| LiMn2O4 spinel was believed to be the most prospective cathode material because of its abundant resources, cheapness, little pollution and simple synthesis process. The low initial capacity and its rapid decrease of the spinel, however, haven't been improved up to now. Through the most widely adopted method to overcome the problems was cation substitution, the improvement on cyclability was at the cost of initial capacity, so the method need to be made better. In addition, the range of charge/discharge voltage was limited in 4V region due to the extensive decrease of capacity in 3V region. If the cyclability in 3v region can be improved, the theory capacity of the material will be doubled and the actual capacity will be elevated a lot. Thus, the research focused on the both above questions.The first-principal calculation indicated in the course of Li intercalation the charge transferred to O mostly but for Mn which was taken for granted by traditional theories, that is to say, the anion played a most important role in the material. According to the calculation results, the research emphasized on anion substitution and the results that the initial capacity of cation-doping spinel was elevated and the cyclability in 3V region was improved were expected.After F-doping and F-Co-doping spinels were synthesized, their structures and electrochemical properties were characterized. The average valence of Mn was decreased by F substitution, accordingly, the amount of Mn3+ were increased, therefore, the initial capacity was elevated and sample c (LiMn2O3.5F0.5) had the highest capacity (127mAh/g). Despite of the elevated initial capacity, the single F substitution deteriorated the cyclability. F-Co compound substitution overcame the defects of single anion substitution and cation substitution. The Jahn-Teller deformation hardly can be found in the XRD spectra of the cathode materials after 30 cycles and the amount of Mn dissolution was decreased so that the cathode materials with high initial capacity (125 mAh/g) and good cyclability (the ratio of retained capacity amount to 93.6%) were obtained.The other emphasis in the research was the S and S-Co substitution. Thesolid method and sol-gel method were both used to synthesize the cathode materials and their structure characters and electrochemical properties both indicated the latter method was better. S substitution had not obvious influence on the electrochemical properties in 4V region, but it improved the cyclability in 3V region to a great extent. In 3V region, the capacity did not decrease but increased in the first 20 cycles. The improved cyclability in 3V region extended the charge/discharge voltage range, which doubled the theory capacity. The reason of the improved cyclability in 3V region was proved to be that S substitution eliminated Jahn-Teller deformation. S-Co substitution combined the good cyclability of Co-doping material in 4V region and the increasing capacity of S-doping material in 3V region. In the range 2.4-4.3V, the initial capacity of S-Co-doping cathode material LiCo0.1MnL9O3.96S0.04 was 170mAh/g and increased to 194.3 mAh/g in the first 20 cycles. The conclusion can be drawn that S-Co compound substitution elevated the capacity and improved the cyclability in both 3V and 4V regions.
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