Patent Application
20230387389
The present technology is generally related to lithium rechargeable batteries. More particularly the technology relates to coating materials for secondary rechargeable batteries, such as lithium ion batteries (LIBs).
It has now been found that lithium transition metal phosphorus oxide (Li-M-P-O) materials may be used as coating materials on the surface of cathode active materials or on other components in lithium ion batteries (LIBs). The coatings are ionically conductive while being electronically insulating, and they can protect the underlying cathode active material from reaction with more conventional coating materials or electrolyte degradation products. Accordingly, the present disclosure provides for coatings based upon such lithium transition metal phosphorus oxides, methods for the preparation, and methods for their incorporation into LIBs.
One of the most common methods to prevent battery degradation, especially on the cathode side that experiences high voltage, is to utilize a protective coating. Typically, oxide type coatings are used to withstand the harsh, unexpected operating conditions of the LIBs. Three major roles of coatings are: 1) formation of modified cathode electrolyte interface (CEI), which help stabilize the interface between electrode and electrolyte, in particular in the event of electrolyte decomposition; 2) improves the electrolyte wetting to ensure uniform Li+ ion (de-)insertion; and, 3) suppress surface phase transition of cathode material (i.e., surface decomposition) as a physical barrier.
The present technology addresses the current need for oxide coatings with properties superior to the current state of the art. Lithium transition metal phosphorus oxide (“Li-M-P-O”) coatings provide help with thermal and electrochemical stability when applied to high Ni cathode materials. Li-M-P-O coatings also improve performance of LIBs by scavenging problematic compounds such as HF and PF5− while simultaneously being stable with nickel-rich cathodes.
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 electroactive species, particularly with regard to the cathode active materials used in the batteries. Typically, metal oxide-type coatings are used to withstand the harsh operating conditions within the LIBs. 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, LiCoO2, 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, where a+b+c=1, d+e+f+g=1 and α+β=1. Coatings on such cathode active material provide for: 1) formation of a modified solid electrolyte interface (SEI) and/or cathode electrolyte interface (CEI), 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.
LiNMC materials can operate at high voltage—e.g. above 4 V vs. Li/Li′. At such high voltages, especially during the first cycle charge cell formation step, electrolyte decomposition is prevalent, typically starting at about 4.2 V vs. Li/Li+. Al2O3 has been one of the more studied binary oxide coatings that have been utilized in LIBs. From a cell cycling perspective, it is beneficial to incorporate Al2O3 or other binary metal oxide materials as electrode coating materials. However, it has now been found that when applied to LiNMC, the Al2O3 consumes Li ions and undergoes a phase transition. For example, when Ni-rich LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode active material reacts with a Al2O3 coating, the following reaction takes place:
0.319 LiNi0.8Mn0.1Co0.1O2+0.681 Al2O3→0.082 Ni3O4+0.006 Li4MnCo5O12+0.003 LiO8+0.273 LiAl5O8+0.008 Li2Mn3NiO8
This reaction exhibits an enthalpy (Erxn) of −0.033 eV/atom. It is evident that Al2O3 is not consumed upon activation, but it causes the NMC811 cathode material to decompose. However, it has now been found that if particular Li-M-P-O compounds (described herein) are used as part of the coating, it is stable when in contact with NMC811. Accordingly, the present technology provides for coatings based upon such lithium transition metal phosphorus oxides (“Li-M-P-Os”) as well as their incorporation into LIBs.
Thus, in an aspect, an electrode composition is provided that includes a lithium transition metal phosphorous oxide (Li-M-P-O) coating on at least a portion of a surface of a particulate bulk cathode active material, wherein the particulate bulk cathode active material has a layered-type structure. In any embodiment herein, the coating may include a lithium transition metal phosphorous oxide other than LiFePO4. In any embodiment herein, the lithium transition metal phosphorous oxide may have an olivine-type structure and/or the coating may include an olivine-type structure. Crystal structures of cathode active materials and/or coatings may be classified by lithium ion mobility through a 2-D framework (layered-type structure), a 3-D framework (spinel-type structure), and a 1-D framework (olivine-type structure). The structural classification may correspond to thermal stability, ion diffusion pathways, and/or activation energy that may govern lithium ion transport in the electrode. A layered-type structure may be characterized as a two-dimensional lithium ion transport and an olivine-type structure may be characterized as uni-dimensional lithium ion transport. In any embodiment herein, the Li-M-P-O coating may include one or more of the following: a greater NMC811 stability score when normalized to that of LiFePO4 at 100%, or a greater PF5− score when normalized to that of LiFePO4 at 100%, or a greater HF score when normalized to that of LiFePO4 at 100%, or a lower LiF score when normalized to that of LiMnPO4 at 100%, or a greater LiOH score when normalized to that of LiFePO4 at 100%. Thus, the coatings described herein provide equivalent or superior protection to that of LiFePO4.
