This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 3193 papers online from Dec 1, 2020 to Jan 31, 2021. 100 of them were selected to be highlighted. High-nickel ternary layered and Li-rich oxide cathode materials are still under extensive investigations for surface coating, preparation of precursors and structural evolution with cycling. The methods for improving the cycling properties of Si-based anode focus on coating Si particles and 3D structure design of the composite Si/C and Si/Cu anodes, while 3D structure design and surface reconstruction are used for metallic lithium anode. Solid state electrolyte including oxide, sulfide and composite materials have been studied. Meanwhile, large efforts are still devoted to liquid electrolytes for the optimizing the electrolyte for graphite anode, the high-voltage spinel and LiCoO₂, ternary layered, and Li-rich oxide cathode materials. For solid-state batteries, there are a few papers related to the design of composite cathode, bi-layer electrolyte, and modification of Li metal anodes. Other relevant works are also presented to the 3D structure design of S-based cathodes and the effects of electron-conductive additives in to electrodes. The characterization techniques are focused on Li deposition, swelling of Si-based anode, micostructures of cathodes and gassing of cells. Theoretical simulations is mainly on the formation mechanism of SEI and kinetics of thick electrodes. The interfaces of layered cathode and solid/liquid electrolyte, liquid electrolyte/anode, and solid state electrolyte/Li are also widely studied.

The rapid development of electric vehicle (EV) and hybrid electric vehicle (HEV) has put forward higher requirements on the energy density and cycle life of lithium-ion batteries. Cathode material is one of the most critical parts in determining the performance of lithium-ion batteries. Lithium-rich manganese-based layered oxides (LMLOs) are considered to be the most promising cathode materials for next-generation power batteries due to their high specific capacity (>250 mA·h/g), high work voltage, low cost and high safety. However, low initial coulombic efficiency, severe voltage fading, and poor cycle and rate performance prevent their practical application. This review summarizes the causes of the above-mentioned problems, including irreversible oxygen release, irreversible transformation from layered structure to spinel phase, and migration and valence change of transition metal ions. What’s more, some typical solutions reported by domestic and overseas researchers in recent years are also summarized from the following four aspects: surface coating, surface/bulk doping, crystal-facet control, and surface integrated structure, respectively.

As a novel anode material for lithium-ion batteries, red phosphorus shows a high specific capacity and rate capability in lithium storage and has attracted increasing attention in recent years. In this paper, the research progress on red phosphorus-based anode materials is briefly reviewed, particularly the crucial parameters involved in practical battery applications (e.g., binders, electrochemical characteristics of the electrode, and expansion and contraction rates of the electrode). It is also compared with other new anode materials. The practicability of the red phosphorus anode is emphatically analyzed. The advantages and disadvantages of the red phosphorus anode and the key problems needed to be solved before application are discussed.

Carbon-based materials are widely used as cathode materials for aluminum-ion batteries (AIBs) because of their easy availability and structural diversity. In this article, we summarize the vital roles of carbon-based materials in the application of AIBs, review the aluminum storage mechanism and the research progress of carbon materials as aluminum-ion electrode materials, and focus on regulating the structure of electrode materials to improve the electrochemical performance of batteries. Furthermore, improving the electrochemical performance of electrode materials through structural design is emphasized. In terms of carbon cathode materials, the influence of the diversity morphology and structure of cathode materials (such as graphite, graphene, and carbon nanotubes) on the electrochemical performance was mainly summarized in this paper. Finally, the problems that need to be solved by carbon-based materials in the field of AIBs are discussed to improve the application performance of AIBs.

Silicon-based materials are promising anode materials for the application of lithium-ion batteries. However, silicon-based anode materials also have problems such as mechanical and electrochemical instability, which limits their practical application as anode material for lithium-ion batteries. In amorphous nanostructured silicon powder, the mechanical and electrochemical instability can be effectively alleviated by reducing the particle size to nanoscale and translating the structure from crystalline to amorphous. Thus, the effective preparation of amorphous nanosilicon powder is of great significance for improving the performance of lithium-ion batteries. The preparation of amorphous nanostructured silicon powder is based on the following principles: reduction of silicon oxides or halides by adding metals or nonmetals with a strong reductant, quick freezing of liquid or gaseous silicon, and thermal decomposition of gaseous silicon. The preparations of amorphous nanosilicon powder are reviewed, including mechanical ball milling, chemical reduction, solvent heating, liquid phase quenching, and vapor deposition. The advantages and disadvantages of various preparation methods are introduced considering their economics, feasibility of industrial production, and so on. In addition, other possible methods such as plasma evaporation-condensation, spray drying, self-propagating combustion, improved Siemens method, and electrodeposition technology are described to offer more references for the preparation of amorphous nanosilicon powder.

Lithium deposition reactions of lithium-ion batteries under different conditions are studied using three-electrode batteries. The corresponding material characterization is performed using X-ray diffraction (XRD) and atomic absorption spectrophotometry (AAS). Considering the changes in the electrode potential of low negative to positive ratio (N/P) batteries and low-temperature charging batteries during charging and discharging processes, the results show that once the lithium deposition reaction occurs, an additional potential plateau appears around 0 V during the charging process, and another additional potential plateau appears around 0 V during the next discharging process. The pair of additional potential plateaus that appeared around 0 V during the charging and discharging processes can be used as the criteria for the formation and stripping of lithium dendrite, expressed as Li⁺ + e^- ? Li. In addition, because the potential plateaus are referred to as the phase transitions in the electrodes, the proportion of reversible and irreversible lithium can be quantitatively analyzed using the corresponding charging or discharging time of the potential plateaus and the corresponding current. Furthermore, it is demonstrated that part of the deposited lithium on the anode surface can reinsert into the graphite layer during the next relaxation process at room temperature. The main reason is that concentration cells are formed between the deposited lithium and the graphite bulk, and partial discharge occurs during shelving, causing some of the deposited lithium to reinsert into the graphite layer. This work provides a quantitative analysis method for the lithium deposition reaction. It can be used as an experimental basis to predict the occurrence of lithium dendrites, which has a certain significance for the failure processes.

