Accurate and reliable fault diagnosis technique is crucial to guarantee the safe, stable and reliable operation of lithium-ion batteries. First, the common fault types of battery system are briefly summarized and the failure initiation mechanisms of battery are elaborated. Then, the current developed fault diagnosis techniques for battery system are classified. Moreover, several typical fault diagnosis methods and their corresponding application cases for battery system are reviewed. Finally, the challenging and future research direction of fault diagnosis for lithium-ion batteries are proposed.

Batteries for electric buses are mainly lithium iron phosphate batteries. Large numbers of spent batteries will be produced after the cycle life termination and cause a significant problem that how to deal with the spent batteries. In this paper, the current status of spent batteries recycling is introduced, as well as the main valuable components of the spent LiFePO₄ battery. The recycling and reusing methods of the spent LiFePO₄ materials such as solution-precipitation method, solid phase direct recycling and regeneration process, bio-dissolution technique, and mechanochemical treatment are introduced in detail. The vacuum pyrolysis process, organic solvent extraction and supercritical CO₂ extraction recovery electrolyte are presented as well. In addition, the separation process and modification method of negative electrode materials are introduced. The products recovered by precipitation method are industrial raw materials containing lithium and iron. This kind of method is easy to implement large-scale application, but it will produce a large number of acid and alkali waste liquor. The process of solid phase direct recycling and regeneration is shorter, but to remove the impurity is the difficulty for large-scale application. At last, the different recycling methods are proposed for different types of recycled materials to provide reference for the recycling of batteries.

The latest research progress of MnO₂/graphene based binary and ternary composites in supercapacitors are reviewed. Due to the stacking caused by van der Waals forces, the actual specific capacitance of graphene is not very high. The theoretical specific capacitance of MnO₂ is as high as 1370 F/g, but its pseudo capacitance is limited by the thickness of MnO₂, and the actual specific capacitance is much smaller than the theoretical value. The combination of graphene and MnO₂, where MnO₂ nanostructures anchored between graphene nanosheets as spacers, can effectively inhibit the stacking of graphene and enhance the interface charge transfer. With the synergistic effect of both functions, it is expected to achieve high specific capacitance and high conductivity and good cycling stability. The preparation method and electrochemical performance of MnO₂/graphene composites are introduced. The electrochemical performance of MnO₂/graphene ternary composites are analyzed. The introduction of metal oxides or conductive polymers can further improve the electrochemical performance. Finally, a series of issues for the application of MnO₂/graphene-based multi-component composites and devices are analyzed, such as safety and reliability, large-scale production and cost reduction. With the mature and break-through of technology, it is expected to achieve applications in industry, transportation and daily electronics.

Based on the test of charge-discharge cycle on NCM power lithium-ion battery applied in electric vehicles under different conditions, the degree of attenuation on life of battery and influenced factors are analyzed. The internal structure of NCM power lithium-ion battery before and after charge-discharge cycle tests at different rates are tested by using X-ray non-destructive testing technology, meanwhile the degree of safety failure and decay on life of battery are evaluated. A new method to study the decline in life of battery and its safety failure is proposed. In the process of charge-discharge cycle, with the continuous decline on capacity of battery, the internal structure of the battery appears more and more obvious defects based on non-destructive testing technology, therefore it indicates the rate of attenuation on life of battery increases faster and the safety of battery gets worse. Based on the comparison on tomographic images of internal structures under different SOH states, the internal structure of the NCM power lithium-ion battery used for electric vehicles has changed on varying degrees after charge-discharge cycle tested by different ratio values of current, therefore it demonstrates that service life of battery has been greatly reduced on different levels.

The internal resistance of the battery is one of the most important characteristic parameters of the battery, and it is also an important indicator for evaluating the performance of the battery. In order to solve the problem that the existing measurement methods of battery internal resistance, which can't be measured online and require special equipment measurement, the paper proposes a calculation method for online measurement of battery internal resistance. The method is based on the current and voltage detected by the battery in the process of charge and discharge, according to the characteristic that the current have a zero-crossing in the charge and discharge process, the definite integral of the current is used to counteract the change of the internal resistance of the battery caused by the internal chemical reaction of the battery during the calculation of the internal resistance of the battery, through a series of calculations to estimate the internal resistance of the battery. The battery internal resistance estimation algorithm is written in MATLAB, and the simulation verification is realized. The results show that the calculation method can realize online estimate the internal resistance without the aid of auxiliary equipment and test equipment, it has the advantages of simple and convenient, accurate calculation and easy implementation.

