Mitigating Lattice Distortion of High‑Voltage LiCoO_(2)via Core‑Shell Structure Induced by Cationic Heterogeneous Co‑Doping for Lithium‑Ion Batteries

Inactive elemental doping is commonly used to improve the structural stability of high-voltage layered transition-metal oxide cathodes.However,the one-step co-doping strategy usually results in small grain size since the low diffusivity ions such as Ti^(4+)will be concentrated on grain boundaries,which hinders the grain growth.In order to synthesize large single-crystal layered oxide cathodes,considering the different diffusivities of different dopant ions,we propose a simple two-step multi-element co-doping strategy to fabricate core–shell structured LiCoO_(2)(CS-LCO).In the current work,the high-diffusivity Al^(3+)/Mg^(2+)ions occupy the core of single-crystal grain while the low diffusivity Ti^(4+)ions enrich the shell layer.The Ti^(4+)-enriched shell layer(~12 nm)with Co/Ti substitution and stronger Ti–O bond gives rise to less oxygen ligand holes.In-situ XRD demonstrates the constrained contraction of c-axis lattice parameter and mitigated structural distortion.Under a high upper cut-off voltage of 4.6 V,the single-crystal CS-LCO maintains a reversible capacity of 159.8 mAh g^(−1)with a good retention of~89%after 300 cycles,and reaches a high specific capacity of 163.8 mAh g^(−1)at 5C.The proposed strategy can be extended to other pairs of low-(Zr^(4+),Ta^(5+),and W6+,etc.)and high-diffusivity cations(Zn^(2+),Ni^(2+),and Fe^(3+),etc.)for rational design of advanced layered oxide core–shell structured cathodes for lithium-ion batteries.

Generation and modulation of multiple 2D bulk photovoltaic effects in space-time reversal asymmetric 2H-FeCl_(2)

The two-dimensional(2D)bulk photovoltaic effect(BPVE)is a cornerstone for future highly efficient 2D solar cells and optoelectronics.The ferromagnetic semiconductor 2H-FeCl_(2) is shown to realize a new type of BPVE in which spatial inversion(P),time reversal(T),and space−time reversal(PT)symmetries are broken(PT-broken).Using density functional theory and perturbation theory,we show that 2H-FeCl_(2) exhibits giant photocurrents,photo-spin-currents,and photo-orbital-currents under illumination by linearly polarized light.The injection-like and shift-like photocurrents coexist and propagate in different directions.The material also demonstrates substantial photoconductance,photo-spin-conductance,and photo-orbital-conductance,with magnitudes up to 4650(nm·μA/V^(2)),4620[nm·μA/V^(2)/(2e)],and 6450(nm·μA/V^(2)/e),respectively.Furthermore,the injection-currents,shift-spin-currents,and shift-orbital-currents can be readily switched via rotating the magnetizations of 2H-FeCl_(2).These results demonstrate the superior performance and intriguing control of a new type of BPVE in 2H-FeCl_(2).

Numerical Analysis on Nanoparticles-laden Gas Film Thrust Bearing

Nanoparticles can be taken as additives and added into various fluids to improve their lubricating performances. At present, researches in this area are mainly concentrated on the improvement effects of nanoparticles on the lubricating performances of liquid such as oil and water. Nanoparticles will also affect gas lubrication, but few related studies have been reported. Nanoparticles-laden gas film (NLGF) is formed when adding nanoparticles into gas bearing. Then, the lubricating performances of gas bearing including pressure distribution and load-carrying capacity will change. The variations of pressure distribution and load-carrying capacity in nanoparticles-laden gas film thrust bearing are investigated by numerical method. Taking account of the compressibility of gas and the interactions between gas and nanoparticles, a computational fluid dynamics model based on Navier-Stokes equations is applied to simulate the NLGF flow. The effects of inlet nanoparticles volume fraction and orifice radius on film pressure distribution and load-carrying capacity of the NLGF are calculated. The numerical calculation results show that both of the film land pressure and the maximum film pressure both increase when the nanoparticles are added into gas bearing, and the film pressures increase with the rising of the inlet nanoparticles volume fraction. The nanoparticles have an enhancement effect on load-carrying capacity of the studied bearing, and the enhancement effect becomes greater as the film thickness decrease. Therefore, nanoparticles can effectively improve the lubricating performance of gas bearing. The proposed research provides a theoretical basis for the design of new-type nanoparticles-laden gas film bearings.

Bone-inspired(GNEC/HAPAAm)hydrogel with fatigue-resistance for use in underwater robots and highly piezoresistive sensors

A novel bone-inspired fatigue-resistant hydrogel with excellent mechanical and piezoresistive properties was developed,and it exhibited great potential as a load and strain sensor for underwater robotics and daily monitoring.The hydrogel was created by using the high edge density and aspect ratio of graphene nanosheet-embedded carbon(GNEC)nanomaterials to form a three-dimensional conductive network and prevent the expansion of microcracks in the hydrogel system.Multiscale progressive enhancement of the organic hydrogels(micrometer scale)was realized with inorganic graphene nanosheets(nanometer scale).The graphene nanocrystals inside the GNEC film exhibited good electron transport properties,and the increased distances between the graphene nanocrystals inside the GNEC film caused by external forces increased the resistance,so the hydrogel was highly sensitive and suitable for connection to a loop for sensing applications.The hydrogels obtained in this work exhibited excellent mechanical properties,such as tensile properties(strain up to 1685%)and strengths(stresses up to 171 kPa),that make them suitable for use as elastic retraction devices in robotics and provide high sensitivities(150 ms)for daily human monitoring.

