Revisiting the corrosion mechanism of LiFSI based electrolytes in lithium metal batteries

Lithium bis(fluorosulfonyl)imide (LiFSI), regarded as one of the most promising alternative of lithium hexafluorophosphate (LiPF6), seriously weakens the electrochemical performance of lithium metal batteries at high voltages, due to its extreme corrosion in nonaqueous electrolyte towards some components of the batteries. Though studies have shown that the aluminum (Al) collector will be corroded in LiFSI electrolytes, few attentions have been paid to the corrosion of steel components of lithium metal batteries, the corrosion intensity of which is much more severe than that of Al. Herein, by comparing the electrochemical corrosion behaviors of Al foil and stainless steel (SS) in LiFSI electrolytes, the corrosion products were characterized and analyzed, and the corrosion mechanism of SS was further proposed. Based on the corrosion mechanism, a strategy to inhibit the corrosion by using high concentration electrolyte (HCE) was also proposed. Moreover, introduction of 1,1,2,2tetrafluoroethyl 2,2,2-trifluoroethyl ether into HCE, forming a localized high concentration electrolyte (LHCE), which not only addresses the viscosity and wettability issues of HCE but also inhibits the corrosion in conventional concentration electrolyte. As a result, Li||LiCoO2 coin cells using HCE and LHCE show excellent cycling stability with capacity fading rates of 0.53% and 0.26% per cycle, respectively, at 1 C (1 C = 180 mAh g 1) between 3 - 4.45 V. The same corrosion inhibition regular also has been proved in pouch cells.