Patent Application
20230387390
This disclosure is generally directed to coating materials for cathode active materials useful in lithium ion batteries (LIBs). The coatings include a metal fluoride (MFx), a lithium metal fluoride (Li-M-F), or both, which are stable with cathode materials such as LiFePO4, and helpful in protecting against battery degradation materials (i.e., HF, LiF, PF5−, and LiOH).
The present technology is directed towards cathode compositions including metal fluoride and/or lithium metal fluoride-containing coatings that provide stability with cathodes (e.g., such as cathodes containing LiFePO4). The present technology addresses the current need for coatings with properties superior to the current state of the art. These and other aspects and implementations are discussed in detail below.
The foregoing information and the following detailed description include illustrative examples of various aspects and implementations, and provide an overview or framework for understanding the nature and character of the claimed aspects and implementations. The drawings provide illustration and a further understanding of the various aspects and implementations, and are incorporated in and constitute a part of this specification. The foregoing information and the following detailed description and drawings include illustrative examples and should not be considered as limiting.
Various embodiments are described hereinafter. It should be noted that the specific embodiments are not intended as an exhaustive description or as a limitation to the broader aspects discussed herein. One aspect described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced with any other embodiment(s).
As used herein, “about” will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, “about” will mean up to plus or minus 10% of the particular term.
The phrase “and/or” as used in the present disclosure will be understood to mean any one of the recited members individually or a combination of any two or more thereof—for example, “A, B, and/or C” would mean “A, B, C, A and B, A and C, B and C, or the combination of A, B, and C.”
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the elements (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better illuminate the embodiments and does not pose a limitation on the scope of the claims unless otherwise stated. No language in the specification should be construed as indicating any non-claimed element as essential.
One option to prevent degradation in lithium ion batteries (“LIBs”) is to utilize a protective coating on the electrode active materials, particularly with regard to the cathode active materials used in the batteries. Cathode decomposition may occur during the structural phase transition (i.e., where lithium ions (de-)insert from the electrode material) and/or when in contact with other components of the LIBs, such as the electrolytes and current collectors. Illustrative commercially available cathode active materials include, but are not limited to, LiFePO4 (also referred to as LFP materials), LiMn1-xFePO4 (also referred to as LMFP materials), LiCoO2 (also referred to as LCO materials), Li(NiaMnbCoc)O2 (also referred to as LiNMC materials), Li(NiaCobAlc)O2 (also referred to as LiNCA materials), Li(NidCoeMnfAlg+)O2 (also referred to as LiNCMA materials), and Li(MnαNiβ)2O4 (also referred to as LNMO materials), where 0<x<1, a+b+c=1, d+e+f+g=1 and α+β=1.
In general, coatings on cathode active material provide for: 1) formation of a modified solid electrolyte interface (SEI), which helps stabilize the interface between the electrode and electrolyte; 2) improvements in electrolyte wetting to ensure uniform Li+ ion insertion and de-insertion; and, 3) suppression of surface phase transitions of cathode material (i.e., surface decomposition) as a physical barrier.
Typically, metal oxide-type coatings are used to withstand the harsh operating conditions within the LIBs. LiFePO4 tends to adsorb moisture from the surrounding due to its high surface area (e.g., composed of nano-sized primary particles and their aggregates). There are two mechanisms that can accelerate the water adsorption. The first mechanism involves hydrogen bonding formation in the surface oxygen groups of LiFePO4, especially in the uncoated area where carbon coating is not present. The second mechanism may involve the carbon coating characteristics, distribution of sp2 vs. sp3 carbon.
However, achieving uniform carbon coating on LiFePO4 without carbon defect derivatives are not an easy task. Fluoridation can help increase the hydrophobicity of oxide materials, as shown schematically in
Thus, in an aspect, the present technology provides a cathode composition that includes a metal fluoride (“MFx”) and/or a lithium metal fluoride (“Li-M-F”) coating on at least a portion of a surface of a particulate bulk cathode active material, where the coating includes a greater LiFePO4 stability score when normalized to that of AlF3 at 100%. In any embodiment herein, the coating may include the metal fluoride and may optionally further include a greater LiOH score when normalized to that of FeF2 at 100%. In any embodiment herein, the coating may include the metal fluoride and may optionally further include a greater HF score when normalized to that of Li2NiF4 at 100% and/or a greater PF5− score when normalized to that of Li2NiF4 at 100%. Thus, the coatings described herein provide equivalent or superior protection to that of AlF3, FeF2, and/or Li2NiF4 in the respective tested measurable statistics. The metal fluoride and/or lithium metal fluoride included in the coating may be crystalline (e.g., if more than few atomic layers) or amorphous (e.g., if very thin, or does not tend to crystallize).
As used herein, the LiFePO4 stability score, LiOH score, PF5− score, and HF score are determined based upon the model reaction that is to be run, as discussed in the working examples. For example, the molar ratio of components (MFx or Li-M-F) to LiFePO4 is first determined (ratio 1). The ratio is then normalized to the ratio for the baseline reaction of AlF3 by dividing ratio 1 (for AlF3) by ratio 1 (for the MFx or Li-M-F of interest) to arrive at value 1. The enthalpy of reaction (Erxn) in eV/atom is then determined from the calculation, however this is then normalized to the Erxn for AlF3 dividing the Erxn (for the MFx or Li-M-F of interest) by Erxn (for AlF3) to arrive at value 2. Value 1 and 2 are then summed, however they are based upon molar ratios. To convert the values to weight-based values, the sum is then divided by the molecular weight of the MFx or Li-M-F multiplied by 1000. The LiFePO4 stability score is then determined by dividing the per weight value for the AlF3 by the per weight value of the MFx or Li-M-F multiplied by 100. Expressed another way, the LiFePO4 stability score is a percentage improvement (or diminution) for that reaction compared to the baseline AlF3 value. Illustrative calculations are shown in the examples.
