Anodic behavior of stainless-steel substrate in organic electrolyte solutions containing different lithium salts

• We investigated anodic behavior of stainless-steel in organic electrolytes for advanced capacitor.
• Anion of the electrolyte affected the anodic stability of the alloy.
• Anodic passivation occurs in LiPF6 solution but pitting or active dissolution proceeds in other electrolyte solutions.
• Fluoride source in the solution contributes to forming a stable surface layer on the stainless steel.

The anodic behavior of austenitic stainless-steel, SUS304, as a current collector of positive electrode in lithium-ion battery/capacitor has been investigated in organic electrolyte solutions based on a mixed alkyl carbonate solvent with different lithium salts. Stable passivation characteristics were observed for the stainless-steel in the LiPF6 solution, but pitting corrosion or active dissolution proceeded in the solutions containing other anions, BF4-, (CF3SO2)2N- (TFSA-) and ClO4-. The mass ratios of the dissolved metal species in the solutions of LiTFSA and LiClO4 were equivalent to that of the alloy composition, which suggests that no preferential dissolution occurs during the anodic polarization in these electrolyte solutions. An HF component formed by decomposition of PF6- with the contaminate water will act as an F- source for the formation of a surface fluoride layer, that will contribute to the anodic stability of SUS304 in the LiPF6 solution. The anodic corrosion in the LiTFSA solution was suppressed in part by mixing the PF6 salt or adding HF in the electrolyte.