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

A phenothiazine-based polymer is rationally designed for lithium organic batteries. As a result of raised HOMO energy level, two-electron storage of redox centers can be fully utilized, leading to much improved specific capacity and cycling lifespan. This work contributes to a major advancement of phenothiazine-based polymer design for high performance energy storage applications.

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.