Researchers from two of Sweden’s largest technical universities (the Chalmers University of Technology and KTH Royal Institute of Technology) have developed a new type of structural battery. The researchers believe that their structural battery exhibits qualities related to rigidity, electrical energy storage, and strength that competitively raises its value above previous and existing models. 

 

Dr. Johann Xu wi and Professor Leif Asp with a newly manufactured structural battery cell in Chalmers’ composite lab. Image used courtesy of Chalmers University of Technology 
Dr. Johann Xu wi and Professor Leif Asp with a newly manufactured structural battery cell in Chalmers’ composite lab. Image used courtesy of Chalmers University of Technology 
 

What is a Structural Battery?

A structural battery is a material that can carry a mechanical load and store electrical energy at the same time. In something like an electric vehicle (EV), the weight of a structural battery would be integrated into the load-bearing frame. A system like this is often termed ‘massless’ energy storage. Effectively, this type of multifunctional battery can substantially reduce the weight of EVs. 

 

The Research

Chalmers and KTH research teams developed a battery with an energy density of 24 Wh/kg. This translates to a 20% capacity compared to lithium-ion batteries currently available on today’s market. Although the structural battery exhibits lower capacity, the weight of vehicles can be reduced, and so less energy would be needed to power and drive an EV. Lower energy density can also be beneficial to EV makers and users in terms of increased safety. This coupled with a recorded stiffness of 25 GPa makes the newly developed structural battery a favorable choice among other commonly used construction materials. 

 

The structural battery cell connected to a circuit lights up a light emitting diode (LED) when exposed to mechanical loading. Image used courtesy of Chalmers University of Technology
The structural battery cell connected to a circuit lights up a light-emitting diode (LED) when exposed to mechanical loading. Image used courtesy of Chalmers University of Technology

 

The battery’s negative electrode consists of carbon fiber and the positive electrode is made of lithium iron phosphate-coated aluminum foil. The carbon fibre acts as a host for lithium and it is this that enables energy storage. Together, the aluminum foil and carbon fiber establish the mechanical properties of the structural battery. Fiberglass fabric is used to separate these two electrode materials in a structural electrolyte matrix. Not only does the electrolyte help to transport lithium-ions between the two battery electrodes, it also helps transfer mechanical loads between carbon fibers and other parts. 

The lightweight, multifunctional battery developed by the Chalmers and KTH researchers has displayed properties that make it ten times better in terms of performance than previous models. Despite this, the structural battery will be facing further development in a new project, financed by the Swedish National Space Agency. The aluminum foil (of the positive electrode) will be replaced by carbon fiber to further increase stiffness and energy density. The fiberglass partition will be replaced by a much thinner component which is expected to generate faster-charging cycles. The project is intended to take around two years to complete.

 

Image used courtesy of Chalmers University of Technology 
Image used courtesy of Chalmers University of Technology 

 

A professor at Chalmers and leader of both of the projects outlined in this article, Leif Asp, said he believes that an energy density of 75 Wh/kg and stiffness of 75 GPa could be achieved.

With enhanced structural batteries that display such properties, the world could see the development of lighter consumer electronic goods such as computers and smartphones, EVs, and electric planes.

For more information on the newly developed structural battery, you can read the full research paper here.


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