Ionic Liquid-based Gel Polymer Electrolyte Research Articles

Preparation and characterization of nanocomposite ionic liquid-based gel polymer electrolyte for safe applications in solid-state lithium battery

Gel electrolyte is one of the most direct and appropriate ways to solve the safety problem of battery before the most challenging technological hurdles to all solid-state batteries have not yet been overcame. A major challenge towards gel polymer electrolyte (GPE) is making an electrolyte that is effectively combine with electrochemical performance, thermal safety and the stability to lithium. Here, PVDF-HFP-LiTFSI/SiO2/EMITFSI polymer electrolyte composite membrane (ILGPE) is prepared via solution casting method, in which nano-silica and ionic liquid positively effect on the performance of polymer electrolytes, such as ionic conductivity, electrochemical stability and thermal safety stability. It remarkably enhances the interface compatibility between ILGPEs and lithium metal. Significantly, we characteristically elucidate the possible transmission mechanism and interaction within the materials of ILGPE. Furthermore, Li/LiFePO4 battery based on such ILGPEs can exhibit fascinating interfacial stability and cycling performance. Herein, cells based on ILGPEs can overcome the drawbacks of solid electrolytes and volatile organic liquid electrolytes, which suggest a promising method for highly secure lithium batteries with appreciably enhanced performance.

Electrochemical characterization of ionic liquid based gel polymer electrolyte for lithium battery application

High molecular weight polymer poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP), ionic liquid 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIMFSI), and salt lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based free-standing and conducting ionic liquid-based gel polymer electrolytes (ILGPE) have been prepared by solution cast method. Thermal, electrical, and electrochemical properties of 80 wt% IL containing gel polymer electrolyte (GPE) are investigated by thermogravimetric (TGA), impedance spectroscopy, linear sweep voltammetry (LSV), and cyclic voltammetry (CV). The 80 wt% IL containing GPE shows good thermal stability (~ 200 °C), ionic conductivity (6.42 × 10−4 S cm−1), lithium ion conductivity (1.40 × 10−4 S cm−1 at 30 °C), and wide electrochemical stability window (~ 4.10 V versus Li/Li+ at 30 °C). Furthermore, the surface of LiFePO4 cathode material was modified by graphene oxide, with smooth and uniform coating layer, as confirmed by scanning electron microscopy (SEM), and with element content, as confirmed by energy dispersive X-ray (EDX) spectrum. The graphene oxide-coated LiFePO4 cathode shows improved electrochemical performance with a good charge-discharge capacity and cyclic stability up to 50 cycles at 1C rate, as compared with the without coated LiFePO4. At 30 °C, the discharge capacity reaches a maximum value of 104.50 and 95.0 mAh g−1 for graphene oxide-coated LiFePO4 and without coated LiFePO4 at 1C rate respectively. These results indicated improved electrochemical performance of pristine LiFePO4 cathode after coating with graphene oxide.

Improved electrochemical performance of EMIMFSI ionic liquid based gel polymer electrolyte with temperature for rechargeable lithium battery

Free-standing, flexible ionic liquid based gel polymer electrolyte (ILGPE) membranes containing polymer PVdF-HFP, imidazolium-based ionic liquid EMIMFSI with lithium salt LiTFSI are synthesized and characterized by various techniques. Thermal, electrochemical and electrical properties of prepared ILGPE membranes are investigated by thermogravimetric analysis, linear sweep voltammetry, cyclic voltammetry and impedance spectroscopy techniques. Prepared membranes are found to be thermally stable upto 200 °C. The ionic conductivity is found to be ∼3.8 × 10−4 S cm−1 at 25 °C and ∼6.0 × 10−4 S cm−1 at 50 °C for 40 wt% IL containing GPE. Lithium transference number and lithium ion conductivity of 40 wt% IL containing GPE shows the maximum value ∼0.4 and ∼1.5 × 10−4 S cm−1 respectively with electrochemical window ∼4.7 V versus Li/Li+ at 25 °C. The 40 wt% IL containing GPE is used for battery application because of its better compatibility with lithium electrode compared to other prepared ILGPEs. The discharge capacity attains a maximum value ∼141.2 mAh g−1 and ∼160.3 mAh g−1 at 25 °C and 50 °C respectively at 0.1C. About ∼99% Coulombic efficiency is obtained upto 100th cycles at 50 °C. These results indicate that the Li/40 wt% IL containing GPE/LiFePO4 cell shows high Coulombic efficiency, good charge-discharge capacity and cyclic stability upto 100th cycles.

