Dibenzo[a,e]Cyclooctatetraene‐Functionalized Polymers as Potential Battery Electrode Materials

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.

Concealed antiaromaticity

“…To start with some structurally simple examples, both cyclooctatetraene and dibenzocyclooctatetraene feature Type I-CA, as both molecules planarize and become aromatic upon twofold reduction (Figure 3a). 21,31,32 Similarly, dibenzopentalene (Figure 2d bottom) becomes globally aromatic upon reduction to the dianion or oxidation to the dication. 33,34 Tetraoxa [8]circulene (Figure 2a top) and the large molecular propeller based on this structure (Figure 2a bottom) also switch to a globally aromatic state upon reduction.…”

Conjugated Copolymer Design in Phenothiazine-Based Battery Materials Enables High Mass Loading Electrodes

“…Their amorphous structures can enable the fabrication of mechanically flexible batteries . Many types of organic electrode materials have been reported, including small molecule and polymeric materials, , covering a wide range of redox potentials − and cell chemistries . Most organic materials, however, lack internal electronic conductivity, and hence, large amounts of conductive carbon additives are required to obtain well-functioning composite electrodes. − This significantly reduces the specific capacity of the entire electrode and makes the materials less competitive compared to established technologies .…”

Bridging the Gap between Small Molecular π-Interactions and Their Effect on Phenothiazine-Based Redox Polymers in Organic Batteries

“…Organic compounds have attracted significant attention as alternative, metal-free, and “greener” electrode materials for rechargeable batteries. − Their advantages lie in the high natural abundance of the constituting elements, mostly C, H, O, S, and N, in their more cost-effective synthesis, in their easier recycling, and in the relative ease of functionalization of organic compounds allowing for a tuning of their electrochemical or chemical properties, compared to traditional metal-oxide-based electrode materials, as used in lithium-ion batteries. , A large variety of organic redox polymers has been synthesized and investigated as electrode materials, − mostly in organic electrode | lithium metal cells but also in all-organic cells , or cells using multivalent metals as negative electrodes . Both low electrode potentials for n-type polymers, − typically used as negative electrode materials, as well as high potentials of up to 4.1 V vs Li/Li + for p-type polymers, , typically used as positive electrode materials, have been reached. Furthermore, high cycling stabilities, rate capabilities, and good specific capacities have been obtained. , Yet, there is still potential for improvement .…”