Imide Salt Research Articles

Long cycle-life prototype lithium-metal all-solid-state pouch cells employing garnet-rich composite electrolyte

All-solid-state batteries (SSB) emerge as a promising candidate to exceed the performance of conventional lithium ion batteries (LIB) due to their improved energy density, durability and safety. However, very few reports have demonstrated a long-term stable cycling and safety of pouch SSB. Herein, solid state pouch cell with nominal capacity of 0.3 Ah is successfully developed employing current-collector-free thin Li metal anode, double-sided composite LiFePO 4 cathode, and garnet-rich composite solid electrolyte (CSE) containing a doping of Li 7 La 3 Zr 1.75 Nb 0.25 O 12 garnet in a ratio 1:1 relative to poly(ethylene oxide) (PEO) host polymer, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. All-solid-state Li/CSE/LiFePO 4 prototype pouch cells tested under 0.2C/0.5C protocol at 60°C exhibit long cycle life (>4,100 cycles) and excellent safety attributed to the improved electrochemical properties, thermal and mechanical stability of the garnet-rich CSE. To the best of our knowledge, this is the longest lifetime up to date reported for bulk Li metal SSB. These outstanding results may pave the way for industrial development of advanced Li metal SSB towards practical application.

Temperature and concentration dependence of the ionic transport properties of poly(ethylene oxide) electrolytes

Even though batteries operate at different temperatures depending on their use and state of charge, little work has been done to understand the effects of temperature on the ionic transport properties of the electrolyte. The temperature dependence of these properties is important for predicting how the performance of the battery will change as a function of temperature, along with gaining fundamental insights into the underpinnings of ion transport in these electrolytes. In this study we provide the first investigation of the effect of temperature on ionic conductivity, salt diffusion coefficient, transference number, and the thermodynamic factor of a model polymer electrolyte: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt dissolved in poly(ethylene oxide) (PEO). These properties were measured at 70, 90, and 110 °C. As expected, we see monotonic increases in conductivity and diffusion with increasing temperature. Additionally, monotonic dependencies on temperature were obtained for the transference number and the thermodynamic factor. One presumes that concentration polarization decreases with increasing temperature due to more rapid ion transport. We use concentrated solution theory to predict concentration polarization in lithium-PEO/LiTFSI‑lithium symmetric cells and thereby quantify the effect of temperature on concentration polarization.

NaFSI and NaTFSI Solutions in Ether Solvents from Monoglyme to Poly(ethylene oxide)-A Molecular Dynamics Study.

Classical molecular dynamics simulations have been performed for a series of electrolytes based on sodium bis(fluorosulfonyl)imide or sodium bis(trifluoromethylsulfonyl)imide salts and monoglyme, tetraglyme, and poly(ethylene oxide) as solvents. Structural properties have been assessed through the analysis of coordination numbers and binding patterns. Residence times for Na–O interactions have been used to investigate the stability of solvation shells. Diffusion coefficients of ions and electrical conductivity of the electrolytes have been estimated from molecular dynamics trajectories. Contributions to the total conductivity have been analyzed in order to investigate the role of ion–ion correlations. It has been found that the anion–cation interactions are more probable in the systems with NaTFSI salts. Accordingly, the degree of correlations between ion motions is larger in NaTFSI-based electrolytes.

Pragmatic Approaches to Correlate between the Physicochemical Properties of a Linear Poly(ethylene oxide)-Based Solid Polymer Electrolyte and the Performance in a High-Voltage Li-Metal Battery

Given its abundance, costs and compatibility with Li, and relatively simple processing, a poly(ethylene oxide)-based solid electrolyte (PEO-based SE) is a reasonable benchmark SE system for solid-state lithium batteries. On the basis of recent pragmatic achievements in cell design and characterization methodology, the physicochemical properties of a PEO-based SE are effectively determined as a function of lithium bis-(trifluoromethyl sulfonyl)-imide (LiTFSI) salt concentration and correlated with the performance in LiNi0.6Mn0.2Co0.2O2 (NMC622)||lithium cells. Even though higher LiTFSI concentrations decrease the crystalline phases with a plasticizing effect and soften the SE membrane, the accompanying increase in amorphous phases enhances the Li+ diffusion coefficient, as galvanostatically obtained from the Sand equation. Both the increased diffusivity of Li+ and the overall amount of charge carriers lead to improved ionic conductivities with a higher LiTFSI concentration, particularly below the melting point (Tm < 60 °C). In terms of anodic behavior, neither SE decomposition nor Al current collector dissolution is relevantly affected by the LiTFSI concentration, revealing a bulk electrolyte stability of 4.6 V vs Li|Li+ and an Al dissolution tendency as low as in LiPF6-containing liquid organic electrolytes. Finally, at an operation temperature below Tm, a higher LiTFSI concentration sensitively increases the specific capacities and Coulombic efficiencies.

