Limited by the sluggish kinetics at the cathode of proton exchange membrane fuel cells(PEMFCs),optimizing platinum-based alloy catalysts for oxygen reduction reaction remains a key target toward industrialization.Stra...Limited by the sluggish kinetics at the cathode of proton exchange membrane fuel cells(PEMFCs),optimizing platinum-based alloy catalysts for oxygen reduction reaction remains a key target toward industrialization.Strain engineering is widely employed to tune Pt-M catalysts,but its impact on the structure-property relationship is often interwoven with multiple factors.In this work,we propose a bi-stage strain tuning method and demonstrate it on the most common PtCo catalysts.Macro-strain is introduced by synthesizing single-crystal PtCo nanodendrites,whereas mild acid etching introduces micro-strain to the surface.The half-wave potential of as-treated catalysts reaches 0.959 V,and mass activity is up to 0.69 A mg^(−1)_(Pt).A minimal decrease of 2 mV is observed for half-wave potential after 10,000 cycles.Detailed analysis using advanced transmission electron microscopy,wide-angle X-ray scattering,etc.provides direct evidence that surface disorder at the atomic scale accounts for the enhanced activity and stability.In contrast,the simplicity of this approach allows for scaling up on Pt-M catalysts,as demonstrated on PEMFCs.The bi-stage strain tuning strategy provides a new perspective and reference for improving the activity and durability of Pt-M catalysts.展开更多
High nickel content worsens the thermal stability of layered cathodes for lithium-ion batteries,raising safety concerns for their applications.Thoroughly understanding the thermal failure process can offer valuable gu...High nickel content worsens the thermal stability of layered cathodes for lithium-ion batteries,raising safety concerns for their applications.Thoroughly understanding the thermal failure process can offer valuable guidance for material optimization on thermal stability and new opportunities in monitoring battery thermal runaway(TR).Herein,this work comprehensively investigates the thermal failure process of a single-crystal nickel-rich layered cathode and finds that the latent thermal failure starts at∼120℃far below the TR temperature(225℃).During this stage of heat accumulation,sequential structure transition is revealed by atomic resolution electron microscopy,which follows the layered→cation mixing layered→LiMn_(2)O_(4)-type spinel→disordered spinel→rock salt.This progression occurs as a result of the continuous migration and densification of transition metal cations.Phase transition generates gaseous oxygen,initially confined within the isolated closed pores,thereby not showing any thermal failure phenomena at the macro-level.Increasing temperature leads to pore growth and coalescence,and eventually to the formation of open pores,causing oxygen gas release and weight loss,which are the typical TR features.We highlight that latent thermal instability occurs before the macro-level TR,suggesting that suppressing phase transitions caused by early thermal instability is a crucial direction for material optimization.Our findings can also be used for early warning of battery thermal runaway.展开更多
In addition to the three well-known Ag-related precipitates(Ω,X′and Z)in the Al-Cu-Mg-Ag alloys,Ag can also be involved in the formation of the as-cast second phases.However,the effect of Ag ad-dition in Al-Cu-Mg-Ag...In addition to the three well-known Ag-related precipitates(Ω,X′and Z)in the Al-Cu-Mg-Ag alloys,Ag can also be involved in the formation of the as-cast second phases.However,the effect of Ag ad-dition in Al-Cu-Mg-Ag alloys has not been completely studied and even the structure of the as-cast Ag-containing phases is still controversial.By employing the focused ion beam(FIB)combined with transmis-sion electron microscopy(TEM)techniques and density functional theory(DFT)calculations,the forma-tion mechanisms of the Ag-containing phases in the as-cast Al-Cu-Mg-Ag alloys have been investigated.The Ag-containing phases are a series of hexagonal C14-type Laves phases with continuously varying Ag concentrations,described as(Al_(x)Cuy Ag_(1-x-y))_(2)Mg.Moreover,the specific occupancy sites of the atoms in(Al_(x)Cuy Ag_(1-x-y))_(2)Mg were determined.The formation of the(Al_(x)Cuy Ag_(1-x-y))_(2)Mg can be attributed to the stronger Ag-induced aggregation of solute atoms in the initial stage and the establishment of strong Ag-X(X=Al,Mg and Ag)bonding in the Ag-containing phases.Furthermore,our experiments have revealed the solidification sequence of Al-Cu-Mg-Ag alloys,and pointed out that(Al_(x)Cuy Ag_(1-x-y))_(2)Mg is formed at a lower temperature(493.9℃)through the reaction L■Al_(2)CuMg+(Al_(x)Cuy Ag_(1-x-y))_(2)Mg.The study could have positive implications for refinement of the Al-Cu-Mg-Ag quaternary phase diagram and promote the composition-property design of novel aluminum alloys based on(Al_(x)Cuy Ag_(1-x-y))_(2)Mg in the future.展开更多
