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At least 757 records · Page 42

Review of Multifunctional Separators: Stabilizing the Cathode and the Anode for Alkali (Li, Na, and K) Metal–Sulfur and Selenium Batteries

Alkali metal batteries based on lithium, sodium, and potassium anodes and sulfur-based cathodes are regarded as key for next-generation energy storage due to their high theoretical energy and potential cost effectiveness. However, metal–sulfur batteries remain challenged by several factors, including polysulfides’ (PSs) dissolution, sluggish sulfur redox kinetics at the cathode, and metallic dendrite growth at the anode. Functional separators and interlayers are an innovative approach to remedying these drawbacks. Here we critically review the state-of-the-art in separators/interlayers for cathode and anode protection, covering the Li–S and the emerging Na–S and K–S systems. The approaches for improving electrochemical performance may be categorized as one or a combination of the following: Immobilization of polysulfides (cathode); catalyzing sulfur redox kinetics (cathode); introduction of protective layers to serve as an artificial solid electrolyte interphase (SEI) (anode); and combined improvement in electrolyte wetting and homogenization of ion flux (anode and cathode). It is demonstrated that while the advances in Li–S are relatively mature, less progress has been made with Na–S and K–S due to the more challenging redox chemistry at the cathode and increased electrochemical instability at the anode. Throughout these sections there is a complementary discussion of functional separators for emerging alkali metal systems based on metal–selenium and the metal–selenium sulfide. The focus then shifts to interlayers and artificial SEI/cathode electrolyte interphase (CEI) layers employed to stabilize solid-state electrolytes (SSEs) in metal–sulfur solid-state batteries (SSBs). The discussion of SSEs focuses on inorganic electrolytes based on Li- and Na-based oxides and sulfides but also touches on some hybrid systems with an inorganic matrix and a minority polymer phase. The review then moves to practical considerations for functional separators, including scaleup issues and Li–S technoeconomics. The review concludes with an outlook section, where we discuss emerging mechanics, spectroscopy, and advanced electron microscopy (e.g. cryo-transmission electron microscopy (cryo-TEM) and cryo-focused ion beam (cryo-FIB))-based approaches for analysis of functional separator structure–battery electrochemical performance interrelations. Finally, throughout the review we identify the outstanding open scientific and technological questions while providing recommendations for future research topics.

25 ENERGY STORAGE↗

Influence of Added Salt on Chain Conformations in Poly(ethylene oxide) Melts: SANS Analysis with Complications

Poly(ethylene oxide) (PEO)-based electrolytes have gained increasing attention in both the rechargeable battery industry and fundamental research, but any influence of the ions on the polymer conformation is not fully understood. Small-angle neutron scattering (SANS) is a powerful means to determine single-polymer chain conformations. We conducted SANS experiments on 50:50 blends of perdeuterated PEO (dPEO) and hydrogenous PEO (hPEO) of two different molecular weights (20 and 40 kDa) doped with two different salts (LiTFSI and LiClO 4 ) at various concentrations. An additional measurement with LiI is also reported. The scattering profiles of salt-doped dPEO/hPEO blends were measured, and the incoherent scattering from dPEO and hPEO doped with salt was measured separately. A strong low q upturn was observed in some of the blends and in the pure dPEO homopolymers. The statistical segment lengths of PEO–salt mixtures were derived using a Kratky analysis. The segment length decreases modestly with increasing amounts of LiTFSI but apparently first increases then decreases with added LiClO 4 . At the highest salt concentration examined (r = [Li+]/[EO] = 0.125), a roughly 10% decrease in the statistical segment length was observed in both LiTFSI and LiClO 4 -doped PEOs, for both molecular weights. This work confirms that added salt causes a contraction of the PEO chain dimensions, but the effect appears slightly weaker than reported recently. Certain difficulties in data analysis are also discussed, including the unexplained low q scattering even in pure deuterated polymers, uncertainties in background subtraction, and inappropriate application of the Debye function.

