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Wen-Zhe Shen,Yi Ma,Yaochun Yao,Feng Liang 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2019 NANO Vol.14 No.8
Ni-rich Li(Ni0.8Co0.1Mn0.1)O2 cathode material is widely recognized as one of the most cathode materials for lithium-ion batteries due to its high specific capacity, high energy density and low cost. In this paper, the NCM cathode material precursor Ni0.8Co0.1Mn0.1(OH)2 was prepared by coprecipitation method and the optimum experimental conditions were investigated. The effects of water bath temperature on the electrochemical performances of the prepared materials were investigated by controlling the morphology. The results showed that 60 ℃ was the best bath temperature for the precursor which has a regular spheroidal morphology and uniform particles with the diameter of 10 μm. After coprecipitation, the samples calcined under oxygen atmosphere displayed good electrochemical properties. The discharge specific capacity is up to 194 mA · h · g -1 and 134 mA · h · g -1 at 0.2 ℃ and 5 ℃, respectively. The initial coulombic efficiency is 87.57% at 0.2 ℃.
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Xiaopeng Huang,Feng Liang,Yuanchao Du,Keyu Zhang,Yaochun Yao,Yongnian Dai 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.11
A systematic approach was used to develop the empirical model for optimizing the preparation process parameters for the synthesis of LiFe1-x-yMgxTiyPO4/C composite cathode material. For optimizing the production parameters, response surface methodology (RSM) was applied to develop a linear regression model and maximize the discharge capacity. Analysis of the variance (ANOVA) showed that the three variables (Mg-dopant, Ti-dopant and sintering temperature) and the interactions among them were significant factors. Response surfaces formed by RSM illustrated that the doping of Mg and Ti on Fe site had obviously synergistic effect on the discharge capacity. In the process optimization, the parameters were 2.9% of Mg-dopant, 3.0% of Ti-dopant and sintering temperature of 678.5℃, corresponding to a discharge capacity of 136.7 mAh/g predicted by the model. This predicted value was in good agreement with the actual value (136.4 mAh/g) by confirmatory experiment. The optimized LiFe0.941Mg0.029Ti0.030PO4/C composite exhibits a good rate performance and cycling stability due to the enhancement of electronic conductivity and lithium diffusion coefficient (3.1 X 10-12 cm2 /s) by the co-doping of Mg and Ti ions.
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Yin Li,Keyu Zhang,Zhengjie Chen,Yunke Wang,Li Wang,Feng Liang,Yaochun Yao 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2020 NANO Vol.15 No.02
The olivine LiFePO4 with various morphologies and different growth lattice planes was prepared by a controllable hydrothermal method with changing precursor concentration and using phytic acid as phosphorus source. The microstructure, crystal orientation and electrochemical performance of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and charge–discharge tests. The results show that the morphologies of all samples change from spindle-like to hierarchical plate-like and then to long plate-like shape, and the main exposed facets transform from (100) to (001). This indicates that the precursor concentration and phytic acid play important roles in exposing facets and controlling the morphology of LiFePO4. In order to illustrate these phenomena, a reasonable assembly process is provided and the formation is explained. Li ion diffusion coefficient along [100] and [001] directions was calculated by using electrochemical impedance spectroscopy (EIS). The results show that the diffusion coefficient of (100) facet is higher than that of (001) facet, indicating a good electrochemical performance for (100) facet. In addition, the capacity test is carried out, which also confirms the above results. With the precursor concentration of 0.5 M, the obtained LiFePO4 with self-assembled hierarchical structure, smaller size and (100) facet shows the best electrochemical performance: 162.1 mAh/g at 0.1C and 112.4 mAh/g at 10 C. Using phytic acid as phosphorus source and controlling precursor concentration to prepare high performance LiFePO4 open up a new prospect for the production of cathode materials for lithium ion batteries.
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Keyu Zhang,Xiaoyan Yang,Jian Wu,Xiaopeng Huang,Yaochun Yao 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2016 NANO Vol.11 No.11
This study investigates the optimal conditions for the synthesis of battery-grade ferrous oxalate as a raw material for preparing cathode material. Ferrous oxalate was prepared by liquid-phase precipitation method using ferrous sulfate and oxalic acid. Central composite design (CCD) was used to determine the effects of three preparation variables on purity and particle size: reaction temperature, aging time and concentration of ferrous sulfate. Based on CCD, the significant factors on each experimental design response identified the analysis of variance (ANOVA). The optimum ferrous oxalate preparation conditions were obtained reaction temperature of 31.32℃, aging time of 56.52 min, and ferrous sulfate concentration of 5%. Under these optimum conditions, ferrous oxalate with purity of 99.69% and particle size of 4.92 µm was obtained as best product which met and exceed the requirements of battery-grade ferrous oxalate. In addition, the special morphologies of ferrous oxalate prepared under different dispersant proportion was characterized by scanning electron microscope (SEM) to analyze the mechanism of synthesis. Morphology control study revealed that the dispersant could effectively change the surface energy between crystallographic planes, then result in anisotropic growth of the crystal structure and change the morphology of synthetic products.
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