Patent Application
20230369585
The present technology is generally related to lithium rechargeable batteries. More particularly the technology relates to sacrificial additives that may be added to the cathode or anode to supply additional lithium ions or enhance the SEI layer.
In one aspect, an electrode includes an electrode active material and a lithium generating species that includes a mixture of Li3N and MNx, wherein MNx may be a metal nitride where the metal (M) may comprise Na, K, Ca, Mg, Ba, V, Nb, Ti, Zr, or Sr, or a mixture of any two or more thereof. In some embodiments, the MNx may be Ba3N2, NaN3, KN3, VN, NbN, TiN, ZrN, Sr3N2, Ca3N2, or Mg3N2, or a mixture of any two or more thereof.
In another aspect, a battery includes comprising the above electrode, a counter electrode, and an electrolyte comprising a halogen-containing species. In some embodiments, the electrode may be a cathode and the counter electrode an anode. In any of the above embodiments, the halogen-containing species is a fluoride-containing compound. In such embodiments, the fluoride-containing compound may be HF.
In one aspect, a cathode for a lithium ion battery includes a cathode active material and coating of a ternary lithium metal oxide, a ternary lithium transition metal phosphate, or a mixture thereof, wherein the metal of the ternary lithium metal oxide may comprise Ti, Mo, Mn, Co, Fe, Bi, W, or Ni, or a mixture of any two or more thereof; and the transition metal of the ternary lithium transition metal phosphate may comprise V or Cr, or a mixture thereof. In some embodiments, the ternary lithium metal oxide may comprise LiTiO2, LiMoO2, Li7Ti11O24, Li6MnO4, Li6CoO4, Li5Ti3O8, Li2CoO2, Li6FeO4, Li8BiO6, LiW2O6, or Li6NiO4, or a mixture of any two or more thereof. In any such embodiments, the ternary lithium transition metal phosphate may include LiVPO4 or LiCrPO4, or a mixture thereof. In another aspect, a battery is provided that include any of the cathodes described herein.
In a further aspect, a method of producing an electrode having a protective coating includes forming in a liquid medium a slurry including an electrode active material and a lithium generating species including a mixture of Li3N and MNx, wherein MNx is a metal nitride where the metal (M) may comprise Na, K, Ca, Mg, Ba, V, Nb, Ti, Zr, or Sr, or a mixture of any two or more thereof; applying the slurry to a current collector; removing the liquid medium to form an electrode; immersing the electrode in an electrolyte comprising a halogen-containing species; and applying a voltage to the electrode to generate an electrode having a protective coating; wherein: protective coating comprises a reaction product of the Li3N, MNx, and the halogen-containing species; the protective coating is electrically insulating and ionically conductive. In some embodiments, the halogen-containing species is HF.
Such batteries may comprise a bank of battery cells, a power unit in a vehicle, or a battery or battery cell within an electric vehicle. In further aspect, an electric vehicle comprises any of the batteries or battery cells embodied herein.
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 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.
It has now been found that a mixture of Li3N and binary nitride (MNx) materials at the battery electrode surfaces may decompose to Li+ ions and other stable phase(s) that can provide beneficial properties to a battery in which they are incorporated. In some instances, the Li3N and MNx may react to form a ternary Li-M-N compound as an intermediate species. Upon battery cell formation and activation, nitrogen or ammonia may be evolved due during the decomposition reactions. The remaining ions may then scavenge the available HF that may be present due to electrolyte decomposition, the scavenging of which can further lead to the formation of protective coating layer at the electrode surfaces.
In lithium ion batteries, fresh anode electrode surfaces consume a portion of the Li+ ions that are transported from the cathode side during the first few cycles of operation to form a stable, passivating solid electrolyte interface, or “SEI.” If the anode surface area is higher (e.g., high surface area carbon, etc.), then a larger volume of SEI will form, trapping more Li+ ions from the cathode side. These trapped Li+ ions are no longer reversible for the rechargeable battery, leading to a significant decrease for the overall cell energy density. One strategy to account for the Li+ ion loss is to use a “cathode additive” with a high concentration of Li+ ions that can supply excess amount of Li ion sources. Using Li3N as a “sole” cathode additive can balance the Li+ loss through N2 gas evolution during the 1st cycle formation cycle. The N2 can be vented from the cell to prevent pressure build-up. Here, it has been found that by adding MNK species with the LiN3, enhanced SEI layers may be formed, as well as providing protective metal fluoride coatings and other ternary lithium metal oxides to protect the electrode active materials. It has also been found that similar result, but without the generation of N2 or other gases, may be achieved by adding a ternary transition metal oxide to the electrodes, which, upon charging, decomposes into Li+ and a transition metal oxide that is stable on the surface of, and protective of, the electrode active material.
