Developing diluted low-concentration electrolyte with a high anion-to-solvent ratio for high-voltage lithium metal batteries

Abstract

Low-concentration electrolyte demonstrates significant advantages in terms of low cost, low viscosity, and high wettability. However, its high solvent ratio usually induces a fragile organic-rich solid electrolyte interphase (SEI), which is not compatible with high-voltage lithium metal batteries (LMBs). Herein, a screening rule for diluents has been established based on the electrostatic potential, which guides the rational design of diluted low-concentration electrolyte (DLCE) with a high anion-to-solvent ratio. Specifically, the anti-solvating power of a diluent is positively correlated with its value of the most positive surface potential (ESP_max), and thus diluents with a high ESP_max value easily cause salt precipitation when diluting concentrated electrolyte to low concentration (<1 M). In light of this observation, a diluent with a low ESP_max value is selected to ensure the preparation of a transparent DLCE, thus maintaining a high anion-to-solvent ratio in DLCE. As an exemplary study, a 0.5 M ether-based DLCE is developed for high-voltage LMBs. Due to the high anion-to-solvent ratio, a robust LiF-rich SEI is formed and enables the stable operation of LMBs under high voltage (4.5 V) and a wide temperature range (−20 to 55 °C). This work offers a guideline for screening diluents to design high-performance LCEs for high-voltage batteries.