Patent Application
20250201826
The present disclosure generally relates to an anode for a lithium-ion battery, and anode compositions thereof. In particular, the anode of the present disclosure comprises an anode composition comprising micro silicon active material particles, wherein the micro silicon active material particles comprise a low surface area and high purity. The present disclosure also relates to a method of incorporating the anode composition into an electrochemical cell.
Conventional lithium-ion (Li-ion) batteries typically employ a graphite-dominant anode as an intercalation material for lithium. Silicon-dominant anodes, however, offer improvements compared to graphite-dominant Li-ion batteries. Silicon (based on Li3.75Si) exhibits both higher gravimetric (3579 mAh/g vs. 372 mAh/g for graphite) and volumetric capacities (˜2194 mAh/cm3 vs. ˜750 mAh/cm3 for graphite in a fully lithiated state). In addition, silicon-based anodes have a low lithiation/delithiation voltage plateau at about 0.3-0.4V vs. Li/Li+, which allows it to maintain an open circuit potential that avoids undesirable Li plating and dendrite formation. While silicon shows excellent electrochemical activity, achieving a stable cycle life for silicon-based anodes is challenging due to silicon's large volume changes during lithiation and delithiation. Silicon active materials and regions may lose electrical contact from the anode as large volume changes coupled with its low electrical conductivity separate the silicon from surrounding materials in the anode.
In addition, the large silicon volume changes exacerbate solid electrolyte interphase (SEI) formation, which can further lead to electrical isolation and, thus, capacity loss. Expansion and shrinkage of silicon particles upon charge-discharge cycling causes pulverization of silicon particles, which increases their specific surface area. As the silicon surface area changes and increases during cycling, SEI repeatedly breaks apart and reforms. The SEI thus continually builds up around the pulverizing silicon regions during cycling into a thick electronic and ionic insulating layer. This accumulating SEI increases the impedance of the electrode and reduces the electrode electrochemical reactivity, which is detrimental to cycle life. Because of its high specific capacity, abundance and low cost, silicon is a promising active material for Li-ion anodes. However its large volume change during lithiation and delithiation (>280% volume change for the Li3.75Si1 phase) creates mechanical degradation of the electrode and an unstable SEI which leads to electrode swelling and poor cell cycle life.
Therefore, there is a need to provide new and alternative anode compositions for lithium ion batteries, particularly those comprising a majority silicon active material, that can control the expansion effects of silicon and significantly extend the stability and/or cycle life of the anode.
The present disclosure provides an anode composition comprising micro silicon active material particles, wherein the silicon content is at least 60 wt. % based on the total weight of the anode composition. The present disclosure also provides a method of incorporating an anode comprising the anode composition into a electrochemical cell and an electrochemical cell so formed, whereby the anode paired with the method of integration into the electrochemical cell can extend the stability and/or cycle life of the anode.
In one aspect there is provided an anode composition comprising micro silicon active material particles, wherein the micro silicon active material particles have one or more of the following (i) a measured BET surface area between about 0.1 m2/g and about 10 m2/g, (ii) a D50 particle size between about 0.1 μm and about 10 μm, and (iii) a ratio of D50:BET surface area between about 0.1 and about 10, and wherein the amount of the micro silicon active material particles present in the anode composition is between about 60 wt. % and about 95 wt. % based on the total weight % of the anode composition. In some embodiments, the amount of the micro silicon active material particles present in the anode composition may be between about 70 wt. % and about 95 wt. % based on the total weight % of the anode composition. In some embodiments, the purity of the micro silicon active material particles (without oxygen) may be at least 95 wt. %.
In some embodiments, the anode composition may further comprise one or more binders. The amount of binder present in the anode composition may be between about 2.5 wt. % to about 15 wt. % based on the total weight of the anode composition.
In some embodiments, the anode composition may further comprise one or more conductive materials. The amount of conductive material present in the anode composition may be between about 2.5 wt. % to about 40 wt. % based on the total weight of the anode composition.
In some embodiments, the micro silicon active material particles and/or the anode composition may be prelithiated. The prelithiation level of the micro silicon active material particles and/or the anode composition may be between about 1% and about 30% silicon lithiation.
In another aspect there is provided an electrochemical cell comprising: an anode; a cathode; an electrolyte; and a separator, wherein the anode comprises the anode composition defined in any one or more embodiments or examples described herein, wherein the lithium uptake capacity of the anode is greater than the lithium release capacity of the cathode. In some embodiments, the capacity of the lithium uptake capacity of the anode may not be fully utilized during charging of the lithium ion battery. In an example, the anode may be only partially lithiated in the fully charged state. In some embodiments, the degree of silicon lithiation may be limited to about 20% to about 80% of the theoretical maximum. In some embodiments, a capacity ratio (N/P ratio) of the anode and the cathode may be between about 1.05 and about 7. In other embodiments, the lower cut-off voltage may be between about 2.0V and 3.5V.
In some embodiments, the prelithiation level of the anode may be between about 1% and about 30% silicon lithiation. The cathode may be selected from the group comprising lithium nickel cobalt manganese oxide (NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LNMO), lithium nickel cobalt aluminium oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), and a sulphur composite. The electrolyte may be selected from a non-aqueous electrolyte solution comprising one or more lithium salts.
In some embodiments, the electrochemical cell may be an energy storage device. The energy storage device may be a battery, preferably a secondary battery. For example, the battery may be a lithium-ion battery.
In another aspect there is provided a method for improving cycling stability of a lithium-ion battery having an anode and a cathode, at least one electrolyte, and a separator, wherein the anode composition is defined by any one or more embodiments or examples described herein. In some embodiments, the anode within the battery delivers a specific capacity of at least about 450 mAh/g, 500 mAh/g, 600 mAh/g, 800 mAh/g, 1000 mAh/g, 1200 mAh/g, or 1500 mAh/g and retains at least about 80% of its initial capacity after 100, 200, 400, 600, 800, 1000 or 1500 cycles of the battery.
In another aspect there is provided a use of an anode composition in an electrochemical cell, wherein the anode composition is at least partially applied to a current collector material, and wherein the anode composition is as defined by any one or more embodiments or examples described herein.
In another aspect there is provided a process for preparing an anode for an electrochemical cell, comprising the steps of: (i) preparing an anode slurry comprising micro silicon active material particles, optionally one or more further active materials, optionally one or more binders, optionally one or more conductive materials, optionally one or more additives, and a solvent system; and (ii) casting a layer of the anode slurry onto a current collector material to provide a wet anode composition layer on the current collector material.
In another aspect there is provided an anode prepared as defined by the process in any one or more embodiments or examples described herein.
In another aspect there is provided a process for assembling an electrochemical cell, whereby the process comprises the following steps: preparing an anode as defined by the process in any one or more embodiments or examples as described herein, wherein the anode comprises an anode composition as defined in any one or more embodiments or examples as described herein; and assembling the anode into an electrochemical cell.
Preferred embodiments of the present disclosure will be further described and illustrated, by way of example only, with reference to the accompanying drawings in which:
The present disclosure describes the following various non-limiting examples, which relate to investigations undertaken to identify alternative and improved anodes comprising a majority micro silicon anode composition for lithium ion batteries, to any methods of incorporating the anodes into electrochemical cells, to electrochemical cells so formed and to use thereof.
In the following description, reference is made to the accompanying drawings which form a part hereof, and which is shown, by way of illustration, several embodiments. It is understood that other embodiments may be utilised and structural changes may be made without departing from the scope of the present disclosure.
With regards to the definitions provided herein, unless stated otherwise, or implicit from context, the defined terms and phrases include the provided meanings. In addition, unless explicitly stated otherwise, or apparent from context, the terms and phrases below do not exclude the meaning that the term or phrase has acquired by a person skilled in the relevant art. The definitions are provided to aid in describing particular embodiments, and are not intended to limit the claimed invention, because the scope of the invention is limited only by the claims. Furthermore, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.
All publications discussed and/or referenced herein are incorporated herein in their entirety.
Throughout this disclosure, unless specifically stated otherwise or the context requires otherwise, reference to a single step, composition of matter, group of steps or group of compositions of matter shall be taken to encompass one and a plurality (i.e., one or more) of those steps, compositions of matter, groups of steps or groups of compositions of matter. Thus, as used herein, the singular forms “a”, “an” and “the” include plural aspects unless the context clearly dictates otherwise. For example, reference to “a” includes a single as well as two or more; reference to “an” includes a single as well as two or more; reference to “the” includes a single as well as two or more and so forth.
Those skilled in the art will appreciate that the disclosure herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the disclosure includes all such variations and modifications. The disclosure also includes all of the examples, steps, features, methods, compositions, and processes, referred to or indicated in this specification, individually or collectively, and any and all combinations or any two or more of said steps or features.
The term “and/or”, e.g., “X and/or Y” shall be understood to mean either “X and Y” or “X or Y” and shall be taken to provide explicit support for both meanings or for either meaning.
Unless otherwise indicated, the terms “first,” “second,” etc. are used herein merely as labels, and are not intended to impose ordinal, positional, or hierarchical requirements on the items to which these terms refer. Moreover, reference to a “second” item does not require or preclude the existence of lower-numbered item (e.g., a “first” item) and/or a higher-numbered item (e.g., a “third” item).
As used herein, the phrase “at least one of”, when used with a list of items, means different combinations of one or more of the listed items may be used and only one of the items in the list may be needed. The item may be a particular object, thing, or category. In other words, “at least one of” means any combination of items or number of items may be used from the list, but not all of the items in the list may be required. For example, “at least one of item A, item B, and item C” may mean item A; item A and item B; item B; item A, item B, and item C; or item B and item C. In some cases, “at least one of item A, item B, and item C” may mean, for example and without limitation, two of item A, one of item B, and ten of item C; four of item B and seven of item C; or some other suitable combination.
It is to be appreciated that certain features that are, for clarity, described herein in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features that are, for brevity, described in the context of a single embodiment, may also be provided separately or in any sub-combination.
Throughout the present specification, various aspects and components of the invention can be presented in a range format. The range format is included for convenience and should not be interpreted as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible sub-ranges as well as individual numerical values within that range, unless specifically indicated. For example, description of a range such as from 1 to 5 should be considered to have specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 5, from 3 to 5 etc., as well as individual and partial numbers within the recited range, for example, 1, 2, 3, 4, 5, 5.5 and 6, unless where integers are required or implicit from context. This applies regardless of the breadth of the disclosed range. Where specific values are required, these will be indicated in the specification.
Throughout this specification the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated element, integer or step, or group of elements, integers or steps, but not the exclusion of any other element, integer or step, or group of elements, integers or steps.
Throughout this specification, the term “consisting essentially of” is intended to exclude elements which would materially affect the properties of the claimed composition.
The terms “comprising”, “comprise” and “comprises” herein are intended to be optionally substitutable with the terms “consisting essentially of”, “consist essentially of”, “consists essentially of”, “consisting of”, “consist of” and “consists of”, respectively, in every instance.
Herein the term “about” encompasses a 10% tolerance in any value or values connected to the term.
Herein the term “weight %” may be abbreviated to as “wt. %”.
Herein the term “lithiation” encompasses lithiation of either the anode or the cathode and is intended to denote the insertion or alloying of Li+ with the active material.
Herein the term “de-lithiation” encompasses de-lithiation of either the anode or the cathode and is intended to denote the extraction or dealloying of Li+ with the active material.
The term “charge” can be used in the context of a full cell and a half cell. In the full cell, the term “charge” encompasses the involuntary process of forcing Li+ to migrate from the cathode into the anode upon assembly of a full cell (initial pairing of anode and cathode) and denotes a rise in the cell voltage. In the half cell, the term “charge” encompasses the involuntary process of Li+ extraction from the working electrode and deposition on the reference electrode (lithium metal foil) and denotes a rise in cell voltage.
The term “discharge” can be used in the context of a full cell and a half cell. In the full cell, the term “discharge” encompasses the voluntary process of extracting Li+ ions from the anode and their migration from the anode to the cathode upon assembly and denotes a decrease in the cell voltage. In the half cell, the term “discharge” encompasses the voluntary process of Li+ dissolution from the reference electrode (lithium metal foil) and the insertion of Li+ into the working electrode and denotes a decrease in the cell voltage.
