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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). (Yusheng Ye/Stanford University)

Batteries

New Approach To Li-Ion Battery Efficiency At Stanford Puts Out Fires

There’s a new approach that is boosting the efficiency of lithium-ion batteries that also puts out fires — making the batteries fireproof. The new approach, according to scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory, is the reengineering of one of the heaviest components in batteries: sheets of copper or aluminum foil that are used to collect currents.

There’s a new approach that is boosting the efficiency of lithium-ion batteries that also puts out fires — making the batteries fireproof. The new approach, according to scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory, is the reengineering of one of the heaviest components in batteries: sheets of copper or aluminum foil that are used to collect currents. These have been redesigned so that they weigh 80% less. They also immediately quench any fires that flare up. The research team shared their work in Nature Energy Today.

Yi Cui, a professor at SLAC and Stanford and investigator with the Stanford Institute for Materials and Energy Sciences (SIMES), led the research. “The current collector has always been considered dead weight, and until now it hasn’t been successfully exploited to increase battery performance.” Cui added, “But in our study, making the collector 80% lighter increased the energy density of lithium-ion batteries — how much energy they can store in a given weight — by 16–26%. That’s a big jump compared to the average 3% increase achieved in recent years.”

The researchers noted that if the technology is adopted, it will address two major goals of battery research:

1. Extending the driving range of EVs.

2. Reducing the danger that laptops, smartphones, and other devices will burst into flames.

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). (Yusheng Ye/Stanford University)

The Need for Weight Loss

Turns out that batteries have a weight problem just as humans do. In either cylinder form or pouches, lithium-ion batteries have two current collectors for each electrode. These distribute the current that flows in or out of the electrode and account for 15% to 50% of the weight of some high-power or ultrathin batteries. Shedding some of the battery’s weight would enable lighter devices while reducing the amount of weight EVs have to carry around. Doing this would also enable the battery to store more energy per given weight and allow for both EVs and devices to go longer between charges.

Another benefit of reducing the weight and the flammability would have a big impact on recycling. This would make the transportation of recycled batteries less expensive, according to Cui.

Yusheng Ye, a postdoctoral researcher in Cui’s lab, carried out experiments with visiting scholar Lien-Yang Chou. Ye pointed out that the researchers in the battery industry have been tackling a challenge while trying to reduce the weight of current collectors. The researchers have been trying to make them thinner or more porous, but the challenges were the unwanted side effects. These came in the forms of fragility — the batteries became more fragile, as well as chemically unstable. Or they would require more electrolytes, which raises the cost.

Regarding safety, Ye said, “People have also tried adding fire retardant to the battery electrolyte, which is the flammable part, but you can only add so much before it becomes viscous and no longer conducts ions well.”

A redesigned current collector for lithium-ion batteries makes batteries lighter, more energy-efficient, and safer. It could also cut costs by replacing copper with cheaper polymer and by reducing the cost of transporting batteries for recycling. (Greg Stewart/SLAC National Accelerator Laboratory)

New Diet: Polymer-Foil Sandwich 😋

Cui, Ye, and Liu put their heads together to find a solution to the problem and ended up designing experiments for making and testing current collectors based on a lightweight polymer known as polyimide. Polyimide resists fire and is able to take on the high temperatures created by fast battery charging. A fire retardant, triphenyl phosphate (TPP), was embedded in the polymer and then coated on both surfaces with an ultrathin layer of copper.

This resulted in the copper protecting the polymer and its fire retardant while still being able to distribute the current as usual. This change reduced the weight of the current collector by 80% compared to today’s versions, Ye noted. This meant an energy density increase of 16–26% in various types of batteries along with the ability to conduct current just as well as regular collectors with no degradation.

When exposed to open flame, lithium-ion pouch batteries made with today’s commercial current collectors (top row) caught fire 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. (Yusheng Ye/Stanford University).

Ye noted that when pouch batteries made with today’s commercial current collectors were exposed to an open flame from a lighter, they caught fire and burned intensely until all of the electrolyte was burned away. However, the batteries with the new flame-retardant collectors didn’t really catch. The fire never really got going and the flames that were produced were very weak and went out within a few seconds — without flaring up again even when the researchers tried to re-light it.

A major advantage to this approach, Cui pointed out, was that the new collector should be easy to manufacture and it’s cheaper since it replaces some of the copper with an inexpensive polymer. Scaling it up for commercial production, he said, “should be very doable.” The researchers also applied for a patent through Stanford and Cui said that they plan to contact battery manufactures to explore the possibilities. The scientific research was supported by the DOE’s Office of Energy Efficiency and Renewable Energy, Vehicle Technologies Office under the eXtreme Fast Charge Cell Evaluation of Lithium-ion Batteries (XCEL) program.

The Benefit of “Fire-Proof” Batteries

Back in August, Forbes noted that one of the most popular myths surrounding EVs is that the batteries are a fire risk. This myth is often used by EV haters or those who are terrified of owning an EV due to this fear. The article brings up that many critics point to the crashing of a Rimac Concept_One electric hypercar. Although, critics skip over the point that the car didn’t crash dramatically because it was an EV, but because the driver made a spectacular mistake after driving in too risky a way at high speed. They used this as an example, though, showing that all EVs are flammable and feeding into fear around that topic. Never mind that if you smoke a cigarette at a gas station you could accidentally blow up the entire block.

Cutting fire risk completely could be helpful in some number of cases, and it also breaks down one of the barriers to faster EV adoption.

 
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