Ni/MH电池过充电过程热效应分析

论文采用二维热模型分析了圆柱型Ni/MH电池在过充电过程中的热效应.实验提供了更为精准的数据以建立精确的热模型.利用石英频率微量热仪对电池的热容量以及电池在不同电流过充电时的发热量和散热速率进行了测量,继而将散热速率曲线拟合成线性函数和三段不同的指数函数.线性阶段之后的散热过程符合数学微分表达式,这些表达式有助于理解过渡阶段和过充电阶段散热速率的变化规律.热传导方程中产热速率采用理论计算值.最后使用FEM模拟了电池在1C,3C,5C充电过程每一阶段末时刻的电池内部温度场分布,结果相对准确.     

The heat generation rate of nickel-metal hydride battery during charging/discharging

The heat generation rate of nickel-metal hydride battery is investigated during charging/discharging in this study. The heat capacity of 8 Ah cylindrical Ni-MH battery is measured using a large-scale calorimeter. An accelerating rate calorimeter is employed to provide an adiabatic environment for the battery. The generation rates of reaction heat, polarization heat, and combination heat are calculated through curve fitting. Results show that there exits a linear relationship between each generation rate of the three heat items and the charging/discharging currents. It is suggested that the ohm internal resistance of the battery needs to be as low as possible for reducing the ohm heat. In addition, it is better to avoid overcharging in the higher rate of 5 C for battery safety.     

Influence of accidental overcharging on the performance and degradation mechanisms of LiCoO<Subscript>2</Subscript>/mesocarbon microbead battery

The accidental overcharging is emulated in fully charged LiCoO₂/mesocarbon microbeads (MCMB) batteries through initial one-off overcharging and successive long-term normal cycling. The aging mechanism and effect of accidental overcharging on the performance of LiCoO₂/MCMB battery is studied by the electrochemical tests and physical characterizations. The result clearly shows that not all accidentally overcharged batteries should be discarded and the extent of the degradation is highly dependent on the overcharging cutoff voltages. Compared with the blank batteries, low overcharging cutoff voltages have almost no influence on the performance degradation during successive long-term normal cycling. Under this condition, the aging is primarily due to the consumption of active lithium. However, high overcharging cutoff voltages, even just one time, decay the battery. Furthermore, further cycling accelerates the aging and changes the aging mechanism of battery under normal operation condition. Under this condition, the surface structure destruction of the LiCoO₂ is revealed as the primary contributor to battery degradation, which is related to the dissolution and reduction of cobalt ions after overcharging at high cutoff voltages and successive long-term normal cycling.     

电压敏感性聚三苯胺修饰隔膜用于锂硫电池过充保护

本文以三苯胺为原料,通过化学氧化法制备了具有电压敏感性的聚三苯胺(PTPAn)并将其成功应用到锂硫电池隔膜上。电导率测试结果表明,PTPAn/聚丙烯(PP)隔膜的离子电导率达1.56 mS·cm^-1;循环伏安(CV)测试结果表明,PTPAn/PP隔膜在3.5–4.2 V内具有氧化还原峰。在0.1C倍率下,采用PTPAn/PP隔膜和空白PP隔膜的锂硫电池在经200周循环后,放电比容量分别为424.8和407.2 mAh·g^-1,库伦效率分别为99.38%和98.59%,倍率测试表明(0.1C、0.2C、0.5C、1C),采用PTPAn/PP隔膜的锂硫电池在不同倍率下放电比容量均高于采用空白PP隔膜的锂硫电池。与此同时,对采用PTPAn/PP隔膜的锂硫电池进行过充实验,在第4周过充时,充电比容量为843.1 mAh·g^-1,放电比容量为839.8 mAh·g^-1;第10周过充时,充电比容量为690.2 mAh·g^-1,放电比容量为669.2 mAh·g^-1。第16周过充时,电池的充电比容量为538.7 mAh·g^-1,放电比容量为512.9 mAh·g^-1。倍率过充测试表明,经过不同倍率过充实验后,采用PTPAn/PP隔膜的锂硫电池仍能正常工作,在1C倍率下过充,电池电压稳定保持在3.9 V,充电比容量为349.8 mAh·g^-1,放电比容量为328.7 mAh·g^-1。     

磷酸铁锂电池的热效应研究

以磷酸铁锂为正极材料,石墨为负极材料,制备了1865型磷酸铁锂电池,研究了该电池在绝热、隔热和自然散热条件下,不同大小电流充放电过程的热效应.研究结果表明,磷酸铁锂电池充放电过程中所放出的热量主要来源于不可逆发热,即电子、离子在传导过程中克服电池内部阻力所产生的热量.发热量与电流呈线性关系,随着电流的增大而增大.这些结...     

