Improvement of high-voltage cycling behavior of Li(Ni1/3Co1/3Mn1/3)O2 cathodes by Mg, Cr, and Al substitution

To improve the electrochemical properties of LiNi_1/3Co_1/3Mn_1/3]O₂ 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 )O₂ (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 LiNi_1/3Co_1/3Mn_1/3]O₂ 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 LiNi_1/3Co_1/3Mn_1/3]O₂. 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)O₂ 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.