I said we needed to sort the wheat from the chaff. Where better to start than at the beginning? There a number of descriptions of how a nickel-iron battery works offered on the web. Most are close to the truth while many are wildly inaccurate.

The first point of confusion arises from the fact that one typically expects a cathode to be the emitter of electrons. However, this is only true externally of a battery. Internally things are backwards. Electrons flow from the positive terminal to the negative. The battery’s cathode is the positive electrode. This point is not unique to nickel-iron batteries but it is important to understand nonetheless. The anode then is the terminal that sends electrons out into the cold cruel world to do work until they return to the cathode spent and thoroughly exhausted.

Remember: The anode is the negative terminal. Like the cathode, I’m quite positive about this.

It’s been claimed that the nickel-iron battery (NiFe battery) is a storage battery having a nickel (III) oxide-hydroxide cathode and an iron anode, with an electrolyte of potassium hydroxide. (Lithium hydroxide is added to improve performance.)

It’s not clear if this is a description of the battery in a charged or discharged state and as we shall see, this will be the second point of confusion to clarify. In any event, the NiFe cell is composed of the following components:

1. A Positive Electrode (the Cathode)
2. A Negative Electrode (the Anode)
3. An Electrolyte (KOH or possibly NaOH, w/LiOH)
4. A casing to safely contain them (Nickel plated or Alkali resistant)

Here are some of the specifics gleaned from Edison’s Patents and Battery Manual:
• Negative Electrode is an Iron Oxide (Wait! What? Which? Not pure iron?)
• Positive Electrode is a Nickel Oxide (Oh sure, there are at least 3 of them.)
• Nominal cell output voltage is 1.2 Volts/cell
• Charge voltage is in the 1.6-1.7 Volt /cell range
• Float voltage is 1.4 Volts/cell
• Equalization charge is 1.65 Volts/cell
• Electrolyte is a 21%-30% solution of KOH in distilled water
• Specific gravity is around 1.2-1.3 (and does not indicate state of charge)
• Charge is about 13-15 watt hours per pound of cells
• Can accept 3x charge rate for 30 minutes provided solution stays < 115 ˚ F