The role of SO2 as an additive to organic Li-ion battery electrolytes

Previous work has shown that the addition of a large amount of sulfur dioxide (SO2) (similar to 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. Vile have performed a series of conductivity studies along with electrochemical experiments at varying SO2 concentrations. The electrolyte solutions were composed of either 1 ill LiAsF6 or 1 M LiPF6. We found that the specific conductance values of the organic electrolytes containing SO2 were increased dramatically. Cyclic voltammetry and Fourier transform infrared measurements show that the use of SO2 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 SO2 and solvent reduction products. The SO2 reduction products are primarily responsible for the improved characteristics of the Li-ion cells containing these SO2-based electrolytes.