Effect of microphase separation on the limiting current density in hybrid organic-inorganic copolymer electrolytes

Hybrid organic-inorganic block copolymer electrolytes are of interest to enable batteries containing lithium metal anodes. The conductive block is a standard polymer electrolyte of poly(ethylene oxide) and the mechanically rigid block is an inorganic poly(acryloisobutyl polyhedral oligomeric silsesquioxane) polymer. In this paper, we compare a poly(acryloisobutyl polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-b-poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS) triblock copolymer and a poly(ethylene oxide)-b- poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (PEO-POSS) diblock copolymer mixed with lithium bis(trifluoromethanesulfonyl)imide salt. We have experimentally measured the limiting current density in lithium symmetric cells containing hybrid organic-inorganic electrolytes at 90 °C. The cells were polarized at a large range of applied current density. The diblock copolymer electrolyte exhibited a clear plateau in cell potential at all current densities below the limiting current density. At low applied current density, the triblock copolymer electrolyte also exhibited a clear plateau in cell potential. At currents approaching the limiting current density, the triblock copolymer electrolyte exhibited an underdamped potential profile. The cell potential did not reach a plateau at current densities above the limiting current in both systems. The diblock and triblock copolymer electrolytes were fully characterized using electrochemical methods to determine the ionic conductivity, cation current fraction, salt diffusion coefficient, and open circuit voltage as a function of salt concentration. Cell potential and salt concentration as functions of position in the cell at various current densities were calculated using Newman's concentrated solution theory. The theoretical limiting current density was calculated to be the current density at which salt is depleted at the cathode. We see quantitative agreement between experimental measurements and theoretical predictions for the limiting current density in the diblock copolymer electrolyte which has an ordered structure at all salt concentrations, while the experimental limiting current density is lower than the theoretical prediction for the triblock copolymer electrolyte, which exhibits a disordered morphology at high salt concentrations.

Modifying Li+ and Anion Diffusivities in Polyacetal Electrolytes: A Pulsed-Field-Gradient NMR Study of Ion Self-Diffusion

Polyacetal electrolytes have been demonstrated as promising alternatives to liquid electrolytes and poly(ethylene oxide) (PEO) for rechargeable lithium-ion batteries; however, the relationship between polymer structure and ion motion is difficult to characterize. Here, we study structure–property trends in ion diffusion with respect to polymer composition for a systematic series of five polyacetals with varying ratios of ethylene oxide (EO) to methylene oxide (MO) units, denoted as P(xEO-yMO), and PEO. We first use 7Li and 19F pulsed-field-gradient NMR spectroscopy to measure cation and anion self-diffusion, respectively, in polymer/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt mixtures. At 90 °C, we observe modest changes in Li+ diffusivity across all polymer compositions, while anion (TFSI–) self-diffusion coefficients decrease significantly with increasing MO content. At a given reduced temperature (T – Tg), all polyacetal electrolytes exhibit faster Li+ self-diffusion than PEO. Intriguingly, P(EO-MO) and P(EO-2MO) also show slower TFSI– anion self-diffusion than PEO at a given reduced temperature. Molecular dynamics simulations reveal that shorter distances between acetal oxygen atoms (O–CH2–O) compared to ether oxygens (O–CH2–CH2–O) promote more diverse, often asymmetric, Li+ coordination environments. Raman spectra reveal that anion-rich ion clusters in P(EO-MO) and P(EO-2MO) lead to decreased anion diffusivity, which along with increased cation diffusivity, support the viability of polyacetals as high-performance polymer electrolytes.

