Electrochemical performance of electrospun poly(vinylidene fluoride-co-hexafluoropropylene)-based nanocomposite polymer electrolytes incorporating ceramic fillers and room temperature ionic liquid

In view of the safety concerns and the requirements of high energy density lithium batteries, the room temperature ionic liquids (RTILs) are being investigated as suitable candidates to substitute organic electrolytes in polymer electrolytes. In this article, we report synthesis, characterization, and electrochemical properties of nanocomposite polymer electrolytes (NCPEs) comprising of a RTIL [n-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BMITFSI)] and nano-sized ceramic fillers (SiO₂, Al₂O₃ or BaTiO₃) hosted in electrospun poly(vinylidene fluoride-co-hexafluoropropylene) [P(VdF-HFP)] membranes. The addition of BMITFSI and ceramic fillers in polymer electrolytes results in high ionic conductivity at room temperature. The cells prepared with BMITFSI and different NCPEs show good interfacial stability and oxidation stability at >5.5 V with the highest value of 6.0 V for the NCPE incorporating BaTiO₃. The cell with the NCPE containing BaTiO₃ delivers high initial discharge capacity of 165.8 mA h g⁻¹, which corresponds to 97.5% utilization of active material under the test conditions, and showed the least % capacity fade after prolonged cycling.     

Ionic liquid mediated nano-composite polymer gel electrolyte for rechargeable battery application

ABSTRACT

Nano-composite polymer gel electrolytes (NPGEs) based on polymer poly(vinylidene fluoride-co-hexafluoropropylene) PVdF-HFP, ionic liquid, 1-butyl-3- methylimidazolium bis(trifluoromethanesulfonyl)imide BMIMTFSI, Li-salt along with the addition of SiO₂ nanoparticles have been synthesized and characterized by various techniques. Prepared NPGEs show high room temperature ionic conductivity (~10^?3 S/cm) and have a wide electrochemical window (ECW) (~3.3–3.5 V). The galvanostatic charge/discharge profile was studied by sandwiching best performing NPGEs between a LiFePO₄ cathode and lithium metal anode. The specific discharge capacity of the cell (Li/NPGE/LiFePO₄) room temperature at 0.1C rate is found to be 138 mAh/g.     

Preparation and application of poly(ethylene oxide)-based all solid-state electrolyte with a walnut-like SiO2 as nano-fillers

Poly(ethylene oxide) (PEO) is one of the most promising candidates in polymer solid-state electrolyte. However, the polymer matrix has a high degree of crystallinity and thus manifests low conductivity, which restricts its application in all solid-state lithium-ion battery. Herein, a new composite polymer electrolyte (PLWLS), which is comprised of PEO, LiClO₄, and the independently synthetized walnut-like SiO₂ (WLS) as nano-fillers, is designed and prepared by the tape-casting way. The optimum mass fraction of walnut-like SiO₂ is determined by physical and electrochemical characterization. The result shows that the PLWLS-15 with 15 wt % walnut-like SiO₂ nanoparticles has a crystallinity of 13.7%. Similarly, the maximum tensile strength is improved greatly. The assembled all-solid-state lithium-ion battery with LiFePO₄/PLWLS-15/Li exhibits a higher discharge capacity of 167 mAh g⁻¹ at 0.1 C (1C = 170 mAh g⁻¹) and 143 mAh g⁻¹ at 0.5 C in first cycle, lower voltage polarization and better cycle performance. Therefore, adding nanoparticle into PEO-based solid-state electrolyte could effectively promote the mechanical property and electrochemical performance, and thus provide a possibility of application for PLWLS-15 in next generation all solid-state lithium battery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48810.     

