Lithium ions, as the name implies, work by shuffling lithium atoms between a battery’s two electrodes. So, increasing a battery’s capacity is largely about finding ways to put more lithium into those electrodes. These efforts, however, have run into significant problems. If lithium is a large fraction of your electrode material, then moving it out can cause the electrode to shrink. Moving it back in can lead to lithium deposits in the wrong places, shorting out the battery.
Now, a research team from Stanford has figured out how to wrap lots of lithium in graphene. The resulting structure holds a place open for lithium when it leaves, allowing it to flow back to where it started. Tests of the resulting material, which they call a lithium-graphene foil, show it could enable batteries with close to twice the energy density of existing lithium batteries.
Lithium behaving badly
One obvious solution to increasing the amount of lithium in an electrode is simply to use lithium metal itself. But that’s not the easiest thing to do. Lithium metal is less reactive than the other members of its column of the periodic table (I’m looking at you, sodium and potassium), but it still reacts with air, water, and many electrolyte materials. In addition, when lithium leaves the electrode and returns, there’s no way to control where it re-forms metal. After a few charge/discharge cycles, the lithium electrode starts to form sharp spikes that can ultimately grow large enough to short out the battery.
To have better control over how lithium behaves at the electrode, the Stanford group has looked into the use of some lithium-rich alloys. Lithium, for example, forms a complex with silicon where there are typically over four lithium atoms for each atom of silicon. When the lithium leaves the electrode, the silicon stays behind, providing a structure to incorporate the lithium when it returns on the other half of the charge/discharge cycle.
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Source: Ars Technica