THERMALLY STABLE ELASTIC POLYMER-ENCAPSULATED ANODE PARTICLES FOR LITHIUM BATTERIES AND METHOD OF MANUFACTURING

Abstract

A composite particulate for a lithium battery, wherein the composite particulate has a diameter from 10 nm to 50 μm and comprises one or more than one anode active material particles that are dispersed in a high-elasticity polymer matrix or encapsulated by a high-elasticity polymer shell, wherein the high-elasticity polymer matrix or shell has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10.sup.−8 S/cm at room temperature and wherein the high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof.

Claims

1. A composite particulate for a lithium battery, wherein said composite particulate has a diameter from 10 nm to 50 μm and comprises one or more than one anode active material particles that are dispersed in a high-elasticity polymer matrix or encapsulated by a high-elasticity polymer shell, wherein said high-elasticity polymer matrix or shell has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10.sup.−8 S/cm at room temperature and wherein said high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof.

2. The composite particulate of claim 1, wherein the fluorinated monomer is selected from the group consisting of fluorinated vinyl carbonates, fluorinated vinyl monomers, fluorinated esters, fluorinated vinyl esters, and fluorinated vinyl ethers and combinations thereof.

3. The composite particulate of claim 1, wherein the sulfone or sulfide is selected from vinyl sulfone, allyl sulfone, alkyl vinyl sulfone, aryl vinyl sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, vinyl sulfide, a vinyl-containing variant of TrMS, MTrMS, TMS, EMS, MMES, EMES, EMEES, or a combination thereof: ##STR00017##

4. The composite particulate of claim 2, wherein the vinyl sulfone or sulfide is selected from ethyl vinyl sulfide, allyl methyl sulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, allyl phenyl sulfone, allyl methyl sulfone, divinyl sulfone, or a combination thereof, wherein the vinyl sulfone does not include methyl ethylene sulfone and ethyl vinyl sulfone.

5. The composite particulate of claim 1, wherein the nitrile comprises a dinitrile or is selected from AND, GLN, SEN, or a combination thereof: ##STR00018##

6. The composite particulate of claim 1, wherein the siloxane or silane is selected from alkylsiloxane (Si—O), alkyylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—), or a combination thereof.

7. The composite particulate of claim 1, wherein said high-elasticity polymer contains a cross-linked network of chains crosslinked by a crosslinking agent to a degree of crosslinking that imparts an elastic tensile strain from 5% to 500%.

8. The composite particulate of claim 7, wherein said crosslinking agent is selected from poly(diethanol) diacrylate, poly(ethyleneglycol)dimethacrylate, poly(diethanol) dimethylacrylate, poly(ethylene glycol) diacrylate, N,N-methylene bisacrylamide, epichlorohydrin, 1,4-butanediol diglycidyl ether, tetrabutylammonium hydroxide, cinnamic acid, ferric chloride, aluminum sulfate octadecahydrate, diepoxy, dicarboxylic acid compound, poly(potassium 1-hydroxy acrylate) (PKHA), glycerol diglycidyl ether (GDE), ethylene glycol, polyethylene glycol, polyethylene glycol diglycidyl ether (PEGDE), citric acid, acrylic acid, methacrylic acid, a derivative compound of acrylic acid, a derivative compound of methacrylic acid, glycidyl functions, N,N′-Methylenebisacrylamide (MBAAm), Ethylene glycol dimethacrylate (EGDMAAm), isobornyl methacrylate, poly (acrylic acid) (PAA), methyl methacrylate, isobornyl acrylate, ethyl methacrylate, isobutyl methacrylate, n-Butyl methacrylate, ethyl acrylate, 2-Ethyl hexyl acrylate, n-Butyl acrylate, a diisocyanate, an urethane chain, a chemical derivative thereof, or a combination thereof.

9. The composite particulate of claim 7, wherein the crosslinking agent comprises a compound having at least one reactive group selected from a phenylene group, a hydroxyl group, an amino group, an imino group, an amide group, an acrylic amide group, an amine group, an acrylic group, an acrylic ester group, or a mercapto group in the molecule.

10. The composite particulate of claim 1, wherein the polymer is synthesized with an initiator selected from an azo compound, azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide tert-butyl peroxide and methyl ethyl ketone peroxide, benzoyl peroxide (BPO), bis(4-tert-butylcyclohexyl)peroxydicarbonate, t-amyl peroxypivalate, 2,2′-azobis-(2,4-dimethylvaleronitrile), 2,2′-azobis-(2-methylbutyronitrile), 1,1-azobis(cyclohexane-1-carbonitrile, benzoylperoxide (BPO), hydrogen peroxide, dodecamoyl peroxide, isobutyryl peroxide, cumene hydroperoxide, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate, lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF.sub.3SO.sub.2).sub.2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), or a combination thereof.

11. The composite particulate of claim 1, wherein said high-elasticity polymer matrix or shell further contains from 0.01% to 30% by weight of a graphite, graphene, or carbon material dispersed therein.

12. The composite particulate of claim 11, wherein said graphite, graphene, or carbon material is selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, meso-phase pitch, carbon black, coke, acetylene black, activated carbon, graphite particles, carbon particles, meso-phase microbeads, carbon or graphite fibers, carbon nanotubes, carbon nano-fibers, graphitic nano-fibers, graphene sheets, or a combination thereof and said graphite, graphene, or carbon material forms a 3D network of electron-conducting pathways that are in electronic contacts with said anode material particles.

13. The composite particulate of claim 1, wherein said anode active material is selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), phosphorus (P), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium titanium niobium oxide, lithium-containing titanium oxide, lithium transition metal oxide, ZnCo.sub.2O.sub.4; (f) carbon or graphite particles (g) prelithiated versions thereof; and (h) combinations thereof.

14. The composite particulate of claim 1, wherein said anode active material contains a prelithiated Si, prelithiated Ge, prelithiated Sn, prelithiated SnO.sub.x, prelithiated SiO.sub.x, prelithiated iron oxide, prelithiated V.sub.2O.sub.5, prelithiated V.sub.3O.sub.8, prelithiated Co.sub.3O.sub.4, prelithiated Ni.sub.3O.sub.4, or a combination thereof, wherein x=1 to 2.

15. The composite particulate of claim 1, wherein said anode active material particles, the composite particulates, or both are porous.

16. The composite particulate of claim 1, wherein one or a plurality of said particles is coated with a layer of carbon or graphene disposed between said one or said plurality of particles and said high-elasticity polymer matrix.

17. The composite particulate of claim 1, wherein said high-elasticity polymer has a lithium ion conductivity from 10.sup.−6 S/cm to 10.sup.−2 S/cm.

18. The composite particulate of claim 1, wherein said composite particulate is further coated with or encapsulated by a shell of a conducting material selected from carbon, graphene, a conducting polymer, a conducting composite, or a combination thereof.

19. The composite particulate of claim 1, wherein said high-elasticity polymer matrix or shell further comprises from 0.1% to 50% by weight of a lithium ion-conducting additive dispersed therein.

20. The composite particulate of claim 1, wherein said high-elasticity polymer forms a mixture or co-polymer with an elastomer selected from natural polyisoprene, synthetic polyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber, ethylene propylene rubber, ethylene propylene diene rubber, epichlorohydrin rubber, polyacrylic rubber, silicone rubber, fluorosilicone rubber, perfluoroelastomers, polyether block amides, chlorosulfonated polyethylene, ethylene-vinyl acetate, thermoplastic elastomer, protein resilin, protein elastin, ethylene oxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer, or a combination thereof.

21. The composite particulate of claim 1, wherein said high-elasticity polymer contains a lithium ion-conducting additive dispersed therein wherein said lithium ion-conducting additive is selected from Li.sub.2CO.sub.3, Li.sub.2O, Li.sub.2C.sub.2O.sub.4, LiOH, LiX, ROCO.sub.2Li, HCOLi, ROLi, (ROCO.sub.2Li).sub.2, (CH.sub.2OCO.sub.2Li).sub.2, Li.sub.2S, Li.sub.xSO.sub.y, or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1, 1≤y≤4.

