Elastomer-Encapsulated particles of high-capacity anode active materials for lithium batteries

Abstract

Provided is an anode active material layer for a lithium battery. This layer comprises multiple particulates of an anode active material, wherein at least a particulate is composed of one or a plurality of particles of a high-capacity anode active material being encapsulated by a thin layer of elastomeric material that has a lithium ion conductivity no less than 10.sup.−7 S/cm (preferably no less than 10.sup.−5 S/cm) at room temperature and an encapsulating shell thickness from 1 nm to 10 μm, and wherein the high-capacity anode active material (e.g. Si, Ge, Sn, SnO.sub.2, Co.sub.3O.sub.4, etc.) has a specific capacity of lithium storage greater than 372 mAh/g (the theoretical lithium storage limit of graphite).

Claims

1. An anode active material layer for a lithium battery, said anode active material layer comprising multiple particulates of an anode active material, wherein a particulate is composed of one or a plurality of particles of a high-capacity anode active material being encapsulated by a thin layer of elastomeric material that has a lithium ion conductivity no less than 10.sup.−7 S/cm at room temperature and an encapsulating shell thickness from 1 nm to 10 μm, and wherein said high-capacity anode active material has a specific capacity of lithium storage greater than 372 mAh/g.

2. The anode active material layer 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), 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-containing titanium oxide, lithium transition metal oxide; (f) prelithiated versions thereof; (g) particles of Li, Li alloy, or surface-stabilized Li having at least 60% by weight of lithium element therein; and (h) combinations thereof.

3. The anode active material layer of claim 1, wherein said Li alloy contains from 0.1% to 10% by weight of a metal element selected from Zn, Ag, Au, Mg, Ni, Ti, Fe, Co, V, or a combination.

4. The anode active material layer 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 VO.sub.2, prelithiated Co.sub.3O.sub.4, prelithiated Ni.sub.3O.sub.4, or a combination thereof, wherein x=1 to 2.

5. The anode active material layer of claim 1, wherein said anode active material is in a form of nano particle, nano wire, nano fiber, nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet, or nano horn having a thickness or diameter from 0.5 nm to 100 nm.

6. The anode active material layer of claim 5, wherein said anode active material has a dimension less than 20 nm.

7. The anode active material layer of claim 1, wherein said one or a plurality of particles is coated with a layer of carbon disposed between said one or said plurality of particles and said elastomeric material layer.

8. The anode active material layer of claim 1, wherein said particulate further contains a graphite or carbon material therein.

9. The anode active material layer of claim 8, wherein said graphite 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, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, or a combination thereof.

10. The anode active material layer of claim 5, wherein said nano particle, nano wire, nano fiber, nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet, or nano horn is coated with or embraced by a conductive protective coating selected from a carbon material, electronically conductive polymer, conductive metal oxide, or conductive metal coating.

11. The anode active material layer of claim 10, wherein said nano particle, nano wire, nano fiber, nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet, or nano horn is pre-intercalated or pre-doped with lithium ions to form a prelithiated anode active material having an amount of lithium from 0.1% to 54.7%% by weight of said prelithiated anode active material.

12. The anode active material layer of claim 1, wherein said elastomeric material has a lithium ion conductivity no less than 10.sup.−5 S/cm.

13. The anode active material layer of claim 1, wherein said elastomeric material has a lithium ion conductivity no less than 10.sup.−4 S/cm

14. The anode active material layer of claim 1, wherein said elastomeric material is a neat polymer having no additive or filler dispersed therein.

15. The anode active material layer of claim 1, wherein said elastomeric material is an elastomer matrix composite containing from 0.1% to 50% by weight of a lithium ion-conducting additive dispersed in an elastomer matrix material.

16. The anode active material layer of claim 1, wherein said elastomeric material contains a material 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.

17. The anode active material layer of claim 1, wherein said elastomeric material is an elastomer matrix composite containing a lithium ion-conducting additive dispersed in an elastomer matrix material, 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, x=0-1, y=1-4.

18. The anode active material layer of claim 1, wherein said elastomeric material is an elastomer matrix composite containing a lithium ion-conducting additive dispersed in an elastomer matrix material, wherein said lithium ion-conducting additive 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-metasulfonate, 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, lithium nitrate, LiNO.sub.3, Li-Fluoroalkyl-Phosphates, LiPF.sub.3(CF.sub.2CF.sub.3).sub.3, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithium bis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide, lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-based lithium salt, or a combination thereof.

