Investigation of mechanical properties of polyvinyl chloride-polyethylene oxide (PVC-PEO) based polymer electrolytes for lithium polymer cells

Polymer electrolytes composed of a blend of polyvinyl chloride-polyethylene oxide (PVC-PEO) as a host polymer, lithium triflate (LiCF₃SO₃) as a salt, mixture of ethylene carbonate (EC) and dibuthyl phthalate (DBP) as plasticizers and silica (SiO₂) as the nanocomposite filler were studied. Results suggest that PVC-PEO blending exhibits improved mechanical strength compared to that of pure PEO. The introduction of LiCF₃SO₃ changes the mechanical properties of PVC-PEO blends from hard and brittle to soft and tough. In PVC-PEO:LiCF₃SO₃ (70:30) system, the Young’s modulus value decreases from 5.30 × 10⁻¹ MPa to 4.78 × 10⁻⁴ MPa and the elongation at peak value increases from 3.71 mm to 32.09 mm with the incorporation of DBP and EC. The deteriorated mechanical properties with the addition of plasticizers are overcome with the addition of SiO₂ as nanocomposite filler. In PVC-PEO-LiCF₃SO₃-DBP-EC system, the addition of 5% SiO₂ increases the Young’s modulus value from 4.78 × 10⁻⁴ MPa to 1.51 × 10⁻³ MPa. The improvement of the mechanical properties reveals greater dispersion of SiO₂ particles in PVC-PEO blend based polymer electrolytes. In practical lithium polymer cells, inorganic fillers are frequently added to improve the mechanical strength of the electrolyte films.     

Ionic conductivity and compatibility studies of blends of poly(methyl methacrylate) and poly(propylene glycol) complexed with LICF3SO3

Stable to atmospheric moisture, adhesive and transparent polymer electrolytes have been prepared by blending poly(methyl methacrylate) (PMMA) with poly(propylene glycol)-425/LiCF₃SO₃ complexes. The blending of the polymers has been achieved by a method developed in our laboratory: free radical polymerization of methylmethacrylate in the polyether/salt matrix. A series of polymer blend complexes varying in PMMA content (up to 20% by weight) and oxygen/metal ratios (25, 16, and 8) have been synthesized and their properties studied. All the samples prepared in this study were found to be optically clear unlike the higher molecular weight poly(propylene glycol)-2000 (PPG-2000) system which required a minimum salt concentration to compatibilize a specific amount of PMMA with PPG. The mechanisms by which the salt holds the otherwise incompatible polymers together in a single phase have been investigated by FT-IR. Our studies show a weak coupling of the ether oxygens in the PPG with the ester groups of the PMMA through the lithium cations. Discrete changes has been observed in the FT-IR spectrum of PMMA when doped with the lithium salt hitherto unnoticed with other dopants. Gel permeation chromatography results of the PMMA samples isolated from the solid electrolytes indicate the molecular weight to vary between 43000 and 121000 with relatively narrow distributions, 1.6?2.0. The ionic conductivities of the polymer blend electrolytes were fairly high (10^?5 S/cm) at room temperature. The PMMA neither significantly influenced the T_g of the blend complexes nor effected the ionic conductivities drastically. The ionic conductivity as a function of temperature followed the empirical Vogel-Tammann-Fulcher equation. The blending of PMMA with PPG/LiCF₃SO₃ complexes was found to impart good adhesiveness to the solid electrolytes while making them stable to atmospheric moisture. © 1992 John Wiley & Sons, Inc.     

Thermal and ionic conductivity studies of plasticized PMMA/PVdF blend polymer electrolytes

Poly(methylmethacrylate) (PMMA)/poly(vinylidene fluoride) (PVdF) blend based electrolyte films containing different lithium salt concentrations are prepared using solvent casting technique. The complexation has been confirmed using XRD and FTIR spectral studies. Ionic conductivity and thermal behaviour of PMMA/PVdF complexes were studied with various salt concentrations, temperature and plasticizer content. The network structure of the polymer complexes are also investigated using SEM. The maximum value of conductivity 4.2×10⁻³ S/cm is obtained for the PMMA(7.5)-PVdF(17.5)-LiClO₄(8)-DMP(67) polymer complex at 303 K.     

