Electrochemical Energy Storage in Poly(dithieno[3,2-b:2′,3′-d]pyrrole) Bearing Pendant Nitroxide Radicals

Abstract

The design and electrochemical synthesis of a conjugated radical polymer (CRP), poly(dithieno[3,2-b:2′,3′d]pyrrole) bearing pendant nitroxide radicals, is reported. Conjugated radical polymers potentially offer simultaneous conductivity and redox activity in the context of organic energy storage. One challenge is understanding the internal electron transfer that occurs in CRPs, which affects the electrochemical energy storage properties. The CRP here is purposefully designed to examine the case of when the conjugated backbone's redox potential is less than that of the organic radical group. Cyclic voltammetry on the as-prepared CRP exhibits two wellresolved redox peaks at E pa1 = 3.15 V and E pa2 = 3.61 V vs Li/Li + , corresponding to the redox activities of the (dithieno[3,2b:2′,3′-d]pyrrole) (DTP) backbone and nitroxide radical, respectively. Galvanostatic charge/discharge studies also reveal a twostep charge/discharge process. The lower oxidation potential of DTP contributes to a conductive pathway during the charge/ discharge process. An internal electron transfer process occurs during the decay of the open circuit potential, as the final potential stabilizes around 3 V. This strategy emphasizes the effects on energy storage when the redox active polymer contains two moieties that are redox active at different potentials, thus impacting future CRP design.

Sustainable Energy Storage: Recent Trends and Developments toward Fully Organic Batteries

“…The cell delivered a stable discharge voltage of 1.0 V, a remarkable rate capability, and an initial specific capacity of 80 mAh g −1 , which retained 70 % after 1000 cycles (Figure ). Alternatively, TEMPO units were coupled to a conjugated polymer, namely poly(dithieno[3,2‐b:2′,3′‐d]pyrrole, for enhanced charge transfer . Electrodes without additives were prepared via electropolymerization, leading only to a small mass loading of 0.1 mg cm −2 .…”

“…Alternatively, TEMPO units were coupled to ac onjugated polymer,n amely poly(dithieno[3,2-b:2',3'-d]pyrrole, for enhanced charge transfer. [114] Electrodes without additives were prepared via electropolymerization, leadingo nly to as mallm ass loading of 0.1 mg cm À2 .T he resulting hybrid lithium-ion cell revealed a decreasing dischargev oltage around3 .3 Va nd an initial capacity of 60 mAhg À1 .…”

“…Polypyrrole, polythiophene, polyaniline, and their derivatives (e.g.,P EDOT) belong to the most common conjugated poly-mers and are applied in various optical, electronic, and electroopticald evicesd ue to their advantageous redox and optical properties. Thus, they were also tested as active battery materials, namely polypyrrole, [127] polythiophene, [128] PEDOT, [129] poly(dithieno[3,2-b:2',3'-d]pyrrole), [114] and polyaniline. [115,130] However, all the presented systemss howeds ignificantly sloping discharge voltages or strongly decreasing capacities,w hich makest hem unsuitable for battery application.…”

A New Conducting Copolymer Bearing Electro‐Active Nitroxide Groups as Organic Electrode Materials for Batteries

“…Indeed, organic and polymer chemistry can provide different nitroxide‐containing materials for their anchoring onto capacitive materials to get polymers. Architectures such as polythiophene‐TEMPO, poly(3,4‐ethylenedioxythiophene) (PEDOT)‐TEMPO, or poly(dithieno[3,2‐ b :2,3‐ d ]pyrrole)‐bearing TEMPO exhibit good conductivity and high theoretical capacity. This strategy emphasizes the importance to match redox‐active polymer potentials with those of electroactive groups.…”

A novel polyphosphazene with nitroxide radical side groups as cathode‐active material in Li‐ion batteries

“…Furthermore, inorganic lithium transition metal oxide cathodes utilized in the rechargeable batteries contain toxic heavy metals. Thus, development of fast charging and discharging new cathode‐active materials, which are also environmentally friendly, is still required and vital in research area for rechargeable LIBs . Therefore, redox‐active and stable radical polymers have proposed as alternative class of cathode materials to inorganic metal oxide cathodes .…”