Toward High Performance Thiophene‐Containing Conjugated Microporous Polymer Anodes for Lithium‐Ion Batteries through Structure Design

Poly(thiophene) as a kind of n‐doped conjugated polymer with reversible redox behavior can be employed as anode material for lithium‐ion batteries (LIBs). However, the low redox activity and poor rate performance for the poly(thiophene)‐based anodes limit its further development. Herein, a structure‐design strategy is reported for thiophene‐containing conjugated microporous polymers (CMPs) with extraordinary electrochemical performance as anode materials in LIBs. The comparative study on the electrochemical performance of the structure‐designed thiophene‐containing CMPs reveals that high redox‐active thiophene content, highly crosslinked porous structure, and improved surface area play significant roles for enhancing electrochemical performances of the resulting CMPs. The all‐thiophene‐based polymer of poly(3,3′‐bithiophene) with crosslinked structure and a high surface area of 696 m² g^?1 exhibits a discharge capacity of as high as 1215 mAh g^?1 at 45 mA g^?1, excellent rate capability, and outstanding cycling stability with a capacity retention of 663 mAh g^?1 at 500 mA g^?1 after 1000 cycles. The structure–performance relationships revealed in this work offer a fundamental understanding in the rational design of CMPs anode materials for high performance LIBs.     

Redox Poly-Counterion Doped Conducting Polymers for Pseudocapacitive Energy Storage

Conducting polymers (CPs) have been widely studied for electrochemical energy storage. However, the dopants in CPs are often electrochemically inactive, introducing “dead-weight” to the materials. Moreover, commercial-level electrode materials with high mass loadings (e.g., >10 mg cm⁻²) often encounter the problems of inferior electrical and ionic conductivity. Here, a redox-active poly-counterion doping concept is proposed to improve the electrochemical performance of CPs with ultra-high mass loadings. As a study prototype, heptamolybdate anion (Mo₇O₂₄⁶⁻) doped polypyrrole (PPy) is synthesized by electro-polymerization. A 2 mm thick PPy electrode with mass loading of ≈192 mg cm⁻² reaches a record-high areal capacitance of ≈47 F cm⁻², competitive gravimetric capacitance of 235 F g⁻¹, and volumetric capacitance of 235 F cm⁻³. With poly-counterion doping, the dopants also undergo redox reactions during charge/discharge processes, providing additional capacitance to the electrode. The interaction between polymer chains and the poly-counterions enhances the electrical conductivity of CPs. Besides, the poly-counterions with large steric hindrance could act as structural pillars and endow CPs with open structures for facile ion transport. The concept proposed in this work enriches the electrochemistry of CPs and promotes their practical applications.     

Systematic Investigation of Side‐Chain Branching Position Effect on Electron Carrier Mobility in Conjugated Polymers

Recently, polymer field‐effect transistors have gone through rapid development. Nevertheless, charge transport mechanism and structure‐property relationship are less understood. Here we use strong electron‐deficient benzodifurandione‐based poly(p‐phenylene vinylene) ( BDPPV ) as polymer backbone and develop six BDPPV ‐based polymers ( BDPPV‐C1 to C6 ) with various side‐chain branching positions to systematically study the side‐chain effect on device performance. All the polymers exhibited ambient‐stable n‐type transporting behaviors with the highest electron mobility of up to 1.40 cm² V^?1 s^?1. The film morphologies and microstructures of all the six polymers were systematically investigated. Our results demonstrate that the interchain π–π stacking distance decreases as moving the branching position away from polymer backbones, and an unprecedentedly close π–π stacking distance down to 3.38 Å is obtained for BDPPV‐C4 to C6 . Nonetheless, closer π–π stacking distance does not always correlate with higher electron mobility. Polymer crystallinity, thin film disorder, and polymer packing conformation, which all influenced by side‐chain branching position, are proved to show significant influence on device performance. Our study not only reveals that π–π stacking distance is not the decisive factor on carrier mobility in conjugated polymers but also demonstrates that side‐chain branching position engineering is a powerful strategy to modulate and balance these factors in conjugated polymers.     

