A novel sandwiched membrane as polymer electrolyte for application in lithium-ion battery

A novel kind of sandwiched polymer membrane was prepared, which consists of two outer layers of electrospun poly(vinyl difluoride) (PVDF) fibrous films and one inner layer of poly(methyl methacrylate) (PMMA) film. Its characteristics were investigated by scanning electron microscopy and X-ray diffraction. The membrane can easily absorb non-aqueous electrolyte to form gelled polymer electrolytes (GPEs). The resulting gelled polymer electrolytes had a high ionic conductivity up to 1.93 × 10⁻³ S cm⁻¹ at room temperature, and exhibited a high electrochemical stability potential of 4.5 V (vs. Li/Li⁺). It is of great potential application in polymer lithium-ion batteries.     

Conductivity and thermal behavior of proton conducting polymer electrolyte based on poly (N-vinyl pyrrolidone)

The polymer electrolytes based on poly N-vinyl pyrrolidone (PVP) and ammonium thiocyanate (NH₄SCN) with different compositions have been prepared by solution casting technique. The amorphous nature of the polymer electrolytes has been confirmed by XRD analysis. The shift in T_g values and the melting temperatures of the PVP-NH₄SCN electrolytes shown by DSC thermo-grams indicate an interaction between the polymer and the salt. The dependence of T_g and conductivity upon salt concentration have been discussed. The conductivity analysis shows that the 20 mol% ammonium thiocyanate doped polymer electrolyte exhibit high ionic conductivity and it has been found to be 1.7 × 10⁻⁴ S cm⁻¹, at room temperature. The conductivity values follow the Arrhenius equation and the activation energy for 20 mol% ammonium thiocyanate doped polymer electrolyte has been found to be 0.52 eV.     

Compositional effect of PVdF-PEMA blend gel polymer electrolytes for lithium polymer batteries

Owing to their improved mechanical properties and good polymer miscibility, the blend gel polymer electrolytes of poly (vinylidene fluoride) (PVdF)-poly(ethyl methacrylate) (PEMA) have been prepared using solvent casting technique and characterized for their electrochemical performances. The electrolyte shows a maximum ionic conductivity of 1.5 × 10⁻⁴ S cm⁻¹ at 301 K for the 90:10 blend ratio of PVdF:PEMA system with good transport property. The ionic conductivity is enhanced, in accompany with improved microstructural homogeneity, at low PEMA contents, while the decreased conductivity at high contents has been attributed to increasing crystalline PEMA domains. With the optimum PVdF:PEMA ratio, the complex system was found to facile reasonable ionic transference number and exhibit superior interfacial stability with Li electrode.     

Ionic transport in P(VDF-HFP)-PMMA-LiCF3SO3-(PC + DEC)-SiO2 composite gel polymer electrolyte

Composite gel polymer electrolytes composed of poly(vinylidene fluoride-co-hexafluoropropylene) P(VDF-HFP) and polymethylmethacrylate PMMA polymers, PC + DEC as plasticizer and LiCF₃SO₃ as salt and fumed silica as filler have been synthesized by solvent casting technique with varying plasticizer-filler ratio systematically. Films of thickness in the range of 40-70 μm were characterized by a.c. impedance measurements in the temperature range 303 K to 373 K. Addition of filler to the polymer electrolyte was found to result in an enhancement of the ionic conductivity. A maximum electrical conductivity of ∼1 × 10⁻³ S/cm at 303 K and ∼2.1 × 10⁻³ S/cm at 373 K has been achieved with the dispersion of the SiO₂. FTIR spectral studies confirmed the polymer-salt interaction. XRD patterns exhibit the increased amorphicity in the blended composite gel polymer electrolytes. Scanning electron micrograph shows the dispersion of SiO₂ particle in the polymer electrolyte.     

