Achieving the goal of "carbon neutrality and carbon peak" will lead to a profound energy and industrial revolution, which will have a far-reaching impact on social and economic life in the future. Energy storage is the key supporting technology to achieve the "30·60" target and energy revolution, and the development of energy storage is of great strategic significance. In this paper, the strategic position and role of energy storage under the goal of "carbon peak neutral and carbon neutral" in China are expounded, the present development situation and future development trend of energy storage are discussed in depth, and then the policy requirements and suggestions for energy storage strategy development are given.

Compressed air energy storage (CAES) is acknowledged to be the most promising physical energy storage technology. In CAES system, the gas storage device as key link has important influence on the efficient, stable, and safe operation of system. In recent years, with the rapid development of CAES technology, the research of gas storage devices has attracted much attention. The characteristics of gas storage devices mainly depend on their material properties, so they were classified according to material, including underground cavern, artificial cavern, metal gas storage device and composite material gas storage device. The application of different types of gas storage devices were discussed emphatically. The contrastive analysis showed that underground cavern had large scale and low cost, but depended on special geological and geographical conditions. Therefore, new gas storage devices with flexible layout characteristics should be explored actively. Further, the challenges faced by current gas storage devices were revealed in this work. The key points and difficulties in establishing the precise thermodynamic model of gas storage device, evaluating the stability of underground cavern and studying the structure characteristics of composite material gas storage devices were discussed respectively. Moreover, the development and research hotspots of gas storage devices were also prospected and summarized. Finally, the purpose of this work is to offer guidance for reasonable selection and theoretical research of gas storage devices in CAES system and to provide reference for improving the performance of gas storage devices and CAES system.

Adjusting trigeneration of adiabatic compressed air energy storage system (A-CAES) to match the variable loads of the supply objects in different seasons can greatly promote the practical application of A-CAES system. In this paper, the simulation model of A-CAES system was developed. The charging and discharging period of system were simulated to investigate the characteristics of system trigeneration. The cooling, heating and electric load of a typical residential area in different seasons was analyzed. Then the load of residential area and trigeneration of system was matched to find the matching performance between them. Finally, through economic analysis the energy cost of a traditional residential area and a new residential area whose energy is supplied by A-CASE system was compared. The simulation results show that the cooling and heating load of households varies greatly in different seasons, but the difference of electric load is small. The mass flow rate of chilled water has little effect on the cooling, heating and electric output, so the minimum value is suggested to improve the quality of chilled water. The mass flow rate of preheating hot water in the discharging period can greatly change cooling, heating and electric output of system. By matching system trigeneration characteristics and residential load, optimum heating hot water flow for summer, spring and autumn, and winter was selected as 3.9 kg/s, 3.9 kg/s and 1.6 kg/s. It is advisable to use higher hot water flow rate to maximize electricity production in summer. The economic analysis found that the annual energy supply cost of the residential area whose energy is supplied by A-CAES system is 23.1% lower than that of the conventional residential area. The annual energy supply cost of residential area decreases 1.56 million CNY. Combined with the equipment cost, the static investment payback period of the system was calculated as 15.6 years.

An ejector can be applied in an adiabatic compressed air energy storage (A-CAES) system to intensify the charging process and improve its overall system performance. In this instance, the ejector will employ high-pressure air from the outlet of a compressor and use it as a primary fluid for entraining low-pressure air from ambient or outlet of earlier stage compressor. The use of an ejector can increase air charging speed and reduce thermodynamic loss of the throttle valve. In this work, the presence of a multiple ejector A-CAES (MEA-CAES) and a single ejector A-CAES (SEA-CAES) in the charging process was researched, respectively, and thermodynamic models of the two systems were constructed. The simulation results showed improved round-trip efficiency of an MEA-CAES under a constant-pressure operation mode and a SEA-CAES under a sliding-pressure operation mode compared with an A-CAES with a constant-pressure operation mode; the maximum increase of the two systems was 2.34%, and 2.73%, respectively. For the MEA-CAES, the work-time of ejectors and the cumulative mass of the ambient air entrained by ejectors both decreased when the entrainment ratio increased. The improvement in the round-trip efficiency of the MEA-CAES was larger in the lower initial storage pressure. It reflected a smaller entrainment ratio and a smaller heat-transfer temperature difference in the heating/cooling exchangers condition. At a fixed initial storage pressure, the SEA-CAES jam margin was larger than the A-CAES when using a sliding-pressure operational mode, and the jam margin decreased when the entrainment ratio increased. The improvement of round-trip efficiency for the SEA-CAES was larger in the higher initial storage pressure and the larger entrainment ratio condition. The study results provide a reference for the further optimization of compressed air energy storage.

Compressed- air energy storage (CAES) is considered the most promising large-scale energy storage technology; however, CAES systems are faced with complex operating conditions, including pressure change in the air storage chamber and input/output power changes. Because of the demand for off-design conditions of CAES systems and the limitations of low control accuracy and large pressure loss in the throttle valve decompression regulating the inlet pressure of turbines, a pressure control unit combined with the valve combinations and expansion tank is proposed herein to regulate the inlet pressure of turbines and meet the output power demand. A thermodynamic model of a 10 MW CAES system with thermal storage integrated pressure control unit was established. Then, the variations of important parameters, including pressure, temperature, mass flow rate, and power, with time in the charging and discharging processes were investigated. Furthermore, the mechanism and effect of the pressure control unit combined with the valve combination and expansion tank in regulating the inlet pressure of the turbine were assessed. Compared with the throttle decompression mode, the total exergy destruction of the pressure control unit in the discharge process was reduced by 1.56×10⁸ J, and the energy storage efficiency and density was increased by 0.24% and 0.04 MJ/m³. The pressure control unit can smoothly regulate the inlet pressure of the turbine, which ensures the stable and efficient operation of the CAES system and improves the comprehensive performance of the system.