Hexanoyl chitosan/ENR25 blend polymer electrolyte system for electrical double layer capacitor

Single salt polymer electrolytes based on hexanoyl chitosan‐ENR25 were prepared by employing LiN (CF₃SO₂)₂ or LiCF₃SO₃ as the doping salt. Elastic property of hexanoyl chitosan was enhanced with the incorporation of ENR25. DSC studies revealed immiscibility of hexanoyl chitosan and ENR25, and dissolution of salt was favored in ENR25 phase. Conductivity enhancement was observed in the blends as compared with the neat hexanoyl chitosan. The maximum conductivities achieved for LiCF₃SO₃‐ and LiN (CF₃SO₂)₂‐comprising electrolyte systems were 1.6 × 10^?8 and 5.0 × 10^?7 S cm^?1, respectively. Deconvolution of spectra bands in the v_as (SO₂^?) mode of LiN (CF₃SO₂)₂ and v_s (SO₃^?) mode of LiCF₃SO₃ has been carried out to estimate the relative percentage of free ions and associated ions. The findings were in good agreement with conductivity results. Electrical double layer capacitor (EDLC) was fabricated with hexanoyl chitosan/ENR25 (90:10)‐LiN (CF₃SO₂)₂‐EmImTFSI electrolyte and activated carbon‐based electrodes. The conductivity and electrochemical stability window of hexanoyl chitosan/ENR25‐LiN (CF₃SO₂)₂‐EmImTFSI were ~10^?6 S cm^?1 and 2.7 V, respectively. The performance of the EDLC was analyzed by cyclic voltammetry (CV) and galvanostatic charge‐discharge (GCD). From GCD, the specific capacitance of EDLC was 58.0 F g^?1 at 0.6 mA cm^?2. The specific capacitance was found to decrease with increasing current density.     

Structural,thermal, vibrational,and electrochemical behavior of lithium ion conducting solid polymer electrolyte based on poly(vinyl alcohol)/poly(vinylidene fluoride) blend

The present study focuses on the preparation and characterization of poly(vinyl alcohol)/poly(vinylidene fluoride) blend polymer electrolyte doped with lithium triflate (LiCF₃SO₃). Interaction of lithium triflate with the host polymer in the solid polymer electrolyte was studied using X-ray diffraction, Fourier transform infrared spectroscopy and differential scanning calorimetry analysis. It was found that 15% salt doped polymer electrolyte possesses the highest ionic conductivity (2.7 × 10^–3 S/cm) at 303 K, the higher thermal stability at 175°C. Linear sweep voltammetry results revealed that the film is electrochemically stable up to 3.4 V.     

Additive Effects of Lithium Salts with Various Anionic Species in Poly (Methyl Methacrylate)

We report that lithium salts in lithium-ion batteries effectively modify the physical properties of poly (methyl methacrylate) (PMMA). The glass transition temperature (T_g) is an indicator of the heat resistance of amorphous polymers. The anionic species of the salts strongly affected the glass transition behavior of PMMA. We focused on the additive effects of various lithium salts, such as LiCF₃SO₃, LiCOOCF₃, LiClO₄, and LiBr, on the T_g of PMMA. The large anions of the former three salts caused them to form macroscopic aggregates that acted as fillers in the PMMA matrix and to combine the PMMA domains, increasing T_g. On the other hand, LiBr salts dispersed microscopically in the PMMA matrix at the molecular scale, leading to the linking of the PMMA chains. Thus, the addition of LiBr to PMMA increased T_g as well as the relaxation time in the range of glass to rubber transition.     

Viscoelastic properties of poly(methyl methacrylate) with high glass transition temperature by lithium salt addition

The effect of ion‐dipole interaction between lithium cations and oxygen atoms in poly(methyl methacrylate) (PMMA), which leads to the great enhancement of glass transition temperature (T_g), on the linear viscoelastic properties is studied using binary blends of PMMA and lithium trifluoromethanesulfonate (LiCF₃SO₃). The strong interaction at low temperature leads to the high modulus in the glassy region even near T_g. The interaction becomes weak as increasing the temperature. Consequently, the rheological terminal region is clearly detected without a marked enhancement of steady‐state compliance, although the zero‐shear viscosity increases by the LiCF₃SO₃ addition. The result indicates that the crosslinking due to the ion‐dipole interaction has a lifetime that decides the longest relaxation time. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 2388–2394     

Application of polyacrylonitrile-based polymer electrolytes in rechargeable lithium batteries

Polyacrylonitrile (PAN)-based polymer electrolytes have obtained considerable attention due to their fascinating characteristics such as appreciable ionic conductivity at ambient temperatures and mechanical stability. This study is based on the system PAN–ethylene carbonate (EC)–propylene carbonate (PC)–lithium trifluoromethanesulfonate (LiCF₃SO₃). The composition 15 mol% PAN–42 mol% EC–36 mol% PC–7 mol% LiCF₃SO₃ has shown a maximum room temperature conductivity of 1.2?×?10^?3 S cm^?1. Also, it was possible to make a thin, transparent film out of that composition. Cells of the form, Li/PAN–EC–PC–LiCF₃SO₃/polypyrrole (PPy)–alkylsulfonate (AS) were investigated using cyclic voltammetry and continuous charge–discharge tests. When cycled at low scan rates, a higher capacity could be obtained and well-defined peaks were present. The appearance of peaks elucidates the fact that redox reactions occur completely. This well proves the reason for higher capacity. The average specific capacity was about 43 Ah kg^?1. Cells exhibited a charge factor close to unity during continuous charging and discharging, indicating the absence of parasitic reactions.     

