When it comes to soothing EV range anxiety, the lithium-sulfur combo offers a lot of promise, but until now there’s been a catch (there’s always a catch). Li-S batteries have a much shorter life cycle than the gold standard, lithium-ion, which makes them a poor bet for the mass market. However, researchers at Pacific Northwest National Laboratory (PNNL) may be on to a solution.
If the research leaps the Valley of Death from the lab to the market, that could spell the end of the gasmobile as we know it. According to PNNL, an Li-S battery could store up to four times more energy per mass than an Li-ion battery.
The Sulfur Cure For EV Range Anxiety
As noted above, Li-S offers far greater energy storage potential than Li-ion, but as of right now if you had an Li-S battery in your EV, you would have range anxiety on an epic scale.
The problem is the sulfur cathode (the positively charged electrode). The cathode sits in an electrolyte bath and researchers have been stuck on how to get the sulfur to stop disintegrating into the bath.
Since the disintegration is not reversible, the cathode quickly loses sulfur and there goes your Li-S battery.
A Better Sulfur Battery
Last spring, researchers at Oak Ridge National Laboratory announced one pathway to solving the life cycle problem last spring, based on a solid electrolyte in combination with a sulfur-enriched cathode and a lithium anode (the negatively charged electrode).
The new PNNL solution focuses in on a “unique, powdery nanomaterial” that can ensnare polysulfides in the cathode. Called a metal organic framework, it is a crystalline compound of metal clusters linked by organic molecules, which self-assemble into a porous structure.
If that sounds familiar, you may be thinking of gas-trapping technology based on metal organic frameworks. Their use in EV batteries represents a new field.
Think of a metal organic framework as a high tech, nanoscale sponge and you’re on the right track. Since nickel interacts strongly with sulfur, the heart of the PNNL “sponge” is a positively charged nickel center.
So far, the research team has been able to get their Li-S battery to retain 89 percent of its initial capacity after 100 charging cycles. The next step is to improve the storage capacity of the cathode and scale the whole thing up.
EV Supply Chain Anxiety
One of the concerns about transitioning to a full-on global EV market is the availability of specialty materials that go into EV batteries.
That opens up a whole new can of worms in terms of supply chain geopolitics.
In that context, sulfur does not open up a new can of worms. It is a common material (“practically free,” enthuses one enthusiastic Oak Ridge scientist), and vast quantities are produced as a byproduct of fossil fuel refining. Researchers at the University of Arizona are already finding that waste sulfur from fossil fuel refining can be used in Li-S batteries (it can also be converted to plastic, for that matter).
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