Constructing robust surface and bulk structure is the prerequisite for realizing high performance high voltage LiCoO_(2)(LCO).Herein,we manage to synthesize a surface Mg-doping and bulk Al-doping coreshell structured ...Constructing robust surface and bulk structure is the prerequisite for realizing high performance high voltage LiCoO_(2)(LCO).Herein,we manage to synthesize a surface Mg-doping and bulk Al-doping coreshell structured LCO,which demonstrates excellent cycling performance.Half-cell shows 94.2%capacity retention after 100 cycles at 3.0-4.6 V(vs.Li/Li^(+))cycling,and no capacity decay after 300 cycles for fullcell test(3.0-4.55 V).Based on comprehensive microanalysis and theoretical calculations,the degradation mechanisms and doping effects are systematically revealed.For the undoped LCO,high voltage cycling induces severe interfacial and bulk degradations,where cracks,stripe defects,fatigue H2 phase,and spinel phase are identified in grain bulk.For the doped LCO,Mg-doped surface shell can suppress the interfacial degradations,which not only stabilizes the surface structure by forming a thin rock-salt layer but also significantly improves the electronic conductivity,thus enabling superior rate performance.Bulk Al-doping can suppress the lattice"breathing"effect and the detrimental H3 to H1-3 phase transition,which minimizes the internal strain and defects growth,maintaining the layered structure after prolonged cycling.Combining theoretical calculations,this work deepens our understanding of the doping effects of Mg and Al,which is valuable in guiding the future material design of high voltage LCO.展开更多
Enhancing the lifetime of perovskite solar cells(PSCs)is one of the essential challenges for their industrialization.Although the external encapsulation protects the perovskite device from the erosion of moisture and ...Enhancing the lifetime of perovskite solar cells(PSCs)is one of the essential challenges for their industrialization.Although the external encapsulation protects the perovskite device from the erosion of moisture and oxygen under various harsh conditions.However,the perovskite devices still undergo static and dynamic thermal stress during thermal and thermal cycling aging,respectively,resulting in irreversible damage to the morphology,component,and phase of stacked materials.Herein,the viscoelastic polymer polyvinyl butyral(PVB)material is designed onto the surface of perovskite films to form flexible interface encapsulation.After PVB interface encapsulation,the surface modulus of perovskite films decreases by nearly 50%,and the interface stress range under the dynamic temperature field(−40 to 85°C)drops from−42.5 to 64.8 MPa to−14.8 to 5.0 MPa.Besides,PVB forms chemical interactions with FA+cations and Pb^(2+),and the macroscopic residual stress is regulated and defects are reduced of the PVB encapsulated perovskite film.As a result,the optimized device's efficiency increases from 22.21%to 23.11%.Additionally,after 1500 h of thermal treatment(85°C),1000 h of damp heat test(85°C&85%RH),and 250 cycles of thermal cycling test(−40 to 85°C),the devices maintain 92.6%,85.8%,and 96.1%of their initial efficiencies,respectively.展开更多
Cathode electrolyte interphase(CEI)layer plays a crucial role in determining the electrochemical performance of lithium-ion batteries.Limited by the sensitive nature of CEI and the lack of characterization techniques,...Cathode electrolyte interphase(CEI)layer plays a crucial role in determining the electrochemical performance of lithium-ion batteries.Limited by the sensitive nature of CEI and the lack of characterization techniques,its dynamic evolution during cycling,its formation mechanism,and its specific impact on battery performance are not yet fully understood.Herein,we systematically investigate the dynamic evolution of CEI layer and its critical effect on the cycling performance of LiCoO_(2)cathode by diverse characterization techniques.We find that cycling voltage plays a key role in affecting CEI formation and evolution,and a critical potential(4.05 V vs.Li)is identified,which acts as the switching potential between CEI deposition and decomposition.We show that CEI starts deposition in the discharge process when the potential is below 4.05 V,and CEI decomposition occurs when the potential is higher than 4.05 V.When the battery is cycled below such a critical potential,a stable CEI layer is developed,which leads to superior cycling stability.When the battery is cycled above such a critical potential,a CEI-free cathode interface is observed,which also demonstrates good cycle stability.However,when the critical potential falls in the cycling voltage range,CEI deposition and decomposition are repeatedly switched on during cycling,leading to the dynamically unstable CEI layer.The unstable CEI layer causes continuous interfacial reaction and degradation,resulting in battery performance decay.Our work deepens the understanding of the CEI formation and evolution mechanisms,and clarifies the critical effect of CEI layer on cycling performance,which provides new insights into stabilizing the electrode-electrolyte interface for high-performance rechargeable batteries.展开更多
Since titanium has high affinity for hydrogen and reacts reversibly with hydrogen,the precipitation of titanium hydrides in titanium and its alloys cannot be ignored.Two most common hydride precipitates in α-Ti matrix...Since titanium has high affinity for hydrogen and reacts reversibly with hydrogen,the precipitation of titanium hydrides in titanium and its alloys cannot be ignored.Two most common hydride precipitates in α-Ti matrix areγ-hydride and δ-hydride,however their mechanisms for precipitation are still unclear.In the present study,we find that both γ-hydride and δ-hydride phases with different specific orientations were randomly precipitated in the as-received hot forged commercially pure Ti.In addition,a large amount of the titanium hydrides can be introduced into Ti matrix with selective precipitation by using electrochemical treatment.Cs-corrected scanning transmission electron microscopy is used to study the precipitation mechanisms of the two hydrides.It is revealed that the γ-hydride and δ-hydride precipitations are both formed through slip+shuffle mechanisms involving a unit of two layers of titanium atoms,but the difference is that the γ-hydride is formed by prismatic slip corresponding to hydrogen occupying the octahedral sites of α-Ti,while the δ-hydride is formed by basal slip corresponding to hydrogen occupying the tetrahedral sites ofα-Ti.展开更多
