Insights into Nano-and Micro-Structured Scaffolds for Advanced Electrochemical Energy Storage

Adopting a nano-and micro-structuring approach to fully unleashing the genuine potential of electrode active material benefits in-depth understandings and research progress toward higher energy density electrochemical energy stor-age devices at all technology readiness levels.Due to various challenging issues,especially limited stability,nano-and micro-structured(NMS)electrodes undergo fast electrochemical performance degradation.The emerging NMS scaffold design is a pivotal aspect of many electrodes as it endows them with both robustness and electrochemical performance enhancement,even though it only occupies comple-mentary and facilitating components for the main mechanism.However,extensive efforts are urgently needed toward optimizing the stereoscopic geometrical design of NMS scaffolds to minimize the volume ratio and maximize their functionality to fulfill the ever-increasing dependency and desire for energy power source supplies.This review will aim at highlighting these NMS scaffold design strategies,summariz-ing their corresponding strengths and challenges,and thereby outlining the potential solutions to resolve these challenges,design principles,and key perspectives for future research in this field.Therefore,this review will be one of the earliest reviews from this viewpoint.

Facet-dependent catalytic activity of two-dimensional Ti_(3)C_(2)T_(x) MXene on hydrogen storage performance of MgH_(2)

Two-dimensional Ti_(3)C_(2)T_(x) MXenes exposing different active facets are introduced into MgH_(2), and their catalytic effects are systematically investigated in depth through experimental and theoretical approaches. Excluding factors such as interlayer space, surface functional groups and experimental contingency, the exposed facets is considered to be the dominant factor for catalytic activity of Ti_(3)C_(2)T_(x) towards MgH_(2).More exposed edge facets of Ti_(3)C_(2)T_(x) displays higher catalytic activity than that with more exposed basal facets, which also leads to different rate-controlling steps of MgH_(2) in the de/hydrogenation process. The low work function, strong hydrogen affinity and high content of in situ metallic Ti for the edge facet contribute the high catalytic activity. This work will give insights into the structural design of two-dimensional Ti_(3)C_(2)T_(x) MXene used for enhancing the catalytic activity in various fields.

Layered double hydroxides as electrode materials for flexible energy storage devices

To prevent and mitigate environmental degradation,high-performance and cost-effective electrochemical flexible energy storage systems need to be urgently developed.This demand has led to an increase in research on electrode materials for high-capacity flexible supercapacitors and secondary batteries,which have greatly aided the development of contemporary digital communications and electric vehicles.The use of layered double hydroxides(LDHs)as electrode materials has shown productive results over the last decade,owing to their easy production,versatile composition,low cost,and excellent physicochemical features.This review highlights the distinctive 2D sheet-like structures and electrochemical characteristics of LDH materials,as well as current developments in their fabrication strategies for expanding the application scope of LDHs as electrode materials for flexible supercapacitors and alkali metal(Li,Na,K)ion batteries.

Design of Flexible Films Based on Kinked Carbon Nanofibers for High Rate and Stable Potassium-Ion Storage

With the emergence of wearable electronics,flexible energy storage materials have been extensively studied in recent years.However,most studies focus on improving the electrochemical properties,ignoring the flexible mechanism and structure design for flexible electrode materials with high rate capacities and long-time stability.In this study,porous,kinked,and entangled network structures are designed for highly flexible fiber films.Based on theoretical analysis and finite element simulation,the bending degree of the porous structure(30%porosity)increased by 192%at the micro-level.An appropriate increase in kinking degree at the meso-level and contact points in entanglement network at the macro-level are beneficial for the flexibility of fiber films.Therefore,a porous and entangled network of sulfur-/nitrogen-co-doped kinked carbon nanofibers(S/N-KCNFs)is synthesized.The nanofiber films synthesized from melamine as nitrogen sources and segmented vulcanization exhibited a porous,kinked,and entangled network structure,and the stretching degree increased several times.The flexible S/N-KCNFs anode delivered a higher rate performance of 270 mAh g−1 at a current density of 2000 mA g−1 and a higher capacity retention rate of 93.3%after 2000 cycles.Moreover,the foldable pouch cell assembled by potassium-ion hybrid supercapacitor operated safely at large-angle bending and showed long-time stability of 88%capacity retention after 4000 cycles.This study provides a new idea and strategy for the flexible structure design of high-performance potassium-ion storage materials.

High-throughput computational screening and design of nanoporous materials for methane storage and carbon dioxide capture

The globally increasing concentrations of greenhouse gases in atmosphere after combustion of coal-or petroleum-based fuels give rise to tremendous interest in searching for porous materials to efficiently capture carbon dioxide(CO_2) and store methane(CH4), where the latter is a kind of clean energy source with abundant reserves and lower CO_2 emission. Hundreds of thousands of porous materials can be enrolled on the candidate list, but how to quickly identify the really promising ones, or even evolve materials(namely, rational design high-performing candidates) based on the large database of present porous materials? In this context, high-throughput computational techniques, which have emerged in the past few years as powerful tools, make the targets of fast evaluation of adsorbents and evolving materials for CO_2 capture and CH_4 storage feasible. This review provides an overview of the recent computational efforts on such related topics and discusses the further development in this field.

