The final goal is to make full use of lithium battery. In order to realize it, lithium battery performance has been studied from different perspectives since it has been widely used. It is an important foundations for improving the safety, reliability and availability of the energy storage system that include accurately describing internal working principle, evaluating the current operation state and predicting future working ability of battery. In order to achieve the final goal, the research work starts from internal principle study. After summarizing and arranging lithium battery modeling methods, it analyzes and compares the advantages and disadvantages of different modeling methods. Then it summarizes many characteristic parameters that can represent the current operation state, health state and future working ability of the battery, such as state of charge （SOC）, state of health （SOH） and remaining useful life （RUL）. This paper compares the advantages and disadvantages of many SOC traditional estimation methods. Then it point that SOC estimation method based on battery model is common application method. It summarizes the characteristics of mathematical algorithm used in SOC estimation method based on battery model, and point put different characteristic of these algorithm. Then it point out that the latest research hotspot is SOC estimation method based on fusion model, then explain its advantages and risks. For SOH evaluation method, it summarizes three different evaluation parameters and SOH estimating method based on different evaluation parameters. After summarizing and comparing, it is widely application engineering method to estimating SOH through impedance of equivalent circuit of battery model. And the hot research direction in the future is SOH estimation based on fusion model. Then it analyzes advantages and disadvantages of mathematical algorithm involved in different SOH estimation methods. This paper summarizes and classifies RUL estimation methods. After analyzing and comparing, the important methods are RUL based on empirical decay model and RUL based on artificial intelligence algorithm. Then it gives several mature cases based on empirical decay model and sorts out the research cases of RUL based on fusion model as future hotspot research. Through evaluation methods of different application stages in lithium battery life cycle, such as SOC, SOH and RUL, which can engineering practicability realize battery state evaluation, it provides accurate quantitative analysis basis for optimization useful of battery system.

This review discusses four evaluation criteria of energy storage technologies: safety, cost, performance and environmental friendliness. The constraints, research progress, and challenges of technologies such as lithium-ion batteries, flow batteries, sodiumsulfur batteries, and lead-acid batteries are also summarized. In general, existing battery energy-storage technologies have not attained their goal of “high safety, low cost, long life, and environmental friendliness”. Finally, the possible development routes of future battery energy-storage technologies are discussed. The coexistence of multiple technologies is the anticipated norm in the energy-storage market.

This study simulates a hydrogen storage tank assuming lumped hydrogen gas and one-dimensional heat transfer through the tank wall. The model was verified on reported data and then applied in a refueling simulation that investigated the effect of tank structure on the temperature rise of the enclosed hydrogen. During refueling of a Type III tank, most of the simulated hydrogen heat was passed into the tank wall, only 2% of the heat was dissipated from the tank into the environment. Owing to its higher thermal conductivity and significantly lower temperature gradient in the radial direction, the aluminum liner layer exchanged more hydrogen heat than the wrap layer. Reducing the liner layer thickness acceleratted the temperature rise. The hydrogen refueling temperature rise was 10 ℃ higher in the tank with a 3-mm-thick liner layer than in the same tank with a 7 mm-thick liner layer. In contrast, the warp layer thickness had an insignificant effect on hydrogen heat exchange owing to its relatively lower heat conductivity than the liner layer. The simulated temperature rise increased by only 1.8 ℃ when the tank wrap layer thickness was reduced from 12 to 8 mm. Therefore, when controlling the hydrogen refueling of a Type III tank, the effect of tank structure on the temperature rise cannot be ignored. To realize fast and safe refueling, the hydrogen fueling rate can be optimized considering the tank wall parameters, especially the thickness of the aluminum liner layer.

This study experimentally evaluated an open air-cooled proton-exchange membrane fuel cell (PEMFC) system to improve its hydrogen utilization under overall working conditions. When operated in dead-end anode mode, the PEMFC demonstrated faster cell voltage decay at higher discharge currents. Therefore, the PEMFC anode end must be periodically opened to ensure its stable running. Moreover, lowering the hydrogen utilization increased the anode inlet pressure. To improve the hydrogen utilization and stabilize the running of the PEMFC, the anode purge period should be prolonged in low-current operation and shortened otherwise. At PEMFC discharge currents of 2, 5, and 8 A with a uniform purge period, the hydrogen utilizations were 0.6421, 0.9280, and 0.9746, respectively. That is, reducing the discharge current lowered the hydrogen utilization. The optimal anode purge period varied with discharge current, being prolonged to 30 and 20 s at 2 and 5 A, respectively, and it was unchanged between 5 and 8 A. The hydrogen utilization always exceeded 0.95. After approximately 1 h, the actual hydrogen consumptions were 0.1241 and 0.1317 g, respectively; approximately 5.77% of hydrogen amount was saved under optimized purge mode.

In this paper, the cost of hydrogen production by renewable energy electrolysis was systematically analyzed, and the levelized cost of hydrogen (LCOH) from alkaline and PEM electrolyzers were compared. The effects of scale, hydrogen pressure, compression and liquefaction, and input power fluctuation on the cost of hydrogen production by alkaline and PEM electrolysis were investigated. The results showed that the cost of hydrogen production was reduced with the increase of scale. When the scale of our investigated electrolysis system was increased from 1 MW to 40 MW, its fixed cost was reduced by more than 40%, but its LCOH cost was reduced byless than 25% because electricity is the main cost. The LCOH cost of hydrogen production by high-pressure electrolysis can be significantly reduced without increasing the fixed cost. With the increase of electrolysis pressure from 1 atm to 30 atm, the cost of hydrogen further compression to 700 atm will be reduced from 1 $/kg to 0.3 $/kg. The liquefaction cost was significantly affected by the scale, and the levelized cost of hydrogen production by electrolysis and liquefaction decreased from 8.7 $/kg to 5.3 $/kg with the increasing of scale from 1 MW to 40 MW. For PEM has good adaptability of renewable energy fluctuation, the LCOH cost of PEM could be lower than that of alkaline electrolysis with an increase of low power (<20% rated power) fluctuation. With the improvement of alkaline electrolysis and PEM electrolysis technology, which is better or worse should be discussed according to the specific situation.