Axial-flow turbines adopted in compressed-air energy storage (CAES) systems are characterized by higher operating pressure, vane with lower aspect ratio, and obvious end-wall secondary flow loss. To increase the efficiency, herein, bowed design is introduced into the vane, and the system is optimized. Moreover, the flow-loss control mechanism of optimal bowed vanes is investigated. The results show an optimal bending angle for maximum isentropic efficiency under each bending height. With an increase in the bending height, the optimal bending angle gradually decreases. The mass flow rate of the axial-flow turbine decreases first and then increases with an increase in the bending angle; a minimum mass flow rate is observed close to the bending angle of 7°. The optimal design results show that when the bending angle and relative bending height are 12.26° and 0.31°, respectively, the isentropic efficiency can be increased by 0.77%, and the mass flow rate increases by only 0.1 kg/s. Although the optimal bowed structure has some negative effects on its own flow field in the vane, it still reduces the inlet flow angle of the rotor blade near the hub, eliminates the stagnation saddle point in front of the rotor-blade leading edge, and limits the influence range of horseshoe vortex and interaction with the end-wall secondary flow. Moreover, the saddle point in the tip leading-edge region moves downstream; limits the influence range of the horseshoe vortex near the suction surface; delays the generation of tip clearance leakage flow, which interacts with the tip clearance upper-passage vortex; and flow loss is reduced.

Expander and compressor are the important components of compressed-air energy storage (CAES) systems. To meet the requirements of off-design and low power consumption, the double cantilever shafting structure is used often. However, the vibration of the double cantilever shafting structure is prominent, whereas there are insufficient studies on it, and the related technology is mostly controlled by foreign giants. Based on this, herein, an experimental study of the vibration of the double cantilever shafting structure was conducted. By several speed-up-and-down experiments, the vibration amplitude curve, vibration spectrum, Bode diagram, and vibration energy distribution spectrum of high-speed shafts are analyzed and the critical speed of the rotor is determined. The influence of speed-up continuity and time on the amplitude through the critical speed is then explored. The results show a critical speed of 14200 r/min for the high-speed shaft of the double-cantilever test piece. The resonance region below the critical speed is about 15%, and that beyond the critical speed is about 9%. When the speed is close to the critical value, the increasing range of other frequencies is 2 μm, which is less than 5% of the fundamental frequency increase. Through the critical speed, the speed-increasing continuity has an impact on the amplitude. This study presents two types of speed-increasing schemes. Although the acceleration of scheme 2 is faster when passing through the critical speed, the vibration energy accumulates as it is close to the critical speed, making the vibration peak of scheme 2 larger than that of scheme 1. Through the critical speed, the vibration peak increases approximately linearly with an increase in the speed-increasing time. When the speed-increasing time is increased from 20 to 60 s, the amplitude increases by about 20%.

The development of compressed-air energy storage (CAES) technology is an effective approach to solve the large-scale integration of renewable energy and an important technical means to implement the goal of “carbon peak, carbon neutral” Axial compressors are one of the important components of a CAES system, which requires to have wide working conditions, large flow, and large pressure ratio Considering NASA Stage35 as a prototype, the coupling relationship between the compound-lean height and angle of the rotor and stator blades is examined using numerical simulations and orthogonal tests, and the system is optimized. After optimization, the stall margin increases by 60.56%, and the reduction of efficiency and pressure ratio is acceptable. Through the range analysis, the blade of the compound lean can generally improve the stall margin; however, the peak efficiency and pressure ratio are generally reduced, and the compound lean angle of the rotor blade has considerable impact on the aerodynamic performance of the compressor. The corner separation of the suction surface is more severe close to the root of the blade. In the region of the middle blade, the intensity of the shock wave is weakened, and the accumulation of low-energy fluid is reduced. At the blade tip, the development of the tip leakage flow is slowed down, and the stall margin is enlarged.

The expansion and heat absorption process in compressed-air energy storage (CAES) systems cause water vapor in the compressed air to freeze, which not only causes mechanical damage to the expander blades but also affects the expander performance. Herein, the interstage water evolution characteristics of multistage piston compressors in the energy storage subsystem are investigated to provide a reference for designing compressor systems and pretreatment of the compressed air before the inlet of the expander. First, the compression and enhancement factors are comprehensively considered, and the water evolution process is derived using the method of moisture evolution coefficient. The expressions of water evolution at different levels were obtained, and the suction and exhaust pressure and temperature, exhaust volume, separator level, and other parameters were sampled. The water evolution characteristics at each stage of the compressor were examined under various operating conditions. As the exhaust pressure of the compressor increased from 1.5 to 9.0 MPa, liquid water was not precipitated when the wet air passed through the first stage of the compressor. The theoretical and experimental results of water discharge at different stages vary from 0 to 10%.

For the large-scale development of renewable energy, the flexible peak-shaving capacity of thermal power is insufficient. Herein, a solution and novel operation strategy for integrated heat-storage systems in conventional thermal power are proposed. Considering a domestic 600-MW coal-fired unit as an example, a system scheme for coupling the unit with molten-salt, concrete, and subcritical-water heat-storage systems is designed. The thermal and peak-shaving performances of each coupled system are analyzed and compared. The results demonstrate that the thermal-power-heat-storage coupling system improves the peak-shaving capacity of the system and the cycle efficiency of the entire process. The coupling scheme with the best thermal performance involves using molten salt to extract reheated steam in the heat-storage process and using the stored heat to heat the high-pressure feedwater during heat release. Its efficiency is increased by >0.8%. However, the best coupling scheme for peak shaving performance involves using molten salt to extract high-pressure cylinder exhaust steam in the heat storage process and using the stored heat to heat the high-pressure feedwater when heat is released. Through the thermal storage unit, the new upper and lower peak shaving depth is 4.83% and 5.93%, respectively. This study provides theoretical and practical guidance for the flexible peak shaving of thermal power units.

Focusing on a miniature compressed air reservoir scroll compressor, the computational fluid dynamics method numerically simulated the working processes of the scroll compressor. Additionally, the internal pressure field, temperature field, and the velocity vector field of the scroll compressor were obtained. The distribution characteristics of the tangential leakage, caused by the radial gap on the flow field of the scroll compressor's working cavity, were studied. The results showed that gas in the high-pressure cavity leaked into the low-pressure cavity through the radial gap, which caused the velocity vector and temperature fields in the cavity were not uniformly distributed, and leakage had little effect on the unevenness of the pressure field distribution; however, it had a greater impact on the unevenness of the temperature and velocity vector fields. The downstream gas in a single cavity was compressed, which gave rise to pressure within the cavity. The distribution was not uniform, and the existence of pressure differences affected changes in the velocity vector field distribution. The offset of the exhaust hole caused pressure asymmetry in the symmetrical cavity. This research presents a theoretical basis for the structural design of scroll compressors.

