Researchers at Hong Kong Polytechnic University (PolyU) have developed a highly flexible, high-energy textile lithium battery that offers more stable, durable, and safe energy supply for wearable electronics with a myriad of applications, including healthcare monitoring and intelligent textiles.
The novel lightweight textile lithium battery demonstrates high energy density of more than 450 Wh/L and excellent flexibility — with a bending radius of <1 mm and foldability of over 1,000 cycles with marginal capacity degradation. In comparison, existing bendable lithium batteries can only reach a bending radius of about 25 mm, and with much lower performance of <200 Wh/L. The battery, which is <0.5 mm thick, is capable of fast charging/discharging. It offers a long cycle life comparable with conventional lithium batteries. The battery was developed by the research team of PolyU's Institute of Textiles and Clothing (ITC).
“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 US $100 billion by 2024,” says Prof. Zheng Zijian, who leads the ITC team. “As all wearable electronics will require wearable energy supply, our novel technology in fabricating textile lithium battery offers promising solution to a wide array of next-generation applications.”
Lithium batteries are currently the dominant rechargeable battery in the market due to their relatively high-energy density and long cycle life. Conventional lithium batteries bulky and heavy, making them hard for use in wearable devices. Over the past decade, scientists worked to develop bendable lithium batteries, often by using metal foils as current collectors. PolyU's textile lithium battery goes further by addressing energy density, flexibility, mechanical robustness, and cycling stability (see Table 1).
Highly conductive metal, copper, and nickel are uniformly and conformally deposited onto pretreated fabrics using PolyU's polymer-assisted metal deposition (PAMD). Such fabricated metallic fabrics, featuring low sheet resistance and large surface area, serve as current collectors in battery. After adding active materials to act as a cathode and an anode, the metallic fabrics, together with a separator and electrolyte, are assembled into the textile lithium battery.
The ITC team conducted tests to demonstrate the battery's extremely high mechanical stability, durability, and safety under deformation. When the battery is repeatedly folded in half, twisted at different angles or freely crumpled, its voltage window remained unchanged. A bending test showed that the battery can be bent more than 1,000 times with marginal capacity degradation. Safety tests conducted by continuous hammering, trimming with scissors, and penetrating with a nail proved that the battery can stably provide power output for the electronic components with no risk of catching fire or bursting.
The findings are published in Chang et al., “Flexible and stable high-energy lithium-sulfur full batteries with only 100% oversized lithium,” Nature Communications, 2018, 9(1): 4480.