Highly Aligned Graphene Aerogels for Multifunctional Composites

Stemming from the unique in-plane honeycomb lattice structure and the sp^(2)hybridized carbon atoms bonded by exceptionally strong carbon–carbon bonds,graphene exhibits remarkable anisotropic electrical,mechanical,and thermal properties.To maximize the utilization of graphene’s in-plane properties,pre-constructed and aligned structures,such as oriented aerogels,films,and fibers,have been designed.The unique combination of aligned structure,high surface area,excellent electrical conductivity,mechanical stability,thermal conductivity,and porous nature of highly aligned graphene aerogels allows for tailored and enhanced performance in specific directions,enabling advancements in diverse fields.This review provides a comprehensive overview of recent advances in highly aligned graphene aerogels and their composites.It highlights the fabrication methods of aligned graphene aerogels and the optimization of alignment which can be estimated both qualitatively and quantitatively.The oriented scaffolds endow graphene aerogels and their composites with anisotropic properties,showing enhanced electrical,mechanical,and thermal properties along the alignment at the sacrifice of the perpendicular direction.This review showcases remarkable properties and applications of aligned graphene aerogels and their composites,such as their suitability for electronics,environmental applications,thermal management,and energy storage.Challenges and potential opportunities are proposed to offer new insights into prospects of this material.

Transition metal carbonate anodes for Li-ion battery: fundamentals,synthesis and modification

Even though transition metal carbonates(TMCs, TM = Fe, Mn, Co, Ni etc.), show high theoretical capacities, rich reserves and environmental friendliness as anodes for lithium-ion batteries(LIBs), they suffer from sluggish electronic/ionic conductivities and huge volume variation, which severely deteriorate the rate capacities and cycling performances. Understanding the intrinsic reaction mechanism and further developing ideal TMC-based anode with high specific capacity, excellent rate capabilities, and longterm cycling stability are critical for the practical application of TMCs. In this review, we firstly focus on the fundamental electrochemical energy-storage mechanisms of TMCs, in terms of conversionreaction process, pseudocapacitance-type charge storage, valence change for charge storage and catalytic conversion mechanisms. Based on the reaction mechanisms, various modification strategies to improve the electrochemical performance of TMCs are summarized, covering:(i) micro-nano structural engineering, in which the influence factors on the morphology are discussed, and multiple architectures are listed;(ii) elemental doping, in which the intrinsic mechanisms of metal/nonmetal elements doping on the electrochemical performance are deeply explored;(iii) multifunctional compositing strategies, in which the specific affections on structure, electronic conductivity and chemo-mechanical stability are summarized.Finally, the key challenges and opportunities to develop high-performance TMCs are discussed and some solutions are also proposed. This timely review sheds light on the path towards achieving cost-effective and safe LIBs with high energy density and long cycling life using TMCs-based anode materials.

Large-scale preparation of high-performance boron nitride/aramid nanofiber dielectric composites

Dielectric polymers featuring high thermal conductivity,excellent mechanical,and stable dielectric properties over a broad temperature range have attracted extensive scientific attention.In this work,a large-scale,layered film was fabricated using blade-coating approach,which integrated aramid nanofibers(ANFs)and boron nitride nanosheets(BNNSs)through a typical solgel transformation procedure.The as-prepared film with 20 wt.%BNNS displays high thermal conductivity(14.03 W·m^(−1)·K^(−1)),103-fold higher than pure ANF film,attributing to massive continuous thermal conduction pathway between BNNSs so as to facilitate fast phonon transmission.The film boasts excellent mechanical properties(stress 97.14±5.17 MPa,strain 19.36±0.35%),high degradation temperature(~542℃),a moderate dielectric constant(~6.9 at 104 Hz),together with low dielectric loss(~0.026 at 104 Hz).Meanwhile,the film reveals high breakdown voltage(310 MV·m^(−1))and volume resistivity(1013Ω·cm).Notably,these dielectric properties remain largely unchanged over a wide temperature range(25 to 200℃).

