Heavily n-Dopable π-Conjugated Redox Polymers with Ultrafast Energy Storage Capabilityby Yanliang Liang, Zhihua Chen, Yan Jing, Yaoguang Rong, Antonio Facchetti, Yan Yao

J. Am. Chem. Soc.


Chemistry (all) / Colloid and Surface Chemistry / Biochemistry / Catalysis


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Heavily n-Dopable #-Conjugated Redox Polymers with Ultrafast Energy Storage Capability

Yanliang Liang, Zhihua Chen, Yan Jing, Yaoguang Rong, Antonio Facchetti, and Yan Yao

J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.5b02290 • Publication Date (Web): 31 Mar 2015

Downloaded from http://pubs.acs.org on April 1, 2015

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Heavily n-Dopable π-Conjugated Redox PolymerswithUltrafast

Energy Storage Capability

Yanliang Liang, †

Zhihua Chen, §

Yan Jing, †

YaoguangRong, †

Antonio Facchetti,* , §

Yan Yao* ,†,¶ †

Department of Electrical and Computer Engineering, University of Houston, Houston, Texas 77204, USA. §

Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, USA. ¶

Texas Center of Superconductivity, University of Houston, Houston, Texas 77204, USA.

Supporting Information Placeholder

ABSTRACT: We report here the firstsuccessful demonstration ofa “π-conjugated redox polymer”simultaneously featuring a πconjugated backbone and integrated redox sites, whichcan be stably and reversibly n-doped to a high doping level of 2.0 with significantly enhanced electronic conductivity. The properties of suchaheavily n-dopable polymer, poly{[N,N’-bis(2-octyldodecyl)1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt-5,5’-(2,2’bithiophene)} (P(NDI2OD-T2)), were compared vis-a-visto those of the corresponding backbone-insulated poly{[N,N’-bis(2octyldodecyl)-1,4,5,8-naphthalenedicarboximide-2,6-diyl]-alt5,5’-[2,2’-(1,2-ethanediyl)bithiophene]} (P(NDI2OD-TET)).

When evaluated as a charge storage material for rechargeable Li batteries, P(NDI2OD-T2) delivers 95% of its theoretical capacity at a high rate of 100C (72 s per charge−discharge cycle) under practical measurement conditions, as well as 96% capacity retention after 3000 cycles of deep discharge−charge.Electrochemical, impedance, and charge transport measurements unambiguously demonstrate that the ultrafast electrode kinetics of P(NDI2OD-T2) are attributed to the high electronic conductivity of the polymerinthe heavily n-doped state.

Organicπ-conjugated polymers are emergingas a materials class for energy-related applications enabling a path to a more sustainable energy landscape without the need of energy-intensive, expensive, and sometimes toxic metal-based compounds.1Furthermore, the possibility to fabricate lightweight and mechanically flexible devices makes polymeric materials even more attractive. Holetransporting(semi)conducting polymers with substantial redox activity and electronic conductivity have been long recognized as electrode materials for batteries, supercapacitors, and thermoelectrics.2 However, all-polymer devices of this type have been difficult to realize due to the limitations of electron-transporting polymers.3Two general classes of electron-transporting polymers are known: π-conjugated polymers and non-conjugated redox polymers.2aElectron-transporting(or n-type) π-conjugated polymers typically need multiple repeating units in the backbone to stabilize injected electrons. Thus, the inability to stably and reversibly store these chargeslimits then-doping level,4 which in turn reduces the amount of free electrons and therefore restricts the electronic conductivity. On the other hand, non-conjugated redox polymers have dedicated redox active sites accepting one or more electrons per repeating unit,5 but lack a π-conjugated backbone as found in πconjugated polymers, which is crucial for efficient electron conduction. Since the advantages of the two classes of polymers perfectly complement each other, the weakness of both polymers could be addressed bya rational combination of the characteristics from each class,such as a “π-conjugated redox polymer” (Figure 1a).Pioneering attempts to construct such a polymer were limited by insufficient reversibility of the doping process,6 unknown doping level,6b, c, 7and/or uninvestigated/poor conductivity of the ndoped state6-7.Thus, it remains a major challenge to develop heavily n-dopable π-conjugated polymers with high electronic conductivity.

Figure 1. (a) Graphical illustration of the structural characteristics of π-conjugated polymers, redox polymers, and π-conjugated redox polymers. (b) Molecular structure of the non-conjugated