Electrochemical and NMR characterizations of mixed polymer electrolytes based on oligoether sulfate and imide salts

Polymer electrolytes based on mixtures of lithium trifluoromethylsulfonylimide, LiTFSI and lithium oligoether sulfates dissolved in poly(oxyethylene) were studied. The properties of these mixed electrolytes i.e. thermal stability, ionic conductivities, transference numbers, diffusion coefficients and electrochemical stabilities were established in a wide range of compositions. A satisfactory compromise was found between high cationic transference numbers and high conductivities, while markedly decreasing the total amount of LiTFSI used. Since lithium oligoether sulfates should be considerably less expensive than LiTFSI and easy to recycle, these mixed polymer electrolytes seem to be promising.     

Chitosan‐based gel film electrolytes containing ionic liquid and lithium salt for energy storage applications

Fabrication, characterization, and a comparative study have been performed for chitosan‐based polymer electrolytes using two different dispersion media. Chitosan gel film (solid) electrolytes are fabricated using acetic acid or adipic acid as the dispersant for chitosan in combination with ionic liquid and lithium salt. This quaternary system of chitosan, acetic acid or adipic acid, 1‐butyl‐3‐methylimadazolium tetrafluoroborate (ionic liquid), and lithium chloride is formed as an electrolyte for potential secondary energy storage applications. The ionic conductivities, thermal, structural, and morphological properties for these electrolytes are compared. The ionic conductivities for chitosan/adipic acid (CHAD) and for chitosan/acetic acid (CHAC) systems are in the range of 3.71 × 10⁻⁴−4.6 × 10⁻³ and 1.3 × 10⁻⁴ −3.2 × 10⁻³ S cm⁻¹, respectively. The thermal stability of CHAD‐based electrolytes is determined to be higher than that of CHAC‐based electrolytes. Preliminary studies are performed to determine the electrochemical stability of these materials as solid film electrolytes for electrochemical supercapacitors. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42143.     

An investigation of lithium ion conductivity of copolymers based on P(AMPS-co-PEGMA)

In this work, a series of novel lithium ion-conducting copolymer electrolytes based on 2-acrylamido-2-methyl-1-propane sulfonic acid (AMPS) and poly(ethyleneglycol) methacrylate (PEGMA) were produced and characterized. The copolymers were synthesized by free-radical polymerization of the corresponding monomers with three different feed ratios to form P(AMPS-co-PEGMA)-based electrolytes. After the polymerization, AMPS units of the copolymers were lithiated via ion exchange. The characterization of the electrolytes was done by ¹H-NMR, FTIR, differential scanning calorimetry (DSC), thermogravimetric analysis, X-ray diffraction, scanning electron microscopy (SEM), and impedance analyzer. The copolymers were thermal stable approximately to 200 °C. Single T_g transitions in DSC curves verified the homogeneity as well as amorphous characteristics. SEM further confirmed the homogeneity of the electrolytes. The lithium ion conductivity of these new polymer electrolytes was studied by impedance dielectric impedance analyzer and the effect of PEGMA contents onto the ionic conductivity of these copolymer electrolytes were investigated. It was observed that the temperature dependence of ionic conductivity was interpreted over Vogel Tammann Fulcher model. The Li ion conductivity increased by PEGMA content and S3 has maximum conductivity of 3 × 10⁻³ mS cm⁻¹ at 100 °C. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47798.     

Synthesis and gelation of fluoroalkyl end‐capped copolymers containing glucosyl segments: Application to new fluorinated conductive polymer electrolytes

Fluoroalkyl end‐capped copolymers containing glucosyl segments were prepared by the copolymerizations of fluoroalkanoyl peroxides with 2‐glucosyoxyethyl methacrylate (GEMA) and comonomers such as acrylic acid (ACA) and methacrylate monomer‐containing poly(oxyethylene) units (PME). Under the non‐cross‐linked conditions, fluoroalkyl end‐capped GEMA–ACA and GEMA–PME copolymers were found to cause a gelation in dimethyl sulfoxide (DMSO), where the aggregations of end‐capped fluoroalkyl segments and the hydrogen‐bonding interaction between hydroxyl segments are involved in establishing a physical gel network, although the corresponding nonfluorinated GEMA copolymers could cause no gelation in DMSO. More interestingly, it was demonstrated that these fluorinated polymeric gelling electrolytes containing lithium salts exhibit a considerably high ionic conductivity of 10^?3 S/cm level at room temperature. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2833–2838, 2002     

