Electrolyte Concentration Regulation Boosting Zinc Storage Stability of High-Capacity K0.486V2O5 Cathode for Bendable Quasi-Solid-State Zinc Ion Batteries

Highlights Moderate-concentration ZnCl 2 (15 m) was found to be effective for suppressing the dissolution of vanadate cathode, which was more stable and had 4 times higher ionic conductivity than 30 m “water-in-salt” electrolyte. K 0.486 V 2 O 5 with huge interlayer space of ~ 0.95 nm was chosen for the first time to assemble aqueous Zn ion batteries, giving rise to excellent rate performance and high energy and power densities. A novel sodium carboxymethyl cellulose-15 m ZnCl 2 hydrogel electrolyte with high ionic conductivity of 10.08 mS cm −1 was designed, enabling a bendable Zn ion battery with outstanding resistance to temperature and pressure. Vanadium-based cathodes have attracted great interest in aqueous zinc ion batteries (AZIBs) due to their large capacities, good rate performance and facile synthesis in large scale. However, their practical application is greatly hampered by vanadium dissolution issue in conventional dilute electrolytes. Herein, taking a new potassium vanadate K 0.486 V 2 O 5 (KVO) cathode with large interlayer spacing (~ 0.95 nm) and high capacity as an example, we propose that the cycle life of vanadates can be greatly upgraded in AZIBs by regulating the concentration of ZnCl 2 electrolyte, but with no need to approach “water-in-salt” threshold. With the optimized moderate concentration of 15 m ZnCl 2 electrolyte, the KVO exhibits the best cycling stability with ~ 95.02% capacity retention after 1400 cycles. We further design a novel sodium carboxymethyl cellulose (CMC)-moderate concentration ZnCl 2 gel electrolyte with high ionic conductivity of 10.08 mS cm −1 for the first time and assemble a quasi-solid-state AZIB. This device is bendable with remarkable energy density (268.2 Wh kg −1 ), excellent stability (97.35% after 2800 cycles), low self-discharge rate, and good environmental (temperature, pressure) suitability, and is capable of powering small electronics. The device also exhibits good electrochemical performance with high KVO mass loading (5 and 10 mg cm −2 ). Our work sheds light on the feasibility of using moderately concentrated electrolyte to address the stability issue of aqueous soluble electrode materials.