Flexible poly(vinylidene fluoride-co-hexafluoropropylene)-based gel polymer electrolyte for high-performance lithium-ion batteries

Fabrication and Evaluation of Filtration Membranes from Industrial Polymer Waste

Polyvinylidene fluoride (PVDF) polymers are known for their diverse range of industrial applications and are considered important raw materials for membrane manufacturing. In view of circularity and resource efficiency, the present work mainly deals with the reusability of waste polymer 'gels' produced during the manufacturing of PVDF membranes. Herein, solidified PVDF gels were first prepared from polymer solutions as model waste gels, which were then subsequently used to prepare membranes via the phase inversion process. The structural analysis of fabricated membranes confirmed the retention of molecular integrity even after reprocessing, whereas the morphological analysis showed a symmetric bi-continuous porous structure. The filtration performance of membranes fabricated from waste gels was studied in a crossflow assembly. The results demonstrate the feasibility of gel-derived membranes as potential microfiltration membranes exhibiting a pure water flux of 478 LMH with a mean pore size of ~0.2 µm. To further evaluate industrial applicability, the performance of the membranes was tested in the clarification of industrial wastewater, and the membranes showed good recyclability with about 52% flux recovery. The performance of gel-derived membranes thus demonstrates the recycling of waste polymer gels for improving the sustainability of membrane fabrication processes.

Electrospun NiPd Nanoparticles Supported on Polymer Membrane Nanofibers as an Efficient Catalyst for NaBH4 Dehydrogenation

Sodium borohydride (SBH) hydrolysis in the presence of cheap and efficient catalysts has been proposed as a safe and efficient method for generating clean hydrogen energy for use in portable applications. In this work, we synthesized bimetallic NiPd nanoparticles (NPs) supported on poly(vinylidene fluoride-co-hexafluoropropylene) nanofibers (PVDF-HFP NFs) via the electrospinning approach and reported an in-situ reduction procedure of the NPs being prepared by alloying Ni and Pd with varying Pd percentages. The physicochemical characterization provided evidence for the development of a NiPd@PVDF-HFP NFs membrane. The bimetallic hybrid NF membranes exhibited higher H₂ production as compared to Ni@PVDF-HFP and Pd@PVDF-HFP counterparts. This may be due to the synergistic effect of binary components. The bimetallic Ni_1-xPd_x(x = 0, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3)@PVDF-HFP nanofiber membranes exhibit composition-dependent catalysis, in which Ni₇₅Pd₂₅@PVDF-HFP NF membranes demonstrate the best catalytic activity. The full H₂ generation volumes (118 mL) were obtained at a temperature of 298 K and times 16, 22, 34 and 42 min for 250, 200, 150, and 100 mg dosages of Ni₇₅Pd₂₅@PVDF-HFP, respectively, in the presence of 1 mmol SBH. Hydrolysis utilizing Ni₇₅Pd₂₅@PVDF-HFP was shown to be first order with respect to Ni₇₅Pd₂₅@PVDF-HFP amount and zero order with respect to the [NaBH₄] in a kinetics study. The reaction time of H₂ production was reduced as the reaction temperature increased, with 118 mL of H₂ being produced in 14, 20, 32 and 42 min at 328, 318, 308 and 298 K, respectively. The values of the three thermodynamic parameters, activation energy, enthalpy, and entropy, were determined toward being 31.43 kJ mol^-1, 28.82 kJ mol^-1, and 0.057 kJ mol^-1 K^-1, respectively. It is simple to separate and reuse the synthesized membrane, which facilitates their implementation in H₂ energy systems.

