Study Of Preparation?Modification And Electrochemical Performance Of LiFePO₄ Composites

For improving the electronic conductivity.structure stability and safety of LiFePO4 as anode material for lithium ion battery,we prepared rodlike LiFePO4 which has uniform particle size and morphology by hydrothermal method,and modified it with specific method.The optimal preparation process conditions were determined by controlling the factors method.The morphology and the performance of LiFePO4 were further optimized by grahene oxide which was prepared by two steps of chemical oxidation method and we got composite LiFeP04/C+RGO.Based on LiFeP04/C+RGO,we prepared LiFeP04/(C+RGO)/Ag-NCs using the self-assembly in situ method of acetaldehyde reducing silver ammonia solution and LiFePO4/(C+RGO)/CuO composite material coated by CuO by in-situ chemical deposition combining with high temperature treatment.The materials and battery were tested by XRD?UV-VIS?SEM?TEM?Electrochemical Workstation?Battery Test System and Battery Safety Test.Specific summarizes as follows:(1)With LiOH·H2O,FeSO4·7H2O and H3PO4 as raw materials,glucose as reductant and carbon source,LiFePO4 with uniform morphology and particle size was prepared by hydrothermal method and high temperature sintering process.The optimum preparation conditions were determined by controlling the factor method.Based on this,we got optimized LiFePO4/C+RGO composite materials coating graphene in situ.Material characterization and electrochemical testing indicated the lithium iron phosphate composite has perfect phase with olivine structure and the microscopic morphology is a rod-like structure with a length of about 500 nm and a diameter of about 200 um,the particles are uniformly distributed and uniform in size.The initial discharge specific capacity is 149.9mAh·g-1 at 0.2C rate and the capacity keeped 94.2%after 100 cycles at the condition of 0.2C rate.(2)On the basis of LiFePO4/C+RGO,LiFePO4/(C+RGO)/Ag-NCs composites modified by 3D conducting network which is built by AgNCs and RGO were prepared by self-assembly in situ method of acetaldehyde reducing silver ammonia solution.Analysis indicated that crystal structure was not changed by modified materials.The silver ammonia solution was reduced and self-assembled into a continuous silver nanochains with a width of about 50nm,and formed a stable and continuous three-dimensional conductive network with graphene.The analysis result indicated that the electrochemical performance and the conductivity were significantly enhanced,the polarization effect was abate,discharge specific capacity,cycle performance and rate performance were significantly improved.(3)In order to improve the structural stability and cycle performance of the materials,we prepared LiFePO4/(C+RGO)/CuO composites coated by CuO by in-situ chemical deposition combining with high temperature treatment.CuO can inhibit the stress generated by the expansion of C axis during Li-ion diffusion process forming zero-stress materials.It also can inhibit the corrosion of the active substances by electrolyte and repair the discontinuity of the graphene coating.The phase and morphology analysis indicated that the modified material did not change its crystal structure.The results of charge-discharge test showed that the electrochemical properties especially the high rate performance and cyclic performance were significantly improved.Safety performance of batteries made by LiFePO4/(C+RGO)/CuO composite was tested and the result display that the battery didn't leak?fire or explode,so the modified LiFePO4/(C+RGO)/CuO composites meet the stability and safety performance requirements.