36 MATERIALS SCIENCE↗

Dual-stage K + ion intercalation in V 2 O 5 -conductive polymer composites

We reported that the incorporation of a conductive polymer into V 2 O 5 materials resulted in an increased interlayer distance of 2.2 nm, favoring K + ion storage in aqueous electrolyte. In situ X-ray diffraction showed that during charging, K + ions were first inserted into the interlayer region of V 2 O 5 through pseudocapacitive intercalation and then continued to be inserted into the [VO 6 ] bi-layer region via diffusion-limited intercalation. Furthermore, this reversible dual-stage insertion/extraction mechanism provides new battery chemistry allowing the storage of around 50% more alkali ions in the intralayer region besides van der Waals gaps.

24 POWER TRANSMISSION AND DISTRIBUTION↗

Electroconvection near an ion-selective surface with Butler–Volmer kinetics

We study the effects of interfacial kinetics on the electro-hydrodynamics of ion transport near an ion-selective surface using a combination of linear stability analysis and numerical simulation. The finite kinetics of the electrolyte–electrode interface affects the ion transfer and electroconvection in many ways. On a surface of fixed topography, such as a metal surface of slow and stable ion deposition or covered by a polymer membrane, the finite kinetics reduces the current in one-dimensional ion diffusion/migration, increases the critical voltage for the onset of the electroconvective instability, changes the dynamics of the electroconvection and the overlimiting current, and enhances the lateral ion diffusion within the interfacial layer. The first three effects are indirectly caused by the reaction kinetics and can be characterized by an effective voltage difference across the liquid electrolyte. In comparison, the last effect is controlled by a direct interplay between kinetics and nonlinear electroconvection. Scaling laws for ion transport and features of electroconvection are proposed. We also analyse the linear stability of a surface which evolves under ion deposition and find that the finite kinetics decreases the growth rate of both electroconvective and morphological instabilities and therefore modifies the wavenumber of the most unstable mode.

Mechanics↗

Dual C–H functionalization of polyolefins for covalent adaptable network formation via cooperative electrolysis

The increasing demand for carbon fibre-reinforced polymer composites with polyolefin thermoset matrices will lead to the generation of large volumes of low molecular weight waste oligomers during the fibre recovery process. To address this challenge, we present a cooperative electrolytic dual C–H bond functionalization strategy for the one-step installation of two key functional groups essential for dynamic linkages of these deconstructed oligomers. Through direct competition studies, we reveal the predominance of tertiary allylic C–H activation along the complex, branched oligomer backbone. The resulting difunctionalized oligomers form covalently adaptable networks with exceptional circularity. By establishing a sustainable pathway for upcycling deconstructed oligomers from carbon fibre-reinforced polymer fibre recovery, this strategy introduces thermoset materials derived directly from waste. Here, it advances sustainable manufacturing practices, contributing to a net-zero waste synthetic ecosystem, and highlights the prospects of mediated electrolysis in macromolecular transformations.

Electrocatalysis↗

In Situ Studies of the Swelling by an Electrolyte in Electrochemical Doping of Ethylene Glycol-Substituted Polythiophene

Organic mixed ionic electronic conductors (OMIECs) have the potential to enable diverse new technologies, ranging from biosensors to flexible energy storage devices and neuromorphic computing platforms. However, a study of these materials in their operating state, which convolves both passive and potential-driven solvent, cation, and anion ingress, is extremely difficult, inhibiting rational material design. In this report, we present a novel approach to the in situ studies of the electrochemical switching of a prototypical OMIEC based on oligoethylene glycol (oEG) substitution of semicrystalline regioregular polythiophene via grazing-incidence X-ray scattering. Here by studying the crystal lattice both dry and in contact with the electrolyte while maintaining potential control, we can directly observe the evolution of the crystalline domains and their relationship to film performance in an electrochemically gated transistor. Despite the oEG side-chain enabling bulk electrolyte uptake, we find that the crystalline regions are relatively hydrophobic, exhibiting little (less than one water per thiophene) swelling of the undoped polymer, suggesting that the amorphous regions dominate the reported passive swelling behavior. With applied potential, we observe that the π–π separation in the crystals contracts while the lamella spacing increases in a balanced fashion, resulting in a negligible change in the crystal volume. The potential-induced changes in the crystal structure do not clearly correlate to the electrical performance of the film as an organic electrochemical transistor, suggesting that the transistor performance is strongly influenced by the amorphous regions of the film.

