Ambient-Condition Strategy for Production of Hollow Ga_(2)O_(3)@rGO Crystalline Nanostructures Toward Efficient Lithium Storage

Crystallineγ-Ga_(2)O_(3)@rGO core-shell nanostructures are synthesized in gram scale,which are accomplished by a facile sonochemical strategy under ambient condition.They are composed of uniformγ-Ga_(2)O_(3)nanospheres encapsulated by reduced graphene oxide(rGO)nanolayers,and their formation is mainly attributed to the existed opposite zeta potential between the Ga_(2)O_(3)and rGO.The as-constructed lithium-ion batteries(LIBs)based on as-fabricatedγ-Ga_(2)O_(3)@rGO nanostructures deliver an initial discharge capacity of 1000 mAh g^(-1)at 100 mA g^(-1)and reversible capacity of 600 mAh g^(-1)under 500 mA g^(-1)after 1000 cycles,respectively,which are remarkably higher than those of pristineγ-Ga_(2)O_(3)with a much reduced lifetime of 100 cycles and much lower capacity.Ex situ XRD and XPS analyses demonstrate that the reversible LIBs storage is dominant by a conversion reaction and alloying mechanism,where the discharged product of liquid metal Ga exhibits self-healing ability,thus preventing the destroy of electrodes.Additionally,the rGO shell could act robustly as conductive network of the electrode for significantly improved conductivity,endowing the efficient Li storage behaviors.This work might provide some insight on mass production of advanced electrode materials under mild condition for energy storage and conversion applications.

Average temperature calculation for straight single-row-piped frozen soil wall

The average temperature of frozen soil wall is an essential parameter in the process of design, construction, and safety manage- ment of artificial ground freezing engineering. It is the basis of calculating frozen soil＇s mechanical parameters, fiarther prediction of bearing capacity and, ultimately, safety evaluation of the frozen soil wall. Regarding the average temperature of sin- gle-row-piped frozen soil wall, this paper summarizes several current calculation methods and their shortcomings. Furthermore, on the basis of Bakholdin＇s analytical solution for the temperature field under straight single-row-piped freezing, two new calcula- tion models, namely, the equivalent trapezoid model and the equivalent triangle model, are proposed. These two approaches are used to calculate the average temperature of a certain cross section which indicates the condition of the whole frozen soil wall. Considering the possible parameter range according to the freezing pipe layout that might be applied in actual construction, this paper compares the average temperatures of frozen soil walls obtained by the equivalent trapezoid method and the equivalent tri- angle method with that obtained by numerical integration of Bakholdin＇s analytical solution. The results show that the discrepancies are extremely small and these two new approaches are better than currently prevailing methods. However, the equivalent triangle method boasts higher accuracy and a simpler formula compared with the equivalent trapezoid method.

Free-standing ternary metallic sulphides/Ni/C-nanofiber anodes for high-performance lithium-ion capacitors

As a promising energy-storage device,the hybrid lithium-ion capacitor coupling with both a large energy density battery-type anode and a high power density capacitor-type cathode is attracting great attention.For the sake of improving the energy density of hybrid lithium-ion capacitor,the free-standing anodes with good electrochemical performance are essential.Herein,we design an effective electrospinning strategy to prepare free-standing MnS/Co4S3/Ni3S2/Ni/C-nanofibers(TMSs/Ni/C-NFs)film and firstly use it as a binder-free anode for hybrid lithium-ion capacitor.We find that the carbon nanofibers can availably prevent MnS/Co4S3/Ni3S2/Ni nanoparticles from aggregation as well as significantly improve the electrochemical performance.Therefore,the binder-free TMSs/Ni/C-NFs membrane displays an ultrahigh reversible capacity of 1246.9 m Ah g-1at 100 m A g-1,excellent rate capability(398 mAh g-1 at2000 mA g-1),and long-term cyclic endurance.Besides,we further assemble the hybrid lithium-ion capacitor,which exhibits a high energy density of 182.0 Wh kg-1at 121.1 W kg-1(19.0 Wh kg-1 at 3512.5 W kg-1)and remarkable cycle life.

