Lithium bis(fluorosulfonyl)imide (LiFSI) has emerged as a promising conducting salt for Li-based batteries, offering numerous advantages, including enhanced solubility, higher ionic conductivity and improved thermal stability compared to conventional lithium hexafluorophosphate (LiPF6) analogue[1,2]. However, within the context of laboratory cells made of stainless steel (SUS) (i.e. CR 2032), the often-overlooked issue of SUS dissolution poses a more significant challenge than the well-known dissolution of aluminum[3–5].
In this work, we have systematically investigated the effect of lithium difluoro(oxalato)borate (LiDFOB) molar concentration within the LiFSI-based electrolyte as well as the impact of Cl- impurity and SUS grade on SUS dissolution. Using linear sweep voltammetry (LSV) and chronoamperometry (CA) measurements supported by SEM investigations, we identified a two-stage dissolution process contributing from Cl- and FSI- anions and proposed a mechanism for SUS dissolution in LiFSI-based electrolyte. Notably, DFOB- anions significantly mitigated SUS dissolution induced by the Cl- and FSI- anions, with a 1:1 molar ratio of LiFSI and LiDFOB effectively overcoming pitting on the steel surface. Based on these results, we propose a mechanism by which LiDFOB inhibits SUS dissolution, potentially through competing anion adsorption or protective film formation. Furthermore, we assess the corrosion resistance of two SUS grades, SUS316 and SUS316L, revealing that SUS316L, with lower carbon content, exhibits better dissolution resistance. Finally, through the incorporation of LiDFOB-containing electrolytes, in combination with high-quality SUS316L coin cell components, a significant enhancement of the electrochemical performances of various chemistries, including NMC811||graphite and NMC811||Si/Gr systems in coin cells CR2032, is proven.

References:
[1] K. Xu, Chem. Rev. 2014, 114, 11503–11618.
[2] L. Li, S. Zhou, H. Han, H. Li, J. Nie, M. Armand, Z. Zhou, X. Huang, Journal of The Electrochemical Society 2011, 158, A74.
[3] Y. Bae, H. G. Lee, Y. J. Kim, G. R. Kim, J.-W. Park, J. Moon, Y.-J. Lee, J.-H. Choi, B. G. Kim, Chemical Engineering Journal 2023, 469, 143804.
[4] C. Luo, Y. Li, W. Sun, P. Xiao, S. Liu, D. Wang, C. Zheng, Electrochimica Acta 2022, 419, 140353.
[5] S. S. Zhang, Journal of The Electrochemical Society 2022, 169, 110515–110515.