Mitigating Stainless Steel Dissolution in LiFSI-based Electrolytes: Insights into Dissolution Mechanisms and Enhancing Cycle Life in Lithium-ion Batteries

Lithium bis(fluorosulfonyl)imide (LiFSI) has gained considerable attention as a promising alternative to lithium hexafluorophosphate (LiPF ₆ ) as conducting salt in battery electrolytes due to its superior physicochemical properties. However, its tendency to promote the dissolution of Al and stainless steel (SUS) compromises the electrochemical performance of lithium ion batteries (LIBs), limiting its practical application with SUS containing cell components with operating conditions exceeding 4 V vs. Li|Li ⁺ . Herein, the dissolution behavior of SUS316 in LiFSI-based electrolytes was investigated using selected complementary electrochemical and surface characterization techniques. The results reveal that Cl ⁻ anions promote the dissolution process by initiating pitting, while subsequent interactions between FSI ⁻ anions and dissolved Fe ²⁺ /Fe ³⁺ lead to the formation of soluble complexes, thereby extending the dissolution process. The dissolution can be effectively suppressed by adding lithium difluoro(oxalato)borate (LiDFOB) in the LiFSI-based electrolyte. The proposed mechanism of action implies that both FSI ⁻ and Cl ⁻ anions are hindered by oxalate anions to reach the surface of SUS. Further improvement has been achieved by incorporating more dissolution resistive SUS316L cell parts, resulting in ≈ 300 cycles until 80% state of health for NMC811||Si-C cell chemistry and ≈ 1150 cycles for NMC811||graphite cell chemistry. This represents a considerable improvement compared to the baseline electrolyte LP57 analogue, which only achieves ≈ 140 cycles for NMC811||Si-C and ≈ 200 cycles for NMC811||graphite cells.