【作者】 李文成；

【导师】 卢世刚；

【作者基本信息】 北京有色金属研究总院 ， 有色金属冶金， 2011， 博士

【摘要】 锂离子动力电池在电动汽车上具有广泛的应用前景,电池的寿命、热行为和安全是电动汽车用锂离子动力电池的关键性能指标。磷酸铁锂动力电池具有寿命长、热稳定性高、安全性好和成本低等优点,被认为是最有应用前景的电动汽车用锂离子动力电池种类之一。本文以制备长寿命、高安全性的电动汽车用磷酸铁锂动力电池为目标,首先研制了不同结构、容量的磷酸铁锂动力电池,并对其充放电性能、安全性能进行了测试,研究了电池结构对电池性能的影响；其次分析了电池的循环性能规律并通过电化学、XRD、SEM和EDS测试方法分析了电池的容量衰减机理；然后运用能量守恒原理仿真分析了电池的热行为,最后研究了充放电方式对电池组性能的影响。采用磷酸铁锂为正极材料,石墨为负极材料研制了圆柱形卷绕结构的13Ah、100Ah和120Ah,方形卷绕结构的9Ah,方形叠层结构的300Ah五种类型的高比能车用锂离子动力电池,其中9Ah和120Ah电池分别实现批量和小批量生产。研究了电池的初始充放电性能和倍率放电性能。结果表明：在小电流放电情况下,电池的容量主要取决于正、负极材料的特性及其负极/正极材料的设计容量比,放电平台电压的变化与电池的结构有关,采用圆柱形结构的电池充放电平台电压差要小于方形结构的电池。随着放电倍率的增加,电池的放电容量、放电平台电压与电池结构及额定容量有关,在电池额定容量相当的情况下,方形结构的9Ah电池和圆柱形结构的13Ah电池的放电容量没有明显差异,13Ah电池的倍率放电性能优于9Ah电池；在相同电池结构、不同电池额定容量的情况下,大容量的120Ah电池的容量衰减速度、放电平台电压的下降幅度均高于13Ah电池,欧姆压降对大容量电池放电平台电压的影响更为明显。对电池的比能量、高低温性能、贮存性能和安全性能进行了测试,结果表明：电池的比能量在100-120Wh/kg之间；13Ah电池55℃高温和-20℃低温放电容量分别是室温放电容量的98.9%和47.9%,电池搁置一年后电池的荷电保持率为71%,其容量恢复率为92%；120Ah和13Ah电池在安全测试中电池未燃烧、未爆炸。采用磷酸铁锂为正极材料、石墨为负极材料的动力电池具有良好的综合性能。研究了五种磷酸铁锂动力电池循环性能。结果表明：电池特性(容量、放电电压等)衰减服从相同的规律,可以分为二个阶段,第一阶段性能衰减缓慢,表现出负极钝化膜增长的特征,第二阶段性能衰减加速,表现出负极表面金属锂沉积的特征。将循环1785周的13Ah电池拆解,分析了正、负极片的容量、结构和组成分析,结果表明：循环后的正极容量保持85%,其容量衰减小于实际电池的容量衰减,循环后正极片还保持完整的橄榄石型结构,其表面形貌与未循环正极片相差不大；负极石墨容量的衰减快于正极LiFePO4容量的衰减,循环后期负极容量损失严重,极片表面的局部区域沉积了金属锂,表面形貌变化很大。第二阶段电池容量、电压的变化与负极有很大关系。研究了电池不同放电电流下的温度变化规律,结果表明：随着放电电流的增加,表面温度变化速度加快,温度逐渐升高。在相同的放电时间里,电池表面温度的变化与放电电流呈抛物线关系,在整个放电过程中电池表面温度的变化与放电电流近似线性。对13Ah电池的热行为进行了分析,结果表明：13Ah电池0.3C、1C、2C和3C放电时总平均产热率分别为0.47W、2.04W.6.04W和11.85W,其中不可逆阻抗热的平均产热率为0.4W,2.0W,6.0W,11.8W。电池内部产热以不可逆阻抗热为主,电池反应的可逆热所占比例很小。小电流放电时,电池表面温度的下降与电池反应的可逆热有关。对300Ah、120Ah、13Ah和9Ah磷酸铁锂动力电池的温度进行仿真分析,结果表明：300Ah、120Ah、13Ah和9Ah电池的比热容分别为2.7JK-1g-1、1.8JK-1g-1、1.8JK-1g-1和1.5JK-1g-1,电池组成、电池壳体材质等对电池比热容有一定的影响。电池总热容、电池与外界的热交换系数对电池表面温度的变化趋势有较大影响。最后研究了充放电方式对13Ah电池组(4只串联)性能的影响。结果表明：串联电池组采用单体电池充放电截止电压的倍数控制电池组的充放电电压的上限和下限,在充放电末期极易引起某只电池的过充或过放。充电时,低容量的电池最先达到截止电压。放电时,大容量的电池最先达到放电截止电压的几率较大。当电流足够大时,内阻大的电池有可能最先达到放电截止电压；将充放电电压范围缩小至11.6-14.2V,采用恒流充放电方式,电池组能够放出额定容量的85%,1C恒流充放电循环900周容量保持85%,电池没有出现过充和过放的现象；电池组循环900周,充电末期电池间的电压差基本没有变化,放电结束时电池间的电压差随循环次数的增加逐渐扩大,容量较小电池电压有增大的趋势,容量较大电池电压则逐渐减小；13Ah电池组短路和挤压试验中,电池组不燃烧、不爆炸,电池组具有良好的抗滥用性能。更多还原

【Abstract】 Lithium-ion power battery has a broad application prospect in electric vehicles where battery life, thermal behavior and safety are key factors. The lithium iron phosphate power battery with long life, high thermal stability, good safety and low cost, is considered one of the most promising lithium-ion power batteries for electric vehicles. This dissertation is targeted at the preparation of the LiFePO4 battery with long life and high safety for electric vehicles. Firstly, the LiFePO4 batteries with different structures and capacities were prepared, and their performances of charge-discharge and safety were tested to study the influence of battery structure on battery performance. Secondly, the cycle performance of battery were analyzed and their capacity fading reasons were tested by the analysis methods of electrochemical, XRD, SEM and EDS. Thirdly, the battery thermal behaviors were simulated using the principle of energy conservation. And finally, the influence of charge-discharge methods on the properties of the battery module has been studied.Using lithium iron phosphate as cathode