As used herein, the term “half cell” describes a reference test system used for research and development purposes consisting of a working electrode (electrode of interest) and reference electrode (e.g. lithium metal foil).
As used herein, the term “full cell” describes a conventional electrochemical cell system pairing a commercially relevant anode (graphite, silicon, LTO) with a commercially relevant cathode (LFP, LCO, NCM, NCA, LMO).
The term “prelithiation” describes the insertion of Li+ into the anode or the anode active material before pairing with a cathode electrode in a full cell format.
The term “N/P ratio” or “negative to positive ratio” refers to the mass balance between the anode (negative electrode) and cathode (positive electrode). The mass balance is determined by the available area capacity per cm2 of the respective electrodes.
The term “area capacity” refers to the available capacity of an electrode (anode or cathode) per area. This may be determined by type and wt. % of active material in the coating as well as the amount of coating loading applied to the current collector substrate in mg/cm2 (or g/m2). The higher the loading in mg/cm2 the higher the area capacity per cm2.
The present disclosure is directed to providing improvements in anodes for lithium ion batteries. The present disclosure covers various research and development directed to identifying and better understanding the failure mechanisms of anodes comprising majority silicon anode compositions and subsequently optimising their formulations such that the degradation (e.g., cracking and delamination), silicon particle fracturing and instability of the solid electrolyte interphase can be controlled, reduced or in some manner ameliorated to improve stability and cyclability of the lithium ion battery.
It has been surprisingly found that the majority silicon anode composition, at least according to some examples as described herein, can demonstrate significant stability and/or cycle life of an anode. It has further been surprisingly found that the majority silicon anode composition paired with the method of integration into the electrochemical cell can control the formation of SEI and the expansion and degradation of silicon, and therefore significantly extend the stability and/or cycle life of the anode.
It has also been found that the majority silicon anode composition for an electrochemical cell (e.g. battery), at least according to some examples as described herein, may provide one or more further advantages such as:
The anode composition as described herein may comprise micro silicon active material particles, wherein the micro silicon active material particles have one or more of the following (i) a measured BET surface area between about 0.1 m2/g and about 10 m2/g, (ii) a D50 particle size between about 0.1 μm and about 10 μm, and (iii) a ratio of D50:BET surface area between about 0.1 and 10, and wherein the amount of silicon present in the anode composition is between about 60 wt. % and about 95 wt. % based on the total weight % of the anode composition.
The anode composition as described herein may comprise micro silicon active material particles, wherein the micro silicon active material particles have (i) a measured BET surface area between about 0.1 m2/g and about 10 m2/g and (ii) a D50 particle size between about 0.1 μm and about 10 μm, or (iii) a ratio of D50:BET surface area between about 0.1 and 10, and wherein the amount of silicon present in the anode composition is between about 60 wt. % and about 95 wt. % based on the total weight % of the anode composition.
The anode composition as described herein may comprise or consist of the micro silicon active material particles, as described herein, optionally one or more further active materials, optionally one or more binders, optionally one or more conductive materials, and optionally one or more additives. In one example, the anode composition as described herein may comprise or consist of micro silicon active material particles, wherein the micro silicon active material particles have one or more of the following (i) a measured BET surface area between about 0.1 m2/g and about 10 m2/g, (ii) a D50 particle size between about 0.1 μm and about 10 μm, and (iii) a ratio of D50:BET surface area between about 0.1 and about 10, and wherein the amount of the micro silicon active material particles present in the anode composition is between about 60 wt. % and about 95 wt. % based on the total weight % of the anode composition; optionally one or more further active materials, optionally one or more binders; optionally one or more conductive materials; and optionally one or more additives. In another example, the anode composition as described herein may comprise or consist of micro silicon active material particles, wherein the micro silicon active material particles have (i) a measured BET surface area between about 0.1 m2/g and about 10 m2/g and (ii) a D50 particle size between about 0.1 μm and about 10 μm, or (iii) a ratio of D50:BET surface area between about 0.1 and about 10, and wherein the amount of the micro silicon active material particles present in the anode composition is between about 60 wt. % and about 95 wt. % based on the total weight % of the anode composition; optionally one or more further active materials, optionally one or more binders; optionally one or more conductive materials; and optionally one or more additives.
In some embodiments or examples, the micro silicon active material particles content of the anode composition may be between about 60 wt. % and about 95 wt. % based on the total weight of the anode composition. It will be appreciated that further advantages may be shown when the the micro silicon active material particles content of the anode composition is greater than 60 wt. %, preferably greater than 70 wt. %. The micro silicon active material particles content may be less than about 95 wt. %, 90 wt. %, 85 wt. %, 80 wt. %, 75 wt. %, 70 wt. %, 65 wt. %, or 60 wt. %. The micro silicon active material particles content may be at least about 60 wt. %, 65 wt. %, 70 wt. %, 75 wt. %, 80 wt. %, 85 wt. %, 90 wt. %, or 95 wt. %. The micro silicon active material particles content of the anode composition may be in a range provided by any two of these upper and/or lower amounts.
In some embodiments or examples, the thickness of the anode composition may be substantially uniform and in the range of about 5 μm to about 70 μm. The thickness (μm) of the anode composition may be less than about 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5. The thickness (μm) of the anode composition may be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70. The thickness of the anode composition may be in a range provided by any two of these upper and/or lower amounts.
In some embodiments or examples, the anode composition may be supported on a current collector material. In some embodiments or examples, the anode composition may be applied to the current collector material as a coating or film. It will be understood that the current collector may be at least partially coated with the anode composition. For example, the anode composition may be applied to only one side of the current collector material. The current collector material for the anode may be selected from the group comprising a copper, aluminium, stainless steel, titanium, carbon, perforated metal foils, metal foams, and metal coated polymer based porous and non-porous membranes. It will be appreciated that the current collector material will be of appropriate dimension, porosity and pore size, encompassing the above materials and acting as the current collector. For example, the anode composition may be applied to a copper current collector material (e.g. copper foil). For example, the anode composition, comprising or consisting of micro silicon active material particles, optionally one or more further active materials, optionally one or more binders, optionally one or more conductive materials, and optionally one or more additives, may be supported on a copper current collector material (e.g. copper foil). In some embodiments, the current collector material for the anode may have a thickness of between about 4 μm and about 25 μm. The thickness of the current collector (in μm) may be less than about 25, 20, 15, 10, 8, 6, or 4. The thickness of the current collector (in μm) may be at least about 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, or 25. The thickness of the current collector (in μm) may be in a range provided by any two of these upper and/or lower amounts. In one example, the current collector material for the anode may be copper foil having a thickness of between about 6 μm and about 12 μm.
In some embodiments or examples, the anode composition may be an anode for a battery. For example, the anode composition may be an anode for a lithium ion battery.
The present invention relates to an anode composition comprising micro silicon active material particles.
In some embodiments or examples, the micro silicon active material particles may be selected from the group comprising or consisting of metallurgical silicon, polycrystalline silicon and monocrystalline silicon. In a preferred example, the micro silicon active material particles are metallurgical silicon.
It will be appreciated that the raw feedstock for any type of elemental silicon is quartz sand (silicon dioxide (SiO2)). In conventional manufacturing processes, SiO2 is reacted with carbon in arc furnaces, where the carbon may be supplied to the process in the form of coke and where were high temperatures (˜1800° C.), are applied to reduce the SiO2 to Si and CO according to the following reaction:
This reaction produces metallurgical grade silicon which may comprise impurities such as Al, Ca, Fe, Ti, P, Cu, Cr, K, V, Ni, Na and others at levels of several hundred to several thousand parts per million (ppm). Metallurgical silicon can be used in various industrial applications including steel production. However, due to the impurities, it cannot be used for electronic applications. The crystal structure of metallurgical silicon is well-defined, but it is neither as pure nor efficient at conducting electricity as monocrystalline silicon. Metallurgical silicon has a metallic crystal structure, which is characterized by its metallic bonding between atoms. In the metallic crystal structure, atoms are arranged in a repeating pattern, but lacking order.
To reduce the impurities of the metallurgical silicon down to parts per billion (ppb), further refinement is required. This process can yield a semiconductor or electronic grade Si (also referred to as polycrystalline silicon). A reaction between metallurgical silicon and dry HCl will form a trichlorosilane (SiHCl3), which is a liquid with a boiling point of 32° C.:
It will be appreciated that some chloride impurities may also form such as FeCl3, but due to the differences between the boiling point of these impurities and SiHCl3, the fractional distillation technique can be used to separate the impurities. During this process, the mixture of SiHCl3 and the chloride impurities are heated, where the vapours are condensed in different distillation towers and held at appropriate temperatures. This will enable the separation of pure SiHCl3 from the impurities. A reaction between SiHCl3 and H2 will result in forming pure polycrystalline silicon.
The crystal structure of polycrystalline silicon is not well-defined, and the small crystals (grain) that make up the material are randomly oriented and typically less than 100 micrometers in size. The grains are separated by grain boundaries and normally have random crystallographic orientations. This results in material that is weaker than monocrystalline silicon and is less efficient at conducting electricity.
Czochralski method is used to convert the pure polycrystalline silicon to single-crystal monocrystalline silicon. A seed crystal is required to grow single-crystal material, which will act as a template for growth. Czochralski method involves heating the polycrystalline silicon in a quartz-lined graphite crucible by resistively heating it to the melting point of Si (1412° C.). Then a seed crystal is lowered into the molten material and raised slowly allowing the crystal to grow onto the seed. During the growth of the crystal a slow rotation is required to average out any temperature variations that might result in an inhomogeneous solidification.
The resulting monocrystalline silicon is often referred to as single-crystal silicon. It consists of silicon, which is characterized by its regular and repeating arrangement of atoms in a three-dimensional lattice, and free from grain limits. Monocrystalline silicon can be treated as an intrinsic semiconductor consisting only of excessively pure silicon. Monocrystalline silicon is known for its high efficiency and high purity, making it ideal for use in electronic applications. Mono-crystalline silicon can be a p-type and n-type silicon by doping with other elements.
It is well known in the art that impurities may be present in any micro silicon active material particle. It is also well known that impurities may be selectively added to any micro silicon active material particle. In some embodiments, impurities selected from the group consisting of Al, Ca, Fe, Ti, P, Cu, Cr, K, V, Ni and Na may be present in the micro silicon active material particle, for example in a total or individual amount of less than about 5000 ppm, less than about 4500 ppm, less than about 4000 ppm, less than about 3500 ppm, or less than about 3000 ppm. In an embodiment, total or individual impurities selected from the group consisting of Al, Ca, Fe, Ti, P, Cu, Cr, K, V, Ni and Na may be present in the micro silicon active material particle in a range between about 0 ppm and about 5000 ppm, preferably between about 0 ppm and about 4000 ppm, more preferably between about 0 ppm and about 3000 ppm.
In one embodiment, the micro silicon active material particles may present any morphology, for example they may take the form of flakes, agglomerates, granules, powders, spheres, pulverized materials or the like, as well as combinations thereof. The micro silicon active material particles may have any desired shape including, but not limited to, cubic, rod like, plate-like, polyhedral, spherical or semi-spherical, quasi spherical, rounded or semi-rounded, angular, irregular, and so forth. In one embodiment, the micro silicon active material particles have an aspect ratio (i.e. the ratio of a length to a width, where the length and width are measured perpendicular to one another, and the length refers to the longest linearly measured dimension) of 1.0 to 10.0, or 1.0 to 5.0, or 1.0 to 4.0, or 1.0 to 2.0. In one embodiment, the micro silicon active material particles may have an aspect ratio of about 1.0 to 5.0 or about 1.0 to 4.0 or about 1.0 to about 3.0, or about 1.0 to about 2.0, for example about 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5 or 5.0.
In some embodiments, the particle size (in μm) of the micro silicon active material particles may be at least about 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, or 30. In some embodiments, the particle size (in μm) of the micro silicon active material particles may be less than about 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, or 0.5. Combinations of any two or more of these upper and/or lower particle sizes are also possible, for example the particle size (in μm) of the micro silicon active material particles may be between about 1 to about 10, about 2 to about 8, about 3 to about 6, or about 2 to about 5. The particle size is taken to be the longest cross-sectional diameter across a micro silicon active material particle. For non-spherical micro silicon active material particles, the particle size is taken to be the distance corresponding to the longest cross-section dimension across the particle.
