Electrochemical and ab initio investigations to design a new phenothiazine based organic redox polymeric material for metal-ion battery cathodes

Versatile Nitrogen-Centered Organic Redox-Active Materials for Alkali Metal-Ion Batteries

Versatile nitrogen-centered organic redox-active molecules have gained significant attention in alkali metal-ion batteries (AMIBs) due to their low cost, low toxicity, and ease of preparation. Specially, their multiple reaction categories (anion/cation insertion types of reaction) and higher operating voltage, when compared to traditional conjugated carbonyl materials, underscore their promising prospects. However, the high solubility of nitrogen-centered redox active materials in organic electrolyte and their low electronic conductivity contribute to inferior cycling performance, sluggish reaction kinetics, and limited rate capability. This review provides a detailed overview of nitrogen-centered redox-active materials, encompassing their redox chemistry, solutions to overcome shortcomings, characterization of charge storage mechanisms, and recent progress. Additionally, prospects and directions are proposed for future investigations. It is anticipated that this review will stimulate further exploration of underlying mechanisms and interface chemistry through in situ characterization techniques, thereby promoting the practical application of nitrogen-centered redox-active materials in AMIBs.

Facile Synthesis of Polyphenothiazine as a High-Performance p-Type Cathode for Rechargeable Lithium Batteries

p-Type electroactive polymers are promising cathodes for dual-ion batteries but cost-effective candidates are still lacking. In this study, the p-type polymer polyphenothiazine (PPTZ) is synthesized by a facile one-step oxidation polymerization from the low-cost phenothiazine (PTZ) monomer. As a cathode for rechargeable lithium batteries, PPTZ shows superior electrochemical performance to previously reported PTZ-based polymers with complicated structures and syntheses. For example, PPTZ has a high reversible capacity of 157 mAh g^-1 within 2.5-4.3 V vs. Li⁺ /Li with an average discharge voltage of 3.5 V, and a high capacity retention of 77 % after 500 cycles. The highly reversible one-electron redox mechanism of PPTZ is also investigated in detail by electrochemical testing, ex situ FT-IR and X-ray photoelectron spectroscopy, and DFT calculations. PPTZ has the potential to serve as an attractive p-type cathode material for practical applications and the facile synthesis may be also extended to other polymer cathodes based on N-heteroaromatic units.

Correlation of electrochemical and ab initio investigations of iron poly-bipyridine coordination complexes for battery applications: impact of the anionic environment and the local geometries of the redox complexes on the electrochemical response

Although they exhibit huge versatility, coordination complexes have been rarely investigated in the field of cathode materials for batteries. Despite their relatively high molecular mass, according to the nature of the metallic center and that of the ligand, the E° value and the electron transfer kinetics can be adjusted to develop a performant material compatible with the electrolyte. Here, we propose to investigate FeII poly-bipyridine complexes with a view to check the impact of the nature of the electrolyte as well as the influence of the distance between two redox centers when polymerized on the electrochemical response in battery conditions. To understand these changes, three lithium salts have been studied: LiClO4, LiPF6 and LiTFSI (TFSI = bis(trifluoromethane)sulfonimide). In order to mimic these impacts, monomer complexes (mono- and binuclear) have been electrochemically studied, whereas, thanks to ab initio calculations, their redox behavior has been correlated to the ligand environment of the metallic center. Finally, despite their expected low mass capacity, these polymeric coordination complexes have been involved in battery conditions.

Symmetric All-Organic Battery Containing a Dual Redox-Active Polymer as Cathode and Anode Material

All-organic batteries are a promising sustainable energy storage technology owing to the wide availability, flexibility, and recyclability of organic/polymeric compounds. The development of all-organic or polymer batteries is still a challenge, as both electrode materials need to be carefully optimized to have a wide difference of redox potential and compatibility with the electrolyte. Herein, dual redox-active polyimides based on phenothiazine and naphthalene tetracarboxylic dianhydride units are presented. After only one optimization step, the electrodes based on these dual redox polymers can be applied simultaneously as anode and cathode in a symmetric all-organic battery. The phenothiazine functional polyimide shows two redox active voltages at around 2.5 and 3.7 V (vs. Li/Li⁺ ) with high discharge capacities of 160 mAh g^-1 . Moreover, the symmetric full battery delivers high power density up to 1542 W kg^-1 with stable cyclability for 1000 cycles. This work demonstrates an efficient strategy to develop dual redox active polymer electrodes for next generation all-polymer batteries.

