Rigid Polymer Backbone Research Articles

Neural Network Inspired Binder Enables Fast Li-Ion Transport and High Stress Adaptation for Si Anode.

Extensive investigations have proven the effectiveness of elastic binders in settling the challenge of structural damage posed by volume expansion of high-capacity anode used in nanoscale silicon. However, the sluggish ionic conductivity of polymer binder severely restricts the electrode reactions, making it unsuitable for practical applications. Inspired by the biological tissues with rapid neurotransmission and robust muscles, we propose a biomimetic binder that contains ionic conductive polymer (by polymerization reaction of poly(ethylene glycol) diglycidyl ether and polyethylenimine) and rigid polymer backbone (polyacrylic acid), which can effectively mitigate both Li-ion transport resistance and lithiation stress to stabilize the silicon nanoparticles during cycles. Consequently, the silicon anode with biomimetic binder achieves a rate capability of 1897 mAh g-1 at 8.0 A g-1 and capacity retention of 87% after 150 cycles under areal capacity upon 3.0 mAh cm-2. These results demonstrate the possibility of decoupling ionic conductivity from mechanical properties toward practical high-capacity anodes for energy-dense batteries.

A high performance, stable anion exchange membrane for alkaline redox flow batteries

The development of cost-effective, safe, and low-corrosion alkaline aqueous redox flow batteries, such as alkaline zinc-iron flow batteries, has motivated the research of hydrocarbon-based anion exchange membranes. These membranes, characterized by their positively charged functional groups, facilitate the transport of hydroxide anions (OH−) in alkaline environments, rendering them as potential alternatives to conventional proton exchange membranes in emerging alkaline redox flow batteries. Herein, a facilely synthesized anion exchange membrane (AEM) with superior chemical stability in alkaline media and outstanding ion conductivity has been developed for use in an alkaline redox flow battery. The membrane consists of a partially imidazolium substituted poly (vinylbenzyl chloride) polymer matrix and low molecular weight polyethylene glycol (PEG) additive. The membrane provides positively charged polymer backbone with hydroxide anion as counter ions. The additive PEG not only augments membrane flexibility through interaction with the rigid polymer backbone, but also enhances the conductivity through conducting ions by the alkalized-ether functionality. The optimized anion exchange membrane demonstrates better ionic conductivity of 58.2 mS cm−1 and comparable permeability compared with commercially Nafion117 membrane, enabling promoted energy efficiency (83.5 %), coulombic efficiency (99.85 %) and excellent stability (280 cycles with negligible capacity degradation) of a zinc-iron flow battery at 80 mA cm−2.

Microphase separation structures facilitated by dipole molecules and hydrogen bonding in poly (biphenyl piperidine-isatin) anion exchange membranes

The anion exchange membranes (AEMs) have the important function of blocking fuel and conducting OH− to make the cell form a circuit, so its alkali stability directly affects the performance of alkaline fuel cells. Currently, AEMs face a “trade-off” between ionic conductivity and stability. In order to solve this problem, we optimize the alkali resistance and conductivity of AEMs by introducing dipole-interacting side chains and hydrophilic hydroxyl side chains acting simultaneously on a rigid polymer backbone. By adopting the design strategy of “1 + 1>2″, the ion channel efficiency also makes a high-speed leap from a “two-wheeled bicycle” to a “four-wheeled car”. This effective microscopic modulation is clearly demonstrated by transmission electron microscope (TEM), where the AEMs after molecular design carry out a more obvious microphase separation structure at 200 nm. Through the PBP-54-IS- [OPD-100-OH-0] membrane, the maximum ionic conductivity is 100.62 mS cm−1 at 80 °C. After 1000 h at 80 °C, the retention rate of OH− conductivity of all AEMs was over 88.24 %. We also test its fuel cell performance for analysis. When the temperature of the two poles is 75 °C/72 °C, the power density is 147.28 mW cm−2. These are in line with the inherent requirements of AEMs for fuel cell applications.

