Magnesium-based energy materials: Progress, challenges, and perspectives

Magnesium-based energy materials, which combine promising energy-related functional properties with low cost, environmental compatibility and high availability, have been regarded as fascinating candidates for sustainable energy conversion and storage. In this review,we provide a timely summary on the recent progress in three types of important Mg-based energy materials, based on the fundamental strategies of composition and structure engineering. With regard to Mg-based materials for batteries, we systematically review and analyze different material systems, structure regulation strategies as well as the relevant performance in Mg-ion batteries(MIBs) and Mg-air batteries(MABs), covering cathodes, electrolytes, anodes for MIBs, and anodes for MABs;as to Mg-based hydrogen storage materials, we discuss how catalyst adding, composite, alloying and nanostructuring improve the kinetic and thermodynamic properties of de/hydrogenation reactions, and in particular, the impacts of composition and structure modification on hydrogen absorption/dissociation processes and free energy modification mechanism are focused;regarding Mg-based thermoelectric materials, the relations between composition/structure and electrical/thermal transport properties of Mg_(3)X_(2)(X = Sb, Bi), Mg_(2)X(X = Si, Ge, Sn) and Mg Ag Sb-based materials, together with the representative research progress of each material system, are summarized and discussed. Finally, by pointing out remaining challenges and providing possible solutions, this review aims to shed light on the directions and perspectives for practical applications of magnesium-based energy materials in the future.

Improved hydrogen storage kinetics of MgH_(2) using TiFe_(0.92)Mn_(0.04)Co_(0.04) with in-situ generated α-Fe as catalyst

While TiFe alloy has recently attracted attention as the efficient catalyst to enhance de/hydrogenation rates of Mg/MgH_(2),the difficulty of its activation characteristics has hindered further improvement of reaction kinetics.Herein,we report that the TiFe_(0.92)Mn_(0.04)Co_(0.04) catalyst can overcome the abovementioned challenges.The synthesized MgH_(2)-30 wt% TiFe_(0.92)Mn_(0.04)Co_(0.04) can release 4.5 wt%of hydrogen in 16 min at 250℃,three times as fast as MgH_(2).The activation energy of dehydrogenation was as low as 84.6 kJ mol^(-1),which is 46.8%reduced from pure MgH_(2).No clear degradation of reaction rates and hydrogen storage capacity was observed for at least 30 cycles.Structural studies reveal that TiFe_(0.92)Mn_(0.04)Co_(0.04) partially decomposes to in-situ generatedα-Fe particles dispersed on TiFe_(0.92)Mn_(0.04)Co_(0.04).The presence ofα-Fe reduces the formation of an oxide layer on TiFe_(0.92)Mn_(0.04)Co_(0.04),enabling the activation processes.At the same time,the hydrogen incorporation capabilities of TiFe_(0.92)Mn_(0.04)Co_(0.04) can provide more hydrogen diffusion paths,which promote hydrogen dissociation and diffusion.These discoveries demonstrate the advanced nature and importance of combining the in-situ generatedα-Fe with TiFe_(0.92)Mn_(0.04)Co_(0.04).It provides a new strategy for designing highly efficient and stable catalysts for Mg-based hydrogen storage materials.

Glucose-derived hydrothermal carbons as energy storage booster for vanadium redox flow batteries

Fabricating of high performance electrodes by a sustainable and cost effective method is essential to the development of vanadium redox flow batteries(VRFBs).In this work,an effective strategy is proposed to deposit carbon nanoparticles on graphite felts by hydrothermal carbonization method.This in-situ method minimizes the drop off and aggregation of carbon nanoparticles during electrochemical testing.Such integration of felts and hydrothermal carbons(HTC)produces a new electrode that combines the outstanding electrical conductivity of felts with the effective redox active sites provided by the HTC coating layer.The presence of the amorphous carbon layers on the felts is found to be able to promote the mass/charge transfer,and create oxygenated/nitrogenated active sites and hence enhances wettability.Consequently,the most optimized electrode based on a rational approach delivers an impressive electrochemical performance toward VRFBs in wide range of current densities from 200 to 500 mAcm^-2.The voltage efficiency(VE)of GFs-HTC is much higher than the VEs of the pristine GFs,especially at high current densities.It exhibits a 4.18 times increase in discharge capacity over the pristine graphite felt respectively,at a high current density of 400 mAcm^-2.The enhanced performance is attributed to the abundant active sites from amorphous hydrothermal carbon,which facilitates the fast electrochemical kinetics of vanadium redox reactions.This work evidences that the glucose-derived hydrothermal carbons as energy storage booster hold great promise in practical VRFBs application.

