Facile Synthesis of Polyphenothiazine as a High‐Performance p‐Type Cathode for Rechargeable Lithium Batteries

Abstract p‐Type electroactive polymers are promising cathodes for dual‐ion batteries but cost‐effective candidates are still lacking. In this study, the p‐type polymer polyphenothiazine (PPTZ) is synthesized by a facile one‐step oxidation polymerization from the low‐cost phenothiazine (PTZ) monomer. As a cathode for rechargeable lithium batteries, PPTZ shows superior electrochemical performance to previously reported PTZ‐based polymers with complicated structures and syntheses. For example, PPTZ has a high reversible capacity of 157 mAh g −1 within 2.5–4.3 V vs. Li + /Li with an average discharge voltage of 3.5 V, and a high capacity retention of 77 % after 500 cycles. The highly reversible one‐electron redox mechanism of PPTZ is also investigated in detail by electrochemical testing, ex situ FT‐IR and X‐ray photoelectron spectroscopy, and DFT calculations. PPTZ has the potential to serve as an attractive p‐type cathode material for practical applications and the facile synthesis may be also extended to other polymer cathodes based on N‐heteroaromatic units.