Rational Design of High‐Mobility Semicrystalline Conjugated Polymers with Tunable Charge Polarity: Beyond Benzobisthiadiazole‐Based Polymers

High‐mobility semiconducting polymers composed of arylene vinylene and dithiophene‐thiadiazolobenzotriazole (SN) units are developed by three powerful design strategies, namely, backbone engineering, heteroatom substitution, and side‐chain engineering. First, starting from the quaterthiophene‐SN copolymer, a vinylene spacer is inserted into the quaterthiophene unit for constructing highly‐planar backbones. Second, heteroatoms (O and N atoms) are incorporated into the thienylene vinylene moieties to tune the electronic properties and intermolecular interactions. Third, the alkyl side chains are optimized to tune the solubility and self‐assembly properties. As a consequence, a remarkable thin film transistor performance is obtained. The very high hole mobility of 3.22 cm² V^?1 s^?1 is achieved for the p‐type polymer, PSNVT‐DTC8, which is the highest value ever reported for the polymers based on the benzobisthiadiazole and its analogs. Moreover, heteroatom substitution efficiently varies the charge polarity of the polymers as in the case of the N atom substituted PSNVT_z‐DTC16 displaying n‐type dominant ambipolar properties with the electron mobility of 0.16 cm² V^?1 s^?1. Further studies using grazing‐incidence wide‐angle X‐ray scattering and atomic force microscopy have revealed the high crystallinities of the polymer thin films with strong π–π interactions and suitable polymer packing orientations.     

Effect of Spacer Length of Siloxane‐Terminated Side Chains on Charge Transport in Isoindigo‐Based Polymer Semiconductor Thin Films

A series of isoindigo‐based conjugated polymers (PII2F‐C_mSi, m = 3–11) with alkyl siloxane‐terminated side chains are prepared, in which the branching point is systematically “moved away” from the conjugated backbone by one carbon atom. To investigate the structure–property relationship, the polymer thin film is subsequently tested in top‐contact field‐effect transistors, and further characterized by both grazing incidence X‐ray diffraction and atomic force microscopy. Hole mobilities over 1 cm² V^?1 s^?1 is exhibited for all soluble PII2F‐C_mSi (m = 5–11) polymers, which is 10 times higher than the reference polymer with same polymer backbone. PII2F‐C₉Si shows the highest mobility of 4.8 cm² V^?1 s^?1, even though PII2F‐C₁₁Si exhibits the smallest π–π stacking distance at 3.379 Å. In specific, when the branching point is at, or beyond, the third carbon atoms, the contribution to charge transport arising from π–π stacking distance shortening becomes less significant. Other factors, such as thin‐film microstructure, crystallinity, domain size, become more important in affecting the resulting device's charge transport.     

New Anthraquinone‐Based Conjugated Microporous Polymer Cathode with Ultrahigh Specific Surface Area for High‐Performance Lithium‐Ion Batteries

Redox‐active conjugated microporous polymers (RCMPs) polymerized by conventional methods are commonly obtained as irregular insoluble solid particles making the electrode processing difficult. In this work, the synthesis of RCMP based on anthraquinone moieties (IEP‐11) is developed via a two‐step pathway combining miniemulsion and solvothermal techniques that results in polymer nanostructures that are much easier to disperse in solvents facilitating the fabrication of electrodes. Interestingly, this synthetic approach is also found to have an important impact on the inherent morphology of IEP‐11 that exhibits a dual porosity combining micro and mesopores with a specific surface area as high as 2200 m² g^?1, which is one of the highest values reported for RCMPs. Moreover, the compactness of the electrodes is also improved, the resulting electrodes have triple the density than those obtained with conventional methods. Consequently, when these electrodes are tested as cathodes in Li‐ion battery, they deliver high gravimetric capacities (≈100 mAh g^?1) and extraordinary rate capability keeping 76% of discharge capacity when charged–discharged in only 12 min (@5 C). Moreover, the insoluble and robust conjugated porous structure provides IEP‐11‐E12 with an unprecedented cycling stability retain ≈90% and ≈60% of its initial capacity after 5000 (@2 C) and 80 000 cycles (@30 C), respectively.     

