BATTERY TECHNOLOGY Have Finnish researchers found a route to silicon battery anodes?

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Researchers at the University of Eastern Finland have reportedly combined mesoporous silicon microparticles made from organic waste with carbon nanotubes to improve the performance of silicon anodes in lithium-ion batteries.

According to industry commentators, the use of silicon as the anode in a li-ion battery represents the “holy grail” for researchers. “In the future, silicon will gradually replace carbon as the anode material in Li-ion batteries,” said the university in a statement.

This is because silicon has an energy storage capacity around 10 times greater than the graphite anodes currently found in li-ion batteries. “Using silicon in the anode makes it possible to even double the capacity of the total battery cell.” However, silicon is unstable; silicon anodes tend to swell and shrink, causing the electrode to degrade over time. So far, researchers have not been able to find a way to produce pure silicon anodes.

According to the Finnish research team, mesoporous silicon microparticles are less susceptible to this damage. Porous materials have previously been made for use in anodes but by using processes that are unlikely to be able to scale from the laboratory and into real-world applications.

Now, the Finnish researchers claim that they have managed to make mesoporous silicon (PSI) microparticles by using the ash of barley husks. This ash contains natural amorphous porous silica structures, and these can be chemically converted into porous silicon structures via a process known as “chemical conjugation”. These silicon structures are then combined with carbon nanotubes (CNTs) to create a hybrid material. The research team found by using the right conjugation method, both conductivity and durability of the anode was improved.

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The team admits that this has been done before, however, their twist is that they have found a way to pre-treat the PSI and CNTs in ways that allows them to bond chemically after mixing. “With the right type of conjugation, also the electrical conductivity and mechanical durability of the material was improved”. The result is a silicon composite with an average discharge capacity of 2Ah/g at a rate of 0.1C (472mAh/g at 1C).

Next, the research team hopes to produce a complete silicon anode with a solid electrolyte. “The progress of the Li-ion battery research is very exciting,” said University of Eastern Finland professor Vesa-Pekka Lehto, “and we want to contribute to the field with our know-how related to mesoporous structures of silicon.”

The team’s research paper was published in Nature Scientific Reports on March 27.

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