22. The composite particulate of claim 1, wherein said high-elasticity polymer further comprises a lithium ion-conducting additive dispersed therein and said additive is selected from lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF.sub.3SO.sub.2).sub.2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium nitrate (LiNO.sub.3), Li-fluoroalkyl-phosphate (LiPF.sub.3(CF.sub.2CF.sub.3).sub.3), lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, or a combination thereof.

23. The composite particulate of claim 1, wherein said anode active material is lithiated to contain from 0.1% to 54.7% by weight of lithium.

24. An anode comprising multiple composite particulates as defined in claim 1 as an anode material.

25. An anode comprising multiple particles of an anode active material and a conductive additive that are dispersed in, bonded by, or encapsulated by a high-elasticity polymer, wherein said high-elasticity polymer has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10.sup.−8 S/cm at room temperature and wherein said high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof.

26. A process for producing the anode of claim 25, said process comprising (i) dispersing multiple particles of an anode active material and a conductive additive in a precursor polymer solution to form a suspension wherein the precursor solution comprises at least a curing agent dissolved or dispersed in a reactive liquid medium that comprises a monomer or oligomer, wherein the monomer or oligomer is selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof; (ii) dispensing and depositing a layer of the suspension onto a solid substrate surface; and (iii) curing the monomer or oligomer to form the anode.

27. The process of claim 26, further comprising a step of partially or fully removing the liquid solvent before or after step (iii).

28. The process of claim 26, wherein a lithium salt is also dispersed in the precursor polymer solution.

29. The process of claim 26, wherein the reactive liquid medium also includes a non-aqueous liquid solvent.

30. A lithium battery comprising the anode of claim 24, a cathode, and an electrolyte in ionic contact with said anode and said cathode.

31. The lithium battery of claim 30, which is a lithium-ion battery, lithium metal battery, lithium-sulfur battery, lithium-selenium battery, or lithium-air battery.

32. The lithium battery of claim 30, further including a porous separator that electrically isolates said anode from said cathode.

33. A method of manufacturing multiple composite particulates of claim 1, said method comprising: (a) Dispersing multiple particles of an anode active material in a precursor polymer solution to form a suspension wherein these particles are fully embedded or immersed in said precursor solution, which comprises at least a curing agent dissolved or dispersed in a reactive liquid medium that comprises a monomer or oligomer, wherein the monomer or oligomer is selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof; (b) operating a secondary particle-forming procedure to shape the suspension into multiple droplets and remove the liquid solvent from the droplets; and (c) curing the monomer or oligomer to form said composite particulates wherein a particulate comprises one or a plurality of anode active material particles that are dispersed and embedded in a polymer matrix or encapsulated by a polymer shell.

34. The method of claim 33, wherein said secondary particle-forming procedure comprises a procedure selected from solution dipping, coating or casting on a solid substrate, pan-coating, air-suspension coating, centrifugal extrusion, vibration-nozzle encapsulation, spray-drying, coacervation-phase separation, interfacial polycondensation or interfacial cross-linking, in-situ polymerization, matrix polymerization, extrusion and palletization, or a combination thereof.

35. The method of claim 33, wherein said suspension in step (a) further comprises an elastomer or its precursor, an electronically conductive polymer or its precursor, a lithium-ion conducting material, a reinforcement material, a foaming or blowing agent, or a combination thereof that is dispersed therein.

36. The method of claim 33, wherein said anode active material particles, prior to step (a), are pre-coated with a layer of carbon, graphene, a conducting polymer, a conducting composite, or a combination thereof.

37. The method of claim 33, wherein the reactive liquid medium also includes a non-aqueous liquid solvent.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] FIG. 1(A) Schematic of a prior art lithium-ion battery cell, wherein the anode layer is a thin coating of an anode active material itself.

[0058] FIG. 1(B) Schematic of another prior art lithium-ion battery; the anode layer being composed of particles of an anode active material, a conductive additive (not shown) and a resin binder (not shown).

[0059] FIG. 2(A) Schematic illustrating the notion that expansion of Si particles, upon lithium intercalation during charging of a prior art lithium-ion battery, can lead to pulverization of Si particles, interruption of the conductive paths formed by the conductive additive, and loss of contact with the current collector;

[0060] FIG. 2(B) illustrates the issues associated with prior art anode active material; for instance, a non-lithiated Si particle encapsulated by a protective shell (e.g., carbon shell) in a core-shell structure inevitably leads to breakage of the shell and that a pre-lithiated Si particle encapsulated with a protective layer leads to poor contact between the contracted Si particle and the rigid protective shell during battery discharge.

[0061] FIG. 3 Schematic of some examples of porous primary particles.

[0062] FIG. 4(A) A flow chart illustrating a method of producing the multi-functional composite particulates according to certain embodiments of the present disclosure.

[0063] FIG. 4(B) Schematic of three types of composite particulates according to certain embodiments of the present disclosure.

[0064] FIG. 4(C) Schematic of four types of composite particulates comprising high-elasticity polymer-encapsulated anode particles according to certain embodiments of the present disclosure

[0065] FIG. 5(A) Charge/discharge curves of a lithium-ion cell having an anode of unprotected Si micro particles (the first-cycle Coulomb efficiency is from 50% to 56%);

[0066] FIG. 5(B) The specific capacity values of a lithium-ion cell having an anode of unprotected Si active material;

[0067] FIG. 5(C) Charge/discharge curves of a lithium-ion cell having an anode of high-elasticity polymer matrix-protected Si particles (the first-cycle Coulomb efficiency is 90.7% on average;

[0068] FIG. 5(D) The specific capacity values of a lithium-ion cell having an anode featuring high-elasticity polymer matrix-protected Si particles.

DETAILED DESCRIPTION

[0069] This disclosure provides an anode (negative electrode) comprising composite particulates (each having one or more than one anode active material particles dispersed in a high-elasticity polymer matrix or encapsulated by a shell of high-elasticity polymer) for a lithium secondary battery, which is preferably a secondary battery based on a non-aqueous electrolyte, a polymer gel electrolyte, an ionic liquid electrolyte, a quasi-solid electrolyte, or a solid-state electrolyte. The shape of a lithium secondary battery can be cylindrical, square, button-like, etc. The present disclosure is not limited to any battery shape or configuration or any type of electrolyte. For convenience, we will primarily use Si, Sn, and SnO.sub.2 as illustrative examples of a high-capacity anode active material. This should not be construed as limiting the scope of the disclosure.

[0070] As illustrated in FIG. 1(B), a lithium-ion battery cell is typically composed of an anode current collector (e.g. Cu foil), an anode or negative electrode active material layer (i.e. anode layer typically containing particles of an anode active material, conductive additive, and binder), a porous separator and/or an electrolyte component, a cathode or positive electrode active material layer (containing a cathode active material, conductive additive, and resin binder), and a cathode current collector (e.g. Al foil). More specifically, the anode layer is composed of particles of an anode active material (e.g. graphite, Sn, SnO.sub.2, or Si), a conductive additive (e.g. carbon black particles), and a resin binder (e.g. SBR or PVDF). This anode layer is typically 50-300 μm thick (more typically 100-200 μm) to give rise to a sufficient amount of current per unit electrode area.

[0071] In a less commonly used cell configuration, as illustrated in FIG. 1(A), the anode active material is deposited in a thin film form directly onto an anode current collector, such as a layer of Si coating deposited on a sheet of copper foil. This is not commonly used in the battery industry and, hence, will not be discussed further.