The study improved the cycle efficiency and exergy efficiency of a liquefied air energy storage (LAES) system by improving the system's liquefaction unit. The paper established the thermodynamic model of a traditional LAES and its coupling system and studied the improvement of the coupling and traditional systems from the perspectives of heat-transfer oil utilization, system exergy efficiency, and cycle efficiency. The results showed that for the compressed air energy storage system coupled with liquefied natural gas, the use rate of high-temperature heat-transfer oil reached 92.47%. The heat utilization rate of heat-transfer oil could increase by 11.18%. The maximum exergy efficiency of the coupled system reached 66.68%, which was 15.67% higher than for a traditional LAES. The cycle efficiency of the system reached 67.60%, and the highest increase was 17.30%. The coupling system effectively improved the defects linked to incomplete utilization of the heat-transfer oil in a LAES system, improved the system's recycling efficiency, and provided an effective system solution for large-scale energy storage.

To solve the problems of high-energy consumption and the high cost of traditional reverse osmosis (RO) desalination systems, an innovative hybrid adiabatic compressed air energy storage system (ACAES) and RO desalination was proposed. The system was based on the improvement of adiabatic compressed air energy storage on the fluctuation of grid load and its output characteristics. The mathematical model of each part of the hybrid system was established, and the dynamic simulation of the system under different design conditions was carried out using 20 s time steps. The classic Runge-Kutta algorithm was used to solve the problem. Then, the effect of the storage pressure range and seasonal variation on the system's performance was analyzed. Meanwhile, the investment cost was estimated, and the economy of the hybrid system was evaluated under different design conditions. The results showed that, in all of the simulated working conditions, when the end pressure of discharge (EPD) changed within 3～7 MPa, regardless of whether the end pressure of charge (EPC) was within 8～12 MPa, the optimal value of the EPD was 5 MPa; this rendered the specific energy consumption (SEC) of freshwater production by the system the lowest. SEC in high summer temperatures could be reduced by approximately 30% compared to low temperatures in winter. In all simulated working conditions, when the EPC was 12 MPa and the EPD was 5 MPa, the SEC had a minimum value of 1.72 USD/m³. Compared with a traditional RO desalination system, the unit price for producing freshwater using this hybrid system could be reduced by a maximum of 4.4%, thereby achieving better economic performance. This study helps promote the application of A-CAES in the field of RO desalination and provides a theoretical basis for the construction of such a power plant.

Compressed-air energy storage (CAES) is one of the most promising large-scale electrical energy storage technologies. In this study, the method of exergy and economic analysis was adopted, a thermo-economic model for CAES systems was developed. The model was employed to analyze an advanced regenerative CAES system operating in a power system with a time-of-use electricity price. The results show that the system is thermo-economically feasible. Energy cost accounts for a greater portion of the total cost. For the non-energy cost, the gas storage subsystem accounts for the highest proportion, followed by the compression subsystem. Optimizing the compression subsystem significantly reduced the exergy price of the system output, followed by the storage and expansion subsystems. Therefore, to optimize the system, the thermoeconomics of the compressor should first be considered. This study provides technical and economic decision-making reference and basis for research and engineering applications of CAES systems.

The randomness of wind energy is an important reason for the abandonment of wind farms. The configuration of compressed-air energy storage (CAES) systems can effectively balance the randomness of wind power generation and lead to a reduction in wind farms. However, the improper configuration of CAES storage scales causes the loss of economic benefits. Therefore, to improve the rate of wind energy usage, this study examines the capacity configuration of CAES based on the uncertainty of wind energy. First, historical data are used to obtain the typical hourly power distribution of wind power generation. Then, factors, such as user load demand, grid time-of-use electricity price, system investment cost, power shortage cost, and power sales revenue, are considered to develop a CAES system for charging and discharging power and gas storage capacity. The developed CAES system is a model with constraints and maximum benefit as the aim; it is solved using the genetic algorithm. Finally, the established model is used to optimize multiscene operation cases. The simulation results demonstrate that for factory users with a typical hourly load power demand of 3.241 MW, the wind farm maintains four wind turbines running daily, and it is equipped with a CAES system with rated power and capacity of 1 MW and 6.5 MW·h, respectively. The economic benefits are the best, and the amount of wind curtailed can be reduced by 3.84 MWh, thus saving 4208.9 yuan in power purchase costs and realizing the largest daily net income of 699.86 yuan.

This study aimed to clarify the natural gas storage capacity and storage capacity availability of cavern repositories, assuming that the temperature of natural gas in each part of the gas storage was the same and that the rock mass around the gas storage was the same medium. Based on the principle of the conservation of energy and mass, and considering the real compressibility of natural gas, the temperature, and pressure change processes of compressed natural gas in constant-volume cavern gas storage were studied. Furthermore, the calculation method for the storage capacity and the gas storage capacity of a rock cavern for gas storage was proposed. The influence of cushion gas pressure on the gas storage capacity and storage capacity availability of cavern repositories were also analyzed. The results indicated that the cavern repositories' total gas storage capacity increased as the cushion gas pressure increased. Moreover, the injection-production ratio and the storage capacity availability exhibited a trend in which it initially increased before decreasing. When the cushion gas pressure was approximately 3.0 MPa, the storage capacity availability reached the maximum value. Once the gas production stage was completed, the pressure in natural gas stores gradually recovered. As the pressure of the cushion gas increased, less of the natural gas pressure would be recovered. The pressure recovery value of natural gas gradually stabilized once the cushion gas pressure was higher than 3.0 MPa. The study's conclusions provide good theoretical guidance for the feasibility of research and design approaches for various rock-cavern repositories for natural gas storage.

Flywheel energy storage has the high power density characteristics of high efficiency and low losses. It has been widely applied in uninterruptible power supplies and grid frequency regulation. Flywheel bearings play an important role in supporting the weight of a flywheel and reducing frictional resistance. It is the key component for determining energy storage capability, charging and discharging efficiency, and the service life of a flywheel. This paper investigates the mechanical structure of active magnetic, high-temperature superconducting magnetic, and hybrid bearings for a flywheel energy storage system. The results showed that hybrid magnetic bearings had the best performance and could lower the losses and increase the rotating speed of the flywheel. Furthermore, the control strategies for active magnetic bearings, including proportional-integral-differential (PID) control, sliding mode control, model predictive control, neural network control, and decoupling control, were introduced and compared. The flywheel bearings' future development trends were also analyzed. The study concludes that the PID control method can keep the system stable in the flywheel rotor linear working range. Contrastingly, the sliding mode, model predictive, and neural network control approaches showed better performance in a nonlinear working range. The advantage of the decoupling control was a high control accuracy at a high speed. This paper contributes to providing guidelines for the study of the flywheel bearing structure and control system.