In a first aspect, an electrode for a lithium ion battery includes an electrode active material and a lithium generating species. The lithium generating species may include a mixture of Li3N and MNx, wherein MNx is a metal nitride that includes a metal (M) selected from Na, K, Ca, Mg, Ba, V, Nb, Ti, Zr, Sr, or a mixture of any two or more thereof. In other aspects, the electrode may include a coating of a ternary lithium metal oxide, wherein the metal is Ti, Mo, Mn, Co, Fe, Bi, W, or Ni, or a mixture of any two or more thereof, and/or a ternary lithium transition metal phosphate, wherein the transition metal is V or Cr, or a mixture thereof. Such coatings may be stand-alone or in conjunction with the lithium generating species.
Where the lithium generating species includes a mixture of Li3N and MNx, the metal nitride contains one or more metals (M) selected from Na, K, Ca, Mg, Ba, V, Nb, Ti, Zr, and Sr. In various embodiments, the MNx may be any one or more metal nitrides selected from Ba3N2, NaN3, KN3, VN, NbN, TiN, ZrN, Sr3N2, Ca3N2, and Mg3N2. It is to be noted that the value of x (in the MNx) is not provided as it is merely a designation of a metal nitride, the stoichiometry of which may vary and be fractional amounts when normalized to the amount of “M” to be recited. Accordingly, to the extent definition is required it may be from greater than 0 to about 5, including fractional amounts, depending on the stoichiometric ratio of the nitrogen to the metal. Even higher amounts can be expressed as fractional amounts if the metal is normalized to 1.
In some embodiments, the metal nitride is Ba3N2, NaN3, or KN3, or a combination of any two or more thereof. In such embodiments, a molar ratio of Li3N to MNx may be from greater than 0 to about 1. Here, the molar ratio in such embodiment may be greater than about 3, from 2 to 10, from 2 to 8, from 2 to 6, from 2 to 4, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10. In other embodiments, the MNx may be VN, NbN, TiN, or ZrN, or a combination of any two or more thereof. In such embodiments, a molar ratio of Li3N to MNx may be greater than about 2. For example, the molar ratio in such embodiment may be greater than about 3, from 2 to 10, from 2 to 8, from 2 to 6, from 2 to 4, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, or about 10. In still other embodiments, MNx may be Sr3N2, Ca3N2, or Mg3N2, or a combination of any two or more thereof. In such embodiments, a molar ratio of Li3N to MNx may be greater than about 0.5. For example, the molar ratio in such embodiment may be greater than about 0.75, greater than about 1, from 0.5 to 10, from 0.5 to 8, from 0.5 to 6, from 0.5 to 4, about 0.5, about 0.75, about 1, about 2, about 3, about 4, or about 5.
Where the electrode includes a lithium generating species that is a ternary lithium metal oxide, and the ternary lithium metal oxide may be one or more of LiTiO2, LiMoO2, Li7Ti11O24, Li6MnO4, Li6CoO4, Li5Ti3O8, Li2CoO2, Li6FeO4, Li8BiO6, LiW2O6, and Li6NiO4. In some embodiments, the lithium generating species may be one or more of LiTiO2, LiMoO2, LiVPO4, and LiCrPO4.
Where the electrode includes a lithium generating species that is a ternary lithium transition metal phosphate, the ternary lithium transition metal phosphate may be one or both of LiVPO4 and LiCrPO4.
The electrode that includes the lithium generating species may be a cathode or an anode. Where the electrode is present in a battery cell, the electrode that includes the lithium generating species may be a cathode, an anode, or both the cathode and anode. Where the electrode is a cathode, it may contain a cathode active material. Illustrative cathode active materials include, but are not limited to, LiFePO4, LiMnxFe1-xPO4, LiMn2O4, LiNi0.5Mn1.5O4, Li1+xM1−xO2, Li(NiaMnbCocAld)O2, or a mixture of any two or more thereof, wherein 0<x<1, and a+b+c+d=1). Where the electrode is an anode, it may contain an anode active material. Illustrative anode active materials include, but are not limited to, Li metal, graphite, Si, SiOx, Si nanowire, lithiated Si, or a mixture of any two or more thereof.