Unveiling Interfacial Li-Ion Dynamics in Li7La3Zr2O12/PEO(LiTFSI) Composite Polymer-Ceramic Solid Electrolytes for All-Solid-State Lithium Batteries.

Unlocking the full potential of solid-state electrolytes (SSEs) is key to enabling safer and more-energy dense technologies than today's Li-ion batteries. In particular, composite materials comprising a conductive, flexible polymer matrix embedding ceramic filler particles are emerging as a good strategy to provide the combination of conductivity and mechanical and chemical stability demanded from SSEs. However, the electrochemical activity of these materials strongly depends on their polymer/ceramic interfacial Li-ion dynamics at the molecular scale, whose fundamental understanding remains elusive. While this interface has been explored for nonconductive ceramic fillers, atomistic modeling of interfaces involving a potentially more promising conductive ceramic filler is still lacking. We address this shortfall by employing molecular dynamics and enhanced Monte Carlo techniques to gain unprecedented insights into the interfacial Li-ion dynamics in a composite polymer-ceramic electrolyte, which integrates polyethylene oxide plus LiN(CF3SO2)2 lithium imide salt (LiTFSI), and Li-ion conductive cubic Li7La3Zr2O12 (LLZO) inclusions. Our simulations automatically produce the interfacial Li-ion distribution assumed in space-charge models and, for the first time, a long-range impact of the garnet surface on the Li-ion diffusivity is unveiled. Based on our calculations and experimental measurements of tensile strength and ionic conductivity, we are able to explain a previously reported drop in conductivity at a critical filler fraction well below the theoretical percolation threshold. Our results pave the way for the computational modeling of other conductive filler/polymer combinations and the rational design of composite SSEs.

Nonpolar Solvent‐based Electrolytes with a Quasi‐Solid‐State Redox Reaction for Lithium‐Sulfur Batteries

AbstractLi−S batteries are one of the most promising next‐generation batteries because of their high theoretical energy density and abundance of active material sulfur reducing the cost. However, conventional ether‐based electrolytes suffer from active material loss due to side reactions between dissolved polysulfides and Li metal anode, and consequential shuttle phenomenon. Herein, a promising concept of nonpolar solvent‐based electrolytes consisting of nonpolar solvent of 1,4‐difluorobenzene, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and chelating agent for Li+ cations, such as 15‐crown‐5 or 1,3‐dioxolane, is introduced to suppress the dissolution of polar polysulfides. Nonpolar electrolytes show a distinctive reaction mechanism that involved a quasi‐solid‐state redox reaction, compared to conventional ether‐based electrolytes. The discharge and charge process of nonpolar electrolytes include phase transitions with sparingly soluble and insoluble polysulfides. As a result, nonpolar solvent‐based electrolytes show excellent electrochemical performance, such as stable capacity retention and Coulombic efficiency of 93.1 % after 100 cycles at 30 °C.

Small dissymmetry, yet large effects on the transport properties of electrolytes based on imide salts: Consequences on performance in Li-ion batteries

