NCR18650A电池的充放电温度特性与管理

采用实验测试与数值仿真的方法对NCR18650A三元锂电池组在1 ~ 3 C放电和1.6 C充电过程的温升特性进行测试,同时验证所建立电池产热模型的准确性。结果显示,实验测试结果与电池产热模型仿真结果之间的相对误差在合理范围内,满足工程应用需求。电池组在自然冷却的情况下,仅在1 C放电状态下符合其最佳工作区间42.5 ~ 45.0℃的要求,3 C放电倍率下最高温度为89.4℃。提出并建立基于热电致冷主动热管理模型,将热电致冷组件设置在电池组上方,致冷功率为50 W时可有效控制电池组3 C放电过程的温度,在最佳工作区间实现电池单体温差小于5℃,抑制电池组的热失效并实现良好的均温性。     

Plate flat heat pipe and liquid‐cooled coupled multistage heat dissipation system of Li‐ion battery

A thermal management system with the capability of achieving excellent heat dissipation is essential to the development of battery pack for transportation devices. To meet the temperature uniformity requirements of the battery pack, the plate flat heat pipe and liquid‐cooled coupled multistage heat dissipation system had been introduced. In this article, the research status of thermal management systems in battery pack was introduced. And the heat generation and heating power of the Li‐ion cell were studied. Then, the structure model of plate flat heat pipe system was proposed. Finally, the enhanced heat conduction effect of the thermal management system proposed in this article was comprehensively analyzed. Through the analysis of the results, in high discharge rates, the thermal management system proposed in this article could meet the temperature uniformity requirements of battery pack; also, the internal difference would reduce by 30.20%.     

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.     

Research on the heat dissipation performance of lithium‐ion cell with different operating conditions

This paper aims to research the thermal power of lithium‐ion cell with different operating conditions. A 55‐Ah lithium‐ion cell is selected as the research object. Experiment and simulation are chosen as the methods to research the temperature distribution and thermal power of the cell under different conditions. Combining with the thermal power of cells, this paper also researches the heat dissipation performance of battery pack under different operation conditions. The results indicated that average thermal power of a 55‐Ah lithium‐ion cell decreases along with the increase of ambient temperature and the decrease of state of charge and charge and discharge rates. The results achieved through simulation and experiment are consistent, so simulation could be used to research the temperature distribution of cell during charge and discharge. As considering the longitudinal battery pack with steady analysis, high temperature area is in the centre, and the temperature of air inlet is relatively low. The airflow mostly passes the top of battery pack but not through both sides. As considering the longitudinal battery pack with transient analysis, the temperature rise of battery pack is evidently higher than the inner temperature difference by studying three operating conditions (sustained deceleration, sustained acceleration and pulsed discharge). The curves of temperature rise and inner temperature difference rise along with sustained acceleration of the electric vehicle; therefore, even if the electric vehicle begins to decelerate, the fan must still work until the temperature of battery pack decreases. Then, the references are given for researching thermal characteristic during charge and discharge of the cell and the heat dissipation analysis of battery pack. Copyright © 2017 John Wiley & Sons, Ltd.     

动力电池微细通道散热数值分析研究

动力电池对温度敏感度高,高温散热实现难度较大,尤其是极端环境温度和高倍率放电下。设计了一个微细通道电池液冷散热系统,针对系统进行不同放置方式、环境温度、冷却液入口温度、入口流速的影响研究。发现竖直方式电池组可获得较好的温度分布;环境温度变化对电池组温度变化影响较小;电池组温度与冷却液入口温度基本呈线性变化,冷却液入口流速增加可显著降低电池组最高温度,提高温度均匀性。最后对流道进行尺寸优化,增大高度是较好的优化方案。     