Doping sites modulation of T-Nb_(2)O_(5) to achieve ultrafast lithium storage

Heteroatoms doping has been regarded as a promising route to modulate the physiochemical properties of electrode materials,in which the doping sites greatly influence the electrochemical performances.However,very few reports focus on enhancing the lithium storage performances of Nb_(2)O_(5) via heteroatoms doping,yet the effect of different doping sites remains unclear.Herein,nitrogen doping has been proposed to improve the fast-charging capability of orthorhombic Nb_(2)O_(5)(T-Nb_(2)O_(5))via a urea-assisted annealing process.Experimental data and theoretical calculation demonstrate that the N doping sites in T-Nb_(2)O_(5) can be tuned by the heating rate,in which substitutional N can increase the spacing of the Li^(+)transport layer as well as reduce the band gap,while interstitial N can provide an electron-rich environment for Li^(+)transport layer and then reduce the Li^(+)diffusion barrier.Arising from the synergistic effect of N doping at different sites,the N-doped T-Nb_(2)O_(5) without carbon coating delivers impressive rate performance(104.6 mA h g^(-1) at 25 C)as well as enhanced cycle stability with a retention of 70.5%over1000 cycles at 5 C.In addition,the assembled lithium ion capacitor exhibits a high energy density of46.6 Wh kg^(-1) even at high power density of 8.4 kW kg^(-1).

Reducing voltage hysteresis of metal oxide anodes to achieve high energy efficiency for Li-ion batteries

In the past two decades,a lot of high-capacity conversion-type metal oxides have been intensively studied as alternative anode materials for Li-ion batteries with higher energy density.Unfortunately,their large voltage hysteresis(0.8-1.2 V) within reversed conversion reactions results in huge round-trip inefficiencies and thus lower energy efficiency(50%-75%) in full cells than those with graphite anodes.This remains a long-term open question and has been the most serious drawback toward application of metal oxide anodes.Here we clarify the origins of voltage hysteresis in the typical SnO2anode and propose a universal strategy to minimize it.With the established in situ phosphating to generate metal phosphates during reversed conversion reactions in synergy with boosted reaction kinetics by the added P and Mo,the huge voltage hysteresis of 0.9 V in SnO_(2),SnO_(2)-Mo,and 0.6 V in SnO2-P anodes is minimized to 0.3 V in a ternary SnO_(2)-Mo-P(SOMP) composite,along with stable high capacity of 936 mA h g^(-1)after 800 cycles.The small voltage hysteresis can remain stable even the SOMP anode operated at high current rate of10 A g^(-1)and wide-range temperatures from 60 to 30℃,resulting in a high energy efficiency of88.5% in full cells.This effective strategy to minimize voltage hysteresis has also been demonstrated in Fe2O3,Co3O4-basded conversion-type anodes.This work provides important guidance to advance the high-capacity metal oxide anodes from laboratory to industrialization.

