Ionic liquid mediated magnesium ion conduction in poly(ethylene oxide) based polymer electrolyte

Magnesium ion conduction in poly(ethylene oxide) (PEO) based polymer electrolyte incorporated with room temperature ionic liquid (RTIL) is reported. The electrolyte films comprise the PEO complexed with magnesium trifluoromethanesulfonate (or magnesium triflate) added with different amount of ionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf). The polymer electrolyte with ∼50 wt.% of ionic liquid offers a maximum electrical conductivity of ∼5.6 × 10⁻⁴ S cm⁻¹ at room temperature (∼25 °C) with improved thermal and electrochemical stabilities. The Mg²⁺ ion conduction in the PEO-complex is confirmed from cyclic voltammetry, impedance and transport number measurements. A significant increase in the Mg²⁺ ion transport number (tMg2+) is observed with increasing content of the ionic liquid in PEO–Mg salt complex and the maximum value is obtained to be ∼0.45 for ∼50 wt.% of ionic liquid. The interaction of imidazolium cations with ether oxygen of PEO, as evidenced from FTIR and Raman studies, play an important role in the substantial enhancement in the tMg2+ value.     

Effect of a novel amphipathic ionic liquid on lithium deposition in gel polymer electrolytes

A novel dimeric ionic liquid based on imidazolium cation and bis(trifluoromethanesulfonyl) imide (TFSI) anion has been synthesized through a metathesis reaction. Its chemical shift values and thermal properties are identified via ¹H nuclear magnetic resonance (NMR) imaging and differential scanning calorimetry (DSC). The effect of the synthesized dimeric ionic liquid on the interfacial resistance of gel polymer electrolytes is described. Differences in the SEM images of lithium electrodes after lithium deposition with and without the 1,1′-pentyl-bis(2,3-dimethylimidazolium) bis(trifluoromethane-sulfonyl)imide (PDMITFSI) ionic liquid in gel polymer electrolytes are clearly discernible. This occurs because the PDMITFSI ionic liquid with hydrophobic moieties and polar groups modulates lithium deposit pathways onto the lithium metal anode. Moreover, high anodic stability for a gel polymer electrolyte with the PDMITFSI ionic liquid was clearly observed.     

Effect of zwitterionic salt on the electrochemical properties of a solid polymer electrolyte with high temperature stability for lithium ion batteries

In this study, we prepare a kind of solid polymer electrolyte (SPE) based on N-ethyl-N′-methyl imidazolium tetrafluoroborate (EMIBF₄), LiBF₄ and poly(vinylidene difluoride-co-hexafluoropropylene) [P(VdF-HFP)] copolymer. The resultant SPE displays high thermal stability above 300 °C and high room temperature ionic conductivity near to 10⁻³ S cm⁻¹. Its electrochemical properties are improved with incorporation of a zwitterionic salt 1-(1-methyl-3-imidazolium)propane-3-sulfonate (MIm3S). When the SPE contains 1.0 wt% of the MIm3S, it has a high ionic conductivity of 1.57 × 10⁻³ S cm⁻¹ at room temperature, the maximum lithium ions transference number of 0.36 and the minimum apparent activation energy for ions transportation of 30.9 kJ mol⁻¹. The charge-discharge performance of a Li₄Ti₅O₁₂/SPE/LiCoO₂ cell indicates the potential application of the as-prepared SPE in lithium ion batteries.     

Proton conducting membrane containing room temperature ionic liquid

A new proton conducting membrane containing room temperature ionic liquid: 2,3-dimethyl-1-octylimidazolium trifluoromethanesulfonylimide (DMOImTFSI) and polyvinylidenefluoride-co-hexafluoropropylene (PVdF-HFP) has been developed in the present work. The addition of bis(trifluoromethanesulphonyl)imide (HN(CF₃SO₂)₂) to this membrane results in an increase in conductivity by one order of magnitude at 25 °C. The membrane shows a conductivity of 2.74 × 10⁻³ S/cm at 130 °C along with good mechanical stability. The membrane was tested in a commercial fuel cell test station at 100 °C with dry hydrogen and oxygen gas reactants using Pt/C electrodes. The membrane containing the ionic liquid has been found to be electroactive for hydrogen oxidation and oxygen reduction at the platinum electrode and can be developed for use in proton exchange membrane fuel cell (PEMFC) under non-humid conditions at elevated temperatures.     

