Class Of Polymer Electrolytes Research Articles

Nanocellulose as a Sustainable Polymer Electrolyte

Polymer electrolyte membranes in fuel cells and electrolyzers will play a key role in the hydrogen economy. These membranes are generally made of sulfonated fluoropolymers, which have excellent proton conductivity, impressive redox stability, and good gas barrier properties. However, the complex synthetic processes mean that they remain expensive. Their synthesis also involves ecologically damaging perfluorosulfonic acids (PFSAs), otherwise known as “forever chemicals” due to their persistence in the environment. More sustainable and lower cost hydrocarbon electrolytes should therefore be investigated.Cellulose is the most abundant biopolymer in nature, and is derived from plant matter. It is used at vast scale and low cost to make paper and cardboard. Cellulose can be chemically or mechanically treated to break up the fibers to form “nanocellulose”. Nanocellulose is a low-cost nanomaterial which can be formed into thin membranes which are much stronger than conventional cellulosic paper.We propose nanocellulose as an alternative electrolyte to replace sulfonated fluoropolymers in fuel cells. We confirmed that unmodified nanocellulose can conduct protons due to acidic hydroxyl groups. We also showed that nanocellulose membranes present a much better barrier to hydrogen compared to Nafion, and can successfully be used as an electrolyte in fuel cells. However, the current-voltage performance of unmodified nanocellulose was insufficient due to a high membrane resistance.We went on to improve the proton conductivity by introducing sulfonic acid groups and reduced the membrane resistance by using spray deposition to create thinner membranes, resulting in significantly improved fuel cell power density of 160 mW/cm2. We also implemented crosslinking with sulfosuccinic acid to simultaneously improve the ionic conductivity, increase strength, and reduce swelling in water. This work shows that nanocellulose is a promising new class of polymer electrolyte which could significantly reduce the cost and improve sustainability of fuel cell and electrolyser systems.1. Cellulose Nanocrystals Crosslinked with Sulfonic Acid as Sustainable Proton Exchange Membranes for Electrochemical Energy Applications, O. Selyanchyn, T. Bayer, D. Klotz, R. Selyanchyn, K. Sasaki, S. M. Lyth, Membranes 12 (7), 658 (2022)2. Spray Deposition of Sulfonated Cellulose Nanofibers as Proton Conducting Membranes for Fuel Cells, T. Bayer, B. Cunning, R. Selyanchyn, B. Smid, S. Fujikawa, K. Sasaki, S. M. Lyth, Cellulose, 28, 1355–1367 (2021)3. Proton Conductivity in Cellulosic Materials: A Review, O. Selyanchyn, R. Selyanchyn, S. M. Lyth, Frontiers in Energy Research: Fuel Cells, 8, 596164 (2020)4. High Temperature Proton Conductivity in Nanocellulose: Paper Fuel Cells, T. Bayer, R. Selyanchyn, S. Fujikawa, K. Sasaki, and S. M. Lyth, Chemistry of Materials, 28 (13), 4805–4814 (2016)

Understanding Lithium-Ion Dynamics in Single-Ion and Salt-in-Polymer Perfluoropolyethers and Polyethyleneglycol Electrolytes Using Solid-State NMR

