Morphology Control Of LiFePO₄/Carbon Composite And Its Electrochemical Performance

Lithium iron phosphate has shown various advantages in terms of high theoretical capacity,outstanding high-rate capability, prominent long-term cycle performance, safety, environmentalbenignity, and low-cost raw material, and is ongoing to occupy the rapid demand in the market forpower portable electronic devices and plug-in hybrid electric vehicles. Some different morphoiogyLiFePO₄/C composites have been prepared by some facile syntheses. The effect on theelectrochemical properties and performance of LiFePO₄/C composites from different morphoiogy interm of synthesis process has been evaluated and analyzed.1、A facile one-step ball milling synthesis has been developed to prepare LiFePO₄nanosphereswith an average diameter of～300nm lodged in the tridimensional （3D） porous carbon structure.This LiFePO₄/C composite possesses the considerably enhanced electronic conductivity of～10-2Scm^-1and amazing high surface area of166.6m²g^-1, and the lithium ion diffusion coefficient of～10^-15-10^-14cm²s^-1is calculated. The LiFePO₄/C cathode material delivers discharge capacities of155.0mAhg^-1at0.1C and69.5mAhg^-1at20C. Furthermore, the pristine LiFePO₄/C entity hasexhibited discharge capacity of127.8mAhg^-1at0.1C without conductive carbon additives.2、Nanoembossed mesoporous LiFePO₄/C microspheres are synthesized by a template-freeone-step hydrothermal at180℃for6hours. These microspheres show a quite uniform sizedistribution of3⁵μm and are composed of many densely aggregated¹00nm nanoparticles andinterconnected nanochannels. The composite materials’ physical properties are further characterizedby SEM, TEM, XRD, TG and so no. These microspheres as a cathode-active material show high tapdensity (1.3g cm^-3), excellent high rate capability (154mAhg^-1,0.1C,154mAhg^-1,20C)and cyclingstability, possibly fulfilling the requirements of rechargeable lithium batteries for upcoming highpower applications.3、 The tablet-shaped LiFePO₄/C composites are synthesized by hydrothermal, In thehydrothermal reaction, ascorbic acid served as the reducing agent for the partialreduction of ferric ions. The effect on the morphology and electrochemical properties oftablet-shaped LiFePO₄/C composites from different ascorbic acid additive volume of synthesisprocess has been evaluated and analyzed. The tablet-shaped LiFePO₄/C composite prepared withmore ratio of LiFePO₄and ascorbic acid （1:1） shows the improved electrochemical performance, the first discharge and charge delivered the capacity of120mAh/g at0.1C.