Because of high theoretical energy density and large resources of elemental sulfur, lithium sulfur （Li/S） became one of hot topics in the battery community. Due to the complex reaction process and many intermediate products which obviously differ to typical lithium ion batteries, this paper shows my own understanding and opinions about Li/S on four aspects of sulfur cathode, lithium anode, electrolyte and battery. Most of reported sulfur cathode materials can be divided into two categories, that is, mobile sulfur and stationary sulfur, which was briefly summarized in Table 1. The lithium metal anode still is the critical problem and more breakthrough works are required to accelerate the progress of Li/S applications. Safety is the first priority. More attention should be paid to construct intrinsic safe Li/S battery to ensure it highly reliable during all cycle life.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 2731 papers online from Oct. 1, 2019 to Nov. 30, 2019. 100 of them were selected to be highlighted. Layered oxide and high voltage spinel cathode materials are still under extensive investigations for improving their capacity, rate capability and cycling performances by doping and coating. Large efforts were devoted to making Si based composite anode materials with higher columbic efficiency and longer cycling life. Metallic lithium anode were drwan large attentions and artifical SEI and solid state electrolyte are widely studied. There are a few papers related to solid state electrolyte, hybrid electrolyte and liquid electrolyte addtives, solid state battery, Li-S battery and Li-air battery. Fading mechanism of Li-ion battery and solid state battery were investigated by electrochemical and physical methods. Theoretical calculations and simulations help to understand the interface, kinetics and fading mechnism of batteries.

The lithium-ion battery is a new type of secondary energy storage device, representing a new direction of future battery development, and is extensively used in production and daily life. However, the energy density and cycling performance of the commercial lithium-ion batteries remain insufficient to satisfy the demands of productivity development. On seeking better-performing electrode materials for lithium-ion batteries, metal–organic framework materials (MOFs) with their porous structures and high specific surface areas as well as their corresponding derivatives exhibit advantages over traditional electrode materials because of their improved lithium-ion diffusion rate, reduced volume changes, and increased cycling stability, which make them highly promising lithium-ion battery electrode materials. Therefore, this study mainly reviews the MIL, MOF, ZIF, and Prussian blue series MOFs and their derivatives as negative and positive electrodes of lithium batteries based on the discussion of recent related literature. The preparation methods of the above materials and the mechanism of capacity improvement of the lithium-ion batteries are also emphasized. The influence mechanism of the increase in the lithium-ion battery capacity shows that the charge loading capacity and porous structures of MOFs and their derivatives make them superior to conventional lithium-ion battery materials. Finally, based on the most significant issues currently associated with the MOF electrode materials, future research should focus on three development directions, i.e., composites with other conductive materials, mechanochemical syntheses, and the use of inexpensive materials, to realize the commercial development of MOF electrode materials for lithium-ion batteries.

Potassium is abundant in nature and cheap. In electrochemical systems, potassium has a lower redox potential and faster ionic conductivity; thus, potassium-ion batteries (PIBs) are expected to be a promising alternative to lithium-ion batteries (LIBs) in the future. However, because K⁺ (1.38 ?) is considerably larger than Li⁺ (0.76 ?), huge volume expansion and structural damage can be observed after K⁺ intercalation into the electrode materials extensively used in LIBs. These electrodes do not meet the needs of practical applications. To address these issues, increasing number of electrode materials have been recently developed. In this study, current research on anode materials for PIBs is reviewed, with emphasis on the potassium intercalation mechanism and structure-performance relation of carbon-based materials (graphite, hard carbon, and soft carbon), titanium-based materials, alloys, conversion materials, and organic compounds. The advantages and main problems of these anode materials are discussed. Additionally, the two main potassium storage mechanisms (intercalation and pseudocapacitance) in carbon-based electrodes and their effects on electrochemical properties are emphasized. The pseudocapacitance mechanism occurring on the electrode surface appears to be suitable for the fast storage of K⁺, and methods for increasing the contribution of pseudocapacitive behavior are introduced in this study. Simultaneously, the research directions and application prospects of future developments in PIB systems are discussed.

