N-type Redox Research Articles

Unveiling the Role of Charge Dilution and Anionic Chemistry in Enabling High-Rate p-Type Polymer Cathodes for Dual-Ion Batteries.

Herein, we introduce a p-type redox conjugated covalent organic polymer (p-PNZ) as a universal and high-rate cathode for diverse dual-ion batteries. By constructing an n-type redox counterpart (n-PNZ) with an analogous reticular structure and redox-site composition, we also attain a comparative platform to probe how the redox-site nature and counterion chemistry affect the rate performance of polymer cathodes. It is disclosed that the charge dilution in p-type redox sites and bulky anions engenders their weak interaction and rapid anion diffusion in electrodes, while the trivial interaction of the solvent with anions facilitates anion desolvation and interfacial charge transfer. Thus, p-PNZ possesses rapid surface-controlled redox kinetics with a high anion diffusion coefficient regardless of its inferior porosity and conductivity relative to n-PNZ. Along with a long cycle life of over 50000 cycles, the p-PNZ-engaged Zn-based dual-ion battery with a dilute electrolyte delivers nearly constant capacities of ∼149 mAh g-1 at various rates of ≤10 A g-1─such an unusual rate capability has rarely been observed previously─and retains ∼99 mAh g-1 at 40 A g-1, surpassing the n-PNZ counterpart and most existing p-type organic cathodes. The p-PNZ cathode can also be applied to build high-rate Li-based batteries, signifying its universality, while the "ready-to-charge" character of p-PNZ enables anode-free dual-ion batteries with a high-rate capability and long lifespan.

Molecular Designs to Achieve High-Rate and Ultra-Stable Organic Electrode Materials for Future Sustainable Batteries

Organic electrode materials (OEMs) are recently drawing much attention as a promising alternative to conventional transition metal oxide electrodes due to their many advantages, including abundance, sustainability, bio-compatibility, low cost, and easy tunability.[1] Most importantly, the flexible nature of organic materials due to loosely packed intermolecular structures allows fast diffusion for charge-carrying ions, which is essential for the high-rate performance of electrode materials. However, in practice, most OEMs still suffer from slow rate capability and low capacity utilization due to their electrically insulating nature. In a typical battery, the rate capability of an electrode is determined by the kinetic factors for the following three steps during the charge/discharge processes: i) redox reaction of active materials, ii) electron conduction through the active materials and the conductive carbon additives to the current collector, iii) and ion diffusion inside the active materials.[2] Previously, most studies have focused on improving the electrical conductivity of OEMs to achieve high-rate capability; however, such attempts typically sacrificed their specific capacity and/or cycle stability. Here, we present novel molecular design strategies to achieve high-rate capability of OEMs without deterioration of their specific capacity and cycle stability. First, we recently proposed that a small structural reorganization of the redox center during the redox reaction would be a key to achieving fast rate capability in OEMs for the first time.[3] We revealed that a novel p-type redox center phenoxazine (PXZ) had faster redox kinetics than its widely used analogue phenothiazine (PTZ) due to negligibly smaller structural changes, which was evidenced by theoretical calculations using the density functional theory (DFT) method and experimental measurements. In practical coin-cells, such low reorganization of the PXZ center led to high-rate performance (73% capacity retention at 20C) of a PXZ trimer electrode material (3PXZ) with a narrow voltage plateau at 3.7 V vs. Li/Li+. Then, in this presentation, we introduce our new OEMs bearing n-type redox centers with low reorganization energy, including tetrazine (Tz)[4-6] and thieno-isoindigo (TIIG).[7] The new OEMs showed superior rate capability (> 50% capacity retention at 50C) and high cycle stability (> 80% capacity retention after 500 cycles). Finally, we present novel OEMs spontaneously forming various nanostructures via self-assembly after fabricating electrodes.[8] The high surface area of the nanostructured OEMs provided fast electron transfer from the insulating active materials to the conductive carbons and easy access of the charge-carrying ions to the active materials, leading to ultrafast rate performance (> 50% capacity retention at 100C) even with high active content more than 70 wt% in the electrode.