The anode prelithiation technology can supplement the loss of active lithium in the activation process and subsequent cycling of lithium-ion batteries, so as to improve the energy density and cycling life of lithium-ion batteries. However, it is still unclear that the decay mechanism of lithium-ion batteries after anode prelithiation. In this work, we studied the evolution of charge/discharge potential, specific capacity, State of Health (SOH) and electrochemical impedance of the Graphite-LiFePO₄ battery after high rate aging conditions, the surface morphology, crystal structure and thermal stability of electrodes under fading process were also studied. The results indicate that within a certain range of filling amount of lithium, the anode prelithiation technology extends the battery cycle life by overcoming the irreversible loss of active lithium, rather affecting the battery fading mechanism.

The cathode material of lithium-ion batteries must have a large energy density and stable cycle life. Cycle life is directly related to structural changes before and after lithium loss. However, the atomic-level factor affecting the cycle life has not been clearly determined. The core work of exploring and optimizing cathode materials is finding the relationship between microstructures and performance, which requires big data statistics and comparing and analyzing the characteristic parameters of structural changes before and after lithium loss. The volume and elastic modulus of 18 typical positive materials were calculated using the molecular dynamics method. We found that different cathode materials corresponding to different pressures can reflect the shrinkage ability, mainly decided by the product of the volume change rate and elastic modulus. The pressure reflects the system's adaptability during contraction after lithium loss and the difference in the stability of different materials before and after lithium loss. For cathode materials containing transition metals such as Co, Ni, Mn, and Fe, this parameter has a certain linear relationship with the cycling stability; that is, the system with the higher pressure has the better cyclic performance. At the same time, the charge density in the electronic structure layer is also one of the intrinsic factors affecting the cycle performance of lithium-ion batteries. This research also shows that using big data combined with theoretical calculations is an effective method to find the laws of materials. The basic laws obtained have certain theoretical guiding significance for optimizing and improving the cycle life.

A simulation-based design method for batteries can replace the trial-and-error method, which is based on the repeated sampling and design of experiments, significantly shortening the product development cycle, reducing the cost of materials and energy, and improving the product innovation ability. In this work, the influence of the electrode structure parameters on the power, energy, specific power, and specific energy is investigated on the basis of a three-dimensional thermo-electrochemical coupling model. Further, the mechanism is revealed using the overpotential decomposition method with constant cell size and capacity. The results indicate that the electrode structure parameters have different effects on various performances. The following design relations should be considered: First, the electrode structure with considerable thickness and small porosity improves the battery energy but obstructs liquid phase transportation and affects the power. Conversely, the electrode structure with a small thickness and high porosity improves power performance but may increase the total mass of the battery and decrease the specific power. Finally, the effect of thin coating and porous design scheme on the improvement of power performance decreases gradually, and after a certain threshold, reducing the thickness and increasing the porosity will not improve the liquid phase transportation anymore. Other restrictions should be considered in this situation.

Separator is an important component of lithium-ion batteries, whose property is crucial to the battery performance. Mechanical loading, intercalation/deintercalation of lithium ions on the electrode, and temperature can cause the deformation of battery components, which then compresses the soft separator. The response of a porous medium separator under compression is determined by the viscoelastic behavior of the polymer skeleton and the poroelastic behavior due to the electrolyte in the pores. A axisymmetric mathematical model capable of describing the fluid-structure coupling effect of the separator under compression at different strain rates is established in this paper. The model also introduces dynamic properties of porosity and permeability, and is solved by numerical simulation software. The numerical results in this work are closer to the experimental data than the numerical results in the literature. It is found that the poroelastic effect of the separator leads to the inhomogeneous distribution of porosity and permeability. The model is also used to analyze the permeability, geometry, Young's modulus, Poisson's ratio, fluid bulk modulus, and viscosity of the separator and discuss their effects on the poroelastic behavior of the separator during compression. The findings in this study are of benefit to obtain in-depth understanding of the poroelastic behavior of the separator. Meanwhile, they can also provide theoretical basis for optimization of separator materials and geometrical parameters.

A series of activated carbon-based supercapacitors were assembled in an electrolyte consisting of ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF₄) mixed with propylene carbonate (PC) and dimethyl carbonate (DMC) by adjusting the mass ratio of the active materials on the cathode and anode (P/N ratio). The influence of the asymmetric electrode mass design on the overall performance of supercapacitors was investigated through galvanostatic charge/discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. The results show that the oxidation decomposition of the electrolyte at high voltage is restrained. The 3V cycle stability and specific capacitance of the capacitor at low rates are improved by increasing the P/N ratio. However, it also leads to an increase in the discharge voltage drop and equivalent series resistance of the capacitor. The capacitance retention of the capacitor with the P/N ratio of 1.4 is 90.4% after 5000 cycles at 10 mA. Its specific energy and specific power are 9.95 W·h/kg and 4480 W/kg, respectively, at a discharge rate of 50 mA. This reflects better cycle performance but weaker power capability of the asymmetric capacitor than those of the symmetrical one. The research exhibits the merit of the asymmetric electrode structure but points out the difficulty in achieving an improved overall performance of the capacitor.

