The Role of Backbone Polarity on Aggregation and Conduction of Ions in Polymer Electrolytes

Converting a Metal-Coordinating Polymer to a Polymerized Ionic Liquid Improves Li+ Transport

Solid polymer electrolytes (SPEs) with mechanical strength and reduced flammability may also enable next-generation Li+ batteries with higher energy densities. However, conventional SPEs have fundamental limitations in terms of Li+ conductivity. While an imidazole functionalized polymer (PMS-Im) has been previously shown to have ionic conductivity related to the imidazole-Li+ coordination, herein we demonstrate that quaternization of this polymer to form an analogous imidazolium functionalized polymer (PMS-Im+) more efficiently solvates lithium salts and plasticizes the polymer. In addition, inverse Haven ratios as high as 10 indicate positively correlated Li+ transport, possibly due to percolation of nanochannels that significantly improve battery-relevant conductivity. From these combined effects, Li+ conductivity in PMS-Im+ (2.1 × 10-5 S/cm) is over an order of magnitude greater than in PMS-Im at 90 °C (1.6 × 10-6 S/cm).

Influence of Water Sorption on Ionic Conductivity in Polyether Electrolytes at Low Hydration

Ion-containing polymers are subject to a wide range of hydration conditions across electrochemical and water treatment applications. Significant work on dry polymer electrolytes for batteries and highly swollen membranes for water purification has informed our understanding of ion transport under extreme conditions. However, knowledge of intermediate conditions (i.e., low hydration) is essential to emerging applications (e.g., electrolyzers, fuel cells, and lithium extraction). Ion transport under low levels of hydration is distinct from the extreme conditions typically investigated, and the relevant physics cannot be extrapolated from existing knowledge, stifling materials design. In this study, we conducted ion transport measurements in LiTFSI-doped polyethers that were systematically hydrated from dry conditions. A semiautomated apparatus that performs parallel measurements of water uptake and ionic conductivity in thin-film polymers under controlled humidity was developed. For the materials and swelling range considered in this study (i.e., <0.07 g water/g dry polymer electrolyte), ionic conductivity depends nonlinearly on water uptake, with the initial sorbed water weakly affecting conductivity. With additional increases in swelling, more significant increases in conductivity were observed. Remarkably, changes in conductivity induced by water sorption were correlated with the number of water molecules per lithium ion, with the normalized molar conductivity of different samples effectively collapsing onto one another until this unit of hydration exceeded the solvation number of lithium ions under aqueous conditions. These results provide important knowledge regarding the effects of trace water contamination on conductivity measurements in polymer electrolytes and demonstrate that the lithium-ion solvation number marks a key transition point regarding the influence of water on ion transport in ion-containing polymers.

Elastic, strong and tough ionically conductive elastomers

Stretchable elastic materials with high strength, toughness, and good ionic conductivity are highly desirable for wearable devices and stretchable batteries. Unfortunately, limited success has been reported to attain all of these properties simultaneously. Here, we report a family of ionically conductive elastomers (ICEs) without compromise between mechanical properties (high stiffness, reversible elasticity, fracture resistance) and ionic conductivity, by introducing a multiple network elastomer (MNE) architecture into a lowT g polymer. The ICEs with the MNE architecture exhibit a room temperature ionic conductivity of the order of10 - 6 S . cm - 1 and stress at break of ~8 MPa, whereas the simple networks without an MNE architecture show two orders magnitude lower ionic conductivity (10 - 8 S . cm - 1 ) and comparably low strength (<1.5 MPa) at 25 °C than their MNE architecture based counterparts. The MNE architecture with a lowT g monomer combines the stiffness and fracture toughness given by sacrificial bond breakage while improving ionic conductivity through increased segmental mobility.

