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Synthesis and Electrochemical Performance of Positice Materials of Lithium Iron Phosphate Synthesized by a Collaborative-modified Method

Author: HuangWeiJing
Tutor: TongQingSong
School: Fujian Normal University
Course: Physical and chemical
Keywords: lithium ions battery lithium iron phosphate collaborative-modified method doping
CLC: TM912
Type: Master's thesis
Year: 2010
Downloads: 31
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Abstract


Lithium-ion batteries have been widely used in portable electronic devices, such as, cellular phones, digital cameras, laptop computers, because of their advantages for high energy density, long cycle life, good safety, environmentally friendly. In the near future, lithium-ion batteries will be used to drive hybrid vehicles and pure electric vehicles. The cathode material is an important component of lithium ion batteries. Lithium iron phosphate (LiFePO4) with olivine structure is one of promising candidates of cathode materials for lithium ion batteries for its relatively high capacity, perfectly flat discharge voltage plateau, good cyclic stability and thermal stability, low cost and environmentally benign.In this dissertation, scries of olivine-type LiFePO.i composites were prepared using a solid-state sintering and collaborative-modified method. Many advanced techniques, such as, X-ray diffraction, charge-discharge cycling, cyclic voltammetry experiment, electrochemical impedance, Fourier transform infrared spectroscopy, scanning electron microscopy and Transmission electron microscope were employed to investigate the relationships among synthesis conditions, structures and electrochemical performances. The main results are given as follows:1. LiFePO4/C composite with a theoretical composition of Li1.05Fe0.95(P04)0.96/Fe0.05 /I0.04/C was synthesized by adding nanosize iron and I2 agent in the precursor by using a solid-state sintering and collaborative-modified method. The optimal sample exhibits’a capacity of 123.9mAh·g-1 in the first cycle at 2C rate and has good cycling ability and rate capability. The Li-ion diffusion coefficient estimated of the optimal sample is 5.99×10-16cm2s-1. The optimal sample is composed of the particles with size range of 0.1 to 0.5μm and coated by a layer of carbon film with thickness about 4nm.2. Series of Mg-doped LiFePO4 composites were synthesized by adding Mg2(OH)2CO3 as a doping agent, and nanosize iron and I2 as additive agents in the precursor by a solid-state sintering and collaborative-modified method. The experimental results indicate that the samples synthesized by doping Mg2+ in Fe sites shows better electrochemical performances than in Li sites. The optimal sample exhibits a capacity of 131.3mAh·g-1 in the first cycle at 2C rate. The Li-ion diffusion coefficient estimated of the optimal sample is 5.75×10-14cm2s-1. The optimal sample is composed of the particles with size range of 0.5 to 1μm.3. Series of Ni-doped LiFePO4 composites were synthesized by adding Ni2(OH)2CO3 as a doping agent, and nanosize iron and I2 as additive agents in the precursor by a solid-state sintering and collaborative-modified method. The optimal sample exhibits a capacity of 125.6mAh·g-1 in the first cycle at 2C rate, and it shows good cycling performance and rate capability. The Li-ion diffusion coefficient estimated of the optimal sample is 4.33×10-14cm2s-1. The optimal sample is composed of the particles with size range of 0.5 to 1μm.

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CLC: > Industrial Technology > Electrotechnical > Independent power supply technology (direct power) > Battery
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