The micro silicon active material particles may have a particle size distribution, wherein 90% of the micro silicon active material particles (D90) have a particle size of less than about 34, 32, 30, 28, 24, 20, 18, 16, 14, 12, 10, 8, 6, 5 or 4 μm, wherein 50% of the micro silicon active material particles (D50) have a particle size (in μm) of less than about 10, 9, 8 7, 6, 5, 4, 3, 2, 1, 0.8, 0.6, 0.4, 0.2, 0.1, or wherein 10% of the micro silicon active material particles (D10) have a particle size of less than about 4, 3, 2, or 1 μm. In some embodiments, the micro silicon active material particles have a (D50) particle size (in μm) of at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10. In some embodiments, the micro silicon active material particles have a (D50) particle size (in μm) of less than about 10, 9, 8, 7, 6, 5, 4, 3.5, 3, 2.5, 2, 1. 0.9, 0.8, 0.7, 0.6, 0.5, 0.5, 0.4, 0.3, 0.2, or 0.1. Combinations of any two or more of these upper and/or lower particle sizes are also possible, for example the micro silicon active material particles have a (D50) particle size (in μm) of between about 0.1 to about 10, about 0.1 to about 9, about 0.1 to about 8, about 0.1 to about 7, about 0.1 to about 6, about 0.1 to about 5, about 0.5 to about 10, about 0.5 to about 9, about 0.5 to about 8, about 0.5 to about 7, about 0.5 to about 6, about 0.5 to about 5, about 1 to about 10, about 1 to about 9, about 1 to about 8, about 1 to about 7, about 1 to about 6, or about 1 to about 5 μm.
One or more advantages of the present disclosure are provided by micro silicon active material particles having a low surface area. It has been found that the more charge/discharge cycles micro silicon is subjected to, the higher the surface roughness of the micro silicon particles resulting in a higher surface area. The higher the surface area, the greater the loss of Li ions per cycle. This has a significant effect on the cycle life of the anode. It has been found that starting with a low surface area, this effect can be mitigated. In some embodiments or examples, the micro silicon active material particles may have a BET surface area in a range of from about 0.1 m2/g to about 10 m2/g, for example from about 1 m2/g to about 5 m2/g. The micro silicon active material particles may have a BET surface area (m2/g) of at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10 m2/g. In other embodiments or examples, the micro silicon active material particles may have a surface area (m2/g) of less than about 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1 m2/g. Combinations of these surface area values to form various ranges are also possible, for example the micro silicon active material particles may have a surface area (m2/g) of between about 0.1 to about 10, about 0.1 to about 9, about 0.1 to about 8, about 0.1 to about 7, about 0.1 to about 6, about 0.1 to about 5, about 0.5 to about 10, about 0.5 to about 9, about 0.5 to about 8, about 0.5 to about 7, about 0.5 to about 6, about 0.5 to about 5, about 1 to about 10, about 1 to about 9, about 1 to about 8, about 1 to about 7, about 1 to about 6, or about 1 to about 5 m2/g.
The inventors have surprisingly found that there is a relationship between the D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles, and the ratio of those parameters to the electrochemical performance of the anode. In some embodiments or examples, the ratio of D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles may be in a range from about 0.1 to about 10. In some embodiments or examples, the ratio of D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles may be at least about 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10. In some embodiments or examples, the ratio of D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles may be less than about 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0.9, 0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.2, or 0.1. Combinations of these ratios to form various ranges are also possible, for example the ratio of D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles may be in a range between about 0.1 to about 10, about 0.1 to about 9, about 0.1 to about 8, about 0.1 to about 7, about 0.1 to about 6, about 0.1 to about 5, about 0.5 to about 10, about 0.5 to about 9, about 0.5 to about 8, about 0.5 to about 7, about 0.5 to about 6, about 0.5 to about 5, about 1 to about 10, about 1 to about 9, about 1 to about 8, about 1 to about 7, about 1 to about 6, or about 1 to about 5. In one particular example, a ratio of D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles in the range of about 0.1 to about 6 provided by a D50 and BET surface area range of about 2 μm to about 8 μm and about 1 m2/g to about 5 m2/g, respectively, improve the initial coulombic efficiency and capacity retention of the anode. In particular, a ratio of D50 particle size (in μm) of the micro silicon active material particles and the BET surface area (m2/g) of the micro silicon active material particles in the range of about 1.0 to about 3.5 provided by a D50 particle size and BET surface area range of about 3.0 μm to about 6.0 μm and about 1.0 m2/g to about 3.5 m2/g, respectively, advantageously provided the most improved capacity retention in the full cell configuration for the micro silicon anode design. It will be appreciated that a gradual decrease in electrochemical performance is found when the D50 particle size/BET surface area ratio is higher than 3.5 and lower than 1.0. However, a drastic decrease in ICE and capacity retention is found when the D50 particle size/BET surface area ratio is between 0.01 and 0.10 resulting from a D50 particle size range of 0.1 to 2.0 μm and a BET surface of >5 m2/g. Without wishing to be bound by theory, this phenomenon is likely to result from the low surface reactivity of the micro silicon active material particle with the electrolyte forming a thinner and less resistive SEI layer.
It was surprisingly found that an inverse relationship of cycling stability exists when various micro silicon anode grades were cycled in half-cell and full-cell designs, which was governed by their respective particle size, BET surface area and the ratio between the d50 particle size and BET surface area.
In half-cell format where the micro silicon anode is tested under fully lithiated conditions, a fast capacity reduction was evident for samples with a d50>2.0 μm, BET surface area <5 m2/g and a d50 particle size:BET surface area ratio higher than 0.01 to 0.1. When the micro silicon materials are tested at limited capacity full-cell design, the cycling stability observed from the half-cell testing were inversed. Micro silicon materials with a high d50 particle size (preferably 2.0-8.0 μm), low BET surface area (preferably 1.0-5.0 m2/g) and high d50 particle size:BET surface area ratio (preferably 0.1-6.0) result in stable cycling performance with a higher ICE and capacity retention.
Expansion and shrinkage of silicon particles upon charge-discharge cycling causes pulverization of silicon particles, which increases their specific surface area. With an unlimited supply of Li+ ions from the Li metal counter electrode in half-cells, any Li loss from SEI formation reactions with newly formed surfaces can be easily compensated and the Si anode can continue to cycle until the silicon electrode is completely exhausted. Therefore, micro silicon particles with a low d50, high BET surface area and a d50 particle size:BET surface area ratio <0.1 will take longer to reach the complete exhaustion of the silicon electrode due to the presence of a larger silicon surface area, lower average particle size and therefore reduced stresses on the particles, resulting in a relatively stable cycling performance.
In full cell designs where a limited Li reservoir is present, the increased reactivity of micro silicon particles with a larger surface area consisting of a d50<2.0 μm, BET surface area >5 m2/g and a d50 particle size:BET surface area ratio <0.1 during charge-discharge leads to accelerated consumption of Li+ leading to poor capacity retention and cycle life. The low surface reactivity and thus the low irreversible consumption of Li+ ions in the micro silicon materials with a high d50 particle size (preferably 2.0-8.0 μm), low BET surface area (preferably 1.0-5.0 m2/g) and high d50 particle size:BET surface area ratio (preferably 0.1-6.0) during cycling extend the capacity retention and cycle life. It was surprisingly found that specific combinations of d50 and BET surface area can lead to exceptionally good performance in full cells.
In the limited capacity electrochemical full cells, the anode is designed so that its lithium uptake capacity is greater than the lithium release capacity of the cathode. This leads to the lithium uptake capacity of the anode not being fully exploited, i.e., the silicon active material particles of the anode being only partially lithiated, in the fully charged state, and advantageously reducing or preventing the high-volume change typically found for silicon anodes during lithiation/delithiation cycling, which degrades their structure and shortens the lifetime of the battery. In other words, a high N/P ratio may limit the degree of lithiation of the micro silicon, as the amount of Li ion is fixed by the cathode upon cell assembly. For example, the anode may be significantly oversized relative to the amount of lithium that is contained in the cell and provided by the cathode. As the degree of lithiation is limited by the oversized anode, so is the level of expansion of the micro silicon active material particles and its degradation.
In some embodiments or examples, the tap density of the micro silicon active material particles may be in a range of from about 0.5 g/cm3 to about 1.5 g/cm3. The tap density of the micro silicon active material particles may be at least about 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1.0, 1.2, 1.3 or 1.5 g/cm3. In other embodiments or examples, the tap density of the micro silicon active material particles may be less than about 1.5, 1.4, 1.3, 1.2, 1.0, 0.95, 0.9, 0.85, 0.8, 0.75, 0.7, 0.65, 0.6, 0.55, or 0.5 g/cm3. Combinations of these density values to form various ranges are also possible, for example the micro silicon active material particles may have a density of between about 0.5 g/cm3 to about 1.2 g/cm3. The density can be measured by any standard method, for example in accordance with ASTM D7481-18.
Advantageously, the micro silicon active material particles of the present disclosure may be provided in a high purity. In an embodiment or example, the purity of micro silicon active material particles (without oxygen) may be in a range from (by wt. %) about 95 to about 99.9. The purity of micro silicon active material particles (without oxygen) may be at least (by wt. %) about 95, 96, 97, 98, 99, 99.5, or 99.9. The purity of the micro silicon active material particles (without oxygen) may be less than (by wt. %) about 99.9, 99.5, 99, 98, 97, 96, or 95. The purity of micro silicon active material particles (without oxygen) may be in a range provided by any lower and/or upper limit as previously described.
In an embodiment or example, the purity of micro silicon active material particles (with oxygen) may be in a range from (by wt. %) about 79 to about 99.5. The purity of micro silicon active material particles (with oxygen) may be at least (by wt. %) about 75, 80, 85, 90, 95, 96, 97, 98, 99 or 99.5. The purity of the micro silicon active material particles (with oxygen) may be less than (by wt. %) about 99.5, 99, 98, 97, 96, 95, 90, 85, 80, or 75. The purity of micro silicon active material particles (with oxygen) may be in a range provided by any lower and/or upper limit as previously described.
The combination of novel and inventive features of the micro silicon active material particles according to the present disclosure and its use in an anode composition for an anode in a lithium ion battery surprisingly leads to an improvement in the batteries cycle behaviour. It was unexpectedly shown that the lithium-ion batteries, as described herein, have a small irreversible capacity loss in the first charge cycle and a stable electrochemical behaviour with minimal fading in the subsequent cycles. Therefore, with the use of the micro silicon active material particles, as described herein, a lower initial capacity loss and also a low continuous loss of capacity of the lithium-ion batteries can be achieved. Overall, the lithium-ion batteries as described herein provide very good stability and cycle life. Accordingly, a high number of cycles can be achieved with minimal fatigue, for example, as a consequence of mechanical destruction of the anode coating layer, anode material or SEI formation.
The SEI layer is formed during the intercalation of lithium-ions, where the organic electrolyte is reduced on the anode's surface when the anode potential is below about 1V versus Li+/Li. The SEI layer is crucial in preventing the co-intercalation of electrolyte ions into the bulk electrode material, by creating a film that is electrically insulating but ionically conductive. This prevents ongoing excessive decomposition of the electrolyte. However, during the formation of the SEI layer film on the surface of the anode active material, some lithium ions may be irreversibly trapped in the electrode, leading to the consumption of lithium ions.
The initial irreversible lithium loss of anodes can be compensated by adding lithium to the anode via prelithiation. Prelithiation methods can be broadly grouped into electrochemical prelithiation and chemical prelithiation. Electrochemical prelithiation may be further grouped into half-cell prelithiation or short-circuit prelithiation. Chemical prelithiation may be further grouped into methods of chemical synthesis, solution immersion and mechanical processes. Additional methods for prelithiation that may be utilized at the active material particle of the anode coating level are represented by chemical vapor deposition (CVD) type methods and physical vapor deposition methods (PVD). The preferred methods to prelithiate an anode composition include methods that also pre-form an SEI layer and can be carried out in a roll-to-roll process and are cost effective in nature. It will be understood that the preferred prelithiation methods to prelithiate an active material particle before incorporation into an anode composition may differ from the methods that are used to prelithiate an anode composition. It should be noted that the current disclosure is not limited to a particular method of pre-lithiation and that the most suitable method will be chosen to achieve the intended outcome.
