The electric drive will replace the internal combustion engine sooner or later, that is - at least on a political level - a done deal. As early as 2035, there could be a Europe-wide ban on new registrations for gasoline and diesel vehicles. But whether the electric motor will really catch on as quickly as politicians and energy experts would like it to be in road traffic is questionable. There are several factors that keep many drivers from switching to battery-powered cars. There are the short ranges of an average of 350 kilometers compared to a combustion engine and the charging times that are still too long. In addition to the currently high price of the batteries, another obstacle is likely to be safety concerns. Because it still happens that lithium-ion batteries burn or even explode.In addition, the liquid electrolyte can leak and ignite in the event of an accident. Disadvantages that it is hoped to be able to overcome with a new generation of lithium batteries.
Manfred Lindinger
Editor in the “Nature and Science” section.
Follow I follow
Many automakers, including VW and BMW, who are already converting their production lines to electric vehicles, have great hopes for rechargeable solid-state batteries. Depending on the design, this battery technology promises faster charging times and greater ranges, and above all it should make electric cars safer. Because this type of battery no longer has any flammable liquid components. In particular, the electrolyte, i.e. the medium that conducts the lithium ions, consists of a flame-retardant solid. "These can be ion-conducting plastics, oxidic or sulfidic inorganic ceramics or glass-like solids," says Holger Althues from the Fraunhofer Institute for Material and Beam Technology IWS in Dresden. The battery expert who heads the Chemical Surfaces and Battery Technology department,wants to help solid-state batteries achieve a breakthrough with colleagues from other institutes. Like many researchers in this country, he favors sulfidic solid electrolytes - such as crystalline lithium thiophosphate - because of their high conductivity for lithium ions and their advantageous processability.
The conductivity of sulfidic solid electrolytes is now comparable to that of electrolytes based on liquid salts, although the lithium ions cannot move as freely here. The ions migrate through a rigid crystal lattice, repeatedly having to cross grain boundaries. After all, the electrolyte is not a homogeneous, massive single crystal, but is made up of tiny, differently oriented crystallites, so-called grains. In the production of sulfidic electrolytes, the loose grains are baked together at mild temperatures and high pressure (with oxidic electrolytes at high temperatures) so that the lithium ions can migrate through the material without great resistance.
In principle, all materials that are also used in classic lithium-ion batteries can be used for the two electrodes for solid-state batteries: graphite for the anode and, for example, a cobalt-nickel oxide for the cathode, which contains large quantities of lithium ions have it stored. The researchers at the IWS want to do without expensive materials and critical metals such as cobalt and nickel entirely. You therefore rely on sulfur on the cathode side. "The material is cheap, light and can absorb large amounts of lithium," says Althues, describing the advantages of sulfur, which is a waste product of the chemical industry and is unused in large quantities. When the battery is discharged, the lithium ions coming from the anode react with the sulfur in the cathode to form lithium sulfide. The process is reversed when loading.The cracks and breaks in the sulfur cathode associated with the changes in volume can be brought under control by using suitable carbon materials, says Althues.