Cathode materials with high energy density, high power density, and long cycle life are the focus of current research on battery energy storage materials and are also in high demand in the energy storage market. Lithium-rich manganese-based oxide (LRMO) cathode materials are some of the most promising cathode materials owing to their high discharge specific capacity (≥250 mAh/g), high operating voltage (4.2～4.5 V vs. Li/Li⁺), low cost, and environmental friendliness. Although the sequential or simultaneous redox of cations and anions of LRMO materials results in their enhanced capacity compared with other conventional layered oxides, several problems such as high irreversible capacity for the first cycle and poor cycling and rate performance hinder their engineering applications, which are closely related to the anionic redox reactions in the materials. This paper introduces the crystal structure of LRMO materials and then reviews the relationship between the energy band structure of LRMO materials and anionic redox reactions based on molecular orbital theory. In addition, the effects of anionic redox reactions on LRMO cathode materials, including high capacity, irreversible oxygen loss, and transition metal ion migration, are summarized. Moreover, recent modification strategies for mitigating the negative effects of anionic redox reactions are summarized from three perspectives: transition metal ratio adjustment, surface modification, and ion doping. Finally, the paper discusses the future theoretical and application direction of LRMO materials.

This studies the influence of different carbon-coated aluminum foils on high-energy-density LiFePO₄ power batteries. The effect of graphite + Carbon black (GC) and Carbon black (C) as current collectors on the electrochemical performance in lithium iron phosphate soft pack batteries. The physical property comparison shows that the appearance of the GC scheme is dark grey, alternately undulating after being compounded by graphite and Carbon black, and has a fluffy structure with large pore size. On the other hand, the appearance of the C scheme is black, composed of nanoscale C particles, showing a loose structure with a small pore size. The results show that the bonding strength of GC composite coating is 1.18 times that of C coating. Electrochemical performance results show that the two schemes' first coulombic efficiency and discharge platform are consistent.In contrast, the charge transfer impedance of the GC scheme is negligible. The GC scheme improves the cycle performance at room and high temperatures while the C coating in plan C is improved in large magnification and low-temperature performance. The advantage of the composite carbon-coated layer may depend on the structural design advantage, improving the electron transport ability and thermal conductivity in the plane direction.

This paper explored the NCM811 battery as the main research target, focusing on its battery performance under normal working conditions. Specifically, its discharge performance at different ambient temperatures and discharge rates, including battery capacity changes during the first and 2000th cycles, and the voltage curve of the battery were obtained. Then, we compared the results with those of the NCM523 and the NCA batteries. At the same time, due to the thermal safety problem of the NCM811 battery, its voltage and temperature rise under thermal runaway conditions were explored, after which its temperature transmission law was summarized and compared with the experimental results. From the above investigations, we discovered that the NCM811 battery had excellent rate charge and discharge performances under normal working battery conditions, with the battery capacity being well preserved during high-rate charge and discharge. We also discovered that in terms of aging, although the NCM523 battery and the NCA battery showed battery-capacity decay, while the NCM811 battery showed obvious capacity decay similar to the NCM523 battery, the capacity of the NCA battery hardly changed. In terms of high-and low-temperature discharge, however, we observed that the heat production of the battery at a low temperature was higher than that at a high temperature. Under the ambient temperature of 100%, although the temperature rise of the NCM811 battery was the most obvious, with great thermal safety hazards being observed, the temperature rise of the NCM523 battery and NCA battery was relatively gentle when the battery thermal runaway occurred, with the battery voltage suddenly dropping to 0 V and the temperature rising to 1200 K in a short time. Besides, only in the part where thermal runaway occurred did the temperature change significantly with time, with the temperature in the rest appearing constant. Therefore, compared with the experimental process, the thermal runaway trigger time of the simulation process was later, the temperature rise was faster, and the maximum battery temperature was lower.

This study explored the selective leaching of valuable metals Li, Cu, and Fe in the mixed positive and negative electrodes of spent LiFePO₄ batteries under acidic conditions to simulate the recycling and comprehensive application of spent LiFePO₄ batteries in industrial production. The positive and negative electrodes are mechanically crushed and sieved to obtain the mixed powder, which contains high contents of Cu and Al impurities. The carbon and fluorine removal rates are 99.03% and 99.93% after calcination at 700 ℃. When the H⁺/Li⁺ molar ratio equals 0.7, the leaching temperature is 90 ℃, the leaching time is 3 h, and the liquid-solid ratio is 3∶1. Additionally, the leaching rates distribution of Li, Fe, Cu, and Al are 91.88%, 0.0024%, 4.71%, 0.11%, respectively, indicating the satisfactory separation of Li. Saturated Na₂CO₃ successfully recovered the battery-grade lithium carbonate as a precipitant. However, the leaching cinder was calcinated at 450 ℃ to convert Cu into CuO. The metal elements Fe and Cu leaching rates are 0.11% and 92.54%, respectively, under a pH of 1.5, 90 ℃ leaching temperature, 3 h leaching time, and the liquid-solid ratio of 5∶1. Finally, the copper leaching residue was completely dissolved in sulfuric acid. The precipitation rate of ferric phosphate dihydrate reached approximately 95% under adjusting pH to 1.8 by ammonia. The battery-grade ferric phosphate with a purity of 99.48% (weight fraction) was obtained by calcining crystal water.

Solid polymer electrolyte is one of the critical materials in all solid polymer lithium-ion batteries. The main challenge for solid polymer electrolytes is their low conductivity and poor electrochemical stability. In this study, a novel solid polymer electrolyte named PMEA@SSE) was prepared by combining poly (ethylene glycol) methyl ether acrylate (PMEA) with polyethylene oxide (PEO), based on the Li⁺-conducting mechanism of polymer electrolyte. PEO electrolyte (PEO@SSE) was prepared as the control sample. The PMEA@SSE was evaluated by Fourier transform infrared spectrometer, electrochemical impedance spectroscopy, linear sweep voltammetry, scanning electron microscope, energy dispersive spectrometer, X-ray diffraction, and cell testing. The results revealed that the electrochemical stability window of PMEA@SSE was similarly higher than that of PEO@SSE (4.2 V vs. 3.8 V) and that the ion conductivity of PMEA@SSE was higher than that of PEO@SSE (0.13 mS/cm vs 0.018 mS/cm, tested at 30 ℃). Furthermore, the solid-state battery prepared using PMEA@SSE exhibited better cycle performance than PEO@SSE (77 vs. 31 cycles with a capacity retention of 80%). This work demonstrates that partially replacing PEO with PMEA is a feasible strategy for advancing the classical PEO solid electrolyte for application in all solid lithium batteries and provides new insights for further developing solid polymer electrolytes.

