This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 4656 papers online from Aug. 1, 2022 to Sept. 31, 2022. 100 of them were selected to be highlighted. High-nickel ternary layered, high-voltage LCO layered and LNMO spinel cathode materials are still under extensive investigations of the influences of doping and interface modifications on their electrochemical performances and surface and bulk evolution of structures under prolong cycling. For alloying mechanism anode materials, such as silicon-based composite materials, many researchers pay attention to material preparation and optimization of electrode structure to buffer volume changes, and emphasize the application of functional binders. Large efforts were devoted to design the three-dimensional structure electrode, interface modification, and inhomogeneity plating of lithium metal anode. The researches of solid-state electrolytes are mainly focused on synthesis, doping, structure design and stability of pre-existing materials and developing new materials, whereas liquid electrolytes are improved by the optimal design of solvents and lithium salts for different battery systems and adding different additives. For solid-state batteries, the studies are mainly focused on the improvement of ionic and electronic conductivity in cathodes. To suppress the "shuttle effect" of Li-S battery, composite sulfur cathode with high ion/electron conductive matrix and functional binders are studied. Other relevant works are also presented to the design of electrode structure and manufactural SEI. There are a few papers for the characterization techniques are on lithium deposition, volume change of silicon-based anode materials and oxygen release of ternary layered materials. Furthermore, theoretical calculations are done to understand the stability of solid electrolytes and the interface of solid state electrolyte/Li.

The electrolyte of all Vanadium Redox Flow batteries (VRFB) is the solution of a single vanadium element with various valences, which avoids the cross-contamination caused by the penetration of numerous element ions through the membrane. The battery has high cycle times and long service life. VRFB is suitable for peak shaving and valley filling in power stations, new energy power generation and storage, and power supply in remote areas. However, because of the restriction of vanadium ion solubility, the electrolyte concentration of all vanadium flow batteries is relatively low, leading to low battery energy density and large electrolyte storage tank volume. Vanadium battery is more suitable for static energy storage systems, and it is challenging to be used in electric vehicles and electronic products. The electrolyte's high cost also restricts its large-scale commercial application. The study summarizes the approaches and research status of enhancing the concentration and the stability of vanadium electrolytes by introducing various additives, changing supporting electrolytes, and constructing mixed-phase electrolytes based on the solubility of vanadium ions in conventional H₂SO₄ solutions at different acidity and temperature. The mechanism of various additives stabilizing V(V) at high temperatures, the impacts of various acid-supported electrolytes on the solubility of V, the electrochemical properties of the electrolyte, and the internal mechanism of mixed-phase electrolyte for stabilizing the electrolyte are introduced. The possibility and R&D direction of significantly increasing the concentration of vanadium electrolyte prospects is extensively examined as well as the new type of high-concentration vanadium electrolyte reported in a recent study. The comprehensive analysis demonstrates, as a promising study and development direction to significantly enhance the concentration of vanadium electrolyte and increase the energy density of the battery, the changing of conventional H₂SO₄ supporting electrolytes, including the development of HCl/H₂SO_4.

Although lithium-sulfur batteries are attractive for next-generation high-energy-density rechargeable batteries, their practical uses are limited by the severe shuttle effect of polysulfides. In this study, a lithium-doped zeolite (Li@CHA) was effectively prepared using an ion-exchange technique and combined with graphene oxide (GO) to alter the conventional polypropylene separator to alleviate the shuttling problem of lithium-sulfur batteries. The morphology, structure, and electrochemical performance of Li@CHA were thoroughly studied using a scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray powder diffraction, and nitrogen adsorption-desorption technique and electrochemical measurements. The results revealed that the Li@CHA could act as an "ionic sieve" of the separator, efficiently hindering the free shuttle of polysulfide anions and enhancing the transport performance of Li⁺. Additionally, GO could suppress the shuttle effect through chemisorption, and improve the conductivity of the altered layer, thereby reducing the impedance of the battery. Hence, the lithium-sulfur battery employing the modified separator demonstrated enhanced reaction kinetics, excellent rate capability, and stable cycling performance, achieving a high rate capacity of 638 mAh/g at 3 C and a high capacity retention rate of 71.0% after 500 cycles at 0.5 C. This work provides a novel idea for suppressing the shuttle effect of polysulfides, which is anticipated to further promote the practical application of lithium-sulfur batteries.

