Transport, reaction, and storage of Li ions in bulk electrode materials leads to the dynamic evolution of their electronic and crystal structures, microstructures, chemical compositions, and physical properties, which are the important determinants in the electrochemical performance of Li ion batteries. It is extremely important to understand the fundamental physical and chemical properties of electrode materials at a nanometer or even atomic scale to determine their microstructure, morphology, phase, and chemical composition during an electrochemical process. The structure-activity relationship between the electrode materials and macroscopic electrochemical performance of a battery must be considered. These require clear, precise, and advanced in situ characterizations. Among existing in situ characterization techniques, in situ transmission electron microscopy (TEM) is one of the most representative and important methods to conduct these experiments. Its unique advantages include ultra-high spatial and temporal resolution and real-time, dynamic monitoring of the structure, morphology, phase and interface evolution of the electrode materials under the given working conditions. It can precisely evaluate the microscopic dynamic evolution behavior and the reaction mechanism of electrode materials, providing a microscopic basis and innovative ideas for the construction and performance regulation of high-performance electrode materials. In this study, we summarize important progress on in situ TEM investigations of the dynamic evolution and failure mechanism of key electrode materials in Li ion batteries during charge/discharge. These investigations include various cathode materials and high specific capacity anode materials, especially their dynamic evolutions in microstructure, chemical composition, and phases during an electrochemical process. Moreover, the current limitations of in situ TEM and future directions of in situ TEM investigation of secondary batteries are discussed.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 3015 papers online from Apr. 1, 2021 to May 31, 2021. 100 of them were selected to be highlighted. Nickel rich ternary layered oxides and the high-voltage spinel materials are still under extensive investigations for the influences of preparation of precursors, doping and interface modifications on their electrochemical performances. The researches of silicon-based composite anode materials focus mainly on the design of electrode structure, while the researches of lithium metal anode focus on electrolyte additives and further to regulate the growth of SEI and inhibit the formation of lithium dendrites. Solid state electrolytes including oxide, sulfide, polymer and composite materials have been studied. Meanwhile, large efforts are still devoted to liquid electrolytes for the additives to improve the performances of graphite and silicon anodes, the high-voltage spinel and LiCoO₂ and ternary layered structure cathode materials. For solid-state batteries, the design and preparation of composite cathode, surface modification of active materials, and lithium metal/solid electrolyte interface are the main topics. To suppress the "shuttle effect" of Li-S battery, composite sulfur cathode with high ion/electronic conductive matrix and electrolyte additives are studied. The characterization work include the investigations on Li deposition, SEI of Si-based anode, microstructures and interfacial reaction of composite cathodes. Furthermore, there are a few theoretical calculation papers related to the stability of solid electrolyte, the interfaces of solid state electrolyte/Li and Li metal deposition.

Transition metal oxides (TMOs) are considered to be one of the best choices to replace graphite as a negative electrode material for Li ion batteries because of the extremely high theoretical specific capacity of TMOs. However, during charging and discharging, excessive volume expansion and poor electrical conductivity limit its further development. Combining TMO materials with carbon materials can meet the demand for Li storage capacity and avoid excessive volume expansion during charging and discharging. After an investigation of recent literature, research results are summarized regarding the preparation of TMO/C hybrid nanofibers using an electrospinning technology as anode materials for Li ion batteries. The preparation process of TMO/C hybrid nanofibers with porous, core-shell, hollow, and hybrid structures, and the influence of these special structures on the performance of Li ion batteries, are introduced. Comprehensive analysis shows that nanofiber membranes with larger specific surface areas and rich pore structures provide additional active sites for chemical reactions during the charge and discharge cycle and establish a good conductive path for the rapid diffusion and charge transfer of Li ions. This can considerably improve the electrochemical performance of Li ion batteries. Finally, the current limitations and challenges in this field are discussed, and future development directions of TMO-based Li-ion battery anode materials are suggested. Prospective research directions could include the simplification of the preparation process, reduction in the cost of preparation, increase in preparation efficiency, and improvement in mass production. It will be important to discover more suitable materials to combine with TMOs to develop Li ion batteries with a more reasonable structure and improved performance.

