It is discovered that the product of the current and the electric field in a PN junction should be regarded as the rate of work(power)done by the electric field force on moving charges(hole current and electron curren...It is discovered that the product of the current and the electric field in a PN junction should be regarded as the rate of work(power)done by the electric field force on moving charges(hole current and electron current),which was previously misinterpreted as solely a Joule heating effect.We clarify that it is exactly the work done by the electric field force on the moving charges to stimulate the emergence of non-equilibrium carriers,which triggers the novel physical phenomena.As regards to Joule heat,we point out that it should be calculated from Ohm’s law,rather than simply from the product of the current and the electric field.Based on this understanding,we conduct thorough discussion on the role of the electric field force in the process of carrier recombination and carrier generation.The thermal effects of carrier recombination and carrier generation followed are incorporated into the thermal equation of energy.The present study shows that the exothermic effect of carrier recombination leads to a temperature rise at the PN interface,while the endothermic effect of carrier generation causes a temperature reduction at the interface.These two opposite effects cause opposite heat flow directions in the PN junction under forward and backward bias voltages,highlighting the significance of managing device heating phenomena in design considerations.Therefore,this study possesses referential significance for the design and tuning on the performance of piezotronic devices.展开更多
The propagation of an elastic wave(EW)in a piezoelectric semiconductor(PSC)subjected to static biasing fields is investigated.It is found that there exist two coupling waves between electric field and charge carriers....The propagation of an elastic wave(EW)in a piezoelectric semiconductor(PSC)subjected to static biasing fields is investigated.It is found that there exist two coupling waves between electric field and charge carriers.One is stimulated by the action of the polarized electric field in the EW-front on charge carriers(EFC),and the other is stimulated by the action of initial electric field in biasing fields on dynamic carriers(IEC).Obviously,the latter is a man-made and tunable wave-carrier interaction.A careful study shows that IEC can play a leading role in remaking dynamic performance of the wave-front and an inter-medium role in transferring energy from biasing fields to EW-fronts.Hence,a method is proposed to reform the EW performance by biasing-fields:reforming the dispersivity of EW-fronts by promoting competition between IEC and EFC and inverting the dissipation by the IEC to transfer energy from biasing fields to EWfronts.The corresponding tuning laws on the phase-frequency characteristics of an EW show that the wave velocity can be regulated smaller than the pure EW velocity at a lowfrequency and larger than the pure piezoelectric wave velocity at a high-frequency.As for regulating the amplitude-frequency characteristics of the EW by the IEC,analyses show that EWs can obtain amplification only for those with relatively high vibration frequencies(small wave lengths).The studies will provide guidance for theoretical analysis of waves propagating in PSCs and practical application and design of piezotronic devices.展开更多
The electric band energy variation in a bent piezoelectric semiconductor(PSC) nanowire of circular cross-section induced by the mechanical force is analyzed based on a six-band k · p method. The electric-mechanic...The electric band energy variation in a bent piezoelectric semiconductor(PSC) nanowire of circular cross-section induced by the mechanical force is analyzed based on a six-band k · p method. The electric-mechanical fields are first obtained analytically in a cantilever bent PSC nanowire by solving the fully-coupled electro-mechanical equations. Then, the band energy is acquired numerically via the six-band Hamiltonian.By considering further the nonlinear coupling between the piezoelectric and semiconducting quantities, the contribution of the redistribution carriers to the electric field is analyzed from the Gauss’ s law. Numerical examples are carried out for an n-type Zn O nanowire in different locations induced by an applied concentrated end force. They include the electric potential, heavy hole(HH), light hole(LH), spin-orbit split-off(SO),and conduction band(CB) edges along the axial and thickness directions. Our results show that the applied force has a significant effect on the band energies. For instance, on the bottom surface along the axial direction, the bandgaps near the fixed end are greater than those near the loading end, and this trend is reversed on the top surface. Moreover,at a fixed axial location, the energy level of the lower side can be enhanced by applying a bending force at the end. The present results could be of significant guidance to the electronic devices and piezotronics.展开更多