A synchrotron x-ray diffraction and hard x-ray photoelectron spectroscopy study of Zn negative electrodes at different charge and discharge states of Zn/MnO2 batteries using an ionic liquid-based gel polymer electrolyte

Zn/MnO2 batteries including an ionic liquid-based gel polymer electrolyte (IL-GPE) have been discharged or discharged and then recharged reaching different states of charge. The Zn electrodes used in these Zn/MnO2 batteries are studied by HAXPES and synchrotron XRD techniques. Besides, HAXPES measurements are compared with the results obtained by a conventional XPS. Formation of Zn(OH)2 and ZnO is found in intermediate states of charge during charging and discharging. However, only ZnO is observed in the anode when a full discharging was carried out. Conversely, an entire charging process produces a complete reduction of all Zn2+ species to metallic Zn. In addition, various techniques have confirmed the entrance of Triflate anions and NMP solvent molecules in the electrode, accompanying the Zn2+ cations movement during the charging.

Electrical studies on ionic liquid-based gel polymer electrolyte for its application in EDLCs

Ionic liquid-based gel polymer electrolyte (GPE) has been synthesized using standard solution cast technique. Different weight percent of ionic liquid, 1-Butyl-3-methylimidazolium chloride (BMIMCl) and liquid electrolyte, ethylene carbonate (EC)–propylene carbonate (PC)–tetra ethyl ammonium tetra fluoro borate (TEABF4) was incorporated in polymer, poly(vinylidene fluoride-co-hexafluoro propylene (PVdF-HFP) to obtain mechanically stable gel polymer electrolyte film (GPE) having maximum conductivity of ~10−3 S cm−1 at room temperature, which is acceptable from device fabrication point of view. Potential window and ionic transference number has been obtained to examine the potential limit and ionic characteristics of optimized GPE system. Temperature dependence behavior of electrical conductivity curve follows Arrhenius nature in the temperature range of 303–373 K. Pattern of dielectric constant and its loss as a function of frequency and temperature have been studied and is being explained on the basis of electrode interfacial polarization effect. Frequency-dependent conductivity spectra obey the Jonscher’s power law. Further, optimized composition of GPE has been tested successfully for its application in supercapacitor fabrication with activated charcoal as an electrode material. Maximum specific capacitance of 118.6 mF cm−2 equivalent to single electrode specific capacitance of 61.7 F g−1 have been observed for the optimized GPE film.

Organic di-radical rechargeable battery with an ionic liquid-based gel polymer electrolyte

We employed 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (EMImTFSI)-based gel polymer electrolyte (ILPE) of low viscosity to prevent the instability of the di-TEMPO organic (DTO) electrode with enhancement of the cycle ability and rate-capability. The gel polymer electrolyte was prepared by electrospinning process. The DTO//ILPE//Li cell showed high initial capacity of 80mAh g-1 for 1 C and 68mAh g-1 for 10 C-rate, which corresponds to 100 and 85% of theoretical capacity, respectively. The cycle ability and rate-capability were much improved by using of EMImTFSI-based gel polymer electrolyte without self-discharge.

Layer-by-layer fully printed Zn-MnO2 batteries with improved internal resistance and cycle life

This research created direct layer-by-layer printed zinc-based secondary batteries with an ionic liquid-based gel polymer electrolyte to power micro- and meso-scale devices. The use of a gel polymer electrolyte composed of [BMIM][Otf] ionic liquid, ZnOtf salt, and PVDF-HFP polymer binder enabled direct layer-by-layer printing of functional cells. The effects of additive printing methods on cell discharge capacity, cycle life, and internal resistance are discussed. Fully printed cells have demonstrated average discharge capacities of 0.548 mAh/cm2, energy densities of 8.20 mWh/cm3, and specific energies of 2.46 mWh/g with some cells achieving over 1000 cycles without catastrophic failure. Layer-by-layer printed devices exhibited decreased DC internal resistance and longer cycle life over previous mechanically assembled cells.