In situ formed ultrafine metallic Ni from nickel(Ⅱ) acetylacetonate precursor to realize an exceptional hydrogen storage performance of MgH_(2)-Ni-EG nanocomposite

It has been well known that doping nano-scale catalysts can significantly improve both the kinetics and reversible hydrogen storage capacity of MgH_(2) . However, so far it is still a challenge to directly synthesize ultrafine catalysts(e.g., < 5 nm), mainly because of the complicated chemical reaction processes. Here, a facile one-step high-energy ball milling process is developed to in situ form ultrafine Ni nanoparticles from the nickel acetylacetonate precursor in the MgH_(2) matrix. With the combined action of ultrafine metallic Ni and expanded graphite(EG), the formed MgH_(2)-Ni-EG nanocomposite with the optimized doping amounts of Ni and EG can still release 7.03 wt.% H_(2) within 8.5 min at 300 ℃ after 10 cycles. At a temperature close to room temperature(50 ℃), it can also absorb 2.42 wt.% H_(2) within 1 h. It can be confirmed from the microstructural characterization analysis that the in situ formed ultrafine metallic Ni is transformed into Mg_(2)Ni/Mg_(2)NiH_4 in the subsequent hydrogen absorption and desorption cycles. It is calculated that the dehydrogenation activation energy of the MgH_(2)-Ni-EG nanocomposite is also reduced obviously in comparison with the pure MgH_(2) . Our work provides a methodology to significantly improve the hydrogen storage performance of MgH_(2) by combining the in situ formed and uniformly dispersed ultrafine metallic catalyst from the precursor and EG.

Competitive Redox Chemistries in Vanadium Niobium Oxide for Ultrafast and Durable Lithium Storage

Niobium pentoxide(Nb_(2)O_(5))anodes have gained increasing attentions for high-power lithium-ion batteries owing to the outstanding rate capability and high safety.However,Nb2O5 anode suffers poor cycle stability even after modified and the unrevealed mechanisms have restricted the practical applications.Herein,the over-reduction of Nb5+has been demonstrated to be the critical reason for the capacity loss for the first time.Besides,an effective competitive redox strategy has been developed to solve the rapid capacity decay of Nb_(2)O_(5),which can be achieved by the incorporation of vanadium to form a new rutile VNbO_(4)anode.The highly reversible V^(3+)/V^(2+)redox couple in VNbO_(4)can effectively inhibit the over-reduction of Nb^(5+).Besides,the electron migration from V^(3+)to Nb5+can greatly increase the intrinsic electronic conductivity for VNbO4.As a result,VNbO4 anode delivers a high capacity of 206.1 mAh g^(−1)at 0.1 A g^(−1),as well as remarkable cycle performance with a retention of 93.4%after 2000 cycles at 1.0 A g^(−1).In addition,the assembled lithium-ion capacitor demonstrates a high energy density of 44 Wh kg^(−1)at 5.8 kW kg^(−1).In summary,our work provides a new insight into the design of ultra-fast and durable anodes.

Achieving a novel solvent-free regeneration of LiBH_(4) combining hydrogen storage and production in a closed material cycle

LiBH_(4) has been considered as one of the most promising energy storage materials with its ultrahigh hydrogen capacity,which can supply hydrogen through hydrolysis process or realize hydrogen-to-electricity conversion via anodic oxidation reaction of direct borohydride fuel cells(DBFCs).However,the realization of practical hydrogen applications heavily depends on the effective synthesis of high-purity LiBH_(4) and recycling of the spent fuels(LiBO_(2)·xH_(2)O).The present work demonstrates a convenient and high-efficiency solvent-free strategy for regenerating LiBH_(4) with a maximum yield close to 80%,by retrieving its by-products with MgH_(2) as a reducing agent under ambient conditions.Besides,the hydrogen released from the regeneration course can completely compensate the demand for consumed MgH_(2).The isotopic tracer method reveals that the hydrogen stored in LiBH_(4) comes from both MgH_(2) and coordinated water bound to LiBO_(2).Here,the expensive MgH_(2) can be substituted with the readily available and cost-effective MgH_(2)-Mg mixtures to simplify the regeneration route.Notably,LiBH_(4) catalyzed by CoCl_(2) can stably supply hydrogen to proton exchange membrane fuel cell(PEMFC),thus powering a portable prototype vehicle.By combining hydrogen storage,production and utilization in a closed cycle,this work offers new insights into deploying boron-based hydrides for energy applications.