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

To reduce the amount of conducting additives generally required for polynitroxide-based electrodes, a stable radical (TEMPO) is combined with a conductive copolymer backbone consisting of 2,7-bisthiophene carbazole (2,7-BTC), which is characterized by a high intrinsic electronic conductivity. This work deals with the synthesis of this new polymer functionalized by a redox nitroxide. Fine structural characterization using electron paramagnetic resonance (EPR) techniques established that: 1) the nitroxide radicals are properly attached to the radical chain (continuous wave EPR) and 2) the polymer chain has very rigid conformations leading to a set of well-defined distances between first neighboring pairs of nitroxides (pulsed EPR). The redox group combined with the electroactive polymer showed not only a very high electrochemical reversibility but also a perfect match of redox potentials between the de-/doping reaction of the bisthiophene carbazole backbone and the redox activity of the nitroxide radical. This new organic electrode shows a stable capacity (about 60 mAh g^-1 ) and enables a strong reduction in the amount of carbon additive due to the conducting-polymer skeleton.

Phenothiazine-Functionalized Poly(norbornene)s as High-Rate Cathode Materials for Organic Batteries

Organic cathode materials are handled as promising candidates for new energy-storage solutions based on their transition-metal-free composition. Phenothiazine-based polymers are attractive owing to their redox potential of 3.5 V vs. Li/Li+ and high cycling stabilities. Herein, three types of poly(norbornene)s were investigated, functionalized with phenothiazine units through either a direct connection or ester linkages, as well as their crosslinked derivatives. The directly linked poly(3-norbornylphenothiazine)s demonstrated excellent rate capability and cycling stability with a capacity retention of 73 % after 10 000 cycles at a C-rate of 100 C for the crosslinked polymer. The polymer network structure of the crosslinked poly(3-norbornylphenothiazine) was beneficial for its rate performance.

Reversible Anion Insertion in Molecular Phenothiazine-Based Redox-Active Positive Material for Organic Ion Batteries

The increasing demand for rechargeable batteries induces the development of greener and better devices. Significant advances have been made in the last decade together with a renewed interest in organic electrode materials. Thus, stable electron-donating organic materials are candidates for "greener" molecular batteries (metal-free). Herein, we report the design of a monomeric p-type N-substituted phenothiazine salt as an efficient anionic host structure working reversibly in a dual-ion cell configuration using lithium as the negative electrode. Investigation of different electrolyte salts, LiClO₄ , LiPF₆ , and LiTFSI in PC (propylene carbonate), reveals that lithium 4-(10H-phenothiazin-10-yl) benzoate (LiPHB) exhibits a high operating potential (≈3.7 vs. Li⁺ /Li) corresponding to a one-electron process with a reversible specific capacity of 86 mAh g^-1 in a LiClO₄ -based electrolyte, exhibiting an extraordinary cycling stability over 500 cycles at 0.2 C. Such impressive results are rendering LiPHB a promising scaffold for developing next-generation molecular organic batteries.

Hypercrosslinked phenothiazine-based polymers as high redox potential organic cathode materials for lithium-ion batteries

Organic cathode materials have been demonstrated to be highly promising sustainable cathode materials for rechargeable lithium-ion batteries. However, the low redox potentials, low electrical conductivity, and the undesirable dissolution in organic electrolytes greatly limit their applications. Herein, two insoluble hypercrosslinked porous conductive polymers with phenothiazine motifs, HPEPT and HPPT, were successfully accomplished with high and stable discharge potentials at 3.65 and 3.48 V versus Li/Li⁺. HPEPT and HPPT with good electrical conductivity exhibited outstanding rate capabilities (up to 800 mA g⁻¹) even at a high mass loading up to 70 wt%. This study shows that excellent organic cathode materials could be achieved readily through this prudent design.