Because of the ultra-high theoretical capacity density (3680 mA·h·g^-1) and the low reduction potential (-3.04 V versus the standard hydrogen electrode), metallic Li is considered the "Holy Grail" anode material for high energy density battery systems. However, a series of problems such as low Coulombic efficiency, short cycle life, and internal short circuits caused by Li dendritic growth and high reactivity toward electrolytes hinder the practical utilization of Li metal anodes. In a practical electrochemical system, the current collector is the substrate for the plating and stripping of Li. Therefore, its surface properties play a vital role on the cyclic stability of the Li metal anode. In this study, multiple strategies of surface modification and microstructure design on current collectors to stabilize Li metal anodes are systematically summarized, including the fabrication of lithophilic surfaces, the modification of nanoscale electronic/ionic hybrid conductive networks, and the design of surface microstructures. Targeted interface/structure modifications of the current collector can effectively regulate the electrodeposition of Li and promote the practical application of Li metal anodes in high energy density battery systems.

Thermochemical energy storage using salt hydrates has the advantages of high heat storage density, less heat loss, and seasonal storage adaptability. It is an effective method to provide clean heating along with renewable energy, such as solar energy, to achieve carbon neutrality. A heat storage reactor is an important component of salt hydrate-based thermochemical energy storage; moreover, it determines the efficiency and reliability of energy storage systems. However, owing to unsuitable material formulations and structural designs, a heat storage reactor has limitations such as low thermal power, poor cycle stability, and short service life. To address these issues, this study reviewed state-of-the-art methods for reactor optimization in terms of salt hydrate formulation and heat and mass transfer mechanisms. Unlike existing review studies, this study introduced a novel type of material, i.e., a metal-organic framework (MOF), in the field of salt hydrate-based thermochemical energy storage. The results demonstrate that the performance of composite salt hydrates based on MOFs is better than that of traditional skeleton materials. This study summarizes the heat and mass transfer mechanisms and mathematical models of the reactor and related experimental research and performance optimization. Based on an in-depth analysis, this study highlights the priorities of future research, including the development of high-performance composite salt hydrates, a study of the reactor on both micro- and nano-scales, and optimization of the reactor structure. This study is significant for suggesting improvements in the heat mass transfer performance and stability of reactors for thermochemical energy storage.

Using thermoplastic elastomers(SEBS)as the base, four different paraffin(OP44E, Paraffin46-48, OP50E, and OP55E)phase change materials were prepared. These composite materials produced thermal therapy nasal strips with different phase change temperatures that were obtained by physical adsorption and a flat-plate vulcanization system. The hardness, phase change temperature, phase change latent heat of the composite materials, and temperature effects of thermal therapy nasal strips were measured. The results demonstrate that the hardness of the four types of thermal therapy nasal strips are close to 0 HA in the state above the phase change temperature and are in a very soft state such that the thermal therapy nasal strip and one's nose could fit closely together. The phase change temperature is comparable with that of paraffin, and the phase change value is >135 J·g^-1. It is a convenient and fast approach to heat the thermal therapy nasal strip from room temperature to 60 ℃ in only 1.5 min under 80 ℃ water temperature conditions. The appropriate phase change temperature of the thermal therapy nasal strip is from 46 to 48 ℃. Paraffin 46—48/SEBS thermal therapy nasal strips with a thickness of 10 mm can meet the requirements of heat therapy lasting 15—20 min with the nasal temperature maintained at>43 ℃. This study effectively improved the temperature and time problems existing in the treatment of rhinitis symptoms with localized heat therapy and promoted the application of effective heat therapy in rhinitis treatment.

