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The heavy weight of EV batteries is one of the factors that pull down driving range, no matter what other bells and whistles the R&D people come up with. Scientists calculate that simply removing the battery would increase range by 70%, except for one tiny detail, which is the absence of a battery. Or not, as the case may be. The scientists behind that 70% estimate have been hard at work developing a massless EV battery, meaning a battery that adds no extra weight because it pulls double duty as a working part of the vehicle’s structure.
Massless EV Batteries Are Coming, Eventually
The research team, based at Chalmers University in Sweden, has been developing massless EV batteries since at least 2007. The key ingredient is carbon fiber, the same lightweight but tough versatile material that goes into auto body parts.
Early efforts focused mainly on tweaking carbon fiber to behave like a battery. The idea of applying the technology to structural elements soon followed. Once carbon fiber is involved as a conductor, the copper or aluminum current collectors in a typical EV battery can also be eliminated, saving a significant amount of weight.
“By using the battery pack’s container and the battery cells themselves for rigidity, the overall weight of the vehicle can be reduced. Advantages include greater range per kWh of battery pack installed, better handling, and great potential for simplified vehicle assembly (which should reduce cost),” CleanTechnica’s Jennifer Sensiba noted back in 2021, when the Chalmers team reported a new milestone.
That’s not as simple as it seems. The researchers spent a lot of elbow grease to achieve a high-functioning combination of both electrical and mechanical factors. The 2021 breakthrough came from a collaboration of the KTH Royal Institute of Technology, which produced a massless EV battery with 10 times the multi-tasking performance of previous iterations.
Big Milestone For Massless EV Batteries
The Chalmers – KTH team reported an energy density of 24 Wh/kg in 2021. If that seems rather low, it is. The team calculated that their new massless EV batteries had approximately 20% of the capacity of typical Li-ion EV batteries. However, the results were promising enough to warrant a fresh burst of research.
“But since the weight of the vehicles can be greatly reduced, less energy will be required to drive an electric car, for example, and lower energy density also results in increased safety,” the team explained.
“And with a stiffness of 25 GPa the structural battery can really compete with many other commonly used construction materials,” they added. GPa stands for gigapascal, an internationally recognized unit of measurement for the ability of a material to withstand compressive force.
The achievement of 25 GPa for EV batteries represents a good start towards the goal of 75 GPa described by project leader Lief Asp of Chalmers University. At 75 GPa, massless EV batteries would be much lighter than aluminum but just as tough.
The primary goal of the Chalmers-KTH project was to explore how different materials interacted, which explains why they only used carbon fiber for the anode (the negative electrode). They deployed aluminum foil coated with a lithium-iron-phosphate formula for the cathode, and the separator consisted of a flexible fiberglass fabric embedded in the electrolyte.
Want more details? Check out the article, “A Structural Battery and its Multifunctional Performance” in the journal Advanced Energy & Sustainability Research.
The All-Carbon Fiber Massless EV Battery
The researchers have not been letting any grass grow under their feet. Even as they published their 2021 results, they were already at work on a followup project funded by the Swedish National Space Agency.
“The aluminium foil will be replaced with carbon fibre as a load-bearing material in the positive electrode, providing both increased stiffness and energy density,” the team explained. “The fibreglass separator will be replaced with an ultra-thin variant, which will give a much greater effect – as well as faster charging cycles.”
The team also received funding from the Wallenberg Initiative Materials Science for Sustainability. Their new study is described in the journal Advanced Materials under the title, “Unveiling the Multifunctional Carbon Fibre Structural Battery,” published in September of 2024.
True to the task, the researchers replaced the aluminum foil in the cathode with carbon fiber, again coated with the LFP formula. “The carbon fibre used in the electrode material is multifunctional. In the anode it acts as a reinforcement, as well as an electrical collector and active material. In the cathode it acts as a reinforcement, current collector, and as a scaffolding for the lithium to build on,” the team explains.
The new battery achieved a stiffness of 70 GPa, bringing it up to snuff in terms of matching the performance of aluminum with a lower weight.
The energy density measured 30 Wh/kg, so the researchers still have a long way to go before they match Li-ion batteries on energy density. Still, Professor Asp makes a good case for commercial-ready massless EV batteries that trade lower energy density for lighter weight.
“Investing in light and energy-efficient vehicles is a matter of course if we are to economise on energy and think about future generations,” Asp explained in a press statement. “We have made calculations on electric cars that show that they could drive for up to 70 percent longer than today if they had competitive structural batteries.”
Where Are The Sustainable EV Batteries Of The Future?
The pursuit of massless EV batteries is just one element in a broader, sustainability-oriented movement among leading automakers and other energy storage stakeholders. Massless EV batteries are among a number of new developments that deploy the LFP formula to eliminate the supply chain headaches posed by conventional Li-ion batteries that rely on cobalt and manganese. The Chalmers team also used a semi-solid electrolyte instead of the volatile liquid electrolyte of conventional Li-ion batteries (see more solid state background here).
There being no such thing as a free lunch, carbon fiber poses some sustainability issues of its own. The material is energy intensive to produce, and difficult to recycle. Keep an eye out for emerging solutions, such as a recyclable carbon fiber composite developed by the US Department of Energy’s National Renewable Energy Laboratory.
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Image: “Massless” EV batteries are designed to pull double duty as structural elements that add no extra weight to a vehicle, increasing battery range by an estimated 70% (courtesy of Chalmers University).
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