High_Performance Lithium Metal Batteries Enabled by a Fluorinated Cyclic Ether with a Low Reduction Potential

Abstract

Abstract Electrolyte engineering is crucial for developing high_performance lithium metal batteries (LMB). Here, we synthesized two cosolvents methyl bis(fluorosulfonyl)imide (MFSI) and 3,3,4,4_tetrafluorotetrahydrofuran (TFF) with significantly different reduction potentials and add them into LiFSI_DME electrolytes. The LiFSI/TFF_DME electrolyte gave an average Li Coulombic efficiency (CE) of 99.41 % over 200 cycles, while the average Li CEs for MFSI_based electrolyte is only 98.62 %. Additionally, the TFF_based electrolytes exhibited a more reversible performance than the state_of_the_art fluorinated 1,4_dimethoxylbutane electrolyte in both Li Cu half_cell and anode_free Cu LiNi 0.8 Mn 0.1 Co 0.1 O 2 full cell. More importantly, the decomposition product from bis(fluorosulfonyl)imide anion could react with ether solvent, which destroyed the SEI, thus decreasing cell performance. These key discoveries provide new insights into the rational design of electrolyte solvents and cosolvents for LMB.