The thermophysical properties of three different proportions of high-temperature mixed carbonate molten salts were studied to meet the requirements of high-temperature heat transfer and storage in a supercritical carbon dioxide solar thermal power generation system. The results show that the melting points of the mixed carbonate molten salts are 388.7 ℃, 337.9 ℃, and 391.3 ℃; initial crystallization points occur at 454.9 ℃, 639.7 ℃, and 535.4 ℃; and decomposition temperatures of the first and third salts are 916.2 ℃ and 920.4 ℃, respectively. The initial crystallization point of the second mixed carbonate molten salt is high, and its melting latent heat is small. Therefore, the first and third mixed carbonate molten salts are selected to measure specific heat, thermal conductivity, and viscosity. It is found that the specific heat of the first and third salts initially decrease and then increase with increasing temperature within the experimental range. The average thermal conductivity of the first mixed carbonate molten salt is 1.024 W·(m·K)^-1, which is 2.29 times of that of the third salt; the viscosity of these salts gradually decreases with increasing temperature. The minimum viscosity values of the first and third mixed carbonate molten salts are 6.62 and 5.28 mPa·s, respectively.

To accurately calculate the heat transfer and heat storage capacity of a molten salt nanofluid, SiO₂ nanoparticles were dispersed into a binary nitrate mixture (60% NaNO₃-40% KNO₃) by a high-temperature melting method, and then five molten salt nanofluids with different SiO₂ nanoparticles were prepared. Using the Archimedes method to measure the liquid density and the pulling escape method to measure the liquid surface tension, the experimental stand was improved. The surface tension and density of the five molten salt nanofluids were measured, and the experimental data were fitted to obtain the relationships of density and surface tension of the five molten salt nanofluids with temperature, and the experimental correlations of the density, the surface tension of molten salt nanofluids, and the temperature was obtained. The results demonstrated that the density of the base salt and the molten salt nanofluids decreased with increase in temperature, and the density of the molten salt nanofluids did not significantly change after addition of the SiO₂ nanoparticles. The surface tension of the base salt and the five molten salt nanofluids decreased with increasing temperature. A formation mechanism of molten salt nanofluids was proposed, and an explanation was given for the changes in density and surface tension.

An amphoteric ion-exchange membrane (SPEEK/PEI) was prepared in accordance with the demand for the Fe-Cr redox flow battery. An efficient hydrogen bond network was formed by introducing highly hydrophilic polyethyleneimine (PEI) into poly(ether ether ketone) (SPEEK). By introducing PEI with an amino group, the swelling ratio of the SPEEK membrane was effectively reduced, and the permeability of Fe²⁺ and Cr³⁺ was inhibited. Furthermore, high proton conductivity was maintained owing to the formation of hydrophilic channels by PEI. Based on the efficient hydrogen bonding network, SPEEK/PEI membranes can effectively improve the Coulombic efficiency and energy efficiency of Fe-Cr redox flow batteries. The Coulombic efficiency of a 3% SPEEK/PEI membrane was 96.5%, and energy efficiency was 79.4% in the performance testing of the Fe-Cr redox flow battery at an ampere density of 70 mA/cm².

LiNi_0.8Co_0.1Mn_0.1O₂ dry electrodes for lithium-ion batteries were prepared using a solvent-free electrode preparation technology. The morphology and elemental distribution of the dry electrodes were analyzed using a scanning electron microscope and an X-ray energy spectrometer (EDS). The electrochemical performance of LiNi_0.8Co_0.1Mn_0.1O₂ dry electrodes were characterized by the rate of charge/discharge, electrochemical impedance spectroscopy, and cycle charge/discharge. The results show that in the dry electrodes, PTFE fibers are widely distributed around the LiNi_0.8Co_0.1Mn_0.1O₂ particles, which form a dense, complete, and flexible net-like binding structure. Batteries containing the dry electrodes delivered an excellent capacity retention of 94.89% for more than 500 cycles, which is much greater than that of traditional wet-coated electrodes. Inside the dry electrodes after 500 cycles, a stable net-like binding structure was maintained, and there were significantly less cracks on the surface of the LiNi_0.8Co_0.1Mn_0.1O₂ particles than on the wet-coated electrodes. These results indicate that the three-dimensional net-like binding structure formed by PTFE fibers can effectively improve the anti-deterioration performance of the electrodes. No solvents were used in the preparation of the dry electrodes, which can reduce the amount of raw materials and energy consumption, and thus be environmentally friendly. The solvent-free electrode preparation technology provides many practical applications in the preparation of thick electrodes to i ncrease the energy density of lithium-ion batteries.