Symmetric lithium-ion cell based on lithium vanadium fluorophosphate with ionic liquid electrolyte

Lithium vanadium fluorophosphate, LiVPO₄F, was utilized as both cathode and anode for fabrication of a symmetric lithium-ion LiVPO₄F//LiVPO₄F cell. The electrochemical evolution of the LiVPO₄F//LiVPO₄F cell with the commonly used organic electrolyte LiPF₆/EC-DMC has shown that this cell works as a secondary battery, but exhibits poor durability at room temperature and absolutely does not work at increased operating temperatures. To improve the performance and safety of this symmetric battery, we substituted a non-flammable ionic liquid (IL) LiBF₄/EMIBF₄ electrolyte for the organic electrolyte. The symmetric battery using the IL electrolyte was examined galvanostatically at different rates and operating temperatures within the voltage range of 0.01–2.8 V. It was demonstrated that the IL-based symmetric cell worked as a secondary battery with a Coulombic efficiency of 77% at 0.1 mA cm⁻² and 25 °C. It was also found that the use of the IL electrolyte instead of the organic one resulted in the general reduction of the first discharge capacity by about 20–25% but provided much more stable behavior and a longer cycle life. Moreover, an increase of the discharge capacity of the IL-based symmetric battery up to 120 mA h g⁻¹ was observed when the operating temperature was increased up to 80 °C at 0.1 mA cm⁻². The obtained electrochemical behavior of both symmetric batteries was confirmed by complex-impedance measurements at different temperatures and cycling states. The thermal stability of LiVPO₄F with both the IL and organic electrolytes was also examined.     

Effect of cation structure on the electrochemical and thermal properties of ion conductive polymers obtained from polymerizable ionic liquids

Several onium cations having vinyl group formed ionic liquids after coupling with bis(trifluoromethanesulfonyl)imide. These monomers were polymerized, and the relation between onium cation structure and properties of thus polymerized ionic liquids was investigated. The polymerized ionic liquid having ethylimiadzolium cation unit showed the highest ionic conductivity of around 10⁻⁴ S cm⁻¹ at 30 °C among the obtained polymers reflecting the lowest glass transition temperature of −59 °C. These polymers were thermally stable and their decomposition temperatures were about 350 °C. The ionic conductivity of the polymerized ionic liquids decreased by both the addition of lithium bis(trifluoromethanesulfonyl)imide and the polymerization in the presence of cross-linker. However, the polymerized ionic liquid having 1-methylpiperidinium cation structure showed good lithium ion transference number of 0.43 at room temperature.     

Ionic conductivities of solid polymer electrolyte/salt systems for lithium secondary battery

We establish a new ionic conductivity model based on the Nernst-Einstein equation in which the diffusion coefficient is derived from modified double lattice-nonrandom-Pitzer-Debye-Hückel (MDL-NR-PDH) model. The proposed model takes into account the mobility of the salt and the motion of the polymer host simultaneously by expressing the effective chemical potential as the sum of chemical potentials of the salt and the polymer. To describe the segmental motion of the polymer chain, which is the well-known conduction mechanism for solid polymer electrolyte (SPE) systems, the effective co-ordinated unit parameter is introduced. The obtained co-ordinated unit parameter for each state is used to describe the behavior of the ionic conductivities of the given systems. Good agreement is obtained upon comparison with experimental data of various PEO and salt systems in the interested ranges.     

Improved ionic conductivity of nitrile rubber/ionic liquid composites

Polymer electrolytes with high ionic conductivity and good elasticity were prepared by mixing nitrile rubber (poly(acrylonitrile-co-butadiene) rubber; NBR) with ionic liquid, N-ethylimidazolium bis(trifluoromethanesulfonyl)imide (EImTFSI). The NBR/EImTFSI composites were obtained as homogeneous and transparent films when the ionic liquid content was less than 60 wt%. Raman spectroscopy suggested the interaction between nitrile group of NBR and TFSI anion. Sample with ionic liquid content of 50 wt% showed the ionic conductivity of 1.2×10⁻⁵ S cm⁻¹ at 30 °C. Addition of lithium salt to this NBR/EImTFSI composite further enhanced the ionic conductivity to about 10⁻⁴ S cm⁻¹ without spoiling mechanical properties. DSC studies showed two glass transition temperatures for composites indicating microphase separation.     

