Classifications

• • C—CHEMISTRY; METALLURGY
  • C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
  • C09K—MATERIALS FOR MISCELLANEOUS APPLICATIONS, NOT PROVIDED FOR ELSEWHERE
  • C09K21/00—Fireproofing materials
  • C09K21/06—Organic materials
  • C09K21/12—Organic materials containing phosphorus
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/052—Li-accumulators
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0567—Liquid materials characterised by the additives
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0568—Liquid materials characterised by the solutes
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/05—Accumulators with non-aqueous electrolyte
  • H01M10/056—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes
  • H01M10/0564—Accumulators with non-aqueous electrolyte characterised by the materials used as electrolytes, e.g. mixed inorganic/organic electrolytes the electrolyte being constituted of organic materials only
  • H01M10/0566—Liquid materials
  • H01M10/0569—Liquid materials characterised by the solvents
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M10/00—Secondary cells; Manufacture thereof
  • H01M10/42—Methods or arrangements for servicing or maintenance of secondary cells or secondary half-cells
  • H01M10/4235—Safety or regulating additives or arrangements in electrodes, separators or electrolyte
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/381—Alkaline or alkaline earth metals elements
  • H01M4/382—Lithium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/38—Selection of substances as active materials, active masses, active liquids of elements or alloys
  • H01M4/40—Alloys based on alkali metals
  • H01M4/405—Alloys based on lithium
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/02—Electrodes composed of, or comprising, active material
  • H01M4/36—Selection of substances as active materials, active masses, active liquids
  • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
  • H01M4/5805—Phosphides
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
  • H01M4/00—Electrodes
  • H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
  • H01M2004/8678—Inert electrodes with catalytic activity, e.g. for fuel cells characterised by the polarity
  • H01M2004/8684—Negative electrodes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/10—Energy storage using batteries
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
  • Y02E60/30—Hydrogen technology
  • Y02E60/50—Fuel cells

Definitions

• This invention is directed to low flammability and nonflammable electrolytes for stable operation of electrochemical devices, certain embodiments of the electrolytes including an active salt, a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent, and a diluent in which the active salt is insoluble or poorly soluble.
• Embodiments of low flammability and nonflammable localized superconcentrated electrolytes (LSEs, also referred to as localized high concentration electrolytes (LHCEs)) and electrochemical systems including low flammability or nonflammable LSEs are disclosed.
• a low flammability or nonflammable LSE includes an active salt, a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent, and a diluent, wherein the active salt has a solubility in the diluent at least 10 times less than a solubility of the active salt in the solvent.
• the LSE comprises at least 5 wt% of the flame retardant compound.
• the flame retardant compound may comprise an organic phosphate, an organic phosphite, an organic phosphonate, an organic phosphoramide, an organic or inorganic phosphazene, other phosphorus-containing compounds, or any combination thereof.
• the flame retardant compound comprises trimethyl phosphate (TMPa), triethyl phosphate (TEPa), tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2- trifluoroethyl) methyl phosphate; trimethyl phosphite (TMPi), triphenyl phosphite (TEPi), tris(2,2,2- trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl
• phenylphosphonate bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide;
• the solvent may further comprise a cosolvent, wherein the active salt is soluble in the cosolvent.
• the cosolvent comprises an organic carbonate solvent, an ether solvent, an organic sulfoxide, a sulfone, an organic nitrogen-containing solvent, or any combination thereof.
• the cosolvent comprises 1 ,2-dimethoxyethane (DME), 1 ,3-dioxolane (DOL), tetrahydrofuran (THF), allyl ether, diethylene glycol dimethyl ether (i.e.
• DMC dimethyl carbonate
• EMC ethyl methyl carbonate
• DEC diethyl carbonate
• EC ethylene carbonate
• PC propylene carbonate
• VEC vinylene carbonate
• FEC fluoroethylene carbonate
• 4-vinyl-1 ,3-dioxolan-2-one i.e. vinyl ethylene carbonate, VEC
• 4-methylene-1 ,3-dioxolan-2-one i.e.
• MEC methylene ethylene carbonate
• MEC 4,5-dimethylene-1 ,3-dioxolan-2-one
• DMSO dimethyl sulfoxide
• DMS dimethyl sulfone
• EMS ethyl methyl sulfone
• EVS ethyl vinyl sulfone
• tetramethylene sulfone i.e.
• sulfolane TMS
• TMS trifluoromethyl ethyl sulfone
• FMES trifluoromethyl isopropyl sulfone
• FMIS trifluoropropyl methyl sulfone
• FPMS trifluoropropyl methyl sulfone
• AN acetonitrile
• SN succinonitrile
• adiponitrile triallyl amine
• triallyl cyanurate triallyl isocyanurate, or any combination thereof.
• the diluent may comprise a fluoroalkyl ether (also referred to as a hydrofluoroether (HFE)).
• the diluent comprises 1 ,1 ,2,2-tetrafluoroethyl-2,2,2,3- tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1 ,1 ,2,2,-tetrafluoroethyl-2,2,2- trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), or any combination thereof.
• the solvent and the diluent may be miscible.
• the active salt may have a molar concentration in the electrolyte within a range of from 0.5 M to 2 M; (ii) the active salt may have a molar concentration in the solvent of greater than 3 moles of active salt per liter of the solvent; (iii) the molar concentration of the active salt in the electrolyte (including the diluent) is at least 20% less than a molar concentration of the active salt in the solvent in the absence of the diluent, or (iv) any combination of (i), (ii), and (iii). In some embodiments, the molar concentration of the active salt in the electrolyte is at least 20% less than a molar concentration of the active salt in the solvent in the absence of the diluent.
• a molar ratio of the active salt to the solvent may be within a range of from 0.33 to 1 .5; (ii) a molar ratio of the solvent to the diluent may be within a range of from 0.2 to 5; or (iii) both (i) and (ii).
• at least 90% of molecules of the solvent may be associated with cations of the active salt.
• fewer than 10% of molecules of the diluent may be associated with cations of the active salt.
• the active salt may include a lithium salt or lithium salts mixture, a sodium salt or sodium salts mixture, a potassium salt or potassium salts mixture, or a magnesium salt or magnesium salts mixture.
• the active salt comprises lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide
• LiN(S02CF 2 CF3)2, LiBETI lithium (fluorosulfonyl trifluoromethanesulfonyhimide (LiN(S02F)(S0 2 CF3), LiFTFSI), lithium (fluorosulfonyl pentafluoroethanesulfonyl)imide (LiN(S02F)N(S02CF 2 CF3), LiFBETI), lithium cyclo(tetrafluoroethylenedisulfonly)imide (LiN(S02CF2CF 2 S02), LiCTFSI), lithium
• the active salt is (i) LiFSI, LiTFSI, or a combination thereof, or (ii) NaFSI, NaTFSI, or a combination thereof;
• the solvent comprises TMPa, TEPa, or a combination thereof; and the active salt has a molar concentration in the electrolyte within a range of from 0.75 M to 1 .5 M.
• a low flammability or nonflammable LSE includes an active salt; a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent; a diluent, wherein the diluent is immiscible with the solvent and wherein the active salt has a solubility in the diluent at least 10 times less than a solubility of the active salt in the solvent; and a bridge solvent having a different composition than the solvent (i.e., the flame retardant and, if present, the cosolvent) and a different composition than the diluent, wherein the bridge solvent is miscible with the solvent and with the diluent.
• Exemplary bridge solvents include AN, DMC, DEC, PC, DMSO, EMS, TMS, DOL, DME, diglyme, triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), or any combination thereof.
• a battery as disclosed herein include (i) an electrolyte comprising an active salt, a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent, and a diluent, wherein the active salt has a solubility in the diluent at least 10 times less than a solubility of the active salt in the solvent, the active salt has a concentration in the electrolyte within a range of 0.75 to 2 M , and the electrolyte includes at least 5 wt% of the flame retardant compound ; (ii) an anode; and (iii) a cathode, wherein the battery has a coulombic efficiency ⁇ 95%.
• Exemplary flame retardant compounds include TMPa, TEPa, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2- trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.
• the anode is lithium metal;
• the active salt comprises LiFSI, LiTFSI, LiBETI, LiPFe, LiAsFe, LiBF 4 , UCF3SO3, L1CIO4, LiBOB, LiDFOB, Lil, LiBr, LiCI, LiSCN, L1NO3, U2SO4, or any combination thereof;
• the flame retardant compound comprises TMPa, TEPa, or a combination thereof;
• the diluent comprises TTE, BTFE, TFTFE, MOFB, EOFB, or any combination thereof;
• the solvent may further include a cosolvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.
• the anode is sodium metal;
• the active salt comprises NaFSI, NaTFSI, or a combination thereof;
• the flame retardant compound comprises TMPa, TEPa, or a combination thereof;
• the diluent comprises BTFE, TTE, TFTFE, MOFB, EOFB, or any combination thereof;
• the cathode is NaFeP0 4 , Na 2 FeP0 4 F, Na 2 FeP 2 0 7 , Na 3 V 2 (P0 4 )3, Na 3 V2(P0 4 )2F3, NaVP0 4 F, NaVPOPOF, Nai.5VOP0 4 Fo.5, NaCo 2 0 4 , NaFe0 2 , Na x M0 2 where 0.4 ⁇ x ⁇ 1 , and M is a transition metal or a mixture of transition metals, Na2/3Nii/3Mn2/302, Na2/3Fei/2Mni/
• the solvent may further include a cosolvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.
• the solvent and the diluent are immiscible
• the electrolyte further includes a bridge solvent having a different composition than the solvent and a different composition than the diluent, wherein the bridge solvent is miscible with the solvent and with the diluent.
• bridge solvents comprise AN, DMC, DEC, PC, DMSO, EMS, TMS, DOL, DME, diglyme, triglyme, tetraglyme, or any combination thereof.
• FIG. 1 is a schematic illustration of a superconcentrated electrolyte (SE) comprising a lithium salt and a solvent.
• SE superconcentrated electrolyte
• FIG. 2 is a schematic illustration of an exemplary localized superconcentrated electrolyte (LSE) comprising a lithium salt, a solvent in which the lithium salt is soluble, and a diluent, i.e., a component in which the lithium salt is insoluble or poorly soluble compared to the solvent.
• LSE localized superconcentrated electrolyte
• FIG. 3 is a schematic illustration of an exemplary "bridge" solvent molecule between a flame retardant solvent molecule and a diluent molecule.
• FIG. 4 is a schematic diagram of a battery.
• FIGS. 5A and 5B show initial lithium deposition/stripping voltage profiles (FIG. 5A) and coulombic efficiency as a function of cycle number (FIG. 5B) for Li
• FIG. 6 is a graph of coulombic efficiency as a function of cycle number for Li
• EMC ethyl methyl carbonate
• FIG. 7 shows digital photographs demonstrating that addition of b is (2 , 2 , 2-t r if I u o ro et h y I) ether (BTFE) to an LiFSI/EMC electrolyte improved wetting of a battery separator.
• BTFE 2-t r if I u o ro et h y I
• FIGS. 8A and 8B are graphs showing the cycling stability of Li
• FIGS. 9A and 9B how initial lithium deposition/stripping voltage profiles (FIG. 9A) and coulombic efficiency as a function of cycle number (FIG. 9B) for Cu
• Li cells having a lithium areal deposition capacity of 0.5 mAh/cm 2 with electrolytes comprising 7.5 mol/kg LiBF 4 /PC and 2.5 mol/kg LiBF 4 /PC-TTE (PC:TTE 2:1 v:v) (TTE: 1 ,1 ,2,2-Tetrafluoroethyl 2,2,3, 3-tetrafluoropropyl ether).
• FIGS. 10A-10D are Li plating/stripping profiles of Li
• FIGS.1 1A-1 1 D are Li plating/stripping profiles of Li
• FIGS. 12A-12D are scanning electron microscopy images of lithium plated onto copper substrates after 100 cycles (1 mA/cm 2 to 0.5 mAh/cm 2 ) from 1 .0 M LiPFe/EC-EMC (FIG. 12A), 5.5 M LiFSI/DMC (FIG. 12B), 3.7 M LiFSI/DMC (FIG. 12C), and 1 .2 M LiFSI/DMC-BTFE (1 :2) (FIG. 12D) electrolytes.
• FIG. 13 is a graph of coulombic efficiency vs. cycle number for conventional electrolyte, dilute LiFSI/DMC electrolytes, superconcentrated LiFSI/DMC electrolyte, and LSE of 1 .2 M LiFSI/DMC-BTFE (1 :2).
