Oligomeric Electrolyte Research Articles

Tuning the Electrode/Electrolyte Interface Enabled by a Trifunctional Inorganic Oligomer Electrolyte Additive for Highly Stable and High-Rate Zn Anodes.

The practical application of aqueous Zn-ion batteries is still greatly hindered by the unstable Zn anode with severe Zn dendrites growth and side reactions. As it is accessible and economical, the exploitation of electrolyte additives is one of the most promising strategies to stabilize the Zn electrode/electrolyte interface. Herein, the penta-potassium triphosphate (KTPP) as a novel trifunctional electrolyte additive is introduced to tune the electrode/electrolyte interface. First, the KTPP additive can induce an ion-conducting and mechanically robust solid electrolyte interphase film to stabilize the Zn anode. Second, the KTPP can complex with Zn2+ ions to reconstitute the dissolution sheath structure of the Zn2+ ion. Finally, the K+ cations in KTPP adsorb on the tips of the Zn anode surface as a shielding film to regulate Zn2+ ion flux. As a result, Zn//Zn symmetric cells can achieve significantly prolonged cycling stability (e.g., from 1077 to 3800h at 1mA cm-2 /1 mAh cm-2 , from 256 to 2500h at 2mA cm-2 /2 mAh cm-2 ), and ultrahigh cumulative capacity of 6400/7200 mAh cm-2 at high current density (40/20mA cm-2 ). A four-layer Zn-MnO2 pouch full cell with a high capacity of 9 mAh can be constructed, showing impressive practical application potential.

Flame-retardant oligomeric electrolyte additive for self-extinguishing and highly-stable lithium-ion batteries: Beyond small molecules

Preparing both safe and high-performance lithium-ion batteries (LIBs) based on commonly used commercial electrolytes is highly desirable, yet challenging. To overcome the poor compatibility of conventional small-molecular flame-retardants as electrolyte additives for safe LIBs with graphite anodes, in this study, we propose and design a novel low-cost flame-retardant oligomer that achieves an accurate and complete reconciliation of fire safety and electrochemical performance in LIBs. Owing to the integration of phosphonate units and polyethylene glycol (PEG) chains, this oligomer, which is a phosphonate-containing PEG-based oligomer (PPO), not only endows commercial electrolytes with excellent flame retardancy but also helps stabilize the electrodes and Li-ion migration. Specifically, adding 15 wt% of PPO can reduce 70% of the self-extinguishing time and 54% of total heat release for commercial electrolytes. Moreover, LiFePO4/lithium and graphite/lithium cells as well as LiFePO4/graphite pouch full cells exhibit good long-term cycling stability.

Rate-Independent Self-Healing Double Network Hydrogels Using a Thixotropic Sacrificial Network

Tough and self-healing hydrogels can be developed by incorporating non-covalent dynamic bonds in the polymer network as reversible sacrificial bonds to dissipate energy. However, the dynamic nature of the non-covalent bonds results in strong strain rate dependency of the materials. In most applications, strain-rate independent mechanical performances are required. Developing tough self-healing hydrogels showing strain rate-independency is a challenge. In this study, we realize this by adopting the thixotropic hydrogel of an oligomeric electrolyte gelator as a brittle, though self-healing, sacrificial network of tough double network (DN) hydrogels. The hydrogels, synthesized via a facile one-pot approach, show specific features of typical double network materials, including high mechanical strength, strain softening, large mechanical hysteresis, but also self-healing and strain rate-independency. As the strain rate-independent and self-healing mechanical behavior of these novel hydrogels overcome the shortcomings of the existing DN hydrogels, these results expand the application spectrum of DN hydrogels.

Realization of an Asymmetric Non-Aqueous Redox Flow Battery through Molecular Design to Minimize Active Species Crossover and Decomposition.

This communication presents a mechanism-based approach to identify organic electrolytes for non-aqueous redox flow batteries (RFBs). Symmetrical flow cell cycling of a pyridinium anolyte and a cyclopropenium catholyte resulted in extensive capacity fade due to competing decomposition of the pyridinium species. Characterization of this decomposition pathway enabled the rational design of next-generation anolyte/catholyte pairs with dramatically enhanced cycling performance. Three factors were identified as critical for slowing capacity fade: (1) separating the anolyte-catholyte in an asymmetric flow cell using an anion exchange membrane (AEM); (2) moving from monomeric to oligomeric electrolytes to limit crossover through the AEM; and (3) removing the basic carbonyl moiety from the anolyte to slow the protonation-induced decomposition pathway. Ultimately, these modifications led to a novel anolyte-catholyte pair that can be cycled in an AEM-separated asymmetric RFB for 96 h with >95 % capacity retention at an open circuit voltage of 1.57 V.

