Low Cost Synthesis And Properties Of Lithium Iron Phosphate Materials

Over the past decades, the lithium batteries has been widely applied in the portable electronic devices. With the advantages of low cost, environmentally friendly, cycling stability and high-temperature capability, LiFePO4 has been considered as one of the most potential cathode material for lithium ion batteries. Presently, although the synthesis technique of LiFePO4 has been largely enhanced, the commercial application of LiFePO4 still suffers from instable nature of Fe+caused by the synthesis procedure, higher cost caused by the expensive raw materials and complicate synthesis procedure. Therefore, in our study, we propose some simple and economic synthesis to prepare high purity LiFePO4/C composite, and explored the electrochemical performance of it.1. A controllable hydrothermal process was proposed to synthesis a micro-plates LiFePO4 growth along (010) and (001) lattice planesWe obtained the two different LiFePO4 micro-plates which grown in (010) and (001) lattice planes through a controllable hydrothermal process by adjusting the molar ratio of Li: Fe:P of the starting raw materials. The XRD, SEM and HRTEM results implying the crystal growth process of the two different samples. The electrochemical investigation confirms that the diffusion coefficient and capacity of (010) microplates were higher than (001) microplates, and the (010) microplates also have a better cycle stability.2. Preparation and Electrochemical Performance of Nano Sized LiFePO4/C Spherical Materials by nano grinding routeA novel synthesis routine for nano LiFePO4/C composites was proposed, in which LiFePO/C composite was prepared at 500-700℃ using iron powders as the starting Fe source through a combined method of nano grinding, spray drying and high temperature calcinating. The initial discharge capacity of spherical nano LiFePO4/C composite at 0.2C, 0.5C,1C was 164.5 mAh/g,161 mAh/g and 151.1 mAh/g, respectively. After 10 cycles, the capacity retention keeps above 97%, showing good electrochemical performance.3. High purity and porous-spherical LiFePO4/C cathode materials obtained by direct conversion of FePO4·2H2O in a hydrothermal methodThe high purity LiFePO4C was prepared at 180℃ for 4h by a hydrothermal method, the molar ration of Li+, Fe3+, and PO43- was 1.35:1:1. The electrochemical investigations confirm that the high purity LiFePO4/C has excellent performance. Porous spherical and high purity LiFePO4/C composites were obtained by the spray pyrolysis. The initial discharge capacity of LFP/C cathode at 0.1C,0.2C,0.5C was 164.5 mAh/g,161 mAh/g and 151.1 mAh/g, respectively. Meanwhile, the capacity showed hardly fading after 20 cycling.4. High purity LiFePO4/C synthesis by conversation FePO4·2H2O into LiFePO4OHThe LiFePO4OH was prepared at 140℃ for 6h by using LiOH·H2O and FePO4·2H2O as raw materials in a hydrothermal process. After colling naturally to room temperature, the LiFePO4OH precursor solution was mixed with sucrose solution, and then it was used to prepare porous spherical LiFePO4OH/C precursor powder by using a spray pyrolysis technique, and the powder was calcined at 700℃ for 6h, then, the sample(A) obtained. The other sample (sample B) which prepared without a hydrothermal process was made to as a comparison. The electrochemical investigation confirms that the sample(A) showing a better performance than sample B. The initial discharge capacity of LFP/C cathode at 0.1C,0.2C, 0.5C was 168 mAh/g,157 mAh/g and 145 mAh/g.