A single cation or anion dendrimer-based liquid electrolyte

We propose here a novel liquid dendrimer-based single ion conductor as a potential alternative to conventional molecular liquid solvent-salt solutions in rechargeable batteries, sensors and actuators. A specific change from ester (-COOR) to cyano (-CN) terminated peripheral groups in generation-one poly(propyl ether imine) (G1-PETIM)-lithium salt complexes results in a remarkable switchover from a high cation (tLi+ = 0.9 for -COOR) to a high anion (tPF6- = 0.8 for -CN) transference number. This observed switchover draws an interesting analogy with the concept of heterogeneous doping, applied successfully to account for similar changes in ionic conductivity arising out of dispersion of insulator particle inclusions in weak inorganic solid electrolytes. The change in peripheral group simultaneously affects the effective ionic conductivity, with the room temperature ionic conductivity of PETIM-CN (1.9 × 10-5 Ω-1 cm-1) being an order of magnitude higher than PETIM-COOR (1.9 × 10-6 Ω-1 cm-1). Notably, no significant changes are observed in the lithium mobility even following changes in viscosity due to the change in the peripheral group. Changes in the peripheral chemical functionality directly influence the anion mobility, being lower in PETIM-COOR than in PETIM-CN, which ultimately becomes the sole parameter controlling the effective transport and electrochemical properties of the dendrimer electrolytes.

Physicochemical characterization of a new family of small alkyl phosphonium imide ionic liquids

Despite their promising properties, phosphonium based ionic liquids have attracted little attention as compared to their nitrogen-based cation counterparts. This study focuses on the properties of a family of small phosphonium imide ionic liquids, as well as the effect of lithium salt addition to these. The 6 ionic liquids were either alkyl, cyclic or nitrile functionalised phoshonium cations with bis(trifluoromethanesulfonyl)imide, NTf2, or bis(fluorosulfonyl)imide (FSI) as anion. Amongst the properties investigated were ionic conductivity, viscosity, thermal behaviour, electrochemical stability and the reversibility of electrochemical lithium cycling. All ionic liquids showed very promising properties e.g. having low transition temperatures, high electrochemical stabilities, low viscosities and high conductivities. Particularly the trimethyl phosphonium ionic liquids showed some of the highest conductivities reported amongst phosphonium ionic liquids generally. The combination of electrochemical stability, high conductivity and reversible lithium cycling makes them promising systems for energy storage devices such as lithium batteries.

Solid state lithium ion conduction in pyrrolidinium imide–lithium imide salt mixtures

The properties of the binary salt system based on mixtures of methyl ethyl pyrrolidinium bis(trifluoromethane sulfonyl) imide (P₁₂) and lithium bis(trifluoromethane sulfonyl) imide (Li imide) are reported. The lithium containing mixtures were found to be more than two orders of magnitude more conductive than the parent P₁₂ phase and the 33 mol% Li imide systems showed a solid state conductivity around 1×10⁻⁴ S/cm at 20°C. This solid state conductivity is believed to take place in plastic crystal phases of the P₁₂ compound.

Gel electrolytes based on lithium macro-anion salt

Montmorillonites are composed of aluminosilicate layers stacked one above the other, and the layer thickness is approximately 1 nm. In this work lithium modified montmorillonite (Li-MMT) was prepared and used as a lithium macro-anion salt in gel electrolytes. It was found that Li-MMT exhibited good compatibility with poly(ethylene glycol), DMSO and the ionic liquid, 1-ethyl-3-methylimidazolium dicyanamide (EMIdca), and a few of novel gel electrolytes based on Li-MMT were obtained. These gel electrolytes were investigated by X-ray powder diffraction, solid state NMR, conductivity measurements and cyclic voltammetry. High conductivities up to 10^{− 4} to 10^{− 3} S/cm at room temperature were observed with these macro-anion gel electrolytes. These gel materials were promising to be used as lithium conductive electrolytes in electrochemical devices, such as lithium batteries.

NMR and Raman studies of a novel fast-ion-conducting polymer-in-salt electrolyte based on LiCF3SO3 and PAN

We report spectroscopic results from investigations of a novel solid polymeric fast-ion-conductor based on poly(acrylonitrile), (PAN, of repeat unit [CH₂CH(CN)]_n), and the salt LiCF₃SO3 . From NMR studies of the temperature and concentration dependencies of ⁷Li- and ^lH-NMR linewidths, we conclude that significant ionic motion occurs at temperatures close to the glass transition temperature of these polymer-in-salt electrolytes, in accordance with a recent report on the ionic conductivity. In the dilute salt-in-polymer regime, however, ionic motion appears mainly to be confined to local salt-rich domains, as determined from the dramatic composition dependence of the ionic conductivity. FT-Raman spectroscopy is used to directly probe the local chemical anionic environment, as well as the Li⁺–PAN interaction. The characteristic δ_s(CF₃) mode of the CF₃SO₃⁻ anion at _~750–780 cm^−l shows that the ionic substructure is highly complex. Notably, no spectroscopic evidence of free anions is found even at relatively salt-depleted compositions (e.g. N:Li_~60–10:1). A strong Li⁺–PAN interaction is manifested as a pronounced shift of the characteristic polymer C=N stretching mode, found at _~2244 cm^−l in pure PAN, to _~2275 cm^−l for Li⁺-coordinated C=N moieties. Our proton-NMR data suggest that upon complexation of PAN with LiCF3 SO₃, the glass transition occurs at progressively lower temperatures.

