TFSI Anions Research Articles

Modelling Coupled Ion Motion in Electrolyte Solutions for Lithium‐Sulfur Batteries

AbstractWe model coupled ion transport in representative electrolyte solutions for Li−S batteries by applying molecular dynamic (MD) simulations on systems of increasing complexity, namely going from solutions of the Li2S4 salt in pure tetraethylene glycol dimethyl ether (TEGDME) and 1,3‐dioxolane (DOL) solvents, to Li2S4 in solvent mixtures, and finally incorporating lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as a reservoir of Li‐ions. While the motion of Li2S4 salt in DOL is predominantly vehicular, it is governed by a hopping regime in the more viscous TEGDME solvent. Most importantly, when the two salts are mixed, the presence of the TFSI anions does not slow down the diffusion of the polysulfide anion.

Probing the relationship of cations-graphene interaction strength with self-organization behaviors of the anions at the interface between graphene and ionic liquids

The influence of molecular cations on the dynamic self-organization of anion at the interface between graphene and ionic liquid (IL) is investigated by selecting same anion ILs (N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide (BMP-TFSI)) as the top gate of double-gate graphene filed effect transistors (DG-GFETs). The selected ILs have similar viscosity and conductivity but exhibit distinctly different effects on device performance. From electric transport properties of the DG-GFETs and infrared spectroscopy, it is found that stronger BMP-graphene interactions facilitate faster self-organization of the TFSI anions on graphene. The results introduce an important role of the interfacial cation-graphene interactions that contribute to molecular self-organization, and clearly show the significant impact interfacial effects offer for tuning macroscopic device performance.

Ionic liquid based battery electrolytes using lithium and sodium pseudo-delocalized pyridinium anion salts.

The electrolyte salt plays an important role for the overall performance and safety of lithium- and sodium-ion batteries (LIBs and SIBs, respectively). Here, two new lithium and sodium pseudo-delocalized pyridinium anion based salts were used to prepare ionic liquid (IL) based electrolytes. The Li and Na salts of the 1-methylpyridinum 2,6-dicarboxylate anion (MM26py) were synthesized and dissolved in an IL matrix (Pyr14TFSI) - hence creating mixed anion electrolytes. The obtained electrolytes are stable up to 150 and 200 °C and show ion conductivities of 2.8 and 3.2 mS cm-1 at room temperature, for the LIB and SIB electrolytes, respectively. A competitive effect between the MM26py and the TFSI anions to coordinate the alkali metal cations is observed. Finally, the electrochemical stability windows of 2.3 and 2.5 V, respectively, confirm that these electrolytes can be used practically in medium-voltage LIBs and SIBs.

Ionic liquid electrolyte with highly concentrated LiTFSI for lithium metal batteries

Electrolytes that possess both interfacial stability toward lithium metal anodes and compatibility with high voltage cathodes are required for high energy density batteries. Here a high concentration LiTFSI salt firstly dissolves in an ionic liquid Pyr1,3FSI. This electrolyte with synergetic effect of TFSI and FSI anions, which not only effectively suppresses lithium dendrite growth because of the highly concentrated solid electrolyte interphase film, but also beneficially improve the cycling performance of lithium batteries. Lithium plating/stripping tests reveal that the concentrated electrolyte has superior compatibility with a lithium metal anode than an electrolyte with low salt concentration. Furthermore, a lithium metal battery containing the electrolyte and a lithium cobalt oxide cathode achieves high coulombic efficiency and good cycling stability at 4.4 V and high temperature. These results indicate that the highly concentrated ionic liquid electrolyte is promising for use in lithium metal batteries.

