CN111212887A

CN111212887A - Low-flammability electrolyte for stable operation of electrochemical devices

Info

Publication number: CN111212887A
Application number: CN201880066668.2A
Authority: CN
Inventors: 张继光; 陈书如; W·徐; X·曹; X·任
Original assignee: Battelle Memorial Institute Inc
Current assignee: Battelle Memorial Institute Inc
Priority date: 2017-10-19
Filing date: 2018-08-31
Publication date: 2020-05-29
Also published as: EP3697869A1; WO2019078965A1; KR20200059316A; JP2021500704A; EP3697869A4; WO2019078965A9

Abstract

Disclosed are low flammability and non-flammable localized super concentrated electrolytes (LSEs) for stable operation of electrochemical devices such as rechargeable batteries, supercapacitors and sensors. Electrochemical devices, such as rechargeable batteries, supercapacitors and sensors, that include low-flammability and non-flammable LSEs are also disclosed. Low flammability and non-flammable LSEs include 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. In certain embodiments, the LSE also includes a bridging solvent, for example, when the solvent and diluent are immiscible.

Description

Low-flammability electrolyte for stable operation of electrochemical devices

Thank you government support

The invention was made with government support under contract numbers DE-AC05-76RL01830 and DE-AC02-05CH11231 awarded by the U.S. department of energy. The government has certain rights in this invention.

Technical Field

The present invention relates to a low flammable and non-flammable electrolyte for stable operation of an electrochemical device, certain embodiments of the electrolyte comprising 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.

Disclosure of Invention

Embodiments of low-flammability and non-flammable localized super concentrated electrolytes (LSEs, also known as Localized High Concentration Electrolytes (LHCEs)) and electrochemical systems including low-flammability or non-flammable LSEs are disclosed. A low-or non-flammable LSE comprises an active salt, a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent, and a diluent, wherein the solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent. In some embodiments, the LSE comprises at least 5 wt.% of the flame retardant compound. In any or all of the preceding embodiments, the flame retardant compound may comprise an organophosphate, an organophosphite, an organophosphonate, an organophosphamide, an organic or inorganic phosphazene, other phosphorus-containing compounds, or any combination thereof. In some embodiments, 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, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.

In any or all embodiments, the solvent may further comprise a co-solvent, wherein the active salt is soluble in the co-solvent. In some embodiments, the co-solvent comprises an organic carbonate solvent, an ether solvent, an organic sulfoxide, a sulfone, an organic nitrogen-containing solvent, or any combination thereof. In certain embodiments, the co-solvent comprises 1, 2-Dimethoxyethane (DME), 1, 3-Dioxolane (DOL), Tetrahydrofuran (THF), allyl ether, diethylene glycol dimethyl ether (diglyme), dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), Vinylene Carbonate (VC), fluoroethylene carbonate (FEC), 4-vinyl-1, 3-dioxolane-2-one (vie., ethylene carbonate, VEC), 4-methylene-1, 3-dioxolane-2-one (vie., methylene ethylene carbonate, MEC), 4, 5-dimethylene-1, 3-dioxolane-2-one, 4, 5-dioxolane-2-one, Dimethyl sulfoxide (DMSO), dimethyl sulfone (DMS), Ethyl Methyl Sulfone (EMS), Ethyl Vinyl Sulfone (EVS), tetramethylene sulfone (i.e., sulfolane, TMS), trifluoromethyl ethyl sulfone (FMES), trifluoromethyl isopropyl sulfone (FMIS), trifluoropropyl methyl sulfone (FPMS), methyl butyrate, ethyl propionate, gamma-butyrolactone, Acetonitrile (AN), Succinonitrile (SN), adiponitrile, triallylamine, triallylcyanurate, triallylisocyanurate, or any combination thereof.

In any or all embodiments, the diluent may comprise a fluoroalkyl ether (also known as Hydrofluoroether (HFE)). In some embodiments, the diluent comprises 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE), bis (2,2, 2-trifluoroethyl) ether (BTFE), 1,2,2, -tetrafluoroethyl-2, 2, 2-trifluoroethyl ether (TFTFE), Methoxynonafluorobutane (MOFB), Ethoxynonafluorobutane (EOFB), or any combination thereof. In any or all embodiments, the solvent and the diluent may be miscible.

In any or all embodiments, (i) the molar concentration of the active salt in the electrolyte is in the range of 0.5M to 2M; (ii) the active salt is present in the solvent at a molar concentration 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 diluent) is at least 20% less than the 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 the molar concentration of the active salt in the solvent in the absence of the diluent.

In any or all embodiments, (i) the molar ratio of the active salt to the solvent is in the range of 0.33 to 1.5; (ii) the molar ratio of the solvent to the diluent is in the range of 0.2 to 5; or (iii) satisfies both (i) and (ii). In any or all embodiments, at least 90% of the molecules of the solvent are associated with the cation of the active salt. In any or all embodiments, less than 10% of the molecules of the diluent are associated with the cation of the active salt.

In any or all embodiments, the active salt may comprise a lithium salt or mixture of lithium salts, a sodium salt or mixture of sodium salts, a potassium salt or mixture of potassium salts, or a magnesium salt or mixture of magnesium salts. In some embodiments, the active salt comprises lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethanesulfonyl) imide (LiN (SO)₂CF₂CF₃)₂LiBETI, lithium (LiN (SO) imide) (fluorosulfonyl trifluoromethanesulfonyl) imide₂F)(SO₂CF₃) LiFeTFSI, lithium (LiN (SO) penta-fluoroethanesulfonyl) imide₂F)N(SO₂CF₂CF3), LiFBETI), lithium cyclic (tetrafluoroethylene dithio) imide (LiN (SO)₂CF₂CF₂SO₂) LiCTFSI), (trifluoromethanesulfonyl) (n-nineLithium fluorobutanesulfonyl) imide (LiN (SO)₂CF₃)(SO₂-n-C₄F₉) LiTNFSI), sodium bis (fluorosulfonyl) imide (NaFSI), sodium bis (trifluoromethylsulfonyl) imide (NaTFSI), sodium bis (pentafluoroethanesulfonyl) imide (NaN (SO)₂CF₂CF₃)₂NaBETI, sodium (NaN (SO) sulfonyl) imide (sodium salt of trifluoromethanesulfonyl) (nonafluorobutanesulfonyl)₂CF₃)(SO₂-n-C₄F₉) NaTNFSI), lithium bis (oxalate) borate (LiBOB), sodium bis (oxalate) borate (NaBOB), lithium difluoroborate anion (LiDFOB), LiPF₆、LiAsF₆、LiBF₄Lithium trifluoromethanesulfonate (LiCF)₃SO₃Or LiTf), lithium nonafluorobutane sulfonate (LiC)₄F₉SO₃,LiNFBS)、LiClO₄、LiI、LiBr、LiCl、LiSCN、LiNO₃、Li₂SO₃、Li₂SO₄、LiRSO₄(wherein R is alkyl) or any combination thereof. In certain of the foregoing embodiments, 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 molar concentration of the active salt in the electrolyte is in the range of 0.75M to 1.5M.

In some embodiments, a low or non-flammable LSE comprises an active salt; a solvent comprising a flame retardant compound, wherein the active salt is soluble in the solvent; a diluent, wherein the solvent is immiscible with the diluent, and wherein the solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent; and a bridging solvent having a different composition from the solvent (i.e., flame retardant, and co-solvent, if present) and from the diluent, wherein the bridging solvent is miscible with the solvent and with the diluent. Exemplary bridging solvents include AN, DMC, DEC, PC, DMSO, EMS, TMS, DOL, DME, diglyme, triglyme (triglyme), tetraglyme (tetraglyme), or any combination thereof.

Some embodiments of the batteries 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 solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent, the concentration of the active salt in the electrolyte is in the range of 0.75M to 2M, and the electrolyte comprises at least 5 wt% of the flame retardant compound; (ii) an anode; and (iii) a cathode, wherein the cell has a coulombic efficiency of ≧ 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) methyl phosphonate, hexamethylphosphoramide, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof.

In one embodiment of the cell, (i) the anode is lithium metal; (ii) the active salt comprises LiFSI, LiTFSI, LiBETI and LiPF₆、LiAsF₆、LiBF₄、LiCF₃SO₃、LiClO₄、LiBOB、LiDFOB、LiI、LiBr、LiCl、LiSCN、LiNO₃、Li₂SO₄Or any combination thereof; (iii) the flame retardant compound comprises TMPa, TEPa, or a combination thereof; (iv) the diluent comprises TTE, BTFE, TFTFE, MOFB, EOFB, or any combination thereof; and (v) the cathode is Li₁₊ _wNi_xMn_yCo_zO₂(x+y+z+w＝1，0≤w≤0.25)、LiNi_xMn_yCo_zO₂(x+y+z＝1)、LiCoO₂、LiNi_0.8Co_0.15Al_0.05O₂、LiNi_0.5Mn_1.5O₄Spinel, LiMn₂O₄、LiFePO₄、Li_4-xM_xTi₅O₁₂(M ═ Mg, Al, Ba, Sr or Ta; 0. ltoreq. x.ltoreq.1), MnO₂、V₂O₅、V₆O₁₃、LiV₃O₈、LiM^C1 _xM^C2 _1-xPO₄(M^C1Or M^C2Fe, Mn, Ni, Co, Cr, or Ti; x is more than or equal to 0 and less than or equal to 1), Li₃V_2-xM¹ _x(PO₄)₃(M¹Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce; x is more than or equal to 0 and less than or equal to 1), LiVPO₄F、LiM^C1 _xM^C2 _1- _xO₂(M^C1And M^C2Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1), LiM^C1 _xM^C2 _yM^C3 _1-x-yO₂(M^C1、M^C2And M^C3Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1; y is more than or equal to 0 and less than or equal to 1), LiMn_2-yX_yO₄(X-Cr, Al or Fe, 0. ltoreq. y.ltoreq.1), LiNi_0.5-yX_yMn_1.5O₄(X ═ Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0. ltoreq. y<0.5)、xLi₂MnO₃·(1-x)LiM^C1 _yM^C2 _zM^C3 _1-y-zO₂(M^C1、M^C2And M^C3Independently Mn, Ni, Co, Cr, Fe or mixtures thereof; x is 0.3-0.5; y is less than or equal to 0.5; z is less than or equal to 0.5), Li₂M²SiO₄(M²Mn, Fe or Co), Li₂M²SO₄(M²Mn, Fe or Co), LiM²SO₄F(M²Fe, Mn or Co), Li_2-x(Fe_1-yMn_y)P₂O₇(0≤y≤1)、Cr₃O₈、Cr₂O₅Carbon/sulfur composite or air electrode. In any preceding embodiment, the solvent further comprises a co-solvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.

In one embodiment of the cell, (i) the anode is sodium metal; (ii) the active salt comprises NaFSI, NaTFSI, or a combination thereof; (iii) the flame retardant compound comprises TMPa, TEPa, or a combination thereof; (iv) the diluent comprises BTFE, TTE, TFTFE,MOFB, EOFB, or any combination thereof; and (v) the cathode is NaFePO₄、Na₂FePO₄F、Na₂FeP₂O₇、Na₃V₂(PO₄)₃、Na₃V₂(PO₄)₂F₃、NaVPO₄F、NaVPOPOF、Na_1.5VOPO₄F_0.5、NaCo₂O₄、NaFeO₂、Na_xMO₂Wherein 0.4<x is less than or equal to 1, and M is transition metal or mixture of transition metals, Na_2/3Ni_1/3Mn_2/3O₂、Na_2/3Fe_1/ ₂Mn_1/2O₂、Na_2/3Ni_1/6Co_1/6Mn_2/3O₂、NaNi_1/3Fe_1/3Mn_1/3O₂、NaNi_1/3Fe_1/3Co_1/3O₂、NaNi_1/2Mn_1/2O₂A Prussian white simulated cathode or a Prussian blue simulated cathode. In any preceding embodiment, the solvent further comprises a co-solvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.

In some embodiments of the battery, the solvent is immiscible with the diluent, the electrolyte further comprises a bridging solvent having a different composition than the solvent and a different composition than the diluent, wherein the bridging solvent is miscible with the solvent and with the diluent. Exemplary bridging solvents include AN, DMC, DEC, PC, DMSO, EMS, TMS, DOL, DME, diglyme, triglyme, tetraglyme, or any combination thereof.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description, which proceeds with reference to the accompanying drawings.

Drawings

This patent or application document contains at least one drawing executed in color. Copies of this patent or patent application publication with color drawing(s) will be provided by the office upon request and payment of the necessary fee.

Fig. 1 is a schematic view of a super concentrated electrolyte (SE) comprising a lithium salt and a solvent.

Fig. 2 is a schematic diagram of an exemplary localized super-concentrated 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.

Fig. 3 is a schematic diagram 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 at 1mA cm for various concentrated electrolytes with lithium salts contained in carbonate solvents^-2The lower test has 0.5mAh cm^-2Li-area deposition capacity, initial lithium deposition/stripping voltage curve (fig. 5A) and coulombic efficiency as a function of cycle number (fig. 5B).

FIG. 6 is a plot of LiFSI concentration at 0.5mA cm for electrolytes with concentrated LiFSI in Ethyl Methyl Carbonate (EMC) with and without fluoroalkyl ether diluent^-2The lower test has 1mAh cm^-2Li | Cu cell of lithium area deposition capacity, coulombic efficiency as a function of cycle number.

The digital photograph of fig. 7 shows that the addition of bis (2,2, 2-trifluoroethyl) ether (BTFE) to a LiFSI/EMC electrolyte improves the wetting of the battery separator.

FIGS. 8A and 8B are graphs showing Li | | | NMC761410 (LiNi) with concentrated LiFSI/EMC electrolyte with no and with BTFE diluent_0.76Mn_0.14Co_0.10O₂) The cycle stability of the cell at C/3 (fig. 8A) and 1C rate (fig. 8B) (BTFE: bis (2,2, 2-trifluoroethyl) ether).

FIGS. 9A and 9B show a LiBF for a sample having a density of 7.5mol/kg₄PerPC and 2.5mol/kg LiBF₄Electrolyte of/PC-TTE (PC: TTE ═ 2:1v: v) (TTE: 1,1,2, 2-

tetrafluoroethyl

2,2,3, 3-tetrafluoropropyl ether), 0.5mAh/cm²Cu | Li cell for lithium area deposition capacity of (a), initial lithium deposition/stripping voltage curve (fig. 9A) and coulombic efficiency as a function of cycle number (fig. 9B).

FIGS. 10A-10D illustrate the use of a conventional electrolyte (1.0M LiPF)₆Li plating/stripping curves for Li | | | Cu cells of/EC-EMC (4:6, w)) (FIG. 10A), 1.2M LiFSI/DMC (FIG. 10B), 3.7M LiFSI/DMC (FIG. 10C), and 5.5M LiFSI/DMC (FIG. 10D).

FIGS. 11A-11D are Li plating/stripping curves for Li | | | Cu cells using concentrated 3.8M LiFSI/DMC-BTFE (1:0.5) (FIG. 11A), 2.5M LiFSI/DMC-BTFE (1:1) (FIG. 11B), 1.8M LiFSI/DMC-BTFE (1:1.5) (FIG. 11C), and 1.2M LiFSI/DMC-BTFE (1:2) (FIG. 11D). The ratio in parentheses represents the molar ratio of DMC to BTFE.

FIGS. 12A-12D are the compounds consisting of 1.0M LiPF₆Lithium plating of the/EC-EMC (FIG. 12A), 5.5M LiFSI/DMC (FIG. 12B), 3.7M LiFSI/DMC (FIG. 12C) and 1.2M LiFSI/DMC-BTFE (1:2) (FIG. 12D) electrolytes onto copper substrates at 100 cycles (1 mA/cm)²To 0.5mAh/cm²) Later scanning electron microscope images.

FIG. 13 is a plot of coulombic efficiency versus cycle number for the LSEs of conventional electrolyte, dilute LiFSI/DMC electrolyte, super concentrated LiFSI/DMC electrolyte, and 1.2MLiFSI/DMC-BTFE (1: 2).

Fig. 14 is a graph of conductivity versus temperature for a conventional electrolyte, a dilute LiFSI/DMC electrolyte, a super concentrated LiFSI/DMC electrolyte, and certain LSEs as disclosed herein.

Fig. 15A and 15B are graphs showing performance (voltage versus capacity) of Li | | | Li symmetric cells at varying current densities in SE of 5.5M LiFSI/DMC (fig. 15A) and LSE of 1.2M LiFSI/DMC-BTFE (1:2) (fig. 15B).

The current versus voltage curve of fig. 16 illustrates the SE of 5.5M LiFSI/DMC and the anode stability of certain LSEs as disclosed herein.

FIGS. 17A-17D are SEM images showing lithium electroplated from 1.2M LiFSI/DMC (FIGS. 17A, 17B) and 3.7M LiFSI/DMC (FIGS. 17C, 17D) onto copper substrates; FIGS. 17A and 17C are cross-sectional views; fig. 17B and 17D are top views.

Fig. 18A-18D show the electrochemical behavior of Li | | | NMC cells with different electrolytes. Fig. 18A shows cycling stability and coulombic efficiency. FIGS. 18B-18D show LiPF at 1.0M₆/EC-EMC (FIG. 18B), 5.5M LiFSI/DMC (FIG. 18C) and 1.2M LiFSI/DTypical voltage profiles in MC-BTFE (1:2) (FIG. 18D).

Fig. 19 shows rate performance of Li | | | NMC cells using different electrolytes; the battery was charged at a constant C/5 rate, but discharged at an increasing C rate; 1C 2.0mA/cm²。

Figure 20 shows rate performance of Li | | | NMC cells using different electrolytes; the battery was discharged at a constant C/5 rate, but charged at an increasing C rate; 1C 2.0mA/cm²。

Fig. 21A-21F are SEM images showing the morphology of Li metal after plating on Cu substrates in different electrolytes. FIGS. 21A, 21C and 21E are cross-sectional views; fig. 21B, 21D, and 21F are top views of Li metal after plating on a Cu substrate. Electrolyte is 1.0M LiPF₆/EC-EMC (FIGS. 21A, 21B), 5.5M LiFSI/DMC (FIGS. 21C, 21D) and 1.2M LiFSI/DMC-BTFE (1:2) (FIGS. 21E, 21F).

FIGS. 22A-22C are graphs showing that²(FIG. 22A), 5mA/cm²(FIG. 22B) and 10mA/cm²(FIG. 22C) SEM image of the morphology of Li metal after electroplating on Cu substrate in 1.2M LiFSI/DMC-BTFE (1:2) at current density.

FIG. 23 shows the measurement at 1mAh cm^-2At a Li deposition area capacity of 0.5mA cm^-2The Coulombic Efficiency (CE) of Li | | | Cu cells tested below using concentrated LiFSI/DME electrolyte and electrolyte with TTE or BTFE diluent varied with cycle number.

