Electrochemical Kinetic Modulators in Lithium–Sulfur Batteries:From Defect-Rich Catalysts to Single Atomic Catalysts

Lithium–sulfur batteries exhibit unparalleled merits in theoretical energy density(2600 W h kg^(-1))among next-generation storage systems.However,the sluggish electrochemical kinetics of sulfur reduction reactions,sulfide oxidation reactions in the sulfur cathode,and the lithium dendrite growth resulted from uncontrollable lithium behaviors in lithium anode have inhibited high-rate conversions and uniform deposition to achieve high performances.Thanks to the“adsorption-catalysis”synergetic effects,the reaction kinetics of sulfur reduction reactions/sulfide oxidation reactions composed of the delithiation of Li_(2)S and the interconversions of sulfur species are propelled by lowering the delithiation/diffusion energy barriers,inhibiting polysulfide shuttling.Meanwhile,the anodic plating kinetic behaviors modulated by the catalysts tend to uniformize without dendrite growth.In this review,the various active catalysts in modulating lithium behaviors are summarized,especially for the defect-rich catalysts and single atomic catalysts.The working mechanisms of these highly active catalysts revealed from theoretical simulation to in situ/operando characterizations are also highlighted.Furthermore,the opportunities of future higher performance enhancement to realize practical applications of lithium–sulfur batteries are prospected,shedding light on the future practical development.

Characterizing the Exchange Interaction of Sm-Co/Co(and Fe_(65)Co_(35))Magnetic Films

Exchange interaction plays an important role on magnetic properties of nanocomposite magnets consisting of hard- and soft-magnetic phases. Here the exchange interaction in the Sm-Co/Co （and Fe65Co35） magnetic films was characterized by measuring static （mr（H）） and demagnetized （md（H）） remanence curves. According to conventional method： δm（H）=md（H） - [1 - 2mr（H）], the exchange interaction was evaluated. The switching fields H′p and Hp, at which static （mr（H）） and demagnetized （md（H）） remanence show the fastest change, were identified. The relative ratio η=Hp-H′p/Hp of switching fields H′p and Hp has a linear relationship with the maximum value δmmax of δm（H） curves, proposing an alternative way to characterize the exchange interaction.

In-plane current-induced magnetization reversal of Pd/CoZr/MgO magnetic multilayers

High critical current density(>10^(6)A/cm^(2))is one of major obstacles to realize practical applications of the currentdriven magnetization reversal devices.In this work,we successfully prepared Pd/CoZr(3.5 nm)/MgO thin films with large perpendicular magnetic anisotropy and demonstrated a way of reducing the critical current density with a low out-of-plane magnetic field in the Pd/CoZr/MgO stack.Under the assistance of an out-of-plane magnetic field,the magnetization can be fully reversed with a current density of about 10^(4)A/cm^(2).The magnetization reversal is attributed to the combined effect of the out-of-plane magnetic field and the current-induced spin-orbital torque.It is found that the current-driven magnetization reversal is highly relevant to the temperature owing to the varied spin-orbital torque,and the current-driven magnetization reversal will be more efficient in low-temperature range,while the magnetic field is helpful for the magnetization reversal in high-temperature range.

Simultaneously realizing good volumetric entropy change and mechanical strength of La_(0.8)Ce_(0.2)Fe_(11.51)Mn_(0.19)Si_(1.3)H_(y) plates

It is hard to get a high-strength La(Fe,Si)_(13)-based hydrides owing to the brittle feature of hydrides.In this work,we fabricated the La_(0.8)Ce_(0.2)Fe_(11.51)Mn_(0.19)Si_(1.3)plates through hot pressing at 1323 K for various time.Subsequently,the saturated hydrogenization is achieved at 593 K in H_2 atmosphere of 0.13 MPa for 210 min.The microstructure and magnetocaloric properties were investigated by an X-ray diffractometer,a scanning electron microscope and the Versa-Lab.Under magnetic fields of 0-2 T,the maximal volumetric entropy change is 91.4 mJ/(cm^(3)·K)at 297 K for the hydride plates.The hydride plate simultaneously has excellent mechanical properties with the maximum bending strength of 213 MPa,which suggest that the hot pressing followed by hydrogenation could be an effective route of fabricating La(Fe,Si)_(13)-based hydrides for the potential application in the magnetic refrigerator.

