Synthesis and Electrochemical Properties of S-M (M=Cu, Co, Ti) Co-doped Layered LiMnO2 Cathode Materials

Orthorhombic structure LiMnO2 Compounds used as cathode materials for lithium-ion batteries were synthesized by a hydrothermal method, and modified by doping with sulphur ion (S2-), large-sized cation (Cu2+, Co3+, Ti4+) and co-doping with S-M (M=Cu, Co, Ti). The structure and electrochemical performances of the as-prepared materials were studied by X-ray powder diffraction (XRD), X-ray photoelectron microscopy (XPS), transmission electron microscopy (TEM), chronoamperometry and electrochemical impedance spectroscopy (EIS). The synthesized materials exhibit a standard orthorhombic structure and good electrochemical performance after the doping with a spot of above-mentioned ions. The beneficial effect of these cations on improving cyclability was demonstrated, due to that the stability of LiMnO2 orthorhombic structure is enhanced by the doping with these non-Jahn-Teller ions. The electrode of Li1.02Mn0.988Ti0.012O1.989S0.011 shows excellent electrochemical properties with the first discharge capacity of 142.6 mAh.g(-1) and retaining 213.4 mAh.g(-1) after 60 cycles at a current rate 50 mA.g(-1). The electrochemical results reveal that the co-doping of S-M (M=Cu, Co, Ti) combines the advantages of the improvement of Li+ diffusion by cation doping, with the suppression of Jahn-Teller distortion by S2- doping. In the meantime, the co-doped materials also achieve higher capacity and better cyclic performance than the pristine LiMnO2.