Deciphering the capacity degradation mechanism in lithium manganese oxide batteries

Spinel lithium manganese oxide (LiMn₂O₄, LMO) emerges as a promising cathode material for future stationary energy storage applications due to its high voltage, safety, cost-effectiveness, and electrochemical performance. However, LMO suffers from rapid capacity degradation caused by the Jahn-Teller effect, Mn dissolution and side reactions. The mechanism remains unclear and even contradictory across various studies, impeding the advancement of high-performance LMO and its widespread utilization. In this study, 14 Ah commercial-level LMO batteries were manufactured and assessed. The mechanism of capacity attenuation in cycle-aged cells at room temperature (RT, 25 °C) and high temperature (HT, 55 °C) storage cells was systematically investigated through the application of electrochemical quantitative methods. The results indicate specific capacity losses of approximately 6.26% and 2.55% for the cathodes in RT cycle-aged cells and HT storage cells, respectively, in comparison to fresh cells. These values are lower than the 12.54% and 6.99% capacity losses observed in RT cycle-aged cells and HT storage cells. While RT cycle-aging and HT storage conditions do not lead to irreversible capacity loss on the anode side. The results suggest that the primary causes of irreversible capacity degradation are not located on the cathode or anode. Nevertheless, significant polarization arises from the continuous growth of the solid electrolyte interphase (SEI), believed to be catalyzed by Mn deposited on the anode, which is considered harmful. This study elucidates that inhibiting the dissolution of Mn from the cathode, facilitating its transport in the electrolyte, promoting its deposition on the anode, and catalyzing the decomposition of the electrolyte are crucial factors for enhancing the performance of LMO batteries.