ELECTROCHEMICAL-BEHAVIOR OF NICKEL IN SO2-CONTAINING NONAQUEOUS ELECTROLYTE IN RELATION TO SELF-DISCHARGE OF LI-SO2 BATTERIES

In propylene carbonate + LiClO4 (1 M) + SO2 (2.2 M) electrolytes at nickel, sulfur dioxide undergoes reversible electrochemical transformations, viz., cathodic reduction at a potential of E = 2.6 V and oxidation of the cathodic reduction products of SO2 at a potential of E = 3.2 V. The rates of the electrochemical reactions at nickel depend on the properties of the film of metal oxides formed in air and on those of the film of products from the electrochemical reactions involving the electrolyte. At the working potentials of primary Li-SO2 batteries (2 to 3.3 V), the rates of the electrochemical reactions involving nickel are not higher than 0.1-0.5% of the rate of the major current-producing battery reaction at the graphitic carbon electrode. Hence nickel can be regarded as a material suitable for cathodic current collectors in the primary batteries. It was seen when investigating the anodic processes occurring at nickel in the above nonaqueous electrolyte that Ni is not suitable for the cathodic current collectors of secondary batteries, since at a potential of 4.3 V which can be attained during battery charging, the metal undergoes anodic dissolution according to the reaction: Ni - 2 e- --> Ni++.