The electrode as described herein may contain from about 0.1 wt % to about 15 wt % of the lithium generating species. For example, the electrode as described herein may contain from about 0.5 wt % to about 5 wt %, or about 1 wt % to about 3 wt % of the lithium generating species.
The electrodes may also contain 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 (Plpr), 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 cathode 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 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.
In another aspect, a method of introducing the lithium generating species that includes a mixture of the LiN3 and MNx to the electrode is provided. The method includes suspending a cathode or anode active material with the LiN3 and MNx in a solvent to form a slurry, coating the slurry on a current collector, and then driving off the solvent to leave a coated current collector as the electrode. The slurry may also include one or more conductive carbons, binders, and other additives. The MNx may be a metal nitride including one or more metals (M) selected from Na, K, Ca, Mg, Ba, V, Nb, Ti, Zr, and Sr.
Where the lithium generating species is the lithium transition metal oxide or phosphate, a method of introducing the lithium generating species to the electrode or the electrode active material is provided. However, here the lithium transition metal oxide/phosphate may be separately generated and mixed with the cathode or anode active material as described above, or it may include adding lithium transition metal oxide/phosphate precursors to the cathode or anode active material to form a mixture, and sintering the mixture to generate the cathode or anode active material surface-coated with a lithium transition metal oxide or phosphate.
Where the lithium generating species is the lithium transition metal oxide or phosphate, a method of introducing the lithium generating species to the electrode or the electrode active material may also include depositing on the electrode material a lithium transition metal oxide or phosphate using the appropriate stoichiometric ratios of the metal constituents of the layer via chemical vapor deposition (CVD), physical vapor deposition (PVD), pulsed laser deposition (PLD), emulsion, sol-gel, atomic layer deposition (ALD), and/or other deposition techniques. For example, a lithium transition metal oxide or phosphate may be deposited via ALD using precursor materials containing lithium, the metal or metal oxide, and a phosphorus source. In one embodiment, the target precursors are dissolved in H2O and/or organic solvent such EtOH, acetone, methanol, isopropyl alcohol (IPA), and the like, and then slowly evaporating the solvent to form the lithium transition metal oxide or phosphate during the calcination process.
Illustrative conductive carbon species for use in the methods include, but are not limited to, graphite, carbon black, Super P carbon black material, Ketjen Black, Acetylene Black, SWCNT, MWCNT, graphite, carbon nanofiber, and/or graphene, graphite. Illustrative binders include, but are not limited to, polymeric material 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 (Plpr), 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 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, He, Ag, etc.), according to some embodiments. The cathode current collector may include a metal that is 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 embodiment, 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, etc.
The active material may be loaded onto the current collector such that after solvent removal coverage is from about 5 mg/cm2 to about 50 mg/cm2 (“Loading Level”), and the packing density may vary from about 1.0 g/cc to about 5.0 g/cc. More specifically, the loading level may be about 15 mg/cm2 to 35 mg/cm2. The electrode packing density may be greater than 2.0 g/cc, approaching 4.0 g/cc.
In a further aspect, a battery cell is provided that includes a cathode, an anode, an electrolyte, and, optionally a separator between the cathode and anode, wherein the cathode, the anode, or both the cathode and the anode include a lithium generating species as described above. For example, the lithium generating species may be include a mixture of Li3N and MNx, a ternary lithium metal oxide as described above, a ternary lithium transition metal phosphate as described above, or a mixture of any two or more thereof. In the battery cell, the electrolyte may be a solution phase electrolyte or a solid-state electrolyte. Solution phase electrolytes may include a lithium salt such as lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis-trifluoromethanesulfonimide (LiTFSI), or lithium difluoro(oxalate)borate (LiDFOB), and a carbonate solvent such as a dimethyl carbonate (DMC), ethylene carbonate (EC), and diethyl carbonate (DEC), among others. Solid-state electrolytes may include a metal oxide, a metal sulfide, or a metal phosphate crystalline structure that is electronically insulating but ionically conductive (i.e., allows lithium-ion migration). Such battery cells may be prismatic, cylindrical, or pouch type cells.
