【摘要】：動力電池作為電動汽車的核心技術(shù),其動力性與經(jīng)濟(jì)性的改善和提升一直都是研究重點,但是受冷卻結(jié)構(gòu)、材料以及布置空間與使用條件的限制,容易導(dǎo)致電池在工作中產(chǎn)熱累積而引發(fā)熱安全問題,顯然,這已成為了限制動力電池可持續(xù)發(fā)展的技術(shù)瓶頸。因此,亟需開展關(guān)于動力電池在不同工況條件下的熱力學(xué)—電化學(xué)特性行為的研究,從本質(zhì)上了解和掌握電池的工作性能,有助于分析和預(yù)測電池的熱行為,并為電池?zé)峁芾碓O(shè)計與相關(guān)控制策略提供合理可靠的參考依據(jù)。本文分析了鋰離子單體電池在正常放電條件下、內(nèi)部短路以及高溫環(huán)境下三種不同機(jī)制工況條件下的產(chǎn)熱特性和荷電特性。首先基于電池電化學(xué)機(jī)理,建立了片狀鋰離子電池單體的物理模型,分析了電池溫度場、內(nèi)部電流分布、電化學(xué)熱以及焦耳熱的變化機(jī)理,建立了更加系統(tǒng)全面的鋰電池仿真分析。鋰電池單體正常放電條件下的仿真結(jié)果表明:在絕熱環(huán)境下,電池放電倍率直接影響電池單體的平均溫升速率和溫勻性。隨著放電倍率的增大,電池溫升速率增加,溫度均勻性變差。在絕熱環(huán)境下,電池初始溫度直接影響電池單體的溫均性,初始溫度越低,電池單體的溫均性越差,當(dāng)初始溫度較高時,電池平均溫升速率增加,電池工作溫度很快超出合理的工作范圍。荷電狀態(tài)的不同也會影響電池平均溫度的變化,荷電量較少的電池,其溫度升高速率越快。通過分析與總結(jié)諸如短路深度、短路位置、短路截面積以及荷電狀態(tài)等不同因素對鋰離子電池單體工作特性的影響規(guī)律,得出如下結(jié)論:隨著短路深度的增加以及短路截面積的增大,短路區(qū)域的最高溫度以及最大電流會隨之增大。相比于電池中心部位發(fā)生內(nèi)部短路,當(dāng)電池邊緣區(qū)域發(fā)生內(nèi)部短路時,短路區(qū)域的最高溫度顯著增加。另外,當(dāng)電池發(fā)生內(nèi)部短路時,隨著電池的荷電量增加,電池短路區(qū)域最高溫度隨之升高。在內(nèi)部短路發(fā)生過程中,放電倍率對電池短路區(qū)域最高溫度影響作用較小。最后,本文建立了電池置于高溫環(huán)境下的熱濫用模型,分析了溫度變化和表面對流傳熱系數(shù)變化對電池單體特性的影響。仿真結(jié)果表明:當(dāng)電池在較低的環(huán)境溫度下工作時,電池單體僅體現(xiàn)出溫升特性,并不會觸發(fā)電池內(nèi)部各材料的分解副反應(yīng);當(dāng)環(huán)境溫度到達(dá)某一個高溫點時,電池會出現(xiàn)急劇的溫升現(xiàn)象,即觸發(fā)了電池內(nèi)部材料分解的熱失控副反應(yīng);隨著環(huán)境溫度的升高,電池內(nèi)部材料分解的熱失控副反應(yīng)的觸發(fā)時間點會提前。另外,在高溫環(huán)境下,電池表面等效傳熱系數(shù)較低時有利于抑制電池?zé)崾Э胤磻?yīng)的發(fā)生;而較高的電池表面等效傳熱系數(shù),會使電池?zé)崾Э貭顟B(tài)提前觸發(fā)。
[Abstract]:As the core technology of electric vehicles, the improvement and upgrading of power performance and economy is always the focus of research, but it is limited by cooling structure, materials, layout space and use conditions. It is easy to cause thermal safety problems due to the accumulation of heat in battery production. Obviously, this has become the technical bottleneck that limits the sustainable development of power battery. Therefore, there is an urgent need to study the thermodynamics and electrochemical characteristics of power batteries under different operating conditions, to understand and master the working performance of the batteries in essence, and to help to analyze and predict the thermal behavior of the batteries. It also provides reasonable and reliable reference for battery thermal management design and related control strategies. In this paper, the thermal and charging characteristics of Li-ion single cell under normal discharge, internal short circuit and three different operating conditions of high temperature mechanism are analyzed. Firstly, based on the electrochemical mechanism of the battery, the physical model of the single cell was established, and the variation mechanism of the cell temperature field, internal current distribution, electrochemical heat and joule heat was analyzed. A more systematic and comprehensive simulation analysis of lithium battery is established. The simulation results show that under adiabatic environment, the discharge rate of lithium battery directly affects the average temperature rise rate and temperature uniformity. With the increase of discharge rate, the temperature rise rate increases and the temperature uniformity becomes worse. In adiabatic environment, the initial temperature of the cell directly affects the temperature homogeneity of the cell. The lower the initial temperature, the worse the temperature uniformity of the cell. When the initial temperature is high, the average temperature rise rate of the cell increases. The battery temperature quickly exceeds the reasonable working range. The change of the average temperature of the battery is also affected by the different state of charge. The faster the increase rate of the temperature is when the charge is low. By analyzing and summarizing the influence of different factors such as short circuit depth, short circuit position, short circuit cross section and charge state on the performance of lithium ion battery, The conclusions are as follows: with the increase of the short circuit depth and the short circuit cross section, the maximum temperature and the maximum current in the short circuit region will increase. Compared with the inner short circuit in the center of the battery, the maximum temperature of the short circuit region increases significantly when the inner short circuit occurs in the edge region of the battery. In addition, the maximum temperature of the short circuit region increases with the increase of the battery charge. In the process of internal short circuit, the discharge rate has little effect on the maximum temperature in the short circuit region of the battery. Finally, the heat abuse model of the battery under high temperature is established, and the effects of temperature change and surface convection heat transfer coefficient on the cell characteristics are analyzed. The simulation results show that when the battery is working at a lower ambient temperature, the cell only exhibits the characteristics of temperature rise and does not trigger the decomposition side effects of various materials in the battery, and when the ambient temperature reaches a certain high temperature point, There will be a sharp temperature rise in the battery, that is, the thermal runaway side reaction of material decomposition in the battery will be triggered, and with the increase of the ambient temperature, the trigger time of the thermal runaway side reaction of the material decomposition in the battery will be advanced. In addition, at high temperature, the lower surface equivalent heat transfer coefficient of the battery is conducive to inhibit the occurrence of the thermal runaway reaction, and the higher surface equivalent heat transfer coefficient of the battery will trigger the heat runaway state of the battery ahead of time.
【學(xué)位授予單位】：吉林大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2017
【分類號】：TM912

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