"Localized Water-In-Salt" Electrolyte for Aqueous Lithium-Ion Batteries.

"Water-in-salt" (WIS) electrolytes using super-concentrated organic lithium (Li) salts are attracting tremendous interest for high energy aqueous Li-ion batteries, owing to their wide electrochemical stability window that enables the application of high-energy electrode couples. However, the high salt cost, high viscosity, poor wettability and environmental hazards remain a great challenge. Herein, we present a "localized water-in-salt" (LWIS) electrolyte based on low-cost lithium nitrate (LiNO 3 ) salt and 1,5-pentanediol (PD) as inert diluent. The addition of PD not only maintains the solvation structure of the WIS electrolyte and improves the electrolyte stability via hydrogen-bonding interactions with water and NO 3 - molecules, but also dramatically reduces the total salt concentration. Furthermore, by in-situ gelling the LWIS electrolyte with tetraethylene glycol diacrylate (TEGDA) monomer, the electrolyte stability window can be further expanded to 3.0 V. The as-developed Mo 6 S 8 |LWIS gel electrolyte|LiMn 2 O 4 (LMO) batteries delivered outstanding cycling performance with a Coulombic efficiency of 98.53 % at after 250 cycles at 1 C.