Developing Diluted Low Concentration Electrolyte with High Anion to Solvent Ratio for High-Voltage Lithium Metal Batteries

Low concentration electrolyte demonstrates significant advantages in terms of cost, viscosity, and wettability. However, its high solvent ratio usually induces fragile organic-rich solid electrolyte interphase (SEI), which is not compatible with high-voltage lithium metal batteries (LMBs). Herein, a screening rule for diluent has been established based on the electrostatic potential, which guides the rational design of diluted low concentration electrolyte (DLCE) with 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 (ESPmax), thus diluents with high ESPmax value easily cause salt-precipitation when diluting concentrated electrolyte to low concentration (< 1 M). In light of this observation, diluent with low ESPmax value is selected to ensure the preparation of a transparent DLCE, thus maintaining 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 wide temperature (−20 to 55 °C). This work offers a guideline for screening diluent to design high-performance LCEs for high-voltage batteries.