Patent Application
20220246915
The present disclosure relates generally to the field of rechargeable lithium battery and, more particularly, to the anode active materials in the form of high-elasticity polymer-protected particles and the process for producing same.
A unit cell or building block of a lithium-ion battery is typically composed of an anode current collector, an anode or negative electrode layer (containing an anode active material responsible for storing lithium therein, a conductive additive, and a resin binder), an electrolyte and porous separator, a cathode or positive electrode layer (containing a cathode active material responsible for storing lithium therein, a conductive additive, and a resin binder), and a separate cathode current collector. The electrolyte is in ionic contact with both the anode active material and the cathode active material. A porous separator is not required if the electrolyte is a solid-state electrolyte.
The binder in the binder layer is used to bond the anode active material (e.g. graphite or Si particles) and a conductive filler (e.g. carbon black or carbon nanotube) together to form an anode layer of structural integrity, and to bond the anode layer to a separate anode current collector, which acts to collect electrons from the anode active material when the battery is discharged. In other words, in the negative electrode (anode) side of the battery, there are typically four different materials involved: an anode active material, a conductive additive, a resin binder (e.g. polyvinylidine fluoride, PVDF, or styrene-butadiene rubber, SBR), and an anode current collector (typically a sheet of Cu foil). Typically the former three materials form a separate, discrete anode layer and the latter one forms another discrete layer.
The most commonly used anode active materials for lithium-ion batteries are natural graphite and synthetic graphite (or artificial graphite) that can be intercalated with lithium and the resulting graphite intercalation compound (GIC) may be expressed as LixC6, where x is typically less than 1. The maximum amount of lithium that can be reversibly intercalated into the interstices between graphene planes of a perfect graphite crystal corresponds to x=1, defining a theoretical specific capacity of 372 mAh/g.
Graphite or carbon anodes can have a long cycle life due to the presence of a protective solid-electrolyte interface layer (SEI), which results from the reaction between lithium and the electrolyte (or between lithium and the anode surface/edge atoms or functional groups) during the first several charge-discharge cycles. The lithium in this reaction comes from some of the lithium ions originally intended for the charge transfer purpose. As the SEI is formed, the lithium ions become part of the inert SEI layer and become irreversible, i.e. these positive ions can no longer be shuttled back and forth between the anode and the cathode during charges/discharges. Therefore, it is desirable to use a minimum amount of lithium for the formation of an effective SEI layer. In addition to SEI formation, the irreversible capacity loss Qir can also be attributed to graphite exfoliation caused by electrolyte/solvent co-intercalation and other side reactions.
In addition to carbon- or graphite-based anode materials, other inorganic materials that have been evaluated for potential anode applications include metal oxides, metal nitrides, metal sulfides, and the like, and a range of metals, metal alloys, and intermetallic compounds that can accommodate lithium atoms/ions or react with lithium. Among these materials, lithium alloys having a composition formula of LiaA (A is a metal or semiconductor element, such as Al and Si, and “a” satisfies 0<a≤5) are of great interest due to their high theoretical capacity, e.g., Li4Si (3,829 mAh/g), Li4.4Si (4,200 mAh/g), Li4.4Ge (1,623 mAh/g), Li4.4Sn (993 mAh/g), Li3Cd (715 mAh/g), Li3Sb (660 mAh/g), Li4.4Pb (569 mAh/g), LiZn (410 mAh/g), and Li3Bi (385 mAh/g). However, as schematically illustrated in
To overcome the problems associated with such mechanical degradation, three technical approaches have been proposed:
It may be further noted that the coating or matrix materials used to protect active particles (such as Si and Sn) are carbon, sol gel graphite, metal oxide, monomer, ceramic, and lithium oxide. These protective materials are all very brittle, weak (of low strength), and/or non-conducting (e.g., ceramic or oxide coating). Ideally, the protective material should meet the following requirements: (a) The coating or matrix material should be of high strength and stiffness so that it can help to refrain the electrode active material particles, when lithiated, from expanding to an excessive extent. (b) The protective material should also have high fracture toughness or high resistance to crack formation to avoid disintegration during repeated cycling. (c) The protective material must be inert (inactive) with respect to the electrolyte, but be a good lithium ion conductor. (d) The protective material must not provide any significant amount of defect sites that irreversibly trap lithium ions. (e) The protective material must be lithium ion-conducting as well as electron-conducting. The prior art protective materials all fall short of these requirements. Hence, it was not surprising to observe that the resulting anode typically shows a reversible specific capacity much lower than expected. In many cases, the first-cycle efficiency is extremely low (mostly lower than 80% and some even lower than 60%). Furthermore, in most cases, the electrode was not capable of operating for a large number of cycles. Additionally, most of these electrodes are not high-rate capable, exhibiting unacceptably low capacity at a high discharge rate.
Due to these and other reasons, most of prior art composite electrodes and electrode active materials have deficiencies in some ways, e.g., in most cases, less than satisfactory reversible capacity, poor cycling stability, high irreversible capacity, ineffectiveness in reducing the internal stress or strain during the lithium ion insertion and extraction steps, and other undesirable side effects.
Complex composite particles of particular interest are a mixture of separate Si and graphite particles dispersed in a carbon matrix; e.g. those prepared by Mao, et al. [“Carbon-coated Silicon Particle Powder as the Anode Material for Lithium Batteries and the Method of Making the Same,” US 2005/0136330 (Jun. 23, 2005)]. Also of interest are carbon matrix-containing complex nano Si (protected by oxide) and graphite particles dispersed therein, and carbon-coated Si particles distributed on a surface of graphite particles Again, these complex composite particles led to a low specific capacity or for up to a small number of cycles only. It appears that carbon by itself is relatively weak and brittle and the presence of micron-sized graphite particles does not improve the mechanical integrity of carbon since graphite particles are themselves relatively weak. Graphite was used in these cases presumably for the purpose of improving the electrical conductivity of the anode material. Furthermore, polymeric carbon, amorphous carbon, or pre-graphitic carbon may have too many lithium-trapping sites that irreversibly capture lithium during the first few cycles, resulting in excessive irreversibility.
In summary, the prior art has not demonstrated a composite material that has all or most of the properties desired for use as an anode active material in a lithium-ion battery. Thus, there is an urgent and continuing need for a new anode active material that enables a lithium-ion battery to exhibit a high cycle life, high reversible capacity, low irreversible capacity, small particle sizes (for high-rate capacity), and compatibility with commonly used electrolytes. There is also a need for a method of readily or easily producing such a material in large quantities.
Thus, it is an object of the present disclosure to meet these needs and address the issues associated the rapid capacity decay of a lithium battery containing a high-capacity anode active material.
The present disclosure provides a solid powder mass of composite particulates for use as an anode material in a lithium battery, wherein at least one of the composite particulates (preferably a majority or all of these particulates or “secondary particles”) has a diameter from 10 nm to 50 μm (preferably from 50 nm to 10 μm) and comprises one or a plurality of anode active material particles (the “primary particles”) that are dispersed in a high-elasticity polymer matrix or encapsulated by a shell of a high-elasticity polymer having a recoverable tensile strain no less than 5% (typically from 5% to 700% and more typically from 10% to 300%), when measured without an additive or reinforcement, and a lithium ion conductivity no less than 10−8 S/cm (preferably >10−6 S/cm, further preferably >10−4 S/cm, and more preferably >10−3 S/cm) when measured at room temperature, wherein the polymer matrix forms a continuous material phase.
When the high-elasticity polymer serves as a matrix in the composite particulate, this material forms a continuous phase that makes physical and ionic contact with all the anode active material particles dispersed in this continuous phase (matrix).
The disclosed multiple individual composite particulates can form a powder mass. In each particulate, the high-elasticity polymer serves as an encapsulating shell to enclose one or more than one anode primary particles inside the shell of a particulate. In a particulate, the high-elasticity polymer may serve as a matrix in which multiple anode primary particles are dispersed. It may be noted that the high-elasticity polymer here is not a binder for use in forming an anode electrode; once crosslinked, the polymer no longer is capable of serving as a binder. These composite particulates are individual, isolated entities that are not bonded together. During the subsequent anode fabrication procedure (e.g., slurry coating on Cu foil), a binder (e.g., PVDF) will be needed to bond these individual composite particulates, along with a conductive additive together, to form a layer of electrode and to bond this layer of anode electrode to a current collector (e.g., Cu foil).
