Approaches to control π-π-interactions and solubility of heteroatomic redox polymers in rechargeable Li/Organic batteries


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Promising candidates for next generation battery systems are organic materials. In comparison to transition metal-based materials, they are prone to be renewable and have a much lower toxicity while less-limited resources are used for synthesis and a lower amount of energy is needed for production.
Despite the drawbacks of a high solubility in common battery electrolytes and low cycle life of organic electrode-active materials, e.g. quinones, redox polymers have been introduced as a viable alternative. These materials contain redox-active units as part of, or as side groups at, the polymer chain. Most of the reported polymers are p-type and can be used as cathode-active materials in a so-called “dual-ion” mode. During charging, the redox sites of the polymer in the cathode are oxidized and the anions of the electrolyte are inserted for charge balancing. The redox sites should be stable in their oxidation state and decomposition processes should be avoided to reach high cycling stabilities of the battery.
Intensified studies on the redox polymer poly(3-vinyl-N-methylphenothiazine) (PVMPT) were performed which reached an outstanding cycling stability and rate capability. The oxidized redox sites are stabilized via π-π-interactions and a stabilization of the oxidized state of the MPT side chains was identified.
In this poster a systematic development of this concept to structurally similar heteroaromatic polymers which were expected to have altered π-π-interactions and further improved electrochemical properties is presented. The tailored design of the redox polymers had great influence on the performance even when just simply one atom is changed or a side group is substituted. The effects of the polymer structure on the electrochemical behavior and solubility will be highlighted. Moreover, the influence of the choice of electrolyte components will be discussed.

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