As multiple{11■2}twin variants are often formed during deformation in hexagonal close-packed(hcp)titanium,the twin-twin interaction structure has a profound influence on mechanical properties.In this paper,the twin-t...As multiple{11■2}twin variants are often formed during deformation in hexagonal close-packed(hcp)titanium,the twin-twin interaction structure has a profound influence on mechanical properties.In this paper,the twin-twin interaction structures of the{11■2}contraction twin in cold-rolled commercial purity titanium were studied by using electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).Formation of the{11■2}twin variants was found to deviate the rank of Schmid factor,and the non-Schmid behavior was explained by the high-angle grain boundary nucleation mechanism.All the observed twin-twin pairs manifested a quilted-looking structure,which consists of the incoming twins being arrested by the obstacle twins.Furthermore,the quilted-looking{11■2}twin-twin boundary was revealed by TEM and high resolution TEM observations.De-twinning,lattice rotation and curved twin boundary were observed in the obstacle twin due to the twin-twin reaction with the impinging twin.A twin-twin interaction mechanism for the{11■2}twin variants was proposed in terms of the dislocation dissociation,which will enrich the understanding for the propagation of twins and twinning-induced hardening in hcp metals and alloys.展开更多
■ compression twins with high density stacking faults were studied at atomic scale using Cscorrection transmission electron microscopy. On one side of the ■ twin boundary, there were many steps arranged alternately ...■ compression twins with high density stacking faults were studied at atomic scale using Cscorrection transmission electron microscopy. On one side of the ■ twin boundary, there were many steps arranged alternately with the coherent twin boundaries. Most of the steps were linked with stacking faults inside twins. Burgers vector of twinning dislocations and the mismatch strain at steps were characterized. Due to the compressive mismatch strain at steps, the high density stacking faults inside twins were formed at twin tips during twinning process. The localized strain at the steps would be related to the crack nucleation in magnesium alloys.展开更多
Halide perovskites are strategically important in the field of energy materials. Along with the rapid development of the materials and related devices, there is an urgent need to understand the structure–property rel...Halide perovskites are strategically important in the field of energy materials. Along with the rapid development of the materials and related devices, there is an urgent need to understand the structure–property relationship from nanoscale to atomic scale. Much effort has been made in the past few years to overcome the difficulty of imaging limited by electron dose,and to further extend the investigation towards operando conditions. This review is dedicated to recent studies of advanced transmission electron microscopy(TEM) characterizations for halide perovskites. The irradiation damage caused by the interaction of electron beams and perovskites under conventional imaging conditions are first summarized and discussed. Low-dose TEM is then discussed, including electron diffraction and emerging techniques for high-resolution TEM(HRTEM) imaging. Atomic-resolution imaging, defects identification and chemical mapping on halide perovskites are reviewed. Cryo-TEM for halide perovskites is discussed, since it can readily suppress irradiation damage and has been rapidly developed in the past few years. Finally, the applications of in-situ TEM in the degradation study of perovskites under environmental conditions such as heating,biasing, light illumination and humidity are reviewed. More applications of emerging TEM characterizations are foreseen in the coming future, unveiling the structural origin of halide perovskite’s unique properties and degradation mechanism under operando conditions, so to assist the design of a more efficient and robust energy material.展开更多
Interfacial structure evolution and degradation are critical to the electrochemical performance of LiCoO_(2)(LCO),the most widely studied and used cathode material in lithium ion batteries.To understand such processes...Interfacial structure evolution and degradation are critical to the electrochemical performance of LiCoO_(2)(LCO),the most widely studied and used cathode material in lithium ion batteries.To understand such processes requires precise and quantitative measurements.Herein,we use well-defined epitaxial LCO thin films to reveal the interfacial degradation mechanisms.Through our systematical investigations,we find that surface corrosion is significant after forming the surface phase transition layer,and the cathode electrolyte interphase(CEI)has a double layer structure,an inorganic inner layer containing CoO,LiF,LiOH/Li_(2)O and Li_(x)PF_(y)O_(2),and an outmost layer containing Li2CO_(3) and organic carbonaceous components.Furthermore,surface cracks are found to be pronounced due to mechanical failures and chemical etching.This work demonstrates a model material to realize the precise measurements of LCO interfacial degradations,which deepens our understanding on the interfacial degradation mechanisms.展开更多
