Researchers with McGill's Trottier Institute for Sustainability in Engineering and Design have developed a stretchable, eco-friendly battery suitable for use in wearable and implantable devices. The battery, which uses citric or lactic acid and gelatin to achieve flexibility and performance without relying on toxic materials, stands to reduce electronic waste.
"We use a lot of batteries in our lab for wearable devices, and they eventually stop working and get thrown out," said research supervisor Sharmistha Bhadra, Associate Professor of Electrical and Computer Engineering. "This project asked whether we could make something biodegradable and stretchable that still performs well."
Inspired by lemons
The electrodes in conventional batteries are often made of heavy metals. The researchers replaced these harmful components with magnesium and molybdenum, commonly used in biodegradable battery designs, which degrade more easily in the environment. However, earlier studies have shown that magnesium-based biodegradable batteries have lower performance than conventional batteries.
To solve that problem, the researchers tested two naturally occurring acids, lactic acid and citric acid, mixed with gelatin, and found that adding either acid resolved the issue.
"Magnesium can generate a layer that stops the reaction between electrolyte and electrode," explained doctoral student Junzhi Liu, who led battery development and testing. "We found we could break down this layer with citric or lactic acid and increase the battery's lifetime and its voltage."
Bhadra said the idea to use citric acid was inspired by a common children's science project.
"Many people make a lemon battery as kids, where you connect a copper wire to a light. The lemon has enough ions to conduct electricity," she said. "I suggested Junzhi look at citric acid."
Gelatin and kirigami-style design provide stretchability
To make the battery stretchable, the researchers suspended both acids in gelatin. They also cut the battery in a kirigami pattern, a technique that allows materials to bend and stretch without breaking. While kirigami structures have been used before in stretchable electronics, their application to biodegradable batteries is still relatively new. In this design, the researchers found they could stretch the battery up to 80 per cent without affecting its performance.
The team also tested the battery in a pressure sensor to simulate real-world use. They found it produced slightly less power than an AA battery (1.3 volts versus 1.5 volts) when connected to a device.
"We wanted to see if we could run an actual wearable or sensor," Bhadra said. "So Junzhi built a touch-sensitive device worn on a finger and powered by the battery."
She added that the design is ideal for medical implants and wearables but could also power flexible Internet-of-Things devices.
Tackling the problem of e-waste
The team is seeking industry partners to continue development. Next steps include improving performance, miniaturizing the battery for implantable use and integrating the design with biodegradable circuits.
"The whole motivation is to address the growing problem of electronic waste," Bhadra said. "If you go to a landfill, you see discarded electronics piled up for years. We are not very good about recycling [e-waste]; much of it ends up in lower-income countries. Maybe we can solve a part of the problem by developing biodegradable electronics."
About the study
"Gelatin-Organic Acid-Based Biodegradable Batteries for Stretchable Electronics," by Junzhi Liu, Gregory Lazaris, Jinhyuk Lee and Sharmistha Bhadra, was published in Advanced Energy and Sustainability Research in August 2025.
It was funded by the McGill Sustainability Systems Initiative.