Synthesis, characterization, and photophysical properties of dicyanoarylamine‐based semi‐aromatic polymers

AbstractIntroductionFluorescent high‐performance polymers have been extensively used in designing optoelectronic devices due to their low cost, excellent thermal stability, high mechanical strength, low flammability, good chemical and radiation resistance, and good electronic properties. While conventional organic luminophores fluoresce strongly in dilute solutions, they suffer from undesirable aggregation‐caused quenching in concentrated solutions and in the solid state due to extensive π‐π stacking interactions and formation of delocalized excitons or excimers. This phenomenon leads to non‐radiative decay thus, decreased fluorescence emission of the material in the solid film state, which significantly limits their real‐world application as solid light‐emitting materials.ObjectivesTo develop new high‐performance polymers with high photo luminescent efficiency, good processability, film‐forming properties, which could potentially be used in the fabrication of optoelectronic devices.MethodsThe preparation of the polyimide DiCN‐PI was carried out by a one‐step, high‐temperature solution imidization method. In this procedure, 1,2,4,5‐cyclohexanetetracarboxylic dianhydride and the diamine were polymerized in 1‐methyl‐2‐pyrrolidinone and γ‐butyrolactone co‐solvent at 180°C for 15 hours in the presence of isoquinoline as catalyst. On the other hand, polyamide DiCN‐PA was synthesized according to the direct phosphorylation polycondensation technique described by Yamazaki from diamine and trans‐1,4‐cyclohexanedicarboxylic acid using triphenyl phosphite and pyridine as condensing agents.Results and DiscussionBoth polymers were soluble in several polar aprotic solvents and exhibited useful levels of thermal stability. The polymers were emissive with PL emission bands around 555 (bluish‐green) and 498 (cyan) nm in dilute 1‐methyl‐2‐pyrrolidinone solutions for polyimide and polyamide, respectively. In the solid film state, the polymers emit light green and yellow colors, which simulate the PL behavior of their aggregated states, thereby demonstrating aggregation‐induced fluorescence changes.ConclusionsThese results indicate that the incorporation of bulky dicyanoarylamine moiety and alicyclic monomer units into the rigid polymer backbones effectively disrupted the planarity of the chain packing which resulted to the fluorescent high‐performance polymers with desired properties for potential optoelectronic applications.

Highly conductive and dimensionally stable anion exchange membranes enabled by rigid poly(arylene alkylene) backbones

Dimensionally and chemically stable anion exchange membranes with excellent ion conductivity are highly desired in electrochemical energy conversion technologies. Herein, we present a design using rigid arylene units, i.e., p-tetraphenylene and p-terphenylene, to suppress the water sorption of quaternized poly(arylene alkylene) membranes with high ion contents. Of note, side chain double-quaternary ammonium (QA) functionalized poly(q-tetraphenylene-co-p-terphenylene alkylene) membrane P(4PA-co-3PA)-D100 with the IEC value as high as 2.93 mmol g−1 showed very limited water uptake and swelling at 80 °C of 75 wt% and 14 %, respectively. Meanwhile, the immiscibility of hydrophilic double-cation side chain and the hydrophobic poly(arylene alkylene) backbone drives the formation of phase-separated morphology. As a result, P(4PA-co-3PA)-D100 showed an exceptional conductivity of 227.8 mS cm−1 at 80 °C with activation energy of 10.5 kJ mol−1. Despite the rigid poly(arylene alkylene) backbone with highly chemical durability and oxidative stability, the tandem tethered double cation in the side chain showed a 11 % QA moiety loss after a 1000-h treatment in 2 M NaOH at 80 °C. Moreover, a good peak power density of 550 mW cm−2 at the current density of 1.06 A cm−2 was achieved for P(4PA-co-3PA)-D100 with the gases flow of 200 mL min−1. This work demonstrates that, in addition to the approach of cross-linking, the highly conductive AEMs with excellent dimensional stability can be achieved by improving the rigidity of polymer backbones.

