锂离子电池论文：锂离子电池正极材料氟磷酸钒锂的合成及电化学性能研究

1、锂离子电池论文：锂离子电池正极材料氟磷酸钒锂的合成及电化学性能研究【中文摘要】近年来,氟磷酸钒锂（LiVPO4F）因具有优异的热稳定性、高放电平台和较高的理论容量(156 mAh·g-1),被认为是一种具有巨大潜力的锂离子电池正极材料。然而,LiVPO4F较差的电导率导致其高倍率性能较差,从而限制了它的应用。本文针对LiVPO4F电导率低的缺点,通过改进合成方法及离子掺杂制备LiVPO4F/C及其掺杂LiVPO4F/C复合材料,提高LiVPO4F的电导率,从而提高LiVPO4F的电化学性能。通过X射线衍射（XRD）、扫描电子显微镜（SEM）、循环伏安和充放电测试等测试技术,研究合成条

2、件、掺杂铝量对LiVPO4F的结构及其电化学性能的影响,并优化合成条件,制备出电化学性能优异的LiV0.95Al0.05PO4F/C复合材料。以V2O5、NH4H2PO4、葡萄糖和LiF为原料,通过改变反应原料的混合方式,改善传统固相法原料混合不均匀的缺点,改进合成LiVPO4F/C复合正极材料的传统固相法制备工艺,并比较由改进固相法及传统固相法合成LiVPO4F/C复合材料的物理和电化学性能。结果表明,两种方法均可合成三斜结构的LiVPO4F及碳组成的复合正极材料,但改进固相法合成的LiVPO4F/C复合正极材料的放电比容量及循环性能均优于传统固相法合成的LiVPO4F/C复合材料。改进固相

3、法合成的LiVPO4F/C复合正极材料的0.2C、0.5C和1C的放电比容量分别为133.7 mAh·g-1、124.9 mAh·g-1和118.7 mAh·g-1,而传统固相法合成的LiVPO4F/C复合正极材料相应倍率的放电比容量分别为131.2 mAh·g-1、121.4 mAh·g-1和104.9 mAh·g-1。以V2O5、H3PO4、柠檬酸和LiF为原料,通过溶胶凝胶法合成LiVPO4F/C复合正极材料并研究反应条件对复合材料电化学性能的影响,确定合成的最佳条件:V2O5、H3PO4和柠檬酸的摩尔比为1:2:2.4,700

4、焙烧干凝胶6h合成VPO4/C,750焙烧VPO4/C与LiF混合物1h合成LiVPO4F/C复合正极材料。最佳条件下合成LiVPO4F/C的放电比容量及循环性能均高于由固相法合成的复合材料,溶胶凝胶法合成的LiVPO4F/C复合材料1C和5C充放电倍率的放电比容量分别为123.7 mAh·g-1和104.4 mAh·g-1。在溶胶凝胶法成功合成LiVPO4F/C的基础上,以V2O5、H3PO4、柠檬酸、硝酸铝和LiF为原料,通过溶胶凝胶法合成LiV1-xAlxPO4F /C（x=0.03, 0.05, 0.07）复合材料。测试结果表明,LiV1-xAlxPO4F/C的放电

5、电压平台及循环性能随着掺杂铝量的增加而提高,放电比容量随着铝含量的增加而下降,其中LiV0.95Al0.05PO4F/C具有最高的能量密度,大电流充放电性能优于LiVPO4F/C复合材料,其5C放电比容量高达110 mAh·g-1。【英文摘要】Recently, lithium vanadium fluorophosphates, LiVPO4F, has been considered as a potential cathode material for lithium ion batteries due to its excellent thermal stability, h

6、igh discharge voltage and high theoretic capacity of 156 mAh·g-1. However, the poor conductivity of LiVPO4F material results in poor high rate capability and limits its applications in lithium ion batteries.The study in this thesis mainly focuses on the improvement of electrochemical performanc

7、e of LiVPO4F by improving its poor conductivity. The conductivity of LiVPO4F was enhanced by improving the synthesis method and LiV0.95Al0.05PO4F/C with excellent performance was prepared by sol-gel method. The effects of preparation conditions and the content of dopped Al on the structure and elect

8、rochemical performance of LiVPO4F were investigated by X-ray diffraction （XRD）, scanning electron microscope （SEM）, cyclic voltammetry （CV） and charge-discharge tests.LiVPO4F/C composites were prepared by a traditional solid-state method and a modified solid-state method, respectively, using V2O5, N