Although single-atom catalysts significantly improve the atom utilization efficiency,the multistep preparation procedures are complicated and difficult to control.Herein,we demonstrate that one-step in situ synthesis ...Although single-atom catalysts significantly improve the atom utilization efficiency,the multistep preparation procedures are complicated and difficult to control.Herein,we demonstrate that one-step in situ synthesis of the single-atom Pt anchored in single-crystal MoC(Pt_(1)/MoC)by using facile and controllable arc-discharge strategy under extreme conditions.The high temperature(up to 4000℃)provides the sufficient energy for atom dispersion and overall stability by forming thermodynamically favourable metal-support interactions.The high-temperature-stabilized Pt1/MoC exhibits outstanding performance and excellent thermal stability as durable catalyst for selective quinoline hydrogenation.The initial turnover frequency of 3710 h^(-1)is greater than those of previously reported samples by an order of magnitude under 2 MPa H_(2)at 100℃.The catalyst also shows broad scope activity toward hydrogenation containing unsaturated groups of C=C,C=N,and C=O.The facile,one-step,and fast arc-discharge method provides an effective avenue for single-atom catalyst fabrication that is conventionally challenging.展开更多
Electrode interfacial degradations are the key challenges for high-performance rechargeable batteries,usually mitigated through surface modification/coating strategies.Herein,we report a novel mechanism to enhance the...Electrode interfacial degradations are the key challenges for high-performance rechargeable batteries,usually mitigated through surface modification/coating strategies.Herein,we report a novel mechanism to enhance the surface stability of P2 layered cathodes by introducing a high density of dopant-enriched precipitates.Based on microscopic analysis,we show that forming a high density of precipitates at the grain surface can effectively suppress surface cracking and corrosion,which not only improves the surface/interface stability but also effectively suppresses the intergranular cracking issue.Increasing the doping level can lead to a greater density of precipitates at the surface region,which results in higher surface stability and increased cycling stability of the P2 layered cathode for a sodium-ion battery.We further reveal that prolonged cycling can induce the formation of a precipitate-free surface region due to the loss of Zn dopant and Na.Our in-depth microanalysis reveals cycling-induced dynamic structural evolution of the P2 layered cathodes,highlighting that dopant segregation-induced precipitation is a new approach to achieving high interfacial stability.展开更多
Cathode electrolyte interphase(CEI)has a significant impact on the performance of rechargeable batteries and is gaining increasing attention.Understanding the fundamental and detailed CEI formation mechanism is of cri...Cathode electrolyte interphase(CEI)has a significant impact on the performance of rechargeable batteries and is gaining increasing attention.Understanding the fundamental and detailed CEI formation mechanism is of critical importance for battery chemistry.Herein,a diverse of characterization tools are utilized to comprehensively analyze the composition of the CEI layer as well as its formation mechanism by LiCoO_(2)(LCO)cathode.We reveal that CEI is mainly composed of the reduction products of electrolyte and it only parasitizes the degraded LCO surface which has transformed into a disordered spinel structure due to oxygen loss and lithium depletion.Based on the energy diagram and the chemical potential analysis,the CEI formation process has been well explained,and the proposed CEI formation mechanism is further experimentally validated.This work highlights that the CEI formation process is nearly identical to that of the anode-electrolyte-interphase,both of which are generated due to the electrolyte directly in contact with the low chemical potential electrode material.This work can deepen and refresh our understanding of CEI.展开更多
基金the National Natural Science Foundation of China(NO.12274010,12474003)Beijing Nova Program(20240484584)+2 种基金the support from the Shanghai Key Laboratory of Material Frontiers Research in Extreme Environments,China(No.22dz2260800)the Shanghai Science and Technology Committee,China(No.22JC1410300)the National Natural Science Foundation of China(No.52103330)。
文摘Limited by the sluggish kinetics at the cathode of proton exchange membrane fuel cells(PEMFCs),optimizing platinum-based alloy catalysts for oxygen reduction reaction remains a key target toward industrialization.Strain engineering is widely employed to tune Pt-M catalysts,but its impact on the structure-property relationship is often interwoven with multiple factors.In this work,we propose a bi-stage strain tuning method and demonstrate it on the most common PtCo catalysts.Macro-strain is introduced by synthesizing single-crystal PtCo nanodendrites,whereas mild acid etching introduces micro-strain to the surface.The half-wave potential of as-treated catalysts reaches 0.959 V,and mass activity is up to 0.69 A mg^(−1)_(Pt).A minimal decrease of 2 mV is observed for half-wave potential after 10,000 cycles.Detailed analysis using advanced transmission electron microscopy,wide-angle X-ray scattering,etc.provides direct evidence that surface disorder at the atomic scale accounts for the enhanced activity and stability.In contrast,the simplicity of this approach allows for scaling up on Pt-M catalysts,as demonstrated on PEMFCs.The bi-stage strain tuning strategy provides a new perspective and reference for improving the activity and durability of Pt-M catalysts.
