Triple-function eutectic solvent additive for high performance lithium metal batteries

Rational carbonate electrolyte chemistry is critical for the development of high-voltage lithium metal batteries (LMBs). However, the implementation of traditional carbonate electrolyte is greatly hindered by the generation of an unstable electrode interphase and corrosive by-product (HF). Herein, we propose a triple-function eutectic solvent additive of N-methylacetamide (NmAc) with LiNO₃ to enhance the stability and compatibility of carbonate electrolyte. Firstly, the addition of NmAc significantly improves the solubility of LiNO₃ in carbonate electrolyte by forming an eutectic pair, which regulates the Li⁺ solvation structure and leads to dense and homogenous Li plating. Secondly, the hydrolysis of acidic PF₅ is effectively alleviated due to the strong complexation of NmAc with PF₅, thus reducing the generation of corrosive HF. In addition, the optimized cathode electrolyte interphase layer decreases the structural degradation and transition metal dissolution. Consequently, Li||LiNi_0.6Co_0.2Mn_0.2O₂ (NCM622) cells with the designed electrolyte deliver superior long-term cycle reversibility and excellent rate capability. This study unveils the rationale for incorporating eutectic solvent additives within carbonate electrolytes, which significantly contribute to the advancement of their practical application for high-voltage LMBs.