Method of manufacturing conducting elastomer composite-encapsulated particles of anode active materials for lithium batteries

Abstract

A method of producing a powder mass for a lithium battery, comprising: (a) mixing graphene sheets and a sulfonated elastomer or its precursor in a liquid medium or solvent to form a suspension; (b) dispersing a plurality of particles of an anode active material in the suspension to form a slurry; and (c) dispensing the slurry and removing the solvent and/or polymerizing or curing the precursor to form the powder mass comprising multiple particulates, wherein at least one of the particulates is composed of one or a plurality of the particles encapsulated by a thin layer of a sulfonated elastomer/graphene composite having a thickness from 1 nm to 10 μm, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10.sup.−7 S/cm to 5×10.sup.−2 S/cm and an electrical conductivity from 10.sup.−7 S/cm to 100 S/cm.

Claims

1. A method of producing a powder mass of an anode active material for a lithium battery, the method comprising: (a) mixing graphene sheets and a sulfonated elastomer or its precursor in a liquid medium or solvent to form a suspension; (b) dispersing a plurality of particles of an anode active material in the suspension to form a slurry; and (c) dispensing the slurry and removing the solvent and/or polymerizing or curing the precursor to form the powder mass, wherein the powder mass comprises multiple particulates of the anode active material, wherein at least one of the particulates is composed of one or a plurality of the anode active material particles which are encapsulated by a thin layer of a sulfonated elastomer/graphene composite having from 0.01% to 50% by weight of graphene sheets dispersed in said sulfonated elastomer matrix material based on the total weight of the graphene/elastomer composite, and wherein the encapsulating thin layer of sulfonated elastomer/graphene composite has a thickness from 1 nm to 10 μm, a fully recoverable tensile strain from 2% to 500%, a lithium ion conductivity from 10.sup.−7 S/cm to 5×10.sup.−2 S/cm and an electrical conductivity from 10.sup.−7 S/cm to 100 S/cm when measured at room temperature, wherein said step of mixing the graphene sheets and the sulfonated elastomer or its precursor includes a procedure of chemically bonding the sulfonated elastomer or its precursor to the graphene sheets.

2. The method of claim 1, wherein said sulfonated elastomeric matrix material contains a material selected from a sulfonated version of natural polyisoprene, synthetic polyisoprene, polybutadiene, chloroprene rubber, polychloroprene, butyl rubber, styrene-butadiene rubber, nitrile rubber, ethylene propylene rubber, ethylene propylene diene rubber, metallocene-based poly(ethylene-co-octene) elastomer, poly(ethylene-co-butene) elastomer, styrene-ethylene-butadiene-styrene elastomer, 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, and combinations thereof.

3. The method of claim 1, wherein said graphene sheets are selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, nitrogenated graphene, hydrogenated graphene, doped graphene, functionalized graphene, and combinations thereof.

4. The method of claim 1, wherein said graphene sheets comprise single-layer graphene or few-layer graphene, wherein said few-layer graphene is defined as a graphene platelet formed of less than 10 graphene planes.

5. The method of claim 1, wherein said graphene sheets have a length or width from 5 nm to 5 μm.

6. The method 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.

7. The method of claim 6, 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, and combinations thereof.

8. The method 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, lithium titanate, and combinations thereof, wherein 1≤x≤2.

9. The method of claim 1, wherein said step of forming the solution includes (a) sulfonating an elastomer to form a sulfonated elastomer and dissolving the sulfonated elastomer in a solvent to form a polymer solution, or (b) sulfonating the precursor to obtain a sulfonated precursor, polymerizing the sulfonated precursor to form a sulfonated elastomer and dissolving the sulfonated elastomer in a solvent to form said solution.

10. The method of claim 1, wherein step (b) includes concurrently or sequentially adding said graphene sheets and said anode active material particles into said solution to form said suspension.

11. The method of claim 1, wherein step (c) includes operating a micro-encapsulation procedure selected from pan-coating, air-suspension coating, centrifugal extrusion, vibration-nozzle encapsulation, spray-drying, coacervation-phase separation, interfacial polycondensation and interfacial cross-linking, in-situ polymerization, matrix polymerization, and combinations thereof.

12. The method of claim 1, wherein said anode active material is in a form of nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn having a thickness or diameter from 0.5 nm to 100 nm.

13. The method of claim 1, further including coating said one or a plurality of particles with a layer of carbon disposed between said one or said plurality of particles and said sulfonated elastomer/graphene composite layer.

14. The method of claim 1, further includes dispersing particles of a graphite or carbon material in said slurry in such a manner that said particulate further contains particles of said graphite or carbon material encapsulated therein.

15. The method of claim 14, wherein said graphite or carbon material is selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, mesophase 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.

16. The method of claim 12, wherein said nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn is coated with or embraced by a conductive protective coating selected from a carbon material, an electronically conductive polymer, a conductive metal oxide, or a conductive metal coating.

17. The method of claim 12, wherein said nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanobelt, nanoribbon, nanodisc, nanoplatelet, or nanohorn 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.

18. The method of claim 1, further comprising a step of dissolving or dispersing 0.1% to 40% by weight of a lithium ion-conducting additive in said slurry in such a manner that said sulfonated elastomer/graphene composite further contains said lithium ion-conducting additive dispersed in said sulfonated elastomeric matrix material.

19. The method of claim 18, 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.

20. The method of claim 18, 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), ionic liquid-based lithium salts, and combinations thereof.

21. The method of claim 1, further comprising a step of dissolving or dispersing an electron-conducting polymer in said slurry wherein said electron-conducting polymer is selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, a sulfonated derivative thereof, or a combination thereof.

22. The method of claim 1, further comprising a step of dissolving or dispersing a lithium ion-conducting polymer in said slurry wherein said lithium ion-conducting polymer is 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), sulfonated derivatives thereof, and combinations thereof.

23. The method of claim 1, further comprising a step of mixing multiple particulates of said anode active material, a binder resin, and an optional conductive additive to form an anode active material layer, which is optionally coated on an anode current collector.

24. The method of claim 23, further comprising combining said anode active material layer, a cathode layer, an electrolyte, and an optional porous separator into a lithium battery cell.

25. The method of claim 23, wherein said lithium battery cell is a lithium-ion battery, lithium metal battery, lithium-sulfur battery, lithium-selenium battery, or lithium-air battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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.

(2) 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).

