Papers by Author: Yun Bo Chen

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Authors: Hong Quan Liu, Fei Xiang Hao, Feng Lin Yao, Yi Jie Gu, Yun Bo Chen
Abstract: LiFePO4 compound has been paid considerable attention as a promising positive electrode material. In this work, LiFePO4 compound was synthesized by the solid carbon thermal reduction reactions,where Fe2O3, Fe(OH)3 and FeSO4 is used as the iron resource respectively. All the synthesized products are pure phases except that using FeSO4 as the iron resource. The SEM images show porous morphologies, but different iron resource samples show different degree of pore ratio. According to the results of charge/discharge curves, capacity of the sample prepared by Fe(OH)3 as the iron resource shows superior to those of other samples. The result is attributed to more pores in the sample, which is benefit to electrolyte penetrating, short Li-ion diffusion distance.
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Authors: Hong Quan Liu, Fei Xiang Hao, Yi Jie Gu, Yun Bo Chen
Abstract: LiFePO4 has been considered as the most promising positive electrode due to its low cost, high theoretical capacity, stability and low toxicity, all highly required in vehicle applications. In this work, LiFePO4 compound was synthesized by the solid carbothermic reduction reactions with different Li resource. The pure LiFePO4 phase was confirmed for all samples by analysis of the XRD results. The different morphologies were obtained due to different Li resources. The potential plateau of all samples is in the range from 3V to 4V. The sample (LiCO3 as the Li resource) has a higher discharge capacity of 118mAhg−1 at 0.2C 20% greater than that of the sample (LiOH as the Li resource). The reason comes maybe from nano pore characteristics, which reduce Li ion diffusion distance, and increase the utilization efficiency of material.
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Authors: Guo Zhi Ruan, Zhi Hui Zhang, Yun Bo Chen
Abstract: In this paper, silicon carbide materials bonded with superfine SiO2 powder were produced using silicon powder, superfine SiO2 powder and different grain grade silicon carbide as raw materials. At the condition of the same content of silicon powder, the effect of the superfine SiO2 powder content on properties of silicon carbide materials after sintered at 1450°C for 3 h in air atmosphere was studied by means of SEM and other analysis methods. The results showed that silicon powder contributes to both sintering by liquid state and plastic phase combination to improve the strength of samples. When the superfine SiO2 powder content is lower than 3.5%, the density and strength of samples increase and porosity decrease with increasing superfine SiO2 powder content. However when the superfine SiO2 powder content is higher than 3.5%, the density and strength of samples decrease and porosity increase with increasing superfine SiO2 powder content. At the same time, sample with 3.5% superfine SiO2 powder has the best oxidation resistance property at 1100°C.
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Authors: Yi Jie Gu, Fei Xiang Hao, Yun Bo Chen, Hong Quan Liu, Yan Min Wang, Peng Liu, Qing Gang Zhang, Shu Qi Li
Abstract: LiFePO4/C composite cathode materials were synthesized by spray-drying method using LiH2PO4 and Fe2O3 as raw materials and amylum as conductive additive and reducing agent. The microstructure of the samples was characterized by X-ray diffraction; charge/discharge cycling performance and electrochemical impedance spectroscopy (EIS) were used to characterize their electrochemical properties. X-ray diffraction result showed that LiFePO4/C composite has an order olivine structure with space group of Pnma. The charge/discharge tests showed that the cathode material has a high discharge capacity of 140.8mAh/g after 5 cycles at 0.1C rate. And after 100 cycles at 1C rate, the discharge capacity is 108.4mAh/g.
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Authors: Y.C. Chen, Hong Zhi Cui, J. Ding, Yun Bo Chen
Abstract: More than twenty years were needed for people to understand the formation mechanism of the periodic-layered structures not only because of the complications of pattern formation, but also due to the limits of traditional diffusion theories. Based on the general theory of interdiffusion growth proposed by Y.C. Chen et al. [1], the quantitative model of periodic layer formation during solid state reactions has been succeeded [2]. The experimental results shown in this paper proved one of the model’s predicts that the reactive diffusion system Zn/Fe3Si with clamp press annealed at 663K should be mixed controlled. Also, the important influence of the uniaxial compressive stress on the diffusion coefficient was emphasized and the reasons are discussed.
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Authors: Yi Jie Gu, Peng Liu, Yun Bo Chen, Hong Quan Liu, Yan Min Wang, Fei Xiang Hao, Qing Gang Zhang, Shu Qi Li
Abstract: The effect of pH concentrations on the size and morphology of FePO4•xH2O particles synthesized in a hydrothermal reactor was investigated in this work. FePO4•xH2O was prepared through co-precipitation by employing Fe(NO3)3•9H2Oand H3PO4 as raw materials. The LiFePO4 obtained through lithiation of FePO4•xH2O by using glucose as a reducing agent at 700°C. The electrochemical performance of LiFePO4 powder synthesized at 700°C were evaluated using coin cells by galvanostatic charge/discharge .The results indicated that the synthesized LiFePO4/C composites (pH=2) showed a superior electrochemical capacity of 146 mAh/g and possessed a capacity favorable cycling maintenance at the 0.1C rate and high electronic conductivity.
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Authors: Yi Jie Gu, Qing Gang Zhang, Yun Bo Chen, Hong Quan Liu, Yan Min Wang, Fei Xiang Hao, Peng Liu, Shu Qi Li
Abstract: The thermodynamic analysis of Ni2+-Mn2+-NH3-OH--H2O in co-precipitation system was carried out, and the precursor Ni1/2Mn1/2(OH)2 was prepared by hydroxide co-precipitation method. The analysis showed that the best pH value of mixed solution is 11 and the ammonia concentration is 0.4 mol/L, when NaOH is precipitating agent and ammonia is chelating agent. When the pH value is 11, the SEM images confirm that the morphology of Ni1/2Mn1/2(OH)2 is the best.
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