Conductivity and NMR properties of plasticized polyethers complexed with lithium salts

NMR provides a tool whereby the dynamic properties of specific nuclei can be investigated. In the present study, a poly(ethylene oxide-co-propylene oxide) network has been used as the polymer host to prepare solid polymer electrolytes (SPE) containing either LiClO₄ or LiCF₃SO₃. In addition, a low molecular weight plasticizer [propylene carbonate (PC), dimethyl formamide (DMF) or tetraglyme] has been added to several of the samples to enhance the mobility of the polymer and, thus, of the ionic species. The effects of plasticizer and salt concentration on the ionic structure and mobility in these SPEs, as measured by NMR relaxation times, and correlation to the conductivity behaviour in these systems are discussed. Temperature dependent triflate diffusion coefficients, as measured by Pulsed Field Gradient ¹⁹F-NMR, in plasticized SPEs are also reported.

Novel high salt content polymer electrolytes based on high Tg polymers

Conductivities greater than or equal to 10⁻⁸ S cm⁻¹ at T_g are reported in polymer electrolytes based on lithium triflate salt and a series of polymers whose T_g is greater than 90°C. The highest conductivities were observed for poly(acrylonitrile) based systems with salt concentrations greater than 60 wt.%. The conductivity in all cases investigated increases with increasing salt concentration. ¹H-NMR T₂ relaxation measurements suggest that T_g decreases with increasing salt content and confirms that these materials are glassy at room temperature and hence that the conductivity is significantly decoupled from the structural relaxations. It appears that the nature of the polymer is important in determining the level of ionic conductivity, possibly due to differences in polymer coordinating ability or differences in T_g. Polymer-in-salt mixtures based on a tetra-alkyl ammonium imide molten salt and several high T_g polymers are also reported. The conductivities of these mixtures appear to be independent of the polymer type.

Glass transition and free volume behaviour of poly(acrylonitrile)/LiCF3SO3 polymer-in-salt electrolytes compared to poly(ether urethane)/LiClO4 solid polymer electrolytes

Measurements of the glass transition temperature (T_g) and free volume behaviour of poly(acrylonitrile) (PAN) and PAN/lithium triflate (LiTf), with varying salt composition from 10 to 66 wt% LiTf, were made by positron annihilation lifetime spectroscopy (PALS). Addition of salt from 10 to 45 wt% LiTf resulted in an increase in the mean free volume cavity size at room temperature (r.t.) as measured by the orthoPositronium (oPs) pickoff lifetime, τ₃, with little change in relative concentration of free volume sites as measured by oPs pickoff intensity, I₃. The region from 45 to 66 wt% salt displayed no variation in relative free volume cavity size and concentration. This salt concentration range (45 wt%<[LiTf]<66 wt%) corresponds to a region of high ionic conductivity of order 10⁻⁵ to 10⁻⁶ S cm⁻¹ at T_g as measured by PALS. A percolation phenomenon is postulated to describe conduction in this composition region. Salt addition was shown to lower the T_g as measured by PALS; T_g was 115°C for PAN and 85°C for PAN/66 wt% LiTf. The T_g and free volume behaviour of this polymer-in-salt electrolyte (PISE) was compared to a poly(ether urethane)/LiClO₄ where the polymer is the major component, i.e. traditional solid polymer electrolyte (SPE). In contrast to the PISE, the T_g of the SPE was shown to increase with increasing salt concentration from 5.3 to 15.9 wt%. The relative free volume cavity size and concentration at r.t. were shown to decrease with increasing salt concentration. Ionic conductivity in this SPE was of order 10⁻⁵ S cm⁻¹ at r.t., which is over 60°C above T_g, 10⁻⁸ S cm⁻¹ at 25°C above T_g, and conductivity was not measurable at T_g.

Poly methacrylate-plasticiser-salt blends as solid polymer electrolytes

Methoxy-ethylene glycol methacrylates, CH₂=CMeCOO(CH₂CH₂O)_nMe (n = 1, 2, 3), ethoxy-triethylene glycol methacrylate, CH₂=CMeCOO(CH₂CH₂O)₃Et, and N,N-dimethylaminoethyl methacrylate, CH₂=CMeCOOCH₂CH₂NMe₂, were used to synthesise the corresponding polymers. Conductivities of these polymers complexed with lithium perchlorate were investigated. Tetraethylene glycol dimethyl ether was used as plasticiser to increase the conductivity of the materials. A conductivity of 10⁻⁵ S cm⁻¹ was obtained at room temperature for the plasticised polymer samples. Effects of polymer structure, plasticiser, salt concentration and temperature on conductivity and glass transition temperature of the polymer electrolytes are discussed.

