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《Energy Storage Science and Technology》(ESST) (CN10-1076/TK, ISSN2095-4239) is the bimonthly journal in the area of energy storage, and hosted by Chemical Industry Press and the Chemical Industry and Engineering Society of China in 2012,The editor-in-chief now is professor HUANG Xuejie of Institute of Physics, CAS. ESST is focusing on both fundamental and applied aspects of energy storage science and technology. Submissions can be in English or Chinese. It is included in Chinese Sci-tech Core Journal, main indexed by CSCD(China), Ulrichsweb(America), INSPEC(England), CA(America), and others database etc.
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05 July 2020, Volume 9 Issue 4 Previous Issue   
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Contention of Sciences and Technologies of Energy Storage
Electrochemical capacitors clarifying
Ge JING, Dianbo RUAN
2020, 9 (4):  1009-1014.  doi: 10.19799/j.cnki.2095-4239.2020.0025
Abstract ( 103 )   HTML ( 8 )   PDF (852KB) ( 71 )  

In 1957, Becker’s patent initiated the study of electrochemical capacitors. As a new type of energy storage device, electrochemical capacitors exhibit high power and long life and have attracted considerable research attention. With the progress of research, electrochemical capacitors have transitioned from the original electric double-layer capacitors and pseudo-capacitors to today’s hybrid capacitors and other product types. During industrialization and research, electrochemical capacitors have been distinctly named (e.g., “supercapacitors,” “ultracapacitor,” and “golden capacitors”) based on different purposes. Their classifications also exhibit diversity. Thus, the hybrid capacitors are also called “battery-type capacitors.” The non-professional names and classifications have created unnecessary obstacles for industrialization and product standardization. This study attempts to clarify the naming and classification of electrochemical capacitors for future reference.

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Reviews of selected 100 recent papers for lithium batteries(Apr. 01, 2020 to May 31, 2020)
Wenbin QI, Hua ZHANG, Zhou JIN, Hongxiang JI, Mengyu TIAN, Yida WU, Yuanjie ZHAN, Feng TIAN, Yong YAN, Liubin BEN, Hailong YU, Yanyan LIU, Xuejie HUANG
2020, 9 (4):  1015-1029.  doi: 10.19799/j.cnki.2095-4239.2020.0216
Abstract ( 67 )   HTML ( 6 )   PDF (1602KB) ( 62 )  

This bimonthly review paper highlights 100 recent published papers on lithium batteries. We searched the Web of Science and found 3260 papers online from Apr. 01, 2020 to May 31, 2020. 100 of them were selected to be highlighted. Layered oxide cathode materials are still under extensive investigations for studying Li+ intercalation-deintercalation mechanism and evolution of structure, and the influences of doping and interface modifications on their electrochemical performances. The researches of silicon-based composite anode materials mainly focuses on the design of electrode structure, while the researches of lithium metal anode mainly focuses on the design of electrode structure and further to regulate the growth of SEI and inhibit the formation of lithium dendrites. Large efforts were devoted to solid state electrolytes including oxide, sulfide, polymer and composite solid state electrolytes. The research works on liquid electrolytes involves mainly the optimal design of solvents, lithium salts and additives. The structure evolution of materials and the growth of SEI are investigated by using in-situ technologies. Furthermore, there are a few papers related to the theoretical works for the electric structure of materials, Li+ transport and Li metal deposition.

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Energy Storage Materials and Devices
Research progress on the application of graphene for lithium-ion capacitors
Tengyu LIU, Xiong ZHANG, Yabin AN, Chen LI, Yanwei MA
2020, 9 (4):  1030-1043.  doi: 10.19799/j.cnki.2095-4239.2020.0041
Abstract ( 79 )   HTML ( 4 )   PDF (3311KB) ( 38 )  

Lithium-ion capacitors (LICs) are hybrid energy storage devices that can bridge the gap between lithium-ion batteries and supercapacitors. Therefore, they have become a popular research topic owing to their advantages of high energy density, high power density, long cycle life, and good safety. Graphene, which is a two-dimensional (2D) honeycomb lattice of sp2-bonded carbon atoms, is promising for future applications in electrochemical energy storage fields because of its high specific surface area, high conductivity, high capacity, and stable physicochemical properties. In this study, a critical overview of the current progress related to the usage of graphene materials in LICs is presented. The effects of specific surface area, electrical conductivity, and micromorphology on the electrochemical performance of graphene were also summarized. In addition, a brief summary of the structural modification of the graphene electrode materials is presented, followed by a systematic examination of the usage of doped graphene and graphene-based composites as electrode materials in LICs. The effects of heteroatoms on the electronegativity, microstructure, active sites, and electrochemical properties of graphene are also analyzed. Finally, major challenges associated with the future applications of graphene materials in LICs are presented.