Preparation of PVDF/PEO-PPO-PEO blend microporous membranes for lithium ion batteries via thermally induced phase separation process

Microporous poly(vinylidene fluoride)/polyethylene oxide-co-polypropylene oxide-co-polyethylene oxide (PVDF/PEO-PPO-PEO, or PVDF/F127) blend membranes were prepared via thermally induced phase separation (TIPS) process using sulfolane as the diluent. Then they were soaked in a liquid electrolyte to form polymer electrolytes. The effects of F127 weight fraction on the morphology, crystallinity and porosity of the blend membranes were studied. It was found that both electrolyte uptake of blend membranes and ionic conductivity of corresponding polymer electrolytes increased with the increase of F127 weight fraction. The maximum ionic conductivity was found to reach 2.94 ± 0.02 × 10⁻³ S/cm at 20 °C. Electrochemical stability window was stable up to 4.7 V (vs. Li⁺/Li). The testing results indicated that the PVDF/F127 blend membranes prepared via TIPS process can be used as the polymer microporous matrices of polymer electrolytes for lithium ion batteries.     

Self-standing single lithium ion conductor polymer network with pendant trifluoromethanesulfonylimide groups: Li diffusion coefficients from PFGSTE NMR

Solid electrolyte materials have the potential to improve performance and safety characteristics of batteries by replacing conventional solvent-based electrolytes. For this purpose, new candidate single ion conductor self-standing networks were synthesized with trifluoromethane-sulfonylimide (TFSI) lithium salt based monomer using poly(ethyleneglycol) dimethacrylate (PEGDM 750) as crosslinker. The highest ionic conductivity was 3.4 × 10⁻⁷ S cm⁻¹ at 30 °C in the dry state. Thermal and mechanical analyses showed good thermal stability up to 190 °C and rubbery-like properties at ambient temperature. A direct relationship between ionic conductivity and glassy or rubbery state of the membranes was found. Vogel–Tammann–Fulcher behavior was observed in the dry state which is consistent with a lithium conductivity correlated with polymer chain mobility. By swelling the network in propylene carbonate, a self-standing electrolyte gel could be obtained with an ionic conductivity as high as 1 × 10⁻⁴ S cm⁻¹ at 30 °C. The individual diffusion coefficients of mobile species in the material (¹⁹F and ⁷Li) were measured and quantified using pulsed-field gradient nuclear magnetic resonance (PFG-NMR). Diffusion coefficients for the most mobile components of the lithium cations and fluorinated anions at 100 °C in dry membranes have been found to be 3.4 × 10⁻⁸ cm² s⁻¹ and 2.1 × 10⁻⁸ cm² s⁻¹ respectively.     

Synthesis and characterization of a new network polymer electrolyte containing polyether in the main chains and side chains

A new network polymer electrolyte matrix with polyether in the side chains and main chains was synthesized by the azo-macroinitiator method and urethane reaction. The macroinitiator, polymer and network polymer were confirmed by Fourier-transform infrared (FT-IR) spectroscopy and ¹H NMR. FT-IR was also used to study the environment of lithium ions doped in these network polymer electrolytes. Three important groups are considered: N-H, carbonyl, and ether groups. The thermal properties of the polymer electrolytes were measured by differential scanning calorimetry and thermogravimetric analysis. The T_g value of this polymer is less than that of a general comb-like polymer. Added lithium ions interact with the oxygen atoms on ether groups, causing the T_g of the polymer electrolyte to increase. Moreover, the interaction between lithium ions and ether groups decreases the decomposition temperature of the polymer. The conductivity measured by AC impedance reached a maximum of 10⁻⁴ S cm⁻¹. A plot of conductivity vs. temperature fit the Vogel-Tamman-Fulcher equation, indicating that ionic mobility in this network polymer electrolyte is coupled to segmental chain movements.     

