Oxygen-deficient ammonium vanadate for flexible aqueous zinc batteries with high energy density and rate capability at −30 °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 NH₄V₄O_10−x·nH₂O (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 °C, respectively. Moreover, NVOH maintains a 100% capacity retention after 100 cycles at 0.1 A g⁻¹ and ∼94% capacity retention after 2600 cycles at 2 A g⁻¹ and −30 °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.