Innovative materials for electric and hybrid car batteries

Innovative materials for car batteries

The mobility of the future: polymers in electric car batteries

The future will be more and more electric: mobility is progressively giving up fossil fuels to extract motive power from batteries. In 2020, the electric and hybrid car market grew by 40%, while it is estimated that 230 million electric vehicles will be sold worldwide by 2030.

The determining factor of this global success certainly depends on the evolution of the latest generation batteries that will allow better performance and ever shorter charging times. On the production front, industries are working on new technologies and innovative materials to increase scale production at reduced times and costs, assembly speed and greater performance.

Covestro with its high-tech polymers has long been collaborating with the best battery manufacturers to tackle together this unprecedented challenge in the automotive field that will bring undoubted advantages in terms of environmental sustainability and the reduction of fossil fuels.

Electric car batteries: how they work and how they are evolving

Knowing how batteries work, is essential to understand what challenges researchers and manufacturers face. Each battery is made up of smaller cells connected to each other. The cell architecture allows a flow of electrons from an anode (carbon, copper sheet) to a cathode (lithium metal oxide, aluminum sheet). During recharging, the electricity supplied by the grid is converted into chemical energy and the lithium ions move from the cathode to the anode where they are stored. When the battery is used, the lithium ions return to the cathode and the chemical energy is converted back into electrical energy. The flow of electrons moves inside a substance called electrolyte which is liquid but which in the near future will also be found in the solid state. The battery is formed by the union of several cells side by side.

High-tech polymeric materials, polycarbonates, adhesives and thermoplastic materials, play a fundamental role in improving the efficiency and performance of a battery dedicated to the automotive sector. Researchers face challenges in terms of both scale production and safety and performance. The focus is increasingly on batteries that have:

  • reduced weight and dimensions
  • efficient temperature control
  • fast production times
  • corrosion protection
  • impact protection.

Polymers for smaller and lighter batteries

Lightness plays a fundamental role in electric or hybrid traction mobility. Less weight to move means less energy used. For this reason, the use of polymers is winning in all automotive components: from glazing to bodywork, from components to batteries. Covestro laboratories have developed a mixture of PC / ABS. This polycarbonate-based thermoplastic composed of acrylonitrile, butadiene and styrene, has a lower density of about 10% and possesses high mechanical, electrical and thermal properties. In a project called Sonnenwagen, Covestro, in partnership with RWTH Aachen University, has experimented with this material with excellent results for battery packs that power a racing car. The same PC / ABS material was then used by Henkel to create new batteries with an innovative design.

Mixed polycarbonate sheets can be processed easily making scale production possible. Furthermore, compared to semi-crystalline materials, amorphous plastics such as polycarbonates have the advantage of being virtually shrink-free in the injection molding process and have very low water absorption. This facilitates the design of thin-walled, distortion-free components.

In the battery compartment sector, Covestro was able to provide the first polycarbonate-based cover. The battery has achieved a 20% lower weight, while on the productivity front it has been increased by up to 50%. Compared to the use of sheet metal stamped parts, both costs and performance have therefore been improved.

New designs for temperature control and management in batteries

Temperature is a critical factor in batteries for electric and hybrid cars. The optimal operating range is between -10 ° to 40 °. Each battery therefore needs a cooling system in order not to reach high temperatures that compromise its efficiency. Fast charging also causes a noticeable rise in temperature. At 150 ° C and above, ruptured cells in batteries can turn into a self-power cycle called thermal runaway that puts the car occupants at risk. For these reasons, battery thermal management and cooling systems are crucial to ensure safety and efficiency.

Mineral-reinforced polycarbonate has been shown to possess the physical and chemical capabilities to resist deformation at very high temperatures and to be flame retardant. In addition, this polymeric material also allows for innovative designs that combine ease of assembly, weight reduction and temperature control. The versatility and plastic capacity of polycarbonate in fact allows designers to create efficient solutions right from the design stage. Cooling devices can consist of integrated channels between the cells or of cooling plates. The lightness of the material and the ability to withstand modeling with thin and resistant walls are pushing companies to create innovative frames and cell holders with cylindrical cells at reduced weights even for larger battery packs.

Battery protection of electric and hybrid vehicles

Electric vehicle underbody housings must protect batteries from dust, debris and moisture, such as rain, snow or car wash jets. Furthermore, it is essential that the cells are perfectly sealed to avoid the loss of the electrolyte. Manufacturers need to find the best sealants and gaskets that do not deteriorate even in extreme conditions, such as vibrations, intense weather phenomena and high external temperatures. The assembly phase is the most delicate, in which the use of polymeric materials can increase the degree of protection of the battery and improve production times at scale for a reduction in costs.

The Covestro polymeric materials in addition to the known dimensional and thermal stability are perfect because they are resistant to UV rays and have fast hardening times. The collaboration with the multinational Henkel has created a synergy between Covestro composite polyurethane and Henkel brand adhesives. An industrial scale assembly process has been developed in which the cylindrical cell holders for lithium batteries are made with the PC/ABS blend. The cells reach a thickness of only 1mm and the material offers production speeds with short curing cycles while the acrylic adhesive provides strong adhesion to components and a perfect seal.

Protect batteries from impact

Safety is the most important point for battery-powered cars. Countless crash tests have been conducted to verify the behavior of polymeric materials in the event of an impact. In the laboratory it was verified that the battery pack made with traditional materials suffered significant damage. In contrast, the polycarbonate battery housing for the bottom plate has proven to be perfect in dissipating kinetic energy and offers the best combination of impact protection, weight, complexity and cost.

Towards a new battery technology for sustainable mobility

With their physical and chemical characteristics and their complete recyclability, the new polymeric materials make an essential contribution to battery technology.

The new thermoplastics meet the needs of manufacturers of safe, cost-effective and durable lithium-ion battery cells made from lightweight polymer. They form the basis for delivering the battery technology of the future today.

Terry Davis

Principal Engineer/Global Technical Battery Lead

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