Mechanism Analysis of Enhanced Li-Ion Conductivity in Mesoporous Silica-Based Solid Nano-Composite Electrolytes

Solid electrolytes with Li-ion conductivity higher than 1 mS/cm are required for the development of high capacity solid-state Li-ion batteries. In the past decade, several studies were done on the improvement of ion conductivity in composite materials by employing interface enhanced ion conduction at inorganic oxide surfaces such as silica, alumina or titania added to, for example, inorganic or polymer electrolytes. Also, composites of nanoparticles and mesoporous microparticles mixed with ionic-liquid electrolyte (ILE) have been proposed to promote the Li-ion conductivity along the particle or pore surface. However, so far the ionic conductivity was always lower than that of the original ILE due to the interrupted ionic paths by percolation from particle to particle. Monolithic nanoporous silica with ILE confined in the porous structures, also named “ionogels” have shown ion conductivities approaching the ILE bulk conductivity. These ionogels are fabricated by a sol-gel process e.g. by hydrolysis-condensation reaction with tetraethylorthosilicate (TEOS) precursor and typically formic acid where the ILE is added in the solution as the template for the silica to grow around. So far, the ionic conductivity of the confined ILE in the standard nanoporous oxide has never exceeded that of the ILE conductivity itself. By introduction of a surface functional group, an ion conductivity slightly higher than that of the bulk ILE was obtained, showing that surface interactions can be used to tailor the ion conductivity in these materials. In this paper, we show nanocomposite electrolyte (nano-SCE) materials with enhancements in ion conductivity exceeding 200% and ion conductivities up to 3mS/cm. The nano-SCE was fabricated in a similar way as the ionogels: a single-step sol-gel process with a TEOS precursor and with the ionic liquid electrolyte in the homogeneous precursor solution. The processing conditions were such that molecular ordering of the IL molecules was favored and the adsorbed interface layers provided free Li+ ions for enhanced Li-ion conductivity along the surface. Figure 1 shows the ion conductivity of the obtained solid pellet for a model system with (N-butyl- N-methyl pyrrolidinium bis(trifluoromethanesulfonyl) imide ([BMP]TFSI) and bis(trifluoromethanesulfonyl)imide lithium salt (LiTFSI). Importantly, the graph shows the difference between an ionogel material with a confined ILE and our nano-SCE. For the ionogels, the conductivity versus temperature behavior is the same as that for the bulk ILE, albeit with lower conductivity due to the fraction of inactive silica. Both the ionogel composites and the bulk ILE show the melting point of the ILE with a lower conductivity for the solid phase. For the nano-SCE, however, the melting point is no longer observed and the slope indicates that the formed nanocomposite material has a lower activation energy for diffusion than that of the bulk ILE and of the ionogels with the confined ILE. In this paper, we propose a mechanism for the observed behavior based on adsorption of the TFSI anion and subsequent molecular ordering and layering of the BMP cation and TFSI anions. The adsorbed layer has a solid-state like character and is therefore named as the mesophase layer. We will present experimental evidence for the interface interactions from FTIR spectra. Raman measurements confirm that the fraction of free Li+ ions increases in the composites. NMR measurements show that similar enhanced surface diffusion happens at nanoparticle systems but the interconnected pores in the SCE provide continuous pathways throughout the solid electrolyte nanostructure, ensuring the full effect of the surface enhancement is observed in contrast to analogous nanoparticle-ILE composites. To demonstrate the functionality of the nano-SCE as Li-ion electrolyte, cells with LFP cathodes were prepared. A technologically distinguishing feature of the nano-SCE, as for ionogels, is that it is applied as a liquid – via wet chemical coating – and only afterwards is converted into a solid. That way it is perfectly suited to be casted into dense powder electrodes where it fills all cavities and makes maximum contact, just as a liquid electrolyte does. A cell with 200Wh/L at 0.5C is demonstrated by casting of the nano-SCE precursor solution into the electrodes. The possibility of wet application of the nano-SCE precursor makes this technology also compatible with current Li-ion battery fabrication processes. Fig. 1 Temperature dependence of the ion conductivity for the ionic liquid electrolyte (ILE) with Li-TFSI and BMP-TFSI, for two silica ionogels with changing ILE content (x refers to the ratio of ILE to silica) and for our nano-SCE showing different behavior between the nano-SCE and the ILE it contains as a result of the mesophase layer formed on the silica pore surface. Figure 1

Electronic Structure Characterization of Cross-Linked Sulfur Polymers.

