American scientists have developed a hydrogel that makes lithium batteries stretchable. The material is suitable for wearables.
Many electronic devices have a Li-ion battery, from laptops to smart watches and electric cars. Lithium batteries have many qualities: you can recharge them thousands of times before they wear out. American scientists have developed a special battery that you can bend and stretch.
Researchers from the University of California, Berkeley and Georgia Institute joined forces to develop a new electrolyte for lithium batteries, based on a hydrogel with low water content. Compared to earlier, similar experiments, the electrolyte contains no fluorine or other toxic substances and combines high stretchability with self-healing properties.
The hydrogel contains a fluorine-free lithium salt and a polymer structure that ensures stable ion conduction. Thanks to molecular interactions with water molecules and lithium ions, the electrolyte remains functional under normal humidity. The battery works stably for at least a month at room temperature without loss of performance. Even under mechanical stress such as folding, twisting, and punctures, the battery retains its capacity.
Bending, Folding, and Cutting
To substantiate this last claim, the researchers subjected the battery to various tortures. The battery was cut with a razor blade, punctured with a needle, and even heated to 70 °C. The system can recover and function again. The mechanism relies on reversible chemical bonds between functional groups in the hydrogel, including ionic interactions and hydrogen bonds.
A prototype consisting of a stretchable battery and an electronic circuit demonstrated that the system can continue to power an LED, even after damage and recovery. The electrolyte does not leak and is not flammable, making it safer than traditional solutions with organic solvents.
According to the researchers, this technology is applicable in wearable electronics and soft robots, where flexibility and safety are essential. In future applications, they want to further increase the energy density level by using other electrode materials or optimizing the design.