Multi-dimensional hybrid flexible films promote uniform lithium deposition and mitigate volume change as lithium metal anodes

Lithium metal is the ultimate anode material for next-generation high-energy batteries.Yet,the practical application of lithium metal anodes is limited by the formation of Li dendrites and large volume changes.Herein,an effective multi-dimensional hybrid flexible film(MD-HFF)composed of iodine ion(0 dimension),CNTs(1 dimension)and graphene(2 dimensions)is designed for regulating Li deposition and mitigating volume changes.The multi-dimensional components serve separate roles:(1)iodine ion enhances the conductivity of the electrode and provides lithiophilic sites,(2)CNTs strengthen interlaminar conductance and mechanical strength,acting as a spring in the layered structure to alleviate volume changes during Li plating and stripping and(3)graphene provides mechanical flexibility and electrical conductivity.The resulting MD-HFF material supports stable Li plating/stripping and high Coulombic efficiency(99%)over 230 cycles at 1 mA cm^(-2) with a deposition capacity of 1 mAh cm^(-2).Theoretical calculations indicate that LiI contributes to the lateral growth of Li on the MD-HFF surface,thereby inhibiting the formation of Li dendrites.When paired with a typical NCM811 cathode,the assembled MD-HFF‖NCM811 cell exhibit improved capability and stable cycling performance.This research serves to guide material design in achieving Li anode materials that do not suffer from dendrite formation and volume changes.

Highly Flexible Graphene-Film-Based Rectenna for Wireless Energy Harvesting

Herein,we report the design,fabrication,and performance of two wireless energy harvesting devices based on highly flexible graphene macroscopic films(FGMFs).We first demonstrate that benefiting from the high conductivity of up to 1×10^(6)S m^(-1)and good resistive stability of FGMFs even under extensive bending,the FGMFs-based rectifying circuit(GRC)exhibits good flexibility and RF-to-DC efficiency of 53%at 2.1 GHz.Moreover,we further expand the application of FGMFs to a flexible wideband monopole rectenna and a 2.45 GHz wearable rectenna for harvesting wireless energy.The wideband rectenna at various bending conditions produces a maximum conversion efficiency of 52%,46%,and 44%at the 5th Generation(5G)2.1 GHz,Industrial Long-Term Evolution(LTE)2.3 GHz,and Scientific Medical(ISM)2.45 GHz,respectively.A 2.45 GHz GRC is optimized and integrated with an AMC-backed wearable antenna.The proposed 2.45 GHz wearable rectenna shows a maximum conversion efficiency of 55.7%.All the results indicate that the highly flexible graphene-film-based rectennas have great potential as a wireless power supplier for smart Internet of Things(loT)applications.

Cascade excitation of vortex motion and reentrant superconductivity in flexible Nb thin films

High quality Nb films were successfully prepared on both flexible polyimide(PI)and rigid Al2O3substrates and their transport properties were systematically studied at various applied currents,external magnetic fields,and sample orientations.It is found that a curved Nb/PI film exhibits quite different superconducting transition and vortex dynamics compared to the flat Nb/Al2O3film.For the curved Nb/PI film,smooth superconducting transitions were obtained at low currents,while unexpected cascade structures were revealed in theρ(T)curves at high currents.We attribute this phenomenon to the gradient distribution of vortex density together with a variation of superconductivity along the curved film.In addition,reentrant superconductivity was induced in the curved Nb/PI thin film by properly choosing the measurement conditions.We attribute this effect to the vortex pinning from both in-plane vortices and out-of-plane vortices.This work reveals the complex transport properties of curved superconducting thin films,providing important insights for further theoretical investigations and practical developments of flexible superconductors.

Molecular simulation and experimental investigation of thermal conductivity of flexible graphite film

Flexible graphite film(FGF),as a traditional interface heat dissipation material,has high anisotropy.It is a challenge to enhance both in-plane and through-plane thermal conductivity of FGF.For this reason,the effects of oxygen content,layer spacing,density and particle size on the in-plane and through-plane thermal conductivity of FGF were studied by both molecular simulation and experimental investigation.The simulation results indicate that the ways to improve the thermal conductivity of FGF include reducing oxygen content and layer spacing,increasing the density and matching the size of graphite sheets.The FGF prepared from room temperature exfoliated graphite(RTFGF)has a wide range of adjustable density(1.3–2.0 g/cm^(3))and thickness(50–400μm).The thermal conductivity of the RTFGF is significantly improved after heat treatment owing to reduced oxygen content and layer spacing,which is consistent with the simulation results.Moreover,RTFGF with both high in-plane(518 W·m^(-1)·K^(-1))and through-plane(7.2 W·m^(-1)·K^(-1))thermal conductivity can be obtained by particle size matching of graphite.

