The world of battery technology continues to expand at a rapid pace. Advances in tech have led to a reduction in costs and adoption of electric vehicles (EVs), playing a key role in the global clean energy transition.
Batteries are also a critical component of consumer electronics such as smartphones, laptops, and wearables. However, in order to build next-generation wearables that have mechanical conformability with the human user and long-term operative capability, we need high-capacity stretchable batteries.
These next-gen wearables are not like currently existing fitness trackers, smart watches, hearing aids, or earphones. They are different from these commercial counterparts and need mechanical compliance with our body that goes far beyond just softness, stretchability, and flexibility.
While advances have been made in various components like transistors, antennas, sensors, and conductive tracks to enhance their electromechanical properties, they are still powered by the same bulky and rigid batteries.
These batteries limit the form factor and mechanical compliance of future wearables. For these wearables to be able to perform functions like long-term sensor monitoring, wireless data transmission, and data logging, along with autonomous operation, there is a need for an integrated stretchable battery.
With wearables forecasted to grow significantly, it is important that we develop stretchable batteries to help revolutionize technologies for entertainment, communication, food monitoring, health care, and the environment.
According to Aiman Rahmanudin, an assistant professor at Linköping University:
“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.”
Stretchable Batteries are Key to Future Wearables
While stretchable battery designs exist today, they face several limitations in increasing capacity. This is because to yield higher capacity, the active material is to be increased, which then results in thicker and stiffer electrodes with poor stretchability and mechanical compliance.
These batteries utilize the same electrode designs that conventional rigid batteries have, which depend on the mechanical coupling of the redox-active species and the conductive filler.
Now, for a coupled electrode to maintain mechanical integrity within the solid matrix, a binder is needed to hold the components together. This ensures good electronic contact between the components, enabling access to the active material for efficient charging and discharging. However, any loss of this contact due to mechanical stress leads to a decline in battery performance.
The binder can be replaced with an elastomer for stretchability, but higher active material loading needs insulating binders and more conductive fillers.
The resulting thick layers will be more susceptible to higher strain and deformation, which negatively affects mechanical compliance. Thicker electrodes also face mechanical instability, higher electrical resistance, and slow electron-ion transport, resulting in a lower effective volumetric capacity.
So, to design a stretchable battery, we need to take a holistic approach that considers all the components, from active electrodes, separator, and current collector to encapsulation.
There are two ways to facilitate stretchability: one is structural engineering that separates rigid components from major strain within the system, and the other is designing stretchable materials by combining stiff active fillers with an elastomer (a polymeric material with high elasticity) to create gels, porous structures, and composites. Despite advancements, they do not tackle the fundamental issue of the trade-off between battery capacity and mechanical properties.
But what if these batteries make use of what is intrinsically “stretchable”?
A Fluid Battery That Can Take Any Shape
Fluids are highly deformable. They have no fixed shape, and they yield easily to external pressure. In simple terms, a fluid battery should be able to take any shape.
So, inspired by this basic behavior of fluids, researchers at Linköping University have presented a concept to change the physical property of a battery electrode from a solid to a fluid state.
Doing so gives an electrode design that depends on the viscosity of a fluid. This decouples an electrode’s electrochemical and electrical function from its mechanical property, resulting in a redox-active electrofluid that enables ions and electron transport to store energy while enhancing capacity and deformability.
This won’t be the first time that fluids are explored for batteries; they are actually widely used in electrochemical energy storage systems. The thing is, these systems are designed for large-scale stationary batteries that utilize huge storage tanks and pumps to flow the anodic and cathodic fluids reversibly through a current collector.
However, when it comes to wireless and portable wearable devices, there are key design factors such as size, weight, stretchability, and mechanical compliance that must be considered in stretchable batteries. In that regard, few have explored fluids like gallium and EGaIn. But these solid metals come with their own problems.
For instance, gallium can only be used as an anode material; it has a hydrophobic surface, and there’s a risk of it converting into a solid during the discharge, which can result in a loss of fluid.