基金the National Natural Science Foundation of China(12174015)the Natural Science Foundation of Beijing,China(2212003)+1 种基金the China National Petroleum Corporation Innovation Found(2021DQ02-1004)the National Natural Science Foundation of China(12074017,12274010).
文摘High nickel content worsens the thermal stability of layered cathodes for lithium-ion batteries,raising safety concerns for their applications.Thoroughly understanding the thermal failure process can offer valuable guidance for material optimization on thermal stability and new opportunities in monitoring battery thermal runaway(TR).Herein,this work comprehensively investigates the thermal failure process of a single-crystal nickel-rich layered cathode and finds that the latent thermal failure starts at∼120℃far below the TR temperature(225℃).During this stage of heat accumulation,sequential structure transition is revealed by atomic resolution electron microscopy,which follows the layered→cation mixing layered→LiMn_(2)O_(4)-type spinel→disordered spinel→rock salt.This progression occurs as a result of the continuous migration and densification of transition metal cations.Phase transition generates gaseous oxygen,initially confined within the isolated closed pores,thereby not showing any thermal failure phenomena at the macro-level.Increasing temperature leads to pore growth and coalescence,and eventually to the formation of open pores,causing oxygen gas release and weight loss,which are the typical TR features.We highlight that latent thermal instability occurs before the macro-level TR,suggesting that suppressing phase transitions caused by early thermal instability is a crucial direction for material optimization.Our findings can also be used for early warning of battery thermal runaway.
基金supported by the National Key R&D Program of China(Nos.2020YFF0218200,2016YFB0300800 and 2021YFC1910505)the Innovation Fund Project of GRINM and other related projects.
文摘In addition to the three well-known Ag-related precipitates(Ω,X′and Z)in the Al-Cu-Mg-Ag alloys,Ag can also be involved in the formation of the as-cast second phases.However,the effect of Ag ad-dition in Al-Cu-Mg-Ag alloys has not been completely studied and even the structure of the as-cast Ag-containing phases is still controversial.By employing the focused ion beam(FIB)combined with transmis-sion electron microscopy(TEM)techniques and density functional theory(DFT)calculations,the forma-tion mechanisms of the Ag-containing phases in the as-cast Al-Cu-Mg-Ag alloys have been investigated.The Ag-containing phases are a series of hexagonal C14-type Laves phases with continuously varying Ag concentrations,described as(Al_(x)Cuy Ag_(1-x-y))_(2)Mg.Moreover,the specific occupancy sites of the atoms in(Al_(x)Cuy Ag_(1-x-y))_(2)Mg were determined.The formation of the(Al_(x)Cuy Ag_(1-x-y))_(2)Mg can be attributed to the stronger Ag-induced aggregation of solute atoms in the initial stage and the establishment of strong Ag-X(X=Al,Mg and Ag)bonding in the Ag-containing phases.Furthermore,our experiments have revealed the solidification sequence of Al-Cu-Mg-Ag alloys,and pointed out that(Al_(x)Cuy Ag_(1-x-y))_(2)Mg is formed at a lower temperature(493.9℃)through the reaction L■Al_(2)CuMg+(Al_(x)Cuy Ag_(1-x-y))_(2)Mg.The study could have positive implications for refinement of the Al-Cu-Mg-Ag quaternary phase diagram and promote the composition-property design of novel aluminum alloys based on(Al_(x)Cuy Ag_(1-x-y))_(2)Mg in the future.