(3) 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;

(4) 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 prelithiated Si particle encapsulated with a protective layer leads to poor contact between the contracted Si particle and the rigid protective shell during battery discharge.

(5) FIG. 3 Schematic of the presently disclosed sulfonated elastomer/graphene composite-encapsulated anode active material particles (prelithiated or unlithiated). The elasticity of the elastomeric shell enables the shell to expand and contract congruently and conformingly with core particle.

(6) FIG. 4 Schematic of four types of sulfonated elastomer/graphene composite-embraced anode active material particles.

(7) FIG. 5 The specific capacity of a lithium battery having an anode active material featuring sulfonated elastomer/graphene composite-encapsulated Co.sub.3O.sub.4 particles and that having un-protected Co.sub.3O.sub.4 particles.

(8) FIG. 6 The specific capacity of a lithium battery having an anode active material featuring sulfonated elastomer/graphene composite-encapsulated SnO.sub.2 particles and that having un-protected SnO.sub.2 particles.

(9) FIG. 7 The specific capacity of a lithium battery having an anode active material featuring sulfonated elastomer/graphene composite-encapsulated Sn particles, that having carbon-encapsulated Sn particles, and that having un-protected Sn particles.

(10) FIG. 8 Specific capacities of 4 lithium-ion cells having Si nanowires (SiNW) as an anode active material: unprotected SiNW, carbon-coated SiNW, sulfonated elastomer/graphene composite-encapsulated SiNW, and sulfonated elastomer/graphene composite-encapsulated carbon-coated SiNW.

(11) FIG. 9 Ragone plot of 4 lithium-ion cells having Si nanowires (SiNW) as an anode active material: elastomer-encapsulated SiNW, sulfonated elastomer-encapsulated SiNW, elastomer/graphene composite-encapsulated SiNW, and sulfonated elastomer/graphene composite-encapsulated SiNW.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(12) The following includes definitions of various terms and phrases used throughout this specification.

(13) The term “graphene sheets” means a material comprising one or more planar sheets of bonded carbon atoms that are densely packed in a hexagonal crystal lattice in which carbon atoms are bonded together through strong in-plane covalent bonds, and further containing an intact ring structure throughout a majority of the interior. Preferably at least 80% of the interior aromatic bonds are intact. In the c-axis (thickness) direction, these graphene planes may be weakly bonded together through van der Waals forces. Graphene sheets may contain non-carbon atoms at their edges or surface, for example OH and COOH functionalities. The term graphene sheets includes pristine graphene, graphene oxide, reduced graphene oxide, halogenated graphene including graphene fluoride and graphene chloride, nitrogenated graphene, hydrogenated graphene, doped graphene, functionalized graphene, and combinations thereof. Typically, non-carbon elements comprise 0 to 25 weight % of graphene sheets. Graphene oxide may comprise up to 53% oxygen by weight. Graphene sheets may comprise single-layer graphene or few-layer graphene, wherein the few-layer graphene is defined as a graphene platelet formed of less than 10 graphene planes. Graphene sheets may also comprise graphene nanoribbons. “Pristine graphene” means a graphene sheet having substantially no non-carbon elements. “Nanographene platelet” (NGP) refers to a graphene sheet having a thickness from less than 0.34 nm (single layer) to 100 nm (multi-layer).

(14) The term “substantially” and its variations are defined as being largely but not necessarily wholly what is specified as understood by one of ordinary skill in the art, and in one non-limiting embodiment substantially refers to ranges within 10%, within 5%, within 1%, or within 0.5% of a referenced range.

(15) Other objects, features and advantages of the present invention may become apparent from the following figures, description, and examples. It should be understood, however, that the figures, description, and examples, while indicating specific embodiments of the invention, are given by way of illustration only and are not meant to be limiting. In further embodiments, features from specific embodiments may be combined with features from other embodiments.

(16) This disclosure 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 disclosure 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 disclosure.

(17) 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.

(18) 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.

(19) 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: 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. 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 nanoparticles, 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. 3) The approach of using a core-shell structure (e.g. Si nanoparticle 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. 4) Referring to the lower portion of FIG. 2(B), wherein the Si particle has been prelithiated 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 prelithiated 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.

(20) 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.

(21) The present disclosure provides an anode active material layer comprising multiple particulates of an anode active material, wherein at least a particulate is composed of one or a plurality of particles of an anode active material being encapsulated by a thin layer of graphene/elastomer composite that has thickness from 1 nm to 10 μm. Preferably, the graphene/elastomer composite has a fully recoverable tensile strain from 2% to 500% (more typically from 5% to 300% and most typically from 10% to 150%), a thickness from 1 nm to 10 μm, a lithium ion conductivity from 10.sup.−7 S/cm to 10.sup.−2 S/cm (more typically from 10.sup.−5 S/cm to 10.sup.−3 S/cm) and an electrical conductivity from 10.sup.−7 S/cm to 100 S/cm (more typically from 10.sup.−3 S/cm to 10 S/cm) when measured at room temperature on a separate cast thin film 20 μm thick. Preferably, the anode active material is a high-capacity anode active material having a specific lithium storage capacity greater than 372 mAh/g (which is the theoretical capacity of graphite).

(22) Preferably, graphene sheets include pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, graphene chloride, nitrogenated graphene, hydrogenated graphene, doped graphene, or functionalized graphene. Further preferably, graphene sheets include single-layer graphene or few layer graphene (having 2-10 graphene planes). More preferably, the graphene sheets contain 1-5 graphene planes, most preferably 1-3 graphene planes (i.e. single-layer, double-layer, or triple-layer graphene).

(23) As illustrated in FIG. 4, the present disclosure provides four major types of particulates of graphene/elastomer composite-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 nanoparticles), optionally along with other active materials (e.g. particles of graphite or hard carbon, not shown) or conductive additive, which are encapsulated by a graphene/elastomer composite 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 graphene/elastomer composite shell 22. The fourth is a multiple-particle particulate containing multiple anode active material particles 24 (e.g. Si nanoparticles) 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 graphene/elastomer shell 28. These anode active material particles can be prelithiated or non-prelithiated.

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

(25) Alternatively, referring to the lower portion of FIG. 3, wherein the Si particle has been prelithiated with lithium ions; i.e. has been pre-expanded in volume. When a layer of sulfonated elastomer/graphene composite is made to encapsulate around the prelithiated 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 sulfonated elastomer/graphene composite 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 more 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.).

