Energy

Molecular pulleys ease the strain for lithium-ion batteries

Stretchy polymers could point the way forward for silicon anodes.

Silicon is a promising material for use as anodes in lithium-ion batteries, because it can take up more lithium per unit of volume or mass than can graphite, the material currently used.

This means that it could store more energy. But engineers have struggled to make usable silicon anodes because they expand in volume by up to 400% during charging and quickly disintegrate.

Researchers have now devised a molecular-scale ‘pulley system’ that could solve the problem. Jang Wook Choi and his colleagues at the Korea Advanced Institute of Science and Technology in Daejeon attached polysaccharide rings to silicon crystals and then threaded strings of polyethylene glycol polymer through these rings.

As the silicon expanded and contracted, the strings stretched and slid through the rings, keeping the material intact.