Quantification of side reactions in lithium-ion batteries during overcharging at elevated temperatures

Abstract

Lithium-ion batteries experience complex reactions between the electrodes and the electrolyte under non-standard conditions. Investigating these reactions is crucial for ensuring battery durability and safety. In this study, we develop an electrochemical cell capable of controlled overcharging and temperature regulation between 30 and 100 °C. The charge-discharge performance of the cell is evaluated after overcharging. By utilizing synchrotron radiation for X-ray diffraction and absorption fine structure analysis, we track the electronic state of the positive electrode and the crystal structure of the negative electrode during heated overcharging. Our results reveal increased side reactions in the positive electrode at higher temperatures during overcharging, while the negative electrode displays a gradual increase in side reactions in the normal charge-discharge region with increasing temperature. Specifically, at 100 °C, side reactions in the overcharging regions consume 86.5% and 66.1% of the current at the positive and negative electrodes, respectively. These side reactions are induced by the electrolyte oxidative decomposition at the positive electrode. Moreover, they initiate Joule heating during battery overcharging, promoting side reactions and leading to exothermic reactions between the electrodes and electrolyte.