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.

Key words: hydrothermal synthesis, orthorhombic structure, cathode material, co-doping