Electrochemical and structural characterization of carbon coated Li1.2Mn0.56Ni0.16Co0.08O2 and Li1.2Mn0.6Ni0.2O2 as cathode materials for Li-ion batteries

Carbon coated Li1.2Mn0.56Ni0.16Co0.08O2 and Li1.2Mn0.6Ni0.2O2 were synthesized as cathode materials for Li-ion batteries by a self-combustion reaction, and were characterized by XRD, SEM, HRTEM and Raman spectroscopy in conjunction with electrochemical measurements. Initial discharge specific capacities of 270 mAh g−1 and 230 mAh g−1 are obtained for Li1.2Mn0.56Ni0.16Co0.08O2 and Li1.2Mn0.6Ni0.2O2, respectively at slow rates (e.g. C/10) in galvanostatic charge-discharge cycling. The cathode material Li1.2Mn0.56Ni0.16Co0.08O2 can provide a discharge capacity of 110 mAh g−1 at 4 C rate. The importance of the presence of Co in the structure for obtaining high rate capabilities was proven by comparison with Li1.2Mn0.6Ni0.2O2 electrodes, which can exhibit only 80 mAh g−1 at 2 C rate. The electrochemical impedance spectra of Li1.2Mn0.56Ni0.16Co0.08O2 recorded at various potentials during charging indicate that there is a substantial increase in the charge-transfer resistance at voltages higher than 4.4 V, indicating that the kinetics of Li+ ions insertion into this material is controlled by charge-transfer rather than by Li+ ions diffusion, at high potentials.