A safer, symmetric all-organic battery based on temperature-responsive polymers as both cathode and anode

All-organic batteries that employ organic compounds as the cathode- and anode-active materials have emerged as a promising rechargeable battery chemistry system due to their environmental friendliness, sustainability, flexibility and wide raw materials availability. Just like current lithium-ion batteries, if operated improperly, there are also safe concerns mainly caused by thermal runaway in all-organic batteries. However, the safety protection for all-organic batteries has not been explored by far. In this work, a novel type of temperature-responsive symmetric all-organic battery with overheating self-protection function is proposed based on poly(3-octylthiophene) (P3OT) as both cathode- and anode-active materials. P3OT is anchored on carbon nanotube (CNT) surface to boost its p- and n-type redox activity. Rewarded by this, the resulting all-organic battery delivers a reversible capacity of 97.2 mAh g−1 at 50 mA g−1 between 0.01 and 2 V and exhibits an outstanding cycling stability. More importantly, when being charged under overheating conditions, the designed all-organic battery can always maintain the low state-of-charge. It can provide an early warning of battery overheating, and mitigate the release of chemical energy if the battery finally goes to fire. During the discharge process, the all-organic battery will be rapidly switched off, thus avoiding continuous battery damage. The thermal protection is proved to be derived from the thermal dedoping of PF6- from cathode-active P3OT. In addition, the all-organic battery is able to resume its normal function when battery temperature is dropped to room temperature.

Carbon nanotube enables high-performance thiophene-containing organic anodes for lithium ion batteries

Poly(thiophene)-based organic compounds with reversible n-type redox behavior can be employed as anode materials for lithium ion batteries (LIBs). However, their inherent problems such as low redox activity, poor rate performance and processing difficultly limit the practical application in LIBs. Herein, a one-dimensional structure-design is reported for a poly(thiophene) derivative (i.e. poly(3-butylthiophene), briefly denoted as P3BT) with a superior lithium storage capability in LIBs. The experimental study and DFT calculation reveal that carbon nanotubes (CNTs) play a critical role in this structure design to promote the electrochemical performances of P3BT. CNTs act as a highly conductive nano-skeleton, which can facilitate the electron transfer, enlarge the electroactive surface area and shorten the ions diffusion path. Besides, the strong π-π interation between P3BT and CNT not only stabilizes the charged and discharged states of P3BT for enhancing the cycling stability, but also compensates the negative effect of introducing of butyl side chains on the energy gap and electron affinity. To the best of our knowledge, the designed one-dimensional P3BT@CNT nanocomposite exhibits a better electrochemical performance compared with the reported thiophene-containing anode materials. This work provides a new insight for the application of thiophene-containing anode materials for LIBs.

Molecular Tailoring of an n/p-type Phenothiazine Organic Scaffold for Zinc Batteries.

The p-type or n-type redox reactions of organics are being used as the reversible electrodes to build the next-generation rechargeable batteries with sustainable and tunable characteristics. However, the n-type organics that store cations generally exhibit low potential (<0.8 V vs. Zn/Zn2+ ), while the p-type organics that store anions suffer from limited capacity (<100 mAh g-1 ). Herein, we demonstrate that bis(phenylamino)phenothiazin-5-ium iodide (PTD-1) containing both n-type and p-type redox moieties exhibits a hybrid charge storage mechanism (n/p-type at low potential, p-type at high potential). Such a hybrid mechanism combines the advantages of n- and p-type reactions and compensates for the associated drawbacks of each. Accordingly, the aqueous Zn//PTD-1 full cell shows a high voltage (1.8 Vmaximum or 1.1 Vaverage ), a high capacity 188.24 mAh gPTD-1 -1 (achieved at 40 mA g-1 ), a long-life and a supercapacitor-like high power. These results shed new light on the design of advanced organic electrodes.