Cerium-promoted conversion of dinitrogen into high-energy-density material CeN_(6) under moderate pressure

Synthesis pressure and structural stability are two crucial factors for highly energetic materials,and recent investigations have indicated that cerium is an efficient catalyst for N2 reduction reactions.Here,we systematically explore Ce–N compounds through first-principles calculations,demonstrating that the cerium atom can weaken the strength of the N≡N bond and that a rich variety of cerium polynitrides can be formed under moderate pressure.Significantly,P1-CeN_(6) possesses the lowest synthesis pressure of 32 GPa among layered metal polynitrides owing to the strong ligand effect of cerium.The layered structure of P1-CeN_(6) proposed here consists of novel N_(14) ring.To clarify the formation mechanism of P1-CeN_(6),the reaction path Ce+3N2→trans-CeN_(6)→P1-CeN_(6) is proposed.In addition,P1-CeN_(6) possesses high hardness(20.73 GPa)and can be quenched to ambient conditions.Charge transfer between cerium atoms and N_(14) rings plays a crucial role in structural stability.Furthermore,the volumetric energy density(11.20 kJ/cm^(3))of P1-CeN_(6) is much larger than that of TNT(7.05 kJ/cm^(3)),and its detonation pressure(128.95 GPa)and detonation velocity(13.60 km/s)are respectively about seven times and twice those of TNT,and it is therefore a promising high-energy-density material.

Asymmetric Electrolytes Design for Aqueous Multivalent Metal Ion Batteries

With the rapid development of portable electronics and electric road vehicles,high-energy-density batteries have been becoming front-burner issues.Traditionally,homogeneous electrolyte cannot simultaneously meet diametrically opposed demands of high-potential cathode and low-potential anode,which are essential for high-voltage batteries.Meanwhile,homogeneous electrolyte is difficult to achieve bi-or multi-functions to meet different requirements of electrodes.In comparison,the asymmetric electrolyte with bi-or multi-layer disparate components can satisfy distinct requirements by playing different roles of each electrolyte layer and meanwhile compensates weakness of individual electrolyte.Consequently,the asymmetric electrolyte can not only suppress by-product sedimentation and continuous electrolyte decomposition at the anode while preserving active substances at the cathode for high-voltage batteries with long cyclic lifespan.In this review,we comprehensively divide asymmetric electrolytes into three categories:decoupled liquid-state electrolytes,bi-phase solid/liquid electrolytes and decoupled asymmetric solid-state electrolytes.The design principles,reaction mechanism and mutual compatibility are also studied,respectively.Finally,we provide a comprehensive vision for the simplification of structure to reduce costs and increase device energy density,and the optimization of solvation structure at anolyte/catholyte interface to realize fast ion transport kinetics.

Membrane-less MoO_(3-x)@TiO_(2)-bromine battery with excellent rate capability and cyclic stability

Bromine has attracted significant attention as a cathode material for aqueous batteries due to its high reduction potential of 1.05 V(Br_(3)^(-)+2e~-■3Br~-),impressive theoretical specific capacity of 223 mA h g^(-1),and rapid reaction kinetics in the electrolyte.However,searching for compatible anode materials to match with bromine has posed a challenge due to its highly corrosive nature.In this study,we developed oxygen-deficient MoO_(3) with TiO_(2) coating(referred to as MoO_(3-x)@TiO_(2))as an anode material to pair with a bromine cathode in static full batteries.The oxygen deficiency contributes to enhanced electronic and protonic diffusion within the MoO_(3-x)lattice,while the TiO_(2) coating mitigates structural dissolution and proton trapping during cycling.The MoO_(3-x)@TiO_(2) demonstrates fast charge storage kinetics and excellent resistance to bromine corrosion.The impressive compatibility between MoO_(3-x)@TiO_(2) and bromine enables the construction of membrane-less full batteries with exceptional rate capability and cyclic stability.The MoO_(3-x)@TiO_(2)-bromine battery achieves an energy density of70.8 W h kg^(-1)at a power density of 328.1 W kg^(-1),showcasing an impressive long-term cyclic life of 20,000 cycles.Our study provides valuable insights for the development of high-performance aqueous secondary batteries.