Emerging Flexible Thermally Conductive Films:Mechanism,Fabrication,Application

Effective thermal management is quite urgent for electronics owing to their ever-growing integration degree,operation frequency and power density,and the main strategy of thermal management is to remove excess energy from electronics to outside by thermal conductive materials.Compared to the conventional thermal management materials,flexible thermally conductive films with high in-plane thermal conductivity,as emerging candidates,have aroused greater interest in the last decade,which show great potential in thermal management applications of next-generation devices.However,a comprehensive review of flexible thermally conductive films is rarely reported.Thus,we review recent advances of both intrinsic polymer films and polymer-based composite films with ultrahigh in-plane thermal conductivity,with deep understandings of heat transfer mechanism,processing methods to enhance thermal conductivity,optimization strategies to reduce interface thermal resistance and their potential applications.Lastly,challenges and opportunities for the future development of flexible thermally conductive films are also discussed.

Ultrathin Ni_(x)Co_(y)-silicate nanosheets natively anchored on CNTs films for flexible lithium ion batteries

The rapid development of portable and wearable electronics has called for novel flexible electrodes with superior performance.The development of flexible electrode materials with excellent mechanical and electrochemical properties has become one of the key factors for this goal.Here,a Ni_(x)Co_(y)-silicate@CNTs film is developed as a flexible anode for lithium ion batteries(LIBs).On this film,Ni_(x)Co_(y)-silicate nanosheets are firmly and intimately anchored on the surface of CNTs,which have a 3D network structure and link the adjacent nanosheets together.Benefitted from this,the composite film is not only sufficient to withstand various deformations due to its excellent flexibility but also has excellent electrochemical properties,in terms of high reversible capacity of 1047 mAh g^(-1) at 0.1 A g^(-1) as well as a high rate and cycling performance(capacity retention up to 78.13% after 140 cycles).The pouch-type full flexible LIB using this material can stably operate under various bending conditions,showing the great potential of this 3 D Ni_(x)Co_(y)-silicate@CNTs film for flexible energy storage devices with high durability.

Fabrication, properties, and applications of flexible magnetic films

Flexible magnetic devices, i.e., magnetic devices fabricated on flexible substrates, are very attractive in applications such as detection of magnetic field in an arbitrary surface, non-contact actuators, and microwave devices, due to their stretchable, biocompatible, light-weight, portable, and low cost properties. Flexible magnetic films are essential for the realization of various functionalities of flexible magnetic devices. To give a comprehensive understanding for flexible magnetic films and related devices, recent advances in the study of flexible magnetic films are reviewed, including fabrication methods, magnetic and transport properties of flexible magnetic films, and their applications in magnetic sensors, actuators, and microwave devices. Our aim is to foster a comprehensive understanding of these films and devices. Three typical methods have been introduced to prepare the flexible magnetic films, by deposition of magnetic films on flexible substrates, by a transfer and bonding approach or by including and then removing sacrificial layers. Stretching or bending the magnetic films is a good way to apply mechanical strain to them, so that magnetic anisotropy, exchange bias, coercivity, and magnetoresistance can be effectively manipulated. Finally, a series of examples is shown to demonstrate the great potential of flexible magnetic films for future applications.

High-Quality Bi_2Te_3 Single Crystalline Films on Flexible Substrates and Bendable Photodetectors

Recently, great efforts have been made in the fabrication of arbitrary warped devices to satisfy the requirement of wearable and lightweight electronic products. Direct growth of high crystalline quality films on flexible substrates is the most desirable method to fabricate flexible devices owing to the advantage of simple and compatible preparation technology with current semiconductor devices, while it is a very challenging work, and usually amorphous, polycrystalline or discontinuous single crystalline films are achieved. Here we demonstrate the direct growth of high-quality Bi2 Te3 single crystalline films on flexible polyimide substrates by the modified hot wall epitaxy technique. Experimental results reveal that adjacent crystallites are coherently coalesced to form a continuous film, although amounts of disoriented crystallites are generated due to fast growth rate. By inserting a quartz filter into the growth tube, the number density of disoriented crystallites is effectively reduced owing to the improved spiral interaction. Furthermore, flexible Bi2 Te3 photoconductors are fabricated and exhibit strong near-infrared photoconductive response under different degrees of bending, which also confirms the obtained fexible films suitable for electronic applications.

