As anyone with a smartphone, laptop or indeed a whole electric car will know, lithium-ion batteries degrade over time.

Each time you charge and discharge the batteries, they lose a little capacity. Day to day you don't really notice, but over a year, or two, it means being able to use your phone (or car) a little less.

Now, research scientists supported by the Department of Energy have discovered the physical properties behind this loss in capacity.

As Gizmodo reports, it's all to do with how ions moving through the battery change the physical structure of the electrodes.

In a lithium-ion battery, lithium ions move from the anode to cathode through a non-aqueous electrolyte. As they do so, the physical structure of the electrodes is very slightly altered, at an atomic level.

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As ions move across the anode when discharging, they wear away at irregularities on its surface in a non-uniform way. Huolin Xin, a materials scientist at Brookhaven Lab's Center for Functional Nanomaterials (CFN), describes it as the same kind of non-uniform structure as rust creeping across steel.

Unfortunately, these imperfections are necessary for the battery to function. Just as snowflakes form around microscopic dirt particles, explains Xin, so too do particles in a battery require these irregularities to form upon.

The cathode doesn't escape charge-reducing effects, either.

Here, as lithium ions move across the electrode when charging, they form a kind of rock-salt, which acts as an electrically-insulating crust. The thicker this crust, the less charge the battery will accept. Xin says this latter effect is even more pronounced at higher voltages.

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Neither is particularly good for your battery's capacity. So finding a fix for both could be the clue to batteries that retain capacity for much longer periods.

Xin says it might be possible to coat the cathodes with elements that resist crystallization--allowing ions to pass freely between anode and cathode.

A commercially-realistic timescale for such advances may mean years of work, rather than months. But for electric car owners--and anyone else with an electronic device--it could be a step towards vehicles that achieve the same range whether they're brand new, or a decade old.

[Hat tip: Alex Salvador]

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