In any embodiment herein, the metal fluoride may include MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, NdF3, or a mixture of any two or more thereof. In any embodiment herein, the metal fluoride may include SrF2, LaF3, NdF3, or a mixture of any two or more thereof. In any embodiment herein, the metal fluoride may include MgF2, MnF2, FeF2, MoF3, or a mixture of any two or more thereof. In any embodiment herein, the lithium metal fluoride may include Li3AlF6, Li3ScF6, Li2NiF4, LiYF4, LiInF4, Li2SnF6, LiCeF5, LiBiF4, Li3FeF6, or a mixture of any two or more thereof. In any embodiment herein, the lithium metal fluoride may include Li3AlF6, Li3ScF6, Li2NiF4, LiBiF4, Li3FeF6, or a mixture of any two or more thereof. In any embodiment herein, the coating may include LiYF4, LiInF4, Li2SnF6, LiCeF5, or a mixture of any two or more thereof. In any embodiment herein, the coating may include LiFePO4. Such coating materials of any embodiment herein are used at a level sufficient to provide additional protection to the cathode material. For example, this may include where the metal fluoride, the lithium metal fluoride, or both the metal fluoride and the lithium metal fluoride is present from about 0.01 wt % to about 5.0 wt %. The thickness of the coating may also play in role in durability, but it may also be a hindrance to current flow. Accordingly, the coating may have an average thickness on the particulate bulk cathode active material of about 5 nm to about 2 μm. In any embodiment herein, the coating may be continuous or discontinuous. Referring to
Referring to
In any of the above embodiments, the second coating material may overcoat the first coating material, fill in voids of the first coating material on the surface of the particulate bulk cathode active material, or both overcoats the first coating material and fill in voids of the first coating material on the surface of the particulate bulk cathode active material, and the second coating material may be different from the first coating material as well as the particulate bulk cathode active material. The particulate bulk cathode active material may be a single crystal, polycrystalline, or blended (e.g., different size of single crystals, polycrystals, or mixture of single- and polycrystals), where the first and/or second coating material may be different based on the size, morphology, and/or crystallinity.
It is understood that in the commercial coating of the particulate bulk cathode active materials, commercial (i.e. the first) coating materials include voids and other irregularities on the surface of the particulate bulk cathode active material. As the second coating material is deposited onto the particulate bulk cathode active material, they typically nucleate near grain boundaries of the first coating material or the particulate bulk cathode active material. For example, they may deposit on the particulate bulk cathode active material next to the first coating material. They may also then fill the voids or uncoated areas from the first coating deposition and grow in thickness in those areas as the deposition proceeds. Where the second coating material is deposited on top of the first coating material, the second coating material may be thinner. For example, in some embodiments, a thickness of the first and/or second coating material may be about 5 nm to about 2 μm. The first coating material may formed in discontinuous regions on the surface of the particulate bulk cathode active material, and the second coating material, may be formed in the discontinuous regions of the first coating material. A portion of the second coating material formed in the discontinuous regions of the first coating coating material may have a greater thickness than other portions of the second coating material formed as an overcoating.
In any embodiment including a first coating material and a second coating material, the second coating material may be different from the first coating material and from the particulate bulk cathode active material. In any of the above embodiments, the first coating material may include a carbon coating, one or more metal phosphate(s) (for example, including AlPO4), one or more lithium metal phosphate(s) (e.g., a lithium metal phosphate where the metal is a transition or non-transition metal/metalloid with the excluding noble metals, rare earth elements, and radioactive elements, such as LiFePO4), a metal fluoride (such as AlF3, MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, NdF3, or a mixture of any two or more thereof), and/or a lithium metal fluoride (such as Li3AlF6, Li3ScF6, Li2NiF4, LiYF4, LiInF4, Li2SnF6, LiCeF5, LiBiF4, Li3FeF6, or a mixture of any two or more thereof); and the second coating material may include MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, NdF3, Li3AlF6, Li3ScF6, Li2NiF4, LiYF4, LiInF4, Li2SnF6, LiCeF5, LiBiF4, Li3FeF6, or a mixture of any two or more thereof.
