The field of wearable electronics requires flexible materials and batteries that can resist mechanical deformation. To develop new foldable, durable batteries for wearable electronics technologies, a paper published in Materials Today Energy has explored carbon nanotubes as materials.
Study: Ultra-flexible and foldable gel polymer lithium-ion batteries enabling scalable production. Image Credit: Mopic/Shutterstock.com
Wearable Electronics: An Innovative Field
The field of wearable electronics is providing innovative applications for the electronics market. There has been significant focus in the field on flexible storage devices for use in products such as electronic skins, smart clothes, flexible wearable communication devices, smart sensors, and medical devices.
Wearable electronics require advanced materials that can withstand mechanical deformation over multiple uses and possess superior conductivity. They must also be lightweight and comfortable for the wearer. In order to develop wearable electronics and storage devices, there has been much research in recent years into advanced materials for use in the field.
Current Issues with Flexible Batteries
Li-ion batteries have several advantages over other rechargeable battery types, including low self-discharge, long life cycles, reduced memory effects, and relatively high power and energy density. However, conventional batteries are too rigid for use in applications that require flexibility.
To overcome this drawback, flexible batteries have recently been developed and show significant potential for their use in powering wearable electronic devices. However, there are several key issues with the technology which must be overcome if they are to become widespread.
Storage devices, like all elements of a wearable device, must be durable and flexible, able to withstand extreme mechanical deformations such as stretching and folding, and must be lightweight and thin.
Developing New Advanced Materials for Wearable Batteries
Flexible batteries require that all their components can withstand mechanical stresses such as bending and folding. Conventional metal foils that are used as current collectors for positive and negative electrodes include aluminum and copper foils. These, however, are rigid and prone to fatigue failure and have difficulty returning to their original shape after deformation, making them unfit for use in flexible batteries.
Additionally, metal foils suffer from delamination of the active layer when batteries undergo bending. Furthermore, they are heavy, which reduces the battery system’s gravimetric capacity. Therefore, due to these issues, replacing the metal foils with lightweight, thin, flexible current collectors with high levels of conductivity is advantageous.
Recently, carbon-based materials have been explored for their use as current collectors for flexible battery systems. These materials have high conductivity, are chemically stable within a wide range of voltages, and have low density, making them ideal candidates for this application.
Further Reading: Biomimicry Offers Flexible Energy Storage Solution for Wearable Electronics
One-dimensional carbon nanotubes have emerged as particularly interesting materials for use as current collectors.
However, there still exist mechanical property and scalability challenges with carbon-based materials, and much of the research is still at the laboratory stage. A further challenge for flexible batteries lies in safety issues with electrolytes. Solid polymer electrolytes have been proposed to overcome the safety challenges, but they have issues with conductivity and electrochemical performance.
To overcome the issues with electrolytes, gel polymer electrolytes, which combine the advantages of both solid and liquid electrolytes, have been proposed. Gel electrolyte polymers act as both electrolytes and separators and can tolerate changes in the volume of electrode materials during charge and discharge.
Using Carbon Nanotubes and Gel Electrolyte Polymers for Flexible, Wearable Batteries
To this end, the paper published in Materialstoday Energy has developed a new flexible battery using carbon nanotubes and gel electrolyte polymers which provides significant improvements in electrochemical and mechanical performance.
Production of carbon nanotubes is scalable, and the material displays superior mechanical strength, is ultra-thin, lightweight, and has excellent electrical conductivity. The material can withstand thousands of physical deformations.
The thickness of components is minimized, and gravimetric energy density is improved. Increased contact between active layers and current collector are caused by the porous and rough surface characteristics of the carbon nanotubes. Adhesion is improved, and the material is less prone to stress cracking and delamination. The gel electrolyte polymers have high ionic conductivity and superior electrochemical and thermal stability.
These properties make the materials proposed in the paper ideal candidates for flexible energy storage in wearable electronics products, providing a robust and durable technological solution to the problems facing the wearable electronics industry.
Wearable electronics are providing interesting, innovative applications for multiple industries. Research into suitable advanced materials for their components is ongoing. Whilst challenges persist, this research provides an innovative approach for flexible energy storage that may be revolutionary for the industry.
Shen, W et al. (2021) Ultra-flexible and foldable gel polymer lithium ion batteries enabling scalable production [online] sciencedirect.com. Available at: https://www.sciencedirect.com/science/article/abs/pii/S2468606921002549