High-performance Cr₈O₂₁ materials were prepared using a high-temperature solid-phase method to pyrolyse a CrO₃ precursor. The effect of pyrolysis temperature on the properties of Cr₈O₂₁ was explored, and the first discharge mechanism of Cr₈O₂₁ was analyzed. Using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS), and electrochemical techniques, the crystallization degree, morphology, and electrochemical performance of samples prepared at different pyrolysis temperatures were compared and analyzed, and the discharge mechanism was elucidated. The results showed that among the samples, the Cr₈O₂₁ sample prepared at 270 ℃ has the highest crystallinity and an excellent discharge performance. At 0.05 mA/cm², the discharge specific capacity reached 419 mAh/g with an average voltage of 2.99 V. At 1.0 mA/cm², the discharge specific capacity reached 315 mAh/g with an average voltage of 2.82 V. The capacity retention rate was 75.11%. Furthermore, the electrochemical performance of this sample is higher than that of Cr₈O₂₁ samples prepared at other temperatures. When the pyrolysis temperature is lower than 270 ℃, the reaction of the CrO₃ precursor is insufficient. When the pyrolysis temperature is higher than 270 ℃, the impurity phase will be formed. The XPS results showed that the Cr element in Cr₈O₂₁ only contains +3 and +6 valence, and no other valence states exist. The first discharge mechanism of Cr₈O₂₁ is as follows: from 3.5 V to 3.0 V, lithium ion intercalates inside Cr₈O₂₁, and from 3.0 V to the end, lithium ion reacts with Cr₈O₂₁ to generate LiCrO₂ and highly irreversible Li₂O. This study helps to promote the application of high-capacity Cr₈O₂₁ materials in lithium primary batteries and provides an experimental basis for the research and development of high specific energy primary battery techniques.

The rich functional groups on the surface of g-C₃N₄ were used for lithiation to acquire lithiated g-C₃N₄ (L-g-C₃N₄). Bistrifluoromethane sulfonimide lithium salt as the lithium salt and polyvinyl epoxide as the polymer matrix was used to prepare L-g-C₃N₄ composite solid electrolytes using the casting-hot-pressing method. Transmission electron microscopy, X-ray diffractometer, infrared spectrometer, differential scanning calorimetry, linear cyclic voltammetry, DC polarization curve, electrochemical impedance spectroscopy and charge-discharge tests were used to characterize and test the composite solid electrolytes. g-C₃N₄ composite solid electrolyte and L-g-C₃N₄ composite solid electrolyte were compared and their electrochemical properties were evaluated. Simultaneously, composite solid electrolytes with different L-g-C₃N₄ content levels were also studied. The results revealed that the composite solid electrolyte's ionic conductivity is 3.95 × 10^-4 S/cm, the Li⁺ migration number is 0.639, and the electrochemical window is higher than 4.5 V. The Li/LiFePO₄ all-solid-state batteries were gathered with composite solid electrolytes. The battery's initial specific discharge capacity was 163.76 mAh/g for the first discharge when charged-discharged with 0.5 C in 2.5-4.0 V at 60 ℃. After 80 cycles, the capacity was still 160.10 mAh/g, and the capacity retention rate was 97.8%.

Transition metal selenides have drawn extensive attention as electrode materials because of their narrower bandgap and linewidth, higher conductivity, larger interlayer spacing, lower cost, and better theoretical capacity. In this study, the FeSe₂ anode was designed to be doped with expanded graphite to form a three-dimensional conductive network structure composed of interpenetrated and stacked, expanded graphite sheets to address the issues of low-reversible capacity and poor cycle stability of FeSe₂ electrode materials. FeSe₂-C anode material was prepared using a simple and effective solvothermal technique. The crystal structure composition and microstructure morphology of the samples were evaluated using an X-ray diffractometer, scanning electron microscope, transmission electron microscope, N₂ isotherm adsorption, and other characterization methods. Meanwhile, electrochemical test techniques, including galvanostatic cycling with potential limitation, cyclic voltammetry, and alternating current impedance were used to study the impact of expanded graphite doping on the electrochemical properties of FeSe₂. The results demonstrate the hierarchical structure, outstanding lithium storage capacity, high electrochemical performance, and cycling stability of the FeSe₂-C electrode. The first coulombic efficiency is 71.1% at a current density of 0.1 A/g, while the first discharge-specific capacity can reach 720.5 mAh/g, and the charge-specific capacity can reach 512.3 mAh/g. After 1000 cycles at a current density of 5 A/g, the capacity was still 339.1 mAh/g, which is 8.5 times that of the pure FeSe₂ electrode material after the same number of cycles. Expanded graphite construction into a three-dimensional conductive network is a practical way to enhance FeSe₂'s electrochemical performance.

