NiFe Batteries

As happens from time-to-time, my mind drifts to designing a solar-battery-inverter system in my head. This usually happens when it looks likely there will be power outages. With the power flickering periodically throughout the day, it was easy to get my mind to focus on the problem.

There are several main rechargeable battery types used to build stationary battery systems: the lead-acid types (open/closed/agm), lithium ion, and the one that I’m fascinated by: Nickel-Iron batteries.

Nickle-Iron batteries are old. The chemistry was developed in 1899 by Waldemar Jungner before Thomas Edison commercialized them starting from 1901. Edison’s company made batteries until 1975.

There are many things to not like about NiFe batteries: they are big, they are expensive (about $800/kWh), only open-cell designs exist so they require filling with water about once a month, high self-discharge rates (1%/day), and low round trip efficiency (about 65%).

The thing about them that consistently draws my attention is that they will last just about forever. Exiter Battery Corporation discontinued production of Edison’s Nickel-Iron batteries in 1975 and people are still using the batteries produced there, making the newest of these batteries 45 years old. There is even a documented instance of a battery from 1934 functioning at 50% capacity over a hundred years later, though I can’t for the life of my find a link to prove this.

These batteries can also be abused far beyond what other battery chemistries allow. 80% depth of discharge will not noticeably damage the battery. They can be overcharged without catching fire. They work at -22F. There is no long-term degradation in performance beyond the potassium hydroxide electrolyte reacting with atmospheric carbon dioxide and forming potassium carbonate which doesn’t work with the battery chemistry. This makes it necessary to refresh the electrolyte every 10 years or so.

It is the type of battery that you can will to your grand-kids as something other than a boat anchor.