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Freeze-drying assisted synthesis of mno/reduced graphene composite and the improved rate cyclic performance for lithium ion batteries
Tengfei MA, Chao MA, Rui SUN, Hongmei JI, Gang YANG
2020, 9 (4):  1044-1051.  doi: 10.19799/j.cnki.2095-4239.2020.0099
Abstract ( 57 )   HTML ( 1 )   PDF (2477KB) ( 22 )  

Taking advantage of manganese oxide (MnO) with high specific capacity and graphene with high conductivity, the composite of MnO/rGO has been synthesized by using freeze-drying assisted hydrothermal method. The structure, morphology and electrochemical performance of MnO/rGO composite are characterized by X-ray diffraction patterns (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electrochemical tests. MnO nanoparticles in MnO/rGO composite are homogeneously dispersed on and wrapped by rGO nanosheets which is helpful in improving the stability and conductivity of MnO during charging/discharging cycles. MnO/rGO delivers specific capacity of 870.4 mA·h/g after 100 cycles at a current density of 0.1 A/g, and it delivers 178.2 mA·h/g after 100 cycles at a current density of 15 A/g. rGO not only improves the conductivity of the composite and suppresses the volume effect of MnO during cycles. The comparison sample prepared by traditional drying assisted hydrothermal synthesis shows obvious agglomeration, lower discharge capacity and worse rate performance. Freeze drying-assisted hydrothermal synthesis method will be potential in synthesizing homogeneous composites of transitional metal oxides/rGO as high performance anode materials for lithium ion batteries.

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Preparation of high-rate double-layer carbon-coated silicon matrix composite
Xiaohui LI, Beihai CHEN, Ganjie CHEN, Yuewei ZHANG, Jing WANG, Lingxian GU
2020, 9 (4):  1052-1059.  doi: 10.19799/j.cnki.2095-4239.2020.0081
Abstract ( 78 )   HTML ( 3 )   PDF (2205KB) ( 27 )  

Silicon, which is the anode material of lithium-ion batteries, has become a popular research topic owing to its ultrahigh theoretical specific capacity of 4200 mA·h/g. However, the volume of silicon-based materials changes significantly during lithium removal. The expansion and contraction rates become 300%, causing the electrode materials to collapse during charging and discharging and considerably reducing the life cycle of a battery. To resolve this problem, a hydrothermal method is developed to obtain double-layer graphene and carbon-coated silicon for achieving a three-dimensional (3D) conductive network structure. The experimental results show that the silicon/carbon/graphene three-layer structure exhibits an excellent electrochemical performance (e.g., ultralong cycle life and high charge-discharge ratio) as the negative electrode material of the lithium-ion batteries. An electrode having this structure that has been charged and discharged 50 times with a current density of 0.2 A/g has a specific capacity of more than 2469 mA·h/g. When 300 charging and discharging cycles are achieved, a current density of 2 A/g realizes a specific capacity of more than 1500 mA·h/g. The specific capacity remains constant at 471 mA·h/g; however, an excellent recovery ability and rate performance can be observed under a super-large current density of 32 A/g, indicating that the 3D conductive network structure composite material increases the strength, toughness, and conductivity of the original material. Therefore, the method and design of composite materials can considerably inhibit the volume effect of silicon as a negative material, which significantly impacts the research and development of lithium-ion battery electrode materials.

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Study on the effect of electrode lugs arrangement on the performance of AGM lead-carbon batteries
Weiguo HUANG, Pengwei WANG, Li CHEN, Zhibin XU, Zhixue ZHOU, Xiaowei LIU, Qingshan WANG, Yan LI
2020, 9 (4):  1060-1065.  doi: 10.19799/j.cnki.2095-4239.2020.0029
Abstract ( 26 )   HTML ( 1 )   PDF (4829KB) ( 10 )  

In this study, the charge-discharge curves, battery capacities at different temperatures, gas evolution at different voltages, and deep circulation performance of the AGM lead-carbon batteries having two different arrangement modes of electrode lugs (i.e., same side and opposite side) are investigated. The positive active materials before and after the cycle were characterized using SEM and XRD, and a LANHE CT2001D battery cycle performance tester was used to verify the battery performance. Results show that the electrode lug arrangement considerably influences the performance of the lead-carbon batteries. When compared with the same-side arrangement, the opposite-side arrangement of the electrode lugs improves the battery’s discharge platform, delays the softening of positive active materials, and increases cycle life. Additionally, the amount of hydrogen produced by the battery on the opposite side of the electrode lugs was mostly less than that produced on the same side under different voltages. The higher the voltage, the greater will be the discrepancy in gas evolution. This study will provide reference and guidance for achieving further optimization of the lead-carbon battery structure.