Structure–Function Relationships in Membrane-Based Hydrocarbon Separations Using N-Aryl-Linked Spirocyclic Polymers

The separation of crude oil into its many components by distillation is an energy-intensive process. Membrane-based separations that avoid the use of heat can significantly reduce these energy requirements but are not yet able to obtain sufficiently high levels of molecular discrimination. While we have recently demonstrated initial success in the ability of membranes to fractionate crude oil, a better understanding of the relationship of polymer structure to membrane function will be necessary to design the library of membranes necessary to reduce the energy intensity of separation systems. In this work, we explored structural changes to a polymer, SBAD-1, that has shown exemplary membrane performance. The results suggest that, while aromatic interactions between solute and polymer impart favorable separation properties, polymer backbone rigidity has a much greater effect on membrane performance in organic solvent reverse osmosis separations, and an intermediate degree of rigidity is likely to be optimal.

An Amorphous n‐Type Conjugated Polymer with an Ultra‐Rigid Planar Backbone

AbstractHigh charge carrier mobility polymer semiconductors are always semi‐crystalline. Amorphous conjugated polymers represent another kind of polymer semiconductors with different charge transporting mechanism. Here we report the first near‐amorphous n‐type conjugated polymer with decent electron mobility, which features a remarkably rigid, straight and planar polymer backbone. The molecular design strategy is to copolymerize two fused‐ring building blocks which are both electron‐accepting, centrosymmetrical and planar. The polymer is the alternating copolymer of double B←N bridged bipyridine (BNBP) unit and benzobisthiazole (BBTz) unit. It shows a decent electron mobility of 0.34 cm2 V−1 s−1 in organic field‐effect transistors. The excellent electron transporting property of the polymer is possibly due to the ultrahigh backbone stiffness, small π‐π stacking distance, and high molecular weight.

An Amorphous n-Type Conjugated Polymer with an Ultra-Rigid Planar Backbone.

High charge carrier mobility polymer semiconductors are always semi-crystalline. Amorphous conjugated polymers represent another kind of polymer semiconductors with different charge transporting mechanism. Here we report the first near-amorphous n-type conjugated polymer with decent electron mobility, which features a remarkably rigid, straight and planar polymer backbone. The molecular design strategy is to copolymerize two fused-ring building blocks which are both electron-accepting, centrosymmetrical and planar. The polymer is the alternating copolymer of double B←N bridged bipyridine (BNBP) unit and benzobisthiazole (BBTz) unit. It shows a decent electron mobility of 0.34 cm2 V-1 s-1 in organic field-effect transistors. The excellent electron transporting property of the polymer is possibly due to the ultrahigh backbone stiffness, small π-π stacking distance, and high molecular weight.

Dual-Dynamic Chemistries-Based Fast-Reprocessing and High-Performance Covalent Adaptable Networks.

Covalent adaptable networks (CANs) possess multiple functions including reprocessing (or recyclability), self-healing, welding, shape shifting, 3D printing, etc., due to the network rearrangement from dynamic bonds, and favorable performance from their cross-linked feature, and they are supposed to be as sustainable alternatives to thermosets. However, the thermal and mechanical properties, and stability of CANs are often sacrificed for rapid network rearrangement. In this paper, fast-reprocessing CANs with high performance are facilely constructed by in situ polymerization and dynamic cross-linking of styrene (St), maleic anhydride (MA), and acetal diol (BHAD). The rigid and hydrophobic polymer backbone endow the materials with high glass transition temperatures, mechanical performance, and water resistance. Besides, carboxylic group-catalyzed dual dynamic ester and acetal-based networks exhibit faster stress relaxation and realize extrusion reprocessing. This work provides an ingenious and simple strategy of construction of CANs combining rapid network rearrangement and excellent comprehensive performance, which is beneficial for the application of CANs.

