The Role of SO 2 as an Additive to Organic Li‐Ion Battery Electrolytes

Previous work has shown that the addition of a large amount of sulfur dioxide (∼20 weight percent) promotes the reversible intercalation‐deintercalation of Li ions into graphite in selected nonaqueous electrolytes. These electrolytes were previously considered to be incompatible with graphite negative electrodes because of solvent‐graphite interaction, which led to catastrophic graphite exfoliation of the graphitic structure. We have performed a series of conductivity studies along with electrochemical experiments at varying concentrations. The electrolyte solutions were composed of either or . We found that the specific conductance values of the organic electrolytes containing were increased dramatically. Cyclic voltammetry and Fourier transform infrared measurements show that the use of as an additive to the organic solutions, even at very low levels, offers the advantage of forming fully developed passive films on the graphite electrode at potentials much higher than that of the electrolyte reduction itself. These graphite surface films are composed of mixtures of and solvent reduction products. The reduction products are primarily responsible for the improved characteristics of the Li‐ion cells containing these ‐based electrolytes.