基于COMSOL的锂离子电池热失控仿真与防控

动力电池是新能源汽车关键部件,为进一步探究其热失控机理及影响因素,总结热失控发展过程,利用COMSOL软件构建锂离子电池单体模型,结合仿真实验结果详细分析其影响因素,并提出一款利用隔热罩、隔热盖板、隔热底座和可滑动扩容盒延缓热失控效果的可延缓热失控的汽车电池包。研究结果表明：热失控过程大致分为加热阶段、喷射和燃烧阶段、熄灭阶段,受4种副反应产热影响;在超过445.08 K的高温环境下,长时间工作的锂离子电池易发生热失控,失控热源关键在正极活性材料与电解液分解反应;当电池实际温度超过500 K时,温度若无法及时控制将导致火灾事故发生;同时,对流传热系数越高,电池温度变化越快;初始温度越高,热失控可能性越大。     

Experimental and numerical studies on air cooling and temperature uniformity in a battery pack

In this paper, a passive technique is examined by adding an inlet plenum to reduce the maximum temperature and improve temperature uniformity in a simple battery pack. The inlet plenum changes the direction of the flow and dramatically reduces the issues of air recirculation and dead‐air regions between adjacent cells. The dimensions of the plenum and Reynolds number were optimized to enhance cooling and temperature uniformity at the cell and pack level. The results indicated that by increasing the Reynolds number to 7440, the maximum temperature decreased by 18.3% and the temperature uniformity increased 54.6%. However, there was no significant change in the maximum temperature and temperature uniformity beyond the Reynolds number of 7440. The developed battery pack achieved the desired temperature uniformity at the cell and pack level to less than 5°C.     

Numerical investigation on integrated thermal management for lithiumion battery pack with phase change material and liquid cooling

为满足3 C放电倍率下电池组散热要求,提出了PCM\液冷复合式散热方案,利用有限元分析了液体流速、流道排列方式、铝制框架鳍宽和环境温度对电池组温度的影响。结果表明,增加流速可优化电池组散热性能,但当流速大于0.08 m/s时,流速的增加对散热系统无明显优化;各流速下Type I散热方式效果均为最优且电池组满足散热要求;鳍宽为2 mm时可将电池组最高温度进一步降低1.6℃;当环境温度从38℃增至42℃时,复合式散热系统体现了良好的热稳定性能。     

Numerical study on thermal behavior and a liquid cooling strategy for lithium-ion battery

Investigation on the thermal behavior of the lithium-ion battery which includes the temperature response, heat contribution and generation, is of vital importance for their performance and safety. In this study, an electrochemical-thermal cycling model is presented for a 4 Ah 21700 type cylindrical single cell and 3× 3 battery pack and the model is validated by experiment on a single cell. Thermal behavior on a single cell is first analyzed, the results show that the heat generated in the charge is smaller than the discharge, and the polarization heat contributes the most to total heat, especially under higher rate. It can also be concluded from the battery pack that the temperature of the cell inside the battery pack is significantly greater than the external battery, while the temperature difference exists the opposite regular due to the worst heat dissipation of the central cell. Finally, after taking the enhanced liquid cooling strategy, the maximum temperature is 320.6 K that is reduced by 9.38%, and the maximum temperature difference is 4.9 K which is reduced by 69.6% at 2C, meeting the requirements of battery thermal management system.     

Thermal modeling and cooling analysis of high-power lithium ion cells

The heat generation model and three-dimensional computational fluid dynamics model for lithium ion cells were established with boundary conditions defined.In order to provide a better insight about the behaviors of high-power lithium ion cells under realistic discharge conditions,the temperature difference of the cells and an active thermal management system with a pure air-cooling mode were analyzed and predicted with the factors affecting the unevenness of temperature field discussed.The results show a significant effect of the cooling flow rate on the temperature rise of the cells for all discharge rates.Average surface temperatures are relatively uniform at lower discharge rate that makes it easier to control the temperature of the pack.Cell temperatures are expected to rise significantly toward the end of discharge and they show non-uniformity at higher discharge rates.Adequate air flow rate of active cooling is required at high discharge rate and high ambient temperature for practical pack thermal management system.     