Oligomer Electrolytes for Light-Emitting Electrochemical Cells: Influence of the End Groups on Ion Coordination, Ion Binding, and Turn-on Kinetics.

The electrolyte is an essential constituent of the light-emitting electrochemical cell (LEC), since its operating mechanism is dependent on the redistribution of mobile ions in the active layer. Recent developments of new ion transporters have yielded high-performance devices, but knowledge about the interactions between the ionic species and the ion transporters and the influence of these interactions on the LEC performance is lacking. We therefore present a combined computational and experimental effort that demonstrates that the selection of the end group in a star-branched oligomeric ion transporter based on trimethylolpropane ethoxylate has a paramount influence on the ionic interactions in the electrolyte and thereby also on the performance of the corresponding LECs. With hydroxyl end groups, the cation from the salt is strongly coordinated to the ion transporter, which leads to suppression of ion pairing, but the penalty is a hindered ion release and a slow turn-on for the LEC devices. With methoxy end groups, an intermediate coordination strength is seen together with the formation of contact ion pairs, but the LEC performance is very good with fast turn-on. Using a series of ion transporters with alkyl carbonate end groups, the ion transporter:cation coordination strength is lowered further, but the turn-on kinetics are slower than what is seen for devices comprising the methoxy end-capped ion transporter.

Solid-state polymer electrolytes for high-performance lithium metal batteries

Electrochemical cells based on alkali metal anodes are receiving intensive scientific interest as potentially transformative technology platforms for electrical energy storage. Chemical, morphological, mechanical and hydrodynamic instabilities at the metal anode produce uneven metal electrodeposition and poor anode reversibility, which, are among the many known challenges that limit progress. Here, we report that solid-state electrolytes based on crosslinked polymer networks can address all of these challenges in cells based on lithium metal anodes. By means of transport and electrochemical analyses, we show that manipulating thermodynamic interactions between polymer segments covalently anchored in the network and “free” segments belonging to an oligomeric electrolyte hosted in the network pores, one can facilely create hybrid electrolytes that simultaneously exhibit liquid-like barriers to ion transport and solid-like resistance to morphological and hydrodynamic instability.

Synthesis and ionic conductivity of siloxane based polymer electrolytes with pendant propyl acetoacetate groups

Abstract Hydrosilylation reaction of 2.4.6.8-tetrahydro-2.4.6.8-tetramethylcyclotetrasiloxane (D4 H) with allyl acetoacetate at 1:4.1 molar ratios of initial compounds in the presence of platinum hydrochloric acid (0.1 M solution in THF), Karstedt’s catalyst (Pt2[(VinSiMe2)2O]3) and platinum on the carbon have been carried out and D4 R type compounds obtained. Reaction order, rate constants and activation energies for hydrosilylation reactions in the presence of Karstedt’s catalyst have been determined. Ring-opening polymerization reaction of D4 R in the presence of catalytic amounts of powder-like potassium hydroxide has been carried out. A linear methylsiloxane oligomer with regular arrangement of propyl acetoacetate groups in the side chain has been obtained. The synthesized methylorganocyclotetrasiloxane and oligomers were studied by FTIR, 1H, 13C and 29Si NMR spectroscopy. Comb-type oligomers were characterized by gel-permeation chromatography, wide-angle X-ray diffractometry and differential scanning calorimetry. Solid oligomer electrolyte membranes have been obtained via sol–gel processes involving lithium trifluoromethylsulfonate (triflate) or lithium bis(trifluoromethylsulfonyl)imide. The specific volumetric electrical conductivity of the membranes at room temperature covers a wide range, from 10−10 to 10−4 S · cm−1, and depends on the structures of grafted anion receptors and the polymer backbones. Higher values of the specific conductivity are seen for the membranes containing triflate.