• FIG. 14 is a graph of conductivity vs. temperature for conventional electrolyte, dilute LiFSI/DMC electrolytes, superconcentrated LiFSI/DMC electrolyte, and certain LSEs as disclosed herein.
• FIGS. 15A and 15B are graphs demonstrating the performance (voltage vs. capacity) of Li
• FIG. 16 is a graph of current vs. voltage illustrating the anodic stability of SE of 5.5 M LiFSI/DMC and certain LSEs as disclosed herein.
• FIGS. 17A-17D are SEM images showing lithium plated onto copper substrates from 1 .2 M
• FIGS. 17A and 17C are cross- sectional views
• FIGS. 17B and 17D are top views.
• FIGS. 18A-18D show the electrochemical behavior of Li
• FIG. 18A shows the cycling stability and coulombic efficiencies.
• FIGS. 18B-18D show typical voltage profiles in 1 .0 M LiPFe/EC-EMC (FIG. 18B), 5.5 M LiFSI/DMC (FIG. 18C), and 1 .2 M LiFSI/DMC-BTFE (1 :2) (FIG. 18D).
• FIG. 19 shows the rate performance of Li
• NMC batteries using different electrolytes; the batteries were charged at a constant C/5 rate but discharged at an increasing C rate; 1 C 2.0 mA/cm 2 .
• FIG. 20 shows the rate performance of Li
• NMC batteries using different electrolytes; the batteries were discharged at a constant C/5 rate but charged at an increasing C rate; 1 C 2.0 mA/cm 2 .
• FIGS. 21 A-21 F are SEM images showing morphology of Li metal after plating on Cu substrates in different electrolytes.
• FIGS. 21 A, 21 C, and 21 E are cross-section views;
• FIGS. 21 B, 21 D, and 21 F are top views of Li metal after plating on Cu substrates.
• the electrolytes were 1 .0 M LiPF6/EC-EMC (FIGS. 21 A, 21 B), 5.5 M LiFSI/DMC (FIGS. 21 C, 21 D), and 1 .2 M LiFSI/DMC-BTFE (1 :2) (FIGS. 21 E, 21 F).
• FIGS. 22A-22C are SEM images showing morphology of Li metal after plating on Cu substrates in 1 .2 M LiFSI/DMC-BTFE (1 :2) at current densities of 2 mA/cm 2 (FIG. 22A), 5 mA/cm 2 (FIG. 22B), and 10 mA/cm 2 (FIG. 22C).
• FIG. 23 shows the coulombic efficiency (CE) of Li
• FIG. 24 shows the cycling stability of Li
• FIGS. 25A and 25B show initial Na deposition/stripping voltage profiles (FIG. 25A) and CE of Na
• FIGS. 26A and 26B show initial charge/discharge voltage profiles (FIG. 26A) and cycling stability (FIG. 26B) of Na
• FIGS. 27A and 27B show the charge and discharge capacities of Na
• FIGS. 28A and 28B show initial Na deposition/stripping voltage profiles (FIG. 28A) and CE of Na
• NaFSI/DME-BTFE (1 :3) electrolytes The ratios in the parentheses indicate the molar ratios of DME:BTFE in different BTFE diluted LSEs.
• FIGS. 29A-29C show the electrochemical performance of Na
• FIG. 29A shows the initial Na
• FIG. 29B shows the cycling stability over 100 cycles
• FIG. 29C shows the charge and discharge capacities of NaFSI/DME-BTFE (1 :1 :2 in mol) over 100 cycles.
• FIGS. 30A and 30B show initial Li deposition/stripping voltage profiles (FIG. 30A) and CE (FIG. 30B) of the Li
• FIGS. 31 A-31 C show the electrochemical performance of Li-S cells containing low concentration 1 M LiTFSI/DOL-DME, concentrated 3.3M LiTFSI/DOL-DME electrolyte and LSE of 1 .06 M LiTFSI/DOL-DME- TTE electrolyte;
• FIG. 31 A is the initial charge/discharge voltage profiles,
• FIG. 31 B is the cycling
• FIG. 31 C shows the CE of the Li-S cells as a function of cycle number evaluated at 0.1 C (168 mA g- ).
• FIG. 32 shows charge/discharge profiles of L1-O2 cells using LiTFSI-3DMSO (dimethyl sulfoxide) (2.76 M) and UTFSI-3DMSO-3TTE (1 .23 M) electrolytes with limited discharge capacity of 600 mAh g at a current density of 0.1 mA cnr 2 .
• LiTFSI-3DMSO dimethyl sulfoxide
• UTFSI-3DMSO-3TTE (1 .23 M
• FIG. 33 shows cyclic voltammograms of concentrated aqueous electrolyte before and after dilution with TTE with the assistance of different 'bridge' solvents (acetonitrile (AN), dimethyl carbonate (DMC), propylene carbonate (PC), and DMSO), using a stainless steel working electrode and counter electrode, and Ag/AgCI as reference electrode at a scan rate of 10 mV s .
• AN acetonitrile
• DMC dimethyl carbonate
• PC propylene carbonate
• DMSO DMSO
• FIGS. 34A and 34B respectively, show first cycle and second cycle cyclic voltammograms of concentrated aqueous electrolyte diluted with different amounts of TTE with the assistance of PC.
• Stainless steel was the working electrode and counter electrode, and Ag/AgCI was the reference electrode.
• Scan rate 10 mV s "1 .
• the potential was converted to those versus to Li/Li + redox couple.
• FIG. 35 shows optimized molecular structures of DMC and BTFE solvent molecules, LiFSI salt, and DMC+LiFSI and BTFE+LiFSI solvent-salt pairs.
• the Li, O, C, H, S, N, and F atoms are colored as magenta, red, gray, white, yellow, blue, and light blue, respectively.
• FIGS. 36A-36F are molecular models showing adsorption of solvent molecules DMC (FIG. 36A) and BTFE (FIG. 36B), LiFSI salt (FIG. 36C), and DMC-LiFSI solvent-salt pairs (FIGS. 36D-36F) on the lithium(100) anode surface.
• the upper and lower images in each pair are the top and side view structures, respectively.
• FIGS. 37A-37C are molecular models of electrolyte/salt mixtures from AIMD simulations at 303 K - LiFSI-DMC (1 :1 .1) (FIG. 37A); LiFSI-DMC-BTFE (0.94:1 .1 :0.55) (FIG. 37B); LiFSI-DMC-BTFE (0.51 :1 .1 :2.2) (FIG. 37C); the ratios in the parentheses indicate the molar ratios of LiFSI:DMC:BTFE.
• FIG. 38 is a graph of the radial distribution functions of LI-ODMC and LI-OBTFE pairs calculated from AIMD simulation trajectories at 303 K.
• FIGS. 39A and 39B are Raman spectra of pure DMC solvent, pure BTFE solvent, and solvent mixture of DMC-BTFE (2:1);
• FIG. 39B is an enlarged view of FIG. 39A in the wavenumber range of 2000- 200 cm- 1 .
• FIGS. 40A and 40B are Raman spectra of different concentrations of LiFSI/DMC solutions
• FIG. 40A shows different concentrations of BTFE diluted LiFSI/DMC-BTFE solutions.
• FIG. 40B shows different concentrations of BTFE diluted LiFSI/DMC-BTFE solutions.
• FIG. 41 shows diffusion coefficients (Ds) of Li + , FSh and solvent molecules (DMC and BTFE) at 30 °C across the samples plotted with the inverse of viscosity (/7- 1 ), which is denoted with stars.
• FIG. 42 shows diffusion ratios of BTFE, Li, and FSI in DMC - DBTFE/DDMC, DU/DDMC and DFSI/DDMC at
• FIGS. 43A-43C are graphs showing projected density of states (PDOS) for dilute electrolyte (LiFSI/DMC, LiFSLDMC molar ratio 1 :2) (FIG. 43A), superconcentrated electrolyte (5.5M LiFSI/DMC, LiFSLDMC molar ratio 1 :1) (FIG. 43B), and BTFE-diluted electrolyte (LiFSI/DMC-BTFE, LiFSI:DMC:BTFE molar ratio 1 :2:4) (FIG. 43C) on the lithium anode surface.
• PDOS projected density of states
• FIGS. 44A-44D show the Raman spectra of pure triethyl phosphate (TEPa) solvent, 3.2 M
• FIGS. 44B-44C are enlarged views of wavenumber ranges from the full spectra.
• FIG. 45 is a graph of coulombic efficiency as a function of cycle number for 3.8 M LiFSLTEPa
• FIG. 46 is a graph showing the cycling stability of Li
• FIG. 47 is a graph showing the cycling stability of Li
• NCA LiNio.85Coo.1Alo.05O2 with an areal capacity loading of 1 .8 mAh/cm 2
• E40 BTFE diluent
• FIG. 48 is a graph showing the cycling stability of Li
• FIG. 49 is a graph of coulombic efficiency as a function of cycle number for Li
• FIG. 50 is a graph showing the cycling stability of Li
• FIGS. 51 A and 51 B show Li plating/stripping profiles of Li
• FIG. 52 is a graph showing the cycling stability of Li
• FIGS. 53A and 53B show Li plating/stripping profiles of Li
• FIG. 54 is a graph showing the cycling stability of Li
• FIG. 55 is a graph showing the cycling stability of a Li
• FIG. 56 is a graph showing the cycling stability of a Li
• the safety of lithium-ion batteries has always been a great concern because they contain highly flammable organic electrolytes that can lead to fire or even battery explosion under conditions of overcharging, overheating, internal short-circuit, and/or mechanical damage.
• the safety problem also applies to any electrochemical device including a flammable electrolyte.
• Superconcentrated electrolytes also referred to as high concentration electrolytes including flammable solvents, e.g. concentrated LiFSI/DME or concentrated LiFSI/DMC, can enable high coulombic efficiency (CE) operation of lithium metal anodes and/or reversible insertion of Li-ions into the graphite anode, due to the reduced presence of free solvent molecules compared to more dilute electrolytes and/or the formation of stabilized SEI layer.
• the term "superconcentrated” (or high concentration) means an active salt concentration of at least 3 M.
• Superconcentrated electrolytes including fire-retarded solvents may be an effective approach to stabilize these compounds at low potentials and enable the formation of a stable SEI layer on graphite anode.
• LSEs low flammability and nonflammable LSEs are stable in electrochemical cells with alkali metal, alkaline earth metal, or carbon-based (e.g., graphite) anodes and various cathode materials.
• the LSEs comprise an active salt, a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent, and a diluent in which the active salt is insoluble or poorly soluble.
• the performance of an electrochemical device including a low flammability or nonflammable electrolyte as disclosed herein is comparable to an electrochemical device including a flammable electrolyte containing the same active salt.
• the concentration of active salt is lowered by addition of the diluent without significant increase in flammability and/or reduction in the performance of electrochemical devices including the low flammability or nonflammable LSE.
• the performance of electrochemical devices including the low flammability or nonflammable LSE is enhanced compared to a similar LSE that does not include the flame retardant compound.
• Active salt refers to a salt that significantly participates in electrochemical processes of electrochemical devices. In the case of batteries, it refers to charge and discharge processes contributing to the energy conversions that ultimately enable the battery to deliver/store energy. As used herein, the term “active salt” refers to a salt that constitutes at least 5% of the redox active materials participating in redox reactions during battery cycling after initial charging.
• Anode An electrode through which electric charge flows into a polarized electrical device. From an electrochemical point of view, negatively-charged anions move toward the anode and/or positively-charged cations move away from it to balance the electrons leaving via external circuitry. In a discharging battery or galvanic cell, the anode is the negative terminal where electrons flow out. If the anode is composed of a metal, electrons that it gives up to the external circuit are accompanied by metal cations moving away from the electrode and into the electrolyte. When the battery is recharged, the anode becomes the positive terminal where electrons flow in and metal cations are reduced.
• association means coordinated to or solvated by.
• a cation that is associated with a solvent molecule is coordinated to or solvated by the solvent molecule.
• Solvation is the attraction of solvent molecules with molecules or ions of a solute. The association may be due to electronic interactions (e.g., ion-dipole interactions and/or van der Waals forces) between the cation and the solvent molecule.
• Coordination refers to formation of one or more coordination bonds between a cation and electron lone-pairs of solvent atoms. Coordination bonds also may form between the cation and anion of the solute.
• Bridge solvent A solvent having amphiphilic molecules with a polar end or moiety and a nonpolar end or moiety.