Lithium metal batteries with high energy densities can enable a revolution in energy storage and accelerate shifts in electric transportation and electricity generation. However, several morphological and electro-chemo-mechanical challenges impede their development. Solid-state electrolytes such as those based on polymers show great promise in replacing liquid electrolytes in lithium metal batteries. Polyether-based polymer electrolytes are the most investigated but are plagued by low room-temperature ionic conductivity and poor oxidative stability. Hence, there is great need for the development and understanding of ion transport in new classes of polymer electrolytes. Perfluoropolyether (PFPE)-based electrolytes have shown improved oxidative stability, but little is understood about their lithium solvation and transport mechanism. In this work, we use multinuclear solid-state magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy to investigate the lithium cation environment and mobility in crosslinked single-ion and salt-in-polymer PFPE electrolytes and compare it directly to that of well-known polyethylene glycol (PEG) electrolytes. We show that the interaction of the lithium cation with the polymer backbone is weaker in PFPE systems compared to PEG, likely resulting in stronger ion pairing in the PFPE systems. Line shape analyses show lower lithium mobility in PFPE electrolytes despite lower activation energies being derived from spin-lattice relaxation (T1) measurements as compared to those for the PEG systems. The rapid relaxation is instead ascribed to the local fluctuations caused by polymer backbone mobility. By studying different modes of ion binding (single-ion vs salt-in-polymer), we show that differences across polymer backbones (PFPE vs PEG) have a greater effect on mobility than differences in ion binding modes within each polymer class (especially when single-ion conducting site density is not high). Our ability to use MAS NMR to study polymer electrolytes in their native state opens new opportunities to develop and understand novel polymer or hybrid solid-state electrolytes for next-generation lithium metal batteries.

Molecularly Tunable Polyanions for Single-Ion Conductors and Poly(solvate ionic liquids)

Polymer electrolytes (PEs) have attracted tremendous research interest for their potential to offer improved safety and energy capacity in next-generation battery technologies. Among the different classes of PEs, single-ion conductors (SICs) are particularly interesting due to their high transference numbers. Nevertheless, a detailed understanding of how molecular structure impacts the properties of SIC-PEs is absent, limiting the ability to design improved materials. Here, we present the synthesis and characterization of a new class (seven examples provided) of polyanions featuring fluorinated aryl sulfonimide tagged (FAST) anions as side chains. These “polyFAST” salts are shown to outperform the widely used poly[(4-styrenesulfonyl) (trifluoromethanesulfonyl)imide] due to their strongly electron-withdrawing side chains and enhanced distance between anionic sites, providing higher electronic conductivities at all salt concentrations and in some cases superior electrochemical oxidative stability. Moreover, they provide a platform for discovery of fundamental relationships between macromolecular composition, as programmed through monomer structure, and SIC-PE bulk properties. Finally, we leverage the electron-deficient nature of polyFAST salts to demonstrate a new poly(solvate ionic liquid) (polySIL) concept that offers a promising pathway toward high-performance PEO-free SIC-PEs.

Redesigned Solid Polymer Electrolytes By Atomistic Predictions and Supramolecular Chemistry

Advancement in energy dense, yet safe batteries is essential for several applications including portable electronics and transportation. However, a major challenge in energy storage systems is the instability of electrolyte materials due to their limited chemical and electrochemical stability, as well as their flammability. We believe, solid-state polymer electrolytes can address the inherent problems of their liquid counterparts and simultaneously provide new avenues for battery development with unprecedented mechanical design. In this regard, polyethylene oxide (PEO) have been the most widely studied solid electrolyte because of their ability of solvating metal salts for ion transport. However, conductivity of PEO is highly temperature dependent because of their crystallinity and they have limited electrochemical stability due to the ease of electron extraction at high voltages (>3.8V vs Li/Li+). In this talk, I will discuss our recent work of redesigning monomer chemistry of ion conducting polymers by ab-initio calculations. Based on the theoretical predictions, we synthesized a new class of polymer electrolytes and evaluated their ion transport and rheological properties. We further utilized nuclear magnetic resonance (NMR), infrared spectroscopy (FTIR) coupled with molecular dynamics (MD) simulations to understand the solvation structure and ionic aggregations. Finally, we demonstrate the application of these rationally designed polymer electrolytes in a high-voltage lithium metal battery, under specific conditions where conventional PEO electrolytes fail to operate.

