Sulfonimide-Containing Triblock Copolymers for Improved Conductivity and Mechanical Performance

Sequencing polymers to enable solid-state lithium batteries

Rational designs of solid polymer electrolytes with high ion conduction are critical in enabling the creation of advanced lithium batteries. However, known polymer electrolytes have much lower ionic conductivity than liquid/ceramics at room temperature, which limits their practical use in batteries. Here we show that precise positioning of designed repeating units in alternating polymer sequences lays the foundation for homogenized Li+ distribution, non-aggregated Li+-anion solvation and sequence-assisted site-to-site ion migration, facilitating the tuning of Li+ conductivity by up to three orders of magnitude. The assembled all-solid-state batteries facilitate reversible and dendrite-mitigated cycling against Li metal from ambient to elevated temperatures. This work demonstrates a powerful molecular engineering means to access highly ion-conductive solid-state materials for next-generation energy devices.

Anion-tethered Single Lithium-ion Conducting Polyelectrolytes through UV-induced Free Radical Polymerization for Improved Morphological Stability of Lithium Metal Anodes

Single Li+ ion conducting polyelectrolytes (SICs), which feature covalently tethered counter-anions along their backbone, have the potential to mitigate dendrite formation by reducing concentration polarization and preventing salt depletion. However, due to their low ionic conductivity and complicated synthetic procedure, the successful validation of these claimed advantages in lithium metal (Li0 ) anode batteries remains limited. In this study, we fabricated a SIC electrolyte using a single-step UV polymerization approach. The resulting electrolyte exhibited a high Li+ transference number (t+ ) of 0.85 and demonstrated good Li+ conductivity (6.3×10-5  S/cm at room temperature), which is comparable to that of a benchmark dual ion conductor (DIC, 9.1×10-5  S/cm). Benefitting from the high transference number of SIC, it displayed a three-fold higher critical current density (2.4 mA/cm2 ) compared to DIC (0.8 mA/cm2 ) by successfully suppressing concentration polarization-induced short-circuiting. Additionally, the t+ significantly influenced the deposition behavior of Li0 , with SIC yielding a uniform, compact, and mosaic-like morphology, while the low t+ DIC resulted in a porous morphology with Li0 whiskers. Using the SIC electrolyte, Li0 ||LiFePO4 cells exhibited stable operation for 4500 cycles with 70.5 % capacity retention at 22 °C.

Mechanically Robust Poly(ionic liquid) Block Copolymers as Self-Assembling Gating Materials for Single-Walled Carbon-Nanotube-Based Thin-Film Transistors

The proliferation of high-performance thin-film electronics depends on the development of highly conductive solid-state polymeric materials. We report on the synthesis and properties investigation of well-defined cationic and anionic poly(ionic liquid) AB-C type block copolymers, where the AB block was formed by random copolymerization of highly conductive anionic or cationic monomers with poly(ethylene glycol) methyl ether methacrylate, while the C block was obtained by post-polymerization of 2-phenylethyl methacrylate. The resulting ionic block copolymers were found to self-assemble into a lamellar morphology, exhibiting high ionic conductivity (up to 3.6 × 10^-6 S cm^-1 at 25 °C) and sufficient electrochemical stability (up to 3.4 V vs Ag⁺/Ag at 25 °C) as well as enhanced viscoelastic (mechanical) performance (storage modulus up to 3.8 × 10⁵ Pa). The polymers were then tested as separators in two all-solid-state electrochemical devices: parallel plate metal-insulator-metal (MIM) capacitors and thin-film transistors (TFTs). The laboratory-scale truly solid-state MIM capacitors showed the start of electrical double-layer (EDL) formation at ∼10³ Hz and high areal capacitance (up to 17.2 μF cm^-2). For solid-state TFTs, low hysteresis was observed at 10 Hz due to the completion of EDL formation and the devices were found to have low threshold voltages of -0.3 and 1.1 V for p-type and n-type operations, respectively.

