Improvement of the electrochemical performance of LiNi _0.33Mn_0.33Co_0.33O₂ cathode material by chromium doping

LiNi_0.33Mn_0.33-x Co_0.33Cr _x O₂ (x=0, 0.01, 0.025, 0.05) materials were synthesized by Cr ³⁺ substitute of Mn⁴⁺ to enhance their electrochemical properties. The structure and electrochemical properties were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge/discharge tests. The materials maintained the α-NaFeO₂ type layered structure and the discharge capacities were also increase by doping appropriate amount of Cr³⁺. The sample with x = 0.025 exhibited the highest discharge capability of 181.6 mAh g^-1 and the best cycle performance. EIS measurement showed that the Cr-doped electrode had the lower resistance impedance increase during cycling. The chemical diffusion coefficient of Li ⁺ ion (D _Li) was measured by potentiostatic intermittent titration technique (PITT). The result showed that D _Li in Cr-doped electrode was faster than that of the un-doped one.