In certain embodiments, the disclosure provides a composite particulate for a lithium battery, wherein the composite particulate has a diameter from 10 nm to 50 μm and comprises one or more than one anode active material particles that are dispersed in a high-elasticity polymer matrix or encapsulated by a high-elasticity polymer shell, wherein said high-elasticity polymer matrix or shell has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10−8 S/cm at room temperature and wherein the high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof. Quite surprisingly, these polymers are thermally stable inside a lithium battery.
The fluorinated monomer may be selected from the group consisting of fluorinated vinyl carbonates, fluorinated vinyl monomers, fluorinated esters, fluorinated vinyl esters, and fluorinated vinyl ethers and combinations thereof.
The sulfone or sulfide may be selected from vinyl sulfone, allyl sulfone, alkyl vinyl sulfone, aryl vinyl sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, vinyl sulfide, a vinyl-containing variant of TrMS, MTrMS, TMS, EMS, MMES, EMES, EMEES, or a combination thereof:
In certain embodiments, the vinyl sulfone or sulfide is selected from ethyl vinyl sulfide, allyl methyl sulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, allyl phenyl sulfone, allyl methyl sulfone, divinyl sulfone, or a combination thereof, wherein the vinyl sulfone does not include methyl ethylene sulfone and ethyl vinyl sulfone.
The nitrile may comprise a dinitrile or is selected from AND, GLN, SEN, or a combination thereof:
The siloxane or silane may be selected from alkylsiloxane (Si—O), alkyylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—), or a combination thereof.
The high-elasticity polymer may preferably comprise a cross-linked network of chains crosslinked by a crosslinking agent to a degree of crosslinking that imparts an elastic tensile strain from 5% to 500%. The crosslinking agent may be selected from poly(diethanol) diacrylate, poly(ethyleneglycol)dimethacrylate, poly(diethanol) dimethylacrylate, poly(ethylene glycol) diacrylate, N,N-methylene bisacrylamide, epichlorohydrin, 1,4-butanediol diglycidyl ether, tetrabutylammonium hydroxide, cinnamic acid, ferric chloride, aluminum sulfate octadecahydrate, diepoxy, dicarboxylic acid compound, poly(potassium 1-hydroxy acrylate) (PKHA), glycerol diglycidyl ether (GDE), ethylene glycol, polyethylene glycol, polyethylene glycol diglycidyl ether (PEGDE), citric acid, acrylic acid, methacrylic acid, a derivative compound of acrylic acid, a derivative compound of methacrylic acid, glycidyl functions, N,N′-Methylenebisacrylamide (MBAAm), Ethylene glycol dimethacrylate (EGDMAAm), isobornyl methacrylate, poly (acrylic acid) (PAA), methyl methacrylate, isobornyl acrylate, ethyl methacrylate, isobutyl methacrylate, n-Butyl methacrylate, ethyl acrylate, 2-Ethyl hexyl acrylate, n-Butyl acrylate, a diisocyanate, an urethane chain, a chemical derivative thereof, or a combination thereof.
In some embodiments, the crosslinking agent comprises a compound having at least one reactive group selected from a phenylene group, a hydroxyl group, an amino group, an imino group, an amide group, an acrylic amide group, an amine group, an acrylic group, an acrylic ester group, or a mercapto group in the molecule.
In certain embodiments, the polymer is synthesized with an initiator selected from an azo compound, azobisisobutyronitrile, azobisisoheptonitrile, dimethyl azobisisobutyrate, benzoyl peroxide tert-butyl peroxide and methyl ethyl ketone peroxide, benzoyl peroxide (BPO), bis(4-tert-butylcyclohexyl)peroxydicarbonate, t-amyl peroxypivalate, 2,2′-azobis-(2,4-dimethylvaleronitrile), 2,2′-azobis-(2-methylbutyronitrile), 1,1-azobis(cyclohexane-1-carbonitrile, benzoylperoxide (BPO), hydrogen peroxide, dodecamoyl peroxide, isobutyryl peroxide, cumene hydroperoxide, tert-butyl peroxypivalate, diisopropyl peroxydicarbonate, lithium hexafluorophosphate (LiPF6), lithium borofluoride (LiBF4), lithium hexafluoroarsenide (LiAsF6), lithium trifluoro-methanesulfonate (LiCF3SO3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF3SO2)2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF2C2O4), lithium oxalyldifluoroborate (LiBF2C2O4), or a combination thereof.
A high-elasticity polymer refers to a polymer, typically a lightly cross-linked polymer, which exhibits an elastic deformation that is at least 5% when measured (without an additive or reinforcement in the polymer) under uniaxial tension. In the field of materials science and engineering, the “elastic deformation” is defined as a deformation of a material (when being mechanically stressed) that is essentially fully recoverable upon release of the load and the recovery is essentially instantaneous. The elastic deformation is preferably greater than 30%, more preferably greater than 50%, further more preferably greater than 100%, still more preferably greater than 150%, and most preferably greater than 200%.
In certain embodiments, the high-elasticity polymer further contains from 0.01% to 30% by weight of a graphite, graphene, or carbon material dispersed therein. The graphite, graphene, or carbon material is preferably selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, meso-phase pitch, carbon black, coke, acetylene black, activated carbon, graphite particles, carbon particles, meso-phase microbeads, carbon or graphite fibers, carbon nanotubes, carbon nano-fibers, graphitic nano-fibers, graphene sheets, or a combination thereof and said graphite, graphene, or carbon material forms a 3D network of electron-conducting pathways. The 3D network of electron-conducting pathways is in electronic or physical contacts with the anode material particles.
The anode active material may be selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), phosphorus (P), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium titanium niobate, lithium-containing titanium oxide, lithium transition metal oxide, ZnCo2O4; (f) carbon or graphite particles (g) prelithiated versions thereof; and (h) combinations thereof.
In some embodiments, the anode active material contains a prelithiated Si, prelithiated Ge, prelithiated Sn, prelithiated SnOx, prelithiated SiOx, prelithiated iron oxide, prelithiated V2O5, prelithiated V3O8, prelithiated Co3O4, prelithiated Ni3O4, or a combination thereof, wherein x=1 to 2.
It may be noted that pre-lithiation of an anode active material means that this material has been pre-intercalated by or doped with lithium ions up to a weight fraction from 0.1% to 54.7% of Li in the lithiated product.
The anode active material is preferably in a form of nano particle (spherical, ellipsoidal, and irregular shape), nano wire, nano fiber, nano tube, nano sheet, nano belt, nano ribbon, nano disc, nano platelet, or nano horn having a thickness or diameter less than 100 nm. These shapes can be collectively referred to as “particles” unless otherwise specified or unless a specific type among the above species is desired. Further preferably, the anode active material has a dimension less than 50 nm, even more preferably less than 20 nm, and most preferably less than 10 nm.
In some embodiments, the anode active material particles (primary particles) contain sub-micron or micron-scale particles that have a thickness or diameter from 100 nm to 20 μm, preferably less than 2 μm.
The primary particles or the secondary particles (or both) can be porous, having pores to accommodate volume expansion of the primary particles, such as Si particles that can undergo a volume expansion up to 380%.
In some embodiments, a cluster of primary particles may be totally embedded in, engulfed by, and dispersed in a matrix of a high-elasticity polymer wherein the polymer forms a continuous phase (hence, the term “matrix”) and the primary particles are a dispersed or discrete phase. Alternatively or additionally, a carbon layer may be deposited to embrace or encapsulate the primary particles prior to being dispersed in the polymer matrix.
