Polymerized Ionic Liquid Block Copolymers Research Articles

Single‐ion conducting polymer as lithium salt additive in polymerized ionic liquid block copolymer electrolyte

AbstractHerein, we describe the use of single‐ion conducting block copolymer (SIC) as an additional lithium salt additive to a ternary solid polymer electrolyte (SPE), consisting of a poly(styrene‐b‐1‐((2‐acryloyloxy)ethyl)‐3‐butylimidazolium bis(trifluoromethanesulfo‐nyl)imide) (S‐ImTFSI64‐16) block copolymer, a N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) ionic liquid (IL) and a lithium bis(fluorosulfonyl) imide (LiFSI) salt. For this purpose, the S‐ImTFSI64‐16 was substituted by a SIC, based on poly(styrene‐b‐((4‐styrenesulfonyl)(trifluoromethanesulfonyl)imide lithium salt)) (S‐STFSILi64‐16), at various molar ratios. The impact of the SIC concentration on the phase behavior and transport properties of the SPEs was investigated by means of differential scanning calorimetry, electrochemical impedance spectroscopy, and diffusion NMR. In addition, the electrochemical performance of the SPEs was assessed in lithium symmetrical cell at 50 and 80°C. Finally, the cycling performance of a selected SPE was also assessed at 80°C in a Li│NMC111 cell with capacity loading of 1.3 mAh.cm−2 at a C‐rate of 0.1 C. The Li│NMC111 full cell was able to deliver a stable capacity of 0.94 mAh.cm−2 after 20 cycles, corresponding to a capacity of 117 mAh.g−1. These results demonstrates that PIL block copolymer—IL—salt composites represent a promising choice of electrolyte for the next generation of solid‐state high energy density lithium metal batteries.

Poly(ionic liquid) Gating Materials for High-Performance Organic Thin-Film Transistors: The Role of Block Copolymer Self-Assembly at the Semiconductor Interface.

The widespread realization of wearable electronics requires printable active materials capable of operating at low voltages. Polymerized ionic liquid (PIL) block copolymers exhibit a thickness-independent double-layer capacitance that makes them a promising gating medium for the development of organic thin-film transistors (OTFTs) with low operating voltages and high switching speed. PIL block copolymer structure and self-assembly can influence ion conductivity and the resulting OTFT performance. In an OTFT, self-assembly of the PIL gate on the semiconducting polymer may differ from bulk self-assembly, which would directly influence electrical double-layer formation. To this end, we used poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) as a model semiconductor for our OTFTs, on which our PILs exhibited self-assembly. In this study, we explore this critical interface by grazing-incidence small-angle X-ray scattering (GISAXS) and atomic force microscopy (AFM) of P(NDI2OD-T2) and a series of poly(styrene)-b-poly(1-(4-vinylbenzyl)-3-butylimidazolium-random-poly(ethylene glycol) methyl ether methacrylate) (poly(S)-b-poly(VBBI+[X]-r-PEGMA)) block copolymers with varying PEGMA/VBBI+ ratios and three different mobile anions (where X = TFSI-, PF6-, or BF4-). We investigate the thin-film self-assembly of block copolymers as a function of device performance. Overall, a mixed orientation at the interface leads to improved device performance, while predominantly hexagonal packing leads to nonfunctional devices, regardless of the anion present. These PIL gated OTFTs were characterized with a threshold voltage below 1 V, making understanding of their structure-property relationships crucial to enabling the further development of high-performance gating materials.

Ionic Liquid Composite Electrocatalysts for the Oxygen Reduction Reaction in PEM Fuel Cells