[0072] In order to obtain a higher energy density cell, the anode in FIG. 1(B) can be designed to contain higher-capacity anode active materials having a composition formula of Li.sub.aA (A is a metal or semiconductor element, such as Al and Si, and “a” satisfies 0<a≤5). These materials are of great interest due to their high theoretical capacity, e.g., Li.sub.4Si (3,829 mAh/g), Li.sub.4.4Si (4,200 mAh/g), Li.sub.4.4Ge (1,623 mAh/g), Li.sub.4.4Sn (993 mAh/g), Li.sub.3Cd (715 mAh/g), Li.sub.3Sb (660 mAh/g), Li.sub.4.4Pb (569 mAh/g), LiZn (410 mAh/g), and Li.sub.3Bi (385 mAh/g). However, as discussed in the Background section, there are several problems associated with the implementation of these high-capacity anode active materials: [0073] 1) As schematically illustrated in FIG. 2(A), in an anode composed of these high-capacity materials, severe pulverization (fragmentation of the alloy particles) occurs during the charge and discharge cycles due to severe expansion and contraction of the anode active material particles induced by the insertion and extraction of the lithium ions in and out of these particles. The expansion and contraction, and the resulting pulverization, of active material particles, lead to loss of contacts between active material particles and conductive additives and loss of contacts between the anode active material and its current collector. These adverse effects result in a significantly shortened charge-discharge cycle life. [0074] 2) The approach of using a composite composed of small electrode active particles protected by (dispersed in or encapsulated by) a less active or non-active matrix, e.g., carbon-coated Si particles, sol gel graphite-protected Si, metal oxide-coated Si or Sn, and monomer-coated Sn nano particles, has failed to overcome the capacity decay problem. Presumably, the protective matrix provides a cushioning effect for particle expansion or shrinkage, and prevents the electrolyte from contacting and reacting with the electrode active material. Unfortunately, when an active material particle, such as Si particle, expands (e.g. up to a volume expansion of 380%) during the battery charge step, the protective coating is easily broken due to the mechanical weakness and/o brittleness of the protective coating materials. There has been no high-strength and high-toughness material available that is itself also lithium ion conductive. [0075] 3) The approach of using a core-shell structure (e.g. Si nano particle encapsulated in a carbon or SiO.sub.2 shell) also has not solved the capacity decay issue. As illustrated in upper portion of FIG. 2(B), a non-lithiated Si particle can be encapsulated by a carbon shell to form a core-shell structure (Si core and carbon or SiO.sub.2 shell in this example). As the lithium-ion battery is charged, the anode active material (carbon- or SiO.sub.2-encapsulated Si particle) is intercalated with lithium ions and, hence, the Si particle expands. Due to the brittleness of the encapsulating shell (carbon), the shell is broken into segments, exposing the underlying Si to electrolyte and subjecting the Si to undesirable reactions with electrolyte during repeated charges/discharges of the battery. These reactions continue to consume the electrolyte and reduce the cell's ability to store lithium ions. [0076] 4) Referring to the lower portion of FIG. 2(B), wherein the Si particle has been pre-lithiated with lithium ions; i.e. has been pre-expanded in volume. When a layer of carbon (as an example of a protective material) is encapsulated around the pre-lithiated Si particle, another core-shell structure is formed. However, when the battery is discharged and lithium ions are released (de-intercalated) from the Si particle, the Si particle contracts, leaving behind a large gap between the protective shell and the Si particle. Such a configuration is not conducive to lithium intercalation of the Si particle during the subsequent battery charge cycle due to the gap and the poor contact of Si particle with the protective shell (through which lithium ions can diffuse). This would significantly curtail the lithium storage capacity of the Si particle particularly under high charge rate conditions.

[0077] In other words, there are several conflicting factors that should be considered concurrently when it comes to the design and selection of an anode active material in terms of material type, shape, size, porosity, and electrode layer thickness. Thus far, there has been no effective solution offered by any prior art teaching to these often conflicting problems. We have solved these challenging issues that have troubled battery designers and electrochemists alike for more than 30 years by developing the multi-functional composite particulates.

[0078] The present disclosure provides a solid powder mass of composite particulates for a lithium battery, wherein at least one of the composite particulates (preferably a majority or all of these particulates or “secondary particles”) has a diameter from 50 nm to 50 μm and comprises a plurality of anode active material particles (the “primary particles”) that are dispersed in a high-elasticity polymer matrix or encapsulated by a shell of high-elasticity polymer having a recoverable tensile strain no less than 5% (typically from 5% to 700% and more typically from 10% to 300%), when measured without an additive or reinforcement, and a lithium ion conductivity no less than 10.sup.−8 S/cm (preferably >10.sup.−4 S/cm, more preferably >10.sup.−3 S/cm) when measured at room temperature. In the structure of a polymer matrix, the polymer forms a continuous material phase. This continuous phase makes physical and ionic contact with all the anode active material particles dispersed in this continuous phase (matrix).

[0079] In certain embodiments, the disclosure provides a composite particulate for a lithium battery, wherein said composite particulate has a diameter from 10 nm to 50 μm and comprises one or more than one anode active material particles that are dispersed in a high-elasticity polymer matrix or encapsulated by a high-elasticity polymer shell, wherein the high-elasticity polymer matrix or shell has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10.sup.−8 S/cm at room temperature and wherein the high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof.

[0080] Many of these monomers are not known to be polymerizable and, if polymerized, the products are sufficiently elastic to protect the anode materials that can undergo large volume expansion.

[0081] The fluorinated monomer may be selected from the group consisting of fluorinated vinyl carbonates, fluorinated vinyl monomers, fluorinated esters, fluorinated vinyl esters, and fluorinated vinyl ethers and combinations thereof.

[0082] Desirable polymerizable liquid solvents include fluorinated monomers having unsaturation (double bonds or triple bonds) in the backbone or cyclic structure (e.g., fluorinated vinyl carbonates, fluorinated vinyl monomers, fluorinated esters, fluorinated vinyl esters, and fluorinated vinyl ethers). Fluorinated vinyl esters include R.sub.fCO.sub.2CH═CH.sub.2 and Propenyl Ketones, R.sub.fCOCH═CHCH.sub.3, where R.sub.f is F or any F-containing functional group (e.g., CF.sub.2— and CF.sub.2CF.sub.3.sup.−).

[0083] Two examples of fluorinated vinyl carbonates are given below:

##STR00003##

[0084] These liquid solvents, as a monomer, can be cured in the presence of an initiator (e.g., 2-Hydroxy-2-methyl-1-phenyl-propan-1-one, Ciba DAROCUR-1173, which can be activated by UV or electron beam):

##STR00004##

[0085] In some embodiments, the fluorinated carbonate is selected from vinyl- or double bond-containing variants of fluoroethylene carbonate (FEC), DFDMEC, FNPEC, a combination thereof, or a combination thereof with hydrofluoro ether (HFE), trifluoro propylene carbonate (FPC), or methyl nonafluorobutyl ether (MFE), wherein the chemical formulae for FEC, DFDMEC, and FNPEC, respectively (all polymerizable via ring-opening polymerization with an ionic initiator) are shown below:

##STR00005##

[0086] Desirable sulfones as a monomer include, but not limited to, alkyl and aryl vinyl sulfones or sulfides; e.g., ethyl vinyl sulfide, allyl methyl sulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, ethyl vinyl sulfone, allyl phenyl sulfone, allyl methyl sulfone, and divinyl sulfone.

##STR00006##

[0087] Simple alkyl vinyl sulfones, such as ethyl vinyl sulfone, may be polymerized via emulsion and bulk methods. Propyl vinyl sulfone may be polymerized by alkaline persulfate initiators to form soft polymers. It may be noted that aryl vinyl sulfone, e.g., naphthyl vinyl sulfone, phenyl vinyl sulfone, and parra-substituted phenyl vinyl sulfone (R=NH.sub.2, NO.sub.2 or Br), were reported to be unpolymerizable with free-radical initiators. However, we have observed that phenyl and methyl vinyl sulfones can be polymerized with several anionic-type initiators. Effective anionic-type catalysts or initiators are n-BuLi, ZnEt2, LiN(CH.sub.2).sub.2, NaNH.sub.2, and complexes of n-LiBu with ZnEt2 or AlEh. A second solvent, such as pyridine, sulfolane, toluene or benzene, can be used to dissolve alkyl vinyl sulfones, aryl vinyl sulfones, and other larger sulfone molecules.