High-speed rotating flywheel rotors for energy storage are key devices of flywheel energy storage technology (FEST). Under normal operating conditions, the flywheel rotor runs stably in the radial gap between the rotor journal and the protective bearing to support the active magnetic suspension bearings at both ends. When the rotor is disturbed (based on several factors) and deviates from a stable trajectory, its journal may collide with the inner ring of the protective bearing, which may cause system instability. Therefore, it is necessary to study the disturbance energy dissipation and the rubbing behavior's influence on the system stability during the rubbing process and subsequently provide a basis for optimizing the system's contact parameters and system stability. In this paper, a set of dynamic equations describing the rubbing process of the flywheel system is established using the two-degrees-of-freedom spring-damping system model, which considers friction after simplification. The fourth-order Runge-Kutta direct integration method was used to numerically solve the system's rubbing behaviors under different contact parameters. The results showed that, within the range of actual contact stiffness, the stability of the rotor system always indicated the trend of first strengthening slowly and then decreasing rapidly with an increase in the friction coefficient. For a given contact stiffness, there was a matching optimal value range and a maximum allowable value for the friction coefficient. Once the friction coefficient exceeded this maximum value, the rubbing effect caused instability behaviors in the flywheel system, such as low-frequency continuous collision or rubbing against the entire circumference. As the contact stiffness increased, the allowable value range of the friction coefficient continued to become narrower. The damping coefficient of the system also restricted the contact parameters' influence on the rubbing process. The calculation results highlighted a feasible solution as enhancing the stability of the flywheel system by optimizing the material of the friction pair during rubbing, as well as the contact parameters between the rotor journal and the inner ring of the protective bearing.

Inductive displacement sensors are widely used to measure magnetic bearing rotor position because of their high sensitivity, good linearity, and low cost. The sensitivity of inductive sensors is typically positively correlated with power consumption. Power improvement is necessary to obtain high sensitivity, particularly for applying the constant flux axial inductive displacement sensor, which requires high power amplifiers. Accordingly, finding a way to reduce the total power of the sensor without changing its sensitivity will help reduce hardware costs. In this paper, a reactive power compensation technology for the inductive sensors of magnetic bearings is proposed. By paralleling appropriate capacitors at both ends of the excitation coils of the sensor, the study was able to realize a parallel resonance state, thereby greatly reducing the reactive power of the entire circuit. The experimental results showed that, without affecting the sensors' sensitivity, the power amplifier's apparent output power could be reduced by more than 70% at 20～40 kHz. This reduced the maximum output power requirement of the power amplifiers. Following that, the influence of compensation point selection on the compensation effect was tested. The results showed that the compensation point selection demand was very low. Finally, the influence of compensation capacitance precision on the compensation effect was evaluated. The results indicated that reactive compensation did not require high compensation capacitance precision, and the 10% precision capacitor could achieve a satisfactory power optimization effect. Parallel reactive power compensation could significantly reduce the total apparent power of the sensors and the cost of power amplifiers. This technology presents practical value in the field of engineering.

Recently, magnetic bearing systems have undergone development to induce higher speed and better reliability in such systems. This has led to the rotor speed exceeding the first-order bending critical speed. However, due to insufficient damping at a critical frequency, magnetic bearing systems face instability risks. In order to adapt the system's performance and stability around the first-order critical speed, this paper proposes a synchronous damping method to provide the damping required for the rotor to cross the critical speed and to support it in reaching a higher yet stable speed. With a rotor modal constructed using the classic finite element method and combining the modal separation method and mass discretization, the suppression of unbalanced vibration around the first-order critical speed using the synchronous damping method was verified in detail. This result can serve as a foundation for the practical application of the synchronous damping method. Finally, with the addition of the synchronous damping module in the existing magnetic bearing equipment in a laboratory setting, the rotor steadily transited the first-order bending speed of 45,000 r/min, which verified the effectiveness of the synchronous damping method in supporting the flexible rotor to pass through the critical speed.

Compared with fiber reinforced composites, high strength alloy steel flywheel has the advantages of mature material and low manufacturing difficulty, which is suitable for flywheel energy storage rotor shafting with weak weight constraint. This paper analyzes the energy storage density, material strength requirement and kinetic energy storage material cost of typical high strength steel disk flywheel. Based on the requirements of heat treatment hardenability and energy storage, two kinds of flywheel structures, 50 kW·h and 7.5 kW·h, are designed. The 50 kW·h flywheel is 6000 r/min, and the circumferential speed is 376.8 m/s; The speed of 7.5 kW·h flywheel is 18000 r/min, and the circumferential speed is 433.5 m/s. The finite element stress analysis shows that its strength is safe. A 400 kW/7.5 kW·h engineering test prototype was developed. The test speed reached 18000 r/min and the kinetic energy of the rotor was 27 MJ. Through field high-speed dynamic balancing, the maximum vibration amplitude of shafting increases from 70 μm dropped to 20 μm The amplitude is reduced by 70%. During the charging and discharging process of 9000—18000—9000 r/min, the input electric energy is 21.5 MJ and the output electric energy is 19.5 MJ.

The strategic goals of "carbon peak" and "carbon neutral" are getting more and more attention. Flywheel energy storage, as a physical energy storage method, is being gradually promoted because of its high power density, short response time, long life and other characteristics, and efficiency is one of the important preconditions for industrialization promotion. The charging and discharging efficiency of a 500 kW/100 kW·h flywheel energy storage system was measured using the electric energy measurement method. The charging and discharging cycle of the flywheel energy storage system ranged from 4000 to 6000 to 4000 r/min. In the experiment, the system's charge-discharge cycle efficiency was 83.23%. The motor's electrically generated cycle efficiency was 90.49%. The charge-discharge conversion efficiency of the converter was 92%. The test results showed that the motor's efficiency could increase to 97%, the efficiency of the converter could be 98%, and the efficiency of the charge-discharge cycle could increase to above 87%.

