Prepartion And Surface Modification Of LiFePO₄ As The Cathode Material Of Lithium Ion Battery

LiFePO4 samples were synthesized by water/ethano solvothermal method with different volume proportion of water and ethano,and then a heat treatment with surcrose as carbon source was carried out to give carbon-coated LiFeP04(C-LiFePO4)cathodes.The X-ray diffraction(XRD)results indicated that with different proportion of water and ethanol as reaction medium,all the synthesized of LiFeP04 were olivine structure,and with the increment of ethanol proportion in the reaction medium,the 020 peak intensity of LiFeP04 material monotonically increased which was benefit to shortend the lithium ion migration pathway and improved the electrochemical performance.In addition,Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)proved that the particle size of LiFeP04 became smaller.The galvanostatic charge-discharge testing results indicated that LFP-D electrode displayed the best discharge capacity and high-rate performance with 150.6?143.6?133.8?121.4?99.5 and 78.2 mAh.g-1 at 0.2 C?0.5 C?1 C?2 C?5 C and 10 C,respectively.The electrochemical impedance measurements also demonstrated that with the increased of ethanol proportion,the charge-transfer resistance of C-LiFeP04 electrodes decreased significantly.A polytriphenylamne(PTPAn)modified C-LiFeP04(C-LiFePO4/PTPAn)composite as a novel cathode for lithium-ion batteries had been prepared by solution blending both the solvothermal-prepared LiFeP04/carbon(C-LiFePO4)nanocrystalline and the electroactive conducting polymer of PTPAn.The X-ray diffraction(XRD)results indicated that PTPAn has no affect on the crystal structure of the C-LiFeP04.Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)proved that PTPAn can form a compact coating on the surface of C-LiFeP04 by the solution blending method,which constructed an effective electronic/ionic conducting pathway to enhance the electrochemical activity of C-LiFeP04 based composites.The galvanostatic charge-discharge testing results indicated that the C-LiFePO4/10%PTPAn electrode displayed an improved initial discharge capacity of 154.5 mAh·g-1 at 0.1 C and a superior high-rate performance with 114.2mAh-g-1 discharge capacity at 10 C,as well as excellent cycling stability.The measurements on the electrochemical impedance measurements also demonstrated that PTPAn coating decreased the charge-transfer resistance of C-LiFeP04 electrodes significantly.A sulfur aniline copolymer P(An-co-DTAn)modified C-LiFeP04(C-LiFePO4/P(An-co-DTAn))composite as a novel cathode for lithium-ion batteries had been prepared by solution blending both the microwave-prepared LiFePO4/carbon(C-LiFePO4)nanocrystalline and the electroactive conducting polymer of P(An-co-DTAn).The effects of P(An-co-DTAn)coatings on the C-LiFePO4/P(An-co-DTAn)samples were investigated by X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),galvanostatic charge-discharge testing.The results indicated that a small amount of P(An-co-DTAn)coated on the surface C-LiFeP04 materials can effectively improved the charge/discharge capacity and high-rate performance.In all of the samples,the C-LiFePO4/5%P(An-co-DTAn)electrode shown an improved initial discharge capacity of 160.4 mAh·g-1 at 0.1 C,superior high-rate performance with 104.8 mAh·g-1 and 74.6 mAh·g-1 discharge capacity at 10 C and 20 C,respectively,as well as excellent cycling stability.