[0088] Poly(sulfone)s have high oxygen indices and low smoke emission on burning. Poly(sulfone)s are inherently self-extinguishing materials owing to their highly aromatic character. A hydroxy-terminated copoly(ester sulfone) synthesized by melt polycondensation of the diethylene glycol and 4,4-dihydroxydiethoxydiphenyl sulfone with adipic acid can be used as a flame retardant. Some examples are difunctional β-allyl sulfones and 4,4-(m-phenylene-dioxy)bis(benzenesulfonyl chloride):

##STR00007##

[0089] Bisphenol S (BPS) and 4,4′-Dichlorodiphenyl sulfone (DCDPS) are additional examples that can be a part of a polymer structure. Bisphenol S (BPS) is an organic compound with the formula (HOC.sub.6H.sub.4)O.sub.2SO.sub.2:

##STR00008##

4,4′-Dichlorodiphenyl sulfone (DCDPS), having a MP=148° C. is an organic compound with the formula (ClC.sub.6H.sub.4).sub.2SO.sub.2:

##STR00009##

[0090] The sulfone or sulfide may be selected from vinyl sulfone, allyl sulfone, alkyl vinyl sulfone, aryl vinyl sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, vinyl sulfide, a vinyl-containing variant of TrMS, MTrMS, TMS, EMS, MMES, EMES, EMEES, or a combination thereof:

##STR00010##

[0091] In certain embodiments, the vinyl sulfone or sulfide is selected from ethyl vinyl sulfide, allyl methyl sulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, allyl phenyl sulfone, allyl methyl sulfone, divinyl sulfone, or a combination thereof, wherein the vinyl sulfone does not include methyl ethylene sulfone and ethyl vinyl sulfone.

[0092] The nitrile may comprise a dinitrile or is selected from AND, GLN, SEN, or a combination thereof:

##STR00011##

[0093] The silaxane or silane may be selected from alkylsiloxane (Si—O), alkyylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—), or a combination thereof.

[0094] High-elasticity polymer refers to a polymer, typically a lightly cross-linked polymer, which exhibits an elastic deformation that is at least 5% when measured (without an additive or reinforcement in the polymer) under uniaxial tension. In the field of materials science and engineering, the “elastic deformation” is defined as a deformation of a material (when being mechanically stressed) that is essentially fully recoverable and the recovery is essentially instantaneous upon release of the load. The elastic deformation is preferably greater than 30%, more preferably greater than 50%, further more preferably greater than 100%, still more preferably greater than 150%, and most preferably greater than 200%.

[0095] Three examples of the disclosed composite particulates are illustrated in FIG. 4(B). The first one comprises multiple anode active material primary particles 34 (e.g. Si nano particles) and a 3D network of electron-conducting pathways 36 (constituted by CNTs, graphene sheets, CNFs, expanded graphite flakes, etc.) that are dispersed in a high-elasticity polymer matrix 32. The second particulate comprises multiple anode active material particles 44 (e.g., Si nano particles) that are coated by a shell 48 of a conducting material. The composite particulate also comprises pores 50 and a 3D network of electron-conducting pathways 46 (constituted by CNTs, graphene sheets, CNFs, expanded graphite flakes, etc.) that are dispersed in a high-elasticity polymer matrix 42. The third particulate is similar to the first one, but further comprises a conductive protection shell or coating 52 (carbon, graphene, conducting polymer, etc.) deposited on the particulate surface. These anode active material particles can be pre-lithiated or non-prelithiated.

[0096] As illustrated in FIG. 4(C), the present disclosure provides four major types of particulates of elastic polymer-encapsulated anode active material particles. The first one is a single-particle particulate containing an anode active material core 10 encapsulated by a high-elasticity polymer shell 12. The second is a multiple-particle particulate containing multiple anode active material particles 14 (e.g., Si nano particles), optionally along with other active materials (e.g. particles of graphite or hard carbon, not shown) or conductive additive, which are encapsulated by a high-elasticity polymer shell 16. The third is a single-particle particulate containing an anode active material core 18 coated by a carbon layer 20 (or other conductive material) further encapsulated by a high-elasticity polymer shell 22. The fourth is a multiple-particle particulate containing multiple anode active material particles 24 (e.g., Si nano particles) coated with a conductive protection layer 26, optionally along with other active materials (e.g., particles of graphite or hard carbon, not shown) or conductive additive, which are encapsulated by a high-elasticity polymer shell 28. These anode active material particles can be pre-lithiated or non-prelithiated.

[0097] The primary particles themselves may be porous having porosity in the form of surface pores and/or internal pores. FIG. 3 shows some examples of porous primary particles of an anode active material. These pores of the primary particles allow the particle to expand into the free space without a significant overall volume increase of the particulate and without inducing any significant volume expansion of the entire anode electrode.

[0098] This amount of pore volume inside the particulate (surface or internal pores of porous primary anode particles) provides empty space to accommodate the volume expansion of the anode active material so that the polymer matrix and the entire composite particulate would not have to significantly expand (not to exceed 50% volume expansion of the particulate) when the lithium battery is charged. Preferably, the composite particulate does not increase its volume by more than 20%, further preferably less than 10% and most preferably by approximately 0% when the lithium battery is charged. Such a constrained volume expansion of the particulate would not only reduce or eliminate the volume expansion of the anode electrode but also reduce or eliminate the issue of repeated formation and destruction of a solid-electrolyte interface (SEI) phase. We have discovered that this strategy surprisingly results in significantly reduced battery capacity decay rate and dramatically increased charge/discharge cycle numbers. These results are unexpected and highly significant with great utility value.

[0099] Multiple non-lithiated Si particles can be dispersed in or encapsulated by a high-elasticity polymer to form a composite particulate. As the lithium-ion battery is charged, the anode active material particles (e.g. Si) are intercalated with lithium ions and, hence, the Si particle expands. Due to the high elasticity of the polymer, the polymer may simply expand accordingly without breaking up into pieces. That the high-elasticity polymer remains intact prevents the exposure of the embedded Si particles to liquid electrolyte and, thus, prevents the Si from undergoing undesirable reactions with electrolyte during repeated charges/discharges of the battery. This strategy prevents continued consumption of the electrolyte and lithium ions to form additional SEI.

[0100] The particulate may further contain a graphite, graphene, and/or carbon material dispersed in the high-elasticity polymer matrix. The carbon or graphite material may be selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, meso-phase pitch, carbon black, coke, acetylene black, activated carbon, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, carbon nano-tubes (single-walled or multi-walled), carbon nano-fibers (vapor-grown or carbonized polymer fibers), graphitic nano-fibers, graphene sheets, or a combination thereof. Graphene may be selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, functionalized graphene, etc.

[0101] The carbon/graphite/graphene particles, fibers, nanotubes, and/or nano sheets dispersed in the high-elasticity polymer or encapsulated in the high-elasticity polymer shell preferably and typically constitute a 3D network of electron-conducting paths that preferably are in contact with individual primary particles of the anode active material. The high-elasticity polymer matrix, being a continuous phase and making contact with individual primary particles (being substantially totally immersed in the polymer matrix) provide a 3D network of lithium ion-conducting paths. In other words, there are dual networks of conducting pathways for electrons and lithium ions inside the multi-functional composite particulate.

[0102] The anode active material may be selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), phosphorus (P), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium titanium niobium oxide, lithium-containing titanium oxide, lithium transition metal oxide, ZnCo.sub.2O.sub.4; (f) carbon or graphite particles (g) prelithiated versions thereof; and (h) combinations thereof.

[0103] Pre-lithiation of an anode active material can be conducted by several methods (chemical intercalation, ion implementation, and electrochemical intercalation). Among these, the electrochemical intercalation is the most effective. Lithium ions can be intercalated into non-Li elements (e.g. Si, Ge, and Sn) and compounds (e.g. SnO.sub.2 and Co.sub.3O.sub.4) up to a weight percentage of 54.68% (see Table 1 below). For Zn, Mg, Ag, and Au encapsulated inside an elastomer shell, the amount of Li can reach 99% by weight.