In-plane micro-sized energy storage devices:From device fabrication to integration and intelligent designs

The rapid development of micro-electronics raises the demand of their power sources to be simplified,miniaturized and highly integratable with other electronics on a chip.In-plane Micro-sized energy storage devices(MESDs),which are composed of interdigitated electrodes on a single chip,have aroused particular attentions since they could be easily integrated with other miniaturized electronics,reducing the complexity of overall chip design via removing complex interconnections with bulky power sources.This review highlights the achievements in the device fabrication of in-plane MESDs,as well as their integration and intelligent designs.We also discussed the current challenges and future perspectives for the development of in-plane MESDs.

Design and operation problems related to water curtain system forunderground water-sealed oil storage caverns

The underground water-sealed storage technique is critically important and generally accepted for the national energy strategy in China. Although several small underground water-sealed oil storage caverns have been built in China since the 1970s, there is still a lack of experience for large-volume underground storage in complicated geological conditions. The current design concept of water curtain system and the technical instruction for system operation have limitations in maintaining the stability of surrounding rock mass during the construction of the main storage caverns, as well as the long-term stability. Although several large-scale underground oil storage projects are under construction at present in China, the design concepts and construction methods, especially for the water curtain system, are mainly based on the ideal porosity medium flow theory and the experiences gained from the similar projects overseas. The storage projects currently constructed in China have the specific features such as huge scale, large depth, multiple-level arrangement, high seepage pressure, complicated geological conditions, and high in situ stresses, which are the challenging issues for the stability of the storage caverns. Based on years’ experiences obtained from the first large-scale （millions of cubic meters） underground water-sealed oil storage project in China, some design and operation problems related to water curtain system during project construction are discussed. The drawbacks and merits of the water curtain system are also presented. As an example, the conventional concept of “filling joints with water” is widely used in many cases, as a basic concept for the design of the water curtain system, but it is immature. In this paper, the advantages and disadvantages of the conventional concept are pointed out, with respect to the long-term stability as well as the safety of construction of storage caverns. Finally, new concepts and principles for design and construction of the underground water-sealed oil storage caverns are proposed.

Model-based optimal design of phase change ionic liquids for efficient thermal energy storage

The selection of phase change material(PCM)plays an important role in developing high-efficient thermal energy storage(TES)processes.Ionic liquids(ILs)or organic salts are thermally stable,non-volatile,and non-flammable.Importantly,researchers have proved that some ILs possess higher latent heat of fusion than conventional PCMs.Despite these attractive characteristics,yet surprisingly,little research has been performed to the systematic selection or structural design of ILs for TES.Besides,most of the existing work is only focused on the latent heat when selecting PCMs.However,one should note that other properties such as heat capacity and thermal conductivity could affect the TES performance as well.In this work,we propose a computer-aided molecular design(CAMD)based method to systematically design IL PCMs for a practical TES process.The effects of different IL properties are simultaneously captured in the IL property models and TES process models.Optimal ILs holding a best compromise of all the properties are identified through the solution of a formulated CAMD problem where the TES performance of the process is maximized.[MPyEtOH][TfO]is found to be the best material and excitingly,the identified top nine ILs all show a higher TES performance than the traditional PCM paraffin wax at 10 h thermal charging time.

Chemical interaction motivated structure design of layered metal carbonate hydroxide/MXene composites for fast and durable lithium ion storage

Rational architecture design has turned out to be an effective strategy in improving the electrochemical performance of electrode materials for batteries.However,an elaborate structure that could simultaneously endow active materials with promoted reaction reversibility,accelerated kinetic and restricted volume change still remains a huge challenge.Herein,a novel chemical interaction motivated structure design strategy has been proposed,and a chemically bonded Co(CO_(3))_(0.5)OH·0.11 H_(2)O@MXene(CoCH@MXene)layered-composite was fabricated for the first time.In such a composite,the chemical interaction between Co^(2+)and MXene drives the growth of smaller-sized CoCH crystals and the subsequent formation of interwoven CoCH wires sandwiched in-between MXene nanosheets.This unique layered structure not only encourages charge transfer for faster reaction dynamics,but buffers the volume change of CoCH during lithiation-delithiation process,owing to the confined crystal growth between conductive MXene layers with the help of chemical bonding.Besides,the sandwiched interwoven CoCH wires also prevent the stacking of MXene layers,further conducive to the electrochemical performance of the composite.As a result,the as-prepared CoCH@MXene anode demonstrates a high reversible capacity(903.1 mAh g^(-1)at 100 mA g^(-1))and excellent cycling stability(maintains 733.6 mAh g^(-1)at1000 mA g^(-1)after 500 cycles)for lithium ion batteries.This work highlights a novel concept of layerby-layer chemical interaction motivated architecture design for futuristic high performance electrode materials in energy storage systems.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part I:A Conductive and Convective Theoretical Heat Transfer Analysis for Molten Salt Cylindrical Shells at 565℃ and 700℃