A full-coupling model on the current-voltage(J-V)characteristics of PN junctions is put forward in the paper by taking into account both the whole junction and the two electrode regions consisting of metal/semiconduct...A full-coupling model on the current-voltage(J-V)characteristics of PN junctions is put forward in the paper by taking into account both the whole junction and the two electrode regions consisting of metal/semiconductor(M/S)contacts.The depletion layer assumption proposed by the Shockley model is discarded.Gauss’law on the electric potential and the electric field is applied in the whole junction region such that the majority-carrier currents inside and outside the P/N barrier region are able to be exactly defined and clearly calculated.Then,the stable continuity equations of the electron and hole currents are established to show the current conversion between minority-and majority-carriers inside the whole PN junction region.By analyzing all the conversion procedure,the J-V characteristics of a PN junction are obtained with good agreement to the experimental results,which are closely dependent on the minority-carrier lifetime and doping concentrations.Obviously,the study on this topic possesses referential significance to mechanically tuning the performance of piezoelectric PN junctions and piezotronic devices.展开更多
Precisely quantifying transition metal(TM) redox in bulk is a key to understand the fundamental of optimizing cathode materials in secondary batteries. At present, the commonly used methods to probe TM redox are hard ...Precisely quantifying transition metal(TM) redox in bulk is a key to understand the fundamental of optimizing cathode materials in secondary batteries. At present, the commonly used methods to probe TM redox are hard X-ray absorption spectroscopy(hXAS) and soft X-ray absorption spectroscopy(sXAS).However, they are both facing challenges to precisely quantify the valence states of some transition metals such as Mn. In this paper, Mn-L iPFY(inverse partial fluorescence yield) spectra extracted from Mn-L m RIXS(mapping of resonant inelastic X-ray scattering) is adopted to quantify Mn valence states. Mn-L i PFY spectra has been considered as a bulk-sensitive, non-distorted probe of TM valence states.However, the exact precision of this method is still unclear in quantifying practical battery electrodes.Herein, a series of LiMn_(2)O_(4) electrodes with different charge and discharge states are prepared. Based on their electrochemical capacity(generally considered to be very precise), the precision of Mn iPFY in quantifying bulk Mn valence state is confirmed, and the error range is unraveled. Mn-L mRIXS iPFY thus is identified as one of the best methods to quantify the bulk Mn valence state comparing with hXAS and sXAS.展开更多
Based on the mechanical motion equation,Gauss’s law,and the current continuity condition,we study a few typical transient effects in a piezoelectric semiconductor(PS)fiber to realize the startup and turning-off funct...Based on the mechanical motion equation,Gauss’s law,and the current continuity condition,we study a few typical transient effects in a piezoelectric semiconductor(PS)fiber to realize the startup and turning-off functions of common piezotronic devices.In this study,the transient extensional vibration induced by a suddenly applied axial time-dependent force is examined in a cantilevered n-type ZnO nanofiber.Neither the magnitude of the loadings nor the doping concentration significantly affects the propagation caused by disturbance of the axial displacement.However,both of the factors play an important role in the propagation caused by disturbance of the electron concentrations.This indicates that the electromechanical coupling effect can be expected to directly determine the electronic performance of the devices.In addition,the assumption of previous simplified models which neglect the charge carriers in Gauss’s law is discussed,showing that this assumption has a little influence on the startup state when the doping concentration is smaller than 1021 m-3.This suggests that the screening effect of the carriers on the polarized electric field is much reduced in this situation,and that the state is gradually transforming into a pure piezoelectric state.Nevertheless,the carriers can provide a damping effect,which means that the previous simplified models do not sufficiently describe the turning-off state.The numerical results show that the present study has referential value with respect to the design of newly multifunctional PS devices.展开更多
The lightweight,rechargeable lithium-ion battery is one of the dominant energy storage devices globally in portable electronics due to its high energy density,no memory effect,wide operating voltage,lightweight,and go...The lightweight,rechargeable lithium-ion battery is one of the dominant energy storage devices globally in portable electronics due to its high energy density,no memory effect,wide operating voltage,lightweight,and good charge efficiency.However,due to safety concerns,the depletion of lithium reserves,and the corresponding increase of cost,an alternative battery system becomes more and more desirable.To develop alternative battery systems with low cost and high material abundance,for example,sodium,magnesium,zinc,and calcium,it is important to understand the chemical and electronic structure of materials.Soft X-ray spectroscopy,for example,X-ray absorption spectroscopy(XAS),X-ray emission spectroscopy(XES),and resonant inelastic soft X-ray scattering(RIXS),is an element-specific technique with sensitivity to the local chemical environment and structural order of the element of interest.Modern soft X-ray systems enable operando experiments that can be applied to amorphous and crystalline samples,making it a powerful tool for studying the electronic and structural changes in electrode and electrolyte species.In this article,the application of in situ/operando(soft)X-ray spectroscopy in beyond lithium-ion batteries is reviewed to demonstrate how such spectroscopic characterizations could facilitate the interpretation of interfacial phenomena under in situ/operando condition and subsequent development of the beyond lithium-ion batteries.展开更多
