Scientists have once again turned to nature for answers, this time discovering the chemical structure of microfibers found in wood can help store energy in large scale renewable batteries used for wind and solar.
A team of researchers led by Hongli (Julie) Zhu, an assistant professor of mechanical and industrial engineering at Northeastern University, used unique nanomaterials derived from cellulose.
Cellulose is what gives plants their strength and is the most abundant natural polymer on Earth. The membrane the team created, from cellulose nanocrystals, demonstrates superior efficiency over current membranes on the market.
Zhu talks about the teams work:
We try to use polymers from wood, from bark, from seeds, from flowers, bacteria, green tea—from these kinds of plants to replace plastic. It contains important molecular structures to improve batteries, reduce plastic pollution, and power the sort of electrical grids that could support entire communities with renewable energy.
Large scale batteries that store wind and solar energy require special membranes that separate positive hydrogen ions from flowing into one another. Currently “flow batteries” are the most advanced. They are equipped with two separate tanks filled with vanadium ions that are dissolved in acid. One tank has positive ions, the other negatively charged ions. These ions get pumped into a cell, which functions similarly to an engine for the battery. Flow batteries are especially good for storing wind and solar energy because they can be adjusted for the amount of energy stored, without altering the amount of energy generated.
The downfall of these expensive batteries is they require moving pieces of hardware, which over time causes the membrane to decay. This can result in the vanadium ions mixing and ultimately reducing the ability of the battery to store energy.
Northeastern Design
Zhu and her team tested out many different membranes made from cellulose nanocrystals in their quest to make flow batteries more affordable. With support from the Rogers Corporation and its Innovation Center at Northeastern’s Kostas Research Institute, they were able to not only create a cheaper material but a much more durable membrane that will substantially increase the lifecycle of the batteries.
“The cost of our membrane per square meter is 147.68 US dollars. The price quote for the commercialized Nafion membrane is $1,321 per square meter,” said Zhu.
That doesn’t include any marketing costs, but it’s easy to see these renewable batteries are considerably cheaper than current membranes.
The cellular structure of the team’s membrane contains thousands of hydroxyl groups, involving the bonds of oxygen and hydrogen. These are what allow for the transportation of water in plants and trees.
That same molecular structure speeds up the transportation of protons through the membrane in flow batteries. The membranes also contain a vinylidene fluoride-hexafluoropropylene polymer that prevents the positive and negatively charged acids from mixing.
Zhu explains:
“For these materials, one of the challenges is that it is difficult to find a polymer that is proton conductive and that is also a material that is very stable in the flowing acid.”
The good thing about the newly created cellulose membrane is they are constructed from plants, making them easily available, and low cost. Zhu continues about the benefits;
A lot of material in nature is a composite, and if we disintegrate its components, we can use it to extract cellulose. Like waste from our yard and a lot of solid waste that we don’t always know what to do with.