Solid‐State Lithium–Sulfur Battery Enabled by Thio‐LiSICON/Polymer Composite Electrolyte and Sulfurized Polyacrylonitrile Cathode

Solid‐state lithium–sulfur battery (SSLSB) is attractive due to its potential for providing high energy density. However, the cell chemistry of SSLSB still faces challenges such as sluggish electrochemical kinetics and prominent “chemomechanical” failure. Herein, a high‐performance SSLSB is demonstrated by using the thio‐LiSICON/polymer composite electrolyte in combination with sulfurized polyacrylonitrile (S/PAN) cathode. Thio‐LiSICON/polymer composite electrolyte, which processes high ionic conductivity and wettability, is fabricated to enhance the interfacial contact and the performance of lithium metal anodes. S/PAN is utilized due to its unique electrochemical characteristics: electrochemical and structural studies combined with nuclear magnetic resonance spectroscopy and electron paramagnetic resonance characterizations reveal the charge/discharge mechanism of S/PAN, which is the radical‐mediated redox reaction within the sulfur grafted conjugated polymer framework. This characteristic of S/PAN can support alleviating the volume change in the cathode and maintaining fast redox kinetics. The assembled SSLSB full cell exhibits excellent rate performance with 1183 mAh g^?1 at 0.2 C and 719 mAh g^?1 at 0.5 C, respectively, and can accomplish 50 cycles at 0.1 C with the capacity retention of 588 mAh g^?1. The superior performance of the SSLSB cell rationalizes the construction concept and leads to considerations for the innovative design of SSLSB.     

Growth of Vertically Aligned Tunable Polyaniline on Graphene/ZrO2 Nanocomposites for Supercapacitor Energy‐Storage Application

In‐situ hydrothermal method is employed to synthesize graphene/zirconium oxide composite from respective precursors graphene oxide and zirconium oxy‐nitrate. In this method, the graphene oxide is reduced itself to graphene and simultaneously metal oxide gets anchor on the graphene sheets. A novel method is also developed for the preparation of vertically aligned tunable polyaniline on the graphene/zirconium oxide nanocomposite, which leads to achieve high surface area (207.1 m² g^?1), high electrical conductivity (70.8 S cm^?1), high specific capacitance (1359.99 Fg^?1 at 1 mV s^?1), and high electrochemical performances as supercapacitor electrode materials. This vertically aligned conducting polymer gets easy contact with electrolyte ions and provides numerous redox active sites during charging and discharging. Moreover, such a simple and low cost assembly approach can be a pioneer for the large‐scale production of various functional architectures for energy storage and conversions.     

Unconventional Carbon: Alkaline Dehalogenation of Polymers Yields N‐Doped Carbon Electrode for High‐Performance Capacitive Energy Storage

Polymers are important precursors for the fabrication of carbon materials. Herein, halogenated polymers are explored as precursors for the synthesis of high‐quality carbon materials via alkaline dehalogenation. It is found that the halogen elements (F, Cl) connecting to vinylidene units are highly reactive so that dehalogenation can take place a few seconds at room temperature by simple hand grinding in the presence of strong inorganic alkaline. Furthermore, the halogen element‐leaving sites are shown to be susceptible to heteroatom doping (e.g., N doping) to become stable capacitive sites for charge storage (e.g., ions). By using a mixture of NaOEt and KOH as dehalogenation reagents, abundant hierarchical pores (macro/meso/micropores) in the resultant doped carbon matrix for fast mass transportation can be created. Very high capacitance (328 F g^?1 at 0.5 A g^?1) and rate capability (75.3% retention at 50 A g^?1 and 62.5% retention at 100 A g^?1) are observed for the newly developed halogenated polymer‐derived doped carbon materials.     

Impact of Polystyrene Oligomer Side Chains on Naphthalene Diimide–Bithiophene Polymers as n‐Type Semiconductors for Organic Field‐Effect Transistors

A series of naphthalene diimide‐based conjugated polymers are prepared with various molar percentage of low molecular weight polystyrene (PS) oligomer of narrow polydispersity as the side chain. The PS side chains are incorporated through preparation of a macromonomer by chain termination of living anionic polymerization. The effects of the PS side chains amount (0–20 mol%) versus overall sidechain on the electrical properties of the resulting polymers as n‐type polymer semiconductors in field‐effect transistors are investigated. We observe that all the studied polymers show similarly high electron mobility (≈0.2 cm² V^?1 s^?1). Importantly, the polymers with high PS side chain content (20 mol%) show a significantly improved device stability under ambient conditions, when compared to the polymers at lower PS content (0–10 mol%). By comparing this observation to the physical blending of the conjugated polymer with PS, we attribute the improved stability to the covalently attached PS side chains potentially serving as a molecular encapsulating layer around the conjugated polymer backbone, rendering it less susceptible to electron traps such as oxygen and water molecules.     

