New “Designer” Energy Storage Breakthrough Packs 3 Football Fields Into 1 Ounce of Carbon

Lithium-ion technology is still the gold standard for energy storage as demonstrated by the popularity of the new Powerwall battery, Tesla Energy’s much-publicized foray into Li-ion energy storage for homes and businesses. However, some new technologies are sneaking up behind. In the latest development, lithium-sulfur batteries could benefit from a new “designer carbon” engineered by a team of researchers at Stanford University.

Why Natural Is Not Better, Energy Storage Edition

The new designer carbon material could have a variety of applications, but the Stanford University team has zeroed in on the energy storage potential, particularly in respect to lithium-sulfur (Li-S) batteries.

The new material is actually a synthetic form of bio-based activated carbon. For those of you new to the topic, activated carbon is a common material that shows up in water filters and deodorizers, among many other things — but not energy storage devices, at least not yet.

Inexpensive forms of activated carbon are typically made from coconut shells, which involves a lot of high-temperature processing and chemical finishing. The result is a material rich in nanoscale pores, which gives it a high surface area ideal for storing electrical charges.

However, this “natural” form of activated carbon falls flat in terms of transporting a charge, partly because there is little connectivity between the pores. Here’s lead researcher Zhenan Bao describing the problem:

With activated carbon, there’s no way to control pore connectivity. Also, lots of impurities from the coconut shells and other raw starting materials get carried into the carbon. As a refrigerator deodorant, conventional activated carbon is fine, but it doesn’t provide high enough performance for electronic devices and energy-storage applications.

The Designer Carbon Solution

As a workaround, the Stanford team created its own synthetic sheets of carbon from a hydrogel polymer (hydrogel is fancyspeak for a class of super-absorbing “smart” materials). To activate the material, they added potassium hydroxide, which also increased its surface area.

The result is a carbon material with characteristics that can be controlled in two ways: by using different polymers and organic linkers, and by changing the temperature of the fabrication process.

Here are a couple of snippets from the new study:

For example, raising the processing temperature from 750 degrees Fahrenheit (400 degrees Celsius) to 1,650 F (900 C) resulted in a 10-fold increase in pore volume.

Subsequent processing produced carbon material with a record-high surface area of 4,073 square meters per gram – the equivalent of three American football fields packed into an ounce of carbon. The maximum surface area achieved with conventional activated carbon is about 3,000 square meters per gram.

The End Of The Lithium-Ion Era

Li-S energy storage has important advantages over Li-ion in terms of cost, energy density, and toxicity, but until recently, some major drawbacks have stymied the development of Li-S batteries.

Read more: New “Designer” Energy Storage Breakthrough Packs 3 Football Fields Into 1 Ounce of Carbon