Nanocrystaline Beta-Ni(OH)2 Cathodes and Their Nanoelectrofuel Analogs for Flow Batteries

β-Ni(OH)₂ is a discharged form of NiOOH which is common cathode for a family of nickel-based batteries including Ni/Cd, Ni/Fe, Ni/Zn, Ni/MH with theoretical capacity of 289 mAh/g. Previous studies have shown that introduction of nano-size β-Ni(OH)₂ could dramatically increase the electrochemical performance, e.g. smaller polarization and better discharge capacity than commonly used micro-sized Ni(OH)₂ mainly due to the enhancement of proton diffusion in nickel hydroxide electrode [1, 2]_. Ni(OH)₂ and NiOOH have been extensively studied before in bulk form including x-ray diffraction (XRD) and x-ray absorption fine structure (XAFS) techniques [3-6]. In situ EXAFS was used to study the progressive structure change during discharge and compare structures of Ni(OH)₂in charged and discharged state [7, 8].

Our work focuses on the development of a suspension form of Ni(OH)₂electrodes, also called nanoelectrofuels (NEFs). NEFs are stable dispersions of nano-scale battery active materials in the electrolytes that can be used in flow batteries as high energy density liquid energy storage. The main advantage of NEFs compared to traditional flow battery electrolytes is that high concentrations of active materials, and therefore energy density as concentration of nanoparticles in suspensions it is not limited by solubility of redox salts.

The presentation will discuss how different morphologies and crystallinities of β-Ni(OH)₂ nanoparticles can be achieved through a simple one-step synthesis method; analysis with scanning electron microscopy (SEM), XRD, and thermogravimetric analysis (TGA) techniques; electrochemical characterization, including cyclic voltammetry, charge/discharge curves and life cycle analysis for different synthesis products in NEF formulations and compare their performance to the solid state analogs. In addition, we will present results from our in situ XAFS study of structural and electronic changes taking place during charge and discharge cycles in β-Ni(OH)₂ cathodes.

References

[1] Guan X. Y, Deng J. C., Materials Letters, 61 (2007) 621-625.

[2] Han X. J., Xu P., Xu C. Q., Zhao L., Mo Z. B., Liu T., Electrochemica Acta, 50 (2005) 2763-2769.

[3] Pandya K. I., O’Grady W. E., Corrigan D. A., McBreen J., and Hoffman R. W., J. Phys. Chem., 94 (1990) 21-26.

[4] Ichiyanagi Y., Kondoh H., Yokoyama T., Okamoto K., Nagai K., Ohta T., Chemical Physical Letters, 379 (2003) 345-350.

[5] Morishita M., Kakeya T., Ochiai S., Ozaki T., Kawabe Y., Watada M., Sakai T., Journal of Power Sources, 193 (2009) 871-877.

[6] Capehart T. W., Corrigan D. A., Conell R. S., Pandya K. I., Hoffman R. W., Applied Physics Letters, 865 (1991) 58.

[7] Farley N. R. S., Gurman S. J., Hillman A. R., Electrochemica Acta, 46 (2001) 3119-3127.

[8] Farley N. R. S., Gurman S. J., Hillman A. R., J. Synchroton. Rad., 6 (1998) 198-200.