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, prismatic cells, or pouch cells, for example. The battery module 115 can operate as a modular unit of battery cells 120. For example, a battery module 115 can collect current or electrical power from the battery cells 120 that are included in the battery module 115 and can provide the current or electrical power as output from the battery pack 110. The battery pack 110 can include any number of battery modules 115. For example, the battery pack can have one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve or other number of battery modules 115 disposed in the housing 205. It should also be noted that each battery module 115 may include a top submodule 220 and a bottom submodule 225, possibly with a thermal component 215 in between the top submodule 220 and the bottom submodule 225. The battery pack 110 can include or define a plurality of areas for positioning of the battery module 115. The battery modules 115 can be square, rectangular, circular, triangular, symmetrical, or asymmetrical. In some examples, battery modules 115 may be different shapes, such that some battery modules 115 are rectangular but other battery modules 115 are square shaped, among other possibilities. The battery module 115 can include or define a plurality of slots, holders, or containers for a plurality of battery cells 120.
Battery cells 120 have a variety of form factors, shapes, or sizes. For example, battery cells 120 can have a cylindrical, rectangular, square, cubic, flat, or prismatic form factor. Battery cells 120 can be assembled, for example, by inserting a winded or stacked electrode roll (e.g., a jellyroll) including electrolyte material into at least one battery cell housing 230. The electrolyte material, e.g., an ionically conductive fluid or other material, can generate or provide electric power for the battery cell 120. A first portion of the electrolyte material can have a first polarity, and a second portion of the electrolyte material can have a second polarity. The housing 230 can be of various shapes, including cylindrical or rectangular, for example. Electrical connections can be made between the electrolyte material and components of the battery cell 120. For example, electrical connections with at least some of the electrolyte material can be formed at two points or areas of the battery cell 120, for example to form a first polarity terminal 235 (e.g., a positive or anode terminal) and a second polarity terminal 240 (e.g., a negative or cathode terminal). The polarity terminals can be made from electrically conductive materials to carry electrical current from the battery cell 120 to an electrical load, such as a component or system of the electric vehicle 105.
For example, the battery cell 120 can include lithium-ion battery cells. In lithium-ion battery cells, lithium ions can transfer between a positive electrode and a negative electrode during charging and discharging of the battery cell. For example, the battery cell anode can include lithium or graphite, and the battery cell cathode can include a lithium-based oxide material. The electrolyte material can be disposed in the battery cell 120 to separate the anode and cathode from each other and to facilitate transfer of lithium ions between the anode and cathode. It should be noted that battery cell 120 can also take the form of a solid state battery cell developed using solid electrodes and solid electrolytes. Yet further, some battery cells 120 can be solid state battery cells and other battery cells 120 can include liquid electrolytes for lithium-ion battery cells.
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 can be rigid or not rigid (e.g., flexible).
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 can include at least one anode layer 245, at least one cathode layer 255, and an electrolyte layer 260 disposed within the cavity 250 defined by the housing 230. The anode layer 245 can 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 can include an active substance. The active substance can include, for example, an activated carbon or a material infused with conductive materials (e.g., artificial or natural Graphite, or blended), lithium titanate (Li4Ti5O12), or a silicon-based material (e.g., silicon metal, oxide, carbide, pre-lithiated).
The prismatic battery cell 120 (
The present invention, 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 invention.
Rechargeable Batteries. Metal nitride (MNx) compounds were studied for possible use in conjunction with Li3N as an additive in cathodes and anodes for lithium ion batteries. While Li3N may serve as a Li reservoir, the metal nitrides described herein will assist in formation of a stable SEI on the electrode materials during the cell activation, electrolyte decomposition, and cycling. HF, formed during the electrolyte decomposition event, serves as an activation agent to transform MNx to MFx or Li-M-F compounds. The Li-M-F materials formed may be able to benefit in terms of ionic diffusivity in Li-ion batteries, when to compare with a binary MFx compound.
Table 1 summarizes a list of MNx candidate compounds that have been evaluated. The crystal structure and density of the compounds are also provided in Table 1.
The chemical reactivity of the MNx compounds was evaluated vis-à-vis their calculated reactivity with Li3N. As an example,
Type I Reactions.
Type II Reactions.
