Abstract
Utilizing organic redox-active materials as electrodes is a promising strategy to enable innovative battery designs with low environmental footprint during production, which can be hard to achieve with traditional inorganic materials. Most electrode compositions, organic or inorganic, require binders for adhesion and conducting additives to enable charge transfer through the electrode, in addition to the redox-active material. Depending on the redox-active material, many types and combinations of binders and conducting additives have been considered. We designed a conducting polymer (CP), with a soluble, trimeric unit based on 3,4-ethylenedioxythiophene (E) and 3,4-propylenedioxythiophene (P) as the repeat unit, acting as a combined binder and conducting additive. While CPs as additives have been explored earlier, in the current work, the use of a trimeric precursor enables solution processing together with the organic redox-active material. To evaluate this concept, the CP was blended with a redox polymer (RP), which contained a naphthoquinone (NQ) redox group at different ratios. The highest capacity for the total weight of the CP/RP electrode was 77 mAh/g at 1 C in the case of 30% EPE and 70% naphthoquinone-substituted poly(allylamine) (PNQ), which is 70% of the theoretical capacity given by the RP in the electrode. We further used this electrode in an aqueous battery, with a MnSO4 cathode. The battery displayed a voltage of 0.95 V, retaining 93% of the initial capacity even after 500 cycles at 1 C. The strategy of using a solution-processable CP precursor opens up for new organic battery designs and facile evaluation of RPs in such.
Highlights
We showed that using a conducting polymer (CP) backbone with redox pendent groups could result in all-organic[18−22] or hybrid-organic electrode materials without the use of carbon additives since the necessary conductivity was supplied by the CP backbone.[23,24]
To show that pEPE promotes high ion and electron transport rates when used as a combined conducting and binder additive, we investigated pEPE composited with an anthraquinone-based redox polymer (RP), poly(vinylanthraquinone) (PVAQ)
We show that PNQ is suitable in this setting since its redox potential is above the onset potential of the conducting additive
Summary
The push for an environmentally sustainable society has created a huge demand for new and sustainable battery technologies.[1,2] Batteries based on organic redox-active materials are receiving substantial attention in the research community.[3−5] These types of materials enable new and interesting designs thanks to the synthetic possibilities that come with using organic materials that can be produced in low-temperature processes from abundant resources.[6,7] These types of materials are considered environmentally benign compared to inorganic materials in conventional lithium ion or nickel metal hydride batteries requiring hightemperature processes during production and the use of limited resourses.[3,7]. Using a suspension of PEDOT:PSS together with the typical formulation used for lithium ion cathode materials, with lithium iron phosphate as the active component, results in improved rate capabilities.[29,30] PEDOT:PSS can be solution-processed, it is truly a suspension, which is why it cannot be considered a soluble conducting additive Instead of exploring these common paths of creating a composite in which a CP has binder and conducting properties, we choose to further study post-deposition polymerization, where a precursor for a CP in the form of a trimer is deposited on the electrode and subsequently polymerized in situ. To further explore the potential of the formed CP/RP composite polymer, we used the electrode as an anode in a hybrid organic battery with MnO2/Mn2+ as the cathode
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