New soft, stretchable battery can safely power wearables

The battery, developed at Stanford University, uses a special plastic to store power more safely than conventional batteries.

Researchers David Mackanic, Xuzhou Yan, Yi Cui, and Zhenan Bao from Stanford University's engineering school have created a soft, stretchable battery prototype for wearables. The new type of battery relies on a unique plastic to store power in a safer manner, compared to the flammable materials used in conventional batteries, according to a Stanford Engineering Magazine article.

SEE: Apple Watch Series 5: A cheat sheet (free PDF) (TechRepublic)

The use of polymers, or plastics, is not new, according to the magazine article; however, some previous polymers existed as flowable gels that could sometimes leak or burst into flame.  

The new battery is ideal for use in wearables, such as smartwatches, because it's soft and flexible. 

"Current batteries are stiff and rigid, making them non-conformable to the human body. This means the batteries must be small in order to not cause discomfort," said David Mackanic, one of the project's researchers. 

"Additionally, our battery uses a polymer electrolyte, which is safer than the liquid electrolyte currently used for many wearable batteries. Our battery's electrolyte is safer because it is less combustible and flammable, and won't leak," Mackanic said.

Outlined further in the Nature Communications scientific journal, even though it is constructed differently, the battery can still carry an electric charge between battery poles.

In the testing lab, the experimental battery kept consistent power output even when it was folded, squeezed, and stretched to almost twice its original length. 

The battery is thumbnail-sized and is able to store approximately half as much energy as a similar sized traditional battery, according to the Stanford magazine.

What can the battery be used in? 

"We are still experimenting with new ways to incorporate our battery into wearable electronics. This battery could be integrated into things like wristbands for smartwatches, allowing the actual smartwatch to be thinner and more comfortable," Mackanic said. "These batteries could also be incorporated comfortably into clothing, providing a power source for smart textiles." 

While this battery is undoubtedly impressive, it only holds half the power of a traditional battery, which is a serious limiting factor, said Ramon Llamas, research director of mobile devices at International Data Corporation. 

While Mackanic said this battery could be used in smartwatches, hearing aids, smart glasses, smart textiles, footwear, on-body health monitoring patches, and more, Llamas noted that most wearables don't necessarily need a stretchable battery to begin with, especially on systems like fitness trackers or smartwatches. 

The most practical use case currently, based on the battery's size, would be in disposable heart rate monitors. People typically wear heart rate monitors for approximately 24 hours before disposing of them. Stretchable batteries would be great for this application since they are flexible, Llamas said. 

However, Mackanic indicated that future versions of the stretchable battery could be bigger, allowing for more advanced use cases. 

"Right now, the energy density of our battery is lower than conventional lithium-ion batteries," Mackanic said. 

However, since the battery is so flexible, future prototypes can be made bigger, allowing for more power and battery life, without losing comfort, Mackanic said.  

The battery is still being refined and going through the manufacturing process, after which the battery will undergo advanced safety testing. For now, the battery remains a prototype. 

Mackanic said it would likely be between 12 and 18 months until they can provide completely certified test batteries to manufacturers. 

For more, check out How wearable devices and sensors could make some of the most dangerous jobs safer on TechRepublic. 

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