动力锂电池组非稳态射流强化换热数值模拟

为动力锂电池组设计了通风冷却系统,在控制总通风量的前提下,研究了非稳态射流对动力锂电池组的冷却效果,针对26650型锂电池组射流冲击方案进行数值模拟分析,揭示非稳态射流送风周期、送风变化量对电池组温升和温度均匀性的影响。研究结果表明:冲击射流的非稳态特性改善了电池组温度场的均匀性,对电池组总温升影响不明显。     

Experimental investigation on thermal performance of silica cooling plate‐aluminate thermal plate‐coupled forced convection‐based pouch battery thermal management system

The power battery as an indispensable part of electric vehicle has attracted much attention in recent years. Among these, the lithium‐ion battery is the most important option due to the high energy density, good stability, and low discharge rate. However, the thermal safety problem of lithium‐ion battery cannot be ignored. Therefore, it is very necessary to explore an effective thermal management system for battery module. Here, a thermal silica cooling plate‐aluminate thermal plate (SCP‐ATP) coupling with forced convection air cooling system as a thermal management system is proposed for improving the cooling performance of pouch battery module. The results reveal that the heat dissipating performance and temperature uniformity of pouch battery module with SCP‐ATP are greatly improved compared with other thermal management systems. Moreover, the highest temperature can be controlled below 50°C, and the temperature differences can be maintained with 3°C when the SCP‐ATP coupling forced convection is utilized to enhance the heat transfer coefficient. Furthermore, considering the cooling effectiveness and consumption cost comprehensively, the optimal air velocity of the SCP‐ATP coupling forced convection cooling system is 9 m/s. In addition, the SCP‐ATP filling with different proportions of acetone has also been investigated for pouch battery module, indicating that 50% acetone exhibited a better heat transfer effect than the 30% one. Therefore, this research would provide a significant value in the design and optimization of thermal management systems for battery module.     

Analysis of Heat Dissipation Performance between a Horizontal and Longitudinal Battery Pack Based on Forced Air Cooling

A battery pack is the main energy storage element, and directly affects the performance of an electric vehicle. Battery thermal management system research and its development for a modern electric vehicle is required. This paper selects the forced air cooling of battery pack as the research object, and uses simulation methods to research the heat dissipation performance with different structures of battery packs. The results indicate that according to the four types of transient state conditions, the rising temperature of both battery packs are significantly higher than the temperature difference, the maximum temperature rise and temperature difference of a horizontal battery pack are lower than a longitudinal battery pack. When an electric vehicle begins to decrease speed, the curves of temperature rising and temperature difference increase. This shows the internal heat is continuously rising, so even in a electric vehicle beginning to decrease speed, the fan must work. The reference basis for choosing battery pack type and an analysis of heat flow field characteristics, including fan run‐time control, are offered.     

Research on heat dissipation performance and flow characteristics of air‐cooled battery pack

With the depletion of fossil fuels and the aggravation of environmental pollution, the research and development speed of electric vehicles has been accelerating, and the thermal management of battery pack has become increasingly important. This paper selects the electric vehicle battery pack with natural air cooling as the study subject, conducts simulation analysis of the heat dissipation performance of battery packs with and without vents. Then this paper researches on the influence of internal flow field and external flow field. Field synergy principle is used to analyze the effect of velocity field and temperature field amplitude. The results show the following: it is found that the maximum temperature rise and the internal maximum temperature difference of the battery pack with vents are reduced by about 23.1% and 19.9%, raising speed value can improve the heat dissipation performance, and raising temperature value can decrease the heat dissipation performance. Reasonable design of the vents can make the inner and outer flow field work synergistically to achieve the best cooling effect. Then the reference basis for the air cooling heat dissipation performance analysis of electric vehicle, battery pack structure arrangement, and air‐inlet and air‐outlet pattern choosing are offered.     

Experimental study of a direct evaporative cooling approach for Li-ion battery thermal management

A desirable operating temperature range and small temperature gradient is beneficial to the safety and longevity of lithium-ion (Li-ion) batteries, and battery thermal management systems (BTMSs) play a critical role in achieving the temperature control. Having the advantages of direct access and low viscosity, air is widely used as a cooling medium in BTMSs. In this paper, an air-based BTMS is modified by integrating a direct evaporative cooling (DEC) system, which helps reduce the inlet air temperature for enhanced heat dissipation. Experiments are carried out on 18650-type batteries and a 9-cell battery pack to study how relative humidity and air flow rate affect the DEC system. The maximum temperatures, temperature differences, and capacity fading of batteries are compared between three cooling conditions, which include the proposed DEC, air cooling, and natural convection cooling. In addition, a DEC tunnel that can produce reciprocating air flow is assembled to further reduce the maximum temperature and temperature difference inside the battery pack. It is demonstrated that the proposed DEC system can expand the usage of Li-ion batteries in more adverse and intensive operating conditions.     