Developing thin solid-state electrolytes with high ionic conductivity and mechanical properties is essential for preparing high-performance all-solid-state lithium metal batteries. Here, Co²⁺-doped CeO₂ (Co²⁺@CeO₂) nanosheets were first prepared, which were subsequently mixed with polyethylene oxide (PEO) to fabricate a thickness of only 32 μm Co²⁺@CeO₂-based laminar composite solid-state electrolyte (L-CSE) through vacuum filtration. The oxygen-vacancy-rich Co²⁺@CeO₂ nanosheets are critical to enhancing ionic conductivity and mechanical properties, while PEO acts as a binder to ensure close contact between electrolytes and electrodes and enhance flexibility. The oxygen-vacancy content on the nanosheets was controlled by changing the doping amount of Co. Meanwhile, the structural composition, mechanical properties, and electrochemical properties of L-CSE were systematically studied, emphasizing the influence of oxygen-vacancy content on Li⁺ transport properties. The results show that the oxygen-vacancy content on the nanosheets can be accurately controlled by adjusting the doping amount of Co, and the oxygen-vacancy content of 0.33Co²⁺@CeO₂ nanosheets is the highest. The prepared L-CSE displays a thin thickness (32 μm) and good mechanical properties (the elastic modulus reaches 1.147 GPa). At 30 ℃, the ionic conductivity reaches 5.81×10^-5 S/cm. The Li⁺ transference number is 0.59 at 60 ℃. Concurrently, due to the good interfacial stability between the electrolyte and Li anode, the assembled Li symmetric cell can operate stably for more than 40 h at a high current density of 0.7 mA/cm². Moreover, the assembled LFP/L-CSE/Li solid-state battery exhibited excellent cycling stability and rate performance. It could cycle stably for 200 cycles with a capacity retention rate of 83.6% at 0.5 C and 60 ℃. Meanwhile, the discharge-specific capacity of LFP/L-CSE/Li cells can reach 120.7 mAh/g at 2 C and 60 ℃.

In the era background of carbon dioxide emission peak and carbon neutrality, hydrogen energy was the key to energy transformation as clean and green energy. Therefore, hydrogen storage technology as an intermediate bridge between the production and application of hydrogen energy has attracted much attention. Although clathrate hydrates are potential hydrogen storage materials, the slow hydrogen storage rates and low storage capacity hinder its industrialization. Consequently, this work discussed the progress of the kinetics enhancement technology of hydrogen storage in clathrate hydrates, and the kinetics mechanism of hydrogen hydrate nucleation and growth, including the kinetics enhancement technology of hydrogen hydrate (the driving force, the contact area of the gas-liquid interface, and the diffusion channel). Then, we summarized current kinetics enhancement technology from the aspects of hydrogen storage rates and density to support the development of related research. Notably, this paper emphasizes that corresponding works may be performed in the future. First, to deepen research on nucleation, growth, and the stability mechanism of hydrogen hydrate. Second, to seek high efficiency and high driving force thermodynamic promoters in improving driving forces fundamentally. Finally, to combine high-efficiency thermodynamic promoters and improved diffusion channels in achieving the double optimization of high hydrogen-storage rates and storage capacity.

Since the cathodic oxygen reduction reaction (ORR) kinetics of proton-exchange membrane fuel cells is sluggish, developing high-activity and low-cost ORR electrocatalysts are essential for fuel cell evolution. Here, platinum nanoparticles (Pt NPs) are synthesized by reducing chloroplatinic acid in a solution of sodium hydroxide/ethylene glycol by microwave synthesis and are subsequently mixed with Vulcan XC-72R carbon black to prepare a highly dispersible carbon-supported platinum (Pt/C) catalyst. The transmission electron microscopy results propose that Pt NPs are evenly distributed on the carbon black's surface, with an average particle size of approximately 2.8 nm, which is slightly smaller than that of the commercial Pt/C catalyst (～3 nm). Further, the effects of microwave power, dispersionsolvent, and the presence or absence of HCl when supporting carbon on the produced catalysts' dispersion and oxygen reduction activities are investigated. Electrochemical tests show that the optimum microwave Pt/C catalyst has superior ORR catalytic activity than commercial Pt/C catalysts. The half-wave potential of the microwave Pt/C catalyst is 9 mV higher than that of the commercial Pt/C catalyst in a 0.1 mol/L HClO₄ electrolyte. Additionally, the mass and specific activities of microwave Pt/C catalyst are 0.109 A/mg and 0.127 mA/cm² at 0.9 V (vs. RHE), which are higher than those of the commercial Pt/C catalyst (0.093 A/mg^{and 0.118 mA/cm2), respectively. Moreover, microwave Pt/C catalyst has better electrochemical stability than that of the commercial Pt/C catalyst. These should be mainly attributed to the smaller size of Pt NPs uniformly dispersed on the carbon surface. The increased Pt surface area improves ORR activity, and the sturdy insertion of Pt NPs into the pore structure in the carbon support surface enhances the stability. Here, the synthesis route of the Pt/C catalyst by the microwave method is systematically studied and proven suitable for large-scale production.}

Supercapacitors (SCs) have attracted considerable attention owing to their high power density, fast charge-discharge rate and long cycle life. Recently, with the development of science and technology, the applications of SCs have expanded beyond conventional fields, such as large-scale renewable power generation and distribution and rail transportation, to a new generation of precision electronic devices, high-precision military weapons and equipment, and other fields involving extreme working conditions. The extreme working conditions such as extremely high/low temperatures and high tension/compression have posed new challenges and requirements for the structure and composition of SCs. Among them, the electrolyte is a key component that affects the performance, life, and safety of the SCs. Polymer electrolytes with light weight, strong mechanical stability, high flexibility and safety, and good interfacial contact are ideal candidates for fabricating safe and flexible SCs. This article first introduces the classification, composition, and characteristics of SCs. Then, the research progresses of polymer electrolytes for SCs in extreme environments are reviewed in terms of the impact of high/low temperature, high tensile/compression, and high/low humidity. Finally, the key issues faced in the development of carbon electrodes and polymer electrolytes for SCs under extreme conditions and the future directions of development are analyzed and discussed, which may provide a new impetus to the development and practical application of the SCs.