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Crystallographic and electrochemical hydrogen storage properties of Sm substitute Nd for La0.5Nd0.35-xSmxMg0.15Ni3.5 alloys
Xin ZHAO, Dandan KE, Liqiang JI, Feng HU, Ying CAI
2020, 9 (4):  1066-1073.  doi: 10.19799/j.cnki.2095-4239.2020.0068
Abstract ( 48 )   HTML ( 1 )   PDF (1777KB) ( 12 )  

The Nd in the La0.5Nd0.35Mg0.15Ni3.5 alloy has been substituted with Sm to improve the performance to price ratio. Herein, the phase structures, morphologies, and hydrogen storage properties of the La0.5Nd0.35-xSmxMg0.15Ni3.5 alloys are studied using different methods. The Rietveld analysis pattern showed that the phase composition of the alloys containing multiphase structures, including the major phases (i.e., A2B7 and A5B19) and the residual phase (i.e., AB5), remained unchanged after the partial substitution of Sm instead of Nd. Increasing the content of the substituted Sm (x=0-0.30) changes the phase abundance, causing the A2B7 and A5B19 phases to increase before decreasing, whereas the AB5 phase showed the reverse trend. The a-axis parameter, c-axis, and unit cell volume of the major phases and the residual phase gradually decreased with the increasing Sm content. Further, the electrochemical properties of the alloy electrodes were improved by substituting Nd with Sm. The maximum discharge capacity of the alloy electrodes initially increased from 334.6 mA·h/g(x=0)to 346.5 mA·h/g (x=0.20). Then, it decreased to 331.1 mA·h/g(x=0.30). The high-rate dischargeability at a discharge current density of 2000 mA/g(HRD2000)initially increased from 41.4%(x=0) to 63.8% (x=0.20). Subsequently, it decreased to 52.1% (x = 0.30). The cycling capacity retention rate at the 100th cycle monotonically increased from 65.6% (x = 0) to 69.2% (x = 0.30), which should be attributed to the improvement in corrosion resistance of the alloy electrodes during the charge-discharge cycle.

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Effects of the charge-discharge cold cycles on performance of the rock materials
Guoyue LI, Xipeng LIN, Liang WANG, Yifei WANG, Long PENG, Haisheng CHEN, Ningning XIE
2020, 9 (4):  1074-1081.  doi: 10.19799/j.cnki.2095-4239.2020.0067
Abstract ( 58 )   HTML ( 3 )   PDF (2417KB) ( 27 )  

Natural rocks are cryogenic energy storage materials and exhibit a wide suitable temperature range, low cost, and easy availability. Their thermophysical properties and cycle stabilities in cryogenic temperature regions are key factors that affect the performance of the cold storage units. An experimental bench of automatic charge and discharge was designed and constructed to explore the effects of the charge-discharge cold cycles on the properties of the cryogenic energy storage materials. The effects of 1000 charge-discharge cold cycles on the thermophysical properties and strengths of four types of natural rocks (i.e., marble, granite, limestone, and basalt) are studied. Results show that the appearance of marble, basalt, and limestone before and after the charge-discharge cold cycles remains unchanged. However, granite shows some cracks and peelings. The density, thermal conductivity, and specific heat of the rocks were not significantly affected after 1,000 charge-discharge cold cycles. The compressive strengths of marble and basalt are unchanged, and the compressive strengths of granite and limestone are observed to significantly improve. Based on the experimental results, the relations between the thermal conductivity and specific heat of four rock materials and the temperatures in the cryogenic interval from cryogenic to normal temperatures were obtained. Comparative analysis shows that the volume energy storage densities of the four types of rock exhibit a considerable difference. Limestone has the largest volume energy storage density, whereas granite has the smallest volume energy storage density. This research will provide important basic data for developing cryogenic energy storage units and systems.