To gain better insight into the influence of the anion size and symmetry on the transport properties and thermal stability of an electrolyte based on lithium (fluorosulfonyl)(trifluoromethanesulfonyl)-imide (FTFSI) salt, we performed the physical and electrochemical characterization of an electrolyte based on FTFSI incorporated in standard binary (3EC/7EMC) and ternary (EC/PC/3DMC) alkylcarbonate mixtures. By applying the Jones-Dole-Kaminsky (JDK), Eyring and Arrhenius empirical models to the electrolyte viscosity we show that the activation enthalpy and entropy energy barriers (ΔH≠,ΔS≠) for viscous flow are between 12 and 15 kJ·mol−1. They are strongly dependent on the solvent nature and are significantly lower than their symmetric anions LiFSI and LiTFSI (19–20 kJ·mol−1) in the binary mixture. Furthermore, the hydrodynamic radius, rs, calculated by JDK, and the ionicity behavior illustrated by the Walden role, showed that the FTFSI anion is outside the solvation sphere (rs > 0.6 nm) which is smaller in the case of an EC/EMC solvent base. In the 3EC/7EMC solvent mixture, LiFTFSI is less conductive than in the ternary mixture i.e., σmax = 8.9 mS cm−1 at Cmax = 1.1 mol L−1 for 3EC/7EMC and, σmax = 10.5 mS cm−1 at max = 0.7 mol L−1 for EC/PC/3DMC, due to a strong solvation and a greater association of FTFSI ions in the binary solvent mixture. The thermal stability of FTFSI based electrolytes was determined by the shift of the evaporation temperature of the volatile solvents (DMC, EMC) in the presence of salt, towards the higher temperatures. This feature is visible on the thermograms obtained by DSC both with the liquid electrolyte and with charged LMO cathodes in presence of electrolytes. The consequences of these properties on the electrochemical behavior of a graphite (Gr) half-cell, a lithium metal (Li) anode and a manganese lithium oxide (LMO) cathode demonstrated on the one hand the formation of a thick solid electrolyte interphase (SEI) on graphite that consumed a significant amount of lithium i.e., 18% of total capacity of the first charge. Furthermore, LiFTFSI delivered 95% of the initial capacity C = 360 mAh g−1 at C/10 with EC/PC/3DMC versus 91% when it was combined with 3EC/7EMC C = 348 mAh g−1, while the capacities obtained for LiTFSI in EC/PC/3DMC were the lowest (C = 275 mAh g−1) compared to those of the other salts. After 10 cycles, the capacity loss at C/20 is <2% for LiFSI and LiFTFSI with the two solvent mixtures. On the other hand, manganese dissolution from LMO as well as current collector corrosion were confirmed by post-mortem examination of opened coin cells. The incompatibility of the LMO cathode with an electrolyte based on FTFSI was confirmed by the position of the decomposition peak of charged LMO in contact with this electrolyte observed by DSC. These results demonstrate that the nature of the anion as well as the composition of the solvent considerably influence the performance of imide-based lithium salts both on the anode, but especially on the high voltage cathode.

Electrolyte Composition Effects on the Formation of the Solid Electrolyte Interphases of Li-Metal Batteries: A Molecular Dynamics Study

We will present our recent effort to develop new materials for batteries using our nanobattery model able to simulate a much smaller battery containing all the main components of an actual size battery. We are testing Li-metal anodes with sulfur- and metal-oxide-based cathodes together with highly concentrated electrolytes as well as with localized highly concentrated electrolytes. Our approach consists on performing ab initio analysis and ab initio molecular dynamics simulations in order to determine energetics properties as well as reactive force fields to perform larger scale reactive molecular dynamics simulations that eventually will allow us to evaluate prospective battery systems based on cycling stability, formation of benign solid-electrolyte interphases, interfacial stability, ion-transport and its mechanisms, electron-transfer, output voltage, current and charge thresholds, battery capacity, ion-pairing, cluster and death lithium formation, dendrite growth, capacity fading. In the present work, we use molecular dynamics simulations to model a TMP-based electrolyte comprising TMP, lithium, and bis(fluorosulfonyl)imide (LiFSI) salt, exploring the effects of salt concentration on solvation and ion transport. A statistical analysis is performed to study ion pairing, clustering, mobility, and coordination of Li-ion with and without small amounts of diluent materials.

Self-Healing Commodity Polymer Electrolytes for Reliable Li Metal Batteries

As countries worldwide pledge to decarbonize their economy, the global demand for batteries is rapidly increasing, urging the development of high-specific-energy (> 500 Wh/kg at cell level) and low-cost (< 100$/kWh at pack level) batteries.1 The safety and durability of these devices are of primary importance. Polymer electrolytes are safer than traditional liquid electrolytes, and further benefit from highly tunable structures.2 Thus, polymers can be designed to achieve desired properties, including the ability of self-healing from damages, which can greatly extend battery lifetime. While the synthesis of self-healing polymers often requires specifically designed monomers or other polymerization components, it was recently shown that commodity copolymers, based on methyl methacrylate (MMA) and n-butyl acrylate (nBA) or their derivatives, display self-healing behavior.3 The autonomous self-repair of these copolymers with certain compositions is governed by interchain van der Waals forces.Herein, this finding was exploited to prepare self-healing polymer electrolytes that ensured long-term performance of high-energy Li metal batteries. The electrolytes were based on polyethylene oxide (PEO), P(MMA-co-nBA) copolymers and Li bis(trifluoromethanesulfonyl)imide (TFSI) salt. Various structures and compositions were explored, including polymer blends and block copolymers made by atom transfer radical polymerization (ATRP) using a functionalized PEO-macroinitiator (Figure 1). The effect of polymer morphology, architecture, weight fraction of PEO and LiTFSI on electrolyte conductivity, thermal and electrochemical stability, Li transference number, mechanical strength and self-healing ability was analyzed.By recovering ionic conductivity and mechanical strength upon cracks, self-healing electrolytes can suppress the growth of dendrites that hinders the utilization of Li metal anodes.4 Moreover, the viscoelastic nature of these polymers contribute to the creation of conformal interfaces on Li metal.2 Therefore, the optimized commodity self-healing polymer electrolytes were tested in Li metal batteries, demonstrating the ability of the electrolytes to enable long-term stable cycling. In addition, tests were conducted to prove the self-repair of the electrolyte upon damaging the device.