Prelithiation may be applied to anode electrodes. For example, prelithiation may be applied to compensate for the lithium that is lost on first cycle which constitutes one full charge and one full discharge of the electrochemical cell. If the amount of prelithiation is chosen such that an SEI layer is formed but no lithium is intercalated or alloyed with the active material before assembly into a full cell, then the first cycle loss of the anode once incorporated into a full cell will be minimized and any further loss of lithium is expected to be contributed from other sources such as the cathode electrode. The result is that the electrochemical cell now cycles at a higher cell capacity as more lithium is available in subsequent cycles to be passed back and forth between the anode and the cathode during repeated charge and discharge cycling.
Prelithiation may also provide a lithium reservoir in the anode before the anode is assembled into a cell assembly in addition to compensating for any lithium loss that occurs during the first cycle and more generally the initial formation cycles. The lithium reservoir may compensate for ongoing lithium losses over a number of cycles thus reducing capacity fade and extending the useful life of the full cell. In other words, prelithiation may provide one or more advantages for silicon containing anodes and in particular for anodes that contain a high percentage of silicon. Providing the anode with a lithium reservoir using a method that also applies an SEI layer to the active material can also maximize the first cycle efficiency of the cell.
Optionally, the anode composition may provide a prelithiated anode composition. The prelithiation may occur at the anode active material level before the active material is incorporated into the anode composition or the prelithiation may occur after the anode composition has been prepared. One or more advantages of the present disclosure are provided by prelithiating the anode composition which can provide a lithium reservoir in the anode thereby extending its cycle life by compensating for ongoing Li+ losses during charge/discharge cycling, once incorporated into a full cell arrangement.
In some embodiments, the micro silicon active material particles may be prelithiated micro silicon active material particles, wherein prelithiation occurs prior to incorporation of the active material into the anode composition. In other embodiments, the micro silicon active material particles may be prelithiated micro silicon active material particles, wherein prelithiation occurs after the active material has been incorporated into the anode composition. The degree of prelithiation may be chosen such that the created phase is in between Li0Si1 (0% prelithiation) and Li3.75Si1 or Li4.40Si1 (100% prelithiation). Any phase composition in between may be desirable including Li1Si1, Li1.71Si2, Li2Si1, Li3.5Si1, and Li3.75Si1. In some embodiments or examples, the amount of prelithiation of the micro silicon active material particle and/or the anode composition may be between about 1% and about 30%. The amount of prelithiation of the micro silicon active material particle and/or the anode composition may be less than about 30%, 25%, 20%, 15%, 10%, 5% or 1%. The amount of prelithiation of the micro silicon active material particle and/or the anode composition may be at least about 1%, 5%, 10%, 15%, 20%, 25%, or 30%. The amount of prelithiation of the micro silicon active material particle and/or the anode composition may be in a range provided by any two of these upper and/or lower amounts.
Prelithiation of the micro silicon active material particles may be carried out via physical vapor deposition (PVD) or chemical vapor deposition (CVD) or mechanical alloying processes or chemical processes or electrochemical processes. It will be appreciated that a range of suitable methods may be applied to create a silicon-lithium alloy phase prior to the prelithiated micro silicon active material particles being incorporated into the anode composition.
The anode composition as described herein may further comprise one or more further active materials. In some embodiments, the further active materials may be a graphite or a silicon. For example, flake graphite, natural graphite, artificial graphite, silicon oxide where x=0.8 to 2 (SiOx), silicon carbon composites, silicon alloys, or any combination thereof.
The anode composition as disclosed herein may further comprise one or more binders. The binder may be a polymer. In some embodiments, the polymer may be selected from the group consisting of gum arabic, carboxymethyl cellulose (CMC)/citric acid, CMC/styrene-butadiene rubber (SBR), polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), poly(l-trimethylsilyl-1-propyne) (PTMSP), gum binders such as gum arabic, Xanthan gum, and guar gum, natural cellulose based binders, polysaccharides such as sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, sodium alginate, polyacrylates, aliphatic polymers such as polyvinyl butyral, aromatic polymers such as styrene-butadiene rubber. For example, the polymer may be selected from the group consisting of polyvinylpyrrolidone, carboxymethylcellulose, polyacrylic acid (PAA), poly(methacrylic acid), maleic anhydride copolymers including poly(ethylene and maleic anhydride) copolymers, polyvinyl alcohol, carboxymethyl chitosan, natural polysaccharide, Xanthan gum, alginate, polyimide and PAA copolymers including one or several of the following of polyvinylalcohol (PVA), polyurethane (PU), polyimide (PI) or polyacrylonitrile (PAN), In one example, the binder is PAA. The binder may be dissolved in H2O or ethanol or mixtures of H2O and ethanol or N,N′ dimethylformamide or any other solvent that is suitable for the intended purpose. Some binders may be present in the form of water-based emulsions.
In some embodiments or examples, the ratio of binder to micro silicon active material particles may be about 1:40, 1:35, 1:32, 1:30, 1:25, 1:23, 1:20, 1:15, 1:10, 1:9, 1:6, or 1:4. The ratio of binder to micro silicon active material particles may be in a range of about 1:4 to about 1:32. The ratio of binder to micro silicon active material particles may be in a range of about 1:8 to about 1:23. The ratio of binder to micro silicon active material particles may be in a range of about 1:9 to about 1:15.
In some embodiments or examples, the binder (in wt. %) may be present in the anode composition in a range of about 2.5 to 15. The binder (wt. %) may be present in the anode composition in an amount of less than about 15, 12, 10, 8, 5 or 2.5. The binder (in wt. %) may be present in the anode composition in an amount of at least about 2.5%, 5%, 8%, 10%, 12%, or 15%. The binder (in wt. %) may be present in the anode composition in a range provided by any two of these upper and/or lower amounts. For example, the binder (in wt. %) may be present in the anode composition in a range of about 3 to about 8, or about 4 to about 8.
It has been found that the pH of the binder may impact the electrochemical performance of the anode composition. In some embodiments or examples, the pH of the binder may be less than 9, 8, 7, 6, 5, 4, 3, or 2. In some embodiments or examples, the pH of the binder may be at least 2, 3, 4, 5, 6, 7, 8 or 9. The pH of the binder may be in a range provided by any two of these upper and/or lower values. For example, the pH of the binder may be in a range of 4 to 8. Preferably, a binder pH of less than 7 may be beneficial to the electrochemical performance of the micro silicon anode and may be due to (i) the reduced corrosion of pure silicon in the acidic region and/or (ii) silicon's greater affinity to interact with binders, such as for example PAA.
The anode composition as described herein may further comprise one or more conductive materials. In some embodiments or examples, the conductive material may be a carbon-based material. In an embodiment or example, the carbon-based material may be nano-sized or micro-sized carbon particles or flakes, or a combination thereof. In an embodiment or example, the carbon-based material may be selected from the group consisting of activated carbon, carbon nanoparticles, graphite, single walled (SWCNTs) or multiwalled (MWCNTs) carbon nanotubes, branched carbon nanotubes, carbon nanofiber, graphene, graphene oxide, MXene, nano or micro-sized hard carbons, nano or micro-sized porous carbons and conductive polymers. The carbon-based material may be selected from the group consisting of graphene, graphene oxide, graphite, single walled (SWCNTs) or multiwalled (MWCNTs) carbon nanotubes, branched carbon nanotubes, carbon nanofiber, MXene, nano or micro-sized hard carbons, nano or micro-sized porous carbons and conductive polymer. In one example, the carbon-based material may be a carbon nanotube.
In some embodiments or examples, the ratio of conductive material to micro silicon active material particles may be about 1:50, 1:48, 1:45, 1:40, 1:35, 1:30, 1:25, 1:20, 1:18. 1:15, 1:10, 1:8, 1:6, 1:4, 1:3, 1:2, or 1:1.3. The ratio of conductive material to micro silicon active material particles may be in a range of about 1:2 to about 1:30. The ratio of conductive material to micro silicon active material particles may be in a range of about 1:2 to about 1:18. The ratio of conductive material to micro silicon active material particles may be in a range of about 1:2 to about 1:15.
In some embodiments or examples, the conductive material may be present in the anode composition in a range of about 2.5 to 40 wt. % (based on total weight of the anode composition). The conductive material may be present in the anode composition in an amount (based on total weight of the anode composition) of less than about 40 wt. %, 30 wt. %, 20 wt. % 15 wt. %, 10 wt. %, 7 wt. %, 5 wt. % or 2.5 wt. %. The conductive material may be present in the anode composition in an amount (based on total weight of the anode composition) of at least about 2.5 wt. %, 5 wt. %, 7 wt. %, 10 wt. %, 15 wt. %, 20 wt. %, 30 wt. %, or 40 wt. %. The conductive material may be present in the anode composition in an amount provided by any two of these upper and/or lower amounts. For example, the conductive material may be present in the anode composition in an amount between about 7 wt. % and about 25 wt. %.
The present disclosure is directed to providing improvements in anodes for an electrochemical cell. In some embodiments or examples, the present disclosure is directed to an anode for an electrochemical cell comprising an anode composition at least according to some embodiments or examples as described herein.
In some embodiments or examples, an electrochemical cell may comprise: a negative electrode, a positive electrode, at least one electrolyte, and a separator, wherein the anode comprises the anode composition as defined herein. For example, the electrochemical cell may comprise or consist of: an anode; a cathode; at least one electrolyte comprising one or more electrolyte solvents; and a separator, wherein the anode comprises the anode composition as defined herein, and wherein the lithium uptake capacity of the anode is greater than the lithium release capacity of the cathode.
One or more advantages of the present disclosure is provided by the arrangement of the anode and cathode in the electrochemical cell, which has been found to be significantly important to increase the stability and cycle life of the anode composition described herein.
In some embodiments, capacity limitation may be considered in terms of mass loading or area capacity. Mass loading or area capacity refers to an electrochemical cell assembly where the capacity of the anode may be significantly oversized relative to the cathode. The capacity limitation may have the effect of limiting the capacity of the oversized electrode (anode) by only allowing for a partial lithiation to occur as the amount of lithium that is contained in the electrochemical cell is limited by the lithium contained in the cathode upon cell assembly. For example, in an electrochemical cell assembly where the anode possesses an area capacity of x and the cathode possesses an area capacity of y the resulting estimated percentage capacity limitation is calculated by y/x*100. It will be appreciated that this approach to capacity limitation may be particularly useful in situations where the anode contains a high percentage of elemental silicon as the active material which offers specific capacities in excess of 3500 mAh/g.
It will be appreciated that the specific area capacity (in mAh/cm2) corresponds to a specific loading weight (in mg/cm2) provided by the amount of anode composition applied to the current collector. The specific loading weight (in mg/cm2) is based on the total weight of the anode composition, including the micro silicon active material particles, one or more optional further active materials, one or more optional binders, and one or more optional conductive materials. The specific area capacity (in mAh/cm2) is dependent on thickness of the anode composition coating on the current collector, the silicon content in the anode composition, and the degree utilization of the silicon.
In some embodiments, the specific area capacity (in mAh/cm2) corresponding to the full utilization of the active materials contained within the anode composition of the anode may be in between 2.5 mAh/cm2 to 20 mAh/cm2.
In some embodiments, the specific loading weight (in mg/cm2) of the anode composition may be in between 0.95 mg/cm2 to 7.5 mg/cm2.
In some embodiments the anode and cathode are arranged in a way so that the cathode can deliver about 0.5 mAh/cm2 to about 6 mAh/cm2 and the anode can deliver about 1500 mAh/g, 1200 mAh/g, 1000 mAh/g, 800 mAh/g, 600 mAh/g, 500 mAh/g or 400 mAh/g. In another embodiment, the anode and cathode are arranged in a way so that the cathode can deliver about 0.5 mAh/cm2 to about 6 mAh/cm2 and the anode may be utilized to about 80%, 75%, 70%, 65%, 60%, 55%, 50%, 45%, 40%, 35%, 30%, 25%, or 20%.