FIG. 24 shows Li | | | LiFePO with concentrated 4M LiFSI/DME electrolyte without and with TTE or BTFE diluent after 3 formation cycles with C/10 over a voltage range of 2.5-3.7V₄(LFP) cycling stability of the cell at 1C rate.

FIGS. 25A and 25B show the difference between 1.3mAh cm^-2At a Na deposition area capacity of 0.26mA cm^-2After 2 formation cycles at 0.65mA cm^-2Initial Na deposition/peel voltage curves (fig. 25A) and CE as a function of cycle number for the Na | | | Cu cells tested below (fig. 25B).

FIGS. 26A and 26B show Na I Na at C/3 with super concentrated NaFSI/DME electrolyte and LSE with TTE diluent₃V₂(PO₄)₃Initial charge/discharge voltage profile (fig. 26A) and cycling stability (fig. 26B) of the battery cell.

FIGS. 27A and 27B show Na I Na II Na III K I (FIG. 27A) and Na I Na II K I Na III K I T E (DME: TTE molar ratio 1:1) (FIG. 27B) containing 5.2M NaFSI/DME and 2.3M Na₃V₂(PO₄)₃The charge and discharge capacity of the battery cell.

FIGS. 28A and 28B show that for 5.2M NaFSI/DME, 3.1M NaFSI/DME-BTFE (1:1), 2.1M NaFSI/DME-BTFE (1:2) and 1.5M NaFSI/DME-BTFE (1:3) electrolytes at 0.2mA cm^-2After 2 formation cycles at 1mA cm^-2Initial Na deposition/peel voltage curves (fig. 28A) and CE as a function of cycle number for the Na | | | Cu cells tested below (fig. 28B). The ratio in parentheses indicates the molar ratio of DME to BTFE in the different BTFE-diluted LSEs.

FIGS. 29A-29C show Na I Na using 5.2M NaFSI/DME and BTFE-diluted NaFSI/DME-BTFE electrolyte₃V₂(PO₄)₃Electrochemical performance of the battery cell. FIG. 29A shows the initial Na plating/stripping curve; FIG. 29B shows cycling stability over 100 cycles;

FIG. 29C shows the charge and discharge capacity of NaFSI/DME-BTFE (1:1:2 in mol) over 100 cycles.

FIGS. 30A and 30B show LSE using low concentrations of 1M LiTFSI/DOL-DME, 3.3M concentrated LiTFSI/DOL-DME electrolyte, 1.06M LiTFSI/DOL-DME-TTE electrolyte at 1mAh cm^-2At a Li deposition area capacity of 0.2mAcm^-2After 2 formation cycles at 1mA cm^-2Initial Li deposition/peel voltage curves (fig. 30A) and CE versus cycle number for the Li | | | Cu cells tested below (fig. 30B).

FIGS. 31A-31C show the electrochemical performance of Li-S cells containing low concentrations of 1M LiTFSI/DOL-DME, 3.3M concentrated LiTFSI/DOL-DME electrolyte, and 1.06M LiTFSI/DOL-DME-TTE electrolyte; FIG. 31A is an initial charge/discharge voltage curve, FIG. 31B is the cycling performance, and FIG. 31C is shown at 0.1C (168mA g^-1) The CE of the Li-S cells evaluated below varied with cycle number.

FIG. 32 shows that.1mA cm^-2At a current density of 600mAh g^-1Limited discharge capacity of Li-O using LiTFSI-3DMSO (dimethyl sulfoxide) (2.76M) and LiTFSI-3DMSO-3TTE (1.23M) electrolytes₂Charge/discharge curves of the battery cells.

FIG. 33 shows the signal at 10mV s^-1With a stainless steel working and counter electrode and Ag/AgCl as reference electrode, the cyclic voltammograms of the aqueous electrolyte were concentrated before and after dilution with TTE with the aid of different "bridge" solvents (acetonitrile (AN), dimethyl carbonate (DMC), Propylene Carbonate (PC) and DMSO). Potential conversion to Li/Li⁺The potential of the redox couple.

Figures 34A and 34B show cyclic voltammograms of the first and second cycles, respectively, of diluting a concentrated aqueous electrolyte with different amounts of TTE with the aid of PC. Stainless steel is used as a working electrode and a counter electrode, and Ag/AgCl is used as a reference electrode. The scanning rate is 10mV s^-1. Potential conversion to Li/Li⁺The potential of the redox couple.

Fig. 35 shows the molecules of DMC and BTFE solvents, LiFSI salts, and the optimized molecular structures of DMC + LiFSI and BTFE + LiFSI solvent-salt pairs. Li, O, C, H, S, N and F atoms are magenta, red, gray, white, yellow, blue and light blue, respectively.

Fig. 36A-36F are molecular models showing the absorption of the solvent's molecular DMC (fig. 36A) and BTFE (fig. 36B), LiFSI salt (fig. 36C), and DMC-LiFSI solvent-salt pairs (fig. 36D-36F) on the lithium (100) anode surface. The top and bottom views in each pair are top and side views respectively.

FIGS. 37A-37C are molecular models of electrolyte/salt mixtures simulated from AIMD at 303K: 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 ratio in parentheses represents the molar ratio LiFSI to DMC to BTFE.

FIG. 38 is Li-O calculated from AIMD simulated orbitals at 303K_DMCAnd Li-O_BTFEGraph of radial distribution function of pairs.

FIGS. 39A and 39B are pure DMC solvent, pure BTFE solvent and DMC-Raman spectrum of BTFE solvent mixture (2: 1); FIG. 39B is the 200 cm-2000 plot of FIG. 39A^-1Enlargement in the wavenumber range.

FIGS. 40A and 40B are Raman spectra of different concentrations of LiFSI/DMC solutions (FIG. 40A) and different concentrations of BTFE-diluted LiFSI/DMC-BTFE solutions (FIG. 40B).

FIG. 41 is a graph showing the viscosity as the reciprocal (η)^-1) Between the plotted samples, Li⁺、FSI^-And the diffusion coefficient (D) of the molecules of the solvent (DMC and BTFE) at 30 ℃ is represented by a star. The bar indicates the presence of the following from left to right: BTFE, DMC, Li, FSI.

FIG. 42 shows the diffusion ratios of BTFE, Li and FSI in DMC at 30 ℃: d_BTFE/D_DMC、D_Li/D_DMCAnd D_FSI/D_DMC。

Fig. 43A-43C are graphs showing projected state density (PDOS) on the surface of lithium anode of dilute electrolyte (LiFSI/DMC, molar ratio of LiFSI: DMC 1:2) (fig. 43A), super concentrated electrolyte (5.5M LiFSI/DMC, molar ratio of LiFSI: DMC 1:1) (fig. 43B) and BTFE-diluted electrolyte (LiFSI/DMC-BTFE, molar ratio of LiFSI: DMC: BTFE 1:2:4) (fig. 43C).

FIGS. 44A-44D show Raman spectra (FIG. 44A) of pure triethylphosphate (TEPa) solvent, 3.2M LiFSI: TEPa (E37), and different concentrations of BTFE-diluted LiFSI: TEPa electrolyte (E38-E40); FIGS. 44B-44C are magnified images of the wavenumber range from the full spectrum.

FIG. 45 is a graph showing coulombic efficiency as a function of cycle number for 3.8M LiFSL: TEPa (E37), 1.5M LiFSI: TEPa: BTFE (E39), and 1.2M LiFSI: TEPa: BTFE (E40). At 1mAh cm^-2At a Li deposition area capacity of 0.5mA cm^-2The next cycle is performed.

FIG. 46 is a graph showing Li | | | NCA (LiNi) with concentrated LiFSI/TEPa electrolyte without (E37) and with BTFE diluents (E39 and E40)_0.6Mn_0.2Co_0.1O₂The area capacity load is 1.5mAh/cm²) Cycling stability of the cell at C/3 rate, 4.4V charge cutoff.

FIG. 47 is a graph showing LiFSI containing a concentrateLi | NCA (LiNi) for TEPa electrolyte and BTFE diluent (E40)_0.85Co_0.1Al_0.05O₂The area capacity load is 1.8mAh/cm²) Cycling stability of the cell at C/3 rate, 4.4V charge cutoff.

FIG. 48 is a graph showing Li | | | LCO (LiCoO) containing concentrated LiFSI/TEPa electrolyte and BTFE diluent (E39 and E40)₂The area capacity load is 2.2mAh/cm²) Cycling stability of the cell at C/5 and 1C discharge rates, 4.35V charge cutoff.

FIG. 49 is a graph showing Coulomb efficiency as a function of cycle number at 0.5mA cm for a Li | | | Cu cell using LSE diluted with TTE for LiFSI/TEPa-TTE (E41-E43)^-2The lower test has 1mAh cm^-2The lithium area of (a) is deposited with a capacity of Li | | | Cu cell.

FIG. 50 is a graph showing Li | | | NMC (LiNi) containing TTE diluted concentrated LiFSI/TEPa (E43) electrolyte_0.6Mn_0.2Co_0.2O₂The area capacity load is 1.5mAh/cm²) Cycling stability of the cell at C/3 rate, 4.4V charge cutoff.

FIGS. 51A and 51B show Li plating/stripping curves for Li | | | Cu cells using concentrated 4.1M LiFSI/TMPa (E44) (51A) and 1.8M LiFSI/TMPa-BTFE (1:2 in moles) (E45) (51B).

FIG. 52 is a graph showing Li | | | NMC (LiNi) containing BTFE diluted concentrated LiFSI/TMPa (E45) electrolyte_0.6Mn_0.6Co_0.2O₂The area capacity load is 1.5mAh/cm²) Cycling stability at C/3 rate, 4.4V charge cutoff.

FIGS. 53A and 53B show lithium plating/stripping curves for Li | | | Cu cells using 1.6M LiFSI/TMPa-DMC-BTFE (1:1:4 in moles) (E46) (53A) and 1.2M LiFSI/TMPa-DMC-BTFE (1:1:6 in moles) (E47) (53B).

FIG. 54 is a graph showing Li | | | NMC (LiNi) for LSE containing LiFSI/TMPa-DMC-BTFE (E46 and E47) electrolytes_0.6Co_0.2O₂The area capacity load is 1.5mAh/cm²) C/3 rate of battery unitCycling stability at 4.4V charge cutoff.

FIG. 55 is a graph showing the cycling stability of a Li | NMC811 cell with an LSE containing LiFSI-0.3TEPa-0.9DME at C/3 rate and 2.8-4.4V voltage.

FIG. 56 is a graph showing the cycling stability at C/3 rate, 2.8-4.4V voltage of a Li | | | NMC811 cell containing an LSE of LiFSI-0.8TEPa-0.4DME-3 TTE.

Detailed Description

The safety of lithium ion batteries has been a high concern since they contain highly flammable organic electrolytes, which can lead to fires and even explosions in the event of overcharge, overheating, internal short circuits, and/or mechanical damage. Safety concerns also apply to any electrochemical device comprising a flammable electrolyte.

Super concentrated electrolytes (also referred to as high concentration electrolytes) including flammable solvents, such as concentrated LiFSI/DME or concentrated LiFSI/DMC, can achieve high Coulombic Efficiency (CE) operation of lithium metal anodes and/or reversible insertion of lithium ions into graphite anodes due to the presence of free solvent molecules that are reduced and/or the formation of stable SEI layers compared to more dilute electrolytes. The term "super-concentrated" (or high concentration) as used herein means that the concentration of active salt is at least 3M. A super-concentrated electrolyte comprising a flame-retardant solvent may be an effective method for stabilizing these compounds at low potential and capable of forming a stable SEI layer on a graphite anode. However, these super concentrated electrolytes suffer from the above safety risks, high cost, high viscosity and/or poor wetting of the separator and thick cathode electrodes, hindering their practical use. However, many of the flame retardant solvents suggested for improving safety are unstable at low potential (e.g., they react with lithium metal) and/or cannot effectively form a stable Solid Electrolyte Interface (SEI) layer on the anode (e.g., they may destroy the layered structure of the graphite anode), thereby hindering their practical application.

Embodiments of low flammability and non-flammability topical super concentrated electrolytes (LSEs) are disclosed. Certain embodiments of the disclosed low-flammability and non-flammable LSEs are stable in electrochemical cells having alkali metal, alkaline earth metal, or carbon-based (e.g., graphite) anodes and various cathode materials. The LSE comprises 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. Advantageously, in certain embodiments, the electrochemical devices disclosed herein comprising a low flammable or non-flammable electrolyte perform comparably to electrochemical devices comprising flammable electrolytes containing the same active salt. In certain embodiments, the concentration of the active salt is reduced by adding a diluent without significantly increasing the flammability and/or reducing the performance of an electrochemical device comprising a low flammable or non-flammable LSE. In certain embodiments, the performance of an electrochemical device comprising a low-flammable or non-flammable LSE is enhanced compared to a similar LSE that does not comprise a flame retardant compound.

I. Definitions and abbreviations

The following explanations and abbreviations are provided to better describe the present invention and to guide those of ordinary skill in the art in the practice of the present invention. As used herein, the term "comprising" means "including" and the singular forms "a/an" and "the" include plural referents unless the context clearly dictates otherwise. The term "or" refers to a single element or a combination of two or more elements of the described optional elements, unless the context clearly dictates otherwise.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present disclosure, suitable methods and materials are described below. The materials, methods, and examples are illustrative only and not intended to be limiting. Other features of the present disclosure will be apparent from the following detailed description and from the claims.

Unless otherwise indicated, all numbers expressing quantities of ingredients, molecular weights, molar concentrations, voltages, capacities, and so forth, used in the specification or claims are to be understood as being modified by the term "about. Accordingly, unless otherwise indicated implicitly or explicitly or unless otherwise clearly understood by those skilled in the art that the context has a more explicit interpretation, the numerical parameters set forth are approximations that may depend upon the desired properties sought and/or the detection limits under standard test conditions/methods as known to those skilled in the art. In embodiments that are directly and unequivocally distinguishable from the prior art, the embodiment values are not approximations unless the word "about" is recited.

Notwithstanding the existence of alternatives for various components, parameters, operating conditions, etc., recited herein, it is not intended that such alternatives be necessarily equivalent and/or equally effective. Nor does it imply that the alternatives are listed in a preferred order unless otherwise indicated.

Definitions of terms commonly used in chemistry can be found in Richard J.Lewis, Sr. (ed.), Hawley's Condensed Chemical Dictionary, published by John Wiley & Sons, Inc.,1997(ISBN 0-471-.

To facilitate reading of the various embodiments of the present disclosure, an explanation of the following specific terms is provided:

active salt: the term "active salt" as used herein refers to a salt that participates significantly in the electrochemical process of an electrochemical device. In the case of batteries, it refers to the charging and discharging processes that contribute to energy conversion, ultimately enabling the battery to transfer/store energy. The term "active salt" as used herein refers to a salt that, after initial charging, makes up at least 5% of the redox active material participating in the redox reaction during battery cycling.

AN: acetonitrile

Anode: the charge flows into the electrodes of the polarized electronic device. From an electrochemical point of view, negatively charged anions move towards the anode, and/or positively charged cations move away from the anode to balance the electrons exiting through the external circuit. In a discharge cell or galvanic cell, the anode is the negative end from which electrons flow. If the anode is comprised of a metal, electrons to the external circuit are accompanied by metal cations that move away from the electrode and into the electrolyte. When the battery is charged, the anode becomes the positive terminal into which electrons flow and metal cations are reduced.

Association: the term "associate" as used herein refers to coordination or solvation. For example, a cation associated with a solvent molecule coordinates or is solvated by the solvent molecule. Solvation is the attraction of solvent molecules to molecules or ions of the 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 means that one or more coordination bonds are formed between the lone pair of electrons of the cation and the solvent atom. Coordination bonds may also be formed between cations and anions of the solute.

Bridge solvent: a solvent having an amphiphilic molecule with a polar end or portion and a non-polar end or portion.

BTFE: bis (2,2, 2-trifluoroethyl) ether

Capacity: the capacity of a battery is the amount of charge that the battery can deliver. Capacity is typically expressed in mAh or Ah units and represents the maximum constant current that a battery can produce over an hour of time. For example, a battery with a capacity of 100mAh may deliver 100mA for one hour or 5mA for 20 hours. Area capacity (area capacity) or specific area capacity is the capacity per unit area of the electrode (or active material) surface, and is typically in mAh cm^-2Expressed in units.

Cathode: the charge flows out of the electrodes of the polarized electronic device. From an electrochemical point of view, positively charged cations move towards the cathode, and/or negatively charged anions move away from the cathode to balance electrons from an external circuit. In a discharge cell or galvanic cell, the cathode is the positive terminal facing the direction of conventional current flow. This outward charge is carried internally by positive ions moving from the electrolyte to the positively charged cathode, where they can be reduced. When the battery is charged, the cathode becomes a negative terminal where electrons flow out and metal atoms (or cations) are oxidized.

Battery cell (cell): as used herein, a battery cell refers to an electrochemical device for generating a voltage or current from a chemical reaction, or conversely inducing a chemical reaction from a current. Examples include voltaic cells, electrolyte cells, fuel cells, and the like, among others. A battery (battery) includes one or more battery cells. The terms "cell" and "battery" are used interchangeably when referring to a battery containing only one cell.

Button cell (coin cell): small, generally circular cells. Button cells are characterized by their diameter and thickness.

Conversion of the compound: a compound comprising one or more cations that are substituted with another metal upon discharge of the battery. For example, when iron (II) selenide (FeSe) is used as the cathode material, Fe is replaced by Na during Na cell discharge:

cosolvent: a solvent that dissolves the solute together with another solvent.

Coulomb Efficiency (CE): efficiency of transferring charge in a system for facilitating electrochemical reactions. CE may be defined as the amount of charge leaving the battery during a discharge cycle divided by the amount of charge entering the battery during a charge cycle. The CE of a Li Cu or Na Cu cell may be defined as the amount of charge that flows out of the cell during the stripping process divided by the amount of charge that enters the cell during the plating process.

DEC: carbonic acid diethyl ester

DMC: carbonic acid dimethyl ester

DME: 1, 2-dimethoxyethane

DMS: dimethyl sulfone

DMSO, DMSO: dimethyl sulfoxide

DOL: 1, 3-dioxolanes

Number of donors: a quantitative measure of Lewis alkalinity, such as the ability of a solvent to solvate cations. The donor number is defined as the number of donors in dilute 1, 2-dichloroethane solution with 0 donor number in Lewis base and SbCl₅A negative enthalpy value of the 1:1 adduct is formed therebetween. The donor number is usually reported in kcal/mol. For example, acetonitrile has a donor number of 14.1 kcal/mol. As another example, dimethyl sulfoxide has a donor number of 29.8 kcal/mol.

EC: ethylene carbonate

Electrolyte: a free ion-containing substance that acts as a conductive medium. The electrolyte typically comprises ions in solution, but molten electrolytes and solid electrolytes are also known.