Organic Iono-Optoelectronics: From Electrochromics to Artificial Retina

ConspectusOrganic mixed ionic electronic conductors (OMIECs) represent an exciting and emerging class of materials that have recently revitalized the field of organic semiconductors. OMIECs are particularly attractive because they allow both ionic and electronic transport while retaining the inherent benefits of organic semiconducting materials such as mechanical conformability and biocompatibility. These combined properties make the OMIECs ideal for applications in bioelectronics, energy storage, neuromorphic computing, and electrochemical transistors for sensing. Within the realm of OMIECs, a subset of materials and devices known as organic iono-optoelectronics (OIOEs) further leverage the optoelectronic properties of organic semiconductors and functions based on ionic-electronic-photonic interactions. Ionic-electronic coupling can regulate the bandgap of organic semiconducting materials, allowing the tuning of optical properties, which forms the basis for organic electrochromic technology. Additionally, light, as a form of energy, can modulate ionic-electronic coupling, enabling applications such as machine vision and artificial retina.Among these applications, organic electrochromic devices have demonstrated their practical and commercial value due to their rapid, high-contrast color switching capabilities and potential for cost-effective mass production and roll-to-roll manufacturing. Ambilight Inc. has spearheaded this technology, introducing the first organic electrochromic sunroof product, now used in hundreds of thousands of vehicles. Despite these promising advancements, organic electrochromic devices face several challenges. These include achieving optical contrast higher than 90%, improving color switching speed to meet the demands of dynamic display applications, and enhancing durability to ensure stability in extreme environmental conditions, such as prolonged exposure to sunlight. Growing research on light-modulated ionic-electronic coupling suggests that this fundamental process can be used to mimic the ion-flux-dependent light-capturing processes found in biological retina systems, offering a promising approach for constructing future artificial retina (vision). The intrinsic softness and biocompatibility of the OIOEs further enhance the potential of the artificial retina to interface with biological systems for applications in biomedical optoelectronics and human-machine interfaces. Compared to electrochromic technology, artificial retinas and biomedical optoelectronics are still in their infancy. In this Account, we use two representative technologies─electrochromic devices and artificial retina─to introduce the fundamental processes, advancements, and challenges in the field of OIOEs. We begin with an overview of the fundamental processes shared by and unique to these two technologies. Next, we discuss their respective challenges and the approaches taken by our group and others to improve their performance. Finally, we suggest future research directions. We hope this Account will introduce readers to these fascinating materials and devices and inspire further interest in these research areas.

Halogen-Bonding Nanoarchitectonics in Supramolecular Plasticizers for Breaking the Trade-Off between Ion Transport and Mechanical Strength of Polymer Electrolytes for High-Voltage Li-Metal Batteries

The low ionic conductivity of poly(ethylene oxide) (PEO)-based polymer electrolytes at room temperature impedes their practical applications. The addition of a plasticizer into polymer electrolytes could significantly promote ion transport while inevitably decreasing their mechanical strength. Herein, we report a supramolecular plasticizer (SMP) to break the trade-off effect between ionic conductivity and mechanical properties in PEO-based polymer electrolytes. Accordingly, the SMP is constructed by tetraethylene glycol dimethyl ether (G4) and SbF3 through halogen bonds. The SMP-plasticized PEO electrolyte (PEO/SMP) presents a simultaneously enhanced ionic conductivity of 2.4 × 10-4 S cm-1 (25 °C) and a high mechanical strength of 8.1 MPa, compared to those of pristine PEO-based electrolytes. Benefiting from the halogen bonds between G4 and SbF3, the Li-O coordination in PEO/SMP is evidently weakened, and thus rapid Li+ transport is achieved. Furthermore, the PEO/SMP electrolyte possesses a wide electrochemical stability window of 4.5 V and, importantly, derives an inorganic-rich SEI with a low interfacial resistance on a lithium metal surface. By using PEO/SMP, the lithium-metal battery with the LiNi0.5Co0.2Mn0.3O2 cathode exhibits a good rate and long-term cycling performance with a capacity retention of 75.3% (500 cycles). This work offers a rational guideline for the design of polymer electrolytes suitable for high-performance lithium-metal batteries.

Design of Fluorinated Elastomeric Electrolyte for Solid-State Lithium Metal Batteries Operating at Low Temperature and High Voltage

This work demonstrates the low-temperature operation of solid-state lithium metal batteries (LMBs) through the development of a fluorinated and plastic-crystal-embedded elastomeric electrolyte (F-PCEE). The F-PCEE is formed via polymerization-induced phase separation between the polymer matrix and plastic crystal phase, offering a high mechanical strain (≈300%) and ionic conductivity (≈0.23 mS cm-1) at -10 °C. Notably, strong phase separation between two phases leads to the selective distribution of lithium (Li) salts within the plastic crystal phase, enabling superior elasticity and high ionic conductivity at low temperatures. The F-PCEE in a Li/LiNi0.8Co0.1Mn0.1O2 full cell maintains 74.4% and 42.5% of discharge capacity at -10 °C and -20 °C, respectively, compared to that at 25 °C. Furthermore, the full cell exhibits 85.3% capacity retention after 150 cycles at -10 °C and a high cut-off voltage of 4.5 V, representing one of the highest cycling performances among the reported solid polymer electrolytes for low-temperature LMBs. This work attributes the prolonged cycling lifetime of F-PCEE at -10 °C to the great mechanical robustness to suppress the Li-dendrite growth and ability to form superior LiF-rich interphases. This study establishes the design strategies of elastomeric electrolytes for developing solid-state LMBs operating at low temperatures and high voltages.

