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.