Recently, researchers from Vancouver have created a flexible battery that can be stretched, worn, and washed while retaining its ability to provide power and recharge. What challenges do wearable devices face, what dd the researchers develop, and could it be the solution to future wearable power?

Why is power a major problem for wearable devices?

While wearable technology continues to improve performance, most wearable devices on the market are not entirely wearable. Sure, smartwatches can be worn on the wrist, and sunglasses that integrate bone conduction can provide a convenient method for listening to audio, but these wearable devices are fundamentally ridged in shape. This rigidity means that these devices can only be worn in areas that do not move or experience deformation, and their rigidity can also make them uncomfortable to wear.

A true wearable would be a device that can move with the body in a similar fashion to clothes. Unlike most electronic devices currently available on the market, clothes are often stretchable, can be compressed and twisted, will move with the body, and are rarely noticed when worn.

Trying to make electronics flexible to be comfortable to wear is extremely challenging when considering that most materials used to make electronic components are ridged. For example, semiconductors rely on crystal structures to manipulate electron flow, while capacitors depend on the separation of two conductive plates kept at a specific distance between them. However, recent research is overcoming these challenges by developing flexible materials, with one primary example being UK-based semiconductor company PragmatIC. They have been able to create a flexible ARM processor.

But it is not just electronic components that need to be flexible; power sources for wearable devices also need to be flexible. Flexible power sources such as solar and thermal have already been proven to function, but they generally lack the necessary power to run everyday devices. Battery technologies such as lithium-ion are highly used in portable devices due to their high energy density, but making these flexible has presented researchers with major challenges.

One challenge faced with making batteries flexible is that batteries generally require two terminals (dissimilar metals) and an electrolyte that allows for ion transportation. This is easy to achieve for a ridge solid battery, but making such a battery bendable presents a wide range of issues.

A flexible battery would have to allow the electrolyte to be moved and stretched while providing a conductive path for ions to move between the anode and cathode. Furthermore, the bending of the battery must not allow for either electrode to make contact with each other as this would form a short circuit.

Vancouver researchers create a flexible battery

Recently, researchers from Vancouver have developed the world’s first truly flexible battery that shows great commercial promise for future wearable devices. The battery chemistry used by the researchers is based on Zinc and manganese dioxide, and this was chosen as it is far safer for use near skin compared to other battery technologies that can often have toxic compounds.

The battery was created by grinding the electrode materials into a fine powder that was then impregnated into a polymer. To improve electrical characteristics, the battery comprises multiple polymer layers while the electrolyte is kept sealed from the outside air. Furthermore, using a polymer allows the battery to be watertight, allowing it to be exposed to water without degradation.

Testing the battery’s ability to resist water was subjecting the battery to multiple wash cycles. According to the researchers, the batter has experienced up to 39 wash cycles while still being able to produce electricity and charge. It has also been reported that the battery has 75% charge retention after 500 charge cycles and a viable shelf-life where the battery lost 22% of its electrolyte mass after 523 days.

Is this battery technology the solution to future wearable devices?

Unlike many other wearable devices, the battery produced by the research team represents a significant advancement in wearable technologies. As the battery is flexible, stretchable, and washable, it can be easily integrated into clothing while having minimal impact on its performance or comfort. Furthermore, the ability to survive more than 39 wash cycles enables its use in some rarely washed textiles (such as coats and shoes).

Of all energy technologies to have come out regarding wearable technologies, this flexible battery is one of the strongest candidates by far. The next test for the battery will be to see its commercial viability, the amount of energy it can store, and its true durability when used in the real world.