π‐Conjugation Enables Ultra‐High Rate Capabilities and Cycling Stabilities in Phenothiazine Copolymers as Cathode‐Active Battery Materials

In recent years, organic battery cathode materials have emerged as an attractive alternative to metal oxide–based cathodes. Organic redox polymers that can be reversibly oxidized are particularly promising. A drawback, however, often is their limited cycling stability and rate performance in a high voltage range of more than 3.4 V versus Li/Li⁺. Herein, a conjugated copolymer design with phenothiazine as a redox‐active group and a bithiophene co‐monomer is presented, enabling ultra‐high rate capability and cycling stability. After 30 000 cycles at a 100C rate, >97% of the initial capacity is retained. The composite electrodes feature defined discharge potentials at 3.6 V versus Li/Li⁺ due to the presence of separated phenothiazine redox centers. The semiconducting nature of the polymer allows for fast charge transport in the composite electrode at a high mass loading of 60 wt%. A comparison with three structurally related polymers demonstrates that changing the size, amount, or nature of the side groups leads to a reduced cell performance. This conjugated copolymer design can be used in the development of advanced redox polymers for batteries.     

Conductive polypyrrole–bacterial cellulose nanocomposite membranes as flexible supercapacitor electrode

Conductive nanocomposite membranes of polypyrrole/bacterial cellulose (PPy/BC) were fabricated in situ by oxidative polymerization of pyrrole with iron (III) chloride as an oxidant and BC as a template. The morphology of the PPy/BC membrane indicated that PPy nanoparticles deposited on the BC surface connected to form a continuous nanosheath structure by taking along the BC nanofiber. The flexible PPy/BC membrane obtained with the optimized reaction condition exhibited a high electrical conductivity of 3.9 S cm⁻¹, which was hardly affected by bending stress. The PPy/BC membrane could be directly used as flexible supercapacitor electrodes, with a maximum discharge capacity of 101.9 mA h g⁻¹ (459.5 F g⁻¹) at 0.16 A g⁻¹ current density. The capacity decreased with charge/discharge cycling, which is attributed to mechanical degradation of PPy as evidenced by scanning electron microscopy (SEM).     

Doping of Conjugated Polythiophenes with Alkyl Silanes

A strong modification of the electronic properties of solution‐processable conjugated polythiophenes by self‐assembled silane molecules is reported. Upon bulk doping with hydrolized fluoroalkyl trichlorosilane, the electrical conductivity of ultrathin polythiophene films increases by up to six orders of magnitude, reaching record values for polythiophenes: (1.1 ± 0.1) × 10³ S cm^?1 for poly(2,5‐bis(3‐tetradecylthiophen ‐2‐yl)thieno[3,2‐b]thiophene) (PBTTT) and 50 ± 20 S cm^?1 for poly(3‐hexyl)thiophene (P3HT). Interband optical absorption of the polymers in the doped state is drastically reduced, making these highly conductive films transparent in the visible range. The dopants within the porous polymer matrix are partially crosslinked via a silane self‐polymerization mechanism that makes the samples very stable in vacuum and nonpolar environments. The mechanism of SAM‐induced conductivity is believed to be based on protonic doping by the free silanol groups available within the partially crosslinked SAM network incorporated in the polythiophene structure. The SAM‐doped polythiophenes exhibit an intrinsic sensing effect: a drastic and reversible change in conductivity in response to ambient polar molecules, which is believed to be due to the interaction of the silanol groups with polar analytes. The reported electronic effects point to a new attractive route for doping conjugated polymers with potential applications in transparent conductors and molecular sensors.     

