Starving Free Solvents: Toward Immiscible Binary Liquid Electrolytes for Li-Metal Full Cells

Abstract

Current state-of-the-art Li batteries use single-phase electrolytes; however, these electrolytes often encounter difficulty in simultaneously fulfilling the nonidentical electrochemical requirements of cathodes and anodes. Here, a class of immiscible binary liquid electrolyte (BLE) is designed by starving free solvent molecules. Based on their electrochemical stability window, 1,2-dimethoxyethane (DME) and succinonitrile (SN) are selected as model solvents for Li-metal anodes and LiNi0.8Co0.1Mn0.1 (NCM811) cathodes, respectively. Li bis(fluorosulfonyl)imide (LiFSI), which promotes Li+ solvation (i.e., reduces free solvents), enables the phase separation of the miscible solvent mixture (SN-DME), and an increase in its concentration strengthens the coordination of Li+-FSI- in the solvation sheath, thus yielding (anion-derived) fluorine-rich electrode-electrolyte interphases. The resulting BLE allows 4.4 V Li-metal full cells to exhibit a stable capacity retention under a constrained cell condition (Li (20 mu m, 4.1 mAh cm(-2))||NCM811 (3.8 mAh cm(-2)), N (negative)/P (positive) capacity ratio = 1.08), which exceed those of previously reported binary liquid electrolytes.