• the capacity of a battery is the amount of electrical charge a battery can deliver.
• the capacity is typically expressed in units of mAh, or Ah, and indicates the maximum constant current a battery can produce over a period of one hour.
• a battery with a capacity of 100 mAh can deliver a current of 100 mA for one hour or a current of 5 mA for 20 hours.
• Areal capacity or specific areal capacity is the capacity per unit area of the electrode (or active material) surface, and is typically expressed in united of mAh cm 2 .
• Cathode An electrode through which electric charge flows out of a polarized electrical device. From an electrochemical point of view, positively charged cations invariably move toward the cathode and/or negatively charged anions move away from it to balance the electrons arriving from external circuitry. In a discharging battery or galvanic cell, the cathode is the positive terminal, toward the direction of conventional current. This outward charge is carried internally by positive ions moving from the electrolyte to the positive cathode, where they may be reduced. When the battery is recharged, the cathode becomes the negative terminal where electrons flow out and metal atoms (or cations) are oxidized.
• a cell refers to an electrochemical device used for generating a voltage or current from a chemical reaction, or the reverse in which a chemical reaction is induced by a current.
• Examples include voltaic cells, electrolytic cells, and fuel cells, among others.
• a battery includes one or more cells.
• the terms “cell” and “battery” are used interchangeably when referring to a battery containing only one cell.
• Coin cell A small, typically circular-shaped battery. Coin cells are characterized by their diameter and thickness. Conversion compound: A compound comprising one or more cations, which are displaced by another metal when a battery is discharged. For example, when iron (II) selenide (FeSe) is used as a cathode material, Fe is replaced by Na during discharge of a Na battery:
• Cosolvent A solvent that, in conjunction with another solvent, dissolves a solute.
• CE Coulombic efficiency
• Donor number A quantitative measure of Lewis basicity, such as a solvent's ability to solvate cations.
• a donor number is defined as the negative enthalpy value for the 1 :1 adduct formation between a Lewis base and SbCIs in dilute solution in 1 ,2-dichloroethane, which has a donor number of zero.
• the donor number is typically reported in units of kcal/mol.
• Acetonitrile for example, has a donor number of 14.1 kcal/mol.
• dimethyl sulfoxide has a donor number of 29.8 kcal/mol.
• Electrolyte A substance containing free ions that behaves as an electrically conductive medium. Electrolytes generally comprise ions in a solution, but molten electrolytes and solid electrolytes also are known.
• FEC fluoroethylene carbonate
• Flame retardant refers to an agent incorporated into an electrolyte to reduce or eliminate its tendency to ignite during operation of an electrochemical device including the electrolyte.
• Flammable refers to a material that will ignite easily and burn rapidly. As used herein, the term “nonflammable” means that an electrolyte, will not ignite or burn during operation of an electrochemical device including the electrolyte. As used herein, the terms “flame retarded” and “low flammability” are interchangeable and mean that a portion of the electrolyte may ignite under some conditions, but that any resulting ignition will not propagate throughout the electrolyte. Flammability can be measured by determining the self-extinguishing time (SET) of the electrolyte. The SET is determined by a modified Underwriters Laboratories test standard 94 HB.
• SET self-extinguishing time
• An electrolyte is immobilized on an inert ball wick, such as a ball wick having a diameter of ⁇ 0.3-0.5 cm, which is capable of absorbing 0.05-0.10 g electrolyte.
• the wick is then ignited, and the time for the flame to extinguish is recorded. The time is normalized against the sample weight. If the electrolyte does not catch flame, the SET is zero and the electrolyte is nonflammable. Electrolytes having an SET of ⁇ 6 s/g (e.g., the flame extinguishes within ⁇ 0.5 s) are also considered nonflammable. If the SET is > 20 s/g, the electrolyte is considered to be flammable. When the SET is between 6-20 s/g, the electrolyte is considered to be flame retarded or have low flammability.
• Immiscible This term describes two substances of the same state of matter that cannot be uniformly mixed or blended. Oil and water are a common example of two immiscible liquids.
• Intercalation A term referring to the insertion of a material (e.g. , an ion or molecule) into the microstructure of another material.
• a material e.g. , an ion or molecule
• lithium ions can insert, or intercalate, into graphite (C) to form lithiated graphite ( ⁇ ).
• KFSI potassium bis(fluorosulfonyl)imide
• KTFSI potassium bis(trifluoromethanesulfonyl)imide
• LiBETI lithium bis(pentafluoroethanesulfonyl)imide
• LiFSI lithium bis(fluorosulfonyl)imide
• LiTFSI lithium bis(trifluoromethanesulfonyl)imide
• LiBOB lithium bis(oxalato)borate
• LiDFOB lithium difluoro oxalato borate anion
• NaFSI sodium bis(fluorosulfonyl)imide
• NaTFSI sodium bis(trifluoromethylsulfonyl)imide
• NaBOB sodium bis (oxalato) bo rate
• Organophosphorus compound An organic compound that contains phosphorus.
• phosphite refers to an organophosphite having a general formula P(OR)3 or HP(0)(OR)2 where each R independently is alkyl (e.g., C1-C10 alkyl) or aryl. Each alkyl or aryl group may be substituted or unsubstituted.
• alkyl e.g., C1-C10 alkyl
• alkoxy e.g., C1-C10 alkoxy
• At least one R is not hydrogen.
• Each alkyl or aryl group may be substituted or unsubstituted.
• Phosphazene A compound in which a phosphorus atom is covalently linked to a nitrogen atom or nitrogen-containing group by a double bond and to three other atoms or radicals by single bonds.
• SEI solid electrolyte interphase Separator
• a battery separator is a porous sheet or film placed between the anode and cathode. It prevents physical contact between the anode and cathode while facilitating ionic transport.
• Soluble Capable of becoming molecularly or ionically dispersed in a solvent to form a
• soluble means that an active salt has a solubility in a given solvent of at least 1 mol/L (M, molarity) or at least 1 mol/kg (m, molality).
• Solution A homogeneous mixture composed of two or more substances.
• a solute (minor component) is dissolved in a solvent (major component).
• a plurality of solutes and/or a plurality of solvents may be present in the solution.
• Superconcentrated electrolyte refers to an electrolyte having a salt concentration of at least 3 M.
• TEPa triethyl phosphate
• TFTFE 1 ,1 ,2,2,-tetrafluoroethyl-2,2,2-trifluoroethyl ether
• TMPa trimethyl phosphate
• TMS tetramethylene sulfone or sulfolane
• TTE 1 ,1 ,2,2-tetrafluoroethyl-2,2,2,3-tetrafluoropropyl ether
• VEC 4-vinyl-1 ,3-dioxolan-2-one or vinyl ethylene carbonate
• a conventional superconcentrated electrolyte comprises a solvent and a salt with a salt
• FIG. 1 is a schematic illustration of a conventional superconcentrated electrolyte comprising a solvent and a lithium salt. Desirably, all or a large majority of the solvent molecules are associated with a lithium cation in the superconcentrated electrolyte. A reduced presence of free, unassociated solvent molecules increases coulombic efficiency (CE) of a lithium metal anode, facilitates formation of a stabilized SEI layer, and/or increases cycling stability of a battery including the electrolyte.
• CE coulombic efficiency
• superconcentrated electrolytes have disadvantages, such as flammability, high material cost, high viscosity, and/or poor wetting of battery separators and/or cathodes. While dilution with additional solvent can resolve one or more of the disadvantages, dilution results in free solvent molecules and often decreases CE, hinders formation of the stabilized SEI layer, and/or decreases cycling stability of a battery.
• FIG. 2 is a schematic illustration of an exemplary LSE including a lithium salt, a solvent in which the lithium salt is soluble, and a diluent in which the lithium salt is insoluble or poorly soluble.
• the lithium ions remain associated with solvent molecules after addition of the diluent.
• the anions are also in proximity to, or associated with, the lithium ions. Thus, localized regions of solvent-cation-anion aggregates are formed.
• Embodiments of the disclosed low flammability and nonflammable localized superconcentrated electrolytes comprise, consist essentially of or consist of an active salt, a solvent A comprising a flame retardant compound, wherein the active salt is soluble in the solvent A, and a diluent, wherein the active salt is insoluble or poorly soluble in the diluent.
• the diluent has a different chemical composition than the solvent.
• “poorly soluble” means that the active salt has a solubility in the diluent at least 10X less than a solubility of the active salt in the solvent A.
• the electrolyte does not include any component that materially affects the properties of the electrolyte.
• the LSE does not include any electrochemically active component (i.e., a component (an element, an ion, or a compound) that is capable of forming redox pairs having different oxidation and reduction states, e.g., ionic species with differing oxidation states or a metal cation and its corresponding neutral metal atom) other than the active salt in an amount sufficient to affect performance of the electrolyte and does not include a diluent in which the active salt is soluble.
• electrochemically active component i.e., a component (an element, an ion, or a compound) that is capable of forming redox pairs having different oxidation and reduction states, e.g., ionic species with differing oxidation states or a metal cation and its corresponding neutral metal atom
• solvent A further comprises a cosolvent, such as a flammable or nonflammable organic solvent, wherein the cosolvent has a different composition than the flame retardant compound.
• a cosolvent such as a flammable or nonflammable organic solvent
• the amount of flame retardant compound in solvent A is sufficient to render the electrolyte flame-retarded (low flammability) or nonflammable.
• the low flammability or nonflammable LSE may include at least 5 wt% of the flame retardant compound.
• the solubility of the active salt in the solvent A may be greater than 3 M, such as at least 4 M or at least 5 M.
• the solubility and/or concentration of the active salt in the solvent A is within a range of from 3 M to 10 M, such as from 3 M to 8 M, from 4 M to 8 M, or from 5 M to 8 M.
• the concentration may be expressed in terms of molality and the concentration of the active salt in the solvent A (in the absence of diluent) may be within a range of from 3 m to 25 m, such as from 5 m to 21 m, or 10 m to 21 m.
• the molar or molal concentration of the active salt in the low flammability or nonflammable electrolyte as a whole may be at least 20% less than the molar or molal concentration of the active salt in the solvent A, such as at least 30% less, at least 40% less, at least 50% less, at least 60% less, or even at least 70% less than the molar or molal concentration of the active salt in the solvent A.
• the molar or molal concentration of the active salt in the electrolyte may be 20-80% less, 20-70% less, 30-70% less, or 30-50% less than the molar or molal concentration of the active salt in the solvent A.
• the molar concentration of the active salt in the electrolyte is within a range of 0.5 M to 3 M, 0.5 M to 2 M, 0.75 M to 2 M, or 0.75 M to 1 .5 M.
• the active salt is a salt, or combination of salts, that participates in the charge and discharge processes of a cell including the low flammability or nonflammable electrolyte.
• the active salt comprises a cation that is capable of forming redox pairs having different oxidation and reduction states, such as ionic species with differing oxidation states or a metal cation and its corresponding neutral metal atom.
• the active salt is an alkali metal salt, an alkaline earth metal salt, or any combination thereof.
• the active salt may be, for example, a lithium salt, a sodium salt, a potassium salt, a magnesium salt, a mixture of lithium salts, a mixture of sodium salts, a mixture of potassium salts, or a mixture of magnesium salts.
• the active salt is stable towards an alkali metal or alkaline earth metal anode.
• Exemplary salts include, but are not limited to, LiFSI, LiTFSI, LiBETI, NaFSI, NaTFSI, LiBOB, sodium bis(oxalato)borate (NaBOB), LiPFe, LiAsFe, LiBF 4 , UCF3SO3, L1CIO4, LiDFOB, Lil, LiBr, LiCI, LiSCN, UNO3, U2SO4, and combinations thereof.
• the salt is LiFSI, LiTFSI, LiBETI, NaFSI, NaTFSI, or any combination thereof.
• Low flammability or nonflammable solvent A comprises, consists essentially of or consists of a flame retardant compound.
• the flame retardant compound is a liquid at ambient temperature (e.g., 20-25 °C).
• Suitable flame retardant compounds include, but are not limited to, phosphorus containing compounds.
• the flame retardant compound comprises one or more organophosphorus compounds (e.g., organic phosphates, phosphites, phosphonates,
• Organic phosphates, phosphites, phosphonates, phosphoramides include substituted and unsubstituted aliphatic and aryl phosphates, phosphites, phosphonates, and phosphoramides.
• the phosphazenes may be organic or inorganic.
• Exemplary flame retardant compounds include, e.g., TMPa, TEPa, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate, hexamethylphosphoramide,
• the flame retardant compound comprises trimethyl phosphate, triethyl phosphate, or a combination thereof.
