Modeling of steady‐state and transient thermal performance of a Li‐ion cell with an axial fluidic channel for cooling

Thermal management of Li‐ion cells is an important technological problem for energy conversion and storage. Effective dissipation of heat generated during the operation of a Li‐ion cell is critical to ensure safety and performance. In this paper, thermal performance of a cylindrical Li‐ion cell with an axial channel for coolant flow is analyzed. Analytical expressions are derived for steady‐state and transient temperature fields in the cell. The analytical models are in excellent agreement with finite‐element simulation results. The dependence of the temperature field on various geometrical and thermal characteristics of the cell is analyzed. It is shown that coolant flow through even a very small diameter axial channel results in significant thermal benefit. The trade‐off between thermal benefit and reduction in cell volume, and hence capacity due to the axial channel, is analyzed. The effect of axial cooling on geometrical design of the cell, and transient thermal performance during a discharge process, is also analyzed. Results presented in this paper are expected to aid in the development of effective cooling techniques for Li‐ion cells based on axial cooling. Copyright © 2014 John Wiley & Sons, Ltd.     

Research progress on safety of lithium ion battery electrolyte

锂离子电池的能量密度及其安全问题是限制其在电动汽车应用中的主要障碍。随着能量密度的不断提升,当务之急是有效解决锂离子电池的安全性问题。锂离子电池安全问题本质上与当前电解液中使用的高挥发性、易燃的有机溶剂有关。因此,本文主要从电解液的燃烧性角度,介绍了电解液在锂离子电池材料安全性方面的研究现状,包括阻燃添加剂、不燃性氟代有机溶剂、高浓度电解液及固液混合电解质的应用等,分析其对安全性能提升的机理,并对电解液的发展方向进行了展望。     

A novel multiobjective charging optimization method of power lithium‐ion batteries based on charging time and temperature rise

Power lithium‐ion batteries have been widely utilized in energy storage system and electric vehicles, because these batteries are characterized by high energy density and power density, long cycle life, and low self‐discharge rate. However, battery charging always takes a long time, and the high current rate inevitably causes great temperature rises, which is the bottleneck for practical applications. This paper presents a multiobjective charging optimization strategy for power lithium‐ion battery multistage charging. The Pareto front is obtained using multiobjective particle swarm optimization (MOPSO) method, and the optimal solution is selected using technique for order of preference by similarity to ideal solution (TOPSIS) method. This strategy aims to achieve fast charging with a relatively low temperature rise. The MOPSO algorithm searches the potential feasible solutions that satisfy two objectives, and the TOPSIS method determines the optimal solution. The one‐order resistor‐capacitor (RC) equivalent circuit model is utilized to describe the model parameter variation with different current rates and state of charges (SOCs) as well as temperature rises during charging. And battery temperature variations are estimated using thermal model. Then a PSO‐based multiobjective optimization method for power lithium‐ion battery multistage charging is proposed to balance charging speed and temperature rise, and the best charging stage currents are obtained using the TOPSIS method. Finally, the optimal results are experimentally verified with a power lithium‐ion battery, and fast charging is achieved within 1534 s with a 4.1°C temperature rise.     

Electrical‐thermal behaviors of a cylindrical graphite‐NCA Li‐ion battery responding to external short circuit operation

Large amount of heat generated during an external short circuit (ESC) process may cause battery safety events. An experimental platform is established to explore the battery electrothermal characteristics during ESC faults. For 18650‐type nickel cobalt aluminum (NCA) batteries, ESC fault tests of different initial state of charge (SOC) values, different external resistances, or different ambient temperatures are carried out. The test case of a smaller external resistance is characterized by a shorter ESC duration with a faster cell temperature rise, whereas the case of a larger external resistance will last for a longer duration, discharge more electricity, and terminate in a slightly higher temperature. The tested batteries of high initial SOCs generally have higher temperature rise rates, smoother changes at the output current/voltage curves, but a smaller discharged capacity. The batteries of low initial SOCs can be overdischarged by the ESC operations. At low temperatures, say 0°C, the ESC process outputs much less electricity than the process at high temperatures, eg, 30°C. The initial low temperature has little effect on reducing the battery overheat due to ESC operations. The battery thermal behavior is of hysteresis property; analysis of heat generations reveals the subsequent increase of battery surface temperature after the completion of ESC discharge is due to the battery material abusive reaction heats. It is found from analytical and numerical analyses that there can have approximately 30°C temperature difference between the battery core and its surface during ESC operations. The interruption of ESC operation is very probably caused by the high battery core temperature, which leads to the destruction of solid‐electrolyte interface (SEI) film.     

