Swedish startup promises “massless” carbon fibre battery for wind blades, EVs and aircraft

A spinout company from a Swedish university says it is on the cusp of commercialising an energy-storing carbon fibre technology that could lead to what would be a world-first effort at a structural battery.

Sinonus last week appointed a new CEO in Markus Zetterström, an executive from the world’s largest bearings manufacturer SKF Group, to lead the commercialisation of its technology. 

The company launched in 2022, a year after researchers from the university found a way to apply their carbon fibre battery to the real world.

The technology, which uses the crystalline structures within carbon fibre to store energy, has been proposed for aircraft, electric vehicles, and now in the massive blades of wind turbines to store excess power.

“Sinonus has developed an amazing carbon fiber composite that doubles as a battery,” Zetterström said on LinkedIn. 

“By substituting part of the structural material in systems/applications to our multipurpose composite, it’s possible to add electrical storage capacity at sustained weight and volume, or to decrease system weight and volume at sustained battery capacity (and of course some combination thereof).”.

Massless batteries are a real possibility

Sinonus uses technology developed at Chalmers University of Technology in Gothenburg, where researchers have been studying the concept of a structural battery using carbon fibre for years. 

Massless batteries have been something of a holy grail for energy storage since 2007, because the weight of the battery effectively disappears once it is part of the load-bearing structure. The Chalmers team, led by professor Leif Asp, is one of the few to find a material that works. 

Carbon fibre is known for its strength versus weight.

Their work found that carbon fibres with small, poorly oriented crystals are good electrical conductors but less stiff that versions of the material with larger, better oriented crystals. The trade off for stiffness, however, is electrochemical properties that are not good enough to be a battery.  

“A slight reduction in stiffness is not a problem for many applications such as cars. The market is currently dominated by expensive carbon fibre composites whose stiffness is tailored to aircraft use. There is therefore some potential here for carbon fibre manufacturers to extend their utilisation,” Asp, who sits on the Sinonus board, said in a statement when the study was published in 2018. 

He said for aircraft which need very stiff materials, making the carbon fibre thicker might compensate for the reducing stiffness of a battery-level material.

“The key is to optimise vehicles at system level – based on the weight, strength, stiffness and electrochemical properties. That is something of a new way of thinking for the automotive sector, which is more used to optimising individual components.

“Structural batteries may perhaps not become as efficient as traditional batteries, but since they have a structural load-bearing capability, very large gains can be made at system level.

“In addition, the lower energy density of structural batteries would make them safer than standard batteries, especially as they would also not contain any volatile substances.”

Since 2018 when this breakthrough was published, the team have been working through applications as to how it might work in practice. 

In 2021, the team produced a carbon fibre battery with an energy density of 24 Wh/kg, or about 20 per cent capacity compared to comparable lithium-ion batteries at the time. 

The battery had a negative electrode made of carbon fibre, a positive electrode made of a lithium iron phosphate-coated aluminium foil, separated by a fibreglass fabric in an electrolyte matrix. The next plan was to swap out the aluminium foil for load-bearing carbon fibre and a thinner separator. 

At the time, Asp estimated that this battery could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa, or as strong as aluminium but lighter. 

The trade-off for lower energy density is weight: lithium ion batteries are extremely heavy, but if a lighter battery is part of the device then carbon fibre-powered cars or aircraft might start to become a reality.