Identifying the Structural Basis for the Increased Stability of the Solid Electrolyte Interphase Formed on Silicon with the Additive Fluoroethylene Carbonate

To elucidate the role of fluoroethylene carbonate (FEC) as an additive in the standard carbonate-based electrolyte for Li-ion batteries, the solid electrolyte interphase (SEI) formed during electrochemical cycling on silicon anodes was analyzed with a combination of solution and solid-state NMR techniques, including dynamic nuclear polarization. To facilitate characterization via 1D and 2D NMR, we synthesized 13C-enriched FEC, ultimately allowing a detailed structural assignment of the organic SEI. We find that the soluble poly(ethylene oxide)-like linear oligomeric electrolyte breakdown products that are observed after cycling in the standard ethylene carbonate-based electrolyte are suppressed in the presence of 10 vol% FEC additive. FEC is first defluorinated to form soluble vinylene carbonate and vinoxyl species, which react to form both soluble and insoluble branched ethylene-oxide-based polymers. No evidence for branched polymers is observed in the absence of FEC.

Electrodeposited paint-and-varnish nickel–polymer coatings

Specific features of preparation of paint-and-varnish nickel–polymer coatings by joint cathodic electrodeposition of an amine-containing oligomeric electrolyte and nickel were studied. The coatings obtained exhibit layer-by-layer heterogeneity, with the lowest layer constituted by an intermetallic compound of nickel with iron. The coatings are characterized by higher degree of cross-linking compared to the polymer coatings without nickel. A paint-and-varnish formulation based on a nickel–polymer film-forming agent was developed for electrodeposition of corrosion- and wear-resistant coatings.

Obtainment of a metal-polymer coating via the simultaneous combination of electrodeposition on the cathode of oligomeric electrolytes and electrodeposition of metals

The example of a nickel-polymer system is used to propose a new way to obtain an original metal-polymer coating via the simultaneous (in situ) combination of electrodeposition on the cathode of oligomeric electrolytes and electrodeposition of metals. The properties, structures, and morphologies of the resultant coating were examined. It was found that the novel metal-polymer coating exhibits significantly improved protective anticorrosive capabilities and unusual hardness, while preserving its high elasticity.

Geometrical implication of ion transporters employing an ellipsoidal hollow structure in pseudo-solid electrolytes.

We demonstrate facilitated ion transport in oligomer electrolytes by introducing TiO2 hollow particles of ellipsoidal and spherical shapes. It was found that the TiO2 hollow particles of ellipsoidal shape are much more effective in constructing ionic diffusion paths for the Grotthuss mechanism, resulting in highly enhanced diffusion coefficients of ions such as I(-) and I3(-) in oligomer electrolytes. Compared to the hollow spheres of the TiO2 component, the ellipsoidal hollow particles of the TiO2 component provide 11% larger ionic diffusion coefficients, because of their geometry with a relatively small diffusion resistance. Since the facilitated ion transport can render fast redox reactions at both photo and counter electrodes, the solid state dye-sensitized solar cells employing oligomer electrolytes based on the TiO2 hollow ellipsoids exhibit highly improved photovoltaic performances including highly improved energy-conversion efficiency without destabilizing the cell.

The Effect of Ionic Liquid to Dye-Sensitized Solar Cell with Fluorinated Oligomer Electrolyte

The Effect of Ionic Liquid to Dye-Sensitized Solar Cell with Fluorinated Oligomer Electrolyte

TiO 2 hollow spheres as effective additives in oligomer electrolytes for dye-sensitized solar cells

TiO 2 hollow spheres are employed as an additive of oligomer electrolytes for dye-sensitized solar cells (DSSCs). The measurement of steady-state currents confirms that introducing TiO 2 hollow spheres can facilitate ionic diffusion in oligomer electrolytes. Even compared with conventional nanoparticle additives, the hollow spheres are more favorable to increase the diffusion coefficients of I − and I 3 − in oligomer electrolytes. Furthermore, the hollow structure with a submicron size is effective to scatter incident light and thereby enhance the light-harvesting efficiency of DSSCs. The energy-conversion efficiency of the DSSCs with TiO 2 hollow sphere additives significantly improves up to 7.22% due to the facilitated ionic diffusion and the enhanced light-harvesting efficiency.

