Preparation Of Li₃MnO₄ Cathode Materials For Lithium-ion Batteries And Modifications

Lithium-ion batteries have great application prospect in electronic devices, electric vehicles, military, aerospace and many other fields because of its high voltage and energy density, as well as its excellent reversibility. It is believed that the properties of lithium-ion batteries greatly depend on the electrode materials, specially the cathode materials. Common cathode materials like LiCoO2, LiNiO2, LiMn2O4, LiFePO4, etc. all have their own advantages as well as their undesirable drawbacks. Recently, a study suggested that a generally new system Li3MnO4 can be used as a promising cathode material which has great potential because of its considerable theoretical capacities. However, there is still not any report about its optimized preparation process and modifications.In this work, the remarkable cathode Li3MnO4 was chosen as a major subject. The reactant LiMnO4·3H2O (Mn:+7) powders were synthesized by ion exchange technology and the target cathode material Li3MnO4 was successfully synthesized by solid-state reaction at a low temperature. The thermal decomposition behavior of the precursor powder was examined by TG/DSC to determine the temperature of heat-treatment. XRD and FESEM were used to characterize the structures, phase composition and morphology of the prepared powders. The electrochemical properties of Li3MnO4 were also investigated using galvanostatic charge/discharge cycling. The influences of raw materials, intermittent grinding, annealing temperature and time on the quality of Li3MnO4 cathode were explored. The results showed that the best raw material is LiOH·H2O and the best comprehensive behavior is obtained from a sample annealed at 170℃for 2.5h using intermittent grinding among 70℃～125℃, which has an initial discharge capacity of 116.3 mAh/g.What's more, on the basis of the optimized process parameters above, some modification measures were utilized in order to improve the conductivity and structure stability of Li3MnO4. The results showed that:pre-mixing the reactants and graphite in solution can improve the conductive agent dispersed in the cathode materials much better while promoting the mixing of the reactants at the same time. The initial capacity of the Li3MnO4 sample used pre-mixed method reached 138.8 mAh/g. Under these conditions, it's found that the coating amount of the cathode material plays a significant role in its electrochemical properties. The capacity reaches 198.9mAh/g when the cathode coating amount is 2.7mg/cm2.The influences of PO43- doping on structure stability and cycling performance were also studied in this thesis. Conductive agent which is composed of graphite, acetylene black and carbon nanotube was also used to form an excellent conductive network and it's useful to improve the conductivity of the cathode materials.