This study innovatively fabricated seven Na₂CO₃/carbide slag shape-stable phase-change composites (SSPCCs) with carbide slag (industrial solid waste) instead of traditional skeleton materials as skeleton material via the cold-compression hot-sintering method to recycle the industrial solid waste and reduce the cost of thermal energy storage (TES) systems. Then, the TES performance, mechanical property, microstructure, thermal cycling stability, and chemical compatibility were investigated using the differential scanning calorimetry, constant-speed pressuring method, scanning electron microscopy method, high-temperature thermal shock method, X-ray diffraction analysis, and Fourier transform infrared absorption spectroscopy. Results indicated that by combining carbide slag with Na₂CO_3, one might create good SSPCCs. The SSPCC (sample NC5) with the mass fraction of 52.45% carbide slag to 47.5% Na₂CO₃ reached the optimal performance with a TES density of 993 J/g in the range of 100 ℃ to 900 ℃ and compressive strength of 22.02 MPa and a maximal thermal conductivity of 0.62 W/(m·K). Different components are distributed evenly and are compatible with one another in sample NC5. Moreover, sample NC5 still had excellent TES performance after the 100 heating/cooling cycles, which can provide technical support for solid waste recycling and low-cost TES materials development.

High heat storage density and cross-seasonal heat storage are two advantages of thermochemical heat storage. In medium-and high-temperature heat storage, the heat storage material of the calcium oxide/calcium hydroxide heat-storage system is easy to accumulate but is challenging to fluidize. This study wrapped calcium hydroxide pellets in a sintered silicon carbide ceramic shell to create a heat storage pellet with a core-shell structure. Although the internal pores of the shell and core of this core-shell structure particles show different pore size distribution, the pore size of the shell is larger than the pore size of the internal calcium hydroxide core, so the wrapping of the shell has less impact on the internal calcium hydroxide storage and exothermic reaction process. Compared with pure calcium hydroxide, the core-shell structure particles' reaction rate and mechanical properties have also improved. The characterization results show that the shell of the pellets is chemically stable and does not react with calcium hydroxide to cause a decrease in the thermal storage density.In addition, the core-shell structure particles have good cycling stability, and the prepared particles were subjected to 25 exothermic and endothermic cycles under an air atmosphere. It was discovered that the particles' loss in heat storage density was 20% or less, and there was no cracking or fragmentation. However, the reaction of calcium hydroxide with carbon dioxide in the air decreased the heat storage density of the pellets. Still, after high-temperature calcination to make calcium carbonate decompose into calcium hydroxide again, the heat storage density of the pellets could be restored to 96.7% of the initial heat storage density. In summary, preparing heat storage particles in this study is significant for applying thermochemical heat storage technology.

The confined molecules exhibit different physicochemical properties and crystallization behavior from the bulk. Therefore, to explore the effect of confinement on the crystallization behavior of confined phase change materials (PCMs), stearic acid/MXene (SA/MXene) composite PCMs were prepared by hydrothermal method using stearic acid (SA) and MXene as the heat storage medium and matrix, respectively. The crystallization behavior was analyzed using a differential scanning calorimeter (DSC) and polarized microscopy (PM), and the SA and SA/MXene crystallization kinetics were studied by the Avrami, Jeziorny, Mo, and Kissinger models. The effects of confinement on the crystallization behavior of confined stearic acid were also analyzed. The results show that SA and SA/MXene exhibit opposite temperature-dependent crystallization behavior during the isothermal crystallization process. SA presents a larger crystallization rate than SA/MXene at low temperatures, while SA/MXene exhibits a shorter half-crystallization time and a faster crystallization rate at higher temperatures. In the non-isothermal crystallization process, MXene has dual effects on the crystallization behavior of stearic acid, which include promoting heterogeneous nucleation under a low cooling rate and inhibiting the confinement effect at a high cooling rate. The confinement effect increases the energy barriers of the confined molecules during the crystallization process. Therefore, the crystallization activation energy of SA increases from 174 kJ/mol to 208 kJ/mol^{in SA/MXene. Finally, this study can provide a theoretical basis for designing and optimizing shape-stabilized composite phase change materials.}

In this study, Na₂HPO₄·12H₂O(DHPD)and Na₂CO₃·10H₂O(SCD)were melt-blended at a ratio of 6:4 to form a eutectic hydrated salt(EHS), after which its supercooling degree and phase change temperature were reduced using sodium pyrophosphate decahydrate, ammonium sulfate, and urea, respectively. Then, four kinds of superabsorbent polymer(SAP)with different mesh numbers(30—60, 60—100, 120—180, and 200—400 meshes)were added to anchor the above system in its three-dimensional network, obtaining four different systems of phase change gels for cold storage. Among the obtained gels, DSSNU-SAP_200-400 with a phase change temperature of 2.7 ℃, phase transition latent heat of 137.7 J/g, supercooling degree of 1.9 ℃, and thermal conductivity of 0.435 W/(m·k)had the best phase-change performance than the other cold storage gels. Subsequently, this study characterized the microscopic morphology, crystal composition, and contact angle of DSSNU-SAP_200-400, fully verified its chemical compatibility between the components in the system, and expounded its regulatory mechanism of ammonium sulfate, urea, and SAP on EHS performance. The application-based experimental results showed that the cold storage module developed using DSSNU-SAP_200-400 as the core could maintain the grape's ultrahigh freshness within 49 h, fully proving its application potential in cold-chain transportation. Therefore, we propose that this research will help to promote the application of hydrated salts in cold storage, thereby providing a theoretical and experimental basis for the research and development of the phase-change cold-storage gel technology.