Methanol permeability in sulfonated poly(etheretherketone) membranes: A comparison with Nafion membranes

Partially sulfonated poly(etheretherketone) (SPEEK) samples were prepared by modification of corresponding poly(etheretherketone) (PEEK) with concentrated sulfuric acid. Membranes cast from these materials were evaluated as polymer electrolytes for direct methanol fuel cells (DMFCs). SPEEK membranes were characterized by ¹H NMR, FT-IR and TGA. The transverse proton conductivities increased from 4.1 to 9.3 × 10⁻³ S/cm with the increase of the degree of sulfonation (DS) from 0.59 to 0.93. These values were comparable with that of Nafion 117 membrane (1.0 × 10⁻² S/cm) measured under the same condition. Nearly one order magnitude difference between transverse conductivity and longitudinal conductivity was found. The methanol permeabilities of the SPEEK membranes were all lower than that of Nafion 117 membrane. The effects of temperature and methanol concentration on the methanol permeability were also studied. In addition, the selectivities of the SPEEK membranes for protons and methanol were all higher than that of Nafion 117 membrane.     

A novel ternary polymer electrolyte for LMP batteries based on thermal cross-linked poly(urethane acrylate) in presence of a lithium salt and an ionic liquid

A new ternary polymer electrolyte based on thermally cross-linked poly(urethane acrylate) (PUA), lithium bis(trifluoromethansulfonyl)imide (LiTFSI) and the ionic liquid N-butyl-N-methylpyrrolidinium TFSI (PYR₁₄TFSI) was developed and tested for application in LMP batteries. The polymer electrolyte was a transparent yellow self-standing material with quite good mechanical properties, i.e., comparable to that of a flexible rubber. The room temperature ionic conductivity of the dry polymer electrolyte was found to be as high as 0.1 mS cm⁻¹ for the compound containing 40 wt% of ionic liquid (PYR₁₄TFSI) and a O/Li ratio of 15/1 (Li⁺ from LiTFSI). The thermal analysis of the new cross-linked electrolyte showed that it was homogeneous, amorphous and stable over a wide temperature range extending from −40 °C to 100 °C. The homogeneity of the polymer electrolyte was also confirmed by SEM analysis.     

Effect of oleic acid plasticizer on chitosan-lithium acetate solid polymer electrolytes

Plasticized polymer electrolytes composed of chitosan as the host polymer, oleic acid (OA) as the plasticizer and lithium acetate (LiOAc) as the doping salt were prepared by the solution cast technique. These complexes with different amounts of salts and plasticizers were investigated as possible ionic conducting polymers. The highest ionic conductivity of the plasticized chitosan-LiOAc was ∼10⁻⁵ S cm⁻¹ for the film containing 40.0 wt.% LiOAc and 10.0 wt.% of OA. Conductivity for the plasticized LiOAc-doped chitosan polymer was also studied as a function of temperature between 300 and 363 K. The plot of ln(σT) versus 10³/T for each sample obeys Arrhenius rule indicating the conductivity to be thermally assisted. XRD and FTIR spectroscopy techniques have been used for the structural studies.     

A novel gel polymer electrolyte based on poly ionic liquid 1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium iodide

Poly ionic liquid 1-ethyl 3-(2-methacryloyloxy ethyl) imidazolium iodide (PEMEImI) as a single-ion conductor was designed and synthesized. When appropriate amount of suitable plasticizers, I₂ and polyacrylonitrile (PAN) were incorporated into it, the complex formed gel polymer electrolyte. Chemical structure, thermal behavior and ionic conductive properties of the gel polymer electrolyte were investigated by Raman spectra, UV-Vis spectra, differential scanning calorimetry (DSC), and complex impedance analysis, respectively. For the new gel polymer electrolyte, the ionic conductivity of about 1 × 10⁻³ S cm⁻¹ at room temperature was achieved.     

Compositional effect on the morphology and ionic conductivity of thermoplastic polyurethane based electrolytes

Four thermoplastic polyurethanes (TPUs) were synthesized from poly(ethylene glycol) (PEG), 4,4^′-methylenebis(phenyl isocyanate) (MDI), and 1,4-butanediol (1,4-BDO) with different 1,4-BDO/PEG ratios. The effect of polymer structure on the conductivity of the polymer elelctrolytes was investigated. Fourier transform infrared spectroscopy (FT-ir) and differential scanning calorimetry (DSC) were utilized to monitor changes in the morphology of the TPUs as polymeric solid electrolyte doped with LiClO₄. The structure of the TPUs has been investigated by 1H solution nuclear magnetic resonance spectroscopy. Alternating current (AC) impedance experiments were performed to determine the ionic conductivities of TPU films and their corresponding gel type electrolytes. The conductivity depends on the soft-segment concentration and on the degree of phase separation exhibited by these materials. One of the investigated TPU gel type electrolytes exhibits an ionic conductivity as high as 3×10⁻⁴ S/cm at room temperature.     