The cathode catalyst layer (CCL) of the proton exchange membrane fuel cell (PEMFC) cathode requires a high amount of Pt to compensate for the sluggish oxygen reduction reaction (ORR) kinetics. Reducing the Pt loading in the CCL remains the major challenge in commercializing fuel cell devices. Recent developments enable up to 20-fold improvement in the activity of ORR electrocatalysts and facilitate a lower amount of Pt in the catalyst layer.1 However, these low-Pt-loaded cathodes show significant voltage losses at high current densities (HCD).2 These performance losses are associated with local oxygen transport resistances due to higher particle-particle distance and the interfacial resistance between Pt and PFSA-based ionomers.3 The interfacial resistance observed at the catalyst-ionomer interface is exacerbated with the thickness of the ionomer film on catalyst particles4 and specific adsorption of sulfonate groups.5 These challenges can be potentially addressed by modifying the catalyst-ionomer interface at fuel cell cathode. Protic and hydrophobic Ionic liquids (ILs) are known to enhance the ORR performance of state-of-the-art catalysts in half cell experiments.6 Our research group has previously shown that an ionic liquid interlayer on the Pt surface mitigates the specific adsorption of sulfonate groups. Despite remarkable half-cell performance of ionic liquid modified catalysts (100-150%), ionic liquid incorporated CCLs show only a modest improvement (10-15%).7 Inhomogeneous distribution of ionic liquids in the catalyst layer and potential loss of ionic liquids during fuel cell operation are possible reasons behind this discrepancy. The use of sulfonated polymerized ionic liquid block copolymer (SPILBCP) as an ionomer presents a novel method to incorporate ionic liquids in the catalyst layer. SPILBCP has sulfonated domains to enable proton conduction and ionic liquid domains to facilitate oxygen transport and mitigate sulfonate adsorption. In this work, we implement rotating disk electrode (RDE) techniques to analyze a polymeric ionic liquid block copolymer (SPILBCP) as an ionomer for the PEMFC cathode. We found that Pt/C catalyst films prepared using PILBCP show two-fold improvement over those prepared using Nafion, a state-of-the-art ionomer. We use the CO displacement technique to show that PILBCP thin films exhibit a lower degree of sulfonate adsorption than Nafion on a highly ordered Pt surface. Furthermore, thin films of SPILBCP and Nafion show comparable proton conductivity and oxygen permeability. These results support the recent finding showing up to two-fold improvement in the kinetic activity of PEMFCs using SPILBCP as a catalyst binder. 8 References Shao M, Chang Q, Dodelet JP, Chenitz R. Recent Advances in Electrocatalysts for Oxygen Reduction Reaction. Chem Rev. 2016;116(6):3594-3657. doi:10.1021/acs.chemrev.5b00462 Kongkanand A, Mathias MF. The Priority and Challenge of High-Power Performance of Low-Platinum Proton-Exchange Membrane Fuel Cells. J Phys Chem Lett. 2016;7(7):1127-1137. doi:10.1021/acs.jpclett.6b00216 Weber AZ, Kusoglu A. Unexplained transport resistances for low-loaded fuel-cell catalyst layers. J Mater Chem A. 2014;2(41):17207-17211. doi:10.1039/c4ta02952f Sasikumar G, Ihm JW, Ryu H. Dependence of optimum Nafion content in catalyst layer on platinum loading. J Power Sources. 2004;132(1-2):11-17. doi:10.1016/j.jpowsour.2003.12.060 Garrick TR, Moylan TE, Yarlagadda V, Kongkanand A. Characterizing electrolyte and platinum interface in PEM fuel cells using CO displacement. J Electrochem Soc. 2017;164(2):F60-F64. doi:10.1149/2.0551702jes Snyder J, Fujita T, Chen MW, Erlebacher J. Oxygen reduction in nanoporous metal-ionic liquid composite electrocatalysts. Nat Mater. 2010;9(11):904-907. doi:10.1038/nmat2878 Snyder J, Livi K, Erlebacher J. Oxygen reduction reaction performance of [MTBD][beti]-encapsulated nanoporous NiPt alloy nanoparticles. Adv Funct Mater. 2013;23(44):5494-5501. doi:10.1002/adfm.201301144 Li Y, Cleve T Van, Sun R, et al. Modifying the Electrocatalyst-Ionomer Interface via Sulfonated Poly ( Ionic Liquid ) Block Copolymers to Enable High-Performance Polymer Electrolyte Fuel Cells. 2020. Figure 1

Polymerized Ionic Liquid Block Copolymer Electrolytes for All-Solid-State Lithium-Metal Batteries