Mechanical failure is a major problem faced by ternary oxide cathode materials in high-capacity applications. In this paper, single crystal and polycrystalline NMC811 materials were prepared using the molten salt and coprecipitation methods, respectively. The evolution and mechanical properties of single crystal and polycrystalline NMC811 materials during the electrochemical process were studied using XRD, FIB-SEM, and stress analysis. The relationship between crack initiation and propagation, as well as the stress and strain, of single crystal and polycrystalline NMC811 materials during the charging and discharging processes was established, and the cause of the structural stability degradation of the material during lithium intercalation was revealed. The experimental results show that after 100 weeks of charging and discharging at 0.5 ℃, almost no cracks appear, and the residual stress of the single crystal NMC811 material is small. However, after 100 cycles of charging and discharging at 0.5 ℃, a large number of cracks appeared along the grain boundary in the polycrystalline NMC811 material, and the maximum residual stress was three times that of the single crystal material. Thus, the cycle and rate performances of the single crystal NMC811 material are better than that of the polycrystalline NMC811. The preparation and development of single crystal NMC811 materials will be an important method of restraining crack propagation during charging and discharging and improving the life cycle of high nickel ternary materials.

Sodium-ion batteries are one of the next-generation low-cost and high-performance battery technologies in large-scale energy storage, and pre-sodiation technology can efficiently replace irreversible sodium depletion during cycling, therefore it plays a crucial role in the practical application of sodium-ion batteries. This research reviews the current pre-sodiation approaches, including physical pre-sodiation, electrochemical pre-sodiation, chemical reaction pre-sodiation, cathode additives, and over-sodiated cathodes. The benefits and drawbacks of different pre-sodiation technologies are examined, and the issues existing in the present pre-sodiation technologies are indicated considering the safety, operability, high efficiency, and total cost. Finally, we offer an outlook on the commercial prospects and development directions of pre-sodiation technologies in the future sodium-ion batteries. With its safety being its primary issue, physical pre-sodiation is facile and convenient; electrochemical pre-sodiation can obtain stable SEI film, but it is restricted by tedious process steps; although atmosphere has specific requirements, and the solvent is expensive, chemical reaction pre-sodiation can also generate a uniform and dense SEI film; although the cathode additives are easy to operate, there are few studies on the residue and gas production; and although the over-sodiated cathode has excellent electrochemical stability, it is restricted by too few types. Future pre-sodiation research needs to comprehensively consider factors including cost, environmental protection, safety and stability, and the effect mechanism of side reactions and by-products need to be investigated in depth.

With the development of high-performance electrode materials and the study of the mechanism, the electrochemical performance of sodium-ion batteries has been greatly improved. Hard carbon has become recognized as the most mature and commercialized anode material. However, it still faces problems such as low initial coulomb efficiency and poor rate capability. At the same time, great efforts have been devoted to in-depth research on the mechanism of sodium storage in hard carbons, and to explore synthetic methods to improve performance and reduce costs. However, there are still disagreements on the sodium storage mechanism, especially the sodium storage mechanism in the plateau region. Through the study of recent literature, based on the three different sodium storage processes of hard carbon material intercalation, adsorption and nanopore filling, the "intercalation-adsorption", "adsorption-intercalation" and other various forms of composite sodium storage mechanisms are emphatically introduced. Then, the effects of specific surface area, pores, defects, interlayer spacing and functional groups on the rate capability and initial Coulomb efficiency of hard carbon anode materials were analyzed based on the in-depth understanding of the sodium storage mechanism of hard carbon materials. At the same time, the effects of structure optimization and surface modification of coating method on improving the rate performance and initial coulombic efficiency of hard carbon anode materials are introduced. In order to promote the practical application of hard carbon, the effect of electrolyte optimization on improve the performance of ICE and rate capability of hard carbon is expounded. Comprehensive analysis shows that hard carbon material modification and electrolyte optimization are promising to achieve high rate capability, high initial coulombic efficiency and cycle stability at the same time.

Hydrogen is an essential element for a net carbon energy system that provides an alternative to difficult sectors for deep decarbonization, including heavy industry and long-haul transport. Electrolytic hydrogen synthesized through renewables is the most sustainable technology. It offers additional flexibility to integrate intermittent renewable energy and also can be used as seasonal energy storage. High current density, high operating pressure, small electrolyzer size, good integrity, and flexibility are all benefits of proton exchange membrane (PEM) water electrolysis technology. It also has good adaptability to the high volatility of wind and PV power. However, one of the main challenges is its high cost. The cost composition and application status of PEM water electrolysis are summarized in this study, and the research progress in critical materials, preparation technology, and component manufacturing are addressed in depth. According to research, novel structure-design preparation strategies and manufacturing technology are expected to improve electrolyzer design and construction, decrease the cost of raw materials and manufacturing for bipolar plates, decrease ohmic polarization by reducing membrane thickness, and increase the activity and utilization of noble-metal catalysts. Finally, the future R&D direction and target of PEM water electrolysis are proposed. With technology innovation in material performance, optimization of component manufacturing, and an increase in electrolyzer plant scale, significantly reducing the cost of PEM water electrolysis equipment and accelerating the large-scale development of PEM hydrogen production.