Table 5 describes HF reactions of Li-M-N compounds. In the case of Li2ZrN2, it forms a stable Li2ZrF6 compound in addition to NH3 gas. It is expected that Li2ZrF6 is ionically more conductive when to compared with metal fluoride materials. According to Table 2, the Li3N to ZrN molar ratio should be about 1 or greater: i.e., the Li3N:ZrN ratio may be 1:1, 2:1, 3:1, or greater. When the ratio between the Li3N and ZrN is 1:1, formation of Li2ZrF6 is maximized, and can protect the electrode surface. If the ratio of Li3N to ZrN is greater than 1, the excess amount of Li3N may decompose to Li+ ions and N2 gas. In the case of ZrN, incorporation on the cathode side may be beneficial due to the increased Li ionic conductivity.
In the case of Li7VN4, Li7NbN4, and Li5TiN3, all form NH3 and N2 gases that can be released by the cell vent system during the formation step. Another product of the Type II reactions is a very stable LiF protective layer. Li7VN4, Li7NbN4, and Li5TiN3 all produce a small amount of metal nitride as the product, VN, Nb5N6, and TiN, respectively. They may further react with the excess Li3N to repeat the process, but this also means that higher amounts of Li3N may be needed to consume all metal nitride reactants. The Li3N to VN or NbN ratio, therefore, should be greater than 3:1; and the Li3N to TiN ratio should be greater than 2:1.
(eV/atom)
Type III Reactions.
Table 6 is a summary of the HF reactions for ternary Li-M-N compounds that are formed as a result of the reaction between the Li3N and MNx, noted in Tables 2 and 3, i.e., Type III compounds. In the case of LiSrN, LiCaN, and LiMgN (derived from Sr3N2, Ca3N2, and Mg3N2), each is predicted to form a stable LiF phase with MF2, and release NH3 gas. Since the Type III reaction does not provide the excess Li, these material are desirable where the electrode surface needs chemical protection. The formation of both LiF and MF2 may be desirable on the anode side for forming a more stable SEI layer. If excess Li ions were to be required to be produced and to be utilized at the cathode side, the molar ratio of Li3N to Sr3N2, Ca3N2, or Mg3N2 may be greater than 1. See Table 2. An example of Mg3N2 reaction with Li3N is illustrated in
In the case of Li3AlN2 (derived from AlN) and LiGe2N3 (derived from Ge3N4), they lead to the formation of ternary Li3AlF6 and Li2GeF6 (along with Ge5F12), respectively. These compounds may be ionically more conductive than the MFx. They may be used if the electrode materials need to be protected with a Li-conducting fluoride material (similar to Li2ZrF6 case in Table 5), also suitable for protecting the cathode side. In the case of Ge3N4, the molar ratio of Li3N:Ge3N4 would be 1:2 to produce the intermediate LiGe2N3. In the case of AlN, a molar ratio of Li3N:AlN may be approximately 1:1 to produce Li3AlN2. In both cases, higher amounts of Li3N may be used to produce the excess Li ions.
Li3BN2 (produced from BN) and Li3GaN2 (from GaN) lead to the formation of NH3 gas, a stable LiF layer, and BN and GaN, respectively, similar to the Type II compounds of Table 4. In order to consume all of BN or GaN compounds, we suggest the ratio of Li3N to BN or GaN to be greater than 1. See Table 2.
(eV/atom)
Type I. Ba3N2, NaN3, and KN3.
The Type I materials do not chemically react with Li3N. When activated by HF, they will form a stable BaF2, NaF, and KF. A ratio of >0 to 1 between Li3N and the Type I compound may be used, depending on the needs of excess Li ions to compensate for the loss on the anode side vs. protection on the cathode side. Type I materials would be most desired at the cathode electrode side.
Type II: VN, NbN, TiN, and ZrN.
The Type II materials form excess Li ions via reaction with Li3N. They also form secondary, intermediate Li-M-N ternary nitride materials via reaction with Li3N. In the case of Li7VN4, Li7NbN4, and Li5TiN3, they all produce a small amount of binary metal nitride as the side product, when reacting with HF. The ratio of Li3N to VN or NbN may be greater than 3:1; and, a Li3N to TiN ratio may be greater than 2:1, if utilized on the cathode side. This will help reduce the metal nitride that is formed and increases the excess Li+ ions to be supplied to the anode side. In the case of Li2ZrN2, it forms a stable Li2ZrF6 compound, likely more ionically conductive than binary metal fluorides. The molar ratio between Li3N and ZrN should be greater than 1, and would be the best to use these on the cathode electrode side that can help with Li+ ion transport.
