No abstract

In spite of recent progress, there is still a lack of reliable organic electrodes for Li storage with high comprehensive performance, especially in terms of long-term cycling stability. Herein, we report an ideal polymer electrode based on anthraquinone, namely, polyanthraquinone (PAQ), or specifically, poly(1,4-anthraquinone) (P14AQ) and poly(1,5-anthraquinone) (P15AQ). As a lithium-storage cathode, P14AQ showed exceptional performance, including reversible capacity almost equal to the theoretical value (260 mA h g(-1); >257 mA h g(-1) for AQ), a very small voltage gap between the charge and discharge curves (2.18-2.14=0.04 V), stable cycling performance (99.4% capacity retention after 1000 cycles), and fast-discharge/charge ability (release of 69% of the low-rate capacity or 64% of the energy in just 2 min). Exploration of the structure-performance relationship between P14AQ and related materials also provided us with deeper understanding for the design of organic electrodes.

Organic electrode materials are promising alternatives to transition-metal based intercalation compounds for the next generation of high-performance and sustainable batteries. Herein, a novel quinone-based organic, lithium salt of poly(2,5-dihydroxy-p-benzoquinonyl sulfide) (Li 2 PDHBQS), was successfully synthesized through a simple one-step polycondensation reaction, and applied as a cathode for Li-organic batteries. As an oligomeric lithium salt with average polymerization degree of 7, Li 2 PDHBQS combines the advantages of the O/Li/O coordination bond and increased molecular weight, thus solves absolutely the dissolution problem of active material in non-aqueous electrolytes, which has seriously hindered development of organic electrode materials. Benefiting from the high theoretical capacity, intrinsic insolubility, fast reaction kinetics of the quinone group, accelerated Li-ion transport and uniform blending with conductive carbon, as well as the stable amorphous structure, Li 2 PDHBQS shows superior comprehensive electrochemical performance including high reversible capacity (268 mA h g À1 ), high cycling stability (1500 cycles, 90%), high rate capability (5000 mA g À1 , 83%) andhigh Coulombic efficiency (99.9-100.1%). Investigation of the structure-property relationship of Li 2 PDHBQS and its analogues also gives new insights into developing novel quinone-based organic electrode materials, for building better Li-organic or Na-organic batteries beyond traditional Li-ion batteries. Broader contextAll electroactive organics or polymers involving reversible redox reactions have the potential to be applied as organic electrode materials for rechargeable batteries. Aer nearly half a century's exploration, conjugated carbonyl compounds are recognized as one of the most promising types among various electroactive materials, as only they have the potential to achieve simultaneously high energy density, high cycling stability and high power density. The conjugated carbonyl compounds can be divided into small organic molecules, organic polymers and organic salts according to the molecular structure, or quinones, dianhydrides, carboxylates, diketones and so on according to the electroactive group. Usually the redox potential of conjugated carbonyl compounds is between 1.5 and 3.0 V vs. Li + /Li, but carboxylates show relatively low redox potential below 1.0 V vs. Li + /Li, so they have the potential to be applied as either cathode or anode. As the theoretical specic capacity is up to 600 mA h g À1 , it is possible to achieve high energy density, although the redox potential is much lower than that of conventional inorganic cathodes. Research on this topic mainly focuses on solving the dissolution problem of active materials to improve the cycling stability, as well as developing new organic electrode materials with higher energy density.