In-situ UV cured acrylonitrile grafted epoxidized natural rubber (ACN-g-ENR) – LiTFSI solid polymer electrolytes for lithium-ion rechargeable batteries

Solid polymer electrolytes (SPEs) of newly synthesized acrylonitrile grafted epoxidized natural rubber (ACN-g-ENR) were successfully prepared with lithium bis(trifluoromethanesulfonyl)imide salt (LiTFSI) via UV curing technique. The highest ionic conductivity of the SPEs was accomplished at 40 wt% LiTFSI with conductivity value of 1.1 × 10−6 S cm−1 at room temperature. Further analysis indicates that the ion transport of the SPEs follows the VTF model. Chronoamperometry study estimated low lithium ions contribution to overall ionic conductivity (ca. 3%). A persuasive value of 2.7 V was obtained from the electrochemical stability. It is suitable to be applied in lithium-ion rechargeable batteries. An additional investigation by infrared (FTIR) spectroscopy revealed the polymer salt complexation occurred between Li+ of dopant salt with the ether group (C-O-C) oxygen of the epoxy ring. The inclusion of LiTFSI salts was decreased crystallinity, nevertheless, the glass transition temperature (Tg) and thermal stability, as well as the dynamic mechanical properties of the polymer electrolytes were enhanced. All in all, the initial electrochemical characteristics showed a promising potential of ACN-g-ENR host polymeric electrolyte to be used in lithium-ion storage energy applications.

Electrochemical properties of poly(ethylene oxide) electrolytes above the entanglement threshold

Ion transport in electrolytes depends on three transport coefficients, conductivity (κ), salt diffusion coefficient (D), and the cation transference number with respect to the solvent velocity (t+0), and the thermodynamic factor (Tf). Current methods for determining these parameters involve four separate experiments, and the coupled nature of the equations used to determine them generally results in large experimental uncertainty. We present data obtained from 64 independent polymer electrolytes comprising poly(ethylene oxide) (PEO) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. The molecular weights of PEO ranged from 5 to 275 kg mol−1; these samples are all above the entanglement threshold. We minimize the experimental uncertainty in transport and thermodynamic measurements by exploiting the fact that ion transport in entangled polymer electrolytes should be independent of molecular weight. The dependence of κ, D, t+0, and Tf as a function of salt concentration in the range 0.035 ≤ r ≤ 0.30 are presented with a 95% confidence interval, where r is the molar ratio of lithium ions to ethylene oxide monomer units. While κ, D, and Tf are all positive as required by thermodynamic constraints, there is no constraint on the sign of t+0. We find that t+0 is negative in the salt concentration range of 0.093 ≤ r ≤ 0.189.

Ion Pairing, Clustering and Transport in a LiFSI-TMP Electrolyte as Functions of Salt Concentration using Molecular Dynamics Simulations

Battery capacity is highly related to ion-pairing mechanisms in electrolytes, since a cluster formation can lead to dead Li formation, reducing the number of charge carriers and leading to capacity fading. We use molecular dynamics simulations to model an electrolyte comprising trimethyl phosphate (TMP) solvent and a lithium bis(fluorosulfonyl)imide (LiFSI) salt, exploring effects of salt concentration on solvation and ion-transport. We simulate the LiFSI-TMP electrolyte for salt concentrations of 0.7, 1.43 and 3.82 molar. A statistical analysis was performed to study ion-pairing, clustering, diffusivity, conductivity, and coordination of Li-ions, providing insights into relations between molecular structures and transport properties. Molecular structure of ionic components changes as concentration increases, from a predominant solvent separated ion pair (SSIP) and contact ion pair (CIP) to aggregate salt (AGG) and ionic cluster formation. Given the formation of the ionic cluster, the diffusion mechanism followed by Li-ions changes from a hopping/exchange to a vehicular mechanism as concentration increases; this is reflected in a decrease of ionic conductivities. Ionicity was also calculated to reveal how the ionic motion changes from an uncorrelated to a correlated one as the salt concentration increases. We also compared our results with experimental calculations performed for similar electrolyte systems.

