Improvement of high-voltage cycling behavior of Li(Ni _1/3Co _1/3Mn _1/3)O ₂ cathodes by Mg, Cr, and Al substitution

To improve the electrochemical properties of Li[Ni _1/3Co _1/3Mn _1/3]O ₂ at high charge end voltage (4.6 V), a series of the mixed transition metal compounds, Li(Ni _1/3Co _1/3∈-∈x Mn _1/3M _x )O ₂ (M = Mg, Cr, Al; x∈=∈0.05), were synthesized via hydroxide coprecipitation method. The effects of doping Mg, Cr, and Al on the structure and the electrochemical performances of Li[Ni _1/3Co _1/3Mn _1/3]O ₂ were compared by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), galvanostatic charge-discharge tests, and electrochemical impedance spectroscopy. The XRD results show that all the samples keep layered structures with R3m space group as the Li[Ni _1/3Co _1/3Mn _1/3]O ₂. SEM images show that all the compounds have spherical shapes and the Cr-doped sample has the largest particle size. Furthermore, galvanostatic charge-discharge tests confirm that the Cr-doped electrode shows improved cycling performance than the undoped material. The capacity retention of Li(Ni _1/3Co _{1/3∈-∈0.05}Mn _1/3Cr _0.05)O ₂ is 97% during 50 cycles at 2.8-4.6 V. The improved cycling performance at high voltage can be attributed to the larger particle size and the prevention of charge transfer resistance (R _ct) increase during cycling.