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University of Michigan uses recycled Kevlar fiber to solve lithium-sulfur battery life cycle issues

(Credit: University of Michigan)

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The University of Michigan Chemical Sciences and Engineering team, led by Professor Nicholas Kotov, has developed a “new biologically inspired battery membrane” with recycled Kevlar fibers that could quintuple electric vehicle ranges and have a lifespan of 1,000 cycles.

The Ann Arbor, Michigan research facility is one of the best in the world, and Kotov, whose research focuses on the development of biomimetic nanocomposites, the self-assembly of nanoparticles, and chiral nanostructures, has worked to change the narrative on lithium-sulfur cells. “There are a number of reports claiming several hundred cycles for lithium-sulfur batteries, but it is achieved at the expense of other parameters—capacity, charging rate, resilience, and safety,” Kotov said in a press release from the University. “The challenge nowadays is to make a battery that increases the cycling rate from the former 10 cycles to hundreds of cycles and satisfies multiple other requirements including cost.”

Lithium-sulfur batteries can enable five times the capacity of standard lithium-ion cells, which are used in electric vehicles. However, as Professor Kotov mentioned in his quote, the lifespan is significantly decreased due to chemical reactions between molecules. The most common reason for reduced life cycles in lithium-sulfur batteries is dendrites, which are appendages that are designed to receive communications from other cells. These can pierce the membrane of cells, reducing the life span and thus the life cycle of a battery cell.

Another problem is polysulfides, or small molecules of lithium and sulfur, can form and flow to the lithium. They bond and cause blockages, reducing the effectiveness of the membrane. “The membrane is needed to allow lithium ions to flow from the lithium to the sulfur and back—and to block the lithium and sulfur particles, known as lithium polysulfides.”

However, Kevlar, the same material used in bulletproof vests, can stop dendrites from penetrating the membrane using dense aramid fibers found in the material. The cells that Kotov and his team developed use recycled Kevlar fibers. The Kevlar “can enable lithium-sulfur batteries to overcome their Achilles heel of cycle life,” caused by the two previously mentioned reactions between molecules.

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An example of the Kevlar system is shown in the images below, as the typical Celgard membrane on the left allows lithium polysulfides to flow through. The Kevlar membrane (right) blocked the polysulfides from traveling through.

“Just half an hour on, the Celgard membrane (left) leaks lithium polysulfides. However, the U-M membrane (right) completely blocks the lithium polysulfides 96 hours later. Image credit: Ahmet Emre, Kotov Lab.” Credit: University of Michigan

“Achieving record levels for multiple parameters for multiple materials properties is what is needed now for car batteries,” Kotov stated. Kotov added that the design of the lithium-sulfur batteries is “nearly perfect” due to its capacity and efficiency reaching theoretical limits. It can also behave more resiliently than lithium-ion cells in warm and cold weather climates, which both have effects on range and efficiency. However, fast charging could reduce the number of lifespans, Kotov added.

Lithium-sulfur batteries could be a good alternative as sulfur is more readily available and abundant than cobalt, which is controversial due to its mining practices. However, automakers like Tesla are reducing cobalt in their batteries vying for other metals, like nickel, instead. Sulfur’s low lifespan and instability, as it changes in size by 78 percent during charging, reduced the possibility of automakers using it in the past, The Independent reported.

The research was funded by the National Science Foundation and the Department of Defense.

I’d love to hear from you! If you have any comments, concerns, or questions, please email me at joey@teslarati.com. You can also reach me on Twitter @KlenderJoey, or if you have news tips, you can email us at tips@teslarati.com.

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Joey has been a journalist covering electric mobility at TESLARATI since August 2019. In his spare time, Joey is playing golf, watching MMA, or cheering on any of his favorite sports teams, including the Baltimore Ravens and Orioles, Miami Heat, Washington Capitals, and Penn State Nittany Lions. You can get in touch with joey at joey@teslarati.com. He is also on X @KlenderJoey. If you're looking for great Tesla accessories, check out shop.teslarati.com

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Tesla is looking to conduct FSD tests in new Swedish city: report

The proposal appears to have been received rather positively by one of the city’s officials.

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Credit: Tesla Europe & Middle East/X

Recent reports have suggested that Tesla is looking at another city in Sweden to test its Full Self-Driving (FSD) system on public roads. The proposal appears to have been received rather positively by one of the city’s officials.

Tesla FSD tests in Sweden

FSD has already been deployed in numerous territories such as the United States, China, and Australia. However, the system is yet to be released in Europe. As per a recent report from Värmlands Folkblad, Tesla has sent a request for FSD testing to the capital of Värmland, Karlstad. As noted in a CarUp report, Tesla is already testing FSD on motorways after the company secured permission from the Swedish Transport Agency. 

The Municipality of Karlstad has reportedly not issued a decision regarding Tesla’s request yet, though lawmakers seem open to the idea of FSD being tested on public roads. In a comment to VF, municipal councilor Linda Larsson stated that FSD tests in Karlstad “sounds interesting.” Tesla’s FSD tests, if they are approved, will still use safety drivers behind the wheel who will be ready to intervene at any time. 