Aluminum current collector for high voltage Li-ion battery. Part I: A benchmark study with statistical analysis

The protection of current collectors against anodic dissolution at high potential has been identified as crucial for next generation of high energy and safe lithium-ion batteries. Herein, a systematic study of the electrochemical behavior of two grades of aluminum current collectors has been performed in five representative liquid electrolytes. Analysis of electrochemical data and microscopy images have notably shown that aluminum current collectors appear to be stable up to 5 V vs. Li+/Li in the presence of the reactive LiPF6 salt whereas imide salts trigger the aluminum anodic dissolution except in ionic liquid medium. It was also observed that the grade of the tested aluminum current collectors had little impact. To support the robustness of this study dedicated to practical developments of the “5 V” Li-ion battery technology, a statistical analysis has been performed for the most corrosive electrolyte formulation (1 M LiTFSI/[EC/DMC]). These data show the anodic dissolution systematically occurs in a reproducible way whatever the sampling area of the aluminum foil.

Intrinsically Nonflammable Ionic Liquid‐Based Localized Highly Concentrated Electrolytes Enable High‐Performance Li‐Metal Batteries

AbstractThe development of high‐performance Li‐metal batteries (LMBs) requires advanced electrolytes that simultaneously possess high safety, high ionic conductivity, wide electrochemical window, and good ability to suppress Li dendrite growth. Herein an intrinsically nonflammable ionic liquid‐based localized highly concentrated electrolyte (LHCE) composed of lithium bis(fluorosulfonyl)imide (LiFSI) salt, N‐methyl‐N‐propyl‐piperidinium bis(fluorosulfonyl)imide ([PP13][FSI]) as ionic liquid solvent, and 1,1,2,2‐tetrafluoroethyl‐2,2,3,3‐tetrafluoropropylether (HFE) as diluent solvent is designed. The introduction of HFE greatly decreases the viscosity and cost of the pure ionic liquid electrolyte, improves its ionic conductivity, and enhances its ability to wet the separator surface. The Li+ solvation structure, Li deposition behavior, and formation of the solid electrolyte interphase (SEI) layer in LHCE are systematically investigated by using Raman spectroscopy, theoretical simulations, scanning electron microscopy, and X‐ray photoelectron spectroscopy. A rational mechanism is suggested for the stable SEI formation and the homogeneous Li deposition behavior. Due to its excellent ability to suppress Li dendrites, the LHCE exhibits a high average Coulombic efficiency (99.4% over 800 cycles in the Cu/Li cell), extremely stable cycling performance (10 mA cm−2 over 5000 cycles in the Li/Li symmetric cell), and excellent cycling performance and rate capability in the LMB systems of LiFePO4 (LFP)/Li and LFP/Li@Cu.

Effect of crystallization of the polyhedral oligomeric silsesquioxane block on self-assembly in hybrid organic-inorganic block copolymers with salt

We present a DSC and X-ray scattering study investigating the effect of polyhedral oligomeric silsesquioxane (POSS) block crystallinity on the self-assembly of a poly(acryloisobutyl polyhedral oligomeric silsesquioxane)-b-poly(ethylene oxide)-b-poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (POSS-PEO-POSS) triblock copolymer and poly(ethylene oxide)-b- poly(acryloisobutyl polyhedral oligomeric silsesquioxane) (PEO-POSS) diblock copolymers mixed with lithium bis(trifluoromethanesulfonyl)imide salt. The POSS block in all copolymer/salt mixture organizes into a rhombohedral crystal, similar to that of the POSS homopolymer. Semicrystalline polymer/salt mixtures favor morphologies with flat interfaces (i.e., lamellae) despite the asymmetric nature of the copolymers; PEO/salt volume fractions range from 0 to 0.85. Coexisting lamellae and hexagonally packed cylinders as well as coexisting lamellae with different domain spacings are seen in many copolymer/salt mixtures wherein the POSS block is amorphous. Morphological phase transitions in these systems are seen in the vicinity of the POSS crystallization temperature.