In this paper a full theoretical thermal analysis of a large molten salt container,80-foot in diameter and 46-foot high,including a four-foot elliptic shell roof,is presented for two temperatures,the standard 565℃ and a futuristic 700℃,which substantially improves the efficiency of the molten salt containers through the use of a highly stable chloride salt called SS700(SaltStream 700).The theoretical analysis includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed theoretically using conductive heat transfer,however the area surrounding the soil surface around the bottom of the molten salt storage tank had convective heat transfer analysis included.The final designs presented in this paper seek to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃,which determines the thicknesses of the fiberglass and firebrick insulation.

Molten Salts and Applications Ⅱ: 565℃ Molten Salt Solar Energy Storage Design, Corrosion, and Insulation

Excess energy from various sources can be stored in molten salts (MS) in the 565 °C range. Large containers can be used to store energy at excess temperatures in order to generate eight hours or more of electricity, depending on the container size, to be used during peak demand hours or at night for up to a week. Energy storage allows for a stable diurnal energy supply and can reduce the fluctuation due to weather conditions experienced at thermal solar power stations. Supported by Office of Naval Research (ONR), this paper discusses the design considerations for molten salt storage tanks. An optimal molten salt storage tank design layout is presented, as well as alternative designs for the storage tanks. In addition, the costs and corrosion effects of various molten salts are discussed in order to show the effects these considerations have on the design process.

The design and engineering strategies of metal tellurides for advanced metal-ion batteries

Owning various crystal structures and high theoretical capacity,metal tellurides are emerging as promising electrode materials for high-performance metal-ion batteries(MBs).Since metal telluride-based MBs are quite new,fundamental issues raise regarding the energy storage mechanism and other aspects affecting electrochemical performance.Severe volume expansion,low intrinsic conductivity and slow ion diffusion kinetics jeopardize the performance of metal tellurides,so that rational design and engineering are crucial to circumvent these disadvantages.Herein,this review provides an in-depth discussion of recent investigations and progresses of metal tellurides,beginning with a critical discussion on the energy storage mechanisms of metal tellurides in various MBs.In the following,recent design and engineering strategies of metal tellurides,including morphology engineering,compositing,defect engineering and heterostructure construction,for high-performance MBs are summarized.The primary focus is to present a comprehensive understanding of the structural evolution based on the mechanism and corresponding effects of dimension control,composition,electron configuration and structural complexity on the electrochemical performance.In closing,outlooks and prospects for future development of metal tellurides are proposed.This work also highlights the promising directions of design and engineering strategies of metal tellurides with high performance and low cost.

Performance Analysis of Constant-Pressure Pumped Hydro Combined with Compressed Air Energy Storage System Considering Off-Design Model of Compressor

With the wide application of renewable energy, energy storage technology has become a research hotspot. In order to overcome the shortcomings of energy loss caused by compression heating in compressed air energy storage technology, a novel constant-pressure pumped hydro combined with compressed air energy storage system was proposed. To deepen the understanding of the system and make the analysis closer to reality, this paper adopted an off-design model of the compressor to calculate and analyze the effect of key parameters on system thermodynamics performance. In addition, the results of this paper were compared with previous research results, and it was found that the current efficiency considering the off-design model of compressor was generally 2% - 5% higher than the previous efficiency. With increased preset pressure or with decreased terminal pressure, both the previous efficiency and current efficiency of the system increased. The exergy destruction coefficient of the throttle valve reached 4%. System efficiency was more sensitive to changes in water pump efficiency and hydroturbine efficiency.

Design of Mooring System for Oil Storage Vessels

The floating oil storage system has been proposed as a new facility for Strategic Petroleum Reserve (SPR) in China. Mooring is one of the key technologies to ensure the safety, reliability, and performance of the oil storage system. This paper describes the concept, analysis, design and reliability of the mooring system. For mooring system design of these oil vessels, analysis is essential of the behavior of the vessel in connection with mooring facilities of nonlinear resilience. A nonlinear mathematical model for analyzing a moored vessel is established and solved. Some results of numerical simulations are presented. Assessment of the safety regarding the mooring system in terms of failure probability is carried out. Another simulation model for calculating the failure probability of the mooring system is proposed. The design parameters that have an influence on the characteristics of the failure probability have been identified. The simulation results,show that the mooring system has an annual reliability value of 0.999998. The proposed simulation method is proved to be effective in quantitative evaluation of the safety of the mooring system for floating oil storage vessels.

