Tuning crystal structure of MnO2 during different hydrothermal synthesis temperature and its electrochemical performance as cathode material for zinc ion battery

Abstract

Rechargeable zinc ion batteries are characterized by low cost, high safety and high specific power, especially mild aqueous Zn–MnO2 battery. Owing to that manganese dioxide with different crystal types has a great impact on its electrochemical performance, it is necessary to understand the crystal structure transformation process of manganese dioxide during synthesis and its effect on the battery property. Here, the crystal structure transformation during different hydrothermal synthesis temperature and related electrochemical performance of MnO2 are researched in detail. It is found that a mixture of ramsdellite (R–MnO2) and Nsutit (γ-MnO2) can be obtained as the hydrothermal synthesis temperature ranges from 85 °C to 145 °C. While, a single phase of β-MnO2 can be observed as the hydrothermal synthesis temperature ranges from 165 °C to 185 °C. Also, manganese valence increases and BET surface area decreases during the evolution from the mixture of ramsdellite (R–MnO2) and Nsutit (γ-MnO2) to the final single β-MnO2 phase. Electrochemical performance verifies that the as-prepared MnO2 under the hydrothermal synthesis temperature of 85 °C possesses the best rate performance and cyclic property among the as-obtained samples, with a discharge capacity of 50 mAh g−1 at 2 C, and capacity retention of around 60% after 100 cycles at 0.5 C.