With their advantages of zero emissions, long cruising range and quick refueling speed, fuel cell electric vehicles (FCEVs) are have wide potential for long cruising range and heavy load applications. During refueling, the tank of an FCEV and its contained hydrogen are heated by the Joule-Thomson effect. An overheated tank compromises the safety of onboard storage, necessitating a specialized refueling technology. In the US, Japan and Europe, this technology has been developed for Type IV tanks. However, China requires a refueling technology for Type III tanks, currently the only available tank type in the country. This study develops and experimentally analyzes a physical and mathematical model of the refueling process for Type III tanks. The Type III tank parameters, refueling parameters and environmental parameters were varied and their effects on refueling speed, final temperature and target pressure were investigated. The temperature rose rapidly when the initial pressure and filling rate were high. Next, a temperature prediction tool for Type III and Type IV refueling was developed and experimentally validated. The proposed method and the developed tool revealed important differences between Type III and Type IV tank refueling. For instance, the temperature gradients across the tank thickness were significantly different in the Type III and Type IV tanks. Across the inner layer, the temperature was nearly uniform in the Type III tank but increased linearly in the Type IV tank. The larger temperature gradient in the Type IV tank indicates a higher energy requirement for precooling the hydrogen in a Type IV tank than in a Type III tank with the same state of charge. Refueling a 35 MPa Type IV tank requires 0.65 kW·h/kg at an ambient temperature of 38 ℃, which increases the operation cost at the hydrogen station. This work provides important guidelines for the domestic development of hydrogen refueling stations.

This study analyzes the working model and refueling performance of a 35 MPa/70 MPa hydrogen dispenser and assesses the user experience of hydrogen fuel cell vehicles and the restriction conditions of on-board hydrogen storage tanks. Based on the results, a universal evaluation index of the refueling performance of a hydrogen dispenser is proposed. A refueling test was conducted on a 35 MPa/70 MPa hydrogen dispenser for passenger and logistics vehicles, and the refueling performance of the dispenser was measured by the evaluation index. The index is direct and reliable, simple and easy to calculate, and comprehensively reflects the refueling performance of the hydrogen dispenser. The index is applicable to actual performance evaluations of 35 MPa/70 MPa hydrogen dispensers and provides technical and theoretical support for ensuring their reliable operation.

Carbon cloth has played a vital role in battery performance evaluations owing to its low price and abundant pore structure that promotes the reaction mass-transfer process. However, the structure and performance of carbon cloth have not been systematically researched. In this work, porous carbon cloth was used as the electrode material in all-vanadium flow batteries. The surface structures and morphologies of different electrodes were studied by X-ray photoelectron spectroscopy, scanning electron microscopy, Raman spectroscopy, mercury intrusion porosimetry, and other characterization methods. Moreover, the electrochemical performances of the batteries were assessed using polarization curves and chargedischarge tests. A high degree of disorder, abundant defects, high surface content of the carbonyl functional group, and high porosity were found to increase the effective contact area between the electrode and electrolyte, provide more active sites in the redox reaction, and promote the oxygen transfer from H₂O to VO²⁺ and the redox reaction between vanadium ions. Consequently, the battery performance was significantly improved. In evaluation tests, the cell delivered high power density and good cycle stability. Under a current density of 100 mA/cm², the cell achieved a power density of 686.2 mW/cm², and its current, voltage, and energy efficiencies were 97.5%, 84.6%, and 82.4%, respectively. Additionally, the chargedischarge performance remained high under 100300 mA/cm² discharge conditions.

Composite carbon fiber electrodes were manufactured by attaching multi-walled carbon nanotubes (MWCNTs) to carbon paper (CP) using the impregnation and carbonization method. The binder between the carbon fiber surface and MWCNT was carbonized to increase the bonding strength and lower the electrical resistance. The composite electrode was characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, the BrunauerEmmettTeller specific surface area, cyclic voltammetry, and electrochemical impedance spectroscopy. The composite CP/MWCNT electrodes demonstrated higher surface area (99 m²/g), higher electrochemical activity, lower electrical resistance (0.74 Ω·cm²), and greater hydrophilicity than CP. The CP/MWCNT possessed chemically reactive sites and low charge-transfer resistance and achieved higher energy-conversion efficiency than CP in electrochemical tests. The energy efficiency was maintained at 80% under a chargedischarge current density of 200 mA/cm² and its peak power density reached 603.32 mW/cm². This excellent electrochemical performance is mainly attributed to the MWCNT nanostructure formed on the carbon fiber surface. The presented results could pave the way for low-cost electrode manufacturing.

Geothermal regions have excellent application prospects as low-carbon, green energy sources. Geothermal energy-storage systems combine geothermal- and thermal-storage technologies, thereby improving the single-well heating ability, expanding the recharge quantity of single wells, and reducing the running costs. To meet the heating demands of office buildings in Hebei Province (Northern China), this study proposes a peak shaving energy system based on geothermal energy. The economics of the system are evaluated in terms of several economic indicators such as initial investment, operating cost, and net present value. Besides conserving energy, the geothermal energy system with thermal storage reduced the initial investment and operating costs by 42% and 55% from those of the geothermal system without the storage. The net annual value of the proposed system was ￥14392.10.

Based on the analysis of the actual operation of the 200 MW wind farm in the northwest in China and the technical features of flow battery energy storage technology, the wind farm is configured with the flow battery energy storage operation mode, and an energy storage revenue model is established. By comparing the gains obtained by deploying flow battery energy storage systems of different sizes in the wind farm, an optimum energy storage scale is obtained. Under the selected wind field conditions, in small scale peak shifting and tracking plan output operation mode, the 5 MW/10 MW·h flow battery energy storage scale is the best solution, which can achieve the purpose of tracking plan output, reduce wind abandonment, and moderately peak shifting, and to maximize the energy storage value. The energy storage station investment payback period is less than 8 years.

