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

Interface Optimization of Metal Quantum Dots/Polymer Nanocomposites and their Properties: Studies of Multi-Functional Organic/Inorganic Hybrid

Nanomaterials filled polymers system is a simple method to produce organic/inorganic hybrid with synergistic or complementary effects. The properties of nanocomposites strongly depend on the dispersion effects of nanomaterials in the polymer and their interfaces. The optimized interface of nanocomposites would decrease the barrier height between filler and polymer for charge transfer. To avoid aggregation of metal nanoparticles and improve interfacial charge transfer, Pt nanodots filled in the non-conjugated polymer was synthesized with an in situ method. The results exhibited that the absorbance of nanocomposite covered from the visible light region to NIR (near infrared). The photo-current responses to typical visible light and 808 nm NIR were studied based on Au gap electrodes on a flexible substrate. The results showed that the size of Pt nanoparticles was about 1-2 nm and had uniformly dispersed in the polymer matrix. The resulting nanocomposite exhibited photo-current switching behavior to weak visible light and NIR. Simultaneously, the nanocomposite also showed electrical switching responses to strain applied to a certain extent. Well-dispersion of Pt nanodots in the polymer is attributable to the in situ synthesis of metal nanodots, and photo-current switching behavior is due to interface optimization to decrease barrier height between metal filler and polymer. It provided a simple way to obtain organic/inorganic hybrid with external stimuli responses and multi-functionalities.

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.

Core-Shell PMIA@PVdF-HFP/Al2O3 Nanofiber Mats In Situ Coaxial Electrospun on LiFePO4 Electrode as Matrices for Gel Electrolytes

Gel electrolytes show certain advantages over conventional liquid and solid electrolytes, but their mechanical strength and surface adhesion to the electrode remain to be improved. To address the challenges, we design and fabricate herein the core-shell nanofiber mats in situ on the LiFePO₄ electrode as matrices for gel electrolytes, in which the core is poly(m-phenylene isophthalamide) (PMIA) nanofiber and the shell are composite of Al₂O₃ nanoparticles and poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP). The mechanical property of the core-shell polymeric nanofiber mats and their surface interaction with LiFePO₄ electrode are characterized complementarily using dynamic thermomechanical analysis and scanning electron microscopy. The electrochemical properties of the gel electrolytes based on the as-prepared matrices after being loaded with lithium salt solution are studied systematically on half coin cells. It is found that the ultimate strength of the core-shell PMIA@PVdF-HFP/Al₂O₃ mat can reach 6.70 MPa, 2 times higher than that of the PVdF-HFP/Al₂O₃ nanofiber mat. Meanwhile, the shell PVdF-HFP/Al₂O₃ can ensure manifest surface affinity to the LiFePO₄ electrode and enhance lithium-ion conductance. Thus, the as-assembled LiFePO₄ half coin cells using PMIA@PVdF-HFP/Al₂O₃ gel electrolyte show good electrochemical performances, especially the long cycle stability with the capacity retention of 96.6% after 600 cycles under 1C.

Long-Term Cycling Behavior of Electrospun Separators for Lithium-Ion Batteries: A Comparison with Conventional Separators

This paper considered the electrochemical behavior of new electrospun separators for lithium-ion batteries on the basis of nano- and microfibers of polyvinylidene fluoride (PVDF) and its polymer composition, with polytetrafluoroethylene (PTFE) having advanced electroconductive properties over conventionally used separators based on polypropylene (PP) and glass-fibers (GF). Such advancement is associated with the low density of electrospun material leading to lower mechanical strengths. However, its use in the electrochemical systems with middle-voltage anode materials where dendrite growth is excluded is very prospective. The performance at the operation of the separators were investigated in the three-electrode-containing laboratory half-cells having Li4Ti5O12 as the electrode under investigation. Galvanostatic charge and discharge tests of cells were conducted under variation of the experimental conditions: the current varied in the range 0.1 C–1 C, and 1C cycling was conducted over 100 cycles. The working electrode and separator characteristics at cycling were monitored by the electrochemical impedance spectroscopy (EIS) method. The gradual decrease of Li4Ti5O12 transport characteristics at cycling was noticed for all the types of separators. However, the least degradation rate was associated with the PVDF and the PTFE-based separator. This fact is explained by the better conductivity of an electrospun separator compared to others, with therefore a better current distribution on the electrode surface and a lower concentration perturbation in the electrode.

