Recent progress in heterostructured materials for room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur(RT Na-S)batteries are a promising next-generation energy storage device due to their low cost,high energy density(1274 Wh kg^(-1)),and environmental friendliness.However,RT Na-S batteries face a series of vital challenges from sulfur cathode and sodium anode:(i)sluggish reaction kinetics of S and Na_(2)S/Na_(2)S_(2);(ii)severe shuttle effect from the dissolved intermediate sodium polysulfides(NaPSs);(iii)huge volume expansion induced by the change from S to Na_(2)S;(iv)continuous growth of sodium metal dendrites,leading to short-circuiting of the battery;(v)huge volume expansion/contraction of sodium anode upon sodium plating/stripping,causing uncontrollable solid-state electrolyte interphase growth and“dead sodium”formation.Various strategies have been proposed to address these issues,including physical/chemical adsorption of NaPSs,catalysts to facilitate the rapid conversion of NaPSs,high-conductive materials to promote ion/electron transfer,good sodiophilic Na anode hetero-interface homogenized Na ions flux and three-dimensional porous anode host to buffer the volume expansion of sodium.Heterostructure materials can combine these merits into one material to realize multifunctionality.Herein,the recent development of heterostructure as the host for sulfur cathode and Na anode has been reviewed.First of all,the electrochemical mechanisms of sulfur cathode/sodium anode and principles of heterostructures reinforced Na-S batteries are described.Then,the application of heterostructures in Na-S batteries is comprehensively examined.Finally,the current primary avenues of employing heterostructures in Na-S batteries are summarized.Opinions and prospects are put forward regarding the existing problems in current research,aiming to inspire the design of advanced and improved next-generation Na-S batteries.

Hierarchical strain band formation and mechanical behavior of a heterostructured dual-phase material

Dispersive strain bands have been reported as a characteristic deformation feature of heterostructured materials,which helps to improve ductility.However,their formation mechanism is still not well understood.Here we report the formation of dispersed strain bands through dual-level hierarchical strain banding and its effect on the mechanical behavior of a heterostructured Fe-40Cu model material.Specifically,deformation started by the formation and propagation of dispersed microscale strain bands in the heterostructured Fe-40Cu material.High strain gradient was generated within the microscale strain bands during their propagation and was accommodated by the accumulation of geometrically necessary disloca-tions(GNDs).The dispersed microscale strain bands were not uniformly distributed,but instead grouped together to form macroscale strain bands that were uniformly distributed over the entire gage section to accommodate the majority of the applied strain.The formation of this dual-level hierarchical strain bands prevented the formation of large strain localization to fail the sample prematurely.It was also found that increasing the strain hardening capacity of soft copper zones provides more room for the accumulation of GNDs,resulting in higher constraint to microscale strain band propagation and consequently higher ductility.These observations suggest the possibility of tailoring microscale strain bands to optimize tensile performance of heterostructured materials.

Optical properties and applications for MoS_2-Sb_2Te_3-MoS_2 heterostructure materials

Two-dimensional(2D) materials with potential applications in photonic and optoelectronic devices have attracted increasing attention due to their unique structures and captivating properties. However, generation of stable high-energy ultrashort pulses requires further boosting of these materials' optical properties, such as higher damage threshold and larger modulation depth. Here we investigate a new type of heterostructure material with uniformity by employing the magnetron sputtering technique. Heterostructure materials are synthesized with van der Waals heterostructures consisting of MoS_2 and Sb_2Te_3. The bandgap, carrier mobility, and carrier concentration of the MoS_2-Sb_2Te_3-MoS_2 heterostructure materials are calculated theoretically. By using these materials as saturable absorbers(SAs), applications in fiber lasers with Q-switching and mode-locking states are demonstrated experimentally. The modulation depth and damage threshold of SAs are measured to be 64.17%and 14.13 J∕cm^2, respectively. Both theoretical and experimental results indicate that MoS_2-Sb_2Te_3-MoS_2 heterostructure materials have large modulation depth, and can resist high power during the generation of ultrashort pulses. The MoS_2-Sb_2Te_3-MoS_2 heterostructure materials have the advantages of low cost, high reliability, and suitability for mass production, and provide a promising solution for the development of 2D-material-based devices with desirable electronic and optoelectronic properties.

Complementary doping of van der Waals materials through controlled intercalation for monolithically integrated electronics

Doping control has been a key challenge for electronic applications of van der Waals materials.Here,we demonstrate complementary doping of black phosphorus using controlled ionic intercalation to achieve monolithic building elements.We characterize the anisotropic electrical transport as a function of ion concentrations and report a widely tunable resistivity up to three orders of magnitude with characteristic concentration dependence corresponding to phase transitions during intercalation.As a further step,we develop both p-type and n-type field effect transistors as well as electrical diodes with high device stability and performance.In addition,enhanced charge mobility from 380 to 820 cm^2/(V·s)with the intercalation process is observed and explained as the suppressed neutral impurity scattering based on our ab initio calculations.Our study provides a unique approach to atomically control the electrical properties of van der Waals materials,and may open up new opportunities in developing advanced electronics and physics platforms.

Devices and applications of van der Waals heterostructures

Van der Waals heterostructures,composed of individual two-dimensional material have been developing extremely fast.Synthesis of van der Waals heterostructures without the constraint of lattice matching and processing compatibility provides an ideal platform for fundamental research and new device exploitation.We review the approach of synthesis of van der Waals heterostructures,discuss the property of heterostructures and thoroughly illustrate the functional van der Waals heterostructures used in novel electronic and photoelectronic device.

Sub-femto-Joule energy consumption memory device based on van der Waals heterostructure for in-memory computing

In-memory computing has carried out calculations in situ within each memory unit and its main power consumption comes from data writ-ing and erasing.Further improvements in the energy efficiency of in-memory computing require memory devices with sub-femto-Joule energy consumption.Floating gate memory devices based on two-dimensional(2D)material heterostructures have outstanding char-acteristics such as non-volatility,multi-bit storage,and low opera-tion energy,suitable for application in in-memory computing chips.Here,we report a floating gate memory device based on a WSe 2/h-BN/Multilayer-graphene/h-BN heterostructure,the energy consump-tion of which is in sub-femto Joule(0.6 fJ)per operation for pro-gram/erase,and the read power consumption is in the tens of femto Watt(60 fW)range.We show a Hopfield neural network composed of WSe 2/h-BN/Multilayer-graphene/h-BN heterostructure floating gate memory devices,which can recall the original patterns from incorrect patterns.These results shed light on the development of future com-pact and energy-efficient hardware for in-memory computing sys-tems.