Presently, Chinas steel industry works with rich media and low heat resources. Because the industry wastes a wide span of heat energies, operates over a large temperature range, and is intermittent and unstable, the existing technology of heat recovery is insufficient. Phase-changing thermal storage materials have become a research hotspot because their heat storage density is high and their temperature remains constant during heat storage and release. This paper introduces the design and manufacture of test equipment based on NaNO₃/SiO₂ as the phase-change thermal storage material and analyzes its characteristics. In an experimental evaluation of the test equipment, the highest heat storage efficiency was 68.3% and the highest exothermal efficiency reached approximately 60%.

Coordinated control among the energy sources, girds, loads, and storages is vital for the economic operation of a microgrid system, especially when the microgrid system includes energy storage systems. To improve the operation economy of such systems, a model library based on value stream analysis was developed on process simulation software. After calculating the flow and potential variables, the unit price variable was calculated according to the bidirectional flow characteristics of the energy storage system. To verify the reliability of the EnergySystem library in optimizing the control of a microgrid system, the control strategy of its energy storage system was analyzed. The result showed that a reasonable control strategy of the energy storage system must fully consider many boundary conditions, such as the time-of-use electric price, load demand, photovoltaic power generation, and energy-storage system parameters. After implementing a control strategy based on the value stream analysis, the peakvalley arbitrage was 1.8 times higher and the solar power loss was 50% lower than after implementing the strategy of the energy storage provider.

Supercapacitors are widely researched energy-storage systems with many unique characteristics: ultrahigh power density, fast chargedischarge capability, high security, and excellent cycle stability. Porous carbon materials with high Brunauer Emmett Teller (BET) surface area and reasonable pore size distribution are ideal candidates for supercapacitor electrode materials. A simple strategy was used to fabricate the water-soluble pitch-based porous carbons (WPCs) using water soluble pitch (WP) as the precursor and Na₂CO₃ as the activating agent. The rational design of three-dimensional (3D) hierarchical porous architecture enables the material to have excellent properties. The BET specific surface area of the as-obtained WPCs reached 1912 m²/g. Moreover, supercapacitor electrodes based on the WPCs achieved a high specific capacitance (232 F/g at 0.05 A/g) and good cyclic stability (capacitance retention=97.5% after 5000 charge-discharge cycles at 2.0 A/g). This facile synthesis strategy will promote the commercial application of WPCs in supercapacitors.

This paper provides a brief background of industrial energy-storage development. The transformation and adjustment of China's energy structure has opened new opportunities for energy storage technology. For instance, it promises to improve the quality of renewable power generation, reduce the power limitation rate of wind farms and photovoltaic power stations, and enhance multiple aspects of power systems. Energy storage plays an important role in todays emerging third industrial revolution, which will continue into the future energy internet. A central enterprise dedicated to renewable energy development, called the State Power Investment Corporation Research Institute (SPICRI), has developed iron-chromium redox flow batteries for electrical energy storage. These batteries have several advantages such as high roundtrip efficiency, long service life, wide temperature-range operability, modular power design, customized capacity design, high safety, environmental friendliness, and low cost. Therefore, they are suitable for various renewable energy sources such as wind, solar, smart grids, and microgrids. Moreover, the manufacturing technology is expected to upscale to large-scale energy storage. As an engineering case study, this paper introduces the 250 kW/1.5 MW·h ironchromium redox flow batteries developed for an energy-storage demonstration power station, which is under construction by SPICRI. The SPICRI station is Chinas first power station with a hundred-kilowatt-level storage capacity. The rated output power and capacity of the energy storage demonstration power station are 250 kW and 1.5 MW·h, respectively. When operated commercially on large scales, the iron-chromium redox flow battery technology promises new innovations in energy storage technology.

Studies on sodium ion batteries for energy storage have gradually gained momentum, motivating the development of practical applications. However, can the theory, materials, and applications of sodium ion batteries be compatible with those of present lithium ion batteries? What are the competitive advantages of sodium ion batteries? To answer these questions, this article considers the present sodium-storage electrode materials and the current developmental status of lithium ion batteries and analyzes the advantages of sodium ion batteries from an application perspective. It then suggests some feasible research directions of sodium-storage electrode materials and practical solutions for sodium ion battery systems. This paper is intended as a reference for the research and application of sodium ion batteries in the future.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 3295 papers online from Feb. 01, 2020 to Mar. 31, 2020. 100 of them were selected to be highlighted. Layered oxide especially Ni-rich cathode materials are under extensive investigations for studying the failure mechanism and the effects of surface modifications. There are also a few papers on Li-rich and high voltage LiCoO₂ materials. As for anode materials, large efforts were devoted to Si based composite anode materials to improving the cycling performance and columbic efficiency by inhibiting the volume expansion and keeping the electron conductivity. Cycling properties of metallic lithium anode are improved by using different kinds of surface cover layer, electrolyte additives and current collector modifications. Both of inorganic and polymer based solid state electrolyte are burningly researched and new additives and lithium salts are used for liquid electrolyte. Solid state batteries, Li-S and Li-O₂ batteries are still at early stage and new electrode preparation methods are proposed to keep the conducting network and reaction reversibility. Various in-situ technologies are used to observe dynamic changes of morphology, lithium and potential distribution. Theoretical works are related to the mechanism of SEI formation, and some mesoscopic and macroscopic models for kinetic properties.

Solid supercapacitors (SSCs) have become a hotspot of supercapacitor research as they satisfy safety requirements and are environment friendly. SSCs require electrolytes with low electronic conductivity, high ionic conductivity at room temperature, and good mechanical properties. Gel polymer electrolyte (GPE) is a solid polymer electrolyte with high ionic conductivity, zero risk of electrolyte leakage, no toxicity (unlike water systems), and heat resistance properties (unlike flammable organic systems). Depending on the solvent type, GPEs can be prepared as hydrogel polymer electrolytes, organic gel polymer electrolytes, or ionic liquid gel electrolytes. GPE is mainly composed of a polymer matrix, an additive, and a conductive salt. It plays dual roles as an ion-conducting medium and a separator. This article summarizes the latest research progress on GPE in SSCs and suggests the research development trends of future GPE-based SCCs.

