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Published on June 24th, 2014 | by Chris Demorro

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Why Do Lithium-Ion Batteries Degrade When Charged?

June 24th, 2014 by Chris Demorro
 

tesla-battery-packWe all know that over time, the ability of a battery to hold a charge diminishes with repeated recharged. But we haven’t known exactly why that is, especially in lithium-ion batteries, the cornerstone of the electric vehicle industry, until now that is.

Gizmodo reports that researchers seem to have figured out the physical properties of lithium-ion battery decay, and it could lead to longer lasting batteries.

The results of the findings were published in two recent studies, with Huolin Xin, a researcher at Brookhaven’s Lab for Functional Nanomaterials, co-authoring both stories. Xin sums up her findings as such;

“We discovered surprising and never-before-seen evolution and degradation patterns in two key battery materials. Contrary to large-scale observation, the lithium-ion reactions actually erode the materials non-uniformly, seizing upon intrinsic vulnerabilities in atomic structure in the same way that rust creeps unevenly across steel.

Consider the way snowflakes only form around tiny particles or bits of dirt in the air. Without an irregularity to glom onto, the crystals cannot take shape. Our nickel oxide anode only transforms into metallic nickel through nanoscale inhomogeneities or defects in the surface structure, a bit like chinks in the anode’s armor.

As the lithium ions race through the reaction layers, they cause clumping crystallization—a kind of rock-salt matrix builds up over time and begins limiting performance. We found that these structures tended to form along the lithium-ion reaction channels, which we directly visualized under the TEM. The effect was even more pronounced at higher voltages, explaining the more rapid deterioration.”

So what’s it all mean? It means that armed with this new information, battery designers can seek ways to build more robust batteries that are less concerned with fast-charging or repeated charging. That’s a pretty big deal when you think about what it means for electric vehicles.

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About the Author

A writer and gearhead who loves all things automotive, from hybrids to HEMIs, can be found wrenching or writing- or esle, he's running, because he's one of those crazy people who gets enjoyment from running insane distances.



  • Chris_in_Raleigh

    Does anyone know if its better to charge to 100% and run down to ~20%, or to charge to 80% and run down to ~0%?

    I have a Nissan Leaf. I charge to 80% at home multiple times per day and that’s almost always just fine. But occasionally, I get down under 10% and wonder if I should have planned ahead and charged to 100% that day.

    Does is matter?

    (FWIW, after 20k miles, I still have 12 of 12 bars of capacity)

  • PaulScott58

    Chris, I don’t think it matters much at all. Nissan suggests keeping the charge within the 20%-80% range to the extent possible, but charging to 100% and driving to 0% is fine now and then. It does make more of a difference if you charge to 100% and leave it full for a long time, like many days. Same for driving it to near 0% and then leaving it empty for many days. I don’t hesitate to charge to 100% if I know I’m going to drive it the next day. And it’s not a good idea to leave it empty since you’re likely to need the car soon, so best to charge to at least 80% for that reason.

    All that said, it’s not as big a problem since Nissan announced the very reasonable price of $5,500 for a new pack. A lot of LEAF owners are now breathing easy knowing that when their pack no longer gives them enough range, they can easily swap our for a new one.

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