Stiffer is Not Necessarily Better: Requirements Analysis for Binary Solid Polymer Electrolytes that Ensure Stable Lithium Metal Electrodes

Use of lithium metal electrodes in solid state batteries requires well-balanced electrochemical and mechanical properties for high performance yet safe application. We present a new methodology to account for coupling mechanisms between electrochemistry and mechanics, understand morphological stability and deduce stability maps for solid polymer electrolytes adjacent to metal electrodes. We use a rigorous electro-chemo-mechanical description of the polymer electrolyte and its reaction kinetics to predict the interface current density along a deformed electrolyte interface as a function of e.g. mechanical stiffness, transport and interface properties. With these results, we explore the stability of the electrolyte-electrode interface in regard to the tendency for protrusions to grow on the metal electrode. We find that there is a critical Young’s modulus of the electrolyte above which protrusion growth is suppressed. However, the critical Young’s modulus depends on the charging rate, and on the electrochemical transport properties of the electrolyte and the interface. We develop a morphological stability map in which the critical Young’s modulus separating stable and unstable behavior is identified. The results agree well with experimental findings and might help in predicting new classes of polymer electrolytes which are more likely to perform well in the effort to suppress dendrite growth.

Dielectric Relaxation Behavior of a Poly(ethylene carbonate)‐Lithium Bis‐(trifluoromethanesulfonyl) Imide Electrolyte

A new class of polymer electrolytes, consisting of poly(ethylene carbonate) (PEC) and metal salts, is expected to find application in all‐solid‐state batteries because of its excellent performance as an electrolyte. To study the ion‐conductive mechanism in PEC‐based electrolytes, broadband dielectric spectroscopy is used to analyze the correlation between dielectric relaxation and ionic conduction in PEC‐lithium bis‐(trifluoromethanesulfonyl) imide electrolytes over a broad range of salt concentration (0–150 mol%) at 40 °C. The PEC system has two relaxation modes, α and β, associated respectively with the segmental motion and the local motion of PEC chains. The conductivity increases exponentially with increasing salt concentration, while the α relaxation frequency (fα) decreases with increasing strength (Δεα) at low salt concentrations, whereas in contrast fα increases with Δεα being saturated at high salt concentrations above 10 mol%. It is believed that the mobility of PEC segment at high concentration is enhanced by two factors. The first is that intermolecular interactions decrease, given the existence of many ion pairs and aggregated ions around saturated PEC domains where the dissociated ions are highly concentrated. The second is that intramolecular interactions between CO and CH2 are lowered by the ion–dipole interaction. image

Decoupling Ion and Proton Transport from Structural Relaxation in Polymers and Ionic Liquids

Classical theory relates the rate of ion transport to viscosity or rate of structural relaxation in a liquid electrolyte. We present here an overview of the relationship between ion and proton transport and structural relaxation in ionic liquids (IL) and polymer electrolyte. We demonstrate that in contrast to most of ILs, there is a strong decoupling of ionic conductivity from structural dynamics in many polymers, including polymerized ionic liquids (polyIL). This decoupling is caused by frustration in packing of relatively rigid polymer chains. As a result, ions retain high mobility even when structural dynamics is very slow or completely frozen. To provide a systematic picture of ionic conductivity we employ the so-called Walden plot. Application of this analysis to different classes of polymer electrolytes and polyILs helps to identify ‘superionic’ behavior for many polymers. We present several examples of promising polymers with conductivity approaching 10-4 S/cm at room temperature. Similar ideas can be applied to proton conductivity. We demonstrate significant decoupling of proton mobility from structural relaxation and/or viscosity in a series of protic ionic liquids. Mechanism of enhanced proton conductivity is discussed at the end.

Gelation of Solvate Ionic Liquid by Self-Assembly of Block Copolymer and Characterization as Polymer Electrolyte