From ice superlubricity to quantum friction: Electronic repulsivity and phononic elasticity

Superlubricity means non-sticky and frictionless when two bodies are set contacting motion.Although this occurrence has been extensively investigated since 1859 when Faraday firstly proposed a quasiliquid skin on ice,the mechanism behind the superlubricity remains uncertain.This report features a consistent understanding of the superlubricity pertaining to the slipperiness of ice,self-lubrication of dry solids,and aqueous lubricancy from the perspective of skin bond-electron-phonon adaptive relaxation.The presence of nonbonding electron polarization,atomic or molecular undercoordination,and solute ionic electrification of the hydrogen bond as an addition,ensures the superlubricity.Nonbond vibration creates soft phonons of high magnitude and low frequency with extraordinary adaptivity and recoverability of deformation.Molecular undercoordination shortens the covalent bond with local charge densification,which in turn polarizes the nonbonding electrons making them localized dipoles.The locally pinned dipoles provide force opposing contact,mimicking magnetic levitation and hovercraft.O:H−O bond electrification by aqueous ions has the same effect of molecular undercoordination but it is throughout the entire body of the lubricant.Such a Coulomb repulsivity due to the negatively charged skins and elastic adaptivity due to soft nonbonding phonons of one of the contacting objects not only lowers the effective contacting force but also prevents charge from being transited between the counterparts of the contact.Consistency between theory predictions and observations evidences the validity of the proposal of interface elastic Coulomb repulsion that serves as the rule for the superlubricity of ice,wet and dry frictions,which also reconciles the superhydrophobicity,superlubricity,and supersolidity at contacts.

Multiscale frictional behaviors of sp^(2) nanocrystallited carbon films with different ion irradiation densities

sp^(2) nanocrystallited carbon films with large nanocrystallite sizes,smooth surfaces,and relative high hardness were prepared with different ion irradiation densities regulated with the substrate magnetic coil current in an electron cyclotron resonance plasma sputtering system.Their multiscale frictional behaviors were investigated with macro pin‐on‐disk tribo‐tests and micro nanoscratch tests.The results revealed that,at an ion irradiation density of 16 mA/cm^(2),sp^(2) nanocrystallited carbon film exhibits the lowest friction coefficient and good wear resistant properties at both the macroscale and microscale.The film sliding against a Si_(3)N_(4) ball under a contact pressure of 0.57 GPa exhibited a low friction coefficient of 0.09 and a long wear life at the macroscale.Furthermore,the film sliding against a diamond tip under a contact pressure of 4.9 GPa exhibited a stable low friction coefficient of 0.08 with a shallow scratch depth at the microscale.It is suggested that sp^(2) nanocrystallites affect the frictional behaviors in the cases described differently.At the macroscale,the contact interface via the small real contact area and the sp^(2) nanocrystallited transfer layer dominated the frictional behavior,while the sp^(2) nanocrystallited structure in the film with low shear strength and high plastic resistivity,as well as the smooth surface morphology,decided the steady low nanoscratch properties at the microscale.These findings expand multiscale tribological applications of sp^(2) nanocrystallited carbon films.

Superhydrophobic,photo-sterilize,and reusable mask based on graphene nanosheet-embedded carbon(GNEC)film

The 2019 coronavirus disease(COVID-19)has affected more than 200 countries.Wearing masks can effectively cut off the virus spreading route since the coronavirus is mainly spreading by respiratory droplets.However,the common surgical masks cannot be reused,resulting in the increasing economic and resource consumption around the world.Herein,we report a superhydrophobic,photo-sterilize,and reusable mask based on graphene nanosheet-embedded carbon(GNEC)film,with high-density edges of standing structured graphene nanosheets.The GNEC mask exhibits an excellent hydrophobic ability(water contact angle:157.9°)and an outstanding filtration efficiency with 100%bacterial filtration efficiency(BFE).In addition,the GNEC mask shows the prominent photo-sterilize performance,heating up to 110℃quickly under the solar illumination.These high performances may facilitate the combat against the COVID-19 outbreaks,while the reusable masks help reducing the economic and resource consumption.

In-situ TEM studies on stick–slip friction characters of sp^(2) nanocrystallited carbon films

Carbon films with two different kinds of sp^(2) nanocrystallited structure were investigated to study the stick–slip friction with the in-situ and ex-situ tests.In-situ transmission electron microscope(TEM)observation and nanofriction tests revealed that the origins of stick and slip varied with shear stress and film deformation.At the stick stage,shear stress gradually increased with the contact strengthened until reached the shear strength to break the interfacial adhesion;at the slip stage,the shear stress decreased and accompanied with film deformation.During the sliding process,adhesive deformation resulted in the large stick–slip step while ploughing deformation led to a smoother step.Ex-situ nanofriction tests on a series of sp^(2) nanocrystallited carbon films with different irradiation energies showed the expected sliding behavior with the in-situ results.This study first clarified the mechanism of stick–slip friction with the in-situ TEM observation,which plays the important role for the micro and nano application of sp2 nanocrystallited carbon films.

