Battery research: DFG project on more efficient ion lithium batteries

If you are reading this article on a laptop or smartphone, it is likely that a lithium-ion battery is providing the necessary electrical energy. Lithium-ion batteries are so successful because they can store large amounts of energy at high voltages - at such high voltages that these batteries should not actually be stable. 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, decompose at such high cell voltages.

Using a special mixture of different carbonates, scientists succeeded in subsequent 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 large effect on the battery.

A layer that not only protects, but also transports ions

It was only 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. But the layer must also be able to transport lithium ions, otherwise the charge carrier transport in the cell would collapse and the battery would no longer supply energy. The TU Ilmenau and the University of Marburg are investigating for three years in the new research project how this so-called passivation layer must be designed so that it both reliably passivates, i.e. protects the electrolyte from further decomposition, and at the same time can conduct ions. To this end, the researchers are using various in-situ methods, some of them in the nanometre range, i.e. on the smallest scale, to observe how the layer forms, how paths for ion conduction are created and how the layer formation can be improved. Prof. Andreas Bund, head of the Electrochemistry and Electroplating Group, knows that the influence of this boundary layer on the battery, although extremely thin, is enormous:

Optimizing the ion conductivity, the formation rate and the passivation behavior would mean that future lithium-ion batteries can not only be charged faster and more efficiently, but also last longer and are more cost-effective. I am optimistic that we can do this.

Only course of study in electrochemistry and electroplating in Germany

Electrochemistry and electroplating are becoming increasingly important in the course of the energy transition. Due to the strong specialization in electrochemical processes and the broad basic knowledge required for this, there are only a few specialists. With the study programme Electrochemistry and Electroplating, which is unique in Germany, TU Ilmenau offers the best prerequisites for a career in a wide range of industries. Among other things, students acquire in-depth specialist knowledge of the technological fields of electrochemical surface technology and electrochemical energy storage and conversion. The TU Ilmenau works closely with the Central Association for Surface Technology (ZVO) and numerous commercial enterprises in the field of electroplating and surface technology. The ZVO awards three scholarships per year to master students and thus promotes the next generation of scientists in the industry. The amount of the scholarship is 400 euros per month. As a rule, it is awarded over a period of four semesters.