Cross-linked polymers of elemental sulfur are of potential interest for electronic applications as they enable facile thin-film processing of an abundant and inexpensive starting material. Here, we characterize the electronic structure of a cross-linked sulfur/diisopropenyl benzene (DIB) polymer by a combination of soft and hard X-ray photoelectron spectroscopy (SOXPES and HAXPES). Two different approaches for enhancing the conductivity of the polymer are compared: the addition of selenium in the polymer synthesis and the addition of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) during film preparation. For the former, we observe the incorporation of Se into the polymer structure resulting in a changed valence-band structure. For the latter, a Fermi level shift in agreement with p-type doping of the polymer is observed and also the formation of a surface layer consisting mostly of TFSI anions.

Magnesium ion-conductive poly(ethylene carbonate) electrolytes

Magnesium (Mg) electrolytes are presently under investigation for their promising performance capabilities in the next generation of batteries. The present work studies Mg-ion transport in polymers using different types of Mg salts. Polymer electrolytes comprising poly(ethylene carbonate) (PEC) with Mg salts (MgX2; X = TFSI, ClO4) were prepared by solution casting. The structural, thermal, and electrochemical properties of flexible self-standing membranes were studied as potential Mg electrolytes. The impedance results at 90 °C found the highest conductivities of 6.0 × 10−6 S cm−1 for PEC-Mg(TFSI)2, and 5.2 × 10−5 S cm−1 for PEC-Mg(ClO4)2, at 40 mol%. FT-IR measurements revealed changes in the peak fraction from the region of carbonyl group, which explain the interaction with Mg ions. The glass transition temperature of the TFSI system decreased with increasing salt concentration due to the plasticizing effect of TFSI anions. Thermal gravimetric analysis revealed that the highest values of the 5% weight-loss temperature at 40 mol% are 174 °C for PEC-Mg(TFSI)2 and 160 °C for PEC-Mg(ClO4)2. The electrochemical stability of PEC-Mg(TFSI)2 at 40 mol% was up to 2.2 V. To confirm the redox reaction of Mg ions in PEC, CV measurement was carried out using symmetrical cells with quasi Mg electrodes. Cathodic and anodic current peaks were clearly observed, and the presence of these peaks indicates Mg-ion conduction in PEC.

Pyrrolidinium FSI and TFSI-Based Polymerized Ionic Liquids as Electrolytes for High-Temperature Lithium-Ion Batteries

Promising electrochemical and dynamical properties, as well as high thermal stability, have been the driving forces behind application of ionic liquids (ILs) and polymerized ionic liquids (PILs) as electrolytes for high-temperature lithium-ion batteries (HT-LIBs). Here, several ternary lithium-salt/IL/PIL electrolytes (PILel) have been investigated for synergies of having both FSI and TFSI anions present, primarily in terms of physico-chemical properties, for unique application in HT-LIBs operating at 80 °C. All of the electrolytes tested have low Tg and are thermally stable ≥100 °C, and with TFSI as the exclusive anion the electrolytes (set A) have higher thermal stabilities ≥125 °C. Ionic conductivities are in the range of 1 mS/cm at 100 °C and slightly higher for set A PILel, which, however, have lower oxidation stabilities than set B PILel with both FSI and TFSI anions present: 3.4–3.7 V vs. 4.2 V. The evolution of the interfacial resistance increases for all PILel during the first 40 h, but are much lower for set B PILel and generally decrease with increasing Li-salt content. The higher interfacial resistances only influence the cycling performance at high C-rates (1 C), where set B PILel with high Li-salt content performs better, while the discharge capacities at the 0.1 C rate are comparable. Long-term cycling at 0.5 C, however, shows stable discharge capacities for 100 cycles, with the exception of the set B PILel with high Li-salt content. Altogether, the presence of both FSI and TFSI anions in the PILel results in lower ionic conductivities and decreased thermal stabilities, but also higher oxidation stabilities and reduced interfacial resistances and, in total, result in an improved rate capability, but compromised long-term capacity retention. Overall, these electrolytes open for novel designs of HT-LIBs.