Effect of Polystyrene Synthesis Method on Water Sorption and Glass Transition

Commodity PS is synthesized via free radical polymerization, whereas PS in block copolymers (BCPs) is typically synthesized via living anionic polymerization. The purpose of this work is to investigate how the synthesis method impacts important properties such as water sorption and glass transition temperature (T_g). Water sorption is important because the performance of nanostructured polymer membranes in various applications is known to be affected by environmental conditions such as humidity. T_g is important because it dictates processing conditions, both for commodity PS as well as BCPs such as thermoplastic elastomers. Water sorption in commercial PS was found to be 0.5 mg_water/g_polymer at the highest humidities investigated (about 80%), in agreement with literature. On the other hand, syndiotactic PS synthesized anionically at low temperature absorbed more water, up to 1.5 mg_water/g_polymer, due to higher free volume. The greatest impact on water sorption was due to addition of hydrophilic hydroxyl chain ends to atactic PS, which resulted in water sorption of up to 2.3 mg_water/g_polymer. In addition to measuring water sorption and dry T_g separately, the impact of relative humidity on PS T_g was examined. Combined differential scanning calorimetry and dynamic mechanical analysis show that on going from the dry state to high humidity, the T_g of PS decreases by 5 °C. Moreover, the tensile storage modulus of PS decreases from 1.58 GPa at 0% RH to 0.53 GPa at 40% RH. In addition to the practical relevance of this study, this report fills a gap in experimental literature by using a poor solvent system, PS/water, to examine plasticization in the pure polymer limit.

Block copolymers as (single-ion conducting) lithium battery electrolytes

Solid-state batteries are considered the next big step towards the realization of intrinsically safer high-energy lithium batteries for the steadily increasing implementation of this technology in electronic devices and particularly, electric vehicles. However, so far only electrolytes based on poly(ethylene oxide) have been successfully commercialized despite their limited stability towards oxidation and low ionic conductivity at room temperature. Block copolymer (BCP) electrolytes are believed to provide significant advantages thanks to their tailorable properties. Thus, research activities in this field have been continuously expanding in recent years with great progress to enhance their performance and deepen the understanding towards the interplay between their chemistry, structure, electrochemical properties, and charge transport mechanism. Herein, we review this progress with a specific focus on the block-copolymer nanostructure and ionic conductivity, the latest works, as well as the early studies that are fr"equently overlooked by researchers newly entering this field. Moreover, we discuss the impact of adding a lithium salt in comparison to single-ion conducting BCP electrolytes along with the encouraging features of these materials and the remaining challenges that are yet to be solved.

Gyroid-Nanostructured All-Solid Polymer Films Combining High H+ Conductivity with Low H2 Permeability

Gyroid-nanostructured all-solid polymer films with exceedingly high proton conductivity and low H₂ gas permeability have been created via crosslinking polymerization of mixtures of a zwitterionic amphiphilic monomer and a polymerizable imide-type acid that co-organize into bicontinuous cubic liquid-crystalline phases. The gyroid nanostructures are visualized by reconstructing a 3D electron map from the synchrotron X-ray diffraction patterns. These films exhibit high proton conductivity of the order of 10^-1 S cm^-1 and extremely low H₂ gas permeability of the order of 10^-15 mol m m^-2 s^-1 Pa^-1 . These properties can be ascribed to the presence of the ionic liquid-like layer along the gyroid minimal surface. Since these two characteristics are required for improving the performance of proton-exchange membrane fuel cells, the present membrane design represents a promising strategy for the development of advanced devices, pertinent to establishing sustainable energy sources.

Sulfonyl Imide Acid-Functionalized Membranes via Ni (0) Catalyzed Carbon-Carbon Coupling Polymerization for Fuel Cells

Polymer membranes, having improved conductivity with enhanced thermal and chemical stability, are desirable for proton exchange membranes fuel cell application. Hence, poly(benzophenone)s membranes (SI-PBP) containing super gas-phase acidic sulfonyl imide groups have been prepared from 2,5-dichlorobenzophenone (DCBP) monomer by C-C coupling polymerization using Ni (0) catalyst. The entirely aromatic C-C coupled polymer backbones of the SI-PBP membranes provide exceptional dimensional stability with rational ion exchange capacity (IEC) from 1.85 to 2.30 mS/cm. The as-synthesized SI-PBP membranes provide enhanced proton conductivity (107.07 mS/cm) compared to Nafion 211® (104.5 mS/cm). The notable thermal and chemical stability of the SI-PBP membranes have been assessed by the thermogravimetric analysis (TGA) and Fenton's test, respectively. The well distinct surface morphology of the SI-PBP membranes has been confirmed by the atomic force microscopy (AFM). These results of SI-PBP membranes comply with all the requirements for fuel cell applications.

