Mitigation of charge heterogeneity by uniform in situ coating enables stable cycling of LiCoO2 at 4.6V

Abstract

LiCoO2 is a predominant cathode for lithium-ion batteries of portable electronics owing to its merit of high volumetric energy density. Nevertheless, it experiences rapid capacity deterioration under high voltages, concomitant with structural degradation and numerous intragranular cracks. Coating has been recognized as an efficacious strategy to ameliorate the decline in cycling performance of LiCoO2 at high voltages. Hence, a systematic elucidation of the precise mechanisms underlying the mitigation of structural degradation via coating layers assumes paramount importance in the context of advancing the next generation of high-voltage LiCoO2. In this work, the intricate interrelation among lithium-ion diffusion coefficients, charge heterogeneity, and crack distribution is explicated through techniques inclusive of galvanostatic intermittent titration technique (GITT), finite element analysis (FEA), and X-ray computed tomography (XCT). A robustly stable lithium-ion-conducting coating material serves the function of curtailing the occurrence of surface passivation layers, achieved by diminishing side reactions between the LiCoO2 and the electrolyte; while a uniform coating ensures a homogeneous lithium-ion flux, thereby mitigating charge heterogeneity and the resultant mechanical strain as well as intragranular cracks. Both are important elements that collectively allow the coating to effectively protect the surface from structural degradation, thus achieving superior performances upon high-voltage charging.