Room temperature synthesis of the Co-doped δ-MnO2 cathode for high-performance zinc-ion batteries

Manganese oxide (MnO2) is considered as one of the most hopeful cathode materials for aqueous zinc ion batteries (ZIBs) thanks to its nontoxicity, high voltage, and low cost. However, its practical application in ZIBs is hindered by its slow reaction kinetics and poor structural stability. The heteroatom-doped δ-MnO2 prepared by hydrothermal reaction can overcome the inherent defects of δ-MnO2 and significantly improve the performance of ZIBs. Nevertheless, hydrothermal method requires high temperature and high pressure processes, which will increase production costs and energy consumption. To address this issue, herein, the Co-doped δ-MnO2 (Co-δ-MnO2) cathode is synthesized by a one-step route through stirring the solution of MnCl2, CoCl2, and H2O2 in the presence of tetramethylammonium cations at room temperature. The Co-δ-MnO2 cathode displays outstanding zinc ion storage performance with a high specific capacity of 408.9 mAh g−1 at the current density of 0.1 A g−1, a superior rate capability of 232.7 mAh g−1 at 3.0 A g−1, a high energy density of 554.9 Wh kg−1 at 135.2 W kg−1, and good cyclability with a capacity retention rate of 77.8 % after 1000 cycles. Ex-situ tests reveal that the charge storage mechanism of the Co-δ-MnO2 cathode is H+/Zn2+ co-insertion/extraction.