Studies on the standard of lithium ion battery electrolyte

电解液是锂离子电池关键技术之一,在正负极之间起着输送和传导电流的作用,是连接正负极材料的桥梁。它影响着电池的工作电压、能量密度和安全性能等。近年来随着正负极材料的技术进步,电解液为了实现与新材料的匹配,在组分上出现了很大变化,现有的锂电池电解液标准及相应的测试方法也需要进一步更新,才能实现产品的检验规范化和质量标准化。本文介绍了电解液的现状及发展趋势,分析了我国现有电解液相关标准的情况,并对新的电解液国标提出了建议。     

Research progress on cathode materials for high energy density lithium ion batteries

便携式电子设备的微型化、轻量化与电动汽车、电网储能设备的飞速发展,对高能量密度的锂离子电池的研发和性能表现提出了越来越高的要求。锂离子电池正极材料是锂离子电池的核心,其提供锂离子并参与电化学反应,因此改善正极材料性能是提高锂离子电池能量密度的关键。人们需要进一步研究开发成本较低、安全性更好的高能量密度新型锂离子电池正极材料。本文主要从提升正极材料的比容量和工作电压两方面介绍三元、富锂锰基材料和高电位镍锰酸锂等高比能量正极材料的介尺度结构设计、制备与性能调控研发进展。     

Study on electrochemical and thermal characteristics of lithium‐ion battery using the electrochemical‐thermal coupled model

The higher specific energy leads to more heat generation of a battery, which affects the performance and cycle life of a battery and even results in some security problems. In this paper, the capacity calibration, Hybrid Pulse Power Characteristic (HPPC), constant current (dis)charging, and entropy heat coefficient tests of chosen 11‐Ah lithium‐ion batteries are carried out. The entropy heat coefficient increases firstly and then decreases with the increase of the depth of discharge (DOD) and reaches the maximum value near 50% DOD. An electrochemical‐thermal coupled model of the chosen battery is established and then verified by the tests. The simulation voltage and temperature trends are in agreement with the test results. The maximum voltage and temperature error is within 2.06% and 0.4°C, respectively. Based on the established model, the effects of adjustable parameters on electrochemical characteristic are systematically studied. Results show that the average current density, the thickness of the positive electrode, the initial and maximum lithium concentration of the positive electrode, and the radius of the positive electrode particle have great influence on battery capacity and voltage. In addition, the influence degree of the internal resistance of the solid electrolyte interface (SEI) layer, the thickness of negative electrode, and the initial and maximum lithium concentration of the negative electrode on the capacity and voltage is associated with certain constraints. Meanwhile, the influences of adjustable parameters related to thermal characteristic are also systematically analyzed. Results show that the average current density, the convective heat transfer coefficient, the thickness, and the maximum lithium concentration of the positive electrode have great influence on the temperature rise. Besides, the uniformity of the temperature distribution deteriorates with the increase of the convective heat transfer coefficient.     

Sorting methods of lithium ion batteries consistency

锂离子电池因其高能量密度和长循环寿命而得到广泛应用.然而当多个电池通过串联或者并联成组时,电池组往往存在容量衰减过快,寿命较短的问题,这是由于电池单体之间的非一致性而造成的.如何利用简单,可靠的分选方法,筛选出性能尽可能一致的电池用来成组,对锂离子电池在大规模储能中的推广应用具有重要的科学与实践意义.该文综述了目前国内外锂离子电池一致性的分选方法,包括各方法的机理特点,并且简单介绍了作者课题组在这方面的研究进展.采用阻抗谱方法或许是建立准确,快速的评价体系和提高配对电池的一致性的有效分选方法.     

