近日，布鲁克大学-Kenneth J. Takeuchi教授团队等人在JACS上发表重要文章，论文题为“Simultaneous Elucidation of Solid and Solution Manganese Environments via Multiphase Operando Extended X-ray Absorption Fine Structure Spectroscopy in Aqueous Zn/MnO2 Batteries”。采用弱酸性电解液的含水锌锰电池(AZMOB)有望成为潜在的绿色电网级清洁发电储能解决方案。机理理解对于提高应用所需的容量保持率至关重要，但由于正极固相的演变以及溶解-沉积氧化还原过程导致电解质中溶解锰的存在，机理理解非常复杂。这项工作引入了原位多相扩展X射线吸收精细结构(EXAFS)分析，能够同时表征Mn氧化还原反应中涉及的水相和固相。该方法在多种电解质(Zn(CF3O3)2或Zn(CH3COO)2)中成功实施，揭示了相似的锰配位环境，但在固相和溶液相中锰样品的分布存在定量差异。互补拉曼光谱用于鉴定在正极充电下形成的结晶度较低的含锰产物。这通过透射电子显微镜(TEM)进一步增强，揭示沉积固体的形态和表面状况。这些结果证明了一种有效的方法，可对结晶不良的多相固体进行整体表征，同时了解溶液中溶解的过渡金属物种。这项工作为深入了解复杂的电化学机制提供了一种有用的方法，其中固态和溶解的活性物质都是氧化还原活性的重要贡献者。
Figure 1. Synchrotron XRD patterns of (a) discharged and (b) charged cathodes cycled in ZnSO, Zn(CFSO)2 or Zn(CH,COO)2 electrolytes along with pristine electrode and carbon nanotubes.
Figure 2. TEM characterization of the a-MnO2 cathodes discharged in (a, d) ZnSO4 electrolyte, (b, e) Zn(CF,SO3)2 electrolyte, and (c, f) Zn(CH,COO)2 electrolyte showing images of the a-MnO2 rods and the platelet-shaped materials deposited (a-c) and diffraction patterns of the platelet-shaped materials (d-f).
Figure 3. TEM images of the charged a-MnO2 cathodes in (a) ZnSO4, (b) Zn(CF3SO3)2 and (c) Zn(CH,COO)2 electrolytes after one charge cycle demonstrating the formation of surface deposits during charging. Higher-resolution images with inset power spectra and overlaid with filtered images (outlined in red) using the red, circled areas of the power spectra (d-f) for the ZnSO,, Zn(CF,SO)2, and Zn(CH,COO) cycled sample, respectively. In these filtered areas of the images, brighter sections correspond to areas that generate the highlighted signal in the power spectra.
Figure 6. Voltage profile of the operando cells during charge plotted with LCF-calculated average Mn oxidation state for (a) ZnSO4 (b) Zn(CFSO)2 and (c) Zn(CH,CO0)2. Operando XANES evolution of the (d) ZnSO, (c) Zn(CF,SO), and (f) Zn(CH,COO)2 cells.
Figure 7. Operando EXAFS evolution in r-space during discharge for the (a) ZnSO, (b) Zn(CF,SO) and (c) Zn(CH,COO)2 cells.Corresponding EXAFS evolution during charge for the (d) ZnSO, (e) Zn(CFSO)2 and (f) Zn(CH,CO0)2 cells.
Figure 8. XANES-LCF results showing the aqueous/solid Mn weight fraction of the operando cells during the first-cycle (a) ZnSO4, (b) Zn(CF,SO3)2 and (c) Zn(CH,CO0); cells.
Figure 9. EXAFS fitting results of (a) fully discharged operando cell scans and (b) fully charged operando cell scans, (c-e) Theoretical structuresused to perform FEFF calculations during EXAFS fitting.
Figure 10. (a-c) Five-cycle CV results and (d-f) 10-cycle capacity retention. (g, h) Voltage profile evolution over the 10 cycles for ZnSO4 Zn(CFSO) and Zn(CH,COO)2 cells.
【总结】
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球差电镜 | 有限元模拟 | 理论计算
原位XRD、原位Raman、原位FTIR、原位TEM
加急测试
刘老师
研图汇技术经理
182 6975 5918
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