This research was conducted to solve the problem of poor heat-transfer efficiency caused by the low thermal conductivity of phase change materials (PCMs). First, metal foams with high thermal conductivity were added to PCMs to accelerate the solid-liquid phase change process, favoring an improvement of the overall heat storage efficiency. Since the buoyancy force caused an accumulation of high-temperature fluid on top of the heat storage unit, PCMs at the bottom were quite difficult to melt. Hence, the bottom of the heat storage unit was cut off at a certain proportion to improve the refractory phenomenon at the bottom under the precise control of the PCM volume. Then, numerical models were established, and simulations were carried out to evaluate melting rate, heat storage, melting phase interface, velocity distribution, and temperature distribution during the melting process. The results demonstrated that cutting off the bottom of the heat storage unit effectively solved the refractory problem at the bottom, improving the overall heat storage efficiency. Notably, when the bottom cross-cut ratio was 0.7, the complete melting time was the shortest, 18.12% shorter than that of the original round tube. However, after managing the bottom cut, the refractory zone was transferred from the bottom to the cutting edge. This transfer reduced the distance between the heat source and the bottom of the regenerator (refractory zone), shortening the overall phase-change heat-storage time. At the end of melting, the flow rate of the melting phase interface with a cross-cut ratio of 0.7 was 2.10 times higher than that of the circular tube. Therefore, these results show that the bottom cross-cut strengthened the heat transfer at the bottom of the heat storage unit, reduced the low-temperature area at the bottom, and promoted the overall melting process.

Primary frequency regulation is a key technology for energy storage power stations to support the stable operation of new power systems. In this paper, the integrated design of primary frequency modulation of lithium-ion energy storage power station is studied, including the analysis and optimization of response time and overload capacity. The response time is shortened mainly through information collection and transmission, and the operation cycle of strategy algorithm. The switching frequency control scheme of the power device inside the energy storage converter is proposed to improve its overload capacity, the optimization of the above indicators is verified by the 20 MW/10 MWh lithium battery energy storage power station. The results show that when the lithium-ion energy storage power station is applied to the primary frequency regulation condition, the response time of the converter is 60—80 milliseconds, and the overload capacity of the converter can reach 150% within 30 seconds, which improves the power cost performance of the energy storage power station. The energy storage power station can effectively smooth the frequency fluctuation in a frequency regulation test in the isolated network, reduce the operating frequency of the generator set, and provide ideas for the design of the subsequent power energy storage power station.

Lithium-ion batteries can serve as backup power supplies to provide different alternate and direct current power levels for the primary and secondary equipment and communication management of the power system to ensure that the core equipment continues to function normally in emergencies. The parallel energy storage system has higher reliability due to the parallel module backup and can also avoid the barrel effect of traditional series backup power supply. However, the parallel scheme can cause differences in module life due to the inconsistencies between modules. Additionally, differences in voltage distribution within the series-connected batteries can lead to overcharging or over-discharging of the battery cells. Therefore, we propose a multitimescale equalization method for parallel lithium-ion battery storage systems. First, bypass equalization is performed on the single cell within the battery module group with the state of charge as the index to achieve intragroup equalization in the short-time scale of a single charge/discharge cycle. Subsequently, the system is balanced in the long-time scale of life decay through the life equalization between parallel battery module groups. Interestingly, the proposed equalization method can improve the consistency between modules when using a parallel energy storage system, enhance the reliability of parallel modules for mutual backup, reduce the operation and maintenance cost, and improve the efficiency of Li-ion battery use. Furthermore, a simulation model is built to verify the effectiveness of the proposed method under different conditions based on accelerated battery aging experiments to verify the equalization method.

The electrified railway is a large industrial user facility with distinctive characteristics. Here, the traction load fluctuates sharply, the negative sequence current is large, and the regenerative braking energy feeds back to the catenary. Hence, negative sequence current will increase the temperature of local metal parts, even leading to transformer burning, shortening the service life of electrical equipment, accelerating the frequency of equipment part replacement, and increasing the cost of equipment maintenance. Furthermore, regenerative braking energy feedback to the catenary will aggravate the load imbalance between the two power supply arms and make the impact of negative sequence currents more serious. However, the traction power supply system cannot use the energy feedback to the catenary. Therefore, the regenerative braking and power quality, which harnessed a synthetic system in traction substations based on flywheel energy storage, was studied. Transformers were first installed on two power supply arms, after which the flywheel energy storage device was connected with feeders through converters and transformers in the whole electrical circuit. Consequently, the system output AC27.5 kV transformed DC1600 V on the feeder to the flywheel energy storage device, causing the flywheel energy storage system to effectively reduce the basic tariff in dual tariff systems. As an energy storage body, the flywheel energy storage device also had the dual functions of storing and releasing electric energy, thereby effectively absorbing and reusing the regenerative electric energy generated during the braking of locomotives and reduction of power rates. In addition, the flywheel energy storage system solved the power quality problem in electrified railways' negative sequences. Thus, compared with the traditional power quality management method, it could produce economic benefits and solve the problem of no economic power quality management.

This study proposed an integrated physical energy storage system design and control strategy with gravity energy storage as the main and flywheel energy storage as an auxiliary to smooth the fluctuation and intermittency of discharge caused by multi-weight switching in a gravitational energy storage system based on a skip hoist. First, the study evaluates the working principle, control methods of gravitational energy storage system and flywheel energy storage system, and critical components, such as motor/generator and converter, and further constructs gravitational and flywheel energy storage motor grid-connected system model. Then, the study simulates and analyzes the variation of parameters including the phase voltage and phase current on the machine side and network side of two kinds of energy storage system at charge: stand-by and grid-connected stages. Finally, the study constructs the simulation model of the integrated physical energy storage system, carries out the research on the matching operation characteristics of the two energy storage systems, designs the energy management and control strategy of the integrated energy storage system, and simulates its operating characteristics at different operating stages to verify the feasibility of the structure and control strategy of the integrated physical energy storage system.

Here, the flywheel energy storage system is used to stabilize the active power output of wind farms to make the change in active power in the wind farm meet the recommended value range of the active power change limit in the national standard. Based on the low-pass filtering method, the flywheel energy storage system responds to the high-frequency component of the active power output of the wind farm to reduce the impact of grid-connected power fluctuations on the primary frequency modulation of the power grid. A two-level optimization model with different cut-off frequencies and flywheel energy storage system power and capacity is established to obtain the optimal flywheel energy storage system capacity that meets the flywheel energy storage system's constraints and the requirements of wind power grid-connected active power changes and economic indicators. The outer model initializes the cut-off frequency of the frequency divider, obtains the high-frequency power command, and inputs it to the flywheel energy storage system. Conversely, the flywheel responds according to the reference power in the inner model. After connecting with the wind farm's power, the fluctuation degree of the active power of the grid point is verified. Furthermore, the flywheel energy storage system model is established; the simulation results show that the flywheel energy storage system can better respond to the power command and effectively suppress wind power fluctuation.

