Carbon encapsulation and vanadium dissolution restraint in hydrated zinc pyrovanadate to enhance energy storage for aqueous zinc-ion batteries

Hydrated vanadates have gained significant attentions as cathode for aqueous zinc-ion batteries (AZIBs) on account of their broad open channels in the structural framework together with the existence of crystal water for stabilizing the structure. Yet, the lower electronic conductivity and the dissolution of vanadium in the electrolyte both affect the specific capacity and stability. In this work, we successfully prepared a unique hydrated zinc pyrovanadate Zn3(OH)2V2O7·(H2O)2 with broad tunnel structure through a hydrothermal method. The carbon encapsulation strategy was then used to enhance its specific capacity, rate performanc and cycle stability in AZIBs. Further, the cycle stability was improved using a highly concentrated ZnWiS electrolyte capable of inhibiting vanadium dissolution, and improved the cycling time from one month to one year at low current densities with high capacity retention rate. Additionally, the electrochemical performances under high-temperature conditions of 50 °C and 80 °C are also investigated. It is found that an increase in temperature can promote the ionic conductivity of the electrolyte and the kinetics of electrode reactions, thus accelerating charge transfer. Due to the excellent high-temperature resistance of the ZnWiS electrolyte, the assembled AZIBs both achieved calendar-level cycle life at 50 °C and 80 °C. These excellent results demonstrate that the dual-strategy approach of carbon encapsulation to enhance the conductivity and high concentration electrolyte to inhibit vanadium dissolution provides technical support to promote the application of AZIBs in large-scale energy storage devices.