Environmentally assisted cracking of cathodically polarized nickel in LiAlCl4/SOCl2 electrolyte

• Published in: Journal of the Electrochemical Society 1991-08, Vol.138 (8), p.2229-2237
• Main Authors: SCULLY, J. R, CIESLAK, W. R, BOVARD, F. S
• Format: Article
• Language: English
• Subjects: Applied sciences; Direct energy conversion and energy accumulation; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Exact sciences and technology
• ISSN: 0013-4651; 1945-7111
• DOI: 10.1149/1.2085955

The susceptibility of nickel to environmentally assisted cracking was investigated at potentials that are relevant to primary Li /SOCl2 batteries which utilize a 1.5M LiAlCl4/SOCl2 electrolyte. Slow strain rate tests were performed on Ni under conditions which simulate exposure of Ni grid supporting the Li anode, Ni grid supporting the cathode, and exposure to the vapor phase above a LiAlCl4/SOCl2 electrolyte. A mixture of transgranular and intergranular cracking is observed only when polycrystalline Ni is galvanically coupled to Li or polarized to potentials equal to or below 0.0 vs a Li/LiCl reference electrode. Under both of these circumstances, zero valent Li is produced from the cathodic reduction of a LiCl film which forms on exposed Ni surfaces. A Li-induced embrittlement mechanism is proposed whereby (i) LiCl is precipitated from solution at fresh crack tips, (ii) solid Li metal is formed from cathodic reduction of LiCl, (iii) Li promotes initiation of cracks at the Ni surface, and (iv) crack advance occurs at sufficiently high rates to preclude Li diffusion into the Ni ahead of the crack tip, implying a surface-induced cracking process.