Preparation of Al/Ni Reactive Multilayer Foils and its Application in Thermal Battery

The conventional heating materials of thermal battery have the disadvantages of low combustion rate and less heat release, so it is necessary to develop new heating materials. Al/Ni Reactive Multilayer Foils (RMFs) is an ideal heat source due to its high heat release, fast burning speed and no gas generated during combustion. Al/Ni RMFs were prepared by magnetron sputtering, and the heat transfer process of thermal battery using Al/Ni RMFs as heating material was simulated by the COMSOL MULTIPHYSICS simulation. The Al/Ni RMFs combustion reaction mechanism with different Al/Ni ratios was proposed according to DSC and XRD results. The effects of Al/Ni atomic ratio of RMFs on the melting time of electrolyte were investigated, and the temperature distribution during the activation was obtained, indicating the rapid activation process of the thermal battery.     

全固态锂金属电池多物理场耦合下的电化学过程仿真模拟

基于COMSOL Multiphysics多物理场仿真软件对氮氧化锂磷(LiPON)基全固态锂金属电池进行有限元模拟. 使用3次电流分布、 稀物质传递、 固体传热与固体力学等接口实现了多物理场在固态锂电池体系内部的耦合, 并完成了对于全固态锂金属电池本身在给定物理参数的情况下实际运行的电化学性能仿真. 在此模型中, 电池在运作时的热管理以及应力分布均得到有效的计算. 利用锂金属负极表面沉积的数据分析得到了锂枝晶生长的可能原因. 结果表明, 全固态锂电池的容量衰减以及枝晶生长等安全管理的失控并不只是单一因素控制的结果; 体系的浓度梯度、 应力预分布、 传热传质过程的控速步骤与充放电过程的体积变化等都会对电池的性能与安全管理产生不同的影响.     

Influence of additives on the thermal behavior of nickel/metal hydride battery

This study discusses the thermal behavior of the 6.5 Ah cylinder Ni/MH hydride battery with 0.5 wt% ytterbium oxide (Yb₂O₃) in nickel electrode and 1.0 wt% super absorbent polymer (SAP) in hydrogen-storage alloy (MH) electrode during charging to 150% of its rating capacity. Quantity of heat and heat generation rate of the battery during charging are studied by quartz frequency microcalorimeter. Heat generation curve is fitted into a function, and heat transport equation is solved. Using measured data, the internal temperature profiles at the terminal moment of charging at 1C, 3C, and 5C are simulated by FEM. Influence of Yb₂O₃ and SAP on the thermal behavior of Ni/MH battery is examined by the two-dimensional thermal model. Results show that addition of Yb₂O₃ and SAP can achieve substantial improvement for thermal behavior of Ni/MH battery at 1C,3C, and 5C charging.     

Thermal behavior of nickel/metal hydride battery during charging and discharging

This work discusses thermal behavior of Ni/MH battery with experimental methods. The present work not only provides a new way to get more exactly parameters and thermal model, but also concentrates on thermal behavior in discharging period. With heat generation rate gained by experiments with microcalorimeter, heat transport equations are set up and solved. The solutions are compared with experiment results and used to understand the reactions inside the battery. Experiments with microcalorimeter provide more reliable data to create precise thermal model.     

New Li-ion Battery Evaluation Research Based on Thermal Property and Heat Generation Behavior of Battery

We do a new Li-ion battery evaluation research on the effects of cell resistance and polariza-tion on the energy loss in batteries based on thermal property and heat generation behavior of battery. Series of 18650 cells with different capacities and electrode materials are evalu-ated by measuring input and output energy which change with charge-discharge time and current. Based on the results of these tests, we build a model of energy loss in cells' charge-discharge process, which include Joule heat and polarization heat impact factors. It was reported that Joule heat was caused by cell resistance, which included DC-resistance and reaction resistance, and reaction resistance could not be easily obtained through routine test method. Using this new method, we can get the total resistance R and the polarization parameter η. The relationship between R, η, and temperature is also investigated in orderto build a general model for series of different Li-ion batteries, and the research can be used in the performance evaluation, state of charge prediction and the measuring of consistency of the batteries.     