The particulate may further contain a graphite, graphene, and/or carbon material dispersed in the high-elasticity polymer. The carbon or graphite material may be selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, meso-phase pitch, carbon black, coke, acetylene black, activated carbon, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, carbon nano-tubes (single-walled or multi-walled), carbon nano-fibers (vapor-grown or carbonized polymer fibers), graphitic nano-fibers, graphene sheets, or a combination thereof. Graphene may be selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, functionalized graphene, etc.
The carbon/graphite/graphene particles, fibers, nanotubes, and/or nano sheets dispersed in the high-elasticity polymer preferably and typically constitute a 3D network of electron-conducting paths that preferably are in contact with individual primary particles of the anode active material. The high-elasticity polymer matrix, being a continuous phase and making contact with individual primary particles (being substantially totally immersed in the polymer matrix) provide a 3D network of lithium ion-conducting paths. In other words, there are dual networks of conducting pathways for electrons and lithium ions inside the multi-functional composite particulate.
In certain embodiments, a single anode particle or a plurality of anode particles may be encapsulated by a shell of high-elasticity polymer. Some desired amount of carbon, graphite, and/or graphene particles, fibers, nanotubes, and/or nano sheets may also be encapsulated by the high-elasticity polymer; these conductive fillers can constitute a 3D network of electron-conducting paths that preferably are in contact with individual primary particles of the anode active material.
The anode active material primary particles and/or the composite particulates (secondary particles) may be further coated with or embraced by a conductive protective coating, selected from a carbon material, graphene, electronically conductive polymer, conductive metal oxide, or conductive metal coating. Preferably, the anode active material, in the form of a 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.
Preferably and typically, the high-elasticity polymer has a lithium ion conductivity no less than 10−7 S/cm, more preferably no less than 10−5 S/cm, and most preferably no less than 10−4 S/cm. Some of the selected polymers exhibit a lithium-ion conductivity greater than 10−2 S/cm (typically up to 5×10−2 S/cm). In some embodiments, the high-elasticity polymer is a neat polymer containing no additive or filler dispersed therein. In others, the high-elasticity polymer is polymer matrix composite containing from 0.1% to 50% by weight (preferably from 1% to 35% by weight) of a lithium ion-conducting additive dispersed in a high-elasticity polymer matrix material. In some embodiments, the high-elasticity polymer contains from 0.01% by weight to 30% by weight (preferably from 1% to 15%) of a reinforcement nano filament selected from carbon nanotube, carbon nano-fiber, graphene, or a combination thereof, sufficient to exceed a percolation threshold for forming a 3D network of electron-conducting pathways.
In some embodiments, the high-elasticity polymer is a polymer matrix composite containing a lithium ion-conducting additive dispersed therein, wherein the lithium ion-conducting additive is selected from Li2CO3, Li2O, Li2C2O4, LiOH, LiX, ROCO2Li, HCOLi, ROLi, (ROCO2Li)2, (CH2OCO2Li)2, Li2S, LixSOy, or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1, 1≤y≤4.
In some embodiments, the high-elasticity polymer is a polymer matrix composite containing a lithium ion-conducting additive dispersed therein, wherein the lithium ion-conducting additive contains a lithium salt selected from lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium borofluoride (LiBF4), lithium hexafluoroarsenide (LiAsF6), lithium trifluoro-methanesulfonate (LiCF3SO3), bis-trifluoromethyl sulfonylimide lithium (LiN(C F3SO2)2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF2C2O4), lithium nitrate (LiNO3), Li-fluoroalkyl-phosphate (LiPF3(CF2CF3)3), lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, or a combination thereof.
In some embodiments, the high-elasticity polymer is mixed with or forms a co-polymer with an elastomer. The high-elasticity polymer may form a mixture or blend with an electron-conducting polymer selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g., sulfonated versions), or a combination thereof.
In some embodiments, the high-elasticity polymer may form a mixture or blend with a lithium ion-conducting polymer selected from poly(ethylene oxide) (PEO), Polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxy ethoxyethoxide-phosphazene, Polyvinyl chloride, Polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a sulfonated derivative thereof, or a combination thereof. Sulfonation is herein found to impart improved lithium-ion conductivity to a polymer.
The present disclosure also provides an anode electrode that contains the presently invented multi-functional composite particulates, an optional conductive additive (e.g., expanded graphite flakes, carbon black, acetylene black, or carbon nanotube), an optional resin binder, and, optionally, some amount of the common anode active materials (e.g., particles of natural graphite, synthetic graphite, hard carbon, etc.), if so desired.
The disclosure also provides an anode comprising multiple particles of an anode active material and a conductive additive that are dispersed in, bonded by, or encapsulated by a high-elasticity polymer, wherein said high-elasticity polymer has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10−8 S/cm at room temperature and wherein said high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof.
Such an anode electrode may be made by the process of (i) dispersing multiple particles of an anode active material, a conductive additive (e.g. carbon black, graphite flakes, graphene sheets, or carbon nanotubes), and an optional lithium salt in a precursor polymer solution to form a suspension (or slurry) wherein the precursor solution comprises at least a curing agent dissolved or dispersed in a reactive liquid medium that comprises a monomer or oligomer, and an optional non-aqueous liquid solvent, wherein the monomer or oligomer is selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof; (ii) dispensing and depositing a layer of the suspension onto a solid substrate surface (e.g. surface of a Cu foil as a current collector); and (iii) curing the monomer or oligomer to form an anode electrode layer. The process may further comprises a step of partially or fully removing the liquid solvent.
The present disclosure also provides a lithium battery containing an optional anode current collector, the presently invented anode as described above, a cathode active material layer, an optional cathode current collector, an electrolyte in ionic contact with the anode active material layer and the cathode active material layer and an optional porous separator. The lithium battery may be a lithium-ion battery, lithium metal battery (containing lithium metal or lithium alloy as the main anode active material and containing no intercalation-based anode active material), lithium-sulfur battery, lithium-selenium battery, or lithium-air battery.
The present disclosure also provides a method of manufacturing the composite particulates described above, the method comprising: (a) dispersing multiple particles of an anode active material in a precursor polymer solution to form a suspension wherein these particles are fully embedded or immersed in the precursor solution, which comprises at least a curing agent dissolved or dispersed in a reactive liquid medium that comprises a monomer or oligomer, and an optional non-aqueous liquid solvent, wherein the monomer or oligomer is selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof; (b) operating a secondary particle-forming procedure to shape the suspension into multiple droplets and remove the liquid solvent from the droplets; and (c) curing the monomer or oligomer to form the composite particulates wherein a particulate comprises one or a plurality of anode active material particles that are dispersed and embedded in a polymer matrix or encapsulated by a polymer shell. Preferably, the high-elasticity polymer has a lithium-ion conductivity from 1×10−8 S/cm to 5×10−2 S/cm. In some embodiments, the high-elasticity polymer has a recoverable tensile strain from 35% to 700% (more preferably >50%, and most preferably >100%).
These matrix or encapsulating polymers exhibit a unique combination of a high elasticity (high elastic deformation strain) and high lithium-ion conductivity.
The secondary particle-forming procedure can include a procedure selected from extrusion and pelletizing, pan coating, air suspension, centrifugal extrusion, vibrational nozzle, spray-drying, ultrasonic spraying, coacervation-phase separation, interfacial polycondensation, in-situ polymerization, matrix polymerization, or a combination thereof.
In certain embodiments, the step of dispersing includes dispersing or dissolving a reactive phosphazene polymer (or its precursor, such as polymerizing monomer or oligomer), an electronically conductive polymer or its precursor (e.g. polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, a sulfonated derivative thereof, or a combination thereof), a lithium-ion conducting material (e.g. lithium ion-conducting polymer and/or lithium salt), a reinforcement material (e.g. carbon nanotube, carbon nano-fiber, and/or graphene sheets), a foaming or blowing agent, or a combination thereof, in the suspension.
The foaming or blowing agent is used to generate pores in the particulate. The porosity level may be controlled by adjusting the type and the amount of pores in the suspension. The use of a foaming agent in producing foamed or cellular plastics is well-known in the plastic industry. However, the use of a foaming agent to produce pores in a composite particulate for lithium battery electrode application has not been previously taught or suggested.