基金the National Natural Science Foundation of China(12174015)the Natural Science Foundation of Beijing,China(2212003)+1 种基金the China National Petroleum Corporation Innovation Found(2021DQ02-1004)the National Natural Science Foundation of China(12102053)。
文摘Constructing robust surface and bulk structure is the prerequisite for realizing high performance high voltage LiCoO_(2)(LCO).Herein,we manage to synthesize a surface Mg-doping and bulk Al-doping coreshell structured LCO,which demonstrates excellent cycling performance.Half-cell shows 94.2%capacity retention after 100 cycles at 3.0-4.6 V(vs.Li/Li^(+))cycling,and no capacity decay after 300 cycles for fullcell test(3.0-4.55 V).Based on comprehensive microanalysis and theoretical calculations,the degradation mechanisms and doping effects are systematically revealed.For the undoped LCO,high voltage cycling induces severe interfacial and bulk degradations,where cracks,stripe defects,fatigue H2 phase,and spinel phase are identified in grain bulk.For the doped LCO,Mg-doped surface shell can suppress the interfacial degradations,which not only stabilizes the surface structure by forming a thin rock-salt layer but also significantly improves the electronic conductivity,thus enabling superior rate performance.Bulk Al-doping can suppress the lattice"breathing"effect and the detrimental H3 to H1-3 phase transition,which minimizes the internal strain and defects growth,maintaining the layered structure after prolonged cycling.Combining theoretical calculations,this work deepens our understanding of the doping effects of Mg and Al,which is valuable in guiding the future material design of high voltage LCO.
基金the National Natural Science Foundation of China(U21A20172,21975028)the China Postdoctoral Science Foundation under Grant Number 2023 M740167.
文摘Enhancing the lifetime of perovskite solar cells(PSCs)is one of the essential challenges for their industrialization.Although the external encapsulation protects the perovskite device from the erosion of moisture and oxygen under various harsh conditions.However,the perovskite devices still undergo static and dynamic thermal stress during thermal and thermal cycling aging,respectively,resulting in irreversible damage to the morphology,component,and phase of stacked materials.Herein,the viscoelastic polymer polyvinyl butyral(PVB)material is designed onto the surface of perovskite films to form flexible interface encapsulation.After PVB interface encapsulation,the surface modulus of perovskite films decreases by nearly 50%,and the interface stress range under the dynamic temperature field(−40 to 85°C)drops from−42.5 to 64.8 MPa to−14.8 to 5.0 MPa.Besides,PVB forms chemical interactions with FA+cations and Pb^(2+),and the macroscopic residual stress is regulated and defects are reduced of the PVB encapsulated perovskite film.As a result,the optimized device's efficiency increases from 22.21%to 23.11%.Additionally,after 1500 h of thermal treatment(85°C),1000 h of damp heat test(85°C&85%RH),and 250 cycles of thermal cycling test(−40 to 85°C),the devices maintain 92.6%,85.8%,and 96.1%of their initial efficiencies,respectively.
基金the National Natural Science Foundation of China (No.12174015)the Natural Science Foundation of Beijing,China (No.2212003)+1 种基金the Innovative Research Group Project of the National Natural Science Foundation of China (CN) (No.51621003)the Beijing Municipal High Level Innovative Team Building Program (IDHT20190503)。
文摘Cathode electrolyte interphase(CEI)layer plays a crucial role in determining the electrochemical performance of lithium-ion batteries.Limited by the sensitive nature of CEI and the lack of characterization techniques,its dynamic evolution during cycling,its formation mechanism,and its specific impact on battery performance are not yet fully understood.Herein,we systematically investigate the dynamic evolution of CEI layer and its critical effect on the cycling performance of LiCoO_(2)cathode by diverse characterization techniques.We find that cycling voltage plays a key role in affecting CEI formation and evolution,and a critical potential(4.05 V vs.Li)is identified,which acts as the switching potential between CEI deposition and decomposition.We show that CEI starts deposition in the discharge process when the potential is below 4.05 V,and CEI decomposition occurs when the potential is higher than 4.05 V.When the battery is cycled below such a critical potential,a stable CEI layer is developed,which leads to superior cycling stability.When the battery is cycled above such a critical potential,a CEI-free cathode interface is observed,which also demonstrates good cycle stability.However,when the critical potential falls in the cycling voltage range,CEI deposition and decomposition are repeatedly switched on during cycling,leading to the dynamically unstable CEI layer.The unstable CEI layer causes continuous interfacial reaction and degradation,resulting in battery performance decay.Our work deepens the understanding of the CEI formation and evolution mechanisms,and clarifies the critical effect of CEI layer on cycling performance,which provides new insights into stabilizing the electrode-electrolyte interface for high-performance rechargeable batteries.
基金This work was supported financially by the National Natural Science Foundation of China(Nos.51621003,11374028and U1330112)the Scientific Research Key Program of Beijing Municipal Commission of Education(No.KZ201310005002)+1 种基金the Beijing Municipal Found for Scientific Innovation(No.PXM2019014204500031)the Foundation on the Creative Research Team Construction Promotion Project of Beijing Municipal Institution(No.IDHT20190503)。
文摘Since titanium has high affinity for hydrogen and reacts reversibly with hydrogen,the precipitation of titanium hydrides in titanium and its alloys cannot be ignored.Two most common hydride precipitates in α-Ti matrix areγ-hydride and δ-hydride,however their mechanisms for precipitation are still unclear.In the present study,we find that both γ-hydride and δ-hydride phases with different specific orientations were randomly precipitated in the as-received hot forged commercially pure Ti.In addition,a large amount of the titanium hydrides can be introduced into Ti matrix with selective precipitation by using electrochemical treatment.Cs-corrected scanning transmission electron microscopy is used to study the precipitation mechanisms of the two hydrides.It is revealed that the γ-hydride and δ-hydride precipitations are both formed through slip+shuffle mechanisms involving a unit of two layers of titanium atoms,but the difference is that the γ-hydride is formed by prismatic slip corresponding to hydrogen occupying the octahedral sites of α-Ti,while the δ-hydride is formed by basal slip corresponding to hydrogen occupying the tetrahedral sites ofα-Ti.
