Elucidation of Side Reactions in Lithium-ion Batteries with Electrolyte Decomposition Products via Overdischarge for Li[Li<sub>1/3</sub>Ti<sub>5/3</sub>]O<sub>4</sub>/Li[Li<sub>0.1</sub>Al<sub>0.1</sub>Mn<sub>1.8</sub>]O<sub>4</sub> Cells with an Imbalanced State-of-Charge

A major factor in the capacity fading of lithium-ion batteries is the imbalance in the state-of-charge (SOC) between the positive and negative electrodes, which is caused by the difference in the side-reaction current between the two electrodes. Therefore, it is crucial to understand these side reactions to extend battery life. There are two types of side-reaction current, ISR: "intrinsic"-ISR results from electrolyte decomposition, while "additional"-ISR results from the reaction of decomposition products. The "additional"-ISR is closely related to crosstalk reactions. In this study, we conducted overdischarge tests on Li[Li1/3Ti5/3]O4 (LTO)/Li[Li0.1Al0.1Mn1.8]O4 (LAMO) cells with the SOC of the positive and negative electrodes intentionally imbalanced to understand the nature of the "additional"-ISR. While the cell capacity initially increased after the overdischarge, the recovered capacity decreased in subsequent cycles. This phenomenon can be explained well by a side-reaction model that considers the oxidant generated in the cell due to overdischarge, which indicates that the concentrations of oxidants and reductants in the cell are important for the ISR.