In the next few years, batteries used in electric vehicles will become cheap enough that the cost of electric vehicles should not exceed the same size cars with internal combustion engines. However, these electric vehicles will still be heavier than gasoline-powered electric vehicles, especially if the market insists on longer and longer cruising ranges, their battery packs will account for 20% to 25% of the total vehicle weight.
But there is a solution: turn some structural parts of the car into a battery. In doing so, your battery weight will effectively disappear, because no matter what the powertrain, each car still needs the structural parts that hold it together. This method has been used in groups around the world for some time, and when Volvo CTO Henrik Green spoke to Ars in early March, the idea was well explained:
What we have learned… just to give one example: “How to integrate the battery cell into the car most effectively?” Well, if you do it in the traditional way, you can put the cell in a box and call it It is a module; you put many modules in a box and you call this package. You put the packaging in the vehicle, and then with a standardized solution, you can expand it for 10 years and 10 manufacturing slots.
But in essence, this is a very inefficient solution in terms of weight and space. Therefore, you can do more in-depth research here, how to integrate cells directly into the body and get rid of these modules and packaging and the things in between? This is the challenge that our children and grandchildren will face, and it will change the way you fundamentally make cars. You may think that the era of change is over, but it has just been reborn.
As we all know, Tesla is designing new battery modules that can also be used as structural elements, but the California automaker is manufacturing these structural modules with traditional cylindrical batteries. However, there is a more elegant way to solve this problem. A team at Chalmers University of Technology in Sweden led by Professor Leif Asp has made some breakthroughs in this regard, so that every component of the battery is structured. Made of feasible materials as well as electricity.
The structural battery combines a carbon fiber anode and an aluminum foil cathode coated with lithium iron phosphate, which are separated in the structural battery electrolyte matrix material by a glass fiber separator. The anode has a triple role, can hold lithium ions, conduct electrons and strengthen all substances at the same time. The electrolyte and the cathode similarly support structural loads and play a role in moving ions.
The researchers tested several different types of glass fibers (all produced batteries with a nominal voltage of 2.8 V), and achieved better results in battery performance through a thinner plain weave. The battery using this configuration has a specific capacity of 8.55 Ah/kg, an energy density of 23.6 Wh/kg (under 0.05 C), a specific power of 9.56 W/kg (under 3 C), and a thickness of 0.27 mm. To put at least one of these numbers as a background, the energy density of the 4680 batteries that Tesla is moving is 380 Wh/kg. However, the energy density map of cylindrical elements does not include the mass of the structural matrix surrounding them (when used as a structural panel).
Speaking of structural loads, the use of 25.5 GPa ordinary glass fiber braid can also achieve maximum stiffness. Again, this number is roughly similar to glass fiber reinforced plastic, while carbon fiber reinforced plastic will be about 10 times larger, depending on whether it is resin transfer molding or a woven board pre-impregnated with resin (called prepreg) .
Professor Asp’s group is now investigating whether replacing the aluminum foil of the cathode with carbon fiber will improve stiffness (should improve) and electrical performance. The team is also testing thinner separators. He hopes to reach 75 Wh/kg and 75 GPa, which will make the battery slightly harder than aluminum (GPa: 68), but obviously much lighter.
It is still a long-term project to manufacture electric vehicles and even airplanes with structural composite batteries. Even at the best, structural batteries may never reach the performance of special batteries. However, since they will also replace heavier metal structures, the final vehicle should be much lighter overall.
At the same time, Asp believes that other products may see benefits sooner. “The next generation of structured batteries has huge potential. If you look at consumer technology, it is entirely possible to make a smartphone, laptop or electric bicycle that is only half the weight and smaller in a few years. .” Said.
List image by Marcus Folino