Fabrication of High-Haze Flexible Transparent Conductive PMMA Films Embedded with Silver Nanowires

High-haze flexible transparent conductive polymethyl methacrylate （PMMA） films embedded with silver nanowires （AgNWs） are fabricated by a low-cost and simple process. The volatilization rate of the solvent in PMMA solution affects the surface microstructures and morphologies, which results in different haze factors of the composite films. The areal mass density of AgNW shows a significant influence on the optical and electrical properties of composite films. The AgNW/PMMA transparent conductive films with the sheet resistance of 5.5Ω sq ^-1 exhibit an excellent performance with a high haze factor of 81.0% at 550？nm.

Hierarchically Multifunctional Polyimide Composite Films with Strongly Enhanced Thermal Conductivity

The development of lightweight and integration for electronics requires flexible films with high thermal conductivity and electromagnetic interference(EMI) shielding to overcome heat accumulation and electromagnetic radiation pollution.Herein,the hierarchical design and assembly strategy was adopted to fabricate hierarchically multifunctional polyimide composite films,with graphene oxide/expanded graphite(GO/EG) as the top thermally conductive and EMI shielding layer,Fe_(3)O_(4)/polyimide(Fe_(3)O_(4)/PI) as the middle EMI shielding enhancement layer and electrospun PI fibers as the substrate layer for mechanical improvement.PI composite films with 61.0 wt% of GO/EG and 23.8 wt% of Fe_(3)O_(4)/PI exhibits high in-plane thermal conductivity coefficient(95.40 W(m K)^(-1)),excellent EMI shielding effectiveness(34.0 dB),good tensile strength(93.6 MPa) and fast electric-heating response(5 s).The test in the central processing unit verifies PI composite films present broad application prospects in electronics fields.

Flexible one-dimensional photonic crystal films composed of chalcogenide glass and water-soluble polymer for curvature sensing

Curvature sensing plays an important role in structural health monitoring,damage detection,real-time shape control,modification,etc.Developing curvature sensors with large measurement ranges,high sensitivity,and linearity remains a major challenge.In this study,a curvature sensor based on flexible one-dimensional photonic crystal(1D-PC)films was proposed.The flexible 1D-PC films composed of dense chalcogenide glass and water-soluble polymer materials were fabricated by solution processing.The flexible 1D-PC film curvature sensor has a wide measurement range of 33-133 m-1and a maximum sensitivity of0.26 nm/m^(-1).The shift of the transmission peak varies approximately linearly with the curvature in the entire measurement range.This kind of 1D-PC film curvature sensor provides a new idea for curvature sensing and measurement.

Texture and Se vacancy optimization induces high thermoelectric performance in Bi_(2)Se_(3) flexible thin films

Bi_(2)Se_(3)-based flexible thin film with high thermoelectric performance is promising for the waste heat recovery technology.In this work,a novel post-selenization method is employed to prepare n-type Bi_(2)Se_(3)flexible thin films with highly textured structure.The strengthened texture and Se vacancy optimization can be simultaneously achieved by optimizing the selenization temperature.The highly oriented texture leads to the increased carrier mobility and results in a high electric conductivity of~290.47 S·cm^(-1)at 623 K.Correspondingly,a high Seebeck coefficient(>110μW·K-1)is obtained due to the reduced carrier concentration,induced by optimizing vacancy engineering.Consequently,a high power factor of 3.49μW·cm^(-1)·K^(-2)at 623 K has been achieved in asprepared highly-bendable Bi_(2)Se_(3)flexible thin films selenized at 783 K.This study introduces an effective post-selenization method to tune the texture structure and vacancies of Bi_(2)Se_(3)flexible thin films,and correspondingly achieves high thermoelectric performance.

