Developing high-performance Zn²⁺-pre-inserted MnO₂<i>via in situ</i> electrodeposition for aqueous Zn-ion batteries

Rechargeable aqueous zinc-ion batteries (AZIBs) are considered to be a promising alternative to lithium-ion batteries (LIBs), because they are more environmentally friendly, cheaper and safer than LIBs. Although manganese dioxide (MnO₂) has many advantages as a cathode material for use in AZIBs, its structural degradation and slow ion diffusion seriously hinder its electrochemical performance. Herein, Zn²⁺-pre-inserted MnO₂ (Zn-MnO₂) was prepared by a simple <i>in situ</i> electrodeposition method. The specific capacity and cycling performance of AZIBs based on Zn-MnO₂ cathodes were significantly improved compared to those of AZIBs with original MnO₂ cathodes. The capacity decay of a Zn//Zn-MnO₂ cell was only 0.029% per cycle at a current density of 1 A g^-1 for 1000 cycles. The pre-inserted Zn²⁺ not only reinforces the structure of MnO₂, but it also reduces the voltage difference between the charge and discharge curves. In addition, the mechanism of the co-insertion of H⁺ and Zn²⁺ during the discharge of AZIBs was elucidated based on the galvanostatic intermittent titration technique (GITT). This work will inspire and promote the development of aqueous zinc-ion batteries.