Synthesis, Structure And Performance Of Mesoporous Titanium Phosphate As Cathode Materials

Poly-anion compounds have advantages of steady framework and easily adjustable potential plat, and thus give good cyclic performance. Because of this, they may become a third era lithium ion battery cathode materials. However, the low electrical conductivity is bad for the poly-anion compounds electrochemical performace at the high current density. In order to improve their performance, carbon coating and metal doping are two conventional methods. We have investigated some materials with mesoporous structure for improving their ionic transport behaviour. Mesoporous structure has distinct effects on the electrode materials' performance, and then overcome the drawback of the low electrical conductivity of the materials. The sol-gel template combinded with the calcination method was used in our study. During this preparation process, there are many factors, such as a suitable phosphorus source, temperature, humidity, solvent vaporizing speed and aging time of the sol, have some influence on mesoporous structure synthesis. It was found that both solvent-vaporing speed and too short sol-aging time wouldn't build ordered mesoporous structure, and PCl₃ is a better phosphorus source, and it was unadvisable to use too high temperature and too high humidity.In order to get ordered mesostructure, a modified sol-gel template method was established to synthesize mesoporous materials. We successfully synthesized a series of different mesoporous titanium phosphate materials, and at the same time, other effects were also considered, such as template, solvent, template removing time, calcination temperature and calcination method during the synthesis. In our study, it is confirmed that P123 with larger hydropobic PO units were used as template resulting in a highly ordered hexagonal mesoporous titanium phosphate materials, and these materials were in possession of a larger surface area and a larger pore volume. And on the other hand, F108 with a larger hydrophilic EO chain is good for synthesizing titanium phosphate with a narrower pore size and a cubic mesostructure. Ethanol as solvent can get long-range ordering of the mesopore. The longer time was spent on removing template or calcination, and the smaller surface area and pore volume of mesoporous titanium phosphate materials were made. Compared with one step calcination, two steps calcination made mesoporous titanium phospahte with a larger surface area and pore volume. In addition, it was proved that calcination temperature is a key factor during the calcination process, and calcination can optimize titanium phosphate mesostructure, and however, too high calcination temperature, for example 800℃, results in collapse of materials mesostructure, and at the same time amorphous titanium phosphate slowly changed into cystalline titanium phosphate.In our study on titanium phosphate electrochemical performance, it was showed that mesoporous titanium phosphate, compared with no porous titanium phospahte, gave a better performance especially at the high current density. Mesoporous titanium phosphate, which had either highly ordered mesostructure or larger pore size, can deliver higher capacity especially at the hugh current density.