A fully-coupled model for a piezoelectric hetero-junction subjected to a pair of stresses is proposed by discarding the depletion layer approximation.The effect of mechanical loadings on PN junction performance is dis...A fully-coupled model for a piezoelectric hetero-junction subjected to a pair of stresses is proposed by discarding the depletion layer approximation.The effect of mechanical loadings on PN junction performance is discussed in detail.Numerical examples are carried out for a p-Si/ZnO-n hetero-junction under a pair of stresses acting on the ntype ZnO portion near the PN interface,where ZnO has the piezoelectric property while Si is not.It is found that the bottom of conduction band is lowered/raised near the two loading points due to the decrease/increase in the electron potential energy there induced by a tensile-stress mode via sucking in majority-carriers from two outside regions,which implies appearance of a potential barrier and a potential well near two loading points.Furthermore,the barrier height and well depth gradually become large with increasing tensile stress such that more and more electrons/holes are inhaled in loading region from the n-/p-zone,respectively.Conversely,rising/dropping of conduction band bottom is brought out near the two loading points by a compressive-stress mode due to the increase/decrease in the potential energy of electrons by pumping out the majority-carriers from the loading region to the two outside regions.Therefore,a potential well and a potential barrier are induced near the two loading points,such that more and more electrons/holes are driven away from the loading region to the n-zone/p-zone,respectively,with the increasing compressive stress.These effects are important to tune the carrier recombination rate near the PN interface.Thus,the present study possesses great referential significance to piezotronic devices.展开更多
The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal(TM)oxide studies in various fields,especially on the fervent topic of oxygen redox states in battery electrodes.However,criti...The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal(TM)oxide studies in various fields,especially on the fervent topic of oxygen redox states in battery electrodes.However,critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions,which has been a popular practice in the battery field.This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements,structures,and electrochemical states through combined experimental and theoretical analyses.It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states.Furthermore,the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window,leading to a summary map of the relative energy positions of the low-lying TM states,with higher TM oxidation states at lower energies,corresponding to higher electrochemical potentials.The results naturally clarify some unusual redox reactions,such as Cr^(3+/6+).This work provides a critical clarification on O-K pre-edge interpretation and more importantly a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.展开更多
In the emergency management of disruptions,efficient emergency material scheduling(EMS) is a key factor to save people’s lives and reduce loss.Based on the literature of EMS and related areas in recent years,the rese...In the emergency management of disruptions,efficient emergency material scheduling(EMS) is a key factor to save people’s lives and reduce loss.Based on the literature of EMS and related areas in recent years,the research was summarized from two aspects of EMS optimization model and algorithms.It is concluded that the EMS optimization models mainly aim at the shortest time,shortest distance,minimum cost,maximum satisfaction and fairness,etc.The constraints usually include the quantity of supply depots,relief supply and vehicles,the types of commodities,the road network conditions,the budgets and the demand forecast of emergency materials.Multi-objective model is more complex and it usually considers more than one objective.To find the optimized solution,the multiobjective model with complex constraints needs more efficient algorithms.The existing algorithms,including mathematic algorithm and heuristic algorithm,have been categorized.For NP-hard(non-deterministic polynomial hard) problems,heuristic algorithms should be designed,which mainly include genetic algorithm(GA),ant colony optimization(ACO),particle swarm optimization(PSO),etc.Based on the characteristics of the optimization model and various algorithms,appropriate algorithm or tools should be chosen and designed to obtain the optimized solution of EMS model.Finally,the development trends of EMS optimization model and algorithm in the future are proposed.展开更多
We study transient bending vibration of a ZnO piezoelec trie semiconduc tor nanofiber fixed at one end with a suddenly applied shear force at the other end.A one-dimensional model based on the phenomenological t heory...We study transient bending vibration of a ZnO piezoelec trie semiconduc tor nanofiber fixed at one end with a suddenly applied shear force at the other end.A one-dimensional model based on the phenomenological t heory of piezoelec trie semiconductors consisting of the equations of piezoelectricity coupled to the continuity equation of electrons is used.An approximate theoretical analysis is performed,accompanied by a finite element analysis using COMSOL.The evolutions of deflection,elec trie pot ential and elec tron dist ribution are calculated and examined.It is found that when the fiber reaches its largest deflection,the distributions of the electromechanical fields are qualitatively similar to those in the case of static loading under the same shear force,but the amplitudes of the fields are about twice as large roughly.展开更多