Lithium-sulfur battery is considered the most promising battery in the field of energy storage in the future due to its high energy density and theoretical specific capacity, rich reserves of elemental sulfur as the primary positive material, and low production cost. However, before its practical application, there are still some technical issues to be addressed, such as poor conductivity of the active material sulfur, cathode volume expansion, the shuttle effect, and other issues that seriously affect the battery's cycle stability, especially the "shuttle effect" caused by the migration of soluble long-chain polysulfide intermediates back and forth between the positive and negative electrodes. As the key inner component of the lithium-sulfur battery, the separator is located between the positive and the negative electrodes and is a crucial barrier to preventing the shuttling of polysulfides. However, although it is essential to design a functional separator to prevent the shuttling of polysulfides to enhance the comprehensive performance of lithium-sulfur batteries, the commercial polyolefin separators on the market have a large pore diameter that makes it simple for polysulfides to pass through, and this type of separator cannot capture polysulfides. The approaches to inhibiting polysulfide shuttle are further divided, according to the interaction between polysulfides and the separator coating, into physical restriction and chemical restriction. The research progress of polypropylene-based and new cellulose-based separators is primarily introduced. Finally, the future development direction of lithium-sulfur battery separator with the function of inhibiting polysulfide shuttle is prospected.

Phase change materials (PCM) can realize energy storage through absorbing and releasing latent heat during phase change processes. PCM is extensively known in thermal energy storage and management because of its stable phase change temperature and high energy storage density. Nevertheless, it usually suffers from low thermal conductivity, which needs to be aggregated with heat transfer improvement technologies. Based on adopting only one particular improvement technology, the "composite heat transfer enhancement technology," which combines more than one heat transfer enhancement technology, has become a research hotspot of heat transfer enhancement and phase change heat-storage performance improvement. The major research in composite heat transfer technology is summarized in this research, covering studies based on fins or porous material, heat pipe joined independently, nanomaterials, and cascade heat storage. It was discovered that the best results were attained by combining heat pipes with fins or porous material. Under the same conditions, combining nanoparticles with fins or porous material is more efficient than utilizing nanomaterials alone. Compared with single cascade phase change, cascade PCM combined with fins or foam metal has faster heat storage and release rate and a more uniform fluid outlet temperature. Further studies are proposed to explore more composite improvement techniques. The influence of structural design or detail parameters needs additional experimental confirmation and enhancement, which can optimize the performance of PCM-based thermal storage systems.

Carbon-coating is a simple and practical method to improve the electrochemical performance of soft carbon anode for fast-charging lithium-ion battery, e.g., reducing the loss of active lithium during the formation of the solid electrolyte interface (SEI) film, and thereby improving the initial coulombic efficiency. However, the systematic study of relationships between carbon-coating layer properties and electrochemical performances is still lacking. Therefore, two soft carbon materials with different carbon-coating layers were used as model materials, which were prepared by vapor-phase method and solid-phase method, respectively. SEM, TEM, XRD and Raman were conducted to characterize the structural evolution of the soft carbon in the coating process. CV, GCPL, EIS and GITT were conducted to analyze the electrochemical performance of carbon-coating soft carbon. This work provides a good guidance for the development of fast-charging soft carbon material.

Cascaded latent heat storage technology has been proven as an effective method for solving the poor thermal conductivity of phase change materials (PCMs). Previous numerical studies on cascaded latent heat storage systems were based on one-or two-dimensional mathematical models, and most of them focused on the charging process. In this paper, a fin-enhanced three-tube cascaded latent heat storage system is proposed, and a three-dimensional numerical model is established to study the thermal performance of PCMs at each stage of the discharging process and to explore the effect of the inlet velocity of the heat transfer fluid and initial temperature of PCMs on system thermal performance. The results show that during the discharging process, the phase change of PCMs at each stage do not occur simultaneously, and the PCMs are mainly affected by the phase change temperature and latent heat. The increase of the inlet velocity of the heat transfer fluid increases the discharging rate of the PCMs. With a further increase of the inlet velocity, the enhancement effect of the discharging rate is weakened. The initial temperature of the PCMs has a certain influence on the sensible heat discharging process but limitedly affects the latent heat discharging stage.