聚合物基镁离子固态电解质的研究进展Q

镁离子电池因其比容量高、资源丰富、环境友好、安全性高(无枝晶)等优势,在储能电池领域脱颖而出.然而,镁金属负极在液态电解质中易钝化,导致其电化学性能不佳.因此,开发高效适用的固态电解质对实现高性能、实用化镁离子电池至关重要.聚合物电解质具有优异的机械稳定性、电化学稳定性、热稳定性且离子电导率高、成本低.但镁离子较高的电荷密度和较强的溶剂化作用限制了其在固态电解质中的解离与扩散.从纯固态聚合物电解质、凝胶聚合物电解质、复合聚合物电解质3个方面综述了国内外聚合物基镁离子固态电解质的离子电导率对解决镁金属负极钝化效应的贡献及其应用研究进展,指出聚合物基镁离子固态电解质当前面临的挑战并对其研究方向进行了建议和展望.     

Enhanced high-temperature polymer electrolyte membrane for fuel cells based on polybenzimidazole and ionic liquids

Polybenzimidazole (PBI)/ionic liquid (IL) composite membranes were prepared from an organosoluble, fluorine-containing PBI with ionic liquid, 1-hexyl-3-methylimidazolium tri?uoromethanesulfonate (HMI-Tf). PBI/HMI-Tf composite membranes with different HMI-Tf concentrations have been prepared. The ionic conductivity of the PBI/HMI-Tf composite membranes increased with both the temperature and the HMI-Tf content. The composite membranes achieve high ionic conductivity (1.6 × 10⁻² S/cm) at 250 °C under anhydrous conditions. Although the addition of HMI-Tf resulted in a slight decrease in the methanol barrier ability and mechanical properties of the PBI membranes, the PBI/HMI-Tf composite membranes have demonstrated high thermal stability up to 300 °C, which is attractive for high-temperature (>200 °C) polymer electrolyte membrane fuel cells.     

提高凝胶电解质电导率的最新研究进展

综述了一种新型功能高分子材料——凝胶电解质近几年来的研究进展.说明了凝胶电解质的类型:固态聚合物电解质、凝胶聚合物电解质、复合凝胶聚合物电解质.重点阐述了提高凝胶电解质导电性能的方法.主要包括:采用电导率高和化学稳定性高的锂盐,采用交联、共聚和共混等方法对分子结构进行改性,降低结晶性能,添加增塑剂,添加无机填料等.并预...     

Li NMR spectroscopy and ion conduction mechanism of composite gel polymer electrolyte: A comparative study with variation of salt and plasticizer with filler

Microporous composite gel polymer electrolyte (CGPE) has been prepared by incorporating the home-made silica aerogel (SAG) particles into the poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer/LiClO₄ matrix. The ionic transport behavior of the electrolyte is studied with various experimental techniques such as AC impedance, X-ray diffraction (XRD), infrared (IR) spectra, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA), etc. The results reveal that the SAG particles are well dispersed in the electrolytes and incorporate with the other components of the CGPEs. The solid-state ⁷Li NMR study has confirmed the interactions of lithium ion with SAG, polymer and plasticizers, causing to form the microporous structure and reduce the glass transition temperature and crystallinity, resulting in an increase in ionic conductivity of the CGPE. The best ionic conductivity (1.04 × 10⁻² S/cm at room temperature) is obtained from the composite polymer electrolyte containing 4 wt% of SAG, which is approximately four times higher than the ionic conductivity of the electrolyte without the filler.     

Ionic liquid mediated nano-composite polymer gel electrolyte for rechargeable battery application

ABSTRACT

Nano-composite polymer gel electrolytes (NPGEs) based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP, ionic liquid, 1-butyl-3- methylimidazolium bis(trifluoromethanesulfonyl)imide BMIMTFSI, Li-salt along with the addition of SiO₂ nanoparticles have been synthesized and characterized by various techniques. Prepared NPGEs show high room temperature ionic conductivity (~10^?3 S/cm) and have a wide electrochemical window (ECW) (~3.3–3.5 V). The galvanostatic charge/discharge profile was studied by sandwiching best performing NPGEs between a LiFePO₄ cathode and lithium metal anode. The specific discharge capacity of the cell (Li/NPGE/LiFePO₄) room temperature at 0.1C rate is found to be 138 mAh/g.     