Ion Transport in Polymer Electrolytes: Building New Bridges between Experiment and Molecular Simulation

ConspectusPolymer electrolytes constitute a promising type of material for solid-state batteries. However, one of the bottlenecks for their practical implementation lies in the transport properties, often including restricted Li+ self-diffusion and conductivity and low cationic transference numbers. This calls for a molecular understanding of ion transport in polymer electrolytes in which molecular dynamics (MD) simulation can provide both new physical insights and quantitative predictions. Although efforts have been made in this area and qualitative pictures have emerged, direct and quantitative comparisons between experiment and simulation remain challenging because of the lack of a unified theoretical framework to connect them.In our work, we show that by computing the glass transition temperature (Tg) of the model system and using the normalized inverse temperature 1000/(T - Tg + 50), the Li+ self-diffusion coefficient can be compared quantitatively between MD simulations and experiments. This allows us to disentangle the effects of Tg and the polymer dielectric environment on ion conduction in polymer electrolytes, giving rise to the identification of an optimal solvating environment for fast ion conduction.Unlike Li+ self-diffusion coefficients and ionic conductivity, the transference number, which describes the fraction of current carried by Li+ ions, depends on the boundary conditions or the reference frame (RF). This creates a non-negligible gap when comparing experiment and simulation because the fluxes in the experimental measurements and in the linear response theory used in MD simulation are defined in different RFs. We show that by employing the Onsager theory of ion transport and applying a proper RF transformation, a much better agreement between experiment and simulation can be achieved for the PEO-LiTFSI system. This further allows us to derive the theoretical expression for the Bruce-Vincent transference number in terms of the Onsager coefficients and make a direct comparison to experiments. Since the Bruce-Vincent method is widely used to extract transference numbers from experimental data, this opens the door to calibrating MD simulations via reproducing the Bruce-Vincent transference number and using MD simulations to predict the true transference number.In addition, we also address several open questions here such as the time-scale effects on the ion-pairing phenomenon, the consistency check between different types of experiments, the need for more accurate force fields used in MD simulations, and the extension to multicomponent systems. Overall, this Account focuses on building new bridges between experiment and simulation for quantitative comparison, warnings of pitfalls when comparing apples and oranges, and clarifying misconceptions. From a physical chemistry point of view, it connects to concentrated solution theory and provides a unified theoretical framework that can maximize the power of MD simulations. Therefore, this Account will be useful for the electrochemical energy storage community at large and set examples of how to approach experiments from theory and simulation (and vice versa).

Enhanced ionic conductivity in block copolymer electrolytes through interfacial passivation using mixed ionic liquids

We present a strategic approach for enhancing the ionic conductivity of block copolymer electrolytes. This was achieved by introducing mixed ionic liquids (ILs) with varying molar ratios, wherein the imidazolium cation was paired with either tetrafluoroborate (BF4) anion or bis(trifluoromethylsulfonyl)imide (TFSI) anion. Two polymer matrices, poly(4-styrenesulfonate)-b-polymethylbutylene (SSMB) and poly(4-styrenesulfonyl (trifluoromethanesulfonyl)imide)-b-polymethylbutylene (STMB), were synthesized for this purpose. All the SSMB and STMB containing mixed ILs showed hexagonal cylindrical structures, but the type of tethered acid group significantly influenced the interfacial properties. STMB electrolytes demonstrated enhanced segregation strength, which was attributed to strengthened Coulomb and hydrogen bonding interactions in the ionic domains, where the ILs were uniformly distributed. In contrast, the SSMB electrolytes exhibited increased concentration fluctuations because the BF4 anions were selectively sequestered at the block interfaces. This resulted in the effective confinement of imidazolium TFSI along the ionic domains, thereby preventing ion trapping in dead zones and facilitating rapid ion diffusion. Consequently, the SSMB electrolytes with mixed ILs demonstrated significantly improved ionic conductivities, surpassing the expected values based on the arithmetic average of the conductivities of each IL, whereas the ionic conductivity of the STMB was aligned with the expected average. The methodology explored in this study holds great promise for the development of solid-state polymer electrolytes.