We report a new class of polymer electrolytes that exhibit high Li+-ionic conductivity and thermal stability up to 200 °C. The polymer electrolyte consists of a solvate ionic liquid ([Li(G4)][TFSA]), comprising an equimolar mixture of lithium bis(trifluoromethanesulfonyl)amide (Li[TFSA]) and tetraglyme (G4), and a well-defined ABA-triblock copolymer, polystyrene-b-poly(methyl methacrylate)-b-polystyrene (PSt-b-PMMA-b-PSt, SMS). The electrolyte is formed by the self-assembly of SMS, where the solvatophobic PSt segments serves as physical cross-linking points, and the solvatophilic PMMA segment with preferentially dissolved [Li(G4)][TFSA] forms ion-conduction paths. In the electrolyte, the preservation of the complex cation [Li(G4)]+ in the PMMA phase was demonstrated by pulsed-field gradient spin–echo (PGSE) NMR, Raman spectra, and thermogravimetric analysis. Because of the preservation of [Li(G4)]+, which hinders the direct interaction of Li+ with the polymer segment and the coupling of the ionic transport from the segmental motion, the room temperature ionic conductivity of the electrolyte reached an appreciable level (10–4–10–3 S cm–1).

Electrospun polymer membrane activated with room temperature ionic liquid: Novel polymer electrolytes for lithium batteries

A new class of polymer electrolytes (PEs) based on an electrospun polymer membrane incorporating a room-temperature ionic liquid (RTIL) has been prepared and evaluated for suitability in lithium cells. The electrospun poly(vinylidene fluoride- co-hexafluoropropylene) P(VdF-HFP) membrane is activated with a 0.5 M solution of LiTFSI in 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI) or a 0.5 M solution of LiBF 4 in 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF 4). The resulting PEs have an ionic conductivity of 2.3 × 10 −3 S cm −1 at 25 °C and anodic stability at >4.5 V versus Li +/Li, making them suitable for practical applications in lithium cells. A Li/LiFePO 4 cell with a PE based on BMITFSI delivers high discharge capacities when evaluated at 25 °C at the 0.1 C rate (149 mAh g −1) and the 0.5 C rate (132 mAh g −1). A very stable cycle performance is also exhibited at these low current densities. The properties decrease at the higher, 1 C rate, when operated at 25 °C. Nevertheless, improved properties are obtained at a moderately elevated temperature of operation, i.e. 40 °C. This is attributed to enhanced conductivity of the electrolyte and faster reaction kinetics at higher temperatures. At 40 °C, a reversible capacity of 140 mAh g −1 is obtained at the 1 C rate.

Organic–Inorganic Hybrid Membranes for a PEMFC Operation at Intermediate Temperatures

Recently, polymer electrolyte membrane fuel cells (PEMFCs) have been investigated extensively as a future energy source to solve a global energy and environmental problem due to their high energy conversion efficiency. As a membrane is recognized to be a key element for more efficient PEMFCs, new classes of polymer electrolytes have been investigated elsewhere. We have also studied new temperature-tolerant electrolytes using organic–inorganic materials such as polydimethylsiloxane, polytetramethylene oxide (PTMO), zirconia, and titania materials. 12-phosphotungstic (PWA) and phosphoric acids as a proton source were incorporated in the hydrophilic interface of organic–inorganic hybrid membranes. In this paper, they were synthetically displayed, and the cell performance for intermediate temperature PEFC using a single membrane electrolyte assembly cell was also investigated. The maximum power densities for zirconium phosphate–PTMO and titania–PTMO–PWA composite membranes were 13 and , respectively. The cell performance of the membranes increased with increasing cell temperature up to 130°C under saturated humidity conditions. The organic–inorganic hybrid electrolytes synthesized from PTMO with metal alkoxides show promise for applications in intermediate temperature PEFCs.

Structural Study of Inorganic Oxides in a Hybrid Organic−Inorganic Solid Polymer Electrolyte

Polymer−inorganic composite electrolytes very often show superior properties as compared to simple polymer electrolytes, and this enhancement is often ascribed to the structure and interfacial properties of the composite. Here, the structure of aluminosilica (AlSi) domains formed within organic−inorganic solid polymer electrolytes was studied using solid state 29Si and 27Al magic angle spinning (MAS) NMR, transmission electron microscopy (TEM), and nitrogen sorption experiments following material calcinations, to determine how the composite affects the properties in this class of polymer electrolytes. The major feature of all the calcined AlSi's based on 600 MW poly(ethylene glycol) (PEG) is the presence of two types of morphologies: nanoparticles with sizes of about 20−60 nm, and larger platelike particles. Increasing the amount of AlSi in the organic−inorganic composite material (OICM) increases the fraction of platelike particles relative to nanoparticles. The nanoparticles are practically nonporous, ...

