Communication—Lithium Bis(fluorosulfonyl)imide (LiFSI) as a Promising Salt to Suppress Solid Electrolyte Interphase Degradation at Elevated Temperatures

This study demonstrates that lithium/silicon monoxide (SiO) cell degradation can be avoided when lithium bis(fluorosulfonyl)imide (LiFSI) is utilized as an electrolyte salt. In our previous work, the solid electrolyte interphase (SEI) was damaged at elevated temperatures by the attack of the Lewis acidic phosphorus pentafluoride (PF5), which is the thermal decomposition product of lithium hexafluorophosphate (LiPF6). This leads to growth of film thickness and cell polarization, causing severe cell failure. However, when LiPF6 is replaced with LiFSI, the SEI degradation is significantly suppressed, resulting in decreased cell polarization and improved cell performance, due to the high thermal stability of LiFSI.