Metal Substitution within Nanostructured Nickel Hydroxides for Aqueous Rechargeable Nickel–Zinc Batteries




Kimmel, Samuel W.

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Developing batteries with high gravimetric and volumetric energy density, improved safety, and lower cost is a critical need for a wide range of applications including electric vehicles, portable electronic devices, and grid-level energy storage. Although lithium-ion is currently the go-to high-energy battery technology, the inherent safety issues of Li-ion persist and represent a challenge for large-format applications. The alkaline nickel–zinc (Ni–Zn) battery is an attractive alternative to Li-ion due to its use of nonflammable aqueous electrolyte. The monolithic three-dimensional zinc “sponge” developed at the U.S. Naval Research Laboratory solves long-standing performance limitations for zinc anodes and paves the way for next generation Ni–Zn batteries that approach the specific energy of Li-ion systems. To match these new levels of zinc anode function in terms of capacity and rate capability, improved alkaline cathode materials and architectures are required. To meet this need, the effect of isomorphic substitution of metal ions (aluminum, cobalt, manganese and zinc) into α-Ni(OH)2 by microwave synthesis was investigated because α-Ni(OH)2 can accommodate more than one-electron charge storage when stabilized, which otherwise converts to lower-capacity β-Ni(OH)2 with cycling in alkaline electrolytes. A rapid and scalable microwave-assisted route was used to synthesize substituted α-Ni(OH)2 with a nanosheet morphology. The effect of metal-ion substituents on the structure and morphology of α-Ni(OH)2 was determined using scanning electron microscopy, X-ray diffraction, nitrogen porosimetry and Raman spectroscopy. Electrochemical charge–storage behavior was evaluated using galvanostatic cycling and differential-capacity measurements under device-relevant conditions. The results show that when α-Ni(OH)2 is synthesized by a microwave-assisted hydrothermal route with a partial substitution at a Ni2+ -to- Mz+ ratio of 9:1 (nominally Ni0.9M0.1), the identity of the metal substituent influences the relative concentration of Ni2+ -to- Mz+ incorporated into the α-Ni(OH)2 nanosheets. Manganese incorporated less (Ni0.98Mn0.02) than the nominal substitution ratio while zinc was incorporated to a greater degree (Ni0.81Zn0.19). The identity of a metal substituent also influenced physicochemical and electrochemical properties of microwave synthesized α-Ni(OH)2 nanosheets. Raman spectroscopy indicated the incorporation of ethylene glycol, urea, and two different nitrate environments, and the x-ray diffraction pattern supported the α-phase crystal structure was maintained upon substitution. Specific substituents increased (Co and Zn) or decreased (Al) the aggregate size of the nanosheets while still preserving the mesoporous and microporous structure. Compared with the initial electrochemical discharge capacity of unsubstituted α-Ni(OH)2 nanosheets of 239 mAh g-1active, Al3+ substitution increased the capacity from to 303 mAh g-1 active, whereas Co2+ substitution decreased the capacity to 189 mAh g-1active. Understanding the nature of metal substituents within the α-Ni(OH)2 structure and the resulting effect on the charge storage process furthers the development of energy dense Ni–Zn batteries.



Rechargeable nickel–zinc batteries


Kimmel, S. W. (2020). <i>Metal substitution within nanostructured nickel hydroxides for aqueous rechargeable nickel–zinc batteries</i> (Unpublished thesis). Texas State University, San Marcos, Texas.


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