Engineering a nitrogen-rich functional interfacial layer on Co-free LiMn2O4 to mitigate Mn3+ driven surface degradation at elevated temperature

Lithium manganese oxide (LMO) is a promising positive electrode material for Li-ion batteries (LIBs) owing to its favorable operating voltage, environmental compatibility and three-dimensional framework for Li + ion transport. However, interfacial degradation and Mn dissolution accelerate capacity loss during prolonged cycling, especially at elevated temperatures. Herein, two-dimensional graphitic carbon nitride (g-C 3 N 4 -CN) was uniformly coated onto LMO using a low-cost wet-chemical approach. The structural, morphological and surface characteristics were investigated using XRD, FT-IR, FESEM, HRTEM and XPS. Among the investigated electrodes, LMO@CN-2wt% exhibited excellent electrochemical performance, delivering 124.48 mAh g −1 with 93% capacity retention after 200 cycles at 1C and 101.30 mAh g −1 with 85% retention after 500 cycles at 3C. It also delivered 131.40 mAh g −1 at 55 °C and 66.18 mAh g −1 at 0 °C, retaining 82% and 95% of its initial capacity respectively, after 100 cycles. Post-cycling XRD, FESEM, XPS and UV-vis DRS confirmed that the CN coating retained its structural integrity and suppressed surface degradation. The improved electrochemical stability can be attributed to the protective effect of the CN layer at the electrode-electrolyte interface, which mitigates manganese dissolution and particle cracking. Overall, the uniform g-C 3 N 4 coating effectively enhances the cycling and temperature stability of LMO cathodes.