As noted above, the cathode composition includes a particulate bulk cathode active material. As used herein, the particulate bulk cathode active material is the core of the particle that is coated with a thin layer of the metal fluoride and/or lithium metal fluoride coating on the surface. Generally, the particulate bulk cathode material may include one or more olivine-type cathode active materials (such as LFP and/or LMFP) and/or may include a nickel-rich cathode active material. Olivine-type cathode active materials may be nano-sized particles with a relatively high surface area, where H2O from surrounding environment (e.g., moisture) may adsorb easily; for nickel-rich cathode active materials, a Ni-rich surface may rapidly react with oxygen and/or H2O to transform to Ni-rich carbonate-like structures that may cause process issues (e.g. gelation) during slurry formation. Illustrative particulate bulk cathode active materials include materials such as lithium nickel manganese cobalt oxide (“LiNMC”), lithium nickel manganese oxide, lithium cobalt oxide (LCO), LiNCA, LiNCMA, or mixtures of any two or more thereof. In some embodiments, the particulate bulk cathode active material may include Li(NiaMnbCoc)O2, wherein 0≤a≤1, 0≤b≤1, 0≤c≤1, and a+b+c=1. In some embodiments, the particulate bulk cathode active material may include Li(NiaMnbCoc)O2, wherein 0<a<1, 0<b<1, 0<c<1, and a+b+c=1. In any embodiment herein, the particulate bulk cathode active material may include LiCoO2, Li(NiaMnbCoc)O2, Li(MnαNiβ)2O4, or a mixture of any two or more thereof, wherein a+b+c=1, and α+β=1. In any embodiment herein, the particulate bulk cathode active material may include a Li-rich Mn-rich material such as Li1+x(NiaMnbCoc)1-xO2 where 0<x<0.4 and a+b+c=1. In any embodiment herein, the particulate bulk cathode active material may include LiCoO2, Li(NiaMnbCoc)O2, Li(MnαNiβ)2O4, or a mixture of any two or more thereof, wherein 0<a<1, 0≤b<1, 0≤c<1, a+b+c=1, 0≤α<1, 0<β<1, and α+β=1. As used herein, nickel-rich cathodes are cathode active materials include 70 wt % or greater of nickel, and may include materials with greater than 80 wt % nickel.
Alternatively, or in addition, to a coating of metal fluoride and/or lithium metal fluoride on the bulk cathode active material, the metal fluoride and/or lithium metal fluoride may be coated or deposited on other surfaces within a battery cell or within a battery pouch or within a battery housing. Accordingly, in other aspects, the metal fluoride and/or lithium metal fluoride may be used as a coating on a current collector, on the separator, inside a pouch, or inside a housing.
In another aspect, a current collector includes a metal that is at least partially coated with a metal fluoride and/or lithium metal fluoride where the coating includes a greater LiFePO4 stability score when normalized to that of AlF3 at 100%. In any embodiment herein, the coating may include the metal fluoride and may optionally further include a greater LiOH score when normalized to that of FeF2 at 100%. In any embodiment herein, the coating may include the metal fluoride and may optionally further include a greater HF score when normalized to that of Li2NiF4 at 100% and/or a greater PF5− score when normalized to that of Li2NiF4 at 100%. In any embodiment herein, the metal fluoride may include MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, NdF3, or a mixture of any two or more thereof. In any embodiment herein, the metal fluoride may include SrF2, LaF3, NdF3, or a mixture of any two or more thereof. In any embodiment herein, the metal fluoride may include MgF2, MnF2, FeF2, MoF3, or a mixture of any two or more thereof. In any embodiment herein, the lithium metal fluoride may include Li3AlF6, Li3ScF6, Li2NiF4, LiYF4, LiInF4, Li2SnF6, LiCeF5, LiBiF4, Li3FeF6, or a mixture of any two or more thereof. In any embodiment herein, the lithium metal fluoride may include Li3AlF6, Li3ScF6, Li2NiF4, LiBiF4, Li3FeF6, or a mixture of any two or more thereof. In any embodiment herein, the coating may include LiYF4, LiInF4, Li2SnF6, LiCeF5, or a mixture of any two or more thereof. In any embodiment herein, the coating may include LiFePO4. In any embodiment herein, about 0.1 wt % to about 5 wt % of the metal fluoride, the lithium metal fluoride, or both the metal fluoride and the lithium metal fluoride may be included. In any embodiment herein, the coating may include an average thickness on the particulate bulk cathode active material of about 5 nm to about 2 μm.
The current collector may include a metal that is aluminum, copper, nickel, titanium, stainless steel, or carbonaceous materials. In some embodiments, the metal of the current collector is in the form of a metal foil. In some specific embodiments, the current collector is an aluminum (Al) or copper (Cu) foil. In some embodiments, the current collector is a metal alloy, made of Al, Cu, Ni, Fe, Ti, or combination thereof. In some embodiments, the metal foils maybe coated with carbon: e.g., carbon-coated Al foil, and the like.
The materials described herein are all intended for use in electrochemical devices such as, but not limited to, lithium ion batteries. Accordingly, in another aspect, the present technology provides an electrochemical cell, such as a lithium ion battery (e.g., a lithium secondary battery), that includes a cathode including a particulate bulk cathode active material and optionally a current collector and the lithium ion battery may optionally include a housing. Where the electrochemical cell is a lithium ion battery, the lithium ion battery may also optionally include an anode, a separator, an electrolyte, or a combination of any two or more thereof. The housing may be a pouch in which a battery cell is contained, or it may be the housing the battery in which the pouches are contained. In the lithium ion battery, one or more of the cathode active material, the current collector, or an inner surface of the housing is at least partially coated with a metal fluoride and/or lithium metal fluoride, where the coating includes a greater LiFePO4 stability score when normalized to that of AlF3 at 100%. In any embodiment herein, the coating may include the metal fluoride and may optionally further include a greater LiOH score when normalized to that of FeF2 at 100%. In any embodiment herein, the coating may include the metal fluoride and may optionally further include a greater HF score when normalized to that of Li2NiF4 at 100% and/or a greater PF5− score when normalized to that of Li2NiF4 at 100%. In any embodiment herein, the metal fluoride may include MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, NdF3, or a mixture of any two or more thereof. In any embodiment herein, the metal fluoride may include SrF2, LaF3, NdF3, or a mixture of any two or more thereof. In any embodiment herein, the metal fluoride may include MgF2, MnF2, FeF2, MoF3, or a mixture of any two or more thereof. In any embodiment herein, the lithium metal fluoride may include Li3AlF6, Li3ScF6, Li2NiF4, LiYF4, LiInF4, Li2SnF6, LiCeF5, LiBiF4, Li3FeF6, or a mixture of any two or more thereof. In any embodiment herein, the lithium metal fluoride may include Li3AlF6, Li3ScF6, Li2NiF4, LiBiF4, Li3FeF6, or a mixture of any two or more thereof. In any embodiment herein, the coating may include LiYF4, LiInF4, Li2SnF6, LiCeF5, or a mixture of any two or more thereof. In any embodiment herein, the coating may include LiFePO4. In any embodiment herein, the coating may about 0.1 wt % to about 5 wt % of the metal fluoride, the lithium metal fluoride, or both the metal fluoride and the lithium metal fluoride. In any embodiment herein, the coating may include an average thickness on the particulate bulk cathode active material of about 5 nm to about 2 μm.