Novel investigation strategy for mini-channel liquid-cooled battery thermal management system

Many researchers have focused on liquid-cooled devices with simple structure and high efficiency, which promoted the gradual development of the mini-channel liquid-cooled plate battery thermal management system (BTMS), due to the advancement of liquid cooling technology. This paper has proposed an electrochemical-thermal coupling model to numerically predict the thermal behavior of the battery pack in different parameters of mini-channel cold plates and optimize the parameter combinations. The effects of cooling plate width, mini-channel interval, and inlet mass flow rate on the heat dissipation performance of the system were analyzed at a constant C-rate to provide a reliable experimental basis for the optimization model. Results indicate that increasing the cold plate width and the inlet mass flow rate reduce the temperature and temperature gradients. In addition, the minimum temperature difference is obtained at the mini-channel interval of 6 mm. The optimum cooling plate width (90 mm), mini-channel interval (4 mm), and inlet mass flow rate (80 g/s) are determined using the orthogonal test, analysis of variance, and comprehensive analysis of multi-index results. The addition of an auxiliary cooling system based on the optimized combination further reduces the maximum temperature and temperature difference of the battery pack by 4.9% and 9.2%, respectively. The developed strategy and methods can further improve the performance of the BTMS and provide a reference for the development of a compact battery pack at high discharge rates for engineering applications.     

车用锂离子电池液冷式热管理系统实验研究

锂离子电池组的热管理对电动汽车的性能和安全性具有重要意义。基于多通道蛇形波纹管液冷式热管理系统,以200个18650型锂离子电池组为热管理对象,对电池在各种充放电倍率下所需的冷却液流量、泵功消耗以及热管理收益进行了实验研究。结果表明,热管理系统对动力电池在各种充放电应用条件下都具有较好的热管理效果,电池最大温度和最大温差基本可控制在40℃以下和5℃以内。提高冷却水流速对系统热管理能力的提升具有一定的效果,但是随着流速增大,热管理能力提升的边际效益也更趋明显;而系统运行所消耗的泵功增加导致了热管理收益随冷却水流速增加而大幅降低。从电池的性能安全以及热管理有效性的角度综合考虑,各充放电倍率下热管理系统的冷却水流速都是以保证电池安全和性能指标的最低流速为优。     

Nonlinear coupling between thermal mass and natural ventilation in buildings

An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h.     

Heat dissipation analysis and optimization of the pure electric bus lithium-ion battery pack based on CFD

针对某纯电动客车电池箱散热效果不佳的问题,本文基于CFD技术以该车的电池箱散热系统为研究对象,建立了估算锂离子电池生热速率数学模型,采用三维软件UG建立电池箱的几何模型,并利用软件Star-ccm+对该模型的速度场和温度场进行仿真和分析。通过添加导流板等措施,对电池箱的结构进行了优化改进,并进行了正交仿真实验,确定了电池箱导流散热的最优方案,结果表明,导流板能够降低电池箱内单体电池的最高温度,使电池组温度分布更加均匀。     

圆柱形锂离子电池热管理实验研究

保持合适的运行温度是锂离子电池高效、安全、长寿命的保证,因而对其进行有效的热管理是非常有必要的。本文针对圆柱形锂离子电池,设计了嵌套电池表面的方形金属外壳,以强化电池散热和单体电池间传热。对比自然对流条件下电池单体加壳和无壳时不同放电倍率的温升情况、多个电池并联的温升情况,以及不同通风功率下多个电池并联时嵌套不同外壳的温升情况,发现加壳可以有效促进电池（组）散热。另外,设计了电池组内不同单体电池出现放电不均衡情况,以检验嵌套外壳对减小电池组内单体电池间温差的效果,结果表明,自然对流条件下,加壳后单体电池间最大温差可以降低10℃以上。