An Ionic Transfer Investigation of Tri-Iodine of Solvent-Free Oligomeric Electrolytes in Dye-Sensitized Solar Cells

An Ionic Transfer Investigation of Tri-Iodine of Solvent-Free Oligomeric Electrolytes in Dye-Sensitized Solar Cells

Electrolyte infiltration in phosphazene-based dye-sensitized solar cells

We report here a study of phosphazene polymer and oligomer electrolyte infiltration into high surface area titanium dioxide electrodes and its effect on the performance of dye-sensitized solar cells. The effects of different cell assembly procedures on the electrochemical properties are examined, as well as the infiltration of electrolytes based on poly[bis(2-(2-methoxyethoxy)ethoxy)phosphazene] (MEEP), hexakis(2-(2-methoxyethoxy)ethoxy)cyclotriphosphazene (MEE trimer), and a linear short chain analogue into conventional titanium dioxide electrode mesoporous (nanosphere) films, microcolumns and nanowires. The effects of temperature, co-solvents, and the order of addition of the electroactive components are found to affect both the conductivity of the electrolytes and the electrochemical performance of the cells. Cross-sectional scanning electron microscopy (SEM) imaging is employed to examine the degree of electrolyte infiltration into the nanostructured electrodes as a function of filling conditions. Using these techniques, conditions are identified for achieving a high degree of pore filling by the three electrolyte systems. Increased power conversion efficiency is obtained when iodine is introduced after the heating and evacuation procedures required for maximum infiltration.

Solvation structure and gelation ability of polyelectrolytes: predictions by quantum chemistry methods and integral equation theory of molecular liquids

Abstract Solvation structure and gelation ability of novel oligomeric electrolyte poly(pyridinium-1,4-diyliminocarbonyl-1,4-phenylenemethylene chloride) (1·Cl) as well as its derivatives 1·X obtained by counterion substitution: X − = BF 4 − , PF 6 − , TFSA − , I − , SCN − , DCA − , ClO 4 − , SO 3 CF 3 − have been studied by quantum chemistry methods and integral equation theory of molecular liquids. The interaction energy, ΔE tot , between the counterions and polymer chains has been estimated in the frame of density functional theory and COSMO model. The calculations show that ΔE tot for gel forming polyelectrolytes has rather high values. For cases when gel formation is not observed experimentally, calculated ΔE tot have generally lower values. The excess chemical potential of ions (xμ ion ) in water, methanol, dimethylsulfoxide and acetonitrile at infinite dilution has been estimated by means of the integral equation theory of molecular liquids, 1D-RISM-KH. According to the xμ ion values obtained, the higher gelation ability is observed for 1·X in which counterions X − have the higher absolute values of the solvation free energies. The three-dimensional solvation structure of 1·Cl in aqueous solution has been analyzed by means of 3D-RISM-KH approach.

Mesoscopic study of dynamics and gelation ability of oligomeric electrolyte gelator with dissipative particle dynamics

Abstract The poly[pyridinium-1,4-diyl-iminocarbonyl-1,4-phenylene-methylene chloride] (1-Cl) is a novel oligomeric electrolyte gelator with notable characteristics and multi-functionalities. In this study, we investigate its structural and dynamical properties by means of the dissipative particle dynamics (DPD). The structural properties of 1-Cl in aqueous solution have been analyzed with the help of the radial distribution functions for the coarse grained model of the polymer and the solvent. Diffusion coefficient and the radius of gyration for the coarse grained polymer in solution have been calculated at various concentrations. We find that both structural and dynamical quantities change significantly when the polymer concentration becomes sufficient to form the gel.

Ionic liquids and oligomer electrolytes based on the B(CN)4− anion; ion association, physical and electrochemical properties

The role of B(CN)(4)(-) (Bison) as a component of battery electrolytes is addressed by investigating the ionic conductivity and phase behaviour of ionic liquids (ILs), ion association mechanisms, and the electrochemical stability and cycling properties of LiBison based electrochemical cells. For C(4)mpyrBison and C(2)mimBison ILs, and mixtures thereof, high ionic conductivities (3.4 ≤σ(ion)≤ 18 mS cm(-1)) are measured, which together with the glass transition temperatures (-80 ≤T(g)≤-76 °C) are found to shift systematically for most compositions. Unfortunately, poor solubility of LiBison in these ILs hinders their use as solvents for lithium salts, although good NaBison solubility offers an alternative application in Na(+) conducting electrolytes. The poor IL solubility of LiBison is predicted to be a result of a preferred monodentate ion association, according to first principles modelling, supported by Raman spectroscopy. The solubility is much improved in strongly Li(+) coordinating oligomers, for example polyethylene glycol dimethyl ether (PEGDME), with the practical performance tested in electrochemical cells. The electrolyte is found to be stable in Li/LiFePO(4) coin cells up to 4 V vs. Li and shows promising cycling performance, with a capacity retention of 99% over 22 cycles.