Open sorption heat storage is a novel technology for space heating in buildings driven by solar energy, industrial waste heat or off-peak electricity, which can effectively ease energy stress and reduce the electric load. However, its large-scale applications are hindered by the lack of accurate predictions of the output performances during the discharging process. In this study, we explained how the entrance, motion, and exit processes of the "reaction wave" (the moving reaction section with a constant speed) directly lead to the increasing, stable, and decreasing output temperature curve. The theoretical formula for the lasting time of the stable process was given. Moreover, zeolite 13X, which has been fully used in open sorption heat storage reactors, was chosen as the sorbent to study the main influencing factors on the output performance. Accordingly, an observation device based on an infrared camera is designed and established. The changes in the wave shape and movement of the reaction wave were obtained from calculations based on the recorded sorbent temperature inside the reactor during the whole sorption process. Moreover, the influences on wavelength and wave speed of the relative humidity, air velocity, and the particle size of zeolite 13X were investigated. The calculated and measured values of the lasting time of the stable output process were compared. The results could contribute to designing reactors using zeolite 13X.

Ice slurry is a kind of cold storage medium and secondary refrigerant with good heat transfer performance. Microemulsions of oil in water (O/W) and water in oil (W/O) are prepared to study ice slurry preparation using microemulsion. We used dodecane as the oil phase, hexanol as the cosurfactant, potassium oleate, sodium oleate, ammonium lauryl sulfate, and their mixtures as surfactants. We analyzed the properties and structures of the microemulsion through centrifugal, particle size, conductivity, and thermal conductivity tests. The optimum preparation system of the microemulsion ice slurry is determined according to the subcooling degree and phase change temperature, and its growth process is described. The experimental results show that the surfactant's lipophilicity to form stable microemulsions increases with the increase in the mass ratio of oil and water. The oil–water mass ratio and hexanol concentration of the microemulsion affect the supercooling degree and phase transition temperature of the ice slurry. O/W microemulsion with an oil–water mass ratio of 1:9 has a good performance for preparing ice slurry. Its subcooling degree is not more than 0.3 ℃, and the phase transition temperature is about -0.1 ℃. The stability of the microemulsion and its ice slurry preparation was verified by thermal cycling. After 500 thermal cycles between -5 ℃ and 25 ℃, no stratification is found, indicating that the microemulsion has good stability. The microemulsion may be used to prepare ice slurry for a long time.

Tubular heat exchangers are widely used in phase change heat storage, but heat transfer is usually poor because of the low thermal conductivity of phase change materials (PCM). Therefore, improving the heat transfer efficiency of the phase change heat storage unit and shortening the solid-liquid phase change time are the focus of this research. In this paper, a three-dimensional unsteady simulation was conducted to study the influences of the fin structure, thickness, number, and spiral cycle on the heat storage performance. The mean temperature, liquid fraction, and heat storage of the PCM during the melting process were also discussed. The simulation results showed that the melting time of the PCM of the spiral fin heat storage unit was shortened by 12.21% compared with that of the flat fin. With the increase in the thickness, number, and spiral cycle of spiral fins, the amount of heat storage slightly reduces. However, the PCM melting time was shorter, and the heat transfer performance was improved continuously.

A fractal phase change heat exchanger model was established to study the law of enhanced phase change heat transfer by fractal fins on the basis of phase change heat transfer theory and fractal theory, and the enthalpy-porosity method was used to simulate phase change material (PCM) melting and heat transfer in the fractal fin heat exchanger. The influence of the radial length of the fractal fins, the diameter of the heat exchange pipe, and their ratio on the melting heat transfer of PCM is analyzed. The results show that when Fo < 0.02, the PCM melting rate decreases with the increase in the aspect ratio; when Fo > 0.02, the PCM melting rate increases with the aspect ratio and finally stabilizes. At the same dimensionless time, the uniformity of the PCM temperature distribution increases as the aspect ratio increases. At the initial moment, the heat flux decreases with the increase in the aspect ratio; in the late melting stage, the heat flux increases with the increase in the aspect ratio and maintains a relatively high and stable level over time. During PCM melting, the best ratio between the radial length of the fractal fins and the heat exchanger tube diameter is 12; that is, when the heat exchange tube diameter is 10 mm, the best radial length of the fractal fins is 120 mm. This provides a theoretical basis for the structural design of fractal phase change energy storage.

Energy Saving and New Energy Vehicle Technology Route (version 2.0) puts forward new requirements for vehicle energy saving technology. Traditional vehicles with internal combustion engine (ICE) can only add secondary energy storage devices to recovery of part of braking energy. The Ragone diagramm shows that flywheel energy storage (FES) has many merits such as higher power density, higher efficiency, fast response, environmental-friendly performance and long cycling using life, which becomes an ideal secondary energy storage technology for traditional ICE vehicles. Despite some progress, there is no systematical review on the recent progress of flywheel energy storage system in the automotive industry. The FES is retrieved based on CNKI database, Engineering Village database and Web of Science database, and highlights on the analysis of application of FES technology in the automotive industry. Comprehensive databases show that FES technology has been exploring in the past twenty years. For two typical hybrid electric and mechanical energy storage and power delivery system, the exploration, research and verification process of the hybrid mechanical energy storage and power delivery system in vehicles is emphatically introduced. Meanwhile, the researches elaborate on the basic structure, characteristics, research status and development trend of this system. The comprehensive analyses show that the mechanical hybrid delivery system, through the pure mechanical connection between the flywheel and vehicle powertrain, not only solves the problem of insufficient power and energy-saving effect caused by the power limitation of the electric drive system, but also improves the energy conversion efficiency of the flywheel hybrid powertrain.

