Enhancing Cycling Stability of Lithium Metal Batteries with Nonflammable Electrolytes Using 4-Chloroanisole as a Cosolvent

The practical application of conventional nonflammable electrolytes in lithium metal batteries (LMBs) is significantly hampered by their side reactions with lithium metal, which cause unstable solid electrolyte interphases (SEIs) formation and lithium dendrite growth. To address these challenges, a cosolvent, 4-chloroanisole (PCA), is incorporated into the high-flash-point solvent 3-methyl-2-oxazolidinone (MO) to create a localized high concentration electrolyte (LHCE), designated as MO/PCA. This electrolyte exhibits excellent compatibility with both the lithium anode and the LiFePO4 (LFP) cathode. In combination with the bis(trifluoromethanesulfonyl)imide (TFSI–) anion and fluoroethylene carbonate (FEC) additive, the PCA cosolvent promotes the formation of SEIs enriched with inorganic species such as LiF, LiCl, and Li2O. These robust interphases effectively protect the electrodes and suppress parasitic side reactions with the solvents. The stable, inorganic-rich SEI enables the LFP||Li cell to retain 90% of its capacity after 1000 cycles at 1C. Even under challenging conditions, including high-load LFP cathodes and lithium-deficient environments, it retains over 90% capacity after 220 cycles. The successful operation of LFP||Li pouch cells (90% capacity retention over 60 cycles at 0.5C discharge) demonstrates the practical applicability of MO/PCA. Moreover, PCA can function as a cosolvent in flame-retardant electrolyte systems such as N-methylcaprolactam (NM) and N,N-dimethylpropyleneurea (DMPU), demonstrating its versatile utility in various electrolyte formulations.