XRD evidence for the electrochemical formation of Li+(PC)yCn- in PC-based electrolytes

The reduction of graphite in propylene carbonate (PC) based electrolytes is a complex process involving solvated lithium–graphite intercalation compounds (GICs), Li+(PC)yCn-. XRD performed in situ to cyclic voltammetry allows to monitor the intercalation/de-intercalation of PC-solvated lithium into/from a crystalline graphite electrode, which is associated with up to 374% expansion of the basal plane spacing in c-direction of the graphite structure. The XRD data further allows to estimate the structure and stoichiometry of the ternary GIC: Li+(PC)yCn-, with y ⩾ 4, indicating a 3-dimensional, tetrahedral solvate shell. The stability of ternary GICs vs. reduction is addressed in view of graphite exfoliation and electrode failure. Keywords: In situ XRD, Graphite, Solvent co-intercalation, Solid electrolyte interphase (SEI), Lithium ion battery