Low flammability electrolytes for stable operation of electrochemical devices

1. An electrolyte, comprising:

an active salt comprising 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), LiPF 6 , LiAsF 6 , LiBF 4 , LiCF 3 SO 3 , LiClO 4 , lithium difluoro oxalato borate anion (LiDFOB), Lil, LiBr, LiCI, LiSCN, LiNO 3 Li 2 SO 4 or any combination thereof;

a solvent comprising a flame retardant compound, the flame retardant compound comprising an organic phosphate, an organic phosphite, an organic phosphonate, an organic phosphoramide, a phosphazene, or any combination thereof, wherein the active salt is soluble in the solvent and a molar ratio of the active salt to the solvent is within a range of from 0.7 to 1.5; and

a diluent comprising a fluoroalkyl ether, wherein the active salt has a solubility in the diluent at least 10 times less than a solubility of the active salt in the solvent, and

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

2. The electrolyte of claim 1 , 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.

3. The electrolyte of claim 1 , wherein the solvent further comprises a cosolvent, wherein the active salt is soluble in the cosolvent.

4. The electrolyte of claim 3 , wherein the cosolvent comprises a carbonate solvent, an ether solvent, dimethyl sulfoxide, or any combination thereof.

5. The electrolyte of claim 3 , wherein the cosolvent 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), vinylene carbonate (VC), fluoroethylene carbonate (FEC), 4-vinyl-1,3-dioxolan-2-one (VEC), 4-methylene-1,3-dioxolan-2-one (MEC), 4,5-dimethylene-1,3-dioxolan-2-one, dimethyl sulfoxide (DMSO), dimethyl sulfone (DMS), ethyl methyl sulfone (EMS), ethyl vinyl sulfone (EVS), tetramethylene sulfone (TMS), methyl butyrate, ethyl propionate, gamma-butyrolactone, acetonitrile, succinonitrile, triallyl amine, triallyl cyanurate, triallyl isocyanurate, or any combination thereof.

6. The electrolyte of claim 1 , wherein:

(i) the active salt has a molar concentration in the electrolyte within a range of from 0.5 M to 2 M;

(ii) the active salt has a molar concentration in the solvent of greater than 3 moles of active salt per liter of the solvent;

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

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

7. The electrolyte of claim 1 , wherein:

(i) a molar ratio of the active salt to the solvent is within a range of from 0.7-1.2;

(ii) a molar ratio of the solvent to the diluent is within a range of from 0.2 to 5; or (iii) both (i) and (ii).

8. The electrolyte of claim 1 , wherein:

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

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

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

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

10. The electrolyte of claim 1 , wherein:

the active salt is (i) LiFSI, LiTFSI, or a combination thereof, or (ii) NaFSI, NaTFSI, or a combination thereof;

the solvent comprises trimethyl phosphate, triethyl phosphate, or a combination thereof; and

the active salt has a molar concentration in the electrolyte within a range of from 0.75 M to 1.5 M.

11. 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), 1,1,2,2,-tetrafluoroethyl-2,2,2 -trifluoroethyl ether (TFTFE), methoxynonafluorobutane (MOFB), ethoxynonafluorobutane (EOFB), or any combination thereof.

12. The electrolyte of claim 1 , wherein the solvent and the diluent are immiscible, the electrolyte further comprising a bridge solvent having a different composition than the solvent and a different composition than the diluent, wherein the bridge solvent is miscible with the solvent and with the diluent.

13. The electrolyte of claim 12 , 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 (triethylene glycol dimethyl ether), tetraglyme (tetraethylene glycol dimethyl ether), or any combination thereof.

14. A battery, comprising:

an electrolyte comprising

an active salt comprising 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), LiPF 6 , LiAsF 6 , LiBF 4 , LiCF 3 SO 3 LiC 1 O 4 lithium difluoro oxalato borate anion (LiDFOB), Lil, LiBr, LiCl, LiSCN, LiNO 3 Li 2 SO 4 or any combination thereof,

a solvent comprising a flame retardant compound comprising an organic phosphate, an organic phosphite, an organic phosphonate, an organic phosphoramide, a phosphazene, or any combination thereof, wherein the active salt is soluble in the solvent and a molar ratio of the active salt to the solvent is within a range of from 0.7 to 1.5, and

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

an anode; and

a cathode, wherein the battery has a coulombic efficiency ≤95%.