Ion Solvation Cage Structure in Polymer Electrolytes Determined by Combining X-ray Scattering and Simulations

Solvation structure plays a crucial role in determining ion transport in electrolytes. We combine wide-angle X-ray scattering (WAXS) and molecular dynamics (MD) simulation to identify the solvation cage structure in two polymer electrolytes, poly(pentyl malonate) (PPM) and poly(ethylene oxide) (PEO) mixed with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. As the salt concentration increases, the amorphous halo in the pure polymers is augmented by an additional peak at low scattering angles. The location of this peak and its height are, however, different in the two electrolytes. By decoupling the total intensity into species contributions and mapping scattering peaks to position-space molecular correlations, we elucidate distinct origins of the additional peak. In PPM, it arises from long-range charge-ordering between solvation cages and anions, while in PEO it is dominated by correlations between anions surrounding the same cage. TFSI- ions are present in the PPM solvation cage, but expelled from the PEO solvation cage.

Superionic Bifunctional Polymer Electrolytes for Solid-State Energy Storage and Conversion

Achieving superionic conductivity from solid-state polymer electrolytes is an important task in the development of future energy storage and conversion technologies. Herein, a platform for innovative electrolyte technologies based on a bifunctional polymer, poly(3-hydroxy-4-sulfonated styrene) (PS-3H4S), is presented. By incorporating OH and SO₃ H functional groups at adjacent positions in the styrene repeating unit, "intra-monomer" hydrogen bonds are formed to effectively weaken the electrostatic interactions of the SO₃ ^- moieties in the polymer matrix with embedded ions, promoting rich structural and dynamic heterogeneity in the PS-3H4S electrolyte. Upon the incorporation of an ionic liquid, interconnected rod-like ion channels, which allow the decoupling of ion relaxation from polymer relaxation, are formed in the stiff motif of the polymeric domains passivated by interfacial ionic layers. This results in accelerated proton hopping through the glassy polymer matrix, and proton hopping becomes more pronounced at cryogenic temperatures down to -35 °C. The PS-3H4S/ionic liquid composite electrolytes exhibit a high ionic conductivity of 10^-3 S cm^-1 and high storage modulus of ≈100 MPa at 25 °C, and can be successfully applied in soft actuators and lithium-metal batteries.

Decoupling Ion Transport and Matrix Dynamics to Make High Performance Solid Polymer Electrolytes

Transport of ions through solid polymeric electrolytes (SPEs) involves a complicated interplay of ion solvation, ion-ion interactions, ion-polymer interactions, and free volume. Nonetheless, prevailing viewpoints on the subject promote a significantly simplified picture, likening ion transport in a polymer to that in an unstructured fluid at low solute concentrations. Although this idealized liquid transport model has been successful in guiding the design of homogeneous electrolytes, structured electrolytes provide a promising alternate route to achieve high ionic conductivity and selectivity. In this perspective, we begin by describing the physical origins of the idealized liquid transport mechanism and then proceed to examine known cases of decoupling between the matrix dynamics and ionic transport in SPEs. Specifically we discuss conditions for "decoupled" mobility that include a highly polar electrolyte environment, a percolated path of free volume elements (either through structured or unstructured channels), high ion concentrations, and labile ion-electrolyte interactions. Finally, we proceed to reflect on the potential of these mechanisms to promote multivalent ion conductivity and the need for research into the interfacial properties of solid polymer electrolytes as well as their performance at elevated potentials.

The effect of explicit polarity on the conformational behavior of a single polyelectrolyte chain

In this work using dissipative particle dynamics simulations with explicit treatment of polar species we demonstrate that the molecular nature of dielectric media has a significant impact on swelling and collapse of a polyelectrolyte chain in a dilute solution. We show that the small-scale effects related to the presence of polar species lead to the intensification of the electrostatic interactions when the charges are close to each other and/or their density is high enough. As a result, the electrostatic strength , usually regarded as the main parameter governing the polyelectrolyte chain collapse, does not have a universal meaning: the value of λ at which the coil-to-globule transition occurs is found to be dependent on the specific fixed value of the solvent bulk permittivity ε while varying the monomer unit charge Q and vice versa. This effect is observed even when the backbone and the counterions have the same polarity as the solvent beads, i.e. no dielectric mismatch is present. The reason for such behavior is rationalized in terms of the "effective" dielectric permittivity ε^eff which depends on the volume fraction φ of charged units inside the polymer chain volume; using ε^eff instead of ε collapses all data onto one master curve describing the chain shrinking with λ. Furthermore, it is shown that a polar chain adopts less swollen conformations in the polyelectrolyte regime and collapses more easily compared to a non-polar chain.