Lithium-ion-conductive polyethylene oxide based polymer electrolytes containing tris(pentafluorophyenyl)borane

For enhancement of lithium-ion transference number, lithium-ion-conductive polymer electrolytes have been prepared from polyethylene oxide (PEO), lithium salt of LiCF₃SO₃ or LiF, plasticizer of polyethylene glycol dimethylether (PEGDME), and anion receptor of tris(pentafluorophenyl)borane (TPFB). Transport properties of the resultant polymer electrolytes have been studied by AC impedance spectroscopy. As a result, lithium-ion transference number increased with increasing TPFB due to the restriction of anion conduction by the interaction between anion and anion receptor. Effects of anion receptor on transport properties are discussed.     

A comparison of local structures in crystalline P(EO)3LiCF3SO3 and glyme-LiCF3SO3 systems

The newly discovered crystal structures of CH₃(OCH₂CH₂)OCH₃(LiCF₃SO₃)₂, monoglyme:(LiTf)₂, and CH₃(OCH₂CH₂)₃OCH₃(LiCF₃SO₃)₂, triglyme:(LiTf)₂, are briefly described. The coordination of lithium cations and the CF₃SO₃⁻ anions in these structures is compared with the cation and anion coordination in the crystalline phase of high molecular weight P(EO)₃LiCF₃SO₃. Comparison is also made with the previously reported crystalline phase of CH₃(OCH₂CH₂)₂OCH₃LiCF₃SO₃, diglyme:LiTf. A tendency to form trans-gauche-trans conformations for the bond order -O-C-C-O- is noted in adjacent ethylene oxide sequences interacting with a five-coordinate lithium ion.     

Preparation and characterization of polymer electrolyte membrane from chloroacetate chitosan/chitosan blended with epoxidized natural rubber

Chitosan-based membranes are among the most effective and efficient PEMs for fuel cells, however their low proton conductivity needs to be improved. In this study, chitosan, chloroacetate chitosan (CCS), chitosan blend with epoxidized natural rubber (ENR), and CCS with ENR blend based membranes were prepared by solution casting, crosslinked with NaOH and H₂SO₄, and investigated for physical, chemical, electrical and ionic properties. The functional groups were identified by ATR-FTIR spectroscopy and the peaks matched improved membrane properties. The surface roughness of the membranes was determined by AFM, and it increased with the amount of ENR. The electrical properties measured with an LCR meter showed that the CCS, CS and CS-B had the highest conductance, conductivity, capacitance and dielectric constant, while the CCS10/ENR8, CS10/ENR8 and CS15/ENR3 showed the highest resistance and resistivity. Furthermore, the CCS gave the lowest dissipation factor, which indicates its suitability for use in a PEM. In addition, the contact angle was relatively high for CS-B, CS and CCS.     

Solid Polymer Electrolytes Studied by NMR Spectroscopy and DFT Calculations

Summary: Results obtained recently on polymer electrolytes poly(ethylene oxide) (PEO)/LiCF₃SO₃ and poly(2-ethyl-2-oxazoline) (POZ)/AgCF₃SO₃ by a combination of solid-state ¹³C and ¹H NMR spectroscopy and DFT quantum-chemical calculations are discussed. Essentially the same local structure was found for the amorphous and crystalline phases of semicrystalline PEO/LiCF₃SO₃ polymer electrolyte. The amorphous POZ/AgCF₃SO₃ complex has a defined stoichiometry with two POZ monomeric units per one AgCF₃SO₃. A close contact between the metal salt and polymer was determined for both investigated systems from the Lee-Goldburg cross-polarization ¹H → ¹³C dynamics.     