In this work, we present a polymerized ionic liquid block copolymer (PBCP) film where relevant properties such as ionic conductivity and electrochemical parameters are tailored by using a ternary system comprised of poly(styrene-b-1-((2-acryloyloxy)ethyl)−3-butylimidazolium bis(tri-fluoromethanesulfonyl)imide), LiFSI salt and ethylene carbonate (EC) as a cosolvent. It was found that EC efficiently decreases the glass transition temperature of the ionic block, resulting in an improved ionic conductivity and efficient platting/stripping of lithium. By using an optimal ratio of EC/LiFSI at relatively high LiFSI amount, Li∣Li symmetrical cells at 50 °C show an overpotential as low as 70 mV at 0.1 mA.cm−2 along with a high lithium transport number of 0.56 (tLi+). All-solid-state full cells based on lithium iron phosphate cathode paired with a lithium metal anode reveal a rather stable cycling at both 50 °C and 70 °C. A negligible capacity fading is observed up to 30 cycles where a specific capacity as high as 161 mAh.g−1 is achieved with a coulombic efficiency of 99.9%. Thus, this work demonstrates an important pathway for tailoring the properties of solid state polymer electrolytes for emerging and specially designed block copolymer architectures comprising domains that give both excellent ionic conduction along with desirable mechanical properties.

Ionic Liquid Electrolytes – from Novel Separators to Solid Polymer Electrolytes

One of the significant challenges to the application of ionic liquid electrolytes (ILE’s) is the ability to identify separators that can be effectively ‘wetted’ by the electrolyte. There has been significant work in identifying appropriate commercial separators for these electrolytes, with varying degrees of success [1]. To-date, the most effective separator for ILE’s is glass fibre, however, this material has large, open pore structure and this requires it to relatively thick to prevent short circuits between the electrodes. As a consequence, there is a need to identify new materials / structures that can lead to innovative separators that can allow ILE’s to be effectively used in batteries. To this end, we have examined the use of a “supported” electrospun membrane to be able to “tailor” the interfaces of the electrodes, but also allow effective wetting of the separator with an ILE to enable use in a lithium-ion battery [1]. However, in doing this, we have now made a “simple” separator far more complex in order to address the ILE wetting problem. So the question needs to be asked – can we combine the properties of the complex separator with an ILE into one solution, such as a solid polymer electrolyte? Further, can we improve these materials by exploiting micro-phase structured morphologies to provide us with enhanced mechanical properties as well? One type of these micro-phase structured polymers [2], known as PILBlox, is made of a high Tg block for mechanical strength and a low Tg ionic block for ionic conductivity [3, 4]. Combining PILBlox with a lithium based ionic salt and an ionic liquid forms a polymer electrolyte which ideally maintains the micro-phase separation present of the pure PILBlox polymer, and confines the ionic salt and ionic liquid to the ionic block of the polymer [4, 5]. In this presentation, we will describe our efforts to make innovative separators using electrospinning techniques and the resulting electrochemistry, before turning our attention to the PILBlox materials and examining their physical properties and their potential use in solid state batteries. References Francis. C., et al., manuscript in preparation, 2018.Bates, F.S., Polymer-Polymer Phase-Behavior. Science, 1991. 251(4996): p. 898-905.Dean, J.M., et al., Micellar structure and mechanical properties of block copolymer-modified epoxies. Journal of Polymer Science Part B-Polymer Physics, 2001. 39(23): p. 2996-3010.Nykaza, J.R., et al., Polymerized ionic liquid diblock copolymer as solid-state electrolyte and separator in lithium-ion battery. Polymer, 2016. 101: p. 311-318.Meek, K.M. and Y.A. Elabd, Polymerized ionic liquid block copolymers for electrochemical energy. Journal of Materials Chemistry A, 2015. 3(48): p. 24187-24194.

Cover Feature: Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes (Batteries & Supercaps 2/2019)

Cover Feature: Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes (Batteries & Supercaps 2/2019)

Enabling High Lithium Conductivity in Polymerized Ionic Liquid Block Copolymer Electrolytes

