Liquid Phase Synthesis And Modification Of High-performance LiFePO₄Cathode Material

Compared to other anionic compounds, the olivine-type LiFePO₄shows theadvantages of higher capacity, environmentally friendly, and easily synthesizing.These advantages make it to be one of the most promising cathode materials, andmore suitable for use in the field of large-scale power supply. In this study, LiFePO₄was synthesized via hydrothermal method by using soluble starch as a reducingagent. The influences of hydrothermal temperature, reaction time, sinteringtemperature and sintering time on structure and electrochemical performance ofLiFePO₄were also investigated. LiFePO₄/C of LiFePO₄/Sb₂Te₃composites wereobtained by surface modification and the influences of coating amount werecharacterized by SEM, XRD, charge-discharge and cyclic voltammetry. The processof Li+deintercalation was investigated by CV.The study shows that the optimum process of hydrothermal synthesis is asfollows: using soluble starch as a dispersing agent and reducing agent, choosingCH₃COOLi, Fe（NO₃）₃and NH₄H₂PO₄as starting materials, hydrothermal reactionunder180℃for6h,sintering under700℃for10h in the atmosphere of H2/Ar.The as-synthesized sample shows morphology of micro-sphere with a size of2μm.The peak voltage difference of the sample is-0.44V, the first discharge capacity atthe0.1C is83.9mAhg^-1and the discharge capacity increases to103.0mAhg^-1after30cycles.When amorphous carbon was evenly coated on the surface of LiFePO₄, notonly the electrical conductivity of the material was improved, but also the growth ofthe spherical material is inhibited. The size of carbon modified composite wassignificantly less than2μm, and the process of Fe²⁺conversion to Fe3+wasinhibited. When the amount of soluble starch was3.3g, the peak difference of theas-synthesized LiFePO₄was0.25V, indicating that the material showed good ionreversibility. The first discharge capacity at the0.1C is134.7mAhg^-1and thedischarge capacity increases to146.1mAhg^-1after30cycles.When Sb₂Te₃sheets were coated or interspersed between the spheres, theelectron conductivity was improved which is benefit for the improving ofelectrochemical performances. When the amount of Sb₂Te₃was8%, the peakdifference of the sample was0.15V which is smaller than that of the un-coatedsamples, indicating that the material showed good ion reversibility. The firstdischarge capacity at the0.1C is113.0mAhg^-1and the discharge capacity increasesto134.5mAhg^-1after30cycles.