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Heat storage characteristic and structure optimum inrectangular unit
Huilin ZHOU, Yan QIU
2020, 9 (4):  1082-1090.  doi: 10.19799/j.cnki.2095-4239.2020.0035
Abstract ( 45 )   HTML ( 2 )   PDF (4541KB) ( 43 )  

The melting process of paraffin wax in rectangular unit is simulated by using FLUENT software. The effects of different upper geometry sizes and different wall temperatures on the melting process of different rectangular units are studied separately. The criterion relations between the liquid fraction β and the dimensionless number Fo, Ste, and Ra are obtained by nonlinear fitting. The scheme and basis are provided for optimizing the overall melting rate of PCM (phase change material) in the rectangular unit. The results show that, during the paraffin melting process, the time proportion of natural convection as the dominant heat transfer method increases first and then decreases as the size of the upper part of the rectangular unit increases. The enhancement of heat transfer by natural convection increases with the increase of the unit upper size. However, the average heat storage rate first increases and then decreases with the increase of the upper size of the unit until it tends to be stable, and there is an optimal value. During the paraffin melting process, the time proportion of natural convection as the dominant heat transfer method increases first and then decreases as the size of the upper part of the rectangular unit increases. The temperature difference is one of the key factors affecting the melting of PCM. The temperature difference is increased from 43 °C to 53 °C, and then from 53 °C to 63 °C, as a consequence of this, the melting time is shortened by 14.63% and 24.26% respectively.

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Forced convection heat transfer characteristics in a circular tube with low-melting-point quaternary nitrate
Chunyu ZHANG, Hang GUO, Yuting WU, Cancan ZHANG, Fang YE, Chongfang MA
2020, 9 (4):  1091-1097.  doi: 10.19799/j.cnki.2095-4239.2020.0020
Abstract ( 53 )   HTML ( 1 )   PDF (1273KB) ( 19 )  

The forced convection heat transfer characteristics of a low-melting-point quaternary nitrate in a tube-type heat exchanger are studied under different conditions to verify the applicability of the classical convection heat transfer correlation in this case. Based on the heat transfer experiment of the molten salt in the inner tube and the heat transfer oil on the shell side of the tube-type heat exchanger, the inlet and outlet temperatures of the molten salt and heat transfer oil in the test section of the tube-type heat exchanger are obtained. Further, the total heat transfer coefficients of the molten salt and heat transfer oil are obtained. Using the Wilson separation method, the convective heat transfer coefficient on the molten salt side is obtained from the total heat transfer coefficient to study the convective heat transfer characteristics of molten salt in a circular tube. Results show that the Reynolds number of the low-melting-point quaternary salt is 1 × 104—5 × 104, the Prandtl number is 4.9—15.5, and the total heat transfer coefficient of the molten salt and the heat transfer oil is 670—1300 W·m-2·K-1 in the fully developed turbulent region. The convective heat transfer coefficient on the molten salt side is 2900—7800 W·m-2·K-1. Subsequently, the correlation between convection and heat transfer in case of the low-melting-point quaternary salt in the turbulent section of the tube is obtained according to the experimental data. By comparing the experimental data with the classical convection correlations, the classical convection correlation is observed to be still applicable to convection heat transfer in a tube containing low-melting-point quaternary nitrate. This study provides reference data for the practical application of molten salt in solar thermal power generation.

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Exothermic process and heat transfer of iron foam/paraffin composite phase change energy storage materials
Qian WAN, Luxi HE, Zhengbin HE, Songlin YI
2020, 9 (4):  1098-1104.  doi: 10.19799/j.cnki.2095-4239.2019.0280
Abstract ( 55 )   HTML ( 0 )   PDF (1940KB) ( 43 )  

As a phase change material (PCM), paraffin exhibits high energy storage density. However, its thermal conductivity is low. In this study, paraffin wax was used as the PCM, whereas iron foam was used as the thermal-conductivity-enhancing material. The heat transfer performance of two types of iron foam during the paraffin exothermic process was explored by preparing the iron foam/paraffin composite phase change energy storage material and conducting its exothermic process test. The results denote that iron foam can reduce the heat release time of paraffin and improve the heat release efficiency. The phase transition times of the iron foam/paraffin composite PCMs having thicknesses of 10 and 15 mm are reduced by 1/3 and 1/4, respectively, and the phase change heat release densities are reduced by 1.60% and 3.26%, respectively, whereas the phase change heat release rates are 1.44 and 1.27 times that of the corresponding control group. Simultaneously, during the heat release process of 15 mm iron foam/paraffin composite PCM, the relation between the convective heat transfer coefficient, phase transition time, and material temperature was simulated, and corresponding theoretical formulas were obtained. The simulated value obtained by this formula is similar to the measured value. Thus, this formula can be used to predict the convective heat transfer coefficient of composite PCMs under different heat release times or material temperatures.

