Abstract
A significant amount of work on electrochemical energy storage focuses mainly on current lithium-ion systems with the key markets being portable and transportation applications. There is a great demand for storing higher capacity (mAh/g) and energy density (Wh/kg) of the electrode material for electronic and vehicle applications. However, for stationary applications, where weight is not as critical, nickel-metal hydride (Mi-MH) technologies can be considered with tolerance to deep discharge conditions. Nickel hydroxide has gained importance as it is used as the positive electrode in nickel-metal hydride and other rechargeable batteries such as Ni-Fe and Ni-Cd systems. Nickel hydroxide is manufactured industrially by chemical methods under controlled conditions. However, the electrochemical route is relatively better than the chemical counterpart. In the electrochemical route, a well-regulated OH− is generated at the cathode forming nickel hydroxide (Ni(OH)2) through controlling and optimizing the current density. It produces nickel hydroxide of better purity with an appropriate particle size, well-oriented morphology, structure, et cetera, and this approach is found to be environmentally friendly. The structures of the nickel hydroxide and its production technologies are presented. The mechanisms of product formation in both chemical and electrochemical preparation of nickel hydroxide have been presented along with the feasibility of producing pure nickel hydroxide in this review. An advanced Ni(OH)2-polymer embedded electrode has been reported in the literature but may not be suitable for scalable electrochemical methods. To the best of our knowledge, no such insights on the Ni(OH)2 synthesis route for battery applications has been presented in the literature.
Highlights
Electrical energy storage devices, comprising batteries and capacitors, employ both aqueous and non-aqueous electrolytes in either liquid or solid state
An attempt is made to summarize the information on nickel metal hydride (Ni-MH) battery technology with an emphasis to synthesize routes and bring insights into the chemistry involved and product formation mechanism in nickel hydroxide
The nickel metal hydride (Ni-MH) battery consists of three components, namely, an anode of hydrogen absorbing alloys, a cathode of nickel hydroxide (Ni(OH)2) and an aqueous potassium hydroxide (KOH; typically 5M) electrolyte
Summary
Electrical energy storage devices, comprising batteries and capacitors, employ both aqueous and non-aqueous electrolytes in either liquid or solid state. Ni-MH batteries have been drawing increasing attention due to their high rate discharge with relatively less heat dissipation [9,10] This technology has gained acceptance throughout the world market for their ever-increasing demands for communication, space, and defense applications because of its unique features such as long-term cycle life at deep depth of discharge (DoD). In this perspective, an attempt is made to summarize the information on Ni-MH battery technology with an emphasis to synthesize routes and bring insights into the chemistry involved and product formation mechanism in nickel hydroxide.
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