Vinylidene Fluoride-hexafluoropropylene Research Articles

Preparation and characterization of hydrophobic P(VDF-HFP) flat sheet membranes using Tamisolve® NxG solvent for the treatment of saline water by direct contact membrane distillation and membrane crystallization

• Tamisolve® was used as a non-toxic solvent for P(VDF-HFP) membranes preparation. • The prepared porous P(VDF-HFP) membranes were fully characterized. • The membranes were tested in membrane distillation and membrane crystallization. • Membrane crystallization allowed achieving crystals with rejection greater than 99%. The replacement of the toxic solvents with non-toxic equivalents attracts a great attention in membrane preparation and application processes. The purpose of this work is to study the preparation of poly(vinylidene fluoride-hexafluoropropylene) P(VDF-HFP) flat sheet membranes by non-solvent induced phase separation (NIPS) using Tamisolve® as a non-toxic solvent, for membrane distillation (MD) and membrane crystallization (MCr) applications. The prepared porous P(VDF-HFP) membranes were fully characterized in terms of morphology, porosity, thickness, pore-size, contact angle and pure water permeability (PWP). The effect of additive(s) and polymer content were investigated. Moreover, preliminary DCMD and MCr tests were carried out and the achieved results indicate the good performance of the prepared flat sheet membranes in terms of permeate flux and salt rejection in comparison to a commercial PVDF membrane. The obtained results confirmed the ability of the eco-friendly Tamisolve® NxG to compete with the highly toxic diluents usually used in membrane fabrication by phase inversion method.

Reusable Ag@TiO2-Based Photocatalytic Nanocomposite Membranes for Solar Degradation of Contaminants of Emerging Concern.

Two significant limitations of using TiO2 nanoparticles for water treatment applications are reduced photocatalytic activity under visible radiation and difficulty recovering the particles after use. In this study, round-shaped Ag@TiO2 nanocomposites with a ≈21 nm diameter and a bandgap energy of 2.8 eV were synthesised by a deposition-precipitation method. These nanocomposites were immobilised into a porous poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrix and well-distributed within the pores. The photocatalytic activity of Ag@TiO2/PVDF-HFP against metronidazole (MNZ) under solar radiation was evaluated. Further, an adaptive neuro-fuzzy inference system (ANFIS) was applied to predict the effect of four independent variables, including initial pollutant concentration, pH, light irradiation intensity, and reaction time, on the photocatalytic performance of the composite membrane on MNZ degradation. The 10% Ag@TiO2/PVDF-HFP composite membrane showed a maximum removal efficiency of 100% after 5 h under solar radiation. After three use cycles, this efficiency remained practically constant, demonstrating the membranes’ reusability and suitability for water remediation applications.

PVDF-HFP based polymer electrolytes with high Li+ transference number enhancing the cycling performance and rate capability of lithium metal batteries

Lithium metal batteries are confronted with safety issues in liquid electrolyte systems owing to rapid growth of lithium dendrite and uneven lithium deposition. Exploration of gel polymer electrolytes (GPEs) with excellent ionic conductivity and high Li+ migration number is a possible strategy to replace liquid electrolyte. Herein, a high-powered GPEs relied on poly (vinylidene fluoride-hexafluoro propylene) (PVDF-HFP) modified by polymer polyethylene glycol (PEG) and lithium montmorillonite (LiMNT) via bond interactions is reported. The prepared porous polymer electrolyte presents a captivating ionic conductivity of 1.82 × 10−3 S·cm−1 and lithium ions transference number up to 0.513 at 25 °C. In view of the eminent ionic conductivity and efficient migration number of Li+, the three-dimensional porous polymer electrolyte is very conducive to the fast transport and stable deposition of lithium ions, restraining the occurrence and growth rate of lithium dendrites, which improves the cycle performance and rate capability of lithium battery. LiFePO4| PPL122 electrolyte |Li battery delivers a desired cycling performance with a capacity retention of 92% after 1000 cycles at 1 C.

