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题名: 锂离子电池正极材料的制备与性能研究
作者: 张璐
答辩日期: 2013-05-27
导师: 康雪雅
专业: 微电子学与固体电子学
授予单位: 中国科学院大学
授予地点: 北京
学位: 硕士
关键词: 锂离子电池 ; 正极材料 ; 节能 ; 磷酸铁锂 ; 掺杂 ; 镍锰酸锂
摘要:

动力锂离子电池材料制备过程中的节能性和电池的比能量、寿命、安全性已成为当前电池技术发展的热点。本文以LiFePO4/CLiNi0.5Mn1.5O4作为研究对象,就其合成工艺和掺杂改性等方面进行了深入研究。利用XRDSEM等表征了材料的晶体结构与表面形貌;利用TG-DTA、恒流充放电测试、CVEIS等测试方法对材料进行电化学性能测试。LiOH·H2OH2C2O4·2H2OFePO4·2H2O为原料,采用基于液相还原的快速烧结法制备LiFePO4/C。通过研究草酸添加量、碳源添加量、烧结温度和烧结时间等对材料电化学性能的影响,确定了LiFePO4/C材料的最佳制备工艺。实验结果表明:草酸添加量摩尔比为LiOH·H2O:H2C2O4·2H2O=1:1.5,碳源添加量为10wt%700 下保温2 h制得的材料在0.2 C倍率下首次放电比容量达157.3 mAh·g-1,在0.2 C0.5 C1.0 C2.0 C5.0C倍率下各循环3次后恢复到1.0C倍率下循环3次,放电比容量基本无衰减,表现出良好的电化学性能。同时,对LiFePO4/C材料进行PB掺杂,能有效提高材料的电化学性能。尤其当掺杂量为0.10时,10C倍率下LiFeP0.9B0.1O4-δ/C放电比容量达102.6mAh·g-1,约为0.2 C倍率下的70%分别采用改进的高温固相法和流变相法制备出LiNi0.5Mn1.5O4材料,并探讨了制备过程中各工艺参数对最终产物性能的影响,得到最佳的工艺参数。以LiOH·H2ONiOMnO2为原料,采用原料中添加草酸这一改进的高温固相法,烧结和退火时间分别为10h24 h下制得的LiNi0.5Mn1.5O4材料比传统固相法制得的具有更优良的电化学性能,具有1.0 C倍率下循环充放电100次后97%以上的容量保持率。以醋酸锰、醋酸镍、碳酸锂为原料,采用流变相法制得的LiNi0.5Mn1.5O4材料在0.2 C倍率下首次放电比容量达144.7 mAh g-1,且通过CrF复合掺杂,能显著提高材料的电化学性能。其中掺杂量x=0.05的材料的电化学性能最好,且LiNi0.475Cr0.05Mn1.475O3.95F0.050.2 C0.5 C1.0 C倍率下各循环10次,放电比容量基本无衰减,在0.5C倍率下循环充放电25次后放电比容量保持率达81.6%

LiFePO4/CLiNi0.5Mn1.5O4共混材料的电化学性能进行初步研究发现,两种材料间表现出明显的协同作用:综合了LiFePO4/C材料高充放电比容量和LiNi0.5Mn1.5O4材料高放电电压平台的优点。实验结果表明,两种材料的共混研究是一个值得关注的课题,且有待深入研究。

英文摘要:
Rapid development of EV requests high power Li-ion batteries (LIBs) to have lower energy consumption, higher energy, longer life and better safety than before. The aim of the present study was to focus on the preparation processes and the modification materials of the LiFePO4/C and LiNi0.5Mn1.5O4 as cathode materials for lithium ion batteries.XRD and SEM were applied to characterize the crystal structure and surface morphology of the samples, respectively. TG-DTA, constant current charge-discharge, cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) were used to test the el electrochemical properties of the samples.Using LiOH?H2O, H2C2O4?2H2O and FePO4?2H2O as starting materials, LiFePO4/C samples were synthesized in flowing N2 atmosphere by liquid phase reduction method with heat treatment. The effects of the content of oxalic acid, carbon content, sintering temperature and sintering time on electrochemical performance of LiFePO4/C samples are studied. The results showed that the initial discharge specific capacities of the as-prepared sample, was 157.3 mAh?g-1 at 0.2 C, when the molar ratio of H2C2O4?2H2O to LiOH?H2O was 1.5, the cabon content was about 10wt%, the sintering temperature was 700 ℃ and the sintering time was 2 h. After continuous 3 cycles at different rates of 0.2, 0.5, 1.0, 2.0, 5.0 and 10 C, the discharge capacity of 1.0 C rate can reconvert to the previous value. B-doping at P-site can improve the conductivity of the samples, decrease the polarization of electrode, and enhance the cycling performance and high rate capability effectively. The LiFeP0.9B0.1O4-δ/C composite exhibits the best electrochemical performance. The discharge capacities of LiFeP0.9B0.1O4-δ/C are 102.6 mAh?g-1 at 10 C.The LiNi0.5Mn1.5O4 samples were prepared via improved solid phase method and rheological phase method, The results show that the samples all have well-regulated structure and high crystalinity. A series of experiments were carried out to investigate the optimum technological condition. The results showed that the electrochemical performances of LiNi0.5Mn1.5O4 samples are effectively improved by introduction of appropriate amount of oxalic acid , with retention ratio of 97% at the rates of 1.0 C after 100 cycles, while LiOH?H2O, NiO and MnO2 were used as starting materials, the sintering time and anneal time was 10 h and 14 h, respectively. Meanwhile, the initial discharge specific capacities of the LiNi0.5Mn1.5O4 samples synthesized via rheological phase method was 144.7 mAh g-1, and modification of LiNi0.5Mn1.5O4 by Cr- and F-co-doping was successfully synthesized. The results showed that the retention ratio of the Cr- and F-co-doping samples was greatly improved. After continuous 3 cycles at different rates of 0.2, 0.5 and 1.0 C, the discharge capacity of 0.5 C rate can reconvert to the previous value. The retention ratio of the LiNi0.475Cr0.05Mn1.475O3.95F0.05 samples were 81.6% at 0.5 C after 10 cycles.The research of LiFePO4/C/LiNi0.5Mn1.5O4 blended cathode material on the performance of lithium ion batteries via galvanostatic charge/discharge measurement and EIS at room temperature showed that the electrochemical performances are improved effectively, and it is worthiness for the study of the mixed electrode.
内容类型: 学位论文
URI标识: http://ir.xjipc.cas.cn/handle/365002/2481
Appears in Collections:材料物理与化学研究室_学位论文

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作者单位: 中国科学院新疆理化技术研究所

Recommended Citation:
张璐. 锂离子电池正极材料的制备与性能研究[D]. 北京. 中国科学院大学. 2013.
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