EMC: carbonic acid methyl ethyl ester

EMS: ethyl methyl sulfone

EOFB: ethoxy nonafluorobutane

EVS: ethylvinylsulfone

FEC: fluoroethylene carbonate

Flame retardant: as used herein, the term "flame retardant" refers to an agent that is incorporated into an electrolyte to reduce or eliminate the tendency of the electrolyte to ignite during operation of an electrochemical device comprising the electrolyte.

Inflammable: the term "combustible" refers to materials that readily ignite and rapidly combust. As used herein, the term "non-flammable" means that the electrolyte will not ignite or burn during operation of the electrochemical device comprising the electrolyte. As used herein, the terms "flame retardant" and "low flammability" are interchangeable and mean that a portion of the electrolyte may ignite under certain conditions, but any resulting ignition does not propagate throughout the electrolyte. Flammability can be measured by determining the self-extinguishing time (SET) of the electrolyte. SET was determined by a modified Underwriters Laboratories test standard 94 HB. The electrolyte is fixed on an inert spherical wick, for example a spherical wick of about 0.3-0.5cm in diameter, which is capable of absorbing 0.05-0.10g of electrolyte. The wick was then lit and the time at which the flame extinguished was recorded. Time was normalized to sample weight. If the electrolyte is not on fire, SET is zero and the electrolyte is not flammable. Electrolytes with SET <6s/g (e.g., flame extinguished within about 0.5 s) are also considered nonflammable. If SET >20s/g, the electrolyte is considered flammable. When SET is between 6-20s/g, the electrolyte is considered flame retardant or has low flammability.

Immiscible: this term describes two substances of the same substance morphology that cannot be uniformly mixed or blended. Oil and water are common examples of two immiscible liquids.

Embedding: the term refers to a material (E.g., ions or molecules) are inserted into the microstructure of another material. For example, lithium ions can be intercalated or intercalated into graphite (C) to form lithiated graphite (LiC)₆)。

KFSI: bis (fluorosulfonyl) imide potassium salt

KTFSI: bis (trifluoromethanesulfonyl) imide potassium salt

LiBETI: lithium bis (pentafluoroethanesulfonyl) imide

LiFSI: lithium bis (fluorosulfonyl) imide

And (3) LiTFSI: lithium bis (trifluoromethanesulfonyl) imide

And (3) LiBOB: lithium bis (oxalato) borate

LiDFOB: lithium difluoro (oxalato) borate anion

LSE: local super-concentrated electrolyte

And MEC: methylene ethylene carbonate

MOFB: methoxy nonafluorobutane

NaFSI: bis (fluorosulfonyl) imide sodium salt

NaTFSI: bis (trifluoromethylsulfonyl) imide sodium salt

NaBOB: sodium bis (oxalato) borate

Organic phosphorus compounds: organic compounds containing phosphorus

PC: propylene carbonate

Phosphate ester: as used herein, phosphate refers to a compound having the general formula P (═ O) (OR)₃Wherein each R is independently an alkyl group (e.g., C)₁-C₁₀Alkyl) or aryl. Each alkyl or aryl group may be substituted or unsubstituted.

Phosphite ester: as used herein, phosphite refers to a compound having the general formula P (OR)₃Or HP (O) (OR)₂Wherein each R is independently alkyl (e.g., C)₁-C₁₀Alkyl) or aryl. Each alkyl or aryl group may be substituted or unsubstituted.

Phosphonate ester: having the formula P (═ O) (OR)₂(R ') wherein each R and R' is independently alkyl (e.g., C)₁-C₁₀Alkyl) or aryl. Each alkyl radical orThe aryl group may be substituted or unsubstituted.

Phosphoramide: having the formula P (═ O) (NR)₂)₃Wherein each R is independently hydrogen, alkyl (e.g., C)₁-C₁₀Alkyl) or alkoxy (e.g. C)₁-C₁₀Alkoxy groups). 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 a nitrogen-containing group through a double bond and to three other atoms or groups through single bonds.

SEI: solid electrolyte interface (solid electrolyte interface)

A diaphragm: the battery separator is a porous sheet or membrane located between the anode and cathode. It prevents physical contact between the anode and cathode while facilitating ion transport.

Dissolving: can be dispersed in a solvent in molecular or ionic form to form a homogeneous solution. The term "soluble" as used herein means that the active salt has a solubility in a given solvent of at least 1mol/L (M, molar concentration) or at least 1mol/kg (M, molar mass concentration).

Solution: a homogeneous mixture consisting of two or more substances. The solute (minor component) is dissolved in the solvent (major component). Multiple solutes and/or multiple solvents can be present in the solution.

And (3) super-concentration: the term "super concentrated electrolyte" as used herein refers to an electrolyte having a salt concentration of at least 3M.

TEPa: phosphoric acid triethyl ester

TFTFE: 1,1,2, 2-tetrafluoroethyl-2, 2, 2-trifluoroethyl ether

TMPa: phosphoric acid trimethyl ester

TMS: tetramethylene sulfone or sulfolane

TTE: 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether

VC: vinylene carbonate

VEC: 4-vinyl-1, 3-dioxolan-2-one or ethylene carbonate

Partially hyperconcentrated electrolytes with low or non-flammability

Conventional super concentrated electrolytes comprise a solvent and a salt, wherein the salt concentration is at least 3M. Some super concentrated electrolytes have a salt concentration of at least 4M or at least 5M. In certain instances, the molar mass concentration of the salt can be as high as 20m or greater, e.g., aqueous LiTFSI. Fig. 1 is a schematic view of a conventional super concentrated electrolyte comprising a solvent and a lithium salt. Ideally, all or most of the molecules of the solvent associate with the lithium cations in the super concentrated electrolyte. The reduced presence of free, unassociated solvent molecules increases the Coulombic Efficiency (CE) of the lithium metal anode, promotes the formation of a stable SEI layer, and/or increases the cycling stability of a battery including the electrolyte. However, most organic based super concentrated electrolytes suffer from drawbacks such as flammability, high material cost, high viscosity, and/or poor wetting of the battery separator and/or cathode. While dilution with another solvent may address one or more of the disadvantages, dilution produces free solvent molecules and often reduces CE, prevents the formation of a stable SEI layer, and/or reduces the cycling stability of the battery.

Certain embodiments of the disclosed low-flammability or non-flammable "localized super concentrated electrolytes" (LSEs) comprising a salt, a solvent comprising a flame retardant compound, wherein the salt is soluble in the solvent, and a diluent in which the salt is insoluble or poorly soluble may address some or all of the problems discussed above. Fig. 2 is a schematic of an exemplary LSE comprising 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. As shown in fig. 2, after the diluent is added, the lithium ions remain associated with the molecules of the solvent. The anion is also in proximity to or associated with the lithium ion. Thus, localized regions of solvent-cation-anion aggregates are formed. In contrast, lithium ions and anions are not associated with molecules of the diluent, which remain free in solution. Evidence of this electrolyte structure for molecules with locally concentrated salt/solvent regions and free diluent can be seen by raman spectroscopy (see, e.g., example 10, fig. 39A-B, 40A-B), NMR characterization, and Molecular Dynamics (MD) simulations. Therefore, although the solution as a whole is less concentrated than the solution of fig. 1, a local region of high concentration is present when lithium cations are associated with the molecules of the solvent. There are few or no molecules of free solvent in the diluted electrolyte, thereby providing the benefits of a super concentrated electrolyte without the associated disadvantages.

Embodiments of the disclosed low-flammability or non-flammable localized super concentrated electrolytes (LSEs) 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. As used herein, "poorly soluble" means that the solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent a. As used herein, "consisting essentially of … …" means that the electrolyte does not include any components that would substantially affect the performance of the electrolyte. For example, LSE does not include any electrochemically active components (i.e., components (elements, ions, or compounds) capable of forming redox pairs having different oxidation and reduction states, such as ionic species or metal cations having different oxidation states and their corresponding neutral metal atoms) other than active salts in amounts sufficient to affect electrolyte performance, and does not include solvents in which the active salts are soluble.

In some embodiments, solvent a further comprises a co-solvent, such as a flammable or non-flammable organic solvent, wherein the co-solvent has a different composition than the flame retardant compound. The amount of flame retardant compound in solvent a is sufficient to render the electrolyte flame retardant (low flammability) or nonflammable. In any or all embodiments, a low-flammable or non-flammable LSE may include at least 5 wt.% of the flame retardant compound.

The solubility of the active salt in solvent a (in the absence of a diluent) may be greater than 3M, such as at least 4M or at least 5M. In some embodiments, the solubility and/or concentration of the active salt in solvent a is in a range from 3M to 10M, such as 3M to 8M, 4M to 8M, or 5M to 8M. In certain embodiments, the concentration may be expressed in terms of molal concentration, and the concentration of the active salt in solvent a (in the absence of diluent) may be in the range of 3M to 25M, such as 5M to 21M or 10M to 21M. In contrast, the molar or molar concentration of the active salt in the entire low flammable or nonflammable electrolyte (salt, solvent a, and diluent) may be at least 20% less than the molar or molar concentration of the active salt in 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 molar concentration of the active salt in solvent a. For example, the molar or molar 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 molar concentration of the active salt in solvent a. In some embodiments, the molar concentration of the active salt in the electrolyte is in the range of 0.5M to 3M, 0.5M to 2M, 0.75M to 2M, or 0.75M to 1.5M.

An active salt is a salt or combination of salts that participate in the charging and discharging process of a battery cell that includes a low or non-flammable electrolyte. The active salt comprises cations capable of forming a redox pair having different oxidation and reduction states, such as ionic species or metal cations having different oxidation states and their corresponding neutral metal atoms. In some embodiments, the active salt is an alkali metal salt, an alkaline earth metal salt, or any combination thereof. The active salt can 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. Advantageously, the active salt is stable to alkali or alkaline earth metal anodes. Exemplary salts include, but are not limited to, LiFSI, LiTFSI, LiBETI, NaFSI, NaTFSI, LiBOB, sodium bis (oxalato) borate (NaBOB), LiPF₆、LiAsF₆、LiBF₄、LiCF₃SO₃、LiClO₄、LiDFOB、LiI、LiBr、LiCl、LiSCN、LiNO₃、Li₂SO₄And combinations thereof. In some embodiments, the salt is LiFSI, LiTFSI, LiBETI, NaFSI, NaTFSI, or any combination thereof.

The low flammable or non-flammable solvent a comprises, consists essentially of, or consists of a flame retardant compound. In some embodiments, the flame retardant compound is a liquid at ambient temperature (e.g., 20-25 ℃). Suitable flame retardant compounds include, but are not limited to, phosphorus-containing compounds. In some embodiments, the flame retardant compound comprises one or more organophosphorus compounds (e.g., organophosphates, phosphites, phosphonates, phosphoramides), phosphazenes, or any combination thereof. 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, for example, 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) methyl phosphonate, hexamethylphosphoramide, hexamethoxyphosphazene (cyclotris (dimethoxyphosphazene), hexamethoxycyclotriphosphazene, hexafluorophosphazene (hexafluorotriphosphazene), and combinations thereof 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.

In any or all embodiments, solvent a may further comprise a co-solvent. Advantageously, the co-solvent is miscible with the flame retardant compound and/or the active salt is soluble in the flame retardant compound and the co-solvent. Suitable co-solvents include, but are not limited to, certain carbonate solvents, ether solvents, dimethyl sulfoxide, water, and mixtures thereof. Exemplary co-solvents include DME, DOL, allyl ether, DMC, EMC, DEC, EC, PC, VC, FEC, VEC, MEC, DMSO, DMS, EMS, EVS, TMS (also known as sulfolane), FMES, FMIS, FPMS, methyl butyrate, ethyl propionate, gamma-butyrolactone, acetonitrile, triallylamine, triallylcyanurate, triallylisocyanurate, water, and combinations thereof. In some embodiments, the co-solvent is non-aqueous. In certain embodiments, the co-solvent comprises DME, DOL, DMC, EMC, or a combination thereof. In one embodiment, the co-solvent is DMC, DME, DOL, or a combination thereof. In one embodiment, the co-solvent is DMC. In another embodiment, the cosolvent is DME. In another embodiment, the co-solvent is a combination of DME and DOL. In another embodiment, the co-solvent is EMC. When solvent a further comprises a flammable co-solvent, the amount of flame retardant in solvent a is sufficient to maintain low or non-flammability of the solvent. Such amounts can be determined by one of ordinary skill in the art having the benefit of reading the present disclosure and depend on the co-solvent selected and the amount.

In some embodiments, solvent a comprises, consists essentially of, or consists of a flame retardant compound. In one embodiment, solvent a comprises, consists essentially of, or consists of a flame retardant compound and a co-solvent. As used herein, "consisting essentially of … …" means that solvent a does not include any electrochemically active components sufficient to affect the performance of the electrolyte that includes solvent a.

Solvent a is associated (e.g., solvated or complexed) with the cation of the active salt or salt mixture. When prepared as a super concentrated electrolyte comprising an active salt and solvent a, solvent-cation-anion aggregates are formed. In contrast to conventional electrolytes containing flame retardant compounds, some embodiments of the disclosed low-flammability or non-flammable hyperconcentrated electrolytes are stable to anodes (e.g., metal or carbon based anodes or silicon based anodes), cathodes (including ion intercalation and conversion compounds), separators (e.g., polyolefins), and current collectors (e.g., Cu, Al), which are not stable when lower concentrations of electrolyte are used and/or other solvents are used. As used herein, "stable" means that the electrolyte has negligible chemical and electrochemical reaction with the anode, cathode, separator and current collector. In some embodiments, stability enables battery operation to achieve high coulombic efficiencies, e.g.,>98 percent. In addition, in contrast to conventional low or non-flammable electrolytes,some embodiments of the disclosed LSEs do not undergo significant decomposition of the flame retardant compounds during operation of electrochemical devices comprising low or non-flammable LSEs. As used herein, significant decomposition of the flame retardant compound refers to decomposition of the flame retardant at the anode or cathode during operation of the electrochemical device including LSE, thereby measurably reducing the performance of the electrolyte and/or causing failure of the electrochemical device including the electrolyte in repeated cycling. For example, it has been found that in certain electrolytes, such as 1M LiPF in EC/EMC₆Even a small amount (5 wt%) of TMPa contained may cause reductive decomposition of TMPa at the graphite anode surface and intercalation of TMPa into the graphite anode, leading to capacity fade and/or electrochemical device failure.

As discussed previously, in a super concentrated electrolyte, it is advantageous to have few, substantially no, or no molecules of free solvent, i.e., solvent molecules that are not associated with the cations of the active salt or salt mixture. The concentration of the active salt may be selected to minimize the number of free solvent a molecules in the electrolyte. The molar ratio of active salt to solvent a may be other than 1:1, since the cation of each active salt may associate with more than one a molecule of solvent and/or since the cation of each solvent a may associate with more than one cation of active salt. In some embodiments, the molar ratio of active salt to solvent a (moles of salt/moles of solvent a) is in the range of 0.33 to 1.5, such as in the range of 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 poorly soluble, i.e., has a solubility at least 10 times less than the solubility of the active salt in solvent a. For example, if the salt has a solubility of 5M in solvent a, the diluent is selected such that the salt has a solubility of less than 0.5M in the diluent. In some embodiments, the solubility of the active salt in solvent a is at least 10-fold, at least 15-fold, at least 20-fold, at least 25-fold, at least 30-fold, at least 40-fold, or at least 50-fold greater than the solubility of the active salt in the diluent. The diluent is selected to be stable with the anode, cathode and current collector at low active salt concentrations (e.g., ≦ 3M) or even in the absence of active salt. In some embodiments, a diluent is selected that has a low dielectric constant (e.g., relative dielectric constant ≦ 7) and/or a low donor number (e.g., donor number ≦ 10). Advantageously, the diluent does not destroy the solvating structure of the solvent a-cation-anion aggregates and is considered inert in that it does not interact with the active salt. In other words, there is no significant coordination or association between the diluent molecule and the active salt cation. The active salt cation remains associated with the solvent a molecule. Thus, despite the dilution of the electrolyte, there are few or no free solvent a molecules present in the electrolyte.

In some embodiments, the diluent comprises an aprotic organic solvent. In certain embodiments, the diluent is a fluorinated solvent such as Hydrofluoroether (HFE) (also known as fluoroalkyl ether) with a wide electrochemical stability window (e.g., > 4.5V). HFEs advantageously have low dielectric constants, low donor numbers, reduced stability with metals of the active salt (e.g., lithium, sodium, and/or magnesium), and/or high stability to oxidation due to electron-withdrawing fluorine atoms. Exemplary fluorinated solvents include, but are not limited to, 1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE), bis (2,2, 2-trifluoroethyl) ether (BTFE), 1,2,2, -tetrafluoroethyl-2, 2, 2-trifluoroethyl ether (TFTFE), Methoxynonafluorobutane (MOFB), Ethoxynonafluorobutane (EOFB), and combinations thereof.

Inflammable:

non-flammable:

the diluent may be flammable or non-flammable. However, the electrolyte comprises a sufficient amount of a flame retardant compound, for example at least 5 wt% based on the total mass of the electrolyte, to render the electrolyte (active salt, solvent a (flame retardant and optionally co-solvent) and diluent) flame retardant or non-flammable.

In some embodiments of the disclosed low or non-flammable LSEs, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, or at least 99% of the solvent a molecules are associated (e.g., solvated or complexed) with the cations of the active salt. In certain embodiments, less than 10%, such as less than 5%, less than 4%, less than 3%, or less than 2% of the molecules of diluent are associated with the cation of the active salt. The degree of association can be quantified by any suitable means, such as by raman spectroscopy or by using NMR spectroscopy to calculate the peak intensity ratio of molecules of the solvent associated with the cation to the free solvent.

The relative amounts of solvent a (the flame retardant compound and optionally the co-solvent) and the diluent are selected to reduce the flammability of the electrolyte, reduce the material cost of the electrolyte, reduce the viscosity of the electrolyte, maintain the stability of the electrolyte against oxidation at the high voltage cathode, improve the ionic conductivity of the electrolyte, improve the wetting ability of the electrolyte, promote the formation of a stable SEI layer, or any combination thereof. In one embodiment, the molar ratio of solvent a to diluent (moles of solvent a/moles of diluent) in the low or non-flammable electrolyte is in the range of 0.2 to 5, such as in the range of 0.2 to 4, 0.2 to 3, or 0.2 to 2. In one embodiment, the volume ratio of solvent a to diluent (L solvent/L diluent) in the low flammable or non-flammable electrolyte is in the range of 0.2 to 5, such as in the range of 0.25 to 4 or 0.33 to 3. In another embodiment, the mass ratio of solvent a to diluent (g solvent/g diluent) in the low flammable or nonflammable electrolyte is in the range of 0.2 to 5, such as in the range of 0.25 to 4 or 0.33 to 3.

In some embodiments, low or non-flammable LSEs comprise at least 5% or at least 10% by weight of the flame retardant compound. In certain embodiments, a low or non-flammable LSE comprises 5 to 75 wt.% of a flame retardant compound, such as 5 to 60 wt.%, 5 to 50 wt.%, 5 to 40 wt.%, or 5 to 30 wt.%, 10 to 60 wt.%, 10 to 50 wt.%, 10 to 40 wt.%, or 10 to 30 wt.% of a flame retardant compound.