Hypercrosslinked conductive polymers with phenothiazine motifs were achieved and studied as organic cathode materials, exhibiting excellent electrochemical performance.

Organocatalyzed Controlled Radical Polymerizations

Radical polymerizations are responsible for a significant amount of the World's total polymer production. Free-radical polymerization provides a relatively inexpensive and facile route to produce bulk plastic products, however, it fails in the synthesis of precisely defined macromolecules. To address this issue, controlled radical polymerizations have been developed, which utilize a reversible deactivation mechanism for the synthesis of advanced polymeric architectures. In this chapter, we discuss the mechanisms and applications of organocatalyzed controlled radical polymerizations, specifically atom transfer radical polymerization, photo mediated reversible addition fragmentation chain-transfer polymerization, and reversible complexation mediated radical polymerization, as powerful new methods for precision polymer synthesis.

Raising the redox potential in carboxyphenolate-based positive organic materials via cation substitution

Meeting the ever-growing demand for electrical storage devices requires both superior and “greener” battery technologies. Nearly 40 years after the discovery of conductive polymers, long cycling stability in lithium organic batteries has now been achieved. However, the synthesis of high-voltage lithiated organic cathode materials is rather challenging, so very few examples of all-organic lithium-ion cells currently exist. Herein, we present an inventive chemical approach leading to a significant increase of the redox potential of lithiated organic electrode materials. This is achieved by tuning the electronic effects in the redox-active organic skeleton thanks to the permanent presence of a spectator cation in the host structure exhibiting a high ionic potential (or electronegativity). Thus, substituting magnesium (2,5-dilithium-oxy)-terephthalate for lithium (2,5-dilithium-oxy)-terephthalate enables a voltage gain of nearly +800 mV. This compound being also able to act as negative electrode via the carboxylate functional groups, an all-organic symmetric lithium-ion cell exhibiting an output voltage of 2.5 V is demonstrated.

Organic electrode materials could enable novelty chemistry required by the new generation of batteries. Here the authors show the synthesis and electrochemical performance of Mg(Li₂)-p-DHT as a lithiated cathode material that cycles at 3.4 V due to the presence of a spectator cation in the host structure.

The rise of organic electrode materials for energy storage

Organic electrode materials are very attractive for electrochemical energy storage devices because they can be flexible, lightweight, low cost, benign to the environment, and used in a variety of device architectures. They are not mere alternatives to more traditional energy storage materials, rather, they have the potential to lead to disruptive technologies. Although organic electrode materials for energy storage have progressed in recent years, there are still significant challenges to overcome before reaching large-scale commercialization. This review provides an overview of energy storage systems as a whole, the metrics that are used to quantify the performance of electrodes, recent strategies that have been investigated to overcome the challenges associated with organic electrode materials, and the use of computational chemistry to design and study new materials and their properties. Design strategies are examined to overcome issues with capacity/capacitance, device voltage, rate capability, and cycling stability in order to guide future work in the area. The use of low cost materials is highlighted as a direction towards commercial realization.

Organocatalyzed Atom Transfer Radical Polymerization: Perspectives on Catalyst Design and Performance

The recent development of organocatalyzed atom transfer radical polymerization (O-ATRP) represents a significant advancement in the field of controlled radical polymerizations. A number of classes of photoredox catalysts have been employed thus far in O-ATRP. Analysis of the proposed mechanism gives insight into the relevant photophysical and chemical properties that determine catalyst performance. Discussion of each of the classes of O-ATRP catalysts highlights their previous uses, their roles in the development of O-ATRP, and the distinctive properties that govern their polymerization behavior, leading to a set of design principles for O-ATRP catalysts. Remaining challenges for O-ATRP are presented, as well as prospects for further improvement in the application scope of O-ATRP.