Ultralow-concentration electrolyte boosting K_0.486V₂O₅ for high-performance proton storage

High-concentration electrolytes are considered a promising tool for widening stable electrochemical windows and enhancing the electrochemical performance of aqueous batteries. However, their high cost, high viscosity, and low conductivity remain thorny issues. Because of the special Grotthuss mechanism of protons in water, proton batteries can use a low-concentration electrolyte to obtain sufficient kinetic performance. Herein, we present an unusual, ultralow-concentration sulfuric acid (0.01 mol L⁻¹) electrolyte to boost the electrochemical stability of K-ion pre-intercalated V₂O₅ (K_0.486V₂O₅, KVO). The KVO electrode exhibits a high reversible capacity of approximately 129 mA h g⁻¹ at a low current density of 50 mA g⁻¹ and impressive capacity retention of 78% over 20,000 cycles at 1 A g⁻¹. Ultralow-concentration electrolyte chemistry will open a novel route to exploit durable and low-cost aqueous energy storage systems. [Figure not available: see fulltext.]