Q+A: How Are Engineers Improving the Safety and Performance of E-Bike, Scooter and EV Batteries?

As battery-powered transportation, such as e-bikes, scooters and electric vehicles, become more widely used, the durability and performance of battery technology is increasingly being pushed to its limits. A spate of tragic e-bike fires in New York City over the summer also drew attention to quality control issues with some commercial lithium-ion batteries. While engineers and manufacturers are rushing to improve the safety and performance of the technology as the demand for electric transportation continues to grow, there are a few things users can do now to identify problematic batteries, avoid malfunction and extend battery life.

Wes Chang, PhD, an assistant professor in the College of Engineering, whose lab studies how batteries work, why they malfunction and how they can be improved, recently shared his insight on our current moment in battery technology and transit and how users of electric transportation can safely get the most out of their batteries.

What seems to be the problem with e-bike batteries? Are electric scooters having the same issues? Are EVs likely to experience similar problems?

There has been an alarming increase in reports of fatalities from e-bike fires, especially in New York City. Luckily, we have not had such incidences reported in Philadelphia, and hopefully it stays that way.

With that said, the increase in the prevalence of e-bikes and e-scooters in dense urban areas necessitates public knowledge of their safe handling and usage procedures, and it is important that the local fire departments and residents alike are familiar with battery fires and how to put them out.

Many of these e-bikes and e-scooters are purchased from vendors without much information on the battery pack quality: where the batteries originated from, their quality, how the cells were assembled, whether the packs passed safety tests. EVs, on the other hand, go through a series of stringent safety checks and qualifications, as most EVs today are produced from large automobile manufacturers in partnership with large battery manufacturers. 

How do you know if you have a defective battery? What are some indicators users might notice?

In the best-case scenario, defective batteries simply experience faster capacity fade, so your battery dies faster than expected. In the worst-case scenario, the battery may overheat, leading to a potential life-endangering fire and explosion. This is called “thermal runaway” and can happen in mere seconds.

Batteries come in different shapes and sizes. Sometimes, they are made using soft pouches, which can bloat up like a balloon and fill with gas after overheating. In other cases, such as most e-bikes, they are made with hard cylindrical casings, which have built-in vent caps for releasing a sudden build-up of gas. In either case, e-bikes and e-scooters are subject to much harsher conditions than phones and cars. E-bikes and scooters are left outside in the dead of winter, where they experience extreme cold. They are also tossed around and the battery pack is much more exposed to vibrations. As batteries are built to be used at no lower than 15 degrees Celsius and with minimal external vibration, these conditions can worsen the health of the battery faster. 

Are there general safety procedures riders should follow because of the prevalence of these defective batteries? 

Riders should take care to use the charger that their e-bike or e-scooter comes with or is rated for. Also, riders should make sure that they do not charge their e-bikes and e-scooters in temperatures below freezing, as this can lead to rapid battery deterioration. 

What are some good maintenance guidelines for lithium-ion batteries to preserve performance and avoid malfunction?

Riders should take care to purchase their e-bikes and e-scooters from trusted vendors with battery packs that pass safety inspections. If purchased online or second hand, they may want to take them to a shop to get the batteries checked. They should be charged at no lower than 15 degrees Celsius, and under charging conditions that meet the specifications of the battery pack.

How might your work help manufacturers identify defects before batteries make it to the market?

Our group is interested in using and developing new techniques that can look inside batteries either during or after manufacturing. Hardware that is fast, low cost and portable would be ideal for high throughput diagnostics of many batteries at once.  

One example of this is ultrasound, which is increasingly being used as a non-destructive analysis tool. Another example is X-ray CT, which can show what the internal structure looks like.   Drexel has several unique tools in our Materials Characterization Center, such as the state-of-the-art X-ray tomography, that could be used for battery research. Within our lab, we are also concurrently working on ways to look at both battery chemistry and battery mechanical properties, which should give better insight to the origins of failure in different battery technologies.

How are engineers who work on battery design approaching the challenge of improving battery performance and safety as the demand for electric vehicles continues to grow?

There are two main ways to improve battery safety: using intrinsically safer chemistries and engineering enhanced safety features into the battery.

Regarding the former, lithium iron phosphate (LFP) is of increasing interest because this positive electrode chemistry is much safer than our typical nickel manganese cobalt oxides (NMC) or lithium cobalt oxide (LCO).

Regarding the engineering factors, material coatings and/or nonflammable additives have been studied to determine if they can decrease the likelihood of thermal runaway or at least decrease the intensity of a potential fire.

Within our lab, we are testing potential solutions from both a materials and cell engineering approach, and we try to make sure that our findings hold true for larger cells as well.

But these materials and engineering innovations, while important, can only lead to battery safety in the real world if the manufacturing process itself is improved such that defects are minimized and quality checks can decidedly find and toss the defective cells. 

Reporters interested in speaking with Chang should contact Britt Faulstick, bef29@drexel.edu

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