Advancements in Sustainable PVDF Copolymer Membrane Preparation Using Rhodiasolv® PolarClean As an Alternative Eco-Friendly Solvent

In this work, Rhodiasolv® PolarClean was employed as a more sustainable solvent for the preparation of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) flat sheet membranes via phase inversion technique by coupling vapour induced phase separation (VIPS) and non-solvent induced phase separation (NIPS) processes. Preliminary calculations based on Hansen solubility parameters well predicted the solubilization of the polymer in the selected solvent. The effect of exposure time on humidity and the influence of polyethylene glycol (PEG), polyvinyl pyrrolidone (PVP) and sulfonated polyether sulfone (S-PES) on membrane properties and performance, were evaluated. Three different coagulation bath compositions were also explored. The obtained membranes, prepared using a more sustainable approach, were compared with those produced with the traditional toxic solvent N-methyl-2-pyrrolidone (NMP) and characterised in terms of morphology, porosity, wettability, pore size, surface roughness and mechanical resistance. The potential influence of the new solvent on the crystallinity of PVDF-HFP-based membranes was also evaluated by infrared spectroscopy. The adjustment of the parameters investigated allowed tuning of the membrane pore size in the microfiltration (MF) and ultrafiltration (UF) range resulting in membranes with various morphologies. From the water permeability and rejection tests, performed with methylene blue dye, the prepared membranes showed their potentiality to be used in MF and UF applications.

In Situ Growing BCN Nanotubes on Carbon Fibers for Novel High-Temperature Supercapacitor with Excellent Cycling Performance.

Carbon nanomaterials have elicited much research interest in the energy storage field, but most of them cannot be used at high temperatures. Thus, a supercapacitor with high energy and desired stability at high temperatures is urgently required. Herein, BCN nanotubes (BCNNTs) with excellent performance at high temperatures are generated on carbon fibers by optimizing the ratio of B and N. The nanotubes' morphology can effectively alleviate the structural damage caused by the rapid adsorption/desorption of the electrolyte during long-time charge/discharge cycles at high temperatures, thus improving the high-temperature cycle stability. The symmetric supercapacitors that are assembled with the binder-free BCNNT electrode in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIM·BF4 ) exhibited a high areal capacitance of 177.1 mF cm-2 at a current density of 5mA cm-2 , and capacitance retention is maintained up to 86.1% for 5000cycles at 100°C. Moreover, the flexible supercapacitor based on BCNNTs in poly(vinylidenefluoride hexafluoropropylene)/EMIM·BF4 /succinonitrile gel electrolyte also exhibits good volumetric capacitance (1.98 mWh cm-3 at a current density of 5mA cm-2 ) and cycling stability (92.6% retention after 200 charge/discharge cycles) at a temperature of 100°C. This work shows that binder-free BCNNTs are promising materials for high-temperature flexible energy storage devices.

Inverse design, fabrication, and tolerance to extreme environments of radiative cooling coating

Alternative to the traditional force cooling technologies, daytime radiative cooling (DRC) has drawn widespread attention for its zero-power. A porous polymer coating based on poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) has been reported as it has excellent DRC capacity. However, performance of the PVDF-HFP coating is affected substantially by its preparation conditions, restricting its application. To resolve the issue, we utilize an artificial neural network (ANN) to predict its DRC capacity and obtain the best preparation condition by siftings. In this work, the predicted solar reflectance ( R ¯ s o l a r ) and emittance of the atmospheric transmittance window ( ε ¯ a t w ), under the optimal preparation condition, reach 0.983 and 0.932, with a 1.865% and 0.107% error from the experimental value, correspondingly. Noticeably, the optimal PVDF-HFP coating achieves about 6℃ temperature drops below ambient temperature during daytime. In addition, to extend its applications in space, we conduct the extreme environmental experiment on the PVDF-HFP coating. After exposing in the extreme environment, R ¯ s o l a r of the coating has degradation rate over 11%. Consequently, these simulative methods and experimental results provide a positive direction for fabricating the high-performance DRCs.

