Seaweed Could be Next Binder in Lithium-Ion Batteries

Researchers have identified a new binder material that could eventually increase the energy storage capacity of lithium-ion batteries and also eliminate the use of the toxic compounds that are currently used for manufacturing the batteries' components. The binder is a critical component for suspending silicon or graphite particles in a battery. These particles actively interact with the electrolyte that provides battery power.

Known as alginate, the new binder material is extracted from brown algae, or seaweed. Current test results indicate that the material boosts energy storage and output for both the graphite-based electrodes used in existing batteries and the silicon-based electrodes being developed for future batteries. The discovery that seaweed can be used as a binder material stems from Gleb Yushin, an assistant professor in the school of materials science at the Georgia Institute of Technology (Georgia Tech; Atlanta) and Igor Luzinov, a professor in the school of materials science and engineering at Clemson University (Clemson, SC).

"We specifically looked at materials that had evolved in natural systems, such as aquatic plants which grow in salt water with a high concentration of ions," Luzinov explains. "Since electrodes in batteries are immersed in a liquid electrolyte, we felt that aquatic plants--in particular, plants growing in such an aggressive environment as salt water--would be excellent candidates for natural binders."

Alginates are attractive because of their uniformly distributed carboxylic groups. The material is extracted from the seaweed using a simple soda (Na₂CO₃)-based process that generates a uniform material. The anodes can then be produced using a water-based slurry to suspend the silicon or graphite nanoparticles. The alginate electrodes are compatible with existing production techniques and can be integrated into existing battery designs, Yushin remarks.

The use of alginate may help address one of the most difficult problems limiting the use of high-energy silicon anodes. When batteries begin to operate, the decomposition of the lithium-ion electrolyte forms a solid electrolyte interface (SEI) on the surface of the anode. The SEI must be stable and allow lithium ions to pass through it, yet it must restrict the flow of fresh electrolyte.

With graphite particles, whose volume does not change, the SEI remains stable. However, because the volume of silicon nanoparticles changes while the battery is in operation, cracks can form, allowing additional electrolyte decomposition until the pores that allow ion flow become clogged. This process results in battery failure. Alginate not only binds silicon nanoparticles to each other and to the metal foil of the anode, but it also coats the silicon nanoparticles themselves and provides a strong support for the SEI, preventing degradation.

Thus far, the researchers have demonstrated that the alginate can produce battery anodes with reversible capacity eight times greater than that of today's best graphite electrodes. The anode also demonstrates a coulombic efficiency approaching 100% and has operated through more than 1000 charge-discharge cycles without failure.

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