Charge storage mechanism of MnO 2 cathodes in Zn/MnO 2 batteries using ionic liquid-based gel polymer electrolytes

Cathode reactions in Zn/MnO2 batteries using aqueous electrolytes have been usually interpreted by the reduction of Mn4 + to Mn3 + while protons and/or cations penetrate inside the cathode. However, until now, the MnO2 storage charge mechanism using a non-aqueous gel polymer electrolyte (GPE) has not been investigated. In this work, ionic liquid-based GPEs including BMIM Tf and ZnTf2 have been employed in Zn/MnO2 batteries. Different states of charge of MnO2 cathodes used in Zn/IL-GPE/MnO2 batteries have been analyzed by XPS and EDX techniques. XPS analysis showed that Mn4 + is reduced during the discharge process at the same time as Zn2 + cations are incorporated into the cathode. Besides, Zn2 + cations insertion is accompanied by triflate anions.

Interaction between Zn2+ cations and n-methyl-2-pyrrolidone in ionic liquid-based Gel Polymer Electrolytes for Zn batteries

Gel Polymer Electrolytes (GPEs) composed by 1-Ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (EMIM TFSI), ZnTf2 salt, and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) are synthesized using n-methyl-2-pyrrolidone (NMP) as solvent. Structural and Thermal characterization of GPEs with different ZnTf2 concentrations are analyzed by ATR-FTIR, XRD, DSC and TG. Ionic conductivity versus temperature plots obeys the Vogel-Tammen-Fulcher (VTF) behavior and activation energy values are deduced from the slopes. Use of NMP solvent turns out to be a key factor for improving the Zn2+ transport inside the GPE due to the interaction between Zn2+ cations and carbonyl groups of the NMP. High values of ionic conductivity and low activation energy values, together with the high reversibility and high current density obtained in the voltammograms reveal these GPEs as good candidates to be used in Zn batteries. Furthermore, ionic liquids-based GPEs are probed in Zn/MnO2 batteries, resulting specific capacities of 125mAhg−1.

Protic ionic liquid-based gel polymer electrolyte: structural and ion transport studies and its application in proton battery

Proton-conducting free standing gel polymer electrolyte (GPE) films containing protic ionic liquid, 1-butyl-3-methylimidazolium hydrogen sulphate, immobilized in blend of poly(vinylidenefluoride-co-hexafluoropropylene) and poly(vinylpyrrolidone) have been prepared by solution-cast technique. Films have been characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscope (SEM), differential scanning calorimetry (DSC), complex impedance spectroscopy, and cyclic voltammetry. Ionic conductivity of the semicrystalline and porous GPE films has been obtained as ~3.9 × 10−3 S cm−1 at room temperature. Protonic nature of conduction in the films has been established by performing cyclic voltammetry and complex impedance spectroscopy on the cells having both blocking (stainless steel) and both reversible electrodes (Zn + ZnSO4.7H2O). The electrochemical stability window of the films has been found as ~3.8 V. The highest conducting film has been used as a separator and proton conductor to fabricate a proton battery of configuration Zn + ZnSO4.7H2O |GPE film| PbO2 + V2O5. The battery shows an open circuit voltage of ~1.62 V. Energy density of the cell has been obtained as 35.2 W h kg−1 for low current drain. Rechargeability of the cell has been tested for ten cycles. The maximum discharge capacity of the cell has been obtained as ~2.50 mA h g−1 during the first discharge cycle.

