Study On Morphology Contral Of Lithium Iron Phosphate

Aiming at the problem of low energy density of LiFePO₄/C material,the effect of drying method on the morphology of LiFePO₄/C and the influence of particle size and sphericity of microspheres on the performance of LiFePO₄/C were investigated on the basis of morphology control,and the high energy density LiFePO₄/C material was prepared.In order to solve the problem of poor processing performance of LiFePO₄/C fines,the two granulating processes and the technology of matching with LiFePO₄/C microspheres material were used.The main characterization methods are XRD,SEM,physical properties test,processing performance test and electrochemical performance test.Main works are as follows:The effects of drying methods on the morphology and properties of LiFePO₄/C were studied.The results indicate that:Compared with microwave drying method,the LiFePO₄/C sample prepared by spray drying method has regular spherical morphology,higher tap density and compaction density,which are 1.28 and 2.55 g·cm^-3,respectively,higher than 0.88 and 2.33 g·cm^-33 for microwave drying materials.The volume energy density of spray drying sample reaches 243.4 Wh·L^-1,which is 5.8%higher than that of microwave drying sample.However,due to the large particle size of microspheres,the carbon shells of microspheres are seriously shedding after the preparation of polar plates.The surface of polar plates is rough,the processing and electrochemical properties are not satisfactory.The effects of spray conditions on particle size of LiFePO₄/C microspheres and the influence of microsphere size on the electrochemical and processing properties of the materials were studied.The results indicate that:Compared with centrifugal spray,the LiFePO₄/C microspheres prepared by pressure spray have smaller particle size.The smaller the particle size of LiFePO₄/C microsphere,the thinner the carbon shell,the more homogeneous the carbon distribution,the higher conductivity.After making into polar plates,the carbon shells of microspheres are well preserved and the electrochemical performance is better.The capacity of sample prepared by pressure spray reaches 537.5mAh at large discharge rate of 10C.However,as the particle size of LiFePO₄/C microspheres decrease,the sphericity becomes worse,the density of compaction and compaction decrease,resulting in poor processability.The effect of primary particle size on the sphericity of LiFePO₄/C microspheres was studied.The results indicate that:Prolonging the milling time and decreasing the particle size can improve the sphericity of LiFePO₄/C microspheres,improve the density,processability and electrochemical performance.The tap density of sample prepared by grinding 4 h reaches 1.68 g·cm^-3,the discharge capacity of 0.5C is 597.8 mAh and the volume energy density reaches 248.7 Wh·L^-1,which is 8.0%higher than that of microwave drying sample.Two kinds of lithium iron phosphate fine powder utilization methods were studied.One is the two granulation process.After treated,the D₅₀0 of sample changes from 0.78?m to 1.11?m,and the tap density increases from 0.65 g·cm^-33 to 1.13 g·cm^-3,and the processing performance is significantly improved.Another method is matching with LiFePO₄/C microspheres material.When the mass ratio of LiFePO₄/C fine powder to LiFePO₄/C microspheres is 3:7,the particle size distribution curve is better,and the tap density is the highest,reaching 1.58 g·cm^-3.And the mixed sample has good processability and electrochemical performance.