Effect of Added Salt on Disordered Poly(ethylene oxide)-Block-Poly(methyl methacrylate) Copolymer Electrolytes

We studied the effect of salt addition on a diblock copolymer system with a negative Flory–Huggins interaction parameter, χ, indicative of attractive interactions between the two blocks. The system studied is poly(ethylene oxide)-block-poly(methyl methacrylate) (PEO-PMMA) with added lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt. We studied two asymmetric block copolymers, PEO-PMMA(10–33) and PEO-PMMA(10–64), where the numbers refer to the molar masses of the blocks in kg mol–1. The small-angle X-ray scattering (SAXS) profiles for PEO-PMMA(10–33) were featureless at all salt concentrations. In contrast, PEO-PMMA(10–64) exhibited SAXS peaks when the salt concentration was between 0.22 ≤ m (mol Li/kg polymer) ≤ 0.44. The appearance of SAXS peaks only in PEO-PMMA(10–64) is consistent with the predictions of ionic self-consistent field theory developed by de la Cruz and co-workers, which predicts that in systems with negative χ, ordered phases are only found when the volume fraction of the ionic block is about 10%.

Spectroscopic Insight into Efficient and Stable Hole Transfer at the Perovskite/Spiro-OMeTAD Interface with Alternative Additives.

A stable and efficient carrier transfer is a prerequisite for high-performance perovskite solar cells. With optimized additives, a significantly improved charge carrier transfer can be achieved at the interface of perovskite/2,2',7,7'-tetrakis-(N,N-di-4-methoxyphenylamino)-9,90-spirobifluorene (Spiro-OMeTAD) with significantly boosted photostability. Using time-dependent spectroscopic techniques, we investigated charge carrier and mobile-ion dynamics at the perovskite/Spiro-OMeTAD interface, where the Spiro-OMeTAD contains different bis(trifluoromethanesulfonyl)imide (TFSI) salts additives (Li-TFSI, Mg-TFSI2, Ca-TFSI2). The pristine response and the dynamic changes under continuous illuminations are presented, which is correlated to the different behaviors of mobile-ion accumulations at the perovskite/Spiro interface and ascribed to the improved hole mobilities in Spiro-OMeTAD, ultimately contributing to the favorable behaviors in solar cells. It is demonstrated that the hole mobility and conductivity of hole transport layers play an important role in suppressing mobile-ion accumulation at the interfaces of solar cells. With the engineering of mixed-cation mixed-halide perovskite, optimal engineering of additives in hole transport materials is an efficient strategy. Therefore, it should be emphasized for accelerating perovskite photovoltaic commercialization.

NMR and DFT studies of the aggregation behavior of dicationic dialkyl DABCO bistriflimide salts in solution

In this study, various derivatives of 1,4-dialkyl-diazabicyclo[2.2.2]octane-1,4-diium bis(trifluoromethanesulfonyl)imide salts, [Cn.DABCO.Cn][Tf2N]2, with different alkyl groups, were synthesized and characterized by their melting points and NMR spectra. Moreover, various solutions of [C4.DABCO.C4][Tf2N]2 and [C8.DABCO.C8][Tf2N]2 salts in deuterated methanol and acetone in different concentrations were prepared. The effect of solvent polarity, concentration and charge density of the cation on the aggregation behavior of these salts were investigated using ESI-mass spectrometry, 1HNMR, DOSY NMR experiments and DFT calculations. The obtained results showed that in methanol, a protic and very polar solvent, the chemical shift of DABCO protons and the diffusion coefficient of the cation are almost independent of the concentration, except for relatively high concentrations. Thus, in this solvent and in the low concentration regime, aggregation is not favored and in high concentration small aggregates can be formed. In contrast, when dissolved in acetone, a less polar solvent, aggregates formation is favored. As a result, chemical shift of DABCO protons and diffusion coefficient of the cation in acetone are more strongly dependent on the concentration.