Ion conduction of poly[methoxy oligo (oxyethylene) propylene] synthesized by the Et(Ind)2ZrCl2-MAO catalyst

Poly[methoxy oligo (oxyethylene) propylene] was synthesized by means of the Et(Ind)₂ZrCl₂-MAO catalyst. The ionic conductivity of poly[methoxy oligo (oxyethylene) propylene] with the lithium salt depends on the content of the lithium salt. The temperature dependence of conductivity was determined and the Vogel–Tammann/Hesser–Fulcher (VTF) plot agreed well with theoretical values, confirming the influence of the polymer segmental motion on conductivity. The ionic conductivity as high as 10^−4.7 s/cm can be obtained at room temperature, and this can be increased one or two orders of magnitude by blending the polyelectrolyte with hydroxyl-containing additives such as tetraethylene glycol. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1397–1400, 1999     

Comb-shaped High Molecular Weight Polyether Consisting of Oxyethylene Units for Polymer Solid Electrolyte

Novel high molecular weight comb-shaped polyethers were synthesized and used as the matrix of a polymer solid electrolyte. Both the main chain and the side chain of these polyethers consist of oxyethylene units. The new polyethers possess film-forming properties, because the weight-average molecular weights were over 10⁶. The short side chains of oxyethylene units gave rise to less crystallization of poly(oxyethylene) segments and to an increase of ionic conductivity when doped with lithium perchlorate. © 1997 SCI.     

Hyperbranched Poly(Glycidol)-Grafted Silica Nanoparticles for Enhancing Li-Ion Conductivity of Poly(Ethylene Oxide)

Silica nanoparticles bearing hyperbranched polyglycidol (hbP) grafts are synthesized and blended with poly(ethylene oxide) (PEO) for the fabrication of composite solid polymer electrolytes (SPEs) for enhancing Li-ion conductivity. Different batches of hbPs are prepared, namely, the 5th, 6th, and 7th with increasing molecular weights using cationic ring-opening polymerization and grafted the hbPs onto the silica nanoparticles using quaternization reaction. The effect of end functionalization of hbP-grafted silica nanoparticles with a nitrile functional group (CN–hbP–SiO₂) on the ionic conductivity of the blends with PEO is further studied. High dipole moments indicate polar nature of nitriles and show high dielectric constants. Among all the hbPs, the 6th-batch CN–hbP–SiO₂ nanoparticles exhibit better ionic conductivity on blending with PEO showing ionic conductivity of 2.3 × 10⁻³ S cm⁻¹ at 80 °C. The blends show electrochemical stability up to 4.5 V versus lithium metal.     

Novel PEO-based solid composite polymer electrolytes with inorganic–organic hybrid polyphosphazene microspheres as fillers

Novel solid-state composite polymer electrolytes based on poly (ethylene oxide) (PEO) by using LiClO₄ as doping salts and inorganic–organic hybrid poly (cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) microspheres as fillers were prepared. Electrochemical and thermal properties of PEO-based polymer electrolytes incorporated with PZS microspheres were studied. Differential scanning calorimetry (DSC) results showed there was a decrease in the glass transition temperature of the electrolytes and the crystallinity of the samples in the presence of the fillers. Maximum ionic conductivity values of 1.2 × 10⁻⁵ S cm⁻¹ at ambient temperature and 7.5 × 10⁻⁴ S cm⁻¹ at 80° were obtained and lithium ion transference number was 0.29. Compared with traditional ceramic fillers such as SiO₂, the addition of PZS microspheres increased the ionic conductivity of the electrolytes slightly and led to remarkable enhancement in the lithium ion transference number.     

