Preparation And Characterization Of FEPO₄·2H₂O Nanometer Precursor And Spherical LIFEPO₄/C Cathode Material

Lithium ion battery cathode material LiFePO4, which has a lot of advantages such as high energy density, low cost, non-toxic, high safety, good thermal stability and good charge and discharge performance and so on. It has smooth discharge platform of3.4V and its theoretical specific capacity can reached170mAh/g. The synthesis conditions and electrochemical characteristics of LiFePO4materials mainly depends on its precursor, a good precursor could provide the better electrochemical performance for material. Iron phosphate which has a lot of advantages such as its stable structure, low cost, high safety, environment friendly and so on. The most important thing is that the Iron phosphate’s crystal structure and crystal cell parameters are similar to the lithium iron phosphate. Using iron phosphate as a precursor to synthesis of lithium iron phosphate, can control the size of the lithium iron phosphate particle effectively. Therefore, iron phosphate is an ideal precursor.In this paper with seven hydrated ferrous sulfate and phosphate acid as reactants, before and after adding oxidant, adjust the pH of the reaction solution twice, iron phosphate powder material is prepared. Using XRD、SEM、TG-DTA、FT-IR and Roman analysis of iron phosphate material. The results show that: before and after adding oxidant hydrogen peroxide, Using low concentration of NaOH to adjust pH value reach2.0in the reaction solution, Under this condition can be generated spherical morphology FePO4·2H2O. Eventually the highest tap density of iron phosphate can reach1.22g/cm3. Then put the material in the500℃heating4hours to take off the crystal water, use water as a medium, mixed with lithium carbonate and sucrose in ball mill to grind, then under inert gas protection, after the mixture calcination12hours in a temperature of700degrees can synthesis of lithium iron phosphate material. Also found that the dosage of the sucrose can affect the morphology of lithium iron phosphate. The finally experimental conditions is:FePO4, Li2CO3and sucrose mixture in accordance with the molar ratio1:0.52:0.1to synthesis of lithium iron phosphate, and the conductive carbon film can be evenly coated on the surface of LiFePO4particles. Its tap density can reached1.32g/cm3. The electrochemical properties of the lithium iron phosphate were studied by cyclic voltammetry. In the LiOH-H2O, LioCO3, LiNO3and Li2SO4·H2O four different types of electrolyte, comparison of the cycle volt-ampere curve of lithium iron phosphate. Final choice LiaSO4·H2O for testing electrolyte. With the decrease of the scanning speed, the electrochemical reversibility of lithium iron phosphate increased gradually. The material has excellent reversibility under low sweep speed.