Wed. Sep 28th, 2022
Cylinder with nickel and hydrogen

A prototype test cell for nickel-hydrogen batteries.

Wei Chen, Yang Jin, Jie Zhao, Nian Liu and Yi Cui

Battery technology is hugely important to a world that uses more and more renewable energy. Renewable energy is variable – electricity cannot be produced if the sun is not shining and the wind is not blowing – so being able to store excess electricity made when those renewable sources to be producing is the key to putting more of it on the net.

The problem is that very large batteries can be expensive. There has been a lot of research into making batteries lighter and smaller, given the focus we have placed on consumer technology over the past decades. But now, researchers are relaxing size and weight restrictions and are instead trying to find battery chemistry that is cheap and extremely durable.

Researchers from Stanford and the Georgia Institute of Technology (GT) suggest a new nickel-hydrogen battery configuration that could be cheap enough for mass adoption on the grid. Traditional nickel-hydrogen batteries can last up to 30,000 cycles and are extremely reliable and durable, making them ideal for mains use. But they often rely on a platinum catalyst which can make them unaffordable for large installations.

In the new work, the researchers replaced the platinum that would have been part of a nickel-hydrogen battery and replaced it with a “bifunctional nickel-molybdenum-cobalt electrocatalyst as the hydrogen anode.” The estimated cost of a full version of this battery is approximately $83 per kilowatt hour, below the Department of Energy’s 2040 target of $100/kWh target for grid-connected storage. By comparison, last year Tesla appeared to offer a record price for the installation of lithium-ion batteries at the Hornsdale wind farm in Australia, at $250/kWh.

Reduce costs

The researchers started their work by building a manganese-hydrogen battery, which stores energy by splitting water and producing hydrogen in a reversible reaction. They eventually replaced the manganese with a nickel-dominant cathode that achieved a superior 35 milliamp-hours (mAh) per square centimeter. They included the nickel-molybdenum-cobalt electrocatalyst to lower the battery’s cost, and with a wet electrolyte (a potassium hydroxide solution), the battery had an energy density of about 140 watt-hours per kilogram. The researchers saw no loss of capacity over 1500 cycles.

The battery prototype is housed in a cylindrical container, with the cathode and anode coiled “similar to the manufacture of commercial AA batteries,” notes the paper.

The nickel-hydrogen battery was found to have a Coulomb efficiency of about 98.5 percent. Coulomb efficiency is a measure of how well electrons are transferred through the system.

The researchers also tried to charge the battery under different current densities. Sometimes high currents can cause a battery to permanently lose its discharge capacity, but this nickel hydrogen battery seemed to hold up well until the higher current range was applied, then the Coulomb efficiency decreased slightly.

Of course, this battery is just a prototype, albeit a promising one. The researchers hope to refine their system and explore ways to further reduce the cost of this next-generation rechargeable battery. But hitting $83 per kWh would be a significant step forward for grid-scale storage.

PNAS2018. DOI: https://doi.org/10.1073/pnas.1809344115 (About DOIs).

By akfire1

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