Consumer Electronics

Flexible and wearable batteries

16 February 2024
The evolution of flexible and stretchable batteries marks a leap forward in powering wearable devices. Source: Yu Lin/University of California San Diego

In portable electronics and wearable devices, the demand for energy storage solutions that are both flexible and lightweight has seen a surge of interest. Traditional rigid and bulky batteries pose potential design constraints in some applications, such as limiting the integration of electronics into everyday wearables and flexible gadgets. The advent of flexible and wearable batteries marks an interesting shift in battery design, offering innovative energy storage mechanisms that conform to the dynamic shapes and movements inherent in wearable technology.

Building blocks of flexibility

The evolution of flexible and stretchable batteries marks a leap forward in powering wearable devices, offering a seamless integration with the dynamic nature of human movement and wear. Unlike traditional power sources characterized by their bulkiness and rigidity, these batteries are flexible and stretchable, meeting the demands of a wide array of wearable technologies.

Central to these advancements are the novel approaches in fabricating free-standing electrodes that can bend, twist and stretch without losing functionality. This is achieved through the use of materials such as conductive polymers, graphene and thin lithium compounds, known for their exceptional electrical properties and mechanical resilience. The design of these batteries often involves creative configurations, such as honeycomb or zigzag patterns, ensuring that they can withstand physical stress without compromising performance.

Flexible electrolytes and separators

A crucial aspect of these batteries is the development of flexible and stretchable electrolytes and separators, which not only facilitate ionic movement but also maintain structural integrity under deformation. These components are pivotal in ensuring the batteries' efficiency and durability, making them suitable for a broad spectrum of wearable applications.

One of the primary engineering challenges is maintaining a consistent electrical connection between all components of the battery under deformation. This issue is addressed through the use of highly elastic binders and conductive additives that ensure the integrity of the electrical pathways, even when stretched or bent. Another challenge is the packaging of these batteries, as conventional metal casings would negate the flexibility. Instead, soft, resilient and sometimes even stretchable polymeric materials are used to encase the battery cells, providing protection without compromising flexibility.

To enhance the energy density and efficiency of flexible batteries, researchers are exploring various nanoengineering techniques to increase the surface area of electrodes, thereby boosting the battery's capacity to store energy. Additionally, solid-state electrolytes are being developed to replace liquid ones, offering improved safety and potentially enabling thinner, more flexible battery designs.

Flexible and wearable batteries in action

Flexible and wearable batteries are carving out their own niche across various industries, due to their adaptability and the growing demand for portable and wearable electronics. These innovative power sources are finding applications in healthcare, fashion and consumer electronics, among other fields, transforming how devices are designed and utilized.

Healthcare integration

In the healthcare sector, flexible batteries can be applied to patient monitoring and diagnostics. Wearable devices equipped with these batteries can be designed as lightweight patches, smart garments or even implantable sensors, providing continuous health monitoring without impeding patient comfort or mobility. For instance, a smart bandage embedded with a flexible battery can monitor wound healing, moisture levels and deliver drug treatments as needed, directly benefiting patient care with real-time data and interventions.

Fashion and smart textiles

Flexible battery design on clothing. Source: CSIROFlexible battery design on clothing. Source: CSIRO

The fashion industry is embracing flexible batteries to power smart textiles, blending aesthetics with functionality. These batteries are being sewn into fabrics to allow the charging of devices, to power LED displays, heating elements or sensors that can adjust to environmental changes or monitor physiological signals. A notable example is a jacket with integrated flexible batteries and solar cells, allowing wearers to charge their devices on the go, marrying convenience with sustainable energy use.

Consumer electronics

In consumer electronics, the demand for sleek, lightweight, and wearable devices is driving the integration of flexible batteries. From smartwatches and fitness trackers to wireless earbuds, these batteries enable slimmer designs and more ergonomic devices that conform to the user's body or clothing, enhancing user experience without sacrificing battery life. An innovative application is in foldable smartphones, where the battery's flexibility is needed to accommodate the bending motion without compromising performance or safety.

Innovations

Health monitoring tattoo: A research team developed an ultra-thin, flexible battery that powers a skin-mounted electronic tattoo, capable of monitoring vital signs like heart rate and body temperature, showcasing the potential for unobtrusive health monitoring solutions.

Energy-harvesting shoes: Incorporating flexible batteries into the soles of shoes, this innovation captures and stores energy generated from walking, potentially powering wearable devices and contributing to sustainable energy practices.

A person wearing running shoes on a stairway. Source: CC BY 3.0 DEEDA person wearing running shoes on a stairway. Source: CC BY 3.0 DEED

These applications underscore the versatility and utility of flexible and wearable batteries, highlighting their potential to transform everyday objects into smart, connected devices.

Challenges in development

The advent of flexible and wearable batteries brings with it a unique set of challenges and considerations, particularly in terms of scalability, durability and safety. Despite the promising applications, these hurdles must be addressed to ensure the widespread adoption and long-term success of these technologies.

One of the primary challenges in the field of flexible batteries is the issue of scaling production while maintaining quality and performance. The intricate designs and specialized materials required for these batteries often involve complex manufacturing processes that are difficult to scale up.

The very flexibility that makes these batteries appealing also introduces concerns regarding their durability and lifespan. Repeated bending, twisting and stretching can lead to material fatigue, potentially causing a decrease in battery performance over time. Ensuring that these batteries can withstand the rigors of daily use without significant degradation is necessary for their practical application, necessitating ongoing research into more resilient materials and designs.

Safety is paramount, especially when integrating batteries into wearable devices that maintain close contact with the body. Issues such as overheating, leakage of hazardous materials and potential short circuits need to be addressed. Furthermore, regulatory standards for these new types of batteries are still evolving, with a need for comprehensive guidelines that ensure user safety while fostering innovation.

Future outlook and emerging trends

Continued advancements in nanotechnology and materials science are expected to yield batteries with higher energy densities, improved safety profiles and even greater flexibility. Innovations such as self-healing batteries and energy-harvesting technologies are on the horizon, which could extend the lifespan and functionality of wearable devices.

The market for flexible and wearable batteries is projected to grow significantly as these technologies mature and find their way into more consumer products. The increasing demand for portable and wearable electronics, coupled with the push for more sustainable energy sources, is likely to drive further investment and research in this area.

About the author

Jody Dascalu is a freelance writer in the technology and engineering niche. She studied in Canada and earned a Bachelor of Engineering. As an avid reader, she enjoys researching upcoming technologies and is an expert on a variety of topics.

To contact the author of this article, email GlobalSpecEditors@globalspec.com


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