The cathodes may include, in addition to the particulate bulk cathode active material, one or more of a current collector, a conductive carbon, a binder, or other additives. The anodes of the electrochemical cells may include lithium. In some embodiments, the anodes may also include a current collector, a conductive carbon, a binder, and other additives, as described above with regard to the cathode current collectors, conductive carbon, binders, and other additives. In some embodiments, the electrode may comprise a current collector (e.g., Cu foil) with an in situ-formed anode (e.g., Li metal) on a surface of the current collector facing the separator or solid-state electrolyte such that in an uncharged state, the assembled cell does not comprise an anode active material.
The cathodes and anodes may also each contain, independently of each other, other materials such as conductive carbon materials, current collectors, binders, and other additives. Illustrative conductive carbon species include graphite, carbon black, Super P carbon black material, Ketjen Black, Acetylene Black, SWCNT, MWCNT, graphite, carbon nanofiber, and/or graphene, graphite. Illustrative binders may include, but are not limited to, polymeric materials such as polyvinylidenefluoride (“PVDF”), polyvinylpyrrolidone (“PVP”), styrene-butadiene or styrene-butadiene rubber (“SBR”), polytetrafluoroethylene (“PTFE”) or carboxymethylcellulose (“CMC”). Other illustrative binder materials can include one or more of: agar-agar, alginate, amylose, Arabic gum, carrageenan, caseine, chitosan, cyclodextrines (carbonyl-beta), ethylene propylene diene monomer (EPDM) rubber, gelatine, gellan gum, guar gum, karaya gum, cellulose (natural), pectine, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS), polyacrilic acid (PAA), poly(methyl acrylate) (PMA), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), polyacrylonitrile (PAN), polyisoprene (PIpr), polyaniline (PANi), polyethylene (PE), polyimide (PI), polystyrene (PS), polyurethane (PU), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), starch, styrene butadiene rubber (SBR), tara gum, tragacanth gum, fluorine acrylate (TRD202A), xanthan gum, or mixtures of any two or more thereof. The current collector may include a metal that is aluminum, copper, nickel, titanium, stainless steel, or carbonaceous materials. In some embodiments, the metal of the current collector is in the form of a metal foil. In some specific embodiments, the current collector is an aluminum (Al) or copper (Cu) foil. In some embodiments, the current collector is a metal alloy, made of Al, Cu, Ni, Fe, Ti, or combination thereof. In another embodiment, the metal foils maybe coated with carbon: e.g., carbon-coated Al foil and the like.
In another aspect, a process for manufacturing a cathode for a lithium ion battery is provided. The process includes mixing a metal fluoride and/or lithium metal fluoride coated particulate bulk cathode active material (of any embodiment of the present technology) with conductive carbon and a binder in a solvent to form a slurry, coating the slurry onto a cathode current collector, and removing the solvent.
Generally, the conductive carbon species may include graphite, carbon black, carbon nanotubes, and the like. Illustrative conductive carbon species include graphite, carbon black, Super P carbon black material, Ketjen Black, Acetylene Black, SWCNT, MWCNT, graphite, carbon nanofiber, and/or graphene, graphite.
Illustrative binders may include, but are not limited to, polymeric materials such as polyvinylidenefluoride (“PVDF”), polyvinylpyrrolidone (“PVP”), styrene-butadiene or styrene-butadiene rubber (“SBR”), polytetrafluoroethylene (“PTFE”) or carboxymethylcellulose (“CMC”). Other illustrative binder materials can include one or more of: agar-agar, alginate, amylose, Arabic gum, carrageenan, caseine, chitosan, cyclodextrines (carbonyl-beta), ethylene propylene diene monomer (EPDM) rubber, gelatine, gellan gum, guar gum, karaya gum, cellulose (natural), pectine, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT-PSS), polyacrilic acid (PAA), poly(methyl acrylate) (PMA), poly(vinyl alcohol) (PVA), poly(vinyl acetate) (PVAc), polyacrylonitrile (PAN), polyisoprene (PIpr), polyaniline (PANi), polyethylene (PE), polyimide (PI), polystyrene (PS), polyurethane (PU), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), starch, styrene butadiene rubber (SBR), tara gum, tragacanth gum, fluorine acrylate (TRD202A), xanthan gum, or mixtures of any two or more thereof. The current collector may include a metal that is aluminum, copper, nickel, titanium, stainless steel, or carbonaceous materials. In some embodiments, the metal of the current collector is in the form of a metal foil. In some specific embodiments, the current collector is an aluminum (Al) or copper (Cu) foil. In some embodiments, the current collector is a metal alloy, made of Al, Cu, Ni, Fe, Ti, or combination thereof. In another embodiment, the metal foils maybe coated with carbon: e.g., carbon-coated Al foil and the like.
