Application of Hydrate-Melt Electrolytes to High-Rate and High-Capacity Organic Lithium-Ion Batteries

Lithium croconate molecules (C₅O₅Li₂), a 4 V-class high-voltage organic cathode material, offer a possibility to develop high-energy-density, rare-metal-free, and environmentally friendly organic secondary batteries. However, organic molecules generally have a serious problem of dissolution into electrolytes, leading to poor cycling performance. Here, we demonstrate the water-based hydrate-melt electrolyte for improving cycling performance of organic batteries and evaluate the relationship between battery performance and solubility behavior of croconate molecules into the electrolytes. Hydrate-melt electrolyte Li(TFSI)_0.7(BETI)_0.3(H₂O)₂ effectively suppresses the dissolution of pristine C₅O₅Li₂ and C₅O₅ molecules (in their two-electron charged state), leading to improved cycling performance and coulombic efficiency. This result can be ascribed to the unique solution structure having less free-water in hydrate-melt electrolytes. Moreover, a C₅O₅Li₂/Li₄Ti₅O₁₂ cell with hydrate-melt electrolyte exhibits an ultrafast redox reaction with no capacity fading at higher C-rate up to 10 C. This insight is beneficial to construct high-power and high-energy-density croconate-based storage systems.