• the flame retardant compound comprises tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate, trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite, dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate, hexamethylphosphoramide,
• solvent A may further comprise a cosolvent.
• the cosolvent is miscible with the flame retardant compound and/or the active salt is soluble in both the flame retardant compound and the cosolvent.
• suitable cosolvents include, but are not limited to, certain carbonate solvents, ether solvents, dimethyl sulfoxide, water, and mixtures thereof.
• cosolvents include DME, DOL, allyl ether, DMC, EMC, DEC, EC, PC, VC, FEC, VEC, MEC, DMSO, DMS, EMS, EVS, TMS (also called sulfolane), FMES, FMIS, FPMS, methyl butyrate, ethyl propionate, gamma-butyrolactone, acetonitrile, triallyl amine, triallyl cyanurate, triallyl isocyanurate, water, and combinations thereof.
• the cosolvent is nonaqueous.
• the cosolvent comprises DME, DOL, DMC, EMC, or a combination thereof.
• the cosolvent is DMC, DME, DOL, or a combination thereof. In one embodiment, the cosolvent is DMC. In another embodiment, the cosolvent is DME. In yet another embodiment, the cosolvent is a combination of DME and DOL. In still another embodiment, the cosolvent is EMC.
• solvent A further comprises a flammable cosolvent, the amount of flame retardant in solvent A is sufficient to maintain low flammability or nonflammability of the solvent. Such amounts can be determined by those of ordinary skill in the art having had the benefit of reading this disclosure, and depends on the cosolvent chosen as well as the amount.
• the solvent A comprises, consists essentially of, or consists of a flame retardant compound. In one embodiment, the solvent A comprises, consists essentially of, or consists of a flame retardant compound and a cosolvent. As used herein, "consists essentially of means that solvent A does not include any electrochemically active component in an amount sufficient to affect performance of an electrolyte including the solvent A.
• the solvent A associates with (e.g., solvates or coordinates) cations of the active salt or salt mixture.
• solvent- cation-anion aggregates form.
• some embodiments of the disclosed low flammability or nonflammable superconcentrated electrolytes are stable toward anodes (e.g., a metal or carbon-based anode or silicon-based anode), cathodes (including ion intercalation and conversion compounds), separators (e.g., polyolefin) and current collectors (e.g., Cu, Al) that may be unstable when lower concentration electrolytes are used and/or when other solvents are used.
• anodes e.g., a metal or carbon-based anode or silicon-based anode
• cathodes including ion intercalation and conversion compounds
• separators e.g., polyolefin
• current collectors e.g., Cu, Al
• the stability enables high Columbic efficiency, e.g. , >98% of battery operation.
• some embodiments of the disclosed LSEs do not suffer from significant decomposition of the flame retardant compound during operation of an electrochemical device including the low flammability or nonflammable LSE.
• significant decomposition of the flame retardant compound means that the flame retardant decomposes at the anode or cathode during operation of an electrochemical device including the LSE, thereby measurably reducing performance of the electrolyte over repeated cycling and/or resulting in failure of an electrochemical device including the electrolyte.
• the concentration of the active salt may be selected to minimize the number of free solvent A molecules in the electrolyte. Because more than one molecule of solvent A may be associated with each cation of the active salt and/or because more than cation of the active salt may be associated with each molecule of solvent A, the molar ratio of active salt to solvent A may not be 1 :1 .
• a molar ratio of the active salt to the solvent A is within a range of from 0.33 to 1 .5, such as within a range of from 0.5 to 1 .5, 0.67 to 1 .5, 0.8 to 1 .2, or 0.9 to 1 .1 .
• the diluent is a component in which the active salt is insoluble or has poor solubility, i.e., a solubility at least 10X less than the active salt's solubility in the solvent A. For instance, if the salt has a solubility of 5 M in the solvent A, the diluent is selected such that the salt has a solubility of less than 0.5 M in the diluent. In some embodiments, the active salt has a solubility in the solvent A that is at least 10 times, at least 15 times, at least 20 times, at least 25 times, at least 30 times, at least 40 times, or at least 50 times greater than the active salt's solubility in the diluent.
• the diluent is selected to be stable with the anode, cathode, and current collectors at low active salt concentrations (e.g., ⁇ 3 M) or even without the active salt.
• the diluent is selected to have a low dielectric constant (e.g., a relative dielectric constant ⁇ 7) and/or low donor number (e.g., a donor number ⁇ 10).
• the diluent does not disrupt the solvation structure of solvent A-cation-anion aggregates and is considered inert because it is not interacting with the active salt. In other words, there is no significant coordination or association between the diluent molecules and the active salt cations. The active salt cations remain associated with solvent A molecules. Thus, although the electrolyte is diluted, there are few or no free solvent A molecules in the electrolyte.
• the diluent comprises an aprotic organic solvent.
• the diluent is a fluorinated solvent having a wide electrochemical stability window (e.g., >4.5 V), such as a hydrofluoroether (HFE) (also referred to as a fluoroalkyl ether).
• HFEs advantageously have low dielectric constants, low donor numbers, reductive stability with the metal of the active salt (e.g., lithium, sodium, and/or magnesium), and/or high stability against oxidation due to the electron-withdrawing fluorine atoms.
• Exemplary fluorinated solvents include, but are not limited to, 1 ,1 ,2,2-tetrafluoroethyl-2,2,2,3- tetrafluoropropyl ether (TTE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1 ,1 ,2,2,-tetrafluoroethyl-2,2,2- trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), and combinations thereof.
• TTE 1 ,1 ,2,2-tetrafluoroethyl-2,2,2,3- tetrafluoropropyl ether
• BTFE bis(2,2,2-trifluoroethyl) ether
• TFTFE 1,1 ,2,2,-tetrafluoroethyl-2,2,2- trifluoroethyl ether
• MOFB meth
• the diluent may be flammable or nonflammable.
• the electrolyte comprises a sufficient amount of a flame retardant compound, e.g., at least 5 wt% based on a total mass of the electrolyte, to render the electrolyte - active salt, solvent A (flame retardant and, optionally, a cosolvent) and diluent - flame retarded or nonflammable.
• a flame retardant compound e.g., at least 5 wt% based on a total mass of the electrolyte, to render the electrolyte - active salt, solvent A (flame retardant and, optionally, a cosolvent) and diluent - flame retarded or nonflammable.
• At least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the molecules of solvent A are associated (e.g., solvated or coordinated) with cations of the active salt. In certain embodiments, fewer than
• 10%, such as fewer than 5%, fewer than 4%, fewer than 3%, or fewer than 2% of the diluent molecules are associated with cations of the active salt.
• the degree of association can be quantified by any suitable means, such as by calculating the peak intensity ratio of solvent molecules associated with cations and free solvent in Raman spectra or by using NMR spectra.
• the relative amounts of the solvent A (flame retardant compound and, optionally, a cosolvent) and diluent are selected to reduce the flammability of the electrolyte, reduce the cost of materials for the electrolyte, reduce viscosity of the electrolyte, maintain stability of the electrolyte against oxidation at high- voltage cathodes, improve ionic conductivity of the electrolyte, improve wetting ability of the electrolyte, facilitate formation of a stable SEI layer, or any combination thereof.
• a molar ratio of the solvent A to the diluent (moles solvent A/moles diluent) in the low flammability or nonflammable electrolyte is within a range of from 0.2 to 5, such as within a range of from 0.2 to 4, 0.2 to 3, or 0.2 to 2.
• a volumetric ratio of the solvent A to the diluent (L solvent/L diluent) in the low flammability or nonflammable electrolyte is within a range of from 0.2 to 5, such as within a range of from 0.25 to 4 or 0.33 to 3.
• a mass ratio of the solvent A to the diluent (g solvent/g diluent) in the low flammability or nonflammable electrolyte is within a range of from 0.2 to 5, such as within a range of from 0.25 to 4 or 0.33 to 3.
• a low flammability or nonflammable LSE comprises at least 5 wt% or at least 10 wt% of the flame retardant compound. In certain embodiments, the low flammability or nonflammable LSE comprises 5-75 wt% of the flame retardant compound, such as 5-60 wt%, 5-50 wt%, 5-40 wt% or 5- 30 wt%, 10-60 wt%, 10-50 wt%, 10-40 wt%, or 10-30 wt% of the flame retardant compound.
• certain embodiments of the disclosed low flammability or nonflammable LSEs allow significant dilution of the active salt without sacrificing performance of the electrolyte.
• the electrolyte performance is enhanced compared to a comparable low flammability or nonflammable superconcentrated electrolyte that does not include the diluent. Due to the interactions between cations of the active salt and molecules of solvent A, the behavior of the electrolyte corresponds more closely to the concentration of the active salt in the solvent A. Because the diluent is present, however, the active salt may have a molar concentration in the electrolyte that is at least 20% less than the molar concentration of the active salt in the solvent A.
• the molar concentration of the active salt in the electrolyte is at least 25% less, at least 30% less, at least 40% less, at least 50% less, at least 60% less, at least 70% less, or even at least 80% less than the molar concentration of the active salt in the solvent A.
• the formation of cation-anion-solvent aggregates also reduces the lowest unoccupied molecular orbital (LUMO) energy of the anion (such as FSI ) of the salt so they can form a stable SEI.
• LUMO lowest unoccupied molecular orbital
• the solvent molecules such as DMC
• the solvent molecules are reductively decomposed first at the anode, leading to a SEI layer which is rich in organic or polymeric component and less mechanically stable, therefore leads to fast capacity degradation upon cycling.
• the diluent is miscible with solvent A.
• the diluent is immiscible with solvent A, i.e., the flame retardant compound and/or the co-solvent (if present).
• the electrolyte may not be effectively diluted with the diluent.
• the low flammability or nonflammable electrolyte further comprises a bridge solvent.
• the bridge solvent has a different chemical composition than either the solvent A or the diluent.
• the bridge solvent is selected to be miscible with solvent A (flame retardant compound and optional cosolvent) and the diluent, thereby
• molecules of the bridge solvent are amphiphilic, including both a polar end or moiety, and a non-polar end or moiety, such that molecules of the bridge solvent will associate both with molecules of solvent A and molecules of the diluent as shown in FIG. 3, thereby improving the miscibility between solvent A, and the diluent.
• Exemplary bridge solvents include, but are not limited to, acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate, dimethyl sulfoxide, 1 ,3-dioxolane, 1 ,2-dimethoxyethane, diglyme (bis(2-methoxyethyl) ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), and combinations thereof.
• Exemplary solvent, diluent, and, in some instances, bridge solvent combinations include TEPa- BTFE, TEPa-TTE, TMPa-BTFE, TMPa-TTE, TEPa-DMC-BTFE, TEPa-DMC-TTE, TMPa-DMC-BTFE, TEPa- DME, TEPa-DME-TTE, TEPa-EC-TTE, TMPa-DME, TMPa-DME-TTE, TMPa-EC-TTE, TMPa-DMC-TTE, EMC-BTFE, EMC-TTE, DMC-BTFE, DME-BTFE, DME-TTE, DOL-DME-TTE, DMSO-TTE, H2O-DMC-TTE, H2O-PC-TTE, H2O-AN-TTE, and H2O-DMSO-TTE.
• the active salt is LiFSI, LiTFSI, NaFSI, or NaTFSI.
• the active salt is LiFSI or NaFSI
• the solvent is DMC, DME, EMC, or EC
• the diluent is TTE, or BTFE.
• the salt is LiTFSI or NaTFSI
• the solvent is DMSO or a mixture of DME and DOL
• the diluent is TTE.
• the salt is LiTFSI or NaTFSI
• the solvent is H2O
• the diluent is TTE
• the bridge solvent is DMC, propylene carbonate (PC), acetonitrile (AN), or DMSO.