Poly(ethylene oxide)‐based block copolymer electrolytes for lithium metal batteries

Nanostructured block copolymer electrolytes (BCEs) based on poly(ethylene oxide) (PEO) are considered as promising candidates for solid‐state electrolytes in high energy density lithium metal batteries (LMBs). Because of their self‐assembly properties, they confer on electrolytes both high mechanical strength and sufficient ionic conductivity, which linear PEO cannot provide. Two types of PEO‐based BCEs are commonly known. There are the traditional ones, also called dual‐ion conducting BCEs, which are a mixture of block copolymer chains and lithium salts. In these systems, the cations and anions participate in the conduction, inducing a concentration polarization in the electrolyte, thus leading to poor performances of LMBs. The second family of BCEs are single‐lithium‐ion conducting BCEs (SIC‐BCEs), which consist of anions being covalently grafted to the polymer backbone, therefore involving conduction by lithium ions only. SIC‐BCEs have marked advantages over dual‐ion conducting BCEs due to a high lithium ion transference number, absence of anion concentration gradients as well as low rate of lithium dendrite growth. This review focuses on the recent developments in BCEs for applications in LMBs with particular emphasis on the physicochemical and electrochemical properties of these materials. © 2018 Society of Chemical Industry     

Preparation and performance analysis of barium titanate incorporated in corn starch‐based polymer electrolytes for electric double layer capacitor application

Polymer electrolyte membranes composing of corn starch as host polymer, lithium perchlorate (LiClO₄) as salt, and barium titanate (BaTiO₃) as composite filler are prepared using solution casting technique. Ionic conductivity is enhanced on addition of BaTiO₃ by reducing the crystallinity and increasing the amorphous phase content of the polymer electrolyte. The highest ionic conductivity of 1.28 × 10^?2 S cm^?1 is obtained for 10 wt % BaTiO₃ filler in corn starch‐LiClO₄ polymer electrolytes at 75°C. Glass transition temperature (T_g) of polymer electrolytes decreases as the amount of BaTiO₃ filler is increased, as observed in differential scanning calorimetry analysis. Scanning electron microscopy and thermogravimetric analysis are employed to characterize surface morphological and thermal properties of BaTiO₃‐based composite polymer electrolytes. The electrochemical properties of the electric double‐layer capacitor fabricating using the highest ionic conductivity polymer electrolytes is investigated using cyclic voltammetry and charge‐discharge analysis. The discharge capacitance obtained is 16.22 F g^?1. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43275.     

Lithium ionic conductivity in poly(ether urethanes) derived from poly(ethylene glycol) and lysine ethyl ester

Poly(ether urethanes) obtained by the copolymerization of poly(ethylene glycol) (PEG) and lysine ethyl ester (LysOEt) are elastomeric materials that can be processed readily to form flexible, soft films. In view of these desirable physicomechanical properties, the potential use of these new materials as solid polymer electrolytes was explored. Solid polymer electrolytes were prepared with copolymers containing PEG blocks of different lengths and with different concentrations of lithium triflate (LiCF₃SO₃). Correlations between the length of the PEG block, the concentration of lithium triflate in the formulation, and the observed Li⁺ ion conductivity were investigated. Solid electrolyte formulations were characterized by differential scanning calorimetry for glass transition temperatures (T_g), melting points (T_m), and crystallinity. Ionic conductivity measurements were carried out on thin films of the polymer electrolytes that had been cast on a microelectrode assembly using conventional ac-impedance spectroscopy. These polymer electrolytes showed inherently high ionic conductivity at room temperature. The optimum concentration of lithium triflate was about 25–30% (w/w), resulting at room temperature in an ionic conductivity of about 10⁻⁵ S cm⁻¹. For poly(PEG₂₀₀₀-LysOEt) containing 30% of LiCF₃SO₃, the activation energy was ∼ 1.1 eV. Our results indicate that block copolymers of PEG and lysine ethyl ester are promising candidates for the development of polymeric, solvent-free electrolytes. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1449–1456, 1997     

Synthesis and electrochemical characterization of PEO-based polymer electrolytes with room temperature ionic liquids

New gel polymer electrolytes containing 1-butyl-4-methylpyridinium bis(trifluoromethanesulfonyl)imide (BMPyTFSI) ionic liquid are prepared by solution casting method. Thermal and electrochemical properties have been determined for these gel polymer electrolytes. The addition of BMPyTFSI to the P(EO)₂₀LiTFSI electrolyte results in an increase of the ionic conductivity, and at high BMPyTFSI concentration (BMPy⁺/Li⁺ = 1.0), the ionic conductivity reaches the value of 6.9 × 10⁻⁴ S/cm at 40 °C. The lithium ion transference numbers obtained from polarization measurements at 40 °C were found to decrease as the amount of BMPyTFSI increased. However, the lithium ionic conductivity increased with the content of BMPyTFSI. The electrochemical stability and interfacial stability for these gel polymer electrolytes were significantly improved due to the incorporation of BMPyTFSI.     