Mechanical properties of polyether-plasticiser-salt systems as polymer electrolytes

The mechanical properties of urethane crosslinked poly(ethylene oxide-co-propylene oxide) glyceryl ether-plasticiser (tetraethylene glycol dimethyl ether, or methylformamide)-salt (LiClO₄)-based polymer electrolytes have been studied. It was found that, with increasing concentration of salt, the elastic modulus and tensile strength of the materials unexpectedly decrease. This is interpreted in terms of a predominance of intramolecular coordination of the Li⁺ ions by the polymer.

Poly(triazine imide) with intercalation of Lithium and ChlorideiIons [(C3N3)2(NHxLi1−x)3⋅LiCl]: A Crystalline 2D Carbon Nitride network

Poly(triazine imide) with intercalation of lithium and chloride ions (PTI/Li+Cl−) was synthesized by temperature-induced condensation of dicyandiamide in a eutectic mixture of lithium chloride and potassium chloride as solvent. By using this ionothermal approach the well-known problem of insufficient crystallinity of carbon nitride (CN) condensation products could be overcome. The structural characterization of PTI/Li+Cl− resulted from a complementary approach using spectroscopic methods as well as different diffraction techniques. Due to the high crystallinity of PTI/Li+Cl− a structure solution from both powder X-ray and electron diffraction patterns using direct methods was possible; this yielded a triazine-based structure model, in contrast to the proposed fully condensed heptazine-based structure that has been reported recently. Further information from solid-state NMR and FTIR spectroscopy as well as high-resolution TEM investigations was used for Rietveld refinement with a goodness-of-fit (χ2) of 5.035 and wRp=0.05937. PTI/Li+Cl− (P63cm (no. 185); a=846.82(10), c=675.02(9) pm) is a 2D network composed of essentially planar layers made up from imide-bridged triazine units. Voids in these layers are stacked upon each other forming channels running parallel to [001], filled with Li+ and Cl− ions. The presence of salt ions in the nanocrystallites as well as the existence of sp2-hybridized carbon and nitrogen atoms typical of graphitic structures was confirmed by electron energy-loss spectroscopy (EELS) measurements. Solid-state NMR spectroscopy investigations using 15N-labeled PTI/Li+Cl− proved the absence of heptazine building blocks and NH2 groups and corroborated the highly condensed, triazine-based structure model.

Laboratory model studies of flushing of trapped salt water from a blocked tidal estuary

Results are presented from a series of laboratory model studies of the flushing of saline water from a partially- or fully-closed estuary. Experiments have been carried out to determine quantitatively the response of the trapped saline volume to fresh water flushing discharges Q for different values of the estuary bed slope α and the density difference (∆ρ)_o between the saline and fresh water. The trapped saline water forms a wedge within the estuary and for maintained steady discharges, flow visualisation and density profile data confirm that its response to the imposition of the freshwater purging flow occurs in two stages, namely (i) an initial phase characterised by intense shear-induced mixing at the nose of the wedge and (ii) a relatively quiescent second phase where the mixing is significantly reduced and the wedge is forced relatively slowly down and along the bed slope. Scalings based upon simple energy balance considerations are shown to be successful in (i) describing the time-dependent wedge behaviour and (ii) quantifying the proportion of input kinetic energy converted into increasing the potential energy of the wedge/river system. Measurements show that the asymptotic value of the energy conversion factor increases with increasing value of the river Froude number Fr_o at small values of Fr_o, thereafter reaching a maximum value and a gradual decrease at the highest values of Fr_o. Dimensional analysis considerations indicate that the normalised, time-dependent wedge position (x_w)³(g')o/q² can be represented empirically by a power-law relationship of the form (x_w)[(g')_o/q²]^1/3 =C [(t)[(g')_o²/q]^1/3]"where the proportionality coefficient C is a function of both Fr_o and the slope angle α and the exponent n has a value of 0.24. Successful attempts are made to relate the model data to existing field observations from a microtidal estuary.

Experiments with multiple, intermittent periodic flushing flows confirm the importance of the starting phase of each flushing event for the time dependent behaviour of the saline wedge after reaching equilibrium in the intervals between such events. For the parameter ranges investigated and for otherwise-identical external conditions, no significant differences are found in the position of the wedge between cases of sequential multiple flushing flows and steady single discharges of the same total duration.

Observation of inter- and intramolecular C---H...F hydrogen bonding in Gingras' salt: [n-Bu4N]+[Ph3SnF2]-

The crystal and molecular structure of Gingras' salt [n-Bu₄N]^₊ [Ph₃SnF₂]⁻ is reported, which reveals a variety of inter- and intramolecular C---H...F hydrogen bonding interactions. A ¹¹⁹Sn MAS-NMR spectrum was recorded and a tensor analysis has been performed according to the method of Herzfeld and Berger. The results are discussed in terms of the molecular structure and are compared with the parent compound Ph₃SnF as well as with Mes₃SnF (Mes=mesityl).