By virtue of their high specific capacity and long service life, lithium ion batteries are popularly installed in mobile electronic equipment, electric vehicles, and energy storage systems. A battery separator is a vital component as it sustains the battery usage at high temperatures. New electric vehicles are increasing the energy density and safety performance demands of lithium ion batteries, placing more stringent requirements on the heat resistance, mechanical properties, and electrolyte infiltration of lithium-ion battery separators. Existing industrial-scale separators are polyolefin porous membranes, which deliver high performance at low cost. However, the poor thermal stability of polyolefins has become the safety bottleneck of high-energy lithium batteries. Excessively high temperatures cause severe thermal contraction, resulting in short-circuiting between the positive and negative electrodes of the battery, and possible burnout or explosion of the battery. In contrast, nonwoven fabric-based separators deliver excellent heat resistance, so they are expected in the next generation of high-energy lithium battery systems. This paper reviews the research progress of nonwoven fabric-based separators in lithium ion batteries. At present, nonwoven composite separators and nonwoven fabric-based separators are formed by the wet-laid process and electrostatic spinning. These fabrication processes are separately described in detail. Nonwoven fabric-based separators in power lithium-ion batteries are still being tested in small-scale trials. To realize their large-scale industrial production and application, we must overcome technical bottlenecks, i.e., the thickness, pore size, and cost control of the separator. Prompt and effective solutions to these problems would help realize safe batteries with high specific capacity.

According to research on thermal energy storage, salt hydrates are effective thermochemical heat-storage materials that store low- and medium-temperature heat for long periods. Salt hydrates store and release heat through reversible dehydration and hydration reactions. This paper describes the types and properties of salt hydrates and introduces progressive research on pure salt hydrates, composite salt hydrates, and binary salts. Pure salt hydrates have high theoretical heat storage densities, but their practical applications are limited by deliquescence, strong corrosiveness and poor cycling stability. To improve their heat- and mass-transfer properties, pure salt hydrates can be filled into porous materials. Recently, high-performance binary mixtures of salt hydrates have been developed. Furthermore, binary salt hydrates have been filled into the pores of porous materials, providing composite materials with high heat-storage density and good cycling stability. The thermochemical heat-storage materials of salt hydrates can be optimized from two perspectives: heat and mass transfer enhancement of composite materials and optimal composition of binary salt hydrates.

As a typical pseudocapacitor material for supercapacitors, MnO₂ has the advantages of low cost and high specific capacitance, but its electrochemical performance is degraded by poor conductivity and structural instability in the working process. At present, the electrochemical performance of MnO₂ is improved by binary composites. This paper reviews the research progress on supercapacitor-based MnO₂ and dual-layered MnO₂, and pseudocapacitor binary composite materials. After analyzing and comparing the electrochemical performances of MnO₂ binary composites, it is proposed that composite MnO₂ and pseudo-capacitive materials, or composites with coreshell heterogeneous structures, are competitive candidates for improving the electrochemical performance.

The stability of Li-metal anodes seriously limits the development of Li-oxygen batteries (LOBs). An artificial solid electrolyte interface (SEI) film constructed on Li is effectively protective, self-healing, and easily achievable. In this work, an artificial SEI film based on LiF/Ag was formed in situ on the surface of the Li-metal anode by a facile pretreatment with silver fluoride (AgF) solution. The film significantly suppressed the growth of Li-dendrites, improved the stability of Li-metal anodes, and prolonged the cycle life of the LOB more than fourfold.

To investigate the fast-decay problem of Li(Ni_0.8Co_0.1Mn_0.1)O₂/graphite system cells in high-temperature cycling, the structures and morphologies of the cathode and anode were systematically analyzed in fresh and cycled cells. The characterizations were performed by X-ray diffraction, scanning electron microscopy, and inductively coupled plasma spectroscopy. After cycling, the Li/Ni cation mixing degree increased and the cathode materials cracked from the inside (even pulverized at 45 ℃). These processes reduced both the electrolyte consumption and internal resistance of the cell and hence degraded the cycling performance. After doping the cathode material, the high-temperature cycling performance can be significantly improved, with a capacity retention of 87% after 1000 cycles at 45 ℃.

With their large layer spacing and controllable pore and defect structures, hard biomass carbon materials are suitable anode materials for lithium ion batteries (LIB). In this paper, impurities were removed from a water-chestnut shell precursor by hydrothermal treatment, which is safer and more environmentally friendly than pickling and saves material preparation time. The hard carbons derived from the water chestnut shells were prepared as the anode materials at different high temperatures (HT-x). The morphologies, microcrystalline structures, and microstructures of the specimens were characterized by scanning electron microscopy, X-ray diffraction analysis, Raman spectroscopy, and transmission electron microscopy. As clarified in the results, the impurities were substantially removed from the precursor. The carbonization temperature significantly affected the microstructure and lithium storage performance of the material. Sample HT-1100 exhibited a large layer spacing (d₀₀₂=0.39 nm) and a moderate specific surface area (76.82 m²/g). Under a current density of 0.1 C (1 C=250 mA/g), the reversible discharge specific capacity of this sample reached 405.6 mA·h/g. The rate performance was also high, with a specific capacity of 181.3 mA·h/g at 4 C. After 300 cycles at a current density of 0.4 C, the capacity remained at 382.5 mA·h/g, showing excellent cycle performance. By applying hard carbon derived from water chestnut shells as the anode material in LIB, we provide experimental support for converting a waste product into a valuable commodity, ultimately realizing green and efficient resource utilization.