Poly(catechol)s As Universal Electrode Materials for Advanced Organic Batteries

This decade has been witnessing the resurgence of redox-active polymer (RAP) based organic electrode materials in the quest of building large-scale, safe, economical, and sustainable electrochemical energy storage technologies (EESTs) after their brief silence. [1] Most of these RAPs mainly fall under the category of quinone, imide, organosulfur or radical polymers that have demonstrated admirable electrochemical performances. However, it is further necessary to design novel electrode materials with outstanding properties for the development of “next-generation” “high-performance” advanced organic batteries.Here, I present the macromolecular engineering of RAPs bearing catechol pendants of different functionality/composition that dictate their overall electrochemical performances in different battery technologies.Firstly, electrochemical performance of poly(catechol) cathodes in lithium-ion batteries will be presented. By tuning the pendant catechol structure, specific capacity of the homopolymer was boosted from 217 [for P(DA)] to 350 [for P(4VC)] mAh g‒1.[2] Furthermore, incorporation of cation conducting styrene sulfonates within the polymer chain in P(4VC-stat-LiSS) drastically improved the rate capability compared to P(4VC). Moreover, a voltage gain of +350 mV was demonstrated when catechol pendants were confined to an electron-withdrawing poly(ionic liquid) backbone, compared to the same redox groups groups in neutral poly(acrylamide) backbone.[3]Secondly, the application of poly(catechol) as organic cathodes for aqueous Zinc-ion batteries will be presented.[4] The Zn||P(4VC86-stat-SS14) cell in the optimized Zn(TFSI)2-H2O electrolyte simultaneously delivered high gravimetric capacity (324 mAh g‒1), high areal capacity (5.5 mAh cm‒2) at 1C, with remarkable capacity of 98 mAh g‒1 at 450C, extremely low capacity fading rate of 0.00035% per cycle over 48 000 cycles at 30 C rate and low temperature operativity (178 mAh g‒1 at –35 °C).Finally, all-polymer aqueous battery comprising poly(catechol) cathode and poly(imide) anode will be presented.[5] Interestingly, full cell exhibited tunable cell voltage depending on the salt used in the aqueous electrolyte, i.e., 0.58, 0.74, 0.89, and 0.95 V, respectively, when Li+, Zn2+, Al3+, and Li+/H+ were utilized as charge carriers. The full-cell delivered best rate performance (a sub-second charge/discharge) and cycling stability (80% capacity retention over 1000 cycles at 5 A g‒1) in Li+. Furthermore, maximum energy/power density of 80.6 Wh kganode+cathode ‒1/348 kW kganode+cathode ‒1 was achieved in Li+/H+, superior than most of the previously reported aqueous all–polymer batteries.Taking together, by the applicability of poly(catechol) as organic electrode material in different battery technologies, the following general conclusions can be drawn. They are quite universal- and accommodate reversibly numerous cations, ranging from H+, and Li+ to Al3+. This unprecedented approach is based on a simple catecholato–cation complex charge storage mechanism (n-type redox molecules). Development of such universal organic electrodes is particularly intriguing, and gaining popularity among the battery community due to the fact that it demands minimal electrode/device engineering efforts.

Dual Electroactivity in a Covalent Organic Network with Mechanically Interlocked Pillar[5]arenes.

The synthesis and characterization of a polyrotaxanated covalent organic network (CON) based on the association between the viologen and pillar[5]arene (P[5]OH) units are reported. The mechanical bond allows for the irreversible insertion of n-type redox centers (P[5]OH macrocycles) within a pristine structure based on p-type viologen redox centers. Both redox units are active on a narrow potential range and, in water, the presence of P[5]OH greatly increases the electroactivity of the material.

Radical polymer-grafted carbon nanotubes as high-performance cathode materials for lithium organic batteries with promoted n-/p-type redox reactions

Here we present the covalently grafting organic radical polymer, poly(2,2,6,6-tetramethylpiperidin-1-oxyl-4-yl methacrylate) (PTMA), onto the surface of multi-walled carbon nanotubes (MWNT) via free radical polymerization, affording MWNT-g-PTMA. The free-standing MWNT-g-PTMA-based electrode exhibits a high specific capacity of 262.9 mAh g−1 and a >60% capacity retention (144 mAh g−1) after 250 cycles, superior to that of physically mixed MWNT/PTMA electrode. Investigating the charge/discharge process by ex situ electron paramagnetic resonance (EPR) and X-ray photoelectron spectroscopy (XPS), the excellent electrochemical performance of MWNT-g-PTMA-based electrode is attributed to the mutual participation of both p- and n-type redox reactions of PTMA with both cationic and anionic ions insertion/extraction into/from the electrode. Moreover, the capacity fading mainly results from irreversible side reactions during the n-type doping process of PTMA as investigating the charge/discharge process in two separate voltage ranges. This study may contribute to the understanding of energy storage mechanisms of radical polymers in the right way.