TABLE-US-00001 TABLE 1 Lithium storage capacity of selected non-Li elements. Atomic Atomic weight of Intercalated weight of Li, active material, Max. compound g/mole g/mole wt. % of Li Li.sub.4Si 6.941 28.086 49.71 L1.sub.4.4Si 6.941 28.086 54.68 Li.sub.4.4Ge 6.941 72.61 30.43 Li4.4Sn 6.941 118.71 20.85 Li.sub.3Cd 6.941 112.411 14.86 Li.sub.3Sb 6.941 121.76 13.93 Li.sub.4.4Pb 6.941 207.2 13.00 LiZn 6.941 65.39 7.45 Li.sub.3Bi 6.941 208.98 8.80

[0104] The particles of the anode active material may be in the form of a nano particle, nano wire, nano fiber, nano tube, nano sheet, nano platelet, nano disc, nano belt, nano ribbon, or nano horn. They can be non-lithiated (when incorporated into the anode active material layer) or pre-lithiated to a desired extent (up to the maximum capacity as allowed for a specific element or compound.

[0105] Preferably and typically, the high-elasticity polymer has a lithium ion conductivity no less than 10.sup.−5 S/cm, more preferably no less than 10.sup.−4 S/cm, further preferably no less than 10.sup.−3 S/cm, and most preferably no less than 10.sup.−2 S/cm. In some embodiments, the high-elasticity polymer is a neat polymer having no additive or filler dispersed therein. In others, the high-elasticity polymer is a polymer matrix composite containing from 0.1% to 50% (preferably 1% to 35%) by weight of a lithium ion-conducting additive dispersed in the high-elasticity polymer matrix material. The high-elasticity polymer should have a high elasticity (elastic deformation strain value >5%).

[0106] An elastic deformation is a deformation that is fully recoverable and the recovery process is essentially instantaneous (no significant time delay) upon release of the mechanical stress. The high-elasticity polymer can exhibit an elastic deformation from 5% up to 1,000% (10 times of its original length), more typically from 10% to 800%, and further more typically from 50% to 500%, and most typically and desirably from 70% to 300%.

[0107] It may be noted that although a metal typically has a high ductility (i.e. can be extended to a large extent without breakage), the majority of the deformation is plastic deformation (non-recoverable) and only a small amount of elastic deformation (typically <1% and more typically <0.2%).

[0108] Typically, a high-elasticity polymer is originally in a monomer, oligomer, or linear or branched chain states that can be cured to form a cross-linked polymer that is highly elastic. Prior to curing, these polymers or oligomers are soluble in an organic solvent or, preferably, water to form a polymer solution. Particles of an anode active material (e.g. SnO.sub.2 nano particles and Si nano-wires) can be dispersed in this polymer solution to form a suspension (dispersion or slurry) of an active material particle-polymer (monomer or oligomer) mixture. This suspension can then be subjected to a solvent removal treatment. The polymer (or monomer or oligomer) precipitates out to form a continuous phase or matrix in which the active material primary particles are dispersed (if a polymer content is high), or to form a coating encapsulating the anode particles (if a polymer content is low). This can be accomplished, for instance, via solution dipping, coating or casting on a solid substrate surface, spray drying, ultrasonic spraying, air-assisted spraying, aerosolization, and other secondary particle formation procedures.

[0109] It is essential for these materials to form a lightly cross-linked network of polymer chains. In other words, the network polymer or cross-linked polymer should have a relatively low degree of cross-linking or low cross-link density to impart a high elastic deformation.

[0110] The cross-link density of a cross-linked network of polymer chains may be defined as the inverse of the molecular weight between cross-links (Mc). The cross-link density can be determined by the equation, Mc=ρRT/Ge, where Ge is the equilibrium modulus as determined by a temperature sweep in dynamic mechanical analysis, p is the physical density, R is the universal gas constant in J/mol*K and T is absolute temperature in K. Once Ge and p are determined experimentally, then Mc and the cross-link density can be calculated.

[0111] The magnitude of Mc may be normalized by dividing the Mc value by the molecular weight of the characteristic repeat unit in the cross-link chain or chain linkage to obtain a number, Nc, which is the number of repeating units between two cross-link points. We have found that the elastic deformation strain correlates very well with Mc and. Nc. The elasticity of a cross-linked polymer derives from a large number of repeating units (large Nc) between cross-links. The repeating units can assume a more relax conformation (e.g. random coil) when the polymer is not stressed. However, when the polymer is mechanically stressed, the linkage chain uncoils or gets stretched to provide a large deformation. A long chain linkage between cross-link points (larger Nc) enables a larger elastic deformation. Upon release of the load, the linkage chain returns to the more relaxed or coiled state. During mechanical loading of a polymer, the cross-links prevent slippage of chains that otherwise form plastic deformation (non-recoverable).

[0112] Preferably, the Nc value in a high-elasticity polymer is greater than 5, more preferably greater than 10, further more preferably greater than 100, and even more preferably greater than 200. These Nc values can be readily controlled and varied to achieve different elastic deformation values by using different cross-linking agents with different functionalities, and by designing the polymerization and cross-linking reactions to proceed at different temperatures for different periods of time.

[0113] Alternatively, Mooney-Rilvin method may be used to determine the degree of cross-linking. Crosslinking also can be measured by swelling experiments. In a swelling experiment, the crosslinked sample is placed into a good solvent for the corresponding linear polymer at a specific temperature, and either the change in mass or the change in volume is measured. The higher the degree of crosslinking, the less swelling is attainable. Based on the degree of swelling, the Flory Interaction Parameter (which relates the solvent interaction with the sample, Flory Huggins Eq.), and the density of the solvent, the theoretical degree of crosslinking can be calculated according to Flory's Network Theory. The Flory-Rehner Equation can be useful in the determination of cross-linking.

[0114] The high-elasticity polymer matrix may contain a simultaneous interpenetrating network (SIPN) polymer, wherein two cross-linking chains intertwine with each other, or a semi-interpenetrating network polymer (semi-IPN), which contains a cross-linked polymer and a linear polymer.

[0115] The aforementioned high-elasticity polymers may be used alone to serve as a matrix. Alternatively, the high-elasticity polymer can be mixed with a broad array of elastomers, electrically conducting polymers, lithium ion-conducting materials, and/or strengthening materials (e.g. carbon nanotube, carbon nano-fiber, or graphene sheets).

[0116] A broad array of elastomers can be mixed with a high-elasticity polymer. Substantially all the anode primary particles in a particulate are fully embedded in and surrounded by the polymer, preventing direct contact between the particle(s) and the liquid electrolyte in the battery.

[0117] The high-elasticity polymer may further contain an elastomeric material selected from natural polyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR for isoprene rubber), polybutadiene (BR for butadiene rubber), chloroprene rubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber (copolymer of isobutylene and isoprene, IIR), including halogenated butyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR), styrene-butadiene rubber (copolymer of styrene and butadiene, SBR), nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM (ethylene propylene rubber, a copolymer of ethylene and propylene), EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene-component), epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such as Viton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM: Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA), chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinyl acetate (EVA), thermoplastic elastomers (TPE), protein resilin, protein elastin, ethylene oxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer, and combinations thereof.

[0118] The urethane-urea copolymer usually consists of two types of domains, soft domains and hard ones. Entangled linear backbone chains consisting of poly(tetramethylene ether) glycol (PTMEG) units constitute the soft domains, while repeated methylene diphenyl diisocyanate (MDI) and ethylene diamine (EDA) units constitute the hard domains. The lithium ion-conducting additive can be incorporated in the soft domains or other more amorphous zones.

