A Leap in Flexible Electronics: Revolutionary Stretchable Lithium-Ion Battery

Stretchable lithium-ion batteries with entirely elastic components offer a promising step forward for wearable or implantable devices.

Flexible electronics are on the rise, especially in the realm of wearable health monitors, and their success hinges on the development of equally flexible batteries. Addressing this need, researchers from ACS Energy Letters have unveiled a lithium-ion battery that boasts entirely stretchable components. This innovative battery features an electrolyte layer capable of expanding by an astonishing 5000% while maintaining its charge storage capacity after nearly 70 charge/discharge cycles.

The challenge in creating such adaptable batteries lies in ensuring all components, from electrodes to the electrolyte layer, possess the necessary elasticity. Previous attempts involved woven conductive fabric or rigid components folded into flexible shapes akin to origami. However, these designs often resulted in moderate elasticity, complicated assembly processes, or limited energy storage capacity, particularly with repeated use. This is often due to weak connections between the electrolyte layer and electrodes or instability in the liquid electrolyte, which can shift when the battery deforms.

To overcome these limitations, Wen-Yong Lai and his team embarked on a novel approach. They integrated the electrolyte into a polymer layer positioned between two flexible electrode films, forming a solid, stretchable battery. This innovative design eliminates the need for a liquid electrolyte, enhancing the stability and performance of the battery under strain.

The creation of this fully elastic battery involved several meticulous steps. The team first spread a conductive paste, containing silver nanowires, carbon black, and lithium-based cathode or anode materials, onto a plate. A layer of polydimethylsiloxane (PDMS), a material known for its flexibility and common use in contact lenses, was then applied over the paste. Next, a mixture of lithium salt, a highly conductive liquid, and ingredients for a stretchy polymer was added. Upon light activation, these components formed a solid, rubbery layer capable of stretching to 5000% of its original length and effectively transporting lithium ions. The final assembly involved topping this stack with another electrode film and sealing the entire device in a protective coating.

Comparative tests showcased the superior performance of this solid, stretchy battery. It exhibited approximately six times higher average charge capacity at a fast-charging rate than a similar device with a traditional liquid electrolyte. Furthermore, the solid battery demonstrated a more stable capacity over 67 charging and discharging cycles. In prototypes with solid electrodes, the polymer electrolyte maintained steady operation over 1000 cycles, with only a 1% drop in capacity in the first 30 cycles compared to a 16% drop for the liquid electrolyte.

While there are still improvements to be made, this pioneering method of creating fully stretchable, solid batteries marks a significant advancement in the development of wearable or implantable devices that need to flex and move with the body.

For more detailed insights, the paper “Elastic Polymer Electrolytes Integrated with In Situ Polymerization-Transferred Electrodes toward Stretchable Batteries” is available here.