Unraveling the Anionic Redox Chemistry in Aqueous Zinc‐MnO2 Batteries

Abstract

Activating anionic redox reaction (ARR) has attracted a great interest in Li/Na‐ion batteries owing to the fascinating extra‐capacity at high operating voltages. However, ARR has rarely been reported in aqueous zinc‐ion batteries (AZIBs) and its possibility in the popular MnO2‐based cathodes has not been explored. Herein, the novel manganese deficient MnO2 micro‐nano spheres with interlayer “Ca2+‐pillars” (CaMnO‐140) are prepared via a low‐temperature (140 °C) hydrothermal method, where the Mn vacancies can trigger ARR by creating non‐bonding O 2p states, the pre‐intercalated Ca2+ can reinforce the layered structure and suppress the lattice oxygen release by forming Ca−O configurations. The tailored CaMnO‐140 cathode demonstrates an unprecedentedly high rate capability (485.4 mAh g−1 at 0.1 A g−1 with 154.5 mAh g−1 at 10 A g−1) and a marvelous long‐term cycling durability (90.6% capacity retention over 5000 cycles) in AZIBs. The reversible oxygen redox chemistry accompanied by CF3SO3− (from the electrolyte) uptake/release, and the manganese redox accompanied by H+/Zn2+ co‐insertion/extraction, are elucidated by advanced synchrotron characterizations and theoretical computations. Finally, pouch‐type CaMnO‐140//Zn batteries manifest bright application prospects with high energy, long life, wide‐temperature adaptability, and high operating safety. This study provides new perspectives for developing high‐energy cathodes for AZIBs by initiating anionic redox chemistry.