Hong Kong researchers develop flexible battery for wearables
May 30, 2019
Researchers at the Hong Kong Polytechnic University (PolyU) have developed a flexible, high-energy textile lithium battery that is said to offer more stable, durable and safe energy supply for wearable electronics in applications such as in healthcare monitoring, intelligent textiles, smartphones, GPS tracking and the IoT.
The battery demonstrates an energy density of more than 450Wh/L, flexibility with a bending radius of less than 1mm, and foldability of over 1000 cycles with marginal capacity degradation. In comparison, existing bendable lithium batteries can only reach a bending radius of about 25mm, and less than 200Wh/L.
The textile lithium battery is less than 0.5mm thick, has a fast charging and discharging capability, and has a cycle life comparable with conventional lithium batteries.
The innovation developed by the research team of PolyU's Institute of Textiles & Clothing (ITC) snatched three prizes at last month’s International Exhibition of Inventions of Geneva – a gold medal and two special merit awards.
"Wearable technology has been named as the next global big market opportunity after smartphones,” said professor Zheng Zijian (pictured), who leads the ITC research team. “Global market revenues for wearable devices are forecasted to grow by leaps and bounds, of over 20% annually, to reach US$100bn by 2024. As all wearable electronics will require wearable energy supply, our novel technology in fabricating textile lithium battery offers a promising solution to a wide array of next-generation applications, ranging from healthcare, infotainment, sports, aerospace, fashion, IoT to any sensing or tracking uses that may even exceed our imagination of today."
Lithium is the dominant rechargeable battery technology in the market due to its relatively high energy density and long cycle life. As a conventional bulky heavy lithium battery is hard for use in wearable devices, over the past decade scientists have put in efforts to develop a bendable lithium battery, often by using metal foils as current collectors. However, PolyU believes the textile lithium battery will address the bottlenecks over energy density, flexibility, mechanical robustness and cycling stability.
Applying PolyU's patented technology of polymer-assisted metal deposition (PAMD), highly conductive metal, copper and nickel are uniformly and conformally deposited onto pre-treated fabrics. Such fabricated metallic fabrics, featuring low sheet resistance and large surface area, serve as current collectors in the battery. After adding active materials to act as cathode and anode, the metallic fabrics, together with separator and electrolyte, are assembled into the textile lithium battery.
Laboratory tests conducted by the ITC team have proven the high mechanical stability, durability and safety of the battery under deformation. When the battery was repeatedly folded in half, twisted at different angles or freely crumpled, its voltage window remained unchanged. Bending tests showed the battery could be bent over 1000 times with marginal capacity degradation. Safety tests conducted by continuous hammering, trimming with scissors and penetrating with nails proved the battery can stably provide power output for electronic components with no risk of catching fire or bursting.