As used herein, the NMC811 stability, HF, PF5−, LiF, and LiOH scores 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 (HF or PF5) to Li-M-P-O is first determined (ratio 1). The ratio is then normalized to the ratio for the baseline reaction of LiFePO4 by dividing ratio 1 (for LiFePO4) by ratio 1 (for the Li-M-P-O of interest) to arrive at value 2. The enthalpy of reaction (Erxn) in eV/atom is then determined from the calculation, however this is then normalized to the Erxn for LiFePO4 dividing the Erxn (for the Li-M-P-O of interest) by Erxn (for LiFePO4) 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 Li-M-P-O multiplied by 1000. The PF5− or HF score is then determined by dividing the per weight value for the LiFePO4 by the per weight value of the Li-M-P-O multiplied by 100. Expressed another way, the PF5− or HF score is a percentage improvement (or diminution) for that reaction compared to the baseline LiFePO4 value. Illustrative calculations are shown in the examples.
In some embodiments, the lithium transition metal phosphorous oxide includes LiMnPO4, LiCoPO4, LiNiPO4, LiSnPO4, LiV(PO3)4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof. In some embodiments, the lithium transition metal phosphorous oxide includes LiCoPO4, LiNiPO4, LiSnPO4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof. In some embodiments, the lithium transition metal phosphorous oxide includes LiCoPO4, LiSnPO4, Li3Mn3(PO4)4, or a mixture of any two or more thereof. In any embodiment herein, the lithium transition metal phosphorus oxide may also include LiFePO4 in addition to one or more lithium transition metal phosphorus oxides that are not 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 lithium transition metal phosphorous oxide is present from about 0.01 wt % to about 5.0 wt % of the electrode composition. 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 nm. 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 (e.g., 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 um. The first coating material may be 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 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 LiFePO4 and/or one or more other lithium metal oxide(s); and the second coating material may include includes LiMnPO4, LiCoPO4, LiNiPO4, LiSnPO4, LiV(PO3)4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof.
In any embodiment herein, the lithium transition metal phosphorous oxide coating may include a redox voltage greater than 4 V vs. Li/Li′. Such a redox voltage is much higher than LiFePO4, where particulate olivine-type materials having a redox voltage greater than 4V vs. graphite include but are not limited to—LiCoPO4, LiNiPO4, LiSnPO4, a mixture of any two more thereof, or a mixture of any one or more thereof with LiFePO4 and/or LiMnPO4. In any embodiment herein, the lithium transition metal phosphorous oxide coating may include a redox voltage (vs. Li/Li+) greater than LiFePO4, LiMnPO4, or a combination of LiFePO4 and LiMnPO4. In any embodiment herein, the lithium transition metal phosphorous oxide coating may include LiFePO4 and a dopant, wherein the dopant increases a de-lithiation voltage of the coating (thus reducing potential de-lithiation) relative to the coating without the dopant. Suitable dopants include, but are not limited to, Co, Si, Sn, Al, Cu, Zn, Ga, Y, Zr, and/or Hf and may provide a material according to the formula LiFe1-xMxPO4 or the formula LiMn1-xMxPO4, where in each formula M is independently Co, Ni, and/or Sn and 0<x<1. In an olivine-type structured lithium transition metal phosphorous oxide, at least a portion of the lithium transition metal phosphorous oxide may be crystalline.
As noted above, the electrode composition includes a particulate bulk cathode active material having a layered-type structure. As used herein, the particulate bulk cathode active material is the core of a particle that is coated with a thin layer of the lithium transition metal oxide coating on the surface. Generally, the particulate bulk cathode active material may be a nickel-rich cathode active material. Illustrative particulate 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 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<a<1, 0<β<1, and α+β=1. As used herein nickel-rich cathodes are cathode active materials including 70 wt % or greater of nickel. This may include materials with greater than 80 wt % nickel.
