Irreversible capacity of lithium secondary battery using meso-carbon micro beads as anode material

One of the most important problems in lithium secondary battery using carbon anodes is the difference between the charge and discharge capacity, the so-called ‘retention’. It is caused partly by the reaction of Li ion with functional groups on the surface of the carbon. Especially, carbons heat-treated at lower temperatures than 1000 °C, have many functional groups such as −COOH and −OH on the surface. As these functional groups are very reactive, Li ions might smoothly react with them in the initial charge-reaction process. In order to evaluate these contributions to the irreversible capacity, the n-butyllithium method was applied for meso-carbon micro beads (MCMB) heat-treated at lower temperatures than 1000 °C. As a result, there are some reactive sites such as functional groups and cavities against Li ions except interlayers. However, the irreversible capacity due to the functional groups is a minor factor, and the dominant factor is due to the decomposition of the solvent followed by the film formation on the surface of the carbon electrode or/and the doping of Li species into the reactive sites such as cavities.