Battery concept multiplies driving range for e-vehicles
The problem with today’s batteries is that they occupy too much space for the energy they store. Researchers from the Fraunhofer Institute for Ceramic Technologies and Systems (IKTS) in Dresden found that the energy density of such batteries can be increased significantly if the cells are arranged differently in the battery pack: In today’s cars, each one of the hundreds of cells in a drivetrain battery is surrounded by a housing, connected to the car via connectors and lines and monitored by sensors. Enclosure and contacting occupy more than 50 percent of the space. The cells can thus not be packed together as desired. Another problem: The connections used for this fragmented assembly feature electrical resistances, which in turn reduce the power.
Here, the Fraunhofer IKTS steps in. Along with industry partners, the researchers transferred the bipolar principle known from the fuel cell to the lithium battery under the brand name EMBATT. In this approach, individual battery cells are not stacked separately side-by-side, but stacked directly one above the other over a large area. The entire structure for the housing and the contacting is thus eliminated, more battery cells fit into the car. Through the direct connection of the cells in the stack the current flows over the entire surface of the battery. The electrical resistance is thereby reduced considerably. The electrodes of the battery are designed so that they can dissipate energy very quickly and resume. “With our new packaging concept, we hope to increase the range of electric cars in the medium term up to 1000 kilometers,” says Mareike Wolter, project manager at Fraunhofer IKTS. In the laboratory the approach already works. Partners are ThyssenKrupp System Engineering and IAV Automotive Engineering.
The most important component of the battery is the bipolar electrode – a metallic foil that is coated on both sides with ceramic storage materials. One side becomes the anode, the other the cathode. As the heart of the battery, it stores the energy. “We use our know-how in ceramic technologies to design the electrodes in such a way that they need as little space as possible, save a lot of energy, are easy to manufacture and have a long life,” says Wolter. The scientists mix the ceramic materials in powder form with polymers and electrically conductive materials to form a suspension. “This formulation has to be specially developed – adapted for the front and back of the film,” explains Wolter. The suspension is applied to the film by the Fraunhofer IKTS in a roll-to-roll process. “One of the core competencies of our institute is to bring ceramic materials from the laboratory to the laboratory scale and reliably reproduce them,” says Wolter, describing the expertise of the Dresden scientists. The next step is to develop larger battery cells and install them in electric cars. Initial tests in the vehicle are aimed at the partners by 2020.
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