Type III: Li-M-N Ternary Compound Formation.
Sr3N2, Ca3N2, and Mg3N2 lead to the formation of LiF and MF2, as a suitable species to protect anode SEI. If used on the cathode side to produce excess Li+ ions, the molar ratio of Li3N to Sr3N2, Ca3N2, or Mg3N2 may be greater than 1. In the case of Li3AlN2 (derived from AlN) and LiGe2N3 (derived from Ge3N4), they lead to the formation of ternary Li3AlF6 and Li2GeF6 (along with Ge5F12), respectively. We expect the Li-M-F compounds to be more ionically conductive than binary metal fluoride compounds. In order to be utilized on the cathode side, the molar ratio of Li3N:Ge3N4 may be greater than 1:2, and Li3N:AlN may be greater than 1:1. Li3BN2 (produced from BN) and Li3GaN2 (from GaN) lead to the formation stable LiF layers, but a small amount of BN and GaN are produced as a byproduct. Therefore, the ratio of Li3N to BN or GaN may be greater than 1 to consume metal nitride and to produce excess Li+ ions.
Preparation of Electrode Materials with Li3N and MNx.
The targeted metal precursor chemicals containing MNx and Li3N may be pre-mixed under a reducing environment (e.g., Ar or N2 atmosphere). These materials, as an additive from 0.1 to 15 wt %, can be blended together with commercially available electrode materials including but not limited to LiFePO4, NMC, LMNO, graphite, Si/SiOx, etc. The ratio of Li3N and MNx can vary from 0 to 1. In another embodiment, the Li3N content may be increased if further excess Li ions are desired. Similarly, if fewer excess Li ion are desired, the Li3N content may be decreased.
The additive containing cathode/anode active materials will be mixed with conductive carbon and binder materials in N-methylpyrrolidone (NMP) solution, or other suitable solvent, to form a slurry. The slurry will be coated on to Al/Cu foil, and then dried in the oven to remove the solvent. The loading level of cathode materials may vary from 5 to 50 mg/cm2 and the packing density can vary from 1.0 to 5.0 g/cc. These electrodes may be separated a layer of separator if liquid electrolyte is used. In the case of all solid-state batteries, polymer or solid-state electrolyte may be used.
Cathode active materials may include LiFePO4, LiMnxFe1-xPO4, LiMn2O4, LiNi0.5Mn1.5O4, Li(NiaMnbCocAld)O2 (where, a+b+c+d=1), or Li-rich Mn-rich layered oxide cathodes (e.g., Li1+xM1−xO2), but are not limited to these cathode active materials. The anode materials may include Li metal, graphite, Si, SiOx, Si nanowire, lithiated Si, or mixture thereof. A traditional liquid electrolyte with LiPF6 salt, dissolved in carbonate solutions may be used. In other embodiments, a solid-state electrolyte including but not limited to oxide, sulfide, or phosphates-based crystalline structure may replace the liquid electrolyte. The cell configuration may be prismatic, cylindrical, or pouch type. Each cell may be further configured together to design pack, module, or stack with desired power output.
The cell may undergo electrolyte filling, re-filling, charging, discharging, aging, high temperature storage, or a combination of any two or more thereof. In order to promote some MFx and Li-M-Fx, the moisture level of the electrode and/or liquid electrolyte materials may be controlled at the ppm level. In one embodiment, high Ni cathode materials may contain a surface Li salts that may promote the formation of H2O, enough to form a small amount of HF to convert MNx or Li-M-N to MFx or Li-M-F. In another embodiment, nanosized LiFePO4 may be aged at the ambient atmosphere, which can increase the water content from several hundred ppm to approximately 1,000 ppm or more.
Low Voltage Oxide Materials as Sacrificial Additives for Rechargeable Batteries. Ternary lithium metal oxide or phosphate (Li-M-O or Li-M-P—O, respectively) compounds at the battery cathode surface may release Li+ ions to account for loss of lithium in the battery due to SEI formation in a first, and subsequent, charging cycle, with the metal oxide or phosphate then forming binary oxide/phosphate coating phases. Contrary to the materials in Example 1, the ternary oxide/phosphate compounds do not require a separate degassing step when the Li+ ions are electrochemically extracted during the 1st cycle formation cycle.