(26) 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.

(27) Prelithiation 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.

(28) TABLE-US-00001 TABLE 1 Lithium storage capacity of selected non-Li elements. Intercalated Atomic weight Atomic weight of Max. wt. % compound of Li, g/mole active material, 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 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

(29) The particles of the anode active material may be in the form of a nanoparticle, nanowire, nanofiber, nanotube, nanosheet, nanoplatelet, nanodisc, nanobelt, nanoribbon, or nanohorn. They can be non-lithiated (when incorporated into the anode active material layer) or prelithiated to a desired extent (up to the maximum capacity as allowed for a specific element or compound.

(30) Preferably and typically, the sulfonated elastomer/graphene composite has a lithium ion conductivity from 10.sup.−7 S/cm to 5×10.sup.−2 S/cm, more preferably and typically greater than 10.sup.−5 S/cm, further more preferably and typically greater than 10.sup.−4 S/cm, and most preferably no less than 10.sup.−3 S/cm. In some embodiments, the composite further contains from 0.1% to 40% (preferably 1% to 35%) by weight of a lithium ion-conducting additive dispersed in a sulfonated elastomer matrix material.

(31) The sulfonated elastomer/graphene composite must have a high elasticity (high elastic deformation value). By definition, an elastic deformation is a deformation that is fully recoverable upon release of the mechanical stress 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). Sulfonation of the rubber reduces the elasticity to 800%. With the addition of 0.01%-50% of graphene sheets, the tensile elastic deformation of a sulfonated elastomer/rubber is reduced to typically from 2% 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 elastic deformation occurs to only a small extent (typically <1% and more typically <0.2%).

(32) A broad array of sulfonated elastomer/graphene composites 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 matrix material may be selected from a sulfonated version of 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), metallocene-based poly(ethylene-co-octene) (POE) elastomer, poly(ethylene-co-butene) (PBE) elastomer, styrene-ethylene-butadiene-styrene (SEBS) elastomer, 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.

(33) 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.

(34) For the present electrode use, the preferred thickness of a graphene sheet or nanographene platelet (NGP) is <10 nm, more preferably <3 nm (or <10 layers), and most preferably single-layer graphene. Thus, the presently disclosed sulfonated elastomer/graphene composite shell preferably contains mostly single-layer graphene, but could make use of some few-layer graphene. The graphene sheet may contain a small amount (typically <25% by weight) of non-carbon elements, such as hydrogen, nitrogen, fluorine, and oxygen, which are attached to an edge or surface of the graphene plane.

(35) In the present disclosure, graphene preferably or primarily refers to those graphene sheets containing no or low oxygen content; but, they can include graphite oxide or graphene oxide (GO) of various oxygen contents. Further, graphene may be fluorinated to a controlled extent to obtain graphite fluoride, or can be doped using various dopants, such as boron and nitrogen.

(36) Graphite oxide may be prepared by dispersing or immersing a laminar graphite material (e.g., powder of natural flake graphite or synthetic graphite) in an oxidizing agent, typically a mixture of an intercalant (e.g., concentrated sulfuric acid) and an oxidant (e.g., nitric acid, hydrogen peroxide, sodium perchlorate, potassium permanganate) at a desired temperature (typically 0-70° C.) for a sufficient length of time (typically 30 minutes to 5 days). In order to reduce the time required to produce a precursor solution or suspension, one may choose to oxidize the graphite to some extent for a shorter period of time (e.g., 30 minutes) to obtain graphite intercalation compound (GIC). The GIC particles are then exposed to a thermal shock, preferably in a temperature range of 600-1,100° C. for typically 15 to 60 seconds to obtain exfoliated graphite or graphite worms, which are optionally (but preferably) subjected to mechanical shearing (e.g. using a mechanical shearing machine or an ultrasonicator) to break up the graphite flakes that constitute a graphite worm. The un-broken graphite worms or individual graphite flakes are then re-dispersed in water, acid, or organic solvent and ultrasonicated to obtain a graphene polymer solution or suspension.

(37) The pristine graphene material is preferably produced by one of the following three processes: (A) Intercalating the graphitic material with a non-oxidizing agent, followed by a thermal or chemical exfoliation treatment in a non-oxidizing environment; (B) Subjecting the graphitic material to a supercritical fluid environment for inter-graphene layer penetration and exfoliation; or (C) Dispersing the graphitic material in a powder form to an aqueous solution containing a surfactant or dispersing agent to obtain a suspension and subjecting the suspension to direct ultrasonication.

(38) In Procedure (A), a particularly preferred step comprises (i) intercalating the graphitic material with a non-oxidizing agent, selected from an alkali metal (e.g., potassium, sodium, lithium, or cesium), alkaline earth metal, or an alloy, mixture, or eutectic of an alkali or alkaline metal; and (ii) a chemical exfoliation treatment (e.g., by immersing potassium-intercalated graphite in ethanol solution).

(39) In Procedure (B), a preferred step comprises immersing the graphitic material to a supercritical fluid, such as carbon dioxide (e.g., at temperature T>31° C. and pressure P>7.4 MPa) and water (e.g., at T>374° C. and P>22.1 MPa), for a period of time sufficient for inter-graphene layer penetration (tentative intercalation). This step is then followed by a sudden de-pressurization to exfoliate individual graphene layers. Other suitable supercritical fluids include methane, ethane, ethylene, hydrogen peroxide, ozone, water oxidation (water containing a high concentration of dissolved oxygen), or a mixture thereof.

(40) In Procedure (C), a preferred step comprises (a) dispersing particles of a graphitic material in a liquid medium containing therein a surfactant or dispersing agent to obtain a suspension or slurry; and (b) exposing the suspension or slurry to ultrasonic waves (a process commonly referred to as ultrasonication) at an energy level for a sufficient length of time to produce the separated nanoscaled platelets, which are pristine, non-oxidized NGPs.