In other embodiments, capacity limitation may be considered in terms of the phase composition of the LiSi alloy. For example, Li3.75Si1 or Li44Si1 corresponds to the maximum accessible capacity of 3590 mAh/g or the highest theoretic state of lithitation of 4200 mAh/g. It will be understood that if utilization of the anode is limited this may translate into specific phase compositions of the LiSi alloy. Specific phase compositions may also translate into a specific capacity (mAh/g). For example, Li1.71Si1 may correspond to a specific capacity of up to 1636 mAh/g, Li2.33Si1 may correspond to a specific capacity of up to 2227 mAh/g, Li3.25Si1 may correspond to a specific capacity of up to 3101 mAh/g, Li3.75Si1 may correspond to a specific capacity of up to 3579 mAh/g and Li44Si1 may correspond to a specific capacity of up to 4199 mAh/g.
In yet another embodiment, capacity limitation may be considered in terms of the voltage of the anode during charge and/or discharge. It will be understood that amount of silicon lithiation after discharge may be configured by a discharge voltage of the anode.
For example, it will be appreciated that the N/P ratio balance between anode and cathode may be in between about 1.05 and about 7, and/or the voltage range may be controlled with respect to level of discharge of the electrochemical cell. In some embodiments or examples, the capacity of the lithium uptake capacity of the anode may not be fully utilized during charging of the lithium ion battery. In some embodiments or examples, the specific area capacity of the anode may be greater than the specific area capacity of the cathode. In other words, the anode is only partially lithiated in the fully charged state. Fully charged refers to the state of the electrochemical cell (e.g., Li-ion battery) in which the anode, in particular the micro silicon active material, has its highest degree of lithiation in accordance with the disclosure described herein. Partial lithiation of the anode means that the maximum lithium uptake capacity of the anode active material in the anode is not fully exploited. In some embodiments, the amount of lithium stored in the cathode (mAh/cm2) may be at least 2× smaller than the lithium storage capacity of the anode (mAh/cm2). For example, the amount of lithium stored in the cathode (mAh/cm2) may be in a range between 0.05× to 7× smaller than the lithium storage capacity of the anode (mAh/cm2)
In some embodiments, the Li/Si ratio of an electrochemical cell (e.g. Li-ion battery) may be set by the anode to cathode ratio (N/P). In some embodiments, the N/P ratio between anode and cathode may be in between about 1.05 and about 7, about 2 and about 5, or about 3 and about 4. The N/P ratio may be than about 7, 6, 5, 4, 3, 2, or 1.05. The N/P ratio may be at least about 1.05, 2, 3, 4, 5, 6, or 7. The N/P ratio may be in a range provided by any two of these upper and/or lower values. For example, the N/P ratio between anode and cathode may be in between about 1.5 and about 4, or between about 1.8 and about 3.5.
In some embodiments, the capacity limitation (in %) may be at least about 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 99. In some embodiments, the capacity limitation (in %) may be less than about 99, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, or 20. The capacity limitation (in %) may be in a range provided by any two of these upper and/or lower values. For example, the capacity limitation (in %) may be in between about 25 and about 90, or between about 30 and about 80.
The present disclosure advantageously provides an electrochemical cell that is designed so that the lithium uptake capacity of the anode is greater than the lithium release capacity of the cathode. This leads to the lithium uptake capacity of the anode not being fully exploited, i.e. the silicon active material particles of the anode being only partially lithiated, in the fully charged state, and advantageously reducing or preventing the high volume change typically found for silicon anodes during lithiation/delithiation cycling, which degrades their structure and shortens the lifetime of the battery. In other words, a high N/P ratio may limit the degree of lithiation of the micro silicon, as the amount of Li ion is fixed by the cathode upon cell assembly. For example, the anode may be significantly oversized relative to the amount of lithium that is contained in the cell and provided by the cathode. As the degree of lithiation is limited by the oversized anode so is the level of expansion of the micro silicon active material particles and its degradation. In some embodiments or examples, the degree of silicon lithiation may be in a range of about 20% to about 80%. Unexpectedly, the degree of silicon lithium in this range may have a stabilizing effect on the electrochemical cells performance.
In another embodiment, the capacity of the electrochemical cell can be limited by limiting the lower cut-off voltage. In some embodiments or examples, the lower cut-off voltage may be between about 2.5V and about 3.0V. For example, the lower cut-off voltage may be between 2.8V and about 3.0V. It will be appreciated that a voltage limitation may be applied by restricting the lower cut-off voltage. This can prevent the complete delithiation of the micro silicon active material particles at each cycle and mitigate its expansion, leading to less degradation and consequently extended cycle life.
In another embodiment, the capacity of the electrochemical cell can be limited by limiting the upper cut-off voltage. In some embodiments or examples, the upper cut-off voltage may be between about 3.6V and about 4.25V.
It will be appreciated that both limitations, by capacity and voltage may be used simultaneously.
It will be understood that the anode composition may be prelithiated as described in any one of more of the embodiments or examples described herein. In some embodiments, prelithiation may occur prior to incorporation of the active material into the anode composition. In other embodiments, prelithiation may occur after the active material has been incorporated into the anode composition. Prelithation can be performed through direct contact between lithium metal and the active anode material in the electrolyte. Due to the potential difference between lithium metal and the anode material an electric field is formed, which will enable the electrons to transfer from the low potential region to the high potential region at the point of contact under the action of the electric field. In an electrically neutral environment, the Li metal will release lithium ions that pass through the electrolyte and embed into the anode material. For the direct contact prelithiation methods lithium metal powder or lithium metal foil may be used. During prelithiation, the lithium metal foil or powder will self-discharge upon contact which is a relatively simple and efficient process. In some embodiments or examples, the amount of prelithiation of the anode composition may be between about 1% and about 30%. The amount of prelithiation of the anode composition may be less than about 30%, 25%, 20%, 15%, 10%, 5% or 1%. The amount of prelithiation of the anode composition may be at least about 1%, 5%, 10%, 15%, 20%, 25%, or 30%. The amount of prelithiation of the anode composition may be in a range provided by any two of these upper and/or lower amounts.
In some embodiments, the amount of lithium contained in the anode may be about 30% of its maximum storage capacity while the cathode may contain 100% of its maximum storage capacity. In some embodiments, the amount of lithium contained in the anode may be about 20% of its maximum storage capacity while the cathode may contain 100% of its maximum storage capacity. In some embodiments, the amount of lithium contained in the anode may be about 10% of its maximum storage capacity while the cathode may contain 100% of its maximum storage capacity.
In one embodiment, to perform an electrochemical prelithiation a half-cell method may be used. A silicon containing electrode is assembled in a half cell set-up using a lithium foil reference electrode and the degree of prelithiation is controlled by setting the appropriate parameters in a galvanostatic charge/discharge cycling program. To create the SEI layer and a lithium reservoir of up to 30% lithium in the anode, the half-cell will go through the first cycle by partially or fully lithiating the silicon containing electrode followed by full delithiation.
Whereas when creating a lithium reservoir in the anode a partial lithiation up to the desired degree of lithium reservoir is required. Subject to the composition and associated material properties of the silicon containing anode a first cycle loss can be estimated upon having tested the corresponding composition in a half cell against a lithium metal foil reference electrode and having so determined the anode compositions first cycle loss. If the first cycle loss is estimated to be x %, then to create a lithium reservoir of y %, the initial lithiation step during the prelithiation process needed to achieve a lithiation level of the silicon anode composition of z % needs to account for x %+y %. If in one particular embodiment an anode composition shows a first cycle loss of 10%, then this loss needs to be taken into account when calculating the desired degree of prelithiation to obtain the resulting lithium reservoir. For example, to achieve a 10% lithium reservoir the anode may be lithiated up to 20% of its expected design capacity (mAh/g) where the initial ˜10% aim to compensate for the irreversible lithium loss during the first cycle and the additional are stored in the anode or the silicon material and thus form the desired lithium reservoir. It will be understood that higher levels of prelithiation may be applied to achieve other desired levels of lithium reservoirs. The maximum desired level of a lithium reservoir may be 30%.
It has been found that pairing prelithiation and capacity limitation may provide the electrochemical cell of the present disclosure with one or more further advantages. For example, while the capacity of the anode that is occupied by lithium that is supplied by the cathode and stored in the anode on first lithiation will be the same with and without prelithiation notwithstanding any loss of lithium on first cycle, the lithium reservoir in the anode can compensate for the gradual loss of lithium during repeated charge and discharge cycling for a number of cycles.
In some embodiments, the anode composition may be applied to a current collector material as a coating or film. The current collector material for the anode may be selected from the group comprising a copper, aluminium, stainless steel, titanium, carbon, perforated metal foils, metal foams, and metal coated polymer based porous and non-porous membranes. For example, the anode composition may be applied to a copper current collector material (e.g. copper foil). It will be appreciated that the current collector material will be of appropriate dimension, porosity and pore size, encompassing the above materials and acting as the current collector.
In some embodiments, the current collector material for the anode may have a thickness of between about 4 μm and about 25 μm. The thickness of the current collector (in μm) may be less than about 25, 20, 15, 10, 8, 6, or 4. The thickness of the current collector (in μm) may be at least about 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, or 25. The thickness of the current collector (in μm) may be in a range provided by any two of these upper and/or lower amounts. In one example, the current collector material for the anode may be copper foil having a thickness of between about 6 μm and about 12 μm.
In some embodiments, the thickness of the anode composition may be substantially uniform and in the range of about 5 μm to about 45 μm. The thickness (μm) of the anode composition may be less than about 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5. The thickness (μm) of the anode composition may be at least about 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70. The thickness of the anode composition may be in a range provided by any two of these upper and/or lower amounts.
It will be appreciated that the cathode active material is also applied to a current collector material. The current collector material for the cathode may be selected from the group comprising an aluminium, stainless steel carbon, perforated metal foils, metal foams, and metal coated polymer based porous and non-porous membranes. It will be appreciated that the current collector material will be of appropriate dimension, porosity and pore size, encompassing the above materials and acting as the current collector. For example, the cathode composition may be applied to an aluminium current collector material (e.g. aluminium foil).
In some embodiments, the current collector material for the cathode may have a thickness of between about 10 μm and about 30 μm. The thickness of the current collector (in μm) may be less than about 30, 25, 20, 15, or 10. The thickness of the current collector (in μm) may be at least about 10, 12, 14, 16, 18, 20, 25, or 30. The thickness of the current collector (in μm) may be in a range provided by any two of these upper and/or lower amounts. In one example, the current collector material for the cathode may be aluminium foil having a thickness of between about 10 μm and about 30 μm.
In some embodiments, the cathode may be selected from the group consisting of lithium nickel cobalt manganese oxide (NCM), lithium iron phosphate (LFP), lithium nickel manganese spinel (LNMO), lithium nickel cobalt aluminium oxide (NCA), lithium manganese oxide (LMO), lithium cobalt oxide (LCO), and sulphur or sulphur composite including sulphur and carbon mixtures.
In some embodiments or examples, the electrolytes may be selected from a non-aqueous solution of one or more lithium salts (e.g. in Li-ion cells). The one or more lithium salts may be selected from the group comprising lithium bis(trifluoromethane sulfone)imide, lithium hexafluorophosphate, lithium hexafluoroarsenate, lithium bis(trifluorosulfonylimide), lithium trifluoromethanesulfonate, lithium fluoroalkylsulfonimides, lithium fluoroarylsulfonimides, lithium bis(oxalate borate), lithium tris(trifluoromethylsulfonylimide) methide, lithium difluoromethane sulfonate, trifluoromethanesulfonic acid lithium salt (lithium triflate), lithium bis(oxalato) borate, lithium tetrafluoroborate, lithium perchlorate, lithium tetrachloroaluminate, lithium hexafluoroarsenate, lithium hexafluoroantimonate, 4,5-dicyano-2-(trifluoromethyl) imidazolide (LiTDI), LiPF3 (C2F5)3(LiFAP), LiBF3(C2F5), lithium chloride, and combinations thereof. For example, the electrolyte may comprise lithium hexafluorophosphate.