Mechanisms leading to electric vehicle safety accidents are usually complex, multifactor, and interrelated, and new types of failures appear gradually during electric vehicle usage, making it difficult to determine root causes of accidents. This study summarizes how electric vehicle accidents are caused and evolve owing to a lithium-ion battery thermal runaway. The mechanisms triggering thermal runaway in electric vehicles and associated processes are discussed, including mechanical abuse, electric abuse, thermal abuse, and internal short-circuiting. Based on literature research, recommended strategies for accident investigation are proposed, including data analysis by the measurement of battery management systems, deformation studies at micro and macro levels, and the elemental identification of residuals after a battery failure. The study provides guidance on the establishment of an accident database for electric vehicles and helps equip investigators with scientific methods to build an evidence chain. It is beneficial for revealing the original mechanism of accidents and improving the efficiency of an accident investigation.

In this study, the 18650-type lithium-ion ternary battery pack was selected as a research object to investigate the burning characteristics of power lithium battery packs. A series of experiments with thermal runaway induced by heating was conducted in a confined space. Some typical characteristic parameters were studied at various heating locations and varying power by measuring temperature data and recording a high-digital video, including the ignition time, flame shape, and critical temperature of thermal runaway. Besides, a fire extinguishing test with water mist was conducted to test the effect of fire suppression and cooling. Results demonstrated that the thermal runaway temperature was at 120—139 ℃ for the lithium ternary battery pack. The maximum burning temperature increased with increased heating power, and peak value was up to 800 ℃. The burning intensity of the lithium battery weakened as spacing between the battery and heating source increased when the battery pack was heated from the side. In such cases, several intermittent reburning instances occurred. We observed that the burning intensity of the battery pack with bottom overheating was stronger than that with side overheating. Unlike in side overheating, the batteries were continuously burned by spraying in bottom overheating. Meanwhile, ignition time was reduced, and burning intensity was increased with increased external heat source power. Herein, the burning batteries were effectively suppressed and cooled using water mist. The main reason was that internal temperature in the battery pack was reduced below the critical value so that reburning was prevented effectively. However, we noted that secondary damage caused by water pollution and short-circuit discharge must be carefully considered according to fire suppression needs although water mist can be used as an effective fire-fighting method for lithium battery fire exhaustion.

Comma roll transfer coating is a common coating method in the production of lithium battery electrodes. Studying the relationship between the height of the coater gap on the coating equipment and the coating's wet thickness has important theoretical significance and practical value. In this work, we first simplify the basic two-dimensional equation of fluid mechanics, the Navier-Stokes equations, into a one-dimensional Reynolds lubrication equation according to the comma roll coating conditions and then apply it to the research. In this flow field, combined with its geometric parameters, a differential equation of pressure is established. Then, with zero pressure at the inlet and outlet of the flow field as boundary conditions, the equation is solved by integration, and the relationship between the coating wet thickness and the geometric parameters of the flow field is obtained. The study found that the ratio of the coating wet thickness H_w to the blade slit height H₀ is close to 2/3 (0.66) within the range of geometric parameter K=R/2H₀ (10—2000). Even if there is a significant difference in the upstream geometric dimensions, its dimensionless pressure-position curve is almost coincident. To verify this theory, we established a 2D model of lithium battery electrode coating with Fluent software and changed the radius of the doctor roller and coating roller and the height of the gap, coating speed, and coating slurry viscosity in the software parameter settings. The results of the software simulation and theoretical calculation of coating thickness and flow field pressure distribution are highly consistent. Both results show that the ratio of coating wet thickness H_w to blade slit height H₀ is not affected by changes in coating slurry viscosity and coating speed. The results of this study can be practically used by coating technicians to predict the coating thickness of electrodes, which helps improve the efficiency of the coating process and reduce material loss.

The fuel cell vehicle commercialization demonstration operation project aims to study the commercial application prospect of fuel cell vehicles and improve fuel cell vehicles in terms of economy, reliability, and life. It is an important way to promote the commercial development of fuel cell vehicles. The fuel cell system's service life is the main factor restricting the commercial development of fuel cell vehicles. Therefore, it is important to improve the service life of fuel cell vehicles, analyze the performance attenuation process of fuel cell systems under road working conditions, and clarify the performance degradation mechanism of fuel cell systems through the research work of the demonstration operation project. On the basis of the discussions of related studies, this paper reviews the research progress of the fuel cell vehicle demonstration operation project, introduces methods to analyze fuel cell system performance degradation, and points out that the main research contents of the demonstration operation project mainly include operating condition and performance degradation analyses of fuel cell stacks. The data-driven and model-based analysis methods are introduced emphatically. The function to fit the steady-state polarization characteristics is deduced from the polarization curve used in fuel cell voltage analysis. The fitting results of the steady-state polarization characteristics are only applicable to specific operating environments and have no wide applicability. Finally, this paper summarizes the emphases of the fuel cell vehicle demonstration operation project research and the development trend of the analysis methods to provide a reference for fuel cell research based on demonstration operation.

Compared with the traditional lithium-ion battery module, the lithium-sulfur battery module based on high energy density lithium-sulfur battery has higher specific energy, which is an important development direction for the power battery industry in the future. Developing a lithium-sulfur battery module requires meeting the VW (Volkswagen) battery module structure strength standard and actual car-loading demand. To do so, a project based on automobile V mode development sorted out the demand definition of the basic functions of the battery module, combined with the research on cathode and anode materials, thermal and cycle characteristics of the lithium-sulfur battery in the early stage of the project, and the Volkswagen standard of mechanical shock and crash test requirements. Finally, the design requirements of the lithium-sulfur battery module are summarized. During design verification, the project finished the function and structure design of the lithium-sulfur battery cell and module and completed the whole development process of the lithium-sulfur battery module through a sample trial production and test verification. The lithium-sulfur battery module designed and developed in this paper uses a magnesium alloy, PC (polycarbonate), ABS (acrylonitrile butadiene styrene) and other lightweight high-strength materials. Its energy density reaches 250 W·h/kg, which passed the mechanical property test required by the VW standard. This module structure design improves the module's energy density, maintains sufficient structural strength, and has good heat dissipation performance. Because the structural strength design of the battery module maintains the preset preload between lithium-sulfur batteries, its cycle performance is also improved correspondingly.

