In recent years, lithium-ion (li-ion) batteries have become leading portable energy sources for a wide range of applications. Due to their intensive use in numerous applications, increasing their efficiency and performance while reducing their cost is obviously an attractive goal for researchers and battery makers. Generally, the final price depends mostly on the costs of the materials and the production process.
The costs of the latter can be lowered by simplifying the complexity of the process. With that in mind, researchers from the Fraunhofer Institute for Environmental, Safety, and Energy Technology UMSICHT in Oberhausen, Germany have developed an innovative battery technology based on an extremely thin bipolar plate that has enabled a cost-effective manufacturing process.
The idea came from the fact that existing battery designs are extremely complex. They are based on a series of interconnected cells, which cause difficulties with their efficiency and the process for manufacturing them. Because the individual cells are connected via wires, not only is manufacturing them complex, but there’s a risk that the wire can be damaged by hot spots caused by overheating.
In constrast, the bipolar battery configuration from Fraunhofer includes compact stacks of individual cells interconnected using flat bipolar plates. Producing the bipolar plates is not without its challenges: if they are made of metal, they’re prone to corrosion; in case of carbon-polymer composite plates, they need to be at least several millimeters thick, due to the nature of the manufacturing process.
The German researchers circumvent these issues by producing bipolar plates made from electrically conductive polymers. The research has resulted not only in an innovative material, but also an innovative manufacturing process. Dr. Engineer Anna Grevé, department head at Fraunhofer UMSICHT, said, “In this way, we can produce very thin plates and – compared with conventional cells connected by wires – save over 80 percent of the material used.”
This new solution has many other advantages, such as the fact that the material does not corrode and can also be subsequently reshaped, allowing for embossing structures (important for fuel cells). Additionally, the bipolar plates are absolutely tightened together. This is because the plates can be perfectly welded together so that gases and liquids cannot pass through the joints. The new material is flexible and can be adapted to specific requirements. “We can make plates that are so flexible that you can wrap them around your finger, as well as ones that are completely stiff,” Grevé explained.
The material is primarily composed of graphite, at about 80 percent, with 20 percent polymer. It is processed using a roll-to-roll method, enabling cost-effective manufacturing and the production of plates in any size. All components of the material must be homogeneously distributed and the plates must be stable and tight.
The Fraunhofer UMSICHT researchers were able to take this manufacturing process a step further, modifying the plate production technique to create a continuous, mass manufacturing process. As a result the batteries are more stable, easier to manufacture, and still significantly cost-effective when compared to the systems currently used to manufacture batteries.