Herein, a two-area grid model is established to analyze the effect of primary frequency modulation of thermal power units with the auxiliary of flywheel energy storage. The effects of the system and the output power situations of frequency-modulation resources with or without flywheel energy storage in the case of step and continuous disturbance are analyzed using MATLAB/Simulink. The simulation results show that, compared with the separate frequency modulation of thermal power units, because the flywheel energy storage can quickly respond to the frequency deviation signal, the maximum transient deviation of frequency in the process of frequency modulation can be reduced. The steady-state frequency deviation of the system is reduced by 7.58×10^-5 per unit under step disturbance, and the maximum frequency deviation of the two areas is reduced by 2.02×10^-4 and 1.47×10^-4 per unit under continuous disturbance with flywheel energy storage. Moreover, the maximum change of exchange power is reduced by 2.84 × 10^-4 and 1.52 × 10^-3 per unit under the step and continuous disturbance, respectively. Because flywheel energy storage undertakes part in the frequency-modulation task, the steady-state output-power variation of thermal power units under step disturbance is reduced by 1.517 × 10^-3 per unit, and the variation range of the output power of the thermal power units is reduced in the entire frequency modulation process under continuous disturbance. Excessive charge or discharge does not significantly influence the life of flywheel energy storage. Hence, the upper and lower limits of its state of charge can be set higher. The state of charge of flywheel energy storage is constrained by logistic functions, the discharge power is limited when the state of charge is low, and the charge power is limited when the state of charge is high. In the entire process of primary frequency modulation simulation, the state of charge of flywheel energy storage is in a good range. Herein, the special case of the initial value of the state of charge being one and zero is simulated, and the results show that the function can help the state of charge gradually recover from the dangerous range to the normal range. Comprehensive analysis shows that using flywheel energy storage to assist primary frequency modulation can reduce the frequency deviation of power systems, the variation range of exchange power, the frequency-modulation burden of the thermal power units, and the variation range of the output power of the thermal power units, and increase the life of the thermal power units.

The energy recovery efficiency of motor regenerative braking recovery systems is affected by the chemical reaction speed of the battery electrode "active substance.?" To address this issue, an electromagnetic coupling flywheel energy recovery system (ECFESS) is proposed herein owing to the high instantaneous power, high efficiency, long cycle life, and fast response of flywheels. The energy conversion route of the system under vehicle acceleration and deceleration was analyzed. Simulink was employed to analyze the energy recovered from batteries in the deceleration-cruise process of the motor energy recovery system and ECFESS. Through the simulation test platform, the energy transfer characteristics of each port of the electromagnetic coupler were confirmed. The result of ECFESS shows that 55.93% of the vehicle kinetic energy is directly stored in the flywheel, and 44.07% in the battery through the electrical port of the electromagnetic coupler, reducing the degree of the battery participating in the energy recovery process.

Because of its long operational life, high safety features, high power ratio, fast power response speed, and high control accuracy, flywheel energy storage is receiving ever more attention in the field of fire storage with combined frequency modulation. This paper analyzed the compensation policy of a thermal power plant frequency regulation in Central China. It obtained several key performance indexes of the flywheel energy storage that participated in fire storage with combined frequency modulation and conducted a performance test on a set of 500 kW/100 kW·h flywheel energy storage systems. According to the test results, the AGC command daily typical 300 MW thermal power unit data are combined, a set of control strategies that combined the frequency modulation of flywheel energy storage systems and thermal power units were designed. The compensation income of the frequency modulation was simulated and calculated. Compared with the compensation income obtained by a thermal power unit participating in FM only, the additional benefits obtained after increasing the flywheel energy storage system were analyzed. The conclusion was that flywheel energy storage reflected a good life-cycle economy in applying fire storage with combined frequency regulation.

A Co₃O₄/CoO system has broad application prospects in the contexts of medium and high-temperature thermochemical energy storage due to its high-energy storage density and good reaction characteristics. This study used thermogravimetry and differential scanning calorimetry to study the influence of different oxygen concentrations and heating/cooling rates on the redox process of a Co₃O₄/CoO system and analyzed the reduction reaction kinetics. The experimental results showed that increasing the oxygen concentration and heating/cooling rate could increase the redox reaction rate. However, a higher oxygen concentration could inhibit the reduction reaction. The effects of oxygen concentration and heating rate on the enthalpy of the reduction were not obvious. The kinetic analysis results showed that the reduction reaction conformed to the Avrami-Erofeyev random nucleation model (A2). Following optimized calculation, a more accurate kinetic model of reduction reaction was obtained, which provided a theoretical basis for the design of a thermochemical energy storage reactor, based on metal oxide systems.

Phase change thermal energy storage technology has remarkable application potential in the use of solar energy and the recovery of waste heat, based on its advantages of high thermal storage density, low-temperature variation, and low cost. However, its practical application is limited by the low thermal conductivity of phase-change materials (PCMs). Thus, in this paper, paraffin/nano-iron oxide (Fe₃O₄) composite PCMs with different fraction masses were prepared using a two-step technique to enhance the thermal conductivity of the PCMs, and its thermo-physical properties were comprehensively characterized. In addition, the charging and discharging performance of composite PCMs were investigated and compared with that of pure paraffin. The results showed that adding nano-Fe₃O₄ could effectively improve the thermal conductivity of composite PCMs compared with pure paraffin. When the mass fraction of nano-Fe₃O₄ was 5%, the thermal conductivity of composite PCMs could be enhanced by 53% in a solid-state and by 79% in a liquid state, and the total melting and solidification time could be shortened by 29.69% and 29.81%, respectively. Although the stored and released heat declined by 5.62% and 7.32%, the exergy efficiency was improved by 0.43% and 3.37% during the charging and discharging processes. The intensity of natural convection heat transfer in the charging and discharging processes was weakened by nano-Fe₃O₄.

This study aimed to develop a type of low-cost heat-storage material with good thermal performance. Chloride salt (CaCl₂-NaCl-KCl) was selected as the phase-change material, alumina (α-Al₂O₃) was used as the matrix material, and expanded graphite (EG) was used as a thermal conductivity enhancer. A mixed sintering method prepared the CaCl₂-NaCl-KCl/α-Al₂O₃/EG stable composite material. Based on X-ray diffraction results, chloride, alumina, and the EG physically mixed, but no chemical reaction occurred. Scanning electron microscopy was used to observe the microstructure of the EG. Chloride and alumina were evenly mixed and adhered to the pores of the EG. The pores formed by the EG helped to prevent liquid leakage. The results showed that the melting point of the composite was almost the same as that of chloride. By measuring the thermal properties of the composite material, the results showed that the specific heat capacity of the CaCl₂-NaCl-KCl/α-Al₂O₃/EG composite material was 1.35 J/(g·K) before the phase change (150～450 ℃), and the thermal conductivity was 5.03 W/(m·K). After the phase change (520～640 ℃), the specific heat capacity was 1.43 J/(g·K), and the thermal conductivity was 5.03 W/(m·K). Compared with the chloride salt, the melting point of the composite material essentially remained unchanged. In the application range of 100～700 ℃, the composite material's heat storage per unit mass was 902.5 J/g, increasing 8.3% compared with the pure chloride salt. In the prepared CaCl₂-NaCl-KCl/α-Al₂O₃/EG composite material, the chloride salt avoided direct contact with the container during use, thereby reducing its corrosiveness. Concurrently, the thermal performance greatly improved. This study provides an alternative low-cost and good comprehensive performance heat-storage material for high-temperature heat-storage contexts. It provides an experimental basis for promoting the practical application of chloride in high-temperature heat-storage environments.