Characterization and application of N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide ionic liquid–based gel polymer electrolyte prepared in situ by photopolymerization method in lithium ion batteries

Ionic liquid gel polymer electrolyte (IL-GPE) was prepared in situ by photocuring of a mixture containing N-methyl-N-propylpiperidinium bis(trifluoromethanesulfonyl)imide (IL), lithium bis(trifluoromethane-sulphonyl)imide and ethoxylated bisphenol A diacrylate. The obtained IL-GPE was characterized by differential scanning calorimetry (DSC), electrochemical impedance spectroscopy (EIS), cyclic and linear sweep voltammetry (CV and LSV) and galvanostatic charging/discharging. Ionic conductivity of the IL-GPE reached 0.64·10−4 S cm−1 at 25°C and increased with a rise in temperature to 4.8 10−3 S cm−1 at 95°C. Electrochemical stability of the IL-GPE is ca. 4.8V vs. Li/Li+. The assembled cell consisting of the Li/IL-GPE/LiFePO4 exhibited stable cycle properties and high capacity above 162 mAh g−1 after 50 cycles (96% of theoretical capacity, which for LiFePO4 is 170 mAh g−1) at the C/20 rate and 25°C. The results obtained indicate that the new IL-GPE is a promising candidate as an electrolyte for flexible lithium ion batteries.

Influence of temperature on ionic liquid-based gel polymer electrolyte prepared by electrospun fibrous membrane

Ionic liquid gel polymer electrolytes (ILPEs) based on electrospun P(VdF-HFP) membrane were prepared by incorporating RTILs, BMImTFSI or BMImBF4. A suitable BMIm cation based ionic liquid with lithium salt and influence of temperature on electrochemical performance was investigated. The BMImTFSI-based polymer electrolyte with LiTFSI salt showed better electrochemical properties and the properties increase with increasing the operation temperature to 40 ˚C, to 140 mAh g−1 discharge capacity at 1 C-rate. However, after 40 ˚C the properties remained the same even when the temperature was increased at high current density.

Fabrication and characterization of electrochemical double layer capacitors using ionic liquid-based gel polymer electrolyte with chemically treated activated charcoal electrodes

The present investigation deals with electrochemical double layer capacitors (EDLCs) made up of ionic liquid (IL)-based gel polymer electrolytes with chemically treated activated charcoal electrodes. The gel polymer electrolyte comprising of poly(vinylidine fluoride-co-hexafluropropylene) (PVdF-HFP)–1-ethyl-2,3-dimethyl-imidazolium-tetrafluroborate [EDiMIM][BF4]–propylene carbonate (PC)–magnesium perchlorate (Mg(ClO4)2) exhibits the highest ionic conductivity of ~8.4 × 10−3 S cm−1 at room temperature (~20 °C), showing good mechanical and dimensional stability, suitable for their application in EDLCs. Activation of charcoal was done by impregnation method using potassium hydroxide (KOH) as activating agent. Brunauer–Emmett–Teller (BET) studies reveal that the effective surface area of treated activated charcoal powder (1,515 m2 g−1) increases by more than double-fold compared to the untreated one (721 m2 g−1). Performance of EDLCs has been tested using cyclic voltammetry, impedance spectroscopy, and charge–discharge techniques. Analysis shows that chemically treated activated charcoal electrodes have almost triple times more capacitance values as compared to the untreated one.

Cycling Performance of Li4Ti5O12Electrodes in Ionic Liquid-Based Gel Polymer Electrolytes

electrodes in ionic liquid-based gel polymer electrolytes exhibitedreversible cycling behavior with good capacity retention. Cycling data and electrochemical impedancespectroscopy analyses revealed that the optimum content of the cross-linking agent necessary to ensure bothacceptable initial discharge capacity and good capacity retention was about 8 wt %. Key Words : Anode, Ionic liquid, Gel polymer electrolyte, Lithium-ion battery, Li

Rheological characterizations of ionic liquid-based gel polymer electrolytes and fumed silica-based composite polymer electrolytes

In this work, two different polymeric systems were investigated. Ionic liquid-based gel polymer electrolytes (IL-GPEs) are designated as the first system and composite polymer electrolytes (CPEs) with addition of nano-sized fumed silica (SiO2) are assigned as the second system. From amplitude sweep and oscillatory shear sweep tests, it was found out that the values of storage modulus (G′) are much higher than loss modulus (G″), indicating the elastic behavior of these samples. No behavioral transition of samples was observed in the tests. Linear visco-elastic range (LVE) of samples becomes wider with increasing content of ionic liquid and SiO2. Long-term structural stability was enhanced upon addition of ionic liquid. In the frequency sweep test, the absence of G″ further confirmed the solid properties of samples. The inclusion of SiO2 did not show any improvement in the frequency sweep test. The zero-shear viscosities were reduced upon inclusion of ionic liquid and SiO2. In the viscosity curve, the decrement of viscosity was shown as increase in shear rate due to the structural changes.