The anode active material may be selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), phosphorus (P), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium titanium niobium oxide, lithium-containing titanium oxide, lithium transition metal oxide, ZnCo2O4; (f) carbon or graphite particles (g) prelithiated versions thereof; and (h) combinations thereof.
In some embodiments, one or a plurality of anode active material particles is coated with a layer of carbon, graphene, or any other conducting material prior to being dispersed in the polymer matrix.
In some embodiments, the composite particulate is further protected by a coating of a conducting carbon, graphite or graphene material. The graphene sheets may be selected from pristine graphene (e.g., that prepared by CVD or liquid phase exfoliation using direct ultrasonication), graphene oxide, reduced graphene oxide (RGO), graphene fluoride, doped graphene, functionalized graphene, etc.
This disclosure provides an anode (negative electrode) comprising composite particulates (each having one or more than one anode active material particles dispersed in a high-elasticity polymer matrix or encapsulated by a shell of high-elasticity polymer) for a lithium secondary battery, which is preferably a secondary battery based on a non-aqueous electrolyte, a polymer gel electrolyte, an ionic liquid electrolyte, a quasi-solid electrolyte, or a solid-state electrolyte. The shape of a lithium secondary battery can be cylindrical, square, button-like, etc. The present disclosure is not limited to any battery shape or configuration or any type of electrolyte. For convenience, we will primarily use Si, Sn, and SnO2 as illustrative examples of a high-capacity anode active material. This should not be construed as limiting the scope of the disclosure.
As illustrated in
In a less commonly used cell configuration, as illustrated in
In order to obtain a higher energy density cell, the anode in
In other words, there are several conflicting factors that should be considered concurrently when it comes to the design and selection of an anode active material in terms of material type, shape, size, porosity, and electrode layer thickness. Thus far, there has been no effective solution offered by any prior art teaching to these often conflicting problems. We have solved these challenging issues that have troubled battery designers and electrochemists alike for more than 30 years by developing the multi-functional composite particulates.
The present disclosure provides a solid powder mass of composite particulates for a lithium battery, wherein at least one of the composite particulates (preferably a majority or all of these particulates or “secondary particles”) has a diameter from 50 nm to 50 μm and comprises a plurality of anode active material particles (the “primary particles”) that are dispersed in a high-elasticity polymer matrix or encapsulated by a shell of high-elasticity polymer having a recoverable tensile strain no less than 5% (typically from 5% to 700% and more typically from 10% to 300%), when measured without an additive or reinforcement, and a lithium ion conductivity no less than 10−8 S/cm (preferably >10−4 S/cm, more preferably >10−3 S/cm) when measured at room temperature. In the structure of a polymer matrix, the polymer forms a continuous material phase. This continuous phase makes physical and ionic contact with all the anode active material particles dispersed in this continuous phase (matrix).
In certain embodiments, the disclosure provides a composite particulate for a lithium battery, wherein said composite particulate has a diameter from 10 nm to 50 μm and comprises one or more than one anode active material particles that are dispersed in a high-elasticity polymer matrix or encapsulated by a high-elasticity polymer shell, wherein the high-elasticity polymer matrix or shell has a recoverable elastic tensile strain no less than 5%, when measured without an additive or reinforcement dispersed therein, and a lithium ion conductivity no less than 10−8 S/cm at room temperature and wherein the high-elasticity polymer comprises a polymer derived from a monomer selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof.
Many of these monomers are not known to be polymerizable and, if polymerized, the products are sufficiently elastic to protect the anode materials that can undergo large volume expansion.
The fluorinated monomer may be selected from the group consisting of fluorinated vinyl carbonates, fluorinated vinyl monomers, fluorinated esters, fluorinated vinyl esters, and fluorinated vinyl ethers and combinations thereof.
Desirable polymerizable liquid solvents include fluorinated monomers having unsaturation (double bonds or triple bonds) in the backbone or cyclic structure (e.g., fluorinated vinyl carbonates, fluorinated vinyl monomers, fluorinated esters, fluorinated vinyl esters, and fluorinated vinyl ethers). Fluorinated vinyl esters include RfCO2CH═CH2 and Propenyl Ketones, RfCOCH═CHCH3, where Rf is F or any F-containing functional group (e.g., CF2— and CF2CF3−).
Two examples of fluorinated vinyl carbonates are given below:
These liquid solvents, as a monomer, can be cured in the presence of an initiator (e.g., 2-Hydroxy-2-methyl-1-phenyl-propan-1-one, Ciba DAROCUR-1173, which can be activated by UV or electron beam):
In some embodiments, the fluorinated carbonate is selected from vinyl- or double bond-containing variants of fluoroethylene carbonate (FEC), DFDMEC, FNPEC, a combination thereof, or a combination thereof with hydrofluoro ether (HFE), trifluoro propylene carbonate (FPC), or methyl nonafluorobutyl ether (MFE), wherein the chemical formulae for FEC, DFDMEC, and FNPEC, respectively (all polymerizable via ring-opening polymerization with an ionic initiator) are shown below:
Desirable sulfones as a monomer include, but not limited to, alkyl and aryl vinyl sulfones or sulfides; e.g., ethyl vinyl sulfide, allyl methyl sulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, ethyl vinyl sulfone, allyl phenyl sulfone, allyl methyl sulfone, and divinyl sulfone.
Simple alkyl vinyl sulfones, such as ethyl vinyl sulfone, may be polymerized via emulsion and bulk methods. Propyl vinyl sulfone may be polymerized by alkaline persulfate initiators to form soft polymers. It may be noted that aryl vinyl sulfone, e.g., naphthyl vinyl sulfone, phenyl vinyl sulfone, and parra-substituted phenyl vinyl sulfone (R=NH2, NO2 or Br), were reported to be unpolymerizable with free-radical initiators. However, we have observed that phenyl and methyl vinyl sulfones can be polymerized with several anionic-type initiators. Effective anionic-type catalysts or initiators are n-BuLi, ZnEt2, LiN(CH2)2, NaNH2, and complexes of n-LiBu with ZnEt2 or AlEh. A second solvent, such as pyridine, sulfolane, toluene or benzene, can be used to dissolve alkyl vinyl sulfones, aryl vinyl sulfones, and other larger sulfone molecules.
Poly(sulfone)s have high oxygen indices and low smoke emission on burning. Poly(sulfone)s are inherently self-extinguishing materials owing to their highly aromatic character. A hydroxy-terminated copoly(ester sulfone) synthesized by melt polycondensation of the diethylene glycol and 4,4-dihydroxydiethoxydiphenyl sulfone with adipic acid can be used as a flame retardant. Some examples are difunctional β-allyl sulfones and 4,4-(m-phenylene-dioxy)bis(benzenesulfonyl chloride):
Bisphenol S (BPS) and 4,4′-Dichlorodiphenyl sulfone (DCDPS) are additional examples that can be a part of a polymer structure. Bisphenol S (BPS) is an organic compound with the formula (HOC6H4)O2SO2:
4,4′-Dichlorodiphenyl sulfone (DCDPS), having a MP=148° C. is an organic compound with the formula (ClC6H4)2SO2:
The sulfone or sulfide may be selected from vinyl sulfone, allyl sulfone, alkyl vinyl sulfone, aryl vinyl sulfone, methyl vinyl sulfone, ethyl vinyl sulfone, vinyl sulfide, a vinyl-containing variant of TrMS, MTrMS, TMS, EMS, MMES, EMES, EMEES, or a combination thereof:
In certain embodiments, the vinyl sulfone or sulfide is selected from ethyl vinyl sulfide, allyl methyl sulfide, phenyl vinyl sulfide, phenyl vinyl sulfoxide, allyl phenyl sulfone, allyl methyl sulfone, divinyl sulfone, or a combination thereof, wherein the vinyl sulfone does not include methyl ethylene sulfone and ethyl vinyl sulfone.
