Single Halide Electrolytes for High‐Performance Mn Metal Batteries

Abstract Rechargeable manganese (Mn) batteries have risen as a highly promising battery technology for sustainable energy storage due to rich abundance, high capacity and low working potential of Mn metal. The key challenge lies at developing advanced Mn‐based electrolyte ensuring reversible Mn plating/stripping. Herein, we report new Mn electrolytes based on low‐cost single halide (MnBr 2 or MnCl 2 ), relative to the benchmark hybrid system (MnCl 2 ‐AlCl 3 ‐Mn(TFSI) 2 ; TFSI = bis(trifluoromethanesulphonyl)imide), for high‐performance Mn metal batteries (MMBs). In the optimized solvent system, for instance, MnBr 2 dissociates as various solvated [MnBr x ] 2− x (0 ≤ x ≤ 4) ions with assistance of triethyl phosphate. No passivation layer is formed on Mn anode owing to non‐reducibility of Br − . The MnBr 2 electrolyte displays superior Mn plating/stripping stability (>1300 h) with near integer Coulombic efficiency under practical areal capacities of 1–50 mAh cm −2 . The overpotential is suppressed as low as <200 mV at 0.5 mA cm −2 . When paring the Mn metal anode with different cathodes like organic Mn 2+ hosts, activated carbon and even a Br − /Br 0 conversion cathode, high‐performance MMBs have been demonstrated with long cycling life (>2000 cycles) and high voltage (1.6 V). Our work represents a brand‐new electrolyte design concept for advanced MMBs and can be readily expanded to other multivalent metal batteries.