The solvent used in the slurry formation may be a ketone, an ether, a heterocyclic ketone, and/or distilled water. One illustrative solvent is N-methylpyrrolidone (“NMP”). The solvent may be removed by allowing the solvent to evaporate at ambient or elevated temperature, or at ambient pressure or reduced pressure. Handling of the cathode and other lithium ion battery internal components may be conducted under an inert atmosphere (N2, Ar, etc.) and/or conducted under an reducing atmosphere (e.g., H2), according to some embodiments. In some embodiments, vacuum-assisted heat treatment conditions may be utilized. Due to the hydrophobic nature of MFx and Li-M-F coatings, agglomeration and/or gelation caused by adsorption of H2O molecules in the electrodes may be significantly reduced, as depicted in
In any embodiment herein, a metal-containing precursor chemical including but not limited to metal nitrates, chloride, sulfate, etc. may be dissolved in water or an organic solvent. In some embodiments, LiOH and/or NH4F may be added to the mixture. In some embodiments, the solution may be mixed with LiFePO4 precursors (including carbon coating sources such as sucrose or citric acid) at room temperature or elevated temperature with an aging time varying from 5 min to 24 hours. The nominal MFx or Li-M-F may be targeted to be from about 0.1 wt % to about 5 wt % of the LiFePO4 powders. The pH of the solution may be controlled by the presence of acid or base in order to precipitate well-mixed precursor compounds. The mixture may be annealed at elevated temperature may be any of the following values or in a range of any two of the following values: 200° C., 400° C., 600° C., 800° C., and 1,000° C. The aging time may be any of the following values or in a range of any two of the following values: 1, 2, 3, 4, 8, 12, 16, 24, 36, 48, 60 and 72 hours.
In any embodiment herein, variously sized MFx or Li-M-F containing LiFePO4 cathode materials may be synthesized via a solid-state method. The primary particle size range for LiFePO4 may any of the following values or in a range of any two of the following values: 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, and 200 nm. In some embodiments, the secondary size range may any of the following values or in a range of any two of the following values: 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, 10, 11, 12, 13, 14, 15, and 20 μm. One exemplary, but not limiting, method of performing solid-state synthesis is a ball-milling process. In some embodiments, the solid-state method may be followed by an optional spray dryer processing step to facilitate the drying and secondary particle formation. The optimal amount of metal fluorides and/or lithium metal fluorides and its chemical composition at the electrode material surface may be tuned by the secondary heat-treatment conditions that may be any of the following values or in a range of any two of the following values: 200° C., 400° C., 600° C., 800° C., and 1,000° C. in the presence of reducing gas such as N2, Ar, H2, or gas mixture thereof. A person of ordinary skill in the art based on the present disclosure would readily understand that, depending on the particular cathode active material (e.g., LiNMC, LCO, LiNCA, LiNCMA, LNMO, Li1+x(NiaMnbCoc)1-xO2, or mixtures of any two or more thereof), heat treatment conditions may be oxidizing in the presence of oxidizing gas such as Air, O2, or gas mixture thereof.
In other embodiments, metal fluoride or Li-M-F coating materials may be deposited on the synthesized electrode active materials, as a post-treatment step. Non-limiting examples of deposition techniques include chemical vapor deposition, etching techniques, physical vapor deposition, pulsed laser deposition, emulsion, sol-gel, atomic layer deposition, and/or other deposition techniques. In some embodiments, such as atomic layer deposition, the choice of precursor chemicals may be limited to certain chemical composition as readily appreciated by a person of ordinary skill in the art.
In any embodiment herein, the loading level of cathode materials may vary from about 5 mg/cm2 to about 50 mg/cm2 and the packing density may vary from about 1.0 g/cc to about 5.0 g/cc. In some embodiments, the electrode may be assembled as the cathode in Li-ion batteries, where the anode materials may be Li metal, graphite, Si, SiOx, Si nanowire, lithiated Si, or mixture thereof. In some embodiments, a traditional liquid electrolyte including lithium hexafluorophosphate (LiPF6) dissolved in a carbonate solution may be used. In other embodiments, a solid state electrolyte including but not limited to a polymer and/or an oxide, sulfide, and/or phosphate-based crystalline structure may replace the liquid electrolyte. The cell configuration may be prismatic, cylindrical, or pouch type. Each cell can further configure together to design pack, module, or stack with desired power output.
In another aspect, the present disclosure provides a battery pack comprising the cathode active material, the electrochemical cell, or the lithium ion battery of any one of the above embodiments. The battery pack may find a wide variety of applications including but are not limited to general energy storage or in vehicles.
