Benzotriazinyl radical containing polymers as bipolar active electrode material in organic secondary batteries

• Applicant: Professor Dr. Ulrich S. Schubert
• Subject Area: Polymer Materials
• Term: from 2016 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 328403339

The growing interest in mobile devices and their increasing integration into the World Wide Web (Internet of Things) necessitates the availability and development of small and flexible energy-storage systems. However, lithium ion batteries, which represent the current benchmark technology, do not allow the assembly of flexible batteries and demand environmentally questionable techniques for production and processing of raw materials as well as for the final disposal of disused devices. Hence, current research focuses more and more on thin film batteries that are based on organic redox active molecules, which are prepared through organic synthesis and disposed free of residues via burning. Furthermore, their (electro)chemical properties can be easily tuned through choosing a suitable chemical structure. Unfortunately, small molecules tend to dissolve in the used electrolyte leading to a significantly decreased lifetime of the battery. Thus, the monomeric redox active units are integrated into long chain polymers, which possess a substantially decreased solubility.In the course of the project, in particular polymers that are based on the benzo-1,2,4-triazinyl radical are developed. This molecule features electrochemical reversibility, high stability against air and moisture, as well as facile synthetic accessibility. Its redox characteristics can be, furthermore, easily tuned through the molecular substitution pattern, which enables even the preparation of systems that can serve both as anode and cathode material, allowing the construction of bipolar, i. e. poleless, batteries.The increase of the batteries still low theoretical capacity (from around 60 to over 100 mAh g-1) represents a central goal, which should be mainly achieved through the reduction of the molar mass of the monomer. (Electro)chemical stability, cell voltages of around 1.2 V (to allow for aqueous electrolytes), and polymerizability of the molecule have to be maintained, which is ensured through the investigation of structure-property relationships in the course of substituent variations to enable a systematic optimization of the system. The characterization process comprises the preliminary characterization of the monomeric and polymeric compounds in solution and in the solid state, the processing of the polymers with conductive additives and binder materials toward thin film composite electrodes and their subsequent characterization, as well as the assembly and comprehensive investigation of half-organic (using lithium or sodium as anode material) and full organic cells. Furthermore, the preparation of the batteries is optimized, in particular with regard to the used additives and the thin-film processing (doctor blading, inkjet printing).

• DFG Programme: Research Grants