High Pressure Effect on the Structure and Ionic Conductivity in Layered Cobaltite LiCoO2
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摘要: 采用金刚石对顶砧(DAC)高压产生装置，结合同步辐射X射线衍射(XRD)，对钴酸锂(LiCoO2)粉末样品进行室温下原位高压X射线衍射实验，最高压强达到20.3 GPa。研究结果表明：在20.3 GPa下，LiCoO2的晶体结构非常稳定，并没有发生结构相变；在20.3 GPa范围内测量了晶体沿不同晶轴a、c方向的压缩比，发现LiCoO2沿c轴方向的压缩率是沿a轴方向的4.5倍；使用二阶Birch-Murnagha方程拟合出钴酸锂样品的等温状态方程。另外还采用高压原位交流阻抗谱技术(EIS)，测量了不同压强下钴酸锂中锂离子导电率，最高压强达到16.8 GPa时，发现在实验的压强范围内，随着压强的增加，离子导电率减小。最后将高压下锂离子的电导率与钴酸锂的晶体结构进行联系，进一步阐述了高压下钴酸锂的微观结构和电学性能之间的关系。Abstract: The high pressure effect on layered lithium cobaltite oxides (LiCoO2) was investigated using synchrotron X-ray diffraction (XRD) up to 20.3 GPa.In this pressure range, no structural transition was observed and the crystal structure of LiCoO2 keeps stable; therefore, the compressibility of the parameter c was 4.5 times that of the parameter a, exhibiting a larger anisotropic compression; the isothermal equation of the state of LiCoO2 was fitted using the second orders Birch-Murnagha of state.Moreover, the ionic conductivity of LiCoO2 was measured by electrochemical impedance spectroscopy up to 16.8 GPa.The results of the high pressure impedance spectroscopy demonstrated that the Li ionic conductivity decreased rapidly with the increase of pressure.This research provided deep insight into the complex relationship of crystal structure with Li ionic conductivity in LiCoO2.
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Key words:
- LiCoO2 /
- DAC /
- X-ray diffraction /
- ionic conductivity
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图 1 常温常压下LiCoO2的晶体结构模型
Figure 1. Crystal structure of LiCoO2 under atmospheric pressure
图 2 LiCoO2不同压强下原位同步辐射X射线衍射谱
Figure 2. In-situ synchrotron radiation X-ray diffraction patterns of LiCoO2 under different pressures
图 3 LiCoO2在压强6.8 GPa和18.4 GPa下XRD精修图
Figure 3. Representative Rietveld refinement for LiCoO2 with R-3m space group under the pressure of 6.8 and 18.4 GPa
图 4 LiCoO2晶胞参数a、c和压强的关系
Figure 4. Structural parameters of LiCoO2 as a function of pressure
图 5 LiCoO2的p-V曲线状态方程的拟合
Figure 5. p-V data of LiCoO2 and fitted Birch-Murnagha relation
图 6 LiCoO2中Li—O和Co—O键长随压强变化关系
Figure 6. Li—O and Co—O bond length data of LiCoO2 varies with pressure
图 7 LiCoO2中Li的跃迁过程
Figure 7. Li hops between octahedral sites through an intermediate tetrahedral site in LiCoO2
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