(41) The present disclosure may utilize graphene oxide, preferably with an oxygen less than 25% by weight, further preferably below 20% by weight, further preferably below 5%. Typically, the oxygen content is between 5% and 20% by weight. The oxygen content can be determined using chemical elemental analysis and/or X-ray photoelectron spectroscopy (XPS). The laminar graphite materials used in the prior art processes for the production of the GIC, graphite oxide, and subsequently made exfoliated graphite, flexible graphite sheets, and graphene platelets are, in most cases, natural graphite. However, the present disclosure is not limited to natural graphite. The starting material may be selected from the group consisting of natural graphite, artificial graphite (e.g., highly oriented pyrolytic graphite, HOPG), graphite oxide, graphite fluoride, graphite fiber, carbon fiber, carbon nanofiber, carbon nanotube, mesophase carbon microbead (MCMB) or carbonaceous microsphere (CMS), soft carbon, hard carbon, and combinations thereof. All of these materials contain graphite crystallites that are composed of layers of graphene planes stacked or bonded together via van der Waals forces. In natural graphite, multiple stacks of graphene planes, with the graphene plane orientation varying from stack to stack, are clustered together. In carbon fibers, the graphene planes are usually oriented along a preferred direction. Generally speaking, soft carbons are carbonaceous materials obtained from carbonization of liquid-state, aromatic molecules. Their aromatic ring or graphene structures are more or less parallel to one another, enabling further graphitization. Hard carbons are carbonaceous materials obtained from aromatic solid materials (e.g., polymers, such as phenolic resin and polyfurfuryl alcohol). Their graphene structures are relatively randomly oriented and, hence, further graphitization is difficult to achieve even at a temperature higher than 2,500° C. But, graphene sheets do exist in these carbons.

(42) Pristine graphene may be produced by direct ultrasonication (also known as liquid phase production) or supercritical fluid exfoliation of graphite particles. These processes are well-known in the art. Multiple pristine graphene sheets may be dispersed in water or other liquid medium with the assistance of a surfactant to form a suspension.

(43) Fluorinated graphene or graphene fluoride is herein used as an example of the halogenated graphene material group. There are two different approaches that have been followed to produce fluorinated graphene: (1) fluorination of pre-synthesized graphene: This approach entails treating graphene prepared by mechanical exfoliation or by CVD growth with fluorinating agent such as XeF.sub.2, or F-based plasmas; (2) Exfoliation of multilayered graphite fluorides: Both mechanical exfoliation and liquid phase exfoliation of graphite fluoride can be readily accomplished [F. Karlicky, et al. “Halogenated Graphenes: Rapidly Growing Family of Graphene Derivatives” ACS Nano, 2013, 7 (8), pp 6434-6464].

(44) Interaction of F.sub.2 with graphite at high temperature leads to covalent graphite fluorides (CF).sub.n or (C.sub.2F).sub.n, while at low temperatures graphite intercalation compounds (GIC) C.sub.xF (2≤x≤24) form. In (CF).sub.n carbon atoms are sp3-hybridized and thus the fluorocarbon layers are corrugated consisting of trans-linked cyclohexane chairs. In (C.sub.2F).sub.n only half of the C atoms are fluorinated and every pair of the adjacent carbon sheets are linked together by covalent C—C bonds. Systematic studies on the fluorination reaction showed that the resulting F/C ratio is largely dependent on the fluorination temperature, the partial pressure of the fluorine in the fluorinating gas, and physical characteristics of the graphite precursor, including the degree of graphitization, particle size, and specific surface area. In addition to fluorine (F.sub.2), other fluorinating agents may be used, although most of the available literature involves fluorination with F.sub.2 gas, sometimes in presence of fluorides.

(45) For exfoliating a layered precursor material to the state of individual layers or few-layers, it is necessary to overcome the attractive forces between adjacent layers and to further stabilize the layers. This may be achieved by either covalent modification of the graphene surface by functional groups or by non-covalent modification using specific solvents, surfactants, polymers, or donor-acceptor aromatic molecules. The process of liquid phase exfoliation includes ultra-sonic treatment of a graphite fluoride in a liquid medium.

(46) The nitrogenation of graphene can be conducted by exposing a graphene material, such as graphene oxide, to ammonia at high temperatures (200-400° C.). Nitrogenated graphene could also be formed at lower temperatures by a hydrothermal method; e.g. by sealing GO and ammonia in an autoclave and then increased the temperature to 150-250° C. Other methods to synthesize nitrogen doped graphene include nitrogen plasma treatment on graphene, arc-discharge between graphite electrodes in the presence of ammonia, ammonolysis of graphene oxide under CVD conditions, and hydrothermal treatment of graphene oxide and urea at different temperatures.

(47) In some embodiments, the elastomeric composite further contains a lithium ion-conducting additive dispersed in a sulfonated elastomer 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.

(48) Alternatively, the lithium ion-conducting additive may contain 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), ionic liquid-based lithium salts, and combinations thereof.

(49) The elastomeric matrix material may contain a mixture or blend of a sulfonated 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.

(50) In some embodiments, the elastomeric matrix material contains a mixture or blend of a sulfonated 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-phosphazene, polyvinyl chloride, polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), derivatives thereof (e.g. sulfonated versions), and combinations thereof.

(51) 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. Graphene sheets can be chemically functionalized to contain functional groups (e.g. —OH, —COOH, NH.sub.2, etc.) that can react with the polymer or its oligomer. The graphene-bonded oligomer or polymer may then be dispersed in a liquid medium (e.g. a solvent) to form a solution or suspension. Particles of an anode active material (e.g. SnO.sub.2 nanoparticles and Si nanowires) can be dispersed in this polymer solution or suspension to form a 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 graphene-bonded polymer precipitates out to deposit on surfaces of these active material particles. This can be accomplished, for instance, via spray drying.

(52) 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),

(53) 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. Graphene sheets can be solution- or melt-dispersed into the elastomer to form a graphene/elastomer composite. Each of these graphene/elastomer composites 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.

(54) 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.

(55) 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.

(56) 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.

(57) Pan-Coating Method:

(58) 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.

(59) Air-Suspension Coating Method:

(60) 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.

(61) 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.

(62) Centrifugal Extrusion:

(63) 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.

(64) Vibrational Nozzle Encapsulation Method:

(65) 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).

(66) Spray-Drying:

(67) 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.

(68) Coacervation-Phase Separation:

(69) This process consists of three steps carried out under continuous agitation: (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. (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 (c) Hardening of encapsulating shell material: shell material being immiscible in vehicle phase and made rigid via thermal, cross-linking, or dissolution techniques.

(70) Interfacial Polycondensation and Interfacial Cross-Linking:

(71) 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.

(72) In-Situ Polymerization:

(73) In some microencapsulation 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.

(74) Matrix Polymerization:

(75) 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.