A novel approach for development of improved polymer electrolytes for lithium batteries

Polymer electrolyte lithium batteries represent the future of safe, high-energy battery systems. Although great strides have been made in the development of new polymer electrolytes and in understanding how these systems function, progress has been evolutionary in its scope. Further advancement of ambient temperature polymer electrolyte batteries will require new approaches that break with tradition. This report deals with new types of liquid polymers that have not been extensively described in the literature. The work presented in this report represents the beginning of the development of new solid polymer electrolytes. These heteroatomic materials combine the better features of several elements to solubilize and transport select lithium salts more efficiently than traditional ethylene oxide-type polymers. Ambient temperature ionic conductivities of >1×10 −3 S/cm are common with this class of polymer electrolytes. An overview and rationale of the approach together with reported materials properties are reported.

Advanced electrolyte and electrode materials for lithium polymer batteries

The most recent results obtained in our laboratory on the characterization of two classes of polymer electrolytes and of olivine-type lithium iron phosphate electrodes are reviewed and discussed, especially in view of their application in advanced lithium batteries.

Amphiphilic Organic/Inorganic Nanohybrid Macromolecules for Intermediate-Temperature Proton Conducting Electrolyte Membranes

Proton exchange membrane fuel cells (PEMFCs) have been considered to be a key technology for renewable energy systems such as an alternative battery for electric vehicles (EVs), stationary power generators, and mobile phones. Intermediate temperature operation of PEMFCs overcome most of the technological problems of the current PEM system such as CO poisoning, cathode overpotential, and complicated water and heat management. As a membrane is recognized to be a key element for more efficient PEMFCs, new classes of polymer electrolytes have been investigated elsewhere. In this paper, a new class of amphiphilic organic/inorganic hybrid membranes have been synthesized through sol-gel processing of bridged polysilsesquioxanes. The membrane doped with acidic moieties such as 12-phosphotungstic acid shows large protonic conductivities at intermediate temperatures up to 140°C and was found to be flexible as well as thermally stable due to the temperature tolerant inorganic frameworks in the hybrids. The fast ionic transport through the hybrid macromolecules has been possibly ascribed to nanosized phase separation of amphiphilic macromolecules. The proton conductivity of the hybrid was at 140°C without degradation, which can potentially be used as an advanced PEM electrolyte membrane for intermediate temperature operation. © 2002 The Electrochemical Society. All rights reserved.

Ion Transport in Glassy Polymer Electrolytes

The existence is reported of a new class of polymer electrolytes, containing polyether backbones and pendent mesogenic groups. These are amorphous (and sometimes liquid crystalline) polymeric solids with sub-Tg conductivities approaching 10-5 S cm-1 at ambient temperatures. The apparent decoupling of ion transport from structural relaxations in the host material implies the existence of a truly “solid” polymer electrolyte, which also implies a link between ion-transport mechanisms in glasses and in polymeric materials. In future it should be possible to develop materials for a variety of electrochemical applications, based on this new design strategy.

Methacryl-terminated macromers by living polymerization as precursors of IPN polymer electrolytes