In recent decades, China and the World have been devoting a significant effort to the development of energy storage technologies. Energy storage can support electrical grids in terms of peak-shaving, frequency regulation, black start, demand side response, and help resolving challenges associated with intermittency and fluctuation of renewables. This article reviews technical and economical evaluation indicators of a variety of energy storage technologies and introduces an evaluation method by Charles J. Barnhart and Sally M. Benson with a focus on energetic costs of storage. This leads to a new metric based on the energetic cost:energy stored on Investment (ESOI). A higher ESOI indicates that more "net energy" is returned. Through studying ESOI for different energy storage technologies, we found that the ESOI of mechanical based energy storage technologies is far higher than the chemical based energy storage technologies. The commonly used lead-acid (PbA) batteries only have an ESOI of 2.

With the new round of power market in-depth reform, we propose an concept of large-scale aggregation management and establish an optimization model for distributed energy storage aggregation providers to participate in power grid peaking scheduling in the form of bidding. In the day-to-day scheduling, the aggregation providers participate in the bidding by predicting the characteristics of distributed energy storage system behavior according to the next-day peaking demand announced by the power trading center; the power trading center optimizes the dispatch plan with a goal of minimizing the peaking scheduling cost. In the real-time scheduling, the aggregation providers optimize the charge and discharge outputs with a goal of maximizing its own interests considering the energy storage system characteristics of the previous prediction error and losses so that the aggregation providers could profit from the market electricity price while satisfying the previous successful bid. Simulation examples show that distributed energy storage aggregation providers participating in the grid dispatching could reduce the cost of peak shaving scheduling and achieve the effect of peak shaving in the form of bidding. The loss cost of energy storage system is the key factor affecting the outputs of charge and discharge.

The polarization resistance of lithium-ion batteries is the key parameter for irreversible heat testing. In order to obtain more precise results of polarization resistance, hybrid pulse power characterization (HPPC) test, entropy thermal coefficient test, and the temperature measurements of the cell in charging and discharging were carried out for a soft-packed NCM lithium-ion battery. Two methods were used to calculate the polarization resistance. One was obtained by dividing the amount of voltage change by the current, the other was identified by establishing a second-order RC model combined with the HPPC test condition. The temperature field simulation under 1C charging and 0.5C, 1C and 2C discharge was carried out by combining with Bernardi's heat generation rate model formula, and compared with the temperature distribution recorded by the infrared thermal imager. The results show that the polarization resistance obtained by second-order RC model is in good agreement with the experimental data, which indicates that the polarization resistance obtained by the second-order RC model is more suitable for the thermal analysis of the battery's continuous charge-discharge process. The model simulates well the temperature field information under different charge-discharge ratios of the battery, which plays a key role in the thermal analysis and thermal management of the battery.

In order to satisfy the requirement of distributed energy storage system for high power applications, developing new power anode with high capacity for lithium-ion batteries is necessary. In this paper, a novel anode with controllable pores for rechargeable lithium-ion battery was developed. The structures of the materials were characterized by X-ray diffraction (XRD), Raman, N₂ adsorption-desorption and scanning electron microscopy (SEM) methods. The capacity, coulombic efficiency and rate capability were investigated. It has been found that the pores can be controlled by changing the space velocity during carbonization. When the space velocity ≥ 0.5 m·min^-1, the amorphous carbon anode achieved a 0.2C capacity of~260 mA·h/g and 2C rate of~137 mA·h/g.

Influence of ceramic separators with different base film on the performance of LiNi_0.8Co_0.15Al_0.05O₂ high power battery is researched, with conventional polyolefin separator as control experiment. The intrinsic performance of these three kinds of separators including micro-morphology, gurley number, and ion conductivity are investigated. For dry process base film ceramic separator, wet process base film ceramic separator and polyolefin separator, the air permeability are 165sec/100cc, 200sec/100cc and 520sec/100cc, respectively. The ion conductivity are 0.952 mS/cm², 0.703 mS/cm², and 0.622 mS/cm². Pouch cells of 2 A·h were prepared with three kinds of separators. Rate performance, cycle and capacity retention were tested. The results exhibit that the ceramic separator can improve voltage plateau compared with polyolefin separator, and the role of dry process base film ceramic separator in improving cell power performance is more evident than the wet process base film ceramic separator, especially when the discharge rate is increased to a margin level of the cell design.

