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Continuous capacity increase in electrochemical cycling, termed as electrochemical activation, is a frequently observed but rarely systematically studied phenomenon. Such phenomenon is noted in a preliminary study of carbon cathode for dual ion battery, showing gradual discharge capacity growth from 186 mAh g−1 (the 1st) to 320 mAh g−1 (the 300th). Systematical characterizations are carried out to investigate this phenomenon occurred on the carbon cathode, hydrothermally reduced graphene oxide (HrGO). The electrochemical activation comes from surface area increment, originated from multilayer reduced graphene oxide rolls formation and accumulation and structural order increase in cycling. The formation of rolls is plausibly a result of strain release of reduced graphene layers after electrochemical interaction with PF6−. Additionally, charge storage mechanism of HrGO is revealed. At active surface sites of HrGO, PF6− is consistently stored in a pseudocapacitive manner. In contrast, at well-crystallized domains, pseudocapacitive PF6− uptake occurs at low voltage region while PF6− intercalation dominates at higher potentials. Supportive lithium storage also contributes to total capacity. Comprehensively, this work offers valuable insights of electrochemical activation and carbon cathodes’ electrochemical behaviors and will facilitate the construction of high-capacity carbon cathodes.

Inspired by the unique layered structure and the superior resistance to thermal impulse exhibited by the shells of snails inhabiting the deep-sea hydrothermal environment, here we attempt to reveal the underlying structure–property relationship by investigating the temperature response of a bilayer subjected to a thermal impulse on one side. A semi-analytical solution to the transient temperature field is obtained, allowing us to examine the effects of the layout sequence and volume fractions of the constitutive layers on the thermal impulse resistance of the shell. For two layers made of given materials, the proper layout sequence and optimal thickness ratio are proposed, giving rise to a highest resistance to thermal impulse. The results of our work not only account for the physiological functionality of the unique laminated design of the snail shells from deep-sea hydrothermal environments but also provide operational guidelines for the development of thermal barriers in engineering.

The commercialization of TiO2 materials for lithium-ion battery (LIB) anodes has been seriously limited due to unsatisfactory capacities and high voltage plateaus vs. Li/Li+ (∼1.75 V). In this work, we synthesized unique dual-phase TiO2 nanowires composed of anatase and TiO2–B phases with tunable phase ratios and studied their electrochemical performance in the extended potential range of 0.01–3.0 V. It was found that the dual-phase nanowire with a phase ratio of ∼1.0, named TiO2-350, possesses the best rate and cyclic performance. More importantly, lowering the discharge cut-off voltage from 1.0 V to 0.01 V significantly increases the capacities, and moreover results in a decreased average discharge voltage of ∼0.58 V vs. Li/Li+. At the rates of 0.5C and 1C, TiO2-350 delivers the ultrahigh capacities of 518.0 and 444.5 mA h g−1 and remarkable long-term cyclic stability, which are strikingly higher than those reported in the literature and the theoretical capacity of TiO2. Cyclic voltammetry results indicated that the ultrahigh capacity of the TiO2 nanowire is the main reason that the capacitive contribution is below 1.0 V. Structural analyses indicated the solid solution reaction of TiO2-350 nanowires with Li+ and the excellent structure stability during cycling, which contributes to the excellent cyclic performance of nanowires. Furthermore, the TiO2-350 anode exhibits superb low-temperature performance between 0.01 V and 3.0 V at 273 K and 248 K. This work demonstrates a TiO2-based anode with ultrahigh capacity and low working potential, and will promote the practical application of TiO2-based materials for all-climate LIB anodes.

