Designing Li4Ti5O12/LiMn2O4 Cells: Negative-to-Positive Ratio and Electrolyte

Abstract

Li4Ti5O12/LiMn2O4 (LTO/LMO) system is a promising candidate for behind-the-meter storage (BTMS) applications due to its critical-material-free chemistry exhibiting good safety and long lifetime. Here, we design LTO/LMO cells to mitigate their major degradation mechanism, loss of Li inventory, and improve their long-term cyclability. First, LMO electrodes with different loadings (2.61, 3.29, and 4.26 mAh cm−2) are paired with an LTO electrode (3.35 mAh cm−2) to create varying negative-to-positive ratios (N/P>1, =1, and <1). Additionally, conventional ethylene carbonate (EC)/ethyl methyl carbonate (EMC) mixture electrolyte and safety enhanced EC-only electrolyte are examined. We show that storing additional Li inventory in the cathode (i.e., using a thicker electrode and having N/P<1) is a convenient method to enhance the capacity retention of LTO/LMO cells, but only if the electrode utilization is not limited by the Li+ ion transport. For systems that suffer from limited transport properties, prelithiating the anode will be more effective since LTO (∼165 mAh g−1 LTO) can store the same amount of capacity using less material compared to LMO (∼100 mAh g−1 LMO). In this work, we demonstrate how the electrolyte properties and the electrode thickness of LTO/LMO cells can be designed to enhance their performance.