[0119] In some embodiments, a high-elasticity polymer can form a polymer matrix composite containing a lithium ion-conducting additive dispersed in the high-elasticity polymer matrix material, wherein the lithium ion-conducting additive is selected from Li.sub.2CO.sub.3, Li.sub.2O, Li.sub.2C.sub.2O.sub.4, LiOH, LiX, ROCO.sub.2Li, HCOLi, ROLi, (ROCO.sub.2Li).sub.2, (CH.sub.2OCO.sub.2Li).sub.2, Li.sub.2S, Li.sub.xSO.sub.y, or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1, 1≤y≤4.

[0120] In some embodiments, the high-elasticity polymer can be mixed with a lithium ion-conducting additive, which contains a lithium salt selected from lithium perchlorate (LiClO.sub.4), lithium hexafluorophosphate (LiPF.sub.6), lithium borofluoride (LiBF.sub.4), lithium hexafluoroarsenide (LiAsF.sub.6), lithium trifluoro-methanesulfonate (LiCF.sub.3SO.sub.3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF.sub.3SO.sub.2).sub.2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF.sub.2C.sub.2O.sub.4), lithium nitrate (LiNO.sub.3), Li-fluoroalkyl-phosphate (LiPF.sub.3(CF.sub.2CF.sub.3).sub.3), lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, or a combination thereof.

[0121] The high-elasticity polymer may form a mixture or blend with an electron-conducting polymer selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g. sulfonated versions), or a combination thereof.

[0122] In some embodiments, the high-elasticity polymer may form a mixture with a lithium ion-conducting polymer selected from poly(ethylene oxide) (PEO), Polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxy ethoxyethoxide-phosphazene, Polyvinyl chloride, Polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivative thereof (e.g. sulfonated versions), or a combination thereof.

[0123] The present disclosure also provides a method of producing composite particulates comprising anode active material particles dispersed in a high-elasticity polymer. As schematically illustrated in FIG. 4(A), the method comprises mixing reactants (phosphazene monomer, initiator, and curing or crosslinking agent) or at least a reactive phosphazene polymer, primary particles of an anode active material, optional reinforcement material, and optional lithium ion-conducting additive to form a reactive slurry. One may mix these ingredients sequentially or concurrently. For instance, one may mix all of these ingredients to form the reactive slurry in one pot (one container) all at once and then rapidly form the reactive slurry into micro-droplets, allowing the reactants to react with one another for polymerizing and crosslinking to form the networks of crosslinked polymer chains. The anode active material particles are dispersed in the polymer or encapsulated by the polymer or encapsulated by the polymer.

[0124] Alternatively, one may first mix certain ingredient(s) in one pot and other ingredients in other pot(s) and then combine them together in one pot. For instance, one may mix the monomer and the initiator in one pot, allowing the mixture to proceed to form a reactive oligomer (low molecular weight chains). A separate pot may be used to contain the curing agent (crosslinker). The primary particles of anode active material and other ingredients may be dispersed into either pot or both pots. The ingredients in two pots are then combined together and then heated or radiation-exposed to initiate the polymerization and crosslinking reactions (if appropriate).

[0125] The present disclosure also provides a method of manufacturing the composite particulates described above, the method comprising: (a) dispersing multiple particles of an anode active material in a precursor polymer solution to form a suspension wherein these particles are fully embedded or immersed in the precursor solution, which comprises at least a curing agent dissolved or dispersed in a reactive liquid medium that comprises a monomer or oligomer, and an optional non-aqueous liquid solvent, wherein the monomer or oligomer is selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof; (b) operating a secondary particle-forming procedure to shape the suspension into multiple droplets and remove the liquid solvent from the droplets; and (c) curing the monomer or oligomer to form said composite particulates wherein a particulate comprises one or a plurality of anode active material particles that are dispersed and embedded in a polymer matrix or encapsulated by a polymer shell. Preferably, the high-elasticity polymer has a lithium-ion conductivity from 1×10.sup.−8 S/cm to 5×10.sup.−2 S/cm. In some embodiments, the high-elasticity polymer has a recoverable tensile strain from 35% to 700% (more preferably >50%, and most preferably >100%).

[0126] Several composite droplet forming processes require the high-elasticity polymer or its precursor (monomer or oligomer) to be dissolvable in a solvent. Fortunately, all the high-elasticity polymers or their precursors used herein are either in a liquid state at room temperature or are soluble in some common solvents. The un-cured polymer or its precursor can be readily dissolved in a common organic solvent or water to form a solution. This solution can then be used to embed, immerse, engulf or encapsulate the solid particles (anode particles along with other additive or reinforcement materials) via several of the micro-droplet-forming methods to be discussed in what follows. Upon formation of the droplets, the polymer matrix is then polymerized and cross-linked.

[0127] There are three broad categories of micro-encapsulation methods that can be implemented to produce high-elasticity polymer composite: physical methods, physico-chemical methods, and chemical methods. The physical methods include extrusion and pelletizing, solution dipping and drying, suspension coating or casting on a solid substrate (e.g. slot-die coating, Comma coating, spray-coating) followed by drying and scratching off particles from the substrate, pan-coating, air-suspension coating, centrifugal extrusion, vibration nozzle, and spray-drying methods. The physico-chemical methods include ionotropic gelation and coacervation-phase separation methods. The chemical methods include interfacial polycondensation, interfacial cross-linking, in-situ polymerization, and matrix polymerization.

[0128] It may be noted that some of these methods (e.g. pan-coating, air-suspension coating, and spray-drying) may be used to coat or encapsulate primary particles or particulates (secondary particles) by adjusting the solid content, degree of dispersion, spraying and drying conditions, etc. Similar processes may be used to produce composite particulates wherein the particles are fully dispersed in a polymer matrix, not just coating on some surfaces. This can be accomplished by providing a higher amount of the reacting monomer, oligomer, or polymer with respect to the anode particles, for instance.

[0129] Pan-coating method: The pan coating process involves tumbling the anode active material primary particles (along with any desired additive or reinforcement materials) in a pan or a similar device while the matrix material (e.g., monomer/oligomer liquid or uncured polymer/solvent solution; possibly containing a lithium salt dispersed or dissolved therein) is applied slowly until a desired amount of matrix is attained.

[0130] Air-suspension coating method: In the air suspension coating process, the solid primary particles of anode active material are dispersed into the supporting air stream in an embedding chamber. A controlled stream of a reactive precursor solution (e.g., polymer or its monomer or oligomer dissolved in a solvent; or its monomer or oligomer alone in a liquid state) is concurrently introduced into this chamber, allowing the solution to hit and embed the suspended particles. These suspended particles are embedded in the reactive precursor (monomer, oligomer, etc. which is polymerized/cured concurrently or subsequently) while the volatile solvent is removed, leaving behind a composite comprising a matrix of conducting network polymer and anode active material particles. This process may be repeated several times until the required parameters, such as full embedding, are achieved. The air stream which supports the anode particles also helps to dry them, and the rate of drying is directly proportional to the temperature of the air stream, which can be adjusted for optimized polymer network amount.

[0131] In a preferred mode, the particles in the embedding zone portion may be subjected to re-circulation for repeated embedding. Preferably, the chamber is arranged such that the particles pass upwards through the embedding zone, then are dispersed into slower moving air and sink back to the base of the encapsulating chamber, enabling repeated passes of the particles through the embedding zone until the desired matrix amount is achieved.

[0132] Centrifugal extrusion: Primary anode particles may be embedded in a polymer network or precursor material using a rotating extrusion head containing concentric nozzles. In this process, a stream of core fluid (slurry containing anode particles dispersed in a solvent) is surrounded by a sheath of shell solution or melt containing the polymer or precursor. As the device rotates and the stream moves through the air it breaks, due to Rayleigh instability, into droplets of core, each coated with the shell solution. While the droplets are in flight, the molten shell may be hardened or the solvent may be evaporated from the shell solution. If needed, the capsules can be hardened after formation by catching them in a hardening bath. Since the drops are formed by the breakup of a liquid stream, the process is only suitable for liquid or slurry. A high production rate can be achieved. Up to 22.5 kg of microcapsules can be produced per nozzle per hour and extrusion heads containing 16 nozzles are readily available.