19. The anode active material layer of claim 1, wherein said elastomeric material contains a mixture or blend of an elastomer and an electron-conducting polymer selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, a sulfonated derivative thereof, or a combination thereof.

20. The anode active material layer of claim 1, wherein said elastomeric material contains a mixture or blend of an elastomer and 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-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonated derivative thereof, or a combination thereof.

21. A powder mass of an anode active material for a lithium battery, said powder mass comprising multiple particulates wherein at least a particulate is composed of one or a plurality of particles of a high-capacity anode active material being encapsulated by a thin layer of elastomeric material that has a lithium ion conductivity no less than 10.sup.−7 S/cm at room temperature and an encapsulating shell thickness from 1 nm to 10 μm, and wherein said high-capacity anode active material has a specific capacity of lithium storage greater than 372 mAh/g.

22. The powder mass of claim 21, further comprising graphite particles, carbon particles, meso-phase microbeads, carbon or graphite fibers, carbon nanotubes, graphene sheets, or a combination thereof.

23. The powder mass of claim 21, wherein said high-capacity anode active material is pre-lithiated to contains from 0.1% to 54.7% by weight of lithium.

24. A lithium battery containing an optional anode current collector, the anode active material layer as defined in claim 1, a cathode active material layer, an optional cathode current collector, an electrolyte in ionic contact with said anode active material layer and said cathode active material layer, and an optional porous separator.

25. The lithium battery of claim 24, which is a lithium-ion battery, lithium metal battery, lithium-sulfur battery, lithium-selenium battery, or lithium-air battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] 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.

[0034] 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).

[0035] 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;

[0036] 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.

[0037] FIG. 3 Schematic of the presently invented elastomer-encapsulated anode active material particles (pre-lithiated or unlithiated). The elasticity of the elastomeric shell enables the shell to expand and contract congruently and conformingly with core particle.

[0038] FIG. 4 Schematic of four types of elastomer-embraced anode active material particles.

[0039] FIG. 5 The specific capacity of a lithium battery having an anode active material featuring elastomer-encapsulated Co.sub.3O.sub.4 particles and that having un-protected Co.sub.3O.sub.4 particles.

[0040] FIG. 6 The specific capacity of a lithium battery having an anode active material featuring elastomer-encapsulated SnO.sub.2 particles and that having un-protected SnO.sub.2 particles.

[0041] FIG. 7 The specific capacity of a lithium battery having an anode active material featuring elastomer-encapsulated Sn particles, that having carbon-encapsulated Sn particles, and that having un-protected Sn particles.

[0042] FIG. 8 Specific capacities of 4 lithium-ion cells having Si nanowires (SiNW) as an anode active material: unprotected SiNW, carbon-coated SiNW, elastomer-encapsulated SiNW, and elastomer-encapsulated carbon-coated SiNW.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0043] This invention is directed at the anode active material layer (negative electrode layer, not including the anode current collector) containing a high-capacity anode material 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 invention is not limited to any battery shape or configuration. 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 invention.

[0044] 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.

[0045] 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 sheet of copper foil. This is not commonly used in the battery industry and, hence, will not be discussed further.

[0046] 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: [0047] 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. [0048] 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.

[0049] 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. [0050] 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. [0051] 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.

[0052] In other words, there are several conflicting factors that must 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 elastomer-protected anode active material.

[0053] The present invention provides an anode active material layer comprising multiple particulates of an anode active material, wherein a particulate is composed of one or a plurality of particles of a high-capacity anode active material being encapsulated by a thin layer of elastomeric material that has a lithium ion conductivity no less than 10.sup.−7 S/cm at room temperature and an encapsulating shell thickness from 1 nm to 10 μm, and wherein said high-capacity anode active material has a specific capacity of lithium storage greater than 372 mAh/g (which is the theoretical capacity of graphite).

[0054] As illustrated in FIG. 4, the present invention provides four major types of particulates of elastomer-encapsulated anode active material particles. The first one is a single-particle particulate containing an anode active material core 10 encapsulated by an elastomer 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 an elastomer 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 an elastomer 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 an elastomer shell 28. These anode active material particles can be pre-lithiated or non-prelithiated.