High performance of boehmite/polyacrylonitrile composite nanofiber membrane for polymer lithium-ion battery

In this study, a novel boehmite/polyacrylonitrile (BM/PAN) composite nanofiber membrane was prepared using the electrospinning technique. The physical and electrochemical properties of different contents of BM/PAN composite nanofiber membranes were investigated as separators for lithium ion batteries (LIBs). Compared to the commercial polypropylene (PP) separator, the experimental results show that the BM/PAN composite nanofiber separator possesses a unique three-dimensional (3D) interconnected structure and exhibits higher porosity, greater electrolyte up-take, higher thermal stability and better electrochemical performance in a LiCoO₂/Li cell. Besides, batteries containing 30 wt% BM/PAN membranes display the highest ionic conductivity (2.85 mS cm⁻¹), widest electrochemical stability window (5.5 V vs. Li⁺/Li), leading to the highest initial discharge capacity (162 mA h g⁻¹) and the largest capacity retention ratio (90.7%) at 0.5C after 100 cycles. These findings reveal that the BM/PAN composite nanofiber membranes are promising candidates as commercial separators for high performance LIBs.

In this study, a novel boehmite/polyacrylonitrile (BM/PAN) composite nanofiber membrane was prepared using the electrospinning technique.

Flame-Retardant Bilayer Separator with Multifaceted van der Waals Interaction for Lithium-Ion Batteries

Safety issues induced by a flammable organic electrolyte challenge the practical applications of high-specific energy lithium-ion batteries (LIBs). Here, we develop a robust bilayer separator by incorporating MoO₃ and Al-doped Li_6.75La₃Zr_1.75Ta_0.25O₁₂ (LLZTO). The bilayer separator is highly flame-resistive and manages to endure intense fire. Density functional calculations reveal that abundant hydrogen bonds and van der Waals forces within the bilayer separator greatly suppress the combustion with interfacial adhesion of MoO₃ and LLZTO to poly(vinylidene fluoride-hexafluoropropylene). With MoO₃ and LLZTO, the graphitized carbon content of the carbon residues is increased, and the formation of molybdenum fluoride (MoF_x) and lanthanum fluoride (LaF_x) is induced during combustion, thus suppressing heat accumulation. The bilayer separator owns a large ductility (227%) and low thermal shrinkage (5%) after annealing at 160 °C for 4 h. Based on the bilayer separator, Li/LiFePO₄ cells deliver a remarkable discharge capacity of 162 mA h/g at 0.5 C with a high capacity retention of 95% after 100 cycles. This work provides a new strategy for achieving safe LIBs.

A Review on Inorganic Nanoparticles Modified Composite Membranes for Lithium-Ion Batteries: Recent Progress and Prospects

Separators with high porosity, mechanical robustness, high ion conductivity, thin structure, excellent thermal stability, high electrolyte uptake and high retention capacity is today's burning research topic. These characteristics are not easily achieved by using single polymer separators. Inorganic nanoparticle use is one of the efforts to achieve these attributes and it has taken its place in recent research. The inorganic nanoparticles not only improve the physical characteristics of the separator but also keep it from dendrite problems, which enhance its shelf life. In this article, use of inorganic particles for lithium-ion battery membrane modification is discussed in detail and composite membranes with three main types including inorganic particle-coated composite membranes, inorganic particle-filled composite membranes and inorganic particle-filled non-woven mates are described. The possible advantages of inorganic particles application on membrane morphology, different techniques and modification methods for improving particle performance in the composite membrane, future prospects and better applications of ceramic nanoparticles and improvements in these composite membranes are also highlighted. In short, the contents of this review provide a fruitful source for further study and the development of new lithium-ion battery membranes with improved mechanical stability, chemical inertness and better electrochemical properties.

Facile Fabrication of Multi-Structured SiO₂@PVDF-HFP Nanofibrous Membranes for Enhanced Copper Ions Adsorption

The low-cost, heavy metal ion (Cu(II)) adsorptive multi-structured nanofibrous membranes of silicon oxide naonoparticles in-situ anchored polyvinylidene fluoride-hexafluoropropylene (SiO₂@PVDF-HFP) fibers were fabricated by the facile electrospinning technique combined with sol⁻gel strategy. To explore the benefits of the structure-related Cu(II) adsorption capacity, the fiber diameters of SiO₂@PVDF-HFP nanofibrous membranes were changed which also resulted in the change of their porosity. Taking advantage of the constructed multi-structures and efficient fiber morphology regulation which not only changed the PVDF-HFP nanofibrous membrane from hydrophobic to superhydrophilic but also increased the porosity of the membrane, the SiO₂@PVDF-HFP nanofibrous membrane with a smaller diameter and a larger porosity exhibits higher Cu(II) adsorption capacity. The adsorption amount was approximate to 21.9 mg per gram of the membrane, which was higher than that of membranes with larger fiber diameter (smaller porosity) and the smooth one. Furthermore, the model isotherms of Freundlich and Langmuir, as well as the kinetic models of pseudo-first-order and pseudo-second-order were preferred to analyze the adsorption equilibrium data. The Freundlich model and the pseudo-first-order were well fitted to the adsorption experimental data. It not only uncovers the structure-related-property of multi-structured nanofibrous membranes, but also provides an efficient and facile way to design heavy metal ion adsorption materials.

