Fusing thiadiazol and terephthalate: A concept to promote the electrochemical performance of conjugated dicarboxylates.

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 reversibility 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, we report on a new strategy in the design of conjugated carboxylates by fusing a thiadiazole heterocycle to the terephthalate core. We investigate for the first time the synthesis and electrochemical performance of dilithium-2,1,3-benzothiadiazole-4,7-dicarboxylate (Li2-DCBTZ) as positive electrode material. Next to being a new structural design, the presence of the thiadiazole ring enables (i) a better conjugation of p-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 Li4-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.