• Exemplary electrolytes include, but are not limited to, LiFSI/TEPa-BTFE, LiFSI/TEPa-TTE,
• LiFSI/TMPa-BTFE LiFSI/TMPa-TTE, LiFSI/TEPa-DMC-BTFE, LiFSI/TEPa-DMC-TTE, LiFSI/TMPa-DMC-BTFE, LiFSI/TMPa-DMC-TTE, LiFSI/DMC-BTFE, LiFSI/DME-BTFE, LiFSI/DME-TTE, LiFSI/EMC-BTFE, LiFSI/EMC-TTE, LiFSI/TEPa-DME-TTE, LiFSI/TEPa-DME, NaFSI/TEPa-BTFE, NaFSI/TEPa-TTE,
• NaFSI/TMPa-BTFE NaFSI/TMPa-TTE, NaFSI/TEPa-DMC-BTFE, NaFSI/TEPa-DMC-TTE, NaFSI/TMPa- DMC-BTFE, NaFSI/TMPa-DMC-TTE, NaFSI/DME-TTE, NaFSI/DME-BTFE, NaFSI/DMC-BTFE,
• the electrolyte isLiFSI/TEPa-BTFE, LiFSI/TEPa-TTE, LiFSI/TMPa-BTFE, LiFSI/TMPa-TTE, LiFSI/TEPa-DMC-BTFE, LiFSI/TEPa-DMC-TTE, LiFSI/TMPa-DMC-BTFE, LiFSI/TMPa-DMC-TTE, NaFSI/TEPa-BTFE, NaFSI/TEPa-TTE, NaFSI/TMPa- BTFE, NaFSI/TMPa-TTE, NaFSI/TEPa-DME-TTE, NaFSI/TEPa-DMC-BTFE, NaFSI/TEPa-DMC-TTE, NaFSI/TMPa-DMC-BTFE, or NaFSI/TMPa-DMC-TTE.
• Embodiments of the disclosed low flammability or nonflammable LSEs are useful in batteries (e.g., rechargeable batteries), sensors, and supercapacitors.
• Suitable batteries include, but are not limited to, lithium metal batteries, lithium ion batteries, lithium-sulfur batteries, lithium-oxygen batteries, lithium-air batteries, sodium metal batteries, sodium ion batteries, sodium-sulfur batteries, sodium-oxygen batteries, sodium-air batteries, potassium metal batteries, potassium ion batteries, and magnesium ion batteries.
• a rechargeable battery comprises a low flammability or nonflammable LSE as disclosed herein, a cathode, an anode, and optionally a separator.
• FIG. 4 is a schematic diagram of one exemplary embodiment of a rechargeable battery 100 including a cathode 120, a separator 130 which is infused with an electrolyte (i.e., a low flammability or nonflammable LSE), and an anode 140.
• the battery 100 also includes a cathode current collector 1 10 and/or an anode current collector 150.
• the current collectors can be a metal or another conductive material such as, but not limited to, nickel (Ni), copper (Cu), aluminum (Al), iron (Fe), stainless steel, or conductive carbon materials.
• the current collector may be a foil, a foam, or a polymer substrate coated with a conductive material.
• the current collector is stable (i.e., does not corrode or react) when in contact with the anode or cathode and the electrolyte in an operating voltage window of the battery.
• the anode and cathode current collectors may be omitted if the anode or cathode, respectively, are free standing, e.g., when the anode is metal or a free-standing film comprising an intercalation material or conversion compound, and/or when the cathode is a free-standing film.
• free-standing is meant that the film itself has sufficient structural integrity that the film can be positioned in the battery without a support material.
• the anode is a metal (e.g., lithium, sodium), an intercalation material, or a conversion compound.
• the intercalation material or conversion compound may be deposited onto a substrate (e.g., a current collector) or provided as a free-standing film, typically, including one or more binders and/or conductive additives.
• Suitable binders include, but are not limited to, polyvinyl alcohol, polyvinyl chloride, polyvinyl fluoride, ethylene oxide polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, epoxy resin, nylon, and the like.
• Suitable conductive additives include, but are not limited to, carbon black, acetylene black, Ketjen black, carbon fibers (e.g., vapor-grown carbon fiber), metal powders or fibers (e.g., Cu, Ni, Al), and conductive polymers (e.g., polyphenylene derivatives).
• Exemplary anodes for lithium batteries include, but are not limited to, MoeSs, T1O2, V2O5, Li4MnsOi2, Li4TisOi2, C/S composites, and polyacrylonitrile (PAN)-sulfur composites.
• Exemplary anodes for sodium batteries include, but are not limited to NaTi 2 (P0 4 )3; TiS 2 , CuS, FeS 2 , N1C02O4, Cu 2 Se, and Lio.5Na 0 .5Ti2(P04)3.
• the cathode is a lithium conversion compound, such as U2O2, L12S, or LiF.
• Exemplary cathodes for sodium batteries include, but are not limited to, NaFeP0 4 , Na2FeP04F, Na 2 FeP 2 0 7 , Na 3 V2(P0 4 )3, Na 3 V2(P0 4 )2F3, NaVP0 4 F, NaVPOPOF, Nai. 5 VOP0 Fo.5, NaCo 2 0 4 , Na 2 Ti 3 0 7 , and Na x M02 where 0.4 ⁇ x ⁇ 1 , and M is a transition metal or a mixture of transition metals (e.g.
• NaCr02, NaCo02, Na x Co02 (0.4 ⁇ x ⁇ 0.9), Na2/3Nii/3Mn2/302, Na2/3Fei/2Mni/202, Na2/3Nii/6C0i/6Mn2/3O2,
• NaNii/3Fei/3Mni/302, NaNii/3Fei/3Coi/302, NaNii/2Mni/202, Prussian white analogue cathodes e.g., sodium NiNii/3Fei/3Mni/302, NaNii/3Fei/3Coi/302, NaNii/2Mni/202, Prussian white analogue cathodes (e.g.,
• the cathode is a sodium conversion compound in which sodium displaces another cation, such as FeSe, CuW0 4 , CuS, CuO, CuCI, or CuC .
• Exemplary cathodes for magnesium batteries include, but are not limited to, zirconium disulfide, cobalt (I I, II I) oxide, tungsten selenide, V2O5, molybdenum-vanadium oxide, stainless steel, ⁇ ,
• Mg2M06S8, M0S2, MoeSs-ySey where y 0, 1 , or 2, Mg x S30 4 where 0 ⁇ x ⁇ 1 , MgCoSi0 4 , MgFeSi0 4 , MgMnSi0 4 , V2O5, WSe2, sulfur, poly(2,2,6,6-tetramethylpiperidinyloxy-4-yl methacrylate)/graphene, Mn02/acetylene black, and carbyne polysulfide.
• the separator may be glass fiber, a porous polymer film (e.g., polyethylene- or polypropylene-based material) with or without a ceramic coating, or a composite (e.g. , a porous film of inorganic particles and a binder).
• a porous polymer film e.g., polyethylene- or polypropylene-based material
• a composite e.g. , a porous film of inorganic particles and a binder.
• One exemplary polymeric separator is a Celgard® K1640 polyethylene (PE) membrane.
• Another exemplary polymeric separator is a Celgard® 2500 polypropylene membrane.
• Another exemplary polymeric separator is a Celgard® 3501 surfactant-coated polypropylene membrane.
• the separator may be infused with an electrolyte, as disclosed herein.
• a battery includes a lithium metal anode, a cathode suitable for a lithium battery as disclosed above, a separator, and a low flammability or nonflammable LSE comprising (i) an active salt selected from LiFSI , LiTFSI , or a combination thereof, (ii) a flame retardant compound selected from TMPa, TEPa, tributyl phosphate, triphenyl phosphate, tris (2 , 2 , 2-trif I u 0 ro eth y I) phosphate, bis(2,2,2- trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl)
• a battery includes a lithium metal anode, a cathode suitable for a lithium battery as disclosed above, a separator, and a low flammability or nonflammable LSE comprising (i) an active salt selected from LiFSI, LiTFSI , or a combination thereof, (ii) a flame retardant compound selected from trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate;
• the flame retardant compound is trimethyl phosphate, triethyl phosphate, or combination thereof.
• the flame retardant compound is tributyl phosphate, triphenyl phosphate, tris(2,2,2- trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide;
• the low flammability or nonflammable LSE may further comprise a bridge solvent having a different composition than the flame retardant compound and cosolvent, if present, and a different composition than the diluent, wherein the bridge solvent is miscible with the flame retardant compound, cosolvent (if present), and the diluent.
• the bridge solvent may be selected from acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate, dimethyl sulfoxide, 1 ,3-dioxolane, dimethoxyethane, diglyme (bis(2-methoxyethyl) ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), or any combination thereof.
• the cathode comprises LiNixMn y Co z 02 (NMC), sulfur/carbon, or an air electrode.
• a battery includes a sodium metal anode, a cathode suitable for a sodium battery as disclosed above, a separator, and a low flammability or nonflammable LSE comprising (i) an active salt selected from NaFSI, NaTFSI, or a combination thereof, (ii) a flame retardant compound selected from TMPa, TEPa, tributyl phosphate, triphenyl phosphate, tris (2 , 2 , 2-trif I u o ro eth y I) phosphate, bis(2,2,2- trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphospho
• a battery includes a sodium metal, a cathode suitable for a sodium battery as disclosed above, a separator, and a low flammability or nonflammable LSE comprising (i) an active salt selected from NaFSI, NaTFSI, or a combination thereof, (ii) a flame retardant compound selected from trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2- trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate; hexa
• the flame retardant compound is trimethyl phosphate, triethyl phosphate, or combination thereof.
• the flame retardant compound is tributyl phosphate, triphenyl phosphate, tris(2,2,2- trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide;
• the low flammability or nonflammable LSE may further comprise a bridge solvent having a different composition than the flame retardant compound and cosolvent, if present, and a different composition than the diluent, wherein the bridge solvent is miscible with the flame retardant compound, cosolvent (if present), and the diluent.
• the bridge solvent may be selected from acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate, dimethyl sulfoxide, 1 ,3-dioxolane, dimethoxyethane, diglyme (bis(2-methoxyethyl) ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), or any combination thereof.
• the cathode is Na 3 V2(P0 4 )3.
• a battery including a low flammability or nonflammable LSE as disclosed herein has a performance equal to, or even better than, a comparable battery including a superconcentrated electrolyte comprising a flame retardant compound.
• the battery including the low flammability or nonflammable LSE may have a CE greater than or equal to a comparable battery including a low flammability or nonflammable concentrated electrolyte.
• the battery has a CE ⁇ 95%, such as ⁇ 96%, ⁇ 97%, ⁇ 98%, ⁇ 99%, or even ⁇ 99.5%.
• the battery also may have a greater discharge capacity and/or cycling stability compared to a battery including a low flammability or nonflammable superconcentrated electrolyte.
• the low flammability or nonflammable LSE provides dendrite-free plating on the anode at high current densities (e.g., 0.5-10 mA cm 2 ) with CE greater than 99%.
• Embodiments of batteries including low flammability or nonflammable LSEs as disclosed herein demonstrate stable cycling performance (e.g., as evidenced by a stable CE and/or specific capacity) over a period of at least 10 cycles, at least 25 cycles, at least 50 cycles, at least 75 cycles, at least 100 cycles, at least 200 cycles, or at least 300 cycles.
• the battery may demonstrate stable cycling performance for 10- 500 cycles, such as 25-500 cycles, 50-500 cycles, 100-500 cycles, 200-500 cycles, or 300-500 cycles.
• synergistic effects arising from lower viscosity and higher conductivity of the disclosed low flammability and nonflammable LSEs also contribute to the superior electrochemical performances of electrochemical devices including certain embodiments of the disclosed low flammability and nonflammable LSEs.
• Cu cells including an electrolyte comprising 1 .2-1 .5 M LiFSI:TEPa:BTFE were demonstrated to have a comparable or superior coulombic efficiency to an electrolyte comprising 3.2 M
• LiFSI/TEPa (Example 1 1 , FIG. 45). Li
• certain embodiments of the disclosed low flammability and nonflammable LSEs are safer than conventional, flammable electrolytes, are cost-effective, enable dendrite-free plating, provide high CE, and/or greatly enhance fast charging and/or stable cycling of batteries.
• the advantages of certain embodiments of the disclosed low flammability and nonflammable LSEs are due to the 'inert' nature of the hydrofluoroether diluent that does not break the localized salt/solvent high concentration solvation structures, but plays an important role in improving the interfacial stablity of the metal anode. This outstanding performance is even superior over than that achieved in low flammability or nonflammable superconcentrated electrolytes, e.g., 4.1 M LiFSLTEPa or
• Embodiments of the disclosed low flammability and nonflammable LSEs are useful with many battery types, such as lithium-lithium intercalation compounds or lithium intercalation compounds, lithium-sulfur batteries, lithium-oxygen batteries, lithium-air batteries, sodium metal batteries, sodium ion batteries, sodium-air batteries, sodium-sulfur batteries, sodium-oxygen batteries, and magnesium ion batteries.