[0133] Vibrational nozzle encapsulation method: matrix-encapsulation of anode particles can be conducted using a laminar flow through a nozzle and vibration of the nozzle or the liquid. The vibration has to be done in resonance with the Rayleigh instability, leading to very uniform droplets. The liquid can include any liquids with limited viscosities (1-50,000 mPa.Math.s): emulsions, suspensions or slurry containing the anode active material particles and the polymer or precursor.

[0134] Spray-drying: Spray drying may be used to encapsulate and embed anode particles when the particles are suspended in a melt or polymer/precursor solution to form a suspension. In spray drying, the liquid feed (solution or suspension) is atomized to form droplets which, upon contacts with hot gas, allow solvent to get vaporized and a polymer matrix to fully embed the particles.

[0135] In-situ polymerization: In some micro-encapsulation processes, anode particles are fully embedded in a monomer or oligomer first. Then, direct polymerization of the monomer or oligomer is carried out with the presence of these material particles dispersed therein.

[0136] Matrix polymerization: This method involves dispersing and embedding anode primary particles in a polymeric matrix during formation of the particles. This can be accomplished via spray-drying, in which the particles are formed by evaporation of the solvent from the matrix material. Another possible route is the notion that the solidification of the matrix is caused by a chemical change.

[0137] In summary, in certain embodiments, the disclosure provides a method of producing the multi-functional particulates, the method comprising (A) dispersing a plurality of primary particles of an anode active material, having a diameter or thickness from 0.5 nm to 20 μm, in a liquid mixture of a monomer or oligomer of a phosphazene compound or derivative, an initiator, and a cross-linking agent to form a reactive slurry; (B) forming the reactive slurry into micro-droplets and polymerizing and curing the monomer or oligomer in the micro-droplets to form the multi-functional particulates. The reactive mixture may further comprise a dopant, a reinforcement material, a lithium ion-conducting additive, an electron-conducting additive, or a combination thereof.

[0138] A foaming agent or blowing agent may be introduced into the reactive slurry and can be activated to produce pores in the micro-droplets when the reactive species are polymerized or crosslinked.

[0139] In some embodiments, the reactive slurry further comprises a high-strength material selected from carbon nanotubes, carbon nano-fibers, carbon or graphite fibers, graphene sheets, expanded graphite flakes, polymer fibrils, glass fibers, ceramic fibers, metal filaments or metal nano-wires, or a combination thereof. Some of these high-strength materials are electron-conducting.

[0140] The step (B) of forming micro-droplets may comprise a procedure selected from solution dipping, coating or casting on a solid substrate, pan-coating, air-suspension coating, centrifugal extrusion, vibration-nozzle encapsulation, spray-drying, coacervation-phase separation, interfacial polycondensation or interfacial cross-linking, in-situ polymerization, matrix polymerization, extrusion and palletization, or a combination thereof.

[0141] In certain embodiments, the micro-droplets as formed may contain a liquid solvent and the method further comprises a step of removing the solvent.

[0142] The following examples serve to provide the best modes of practice for the present disclosure and should not be construed as limiting the scope of the disclosure:

Example 1: Composite Particulates Containing FEC and PEGDA Polymer-Protected Micron-Scale Si Particles

[0143] Si particles were encapsulated with a high-elasticity polymer. In one example, FEC and poly(ethyleneglycol) diacrylate (PEGDA) (structures shown below),

##STR00012##

were stirred under the protection of argon gas until a homogeneous solution was obtained. Subsequently, lithium hexafluoro phosphate (4%) and, lithium trifluoro-methanesulfonate, LiCF.sub.3SO.sub.3 (1% by weight) were then added and dissolved in the above solution to obtain a reactive mixture solution, wherein the weight, fractions of fluorinated vinylene carbonate, polyethyleneglycol diacrylate, and lithium salts were 85 wt %, 10 wt %, and 5 wt %, respectively. Si particles were then added into the solution to form a slurry, which was partially dried in a vacuum oven to obtain a reactive mass. The reactive mass was then irradiated with electron beam at room temperature until a total dosage of 40 Gy was reached, resulting in the formation of an elastic polymer.

[0144] On a separate basis, some amount of the reactive solution without Si was cast onto a glass surface to form a wet film, which was thermally dried and then cured under similar conditions to form a film of polymer. Several tensile testing specimens were cut from each polymer film and tested with a universal testing machine. The representative tensile stress-strain curves indicate that this series of network polymers have an elastic deformation from approximately 15% to 115%.

[0145] For electrochemical testing, the working electrodes were prepared by mixing 85 wt. % active material particles (polymer-protected and non-protected particulates of Si, separately), 7 wt. % acetylene black (Super-P), and 8 wt. % polyvinylidene fluoride (PVDF) binder dissolved in N-methyl-2-pyrrolidinoe (NMP) to form a slurry of 5 wt. % total solid content. After coating the slurries on Cu foil, the electrodes were dried at 120° C. in vacuum for 2 h to remove the solvent before pressing. Then, the electrodes were cut into a disk (ϕ)=12 mm) and dried at 100° C. for 24 h in vacuum. Electrochemical measurements were carried out using CR2032 (3V) coin-type cells with lithium metal as the counter/reference electrode, Celgard 2400 membrane as separator, and 1 M LiPF.sub.6 electrolyte solution dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v). The cell assembly was performed in an argon-filled glove-box. The CV measurements were carried out using an-6 electrochemical workstation at a scanning rate of 1 mV/s. The electrochemical performance of the particulates of high-elasticity polymer-encapsulated Si particles and non-protected Si particles were evaluated by galvanostatic charge/discharge cycling at a current density of 50-200 mA/g, using an electrochemical workstation.

[0146] FIG. 5(A) shows the charge/discharge curves of a lithium-ion cell having an anode of unprotected sub-micron Si particles. The first-cycle Coulomb efficiency of this cell is only from 50.2% to 55.9%, indicating that up to 49.2% of the active lithium ions intercalated into micron-scaled Si particles have become in-activated, no longer being able to return to the cathode side during the first discharge. As shown in FIG. 5(B), the specific capacity values of such a cell suffers from a rapid capacity decay.

[0147] In contrast, as demonstrated FIG. 5(C), the lithium-ion cell having an anode of high-elasticity polymer matrix-protected Si particles delivers an average first-cycle Coulomb efficiency of greater than 92.7%, which is among the very best for all Si-based anodes reported in open literature. As shown in FIG. 5(D), such a cell also exhibits a relatively stable charge/discharge cycling behavior.

Example 2: Encapsulating Polymer from a Fluorinated Vinyl Carbonate

[0148] Similar procedure as in Example 1 was followed, but the monomer was a fluorinated vinyl carbonate, given below:

##STR00013##

which was cured with an initiator, 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (Ciba DAROCUR-1173), with the assistance of electron beam irradiation.

Example 3: Encapsulating Polymer from 2-(Trifluoromethyl)Acrylic Acid

[0149] Similar procedure as in Example 1 was followed, but the monomer was 2-(Trifluoromethyl)acrylic acid, as shown below (melting point=52° C.):

##STR00014##

Polyethylene glycol) diacrylate was used as an initiator and mixing was conducted at 60° C.

Example 4: High-Elasticity Vinyl Sulfite Polymer Matrix-Protected Tin Oxide Particulates

[0150] Tin oxide (SnO.sub.2) nano particles were obtained by the controlled hydrolysis of SnCl.sub.4.5H.sub.2O with NaOH using the following procedure: SnCl.sub.4.5H.sub.2O (0.95 g, 2.7 m-mol) and NaOH (0.212 g, 5.3 m-mol) were dissolved in 50 mL of distilled water each. The NaOH solution was added drop-wise under vigorous stirring to the tin chloride solution at a rate of 1 mL/min. This solution was homogenized by sonication for 5 m in. Subsequently, the resulting hydrosol was reacted with H.sub.2SO.sub.4. To this mixed solution, few drops of 0.1 M of H.sub.2SO.sub.4 were added to flocculate the product. The precipitated solid was collected by centrifugation, washed with water and ethanol, and dried in vacuum. The dried product was heat-treated at 400° C. for 2 h under Ar atmosphere.