Ionic Liquid-Based Thermoplastic Solid Electrolytes Processed by Solvent-Free Procedures.

A series of thermoplastic polymer electrolytes have been prepared employing poly(ethylene oxide) (PEO) as a polymer matrix, bis(trifluoromethane sulfonimide) (LiTFSI), and different room-temperature ionic liquids (RTIL) with bis(fluorosulfonyl)imide (FSI) or TFSI anions. This formulation makes them safe and non-flammable. The electrolytes have been processed in the absence of solvents by melt compounding at 120 °C, using sepiolite modified with d-α-tocoferol-polyethyleneglycol 1000 succinate (TPGS-S) as a physical cross-linker of PEO. Several concentrations of RTILs, lithium salt, and TPGS-S have been tested in order to obtain the highest ionic conductivity (σ) without losing electrolytes’ mechanical stability. The materials’ rheology and ionic conductivity have been extensively characterized. The excellent crosslinking ability of TPGS-S makes the electrolytes behave as thermoplastic materials, even those with the highest liquid concentration. The electrolytes with the highest concentrations of FSI anion present a σ over 10−3 S·cm−1 at 25 °C and close to 10−2 S·cm−1 at 70 °C, and notably behave as solids at temperatures up to 90 °C despite over 65 wt % of their formulation being liquid. The electrolytes thus obtained are safe solid thermoplastics prepared by industrially scalable procedures and are suitable for energy storage devices, proving the adequacy of polymer-based materials as solid electrolytes for batteries or supercapacitors.

Ionic liquid‐based organic–inorganic hybrid electrolytes: Impact of in situ obtained and dispersed silica

ABSTRACTOrganic–inorganic hybrid electrolytes based on PEO‐NaTFSI‐ionic liquid (HMIMTFSI)‐silica (in situ production via sol gel process) are being reported in this article. The variation in conductivity with ionic liquid (IL) addition has been explained on the basis of number of free TFSI anions evaluated using ATR‐IR data. The deconvolution of the IR spectra of these hybrid electrolytes has given evidence of ion‐pair formation which has been compared vis‐á‐vis the conductivity variation. The hybrid electrolyte with maximum conductivity comprises the highest number of free imide ions and has lowest glass transition temperature. FESEM has displayed a porous and layered surface morphology with dispersed silica nanoparticles. In addition, the optimized hybrid electrolyte has been compared with 5 wt% (limit of mechanical stability) ex situ silica added composite where the temperature cycling of conductivity has shown that the ex situ dispersed hybrid electrolytes do not retrace their conductivity path contrary to the in situ prepared hybrid electrolytes. This behavior has been explained to be due to the hindrance offered by the ex situ added silica in the recrystallization kinetics of PEO. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 207–218

Self-Organization of Ions at the Interface between Graphene and Ionic Liquid DEME-TFSI.

Electrochemical effects manifest as nonlinear responses to an applied electric field in electrochemical devices, and are linked intimately to the molecular orientation of ions in the electric double layer (EDL). Herein, we probe the origin of the electrochemical effect using a double-gate graphene field effect transistor (GFET) of ionic liquid N,N-diethyl-N-(2-methoxyethyl)-N-methylammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) top-gate, paired with a ferroelectric Pb0.92La0.08Zr0.52Ti0.48O3 (PLZT) back-gate of compatible gating efficiency. The orientation of the interfacial molecular ions can be extracted by measuring the GFET Dirac point shift, and their dynamic response to ultraviolet-visible light and a gate electric field was quantified. We have observed that the strong electrochemical effect is due to the TFSI anions self-organizing on a treated GFET surface. Moreover, a reversible order-disorder transition of TFSI anions self-organized on the GFET surface can be triggered by illuminating the interface with ultraviolet-visible light, revealing that it is a useful method to control the surface ion configuration and the overall performance of the device.

TFSI and TDI Anions: Probes for Solvate Ionic Liquid and Disproportionation-Based Lithium Battery Electrolytes.

