Structural Design And Electrochemical Characterization Of Lithium-ion Battery Cathode Materials

In recent years, environmental problems, such as greenhouse effect and acid rain, become more serious due to excessive consumption of traditional fossil fuels. At the same time, the further development of mobile electronics market, inherent intermittent of the renewable energy（solar energy, tidal energy） and the increasing demand for electric vehicles are calling for green and efficient energy storage and conversion systems. Lithium-ion battery, having both the highest gravimetric and volumetric energy densities among all secondary batteries, is one of the most important energy storage and conversion solution. In order to overcome the insufficient of traditional lithium-ion batteries, development of lithium-ion battery cathode materials plays a key role.In this paper, the development of the lithium-ion cathode materials and the process were reviewed. In the aim of low environmental toxicity and low cost, Li_1.2Ni_0.2Mn_0.6O₂ and LiNi_1/3Co_1/3Mn_1/3O₂ were chosen, morphological modified and electrochemically studied. The main content of the research are as follows:（1） Ordered mesoporous silica, KIT-6, was synthesized. Ordered mesoporous Li_1.2Ni_0.2Mn_0.6O₂ cathode materials was further synthesized, using KIT-6 as template. The average pore width of the cathode material is 4.882 nm. A large specific surface area of 60.682 m2 g-1 was also achieved. The mesoporous cathode material has the same crystal structure with materials synthesized by a sol-gel method. While used as lithium-ion battery cathode, it exhibited remarkably enhanced electrochemical performances. Specifically, mesoporous Li_1.2Ni_0.2Mn_0.6O₂ achieved a high discharge capacity of 210 mA h g-1 at 0.2 C with 84% capacity retention after 50 cycles. The bulk Li_1.2Ni_0.2Mn_0.6O₂ only achieved a discharge capacity of 175 mA h g-1 at 0.2 C with 81% capacity retention after 50 cycles.（2） Ca0.2Co0.4Mn0.4CO3 microspheres were synthesized using a co-precipitation method. CoMnO3 templates were outcomes of triple carbonate precipitate Ca0.2Co0.4Mn0.4CO3 after decomposition, etching and calcination. Porous nano-micro hierarchical LiNi_1/3Co_1/3Mn_1/3O₂ microspheres were further synthesized by heating Li and Ni into porous CoMnO3 microsphere templates with a solid state method to form layered crystal structure, barely damaging the morphology of CoMnO3 templates. When used as the cathode material for lithium-ion batteries, the as-synthesized microspheres exhibited remarkably enhanced electrochemical performances with higher capacity, excellent cycling stability and better rate capability, compared with the bulk counterpart. Specifically, hierarchical LiNi_1/3Co_1/3Mn_1/3O₂ achieved a high discharge capacity of 159.6 mA h g-1 at 0.2 C with 98.7% capacity retention after 75 cycles and 133.2 m A h g-1 at 1 C with 90% capacity retention after 100 cycles. A high discharge capacity of 135.5 mA h g-1 even at a high current of 750 mAg-1（5 C） was also achieved.