Mechanism and mitigation of stainless steel dissolution in LiFSI-based lithium-ion battery electrolytes

Lithium bis(fluorosulfonyl)imide has emerged as a promising alternative to lithium hexafluorophosphate as conducting salt in battery electrolytes due to its favorable physicochemical properties. However, its tendency to promote the dissolution of Al and stainless steel severely limits its practical application, particularly in lithium ion batteries operating above 4 V vs. Li/Li⁺. Here we show that the dissolution of SUS316 in lithium bis(fluorosulfonyl)imide-based electrolytes is governed by a synergistic mechanism involving trace Cl^- impurities and FSI^- anions. Cl^- initiates localized pitting, while subsequent interactions between FSI^- anions and dissolved iron species lead to the formation of soluble complexes, thereby extending the dissolution process. We further demonstrate that the dissolution can be effectively suppressed by adding lithium difluoro(oxalato) borate. The proposed mechanism involves preferential adsorption of oxalate anions at surface of stainless steel, which limits the access of aggressive anions. Additional improvement is achieved by incorporating more dissolution resistive SUS316L components, resulting in ≈300 cycles until 80 % state of health in silicon-graphite | |LiNi_0·8Co_0·1Mn_0·1O₂ cells. Furthermore, this improvement has also been confirmed in silicon-graphite | |LiNi_0·8Co_0·1Mn_0·1O₂ pouch cells.