Cesium-doped ammonium vanadium bronze nanosheets as high capacity aqueous zinc-ion battery cathodes with long cycle life and superb rate capability

Abstract

Aqueous zinc-ion batteries (AZIBs) are emerging as a promising candidate for large grid energy storage due to their abundant availability and high safety. To meet long cycle life requirements, developing a stable cathode with high rate capability is of great importance. Herein, cesium-doped ammonium vanadium bronze Cs_0.07NH₄V₄O₁₀·0.28H₂O (CNVO) is synthesized and proposed as a potential cathode material in AZIBs. The doping of Cs⁺ ions expands the interlayer spacing of the (001) plane from 9.7 to 10.5 Å, which leads to enhanced kinetics and a low energy barrier for the intercalation of Zn²⁺ ions. The as-synthesized CNVO boasts a two-dimensional (2D) sheet-like morphology with a lateral dimension of about 500 and a low thickness of 9 nm, which enables robust stability during cycling. Additionally, the synergistic interactions among Cs, NH₄ and V enhance the electrochemical stability of CNVO during the Zn²⁺/H⁺ intercalation/deintercalation reactions. The three-pronged approaches make CNVO nanosheet cathodes deliver a high specific capacity of 475.6 mA h g⁻¹ at 0.1 A g⁻¹, a high energy density of 347.4 W h kg⁻¹ at 74.4 W kg⁻¹ and superb cycling stability with 90.1% capacity retention after 5000 cycles at 10 A g⁻¹. Electrochemical studies indicate that Zn²⁺ ion storage in CNVO is a comprehensive process involving intercalation and pseudocapacitance, with the latter not only providing extra capacity but also facilitating fast charge–discharge capability.