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A team at Japan’s Yokohama National University has developed a stretchable packaging film for lithium-ion batteries used in wearable devices, particularly those important in the medical field.
The packaging is aimed at extending battery life while protecting it from atmospheric moisture and gases.
“Currently, the use of solid and large batteries for stretchable devices is a problem because while sensors and interfaces are soft, the batteries are still hard,” Hiroki Ota, one of the researchers involved in the development, said in a media statement. “Soft and stretchable batteries have been studied in the world but the issue is that they cannot be used yet due to the high gas and moisture permeability of their packaging materials.”
In a paper published in the journal ACS Applied Materials & Interfaces, Ota and his colleagues explain that to create this flexible film with a high gas barrier, they coated a thin layer of liquid metal onto a gold-deposited thermoplastic polyurethane film using the layer-by-layer method. This method allowed for the desired deformability, unlike aluminum-laminated films, which were used previously to address the issue of gas and moisture permeability but failed to allow for the needed flexibility.
According to the researchers, the resulting film shows excellent oxygen gas impermeability under mechanical strain and also extremely low moisture permeability. In fact, the stretchable lithium-ion battery that they assembled for this study was able to operate reliably at room conditions due to the new barrier.
“It is exciting that in addition to the development of a stretchable battery, which could be used in the next generation of smart devices, including future wearable devices, films with high gas and moisture barrier properties can be achieved by using a novel material called liquid metal,” Ota said.
In the scientist’s view, these results are a very good first step towards the implementation of high energy density, high working voltage, long-term stability and highly deformable — as opposed to bulky and inflexible — wearable devices.
Ota pointed out that more work lies ahead, with the next steps including the enhancement of the moisture protection ability of the film by modifying the materials and making the film cost-effective to facilitate scalability.
“Further cost reductions of the developed film will lead to the implementation of stretchable batteries,” Ota said. “In addition, the film could be useful as a barrier film for organic electronics and so on.”