Highly concentrated electrolytes based on Li-salts and chelating solvents, such as glymes, are promising as electrolytes for lithium batteries. This is due to their unique properties, such as higher electrochemical stabilities, compliance with high-voltage electrodes, low volatility and flammability, and inertness toward aluminum current collector corrosion. The nature of these properties originates from the molecular-level structure created in either solvate ionic liquids (SILs) or the less common ionic aggregates by disproportionation reactions. The nature of the anion plays a crucial role, and here, we present a computational study using TFSI and TDI anions as probes, revealing increasing differences upon increased salt concentration. TFSI-based electrolytes preferably form SILs, while TDI-based electrolytes form ionic aggregates. The latter lead to an unexpected creation of "free" cationic species even at (very) high salt concentrations and thus promise of ample lithium ion transport.

A stable graphite electrode in superconcentrated LiTFSI-DME/DOL electrolyte and its application in lithium-sulfur full battery

Herein, prelithiated graphite anodes are coupled with sulfur composite cathodes to form a Li–S full cell in superconcentrated ether electrolyte. This novel system is effective in avoiding sever corrosion of Li-metal anode and significantly improving the safety of present Li–S cell, owing to the replacement of Li-metal anode with graphite. The introduced superconcentrated ether electrolyte has a unique networking structure of Li cations and TFSI anions with Li+-solvating DME/DOL solvents, which is conducive to form a stable TFSI-derived surface film on the graphite electrode. The stable and dense TFSI-derived film inhibits further electrolyte decomposition and graphite exfoliation caused by co-intercalation of solvents, allowing reversible lithium intercalation and de-intercalation at a graphite electrode. Besides, the severe polysulfides shuttle is also suppressed by the concentrated ether-based solutions. Consequently, the assembled graphite-sulfur full battery retains outstanding capacity of 686mAhg−1sulfur at 0.1C rate after 105 cycles, along with high Coulombic efficiency.

A bis(fluorosulfonyl)imide based ionic liquid as safe and efficient electrolyte for Si/Sn-Ni/C/Al composite anode

The composite material Si0.26Ni0.13Sn0.15Al0.04C0.42 (Si/Sn-Ni/C/Al) exhibits a high reversible capacity (>600mAhg−1) at a low potential and can be cycled for more than 100 cycles. Moreover fast rates of charge and discharge can be achieved without any significant loss in capacity. In order to optimize the performances of this material and especially to obtain larger and stable cycling results, the use of room temperature ionic liquids (RTIL) as electrolyte is investigated. RTIL selected for this purpose contain the FSI (bis(fluorosulfonyl)imide) or TFSI (bis(trifluoromethylsulfonyl)imide) anions and pyrrolidium (methyl-propylpyrrolidinium, PYR13 or methyl-butylpyrrolidinium, PYR14) and ethyl-methylimidazolium (EMI) as cations. Charge/discharge cycling tests of Li|Si/Sn-Ni/C/Al half-cells containing RTIL based on the FSI or TFSI anions have been performed. Results revealed significantly higher capacities and improved capacity retention (73% of the discharge capacity after 100 cycles at a C/5 rate) for cells containing FSI anions as components of the electrolyte. The choice of the RTIL cation has also an impact on the cycling stability and mean capacity of the cell. Using the EMIFSI ionic liquid and 1molL−1 of LiFSI, the mean capacity during 100 cycles at C/5 rate (635mAhg−1) is higher than with [PYR13][FSI] (579mAhg−1) or [PYR14][FSI] (550mAhg−1) ionic liquids. For comparison, the capacity of a half-cell containing a classical alkylcarbonate mixture with 1molL−1 of LiFSI drops to 206mAhg−1 after 20 cycles. It is concluded that the Si/Sn-Ni/C/Al/electrolyte interface is more stable in the presence of FSI anions and especially in the presence of the [EMI][FSI] ionic liquid.