15. The battery of claim 14 , 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.

16. The battery of claim 14 , wherein:

the anode is lithium metal;

the active salt comprises LiFSI, LiTFSI, LiPF 6 , LiAsF 6 ,LiBF 4 , LiCF 3 SO 3 ,LiCIO 4 ,LiBOB, LiDFOB, Lil,LiBr, LiCI, LiSCN, LiNO 3 , Li 2 SO 4 ,or any combination thereof;

the flame retardant compound comprises trimethyl phosphate triethyl phosphate, or a combination thereof:

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

the cathode is Li 1+w Ni x Mn y Co z O 2 (x+y+z+w=1, 0≤w≤0.25), LiNi x Mn y Co z O 2 (x+y+z=1), LiCoO 2 , LiNi 0.8 Co 0.15 AI 0.05 O 2 , LiNi 0.5 Mn 1.5 O 4 spinel, LiMn 2 O 4 ,LiFePO 4 ,Li 4−x M x Ti 5 O 12 (M=Mg, Al, Ba, Sr, or Ta; 0≤x≤1), MnO 2 , V 2 O 5 , V 6 O 13 , LiV 3 O 8 , LiM C1 x M C2 1−x PO 4 (M C1 or M C2 =Fe, Mn, Ni, Co, Cr, or Ti; 0≤x≤1), Li 3 V 2−x M 1 x (PO 4 ) 3 (M 1 =Cr, Co, Fe, Mg, Y, Ti, Nb, or Ce; 0≤x≤1), LiVPO 4 F, LiM C1 x M C2 1−x O 2 ((M C1 and M C2 independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1), LiM C1 x M C2 y M C3 1−x−y O 2 ((M C1 , M C2 , and M C3 independently are Fe, Mn, Ni, Co, Cr, Ti, Mg, or Al; 0≤x≤1; 0≤y≤1), LiMn 2−y X y O 4 (X=Cr, Al, or Fe, 0≤y≤1), LiNi 0.5−y X y Mn 1.5 O 4 (X=Fe, Cr, Zn, Al, Mg, Ga, V, or Cu; 0≤y<0.5), xLi 2 MnO 3 .(1−x)LiM C1 y M C2 z M C3 1−y−z O 2 (M C1 , M C2 , and M C3 independently are Mn, Ni, Co, Cr, Fe, or mixture thereof; x=0.3-0.5; y≤0.5; z≤0.5), Li 2 M 2 SiO 4 (M 2 =Mn, Fe, or Co), Li 2 M 2 SO 4 (M 2 =Mn, Fe, or Co), LiM 2 SO 4 F (M 2 =Fe, Mn, or Co), Li 2−x (Fe 1−y Mn y )P 2 O 7 (0≤y≤1). Cr 3 O 8 , Cr 2 O 5 , a carbon/sulfur composite, or an air electrode.

17. The battery of claim 14 , wherein:

the anode is sodium metal;

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

the flame retardant compound comprises trimethyl phosphate, triethyl phosphate, or a combination thereof;

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

the cathode is NaFePO 4 , Na 2 FePO 4 F, Na 2 FeP 2 O 7 , Na 3 V 2 (PO 4 ) 3 , Na 3 V 2 (PO 4 ) 2 F 3 , NaVPO 4 F, NaVPOPOF, Na 1.5 VOPO 4 F 0.5 , NaCo 2 O 4 , NaFeO 2 , Na x MO 2 where 0.4<x≤1, and M is a transition metal or a mixture of transition metals, Na 2/3 Ni 1/3 Mn 2/3 O 2 , Na 2/3 Fe 1/2 Mn 1/2 O 2 , Na 2/3 Ni 1/6 Co 1/6 Mn 2/3 O 2 , NaNi 1/3 Fe 1/3 Mn 1/3 O 2 , NaNi 1/3 Fe 1/3 CO 1/3 O 2 , NaNi 1/2 Mn 1/2 O 2 , a Prussian white analogue cathode, or a Prussian blue analogue cathode.

18. The battery of claim 14 , wherein the solvent further comprises a cosolvent comprising a carbonate solvent, an ether solvent, dimethyl sulfoxide, or a combination thereof.

19. The battery of claim 14 , wherein the solvent and the diluent are immiscible, the electrolyte further comprising a bridge solvent having a different composition than the solvent and a different composition than the diluent, wherein the bridge solvent is miscible with the solvent and with the diluent.