Microcalorimetric Study of the Reactivity of Lithiated HOPG with Organic Electrolytes

For the first time, the reactivity of lithiated graphite (HOPG) with organic electrolytes has been followed by calorimetric measurements. The role of three different solvents, ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and their binary and ternary mixtures, has been investigated, with or without LiPF 6 . The lithiated HOPG is shown to react totally with DEC, whereas with EC and DMC the reaction is only partial. This has been attributed to the formation of a passivating film on the surface of the lithiated HOPG. The importance of EC on the film composition and heat exchanged during its formation is demonstrated. LiPF 6 seems to enhance the reactivity with EC-based electrolytes whereas it lessens the heat exchanged with DMC or DMC−DEC. Reaction mechanisms have been considered, and the composition of the film has been discussed with regard to the calorimetric data.