Preparation And Research Of The Lithium Ion Battery LiFePO₄Materials

Olivine-type lithium iron pHospHate （LiFePO₄） has recently received substantialinterest as one of the most promising cathode materials for Li-ion batteries （LIBs）,because of its low cost, environmental compatibility, superior capacity retention,thermal stability and safety. However, the poor electronic conductivity of pure LiFePO₄pHase which leads to significantly low rate performance and the low tap-density, leads abottleneck for its wide commercialization.Herein, we report a novel two-step route to synthesize porous LiFePO₄and carbonnanotube （LiFePO₄/CNT） composite microspHeres, by which carbon nanotube （CNT）as an effective conductive component is in-situ and uniformly embedded into theLiFePO₄microspHeres to form the conductive CNT network. Our results provide afacile approach for simultaneously achieving the microspHerical morpHology andexcellent electronic conductivity for LiFePO₄materials. The obtained LiFePO₄/CNTmicrospHeres exhibit greatly increased volumetric energy density and good ratecapability as the high-performance cathode materials for LIBs.SpHerical FePO₄precursors were prepared by hydrothermal synthesis with thecontrol of the PH and reaction temperature of the system. In brief, Fe³⁺ions dissolved inthe solution were firstly anchored on CNT surfaces by the electrostatic interactionbetween Fe³⁺ions and the negatively charged CNT surfaces that were developed byrefluxing CNT in strong acid solutions. After that, FePO₄nanoparticles were formed onthe CNT surfaces by adjusting pH value of the solution to reduce the FePO₄solubility.During the subsequent hydrothermal process, the FePO₄nanoparticles then grew andassembled into porous microspHeres with CNT simultaneously embedded. TheFePO₄/CNT precursors were finally transformed to LiFePO₄/CNT microspHeres b bysolid state method at high temperatures.The material was characterized by XRD, SEM and charge-discharge test. Theresults show that initial discharge capacity of LiFePO₄/C/CNTs at the rates of0.1C,1C,5C and10C were152mAh/g,141mAh/g,120mAh/g and103mAh/g with the tap density of1.40g/cm³. After cycling for1000times at5C charge-discharge rate and10C charge-discharge rate, the capacity loss was just5.9%and8.3%.