Unraveling Influential Factors of Stainless-Steel Dissolution in High-Energy Lithium Ion Batteries with LiFSI-Based Electrolytes

Abstract

Leveraging physicochemical advantages over lithium hexafluorophosphate (LiPF₆), lithium bis(fluorosulfonyl)imide (LiFSI) is being investigated as a conducting salt for lithium manganese-rich cathodes (LMR) and micro-crystalline silicon anodes (μ-Si). Nevertheless, its behavior towards the aluminum (Al) current collector and stainless-steel (SUS) coin cell parts limits its application under operating conditions requiring potentials higher than 3.9 V vs. Li|Li⁺. Using a mixture of organic carbonate-based solvents, various functional additives, and LiPF₆ lithium salt concentrations up to 1.0 M, the instability issue of the Al current collector in the presence of LiFSI is avoided. However, stainless-steel dissolution remains, being confirmed by both potentiodynamic measurements and SEM morphology investigations of the coin cell components after linear sweep voltammetry measurements carried out to 5.0 V. The results also indicate that the amount of stainless-steel dissolution is influenced by both the LiFSI amount in the electrolyte and the quality (grade) of stainless-steel used. Using Al-coated SUS 316L coin cell parts and/or high concentration electrolytes (HCE) with LiFSI (≈4 M LiFSI), the observed stainless-steel dissolution process can be fully avoided, allowing the evaluation of the electrochemical performance of LMR cathodes with μ-Si anodes in LiFSI-based electrolytes.