Alternatively, or in addition, to a Li-M-P-O coating on particulate bulk cathode active material, a Li-M-P-O may be coated or deposited on other surfaces within a battery cell or within a battery pouch or within a battery housing where the Li-M-P-O coating may include one or more of the following: a greater NMC811 stability score when normalized to that of LiFePO4 at 100%, or a greater PF5− score when normalized to that of LiFePO4 at 100%, or a greater HF score when normalized to that of LiFePO4 at 100%, or a lower LiF score when normalized to that of LiMnPO4 at 100%, or a greater LiOH score when normalized to that of LiFePO4 at 100%. Accordingly, in other aspects, the Li-M-P-O may be used as a coating on a current collector, on the separator, inside a pouch, or inside a housing, where the Li-M-P-O coating may include one or more of the following: a greater NMC811 stability score when normalized to that of LiFePO4 at 100%, or a greater PF5− score when normalized to that of LiFePO4 at 100%, or a greater HF score when normalized to that of LiFePO4 at 100%, or a lower LiF score when normalized to that of LiMnPO4 at 100%, or a greater LiOH score when normalized to that of LiFePO4 at 100%.
Thus, in another aspect, a current collector includes a metal that is at least partially coated with a lithium transition metal phosphorus oxide (a “Li-M-P-O coating”). In any embodiment herein, it may be that the Li-M-P-O coating includes a lithium transition metal phosphorous oxide other than LiFePO4. In any embodiment herein, the Li-M-P-O coating may include one or more of the following: a greater NMC811 stability score when normalized to that of LiFePO4 at 100%, or a greater PF5− score when normalized to that of LiFePO4 at 100%, or a greater HF score when normalized to that of LiFePO4 at 100%, or a lower LiF score when normalized to that of LiMnPO4 at 100% (e.g., down to 0%), or a greater LiOH score when normalized to that of LiFePO4 at 100%. In some embodiments, the lithium transition metal phosphorous oxide includes LiMnPO4, LiCoPO4, LiNiPO4, LiSnPO4, LiV(PO3)4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof. In some embodiments, the lithium transition metal phosphorous oxide includes LiCoPO4, LiNiPO4, LiSnPO4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof. In some embodiments, the lithium transition metal phosphorous oxide includes LiCoPO4, LiSnPO4, Li3Mn3(PO4)4, or a mixture of any two or more thereof. In any embodiment herein, the lithium transition metal phosphorus oxide may also include LiFePO4 in addition to one or more lithium transition metal phosphorus oxides that are not LiFePO4.
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 a current collector and the lithium ion battery also includes 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 particulate bulk cathode active material, the current collector, or an inner surface of the housing is at least partially coated with a lithium transition metal oxide (a “Li-M-P-O coating”). In any embodiment herein, it may be that the Li-M-P-O coating includes a lithium transition metal phosphorous oxide other than LiFePO4. In any embodiment herein, the Li-M-P-O coating may include one or more of the following: a greater NMC811 stability score when normalized to that of LiFePO4 at 100%, or a greater PF5− score when normalized to that of LiFePO4 at 100%, or a greater HF score when normalized to that of LiFePO4 at 100%, or a lower LiF score when normalized to that of LiMnPO4 at 100% (e.g., down to 0%), or a greater LiOH score when normalized to that of LiFePO4 at 100%. In some embodiments, the lithium transition metal phosphorous oxide includes LiMnPO4, LiCoPO4, LiNiPO4, LiSnPO4, LiV(PO3)4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof. In some embodiments, the lithium transition metal phosphorous oxide includes LiCoPO4, LiNiPO4, LiSnPO4, LiCrP2O7, Li3Mn3(PO4)4, Li2MnP2O7, Li2FeP2O7, LiCo(PO3)3, or a mixture of any two or more thereof. In some embodiments, the lithium transition metal phosphorous oxide includes LiCoPO4, LiSnPO4, Li3Mn3(PO4)4, or a mixture of any two or more thereof. In any embodiment herein, the lithium transition metal phosphorus oxide may also include LiFePO4 in addition to one or more lithium transition metal phosphorus oxides that are not LiFePO4. 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 a particulate cathode active material of any embodiment herein, 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 (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 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 an electrode composition (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. The loading level of cathode materials on the cathode current collector (after solvent removal) may range 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.
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 (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, Ar, etc.), under an oxidizing atmosphere (O2, air, etc.), and/or under a reducing atmosphere (e.g., H2), according to some embodiments.
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; alternatively, in any embodiment herein, a dry (solventless) mixture may include the metal-containing precursor chemical. In some embodiments, LiOH, (NH4)2HPO4, and/or NH4F may be added to the solution/dry mixture containing the metal-containing precursor chemical(s). In some embodiments, the solution/dry mixture may be mixed with Li-M-P-O 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 to potentially 1 week. The nominal Li-M-P-O may be targeted to be from about 0.1 wt % to about 5 wt % of the electrode composition. 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 Li-M-P-O coated cathode materials may be synthesized via a solid-state method. The primary particle size range for Li-M-P-O coated cathode materials 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 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 Li-M-P-O 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 an oxidizing gas (e.g., O2 and/or air), an inert gas (e.g., N2 and/or Ar), a reducing gas (e.g., H2), or gas mixture of any two or more thereof.