[0055] As schematically illustrated in the upper portion of FIG. 3, a non-lithiated Si particle can be encapsulated by an elastomeric shell to form a core-shell structure (Si core and elastomer shell in this example). As the lithium-ion battery is charged, the anode active material (elastomer-encapsulated Si particle) is intercalated with lithium ions and, hence, the Si particle expands. Due to the high elasticity of the encapsulating shell (elastomer), the shell will not be broken into segments (in contrast to the broken carbon shell). That the elastomeric shell remains intact prevents the exposure of the underlying Si to 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 to form additional SEI.

[0056] Alternatively, referring to the lower portion of FIG. 3, wherein the Si particle has been pre-lithiated with lithium ions; i.e. has been pre-expanded in volume. When a layer of elastomer is encapsulated around the pre-lithiated Si particle, another core-shell structure is formed. When the battery is discharged and lithium ions are released (de-intercalated) from the Si particle, the Si particle contracts. However, the elastomer is capable of elastically shrinking in a conformal manner; hence, leaving behind no gap between the protective shell and the Si particle. Such a configuration is amenable to subsequent lithium intercalation and de-intercalation of the Si particle. The elastomeric shell expands and shrinks congruently with the expansion and shrinkage of the encapsulated core anode active material particle, enabling long-term cycling stability of a lithium battery featuring a high-capacity anode active material (such as Si, Sn, SnO.sub.2, Co.sub.3O.sub.4, etc.).

[0057] The anode active material may be selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), 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-containing titanium oxide, lithium transition metal oxide; (f) prelithiated versions thereof; (g) particles of Li, Li alloy, or surface-stabilized Li; and (h) combinations thereof Particles of Li or Li alloy (Li alloy containing from 0.1% to 10% by weight of Zn, Ag, Au, Mg, Ni, Ti, Fe, Co, or V element), particularly surface-stabilized Li particles (e.g. wax-coated Li particles), were found to be good anode active material per se or an extra lithium source to compensate for the loss of Li ions that are otherwise supplied only from the cathode active material. The presence of these Li or Li-alloy particles encapsulated inside an elastomeric shell was found to significantly improve the cycling performance of a lithium cell.

[0058] 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 weight of Max. Intercalated of Li, active material, wt. % compound g/mole g/mole of Li Li.sub.4Si 6.941 28.086 49.71 Li.sub.4.4Si 6.941 28.086 54.68 Li.sub.4.4Ge 6.941 72.61 30.43 Li.sub.4.4Sn 6.941 118.71 20.85 Li.sub.3Cd 6.941 112.411 14.86 Li3Sb 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

[0059] 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.

[0060] Preferably and typically, the elastomeric material has a lithium ion conductivity no less than 10.sup.−7 S/cm, more preferably no less than 10.sup.−5 S/cm, further preferably no less than 10.sup.−4 S/cm, and most preferably no less than 10.sup.−3 S/cm. In some embodiments, the elastomeric material is a neat polymer having no additive or filler dispersed therein. In others, the elastomeric material is an elastomer matrix composite containing from 0.1% to 50% (preferably 1% to 35%) by weight of a lithium ion-conducting additive dispersed in an elastomer matrix material. The elastomeric material must have a high elasticity (high elastic deformation value). An elastic deformation is a deformation that is fully recoverable and the recovery process is essentially instantaneous (no significant time delay). An elastomer, such as a vulcanized natural rubber, can exhibit an elastic deformation from 2% 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 100% to 500%. 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%).

[0061] A broad array of elastomers, as a neat resin alone or as a matrix material for an elastomeric matrix composite, can be used to encapsulate an anode active material particle or multiple particles. Encapsulation means substantially fully embracing the particle(s) without allowing the particle to be in direct contact with electrolyte in the battery. The elastomeric material may be 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.

[0062] The urethane-urea copolymer film 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.

[0063] In some embodiments, the elastomeric material is an elastomer matrix composite containing a lithium ion-conducting additive dispersed in an elastomer matrix material, 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, x=0-1, y=1-4.

[0064] In some embodiments, the elastomeric material is an elastomer matrix composite containing a lithium ion-conducting additive dispersed in an elastomer matrix material, wherein said lithium ion-conducting additive 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-metasulfonate, 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, lithium nitrate, LiNO.sub.3, Li-Fluoroalkyl-Phosphates, LiPF.sub.3(CF.sub.2CF.sub.3).sub.3, lithium bisperfluoro-ethysulfonylimide, LiBETI, lithium bis(trifluoromethanesulphonyl)imide, lithium bis(fluorosulphonyl)imide, lithium trifluoromethanesulfonimide, LiTFSI, an ionic liquid-based lithium salt, or a combination thereof.