100th Anniversary of Macromolecular Science Viewpoint: Block Copolymers with Tethered Acid Groups: Challenges and Opportunities

Scientific research on advanced polymer electrolytes has led to the emergence of all-solid-state energy storage/transfer systems. Early research began with acid-tethered polymers half a century ago, and research interest has gradually shifted to high-precision polymers with controllable acid functional groups and nanoscale morphologies. Consequently, various self-assembled acid-tethered block polymer morphologies have been produced. Their ion properties are profoundly affected by the multiscale intermolecular interactions in confinements. The creation of hierarchically organized ion/dipole arrangements inside the block copolymer nanostructures has been highlighted as a future method for developing advanced single-ion polymers with decoupled ion dynamics and polymer chain relaxation. Several emerging practical applications of the acid-tethered block copolymers have been explored to draw attention to the challenges and opportunities in developing state-of-the-art electrochemical systems.

All-Solid-State Lithium-Organic Batteries Comprising Single-Ion Polymer Nanoparticle Electrolytes

Advances in lithium battery technologies necessitate improved energy densities, long cycle lives, fast charging, safe operation, and environmentally friendly components. This study concerns lithium-organic batteries comprising bioinspired poly(4-vinyl catechol) (P4VC) cathode materials and single-ion conducting polymer nanoparticle electrolytes. The controlled synthesis of P4VC results in a two-step redox reaction with voltage plateaus at around 3.1 and 3.5 V, as well as a high initial specific capacity of 352 mAh g^-1 . The use of single-ion nanoparticle electrolytes enables high electrochemical stabilities up to 5.5 V, a high lithium transference number of 0.99, high ionic conductivities, ranging from 0.2×10^-3 to 10^-3  S cm^-1 , and stable storage moduli of >10 MPa at 25-90 °C. Lithium cells can deliver 165 mAh g^-1 at 39.7 mA g^-1 for 100 cycles and stable specific capacities of >100 mAh g^-1 at a high current density of 794 mA g^-1 for 500 cycles. As the first successful demonstration of solid-state single-ion polymer electrolytes in environmentally benign and cost-effective lithium-organic batteries, this work establishes a future research avenue for advancing lithium battery technologies.

Tuning the Properties of a UV-Polymerized, Cross-Linked Solid Polymer Electrolyte for Lithium Batteries

Lithium metal anodes have been pursued for decades as a way to significantly increase the energy density of lithium-ion batteries. However, safety risks caused by flammable liquid electrolytes and short circuits due to lithium dendrite formation during cell cycling have so far prevented the use of lithium metal in commercial batteries. Solid polymer electrolytes (SPEs) offer a potential solution if their mechanical properties and ionic conductivity can be simultaneously engineered. Here, we introduce a family of SPEs that are scalable and easy to prepare with a photopolymerization process, synthesized from amphiphilic acrylic polymer conetworks based on poly(ethylene glycol), 2-hydroxy-ethylacrylate, norbornyl acrylate, and either lithium bis (trifluoromethanesulfonyl) imide (LiTFSI) or a single-ion polymethacrylate as lithium-ion source. Several conetworks were synthesized and cycled, and their ionic conductivity, mechanical properties, and lithium transference number were characterized. A single-ion-conducting polymer electrolyte shows the best compromise between the different properties and extends the calendar life of the cell.

Development of Hierarchically Porous Ionomer Membranes for Versatile and Fast Metal Ion Conduction

Innovative design concepts can play a key role in the realization of high-performance ionomer membranes that are capable of exclusive metal ion conduction and potentially applicable in electrochemical devices including sensors, fuel cells, and high-energy batteries. Herein, we report on the development of new ionomers, based on sulfonated poly(ether ether ketone) (SPEEK), engineered to conduct a variety of ions, namely, Li⁺, Na⁺, K⁺, Zn²⁺, and Mg²⁺, when soaked with nonaqueous solvents. Application of a facile phase-inversion method results in M-SPEEK (M = Li/Na/K/Zn/Mg) membranes with a hierarchical porous network, facilitating organic solvent infusion that is necessary to promote dissociation and rapid transport of cations between anionic sulfonate groups on the polymer chains. This strategy leads to membranes with alkali ion conductivities approaching 10^-4 S cm^-1 at room temperature, and near unity cation transference numbers (t _M⁺ ≥ 0.9). Furthermore, an exceptionally high Zn-ion conductivity of 10^-2 S cm^-1 is obtained for the water-infused Zn-SPEEK membrane. In comparison, the dense membranes demonstrate 2-3 orders of magnitude lower conductivities because of insufficient solvent infusion. Preliminary electrochemical studies with solvent-infused ionomer membranes as the electrolyte look promising.

