Difluorophosphate additive compounds and methods thereof for use in energy storage devices
The present disclosure relates to the synthesis and evaluation of difluorophosphate additives for use in energy storage devices. The difluorophosphate additive may be selected from the group consisting of lithium difluorophosphate (LFO), sodium difluorophosphate (NaFO), ammonium difluorophosphate (AFO), tetramethylammonium difluorophosphate (MAFO), potassium difluorophosphate (KFO), and combinations thereof. In some instances, the difluorophosphate additive is not lithium difluorophosphate (LFO).
1 . An energy storage device, comprising:
an anode comprising an anode active material consisting of a carbon material;
a cathode;
a housing; and
an electrolyte comprising a lithium salt, a solvent, and an additive consisting of sodium difluorophosphate (NaFO) and at least one additional difluorophosphate additive selected from the group consisting of: lithium difluorophosphate (LFO), ammonium difluorophosphate (AFO), tetramethylammonium difluorophosphate (MAFO), potassium difluorophosphate (KFO), and combinations thereof;
wherein the anode, cathode and electrolyte are positioned within the housing;
wherein the electrolyte comprises 0.1 wt. % to 5 wt. % of NaFO, and 0.1 wt. % to 5 wt. % of the additional difluorophosphate additive; and
wherein the device has a charge transfer resistance (R ct ) of less than about 60 Ohms/cm 2 after formation at a voltage of 4.3V-4.4V.
2 . The device of claim 1 , wherein the additional difluorophosphate additive is selected from the group consisting of: ammonium difluorophosphate (AFO), tetramethylammonium difluorophosphate (MAFO), potassium difluorophosphate (KFO), and combinations thereof.
3 . The device of claim 1 , wherein the additional difluorophosphate additive does not comprise lithium difluorophosphate (LFO).
4 . The device of claim 1 , wherein the electrolyte comprises about 1 wt. % of NaFO.
5 . The device of claim 1 , wherein the carbon material is selected from the group consisting of a graphitic material, a graphite, a graphene-containing material, a hard carbon, a soft carbon, carbon nanotubes, a porous carbon, a conductive carbon, and combinations thereof.
6 . The device of claim 1 , wherein the cathode comprises a cathode active material selected from the group consisting of: lithium nickel manganese cobalt oxide (NMC), lithium manganese oxide (LMO), lithium iron phosphate (LFP), lithium cobalt oxide (LCO), lithium titanate (LTO), lithium nickel manganese oxide (LNMO), lithium nickel cobalt aluminum oxide (NCA), lithium nickel manganese aluminum oxide (NMA) and combinations thereof.
7 . The device of claim 1 , wherein the lithium salt is selected from the group consisting of: LiPF 6 , LiBF 4 , LiCIO 4 , LiN(SO 2 CF 3 ) 2 , LiSO 3 CF 3 , LiB(C 2 O 4 ) 2 , LiN(SO 2 F) 2 , LiC 2 BF 2 O 4 , and combinations thereof.
8 . The device of claim 1 , wherein the electrolyte comprises a solvent selected from the group consisting of: ethylene carbonate (EC), propylene carbonate (PC), vinyl ethylene carbonate (VEC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl acetate (MA), and combinations thereof.
9 . The device of claim 1 , wherein the device has a charge transfer resistance (R ct ) after formation at 4.3V of less than about 60 Ohms/cm 2 .
10 . The device of claim 1 , wherein the device has a charge transfer resistance (R ct ) after formation at 4.4V of less than about 60 Ohms/cm 2 .
11 . The device of claim 1 , wherein the device has a capacity after 2000 cycles relative to a capacity after a third cycle (Qd2000/Qd3) at 40° C. and upper cutoff voltage of 4.4V of at least about 0.8.
12 . The device of claim 1 , wherein the device has a capacity after 2500 cycles relative to a capacity after a third cycle (Qd2500/Qd3) at 40° C. and upper cutoff voltage of 4.3V of at least about 0.8.
13 . The device of claim 1 , wherein the energy storage device is a battery.
14 . A method of fabricating an energy storage device, comprising:
positioning an anode, a cathode and an electrolyte within a housing, wherein the electrolyte comprises a lithium salt, a solvent, and an additive consisting of sodium difluorophosphate (NaFO) and at least one additional difluorophosphate additive selected from the group consisting of: lithium difluorophosphate (LFO), ammonium difluorophosphate (AFO), tetramethylammonium difluorophosphate (MAFO), potassium difluorophosphate (KFO), and combinations thereof;
wherein the anode comprises an anode active material consisting of a carbon material;
wherein the electrolyte comprises 0.1 wt. % to 5 wt. % of NaFO, and 0.1 wt. % to 5 wt. % of the additional difluorophosphate additive;
sealing the housing to form an energy storage device; and
forming a solid-electrolyte interphase (SEI) at the anode, wherein forming the SEI comprises charge cycling the energy storage device to a voltage of at least about 4.3V.
15 . The device of claim 1 , wherein the additional difluorophosphate additive is LFO.
16 . The device of claim 1 , wherein the additional difluorophosphate additive is selected from AFO and MAFO.
17 . The device of claim 1 , wherein the additive consists of NaFO and the at least one additional difluorophosphate additive.
18 . The device of claim 1 , wherein the electrolyte consists of the lithium salt, the solvent, and the additive.
19 . The method of claim 14 , wherein the electrolyte consists of the lithium salt, the solvent, and the additive.
20 . The device of claim 5 , wherein the carbon material is a graphite.