A multiple electrolyte concept for lithium-metal batteries

A cross-linked polymer membrane formed by poly(ethylene oxide) (PEO), N-methoxyethyl-N-methylpyrrolidium (fluorosulfonyl)(trifluoromethanesulfonyl)imide (Pyr12O1FTFSI) ionic liquid and LiFTFSI salt is proposed as the electrolyte for lithium-metal batteries. The ternary membrane has a PEO:Pyr12O1FTFSI:LiFTFSI composition of 20:6:4 by mole, which ensures thermal stability up to 220 °C, overall ionic conductivity of 10− 3 S cm− 1 at 40 °C and suitable Li+ transport properties. Combined with the LiFePO4 composite electrode, whose pores are filled with the Pyr12O1FTFSI:LiFTFSI electrolyte, and Li-metal anode, it yields Li/LiFePO4 cells delivering at 40 °C stable capacity (150 mAh g− 1 or 0.7 mAh cm− 2) with coulombic efficiency higher than 99.5%. Impedance spectroscopy measurements reveal low resistance of the electrode/electrolyte interface at both the anode and the cathode. Preliminary results at 20 °C indicates a capacity of 130 mAh g− 1 at C/10 rate (17 mA g− 1) with coulombic efficiency higher than 99.5%, thereby suggesting PEO:Pyr12O1FTFSI:LiFTFSI as suitable electrolyte for lithium-metal polymer batteries for stationary storage applications, coupled for example with PV and wind generation.