Charge/discharge characteristics of Li‐ion batteries with two‐phase active materials: a comparative study of LiFePO4 and LiCoO2 cells

A comparative study of LiFePO₄ and LiCoO₂ cells was conducted using two mathematical models to identify the physical characteristics of the two‐phase electrode compared with the single‐phase electrode under both charge and discharge conditions. First, the electrical conductivity of the LiFePO₄ electrode was examined applying a two‐dimensional electrical conduction model. The calculation results showed that the electrical conductivity of the LiFePO₄ electrode could be improved significantly by coating the LiFePO₄ particles with a conductive substance. Second, a modified physics‐based cell model was applied to simulate the phase‐change phenomena at the equilibrium boundary inside the LiFePO₄ particles. The cell performance using LiFePO₄ electrode was degraded significantly owing to the increase in ohmic loss and concentration loss caused by the low electrical conductivity and phase‐change characteristics of LiFePO₄ under high C‐rate conditions. The present model was validated with experimental data and showed good agreement. Copyright © 2016 John Wiley & Sons, Ltd.     

Surface modification of LiNi0.5Co0.2Mn0.3O2 cathode materials with Li2O‐B2O3‐LiBr for lithium‐ion batteries

LiNi_0.5Co_0.2Mn_0.3O₂ (NCM523) cathode material suffers from phase transformation and electrochemical performance degradation as its main drawbacks, which are strongly dependent on the surface state of NCM523. Herein, an effective surface modification approach was demonstrated; namely, the fast lithium‐ion conductor (Li₂O‐B₂O₃‐LiBr) was coated on NCM523. The Li₂O‐B₂O₃‐LiBr coating layer as a protecting shell can prevent NCM523 particles from corrosion by the acidic electrolyte, leading to a superior discharge capacity, rate capability, and cycling stability. At room temperature, the Li₂O‐B₂O₃‐LiBr–coated NCM523 exhibited an excellent capacity retention of 87.7% after 100 cycles at the rate of 1 C, which is remarkably better than that (29.8%) without the uncoated layer. Furthermore, the coating layer also increased the discharge capacity of NCM523 cathode material from 68.7 to 117.0 mAh g^?1 at 5 C. Those can be attributed to the reduction in the electrode polarization and improvement in the electrode conductivity, which was supported by electrochemical impedance spectroscopy and cyclic voltammetry measurements.     

Fundamental scientific aspects of lithium ion batteries (Ⅸ)----Nonaqueous electrolyte materials

电解质是锂离子电池的重要组成部分,它起着在正负极之间传输Li⁺的作用.因此,电解质的研究与开发对锂离子电池来说至关重要,然而综合性能优异,满足不同应用的电解液并不容易开发.本文简介了非水液体电解质的发展历史和基本性质,然后分别从锂盐,溶剂和添加剂方面进行论述,最后介绍了离子液体,凝胶聚合物电解质和高电压电解质,认为未来锂离子电池电解质要解决的问题有:电解液和电池的安全性,提高电解质的工作电压,拓宽其工作温度范围,延长电池寿命和降低成本.     

Niobium carbide/reduced graphene oxide hybrid porous aerogel as high capacity and long‐life anode material for Li‐ion batteries

Two‐dimensional material MXenes owing to their hydrophilic nature, surface termination, and high conductivity can be used in the energy storage device as an anode material. However, poor ion transfer and less available intercalating sites due to self‐stacking of MXene sheets prevent comprehensive utilization of their electrochemical properties. To resolve this problem, a facile method is introduced in this paper to disperse MXene sheets onto reduced graphene oxide sheets to form a porous structure by enhancing electrostatic interactions between two components, which can facilitate ion movement and provide access of ions to more intercalating sites. This hybrid material delivered a capacity of 357 mAh g^?1 at 0.05 A g^?1 as anode in case of lithium‐ion batteries. Furthermore, the hybrid material showed exceptional stability even after 1000 cycles at 1 A g^?1. Current work offers an easy approach for the synthesis of high‐performance niobium carbide‐based hybrid energy storage materials.     