In some embodiments or examples, the lithium salt may be dissolved in an organic solvent. The lithium salt may be dissolved in an organic solvent selected from ethers, esters, carbonates, and acetals. In one example, the solvent may be selected from dimethoxyethane, diglyme, triglyme, tetraglyme, ethylene carbonate, propylene carbonate, dimethyl carbonate, tetrahydrofuran, and dioxolane. In some embodiments or examples, the lithium salt may be dissolved in an organic solvent selected from the group comprising ethylene carbonate, propylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, methylpropyl carbonate, butylmethyl carbonate, ethylpropyl carbonate, dipropyl carbonate, cyclopentanone, sulfolane, dimethyl sulfoxide, 3-methyl-1,3-oxazolidine-2-one, γ-butyrolactone, 1,2-diethoxymethane, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,2-dimethoxyethane, methyl acetate, ethyl acetate, nitromethane, 1,3-propane sultone, γ-valerolactone, methyl isobutyryl acetate, 2-methoxyethyl acetate, 2-ethoxyethyl acetate, diethyl oxalate, an ionic liquid, and any combinations thereof. In some embodiments or examples, the lithium salt may be dissolved in an organic solvent selected from the group comprising ethylene carbonate, dimethyl carbonate, diethyl carbonate, and any combinations thereof.
The electrolyte may comprise an additive selected from one or more alkali metal salts of LiPF6 LiBF4, LiAsF6, LiSbF6, LiClO4, LiAlCl4, LiGaCl4, LiC(SO2CF3)3, LIN (SO2CF3)2, LiSCN, LiSO2CF2CF3, LiC6F5SO3, LiO2CCF3, LiSO3F, LiB(C6H5)4, LiCF3SO3, LiNO3, and mixtures thereof. In other embodiments, the additive may be selected from one or more of flouroethylene carbonate (FEC), vinylethylene carbonate (VEC), vinyl carbonate (VC), propylene carbonate (PC), ethylmethyl carbonate (EMC), propane sultone (PS), and mixtures thereof. Electrolyte additives can further improve certain characteristics of the cell. For example, the electrolyte (e.g. lithium hexafluorophosphate) may comprise an additive (e.g. flouroethylene carbonate) dissolved in an organic solvent (e.g. diethyl carbonate).
In some embodiments or examples, the lithium salt may be dissolved in one or more organic solvents as described above, wherein the one or more organic solvents are present in a volume to volume ratio ranging from 10 to 1 to 1 to 10. For example, the lithium salt (e.g., 1M LiPF6) may be dissolved in FEC/DEC (2:8) v %, FEC:EMC (3:7) w/w+2 wt. % VC, EC/EMC/DEC (3/5/2 vol %)+1 wt. % VC+10 wt. % FEC, or EC/EMC (3:7) wt. %+1 wt. % VC.
In some embodiments or example, a separator is used to electrically separate the anode from the cathode, and allowing free passage of lithium ions in the electrolyte. The separator may be selected from a range of different porous polymer films. It will be appreciated that any porous polymer film may be selected for use as a separator that have a suitable porosity, tortuosity and thickness. For example, a polymer film-based separator material may be selected. In an embodiment or example, the separator may be selected from a polyethylene (PE), polypropylene (PP), or polyethylene terephthalate (PET). In another embodiment a non-woven fibrous material be selected as the separator, comprising of fibres selected from nylon, polyethylene terephthalate (PET), cellulose, aramid or polyacrylonitrile.
In some embodiments or examples, the electrochemical cell may be an energy storage device. The energy storage device may be a battery. For example, the battery may be a secondary battery. In one particular example, the battery may be a lithium ion battery (Li-ion battery).
In some embodiments or examples, the present disclosure also provides a method for improving cycling stability of a battery having an anode and a cathode, at least one electrolyte, and optionally a separator, wherein the anode comprises the anode composition as described herein. It has been found that the anode comprising the anode composition provides a particularly effective anode for use in a battery (e.g. Li-ion battery) capable of maintaining a long-term capacity retention. In some embodiments or examples, the anode inside a battery may have a discharge capacity of at least about 800 mAh/g for at least 100 cycles of the battery. In some embodiments or examples, the specific capacity (mAh/g) may be at least about 500, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000 or 3500. In some embodiments or examples, the specific capacity (mAh/g) may be less than about 3500, 3400, 3200, 3000, 2800, 2600, 2400, 2200, 2000, 1800, 1600, 1400, 1200, 1000, 800, 600 or 500. The specific capacity (mAh/g) may be in a range provided by any two of these upper and/or lower values. In some embodiments or examples, the number of cycles may be at least 80, 100, 120, 140, 160, 180, 200, 220, 240, 260, 280, 300, 320, 340, 360, 380, 400, 420, 440, 460, 480, 500, 1000 or 1500.
The long term cyclic performance of an electrochemical cell (e.g. Li-ion battery) comprising the anode composition may be tested for high silicon content anodes (i.e. about 70% silicon content) with varying capacity limitation. The initial discharge capacity of the anode comprising the anode composition, according to at least some embodiments or examples as described herein, can be at least about (in mAh/g) 600, 800, 1100, 1200, 1300, 1400, 1500, or 1600. At least according to some embodiments or examples, at least about 80% of the discharge capacity may be retained after cycles of 100, 200, 300, 400, 500, 800, 1000 or 1500.
It will be appreciated that galvanostatic charge-discharge cycling experiments may typically be used to evaluate the performance metrics of a battery:capacity, rate capability, coulombic efficiency, and capacity retention upon cycling.
In some embodiments or examples, the present disclosure is also directed to a use of the anode comprising an anode composition, as described herein, in an electrochemical cell. For example, the electrochemical cell may be an energy storage device, such as a battery, preferably a secondary battery. More particularly, the battery may be a lithium-ion battery.
In some embodiments or examples, the present disclosure is also directed to an anode comprising an anode composition, wherein the anode may be a battery anode. More particularly, a lithium ion battery anode.
It has been found that the anode composition, which may comprise or consist of micro silicon active material particles, optionally one or more binders, optionally one or more conductive materials, and optionally one or more additives, significantly reduces effects shown by SEI formation and silicon expansion and degradation, and therefore provides improved performance of Li-ion batteries. The anode composition provides a high first cycle efficiency, and further advantages providing controlled silicon utilization, which, in turn, improves the high current response and performance of the battery. For example, an electrochemical cell (e.g., Li-ion battery) comprising the anode composition as described herein, allows partially utilization/lithiation of silicon and the specific capacity of the anode is reduced and controlled by the amount of lithium the cathode is able to supply, providing an improved average Coulombic efficiency (CE) of at least about 75, 80, 85, 90, 95, 98%, 99% or 99.5% or 99.8% or 99.9 or higher or less than 100% over at least 200 cycles. In another example, use of the anode composition as an anode, provides improved performance of Li-ion batteries showing cyclic stability after at least 200 cycles at C/2.
Further, it has been surprisingly found that if the N/P ratio for an anode that contains majority micro-silicon (e.g., >70%) is manipulated to a value of above 3 (e.g., 3.3), stable cycling of the anode can be provided to achieve more than 200 cycles at greater than 80% capacity retention. In other words, the high N/P ratio limits the degree of lithiation of the micro-silicon, as the amount of Li+ is fixed by the cathode upon cell assembly. This leads to a degree of silicon lithiation of about 20% to about 80%, instead of 80% to 90% as seen for the conventional cell assembly where the anode comprises majority graphite, which has a stabilizing effect on the cells performance. It will be understood that the anode is significantly oversized relative to the amount lithium that is contained in the cell and provided by the cathode. Advantageously, as the degree of lithiation is limited by the oversized anode so is the level of expansion of the silicon and its degradation.
In some embodiments or examples, the present disclosure is directed to a process for preparing an anode for an electrochemical cell. The process may be for preparing an anode according to any embodiments or examples as described herein. It will be appreciated that the anode prepared by the process may comprise an anode composition comprising micro silicon active material particles. It will also be appreciated that the anode prepared by the process may comprise or consist an anode composition comprising micro silicon active material particles, optionally one or more further active materials, optionally one or more binders, optionally one or more conductive materials, optionally one or more additives, and optionally a solvent. The micro silicon active material particles, one or more further active materials, one or more optional binder, one or more optional conductive materials, one or more optional additives, and one or more optional solvents may be selected from any one or more of the embodiments or examples as described herein.
In some embodiments, or examples, a process for preparing of an anode for an electrochemical cell, comprising the steps of: (i) preparing an anode slurry comprising micro silicon active material particles, optionally one or more further active materials, optionally one or more binders, optionally one or more conductive materials, optionally one or more additives, and a solvent system; and (ii) casting a layer of the anode slurry onto a current collector material to provide a wet anode composition layer on the current collector material.
In some embodiments or examples, the process may further comprise step (iii) solidifying the wet anode layer by solvent evaporation to provide a dry anode composition layer on the current collector material.
In some embodiments or examples, the solvent may be an organic solvent selected from aromatics, halogenated aromatics, halogenated aliphatic hydrocarbons, aliphatic hydrocarbons, glycols, ethers, glycol ethers, esters, alcohols, ketones, or combinations thereof. In some embodiments or examples, the solvent may be present in an amount (by weight % of total anode composition) between about 40 wt. % and 90 wt. %, between about 40 wt. % and 70 wt. %, or between about 40 wt. % and 60 wt. %. The solvent may be a low boiling point organic solvent, or a mixture of one or more of such solvents. In some embodiments or examples, the solvent may be selected from the group comprising water, methanol, ethanol, n-propanol, isopropanol, tetrahydrofuran, methylene chloride, chloroform, diethyl ether, room temperature ionic liquids, ethylene glycol, glycerol, formamide, N-methylformamide, dimethylformamide, N-methylsydnone, an aqueous solution thereof, and any mixtures thereof. For example, the solvent may be water, ethanol, N,N′ dimethylformamide, or a combination thereof.
In some embodiments or examples, the ratio of binder to micro silicon active material particles may be about 1:40, 1:35, 1:32, 1:30, 1:25, 1:23, 1:20, 1:15, 1:10, 1:9, 1:6, or 1:4. The ratio of binder to micro silicon active material particles may be in a range of about 1:4 to about 1:32. The ratio of binder to micro silicon active material particles may be in a range of about 1:8 to about 1:23. The ratio of binder to micro silicon active material particles may be in a range of about 1:9 to about 1:15.
In some embodiments or examples, the binder (in wt. %) may be present in the anode composition in a range of about 2.5 to 15. The binder (wt. %) may be present in the anode composition in an amount of less than about 15, 12, 10, 8, 5 or 2.5. The binder (in wt. %) may be present in the anode composition in an amount of at least about 2.5%, 5%, 8%, 10%, 12%, or 15%. The binder (in wt. %) may be present in the anode composition in a range provided by any two of these upper and/or lower amounts. For example, the binder (in wt. %) may be present in the anode composition in a range of about 3 to about 8, or about 4 to about 8.
It has been found that the pH of the binder may impact the electrochemical performance of the anode composition. In some embodiments or examples, the pH of the binder may be less than 9, 8, 7, 6, 5, 4, 3, or 2. In some embodiments or examples, the pH of the binder may be at least 2, 3, 4, 5, 6, 7, 8 or 9. The pH of the binder may be in a range provided by any two of these upper and/or lower values. For example, the pH of the binder may be in a range of 4 to 8. Preferably, a binder pH of less than 7 may be beneficial to the electrochemical performance of the micro silicon anode and may be due to (i) the reduced corrosion of pure silicon in the acidic region and/or (ii) silicon's greater affinity to interact with binders, such as for example PAA.
In some embodiments or examples, the viscosity of the anode slurry may be in a range between about 10 mPas and 100,000 mPas. The viscosity (mPas) may be less than about 100,000, 90,000, 80,000, 70,000, 60,000, 50,000, 40,000, 30,000, 20,000, 10,000, 8000, 6000, 4000, 2000, 1000, 800, 600, 400, 200, 100, 50, or 10. The viscosity may be at least about 10, 20, 40, 60, 80, 100, 300, 500, 700, 900, 1000, 3000, 5000, 7000, 9000, 10,000, 20,000, 30,000, 40,000, 50,000, 60,000, 70,000, 80,000, 90,000, or 100,000. The viscosity (mPas) of the anode slurry may be in a range provided by any two of these upper and/or lower amounts. For example, viscosity (mPas) of the anode slurry may be in a range of about 2500 mPas to about 8000 mPas. All viscosity values recited herein may be at a given shear rate. In embodiments the shear rate may be that as used in any accepted standard testing approach in the art.
In some embodiments or example, the thickness of the dry anode composition may be in a range between about 5 μm to about 45 μm. The thickness (μm) of the dry anode composition may be less than about 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 8, 6, or 5. The thickness (μm) of the dry anode composition may be at least about 5, 6, 8, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, or 70. The thickness (μm) of the dry anode composition may be in a range provided by any two of these upper and/or lower values.
