Tiny-Ligand Solvation Electrolyte Enabled Fast-charging Aqueous Batteries

Abstract

The H-bond network among H2O molecules enables ultrafast diffusion of H+ and OH- via a hopping mechanism, making aqueous batteries attractive competitors for next-generation fast-charging energy storages. Ideal aqueous electrolyte for the widely used lithium-ion batteries is expected to have the wide electrochemical stability window (>5 volts), fast charging (≤15 minutes) without gas evolution, and low cost. However, the hydrogen evolution reaction (HER) associated with narrow voltage window of water (1.23 V) limits their practical applications. Herein, we built a new guideline for designing tiny-ligand electrolytes by utilizing sterically hindered groups with low binding energy. Cosolvent tetraethyl orthocarbonate (TEOC), with large-sized ethoxy groups and hydrogen-bond-captured ability, forces free H2O and anion TFSI- into the Li+ first solvation shell. Hence, inhibition of HER takes place by means of immobilized H2O activity and formation of hydrogen-bonding networks—C-O···H between TEOC and H2O. This unique structure with ultra-small sheath volume thereby facilitates the formation of LiF-rich SEI and fast ion-conduction. The lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in TEOC/H2O electrolyte exhibits wide electrochemical window of 5.7 V, enabling LiMn2O4/Li4Ti5O12 pouch cells to achieve 1200 cycles under rapid 10 C rate. This engineering of tiny-ligand solvation opens new pathways for developing advanced electrolyte that balance performance with sustainability.