Single lithium-ion conducting solid polymer electrolytes: advances and perspectives

Electrochemical energy storage is one of the main societal challenges to humankind in this century. The performances of classical Li-ion batteries (LIBs) with non-aqueous liquid electrolytes have made great advances in the past two decades, but the intrinsic instability of liquid electrolytes results in safety issues, and the energy density of the state-of-the-art LIBs cannot satisfy the practical requirement. Therefore, rechargeable lithium metal batteries (LMBs) have been intensively investigated considering the high theoretical capacity of lithium metal and its low negative potential. However, the progress in the field of non-aqueous liquid electrolytes for LMBs has been sluggish, with several seemingly insurmountable barriers, including dendritic Li growth and rapid capacity fading. Solid polymer electrolytes (SPEs) offer a perfect solution to these safety concerns and to the enhancement of energy density. Traditional SPEs are dual-ion conductors, in which both cations and anions are mobile and will cause a concentration polarization thus leading to poor performances of both LIBs and LMBs. Single lithium-ion (Li-ion) conducting solid polymer electrolytes (SLIC-SPEs), which have anions covalently bonded to the polymer, inorganic backbone, or immobilized by anion acceptors, are generally accepted to have advantages over conventional dual-ion conducting SPEs for application in LMBs. A high Li-ion transference number (LTN), the absence of the detrimental effect of anion polarization, and the low rate of Li dendrite growth are examples of benefits of SLIC-SPEs. To date, many types of SLIC-SPEs have been reported, including those based on organic polymers, organic-inorganic hybrid polymers and anion acceptors. In this review, a brief overview of synthetic strategies on how to realize SLIC-SPEs is given. The fundamental physical and electrochemical properties of SLIC-SPEs prepared by different methods are discussed in detail. In particular, special attention is paid to the SLIC-SPEs with high ionic conductivity and high LTN. Finally, perspectives on the main challenges and focus on the future research are also presented.

Structure design, fabrication and property investigation of water-based polyesters with notable surface hydrophilicity

Environmentally friendly waterborne polyesters (WPEs) were obtained by copolymerization of diethylene glycol (DEG), isophthalic acid (IPA) and 5-sulfoisophthalic acid monosodium salt (5-SSIPA).

Thiol-ene synthesis and characterization of lithium bis(malonato)borate single-ion conducting gel polymer electrolytes

The development of high capacity anodes and high voltage cathodes for advanced lithium-ion batteries motivates the search for new polymer electrolytes that exhibit superior electrochemical stabilities and high ionic conductivities. We report a convenient, three-step synthesis of lithium bis(non-8-enyl-malonato)borate (LiBNMB) as a α,ω-diene monomer, which undergoes thermally initiated thiol-ene crosslinking polymerizations in propylene carbonate to yield gel polymer electrolytes with high lithium ion concentrations (∼0.9 M). By conducting these crosslinking polymerizations using mixtures of di- and tri-thiols and LiBNMB with [thiol] : [ene] = 1 : 1, we synthesized a series of gel networks with dynamic elastic moduli ranging from G' = 40-79 kPa that increase monotonically with trifunctional crosslinker content. While ionic conductivities for these polymer gels measured by electrochemical impedance spectroscopy at 22 °C are σ = 0.82-2.5 × 10^-6 S cm^-1, we show that the conductivity of propylene carbonate-solvated lithium ions though the bulk of these gel electrolytes is 8.5 × 10^-5 S cm^-1 independent of crosslinker density. However, the conductivities of the gel interfaces depend sensitively on crosslinker content, suggesting the importance of segmental rearrangement dynamics at the electrode interface in limiting the rate of ion motion. Thus, the design of highly conductive polymer electrolytes for advanced batteries demands careful design of both the internal and interfacial properties of these new materials.