A composite microporous gel polymer electrolyte prepared by ultra-violet cross-linking

A new type of composite microporous gel polymer electrolyte was prepared by directly coating the hydrolyzed prepolymers onto PVdF microporous membrane, and then polymerizing and cross-linking with ultra-violet (UV). Their chemical, thermal, surface microscopic configuration, swelling ability and electrochemical properties have been investigated for various prepolymer’s solution concentrations. The swelling ability and ionic conductivity of the membrane supporting hybrid gel electrolyte (MSHGE) could reach an extreme point at 0.15 g/ml of the prepolymer’s solution. It is thought that their performance can be affected by the surface microscopic configuration and the quality of coated copolymer. The Arrhenius-type relationship was observed in the temperature dependence of ionic conductivity. The ionic conductivity of MSHGE (PVdF-15) at room temperature can reach 6.18 × 10⁻³ S cm⁻¹, and its electrochemical stability window is about 4.9 V.     

Electro chemical properties of porous PVdF-HFP membranes prepared with different nonsolvents

Porous poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) membranes were prepared by solvent–nonsolvent evaporation technique. Morphology and porosity of the membranes were varied with different nonsolvents and had an effect on electrochemical properties. The porous membranes were functionalized with different liquid electrolyte solutions such as p-toluene sulfonic acid/phosphoric acid/sulfuric acid. Maximum electrolyte uptake and minimal electrolyte leakage were tailored by the optimized porosity of the membranes. Thermal behavior obtained in this study ensures the complete evaporation of nonsolvents and ensures its thermal stability. The pTSA-activated PVdF-HFP/THF membrane exhibited high ionic conductivity of about 27.27 mS/cm and a lower methanol permeability in the range of 9.7 × 10⁻⁸ cm²/s. High compatibility between pTSA solution and porous PVdF-HFP polymer electrolyte membrane enhances its electro chemical behavior than that of conventional liquid electrolytes.     

Novel composite polymer electrolytes based on poly(ether-urethane) network polymer and modified montmorillonite

Novel composite solid polymer electrolytes (CSPEs) and composite gel polymer electrolytes (CGPEs) have been prepared. CSPE consists of poly(ether-urethane) network polymer, which is superior to poly(ethylene oxide) in mechanical stability due to its cross-linked structure, modified montmorillonite (MMMT) and LiClO₄, and CGPE with good mechanical strength comprises of the CSPE and LiClO₄–PC (propylene carbonate) solution. The ionic conductivity can be enhanced after the addition of MMMT, and CGPE exhibits ionic conductivity in the order of 10⁻³ S/cm at room temperature. The temperature dependence of the ionic conductivity of the CSPE follows the Vogel–Tamman–Fulcher (VTF) equation. The effects of MMMT on the interactions in these systems and the possible conduction mechanisms are also discussed.     

Conductivity studies of polymer electrolytes based on aliphatic polyesters

A series of aliphatic polyesters of sebacoyl chloride and poly(ethylene glycol) containing a different number of ethylene oxide groups was synthesized and characterized. These polyesters were complexed with lithium perchlorate to obtain a new class of polymer electrolyte. The relationships between the structure and properties of these polymer electrolytes were investigated. The main factor that affects the ionic conductivity in these systems was found to be the solvating capacity of the polyester for the lithium salt. These polymer electrolytes showed ionic conductivities up to 10^?5 ? 10^?4 S/cm at 25°C. The mechanical strength was improved by cross-linking, and the cross-linked polyester complexed with a LiCIO₄ salt showed an ionic conductivity of 2 × 10^?5 S/cm at room temperature. ⁷Li NMR spin-spin relaxation and dielectric relaxation studies were also carried out to investigate the local environments and dynamics of ions in the polymer electrolytes. © 1995 John Wiley & Sons, Inc.     

