Quantifying and Inhibiting Manganese Dissolution in Li-Rich Mn-Based Cathode Materials

The development of lithium-ion batteries has propelled electronics and electric vehicles, with lithium-rich manganese-based (LRMO) materials becoming promising high-energy-density cathodes. However, Mn dissolution remains a major challenge, leading to structural instability and performance degradation. This study elucidates the Mn dissolution mechanism in LRMO materials and validates it through surface modification. Between 2.5 and 3.5 V, Mn dissolution is primarily driven by Mn⁴⁺ reduction to Mn³⁺ during cycling, followed by disproportionation to Mn²⁺. Above 4.3 V, lattice oxygen release causes structural densification, impeding lithium-ion transport and promoting Mn dissolution. Within 3.5-4.3 V, Mn dissolution is higher than that in other voltage regions, primarily due to the Jahn-Teller effect and electrolyte side reactions. Contrary to conventional beliefs, Mn dissolution remains substantial, even within this moderate voltage range. To verify the mechanism and enhance stability, an ALD-based LPO nanocoating is applied, effectively suppressing electrode/electrolyte side reactions and improving voltage retention. Quantitative analysis shows a significant reduction in the level of Mn dissolution, confirming the critical role of electrolyte interactions. Overall, this work highlights the complex role of Mn dissolution across different voltage ranges, along with the demonstrated effectiveness of surface engineering in stabilizing LRMO cathodes.