The nitrile may comprise a dinitrile or is selected from AND, GLN, SEN, or a combination thereof:
The silaxane or silane may be selected from alkylsiloxane (Si—O), alkyylsilane (Si—C), liquid oligomeric silaxane (—Si—O—Si—), or a combination thereof.
High-elasticity polymer refers to a polymer, typically a lightly cross-linked polymer, which exhibits an elastic deformation that is at least 5% when measured (without an additive or reinforcement in the polymer) under uniaxial tension. In the field of materials science and engineering, the “elastic deformation” is defined as a deformation of a material (when being mechanically stressed) that is essentially fully recoverable and the recovery is essentially instantaneous upon release of the load. The elastic deformation is preferably greater than 30%, more preferably greater than 50%, further more preferably greater than 100%, still more preferably greater than 150%, and most preferably greater than 200%.
Three examples of the disclosed composite particulates are illustrated in
As illustrated in
The primary particles themselves may be porous having porosity in the form of surface pores and/or internal pores.
This amount of pore volume inside the particulate (surface or internal pores of porous primary anode particles) provides empty space to accommodate the volume expansion of the anode active material so that the polymer matrix and the entire composite particulate would not have to significantly expand (not to exceed 50% volume expansion of the particulate) when the lithium battery is charged. Preferably, the composite particulate does not increase its volume by more than 20%, further preferably less than 10% and most preferably by approximately 0% when the lithium battery is charged. Such a constrained volume expansion of the particulate would not only reduce or eliminate the volume expansion of the anode electrode but also reduce or eliminate the issue of repeated formation and destruction of a solid-electrolyte interface (SEI) phase. We have discovered that this strategy surprisingly results in significantly reduced battery capacity decay rate and dramatically increased charge/discharge cycle numbers. These results are unexpected and highly significant with great utility value.
Multiple non-lithiated Si particles can be dispersed in or encapsulated by a high-elasticity polymer to form a composite particulate. As the lithium-ion battery is charged, the anode active material particles (e.g. Si) are intercalated with lithium ions and, hence, the Si particle expands. Due to the high elasticity of the polymer, the polymer may simply expand accordingly without breaking up into pieces. That the high-elasticity polymer remains intact prevents the exposure of the embedded Si particles to liquid electrolyte and, thus, prevents the Si from undergoing undesirable reactions with electrolyte during repeated charges/discharges of the battery. This strategy prevents continued consumption of the electrolyte and lithium ions to form additional SEI.
The particulate may further contain a graphite, graphene, and/or carbon material dispersed in the high-elasticity polymer matrix. The carbon or graphite material may be selected from polymeric carbon, amorphous carbon, chemical vapor deposition carbon, coal tar pitch, petroleum pitch, meso-phase pitch, carbon black, coke, acetylene black, activated carbon, fine expanded graphite particle with a dimension smaller than 100 nm, artificial graphite particle, natural graphite particle, carbon nano-tubes (single-walled or multi-walled), carbon nano-fibers (vapor-grown or carbonized polymer fibers), graphitic nano-fibers, graphene sheets, or a combination thereof. Graphene may be selected from pristine graphene, graphene oxide, reduced graphene oxide, graphene fluoride, hydrogenated graphene, nitrogenated graphene, functionalized graphene, etc.
The carbon/graphite/graphene particles, fibers, nanotubes, and/or nano sheets dispersed in the high-elasticity polymer or encapsulated in the high-elasticity polymer shell preferably and typically constitute a 3D network of electron-conducting paths that preferably are in contact with individual primary particles of the anode active material. The high-elasticity polymer matrix, being a continuous phase and making contact with individual primary particles (being substantially totally immersed in the polymer matrix) provide a 3D network of lithium ion-conducting paths. In other words, there are dual networks of conducting pathways for electrons and lithium ions inside the multi-functional composite particulate.
The anode active material may be selected from the group consisting of: (a) silicon (Si), germanium (Ge), tin (Sn), lead (Pb), antimony (Sb), phosphorus (P), bismuth (Bi), zinc (Zn), aluminum (Al), titanium (Ti), nickel (Ni), cobalt (Co), and cadmium (Cd); (b) alloys or intermetallic compounds of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Ni, Co, or Cd with other elements; (c) oxides, carbides, nitrides, sulfides, phosphides, selenides, and tellurides of Si, Ge, Sn, Pb, Sb, Bi, Zn, Al, Ti, Fe, Ni, Co, V, or Cd, and their mixtures, composites, or lithium-containing composites; (d) salts and hydroxides of Sn; (e) lithium titanate, lithium manganate, lithium aluminate, lithium titanium niobium oxide, lithium-containing titanium oxide, lithium transition metal oxide, ZnCo2O4; (f) carbon or graphite particles (g) prelithiated versions thereof; and (h) combinations thereof.
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. SnO2 and Co3O4) 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.
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.
Preferably and typically, the high-elasticity polymer has a lithium ion conductivity no less than 10−5 S/cm, more preferably no less than 10−4 S/cm, further preferably no less than 10−3 S/cm, and most preferably no less than 10−2 S/cm. In some embodiments, the high-elasticity polymer is a neat polymer having no additive or filler dispersed therein. In others, the high-elasticity polymer is a polymer matrix composite containing from 0.1% to 50% (preferably 1% to 35%) by weight of a lithium ion-conducting additive dispersed in the high-elasticity polymer matrix material. The high-elasticity polymer should have a high elasticity (elastic deformation strain value >5%).
An elastic deformation is a deformation that is fully recoverable and the recovery process is essentially instantaneous (no significant time delay) upon release of the mechanical stress. The high-elasticity polymer can exhibit an elastic deformation from 5% up to 1,000% (10 times of its original length), more typically from 10% to 800%, and further more typically from 50% to 500%, and most typically and desirably from 70% to 300%.
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%).
Typically, a high-elasticity polymer is originally in a monomer, oligomer, or linear or branched chain states that can be cured to form a cross-linked polymer that is highly elastic. Prior to curing, these polymers or oligomers are soluble in an organic solvent or, preferably, water to form a polymer solution. Particles of an anode active material (e.g. SnO2 nano particles and Si nano-wires) can be dispersed in this polymer solution to form a suspension (dispersion or slurry) of an active material particle-polymer (monomer or oligomer) mixture. This suspension can then be subjected to a solvent removal treatment. The polymer (or monomer or oligomer) precipitates out to form a continuous phase or matrix in which the active material primary particles are dispersed (if a polymer content is high), or to form a coating encapsulating the anode particles (if a polymer content is low). This can be accomplished, for instance, via solution dipping, coating or casting on a solid substrate surface, spray drying, ultrasonic spraying, air-assisted spraying, aerosolization, and other secondary particle formation procedures.
It is essential for these materials to form a lightly cross-linked network of polymer chains. In other words, the network polymer or cross-linked polymer should have a relatively low degree of cross-linking or low cross-link density to impart a high elastic deformation.
The cross-link density of a cross-linked network of polymer chains may be defined as the inverse of the molecular weight between cross-links (Mc). The cross-link density can be determined by the equation, Mc=ρRT/Ge, where Ge is the equilibrium modulus as determined by a temperature sweep in dynamic mechanical analysis, p is the physical density, R is the universal gas constant in J/mol*K and T is absolute temperature in K. Once Ge and p are determined experimentally, then Mc and the cross-link density can be calculated.
The magnitude of Mc may be normalized by dividing the Mc value by the molecular weight of the characteristic repeat unit in the cross-link chain or chain linkage to obtain a number, Nc, which is the number of repeating units between two cross-link points. We have found that the elastic deformation strain correlates very well with Mc and. Nc. The elasticity of a cross-linked polymer derives from a large number of repeating units (large Nc) between cross-links. The repeating units can assume a more relax conformation (e.g. random coil) when the polymer is not stressed. However, when the polymer is mechanically stressed, the linkage chain uncoils or gets stretched to provide a large deformation. A long chain linkage between cross-link points (larger Nc) enables a larger elastic deformation. Upon release of the load, the linkage chain returns to the more relaxed or coiled state. During mechanical loading of a polymer, the cross-links prevent slippage of chains that otherwise form plastic deformation (non-recoverable).