(76) A variety of synthetic methods may be used to sulfonate an elastomer or rubber: (i) exposure to sulfur trioxide in vapor phase or in solution, possibly in presence of Lewis bases such as triethyl phosphate, tetrahydrofuran, dioxane, or amines; (ii) chlorosulfonic acid in diethyl ether; (iii) concentrated sulfuric acid or mixtures of sulfuric acid with alkyl hypochlorite; (iv) bisulfites combined to dioxygen, hydrogen peroxide, metallic catalysts, or peroxo derivates; and (v) acetyl sulfate.

(77) Sulfonation of an elastomer or rubber may be conducted before, during, or after curing of the elastomer or rubber. Further, sulfonation of the elastomer or rubber may be conducted before or after the particles of an electrode active material are embraced or encapsulated by the elastomer/rubber or its precursor (monomer or oligomer). Sulfonation of an elastomer or rubber may be accomplished by exposing the elastomer/rubber to a sulfonation agent in a solution state or melt state, in a batch manner or in a continuous process. The sulfonating agent may be selected from sulfuric acid, sulfonic acid, sulfur trioxide, chlorosulfonic acid, a bisulfate, a sulfate (e.g. zinc sulfate, acetyl sulfate, etc.), a mixture thereof, or a mixture thereof with another chemical species (e.g. acetic anhydride, thiolacetic acid, or other types of acids, etc.). In addition to zinc sulfate, there are a wide variety of metal sulfates that may be used as a sulfonating agent; e.g. those sulfates containing Mg, Ca, Co, Li, Ba, Na, Pb, Ni, Fe, Mn, K, Hg, Cr, and other transition metals, etc.

(78) For instance, a triblock copolymer, poly(styrene-isobutylene-styrene) or SIBS, may be sulfonated to several different levels ranging from 0.36 to 2.04 mequiv./g (13 to 82 mol % of styrene; styrene being 19 mol % of the unsulfonated block copolymer). Sulfonation of SIBS may be performed in solution with acetyl sulfate as the sulfonating agent. First, acetic anhydride reacts with sulfuric acid to form acetyl sulfate (a sulfonating agent) and acetic acid (a by-product). Then, excess water is removed since anhydrous conditions are required for sulfonation of SIBS. The SIBS is then mixed with the mixture of acetyl sulfate and acetic acid. Such a sulfonation reaction produces sulfonic acid substituted to the para-position of the aromatic ring in the styrene block of the polymer. Elastomers having an aromatic ring may be sulfonated in a similar manner.

(79) A sulfonated elastomer also may be synthesized by copolymerization of a low level of functionalized (i.e. sulfonated) monomer with an unsaturated monomer (e.g. olefinic monomer, isoprene monomer or oligomer, butadiene monomer or oligomer, etc.).

Example 1: Sulfonation of Triblock Copolymer Poly(Styrene-Isobutylene-Styrene) or SIBS

(80) An example of the sulfonation procedure used in this study is summarized as follows: a 10% (w/v) solution of SIBS (50 g) and a desired amount of graphene oxide sheets (0.15 to 40% by weight) in methylene chloride (500 ml) was prepared. The solution was stirred and refluxed at approximately 40 8 C, while a specified amount of acetyl sulfate in methylene chloride was slowly added to begin the sulfonation reaction. Acetyl sulfate in methylene chloride was prepared prior to this reaction by cooling 150 ml of methylene chloride in an ice bath for approximately 10 min. A specified amount of acetic anhydride and sulfuric acid was then added to the chilled methylene chloride under stirring conditions. Sulfuric acid was added approximately 10 min after the addition of acetic anhydride with acetic anhydride in excess of a 1:1 mole ratio. This solution was then allowed to return to room temperature before addition to the reaction vessel.

(81) After approximately 5 h, the reaction was terminated by slowly adding 100 ml of methanol. The reacted polymer solution was then precipitated with deionized water. The precipitate was washed several times with water and methanol, separately, and then dried in a vacuum oven at 50 8 C for 24 h. This washing and drying procedure was repeated until the pH of the wash water was neutral. After this process, the final polymer yield was approximately 98% on average. This sulfonation procedure was repeated with different amounts of acetyl sulfate to produce several sulfonated polymers with various levels of sulfonation or ion-exchange capacities (IECs). The mol % sulfonation is defined as: mol %=(moles of sulfonic acid/moles of styrene)×100%, and the IEC is defined as the mille-equivalents of sulfonic acid per gram of polymer (mequiv./g).

(82) After sulfonation and washing of each polymer, the S-SIBS samples were dissolved in a mixed solvent of toluene/hexanol (85/15, w/w) with concentrations ranging from 5 to 2.5% (w/v). Desired amounts of anode active material particles, along with a desired amount of graphene sheets I if not added at an earlier stage) were then added into the solution to form slurry samples. The slurry samples were separately spray-dried to form sulfonated elastomer-embraced particles.

(83) Alternatively, sulfonation may be conducted on the elastomer/graphene composite layer after this encapsulating layer is form. (e.g. after the anode active material particle(s) is/are encapsulated.

Example 2: Synthesis of Sulfonated Polybutadiene (PB) by Free Radical Addition of Thiolacetic Acid (TAA) Followed by In Situ Oxidation with Performic Acid

(84) A representative procedure is given as follows. PB (8.0 g) was dissolved in toluene (800 mL) under vigorous stirring for 72 h at room temperature in a 1 L round-bottom flask. Benzophenone (BZP) (0.225 g; 1.23 mmol; BZP/olefin molar ratio=1:120) and TAA (11.9 mL; 0.163 mol, TAA/olefin molar ratio=1.1) and a desired amount of graphene sheets (0.1%-40% by wt.) were introduced into the reactor, and the polymer solution was irradiated for 1 h at room temperature with UV light of 365 nm and power of 100 W.

(85) The resulting thioacetylated polybutadiene (PB-TA)/graphene composite was isolated by pouring 200 mL of the toluene solution in a plenty of methanol and the polymer recovered by filtration, washed with fresh methanol, and dried in vacuum at room temperature (Yield=3.54 g). Formic acid (117 mL; 3.06 mol; HCOOH/olefin molar ratio=25), along with a desired amount of anode active material particles, from 10 to 100 grams) were added to the toluene solution of PB-TA at 50° C. followed by slow addition of 52.6 mL of hydrogen peroxide (35 wt %; 0.61 mol; H.sub.2O.sub.2/olefin molar ratio=5) in 20 min. We would like to caution that the reaction is autocatalytic and strongly exothermic. The resulting slurry was spray-dried to obtain sulfonated polybutadiene (PB-SA)/graphene composite-encapsulated anode active material particles (Si, SiO, Sn, SnO.sub.2, Co.sub.3O.sub.4, separately).