Through layer-layer coating and series chemical reaction, the sandwich structure of SiO@C@Al₂O₃ and Li-Si-O@C@LiAlO₂ was prepared by using SiO, pitch, aluminum nitrate and LiH as the main raw materials. The morphology and the phase structure of the samples were characterized by SEM, TEM, XRD and laser particle size analyzer. It was adopted by CR2032 cell to evaluate the reversible capacity, initial coulombic efficiency and capacity retention of different products. The results showed that compared with the common SiO@C, the modified SiO@C@Al₂O₃ and Li-Si-O@C@LiAlO₂ composites had excellent electrochemical performance in initial Coulombic efficiency and capacity retention. This preparation was simple operation, low cost and suitable for industrial production.

This work focused on the electrochemical-thermal coupled simulation of lithium-ion battery based on three-dimensional multi-layer structure. Temperature and current characteristics of the smallest unit of prismatic battery were analyzed, and tab size was optimized. Temperature and voltage results of experiments under 0.5 C, 1 C, and 2 C constant current discharge processes agreed well with the simulation, and indicated that the model could be furtherly used to analyze the electrochemical and thermal characteristics of the batteries. It was found that with the increase of discharge rate, the maximum temperature rise of the battery at the end of discharge increased in the trend of the convex curve, and it was high to 33.83 ℃ at the end of 2 C discharge process. And The increasing trend of the maximum temperature difference was in the concave curve, which was 1.6645 ℃ at 2 C discharge process. Both the average current density perpendicular to the separator and the current density difference were found linearly increased with the increasing discharge rate. At the end of 2 C discharge process, they were 43.62 A/m² and 2.0 A/m², respectively. Besides, the temperature rise and maximum temperature difference of the battery were significantly correlated with the resistance ratio of the negative tab to positive tab (Sc). The optimal Sc value was considered to be around 0.875. When Sc was less than 0.875, the maximum temperature rise and maximum temperature difference decreased rapidly at a rate of 1.52 ℃/Sc and 5.2 ℃/Sc respectively. When Sc was greater than 0.875, the maximum temperature rise decreased at a slow rate of 0.2021 ℃/Sc, and the maximum temperature difference increasing rate was 0.1934 ℃/Sc. In addition, the average current density perpendicular to the separator and the current density difference were found little affected by Sc.

Heat transfer was experimentally investigated in a sintered flat heat pipe. The shell of the heat pipe was fabricated from oxygen-free copper, and the working medium was a mixture of water and ethanol. The wick of the heat pipe was a sintered copper ball. The sintered flat heat pipe was 3.2 mm thick, 8 mm wide, and 400 mm long. Its bending radius was 20 mm, and its bending angle was varied as 30°, 50°, 70°, and 90°. The heat transfer performance of the pipe was evaluated for heat sources of different temperatures (50 ℃, 60 ℃, 70 ℃, and 80 ℃), generated by heating quantitative cold water. In a preliminary test, the temperature difference in each part of the heat pipe was not significantly affected by the bending angle. Even the pipe bent at 90° showed good isothermal properties. In a further study, the thermal resistance of the heat pipe was reduced by increasing the source temperature and reducing the bending angle. The heat resistance performance of the heat pipe mainly depended on the bending angle. When the bending angle increased from 30° to 90°, the thermal resistance increased by more than 60% because the bend crushed the liquid core and deformed the flow of the absorption liquid working medium. Consequently, the fluid flow was hindered and the heat transfer performance declined. Moreover, changing the temperature of the heat source altered the heat transfer capacity in the evaporation section of the heat pipe. As the source temperature increased, the heat resistance of the heat pipe decreased. Finally, sensitive heat storage was investigated in a bent flat heat pipe. At higher source temperatures and lower bending angles of the heat pipe, the time of the sensible heat storage was lowered and the rate of sensible heat storage increased.

Spent NCM523 was regenerated by a green method which is simple, feasible, and innovative. A low-eutectic mixture (LiNO₃-LiOH) was used as the lithium salt for regeneration in an air atmosphere. The regenerated product was characterized by X-ray diffraction, inductively coupled plasma spectroscopy, and scanning electron microscopy. The composition and crystal structure confirmed that the spent cathode was restored to its original state. Moreover, electrochemical results show that under the condition 300 ℃/3 h～850 ℃/4 h, the specific capacity of the regenerated material reached 161.2 mA·h/g(0.1 C, 2.8～4. 25 V) in the first discharge, and the coulomb efficiency was 87.8%. After 100 cycles at 1 C, the specific discharge capacity was 133.6 mA·h/g, confirming the high electrochemical performance of the rejuvenated material. The rate and recycling performance were much improved from those of untreated cathode materials and were similar to those of commercial anode materials. This research can promote the industrialization of cathode material recovery and provides a unique idea for the green recovery of other cathode materials such as LiMn₂O₄ and LiFePO₄. This method has good application prospects in lithium battery recovery.

The specific surface area of a vitrified lead-foam grid formed from polyurethane foam as the raw material was several tens of times higher than that of a common grid. After comparing the performances of different number of holes in a polyurethane foam substrate and different amounts of lead plated on the positive foam, the technological scheme was optimized as polyurethane foam substrate with a hole density of 15 PPI and 20 g lead plated on a positive grid. Under the optimized scheme, the specific surface area and coating thickness of the positive lead-foam grid were 19.1 cm²/cm³ and 39.1 μm, respectively, and those of the corresponding negative lead-foam grid were 33.1 cm²/cm³ and 13.3 μm, respectively. The foam grid can improve the utilization of active material and the specific energy of lead acid batteries. Moreover, the high rate discharge performance and cycle life of electric moped batteries with the foam grid can meet the requirements of national standards.