Electrospun Co Nanoparticles@PVDF-HFP Nanofibers as Efficient Catalyst for Dehydrogenation of Sodium Borohydride

Metallic Co NPs@poly(vinylidene fluoride-co- hexafluoropropylene) nanofibers (PVFH NFs) were successfully synthesized with the help of electrospinning and in situ reduction of Co²⁺ ions onto the surface of PVFH membrane. Synthesis of PVFH NFs containing 10, 20, 30, and 40 wt% of cobalt acetate tetrahydrate was achieved. Physiochemical techniques were used to confirm the formation of metallic Co@PVFH NFs. High catalytic activity of Co@PVFH NFs in the dehydrogenation sodium borohydride (SBH) was demonstrated. The formulation with 40 wt% Co proved to have the greatest performance in comparison to the others. Using 1 mmol of SBH and 100 mg of Co@PVFH NFs, 110 mL of H₂ was produced in 19 min at a temperature of 25 °C, but only 56, 73, and 89 mL were produced using 10, 20, and 30 wt% Co, respectively. With the rise of catalyst concentration and reaction temperature, the amount of hydrogen generated increased. By raising the temperature from 25 to 55 °C, the activation energy was lowered to be 35.21 kJ mol^-1 and the yield of H₂ generation was raised to 100% in only 6 min. The kinetic study demonstrated that the reaction was pseudo-first order in terms of the amount of catalyst utilized and pseudo-zero order in terms of the SBH concentration. In addition, after six cycles of hydrolysis, the catalyst showed outstanding stability. The suggested catalyst has potential applications in H₂ generation through hydrolysis of sodium borohydride due to its high catalytic activity and flexibility of recycling.

Phosphonate-Functionalized Ionic Liquid Gel Polymer Electrolyte with High Safety for Dendrite-Free Lithium Metal Batteries

The conventional lithium-ion battery technology relies on the liquid carbonate-based electrolyte solution, which causes excessive side reactions, serious risk of electrolyte leakage, high flammability, and significant safety hazards. In this work, phosphonate-functionalized imidazolium ionic liquid (PFIL) is synthesized and used as a gel polymer electrolyte (GPE) to replace the organic carbonate-based electrolyte solution. The as-prepared ionic liquid-based gel polymer electrolyte (IL-GPE) shows low crystallinity, flame retardance, and excellent electrochemical performance. Thanks to the fast double channel transport of lithium ions in the IL-GPE electrolyte, a high ionic conductivity of 0.48 mS cm^-1 and a lithium-ion transference number of 0.37 are exhibited. Symmetrical lithium cells with IL-GPE retain stable cycling even after 3000 h under 0.1 mA cm^-2. IL-GPE exhibits good compatibility toward lithium metal, yielding excellent long-term electrochemical kinetic stability. IL-GPE induces the formation of a uniform and robust SEI layer, inhibiting the growth of lithium dendrites and improving the rate performance and cycle stability. Furthermore, Li/LiFePO₄ cells exhibit a specific capacity of 63 mA h g^-1 after 150 cycles at 5.0 C, with a capacity retention of 90.2%. It is foreseen that this GPE is a promising candidate to enhance the safety of high-performance lithium metal batteries.

Phase behavior of binary and ternary fluoropolymer (PVDF-HFP) solutions for single-ion conductors

A fluoropolymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) has a dielectric constant of ∼11, providing charge screening effects. Hence, this highly polar PVDF-HFP material has been employed as a matrix for solid polymer electrolytes (SPEs). In this study, the phase behavior of binary PVDF-HFP solutions was analyzed using the Flory-Huggins theory, in which ethylene carbonate, propylene carbonate, dimethyl carbonate, γ-butyrolactone, and acetone were employed as model solvents. In particular, for the binary PVDF-HFP/acetone system, the solid-liquid and liquid-liquid phase transitions were qualitatively described. Then, the phase diagram for ternary acetone/PVDF-HFP/polyphenolate systems was constructed, in which the binodal, spinodal, tie-line, and critical point were included. Finally, when a polyelectrolyte lithium polyphenolate was mixed with the PVDF-HFP matrix, it formed a single-ion conductor with a Li⁺ transference number of 0.8 at 23 °C. In the case of ionic conductivity, it was ∼10^-5 S cm^-1 in solid state and ∼10^-4 S cm^-1 in gel state, respectively.

