Preparation Of Lithium Iron Phosphate/three-dimensional Carbon Architecture Composite And Its Electrochemical Performance Study

In recent years,with the rapid development of electric vehicles,people have put forward higher requirements on the energy density and power supply for automobile power batteries.As a promising cathode material,olivine lithium iron phosphate has been regarded as one of the best choices for cathode materials of lithium ion power batteries with the advantage of its excellent physico-chemical stability,high specific capacity(170 mAh g^-1),abundant raw material supply and environment-friendly characterization.However,the poor electron conductivity(¹0^-9-10^-10 S cm^-1)and slow ion diffusion rate(10^-1210^-14 cm² S^-1)severely limit its large-scale application at high rate performance.This work focused on the preparation of the composites of three-dimensional carbon architecture and lithium iron phosphate,which is expected to improve its electrochemical performance.The main contents are as follows:First,carbon nanotubes were mixed with the precursor of lithium iron phosphate by solid ball milling to build three-dimensional carbon skeleton,and then the composite was prepared in situ with lithium iron phosphate.In addition,we further investigate the electrical properties of the composite.With the addition of carbon nanotubes or modified carbon nanotubes,it not only reduced the charge transfer impedance from 461?to 148?,but also effectively inhibited the formation of impurity phase in the process of high temperature crystallization,which could improve the diffusion coefficient of lithium ion.At the rate of 0.1 C,the discharge capacities of LiFePO₄/C-CNTN was 162.3 mAh g^-1.Increasing the rate to 20 C,the discharge capacity of the LiFePO₄/C-CNTN was still up to 103.9 mAh g^-1 and maintained a good retention rate of 95.4%after 400 cycles.Subsequently,Phenolic resin was adopted as carbon skeleton builted by in-situ polymerization method,and then a well-coated LiFePO₄/Resin composite material was successfully prepared.The carbon content of this composite is just 6.89%measured by TG.Compared with the ordinary carbon coating material?LiFePO₄/Glucose?,the specific surface area of the three-dimensional porous LiFePO₄/Resin composites increased from 43.45 m² g^-11 to 92.75 m² g^-1,and the pore volume increased from 0.1006 cm³ g^-1 to 0.1456 cm³ g^-1.At the rate of 0.1 C and 20 C,the discharge specific capacities could reach 169.3 mAh g^-1 and 105.8 mAh g^-1respectively,showing excellent electrochemical performance.