Ultralow-water-activity electrolyte endows vanadium-based zinc-ion batteries with durable lifespan exceeding 30 000 cycles

Vanadium-based cathodes with high specific capacity have attracted wide attention in aqueous zinc ion batteries . The main barriers of the development of vanadium-based cathodes are vanadium dissolution, structure degradation, instability of cathode electrolyte interlayer (CEI) and parasitic reactions in aqueous electrolyte. In this work, for the first time, we propose a new type of ultralow-water-activity electrolyte that tackles all these problems. Our design is realized by the introduction of pioneering inert electrolyte filler (trimethyl phosphate). It is discovered that highly concentrated ZnCl 2 H 2 O clusters are surrounded by this electrolyte filler, reaching the lowest free solvation water composition (2.5%) reported so far. The ultralow water activity significantly inhibits parasitic reactions and vanadium dissolution, boosting the achievement of the highest columbic efficiency (99.98%). The biggest bottleneck of vanadium-based cathodes dissolution and water shuttle has been broken through by stable CEI. As a proof of concept , the V 6 O 13 cathode demonstrates exceptional stability of 99.43% capacity retention after 3 000 cycles at 1 A g −1 , and sets a new record for cycle life of 30 000 cycles (capacity retention of 90.34% at 10 A g −1 ) in zinc ion batteries , even reaching the level of supercapacitors (∼100 000 cycles).