[0065] The elastomeric material may contain a mixture or blend of an elastomer and an electron-conducting polymer selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g. sulfonated versions), or a combination thereof.

[0066] In some embodiments, the elastomeric material contains a mixture or blend of an elastomer and 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-phosphazenex, Polyvinyl chloride, Polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivative thereof (e.g. sulfonated versions), or a combination thereof.

[0067] Some elastomers are originally in an unsaturated chemical state (unsaturated rubbers) that can be cured by sulfur vulcanization to form a cross-linked polymer that is highly elastic (hence, an elastomer). Prior to vulcanization, these polymers or oligomers are soluble in an organic solvent 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 mixture. This suspension can then be subjected to a solvent removal treatment while individual particles remain substantially separated from one another. The polymer precipitates out to deposit on surfaces of these active material particles. This can be accomplished, for instance, via spray drying.

[0068] Unsaturated rubbers that can be vulcanized to become elastomer include 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),

[0069] Some elastomers are saturated rubbers that cannot be cured by sulfur vulcanization; they are made into a rubbery or elastomeric material via different means: e.g. by having a copolymer domain that holds other linear chains together. Each of these elastomers can be used to encapsulate particles of an anode active material by one of several means: melt mixing (followed by pelletizing and ball-milling, for instance), solution mixing (dissolving the anode active material particles in an uncured polymer, monomer, or oligomer, with or without an organic solvent) followed by drying (e.g. spray drying), interfacial polymerization, or in situ polymerization of elastomer in the presence of anode active material particles.

[0070] Saturated rubbers and related elastomers in this category include 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, and protein elastin. Polyurethane and its copolymers (e.g. urea-urethane copolymer) are particularly useful elastomeric shell materials for encapsulating anode active material particles.

[0071] Several micro-encapsulation processes require the elastomer materials to be dissolvable in a solvent. Fortunately, all the elastomers used herein are soluble in some common solvents. Even for those rubbers that are not very soluble after vulcanization, the un-cured polymer (prior to vulcanization or curing) can be readily dissolved in a common organic solvent to form a solution. This solution can then be used to encapsulate solid particles via several of the micro-encapsulation methods to be discussed in what follows. Upon encapsulation, the elastomer shell is then vulcanized or cured. Some examples of rubbers and their solvents are polybutadiene (2-methyl pentane+n-hexane or 2,3-dimethylbutane), styrene-butadiene rubber (toluene, benzene, etc.), butyl rubber (n-hexane, toluene, cyclohexane), etc. The SBR can be vulcanized with different amounts sulfur and accelerator at 433° K in order to obtain different network structures and crosslink densities. Butyl rubber (IIR) is a copolymer of isobutylene and a small amount of isoprene (e.g. about 98% polyisobutylene with 2% isoprene distributed randomly in the polymer chain). Elemental sulfur and organic accelerators (such as thiuram or thiocarbamates) can be used to cross-link butyl rubber to different extents as desired. Thermoplastic elastomers are also readily soluble in solvents.

[0072] There are three broad categories of micro-encapsulation methods that can be implemented to produce elastomer-encapsulated particles of an anode active material: physical methods, physico-chemical methods, and chemical methods. The physical methods include 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.

[0073] Pan-coating method: The pan coating process involves tumbling the active material particles in a pan or a similar device while the encapsulating material (e.g. elastomer monomer/oligomer, elastomer melt, elastomer/solvent solution) is applied slowly until a desired encapsulating shell thickness is attained.

[0074] Air-suspension coating method: In the air suspension coating process, the solid particles (core material) are dispersed into the supporting air stream in an encapsulating chamber. A controlled stream of a polymer-solvent solution (elastomer 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 coat the suspended particles. These suspended particles are encapsulated (fully coated) with polymers while the volatile solvent is removed, leaving a very thin layer of polymer (elastomer or its precursor, which is cured/hardened subsequently) on surfaces of these particles. This process may be repeated several times until the required parameters, such as full-coating thickness (i.e. encapsulating shell or wall thickness), are achieved. The air stream which supports the 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 shell thickness.