Investigation of PEO-Imidazole Ionic Liquid Oligomer and Polymer Electrolytes for Dye-Sensitized Solar Cells

Ionic liquid oligomer, 1-oligo(ethyleneoxide)-3-methylimidazolium salt (PEO(X)MIm) and Ionic liquid polymer, poly(1-oligo (ethylene glycol) methacrylate-3-methylimidazolium) salt (P(MOEMIm)) prepared by incorporating imidazolium ionic liquid with PEO oligomer and polymer were investigated as electrolytes for dye-sensitized solar cells (DSCs). Ionic liquid electrolytes were composed of LiI, I2, and PEO(X)MImCl or the mixture of 1-hexyl-3-methylidazolium iodide (HMImI), 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4) and PEO(X)MImCl. Quasi-solid-state electrolytes were prepared by employing the imidazole polymers P(MOEMImCl) to solidify the liquid electrolyte containing lithium iodide, iodine and ethylene carbonate (EC)/propylene carbonate (PC) mixed solvent. Ionic liquid based quasi-solid state electrolytes were prepared by solidifying the ionic liquid electrolytes containing HMImI or a binary mixture of HMImI and EMImBF4 with an ionic liquid polymer P(MOEMImCl), respectively. The influences of PEO molecular weight, polymer content, addition of alkyl ionic liquid and various anions of the ionic liquid oligomers and polymer on the ionic conductivity, apparent diffusion coefficient of the redox species in the electrolytes and the performance of solar cells were examined. The influences on the kinetic behaviors of dye regeneration and triiodide reduction reactions taken place at nanocrystalline TiO2 electrode and Pt counter-electrode, respectively, were also studied by cyclic-voltammetry and electrochemical impedance spectroscopy measurements. By using ternary ionic liquid electrolyte containing 1M lithium iodide and 0.5M iodine in the ionic liquid of the ionic liquid mixture of PEO(X)MImCl), HMImI and EMImBF4, quasi-solid-state electrolytes and ionic liquid based quasi-solid state electrolytes the photoelectron conversion efficiency of DSCs is 7.89%, 7.6% and 6.1%, respectively(AM 1.5, 100mWcm−2). These results show the potential application of PEO based ionic liquid in SCs.

Tuning of solubility and gelation ability of oligomeric electrolyte by anion exchange

To tune the miscibility of the gel-forming oligomeric electrolyte, we examined anion exchange reactions using appropriate ammonium or alkali-metal salts. Nine oligomeric electrolytes with different anions were obtained in high yields by the reactions. The solubility of these oligomeric electrolytes in organic solvents was carefully tested. Although the starting material with chloride as a counter anion was not soluble in any organic solvents, excellent miscibility and gelation ability of the oligomeric electrolytes with different anions were consequently observed with dipolar protophilic and aprotic solvents such as N,N-dimethylformamide, dimethylsulfoxide and N,N-dimethylacetamide. Furthermore, ionogels based on aliphatic ionic liquids were readily formed using the oligomer with bis(trifluoromethanesulfonyl)amide anion at a 40 g l−1 concentration. It is remarkable that the ionic conductivity of the above-mentioned ionogels is almost identical to that of neat ionic liquids, despite the significant increase in the apparent viscosity. This study shows a novel and convenient approach to gelators for multiple solvents. New oligomeric electrolytes with a number of different anions were obtained in high yields by anion exchange reactions. Although the starting material with chloride as a counter anion was not soluble in any organic solvent, the excellent miscibility and gelation ability of the oligomeric electrolytes were consequently observed with dipolar protophilic and aprotic solvents. Furthermore, the ionogels based on aliphatic ionic liquids were readily formed using the oligomer with bis(trifluoromethanesulfonyl)amide anion at a 40 g l−1 concentration.