Stretchable Fluid Battery Can Flex Without Losing Power

Scientists at Linköping University have developed a stretchable battery that can conform to any shape, thanks to its fluid electrodes.

Made from conductive polymers and natural lignin, the soft battery could be a breakthrough for powering wearable technology – such as insulin pumps, pacemakers and other health monitoring sensors – as well as for soft robotics and e-textiles.  

The research was published in Science Advances.

Beating the bulk

Wearable technology is an important new frontier for healthcare monitoring. But with ever more Internet of Things-enabled gadgets finding their way into our lives, the applications of a flexible and malleable power source are manifold. However, creating such a battery is not without its challenges.

“Soft batteries are important to power next-generation wearables and electronics that interface closely with the human body. Soft electronic components are more advanced, but engineering a soft battery is challenging,” study author Dr. Aiman Rahmanudin, assistant professor in materials chemistry at Linköping University, told Technology Networks. “Batteries are typically bulky and rigid, since capacity scales with volume.”

While soft batteries do exist, they are still made from solid parts. Rahmanudin likens current soft batteries to a piece of rubber – while rubber does stretch, thicker chunks of material will require more force to deform. The same is true for soft batteries; thicker batteries have a better capacity for powering devices, but their increased stiffness makes them less suitable for use in the wearable electronics they were supposed to power.

“The key innovation of our work is converting the physical property of a battery electrode from a solid to a fluid state,” Rahmanudin said. “Why fluid? We can add more active materials to gain capacity without stiffening the electrode, and despite it changing shape easily under strain, the battery performance is retained.”

An advanced fluid battery

Fluid electrodes are also not a completely new concept. However, previous battery designs with fluid or semi-solid electrodes generally relied on the use of liquid metals, such as gallium. This is not an ideal solution as there is some risk of the gallium solidifying during the charge/discharge cycle.

Gallium, as well as several other metals that are commonly used in advanced battery designs, is also considered to be a “critical material” – a designation that reflects its central importance to the energy industry but also a high risk of supply chain disruption.

The new stretchable battery avoids the use of such materials, instead opting for conductive polymers suspended in an electrolyte.

“We used two main active materials: modified lignin (a natural polymer and waste product from the paper industry) and a synthetic conjugated polymer called PACA (poly(alkyl cyanoacrylate)),” said Rahmanudin. “Both were combined with a conducting polymer (PEDOT (poly(3,4-ethylenedioxythiophene)) and carbon additives, to ensure good electrical conductivity.”

“These materials are suspended in a liquid electrolyte to create a fluid electrode. Fluids have no fixed shape and yield easily to external pressure, making them intrinsically ‘stretchable’ or highly deformable. Under applied mechanical strain, the suspended particles slide over each under (i.e., reversibly break and reform the contact points) while maintaining the connected pathways that are essential for electronic transport and energy storage,” Rahmanudin explained.

Constructing this battery is a more involved process than making a traditional battery, Rahmanudin admits. However, the team have been able to streamline the process to keep production scalable.

“Instead of casting and drying (or baking) solid electrodes into a film, we fill the fluids into sealed compartments – kind of like injecting toothpaste into a pouch,” Rahmanudin explained. “Another key design consideration is [having] customised stretchable components for the full battery cell, like a stretchable current collector, a porous membrane (that lets ions move but keeps the cathode and anode fluids on their respective sides) and a low-permeability encapsulation elastomer to prevent the fluids from drying out or oxygen and air from entering. It’s more complex, but the techniques are scalable, and we believe they could be adapted for manufacturing wearable electronics in the future.”

The future of wearable electronics

The Linköping research team’s battery showed excellent capacity retention even after 500 charge and discharge cycles. Additionally, it can be stretched out to twice its original length and still retain its performance.

But the battery is not without its limitations; it operates at just 0.9 Volts. Improving these performance metrics is a key part of the team’s continued research, though they believe that the current device provides a good proof-of-concept showing what is possible for the future of wearable electronics.

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“We’re currently looking into using pH-neutral and more biocompatible electrolytes to make the battery even safer for on-skin or implantable wearables. We also want to explore other sustainable active materials with higher energy density, such as zinc-manganese oxide battery chemistries,” Rahmanudin said.

“Long-term, we’re looking to exploit the intrinsic fluidity and ‘shape-ability’ of the electrodes to build truly form-factor-free power sources. Most electronics are typically designed around the bulky battery – think of your smartphone or any electronics, the battery is always the largest component. We think that with a fluid battery, we will open the design space for next-generation soft wearable devices by instead designing the battery around the electronic components.”

Reference: Mohammadi M, Mardi S, Phopase J, et al. Make it flow from solid to liquid: Redox-active electrofluids for intrinsically stretchable batteries. Sci Adv. 2025;11(15):eadr9010. doi: 10.1126/sciadv.adr9010

About the interviewee:

Dr. Aiman Rahmanudin is an assistant professor of materials chemistry and a research leader in the Soft Electronics Group at Linköping University, focusing on developing sustainable functional materials and device concepts for soft and stretchable energy applications.

Rahmanudin obtained his MChem degree in chemistry with business and management from the University of Manchester (UoM) in 2013. He then pursued his PhD in chemistry at the École Polytechnique Fédérale de Lausanne under the supervision of Professor Kevin Sivula, researching organic semiconductors for optoelectronic devices. Upon graduating in 2018, he went back to UoM as a postdoctoral research associate at the Organic Materials Innovation Centre to focus on developing green synthesis and processing methodologies for large-area organic electronic applications.

He joined the Soft Electronics Group at the Laboratory of Organic Electronics with Professor Klas Tybrandt after being awarded a Marie Skłodowska-Curie Actions Seal of Excellence research fellowship by the Swedish Governmental Agency for Innovation Systems (VINNOVA). Since then, he has expanded the research direction within the Soft Electronics Group from soft and stretchable electronic materials and devices to include soft energy devices. In late 2024, he was awarded the Zenith Career Development Grant from Linköping University, was promoted to assistant professor and became a research leader in the Soft Electronics Group.