As the permeability of renewable energy power generation increases year by year, its inherent randomness and volatility brought challenges to the frequency security of power systems. This paper proposes a hybrid energy storage scheme with pumped storage and flywheel energy storage system(FESS) to improve the frequency regulation capacity of the regional system. Based on the state of charge(SOC) and the area control error(ACE), the paper designs a grey-fuzzy-correction control which contains two fuzzy controller and a grey prediction to correct the energy distribution of the FESS and the pumped storage. Therefore, the FESS and the pumped storage can participate in the frequency regulation in a coordinated way. In the flywheel energy storage control module, the SOC signal is divided into different intervals and using Sigmoid and Logistic regression model the paper constructs the charge and discharge constraints of FESS and the self-recovery mode on the basis of real-time state perception and comprehensive evaluation to ensure that the flywheel runs healthily and efficiently. In MATLAB/Simulink, a two-region load frequency control model is constructed and the effects of the system and the output power situations of frequency-modulation resources with or without hybrid energy storage system and control strategy in the case of step and continuous disturbance are analyzed. As far as the frequency regulation effect is concerned, the simulation results show that, compared with the separate frequency modulation of conventional power generation in scheme 1, the effects of frequency regulation can be enhanced because of the quick response capability of hybrid energy storage system. The frequency regulation effect of the scheme proposed in this article is only slightly inferior to that of scheme 3, which has no power and capacity limitations for the flywheel energy storage. Focusing on the state of the flywheel energy storage, the simulation results show that the SOC of the flywheel in the proposed scheme has the best maintenance effect, and in scheme 2, it approaches to the maximum value many times, while the SOC of flywheel in scheme 3 even exceeds the allowable range. Moreover, the proposed scheme improves the frequency regulation participation of pumped storage and liberates conventional power generation from frequency regulation compared with the comparison schemes.Comprehensive analysis shows that the proposed scheme and strategy have advantages in improving the system frequency regulation ability, reducing frequency regulation engagement for conventional energy sources, improving the utilization rate of the hybrid energy storage system and improving the maintenance effect of the flywheel SOC.

Coordinated optimization of flexible loads and multitype energy storages is a key strategy to achieve a power balance in the system. With large-scale flexible loads widely connected to the grid and participating in demand-side response, the heterogeneous characteristics of flexible loads make them difficult to adapt to the large-scale regulation demand of the grid and prevent them from exploring the full potential for regulation. Accordingly, this study proposes an optimal configuration strategy for multitype energy storages considering flexible heterogeneous loads and establishes a generalized model to match load characteristics and grid regulation demands using clustering flexible heterogeneous loads. First, according to the differentiated power consumption curve and regulation potential of flexible heterogeneous loads, the typical heterogeneous loads are clustered into transferable, cuttable, and adjustable loads with the corresponding generalization model. Accordingly, the coordinated optimization strategy of flexible heterogeneous loads and multitype energy storages is proposed. Meanwhile, with the optimization objective of total system-operating cost considering the cost of generations, grid, energy storages, and loads, the optimal configuration of multitype energy storages is achieved by mixed integer linear programming. Finally, the feasibility and validity of the proposed coordinated optimization strategy are verified using a comparative analysis of cases. Compared with flexible loads or energy storages participating in system regulation alone, coordinated optimization of flexible loads and multitype energy storages can achieve a power balance of regional grids, reduce system operating costs, and enhance grid economic benefits.

Multiple virtual power plants (VPP) will cooperate and compete with each other in the operation of the future power grid because of the constant growth of the scale of new energy sources and the entry of diverse capitals into the power market. A collaborative optimal operation model between multi-energy VPPs based on the Nash bargaining theory is proposed to solve the problem of optimal power grid operation and market players' interest distribution. First, for the multi-energy VPP, including the gas turbine, heat pump, various energy storage devices, electric load, thermal load, cooling load, etc., a multi-energy VPP group optimization operation model based on Nash negotiation theory is constructed. Second, to solve the complex non-convex nonlinear optimization problem, based on the mean value inequality, the model is transformed into two sub-problems of multi-energy VPP benefit maximization and energy payment value between multi-energy VPPs. Third, considering the information privacy and security between VPPs, the alternating direction method of multipliers (ADMM) is employed to solve the above two sub-problems in a distributed manner. Three multi-energy VPPs were selected for this study's example analysis. The results show that when fairness is considered, the optimization method proposed in this study can improve both the income and overall income of each VPP.

Lithium-ion power batteries are crucial for the development of electric vehicles and they have widespread application in different scenarios. To study the variation laws of the voltage, temperature, and capacity, the charging and discharging cycle experiments are used considering the availability and safety of the square ternary lithium battery in a wide temperature range. According to the concavity and convexity of the voltage curve, the piecewise fitting analysis is performed to explore the voltage plateau characteristics of lithium batteries at different working conditions. The results revealed that, the voltage drops from 3.8 V to 3.1 V at ambient temperatures of 10 ℃, 25 ℃, 40 ℃, and 55 ℃ and current rate of 1 C. Moreover, at the ambient temperature of -20 ℃ and -5 ℃, the voltage drops from 3.39 V to 3.05 V and 3.68 V to 3.07 V, respectively. Furthermore, the battery terminal voltage changes gradually during the voltage plateau period, surface temperature rise does not reach a peak, discharge capacity accounts for approximately 90%, and the battery has excellent operating performance. However, when the ambient temperature drops to -35 ℃, the discharge capacity in the voltage plateau period accounts for 66.08% of the total discharge capacity; moreover, the impact of low temperature on energy loss is substantial. The research results provide a reference for the modeling and control strategy design of lithium-ion power batteries battery in electric vehicle of an energy storage system.