Plasticiser interactions with polymer and salt in PVC-LiCF3SO3-DMF electrolytes

The IR spectra of pure DMF, LiCF₃SO₃, PVC, PVC-LiCF₃SO₃, LiCF₃SO₃-DMF, PVC-DMF and PVC-LiCF₃SO₃-DMF have been studied as part of a systematic research on the interactions between the components of the PVC-based electrolytes. It has been found that Li⁺ ions interact with the chlorine atoms of PVC in PVC-LiCF₃SO₃ samples. In LiCF₃SO₃-DMF samples interactions between Li⁺ is observed to be with both the oxygen and nitrogen atoms of DMF. PVC-DMF interactions are evident from the disappearance of the C-Cl stretching vibrations and the shifts in some peaks attributed to DMF. Free ions and ion pairs are observed to be present in the PVC-LiCF₃SO₃-DMF samples which affect the ionic conductivity of the samples.     

Thermal and kinetic studies of epoxidized natural rubber in lithium salts-epoxidized natural rubber polymer electrolytes

The thermal and kinetic studies of epoxidized natural rubber (ENR) and its polymer electrolytes, LiX/ENR PEs, (where X = ClO ₄ ^? , CF₃SO ₃ ^? , COOCF ₃ ^? , I^?, and BF ₄ ^? ) were carried out using thermogravimetric analysis at different heating rates. The thermal behaviors for LiX/ENR PEs are closely related to the morphology and interactions between the LiX and ENR chains. The LiCF₃SO₃, LiCOOCF₃, and LiI form pseudo-crosslinking within the ENR; their thermal behavior resembled purified ENR. The LiClO₄ tends to form aggregates within the ENR. This phenomenon has promoted a much earlier decomposition of epoxide in the ENR. The occurrence of ring-opening and complexation or cross-linking reactions in and between the ENR chains in the LiBF₄/ENR has produced a thermally stable macrostructure. The activation energy for the thermal degradation (E _d) of purified ENR was 239.8 and 239.9 kJ mol^?1 using Kissinger and FWO methods, respectively. According to the Coats–Redfern method, the degradation mechanism of purified ENR follows the F₁ type model, while the Criado method revealed that the degradation starts with F₁ followed by D₃ type models. The E _d for LiX/ENR (X = COOCF ₃ ^? , CF₃SO ₃ ^? , I^?, and BF ₄ ^? ) PE’s obtained via the Kissinger method are 258.5, 257.0, 251.0, and 198.9 kJ mol^?1, respectively, and the corresponding E _d values obtained by FWO are 236.0, 223.6, 349.7, and 206.6 kJ mol^?1, respectively. The degradation of ENR in these PEs followed the D₃ type model. However, for LiClO₄/ENR, the presence of two distinct degradations of ENR gave two E _d values. These are 174.5 and 234.7 kJ mol^?1 using Kissinger and 117.8 and 293.6 kJ mol^?1 using FWO method. The degradation mechanism of ENR in the LiClO₄/ENR PE was similar to purified ENR that is F₁ followed by D₃ type models.     

Evaluation of air permeability characteristics on the hybridization of carbon black with graphene nanoplatelets in bromobutyl rubber/epoxidized natural rubber composites for inner‐liner applications

Nanotechnology has been explored recently as a means of enhancing the properties of conventional elastomers for engineering applications. In the current study, the effect of nanofillers on air impermeability properties of Brominated isobutylene‐isoprene rubber (BIIR)/Epoxidized natural rubber (ENR) blend has analyzed for automotive applications. The ENR chosen is ENR 25 and ENR 50 (25 and 50% epoxidation) and prepared the blends in a ratio of 75:25 (BIIR:ENR), and from both blend based composites, a part of carbon black replaced with graphene nanoplatelets (GNP). The physical and thermal properties were compared for both binary blend nanocomposites to study the level of exfoliation and reinforcement behavior of GNP. Morphology studies were employed to reveal the level of interaction between GNP and carbon black in both blends. The influence of epoxidation in the formation of nanostructures in both blends have been evaluated, and the effect of nanostructures on air permeability properties was studied. The air impermeability of BIIR‐ENR 50 nanocomposites were improved with increasing platelet concentration, a 30% improvement in air permeability is obtained for BIIR‐ENR 50 composites over BIIR ‐ENR 25.     