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Thermal behavior of the nanoenhanced phase change materials
Lihui LIU, Yajing MO, Xiaoqin SUN, Jie LI, Chuanchang LI, Baoshan XIE
2020, 9 (4):  1105-1112.  doi: 10.19799/j.cnki.2095-4239.2020.0044
Abstract ( 53 )   HTML ( 0 )   PDF (2014KB) ( 24 )  

Highly conductive particles have been used to improve the thermal conductivity of phase change materials (PCMs). To investigate the influence of the type and concentration of nano-particles and dispersants on the heat transfer process of PCMs, nano graphite (NG) and nano coconut shell based-carbon (NC) were used in the study to improve the thermal conductivity of paraffin. Type T thermocouples were used to monitor the temperature variation during melting under different boundary temperatures in a climate chamber. Thermovision tests were conducted to illustrate the temperature distribution. It was found that nano-particles were able to enhance the heat transfer of PCMs. The heat transfer of the PCMs with NG outperformed the PCMs with NC under same concentration. However, the distribution of nano-particles within the PCMs was not uniform. Dispersant, especially oleic acid, was able to improve the distribution of nano-particles, resulting in the improvement of heat transfer of NePCMs. When the nano-particles distributed evenly in the PCMs, the heat transfer rate of NePCMs increased with increasing concentration.

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Energy Storage System and Engineering
Thermal runaway characteristics and mechanisms of Li-ion batteries for electric vehicles under nail penetration and crush
Huiyong XU, Yafei FAN, Zhiping ZHANG, Renzong HU
2020, 9 (4):  1113-1126.  doi: 10.19799/j.cnki.2095-4239.2020.0028
Abstract ( 117 )   HTML ( 2 )   PDF (3630KB) ( 128 )  

Thermal runaway of battery is an irreversible failure mode that can, in its most severe form, cause battery combustion and explosion, which can trigger the combustion of electrical vehicles, resulting in heavy loss of property and danger to human life. Therefore, it is considerably significant to study thermal runaway for understanding the failure mechanisms of the Li-ion batteries and improving the battery quality by optimizing the design to reduce the risk of battery combustion and explosion. Based on the electrical vehicle incident investigations, thermal runaway can be mainly attributed to mechanical abuse. In this study, the research progress with respect to the effects of nail penetration and crushing on the thermal runaway of the Li-ion vehicle batteries is summarized. In additional, the factors that influence the thermal runaway of Li-ion batteries are systematically analyzed, including battery materials and structures. Results show that under nail penetration and crushing, the battery charge states, internal structural design, and chemical systems considerably influence the thermal runaway results. Among them, the internal structural design and chemical systems of the batteries affect their thermal safety performance. Furthermore, mechanical abuses, such as nail penetration and crushing, trigger thermal runaway by causing large-scale internal short circuits in the batteries. Hence, rationalization proposals with respect to battery safety design have been proposed based on the related research results to avoid internal short circuits.

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The structural engineering for achieving high energy density Li-ion batteries
Xulai YANG, Zheng ZHANG, Yong CAO, Chengshi LIU, Xinping AI
2020, 9 (4):  1127-1136.  doi: 10.19799/j.cnki.2095-4239.2020-0147
Abstract ( 35 )   HTML ( 1 )   PDF (1354KB) ( 62 )  

Electric vehicle (EV) market has had an aggressive development in the last years, and Chinese market has more than 50% share of global capacity. However, there are still some important social barriers that must be overcome to get the expected BEV market penetration, mostly related to the cost, distance range capacity, charging time and infrastructure. Range anxiety is a key reason that consumers are reluctant to embrace EVs. To be truly competitive with gasoline vehicles, EVs should allow drivers to recharge quickly anywhere in any weather, like refueling gasoline cars, or carry more useful energies with high energy density lithium-ion batteries (LIBs). The need to improve performances and reduce costs of LIBs encourages different research strategies. In general, the methods toward achieving higher energy density LIBs can be summarized in two ways: ① the development of novel battery chemistries with higher specific capacity and ② the exploration of advanced battery configurations with increased electrochemical active material ratio via electrode architecture engineering. However, the novel battery chemistries have a long journey to be used industrially, structural engineering provides a feasible and universal way to further improve the energy density of LIBs without changing the fundamental battery chemistries. Recently the attention is focusing on increasing the electrodes areal capacity to enable the substantial reduction of the current collectors, porous separator, and electrolyte resulting in large gravimetric and volumetric energy density improvements as well as cost savings. Moreover, increasing electrode thickness and density is a most effective approach to achieve high energy density of LIBs, but high tortuosity and low wettability in the electrodes deteriorate the LIB performance, such power density and cycling life. Herein, we introduce various methods to create low tortuosity nanostructures, such as templating and micro fabrications, and the structural designs by adopting laser-structured or multi-layer coating technologies to realize a low tortuosity electrode in the commercialized LIBs are highlighted.