In another aspect, a plurality of battery cells as described above may be used to form a battery and/or a battery pack that may find a wide variety of applications such as general storage, or in vehicles. By way of illustration of the use of such batteries or battery packs in an electric vehicle,
The battery modules 115 can each include a plurality of battery cells 120. The battery modules 115 can be disposed within the housing 205 of the battery pack 110. The battery modules 115 can include battery cells 120 that are cylindrical cells (e.g.,
As noted above, battery cells 120 have a variety of form factors, shapes, or sizes. For example, battery cells 120 may have a cylindrical, rectangular, square, cubic, flat, or prismatic form factor.
The battery cell 120 can be included in battery modules 115 or battery packs 110 to power components of the electric vehicle 105. The battery cell housing 230 can be disposed in the battery module 115, the battery pack 110, or a battery array installed in the electric vehicle 105. The housing 230 can be of any shape, such as cylindrical with a circular (e.g., as depicted), elliptical, or ovular base, among others. The shape of the housing 230 can also be prismatic with a polygonal base, such as a triangle, a square, a rectangle, a pentagon, and a hexagon, among others.
The housing 230 of the battery cell 120 can include one or more materials with various electrical conductivity or thermal conductivity, or a combination thereof. The electrically conductive and thermally conductive material for the housing 230 of the battery cell 120 can include a metallic material, such as aluminum, an aluminum alloy with copper, silicon, tin, magnesium, manganese, or zinc (e.g., aluminum 1000, 4000, or 5000 series), iron, an iron-carbon alloy (e.g., steel), silver, nickel, copper, and a copper alloy, among others. The electrically insulative and thermally conductive material for the housing 230 of the battery cell 120 can include a ceramic material (e.g., silicon nitride, silicon carbide, titanium carbide, zirconium dioxide, beryllium oxide, and among others) and a thermoplastic material (e.g., polyethylene, polypropylene, polystyrene, polyvinyl chloride, or nylon), among others.
The battery cell 120 may include at least one anode layer 245, which may be disposed within the cavity 250 defined by the housing 230. The anode layer 245 may receive electrical current into the battery cell 120 and output electrons during the operation of the battery cell 120 (e.g., charging or discharging of the battery cell 120). The anode layer 245 may include an active substance.
The battery cell 120 may include at least one cathode layer 255 (e.g., a composite cathode layer compound cathode layer, a compound cathode, a composite cathode, or a cathode). The cathode layer 255 may be disposed within the cavity 250. The cathode layer 255 may output electrical current out from the battery cell 120 and may receive electrons during the discharging of the battery cell 120. The cathode layer 255 may also release lithium ions during the discharging of the battery cell 120. Conversely, the cathode layer 255 may receive electrical current into the battery cell 120 and may output electrons during the charging of the battery cell 120. The cathode layer 255 may receive lithium ions during the charging of the battery cell 120.
The battery cell 120 may include a polymer separator comprising a liquid electrolyte in the case of Li-ion batteries or a solid-state electrolyte layer 260 in the case of solid-state batteries, disposed within the cavity 250. The separator or solid-state electrolyte layer 260 may be arranged between the anode layer 245 and the cathode layer 255 to separate the anode layer 245 and the cathode layer 255. The liquid electrolyte or solid-state electrolyte layer 260 may transfer ions between the anode layer 245 and the cathode layer 255. The liquid or solid electrolytes can transfer cations (e.g., Li+ ions) from the anode layer 245 to the cathode layer 255 during a discharge operation of the battery cell 120. The liquid or solid electrolyte can transfer cations (e.g., Li+ ions) from the cathode layer 255 to the anode layer 245 during a charge operation of the battery cell 120.
The battery cell 120 may also include a pressure vent 270. The pressure vent 270 may be disposed in the housing 230. The pressure vent 270 may provide pressure relief to the battery cell 120 as pressure increases within the battery cell 120. For example, gases may build up within the housing 230 of the battery cell 120. The pressure vent 270 may provide a path for the gases to exit the housing 230 when the pressure within the battery cell 120 reaches a threshold.
The present technology, thus generally described, will be understood more readily by reference to the following examples, which are provided by way of illustration and are not intended to be limiting of the present technology.
General. First-principles density functional theory (DFT)-based methodologies can be used to determine, understand, and pre-select MF compounds and Li-M-F compounds for coating materials. The DFT algorithms are used calculate the thermodynamic stability of the materials, to identify those material shaving stable ground state structures vs. high-energy structures.
The screening strategy employed the following criteria to identify additional protective coating materials and compare them to AlF3 as an illustrative example of a coating material. The criteria included: (a) cathode stability by predicting an equilibrium or no reaction with illustrative cathode material LiFePO4; (b) stability against H2O; and (c) electrolyte stability by predicting an equilibrium or no reaction with HF, PF5−, LiF, and LiOH.
Here, first-principles density functional theory (DFT) methodologies are used to model the stability of AlF3 and LiFePO4 cathode materials using the interface app in materialproject.org, an open access materials database that is open to public.
The chemical stability for 74 MxFy compounds was tested against LiFePO4, as shown in Table 1. Table 1 shows the chemical reaction of a MFx and its corresponding reaction enthalpy when in contact with LiFePO4.
