A team of Swedish researchers has created a flexible, stretchable battery that can be shaped like toothpaste and embedded in a wide variety of wearable tech and medical devices.
Unlike conventional bulky batteries, this one uses liquid electrodes made from sustainable materials like lignin, a paper industry byproduct, and conductive plastics. It maintains performance even when stretched to double its length and can be recharged hundreds of times. With major design and environmental advantages, the innovation could revolutionize how we power the billions of smart gadgets expected in the coming decade.
Shapable Soft Batteries Break the Mold
Researchers at Linköping University have developed a new kind of battery that can be molded into virtually any shape, thanks to its fluid-based electrodes. This soft, flexible design opens the door to integrating batteries into future technologies in entirely new ways. The findings are published today (April 11) in Science Advances.
“The texture is a bit like toothpaste. The material can, for instance, be used in a 3D printer to shape the battery as you please. This opens up for a new type of technology,” says Aiman Rahmanudin, assistant professor at Linköping University.
In the next ten years, over a trillion devices are expected to connect to the Internet. Alongside familiar gadgets like smartphones, smartwatches, and laptops, this explosion of connectivity will include wearable medical devices such as insulin pumps, pacemakers, hearing aids, and health monitors. Looking further ahead, it may also extend to soft robotics, electronic textiles, and nerve-connected implants.
The Need for Flexible Battery Innovation
To power this vast array of devices, many of which will be worn or embedded in the body, batteries need to be smaller, softer, and more adaptable.
“Batteries are the largest component of all electronics. Today they are solid and quite bulky. But with a soft and conformable battery, there are no design limitations. It can be integrated into electronics in a completely different way and adapted to the user,” says Aiman Rahmanudin.
Together with his colleagues at the Laboratory of Organic Electronics, LOE, he has developed a battery that is soft and malleable. The key has been a new approach – converting the electrodes from a solid to a liquid form.
Rethinking Battery Structure for Stretchability
Previous attempts to manufacture soft and stretchable batteries have been based on different types of mechanical functions, such as rubbery composite materials that can be stretched out or connections that slide on each other. But this does not deal with the core of the problem – a large battery has higher capacity, but having more active materials means thicker electrodes and thus higher rigidity.
“Here, we’ve solved that problem, and we’re the first to show that capacity is independent of rigidity,” says Aiman Rahmanudin.
Fluid electrodes have been tested in the past but without any great success. At that time, liquid metals such as gallium were used. But then the material can only function as an anode and has the risk of being solidified during charging and discharging – losing its fluid nature. In addition, many of the stretchable batteries previously made have used rare materials that have a major environmental impact when mined and processed.
A Battery Made of Paper Waste and Plastic
The researchers at LiU Campus Norrköping have instead based their soft battery on conductive plastics (conjugated polymers) and lignin, a byproduct from paper production. The battery can be recharged and discharged over 500 times and still maintain its performance. It can also be stretched to double the length and still work just as well.
“Since the materials in the battery are conjugated polymers and lignin, the raw materials are abundant. By repurposing a byproduct like lignin into a high-value commodity such as a battery material we contribute to a more circular model. So, it’s a sustainable alternative,” says Mohsen Mohammadi, postdoctoral fellow at LOE and one of the lead authors behind the article published in Science Advances.
The next step is to try to increase the electrical voltage in the battery. According to Aiman Rahmanudin, there are currently some limitations that they need to overcome.
“The battery isn’t perfect. We have shown that the concept works but the performance needs to be improved. The voltage is currently 0.9 volts. So now we’ll look at using other chemical compounds to increase the voltage. One option that we are exploring is the use of zinc or manganese, two metals that are common in the Earth’s crust,“ says Aiman Rahmanudin.
Reference: “Make it flow from solid to liquid: Redox-active electrofluids for intrinsically stretchable batteries” by Mohsen Mohammadi, Saeed Mardi, Jaywant Phopase, Filippa Wentz, Jibin J. Samuel, Ujwala Ail, Magnus Berggren, Reverant Crispin, Klas Tybrandt and Aiman Rahmanudin, 11 April 2025, Science Advances.
DOI: 10.1126/sciadv.adr9010
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