基金financially supported by the National Natural Science Foundation of China(Grants Nos.11374028 and U1330112)the Key Project of Beijing Natural Science Foundation(No.KZ201310005002)
文摘As multiple{11■2}twin variants are often formed during deformation in hexagonal close-packed(hcp)titanium,the twin-twin interaction structure has a profound influence on mechanical properties.In this paper,the twin-twin interaction structures of the{11■2}contraction twin in cold-rolled commercial purity titanium were studied by using electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM).Formation of the{11■2}twin variants was found to deviate the rank of Schmid factor,and the non-Schmid behavior was explained by the high-angle grain boundary nucleation mechanism.All the observed twin-twin pairs manifested a quilted-looking structure,which consists of the incoming twins being arrested by the obstacle twins.Furthermore,the quilted-looking{11■2}twin-twin boundary was revealed by TEM and high resolution TEM observations.De-twinning,lattice rotation and curved twin boundary were observed in the obstacle twin due to the twin-twin reaction with the impinging twin.A twin-twin interaction mechanism for the{11■2}twin variants was proposed in terms of the dislocation dissociation,which will enrich the understanding for the propagation of twins and twinning-induced hardening in hcp metals and alloys.
基金supported financially by the National Natural Science Foundation of China (Nos. 11374028, U1330112 and 51621003)the National Natural Science Fund for Innovative Research Groups (No. 51621003)the Scientific Research Key Program of Beijing Municipal Commission of Education (No. KZ201310005002)
文摘■ compression twins with high density stacking faults were studied at atomic scale using Cscorrection transmission electron microscopy. On one side of the ■ twin boundary, there were many steps arranged alternately with the coherent twin boundaries. Most of the steps were linked with stacking faults inside twins. Burgers vector of twinning dislocations and the mismatch strain at steps were characterized. Due to the compressive mismatch strain at steps, the high density stacking faults inside twins were formed at twin tips during twinning process. The localized strain at the steps would be related to the crack nucleation in magnesium alloys.
基金the Beijing Municipal High Level Innovative Team Building Program (IDHT20190503)the National Natural Science Fund for Innovative Research Groups of China (51621003)the National Natural Science Foundation of China (12074017)。
文摘Halide perovskites are strategically important in the field of energy materials. Along with the rapid development of the materials and related devices, there is an urgent need to understand the structure–property relationship from nanoscale to atomic scale. Much effort has been made in the past few years to overcome the difficulty of imaging limited by electron dose,and to further extend the investigation towards operando conditions. This review is dedicated to recent studies of advanced transmission electron microscopy(TEM) characterizations for halide perovskites. The irradiation damage caused by the interaction of electron beams and perovskites under conventional imaging conditions are first summarized and discussed. Low-dose TEM is then discussed, including electron diffraction and emerging techniques for high-resolution TEM(HRTEM) imaging. Atomic-resolution imaging, defects identification and chemical mapping on halide perovskites are reviewed. Cryo-TEM for halide perovskites is discussed, since it can readily suppress irradiation damage and has been rapidly developed in the past few years. Finally, the applications of in-situ TEM in the degradation study of perovskites under environmental conditions such as heating,biasing, light illumination and humidity are reviewed. More applications of emerging TEM characterizations are foreseen in the coming future, unveiling the structural origin of halide perovskite’s unique properties and degradation mechanism under operando conditions, so to assist the design of a more efficient and robust energy material.
基金Supported by the National Natural Science Fund for Innovative Research Groups(China)(Grant No.51621003)the National Key Research and Development Program of China(Grant No.2016Yu7FB0700700)+2 种基金the Beijing Municipal Fund for Scientific Innovation(Grant No.PXM2019014204500031)the Beijing Municipal High Level Innovative Team Building Program(Grant No.IDHT20190503)The film growth is supported by the U.S.Department of Energy(DOE),Office of Science,Office of Basic Energy Science,Early Career Research Program under Award#68272performed using EMSL(grid.436923.9),a DOE Office of the Science User Facility sponsored by the Biological and Environmental Research Program。
文摘Interfacial structure evolution and degradation are critical to the electrochemical performance of LiCoO_(2)(LCO),the most widely studied and used cathode material in lithium ion batteries.To understand such processes requires precise and quantitative measurements.Herein,we use well-defined epitaxial LCO thin films to reveal the interfacial degradation mechanisms.Through our systematical investigations,we find that surface corrosion is significant after forming the surface phase transition layer,and the cathode electrolyte interphase(CEI)has a double layer structure,an inorganic inner layer containing CoO,LiF,LiOH/Li_(2)O and Li_(x)PF_(y)O_(2),and an outmost layer containing Li2CO_(3) and organic carbonaceous components.Furthermore,surface cracks are found to be pronounced due to mechanical failures and chemical etching.This work demonstrates a model material to realize the precise measurements of LCO interfacial degradations,which deepens our understanding on the interfacial degradation mechanisms.
