Eu doping β-MnO2 as cathode materials for high specific capacity aqueous zinc ion batteries

Aqueous zinc ion batteries (AZIB) have become a research hotspot for energy storage systems (ESS) in recent years due to some advantages such as their low risk and low cost. However, the structural collapse during charging and discharging affects the reversibility of the battery, which is a very serious blow to manganese-based materials and will affect their subsequent development in batteries. Therefore, β-MnO2 cathode materials doped by the rare earth element europium (Eu) were prepared by a simple hydrothermal method. Compared with β-MnO2, Eu-doped MnO2 possessed a high specific capacity of 409 mA h g−1 at 0.2 A g−1. The initial specific capacity of Eu-doped MnO2 at 1 A g−1 was 200.23 mA h g−1 and the maximum discharge specific capacity of 254 mA h g−1 was reached at 128 cycles. The energy storage mechanism of the electrodes was investigated by ex-situ XRD and ex-situ XPS tests. It was found that Eu element doping to β-MnO2 not only maintains the stability of the crystal structure during redox reaction, but also promotes the embedding reaction of H+/Zn2+. The combination of rare earth elements Eu and MnO2 is a new direction in the development path of aqueous zinc ion batteries.