A novel titania nanorods‐filled composite solid electrolyte with improved room temperature performance for solid‐state Li‐ion battery

Solid‐state batteries (SSBs) with room temperature (RT) performances had been one of the most promising technologies for energy storage. To achieve a chemical stable and high ionic conductive solid electrolyte, herein, a titania (TiO₂) (B) nanorods‐filled poly(propylene carbonate) (PPC)‐based organic/inorganic composite solid electrolyte (CSE) was prepared for the first time. It was found that by using TiO₂(B) nanorods, the ionic conductivity of the CSE membrane could be improved to 1.52 × 10^?4 S/cm, the electrochemical stable window was more than 4.6 V, and the tensile strength reaches 27 MPa with a strain less than 6%. The CSE was applied for SSB and showed excellent room temperature electrochemical performances. At 25°C, the LiFePO₄/CSE/Li SSB with 3%TiO₂‐filled CSE had the first cycle specific discharge capacity of 162 mAh/g with a capacity retention of 93% after 100 cycles at 0.3C. While the NCM622/CSE/Li SSB with 3%TiO₂‐filled CSE had the first specific discharge capacity of 165 mAh/g with a capacity retention of 88% after 100 cycles at 0.3C. The enhancement effect of TiO₂(B) nanorods could be ascribed that the rod‐like fillers provide more continuous Li‐ion transport path compared with nano particles, and the surface porosity and composition of TiO₂(B) nanorods could also improve the interfacial contact and Lewis acid‐base reaction sites between polymer and fillers. The TiO₂(B) nanorods‐filled CSE with high chemical stability, potential window, and ionic conductivity was promising to meet the requirements of SSBs.     

Computational study about the effect of electrode morphology on the performance of lithium‐ion batteries

Electrode morphology has significant influence on the performance of lithium‐ion batteries in that it controls electrical conductivity and electrode utilization by establishing electrical connectivity in the electrode. The present study investigates the effect of the electrode morphology on battery performance by combining two different mathematical models. First, a two‐dimensional, direct numerical simulation (DNS) model is introduced, which stochastically generates electrode morphology and calculates electrical conduction and electrode utilization. Various simulations are conducted to evaluate the effect of the active particle coating, conductive agent loading, particle size, and electrode compression by using the DNS model. Second, data acquired from the DNS model are applied to the blended‐electrode model to evaluate battery performance. Calculation result confirms that electrode morphologies have significant effects on both capacity and power of lithium‐ion batteries. Copyright © 2016 John Wiley & Sons, Ltd.     

Introducing the energy efficiency map of lithium‐ion batteries

The charge, discharge, and total energy efficiencies of lithium‐ion batteries (LIBs) are formulated based on the irreversible heat generated in LIBs, and the basics of the energy efficiency map of these batteries are established. This map consists of several constant energy efficiency curves in a graph, where the x‐axis is the battery capacity and the y‐axis is the battery charge/discharge rate (C‐rate). In order to introduce the energy efficiency map, the efficiency maps of typical LIB families with graphite/LiCoO₂, graphite/LiFePO₄, and graphite/LiMn₂O₄ anode/cathode are generated and illustrated in this paper. The methods of usage and applications of the developed efficiency map are also described. To show the application of the efficiency map, the effects of fast charging, nominal capacity, and chemistry of typical LIB families on their energy efficiency are studied using the generated maps. It is shown how energy saving can be achieved via energy efficiency maps. Overall, the energy efficiency map is introduced as a useful tool for engineers and researchers to choose LIBs with higher energy efficiency for any targeted applications. The developed map can be also used by energy systems designers to obtain accurate efficiency of LIBs when they incorporate these batteries into their energy systems.     

Experimental and numerical investigation of heat transfer in Li‐ion battery pack of a hoverboard

Li‐ion cells are used for energy storage and conversion in electric vehicles and a variety of consumer devices such as hoverboards. Performance and safety of such devices are severely affected by overheating of Li‐ion cells in aggressive operating conditions. Multiple recent fires and accidents in hoverboards are known to have originated in the battery pack of the hoverboard. While thermal analysis and measurements have been carried out extensively on large battery packs for electric vehicles, there is relatively lesser research on smaller devices such as hoverboards, where the extremely limited thermal management design space and the critical importance of user safety result in severe thermal management challenges. This paper presents experimental measurements and numerical analysis of a novel approach for thermal management of the battery pack of a hoverboard. Measurements indicate that temperature rise in cells in the pack can be as large as 30°C at 4C discharge rate, which, although unlikely to be a standard discharge rate, may result from a malfunction or accident. A novel thermal management approach is investigated, wherein careful utilization of air flow generated by hoverboard motion is shown to result in significant temperature reduction. Measurements also indicate the key role of the metal housing around the battery pack in thermal management. Measurements are found to be in good agreement with finite element simulations, which indicate that the battery pack can be cooled as effectively in presence of a perforated metal casing as without the casing at all. Experimental data and simulation model presented here offer critical insights into the design of hoverboard thermal management and may result in safer, high performance hoverboard battery packs.     