Catalytic reduction of TFSI-containing ionic liquid in the presence of lithium cations

The influence of the electrochemical double layer (EDL) structure on the electrochemical processes in ionic liquids is an intriguing subject. The complex layered structure of the EDL and its restructuring have been shown to strongly affect metal deposit morphology and electrochemical reaction kinetics. In this work, we demonstrate that the breakdown of an ionic liquid containing TFSI anions can be catalyzed through the addition of Li+ cations. We ascribe this catalytic effect to the change in the EDL structure: the Li+ cations preferentially adsorb on the electrode surface and drag the TFSI anions with them, facilitating their reduction. The decomposition of the ionic liquid leads to the formation of an SEI layer, which is studied using an electrochemical quartz crystal microbalance.

X-ray Photodecomposition of Bis(trifluoromethanesulfonyl)imide, Bis(fluorosulfonyl)imide, and Hexafluorophosphate

X-ray photoelectron spectroscopy is one of the workhorses in today’s battery analysis and research. The potential of X-ray radiation damage and degradation during measurements with regularly used salts and organic compounds are often overlooked. In this study, we show that, under common analysis conditions, the exiting X-ray radiation (1468.6 eV) during the XPS analysis does have significant effect on some Mg and Li salts based on TFSI, FSI, and PF6 anions. In all cases, we show that the salts undergo significant photodegradation during the XPS measurements. With XPS, the photodegradation is detected as the solid degradation products remaining on the sample holder, and they are clearly identified by formation of new peaks at lower binding energies for the relevant elements. We were also able to show that in some cases, as expected, some gaseous byproducts evolve during the photodegradation process.

Plasticization of NaX-PEO solid polymer electrolytes by Pyr13X ionic liquids

Addition of moderate contents (≤20wt%) of ionic liquids (ILs) to binary solid polymer electrolytes (SPEs) is made to alter the overall SPE properties, foremost to increase the room temperature ionic conductivity. Sodium conducting ternary electrolytes, based on sodium salts; NaTFSI and NaFSI, the polymer poly(ethylene oxide) (PEO), and pyrrolidinium ILs; Pyr13TFSI and Pyr13FSI, with different compositions: NaX(PEO)n – Pyr13X (X=TFSI, FSI), have been prepared. Raman and dielectric spectroscopy as well as differential scanning calorimetry have been used to evaluate the plasticizing effect of the Pyr13 IL cation and the accompanying TFSI and FSI IL anions via changes in ionic association, crystallinity, polymer chain dynamics, and total ionic conductivity. While all the TFSI based systems seem rather insensitive to the addition of IL with respect to speciation, the situation is much less clear for the FSI based systems. Furthermore, the addition of ILs seems beneficial for inhibiting PEO crystallization, especially for the FSI anion, and also for enhancing the polymer chain dynamics, but yet the FSI based ternary electrolytes show lower ion conductivities as compared to the analogous TFSI based systems.

Sulfonated Polymerized Ionic Liquid Block Copolymers.

The successful synthesis of a new diblock copolymer, referred to as sulfonated polymerized ionic liquid (PIL) block copolymer, poly(SS-Li-b-AEBIm-TFSI), is reported, which contains both sulfonated blocks (sulfonated styrene: SS) and PIL blocks (1-[(2-acryloyloxy)ethyl]-3-butylimidazolium: AEBIm) with both mobile cations (lithium: Li(+) ) and mobile anions (bis(trifluoromethylsulfonyl)imide: TFSI(-) ). Synthesis consists of polymerization via reversible addition-fragmentation chain transfer, followed by post-functionalization reactions to covalently attach the imidazolium cations and sulfonic acid anions to their respective blocks, followed by ion exchange metathesis resulting in mobile Li(+) cations and mobile TFSI(-) anions. Solid-state films containing 1 m Li-TFSI salt dissolved in ionic liquid result in an ion conductivity of >1.5 mS cm(-1) at 70 °C, where small-angle X-ray scattering data indicate a weakly ordered microphase-separated morphology. These results demonstrate a new ion-conducting block copolymer containing both mobile cations and mobile anions.