[0075] In a preferred mode, the particles in the encapsulating zone portion may be subjected to re-circulation for repeated coating. Preferably, the encapsulating chamber is arranged such that the particles pass upwards through the encapsulating 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 encapsulating zone until the desired encapsulating shell thickness is achieved.

[0076] Centrifugal extrusion: Anode active materials may be encapsulated using a rotating extrusion head containing concentric nozzles. In this process, a stream of core fluid (slurry containing particles of an anode active material dispersed in a solvent) is surrounded by a sheath of shell solution or melt. 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.

[0077] Vibrational nozzle method: Core-shell encapsulation or matrix-encapsulation of an anode active material 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 consist of any liquids with limited viscosities (1-50,000 mPa.Math.s): emulsions, suspensions or slurry containing the anode active material. The solidification can be done according to the used gelation system with an internal gelation (e.g. sol-gel processing, melt) or an external (additional binder system, e.g. in a slurry).

[0078] Spray-drying: Spray drying may be used to encapsulate particles of an active material when the active material is dissolved or suspended in a melt or polymer solution. 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 thin polymer shell to fully embrace the solid particles of the active material.

[0079] Coacervation-phase separation: This process consists of three steps carried out under continuous agitation: [0080] (a) Formation of three immiscible chemical phases: liquid manufacturing vehicle phase, core material phase and encapsulation material phase. The core material is dispersed in a solution of the encapsulating polymer (elastomer or its monomer or oligomer). The encapsulating material phase, which is an immiscible polymer in liquid state, is formed by (i) changing temperature in polymer solution, (ii) addition of salt, (iii) addition of non-solvent, or (iv) addition of an incompatible polymer in the polymer solution. [0081] (b) Deposition of encapsulation shell material: core material being dispersed in the encapsulating polymer solution, encapsulating polymer material coated around core particles, and deposition of liquid polymer embracing around core particles by polymer adsorbed at the interface formed between core material and vehicle phase; and [0082] (c) Hardening of encapsulating shell material: shell material being immiscible in vehicle phase and made rigid via thermal, cross-linking, or dissolution techniques.

[0083] Interfacial polycondensation and interfacial cross-linking: Interfacial polycondensation entails introducing the two reactants to meet at the interface where they react with each other. This is based on the concept of the Schotten-Baumann reaction between an acid chloride and a compound containing an active hydrogen atom (such as an amine or alcohol), polyester, polyurea, polyurethane, or urea-urethane condensation. Under proper conditions, thin flexible encapsulating shell (wall) forms rapidly at the interface. A solution of the anode active material and a diacid chloride are emulsified in water and an aqueous solution containing an amine and a polyfunctional isocyanate is added. A base may be added to neutralize the acid formed during the reaction. Condensed polymer shells form instantaneously at the interface of the emulsion droplets. Interfacial cross-linking is derived from interfacial polycondensation, wherein cross-linking occurs between growing polymer chains and a multi-functional chemical groups to form an elastomer shell material.

[0084] In-situ polymerization: In some micro-encapsulation processes, active materials particles are fully coated with a monomer or oligomer first. Then, direct polymerization of the monomer or oligomer is carried out on the surfaces of these material particles.

[0085] Matrix polymerization: This method involves dispersing and embedding a core material 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.

EXAMPLE 1

Cobalt Oxide (Co.SUB.3.O.SUB.4.) Anode Particulates

[0086] An appropriate amount of inorganic salts Co(NO.sub.3).sub.2.6H.sub.2O and ammonia solution (NH.sub.3.H.sub.2.O, 25 wt. %) were mixed together. The resulting suspension was stirred for several hours under an argon flow to ensure a complete reaction. The obtained Co(OH).sub.2 precursor suspension was calcined at 450° C. in air for 2 h to form particles of the layered Co.sub.3O.sub.4. Portion of the Co.sub.3O.sub.4 particles was then encapsulated with a urea-urethane copolymer with the encapsulating elastomer shell thickness being varied from 17 nm to 135 nm.

[0087] For electrochemical testing, the working electrodes were prepared by mixing 85 wt. % active material (encapsulated or non-encapsulated particulates of Co.sub.3O.sub.4, 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 a CH-6 electrochemical workstation at a scanning rate of 1 mV/s.

