rom Stephen Cass in the MIT Technology Review, a report that researchers at the Georgia Institute of Technology and Clemson University have found that a polymer alginate made from brown algae—widely used as a gelling agent and a food additive – may make lithium-ion batteries more efficient, as well as cleaner and cheaper to manufacture.
Lithium-ion batteries store energy by accumulating ions at the anode. During use, these ions migrate, via an electrolyte, to the cathode. The anodes are typically made by mixing an electroactive graphite powder with a polymer binder—typically polyvinylidene fluoride (PVDF) –dissolved in a solvent called NMP. The resulting slurry is spread on the metal foil used to collect electrical current, and dried.
If silicon particles are used as the basis of the electroactive powder, the battery’s anode can hold more ions. But 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. In the research, published in Science, the Georgia Tech and Clemson scientists showed 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.