36 MATERIALS SCIENCE↗

The impact of residual solvent on catholyte performance in solid-state batteries

All-solid-state batteries (ASSBs) are attractive due to their safety, use of the Li metal anode, high energy density, and innovative processing routes. However, high interfacial resistance, especially on the cathode side, is one of the major challenges for commercialization of ASSBs. Catholyte, either a liquid or solid, is added to lower the cathode/electrolyte interfacial resistance. In this study, we find that residual N-methylpyrrolidone solvent remaining in a PVDF/LiTFSI solid polymer catholyte after incomplete drying can dramatically lower the interfacial resistance between the Li 6.25 Al 0.25 La 3 Zr 2 O 12 electrolyte and LiNi 1/3 Mn 1/3 Co 1/3 O 2 cathode-active material. Cells with varying amounts of residual solvent are compared to optimize the residual solvent loading. With moderate residual solvent, the discharge capacity reaches 142 mA h g -1 when cycled at 25 °C and 0.5 C and the capacity retention is 60.5% after 125 cycles. Discharge capacity retention is improved at -10 °C. The conductivity of the free-standing PVDF/LiTFSI film, mimicking the PVDF/LiTFSI catholyte, verifies the role of residual NMP in the cathode. Finally, this study demonstrates the possibility of widely differing results for ASSBs when the cathode is not completely dried. Also, it provides a hint for a potential method to lower the cathode/electrolyte interfacial resistance.

25 ENERGY STORAGE↗

The Study of the Binder Poly(acrylic acid) and Its Role in Concomitant Solid–Electrolyte Interphase Formation on Si Anodes

In this work we use neutron reflectometry to study how the polymeric binder, poly(acrylic acid) (PAA), affects the in situ formation and chemical composition of the solid–electrolyte interphase (SEI) formation on a silicon anode at various states of charge. The reflectivity is correlated with electrochemical quartz crystal microbalance to better understand the viscoelastic effects of the polymer during cycling. The use of model thin films allows for a well-controlled interface between the amorphous Si surface and the PAA layer. If the PAA perfectly coats the Si surface and standard processing conditions are used, the binder will prevent the lithiation of the anode. The PAA suppresses the growth of a new layer formed at early states of discharge (open circuit voltage to 0.8 V vs Li/Li+), protecting the surface of the anode. At 0.15 V, the SEI layer underneath the PAA changes in chemical composition as indicated by an increase in the scattering length density and thickness as the layer incorporates components from the electrolyte, most likely the salt. At lithiated and delithiated states, the SEI layer changes in chemical composition and grows in thickness with delithiation and shrinks during lithiation.

36 MATERIALS SCIENCE↗

The hierarchical structure of organic mixed ionic–electronic conductors and its evolution in water

Polymeric organic mixed ionic–electronic conductors underpin several technologies in which their electrochemical properties are desirable. These properties, however, depend on the microstructure that develops in their aqueous operational environment. We investigated the structure of a model organic mixed ionic–electronic conductor across multiple length scales using cryogenic four-dimensional scanning transmission electron microscopy in both its dry and hydrated states. Four-dimensional scanning transmission electron microscopy allows us to identify the prevalent defects in the polymer crystalline regions and to analyse the liquid crystalline nature of the polymer. The orientation maps of the dry and hydrated polymers show that swelling-induced disorder is mostly localized in discrete regions, thereby largely preserving the liquid crystalline order. Therefore, the liquid crystalline mesostructure makes electronic transport robust to electrolyte ingress. Furthermore, this study demonstrates that cryogenic four-dimensional scanning transmission electron microscopy provides multiscale structural insights into complex, hierarchical structures such as polymeric organic mixed ionic–electronic conductors, even in their hydrated operating state.

