Coupling Electro-Chemo- Thermodynamics with Water in Salt (WIS) Electrolyte for Enhanced Pseudocapacitive Charge Storage

Distinguishing and fundamental understanding of different charge storage mechanisms is critical for advancing sustainable energy developments. Pseudocapacitive materials combine the Faradaic charge transfer and partial surface-controlled process with the advantages of large energy density and fast response compared to electrical double-layer capacitors and batteries. Electrochromic oxides thin films, as an emerging class of energy storage materials, allow the synchronous visible color change to indicate the energy level. This work involves comprehensive research on the effect of the electrolyte concentration, solvent, and temperature on the charge storage behavior at the interface and the electrochromic properties of amorphous WO3-x films. The Li+ and e- dual insertion/extraction process depends not only on the electrochemical kinetics but also related to the viscosity of the ionic liquid LiCl water-in-salt (WIS) electrolyte varying from room temperature to 70°C. The de-solvation-free cations insertion feature differs the WIS from the low concentration. The electro-chemo coupling thermo-dynamics significantly improve the peak current (by a factor of 10 from 0.15 to 1.5 mA/cm2), charge capacity, and meanwhile shift the redox peak to lower potential (1.0 to 0.5V). This finding opens new avenues to developing safe, inexpensive, and high-capacity aqueous energy storage devices. Figure 1