[0088] The electrochemical performance of the particulates of elastomer-encapsulated Co.sub.3O.sub.4 particles and that of non-protected Co.sub.3O.sub.4 were evaluated by galvanostatic charge/discharge cycling at a current density of 50 mA/g, using a LAND electrochemical workstation. The results indicate that the charge/discharge profiles for the encapsulated Co.sub.3O.sub.4 particles and un-protected Co.sub.3O.sub.4 particle-based electrodes show a long voltage plateau at about 1.06 V and 1.10 V, respectively, followed by a slopping curve down to the cut-off voltage of 0.01 V, indicative of typical characteristics of voltage trends for the Co.sub.3O.sub.4 electrode.

[0089] As summarized in FIG. 5, the first-cycle lithium insertion capacity is 752 mAh/g (non-encapsulated) and 751 mAh/g (encapsulated), respectively, which are higher than the theoretical values of graphite (372 mAh/g). Both cells exhibit some first-cycle irreversibility. The initial capacity loss might have resulted from the incomplete conversion reaction and partially irreversible lithium loss due to the formation of solid electrolyte interface (SEI) layers.

[0090] As the number of cycles increases, the specific capacity of the bare Co.sub.3O.sub.4 electrode drops precipitously. Compared with its initial capacity value of approximately 752 mAh/g, its capacity suffers a 20% loss after 150 cycles and a 35.88% loss after 220 cycles. By contrast, the presently invented elastomer-encapsulated particulates provide the battery cell with a very stable and high specific capacity for a large number of cycles, experiencing a capacity loss of less than 2.7% after 220 cycles. These data have clearly demonstrated the surprising and superior performance of the presently invented particulate electrode materials compared with prior art un-encapsulated particulate-based electrode materials.

[0091] It may be noted that the number of charge-discharge cycles at which the specific capacity decays to 80% of its initial value is commonly defined as the useful cycle life of a lithium-ion battery. Thus, the cycle life of the cell containing the non-encapsulated anode active material is approximately 150 cycles. In contrast, the cycle life of the presently invented cells (not just button cells, but large-scale full cells) is typically from 1,000 to 4,000.

EXAMPLE 2

Elastomer-Encapsulated Tin Oxide Particulates

[0092] 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. A dilute elastomer-solvent solution (0.01-0.1 M of cis-polyisoprene in cyclohexane and 1,4-dioxane) was used as a coating solution in an air-suspension method to produce elastomer-encapsulated SnO.sub.2 particles having a shell thickness of 2.3 nm to 124 nm.

[0093] The battery cells from the elastomer-encapsulated particulates (nano-scaled SnO.sub.2 particles) and non-coated SnO.sub.2 particles were prepared using a procedure described in Example 1. FIG. 6 shows that the anode prepared according to the presently invented elastomer-encapsulated particulate approach offers a significantly more stable and higher reversible capacity compared to the un-coated SnO.sub.2 particle-based.

EXAMPLE 3

Tin (Sn) Nano Particles Encapsulated by a Styrene-Butadiene Rubber (SBR)

[0094] Nano particles (76 nm in diameter) of Sn were encapsulated with a thin layer of SBR shell via the spray-drying method, followed by curing of the butadiene segment of the SBR chains to impart high elasticity to the SBR. For comparison, some amount of Sn nano particles was encapsulated by a carbon shell. Carbon encapsulation is well-known in the art. Un-protected Sn nano particles from the same batch were also investigated to determine and compare the cycling behaviors of the lithium-ion batteries containing these particles as the anode active material.

[0095] Shown in FIG. 7 are the discharge capacity curves of three coin cells having three different Sn particles as the anode active material: elastomer-encapsulated Sn particles, carbon-encapsulated Sn particles, and un-protected Sn particles. These results have clearly demonstrated that elastomer encapsulation strategy provides the very best protection against capacity decay of a lithium-ion battery featuring a high-capacity anode active material. Carbon encapsulation is not good enough to provide the necessary protection.

EXAMPLE 4

Si Nanowire-Based Particulates

[0096] In a typical procedure, approximately 2.112 g of silicon powders (average diameter 2.64 μm) were mixed with 80 ml of a 0.1M aqueous solution of Ni(NO.sub.3).6H.sub.2O and vigorously stirred for 30 min. Then, water was evaporated in a rotary evaporator and the solid remnants were completely dried in an oven at 150° C. The final sample (Ni-impregnated Si powers) was obtained by grinding the solids in a mortar.