Geant4 simulation of fast-electron bremsstrahlung imaging at the HL-3 tokamak

To further research on high-parameter plasma,we plan to develop a two-dimensional hard X-ray(HXR)imaging system at the HL-3 tokamak to measure HXRs with energies ranging from 20 to 300 keV.The application of an array-structured detector ensures that this system can measure HXR-radiation spectra from the entire plasma cross section.Therefore,it is suitable for the study of fast-electron physics,such as radio-frequency wave current drives,fast electrons driving instabilities,and plasma disruptions in fusion research.In this study,we develop a simulation for calculating fast-electron bremsstrahlung in the HL-3 tokamak based on the Monte Carlo simulation code Geant4,in which the plasma geometry and forward scattering of fast-electron bremsstrahlung are considered.The preliminary calculation results indicate that the HXR energy deposi-tion on the detector is symmetrically distributed,even though the plasma distribution is asymmetric owing to the toroidal effect.These simulation results are helpful in constructing the relationship between the energy deposition on the detector and parameter distribution on the plasma cross section during HL-3 experiments.This is beneficial for the reconstruction of the fast-electron-distribution function and for optimizing the design of the HXR-imaging system.

Interfacial chemistry of anode/electrolyte interface for rechargeable magnesium batteries

Rechargeable magnesium batteries(RMBs),as a low-cost,high-safety and high-energy storage technology,have attracted tremendous attention in large-scale energy storage applications.However,the key anode/electrolyte interfacial issues,including surface passivation,uneven Mg plating/stripping,and pulverization after cycling still result in a large overpotential,short cycling life,poor power density,and possible safety hazards of cells,severely impeding the commercial development of RMBs.In this review,a concise overview of recently advanced strategies to address these anode/electroyte interfacial issues is systematically classified and summarized.The design of magnesiophilic substrates,construction of artificial SEI layers,and modification of electrolyte are important and effective strategies to improve the uniformity/kinetics of Mg plating/stripping and achieve the stable anode/electrolyte interface.The key opportunities and challenges in this field are advisedly put forward,and the insights into future directions for stabilizing Mg metal anodes and the anode/electrolyte interface are highlighted.This review provides important references fordeveloping the high-performance and high-safety RMBs.

In situ formed Mg(BH_(4))_(2) for improving hydrolysis properties of MgH_(2)

The hydrolysis of MgH_(2) delivers high hydrogen capacity(15.2 wt%),which is very attractive for real-time hydrogen supply.However,the formation of a surface passivation Mg(OH)_(2) layer and the large excess of H_(2)O required to ensure complete hydrolysis are two key challenges for the MgH_(2) hydrolysis systems.Now,a low-cost method is reported to synthesize MgH_(2)@Mg(BH_(4))_(2) composite via ball-milling MgH_(2) with cheap and widely available B_(2)O_(3)(or B(OH)_(3)).By adding small amounts of B_(2)O_(3),the in-situ formed Mg(BH_(4))_(2) could significantly promote the hydrolysis of MgH_(2).In particular,the MgH_(2)–10 wt%B_(2)O_(3) composite releases 1330.7 mL·g^(−1) H_(2)(close to 80%theoretical hydrogen generation H_(2))in H_(2)O and 1520.4 mL·g^(−1) H_(2)(about 95%)in 0.5 M MgCl_(2) in 60 min at 26℃ with hydrolysis rate of 736.9 mL·g^(−1)·min^(−1) and 960.9 mL·g^(−1)·min^(−1) H_(2) during the first minute of the hydrolysis,respectively.In addition,the MgCl_(2) solution allows repeated use by filtering and exhibits high cycle stability(20 cycles),therefore leading to much reduced capacity loss caused by the excess H_(2)O.We show that by introducing B_(2)O_(3) and recycling the 0.5 M MgCl_(2) solution,the system hydrogen capacity can approach 5.9 wt%,providing a promising hydrogen generation scheme to supply hydrogen to the fuel cells.