Many stretchable battery attempts have also made use of rare materials, but they have an energy-intensive mining and extraction process, which also has a major environmental impact.
This makes it important that future stretchable battery designs can address the electrochemical, mechanical, and sustainability considerations simultaneously.
So, the Linköping University researchers published a study in Science Advances1 that details the development of a battery that can take any shape, thanks to using electrodes in a fluid form. This conformable battery is made from conjugated polymers and biopolymers and showcases the potential to be integrated into future wearables in an entirely new way.
Click here to learn how ultra-durable batteries will last decades.
Fluid-based Electrodes for Maximum Capacity
The study showcased a flexible battery design that is based on redox-active cathodic and anodic electrofluid electrodes that are intrinsically deformable, which are incorporated into a full cell by a customized stretchable current collector and separator membrane.
Among its key innovations are the mass loading of the fluids and their resulting battery capacity, which does not influence the cell’s axial stiffness, which the team called an “important characteristic that has yet to be demonstrated by existing stretchable battery designs.” Also, they used a sustainable redox couple as active materials in the fluids.
Interestingly, the fluid has a toothpaste-like consistency and is extruded from a syringe. According to Rahmanudin, one of the study authors:
“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 a new type of technology.”
This soft and malleable battery overcomes the problem with previous attempts at manufacturing stretchable batteries that have been based on different types of mechanical functions. While those attempts used materials that can be stretched out or connections that slide on each other, they didn’t really address the main problem. As noted above, having more active material, as a large battery has higher capacity, leads to thicker electrodes and, in turn, higher rigidity.
“Here, we’ve solved that problem, and we’re the first to show that capacity is independent of rigidity.”
– Rahmanudin
Now, to overcome the problem of materials’ sustainability, the researchers at the Laboratory of Organic Electronics (LOE) based their soft battery on conductive plastics and lignin.
Lignin is a biopolymer that is found in abundance on Earth. This organic polymer is found in the plant’s cell walls, particularly in wood and bark. It is usually a waste product from the pulp industry and ethanol biorefinery. From the 100 million tons of lignin extracted annually, less than 5% is considered a value-added commodity, with the rest discarded or burned for energy.
By using modified lignin as a cathode active material, the study effectively repurposes a waste product into a battery material.
“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.”
– Co-lead author Mohsen Mohammadi, who’s a postdoc fellow at LOE
When it comes to battery performance, it can be recharged and discharged more than 500 times while still maintaining its performance. What’s more, it has a mechanical robustness of up to 100% strain, which means it can be stretched to double its length and still work just fine.
In the next steps, the team will work to increase the electrical voltage in the battery and try to overcome some of its current limitations.
“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.”
– Rahmanudin
Innovative Company
Amprius Technologies (AMPX -4.89%)
In the wearable tech space, giants like Apple (AAPL) with its Apple Watch and AirPods, and Google (GOOG) through Fitbit are leading the market. Garmin Ltd. (GRMN) is another prominent name in the sector that builds smart wearables for fitness, health, and navigation.
But today, we’ll take a deeper look at a company involved in battery technology. While this particular research focused on fluid batteries, that technology is still mostly in the research phase. So, we’ll cover a player who is advancing the battery tech in general. And our focus today is Amprius Technologies, which manufactures lithium-ion batteries.
The company’s focus is on the commercialization of silicon anode batteries that allow for greater energy and power density with up to 450 Wh/kg, 0% to 80% charging in as little as six minutes, reliable performance in extreme temperatures from -30°C to 55°C, and maintaining performance through 1,300 full charge cycles.
In particular, Amprius operates through two commercially available product platforms, SiMaxx and SiCore. The company’s products are used in a wide range of applications, including drones, defense, e-bikes, electric vehicles, AI, and robotics.