New high-temperature thermal storage/storage materials with higher service temperatures must be developed to improve the efficiency of third-generation concentrated solar thermal power generation technology and reduce the system's operating costs. Based on the same-cation principle, three molten salts, i.e., sodium nitrate (NaNO₃), sodium chloride (NaCl), and sodium carbonate (Na₂CO₃) of the same sodium ion, were selected as base salts, and the phase diagram principle guided the preparation of mixed molten salts. The phase diagram thermodynamic calculation of the NaNO₃-NaCl-Na₂CO₃ ternary system was carried out using the FactSage software program. The thermophysical analysis of several groups of eutectic salts near the lowest eutectic point was carried out using a differential scanning calorimeter. The results showed that when the molar ratio of the molten salts in the ternary system(NaNO₃:NaCl:Na₂CO₃) was 0.92:0.064:0.016, the melting point of the system was the lowest, the lowest eutectic point was 279.9 ℃, and the latent heat was 194.1 J/g. These results were essentially consistent with the theoretical calculation result (291 ℃), verifying the model's accuracy. Other thermophysical properties of the system at the lowest eutectic point were measured. The decomposition temperature of the system at this ratio was 648 ℃ (the mass loss rate was 5%), and the specific heat value was 1.60 J/(g·K) (500 ℃). The measured specific heat value increased by 0.12 compared with Solar Salt and 0.28 compared with Hitec salt. The new ternary system had large latent heat of molten salts and a broad temperature range. It showed significant potential in the preparation of latent heat storage involving composite materials. The system can be used as a reference for developing new thermal storage/storage materials for solar power generation and as a guide for the development of mixed molten salts using phase diagram theory.

Thermochemical energy storage is a promising energy storage method because of its high-energy storage density, long-term storage capability, and broad temperature ranges. A fluidized bed reactor has excellent heat and mass transfer performance, suitable for a thermochemical heat-storage system. This study established a two-dimensional axisymmetric unsteady numerical model that included the multiphase flow and chemical reaction, based on the Eulerian–Eulerian model and heat-transfer and reaction kinetics equations. The effects of bed expansion ratio and gas flow rate on the heat storage and release efficiency were analyzed based on the investigation of the reaction processes and using magnesium hydroxide and magnesium oxide as the thermochemical heat storage materials. The authors validated the numerical model and investigated the energy flow and energy consumption optimization in the fluidized bed reactor by conducting experiments. The results indicated that the heat-transfer efficiency did not limit the bed temperature. The temperature differences among the different regions inside the reactor and between the gas phase and the solid phase were less than 1.0 K. The exothermic reaction kinetics limited the performance of the reactor. A high-temperature gas-solid reaction can significantly increase the bed's expansion rate; additionally, the bed expansion ratio and gas flow rate significantly influenced the heat storage efficiency but had little influence on the heat release efficiency. The gas that was preheated in the heat release process, as well as the sensible heat within particles in the heat-storage process, were key aspects of the reactor energy optimization. This research reflects guiding value for the numerical modeling and experimental optimization of a fluidized bed reactor in a thermochemical heat storage system.

In this paper, a prototype of a plate-type phase-change heat exchanger (PPCHE) is designed, and the influence of geometric parameters on the performance of the PPCHE is studied. Five PPCHEs models with different plate-type phase-change units (PPCUs) were constructed to control the heat exchanger volume and the PCM mass. Numerical simulation optimized the heat-transfer fluid (HTF) inlet temperature and velocity. The results showed that increasing the number of PPCUs increased the heat-transfer rate, but the pressure drop also increased. When the PPCUs numbered five in total, the heat-transfer efficiency was the best. The energy storage efficiency was proportional to the fluid velocity and inversely proportional to the pressure drop. The heat-transfer rate increased with an increasing HTF temperature; however, the increased rate decreased with an increase in HTF velocity or temperature. In this study, the best condition for the highest energy storage performance was v=0.5 m/s and N=5. In practical application, the design of the internal structure of the heat exchanger when the flow rate is low should be a primary focus.

When a coil heat exchanger is placed in a single-tank molten-salt heat storage system, the heat release power of the system decreases with an increase in the heat release time. To achieve stable heat release, in this study, the influence of the change in the heat exchange area on the heat release power of single-tank heat storage systems was examined by experiment using low-melting-point molten salt and air as the heat extraction mediums. By continuously adjusting the heat exchanger area, the outlet temperature of the heat exchanger could be stabilized at the set target value for a long time, and the heat release power could be stabilized. Experimental analysis demonstrated that continuous adjustment of the heat transfer area with a stable heat release is preferred, and the stable heat release time accounts for ～98% of the total heat release time. By continuously adjusting the heat exchange area, stable outlet temperature and heat release power could be obtained.

To increase the flexibility of the power system and the consumption of energy, a 100 MW molten-salt heat storage system is proposed herein. The molten-salt heat storage system with a large capacity and high temperature was embedded between the boiler and turbine in a thermal power system of a thermal power unit to decouple thermal and electric energy. The 100 MW molten-salt heat storage system could enable the turbine to operate at the lowest output while ensuring the safe operation of the boiler without stopping it, thereby greatly increasing the deep peak-shaving capacity of the thermal power unit. To ensure the safety of the boiler and the manufacturing ability of the salt-water heat exchanger, the heat storage system is designed with high main steam pressure and high subcooled high-pressure water temperature. It can effectively increase the temperature of the hot molten salt and reduce the amount of molten salt, reducing the initial investment capital of molten-salt energy storage systems. The theoretical calculation of each module of the 100 MW molten-salt heat storage technology shows that the comprehensive storage efficiency of the system is as high as 77.8%; thus, it has broad application prospects in large-scale energy storage.