Rechargeable Li/LiFePO4 cells using N-methyl-N-butyl pyrrolidinium bis(trifluoromethane sulfonyl)imide-LiTFSI electrolyte incorporating polymer additives

We have incorporated polymer additives such as poly(ethylene glycol) dimethyl ether (PEGDME) and tetra(ethylene glycol) dimethyl ether (TEGDME) into N-methyl-N-butylpyrrolidinium bis(trifluoromethane sulfonyl)imide (PYR₁₄TFSI)-LiTFSI mixtures. The resulting PYR₁₄TFSI + LiTFSI + polymer additive ternary electrolyte exhibited relatively high ionic conductivity as well as remarkably low viscosity over a wide temperature range compared to the PYR₁₄TFSI + LiTFSI binary electrolytes. The charge/discharge cyclability of Li/LiFePO₄ cells containing the ternary electrolytes was investigated. We found that Li/PYR₁₄TFSI + LiTFSI + PEGDME (or TEGDME)/LiFePO₄ cells containing the two different polymer additives showed very similar discharge capacity behavior, with very stable cyclability at room temperature (RT). Li/PYR₁₄TFSI + LiTFSI + TEGDME/LiFePO₄ cells can deliver about 127 mAh/g of LiFePO₄ (74.7% of theoretical capacity) at 0.054 mA/cm² (0.2C rate) at RT and about 108 mAh/g of LiFePO₄ (63.4% of theoretical capacity) at 0.023 mA/cm² (0.1C rate) at −1 °C for the first discharge. The cell exhibited a capacity fading rate of approximately 0.09-0.15% per cycle over 50 cycles at RT. Consequently, the PYR₁₄TFSI + LiTFSI + polymer additive ternary mixture is a promising electrolyte for cells using lithium metal electrodes such as the Li/LiFePO₄ cell reported here. These cells showed the capability of operating over a significant temperature range (∼0-∼30 °C).     

High performance electrospun PVdF‐HFP/SiO2 nanocomposite membrane electrolyte for Li‐ion capacitors

Electrospun poly[(vinylidene fluoride)‐co ‐hexafluoropropylene]/silica (PVdF‐HFP/SiO₂) nanocomposite polymer membranes (esCPMs) were prepared by incorporating different weight percentages of SiO₂ nanoparticles onto electrospun PVdF‐HFP by electrospinning technique. The surface morphology of electrospun PVdF‐HFP nanocomposite membranes was characterized by scanning electron microscopy. The effect of SiO₂ nanoparticles incorporation onto electrospun PVdF‐HFP polymer membranes (esPMs) has been studied by XRD, DSC, TGA, and tensile analysis. The electrospun PVdF‐HFP/SiO₂ based nanocomposite membrane electrolytes (esCPMEs) were prepared by soaking the corresponding esCPMs into 1 M LiPF₆ in EC:DMC (1:1 vol/vol %). The ionic conductivity of the esCPMEs was studied by AC‐impedance studies and it was found that the incorporation of SiO₂ nanoparticles into PVdF‐HFP membrane has improved the ionic conductivity from 1.320 × 10^?3 S cm^?1 to 2.259 × 10^?3 S cm^?1. The electrochemical stability of the esCPME was studied by linear sweep voltammetry studies and it was found to be 2.87 V. Finally, a prototype LiCo_0.2Mn_1.8O₄//C Li‐ion capacitor (LIC) cell was fabricated with esCPME, which delivered a discharge capacitance of 128 F g^?1 at the current density of 1 A g^?1 and retained 86% of its discharge capacitance even after 10,000 cycles. These results demonstrated that the esCPMEs could be used as promising polymer membrane electrolyte for LICs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45177.     

