Harvesting Mn ²⁺ by Encapsulated MnO _x With sp ² ‐Carbon to Enhance the Mn ²⁺ /MnO ₂ Conversion for High‐Capacity Zn‐Ion Batteries

ABSTRACT Manganese oxide is a promising cathode material for aqueous Zn‐ion batteries (AZIBs), of which the key is to inhibit the dissolution of Mn ²⁺ and harvest Mn ²⁺ to achieve high‐capacity and long‐life. Herein, MnO _x cathode is encapsulated into in situ formed sp ² ‐carbon shell (denoted as CMC) via coating Mn‐based metal organic framework by coal tar pitch for Zn ²⁺ storage. Thanks to the in situ formed sp ² ‐carbon shell in CMC, the formation energy of Mn vacancy is significantly increased, thus effectively inhibiting the dissolution of Mn ²⁺ . Meanwhile, a reversible Mn ²⁺ /MnO ₂ conversion is achieved by harvesting Mn ²⁺ via electrostatic attraction, and preventing the formation of massive zinc hydroxide sulfate via repelling SO ₄ ²⁻ and OH ⁻ . Moreover, the sp ² ‐carbon shell with excellent conductivity enables effective re‐deposition of Mn ²⁺ to MnO ₂ . As expected, the novel CMC cathode delivers an exceptional capacity of 438.2 mAh g ⁻¹ (889.5 mAh g ⁻¹ based on the mass of MnO _x ) at 0.2 A g ⁻¹ with a capacity retention up to 91.1% over 5000 cycles at 2 A g ⁻¹ . This work proposes an effective strategy to synthesize advanced Mn‐based cathode materials to harvest Mn ²⁺ through interface engineering for AZIBs.