New energy storage materials comprising Prussian blue and its analogues exhibit promising application potential as positive electrode materials for sodium-ion batteries because of their open frame structure, which is beneficial for the storage and rapid migration of sodium ions. Among these, Fe-based Prussian blue has attracted considerable attention due to its abundant resources, simple preparation, and high specific capacity. The electrochemical performance of Prussian blue is strongly correlated with its lattice structure, especially the sodium content, vacancy concentration, and crystal water. The lattice structure of Prussian blue can be tuned by controlling the processing parameters. Herein, two types of Na-enriched Fe-based Prussian blue cathode materials were synthesized via a facile coprecipitation method with and without a chelating agent, i.e., sodium citrate. The effects of sodium citrate on the crystal structure formation and sodium storage performances were investigated using X-ray diffraction （XRD）, scanning electron microscopy, thermogravimetric analysis （TGA）, and electrochemical characterization techniques. The results denoted that the Fe-based Prussian blue material prepared using the chelating agent exhibited a monoclinic structure. The material exhibited a well-defined cubic particle morphology with an average size of approximately 400 nm and good crystallinity as well as particle dispersibility. However, the Prussian blue sample prepared without the chelating agent displayed a cubic lattice structure. The particles exhibited a spherical morphology with a size of approximately 150 nm and presented significant particle agglomeration. XRD and TGA revealed that the sample with a monoclinic structure had a high sodium content but a low water content per formula unit when compared to the cubic structure. As a sodium-ion battery cathode, the sample with the monoclinic structure exhibited a high reversible capacity of 129.9 mA·h/g, a high first-cycle coulombic efficiency of 99.5%, and a remarkable cycling performance with a capacity retention of 75.7% after 100 cycles at a current density of 30 mA/g. This electrode exhibited a good rate performance, and the reversible specific capacities were 129.3, 121.7, 116.7, 110.7, 87.8, 63.6, and 45.3 mA·h/g at a current density of 30, 50, 100, 200, 400, 600, and 800 mA/g, respectively. When the current density returned to 30 mA/g, the reversible specific capacity was restored to 117.3 mA·h/g. The cyclic voltammetry and electrochemical impedance tests indicated that the monoclinic Prussian blue electrode exhibited lower electrode polarization and charge transfer resistance when compared with that exhibited by the cubic sample, resulting in faster electrode reaction kinetics and an excellent electrochemical performance. The role of the chelating agent, i.e., sodium citrate, in the Prussian blue particle nucleation and growth processes is also discussed.

Three-dimensional porous graphene (TDPG) is extensively used as an electrode material for supercapacitors because of its unique three-dimensional structure, high specific surface area, high conductivity, and multilevel pore diameters. However, the specific capacitance per unit area of TDPG is only approximately 5.35 μF/cm², which is considerably lower than the theoretical value of a carbon-based material (~21 μF/cm²). A TDPG with a high specific surface area was selected for this study to improve the specific capacitance per unit area. The effect of high-temperature heat treatment on the conductivity of TDPG was investigated along with the effect of the changes in conductivity on its electrochemical properties. The results denoted that the specific surface area of TDPG was drastically reduced from 2009.8 to 1301.0 m²/g after the high-temperature heat treatment, which was mainly due to the shrinkage of the graphene particles and the reduction of pore volume. The Raman spectrum results demonstrated that high-temperature heat treatment could improve the degree of graphitization of TDPG and increase the conductivity of the electrode materials. Electron impact spectroscopy verified that the equivalent series internal resistance of button supercapacitors with TDPG as the electrode was reduced from 4.0 Ω to 1.4 Ω after heat treatment. The increase in conductivity helped to increase the specific capacity retention rate from 34.8% to 45.2%, indicating that the specific capacitance per unit area of TDPG was considerably improved by high-temperature heat treatment. The study provides a theoretical basis for the controllable preparation of the TDPG electrode materials.

The high conductivity, high specific surface area, and excellent chemical stability and mechanical properties of graphene make it attractive as a conductive additive in cathodes for lithium-ion batteries （LIBs）. Unlike conventional additives, such as carbon black, graphite, and carbon nanotubes （CNTs）, flexible ultrathin graphene with a unique two-dimensional structure provides “plane-to-point” contact with the active materials, realizing long-range conduction while promoting fast electron transportation in the electrode. In this study, recent progress in graphene conductive additives used for cathodes in LIBs in fundamental research and industrial applications is reviewed. The combination of graphene with carbon black and/or CNTs as hybrid conductive additives can create a vast conductive network, including the “plane-to-point,” “point-to-point,” and “line-to-point” conducting modes; thus, this combination of long-range and short-range conduction increases the overall electrode conductivity. The obtained improvement in electrochemical performance not only affects the efficiency but also reduces the overall electrode production cost, realizing myriad potential applications in the industrial sector. Finally, the challenges and future prospects of graphene conductive additives are outlined.

Lithium-sulfur batteries have attracted considerable attention due to their high energy density. Their battery performance is closely related to the sulfur loading, sulfur content of the cathode, and amount of electrolyte. The complexity of the lithium-sulfur battery systems causes data distortion with coin cells. Literature reports on the performance evaluation of soft-packed batteries are rare. Six ether-based electrolytes were studied by linear sweep voltammetry and galvanostatic charge-discharge methods along with the physicochemical parameters, conductivity, and viscosity. The electrolyte lithium salts were lithium bis（trifluoromethanesulfonyl）imide （LiTFSI）, lithium hexafluorophosphate （LiPF₆）, and lithium tetrafluoroborate （LiBF₄）. The mixed solvent volume ratios of 1,2-dimethoxyethane （DME） to 1, 3-dioxane ring （DOL） were 1∶1 and 2∶1. The effects of six electrolytes on the first charge-discharge cycle, median discharge voltage, cycling performance, and charge-discharge efficiency were analyzed using an electrolyte/sulfur ratio of 3.5∶1 with 1.8 A·h lithium-sulfur soft-packed batteries. The results denoted that LiPF₆ was suitable for lithium-sulfur batteries as well as the conventional LiTFSI and mixed solvents in case of DME∶DOL = 2∶1, exhibiting better discharging capacity and a more effective cycling performance. The results based on Li-S soft-packed batteries are of high practical value.