9、H4H2PO4, glucose and LiF as raw materials. Defect of uneven mixing of raw materials resulted from traditional solid-state method was overcomed by modified solid-state method through the improved mixing procedure. Comparative study of physical and electrochemical properties of LiVPO4F/C composites pr

10、epared by traditional and modified solid-state methods, respectively, was carried out. Results suggest that the two synthesis methods are effective to prepare composite cathode materials consisting of triclinic LiVPO4F and carbon. But the discharge capacity and cyclability of LiVPO4F/C composite syn

11、thesized by modified solid-state method are better than that composite prepared by traditional solid-state method. The discharge capacities of LiVPO4F/C composite prepared by modified solid-state method at 0.2, 0.5 and 1C are 133.7, 124.9 and 118.7 mAh·g-1, respectively, while the LiVPO4F/C com

12、posite prepared by traditional solid-state method exhibits 131.2, 121.4 and 104.9 mAh·g-1 at the corresponding above-mentioned current rates, respectively.LiVPO4F/C composite cathode materials were prepared by a sol-gel method using V2O5, H3PO4, citric acid and LiF as raw materials and the effe

13、cts of preparation conditions on the electrochemical performance of composites were investigated. The results reveal the optimum preparation conditions as follows: mole ratios of V2O5, H3PO4 and citric acid are 1:2:2.4; VPO4/C was prepared by calcination of dried gel at 700for 6h; preparation of LiV

14、PO4F/C by sintering mixture of VPO4/C and LiF at 750for1 h. The discharge capacity and cyclability of LiVPO4F/C composite prepared by sol-gel method at optimum conditions are better than that of LiVPO4F/C composite prepared by solid-state method. The discharge capacities of LiVPO4F/C composite prepa

15、red by sol-gel method are 123.7 and 104.4 mAh·g-1 at 1C and 5C, respectively.Based on the preparation of LiVPO4F/C composite by sol-gel method, LiV1-xAlxPO4F/C （x=0.03, 0.05 and 0.07） composites were synthesized by sol-gel method using V2O5, H3PO4, citric acid, Al（NO3）3·9H2O and LiF as raw

16、 materials, and the electrochemical performance was investigated. The discharge voltage plateau and cyclability of LiV1-xAlxPO4F/C are improved with the increase in doped-Al content, while the discharge capacity decreases with the increase of doped-Al content and LiV0.95Al0.05PO4F/C exhibits highest

17、 energy density among the above-mentioned LiV1-xAlxPO4F/C composites. The high rate discharge capacity of LiV0.95Al0.05PO4F/C is higher than that of LiVPO4F/C composite and displays high capacity of 110 mAh·g-1 at 5C.【关键词】锂离子电池 正极材料 氟磷酸钒锂 LiVPO4F Al掺杂【英文关键词】Li-ion batteries cathode material lit

18、hium vanadium fluorophosphate LiVPO4F Al doped【目录】锂离子电池正极材料氟磷酸钒锂的合成及电化学性能研究摘要4-5Abstract5-6第1章 绪论9-221.1 引言91.2 锂离子电池概述9-121.2.1 锂离子电池的结构9-101.2.2 锂离子电池的工作原理10-111.2.3 锂离子电池的特点和存在的问题11-121.3 锂离子电池正极材料的研究进展12-171.3.1 过渡金属氧化物正极材料12-151.3.2 聚阴离子型正极材料15-171.4 氟磷酸钒锂LiVP0_4F 正极材料的研究进展17-201.4.1 氟磷酸钒锂的结构与特

19、点17-181.4.2 氟磷酸钒锂的制备方法18-191.4.3 LiVP0_4F 材料的缺点和改进的方法19-201.5 本论文研究的意义及内容20-22第2章 实验22-272.1 主要实验仪器与药品22-232.1.1 主要实验仪器22-232.1.2 主要实验药品232.2 实验方法23-242.2.1 高温固相法制备LiVP0_4F/C232.2.2 改进的固相法制备LiVP0_4F/C23-242.2.3 溶胶凝胶法制备LiVP0_4F/C242.2.3.1 溶胶凝胶法制备LiV_(1-x)Al_xP0_4F/C242.3 LiVP0_4F 正极材料的表征24-252.3.1 物相分析242.3.2 形貌分析242.3.3 热重分析24-252.3.4 碳含量分析252.4 扣式模拟电池的组装252.5 材料的电化学性能测试252.6