Surface topography has been demonstrated as an effective nonchemical strategy for controlling the fouling resistance of a surface, but its impact on optical transparency remains a barrier to the application of this strategy in optical materials. To reconcile the conflicting effects of surface topography on optical transparency and fouling resistance, here we study the optical properties and antifouling performance of nanowrinkled surfaces inspired by the corneal surface of zebrafish (

Inspired by Namib desert beetle’s bumpy structures, condensing droplet shedding from various super-hydrophobic bumps with a hydrophilic patch present on their top was numerically studied using the lattice Boltzmann method (LBM). The droplet grows on the top patch due to condensation and then sheds from the bump due to gravity. A parametric study has been conducted. It was revealed that the bump shape, diameter, height, inclination and wettability all affect the shedding volume (volume at which the droplet sheds from the bump) of the droplet. The shedding volume decreases with the bump height till a threshold height, defined as the critical bump height, beyond which the shedding volume does not change any more. With the same patch area, the shedding volume is smaller on the bump with a hemispherical top compared to the bump with a circular cylindrical top. The shedding volume increases with bump diameter, but decreases with the patch contact angle and surface inclination angle. The same trends were also found for the critical bump height. Furthermore, compared to milli-scale bumps, droplet removal followed by shedding on micro-scale bumps was found to be inefficient. Based on the simulation results, a scaling law was obtained by data fitting to estimate the critical bump height for bumps with a cylindrical top, which can be used to guide the design of desert-beetle-inspired bumps for efficient water collection from fog.

Bombardier beetles, as their name implies, defend themselves against the potential predators by spraying boiling-hot and corrosive chemicals which are products of an explosive biochemical reaction taking place in the paired organs called reaction chambers (RCs). Why these beetles can withstand the explosive reaction that takes place in their bodies? Knowledge of thermal properties of the RCs will help to shed light on this puzzle. However, the submillimeter dimension and irregular shape of the RCs discourage the traditional methods for thermal characterization. To overcome this challenge, in this paper a method is developed particularly for measuring the thermal conductivity of a material with dimension as small as submillimeter. The measurement results by this method are demonstrated reliable especially for polymeric or organic materials including the RCs of bombardier beetles. The results in this paper not only help to understand the superior thermal insulation of the RC wall but also offer a facile approach to measuring the thermal conductivity of materials in submillimeter scale.

The sodium-ion battery is a promising battery technology owing to its low price and high abundance of sodium. However, the sluggish kinetics of sodium ion makes it hard to achieve high-rate performance, therefore impairing the power density. In this work, a fiber-in-tube Co9 S8 -carbon(C)/Co9 S8 is designed with fast sodiation kinetics. The experimental and simulation analysis show that the dominating capacitance mechanism for the high Na-ion storage performance is due to abundant grain boundaries, three exposed layer interfaces, and carbon wiring in the design. As a result, the fiber-in-tube hybrid anode shows a high specific capacity of 616 mAh g-1 after 150 cycles at 0.5 A g-1 . At 1 A g-1 , a capacity of ca. 451 mAh g-1 can be achieved after 500 cycles. More importantly, a high energy density of 779 Wh kg-1 and power density of 7793 W kg-1 can be obtained simultaneously.

Adhesion between cells and blood vessel wall plays an essential role in many biological processes such as immune response and cancer metastasis. Unlike the other adhesion processes taking place in relatively quiescent milieu, cells in blood vessel tend to be subjected to hydrodynamic impact from the blood flow. Understanding the kinetic response of cells to the blood flow helps in shedding light on the related biological processes. In this paper, a theoretical model is established to depict the kinetic behavior of a cell in shear flow by equating cell adhesion, which is mediated by ligand-receptor reactions, as speed-dependent inter-surface interaction in combination with the kinetics of a rolling object. Our results indicate that the steady state of the cell depends on the shear rate of the flow. In a flow with relatively low shear rate, the cell would finally rest on the vessel wall. If the shear rate is sufficiently high, the cell would be rolling at a steady speed on the wall. In a flow with intermediate shear rate, the cell would either rest or roll at a steady speed on the vessel, depending on its initial status. These predictions are verified by Monte Carlo simulations and are also consistent with the ‘bistability’ phenomenon of the rolling cell as reported in literature. Our findings not only shed light on the mechanics of adhesive rolling of cells on vessel wall but also have potential applications in the design of biomedical systems such as microscopic carriers for drug delivery in blood circulation.