N-Type Redox-active Benzoylpyridinium-substituted Supramolecular Gel for an Organogel-based Rechargeable Device

A supramolecular benzoylpyridinium-substituted cyclohexanediamine gelator with n-type redox properties was synthesized. The gelator formed a robust supramolecular network consisting of cyclohexaned...

Macromolecular aggregation and electrochemical behavior of pyrrolyl-, anilynyl- and thiophenyl-silicon compounds as precursors for thin hybrid films

Aniline, pyrrole and thiophene substituted with methoxysilyl propyl side chains were investigated by means of spectroscopic and electrochemical techniques. The effect of hydrolysis and ex-situ irradiation of solutions prepared in different solvent mixtures, containing either methanol or methylacetate in excess, was considered also. The development of stable intermediate species in solution is governed by intramolecular polarization of the hydrolyzed monomer rather than by ex-situ photoxidation or electro-oxidation of the monomer head group. Cooperative non-covalent OH-π interactions between the electron deficient silanol (SiOH) and the electron rich aromatic π system leading to mixed- n-p type redox behavior of the hybrid films are confirmed for the case of N-substituted pyrrolyl-silicon derivative. Less efficient interactions of the more basic N-AnSi derivative result from the deprotonation and self-condensation of SiOH, being supported by the prevalent p-type charge transport of the related hybrid film. For the case thiophenyl-silicon derivatives, charge trapping manifesting n-type redox behavior dominates for the case of α-substituted thiophene rather than for the parent β-substituted derivative but with jellification, indicating effective OH-π stabilization of σ-coupled α,α’ dimer structures by a short-range intramolecular mechanism. The establishment and modulation of constructive OH-π interactions determine the macromolecular aggregation and redox behavior of the hybrid films. The diverse properties exhibited by the hybrid precursors support different protection mechanisms against corrosion.

Metallopolyyne polymers with ferrocenyl pendant ligands as cathode-active materials for organic battery application

Two bis(acetylide)-functionalized platinum(II) polymers containing ferrocenyl pendant ligands, trans-[{-Pt(PBun3)2-C≡CRC≡C-}nP1 (R = 9-ferrocenylmethylene-2,7-diethynylfluorene) and P2 (R = ferrocenylmethylene-2,5-diethynylbenzene), were prepared in good yields and were characterized by NMR spectroscopy and GPC. Electrochemical characteristics with copolymers P1 and P2 as the cathode active materials for rechargeable lithium batteries showed chemical and electrochemical reversibility. The thin layer polymer electrodes of P1 and P2 exhibited reversible redox peaks at the potentials of 0.54 and 0.64 V (vs. Ag/AgCl), respectively. The P1 or P2/carbon composites are also used as cathode-active materials to enhance the conductivity and durability. The electrodes exhibited good cycle life of over 50 charging/discharging cycles and no reversible n-type redox abilities seemed to be available.

Synthesis of Pendant Nitronyl Nitroxide Radical-Containing Poly(norbornene)s as Ambipolar Electrode-Active Materials

Ambipolar redox-active polymers with a reversible charging and discharging capability were synthesized via ring-opening metathesis polymerization (ROMP) of nitronyl nitroxide radical (NN) mono- and disubstituted norbornenes which exhibited p- and n-type redox processes (i.e., one-electron oxidation and reduction per NN group, respectively), using Grubbs catalyst to avoid side reactions of the radical moiety allowing over 95% of radicals to survive after ROMP. ROMP of the NN monomers was accomplished with well-controlled molecular weights of the resulting NN polymers which were coincident with theoretical values in the ratio of [monomer]/[catalyst] = 25–200, narrow polydispersity index (ca. 1.2), and high yields even with [monomer]/[catalyst] > 600. The living character for the ROMP of the NN monomers also allowed block copolymerization. NN-containing block copolymers were synthesized through sequential ROMP with benzyl ether-containing norbornene in high yields. The NN polymer/carbon composite electrode exhibited both p- and n-type charging/discharging with plateau potentials near the redox potentials of the polymer at 0.78 and −0.80 V vs Ag/AgCl, respectively. The spin-coated layer electrode of the NN polymer immobilized on a current collector also demonstrated a fast charging/discharging performance in the range of 10–100 C rates and a cycle stability especially for the p-type reaction. These results made the NN polymer accessible as ambipolar electrode-active materials and also encouraged other organic radicals to be candidates for electroactive polymers.