Preferably, the Nc value in a high-elasticity polymer is greater than 5, more preferably greater than 10, further more preferably greater than 100, and even more preferably greater than 200. These Nc values can be readily controlled and varied to achieve different elastic deformation values by using different cross-linking agents with different functionalities, and by designing the polymerization and cross-linking reactions to proceed at different temperatures for different periods of time.
Alternatively, Mooney-Rilvin method may be used to determine the degree of cross-linking. Crosslinking also can be measured by swelling experiments. In a swelling experiment, the crosslinked sample is placed into a good solvent for the corresponding linear polymer at a specific temperature, and either the change in mass or the change in volume is measured. The higher the degree of crosslinking, the less swelling is attainable. Based on the degree of swelling, the Flory Interaction Parameter (which relates the solvent interaction with the sample, Flory Huggins Eq.), and the density of the solvent, the theoretical degree of crosslinking can be calculated according to Flory's Network Theory. The Flory-Rehner Equation can be useful in the determination of cross-linking.
The high-elasticity polymer matrix may contain a simultaneous interpenetrating network (SIPN) polymer, wherein two cross-linking chains intertwine with each other, or a semi-interpenetrating network polymer (semi-IPN), which contains a cross-linked polymer and a linear polymer.
The aforementioned high-elasticity polymers may be used alone to serve as a matrix. Alternatively, the high-elasticity polymer can be mixed with a broad array of elastomers, electrically conducting polymers, lithium ion-conducting materials, and/or strengthening materials (e.g. carbon nanotube, carbon nano-fiber, or graphene sheets).
A broad array of elastomers can be mixed with a high-elasticity polymer. Substantially all the anode primary particles in a particulate are fully embedded in and surrounded by the polymer, preventing direct contact between the particle(s) and the liquid electrolyte in the battery.
The high-elasticity polymer may further contain an elastomeric material selected from natural polyisoprene (e.g. cis-1,4-polyisoprene natural rubber (NR) and trans-1,4-polyisoprene gutta-percha), synthetic polyisoprene (IR for isoprene rubber), polybutadiene (BR for butadiene rubber), chloroprene rubber (CR), polychloroprene (e.g. Neoprene, Baypren etc.), butyl rubber (copolymer of isobutylene and isoprene, IIR), including halogenated butyl rubbers (chloro butyl rubber (CIIR) and bromo butyl rubber (BIIR), styrene-butadiene rubber (copolymer of styrene and butadiene, SBR), nitrile rubber (copolymer of butadiene and acrylonitrile, NBR), EPM (ethylene propylene rubber, a copolymer of ethylene and propylene), EPDM rubber (ethylene propylene diene rubber, a terpolymer of ethylene, propylene and a diene-component), epichlorohydrin rubber (ECO), polyacrylic rubber (ACM, ABR), silicone rubber (SI, Q, VMQ), fluorosilicone rubber (FVMQ), fluoroelastomers (FKM, and FEPM; such as Viton, Tecnoflon, Fluorel, Aflas and Dai-El), perfluoroelastomers (FFKM: Tecnoflon PFR, Kalrez, Chemraz, Perlast), polyether block amides (PEBA), chlorosulfonated polyethylene (CSM; e.g. Hypalon), and ethylene-vinyl acetate (EVA), thermoplastic elastomers (TPE), protein resilin, protein elastin, ethylene oxide-epichlorohydrin copolymer, polyurethane, urethane-urea copolymer, and combinations thereof.
The urethane-urea copolymer usually consists of two types of domains, soft domains and hard ones. Entangled linear backbone chains consisting of poly(tetramethylene ether) glycol (PTMEG) units constitute the soft domains, while repeated methylene diphenyl diisocyanate (MDI) and ethylene diamine (EDA) units constitute the hard domains. The lithium ion-conducting additive can be incorporated in the soft domains or other more amorphous zones.
In some embodiments, a high-elasticity polymer can form a polymer matrix composite containing a lithium ion-conducting additive dispersed in the high-elasticity polymer matrix material, wherein the lithium ion-conducting additive is selected from Li2CO3, Li2O, Li2C2O4, LiOH, LiX, ROCO2Li, HCOLi, ROLi, (ROCO2Li)2, (CH2OCO2Li)2, Li2S, LixSOy, or a combination thereof, wherein X=F, Cl, I, or Br, R=a hydrocarbon group, 0<x≤1, 1≤y≤4.
In some embodiments, the high-elasticity polymer can be mixed with a lithium ion-conducting additive, which contains a lithium salt selected from lithium perchlorate (LiClO4), lithium hexafluorophosphate (LiPF6), lithium borofluoride (LiBF4), lithium hexafluoroarsenide (LiAsF6), lithium trifluoro-methanesulfonate (LiCF3SO3), bis-trifluoromethyl sulfonylimide lithium (LiN(CF3SO2)2), lithium bis(oxalato)borate (LiBOB), lithium oxalyldifluoroborate (LiBF2C2O4), lithium nitrate (LiNO3), Li-fluoroalkyl-phosphate (LiPF3(CF2CF3)3), lithium bisperfluoro-ethylsulfonylimide (LiBETI), lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium trifluoromethanesulfonimide (LiTFSI), an ionic liquid-based lithium salt, or a combination thereof.
The high-elasticity polymer may form a mixture or blend with an electron-conducting polymer selected from polyaniline, polypyrrole, polythiophene, polyfuran, a bi-cyclic polymer, derivatives thereof (e.g. sulfonated versions), or a combination thereof.
In some embodiments, the high-elasticity polymer may form a mixture with a lithium ion-conducting polymer selected from poly(ethylene oxide) (PEO), Polypropylene oxide (PPO), poly(acrylonitrile) (PAN), poly(methyl methacrylate) (PMMA), poly(vinylidene fluoride) (PVdF), Poly bis-methoxy ethoxyethoxide-phosphazene, Polyvinyl chloride, Polydimethylsiloxane, poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), a derivative thereof (e.g. sulfonated versions), or a combination thereof.
The present disclosure also provides a method of producing composite particulates comprising anode active material particles dispersed in a high-elasticity polymer. As schematically illustrated in
Alternatively, one may first mix certain ingredient(s) in one pot and other ingredients in other pot(s) and then combine them together in one pot. For instance, one may mix the monomer and the initiator in one pot, allowing the mixture to proceed to form a reactive oligomer (low molecular weight chains). A separate pot may be used to contain the curing agent (crosslinker). The primary particles of anode active material and other ingredients may be dispersed into either pot or both pots. The ingredients in two pots are then combined together and then heated or radiation-exposed to initiate the polymerization and crosslinking reactions (if appropriate).
The present disclosure also provides a method of manufacturing the composite particulates described above, the method comprising: (a) dispersing multiple particles of an anode active material in a precursor polymer solution to form a suspension wherein these particles are fully embedded or immersed in the precursor solution, which comprises at least a curing agent dissolved or dispersed in a reactive liquid medium that comprises a monomer or oligomer, and an optional non-aqueous liquid solvent, wherein the monomer or oligomer is selected from the group consisting of vinyl sulfite, ethylene carbonate, methyl methacrylate, vinyl acetate, fluorinated monomers having unsaturation for polymerization, sulfones, sulfides, nitriles, sulfates, siloxanes, silanes, and combinations thereof; (b) operating a secondary particle-forming procedure to shape the suspension into multiple droplets and remove the liquid solvent from the droplets; and (c) curing the monomer or oligomer to form said composite particulates wherein a particulate comprises one or a plurality of anode active material particles that are dispersed and embedded in a polymer matrix or encapsulated by a polymer shell. Preferably, the high-elasticity polymer has a lithium-ion conductivity from 1×10−8 S/cm to 5×10−2 S/cm. In some embodiments, the high-elasticity polymer has a recoverable tensile strain from 35% to 700% (more preferably >50%, and most preferably >100%).
