Oxygen-deficient ammonium vanadate for flexible aqueous zinc batteries with high energy density and rate capability at-30 degrees C

Aqueous zinc batteries (AZBs) have received significant attention owing to environmental friendliness, high energy density and inherent safety. However, lack of high-performance cathodes has become the main bottleneck of AZBs development. Here, oxygen-deficient NH4V4O10-x center dot nH(2)O (NVOH) microspheres are synthesized and used as cathodes for AZBs. The experimental test and theoretical calculations demonstrate that the oxygen vacancies in the lattice lower the Zn2+ diffusion energy barrier, which enables fast Zn2+ diffusion and good electrochemical performance in a wide temperature range. The suppressed side reactions also can help to improve the low temperature performance. NVOH shows a high energy density of 372.4 Wh kg(-1) and 296 Wh kg(-1) at room temperature and -30 degrees C, respectively. Moreover, NVOH maintains a 100% capacity retention after 100 cycles at 0.1 A g(-1) and similar to 94% capacity retention after 2600 cycles at 2 A g(-1) and -30 degrees C. Investigation into the mechanism of the process reveals that the capacity contribution of surface capacitive behaviors is dominant and capacity attenuation is mainly caused by the decay of diffusion-controlled capacity. Furthermore, flexible AZBs can steadily power portable electronics under different bending states, demonstrating its great potential in wide-temperature wearable device.