• Lithium hexafluorophosphate LiPFe
• dimethyl carbonate DMC
• ethylene carbonate EC
• ethyl methyl carbonate EMC
• Trimethyl phosphate TMPa, >99%
• Triethyl phosphate TEPa, >99%
• BTFE bis(2,2,2-trifluoroethyl) ether
• TTE 1 ,1 ,2,2-tetrafluoroethyl-2,2,2,3-tetrafluoropropyl ether
• LiFSI bis(fluorosulfonyl)imide
• the NMC (LiNii/3Mni/3Coi/302 andLiNio.6Mno.2Coo.2O2) cathode electrode was prepared in the Advanced Battery Facility (ABF) located at Pacific Northwest National Laboratory by mixing NMC, super C carbon, polyvinylidene fluoride (PVDF) binder at a mass ratio of 96:2:2 in N-Methyl-2- pyrrolidone (NMP) and coating the slurry onto Al foil.
• ABSF Advanced Battery Facility
• NCA LiNio.85Coo.1Alo.05O2
• LCO U0O2
• the electrode laminates were punched into discs (1 .27 cm 2 ) after being pre-dried and further dried at -75 °C under vacuum for 12 h.
• the materials were stored and handled in an MBraun LABmaster glove box (Stratham, NH) with an argon atmosphere (O2 ⁇ 0.1 ppm and H2O ⁇ 0.1 ppm).
• Raman spectra were collected using a Raman spectrometer (Horiba LabRAM HR) with sub-1 cnr spectral resolution, with all the samples sealed in a test glass tube.
• the viscosity ( ⁇ ) of the electrolytes was measured on a Brookfield DV-II+ Pro Viscometer (Middleboro, MA) at temperatures of 5 °C and 30 °C.
• S(g) and S(0) are peak intensities at a gradient strength of g and 0, respectively
• D is diffsuion coeffcient
• y is the gyromagnetic ratio of observing nuclei
• ⁇ and ⁇ are the gradient pulse length and the duration of the two gradient pulses, respectively, ⁇ and ⁇ were fixed at 2 ms and 30 ms for all
• Ionic conductivity was measured using BioLogic MCS 10 Fully Integrated Multichannel Conductivity Spectroscopy with a cell made of two parallel Pt electrodes over a temperature range of 5 to 30 °C.
• the conductivity cell constants were pre-determined using conductivity standard solution from Okalon Inc.
• Electrochemical cycling tests were carried out using CR2032-type coin cells of a two-electrode configuration with constant current mode on battery testers (Land BT2000 and Arbin BT-2000, Arbin Instruments, College Station, TX) at 30 °C in environmental chambers.
• Coin cells Li
• Celgard ® 2500 polypropylene membrane was used as the separators except for cells with concentrated LiFSI/DMCelectrolytes for which Celgard ® 3501 surfactant-coated polypropylene membranes were used to ensure good wetting due to the wettability issue with Celgard ® 2500 membrane.
• 200 ⁇ of electrolyte (excess amount) was added in each coin cell despite some spilling during cell crimping process.
• the effective area of the Cu foil for Li deposition was 2.1 1 cm 2 (diameter 1 .64 cm).
• Li symmetric cells were assembled with Li metal used as the working and counter electrodes. All the Li
• LSV Linear sweep voltammetry
• n is the cycle number at the charge capacity of Q C ycie,stnp and discharge capacity of Q cy cie
• P iate, Qstnp is the charge capacity during the final stripping
• Qresemor is the amount of deposition lithium during step 2.
• Electron-ion interactions were described by the projector-augmented wave (PAW) pseudopotentials with the cutoff energy of 400 eV (Blochl, Phys Rev B 1994, 50:17953-17979; Kresse et al. , Phys Rev B 1999, 59:1758-1775).
• the exchange-correlation functional was represented using the
• AIMD simulations of electrolyte-salt mixtures were performed in the canonical (NVT) ensemble at 303 K.
• the constant temperature of AIMD simulation systems was controlled using the Nose thermostat method with a Nose-mass parameter of 0.5.
• the time step of 0.5 fs was used in all AIMD simulations.
• Monkhorst-Pack k-point mesh grid scheme (2 ⁇ 2 ⁇ 2) was used in AIMD simulations.
• the total AIMD simulation time for each electrolyte/salt system was 15 ps.
• the AIMD trajectory of final 5 ps was used to obtain radial distribution functions of Li-O pairs.
• Lithium Metal Batteries with LiFSI/EMC-B TFE and LiFSI/EMC-TTE Electrolytes The coulombic efficiencies (CEs) of Li
• the solubility of different salts in carbonate solvents, e.g. EMC, is different, as reflected by the Li salt:solvent molar ratios shown in FIG. 5A.
• the LiPF6:EMC ratio is ca. 1 :2.35 in a saturated LiPF6/EMC solution
• the LiFSLEMC ratio could be as high as 1 :1 .1 in a saturated LiFSI/EMC solution.
• Cu cells were cycled at 1 mA cm 2 , with lithium deposition/stripping areal capacity of 0.5 mAh cnr 2 in each cycle.
• the CE data in FIG. 5B shows that only the concentrated electrolytes based on LiFSI salt, for example LiFSI/EMC (molar ratio 1 :1 .1 , 8.73 mol kg 1 ), could enable the reversible Li deposition/stripping with a stabilized CE of ⁇ 97%.
• Fluoroalkyi ethers were used to dilute the concentrated LiFSI/EMC (molar ratio 1 :1 .1 , 8.73 mol kg ) electrolyte.
• the LiFSI salt was confirmed insoluble in the fluoroalkyi ethers, e.g., TTE.
• TTE is misable with EMC. Therefore, the fluoroalkyi ethers are considered an 'inert' diluent of the electrolyte without participating in the solvation of LiFSI.
• the electrolyte formulations and the corresponding mole numbers of these electrolytes are shown in Table 1 . Table 1. Electrolyte number and formulations
• LiFSI/EMC (1 :1 .1) solvation cation-anion aggregates are well maintained, beneficial for achieving higher CE for reversible Li deposition/stripping.
• the formation of Li + -FSI --solvent aggregates also reduces the lowest unoccupied molecular orbital (LUMO) energy of the FSI- anions so they can be decomposed first to form a stable SEI.
• LUMO lowest unoccupied molecular orbital
• LiFSI/EMC-TTE (2:1).
• TTE fluoroalkyi ethers
• BTFE BTFE
• Cu cells from 3 rd to 86 th cycles are up to 98.95%, which is comparable to that of the parent superconcentrated LiFSI/EMC electrolyte (98.93%).
• FIG. 8A shows that the addition of BTFE as diluent largely shortened the rest time required to wet the electrode/separator. Cycling performance result shows that the Li
• the result suggests that addition of BTFE or TTE as a diluent does not compromise the oxidative stability of the concentrated electrolyte.
• L1BF4 was evaluated in propylene carbonate (PC).
• PC propylene carbonate
• the initial two cycles were performed at 0.2 mA/cm 2 with further cycles at 1 mA/cm 2 .
• the results are shown in FIGS. 9A and 9B.
• the LiBF 4 /PC electrolyte had an initial CE of approximately 50%. When diluted with TTE, the electrolyte had an average CE over 50 cycles of less than 50%.
• LiFSI/EMC LiFSI/EMC-BTFE
• LiFSI-EMC-TTE electrolytes with CE values up to 98.95%.
• LiTFSI-tetraglyme also produces poor CE results.
• LiFSI/DMC-BTFE Electrolyte Performance in Lithium Metal Batteries The concept of dilution and formation of the localized concentrated electrolyte solution structure was proven in DMC solvent-based electrolytes.
• the electrolyte formulations of various concentrations of LiFSI/DMC-BTFE solutions are listed in Table 2. With addition of BTFE, the concentration of 5.5 M
• LiFSI/DMC electrolyte was diluted to as low as 1 .2 M.
• Table 2 Electrolyte number, formulations and viscosity.
• Cu cells using 1 .0 M LiPFe/EC-EMC (E4), 1 .2 M LiFSI/DMC (E5), 3.7 M LiFSI/DMC (E6), and 5.5 M LiFSI/DMC (E7) are presented in FIGS. 10A-10D, respectively.
• the profiles were obtained using the following protocol: 1) one initial formation cycle with Li plating of 5 mAh cnv 2 on Cu at 0.5 mA cm 2 ; and then Li stripping at 0.5 mA cnr 2 to 1 V; 2) plate 5 mAh cnr 2 Li on Cu at 0.5mA cnr 2 as Li reservoir; 3) strip/plate Li with 1 mAh cnr 2 with 20% depth for 9 cycles; 4) strip all Li at 0.5 mA cnr 2 to 1 V.
• the average CE is calculated by dividing the total Li stripping capacity by the total Li plating capacity.
• Li metal cycling efficiency is so low ( ⁇ 50%) that significant overpotential arises for stripping within only couples of cycles.
• the CEs can reach >99.0% for 3.7 M and 5.5 M LiFSI/DMC.
• the average CEs of diluted LiFSI/DMC-BTFE electrolytes were also measured using the same protocol as shown in FIGS. 1 1A-1 1 D.
• the BTFE-diluted LSEs exhibited CEs that were even higher than the superconcentrated 5.5 M LiFSI/DMC (CE 99.2%) with CEs ranging from 99.3 to 99.5%.
• the results illustrate that the dilution with BTFE does not alter the localized superconcentrated structures and minimizes the presence of free DMC solvent molecules, therefore maintaining the high stability of the electrolyte toward Li metal anode during repeated plating/stripping processes.
• FIGS. 12A-12D are scanning electron microscopy images of lithium plated onto copper substrates at the 100th cycle (1 mA/cm 2 to 0.5 mAh/cm 2 ) from 1 .0 M LiPFe/EC-EMC (4:6, w) (FIG. 12A), 5.5 M LiFSI:DMC (1 :1) (FIG. 12B), 3.7 M LiFSI/DMC (1 :2) (FIG.
• FIG. 12C Cells with the highly concentrated 5.5 M LiFSI/DMC and highly diluted 1 .2 M LiFSI/DMC-BTFE (1 :2) electrolytes were stably cycled for >200 cycles (FIG. 13) with average CE of ⁇ 99%. Due to better conductivity and lower viscosity (FIG. 14, Table 2), the cell polarization during charge-discharge in the diluted electrolyte was much smaller than that in the highly concentrated electrolyte, and this difference became more obvious with increasing current densities (FIGS. 15A, 15B).
• FIGS. 17A-17D are photomicrographs showing the morphology of lithium metal after plating on Cu substrates in low and moderate concentration electrolytes of LiFSI in DMC - 1 .2 M LiFSI/DMC (FIGS. 17A, 17B) and 3.7 M LiFSI/DMC (FIGS. 17C, 17D).
• NMC cells were assembled to evaluate the performance of a dilute 1 .2 M LiFSI/DMC-BTFE electrolyte, by using NMC electrodes of high areal capacity of ⁇ 2.0 mAh/cm 2 .
• NMC cells with concentrated 5.5 M LiFSI/DMC and conventional 1 .0 M LiPFe/EC-EMC were also assembled and tested for comparison.
• FIGS, 18A-18D show the long-term cycling performance and corresponding voltage profile evolution of the Li
• NMC cells delivered similar specific discharge capacities of ca. 160 mAh g of NMC, corresponding to a norminal areal capacity of 2.0 mAh/cm 2 .
• NMC cell with the 1 .0 M LiPFe/EC-EMC electrolyte showed a drastic increase of electrode polarization and fast capacity degradation with ⁇ 30% retention after 100 cycles (FIGS.
• NMC cells were evaluated to determine the electrochemical reaction kinetics of the BTFE diluted electrolyte.
• the rate capability was tested using two charge/discharge protocols, i.e., (i) charge at same C/5 and discharge at increasing rate; (ii) charge at increasing rate and discharge at same C/5.
• NMC cell with BTFE-diluted electrolyte (1 .2 M LiFSI/DMC-BTFE) showed superior charging and discharging capability as compared to the concentrated 5.5 M LiFSI/DMC electrolyte and the baseline 1 M LiPF6 dilute electrolyte.
• protocol (i) when discharging at 5C (i.e.
• the cell using 1 .2 M LiFSI/DMC-BTFE electrolyte delivered a high discharge capacity of 141 mAh/g, significantly higher than 1 16 mAh/g for the concentrated 5.5 M LiFSI/DMC electrolyte and 68 mAh/g for the 1 M LiPF6 dilute electrolyte.