Various factors, including slow temperature rise, insufficient heat storage, and rapid heat release rate, are observed to affect the promotion of distributed electric heating in the market according to the feedback analysis of the practical application of distributed electric heating in recent years. This can be mainly attributed to the user environment of distributed electric heating, including specific user conditions and the electric heating equipment. This study proposes the usage of a high-temperature phase change thermal-storage material as the thermal storage medium for a high-temperature phase change thermal-storage electric heater based on the equipment itself. The proposed material comprises a carbonate ceramic matrix composite, which is composed of a microporous ceramic matrix and carbonate with high viscosity, and exhibits a stable structure in the phase change state. To study the variables, such as the heating rate, heat storage, heat release rate, and user usage effect of a high-temperature phase change heat-storage electric heater, a mathematical model of the high-temperature phase change heat-storage electric heater is initially established using the ICEPAK commercial software. The heating operation of the electric heater is studied via a numerical simulation, and the temperature distribution diagram and temperature increase curve diagram are obtained with respect to a non-steady state heat storage process when the electric heater is in a stable state. Further, the accuracy of the simulation results can be verified using the same heating curve as the heat storage process. Real-time online monitoring method of the user’s room temperature is adopted to test the practical effects of the high-temperature phase change electric heater; the obtained temperature rise curve is consistent with the simulation and test results, and the room temperature is maintained at 18–20 °C, satisfying the heat demand of the users.

The development of energy storage materials can improve the solar energy utilization efficiency. Paraffin wax is a phase change energy storage material that exhibits high heat storage density and latent heat of phase change but low thermal conductivity. Iron foam was used to enhance the thermal conductivity of the paraffin-based phase change energy storage materials (PCMs). Further, the thermal storage properties of paraffin and iron foam/paraffin composite PCM were investigated through by preparing PCMs of different thickness and by testing the temperature increase at a drying medium temperature of 70 °C. The results reveal that the addition of iron foam can effectively improve the thermal conductivity of the iron foam/paraffin composite PCM, increase the heat transfer rate, and reduce the heat transfer duration. When compared with the control group, the mass fractions of paraffin in the composite (with thicknesses of 10 and 15 mm) decreased by 5.56% and 3.68%, respectively, and the time of phase change commencement was reduced by 15 and 17 min, respectively. The phase change duration was reduced by 42 and 31 min, respectively. The heat storage densities of the 10- and 15-mm composite PCM were 139.75 and 143.85 J·cm^-3, respectively, which were 8.81% and 8.01% lower than those of the control group. The heat storage rates were 3.05 and 3.96 J·s^-1, respectively, which were 1.22 and 1.11 times higher than those of the corresponding control group.

Solar energy is the first choice for developing clean energy because of its wide distribution, large reserves, and easy access. However, solar energy is affected by adverse weather conditions and seasons. Efficient methods for storing solar energy remain an urgent problem. Thus, understanding the factors that influence the thermal storage process of the phase change materials (PCMs) is important to improve the solar energy utilization rate. In this study, a two-dimensional (2-d) computational fluid dynamics model is developed on a shell-and-tube phase change energy storage heat exchanger. The melting process of the PCMs (paraffin wax) is numerically simulated using a solidification and melting model in FLUENT. The effects of the natural convection, paraffin thickness, and wall temperature on the heat transfer characteristics of the heat exchanger are studied during the charging process. Natural convection is demonstrated to significantly affect the growth of the PCM interface shape. The total melting time of paraffin increases with its thickness; however, it is not clear if a higher wall temperature of the heat-carrier fluid results in a faster melting rate. The influence of the wall temperature on the melting time significantly weakens when it exceeds the threshold.

Copper foam, nickel foam, and aluminum foam were used as supporting materials, and paraffin was used as the main material. Multiple composite phase change materials were prepared by constant temperature impregnation and pouring methods. Herein, the effects of adsorption temperature and time on the paraffin content of metal foam/paraffin composites and optimal conditions for preparing composite phase change materials by the constant temperature impregnation method are established. Adsorption was conducted at 70 °C for 10 min. The temperature field distribution and thermal conductivity of the multiple composite phase change materials prepared under the optimal condition were tested by the thermal conductivity measurement technology （based on the guarded hot-plate method and infrared imaging technology）. The results indicate that the copper foam/ paraffin composites were the most stable and exhibited the most uniform temperature field distribution during the thermal storage and release process. With a composite thermal storage material released between 35 °C and 50 °C, the shortest duration was revealed by the aluminum foam/ paraffin composite phase change material. The thermal conductivity of composite phase change materials prepared by constant temperature impregnation was 5-9 times higher than that of pure paraffin. The composite materials were prepared by pouring 6-13 times. This study is helpful in promoting the manufacture of metal foam/ paraffin composite phase change materials and provides an experimental basis for conducting future study on the temperature field distribution of the composite phase change materials.

