Mechano-Electrochemical Interaction and Degradation in Graphite Electrode with Surface Film

Lithium ion batteries (LIBs) exhibit significant capacity and performance degradation with cycling owing to extensive decrepitation of anodes associated with lithiation-delithiation induced volumetric expansion and contraction. Microcrack formation in the active material and solid electrolyte interphase layer contribute to deleterious effects including hindered diffusion, particle isolation, and loss of cyclable Li inventory, with detrimental performance ramifications. In this work, a stochastic computational methodology, utilizing lattice spring formalism, is extended to probe effect of surface film characteristics on diffusion induced damage in graphite anodes with a direct correlation to LIB performance. Film geometric and mechanical properties of interest, with a direct impact on fracture characteristics, are identified and parametric variations are explored to ascertain the relative influence of each property. Reduction of surface film stiffness is found to substantially ameliorate fracture damage inside both active material and film. Film thickness and fracture threshold energy primarily affect the fracture characteristics inside film with a less discernible impact on the anode active material. Extensive damage density data based regression as well as rate performance study is performed to strengthen the hypothesis and desirable film properties are outlined for improved LIB performance, specifically, low stiffness and high fracture threshold energy film with optimal thickness. (C) 2018 The Electrochemical Society.