[0097] Subsequently, 0.03 g of Ni-impregnated Si particles was placed in a quartz boat, and the boat was placed in a tube furnace. The sample was reduced at 500° C. for 4 hours under flowing Ar (180 sccm) and H.sub.2 (20 sccm), then the temperature was raised to 990° C. to catalytically synthesize Si nanowires; Si nanowires were found to emanate from original micron-scaled Si particles. For the purpose of separating Si nanowires, for instance, every 0.1 g of the reacted Si powders was mixed with 10 ml of ethanol and the resulting mixture was sonicated for 1 hour. Subsequently, Si nanowires were separated from the Si powders by centrifuge at 5,000 rpm for 10 min.

[0098] Some Si nanowires were encapsulated with cis-polyisoprene elastomer. Some Si nanowires were coated with a layer of amorphous carbon and then encapsulated with cis-polyisoprene elastomer. For comparison purposes, Si nanowires unprotected and protected by carbon coating (but no elastomer encapsulation), respectively, were also prepared and implemented in a separate lithium-ion cell. In all four cells, approximately 25-30% of graphite particles were mixed with the protected or unprotected Si nanowires (SiNW), along with 5% binder resin, to make an anode electrode. The cycling behaviors of these 4 cells are shown in FIG. 8, which indicates that elastomer encapsulation of Si nanowires, with or without carbon coating, provides the most stable cycling response. Carbon coating alone does not help to improve cycling stability by much.

EXAMPLE 5

Effect of Lithium Ion-Conducting Additive in an Elastomer Shell

[0099] A wide variety of lithium ion-conducting additives were added to several different elastomer matrix materials to prepare encapsulation shell materials for protecting core particles of an anode active material. We have discovered that these elastomer composite materials are suitable encapsulation shell materials provided that their lithium ion conductivity at room temperature is no less than 10.sup.−7 S/cm. With these materials, lithium ions appear to be capable of readily diffusing in and out of the encapsulation shell having a thickness no greater than 1 μm. For thicker shells (e.g. 10 μm), a lithium ion conductivity at room temperature no less than 10.sup.−4 S/cm would be required.

TABLE-US-00002 TABLE 2 Lithium ion conductivity of various elastomer composite compositions as a shell material for protecting anode active material particles. Sample Lithium-conducting No. additive Elastomer (1-2 μm thick) Li-ion conductivity (S/cm) E-1 Li.sub.2CO.sub.3 + (CH.sub.2OCO.sub.2Li).sub.2 70-99% polyurethane 2.7 × 10.sup.−6 to 1.8 × 10.sup.−3 S/cm E-2 Li.sub.2CO.sub.3 + (CH.sub.2OCO.sub.2Li).sub.2 65-99% polyisoprene 6.1 × 10.sup.−6 to 3.6 × 10.sup.−4 S/cm E-3 Li.sub.2CO.sub.3 + (CH.sub.2OCO.sub.2Li).sub.2 65-99% SBR 6.5 × 10.sup.−6 to 5.2 × 10.sup.−4 S/cm D-4 Li.sub.2CO.sub.3 + (CH.sub.2OCO.sub.2Li).sub.2 70-99% urethane-urea 7.4 × 10.sup.−7 to 4.3 × 10.sup.−4 S/cm D-5 Li.sub.2CO.sub.3 + (CH.sub.2OCO.sub.2Li).sub.2 75-99% polybutadiene 8.7 × 10.sup.−6 to 3.6 × 10.sup.−3 S/cm B1 LiF + LiOH + Li2C.sub.2O.sub.4 80-99% chloroprene 8.7 × 10.sup.−7 to 2.1 × 10.sup.−4 S/cm rubber B2 LiF + HCOLi 80-99% EPDM 2.1 × 10.sup.−6 to 8.6 × 10.sup.−4 S/cm B3 LiOH 70-99% polyurethane 2.8 × 10.sup.−5 to 1.2 × 10.sup.−3 S/cm B4 Li.sub.2CO.sub.3 70-99% polyurethane 4.4 × 10.sup.−5 to 3.9 × 10.sup.−3 S/cm B5 Li.sub.2C.sub.2O.sub.4 70-99% polyurethane 9.3 × 10.sup.−6 to 7.7 × 10.sup.−4 S/cm B6 Li.sub.2CO.sub.3 + LiOH 70-99% polyurethane 1.4 × 10.sup.−5 to 1.6 × 10.sup.−3 S/cm C1 LiClO.sub.4 70-99% urethane-urea 4.8 × 10.sup.−5 to 2.2 × 10.sup.−3 S/cm C2 LiPF.sub.6 70-99% urethane-urea 2.4 × 10.sup.−5 to 8.2 × 10.sup.−4 S/cm C3 LiBF.sub.4 70-99% urethane-urea 1.2 × 10.sup.−5 to 1.2 × 10.sup.−4 S/cm C4 LiBOB + LiNO.sub.3 70-99% urethane-urea 6.8 × 10.sup.−6 to 1.2 × 10.sup.−4 S/cm S1 Sulfonated polyaniline 85-99% SBR 6.3 × 10.sup.−6 to 4.2 × 10.sup.−4 S/cm S2 Sulfonated SBR 85-99% SBR 5.2 × 10.sup.−6 to 2.2 × 10.sup.−4 S/cm S3 Sulfonated PVDF 80-99% chlorosulfonated 3.3 × 10.sup.−6 to 2.8 × 10.sup.−4 S/cm polyethylene (CS-PE) S4 Polyethylene oxide 80-99% CS-PE 4.9 × 10.sup.−6 to 3.7 × 10.sup.−4 S/cm