Optimal Design for Main Dimensions of a 75000t Floating Production and Storage Vessel

The basis, process and results of the demonstration of the main dimensions of a 75000t floating production and storage vessel are discussed in this paper. A simple but reliable orthogonal design method is applied in the main dimension optimization. The ideas of gradual approximation and feedback from various aspects are put into effect. During the demonstration, in order to make the model tally with the actual situation, the draft design is closely related to the computational analysis, so that the demonstration model can be verified at any time; the handling of the overall system is closely related to the research of each item, which is beneficial not only to the mastery of various regularities, but also to the balance of decisions. Finally, according to the computational results and the regularities obtained from analysis, the main dimensions are determined.

Comprehensive Molten Salt Storage Shell and Supporting Structure Design and Analysis-Part II:A Conductive and Convective Numerical Finite Element Heat Transfer Analysis for Molten Salt Cylindrical Shells at 700℃,and Comparison with Theoretical Analysis

In this paper a finite element thermal analysis model-using COMSOL-of a large molten salt container,80-foot in diameter and 46-foot high that includes a four-foot elliptic shell roof,is presented for a futuristic 700℃ design,which uses a highly stable chloride salt called SS700(SaltStream 700)that improves the efficiency of the tank when compared to the traditional 565℃.The FEA(finite element analysis)includes conductive and convective heat transfer analysis in the steel container,elliptic roof shell,the fiberglass insulation,and firebrick insulation,and includes thermal insulation designs to safeguard against energy losses at high temperatures.The underlying soil and the high temperature concrete foundation were analyzed by finite element using conductive heat transfer,however the area surrounding the soil surface around the bottom of the MS storage tank had convective heat transfer analysis included.The finite elements analyses presented are to verify the final fiberglass and firebrick insulation designs,which seeks to limit heat losses to a maximum of 250 W/m^(2) while being able to operate at a minimum external ambient temperature of-10℃.These results are also compared to previously calculated theoretical results.

Design of Zr-based AB_2 type hydrogen storage alloys

The influences of the ratio of the radius of atom A（rA） to radius of atom B（rB）, electronegativity and electron number were discussed on the Laves phase formation and the characteristics of Zr-based AB2 type hydrogen storage alloy. An enthalpy model of Zr-based AB2 alloy was obtained from known data and twelve Zr-based alloys were designed to test the model. The results show that the predicted values are in good agreement with the experimental values. The model can be used for predicting enthalpy values of Zr-based hydrogen storage alloys and settles a foundation for experiments.

Design Strategy of Diagonal Compressors in Compressed Air Energy Storage System

As a kind of large-scale physical energy storage,compressed air energy storage(CAES)plays an important role in the construction of more efficient energy system based on renewable energy in the future.Compared with traditional industrial compressors,the compressor of CAES has higher off-design performance requirements.From the perspective of design,it needs to pay attention not only to the performance of the design point,but also to the performance of all the stable working range.However,from the previous literature,no diagonal compressor was used in CAES which can meet the requirements,which also reflects the design program can be further improved.Therefore,this paper studies the design strategy of high efficient diagonal compressor for large-scale CAES,and gives the complete strategy algorithms used for different program modules.The pressure ratio,isentropic efficiency and stable working range are comprehensively considered.In the design process,the criteria for the key parameters of the diagonal flow angle of the diagonal compressor are given for the first time.The results show that the isentropic efficiency at the design point is 92.7%,the total pressure ratio is1.97,and the stable working range exceeds 20%,which meets the design requirements of the compressor for CAES and exceeds the overall performance of the previous compressors in the entire working range.

Design strategies of high-performance lead-free electroceramics for energy storage applications

A greater number of compact and reliable electrostatic capacitors are in demand due to the Internet of Things boom and rapidly growing complex and integrated electronic systems,continuously promoting the development of high-energy-density ceramic-based capacitors.Although significant successes have been achieved in obtaining high energy densities in lead-based ferroelectric ceramics,the utilization of lead-containing ceramies has been restricted due to environmental and health hazards of lead.Lead-free ferroelectric ceramics have garnered tremendous attention and are expected to replace lead-based ceramics in the near future.However,the energy density of lead-free ceramics is still lagging behind that of lead-containing cou.nterparts,severely limiting their applications.Significant efforts have been made to enhance the energy storage performance of lead-free ceramics using multi-scale design strategies,and exciting progress has been achieved in the past decade.This review briefly discusses the energy storage mechanism and fundamental characteristics of a dielectric capacitor,summarizes and compares the state-of-the-art design strategies for high-energy-density lead-free ceramics,and highlights several critical issues and requirements for industrial production.The prospects and challenges of lead-free ceramics for energy storage applications are also discussed.