Magneto-dielectric and magneto-conducting fillers based polymer composites: Effect of functionalization,coating and dispersion process on electromagnetic shielding properties

Electromagnetic interference shielding of magneto-dielectric (BaTiO₃-Fe₃O₄) and magneto-conducting (f-MWCNT-Fe₃O₄) fillers based polymer electrolyte composites in the X-band have been studied in the present work. Magneto-dielectric and magneto-conducting fillers have been obtained by in situ preparation of Fe₃O₄ nanoparticles by chemical precipitation in the presence of BaTiO₃ and functionalized multiwalled carbon nanotubes (f-MWCNT). Functionalization of MWCNT has resulted in their strong bonding with the polymer electrolyte adversely affecting the charge transport properties and shielding effectiveness. Dielectric, magnetic and conducting properties of the magneto-dielectric and magneto-conducting fillers are found to be significantly different as a result of coating by Fe₃O₄ nanoparticles on BaTiO₃ and f-MWCNT. Combining two fillers in a single nanocomposite has exhibited non-complimentary addition of their individual properties. The ultra-sonication method of dispersion of the magneto-conducting filler has been found to give better conducting and shielding effectiveness in comparison to the homogenization method due to better disentanglement of the nanotubes.     

Effect of Al2O3 nanoparticles on the electrochemical characteristics of P(VDF-HFP)-based polymer electrolyte

Alumina (Al₂O₃) nanoparticles have been used as fillers in the preparation of poly(vinylidenefluoride-co-hexafluorpropylene) (P(VDF-HFP))-based porous polymer electrolyte. The degree of crystallization of polymer film filled with Al₂O₃ nanoparticles decreases with increase of the mass fraction of Al₂O₃ nanoparticles and the amorphous phases of polymer film expand accordingly. The Al₂O₃ nanoparticles play the role of solid plasticizer for polymer matrix. Nevertheless that excessive Al₂O₃ nanoparticles existing in polymer matrix leads to micro-phase separation between polymer matrix and fillers. As a result, both ionic conductivity and lithium ions transference number reduces whereas the activation energy for ions transport increases. When the polymer film is filled with 10% of the mass fraction of Al₂O₃ nanoparticles, polymer electrolyte possesses the ionic conductivity up to 1.95 × 10⁻³ S cm⁻¹ and the lithium ions transference number to 0.73 while the activation energy for ions transport of them falls to 5.6 kJ mol⁻¹. Effect of Al₂O₃ on the electrochemical properties of polymer electrolyte has been investigated in this paper. Analysis of FTIR spectra shows that there is the interaction between Al₂O₃ nanoparticles and polymer chains.     

Preparation and performance of poly(ethylene oxide)-based composite solid electrolyte for all solid-state lithium batteries

Poly(ethylene oxide)-based solid electrolyte is attractive for using in all solid-state lithium batteries. However, the polymer has a certain degree of crystallization, which is adverse to the conduction of lithium ions. In order to overcome this drawback, a flexible composite polymer electrolyte (CPE) containing TiO₂ nanoparticles is elaborately designed and synthesized by tape casting method. The effects of different molar ratios of EO: Li and mass fraction of TiO₂ on the physical and electrochemical performances are carefully studied. The results show the CPE10 having 10 wt % TiO₂ has the lowest degree of crystallinity of 9.04%, the lowest activation energy of 8.63 × 10⁻⁵ eV mol⁻¹. Besides, the CPE10 shows a lower polarization and higher decomposition voltage. Thus, prepared all solid-state battery LiFePO₄/CPE10/Li shows a high initial capacity of 160 mAh g⁻¹ at 0.1 C, 134 mAh g⁻¹ at 0.5 C and higher capacity retention of 93.2% after 50 cycles at 0.5 C (1 C = 170 mAh g⁻¹). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47498.     

Electrochemical properties of carbon-mixed LiFePO4 cathode material synthesized by the ceramic granulation method

LiFePO₄/carbon composite cathode material was prepared using polyvinyl alcohol (PVA) as carbon source by pelleting and subsequent pyrolysis in N₂. The samples were characterized by XRD, SEM and TGA. Their electrochemical performance was investigated in terms of charge–discharge cycling behavior. It consists of a single LiFePO₄ phase and amorphous carbon. The special micro-morphology via the process is favorable for electrochemical properties. The discharge capacity of the LiFePO₄/C composite was 145 mAh/g, closer to the theoretical specific capacity of 170 mAh/g at 0.1 C low current density. At 3 C modest current density, the specific capacity was about 80 mAh/g, which can satisfy for transportation applications if having a more planar discharge flat.     

