The lithium-ion battery can heal itself after being cut in half
By Charles Q. Choi
A new lithium-ion battery can not only withstand stretching and twisting, but can get stabbed with needles and cut in half with razor blades—and then heal itself to continue providing power to a device.
Wearable electronics, soft robots, and other devices could benefit from soft, stretchable lithium-ion batteries. However, most commercial lithium-ion batteries are hermetically sealed in rigid packages to keep out moisture that can degrade their performance, and to prevent toxic and flammable electrolytes from leaking out.
Previous research had investigated stretchable batteries that used hydrogels as their electrolytes. By using water as their solvent, these hydrogel batteries would prove nonflammable and less sensitive to moisture than commercial lithium-ion batteries. However, prior devices suffered from a number of limitations. Some only proved stable in relatively low voltages. Others depended on toxic, expensive flourine-loaded compounds.
In the new study, researchers developed a new water-based hydrogel lithium-ion battery that does not contain fluorine. “Many materials we used are non-standard to conventional lithium-ion batteries,” says a postdoctoral researcher of mechanical engineering at the University of California, Berkeley Peisheng He. “We surmounted those challenges by learning lessons from unsuccessful trials, building and constantly improving fabrication and testing protocols.”
Previous stretchable batteries have proven sturdy, surviving twisting and even strikes from a hammer. The new battery displays another level of durability, not only enduring stretching, twisting, and folding, but continuously powering a yellow light even while being repeatedly punctured with needles. In addition, “the battery can be cut in half, put together, and self-heal to still maintain more than 90 percent of its capacity,” says a professor of mechanical engineering at the University of California, Berkeley Liwei Lin.
New Durable Hydrogel Lithium-Ion Battery
The new battery proved stable up to 3.11 volts. Past hydrogel batteries were only stable up to 1.23 volts. Moreover, over the course of a month, it operated stably over 500 cycles of charging and discharging, on average discharging 95 percent of the electric charge it received.
“Integrating our batteries into the wristband of a smart watch can multiply the watch’s battery capacity, such that one may only need the recharge once a week or longer,” says an assistant professor of materials science and engineering at the Georgia Institute of Technology Anju Toor.
The scientists caution that the energy density of their battery is only about one-tenth of the lithium-ion batteries on the market, “so there is work to be done,” He says. “We expect optimizations on the electrode structure, high capacity electrodes, and electrolyte chemistry will further improve the energy density in future.”
Still, “even without these improvements, the current prototype would be enough to replace the polymer band of a smart watch to provide additional power,” Lin says.
The researchers are now trying to push this technology from lab-scale fabrication to industry-level high-throughput manufacturing through a roll-to-roll process, Toor says.
The scientists detailed their findings 9 April in the journal Science Advances.
- Q. Choi is a contributing editor for IEEE Spectrum.