A new scheme for integrating cogeneration units and compressed air energy storage systems is proposed to improve the regulation flexibility of cogeneration units in thermal power plants and increase the peak load regulation capacity of systems and the proportion of renewable energy into the grid. In the enhanced heating stage, a compressed air energy storage system is used to store electric energy, and the compressed heat is used for heating to improve the heating ratio of the system. In the enhanced power supply stage, the extraction steam of a cogeneration unit is used to heat the inlet air of the expander to increase the power generation ratio of the system. Compared with that of the reference system, the scheme's exergy efficiency can be increased by 4%—31.4%, and the heat to power ratio has been widened. The effects of different component parameters on the thermal efficiency, exergy efficiency, and thermoelectric decoupling performance of the system are compared. On this basis, the basic points of several heating conditions are analyzed. The results show that the airflow rate of the compressed air energy storage system has a great influence on the thermal efficiency of the new integrated system, whereas the inlet air temperature of the expander has a greater impact on the thermoelectric ratio of the new integrated system. With the increase in the main steam flow into the steam turbine, the system's total process efficiency and thermal efficiency increase by 5% and 8%, respectively. The loss analysis shows the loss of boiler components. The largest proportion is about 20%, followed by cold source loss, which is about 10%.

With the world's increasing attention to the development of the solar energy industry, the efficient use of solar energy technology has become a hot spot of renewable energy research. However, because of the intermittent, fluctuating, and lower energy density characteristics of solar energy, there are some problems in solar energy storage and utilization, such as high cost, complex process, and low overall utilization rate. The organic combination of solar power generation and hydrogen production technology can convert solar energy into hydrogen for storage, which realizes energy-efficient conversion and utilization and effectively solve the above problems. This study presents a combined heat power and hydrogen production system based on solar energy and the Rankine cycle. This system mainly consists of a solar dish collector, solid oxide electrolyzer, and the Rankine cycle, which can simultaneously provide electricity, heat, and hydrogen. The system's mathematical model is established, and the parameters of the system and its subsystems are analyzed. The effects of operating parameters such as operating temperature, current density, and solar radiation on the system energy and exergy efficiency are obtained, and the internal reason for the exergy destruction of each system component is determined. The results show that high radiation, relatively high operating temperature, and current density can improve the system's thermodynamic performance. The total efficiency and hydrogen production efficiency are 49% and 25%, respectively. The maximum exergy destruction occurred at a solar dish collector, taking up 50% of the total exergy destruction.

The energy management problem of microgrids in an independent community is investigated in this paper. A multiobjective optimization mathematical model of microgrids considering electric vehicle charging or discharging and demand response (DR) is constructed, and an energy management strategy including load and source-load levels is proposed. Charging or discharging electric vehicles is orderly guided in the load level according to the owner's travel habits and time-of-use electricity price to reduce the microgrids' peak-valley difference. The load curve is optimized at the source-load level by adjusting the residential electricity consumption method through DR. PV, battery energy system, and electric vehicles are used preferentially. The car's output and the remaining "net load" are absorbed by the micro-gas-turbine to minimize the operating cost of the microgrid, the amount of polluting gas emissions, and the energy waste rate. According to the model's multiobjective, multiconstraint, nonlinear, and other characteristics, a nondominated sorting genetic algorithm with elite strategy is used to solve, compare, and analyze the operations of typical community microgrids with different energy management schemes. The correctness and effectiveness of the optimization model and strategy are verified.

Under the trends of energy transformation, energy conservation, and emission reduction, photovoltaic buildings combined with DC power supply have become a research hotspot, and the role of energy storage is crucial. However, the standards of electrochemical energy storage are still insufficient domestically, and the standards of building electrochemical energy storage applications are even lower. This paper analyzes the functions of energy storage in photovoltaic DC power supply buildings: coordinating control of charging and discharging power and energy of energy storage, realizing the maximum utilization of photovoltaic power generation and self-consumption, smoothing the fluctuation of photovoltaic power generation and load, improving the efficiency of building power distribution access to the grid, and ensuring the power supply of important loads. We propose the principles of reliability, economy, and adaptability of electrochemical energy storage used in photovoltaic buildings. These principles also provide references for the research and development of photovoltaic building energy storage technology standards. Under the current technical conditions, the main bases for using Pb-C batteries for photovoltaic building energy storage are safety and adaptability under partially charged states. According to the above energy storage principles, this low-voltage DC power supply photovoltaic building project is equipped with a containerized Pb-C battery energy storage system, including a 178 kW·h Pb-C battery and thermal and battery management systems. The installed capacity of the project is 112.6 kWp, which adopts a DC power supply system. The energy management system can be operated both in-grid and off-grid. The energy time-shift of the photovoltaic building for a whole day was analyzed in detail using data on in-grid operation on a certain day. The maximum utilization of photovoltaic power, peak cutting, and valley-filling and a constant power supply were demonstrated. The project can provide a reference for promoting distributed energy storage in photovoltaic buildings.