In this study, a size-dependent composite laminated skew Mindlin plate model is proposed based on a new modified couple stress theory. This plate model can be viewed as a simplified couple stress theory in engineering...In this study, a size-dependent composite laminated skew Mindlin plate model is proposed based on a new modified couple stress theory. This plate model can be viewed as a simplified couple stress theory in engineering mechanics. Governing equations and related boundary conditions are derived based on the principle of minimum potential energy. The Rayleigh–Ritz method is employed to obtain the numerical solutions of the center deflections of simply supported plates with different ply orientations. Numerical results show that the normalized center deflections obtained by the proposed model are always smaller than those obtained by the classical one, i.e. the present model can capture the scale effects of microstructures. Moreover, a phenomenon reveals that the ply orientation would make a significant influence on the magnitude of scale effects of composite laminated plates at micro scale. Additionally, the present model of thick skew plate can be degenerated to the model of Kirchhoff plate based on the modified couple stress theory by adopting the assumptions in Bernoulli–Euler beam and material isotropy.展开更多
Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage ...Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage solely relies on the disordered region of the carbon materials in a carbonate-based electrolyte. The solvent co-intercalation mechanism for Na ions has been recently reported in natural graphite anodes for Na-ion batteries with ether-based electrolytes, but their capacities are still unsatisfactory. We show here for the first time that by combining regular Na ion storage in the disordered carbon layer and solvent co-intercalation mechanism in the graphitized layer of a commercial N330 carbon black as an anode material for Na-ion batteries in ether-based electrolyte, the reversible capacity could be fully realized and doubled in magnitude. This unique sodium intercalation process resulted in a significantly improved electrochemical performance for the N330 electrode with an initial reversible capacity of 234 mAh.g-1 at 50 mA.g-1 and a superior rate capability of 105 mAh.g-1 at 3,200 mA-g-1. When cycled at 3,200 mA.g-1 over 2,000 cycles, the electrode still exhibited a highly reversible capacity of 72 mAh.g-1 with a negligible capacity loss per cycle (0.0167%). Additionally, surface-sensitive C K-edge X-ray absorption spectroscopy, with the assistance of electrochemical and physicochemical characterizations, helped in identifying the controlled formation and evolution of a thin and robust solid electrolyte interphase film. This film not only reduced the resistance for sodium ion diffusion, but also maintained the structural stability of the electrode for extended cycle reversibility. The superior electrochemical performance of N330 carbon black strongly demonstrated the potential of applying ether-based electrolytes for a wide range of carbon anodes apart from natural graphite.展开更多
Eukaryotic transcription begins with the assembly of general transcription factors(GTFs)including TFIID,IIA,IIB,IIE,IIF,and IIH,which help Pol II to engage with promoters.The binding of TATA-box binding protein(TBP)to...Eukaryotic transcription begins with the assembly of general transcription factors(GTFs)including TFIID,IIA,IIB,IIE,IIF,and IIH,which help Pol II to engage with promoters.The binding of TATA-box binding protein(TBP)to DNA,which causes the bending of TATA sequence,is the first step of the preinitiation complex(PIC)formation,and TBP is essential for almost all gene expression.TBP is an integral part of the TFIID complex which includes 13 other TBP-associated factors(TAFs)and can be separated into 3 submodules(TFIID-A,-B and-C)(Chen et al.,2021a).展开更多
基金the National Natural Science Foundation of China(Nos.12232007,11972164,and 12102141)。
文摘It is discovered that the product of the current and the electric field in a PN junction should be regarded as the rate of work(power)done by the electric field force on moving charges(hole current and electron current),which was previously misinterpreted as solely a Joule heating effect.We clarify that it is exactly the work done by the electric field force on the moving charges to stimulate the emergence of non-equilibrium carriers,which triggers the novel physical phenomena.As regards to Joule heat,we point out that it should be calculated from Ohm’s law,rather than simply from the product of the current and the electric field.Based on this understanding,we conduct thorough discussion on the role of the electric field force in the process of carrier recombination and carrier generation.The thermal effects of carrier recombination and carrier generation followed are incorporated into the thermal equation of energy.The present study shows that the exothermic effect of carrier recombination leads to a temperature rise at the PN interface,while the endothermic effect of carrier generation causes a temperature reduction at the interface.These two opposite effects cause opposite heat flow directions in the PN junction under forward and backward bias voltages,highlighting the significance of managing device heating phenomena in design considerations.Therefore,this study possesses referential significance for the design and tuning on the performance of piezotronic devices.
