High-Performance Stretchable Gallium Battery for Wearable Electronics, Through Synthesis of Foam Electrodes

The demand for sustainable and stretchable thin-film printed batteries for bioelectronics, wearables, and e-textiles is rapidly increasing. Recently, we developed a fully 3D-printed soft-matter thin-film Ga-Ag₂O battery with 3R characteristics: resilient to mechanical strain, repairable after damage, and recyclable. This battery achieved a record-breaking areal capacity of 26.37 mAh cm⁻², increasing to 30.32 mAh cm⁻² after 10 cycles under 100% strain. This performance stems from the synergistic effects of gallium's liquid metal properties and the styrene-isoprene-styrene polymer in the anode. Gallium's high specific capacity (1153.2 mAh g⁻¹), deformability, and self-healing abilities, supported by its supercooled liquid phase, significantly enhance the battery's resilience and efficiency. However, the cathode's lower theoretical capacity, due to Ag₂O (231.31 mAh g⁻¹), remains a limitation. Traditional Ag₂O-carbon black-styrene-isoprene-styrene cathodes experience rapid capacity decay as only the surface area of the active materials interacts with the electrolyte. To overcome this, we designed a carbon-filled Ag₂O foam electrode using a sacrificial sugar template, increasing the effective surface area. This optimization enhanced ion-exchange efficiency, specific capacity, and cyclability, achieving a specific capacity of 221.16 mAh g⁻¹. Consequently, the Ga-Ag₂O stretchable battery attained a record areal capacity of 40.91 mAh cm⁻²—double that of nonfoam electrodes—and exhibited fivefold improved charge–discharge cycles. Using ultrastretchable Ag-EGaIn-styrene-isoprene-styrene and carbon black-styrene-isoprene-styrene current collectors, the battery's specific capacity increased by 33% under 50% strain. Integrated into a soft-matter smart wristband for temperature monitoring, the battery demonstrated its promise for wearable electronics.