Renewable energy is characterized by intermittency and instability because of weather, region, and season, resulting in a mismatch between supply and demand. Seasonal thermal storage is an effective technology to solve the abovementioned problems. However, the traditional seasonal underground thermal storage has the disadvantages of single storage modes and severe heat loss. In this study, the underground hot water energy storage (HWES) and borehole thermal energy storage (BTES) modes were combined to establish a composite seasonal thermal storage system, and a numerical model was developed and confirmed by comparing with experiments. On this basis, the effects of parameters, such as store/release flow rate, scale matching, number of boreholes, and soil thermal conductivity, on the temperature, thermal energy store/release capacity and power, and heat loss of the composite system were analyzed. The performance law of the composite thermal storage system was examined to maximize efficiency. The results show that with an increase in the store/release mass flow rate, the system efficiency gradually increases. The system efficiency increases with an increase α value of scale matching. However, an increase in the volume ratio of the water tank causes more heat loss. Therefore, scale matching should be comprehensively considered not only to achieve higher system efficiency and obtain larger heat store/release power but also to minimize investment cost and reduce heat loss. Increasing the number of buried pipes increases the thermal energy store/release capacity and improves the system efficiency; however, it increases the investment cost. An increase in the space between the borehole rings increases the soil volume, thus reducing the storage temperature, which is not conducive to energy release and decreases the system efficiency. With an increase in the soil thermal conductivity, heat transfer in the soil, energy store power of boreholes, and peak temperature of energy storage increase. However, heat loss becomes faster, and the energy release power decreases, thereby decreasing the system efficiency.

The volute tongue could markedly influence the performance of pump and turbine. In order to study the hydraulic characteristic of pump as turbine with the variance of volute tongue angle under the direct and reverse modes, a numerical simulation is carried out to analyze the inner flow of low specific speed centrifugal pump with four volute types of different tongue angle, which is validated by experiment. Combining the entropy generation analysis and loss calculation, the change laws of pump head, required head of turbine, efficiency and internal loss are investigated. The results show that an increase of volute tongue angle could improve the pump head, reduce the turbine required head, and make both efficiencies rise, and the efficiency-discharge curves move to the right with the discharge of the best efficiency point increasing, while the pump efficiency decreases when the angle value exceeds a certain range. The loss in the volute region accounts for the major part of hydraulic loss under both modes, and the loss is more likely to be affected by angle changing than it in the runner. As the angle increasing, the pump efficiency rise is attributed to the loss decrease in the outlet region of volute, while the loss reduction in the gap between runner and volute tongue, and the area near volute wall is the main cause instead of the restricted separation in the runner for the improvement of the turbine efficiency.

Hydropower has the advantages of clean and low-operation cost, and the reasonable development of hydropower resources is of great significance to promote the social sustainable development, specifically, the pumped-storage power stations will improve the stability and reliability of the power grid operation, as its distinct natures of efficient energy storage. However, the development of the traditionally pumped-storage power station is also restricted by many factors such as the geographical conditions. In order to better utilize the hydropower resources, this work explores a new pathway of the conventional and energy-storage hybrid hydropower concept, and takes the development of hydropower in the Manas River in Xinjiang as an example. Based on the planned three typical storage-type hydropower plants, four optimized development schemes are proposed. According to the waterhead and daily adjustment capacity of storage, the diameter of the pressure pipe of the power tunnel and the cross-sectional area of the waterway are increased to improve increase the plant hydropower capacity, the comprehensive utilization benefits of the hydropower resource will be evidently enhanced. Compared to the original development plan for the graded utilization of hydropower resource, the maximum installed capacity and total annual power generation of the energy-storage hybrid hydropower scenario will improve to 2.7 million kW and 6.012 billion kW·h, which are 3.9 times and 4 times higher than the original one, respectively. Moreover, this scenario is able to consume the surplus electricity of 5.724 billion kW·h of the solar/wind power or the off-peak power load, which will enhance the efficient utilization of hydropower resources. This positive method provides an alternative route for optimizing the exploration of hydropower resources.

Pumped thermal electricity storage (PTES) systems are a novel type of physical energy storage technology with low capital cost, high energy density, and no geographical restriction. In this study, the transient behavior of PTES systems based on the Brayton cycle was explored under cyclic stable state by coupling dynamics analysis method, transient heat transfer, and finite-time thermodynamics. The performance of the two concepts of PTES systems proposed by Isentropic Ltd. and Saipem S.A. company (hereafter, Is-PTES and Sa-PTES system, respectively) was analyzed and compared, and the influence of the working fluid, system maximum temperature, and volume of thermal energy storage reservoirs on the performance of the system are discussed. Under standard operating conditions, the round-trip efficiency of the Sa-PTES system is higher, whereas the Is-PTES system exhibits better output stability. The round-trip efficiency of the Is-PTES and Sa-PTES systems reaches 56.42% and 64.28%, respectively, and the performance of the PTES system using He is the best, followed by that of the system using air, and that of the system using Ar is the worst. Exergy analysis demonstrated that the compressors and expanders account for the highest proportion of exergy loss in the Is-PTES system, which was converted into heat exchangers and thermal energy storage reservoirs in the Sa-PTES system. When the allowable upper limit temperature of the PTES system is low, the performance of the Is-PTES system becomes better than that of the Sa-PTES system. For the Sa-PTES system, better performance can be obtained under high upper-temperature conditions, and it is affected more by the volume of packed beds.

Liquid carbon dioxide (CO₂) energy storage (LCES) is an effective method for expanding the scale of renewable energy utilization and ensuring the stable use of renewable energy. To solve the problem related to the effective condensation of subcritical CO₂ in an LCES system, a novel liquid energy storage system (LMES), based on a CO₂ mixture, is proposed in this paper. Two organic working mediums, R32 and R161, were selected to mix with CO₂. By establishing the thermodynamic model of the system, the effects of five key parameters on the system's performance were studied, i.e., the mass fraction of the organic working medium, compressor pressure ratio, pump pressure ratio, cooling temperature (T₆), and ambient temperature. The results showed that the mixing of an organic working medium and CO₂ could significantly increase the critical temperature of the working medium and solve the problem of CO₂ condensation in an LCES system. In a system with the CO₂/R32 mixture as a working medium, the increase in the organic working medium mass fraction slightly reduced the round-trip efficiency and energy density of the system, but it effectively reduced the working pressure of the system. The energy density of the system could be increased by increasing the compressor pressure ratio, thus increasing the cooling temperature and decreasing the ambient temperature. In the system that employed both mixtures, an optimal cooling temperature existed to maximize the system's round-trip efficiency. When the CO₂/R32 mixture was used, the optimal cooling temperature was 42 ℃, and the round-trip efficiency of the system was 57.65%. When the CO₂/R161 mixture was used, the optimal cooling temperature was 45 ℃, and the round-trip efficiency of the system was 50.54%. The research also found that, compared with the CO₂/R161 mixture, the application of the CO₂/R32 mixture as the working medium of the energy storage system obtained a higher round-trip efficiency and energy density.