In this study, three types of alkyl sulfonate anthraquinones, (1-hydroxy-2-oxopropane sulfonic acid anthraquinone (1,2-AQPSH₂), 2,6-dioxopropane sulfonic acid anthraquinone (2,6-AQDPSH₂), and 1-hydroxy-2-oxopropane sulfonic acid anthraquinone (1,4-AQPSH₂), were synthesized using propane sultone from 1,2-dihydroxyanthraquinone, 2,6-dihydroxyanthraquinone and 1,4-dihydroxyanthracene, respectively. Solubility and the oxidation-reduction properties of these three anthraquinones in 1 mol/L NaCl aqueous solution under neutral conditions were studied in detail. 1,4-AQPSH₂ was selected and used as an anodolyte, 2,2,6,6-tetramethylpiperidinol (4-OH-TEMPO) was used as a catholyte, and Nafion 212 was used as an ion-exchange membrane to assemble a neutral water-based organic redox flow battery cell. Open circuit voltage of the flow battery was about 1.0 V; at a current density of 60 mA·cm^-2, the Coulombic efficiency, energy efficiency, and voltage efficiency of the cell were 97%, 68%, and 69%, respectively. At a current density of 60 mA·cm^-2, there was no substantial reduction in the discharge capacity of the battery after 75 charging and discharging cycles. These results demonstrate that 1,4-AQPSH₂ shows promise as an anolyte for neutral water-based organic redox flow batteries.

In order to explore the influence of the N/P ratio on the performance of lithium iron phosphate batteries, four kinds of N/P ratios of lithium-ion batteries were fabricated by using lithium iron phosphate as the cathode material and artificial graphite as the anode material. The effects of the first discharge efficiency; charge and discharge performance at different current intensities; charge and discharge DCR; discharge capacity at high and low temperatures; and cycle performance at 45 ℃ using different N/P ratios were studied by electrochemical technology. The results show that the charge DCRs of lithium-ion batteries at 1.10 and 1.14 are about 4 MΩ smaller than those of N/P ratios (1.02 and 1.06) at 60% and 30% SOC, making them less polarized under high current intensities and low temperature conditions. With the increase of N/P, the charging constant current ratio and capacity retention rate at 0 ℃ are improved. The capacity retention rate is still 91.8% after 1000 cycles at 45 ℃ when N/P is 1.10, which is significantly higher than other groups (N/P ratios at 1.02 and 1.06). This research could provide a theoretical basis for future investigation of the design and use of lithium iron phosphate batteries.

Aqueous Li ion batteries have been extensively studied for their safety and high ionic conductivity. As an important cathode material, LiMn₂O₄ is limited because of its poor cyclic stability in aqueous Li ion batteries. Al-doped LiMn₂O₄ cathode materials were synthesized by a simple high-temperature solid phase method, using acetylene black as the template, and applied to aqueous Li ion batteries. The discharge specific capacity of LiMn₂O₄ (125.5 mA·h·g^-1) at 0.1A·g^-1 is slightly higher than that of LiMn_1.9Al_0.1O₄(121.6 mA·h·g^-1). The capacity retention of LiMn_1.9Al_0.1O₄ cathode materials at 0.1 A·g^-1 is 90% after 200 cycles, which is higher than that of LiMn₂O₄ (78%). At a high current density of 1 A·g^-1, the LiMn_1.9Al_0.1O₄ sample displays 88% capacity retention after 500 cycles, which is considerably higher than the LiMn₂O₄ sample (57%). These results confirm that Al-doped LiMn₂O₄ cathodes can alleviate the dissolution of Mn, inhibit the Jahn-Teller effect, and improve the cycling performance.

