They have a lot in common, yet are so different. A passing glance at the Tesla Model S and the BMW i3 shows two electric cars that have helped shape the future of mobility—but a second look reveals that the two are taking very different approaches. On one side you have Tesla, a disruptive tech company, that in typical American fashion is betting on cars built from steel and aluminum that can travel long distances. And then there is the BMW i3, better suited to urban spaces, a lightweight construction with a passenger compartment made of 100 percent carbon fiber-reinforced plastics. These differing concepts beg the question: Which is the most promising approach? Or will we need other approaches?
It is hardly surprising that a wide variety of different scenarios are currently being considered. The automotive industry finds itself in the midst of a revolutionary transformation, with increasing numbers of tech companies beginning to compete with traditional carmakers.
Combustion car engines must significantly reduce their carbon-dioxide emissions, whereby the weight of the steel/aluminum car bodies, as well as of the engines, does not leave much room for further reductions. In turn, the alternative drives need to extend their range to gain greater acceptance among the car-buying public.
What car body construction may look like in the future can be seen in the example of the BMW 7 Series, which combines both of the materials mentioned above. For this combustion engine car, BMW relies on a combination of carbon fiber-reinforced polymer (CFRP), largely with material supplied by SGL Carbon, in conjunction with steel and aluminum—whereby CFRP is used only where it genuinely offers added value. It is primarily utilized in roof frames, side skirts and the pillars.
How mixed materials will support novel structures in modern vehicle concepts is demonstrated by the Carbon Carrier, an OEM-neutral technology carrier. It was jointly developed by SGL Carbon and Bertrandt for the front vehicle interior of a convertible/sport sedan with an electric drive and contains all the important functional parts and trim of a traditional instrument panel.
SGL Carbon worked with BMW to further develop the materials and carbon fibers so that they can be optimally used in large-scale, hence fully automatic mass production.
Further examples also indicate that hybrid construction techniques are the future. Audi, for instance, utilizes a similar solution in the A8; CFRP is used primarily in the rear panel and ensures better vehicle stability with concurrent weight reduction for the component. Volvo in turn uses a leaf spring made of SGL Carbon glass fiber-reinforced composite, which weighs 65 percent less than conventional heavy steel springs.
Mixed materials will also allow novel structures in the modern vehicle concepts of the future, as demonstrated by the Carbon Carrier, which SGL Carbon developed in cooperation with the development solutions specialist Bertrandt. The flexible, OEM-neutral technology carrier was developed for the front vehicle interior of a convertible/sport sedan with an electric drive. The model contains all the important functional parts and trim of a traditional instrument panel. Even the structural components were redesigned. Taken together it gives the interior an airy, light and free-floating feeling.
While designing the Carbon Carrier, we made sure that the components, technologies and assembly concepts used were ready for large-scale production either today or in the near future
Michael Hage, Head of Body Development/CAE at Bertrandt
Alongside lightweight construction, emissions-free drives rank among the important elements of future mobility. Lithium-ion batteries have become the accepted standard. SGL Carbon has been a partner in this area from the very start and is the leading manufacturer of synthetic graphite for anode materials in this market. One of the company’s main strengths is its close collaboration with its customers, continuously optimizing the technology for the material used in the anodes, which is based on synthetic graphite. At the same time SGL Carbon participates in various research and development co-operations: For instance, the Fab4Lib project is advancing the potential German mass production of LIB cells.
Graphite is an irreplacable component of anodes in these battery cells. In fact, there is more graphite than lithium in these batteries, despite the LIB name: about one kilogram per kilowatt-hour of battery capacity in the car. By way of example, a car like the Tesla S 90 contains almost 90 kilograms of graphite.
Synthetic graphite has proven to be more advantageous for LIBs than natural graphite. As SGL Carbon’s Head of Battery Solutions Dr. Peter Roschger explains: “Firstly, its performance profile can be systematically controlled through its synthetic production. Secondly, the reproducible production process means consistent quality.”
To increase the capacity of both the anode and the LIB, SGL Carbon is working on improving the formulas and processes, such as a compound of carbon and silicon, known as a carbon-silicon composite. The market has very high expectations for silicon with respect to improved energy density. Even though silicon combined with graphite will be adopted as a complementary technology in special fields of application, it is expected that graphite will continue to be the dominant feature in LIB anodes due to its outstanding price/performance profile.
Fuel cells where cars are powered with hydrogen, rather than with gas or diesel, are looking promising again. Vehicles with this technology run very efficiently, and like electric cars are extremely quiet when in operation and, above all, have no harmful emissions. Additionally, their technology has improved tremendously.
This is why for the past several years car manufacturers and their partners, including SGL Carbon, having been putting a lot of work into fuel cell development. The so-called gas-diffusion layer (GDL) based on carbon fiber paper is one of the fuel cell’s key components. These interlayers ensure an even distribution of gas to the catalyst, which is applied to both sides of the ion-exchange membrane that converts hydrogen and atmospheric oxygen into electricity and water. One of SGL Carbon’s activities to further promote the use of this material is its participation since 2016 in the EU-sponsored INSPIRE project, which aims to develop a new generation of long-lasting high-performance fuel cells. Moreover, the company is also working on a number of customer projects dealing with fuel cells. The SGL team recently finalized an expanded co-operation with Hyundai. Specifically, SGL Carbon delivers the gas-diffusion layers for the fuel-cell car NEXO, which has been on the market as a production model since March of this year.
The best way to predict the future is to create it.
Alan Kay, Computer Scientist
At the moment, work is proceeding on many solutions without anyone being able to say for certain what the future of mobility will look like exactly. Yet it is these very processes – tinkering and developing with current concepts – that are so important, allowing innovations to move from mere ideas to tangible benefits for society.