In this paper, the thermal conductivities (κ) of polycrystalline graphene (PG) with varying average grain size are investigated using reverse nonequilibrium molecular dynamics method. Due to the pr...

Lithiation process of Si has been widely studied, while most of the previous works neglected the effects of mechanical constraint from the accessory materials such as binder and conductive additive on Si. In this paper, we carry out molecular dynamics simulations to investigate the effects of mechanical constraint on the performances, such as capacity and lithiation rate, of Si nanosheets as the anode material for lithium-ion batteries. Our results show that strong mechanical constraint would largely affect the capacity and lithiation rate of Si nanosheets. Remedial strategies for improving the capacity and lithiation rate of the constrained Si nanosheets are proposed, giving rise to guidelines for the design of Si-based anode material for high-performance lithium-ion batteries.

Using the lattice Boltzmann method, a numerical study was conducted to investigate the oblique impact of two successive droplets on a flat surface. The focus was placed on the effects of surface inclination, lateral/longitudinal offset, the impact dynamics of the two droplets and the subsequent dynamics of the combined droplet. The evolution of the topology, contact lines and spread factor of the two droplets under various conditions was compared and analyzed. It was found that, compared to single droplet impact, the impact of successive droplets shows quite different dynamics due to the involved coalescence process. The surface inclination causes asymmetric spreading of the droplets. The increase in surface inclination leads to faster downward spreading and reduced lateral spreading. The non-zero offset between the two droplets further enhances this asymmetry. Furthermore, the intermixing between the two droplets during the oblique impact was also examined. It was observed that the surface inclination changes the mass distribution of the combined droplet.

Mechanical exfoliation is an approach widely applied to prepare high-quality two-dimensional (2D) materials for investigating their intrinsic physical properties. During mechanical exfoliation, in-plane cleavage results in new edges whose orientations play an important role in determining the properties of the as-exfoliated 2D materials especially those with high anisotropy. Here, we systematically investigate the factors affecting the edge orientation of 2D materials obtained by mechanical exfoliation. Our theoretical study manifests that the fractured direction during mechanical exfoliation is determined synergistically by the tearing direction and material anisotropy of fracture energy. For a specific 2D material, our theory enables us to predict the possible edge orientations of the exfoliated flakes as well as their occurring probabilities. The theoretical prediction is experimentally verified by examining the inter-edge angles of the exfoliated flakes of four typical 2D materials including graphene, MoS2, PtS2, and black phosphorus. This work not only sheds light on the mechanics of exfoliation of the 2D materials but also provides a new approach to deriving information of edge orientations of mechanically exfoliated 2D materials by data mining of their macroscopic geometric features.

In this study, the mechanical properties of grain boundaries (GBs) in planar heterostructures of graphene and hexagonal boron nitride (h-BN) were studied using the molecular dynamics method in combination with the density functional theory and classical disclination theory. The hybrid interface between graphene and h-BN grains was optimally matched by a non-bisector GB composed of pentagon-heptagon defects arranged in a periodic manner. GB was found to be a vulnerable spot to initiate failure under uniaxial tension; moreover, the tensile strength was found to anomalously increase with an increase in the mismatch angle between graphene and h-BN grains, i.e., the density of pentagon-heptagon defects along the GBs. The disclination theory was successfully adopted to predict the stress field caused by lattice mismatch at the GB. Comparison between stress contours of GBs with different mismatch angles demonstrates that the arrangement of 5-7 disclinations along the GB is crucial to the strength, and the stress concentration at the GB decreases with an increase in disclination density; this results in an anomalous increase of strength with an increase in the mismatch angle of grains. Moreover, the thermal transfer efficiency of the hybrid GB was revealed to be dependent not only on the mismatch angle of grains but also on the direction of the thermal flux. Thermal transfer efficiency from graphene to h-BN is higher than that from h-BN to graphene. Detailed analyses for the phonon density of states (PDOS) of GB atoms were carried out for the mismatch angle-dependence of interfacial conductance. Our results provide useful insights for the application of two-dimensional polycrystalline heterostructures in next-generation electronic nanodevices.