AbstractHerein, the use of a novel block copolymer host, based on a polymerized ionic liquid block copolymer, is proposed. Mechanically robust solid polymer electrolytes (SPEs) with high lithium conductivity are developed using a ternary polymer electrolyte system, consisting of a poly(styrene‐b‐1‐((2‐acryloyloxy)ethyl)‐3‐butylimidazolium bis(trifluoromethanesulfo‐nyl)imide) (S‐PIL64‐16) block copolymer, a N‐propyl‐N‐methylpyrrolidinium bis(fluorosulfonyl)imide (C3mpyrFSI) ionic liquid (IL) and a lithium bis (fluorosulfonyl) imide (LiFSI) salt. The impact of both IL and lithium salt concentration on the morphology, ion migration processes and electrochemical performance of the electrolytes is characterized. High lithium ion conductivity is achieved when anion to Li+ molar ratio was kept below a value of 1.5, resulting in a lithium transport number ( ) as high as 0.53 at 50 °C. Finally, the cycling performance in a Li|LiFePO4 full cell is assessed using an in‐house formulated solid‐state high loading cathode (LiFePO4 loading=10 mg cm−2, 1.8 mAh cm−2). 98 % of the theoretical discharge capacity (167 mA g−1) is achieved for the first cycle at a C‐rate of C/20 at 50 °C. The results herein reported are the first demonstration of a PIL block copolymer‐IL‐salt composite electrolyte operating at near‐practical levels, making them a promising choice of electrolyte for the next generation of solid‐state high capacity lithium‐metal batteries.

Effect of alkaline exchange polymerized ionic liquid block copolymer ionomers on the kinetics of fuel cell half reactions

Rotating disk electrode (RDE) half-cell experiments were used to determine the impact of a hydroxide-conducting polymerized ionic liquid block copolymer (PILBCP) ionomer on the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) activity of a commercial Pt/C catalyst at three PILBCP loadings (23, 41, and 57wt.% total solids). Increasing loadings of PILBCP resulted in reduced surface coverage of both the hydrogen (HUPD) and hydroxide/oxide (OHad/Oad) as evidenced by the cyclic voltammograms due to both a physical blocking of surface catalytic sites and a water/ion diffusional resistance imparted by the presence of the film. With the maximum loading of 57wt.% PILBCP, a decrease of 88% for the kinetic current density (Jk) and 42% for the diffusion limited current (Id) in the ORR and a decrease of 29% for the Id in the HOR compared to bare Pt/C nanoparticles was observed. Similar trends were observed with 60wt.% Nafion on Pt/C nanoparticles. These results indicate that while substantial, the detrimental effects of PILBCP ionomers on the half-cell reaction kinetics are no worse than those observed with the Nafion ionomer. AEMFC performance optimization for polymers with sufficient hydroxide conductivities should focus on AEM ionomer integration strategies with the goal of optimizing the triple phase boundary and limiting the interfacial resistance between the AEM and the corresponding ionomer in the catalyst layer.

Polymerized ionic liquid diblock copolymer as an ionomer and anion exchange membrane for alkaline fuel cells

Alkaline fuel cells have the potential to provide sustainable portable energy without high-cost platinum if robust, chemically stable anion exchange polymers can be discovered. In this study, a polymerized ionic liquid (PIL) diblock copolymer, poly(MMA-b-MUBIm-HCO3), composed of an ionic liquid monomer, (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bicarbonate) (MUBIm-HCO3), and a non-ionic monomer, methyl methacrylate (MMA), was produced via anion exchange metathesis from the precursor bromide conducting PIL block copolymer, poly(MMA-b-MUBIm-Br), at two PIL compositions (20.0 and 37.9mol%). Prior to anion exchange, the precursor block copolymer was synthesized via the reverse addition fragmentation chain transfer (RAFT) polymerization technique. Non-porous, dense membranes fabricated from this PIL block copolymer were highly conductive, transparent, flexible, and water insoluble. Membrane electrode assemblies were fabricated with this polymer as both the solid-state membrane separator and the ionomer in the catalyst layers using three different techniques: Painted Gas Diffusion Layer (GDL), Air Spray GDL, and Decal Transfer. Alkaline fuel cell (AFC) performance was measured as a function of fuel cell operating conditions, MEA fabrication technique, membrane thickness, and ionomer in different anion exchanged forms. AFC maximum power density of approximately 30mWcm−1 was obtained for H2/O2 fuel, 25psig (172kPa) back pressure, 50μm thick membrane using the Painted GDL MEA fabrication technique. For the first time, these results demonstrate the feasibility of using PIL block copolymers as the membrane and ionomer in alkaline fuel cells.

