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USA: Carbon Nanofibers Improve Silicon Electrodes for Li-ion Batteries, But Is It Enough?

For the last couple of years the big news for lithium-ion (Li-ion) batteries has been the replacement of graphite in the anodes with silicon.

This move from graphite to silicon has been eagerly pursued in order to address one of the fundamental operations of Li-ion batteries: the movement of lithium ions from the cathode to the anode and their storage there. The more lithium ions that the anode can store, the longer the battery will stay charged. The charge can be increased by a factor of ten by replacing the graphite with silicon.

But there is a drawback with these silicon electrodes. They swell to three times their original size when charged and the charging and discharging of the battery soon renders the silicon useless as an electrode in a battery. For this reason, researchers have been working with various nanostructured silicon materials that take advantage of the superior storage capacity of silicon but are not as susceptible to the deterioration caused by charge-discharge cycles.

Now researchers at Pacific Northwest National Laboratory (PNNL) are taking a closer look at why these nanostructured silicon electrodes perform better than the graphite variety. “The electrodes expand as they get charged, and that shortens the lifespan of the battery,” lead researcher Chongmin Wang at the Department of Energy’s Pacific Northwest National Laboratory, was quoted as saying. “We want to learn how to improve their lifespan, because silicon-carbon nanofiber electrodes have great potential for rechargeable batteries.”

The research, which was published in the journal Nano Letters, first tested how much lithium the electrodes could hold and how long they would last by putting the electrodes—which were made from carbon nanofibers wrapped by a thin layer of silicon—into a half-cell.
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