For the regeneration of spent graphite: The exploring of structural failure mechanism about commercial graphite

Abstract

Along with the wide application of electric automobiles, the great “wave” of recycling for lithium-ion batteries would be upcoming due to their limited cycling lifespan. As the main components but without valuable elements, spent graphite suffers from effective recycling manners. Although the regeneration method has been deemed as a promising manner, the clarifying of their failure mechanism is prerequisite to the exploring of regeneration methods. Herein, commercial graphite with different healthy states is prepared through the disassembling of cells at different cycles. Assisted by the detailed structural analysis, the systematic failure process is clearly illustrated. At initial cycling, the shuttling of lithium ions renders the decomposing of unstable carbon atoms and some weak interlayer structures. With further cycling, the interlayer architecture and large-size grains were further damaged, to form small-size grains, accompanying enhanced anisotropy, finally resulting in the increasing internal resistance. Moreover, owing to the ion-diffusion behaviors, graphite sheets have an obvious moving, resulting in the transformation from 2H-phase to 3R-phase with the decreasing of energy-storage activity. Thus, from the perspective of internal structure, the decreasing of graphitized grains and the formation of 3R-phase served as crucial failure factors. Given this, the work is anticipated to illustrate the failure mechanism of graphite, meanwhile offering the basic regeneration direction of spent graphite samples.