In recent years, organic battery cathode materials have emerged as an attractive alternative to metal oxide–based cathodes. Organic redox polymers that can be reversibly oxidized are particularly promising. A drawback, however, often is their limited cycling stability and rate performance in a high voltage range of more than 3.4 V versus Li/Li+. Herein, a conjugated copolymer design with phenothiazine as a redox‐active group and a bithiophene co‐monomer is presented, enabling ultra‐high rate capability and cycling stability. After 30 000 cycles at a 100C rate, >97% of the initial capacity is retained. The composite electrodes feature defined discharge potentials at 3.6 V versus Li/Li+ due to the presence of separated phenothiazine redox centers. The semiconducting nature of the polymer allows for fast charge transport in the composite electrode at a high mass loading of 60 wt%. A comparison with three structurally related polymers demonstrates that changing the size, amount, or nature of the side groups leads to a reduced cell performance. This conjugated copolymer design can be used in the development of advanced redox polymers for batteries.

Organic electrode materials based on conjugated dicarboxylate moieties are particularly attractive to develop metal-ion organic batteries. Exhibiting good stability properties in liquid electrolytes, such organic electrode materials can reversibly store alkali metal ions (Li, Na or K) at low working potential. Although many molecular designs have been investigated in the last decade, conjugated dicarboxylates are impeded by low coulombic efficiencies, especially at the first cycle, and sluggish kinetics in most cases. Herein, a new strategy in the design of conjugated carboxylates by fusing a thiadiazole heterocycle to the terephthalate core is reported. The synthesis and electrochemical performance of dilithium-2,1,3-benzothiadiazole-4,7-dicarboxylate (Li 2 -DCBTZ) as positive electrode material is investigated for the first time. Next to being a new structural design, the presence of the thiadiazole ring enables (i) a better conjugation of π-n electrons leading to a benefit in terms of rate capability, and (ii) a better stabilizing coordination network for Li ions through both oxygen and nitrogen atoms. In addition, the reduced state in Li 4 -DCBTZ is stabilized due to a maintained aromaticity in the heteroaromatic core in comparison to the parent terephthalate. Theoretical calculations on the Li-ion storage mechanism and bonding character support the experimental work.