Several composite droplet forming processes require the high-elasticity polymer or its precursor (monomer or oligomer) to be dissolvable in a solvent. Fortunately, all the high-elasticity polymers or their precursors used herein are either in a liquid state at room temperature or are soluble in some common solvents. The un-cured polymer or its precursor can be readily dissolved in a common organic solvent or water to form a solution. This solution can then be used to embed, immerse, engulf or encapsulate the solid particles (anode particles along with other additive or reinforcement materials) via several of the micro-droplet-forming methods to be discussed in what follows. Upon formation of the droplets, the polymer matrix is then polymerized and cross-linked.
There are three broad categories of micro-encapsulation methods that can be implemented to produce high-elasticity polymer composite: physical methods, physico-chemical methods, and chemical methods. The physical methods include extrusion and pelletizing, solution dipping and drying, suspension coating or casting on a solid substrate (e.g. slot-die coating, Comma coating, spray-coating) followed by drying and scratching off particles from the substrate, pan-coating, air-suspension coating, centrifugal extrusion, vibration nozzle, and spray-drying methods. The physico-chemical methods include ionotropic gelation and coacervation-phase separation methods. The chemical methods include interfacial polycondensation, interfacial cross-linking, in-situ polymerization, and matrix polymerization.
It may be noted that some of these methods (e.g. pan-coating, air-suspension coating, and spray-drying) may be used to coat or encapsulate primary particles or particulates (secondary particles) by adjusting the solid content, degree of dispersion, spraying and drying conditions, etc. Similar processes may be used to produce composite particulates wherein the particles are fully dispersed in a polymer matrix, not just coating on some surfaces. This can be accomplished by providing a higher amount of the reacting monomer, oligomer, or polymer with respect to the anode particles, for instance.
Pan-coating method: The pan coating process involves tumbling the anode active material primary particles (along with any desired additive or reinforcement materials) in a pan or a similar device while the matrix material (e.g., monomer/oligomer liquid or uncured polymer/solvent solution; possibly containing a lithium salt dispersed or dissolved therein) is applied slowly until a desired amount of matrix is attained.
Air-suspension coating method: In the air suspension coating process, the solid primary particles of anode active material are dispersed into the supporting air stream in an embedding chamber. A controlled stream of a reactive precursor solution (e.g., polymer or its monomer or oligomer dissolved in a solvent; or its monomer or oligomer alone in a liquid state) is concurrently introduced into this chamber, allowing the solution to hit and embed the suspended particles. These suspended particles are embedded in the reactive precursor (monomer, oligomer, etc. which is polymerized/cured concurrently or subsequently) while the volatile solvent is removed, leaving behind a composite comprising a matrix of conducting network polymer and anode active material particles. This process may be repeated several times until the required parameters, such as full embedding, are achieved. The air stream which supports the anode particles also helps to dry them, and the rate of drying is directly proportional to the temperature of the air stream, which can be adjusted for optimized polymer network amount.
In a preferred mode, the particles in the embedding zone portion may be subjected to re-circulation for repeated embedding. Preferably, the chamber is arranged such that the particles pass upwards through the embedding zone, then are dispersed into slower moving air and sink back to the base of the encapsulating chamber, enabling repeated passes of the particles through the embedding zone until the desired matrix amount is achieved.
Centrifugal extrusion: Primary anode particles may be embedded in a polymer network or precursor material using a rotating extrusion head containing concentric nozzles. In this process, a stream of core fluid (slurry containing anode particles dispersed in a solvent) is surrounded by a sheath of shell solution or melt containing the polymer or precursor. As the device rotates and the stream moves through the air it breaks, due to Rayleigh instability, into droplets of core, each coated with the shell solution. While the droplets are in flight, the molten shell may be hardened or the solvent may be evaporated from the shell solution. If needed, the capsules can be hardened after formation by catching them in a hardening bath. Since the drops are formed by the breakup of a liquid stream, the process is only suitable for liquid or slurry. A high production rate can be achieved. Up to 22.5 kg of microcapsules can be produced per nozzle per hour and extrusion heads containing 16 nozzles are readily available.
Vibrational nozzle encapsulation method: matrix-encapsulation of anode particles can be conducted using a laminar flow through a nozzle and vibration of the nozzle or the liquid. The vibration has to be done in resonance with the Rayleigh instability, leading to very uniform droplets. The liquid can include any liquids with limited viscosities (1-50,000 mPa·s): emulsions, suspensions or slurry containing the anode active material particles and the polymer or precursor.
Spray-drying: Spray drying may be used to encapsulate and embed anode particles when the particles are suspended in a melt or polymer/precursor solution to form a suspension. In spray drying, the liquid feed (solution or suspension) is atomized to form droplets which, upon contacts with hot gas, allow solvent to get vaporized and a polymer matrix to fully embed the particles.
In-situ polymerization: In some micro-encapsulation processes, anode particles are fully embedded in a monomer or oligomer first. Then, direct polymerization of the monomer or oligomer is carried out with the presence of these material particles dispersed therein.
Matrix polymerization: This method involves dispersing and embedding anode primary particles in a polymeric matrix during formation of the particles. This can be accomplished via spray-drying, in which the particles are formed by evaporation of the solvent from the matrix material. Another possible route is the notion that the solidification of the matrix is caused by a chemical change.
In summary, in certain embodiments, the disclosure provides a method of producing the multi-functional particulates, the method comprising (A) dispersing a plurality of primary particles of an anode active material, having a diameter or thickness from 0.5 nm to 20 μm, in a liquid mixture of a monomer or oligomer of a phosphazene compound or derivative, an initiator, and a cross-linking agent to form a reactive slurry; (B) forming the reactive slurry into micro-droplets and polymerizing and curing the monomer or oligomer in the micro-droplets to form the multi-functional particulates. The reactive mixture may further comprise a dopant, a reinforcement material, a lithium ion-conducting additive, an electron-conducting additive, or a combination thereof.
A foaming agent or blowing agent may be introduced into the reactive slurry and can be activated to produce pores in the micro-droplets when the reactive species are polymerized or crosslinked.
In some embodiments, the reactive slurry further comprises a high-strength material selected from carbon nanotubes, carbon nano-fibers, carbon or graphite fibers, graphene sheets, expanded graphite flakes, polymer fibrils, glass fibers, ceramic fibers, metal filaments or metal nano-wires, or a combination thereof. Some of these high-strength materials are electron-conducting.
The step (B) of forming micro-droplets may comprise a procedure selected from solution dipping, coating or casting on a solid substrate, pan-coating, air-suspension coating, centrifugal extrusion, vibration-nozzle encapsulation, spray-drying, coacervation-phase separation, interfacial polycondensation or interfacial cross-linking, in-situ polymerization, matrix polymerization, extrusion and palletization, or a combination thereof.
In certain embodiments, the micro-droplets as formed may contain a liquid solvent and the method further comprises a step of removing the solvent.
The following examples serve to provide the best modes of practice for the present disclosure and should not be construed as limiting the scope of the disclosure:
Si particles were encapsulated with a high-elasticity polymer. In one example, FEC and poly(ethyleneglycol) diacrylate (PEGDA) (structures shown below),
were stirred under the protection of argon gas until a homogeneous solution was obtained. Subsequently, lithium hexafluoro phosphate (4%) and, lithium trifluoro-methanesulfonate, LiCF3SO3 (1% by weight) were then added and dissolved in the above solution to obtain a reactive mixture solution, wherein the weight, fractions of fluorinated vinylene carbonate, polyethyleneglycol diacrylate, and lithium salts were 85 wt %, 10 wt %, and 5 wt %, respectively. Si particles were then added into the solution to form a slurry, which was partially dried in a vacuum oven to obtain a reactive mass. The reactive mass was then irradiated with electron beam at room temperature until a total dosage of 40 Gy was reached, resulting in the formation of an elastic polymer.
On a separate basis, some amount of the reactive solution without Si was cast onto a glass surface to form a wet film, which was thermally dried and then cured under similar conditions to form a film of polymer. Several tensile testing specimens were cut from each polymer film and tested with a universal testing machine. The representative tensile stress-strain curves indicate that this series of network polymers have an elastic deformation from approximately 15% to 115%.