A series of sulfonated polyoxadiazoles (SPOD) with different monomer ratios were synthesized by using hydrazine sulfate (HS), terephthalic acid (TPA) and 4,4'-diphenyl ether dicarboxylic acid (DPE) as monomers, fuming sulfuric acid as solvent and dehydrating agent. Then, the SPOD films were obtained by the solution casting method. Finally, the SPOD films were neutralized with lithium hydroxide to form Li-SPOD polymer electrolytes films. The effects of two monomer ratios of TPA and DPE on the structure and properties of Li-SPOD were studied. Results show that SPOD can be obtained with different monomer ratios, and the sulfonic acid group was grafted on the benzene ring of DPE chain segments. The aggregation structure difference among Li-SPOD electrolyte films is small. Their thermal stabilities are excellent, and the initial thermal decomposition temperature are all above 450℃. The mechanical properties of Li-SPOD films decrease slightly with the increase of DPE contents. The conductivities of Li-SPOD electrolyte films are about 10^-5S·cm^-1, and gradually decrease with the increase of DPE content. Their electrochemical stability are good, and the decomposition voltages are all above 4.0 V.

To overcome the discontinuity and instability of solar energy and achieve energy supply and demand regulation and all-weather continuous heating supply of a solar heating system, a solar multi-mode heating method based on latent heat thermal energy storage is proposed. A solar heating system combining integrating vacuum-tube collectors with a latent heat thermal energy storage device is established in a building in Linzhi city, Tibet. The system can perform automatic control and operation of solar multi-mode heating according to the operating condition of solar collectors and external heating demand. Experimental studies show that the vacuum-tube solar collectors can work collaboratively with the latent heat thermal energy storage device. During the daytime, the latent heat thermal energy storage device performs a heat storage with an average charging power of 10.63 kW and a storage capacity of 92.67 kW·h, and the temperature platform of phase change can be apparently observed. At night, the thermal energy storage device can provide a 10-hour continuous discharging process with a total heat output of 85.23 kW·h at a stable discharging power and temperature. The charging-discharging efficiency of the storage device is 92%, and its heat storage density can reach 3.6 times that of a traditional hot-water storage tank. The results indicate that the solar heating system can achieve all-weather continuous heating supply. The present study can provide guidelines for implementation of solar heating in Tibet.

This paper concerns the application of the electromagnetic induction heating technology in heating molten salt in a heat storage system. An experimental system was set up for electromagnetic induction heating of molten salt and temperature variation of molten salt and coil cooling water under different molten salt velocity and coil current conditions were investigated. The results showed that the electromagnetic induction heater can heat the molten salt quickly. The temperature rise of molten salt occurred mainly in the first 80-240 s after starting the heating process, and the temperature rising rate reached maximum at~100s. A change in the coil current or molten salt velocity can produce molten salts with different final temperatures. When the velocity was 0.177m/s, the outlet temperature of molten salt at different currents was 201.45℃, 203.89℃, 207.60℃, 212.98℃ and 221.45℃. When the velocity of molten salt was constant, the heat absorption of molten salt and coil cooling water increased with increasing coil current. When the coil current was constant, the heat absorption of molten salt increased with increasing velocity, while the heat absorption of cooling water decreased. When the velocity of molten salt was 0.296 m/s and the current of coil was 600 A, the heating efficiency of molten salt was 69.28% and the corresponding heat loss of the cooling water was 16.45%.

The mannitol based phase change material has phase transition temperature of 2-3℃ required for micro-frozen storage of aquatic products. Such a material has an issue of supercooling. This article aims to understand the supercooling characteristics of mannitol based phase change system under an ultrasonic action from both single and double external fields. The sound pressure model under the action of an external ultrasonic field and the associated influence on the supercooling characteristics of phase change solution were discussed. An experimental system for studying the supercooling characteristics of the phase change system was constructed. It was found that the cavitation effect caused by ultrasonic waves can change the degree of subcooling of the mannitol based phase change system. The supercooling degree of the 3% mannitol based phase change system and the mannitol phase change system containing K₂SO₄ decreased first and then increased with an increase in the ultrasonic power. When the ultrasonic power was too high, the use of cavitation bubbles would reduce the cavitation effect, leading to an increased the degree of supercooling. The K₂SO₄-containing mannitol phase change system showed the best effect under a double ultrasonic field of 150W+150W. When the concentration of K₂SO₄ was 1%, the degree of supercooling was 0.8℃. For the carbon nanotube water dispersant (TNWDIS) mannitol phase change nanofluid, a 50W+50W double ultrasonic external field effect was optimal at a MWCNT concentration of 0.4% and 0.5%, with a supercooling degree of only 0.1℃.