Here, a number of Li-M-O or Li-M-P—O compounds were initially identified having an average voltage from about 0.2 to 2.7 V vs. Li/Li+. Then, based upon the actual or predicted polymorphism, thermodynamic stability of the corresponding lithiated and de-lithiated species, and their decomposition products, the compounds of interest was further focused. Table 7 provides a summary the some of the Li-containing transition metal oxide/phosphate compounds that were initially evaluated. The table illustrates the chemical formula of the lithiated and de-lithiated species in the first column. For example, in the first row, Li0-1Ti8O13 involves the reaction between Ti8O13 and LiTi8O13. The second column shows the Hall space group notation of a given compound. In this notation, rotation, translation, and axis direction symbols are separated and inversion centers are defined by the Hall symbols. The next column shows the average voltage between the lithiated and de-lithiated species. The ability to store Li+ ions is measured by its mass (i.e., gravimetric capacity) or volume (i.e., volumetric capacity) in the next two columns. The specific energy or energy density is a measure of how much energy the battery material contains in comparison to its weight or volume, respectively.
Polymorph and Thermodynamic Stability.
The materials from Table 7 in terms of thermodynamic stability, using a convex hull distance (Ehull). When a convex hull distance is a positive number, this means that there are more stable phase mixtures at this chemical composition. For example, Li5Ti3O8 is predicted to decompose to Li2TiO3 and LiTiO2, where the Ehull is 22 meV/atom. At room temperature kBT=25 meV, the kinetic energy of any given molecule at room temperature is −36 meV, and therefore, any compound with Ehull less than ˜40 meV as defined as “nearly-stable” at room temperature conditions. In addition, some of materials listed in Table 7 are polymorphs (defined herein as when two or more crystalline phases, having different atomic arrangement in the solid state, have the same atomic content). For determining lithium transition metal oxides and phosphates of interest, only the lowest energy structure, also known as a ground state structure, was used for any polymorphic compounds. Table 8 is a list of lithiated compounds that were evaluated with regard to thermodynamic stability and polymorphism. The convex hull energy, crystal system, and space group of the candidate materials are listed in Table 8.
Voltage of Li Extraction.
Table 9 summarizes the charging reaction of lithiated compounds listed in Table 8. The second column, “Net Reactions”, describes the overall Li chemical extraction reaction (i.e., charging reaction). For example, LiTiO2 converts to TiO2, giving one molar unit of Li per LiTiO2 compound at 1.43 V vs. Li/Li+, as shown in the last column. However, this net reaction is composed of a two-step reaction: Li1TiO2→Li0.5TiO2→Li0TiO2, as shown in Table 9 and
As shown in Table 9, few of the lithiated compounds, such as LiTiO2, Li6CoO4, Li6FeO4, and LiW2O6, proceed via two-step reactions. The remaining materials undergo a one-step charging reaction, where the example for LiVPO4 is shown in
Charged Compound Stability Analysis.
Table 10 summarizes the chemical stability of delithiated compounds in Table 9. TiO2, VPO4, MoO2, CrPO4, Li7BiO6, WO3, Li5NiO4 are thermodynamically stable, even after the Li extraction from the parent compound.
Other compounds in Table 10 tend to decompose to more stable phase mixtures, where some of these compounds are known experimentally. For example, Li4Ti11O24 decomposes to Li4Ti5O12 (anode material at 1.5 V vs. Li/Li+) and TiO2. Li5MnO4 decomposes to LiMnO2 (an approximately 3 V cathode material), Li4Ti3O8 decomposes to Li4Ti5O12 anode and Li2TiO3 (4.5 V cathode material), Li1.6CoO2 decomposes to LiCoO2 (3.7 V cathode material), and Li4.5FeO4 decomposes to Li5FeO4 (an approximately 3-4 V material) and Li2FeO3 (an approximately 4 V cathode material), respectively. Some high voltage cathode materials may additionally contribute to increasing the energy density of the battery cell, especially during cell degradation/cycling.
Materials Selection.
Material selection and evaluation is summarized in Table 11 based on thermodynamic stability, average voltage, utilized Li percentage, delithiated species stability, and decomposition products.
Of the materials listed in Table 11, a number of the compounds were found to be stable and have acceptable stability for use in battery materials.
