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Nickel-metal hydride batteries

This article explores how nickel-metal hydride batteries work.

Nickel-metal hydride (NiMH) batteries were introduced to the market in 1989 and are commonly used in portable devices like phones and computers (Berg, 2015).

These batteries work by moving hydrogen ions (H⁺ or protons) within the battery to store and release electrical energy.

Inside the battery there are two main parts: the positive side made of nickel oxyhydroxide (NiOOH) and the negative side made of metal alloys like nickel-titanium alloys (TiNi₂ and Ti₂Ni) and nickel zirconium (ZrNi). These two parts are separated by a membrane and surrounded by a liquid electrolyte containing potassium hydroxide (KOH).

When the battery is in use (discharging), the hydrogen ions move from the metal alloy toward the positive side and react with hydroxide (OH^–). When the battery is being recharged, the hydrogen ions move back from the positive side to the negative. This back-and-forth movement of hydrogen ions is what allows the battery to store and release energy (Berg, 2015; Skyllas-Kazacos, 2010).

Diagram showing the flow of ions within a nickel-metal hydride battery. _{Based on information from Berg, 2015 and Skyllas-Kazacos, 2010}

Hopefully you have completed the task in Step 1.8, to research nickel-cadmium (NiCad) batteries. Compare what you’ve learned about NiCad batteries to NiMH, in terms of their charge/discharge mechanism and advantages and disadvantages. Share some findings in the comments below.

References

Berg, H. (2015). Batteries for electric vehicles: materials and electrochemistry. Cambridge University Press.

Skyllas-Kazacos, M. (2010). Electro-chemical energy storage technologies for wind energy systems. Stand-alone and hybrid wind energy systems, 323-365.