Unraveling the Roles of Dissolved Mn(2+) and Its Impact on the Electrode–Electrolyte Interface under Realistic Conditions

NMC532 (LiNi0.5Mn0.3Co0.2O2) is a cost-effective and structurally stable cathode material that is widely used in batteries. Despite its stability, it undergoes irreversible phase transitions and transition metal (TM) dissolution during long-term cycling, which significantly impacts cell performance. This study pioneered a methodology to investigate the solid electrolyte interface (SEI) layers in depth, employing advanced analytical techniques: time-of-flight secondary ion mass spectrometry (TOF-SIMS) and cluster analysis. By utilizing these techniques, we specifically examined the impact of Mn dissolution on the interface evolution of graphite during calendar degradations. Additionally, we explored the relationship between Mn dissolution and cell performance in a graphite||NMC532 pouch cell. The results demonstrate that the competition between Mn dissolution and electrolyte depletion governs cell degradation. In particular, Mn dissolution accelerates the decomposition of the electrolyte, ultimately causing SEI layer growth. These findings provide a deeper understanding of battery performance and degradation mechanisms.