The study of similar modeling characteristics of turbo-expanders with different working fluids is not only the important technical means and necessary method for the research and development of turbo-expanders with special working fluids but also an effective approach to improve the efficiency of research and development and save cost. In this study, a new modeling method based on rotational speed, inlet total temperature, adiabatic index, and gas constant is proposed. The modeling method is suitable for varying the working fluids of turbo-expanders, and it is numerically confirmed using supercritical CO₂ and air in a turbo-expander. It exhibits high accuracy in modeling the overall performance parameters and has a good modeling effect in predicting the internal flow field (Mach number, velocity distribution). This method is suitable for modeling the work process of supercritical CO₂ energy storage at high temperatures and high pressure using air.

Energy storage is an important technology to realize the large-scale utilization of renewable energy sources; however, the supercritical compressed carbon dioxide energy storage (SC-CCES) system has advantages of compact equipment, high efficiency and security, and it is one of the most promising large-scale energy storage technologies. The models of conventional and advanced exergy analysis of SC-CCES are established in order to the investigate exergy destruction in each process and component of the system, and its causes are revealed. The characteristics of avoidable/unavoidable and endogenous/exogenous exergy destruction, correlations among different processes and components are determined. The simulation results show that the system efficiency is 60.30%. Considering the components, compressors exhibit the largest exergy destruction, accounting for 33.85% of the total exergy destruction, followed by the expander, throttle valve, cooler, recuperator, mixer and heater. For advanced exergy analysis, the compressor and expander still exhibit the highest avoidable exergy destruction, whereas the throttle valve and mixer have a small potential. As the endogenous/exogenous exergy analysis show, the exogenous exergy destruction of almost all components only accounted for a small part of the total destruction, which means the interactions between the components are weak. In a short word, advanced exergy analysis method might lead to a different optimization priority and indicate the interactions between components, which are weak and intricate at the same time. The advanced exergy analysis is a powerful complement to conventional exergy analysis. Furthermore, sensitivity investigations revealed the effects of energy charge/discharge pressure, compressor and expander efficiency on the system performance. It's obvious that high charge/discharge pressure and small heat exchange temperature differences bring a positive influence on the performance of the system. The research in this paper provides a reference for SC-CCES optimization design and application.

This study introduced several high-pressure gaseous hydrogen storage containers, including high-pressure hydrogen storage cylinders, high-pressure composite hydrogen storage tanks, and glass hydrogen storage containers. High-pressure hydrogen storage cylinders include all-metal gas cylinders and fiber composite material-wound gas cylinders. The only commercially available high-pressure hydrogen storage container has the advantages of easy hydrogen release and high hydrogen concentration. The high-pressure composite hydrogen storage tank used hydrogen storage materials to store hydrogen and achieve solid hydrogen storage; the gap between the powder materials also participated in hydrogen storage to accomplish gas-solid mixed hydrogen storage. This method had the advantages of high volumetric hydrogen storage density, fast hydrogen charging speed, and good working performance at low temperatures. The glass hydrogen storage containers included hollow glass microspheres and a capillary glass array. This was a new type of high-pressure hydrogen storage container that had the advantages of high mass and volume density, good safety, low-cost parameters, and did not undergo hydrogen embrittlement. It was initially anticipated that this type of container would be combined with fuel cells and applied to various electronic mobile devices. However, due to imperfections in its related supporting devices, additional development is required for its commercial application. This paper compared the performance of several commercial high-pressure hydrogen storage tanks. It focused on the hydrogen storage mechanism, the technical status, and the research related to glass hydrogen storage tanks. It posited future technical research directions related to several types of hydrogen storage tanks.

Considering the uncertainty of new energy's output, economic and optimal operation of multiple virtual power plants have attracted considerable attention. Herein, a two-stage coordinated optimal scheduling method for multiple virtual power plants based on economic model predictive control is proposed. First, distributed power models, including wind turbines, gas turbines, and energy storage batteries models, are established, and an interruptible load model that participates in demand response is developed. Then, the day-ahead scheduling maximizes the revenue of multiple virtual power plants, employing Nash optimal decision-making to achieve optimal economic scheduling of multiple virtual power plants based on improved economic model predictive control. The length of the prediction domain is adaptively selected as per the wind power forecast error to reduce the impact of wind-power forecast uncertainty on the dispatch model. Furthermore, a real-time feedback scheduling strategy considering the economy is developed to make up for the power deviation of the day-ahead. Analysis of the case demonstrates that, compared with a single virtual power plant trading with only a large power grid, the total profit of the joint operation of multiple virtual power plants increases by 26.75%. Furthermore, compared with the fixed step size, the transaction power error is reduced by 78.28% under the adaptive domain step size. The proposed scheduling scheme effectively copes with the uncertainty of wind power and improves scheduling accuracy while realizing the overall optimal economic operation of multiple virtual power plants; thus, the correctness and feasibility of the scheduling model are confirmed.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 2739 papers online from Jun. 1, 2021 to Jul. 31, 2021. 100 of them were selected to be highlighted. Layered oxide cathode including Ni-rich oxides, lithium-rich materials, and spinel materials are still under extensive investigations for the modification of doping and coating. Large efforts were devoted to design the three-dimensional electrode structure, surface modification, and plating inhomogeneity of lithium metal anode. For silicon-based anode materials, beside 3D structure design, the researches focused on the development of electrode binders, aiming at buffering the volume change during cycling. The researches of solid-state electrolytes mainly focused on optimizing pre-existing materials and developing new materials, whereas liquid electrolytes mainly focused on the optimal design of solvents and lithium salts for different battery systems and developing new additives. The works of solid-state battery involve mainly the modification of interfaces, and suppressing the "shuttle effect" is the main task for Li-S battery. 3D lithium metal plating and electrode behavior under high current density were characterized by in-situ and ex-situ technologies. Theoretical calculation papers were related to ion transport and some interfacial reaction works were related to the SEI analysis. There are also a few papers related to the investigation of current collectors' modification and pre-lithiation techniques.