A high-strength PPESK/PVDF fibrous membrane prepared by coaxial electrospinning for lithium-ion battery separator

Electrospinning fibrous membranes have attracted a great deal of attention because of their advantages, including uniform pore size, large ratio surface area, and high porosity. For extended application in lithium-ion battery, it is essential to further improve their electrochemical, mechanical, and thermal properties. In this work, a new poly (phthalazine ether sulfone ketone) (PPESK)/polyvinyli-denefluoride (PVDF) core/shell fibrous membrane was fabricated via the coaxial electrospinning technique, followed by hot press. The PPESK/PVDF membrane hot pressed at 160°C exhibits excellent comprehensive performance, including large porosity (80%), high electrolyte uptake (805%), and excellent thermal stability (at 200°C). Moreover, due to the improved bonding effect derived from the solidification of the PVDF shell layer after the hot press, the mechanical property of the membrane is effectively enhanced. The electrochemical tests also indicate that the PPESK/PVDF membrane shows larger ionic conductivity and lower interfacial resistance when compared with commercial microporous polypropylene separator. In addition, simulated cells assembled with the PPESK/PVDF membrane present superior discharge capacity, stable cycle performance, and excellent rate capability. Therefore, the hot-pressed coaxial PPESK/PVDF fibrous membrane has the potential to be a promising candidate as the separator for high-performance lithium-ion battery.

In situ grown nickel selenide on graphene nanohybrid electrodes for high energy density asymmetric supercapacitors

Nickel selenide (NiSe) nanoparticles uniformly supported on graphene nanosheets (G) to form NiSe-G nanohybrids were prepared by an in situ hydrothermal process. The uniform distribution of NiSe on graphene bestowed the NiSe-G nanohybrid with faster charge transport and diffusion along with abundant accessible electrochemical active sites. The synergistic effect between NiSe nanoparticles and graphene nanosheets for supercapacitor applications was systematically investigated for the first time. The freestanding NiSe-G nanohybrid electrode exhibited better electrochemical performance with a high specific capacitance of 1280 F g-1 at a current density of 1 A g-1 and a capacitance retention of 98% after 2500 cycles relative to that of NiSe nanoparticles. Furthermore, an asymmetric supercapacitor device assembled using the NiSe-G nanohybrid as the positive electrode, activated carbon as the negative electrode and an electrospun PVdF membrane containing 6 M KOH as both the separator and the electrolyte delivered a high energy density of 50.1 W h kg-1 and a power density of 816 W kg-1 at an extended operating voltage of 1.6 V. Thus, the NiSe-G nanohybrid can be used as a potential electrode material for high-performance supercapacitors.

A facile approach to preparation of silica double-shell hollow particles, and their application in gel composite electrolytes

Double-shell hollow particles (DSHPs) have attracted significant attention due to their diverse potential applications. DSHPs are usually obtained by multi-step sacrificial template method which is tedious and inefficient. In this work, a facile synthesis of silica DSHPs has been developed via a novel one-step template method, which is using single-hole hollow particles (SHHPs) as the templates. The shapes and internal structures of the DSHPs were determined by SEM and TEM, and the average diameters of inner and outer shells were about 0.6 and 1.6 μm, respectively. According to FTIR analyses, the compositions of silica DSHPs were identified as well. Furthermore, the silica DSHPs was applied to Li-ion batteries as a modifier of gel polymer electrolyte (GPEs), and the results showed that the gel composite electrolytes (GCEs) could display higher capability, higher ionic conductivity and better rate performance at high current density for GCEs-cell. Properties of the silica DSHPs such as larger specific surface area, more porous structures and Lewis acid-base effect were important for high-performance Li-ion batteries.

Durable Sodium Battery with a Flexible Na3Zr2Si2PO12-PVDF-HFP Composite Electrolyte and Sodium/Carbon Cloth Anode

High-performance electrolytes and electrode materials play a critical role in advanced sodium-ion batteries with higher energy densities. In this work, we prepared a poly(methyl methacrylate)-filled composite electrolyte (named as GHSE) by in situ polymerization of methyl methacrylate in the porous Na₃Zr₂Si₂PO₁₂-polymer vinylidene fluoride-hexafluoropropylene composite membrane for the first time. The GHSE membrane exhibits a high ionic conductivity (2.78 × 10^-3 S cm^-1), wide electrochemical window (∼4.9 V), high Na⁺ ion transference number (∼0.63), good thermal stability and flexibility, as well as smaller interfacial resistance. Moreover, a composite Na/C anode was prepared, which shows good dendrite suppression ability. The full cell Na_0.67Ni_0.23Mg_0.1Mn_0.67O₂ |GHSE|Na/C exhibits excellent rate capability with an initial discharge capacity of 96 mAh g^-1 even at a higher current density of 192 mA g^-1 and excellent cyclability for 600 cycles. These results suggest that the GHSE and Na/C anode are promising electrolyte and anode materials for Na-ion batteries, respectively.