As the key technology associated with the battery management systems of electric vehicles, the state of charge (SOC) of lithium-ion batteries describes the residual capacity and indicates the remaining mileage of electric vehicles. An extended Kalman filter (EKF), which is optimized by the improved Firefly algorithm, is proposed to research the estimation of the SOC of lithium-ion batteries for electric vehicles. The state-space representation of the battery model is estimated based on the second-order resistor-capacitor (RC) equivalent circuit model, which uses a pulse power characteristic test experiment to rapidly estimate the model parameters. Subsequently, the Firefly algorithm is applied to optimize the covariance of the system noise matrix and measurement matrix in the EKF to improve the SOC estimation accuracy. After performing the simulation experiments under dynamic and static conditions, the results denote that an algorithm for the estimation of SOC based on IFA–EKF results in a lower absolute maximum error and average absolute error when compared with those obtained via the EKF algorithm. Furthermore, the proposed algorithm offers improved accuracy and practicality.

The stacked lithium-ion batteries comprise many identical electrode-cell combinations. The internal physicochemical properties of each electrode significantly affect the battery performance. However, these properties are difficult to be experimentally measured. In this study, a three-dimensional electrochemical-thermal coupling model is proposed by coupling the mass, charge, energy, and electrochemical kinetic equations. The time-space distribution of the electrochemical behavior and thermal properties of a stacked lithium-ion battery is studied. The simulation results denote that during the discharge process, a significant distribution gradient can be observed between the potential distribution and the current density distribution with respect to the connection between the pole and plate; furthermore, the current density is the highest at the positive pole, the increase in temperature is the highest, and the increase in temperature is reached at the end of discharge. The maximum temperature is 8 °C. The rate of increase in temperature differs at different positions of the battery. In the early discharge stage, the rate of increase in temperature is higher near the ear area and lower away from the ear; as the discharge process is deeper, the rate of increase in temperature increases away from the ear. The model established in this study can accurately predict the electrochemical behavior and temperature field distribution inside a lithium-ion battery, which will help to provide a relevant basis for subsequent structural optimization and thermal management of the batteries.

Battery state estimation (state of charge, SOC) is particularly important in a battery management system (BMS). It is difficult to ensure its accuracy because SOC estimation is vulnerable to temperature, load, charging and discharging efficiency, and other external factors. Currently, many scholars use machine learning algorithms to estimate the SOC. However, the estimation accuracy of a neural network (NN) is dependent on the number of samples. The support vector machine (SVM) falls into a local optimum in parameter optimization. An online estimation method is proposed based on Gaussian process regression (GPR) for lithium-ion batteries to improve the estimation accuracy of the SOC. Based on the battery measurement parameters, including current, voltage, and temperature, as input to the GPR model and the SOC as an output of the model, the model is trained, and the parameters are optimized using the gradient descent method. The validity of the model is verified by simulation and data collected from the constant current charging and discharging experiments. Compared with the SVM, LSSVM, and NN, the validity and feasibility of the model are verified.

Accurately predicting the declining trend with respect to the capacity of a battery is important for strengthening the management and maintenance of the battery system. Lithium-ion batteries are the research object; the battery capacity decline trend is predicted based on a source data set analysis published by NASA Laboratories. The data for a full-cycle charge-discharge test of a battery, obtained at room temperature and constant current, are denoised and optimized by a compact set orthogonal wavelet analysis to obtain a more stable and regular battery capacity decay process. The ant colony optimization (ACO) algorithm is subsequently used to optimize the initial weight of the BP neural network. And threshold, based on the ACO-BP neural network model to predict the capacity decline of lithium-ion batteries, and compared with BP neural network alone. The results denote that the ACO-BP neural network generates better prediction results when compared with that generated by the BP neural network alone; with more training samples, it contains more information on battery capacity degradation, and the prediction accuracy is significantly improved. The predicted average error is 1.46% when 80 charge and discharge cycles are used as training samples. If the training samples are further expanded, the prediction effect will improve. This study helps to strengthen the management of the battery systems and provides a technical reference for efficiently predicting the degradation trajectory of the lithium-ion batteries.

Accurate estimation of the state-of-charge （SOC） with respect to the power in a lithium battery is the key to its safe and reliable use. Temperature significantly influences the usage of the lithium power battery. The advantages and disadvantages are compared by comprehensively analyzing the impact of various factors on the SOC for lithium batteries combined with various existing SOC estimation methods. Considering a temperature change from -10 ℃ to 40 ℃, a hybrid pulse power characteristic was obtained with respect to an AVIC 50 A·h lithium battery at intervals of 10 ℃. Based on the experimental data, the battery’s parameters were identified according to the least squares principle. The characteristics of the battery were explored with different temperature parameters, and the Thévenin equivalent circuit model （adapted for temperature changes） was established. The error variance matrix may gradually lose its positive definiteness or symmetry, resulting in filter divergence, because all the computer algorithm programs may be affected by word limitations or calculation errors. To solve this problem, the extended Kalman filter （EKF） algorithm is improved by square root decomposition of the EKF algorithm to accurately estimate the SOC. Through the simulation of the vehicle operating conditions of the China National Aviation’s ternary lithium battery, the simulation verification algorithm is used to estimate the effect under variable temperature conditions. The results reveal that the maximum error of SOC estimation based on the Thévenin equivalent circuit model at the considered variable temperature is less than 1.5% with an average error of 0.37%, which is better than that of the EKF algorithm. The improved EKF algorithm based on square root decomposition can rectify the error of the initial value of SOC and realize SOC estimation at different temperatures without depending on the accuracy of the initial value.

