Surface-segregated, high-voltage spinel lithium-ion battery cathode material LiNi_0.5Mn_1.5O₄cathodes by aluminium doping with improved high-rate cyclability

A series of Al-doped Li_1+xNi_0.5Al_xMn_1.5-xO₄cathode materials for lithium ion batteries are successfully synthesized via a co-precipitation method. Raman spectroscopy studies reveal that the cation-disordered tends to increase with the content of Al. The data of X-ray photoelectron spectroscopy (XPS) depth profiles reveal that the inert Al³⁺ions segregates preferentially to the surface during the synthesis process. The results of the electrochemical tests suggest that the substitution of a small amount of Al has the ability to improve the rate capability of LiNi_0.5Mn_1.5O₄spinel with conventional electrolytes. Especially, the Al-doped (x = 0.06) sample delivers a long cycle-life at high rate (20 C). The enhanced performance is attributed to the formation of Al-enriched surface, providing a more stable interface with the electrolyte at high voltage (∼4.7 V), along with the stabilization of the spinel structure with a disordering of the cations and improved Li-ion diffusion, based on results of the potentiostatic intermittent titration technique.