Each MFx compound was further evaluated in comparison with AlF3 for stability when in contact with LiFePO4, as illustrated in Table 2. It is desirable for a new metal fluoride coating to have a more stable interface with LiFePO4 cathode materials. For example, AlF3:LiFePO4 is 0.455:0.545=0.83. It is beneficial when the “Ratio” between the metal fluorides to LiFePO4 is low—for example, VF2:LiFePO4=0.33 which is lower than the AlF3 to LiFePO4 ratio (0.83). LiF, MgF2, CaF2, ScF3, SrF2, BaF2, LaF3, and NdF3 do not react at all with LiFePO4 cathode materials; this means that when these compounds are in contact with LiFePO4, neither the compound nor the LiFePO4 cathode material will undergo decomposition reactions. All other metal fluoride materials vs. AlF3 (“Ratio vs. AlF3”) are shown in the next column in Table 2, where it is beneficial when this value is less than 1 (i.e., less reactive against LiFePO4). For example, ratio score for VF2 is 0.33/0.83=0.40. Another key criterion is the reaction enthalpy (“Erxn”), where for the AlF3 reaction with LiFePO4 the Erxn=−0.017 eV/atom. All metal fluoride materials are compared vs. AlF3 in the “Erxn vs. AlF3,” where it is beneficial when this value is less than 1 (i.e., interfacial reaction between LiFePO4 and metal fluoride is rather unfavorable and less favorable than for AlF3). For example, NaF has Erxn value of −0.009 eV/atom and therefore “Erxn vs. AlF3,” for NaF is −0.009/−0.017=0.53. The next column, “Sum” adds the two values that are referenced to AlF3 for molar ratio and reaction enthalpy. Since these values are evaluated based on the molar fraction, these values are converted to by dividing my molecular weight in the “per mg” column: e.g., 2.00/83.98×1,000=23.8 for AlF3. Lastly, the “LiFePO4 stability score” provides the percentage improvement vs. AlF3 for all materials (e.g., 23.8/21.8×100=109.5% for MnF2).
Using the above-described assessment better or comparable coating materials for a LiFePO4 cathode can be determined as compared with AlF3. As illustrated in Table 2, LiF, MgF2, CaF2, ScF3, SrF2, BaF2, LaF3, and NdF3 do not react at all with LiFePO4 cathode materials, i.e., ideal for a coating material. In addition, Ge3F8, Ge5F12, MoF3, InF3, SnF2, SnF3, Sn3F8, Sb2F7, SbF3, Sb7F29, Sb11F43, CeF3, CeF4, HfF4, WF6, and BiF3 are better coating candidates than AlF3 (i.e., at least 25% more protective per the “LiFePO4 stability score”), and MnF2, FeF2, NiF2, and YF3 are comparable to AlF3, i.e., greater than 100% but less than 125% per the “LiFePO4 stability score”).
In a similar fashion as described for LiFePO4, reactivity between the MFx and H2O was assessed. The results are illustrated in Table 3, thus identifying metal fluorides that are more protective against H2O: LiF, MgF2, AlF3, CaF2, ScF3, MnF2, FeF2, NiF2, SrF2, YF3, MoF3, InF3, SnF2, SnF3, Sn3F8, SbF3, BaF2, LaF3, CeF3, CeF4, NdF3, and BiF3 do not react with H2O; Ge3F8, Ge5F12, Sb2F7, Sb7F29, Sb11F43, HfF4, and WF6 have a decomposition reaction with H2O.
HF can form in the liquid electrolyte when residual water/moisture is present to react with LiPF6 salt in the battery cell: LiPF6+H2O↔POF3+2HF+LiF. HF is an acid that can degrade subcomponents in battery cell. In particular, LiFePO4 can react with HF in the reactions illustrated in Table 4. Table 4 illustrates that in all ratios between HF and LiFePO4, LiFePO4 cathode material will decompose to another species; therefore, cathode materials will be lost along with their capacity to (de-)insert Li+ ions.
Typically, oxide or PO4-based coatings will be chemically converted to a fluoride-containing compound by scavenging HF where such converted materials may form a stable cathode solid electrolyte interface (“c-SEI”). However, for hydrophobic coating materials for cathode materials such as LiFePO4, materials that are stable against HF (i.e., providing a physical barrier by use as a coating) are more desirable than chemical scavengers. The HF reactivity was therefore determined for identified MFx compounds and the results shown in Table 5. LiF, CaF2, SnF2, Sn3F8, SbF3, and BaF2 were found to be reactive with HF.
PF5− is a species that forms from LiPF6 salt decomposition: LiPF6↔LiF+PF5−. Similar to HF, PF5− will decompose battery subcomponents such as LiFePO4 (see Table 6). Thus, similar to the determination of HF reactivity, the PF5− reactivity for MO(OH) candidates was determined, where an ideal MFx coating should act as a physical barrier against PF5−. As illustrated in Table 7, all MFx compounds that were stable against HF were found to be stable against PF5.
Electrolyte decomposition leads to the formation of the desirable solid electrolyte interface (SEI). The SEI is primarily composed of LiF, Li2O, Li2CO3 and other insoluble products. Enriching the SEI with LiF has recently gained popularity to improve Li cyclability. Here, it is desirable that the coatings not to consume LiF, so that it remains available for the SEI formation. Similar to the determination of HF reactivity and PF5− reactivity discussed above, the LiF reactivity for MFx compounds was determined and the results are provided in Table 8. As illustrated in Table 8, 0.25 AlF3 reacts with 0.75 LiF to form 0.25 Li3AlF6 whereas MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, CeF3, and NdF3 are stable when in contact with LiF. Thus, as used herein and in the claims, MgF2, MnF2, FeF2, SrF2, MoF3, LaF3, CeF3, and NdF3 have a greater “LiF score” than AlF3.