基金Project supported by the National Natural Science Foundation of China(Nos.12232007,12102141,U21A20430,and 11972164)the Chinese Postdoctoral Science Foundation(No.2022M711252)。
文摘The propagation of an elastic wave(EW)in a piezoelectric semiconductor(PSC)subjected to static biasing fields is investigated.It is found that there exist two coupling waves between electric field and charge carriers.One is stimulated by the action of the polarized electric field in the EW-front on charge carriers(EFC),and the other is stimulated by the action of initial electric field in biasing fields on dynamic carriers(IEC).Obviously,the latter is a man-made and tunable wave-carrier interaction.A careful study shows that IEC can play a leading role in remaking dynamic performance of the wave-front and an inter-medium role in transferring energy from biasing fields to EW-fronts.Hence,a method is proposed to reform the EW performance by biasing-fields:reforming the dispersivity of EW-fronts by promoting competition between IEC and EFC and inverting the dissipation by the IEC to transfer energy from biasing fields to EWfronts.The corresponding tuning laws on the phase-frequency characteristics of an EW show that the wave velocity can be regulated smaller than the pure EW velocity at a lowfrequency and larger than the pure piezoelectric wave velocity at a high-frequency.As for regulating the amplitude-frequency characteristics of the EW by the IEC,analyses show that EWs can obtain amplification only for those with relatively high vibration frequencies(small wave lengths).The studies will provide guidance for theoretical analysis of waves propagating in PSCs and practical application and design of piezotronic devices.
基金Project supported by the National Natural Science Foundation of China(Nos.11972164,11672113,11472182)the Key Laboratory Project of Hubei Province of China(No.2016CFA073)。
文摘The electric band energy variation in a bent piezoelectric semiconductor(PSC) nanowire of circular cross-section induced by the mechanical force is analyzed based on a six-band k · p method. The electric-mechanical fields are first obtained analytically in a cantilever bent PSC nanowire by solving the fully-coupled electro-mechanical equations. Then, the band energy is acquired numerically via the six-band Hamiltonian.By considering further the nonlinear coupling between the piezoelectric and semiconducting quantities, the contribution of the redistribution carriers to the electric field is analyzed from the Gauss’ s law. Numerical examples are carried out for an n-type Zn O nanowire in different locations induced by an applied concentrated end force. They include the electric potential, heavy hole(HH), light hole(LH), spin-orbit split-off(SO),and conduction band(CB) edges along the axial and thickness directions. Our results show that the applied force has a significant effect on the band energies. For instance, on the bottom surface along the axial direction, the bandgaps near the fixed end are greater than those near the loading end, and this trend is reversed on the top surface. Moreover,at a fixed axial location, the energy level of the lower side can be enhanced by applying a bending force at the end. The present results could be of significant guidance to the electronic devices and piezotronics.
基金Project supported by the National Natural Science Foundation of China (Nos.11972164,11672113,11472182)the Key Laboratory Project of Hubei Province of China (No.2016CFA073)。
文摘A full-coupling model on the current-voltage(J-V)characteristics of PN junctions is put forward in the paper by taking into account both the whole junction and the two electrode regions consisting of metal/semiconductor(M/S)contacts.The depletion layer assumption proposed by the Shockley model is discarded.Gauss’law on the electric potential and the electric field is applied in the whole junction region such that the majority-carrier currents inside and outside the P/N barrier region are able to be exactly defined and clearly calculated.Then,the stable continuity equations of the electron and hole currents are established to show the current conversion between minority-and majority-carriers inside the whole PN junction region.By analyzing all the conversion procedure,the J-V characteristics of a PN junction are obtained with good agreement to the experimental results,which are closely dependent on the minority-carrier lifetime and doping concentrations.Obviously,the study on this topic possesses referential significance to mechanically tuning the performance of piezoelectric PN junctions and piezotronic devices.
