Braided wires boost energy density in lithium-ion batteries for wearable electronics

In a recent article published in Angewandte Chemie International Edition, researchers have reported that incorporating an ultrathin braided wire in the core of an electrode can significantly increase the energy density of lithium-ion batteries. Such batteries could be integrated into functional textiles and used to power electronic devices while they are being worn. By replacing the single continuous wire current collector with a braided structure, ion transport within the electrode is improved, leading to an increase in charge density.

Lithium-ion batteries are commonly used in a wide range of devices, from smartphones to electric cars. Traditionally, these batteries are made up of a stack of electrodes, resulting in bulky or cylindrical designs. However, a new variant has been developed that reduces the stack to the dimensions of a thread made up of two long electrode fibers. These fiber batteries are lightweight and can be woven into fabric, making them ideal for wearable electronics. In fact, they were declared one of IUPAC’s Top Ten Emerging Technologies in Chemistry in 2022.

Despite their potential, there is a problem with using fiber batteries to supply power to functional clothing and tents – the energy density in long fibers is too low to be useful. To address this issue, Huisheng Peng and his team at Fudan University in Shanghai decided to redesign the current collector of the electrode.

The team replaced the continuous, thin metal wire inside the graphite electrode with a braid made up of several much thinner metal threads. To produce the braid, they unwound ultra-thin metal threads from spindles and braided them into a central braided thread. This thread was then coated with graphite over the whole electrode.

Tests demonstrated that the new braided current collector led to an increase in energy density, as the braiding structure led to channels filled with active materials, reducing obstruction to lithium ion transport and increasing the loading capability of active materials. A woven textile was produced containing 40 one-meter-long fiber batteries with braided current collectors, which was able to charge a smartphone from 30% to 57%. In contrast, the conventional fiber battery design using a continuous current collector wire only managed to reach 52%.

The increase in efficiency was achieved through a relatively simple change in the design of the current collector, which is particularly important for long fiber batteries that need to be robust, stable, and light.

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