Research On The Synthesis And Modification Of LiFePO₄for Cathode Material Of Power Battery

The olivine-type structure lithium iron phosphate（LiFePO₄）, as cathode materials,has advantages of its rich resource, low cost,and no pollution, which is in line with therequirement of modern development. Due to its good performance in thermal stabilityand cycle, it has becomes the most promising cathode materials for lithium-ionbatteries. However, its disadvantages like low electronic conductivity and slow ionconduction rate.etc, has prevent its further development as power batteries. In thisarticle, by using different raw materials and synthetic methods, we explore the syntheticof LiFePO₄/C composite material and its electrochemical performance, in order tosynthesize LiFePO₄cathode materials with excellent electrochemical performance.The LiFePO₄/C composites were synthesized by solid-phase method, usingLi₂CO₃, FeC₂O₄·2H₂O, NH4H₂PO₄as raw material, modified starch as carbon source.The influencing factors on the properties of LiFePO₄/C composite materials, such assintering time, sintering temperature, the amount of added carbon source were explored.The results showed that: With the increase of sintering time, product particles becomelarger,10h is the best reaction time, its initial specific capacity was141mAh/g at0.1C;sintering temperature have a great impact on the crystal structure, With the increase ofsintering temperature, the crystal structure become perfect. But when the temperaturewas raised to750℃, Fe2P and Li₃PO₄impurities have great effect on theelectrochemical performance of LiFePO₄/C composites.700℃is the best synthesistemperature, its initial specific capacity was148mAh/g at0.1C; with the increase of theamount of added carbon source, the material particle become smaller, the dispersionwere better,6%is the best amount, its initial specific capacity was150mAh/g at0.1C.LiFePO₄/C composite materials were synthesized by gelatin-gel method. Gelatinwas used to be a thickener to improve the dispersion of the synthetic material. Theeffects of gelatin,and glucose as a carbon source and adding CTAB on the synthesis ofLiFePO₄/C composite materials were investigated. The results show that: LiFePO₄/Ccomposite material with a good dispersion was successfully synthesized by usingfreeze-drying technology when gelatin as a carbon source. But gelatins have noobvious improvements on the electrochemical performance of LiFePO₄. When theamount of gelatin was2g,the capacity was128mAh/g（max） at0.1C; When glucose as a carbon source its initial capacity was161mAh/g at0.1C; CTAB is helpful in formingspherical morphology after the high-temperature sintering,which have the advantageof the high tap density.in the industry.LiFePO₄/C composite composites were synthesized by solid-phase method, usingLi₂CO₃, FePO₄·2H₂O as raw material. Sintering temperature, carbon content, sinteringtime as investigated factors, we optimize the process conditions by orthogonalexperiments using homemade starch, homemade carbon aerogels, PEG-20000ascarbon source to synthesize LiFePO₄/C composites. The results showed that: usinghome-made modified starch coating of LiFePO₄, the best reaction conditions: sinteringtemperature:700℃, the added amount of carbon source:6%, sintering time:6h, itsdischarge capacity is148mAh/g at0.1C,118mAh/g at2C. Modified starch hascavernous structure, it improves the electrochemical performance of LiFePO₄in iondiffusion and electrolyte infiltration; Using homemade carbon aerogels coating ofLiFePO₄, the best reaction conditions: sintering temperature:650℃, the added amountof carbon source:6%, the sintering time:14h, its discharge capacity is155mAh/g at0.1C,124mAh/g at2C. Carbon aerogels’ good conductivity and spatial structure has atremendous advantage in the lithium-ion battery development; PEG-20000coatingLiFePO₄, the best reaction conditions: sintering temperature:700℃, the added amountof carbon source:10%, the sintering time:10h, its discharge capacity is142mAh/g at0.1C,110mAh/g at2C, macromolecular PEG coating cannot be uniform, resulting inthe electrochemical performance of LiFePO₄is not stable enough which affect the cycleperformance.