Syntyesis And Electrochemical Performances Of Polyanion As Cathode Material For Lithium Ion Batteries

Polyanion iron-base cathode is a very promising cathode materialused in lithium ion batteries due to thermal safety, low cost and environmentalcompatibility. In this paper, LiFePO4、 LiCoPO4、 Li2CoPO4F andFe(OH)SO4were synthesized, and he morphology, structure of particles andelectrochemical performance were characterized by XRD、FTIR、thermalgravimetric analysis and electrochemical performance testing.LiFePO4was synthesized by precipitation-carbonthermal reductionmethod，with self-made FePO4、NH4H2PO4、LiOH and sucrose asstarting materials.The results show that under the optimized conditions of700℃and6h, the obtained LiFePO4/C cathode material exhibited superiorelectrochemical performance, delivering a discharge capacity of147.1mAh/g at10mA/g and showed good cycling ability with anegligible capacity fade of50cycles.LiCoPO4was synthesized by solid phase method method, withself-made Co(Ac)2、NH4H2PO4and LiOH as starting materials. Theresults show that under the optimized conditions of700℃and16h, theobtained LiCoPO4cathode material exhibited superior electrochemicalperformance, delivering a discharge capacity of125.8mAh/g at10mA/g,but capacity fade fast, the discharge capacity was only45.7mAh/gafter50cycles; The carbon-coated LiCoPO4/C was prepared, and foundlittle effects on the electrochemical performance. Consequently,Li2CoPO4Fwas synthesized in the same way by adding LiF,which had thedischarge specific capacity of132.3mAh/g at30mA/g、121.4mAh/g at150mA/g and114.8mA/g at300mA/g, and showed poor cycling ability.Fe(OH)SO4was synthesized by heat-treating FeSO4·7H2O withtwo steps. The results show that under the optimized conditionsdelivering a discharge capacity of134.5mAh/g at15mA/g, but capacityfade fast, the discharge capacity was72.6mAh/g after50cycles; thecycling ability was improved by carbon-coating.