基金the support from the key research and development and promotion of special projects (scientific and technological research) of Henan province (212102210188)the National Natural Science Foundation of China (51604244)the Energy Storage Materials and Processes Key Laboratory of Henan Province Open Fund (2021003)。
文摘Precisely quantifying transition metal(TM) redox in bulk is a key to understand the fundamental of optimizing cathode materials in secondary batteries. At present, the commonly used methods to probe TM redox are hard X-ray absorption spectroscopy(hXAS) and soft X-ray absorption spectroscopy(sXAS).However, they are both facing challenges to precisely quantify the valence states of some transition metals such as Mn. In this paper, Mn-L iPFY(inverse partial fluorescence yield) spectra extracted from Mn-L m RIXS(mapping of resonant inelastic X-ray scattering) is adopted to quantify Mn valence states. Mn-L i PFY spectra has been considered as a bulk-sensitive, non-distorted probe of TM valence states.However, the exact precision of this method is still unclear in quantifying practical battery electrodes.Herein, a series of LiMn_(2)O_(4) electrodes with different charge and discharge states are prepared. Based on their electrochemical capacity(generally considered to be very precise), the precision of Mn iPFY in quantifying bulk Mn valence state is confirmed, and the error range is unraveled. Mn-L mRIXS iPFY thus is identified as one of the best methods to quantify the bulk Mn valence state comparing with hXAS and sXAS.
基金the National Natural Science Foundation of China(No.11972164)the Key Laboratory Project of Hubei Province of China(No.2016CFA073)。
文摘Based on the mechanical motion equation,Gauss’s law,and the current continuity condition,we study a few typical transient effects in a piezoelectric semiconductor(PS)fiber to realize the startup and turning-off functions of common piezotronic devices.In this study,the transient extensional vibration induced by a suddenly applied axial time-dependent force is examined in a cantilevered n-type ZnO nanofiber.Neither the magnitude of the loadings nor the doping concentration significantly affects the propagation caused by disturbance of the axial displacement.However,both of the factors play an important role in the propagation caused by disturbance of the electron concentrations.This indicates that the electromechanical coupling effect can be expected to directly determine the electronic performance of the devices.In addition,the assumption of previous simplified models which neglect the charge carriers in Gauss’s law is discussed,showing that this assumption has a little influence on the startup state when the doping concentration is smaller than 1021 m-3.This suggests that the screening effect of the carriers on the polarized electric field is much reduced in this situation,and that the state is gradually transforming into a pure piezoelectric state.Nevertheless,the carriers can provide a damping effect,which means that the previous simplified models do not sufficiently describe the turning-off state.The numerical results show that the present study has referential value with respect to the design of newly multifunctional PS devices.
基金supported as part of the Joint Center for Energy Storage Research(JCESR)an Energy Innovation Hub funded by the U.S.Department of Energy(DOE),Office of Science,Basic Energy Sciences
文摘The lightweight,rechargeable lithium-ion battery is one of the dominant energy storage devices globally in portable electronics due to its high energy density,no memory effect,wide operating voltage,lightweight,and good charge efficiency.However,due to safety concerns,the depletion of lithium reserves,and the corresponding increase of cost,an alternative battery system becomes more and more desirable.To develop alternative battery systems with low cost and high material abundance,for example,sodium,magnesium,zinc,and calcium,it is important to understand the chemical and electronic structure of materials.Soft X-ray spectroscopy,for example,X-ray absorption spectroscopy(XAS),X-ray emission spectroscopy(XES),and resonant inelastic soft X-ray scattering(RIXS),is an element-specific technique with sensitivity to the local chemical environment and structural order of the element of interest.Modern soft X-ray systems enable operando experiments that can be applied to amorphous and crystalline samples,making it a powerful tool for studying the electronic and structural changes in electrode and electrolyte species.In this article,the application of in situ/operando(soft)X-ray spectroscopy in beyond lithium-ion batteries is reviewed to demonstrate how such spectroscopic characterizations could facilitate the interpretation of interfacial phenomena under in situ/operando condition and subsequent development of the beyond lithium-ion batteries.
