【作者】 谭俐；

【导师】 郑洪河；

【作者基本信息】 苏州大学 ， 凝聚态物理， 2013， 硕士

【摘要】 磷酸铁锂电池具有安全性高、循环寿命长、环境友好等突出的优点，是最有希望成为电动汽车电源的候选者之一。然而，要作为动力电池使用还需要进一步提升电池的循环寿命，解决电池在高温下容量迅速衰减的问题，这需要对磷酸铁锂电池容量衰减规律和机理进行深入研究。影响磷酸铁锂电池容量衰减的主要相互作用：铁溶解和锂离子消耗成为研究磷酸铁锂电池容量衰减的主要内容。本文中使用商业化的磷酸铁锂电池材料来研究其在电解液中的溶解规律，综合考虑温度、时间、电解液溶剂、电解液溶质以及正极的充电状态这五个影响因素对铁溶解的影响。发现高温、与电解液接触时间变长以及电池处于高充电状态下时电解液中的铁溶解量会增加，而使用不同的锂盐和不同溶剂对其在电解液中的溶解影响较小。分别研究了18650型磷酸铁锂电池在的循环状态下和放置状态下的容量衰减规律。在不同温度下循环LiFePO₄电池中，60℃下循环的电池容量衰减迅速，循环寿命比在25℃循环的电池缩短了约55%，在电池循环的大部分时间内，各温度下电池容量基本呈现线性衰减；在放置状态下，100%充电状态下的LiFePO₄电池容量衰减最快,随着充电状态的降低，电池的容量衰减速度变缓。对LiFePO₄电池的容量衰减分析发现，电池的正极容量并没有降低，只是在第一次脱锂过程中缺少了一部分锂离子，并且正极缺失的锂离子的比例与电池容量衰减的比例基本吻合，这说明磷酸铁锂电池容量衰减的主要原因在电池中可循环的锂离子被消耗。使用ICP定量分析了磷酸铁锂电池中的负极对立离子的消耗，发现负极中的锂离子含量与正极中的锂离子缺失有着一致的对应关系。电池容量的损失、正极中锂离子损失和负极中锂离子含量这三者的对应关系充分说明了磷酸铁锂电池的容量衰减的主要原因是电池中可循环的锂离子不断被负极消耗。更多还原

【Abstract】 Lithium-ion phosphate battery is one of the most promising candidate power sourcesfor electrical vehicles with the outstanding advantages such as high safety, long cycle lifeand environmentally friendly. However, the cycle life must be further improved and therapid capacity fade problem at high temperature must be solved before its automotiveapplication, which need intensive study on the capacity fade behavior and relatedmechanism in lithium-ion phosphate battery. Iron dissolution and lithium consumption aretwo of the main interactions which lead to capacity fade, hence becoming the main contentof the study.In this thesis, commercial LiFePO₄cathode material was used to study irondissolution behavior in electrolytes. Up to five factors involving temperature, time,solvents, lithium salts and the states of charge of the cathode were used to comprehensivelyevaluate the behavior and mechanisms of iron dissolution. The results suggest evaluateelevated temperature, longer electrolyte residence time and high sate of charge of thecathode can increase iron dissolution, while the kinds of electrolyte solvents and lithiumsalts have smaller influence.Capacity fade behavior of18650style LiFePO₄battery under cycle and steady statewas studied respectively. Batteries cycled at different temperatures showed different cycleperformances. Rapid capacity fade was observed at60℃and the cycle life shortenedabout55%compared with the cell cycled at25℃，and all the capacity fade curvesdelivered linear decreasing trend during most of the test time. On standing condition, thecell charged to100%state of charge suffered severe capacity fade, with the decrease of thecharging status, the capacity fade slowed down. Based on the analysis on the capacity fade of the LiFePO₄batteries, we found that thecapacity of the cathode maintained, while a part of lithium inventory was lost during thefirst de-intercalation process, and the lost amount of lithium inventory in the cathodescorrelated well with the capacity fade of the LiFePO₄battery. A quantitative study of thelithium content in the negative electrode was carried out by ICP, and it was amazing to findthat the lithium content in the negative electrode correlated well with the lithium inventoryloss of the cathode. The consistent relationship between capacity fade of the cell, thelithium inventory lose in the cathode and lithium consumptions in the anode fully showsthat the loss of recyclable lithium which was consumed in the anode is the main cause ofthe capacity fade in LiFePO₄battery.更多还原