Two-dimensional (2D) materials as exemplified by graphene have received a bunch of attention for their outstanding properties and enormous application potential. Recently, a macroscopic graphene-based material was fabricated simply by stacking the few-layer graphene flakes. The resulting film, called SGA, exhibits unusual mechanical behavior, which implies the existence of tension-compression asymmetry in its mechanical property. However, direct experimental verification of such unique mechanical property of the SGA remains deficient because of the difficulty in fixturing and applying load on the samples. In this work, we tackle these problems by transferring the SGA film onto a polyethylene (PE) substrate which can elongate and contract in response to the variation of the ambient temperature. Tensile and compressive loads thus can be controllably applied to the SGA samples through the SGA/PE interface by tuning the temperature variation. The stress-strain curves of the SGA, including tensile and compressive, are deduced based on the Stoney equation for thin film-substrate systems, showing the tension-compression asymmetry as expected. Theoretical modeling is carried out and reveals the structural basis of such unique mechanical behavior. This work not only provides a facile yet effective approach to measuring the stress-strain behavior of less-cohesive materials like SGA but also is of great value to the design and applications of SGA and other stacked assemblies of 2D materials in flexible sensors and actuators.

Helical structures are ubiquitous in nature at length scales of a wide range. In this paper, we studied a helical architecture called microscopic screw dislocation (μ-SD), which is prevalently present in biological laminated composites such as shells of mollusks P. placenta and nacre of abalone. Mechanical characterization indicated that μ-SDs can greatly enhance resistance to scratching. To shed light on the underlying reinforcing mechanisms, we systematically investigated the mechanical behaviors of μ-SD using theoretical modeling in combination with finite element simulation. Our analysis on an individual μ-SD showed that the failure of a μ-SD under tension involves the delamination of the prolonged spiral interface, giving rise to much higher toughness compared to those of the planar counterpart. The corporation of multiple μ-SDs was further investigated by analyzing the effect of μ-SD density on the mechanical reinforcement. It was found that higher areal density of μ-SD would lead to more improvement in toughness. However, the operation of such reinforcing mechanism of μ-SD requires proclivity of cracking along the spiral interface, which is not spontaneous but conditional. Fracture mechanics-based modeling indicated that the proclivity of crack propagation along the spiral interface can be ensured if the fracture toughness of the interface is less than 60% of that of the lamina material. These findings not only uncover the reinforcing mechanisms of μ-SDs in biological materials but imply a great promise of applying μ-SDs in reinforcing synthetic laminated composites.

Dual ion battery (DIB) with graphite cathode is a renewable energy storage system but suffers from low capacity. Addition of lithium ion battery (LIB) cathode to graphite cathode not only facilitates capacity increment but also serves as proof-of-concept for LIB-DIB hybridization. In this study, a hybrid cathode, incorporating a physical mixture of high working potential graphite and nontoxic lithium iron phosphate (LiFePO4, LFP), is proposed and examined. The graphite interacts with anion and works as electrically conductive matrix. While additive LFP is active to cation, serving as capacity facilitator. Characterization results reveal that, during charging, the hybrid cathode starts with LFP delithiation in lower voltage region and finishes with anion intercalation in graphite at higher voltage region. During discharging, processes are reversed with stepwise anion deintercalation and cation insertion, without interfering individual constituent's proper functioning. The transfer of two polarity distinct ions inside the hybrid cathode maintains high independence, without any added kinetical difficulties. Such hybrid cathode is demonstrated to work stably with varied LFP-graphite proportions. The addition of 40 wt% LFP to graphite cathode shows doubled capacity and excellent long-term cyclability. And the hybrid cathode is also cyclable in a full cell configuration.

