Synthesis And Electrochemical Property Of LiMn_0.8Fe_0.2PO₄/Graphene And FeF₃/Graphene

Since the1990s. the development of portable electronic products such as video cameras, notebook computers,and cell phones led to a growing need for superiority rechargeable batteries with greater capacity, or reduced size and weight for a given capacity. However, conventional rechargeable batteries such as lead-acid batteries and nickel-cadmium batteries, as well as nickel-metalhydride batteries could not meet the demand of the portable products. The lithium-ion batteries has aroused the attention of researchers for its superior battery performance, and quickly occupied the battery market of portable electronic products. LiCoO2and graphite were used as the cathode material and anode material for commercial lithium-ion batteries. Its energy density was poor, high cost and the relatively toxicity of cobalt. Now looking for high energy density, low cost, low toxicity, safety, good of cycle and higher capacity cathode material to replace LiCoO2becomes the hotspot. At the same time, nano-material technology for the development of lithium-ion battery to provide a more effective method.In this text, first we simply introduced the lithium-ion batteries. Then we explored the preparation, characterization and constant-current charging and discharging test of LiMno.8Feo.2PO4/Graphene and FeF3/Graphene nano-particles The details and results as follows:1. LiMno.8Feo.2PO4/graphene powders were successfully prepared by the pyrolysis then ball milling, The materials were characterized by XRD, SEM, TEM, HRTEM,FTIRand constant-current charging and discharging test. We found that the content of graphene have a larger impact on the electrochemical properties of LiMno.8Feo.2PO4. In the rate of0.2C and0.5C,1C, the voltage is the range of2.4～4.5V electrochemical tests. We found that the optimum conditions for the content of graphene40%(mass ratio)。At0.2C, the capacity remained at about170mAh/g; at0.5C,the capacity remained at about150mAh/g; at1C,the capacity remained at about120mAh/g. The results showed that LiMno.gFeo.2PO4/graphene with high capacity and good cyclic performance was a good cathode electrode material for lithium-ion battery.2. We synthesis FeF3nanoparticles by using a simple method. The FeF3material was characterized by TG, XRD, SEM, TEM and HRTEM.The precursor wascalcined at400℃for2h under high-purity argon to remove the organic residues. In order to improve the conductivity of the material, The FeF3/graphene nanocomposites were prepared by mechanical ball-milling for4h (graphene/FeF3=15%;30%;45%;50%by weight). FeF3/graphene composite was tested by constant current density30mA/g under voltage1.0-4.5V charging and discharging test. The discharging capacity was about750mAh/g in the first cycle. After10cycles, the capacity was about725mAh/g. it close to the theoretical capacity. Experimental results show that FeF3/graphene composite electrode material is a good electrochemical properties of lithium-ion battery cathode material.