Evaluation and investigation on the effect of ionic liquid onto PMMA-PVC gel polymer blend electrolytes

1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl imide), BmImTFSI based poly(methyl methacrylate)-poly (vinyl chloride), PMMA-PVC gel polymer electrolytes were prepared by solution casting technique. These ionic liquid-based gel polymer electrolytes exhibit Arrhenius type temperature dependence of ionic conductivity. The highest ionic conductivity of (8.08 ± 0.01) × 10 − 4 Scm −1 was achieved at 80 °C upon addition of 60 wt.% of BmImTFSI. X-ray diffraction (XRD) and scanning electron microscopy (SEM) studies revealed the amorphous nature and morphology of these polymer electrolytes, respectively. The lower coherence length of the peak inferred the higher amorphous degree in these polymer matrices. Decreases in T g and T m indicate the flexibility of polymer backbone. The amorphous behavior of these ionic liquid-based gel polymer electrolytes are also enhanced as shown in differential scanning calorimetry (DSC) analysis. On the contrary, thermogravimetric analysis (TGA) divulges that the thermal stability of polymer electrolytes has been improved upon impregnation of BmImTFSI.

Ionic liquid-based gel polymer electrolyte for LiMn 0.4Fe 0.6PO 4 cathode prepared by electrospinning technique

Two polymer electrolytes (PEs), one consisting of 1 M LiPF 6 in ethylene carbonate (EC)/dimethyl carbonate (DMC) (PE EC/DMC) and the other consisting of LiTFSI in room temperature ionic liquid (RTIL), 1-ethyl-3-methyl imidazolium bis(trifluoromethane sulfonyl)imide (EMITFSI) (PE IL), were prepared by using electrospun P(VdF-HFP) membranes. The PEs showed typical impedance spectroscopic responses with high conductivity and good anodic stability . The PEs were applied with carbon coated LiMn 0.4Fe 0.6PO 4 cathode material prepared by sol–gel method. The charge–discharge kinetics of LiMn 0.4Fe 0.6PO 4 cathode cells were studied by electrochemical impedance spectroscopy. The excellent performance with high capacity and good cycle stability was observed for both the cells. The cell comprising of PE IL showed a better performance than the other cell. The cells having PE EC/DMC and PE IL delivered discharge capacities of 150 and 141 mAh g −1, and 168 and 162 mAh g −1, respectively, after cycle 1 and 50. The differences in the performance of the PEs originate from the differences in viscosity, ionic conductivity and also from the different levels of interactions of a RTIL and EC/DMC with the polymer. The evaluation of lithium ion diffusion coefficients shows its fast diffusion in both the cases, the trend of which changed with the increase in the number of cycles.

Lithium ion conduction in ionic liquid-based gel polymer electrolyte

The conduction mechanism of gel electrolyte system consisting of poly(ethylene oxide) branched poly(methyl methacrylate) (PEO-PMA) matrix and ionic liquid containing lithium salt has been investigated. The kinetics of ion conduction and the mobility of lithium ion are different by the kind of ionic liquid; 1-ethyl-3-methyl imidazolium bis(trifluoromethane sulfone)imide (EMITFSI) or hexyltrimethylammonium bis(trifluoromethane sulfone)imide (HTMATFSI). Lithium ion exhibits a significant contribution for ion conduction in the gel electrolyte containing HTMATFSI. In contrast, the mobility of lithium ion is not obvious in the gel electrolyte containing EMITFSI. Such difference is considered to originate from the difference in ‘miscibility’ of polymer component in ionic liquid.