Electronics designed to bend and stretch require batteries that possess the same flexible characteristics. Many attempts to construct such batteries have utilized conductive fabric woven into expandable forms or rigid components arranged in origami-like configurations. However, for optimal flexibility, all components of the battery, including the electrodes that gather charge and the central electrolyte layer that balances the charge, need to be inherently stretchable. Existing prototypes of truly flexible batteries often display only moderate elasticity, involve complex manufacturing processes, or suffer from limited energy storage capabilities that diminish with each charging cycle. This degradation in performance is frequently due to poor connections between the electrolyte layer and the electrodes or the instability of the liquid electrolyte, which may shift position as the battery's shape changes. Addressing these challenges, researchers have now developed a lithium-ion battery composed entirely of stretchable components that feature an electrolyte layer capable of expanding by 5000%, maintaining its charge capacity even after almost 70 charge and discharge cycles.

The completely solid, stretchy battery was created by scientists at Nanjing University of Posts & Telecommunications (Nanjing, China) by incorporating the electrolyte into a polymer layer fused between two flexible electrode films. To construct the electrodes for this fully stretchable battery, the researchers spread a thin layer of conductive paste made from silver nanowires, carbon black, and lithium-based cathode or anode materials onto a surface. They then applied a layer of polydimethylsiloxane—a flexible polymer commonly found in contact lenses—over the paste. Directly on this layer, they added lithium salt, a conductive liquid, and the components needed to create an elastic polymer, which solidified into a rubber-like material under light activation. This material could stretch to 5000% of its original size and effectively transport lithium ions. The stack was topped with another electrode film with the entire device sealed in a protective coating.

According to research published in ACS Energy Letters, when compared to a similar stretchy battery design using a traditional liquid electrolyte, this novel solid-state battery exhibited approximately six times the average charge capacity at a fast-charging rate. Additionally, it maintained a more consistent capacity over 67 charging cycles. Comparatively, other prototypes with solid electrodes showed that the polymer electrolyte performed reliably across 1000 cycles, with only a 1% capacity reduction in the first 30 cycles, a significant improvement over the 16% reduction seen in batteries with liquid electrolytes. While further enhancements are needed, this breakthrough in creating fully stretchable, solid-state batteries marks a significant advancement in the development of wearable or implantable devices that need to flex and move with the human body. 

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