The development of stretchable lithium-ion batteries marks a significant advancement in the realm of flexible electronics, particularly for wearable health monitors. Researchers, as reported in ACS Energy Letters, have introduced a lithium-ion battery with entirely stretchable components, including an electrolyte layer that can expand by 5000%. Remarkably, this battery retains its efficient charge storage after 70 charge/discharge cycles.
Traditional batteries are rigid, but flexible electronics require equally flexible power sources. Previous attempts at creating such batteries involved woven conductive fabrics or rigid components folded into expandable shapes, akin to origami. However, for a truly malleable battery, every part—including the charge-collecting electrodes and the charge-balancing electrolyte layer—must be elastic.
Existing prototypes of stretchable batteries often face challenges like moderate elasticity, complex assembly processes, or limited energy storage capacity. These issues arise from weak connections between the electrolyte layer and electrodes or the instability of liquid electrolytes, which can shift when the battery changes shape. Wen-Yong Lai and his team aimed to address these problems by incorporating the electrolyte into a polymer layer fused between two flexible electrode films, resulting in a completely solid, stretchy battery.
To create the electrodes, the team spread a thin film of conductive paste containing silver nanowires, carbon black, and lithium-based cathode or anode materials onto a plate. They then applied a layer of polydimethylsiloxane, a flexible material commonly used in contact lenses, on top of the paste. On this film, they added a lithium salt, a highly conductive liquid, and ingredients to form a stretchy polymer. When activated by light, these components formed a solid, rubbery layer capable of stretching to 5000% of its original length and transporting lithium ions. The stack was topped with another electrode film and sealed in a protective coating.
This innovative solid stretchy battery demonstrated about six times higher average charge capacity at a fast-charging rate compared to a similar device with a traditional liquid electrolyte. It maintained 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% capacity drop in the first 30 cycles, compared to a 16% drop for the liquid electrolyte.
While further improvements are necessary, this new approach to creating fully stretchable, solid batteries represents a promising step forward for wearable or implantable devices that must flex and move with the body.