LiOH may also be present at the surface of cathode materials, depending on the choice of Li salt precursors. The presence of LiOH leads to the formation of H2O within the cell, and this can subsequently form HF. For most LiFePO4, LiOH may be included as a Li+ salt because Li2CO3 typically does not fully decompose in the temperature range in which LiFePO4 is synthesized. For example, LiFePO4 reacts with LiOH according to following reaction with a Erxn of −0.054 eV/atom: 0.333 LiFePO4+0.667 LiOH→0.333 FeO+0.333 Li3PO4+0.333 H2O. Similar to LiF, it is desirable that the LiOH reaction not take place when in contact with the MFx compounds in order to avoid H2O formation. Thus, similar to the determination of LiFePO4 stability, FH reactivity, and PF5− reactivity discussed above, the LiOH reactivity for MFx compounds was determined then normalized to the case of FeF2 (as AlF3 was determined to not be stable to LiF, as discussed above) to ultimately provide a “LiOH score,” as indicated in Table 9. As shown in Table 9, SrF2 is stable against LiOH, LaF3 and NdF3 are each significantly more stable than FeF2, and MgF2, MnF2, and MoF3 have comparable LiOH stability as FeF2 (89.5 to 106.8% vs. FeF2); CeF3 was determined to release H2 gas as byproduct.
Preliminarily identified ternary Li-M-F compounds are shown in Table 10 below along with the associated molecular weight and bandgap (“Eg”), where several are from Table 8 (where certain MFx compounds reacted with LiF to form a ternary Li-M-F compounds) and others are based on compositional search extending binary metal fluorides that are found to be top candidates.
Similar to the assessment for MFx compounds, each Li-M-F compound was further evaluated in comparison with AlF3 for stability when in contact with LiFePO4, as illustrated in Table 11. As illustrated by the “LiFePO4 stability score” in Table 11, 11 out of 17 Li-M-F compounds had a greater “LiFePO4 stability score” than AlF3. These 11 Li-M-F compounds were further assessed for reactivity with H2O and found not to react with H2O.
The 11 Li-M-F compounds with a greater “LiFePO4 stability score” than AlF3 were further assessed for reactivity with H2O and found not to react with H2O. The HF reactivity was also determined for the 11 Li-M-F compounds where, because AlF3 is stable against HF, Li2NiF4 was used as the reference material to provide an “HF score” and the results shown in Table 12.
For the 10 Li-M-F compounds with an HF score of 100% or greater, the LiF reactivity was determined and it was found that LiFe2F6 reacts with LiF. For the 9 Li-M-F compounds stable to LiF, the PF5− reactivity for these Li-M-F candidates was determined as compared to Li2NiF4 to provide a “PF5− score” (similar to the determination of HF score) as illustrated in Table 13. Further, similar to the determination of LiFePO4 stability, HF reactivity, and PF5− reactivity, the LiOH reactivity for the 9 Li-M-F compounds was determined then normalized to the case of Li2NiF4 to provide a “LiOH score,” as indicated in Table 14.
While certain embodiments have been illustrated and described, it should be understood that changes and modifications can be made therein in accordance with ordinary skill in the art without departing from the technology in its broader aspects as defined in the following claims.
The embodiments, illustratively described herein may suitably be practiced in the absence of any element or elements, limitation or limitations, not specifically disclosed herein. Thus, for example, the terms “comprising,” “including,” “containing,” etc. shall be read expansively and without limitation. Additionally, the terms and expressions employed herein have been used as terms of description and not of limitation, and there is no intention in the use of such terms and expressions of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the claimed technology. Additionally, the phrase “consisting essentially of” will be understood to include those elements specifically recited and those additional elements that do not materially affect the basic and novel characteristics of the claimed technology. The phrase “consisting of” excludes any element not specified.
The present disclosure is not to be limited in terms of the particular embodiments described in this application. Many modifications and variations can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. Functionally equivalent methods and compositions within the scope of the disclosure, in addition to those enumerated herein, will be apparent to those skilled in the art from the foregoing descriptions. Such modifications and variations are intended to fall within the scope of the appended claims. The present disclosure is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled. It is to be understood that this disclosure is not limited to particular methods, reagents, compounds, compositions, or devices, which can of course vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
In addition, where features or aspects of the disclosure are described in terms of Markush groups, those skilled in the art will recognize that the disclosure is also thereby described in terms of any individual member or subgroup of members of the Markush group.
As will be understood by one skilled in the art, for any and all purposes, particularly in terms of providing a written description, all ranges disclosed herein also encompass any and all possible subranges and combinations of subranges thereof. Any listed range can be easily recognized as sufficiently describing and enabling the same range being broken down into at least equal halves, thirds, quarters, fifths, tenths, etc. As a non-limiting example, each range discussed herein can be readily broken down into a lower third, middle third and upper third, etc. As will also be understood by one skilled in the art all language such as “up to,” “at least,” “greater than,” “less than,” and the like, include the number recited and refer to ranges which can be subsequently broken down into subranges as discussed above. Finally, as will be understood by one skilled in the art, a range includes each individual member.
All publications, patent applications, issued patents, and other documents referred to in this specification are herein incorporated by reference as if each individual publication, patent application, issued patent, or other document was specifically and individually indicated to be incorporated by reference in its entirety. Definitions that are contained in text incorporated by reference are excluded to the extent that they contradict definitions in this disclosure.
Other embodiments are set forth in the following claims.
