Co-modification by LiAlO2-coating and Al-doping for LiNi0.5Co0.2Mn0.3O2 as a high-performance cathode material for lithium-ion batteries with a high cutoff voltage

LiAlO2-coated and Al-doped LiNi0.5Co0.2Mn0.3O2 (Al-modified NCM) materials are successfully synthesized via a facile coprecipitation method. The lattice parameters calculated from X-ray diffraction (XRD) patterns reveal that the slab spacing of the modified material is broadened after Al substitution. A continuous and uniform LiAlO2 coating layer with a thickness of ∼4.3 nm on the surface of Al-doped LiNi0.5Co0.2Mn0.3O2 is confirmed by transmission electron microscopy (TEM). Al-modified NCM shows remarkable improvements in cycling and rate performance and possesses a high capacity retention of 82.06% at 0.5 C after 200 repeated cycles in the voltage range of 3.0-4.6 V, whereas the capacity retention of pristine NCM is only 60.04%. Even at a high current density and an elevated temperature, the Al-modified sample still shows better cycling performance than that of pristine NCM, with capacity retentions of 67.68% (25 °C) and 57.36% (85 °C) after 100 cycles at 10 C. Furthermore, Al-modified NCM delivers a high discharge specific capacity of 142.73 mAh g−1 at a current density of 10 C. The improved electrochemical performance could be ascribed to the synergistic effect of the LiAlO2 coating and Al doping. The enlarged slab spacing resulting from Al substitution and the Li+-conducting LiAlO2-coating layer benefits lithium ion diffusion. Moreover, the LiAlO2-coating layer acts as a protective shell and can suppress the increase in impedance during repeated cycling.