Video Shows Why Recharging Kills Batteries

sciencehabit writes with this except from Science: "You may not give a lot of thought to what happens inside the battery of your laptop or cell phone, but to judge from this video, it's not a dull place. The battery in question is a miniature rechargeable lithium-ion device, and the clip shows what happens when it is charged. As lithium ions flow from the positively charged cathode into the 200-nanometre diameter wires of tin oxide that make up the negatively charged anode, the nanowires writhe and bulge, causing them to expand up to 2.5 fold. The wires also change structure from a neatly ordered crystal to a disordered glassy material. These distortions may explain why such batteries ultimately wear down. Knowing more about the process may help researchers develop longer lasting, and perhaps much smaller, batteries in the future."

Comments

What we don't know why or how?

[Twinbee]

I find it pretty amazing that we don't really still understand why these things wear out. It's a bit more forgivable for something like the human brain which is much more complicated, and where we can't easily poke around for obvious reasons.

But batteries?

I'm guessing our tools to get a peak of the microscopic realm must still be in their early stages technogically.

Re:What we don't know why or how?

[jeffmeden]

We do know why, and it's simple; parts of the insides of the battery end up in different places over time. The chemical reactions that take place during charging and discharging don't happen with perfect symmetry in forward and reverse, therefore each cycle will leave a little less reactive material than before. Making a battery with such perfect symmetry might be theoretically possible but it's not been achieved with any cost-beneficial success.

The bottom line is that batteries, like many other things, are only gradually improved since the process of production that establishes their characteristics can only be gradually improved. The lithium-ion system was a LONG time coming from the days of lead and nickel, but nevertheless it's just another stop on the road to better things.

Re:What we don't know why or how?

[koolguy442]

TEM Comments
This experiment was actually quite a bit harder to carry out than you think. (I imagine, as I wasn't involved in this study but do similar work.) Doing these experiments is like traveling to the moon in that the principles are relatively simple, but it's the details that are hard. While operation of the TEM is relatively easy, preparation of samples is extremely tedious even when the sample is relatively robust and isotropic and it doesn't matter where you need to look on the sample. Constructing a TEM specimen with the intention of looking at a tiny little feature of some larger piece of material is extremely difficult, taking hours or days, if even possible. It's even more difficult to prepare a specimen and have the right equipment set up to control and observe dynamic processes, such as lithium discharge from a single nanofiber. And viewing dynamics in a complicated system, like a battery, which contains at a very minimum three active components, anode, cathode, and electrolyte, is another order of magnitude harder. Plus you have to find a way to make the thing less than 20 nanometers thick and get it into a microscope at high vacuum without breaking or contaminating it, which is nontrivial. There's also the cost of the equipment, which is between $500,000 and $10 million for the microscope itself and another couple hundred thousand dollars for the specialized probes required to do this experiment. I do this for a living myself, as do many people across the world who are either pursuing or already have PhDs in microscopy and analysis, and if it were easy, it'd've already been done and we'd be out of the job.

Battery comments
We understand pretty much exactly why batteries wear out. Though the anodes in "real" batteries are usually some form of graphite, which expands less than 10% versus the SnOx in the video (~250%), there is still jostling of all the little powders that form the battery upon charging and discharging that eventually lead to the individual particles separating from the electrodes as a whole and essentially becoming dead micro-paperweights within the battery cell. It's just very hard to image them dynamically in a realistic operation because air and water vapor tend to destroy the materials nearly instantly.