Capacity fading mechanism of thick electrode in Lithium-ion rechargeable batteries

Abstract

In order to achieve the higher energy density batteries, increasing loading level of cathode material is considered as a promising method in the practical point of view. However, when the loading level of cathode material increases, capacity retention of the electrode significantly deteriorates. In this study, two different loading levels of cathode material (20 mg cm-2 and 28 mg cm-2 of LiNi¬0.6Co0.2Mn0.2O2, NCM622) are prepared as models for the study and I found that the state of charge inhomogeneity of 28 mg cm¬-2 loading level electrode is much severer than that of 20 mg cm-2. Furthermore, I found that of NCM622 near separator side actively oxidize/reduces, while the particles being near the current collector remains almost inert in 28 mg cm-2 electrode. Such discrepancy between separator and current collector side in 28 mg cm-2 electrode can be explained by sluggish ion transport in thick electrode after cycling. In case of charging, Li-ion is difficult to be extracted from the active material near the current collector side due to elongated Li-ion pathway in 28 mg cm-2 electrode. In case of discharging, Li-ion from electrolyte cannot reach to active material near the current collector side. Therefore, the active materials near the separator side participates the reaction more vigorously than current collector side ones, leading to the severe capacity fading of thick electrode due to its current hot spot. Here, I studied the relationships with the state of charge inhomogeneity and capacity fading of thick LiNi0.6¬Co0.2Mn0.2O2 electrode.