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Researchers with McGill鈥檚听Trottier Institute for Sustainability in Engineering and Design听have developed a stretchable, eco-friendly battery听suitable for听use in听wearable and implantable devices. The battery, which听uses听citric or听lactic听acid and gelatin to achieve flexibility and performance without relying on toxic materials, stands to reduce electronic waste.
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鈥淲e use a lot of batteries in our lab for wearable devices, and they eventually stop working and get thrown out,鈥澨齭aid听research听supervisor听Sharmistha Bhadra, Associate Professor of Electrical and Computer Engineering.听鈥淭his project asked whether we could make something biodegradable and stretchable that still performs well.鈥澨�

Inspired by lemons听

The electrodes in conventional batteries are often made of heavy metals.听The researchers replaced these harmful components with magnesium and molybdenum,听commonly used in biodegradable battery designs,听which degrade more easily in the environment.听However,听earlier studies have shown that magnesium-based biodegradable batteries have听lower听performance听than conventional batteries.听

To solve that problem, the researchers tested two naturally occurring acids, lactic acid and citric acid,听mixed with gelatin, and found that听adding听either听acid听resolved the issue.听

鈥淢agnesium can generate a layer that stops the reaction between electrolyte and electrode,鈥澨齟xplained doctoral student听Junzhi听Liu, who led battery development and testing. 鈥淲e found we could break down this layer with听citric听or lactic听acid听and increase the battery鈥檚 lifetime and its voltage.鈥濃��听

Bhadra said the idea to use citric acid was inspired by a common children鈥檚 science project.听

鈥淢any people make a lemon battery听as听kids, where you connect a copper wire to a light. The lemon has enough ions to conduct electricity,鈥� she said.听鈥淚 suggested听Junzhi听look at citric acid.鈥澨�

Gelatin and听kirigami-style design provide stretchability听

To make the battery stretchable, the researchers suspended听both听acids听in gelatin.听They also cut the battery in a听kirigami听pattern, a technique that allows materials to bend and stretch without breaking. While听kirigami听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听affecting听its performance.听

The team also tested the battery in a pressure sensor to simulate real-world use. They听found it produced slightly less power than an AA battery (1.3 volts versus 1.5 volts) when connected to a device.听

鈥淲e wanted to see if we could run an actual wearable or sensor,鈥� Bhadra said. 鈥淪o听Junzhi听built a touch-sensitive device听worn on听a听finger听and听powered by the battery.鈥澨�

She added that the design is ideal for medical implants听and wearables听but could also power flexible Internet-of-Things devices.听听

Tackling the problem of e-waste听

The team is seeking industry partners to continue development. Next steps include improving performance, miniaturizing the battery for implantable听use听and integrating the design with听biodegradable听circuits.听

鈥淭he whole motivation is to address the growing problem of electronic waste,鈥� Bhadra said. 鈥淚f you go to a landfill, you see discarded electronics piled up for years. We are not听very good听about recycling [e-waste]; much of it ends up in lower-income countries.听Maybe we听can solve a part of the problem by developing biodegradable electronics.鈥澨�

About the study鈥�听

鈥溙齜y听Junzhi听Liu, Gregory Lazaris,听Jinhyuk听Lee听and听Sharmistha Bhadra, was published in听Advanced Energy and Sustainability Research听in August 2025.听听

It was听funded听by the 51吃瓜网Sustainability Systems Initiative.听