Two‐Electron Phenothiazine Based Cathode Achieved by Raising HOMO Energy Level for High Performance Lithium Organic Battery

Abstract Redox‐active p ‐type phenothiazine based organic cathodes have captured increasing attention for lithium‐organic batteries due to their high voltage output and rich chemical modification. However, their capacities are generally limited to one redox event per molecule; while the di‐cation states are subject to rapid decomposition and cannot be effectively utilized. Herein, a scalable synthesis of phenothiazine‐based polymer ( MPT‐CC ) is reported, that can fully utilize the two‐electron storage by raising its highest occupied molecular orbital (HOMO). Lithium‐organic batteries using this polymer as cathode displayed a high specific capacity of 178 mAh g −1 at 0.2 A g −1 . This polymer also displays excellent cycling stability. After 1000 cycles at 0.2 A g −1 , a stable capacity of 194 mAh g −1 with ≈100% capacity retention can be obtained. Even at 2 A g −1 after 10,000 cycles, 98 mAh g −1 can be reversibly achieved. Its practical applicability has been successfully demonstrated in MPT‐CC //graphite full cell, also displaying good performance. This work contributes to a major advancement of phenothiazine‐based polymer design for high performance energy storage devices.