The Lithium-Ion Battery With Built-In Fire Suppression

New design also increases energy density for Li-ion batteries

4 min read
Comparison of current lithium-ion pouch batteries (top) vs new flame-retardant collectors showing effects when exposed to an open flame.
In a study at Stanford and SLAC, lithium-ion pouch batteries made with today's commercial current collectors (top row) caught fire when exposed to an open flame and burned vigorously until all the electrolyte burned away. Batteries with the new flame-retardant collectors (bottom row) produced weak flames that went out within a few seconds, and did not flare up again even when the scientists tried to relight them.
Image: Yusheng Ye/Stanford University

If there are superstars in battery research, you would be safe in identifying at least one of them as Yi Cui, a scientist at Stanford University, whose research group over the years has introduced some key breakthroughs in battery technology.

Now Cui and his research team, in collaboration with SLAC National Accelerator Laboratory, have offered some exciting new capabilities for lithium-ion batteries based around a new polymer material they are using in the current collectors for them. The researchers claim this new design to current collectors increases efficiency in Li-ion batteries and reduces the risks of fires associated with these batteries.

Current collectors are thin metal foils that distribute current to and from electrodes in batteries. Typically these metal foils are made from copper. Cui and his team redesigned these current collectors so that they are still largely made from copper but are now surrounded by a polymer.

The Stanford team claim in their research published in the journal Nature Energy that the polymer makes the current collector 80 percent lighter, leading to an increase in energy density from 16 to 26 percent. This is a significant boost over the average yearly increase of energy density for Li-ion batteries, which has been stuck at 5 percent a year seemingly forever.

Scientists at Stanford and SLAC redesigned current conductors - thin metal foils that distribute current to and from electrodes - to make lithium-ion batteries lighter, safer and more efficient. They replaced the all-copper conductor, middle, with a layer of lightweight polymer coated in ultrathin copper (top right), and embedded fire retardant in the polymer layer to quench flames (bottom right). Scientists at Stanford and SLAC redesigned current conductors, thin metal foils that distribute current to and from electrodes, to make lithium-ion batteries lighter, safer and more efficient. They replaced the all-copper conductor, middle, with a layer of lightweight polymer coated in ultrathin copper (top right), and embedded fire retardant in the polymer layer to quench flames (bottom right). Image: Yusheng Ye/Stanford University

This method of lightening the batteries is a bit of a novel approach to boosting energy density. Over the years we have seen many attempts to increase energy density by enlarging the surface area of electrodes through the use of new electrode materials—such as nanostructured silicon  in place of activated carbon. While increased surface area may increase charge capacity, energy density is calculated by the total energy over the total weight of the battery.

The Stanford team have calculated the increase of 16 to 26 percent in the gravimetric energy density of their batteries by replacing the commercial  copper/aluminum current collectors (8.06 mg/cm2 for copper and 5.0 mg/cm2 for aluminum) with their polymer collections current collectors (1.54 mg/cm2 for polymer-copper material and 1.05 mg/cm2 for polymer-aluminum). 

“Current collectors don’t contribute to the total energy but contribute to the total weight of battery,” explained Yusheng Ye, a researcher at Stanford and co-author of this research. “That’s why we call current collectors ‘dead weight’ in batteries, in contrast to ‘active weight’ of electrode materials.”

Whenever the battery has combustion issues, our current collector will instantaneously release the fire retardant and extinguish the fire.

By reducing the weight of the current collector, the energy density can be increased, even when the total energy of the battery is almost unchanged. Despite the increased energy density offered by this research, it may not entirely alleviate so-called “range anxiety” associated with electric vehicles in which people have a fear of running out of power before reaching the next charge location. While the press release claims that this work will extend the range of electric vehicles, Ye noted that the specific energy improvement in this latest development is based on the battery itself. As a result, it is only likely to have around a 10% improvement in the range of an electric vehicle.

“In order to improve the range from 400 miles to 600 miles, for example, more engineering work would need to be done taking into account the active parts of the batteries will need to be addressed together with our ultra-light current collectors,” said Ye.

Beyond improved energy density efficiency, the polymer-based charge collectors are expected to help reduce the fires associated with Li-ion batteries. Of course, traditional copper current collectors don’t contribute to battery combustion on their own. The combustion issues in Li-ion batteries  are related to the electrolyte and separator that are not used within the recommended temperatures and voltage windows.

“One of the key innovations in our novel current collector is that we are able to embed fire retardant inside without sacrificing the energy density and mechanical strength of the current collector,” said Ye. “Whenever the battery has combustion issues, our current collector will instantaneously release the fire retardant and extinguish the fire. Such function cannot be achieved with traditional copper or aluminum current collector.”

The researchers have patented the technology and are in discussions with battery manufacturers for commercialization. Cui and his team have already worked out some of the costs associated with adopting the polymer and they appear attractive. According to Ye, the cost of the polymer composite charge collector is around $1.3 per m2, which is a bit lower than the cost of copper foil, which is around $1.4 per m2. With these encouraging numbers, Ye added: “We are expecting industry to adopt this technology within the next few years.”

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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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