Thermal runaway and fire behavior investigation of lithium ion batteries using modified cone calorimeter

The lithium ion battery has been widely used, but it has high fire risk due to its flammable materials. In this study, a series of combustion tests are conducted on the 18650-type lithium ion batteries using the modified cone calorimeter. The temperature and voltage variation of the battery, heat release rate and gas generation during combustion are measured in this study. The battery is heated evenly by the self-made heater, and the reliable trigger temperatures of thermal runaway are obtained for different states of charge (SOCs) batteries in this study. The fire behavior of the 100% SOC batteries is shown in this paper. The net heat absorption by the battery before thermal runaway is calculated based on the heat transfer theory. It ranges from 56.81 to 64.05 kJ for 0 to 100% SOC batteries, which shows a decreasing trend as SOC increases. The peak combustion heat release rate of 100% SOC batteries is 3.747?±?0.858 kW. CH₄ and CO gases are detected before and after thermal runaway. The generation of CO shows an increasing trend as SOC increases. Some suggestions on the early warning system of battery thermal runaway are proposed based on this study.

     

Effects of iron phthalocyanine on the inner pressure of MH/Ni battery

The inner gas pressure of the battery beyond 1.01 106 Pa can cause a release of gas from the safety valve for a normal sealed cell, leading to a drying out of electrolyte solution[1], and gradually decreasing the performance of the battery until finally destroying it. During overcharging, oxygen is produced rapidly on the nickel electrode, and it is necessary to eliminate the oxygen and restrain the rising speed of inner pres-sure so as to improve the performance of MH/Ni bat-tery. Phthalocy…     

Analysis of the heat generation of lithium-ion battery during charging and discharging considering different influencing factors

Operating temperature of lithium-ion battery is an important factor influencing the performance of electric vehicles. During charging and discharging process, battery temperature varies due to internal heat generation, calling for analysis of battery heat generation rate. The generated heat consists of Joule heat and reaction heat, and both are affected by various factors, including temperature, battery aging effect, state of charge (SOC), and operation current. In this article, a series of experiments based on a power-type lithium manganese oxide/graphite battery was implemented under different conditions. The parameters for Joule heat and reaction heat are determined, and the Joule heat, reaction heat as well as total heat generation rate is detailed and analyzed considering the influence of temperature, aging, SOC, and current. In order to validate the accuracy of heat generation rate, a lumped battery heat transfer model is applied to calculate the temperature variation, and the estimated temperature variation shows good correspondence with experimental results under different currents and aging conditions. Due to its simplicity, the temperature variation estimation method is suitable for real time applications.     

In-situ Study of Charge and Discharge of Ni-MH Battery Using the Combined Method of Electrochemistry and Microcalorimetry

An apparatus to study the battery system has been set up. The thermal effects of charge and discharge of Ni-MH batteries have been studied. The calorimetric measurements indicate that the net heat dissipation during charging is larger than that during discharging. It is observed that the ratio of heat dissipation to charging energy varies with charging capacity, and almost 90 percent of charging energy is lost as heat dissipation near the end of the charging process at 97.7 mA. A jump of thermal curve near the end of discharge due to a secondary electrode reaction has been observed.This revised version was published online in November 2005 with corrections to the Cover Date.     

A unique control strategy to improve the life cycle of the battery and to reduce the thermal runaway for electric vehicle applications

This paper presents a unique thermal control strategy to improve the ageing of the battery and to maintain the internal temperature of the battery within the optimum limit of 20 °C–40 °C for electric vehicle (EV) applications. The hybrid EV system encompasses photovoltaic (PV) module, high power density device supercapacitor (SC) and high energy density Li-ion battery (LIB) as an energy storage element. The vehicle dynamics encounter frequent voltage fluctuations in the direct current (DC) bus, which ultimately reduces the lifecycle of the battery and also the heat is generated inside the battery when it is connected in parallel to the DC bus. The frequent charging/discharging of LIB is controlled by the unique thermal control strategy of the hybrid EV system. The DC bus voltage is controlled by the SC bi-directional converter (BDC) where, the battery BDC delivers the essential constant current from the main source (PV) to the DC bus. This unique thermal control strategy supports the distribution of power from the PV/LIB/SC hybrid source system to the EV and also improves the battery life cycle. Due to constant charging/discharging of battery the thermal runaway (TR) problem such as leak, smoke, gas venting, rapid disassembly, flames etc., can be eliminated. Decoupling of load power and battery power comprises the growth in the battery lifecycle and to maintain the optimum internal temperature of the LIB by conditional flow of current through hybrid thermal management system (HTMS). To certify the thermal control strategy and to estimate the performance of HTMS, a simulation of a hybrid source system with vehicle dynamics is performed in MATLAB/Simulink. Numerical analysis of the LIB during constant charging/discharging is performed using ANSYS fluent software to validate the temperature effect of HTMS.

