A battery that has crucial parts made from seaweed could pave the way to greener energy storage.
Most batteries in smartphones, electric cars and laptops rely on lithium. This metal is in short supply, though, and is often mined by workers in poor conditions and is refined using methods that damage the environment. The shortage of lithium is only likely to worsen as the world shifts away from fossil fuels towards using more renewable electricity stored in batteries.
at the University of Bristol, UK, says finding a replacement battery technology is essential, but that there are still problems to overcome for one of the big contenders: sodium-metal batteries. In these, sodium is used instead of lithium.
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When sodium-metal batteries are charged and depleted over time, metal deposits known as dendrites build up on their electrodes, eventually growing so large that they puncture the non-conductive separator between them and cause a short circuit that destroys the battery.
Eichhorn and his team have now solved this by creating a separator made, in part, from brown seaweed harvested on the Scottish coast. He says that because sodium itself can easily be harvested from the salt in seawater, that effectively means the critical parts of these new batteries can be 鈥渕ade out of the sea鈥�.听
To make the separator, the researchers spun a plastic called polyetherimide into fibres and impregnated these with cellulose nanocrystals about 10 nanometres in diameter and 200 nanometres long that they had extracted from the seaweed. They ejected this composite material through a fine syringe by applying a charge of up to 30 kilovolts in a process called electrospinning. The resulting fine threads can form battery separators that are strong enough to resist puncturing and allow long-lasting batteries.
鈥淣ormally, seaweed doesn鈥檛 have a particularly high cellulose content, but this one does, this cultivar. So we extracted it from that,鈥� says Eichhorn. 鈥淵ou can extract these nanocrystals from anything: wood, miscanthus, flax. But the seaweed ones are interesting because they actually are quite long, and that鈥檚 critical for reinforcement.鈥�
The use of seaweed-derived crystals has another benefit in that, in experiments, it allowed for greater storage capacity and efficiency than previous materials, increasing the lifetime of the battery. The team found that the design continued to work well even after 1000 charging cycles.
Advanced Materials