ε‐Branched Flexible Side Chain Substituted Diketopyrrolopyrrole‐Containing Polymers Designed for High Hole and Electron Mobilities

Based on the integrated consideration and engineering of both conjugated backbones and flexible side chains, solution‐processable polymeric semiconductors consisting of a diketopyrrolopyrrole (DPP) backbone and a finely modulated branching side chain (ε‐branched chain) are reported. The subtle change in the branching point from the backbone alters the π?π stacking and the lamellar distances between polymer backbones, which has a significant influence on the charge‐transport properties and in turn the performances of field‐effect transistors (FETs). In addition to their excellent electron mobilities (up to 2.25 cm² V^?1 s^?1), ultra‐high hole mobilities (up to 12.25 cm² V^?1 s^?1) with an on/off ratio (I_on/I_off) of at least 10⁶ are achieved in the FETs fabricated using the polymers. The developed polymers exhibit extraordinarily high electrical performance with both hole and electron mobilities superior to that of unipolar amorphous silicon.     

Synergistic Effect of Multi-Walled Carbon Nanotubes and Ladder-Type Conjugated Polymers on the Performance of N-Type Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) have the potential to revolutionize the field of organic bioelectronics. To date, most of the reported OECTs include p-type (semi-)conducting polymers as the channel material, while n-type OECTs are yet at an early stage of development, with the best performing electron-transporting materials still suffering from low transconductance, low electron mobility, and slow response time. Here, the high electrical conductivity of multi-walled carbon nanotubes (MWCNTs) and the large volumetric capacitance of the ladder-type π-conjugated redox polymer poly(benzimidazobenzophenanthroline) (BBL) are leveraged to develop n-type OECTs with record-high performance. It is demonstrated that the use of MWCNTs enhances the electron mobility by more than one order of magnitude, yielding fast transistor transient response (down to 15 ms) and high μC* (electron mobility × volumetric capacitance) of about 1 F cm^?1 V^?1 s^?1. This enables the development of complementary inverters with a voltage gain of >16 and a large worst-case noise margin at a supply voltage of <0.6 V, while consuming less than 1 µW of power.     

Open‐Shell Donor–Acceptor Conjugated Polymers with High Electrical Conductivity

Conductive polymers largely derive their electronic functionality from chemical doping, processes by which redox and charge‐transfer reactions form mobile carriers. While decades of research have demonstrated fundamentally new technologies that merge the unique functionality of these materials with the chemical versatility of macromolecules, doping and the resultant material properties are not ideal for many applications. Here, it is demonstrated that open‐shell conjugated polymers comprised of alternating cyclopentadithiophene and thiadiazoloquinoxaline units can achieve high electrical conductivities in their native “undoped” form. Spectroscopic, electrochemical, electron paramagnetic resonance, and magnetic susceptibility measurements demonstrate that this donor–acceptor architecture promotes very narrow bandgaps, strong electronic correlations, high‐spin ground states, and long‐range π‐delocalization. A comparative study of structural variants and processing methodologies demonstrates that the conductivity can be tuned up to 8.18 S cm^?1. This exceeds other neutral narrow bandgap conjugated polymers, many doped polymers, radical conductors, and is comparable to commercial grades of poly(styrene‐sulfonate)‐doped poly(3,4‐ethylenedioxythiophene). X‐ray and morphological studies trace the high conductivity to rigid backbone conformations emanating from strong π‐interactions and long‐range ordered structures formed through self‐organization that lead to a network of delocalized open‐shell sites in electronic communication. The results offer a new platform for the transport of charge in molecular systems.     

The Effects of Crystallinity on Charge Transport and the Structure of Sequentially Processed F4TCNQ‐Doped Conjugated Polymer Films