Unraveling the Role of Neutral Units for Single-Ion Conducting Polymer Electrolytes

With the cationic transference number close to unity, single-ion conducting polymer electrolytes (SICPEs) are recognized as an advanced electrolyte system with improved energy efficiency for battery application. The relatively low ionic conductivity for most of the SICPEs in comparison with liquid electrolytes remains the major "bottleneck" for their practical applications. Polyethylene oxide (PEO) has been recognized as a benchmark for solid polymer electrolytes due to its high salt solubility and reasonable ionic conductivity. PEO has two advantages: (i) the polar ether groups coordinate well with lithium ions (Li⁺) providing good dissociation from anions, and (ii) the low T_g provides fast segmental dynamics at ambient temperature and assists rapid charge transport. These properties lead to active use of PEO as neutral plasticizing units in SICPEs. Herein, we present a detailed comparison of new SICPEs copolymerized with PEO units vs SICPEs copolymerized with other types of neutral units possessing either flexible or polar structures. The presented analysis revealed that the polarity of side chains has a limited influence on ion dissociation for copolymer-type SICPEs. The Li⁺-ion dissociation seems to be controlled by the charge delocalization on the polymerized anion. With good miscibility between plasticizing neutral units and ionic conductive units, the ambient ionic conductivity of synthesized SICPEs is still mainly controlled by the T_g of the copolymer. This work sheds light on the dominating role of PEO in SICPE systems and provides helpful guidance for designing polymer electrolytes with new functionalities and structures. Furthermore, based on the presented results, we propose that designing polyanions with a highly delocalized charge may be another promising route for achieving sufficient lithium ionic conductivity in solvent-free SICPEs.

Relationship between Ionic Conductivity, Glass Transition Temperature, and Dielectric Constant in Poly(vinyl ether) Lithium Electrolytes

We report a partial elucidation of the relationship between polymer polarity and ionic conductivity in polymer electrolyte mixtures comprising a homologous series of nine poly(vinyl ether)s (PVEs) and lithium bis(trifluoromethylsulfonyl)imide. Recent simulation studies have suggested that low dielectric polymer hosts with glass transition temperatures far below ambient conditions are expected to have ionic conductivity limited by salt solubility and dissociation. In contrast, high dielectric hosts are expected to have the potential for high ion solubility but slow segmental dynamics due to strong polymer-polymer and polymer-ion interactions. We report results for PVEs in the low polarity regime with dielectric constants of about 1.3 to 9.0. Ionic conductivity measured for the PVE and salt mixtures ranged from about 10^-10 to 10^-3 S/cm. In agreement with the predictions from computer simulations, the ionic conductivity increased with dielectric constant and plateaued as the dielectric approached 9.0, comparable to the dielectric constant of the widely used poly(ethylene oxide).

Theory of ionic conductivity with morphological control in polymers

We present a general theory of ionic conductivity in polymeric materials consisting of percolated ionic pathways. Identifying two key length scales corresponding to inter-path permeation distance ξ and one-dimensional hopping conduction path length mλ, we have derived closed-form formulas in terms of the energy U required to unbind a conductive ion from its bound state and the partition ratio ξ/mλ between the three-dimensional permeation and one-dimensional hopping pathways. The results provide design strategies to significantly enhance ionic conductivity in single-ion conductors. For large barriers to dissociate an ion, corrections to the Arrhenius law are presented. The predicted dependence of ionic conductivity on the unbinding time is in agreement with results in the literature based on simulations and experiments. This theory is generally applicable to conductive systems where the two mechanisms of permeation and hopping occur concurrently.

Molecular Characterization of Polymer Networks

Polymer networks are complex systems consisting of molecular components. Whereas the properties of the individual components are typically well understood by most chemists, translating that chemical insight into polymer networks themselves is limited by the statistical and poorly defined nature of network structures. As a result, it is challenging, if not currently impossible, to extrapolate from the molecular behavior of components to the full range of performance and properties of the entire polymer network. Polymer networks therefore present an unrealized, important, and interdisciplinary opportunity to exert molecular-level, chemical control on material macroscopic properties. A barrier to sophisticated molecular approaches to polymer networks is that the techniques for characterizing the molecular structure of networks are often unfamiliar to many scientists. Here, we present a critical overview of the current characterization techniques available to understand the relation between the molecular properties and the resulting performance and behavior of polymer networks, in the absence of added fillers. We highlight the methods available to characterize the chemistry and molecular-level properties of individual polymer strands and junctions, the gelation process by which strands form networks, the structure of the resulting network, and the dynamics and mechanics of the final material. The purpose is not to serve as a detailed manual for conducting these measurements but rather to unify the underlying principles, point out remaining challenges, and provide a concise overview by which chemists can plan characterization strategies that suit their research objectives. Because polymer networks cannot often be sufficiently characterized with a single method, strategic combinations of multiple techniques are typically required for their molecular characterization.