Biofouling refers to the adverse attachment and colonization of fouling organisms, including macromolecules, bacteria, and sessile invertebrates, on the surfaces of materials submerged in aquatic environments. Almost all structures working in watery surroundings, from marine infrastructures to healthcare facilities, are affected by this sticky problem, resulting in massive direct and indirect economic loss and enormous cost every year in protective maintenance and remedial cleaning. Traditional approaches to preventing marine biofouling primarily rely on the application of biocide-contained paints, which certainly impose adverse effects on the ocean environment and marine ecology. Biomimicry offers an efficient shortcut to developing environmentally friendly antifouling techniques and has yielded encouraging and promising results. The antifouling strategies learned from nature can be broadly classified into two categories according to the nature of the cues applied for biofouling control. One is the chemical antifouling techniques, which are dedicated to extracting the effective antifoulant compounds from marine organisms and synthesizing chemicals mimicking natural antifoulants. In contrast, the physical biomimetic (BM) antifouling practices focus on the emulation and optimization of the physical cues such as micro and nanoscale surface topographies learned from naturally occurring surfaces for better antifouling efficacy. In this review, a synopsis of the techniques for manufacturing the BM and bioinspired (BI) antifouling surface topographies is introduced, followed by the bioassay to assess the antifouling performance of the structured surfaces. Then, the BM and BI surface topographies that were reported to possess enhanced antifouling competence are introduced, followed by a summary of theoretical modeling. The whole paper is concluded by summarizing the studies' deficiencies so far and outlooking the research directions in the future.

Summary Hollow graphitic carbon nanofibers (HGCNFs) have great promise for many important applications, such as catalysis, sensors, energy conversion, gas storage, and electronic devices. Here, we report a catalytic etching-wetting-dewetting mechanism in synthesizing HGCNFs with both hollow spherical-like and tunnel-like pores. With in situ transmission electron microscope imaging, we show that the spherical pores are formed by the evaporation of encapsulated Ni on the surface of amorphous carbon nanofiber and that hollow tunnels are developed through continuous etching of the amorphous carbon under catalysis of Ni nanoparticles. Theoretical calculations and simulations reveal that continuous tunnel etching is driven by the wetting-to-dewetting transition of the Ni-tunnel wall interaction during the catalytic graphitization of the amorphous carbon wall. In a typical application, we demonstrate that the synthesized HGCNFs, with a capacity about three times higher than that of their non-hollow counterparts, are excellent potential candidates for CO 2 capture.

In this paper, the in-plane torsional properties of two dimensional nanomaterials are revealed to be tunable by surface functionalization using molecular dynamics simulations. The torsional strengths of both graphene and graphyne under circular shearing are found to first decrease and then increase anomalously with the increase of the hydrogenation ratio. The minimum strength of such U-shaped strength evolution appears at different hydrogenation ratios H for graphene (H = 50%) and graphyne (H = 70%), demonstrating a correlation between hydrogenation and the unit lattices of 2D nanomaterials. By studying the torsional characteristics of a graphene annulus with varying outer-to-inner boundary radius ratios, the anomalous increase of torsional strength at a high hydrogenation ratio is revealed to be the result of wrinkling deformation as well as chemical bond hybridization. Further analyses of the local stress distribution are carried out for understanding the mechanism of surface hydrogenation tuned in-plane torsional strength of graphene and graphyne. Torsional strength of the graphene annulus with an elliptical outer boundary also shows a U-shaped evolution with hydrogenation ratio, while the shape effect of the graphene annulus can smooth the change of the torsional characteristics with hydrogenation. Our results provide novel insights into the development of 2D nanomaterial-based annular devices.