基金This work was financially supported by the National Key Research and Development Program of China(2016YFB0901600)the NSF of China(21872166)the Key Research Program of Chinese Academy of Sciences(QYZDJ-SSW-JSC013 and KGZD-EW-T06).
文摘Although single-atom catalysts significantly improve the atom utilization efficiency,the multistep preparation procedures are complicated and difficult to control.Herein,we demonstrate that one-step in situ synthesis of the single-atom Pt anchored in single-crystal MoC(Pt_(1)/MoC)by using facile and controllable arc-discharge strategy under extreme conditions.The high temperature(up to 4000℃)provides the sufficient energy for atom dispersion and overall stability by forming thermodynamically favourable metal-support interactions.The high-temperature-stabilized Pt1/MoC exhibits outstanding performance and excellent thermal stability as durable catalyst for selective quinoline hydrogenation.The initial turnover frequency of 3710 h^(-1)is greater than those of previously reported samples by an order of magnitude under 2 MPa H_(2)at 100℃.The catalyst also shows broad scope activity toward hydrogenation containing unsaturated groups of C=C,C=N,and C=O.The facile,one-step,and fast arc-discharge method provides an effective avenue for single-atom catalyst fabrication that is conventionally challenging.
基金P.Y.thank the National Natural Science Foundation of China(No.12174015)the Natural Science Foundation of Beijing,China(No.2212003)+4 种基金M.S.thank Innovative Research Group Project of the National Natural Science Foundation of China(grant no.51621003)Beijing Municipal High Level Innovative Team Building Program(IDHT20190503)K.W.thanks National Natural Science Foundation of China(No.12104024)China Postdoctoral Science Foundation(2020M680273)China National Postdoctoral Program for Innova-tive Talents(BX2021024).
文摘Electrode interfacial degradations are the key challenges for high-performance rechargeable batteries,usually mitigated through surface modification/coating strategies.Herein,we report a novel mechanism to enhance the surface stability of P2 layered cathodes by introducing a high density of dopant-enriched precipitates.Based on microscopic analysis,we show that forming a high density of precipitates at the grain surface can effectively suppress surface cracking and corrosion,which not only improves the surface/interface stability but also effectively suppresses the intergranular cracking issue.Increasing the doping level can lead to a greater density of precipitates at the surface region,which results in higher surface stability and increased cycling stability of the P2 layered cathode for a sodium-ion battery.We further reveal that prolonged cycling can induce the formation of a precipitate-free surface region due to the loss of Zn dopant and Na.Our in-depth microanalysis reveals cycling-induced dynamic structural evolution of the P2 layered cathodes,highlighting that dopant segregation-induced precipitation is a new approach to achieving high interfacial stability.
基金Natural Science Foundation of Beijing,China,Grant/Award Number:2212003National Natural Science Foundation of China for Youth Science Fund,Grant/Award Number:12204025+2 种基金National Natural Science Fund for Innovative Research Groups,Grant/Award Number:51621003Beijing municipal high level innovative team building program,Grant/Award Number:IDHT20190503The U.S.Department of Energy(DOE),Office of Science,Basic Energy Sciences,Division of Materials Sciences and Engineering,Synthesis and Processing Science Program,Grant/Award Number:10122。
文摘Cathode electrolyte interphase(CEI)has a significant impact on the performance of rechargeable batteries and is gaining increasing attention.Understanding the fundamental and detailed CEI formation mechanism is of critical importance for battery chemistry.Herein,a diverse of characterization tools are utilized to comprehensively analyze the composition of the CEI layer as well as its formation mechanism by LiCoO_(2)(LCO)cathode.We reveal that CEI is mainly composed of the reduction products of electrolyte and it only parasitizes the degraded LCO surface which has transformed into a disordered spinel structure due to oxygen loss and lithium depletion.Based on the energy diagram and the chemical potential analysis,the CEI formation process has been well explained,and the proposed CEI formation mechanism is further experimentally validated.This work highlights that the CEI formation process is nearly identical to that of the anode-electrolyte-interphase,both of which are generated due to the electrolyte directly in contact with the low chemical potential electrode material.This work can deepen and refresh our understanding of CEI.