Electrostrictive and Structural Properties of Poly(Vinylidene Fluoride-Hexafluoropropylene) Composite Nanofibers Filled with Polyaniline (Emeraldine Base).

Previous studies have reported that poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymers can exhibit large electrostrictive strains depending on the filler. This work examines the electrostrictive and structural properties of P(VDF-HFP) nanofibers modified with conductive polymer polyaniline (PANI). The P(VDF-HFP)/PANI composite nanofibers were prepared by an electrospinning method with different PANI concentrations (0, 0.5, 1, 1.5, 3 and 5 wt.%). The average diameter, water contact angle and element were analyzed by SEM, WCA and EDX, respectively. The crystalline, phase structure and mechanical properties were investigated by XRD, FTIR and DMA, respectively. The dielectric properties and electrostrictive behavior were also studied. The results demonstrated that the composite nanofibers exhibited uniform fibers without any bead formation, and the WCA decreased with increasing amount of PANI. However, a high dielectric constant and electromechanical response were obtained. The electrostrictive coefficient, crystalline, phase structure, dielectric properties and interfacial charge distributions increased in relation to the PANI content. Moreover, this study indicates that P(VDF-HFP)/PANI composite nanofibers may represent a promising route for obtaining electrostrictive composite nanofibers for actuation applications, microelectromechanical systems and sensors based on electrostrictive phenomena.

Superhydrophilic mixed matrix membranes by using strategy of internal and external coupling for oil-in-water emulsion separation

The intrinsic hydrophobicity of Poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HPF) membranes seriously hampers its application in the field of oily sewage treatment. The superhydrophilic surface transition of PVDF-HPF membranes can be achieved by the addition of inorganic nanoparticles. Nevertheless, the improvement of water remediation capacity may not be outstanding due to the addition of small or excessive amounts of nanomaterials. Herein, a highly active mixed matrix membranes (MMMs) were prepared by an internal and external coupling strategy of mixing and surface modification. Firstly, (3-mercaptopropyl) trimethoxysilane (KH590)-modified sodium bentonite (KNa-Bentonite) was used as nanofiller to prepare PVDF-HPF MMMs by phase inversion method. Subsequently, the assembly of plant-derived gallic acid (GA) and γ-aminopropyltriethoxysilane (APTES) couple KNa-Bentonite and polyethyleneimine (HPEI) as an intermediate component aims to constructed a nanostructured coating. The excellent superhydrophilicity could be achieved on PVDF-HPF MMMs by nanopapillae-like structures and sulfhydryl-quinone-amino covalent bridge. The optimal PVDF-HPF MMMs possessed favorable water flux (5966.31 ± 21 L·m−2·h−1 under 0.2 MPa, 266% higher than the pristine membrane), highly efficient separation ability for oil-in-water (O/W) emulsion (2369.5 ± 49 L·m−2·h−1) and operable antifouling performance (the flux recovery rate decreased by 10.24% after 10 cycles). Moreover, the oil rejection could be almost wholly restored after one month of standing at room temperature, indicating that the modified MMMs possessed good antioxidant property. The cost-effective strategy of internal and external coupling may offer new prospects for design and fabrication of super-wet membranes for O/W separation.

Effect of ultrahigh diluted homeopathic medicines on the electrical properties of PVDF-HFP

In an effort to improve the electrical properties of the electroactive Poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP), we introduced a novel and simple approach to synthesize PVDF-HFP composite films by incorporating ultrahigh dilutions of two homeopathic medicines Ferrum metallicum (FM) and Zincum oxidatum (ZO) in different potencies. The homeo-PVDF-composite films (HPCF) were synthesized by simple solution casting technique. XRD, FESEM, FTIR studies were performed to check the presence of nanoparticles in the film. The electrical properties of the HPCF samples get enhanced significantly due to the incorporation of the medicines and the effect increases with the increase in potency of the medicines.