In low-temperature environments, the performance of lithium-ion batteries is degraded, making charging and discharging difficult, which seriously affects the use of electric vehicles. The use of pulse heating is an effective strategy to solve this problem. Therefore, in this paper, a ternary lithium-ion battery was used, after which we established an electrochemical-thermal coupling model by comparing the experimental and simulated values from the discharge voltage and temperature rise curves, including those of the electrochemical and thermal characteristics of the lithium-ion battery. Then, a simulation analysis of an ion battery under pulsed heating was conducted, followed by heat production distribution at ambient temperature. The results showed that the temperature rise of the 4 C pulse-heated battery was 2.25 times higher than that of the 2 C-pulse-heated battery at -8 ℃ ambient temperature, with ohmic heat and polarization heat determining the size of the total heat production. We also observed that although the lower the ambient temperature, the more severe the polarization of the lithium-ion battery, the polarization moderated as the pulse progressed. Pulse heating at a high pulse current and a lower temperature also had a larger temperature rise rate. Hence, after pulse heating, the battery surface's maximum temperature was at the geometric centre's lower position, the maximum temperature difference did not exceed 2 ℃, and the temperature uniformity was good.

Lithium-ion batteries have been widely used in new energy fields, including electric vehicles, among others. Therefore, to facilitate the designing of thermal management schemes for reducing the uneven temperature variation in battery modules and improving battery durability, this study develops a three-dimensional electrochemical-thermal model that can show the heat spatiotemporal production rate and the temperature distribution of battery cells. Besides, the model can predict the electrical characteristics of different parts of electrode pairs and the temperature distribution of battery cells. Specifically, the single-cell thermal model is extended to a thermal model of a battery module comprising three single cells connected in parallel to investigate temperature aggregation phenomenon reduction in the battery modules. The experimental results verify the validity of the proposed electrochemical-thermal model. Specifically, single-cell and three-cell parallel battery strings are placed in an insulation box with a constant temperature of 25 ℃ and discharged at a constant current rate to provide quantitative data on the electrical and thermal behavior. The current model prediction agrees well with the experimental data. The average absolute errors of the cell terminal voltage and temperature are less than 0.016 V and 0.36 ℃, respectively, under the constant discharge current conditions of 0.5 C, 1 C, 2 C, and 3 C. however, the average temperature error of each surface of the three-cell parallel batteries does not exceed 0.4 ℃ under constant discharge current conditions of 0.5 C, 0.75 C, 1 C, 1.25 C, and 1.5 C. Further analyses show that the current density in the cathode material is related to the discharge depth and electrochemical reaction area. In the early and middle stages of discharge, the electrochemical reaction area is mainly at the tab, where the current density is the highest. Conversely, the electrochemical reaction area is mainly at the bottom of the cathode material, where the current density at the bottom is greater than that at the tab in the later stages of discharge. The temperature of a three-cell parallel battery module is not a simple superposition of the temperatures of single cells. Additionally, the temperature of the middle cell is higher than that of the two cells at the sides. In the battery module, when boundary conditions are consistent, the temperature of the two side batteries becomes distributed symmetrically. Furthermore, a temperature aggregation effect caused by air non-circulation among the cells exists. Therefore, the temperature of intermediate cells can be reduced by reducing the gap between monoliths or adding materials with high thermal conductivity to them as heat transfer media.

Lithium-ion batteries have become a hot spot with the emergence of energy problems. This study takes the 18650 NCM811 lithium-ion battery as the research object. It overcharges the battery to three different cut-off voltages (4.3 V, 4.4 V, and 4.5 V) and cycles it several times (180 times) until the battery capacity decays significantly. The test and analysis of the 4.5 V overcharged circulating battery's AC impedance spectrum and capacity increment curve reveal the mechanism of battery capacity decay, which is studied both qualitatively and quantitatively. It was discovered that the main cause of battery capacity attenuation is the loss of active lithium ions and active materials, whereas the loss of battery conductivity has little effect. The thermal runaway characteristic parameters (self-heating starting temperature T₁, thermal runaway triggering temperature T₂, maximum thermal runaway temperature T₃) of new batteries, 4.3 V, 4.4 V, and 4.5 V, overcharged circulating batteries at 100% SOC, which was investigated by adiabatic rate calorimeter. It was found that in the thermal runaway process when the battery reached the same temperature, the temperature rise rates of the four batteries were new battery<4.3 V overcharge cycle battery<4.4 V overcharge cycle battery<4.5 V overcharge cycle battery, respectively. The thermal stability of the battery becomes worse after the overcharge cycle. After the overcharge cycle, the starting temperature of the self-generated heat of the battery decreases. In addition, the trigger temperature of the thermal runaway decreases.

Recently, the thermal runaway combustion of new energy vehicles has been reported frequently, which not only endangers the safety of consumers' lives and property but also affects the public's trust and acceptance of electric vehicles, causing severe obstacles to the promotion and popularization of the new energy vehicle market. This study first established an electrochemical-aging-thermal runaway-thermal coupling model based on the heat and mass transfer of the battery to fundamentally provide effective guidance for the prevention and control of thermal runaway. Then, the finite element software was used to establish a simulation model for the ternary lithium soft-packed battery and conduct a preliminary verification. Finally, aiming at the thermal runaway problem of internal short circuits caused by battery aging characterized by cycle times, this paper establishes a simulation model to explore the influence of different aging degrees on the temperature rise of the battery and designs the dimensionless risk index β of "the speed of reaching the threshold temperature of the side reaction" and obtains the critical risk index of thermal runaway, which is helpful for the prediction and prevention of thermal runaway in daily use.

Lithium-ion battery's remaining useful life (RUL) is an important indicator of battery health management. Therefore, in this paper, using battery capacity as an indicator of health status, including modal decomposition and machine learning algorithms, a CEEMDAN-RF-SED-LSTM method was proposed to predict lithium battery RUL. First, adaptive white-noise full-ensemble empirical-mode decomposition (CEEMDAN) was used to decompose the battery capacity data. Then, to avoid the influence of the noise in the fluctuation component on the prediction ability of the model and not completely discard the characteristic information in the fluctuation component, this paper used the Random Forest algorithm to obtain important values for each fluctuation component, after which sexual ranking and numerical values were used as weights for each component's ability to explain the original data. Subsequently, the weight value and prediction result obtained by the neural network model constructed by different fluctuation components were weighted and reconstructed, resulting in the RUL prediction of the lithium-ion battery. Next, this research compared the prediction accuracy of the single model and the combined model, followed by the addition of the combined model prediction accuracy of RF, to improve the performance of the five neural networks further, after which the Simple Encoder-Decoder (SED) mechanism was introduced for the two networks with better performance, LSTM and GRU, to better learn the global temporal features and long-range dependencies of sequence data. We finally tested the method's performance using the NASA dataset as the research object. The experimental results showed that although the CEEMDAN-RF-SED-LSTM model performed well in battery RUL prediction, the prediction results had lower errors than the single model.

