Study On The Application Of Lithium Iron Phosphate Cathode Material Prepared By Hydrothermal Synthesis Process

In the present work, the products of lithium iron phosphate（LFP） can be synthesized by solid state reaction and hydrothermal method. The products synthesized by hydrothermal method become high-end products because of following advantages, such as chosing to grow in aqueous solution, high crystallinity and purity, uniform and small particles and so on. By now, there is still no hydrothermal products in China. As electrode materials, they need to meet the demands of good electrochemical properties and excellent machinability etc. Different ways or processes result in various physical and chemical properties of LFP which may cause the difference applicant performance. The technological parameters of hydrothermal method that to synthesize LFP have been widely studied, but there still need particular study on the application of the materials.The qualities of the slurry that made by LFP/C was studied. The best pulp formula was obtained through testing solid content of the slurry, surface resistance and surface density of the electrode plate when changed the content and diverse proportion of conductive agent. When the pulp formula is Li FePO₄: PVDF: Super-P: KS-6= 93.5:3.5:2:1, the slurry has the best stability and well dispersion performances, and the consistency of the electrode is the best.The sensibility of the LFP prepared by hyrothermal process to acidity of electrolyte was studied, and compared with the products made by solid state method. The electrolyte was exposed in air for 10-30 minutes to change the acidity and moisture content. With the increase of acidity and moisture content in electrolyte, the charge plateau increase 0.02-0.05 V. But their capacity, rate property and cycle performance display superior results when the acidity in electrolyte is 59.2 ppm. However, both rate properties of the two materials have downtrend, as the acidity of electrolyte increase to 110.6 ppm. Compared with the solid state reaction LFP, the hydrothermal LFP is more sensible to acidity of electrolyte.Three compaction densities was set, they were 2.15, 2.25 and 2.30 g·cm-3,.The discharge curve show that the battery has the largest discharge capacity and high voltage platform when the compaction density is 2.25 g·cm-3.The performances of 26650 cells used LFP prepared by hydrothermal method as cathode material were tested. And compared with the product of Süd-Chemie Life Power®ï¼ˆP2） via hydrothermal method and the product of Changyuan prepared by solid state reaction. The specific capacity of hydrothermal products is 144.2, 142.0 mAh·g-1 respectively, which is higher than the product synthesized by the solid state reaction, which is 128.0 mAh·g-1. The products of lithium iron phosphate, using hydrothermal method, made in our laboratory have the excellent rate performance. The capacity ratio of the batteries at the rate of 0.5 C, 1 C, 3 C and 5 C are 98.78%, 97.25%, 96.94% and 96.64% respectively. After high-temperature storage, the capacity retention ratio and capacity recovery ratio are 96.23% and 96.64%. And its internal resistance increased is little and the voltage decrease value is 0.049 V. After 100 times cycles, the capacity retention is 98.91%, 97.61% after 500 times, 93.97% after 1000 times.