Enhancement of electrochemical performance of LiNi_1/3Co_1/3Mn_1/3O₂ by surface modification with MnO₂

LiNi_1/3Co_1/3Mn_1/3O₂ is successfully coated with MnO₂ by a chemical deposition method. The X-ray diffraction (XRD), scanning electron microscope (SEM) and high resolution transmission electron microscope (HRTEM) results demonstrate that MnO₂ forms a thin layer on the surface of LiNi_1/3Co_1/3Mn_1/3O₂ without destroying the crystal structure of the core material. Compared with pristine LiNi_1/3Co_1/3Mn_1/3O₂, the MnO₂-coated sample shows enhanced electrochemical performance especially the rate capability. Even at a current density of 750 mA g⁻¹, the discharge capacity of MnO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂ is 155.15 mAh g⁻¹, while that of the pristine electrode is only 132.84 mAh g⁻¹ in the range of 2.5–4.5 V. The cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS) curves show that the MnO₂ coating layer reacts with Li⁺ during cycling, which is responsible for the higher discharge capacity of MnO₂-coated LiNi_1/3Co_1/3Mn_1/3O₂. Electrochemical impedance spectroscopy (EIS) results confirmed that the MnO₂ coating layer plays an important role in reducing the charge transfer resistance on the electrolyte–electrode interfaces. - Highlights: • MnO₂ coated LiNi_1/3Co_1/3Mn_1/3O₂ cathode material is synthesized for the first time. • MnO₂ offers available sites for insertion of extracted lithium. • The preserved surface and crystal structures results in the improved kinetics.