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Low temperature charging aging modeling and optimization of charging strategy for lithium batteries
Taihua WANG, Shujie ZHANG, Jingan CHEN
2020, 9 (4):  1137-1146.  doi: 10.19799/j.cnki.2095-4239.2020.0078
Abstract ( 91 )   HTML ( 2 )   PDF (2529KB) ( 64 )  

The aging of lithium-ion batteries in case of low-temperature charging and a control strategy for low-temperature charging should be investigated to promote the use of new energy vehicles in cold regions. Further, a multi-stress low-temperature charging aging model was established using a large number of low-temperature charging experimental data. By considering temperature as the main influencing factor, the influence of the charging cut-off voltage, rate, and cycle times with respect to battery aging was considered. A decay acceleration factor is introduced, and several charging stresses are combined to measure their effects on the model. By introducing the genetic algorithm to optimize the charging control strategy based on the charging voltage, charging to the cut-off voltage is divided into several stages. Each stage’s charging current becomes the genetic sequence of a genetic algorithm. The charge rate of aging and charging time are considered to be the optimization objectives, creating an iterative optimization procedure. The simulation results show that the low-temperature charging aging model exhibits high parameter estimation accuracy and that the charging control strategy can effectively reduce battery aging and the charging time. The charging strategy is verified using the designed charging controller, and the test results are identical to the simulation results. These experiments explore the law of influence of low-temperature charging on the battery-life decline, and the data, the aging model, and the charging strategy optimization method offer direct reference value.

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State of charge estimation of Li-ion battery based on adaptive extended Kalman filter
Jiabo LI, Meng WEI, Zhongyu LI, Shengjie JIAO, Min YE, Xinxin XU
2020, 9 (4):  1147-1152.  doi: 10.19799/j.cnki.2095-4239.2020.0071
Abstract ( 20 )   HTML ( 0 )   PDF (1687KB) ( 6 )  

The state of charge (SOC) of the Li-ion battery is an important parameter associated with a battery management system. However, when estimating the SOC, external factors, such as the accuracy of the measuring equipment and noise, can interfere and reduce the SOC estimation accuracy. In this study, an adaptive extended Kalman filter (EKF) is proposed to improve the estimation accuracy and stability of SOC. Compared with traditional EKF, the estimation error of our method can be controlled within 3%, demonstrating the validity of the proposed model.

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Battery state estimation of least squares support vector machinebased on particle swarm optimization
Yuyuan WANG, Jiabo LI, Fu ZHANG
2020, 9 (4):  1153-1158.  doi: 10.19799/j.cnki.2095-4239.2020.0075
Abstract ( 54 )   HTML ( 1 )   PDF (1294KB) ( 13 )  

As one of the important parameters of battery management system (BMS), it is very important to estimate SOC accurately. It is difficult to estimate SOC accurately because SOC is often affected by many factors such as voltage, current, charge discharge efficiency and so on. In order to improve the accuracy of SOC estimation, the least square support vector machine (LSSVM) based SOC estimation model for lithium-ion battery is proposed. The current, voltage and temperature of the battery are taken as the input vector and SOC as the output vector of the model. In order to better obtain the parameters of LSSVM model, an adaptive particle swarm optimization algorithm is proposed to optimize the parameters, so as to obtain a high-precision SOC estimation model. Compared with the PSO optimized LSSVM and support vector machine (SVM) neural network (NN), the accuracy error of SOC estimation of the proposed model is 1.63%, which proves the effectiveness of the algorithm.

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Three-vector-based model predictive current control for energy-stored quasi-Z-source PV inverter
Min’an TANG, Shangmei YANG, Xiyuan XU
2020, 9 (4):  1159-1166.  doi: 10.19799/j.cnki.2095-4239.2020.0039
Abstract ( 44 )   HTML ( 0 )   PDF (2762KB) ( 15 )  

In this study, a three-vector-based model predictive current control (MPCC) is proposed for an energy-storage quasi-Z-source inverter because of the low accuracy of MPCC that can be attributed to large current ripples. The current in a synchronously rotating coordinate system is considered to be the control variable, and six virtual voltage vectors are constructed according to the nearest three vectors principle; thus, the output voltage vector range of the inverter can cover any direction and amplitude. Then, the minimum current error principle with respect to the direct and quadrature axes is used to calculate the duration of each discrete voltage vector. Finally, the optimal voltage vector acting on the inverter is obtained via six current predictions. The simulation results show that the current distortion rate of this method is 2.92% less than that of the traditional MPCC. Furthermore, the current ripple is smaller, and the output performance of the inverter is superior.