Ocean uptake of anthropogenic CO

The attachment efficiency of biofouling organisms on solid surfaces depends on a variety of factors, including fouler species, nutrition abundance, flow rate, surface morphology and the stiffness of the solid to which attachment is to be made. So far, extensive research has been carried out to investigate the effects of these factors on the attachment of various fouling species. However, the results obtained are species-dependent and scattered. There is no universal rule that can be applied to predict the attachment efficiency of different species. To solve this problem, the authors carried out meta-analysis of the effects of ten selected factors on attachment efficiency, resulting in a universal correlation between the attachment density and the selected factors, which was validated by attachment tests of tubeworms on PDMS surfaces. The results provide a practical approach to predicting the attachment efficiency of fouling organisms and should be of great value in the design of anti-biofouling materials.

Silicon (Si) has long been regarded as one of the most promising anode materials for the next-generation lithium-ion batteries (LIBs) due to its exceptional specific capacity and apt working voltage. However, the drastic volume change of Si during lithiation/delithiation processes tends to cause various mechanical failure problems including the delamination between current collector and electrode materials, resulting in poor stability and degradation of LIBs. Inspired by the functional graded design in natural biomaterials, we propose to solve the interfacial delamination problem by reallocating the Si in the electrode in a graded manner. The prepared graded electrodes especially those after gradient optimization are found quite successful in alleviating the interfacial delamination, resulting in higher capacity and capacity retention, higher coulombic efficiency, higher effective mass loading in comparison to the traditional ones. Specifically, the optimal graded electrode shows a charge capacity of 1299 mAh g−1 after 50 cycles, which is much higher than that of the homogeneous electrode (66 mAh g−1). Such a graded electrode can be easily implemented by existing manufacturing techniques and synergize with other strategies for solving the large-volume-change problem of Si. Our work provides a guideline for the design and manufacture of the graded Si-based electrodes for LIBs. Keywords: Delamination, Functionally graded materials, Energy materials, Heterogeneity, Lithium-ion batteries

In this paper, silicon nanosheets (Si-NSs) are chemically synthesized by using graphene oxide nanosheets as the template. The obtained Si-NSs, which are aggregations of silicon nanocrystals with a size of ∼10 nm, are applied directly as the anode material for lithium ion batteries, delivering a reversible capacity of 800 mA h g−1 after 900 cycles at a rate as high as 8400 mA g−1. Ex situ measurements and in situ observations show the positive effect of the mesoporous structure on the structural stability of Si-NSs. The evolution and survivability of the porous structures during lithiation and delithiation processes are investigated by molecular dynamics simulations, demonstrating that the porous structure can enhance the amount of “active” Li atoms during the stable stage of cycling and therefore promote mass capacity. The longer the survival of the porous structure, the longer the high mass capacity can be retained.

We report damage-healable supramolecular silicone coatings with high adhesion to solid and low adhesion to oils., Polymer coatings with a combined competence of strong bonding to diverse substrates, broad liquid repellency, and readily damage healing are in substantial demand in a range of applications. In this work, we develop damage-healable, oil-repellent supramolecular silicone (DOSS) coatings to harvest abovementioned properties by molecular engineering siloxane oligomers that can self-assemble onto coated substrates via multivalent hydrogen bonding. In addition to the readily damage-healing properties provided by reversible association/dissociation of hydrogen bonding motifs, the unique molecular configuration of the siloxane oligomers on coated substrates enables both robust repellency to organic liquids and strong bonding to various substrates including metals, plastics, and even Teflon. We envision that not only DOSS coatings can be applied in a range of energy, environmental, and biomedical applications that require long-term services in harsh environmental conditions but also the design strategy of the oligomers can be adopted in the development of supramolecular materials with desirable multifunctionality.

