Long-term cyclability of Li4Ti5O12/LiMn2O4 cells using carbonate-based electrolytes for behind-the-meter storage applications

Li4Ti5O12/LiMn2O4 (LTO/LMO) chemistry was evaluated as a potential candidate for behind-the-meter storage (BTMS) applications. Its long-term cycle performance at 45 degrees C was tested using ethylene carbonate (EC) and propylene carbonate (PC) solvent electrolytes. Over 1000 cycles, LTO/LMO cells exhibited similar to 80% capacity retention and Coulombic efficiency higher than 99.96%. Electrochemical test results showed the major degradation mode of LTO/LMO cells arises from continuous electrolyte decomposition at the LTO anode and loss of Li inventory. EC and PC electrolytes created distinct surface layers, where the EC reduction products were more effective in passivating the LTO electrode surface. Dissolution and migration of Mn from the cathode was probed as Mn2+ species distributed throughout the surface layer at the anode. By utilizing a prelithiated LTO electrode, the LTO/LMO cell performance was significantly enhanced with EC electrolyte. On the other hand, PC electrolyte resulted in accelerated electrolyte decomposition at the lithiated LTO surface due to the lack of surface passivation. Thus, mitigating parasitic reactions at the LTO electrode is the key to developing successful LTO/LMO cells.

Automated summary

The LTO/LMO chemistry shows promising potential for BTMS applications, with good long-term cycle performance but facing degradation issues such as continuous electrolyte decomposition at the anode and loss of Li inventory. Addressing these challenges will be key to developing successful LTO/LMO cells.