The power generation system based on PEMFC has been proven to be clean and efficient, which mainly consists of fuel supply and fuel cell subsystems. High-efficiency, safe and economic hydrogen storage technology is still the crucial factor affecting the large-scale practical applications of the PEMFC power generation system. The solid-state hydrogen storage method by chemisorption has the advantages of high capacity, good safety, and reversibility, thus being widely used as hydrogen sources and generally affecting the output properties of the power system. In this work, the models of the solid-state hydrogen storage reactor based on metal hydride and the PEMFC are established. Besides, the coupling process between the reactor and the fuel cell is modeled by MATLAB/SIMULINK to investigate the coupling characteristics. Based on the model, the effects of the important operating and design parameters, including hydrogen pressure, oxygen pressure, fuel cell temperature, and proton exchange membrane area, on the output performance of the power generation system are investigated. The simulation results show that the elevated temperature of the hydrogen storage reactor facilitates the improvement of power output of the system. This is because that the higher reaction temperature results in the higher hydrogen supply pressure, accordingly enhancing the fuel cell performance. In addition, the output power of the system also increases with the increase of the hydrogen pressure, fuel cell temperature and proton exchange membrane area. The corresponding power sensitivity coefficient of the three parameters is calculated to be 1.81, 0.73, and 0.036, respectively.

Energy storage is characterized by fast response and high flexibility and can provide several auxiliary services for a power grid, which is an important flexible resource that can absorb a considerable proportion of renewable energy. With the rapid decline in energy storage costs, the application of centralized and distributed energy storage in a power grid has recently become the focus of attention of international researchers. This study proposes a two-layer optimization model for the optimal placement and sizing of distributed electrochemical energy storage considering the uncertainty and intermittency associated with the renewable energy output. First, the study establishes an optimal objective function for electrochemical energy storage investment and operating costs considering the renewable energy uncertainty. Second, a two-layer optimization algorithm is applied to solve the sizing and placement of energy storage. The outer layer adopts the branch definition method to determine the energy storage location, whereas the inner layer uses the improved genetic algorithm to obtain the optimal capacity as well as the discharging/charging operation strategy of the storage system. Finally, the proposed method is applied using the IEEE-39 bus test system, and the validity and efficiency of the proposed method are verified.

The variations in light intensity and temperature induce the photovoltaic power generation to become random and intermittent, causing the photovoltaic output power to fluctuate considerably and affecting the safe operation of the power grid. Thus, a hybrid energy storage system comprising a storage battery and supercapacitor is investigated to reduce photovoltaic power fluctuation. This study proposes a power allocation method for variational mode decomposition. Combined with the photovoltaic power volatility and energy storage response characteristics, the photovoltaic power is classified as grid-connected power, which satisfies the national standard, and high and low compensation power; supercapacitors and batteries are used to provide high and low compensation power. A capacity optimization configuration model is established by considering the minimum annual comprehensive cost of the hybrid energy storage system as the objective function. Considering constraints, including the power balance, charge and discharge power limitation, and state of charge, an improved particle swarm optimization algorithm based on the Gaussian weighting of fitness values is used. The capacity configuration of energy storage equipment that meets the system compensation requirements is obtained, and the annual comprehensive cost of the hybrid energy storage system is minimized. Using this example, the mixed storage capacity allocations and costs of variational and empirical mode decomposition are compared and analyzed, and the capacity allocation results of mixed and single energy storage based on variational mode decomposition are compared and analyzed. The proposed method can suppress photovoltaic power fluctuation, reduce the energy storage capacity and annual comprehensive cost, and improve the system reliability and economy.

The energy storage technology is an effective method for solving the problem of poor power quality caused by intermittent and fluctuating power output. However, a single energy storage system has issues with low energy density or power density; therefore, a hybrid energy storage system （HESS） is extensively used to ensure the safe and stable operation of the power system. According to the structure and operational characteristics of the existing battery-supercapacitor HESS, this study proposes a bidirectional DC/DC converter for the HESS, which uses a battery as the main power supply and a supercapacitor as the auxiliary power supply. Meanwhile, the HESS includes a supercapacitor pre-charging circuit to ensure that the energy storage unit （supercapacitor） exhibits a good state of charge. The working principle and three working modes of the HESS （supercapacitor pre-charging cold stand-by mode, boost mode, and buck mode） are analyzed in detail, and the voltage conversion ratios of the boost and buck modes are determined. Further, the main waveforms are verified by building a simulation model using the MATLAB/Simulink software. The results show that the system has the advantages of low voltage stress and switching loss from switching devices, providing a high current and improved battery life. This study is helpful in promoting the application of a bidirectional DC/DC converter in the HESS and provides an experimental, theoretical, and simulation basis for the research and development of an efficient and stable hybrid energy storage technology.

