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 ZnCl2H2O 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 V6O13 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).