(86) It may be noted that graphene sheets may be added at different stages of the procedure: before, during or after BZP is added or before/during/after the anode active material particles are added.

Example 3: Synthesis of Sulfonated SBS

(87) Sulfonated styrene-butadiene-styrene triblock copolymer (SBS) based elastomer was directly synthesized. First, SBS (optionally along with graphene sheets) is first epoxidized by performic acid formed in situ, followed by ring-opening reaction with an aqueous solution of NaHSO.sub.3. In a typical procedure, epoxidation of SBS was carried out via reaction of SBS in cyclohexane solution (SBS concentration=11 g/100 mL) with performic acid formed in situ from HCOOH and 30% aqueous H.sub.2O.sub.2 solution at 70° C. for 4 h, using 1 wt % poly(ethylene glycol)/SBS as a phase transfer catalyst. The molar ratio of H.sub.2O.sub.2/HCOOH was 1. The product (ESBS) was precipitated and washed several times with ethanol, followed by drying in a vacuum dryer at 60° C.

(88) Subsequently, ESBS was first dissolved in toluene to form a solution with a concentration of 10 g/100 mL, into which was added 5 wt % TEAB/ESBS as a phase transfer catalyst and 5 wt % DMA/ESBS as a ring-opening catalyst. Herein, TEAB=tetraethyl ammonium bromide and DMA=N,N-dimethyl aniline. An aqueous solution of NaHSO.sub.3 and Na.sub.2SO.sub.3 (optionally along with graphene sheets, if not added earlier) was then added with vigorous stirring at 60° C. for 7 h at a molar ratio of NaHSO.sub.3/epoxy group at 1.8 and a weight ratio of Na.sub.2SO.sub.3/NaHSO.sub.3 at 36%. This reaction allows for opening of the epoxide ring and attaching of the sulfonate group according to the following reaction:

(89) ##STR00001##
The reaction was terminated by adding a small amount of acetone solution containing antioxidant. The mixture was washed with distilled water three times, then precipitated by ethanol, followed by drying in a vacuum dryer at 50° C. It may be noted that particles of an electrode active material and graphene sheets may be added during various stages of the aforementioned procedure (e.g. right from the beginning, or prior to the ring opening reaction).

Example 4: Synthesis of Sulfonated SBS by Free Radical Addition of Thiolacetic Acid (TAA) Followed by In Situ Oxidation with Performic Acid

(90) A representative procedure is given as follows. SBS (8.000 g) in toluene (800 mL) was left under vigorous stirring for 72 hours at room temperature and heated later on for 1 h at 65° C. in a 1 L round-bottom flask until the complete dissolution of the polymer. Thus, benzophenone (BZP, 0.173 g; 0.950 mmol; BZP/olefin molar ratio=1:132) and TAA (8.02 mL; 0.114 mol, TAA/olefin molar ratio=1.1) were added, and the polymer solution was irradiated for 4 h at room temperature with UV light of 365 nm and power of 100 W. To isolate a fraction of the thioacetylated sample (S(B-TA)S), 20 mL of the polymer solution was treated with plenty of methanol, and the polymer was recovered by filtration, washed with fresh methanol, and dried in vacuum at room temperature. The toluene solution containing the thioacetylated polymer was equilibrated at 50° C., and 107.4 mL of formic acid (2.84 mol; HCOOH/olefin molar ratio=27.5) and 48.9 mL of hydrogen peroxide (35 wt %; 0.57 mol; H.sub.2O.sub.2/olefin molar ratio=5.5) were added in about 15 min. It may be cautioned that the reaction is autocatalytic and strongly exothermic! Particles of the desired anode active materials were added before or after this reaction. The resulting slurry was stirred for 1 h, and then most of the solvent was distilled off in vacuum at 35° C. Finally, the slurry containing the sulfonated elastomer was coagulated in a plenty of acetonitrile, isolated by filtration, washed with fresh acetonitrile, and dried in vacuum at 35° C. to obtain sulfonated elastomers.

(91) Other elastomers (e.g. polyisoprene, EPDM, EPR, polyurethane, etc.) were sulfonated in a similar manner. Alternatively, all the rubbers or elastomers can be directly immersed in a solution of sulfuric acid, a mixture of sulfuric acid and acetyl sulfate, or other sulfonating agent discussed above to produce sulfonated elastomers/rubbers.

(92) Again, both graphene sheets and anode active material particles may be added at various stages of the procedure.

Example 5: Graphene Oxide from Sulfuric Acid Intercalation and Exfoliation of MCMBs

(93) MCMB (mesocarbon microbeads) were supplied by China Steel Chemical Co. This material has a density of about 2.24 g/cm.sup.3 with a median particle size of about 16 μm. MCMBs (10 grams) were intercalated with an acid solution (sulfuric acid, nitric acid, and potassium permanganate at a ratio of 4:1:0.05) for 48 hours. Upon completion of the reaction, the mixture was poured into deionized water and filtered. The intercalated MCMBs were repeatedly washed in a 5% solution of HCl to remove most of the sulfate ions. The sample was then washed repeatedly with deionized water until the pH of the filtrate was neutral. The slurry was dried and stored in a vacuum oven at 60° C. for 24 hours. The dried powder sample was placed in a quartz tube and inserted into a horizontal tube furnace pre-set at a desired temperature, 800° C.-1,100° C. for 30-90 seconds to obtain graphene samples. A small quantity of graphene was mixed with water and ultrasonicated at 60-W power for 10 minutes to obtain a suspension. A small amount was sampled out, dried, and investigated with TEM, which indicated that most of the NGPs were between 1 and 10 layers. The oxygen content of the graphene powders (GO or RGO) produced was from 0.1% to approximately 25%, depending upon the exfoliation temperature and time.