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Simulation study of a battery discharge power balance system based on the external energy storage method
Zheng ZHENG, Weixing GAO, Xi ZHANG
2020, 9 (4):  1167-1177.  doi: 10.19799/j.cnki.2095-4239.2020.0016
Abstract ( 37 )   HTML ( 0 )   PDF (1986KB) ( 20 )  

Battery packs exhibit inconsistent charge-discharge rates during their work cycles because of the differences among single cells, resulting in low work efficiency, low energy utilization, and short service life. To resolve these issues, a positive balancing circuit is designed for the power battery of a flyback multi-winding transformer based on a supercapacitor. By considering the battery voltage and state of charge as the judgment control conditions, the supercapacitor, which is an external energy storage component, cooperates with the multi-winding transformer to balance the energy of the cell. Simulation results show that the equalization circuit and control strategy can effectively weaken the barrel effect during the work cycle of the battery pack, improving its working efficiency, endurance, and service life.

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Solar air conditioning system for automobiles based on thermoelectric refrigeration
Fang LOU, Hengyun ZHANG, Daochang XIE, Junliang LIU, Dewen MAO, Qifu SUN, Yuanjie LI
2020, 9 (4):  1178-1185.  doi: 10.19799/j.cnki.2095-4239.2020.0031
Abstract ( 49 )   HTML ( 2 )   PDF (1819KB) ( 29 )  

In this study, a solar air conditioning system for automobiles is experimentally investigated based on thermoelectric refrigeration. The proposed system can achieve independent power supply and regulate the temperature in a simulated compartment space. The system includes a solar panel, lithium batteries, and other energy supply devices as well as the air conditioning and refrigeration systems containing semiconductor thermoelectric chips. The batteries comprise 1 × 4 prismatic lithium iron phosphate batteries connected in series. The size of the simulation box is 400 mm× 400 mm× 400 mm, and six temperature sensors are placed in the box to measure the air temperature. The thermocouples and heat flow meters are installed on the side wall to measure the wall temperature and heat flow through the wall. Subsequently, an experiment is conducted to examine the solar air conditioner’s performance in case of TECs connected in series or parallel. Subsequently, the cooling curves are obtained, the heat flow across the side wall is measured, and the refrigeration coefficient is calculated for both the connections. Results show that when cooling is performed at the ambient temperature of 27 C for 30 min, the average temperature in the closed box can reduce to 18.3 °C. In a series connection, he average refrigeration coefficient is 1.03 and the effective refrigeration coefficient is 0.79 (excluding the heat flow on the side wall). In a parallel connection, the average temperature reduces to 16.7 °C and the average refrigeration coefficient and effective refrigeration coefficients are 0.38 and 0.28 (excluding wall heat flow), respectively.

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Energy Storage Test: Methods and Evaluation
Simulation analysis of flywheel energy storage beam pumping unit
Chuanjun HAN, Degao TIAN, Yong ZHOU
2020, 9 (4):  1186-1192.  doi: 10.19799/j.cnki.2095-4239.2020.0033
Abstract ( 63 )   HTML ( 10 )   PDF (2852KB) ( 12 )  

In this study, a mathematical model affecting the output power of the motor is theoretically deduced and a virtual prototype of a flywheel energy storage pumping unit is developed to investigate the influence of an energy storage flywheel on the performance of a beam pumping unit and the energy-saving effects. The feasibility of the proposed model is verified via ADAMS simulation analysis, and the effects of different transmission ratios and moments of inertia on the performance of the beam pumping units are discussed. Results show that the flywheel releases energy when the pumping unit works in the upstroke mode and absorbs energy when the pumping unit works in the downstroke mode. Therefore, the installation of an energy storage flywheel in a beam pumping unit could effectively reduce the initial torque of the motor and reduce the fluctuation amplitude with respect to the motor torque, power, and speed. The fluctuation amplitude of each parameter decreases with the increasing rotational inertia of the energy storage flywhee; however, the starting time of the motor will be prolonged to a certain extent. Based on the power consumption of the motor, the flywheel is observed to inhibit reverse power generation under different rotational inertias. Furthermore, the average power consumed by the motor will decrease with the increasing rotational inertia, improving the energy-saving effect of the beam pumping unit.

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SOC estimation of aging lithium battery based on adaptive CKF
Tao ZHENG, Li ZHANG, Yangcheng HOU, Wei CHEN
2020, 9 (4):  1193-1199.  doi: 10.19799/j.cnki.2095-4239.2020.0005
Abstract ( 47 )   HTML ( 1 )   PDF (1589KB) ( 14 )  

The state of charge (SOC) of a lithium battery is an important parameter associated with electric vehicle system management and energy control. During SOC estimation, the changes in battery parameters and aging problems will considerably affect the results. Therefore, the recursive least square (RLS) algorithm is used to identify the parameters of the lithium battery model and update the battery capacity. The SOC of the lithium battery can be estimated based on the cubature Kalman filter (CKF). Further, the SOC can be accurately estimated by combining RLS and CKF even though this causes the battery parameters to changes. The accuracy of the proposed algorithm can be verified by estimating the SOC of the lithium iron phosphate battery online.

