Tuning the Nanoarea Interfacial Properties for the Improved Performance of Li-Rich Polycrystalline Li-Mn-O Spinel.

The nontoxicity and low cost make LiMn2O4 a competitive cathode material for lithium-ion batteries. LiMn2O4 has a high theoretical capacity (296 mAh g-1) when cycled in the 3 and 4 V regions. However, it displays a low practical capacity (∼120 mAh g-1) because of the unavailability of the 3 V region caused by severe Jahn-Teller distortion. The present work investigated the full utilization of LiMn2O4 in both 3 and 4 V by tuning the nanoscale interfacial properties. Li-rich structures at the surface and interface of the spinel material and nanograin strain were introduced to improve the performances and were achieved by grinding LiMn2O4 and Li2O at 700 rpm for 10 h under an argon atmosphere. The product shows a high initial discharge capacity of 287.9 mAh g-1 at 0.05 C between 1.2 and 4.6 V and retains 83.2% of the capacity after 50 cycles. The nanoscale interfacial structure was clarified by spherical aberration-corrected microscopy and XRD refinement, and complex occupancies of Li and Mn were found at the interface. A correlation between the interfacial properties and electrochemical performance was established, and the improved performance could be attributed to the polycrystalline nature of the material, the unique Li-rich interfacial structure, and the slightly elevated valence state of Mn. The present results may provide insight for further evaluating the complex mechanism of controlling the electrochemical performance of LiMn2O4.