New Flow Battery Ups Storage Capacity by Factor of Ten

Redox flow lithium battery could store energy from wind and solar

2 min read
New Flow Battery Ups Storage Capacity by Factor of Ten
Illustration: Jia et al/Science Advances

To smooth out the peaks and valleys inherent in generating electric power from the sun and the wind, utility companies want massive battery farms capable of storing the surplus energy from renewable power sources for use when the sun goes down and the wind isn’t blowing. One candidate for this application is a redox flow battery that uses liquids to store and release energy.

Redox flow batteries possess a number of features that make them attractive for large-scale energy storage for power girds. For instance, their cost per kilowatt-hour is lower than the lithium-ion batteries often used in mobile devices, and their overall energy capacity can easily be expanded by adding more fluid to match a grid's growing needs.

Heretofore, they’ve been limited by low energy density—that is, energy stored per unit volume. To offer the storage needed by a local or regional power grid, they would need a lot of space, which is often limited in the cities they are intended to power. For example, the energy density of the vanadium redox-flow battery, the most developed type of redox flow battery, is roughly one-tenth that of lithium-ion batteries.

But in a paper published in the 27 November online edition of the journal Science Advancesscientists in Singapore reported that they have developed new redox flow lithium batteries whose energy densities match those of their lithium-ion counterparts. “The energy density of redox flow lithium batteries can be about eight to 10 times as high as conventional redox flow batteries,” says Qing Wang, a materials scientist at the National University of Singapore who is a member of the team that made the breakthrough.

The key innovation: solid granules in the electrolyte tanks made from the same kinds of compounds that make up the anodes and cathodes in lithium-ion batteries. 

Previous research had explored using solid materials in redox flow batteries. But prior approaches used viscous slurries of solid materials, which can take a lot of energy to pump through a battery’s interior. The new redox flow lithium battery keeps the solid granules stationary, and only pumps the electrolytes around.

The scientists used granules of lithium iron phosphate for the cathode material and titanium dioxide for the anode material. The granules are porous, to increase the amount of surface area available for electricity-generating chemical reactions.

One challenge the scientists faced in developing this battery was fabricating the membrane separating the electrolytes. The membrane needed to possess high permeability to lithium ions, low permeability to other chemicals, and good mechanical and chemical stability. The researchers ultimately settled on a lithium-loaded composite membrane made of the commercially available electroactive polymer Nafion, which is commonly used in fuel cells, plus polyvinylidene difluoride, a tough plastic that is resistant to flame, electricity, and attack by most chemicals.

Still, says Wang, the membrane they used is not good enough for transporting lithium ions at the scale necessary for power storage applications. Future research is needed to improve the membrane and other parts of the battery before before the improved redox flow battery can be used by utilities.

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Smokey the AI

Smart image analysis algorithms, fed by cameras carried by drones and ground vehicles, can help power companies prevent forest fires

7 min read
Smokey the AI

The 2021 Dixie Fire in northern California is suspected of being caused by Pacific Gas & Electric's equipment. The fire is the second-largest in California history.

Robyn Beck/AFP/Getty Images

The 2020 fire season in the United States was the worst in at least 70 years, with some 4 million hectares burned on the west coast alone. These West Coast fires killed at least 37 people, destroyed hundreds of structures, caused nearly US $20 billion in damage, and filled the air with smoke that threatened the health of millions of people. And this was on top of a 2018 fire season that burned more than 700,000 hectares of land in California, and a 2019-to-2020 wildfire season in Australia that torched nearly 18 million hectares.

While some of these fires started from human carelessness—or arson—far too many were sparked and spread by the electrical power infrastructure and power lines. The California Department of Forestry and Fire Protection (Cal Fire) calculates that nearly 100,000 burned hectares of those 2018 California fires were the fault of the electric power infrastructure, including the devastating Camp Fire, which wiped out most of the town of Paradise. And in July of this year, Pacific Gas & Electric indicated that blown fuses on one of its utility poles may have sparked the Dixie Fire, which burned nearly 400,000 hectares.

Until these recent disasters, most people, even those living in vulnerable areas, didn't give much thought to the fire risk from the electrical infrastructure. Power companies trim trees and inspect lines on a regular—if not particularly frequent—basis.

However, the frequency of these inspections has changed little over the years, even though climate change is causing drier and hotter weather conditions that lead up to more intense wildfires. In addition, many key electrical components are beyond their shelf lives, including insulators, transformers, arrestors, and splices that are more than 40 years old. Many transmission towers, most built for a 40-year lifespan, are entering their final decade.

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