Tesla pledges to work with the municipality

In its request, Tesla noted that Karlstad is an interesting municipality in which to conduct its tests. The company also stated that it would conduct its operations and tests in close collaboration with the municipality, as well as local entities. Considering the municipal councilor’s comments, it does appear that Tesla might have a solid chance at attaining permission to test FSD on Karlstad’s roads. 

Tesla’s success for FSD tests in Sweden has been mixed. A few months ago, reports emerged stating that the company’s request to test FSD in Stockholm had been rejected by the Swedish Traffic Department. 

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“The Traffic Office is currently working on updating its approach to automation. At the same time, the city and the office are under heavy pressure from other ongoing innovation tests. Our ambition is to actively participate in and learn from the continued development in the field of automation. 

“Based on this, and in combination with the fact that the current test is the first of its kind, which entails certain risks for both infrastructure and third parties, and that it is planned to be carried out throughout the city, the City of Stockholm considers it is currently not possible to approve the implementation of the test,” the Swedish Traffic Department stated.

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Waymo faces federal probe after self-driving taxi fails to stop for school bus

In a statement, a Waymo representative stated that the company has “already developed and implemented improvements” that should help its fleet avoid similar incidents in the future.

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Credit: Waymo

Federal regulators have launched an investigation into Waymo’s self-driving vehicles after reports that one of its autonomous taxis failed to stop properly for a school bus. 

The U.S. National Highway Traffic Safety Administration (NHTSA) stated that it’s reviewing around 2,000 Waymo vehicles following concerns that its autonomous systems may have violated traffic laws.

Waymo under review

According to a Reuters report, the NHTSA’s Office of Defects Investigation began the probe after flagging a media report involving a Waymo self-driving taxi that did not remain stationary when approaching a school bus. At the time of the incident, the school bus had its red lights flashing, its stop arm was deployed, and its crossing control arm was extended.

As per the ODI’s report, the Waymo initially stopped beside the bus before maneuvering around its front. This resulted in the vehicle passing the school bus’ extended stop arm and crossing control arm. Students from the bus were disembarking when the Waymo committed the error. The vehicle was operating without a safety driver at the time, and it was equipped with Waymo’s fifth-generation Automated Driving System (ADS).

Software fix already in place

In a statement, a Waymo representative stated that the company has “already developed and implemented improvements related to stopping for school buses and will land additional software updates in our next software release.” The spokesperson also highlighted that Waymo prioritizes the safety of pedestrians, especially children, in its vehicles’ operations. 

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“Driving safely around children has always been one of Waymo’s highest priorities. In the event referenced, the vehicle approached the school bus from an angle where the flashing lights and stop sign were not visible and drove slowly around the front of the bus before driving past it, keeping a safe distance from children,” Waymo noted.

Waymo, which is owned by Alphabet, operates a fleet of more than 1,500 robotaxis in major U.S. cities, including Phoenix, Los Angeles, San Francisco, and Austin. The company continues to expand its footprint and plans future operations in Tokyo and London.

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Kia and Tesla top list in Swedish study of strongest EV batteries

A major Swedish study has revealed which electric vehicles hold their battery health the best, and Kia and Tesla came out on top. 

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Credit: Tesla Asia/X

A major Swedish study has revealed which electric vehicles hold their battery health the best, and Kia and Tesla came out on top. 

Swedish car broker Kvdbil initiated a test of more than 1,300 used BEVs and plug-in hybrids to determine which models retain the best battery capacity over time. Based on the study’s results, the Kia EV6, Kia e-Niro, and the Tesla Model Y were deemed the best.

Kia and Tesla lead the pack

Kvdbil’s test results are bullish for electric vehicles as a whole. The study showed that eight out of ten used electric cars still had at least 90% of their original battery capacity. Kia’s EV6 and e-Niro finished first and second in the rankings, while Tesla’s Model Y came in third. As per CarInfo data, Sweden currently has 12,148 Kia EV6 registered, while there are 48,488 Model Y.

In a comment to the media, test manager Martin Reinholdsson stated, “They are actually better than we thought. We were a bit surprised that there were so many that were this good.”

In a way, Tesla’s strong performance in the test carries extra weight since the Model Y is one of Sweden’s best-selling EVs, giving the test a much larger sample size compared to Kia’s smaller but highly rated fleet. 

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Battery tech, driver habits, and age all play a role

Kvdbil noted that the test’s standout results could be attributed to advanced battery management systems and careful engineering, as noted in a report from the Sweden Herald. At the same time, the study also found that factors like charging routines, driving style, and the age of a vehicle can influence capacity retention.

Rounding out the top ten were entries from Opel, Mazda, Audi, Fiat, Volvo, Citroën, and Volkswagen, as noted in a CarUp report.

This is not the first time that Tesla’s battery prowess has shown its strength. Last year, reports emerged stating that a Tesla Model S 90D from Chesterfield, UK, had traveled 430,000 miles on its original motors and batteries. Over that period, which was comprised of constant Supercharging sessions due to the car being used as an airport taxi, the Model S 90D only lost 65 miles of range.

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