The grafting yield must be kept in a proper range to obtain a satisfactory gating property of membranes. An optimization strategy for EV charging with wind power consumption in mind was proposed to make full use of wind power in EV charging stations and reduce the negative impact of charging load on the distribution system operation. First, a Monte Carlo simulation method is used to predict the charging load of different numbers of EV. Then, considering wind power output and on the basis of the electric car charge demand, according to the fluctuation of wind power, we dynamically adjusted the time-of-use (TOU) pricing to include the charging load of the distribution network and user charge. With the lowest minimum peak valley load difference as the control target, a coordinated charging model is set up, using an improved particle swarm optimization algorithm to solve the model. In addition, through the electric vehicle charging directly connected to the distribution network of uncoordinated situation comparison, the results show that the proposed strategy on the impact of power distribution network at the same time effectively reduce the charging behavior can directly promote the wind power given, improve the economic benefit of charging users.

For understanding the variation process of humidity in an underground cavern for compressed air storage and its influence on the thermodynamic processes of compressed air, the heat transfer mechanisms of vapor phase change were analyzed. A thermodynamic model for compressed air taking the humidity of air into account was suggested and validated. The influence of humidity variation on the temperature and pressure of compressed air and condensation and evaporation effects in the cavern were analyzed. The results show that vapor quantity included in inflowing compressed air has a significant influence on temperature variation but only a slight influence on pressure variation of the compressed air in the cavern. During compressed air discharge, relative humidity in the cavern rises gradually and could go up to 100%, and condensation happens. During air charging, relative humidity in the cavern decreases gradually, and evaporation occurs. The quantity of condensed water is far greater than that of evaporated water. The problem of water treatment after the cavern experienced a long-term operation should be considered in engineering designs.

Lithium batteries undergo chemical reactions and material deformation all the time during use, causing their shape to continue to change with the state of use. Both hard- and soft-shell materials of lithium batteries have a certain degree of ductility. In early stages of thermal runaway of lithium batteries, a series of physical and chemical changes will create pressure inside the lithium batteries. As time goes by, lithium batteries will swell significantly, causing significant pressure changes between battery cells. Therefore, studying the mechanism of lithium battery expansion is extremely important for early detection and early warning of thermal runaway of lithium batteries. This article reviews the research on the expansion and formation mechanisms of lithium batteries at home and abroad, sums up the main reasons for the expansion of lithium batteries, and starts from five aspects of lithium battery electrode materials, electrolyte, charge and discharge temperature, charge and discharge voltage, and charge and discharge current. We analyzed their impact on the expansion of lithium batteries. Finally, through the research results of various influencing factors, future methods and directions for controlling gas swelling of lithium batteries are explored, and more effective early warning suggestions are put forward for the early detection and early warning systems of lithium battery thermal runaway.

The thermal power of a thermal runaway cell is calculated using its temperature obtained by existing ARC tests. The power is assigned to cells in a hybrid locomotive traction battery system, and the transient temperature of other cells around it is simulated. The simulation shows that one cell's thermal runaway cannot incur propagation when it is cooled by an air-conditioner. However, it will lead to propagation without an air-conditioner in modules, and the parallel cells' thermal runaway will cause propagation in the upper package. Lastly, preventing thermal runaway propagation was studied.

Lithium batteries are widely used in new energy electric vehicles and energy storage because of their superior performance. However, micro-short circuits in lithium batteries are a safety hazard during the use of battery packs. This paper proposes a method to diagnose micro-short circuits on the basis of the change in the relative charging time of the cell to determine whether the battery pack is micro-short and judge the micro-short circuit cell. At the end of the battery pack charging, this method uses the voltage curve of the cell that first reaches the charge cut-off voltage as a reference, analyzes the charging times for other cells to reach the charge cut-off voltage under the condition that they can continue to be charged, and characterizes these with the relative charging time. Because of the micro-short circuit battery's continuous consumption of electrical energy, its relative charging time increases with the number of charging times. Accordingly, each cell's relative charging time in the battery pack is analyzed, and abnormality detection is performed through the box diagram. Among the abnormal monomers detected, the micro-short circuit cell has the most repeated occurrences. While analyzing the relative charging time, analyzing the influence of the DC internal resistance on the diagnosis result is necessary to improve the result's accuracy. After a comparative analysis, the diagnosis results are highly consistent with the actual results. The implementation of this method does not require special tests on the battery pack; the operation is convenient, which can guide battery pack safety testing.

In this work, the factors that influence the cycle life of battery systems, such as the internal resistance, temperature, and the voltage difference between the cells, were systematically studied. We determined a fitting equation for the cycle life of battery systems and found that their discharge capacity showed an exponential decay. This characteristic can serve as a basis to predict and estimate the actual service life of battery systems. We also studied the capacity variation of battery cells for different discharge depths at different temperatures.

Recently, 48 V light hybrid vehicles have been frequently seen as a transition product from fuel vehicles to electric vehicles. The 48 V battery pack can drive a more powerful vehicle system, and it is easy to generate high discharge rate during normal use. Controlling the battery temperature below 45 ℃ is necessary to efficiently run the battery under the premise of high safety performance. Therefore, it is very important to study the thermal management of the battery pack. With the pouch lithium iron phosphate battery as the research object, we study the mechanism for battery thermogenesis using multiple battery monomers in test experiments of resistance and electromotive force coefficients of temperature rise and machine learning polynomial regression for data processing. At the same time, the temperature distribution characteristics of the battery were investigated, and a relatively perfect battery heat generation model was obtained. Because of the battery cell's structural characteristics and thermal conductivity, it is difficult to export the battery heat produced. In this paper, using aluminum, heat pipe, and graphene materials, we designed the heat dissipation structure of the 48 V soft package battery pack. The temperature evolution rule of the battery pack was revealed through simulations, and the temperature control mechanism of the heat dissipation structure of the battery was explored. The battery pack's heat dissipation structure can control the battery's temperature below 45 ℃ and the temperature difference between the battery cell and the battery pack within 2 ℃, ensuring a safe and efficient operation of the battery pack under high rate discharge conditions.

