MnO2 cathode materials with the improved stability via nitrogen doping for aqueous zinc-ion batteries

Abstract

The research and exploration of manganese-based aqueous zinc-ion batteries have been controversial of cycle stability and mechanism investigation, thus improving the stability and exploring storage mechanism are still the most main issue. Defect engineering has become an effective method to improve cycle stability. Herein, a nitrogen-doped ε-MnO2 (MnO2@N) has been prepared using electrochemical deposition and heat treatment under nitrogen atmosphere. As the cathode for zinc-ion batteries, the capacity retention rate of MnO2@N cathode is close to 100% after 500 cycles at 0.5 A g−1, while the capacity retention rate for the initial MnO2 cathode is 62%. At 5 A g−1, the capacity retention rate of MnO2@N cathode is 83% after 1000 cycles, which is much higher than the 27% capacity retention rate for the original MnO2 cathode. And it can be found that the oxygen vacancies increase after nitrogen doping, which can improve the conductivity of the MnO2@N cathode. Also, there is Mn-N bond in MnO2@N, which can enhance the electrochemical stability of MnO2@N cathode. In addition, the electrochemical mechanism of MnO2@N cathode has been explored by the CV, GCD and GITT tests. It is found that nitrogen doping promotes the intercalation of H+ and the corresponding capacity contribution. Compared with the original MnO2 cathode, the diffusion coefficient of H+ and Zn2+in MnO2@N cathode increases. Also, the reactions during the charging and discharging process are explored through the ex-situ XRD test. And this work may provide some new ideas for improving the stability of manganese-based zinc-ion batteries.