A Novel Method of Fabricating Flexible Transparent Conductive Large Area Graphene Film

We fabricate flexible conductive and transparent graphene films on position-emission-tomography substrates and prepare large area graphene films by graphite oxide sheets with the new technical process. The multi-layer graphene oxide sheets can be chemically reduced by HNO3 and HI to form a highly conductive graphene film on a substrate at lower temperature. The reduced graphene oxide sheets show a high conductivity sheet with resistance of 476Ω/sq and transmittance of 76% at 550nm （6 layers）. The technique used to produce the transparent conductive graphene thin film is facile, inexpensive, and can be tunable for a large area production applied for electronics or touch screens.

Recent advances of flexible perovskite solar cells

In few years only, the efficiency record of perovskite solar cells（PSCs） has raised quickly from 3.8% to over 22%. This emerging photovoltaic technology has primarily shown its great potential of industrialization. Flexible PSCs are thought to be one of the most priority options for mass production, related to the intrinsic advantage of perovskite thin films which could be deposited by facile solution processes at low temperature. Flexible PSCs have at least four advantages in comparison to the rigid counterpart：（1） it can generate higher power output at lighter weight,（2） it is easily portable,（3） it can be easily attached to architectures or textiles with diverse shapes, and（4） it is compatible with roll-to-roll fabrication in a large scale. In this review, we have summarized recent development of the key materials and technologies applied in flexible PSCs. The key materials including flexible substrates, transparent and conductive electrodes, and interfacial materials; some key technologies about roll-to-roll manufacture, encapsulation technology have been overviewed. Finally, a prospect on possible application directions of flexible PSCs has been discussed.

The Effective Surface Metallization of Hollow Glass Microspheres for Flexible Electromagnetic Shielding Film

The surface of hollow glass microspheres (HGMs) was roughened by a HCl+NH_(4)F strategy,which achieved a broken ratio as 16.10%,and then metallized by electroless plating by Co nanoparticles up to 90 wt% (abbreviated as Co-HGMs).The average grain size of Co was measured to range from 0.4 to 0.5 μm.Then Co-HGMs were mixed with liquid silicone rubber and xylene,and cured on a perspex plate applicable for flexible electromagnetic shielding.By attentive parameter optimization,a film about 0.836 mm in thickness was obtained with a density of 0.729 g/cm^(3),showing a shielding effectiveness of 15.2 dB in the X-band (8.2-12.4 GHz) at room temperature,which was ascribed to the formation of a conductive network of Co-HGMs inside the film.Simultaneously,the tensile strength of 0.89 MPa at an elongation ratio of 194.5% was also obtained,showing good mechanical properties and tensile strength.

Sub-nanoscale Engineering of MoO_(2) Clusters for Enhanced Sodium Storage

Smart construction of battery-type anodes with high rate and good mechanical properties is significant for advanced sodium ion capacitors(SICs).Herein,a flexible film consisting of MoO_(2) subnanoclusters encapsulated in nitrogen-doped carbon nanofibers(MoO_(2) SCs@N-CNFs)is designed and synthesized via electrospinning toward SICs as anodes.The strong N-Mo interaction guarantees the stable yet uniform dispersion of high loading MoO_(2) SCs(≈40 wt.%)in the flexible carbonaceous substrate.The sub-nanoscale effect of SCs restrains electrode pulverization and improves the Na+diffusion kinetics,rendering better pseudocapacitance-dominated Na+-storage properties than the nanocrystal counterpart.The MoO_(2) SCs@N-CNFs paper with mass loadings of 2.2–10.1 mg cm^(−2) can be directly used as free-standing anode for SICs,which exhibit high reversible gravimetric/areal capacities both in liquid and quasi-solid-state electrolytes.The assembled flexible SICs competitively exhibit exceptional energy density and cycling stability.More significantly,the sub-nanoscale engineering strategy here is promisingly generalized to future electrode design for other electrochemical energy-related applications and beyond.