Tin‐based materials as negative electrodes for Li‐ion batteries: Combinatorial approaches and mechanical methods

Graphite has been used as the negative electrode in lithium‐ion batteries for more than a decade. To attain higher energy density batteries, silicon and tin, which can alloy reversibly with lithium, have been considered as a replacement for graphite. However, the volume expansion of these metal elements upon lithiation can result in poor capacity retention. Alloying the active metal element with an inactive material can limit the overall volume expansion and improve cycle life. This paper presents a summary of tin‐based materials as negative electrodes. After reviewing attempts to improve and understand the electrochemical behaviour of metallic tin and its oxides, the focus turns to alloys of tin with a transition metal (TM) and, optionally, carbon. To do so, a combinatorial sputtering technique was used to simultaneously prepare many different compositions of Sn‐TM‐based materials. The structural and electrochemical results of these samples are presented and they show that cobalt is the preferred TM to give optimal performance. Finally, a comparison of a Sn–Co–C negative electrode material prepared by a rapid quenching method (sputtering) with a material prepared by an economical milling method (mechanical attrition) is presented and discussed. Copyright © 2010 John Wiley & Sons, Ltd.     

The progress of novel binder as a non‐ignorable part to improve the performance of Si‐based anodes for Li‐ion batteries

In this review, we highlight recent achievements of polymer binders used for Si‐based anodes in Li‐ion batteries. We classify the polymer binders, depending on their polymer structures and the function on performances of Si‐based anodes, into 3 types: cellulose‐type, conductive‐type and self‐healing‐type binders. The relationship between polymer structures and enhanced electrochemical performances of Si‐based anodes is discussed in details. We investigate how the binders make an extraordinary improvement on the specific capacity, cycling stability and rate performances of Si‐based anodes. The reasons of the noticeable effect on Si‐based anodes especially the controlling of swelling during cycling are also researched. In a word, the main aim of this review is to analyze recent research achievements and propose perspectives of polymer binders used for Si‐based anodes in promising Li‐ion batteries.     

Thermal management of lithium‐ion batteries for electric vehicles

Thermal issues associated with electric vehicle battery packs can significantly affect performance and life cycle. Fundamental heat transfer principles and performance characteristics of commercial lithium‐ion battery are used to predict the temperature distributions in a typical battery pack under a range of discharge conditions. Various cooling strategies are implemented to examine the relationship between battery thermal behavior and design parameters. By studying the effect of cooling conditions and pack configuration on battery temperature, information is obtained as to how to maintain operating temperature by designing proper battery configuration and choosing proper cooling systems. It was found that a cooling strategy based on distributed forced convection is an efficient, cost‐effective method which can provide uniform temperature and voltage distributions within the battery pack at various discharge rates. Copyright © 2012 John Wiley & Sons, Ltd.     

Resistance exterior force property of lithium‐ion pouch batteries with different positive materials

Lithium‐ion pouch battery (LIPB) is widely applied in different engineering fields, such as electric vehicles, aeronautics, astronautics, and among others. However, few complete mechanical models with deformation field are presented to predict internal short circuit (ISC) and resistance exterior force property of LIPB under exterior loading. In the present research, the indentation theoretical models with sinusoidal shape function are established to investigate resistance exterior force property of batteries with different positive materials under different punch shapes loading. The effects of indentation displacement and deformation region on indentation force are carried out. By the comparison of indentation force, present theoretical and numerical results are consistent with previous experimental results. The indentation force increases with the punch radius increase, but decreases with the indentation displacement increase. On the basis of energy conservation law, it is concluded that LIPB is more likely to produce mechanical failure and ISC when normalized deformation region is greater than or equal to 0.4 and plastic strain energy ratio is greater than or equal to 1.5. In addition, from resistance exterior force property point of view, LIPB has a better property to resist external force when LiMnNiCoO₂, rather than LiCoO₂ and Nanophosphate, is used as positive material. The research provides a reference for assessing the safety of LIPB and selecting suitable positive material, which possesses high energy capacity and resistance exterior force property.