Preparation Of LiFePO₄/C Cathode Material By Spray-drying Method

Lithium iron phosphate (LiFePO4) is a kind of positive electrode materials, which has olivine structure, because of its high working voltage and specific capacity (170mah/g), good life, a wide range of sources, low cost, environment friendly, safe and stable, becomes one of the hot issues by many scientists, also has been regarded as the top development potential of lithium ion battery cathode material because the lots of advantages. But, it also has some faults, for example, low electrical conductivity, lithium iron phosphate lithium ion migration rate and low bulk density. Related studies found that doping or coated modification method can improve the electrochemical performance of LiFePO4.This paper summarized the existing preparation methods of lithium iron phosphate, prepared the spherical LiFePO4/C anode material by spray drying method, optimized the technological parameters of spray drying and the ratio between the oxalic acid and citric acid,discussed the carbon coating process, improved the conductivity and lithium ion diffusion coefficient, and combined with the characterization methods such as SEM, XRD, TG-DTA, etc. and researched on the material.l.The effect of process parameters on the synthesis of LiFePO4.Firstly,with FeSO4.7H2O, H3PO4H2O2and NH3.H2O as raw materials and the oxidation of co-precipitation to synthesis FePO4.2H2O precursor, then by ball-milling and spray drying method to get the precursor powder of LiFePO4. Seen from the result of SEM that the best parameters of spray drying, namely that when the inside diameter of nozzle ψp=0.5mm and the solid content is5%, the dissolution was completely, the inlet air temperature is160℃, the rate of the spray is750ml/h the particle’s sphericity was uniformed and better.2. The precursor powder was burned under650℃to get a single phase of LiFePO4/composites. Seen from the SEM,XRD,TG-DTA and so on, the particle’s morphology and size can be modified by adjust the amount of the oxalic acid (OA) and the citric acid (CA). According to the result, the proportion of oxalic acid and citric acid had no effect on the precursor powder. The partical are almost spherical and the size distribution is wild, they bond heavily and cause the situation of "unite". The particles’ sphericity will be better after adding sucrose to it and when the sucrose content was20%, the particles’ surface become smooth and smaller. As is shown by the test of tap-density measurement and electrochemical performance, Tap density decreased with the sucrose content increases. LiFePO4/C first discharge specific capacity has increased significantly compare to LiFePO4, and when the sucrose content was20%, the cycle performance of LiFePO4/C composite material is the best.