Everybody knows that lithium-ion batteries are the gold standard for energy storage, but there’s always room for improvement and some clever folks over at the University of Michigan have been tackling the dendrite problem. Dendrites on the lithium-ion battery might sound like something Mr. Scott should worry about, and it certainly is, so let’s take a look and see what the Michigan team is up to.
For those of you new to the topic, among many applications lithium-ion batteries have been the key to the development of the global electric vehicle market. No other mobility-friendly energy storage technology has come close — at least not yet.
The Dendrite Problem
Dendrites are nanoscale, fernlike growths that can occur in lithium-ion batteries. In addition to posing a potential fire risk, they cut down on efficiency. Here’s a good rundown from Lawrence Berkeley National Laboratory:
Over the course of several battery charge/discharge cycles, particularly when the battery is cycled at a fast rate, microscopic fibers of lithium, called “dendrites,” sprout from the surface of the lithium electrode and spread like kudzu [a highly invasive weed] across the electrolyte until they reach the other electrode.
An electrical current passing through these dendrites can short-circuit the battery, causing it to rapidly overheat and in some instances catch fire.
Former Energy Secretary Steven Chu is among those who have been tackling the dendrite problem, just to indicate how critical the issue is. He was working on it before he joined the Obama Administration, and after he finished his tenure there he jumped right back into it with a project focusing on carbon nanotubes.
Dendrites And Lightweighting
To be clear, gasoline also poses a potential — and very clear — fire risk, so electric vehicles and gasmobiles are even on that score. For that matter millions of drivers seem perfectly comfortable with the idea of speeding down a crowded highway while sitting on ten or so gallons of highly volatile liquid.
The point is that although the dendrite problem has been engineered down to an adequate level, if you can figure out a way to do it more effectively, at a lower cost, then you’re golden.
We’ve been hearing a lot about vehicle lightweighting recently (Ford, for example, just knocked 700 pounds off its F-150 pickup), so if you can resolve the dendrite issue in a way that makes your lithium-ion battery thinner and lighter, then you’ve hit double platinum.
The Bullet Proof Energy Storage Solution
That’s just what the U-M team has done.
If you know your Kevlar, you know that this iconic “Dare Bigger” DuPont product is made from aramid, a synthetic material related to nylon. It’s so strong that it can stave off bullets among other projectiles, although DuPont is eager to point out that it has a wide variety of uses.
In its “raw” state aramid resembles yellow fuzz, as you can see from the image above. It also happens to be a good insulator, and that is the key.
In a new paper just published at Nature.com titled “A dendrite-suppressing solid ion conductor from aramid nanofibers,” the U-M team described how they extracted nanofibers of aramid from Kevlar, and layered them on top of each other in the form of thin sheets to create a new membrane.
The basic idea was to engineer a membrane with pores big enough to allow lithium ions to hop through, but too small to admit dendrites.
As described by U-M, the tip of a dendrite fern ranges from 20 to 50 nanometers across, but conventional membranes typically have pores in the hundreds-of-nanometers range, allowing for relatively easy passage.
In contrast, the aramid fiber membrane has pores that only range between 15 and 20 nanometers, blocking all but the very smallest dendrites.
That takes care of those dendrites, now what about lightweighting? Well, it seems that the U-M team got a twofer. Because the aramid membrane is extremely thin, it improves energy density, so you can shrink the size of the battery cell and still get the same energy. Alternatively, you can have a battery cell the same size, but with more energy.
The next step for the team is to improve the flow of lithium ions through the membrane, with the aim of developing improved fast-charging (and fast-discharging) batteries.
Meanwhile, the team has already spun off a company called Elegus Technologies to market the new membrane material, with commercial production expected late in 2016.
For the record, the research was funded partly by the National Science Foundation, the Office of Naval Research, and the Air Force Office Scientific Research, so go ahead and give yourselves a pat on the back all you taxpayers out there for yet another energy storage breakthrough.
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