Self-Healing Flexible Batteries: Safer and Better for Wearables

In an era where energy efficiency and flexibility are paramount, the evolution of energy storage technologies has taken center stage. Among the latest advancements, Micro Flexible Energy Storage Devices (MFESDs) have emerged as a promising solution to address the growing demand for compact, adaptable, high-performance energy storage systems.

However, aqueous micro batteries (AMBs) have garnered significant attention as a leading choice for Micro Flexible Energy Storage Devices (MFESDs). Utilizing water-based solutions as electrolytes, AMBs offer enhanced safety and cost-effectiveness compared to traditional lithium-ion batteries. Despite their lower energy density, their reduced flammability and affordability make them ideal for wearable technology applications. Recent advancements focus on improving their flexibility and durability, which are essential for the dynamic nature of wearable devices.

Self-healing AMBs

Researchers have invented a safer, cheaper, and more flexible AMB for wearable technology, as detailed in Nano Research Energy. This new battery, ideal for fitness trackers and smartwatches, combines ammonium ions and hydrogel for self-healing properties and enhanced performance. Testing revealed excellent energy density, cycle life, and flexibility, significantly advancing wearable energy storage solutions.

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“Up till now, sadly, AMBs have not lived up to their potential,” stated Ke Niu, a materials scientist with the Guangxi Key Laboratory of Optical and Electronic Materials and Devices at the Guilin University of Technology—one of the lead researchers on the team. “To be able to be used in a wearable device, they need to withstand a certain degree of real-world bending and twisting. But most of those explored so far fail in the face of such stress.”

Non-metallic charge carriers

Researchers of the team opted for non-metallic charge carriers in their new battery design to enhance durability and performance. Metallic compounds used previously in self-healing AMBs react strongly with electrode materials, reducing the battery's reaction rate and overall performance. Nevertheless, non-metallic charge carriers, such as ammonium ions, avoid these interactions, ensuring better compatibility with electrode materials. This approach minimizes performance degradation and supports the self-healing mechanism, allowing the battery to withstand real-world stress like bending and twisting, making it ideal for wearable devices. The new design significantly improves battery reliability and efficiency by eliminating the negative side effects of metal ions.

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“But ammonium ions are not the only ingredient in the recipe needed to make our batteries self-healing,” said Long Zhang, the third leading member of the research team with the School of Physics and Center for Nanoscale Characterization & Devices (CNCD) at the Huazhong University of Science and Technology in Wuhan.

The researchers used a hydrogel matrix in their new battery design to provide flexibility and self-healing properties. Hydrogels, such as polyvinyl alcohol (PVA), can absorb and retain large amounts of water while maintaining their structure, which imparts impressive flexibility. This flexibility is crucial for wearable devices that must withstand bending and twisting. Additionally, the hydrogel matrix supports the self-healing mechanism by allowing the battery to recover from physical damage or stress. By incorporating the ammonium salts into the hydrogel, the battery gains the necessary mechanical resilience and durability to function reliably in dynamic, real-world conditions.

With further optimization efforts underway, the team envisions a future where their innovation revolutionizes the wearable device energy storage landscape. By enhancing comfort, reliability, and performance in energy storage, this innovation paves the way for more efficient and versatile wearable devices, improving user experience and expanding potential applications.