Facet-dependent Thermal and Electrochemical Degradation of Lithium-rich Layered Oxides

Lithium-rich layered oxides(LLOs)are promising candidate cathode materials for safe and inexpensive high-energy-density Li-ion batteries.However,oxygen dimers are formed from the cathode material through oxygen redox activity,which can result in morphological changes and structural transitions that cause performance deterioration and safety concerns.Herein,a flake-like LLO is prepared and aberration-corrected scanning transmission electron microscopy(STEM),in situ high-temperature X-ray diffraction(HT-XRD),and soft X-ray absorption spectrum(sXAS)are used to explore its crystal facet degradation behavior in terms of both thermal and electrochemical processes.Void-induced degradation behavior of LLO in different facet reveals significant anisotropy at high voltage.Particle degradation originates from side facets,such as the(010)facet,while the close(003)facet is stable.These results are further understood through ab initio molecular dynamics calculations,which show that oxygen atoms are lost from the{010}facets.Therefore,the facet degradation process is that oxygen molecular formed in the interlayer and accumulated in the ab plane during heating,which result in crevice-voids in the ab plane facets.The study reveals important aspects of the mechanism responsible for oxygen-anionic activity-based degradation of LLO cathode materials used in lithium-ion batteries.In particular,this study provides insight that enables precise and efficient measures to be taken to improve the thermal and electrochemical stability of an LLO.

Dynamic Simulation of Distribution Networks Using Multi-stage Discontinuous Galerkin Method

Dynamic simulation plays a fundamental role in security evaluation of distribution networks(DNs).However,the strong stiffness and non-linearity of distributed generation(DG)models in DNs bring about burdensome computation and noteworthy instability on traditional methods which hampers the rapid response of simulation tool.Thus,a novel L-stable approximate analytical method with high accuracy is proposed to handle these problems.The method referred to as multistage discontinuous Galerkin method(MDGM),first derives approximate analytical solutions(AASs)of state variables which are explicit symbolic expressions concerning system states.Then,in each time window,it substitutes values for symbolic variables and trajectories of state variables are obtained subsequently.This paper applies MDGM to DG models to derive AASs.Local-truncation-error-based variable step size strategy is also developed to further improve simulation efficiency.In addition,this paper establishes detailed MDGM-based dynamic simulation procedure.From case studies on a numerical problem,a modified 33-bus system and a practical large-scale DN,it can be seen that proposed method demonstrates fast and dependable performance compared with the traditional trapezoidal method.

Analysis for integrated energy system:Benchmarking methods and implementation

The selection of suitable models and solutions is a fundamental requirement for con-ducting energy flow analysis in integrated energy systems(IES).However,this task is challenging due to the vast number of existing models and solutions,making it difficult to comprehensively compare scholars'studies with current work.In this paper,we aim to address this issue by presenting a comprehensive overview of mainstream IES models and clarifying their relationships,thereby providing guidance for scholars in selecting appro-priate models.Additionally,we introduce several widely used solvers for solving algebraic and differential equations,along with their detailed implementations in the energy flow analysis of IES.Furthermore,we conduct extensive testing and demonstration of these models and methods in various cases to establish benchmarking datasets.To facilitate reproducibility,verification and comparisons,we provide open‐source access to these datasets,including system data,analysis settings and implementations of the various solvers in the mainstream models.Scholars can utilise the provided datasets to reproduce the results,verify the findings and perform comparative analyses.Moreover,they have the flexibility to customise these settings according to their specific requirements.

Improving Operational Flexibility of Integrated Energy Systems Through Operating Conditions Optimization of CHP Units

As a type of energy system with bright application prospects,the integrated energy system(IES)is environmentally friendly and can improve overall energy efficiency.Tight coupling between heat and electricity outputs of combined heat and power(CHP)units limits IES operational flexibility significantly.To resolve this problem,in this paper,we integrate operating mode optimization of the natural gas combined cycle CHP unit(NGCC-CHP)into dispatch of the IES to improve flexibility of the IES.First,we analyze operational modes of the CHP units from the perspectives of thermal processes and physical mechanisms,including the adjustable extraction mode,backpressure mode,and switching mode.Next,we propose an explicit mathematical model for full-mode operation of the CHP units,in which the heat-electricity feasible region,switching constraints,and switching costs are all formulated in detail.Finally,a novel economic dispatch model is proposed for a heat and electricity IES,which uses the full-mode operation of CHP units to improve operational flexibility.The Fortuny-Amat transformation is used to convert the economic dispatch model into a mixed-integer quadratic programming model,which can then be solved using commercial solvers.Case studies demonstrate the proposed method can reduce operational costs and obviously promotes wind power utilization.