Degradation Effects in Li₄Ti₅O₁₂-Based Cells─Learning from Electrode Potential Profiles

Li₄Ti₅O₁₂ (LTO) is a promising negative electrode active material for high-power applications of lithium-ion batteries due to its structural and dimensional stability, high safety properties, and rate capability. However, there are still challenges regarding the cyclic aging behavior of LTO-based cells, especially when it comes to the origin of gas evolution that needs to be resolved in order to enable an optimized cell design and prolonged cycle life. Using a three-electrode setup provides operando insights into the cyclic aging behavior of LiNi_1/3Co_1/3Mn_1/3O₂ (NCM111)||LTO cells. The results demonstrated that an initial slight increase in specific capacity followed by an intense decrease after 40 cycles could be attributed to a relative shift of the individual electrode potential profiles caused by loss of lithium inventory and associated electrolyte consumption during cyclic aging. By using higher formation temperatures, the capacity decrease, an associated loss of lithium inventory, and continuous electrolyte consumption were successfully suppressed. Moreover, the results suggested that gas evolution in Li₄Ti₅O₁₂-based cells majorly originates from the reductive decomposition of moisture residues and the electrolyte at the Li₄Ti₅O₁₂ electrode surface.