Vacancy-rich Al-doped MnO2 cathodes break the trade-off between kinetics and stability for high-performance aqueous Zn-ion batteries

Abstract

Rechargeable aqueous zinc ion batteries (RAZIBs) have the potential for large scale energy storage due to their environmental friendliness, high safety and low cost. The trade-off between charging/discharging kinetics and stability has been the bottleneck of most cathode materials, which impedes the rate performance and cycle life of RAZIBs. Here we break the trade-off by designing vacancy-rich and Al-doped birnessite-type MnO₂ nanosheet (Al_x–MnO₂) electrodes, which are synthesized by electrochemically oxidizing manganese based layered double hydroxides (MnAl-LDHs). Rich Al cation vacancies formed during the process of electrochemical oxidation provide three-dimensional diffusion channels for the storage of Zn ions, and the remaining Al atoms benefit the structural stability by suppressing the Jahn–Teller distortion of Mn(III)O₆ polyhedra during battery cycling. As a result, by employing the optimized cathode (Al_0.1–MnO₂), the rate capability and stability of the RAZIBs are spontaneously enhanced. Specifically, the battery exhibits a large specific capacity (327.9 mA h g⁻¹ at 0.2 A g⁻¹), superior rate performance (135.8 mA h g⁻¹ at 8 A g⁻¹) and high capacity retention (87% after 1000 cycles at 1 A g⁻¹) that exceeds that of most of the reported manganese and vanadium based cathode materials.