Hydrated ammonium manganese phosphates by electrochemically induced manganese-defect as cathode material for aqueous zinc ion batteries

Abstract

Aqueous zinc ion batteries (AZIBs) with the merits of low cost, low toxicity, high safety, environmental benignity as well as multi-valence properties as the large-scale energy storage devices demonstrate tremendous application prospect. However, the explorations for the most competitive manganese-based cathode materials of AZIBs have been mainly limited to some known manganese oxides. Herein, we report a new type of cathode material NH₄MnPO₄·H₂O (abbreviated as AMPH) for rechargeable AZIBs synthesized through a simple hydrothermal method. An in-situ electrochemical strategy inducing Mn-defect has been used to unlock the electrochemical activity of AMPH through the initial charge process, which can convert poor electrochemical characteristic of AMPH towards Zn²⁺ and NH₄⁺ into great electrochemically active cathode for AZIBs. It still delivers a reversible discharge capacity up to 90.0 mAh/g at 0.5 A/g even after 1000^th cycles, which indicates a considerable capacity and an impressive cycle stability. Furthermore, this cathode reveals an (de)insertion mechanism of Zn²⁺ and NH₄⁺ without structural collapse during the charge/discharge process. The work not only supplements a new member for the family of manganese-based compound for AZIBs, but also provides a potential direction for developing novel cathode material for AZIBs by introducing defect chemistry.