A Novel Method For The Synthesis Of LiFePO₄/C

Pure LiFePO₄shows initial capacity loss, poor rate capability and charge-dischargecharacteristics at high current density due to its poor electronic conductivity. That preventLiFePO₄to be put into commercially used.In order to overcome it’s shortcomings, we chose PAAM as dispersant, in themeantime，as carbon source and reductant. It was applied to solid state method andinvented low temperature vapour reaction-elevated temperature crystallization method.Successfully, we obtained LiFePO₄with morphology uniformly and small and performancesteadily.Firstly, FePO₄/PAAM powders with nano-size were synthesized with PAAM asdispersant. PAAM was proved a very efficacious dispersant in the experiment. PAAMplayed a part in adsorbing the particles surface of FePO₄, cladding and segregation. Thatprevented condensation and enlargement turning up. The results indicated that PAAMeffectively dispersed the particles, the optimum containing was12%.We synthesized lithium iron phosphate with the solid state method and used PAAM asdispersant and carbon source. In the process of preparing composite materials, the sinteringtemperature had great effects on the material’s properties. The results showd thatLiFePO₄/C powders with nano-size can be obtained by FePO₄/PAAM powders withnano-size synthesized with PAAM as dispersant, an average particle size of below200nm,optimum reaction condition was450℃（5h）-650℃（5h）. But the size of LiFePO₄/C waslarger than the precursor. Agglomeration partly and vegetating distinctly of LiFePO₄/Ccame forth in the synthesize. The reason may be that transmission of lithium salt did greatdamage to the carbon film in the crystallization.For this reason, the synthesis of LiFePO₄was used improved solid-state reaction, weinvented low temperature vapour reaction-elevated temperature crystallization method. Weput FePO₄/PAAM and lithium salt in the reaction kettle then treated them in the lowtemperature vapour condition, after elevated temperature crystallization, finally obtainedLiFePO₄/C Powders with nano-size. That prevented transmission of lithium salt did greatdamage to the carbon film in the crystallization and held back the LiFePO₄vegetating inthe crystallization. In the article, we investigated separately using LiOH·H2O and CH3COOLi·2H2O as lithium source, the effect of temperature in the pressure reaction kettleto LiFePO₄/C.In the result, in the low temperature in the pressure reaction kettle generatedLiFe（PO₄）（OH）, it broke down in elevated temperature crystallization. That managedeffectively agglomeration and vegetating of LiFePO₄/C. The particle size was uniformedand the electrochemical properties were improved, the charge and discharge curves showedmore flat work voltages and larger capacities, when we chosed the CH3COOLi.2H2O as thesource of iron with method of low temperature vapour reaction-elevated temperaturecrystallization.