H. Pan, Tiantian Wang, Tiantian Wang, Yanxin Jiang, Jingjing Ouyang, L. Chen, Zeyi Wang, Chunlei Song, Nanshan Chen, Qing Yan, Xin Li, Shumin Wu, Tianshuai Wang, Tianshuai Wang, Yiju Li
The localized high-concentration electrolyte based on the low-cost, low-density, low-viscosity, and low-fluorine-substitution fluorobenzene diluents and 1,2-dimethoxyethane solvents has been successfully demonstrated in high-performance lithium metal batteries. However, it requires high salt-to-solvent molar ratio, which causes high production costs and great environmental burden. Decreasing the salt-to-solvent molar ratio without sacrificing its electrochemical performance remains a challenge. Herein, we reveal that as the salt-to-solvent molar ratio is decreased, the compatibility of the fluorobenzene-diluted 1,2-dimethoxyethane-based electrolyte with lithium metals transitions from compatible to incompatible. We elucidate the degradation mechanism of the fluorobenzene-diluted 1,2-dimethoxyethane-based electrolyte undergoing severe side reactions with lithium metals. Inspired by these findings, we develop a fluorobenzene-diluted dimethyl acetal-based electrolyte, which enhances the stability of the electrolyte under a reduced lithium-salt concentration, making it show good compatibility with lithium metal (Coulombic efficiency: 99.43% at 25 °C, 97.74% at −40 °C). Moreover, the assembled Li | |SPAN battery displays a high capacity retention of 83% after cycling 500 cycles and can operate at −60 °C. Besides, a high specific energy of 334.53 Wh kg−1 (excluding package) can be achieved for the Li | |SPAN pouch cell. This work prompts us to re-examine the applicability of fluorobenzene as diluents in ether-based electrolytes for lithium metal batteries. Decreasing salt-to-solvent molar ratio without sacrificing electrochemical performance remains a challenge in high-performance lithium metal batteries. Here, authors show that compatibility of fluorobenzene-diluted 1,2-dimethoxyethane-based electrolyte with Li metal is reduced in smaller salt-to-solvent molar ratios and design a fluorobenzene-diluted dimethyl acetal-based electrolyte with significantly enhanced stability towards Li metal under a reduced Li salt concentration.