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

The nontoxicity and low cost make LiMn 2 O 4 a competitive cathode material for lithium-ion batteries. LiMn 2 O 4 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 LiMn 2 O 4 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 LiMn 2 O 4 and Li 2 O 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 LiMn 2 O 4 .