Organic Cathode Materials for Magnesium Batteries

• Applicant: Dr. Clemens Liedel
• Subject Area: Polymer Materials ; Preparatory and Physical Chemistry of Polymers
• Term: from 2017 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 390075497

In Germany there is a great consensus about the necessity of developing new sources of renewable energy. However, many of these, like wind or solar power, are not continuously available, and research on energy storage materials becomes necessary. In electromobility applications this will be even more important when it comes to expanding the reach of electric cars or unmanned aerial vehicles for private, economic, public or military applications. Compared to lithium, not only is magnesium more abundant in the earth crust, cheaper, and less dangerous, it also has a similar specific and higher volumetric capacitance while the standard electrode potential is only slightly less negative. This makes magnesium a promising material for next generation rechargeable batteries. Currently, major challenges besides insufficient electrochemical stability of many electrolytes are the slow kinetics, bad reversibility, and low density of magnesium ion incorporation into electrodes, preventing such batteries from being realized. One major problem for sluggish incorporation into host materials as necessary for fast charge-discharge processes in, e.g., electromobility is the high charge density of bivalent magnesium ions. As an alternative to currently investigated intercalation electrodes, this project hence focusses on research about organic polymer electrode materials. Because of a high specific surface area, interactions between redox active groups within the polymer and magnesium ions will only be at the electrode surface, enabling faster charging and discharging. Lignin, which is omnipresent in all plant biomass, will be used as electroactive polymer species. There is already literature about using it for organic battery applications in combination with conductive polymers. Also there, a high specific surface area is crucial. In this project, porous conductive lignin fibers with a high specific surface area will be gained by electrospinning. First, a combination of lignin, a water-soluble auxiliary polymer, and a conductive polymer or its precursor or carbon nanotubes will be spun, followed by dissolution of the auxiliary polymer. The project contains different issues of lignin. On the one hand it deals with lignin based polymer materials, its structures, and with structuring a ternary polymeric mixture. On the other hand the electrochemistry of lignin and interaction with ions is in focus. Combining both subjects will enable creation of bio-based polymeric electrode materials. Through a better understanding of electrochemical magnesium conduction and deposition in polymer materials and intricate settings, an important step towards future energy storage materials will be completed.

• DFG Programme: Research Grants