Cycle life at ambient temperatures is an important indicator of power battery applications. With a stable cathode and a simple electrolyte, the analysis of the capacity fading mechanism in lithium iron phosphate (LFP) power batteries is of great significance for a comprehensive understanding of capacity fading in these power batteries and for improving electrochemical performance. This study discusses the capacity fading mechanism in ambient cycling based on commercial lithium iron phosphate power batteries at different states of health (SOH). Electrochemical differential capacity analysis is applied to batteries cycled at ambient temperature to determine the polarization alteration. The area charge of peaks on a differential capacity curve is used to analyze the source of the capacity loss. Capacity loss is mainly derived from the reaction of graphite on the third plateau, not from the result of polarization upon cycling. Charge transfer resistance of the anode is found to increase significantly in electrochemical impedance spectroscopy collected on tri-electrode cells. No evident capacity losses of positive and negative electrodes are observed on coin cells whose electrodes were collected from LFP batteries of different SOH, indicating no deterioration in cathode and anode materials. The investigation shows that the capacity fading at ambient temperature cycling is mainly caused by the active lithium loss from side reactions and kinetic fading of the anode. The kinetic fading of the anode is commonly exhibited during the cycles by the thickening of the SEI and stress on the batteries.

At present, the safety problem caused by thermal runaway (TR) of lithium-ion batteries (LIBs) has been the bottleneck for the promotion of electric vehicles and large-scale energy storage stations. To tackle this problem, great efforts have been made to study the TR characteristics of LIBs. The electrical abuse and the thermal abuse are two key reasons that induce the TR. In this paper, based on the TR model, the electrical and thermal response of LIB are systematically studied under different abuse conditions. Three influencing impacts are comprehensively investigated, including charging rate, ambient temperature and heat dissipation. These results show that compared with the TR induced by the overcharge, the TR would occur at lower SOC under the combined overcharge and overheating condition. In the face of extreme high temperature environment, the TR could even occur at the early charge stage. Moreover, under the overheat condition with low surface heat transfer coefficient, the charging rate has little effect on trigger SOC of thermal runaway; While under the overheat condition with natural convection condition, the thermal runaway would occur at higher SOC with the increase of charging rate, but the thermal runaway time would be reduced. This study provides support for the development of reliable battery safety early warning technology.

The long-term stable operation of renewable battery energy storage systems is closely related to the heat management of energy storage systems, and a reasonable heat management strategy can guarantee the economy and safety of the system. In order to determine a way to carry out the heat management of energy storage systems reasonably and effectively, this study proposes a scheduling strategy for energy storage power plants that considers heat management and battery life with an optimization target of high net profit in intraday real-time scheduling. It also uses the piecewise McCormick method to linearize the bilinear term and then uses Gurobi for a fast solution to meet the intraday real-time scheduling requirements. The case simulation shows that the proposed model can balance heat management and plant economy, which is significantly superior to the traditional scheduling strategy. The piecewise McCormick method offers better results than the general intelligent algorithm in terms of solution time and smaller errors.

Thermal characteristics are a major factor affecting the performance of lithium-ion batteries. When a battery is charged and discharged at a high rate, heat accumulation causes the temperature to rise rapidly, affecting the battery performance and even causing the danger of combustion or explosion. In this study, the heat generation mechanism of lithium-ion batteries is studied by combining theory with experiment. The HPPC pulse current method is used to identify the internal ohmic resistance and internal polarization resistance of the battery offline, and the heat transfer coefficient of the flat heat pipe is identified by the least square method. Under various working conditions, the average temperature and the maximum temperature difference at the battery surface were calculated, and the accuracy of the thermal management model was experimentally verified. At an ambient temperature of 20 ℃, a cooling wind speed of 5 m/s, and the discharge of the battery pack at the cut-off voltage of 1 C, the average temperature of the battery pack is 38 ℃, and the maximum temperature difference is 1.9 ℃. When the heat exchange area increases, the heat exchange efficiency improves. This research promotes the application of flat heat pipes in the heat dissipation of power batteries and provides a basis for ensuring the safety and efficiency of batteries under high-rate charging and discharging.

The cold storage heat exchanger is an important part of a supercritical compressed air energy storage system. In order to explore the influence of design parameters on the processing cost and performance of the cold storage device, a supercritical packed bed cold storage heat exchanger is designed with solid sodium chloride as the cold storage material. According to the required parameters of the system and the constraint equation of the size of the pressure vessel, the 10 MW cold storage heat exchanger is optimized in order to minimize the tank mass and processing costs, minimize the cooling loss, and increase the cold storage efficiency. It is found that with increasing height of the heat exchanger, the tank mass and cost rise gradually. Analyzing the efficiency of the cold storage device under different powers ranging from 0.5MW to 10 MW, we determined that the cold storage efficiency increases gradually from 94.65% to 96.08% with increasing power when the aspect ratio is constant; the cold loss also increases with the power. Finally, in fourteen sets of optimized data, the cold loss of the heat exchanger is relatively low under optimal parameters, with the cold storage efficiency being 96.08%. The processing cost also falls within the acceptable range.