A new class of polymer electrolytes, based on the interpenetrating polymer network approach, was obtained starting from functionalised macromers, of poly-ether nature, in the presence of a lithium salt (LiBF 4, LiClO 4, LiCF 3SO 3) and propylene carbonate (PC) or tetraethyleneglycol dimethylether (TGME), as plasticizers. The macromers were synthesised by living polymerisation employing a HI/I 2 system as the initiator. The macromer has a polymerisable end group, which can undergo radical polymerisation, attached to a monodisperse poly-vinylether, containing suitable ethylene oxide groups for ion coordination. Monomers and macromers were characterised by FTi.r., u.v.–vis, 1H- and 13C-n.m.r. Self-consistent and easily handled membranes were obtained as thin films by a dry procedure using u.v. radiation to polymerise and crosslink the network precursors, directly on suitable substrates, in the presence of the plasticizer and the lithium salt. The electrolytic membranes were studied by complex impedance and their thermal properties determined by differential scanning calorimetry analysis. Ionic conductivities ( σ) were measured for PC and TGME-based membranes at various plasticizer and salt contents as a function of T (60 to −20°C). LiClO 4/PC/PE electrolytes, with 3.8% (w/w) salt and 63% PC, have the highest σ (1.15×10 −3 and 3.54×10 −4 S cm −1 at 20°C and −20°C, respectively). One order of magnitude lower conductivities are achieved with TGME; samples with 6% (w/w) LiClO 4 and 45% (w/w) TGME exhibit σ values of 2.7×10 −4 and 2.45×10 −5 S cm −1 at 20°C and −20°C.

Conducting polymers: advanced materials for new design, rechargeable lithium batteries

The results obtained in our laboratory on the characterization of two families of ionically-conducting membranes, i.e. poly(ethylene oxide)-based and gel-type polymer electrolytes, are reviewed here. Particular attention is devoted to the description of the conditions of the lithium electrode interface and to the approaches which may be undertaken to improve its stability. The most promising applications of the two classes of polymer electrolytes are also outlined. © 1998 Society of Chemical Industry

A New Class of Advanced Polymer Electrolytes and Their Relevance in Plastic‐like, Rechargeable Lithium Batteries

The synthesis, properties, and application of a new class of polymer electrolytes, are here reported and discussed. The electrolytes have a very high ionic conductivity, an acceptable lithium ion transport number, and a wide electrochemical stability window. The members of the family which appear most promising in terms of stability of the lithium electrode interface have been tested as electrolyte separators in high voltage, thin layer, laminated rechargeable batteries. Preliminary results provided indications of promising performance in terms of voltage output and cyclability.

Conductivity studies of polymer electrolytes based on aliphatic polyesters

AbstractA series of aliphatic polyesters of sebacoyl chloride and poly(ethylene glycol) containing a different number of ethylene oxide groups was synthesized and characterized. These polyesters were complexed with lithium perchlorate to obtain a new class of polymer electrolyte. The relationships between the structure and properties of these polymer electrolytes were investigated. The main factor that affects the ionic conductivity in these systems was found to be the solvating capacity of the polyester for the lithium salt. These polymer electrolytes showed ionic conductivities up to 10−5 ˜ 10−4 S/cm at 25°C. The mechanical strength was improved by cross‐linking, and the cross‐linked polyester complexed with a LiCIO4 salt showed an ionic conductivity of 2 × 10−5 S/cm at room temperature. 7Li NMR spin‐spin relaxation and dielectric relaxation studies were also carried out to investigate the local environments and dynamics of ions in the polymer electrolytes. © 1995 John Wiley & Sons, Inc.

Effect of grafting degree and side PEO chain length on the ionic conductivities of NBR‐g‐PEO based polymer electrolytes

AbstractComb‐shaped graft polymers were synthesized and complexed with a LiCF3SO3 salt to form a new class of polymer electrolytes. The polymers based on an acrylonitrile‐butadiene copolymer (NBR) have pendant, short‐chain poly(ethylene oxide) (PEO) grafted onto a butadiene unit. The characteristics of these polymer electrolytes were investigated in terms of number of pendant EO groups and grafting degree in the graft copolymer. The maximum conductivity was observed at the optimum side PEO chain length, and the PEO chain length for the maximum conductivity decreased with an increase in the grafting degree. And a solid 7Li NMR relaxation technique was used to study the local environments and dynamics of the ions in the polymer electrolytes. The maximum conductivity value obtained from our study was three orders of magnitude higher than that of classical PEO‐based electrolytes at ambient temperature. These improved low temperature conducting polymers with higher relative mechanical strength are expected to be suitable for practical applications, such as in rechargeable lithium batteries or electrochromic devices.