The structural spectra of high dilutions and their unconventional application

Until few years, the so-called implausible science, homeopathy, was on the verge of being rejected on conventional physicochemical grounds. The mere selection of ultrahigh dilutions (UHD) (homeopathic potencies) for experimentation by mainstream scientists seemed impossible, but the curiosity to explore the science behind homeopathy kept igniting intellectual alma mater who subjected homeopathy to laboratories and test tubes, to know beyond its clinical application.
 Still, there exist a huge gap and a challenge to convince a conventional scientist to go beyond his domains and look for something which is apparently invisible (beyond Avogadro). But gradually we are overcoming this dogma and exploring the finer aspects and applications of UHDs. Much research has been undertaken, at least, to protect the identity of UHDs, and we are now verge of proving the plausibility of homeopathy from every aspect. 
 This issue of International Journal of High Dilution Research features two interesting articles on nature of UHDs and their unconventional application.
 The first article by NC Sukul et al aimed to decipher the nature of the water structure of UHDs of two commonly used homeopathic drugs Natrum muriaticum and Sulphur by Laser Raman Spectroscopy. This work is in the series undertaken by the group, who earlier experimented using Nuclear Magnetic Resonance; Electronic, Vibrational and Raman spectroscopy to shown differences in UHDs of various drugs. The present experiment could differentiate the intensities (potencies) of Nat-m and Sulph when compared to their controls, on the basis of hydrogen bond strength and free OH groups. 
 The second article by Nandy et al proposes a new dimension to the application of UHD. In an interesting manner, the author used UHDs of Ferrum metallicum and Zincum oxidatum to improve the electrical properties of the electroactive Poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP). The PVDF-HFP composite films were synthesized in their usual way, but an incorporation of Ferrum and Zinc-o could make the film as homeo-PVDF-composite. This enhancement of the electrical properties and are possibly due to the presence of nanoparticle, as hypothesized by the group. 
 The nature and application of UHDs are promising but challenging areas, which can only be validated through extensive research and validation. The realm of UHDs is expanding, and the day is not far when plausibility of homeopathy would be proved from every aspect, but at the same time we should also keep the momentum of research at pace in clinical research too!

Interfacial and Bulk Polarization of P(VDF-HFP) Investigated by Dielectric Spectroscopy

Capacitors in electrical and electronic systems composed of thin film dielectrics operate under extremely high electric fields. Dynamics of charge transport and relaxation are closely correlated to the energy storage properties and electrical degradation of thin film dielectrics for capacitive applications. In this paper, the dielectric relaxation properties of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) copolymer films are investigated over a broad frequency range from 10 mHz to 10 MHz and temperature range from -130 °C to 130 °C. The dielectric responses correlated to bulk and interfacial processes are clarified by varying the thickness and interfacial contact status of P(VDF-HFP) films. A low frequency process originating from the quasi-DC (QDC) process and a dielectric dispersion process correlated to the interfacial polarization are identified based on the Dissado-Hill dielectric response model and the equivalent circuit analysis. The high permittivity and high operation electric field of P(VDF-HFP) for capacitive energy storage give rise to improved blocking capacitance associated with the interface, suggesting the enhanced interfacial polarization. This work provides insights into the bulk and interface charge dynamics of polymer thin film dielectrics.

Electrospun Composite Gel Polymer Electrolytes with High Thermal Conductivity toward Wide Temperature Lithium Metal Batteries

