Study On Development And Application Of Lithium Manganese Oxide For Power Lithium-ion Batteries

The spinel lithium manganese oxide cathode materials for lithium-ion power batteries were synthesized by solid-state method, and the 18650S cells using the as-prepared cathode materials were prepared. The lithium manganese oxide with better electrochemical performance was prepared by multidoping. The pilot-scale production of modified LiMn₂O₄ was performed. The modification effects of coated-carbon and mixing lithium cobalt oxide on the spinel lithium manganese were studied respectively. The power batteries with good performances were developed. The main contents of this dissertation are as follows:The effects of doping concentration on the phase structure and electrochemical performance of the produced cathode were systematically investigated with several kinds of cations mono-doped separately. Attempts were made in choosing the doping ions Zr and rare earth elements La, Ce and Nd for the spinel lithium manganese modification, which have larger ionic radius than Mn³⁺ while have much stronger M-O bond energy. It was proved that their doping is propitious to the produced spinel cathode and rare earth elements have greatly improved the cycle performance at elevated temperatre(55℃). The binary-cation doping has much better effects on improving the electrochemical performance. The modified spinel cathode with two cations and one anion multiplex doped were synthesized. By choosing the doping ions combination scheme and controlling the doping quantum, perfect spinel lithium manganese cathode LiCo_0.02La_0.01Mn_1.97O_3.98Cl_0.02 was produced for the first time, which has high initial capacity as well as good cycle performances at both room temperature and high temperature. The properties of 5V spinel material were also characterized.The pilot-scale production technics of modified LiMn₂O₄ were investigated and the role of particle size in the cathode performance was also studied. So the pilot-scale samples have nearly good performance as that made in the lab. The coated-carbon composite cathode materials were made with glucose and polyvinyl alcohol as carbon additive, which has higher dischargeplateau and higher capacity. The well performed lithium cobalt oxide cathode was synthesized to modify the as-prepared spinel by directly mixing and by solid-state reactions using the mixture as precursors. The best mixing mass proportion of the two kinds of cathode materials was got from the experiments. When the direct mixing mass proportion of LiMn₂O₄ and LiCoO₂ was 90 : 10, the sample exhibits the superiority of the both kinds of materials. The mixture of the two with the mass proportion of 90 : 5 after heat treatment shows the best cycle stability with acceptable capacity.18650S-1300mAh cells used for powered tools were made with the self-productive materials as cathode. The power batteries had good high-rate discharge performance and good cycleability at room and high temperature. The cells also had passed some safety tests. In the end the factors influencing the cell safety were also evaluated and methods which could improve the safety of the lithium-ion batteries were also put forward. The safety of the lithium manganese oxide cathode was explained from the energy states. It is concluded that stable electrode material is the most important essential to the cell safety.