Study On Synthesis And Characterization Of LiFePO₄/C Composite Cathode Material By Precipitation Method

Owing to its high capacity, thermal stability, low toxicity and wide raw materials, LiFePO₄ has become one of the most promising cathode materials for next generation rechargeable lithium ion batteries.In recent years,great efforts have been made to improve the performance of this material, however,the electrical conductivity and lithium ion diffusion coefficient of LiFePO₄ is still low,which is largely limit its electrochemical performance. With more and more researches,the synthesis and properties of LiFePO₄ have achieved fruitful results.On the basis of previous studies,this paper continue to study the synthesis process of LiFePO₄,used different precipitation method to synthesize LiFePO₄/C composites,compared the advantage and disadvantages of different methods,and optimized the synthesis process of oxidation precipitation method .Synthetic methods have great effect on electrochemical properties of materials.Compared with the solid phase method, co-precipitation method can control the material chemical composition and particle size to prepare uniform fine particles and improve the electrochemical properties of materials effectively.LiFePO₄/C synthesized by different precipitation method have different performance.This is mainly due to different precipitation have different reaction in aqueous solution.In this paper,I used the oxide precipitation and adjust pH precipitation method to synthesize the target prouduct.Oxide precipitation method is relatively easier and the capacity of the product is higher.However, due to H₂O₂ is not stability,lead to batch instability and the material have a low tap density. Adjust pH precipitation method can make the material have a higher tap density, but the pH range of precipitation can generate a lot of impurities precipitation, therefore the capacity of the product is not high.In addition,through charge/discharge performance test and the physical and chemical properties test, the technological parameter of the oxidation precipitation method have a preliminary optimization and choose technologcial conditions for coprecipitation:the amount of H₂O₂ is 0.98 times the oretical amount ;concentration is 0.5 mol/L;stirring time is 6h;mixing temperature is 50℃;16% glucose content;calcination temperature is 650℃.The properties of LiFePO₄/C were systemically characterized by the methods of XRD,SEM etc.The results showed that LiFePO₄/C were both simple pure phase olivine-type crystal structure,had better discharge specific capacity and rate cycle performance.The particle size distribution is narrow, the precursor D50 is 1.288μm, the D50 of the target material is 0.995μm.