EXAMPLE 6

Cycle Stability of Various Rechargeable Lithium Battery Cells

[0100] In lithium-ion battery industry, it is a common practice to define the cycle life of a battery as the number of charge-discharge cycles that the battery suffers 20% decay in capacity based on the initial capacity measured after the required electrochemical formation. Summarized in Table 3 below are the cycle life data of a broad array of batteries featuring presently invented elastomer-encapsulated anode active material particles vs. other types of anode active materials.

TABLE-US-00003 TABLE 3 Cycle life data of various lithium secondary (rechargeable) batteries. Initial Sample Type & % of anode active capacity Cycle life ID Protective means material (mAh/g) (No. of cycles) Si-1 SBR-encapsulation 25% by wt. Si nano 1,120 1,230-1,575 particles (80 nm) + 67% graphite + 8% binder Si-2 Carbon 25% by wt. Si nano 1,242 251 encapsulation particles (80 nm) SiNW-1 Urea-Urethane 35% Si nanowires 1,258 1,455 encapsulation (diameter = 90 nm) SiNW-2 ethylene oxide- 45% Si nano particles, 1,766 1,420 (pre- epichlorohydrin pre-lithiated or non- lithiated); 1,125 copolymer prelithiated (no pre-Li) (no prelithiation) VO.sub.2-1 Polyurethane 90%-95%, VO.sub.2 nano 255 1689 encapsulation ribbon Co.sub.3O.sub.4-2 Polyisoprene 85% Co.sub.3O4 + 8% 720 2,356 (Pre-lithiated); encapsulation graphite platelets + 1,722 (no pre-Li) binder Co.sub.3O.sub.4-2 No encapsulation 85% Co.sub.3O.sub.4 + 8% 725 266 graphite platelets + binder SnO.sub.2-2 polybutadiene 75% SnO.sub.2 particles 740 1,138 encapsulation (3 μm initial size) SnO.sub.2-2 EPDM 75% SnO.sub.2 particles 738 3,245 (Pre-Li); encapsulation (87 μm in diameter) 1,856 (non pre-Li) Ge-1 butyl rubber 85% Ge + 8% graphite 850 1,226 encapsulation of platelets + binder C-coated Ge Ge-2 Carbon-coated 85% Ge + 8% graphite 856 120 platelets + binder Al-Li-1 Polyurethane Al/Li alloy (3/97) 2,850 1,544 encapsulation particles Al-Li-2 None Al/Li alloy particles 2,856 155 Zn-Li-1 Cis-polyisoprene C-coated Zn/Li alloy 2,626 1,239 encapsulation (5/95) particles Zn-Li-2 None C-coated Zn/Li alloy 2,631 146 (5/95) particles

[0101] These data further confirm: [0102] (1) The elastomer encapsulation strategy is surprisingly effective in alleviating the anode expansion/shrinkage-induced capacity decay problems. [0103] (2) The encapsulation of high-capacity anode active material particles by carbon or other non-elastomeric protective materials does not provide much benefit in terms of improving cycling stability of a lithium-ion battery [0104] (3) Pre-lithiation of the anode active material particles prior to elastomer encapsulation is beneficial. [0105] (4) The elastomer encapsulation strategy is also surprisingly effective in imparting stability to lithium metal or its alloy when used as the anode active material of a lithium metal battery.