An on-line transient study on gassing mechanism of lithium titanate batteries

Gassing at elevated temperature is the main reason for the performance degradation of lithium titanate (Li₄Ti₅O₁₂, LTO) batteries. In this study, an in-situ device was developed and used to study on-line the transient gassing of custom-made 4.5Ah LTO/NCM pouch batteries at 1C cycling at 55°C. The gas volume and internal pressure of the batteries were recorded on-line for 1000 h, and the composition of the gas components at different times was also analyzed by on-line gas chromatography. The results show that H₂ and CO₂ are the main gas components. The H₂ percentage decreases, while the CO₂ percentage increases gradually during the process of gassing. According to the rate-controlling step of gassing from H₂ formation reaction to CO₂, a stage-by-stage mixed gassing mechanism is proposed, where the water decomposition is dominant in the initial stage and solvent decomposition is dominant in the subsequent stage. The gassing of LTO batteries aged at 55°C was studied on-line at different states of charge (0%, 50%, 100% SOC). The results show that the volume and composition of the gas are essentially independent of the SOC of batteries and that formation of SEI at LTO interface is the main reason for the gassing rate reduction when aged and cycled (final phase) at 55°C.