Ionic conductivity enhancement of the plasticized PMMA/LiClO4 polymer nanocomposite electrolyte containing clay

This work has demonstrated that the addition of an optimum content of dimethyldioctadecylammonium chloride (DDAC)-modified montmorillonite clay (Dclay) enhances the ionic conductivity of the plasticized poly(methyl methacrylate)-based electrolyte by nearly 40 times higher than the plain system. Specific interactions among silicate layer, carbonyl group (CO) and lithium cation have been investigated using Fourier-transform infrared (FTIR), solid-state NMR, alternating current impedance. The FTIR characterization confirms that both of the relative fractions of ‘complexed’ CO sites and ‘free’ anions increase with the increase of the Dclay content, indicating that strong interaction exists between the CO group and the lithium salt. In addition, the solid-state NMR demonstrates that the interaction between the PMMA and the clay mineral is insignificant. The addition of clay mineral promotes the dissociation of the lithium salt and thus, the specific interaction can be enhanced between the CO and the free lithium cation. However, the balanced attractive forces among silicate layers, CO groups, lithium cations and anions is critical to result in the higher ionic conductivity.     

Polymer electrolyte with large temperature-dependent conductivity for novel electrochromic imaging

Novel polymer electrolyte aimed for space-selective electrochromic imaging was prepared with poly(vinylbutyral) (PVB), poly(ethyleneglycole) (PEG2000) and tetrabutylammonium perchlorate (TBAP). A spreading of the electrochromic image is a shortcoming when the electrochromic image is space-selectively formed by electrochemical reaction. This is due to a cell formation between colored and uncolored parts through ionic conductor. In order to inhibit the spreading, it would be effective to apply a polymer electrolyte with very low ionic conductivity at room temperature to the imaging system. On this basis, the present electrolyte was designed to have large difference in ionic conductivity between high and low temperatures. Namely, this polymer electrolyte enables writing and erasing at high temperature due to high ionic conductivity, and the image is expected to be preserved without change at ambient temperature due to very low ionic conductivity. The thermal and conductive properties of the polymer electrolyte were analyzed. Further, space-selective electrochromic image was formed on the device with the present polymer electrolyte at 100 °C, and was revealed to be stable without change for more than a week when the device was kept at 20 °C.     

Electrochemical properties of Li ion polymer battery with gel polymer electrolyte based on polyurethane

Gel polymer electrolyte (GPE) was prepared using polyurethane acrylate as polymer host and its performance was evaluated. LiCoO₂/GPE/graphite cells were prepared and their electrochemical performance as a function of discharge currents and temperatures was evaluated. The precursor containing a 5 vol % curable mixture had a viscosity of 4.5 mPa s. The ionic conductivity of the GPE at 20 °C was about 4.5 × 10^–3 S cm^–1. The GPE was stable electrochemically up to a potential of 4.8 V vs Li/Li⁺. LiCoO₂/GPE/graphite cells showed a good high rate and low-temperature performance. The discharge capacity of the cell was stable with charge–discharge cycling.     

Study of ionic conductivity and microstructure of a cross-linked polyurethane acrylate electrolyte

A cross-linked polyurethane acrylate (PUA) was synthesized by end capping 4,4′-methylene bis(cyclohexyl isocyanate), H₁₂MDI/poly-(ethylene glycol), PEG based prepolymer with hydroxy ethyl acrylate (HEA). Significant interactions of the Li⁺ ions with the soft and hard segments of the host polymer have been observed for the PUA complexed with lithium perchlorate (LiClO₄) by means of differential scanning calorimetry (DSC), Fourier transform infra-red (FTIR) spectroscopy, ⁷Li magic angle spinning (MAS) NMR measurements and thermogravimetric analysis (TGA). The ⁷Li MAS NMR investigation of the PUA indicates the presence of at least three distinct Li⁺ sites at lower temperature, which merge to a single one at higher temperature in similar line with uncross-linked polyurethane. The results of TGA, DSC and FTIR spectroscopy support the formation of different types of complexes by the interaction of the Li⁺ ions with different coordination sites of PUA. No detectable interactions could be observed between Li⁺ ions and groups in HEA. The DSC data indicates the formation of transient cross-links with the ether oxygens of the soft segment and mixing of soft and hard phases induced by the Li⁺ ions. In addition, a Vogel-Tamman-Fulcher (VTF) like temperature dependence of ionic conductivity implies coupling of the ion movement with the segmental motion of the polymer chains in the cross-linked environment. Predominant formation of contact ion pairs of LiClO₄ has been consistently observed through AC conductivity, DSC and NMR spectroscopic results. Swelling measurements of PUA with plasticizers reveal the improved dimensional stability for these cross-linked PUA in comparison with uncross-linked polyurethane.     