Accurate estimation state of health (SOH) of lithium-ion batteries is the key to ensuring the efficient, safe, and sustainable operation of electric vehicles. The accuracy of SOH estimation can be improved with a data-driven method. However, the accuracy of SOH estimation in this method is highly dependent on the selected feature and estimation model. The redundancy between features and the lack of generalization of the estimation model will affect the accurate estimation of battery SOH. According to principal component analysis and whale optimization algorithm (WOA)-Elman, a new SOH estimation method is proposed to reduce the redundancy of input features, increase the model's generalization, and improve the accuracy of SOH estimation. Firstly, the features highly related to the aging of lithium-ion batteries were extracted and selected from the charging process curve. Principal component analysis was used to decrease the dimension of features and reduce the redundancy between features. Then, the WOA method was used to optimize the initial weights and thresholds of the Elman model to establish the WOA-Elman model. The B01 battery was used to train the model while B02 and B03 batteries were used to verify the model. Simultaneously, comparing the commonly used long short-term memory neural network, support vector regression, extreme learning machine, and the unoptimized Elman model. The results show that the root-mean-square error of the WOA-Elman estimation model is 1.2113%. Finally, the SOH of the remaining two groups of batteries was estimated and verified by alternating test data of three groups of batteries as training sets, and the maximum root-mean-square deviation of the estimated results was only 0.1771%. Therefore, the proposed method can estimate battery SOH more accurately and perform better generalization.

The battery system's state of health(SOH)characteristic is a crucial indicator for the large-scale application of the new system for improving the battery energy storage system's dispatchability and operating economy. Based on the self-developed all-vanadium redox flow battery system test platform, this study simulates the actual operating conditions of the all-vanadium redox flow battery system for approximately two years of charging and discharging. Here, the capacity, energy efficiency, comprehensive valence state, and internal resistance changes of the all-vanadium redox flow battery test platform are summarized and analyzed. This study's experimental data show that under operating conditions, the annual SOH reduction of the all-vanadium redox flow battery system is approximately 4%, and the energy efficiency remains stable. Furthermore, the analysis found that the rapid increase in the concentration polarization internal resistance at the end of discharge caused by the average valence state change is the main reason for the capacity decline of the all-vanadium flow battery system. Moreover, the SOH of the all-vanadium redox flow battery system also shows a pronounced difference from other solid-state batteries, implying that the SOH of the all-vanadium redox flow battery can be 100% recoverable.

Trace water contamination in the electrolyte is an important cause for gassing and rapid failure of lithium-ion batteries. However, there is lack of nondestructive techniques to detect trace water in cells. In this study, based on the sensitivity of ultrasonic nondestructive imaging technique to trace gassing side reactions, ultrasonic transmission scanning imaging was performed to analyze the gassing behavior of commercial NCM523/AG pouch cells with different water contents during formation, storing, and cycling. Using electrochemical impedance spectroscopy, scanning electronic microscopy, and charge/discharge characterization, the aging and failure mechanisms were analyzed. The results show that the presence of trace water causes consumption of electrolyte, accelerates gas generation, and increases interfacial impedance and polarization voltage. These characteristics can further cause the reduction of coulomb efficiency and capacity decay, thus accelerating battery failure. This study has guiding significance for quality control in the battery production process and failure mechanism analysis during battery usage.

This paper takes SPE electrolytic hydrogen renewable energy project as the research object and analyzes the total investment, total cost, operating cost and profit of 1000 Nm³/h plant through the engineering economics of methodology, which obtains the key financial indicators such as accumulative NPV, IRR and static investment payback period (P_t ).The total investment of the hydrogen plant is 11.178 million yuan with the area of 10.47 mu(1 mu=666.67 m²).The result shows the electricity consumption accounts for 86.4% of the operating cost, which is the largest cost during the operation. Under the calculation conditions,the relevant financial indicators of the SPE hydrogen technology plant are NPV=21.7321 million Yuan≥0.P_t =8.8 years and IRR=11.63%. At the same time, it is found that the economic values of SPE electrolytic hydrogen renewable energy project is very sensitive to equipment purchase cost, muzzle price of hydrogen refueling station, green electricity price and government subsidies. Investors need to fully consider the local situations to make a decision. The study also points out that when the capacity of the hydrogen plant has reached 308 Nm³/h, i.e., the production capacity utilization ratio (EBP) is 30.08%, it begins to reach the balance point. The balance point is rising with the years of operating, that means hydrogen plant should be fully operated to make more profits by maximum production with highest efficiency. Meanwhile, IRR is 11.05% based on one time overhaul and 20% of the equipment cost during the life span. If the government subsidies last for 15 years, the IRR is 8.1% (one time overhaul) and the NPV is 74.386 million.

Ammonia (NH₃) is one of the most important chemical products in modern society, which has important applications in many fields, such as agriculture and industry. However, since, at present, the production of raw hydrogen in the process of ammonia synthesis in China is mainly based on fossil energy, achieving the goal of "carbon peak" and "carbon neutrality" to effectively alleviate the problems of high carbon emission, electrolysis of water for hydrogen production, and clean ammonia utilization technologies are important breakthroughs. Therefore, this paper understudied the current situation and future trends in China's synthetic ammonia sector, after which we simulated the trend of hydrogen consumption and carbon emission in China's synthetic ammonia industry from 2020 to 2060 based on the Long-range Energy Alternatives Planning System (LEAP) model combined with economic drivers, taking hydrogen price and policy as the main driving factors and considering the substitution of synthetic ammonia with different raw materials. The results showed that in 2060, China's hydrogen demand for synthetic ammonia could reach 21.28 million tons, with the demand mainly coming from new fields like shipping ammonia fuels and coal-fired ammonia blending, which exceeded 50% of the hydrogen demand for synthetic ammonia. Hence, there is great potential for China's synthetic ammonia industry to convert from fossil energy to renewable energy. With a reduction in the cost of hydrogen production from renewable energy, we also observed that the proportion of synthetic ammonia produced from renewable energy increased significantly and may reach more than 97% in the future. Besides, in terms of carbon emission, while China's synthetic ammonia industry could reach a peak around 2025, with a peak of 221.8 million tons, the carbon emission of the synthetic ammonia industry would be about 9.2 million tons in 2060. Thus, to achieve the goal of carbon neutralization, China should give priority to the demonstration project of hydrogen production from electrolytic water and ammonia synthesis in areas rich in renewable energy, thereby strengthening key technologies and applications of electrolytic hydrogen production and ammonia synthesis under mild conditions, realizing the large-scale application of low-carbon ammonia synthesis technology as soon as possible, and increasing research on ammonia fuel engines and ammonia-doped power generation in ammonia application.