Advantageously, certain embodiments of the disclosed low or non-flammable LSEs allow significant dilution of the active salt without sacrificing electrolyte performance. In some examples, the performance of the electrolyte is improved compared to a comparable low-flammability or non-flammable super concentrated electrolyte that does not include a diluent. The behavior of the electrolyte is more closely related to the active salt concentration in solvent a due to the interaction between the cations of the active salt and the molecules of solvent a. However, due to the presence of the diluent, the active salt may have a molarity in the electrolyte that is at least 20% less than the molarity of the active salt in solvent a. In certain embodiments, 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 solvent a.

In some embodiments, the formation of cation-anion-solvent aggregates also reduces the anion of the salt (e.g., FSI)^-) So that it can form a stable SEI. As described in example 10, when LUMO of the conduction band is located at a molecule of a solvent (e.g., DMC), the molecule of the solvent is first reductively decomposed at the anode, resulting in an SEI layer rich in an organic or polymer component and poor mechanical stability, thus resulting in a rapid decrease in capacity upon cycling. In contrast, in certain embodiments of the disclosed LSEs, the anion of the salt (e.g., FSI)^-) Is lower than the lowest level conduction band of the solvent (e.g., DMC), indicates that the anion of the salt, rather than the solvent molecule, is decomposed to form a stable SEI layer rich in inorganic components (e.g., LiF, Li)₂CO₃、Li₂O, etc.) and has mechanical strength, and thus can prevent degradation of the anode during subsequent cycles.

In some embodiments, the diluent is miscible with solvent a. In other embodiments, the diluent is immiscible with solvent a, i.e., the flame retardant compound and/or the co-solvent (if present). When solvent a is immiscible with the diluent, the electrolyte may not be diluted effectively with the diluent.

Thus, in some embodiments, when the diluent is immiscible with solvent a, the low or non-flammable electrolyte further comprises a bridging solvent. The bridging solvent has a different chemical composition than solvent a or the diluent. The bridging solvent is chosen to be miscible with both solvent a (the flame retardant compound and optionally the co-solvent) and the diluent, thereby "bridging" the immiscibility of solvent a with the diluent and enhancing the actual miscibility of solvent a and the diluent. In some embodiments, the molecules of the bridging solvent are amphiphilic, including polar ends or moieties and non-polar ends or moieties, such that the molecules of the bridging solvent will associate with both the molecules of solvent a and the molecules of the diluent as shown in fig. 3, thereby improving miscibility between solvent a and the diluent. Exemplary bridging 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 (triglyme), tetraglyme (tetraglyme), and combinations thereof.

Exemplary combinations of solvents, diluents, and (in some cases) bridging solvents include TEPa-BTFE, TEPa-TTE, TMPa-BTFE, TMPa-TTE, TEPa-DMC-BTFE, TEPa-DMC-TTE, TMPa-DMC-BTFE, TEPa-DME-TTE, TEPa-EC-TTE, TMPa-DME-TTE, TMPa-EC-TTE, TMPa-TTE, EMC-BTFE, EMC-TTE, DMC-BTFE, DME-TTE, DOL-DME-TTE, DMSO-TTE, HDMC-BTFE, and so forth₂O DMC TTE、H₂O PC-TTE、H₂O-AN-TTE and H₂O-DMSO-TTE. In some embodiments, the active salt is LiFSI, LiTFSI, NaFSI, or NaTFSI.

In some examples, the active salt is LiFSI or NaFSI, the solvent is DMC, DME, EMC, or EC, and the diluent is TTE or BTFE. In certain examples, the salt is LiTFSI or NaTFSI, the solvent is DMSO or a mixture of DME and DOL, and the diluent is TTE. In another embodiment, the salt is LiTFSI or NaTFSI and the solvent is H₂O, the diluent is TTE, and the bridging 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-TTE, LiFSI/EMC-BTFE, LiFSI/EMC-TTE, LiFSI/TEPa-DME-TTE, and,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、NaFSI/EMC-BTFE、NaFSI/EMC-TTE、NaFSI/TEPa-EC-TTE、NaFSI/TEPa-DME-TTE、LiTFSI/DMSO-TTE、LiTFSI/DME-DOL-TTE、NaTFSI/DMSO-TTE、NaTFSI/DME-DOL-TTE、LiTFSI/H₂O-DMC-TTE、LiTFSI/H₂O-PC-TTE、LiTFSI/H₂O-AN-TTE、LiTFSI/H₂O-DMSO-TTE、NaTFSI/H₂O-DMC-TTE、NaTFSI/H₂O-PC-TTE、NaTFSI/H₂O-AN-TTE、NaTFSI/H₂O-DMSO-TTE. In some embodiments, the electrolyte is 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, NaFSI/TEPa-BTFE, NaFSI/TEPa-TTE, NaFSI/TMPa-BTFE, NaFSI/TEPa-DME-TTE, NaFSI/TEPa-DMC-BTFE, NaFSI/TEPa-DMC-TTE, NaFSI/TMPa-DMC-BTFE, or NaFSI/TEPa-DMC-TTE.

III. Battery

Embodiments of the disclosed low or non-flammable LSEs are suitable for use 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.

In some embodiments, a rechargeable battery comprises a low or non-flammable LSE as disclosed herein, a cathode, an anode, and optionally a separator. Fig. 4 is a schematic diagram of an exemplary embodiment of a rechargeable battery 100, the rechargeable battery 100 including a cathode 120, a separator 130 impregnated with an electrolyte (i.e., low flammable or non-flammable LSE), and an anode 140. In some embodiments, battery 100 further includes a cathode current collector 110 and/or an anode current collector 150.

The current collector may be a metal or another conductive material such as, but not limited to, nickel (Ni), copper (Cu), aluminum (Al), iron (Fe), stainless steel, or a conductive carbon material. The current collector may be a foil, foam or polymer substrate coated with a conductive material. Advantageously, the current collector is stable (i.e., does not corrode or react) when in contact with the anode or cathode and the electrolyte during the operating voltage window of the cell. The anode and cathode current collectors may be omitted if the anode or cathode, respectively, is self-supporting, for example when the anode is a metal or a free-standing film comprising intercalation materials or conversion compounds, and/or when the cathode is a self-supporting film. By "self-supporting" is meant that the membrane itself has sufficient structural integrity that the membrane can be placed in a battery without the need for a support material.

In some embodiments, the anode is a metal (e.g., lithium, sodium), intercalation material (intercalation material), or conversion compound. The intercalation material or conversion compound may be deposited onto a substrate (e.g., a current collector) or provided as a self-supporting film that typically includes 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, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, epoxy, nylon, and the like. Suitable conductive additives include, but are not limited to, carbon black, acetylene black, Ketjen black (Ketjen black), carbon fibers (e.g., vapor grown carbon fibers), 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, Mo₆S₈、TiO₂、V₂O₅、Li₄Mn₅O₁₂、Li₄Ti₅O₁₂C/S complexes and Polyacrylonitrile (PAN) -sulfur complexes. Exemplary anodes for sodium batteries include, but are not limited to, NaTi₂(PO₄)₃；TiS₂、CuS、FeS₂、NiCo₂O₄、Cu₂Se and Li_0.5Na_0.5Ti₂(PO₄)₃。

Exemplary cathodes for lithium batteries include, but are not limited to, Li-rich Li_1+wNi_xMn_yCo_zO₂(x+y+z+w＝1，0≤w≤0.25)、LiNi_xMn_yCo_zO₂(NMC，x+y+z＝1)、LiCoO₂、LiNi_0.8Co_0.15Al_0.05O₂(NCA)、LiNi_0.5Mn_1.5O₄Spinel, LiMn₂O₄(LMO)、LiFePO₄(LFP)、Li_4-xM_xTi₅O₁₂(M ═ Mg, Al, Ba, Sr or Ta; 0. ltoreq. x.ltoreq.1), MnO₂、V₂O₅、V₆O₁₃、LiV₃O₈、LiM^C1 _xM^C2 _1-xPO₄(M^C1Or M^C2Fe, Mn, Ni, Co, Cr, or Ti; x is more than or equal to 0 and less than or equal to 1), Li₃V_2-xM¹ _x(PO₄)₃(M¹Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce; x is more than or equal to 0 and less than or equal to 1), LiVPO₄F、LiM^C1 _xM^C2 _1-xO₂(M^C1And M^C2Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1), LiM^C1 _xM^C2 _yM^C3 _1-x-yO₂(M^C1、M^C2And M^C3Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1; y is more than or equal to 0 and less than or equal to 1), LiMn_2-yX_yO₄(X-Cr, Al or Fe, 0. ltoreq. y.ltoreq.1), LiNi_0.5- _yX_yMn_1.5O₄(X ═ Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0. ltoreq. y<0.5)、xLi₂MnO₃·(1-x)LiM^C1 _yM^C2 _zM^C3 _1-y-zO₂(M^C1、M^C2And M^C3Independently Mn, Ni, Co, Cr, Fe or mixtures thereof; x is 0.3-0.5; y is less than or equal to 0.5; z is less than or equal to 0.5), Li₂M²SiO₄(M²Mn, Fe or Co), Li₂M²SO₄(M²Mn, Fe or Co), LiM²SO₄F(M²Fe, Mn or Co), Li_2-x(Fe_1-yMn_y)P₂O₇(0≤y≤1)、Cr₃O₈、Cr₂O₅A carbon/sulfur composite, or an air electrode (e.g., a carbon-based electrode comprising graphitic carbon and optionally comprising a metal catalyst such as Ir, Ru, Pt, Ag, or Ag/Pd). In one embodiment, the cathode is a lithium conversion compound, such as Li₂O₂、Li₂S or LiF.

Exemplary cathodes for sodium cells include, but are not limited to, naffepo₄、Na₂FePO₄F、Na₂FeP₂O₇、Na₃V₂(PO₄)₃、Na₃V₂(PO₄)₂F₃、NaVPO₄F、NaVPOPOF、Na_1.5VOPO₄F_0.5、NaCo₂O₄、Na₂Ti₃O₇And Na_xMO₂Wherein 0.4<x ≦ 1, and M is a transition metal or a mixture of transition metals (e.g., NaCrO₂、NaCoO₂、Na_xCoO₂(0.4≤x≤0.9)、Na_2/3Ni_1/3Mn_2/3O₂、Na_2/3Fe_1/2Mn_1/2O₂、Na_2/3Ni_1/6Co_1/6Mn_2/3O₂、NaNi_1/3Fe_1/3Mn_1/3O₂、NaNi_1/ ₃Fe_1/3Co_1/3O₂、NaNi_1/2Mn_1/2O₂Prussian white simulated cathode (e.g., Na)₂MnFe(CN)₆And Na₂Fe₂(CN)₆) Prussian Blue Analog (PBA) cathode (Na)_2-xM_a[M_b(CN)₆]_1-y·nH₂O, wherein M_aAnd M_bIndependently Fe, Co, Ni or Cu, x ═ 0 to 0.2, y ═ 0 to 0.2, n ═ 1 to 10). Other sodium intercalation materials include Na₄Ti₅O₁₂、Fe₃O₄、TiO₂、Sb₂O₄Sb/C complexes, SnSb/C complexes, BiSb/C complexes and amorphous P/C complexes. In one embodiment, the cathode is sodium transitionCompounds in which sodium is substituted for another cation, e.g. FeSe, CuWO₄CuS, CuO, CuCl or CuCl₂。

Exemplary cathodes for magnesium cells include, but are not limited to, zirconium disulfide, cobalt (II, III) oxide, tungsten selenide, V₂O₅Molybdenum-vanadium oxide, stainless steel, Mo₆S₈、Mg₂Mo₆S₈、MoS₂、Mo₆S_8-ySe_y(wherein y is 0, 1 or 2), Mg_xS₃O₄(wherein 0)<x<1)、MgCoSiO₄、MgFeSiO₄、MgMnSiO₄、V₂O₅、WSe₂Sulfur, poly (2,2,6, 6-tetramethylpiperidinyloxy-4-ylmethacrylate)/graphene, MnO₂Acetylene black and carbyne polysulfides.

The separator may be a glass fiber, a porous polymer film (e.g., a polyethylene-based or polypropylene-based material) with or without a ceramic coating, or a composite (e.g., a porous film of inorganic particles and a binder). An exemplary polymer separator is

K1640 Polyethylene (PE) film. Another exemplary polymer membrane is a 2500 polypropylene membrane. Another exemplary polymer membrane is coated

3501 polypropylene film of surfactant. The separator may be impregnated with an electrolyte as disclosed herein.

In some embodiments, a battery comprises a lithium metal anode, a cathode suitable for a lithium battery as disclosed above, a separator, and a low flammable or non-flammable LSE comprising (i) an active salt selected from LiFSI, LiTFSI, or a combination thereof, (ii) an active salt selected from 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, and (iii) a diluent selected from TTE, BTFE, TFTFE, MOFB, EOFB, or any combination thereof. In certain embodiments, a battery comprises a lithium metal anode, a cathode suitable for a lithium battery as described above, a separator, and a low flammable or non-flammable 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, hexamethylphosphoramide, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof, (iii) a flame retardant compound selected from DMC, DME, hexamethylphosphoramide, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof, (iii) a low flammable or non-flammable LSE, (iii) a co-solvent of DOL, DEC, EMC, DMSO, EMS, TMS, or any combination thereof, and (iv) a diluent selected from TTE, BTFE, TFTFE, MOFB, EOFB, or any combination thereof. In certain embodiments, the flame retardant compound is trimethyl phosphate, triethyl phosphate, or a combination thereof. In certain embodiments, 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, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof. When the flame retardant compound (and/or optional co-solvent (s)) is immiscible with the diluent, the low-flammable or non-flammable LSE may further comprise a bridging solvent having a different composition than the flame retardant compound and co-solvent (if any) and different composition than the diluent, wherein the bridging solvent is miscible with the flame retardant compound, co-solvent (if any) and diluent. The bridging solvent is 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. In certain embodiments, the cathode comprises LiNi_xMn_yCo_zO₂(NMC), sulfur/carbon or air electrodes.

In some embodiments, a battery comprises a sodium metal anode, a cathode suitable for a sodium battery as disclosed above, a separator, and a low flammable or non-flammable LSE, the LSE comprises (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-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) methyl phosphonate, hexamethylphosphoramide, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof, and (iii) a diluent selected from BTFE, TTE, TFTFE, MOFB, EOFB, or any combination thereof. In certain embodiments, a battery comprises sodium metal, a cathode suitable for a lithium battery as described above, a separator, and a low flammable or non-flammable 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, hexamethylphosphoramide, hexamethoxyphosphazene, hexafluorophosphazene, or any combination thereof, (iii) a flame retardant compound selected from DMC, DME, DOL, or any combination thereof, (iii) a lithium metal salt, (iii) a co-solvent of DEC, EMC, DMSO, EMS, TMS, or any combination thereof, and (iv) a diluent selected from TTE, BTFE, TFTFE, MOFB, EOFB, or any combination thereof. In certain embodiments, the flame retardant compound is trimethyl phosphate, triethyl phosphate, or a combination thereof. In certain embodiments, 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, hexamethoxyphosphazene, hexafluorophosphazene or any combination thereof. When the flame retardant compound (and/or optional co-solvent (s)) is immiscible with the diluent, the low-flammable or non-flammable LSE may further comprise a bridging solvent having a different composition than the flame retardant compound and co-solvent (if any) and different composition than the diluent, wherein the bridging solvent is miscible with the flame retardant compound, co-solvent (if any) and diluent. The bridging solvent may be selected from acetonitrile, dimethyl carbonate, diethyl carbonate, propylene carbonate, dimethyl sulfoxide, 1, 3-dioxolane, dimethoxyethane, diglyme (bis (2-methoxyethyl) ether), triglyme (triglyme), tetraglyme (tetraglyme), or any combination thereof. In one embodiment, the cathode is Na₃V₂(PO₄)₃。

In some embodiments, a battery comprising a low flammable or non-flammable LSE as disclosed herein has equivalent or even better performance than a similar battery comprising a super concentrated electrolyte comprising a flame retardant compound. For example, a cell comprising a low-flammable or non-flammable LSE may have a larger or equivalent CE than a similar cell comprising a low-flammable or non-flammable concentrated electrolyte. In some embodiments, the battery has a CE of greater than or equal to 95%, such as greater than or equal to 96%, greater than or equal to 97%, greater than or equal to 98%, greater than or equal to 99%, or even greater than or equal to 99.5%. The battery may also have a greater discharge capacity and/or cycle stability compared to batteries including a low flammable or non-flammable hyperconcentrated electrolyte. In some embodiments, low or non-flammable LSEs provide for high current densities (e.g., 0.5-10mAcm @)^-2) There was no dendritic plating on the anode, CE was greater than 99%. Embodiments of batteries comprising low-flammability or non-flammable LSEs as disclosed herein exhibit stability over 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 cyclesAs evidenced, for example, by stable CE and/or specific capacity. For example, the cell may exhibit 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. In addition, the synergistic effect resulting from the lower viscosity and higher electrical conductivity of the disclosed low-flammability and non-flammable LSEs also contributes to the excellent electrochemical performance of electrochemical devices, including certain embodiments of the disclosed low-flammability and non-flammable LSEs.

In one embodiment, Li | | Cu cells comprising an electrolyte comprising 1.2-1.5M LiFSI: TEPa: BTFE demonstrated comparable or higher coulombic efficiencies than electrolytes comprising 3.2M LiFSI/TEPa (example 11, fig. 45). Li | | | NMC cells using BTFE diluted electrolyte had higher discharge capacity and better cycling stability compared to 3.2M LiFSI/TEPa electrolyte (example 11, fig. 46). Similar results were found with LiFSI: TEPa: TTE electrolyte (example 12, FIG. 49, FIG. 50). LiFSI: TMPa: BTFE electrolyte (99.2%) provided higher coulombic efficiency than 4.1M LiFSI/TMPa electrolyte (98.5%) (example 13, FIGS. 51A-51B), and exhibited high capacity, good cycling stability, and high efficiency (example 13, FIG. 52). Electrolytes containing co-solvents (i.e., LiFSI: TMPa: DMC: BTFE) provide coulombic efficiencies > 99.3% in Li | | Cu cells.

In summary, certain embodiments of the disclosed low or non-flammable LSEs are safer, cost-effective than conventional flammable electrolytes, capable of dendrite-free electroplating, provide high CE, and/or greatly enhance rapid charging and/or stable cycling of the battery. Without wishing to be bound by a particular theory of operation, certain embodiments of the disclosed low flammable and non-flammable LSEs have the advantage of not destroying localized salt/solvent high concentration solvated structures due to the "inert" nature of the hydrofluoroether diluent, but play an important role in improving the interfacial stability of the metal anode. This superior performance is even more excellent than that achievable with low flammability or nonflammable hyperconcentrated electrolytes (e.g., 4.1M LiFSI: TEPa or 4.1M LiFSI: TMPa). The disclosed embodiments of low-flammability and non-flammable LSEs may be used in many types of batteries, 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.

