Researchers at the University of Cambridge are claiming to have created a lithium-air battery chemistry that solves many of the outstanding problems with that design and could revolutionize the battery industry in a way not seen since the introduction of lithium-ion. That’s a hefty claim for any organization. But if the claims prove true, the research teams might not be exaggerating.
Lithium-ion batteries have given us electric vehicles, laptops and smartphones, and much of the modern digital ecosystem, but they aren’t particularly power efficient or energy dense. Lithium-ion’s energy density (measured either in terms of weight or volume) is terrible compared with just about everything.
You’ll see zinc-air batteries. These may pale in comparison to the fossil fuels, but they illustrate a tremendous improvement over the status quo. Lithium-air batteries can theoretically pack far more power than zinc air batteries. Estimates vary for the two chemistries, but lithium-air batteries have a theoretical energy density of 18.75MJ/kg (including oxygen) and 43MJ/kg (excluding oxygen). Either way you slice it, this battery technology is lighter and far more energy dense than lithium-ion. Smartphones and laptops with lithium-air batteries at current lithium-ion weights and sizes wouldn’t need an asterisk to claim “All day” operation.
They’d just offer it.
The lithium-air (top bar) against other types of batteries, including sodium-air, lithium-sulfur, and lithium-ion. Note that the energy density of lithium-air is up to 10x higher than lithium-ion.
So where’s the batteries?
Here’s the ten-thousand-foot view of the problem: Building a better battery than lithium-ion is easy, and we’ve known how to do it since at least the 1970s. Multiple primary cell batteries (non-rechargeable) are known that offer 4x to 8x better energy density than conventional lithium-ion batteries — though, of course, these batteries have to be replaced, since they can’t be recharged. A Tesla Model S-equivalent vehicle that travels 2,000 miles per charge, but needs $10,000 worth of batteries, isn’t particularly practical.
Creating higher energy densities is easy. But mass producing batteries that won’t explode, suffer thermal runaway, are durable, don’t produce toxic byproducts during the charge/discharge cycle, and are inexpensive is extremely difficult. Many of these problems have held lithium-air batteries back from commercialization — such designs degrade rapidly when recharged, are damaged by the presence of water (a problem on planet Earth), or don’t hold up under multiple charge cycles. A battery that only retains 90% of its charge after 5 cycles and degrades to 50% charge after 10 cycles, again, isn’t very useful.
The University of Cambridge research “relies on a highly porous, ‘fluffy’ carbon electrode made from graphene (comprising one-atom-thick sheets of carbon atoms), and additives that alter the chemical reactions at work in the battery, making it more stable and more efficient.” “What we’ve achieved is a significant advance for this technology and suggests whole new areas for research — we haven’t solved all the problems inherent to this chemistry, but our results do show routes forward towards a practical device,” said Professor Clare Grey of Cambridge’s Department of Chemistry, the paper’s senior author.
The new design discussed in the paper relies on lithium hydroxide, and is far more water-tolerant than previous designs. The team redesigned the battery electrode and shifted the makeup of the electrolyte, reducing the voltage gap between the charge and discharge states. Dendrite formations, however, remain a problem, and the demonstrator battery can only be cycled in pure oxygen. That’s a significant problem for any battery that’s intended to run in the atmosphere. These barriers are part of why the researchers are still cautioning that their cells remain a decade away from commercial use.