Solid-State Redox-Active Pseudocapacitor with Improved Performance at High Temperature
Authors: Lashkari Sima , Zanata Daniela de Morais , Goujon Nicolas , Camara Ousmane , Mecerreyes David , Villaluenga Irune 
Published: February 2024

With the emergence of environmental issues such as global warming as well as our new demand for efficient energy storage systems (EES) that can power portable electronics; batteries and supercapacitors are gaining more attention in the latest literature. Batteries can provide high energy density and lower power densities (e.g. for LIB, 1kW.kg-1 vs. 150-200 Wh.kg-1), while supercapacitors are high power devices with low energy densities (e.g. for most commercial devices ⁓ 10 kW.kg-1 vs. 5-10 Wh.kg-1). In order to couple high energy and high power densities of both devices, pseudocapacitance was introduced in 1991 by Conway 1 using metal oxide. Pseudocapacitance is a fast and reversible surface faradaic process with performance similar to double layer capacitors but higher energy densities closer to that of batteries. Aside from metal oxides, conductive polymers also demonstrate pseudocapacitance. In this regards, the use of conductive polymers as nontoxic, abundant, low cost and sustainable organic material is on the rise. Nevertheless, the inherent issue related to instability of the conductive polymer especially at high degree of oxidation had restricted their application in EES. However, redox active polymers (RAPs) with non-conjugated backbone and redox active pendant group demonstrates improved performance and structural diversity with more distinct redox potentials. 2 Amongst them, quinone-containing polymers with their high theoretical capacities, facile kinetics and tunable redox potential are at the top of the list. Particularly, catechol, a bioinspired ortho-quinone based polymer has gain popularity following a work by Detrembleur et al. 3 However; the solubility of the organic materials in organic solvents hinders their application in EES. To this end, using solid-state electrolyte can help alleviate the issue. Nevertheless, solid-state design stimulate sluggish kinetics and reduce electrode/electrolyte interfacial area, a component required to achieve high pseudocapacitance. Consequently, nano-structuring the redox polymer can help improve the contact resistance as well as increasing the surface area. In addition, the nanoparticles structure will promote more distinct redox processes. 4

In this study, we demonstrate for the first time, a prototype pouch cell based on all-solid-state organic hybrid supercapacitor bearing catechol redox active moieties. Using emulsion polymerization, catechol based RAP nanoparticles of size ranging from 50 to 150 nm were synthesized 4 and together with activated carbon was used as working electrode. Block-co-polymers based solid electrolyte was employed as electrolyte as well as binder for both cathode and anode. Using this design, discharge capacities of ⁓ 10 and 60 mAh/g at room temperature and at 50 °C were obtained, respectively.
References:
(1) Conway, B. E. Transition from “Supercapacitor” to “Battery” Behavior in Electrochemical Energy Storage. J. Electrochem. Soc.
1991, 138 (6), 1539. https://doi.org/10.1149/1.2085829.
(2) Casado, N.; Mecerreyes, D. Redox Polymers for Energy and Nanomedicine; Royal Society of Chemistry, 2020.
(3) Patil, N.; Aqil, M.; Aqil, A.; Ouhib, F.; Marcilla, R.; Minoia, A.; Lazzaroni, R.; Jérôme, C.; Detrembleur, C. Integration of Redox-Active Catechol Pendants into Poly(Ionic Liquid) for the Design of High-Performance Lithium-Ion Battery Cathodes. Chem. Mater.
2018, 30 (17), 5831–5835. https://doi.org/10.1021/acs.chemmater.8b02307.
(4) Gallastegui, A.; Camara, O.; Minudri, D.; Goujon, N.; Patil, N.; Ruipérez, F.; Marcilla, R.; Mecerreyes, D. Aging Effect of Catechol Redox Polymer Nanoparticles for Hybrid Supercapacitors. Batter. Supercaps
2022, 5 (9), e202200155. https://doi.org/10.1002/batt.202200155.