For electrochemical testing, the working electrodes were prepared by mixing 85 wt. % active material particles (polymer-protected and non-protected particulates of Si, separately), 7 wt. % acetylene black (Super-P), and 8 wt. % polyvinylidene fluoride (PVDF) binder dissolved in N-methyl-2-pyrrolidinoe (NMP) to form a slurry of 5 wt. % total solid content. After coating the slurries on Cu foil, the electrodes were dried at 120° C. in vacuum for 2 h to remove the solvent before pressing. Then, the electrodes were cut into a disk (ϕ)=12 mm) and dried at 100° C. for 24 h in vacuum. Electrochemical measurements were carried out using CR2032 (3V) coin-type cells with lithium metal as the counter/reference electrode, Celgard 2400 membrane as separator, and 1 M LiPF6 electrolyte solution dissolved in a mixture of ethylene carbonate (EC) and diethyl carbonate (DEC) (EC-DEC, 1:1 v/v). The cell assembly was performed in an argon-filled glove-box. The CV measurements were carried out using an-6 electrochemical workstation at a scanning rate of 1 mV/s. The electrochemical performance of the particulates of high-elasticity polymer-encapsulated Si particles and non-protected Si particles were evaluated by galvanostatic charge/discharge cycling at a current density of 50-200 mA/g, using an electrochemical workstation.
In contrast, as demonstrated
Similar procedure as in Example 1 was followed, but the monomer was a fluorinated vinyl carbonate, given below:
which was cured with an initiator, 2-Hydroxy-2-methyl-1-phenyl-propan-1-one (Ciba DAROCUR-1173), with the assistance of electron beam irradiation.
Similar procedure as in Example 1 was followed, but the monomer was 2-(Trifluoromethyl)acrylic acid, as shown below (melting point=52° C.):
Polyethylene glycol) diacrylate was used as an initiator and mixing was conducted at 60° C.
Tin oxide (SnO2) nano particles were obtained by the controlled hydrolysis of SnCl4.5H2O with NaOH using the following procedure: SnCl4.5H2O (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 H2SO4. To this mixed solution, few drops of 0.1 M of H2SO4 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.
Under the protection of argon, lithium hexafluorophosphate with the mass fraction of 5% was added into vinyl sulfite to form a solution, which was stirred uniformly. Then azodiisobutyronitrile with the mass fraction of 0.5% was added into the solution, which was stirred to obtain a uniformly mixed solution. SnO2 nano particles were then added into the solution to prepare a slurry. The slurry was cured at the temperature of 40° C. for 4 hours.
Separately, the reacting mass was cast onto a glass surface to form several films which were cured to obtain polymers. Tensile testing was conducted on these films. This series of polymers can be elastically stretched up to approximately 68%.
Under the protection of argon, 10 mass percent of lithium bis(trifluoromethyl)sulfonyl imide was added into ethylene carbonate, which was stirred to achieve a uniform solution. Subsequently, 3 mass percent of benzoyl peroxide was into the solution, followed by addition of anode active material particles (Si nanowires) to obtain a slurry. The slurry was cured and dried at 60° C. in a vacuum oven for 5 hours to polymerize the vinylene trithiocarbonate. The resulting solid was subjected to mechanical shearing in a food blender to produce powder of composite particulates.
Under the protection of argon, 30% by mass of lithium perchlorate was added into methyl vinyl sulfone and then uniformly stirred to produce a solution. Then, 1% by mass of dimethyl azodiisobutyrate was added into the solution. To this solution were added SiO particles to obtain a slurry, which was dried in a vacuum oven at 80° C. for 7 hours to polymerize the methyl vinyl sulfone. The solid mass was then lightly ball-milled to produce composite particulates.
Additionally, polymer films without the anode particles were cast on a glass surface and were subjected to the same polymerization conditions. The tensile elastic strains were found to be from 16% to 62%.
Under the protection of argon, vinyl sulfite and ethyl vinyl sulfone were mixed together according to a molar ratio of 10:1. Subsequently, 2 mass percent of lithium bis(oxalato)borate and 0.1 mass percent of methyl ethyl ketone peroxide were added and stirring was continued for 15 minutes to obtain a mixed solution. Si nano particles and nanowires were separately added into a solution to form two slurry samples. The samples were cast on a glass surface and then heated to 30° C. for 2 hours to polymerize vinyl sulfite and ethyl vinyl sulfone. Powder of composite particulates was obtained by low-intensity ball-milling of the resulting product.
Under the protection of argon, ethylene carbonate and vinyl acetate are mixed according to the molar ratio of 5:1. The mixture was stirred uniformly, and then benzoyl peroxide with a mass fraction of 5% was added in a droplet-wise manner into the mixture to form a homogeneous solution. Anode particles (Co3O4) were then added into the solution to prepare a slurry. The slurry in a glass container was housed in a bag and heated at a vacuum oven at 40° C. for 4 hours while under electron beam irradiation to polymerize and cure vinyl ethylene sulfite.
Under the protection of argon, vinyl sulfite, methyl vinyl sulfone and methyl methacrylate were mixed according to a molar ratio of 5:2:3. After some stirring, 1 mass percent of benzoyl peroxide tert-butyl ester was added into the mixture solution. Anode particles (Sn particles) were then dispersed into this solution, which was further stirred and mixed uniformly to obtain a slurry. The slurry was heated in a vacuum oven at 70° C. for 4 hours, allowing the vinyl sulfite, methyl vinyl sulfone and methyl methacrylate to get co-polymerize and cured.
Phenyl vinyl sulfide, CTA (chain transfer agent, shown below), AIBN (initiator, 1.0%), and Si nano particles were mixed and heated at 60° C. to obtain a cured dry mass. The dried solid was then ball-milled to obtain powder of composite particulates.
The reaction of vinyl sulfones (e.g., ethyl vinyl sulfone, EVS), acrylates (e.g. hexanethiol, HA) and/or 1-Hexanethiol (HT) as a co-reactant or curing agent, and triethylamine (TEA) as an initiator was investigated. Hexanethiol (HT), ethyl vinyl sulfone (EVS) and hexyl acrylate (HA) were prepared at a molar ratio from 1:1:0.1 (no unreacted HA) to 1:1:0.3 (20% of HA remained unreacted). The thiol reactant and the initiator, along with SiO particles, were added to a glass vial and thoroughly mixed. Varying stoichiometric amounts of vinyl sulfone and acrylate were added to the mixture, which was mixed vigorously and then allowed start the thiol—Michael addition reaction. With a 2.0% TEA initiator, the reaction can be concluded in approximately 20-40 minutes, generating a network of crosslinked chains. The use of acrylates via thiol—Michael addition reaction in ternary systems was used to control gelation behavior in crosslinked polymer networks formed by thiol—Michael addition reactions.
Phenyl vinyl sulfone (PVS) can be polymerized with several anionic-type initiators; e.g., n-BuLi, ZnEt2, LiN(CH2)2, and NaNH2. The second solvent may be selected from pyridine, sulfolane, toluene or benzene, which may be removed before or after polymerization.
In an example, a mixture of PVS, n-BuLi (1.0%), LiBF4 (0.5 M), and sulfolane was thoroughly mixed and was maintained at 30° C. overnight to cure the polymer.
A monomer solvent 4,4′-(1,4-Butylenedioxy)dibenzonitrile (BDDN) was used, along with trifluoromethanesulfonic acid (CF3SO3H) as an initiator dissolved in o-dichlorobenzene (o-DCB) in the polymerization reaction.
The reaction was carried out in o-DCB under nitrogen for 30 min, having [BDDN]=0.125 M; and [CF3SO3H]=0.5 M. A typical experimental procedure for the polymerization of BDDN is given in the following as an example. In a 20 mL test tube equipped with a magnetic stirrer were placed BDDN (0.25 mmol) and CF3SO3H (1 mmol) in 2 mL o-DCB. The mixture solution was added with particles of an anode active material and the resulting slurry was stirred at room temperature for 5 minutes and then allowed to proceed with reactions for 1 hour.
The present study led to the following additional observations:
