An Environmentally Benign Electrolyte for High Energy Lithium Metal Batteries

A hybrid electrolyte comprising a high content of H₂O for a lithium metal cell is reported. At high LiFSI salt concentration, the N-methyl-N-propyl-piperidinium bis(fluorosulfonyl) imide (PMpipFSI) electrolyte can tolerate up to 1 M H₂O addition without sacrificing its redox stability on both lithium nickel manganese cobalt oxide (NMC) cathode and lithium metal anode. Molecular dynamics simulations revealed the underpinned mechanism that, at high salt concentrations, H₂O molecules are embedded in the Li⁺, PMpip⁺, and FSI^- bulk as a structural material with a strong solvation with Li⁺ and are orderly distributed at the surface of both electrodes. This electrolyte eliminates the critical moisture controls required for the state-of-the-art (SOA) carbonate/LiPF₆ electrolyte, electrode, separator and cell assembly, thus significantly reducing the cost of the mass production of the batteries.