On November 1, the TU Ilmenau will launch a research project that will not only make it possible to charge lithium-ion batteries faster and more efficiently, also ensure a longer service life and more cost-effective production of the batteries. The team of researchers from TU Ilmenau led by Prof. Andreas Bund together with scientists from the University of Marburg will investigate how a layer of decomposition products, that forms during battery operation, can be positively influenced on a very small scale so that it can conduct ions and the materials do not decompose even at high voltages. The research project, which is scheduled to last three years, is being funded by the Deutsche Forschungsgesellschaft (DFG) with 324,000 euros.
If you are reading this article on a laptop or smartphone a lithium-ion battery is probably providing the necessary electrical energy. Lithium-ion batteries are successful because they can store large amounts of energy at high voltages - at such high voltages that these batteries should not actually be stable at all. Why lithium-ion batteries nevertheless work and how this knowledge can improve batteries is the subject of the new research project "Investigation of the transport properties and the formation and growth mechanisms of the solid electrolyte interphase (SEI) on carbon model electrodes" at TU Ilmenau.
Rechargeable lithium-ion batteries have been on the market since the early 1990s. While other batteries usually have voltages of one to two volts, the voltage of lithium-ion batteries is four volts - which caused problems especially in the early days of lithium-ion batteries: Many materials, especially the battery electrolytes available at the time, which are needed in batteries to transport ions, degrade at such high cell voltages.
The right choice of carbonates
Using a special mixture of different carbonates, scientists succeeded in the following years in producing electrolytes that remained stable for much longer. For example, a mixture of ethylene carbonate and dimethyl carbonate had very positive properties. However, if the ethylene carbonate was replaced with the chemically very similar propylene carbonate, very poor batteries were obtained, which failed after only a few charging and discharging processes. At the time, it was completely unclear why such a small change in the use of a material had such a big impact on the battery.
It wasn't until years later that researchers found the answer. If the "wrong" carbonates are used, they are not stable at high cell voltages, but continue to decompose until the battery fails. With the right choice of carbonates, on the other hand, the decomposition products form a stable layer that is only a few nanometers thick and protects the electrolyte from further decomposition.
