Ultralow-concentration electrolyte unlocking the high-stable proton storage in (NH4)0.5V2O5 electrode

High-concentration electrolytes have been proven to be an effective strategy to improve the electrochemical performance of aqueous batteries. However, dramatically increasing the salt concentration will leads to high cost, high viscosity, and low conductivity. Here, we propose an ultralow-low concentration electrolyte of 1 mM H2SO4 solution for the practical application of aqueous batteries for the first time. Surprisingly, the (NH4)(0.5)V2O5 (NVO) achieves good electrochemical performance benefitting from the special Grotthuss mechanism of proton and structural stability of electrode material in dilute acidic electrolyte. The NVO electrode exhibits a high reversible capacity of about 150 mAh g(-1) at a low current density of 50 mA g(-1) and impressive capacity retention of 80% over 70,000 cycles at 2 A g(-1). The low concentration electrolyte chemistry will open a novel route for the exploitation of durable and low-cost aqueous batteries.