| Basing on studying of LiCoO2, we researched one or several metal substituents(both electrochemically-active and inactive) in LiCoO2. Another approach to improve the cycling stability of cathode materials is surface coating treatment.In this work, we studied the structural and electrochemical properties of Al-substituted LiCo1-xAlxO2 and co-doped LiCo0.7Al0.3-xMgxO2 cathode materials thatwere synthesized by a sol-gel method from citrate precursors. The powders werecharacterized by means of X-ray diffraction (XRD) and charge-discharge test. It wasshown by XRD that the layered pure phases of LiCo1-xAlxO2 were made for thesolubility of the Al doping. With the increasing content of Al in LiCo1-xAlxO2, thecrystal structure was not changed. The research indicated that the first dischargecapacity of LiCo1-xAlxO2 was 131.2mAh·g-1, and has the higher charge voltage thanLiCoO2. But cyclic efficiency decreased with increasing the cycle number, thecapacity was faded at the same time. The best electrochemical performance is gottenwhen the doping amount of Al is 0.1. It could export 125.7 mAh·g-1 of the dischargespecific capacity at initial cycle and remain 86.03％of the initial capacity after 30cycles.The LiCo0.7Al0.3-xMgxO2 particles possesses spherical morphology anduniform particle size with theα-NaFeO2 layerd structure.The voltage of charge wasdecreased slightily after doping. Also the cyclic properties for charge-discharge wereimproved obviously. The best electrochemical performance is gotten when thedoping amount of Mg is 0.05. It could export 122.10mAh·g-1 of the dischargespecific capacity at initial cycle and remain 95.03％of the initial capacity after 30cycles.In this study, the LiCoO2 and LiCo0.7Al0.3O2 cathode materials were also modifiedby applying surface coating of MgO at the different conditions. MgSO4 andNH3·H2O were used to coat LiCoO2 through co-precipitation method. Through the battery's performance tests, we found that the structure of the coated materials wasnot changed. And the cycling performance and charge-discharge reversibility of thecoated materials was improved. The material's charge voltage was increased. In theLiCo0.7Al0.3O2 coated by MgO materials, the best electrochemical performance isgotten when the coating amount of MgO is 1.0％. It could export 120.17mAh·g-1 ofthe discharge specific capacity at initial cycle and remain 89.3％of the initialcapacity after 30 cycles...
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