In other embodiments, Li-M-P-O 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, 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 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 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 electrode composition, the electrochemical cell, and/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 sub stance.
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 LiMPO4 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 using LiMn0.1Co0.1Ni0.8O2 (NMC811) powders as an illustrative example of LiNMC materials more generally. The criteria included: (a) stability/synthesizability; (b) equilibrium with the NMC811 cathode material; and (c) electrolyte stability by predicting an equilibrium or no reaction with HF, LiF, and LiOH while scavenging corrosive species such as PF5−.
In addition to LiMnPO4, LiFePO4, LiCoPO4, LiNiPO4, and LiSnPO4, 18 additional Li-M-P-O compounds were identified that were thermodynamically stable as well as had predicted average voltage values greater than 4.3 V vs. Li/Li′. The thermodynamic stability is quantified based on the energy of the compound above the convex hull (Emu) in the chemical space of elements which make up the material and such data are readily acquired from the materials project database. A compound with Ehull=0 lies in the energy convex hull and is a thermodynamically stable phase at T=0 K. A compound with Ehull>0 is thermodynamically metastable and a material with a high energy above hull (e.g., >50 meV/atom) may have a strong driving force to decomposition and would be difficult to synthesize experimentally. Table 1 provides the 18 additional Li-M-P-O compounds identified to be thermodynamically stable according to the above-described parameters and, as predicted by DFT, have average voltage values of greater than 4.3 V vs. Li/Li+.
As noted above, another screening step included determining if the Li-M-P-O compounds exhibit chemical equilibrium with the NMC811 cathode material. It is preferred that either no reaction is found, or if there is a reaction it is at equilibrium so that overall compositional changes are not imparted to the electrode. To compute whether a compound exhibits equilibrium with the electrode materials, the convex hull method was used. For each candidate compound, the convex hull is calculated for the set of elements defined by the compound plus the electrolyte material. Within the convex hull, tie lines connecting the candidate compound with the electrolyte material are analyzed. The presence of a tie line is an indication that the candidate compound does exhibit stable equilibrium with the electrode. The absence of such a tie line indicates that the candidate compound does not exhibit stable equilibrium with the electrolyte but rather reacts.
0.595 Li1Mn0.1Co0.1Ni0.8O2+0.405 LiFePO4→0.202 Fe2NiO4+0.012 Li4MnCo5O12+0.14 LiNiPO4+0.021 Mn(Ni3O4)2+0.009 Li2Mn3NiO8+0.265 Li3PO4
This reaction has a Erxn value of −0.125 eV/atom.
Similarly, Table 2 provides the performance of LiMnPO4, LiFePO4, LiCoPO4, LiNiPO4, LiSnPO4, and those compounds listed in Table 1 with respect to generation of O2, indicative of release of O2 gas. When more than 0.05 O2 is formed, these compounds are considered to have “high” O2 evolution and thus may pose safety concerns.
LiFePO4 is a known coating material for Li-ion battery cathode powders, and is generally considered to provide a stable protective layer. Accordingly, Table 3 provides the stability of the Li-M-P-O compounds that do not release or release less than 0.05 O2 as determined with respect to NMC811, and this was then normalized to the case of LiFePO4. In the Table, LiMnPO4 has a ratio for LiMnPO4:NMC811 (“Ratio”) of 0.34, and a “Ratio vs LiFePO4” of 0.50. For NMC811 reaction, it is beneficial if the “Ratio” value of the coating is lower when compared to that of LiFePO4:NMC811, or in other words, the coating consumes less NMC811 than LiFePO4. Similarly, it is desirable that the Erxn of NMC811 versus the compound be higher (i.e., less favorable to react with NMC811) compared to NMC811 vs. LiFePO4 reaction. The Erxn of the screened Li-M-P-O coatings vs. LiFePO4 is presented in the column marked “Erxn vs. LiFePO4.”
The two values that are referenced to LiFePO4 for molar ratio and reaction enthalpy are then added (“Sum”). Because these values are evaluated based on the molar fraction, they are then converted by dividing by molecular weight: e.g., 2.00/157.76×1,000=12.68 for LiFePO4. In the last column (the ‘NMC811 stability score’), the percentage improvement vs. LiFePO4 is provided. For example, for LiMnPO4, the calculation is: 12.68/9.62×100=131.84%. An “NMC811 stability score” >100 indicates that the Li-M-P-O compound is expected to have better stability with regard to NMC811, compared to LiFePO4. All compounds listed in Table 3 exhibit better performance for NMC811 stability, when compared with the state-of-art LiFePO4 material.