Alkaline anion exchange membrane containing pyrene-based π-π stacking interactions

Highly conductive and chemically resistant alkaline anion exchange membranes (AAEMs) are highly desirable in various electrochemical devices such as alkaline anion exchange membrane fuel cells (AAEMFCs) and water electrolysis. Here we present the novel AAEMs with pyrene-containing ether-free polymer backbones bearing piperidinium cations. Both morphology analyses and simulations verify that the π-π stacking of pyrene units in polymer backbones can actuate the neighboring piperidinium cations to aggregate and form ion conducting channels, thus enhancing the ion conductivity of AAEMs (153 mS cm−1 at 90 °C). Additionally, the resultant aryl ether-free poly(aryl piperidinium) structure guarantees the chemical durability of the AAEMs, which has 91.5% OH− conductivity retention after treatment in 2 M NaOH at 80 °C for1080 h. Meanwhile, the rigid pyrene units increase the rigidity of polymer backbones, resulting in excellent mechanical strength (46.3 MPa) and dimensional stability (swelling ratio of 11.8% at 90 °C). The molecular design provides an attractive strategy for advancing the development of high-performance AAEMs.

Mechanically robust and highly conductive semi-interpenetrating network anion exchange membranes for fuel cell applications

A series of highly transparent semi-interpenetrating polymer network anion exchange membranes (SIPN AEMs) composed of a flexible and cation cross-linked polystyrene-b-poly(ethylene-co-butylene)-b-polystyrene (cQSEBS) component, and a rigid, highly-charged quaternized poly(2,6-dimethyl phenylene oxide) (QPPO) component are prepared. Flexible and rigid polymer backbones endow SIPN AEMs with excellent flexibility and mechanical strength. High charge content and well defined hydrophilic/hydrophobic phase separation patterns ensure SIPN AEMs with improved ionic conductivity. Alkali-resistant SEBS, enhanced dimensional stability and ordered microphase separation morphology contribute to the good chemical stability of SIPN-AEMs. Among these AEMs, SIPN-cQSEBS/QPPO-10 with an IEC of 1.93 mmol g−1 achieves a better trade-off between tensile strength (19.36 MPa at 25 °C in wet state), flexibility (58.43% at 25 °C in wet state) and OH− conductivity (103.1 mS cm−1 at 80 °C). Besides, SIPN-cQSEBS/QPPO-10 shows low swelling degree (15.4% at 80 °C) and high chemical stability (95.9%, 88.7%, 82.7% and 88.5% retention in weight, OH− conductivity, tensile strength and elongation at break, respectively, after immersing in 1 M NaOH at 80 °C for 30 days). Importantly, a fuel cell peak power density of 1.174 W cm−2 is obtained at 80 °C by using SIPN-cQSEBS/QPPO-10 as the separator.

Effects of polysaccharides' molecular structure on membrane fouling and the related mechanisms.

Fouling behaviors of polysaccharides vary with their structure, while the mechanisms underlying this phenomenon remain unexplored. This work was carried out to explore the thermodynamic fouling mechanisms of polysaccharides with different structure. Carrageenan and xanthan gum were selected as the model polysaccharides with structure of straight and branch chains, respectively. Batch filtration experiments showed that xanthan gum solution corresponded to a more rapid flux decline trend, and specific filtration resistance (SFR) of xanthan gum (2.32 × 1015 m-1 kg-1) was over 10 times than that of carrageenan (2.21 × 1014 m-1 kg-1). It was found that, xanthan gum possessed a more disordered structure and a rather higher viscosity (15.03 mPa·s V.S. 1.98 mPa·s for carrageenan). Calculation of extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory showed higher adhesion energy of xanthan gum (-42.82 my m-2 V.S. -23.26 mJ m-2 for carrageenan). Scanning electron microscopy (SEM) analyses showed that xanthan gum gel layer had a more homogenous structure and rigid polymer backbone, indicating better mixing with water to form a gel. As verified by heating experiments, such a structure tended to contain more bound water. According to this information, Flory-Huggins lattice theory was introduced to build a bridge between polymeric structure and SFR. It was revealed that branch structure corresponded to higher chemical potential change during gel layer formation, and higher ability to carry bound water, resulting in higher filtration resistance during filtration process. This work revealed the fundamental thermodynamic mechanism of membrane fouling caused by polysaccharides with different structure, deepening understanding of membrane fouling.