Renewable energy contains embedded uncertainties, such as wind energy, solar energy, and load demand. This uncertainty adds ambiguity to smart grid planning. The existing research only focuses on intelligent optimization algorithms or the uncertain output of the source load to solve the optimal configuration problem of the independent microgrid; it fails to combine the intelligent optimization algorithm with the uncertainty processing method. Monte Carlo simulation （MCS） can successfully simulate the system output in a certain timescale to effectively deal with the uncertainty factors associated with the system. Furthermore, the gravitational search algorithm （GSA） is fast and accurate when dealing with this kind of optimal allocation. An MCS-embedded universal gravitation search algorithm （GSA-MCS） is proposed for solving the optimization model to effectively improve the economy of independent microgrids （by fully considering the reliability of microgrid power supply and renewable energy waste） and aiming at the optimization of system levelized energy cost （LCOE）. The main objective of GSA-MCS is to simulate the uncertainty of wind load through an MCS and substitute the simulated load data into the universal gravitation search algorithm to solve the capacity optimization configuration model. First, an MCS is applied to deal with the uncertainty of wind, light, and load, and the global optimization of wind, light, and storage is conducted using a gravitational search algorithm. The allocation scheme determines the allocation capacity at different cumulative probability levels. This study considers an island microgrid as an example to conduct simulation analysis and verify the effectiveness of the method used herein. The simulation results reveal that under different cumulative probability levels, the number of microgrid fans, photovoltaic panels, and energy storage cells reduce when compared with those obtained using traditional methods, and the LCOE is also reduced. When compared with the traditional optimization method, the proposed model can provide a compromise and flexible scheme for the capacity allocation of microgrid systems.

Pure electric buses have gradually become the main mode of urban public transport in China. One of the key issues associated with this development is how to provide rapid and timely electric power supply for the electric buses while avoiding the potential safety and economic impacts associated with a power grid system. This study proposes a charging strategy optimization method for pure electric buses using a double-level optimization model and a rolling optimization method while considering multiple factors that affect the charging strategy in a complex operating environment. First, this study establishes a two-tier optimization model for rapidly charging pure electric buses, aiming to minimize the costs associated with the charging and battery loss. The upper tier predicts a forecast charging plan for pure electric buses based on the expected full load rate, traffic index and time-of-use electricity cost. The lower tier is the model-dispatching level, which performs rolling optimization of the forecasted charging plan according to the real-time operation data. The MATLAB simulation results reveal that the proposed method can effectively optimize the pure electric bus charging process, improve the economy of rapid charging, and reduce the impact of concentrated charging of a large number of pure electric buses on the power grid.

This study aims to examine the significant impact of the frequent starting and braking of the urban rail trains on the voltage of the traction network. A hybrid energy storage system comprising a supercapacitor and battery, which can satisfy the high energy and power requirements of urban rail trains and maintain the voltage stability of the DC traction network to ensure its safe operation, is proposed. A power allocation strategy is designed for a hybrid energy storage system by considering the over-charge, over-discharge, and compensation range of the energy storage elements. Based on the low-pass filtering method, the power allocation strategy combines the supercapacitor’s state-of-charge to allocate and manage the power and energy of the hybrid energy storage system through a low-pass filter. The supercapacitor compensates for the variable high-frequency power, whereas the battery compensates for the corresponding low-frequency power. The simulation results reveal that the voltage of the DC traction network can fluctuate at approximately 1500 V; the battery and supercapacitor can operate within their respective states of charge and will not over-charge or over-discharge. The supercapacitor protects the battery from large shocks and increases the service life of the battery. The proposed hybrid energy storage system and control strategy can not only ensure that the voltage of the DC traction network fluctuates within the required range but also prolong the service life of the energy storage elements; the feedback energy of the urban rail trains can be captured to improve the energy utilization rate.

Aiming to solve the high energy consumption, large fluctuation of internal temperature and humidity issues of the conventional cold chain transportation containers, this paper presents a phase change materials (PCMs）-based cold thermal energy storage (TES） container for cold chain application. By installing 10 cold TES plates in a 40ft insulation container, the cooling of the interior of container can be achieved through the released cold during the solid-liquid phase transition of the PCMs inside the plates. The separate charging facility was introduced and the charging performance of the TES conditioner was studied. Experimental investigations of the internal temperature and humidity of the container with time have been carried out, the cooling time, the time evolution of the internal temperature and humidity under the dynamic condition are obtained. The charging time was found to be 6 hours. The dynamic discharging experiments showed that the cooling time of the TES container was long, and the internal relative humidity could be maintained between 85% and 95%. Compared with the conventional refrigeration container, the operation cost can be saved by 61.9%, with a payback period of 0.58 years. Higher internal relative humidity and longer cooling time, together with the benefits of operating costs, indicate the feasibility of the TES container for the cold chain application.

Although research on the fluoride-ion battery （FIB） as a new energy storage system is in its infancy, FIB has attracted increasing attention because of its high energy density, wide electrochemical window, and excellent charge transport kinetics. The difficulty in achieving high performance FIB lies in the exploration of electrolytes which allow rapid transportation of F^-during electrochemical reactions and the development of electrode materials for fluorine-based electrochemical reactions. In this review, the research progress in terms of the electrolyte and electrode materials of FIBs since the first proof of feasibility for a rechargeable FIB was presented in 2011 is summarized by introducing the developed solid electrolytes, liquid electrolytes, and conversion-and intercalation-based electrode materials. These research results expound the ion conduction mechanism of different prototype solid electrolytes and solve issues related to insoluble fluoride salts and the fact that the FIB can only be used at high temperatures. They also highlight the key factors that result in capacity decay during cycling.