Lithium-ion batteries have been extensively applied in novel energy vehicles and other fields. Their reliability directly influences vehicle conditions. The lithium-ion battery pack must rely on an efficient thermal management system to guarantee its safe and reliable operation. The liquid cooling system has a good effect on the total temperature regulation of the battery module and the temperature uniformity control. The heat dissipation effects of the serpentine and double inverted U-shaped cooling channels on the battery pack are simulated and compared using the established finite element simulation model of the liquid-cooled lithium-ion battery pack. The maximum temperature of the battery pack is reduced by 17.2 ℃, and the temperature difference is reduced by 12.1 ℃ when twin inverted U-shaped cooling channels are used instead of serpentine cooling channels. The double inverted U-shaped cooling channel with a better cooling effect is used as the structure to be optimized, the overall temperature of the battery pack is reduced, and the temperature uniformity is improved by adjusting the inlet temperature and flow rate of the cooling liquid and adding graphene films. The problem of local overheating has been alleviated, the battery pack's reliability has increased, and the maximum temperature of the battery pack has been reduced by 32.2%. The temperature difference has also been reduced by 59.2%.

The electrode of a lithium ion battery is the crucial factor in determining the performance of the battery. According to the porous electrode theory, fractal theory is introduced to reconstruct the microstructure of the electrode. The theoretical model of the effective diffusion coefficient of lithium-ion in solid and liquid phases is deduced, and its influencing factors are analyzed, taking into account the impact of structural characteristics and temperature on the effective diffusion coefficient. The relationship between the thermal and electrochemical models is established, and the thermal chemical coupling model is examined. The discharge process is simulated to explore the effects of different solid and liquid effective diffusion coefficients on the discharge performance. The results demonstrate that the effective diffusion coefficient of lithium-ion in the liquid phase increases with the increasing porosity, temperature, and area fractal dimension while decreasing with increasing tortuous fractal dimension. The solid diffusion coefficient decreases with the increase in area fractal dimension. In the case of comparatively high rate discharge, altering the particle size and distribution of the negative electrode changes the microstructure of the electrode so that the effective diffusion coefficient of lithium-ion in the solid and liquid phases changes, which further influences the maximum discharge capacity of the battery. This result provides basic theoretical knowledge for manufacturing lithium-ion battery electrodes.

Under a "Double Carbon" goal, the vigorous development of renewable energy not only threatens the stable operation of the power grid but brings considerable demand for frequency controlling. Thermal energy storage frequency controlling, which as the high-quality frequency modulation resource was be extensive research. In the thermal energy storage frequency controlling project in Guangdong, the power control, power conversion efficiency, and response time and accuracy between the low-voltage parallel and high-voltage cascaded chemical energy storage systems were compared by testing the connections to the power grid, and the latter performed better. The high-voltage cascaded chemical energy storage system is beneficial for improving the stability and security of the project and is more competitive in the frequency modulation market. Based on the advantages of high-voltage cascaded chemical energy storage system and frequency modulation demand of the power plant, the largest thermal energy storage frequency controlling project in China was designed to improve the response in frequency controlling and research on control strategies to provide a reference for thermal energy storage frequency controlling projects.

The issue of power imbalance is brought on by the large-scale access to wind power, photovoltaic and other renewable energy sources in the system. In this paper, we suggested a method to optimize energy storage allocation considering peak and frequency regulation demands. In order to quantify the contribution of energy storage to system peaking and frequency response, i.e., intra-day frequency regulation with contact line deviation control and day-ahead peaking with carbon footprint constraints, a typical daily multi-timescale operation simulation model is first established. Then, a two-layer energy storage configuration-operation optimization model is established. The lower model is a simulation of different typical day operations, solved by a hybrid algorithm of differential evolutionary algorithm & Gurobi solver. The upper model aims to minimize the sum of typical day-set operation cost and energy storage investment cost to determine the energy storage capacity. Finally, the calculation example demonstrates that the configuration results taking into account the dual application scenarios with energy storage participation are more reasonable, the overall system operation cost is lower, and the carbon emission is less.

It is necessary to accurately estimate the state of energy (SOE) of a battery to make full use of the energy stored in the battery and prevent over-discharge and over-charge. Generally, SOE is defined as the ratio of the remaining energy to the standard rated energy. The current SOE estimation algorithms have not fully considered the influence of temperature, operating conditions, etc., leading to low accuracy of the estimation results. This study proposes an adaptive extended Kalman filter (S-H EKF) based on Sage-Husa to accurately estimate the energy state of a battery. The algorithm's energy state estimation approach for lithium-ion batteries is compared with the traditional SOE estimation algorithm based on the EKF. First, the influence of temperature on the battery's energy characteristics was examined, and the standard energy of the battery at various temperatures was obtained. Then, a second-order RC equivalent circuit model considering the variation of parameter values with temperature and SOE value is established. Combined with an experiment of mixed pulse power characteristics, the least squares approach is employed to identify the model parameters, and the model accuracy is verified. With a good simulation of the battery's terminal voltage having high accuracy, the verification findings reveal that the model can be compared better. Finally, by employing S-H EKF and EKF to estimate the SOE under dynamic conditions and intermittent high-rate charging conditions, the comparison results demonstrate that: taking the mean absolute error as the comparison standard, the estimation accuracy of S-H EKF is 20.72% higher than that of EKF, and the maximum SOE estimation is the absolute error is less than 3%, which is more appropriate for energy estimation of lithium-ion batteries.