Study of poly(organic palygorskite-methyl methacrylate)/poly(ethylene oxide) blended gel polymer electrolyte for lithium-ion batteries

In this study, the composite polymer was prepared by blending poly(ethylene oxide) (PEO) and POPM (the copolymer of methyl methacrylate [MMA] and organically modified palygorskite), and then the composite polymer based membrane was obtained by phase-inversion method. The scanning electron microscopy results showed that the composite polymer membrane has a three-dimensional network structure. X-ray diffraction results indicated that the crystalline region of PEO is disappeared when introduction of a certain amount of the PEO. Meanwhile, the elongation of composite polymer membrane increased when increasing PEO concentration, but the value of tensile strength of PEO-POPM membrane decreased. When the mass fraction of PEO was 24%, the porosity and maximum value of ionic conductivity of the composite polymer membrane were 54% and 2.41 mS/cm, respectively. The electrochemical stability window of Li/gel composite polymer electrolyte/stainless steel batteries was close to 5.3 V (vs. Li⁺/Li), and the battery of Li/gel composite polymer electrolyte/LiFePO₄ showed good cycling performance and the discharge capacity of the battery were between 169.8 and 155 mAh/g. Meanwhile, the Coulombic efficiency of the battery maintained over 95% during the 80 cycles.     

One-step hydrothermal synthesis of 3D porous microspherical LiFePO4/graphene aerogel composite for lithium-ion batteries

Three-dimensional (3D) porous LiFePO₄/graphene aerogel (LFP/GA) composite was successfully prepared by an in-situ hydrothermal process. In this composite, the LiFePO₄ microspheres assembled by nanoparticles were embedded in a three-dimensional framework intertwined with the graphene sheets, which acts as a bridge for transfer of electron and diffusion of lithium ion. The large specific surface of the composite structure enables the increased infiltration area and utilization of the active material. The content of the graphene sheet is analyzed and is found important for the Li-storage characteristics of LiFePO₄. An aerogel composite with 10% of graphene displays the best electrochemical performance, with the specific discharge capacities of 168 mAh g⁻¹ and 155 mAh g⁻¹ at respectively 0.1C and 1C, and the capacity retains 96.3% for up to 800 cycles. This novel 3D porous aerogel composite is identified as a promising cathode material for the rechargeable Li battery, and the simple strategy may be applied to construct other high performing composite structure and materials.     

Metallic-lithium, LiFePO4-based polymer battery using PEO—ZrO2 nanocomposite polymer electrolyte

A study of the electrochemical properties of a PEO-based polymer electrolyte with nanometric ZrO₂ as ceramic filler has been carried out in order to confirm an earlier reported model dealing with the role of ceramic fillers within PEO-based polymer electrolytes as components that enhance such properties as conductivity, lithium transference number, compatibility with lithium metal electrodes and cyclability. A prototype of a lithium polymer battery, based on a membrane made from a nanocomposite polymer electrolyte doped with ZrO₂, utilizing LiFePO₄ + 1%Ag as cathode, has been assembled and galvanostatically cycled, resulting in excellent performance at temperatures ranging from 100 °C to 60 °C (close to the crystallization temperature of PEO).     

Enhancement of electrochemical properties of hot-pressed poly(ethylene oxide)-based nanocomposite polymer electrolyte films for all-solid-state lithium polymer batteries

PEO₁₆-LiClO₄-ZnAl₂O₄ nanocomposite polymer electrolyte (NCPE) films prepared by hot-pressing method have been investigated. In order to compare with the hot-pressed NCPEs, the NCPE films have also been prepared using the conventional solution-casting method. Field emission scanning electron microscopy (FESEM), differential scanning calorimetry (DSC), conductivity (σ) and interface property studies have been carried out on above two kinds of films. The results show that the NCPE film prepared by hot-pressing method has smoother surface, higher interface stability, lower crystallization and melting temperature values than that prepared by solution-casting method. An all-solid-state lithium polymer battery using the hot-pressed NCPE film as electrolyte, lithium metal and LiFePO₄ as anode and cathode respectively, shows high discharge specific capacity, good rate capacity, high coulombic efficiency, and excellent cycling stability as revealed by galvanostatical charge/discharge cycling tests.     

