Synthesis And Characterization Of LiFePO₄Thin Films With One-dimensional Nanoarrays

The lithium-ion battery as a typical, lightweight, repeatable charging anddischarging of electrochemical energy storage and conversion devices, has developedrapidly and has become a new type of storage batteries. In all phosphate of lithium-ionbattery, LiFePO₄（LFP） with olivine structure has a high theoretical capacity. In addition,LiFePO₄has attracted a lot of attention because of its non-toxic, safe advantage, and hasbecome one of the most potential for lithium ion battery cathode material. But LiFePO₄also has a drawback, its inherent low electronic conductivity, which results in poor ratecapacity. A lot of approaches such as reducing the particle size, doping metal ions,coating carbon have been considered to overcome LiFePO₄poor conductivity. In thiswork, LiFePO₄nanoarrays’ size is reduced through template-assisted synthesis.Template-assisted synthesis is one of the most effective methods for1D nanostructuresfabrication.1.AAO template was synthetized in0.3M solution of oxalic acid,0℃,40V by twoanode oxidation method. AAO template with pore size of90nm is highly uniform,Thickness of template increased with increasing oxidation time.2. LiFePO₄sol was prepared by FeSO₄·7H2O, C2H3O2Li·2H2O as well as phosphoricacid, Under a complexing agent, citric acid. We presented the development of highlyordered and vertically oriented LiFePO₄nanoarrays using a sol-gel method with porousanodic aluminum oxide （AAO） as the template. The LiFePO₄films attached withnanoarrays were successfully fabricated. The LiFePO₄nanorods with rough surfacewere parallel to each other to form orderly arrays, and diameter was90nm. The samplewas characterized by XRD, SEM and TEM. The preparation of LiFePO₄nanorods indifferent conditions has showed increased the deposition rate of LiFePO₄sol to100%;Increasing the sol concentration and the time of deposition were in favour of deposition of LiFePO₄in a certain range; Vacuum freeze drying could reduce the surface tensionand prevent the agglomeration of the LiFePO₄nanorods significantly. Herein we get theoptimized conditions for preparation of ordered LiFePO₄nanorods arrays: solconcentration was0.25mol/L for vacuum deposition3times, in vacuum freeze-dryingafter removing template40min.3. The passage have researched the mechanism of the AAO template-the sol-gel methoddespositing LiFePO₄nanorods.There are three main forces in the despotion process.LiFePO₄sol with a positive charge and negative electrostatic attraction between thetemplate, the template pore of capillary force, get rid of the negative pressure when theatmospheric pressure. Under the electrostatic attractive force, with the positivelycharged sol adsorbed on the wall of the pore. if the deposition times fewer, the solconcentration is lower, then the nanotube is formed after heating treatment, and viceversa, if the deposition times more, channels within a high solid content, result in theformation of nanowires. The presence of these three forces promotes the deposition ofthe LiFePO₄sol.