In some embodiments or examples, the wet anode composition layer may be maintained at a temperature of between about 40° C. and about 60° C. in step (iii) (a) for about 30 seconds to about 5 minutes. The wet anode composition may be maintained at a temperature (° C.) of less than about 60, 55, 50, 45, or 40. The wet anode composition may be maintained at a temperature (° C.) of at least about 40, 45, 50, 55, or 60. The wet anode composition may be maintained at a temperature (° C.) in a range provided by any two of these upper and/or lower values. The wet anode composition may be maintained at a temperature as described herein for less than about 24 hours, 12 hours, 8 hours, 4 hours, 2 hours, 1 hours, 30 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, 1 minute, or 30 seconds. The wet anode composition may be maintained at a temperature as described herein for at least about 30 seconds, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 10 hours, 12 hours, or 24 hours. The wet anode composition may be maintained at a temperature as described herein for a time in a range provided by any two of these upper and/or lower values.
In some embodiments or examples, the wet anode composition may be maintained at a temperature of between about 90° C. and about 180° C. in step (iii) (b) for about 30 seconds to about 5 minutes. The wet anode composition may be maintained at a temperature (° C.) of less than about 180, 170, 160, 150, 140, 130, 120, 115, 110, 105, 100, 95 or 90. The wet anode composition may be maintained at a temperature (° C.) of at least about 90, 95, 100, 105, 110, 115, 120, 130, 140, 150, 160, 170, or 180. The wet anode composition may be maintained at a temperature (° C.) in a range provided by any two of these upper and/or lower values. The wet anode composition may be maintained at a temperature as described herein for less than about 24 hours, 12 hours, 8 hours, 4 hours, 2 hours, 1 hours, 30 minutes, 5 minutes, 4 minutes, 3 minutes, 2 minutes, 1 minute, or 30 seconds. The wet anode composition may be maintained at a temperature as described herein for at least about 30 seconds, 1 minute, 2 minutes, 3 minutes, 4 minutes, 5 minutes, 30 minutes, 1 hour, 2 hours, 4 hours, 10 hours, 12 hours, or 24 hours. The wet anode composition may be maintained at a temperature as described herein for a time in a range provided by any two of these upper and/or lower values.
In some embodiments or examples, the anode slurry can be made homogeneous to provide further advantages/improvements.
In some embodiments or examples, the present disclosure is directed to a process for assembling an electrochemical cell, whereby the process may comprise the steps of: preparing an anode as defined by the process at least according to any one of the examples described herein, wherein the anode may comprise an anode composition comprising micro silicon active material particles; and assembling the anode into an electrochemical cell. In some other embodiments or examples, the present disclosure is directed to a process for assembling an electrochemical cell, whereby the process may comprise the steps of: preparing an anode as defined by the process at least according to any one of the examples described herein, wherein the anode may comprise or consist of an anode composition comprising micro silicon active material particles, optionally one or more further active materials, optionally one or more binders, and optionally one or more conductive materials, at least according to any one of the examples described herein; and assembling the anode into an electrochemical cell.
Upon formation of the anode slurry, some or all of the solvent may be removed (e.g., by natural evaporation, forced evaporation or under vacuum) to generate a solid or viscous anode slurry. The anode slurry may be formed or moulded in any desired shape, such as an anode.
In some embodiments or examples, the anode slurry may also be deposited on a current collector material, as defined herein, to generate an anode. It will be appreciated that the anode is the combination of the current collector material and the anode composition, also referred to as an anode composition applied to a current collector material. The current collector material can be selected from any current collector material referred to herein.
During preparation of an anode, the anode composition may be applied to only a portion of the surface of the current collector material. In some embodiments or examples, the portion (%) may be less than about 100, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5. In some embodiments or examples, the anode composition may be applied by casting on the current collector material (e.g. roll-to-roll processing).
It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the above-described embodiments, without departing from the broad general scope of the present disclosure. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
The present disclosure is further described by the following examples. It is to be understood that the following description is for the purpose of describing particular examples only and is not intended to be limiting with respect to the above description.
Various commercially available silicon materials may be used to prepare the anode compositions, as described herein, and further exemplified in the Examples. An example of a select number of characteristics including its PSD, BET surface area and measured impurities (measured via ICP-AES) of such a silicon material is given in Table 1 below.
It will be appreciated that impurities may be present in the silicon material, one such example is as shown in Table 1 above. Such impurities may be present in the micro silicon active material particle, preferably in the quantities of less than about 3000 ppm total impurities.
To prepare the anode slurry, a binder solution and a conductive material are combined using a planetary-centrifugal mixer. The mixture is then incorporated at 2000 rpm for 2 minutes, manually mixed with a spatula, and then mixed for another 2 minutes. The micro silicon active material particles and required amounts of additional water are added and the mixing steps are repeated. An active graphite is added, and the mixing steps are repeated. Unless otherwise mentioned a pre-determined amount of anode slurry is transferred to a Dispermat-compatible container and is mixed at 6000 rpm using an overhead mixer (e.g.: VMA-Getzmann Dispermat) for 5 minutes.
In a full cell assembly, the slurries were cast onto copper foil and dried at 60° C. then cut for coin cell assembly. The electrodes (coated anodes and commercially supplied NCM 523 cathodes) were further dried under vacuum for 12 h at 110° C. 150 μL of an electrolyte (e.g. 1M LiPF6 in FEC/DEC (2:8) vol. %) was used and a separator (e.g. Whatman fiberglass) for the coin cell (CR 20232 type) assembly. For charge/discharge cycling tests, the coin cells were activated at 0.05C for 1 cycle and then cycled at 0.5C for long-term stability testing. The C rates were based on the mass of active material (Si particles, graphite) in the electrodes. The voltage range for charge/discharge tests was 4.2-2.5V during formation and 4.2-3V during cycling. The charge/discharge tests were conducted on Neware multi-channel battery testers controlled by a computer. Four replicate cells were made and tested for each condition.
In a half cell assembly, the slurries were cast onto copper foil and dried at 60° C. then cut for coin cell assembly. The electrodes were further dried under vacuum for 12 h at 110° C. Lithium (Li) metal was used as the counter electrode. 150 μL of an electrolyte (e.g. 1M LiPF6 in FEC/DEC (2:8) vol. %) was used and a separator (e.g. Celgard 2500) for the coin cell (CR 2032 type) assembly. For charge/discharge cycling tests, the coin cells were activated at 0.05C for 1 cycle followed by two cycles at 0.1C and then cycled at 0.5C for long-term stability testing. The C rates were based on the mass of active material (Si particles, graphite) in the electrodes. The voltage range for charge/discharge tests was 0.005-1.50 V vs. Li. The charge/discharge tests were conducted on Neware multi-channel battery testers controlled by a computer. Four replicate cells were made and tested for each condition.
Each silicon material was tested using the micro-silicon anode composition, as described in Example 1, wherein the micro-silicon active material particles content is about 70%.
It will be appreciated that one (1) battery slurry is fabricated per micro-silicon sample.
For each silicon anode configuration assembled:
All micro-silicon containing anodes were paired with a NCM 523 cathode in a 30 to 36% limited capacity test set-up. The 30 to 36% capacity limitation refers to the degree to which the anode is utilized. In practical terms this means that the anode area capacity is oversized in comparison to the cathode. Given that the cathode contains the lithium stock of the cell upon cell assembly, the area capacities of both electrodes were chosen such that only a maximum of 30 to 36% of anode lithiation is possible upon first charge.
The specific coating capacity for the anode was calculated by dividing the capacity the full cell delivers per cm2 of cathode by the weight of the anode coating in g per cm2. The resulting cycling capacity values at a rate of C/2 (2nd cycle onwards) fall within the target range of 600 to 700 mAh/g for all anode configurations. The cycling graph comparison based on the specific anode coating capacity is shown in
The specific coating capacity for the cathode was calculated by dividing the capacity the full cell delivers per cm2 of cathode by the weight of the cathode coating in g per cm2. The resulting values for all anode configurations fall within the target range of 160 to 165 mAh/g. This capacity figure is expected given the NCM 523 cathode material that is used.
An anode composition consisting of 70% micro-silicon was fabricated. The specific electrode composition used for all experiments in Example 2 is shown in Table 2 below.
Material quantities specified in Table 2 were used for the slurry preparation process of Elkem 1, 2, 3 and 4 micro-silicon materials. The slurries were prepared using the procedure in Example 1.
The electrochemical test set-up used for full cells is as described in Example 1. The test program is detailed in Table 3 below.
Current density used for cycling test is based on electrode capacity obtained for the last delithiation step of formation program.
The Elkem 1, 2 and 3 silicon materials showed superior electrochemical performance compared to Elkem 4 resulting an ICE of >89% and a higher capacity retention. At 95.3% capacity retention, Elkem 2 showed 24 more cycles compared to Elkem 1, 29 cycles compared to Elkem 3 and 131 cycles compared to Elkem 4. Decreasing the SSA has resulted in improving the electrochemical behavior by increasing ICE and extending the cycle life of the Si anode.
An overview of the limited capacity full cell electrochemical data is shown in Table 5 below.
The following table provides the micro silicon active material particle D50 particle size, BET surface area and the ratio of D50 to BET surface area.
The ranges for D50 particle size, BET surface area and the ratio between D50 particle size to BET surface area in Table 6 were defined as a representative range for obtained measured values.
The silicon material with 1.0 to 3.5 ratio of D50 particle size to BET surface area resulting from the 3.0 to 6.0 μm D50 particle size and the BET surface area range of 1.0 to 3.5 m2/g exhibited a superior cycle life when compared to higher (3.5-6.0) or lower (0.01-1.0) ratios of D50 particle size to BET surface area resulting from both higher (6.0-8.0 μm) and lower (0.1-3.0 μm) D50 particle sizes and higher BET surface areas (>3.5 m2/g).
The electrochemical test set-up used for half-cells is as described in Example 1. The test program is detailed in Table 7 below.
Current density used for cycling test is based on electrode capacity obtained for the last delithiation step of formation program.
All half cells were tested under full lithiation conditions.
The following Table provides a summary of the micro silicon active material D50 particle size, BET surface area, ratio of D50 particle size to BET surface area and the corresponding electrochemical data for half-cell measurements.
Each micro-silicon containing anode was paired with a NCM 523 cathode in a 30%, 50% and full capacity test set-up. The degree of capacity limitation refers to the degree to which the anode is utilized. In practical terms this means that the anode area capacity is oversized in comparison to the cathode. Given that the cathode contains the lithium stock of the cell upon cell assembly, the area capacities of both electrodes were chosen such that only a maximum capacity that translates to the chosen degree of anode lithiation is utilized upon first charge.
An anode composition consisting of 70% micro-silicon was fabricated. The specific electrode composition used for all experiments is shown in Table 10 below.
Firstly, polyacrylic acid (18.20 g) (PAA, 250 kDa, 25% neutralised) and conductive carbon black Super C65 (0.91 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (24.20 g) and micro-silicon (31.85 g), and the mixing steps were repeated. Finally, flaked graphite (9.10 g) was added and the mixing steps were repeated. 64.81 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 6000 rpm for 5 minutes.
The full cells were assembled using the procedure described in Example 1. Cycling program is a shown in Table 3 and 4 above.
Increasing the capacity limitation increases the stress on the tested anode composition in the full cells, where ICE increases with higher capacity utilisation and the capacity retention decrease. At 99% capacity limitation, the ICE was 0.4% higher than the 35% capacity limitation (Table 11). Limiting the capacity down to 35% the cycle life was extended by more than 258 cycles to reach the same level of capacity retention as 99% capacity limitation (
An anode composition consisting of 70% micro-silicon was fabricated. The specific electrode composition used for all experiments is shown in Table 12 below.
Firstly, polyacrylic acid (18.20 g) (PAA, 250 kDa, 25% neutralised) and conductive carbon black Super C65 (0.91 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (24.20 g) and micro-silicon (31.85 g), and the mixing steps were repeated. Finally, flaked graphite (9.10 g) was added and the mixing steps were repeated. 64.81 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 6000 rpm for 5 minutes.