Sulfonated Polymerized Ionic Liquid Block Copolymers.

The successful synthesis of a new diblock copolymer, referred to as sulfonated polymerized ionic liquid (PIL) block copolymer, poly(SS-Li-b-AEBIm-TFSI), is reported, which contains both sulfonated blocks (sulfonated styrene: SS) and PIL blocks (1-[(2-acryloyloxy)ethyl]-3-butylimidazolium: AEBIm) with both mobile cations (lithium: Li(+) ) and mobile anions (bis(trifluoromethylsulfonyl)imide: TFSI(-) ). Synthesis consists of polymerization via reversible addition-fragmentation chain transfer, followed by post-functionalization reactions to covalently attach the imidazolium cations and sulfonic acid anions to their respective blocks, followed by ion exchange metathesis resulting in mobile Li(+) cations and mobile TFSI(-) anions. Solid-state films containing 1 m Li-TFSI salt dissolved in ionic liquid result in an ion conductivity of >1.5 mS cm(-1) at 70 °C, where small-angle X-ray scattering data indicate a weakly ordered microphase-separated morphology. These results demonstrate a new ion-conducting block copolymer containing both mobile cations and mobile anions.

(Invited) Polymerized Ionic Liquid Block Copolymers As Solid-State Electrolytes in Alkaline Fuel Cells

Alkaline fuel cells (AFCs) that employ solid-state anion exchange membranes (AEMs) as the electrolyte separator are of great interest as they produce high power densities at low operating temperatures (< 200 °C) and enable the use of non-platinum electrodes (e.g., nickel), significantly reducing cost relative to proton exchange membrane fuel cells. Several challenges limiting the wide scale use of membrane-based AFCs is the alkaline chemical stability and ion transport of polymers used as AEMs. Recently, polymerized ionic liquid (PIL) block copolymers with a range of chemically stable heterocyclic cations have become candidates to investigate for AFCs. PIL block copolymers constitute an emerging class of polymers and a distinct set of block copolymers that synergistically combine the advantageous properties of both PILs and block copolymers and are synthetically highly versatile with numerous cation and anion chemistries available. Specifically, the unique physiochemical properties of PILs, such as high solid-state ionic conductivity, high chemical, thermal and electrochemical stability, and widely tunable physical properties (e.g., via anion exchange), are incorporated in the block copolymer architecture, which allows for self-assembly into a range of nanostructures, where morphology type and domain size are tunable. In this talk, the synthesis, alkaline chemical stability, and ion transport of numerous PIL block copolymers developed in our research group will be discussed. More specifically, both the cation and backbone chemistry have a significant effect on alkaline chemical stability and various chemistries and chain architectures have a significant impact on ion conductivity. The AFC performance of PIL block copolymers as both the electrolyte and ionomer in the catalyst layer will also be discussed.

Anhydrous Proton Transport in Polymerized Ionic Liquid Block Copolymers: Roles of Block Length, Ionic Content, and Confinement

Anhydrous proton transport has been investigated in a series of proton conducting polystyrene-block-polymerized ionic liquid (PS-b-PIL) copolymers spanning a range of molecular weights and compositions. The PIL is a macromolecular analogue of imidazolium bis(trifluoromethane sulfonimide) (ImTFSI), a well-known proton conducting ionic liquid, and consists of imidazole linked to a polymer backbone via the 5-carbon. In contrast to prior work on nitrogen-linked imidazolium PILs, carbon-linked imidazolium has two nitrogens which can both function as proton donor/acceptors and participate in Grotthus mechanism conduction. The conductivity of the PIL block is shown to be dramatically impacted upon confinement by a PS block and can exceed the conductivity of the homopolymer in the range of 30–130 °C for PIL-rich block copolymer composition. At high temperature the conductivities track with ionic content while at room temperature the conductivities are nonmonotonic. X-ray scattering reveals a suppression of the pe...