Ion transport properties of lithium ionic liquids and their ion gels

A new series of lithium ionic liquids were prepared by introducing of two electron-withdrawing trifluoroacetyl groups in borate salts containing two methoxy-oligo(ethylene oxide) groups in the structures. Successive substitution reactions of oligo-ethylene glycol monomethyl ether and trifluroacetic acid from LiBH₄ yielded the lithium salts, which were clear and colorless liquids at room temperature. The fundamental physicochemical properties, such as density, thermal property, viscosity, ionic conductivity, self-diffusion coefficients, and electrochemical stability, were measured. The lithium ionic liquids had self-dissociation ability and conducted ions even in the absence of organic solvents. New polymer electrolytes, named ‘ion gels’, were prepared by radical cross-linking reactions of a poly(ethylene oxide-co-propylene oxide)tri-acrylate macromonomer in the presence the lithium ionic liquid. An increase in the glass transition temperatures (T_g) of the ion gels was very small even with increasing lithium ionic liquid concentration, and the T_g's were lower than that of the ionic liquid itself. The ionic conductivity of the ion gels surpassed that of the lithium ionic liquid in the bulk at certain compositions.     

Evidence for enhancing charge collection efficiency with an alternative cost-effective binary ionic liquids electrolyte based dye-sensitized solar cells

To mitigate the mass transfer limitations of a highly viscous room temperature ionic liquid (RTIL) electrolyte, systematic characterizations of viscosity, ionic conductivity, apparent triiodide diffusion coefficient and photovoltaic response of an alternative cost-effective and highly conductive binary RTIL mixture of 1-ethyl-3-methylimidazolium trifluoroacetate (EMIATF) and 1-methyl-3-propylimidazolium iodide (PMII) were investigated. An emphasis was placed on the dynamics of electron transport and charge recombination processes; specifically, a focus was placed on the effective electron diffusion length and charge collection efficiency in the devices. Notably, the introduction of perfluorinated anions, with a strong delocalization of the negative charge over the anion backbone, was able to weaken the hydrogen bonding with the imidazolium cations and, thus, decrease the viscosity and increase the ionic conductivity of the electrolyte. A sealed device that employed the binary RTIL achieved an overall conversion efficiency of 5.22% under irradiation of 100 mW cm⁻², which increased the value by 30% compared to a device with a blank PMII-based RTIL electrolyte. Electrochemical impedance spectroscopy and intensity-modulated photovoltage/photocurrent spectroscopy analysis revealed that employment of this alternative binary RTIL electrolyte system was able to significantly decrease the diffusion resistance of triiodide species in the electrolyte and retard the charge recombination between the injected electrons with triiodide anions in the electrolyte, thus improving the effective electron diffusion length and charge collection efficiency in the device. The charge collection efficiency was certified to be the dominant parameter governing the short-circuit photocurrent density and the overall conversion efficiency of devices with RTIL electrolyte.     

Polyterthiophene/CNT composite as a cathode material for lithium batteries employing an ionic liquid electrolyte

A polyterthiophene (PTTh)/multi-walled carbon nanotube (CNT) composite was synthesised by in situ chemical polymerisation and used as an active cathode material in lithium cells assembled with an ionic liquid (IL) or conventional liquid electrolyte, LiBF₄/EC-DMC-DEC. The IL electrolyte consisted of 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄) containing LiBF₄ and a small amount of vinylene carbonate (VC). The lithium cells were characterised by cyclic voltammetry (CV) and galvanostatic charge/discharge cycling. The specific capacity of the cells with IL and conventional liquid electrolytes after the 1st cycle was 50 and 47 mAh g⁻¹ (based on PTTh weight), respectively at the C/5 rate. The capacity retention after the 100th cycle was 78% and 53%, respectively. The lithium cell assembled with a PTTh/CNT composite cathode and a non-flammable IL electrolyte exhibited a mean discharge voltage of 3.8 V vs Li⁺/Li and is a promising candidate for high-voltage power sources with enhanced safety.