Structural Battery Materials – The Key to Electric Planes?

Electrification is the trend in the world of transportation – in the quest for more environmentally sustainable and emission friendly forms of transportation, electric cars and buses have taken all of the headlines. Battery technologies have reached the point where they are economically viable and in some cases, even favourable. This trend is only continuing to rise, as more competitors are entering the EV market, Tesla’s Semi truck is on the horizon, and talk about electrifying the grid and increasing EV charger availability is becoming more and more common. All signs of how the trend of electrification is changing ground transportation as we know it.
However, there is one place we have yet to look with this trend of electrification – the skies. Futurists and fanatics alike have explored the prospects of electric planes, but dreams of transatlantic travel have been deterred by one factor: the fundamentals of flight. The thrust-to-weight ratio of a plane determines whether or not it will be able to achieve flight, and for how long. The energy density of conventional rechargeable lithium ion batteries such as those found in electric cars is not comparable to that of conventional fuels – you would need more weight in batteries than fuel to produce the same amount of power. So, current electric plane prototypes like those from Rolls-Royce and Airbus are too heavy to achieve long distance flight.
A recent breakthrough by researchers from Chalmers University of Technology could change this. This is based around structural battery materials – also known as ‘massless’ energy storage. Project leader Lief Asp published his first paper on structural battery materials in 2010, and has come a long way since, as work on the current structural battery was presented by Physics World as one of 2018’s ten biggest scientific breakthroughs.
These are materials that serve as both structural elements and batteries. Vehicles such as cars or planes would be made out of these materials – the doors, wings, and other body elements, instead of having to carry battery packs, allowing them to be lighter, and achieve longer term flight.
The structural battery uses carbon fiber as a negative electrode, and a lithium iron phosphate-coated aluminum foil as the positive electrode. The carbon fiber acts as a host for the lithium and thus stores the energy. The battery has an energy density of 24 Wh/kg, meaning approximately 20 percent capacity compared to conventional battery technologies. Leif Asp, who is leading this project too, estimates that such a battery could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa. This would make the battery about as strong as aluminum, but with a comparatively much lower weight, and would allow it to reach about 62.5% capacity compared to conventional batteries.
While the figures seem underwhelming on a surface level, the potential for growth in the field is very encouraging, as we are faced with a new frontier for battery technologies altogether. Currently, Chalmers University of Technology is working with carbon fiber, but who knows what composites we may be looking at ten years from now?
Regardless, structural battery materials provide a potential solution to the seemingly impassable hurdle that long-distance electric-powered planes have faced. By making the body of the plane out of its own battery, we can hope to achieve the power to weight ratio to achieve long distance, electric flight.
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