Influence of Barium Titanate on poly(vinyl pyrrolidone)‐based composite polymer blend electrolytes for lithium battery applications

Nanocomposite polymer blend electrolytes based on poly (ethylene oxide), poly (vinyl pyrrolidone) that contained lithium perchlorate as a dopant, propylene carbonate (PC) as a plasticizer and Barium Titanate (BaTiO₃) as a filler were prepared for various concentrations of BaTiO₃ using solvent casting technique. The structural and complex formations of the composite electrolyte membranes were confirmed by X‐ray diffraction and FTIR analysis. The addition of BaTiO₃ nanofillers improved the ionic conductivity of the polymer electrolytes to some extent when the content of the BaTiO₃ is 10 wt%. The addition of BaTiO₃ also enhanced the thermal stability of the electrolyte. The surface morphology of the sample having a maximum ionic conductivity was studied by AFM. Molecular motion in the polymeric media was supported by fluorescence studies. The charge transfer arises between the polymer blend and Li‐ions were confirmed by UV‐Vis analysis. POLYM. COMPOS., 36:302–311, 2015. © 2014 Society of Plastics Engineers     

Enhanced energy storage performance of nanocomposites filled with paraelectric ceramic nanoparticles by weakening the electric field distortion

Polymer-based dielectric nanocomposites, which combines the high dielectric constant of ceramic materials and the high breakdown strength of polymer materials, has emerged as one of the most effective progress for the advanced dielectric energy storage materials. To improve energy storage performance, the core-shell structured SiO₂@SrTiO₃ paraelectric nanoparticles are used as fillers in constructing the polymer-based nanocomposites. Hence, this paper systematically investigates the impacts of filler content on energy storage performance and breakdown strength, and provides insight into the polarization behavior of different composites filled with paraelectric and ferroelectric nanoparticles (SiO₂@BaTiO₃), respectively. Combined finite element simulations, it is shown that the dielectric constant of the paraelectric ceramic is more similar to the polymer matrix, resulting in weakening the electric field distortion in the dielectric. Furthermore, due to the paraelectric characteristics of SrTiO₃ nanoparticles and the diminution of interface polarization, the remnant polarization of the nanocomposites can be significantly reduced. The polymer-based dielectric nanocomposites exhibit more impressive energy storage, of 11.42 J/cm³ at 350 MV/m with 2.5 vol% paraelectric SiO₂@SrTiO₃ nanoparticles, which is superior to the composite filled with ferroelectric nanoparticles. Overall, this finding not only establishes a new direction for the structural design of fillers but also provides insight into an underlying mechanism to control interface polarization in the dielectric composites.     

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.     

Improving room-temperature electrochemical performance of solid-state lithium battery by using electrospun La2Zr2O7 fibers-filled composite solid electrolyte

Low ionic conductivity at room temperature and poor interfacial compatibility are the main obstacles to restrain the practical application of polymer solid electrolytes. In this work, lanthanum zirconate (LZO) fibers were prepared by electrospinning method and used for the first time as fillers in sandwich polypropylene carbonate (PPC)-based solid electrolyte. Meanwhile, a graphite coating was applied on one surface of the composite solid electrolyte (CSE) membrane. The results show that the LZO fibers significantly increases the room-temperature electrochemical performance of the CSE, and the graphite coating enhances the interfacial compatibility between electrolyte and lithium anode. Furthermore, an ultra-thin PPC-LZO CSE with a total thickness of 22 μm was prepared and used in NCM622/CSE/Li solid-state cell, which shows an initial discharge capacity of 165.6 mAh/g at the current density of 0.5C and a remaining capacity of 113.0 mAh/g after 250 cycles at room temperature. Rise to 1C, the cell shows an initial discharge capacity of 154.2 mAh/g with a remaining capacity of 95.6 mAh/g after 250 cycles. This ultra-thin CSE is expected to be widely applied in high energy-density solid-state battery with excellent room-temperature electrochemical performances.     