Electrochemical test-program is set up as follows:
The slurries were cast onto copper foil and dried at 60° C. then cut for coin cell assembly. The electrodes were further dried under vacuum for 12 h at 110° C. Lithium (Li) metal was used as the counter electrode and Celgard separator was used. 150 μL 1M LiPF6 in FEC/DEC (2:8) vol. % was used as electrolyte for the coin cell assembly. The coin cells were lithiated at 0.05C for 1 cycle and stopped when capacity reached the required degree of prelithiation. The C rates were based on the mass of active material (Si particles, graphite) in the electrodes. Two replicate cells were made and tested for each condition.
Coin cells were taken down and introduced to the glove box (under Ar atmosphere) and disassembled for full cell preparation. Anodes were washed with DMC and dried prior to assembly. The full cells were assembled using the procedure described in Example 1. Please see Table 3 and 4 for the cycling program.
Similar capacity limitation was used to compare the prelithiated and the unlithiated full cells. Initial Coulombic efficiency increased on average by 1% from 89% up to 90%.
Cycling capacity and average coulombic efficiency increased substantially. Negligible capacity loss was observed over the initial 330 cycles. A lithium reservoir of 20% reached 95% capacity retention at 260 cycle and 80% retention after 680 cycles (
An anode composition consisting of 70% micro-silicon was fabricated. The specific electrode composition used for all experiments is shown in Table 15 below.
Firstly, polyacrylic acid (19.24 g) (PAA, 250 kDa, 25% neutralised) and conductive carbon black Super C65 (0.94 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (14.91 g) and micro-silicon (33.67 g), and the mixing steps were repeated. Next, flaked graphite (9.62 g) was added and the mixing steps were repeated. Finally, pre-dispersed carbon nanotube solution (6.01 g) was added, and the mixing steps were repeated. 60.31 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 6000 rpm for 5 minutes.
Direct contact experimental setup:
The slurries were cast onto copper foil and dried at 60° C. and then cut for coin cell assembly. The electrodes (coated anodes and commercially supplied NCM 523) were further dried under vacuum for 12 h at 110° C. The electrodes were then introduced inside Ar glove box where the prelithiation process was performed. The silicon anode was brought into direct contact with the lithium foil for a specific time (Table 16) with an electrolyte medium between them (2.0 ml of 1 M LiPF6 in FEC/December 2:8 V %). Pressure (certain weight) was applied to establish a direct contact between the silicon and lithium foil (Table 16) thereby initiating the prelithiaton process. The prelithiation process outcome and the degree of the prelithiation are dependent on contact duration, applied pressure and the homogeneity of the contact.
Based on thermodynamics, the lithium metal foil will spontaneously react with silicon (Si) to form Li—Si alloy as follows:
where ΔG was the Gibbs free energy of the total reaction, E was the potential of the total reaction, and F the Faraday constant. E was assumed to be ˜0.1 V according to experimental data.
The prelithiated electrodes were then assembled onto full cells using the procedure described in Example 1. Please see Table 3 and 4 for the cycling program.
The direct contact prelithiation increased ICE for every electrode compared to the control. The percentage lithiation that can be achieved is a factor of contact time and the applied pressure. Table 17 shows the capacity retention of the cells at cycle 90, where both the 200 g/5 min and 100 g/5 min (pressure/time) have the same capacity retention (98.9%) and best performing samples the 200 g/10 min and 100 g/15 min also have the same capacity retention (101%). It is evident that the degree of prelithiation can be controlled by controlling contact time and the applied pressure.
The specific electrode composition used for this experiment is shown in Table 18 below.
Firstly, carboxymethyl cellulose binder (52.00 g, CMC) and conductive carbon black Super C65 (0.52 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (18.30 g) and micro-silicon (18.20 g), and the mixing steps were repeated. Next, flaked graphite (5.20 g) was added and the mixing steps were repeated. Finally, styrene-butadiene rubber (2.08, SBR) was added and mixed at 900 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. 72.47 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 900 rpm for 5 minutes.
Firstly, polyacrylic acid (18.20 g) (PAA, 250 kDa, 25% neutralised) and conductive carbon black Super C65 (0.91 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (19.25 g) and micro-silicon (31.85 g), and the mixing steps were repeated. Finally, flaked graphite (9.10 g) was added and the mixing steps were repeated. 61.01 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 3000 rpm. Extra water (3.81 g) was added to the mixture dropwise and the mixing speed was increased to 6000 rpm for 5 minutes.
The full cells were assembled using the procedure described in Example 1. The cycling program is as shown in Table 3 and 4 above.
Full cell results using 8% PAA binder were used to compare the effect of binders on the electrochemical performance of 70% micro-Si anode. The use of CMC/SBR binder have improved ICE by 0.6% when compared to PAA binder. However, the CMC/SBR full cells lost 20% of capacity after only ˜155 cycles whereas the PAA full cells lost the same amount of capacity after 277 cycles (
The degree of PAA neutralisation with LiOH, thus the resultant binder pH, showed a direct impact on the micro silicon anode electrochemical performance. A binder pH between 4 to 5 results was found to be particularly beneficial, leading to improved capacity retention while requiring lower amounts of conductive additive for further enhancement in electrode performance. When the pH of the PAA binder is above 7, the capacity retention of micro-silicon anode significantly degrades. High binder pH also leads to the requirement of higher quantities of conductive additives.
The gradually degrading electrochemical performance of the micro silicon anode at pH that is approaching 7 or above may result from the exposure of Si particles to LiOH causing the oxidation of Si. In addition, the reduced number of —COOH groups at pH above 7 may reduce the degree of esterification of siloxyl groups on the surface of Si particles that enable the formation of strong bonds between the polymer chains and the Si. This will cause PAA binder to be less efficient in countering the effects of volumetric changes of Si particles in the electrode matrix. In addition, the differences in solid content to achieve a processable slurry viscosity based on the binder pH may impact the micro silicon anode morphology further contributing to the variations in electrochemical performance.
An anode composition consisting of 70% Elkem 2 micro-silicon was fabricated. The specific electrode compositions used for all the experiments in Example 6.1 are shown in Table 20 below.
The material compositions described in Table 20 were used for slurry preparation.
The slurries without the carbon nanotubes were prepared using the procedure described in Example 1. The final mixing step with the Dispermat was omitted only for the slurry with Li0.95PAA binder.
The carbon nanotube incorporated slurries with Li0.25PAA and Li0.95PAA binder systems were prepared using the procedure described in Example 4.2 (b).
The full cells were assembled using the procedure described in Example 1. Cycling program is as shown in Table 3 and 4 above.
Overall, the addition of CNTs has improved the ICE and extended the cycle life. In the case of 25% neutralised PAA [Li0.25PAA], the addition of 0.05 wt % CNTs has increased the cycle life by 80 cycles when compared to 0% CNTs. For the 95% neutralised PAA [Li0.95PAA] example, the CNTs addition has slightly increased the ICE but the capacity retention decreased by 26 cycles (
Further, the micro-silicon electrode resulted from the anode formulation consisting of 95% neutralised PAA binder showed a relatively loosely packed morphology, which is more prone to particle disintegration and thus electrical isolation during cycling resulting poor capacity retention. In contrast, a relatively densely packed electrode morphology was resulted from the anode formulation consisting of 25% neutralised PAA binder suggesting it is less likely to undergo capacity loss due to electrical isolation of the Si particles.
The specific electrode composition used for all experiments is shown in Table 23 below.
PAA-copolymer with hydrophilic moieties (37.14 g, 9.8 wt. % solution) and conductive carbon black Super C65 (0.91 g, Nanografi, Turkey) were combined using a Thinky Mixer ARE-250 CE (Thinky Corp, USA) centrifugal-planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed in between with spatula. This was followed by the addition of water (18.05 g) and micro silicon (31.85 g), and the mixing steps were repeated. Finally, flaked graphite (9.10 g, KS6L, Imerys, Malaysia) was added and the mixing steps were repeated. 74.65 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 3000 rpm using an overhead mixer (VMA-Getzmann Dispermat, Germany). 3.81 g of water were added to the mixture dropwise (1-2 drops/second). The speed was increased to 6000 rpm and left to mix for 5 minutes.
The full cells were assembled using the procedure described in Example 1. Cycling program is as shown in Table 3 and 4 above.
The use of PAA co-polymer (hydrophilic moieties) binder showed an ICE of 90.3% and a discharge capacity of 165 mAh/g based on the weight of the cathode coating and 1357 mAh/g based on the weight of the anode coating at a rate of C/20.
A silicon dominant anode design enables accessing a high energy density compared to commercial state of the art anode formulations containing silicon as an additive material. While 70 wt % micro-silicon anode design is an already a silicon dominant system, further increment in silicon content to 90 wt % will reduce the degree of silicon utilization required to achieve the same capacity as from a 70 wt % micro-silicon anode design.
For example, if the 70 wt % micro-silicon anode design can deliver 800 mAh/g of coating capacity at 30% capacity limitation, a 1000 mAh/g can be accessed by the 90 wt % micro-silicon anode design at the same capacity limitation. This will enable designing thinner electrodes with faster Lit ion diffusion capability paving the path to new light weight battery design possibilities. In addition, the 90 wt % micro-silicon anode design can further increase the energy density and support high-rate capability.
An anode composition consisting out of 70% and 90% Elkem 2 micro-silicon was fabricated. The specific electrode composition used for all experiments is shown in Table 25 below.
The slurries were prepared using the compositions in Table 25. The procedure described in Example 4.2 (b) was used for the slurry preparation process.
The full cells were assembled using the procedure described in Example 1. Please see Table 3 and 4 for the cycling program.
The effect of mSi content (70 and 90%) was examined (
CNTs was found to improve the conductivity for LIB electrodes when used as a conductive additive, which also provides an effective conductive network for Si anode. Physical mixing is a simple and effective way to improve conductivity of Si based anode, with the disadvantage of low homogeneity and thus the lack of consistency in cycling performance. The use of CNTs during the physical mixing was found to affect the slurry viscosity, with no direct impact on slurry processibility and anode structure. Fortunately, many advantages were observed after adding the CNTs into the anode composition. An improvement in conductivity and charge transfer through the reduction of resistance was concluded, and based on the cycling tests it has extended the lifecycle by ˜90 cycles.
An anode composition consisting of 70% micro-silicon was fabricated. The specific electrode composition used is shown in Table 27 below.
Firstly, polyacrylic acid (18.20 g) (PAA, 250 kDa, 25% neutralised) and conductive carbon black Super C65 (0.91 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (19.25 g) and micro-silicon (31.85 g), and the mixing steps were repeated. Finally, flaked graphite (9.10 g) was added and the mixing steps were repeated. 61.01 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 3000 rpm using an overhead mixer (VMA-Getzmann Dispermat). 3.81 g of water were added to the mixture dropwise (1-2 drops/second). The speed was increased to 6000 rpm and left to mix for 5 minutes.
An anode composition consisting out of 70% micro-silicon was fabricated. The specific electrode composition used for all experiments is shown in Table 28 below.
Firstly, polyacrylic acid (18.20 g) (PAA, 250 kDa, 25% neutralised) and conductive carbon black Super C65 (0.89 g) were combined using a Thinky Mixer ARE-250 CE planetary mixer. The mixture was incorporated at 2000 rpm for 2 minutes and then repeated for another 2 minutes. Manual mixing was needed with a spatula in between. This was followed by the addition of water (18.53 g) and micro-silicon (31.85 g), and the mixing steps were repeated. Next, flaked graphite (9.10 g) was added and the mixing steps were repeated. Finally, pre-dispersed carbon nanotube (CNTs) solution (5.69 g) was added, and the mixing steps were repeated. 60.46 g of this complete mixture was transferred to a Dispermat-compatible container and mixed at 6000 rpm for 5 minutes.
The full cells were assembled using the procedure described in Example 1. Cycling program is as shown in Table 3 and 4.
The effect of CNTs addition was examined on the 70 wt % mSi anode, it was found that 0.05 wt % CNTs has increased the ICE by 0.3% and extended the cycle life by 85 cycles at 80% capacity retention when compared to 0% CNTs (
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022900553 | Mar 2022 | AU | national |
This application is the United States national phase of International Patent Application No. PCT/AU2023/050153 filed Mar. 7, 2023, and claims priority to Australian Patent Application No. 2022900553 filed Mar. 7, 2022, the disclosures of which are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/AU2023/050153 | 3/7/2023 | WO |
