Analysis for Mechanical Failure of DISs with Graphite Anode in Lithium ion Batteries for Electric Vehicles

Graphite-based anode materials undergo electrochemical reactions, coupling with mechanical degradation during battery operation, can affect or deteriorate the performance of lithium-ion batteries dramatically, and even lead to the battery failure in electric vehicle. First, a single-particle model based on kinetics of electrochemical reactions was built in this article. Then, the lithium-ion concentration and evolution of diffusion induced stresses within the single-particle model under galvanostatic operating conditions were analyzed by utilizing a mathematical method. Next, evolutions of stresses or strains in the single-particle model, together with mechanical degradation of anode materials, were elaborated in detail. Finally, in order to verify the aforementioned hypothesis, surface and morphology of the graphite-based anode dismantled from fresh and degraded cells after galvanostatic charge/discharge cycling were analyzed by X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy. The results show that large volume changes of anode materials caused diffusion-induced stresses during lithium-ion insertion and extraction within the active particles. The continuous accumulations of diffusion-induced stresses brought about mechanical failure of the anode eventually.