Example 6: Oxidation and Exfoliation of Natural Graphite

(94) Graphite oxide was prepared by oxidation of graphite flakes with sulfuric acid, sodium nitrate, and potassium permanganate at a ratio of 4:1:0.05 at 30° C. for 48 hours, according to the method of Hummers [U.S. Pat. No. 2,798,878, Jul. 9, 1957]. Upon completion of the reaction, the mixture was poured into deionized water and filtered. The sample was then washed with 5% HCl solution to remove most of the sulfate ions and residual salt and then repeatedly rinsed with deionized water until the pH of the filtrate was approximately 4. The intent was to remove all sulfuric and nitric acid residue out of graphite interstices. The slurry was dried and stored in a vacuum oven at 60° C. for 24 hours.

(95) The dried, intercalated (oxidized) compound was exfoliated by placing the sample in a quartz tube that was inserted into a horizontal tube furnace pre-set at 1,050° C. to obtain highly exfoliated graphite. The exfoliated graphite was dispersed in water along with a 1% surfactant at 45° C. in a flat-bottomed flask and the resulting graphene oxide (GO) suspension was subjected to ultrasonication for a period of 15 minutes to obtain a homogeneous graphene-water suspension.

Example 7: Preparation of Pristine Graphene Sheets

(96) Pristine graphene sheets were produced by using the direct ultrasonication or liquid-phase exfoliation process. In a typical procedure, five grams of graphite flakes, ground to approximately 20 μm in sizes, were dispersed in 1,000 mL of deionized water (containing 0.1% by weight of a dispersing agent, Zonyl® FSO from DuPont) to obtain a suspension. An ultrasonic energy level of 85 W (Branson 5450 Ultrasonicator) was used for exfoliation, separation, and size reduction of graphene sheets for a period of 15 minutes to 2 hours. The resulting graphene sheets were pristine graphene that had never been oxidized and were oxygen-free and relatively defect-free. There are substantially no other non-carbon elements.

Example 8: Preparation of Graphene Fluoride (GF) Sheets

(97) Several processes have been used by us to produce GF, but only one process is herein described as an example. In a typical procedure, highly exfoliated graphite (HEG) was prepared from intercalated compound C.sub.2F.xClF.sub.3. HEG was further fluorinated by vapors of chlorine trifluoride to yield fluorinated highly exfoliated graphite (FHEG). A pre-cooled Teflon reactor was filled with 20-30 mL of liquid pre-cooled ClF.sub.3, and then the reactor was closed and cooled to liquid nitrogen temperature. Subsequently, no more than 1 g of HEG was put in a container with holes for ClF.sub.3 gas to access the reactor. After 7-10 days, a gray-beige product with approximate formula C.sub.2F was formed. GF sheets were then dispersed in halogenated solvents to form suspensions.

Example 9: Preparation of Nitrogenated Graphene Sheets

(98) Graphene oxide (GO), synthesized in Example 2, was finely ground with different proportions of urea and the pelletized mixture heated in a microwave reactor (900 W) for 30 s. The product was washed several times with deionized water and vacuum dried. In this method graphene oxide gets simultaneously reduced and doped with nitrogen. The products obtained with graphene/urea mass ratios of 1/0.5, 1/1 and 1/2 are designated as N-1, N-2 and N-3 respectively and the nitrogen contents of these samples were 14.7, 18.2 and 17.5 wt. % respectively as determined by elemental analysis. These nitrogenated graphene sheets remain dispersible in water.

Example 10: Cobalt Oxide (Co.SUB.3.O.SUB.4.) Anode Particulates

(99) An appropriate amount of inorganic salts Co(NO.sub.3).sub.2.6H.sub.2O and ammonia solution (NH.sub.3—H.sub.2O, 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.

(100) For electrochemical testing, the working electrodes were prepared by mixing 85 wt. % active material (elastomer composite 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 (4=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.

(101) The electrochemical performance of the particulates of elastomer composite-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.

(102) 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.

(103) 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 42.7% loss after 360 cycles. By contrast, the presently disclosed 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 3.5% after 360 cycles. These data have clearly demonstrated the surprising and superior performance of the presently disclosed particulate electrode materials compared with prior art un-encapsulated particulate-based electrode materials.

(104) 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 disclosed cells (not just button cells, but large-scale full cells) is typically from 1,000 to 4,000.

Example 11: Elastomer Composite-Encapsulated Tin Oxide Particulates

(105) Tin oxide (SnO.sub.2) nanoparticles 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.

(106) The battery cells from the elastomer-encapsulated particulates (nanoscaled 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 disclosed graphene/elastomer composite-encapsulated particulate approach offers a significantly more stable and higher reversible capacity compared to the un-coated SnO.sub.2 particle-based.

Example 12: Tin (Sn) Nanoparticles Encapsulated by a Sulfonated Styrene-Butadiene Rubber (SBR)/Graphene Composite

(107) Nanoparticles (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 nanoparticles was encapsulated by a carbon shell. Carbon encapsulation is well-known in the art. Un-protected Sn nanoparticles 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.

(108) Shown in FIG. 7 are the discharge capacity curves of three coin cells having three different Sn particles as the anode active material: graphene/elastomer composite-encapsulated Sn particles, carbon-encapsulated Sn particles, and un-protected Sn particles. These results have clearly demonstrated that graphene/elastomer composite 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 13: Si Nanowire-Based Particulates

(109) Si nanowires were supplied from Angstron Energy Co. (Dayton, Ohio). Some Si nanowires were encapsulated with graphene-reinforced cis-polyisoprene elastomer. Some Si nanowires were coated with a layer of amorphous carbon and then encapsulated with graphene-reinforced 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 graphene/elastomer composite 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.

(110) FIG. 9 shows the Ragone plots (power density vs. energy density curves) of 4 lithium-ion cells having Si nanowires (SiNW) as an anode active material: elastomer-encapsulated SiNW, sulfonated elastomer-encapsulated SiNW, elastomer/graphene composite-encapsulated SiNW, and sulfonated elastomer/graphene composite-encapsulated SiNW. These and similar data for other types of anode materials demonstrate that the approaches of sulfonation and/or graphene addition enable a higher energy density and/or higher power density to lithium cells featuring a high-capacity anode active material. Graphene sheets appear to impart stability and sulfonation appears to impart lithium ion conductivity (hence, rate capability) to the protecting elastomer shell encapsulating anode active material particles.

Example 14: Effect of Lithium Ion-Conducting Additive in an Elastomer Shell

(111) A wide variety of lithium ion-conducting additives were added to several different sulfonated elastomer/graphene composites 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.

