Mixed phase sodium manganese oxide as cathode for enhanced aqueous zinc-ion storage

Aqueous zinc-ion batteries have been regarded as a promising alternative to large-scale energy storage, due to associated low-cost, improved safety and environmental friendliness. However, a high-performance cathode material for both rate capability and specific capacity is still a challenge. One kind of the more promising candidates are sodium manganese oxide (NMO) materials, although they suffer from individual issues and need to be further improved. Herein, we present a novel mixed phase NMO material composed of nearly equal amounts of Na0.55Mn2O4 and Na0.7MnO2.05. The structured configuration with particle size of 200-500 nm is found to be beneficial towards improving the ion diffusion rate during the charge/discharge process. Compared with Na0.7MnO2.05 and Na0.55Mn2O4, the mixed phase NMO demonstrates an enhanced rate capability and excellent long-term cycling stability with a capacity retention of 83% after 800 cycles. More importantly, the system also delivers an impressive energy density and power density, as 378 W.h.kg(-1) at 68.7 W.kg(-1), or 172 W.h.kg(-1) at 1705 W.kg(-1). The superior electrochemical performance is ascribed to the fast Zn2+ diffusion rate because of a large ratio of capacitive contribution (63.9% at 0.9 mV.s(-1)). Thus, the mixed phase route provides a novel strategy to enhance electrochemical performance, enabling mixed phase NMO as very promising material towards large-scale energy-storage applications. (C) 2020 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.