At the convergence of 3D-printing and lithium battery technology, Hong Kong researchers develop a promising textile-based, foldable battery that may find its way onto IoT-connected fabrics within automotive, aerospace, and medical industries.
A researcher team at the Hong Kong Polytechnic University (PolyU) have leveraged a previously patented PolyU additive manufacturing technology – polymer-assisted metal deposition (PAMD) – to develop a highly flexible, high-energy textile lithium battery. While bendable batteries have been a focus of research for the past decade, PolyU researchers have confirmed the textile lithium battery’s promising level of stability, durability, and safety in what may be a breakthrough for wearable electronics.
With applications ranging from healthcare monitoring, intelligent textiles, smartphones, Global Positioning System (GPS) tracking, and Internet of Things (IoT), PolyU's lightweight textile lithium battery demonstrates high energy density of more than 450 watt-hours per liter and excellent flexibility – with a bending radius of less than one millimeter and foldability of over 1,000 cycles with marginal capacity degradation.
In comparison, the existing bendable lithium batteries can only reach a bending radius of about 25 millimeters at less than 200 watt-hours per liter. The less-than-one-half-millimeter-thick textile lithium battery also possesses fast charge and discharge capabilities and cycle life comparable to conventional lithium batteries.
“Wearable technology has been named as the next global big market opportunity after smartphones. Global market revenues for wearable devices are forecasted to grow by leaps and bounds, of over 20 percent annually, to reach $100 billion by 2024,” says Professor Zheng Zijian, who lead the PolyU Institute of Textiles and Clothing research team.
“As all wearable electronics will require wearable energy supply, our novel technology in fabricating [the] textile lithium battery offers 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,” concludes Zijian.
Lithium battery technology currently dominates the rechargeable battery market due to its relatively high energy density and long cycle life. Previous attempts at developing thin, bendable lithium batteries for use in wearable devices, typically resulted in the use of metal foils as current collectors. However, complications with this method resulted in various combinations of low energy density, inflexibility, lack of mechanical robustness, and poor cycling stability.
Image courtesy: The Hong Kong Polytechnic University
Through PolyU's novel PAMD additive manufacturing technology, researchers uniformly and conformally deposited highly conductive copper and nickel metals onto pre-treated fabrics, which then serve as current collectors. Additional active materials are then added to the material to act as cathode and anode. The metallic textile is then combined with a separator and electrolyte and assembled into the final textile lithium battery.
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These metallic fabrics feature low sheet resistance and large surface area – two important characteristics of conductive materials:
- Sheet resistance is the quantifiable measurement of how long it takes to transport charge in a material: the lower the sheet resistance, the faster the transfer of charge.
- Larger surface areas allow for loading more anode and cathode materials, which increases stability and allows for higher charge and discharge speed and better flexibility is the battery. The use of PolyU PAMD technology allows for precise control of the deposition time, thickness, and sheet resistance of the metallic yarns. The surface area of a sheet of woven 3D metallic yarn is much greater than that of a similarly sized foil sheet.
Laboratory tests conducted by the ITC team have shown extremely high mechanical stability, durability, and safety of PolyU’s battery under deformation. When the battery is repeatedly folded in half, twisted at different angles, or freely crumpled, its voltage window remained unchanged. Safety tests conducted by continuous hammering, trimming with scissors, and nail penetration demonstrate that the battery can stably provide power output for electronic components with no risk of catching fire or bursting.
So far, the innovation has won three prizes at the 47th International Exhibition of Inventions of Geneva: a Gold Medal and two Special Merit Awards.
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William Kucinski is content editor at SAE International, Aerospace Products Group in Warrendale, Pa. Previously, he worked as a writer at the NASA Safety Center in Cleveland, Ohio and was responsible for writing the agency’s System Failure Case Studies. His interests include literally anything that has to do with space, past and present military aircraft, and propulsion technology.
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