Example IV

Material

Lithium hexafluorophosphate (LiPF)₆) Dimethyl carbonate (DMC), Ethylene Carbonate (EC) and Ethyl Methyl Carbonate (EMC) (all cell grade purities) were obtained from BASF corporation (Florham Park, NJ). Trimethyl phosphate (TMPa,. gtoreq.99%) and triethyl phosphate (TEPa,. gtoreq.99%) from Sigma Aldrich, as well as bis (2,2, 2-trifluoroethyl) ether (BTFE, 99%) and 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE, 99%) from SynQuest Labs were dried over molecular sieves before use. Lithium bis (fluorosulfonyl) imide (LiFSI) was obtained from Nippon Shokubai (japan) and used after drying in vacuum at 120 ℃ for 24 h. The electrolyte is prepared by dissolving the required amount of salt in a solvent. Li chips were purchased from MTI (Richmond, CA). Cu and Al Foils were purchased from All Foils (Strongsville, OH). NMC (LiNi)_1/3Mn_1/3Co_1/3O₂And LiNi_0.6Mn_0.2Co_0.2O₂) The cathode electrode was prepared from Advanced Battery Facility (ABF) in Pacific Northwest National Laboratory by mixing NMC, super C carbon, polyvinylidene fluoride (PVDF) binder in a mass ratio of 96:2:2 in N-methyl-2-pyrrolidone (NMP) and coating the slurry onto Al foil. NCA (LiNi)_0.85Co_0.1Al_0.05O₂) And LCO (LiCoO)₂) The cathode electrode was obtained from the Argonne National Laboratory. After predrying and further drying at about 75 ℃ under vacuum for 12h, the electrode laminate was punched into disks (1.27 cm)²). In the presence of argon (O)₂<0.1ppm and H₂O<0.1ppm) was stored and processed in MBraun LABmaster glove box (Stratham, NH).

Material characterization

Morphological Observation of cycling electrodes on a FEI Quanta OR Helios focused ion Beam Scanning Electron Microscope (SEM) (Hillsboro, OR) at 5.0kVEXPERIMENT AND EDS MEASUREMENT, to prepare the samples, the circulating electrode was soaked in pure DMC for 10min, then rinsed at least 3 times with pure DMC to remove the remaining electrolyte, and finally dried under vacuum^-1Raman spectra were collected by a Raman spectrometer with spectral resolution (Horiba LabRAM HR.) the viscosity of the electrolyte was measured on a Brookfield DV-II + Pro viscometer (Middleboro, MA) at 5 ℃ and 30 ℃ (η).

On a 600MHz NMR spectrometer (Agilent Tech, Santa Clara, Calif.) equipped with a 5mm liquid NMR probe (Doty Scientific, Columbia, SC) at about 31T m^–1The maximum gradient strength of the alloy is within the temperature range of 0-50 ℃ and the alloy is used⁷Li、¹⁹F and¹separate measurement of Li by H-pulse gradient field (PFG) NMR⁺Cation, FSI^-Diffusion coefficients of anion and solvent molecules (DMC and BTFE), expressed as D_Li、D_FSI、D_DMC/D_BTFE. To for¹H、¹⁹F and⁷larmor frequency for Li PFG-NMR was 599.8MHz, 564.3MHz, and 233.1MHz, respectively, with a bipolar pulse gradient stimulus echo sequence (Dbppste in VNMRJ, a sequence supplied by the supplier) with pulse lengths of 5.5, 7, and 12 μ s of 90 degrees. Fitting the echo curve S (g) obtained as a function of the gradient strength (g) to the Stejskal-Tanner equation [1](Stejskal et al, J.chem.Phys.1965,42: 288-:

S(g)＝S(0)exp[-D(γδg)²(Δ-δ/3)][1]

where S (g) and S (0) are the peak intensities at gradient intensities g and 0, respectively, D is the diffusion coefficient, γ is the gyromagnetic ratio of the observed nuclei, and δ and Δ are the gradient pulse length and the duration of the two gradient pulses, respectively. For all measured and varied g values, δ and Δ are fixed at 2ms and 30ms to obtain sufficient decay in the echo curve.

Electrochemical measurements

Ionic conductivity was measured with a cell made of two parallel Pt electrodes using a BioLogic MCS 10 fully integrated multi-channel conductivity spectrometer over a temperature range of 5 ℃ to 30 ℃. Conductivity cell constants were predetermined using conductivity standard solutions from Okalon inc.

Electrochemical cycling tests were performed in a constant current mode on a battery tester (Land BT2000 and Arbin BT-2000, Arbin instruments, College Station, TX) in an environmental chamber at 30 ℃ using a button cell type CR2032 with a two-electrode configuration. Button cells (Li | | Cu, Li | | Li, Li | | | NMC, Li | | NCA and Li | | | LCO) are assembled in a glove box, and a Li chip is used as a counter electrode and a reference electrode. Use of

2500 polypropylene films as separators, in addition to cells with concentrated LiFSI/DMC electrolyte, due to

2500 film wettability problem, cell use with concentrated LiFSI/DMC electrolyte

3501 polypropylene film of surfactant to ensure good wetting. For test standardization, 200 μ L of electrolyte was added to each button cell (excess), although some spillage occurred during the cell sealing process. For a Li | | Cu cell, the effective area of the Cu foil for Li deposition is 2.11cm²(diameter 1.64 cm). During each cycle, the desired amount of Li metal was deposited on the Cu substrate at various current densities and subsequently stripped until the potential was opposite to Li/Li⁺Reaching 1.0V. Li | Li symmetric cells were assembled using Li metal as the working and counter electrodes. All Li NMC, Li NCA and Li LCO cells were assembled using aluminum-clad coin cell cans for the cathode portion to eliminateExcept corrosion to stainless steel tank and side effect under high voltage. The cells were tested between 2.7 to 4.3V for Li NMC333, between 2.8 to 4.4V for Li NMC622 and Li NCA, and between 3.0 to 4.35V for Li LCO cells. 1C equals 160mAg^-1Active NMC333 and LCO of (1), 180mA g^-1NMC622, and 190mA g^-1The NCA material of (1).

On a CHI660C bench (CH Instruments, Inc., Austin, TX) at a scan rate of 0.2mV/s from OCV (open circuit voltage) to 6V using 2.11cm²As working electrode in coin cells Linear Sweep Voltammetry (LSV) studies of the electrolyte solution were performed.

Coulombic Efficiency (CE) measurement

The average CE of Li metal anodes was measured using Li | | | Cu coin cells using the following protocol: 1) an initial formation cycle at 5mAh/cm²Plating Li on Cu and stripping to 1V; 2) at 5mAh/cm²Plating Li on Cu as Li reservoir; 3) at 1mAh/cm²Repeated stripping/plating of Li (or if desired)>Overpotential of 1V to 1mAh/cm²Stripping Li, then stripping to 1V) for 9(n ═ 9) cycles; 4) all Li was stripped to 1V. Current: 0.5mA/cm². The average CE was calculated by dividing the total stripping capacity by the total plating capacity based on the following formula:

wherein n is Q_{Circulation, stripping}Charge capacity and Q_{Circulation, electroplating}Number of cycles at discharge Capacity, Q_{Peeling off}Is the charge capacity and Q during the final stripping_{Storage warehouse}Is the amount of lithium deposited during step 2.

MD simulation

DMC-LiFSI solvation structure in the local super concentrated electrolyte was characterized using first-principles Density Functional Theory (DFT) and Ab Initio Molecular Dynamics (AIMD) simulations. From scratch simulation software package (VASP) using vienna (Kresse et al, phys96,54: 11169-11186; kressee et al, Phys. Rev.B 1993,47: 558. 563; kresse et al, Phys. Rev.B1994,49: 14251-. Electron-ion interactions are described by projected extended wave (PAW) pseudopotentials with a cutoff energy of 400eV (Blochl, Phys Rev B1994, 50: 17953-. The exchange-correlation functional (Perew et al, Phys Rev Lett 1996,77: 3865-. The electrolyte and LiFSI salts interacting with the Li metal anode surface system were calculated using an exchange correlation functional with a Gaussian spread width term (Gaussian smearing width term) of 0.05 eV. An optimized Li anode surface and absorption of ground state electrolyte and salt molecules was obtained using the Monkhorst-Pack k-point grid scheme (4 × 4 × 1). The convergence criterion for the electron self-consistent iteration and ion relaxation was set to 1 × 10^-5eV and 1X 10^-4eV. AIMD simulations of electrolyte-salt mixtures were performed at 303K with a canonical (NVT) ensemble. The constant temperature of the AIMD simulation system was controlled using the Nose constant temperature method with a Nose mass parameter of 0.5. A time step of 0.5fs was used in all AIMD simulations. The Monkhorst-Pack k-point grid scheme (2X 2) was used in AIMD simulations. The total AIMD simulation time for each electrolyte/salt system was 15 ps. The radial distribution function of the Li-O pair was obtained using the last 5ps AIMD tracks.

Example 1

Lithium metal battery with LiFSI/EMC-BTFE and LiFSI/EMC-TTE electrolytes

Coulombic Efficiency (CE) of Li | | | Cu cells using different super-concentrated Li salts in carbonate solvents was evaluated. Li salt as shown in fig. 5A: the solvent molar ratio reflects the different salts differing in solubility (e.g., EMC) in the carbonate solvent. For example, in saturated LiPF₆LiPF in EMC solution₆EMC ratio of about 1:2.35, while the LiFSI: EMC ratio in saturated LiFSI/EMC solution can be as high as 1: 1.1. Li | | | Cu cell unit with 1mA cm^-2Cycles with a lithium deposition/stripping area capacity of 0.5mAh cm per cycle^-2. The CE data in FIG. 5B show only concentrated electrolytes based on LiFSI salts, e.g., LiFSI/EMC (molar ratio 1:1.1, 8.73mol kg)^-1) Can be used forAllowing reversible Li deposition/exfoliation with a stable CE of about 97%.

Concentrated LiFSI/EMC was diluted with fluoroalkyl ether (molar ratio 1:1.1, 8.73mol kg)^-1) An electrolyte. LiFSI salts proved insoluble in fluoroalkyl ethers, such as TTE. On the other hand, TTE is miscible with EMC. Therefore, fluoroalkyl ethers are considered to be 'inert' diluents for the electrolyte and do not participate in the solvation of LiFSI. The electrolyte formulations and the corresponding moles of these electrolytes are shown in table 1.

TABLE 1 electrolyte numbering and formulation

In E2 and E3, the local super concentrated LiFSI/EMC (1:1.1) solvated cation-anion Aggregates (AGG) were well preserved, beneficial to reach higher CEs for reversible Li deposition/exfoliation. Li⁺-FSI^--Formation of solvent aggregates also reduces FSI^-The Lowest Unoccupied Molecular Orbital (LUMO) energy of the anion, so it can decompose first to form a stable SEI. The concentration of LiFSI/EMC-fluoroalkyl ether was greatly reduced by adding fluoroalkyl ether to EMC: fluoroalkyl ether at a ratio of 2:1, calculated to be 4.66mol kg for LiFSI/EMC-BTFE (2:1)^-1And a concentration of 4.13mol kg for LiFSI/EMC-TTE (2:1)^-1. As shown in fig. 6, by adding fluoroalkyl ethers (i.e., TTE, BTFE) as diluents, the average CE of Li | | Cu cells from cycle 3 to 86 was as high as 98.95%, which is comparable to the CE of the parent super-concentrated LiFSI/EMC electrolyte (98.93%).

The cycling performance of Li | | | NMC cells with concentrated LiFSI/EMC electrolyte with and without BTFE diluent was investigated. As shown in FIG. 7, visual observation was made after addition of BTFE

2500 separator wetting was improved. The cells were cycled at C/3 or 1C at a charge cutoff voltage of 4.5V. FIG. 8A shows that the addition of BTFE as a diluent greatly shortens the need to wet the electrode/separatorRest time (rest time). The cycling performance results show that Li | | | NMC cells using BTFE diluted LiFSI/EMC-BTFE (2:1) electrolyte exhibit comparable discharge capacity, cycling stability, and CE during cycling at C/3 and 1C rates, respectively, as shown in fig. 8A and 8B. The results show that the addition of BTFE or TTE as a diluent does not compromise the oxidative stability of the concentrated electrolyte.

Not all salt/solvent combinations provide such excellent results. Evaluation of LiBF in Propylene Carbonate (PC)₄. At a concentration of 0.5mAh/cm²In a Li [ l ] Cu cell comparing 7.5mol/kgLiBF in PC₄And 2.5mol/kg LiBF in PC-TTE₄(2:1v: v) cycle performance. At 0.2mA/cm²The initial two cycles were performed, with the other cycles at 1mA/cm²The process is carried out as follows. The results are shown in fig. 9A and 9B. LiBF₄the/PC electrolyte had an initial CE of about 50%. The electrolyte has an average CE of less than 50% over 50 cycles when diluted with TTE. This is in sharp contrast to LiFSI/EMC, LiFSI/EMC-BTFE and LiFSI-EMC-TTE electrolytes, which have CE values as high as 98.95%. LiTFSI-tetraglyme also produced poor CE results.

Example 2

LiFSI/DMC-BTFE electrolyte performance in lithium metal batteries

The concept of diluting and forming a locally concentrated electrolyte solution structure is demonstrated in DMC solvent based electrolytes. The electrolyte formulations of various concentrations of LiFSI/DMC-BTFE solutions are listed in Table 2. The concentration of 5.5M LiFSI/DMC electrolyte was diluted down to 1.2M by addition of BTFE.

Table 2 electrolyte number, formulation and viscosity

The use of 1.0M LiPF is shown in FIGS. 10A-10D, respectively₆Li plating/stripping curves for Li | | | Cu cells of/EC-EMC (E4), 1.2M LiFSI/DMC (E5), 3.7MLiFSI/DMC (E6), and 5.5M LiFSI/DMC (E7). The curves were obtained using the following protocol: 1) one initial cycle of formation at 0.5mA cm^-2Electroplating of 5mA on Cuh cm^-2Li; and then at 0.5mA cm^-2Lower Li to 1V; 2) at 0.5mA cm^-2Electroplating 5mAh cm on Cu^-2Li as Li reservoir; 3) at 1mAhcm^-2Next 9 cycles of Li stripping/plating at 20% depth; 4) at 0.5mA cm^-2All Li was stripped down to 1V. The average CE was calculated by dividing the total Li stripping capacity by the total Li plating capacity. Using 1.0M LiPF₆EC-EMC electrolyte and 1.2M LiFSI/DMC electrolyte, Li metal cycle inefficiency (II) ((III))<50%) to such an extent that a significant overpotential is generated for stripping in only a few cycles. CE can be achieved for LiFSI/DMC of 3.7M and 5.5M>99.0％。

The average CE of the diluted LiFSI/DMC-BTFE electrolyte was also measured using the same protocol as shown in fig. 11A-11D. The BTFE-diluted LSE exhibited an even higher CE than the super concentrated 5.5M LiFSI/DMC (CE 99.2%), with a CE in the range of 99.3% to 99.5%. The results demonstrate that dilution with BTFE does not alter the local super-concentrated structure and minimizes the presence of free DMC solvent molecules, thus maintaining high stability of the electrolyte to the Li metal anode during repeated plating/stripping processes.

The evolution of Li plating/stripping curves and CE during long-term cycling in different electrolytes was examined by repeated plating/stripping cycles in Li Cu cells. The cell size was 0.5mA cm²Current density cycling of; the working area of the Cu electrode is 2.11cm². FIGS. 12A-12D show the 100 th cycle (1 mA/cm)²To 0.5mAh/cm²) From 1.0M LiPF₆Scanning electron microscope images of lithium plated onto copper substrates with the/EC-EMC (4:6, w) (FIG. 12A), 5.5M LiFSI: DMC (1:1) (FIG. 12B), 3.7M LiFSI/DMC-BTFE (1:2) (FIG. 12C), and 1.2MLiFSI/DMC-BTFE (0.51:1.1:2.2) (FIG. 12D) electrolytes. Cell stabilization cycling with highly concentrated 5.5M LiFSI/DMC and highly diluted 1.2M LiFSI/DMC-BTFE (1:2) electrolyte>200 cycles (FIG. 13), with an average CE of about 99%. Due to better conductivity and lower viscosity (fig. 14, table 2), the cell polarization during charge-discharge in diluted electrolyte was much smaller than in highly concentrated electrolyte, and this difference became more pronounced with increasing current density (fig. 15A, 15B).

Example 3

Lithium ion battery with LiFSI/DMC-BTFE electrolyte

The stability of the concentrated electrolyte and the BTFE-diluted electrolyte at high voltage was first studied by Linear Sweep Voltammetry (LSV) at a sweep rate of 0.2mV/s in a cell with Al as the working electrode. The results show that the BTFE-diluted electrolyte shows anodic stability at 4.5V or higher, although stability decreases with increasing BTFE concentration at high voltage (fig. 16). Fig. 17A-17D are photomicrographs showing the morphology of lithium metal after electroplating on Cu substrates in low and medium concentration electrolytes of LiFSI in DMC, 1.2M LiFSI/DMC (fig. 17A, 17B) and 3.7M LiFSI/DMC (fig. 17C, 17D).

Next, Li | | NMC battery cells were assembled by using cells having about 2.0mAh/cm²High area capacity NMC electrodes were used to evaluate the performance of dilute 1.2M LiFSI/DMC-BTFE electrolytes. A composition with concentrated 5.5M LiFSI/DMC and conventional 1.0M LiPF was also assembled₆Li | | | NMC cells from/EC-EMC and tested for comparison. Fig. 18A-18D show the long-term cycling performance and corresponding voltage curve evolution of Li | | | NMC cells. At 0.67mA/cm²After 3 formation cycles (1/3 hours magnification), all cells were subjected to 2.0mA/cm²(1 hour rate) cycling at high current density to demonstrate the stability of Li metal anodes under this harsh condition for these electrolytes. During the formation cycle, the Li NMC cell delivers about 160mAhg^-1Similar specific discharge capacity of NMC, corresponding to 2.0mAh/cm²Nominal area capacity of. When the concentration is 2.0mA/cm²At lower cycle, 1.0M LiPF₆The Li | NMC battery unit of the/EC-EMC electrolyte shows that the electrode polarization is increased violently and the capacity is reduced rapidly after 100 cycles, and the Li | NMC battery unit of the/EC-EMC electrolyte retains<30% (fig. 18A, 18B), which is due to severe corrosion reactions between Li metal and the electrolyte. When concentrated 5.5M LiFSI/DMC was used, the stability of the Li metal was greatly improved as reflected by the much higher CE of the Li metal itself. However, Li NMC cells with concentrated 5.5M LiFSI/DMC still showed continued capacity decline and electrode polarization increase, with about 70% capacity remaining after 100 cycles% (FIG. 18C). The unsatisfactory cycling performance of concentrated 5.5M LiFSI/DMC is due to the slow electrode reaction kinetics resulting from the high viscosity, low conductivity and poor wetting ability of the super concentrated electrolyte. In sharp contrast, using a BTFE diluted 1.2M LiFSI/DMC-BTFE electrolyte, significantly improved long-term cycling stability and limited increase in electrode polarization were achieved (fig. 18D). At 2.0mA/cm²After 300 cycles at high current density, the cell displays>High capacity retention of 95%, which was once reported as the best performance for Li metal batteries. This finding indicates that LSEs with low Li salt concentrations can achieve fast charging and stable cycling of Li Metal Batteries (LMB).

