Replacing Silicon with Graphite
In view of the environmental and capacitance pitfalls that come from using graphite-based anodes in lithium-ion batteries (LIBs), UEF scientists (including junior researcher Timo Ikonen, and Professor Vesa-Pekka Lehto) have developed a hybrid material that suggests that silicon should—and perhaps eventually will—replace graphite.
According to UEF’s release, silicon is ten times higher in its capacity than graphite, and a LIB that holds a silicon anode may see as much as a two-fold improvement in the total capacity of the battery cell itself. The researchers also intend to improve on what is currently the unstable nature of LIBs’ solid electrolyte interfaces.
Research Challenges, Solutions, and Processes
The above is not to say, however, that making batteries more silicon-based is completely safe.
At the time of writing, for instance, battery manufacturers have to consider a balancing act: silicon may have an excellent ability to absorb lithium ions—but previous research has long shown that it swells greatly when doing so (whereas graphite’s size changes very little under the same conditions). The UEF’s research also explains that presently no technology exists to produce feasible anodes from silicon alone.
Nevertheless, the Eastern Finland-based researchers’ current approach is to minimise the reducing effect of silicon’s high charging rates by developing a hybrid material that consists of mesoporous silicon (PSi) microparticles (produced from the agricultural residue barley husk ash—for want of a lower carbon footprint than tradition silicon production) and carbon nanotubes (CNTs).
The PSi and CNTs had to become chemically bonded (a process known as chemical conjugation, the specifics of which the UEF researchers discuss in Nature Research’s Scientific Reports).
A scanning electron microscope’s photograph of the University of Eastern Finland’s (UEF) hybrid material, created in the interest of improving lithium-ion battery performance. Image Credit: UEF via TechSpot.
Research Implications and Intentions
The discovery of UEF’s hybrid material follows its late-2017 paper that concluded that dealing with silicon in batteries required the use of particles at the micrometre, or μm, level (ideally between 10 μm and 20 μm in size). This challenged original research that nanometre-level particles are ideal for implementing silicon within batteries.
It was in that same paper that UEF’s Professor Vesa-Pekka Lehtol stated that “the silicon we’ve been using is too expensive for commercial use, and that’s why we are now looking into the possibility of manufacturing a similar material from agricultural waste, for example from barley husk ash”. Less than three years on, and it’s clear that the UEF’s interest in a less resource-intensive material has paid dividends.
Improving Li-ion Battery Sustainability
Now, having realised the use of barley husk ash, as well as PSi microparticles and NCTs, the University of Eastern Finland researchers have made great strides in their aim to improve, not only lithium-ion battery performance, but also the devices’ overall efficiency and sustainability—particularly in the interest of climate neutrality.
Alongside their eco-friendly use of barley husk ash, the researchers believe their work will benefit from Europe’s Battery 2030+ roadmap, which (to quote the document’s Executive Summary) aims to one day render battery production processes ‘more sustainable, safe, ultrahigh performing, and affordable’:
“Hopefully, the EU will invest more in the basic research of batteries to pave the wave for high-performance batteries,” says Letho. “The Battery 2030+ roadmap would be essential in supporting this progress.”