Nickel-cobalt-manganese （NCM） lithium-ion batteries were selected for usage in electric passenger vehicles to study the variation in temperature, voltage, and characteristics of explosion venting and fire during thermal runaway. Battery thermal runaway and fire tests were performed during overheating and overcharging by temperature and voltage measurements and high-speed photography. The tests determined the relation between the temperature and voltage variation laws and the explosion venting process. Under overheating conditions, the dominant side reaction involved the positive electrode and electrolyte, resulting in the production of large amounts of oxygen and combustible hydrocarbons, and the time span from battery expansion to explosion venting near the electrode tab was only 0.5 s, during which a jet flame initially appeared. Under overcharging conditions, the dominant side reaction involved the negative electrode and electrolyte; this initially produced a solid-liquid-gas mixture during explosion venting and formed a jet flame after a period of continuous venting. Under the two trigger conditions, the battery burning times were less than 50 s, the highest temperatures were approximately 700 °C, the combustion residue temperatures exceeded 500 °C, and the voltages did not change significantly before explosion venting. When compared with the experimental data obtained by previous scholars, the safety of the NCM battery series is ranked from 333, 622, 811 from high to low. This study provides an experimental basis for the practical application, thermal runaway fire prevention, and early warning technology for high-specific-energy lithium-ion batteries.

Thermal safety is the main safety problem associated with lithium-ion batteries . High temperatures are extremely harmful to lithium batteries, affecting their service life and potentially endangering their safety. A ternary cylindrical high-nickel lithium-ion battery is the object of this study, and the heat–wait–seek mode of an adiabatic accelerating rate calorimeter is used to study the thermal parameters of a lithium-ion battery when high-temperature thermal runaway occurs under five groups of operating conditions [state of charge (SOC) = 0, 25%, 50%, 75%, and 100%]. The experimental results show that 1) in a lithium-ion battery, the initial temperature of self-generated heat is minimally affected by the battery SOC and is mainly dependent on the solid electrolyte interface film decomposition, 2) the thermal runaway onset temperature tends to decrease as the SOC increases, and the reaction between the positive electrode and electrolyte produces heat, which is the main cause of thermal runaway, 3) the temperature at which the voltage line drop and safety valve damage occur during the thermal runaway process decreases as the battery SOC increases, and 4) the higher the SOC of the lithium-ion battery, the higher will be the maximum temperature in the thermal runaway process, the higher will be the rate of temperature increase, and the more severe will be the damage to the lithium-ion battery.

In the prediction method of the power lithium battery state of charge （SOC）, there are problems such as the cumulative error of the ampere-time integration method and the divergence of the estimation result of the extended Kalman filter algorithm. This paper proposes a soc estimation strategy based on the interactive multi-model unscented Kalman filter （IMM-UKF） algorithm. Firstly, the second-order RC battery equivalent model is established，The recursive least squares method with forgetting factor is used to identify the battery equivalent model parameters online, and consider the battery's actual capacity change and sensor noise caused by the discharge of the battery under different magnification conditions. Three different parameters of the battery model of current, medium current and small current, then study the Markov chain between the three models, determine the transition probability and model probability between each model based on the prior information, and finally build the matlab simulation model，The experimental results show that the average error of IMM-UKF is less than 1%, the adaptability of the algorithm is enhanced, and the prediction accuracy is improved, which has better prediction effect than the current mainstream prediction methods.

The thermal characteristics of the lithium-ion battery packs are of considerable significance for their operation and maintenance. In this study, a cell thermal model is simplified into a uniform heating unit to simplify the computation during the simulation process. The novel model structure is validated through thermal simulation using a lithium-ion battery pack, and its accuracy can be experimentally verified. Further, the thermal characteristic parameters of the lithium-ion cells are acquired via an accelerating rate calorimeter. Subsequently, a lithium-ion battery pack thermal model is constructed and solved using computational fluid dynamics and computer-aided design programs based on the simplified cell thermal model and considering an air cooling scenario. The internal flow field distribution and in-service temperature data of the battery pack are analyzed. Finally, the accuracy of the simulation result is verified through a prototype experiment. When charged and discharged at a constant current of 0.5C, the simulated temperature of this battery pack exhibits the same variation profile as that exhibited by the experimental measurement with an error of 0.9 °C being observed with respect to the maximum temperature and 0.2 °C being observed with respect to the temperature difference in case of the simulation and experimental results.

During the previous two years, China’s energy storage industry has witnessed explosive growth. Compared with other energy storage technologies, lithium-ion batteries are more competitive due to rapid advances in production technology and a gradual decline in manufacturing costs, and the market penetration rate in the field of energy storage is continuously increasing. As an electronic device for monitoring and managing a battery, the battery management system (BMS) is the core component of an energy storage system. Its functional safety is related to the safe and stable operation of an entire lithium-ion battery power station. To accurately and efficiently implement the design and verification of function safety in the BMS of the energy storage system, the analysis and design of a BMS to achieve functional safety, which is primarily described through system hazard identification and risk analysis, overall safety requirements and safety function allocation, and safety integrity verification, are outlined by incorporating the characteristics of a lithium-ion battery energy storage system BMS according to IEC 61508, GB/T 20438, and other related reference standards. The analysis shows that the failure mode effects and diagnostic analysis, the risk matrix, and the reliability block diagram are suitable for the functional safety analysis and design of the BMS of the energy storage system. Based on the IEC 61508 and IEC 60730-1 standards, combined with the characteristics of the energy storage system, an accurate analysis design ensures that the functional safety integrity level of the energy storage system BMS is effectively achieved. These provide a reference for the design and development of the energy storage power stations.