[0151] Under the protection of argon, lithium hexafluorophosphate with the mass fraction of 5% was added into vinyl sulfite to form a solution, which was stirred uniformly. Then azodiisobutyronitrile with the mass fraction of 0.5% was added into the solution, which was stirred to obtain a uniformly mixed solution. SnO.sub.2 nano particles were then added into the solution to prepare a slurry. The slurry was cured at the temperature of 40° C. for 4 hours.

[0152] Separately, the reacting mass was cast onto a glass surface to form several films which were cured to obtain polymers. Tensile testing was conducted on these films. This series of polymers can be elastically stretched up to approximately 68%.

Example 5: Polymerized Vinylene Trithiocarbonate as the Encapsulating Polymer

[0153] Under the protection of argon, 10 mass percent of lithium bis(trifluoromethyl)sulfonyl imide was added into ethylene carbonate, which was stirred to achieve a uniform solution. Subsequently, 3 mass percent of benzoyl peroxide was into the solution, followed by addition of anode active material particles (Si nanowires) to obtain a slurry. The slurry was cured and dried at 60° C. in a vacuum oven for 5 hours to polymerize the vinylene trithiocarbonate. The resulting solid was subjected to mechanical shearing in a food blender to produce powder of composite particulates.

Example 6: Matrix Polymer from Methyl Vinyl Sulfone

[0154] Under the protection of argon, 30% by mass of lithium perchlorate was added into methyl vinyl sulfone and then uniformly stirred to produce a solution. Then, 1% by mass of dimethyl azodiisobutyrate was added into the solution. To this solution were added SiO particles to obtain a slurry, which was dried in a vacuum oven at 80° C. for 7 hours to polymerize the methyl vinyl sulfone. The solid mass was then lightly ball-milled to produce composite particulates.

[0155] Additionally, polymer films without the anode particles were cast on a glass surface and were subjected to the same polymerization conditions. The tensile elastic strains were found to be from 16% to 62%.

Example 7: Si Nano Particle- and Nanowire-Based Particulates Dispersed in a High-Elasticity Polymer Matrix

[0156] Under the protection of argon, vinyl sulfite and ethyl vinyl sulfone were mixed together according to a molar ratio of 10:1. Subsequently, 2 mass percent of lithium bis(oxalato)borate and 0.1 mass percent of methyl ethyl ketone peroxide were added and stirring was continued for 15 minutes to obtain a mixed solution. Si nano particles and nanowires were separately added into a solution to form two slurry samples. The samples were cast on a glass surface and then heated to 30° C. for 2 hours to polymerize vinyl sulfite and ethyl vinyl sulfone. Powder of composite particulates was obtained by low-intensity ball-milling of the resulting product.

Example 8: Polymerized Ethylene Carbonate and Vinyl Acetate as an Encapsulating Polymer

[0157] Under the protection of argon, ethylene carbonate and vinyl acetate are mixed according to the molar ratio of 5:1. The mixture was stirred uniformly, and then benzoyl peroxide with a mass fraction of 5% was added in a droplet-wise manner into the mixture to form a homogeneous solution. Anode particles (Co.sub.3O.sub.4) were then added into the solution to prepare a slurry. The slurry in a glass container was housed in a bag and heated at a vacuum oven at 40° C. for 4 hours while under electron beam irradiation to polymerize and cure vinyl ethylene sulfite.

Example 9: Polymer from Vinyl Sulfite, Methyl Vinyl Sulfone and Methyl Methacrylate

[0158] Under the protection of argon, vinyl sulfite, methyl vinyl sulfone and methyl methacrylate were mixed according to a molar ratio of 5:2:3. After some stirring, 1 mass percent of benzoyl peroxide tert-butyl ester was added into the mixture solution. Anode particles (Sn particles) were then dispersed into this solution, which was further stirred and mixed uniformly to obtain a slurry. The slurry was heated in a vacuum oven at 70° C. for 4 hours, allowing the vinyl sulfite, methyl vinyl sulfone and methyl methacrylate to get co-polymerize and cured.

Example 10: Polymerized Phenyl Vinyl Sulfide

[0159] Phenyl vinyl sulfide, CTA (chain transfer agent, shown below), AIBN (initiator, 1.0%), and Si nano particles were mixed and heated at 60° C. to obtain a cured dry mass. The dried solid was then ball-milled to obtain powder of composite particulates.

##STR00015##

Example 11: Polymerized Ethyl Vinyl Sulfone

[0160] The reaction of vinyl sulfones (e.g., ethyl vinyl sulfone, EVS), acrylates (e.g. hexanethiol, HA) and/or 1-Hexanethiol (HT) as a co-reactant or curing agent, and triethylamine (TEA) as an initiator was investigated. Hexanethiol (HT), ethyl vinyl sulfone (EVS) and hexyl acrylate (HA) were prepared at a molar ratio from 1:1:0.1 (no unreacted HA) to 1:1:0.3 (20% of HA remained unreacted). The thiol reactant and the initiator, along with SiO particles, were added to a glass vial and thoroughly mixed. Varying stoichiometric amounts of vinyl sulfone and acrylate were added to the mixture, which was mixed vigorously and then allowed start the thiol—Michael addition reaction. With a 2.0% TEA initiator, the reaction can be concluded in approximately 20-40 minutes, generating a network of crosslinked chains. The use of acrylates via thiol—Michael addition reaction in ternary systems was used to control gelation behavior in crosslinked polymer networks formed by thiol—Michael addition reactions.

Example 12: Polymerized Phenyl Vinyl Sulfone

[0161] Phenyl vinyl sulfone (PVS) can be polymerized with several anionic-type initiators; e.g., n-BuLi, ZnEt2, LiN(CH.sub.2).sub.2, and NaNH.sub.2. The second solvent may be selected from pyridine, sulfolane, toluene or benzene, which may be removed before or after polymerization.

[0162] In an example, a mixture of PVS, n-BuLi (1.0%), LiBF.sub.4 (0.5 M), and sulfolane was thoroughly mixed and was maintained at 30° C. overnight to cure the polymer.

Example 13: Cured Polymer from a Dinitrile Monomer

[0163] A monomer solvent 4,4′-(1,4-Butylenedioxy)dibenzonitrile (BDDN) was used, along with trifluoromethanesulfonic acid (CF.sub.3SO.sub.3H) as an initiator dissolved in o-dichlorobenzene (o-DCB) in the polymerization reaction.

##STR00016##

The reaction was carried out in o-DCB under nitrogen for 30 min, having [BDDN]=0.125 M; and [CF.sub.3SO.sub.3H]=0.5 M. A typical experimental procedure for the polymerization of BDDN is given in the following as an example. In a 20 mL test tube equipped with a magnetic stirrer were placed BDDN (0.25 mmol) and CF.sub.3SO.sub.3H (1 mmol) in 2 mL o-DCB. The mixture solution was added with particles of an anode active material and the resulting slurry was stirred at room temperature for 5 minutes and then allowed to proceed with reactions for 1 hour.

[0164] The present study led to the following additional observations: [0165] (1) The high-elasticity polymer matrix embedding or shell encapsulating strategy is surprisingly effective in alleviating the anode expansion/shrinkage-induced capacity decay problems. Such a strategy appears to have significantly reduced or eliminated the possibility of repeated SEI formation and breakage that would otherwise continue to consume electrolyte and active lithium ions. [0166] (2) It is quite surprising that the group of polymers herein investigated (commonly used as an additive in a battery liquid electrolyte) can be so elastic and lithium ion-conducting (even without the presence of a lithium salt), having a lithium ion conductivity typically in the range from 10.sup.−6 to 10.sup.−3 S/cm at room temperature. [0167] (3) The encapsulation of high-capacity anode active material particles by carbon or other protective materials without high elasticity polymer protection does not provide much benefit in terms of improving cycling stability of a lithium-ion battery.