Synthesis Of Lithium-ion Battery Cathode Material LiFePO₄Controlled By Mixed Solvent Thermal Method

Water or solvent thermal method is the commonly used method for synthesis of lithium-ion batteries cathode material LiFePO4. However, the application and development of single solvent are subjected to some degree of restriction due to their own different weaknesses. The mixed solvent thermal method of water and organic solvent is an effective method based on the water or solvothermal method, which makes full use of their own physicochemical properties of water and organic solvent. In this paper, we selected three organic solvents including ethylene glycol (EG), triethanolamine (TEA) and N, N-dimethylformamide (DMF) and water (H2O) which composed of binary or ternary mixed solvents in order to control and synthesize LiFePO4cathode materials. We successfully obtained the sample materials of rule structure and dispersed uniformity. Then, the obtained active materials were characterized and tested by the means of X-ray diffraction (XRD), field emission scanning electron microscope (FESEM), field emission transmission electron microscope (FETEM) and electrochemical performance tests.The results show that the prepared LiFePO4samples possess spherical, rectangular block and cubic crystal morphology, of which the spherical size is approximately500nm. The rectangular block structure of crystalline materials is about length of1.5μm and thickness of300nm. However, cubic crystal is the minimum size about100nm. Furthermore, H2O-EG and H2O-DMF act as mixed solution to investigate the effect of surfactant, the solvent volume ratio of the mixed solution, pH on the morphology, the influence of electrochemical properties and the cathode material LiFePO4synthesized by mixed solvent thermal method. In the mixed system of H2O and EG adding small amount of anionic surfactant make the volume ratio of H2O and the ratio of EG reach the proportion of1:1to1:3. It is benefit to obtain the optimal crystalline morphology and electrochemical properties of LiFePO4materials. At the same time it is helpful to obtain good properties of the LiFePO4sample materials in the mixed system of H2O and DMF when the pH of the mixed solution keeps the scale of8to9.Henceforth, we studied the obtained pure phase LiFePO4sample materials which dealt with the carbon coating process. The electrochemical performance of LiFePO4material after carbon coating on the surface has been significantly improved, which may be the enhancement of its conductivity and ionic conductivity.Last but not the least, the electrochemical performance of the modified LiFePO4 material through the ternary mixed solvent comprised of H2O, TEA and DMF is optimum. And it has a specific charge capacity of151.13mA-h/g at the magnification of0.1C. In the mixed system of H2O and DMF, the influence on the performance of the synthesised LiFePO4material by the binary solvent thermal method is explored by changing the modification form. The results reveal that the initial specific charge capacity for LiFePO4crystalline material by the two-step and one-step methods are respectively135.1mA-h/g and148.27mA·h/g at the magnification of0.1C.