Ocean uptake of anthropogenic CO2 causes ocean acidification (OA), which not only decreases the calcification rate, but also impairs the formation of calcareous shells or tubes in marine invertebrates such as the dominant biofouling tubeworm species, Hydroides elegans. This study examined the ability of tubeworms to resume normal tube calcification when returned to ambient pH 8.1 from a projected near-future OA level of pH 7.8. Tubeworms produced structurally impaired and mechanically weaker calcareous tubes at pH 7.8 compared to at pH 8.1, but were able to recover when the pH was restored to ambient levels. This suggests that tubeworms can physiologically recover from the impacts of OA on tube calcification, composition, density, hardness and stiffness when returned to optimal conditions. These results help understanding of the progression of biofouling communities dominated by tubeworms in future oceans with low pH induced by OA.

Hollow carbon nanospheres embedded with ultrafine Fe 3 O 4 nanoparticles (Fe 3 O 4 @HCNS) were synthesized by using carboxyl functionalized polystyrene latexes as template and poly dopamine as carbon precursor. The ultrafine Fe 3 O 4 nanoparticles (NPs) had a small size of 3 ∼ 5 nm and the HCNS had a thin shell thickness of 15 nm in the Fe 3 O 4 @HCNS. As a promising anode material for lithium-ion batteries, the Fe 3 O 4 @HCNS exhibited high reversible capacity, excellent cycling stability (1380 mA h g −1 after 200 cycles at 1 A g −1 ) and high-rate capability (475 mA h g −1 at 5 A g −1 , 290 mA h g −1 at 10 A g −1 ). The outstanding performance was attributed to the unique structure of the Fe 3 O 4 @HCNS, which greatly shorten the path of Li ions intercalation during charging and discharging.

Yolk-shell carbon-coated silicon nanoparticles (Si@void@C NPs) have been demonstrated to have a great promise in solving the problem of significant volume change of silicon-based anode materials during lithiation and delithiation cycling. However, our in situ lithiation experiments show that Si@void@C NPs may still subject to fracture upon lithiation, depending on their characteristic structural features such as the size of Si yolk, the thickness of carbon shell, and the interspace between the yolk and shell. Given the size of Si yolk, to ensure structural integrity of Si@void@C NPs during lithiation and delithiation, thicker carbon shell and larger yolk-shell interspace are preferred. On the other hand, from the perspective of attaining higher effective capacity, thinner carbon shell and smaller yolk-shell interspace are favored. To find the optimal structural design which yields the maximum capacity and meanwhile ensure the integrity of Si@void@C NPs during lithiation, mechanics-based theoretical modeling is carried out. A diagram for structural optimizations is obtained, by which the optimized Si@void@C NPs are synthesized and found to have improved capacity and capacity retention compared to the unoptimized ones. The results of this paper provide a guideline for the design of Si@void@C NPs as anode materials for high-capacity lithium ion battery.

Previous studies on silicon (Si) indicate that lithiation-induced fracture of crystalline Si nanoparticles can be greatly inhibited if their diameter is reduced to below a critical scale of around 150 nm. In this paper, in situ lithiation of individual carbon-coated Si nanoparticles (Si@C NPs) is conducted which shows that Si@C NPs will fracture during lithiation even though their diameter is much smaller than 150 nm, implying a deleterious effect of the carbon coating on the integrity of the Si@C NPs during lithiation. To shed light on this effect, finite element analysis is carried out which reveals that the carbon coating, if fractured during lithiation, will induce cracks terminating at the C/Si interface. Such cracks, upon further lithiation, can immediately propagate into the Si core due to the elevated driving force caused by material inhomogeneity between the coating and core. To prevent the fracture of the carbon coating so as to protect the Si core, a design guideline is proposed by controlling the ratio between the diameter of Si core and the thickness of carbon coating. The results in this paper should be of practical value to the design and application of Si-based core-shell structured anode materials for lithium ion batteries.

