From electrode saturation to structural collapse: unraveling the rollover failure in a lithium-rich manganese/graphite pouch cell at elevated temperature

Abstract

The abrupt capacity rollover failure of medium-voltage lithium-rich manganese-based oxide (LRMO) batteries at elevated temperatures severely limits their practical application. This study systematically investigated the underlying failure mechanism of a 0.2Li₂MnO₃·0.8LiMn_0.33Ni_0.33Co_0.33O₂-graphite (LRMO-Gr) pouch cell cycled at 45 °C. Through combined differential voltage analysis, alternating current (AC) impedance measurements, and post-mortem characterization, we revealed that lithium plating on the anode surface acts as the primary trigger of rollover failure. This plating is driven by electrode saturation, which originates from the faster loss of the anode active material relative to the cathode. This imbalance stems from the structural degradation of a graphite anode induced by cathode-derived active lithium compensation and transition metal (TM) dissolution–migration–deposition. The migrated TMs and plated lithium further catalyze electrolyte decomposition, leading to gas evolution, electrode exfoliation, and rapid capacity collapse. These insights provide a fundamental basis for mitigating failure in high-energy LRMO-based batteries under realistic operating conditions.