Mechanical degradation of electrode materials within single particle model in Li-ion batteries for electric vehicles

Mechanical degradation of electrode materials, in the form of particle cracking and fragmentation, disintegration, fracturing, and loss in contact between current collectors and the active electrode materials, can affect or deteriorate the performance of Li-ion batteries dramatically and even lead to the battery failure in electric vehicle. This paper firstly built a single particle model (SPM) based upon kinetics of electrochemical reactions. Then the Li-ion concentration, evolution of diffusion induced stresses within the SPM under potentiostatic or galvanostatic operating conditions were analyzed by utilizing a mathematical method. Next, evolution of stresses or strains in the SPM, at the core of relates with mechanical degradation of electrode materials, are elaborated in detail. Finally, surface and morphology of the electrodes dismantled from fresh and degraded cells after galvanostatic charge/discharge cycling have been analyzed to verify the hypothesis aforementioned by observing scanning electron microscopy and analyzing X-ray diffraction.