It is crucial for the battery management system of electric vehicles to accurately estimate the state of charge (SOC) of lithium batteries. The offline parameter identification and the online parameter identification approaches of recursive least squares with forgetting factor are employed to identify the parameters in the equivalent circuit, where the second-order RC equivalent circuit model is employed to accurately model the battery, and, after ensuring the accuracy of the model meets the requirements, the extended Kalman filter (EKF) algorithm is employed to accurately estimate the battery's SOC. The simulation experiment was conducted with the federal urban driving schedule (FUDS) and urban dynamometer driving schedule (UDDS), and the standard SOC value in the experiment is compared with the SOC estimation values of offline identification and online identification. The experimental findings demonstrate that the average error of SOC estimation using the EKF algorithm under FUDS and UDDS conditions is less than 2.5%, and the average error of the online parameter identification model decreased by 0.7% and 0.9% than offline parameter identification model, respectively. The battery model under the online parameter identification approach is shown to have higher estimation accuracy and it is proved that the EKF algorithm can realize an accurate estimation of battery SOC.

A retired lithium-ion battery-sorting approach based on SOM (self-organizing feature mapping network)+SVM (support vector machine) is proposed to address the shortage of sorting methods for retired power batteries. A battery test was performed on retired batteries. Battery test systems were used to record the changes in battery current, voltage, temperature, and discharge capacity. The battery PNGV (new generation automotive partner) model parameters were identified. Furthermore, the batteries were grouped and sorted according to the characteristics and model parameters, including battery capacity and constant voltage drop time. The retired battery cells in the sorting and classification results were reorganized in parallel, the consistency experiment was performed, and the experimental results were compared and analyzed. The results revealed that the consistency of polarization internal resistance, residual capacity, constant pressure drop time, and temperature conversion rate changed slightly after the recombination cycle operation of the retired battery parameters under this method, and the dispersion of internal ohmic resistance decreased significantly, which is of practical significance in the sorting of retired batteries.

Supercapacitors' service performance and the aging process are closely related to temperature. Excessive temperature will cause thermal runaway and affect the operation safety of supercapacitors. Therefore, it is imperative to monitor the temperature of each unit in the supercapacitor system. However, the conventional sensor monitoring scheme has high costs and complex installation issues. With a commercial supercapacitor module as the research object, this paper suggests a method to estimate the temperature of residual cells in the module according to the temperature of a small number of cells, which can reduce the use of sensors. It is found that there is a strong correlation between cell temperatures by analyzing the temperature data of each cell in the module under various cooling wind speeds with multi-stage constant current charging and discharging. A module temperature estimation model according to BP neural network is established. The best model architecture is determined by comparing the pre-training effects of different cell combinations as input and removing current, voltage, wind speed, and other factors. By comparing the estimation impacts of various algorithms on the same data set, Levenberg Marquardt is chosen as the training algorithm of the model. The model can estimate the temperature of the remaining 9 cells through the temperature of 3 cells. The test data set's average absolute error is 0.06 ℃, and the maximum absolute error is within 0.3 ℃, which meets the energy storage system's requirements for temperature monitoring precision. The suggested method requires simple test conditions and can reduce the purchase cost of temperature sensors, which provides a new method for temperature monitoring of supercapacitor thermal management systems.

In concentrating solar power plant, molten salt is widely used for heat transfer and energy storage medium. It is found that the thermophysical properties of molten salt can be improved by adding nanoparticles to molten salt. In this paper, numerical simulation was used to analyze the flow and heat transfer characteristics of molten salt nanofluids in twisted tubes with different structures. The results show that the convective heat transfer coefficient and pressure drop of molten salt nanofluids in twisted tubes increase with the increase in the ratio of the long axis to short axis, and decrease with the increasing of the pitch. When Re = 10000—35000, the convective heat transfer coefficient of molten salt nanofluids in twisted tubes is 34.6% higher than that in smooth tube, and the maximum pressure drop is 141.3%. The empirical correlations of the nusselt number and resistance coefficient of molten salt nanofluids in twisted tubes are fitted. Through the comprehensive performance and field synergy analysis, it is found that when Re = 30000, the ratio of the long and short axis a/b = 2, and the pitch S = 300 mm. The maximum enhanced heat transfer factor is 1.16, and the synergy angle at the top of the long axis of the twisted tube is the smallest.