(112) TABLE-US-00002 TABLE 2 Lithium ion conductivity of various sulfonated elastomer composite compositions as a shell material for protecting anode active material particles. Graphene-elastomer (1-2 μm thick); Sample Lithium-conducting 5% graphene unless No. additive otherwise noted Li-ion conductivity (S/cm) E-1s Li.sub.2CO.sub.3 + 70-99% polyurethane, 4.4 × 10.sup.−6 to (CH.sub.2OCO.sub.2Li).sub.2 2% RGO 4.3 × 10.sup.−3 S/cm E-2s Li.sub.2CO.sub.3 + 65-99% polyisoprene, 1.3 × 10.sup.−5 to (CH.sub.2OCO.sub.2Li).sub.2 8% pristine graphene 6.8 × 10.sup.−4 S/cm E-3s Li.sub.2CO.sub.3 + 65-80% SBR, 15% RGO 8.7 × 10.sup.−6 to (CH.sub.2OCO.sub.2Li).sub.2 8.4 × 10.sup.−4 S/cm D-4s Li.sub.2CO.sub.3 + 70-99% urethane-urea, 1.4 × 10.sup.−6 to (CH.sub.2OCO.sub.2Li).sub.2 12% nitrogenated 6.3 × 10.sup.−4 S/cm graphene D-5s Li.sub.2CO.sub.3 + 75-99% polybutadiene 1.5 × 10.sup.−5 to (CH.sub.2OCO.sub.2Li).sub.2 7.7 × 10.sup.−3 S/cm B1s LiF + LiOH + 80-99% chloroprene 1.5 × 10.sup.−6 to Li.sub.2C.sub.2O.sub.4 rubber 6.4 × 10.sup.−4 S/cm B2s LiF + HCOLi 80-99% EPDM 5.3 × 10.sup.−6 to 4.1 × 10.sup.−3 S/cm B3s LiOH 70-99% polyurethane 3.5 × 10.sup.−5 to 4.1 × 10.sup.−3 S/cm B4s Li.sub.2CO.sub.3 70-99% polyurethane 5.2 × 10.sup.−5 to 4.9 × 10.sup.−3 S/cm B5s Li.sub.2C.sub.2O.sub.4 70-99% polyurethane 1.5 × 10.sup.−5 to 2.6 × 10.sup.−3 S/cm B6s Li.sub.2CO.sub.3 + LiOH 70-99% polyurethane 2.6 × 10.sup.−5 to 3.8 × 10.sup.−3 S/cm C1s LiClO.sub.4 70-99% urethane-urea 5.3 × 10.sup.−5 to 4.6 × 10.sup.−3 S/cm C2s LiPF.sub.6 70-99% urethane-urea 4.5 × 10.sup.−5 to 1.5 × 10.sup.−3 S/cm C3s LiBF.sub.4 70-99% urethane-urea 2.8 × 10.sup.−5 to 3.8 × 10.sup.−4 S/cm C4s LiBOB + LiNO.sub.3 70-99% urethane-urea 8.2 × 10.sup.−6 to 3.2 × 10.sup.−4 S/cm S1s Sulfonated 85-99% SBR 7.83 × 10.sup.−6 to polyaniline 8.5 × 10.sup.−4 S/cm S2s Sulfonated SBR 85-99% SBR 7.6 × 10.sup.−6 to 5.5 × 10.sup.−4 S/cm S3s Sulfonated PVDF 80-99% chlorosulfonated 4.7 × 10.sup.−6 to polyethylene (CS-PE) 5.2 × 10.sup.−4 S/cm S4s Polyethylene oxide 80-99% CS-PE 6.2 × 10.sup.−6 to 4.5 × 10.sup.−4 S/cm

Example 15: Cycle Stability of Various Rechargeable Lithium Battery Cells

(113) 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 disclosed elastomer-encapsulated anode active material particles vs. other types of anode active materials.

(114) TABLE-US-00003 TABLE 3 Cycle life data of various lithium secondary (rechargeable) batteries. Protective means; Initial Sample 1-25% graphene; Type & % of anode capacity Cycle life (No. ID sulfonated elastomer active material (mAh/g) of cycles) Si-1 SBR-encapsulation, 25% by wt. Si 1,120 1,512-1,833 2% Gn nanoparticles (80 nm) + 67% graphite + 8% binder Si-2 Carbon encapsulation 25% by wt. Si 1,242 251 nanoparticles (80 nm) SiNW-1 Urea-Urethane 35% Si nanowires 1,258 1,630 encapsulation, 5% Gn (diameter = 90 nm) SiNW-2 ethylene oxide- 45% Si nanoparticles, 1,766 1,650 epichlorohydrin prelithiated or non- (prelithiated); copolymer, 8% Gn prelithiated (no pre-Li) 1,285 (no prelithiation) VO.sub.2-1 Polyurethane 90%-95%, VO.sub.2 255 1860 encapsulation, 3% Gn nanoribbon Co.sub.3O.sub.4-2 Polyisoprene 85% Co.sub.3O.sub.4 + 8% 720 2,550 encapsulation, 10% Gn graphite platelets + binder (Prelithiated); 1,930 (no pre-Li) 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 1,440 encapsulation, 2% Gn (3 μm initial size) SnO.sub.2-2 EPDM encapsulation, 75% SnO.sub.2 particles 738 3,502 7% Gn (87 nm in diameter) (Pre-Li); 1,980 (non pre-Li) Ge-1 butyl rubber 85% Ge + 8% graphite 850 1,440 encapsulation of C- platelets + binder coated Ge, 2% Gn Ge-2 Carbon-coated 85% Ge + 8% graphite 856 120 platelets + binder Al—Li-1 Polyurethane Al/Li alloy 2,850 1,825 encapsulation, 25% Gn (3/97) particles Al—Li-2 None Al/Li alloy particles 2,856 155 Zn—Li-1 Cis-polyisoprene C-coated Zn/Li alloy 2,626 1,533 encapsulation, 1% Gn (5/95) particles Zn—Li-2 None C-coated Zn/Li alloy 2,631 146 (5/95) particles

(115) These data further confirm the following: (1) The sulfonated elastomer/graphene composite encapsulation strategy is surprisingly effective in alleviating the anode expansion/shrinkage-induced capacity decay problems. (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 (3) Prelithiation of the anode active material particles prior to graphene/elastomer encapsulation is beneficial. (4) The sulfonated elastomer/graphene composite 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. (5) Sulfonation further improves the lithium ion conductivity of an elastomer and, hence, power density of the resulting battery.