Combining the current developmental renewable energy and hydrogen energy trends in China, this paper summarizes the current developmental status of an underground salt-cavern hydrogen-storage technology at home and abroad. Consequently, it was evident that the abundant renewable energy and underground salt cavern resources in Jiangsu Province, including the good coincidence of resource and energy storage sites, were ideal for developing this technical route. Therefore, we systematically analyzed the feasibility of this coupled power generation renewable energy technology, including that of the salt-cavern hydrogen-energy storage and these technical route's full-cycle power generation costs. Investigations revealed that this technical route recovered renewable energy in the form of chemical energy by electrolyzing water from renewable energy to produce hydrogen, then stored this energy on a large scale through underground salt caverns, which used fuel cells to generate electricity for reusing renewable energy when needed. Next, this paper comprehensively considered and analyzed the cost of hydrogen production, including hydrogen storage and re-power generation, and then conducted a preliminary analysis of the kWh costs of re-power generation for this technical route. The results showed that the current cost of electricity reproduction was high, about 1.88 CNY/kWh, of which the cost of electricity and equipment accounted for 61.1% and 25.6% of the total cost, respectively. We also discovered that if the interference power generated by renewable energy was used to electrolyze water to produce hydrogen, the cost of related equipment in the technical route was reduced to 50% of the current, thereby reducing the electricity cost in the technical route to 0.49 CNY/kWh. Additionally, if reducing the power generation cost of the technical route further was necessary, a reliance on the progress of technological and manufacturing levels was needed to improve the power generation efficiency of the fuel cell further. To this end, we observed that if the fuel cell efficiency was increased to 60%, the cost of the technical route could be further reduced to 0.43 CNY/kWh, which was the same as the current electricity price. It also had practical application values. Hence, we propose that industrial and technological progress should improve China's energy security and competitiveness in the international energy field, helping her realize the optimization and transformation of the energy structure, including her peak carbon dioxide emission and carbon neutrality goals, as soon as possible. Moreover, with an improvement in the technical level and efficiency of equipment, such as electrolyzers and fuel cells, in the future, this technical route could also have extremely high application prospects.

New energy storage is an important technology. While it is a piece of basic equipment supporting new power systems, it is also a reasonable and effective price mechanism, hypothesized as the key to the development of new energy storage. However, simply carrying out research on the price mechanism of independently new energy storage power stations, summarizing the practice and experience of typical foreign countries, and analyzing the relevant exploration of the price mechanism of energy storage power stations in China, including the regulated pricing model and independent participation in the electricity market, are insufficient to support new energy storage power station's large-scale commercial application. Hence, on the basis of the equality of responsibilities, rights of all relevant parties, and transfer factors, this study proposes the price formation mechanism and cost diversion optimization method for energy storage power stations, after which a case is finally used for illustrations to prove our findings. The results show that the transfer factor effectively distributed the benefits of energy storage capacity and the electricity market, ensuring a benefit balance for all stakeholders.

The author believes that independent energy storage power stations in Hunan Province have commercial investment value; that is, they can make the project economic, stable and sustainable through capacity lease income and auxiliary service income based on on-site investigation, in-depth analysis of energy storage policies and auxiliary service rules issued by various provinces, and empirical research on the operation mode of independent energy storage power stations. Regarding capacity lease income, Hunan need large-scale energy storage power stations as supporting power sources based on the current power grid structure of Hunan Province. Presently, the policy of mandatory configuration of energy storage has been issued, which makes the capacity lease mandatory. Simultaneously, the capacity resources are scarce considering the limited number of 220 kV substations under a particular power system structure. The planned energy storage in Hunan Province presently can barely meet only the rental demand of the existing and newly planned projects during the "14th five-year plan." The pumped storage power stations planned for long-term demand should be operational by 2030. Therefore, the short-term capacity leasing market is expected to show supply exceeding demand. Finally, the capacity leasing market will maintain a basic balance between supply and demand before the large-scale production of pumped storage power stations. Presently, regarding auxiliary service income, the profit rules of Hunan energy storage participating in auxiliary services are relatively clear; the charging mode measurement is favorable for the energy storage power station. Furthermore, looking forward to the future power spot market, the spot trading income of energy storage power will show explosive growth. According to the survey, Hunan's independent energy storage power station has a commercial investment value at the current income level.

Energy storage technology is the hub and core technology of new power system development. The Ministry of Education and National Development and Reform Commission actively promote the energy storage-related talent cultivation system reform and promote the construction of the major of "Energy Storage Science and Engineering" to adapt to the energy system reform. Energy storage science and engineering is an "Emerging Engineering Education" major with exceptional requirements for integrating industry and education, in which the multidisciplinary system is complicated and closely connected to the industry. Since the start of preparation in 2019, the major and discipline of Energy Storage Science and Engineering at North China Electric Power University have been under construction for four years. The classes of 2019, 2020, and 2021 have more than 340 undergraduate students enrolled, which makes them the major's current largest undergraduate education scale. Some experience has been accumulated in related majors, discipline construction, and student training. This study focuses on constructing the undergraduate cultivation process of Energy Storage Science and Engineering, and it introduces the construction of its discipline and major, the orientation, and features of the curriculum system. The study also evaluates the role of the tutorial system in the cultivation process. This "Emerging Engineering Education" major's overall plan and training methods are comprehensively summarized from the undergraduate education of Energy Storage Science and Engineering. The main strategies and methods adopted in the undergraduate training process of this major are analyzed.