Pumped thermal electricity storage technology has the benefits of low cost, no geographical limitations, and high energy storage density. It is a promising new large-scale electricity storage technology. Typically having drawbacks including excessive system volume, low energy storage density, and low efficiency, most conventional pumped thermal electricity storage systems employ air as the working fluid and stone as the energy storage medium. A pumped thermal electricity storage system, employing argon as the working fluid and PCMs as the energy storage medium instead of sensible heat material, is proposed to enhance the practicability of this technology. A transient numerical model of a 10 MW/5 h Brayton cycle-based pumped thermal storage system is established. With the system's economics being simultaneously examined, the impacts of compression/expansion ratio, porosity, and isentropic efficiency on the system round-trip efficiency, energy storage density, and power density are simulated and examined to compare with the conventional system. Where this study has a guiding value for the thermodynamic and economic analysis of the Brayton cycle-based pumped thermal electricity storage system, its findings demonstrate that the energy storage density of the energy storage system reaches 182.5 kWh/m³, which is 118.5% higher than that of sensible heat materials, the round-trip efficiency reaches 63.1%, and the power density reaches 175.8 kW/m³. The energy storage cost per unit of the system is approximately 768 CNY/kWh, which is 12% cheaper than the conventional system.

It is crucial to optimize the efficient thermal storage structure of thermal storage systems to address the problem of slow thermal response of phase change materials (PCMs) in conventional rectangular shell-and-tube phase change thermal storage systems. Numerical simulations were employed to examine the melting process of PCM with natural convection in a baseline shell-and-tube phase change thermal storage unit and an optimized structural unit and to perform experimental verification. According to different improved natural convection approaches, such as wedging, internal flow tube eccentricity, and inclined tanks, discuss the evolution of temperature field, heat storage capacity, Fo number, average Nu number, and phase interface. The dynamic thermal behavior of PCM within different improved natural convection approaches was examined to derive optimized solutions for enhancing the heat transfer efficiency of heat storage systems. The findings reveal that the wedge-shaped phase change heat storage unit shell shape can improve the natural convection effect and enhances the heat transfer performance. The complete melting time was reduced by 28% compared to the melting time of the PCM in the reference rectangular structure when the wedge ratio X=5. Although it prolongs the complete melting time and has an opposite effect on the melting efficiency, the eccentric distance has little effect on the heat storage capacity of the PCM in the vertically placed thermal storage system. The research findings have a certain reference significance for the realization of energy conservation and emission reduction and the realization of the dual carbon goal, where the natural convection heat transfer effect reaches its maximum during the early melting, and the heat storage efficiency increases to its maximum, with a 29% increase compared to vertical placement when the wedge-shaped tank is tilted at 75°.

Energy storage technology, particularly heat storage technology, can efficiently solve the intermittency issue of solar energy; thus, enhancing the quality and efficiency of the solar energy usage system. Stable energy flow output for the solar energy system is guaranteed upon this integration with the energy storage sections. A horizontal heat storage tank filled with paraffin and metal foam was designed to address the key problem of low thermal conductivity of phase change materials and low efficiency of heat storage/release systems. The solidification phase change behavior of paraffin-embedded metal foam was examined under the same heat storage condition (70.0 ℃) but at different cooling fluid temperatures (10.0 ℃, 15.0 ℃, 20.0 ℃, 25.0 ℃, and 30.0 ℃). The real-time position of the solidification front was captured by an HD camera, and the internal temperature response features during the solidification process were obtained from the measurements. The experimental findings revealed that the lower the temperature of the cold fluid, the faster the solidification rate. The total solidification time of paraffin was shortened by 52.0% when the cold fluid was 10.0 ℃ compared with the exothermic condition of 30.0 ℃. Although the axial position exerted little impact on the temperature development during the solidification process, the higher the vertical height of the measurement point at the same radial distance, the faster the temperature drop and the higher the temperature response rate. The temperature response rate of point 1a under cooling conditions of 10.0 ℃, 15.0 ℃, 20.0 ℃, 25.0 ℃, and 30.0 ℃ increased by 7.2%, 8.8%, 10.3%, 10.8%, and 11.7%, respectively, based on the temperature response value of point 1b. Providing guidance and help for the structural design and operation parameter selection of solid-liquid phase change applications, this study helps popularize the engineering application of heat storage tanks filled with metal foam.