The company has a market cap of $264.15 million as its shares trade at $2.24, down 19.64% YTD. Its EPS (TTM) is -0.44, and the P/E (TTM) is -5.08. Amprius does not pay any dividends.
Amprius Technologies, Inc. (AMPX -4.89%)
As for the company’s financial results, Amprius ended 2024 with $55.2 million in cash and cash equivalents and no debt.
“We continue to remain lean with a $2.5 million to $3 million monthly run rate, excluding transaction-related costs.”
– CFO Sandra Wallach
Revenue in the entire last year was reported to be $24.2 million, a massive 167% increase from the previous year. As for profitability, gross margin was negative 76% compared to negative 162% in 2023, an improvement directly related to the launch of the SiCore product line.
Operating expenses for the full year were $27.9 million, up from $24 million in 2023, while net loss came in at $44.7 million. Share-based compensation during this period was $7.3 million, a big jump from $3.9 million in 2023, primarily due to changes in the Board of Directors and the non-recurring grant of fully vested shares by Amprius.
In 2024, the company shipped to a total of 235 customers, which includes both new customers and repeat volume orders from long-term partners like Teledyne FLIR, Airbus, Kraus Hamdani, AeroVironment, and BAE Systems. Last year, it also completed the development and qualification of SiMaxx™ safe cells for the U.S. Army’s next-generation Wearable Battery pack.
After the ‘productive’ last year, CEO Kang Sun shared he is “increasingly optimistic” for this year, expecting to “deliver new high-performance batteries, participate in new market segments, engage with more customers, due to additional manufacturing partnerships, and bring our business to another level. We believe that the opportunity ahead of Amprius is tremendous.” Already, the company has made a great start to 2025.
In Jan., Amprius introduced a battery cell with 370 Wh/kg energy density and up to 3,500 W/kg power while supporting high discharge rates to ensure quick power delivery without compromising run time. The new SiCore™ cell was launched as part of the SiCore product platform expansion with an aim to revolutionize high-performance electric mobility that requires both endurance and rapid energy delivery.
Talking about this “significant technical breakthrough,” CTO Dr. Ionel Stefan noted that “by optimizing the silicon anode composition without compromising the other performance metrics of the cell, we have redefined the trade-off between power and energy. This cell is not just about performance but about creating new power possibilities for high-demand applications.”
Then, in February, Amprius secured a $15 million purchase order from a leading Unmanned Aircraft System (“UAS”) manufacturer to produce its SiCoreTM cells that are expected to be shipped in the second half of 2025.
“We anticipate continued momentum with additional high-value orders in the future.”
– Sun
A month ago, Amprius also announced that it had dispatched its latest 6.3Ah 21700 SiCore™ cell, delivering over 25% more capacity than a standard 5.0Ah 21700 cell, to a Fortune 500 organization in the Light Electric Vehicle (LEV) segment for assessment. The commercialization of this cell is set for this year.
Conclusion
With an estimated trillion gadgets—ranging from smartphones, smartwatches, and wearable medical devices to soft robotics and more—expected to be connected to the Internet in the next decade, it is crucial that stretchable batteries become a reality without sacrificing capacity, while still providing enough electrical energy and maintaining a focus on sustainability.
The new class of fluid batteries presented by researchers aims to push the boundaries of design, making next-generation wearable technology possible and more efficient.
By decoupling capacity from rigidity and using natural, abundant materials like lignin, this innovation offers a sustainable, flexible, and high-performance energy source tailored for tomorrow’s devices. As the tech improves, this soft battery might help power the next technological wave.
Click here for a list of top battery stocks.
Studies Referenced:
1. Mohammadi, M., Mardi, S., Phopase, J., Wentz, F., Samuel, J. J., Ail, U., Berggren, M., Crispin, R., Tybrandt, K., & Rahmanudin, A. (2025). Make it flow from solid to liquid: Redox-active electrofluids for intrinsically stretchable batteries. Science Advances, 11(15), eadr9010. https://doi.org/10.1126/sciadv.adr9010