Think alginate, that you may have met quite intimately if you’ve had dental impressions made – the gooey, but not sticky substance that was in the tray which formed to match your teeth. Alginate or more accurately the sodium alginate, the sodium salt of alginic acid, is derived from Macrocystis pyrifera algae, which is also called Giant Kelp or simply brown algae has now been found to apply to lithium-ion battery construction with great results.
Clemson University and Georgia Institute of Technology scientists are reporting in Science Express, a refinement of alginate is a promising new binder material for lithium-ion battery electrodes that not only could boost energy storage, but also eliminate the use of toxic compounds now used to manufacture the components. In tests so far, it has helped boost energy storage and output for both graphite-based electrodes used in existing batteries and silicon-based electrodes being developed for future generations of batteries.
Alginate with Silicon Structure.
Gleb Yushin, an assistant professor in Georgia Tech’s School of Materials Science and Engineering starts the explanation, “Making less-expensive batteries that can store more energy and last longer with the help of alginate could provide a large and long-lasting impact on the community. These batteries could contribute to building a more energy-efficient economy with extended-range electric cars, as well as cell phones and notebook computers that run longer on battery power — all with environmentally friendly manufacturing technologies.”
Working together with Igor Luzinov at Clemson University’s School of Materials Science and Engineering, the scientists looked at ways to improve binder materials in batteries. The binder is a critical component that suspends the silicon or graphite particles that actively interact with the electrolyte that provides battery power.
Luzinov picks up the explanation, “We specifically looked at materials that had evolved in natural systems, such as aquatic plants which grow in saltwater with a high concentration of ions. 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 saltwater – would be excellent candidates for natural binders.” Seems obvious now that the explanation is at hand, still its top of the line situational assessment.
Alginates are low-cost materials already used in foods, pharmaceutical products, paper and other applications. They are attractive because of their uniformly distributed carboxylic groups. This may provide an answer to the silicon anode theoretically offering as much as a tenfold capacity improvement over graphite anodes.
When batteries begin operating, decomposition of the lithium-ion electrolyte forms a solid electrolyte interface on the surface of the anode. The interface must be stable and allow lithium ions to pass through it, yet restrict the flow of fresh electrolyte.
With graphite particles, whose volume does not change, the interface remains stable. However, because the volume of silicon nanoparticles changes during operation of the battery, interface cracks can form and allow additional electrolyte decomposition until the pores that allow the ion flow become clogged, causing battery failure. Alginate not only binds silicon nanoparticles to each other and to the metal foil of the anode, but they also coat the silicon nanoparticles themselves and provide a strong support for the interface, preventing degradation. Eureka!
SEM Alginate Binder and Silicon Electrode.
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 been operated through more than 1,000 charge-discharge cycles without failure. Eureka, indeed.
Luzinov sums up, “Brown algae is rich in alginates and is one of the fastest-growing plants on the planet. This is a case in which we found all the necessary attributes in one place: a material that not only will improve battery performance, but also is relatively fast and inexpensive to produce and is considerably more safe than the some of the materials that are being used now.”
If the silicon anode construction matter is resolved for a very long life and a huge capacity increase – lots of other ideas can get new better footing, too. Time to try scaling up and further operating condition testing. Looking good.
By. Brian Westenhaus
Source: Algae To Make Better Batteries