Studyonthe Preparationand Electrochemical Performanceof 3D Structure LiFePO₄ Nanowire Arrays

Lithium iron phosphate?LiFePO₄?has been widely used as cathode material in lithium ion power batteries due to its environmental benignity,superior safety and lowcost.However,it also exist the shortcomings include low electrical conductivity and low lithium ion diffusion rate,these lead toits poor rate performance.Nowadays,the main way to overcome these problems is to synthesis nanoscale materials.However,the size distribution of the nanoscale materials is usually inhomogeneity,and it can also increase the lithium ion diffusion distance.Therefore,looking for a solution that both can reduce the grain size and improve the conductivity and lithium ion diffusion rate is particularly important.In this paper,the three-dimensional structure of LiFePO₄ nanowire arrays are the designed and synthesized,the unique structure cannot only reduce the size of LiFePO₄ but also improve the conductivity and lithium ion diffusion constant at the same time.AAO template with controllable thickness andpore diameteris systematically studied in this paper.The experimental results show that the control of secondary oxidation time can adjust the thickness of the AAO template.The pore diameter of AAO template can be controlled by adjust the pore expanding time.The 60-400 nm AAO templates are successfully prepared in this word.LiFePO₄ nanoparticles and 1D-nanowires are synthesized by sol-gel method using ferrous chloride,phosphate,lithium carbonate,citric acid as raw material andreductant conductive carbon source.The addition of citric acid can control the particle size?100 nm?and conductivity?3.1×10-3s/cm?,it can also reduce lithium ion diffusion constant?1.15×10-14 cm2/s?.As a result of the structure,good rate performance?156mAh/g at 0.1 C and 88mAh/g at 10 C?and outstandingcycle stability?littledecreaseafter 50 cycles at 10C?are gained.one-dimensional nanowires are obtained by electrostatic spinning,the performance of nanowires are close to nanoparticles,this means that 1D-nanowires can also reduce the size of LiFePO₄,so as to increase the lithium ion diffusion constant and improveits electrochemical performance.The successful preparation of nanoparticles and nanowires provides the possibilityfor the preparation of three-dimensionalLiFePO₄ nanowire arrays.The three-dimensionalLiFePO₄ nanowire arrays are synthesizedby usingAAO templatecombined with the sol-gel method above.The diameter of nanowire arrays and the pore diameter of AAO template are one-to-one correspondence.SEM figure shows that the nanowire arrays are parallel to each other,with diameter of 90 nm.Nanowire arrays have batter rate performance?160mAh/g at 0.1 C and106mAh/g at 10 C?and excellent cycle stability?99.1%after 350 cycles at 1C and 89.6% after 350 cycles at 10C?compared with nanoparticles.The remarkable electrochemical performanceof nanowire arrays is due to the unique orientationstructure,thus thelithium ion can transport in the unique channel,shortening the distance of lithium ion diffusion.