In situ Raman study on the structural degradation of a graphite composite negative-electrode and the influence of the salt in the electrolyte solution

Structural changes in the surface of graphite composite electrodes in the 1st charge/discharge cycle were studied by ex situ and in situ Raman spectroscopy. The influence of the salt in the electrolyte solution and the volume of this solution injected into electrochemical cells on the structural degradation of the graphite surface was investigated. The surface crystallinity of graphite was degraded in LiPF6-based electrolyte solution with only a cycle of intercalation/de-intercalation reactions of Li+, compared to that in a LiClO4-based electrolyte. In situ Raman measurements revealed that structural disordering of the graphite surface should occur in an early stage of the initial intercalation reaction of Li+ into graphite.

► Surface crystallinity of graphite lowers in a LiPF6-based electrolyte during the initial charge. ► The structural disordering is greater than that in a LiClO4-based electrolyte. ► The structural degradation should be accelerated by the use of a large quantity of an electrolyte.