The thermal deformation and thermal stress of a resistant based regenerator were analyzed by a combination of theoretical analyses and finite element numerical simulations, aimed at the understanding if thermal deformation of the external resistive regenerator could cause unstable structure of the regenerator. The thermal stress and thermal deformation equations of different phase change materials under temperature cycling were deduced theoretically, and the numerical simulations were carried out on the thermal stress and its distribution in the regenerator under a certain working condition (case study). The modelling was validated qualitatively by comparing with the operation of an actual thermal storage body.

Phase change heat storage has become a research hot spot in recent years because of high storage capacity per unit volume, and constant heat storage/release process. In this paper, the heat transfer characteristics of a high temperature phase change heat storage unit are studied. The temperature distribution, heat transfer rate and heat storage efficiency during heat storage and release processes are studied using the computational fluid dynamics in FLUENT software environment. The mathematical modeling and simulation analysis focus on the effect of different heat transfer fluid velocity on the performance of the heat storage and release processes. The results show that an appropriate air velocity can be selected to achieve different heat discharge power and heat storage time, to meet various demands of different end users. Physical experiments are carried out, showing that the deviation of simulation results is small from experimental measurements.

This work is motivated by the following two aspects. First, replacement of coal firing to electrical heating has become an effective means to achieve clean heating in the north part of China to combat increasingly serious environmental problems. Second, China's annual use of waste heat, especially in the medium and low temperature ranges, is still inadequate. For both the aspects, the phase change material-based heat storage technology has a great role to play. This article aims to compare heat exchangers consisting of phase change materials. First, a qualitative comparison was made between plate, shell-and-tube, heat pipe and other specially designed heat exchangers (heat storage bricks/balls). Numerical simulations were then carried out using a two-dimensional phase change material melting model for shell-and-tube and plate heat exchangers with the same heat exchange area and boundary conditions. The results showed that the shell-and-tube heat exchanger took about 6 hours to completely melt, and 8.5 hours were needed for the plate heat exchanger mainly due to the difference in the arrangement of the heat exchange tubes/plates. However, the plate heat exchanger is still regarded to have a great potential due to more compact structure, simpler manufacture process and easier to assemble/disassemble, and easier modularization for scale-up.

T This study aims to provide a theoretical basis for the design of a scroll expander for a micro-compressed air energy storage (micro-CAES) system, by using computational fluid dynamics (CFD) to obtain temperature, pressure and velocity fields in the working chambers. The effects of inlet temperatures on the performance of the scroll expander and the flow fields of the working chambers were investigated. The results showed that the output power per unit mass flow increased with increasing inlet temperature. The axial force acting on the orbiting scroll increased with decreasing inlet temperature, and the tangential and radial forces decreased with decreasing inlet temperature. The temperature distributions of the working chambers were not always increasing along the radial direction of the scroll plate. There existed energy losses in the backpressure chambers, and the temperature of the backpressure chambers can be higher than that of the exhaust chambers.

A step-by-step design method based on dual-input is proposed to address issues associated with non-linear factors in the control of a flywheel energy storage unit. This was based on an effective combination of the Backstepping control and passivity methods, enabling the flywheel system speed and current output stabilized. First, the Backstepping method was used to design the q-axis controller of the flywheel during charge. The d-axis controller of the system was designed by coordinating the passivity, making the whole system passive and hence ensuing the asymptotic stability of the system. The whole design process did not use any linearization treatment, ensuring the applicability of the whole control model in the non-linear system and hence an improved stability performance of the system. Simulations were then performed and the results validated the proposed control strategy.

Expandable graphite-paraffin composite phase change materials were prepared by a melt-blending process. The resistivity of natural flake graphite, purified graphite, expandable graphite, paraffin-expanded graphite composite phase change materials formed at different pressures was measured using a semiconductor powder resistivity tester. The results showed that the resistivity of all materials decreased with increasing pressure, seven repeated tests were performed on the material with the best thermal conductivity, and the resistivity of the material varied between 0.210-0.535 Ω·cm, which was lower than 11 Ω·cm and hence can be classified as a low-resistivity material. According to the measurement data, the amount of heat storage per unit volume, density, volume and resistance of the composite phase change materials were calculated. The amount of heat storage per unit volume and density of the material increased with increasing pressure, however, the resistivity and volume showed the opposite as expected. The physical properties of materials were found to be stable when the formation pressure was between 4 and 10 MPa; at about 10 MPa, the resistivity of the phase change material was 884 times larger than that of natural scale graphite, 1.9 times the volume and 0.6 times the density. The amount of heat storage per unit volume was 22.8% higher than that at 4 MPa. It was shown that the expanded graphite/paraffin composite was a low resistivity phase transition material, which can be applied on asphalt pavement, achieving both heating up and cooling down effects.