Bromide and Hydroxide Conductivity–Morphology Relationships in Polymerized Ionic Liquid Block Copolymers

A polymerized ionic liquid (PIL) diblock copolymer, poly(MMA-b-MEBIm-Br), was synthesized at various compositions from an ionic liquid monomer, (1-[(2-methacryloyloxy)ethyl]-3-butylimidazolium bromide) (MEBIm-Br), and a nonionic monomer, methyl methacrylate (MMA), via the reverse addition–fragmentation chain transfer (RAFT) polymerization technique. A hydroxide-conducting PIL diblock copolymer, poly(MMA-b-MEBIm-OH), was also prepared via anion exchange metathesis of the bromide-conducting block copolymer. In a former study, the conductivity and morphology of the bromide- and hydroxide-conducting PIL diblock copolymer were examined at one fixed PIL composition: 17.3 mol %. In this study, additional PIL compositions of (6.6, 11.9, and 26.5 mol %) were explored to fully understand the previous unusual conductivity results. Both bromide and hydroxide conductivities were higher in the PIL block copolymer at PIL compositions of 11.9, 17.3, and 26.5 mol % compared to the PIL homopolymer under the same experiment...

Single ion conducting, polymerized ionic liquid triblock copolymer films: high capacitance electrolyte gates for n-type transistors.

There has been impressive progress in the fabrication and characterization of p-type organic electrolyte-gated transistors (EGTs). Unfortunately, despite the importance of n-type organic transistors for complementary circuits, fewer investigations have focused on developing electrolytes as gate dielectrics for n-type organic semiconductors. Here, we present a novel single ion conductor, a polymerized ionic liquid (PIL) triblock copolymer (PS-PIL-PS) composed of styrene (PS) and 1-[(2-acryloyloxy)ethyl]-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (PIL), that conducts only the TFSI anion. This triblock copolymer acts as a gate dielectric to allow low-voltage n-type organic EGT operation. Impedance characterization of PS-PIL-PS reveals that there are three polarization regions: (1) dipolar relaxation, (2) ion migration, and (3) electric double layer (EDL) formation. These polarization regions are controlled by film thickness, and rapid EDL formation can be obtained in thinner polyelectrolyte films. In particular, a 500 nm-thick polyelectrolyte film exhibits a large capacitance of ∼1 μF/cm(2) at 10 kHz. Employing this single ion conducting PIL triblock copolymer as the gate insulator, we achieved low voltage operation (<1 V supply) of poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) n-type organic EGTs (electron mobility of ∼0.008 cm(2)/(V·s) and ON/OFF current ratio of ∼2 × 10(3)) by preventing electrochemical doping. Furthermore, the recognition that the performance of n-type organic EGTs is diminished by 3D electrochemical doping suggests that it may be necessary to have a unipolar electrolyte to gate n-type organic semiconductors. Finally, we highlight that the use of PIL block copolymer electrolytes as gate insulators opens unique opportunities to explore the role of ion penetration in n-type organic EGTs by tuning the extent of electrochemical doping.

Polymerized ionic liquid block copolymers for electrochemical energy

Polymerized ionic liquid (PIL) block copolymers are an emerging class of polymers that synergistically combine the benefits of both ionic liquids (ILs) and block copolymers into one, where the former possesses a unique set of physiochemical properties and the latter self assembles into a range of nanostructures.

Correction: Polymerized ionic liquid block copolymers for electrochemical energy

Correction for ‘Polymerized ionic liquid block copolymers for electrochemical energy’ by Kelly M. Meek et al., J. Mater. Chem. A, 2015, DOI: 10.1039/c5ta07170d.

Polymerized ionic liquid diblock copolymers with long alkyl side-chain length

A polymerized ionic liquid (PIL) diblock copolymer with a long alkyl side-chain, poly(MMA-b-MUBIm-Br), was synthesized at various compositions from an ionic liquid monomer, (1-[(2-methacryloyloxy)undecyl]-3-butylimidazolium bromide) (MUBIm-Br), and a non-ionic monomer, methyl methacrylate (MMA). The PIL diblock copolymer was synthesized via post-functionalization from its non-ionic precursor PIL diblock copolymer, poly(MMA-b-BrUMA) (BrUMA = 11-bromoundecyl methacrylate), which was synthesized via the reverse addition fragmentation chain transfer (RAFT) polymerization technique. Differential scanning calorimetry reveals two distinct constant glass transition temperatures (Tgs) with a low PIL segment Tg. These PIL block copolymers result in easily processable, flexible, transparent films with high mechanical strength. A high bromide ion conductivity of 64.85 mS cm−1 at 80 °C and 90% RH was measured for the PIL diblock copolymer with an ion exchange capacity (IEC) of 1.44 meq/g (23.3 mol% MUBIm-Br). Interestingly, this result was three times higher than its analogous PIL homopolymer (2.75 meq/g; 100 mol% MUBIm-Br) and an order of magnitude higher than a PIL block copolymer from a previous study with similar chemistry, similar IEC, higher water content, but shorter alkyl side-chain length. Ion conductivity did not scale as expected with water content, which is unusual for water-assisted ion transport (e.g., protons, hydroxide, chloride) in ion-containing polymers, and therefore suggests other mechanisms that impact ion transport in PIL block copolymers.

