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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.

Although organic cathode materials with sustainability and structural designability have great potential for rechargeable lithium batteries, the dissolution issue presents a huge challenge to meet the demands of cycling stability and energy density simultaneously. Herein, we have designed and successfully synthesized two novel small-molecule organic cathode materials (SMOCMs) by the same innovative route, namely 7,14-diazabenzo­[a]­tetracene-5,6,8,13-tetraone (DABTTO) and 7,9,16,18-tetraazadibenzo­[a,l]­pentacene-5,6,8,14,15,17-hexaone (TADBPHO). The integrated p-quinone, o-quinone, and pyrazine groups provide these SMOCMs with attractive theoretical capacities of 473 and 568 mAh g–1 based on 6- and 10-electron reactions, respectively, which were almost fully utilized within 0.8–3.8 V vs Li+/Li. The extended aromatic nucleus of TADBPHO makes it much less soluble than DABTTO and thus able to achieve the highest level of cycling stability (66% @ 500th cycle) for SMOCMs in addition to the exceptional energy density (364 mAh g–1 × 2.56 V = 932 Wh kg–1) within 1.5–3.8 V. In addition to the excellent electrochemical performance, the redox reaction and capacity fading mechanisms have been also investigated in detail. The novel approach to construct extended π-conjugated molecules with o-quinone groups is enlightening for the development of high-energy and stable OCMs for future efficient and sustainable energy storage devices.

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Organic cathode materials (OCMs) for rechargeable Li and Na batteries show great advantages in resource sustainability and huge potential in electrochemical performance but suffer from dissolution problems and costly synthesis. Herein, for the first time, we investigated the copolymer of benzoquinone (BQ) and pyrrole (Py), namely, poly­(benzoquinone-pyrrole) (PBQPy), as an OCM for Li batteries. The low-cost raw materials and solvent-free synthesis provide PBQPy much brighter prospects in large-scale production compared to other carbonyl-based polymer cathode materials. Nevertheless, PBQPy showed one of the best electrochemical performances among all OCMs, including excellent energy density (2.32 V × 255 mAh g–1 = 592 Wh kg–1), rate capability (79%@2000 mA g–1), and cycling stability (81%@1000th cycle). By introducing poly­(benzoquinone-methyl pyrrole) for comparison, as well as employing density functional theory calculations and various characterizations for in-depth understanding, the synthesis mechanism, polymer structure, electrochemical behavior, and redox mechanism were clearly clarified. It is believed that this work will encourage more efforts to develop cost-effective OCMs toward practical organic batteries.

In spite of the recent progress made in organic electrode materials, high-performance candidates are still lacking, especially when taking affordability into account. Herein, we report a novel polymeric lithium salt, namely dilithium salt of poly­(2,5-dihydroxy-1,4-benzoquinone-3,6-methylene) (Li2PDBM), which can be easily synthesized by phenol–formaldehyde condensation, followed by lithiation in LiOH solution to eliminate the negative effect of phenol groups in PDBM. Benefiting from a high theoretical capacity (327 mA h g–1), structure stability, insolubility, and redox reversibility, Li2PDBM exhibits superior electrochemical performance as a cathode for rechargeable lithium batteries, including a high reversible capacity (256 mA h g–1), a high rate capability (79% @ 2000 mA g–1), and a high cycling stability (77% @ 2000th cycle). Besides the cost-effective electrode material synthesis approach, this work also provides an important mechanistic understanding of the structure–performance relationship of carbonyl-based electrode materials, especially those with −OH or −OM (M = Li, Na, and K) substituents.

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