Linker Unit Modulation of Polymer Acceptors Enables Highly Efficient Air-Processed All-Polymer Solar Cells.

A group of regioregular polymer acceptors is synthesized by polymerizing Y6 moieties with different linker units including thiophene, vinylene, 2,2’‐bithiophene, and thieno[3,2‐b]thiophene, and their optoelectrical properties and photovoltaic performances are studied systematically. It is found that the linker units have significant impacts on the backbone planarity, conjugation, and hence optoelectrical properties of polymer acceptors. The vinylene‐based PYF‐V‐o polymer shows a smaller dihedral angle between the end groups and vinylene units and a more rigid polymer backbone, thus affording bathochromic absorption and better electron‐transporting capacity. As a result, the PM6:PYF‐V‐o based all‐polymer solar cells (all‐PSCs) are able to achieve the highest power conversion efficiency of 16.4% with an unprecedented small voltage loss of 0.49 V. Moreover, the PM6:PYF‐V‐o blend exhibits good resistance to environmental stressors and the air‐processed PM6:PYF‐V‐o cells can still maintain a high efficiency of 16.1%, which is the best air‐processed all‐PSC efficiency reported to date. This study provides the structural‐property guidance that can be used to facilitate the development of polymer acceptors for all‐PSCs.

Subnanometer Ion Channel Anion Exchange Membranes Having a Rigid Benzimidazole Structure for Selective Anion Separation.

Ion-conductive polymers having a well-defined phase-separated structure show the potential application of separating mono- and bivalent ion separation. In this work, three side-chain-type poly(arylene ether sulfone)-based anion exchange membranes (AEMs) have been fabricated to investigate the effect of the stiffness of the polymer backbone within AEMs on the Cl-/NO3- and Cl-/SO42- separation performance. Our investigations via small-angle X-ray scattering (SAXS), positron annihilation, and differential scanning calorimetry (DSC) demonstrate that the as-prepared AEM with a rigid benzimidazole structure in the backbone bears subnanometer ion channels resulting from the arrangement of the rigid polymer backbone. In particular, SAXS results demonstrate that the rigid benzimidazole-containing AEM in the wet state has an ion cluster size of 0.548 nm, which is smaller than that of an AEM with alkyl segments in the backbone (0.760 nm). Thus, in the electrodialysis (ED) process, the former exhibits a superior capacity of separating Cl-/SO42- ions relative to latter. Nevertheless, the benzimidazole-containing AEM shows an inability to separate the Cl-/NO3- ions, which is possibly due to the similar ion size of the two. The higher rotational energy barrier (4.3 × 10-3 Hartree) of benzimidazole units and the smaller polymer matrix free-volume (0.636%) in the AEM significantly contribute to the construction of smaller ion channels. As a result, it is believed that the rigid benzimidazole structure of this kind is a benefit to the construction of stable subnanometer ion channels in the AEM that can selectively separate ions with different sizes.

Dielectric Properties of Fluorinated Aromatic Polyimide Films with Rigid Polymer Backbones.

Fluorinated aromatic polyimide (FAPI) films with rigid polymer backbones have been prepared by chemical imidization approach. The polyimide films exhibited excellent mechanical properties including elastic modulus of up to 8.4 GPa and tensile strength of up to 326.7 MPa, and outstanding thermal stability including glass transition temperature (Tg) of 346.3–351.6 °C and thermal decomposition temperature in air (Td5) of 544.1–612.3 °C, as well as high colorless transmittance of >81.2% at 500 nm. Moreover, the polyimide films showed stable dielectric constant and low dielectric loss at 10–60 GHz, attributed to the close packing of rigid polymer backbones that limited the deflection of the dipole in the electric field. Molecular dynamics simulation was also established to describe the relationship of molecular structure and dielectric loss.

