Stringed Nano Beads Could Improve Lifespan of Lithium-Ion Batteries

Researchers continue their work to improve lithium-ion battery design with the latest hope for a longer lifespan found in silicon nanotechnology developed at the University of Maryland.

A team in the university's Nanocenter that included YuHuang Wang, an assistant professor in the department of chemistry and biochemistry, has created nanoscale beads of silicon, about 10,000 times thinner than a piece of paper, that could extend the number of charging cycles lithium-ion batteries can go through by about 10 times the current design. This potentially could allow electric vehicles to travel farther on a single charge, as well as have applications for mobile phones, cameras, and other devices that use lithium-ion batteries.

Graphite is typically the electrode used in current lithium-ion battery design, but silicon is actually a better material, storing up to 10 times more lithium ions than graphite. However, silicon has been tricky to work with because it tends to crack and break with overuse, though researchers have been working for some time to solve this problem.

The work is reminiscent of similar research being done at the University of Southern California under the tutelage of Chongwu Zhou, professor at the USC Viterbi School of Engineering. Researchers there replaced the graphite anodes that are typically used in the batteries with silicon nanowires with pores that allow the silicon to expand and contract without breaking.

Wang and his team took a slightly different approach, but the concept for how the silicon holds together well under the charging and discharging process is quite similar. The University of Maryland researchers, which also included mechanical and materials engineering scientists, grew beads of silicon on a carbon tube less than 50 nanometers wide. They accomplished this by attaching part of a molecule sometimes found in food flavorings along the tube and then flooding it with a gas containing silicon.

Researchers then charged the silicon with lithium ions, creating a more resilient structure for the silicon because the beads are more flexible than a typical flat silicon coating, they said. This resiliency is in part thanks to the organic molecule used to attract the silicon to the tube, which allowed it to bond more strongly and is thus less likely to break during the electrochemical process.

"As the nanobeads of silicon were charged by the lithium, they grew and shrank without cracking or ripping," Wang said in a news release on the university's website.

Researchers published an article about their development in the journal ACS Nano, as well as posted a video online of the beads in action under an electron microscope.

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