Herein, the thermally conductive composite polymer membranes (CPMs) with silica-coated silver nanowires (AgNWs@SiO2) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) are first fabricated by an electrospinning technique. Various composite gel polymer electrolytes (CGPEs) are investigated with different weight percentages of AgNWs@SiO2 with respect to PVDF-HFP in the presence of liquid electrolytes. The CPMs display high thermal conductivity and thermal stability, good mechanical strength, and high electrolyte uptake. The thermal conduction property of CPMs was analyzed by a bidirectional asymmetric heat transfer model. Moreover, the CGPEs with the electrospun CPM as the matrix and AgNWs@SiO2 as fillers (es-CGPEs) possess the high ionic conductivity and excellent electrochemical performance compared to the Celgard separator system. The Li/es-CGPEs/LiFePO4 cell shows an enlarged excellent cycling life and better rate performance at 25 and 60 °C, in comparison to the one without AgNWs@SiO2 fillers. Interestingly, the Li/es-CGPEs/LiFePO4 cell in the presence of 5 wt % of AgNWs@SiO2 still delivers an excellent rate capability at 0 °C. The es-CGPE with AgNWs@SiO2 would be a promising candidate as the electrolyte material toward wide temperature lithium metal batteries.

Significantly enhanced energy density and breakdown strength of polymer nanocomposites using highly textured [111]c BaTiO3 platelets

Polymer-based dielectric films are considered as most promising materials for pulsed power capacitors due to their ultra-high power density and current density, fast discharging speed, excellent cycle lifetime and so on. However, the relatively low energy density and efficiency limit their applications in modern electronics and electrical power systems. Here we demonstrate a remarkable improvement in the breakdown strength and energy density of [111]c-BaTiO3 (BT) textured ceramic platelets synthesized in a poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) matrix. The breakdown strength of 1.0 wt% BT/P(VDF-HFP) composite films is 130 MV/m higher than that of pristine poly(vinylidene fluoride-hexafluoropropylene) films. The highest energy density of 19.5 J/cm³ and discharged energy density of 10.6 J/cm³ are achieved under an electric field of 480 MV/m in the 1.0 wt% BT/P(VDF-HFP) composite films. Fatigue experimental results show that the energy density and efficiency enhanced with the increase of cycles. This study provides a new paradigm to develop the polymer composites with high breakdown strength and energy density, which has great potential for flexible electrical energy storage applications.

Lead-free AgNbO3/poly(vinylidene fluoride‐hexafluoropropylene) antiferroelectric nanocomposite for high energy density capacitor applications

In the past few decades, ceramic/polymer nanocomposites have been extensively studied due to their relatively large dielectric constant, high electric energy density, and large charge–discharge efficiency. Antiferroelectric (AFE) materials possess a low remnant polarization (P r) and relatively high saturation polarization (P s), which can induce higher storage energy density than relaxor ferroelectric materials. In this investigation, AgNbO3-based AFE ceramic nanoparticles were grafted with a layer of poly(methyl methacrylate) (PMMA) to form AgNbO3–g-PMMA nanoparticles and then the obtained nanoparticles were embedded into a poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) matrix to form an AgNbO3–g-PMMA/PVDF-HFP (AN–g-PMMA/HFP) nanocomposite film. After characterization, it was found that the dielectric constant of the AN–g-PMMA/HFP-5 (5% AgNbO3) nanocomposite film was 12.3, which was 43% higher than that of the pristine PVDF-HFP film. The AN–g-PMMA/HFP-5 nanocomposite film exhibited the largest breakdown field of 500 MV m−1 and the highest energy density of 13 J cm−3, which was increased by 32.5% (from 9.82 to 13 J cm−3), as compared with that of the pristine PVDF-HFP film. The AN–g-PMMA/HFP-5 film exhibited a charge–discharge efficiency of 69.5% at 500 MV m−1, which is 9.5% higher than that of the pristine PVDF-HFP film. This AgNbO3-based nanocomposite film shows great promise for AFE nanocomposite for high energy density capacitor applications.

