Ionic Liquid-Based Electrolyte with Multiple Hydrogen Bonding Network Enabling High-Voltage Stable Proton Batteries Across Wide Temperature Range

Abstract

Proton batteries are strong contender for next-generation energy storage due to their high safety and rapid response. However, the narrow electrochemical window of acidic aqueous electrolytes limits their energy density and stability. Here, an ionic liquid (IL)-based electrolyte (EMImOTf-H₃PO₄) containing H₃PO₄ in polar IL solvent 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMImOTf) is developed for stable high-voltage energy storage. H₃PO₄ serving as a proton source interacts with both EMIm⁺ and OTf⁻, forming an intricate hydrogen bonding network that effectively prevents electrolyte decomposition at high voltage. The half-cell in EMImOTf-H₃PO₄ electrolyte and pre-protonated vanadium hexacyanoferrate (H-VHCF) cathode demonstrates a 126% improvement in Coulombic efficiency over aqueous electrolytes at a current density of 1 A g⁻¹. The fabricated PTCDA/MXene//EMImOTf-H₃PO₄//H-VHCF full battery achieves an operating voltage of 2 V at room temperature, surpassing currently reported values for proton batteries. After 30 000 cycles at 5 A g⁻¹, the battery retains 86.1% of its initial capacity. It delivers an energy density of 87.5 Wh kg⁻¹ and a power density of 30.6 kW kg⁻¹ at room temperature, and can maintain stable operation across a temperature range of 110 °C (−60 ∼ 50 °C). These findings present new possibilities for proton batteries in all-weather grid-scale energy storage applications.