36 MATERIALS SCIENCE↗

Molecular dynamics study on the interfacial properties of mixtures of monomers of polyvinylpyrrolidone (PVP)-based battery binders on graphene and graphite surfaces

This study investigates the behavior of two different mixtures of monomers of polyvinylpyrrolidone (PVP)-based battery binders, polyvinylpyrrolidone:polyvinylidene difluoride (PVP:PVDF) and polyvinylpyrrolidone:polyacrylic acid (PVP:PAA), at graphene and graphite interfaces using classical molecular dynamics simulations. The aim is to identify the best performing monomer binder blend and carbon-based material for the design of battery-optimized energy devices. The PVP:PAA monomer binder blend and graphite are found to have the best interaction energies, densification upon adsorption, and more ordered structure. The adsorption of both monomer binder blends is strongly guided by the higher affinity of PVP and PAA monomeric molecules for the surfaces compared to PVDF. The structure of adsorbed layers of PVP:PVDF monomer binder blend on graphene and graphite develops more quickly than PVP:PAA, indicating faster kinetics. This study complements a previous density functional theory study recently reported by our group and contributes to a better understanding of the nanoscopic features of relevant interfacial regions involving mixtures of monomers of PVP-based battery binders and different carbon-based materials. In conclusion, the effect of a blend of commonly used monomer binders on carbon-based materials is essential for obtaining tightly bound anode and cathode active materials in lithium-ion batteries, which is crucial for designing battery-optimized energy devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Importance of Nuclear Quantum Effects on Aqueous Electrolyte Transport under Confinement in Ti 3 C 2 MXenes

Protons display a high chemical activity and strongly affect the charge storage capability in confined interlayer spaces of two-dimensional (2D) materials. As such, an accurate representation of proton dynamics under confinement is important for understanding and predicting charge storage dynamics in these materials. While often ignored in atomistic-scale simulations, nuclear quantum effects (NQEs), e.g., tunneling, can be significant under confinement even at room temperature. Here, using the thermostatted ring polymer molecular dynamics implementation of path integral molecular dynamics (PIMD) in conjunction with the ReaxFF force field, density functional tight binding (DFTB), and NequIP neural network potential simulations, we investigate the role of NQEs on proton and water transport in bulk water and aqueous electrolytes under confinement in Ti 3 C 2 MXenes. Although overall NQEs are relatively small, especially in bulk, we find that they can alter both quantitative values and qualitative trends on both proton transport and water self-diffusion under confinement relative to classical MD predictions. Therefore, our results suggest the need for NQEs to be considered to simulate aqueous systems under confinement for both qualitative and quantitative accuracy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Study on Emulsification/Demulsification Behavior and Mechanism of Produced Liquid from Polymer Flooding on Alaska North Slope

Heavy oil reservoirs on Alaska North Slope (ANS) are unconsolidated and contain abundant clay minerals, where the first-ever field pilot is currently implemented to validate the use of polymer floods for heavy oil enhanced oil recovery (EOR). The polymer molecules and/or fine clay particles carried with the produced liquid could potentially affect the oil/water separation, which is one of the major concerns for field operators. This dissertation aims to investigate the emulsification behavior of produced liquid, understand the emulsifying mechanism, and seek an adaptive and cost-effective method to treat the produced liquid from polymer flooding. Emulsions were prepared by mechanically mixing the actual heavy oil and the produced water from the pilot site, of which the stability was investigated by bottle test method or multiple light scattering method. Drop size distribution and interfacial properties were measured via microscope and pendant drop technique to probe the stability mechanism further. Results showed that oil-continuous or water-continuous emulsion could be generated depending on the water cut, clay types, clay concentration, and polymer concentration. In the crude oil/water system, the increasing water cut triggered the phase inversion of oil-continuous emulsion to water-continuous emulsion, resulting in faster separation and lower emulsion stability. Whereas, clay particles, no matter added to the oil or water phase, resulted in an unfavorable phase inversion from the loose water-continuous emulsion to the tight oil-continuous emulsion as clay concentration increased. For all four types of clay except Ca-montmorillonite, clay particles added to water led to an earlier phase inversion and higher emulsion stability than that added to the oil. The dual function of polymer on emulsion stability was observed. On the one hand, both sheared and unsheared polymer tended to convert the oil-continuous emulsion formed in either crude oil/water system or complex crude oil/water/clay particle system to the water-continuous emulsion, acting as a weak demulsifier to accelerate the oil/water separation. On the other hand, the addition of polymer to the water-continuous emulsion could result in enhanced emulsion stability, which is primarily attributed to the increased viscosity of the continuous phase and the decreased drop size of the dispersed oil phase. Particularly, the sheared polymer had a weaker ability to stabilize the o/w emulsion than the unsheared polymer due to the lower viscosity of the sheared polymer solution resulting from the breakdown of the polymer macromolecules. As for the chemical demulsification tests, the performance of demulsifiers showed a complex dependency upon the water cut, the shearing intensity, demulsifier type and dosage, and the polymer concentration. A compound emulsion breaker, E12+E18, exhibited the most satisfactory demulsification performance despite the varied test conditions. For severe water-continuous emulsions that might require a multi-fold dosage of demulsifier, a less expensive electrolyte, KCl, was proposed to be used in combination with demulsifier E12+E18 to improve the demulsification performance. In the proposed demulsifier formula, the effectiveness of the commercial demulsifier relied on its destructive effect on the interfacial film, while the efficacy of KCl was mainly dependent on its viscosity reduction effect on the continuous phase. This dissertation illustrates that intermediate layer elimination and water clarification are the major challenges for produced liquid treatment from polymer flooding. It also provides practical and theoretical guidance in advance for the demulsification strategy of the produced liquid from the ongoing first-ever polymer flooding pilot on ANS.