Preparation and electrochemical study of PVDF-HFP/LATP/g-C3N4 composite polymer electrolyte membrane

Li1.3Al0.3Ti1.7(PO4)3 powder (LATP) is synthesized by high temperature solid phase method, and then a composite polymer electrolyte membrane Poly(Vinylidene Fluoride-Hexafluoropropylene)/LATP/graphitic-C3N4 is prepared by a simple casting method. Then, the influence of porous layered g-C3N4 on the composite polymer electrolyte membrane is studied by morphology characterization and electrochemical measurement. The experimental results show that the addition of g-C3N4 improves the ionic conductivity (2.55 × 10-5 S cm−1) and lithium ion transference number (0.647) of the composite polymer electrolyte membrane (CPE), and the CPE membrane PVDF-HFP/LATP/g-C3N4 has a broad electrochemical window (up to 5.0 V) and superior electrochemical stability.

Temperature dependence and correlation of polarization processes in P(VDF-HFP) films

Polymer dielectrics are indispensable in electrical and electronic systems, being used as insulation, capacitors, gate dielectric, etc. However, a lot of polymer materials show unsatisfactory efficiency at high temperature and low frequencies, which has been found to be closely related to polarization processes. In this paper, the dielectric spectroscopy of poly (vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) films is investigated over a broad frequency range from 10 mHz to 1 MHz and temperature range from −130 °C to 130 °C based on the Dissado-Hill model. The processes in the entire response are identified and characterized quantitatively. The temperature dependence of major processes contributing to energy storage and dielectric loss are revealed. It is found that the variations of both β polarization and DC conductance coincide with Arrhenius equation, while both α polarization and quasi-DC polarization show Vogel−Fulcher−Tammann (VFT) features. Moreover, α polarization and quasi-DC polarization share the same form parameter of VFT equation, indicating that they have a common origin of microstructure. The origin and correlation of polarization processes could be used to develop a paradigm for rational design of polymer dielectrics to enhance or suppress specific processes for certain purposes.

Highly porous single ion conducting membrane via a facile combined “structural self-assembly” and in-situ polymerization process for high performance lithium metal batteries

A polymer electrolyte with high porosity and enhanced lithium ion transference number, tLi+, can endow lithium metal batteries with high energy density and relieved dendrite growth. Herein, highly porous single ion conducting polymer electrolyte (SIPE), po-PVPB, is successfully prepared via the “structural self-assembly” process occurred in different chemical structures of aliphatic poly (vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) binder and partially aromatic SIPE during membrane preparation process. In particular, the semi-interpenetrating polymer networks are successfully achieved by in-situ polymerization of bis(4-amino benzene sulfonyl)imide (Li-BABSI) and poly (ethylene glycol) diglycidyl ether (PEGDGE) in the poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix during the same membrane preparation process for construction of highly continuous lithium ion transport pathway. The po-PVPB membrane exhibits high porosity of 61.5% and solvent uptake of 116.0 wt% as well as good mechanical strength of 10.5 MPa. The po-PVPB electrolyte is then prepared by impregnating with EC/DMC, v:v = 1:1 solvent and the practical use of the po-PVPB electrolyte is finally evaluated by Li/LFP cell using LiFePO4 (LFP) as cathode active materials and Li metal as anode, respectively. Very important, the po-PVPB electrolyte demonstrates a high tLi+ of 0.9 for suppressing lithium dendrite growth. The Li/LFP cell also exhibit good rate capability and highly stable for over 200 cycles, suggesting its potential application in the lithium metal batteries.

Mechanically Strong and Electrochemically Stable Single-Ion Conducting Polymer Electrolytes Constructed from Hydrogen Bonding.

