Enhanced Electrochemical Performance of Surface-Nitrided MnO Negative Electrode Materials in Li-Ion Batteries

MnO is a negative electrode material that has significant potential for application in high-capacity Li-ion batteries because of its low material cost and the fact that its conversion reaction allows excellent Li storage capability (756 mAh g−1). However, despite its high theoretical capacity, the practical application of MnO is impeded by its low conductivity and the significant volume changes exhibited by the material during lithiation/delithiation. Herein, we report a simple, solvent-free method for synthesizing surface-nitrided MnO by heating a homogeneous mixture of MnO powder and urea in an autogenic reactor. The nitrided layer formed on the surface of the microsized MnO particles acts as a buffer, mitigating volume changes during lithiation and delithiation, and its high conductivity reduces the charge-transfer resistance of MnO. These enhanced properties collectively serve to optimize the electrochemical performance of MnO electrodes. In Li/MnO cell tests (for a 50.0 wt% urea sample), the MnO surface is converted into electrochemically inert Mn2N0.86 during synthesis. It exhibits a slight reduction in reversible capacity but demonstrates significantly improved cyclability and rate capability when compared to bare MnO. This improvement is attributed to the ability of the nitrided layer to stabilize the electrode structure and facilitate more efficient charge transfer. We expect the results of this study to provide insights into simple surface-coating methods and facilitate the application of conversion-type anode materials (such as MnO) in high-capacity Li-ion batteries.