As noted, the lithium transition metal oxides and phosphates, upon initial charging and subsequent cycles, produce lithium ions that can balance out the cell capacity and account for some lithium loss to SEI formation.
Procedure.
A metal-containing precursor chemical solution may be prepared that upon sintering will produce lithium transition metal oxides or phosphates. This method may include, but is not limited to, co-precipitation methods using a continuously stirred tank reactor (CSTR). The solution may be further mixed with cathode materials including, but not limited to, NMC811, LiFePO4, Mn-substituted LiMnxMn1-xPO4 (LMFP), NMC, and LMNO cathode materials (NMC811, NMC, and LMNO are abbreviations for various phases of lithium nickel manganese (cobalt) cathode active materials), or precursors to such materials, at room temperature or elevated temperature with an aging time from 5 min to 24 hours. 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 then be annealed at elevated temperatures. Illustrative elevated temperatures may include any of the following values, or a range of any two of the following values: 200, 400, 600, 800, 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. Depending on the choice of coatings, reducing/oxidizing conditions may vary by presence of different gas agents including but not limited to N2, O2, Air, Ar, H2, CO, CO2, mixture thereof, etc. The materials may include a thin coating layer at the outer surface in the form of an island or a conformal coating.
Particles of Li-M-O or Li-M-P—O cathode additives, of varying sizes, may be synthesized via solid-state methods. They may exhibit primary and secondary particle sizes (i.e. a drupelet structure where the large particles are the secondary size and the smaller particles are the primary size). The primary particle size range may any of the following values or in a range of any two of the following values: 5, 10, 15, 20, 25, 30, 35, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 300, 400, 500, 600, 700, 800, 900 nm. One method of performing solid-state synthesis is a high-energy ball-milling (or, bead-mill) process. 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 cathode additives and its chemical composition at the electrode material surface may be tuned by the secondary heat-treatment conditions may be any of the following values or in a range of any two of the following values: 200, 400, 600, 800, and 1,000° C. in the presence of reducing gas agents such as N2, Ar, H2, or gas mixture thereof. In another embodiment, secondary heat treatment is not applied.
Metal precursor chemicals containing Li-M-O or Li-M-P—O can prepared and blended with the cathode materials. These materials may be added at an amount of about 1 to 10 wt %, when mixed together with commercially-available electrode materials. If additional excess Li ions are desired, Li3N, or other metal nitrides as above, may be used as an additional cathode additive.
In some embodiments, the cathode and/or anode active materials may be mixed with conductive carbon and/or binder materials in a solvent to form a slurry. The slurry may then be coated onto a current collector and dried in the oven to remove the solvent. The loading level of cathode materials may vary from 5 to 50 mg/cm2 on the current collector, and the packing density may vary from 1.0 to 5.0 g/cc. The anodes and cathodes will be separated by a layer of a separator.
Illustrative cathode active materials may include LiFePO4, LiMnxFe1−xPO4, LiMn2O4, LiNi0.5Mn1.5O4, Li(NiaMnbCocAld)O2 (where, a+b+c+d=1), or Li-rich Mn-rich layered oxide cathodes (e.g., Li1+xM1−xO2), but are not limited to these cathode active materials. Anode active materials may include Li metal, graphite, Si, SiOx, Si nanowire, lithiated Si, or mixture of any two or more thereof. A traditional liquid electrolyte with a salt such as, but not limited to, LiPF6 salt, and based upon carbonate solvents may be used. In other embodiments, a solid-state electrolyte may be used. Solid-state electrolytes include oxide, sulfide, or phosphate-based crystalline structures may replace the liquid electrolyte. The cell configuration may be prismatic, cylindrical, or pouch type. Each cell can further configured together to design pack, module, or stack with desired power output. An illustration of cathode and anode stacks is shown in
The cell may undergo extensive formation process which include electrolyte filling, re-filling, charging, discharging, aging, high temperature storage, and mixture thereof. In order to promote formation of MFx and Li-M-Fx, the moisture level of the electrode and/or liquid electrolyte materials may be controlled at ppm level. In one embodiment, high Ni cathode materials may contain lithium salts that the surface to promote the formation of H2O, and enough to form a small amount of HF to convert MNK or Li-M-N to MFx or Li-M-F. In another embodiment, nanosized LiFePO4 may be aged at the ambient atmosphere, increasing the water content from several hundred ppm to 1,000 ppm or more.
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, or compositions that 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.