Network Structure and Strong Microphase Separation for High Ion Conductivity in Polymerized Ionic Liquid Block Copolymers

A series of strongly microphase-separated polymerized ionic liquid (PIL) diblock copolymers, poly(styrene-b-1-((2-acryloyloxy)ethyl)-3-butylimidazolium bis(trifluoromethanesulfonyl)imide) (poly(S-b-AEBIm-TFSI)), were synthesized to explore relationships between morphology and ionic conductivity. Using small-angle X-ray scattering and transmission electron microscopy, a variety of self-assembled nanostructures including hexagonally packed cylinders, lamellae, and coexisting lamellae and network morphologies were observed by varying PIL composition (6.6–23.6 PIL mol %). At comparable PIL composition, this acrylate-based PIL block copolymer with strong microphase separation exhibited ∼1.5–2 orders of magnitude higher ionic conductivity than a methacrylate-based PIL block copolymer with weak microphase separation. Remarkably, we achieved high ionic conductivity (0.88 mS cm–1 at 150 °C) and a morphology factor (normalized ionic conductivity, f) of ∼1 through the morphological transition from lamellar to a coex...

High Hydroxide Conductivity in Polymerized Ionic Liquid Block Copolymers

Herein, we report a polymerized ionic liquid diblock copolymer with high hydroxide conductivity and nanoscale morphology. Surprisingly, the conductivity is not only higher (over an order of magnitude) than its random copolymer analog at the same ion and water content, but also higher than its homopolymer analog, which has a higher ion and water content than the block copolymer. These results should have a significant impact on low-cost (platinum-free), long-lasting, solid-state alkaline fuel cells.

Effect of Nanoscale Morphology on the Conductivity of Polymerized Ionic Liquid Block Copolymers

Polymerized ionic liquid (POIL) block copolymers represent a unique class of materials for fundamental studies of single ion conduction as a function of morphology in microphase-separated polymer electrolytes for energy storage and conversion applications. We describe the synthesis of a series of poly(styrene-b-4-vinylbenzylalkylimidazolium bis(trifluoromethanesulfonyl)imide) (PS-b-PVBn(alkyl)ImTFSI; alkyl = CH3 (Me), n-C4H9 (Bu), n-C6H13 (Hex)) diblock copolymers (2.7–17.0 mol % POIL) via exhaustive functionalization and ion exchange of relatively narrow molecular weight dispersity poly(styrene-b-4-vinylbenzyl chloride) precursors derived from nitroxide-mediated block copolymerizations. The solid-state morphology of these PS-b-PVBn(alkyl)ImTFSI copolymers were studied using a combination of temperature-dependent synchrotron small-angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). From electrochemical impedance spectroscopy measurements, we observe that lamellar samples having similar compositions exhibit comparable values of conductivity (0.1 mS cm–1 at 150 °C) regardless of imidazolium alkyl substituent. The ionic conductivity of a compositionally varied series of PS-b-PVBnHexImTFSI diblocks depends nonlinearly on POIL composition (0.01 mS cm–1 for 8.6 mol % POIL and 0.1 mS cm–1 for 17.0 mol % POIL at 150 °C), thus highlighting the influence of morphology on the observed ionic conductivity of POIL block copolymers for the first time. By using different polymer processing strategies, we further demonstrate that the ionic conductivity of a single sample (8.6 mol % POIL) may vary by more than one order of magnitude depending on the long-range ordering of the microphase separated morphology. These studies indicate that macroscopic connectivity and morphological defects strongly affect the observed conductivity in these materials.