Enhancement of permittivity and energy storage efficiency of poly (vinylidene fluoride-chlorotrifluoroethylene) by uniaxial stretching

Dielectric polymer film capacitors with a high-power density as well as efficient charge and discharge rates have great potential for application to fulfill the miniaturized and lightweight requirements of the electronic and stationary power systems.It was reported that the elastic recovery rate and energy storage density of poly(vinylidene fluoride-chlorotrifluoroethylene)[P(VDF-CTFE)]polymer film can be enhanced through thermostatic uniaxial stretching.But it is unknown about the relationship between the stretching rate and above properties.In this study,we investigated the effect of different stretching rates on the conformation,elastic recovery,dielectric constant,and energy storage density of stretched P(VDF-CTFE)polymer films.It was found that the stretching rate significantly affected the formation of polarβ-crystal phase,causing different dielectric properties.The degrees of elastic recovery of P(VDF-CTFE)film vary with stretching rates.Among them,the elastic recovery rate of the P(VDF-CTFE)94/6 film is 46.5%at a stretching rate of 15 mm/min,the dielectric constant is 12.25 at 100 Hz,and the energy density reaches 3.95 J/cm^(3) with the energy loss of 39%at 200 MV/m field.

A controllable soft-templating approach to synthesize mesoporous carbon microspheres derived from d-xylose via hydrothermal method

Highly dispersed carbon microspheres(CMSs)derived from D-xylose were successfully synthesized under hydrothermal conditions and followed by further carbonization,in which F127 was used as a soft template.As-synthesized products were characterized by scanning electron microscopy(SEM),transmission electron microscopy(TEM),flourier transform infrared spectroscopy(FT-IR),thermal gravimetric(TG)and X-ray diffraction(XRD).The results showed that the morphology and structure of the CMSs prominently depended on the stirring speed during hydrothermal reaction.The resultant CMSs principally had non-porous structure without stirring and had a very smooth surface.When the stirring speed increased to 200 rpm,the synthesized mesoporous carbon microspheres at 220?C for 24 h(CMSs-5)had a uniform size distribution of 1–1.4μm and a specific surface area of 452 m^2/g.Nevertheless,with further increasing to 400 rpm,as-fabricated carbon products were mostly amorphous with a low degree of sphericity.Results demonstrated that the diameter of the products decreased with the increase of stirring speed.Furthermore,the sphericity product yield of CMSs reduced with the increase of stirring speed.XRD result showed that all the obtained samples contained partial graphite phase.In addition,a formation mechanism was proposed that involved polymerization product as the precursors for microsphere formation.The controllable and green strategy may provide a great convenience to study properties and applications of carbon microspheres.

Thermally conductive MWCNTs/Fe_(3)O_(4)/Ti_(3)C_(2)T_(x) MXene multi-layer films for broadband electromagnetic interference shielding

The Ti_(3)C_(2)T_(x)MXene is thought to be a promising candidate for next-generation electromagnetic interference(EMI) shielding materials.However,its broadband shielding capability and thermal conduction performance are insufficient to meet the growing demands.Herein,we reported a layer-by-layer composite film composed of Ti_(3)C_(2)T_(x)MXene,multi-walled carbon nanotubes(MWCNTs),and Fe_(3)O_(4)nanoparticles.Benefitting from the architecture and the synergistic effect of components,the obtained composite film exhibited high comprehensive performance.Specifically,the introduction of Fe_(3)O_(4)magnetic nanoparticles effectively reduced the impedance mismatch between the composite film and air and enhanced the magnetic loss of the composite film.The layered structure prolonged the transmission path of electromagnetic waves inside the composite film and constructed a rich conductive network,causing interfacial polarization and ohmic loss.The results indicated that the composite film(52 μm) delivered a high EMI shielding effectiveness of 49 dB in the frequency range from X-band to Ku-band.Furthermore,the MWCNTs layers in the composite films provided numerous heat transfer channels,reducing phonon scattering during heat transfer and resulting in a maximum thermal conductivity of 8.241 W/(m K).