Ultra‑stretchable anti‑freezing hydrogel electrolytes cross‑linked by liquid metal particle initiators toward soft energy storage devices

As wearable electronics and soft robotics advance, conventional energy storage devices struggle to meet the demands for mechanical flexibility and extreme-temperature operation. Now, researchers from Sungkyunkwan University, led by Professor Sungjune Park, have developed a breakthrough hydrogel electrolyte that enables stretchable supercapacitors to perform reliably from -40°C to 80°C.

Why This Electrolyte Matters

Traditional hydrogel electrolytes face a critical trade-off: high water content enables ionic conductivity but causes freezing at sub-zero temperatures and poor mechanical strength. The novel PSLM/LiCl hydrogel overcomes these limitations by using liquid metal nanoparticles as polymerization initiators and introducing hydrophobic stearyl methacrylate (SMA) associations—creating dense physical cross-linking networks that deliver both ultra-stretchability and anti-freezing capability.

Innovative Design and Mechanism

The material is synthesized through liquid metal-initiated free-radical polymerization, where gallium nanoparticles generate radicals to cross-link acrylamide and acrylic acid within one minute. SMA segments form hydrophobic associations acting as dynamic cross-linking points, while subsequent LiCl immersion disrupts water hydrogen bonding to depress the freezing point below -40°C. This dual-network structure maintains ionic pathways even under severe deformation.

Outstanding Performance

The hydrogel achieves 907% elongation at break, 766 kPa tensile strength, and 4.35 S m^-1 ionic conductivity at 25°C—retaining 3.39 S m^-1 and 897% stretchability at -20°C. Assembled supercapacitors deliver 93.52 mF cm^-2 areal capacitance with exceptional durability: 98% capacitance retention over 45,000 cycles, surpassing most reported hydrogel-based devices. The system operates stably across bending angles up to 180° and temperatures from -20°C to 80°C.

Applications and Future Outlook

Three series-connected units power commercial LEDs for over one minute, demonstrating practical viability for next-generation wearable and cold-climate energy storage. This work establishes a versatile platform for soft, deformable electronics requiring reliable performance in extreme environments.