material, graphite as anode material, the five types of high specific energy Lithium-ion power battery for electric vehicles with cylindrical winding structure for 13Ah,100Ah and 120Ah batteries, square winding structure for 9Ah battery, square laminated structure for 300Ah battery were developed. In the five batteries, the 9Ah and 120Ah battery has been produced in mass production and small quantities, respectively. The performances of initial charge-discharge and large current discharge were studied. The results showed that:the battery capacity depends on the characteristics of the positive and negative materials and the ratio of the design capacity of anode/cathode material when the discharge current is low. The change of discharge plateau voltage was related to the structure of battery, and the difference of charge plateau and discharge plateau of the cylindrical battery is less than that of the square battery. With the discharge rate increasing, the battery discharge capacity and discharge voltage are related to its marked capacity and structure. When the marked capacity of battery was close, the discharge capacities with the square 9Ah battery and the cylindrical 13 Ah battery were not different significantly, but the performance of rate discharge with 13 Ah battery was better than that with 9Ah battery. In the case of same cell structure and different marked capacity, the rate of capacity fading and the decrease of discharge plateau voltage of 120Ah battery are higher than those of 13 Ah battery. For the large capacity battery, the influence of ohmic voltage drop on the discharge plateau voltage is more obvious. The battery’s specific energy, high and low temperature performance, storage performance and safety were tested. The result showed that:the specific energy was between 100-120Wh/kg; for the 13Ah battery, the discharge capacities in 55℃and-20℃were 98.9% and 47.9% of that in room temperature, respectively. The charge retention rate was 71% at room temperature for one year and the capacity recovery rate was 92%. The 120Ah and 13Ah batteries neither explode nor catch fire in the safety test. The Lithium-ion power battery with lithium iron phosphate as cathode material, graphite as anode material has a good combination performance.The cycle performances of five types of lithium iron phosphate power battery were studied. The test results showed that:the fading of battery characteristics (capacity, discharge voltage, etc.) have the same trends which can be divided into two stages. In the first stage, the performances fade slowly, showing a characteristic of the passive film growth in the negative electrode. In the second stage, the performances fade fast, showing the characteristic of lithium deposition in the surface of negative electrode. The study on structures and performances of 13Ah batteries with no cycling and the 1785th cycle showed that:the rate of capacity retention of positive electrode is 85% after cycling which is less than that of battery. The positive electrode after cycling also maintain the integrity of the olivine structure, and its surface morphology are not significantly changed with before cycling; the rate of capacity fade of graphite anode was faster than that of LiFePO4 