Mo doping provokes two electron reaction in MnO2 with ultrahigh capacity for aqueous zinc ion batteries

Rechargeable aqueous zinc ion batteries (AZIBs) based on manganese dioxide (MnO2) have received much attention for large-scale energy storage applications, however, their energy density is mainly limited by the one-electron reaction of Mn4+/Mn3+ redox. Herein, Mo doped δ-MnO2 (Mo-MnO2) is prepared and used as a high-performance cathode for AZIBs, which delivers an ultrahigh specific capacity of 652 mAh·g−1 at 0.2 A·g−1 based on the two-step two-electron redox reaction of Mn4+ ⇌ Mn3+ ⇌ Mn2+. Ex-situ structural analysis and density functional theory calculation reveal that the Mo5+ dopant plays an important role in enhancing the electronic conductivity of Mo-MnO2 and promoting Jahn—Teller distortion of octahedral [MnO6] in ZnMn2O4, which facilitates the second step redox reaction of Mn3+/Mn2+. This work provides a novel cathode materials design with multi-electron redox chemistry to achieve high energy density in AZIBs.