The traditional method of predicting the state of health (SOH) of a battery is generally based on historical data. Predicting the real-time state of a lithium battery or estimating its remaining service life is difficult. Aiming at the real-time prediction of battery SOH, we introduce a large amount of real-vehicle battery data (combined with machine learning and ampere-hour integration method to model and predict SOH) to process features and train data. On the basis of the model test results, this article proposes a real-time SOH hybrid prediction model combining the LightGBM and CatBoost algorithms. By verifying the hybrid model with two real vehicles as the carrier, the measured absolute average error of the real-time SOH prediction is 0.009. Our research intends to obtain the SOH attenuation curve to predict the remaining battery life. Therefore, we establish a long short-term memory (LSTM) neural network model to predict the future decay curve of battery SOH, characterized by the difference in SOH within a fixed time interval. This reduces the fluctuation of the difference and ensures that the data have similar distribution laws. By verifying the real-time monitoring data set provided by an original equipment manufacturer, the absolute average error of the future attenuation curve prediction is 0.021. The overall results show that the real-time SOH prediction model and the remaining life prediction model of the lithium battery studied in the article have high prediction accuracy. The battery user can better grasp the real-time status of the lithium battery and provide a basis for relevant decision making.

Because of the complex working environment of special robots, a state of charge (SOC) estimation method with high precision and strong tracking ability is required for real-time state monitoring and safety control of lithium-ion batteries of special robots. SOC is one of the most important parameters in battery management systems. The working environment of special robots has strong nonlinear characteristics, considering that the commonly used ampere-hour integration method depends heavily on the accuracy of the initial SOC and accumulates errors in the later stages of estimation. Therefore, considering the working characteristics of special robots, a ternary lithium-ion battery is taken as the research object based on the Thevenin equivalent circuit model and experiments under various operating conditions. An improved extended Kalman filter (IEKF) algorithm is used to estimate the SOC of lithium-ion batteries at 10 ℃, 25 ℃, and 35 ℃. The simulation model is built in MATLAB/Simulink and combined with various working condition data for performance analysis. The experimental results show that using the IEKF algorithm to estimate the SOC value of ternary lithium-ion batteries has a good tracking and convergence effect, and the convergence time is within 80 s. At different temperatures, the maximum estimation errors of the HPPC and BBDST conditions are less than 2.235% and 3.004%, respectively, after convergence, which 9.067% and 4.654% less than those of the corresponding maximum estimation errors of the extended Kalman filter (EKF) algorithm. This study verifies that the IEKF algorithm has high accuracy in estimating the SOC of lithium-ion batteries, and it provides an experimental basis for effectively resolving the inaccurate estimation of the SOC values of lithium-ion batteries of special robots.

When the traditional particle filter (PF) algorithm is used to estimate the state of health (SOH) of lithium-ion batteries, several problems arise, such as particle weight degeneration and species decrease, leading to lower prediction accuracy. In this paper, a novel hybrid algorithm, the improved butterfly optimization algorithm based on PF (IBOA-PF), is proposed to solve these problems. This algorithm based on the basic butterfly optimization algorithm (BOA) replaces the stable switching probability with the chaotic maps. It uses the mutualism phase of symbiosis organism search to make up for the limitations of the butterfly algorithm (i.e., it easily falls into the local optimum and has poor development ability) and improve the convergence speed of BOA. Butterflies are used to represent particles, and the process of butterflies moving to the food is similar to the change of particles having better values that are more possibly equal to the true values. This paper proposed an SOH estimation method using IBOA-PF for lithium batteries based on the double exponential model and time index (TI), constructed the state-space model of the nonlinear system, used the simplex method to improve the Gauss-Newton method for parameter fitting, and estimated SOH. The simulation results show that this method is superior to the traditional PF method, with higher accuracy and better adaptability.

The durability and reliability of vehicle fuel cells are key problems restricting the development of commercial fuel cells. Mostly, current fuel cell vibration tests refer to the vibrational spectrum of power batteries, which does not match those of fuel cell influence studies. Its influence mechanism is analyzed, and a novel testing program is designed. In this paper, the power density spectrum of a vibration bench is converted from a typical vehicle driving cycle through smoothing and degradation treatment. An intensified vibration test proceeded using a typical fuel cell stack. By choosing the remarkable influence direction, a 270 h endurance test is done to simulate the impact of a 30000 km actual drive cycle. During the test, an acoustic meter is used to confirm the amplifying effect of the shock absorber on vibration acceleration. After the test, the variation law of fuel cell electrical performance and the sealing property were analyzed through a polarization curve test, airtightness test, and other performance characterization methods. The research shows that long-term durability vibration attenuates fuel cell electrical performance. The inside proton exchange membrane and outer shell package of fuel cell decay to different degrees as well.

Power lithium-ion battery is one of the core "three-power" systems of new energy vehicles. Its accurate battery modeling and state prediction can ensure the safe start and stable operation of battery management systems. With a ternary lithium-ion battery as the research object, the Thevenin equivalent circuit model is constructed. On the basis of the traditional particle filter (PF), the appropriate recommended density function is selected, and an unscented PF (UPF) with a more precise calculation of the mean and variance is proposed to solve particle depletion and detect the state of charge (SOC) of lithium-ion batteries. The method further improves the theoretical analysis and studies the working characteristics of lithium-ion batteries in combination with experiments under different conditions. The results show that when UPF predicts the lithium-ion battery SOC, the system robustness is improved, the follow-up effect is better, and the prediction error is stably controlled within 1.5%, which brings good practical value to the power battery.

