Preparation And Characterization Of LiFePO₄Porous Films

In recent year, by the over-exploitation of coal and petroleum resources, peoplebegin to realize the energy crisis intensely. Meanwhile, the environmental problemscaused by the over-exploitation of resources, such as global warming has had impacton people’s living environment, even the survival. Thus, as a high-powered andreusable green energy resource, the lithium-ion battery has been brought to theforefront. However, LiFePO4, the anode material for lithium ion battery, though hassorts of advantages, such as a good command of thermo stability, being environmentalfriendly, a higher theoretical specific capacity and price moderate, its electricalconductivity is relatively poor. Therefore, it’s important to improve the mobility ofions and electron conduction, in order to make it an ideal material for li-ion batteries.To product a positive electricity of li-ion battery with nano-porous surface, this paperis focused to improve the electrical conductivity of li-ion by decreasing itstransmission range. Base on this, the project will be carried out with the process ofstudying the sol-gel synthesis method of high-performance of LiFePO4powdermaterials and the method to product well-distributed reticular formation of LiFePO4on aluminum substrate by using polystyrene (PS) microsphere as a template combinedwith sol-gel technology.Firstly, the experiment is to get good crystal form and small particles of LiFePO4powder materials by the method of sol-gel. Based on this, LiFePO4porous membranematerial with well-distributed spatial reticulated structure would be produced tocombine with substrate on the template of PS microspheres surface successfullythrough a large number of experiments.Secondly, this paper presents the study of what those effect of calcinationtemperature, the selection of iron source are made on the ingredient, microstructure and electrochemical performance of LiFePO4powder materials. On the one hand, thecalcination temperature influences the electrochemical performance andmicrostructure of LiFePO4. It is testified that through SEM, with the increasingtemperature, the particle of powder materials become larger gradually and the crystalform better, however, with the gradually larger crystal particle, its electricalconductivity becomes worse—the optimum electrochemical performance throughcharge-discharge curves is600℃. On the other hand, different selection of iron sourcehas exerted a different effect on the ingredient, electrochemical conductivity andmicrostructure of LiFePO4powder materials. Among these selections, ferrous oxalateas the iron source produces the purest ingredient of powder materials, whereas, theproducts of the other two (iron nitrate and ferrous sulfate) all contain a certainimpurities. Besides that, the samples produced by ferrous oxalate is electrochemicalperformance optimum. But the particle of powder microstructure produced by ferroussulfate—another iron selection is the smallest, and those produced by the other twoare larger and blocked together.Lastly, the paper also give a study about the effect of different factors of PSmicrosphere template such as the end plate, the film forming process, the way offilming and the diameter of PS microsphere, have made on the porous membrane ofLiFePO4microstructure. By comparing within the help of SEM, it is found thataluminum substrate is suitable than glass substrate to be the PS microsphere template,because the glass substrate has weak adsorption capacity with PS microsphere andhard to form an unbroken porous membrane. From the point of film formingtechnology, compared with secondary film process technology, porous membraneproduced by one time film is poorer on evenness and completeness, because theporous membrane is covered by excrescent LiFePO4gelatin which makes itsinterspace reticulation blur. Moreover, under such circumstance when the adhesiveforce, shear force and capillary force reach the balance, then the well-distributed andtransparent porous membrane will be produced. Above all, in order to produce an unbroken and continuous honeycomb structural LiFePO4thin film, while the600nmPS microsphere adopts the method of dipping tyra daub, the200nmPSmicrosphere is better to spin coating.