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An improved battery state estimation based on support vector machine regression
Jiabo LI, Meng WEI, Zhongyu LI, Min YE, Shengjie JIAO, Xinxin XU
2020, 9 (4):  1200-1205.  doi: 10.19799/j.cnki.2095-4239.2020.0076
Abstract ( 41 )   HTML ( 2 )   PDF (1521KB) ( 10 )  

The state-of-charge (SOC) estimation of a lithium-ion battery is very important with respect to a battery management system (BMS). It is difficult to ensure SOC estimation accuracy because it cannot be measured directly. To improve the SOC estimation accuracy, a least squares support vector machine (LSSVM) is used to establish a relation among voltage, current, and SOC. Further, an improved LSSVM method for SOC estimation is proposed to reduce the SOC estimation accuracy because of the changing voltage and current. The voltage measurement, current measurement, and SOC estimation values of the previous time are considered to be the feedback quantities of the model, and the voltage and current values of the present time are considered to be the input quantities that can be used to estimate the current SOC. The experimental results show that the error of the proposed method is less than 1% when compared with LSSVM, verifying the effectiveness of the proposed method.

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SOC estimation of Li-ion batteries based on Gaussian process regression and UKF
Meng WEI, Jiabo LI, Zhongyu LI, Min YE, Xinxin XU
2020, 9 (4):  1206-1213.  doi: 10.19799/j.cnki.2095-4239.2020.0003
Abstract ( 17 )   HTML ( 0 )   PDF (3795KB) ( 5 )  

The high-precision state-of-charge (SOC) estimation of battery power capacity is the key technology associated with a battery management system, and its estimation accuracy directly influences the energy management efficiency and endurance mileage of electric vehicles. The traditional filter estimation method uses an estimation model and does not consider the accuracy model of a Li-ion battery. To solve this problem, an unscented Kalman filter (UKF) estimation method based on Gaussian process regression (GPR) is presented. GPR can be used to establish a measurement equation for an equivalent circuit model with limited training data, resulting in the connection of UKF and GPR. The proposed model optimally uses the data obtained via the tests and the current to estimate the SOC. The experimental results and comparative analysis of the UKF estimation method based on Gaussian process regression demonstrate the high prediction accuracy of the proposed algorithm during SOC estimation.

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Energy Storage Patent Analysis
Patent analysis of the high-specification and high-voltage lithium-ion battery technology
Dongdong SHENG, Haitao WANG, Yingjie SHI, Hong DU
2020, 9 (4):  1214-1219.  doi: 10.19799/j.cnki.2095-4239.2020.0066
Abstract ( 55 )   HTML ( 4 )   PDF (1254KB) ( 50 )  

Lithium-ion batteries are rechargeable batteries, the operation of which is dependent on the movement of the lithium ions between positive and negative electrodes. The high-specification and -voltage batteries exhibit various advantages such as good cycle performance, low self-discharge, no memory effect, high specific energy, and environmental protection. Thus, they have become the focus of current energy storage and battery research worldwide. In this study, the patent applications with respect to the geographic distribution of lithium-ion battery packs and the main global patent applicants were sorted based on the analysis of the patent application trends and the technical life cycles of the high-specification and -voltage lithium-ion battery packs. Subsequently, the patent layouts are analyzed to guide the relevant research units to effectively avoid patent disputes and reduce infringement risk in case of research and development. Furthermore, we promote technical innovation in key research and development directions through technical analysis.

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Energy Storage Education
Suggestions on university education on energy storage science and engineering majors
Qiang ZHANG, Xiaogang HAN, Hong LI
2020, 9 (4):  1220-1224.  doi: 10.19799/j.cnki.2095-4239.2020.0164
Abstract ( 26 )   HTML ( 2 )   PDF (1468KB) ( 19 )  

The Ministry of Education of China, Nation Development and Reform Commission and National Energy Administration announced a document on Feb.11, 2020 to set up a major course on energy storage in universities. This action is a milestone for the development of energy storage in China. We have proposed a series of courses and study plans, including training targets, requirements and course systems. We hope our suggestions are helpful for the universities which is building energy storage major. From this issue on, the journal “Energy Storage Science and Technology” sets up a column of Education on Energy Storage for the articles on the strategies, suggestions, experiences on online/offline education for students in colleges, universities, institutions as well as enterprises.

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