Vanadium doped ceramic matrix Li6.7La3Zr1.7V0.3O12 enabled PEO-based solid composite electrolyte with high lithium ion transference number and cycling stability

Solid polymer electrolytes (SPEs) have attracted much attention because of their potential in improving energy density and safety. Vanadium doped ceramic matrix Li_6.7La₃Zr_1.7V_0.3O₁₂ (LLZVO) was synthesized by high-temperature annealing, and formed a composite electrolyte with polyethylene oxide (PEO). Compared with pure PEO electrolyte membrane, the composite electrolyte membrane exhibited better ionic conductivity (30 °C: 3.2 × 10^?5 S cm^?1; 80 °C: 3.6 × 10^?3 S cm^?1). The combination of LLZVO was beneficial to improve the lithium ion transference number (t_Li⁺) of SPE, which was as high as 0.81. The Li/SPE/LiFePO₄ battery shows good cycling ability, with a specific capacity of 142 mAh g^?1 after a stable cycle of 150 cycles. Meanwhile, the symmetrical lithium battery with composite electrolyte can work continuously for 1200 h without short circuit at the current density of 0.1 mA cm^?2 at 50 °C, and the capacity is 0.176 mAh. Vanadium doped ceramic matrix LLZVO as an active ionic conductor, improved the overall performance of solid electrolyte.     

Characterization of SiO2 and Al2O3 incorporated PVdF‐HFP based composite polymer electrolytes with LiPF3(CF3CF2)3

Lithium fluoroalkylphosphate (LiPF₃(CF₃ CF₂)₃) based composite polymer electrolytes (CPE) have been prepared in the matrix of polyvinylidenefluoride‐hexafluoropropylene(PVdF‐HFP), using solvent casting technique. The membranes were gelled with ethylene carbonate and diethyl carbonate as a plasticizer and nanosized SiO₂ and nanoporous Al₂O₃ as fillers. These membranes were subjected to a.c. impedance, DSC, SEM, FTIR, and Fluorescence studies. The a.c. impedance studies and activation energy calculation reveal that 2.5 wt % fillers containing membranes only exhibit maximum conductivity for SiO₂ (1.16 mS cm^?1) and Al₂O₃ (0.98 mS cm^?1), compared to fillers free membranes and beyond 2.5 wt % of such fillers the conductivity tends to decrease. The enhancement of conductivity has been explained in terms of Vogel‐Tamman‐Fulcher (VTF) theory. Molecular interactions by FTIR and local viscosity environment by fluorescence studies have been investigated. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhanced mechanical strength and conductivity of PVFM based membrane and its supporting polymer electrolytes

Polyvinyl formal based polymer electrolyte membranes are prepared via the optimized phase inversion method with poly(ethylene oxide) (PEO) blending. The physical properties of blend membranes and the electrochemical properties of corresponding gel polymer electrolytes (GPEs) are characterized by field emission scanning electron microscopy, X‐ray diffraction, differential scanning calorimetry, mechanical strength test, electrolyte uptake test, AC impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge test. The comparative study shows that the appearance of PEO obviously enhances the tensile strength of membranes and the ionic conductivity of corresponding GPEs. When the weight ratio of PEO is 30%, the tensile strength of membrane achieves 12.81 MPa, and its GPE shows high ionic conductivity of 2.20 × 10⁻³ S cm⁻¹, wide electrochemical stable window of 1.9–5.7 V (vs. Li/Li⁺), and good compatibility with LiFePO₄ electrode. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41839.