Rate performance of Li | | NMC cells was evaluated to determine the electrochemical reaction kinetics of BTFE-diluted electrolytes. Rate performance was tested using two charge/discharge schemes, namely (i) charging at the same C/5 and discharging at increased rates; (ii) charged at increasing rates and discharged at the same C/5. As shown in FIGS. 19 and 20, with concentrated 5.5M LiFSI/DMC electrolyte and baseline 1M LiPF₆Compared to dilute electrolytes, Li | | | NMC cells with BTFE diluted electrolytes (1.2M LiFSI/DMC-BTFE) show superior charge and discharge capabilities. Specifically, protocol (i) was used at 5C (i.e., 10 mA/cm)²) Upon discharge, cells using 1.2M LiFSI/DMC-BTFE electrolyte delivered high discharge capacity of 141mAh/g, significantly higher than 116mAh/g and 1M LiPF of concentrated 5.5M LiFSI/DMC electrolyte₆68mAh/g of dilute electrolyte. The enhanced rate performance of the 1.2M LiFSI/DMC-BTFE electrolyte compared to the concentrated 5.5M LiFSI/DMC electrolyte is due to reduced viscosity, increased conductivity, improved electrode/separator wetting, and improved interfacial reaction kinetics.

Example 4

Dendrite-free deposition on Li metal anodes

To gain insight into the superior electrochemical properties of LSE (1.2M LiFSI/DMC-BTFE), the morphological characteristics of Li deposited in different electrolytes were evaluated. The current density is 1.0mA/cm²And the deposition capacity was 1.5mAh/cm². FIGS. 21A-21F show a signal at 1mA/cm²At different current densities ofCross-sectional and surface morphology of Li films deposited on Cu substrates. The electrolytes are as follows: 1.0M LiPF₆/EC-EMC (FIGS. 21A, 21B), 5.5M LiFSI/DMC (FIGS. 21C, 21D) and 1.2M LiFSI/DMC-BTFE (1:2) (FIGS. 21E, 21F). By LiPF₆Electrolyte plating of Li metal produces a highly porous/loose structure with a large number of dendritic Li (fig. 21A, 21B). Dendritic Li deposition was also observed in low (1.2M) and medium (3.7M) concentrations of LiFSI/DMC electrolyte as previously shown in fig. 17A-17D. In contrast, dendritic-free nodular (nodule-like) Li deposits were obtained in both the highly concentrated 5.5M LiFSI/DMC and the diluted low concentration 1.2M LiFSI/DMC-BTFE electrolyte (FIGS. 21C-21F). Larger primary Li particles (about 5 μ M on average) and tighter deposits (about 10 μ M, 1.5mAh cm close to bulk Li) were found in the LSE electrolyte (1.2M LiFSI/DMC-BTFE) than in the concentrated electrolyte^-2(about 7.2 μm) theoretical thickness). Furthermore, as the current density increased (2 mA/cm)²、5mA/cm²And 10mA/cm²) The Li deposits maintained nodular properties in the 1.2MLiFSI/DMC-BTFE electrolyte, despite the slight decrease in particle size (fig. 22A-22C). The formation of large particle size nodular Li deposits can significantly mitigate interfacial reactions with the electrolyte and reduce the risk of Li penetration into the separator, thereby improving the cycle life and safety of LMBs using LSE (dilute 1.2M LiFSI/DMC-BTFE). Dilute electrolytes also produce SEI layers that are more stable than highly concentrated 5.5M LiFSI/DMC. In addition, depositing high density Li is beneficial to reduce the volume change of LMB during the charge/discharge process and highly beneficial to the development of LMB.

Example 5

Lithium metal battery with LiFSI/DME-BTFE and LiFSI/DME-TTE electrolytes

Dilution of the concentrated electrolyte with an ether-based electrolyte (such as DME) is also suitable. An exemplary electrolyte formulation is shown in table 3. The concentration of 4M LiFSI/DME electrolyte was diluted to 2M or 1M by the addition of BTFE or TTE.

TABLE 3 electrolyte numbering and formulation

Electrolyte numbering	Electrolyte formulation	Concentration of
			E12	4M LiFSI/DME(LiFSI:DME 1:1.4)	4mol L^-1
E13	LiFSI/DME+BTFE(DME:BTFE＝3:5,v:v)	2mol L^-1
			E14	LiFSI/DME+TTE(DME:TTE＝3:5,v:v)	2mol L^-1
E15	LiFSI/DME+BTFE(DME:BTFE＝3:8,v:v)	1mol L^-1
			E16	LiFSI/DME+TTE(DME:TTE＝3:8,v:v)	1mol L^-1

Fig. 23 shows CE for Li | | | Cu cells using concentrated LiFSI/DME electrolyte and LiFSI/DME electrolyte with TTE or BTFE diluent. All cells exhibited very similar CE in the first cycle and during long-term cycles. When the concentrations of LiFSI/(DME + BTFE) and LiFSI/(DME + TTE) were diluted to 2M by adding fluoroalkyl ethers (i.e., TTE, BTFE) as diluents, the average CE of the Li | | | Cu cells of the TTE and BTFE diluted electrolyte was 98.83% and 98.94%, which is comparable or even better than the CE (98.74%) of the parent concentrated LiFSI/DME. Even when LiFSI/(DME + BTFE) and LiFSI/(DME + TTE) concentrations were diluted to 1M by adding TTE, BTFE as diluent, the average CE of Li | | | Cu cells for the TTE and BTFE diluted electrolyte was 98.90% and 98.94% and 98.74%, which is very comparable or even better than the CE (98.74%) for the parent concentrated LiFSI/DME.

The cycling performance of Li | | | LFP cells containing concentrated 4M LiFSI/DME electrolyte with and without TTE or BTFE diluent is shown in fig. 24. Using LFP cathode (Hydro-Quebec, 1mAh cm)^-2) Li LFP coin cells were assembled with a lithium metal anode, a piece of Polyethylene (PE) separator, and concentrated ether-based electrolyte before and after dilution. The concentrated LiFSI/DME electrolyte was diluted from 4M to 2M, and Li | | | LFP cells using 2M LiFSI/(DME + BTFE) and 2M LiFSI/(DME + TTE) electrolytes showed similar long-term cycling stability compared to cells using the parent concentrated 4M LiFSI/DME electrolyte. The results were obtained at 1C magnification after 3 formation cycles at C/10 in a voltage range of 2.5-3.7V.

Example 6

Sodium metal battery with NaFSI/DME-TTE and NaFSI-DME-BTFE electrolytes

The concept of locally super-concentrated electrolyte is also applicable in sodium metal batteries. The evaluated electrolyte formulations are shown in table 4. The concentration of 5.2M NaFSI/DME electrolyte was diluted to 1.5M by the addition of TTE.

TABLE 4 electrolyte numbering and formulation used in this example

Electrolyte numbering	Electrolyte formulation	Concentration of
			E17	NaFSI/DME (NaFSI: DME, 1:1, molar ratio)	5.2mol L^-1
E18	NaFSI/DME + TTE (DME: TTE ═ 1:0.5, molar ratio)	3.0mol L^-1
			E19	NaFSI/DME + TTE (DME: TTE ═ 1:1, molar ratio)	2.3mol L^-1
E20	NaFSI/DME + TTE (DME: TTE ═ 1:2, molar ratio)	1.5mol L^-1

For the charge/discharge performance test, Na was used in an argon-filled glove box (MBraun, Inc.)₃V₂(PO₄)₃Constructing Na & lt/EN & gt by cathode, Na metal as anode, glass fiber as diaphragm and NaFSI/DME electrolyte containing TTE diluent and not containing TTE diluent₃V₂(PO₄)₃A button cell. Na (Na)₃V₂(PO₄)₃The cathode contains 80% Na₃V₂(PO₄)₃、10％Super

Carbon black (e.g., available from Fisher Scientific) and 10% PVDF (polyvinylidene fluoride).

FIGS. 25A and 25B show a sample having 1.3mAh cm^-2Na | Cu cell initial Na plating/stripping voltage curve (fig. 25A) and CE versus cycle number (fig. 25A) for Na deposition area capacity25B) In that respect At 1.3mAh cm^-2At a Na deposition area capacity of 0.26mA cm^-2After two formation cycles at 0.65mA cm^-2The CE was tested as a function of cycle number. The initial CE for the NaFSI/DME and NaFSI/DME-TTE electrolytes with 5.2M, 3.0M, 2.3M and 1.5M NaFSI salts were 94.3%, 96.1%, 94.8% and 96.5%, respectively. During the next cycle, the CE of the diluted electrolyte was comparable or higher than that of the parent 5.2m nafsi/DME electrolyte.

FIGS. 26A and 26B show Na I using concentrated 5.2M NaFSI/DME electrolyte and TTE diluted NaFSI/DME-TTE electrolyte (2.3M and 1.5M)₃V₂(PO₄)₃Electrochemical performance of the cell at C/3 rate. The cells using TTE diluted NaFSI/DME-TTE electrolyte showed about 97mAh g compared to concentrated NaFSI/DME electrolyte^-1Similar initial specific discharge capacity (fig. 26B). Fig. 27A and 27B show the charge and discharge capacities of battery cells using 5.2M NaFSI/DME electrolyte and 2.3M NaFSI/DME-TTE electrolyte, respectively.

FIGS. 28A and 28B show that at 5.2M NaFSI/DME, 3.1M NaFSI/DME-BTFE (1:1), 2.1M NaFSI/DME-BTFE (1:2) and 1.5M NaFSI/DME-BTFE (1:3), there is 1.0mAh cm^-2Na deposited area capacity of (a) initial Na plating/stripping voltage curve (fig. 28A) and CE versus cycle number (fig. 28B) for Na | | | Cu cells. The ratio in parentheses is the molar ratio of DME to BTFE. At 0.2mA cm^-2After two formation cycles, the evaluation was carried out at 1mA cm^-2CE as a function of the number of cycles tested. As shown in FIG. 28B, LSE, 2.1M NaFSI/DME-BTFE (1:2) showed stable cycling over 200 cycles with a CE approaching 100%.

FIGS. 29A-29C show Na I using 5.2M NaFSI/DME and BTFE-diluted NaFSI/DME-BTFE electrolyte-3.1M NAFSI/DME-BTFE (1:1), 2.1M NaFSI/DME-BTFE (1:2) and 1.5M NaFSI/DME-BTFE (1:3)₃V₂(PO₄)₃Electrochemical performance of the battery cell. Fig. 29A shows the initial Na plating/stripping voltage curve. FIG. 29B shows cycling stability over 100 cycles at C/10 and C/3 magnification. FIG. 29C shows 2.1M NaFSI/DME-BTFE (1:2mol) over 100 cycles at C/10 and C/3 ratesCharge and discharge capacity. The results indicate that BTFE is an excellent diluent for concentrating NaFSI/DME electrolyte.

Example 7

Li-S battery with LiTFSI/DOL-DME-TTE electrolyte

The concept of locally super-concentrated electrolyte is also applicable to lithium sulfur batteries. The electrolyte formulations evaluated in this example are shown in table 5. The concentration of 3.3M LiTFSI in DOL-DME (1:1, v: v) electrolyte was diluted to 1.06M by the addition of TTE.

TABLE 5 electrolyte numbering and formulation

Electrolyte numbering	Electrolyte formulation	Concentration of
			E21	LiTFSI in DOL-DME (1:1, v: v)	1mol L^-1
E22	LiTFSI in DOL-DME (1:1, v: v)	3.3mol L^-1
			E23	LiTFSI in DOL-DME-TTE (1:1:9, v: v: v)	1.06mol L^-1

For charge/discharge performance testing, a Ketjen black conductive carbon (KB)/S cathode was used in an argon-filled glove box (MBraun, Inc.)Li-S coin cells were assembled with lithium metal as the anode, a sheet of polyethylene as the separator, and LiTFSI/DOL-DME electrolyte with and without TTE diluent. By coating with a composition containing 80% KB/S composite, 10% PVDF and 10%

Conductive carbon slurry to make KB/S cathode. The KB/S complex was prepared by mixing 80% S and 20% KB and then heat treating at 155 ℃ for 12 hr.

FIGS. 30A and 30B show a sample having a 1mAh cm^-2Li deposition area capacity initial Li plating/strip voltage curves (fig. 30A) and CE versus cycle number (fig. 30B) for Li Cu cells. At 1mAh cm^-2At a Li deposition area capacity of 0.2mA cm^-2After 2 formation cycles at 1mA cm^-2The results were obtained as follows. The super concentrated 3.3M LiTFSI/DOL-DME electrolyte showed an initial CE of 91.6%, which is much higher than 70.1% at low concentrations of 1M LiTFSI/DOL-DME electrolyte. Local hyperconcentration of Li by dilution of 3.3M LiTFSI/DOL-DME electrolyte with TTE⁺The structure was solvated, and 1.06M LiTFSI diluted in DOL-DME-TTE (1:1:9, v: v: v) electrolyte showed a higher CE of 96.4% during the initial plating/stripping process.

The electrochemical performance of a Li-S cell containing a conventional low concentration of 1M LiTFSI/DOL-DME, a concentrated 3.3M LiTFSI/DOL-DME electrolyte, and 1.06M LiTFSI diluted in DOL-DME-TTE electrolyte is shown in FIGS. 31A-31C. Fig. 31A shows an initial charge/discharge voltage curve. In FIG. 31A, curve A was obtained for 1.0M LiTFSI/DOL-DME, curve B was obtained for 3.3M LiTFSI/DOL-DME, and curve C was obtained for 1.06M LiTFSI/DOL-DME-TTE. Li-S cells with an electrolyte/sulfur ratio of 50mL/g were cycled at a low current rate of C/10(168 mA/g). Upon dilution of the concentrated LiTFSI/DOL-DME electrolyte from 3.3M to 1.06M, the Li-S cell showed even better long-term cycling stability (fig. 31B) and higher CE (fig. 31C) than the cell using the parent concentrated 3.3M LiTFSI/DOL-DME electrolyte.

Example 8

Li-O with LiTFSI/DMSO-TTE electrolyte₂Battery with a battery cell

The concept of a local super concentrated electrolyte has also been investigated in lithium oxygen batteries. The electrolyte formulations evaluated are listed in table 6. The concentration of 2.76M LiTFSI in DMSO (LiTFSI: DMSO molar ratio 1:3) electrolyte was diluted to 1.23M (LiTFSI: DMSO: TTE molar ratio 1:3:3) by addition of TTE.

TABLE 6 electrolyte numbering and formulation

FIG. 32 shows the color at 0.1mA cm^-2Has a current density of 600mAh g^-1Limited discharge capacity of Li-O using LiTFSI-3DMSO (2.76M) and LiTFSI-3DMSO-3TTE (1.23M) electrolytes₂Charge/discharge curves of the battery cells. Li-O after dilution of LiTFSI concentration from 2.76M to 1.23M₂Cell display and use of high concentration electrolyte Li-O₂The capacities observed in the battery cells were similar. For charge/discharge performance testing, Li-O was assembled in an argon filled glove box (MBraun, Inc.)₂A button cell. A piece of membrane (Whatman glass fiber B) soaked with 200 μ L LiTFSI-DMSO electrolyte with and without TTE diluent was placed between the air electrode disc and the Li metal chip. After sealing, the assembled cell was transferred to a PTFE (polytetrafluoroethylene) container and removed from the glove box. Filling ultra-high purity O in PTFE container₂. Reacting these Li-O₂Cell at O₂Rest in atmosphere for at least 6h, then at room temperature, 0.1mA cm on ArbinBT-2000 Battery tester (Arbin Instruments, College states, TX)^-2Discharge/charge evaluation was performed at the current density of (1).

Example 9

Aqueous electrolyte with bridging solvent

Aqueous electrolytes (e.g., 1kg H) reported to have super concentrated lithium salts, LiTFSI₂21mol LiTFSI in O) broadens its electrochemical stability window to about 3.0V (i.e., 1.9-4.9 vs. Li/Li)⁺). As shown in the above examples, this concentrated aqueous-based electrolyte was diluted while maintaining broad electrochemical performanceThe chemical stability window may be a good strategy to reduce the cost of the electrolyte. However, fluoroalkyl ethers having a low dielectric constant and a low donor number are not miscible with water. Thus, super concentrated aqueous electrolyte (1kg H) was diluted with TTE with the aid of a 'bridge' solvent₂21mol of LiTFSI in O). The evaluated electrolyte formulations are shown in tables 7 and 8. 'bridge' solvents include DMC, PC, AN and DMSO. By mixing H₂The ratio of O to TTE was fixed at 1:1, with careful optimization of the optimum content of 'bridge' solvent. The optimum content of different solvents will vary depending on the ` bridge ` solvent and H₂Strength of interaction between O and TTE diluent.

TABLE 7 electrolyte numbering and formulation

Electrolyte numbering		H₂Weight ratio of O-solvent to TTE	m(mol/kg)	M(mol/L)
					E27	H₂O	1	21	5.04
E28	H₂O-DMC-TTE	1:0.85:1	7.37	3.78
					E29	H₂O-PC-TTE	1:1.05:1	6.89	3.69
E30	H₂O-AN-TTE	1:0.5:1	8.4	3.87
					E31	H₂O-DMSO-TTE	1:1.15:1	6.67	3.69

FIG. 33 shows the signal at 10mV s^-1Using stainless steel working and counter electrodes with Ag/AgCl as reference electrode, with the aid of different 'bridge' solvents (including DMC, PC, AN and DMSO), before and after dilution with TTE, cyclic voltammograms of the aqueous electrolyte were concentrated. Potential conversion to Li/Li⁺The potential of the redox couple. In contrast, dilution with TTE was found not to compromise most of the oxidation and reduction stability using PC as the 'bridge' solvent. However, H at 1:1₂TTE ratio of LiTFSI/H₂The concentration of the O solution was only diluted from 5.04M to 3.69M.

Concentrated LiTFSI/H for further dilution₂O solution, with the addition of increased PC as 'bridge' solvent, more TTE was used. The ratio between PC to TTE in the diluted electrolyte is very close to 1:1. Concentration of LiTFSI/H by increasing PC and TTE addition₂The concentration of the O solution was diluted from 5.04M to 2.92M.

