Synthesis And Performance Study Of LiFePO₄Cathode Material For Lithium-ion Battery

Olivine LiFePO₄has been considered to be a promising cathode material forlithium-ion battery due to its high energy density of550Wh·g^-1, high theoreticalcapacity of170mAh·g^-1, enough and low cost materials, excellent safety, a flatcharge–discharge plat and excellent cycle stability. However, due to the restriction ofits crystal structure，LiFePO₄has the low electronic conductivity and the lithium-iondiffusion rate so that practical specific capacity is low and the rate performance ispoor. Now the LiFePO₄is mainly be studied to improve its performance by thesynthesis technology, carbon coating, ion-doped.1.LiFePO₄/C composites were synthesized by mechanical activation withFeC2O4·2H2O、LiH₂PO₄and glucose as the raw materials. By the results of X-raydiffraction （XRD），scanning electron microscopy （SEM）, and charge-discharge test,the optimized technology of synthesizing LiFePO₄/C is that content of glucose addedis10.8%, sintering temperature is700℃and the sintering time is12h.2. In order to improve the performance of LiFePO₄, synthesize the LiFePO₄/Cdoping with element V by using the the optimized technology and adding the V₂O₅.The results indicated that Li₃V₂（PO₄）₃is informed during the process and theelectrochemical performance of LiFePO₄/C is best when content of the V₂O₅added is11%. The discharge capacity of LiFePO₄/C is158.5，129.4mAh·g^-1at0.1C,2C. Evenat the5C rate, the discharge capacity obtained is120.45mAh·g^-1, which is76.33%，93.1%of the capacity at0.1C,2C. It indicates the good rate performance of thematerial. The excellent cycle performance of the material is also showed with thecapacity retention ratio reaching100.3%after20cycles at2C，96.3%after50cycles at5C. The excellent electrochemical performance of material is attributed to the increaseof electronic conductivity and lithium-ion diffusion.3. Using the PVA as the carbon resource, the LiFePO₄/C is synthesized by usingthe the optimized technology. The results indicate that when the PVA added is7%（thepercent is the weight of PVA in the weight of all raw materials）, the LiFePO₄/C hasthe best electrochemical performance. The discharge capacity of LiFePO₄/C is155.06、137.92and122.45mAh g^-1at0.1C,2C,5C. After50cycles, the dischargecapacity is121.74mAh g^-1at the5C rate，with the capacity retention ratio99.42%. The excellent electrochemical performance of LiFePO₄/C is attributed to the carboncoating when the PVA is decomposed at the high temperature.4. LiFePO₄/C composites were synthesized by microwave method with Li₂CO₃、FeC₂O₄·H₂O、NH₄H₂PO₄and glucose as the raw materials. By the results of X-raydiffraction （XRD），scanning electron microscopy （SEM）, and charge-discharge test,the optimized technology of synthesizing LiFePO₄/C is that microwave power is320W, microwave time is5min, and content of glucose added is11%.