Voltammetric Study and Electrodeposition of Zinc from Room Temperature Ionic Liquid 1-Butyl-1-Methylpyrrolidinium Bis((trifluoromethyl)Sulfonyl)Imide

Voltammetric behavior of Zn(II) introduced into the room temperature ionic liquid 1-butyl-1-methylpyrrolidinium bis((trifluoromethyl)sulfonyl)imide (RTIL BMP-TFSI) via the addition of ZnCl2 or Zn(TFSI)2 salt was studied. It is surprised that ZnCl2 is highly soluble in this IL because many transition metal chlorides are insoluble in the TFSI-based ILs, leading to the retardation of applying the RTIL BMP-TFSI to electrodeposition. Two redox couples both associated to the redox reaction Zn(II) + 2e− ↔ Zn were observed in the ZnCl2 solution, which resulted from the nonchloride-coordinated and chloride-coordinated Zn(II) species, respectively. However, a single redox couple corresponding to Zn(II) + 2e− ↔ Zn was observed in the Zn(TFSI)2 solution (Figure 1). According to the experiments of voltammetric titration, it was supposed that TFSI anions exhibit much stronger coordinating ability towards Zn2+ ions than to other common transition metal ions, resulting in the high solubility of ZnCl2 in BMP-TFSI. A sufficient amount of chloride anion must be introduced in order to observe the chloride-coordinated Zn(II) species in the Zn(TFSI)2 solution. Afterwards, TFSI anions coordinated to Zn2+ ions were gradually replaced by chloride ions continuously introduced into the Zn(TFSI)2 solution. Finally, no zinc redox couple could be observed once Zn2+ions were completely coordinated with chloride ions. Electrodeposition of Zn was achieved by potentiostatic electrolysis using copper substrates as the electrodes from the IL containing ZnCl2 and Zn(TFSI)2, respectively. Crystalline Zn could be obtained from the two different solutions. The crystallinity and surface morphology of the Zn electrodeposits depended on the applied potentials, and nanostructured Zn could be obtained at some particular electrodepositing potentials. An interesting current-vibration behavior was observed during the potentiostatic electrodeposition of Zn from ZnCl2 solution, and this vibration behavior obviously depended on the applied potentials. It was supposed that the current-vibration behavior was due to a chloride-releasing & chloride-combination mechanism accompanied with the diffusion-drove supplementary of electroactive Zn(II) species because the vibration phenomenon was only observed while the applied potentials were set at where the chloride-coordinated Zn(II) species was reduced in the ZnCl2 solution. Figure 1

Performance of solid state supercapacitors based on polymer electrolytes containing different ionic liquids

Abstract Four Ionic Liquid based Polymer Electrolytes (IL-b-PE) were prepared by blending a Polymeric Ionic Liquid, Poly(diallyldimethylammonium) bis(trifluoromethanesulfonyl)imide (PILTFSI), with four different ionic liquids: 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) (IL-b-PE1), 1-butyl-1-methylpyrrolidinium bis(fluorosulfonyl)imide (PYR14FSI) (IL-b-PE2), 1-(2-hydroxy ethyl)-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (HEMimTFSI) (IL-b-PE3), and 1-Butyl-1-methylpyrrolidinium dicyanamide, (PYR14DCA) (IL-b-PE4). Physicochemical properties of IL-b-PE such as ionic conductivity, thermal and electrochemical stability were found to be dependent on the IL properties. For instance, ionic conductivity was significantly higher for IL-b-PE2 and IL-b-PE4 containing IL with small size anions (FSI and DCA) than IL-b-PE1 and IL-b-PE3 bearing IL with bigger anion (TFSI). On the other hand, wider electrochemical stability window (ESW) was found for IL-b-PE1 and IL-b-PE2 having ILs with electrochemically stable pyrrolidinium cation and FSI and TFSI anions. Solid state Supercapacitors (SCs) were assembled with activated carbon electrodes and their electrochemical performance was correlated with the polymer electrolyte properties. Best performance was obtained with SC having IL-b-PE2 that exhibited a good compromise between ionic conductivity and electrochemical window. Specific capacitance (Cam), real energy (Ereal) & real power densities (Preal) as high as 150 F g−1, 36 Wh kg−1 & 1170 W kg−1 were found at operating voltage of 3.5 V.