快充型锂离子电池的性能研究

发布时间：2018-02-10 03:03

  本文关键词： 快充 极化 电池制作工艺 改性 L333三元材料　出处：《江西理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：本文拟开发一种快充型锂离子电池,以LiCoO2为正极材料,石墨为负极材料,设计400mAh的软包电池,并分析了大电流充电条件下电池的电化学性能、电极材料结构与形貌的变化规律、电池热效应等。研究了电池制作工艺参数对快充性能的影响规律。另外,对L333-石墨的快充体系进行了初步研究,重点研究了L333晶体形貌对快充性能的影响。通过充放电测试、交流阻抗(EIS)及电化学循环测试研究了锂离子电池在大电流充电条件下的电化学性能变化规律,发现锂离子电池在大电流充电过程中正负极存在较大的极化,严重影响电池的快充性能,减小极化能够提高电池大电流充电性能,降低电池内阻能够有效减少电池电极极化现象,为此,研究了不同导电剂及其掺入比例、电池制作工艺等的对电池快充性能的影响。结果显示:正负极配料制浆过程中,导电剂与电极活性物质的均匀性与加入比例对电极电阻有影响,当导电剂加入比例加入量在4%时,电池综合性能最佳。在0.2C电流作用下形成的SEI膜内阻相对较小且稳定,在一定程度上改善了极化程度,性能稳定的SEI膜对后期循环性能具有很大的影响。电极材料的面密度越小,大电流充电时电池的极化越小,循环稳定性较好,正极面密度为153g/m2时,6C倍率充电循环1700次后容量保持率仍有80%。当正极材料的压实比为3.6g/cm3时,电池的极化及内阻最小,循环稳定性能好。通过绝热量热测试仪(ARC)测试了大倍率充电情况电池的热量变化及电池的比热容,结果表明电池热容为2.02J/(K*g),在6C充电时电池表面温升为5℃±0.1℃,受温度效应影响,此时电池内热能够提高电化学反应效率,并无安全性影响。对循环前后电池电极材料进行了X射线衍射(XRD)谱,扫描电子显微分析,场发射透射电子显微分析,结果表明,大电流充电作用下,循环1000次后,正极材料晶体结构发生变化,(001)晶面间距变大,晶胞体积增大,结构中存在锂离子的缺失,产生晶格缺陷,晶化程度变低。负极材料的晶面间距变小,且循环后晶格条纹模糊,出现部分非晶化现象。正极材料粒度分布对电池影响电池快充性能。对比分析了不同粒径正极材料的快充性能,结果表明减小正极材料颗粒粒度有利于提高电池倍率充电性能。负极材料的结构特点也影响电池快充效率,研究了层状石墨、球形石墨及中间相碳微球的快充性能。通过KOH溶液对层状石墨负极处理改性后,电池在大电流(6C)充电时能量密度提高至128Wh/kg,循环1000次后容量保持率为80.3%。另外,研究了三元正极材料L333的快充性能,结果表明,颗粒较小的正极材料具有更好的倍率性能,使用改性后的石墨作为负极,6C充放条件下,将快充电池的能量密度提高至130wh/kg时,循环1000次后容量保持80mAh/g。
[Abstract]:In this paper, a fast charging lithium-ion battery with LiCoO2 as cathode material and graphite as negative electrode material is developed, and a 400mAh soft-clad battery is designed. The electrochemical performance, structure and morphology of electrode material are analyzed under the condition of high current charging. The influence of battery fabrication process parameters on the rapid charging performance was studied. In addition, the effect of L333 crystal morphology on the rapid charge performance was studied, with emphasis on the effect of L333 crystal morphology on the rapid charge performance. Ac impedance spectroscopy (EIS) and electrochemical cycle measurements were used to study the electrochemical performance of lithium ion batteries under high current charging conditions. It was found that the positive and negative electrodes of lithium ion batteries were highly polarized during high current charging. The rapid charging performance of the battery is seriously affected, and the polarization reduction can improve the charging performance of the battery with high current and reduce the internal resistance of the battery, which can effectively reduce the polarization phenomenon of the battery electrode. Therefore, different conductive agents and their mixing ratios are studied. The results show that the homogeneity of conductive agent and electrode active material and the proportion of electrode active material have influence on electrode resistance in the process of batching process of positive and negative electrode. When the ratio of conductive agent is 4, the overall performance of the battery is the best. The internal resistance of SEI film formed under the action of 0.2C current is relatively small and stable, and the polarization degree is improved to a certain extent. The lower the surface density of the electrode material, the smaller the polarization of the battery under high current charge, and the better the cycle stability. When the positive electrode surface density is 153g / m ~ 2, the capacity retention rate is still 80 when the charge cycle is 1700 times. When the compaction ratio of the cathode material is 3.6 g / cm ~ 3, the polarization and internal resistance of the battery are minimum. The cycle stability is good. The heat change of the battery and the specific heat capacity of the battery are measured by the adiabatic calorimeter ARC. the results show that the heat capacity of the battery is 2.02J / L KG, and the surface temperature of the battery rises to 5 鈩，

本文编号：1499506