Single Halide Electrolytes for High‐Performance Mn Metal Batteries

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 (MnBr₂ or MnCl₂), relative to the benchmark hybrid system (MnCl₂-AlCl₃-Mn(TFSI)₂; TFSI = bis(trifluoromethanesulphonyl)imide), for high-performance Mn metal batteries (MMBs). In the optimized solvent system, for instance, MnBr₂ 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 MnBr₂ 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 Mn²⁺ hosts, activated carbon and even a Br^-/Br⁰ 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.