Understanding capacity fading mechanism of thick electrodes for lithium-ion rechargeable batteries

The use of thick electrodes with high-loading density of active material is one of the most practical strategies to increase the volumetric/specific energy density of lithium-ion battery, while taking advantage of the current electrode chemistry. However, their use is accompanied by serious deterioration of electrochemical performance, especially exhibiting poor capacity retention with low power capability. Here, the degradation behavior of the LiNi0·6Co0·2Mn0·2O2, one of widely adopted cathodes, is comparatively investigated under high loading levels as high as 28 mg cm−2 over the extended cycling. It is revealed that the charge transport limitation is cumulatively dominated by the lithium ionic diffusion rather than the electronic conduction in the thick electrode. More importantly, as the cycle proceeds, the thick electrode gets exposed to a serious reaction inhomogeneity because of the negative feedback between the accumulated ion transport limitation and locally increasing resistance. It leads to the generation of current hot spot in the electrode and the corresponding local material degradation, which further inhibit the charge transport, resulting in unavoidable capacity fading. This finding proposes that rational electrode architecture detouring the hot spot generation needs to be considered with respect to the ion transport and the electrode material degradation toward the high-loading electrodes.