uni'wissen 01-2015

“Fluorine is the most reactive element around.” analyze the mechanisms behind chemical reac- tions, and break new ground in chemistry. “But it’s not enough to just publish such findings. We need to see to it that they are used.” He has been par- ticularly successful finding a balance between fundamental research and industrial application in his research on weakly coordinating anions. His “outstanding achievements in synthesis and application” earned him the Otto Klung–Weber- bank Award. Krossing’s findings on anions are on the one hand so fundamental that they now have a place in chemistry textbooks, while on the other hand they have the potential to greatly im- prove the concrete inner workings of batteries for hybrid vehicles, mobile phones, and table comput- ers. “We are working on developing even better conductive salts and additives,” says Krossing, who has established a battery laboratory for this purpose in cooperation with the chemical com- pany BASF. Coating Anions with Teflon Salts are composed of ions. This is what chemists call electrically charged atoms or mol- ecules. Anions are always negatively charged: They have more electrons, which carry a nega- tive charge. Cations, on the other hand, have a positive charge, because they are missing elec- trons. Both types of ion are released when salt crystals break up. Conventional salts like table salt need a solvent – in most cases water – and often energy for this to happen: The salt with- draws heat from the water as it dissolves. But modern salts do not need a solvent, and they also need less energy. Their crystal lattice struc- ture often breaks on its own at room temperature. The salts take on a liquid form and are then re- ferred to as ionic liquids. This is what Krossing is focusing on: “In our standard anions, 36 of the 57 atoms are fluorine atoms.” There is a reason for this. Ionic liquids are electrolytes, which means that they can conduct electricity. When batteries produce electricity, anions on the positive pole give off a charge in the form of electrons. To even out the charge again, one cation needs to migrate to the nega- tive pole each time an electron is released. “This movement slows down the process,” explains Krossing. In the course of their migration through the ionic liquid, the cations constantly encounter anions. The oppositely charged particles are at- tracted to each other like magnets. The cations keep getting “stuck” and thus take a long time to reach the other pole. “The trick is to keep this interaction to a minimum,” explains Krossing. To this end, he covered anions with a coat of fluorine- rich polytetrafluorethylene, more commonly known as Teflon. This reduces the negative charge. The anions become weakly coordinated and less “sticky” for cations. Making Predictions on the Computer However, conductive salts need to do more than just conduct electricity. Automotive batteries reach temperatures of up to 80 degrees Celsius when a car is left out in the sun. “Many standard electrolytes can only stand temperatures of 50 to 60 degrees,” says Krossing. When his team of 30 researchers develops new connections, they begin by running a computer simulation to find out what will happen when they add fluorine to a substance. “Computer chemistry enables us to predict which direction the properties will take.” More than 90 percent of the prognoses on viscosity, conductivity, density, melting point, and other parameters are correct. The scientists still need to conduct real experiments to remove any remaining uncertainties in the end, but many less than previously. This reduces the time needed to conduct the research, the cost of chemicals, and the amount of waste, which works to the benefit of the researchers, the budget, and nature in equal measure: One of Krossing’s cooperation partners is the German Environmental Foundation. Krossing has set up a special fluorine labora- tory at his institute to conduct experiments with fluorine concentrations of up to 100 percent. The security area is only accessible to members of his team who have been trained to handle the This new minireactor makes it possible for scientists to introduce fluorine to organic compounds. The next step in miniaturization will be the microreactor – a chip currently under development in Freiburg. 41

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