TABLE 8 electrolyte numbering and formulation

Electrolyte numbering		H₂Weight ratio of O-solvent to TTE	m(mol/kg)	M(mol/L)
					E32	H₂O	1	21	5.04
E33	H₂O-PC-TTE	1:0.55:0.5	10.3	4.30
					E34	H₂O-PC-TTE	1:1.05:1	6.89	3.69
E35	H₂O-PC-TTE	1:1.5:1.5	5.25	3.27
					E36	H₂O-PC-TTE	1:2:2	4.29	2.92

Figures 34A and 34B show cyclic voltammograms of the first and second cycles, respectively, of diluting a concentrated aqueous electrolyte with different amounts of TTE with the aid of PC. Stainless steel is used as a working electrode and a counter electrode, and Ag/AgCl is used as a reference electrode; the scanning rate is 10mV s^-1. Potential conversion to Li/Li⁺The potential of the redox couple. In the first cycle (fig. 34A), the increase in added PC-TTE resulted in a slight increase in reduction instability at about 2.35V as reflected by the higher current response during the negative scan. However, diluting the PC-TTE by an appropriate amount improves the reduction stability and oxidation stability, probably due to the enhanced SEI layer formed on the working electrode (fig. 34B). The optimum dilution of the concentrated electrolyte was determined as H₂The ratio of O to PC to TTE was 1:1.5: 1.5.

Example 10

Molecular simulation

Without wishing to be bound by a particular theory of operation, it is believed that the superior electrochemical performance of LMB achieved in BTFE diluted LiFSI/DMC-BTFE electrolytes stems from its unique highly localized hyperconcentration of Li salt solvation structure. The DMC-LiFSI solvation structure in the local super concentrated electrolyte was characterized using first principles Density Functional Theory (DFT) and de novo computational molecular dynamics (AIMD) simulations. Using the Vienna de novo modeling software package (VASP) (Kresse et al, Phys. Rev.B 1996,54: 11169-11186; Kresse et al, Phys. Rev.B 1993,47: 558-561; Kresse et al, Phys. Rev.B1994,49:14251-14269) proceedsAll calculations are performed. Electron-ion interactions are described by projected extended wave (PAW) pseudopotentials with a cutoff energy of 400eV (Blochl, Phys Rev B1994, 50: 17953-. The exchange correlation functional was expressed using Perew-Burke-Ernzerhof generalized gradient approximation (GGA-PBE) (Perew et al, Phys Rev Lett 1996,77: 3865-. The electrolyte and LiFSI salts interacting with the Li metal anode surface system were calculated using the exchange correlation functional with a gaussian spread width term of 0.05 eV. An optimized Li anode surface and absorption of ground state electrolyte and salt molecules was obtained using the Monkhorst-Pack k-point grid scheme (4 × 4 × 1). The convergence criterion for the electron self-consistent iteration and ion relaxation was set to 1 × 10^-5eV and 1X 10^-4eV. AIMD simulations of electrolyte-salt mixtures were performed at 303K with a canonical (NVT) ensemble. The constant temperature of the AIMD simulation system was controlled using the Nose constant temperature method with a Nose mass parameter of 0.5. A time step of 0.5fs was used in all AIMD simulations. The Monkhorst-Pack k-point grid scheme (2X 2) was used in AIMD simulations. The total AIMD simulation time for each electrolyte/salt system was 15 ps. The radial distribution function of the Li-O pair was obtained using the last 5ps AIMD tracks.

FIG. 35 shows the optimized geometry for vacuum using VASP, DMC, BTFE, LiFSI and DMC/LiFSI, BTFE/LiFSI. Li, O, C, H, S, N and F atoms are magenta, red, gray, white, yellow, blue and light blue, respectively. The above calculation uses only a k-point grid centered at Γ. Similar results were also obtained using the Gaussian 09 software package with PBE and the 6-311+ + G (p, d) base set (Frisch et al, Gaussian 09,2009, Gaussian inc., Wallingford, CT), table 10. LiFSI salts were found to preferentially pass Li-O_DMCBond coordination to DMC, optimized Li-O_DMCThe key length is

And there was a strong interaction (-88.7kJ/mol) between LiFSI and DMC. On the other hand, such as

Li-O of_BTFEBond distance (ratio optimized Li-O)_DMCMuch longer bond) andthe weaker interaction between LiFSI and BTFE of-41.4 kJ/mol reflects that the interaction between LiFSI and another electrolyte solvent BTFE is rather weak.

As shown by previous theoretical studies on Li agglomerates and surfaces (Camacho-Forero et al, J Phys Chem C2015,119: 26828-26839; Doll et al, J Phys Condens Matter 1999,11:5007-5019), the most stable (100) surface of the three low index surface structures (i.e., (100), (110), and (111) crystal planes) was used to simulate the Li anode surface. The periodic Li (100) surface has a p (4 × 4) super cell with seven atomic Li layers. The optimized structures of DMC, BTFE, LiFSI, and DMC/LiFSI pairs on the Li (100) surface are shown in FIGS. 36A-36F.

Beard charge analysis (Bader charge analysis, Henkelman et al, Comut Mater Sci2006,36: 354-. The DFT calculated adsorption energies and the bedd charge for each species are summarized in table 9. Compared to DMC, LiFSI, and DMC/LiFSI pairs, the interaction between BTFE and Li anode surface is very weak and has little reducibility. This indicates that the BTFE molecule is almost inert and is hardly reduced. Whereas the DMC and DMC/LiFSI pairs were slightly reduced by obtaining fractional charges of-0.19 and-0.40 | e | respectively, suggesting that both were reduced, thereby leading to possible decomposition. In summary, BTFE was found to be more stable on Li anodes than DMC and DMC/LiFSI pairs.

To understand the effect of adding the second electrolyte solvent, BTFE, on the microstructure of the DMC/LiFSI mixture, three electrolyte/salt mixture systems, one binary DMC/LiFSI mixture and two ternary DMC/BTFE/LiFSI mixtures with two different molar ratios, were studied using AIMD simulations. The initial structure of each liquid electrolyte/salt mixture system was established by randomly placing the number of DMC, BTFE and LiFSI molecules on the basis of experimental density and molar ratio (concentration). The size of the simulation system is

These initial structures were first relaxed using a homemade classical molecular dynamics simulation method with a flexible force field (Han et al, J Electrochem Soc 2014)161A 2042-2053; soetens et al, J Phys Chem A1998,102: 1055-1061). After system quasi-equilibrium, a total of 15ps of AIMD simulations were performed for each mixture system. The profiles of the three electrolyte/salt mixture systems from the AIMD summation method are shown in figures 37A-37C. FIG. 38 shows Li-O calculated from AIMD simulated orbitals at 303K_DMCAnd Li-O_BTFEThe radial distribution function of the pair. Profiles from three electrolyte/salt mixture systems (FIGS. 37A-37C) and Li-O_DMCAnd Li-O_BTFEThe radial distribution function of the pairs (fig. 38) is evident in that all LiFSI salt molecules are tightly coordinated to DMC and not BTFE. Li-O calculation using the last 5ps AIMD simulation orbit_DMCAnd Li-O_BTFEThe radial distribution function of the pair. As shown in FIG. 38, for all three systems studied, the process was

Identification of Li-O_DMCThe sharp peak of the pair indicates that all LiFSI salts are surrounded by molecules of DMC solvent as the first coordination shell. This is due to the strong attractive interaction between DMC and LiFSI. For two ternary mixture systems with high and low BTFE concentrations, Li-O was found_BTFEThe pair is located at 4.65 and

two small peaks at (c). This indicates that BTFE is not coordinated to LiFSI in the two DMC/BTFE/LiFSI mixtures, clearly indicating the presence of a local excess concentration of DMC/LiFSI pairs, independent of the concentration of molecules of the BTFE diluent.

Raman and NMR spectroscopy were used to study the solvated structures of concentrated LiFSI/DMC electrolyte and BTFE diluted LiFSI/DMC-BTFE electrolyte. FIGS. 39A and 39B show Raman spectra of pure DMC, BTFE, and DMC-BTFE (2:1) solvent mixtures. No raman shift was observed at the peak positions of DMC and BTFE in the DMC and BTFE mixture. This result indicates no significant interaction between DMC and BTFE.

As presented in fig. 40A, in a different aspectDilute LiFSI/DMC (1:9) solutions are characterized by free DMC solvent molecules at about 920cm in the raman spectrum of the LiFSI/DMC solution at concentration^-1Is mainly O-CH₃Telescopic vibrating band and Li⁺-coordination of DMC at about 940cm^-1A secondary vibration band. As the LiFSI concentration increases (higher LiFSI: DMC molar ratio), free DMC decreases and disappears to form contiguous ion pairs (CIP, with Li alone)⁺Ion coordinated FSI^-) And aggregates (AGG, with two or more Li)⁺Ion coordinated FSI^-). By FSI^-The Raman band is 710-780 cm^-1The significant shift in (A) also demonstrates the formation of CIP and AGG in concentrated 5.5M LiFSI/DMC. Fig. 40B shows raman spectra of different concentrations of BTFE diluted LiFSI/DMC solution. Upon dilution with BTFE, Li was found⁺The coordinated DMC solvated structure remained intact and no about 940cm was observed^-1Any displacement of the vibration band at (a). In addition, in different LiFSI/DMC-BTFE solutions, the BTFE is 830-840 cm^-1The vibration band of (a) is unchanged. The results indicate that the diluent BTFE did not participate in Li due to its low dielectric constant and low donor number⁺Solvation of the cation confirms the solvated structure of the LSE. One feature of note is that dilution with BTFE slightly attenuates Li⁺Cation and FSI^-Association between anions by FSI^-Downward moving of Raman band (710-780 cm)^-1) It was confirmed that this would be beneficial to enhance Li⁺The ions diffuse and improve the kinetics of LMB.

NMR data (FIG. 41) show that all diffusion coefficients (D) are related to the inverse of solution viscosity (η)^-1) All proportional, and slightly different in their variation, as predicted by Stokes-Einstein diffusion theory, and depend on ion-ion and ion-solvent interactions (Pregosin et al, Chemical reviews2005,105: 2977-2998)). D was found in pure DMC, BTFE solvent and mixtures thereof_DMC>D_BTFEHowever, with the introduction of LiFSI salts, D_DMCAnd D_BTFEBecome less than and greater than η, respectively^-1. This strongly suggests that Li occurs predominantly from DMC molecules⁺Cationic solvation, BTFE interacts rather weakly with other electrolyte components. Also shown is enhancement of Li by addition of BTFE⁺Cation diffusion (D)_Li≥D_FSI) This is consistent with Raman observation, as opposed to LiFSI/DMC electrolyte (D)_Li≤D_FSI)。

Stable diffusion ratio D_Li/D_DMCAnd D_FSI/D_DMCShows the reaction of Li⁺Cation, FSI^-LSE solvation structure composed of anion and DMC solvent was insensitive to BTFE population in LiFSI/DMC-BTFE electrolyte (fig. 42). The temperature dependence of Ds seems to conform to the Stokes-Einstein diffusion theory, D ═ k_BT/6πηr_sWhere D is the diffusion coefficient, k_BBoltzmann constant (Boltzmann constant), T is absolute temperature, η is viscosity and r is_sIs the hydrodynamic radius of the diffusing molecule. D_Li/D_DMCAnd D_FSI/D_DMCThe value is closer to unity, and D_BTFE/D_DMCThe values are much greater than unity, due to preferential solvation of Li by the DMC molecules⁺A cation. Relatively constant D in DMC BTFE electrolyte_Li/D_DMCAnd D_FSI/D_DMCThe values indicate the formation of Li⁺Cation, FSI^-The solvating structure of the anion and DMC composition 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 are mainly dependent on the Li salt concentration, are less likely to vary with the LiFSI concentration in the DMC BTFE binary electrolyte system.

To understand the stability of the electrolyte components with Li metal, moderately diluted 3.7M LiFSI/DMC, SE (5.5M LiFSI/DMC) and LSE (1.2M LiFSI/DMC-BTFE (1:2)) were simulated by using solutions of 1LiFSI:2DMC, 1LiFSI:1DMC and 1LiFSI:2DMC:4BTFE as the three adsorption configuration types on the most stable Li (100) surface. For moderately diluted solutions, in the case of high concentrations of LiFSI, the LiFSI adsorbs two DMC molecules (fig. 36F), while only the DMC-LiFSI couple adsorbs the Li (100) surface (fig. 36D). As shown in previous studies (Yamada et al, J Am Chem Soc 2014,136:5039-5046), the reduction in LiFSI and DMC of the Li anode was examined using the Lowest Unoccupied Molecular Orbital (LUMO) energy. FIGS. 43A-43C showThe projected density of states (PDOS) of each atom in the adsorbed LiFSI and DMC molecules is shown in three configurations. It is evident that in dilute LiFSI/DMC solutions (FIG. 43A), the LUMO of the conduction band is located at the DMC molecule. Thus, the DMC molecules reductively decompose on the Li anode, resulting in continuous corrosion of the Li metal anode and a rapid drop in capacity of the LMB during cycling. In contrast, for the 5.5M LiFSI concentrated solution (FIG. 43B), the appearance was similar to FSI^-A new LUMO peak associated with the anion. FSI^-The lowest energy level of the conduction band is lower than that of DMC, indicating FSI^-The anion, rather than the DMC solvent, will decompose as the primary reduction reaction, forming a surface film derived from FSI. Importantly, Li was diluted to 1.2M with inert BTFE (FIG. 43C)⁺-DMC-FSI^-The solvated structure is well maintained and the LUMO of the conduction band remains localized in the FSI^-On the anion, not on the DMC or BTFE molecule. In this regard, FSI^-The anions are still preferably reduced, forming a strong FSI-derived surface film on the Li metal, thus making it possible to improve the stability of LMB in such low concentrations of electrolyte (1.2M LiFSI/DMC-BTFE).

TABLE 9 DFT calculated adsorption energy and DMC, BTFE, and LiFSI

Beard charge on the surface of a Li (100) anode

TABLE 10 Mullikan charge of LiFSI salt, DMC and BTFE electrolyte calculated using Gaussian 09

Example 11

Lithium metal battery cell with LiFSI TEPa BTFE electrolyte

Li | Cu and Li | LiNi using different electrolyte formulations were studied at a constant temperature of 30 deg.C_xMn_yCo_zO₂(where x + y + z is 1, i.e., Li | | | NMC) performance of the cell. A High Concentration Electrolyte (HCE) of LiFSI in triethyl phosphate (TEPa), 3.8M LiFSI/TEPa, was prepared and diluted with different amounts of BTFE. The electrolyte formulations and physical properties of these electrolytes are shown in table 11.

TABLE 11 electrolyte numbering and formulation

The concentration of the diluted electrolyte was reduced to 1.2M by adding BTFE to 3.8M HCE, LiFSI: TEPa with a molar ratio of 0.75:1, the LiFSI: TEPa: BTFE molar ratio was 0.75:1: 3. Compared to the original concentrated LiFSI/TEPa, the viscosity of the diluted LSE was reduced by 2 orders of magnitude and the ionic conductivity increased by >2 times. The self-extinguishing time (SET) was found to be effectively zero for all electrolytes in table 11, indicating that they are non-flammable due to the high mass content of TEPa (21-57 wt%).

LiFSI salt is insoluble in BTFE solvent. Thus, BTFE is considered an "inert" diluent for the electrolyte and does not participate in the solvation of LiFSI. Raman spectroscopy was used to detect the solution coordination structures of concentrated LiFSI/TEPa electrolyte and BTFE diluted LiFSI/TEPa-BTFE electrolyte. In BTFE-diluted electrolytes, BTFE and Li⁺No observable raman shift of peak positions of TEPa solvate (fig. 44A-44D). The results show that dilution with BTFE does not change the local high concentration LiFSI-TEPa solvation structure and minimizes the presence of free TEPa solvent molecules, thus maintaining a good high stability of the electrolyte to the Li metal anode during repeated plating/stripping.

Fig. 45 shows CE of Li | | | Cu cells over long-term cycling using concentrated LiFSI/TEPa electrolyte (E37) and those LSEs with BTFE diluent. At 0.5mA cm^-2The following cycle is carried out, the Li deposition area capacity is1mA cm^-2. When BTFE was added as a diluent to reduce the LiFSI concentration to 1.5M (E39) and 1.2M (E40), the average CE of Li | | | Cu cells over 140 cycles was 98.63% and 98.82%, respectively, which was similar to or even better than the original concentrated LiFSI/TEPa (98.60%).

Further studies were conducted on Li | | | NMC (LiNi) using concentrated LiFSI/TEPa electrolyte without (E1) and with BTFE diluents (E39 and E40)_0.6Mn_0.2Co_0.2O₂The area capacity load is 1.5mAh/cm²) A battery cell. Figure 46 shows that Li | | | NMC cells of LSE diluted with BTFE exhibited higher discharge capacity, better cycling stability and cycling efficiency compared to 3.8M LiFSI/TEPa electrolyte. The cycling stability was performed at C/3 magnification, and the charge cut-off voltage was 4.4V.

BTFE-diluted LSE also provides Li | | | NCA cells (LiNi)_0.85Co_0.1Al_0.05O₂The area capacity load is 1.8mAh/cm²As shown in fig. 47) and Li LCO cells (LiCoO)₂The area capacity load is 2.2mAh/cm²As shown in fig. 48) high discharge capacity and good cycle stability. The results show that TEPa-based LSE diluted with non-flammable BTFE can safely and stably cycle LMB. The cycling stability of the Li | | | NCA cell was performed at C/3 rate with a charge cut-off voltage of 4.4V. The cycling stability of the Li | | | LCO battery cell was performed at a C/5 charge rate and a 1C discharge rate, with a charge cutoff voltage of 4.35V.

Example 12

Lithium metal battery cell with LiFSI TEPa TTE electrolyte

As shown in table 12, electrolytes were prepared with LiFSI, TEPa, and varying concentrations of TTE to produce TTE diluted LSE. The concentration of LSE was reduced to 1.9-1.0M using TTE diluent with a TEPa to TTE molar ratio of 1:1 to 1: 3. Due to the high mass content of TEPa (18-33 wt%), the TTE diluted LSE is also not flammable.

TABLE 12 electrolyte numbering and formulation

As shown in fig. 49, with TTE as a diluent, Li | | | Cu cells achieved average CE as high as 98.59-98.82% over 130 cycles, comparable to or even better than the original concentrated LiFSI/TEPa electrolyte (98.60%). At 0.5mAh cm^-2Circulating, and the Li deposition area capacity is 1mAh cm^-2. Similarly, TEPa-based LSE diluted with TTE also provided high capacity, good cycling stability and high efficiency of Li | | NMC cells (fig. 50). Cycling was performed at C/3 magnification, with a charge cut-off voltage of 4.4V.

Example 13

Lithium metal battery cell with LiFSI TMPa BTFE electrolyte

As shown in table 13, electrolytes were prepared with LiFSI, trimethyl phosphate (TMPa) and different concentrations of BTFE. By adding BTFE, the reaction can be performed by using 1: a2 molar ratio of TMPa/BTFE diluted 4.1M LiFSI/TMPa electrolyte to 1.8M. HCE and LSE based on TMPa are not flammable due to the high mass content of TMPa (22-43 wt%).

