Rechargeable lithium-ion batteries currently have graphite anodes. Manufacturers have tried to boost charge by using other materials, such as silicon, but the anodes degrade too quickly. Turns out that partnering silicon with a polymer in seaweed called alginate can boost capacity in rechargeable lithium-ion batteries by eight times, according to new research.
Stephen Cass of Technology Review reports:
Researchers at the Georgia Institute of Technology and Clemson University think they might have found the ingredient that will make silicon anodes work — a common binding agent and food additive derived from algae and used in many household products. They say this material could not only make lithium-ion batteries more efficient, but also cleaner and cheaper to manufacture.
Lithium-ion batteries store energy by accumulating ions at the anode, and then these ions travel via an electrolyte to the cathode. Graphite anodes are made by spreading on metal foil a mixture of graphite powder and a polymeric binder called polyvinylidene fluoride (PVDF) dissolved in a solvent called NMP.
Cass explains the problem with silicon that alginate helps to overcome:
Silicon particles swell as the battery is charged, increasing in volume up to four times their original size. This swelling causes cracks in the PVDF binder, damaging the anode…The Georgia Tech and Clemson scientists show that when alginate is used instead of PVDF, the anode can swell and the binder won’t crack. This allows researchers to create a stable silicon anode that has, so far, been demonstrated to have eight times the capacity of the best graphite-based anodes.
Alginate is a natural polysaccharide made from brown algae, including large kelp. Alginates “are attractive because of their uniformly distributed carboxylic groups,” according to a Clemson University press release.
Using alginate could be cheaper and more environmentally-friendly to manufacture lithium-ion batteries for several reasons. First, alginate is a plant-based material that can be extracted via a soda-based process from plentiful and inexpensive seaweed. Second, manufacturing the anodes would be a water-based process, and not include toxic materials such as PVDF or NMP.
Redesigning batteries to accommodate the new anodes wouldn’t be necessary. “The new alginate electrodes are compatible with existing production techniques and can be integrated into existing battery designs,” Gleb Yushin, one of the researchers and director of the Center for Nanostructured Materials for Energy Storage at Georgia Tech, said in a press release.
More research is needed, however, to create an enhanced cathode. Cass writes:
The full potential of a silicon anode can’t be exploited until researchers develop a matching cathode capable of handling the same amount of lithium ions. But even with existing cathodes, alginate-silicon anodes could increase the capacity of lithium-ion batteries by 30 to 40 percent, according to Yushin.
Source: “Battery Storage Could Get a Huge Boost from Seaweed,” Technology Review, 9/8/11
Source: “Seaweed extract gives lithium batteries a boost,” Chemistry World, 9/8/11
Source: “Powered by seaweed: Polymer from algae may improve battery performance,” Clemson University press release, 9/8/11
Image by NOAA’s National Ocean Service, used under its Creative Commons license.
Rachel Petkewich is a freelance science writer and editor. She has worked as a research scientist in the chemical industry and spent eight years as a staff writer and editor at various science journals and magazines, including Chemical & Engineering News.