Brønsted acid-base polymer electrolyte membrane based on sulfonated poly(phenylene oxide) and imidazole

The Brønsted acid-base polymer electrolyte membrane was prepared by entrapping imidazole in sulfonated poly(phenylene oxide) at the molar ratio of Im/SPPO = 2:1. The hybrid showed a high thermal stability up to 200 °C and peroxide tolerance. Differential scanning calorimetry shows that glass transition temperature is 232 °C. The conductivity increases with temperature exceeding 10⁻³ S/cm above 120 °C and a high conductivity of 6.9 × 10⁻³ S/cm was obtained at 200 °C under 33% RH conditions.     

Preparation of alkaline anion exchange membranes based on functional poly(ether-imide) polymers for potential fuel cell applications

A novel poly(ether-imide)-based alkaline anion exchange membrane with no free base has been prepared and characterized for its ionic conductivity in water, which is a critical metric of its applicability in a liquid-fed direct methanol fuel cell. The poly(ether-imide)-based membranes were prepared by chloromethylation, quaternization and alkalization of commercial poly(ether-imide) and the derivatives were characterized by NMR. The chemical and thermal stabilities were investigated by measuring changes of ionic conductivities when the membranes were placed in various alkaline concentrations and temperatures for 24 h. The membranes were stable at all concentrations of KOH at room temperature, but not at elevated temperatures. The membranes were stable in 1.0 M KOH solution up to 80 °C without losing membrane integrity. The measured conductivity of the formed membrane ranged from 2.28 to 3.51 × 10⁻³ S/cm at room temperature. This preliminary study indicates that functionalized poly(ether-imide) has suitable conductivity suggesting that it can be used as an alkaline anion exchange membrane in fuel cell applications.     

Preparation and performance analysis of PE-supported P(AN-co-MMA) gel polymer electrolyte for lithium ion battery application

Copolymer, poly(acrylonitrile-co-methyl methacrylate) (P(AN-co-MMA)), was synthesized by solution polymerization with different mole ratios of monomers, acrylonitrile (AN) and methyl methacrylate (MMA). Polyethylene (PE) supported copolymer and gel polymer electrolyte (GPE) were prepared with this copolymer and their performances were characterized with FTIR, TGA, SEM, and electrochemical methods. It is found that the GPE using the PE-supported copolymer with AN to MMA = 4:1 (mole) exhibits an ionic conductivity of 2.06 × 10⁻³ S cm⁻¹ at room temperature. The copolymer is stable up to 270 °C. The PE-supported copolymer shows a cross-linked porous structure and has 150 wt% of electrolyte uptake. The GPE is compatible with anode and cathode of lithium ion battery at high voltage and its electrochemical window is 5.5 V (vs. Li/Li⁺). With the application of the PE-supported GPE in lithium ion battery, the battery shows its good rate and initial discharge capacity and cyclic stability.     

Effects of the porous structure on conductivity of nanocomposite polymer electrolyte for lithium ion batteries

A kind of porous nanocomposite polymer membranes (NCPMs) based on poly(vinylidene difluoride-co-hexafluoropropylene) (P(VdF-HFP)) incorporated with different amounts of TiO₂ nanoparticles from in situ hydrolysis of Ti(OC₄H₉)₄ was prepared by a non-solvent induced phase separation (NIPS) technology. The SEM micrographs reveal that a porous structure exists in the NCPMs, which changes with the incorporated amount of TiO₂. The NCPMs incorporated with 9.0 wt.% of mass fraction of TiO₂ possess the highest porosity, 67.3%, and appear as flexile fracture with an elongation ratio, 74.4%. At this content, the ionic conductivity of the NCPE is up to 0.94 × 10⁻³ S cm⁻¹ at room temperature and the activation energy for ions transport reaches the lowest, 18.71 kJ mol⁻¹. It is of great potential application in lithium ion batteries.