Hydrogen bond-bridged phosphorene flexible film for photodynamic inhibiting Staphylococcus aureus

Antibiotics are a widely used and effective treatment for bacterial infections.However,bacteria can gradually evolve during infection,leading to developing resistance to antibiotics,which renders previously effective treatments ineffective.Finding a useful and convenient manner to treat bacterial infections is a great challenge.Here,we report a flexible hydrogen-bond-bridged phosphorene film with photodynamic antibacterial properties and excellent mechanical properties,fabricated from electrochemical exfoliation of black phosphorus(BP).When illuminated under 700 nm light,the hydrogen bond-bridged phosphorene flexible film is capable of converting ground-state triplet oxygen(O_(2))into excited-state singlet oxygen(^(1)O_(2)),destroying the structure of the membrane of Staphylococcus aureus,and eventually leading to bacterial death,via breaking the C=C of unsaturated fatty acids within the bacterial cell membrane after the reaction between^(1)O_(2)and unsaturated fatty acids,thus realizing a highly efficient antibacterial approach,which is supported by gas chromatography-mass spectrometry(GC-MS)technique.This work establishes an effective phototherapy platform for treating bacterial traumatic infections.

An Anisotropic Biomimetic Lemongrass Flexible Piezoelectric Actuator-Inhibitory Regression

At present,the existing piezoelectric stick-slip actuators have an inherent back-slip problem,which greatly limits the development and application of stick-slip actuators.In order to inhibit the regression phenomenon,a new bionic lemongrass stickslip actuator was prepared by using polymer PDMS to replicate natural biological surface.The surface microstructure of the grass was copied by PDMS,and the PDMS film was prepared.The rigid and flexible bionic friction pair was further prepared,and the flexible anisotropic PDMS stick slip actuator was developed.It was found that the anisotropic friction characteristics of the surface microstructure of the grass inhibited the anti-sliding motion,and the elastic potential energy of the PDMS film improved the output characteristics of the driver.By adjusting the input voltage to control the contact between the drive foot and the rotor,the rigid and flexible hybrid drive can be realized and the backsliding phenomenon can be suppressed.The actuator is compact,lightweight and can achieve high speed and high resolution output without preloading force,which has important application value in the field of fast and accurate positioning with load limitation.

Highly sensitive color fine-tuning of diblock copolymeric nano-aggregates with tri-metallic cations,Eu(Ⅲ),Tb(Ⅲ),and Zn(Ⅱ),for flexible photoluminescence films(FPFs)

Luminescence materials have shown promise as display apparatus and lighting devices.The particularly interesting systems are photoluminescence materials that are capable of reversible colors emitting repeatedly on exposure to light.Here we report a series of color tunable flexible and transparent photoluminescence films consisting of multi-metals(Eu^(3+),Tb^(3+)and Zn^(3+))induced polymer aggregates(MIPAs)which are distributed uniformly in the polyacrylonitrile(PAN)films without agglomeration.MIPAs have a unique spherical structure due to the self-assembly of polystyrene-block-polyacrylic acid(PS-b-PAA)induced by metal ions.Notably,when applied in photoluminescence devices,these photoluminescence films exhibit not only red,green,blue colors(RGB)light,but also other tuned various color light covering the whole visible range upon excitation of 345 nm through adjusting the relative ratios of metal complexes.As the most important key point,non-conductive polymers can be used in photoluminescence devices as host medium,which is not realized in electroluminescent devices.Thus,the flexible photoluminescence films(FPFs)innovated herein exhibit the great potential to apply for flexible light-color and light-energy transformation devices.

MoS_(2)-Decorated/Integrated Carbon Fiber:Phase Engineering Well-Regulated Microwave Absorber

Phase engineering is an important strategy to modulate the electronic structure of molybdenum disulfide(MoS_(2)).MoS_(2)-based composites are usually used for the electromagnetic wave(EMW)absorber,but the effect of different phases on the EMW absorbing performance,such as 1T and 2H phase,is still not studied.In this work,micro-1T/2H MoS_(2) is achieved via a facile one-step hydrother-mal route,in which the 1T phase is induced by the intercalation of guest molecules and ions.The EMW absorption mechanism of single MoS_(2) is revealed by presenting a comparative study between 1T/2H MoS_(2) and 2H MoS_(2).As a result,1T/2H MoS_(2) with the matrix loading of 15%exhibits excellent microwave absorption property than 2H MoS_(2).Furthermore,taking the advantage of 1T/2H MoS_(2),a flexible EMW absorbers that ultrathin 1T/2H MoS_(2)grown on the carbon fiber also performs outstanding performance only with the matrix loading of 5%.This work offers necessary reference to improve microwave absorption performance by phase engineering and design a new type of flexible electromagnetic wave absorption material to apply for the portable microwave absorption electronic devices.