Effect of reaction kinetics of polymer electrolyte on the ion‐conductive behavior for poly(oligo oxyethylene methacrylate)–LiTFSI mixtures

The effect of the reaction kinetics on the ionic conductivity for a comblike‐type polyether (MEO) electrolyte with lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) was characterized by DSC, complex impedance measurements, and ¹H pulse NMR spectroscopy. The ionic conductivity of these electrolytes was affected by the reaction condition of the methacrylate monomer and revealed by the glass transition temperature (T_g), spin–spin relaxation time (T₂), steric effects of the terminal groups, and the number of charge carriers indicated by the VTF kinetic parameter. In this system, the electrolytes prepared by the reaction heating rate of 10°C/min of MEO–H and 15°C/min of MEO–CH₃ showed maximum ionic conductivity, σ_i, two to three times higher in magnitude than that of the σ_i of the others at room temperature. As experimental results, the reaction kinetic rate affected the degree of conversion, the ionic conductivity, and the relaxation behaviors of polyether electrolytes. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2149–2156, 2003     

Sol-gel preparation of a di-ureasil electrolyte doped with lithium perchlorate

Solid polymer electrolytes (SPEs) synthesized by the sol-gel process and designated as di-ureasils have been prepared through the incorporation of lithium perchlorate, LiClO₄, into the d-U(2000) organic-inorganic hybrid network. Electrolytes with lithium salt compositions of n (where n indicates the number of oxyethylene units per Li⁺ ion) between ∞ and 0.5 were characterized by conductivity measurements, cyclic voltammetry at a gold microelectrode, thermal analysis and Fourier transform Raman (FT-Raman) spectroscopy. The conductivity results obtained suggest that this system offers a quite significant improvement over previously characterized analogues doped with lithium triflate [S.C. Nunes, V. de Zea Bermudez, D. Ostrovskii, M.M. Silva, S. Barros, M.J. Smith, R.A. Sá Ferreira, L.D. Carlos, J. Rocha, E. Morales, J. Electrochem. Soc. 152 (2) (2005), A429]. “Free” perchlorate ions, detected in all the samples examined, are identified as the main charge carriers in the sample that yields the highest room temperature conductivity (n = 20). In the di-ureasils with n ≤ 10 ionic association is favoured and the ionic conductivity drops.     

Solid polymer electrolytes. VII. Preparation and ionic conductivity of gelled polymer electrolytes based on poly(ethylene glycol) diglycidyl ether cured with α,ω‐diamino poly(propylene oxide)

Crosslinked polymer electrolyte networks were prepared from poly(ethylene glycol) diglycidyl ether blended with an epoxy resin (diglycidyl ether of bisphenol A) in different ratios and then cured with α,ω‐diamino poly(propylene oxide) in the presence of lithium perchlorate (LiClO₄) as a lithium salt. The ionic conductivities of these polymer electrolytes were determined by alternating current (AC) impedance spectroscopy. Propylene carbonate (PC) was used as a plasticizer to form gelled polymer electrolyte networks. The conductivities of the polymer electrolytes containing 46 wt % PC plasticizer were approximately 5 × 10^?4 S cm^?1 at 25°C and approximately 10^?3 S cm^?1 at 85°C. These polymer electrolytes were homogeneous and exhibited good mechanical properties. The effects of the polymer composition, plasticizer content, salt concentration, and temperature on the ionic conductivities of the polymer electrolytes were examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1264–1270, 2004     

Preparation of polymer electrolytes based on the polymerized imidazolium ionic liquid and their applications in lithium batteries

The polymer electrolytes based on a polymerized ionic liquid (PIL) as polymer host and containing 1,2‐dimethyl‐3‐butylimidazolium bis(trifluoromethanesulfonyl)imide (BMMIM‐TFSI) ionic liquid, lithium TFSI salt, and nanosilica are prepared. The PIL electrolyte presents a high ionic conductivity, and it is 1.07 × 10^?3 S cm^?1 at 60°C, when the BMMIM‐TFSI content reaches 60% (the weight ratio of BMMIM‐TFSI/PIL). Furthermore, the electrolyte exhibits wide electrochemical stability window and good lithium stripping/plating performance. Preliminary battery tests show that Li/LiFePO₄ cells with the PIL electrolytes are capable to deliver above 146 mAh g^?1 at 60°C with very good capacity retention. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40928.     