As there is no central heating in most cold winter zones in China, the use of efficient heat pumps is a promising way to achieve clean heating. Based on the principle of phase transformation under supercooling, ice source heat pump uses the latent heat of water near freezing point, which has high energy efficiency and wide applicability. EES (engineering equation solver) software was used to simulate the performance of the ice source heat pump. The influence of parameters such as refrigerant, supercooling degree and condensing temperature on system performance was studied. The results indicated that R22 refrigerant can achieve the highest COP_sys For the system using refrigerant R22, when subcooling degree of subcooled water increased from 1.0 K to 3.5 K, COP_sys decreased from 2.87 to 2.71, which decreased by 5.57%. When the condensing temperature increased from 35 ℃ to 55 ℃, COP_sys decreased significantly from 3.4 to 2.3. What's more, to analyze the operation economy of ice source heat pump, the dynamic change of heating load of 200 m² building in Shanghai and Chongqing was simulated by TRNSYS. The results showed that the operating costs per square meter during heating period were 12.7 yuan/m² and 5.6 yuan/m² respectively. Besides, ice source heat pumps were more economical when operating in Shanghai.

In recent years, the development of energy storage trams has attracted considerable attention. Our current research focuses on a new type of tram power supply system that combines ground charging devices and energy storage technology. Based on the existing operating mode of a tram on a certain line, this study examines the combination of ground-charging devices and energy storage technology to form a vehicle (with a Li battery and a super capacitor) and a ground (ground charging pile) power system. Under the premise of tram operation and safety, an economic model of the integrated power system of ground, vehicle, and ground is established, and a particle swarm optimization (PSO) algorithm is used to obtain the most economical capacity allocation plan. Through a comparative analysis and compared with the existing pure supercapacitor "station charging" mode, the new capacity configuration scheme proposed in this study would reduce the average daily cost by 9.8% and save 10.64 million yuan in the overall cost. The charging power requirements would be reduced by 66.7%.

Equalization control, as an effective way to improve inconsistencies in electric vehicle battery packs, has been developed as one of the key technologies in automobile power batteries. In order to solve the problems of long time and slow balancing speed of inductive topological equalization, this study proposes a multi-staggered symmetric equalization scheme based on Cuk circuits. Taking a single battery for the investigation, the stop parameters were introduced to complete the design and optimization of the equalization strategy, and equalization control was achieved. This equalization scheme, which has the advantages of simple topology and fast balancing speed, overcomes the disadvantages of the long energy transfer path of traditional inductive equalization and achieves the adaptive adjustment of control signal duty cycles of the balancing module. Finally, in order to verify the results, an equalization simulation model of ten batteries was built. The simulation results show that the equalization scheme can improve the equalization speed and the inconsistency of battery packs.

Sodium-ion batteries (SIBs) show promising application prospect in large-scale energy storage, due to the abundant and low-cost sodium resources. Most of the research focuses on the development of new SIB materials such as electrodes and electrolytes. Engineering manufacturing technologies and demonstration applications are still in the exploration stage. To ensure high safety, long life, and high efficiency operation, the battery management systems (BMSs) based on the characteristics of SIBs need to be developed. Accurate state of health (SOH) prediction is one of the core functions of BMS, and single-step-ahead and multi-step-ahead SOH prediction are important for the estimation of state of charge and the prediction of remaining useful life (RUL), respectively. Compared to lithium-ion batteries, SIBs have similar operation mechanism, but the larger sodium ions result in more complicated battery characteristics and aging mechanism, which may make it difficult for accurate SOH prediction for the full SIBs. Based on the SOH time series, a double-exponential model-based Particle filter (DEM-PF) method and a wavelet-analysis-based Gaussian process regression (WA-GPR) method are proposed. In the DEM-PF method, the DEM is utilized to model SOH time series. The PF is used to update the model parameters. In the WA-GPR method, WA is used to decouple the global degradation trend and local capacity regeneration and fluctuations of SOH time series. The GPR with time index input is used to prediction the global degradation trend. The GPR with lag vector input realizes the autoregression of the local capacity regeneration and fluctuation. The two methods are validated and compared in the 1 C charge/discharge aging test of a 1 A·h pouch-type SIB. The results indicates that the WA-GPR method shows better accuracy and stability both in the one-step-ahead SOH and RUL prediction, with the prediction root mean square error of 0.8% for one-step-ahead SOH and minimum error of 3 cycles for RUL.