Thermal storage can solve the intermittent problem of solar energy, which is providing a stable thermal output and improving energy quality. Solid-liquid phase change heat storage has attracted attention due to its advantages of large heat storage density and relatively constant temperature during heat storage/release. However, during solid-liquid phase change heat storage, there is constant inhomogeneity in the melting times and temperatures of the phase change materials (PCMs). The refractory zone greatly prolongs the overall phase change heat storage time. Therefore, this paper proposes improving the unevenness of the melting times by changing the shape of the heat storage tank. Five trapezoidal phase change heat storage tanks with different gradient ratios were designed. The heat storage performance of these tanks were examined using numerical simulations. The results indicated that increasing the proportion of PCMs in the upper region was conducive to the timely transfer of heat to the unmolten PCMs and reduced the resistance of heat transfer, thereby improving the overall heat transfer rate. The complete melting time of Cases 1 and 2 with a larger proportion of PCMs in the upper region was shortened compared to that of Case 3, with reduction ratios of 39.06% and 29.37%, respectively.

To explore the mechanism of eccentric fractional-finned tubes improving the performance of phase change heat storage unit (PCCS), a two-dimensional unsteady simulation was conducted to study the melting of paraffin wax in the PCCS. The heat transfer characteristics of eccentric rectangular fin and eccentric fractal fin are compared considering natural convection. Demonstrating that the eccentric fractal fin enhances natural convection more than the eccentric rectangular fin and the temperature distribution is more uniform, which is consistent with the fact that the fractal fin can enhance heat diffusion from point to the surface, the partial strengthening of the eccentric fractal fin structure was conducted, and three schemes of rectangular fin, Y fin, and split fin were chosen. In the three local strengthening schemes, the eccentric fractal fin has the best strengthening impact, the melting rate is increased in the entire process, and the melting time is shortened by 70%. This offers good theoretical guidance for the performance enhancement of shell and tube phase change heat accumulators and further increases its application prospects in the field of energy storage.

A review of the research progress of the lithium battery electrolyte-conductivity model recently is described from the classic solution model, statistical thermodynamic model, semi-empirical model, and mathematical-statistical method. The statistical thermodynamics theory has gradually replaced the classical solution theory in studies on the transport mechanism of lithium battery electrolytes. To better understand the microstructure and interaction between microscopic particles, a high-level thermodynamic theoretical model is created from the microscopic properties of molecules and ions. The prediction and optimization of the conductivity of lithium battery electrolyte changed from the conventional semi-empirical model to a mathematical, statistical method to obtain ideal test results and draw scientific conclusions with a small-test scale, short test cycle, and low test cost.

The use of fossil fuels as the primary source of energy has caused several negative environmental effects, including global warming and air pollution. Despite having numerous benefits, the storage of hydrogen is a serious issue, as a potential non-carbon-based energy resource, which can replace fossil fuels. It is extensively employed, clean and safe. Underground hydrogen storage (UHS) appears to be a crucial means of a large-scale and long-term energy storage solution. This research analysis underground hydrogen storage projects around the world. The salt cavern has the benefits of good sealing, a stable structure, and easy engineering application when combined with research. This demonstrates that the salt cavern is one of the most promising options for UHS. With a feasible and economical solution for fulfilling the large-scale UHS in the Jintan salt mine being proposed in this study, also introduced are the difficulties associated with underground hydrogen storage. Mechanisms that can compromise well integrity and generate leaks include microbial corrosion, hydrogen embrittlement, cement degradation, elastomer failure, caprock sealing failure, and hydrogen leakage. The difference between supply and demand is reduced by storing the energy converted into hydrogen. The key issues of "production, storage, and transportation of hydrogen" could be solved. This is of great significance for the large-scale storage of renewable energy, the use of green hydrogen sources, and the development of a low-carbon economy.

Shared energy storage adopts unified planning, construction, and scheduling and has the advantages of low initial investment, low operation risk, and guaranteed equipment quality, as well as being conducive for realizing multiple values. In the future, it is expected to become the mainstream model for the coordinated development of energy storage and new energy. The sustainable and healthy development of this model is inseparable from the support of reasonable and effective policies. In this paper, the development status of shared energy storage in China is analyzed, and the system dynamics model of photovoltaic and shared energy storage is established using the system dynamics method. Based on the actual and planning data of a province, the model parameters are determined, and the changes in the installed capacity of photovoltaic and energy storage under different policy scenarios, such as configuration proportion, configuration duration, rental cost, and annual scheduling times, are simulated. The results show that the development of a shared energy storage policy should (1) comprehensively consider the new energy and energy storage planning objectives, system flexibility requirements, and other factors, (2) actively expand energy storage revenue sources, and (3) reasonably allocate energy storage costs to the source, grid, and load to realize the high-quality coordinated development of new energy and energy storage.