During charging and discharging, a supercapacitor used for energy storage generates heat owing to internal resistance, which increases the internal temperature of the capacitor. If temperature inside a supercapacitor is very high, the capacitor's performance deteriorates, cycle life reduces, and electrolyte evaporates and damages the capacitor. This study simulates the charging and discharging processes of a supercapacitor module (single series 40 A charge/519.5 A discharge) and obtains temperature distribution inside the capacitor and the welding point between the supercapacitor terminal and aluminum bar and between the aluminum bar and whole module under natural cooling at 25 °C using Fluent. A heat generation model of the supercapacitor module is established to simulate its heat generation and heat generation rate under cycle conditions, which provides a basis for research on thermal management systems of supercapacitor modules.

The management of the state of health (SOH) and life prediction of Li-ion batteries are of great significance to promote their wide application. In this paper, on the basis of the situation of application of Li-ion batteries, to remedy the real-time estimation difficulty and low precision under various working conditions, a ternary Li-ion battery is taken as the research object, a second-order RC equivalent circuit model is established to characterize the operating characteristics of the battery, and the performance of the Li-ion battery is studied and analyzed on the basis of the experiments under various working conditions. The changes in the state of health were analyzed from two directions: internal resistance increase and capacity fading. The effect of the state of charge (SOC) on internal resistance is considered. The SOC is calibrated under discharge conditions, and the change of internal resistance is analyzed from 0 to 1 s and 1 to 10 s, respectively. We established the corresponding calculation formula of the evaluation method on the basis of the internal resistance increase of the Li-ion battery and determined the changes of state of health under different initial SOCs in two time ranges. The temperature is taken as a parameter, and the measurement interval is extended to reflect the capacity fading at different temperatures more accurately by multiple full charging and discharging experiments. We also established the corresponding mathematical formula of the state of health on the basis of capacity fading for the Li-ion battery and obtained the changes in the battery's state of health at different temperatures. The experimental results show that within 0—1 s, there is no relationship between the state of health of the Li-ion battery and the initial SOC. Within 1—10 s, the decline rate of the state of health is inversely proportional to the initial SOC. The complete discharging experiments at different temperatures show that the Li-ion battery has the best health condition at 25℃, so the test battery should be operated at this temperature as far as possible. It is indicated that the second-order RC equivalent circuit model can estimate the state of health of Li-ion batteries very well; the convergence rate is fast, and the tracking effect is good. The state of health estimation errors based on internal resistance increase and capacity fading are controlled within 1.0% and 0.8%, respectively. Improving the state of health estimation method helps promote the applications of Li-ion batteries.

Accurate estimation of battery state of charge (SOC) is the basic premise for the normal operation of electric vehicles. An extreme learning machine (ELM) based on the gray wolf optimizer (GWO) algorithm was proposed to estimate the SOC of lithium-ion batteries, improve the estimation accuracy, and shorten the estimation time. The traditional ELM generates model parameters randomly. This method runs fast and has good generalization performance. However, the ELM must determine the optimal hidden layer neuron parameters to achieve high accuracy. Therefore, the GWO algorithm was adopted to further optimize the model parameters. The appropriate activation function was selected to make up for the shortcomings of the traditional ELM. Finally, the advantages of this method in battery SOC estimation are verified under different working conditions by comparison with the particle swarm optimization-feedforward neural network algorithm (BPNN-PSO) and the ELM. The result shows that the ELM based on the GWO algorithm has high accuracy, short estimation time, and good robustness, which is better than those of the traditional SOC estimation method. This research helps promote the development and application of new energy vehicle battery management systems and provide support for the research and development of reliable battery management systems.

Energy storage is one of the important technologies to support the stable operation of power system with high renewable proportion. The participation of energy storage technology should be considered in the mechanism design of frequency regulation market in China. This paper first summarizes the status of grid-side energy storage technology in frequency regulation. The grid-side energy storage has advantages on response time and output adjustment to provide frequency regulation service for power grid. The development status of storage that provide frequency regulation service, the foreign market mechanisms for grid-side storage participating in the market, including the market access threshold, competing method and price mechanism, are analyzed from the frequency regulation auxiliary service markets of the United States, Australia and the United Kingdom. The differences of the designs and their influences on energy storage participating the market are analyzed. Finally, based on our current situation, there are still some deficiencies and challenges in the design of energy storage participating in the China's frequency regulation market, including that most region do not definitely take storage as market member, the capacity access threshold of storage in most of the China's frequency regulation markets are twice or more than that in typical frequency regulation markets worldwide, and the lower limit of frequency regulation benefit is too low in certain regions to reflect the capacity value of storage. Based on the experience of foreign markets, frequency regulation could bring more than 6 GW needs for storage with suitable market mechanism design and thus storage should be the market member of frequency regulation market. The access threshold should be timely reduced in the design of China's frequency regulation auxiliary service market along with the development of market and technology to allow the participant of small distributed storage. The price mechanism should consider the two-part payment to reflect the capacity value of storage in frequency regulation and guarantee the minimum payment for storage.

The action plan for the development of energy storage technology is put forward to support and motivate the future development of energy storage. At present, the discipline of energy storage involves many fields, such as power electronics, power system, power market, electrochemical thermal management, and covers a wide range of specialties. Therefore, it is necessary to establish a specialized discipline of energy storage for the development of energy storage technology in China. As the cornerstone of the development of energy storage discipline, the construction of energy storage discipline is also in the measures issued by national policies. According to the current situation of energy storage field, this paper first expounds the significance and necessity of energy storage discipline construction, and then sorts out the current situation of domestic energy storage universities, textbooks and magazines, and finally gives the enlightenment of energy storage discipline construction in China.