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.
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.
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