cathode. In the end of cycling, the capacity of negative electrode lost seriously, and in some place, the lithium was desposited, its surface morphology is significantly changed. The changes of capacity and voltage in the second stage have a great relationship with negative electrode.The analysis on the surface temperature of five categories of lithium iron phosphate battery during discharge showed that:the surface temperature changes faster and the temperature gradually increased when the discharge current increases. The relationship of the surface temperature rising and the discharge current is parabolic at the same discharge time, but the surface temperature rising at the end of discharge is a liner relationship with the discharge current. The analysis on the thermal behavior of 13Ah battery showed that: the total heat generation at 0.3C,1C,2C and 3C rate is about 0.47W,2.04W,6.04W and 11.85W and the average value of irreversible resistive heating at 0.3C,1C,2C and 3C rate is about 0.4W,2.0W,6.0W and 11.8W, respectively. Inside the battery, the irreversible resistive heating is major heat generation source, and the proportion of reversible entropic heat is very small. At low discharge current, the surface temperature drop was dominated by reversible entropic heat. The temperature simulation results of 300Ah,120Ah,13Ah and 9Ah lithium iron phosphate power battery show that:the specific heat capacity of 300Ah,120Ah,13Ah and 9Ah battery were 2.7 JK-1g-1,1.8 JK-1g-1,1.8JK-1g-1 and 1.5 JK-1g-1, respectively. Battery components, battery case material and other will exert some influences for the specific heat capacity of the battery. The total heat capacity of the battery, the battery and the external heat exchange coefficient has a greater impact on the trend of the surface temperature of battery.Eventually, the influences of the charge and discharge mode on the performances of 13 Ah battery module (four series) were analyzed. If the upper and the lower voltage of the series battery module equal the single battery charge and discharge cut-off voltage multiply number the battery number, respectively, the over-charge and over-discharge could easily occur in the end of charge and discharge, The low capacity battery reached firstly cut-off voltage during the charge process. The chance that the large capacity battery reached cut-off voltage during the discharge process is greater. When the current is large enough, the battery of larger resistance may be first to reach cut-off voltage. In the voltage range of 11.6-14.2V, the capacity of battery pack is 85% of marked capacity with constant current charge and discharge. After 900 cycles with 1C at room temperature, the capacity retention rate of 13Ah battery module capacity is 85%. During cycling, the over-charge and over-discharge didn’t occur. Before the 900 cycles, the difference of battery voltage in the end of charge unchanged. In the end of discharge, the difference of battery voltage increased with cycles. The smaller capacity battery voltage increased, and the larger capacity battery voltage is decreased. In short-circuit and compression test, the battery pack is not burning, no explosion, the battery pack has a good anti-abuse properties.更多还原