基金Project supported by the National Natural Science Foundation of China(Nos.11972164 and 12102141)。
文摘A fully-coupled model for a piezoelectric hetero-junction subjected to a pair of stresses is proposed by discarding the depletion layer approximation.The effect of mechanical loadings on PN junction performance is discussed in detail.Numerical examples are carried out for a p-Si/ZnO-n hetero-junction under a pair of stresses acting on the ntype ZnO portion near the PN interface,where ZnO has the piezoelectric property while Si is not.It is found that the bottom of conduction band is lowered/raised near the two loading points due to the decrease/increase in the electron potential energy there induced by a tensile-stress mode via sucking in majority-carriers from two outside regions,which implies appearance of a potential barrier and a potential well near two loading points.Furthermore,the barrier height and well depth gradually become large with increasing tensile stress such that more and more electrons/holes are inhaled in loading region from the n-/p-zone,respectively.Conversely,rising/dropping of conduction band bottom is brought out near the two loading points by a compressive-stress mode due to the increase/decrease in the potential energy of electrons by pumping out the majority-carriers from the loading region to the two outside regions.Therefore,a potential well and a potential barrier are induced near the two loading points,such that more and more electrons/holes are driven away from the loading region to the n-zone/p-zone,respectively,with the increasing compressive stress.These effects are important to tune the carrier recombination rate near the PN interface.Thus,the present study possesses great referential significance to piezotronic devices.
基金supported by the LDRD program at the LBNL and facilitated by a User Program at The Molecular Foundry(TMF)provided by the TMF clusters(managed by the High Performance Computing Services Group,at LBNL)+3 种基金by the National Energy Research Scientific Computing Center(NERSC)supported by the Office of Science of the US DOE under Contract No.DE-AC02-05CH11231support from EERE VTO under the Applied Battery Materials Program of the US DOE with Contract No.DE-AC02-05CH11231supported by the DOE VTO at Argonne National Laboratory
文摘The pre-edges of oxygen-K X-ray absorption spectra have been ubiquitous in transition metal(TM)oxide studies in various fields,especially on the fervent topic of oxygen redox states in battery electrodes.However,critical debates remain on the use of the O-K pre-edge variations upon electrochemical cycling as evidences of oxygen redox reactions,which has been a popular practice in the battery field.This study presents an investigation of the O-K pre-edge of 55 oxides covering all 3d TMs with different elements,structures,and electrochemical states through combined experimental and theoretical analyses.It is shown unambiguously that the O-K pre-edge variation in battery cathodes is dominated by changing TM-d states.Furthermore,the pre-edge enables a unique opportunity to project the lowest unoccupied TM-d states onto one common energy window,leading to a summary map of the relative energy positions of the low-lying TM states,with higher TM oxidation states at lower energies,corresponding to higher electrochemical potentials.The results naturally clarify some unusual redox reactions,such as Cr^(3+/6+).This work provides a critical clarification on O-K pre-edge interpretation and more importantly a benchmark database of O-K pre-edge for characterizing redox reactions in batteries and other energy materials.
基金supported by the China Fundamental Research Funds for the Central Universities under Grant300102228402 and 3100102229103China Xi’an Social Science Planning Fund under Grant 19Z73+1 种基金Shaanxi Natural Science Foundation of China under Grant 2019JLP-07the China Innovation and Entrepreneurship Training Program for College Students under Grant 20191071245
文摘In the emergency management of disruptions,efficient emergency material scheduling(EMS) is a key factor to save people’s lives and reduce loss.Based on the literature of EMS and related areas in recent years,the research was summarized from two aspects of EMS optimization model and algorithms.It is concluded that the EMS optimization models mainly aim at the shortest time,shortest distance,minimum cost,maximum satisfaction and fairness,etc.The constraints usually include the quantity of supply depots,relief supply and vehicles,the types of commodities,the road network conditions,the budgets and the demand forecast of emergency materials.Multi-objective model is more complex and it usually considers more than one objective.To find the optimized solution,the multiobjective model with complex constraints needs more efficient algorithms.The existing algorithms,including mathematic algorithm and heuristic algorithm,have been categorized.For NP-hard(non-deterministic polynomial hard) problems,heuristic algorithms should be designed,which mainly include genetic algorithm(GA),ant colony optimization(ACO),particle swarm optimization(PSO),etc.Based on the characteristics of the optimization model and various algorithms,appropriate algorithm or tools should be chosen and designed to obtain the optimized solution of EMS model.Finally,the development trends of EMS optimization model and algorithm in the future are proposed.