• the enhanced rate capability of 1 .2 M LiFSI/DMC-BTFE electrolyte as compared to concentrated 5.5 M LiFSI/DMC electrolyte is ascribed to the reduced viscosity, increased conductivity, improved electrode/separator wetting, as well as the improved interfacial reaction kinetics.
• FIGS. 21 A-21 F show the cross-section and surface morphologies of Li films deposited on Cu substrates in different electrolytes at a current desity of 1 mA/cm 2 .
• the electrolytes were as follows: 1 .0 M LiPFe/EC-EMC (FIGS. 21 A, 21 B), 5.5 M LiFSI/DMC (FIGS.
• LiFSI/DMC electrolytes as previously shown in FIGS. 17A-17D.
• nodule-like Li deposits without dendrite formation were obtained in both highly concentrated 5.5 M LiFSI/DMC and diluted low
• LiFSI/DMC-BTFE LiFSI/DMC-BTFE
• the Li deposits maintained a nodule-like nature in the 1 .2 M LiFSI/DMC-BTFE electrolyte despite a slight decrease in particle size (FIGS. 22A-22C).
• Formation of nodule-like Li deposits of large particle size can significantly mitigate the interfacial reactions with the electrolyte, and reduce the risk of Li penetration through the separator, hence improving the cycle life and safety of LMBs using LSE (dilute 1 .2 M LiFSI/DMC-BTFE).
• the dilute electrolyte also produced a more stable SEI layer than the highly concentrated 5.5 M LiFSI/DMC.
• deposition of high density Li is beneficial for reducing the volume variation of the LMBs during charge/discharge processes, and is highly desirable for the development of LMBs.
• FIG. 23 shows the CE of Li
• concentration of LiFSI/(DME+BTFE) and LiFSI/(DME+TTE) was diluted to 2M with the addition of fluoroalkyl ethers, i.e. TTE, BTFE as diluent
• Cu cells were 98.83% and 98.94% for TTE and BTFE diluted electrolyte, which is comparable to or even superior over that of the parent concentrated LiFSI/DME (98.74%).
• LiFSI/(DME+TTE) was diluted to 1 M with the addition of TTE, BTFE as diluent, the average CEs of Li
• LFP cells containing concentrated 4 M LiFSI/DME electrolyte without and with TTE or BTFE diluent is shown in FIG. 24.
• LFP coin cells were assembled using LFP cathode (Hydro-Quebec, 1 mAh cm 2 ), lithium metal anode, one piece of polyethylene (PE) separator, and the concentrated ether based electrolyte before and after dilution. Diluting the concentrated LiFSI/DME electrolyte from 4 M to 2 M, the Li
• LiFSI/(DME+TTE) electrolyte show similar long-term cycling stability as compared to the cell using parent concentrated 4 M LiFSI/DME electrolyte. Results were obtained at a 1 C rate after 3 formation cycles at C/10, in the voltage range of 2.5-3.7 V.
• Na3V2(P04)3 coin cells were constructed in an argon- filled glove box (MBraun, Inc.) using a Na3V2(P04)3 cathode, Na metal as the anode, glass fiber as the separator, and NaFSI/DME electrolyte with and without TTE diluent.
• the Na3V2(P04)3 cathode contains 80% Na 3 V2(P04)3, 10% Super P ® carbon black (available, e.g., from Fisher Scientific), and 10% PVDF (polyvinylidene fluoride).
• FIGS. 25A and 25B show the initial Na plating/stripping voltage profiles (FIG. 25A) and CE vs. cycle number of Na
• CE was evaluated as a function of cycle number tested at 0.65 mA cnr 2 after two formation cycles at 0.26 mA cnr 2 , with Na deposition areal capacity of 1 .3 mAh cm 2 .
• the initial CEs for NaFSI/DME and NaFSI/DME-TTE electrolytes with 5.2 M, 3.0 M, 2.3 M and 1 .5 M NaFSI salt were 94.3%, 96.1 %, 94.8% and 96.5%, respectively.
• the CEs of the diluted electrolytes were comparable or higher than that of the parent 5.2 M NaFSI/DME electrolyte.
• FIG. 26A, and 26B show the electrochemical performance of Na
• the cells using TTE diluted NaFSI/DME-TTE electrolytes showed similar initial specific discharge capacity of ca. 97 mAh g as compared to concentrated NaFSI/DME electrolyte (FIG. 26B).
• FIGS. 27A and 27B respectively, show the charge and discharge capacities of the cells using 5.2 M
• FIGS. 28A and 28B show the initial Na plating/stripping voltage profiles (FIG. 28A) and CE vs. cycle number of Na
• the ratios in the parentheses are the mole ratios of DME:BTFE.
• CE was evaluated as a function of cycle number tested at 1 mA cnr 2 after two formation cycles at 0.2 mA cnr 2 .
• the LSE, 2.1 M NaFSI/DME-BTFE (1 :2) exhibited stable cycling with a CE of nearly 100% over 200+ cycles.
• FIGS. 29A-29C show the electrochemical performance of Na
• FIG. 29A shows the initial Na plating/stripping voltage profiles.
• FIG. 29B shows the cycling stability over 100 cycles at rates of C/10 and C/3.
• FIG. 29C shows the charge and discharge capacities of 2.1 M NaFSI/DME-BTFE (1 :2 mol) over 100 cycles at rates of C/10 and C/3. The results indicate that BTFE is a superior diluent for concentrated NaFSI/DME electrolytes.
• the concept of localized superconcentrated electrolyte also works well for lithium sulfur batteries.
• the electrolyte formulations evaluated in this example are shown in Table 5. With addition of TTE, the concentration of 3.3 M LiTFSI in DOL-DME (1 :1 , v:v) electrolyte was diluted to 1.06 M.
• Li-S coin cells were assembled in an argon-filled glove box (MBraun, Inc.) using a Ketjen black conductive carbon (KB)/S cathode, lithium metal as the anode, one piece of polyethylene as separator, and the LiTFSI/DOL-DME electrolytes with or without TTE diluent.
• the KB/S cathode was prepared by coating a slurry containing 80% KB/S composite, 10% PVDF and 10% Super P® conductive carbon.
• the KB/S composite was prepared by mixing 80% S and 20% KB, followed by heat treatment at 155 °C for 12 hrs.
• FIGS. 30A and 30B show the initial Li plating/stripping voltage profiles (FIG. 30A) and CE vs. cycle number (FIG. 30B) of Li
• the results were obtained at 1 mA cnr 2 after 2 formation cycles at 0.2 mA cnr 2 with a Li deposition areal capacity of 1 mAh cnr 2 .
• the superconcentrated 3.3 M LiTFSI/DOL-DME electrolyte showed an initial CE of 91 .6%, which was much higher than the 70.1 % for the low concentration 1 M LiTFSI/DOL-DME electrolyte.
• FIGS. 31 A-31 C shows the initial charge/discharge voltage profiles.
• curves A were obtained with 1 .0 M LiTFSI/DOL-DME
• curves B were obtained with 3.3 M LiTFSI/DOL-DME
• curves C were obtained with 1 .06 M LiTFSI/DOL-DME-TTE.
• the Li-S cells with electrolyte/sulfur ratio of 50 mL/g were cycled at a low current rate of C/10 (168 mA/g). Diluting the concentrated LiTFSI/DOL-DME electrolyte from 3.3 M to 1 .06 M, the Li-S cells showed even better long- term cycling stability (FIG. 31 B) and higher CE (FIG. 31 C) as compared to the cell using parent
• FIG. 32 shows the charge/discharge profiles of L1-O2 cells using UTFSI-3DMSO (2.76 M) and UTFSI-3DMSO-3TTE (1 .23 M) electrolytes with limited discharge capacity of 600 mAh g at a current density of 0.1 mA cm 2 .
• the L1-O2 cells demonstrated similar capacity as those observed in the U-O2 cells using the highly concentrated electrolyte.
• U-O2 coin cells were assembled in the argon-filled glove box (MBraun, Inc.).
• a piece of separator (Whatman glass fiber B) soaked with 200 ⁇ _ of LiTFSI-DMSO electrolyte with and without TTE diluent was placed between an air electrode disc and a Li metal chip. After crimping, the assembled cells were transferred into PTFE (polytetrafluoroethylene) containers and taken out of the glove box. The PTFE containers were filled with ultrahigh purity O2. These U-O2 cells were allowed to rest for at least 6 h in O2 atmosphere and then discharge/charge evaluations were performed at room temperature on an Arbin BT-2000 battery tester (Arbin Instruments, College Stations, TX) at a current density of 0.1 mA cm 2 .
• Arbin BT-2000 battery tester Arbin Instruments, College Stations, TX
• the superconcentrated aqueous electrolyte (21 mol LiTFSI in 1 kg of H2O) was diluted with TTE with the assistance of a 'bridge' solvent.
• the evaluated electrolyte formulations are shown in Tables 7 and 8.
• the 'bridge' solvents included DMC, PC, AN, and DMSO.
• the optimal content of 'bridge' solvent was carefully optimized. The optimal content is different for different solvents, depending on the strength of the interaction between 'bridge' solvent and H2O and TTE diluent.
• FIG. 33 shows the cyclic voltammograms of concentrated aqueous electrolyte before and after dilution with TTE with the assistance of different 'bridge' solvents, including DMC, PC, AN, and DMSO , using a stainless steel working electrode and counter electrode, and Ag/AgCI as reference electrode at a scan rate of 1 0 mV s "1 .
• the potential was converted to those versus to Li/Li + redox couple.
• the concentration of the UTFSI/H2O solution was only diluted from 5.04 M to 3.69 M.
• FIGS. 34A and 34B show the first and second cycle cyclic voltammograms, respectively, of concentrated aqueous electrolyte diluted with different amounts of TTE with the assistance of PC.
• Stainless steel was the working electrode and counter electrode, and Ag/AgCI was the reference electrode; scan rate of 10 mV s "1 . The potential was converted to those versus to Li/Li + redox couple.
• the first cycle
• Monkhorst-Pack k-point mesh grid scheme (4 4 1 ) was used to obtain the optimized Li anode surface and adsorption of electrolyte and salt molecules in the ground state.
• the convergence criteria for electronic self-consistent iteration and ionic relaxation were set to 1x10 5 eV and 1x10 4 eV, respectively.
• AIMD simulations of electrolyte-salt mixtures were performed in the canonical (NVT) ensemble at 303 K.
• the constant temperature of AIMD simulation systems was controlled using the Nose thermostat method with a Nose-mass parameter of 0.5.
• the time step of 0.5 fs was used in all AIMD simulations.
• a Monkhorst-Pack k-point mesh grid scheme (2 ⁇ 2 ⁇ 2) was used in AIMD simulations.
• the total AIMD simulation time for each electrolyte/salt system was 15 ps.
• the AIMD trajectory of final 5 ps was used to obtain radial distribution functions of Li-O pairs.
• FIG. 35 shows the optimized geometries of DMC, BTFE, LiFSI, and pairs of DMC/LiFSI, BTFE/LiFSI in vacuum using VASP.
• the Li, O, C, H, S, N, and F atoms are colored as magenta, red, gray, white, yellow, blue, and light blue, respectively. Only ⁇ -centered k-point mesh was used for above calculations. Similar results were also obtained using the Gaussian 09 package with PBE and the 6-31 1 ++G(p,d) basis set (Frisch et al., Gaussian 09, 2009, Gaussian Inc., Wallingford, CT), Table 10.
• LiFSI salt is preferentially coordinated with DMC via the LI-ODMC bond, with an optimized LI-ODMC bond length of 1 .85 A and strong interaction between LiFSI and DMC (-88.7 kJ/mol).
• the interaction between LiFSI and another electrolyte solvent BTFE is comparatively weak as reflected by the LI-OBTFE bond distance of 2.70 A, which is much longer than the optimized LI-ODMC bond, and much weaker interaction of
• each liquid electrolyte/salt mixture system was set up by randomly placing the numbers of DMC, BTFE and LiFSI molecules on the basis of experimental densities and molar ratios (concentration).
• the size of simulation system is 20 A x 20 A x 20 A.
• FIGS. 37A-37C The snapshots of three electrolyte/salt mixture systems from AIMD summations are shown in FIGS. 37A-37C.
• FIG. 38 shows the radial distribution functions of U-ODMC and U-OBTFE pairs calculated from AIMD simulation trajectories at 303 K.
• FIGS. 39A and 39B show Raman spectra of pure DMC, BTFE, and a DMC-BTFE (2:1) solvent mixture. There is no observable Raman shift in the peak locations of DMC and BTFE in the mixture of DMC and BTFE. This result indicates that there is no significant interaction between DMC and BTFE.
