Nickel Metal Hydride Battery

nickel metal hydride battery

The Nickel Metal Hydride battery has a nickel-hydroxide cathode, a metal hydride (a variety of metal alloys are used) anode, and aqueous potassium hydroxide electrolyte. This is a rechargeable battery chemistry that has been superseded by lithium ion, but has seen a lot of use in Toyota hybrids.

The overall reaction is:

2NiOOH + MH <=> Ni(OH)2 + M

Advantages:

  • High efficiency
  • Environmentally friendly
  • Wide operating temperature range: -30°C to +65°C
  • High abuse tolerance to overdischarging and overcharging
  • Relatively maintenance free
  • Long cycle life: 600 to 1200 cycles to 80% DoD
  • Below 40% SoC the internal resistance increases due to electrode and transport kinetics which reduces the available power
  • Above 80% SoC pressure within the cells causes the onset of hydrogen exchange which decreases the overall specific power
  • The Toyota Prius kept the cells within a 5% window around 56% SoC so as to prolong life, increase safety and ensure a flat voltage profile.

Disadvantages:

  • Low energy density compared to Lithium Ion
About Nigel 279 Articles
Have been making models since I was around 7 years old and using a lathe from the age of 11, a self taught engineer with a passion for making model engines.

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