Degradation Mechanisms Induced by Depth-Dependent Inhomogeneity in High-Areal-Capacity Graphite Electrode

Developing high-energy-density batteries is essential to satisfy the electric vehicle market's demand for longer driving ranges. Among the strategies to enhance the energy densities of lithium-ion batteries, employing thick electrodes with high active material loading is one of the most feasible approaches. However, the use of thick electrodes leads to a significant decline in capacity retention and rate capability. To address this challenge, it is imperative to investigate the degradation mechanism of high loading graphite electrode. Herein, this study reveals that depth-dependent reaction inhomogeneity is more pronounced in graphite thick. Notably, this inhomogeneity contributes to the generation of current hotspots at the top of the electrode, leading to lithium plating and the parasitic formation of solid electrolyte interphase (SEI) layers. Consequently, this results in significant performance decline including increased charge transfer resistance and subsequent capacity fading. In addition, it has been demonstrated that the inhomogeneity and consequent degradation can be regulated with lithium phosphorus oxynitride (LiPON) artificial SEI layer. This coating, known for enhancing lithium-ion diffusivity and suppressing the formation of additional byproducts, effectively mitigates the heterogeneity along the electrode and degradation. This study underscores that addressing reaction inhomogeneity and its impact on thick electrodes is imperative for the application of high loading electrodes in batteries with elevated energy densities, necessitating a comprehensive strategy that encompasses the enhancement of diffusion processes and the regulation of surface reactions.