The boost converter suffers the low convergence speed and chattering phenomenon in the scheme with sliding mode variable structure control. A double power reaching law-based sliding mode hysteresis control strategy is proposed. To achieve the current tracking control, a sliding surface is defined based on the estimated tracking current error. By considering the unmodeled dynamics and the unknown disturbances, the adaptive state observer is established. The adaptation laws are designed based on the Lyapunov function and the adaptive duty ratio is calculated. A double power reaching law is proposed, which can set the parameter selection standard according to the different features of system approaching process and purposefully adjust the dynamic response quality. A sliding mode hysteresis controller is designed, which aims at reducing chattering phenomenon caused by the sign function. Simulation results show that the dynamic response performance and robustness of current control are improved effectively.

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 2472 papers online from Dec. 1, 2018 to Jan. 31, 2019. 100 of them were selected to be highlighted. Layered oxide and high voltage spinel cathode materials are still under extensive investigations for studying Li⁺ intercalation-deintercalation mechanism and evolution of surface structure, and the influences of doping, coating and interface modifications on their cycling performances. Large efforts were devoted to Si and Sn based composite anode materials for analyzing the mechanism for Li storage and SEI formation. The cycling properties of metallic lithium electrode are improved by using different kinds of surface cover layer, substrate and electrolyte additives. In-situ technologies are used to analyze the kinetic process and SEI and theoretical work covers the machnism for Li storage, kinetics, SEI and solid state electrolytes. There are a few papers related to solid state electrolytes, electrolyte additives, solid state lithium batteries, Li/S batteries, and modeling.

This paper concerns the use of energy storage for enhancing transmission capacities and trans-regional reserves of a UHV AC/DC power grid. First, based on the correspondence of power shortage to frequency variation in the receiving system of UHV AC/DC power grid, this paper proposes a model on capability improvement of the receiver and capacity allocation of storage while maintaining the stability of the minimal frequency scenarios. Second, through the analysis of the load characteristics of different intervals during typical days, a model between increasing renewable generation and required capacity of storage for peak shaving is also proposed. Third, considering both the fault support and trans-regional peak shaving reserve as well as their priorities, the capacity configuration and the associated economic feasibility are studied. Finally, verification of the method is done by a simulation which sets Henan Grid as the weak receiving end while Xinjiang Grid as the sending end abundant in renewable energy.

The capacity, DC internal resistance and storage performance at room temperature have been tested for LiFePO₄ batteries retired from electric bus. The charge/discharge rate performance, temperature performance, cycle performance have also been tested. The difference and change regulation of parameter between new batteries and retired batteries have also been analyzed. Then the batteries were recombined and the cycle performance of model have been tested. 1 MW·h secondary use batteried energy-storage system were integrated and participated in wind-power smoothing. The results show that DC internal resistance of battery increase a little, storage performance at room temperature, rate performance and temperature performance decrease slightly, the cycle performance of cell and model is still good, when the capacity of LiFePO₄ battery decreased to about 75% of the initial capacity. These results show that the retired EV batteries has good reuse value.

From the perspective of patent application and layout, this paper analyzes the basic situation of CATL's application trends, application geographical layout, application technology layout, key technology branches, R&D paths, etc., and comprehensively analyzes the above patent information and the company's own development and industry characteristics. The deep reason for its growth as a power battery unicorn enterprise is mainly the parallel of patent application and enterprise development, taking into account the patent layout at home and abroad, improving process continuously, enhancing the research and development focus in the advantageous field, and insisting on independent innovation in the core field. The above successful experience is worth learning for domestic and foreign counterparts or start-ups.

Electrode binder is one of the important auxiliary functional materials for lithium-ion batteries. Although it has no capacity, it is the key to maintain the integrity of the electrode. It determines the adhesion of the electrode coating and the flexibility of the electrode, and affects the rheological properties of the electrode paste. In this article, we discuss the domestic standards on electrode binders and introduce the characteristics and testing methods of electrode binders for lithium-ion batteries. We also propose some suggestions on the formulation of future standards for electrode binders.

Some of typical safety standards and regulations of lithium ion traction batteries are compared, including ISO 12405, IEC 62660, SAE J2464, SAE J2929, UL 2580, ECE R100-02, GB/T 31485, GB/T 31467.3 and FreedomCAR. Safety tests are classified into three type tests, i·e. mechanical, environmental and electrical tests. The specific parameters of each test item in different standards and regulations are introduced in details. The similarities and differences of Chinese national standards with foreign standards are summarized, some shortcomings in the current standards are pointed out, and suggestions for improvement are put forward.