Lithium-ion batteries are used in various energy storage systems on a large scale because of the advantages of high energy density, low discharge rate, long life, and excellent electrochemical performance. The energy storage magnitude is observed to continually increase. However, in the previous two years, safety accidents have frequently occurred in lithium-ion battery energy storage power stations at home and abroad. This study introduces foreign and domestic safety standards of lithium-ion battery energy storage, including the IEC and UL safety standards, China’s current energy storage national standards, industry standards, and energy storage safety standards set by the alliance, to improve and perfect the safety standards of the current domestic energy storage systems. This study briefly analyzes the characteristics of the energy storage safety standards established at home and abroad. Further, the storage system security requirements, battery or cell safety requirements, effects, and system safety requirements are used to analyze the operational requirements of the lithium-ion battery energy storage system, domestic energy storage safety standards, and foreign standards （IEC and UL） according to the specific tests of the lithium-ion battery energy storage system. Finally, the weaknesses and shortcomings of the current domestic energy storage safety standards are revealed. By comprehensively analyzing, comparing, and discussing the safety standards for lithium-ion batteries in energy storage systems at home and abroad, this study proposes suggestions and implementation strategies to improve the safety standards in domestic energy storage power stations to promote the safe, efficient, and long-lasting operation of future energy storage systems.

With continuous strengthening of the national environmental protection efforts, the proportion of new forms of energy power generation has gradually increased, resulting in gradual transformations in the energy structure of China. Because of the fast response rate and high adjustment accuracy of an energy storage system, it has become an important supporting method to improve the power quality and promote the consumption of new types of energy within the energy industry; it has also become the subject of increasing attention. Furthermore, the advancement of the energy storage technology (through the improvement of the product quality and continuous cost reduction) has realized its commercial application. The development of various electrochemical energy storage technologies has gradually expanded the energy storage application possibilities. In addition to technological advances, the promulgation of national policies and regulations and the deepening of power market reforms have promoted the application and support of electrochemical energy storage technologies. This study summarizes the application status of energy storage in the global power industry from a data perspective. It summarizes the development of the energy storage policies and standards of the domestic electrochemical industry and introduces the modes, technical routes, and key technology for the integration of electrochemical energy storage. Additionally, from the perspective of power generation, the use of electrochemical energy storage technology in new, large-scale grid-connected, auxiliary, and microgrid level settings is discussed in terms of the functions, policies, and application projects. Finally, the potential and development trends of electrochemical energy storage technology with respect to future energy systems are considered, and development suggestions for energy storage enterprises are proposed to promote the commercial operation and usage of energy storage.

The development and utilization of renewable energy have posed severe challenges to the normal operation and scheduling of the existing power grid systems. The identification and implementation of cost-effective and sustainable energy storage and conversion systems are particularly important. The energy storage technologies mainly consist of four types, i.e., physical, electrochemical, chemical, and phase change. This study uses the INSPEC database for retrieving research papers. A bibliometric method and the VOSviewer analysis tool are adopted to obtain quantitative statistics and perform cluster analysis; further, the analysis results are visually represented. The output of global papers on energy storage has exhibited a sustained and rapid development trend, and China has become the largest contributor to this type of research. China contributes more than one-fifth of all the energy storage papers and more than 40% of the highly cited papers. China, the United States, Japan, and Germany are interested in the development of supercapacitors, graphene-based energy storage materials, and electrochemical cells. The energy storage technology is interdisciplinary, which provides remarkable application for basic research characteristics and presents a good diversified development trend. Over the previous decade, research has mainly focused on electrochemical energy storage, microgrids with renewable energy source and energy storage systems, phase change materials, and thermal energy storage systems and hybrid energy storage systems. Simultaneously, rapid development and application of these technologies have been observed in related industries.

The development of distributed energy storage in the context of the international market would be impossible without policy support and market rules. Since 2011, more than 10 countries and regions have released distributed energy storage subsidy policies; majority of these policies have focused on encouraging the consumption of distributed solar-plus-storage systems for self-generation and use or supporting independent residential storage systems. These subsidies are primarily provided for the first-time installation of a system, helping to alleviate some financial burdens associated with the purchase, lease, and installation of energy storage systems. Subsidies are most often dispersed at a rate of 30%-60% of the initial cost of a single individual system. With stimulus policies encouraging the rapid development of distributed energy storage, some countries have initiated energy system reforms, which simplify the process for the participation of distributed energy storage in the power market, reduce the capacity size limits for market participation, and allow distributed energy storage to participate in new markets. Such reforms have helped to harness the value of energy storage in contributing to grid stability, safety, and the increased use of renewables in the network while increasing the revenue of the project owners.