Robust low friction performance of graphene sheets embedded carbon films coated orthodontic stainless steel archwires

Reducing the friction force between the commercial archwire and bracket during the orthodontic treatment in general dental practice has attracted worldwide interest.An investigation on the friction and wear behaviors of the uncoated and carbon film coated stainless steel archwires running against stainless steel brackets was systematically conducted.The carbon films were prepared at substrate bias voltages from+5 to+50 V using an electron cyclotron resonance plasma sputtering system.With increasing substrate bias voltage,local microstructures of the carbon films evolved from amorphous carbon to graphene nanocrystallites.Both static and stable friction coefficients of the archwire-bracket contacts sliding in dry and wet(artificial saliva)conditions decreased with the deposition of carbon films on the archwires.Low friction coefficient of 0.12 was achieved in artificial saliva environment for the graphene sheets embedded carbon(GSEC)film coated archwire.Deterioration of the friction behavior of the GSEC film coated archwire occurred after immersion of the archwire in artificial saliva solution for different periods before friction test.However,moderate friction coefficient of less than 0.30 sustained after 30 days immersion periods.The low friction mechanism is clarified to be the formation of salivary adsorbed layer and graphene sheets containing tribofilm on the contact interfaces.The robust low friction and low wear performances of the GSEC film coated archwires make them good candidates for clinical orthodontic treatment applications.

Machine learning accelerated DFT research on platinum-modified amorphous alloy surface catalysts

Pt-modified amorphous alloy(Pt@PdNiCuP)catalyst exhibits excellent electro-catalytic activity and high experimental durability for hydrogen evolution reaction(HER).However,the physical origin of the catalytically active remains unclear.In this paper,we constructed a distance contribution descriptor(DCD)for the feature engineering of machine learning(ML)potential,and calculated the Gibbs free energies(ΔGH)of 46,000*H binding sites on the Pt@Pd Ni Cu P surface by ML-accelerated density functional theory(DFT).The relationship betweenΔGHand DCD revealed that in the H-Pt distance region of 2.0-2.5 A where the parabolic tail and disordered scatters coexist,the H-metal bonding configuration is mainly the bridge-or hollow-bonding type.The contribution analysis of DCD indicates that the joint effect of Pt,Pd and Ni atoms determines the catalytical behavior of amorphous alloy,which agrees well with experimental results.By counting atomic percentages in different energy intervals,we obtained the atomic ratio for the best catalytic performance(Pt:Pd:Ni:Cu:P=0.33:0.17:0.155:0.16:0.185).Projected density of states(PDOS)show that H 1s orbital,Pt 5d orbital,and Pd 4d orbital form a bonding state at-2 e V.These results provide new ideas for designing more active amorphous alloy catalysts.

Current-carrying friction in carbon coated ball bearing

In this work,we proposed a method for coating the whole surfaces of bearing balls uniformly by carbon film with a rotatable ball clamp.We studied the carbon/carbon friction with a self-designed currentcarrying ball bearing friction test system.A notable and instant friction force drop of 28%and significant carbon film wear alleviation were found when currents were applied.By using TEM-,SEM-,and EDS-analysis,special carbon stacks with a mixture of large wear particles and oxide were found in the wear areas under current applied condition.We elucidated the current-carrying friction mechanisms as follows:(1)wear particles formation;(2)wear particles charged by tribomicroplasma;(3)formation of surface passivated carbon stacks under electric force;(4)sliding between passivated carbon surfaces.This work may facilitate the development of novel solid-lubricated ball bearings and lay some foundations for current-carrying rolling friction.

Excited state biexcitons in monolayer WSe_(2)driven by vertically grown graphene nanosheets with high-density electron trapping edges

Interface engineering in atomically thin transition metal dichalcogenides(TMDs)is becoming an important and powerful technique to alter their properties,enabling new optoelectronic applications and quantum devices.Interface engineering in a monolayer WSe_(2)sample via introduction of high-density edges of standing structured graphene nanosheets(GNs)is realized.A strong photoluminescence(PL)emission peak from intravalley and intervalley trions at about 750 nm is observed at the room temperature,which indicated the heavily p-type doping of the monolayer WSe_(2)/thin graphene nanosheet-embedded carbon(TGNEC)film heterostructure.We also successfully triggered the emission of biexcitons(excited state biexciton)in a monolayer WSe_(2),via the electron trapping centers of edge quantum wells of a TGNEC film.The PL emission of a monolayer WSe_(2)/GNEC film is quenched by capturing the photoexcited electrons to reduce the electron-hole recombination rate.This study can be an important benchmark for the extensive understanding of light–matter interaction in TMDs,and their dynamics.