Chang, Hongli↗

Polarons are probes of the dynamic nanoscale environments found in electrochemically doped π-conjugated polymers

Charge carriers (i.e., polarons) in electrochemically doped organic (semi)conductors are proposed to be regulated by several physicochemical features, including the chemical compositions and structures of the π-conjugated frameworks of the semiconductor building blocks, the chemistry of the electrolyte (considering both the salt and solvent), multiscale and time-dependent morphology variations across the material as a function of electrochemical processes, and assorted permutations of these and other factors. To address these hypotheses, we investigate the energetic, optoelectronic, chemical, and local structural properties of negative polarons (radical anions) as a function of electrochemical doping in the donor–acceptor, π-conjugated redox copolymer P(NDI2OD-T2), also referred to as N2200. A critical finding is that there is not just “one type” of polaron in electrochemically doped P(NDI2OD-T2). Rather, an ensemble of polarons exists, with the polarons having optoelectronic signatures that are defined by their nanoscale environments. Importantly, the polaron optical signatures serve as local probes for how the operando electrochemical environments are dynamically working in concert to facilitate charge transport. Collectively, the distinctive and extensive integration of theory and measurement science presented here establishes a baseline for the roles that semiconductor and electrolyte chemistries and dynamic structural features have on polarons in electrochemically doped organic semiconductors and how these factors influence the energetics and rates of polaron transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Nano Scale Poly(vinylidene chloride-co-acrylonitrile) Protection for Reversible and Stable Mg Anode Interface

This study investigates the efficacy of a polymer coating, PVdC-co-AN, in enhancing the stability and reversibility of the electrochemical Mg anode interface. Coated electrodes, immersed in a 0.25 M Mg(TFSI) 2 −0.50 M MgCl 2 /dimethoxyethane (DME) electrolyte, exhibit notable improvements. Cyclic voltammetry demonstrates consistent behavior with the coated electrode, while the uncoated electrode changes dramatically. During extended open circuit potential conditions, the coated electrode maintains much higher coulombic efficiency (93%) compared to the uncoated electrode (62%). Galvanostatic cycling test over 200 cycles further show the benefits of the PVdC-co-AN coating, decreasing the overpotential of Mg plating and improving long-term stability. The coated electrodes also demonstrate improved rate capability at higher current densities. Surface analysis reveals differences in the formation of byproducts between the coated and uncoated electrodes, indicating a more stable and uniform interface in the former. Nuclear magnetic resonance (NMR) spectroscopy suggests that the polymer influences ion mobility through tuning the solvation environments which results in better kinetics and fewer byproducts. In summary, the study affirms that the PVdC-co-AN coating significantly improves the stability and performance of Mg electrochemistry, offering a promising advancement for practical battery applications.