roton exchange membrane fuel cells (PEMFCs) are energy conversion devices that directly convert chemical energy in hydrogen into electric energy via an electrochemical reaction. They are environmentally friendly and exhibit fast startup , high efficiency, and high reliability; thus they are being gradually applied for developing new energy-efficient vehicles. In this study, we present a thermodynamic model of a vehicle fuel cell power system. This system comprises a PEMFC stack, an air compressor, a hydrogen circulating pump, a cooling pump, and a humidifier model. Under dynamic conditions, the effects of the energy consumption of the auxiliary equipment on the efficiency of the fuel cell power system are reported. Moreover, we included an analysis of the mapping relationship between the operating parameters such as working temperature; the inlet humidity of the cathode; and the electric power, electric efficiency, and thermal efficiency of the system. Energy consumption of auxiliary equipment and the net output power, electric efficiency, and thermal efficiency of the system at step currents ranging from 180 to 300 A were obtained. The results demonstrate that, in a 30 kW vehicle PEMFC system, the net output power of the system reaches 22.5 kW, and energy losses of the humidifier, cooling pump, air compressor, and hydrogen circulation pump reach 1.78, 2.18, 3.1, and 2.15 kW, respectively. The maximum electric efficiency and thermal efficiency of the system are 41% and 52.1%, respectively.

In order to address heat dissipation problems in cylindrical lithium-ion battery packs, we designed a new phase change material (PCM) water-jacket liquid-cooled coupling heat dissipation structure model. First, the influence of battery spacing on the surface temperature of the battery pack under the heat dissipation of the PCM model was studied, and the best battery layout of the PCM model was determined. According to this ideal battery layout, the heat dissipation structure model was optimized, that is, we determined the optimal flow channel structure of the PCM heat dissipation model. The simulation analysis shows that under the 6-channel structure model, the PCM water-jacket liquid-cooled coupling heat dissipation model has the largest effect with an 8 mm distance between the batteries. When the 3 C and 5 C high-rate discharges, the battery The maximum surface temperatures of the group were 33.78 ℃ and 41.11 ℃, respectively, which were reduced by 7.23 ℃ and 1.06 ℃, respectively, when compared to the maximum temperatures of the PCM heat dissipation model of the same size. Using the PCM water-jacket liquid-cooled coupling heat dissipation model, the maximum temperature difference between the batteries remains within 5 ℃. These results show that the new PCM water-jacket liquid-cooled coupling heat dissipation structure can ensure reasonably normal operation of a battery pack, as well as to improve its safety and durability.

Because of the complex degradation characteristics of Li-ion batteries, it is a continuing challenge to accurately predict the state of health and remaining useful life of batteries, which limits the development of consumer electronics, electric vehicles, and grid energy storage technologies. The degradation mechanism of the batteries is complex and coupled with each other. Therefore, it is difficult to use a model-based method for accurate modeling. This study proposes a data-driven capacity estimation method for Li-ion batteries. By analyzing the evolution pattern of the voltage-discharge capacity curve with cycle aging, features with an electrochemical concept are selected as the model input, and the capacity of Li-ion batteries can be predicted by the Gaussian process regression (GPR) model. The input features of the model can be obtained online, and the capacity of the battery can be estimated without a full charge-discharge. The experimental verification was completed with the data sets for LCO/graphite batteries and LFP/graphite batteries. The results show that the method has a good generalization ability and can accurately estimate the capacity of different types of batteries. The proposed method is compared to the GPR model with electrochemical impedance spectroscopy as the input, and the results indicate that the proposed method can obtain better estimation accuracy. This highlights that the appropriate selection of various features can significantly affect the performance of the data-driven model for Li-ion batteries and can provide a reference for battery state prediction and diagnosis.

