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Synthesis and Surface Modification of LiFePO4 and LiTi2（PO4）3 for Lithium-ion Batteries Materials

Author: ZhengWei
Tutor: CaoGaoZuo；ZhaoXinBing
School: Zhejiang University
Course: Materials Science
Keywords: Lithium ion battery Cathode material Anode material LiFePO4 LiTi2 PO4 3 Carbon-coated Synthesis temperature
CLC: TM912
Type: Master's thesis
Year: 2010
Downloads: 172
Quote: 1
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Abstract


Olivine-type LiFePO 4 and NASICON the structure of LiTi 2 (PO 4 ), 3 has a low price environment friendly, high thermal stability, chemical compatibility, outstanding cycling stability, etc., is regarded as the lithium ion electrode materials with broad application prospects. But the LiFePO 4 , the / sub> (as PO in the 4 ) 3 low intrinsic conductivity serious impact on the material The electrochemical performance limits of the practical application of the material. This paper to improve LiFePO 4 , and LiTi 2 (PO 4 ), 3 electrode electrochemical properties of the materials for the primary purpose and high temperature solid phase was prepared the LiFePO 4 / the C and LiTi 2 (the PO 4 ) 3 / C composite materials, using X-ray diffraction, scanning electron microscopy and Raman spectroscopy, the crystal structure of the synthetic product, surface morphology and carbon structure were characterized and studied by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and charge-discharge tests on the electrochemical properties of the material testing and analysis, research synthesis temperature and FePO 4 raw material LiFePO 4 the electrochemical properties of the cathode material impact LiTi 2 (PO 4 ), 3 anode material for the synthesis mechanism and surface modification research. Synthesis temperature of LiFePO 4 cathode material. To the FePO 4 · 2H 2 O as a source of iron, Li 2 the CO 3 for lithium source, polypropylene is reductant and carbon source, step solid-phase synthesis in situ carbon-coated lithium iron phosphate (LiFePO 4 / C) composites. The research results show that the pure LiFePO 4 materials can be synthesized when calcination at 500 ℃ ~ 750 ℃. Polypropylene pyrolysis carbon when the synthesis temperature is below 700 ° C can effectively inhibit LiFePO 4 particle growth conducive to shorten the lithium ion migration distance. As the synthesis temperature increases, the degree of carbon graphite material will be increased, thus improving the electronic conductivity of the material. Calcined 8 h at 550 ℃ synthesized LiFePO 4 / C composite grains fine and uniform, size distribution within the range of 50 ~ 300 nm, the best electrochemical performance, at 1 C, 2 C-and 5 C ratio reached its discharge capacity of 151 mAh / g and 139 mAh / g and 127 mAh / g. FePO 4 raw material LiFePO 4 cathode material. In LiFePO 4 cathode material preparation, the iron source FePO 4 particle size of precursor and follow-up after milling calcined product purity, morphology and electrochemical performance than big impact. The the small particles the FePO 4 · 2H 2 O in the milling process can be with raw Li in 2 CO 3 chemical reaction generates Li 3 PO 4 the precursor reaction 550 ℃ calcined process more fully, more nucleation rate, the product of small particles, the product lithium ion diffusion coefficient greater, be the EIS test the apparent diffusion coefficient D by Li 3.12 × 10 -14 cm 2 / s The ionic conductivity of the material σ Li 1.97 × 10 -9 S / cm, the material under a magnification of the 1 C discharge capacity of 151 mAh / g. When the FePO 4 · 2H 2 O when the larger particle size is likely to cause a subsequent reaction incomplete, affecting the purity of the product, while the product of larger particle size, which leads to the electrochemical The performance deterioration, under the magnification of the 1 C discharge capacity of only 116 mAh / g. LiTi 2 (PO 4 ), 3 mechanism of anode materials synthesis and surface modification research. The results show that: TiO 2 , LiH 2 PO 4 and the NH 4 H 2 < / sub> PO 4 as raw material, through high temperature solid-phase synthesis LiTi 2 (PO 4 ) 3 negative The materials process will first form an intermediate product TiP 2 O 7 , and then generate LiTi 2 (the PO 4 ) 3 . Calcination temperature conducive LiTi 2 (as PO in 4 ) 3 pure phase formation can be pure at 950 ℃ for 12 h LiTi 2 (PO 4 ) 3 , 0.1 C magnification first discharge capacity of 42.2 mAh / g, for the first time coulombic efficiency 44.5%. After carbon-coated LiTi 2 (PO 4 ), the conductivity of the anode material can significantly improve the electrochemical properties of the material can be greatly improved. Increase the temperature of carbon-coated help to improve LiTi 2 (as PO in 4 ) 3 / C composites conductivity, 700 ℃ synthesis of LiTi 2 (PO 4 ) 3 / C composite 0.1 C magnification first discharge capacity reached 131 mAh / g, reached a theoretical capacity of 95%, for the first time the coulombic efficiency was 96.4% and 0.5 C discharge capacity of 103.2 mAh / g can be achieved.

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