Stable operation of highly loaded pure Si-Fe anode under ambient pressure via carboxy silane-directed robust solid electrolyte interphase

Incorporation of higher content Si anode material beyond 5 wt% to Li-ion batteries(LIBs)is challenging,owing to large volume change,swelling,and solid electrolyte interphase(SEI)instability issues.Herein,a strategy of diacetoxydimethylsilane(DAMS)additive-directed SEI stabilization is proposed for a stable operation of Si-0.33FeSi_(2)(named as Si-Fe)anode without graphite,which provides siloxane inorganics and organics enrichment that compensate insufficient passivation of fluoroethylene carbonate(FEC)additive and reduce a dependence on FEC.Unprecedented stable cycling performance of highly loaded(3.5 mA h cm^(-2))pure Si-Fe anode is achieved with 2 wt%DAMS combined with 9 wt%FEC additives under ambient pressure,yielding high capacity 1270 mA h g^(-1)at 0.5 C and significantly improved capacity retention of 81% after 100 cycles,whereas short circuit and rapid capacity fade occur with FEC only additive.DAMS-directed robust SEI layer dramatically suppresses swelling and particles crossover through separator,and therefore prevents short circuit,demonstrating a possible operation of pure Si or Sidominant anodes in the next-generation high-energy-density and safe LIBs.

Precise construction of RuPt dual single-atomic sites to optimize oxygen electrocatalytic behaviors for high-performance Zn-air batteries

The development of redox bifunctional electrocatalysts with high performance,low cost,and long lifetimes is essential for achieving clean energy goals.This study proposed an atom capture strategy for anchoring dual single atoms(DSAs)in a zinc-zeolitic imidazolate framework(Zn-ZIF),followed by calcination under an N_(2) atmosphere to synthesize ruthenium-platinum DSAs supported on a nitrogendoped carbon substrate(RuPt DSAs-NC).Theoretical calculations showed that the degree of Ru 5dxz-~*O 2p_x orbital hybridization was high when^(*)O was adsorbed at the Ru site,indicating enhanced covalent hybridization of metal sites and oxygen ligands,which benefited the adsorption of intermediate species.The presence of the RuPtN_6 active center optimized the absorption-desorption behavior of intermediates,improving the electrocatalytic performance of the oxygen reduction reaction(ORR)and the oxygen evolution reaction(DER),RuPt DSAs-NC exhibited a 0.87 V high half-wave potential and a 268 mV low overpotential at 10 mA cm^(-2)in an alkaline environment.Furthermore,rechargeable zinc-air batteries(ZABs)achieved a peak power density of 171 MW cm^(-2).The RuPt DSAs-NC demonstrated long-term cycling for up to 500 h with superior round-trip efficiency.This study provided an effective structural design strategy to construct DSAs active sites for enhanced electrocata lytic performance.

Mode coupling with Fabry-Perot modes in photonic crystal slabs

Fabry–Perot(FP)modes are a class of fundamental resonances in photonic crystal(PhC)slabs.Owing to their low quality factors,FP modes are frequently considered as background fields with their resonance nature being neglected.Nevertheless,FP modes can play important roles in some phenomena,as exemplified by their coupling with guided resonance(GR)modes to achieve bound states in the continuum(BIC).Here,we further demonstrate the genuine resonance mode capability of FP modes PhC slabs.Firstly,we utilize temporal coupled-mode theory to obtain the transmittance of a PhC slab based on the FP modes.Secondly,we construct exceptional points(EPs)in both momentum and parameter spaces through the coupling of FP and GR modes.Furthermore,we identify a Fermi arc connecting two EPs and discuss the far-field polarization topology.This work elucidates that the widespread FPs in PhC slabs can serve as genuine resonant modes,facilitating the realization of desired functionalities through mode coupling.