Poly(ionic liquid)-based polyurethanes having imidazolium, ammonium, morpholinium or pyrrolidinium cations

The synthesis of cationic polyelectrolytes based on condensation-derived backbone is rarely performed due to the difficulty obtaining of the respective ionic monomers in high purity. Despite such an approach is favorable as it results in ionic polymers with well-defined chemical structure and ionic group distribution. In this work two efficient methods are presented for the synthesis of ionic diols in high purity, namely the technique with pyranyl protection of OH-groups and the direct quaternization of tertiary amine alcohols. Applying these methods five novel ionic diols bearing various cations, namely, 1,1-bis(2-hydroxyethyl)pyrrolidin-1-ium bromide, 4,4-bis(2-hydroxyethyl)morpholin-4-ium bromide, N, N-bis(2-hydroxyethyl)-N-methylethanammonium, 1,1′-(pentane-1,5-diyl)bis(1-(2-hydroxyethyl)pyrrolidin-1-ium) dibromide, and 3-(2-hydroxyethyl)-1-(5-(3-(3-hydroxypropyl)-1H-imidazol-3-ium-1-yl)pentyl)-1H-imidazol-3-ium dibromide, were synthesized in high purity and high yields. The tin(II) mediated solution polycondensation of ionic diols with commercial hexamethylene diisocyanate or 4,4′-methylenebis(cyclohexyl isocyanate) resulted in a series of ionic, high molecular weight ( Mw = 2.3 × 104 −8.0 × 104) polyurethanes (PUs). The influence of various reaction parameters including reaction temperature and time, catalyst concentration and solvent nature upon PUs molecular weight was investigated. After the exchange of bromide to (CF3SO2)2N- anion the obtained poly(ionic liquid)s exhibit high thermal stability with onset mass loss above 225°C and demonstrate glass transition temperatures in the wide range from −22°C to 76°C depending on the nature of ionic diol used. Ionic PUs present excellent solubility in most organic solvents and are capable to form tough, flexible films with tensile strength up to 29.7 MPa.

A post-polymerization functionalization strategy for the synthesis of sulfonyl (trifluoromethanesulfonyl)imide functionalized (co)polymers

Synthesis of functional sulfonyl(trifluoromethanesulfonyl)imide (STFSI) derivatives and original (co)polymers containing the STFSI group.

Single lithium-ion conducting poly(tetrafluorostyrene sulfonate) – polyether block copolymer electrolytes

Well-designed BAB triblock copolymers with central polyether and flanking poly(lithium pentafluorostyrene sulfonate) blocks reach very high conductivities in the solid state.

Single-Ion Block Copoly(ionic liquid)s as Electrolytes for All-Solid State Lithium Batteries

Polymer electrolytes have been proposed as replacement for conventional liquid electrolytes in lithium-ion batteries (LIBs) due to their intrinsic enhanced safety. Nevertheless, the power delivery of these materials is limited by the concentration gradient of the lithium salt. Single-ion conducting polyelectrolytes represent the ideal solution since their nature prevents polarization phenomena. Herein, the preparation of a new family of single-ion conducting block copolymer polyelectrolytes via reversible addition-fragmentation chain transfer polymerization technique is reported. These copolymers comprise poly(lithium 1-[3-(methacryloyloxy)propylsulfonyl]-1-(trifluoromethylsulfonyl)imide) and poly(ethylene glycol) methyl ether methacrylate blocks. The obtained polyelectrolytes show low Tg values in the range of -61 to 0.6 °C, comparatively high ionic conductivity (up to 2.3 × 10(-6) and 1.2 × 10(-5) S cm(-1) at 25 and 55 °C, respectively), wide electrochemical stability (up to 4.5 V versus Li(+)/Li), and a lithium-ion transference number close to unity (0.83). Owing to the combination of all mentioned properties, the prepared polymer materials were used as solid polyelectrolytes and as binders in the elaboration of lithium-metal battery prototypes with high charge/discharge efficiency and excellent specific capacity (up to 130 mAh g(-1)) at C/15 rate.

Highly Conductive and Thermally Stable Ion Gels with Tunable Anisotropy and Modulus

A new liquid-crystalline ion gel exhibits unprecedented properties: conductivity up to 8 mS cm(-1) , thermal stability to 300 °C, and electrochemical window to 6.1 V, as well as adjustable transport anisotropy (up to 3.5×) and elastic modulus (0.03-3 GPa). The combination of ionic liquid and magnetically oriented rigid-rod polyanion provides widely tunable properties for use in diverse electrochemical devices.

Vinyl monomers bearing a sulfonyl(trifluoromethane sulfonyl) imide group: synthesis and polymerization using nitroxide-mediated polymerization

A series of water-soluble styrene and propyl (meth)acrylate based monomers bearing a sulfonyl(trifluoromethane sulfonyl) imide (STFSI) group was prepared.

A well-defined polyelectrolyte and its copolymers by reversible addition fragmentation chain transfer (RAFT) polymerization: synthesis and applications

Controlled polymerization and self-assembly of novel block copolymer electrolytes.