| Spinel Li4Ti5O12is a promising candidate of negative electrode materials for lithium ion batteries due to its excellent cycle performance, safety, low cost and volume change. It has been ranked as the secondary negative electrode material for lithium ions power battery by department of energy of USA. Currently the intercalation voltage of commercially used in carbon anode material is0-0.26V, which is very close to the deposition potential of lithium metal, and easy to dissolve out lithium dendritic crystal. As the dendritic crystal grows, it is very possible to puncture the membrane between cathode and anode electrode, thus result in short circuit in the battery. It also causes great security risk in the application of cells especially in power batteries. Meanwhile, it limits the scope application of lithium ion batteries. In this thesis, XRD, DTA, BET, PSD, SEM, charge-discharge test, CV and EIS etc. are employed to investigate the structure, synthesis, improvements, theoretical capacity and electrochemical properties of Li4Ti5O12.Spinel Li4Ti5O12of excellent performance is prepared via optimized solid state method, through exploring the various process conditions on the structure and electrochemical properties. Experiment result indicates that the ratio of raw materials Li/Ti, calcinations temperature and reaction time play an important role in affecting electrochemical performances. The optimized condition for solid state method is:the raw material of Li/Ti at the ratio of0.86is calcinated at800℃for12h. The prepared sample under this developed condition is processed well with distributed morphology, high phase purity and high degree of crystalline. At0.5C discharge, its initial reversible capacity is166.9mAh/g and initial charge-discharge efficiency is97.7%. After80cycles its discharge capacity is158mAh/g and its capacity retention is96.1%.The electrochemical performance of spinel Li4Ti5O12can be affected from production to application. Researches indicate that even at a dew point of-50℃in the dry warehouse, the electrochemical performance of Li4Ti5O12powder will decay in a long period. This thesis further processed the synthesis of spinel Li4Ti5O12via high temperature solid phase method with refined size of particles by using high energy ball milling. Furthermore, in order to improve the electrochemical performance of modified Li4Ti5O12, annealing process is also applied under appropriate temperature. The result indicates that the electrochemical performance of Li4Ti5O12can be well optimized by ball millingl2h and annealing treatment at650℃for4h. The initial discharge is170.7mAh/g, and its reversible specific capacity is168.5at0.5C. After80cycles, the retention capacity is163.8mAh/g and the discharge capacity is134.9mAh/g at5C. Under such condition, the efficiency of rentention capacity is86.8%. It shows that Li4Ti5O12has excellent electrochemical properties at the large charge-discharge rate through these treatments. Therefore, it will provide huge industrial value when applied in industrial production.The disadvantage of spinel Li4Ti5O12is the low electronic conductivity, which prevents the reversible capacity from achieving desired objectives and requirements at a large charge-discharge rate. This thesis explores carbon-coating research to Li4TiO12synthesis prepared via high temperature solid-phase and focuses on the influence of structure and electrochemical performance through different sucrose dosage of the material:m (sucrose)/m (lithium titanate)=5%.10%,15%The results show that the electrochemical performance of carbon-coated Li4TiO12material improves significantly, and as the discharge rate increases, the effect becomes more obvious. All the results indicate that the best sucrose adding amount is10%. Meanwhile, the material has most uniform particle size distribution and best electrochemical performance. At0.5C charge and discharge, the initial discharge capacity is181.5mAh/g, and its efficiency is99.6%. At5C of charge and discharge rate, after80cycles the discharge capacity is128.5mAh/g and the retention capacity efficiency is89.7%. |
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