Promotion of clean heating can improve the livelihoods and contentedness of people in the northern China. Various clean heating technologies are available, each with different characteristics. Among these technologies, thermal energy-storage technology has received much attention. This paper summarizes the technologies of clean heating and thermal energy storage and reviews the development status and trend of thermal energy-storage technologies in clean heating applications. Finally, combining the characteristics of clean heating technology and thermal energy-storage technology, typical thermal energy-storage technologies for clean heating were analyzed. Among the clean heating technologies, we identified clean coal-fired central heating, natural gas heating, electric heating, renewable energy, and other clean heating technologies. Electric heating technologies based on thermal energy storage are widely disseminated as they cooperate with the peak load regulations of power grids and avoid the volatility of renewable energy sources. Thermal energy-storage technologies are divisible into sensible heat, latent heat, and thermochemical heat storage technologies. As the earliest, most widely used, and most mature technology, sensible heat-storage technology has advantages of scalability, long life, low cost, and high technological maturity. Latent heat-storage technology achieves a high heat-storage density, and its temperature remains nearly constant during exothermic processes. This technology has become a research and application hotspot. Thermochemical heat-storage technology achieves the highest energy-storage density over a long storage period, but it is currently in the laboratory verification stage. Thermal energy-storage technologies for clean heating have gradually focused on water-heat storage, high-temperature solid-heat storage, and phase-change heat storage. This study provides a reference and basis for the design and application of clean heating technologies in northern China.

The statistical data at the end of 2018 shows that the new energy power generation is the second largest power generation form in China, but the inherent randomness and volatility of the new energy itself have brought challenges to the stability of the power grid, and the contribution of the new energy units to the peak load regulation and frequency modulation of the power grid can be ignored. One of the ways to deal with this challenge is to build a certain scale of grid level flexible regulation resources represented by flywheel energy storage. The engineering value of flywheel energy storage is reflected by typical application scenarios such as frequency modulation auxiliary service market. By tracking the progress of flywheel energy storage project in recent years, this paper introduces the main subsystem of flywheel energy storage technology and the technical route of major companies and research institutions, and concludes that the engineering application of flywheel energy storage in power system mainly includes grid frequency modulation, renewable energy consumption and micro grid support. When applied to grid frequency modulation, flywheel changes its output according to the area control error of the grid. When applied to renewable energy consumption, flywheel facility has different control modes. In the power output smoothing control mode, the flywheel energy storage facility shall smooth the varying real power output from renewable energy on a continuous basis. By comparing the instantaneous real power output of renewable energy to the average real power output of renewable energy obtained over a field adjustable time period, the flywheel will adjust its power demands to ensure that the average real power output of renewable energy is equal to the sum of the instantaneous real power output of the flywheel and renewable energy. In the dynamic reactive power support control mode, the flywheel energy storage facility shall inject appropriate amount of reactive power at the grid so that the grid reactive power flow nullifies the grid voltage change as a result of average real power injection by renewable energy. The flywheel provide dynamic power support by operating the facility in variable power factor control mode. Reactive power absorption is a continuous function of two variables, one is grid voltage level and another is total real power output from renewable energy and the flywheel. The installation of flywheel energy storage device can make up for the uncertainty of renewable energy generation. However, compared with the power battery energy storage technology, the bottleneck restricting the large-scale application of flywheel energy storage technology lies in the high initial investment cost, and the development direction of grid level flywheel energy storage technology should be higher cost performance, so as to obtain the market share.

This study proposes an adaptive energy-management strategy that enhances the driving range and performance of a hybrid energy-storage system. First, the intention and driving style of the driver is established by fuzzy logic. Using this model, the time constant of the low-pass filter is then adjusted online. The filter divides the motor demand power into the average power and the peak power. To evaluate its performance, the proposed energy management strategy is compared with the logic threshold control strategy and fuzzy control strategy on the ADVISOR simulation platform. The proposed adaptive energy-management strategy achieves lower peak discharge current of the battery than the other control strategies and improves the power distribution of hybrid energy-storage systems in electric vehicles. With these improvements, more braking energy is recovered by the ultracapacitor and the driving mileage is extended.

Thermal management of batteries is typically performed in liquid medium, which is simply structured and accelerates the cooling speed. To explore the heat transfer effect of battery thermal management in liquid medium, this study examined the effect of coolant temperature on the maximum temperature and the maximum temperature difference in a battery pack. Comparison experiments were conducted at different ambient temperatures in a liquid-cooled lithium-ion battery thermal-management system. The overall temperature distribution inside the battery pack was analyzed using simulation software. The study revealed several shortcomings of battery thermal management in liquid media, providing a reference for improving the design of power battery thermal management systems. Placing a liquid-cooled plate at the bottom of the battery pack effectively lowered the maximum temperature of the battery. Increasing the ambient temperature enhanced the heat dissipation effect, but risked a large temperature difference between the upper and lower surfaces of the battery module. Within a certain range, the maximum temperature of the battery decreased with decreasing coolant temperature. Further cooling of the coolant disturbed the uniformity of the temperature concentration at the surface of the battery.

The volume of an underground air-storage cavern is a basic parameter in the planning and engineering of large-scale compressed-air energy-storage power stations. The volume of an isochoric air-storage cavern must be accurately matched with the installed capacity of the power station. This work calculates the energy storage of compressed air in the cavern and determines the energy storage efficiency of the cavern. Based on the energy storage efficiency, it calculates the cavern volume and finally derives the efficiency of the expansion device and the power generation efficiency of a generator set. To assess the correctness and rationality of the calculation method, the main factors affecting the energy storage efficiency and volumetric quantity of the cavern were quantified in numerical examples. As the operation cycles proceeded, the energy storage efficiency gradually improved and the variations decreased, reaching stability in the later stage. The energy storage efficiency decreased with increasing leakage amount of compressed air, and was enhanced by increasing the coefficient of convective heat transfer. The operation pressure difference also increased the energy storage efficiency up to a certain value. Increasing both the storage efficiency and the operation pressure difference reduced the cavern volume that matched the installed capacity. Therefore, to decrease the construction cost of the cavern, the operation scheme should increase the operating pressure and the operating pressure difference as much as possible.

