Credit: © 2009 ACS

In recent years many researchers have been working to improve the performance of lithium-ion batteries, which can power electric cars or store the energy generated from renewable sources. Now a team including Jaephil Cho at Ulsan National Institute of Science & Technology in Korea and Yi Cui at Stanford University in the US have shown that energy storage can be improved by building the battery anode from silicon nanotubes1.

The use of silicon instead of graphite as an anode material can greatly increase the total energy capacity of a battery, because each silicon atom incorporates up to 4.4 lithium ions. However, the silicon tends to expand during use, meaning that the battery can only be recharged a few times before it becomes unusable.

To overcome this problem, Cho, Cui and co-workers made parallel bundles of silicon nanotubes coated in carbon. Each nanotube presents a large functional surface area for the battery, because lithium ions in the electrolyte can accumulate both inside and outside the nanotubes.

The researchers built a lithium-ion cell including the silicon nanotubes and found it had a ten times higher capacity than commercial cells with graphite anodes. More importantly, the new cell retained its high performance even after 200 cycles of charging and discharging.