Tin holds promise as an anode material for lithium-ion batteries (LIBs) because of its high theoretical capacity, but its cycle life is limited by structural degradation. Herein, a novel approach is exploited to insert Sn nanoparticles into the pores of highly stable titanium dioxide–carbon (TiO2−x–C) nanofiber substrates that can effectively localize the postformed smaller Sn nanoparticles, thereby address the problem of structural degradation, and thus achieve improved anode performance. During first lithiation, a Li4.4Sn alloy is inserted into the pores surrounding the initial Sn nanoparticles in TiO2−x–C nanofibers by its large volume expansion. Thereafter, the original Sn nanoparticle with a diameter of about 150 nm cannot be recovered by the delithiation because of the surface absorption between inserted Sn nanoparticles and the TiO2−x–C substrate, resulting in many smaller Sn nanoparticles remaining in the pores. Batteries containing these porous TiO2−x–C–Sn nanofibers exhibit a high capacity of 957 mAh g−1 after 200 cycles at 0.1 A g−1 and can cycle over 10 000 times at 3 A g−1 while retaining 82.3% of their capacity, which represents the longest cycling life of Sn-based anodes for LIBs so far. This interesting method can provide new avenues for other high-capacity anode material systems that suffer from significant volume expansion.

Fabrication of graphitized carbon materials (e.g. carbon nanotubes and graphene) normally entails the assistance of transition metal catalyst. In this paper, a nitrogen doped carbon foam (NCF) with both graphitized and porous carbon structure was fabricated by direct pyrolysis of melamine foam (MF) without using any transition metal catalyst. The graphitized carbon structure was possibly attributed to the triazine moieties in the MF precursor. The introduction of oxygen groups in the oxidation step resulted in the formation of large amount of micro- and mesopores and therefore high specific surface area. The NCF exhibited a three-dimensional cellular network consisting of carbon microfiber with abundant micro- and mesopores and giving rise to a specific surface area over 980 m 2 g −1 . Due to such graphitized porous structure, the NCF was demonstrated to have superior resilience, excellent electrocatalytic activity and good durability for oxygen reduction.

Continuous efforts to discover the novel carbon nanotube ultrahigh frequency resonators or sensors have being made since past two decades. The bending rigidity plays a key role in determining the frequency magnitude. Although it is previously justified that the bending rigidity has the almost linear dependence on the cubic of tube diameter, its dependence on another characteristic scale, i.e., the tube length is missing. Considering that the direct experimental observation faces significant challenge due to the low measurement precision by the inevitable thermodynamic fluctuation, we theoretically explored such size effect by means of three approaches respectively at different scale levels including quantum mechanics lattice dynamics calculations, molecular mechanics simulations and nonlocal continuum modeling for single-walled carbon nanotubes. The results from the different approaches give the consistent conclusion that there exists a strong correlation between the tube length and the bending rigidity, i.e., the rigidity increases with the tube length and converges to the value predicted by continuum theories. Moreover, we also find the nonlocal parameter reflecting the microscopic lattice effect in present continuum modeling almost independent of the chirality and linearly increases with the tube diameter with a scale factor 1.5. The comprehensive study may not only guide the design of ultrahigh frequency carbon nanotube devices but also provide insight to the bending nanomechanics of other devices made from nanotubes, nanobeams and nanowires.

Mechanical characterization of two-dimensional (2D) materials has always been a challenging task due to their extremely small thickness. The current prevailing methods to measure the strength of 2D materials normally involve sophisticated testing facilities and complicated procedures of sample preparation, which are usually costly and time-consuming. In this paper, we propose a cost-effective and rapid approach to characterizing the strength of 2D materials by processing optical microscope images of the mechanically exfoliated 2D materials. Specifically, a machine learning-based model is developed to automate the identification of 2D material flakes of different layers from the optical microscope images, followed by the determination of their lateral size. The statistical distribution of the flakes’ size is obtained and used to estimate the strength of the associated 2D material based on a distribution-property relationship we developed before. A case study with graphene indicates that the present machine learning-based method, as compared to the previous manual one, enhances the efficiency of characterization by more than one order of magnitude with no sacrifice of the accuracy.