Enhanced electrochemical performance of spinel LiNi_0.5Mn_1.5O₄ for Li-ion batteries with moderate Mn³⁺ concentration and nanosized thin Al₂O₃ coating

In this paper, Al₂O₃ was selected as a modifying material to improve the electrochemical performance of spinel LiNi_0.5Mn_1.5O₄ (LNMO) by a simple wet chemical process. SEM and TEM analyses indicated that the Al₂O₃ was coated on the surface of LNMO surface with the thickness of ~ 10 nm. Meanwhile, XRD, Raman, and XPS analyses indicated that the introduction of Al₂O₃ had a slight change in LNMO structure from disordered phase to ordered phase, with the decrease of Mn³⁺ concentration. The optimized LNMO (LNMO@AO-1 wt%) delivered specific capacities of 129 and 109 mA h g⁻¹ at 1 and 20 C rates, respectively. At the 1 C cycling rate, capacity retention of 96% was obtained after 300 cycles, much better than pristine LNMO of 86%. The remarkable performance was attributed to the introduction of Al₂O₃ that can not only form inert coating layer to isolate the contact between electrolyte and electrode surface, but also reduce the Mn³⁺ concentration in materials appropriately, thus alleviating the disproportional reaction and Jahn–Teller distortion effect.