PVDF/6H-SiC composite fiber films with enhanced piezoelectric performance by interfacial engineering for diversified applications

Piezoelectric silicon carbide(SiC)has been quite attractive due to its superior chemical and physical properties as well as wide potential applications.However,the inherent brittleness and unsatisfactory piezoelectric response of piezoelectric semiconductors remain the major obstacles to their diversified applications.Here,flexible multifunctional PVDF/6H-SiC composite fiber films are fabricated and utilized to assemble both piezoelectric nanogenerators(PENGs)and stress/temperature/light sensors.The open cir-cuit voltage(V_(oc))and the density of short circuit current(I_(sc))of the PENG based on the PVDF/5 wt%6H-SiC composite fiber films reach 28.94 V and 0.24μA cm^(-2),showing a significant improvement of 240%and 300%compared with that based on the pure PVDF films.The effect of 6H-SiC nanoparticles(NPs)on inducing interfacial polarization and stress concentration in composite fiber films is proved by first-principles calculation and finite element analysis.The stress/temperature/light sensors based on the composite fiber film also show high sensitivity to the corresponding stimuli.This study shows that the PVDF/6H-SiC composite fiber film is a promising candidate for assembling high-performance energy harvesters and diverse sensors.

Low-Voltage Activating, Fast Responding Electro-thermal Actuator Based on Carbon Nanotube Film/PDMS Composites

The electro-thermal actuators(ETA)are smart devices that can convert electric energy into mechanical energy under electro-heating stimulation,showing great potential in the fields of soft robotics,artificial muscle and aerospace component.In this study,to build a low-voltage activating,fast responding ETA,a robust and flexible carbon nanotube film(CNTF)with excellent electrical and thermal conductivity was adopted as the conductive material.Then,an asymmetric bilayer structured ETA was manufactured by coating a thin layer of polydimethylsiloxane(PDMS)with high coefficient of thermal expansion(9.3×10^(-4)℃^(−1)),low young’s modulus(2.07 MPa)on a thin CNTF(~11μm).The as-produced CNTF/PDMS composite ETA exhibited a large deformation(bending angle~324°)and high electro heating performance(351℃)at a low driving voltage of 8 V within~12 s.The actuated movement and the generated heat could be controlled by adjusting the driving voltages and showed almost the same values in 20 cycles.Furthermore,the influences of the PDMS thickness and driving voltage on CNTF/PDMS composite ETA performance were systematically investigated.The CNTF/PDMS soft robotic hand which can lift 5.1 times and crab 1.3 times of its weight demonstrated its potential capability.

Interlayer engineering in 3D graphene skeleton realizing tunable electronic properties at a highly controllable level for piezoresistive sensors

Three-dimensional(3D)graphene is a promising active component for various engineering fields,but its performance is limited by the hidebound electrical conductivity levels and hindered electrical transport.Here we present a novel approach based on interlayer engineering,in which graphene oxide(GO)nanosheets are covalently functionalized with varied molecular lengths of diamine molecules.This has led to the creation of an unprecedented class of 3D graphene with highly adjustable electronic properties.Theoretical calculations and experimental results demonstrate that ethylenediamine,with its small diameter acting as a molecular bridge for facilitating electron transport,has the potential to significantly improve the electrical conductivity of 3D graphene.In contrast,butylene diamine,with its larger diameter,has a reverse effect due to the enlarged spacing of the graphene interlayers,resulting in conductive degradation.More importantly,the moderate conductive level of 3D graphene can be achieved by combining the interlayer spacing expansion effect and theπ-electronic donor ability of aromatic amines.The resulting 3D graphene exhibits highly tunable electronic properties,which can be easily adjusted in a wide range of 2.56-6.61 S·cm^(-1)compared to pristine GO foam(4.20 S·cm^(-1)).This opens up new possibilities for its use as an active material in a piezoresistive sensor,as it offers remarkable monitoring abilities.

Shape Memory Polymer Fibers:Materials,Structures,and Applications

Shape memory polymer(SMP)is a kind of material that can sense and respond to the changes of the external environment,and its behavior is similar to the intelligent refection of life.Electrospinning,as a versatile and feasible technique,has been used to prepare shape memory polymer fbers(SMPFs)and expand their structures.SMPFs show some advanced features and functions in many felds.In this review,we give a comprehensive overview of SMPFs,including materials,fabrication methods,structures,multifunction,and applications.Firstly,the mechanism and characteristics of SMP are introduced.We then discuss the electrospinning method to form various microstructures,like non-woven fbers,core/shell fbers,hollow fbers and oriented fbers.Afterward,the multiple functions of SMPFs are discussed,such as multi-shape memory efect,reversible shape memory efect and remote actuation of composites.We also focus on some typical applications of SMPFs,including biomedical scafolds,drug carriers,self-healing,smart textiles and sensors,as well as energy harvesting devices.At the end,the challenges and future development directions of SMPFs are proposed.