空気電池：有機負極を目指したポリマー膜の設計

Energy storage by organic redox-active molecules is based on the electromotive force produced from a couple of molecules which are different in redox potentials. Reversible and high-density charge storage by redox polymers ( [Red/Ox]polym ) require charge transport and electroneutralization by electrolyte ions throughout the polymer layer populated in high density with the redox-active groups. Charging/discharging capabilities are accomplished by fabricating organic rechargeable air batteries ((-) M | [Red]polym ↔ [Ox]polym | KOH, H2O | C (catalyst), O2 (+)), using polymer layers as the anode-active material which undergo reversible charging at potentials more negative than that of O2. Nonconjugated polymers with various types of main chains populated with anthraquinone derivatives per repeating unit have been synthesized with a view to unravel their charge transport and storage properties based on the n-type redox reactions. Anthraquinone-functionalized polymers have been proposed as a new class of anodeactive materials with negative charge storage properties and large redox capacities, as a result of the capability of using almost all of the redox sites in the polymer. The polymer/carbon composite layer allowed efficient swelling of the polymer in aqueous electrolyte solutions, giving rise to the rechargeable air battery effect with more than 500 charge/discharge cycle performances.

N-Dopable polythiophenes as high capacity anode materials for all-organic Li-ion batteries

All-organic rechargeable batteries may have low cost, materials sustainability and environmental friendliness, particularly suitable for large scale electric energy storage applications. However, development of such a new generation of batteries is now hindered by the lack of appropriate organic anode materials. In this paper, we report a novel polythiophene/carbon composite, where n-dopable poly (3,4-dihexylthiophene) is in situ chemically polymerized on carbon nanofibers. This organic-carbon composite exhibits an exceptionally high reversible electrochemical capacity of ∼300mAhg−1 (or ∼ 200AhL−1) through n-type redox reactions and superior capacity retention of ⩾95% after a hundred cycles. Based on this n-type redox-active material, an all-organic Li-ion cell using polytriphenylamine as cathode-active material was constructed and found to operate successfully, demonstrating possible applications of this composite as a high capacity anode material for all-organic storage batteries.

N-Type redox behaviors of polybithiophene and its implications for anodic Li and Na storage materials

A polybithiophene-carbon (PBT/C) composite was synthesized by ball-milling chemically polymerized polybithiophene with carbon nanofibers and found to have n-type redox properties with exceptional reversible capacity and cycling stability. The experimental results demonstrated that the as-synthesized (PBT/C) composite can realize a total two-electron redox capacity of ∼850mAhg−1 with half of the capacity delivered at a low potential plateau of 1.25V in Li+ electrolyte, possibly serving as a high capacity organic anode for Li-ion batteries. More significantly, the PBT/C composite can also be cycled in Na+-electrolyte, delivering a reversible redox capacity of ∼500mAhg−1 through the doping–dedoping reactions of Na+ ions into/from the polymer chains. These n-type redox performances suggest a possible application of the polymers of this type as high capacity and cycling-stable anodes for Li-ion and Na-ion batteries.

Cathode- and Anode-Active Poly(nitroxylstyrene)s for Rechargeable Batteries: p- and n-Type Redox Switching via Substituent Effects

Three polystyrenes bearing redox-active nitroxide radical(s) in each repeating unit, poly[4-(N-tert-butyl-N-oxylamino)styrene] (1), poly[3,5-di(N-tert-butyl-N-oxylamino)styrene] (2), and poly[4-(N-tert-butyl-N-oxylamino)-3-trifluoromethylstyrene] (3), were synthesized via free radical polymerization of protected precursor styrenic derivatives and subsequent chemical oxidation. The radicals in these polymers were robust at ambient conditions, and the polymers possessed radical densities of 2.97 × 1021, 4.27 × 1021, and 1.82 × 1021 unpaired electrons/g for 1−3, respectively, resulting in an electrode-active material with a high charge/discharge capacity. Particularly, the dinitroxide functional polymer 2 possessed the highest radical density. Cyclic voltammetry of the poly(nitroxylstyrene) 1 revealed a reversible redox at 0.74 V vs Ag/AgCl, which was assigned to the oxidation of the nitroxide radical to form the oxoammonium cation (p-type doped state). On the other hand, the poly(nitroxylstyrene) ortho-subs...