ABSTRACT
Organic materials are promising candidates for next-generation battery systems. However, many organic battery materials suffer from high solubility in common battery electrolytes. Such solubility can be overcome by introducing tailored high-molecular-weight polymer structures, for example, by cross-linking, requiring enhanced synthetic efforts. We herein propose a different strategy by optimizing the battery electrolyte to obtain insolubility of non-cross-linked poly(3-vinyl-N-methylphenothiazine) (PVMPT). Successive investigation and theoretical insights into carbonate-based electrolytes and their interplay with PVMPT led to a strong decrease in the solubility of the redox polymer in ethylene carbonate/ethyl methyl carbonate (3:7) with 1 M LiPF6. This allowed accessing its full theoretical specific capacity by changing the charge/discharge mechanism compared to previous reports. Through electrochemical, spectroscopic, and theoretical investigations, we show that changing the constituents of the electrolyte significantly influences the interactions between the electrolyte molecules and the redox polymer PVMPT. Our study demonstrates that choosing the ideal electrolyte composition without chemical modification of the active material is a successful strategy to enhance the performance of organic polymer-based batteries.
ABSTRACT
Organic redox polymers are attractive electrode materials for more sustainable rechargeable batteries. To obtain full-organic cells with high operating voltages, redox polymers with low potentials (<2 V versus Li|Li+ ) are required for the negative electrode. Dibenzo[a,e]cyclooctatetraene (DBCOT) is a promising redox-active group in this respect, since it can be reversibly reduced in a two-electron process at potentials below 1 V versus Li|Li+ . Upon reduction, its conformation changes from tub-shaped to planar, rendering DBCOT-based polymers also of interest to molecular actuators. Here, the syntheses of three aliphatic DBCOT-polymers and their electrochemical properties are presented. For this, a viable three-step synthetic route to 2-bromo-functionalized DBCOT as polymer precursor is developed. Cyclic voltammetry (CV) measurements in solution and of thin films of the DBCOT-polymers demonstrate their potential as battery electrode materials. Half-cell measurements in batteries show pseudo capacitive behavior with Faradaic contributions, which demonstrate that electrode composition and fabrication will play an important role in the future to release the full redox activity of the DBCOT polymers.