Effect of overload on the performance of power-type electric double-layered capacitors used for trams is studied via overcurrent, overvoltage, short-circuit discharge, and high- and low-temperature tests. The results show that the electrochemical properties of electric double-layered capacitor cells remain consistent after cycling at the same charging and discharging current. When average current is greater than rated current, a cell produces more heat than usual, which can easily cause electrolyte leakage. The cell can be discharged at a short-circuit current without damage while the instantaneous short-circuit discharge current is 6200 A. The cell shell bursts and burns after charging for 1000 s at the rated current, but the burning phenomenon is quickly extinguished after charging is stopped. Continuous combustion does not occur and the cell does not explode. The high withstand voltage of the cell is 3.0 V. The monomers can be used in the temperature range of -45 ℃ to approximately 65 ℃. As temperature decreases (≥-45 ℃), the performance of a cell improves.

The thermal management of the battery pack is essential to avoid problems such as overheating and thermal runaway. An active cooling system must be used to maintain a safe temperature of the battery and improve the performance and life of the battery. Liquid cooling is an effective cooling method, but parameterized research on the influence of structural parameters on cooling effects is still lacking. In this paper, a liquid cooling method based on a micro channel silicon-based cold plate is used, and a fluid-solid coupling heat dissipation model is established by using computational fluid dynamics. The Latin super vertical method is used to generate parameter combination samples and a cooling system with efficient heat dissipation performance and lower energy consumption is developed through a multi-objective genetic optimization method. Experimental results show that the optimized liquid cooling system is sufficient to control the temperature of the module below 45 ℃, and the temperature deviation between single cells can also be controlled within a small range of 2 ℃. The results of this study will provide effective research ideas for the design and optimization of the thermal management system of battery components, and will help promote the application of batteries in actual products.

Accurate estimation of the SOC can provide a basis for balanced management between batteries and extend the overall service life of a lithium battery pack. In order to address large linear errors in the central differential Kalman filter algorithm (CDKF), an improved CDKF algorithm is proposed. The iterative filtering idea is introduced in the original algorithm, and the measurement information is used to constantly update the estimated value of the state. The observation information is provided iteratively, and the covariance matrix is continuously modified based on the LM optimization method, which effectively reduces the linear error. Based on the second-order resistance-capacitance circuit unit model, the least square parameter identification method is selected to identify the model resistance and capacitance parameters, then HPPC experiments are performed to verify the accuracy of the battery equivalent model. Finally, the improved CDKF algorithm is applied to estimate the SOC and voltage under both constant current conditions and dynamic conditions, and the estimation results are compared to the CDKF algorithm. The results show that the improved CDKF algorithm has higher accuracy, the SOC estimation accuracy can be improved by 1.16%, the maximum error is less than 1.7%, and the algorithm convergence time is shorter than the original algorithm. This improved CDKF algorithm improves the estimation accuracy and robustness and offers numerous application advantages.

Major countries in the world have policies to support the large-scale development of energy storage to promote increase in renewable energy use, improve and optimize existing power systems, and improve overall energy efficiency. Energy storage in China is rapidly developing; however, it is still in a transition period from the policy level to action plans. This study briefly introduces the important role of energy storage in global green energy revolution and the development status of the global energy-storage industry. Moreover, it separates energy-storage policies at the national level in China from the aspects of industrial energy storage plans, incentive policies for energy-storage applications in the electricity market, renewable energy, clean-energy development policies, and incentives for new energy-efficient vehicles. Furthermore, the study analyzes China’s local policies from the aspects of energy planning during the “13th Five-Year Plan” period, operation rules for the peak regulation auxiliary market, local subsidy policies, energy-storage-coordinated renewable energy policies, and peak-valley tariff policies. Moreover, it addresses the recent change in the direction of the energy-storage policy for the State Grid and China Southern Power Grid and analyzes the primary problems existing in China’s energy-storage policy. Finally, this study suggests certain policy changes to promote the development of energy storage in China.