Herein, composite membranes based on a single-ion conducting polymer electrolyte (SIPE) and poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) were prepared by an electrospinning technology. The SIPE with hydrogen bonding was obtained via reversible addition-fragmentation chain transfer (RAFT) copolymerization of 2-(3-(6-methyl-4-oxo-1,4-dihydropyrimidin-2-yl)ureido)ethyl methacrylate (UPyMA), poly(ethylene glycol) methyl ether methacrylate (PEGMA), and lithium 4-styrenesulfonyl (phenylsulfonyl) imide (SSPSILi). The obtained composite membrane exhibited a highly porous network structure, superior thermal stability (>300 °C), and high mechanical strength (17.3 MPa). The fabricated SIPE/PVDF-HFP composite membrane without lithium salts possessed a high ionic conductivity of 2.78 × 10-5 S cm-1 at 30 °C, excellent compatibility with the lithium metal electrode, and high lithium-ion transference number (0.89). The symmetric Li//Li cell exhibited a superior cycle performance without short circuit, indicating the generation of a stable interface between SIPE and the lithium metal electrode during the process of lithium plating/stripping, which could inhibit lithium dendrite growth in lithium metal batteries (LMBs). The Li//LiFePO4 cell also exhibited superior cycle life and excellent rate capability at 60 or 25 °C. In consequence, the composite membrane exhibits a considerable future prospect for advanced LMBs.

Chlorinated dual-protective layers as interfacial stabilizer for dendrite-free lithium metal anode

Lithium metals offer great promises to achieve higher energy density beyond conventional lithium-ion batteries (LIBs) because of its ultrahigh specific capacity (3860 mAh g−1) and the lowest reduction potentials (-3.04 V vs. standard hydrogen electrode). Unfortunately, the application of lithium metal anode has been long-standingly handicapped by uncontrollable dendrite growth, which induces instable solid electrolyte interface (SEI), performance degradation and thermal runaway. Herein, a compositionally favorable and structurally robust dual-protective layer (DPL) is proposed, where at the bottom, in-situ formed LiCl film provides sufficient rigidity (6.5 GPa) and low Li+ diffusion barriers (0.09 eV) against dendrite growth. The poly(vinylidene fluoride-hexafluoropropylene) (PVdF-HFP) gel-electrolyte as the top layer is rationally selected with high flexibility to accommodate volume variation. Due to the synergy of DPL, the instability of interface is ultimately regulated to favor an extremely stabilized SEI with enhanced Li+ diffusion kinetics. Depth profiling of X-ray photoelectron spectroscopy (XPS) revealed a spontaneously-formed gradient SEI hierarchy, a first-of-this-kind structure that enables long-term cycle stability and high rate capability. Cryo-electron microscopy (cryo-EM) provides direct proof on the formation of halide-rich SEI interlayers that strengthen the interfacial stability during cycles. As a consequence, dendrite-proof lithium deposition, critical Li+ flux and fast ion-diffusion kinetics have been synergistically achieved to greatly improve the high-rate cycle stability (10 mA cm−2), high Coulombic efficiency (99.5%), and prolonged cycle lifespan (1600 h) for lithium metal batteries (LMBs). The design of DPL from this contribution has opened up opportunities of lithium chlorides in purpose of constructing dendrite-free and Li+ permeable interface, and provided insights for the realization of high energy density LMBs.

Achieving Concurrent High Energy Density and Efficiency in All-Polymer Layered Paraelectric/Ferroelectric Composites via Introducing a Moderate Layer.

Dielectric polymer capacitors are extensively applied in advanced electronics by virtue of their extremely high power density. However, it remains a challenge to concurrently realize high energy density and high discharge efficiency. In order to solve this conundrum, we herein design a novel all-polymer trilayer structure, where the paraelectric poly(methyl methacrylate) (PMMA) is used as the top layer to obtain a high discharge efficiency, and ferroelectric P(VDF-HFP) is employed as the bottom layer to obtain a high energy density. Particularly, the PMMA/poly(vinylidene fluoride-hexafluoropropylene) (P(VDF-HFP)) blend composite is used as the middle layer to homogenize the electric field inside the trilayer composites, turning out an obviously boosted breakdown strength and elevated energy density. Consequently, an efficiency as high as 85% and an energy density up to 7.5 J/cm3 along with excellent cycling stability are simultaneously realized at an ultrahigh electric field of 490 kV/mm. These attractive characteristics of the all-polymer trilayer structure suggest that the feasible pathway presented herein is significant to realize concurrently a high energy density and discharge efficiency.