A UPS system provides the requisite power for sensitive equipment. The performance of a UPS is dominated by its storage medium and power control. The flywheel energy-storage system (FESS) is more efficient, incurs lower maintenance costs, and is non-polluting than chemical batteries. There are three types of UPS configurations: on-line, off-line, and line-interactive. The off-line configuration has a simpler topology, lower cost, and higher efficiency than the line-interactive configuration, but it is disadvantaged by low dynamic response. This paper proposes an FESS UPS based on a quasi-proportional resonance (quasi-PR) control method with a SCR switch. Combined with quasi-PR and vector controls, the proposed UPS overcomes the shortcomings of the traditional off-line type, achieving both high dynamic response and high power quality. This paper presents the operation mechanism, quasi-PR control, and vector control at the motor/grid side. The good response and high power quality of the proposed UPS are validated in simulations and experiments.

For the problem of the regenerative braking energy in the rail transit, some research on a kind of magnetically suspended flywheel array-based energy recovery system is done. Through analysis on the structure of the traction power supply system, the braking methods and energy consumption during the rail pulling in are introduced. And then the contrast results of the energy consumption are provided before and after adding the energy-storaged equipment. Based on this, a kind of the flywheel energy-storaged array-based DC power recycling system is designed which can be used to achieve a fast braking power absorption during pulling in and power compensation during pulling out of the rail train. With the argumentation of the flywheel key performance indices, the parallel strategy and the capacity assignment are demonstrated. Finally, the experimental platform of the flywheel energy-storaged array is developed with the real test system. The mutual-driven charging and discharging results can be able to demonstrate the effectiveness of the designed.

Determination the capacity ratio in microgrids (MGs) not only lacks a sufficient scientific basis, but also incurs large investment waste, with detrimental impact on subsequent economic dispatching and safe operation of the MG. Therefore, MG construction faces a multi-objective optimization problem. Moreover, there is a complex nonlinear relationship between the capacity of each type of power source and the given index. To solve the capacity ratio optimization problem, this work incorporates the Bettle Antennae Search (BAS) algorithm into the genetic algorithm (GA). Based on the design of a wind-solar-diesel battery hybrid power system, the BAS algorithm improves the ease and speed of finding the global optimal solution and thereby improves the nonlinear planning performance. The input data include the hourly wind speed, hourly solar radiation intensity, and hourly environmental temperature at a certain point in Lanzhou City (Gansu Province, Northwest China), where the power output model has an established dispatching strategy. The primary and secondary goals of the optimal capacity ratio are to maximize the annual power-supply reliability and find the best investment economy, respectively. In all tested cases, the BAS-GA optimized the capacity ratio at faster convergence speed than others and consistently obtained the same result, confirming its stability and reliability. In the BAS-GA with an LPSP of 0.2%, the investment saving was 66%, whereas the basic GA with an LPSP of 0% yielded no investment saving. Moreover, the efficiency/cost ratio obtained by the basic GA (2.3%) exceeded the LPSP. The data of other basic GAs were not comparable with those of BAS-GA. The BAS algorithm effectively prevented the basic GA from falling into the local optima of the capacity- ratio optimization scheme in MG construction.

The neutral-point voltage balance of three-level inverters has always been a research hotspot for researchers worldwide. This paper discusses common-mode voltage suppression and neutral-point voltage balance in three-level inverters for NPC. When constructing virtual vectors, the positive small vectors are neglected as they cause a large common-mode voltage. Second, depending on the voltage difference between the upper and lower capacitors on the DC side, a virtual vector that meets the demand is constructed to balance the neutral point voltage. Finally, a model that predicts the midpoint voltage in the next sampling period is established and an index measuring the quality of the output waveform is input to a function. Each vector allocation time is optimized by Lagrange multiplication. A simulation study conducted in MATLAB/Simulink showed that the proposed scheme suppresses and effectively controls the common-mode voltage.

Supercapacitor energy feedback system is an important development direction of energy storage & feedback system. However, the high cost of supercapacitor limits its application. In order to reduce the cost of the supercapacitor energy storage system, this paper discusses the shortcomings of the traditional bi-directional DC/DC scheme in the supercapacitor energy feedback system from the perspective of broadening the working voltage range of the supercapacitor and improving the energy utilization ratio. Through the comparative study of the three-level circuit, a flying capacitor three-level circuit structure is proposed, which is suitable for the supercapacitor energy feedback system. A PWM control method is proposed for the circuit and the operating modes of the circuit is analyzed in detail. Finally, the correctness of the theoretical analysis is verified by PSIM software simulation. Compared with the traditional two-level DC/DC scheme, the three-level circuit structure proposed in this paper widens the working voltage range of the supercapacitor by 100%, and improves the energy utilization rate of the system. At the same time, the circuit can improve the system withstand voltage, reduce the output harmonic and topology loss, and has a wide application prospect in the high-power charging and discharging occasions such as braking energy & potential energy feedback.

To optimize the structure and operating parameters of solar hot-water storage tanks, this study numerically analyzes 25 tanks with different obstacle structures. The temperature difference between the cold and hot water outlets decreased with increasing vertical spacing of an obstacle with the same horizontal extent, but it was not obviously affected by increasing the horizontal extent of an obstacle with fixed vertical spacing. The temperature was increased below the obstacle, forming a stable thermal-stratification structure in the solar hot-water storage tank. When the vertical distance between the two obstacles is 0.01 m and the horizontal extension of the left and right obstacle is 0, the maximum instantaneous efficiency of the collector is 20.5%. When the temperature at the hot-water inlet increased, the temperature at the hot-water outlet became more sensitive to the flow velocity at the cold-water inlet. Increasing the inlet cold-water velocity first increased and then decreased the effective heat-storage rate of the hot-water storage tank. The maximum effective heat-storage rates in hot-water storage tanks with different structures varied because of the changing inlet velocities of cold water. To increase the temperature difference between the outlets, the solar hot-water storage tank should have a hemispherical top and internal staggered obstacles, rather than a conical top and a single internal obstacle with one hole.

