Juggling Formation of HF and LiF to Reduce Crossover Effects in Carbonate Electrolyte with Fluorinated Cosolvents for High-Voltage Lithium Metal Batteries

Fluorinated solvents emerge as a promising strategy to improve performance of lithium metal batteries (LMBs). However, most of them are prone to produce corrosive HF and deteriorate electrode interface, inducing cathode-to-anode detrimental crossover of transition metal-ions. Here, fluorinated aromatic hydrocarbons in dimethyl carbonate (DMC)-based diluted highly concentrated electrolyte (DHCE) are employed to juggle formation of HF and LiF, enabling stable cycling of high-voltage LiNi0.7Co0.1Mn0.2O2 (NCM712) and LiCoO2 (LCO). The nature of aromatics in this carbonate-based DHCE makes them difficult to undergo beta-hydrogen assisted defluorination, evidencing by the high energy barrier and high bond energy of beta-sites hydrogen. The advanced DHCE restrains HF formation but strengthens LiF formation, which not only suppresses impedance growth, transition-metal dissolution, and stress crack on the cathode, but achieves highly reversible Li stripping/plating with an outstanding average Coulombic efficiency up to 99.3%. The Li||NCM712 cell and Li||LCO cell both exhibits superior cycling stability at high operation voltage. Even under stringent conditions, the 4.4 V Li||NCM712 full battery retains >95% of the initial capacity over 100 cycles, advancing practical high-voltage LMBs. This study designs an efficient electrolyte that generates robust electrode/electrolyte interphases and restrains by-products formation spontaneously, thus shedding new light on electrolyte toward applicable LMBs.

Automated summary

Fluorinated aromatic hydrocarbons in the electrolyte enable stable cycling of high-voltage LiNi0.7Co0.1Mn0.2O2 (NCM712) and LiCoO2 (LCO) by balancing the formation of corrosive HF and LiF. The electrolyte restrains HF formation but strengthens LiF formation, leading to improved cycling stability and high Coulombic efficiency.