Nano lithium aluminate filler incorporating gel lithium triflate polymer composite: Preparation,characterization and application as an electrolyte in lithium ion batteries

Gel polymer composites electrolytes containing nano LiAlO₂ as filler were prepared using a solution cast technique and characterized using different techniques such as X-ray diffraction (XRD), thermal analysis (TG, DSC), Fourier transform infra – red spectroscopy (FT-IR) and scanning electron microscope (SEM). X-ray diffraction analysis showed the effect of lithium tri fluoro methane sulphonate (LiCF₃SO₃), poly vinyl acetate (PVAc) and nano lithium aluminate (LiAlO₂) on the crystalline structure of the poly vinylidene fluoride –co– hexa fluoro propylene (PVDF-co-HFP) matrix containing ethylene carbonate (EC) and diethyl carbonate (DEC) as plasticizers. FT-IR analysis confirmed both the good dissolution of the LiCF₃SO₃ salt and the good interaction of the nano LiAlO₂ filler with the polymer matrix. TG analysis showed the good thermal stability of the LiAlO₂ samples compared to the free one. Also, addition of nano LiAlO₂ filler enhanced the conductivity value of the polymer composites electrolytes. The sample containing 2 wt% of LiAlO₂ showed the highest conductivity value, 4.98 × 10⁻³ Ω ⁻¹ cm⁻¹ at room temperature, with good thermal stability behavior (T_d = 362 °C). This good conductive and thermally stable polymer nano composite electrolyte was evaluated as a promising membrane for lithium ion batteries application.     

Polyimide-polysiloxane-segmented copolymers as high-temperature polymer electrolytes

Based on the fact that the flexibility of the polymer backbone will affect the ion transport and sometimes enhance the ionic conductivity, copolymer electrolytes of 1,2,4,5-benzene-tetracarboxylic dianhydride (PMDA), 4-aminophenyl ether (ODA), and aminopropyldimethyl-terminated polydimethylsiloxane (PSX), with or without doping of lithium triflate, have been prepared and investigated by infrared spectroscopy and electrical conductivity measurements. The PSX was found to be incorporated into PMDA-ODA polyimide to form block copolymers, and the best conductivity (10^-7 s/cm at 300°C) is observed in the lithium triflate-doped PMDA-ODA-PSX copolymer with a composition of 4PMDA: 3DA: 0.6PSX: 2LiCF₃SO₃. This conductivity is about 100 times better than the result of the lithium-doped PMDA, ODA, and 2,5-diaminobenzene sulfonic acid (DABSA) copolymer (4PMDA: 3DA:1DABSA:1LiCF₃SO₃) recently reported by this group. © 1994 John Wiley & Sons, Inc.     

Cycling a Sulfur Electrode in Mixed Electrolytes Based on Sulfolane: Effect of Ethers

The cycling of a sulfur electrode is studied in 1 M LiCF₃SO₃ solutions in sulfolane mixtures with ethers 1,2-dimethoxyethane, dioxolane, and tetrahydrofuran. The results suggest that the electrochemical behavior of sulfur is defined by the forms of existence of lithium polysulfides in the electrolyte.     

Solid state NMR studies of syndiotactic polystyrene/ethylbenzene and poly(ethylene oxide)/LiCF3SO3 molecular complexes

Solvent dynamics and polymer-solvent interactions in syndiotactic (s) polystyrene (PS)/ethylbenzene (PhEt) clathrates, as well as polymer-salt interactions in the poly(ethylene oxide) (PEO)/LiCF₃SO₃ complex, were characterized by solid state ¹H and ¹³C NMR. ¹H static and ¹H MAS NMR spectra have shown that PhEt molecules in s-PS clathrates retain relatively large, but spatially anisotropic mobility. ¹³C CP/MAS (cross polarization/magic angle spinning) spectra and CP dynamics measured for s-PS-dg/PhEt system indicate that at least a part of PhEt molecules are intercalated between phenyl rings of s-PS. ¹³C CP/MAS NMR spectra show that PEO carbons in complex with LiCF₃SO₃ are more shielded in comparison to neat crystalline PEO. The results (distances) obtained from CP dynamics are in agreement with the published crystal structure of the PEO/LiCF₃SO₃ complex. ¹³C spin-lattice relaxation time measurements have shown that the mobility of PEO in the complex is lower than that in neat crystalline PEO.     

Thermochemical and Electrochemical Stability of Electrolyte Systems based on Sulfolane

UV spectroscopy and cyclic voltammetry were used to examine the thermochemical and electrochemical stabilities of liquid sulfolane-based electrolyte systems for lithium and lithium-ion batteries. It was found that solutions of lithium salts in sulfolane are stable in prolonged keeping at 100°C. The thermochemical stability of lithium salt solutions in sulfolane changes in the order LiBF₄ > LiClO₄ ≈ LiN(CF₃SO₂)₂ > LiCF₃SO₃. It was shown that the electrochemical stability of lithium salt solutions in sulfolane is in the range from 5.5 to 5.9 V (relative to Li/Li⁺) and prolonged action of high temperatures (100°C) does not yield electrochemically active thermal destruction products.