• the dilute LiFSI/DMC (1 :9) solution is featured by the dominating O-CH3 stretching vibration band at ⁇ 920 cm "1 for free DMC solvent molecules and the minor vibration band at ⁇ 940 cm 1 for Li + -coordinated
• FIG. 40B shows the Raman spectra of different concentrations of BTFE diluted LiFSI/DMC solutions.
• NMR data shows that all diffusion coefficients (Ds) are globally proportional to the inverse of viscosity (/7 1 ) of solutions while its variations are slightly different depending on the ion-ion and ion-solvent interactions as predicted by the Stokes-Einstein theory of diffusion (Pregosin et al., Chemical Reviews 2005, 105:2977-2998)). It is found DDMC > DBTFE in pure DMC, BTFE solvent and their mixture, but with introduction of LiFSI salt, DDMC and DBTFE become smaller and larger than ⁇ respectively.
• Li + cation solvation occurs mainly by DMC molecules, with BTFE interaction to other electrolyte components being quite weak. It also indicates that Li + cation diffusion is enhanced (Du ⁇ DFSI) by addition of BTFE, which is in line with Raman observation, while is reversed in the LiFSI/DMC electrolytes (Du ⁇ DFSI).
• the stable diffusion ratios DU/DDMC and DFSI/DDMC suggest that the LSE solvation structure composed of Li + cation, FSI " anion and DMC solvent is not sensitive to the population of BTFE in the LiFSI/DMC-BTFE electrolytes (FIG. 42).
• DU/DDMC and DFSI/DDMC values are closer to unity and DBTFE/DDMC values are much larger than the unity due to the preferential solvation of Li + cation by DMC molecules.
• Relatively constant DU/DDMC and DFSI/DDMC values in DMC:BTFE electrolytes suggests that the solvation structure composed of Li + cation, FSh anion and DMC is less sensitive to the concentration of LiFSI and the ratio between DMC:BTFE. It can be concluded that the ion-ion and ion-solvent interactions, which depend strongly on the concentration of Li salt, are less likely to change as a function of LiFSI concentration in a DMC:BTFE binary electrolyte system.
• the moderately dilute 3.7 M LiFSI/DMC, SE (5.5 M LiFSI/DMC), and LSE (1 .2 M LiFSI/DMC-BTFE (1 :2)) are modeled by using solution of 1 LiFSI: 2 DMC, 1 LiFSI: 1 DMC, and 1 LiFSI: 2 DMC: 4 BTFE as three types of adsorption configurations on the most stable Li (100) surface.
• the LiFSI adsorbs with two DMC molecules (FIG. 36F) while only the DMC-LiFSI pair adsorbs the Li (100) surface (FIG.
• FIGS. 43A-43C show projected density of states (PDOS) of each atom in adsorbed LiFSI and DMC molecules for the three configurations.
• PDOS projected density of states
• LiFSI -0.14e
• LiFSI - 0.09
• LiFSI -0.20
• the electrolyte formulations and the physical properties of these electrolytes are shown in Table 1 1 .
• Table 11 Electrolyte number and formulations
• BTFE is considered as an 'inert' diluent of the electrolyte without participating in the solvation of LiFSI.
• Raman spectroscopy was employed to detect the solution coordination structures of concentrated LiFSI/TEPa electrolyte and BTFE diluted LiFSI/TEPa- BTFE electrolytes. There was no observable Raman shift in the peak location of BTFE and Li + -TEPa solvates in the BTFE-diluted electrolytes (FIGS. 44A-44D).
• FIG. 45 shows the CE of Li
• the LiFSI concentration was reduced to 1 .5 M (E39) and 1 .2 M (E40) with the addition of BTFE as diluent
• Cu cells over 140 cycles were 98.63% and 98.82%, respectively, which are comparable to or even superior to that of the original concentrated LiFSI/TEPa (98.60%).
• FIG. 46 shows that the Li
• the BTFE-diluted LSEs also provided high discharge capacities and good cycling stability of Li
• the results suggest that the nonflammable BTFE-diluted TEPa-based LSEs can enable safe and stable cycling of LMBs. Cycling stability of the Li
• Electrolytes were prepared with LiFSI, TEPa, and varying concentrations of TTE to produce TTE- diluted LSEs as shown in Table 12.
• concentration of LSEs was decreased to 1 .9- 1 .0 M with a TEPa:TTE molar ratio of 1 :1 to 1 :3.
• the TTE-diluted LSEs are also nonflammable due to the high mass contents (18-33 wt%) of TEPa.
• Cu cells over 130 cycles were up to 98.59-98.82%, which is comparable to or even superior to that of the original concentrated LiFSI/TEPa electrolyte (98.60%). Cycling was performed at 0.5 mA cnr 2 with a Li deposition areal capacity of 1 mAh cnr 2 . Similarly, the TTE-diluted TEPa-based LSEs also provided high capacity, good cycling stability and high efficiency of Li
• Electrolytes were prepared with LiFSI, trimethyl phosphate (TMPa), and varying concentrations of BTFE as shown in Table 13. With addition of BTFE, a 4.1 M LiFSI/TMPa electrolyte could be diluted to 1 .8 M by using a TMPa/BTFE molar ratio of 1 :2. The TMPa-based HCE and LSE were nonflammable due to the high mass content (22-43 wt%) of TMPa.
• Cu cells using the concentrated 4.1 M LiFSI/TMPa (E44) and 1 .8 M LiFSI/TMPa-BTFE (1 :2 by mol, E45) electrolytes are presented in FIGS. 51 A and 51 B, respectively.
• the following protocol was used: 1) one formation cycle with an initial Li plating of 5 mAh cnr 2 on Cu at 0.5 mA cnr 2 ; and then Li stripping at 0.5 mA cnr 2 to 1 V; 2) plate 5 mAh cm 2 Li on Cu at 0.5 mA cnr 2 as Li reservoir; 3) strip/plate Li with 1 mAh cnr 2 for 10 cycles; 4) strip all Li at 0.5 mA cnr 2 to 1 V.
• the average CE was calculated by dividing the total Li stripping capacity by the total Li plating capacity after the initial formation cycle. Both electrolytes showed very high stability towards Li metal, providing high CE of 98.5% and 99.2% for the HCE and LSE, respectively.
• the BTFE-diluted TMPa-based LSEs also exhibited high capacity, good cycling stability and high efficiency in Li
• Nonflammable LSEs can be modified by replacing portions of the flame retardants (FRs) and diluents with other conventional solvents or additives, while still retaining a sufficiently high content of FRs to maintain the nonflammable characteristics and retain the localized high concentration solvation structures for high stability towards the Li metal anode. Electrolytes were prepared where DMC replaced some of the TMPa in LiFSI:TMPa:BTFE LSEs. The electrolyte formulations and properties are shown in Table 14.
• Li plating/stripping profiles were prepared using the following protocol: 1) one formation cycle with an initial Li plating of 5 mAh cnr 2 on Cu at 0.5 mA cnr 2 ; and then Li stripping at 0.5 mA cnr 2 to 1 V; 2) plate 5 mAh cnr 2 Li on Cu at 0.5 mA cnr 2 as Li reservoir; 3) strip/plate Li at 1 mAh cnr 2 for 10 cycles; 4) strip all Li at 0.5 mA cnr 2 to 1 V.
• the average CE was calculated by dividing the total Li stripping capacity by the total Li plating capacity after the initial formation cycle.
• the electrolytes also provided high capacity, good cycling stability and high efficiency in Li
• LiFSI Lithium Metal Cells with LiFSI: TE Pa.DME, LiFSI:TMS:TTE, and LiFSI: TEPa.DME: TTE Electrolytes
• FIGS. 55 and 56 show the cycling stability of Li
• the LiFSI- 0.3TEP-0.9DME electrolyte has a lower SET values (54 s/g) than that of the baseline electrolyte - 1 M LiPFe in EC EMC (3/7 by wt.) + 2 wt.% VC - (85 s/g).
• LiFSI-0.8TEPa-0.4DME-3TTE electrolyte has a low SET value (7.7 s/g) and is suitable for high-loading, lean-electrolyte conditions.
• An electrolyte comprising: an active salt; a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent; and a diluent, wherein the active salt has a solubility in the diluent at least 10 times less than a solubility of the active salt in the solvent, and wherein the electrolyte comprises at least 5 wt% of the flame retardant compound.
• the flame retardant compound comprises triethyl phosphate, trimethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2- trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2,2-trifluoroethyl) methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.
• EMC diethyl carbonate
• DEC diethyl carbonate
• EC ethylene carbonate
• PC propylene carbonate
• VEC vinylene carbonate
• FEC fluoroethylene carbonate
• VEC 4-vinyl-1 ,3-dioxolan-2-one
• MEC 4-methylene-1 ,3-dioxolan-2-one
• DMSO dimethyl sulfoxide
• DMS dimethyl sulfone
• EMS ethyl methyl sulfone
• EVS tetramethylene sulfone
• TMS tetramethylene sulfone
• LiFSI lithium bis(trifluoromethanesulfonyl)imide
• LiTFSI lithium bis(trifluoromethanesulfonyl)imide
• LiBETI bis(pentafluoroethanesulfonyl)imide
• NaFSI sodium bis(fluorosulfonyl)imide
• LiTFSI bis(trifluoromethylsulfonyl)imide
• LiBOB lithium bis(oxalato)borate
• NaBOB sodium bis(oxalato)borate
• LiPFe LiAsFe
• LiBF 4 LiBF 4 , UCF3SO3, UCIO4
• LiDFOB lithium difluoro oxalato borate anion
• Lil LiBr, LiCI, LiSCN, UNO3, U2SO4, or any combination thereof.
• the active salt is (i) LiFSI, LiTFSI, or a combination thereof, or (ii) NaFSI, NaTFSI, or a combination thereof;
• the solvent comprises triethyl phosphate, trimethyl phosphate, or a combination thereof; and the active salt has a molar concentration in the electrolyte within a range of from 0.75 M to 1 .5 M.
• EOFB ethoxynonafluorobutane
• the bridge solvent comprises acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate, dimethyl sulfoxide, 1 ,3-dioxolane, 1 ,2-dimethoxyethane, diglyme (bis(2-methoxyethyl) ether), triglyme (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), or any combination thereof.
• a battery comprising: (i) an electrolyte comprising an active salt, a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent, and a diluent, wherein the active salt has a solubility in the diluent at least 10 times less than a solubility of the active salt in the solvent, the active salt has a concentration in the electrolyte within a range of 0.75 to 2 M, and the electrolyte comprises at least 5 wt% of the flame retardant compound; (ii) an anode; and (iii) a cathode, wherein the battery has a coulombic efficiency ⁇ 95%.
• the flame retardant compound comprises trimethyl phosphate, triethyl phosphate, tributyl phosphate, triphenyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, bis(2,2,2-trifluoroethyl) methyl phosphate; trimethyl phosphite, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphite; dimethyl methylphosphonate, diethyl ethylphosphonate, diethyl phenylphosphonate, bis(2,2 ,2- trifluoroethyl) methylphosphonate; hexamethylphosphoramide; hexamethoxyphosphazene,
• the anode is lithium metal
• the active salt comprises LiFSI, LiTFSI , LiPFe, LiAsFe, LiBF 4 , UCF3SO3, L1CIO4, LiBOB, LiDFOB, Lil, LiBr, LiCI, LiSCN, UNO3, L12SO4, or any combination thereof
• the flame retardant compound comprises trimethyl phosphate, triethyl phosphate, or a combination thereof
• the diluent comprises TTE, BTFE, TFTFE, MOFB, EOFB, or any combination thereof
• the anode is sodium metal
• the active salt comprises NaFSI , NaTFSI , or a combination thereof
• the flame retardant compound comprises trimethyl phosphate, triethyl phosphate, or a combination thereof
• the diluent comprises BTFE, TTE, TFTFE, MOFB, EOFB, or any combination thereof
• the cathode is NaFeP04, Na2FeP04F, Na2FeP207, Na3V2(P04)3, Na 3 V2(P0 4 )2F3, NaVP0 4 F, NaVPOPOF, Nai .
• Na2/3Nii/6C0i/6Mn2/3O2 NaNii/3Fei/3Mni/302, NaNii/3Fei/3Coi/302, NaNii/2Mni/202, a Prussian white analogue cathode, or a Prussian blue analogue cathode.
• the solvent further comprises a cosolvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.

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