A perspective on the key factors of safety for rechargeable magnesium batteries

Rechargeable Mg batteries(RMBs)have become one of the best subsitutes for lithium-ion batteries due to the high volumetric capacity,abundant resources,and uniform plating behavior of Mg metal anode.However,the safety hazard induced by the formation of high-modulue Mg dendrites under a high current density(10 mA cm^(-1))was still revealed in recent years.It has forced researchers to re-examine the safety of RMBs.In this review,the intrinsic safety factors of key components in RMBs,such as uneven plating,pitting and flammability of Mg anode,heat release and crystalline water decomposition of cathode,strong corrosion,low oxidition stability and flammability of electrolytes,and soforth,are systematacially summarized.Their origins,formation mechanisms,and possible safety hazards are deeply discussed.To develop high-performance Mg anode,current strategies including designing artificial SEI,three-dimensional substrates,and Mg alloys are summarized.For practical electrolytes,the configurations of boron-centered anions and simple Mg salts and the functionalized solvent with high boiling point and low flammability are suggested to comprehensively design.In addition,the future study should more focus on the investigation on the thermal runaway and decomposition of cathode materials and separa-tors.This review aims to provide fundamental insights into the relationship between electrochemistry and safety,further promoting the sustainable development of RMBs.

Thermodynamics-directed bulk/grain-boundary engineering for superior electrochemical durability of Ni-rich cathode

Introducing high-valence Ta element is an essential strategy for addressing the structu ral deterioration of the Ni-rich LiNi_(1-x-y)Co_(x)Mn_(y)O_(2)(NCM)cathode,but the enlarged Li/Ni cation mixing leads to the inferior rate capability originating from the hindered Li~+migration.Note that the non-magnetic Ti~(4+)ion can suppress Li/Ni disorder by removing the magnetic frustration in the transition metal layer.However,it is still challenging to directionally design expected Ta/Ti dual-modification,resulting from the complexity of the elemental distribution and the uncertainty of in-situ formed coating compounds by introducing foreign elements.Herein,a LiTaO_3 grain boundary(GB)coating and bulk Ti-doping have been successfully achieved in LiNi_(0.834)Co_(0.11)Mn_(0.056)O_(2) cathode by thermodynamic guidance,in which the structural formation energy and interfacial binding energy are employed to predict the elemental diffusion discrepancy and thermodynamically stable coating compounds.Thanks to the coupling effect of strengthened structural/interfacial stability and improved Li~+diffusion kinetics by simultaneous bulk/GB engineering,the Ta/Ti-NCM cathode exhibits outstanding capacity retention,reaching 91.1%after 400 cycles at 1 C.This elaborate work contributes valuable insights into rational dual-modification engineering from a thermodynamic perspective for maximizing the electrochemical performances of NCM cathodes.

Regulating Melting Process in the Energy Storage of Solid-Liquid PCM based on Double MRT-LBM Simulation

The melting process of solid-liquid phase change materials(PCM)has a significant impact on their energy storage performance.To more effectively apply solid-liquid PCM for energy storage,it is crucial to study the regulation of melting process of solid-liquid PCM,which is numerically investigated based on double multiple relaxation time lattice Boltzmann method(MRT-LBM)in this work.In this work we pay more attention to the effects of different Stefan numbers(Ste)and Rayleigh numbers(Ra)on the melting process.The results indicate that the PCM melting is greatly influenced by the Ste number and Ra number,which can be divided into the heat conduction dominant stage and the convection dominant stage,according to the onset time of convection Fo_(C).In order to describe the contribution of the heat conduction dominant stage to the whole melting process quantitatively,we firstly propose the ratio of the heat conduction dominant stage R_(pc),which can be defined as the ratio of Fo_(C)to the complete melting time Fo_(M).R_(pc)gradually decreases as the Ra number increases,and when the Ste number rises:R_(pc)=90.0%when Ste=1.0 and Ra=1×10^(5),R_(pc)=39.6%when Ste=0.1 and Ra=1×10^(5),and R_(pc)=14.0%when Ste=1.0 and Ra=1×10~7.A regime map about the effects of different Ste numbers and Ra numbers on R_(pc)has been further summarized.The discovered findings would be helpful in regulating melting process in the energy storage of solid-liquid PCM.