HF can form in the liquid electrolyte when residual water/moisture is present to react with LiPF6 salt in the battery cell: LiPF6+H2O4↔POF3+2HF+LiF. HF is an acid that can degrade subcomponents in battery cell. In particular, NMC811 cathode may react with HF in at least molar factions of 0.083-0.714 to decompose the NMC811 cathode material to other species and consequently reducing the cathode material's capacity to (de-)insert Li ions.
Therefore, it would be beneficial for a Li-M-P-O coating to scavenge HF as much as possible. Accordingly, the HF reactivity for 11 Li-M-P-O compounds was determined and this was then normalized to the case of LiFePO4, where the results are provided in Table 4. In particular, 0.077 LiFePO4 reacts with 0.923 HF to yield 0.308 H3OF, 0.077 LiPF6, and 0.077 FeF2 with Erxn of −0.156 eV/atom. It would be beneficial for a Li-M-P-O coating to scavenge HF more effectively than LiFePO4, where the “Ratio” between HF to Li-M-P-O is higher than the ratio of HF to LiFePO4. In particular, HF:LiFePO4 is 0.923:0.77=11.99, where all other Li-M-P-O materials are normalized vs. LiFePO4 in the “Ratio vs. LiFePO4” column. An example is LiV(PO3)4, where HF:LiV(PO3)4=36.04, and the “Ratio vs. LiFePO4” is 11.99/36.04=0.33. It is beneficial when the “Ratio vs. LiFePO4” is less than 1 (i.e., more reactive against HF). Another criteria is the reaction enthalpy. When LiFePO4 reacts with HF, the corresponding reaction enthalpy (Erxn) is found to be −0.156 eV/atom. The reaction enthalpy for the Li-M-P-O materials was normalized vs. LiFePO4 (“Erxn vs. LiFePO4”) where it is beneficial when this value is less than 1 (i.e., HF scavenging reaction is more favorable). The two values that are referenced to LiFePO4 for molar ratio and reaction enthalpy are then added (“Sum”). Since these values are evaluated based on the molar fraction, we then convert this value by dividing my molecular weight: e.g., 2.00/157.76×1,000=12.68 for LiFePO4. Lastly, the “HF score” provides the improvement vs. LiFePO4 for all materials: 12.68/12.67×100=100.06% for LiMnPO4. As illustrated in Table 4, all Li-M-P-O compounds showed improved performance for HF scavenging reactions when compared with the LiFePO4 material, with the exception of LiCoPO4.
PF5− is a species that forms from LiPF6 salt decomposition: LiPF6↔LiF+PF5−. Similar to HF, PF5− will decompose NMC811. Therefore, it is beneficial if the Li-M-P-O coating materials scavenge PF5−. Thus, similar to the determination of HF reactivity, the PF5− reactivity for 11 Li-M-P-O compounds was determined and this was then normalized to the case of LiFePO4 to provide a “PF5 score,” where the results are provided in Table 5. As shown in this Table, LiSnPO4, LiCrP2O7, Li3Mn3(PO4)4, LiMnP2O7, and Li2FeP2O7 favorably react against PF5− (as compared to LiFePO4).
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 Li-M-P-O coatings not to consume LiF, so that it remains available for the SEI formation. 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. Similar to LiF, it is desirable that the LiOH reaction not take place when in contact with the Li-M-P-O compounds, to avoid the H2O formation.
Similar to the determination of HF reactivity and PF5− reactivity discussed above, the LiF reactivity and LiOH reactivity for 11 Li-M-P-O compounds was determined. For the LiF reactivity, LiFePO4 was found not to react with LiF, therefore the LiF reactivity was determined and then normalized to the case of LiMnPO4 to ultimately provide a “LiF score” as illustrated in Table 6. For the LiF reactivity, it is beneficial if “Ratio” value is lower (i.e., less reaction with LiF) and for the Erxn to be higher (i.e., less favorable to react with LiF). LiCoPO4, LiNiPO4, LiSnPO4, Li2MnP2O7, Li2FeP2O7, and LiCo(PO3)3 were determined to be stable in contact with LiF. For LiOH reactivity, as indicated in Table 7, determinations were made for the indicated Li-M-P-O compounds then normalized to the case of LiFePO4 to provide a “LiOH score.” LiMnPO4, LiSnPO4, and Li3Mn3(PO4)4 were found to be most stable against LiOH.
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.