Gas transport properties of truxene-based network polyimide membrane with flexible hexyl side chains

Crosslinking is a viable way to construct the network polymers which possesses the merits of high rigidity, excellent plasticization resistances, and good thermal stability using in the area of gas separation. However, dependence on crosslinking method often leads to contracted pores among polymer chains and in turn, sacrifices gas permeability seriously. In this work, a novel truxene triamine monomer with flexible hexyl side chains (termed as HTUTA) was designed, synthesized, and subsequently reacted with three different dianhydrides ODPA, BTDA, and 6FDA though polycondensation to obtain a series of network polyimides (PIs) membranes. Among these three designed truxene-based network PIs, HTUTA-6FDA had the best overall gas separation performance rooting from its bulky –C(CF3)2- moieties within the polymer framework. Compared with our previous reported TAPA-6FDA and TAPB-6FDA, the overall gas transport properties of the newly designed truxene-based network PIs are enhanced obviously because of incorporating the bulky and flexible side chains as well as enhancing the polymer backbone rigidity via using the truxene structure as the building block. For instance, the gas permeability of designed HTUTA-6FDA for CO2 and O2 were, respectively, enhanced 261% and 253% in comparison with these of TAPB-6FDA. In addition, benefiting from the flexible hexyl side chains, the partial chain segment motion was increased and accordingly the inter- and intra-chain interactions were minimized. Thus, a broad operating flexibility without the risk of gelation could be achieved during the tridimensional polycondensation process, which is extremely significant to their practical production. We hope this study can open a new insight into the rational design of the network PI membranes with enhanced gas permeability as well as no risk of gelation trend before film-forming.

Ionic Liquid/Sulfonated Polyimide Composite Membranes: Effect of Polyimide Sequence on CO2 Transport Properties

The carbon dioxide capture and storage (CCS) plays an important role in reducing greenhouse gases, but its high energy cost is a critical issue. The CO2 separation is recognized as a key process for reducing cost, and a membrane separation method is one of the promising candidates with a low energy cost. Ion gels comprising polymer networks and ionic liquids (IL), which exhibit unique properties such as non-volatility and CO2 absorption selectivity, have attracted attention as environmentally friendly separation membranes. Previous work in our group has shown that sulfonated polyimide (SPI) with an imidazolium cation exhibits good compatibility with an IL. SPI can hold high content of IL (~75 wt%) and form a uniform, flexible, tough (~10 MPa of Young’s modulus) and thin composite membrane.[1-3] This SPI was synthesized by random copolymerization of a sulfonated ionic monomer and a non-ionic monomer. The composite membranes separated into bicontinuous two phases of ionic and non-ionic domains, which contribute to the formation of gas diffusion path and mechanically tough network, respectively. By using multiblock copolymers of SPI, it is expected that the size and connectivity of each domain are improved, which could lead to the increase of the CO2 permeability and mechanical toughness of the membrane. In this study, we fabricated an 1-buty-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C4mim][NTf2])/SPI composite membranes composed of multiblock-type SPI (mb-SPI) and compared their property with those of random-type SPI (r-SPI).75 wt%[C4mim][NTf2]/mb-SPI composite membranes exhibited higher CO2 permeability (372 barrer) than the corresponding r-SPI (235 barrer) while the gas selectivity (CO2/N2) is 26, which is of the same magnitude as that of r-SPI (CO2/N2 is 28). The mb-SPI can hold higher IL content up to 80 wt% than r-SPI, resulting in higher CO2 permeability (480 barrer; CO2/N2 is 27). The higher ionic conductivity also suggested the higher connectivity of ionic domains in mb-SPI system. On the other hand, from tensile tests, it was found that the mb-SPI membrane was less ductile than the r-SPI membrane. The result of dynamic mechanical analysis (DMA) indicates that the difference of internal structure between the membranes composed of mb-SPI and r-SPI is one of the reasons of the poor mechanical property.To fabricate more strong membrane, we used SPI with more rigid polymer backbone. Rigid mb-SPI exhibits high CO2 permeability (450 barrer) and gas selectivity (CO2/N2 is 24), comparable with the conventional one, and the mechanical property was superior to the conventional one. From these results, we concluded that the mb-SPI membrane having high CO2 permeability and toughness was successfully fabricated.