To ensure the safe operation of electric vehicles, the accurate estimation of the state of charge (SOC) of the lithium-ion battery installed in the vehicle is required. SOC is also an important parameter of battery management systems. However, SOC estimation is influenced by the accuracy of the measuring equipment, applied load, and various other factors. Accordingly, to improve the accuracy of SOC estimation, this study proposes a new SOC estimation model for lithium-ion batteries based on least-squares support vector machine (LSSVM) machine learning. The LSSVM model is trained on the measured current, voltage, and temperature of the lithium ion battery, which are input in vector form, and outputs the SOC vector. To improve the accuracy of SOC estimation, the SOC value estimated at the previous time is added as a feedback vector to the input vector before estimating the SOC at the current time. In an experimental evaluation, the proposed method achieved higher SOC estimation accuracy than the LSSVM, SVM, and neural network models. Moreover, the estimation error was controlled within 1%, establishing the validity of the model.

The state of charge (SOC) of a power battery must be accurately estimated as it determines the endurance mileage and is the basic premise for the energy management of electric vehicles. However, SOC estimation of battery systems is degraded by nonlinearity, instability, and other factors. Accordingly, the characteristic state data of a lithium battery contain nonlinearities, fluctuations, and external interference. This study proposes an SOC prediction method based on Gaussian mixture regression (GMR), which resolves the problems of abnormal values embedded in the state data and noise in the traditional Gaussian procession model (GPM). The hyper-parameters of the Gaussian mixture model are sequentially optimized by k-means clustering and an EM algorithm. The GMR predicts the SOC output. In an experimental validation and a comparative analysis of GMR and GPM, the GMR algorithm achieved superior prediction accuracy and effectiveness in SOC estimation.

This study analyzes the causes of failure of the interval cycle of a high-voltage system. To this end, it compares the relationships among the interval cycle, high-temperature cycle, and storage performance at 45 ℃. During the high-temperature interval cycle, the cathode material structure is destroyed and the metal element dissolves, releasing O₂ that oxidizes and decomposes the electrolyte. The cathode electrolyte interphase and solid electrolyte interface films in the high-temperature and high-voltage state are recombined and repaired, which increases the impedance and accelerates the cycle capacity attenuation. The cell interval cycle life at high temperatures can be obviously increased by improving the structural stability of the cathode material and the cathodeanode interface.

This paper aims to identify the parameters of a simplified electrochemical model. Firstly, the three-parameter partial differential equations of solid lithium-ion diffusion are simplified to ordinary differential equations. This simplification of the ordinary differential equations is based on the single-particle model and considers the concentration in liquid phase, liquid-phase electric potential, and the impedance of the solid electrolyte interface film caused by the potential impact on the terminal voltage. The next contribution is a new electrochemical model, which computes the average current density and volume density of the lithium-ion flow along the electrode thickness direction. The expression for positive open-circuit voltage of the battery was formulated through experiment and simulation. The electrochemical parameters of the model were determined in a parameter sensitivity analysis and identified by an adaptive chaotic particle swarm optimization algorithm. The accuracy of the electrochemical model was verified in further experiments and simulations.

Lithium batteries have become the main power source for new energy vehicles because they provide high energy density at a low self-discharge rate. In actual use, the battery characteristics, temperatures, and self-discharge rates vary among the individual cells of series battery packs. Such inconsistencies reduce the energy utilization rate and service life of a battery pack. To improve this situation, this paper proposes an equalization method based on a flyback converter. The residual power of a single cell is used as the inconsistency index. A set of flyback converters balances the energy in the entire battery and the transfer between arbitrary monomers. The proposed equalization topology requires fewer components and realizes a lower-volume equalization system than the traditional equalization topology. Moreover, the primary side of the energy transfer requires only a set of control signals, which reduces the control difficulty. The effectiveness of the proposed equalization method was evaluated using a simulation model built in MATLAB/Simulink.

To determine the internal parameters of the power battery model under changing load and working conditions, this work designs comprehensive experiments considering the battery capacity, temperature, multiplier, hysteresis, self-discharge, and other factors into comprehensive consideration. By analyzing the relationship between the terminal voltage of the power battery and factors such as ohmic, electrochemical, and concentration polarizations; unbalanced potential; and the hysteresis characteristics, the internal state variables of the power battery were determined and a dynamic integrated equivalent-circuit model was proposed. Dynamic identification was performed using a hybrid pulse-power characteristic method. The performance of the proposed model under varying operating conditions was compared with those of the Rint model, the partnership for a new generation of vehicle model, and the second-order RC model. The performance index was the Akaike information criterion (AIC). The average error of the proposed model was 52.3% lower than that of the other models. Moreover, the AIC and calculation values were moderate, implying that the proposed method better balances accuracy and structural complexity than the comparison methods. This study will be helpful in promoting the application of equivalent circuit models in practical engineering.

The 811 type ternary power battery cell with 21700 shape structure is taken as the research object. After low temperature cooling treatment, it is partially dismantled at the bottom of the single anode, and a thermocouple is arranged in the center of the battery to be arranged on the outer surface of the battery. The film type heat flow sensor quantifies the discharge heat generation rate of the battery at different ambient temperatures by using parameters such as heat flux density and internal temperature. The results show that when the battery is discharged in a low temperature environment, the battery will generate more heat and reduce the power output efficiency of the battery. It is known from the calculation result of the distribution ratio of the total heat generation rate of the battery discharge that a major portion of the heat generation when the battery is discharged is stored inside the battery.

Commercial lithium-ion batteries mostly use liquid electrolytes as electrolyte systems, which have problems such as insufficient electrochemical stability, low thermal stability and poor safety. The inorganic solid-state electrolyte has been a research hotspot in the current energy storage field because of its advantages of high electrochemical stability, high mechanical strength and so on. In this paper, the global patents in the field of inorganic solid-state electrolyte are taken as the research objects. By using patent data mining method, the technical layout, competitive advantage and core technology of the main institutions, and the development trend of the latest technology of sulfide electrolyte and oxide electrolyte are analyzed. Finally, suggestions were put forward to pay attention to the major needs of the country, accelerate the research and development of key technologies, and attach importance to the patent protection strategy.