In situ study of ionic conductivity for polyether-LiCF3SO3 electrolytes with subcritical and supercritical CO2

In situ measurements of the ionic conductivity were performed on polyethers, poly(ethylene oxide) (PEO) and poly(oligo oxyethylene methacrylate) (PMEO), with lithium triflate (LiCF₃SO₃) as crystalline and amorphous electrolytes, and at CO₂ pressures up to 20 MPa. Both PEO and PMEO systems in subcritical and supercritical CO₂ increased more than five fold in ionic conductivity at 40 °C composed to atmospheric pressure. The pressure dependence of the ionic conductivity for PEO electrolytes was positive under CO₂, and increased by two orders of magnitude under pressurization from 0 to 20 MPa, whereas it decreases with increasing pressure of N₂. The enhancement is caused by the plasticizing effect of CO₂ molecules that penetrate into the electrolytes.     

Polymer gel electrolytes containing sulfur-based ionic liquids in lithium battery applications at room temperature

Polymer gel electrolytes comprising a sulfur-based ionic liquid (IL), a lithium salt, and butyrolactone (GBL) as an additive hosted in PVdF-HFP matrix were prepared and characterized. The result shows that adding small amount of GBL to the polymer electrolytes can improve the cathodic stability of the electrolytes, which ensures the lithium plating/stripping in the redox process. Furthermore, cyclic voltammograms studies indicate that the polymer electrolytes have well reversible redox process. When the IL component reaches 75 wt%, the polymer electrolyte has higher ionic conductivity than the other samples and it is 6.32 × 10^?4 S cm^?1. The assembled batteries with the polymer electrolyte have better discharge capacity, and after 100 cycles, the discharge capacity of the battery still retains 148 mAh g^?1.     

Electrochemical behavior of ionically crosslinked polyampholytic gel electrolytes

An ionic complex of anionic and cationic monomers was obtained by protonation of (N,N-diethylamino)ethylmethacrylate (DEA) with acrylic acid (AAc). Free radical copolymerization of the ionic complex and acrylamide (AAm), yielded the ionically crosslinked polyampholytic gel electrolytes [poly(AAc-DEA-AAm), designated as PADA] using two types of organic solvents containing a lithium salt. The PADA gel electrolyte exhibited good thermal stability shown by the DSC thermogram. The impedance analysis at temperatures ranging from −30 to 75 °C indicated that the ionic conductivities of the PADA gel electrolytes were rather close to those of liquid electrolytes. The temperature dependence of the ionic conductivities was found to be in accord with the Arrhenius equation. Moreover, the ionic conductivities of PADA gel electrolytes increased with an increase of the molar ratios of cationic/anionic monomers. The ionic conductivities of PADA gels prepared in solvent mixtures of propylene carbonate, ethyl methyl ether and dioxolane (3:1:1, v/v) were higher than those of PADA gels prepared in propylene carbonate only. Significantly, the ionic conductivities of two kinds of PADA gel electrolytes were in the range of 10⁻³ and 10⁻⁴ S cm⁻¹ even at −30 °C. The electrochemical windows of PADA gel electrolytes measured by cyclic voltammetry were in the range from −1 V to 4.5 V.     

Morphology,crystallinity, and electrochemical properties of in situ formed poly(ethylene oxide)/TiO2 nanocomposite polymer electrolytes

A method to produce nanocomposite polymer electrolytes consisting of poly(ethylene oxide) (PEO) as the polymer matrix, lithium tetrafluoroborate (LiBF₄) as the lithium salt, and TiO₂ as the inert ceramic filler is described. The ceramic filler, TiO₂, was synthesized in situ by a sol–gel process. The morphology and crystallinity of the nanocomposite polymer electrolytes were examined by scanning electron microscopy and differential scanning calorimetry, respectively. The electrochemical properties of interest to battery applications, such as ionic conductivity, Li⁺ transference number, and stability window were investigated. The room‐temperature ionic conductivity of these polymer electrolytes was an order of magnitude higher than that of the TiO₂ free sample. A high Li⁺ transference number of 0.51 was recorded, and the nanocomposite electrolyte was found to be electrochemically stable up to 4.5 V versus Li⁺/Li. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2815–2822, 2003