The properties of molecularly doped films of conjugated polymers are explored as the crystallinity of the polymer is systematically varied. Solution sequential processing (SqP) was used to introduce 2,3,5,6‐tetrafluoro‐7,7,8,8‐tetracyanoquinodimethane (F₄TCNQ) into poly(3‐hexylthiophene‐2,5‐diyl) (P3HT) while preserving the pristine polymer's degree of crystallinity. X‐ray data suggest that F₄TCNQ anions reside primarily in the amorphous regions of the film as well as in the P3HT lamellae between the side chains, but do not π‐stack within the polymer crystallites. Optical spectroscopy shows that the polaron absorption redshifts with increasing polymer crystallinity and increases in cross section. Theoretical modeling suggests that the polaron spectrum is inhomogeneously broadened by the presence of the anions, which reside on average 6–8 Å from the polymer backbone. Electrical measurements show that the conductivity of P3HT films doped by F₄TCNQ via SqP can be improved by increasing the polymer crystallinity. AC magnetic field Hall measurements show that the increased conductivity results from improved mobility of the carriers with increasing crystallinity, reaching over 0.1 cm² V^?1 s^?1 in the most crystalline P3HT samples. Temperature‐dependent conductivity measurements show that polaron mobility in SqP‐doped P3HT is still dominated by hopping transport, but that more crystalline samples are on the edge of a transition to diffusive transport at room temperature.     

Fully Printed Organic Electrochemical Transistors from Green Solvents

To achieve the full potential of scalable and cost‐effective organic electronic devices, developments are being made in both academic and industry environments to move toward continuous solution‐processing techniques that make use of safe and environmentally benign “green” solvents. In this work, the first example of a transistor device that is fully solution processed using only green solvents is demonstrated. This achievement is enabled through a novel multistage cleavable side chain process that provides aqueous solubility for semiconducting conjugated polymers, paired with aqueous inkjet printing of PEDOT:PSS electrodes, and a solution deposited ion gel electrolyte as the dielectric layer. The resulting organic electrochemical transistor devices operate in accumulation mode and reach maximum transconductance values of 1.1 mS at a gate voltage of ? 1 V. Normalizing the transconductance value to the channel dimensions yields g_m/W = 2200 S m^?1 (µC* = 22 F cm^?1 V^?1 s^?1), making these devices suitable for a range of applications requiring small signal amplification such as transistors, biosensors, and ion pumps. This new material design and device process paves the way toward scalable, safe, and efficient production of organic electronic devices.     

Toward High-Performance Dihydrophenazine-Based Conjugated Microporous Polymer Cathodes for Dual-Ion Batteries through Donor–Acceptor Structural Design

Recent studies have demonstrated that dihydrophenazine (Pz) with high redox-reversibility and high theoretical capacity is an attractive building block to construct p-type polymer cathodes for dual-ion batteries. However, most reported Pz-based polymer cathodes to date still suffer from low redox activity, slow kinetics, and short cycling life. Herein, a donor–acceptor (D–A) Pz-based conjugated microporous polymer (TzPz) cathode is constructed by integrating the electron-donating Pz unit and the electron-withdrawing 2,4,6-triphenyl-1,3,5-triazine (Tz) unit into a polymer chain. The D–A type structure enhances the polymer conjugation degree and decreases the band gap of TzPz, facilitating electron transportation along the polymer skeletons. Therefore the TzPz cathode for dual-ion battery shows a high reversible capacity of 192 mAh g⁻¹ at 0.2 A g⁻¹ with excellent rate performance (108 mAh g⁻¹ at 30 A g⁻¹), which is much higher than that of its counterpart polymer BzPz produced from 1,3,5-triphenylbenzene (Bz) and Pz (148 and 44 mAh g⁻¹ at 0.2 and 10 A g⁻¹, respectively). More importantly, the TzPz cathode also shows a long and stable cyclability of more than 10 000 cycles. These results demonstrate that the D–A structural design is an efficient strategy for developing high-performance polymer cathodes for dual-ion batteries.     

Effect of Alkyl Chain Branching Point on 3D Crystallinity in High N‐Type Mobility Indolonaphthyridine Polymers

Herein, this study investigates the impact of branching‐point‐extended alkyl chains on the charge transport properties of three ultrahigh n‐type mobility conjugated polymers. Using grazing incidence wide‐angle X‐ray scattering, analysis of the crystallinity of the series shows that while π–π interactions are increased for all three polymers as expected, the impact of the side‐chain engineering on polymer backbone crystallinity is unique to each polymer and correlates to the observed changes in charge transport. With the three polymers exhibiting n‐type mobilities between 0.63 and 1.04 cm² V^?1 s^?1, these results ratify that the indolonaphthyridine building block has an unprecedented intrinsic ability to furnish high‐performance n‐type organic semiconductors.