Light-Switchable and Self-Healable Polymer Electrolytes Based on Dynamic Diarylethene and Metal-Ion Coordination

Self-healing polymer electrolytes are reported with light-switchable conductivity based on dynamic N-donor ligand-containing diarylethene (DAE) and multivalent Ni²⁺ metal-ion coordination. Specifically, a polystyrene polymer grafted with poly(ethylene glycol-r-DAE)acrylate copolymer side chains was effectively cross-linked with nickel(II) bis(trifluoromethanesulfonimide) (Ni(TFSI)₂) salts to form a dynamic network capable of self-healing with fast exchange kinetics under mild conditions. Furthermore, as a photoswitching compound, the DAE undergoes a reversible structural and electronic rearrangement that changes the binding strength of the DAE-Ni²⁺ complex under irradiation. This can be observed in the DAE-containing polymer electrolyte where irradiation with UV light triggers an increase in the resistance of solid films, which can be recovered with subsequent visible light irradiation. The increase in resistance under UV light irradiation indicates a decrease in ion mobility after photoswitching, which is consistent with the stronger binding strength of ring-closed DAE isomers with Ni²⁺. ¹H-¹⁵N heteronuclear multiple-bond correlation nuclear magnetic resonance (HMBC NMR) spectroscopy, continuous wave electron paramagnetic resonance (cw EPR) spectroscopy, and density functional theory (DFT) calculations confirm the increase in binding strength between ring-closed DAE with metals. Rheological and in situ ion conductivity measurements show that these polymer electrolytes efficiently heal to recover their mechanical properties and ion conductivity after damage, illustrating potential applications in smart electronics.

Glass Transition Temperature and Ion Binding Determine Conductivity and Lithium-Ion Transport in Polymer Electrolytes

Polymer electrolytes with high Li⁺-ion conductivity provide a route toward improved safety and performance of Li⁺-ion batteries. However, most polymer electrolytes suffer from low ionic conduction and an even lower Li⁺-ion contribution to the conductivity (the transport number, t₊), with the anion typically transporting over 80% of the charge. Here, we show that subtle and potentially undetected associations within a polymer electrolyte can entrain both the anion and the cation. When removed, the conductivity performance of the electrolyte can be improved by almost 2 orders of magnitude. Importantly, while some of this improvement can be attributed to a decreased glass transition temperature, T_g, the removal of the amide functional group reduces interactions between the polymer and the Li⁺ cations, doubling the Li⁺ t₊ to 0.43, as measured using pulsed-field-gradient NMR. This work highlights the importance of strategic synthetic design and emphasizes the dual role of T_g and ion binding for the development of polymer electrolytes with increased total ionic conductivity and the Li⁺ ion contribution to it.

The role of anions in light-driven conductivity in diarylethene-containing polymeric ionic liquids

The role of anion character in the photostationary state, magnitude of conductivity, and light-responsive properties of diarylethene-containing polymeric ionic liquids was investigated.

Effects of Solvent Polarity on Li-ion Diffusion in Polymer Electrolytes: An All-Atom Molecular Dynamics Study with Charge Scaling

We herein report an all-atom molecular dynamics study on the role of solvent polarity for Li+ diffusion in polymer electrolytes using PEO-LiTFSI (poly(ethylene oxide)-lithium bis(trifluoromethane)sulfonimide) as a model system. By separating the effect of Tg and the effect of solvent polarity in our simulations, we show that the maximum in the diffusion coefficient of Li+ with respect to the dielectric constant of polymer solvent εp is due to transitions in the transport mechanism. In particular, it is found that the frequent interchain hopping involves the coordination of both PEO and TFSI. This optimal solvating ability of PEO at an intermediate value of εp leads to the fast ion conduction. These findings highlight the synergetic effect of solvent polarity and bond polarity on Li-ion diffusion in solid polymer electrolytes.