Reversible Anion Insertion in Molecular Phenothiazine‐Based Redox‐Active Positive Material for Organic Ion Batteries

The increasing demand for rechargeable batteries induces the development of greener and better devices. Significant advances have been made in the last decade together with a renewed interest in organic electrode materials. Thus, stable electron‐donating organic materials are candidates for “greener” molecular batteries (metal‐free). Herein, we report the design of a monomeric p‐type N‐substituted phenothiazine salt as an efficient anionic host structure working reversibly in a dual‐ion cell configuration using lithium as the negative electrode. Investigation of different electrolyte salts, LiClO4, LiPF6, and LiTFSI in PC (propylene carbonate), reveals that lithium 4‐(10H‐phenothiazin‐10‐yl) benzoate (LiPHB) exhibits a high operating potential (≈3.7 vs. Li+/Li) corresponding to a one‐electron process with a reversible specific capacity of 86 mAh g−1 in a LiClO4‐based electrolyte, exhibiting an extraordinary cycling stability over 500 cycles at 0.2 C. Such impressive results are rendering LiPHB a promising scaffold for developing next‐generation molecular organic batteries. So new, so green, phenothiazine: A one‐electron‐donating phenothiazine derivative is prepared for the first time and used as a non‐polymeric solid‐state stable organic cathode with a reversible specific capacity of 86 mAh g−1 in LiClO4/propylene carbonate and extraordinary cycling stability over 500 cycles at 0.2 C.