Batteries, the core of electric vehicles, are used only to store electricity. Wouldn't it be nice to store material electricity in other skeletons or structures that make up the car?
A research team at the Swedish Chalmers University of Technology, who has studied this imagination for over 10 years, has developed a competitive structural battery published in the journal.
This structural battery is more than ten times higher than the storage capacity of all structural cells available so far. As of yet, it cannot store energy as much as a lithium-ion battery, which is a battery-only battery. However, since there is no additional battery load, the research team said that it can be used in various ways such as smartphones, electric bicycles, home appliances, and electric vehicles.
Batteries make up a significant portion of the electric vehicle's weight, but do not perform any load-bearing function. In contrast, the'structure battery' is an innovative battery of a new concept that functions as a battery while performing the function of the structure of an electric vehicle. For example, a structural battery can also serve as a vehicle body.
The team named the battery as massless energy storage. This is because when the weight of the battery becomes part of the load-bearing structure, it is the same as no battery weight that stores energy. Naturally, this type of multifunctional battery can significantly reduce the weight of an electric vehicle.
Electricity storage capacity and material rigidity increase at the same time
Charmers Institute of Technology has developed structural cells for many years. One of them is a special carbon fiber battery, which is not only durable, but also has the function of chemically storing electrical energy. This study was selected as one of the Top 10 Scientific Advancements of 2018 by Physics World.
The first attempts to make structural cells began in 2007, but until now, it has been difficult to manufacture batteries that exhibit excellent electrical and mechanical properties at the same time.
Meanwhile, the research team at Chammers University collaborated with KTH Royal Technology Institute in Sweden to show a structural battery with characteristics that have not been seen in terms of electric energy storage and material stiffness.
The structural cell consists of a carbon fiber electrode and a lithium iron phosphate electrode, and a structural battery electrolyte is injected to combine mechanical and electrical functions at the same time. Basically, three structural cells are connected in series using a composite laminate material. The nominal voltage of the individual structural cells is 2.8V, and the total voltage of one laminate battery with three cells connected is 8.4V. The stiffness of the laminate is just over 28 GPa.
It is still different from the energy density of lithium-ion batteries. The energy density of the new structured cell is 24 Wh/kg, which has a capacity of about 20% of the equivalent lithium-ion battery currently available. However, since a separate battery is not loaded, the vehicle weight is greatly reduced, and thus the energy required for driving an electric vehicle is reduced. The lower the electrical energy density, the higher the safety. Due to its 25 GPa stiffness, the structural cells can compete with many other commonly used materials.
Professor Leif Asp of Charmers University, the research director said, the structural cells that have been available so far have been incomplete with good mechanical properties or excellent electrical properties. This time, we have succeeded in designing a structural battery with both competitive energy storage capacity and robustness using carbon fiber
Use of carbon fiber, lighter and stronger than aluminum
The new battery has a negative electrode made of carbon fiber and a positive electrode made of lithium iron phosphate-coated aluminum foil. The cathode and anode are separated from the electrolyte matrix with a fiberglass cloth.
Currently, a new project supported by the Swedish National Space Agency is underway, so the performance of the structural cells will be further improved. When aluminum foil is replaced with carbon fiber to increase stiffness and energy density, and fiberglass separator is replaced with an ultra-thin model, storage capacity is expected to increase and charging cycles are expected to be faster.
In that case, Professor Leif Asp predicts that the structural cell could reach an energy density of 75 Wh/kg and a stiffness of 75 GPa. This means that the structural cells are as sturdy as aluminum, but much lighter.
Professor Asp, who published his first paper on structural batteries in 2010, said, "In a few years it will be possible to manufacture smartphones, laptops, and electric bicycles that are small and weigh half the weight of today.
In the long run, electric vehicles, electric planes, and satellites are also expected to be designed and operated with rescue cells.