Ni2+ pre-intercalation and polyindole coating synergy enhance the performance of δ-MnO2 cathode for zinc ion battery

Aqueous zinc ion batteries (AZIBs) with MnO 2 as the positive electrode have attracted extensive attention due to their high theoretical energy density. However, the dissolution of the positive electrode and the poor conductivity during the cycling process affect its development prospects. In this paper, δ-MnO 2 with larger interlayer spacing is adopted, and pre-intercalation of Ni 2+ is used to further expand its interlayer spacing to enhance the diffusion kinetics of Zn 2+ in the cathode. Density functional theory (DFT) calculations show that the charge distribution around Mn and O atoms will be changed to improve the conductivity of the MnO 2 cathode by the Ni 2+ intercalation. However, the intercalation of metal cations will lead to the production of more Mn 3+ . which will lead to further manganese dissolution. Therefore, we prepared a polyindole (PIn) coating layer with high conductivity and can effectively prevent cathode erosion by in-situ polymerization. The formation of a heterogeneous interface between PIn and MnO 2 surface not only provides more active electrochemical sites, but also enhances the conductivity of the cathode and reduces the occurrence of manganese dissolution, which greatly improves the cycle performance and specific capacity of the cathode. Ni-MnO 2 @PIn delivers a discharge capacity of 385 mAh g −1 at a current density of 0.1 A g −1 , and maintains a capacity of 278 mAh g −1 after 200 cycles at a current density of 0.3 A g −1 , with a capacity retention of 95 %.