25 ENERGY STORAGE↗

Metal-ion deposition regulator for suppressing dendrite formation in electrochemical cells

A metal-ion deposition regulator to regulate the flux and deposition of metal ions in an electrochemical cell. The regulator containing two membranes made of a polymer and a plurality of two-dimensional porous nanosheets sandwiched between the two membranes. The regulator is capable of distributing flux of metal ions passing through the metal-ion deposition regulator and regulating the deposition of the metal ions onto the cathode or anode thereby suppressing dendrite growth in the electrochemical cell. An electrochemical cell containing an anode, a cathode, a liquid electrolyte, and a metal-ion deposition regulator. A method of making a metal-ion deposition regulator. The method includes fabricating two-dimensional porous nanosheets utilizing graphene oxide as an expendable template, and sandwiching the porous nanosheets between two membranes made of a polymer such that the nanosheets are in contact with the two membranes.

Pol, Vilas Ganpat↗

Characterizing Hygroscopic Films of Polyzwitterions in Electric Fields Using Neutron and X-ray Reflectometries: Electrostriction or Mass Loss?

Herein we study responses of thermally annealed ultrathin films deposited on silicon substrates and containing polyzwitterions to applied electric fields by using specular neutron reflectometry (NR). In particular, we applied 7 kV under vacuum at 150 °C on the films containing poly(1-(3-sulfonatopropyl)-2-vinylpyridinium) (P2VPPS) and its blends with either a deuterated ionic liquid (EMIMBF 4 - d 11 ), potassium bromide (KBr), or deuterated sodium polystyrenesulfonate (NaPSS-d 7 ). The voltage was applied over an air gap, and the in situ neutron reflectivity measurements allowed us to measure changes in the films. In all the cases, we measured decreases in thicknesses of the films, which varied up to ~8% depending on the added salt. Posteriori X-ray reflectivity (XRR) measurements on the same films at room temperature reveal that these films were highly hygroscopic, which led to the presence of water in these films. Analysis of the NR and the XRR revealed that the decrease in the thickness of the films in the neutron reflectivity experiments on heating resulted from the loss of water and the ionic liquid but not from electrostrictive effects. The in situ NR and posteriori XRR experiments revealed not only the hygroscopic nature of these films but also depth-resolved structural rearrangements due to the applied electric fields in the films containing electrolytes and polyelectrolytes. This work shows that a combination of NR and XRR can be used to distinguish between mass loss and electrostriction in films containing charged polymers such as polyzwitterions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Side chain engineering in indacenodithiophene- co -benzothiadiazole and its impact on mixed ionic–electronic transport properties

Organic semiconductors are increasingly being decorated with hydrophilic solubilising chains to create materials that can function as mixed ionic–electronic conductors, which are promising candidates for interfacing biological systems with organic electronics. While numerous organic semiconductors, including p- and n-type materials, small molecules and polymers, have been successfully tailored to encompass mixed conduction properties, common to all these systems is that they have been semicrystalline materials. Here, we explore how side chain engineering in the nano-crystalline indacenodithiophene-co-benzothiadiazole (IDTBT) polymer can be used to instil ionic transport properties and how this in turn influences the electronic transport properties. This allows us to ultimately assess the mixed ionic–electronic transport properties of these new IDTBT polymers using the organic electrochemical transistor as the testing platform. Using a complementary experimental and computational approach, we find that polar IDTBT derivatives can be infiltrated by water and solvated ions, they can be electrochemically doped efficiently in aqueous electrolyte with fast doping kinetics, and upon aqueous swelling there is no deterioration of the close interchain contacts that are vital for efficient charge transport in the IDTBT system. Despite these promising attributes, mixed ionic–electronic charge transport properties are surprisingly poor in all the polar IDTBT derivatives. Albeit a “negative” result, this finding clearly contradicts established side chain engineering rules for mixed ionic–electronic conductors, which motivated our continued investigation of this system. We eventually find this anomalous behaviour to be caused by increasing energetic disorder in the polymers with increasing polar side chain content. We have investigated computationally how the polar side chain motifs contribute to this detrimental energetic inhomogeneity and ultimately use the learnings to propose new molecular design criteria for side chains that can facilitate ion transport without impeding electronic transport.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