TABLE 13 electrolyte numbering and formulation

Li plating/stripping curves for Li | | | | Cu cells using concentrated 4.1M LiFSI/TMPa (E44) and 1.8M LiFSI/TMPa-BTFE (1:2, E45 molar ratio) electrolytes are shown in fig. 51A and 51B, respectively. The following protocol was used: 1) one forming cycle at 0.5mA cm^-2Down 5mAh cm on Cu^-2The initial Li plating of (2); then at 0.5mA cm^-2Li is stripped to 1V; 2) at 0.5mA cm^-2Electroplating 5mAh cm on Cu^-2Li as Li reservoir; 3) at 1mAh cm^-2Stripping/plating Li down for 10 cycles; 4) at 0.5mA cm^-2Next, all Li was exfoliated to 1V. 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 to lithium metal, providing high CE of 98.5% and 99.2% for HCE and LSE, respectively.

BTFE diluted TMPa-based LSE also exhibited high capacity, good cycling stability and high efficiency in Li | | NMC cells (fig. 52). Cycling was performed at C/3 magnification, with a charge cut-off voltage of 4.4V.

Example 14

Lithium metal battery cell with LiFSI TMPa DMC BTFE electrolyte

The non-flammable LSE can be modified by replacing some of the Flame Retardants (FR) and diluents with other conventional solvents or additives while still retaining a high enough FR content to maintain the non-flammable characteristics and retain a localized high concentration of solvated structures, resulting in high stability to the lithium metal anode. The electrolyte was prepared with DMC replacing some of the TMPa in LiFSI TMPa BTFE LSE. The formulation and properties of the electrolyte are shown in table 14.

TABLE 14 electrolyte numbering and formulation used in the study of example 4

The electrolytes (E46 and E47) both provide a very high CE of 99.34% in Li | | Cu cells (see fig. 53A and 53B, respectively). The following protocol was used to prepare the Li plating/stripping curve: 1) one forming cycle at 0.5mA cm^-2Down 5mAh cm on Cu^-2The initial Li plating of (2); then at 0.5mA cm^-2Li is stripped to 1V; 2) at 0.5mA cm^-2Electroplating 5mAh cm on Cu^-2Li as Li reservoir; 3) at 1mAh cm^-2Stripping/plating Li down for 10 cycles; 4) at 0.5mAcm^-2Next, all Li was exfoliated to 1V. The average CE was calculated by dividing the total Li-stripping capacity by the total Li plating capacity after the initial formation cycle.

The electrolyte also exhibited high capacity, good cycling stability and high efficiency in Li | | NMC cells (fig. 54). Cycling was performed at C/3 magnification, with a charge cut-off voltage of 4.4V.

Example 15

Lithium metal battery cells with LiFSI TEPa DME, LiFSI TMS TTE, and LiFSI TEPa DME TTE electrolytes

As shown in table 15, the flammability and electrochemical performance of several electrolytes were evaluated. FIGS. 55 and 56 show the cycling stability of Li | | | NMC811 cells using LiFSI-0.3TEPa-0.9DME and LiFSI-0.8TEPa-0.4DME-3TTE, respectively. The circulation is carried out at C/3, and the voltage is 2.8-4.4V. The SET value (54s/g) of LiFSI-0.3TEP-0.9DME electrolyte is lower than that of the reference electrolyte (1M LiPF in EC EMC)₆(3/7 by weight) +2 wt% VC (85 s/g)). The cell in FIG. 56 had a 50 μm Li anode with a lithium area deposition capacity of 0.5mAh cm^-2And comprises 3g/Ah of electrolyte. The result shows that the LiFSI-0.8TEPa-0.4DME-3TTE electrolyte has a low SET value (7.7s/g) and is suitable for high-load and dilute electrolyte conditions.

TABLE 15-flammability comparison of selected electrolytes with LiFSI salts

Representative examples of the disclosed electrolytes and batteries are described in the following numbered items.

1. 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 solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent, and wherein the electrolyte comprises at least 5 wt% of a flame retardant compound.

2. The electrolyte of claim 1, wherein the flame retardant compound comprises an organophosphate, an organophosphite, an organophosphonate, an organophosphamide, a phosphazene, or any combination thereof.

3. The electrolyte of claim 2, wherein 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.

4. The electrolyte according to any one of claims 1 to 3, wherein the solvent further comprises a co-solvent, wherein the active salt is soluble in the co-solvent.

5. The electrolyte of item 4, wherein the co-solvent comprises an ether solvent, a carbonate solvent, dimethyl sulfoxide, or any combination thereof.

6. The electrolyte of item 4, wherein the co-solvent comprises 1, 2-Dimethoxyethane (DME), 1, 3-Dioxolane (DOL), allyl ether, diethylene glycol ether, dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), ethylene carbonate (VC), fluoroethylene carbonate (FEC), 4-vinyl-1, 3-dioxolane-2-one (VEC), 4-methylene-1, 3-dioxolane-2-one (MEC), 4, 5-dimethylene-1, 3-dioxolane-2-one, dimethyl sulfoxide (DMSO), dimethyl sulfone (DMS), ethylmethyl sulfone (EMS), ethylvinyl sulfone (EVS), Tetramethylene sulfone (TMS), methyl butyrate, ethyl propionate, gamma-butyrolactone, acetonitrile, succinonitrile, triallylamine, triallylcyanurate, triallylisocyanurate, or any combination thereof.

7. The electrolyte according to any one of claims 1 to 6, wherein:

(i) the molar concentration of the active salt in the electrolyte is in the range of 0.5M to 2M; or

(ii) The active salt is present in the solvent at a molar concentration of greater than 3 moles of active salt per liter of the solvent; or

(iii) The molar concentration of the active salt in the electrolyte is at least 20% less than the molar concentration of the active salt in the solvent in the absence of the diluent; or

(iv) (iv) any combination of (i), (ii), and (iii).

8. The electrolyte according to any one of claims 1 to 7, wherein:

(i) the molar ratio of the active salt to the solvent is in the range of 0.33 to 1.5; or

(ii) The molar ratio of the solvent to the diluent is in the range of 0.2 to 5; or

(iii) Satisfy both (i) and (ii).

9. The electrolyte according to any one of claims 1 to 8, wherein:

(i) at least 90% of the molecules of the solvent are associated with the cation of the active salt; or

(ii) Less than 10% of the molecules of the diluent are associated with the cation of the active salt; or

(iii) Satisfy both (i) and (ii).

10. The electrolyte of any of claims 1-9, wherein the active salt comprises a lithium salt or a mixture of lithium salts, a sodium salt or a mixture of sodium salts, a potassium salt or a mixture of potassium salts, or a magnesium salt or a mixture of magnesium salts.

11. The electrolyte of any one of claims 1 to 9, wherein the active salt comprises lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethanesulfonyl) imide (LiBETI), sodium bis (fluorosulfonyl) imide (NaFSI), sodium bis (trifluoromethylsulfonyl) imide (NaTFSI), lithium bis (oxalato) borate (LiBOB), sodium bis (oxalato) borate (NaBOB), LiPF₆、LiAsF₆、LiBF₄、LiCF₃SO₃、LiClO₄Lithium difluoroborate anion (LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO₃、Li₂SO₄Or any combination thereof.

12. The electrolyte according to any one of claims 1 to 9, wherein:

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 is

The molar concentration of the active salt in the electrolyte is in the range of 0.75M to 1.5M.

13. The electrolyte according to any one of claims 1 to 12, wherein the diluent comprises a fluoroalkyl ether.

14. The electrolyte of any one of items 1 to 12, wherein the diluent comprises 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE), bis (2,2, 2-trifluoroethyl) ether (BTFE), 1,2,2, -tetrafluoroethyl-2, 2, 2-trifluoroethyl ether (TFTFE), Methoxynonafluorobutane (MOFB), Ethoxynonafluorobutane (EOFB), or any combination thereof.

15. The electrolyte of any one of claims 1 to 14, wherein the solvent is immiscible with the diluent, the electrolyte further comprising a bridging solvent having a different composition than the solvent and a different composition than the diluent, wherein the bridging solvent is miscible with the solvent and with the diluent.

16. The electrolyte of claim 15, wherein 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 (triglyme), tetraglyme (tetraglyme), or any combination thereof.

17. A battery, comprising:

(i) an electrolyte comprising

An active salt;

a diluent, wherein the solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent, the concentration of the active salt in the electrolyte is in the range of 0.75M to 2M, and the electrolyte comprises at least 5 wt% of a flame retardant compound;

(ii) an anode; and

(iii) a cathode, wherein the cell has a coulombic efficiency of ≧ 95%.

18. The battery of claim 17, wherein 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, hexafluorophosphazene, or any combination thereof.

19. The battery according to item 17 or 18, wherein:

the anode is lithium metal;

the active salt comprises LiFSI, LiTFSI and LiPF₆、LiAsF₆、LiBF₄、LiCF₃SO₃、LiClO₄、LiBOB、LiDFOB、LiI、LiBr、LiCl、LiSCN、LiNO₃、Li₂SO₄Or 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; and is

The cathode is Li_1+wNi_xMn_yCo_zO₂(x+y+z+w＝1，0≤w≤0.25)、LiNi_xMn_yCo_zO₂(x+y+z＝1)、LiCoO₂、LiNi_0.8Co_0.15Al_0.05O₂、LiNi_0.5Mn_1.5O₄Spinel, LiMn₂O₄、LiFePO₄、Li_4-xM_xTi₅O₁₂(M ═ Mg, Al, Ba, Sr or Ta; 0. ltoreq. x.ltoreq.1), MnO₂、V₂O₅、V₆O₁₃、LiV₃O₈、LiM^C1 _xM^C2 _1-xPO₄(M^C1Or M^C2Fe, Mn, Ni, Co, Cr, or Ti; x is more than or equal to 0 and less than or equal to 1), Li₃V_2-xM¹ _x(PO₄)₃(M¹Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce; x is more than or equal to 0 and less than or equal to 1), LiVPO₄F、LiM^C1 _xM^C2 _1-xO₂(M^C1And M^C2Independently of Fe, Mn, NiCo, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1), LiM^C1 _xM^C2 _yM^C3 _1-x-yO₂(M^C1、M^C2And M^C3Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1; y is more than or equal to 0 and less than or equal to 1), LiMn_2-yX_yO₄(X-Cr, Al or Fe, 0. ltoreq. y.ltoreq.1), LiNi_0.5-yX_yMn_1.5O₄(X ═ Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0. ltoreq. y<0.5)、xLi₂MnO₃·(1-x)LiM^C1 _yM^C2 _zM^C3 _1-y-zO₂(M^C1、M^C2And M^C3Independently Mn, Ni, Co, Cr, Fe or mixtures thereof; x is 0.3-0.5; y is less than or equal to 0.5; z is less than or equal to 0.5), Li₂M²SiO₄(M²Mn, Fe or Co), Li₂M²SO₄(M²Mn, Fe or Co), LiM²SO₄F(M²Fe, Mn or Co), Li_2-x(Fe_1-yMn_y)P₂O₇(0≤y≤1)、Cr₃O₈、Cr₂O₅Carbon/sulfur composite or air electrode.

20. The battery according to item 17 or 18, wherein:

the anode is sodium metal;

the active salt comprises NaFSI, NaTFSI, or a combination thereof;

the diluent comprises BTFE, TTE, TFTFE, MOFB, EOFB, or any combination thereof; and is

The cathode is NaFePO₄、Na₂FePO₄F、Na₂FeP₂O₇、Na₃V₂(PO₄)₃、Na₃V₂(PO₄)₂F₃、NaVPO₄F、NaVPOPOF、Na_1.5VOPO₄F_0.5、NaCo₂O₄、NaFeO₂、Na_xMO₂Wherein 0.4<x is less than or equal to 1, and M is transition metal or mixture of transition metals, Na_2/3Ni_1/3Mn_2/3O₂、Na_2/3Fe_1/2Mn_1/2O₂、Na_2/3Ni_1/6Co_1/6Mn_2/3O₂、NaNi_1/3Fe_1/3Mn_1/3O₂、NaNi_1/3Fe_1/3Co_1/3O₂、NaNi_1/2Mn_1/2O₂A Prussian white simulated cathode or a Prussian blue simulated cathode.

21. The battery of any of claims 17-20, wherein the solvent further comprises a co-solvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.

22. The battery of any one of claims 17-21, wherein the solvent is immiscible with the diluent, the electrolyte further comprising a bridging solvent having a different composition than the solvent and a different composition than the diluent, wherein the bridging solvent is miscible with the solvent and with the diluent.

In view of the many possible embodiments to which the disclosed invention may be applied, it should be recognized that the illustrated embodiments are only preferred examples of the invention and should not be taken as limiting the scope of the invention. Rather, the scope of the invention is defined by the appended claims. We therefore claim as our invention all such embodiments as may come within the scope and spirit of these claims.

Claims

1. An electrolyte comprising:

an active salt;

a diluent, wherein the solubility of the active salt in the diluent is at least 10 times less than the solubility of the active salt in the solvent, and

wherein the electrolyte comprises at least 5 wt% of a flame retardant compound.

4. The electrolyte of claim 1, wherein the solvent further comprises a co-solvent, wherein the active salt is soluble in the co-solvent.

5. The electrolyte of claim 4, wherein the co-solvent comprises an ether solvent, a carbonate solvent, dimethyl sulfoxide, or any combination thereof.

6. The electrolyte of claim 4, wherein the co-solvent comprises 1, 2-Dimethoxyethane (DME), 1, 3-Dioxolane (DOL), allyl ether, diethylene glycol ether, dimethyl carbonate (DMC), Ethyl Methyl Carbonate (EMC), diethyl carbonate (DEC), Ethylene Carbonate (EC), Propylene Carbonate (PC), ethylene carbonate (VC), fluoroethylene carbonate (FEC), 4-vinyl-1, 3-dioxolane-2-one (VEC), 4-methylene-1, 3-dioxolane-2-one (MEC), 4, 5-dimethylene-1, 3-dioxolane-2-one, dimethyl sulfoxide (DMSO), dimethyl sulfone (DMS), ethylmethyl sulfone (EMS), ethylvinyl sulfone (EVS), Tetramethylene sulfone (TMS), methyl butyrate, ethyl propionate, gamma-butyrolactone, acetonitrile, succinonitrile, triallylamine, triallylcyanurate, triallylisocyanurate, or any combination thereof.

7. The electrolyte of claim 1, wherein:

(iv) (iv) any combination of (i), (ii), and (iii).

8. The electrolyte of claim 1, wherein:

(iii) Satisfy both (i) and (ii).

9. The electrolyte of claim 1, wherein:

(iii) Satisfy both (i) and (ii).

10. The electrolyte of claim 1, wherein the active salt comprises a lithium salt or a mixture of lithium salts, a sodium salt or a mixture of sodium salts, a potassium salt or a mixture of potassium salts, or a magnesium salt or a mixture of magnesium salts.

11. The electrolyte of claim 1, wherein the active salt comprises lithium bis (fluorosulfonyl) imide (LiFSI), lithium bis (trifluoromethanesulfonyl) imide (LiTFSI), lithium bis (pentafluoroethanesulfonyl) imide (LiBETI), bis (fluorosulfonyl) imideSodium imide (NaFSI), sodium bis (trifluoromethylsulfonyl) imide (NaTFSI), lithium bis (oxalate) borate (LiBOB), sodium bis (oxalate) borate (NaBOB), LiPF₆、LiAsF₆、LiBF₄、LiCF₃SO₃、LiClO₄Lithium difluoroborate anion (LiDFOB), LiI, LiBr, LiCl, LiSCN, LiNO₃、Li₂SO₄Or any combination thereof.

12. The electrolyte of claim 1, wherein:

13. The electrolyte of claim 1, wherein the diluent comprises a fluoroalkyl ether.

14. The electrolyte of claim 1, wherein the diluent comprises 1,1,2, 2-tetrafluoroethyl-2, 2,3, 3-tetrafluoropropyl ether (TTE), bis (2,2, 2-trifluoroethyl) ether (BTFE), 1,2,2, -tetrafluoroethyl-2, 2, 2-trifluoroethyl ether (TFTFE), Methoxynonafluorobutane (MOFB), Ethoxynonafluorobutane (EOFB), or any combination thereof.

17. A battery, comprising:

an electrolyte comprising

An active salt;

an anode; and

a cathode, wherein the cell has a coulombic efficiency of ≧ 95%.

19. The battery of claim 17, wherein:

the anode is lithium metal;

The cathode is Li_1+wNi_xMn_yCo_zO₂(x+y+z+w＝1，0≤w≤0.25)、LiNi_xMn_yCo_zO₂(x+y+z＝1)、LiCoO₂、LiNi_0.8Co_0.15Al_0.05O₂、LiNi_0.5Mn_1.5O₄Spinel, LiMn₂O₄、LiFePO₄、Li_4-xM_xTi₅O₁₂(M ═ Mg, Al, Ba, Sr or Ta; 0. ltoreq. x.ltoreq.1), MnO₂、V₂O₅、V₆O₁₃、LiV₃O₈、LiM^C1 _xM^C2 _1-xPO₄(M^C1Or M^C2Fe, Mn, Ni, Co, Cr, or Ti; x is more than or equal to 0 and less than or equal to 1), Li₃V_2-xM¹ _x(PO₄)₃(M¹Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce; x is more than or equal to 0 and less than or equal to 1), LiVPO₄F、LiM^C1 _xM^C2 _1-xO₂(M^C1And M^C2Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1), LiM^C1 _xM^C2 _yM^C3 _1-x-yO₂(M^C1、M^C2And M^C3Independently Fe, Mn, Ni, Co, Cr, Ti, Mg or Al; x is more than or equal to 0 and less than or equal to 1; y is more than or equal to 0 and less than or equal to 1), LiMn_2-yX_yO₄(X-Cr, Al or Fe, 0. ltoreq. y.ltoreq.1), LiNi_0.5-yX_yMn_1.5O₄(X ═ Fe, Cr, Zn, Al, Mg, Ga, V or Cu; 0. ltoreq. y<0.5)、xLi₂MnO₃·(1-x)LiM^C1 _yM^C2 _zM^C3 _1-y-zO₂(M^C1、M^C2And M^C3Independently Mn, Ni, Co, Cr, Fe or mixtures thereof; x is 0.3-0.5; y is less than or equal to 0.5; z is less than or equal to 0.5), Li₂M²SiO₄(M²Mn, Fe or Co), Li₂M²SO₄(M²Mn, Fe or Co), LiM²SO₄F(M²Fe, Mn or Co), Li_2-x(Fe_1-yMn_y)P₂O₇(0≤y≤1)、Cr₃O₈、Cr₂O₅Carbon/sulfur composite or air electrode.

20. The battery of claim 17, wherein:

the anode is sodium metal;

the active salt comprises NaFSI, NaTFSI, or a combination thereof;

21. The battery of claim 17, wherein the solvent further comprises a co-solvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.