Thermally Stable PVDF-HFP-Based Gel Polymer Electrolytes for High-Performance Lithium-Ion Batteries

The development of gel polymer electrolytes (GPEs) for lithium-ion batteries (LIBs) has paved the way to powering futuristic technological applications such as hybrid electric vehicles and portable electronic devices. Despite their multiple advantages, non-aqueous liquid electrolytes (LEs) possess certain drawbacks, such as plasticizers with flammable ethers and esters, electrochemical instability, and fluctuations in the active voltage scale, which limit the safety and working span of the batteries. However, these shortcomings can be rectified using GPEs, which result in the enhancement of functional properties such as thermal, chemical, and mechanical stability; electrolyte uptake; and ionic conductivity. Thus, we report on PVDF-HFP/PMMA/PVAc-based GPEs comprising poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and poly(methyl methacrylate) (PMMA) host polymers and poly(vinyl acetate) (PVAc) as a guest polymer. A physicochemical characterization of the polymer membrane with GPE was conducted, and the electrochemical performance of the NCM811/Li half-cell with GPE was evaluated. The GPE exhibited an ionic conductivity of 4.24 × 10-4 S cm-1, and the NCM811/Li half-cell with GPE delivered an initial specific discharge capacity of 204 mAh g-1 at a current rate of 0.1 C. The cells exhibited excellent cyclic performance with 88% capacity retention after 50 cycles. Thus, this study presents a promising strategy for maintaining capacity retention, safety, and stable cyclic performance in rechargeable LIBs.

The plastic crystal composite polyacrylate polymer electrolyte with a semi-interpenetrating network structure for all-solid-state LIBs

Polymer electrolyte semi-interpenetrating network structure of lithium ion battery.

Metal-Organic Framework-Supported Poly(ethylene oxide) Composite Gel Polymer Electrolytes for High-Performance Lithium/Sodium Metal Batteries

Thanks to their high energy density, lithium/sodium metal batteries (LMBs/SMBs) are considered to be the most promising next-generation energy storage system. However, the instability of the electrode/electrolyte interface and dendrite growth seriously hinders commercial application of LMBs/SMBs. In addition, traditional liquid electrolytes are inflammable and explosive. As a key part of the battery, the electrolyte plays an important role in solving the abovementioned problems. Although solid electrolytes can alleviate dendrite growth and liquid electrolyte leakage, their low ionic conductivity and poor interfacial contact are not conducive to improvement of overall LMBs/SMB performances. Therefore, it is necessary to find a balance between liquid and solid electrolytes. Gel polymer electrolytes (GPEs) are one means for achieving high-performance LMBs/SMBs because they combine the advantages of liquid and solid electrolytes. Metal-organic frameworks (MOFs) benefit from high specific surface areas, ordered internal porous structures, organic-inorganic hybrid properties, and show great potential in modified electrolytes. Here, Cu-based MOF-supported poly(ethylene oxide) composite gel polymer electrolytes (CGPEs) were prepared by ultraviolet curing. This CGPE exhibited high ionic conductivity, a wide electrochemical window, and a high ion transference number. In addition, it also exhibited excellent cycle stability in symmetric batteries and LMBs/SMBs. This study showed that CGPE had great practical application potential in the next-generation LMBs/SMBs.

Structural, electrical and electrochemical studies of ionic liquid-based polymer gel electrolyte using magnesium salt for supercapacitor application

In the present studies, the effect of ionic liquid 1-Ethyl-2,3-dimethylimidazoliumtetrafluoroborate (EDiMIM)(BF4) on ionic conductivity of gel polymer electrolyte using poly(vinylidene fluoride-co-hexafluoropropylene) [PVdF(HFP)] and magnesium perchlorate [Mg(ClO4)2] as salt was investigated. The maximum room temperature ionic conductivity for the optimized system was found to be of the order of 8.4 × 10–3 S cm−1. The optimized composition reflects Vogel-Tammann-Fulcher (VTF) behavior in the temperature range of 25 °C to 100 °C. The X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy studies confirm the uniform blending of ionic liquid, polymer, and salts along with the enhanced amorphous nature of the optimized system. Dielectric and modulus spectra studies provide the information of electrode polarization as well as dipole relaxation properties of polymeric materials. The optimized electrolyte system possesses a sufficiently large electrochemical window of the order of 6.0 V with stainless steel electrodes.