     

Numerical investigation on cooling performance of PCM/cooling plate hybrid system for power battery with variable discharging conditions

To solve the cooling problems of power battery with variable discharging conditions, a hybrid thermal management system combined with phase change materials (PCM) and cooling plate is designed. Moreover, the ANSYS FLUENT is adopted to simulate the three-dimensional model. As a result, the effects of water flow direction and variable discharging conditions are discussed on the maximum temperature and maximum temperature difference inside the battery as well as the liquid fraction of PCM. The numerical results indicate that the maximum temperature is governed by the physical parameters of PCM, whereas the water flow direction in the cooling plate plays a dominant role on the maximum temperature difference. Moreover, the flow direction scheme of case 5 is benefit to reduce the maximum temperature and temperature difference simultaneously. Although the cooling performance of hybrid thermal management system can be deteriorated by increasing the pulse duration and heat flux, the melting of PCM dramatically suppresses the increase in maximum temperature and temperature difference. Considering the limited quality of PCM, enhancing the thermal conductivity of PCM and employing cooling scheme with staggered flow direction are recommendable ways to extend the applicability of the hybrid thermal management system for power battery with complex discharging conditions.

     

Thermal Behavior Investigation of LiNi1/3Co1/3Mn1/3O2-Based Li-ion Battery under Overcharged Test

Thermal behavior of its components such as separator, electrolyte, cathode, anode, and each binder were investigated by differential scanning calorimetry and thermal gravimetric (DSC/TG) to explain thermal runaway mechanism of Li‐ion battery under overcharged test. DSC results indicated the decomposition reaction temperature of SEI (solid electrolyte interface) layer in anode was at about 126°C. It was found that heat generation in anode under normal charged state increased obviously with the increasing of charged voltage. When the battery was overcharged to 4.6 V or 5.0 V, the onset temperature and heat generation of thermal reaction in anode changed a little, while those in cathode had large increase. It was proposed that thermal behavior in cathode mainly caused by the reaction of electrolyte with evolutional oxygen played a key role to thermal runaway for the studied Li‐ion battery under overcharged test.     

Experimental study of the heat generations of Li/SOCl2 and Li/SO2 batteries using a phase-change measurement method

A paraffin phase-change measurement method for the heat generation of spirally wound cylindrical Li/SOCl₂ and Li/SO₂ batteries at different ambient temperatures and discharge currents is proposed. The electrical and thermal insulations of the measurement system have been greatly improved, and the accuracy of the measurement system is 4.6 % based on calibration experiments. Compared with accelerated rate calorimetry, isothermal microcalorimetry, and radiation calorimetry methods, the phase-change measurement method is simpler, but with a high accuracy. The experimental results reveal that the heat generation of the batteries during discharge is weakly dependent on the ambient temperature in the range of 38–50 °C, but strongly affected by the discharge current. As the discharge current increases, the heat generated by the Li/SOCl₂ and Li/SO₂ batteries increases as a quadratic polynomial function. The Li/SO₂ battery generates more heat than the Li/SOCl₂ battery at the same discharge current, which is demonstrated by the qualitative analysis of the internal resistance. Furthermore, the phase-change measurement method for heat generation has a strong universality, and can be applicable for heat generation measurement of various battery types.     

Overcharging of nanoparticles in electrolyte solutions

Monte Carlo simulations are performed to investigate the effects of salt concentration, valence and size of small ions, surface charge density, and Bjerrum length on the overcharging of isolated spherical nanoparticles within the framework of a primitive model. It is found that charge inversion is most probable in solutions containing multivalent counterions at high salt concentrations. The maximum strength of overcharging occurs near the nanoparticle surface where counterions and coions have identical local concentrations. The simulation results also suggest that both counterion size and electrostatic correlations play major roles for the occurrence of overcharging.     

导热塑料的研究与应用

随着科学的进步导热塑料应用领域不断扩大,尤其近些年来蓬勃发展的信息产业,为导热塑料提供了新的发展空间.本文对比了高分子材料、金属材料及金属氧化物导热性能,介绍了聚合物的导热机理,并对不同填充含量可适用的导热模型进行了介绍.讨论了提高塑料导热性能的途径和近年来提高导热性能新的研究方法,对非绝缘导热塑料、绝缘导热塑料的应用研究和最新进展作了综述,提出了导热塑料目前存在的问题,展望了导热塑料的应用前景.