Structure-property relationship of low dielectric constant polyimide fibers containing fluorine groups

A series of copolyimide (co-PI) fibers with low dielectric constants and excellent comprehensive properties have been successfully prepared via a two-step wet-spinning method by incorporating 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) into rigid polymer backbones of 3,3′,4,4′-biphenyltetracarboxylic dianhydride (BPDA)/p-phenylenediamine (p-PDA). The dielectric constant of PI fibers were substantially reduced from 3.0 to 2.48 at the frequency of 10 GHz after the introduction of trifluoromethyl (-CF3) groups. Meanwhile, the prepared PI fibers exhibited high thermal stability as well as excellent mechanical properties. The co-PI fibers possessed the optimum tensile strength of 1.4 GPa and modulus of 83.3 GPa at the p-PDA/TFMB molar ratio of 7/3. The 5% weight loss temperature in nitrogen ranged from 523 to 558 °C, and the glass transition temperature decreased from 372 °C to 295 °C with increasing TFMB contents. Both experimental and molecular simulations method were adopted to discuss the influence of fluorine group on the aggregation structure and properties of PI fibers, suggesting that the improved free volume were the crucial factor responsible for low dielectric constant. The molecular ordered degree and orientation degree of co-PI fibers decreased firstly and further increased with increasing TMFB content, which is due to the combined effects of large free volume of trifluoromethyl and polymer regularity variation caused by copolymerization.

Microporous Binder for the Silicon-Based Lithium-Ion Battery Anode with Exceptional Rate Capability and Improved Cyclic Performance.

Silicon anodes have attracted much attention owing to their high theoretical capacity. Nonetheless, an inevitable and enormous volumetric expansion of silicon in the lithiated state restrained the development of the silicon anode for lithium-ion batteries. Fortunately, the utilization of the high-performance binder is a promising and effective way to overcome such obstacles. Herein, a polymer of intrinsic microporosity (PIM) is applied as the binder for the silicon anode, which is composed of a rigid polymer backbone, an intrinsic porous structure, and active carboxyl groups (PIM-COOH). Compared to the traditional binder, both the long-term stability and rate performance of the electrode using PIM-COOH as the binder are significantly improved. The mechanism responsible for the enhanced performance is investigated. The PIM-COOH binder provides stronger adhesion toward the current collector than the conventional binders. The unique rigid polymer backbone and porous structure of the PIM-COOH binder enable a good capability to withstand the volume change and external stress generated by the Si anode. The porous structure of the PIM-COOH binder enhances lithium-ion transportation compared to the SA binder, which improves rate performance of the silicon anode. This work provides a unique insight into design, synthesis, and utilization of the binders for lithium-ion batteries.

Synthesis and Properties of Soluble Fused Thiophene Diketopyrrolopyrrole-Based Polymers with Tunable Molecular Weight

It is challenging to realize both a fully conjugated rigid polymer backbone and high molecular weight at the same time. Previously, we reported a DPP-FT4 polymer with molecular weight up to 30 kDa. A new design and synthesis was required to overcome this limitation. Here, we report the successful synthesis of a conjugated semiconducting polymer with tunable molecular weight over a wide range. Through molecular design and synthesis control, our new polymer can be selectively prepared with number-averaged molecular weight (Mn) ranging from approximately 20 to 100 kDa, realizing both high molecular weight and high solubility at the same time. Four polymers within this range were investigated, with particular emphasis on Mn of 50 kDa (P2) and 97 kDa (P4). The relationships between molecular weight and polymer properties, molecular packing, and electrical behavior are explored in detail. All the polymers in this series are fully soluble in nonchlorinated solvents at room temperature, which is promising for lar...