文摘We study transient bending vibration of a ZnO piezoelec trie semiconduc tor nanofiber fixed at one end with a suddenly applied shear force at the other end.A one-dimensional model based on the phenomenological t heory of piezoelec trie semiconductors consisting of the equations of piezoelectricity coupled to the continuity equation of electrons is used.An approximate theoretical analysis is performed,accompanied by a finite element analysis using COMSOL.The evolutions of deflection,elec trie pot ential and elec tron dist ribution are calculated and examined.It is found that when the fiber reaches its largest deflection,the distributions of the electromechanical fields are qualitatively similar to those in the case of static loading under the same shear force,but the amplitudes of the fields are about twice as large roughly.
基金supported by the National Natural Sciences Foundation of China(No.11572204)
文摘In this study, a size-dependent composite laminated skew Mindlin plate model is proposed based on a new modified couple stress theory. This plate model can be viewed as a simplified couple stress theory in engineering mechanics. Governing equations and related boundary conditions are derived based on the principle of minimum potential energy. The Rayleigh–Ritz method is employed to obtain the numerical solutions of the center deflections of simply supported plates with different ply orientations. Numerical results show that the normalized center deflections obtained by the proposed model are always smaller than those obtained by the classical one, i.e. the present model can capture the scale effects of microstructures. Moreover, a phenomenon reveals that the ply orientation would make a significant influence on the magnitude of scale effects of composite laminated plates at micro scale. Additionally, the present model of thick skew plate can be degenerated to the model of Kirchhoff plate based on the modified couple stress theory by adopting the assumptions in Bernoulli–Euler beam and material isotropy.
文摘Carbonaceous materials have long been considered promising anode materials for Na-ion batteries. However, the electrochemical performance of conventional carbon anodes is generally poor because the sodium ion storage solely relies on the disordered region of the carbon materials in a carbonate-based electrolyte. The solvent co-intercalation mechanism for Na ions has been recently reported in natural graphite anodes for Na-ion batteries with ether-based electrolytes, but their capacities are still unsatisfactory. We show here for the first time that by combining regular Na ion storage in the disordered carbon layer and solvent co-intercalation mechanism in the graphitized layer of a commercial N330 carbon black as an anode material for Na-ion batteries in ether-based electrolyte, the reversible capacity could be fully realized and doubled in magnitude. This unique sodium intercalation process resulted in a significantly improved electrochemical performance for the N330 electrode with an initial reversible capacity of 234 mAh.g-1 at 50 mA.g-1 and a superior rate capability of 105 mAh.g-1 at 3,200 mA-g-1. When cycled at 3,200 mA.g-1 over 2,000 cycles, the electrode still exhibited a highly reversible capacity of 72 mAh.g-1 with a negligible capacity loss per cycle (0.0167%). Additionally, surface-sensitive C K-edge X-ray absorption spectroscopy, with the assistance of electrochemical and physicochemical characterizations, helped in identifying the controlled formation and evolution of a thin and robust solid electrolyte interphase film. This film not only reduced the resistance for sodium ion diffusion, but also maintained the structural stability of the electrode for extended cycle reversibility. The superior electrochemical performance of N330 carbon black strongly demonstrated the potential of applying ether-based electrolytes for a wide range of carbon anodes apart from natural graphite.
基金supported by the National Natural Science Foundation of China (11434006, 11774199, and 51871112)the National Basic Research Program of China (2015CB921502)+1 种基金the 111 Project B13029supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DEAC02-76SF00515。
文摘Eukaryotic transcription begins with the assembly of general transcription factors(GTFs)including TFIID,IIA,IIB,IIE,IIF,and IIH,which help Pol II to engage with promoters.The binding of TATA-box binding protein(TBP)to DNA,which causes the bending of TATA sequence,is the first step of the preinitiation complex(PIC)formation,and TBP is essential for almost all gene expression.TBP is an integral part of the TFIID complex which includes 13 other TBP-associated factors(TAFs)and can be separated into 3 submodules(TFIID-A,-B and-C)(Chen et al.,2021a).