四氟硼酸离子液体的制备及作为锂离子电池电解液的应用

发布时间：2018-05-01 00:23

本文选题：锂离子电池 + 离子液体　；参考：《山东理工大学》2015年硕士论文

【摘要】：锂离子电池有如下优点:平台工作电压相对较高,对环境友好污染程度低,比能量密度比较高,循环时间长衰减小等,因此成为目前主流移动设备的电力来源。但是由于传统的锂离子电池采用的电解液一般为有机溶剂,易挥发,在电池反应中吸收能量发生燃烧,给电池带来极大的安全隐患。因此,开发无毒且安全的新型电解液成为电池领域的重点。离子液体是在常温下即可保持液体状态的完全由离子组成的化合物。它有稳定较宽的电化学窗口,不挥发,不易燃,电导率高,有望解决锂离子电池的安全性问题,成为取代传统的有机电解液最佳之选。本文合成了两种离子液体1-乙基-3-甲基咪唑四氟硼酸盐EMIMBF4,1-正丁基-3-甲基咪唑四氟硼酸盐BMIMBF4。着重研究了离子液体的物理化学性能,并从离子液体作为锂离子电池电解液的角度,研究了与三种正极材料钴酸锂LiCoO2、磷酸铁锂LiFePO4、镍钴锰三元材料LiNi1/3Co1/3Mn1/3O2的相容性。选用N-甲基咪唑为原料,分别采用传统回流方法和微波合成法合成目标离子液体EMIMBF4、BMIMBF4,比较两者产率。结果表明当微波合成法的投料比为C4H9Br:N-甲基咪唑:KBF4=1.0:1.0:1.6、微波功率240 W、反应温度70℃、反应时间20 min时,产率最高达到72%,高于传统法60%的产率。两者在常温下都为液态,黏度分别为51 mm2/s和123 mm2/s,电导率分别为14.0×10-3 S/cm,3.1×10-3 S/cm,热重测试结果显示两者的热分解温度分别为323.7℃和325.7℃,测试EMIMBF4电化学窗口为4.4 V,BMIMBF4的电化学窗口为5.3 V。将锂盐LiPF6分别以0.5 mol/L、0.8 mol/L、1.0 mol/L的浓度溶解于EMIMBF4,BMIMBF4中,室温下0.5 mol/L、0.8 mol/L、1.0 mol/L LiPF6+EMIMBF4的电导率分别为9.2 mS/cm、7.8 mS/cm、5.8 mS/cm。0.5 mol/L、0.8 mol/L、1.0 mol/L LiPF6+BMIMBF4的电导率分别为2.52 mS/cm、2.09 mS/cm、1.4 mS/cm。用钴酸锂为正极材料,锂片为负极,不同浓度锂盐的离子液体加入等体积有机电解液为电解液组装半电池并对其电化学性能进行测试。有机电解液组分为等浓度LiPF6+碳酸乙烯酯EC和碳酸二乙酯DEC的混合液(体积比1:1)。0.8 mol/L和1.0mol/L LiPF6+EMIMBF4(EC+DEC)电解液的首次充电容量分别为98.4 mAh·g-1和95mAh·g-1。高于锂盐浓度为0.5 mol/L时的68.1 mAh·g-1。50次循环后容量保持率分别为110%、96.1%和99.8%。0.8 mol/L LiPF6+BMIMBF4(EC+DEC)电解液首次充电比容量为113 mAh·g-1,放电比容量为98.2 mAh·g-1,库伦效率为86.9%。循环50次容量保持率衰减不明显。综上实验,当使用0.8 mol/L LiPF6+BMIMBF4(EC+DEC)离子液体做电解液时,电池的性能最好。以锂盐浓度为0.8 mol/L时的离子液体为电解液,研究离子液体电解液与正极材料钴酸锂LiCoO2、磷酸铁锂LiFePO4、镍钴锰三元正极材料LiNi1/3Co1/3Mn1/3O2的相容性。分析每种正极材料在0.1C、0.5C和1C电流密度下的循环性能。LiCoO2在这三种正极材料中的表现最差,LiFePO4和LiNi1/3Co1/3Mn1/3O2在0.1C和0.5C电流密度下的电池比容量和循环性能相差不多。在50次循环之后,容量几乎无衰减,容量保持率在95%以上。当电流密度增加到1C时,LiNi1/3Co1/3Mn1/3O2三元材料仍能保持相对较高的充放电比容量,50次循环之后容量保持率为93%,表现出良好的循环性能和倍率充放电性能。
[Abstract]:Lithium-ion batteries have the following advantages: relatively high working voltage on the platform, low pollution to the environment, higher density than energy density, low cycle time attenuation and so on. Therefore, the lithium ion battery has become the power source of current mainstream mobile devices. However, the electrolyte used in traditional lithium ion batteries is generally organic solvent, volatile and in battery reaction. The development of a new type of non-toxic and safe electrolyte has become the focus of the battery field. The ionic liquid is a completely ionic compound that can maintain the liquid state at normal temperature. It has a wide electrochemical window, nonvolatile, nonflammable and high conductivity. It is hopeful to solve the safety problem of lithium ion batteries and become the best choice to replace the traditional organic electrolyte. In this paper, two kinds of ionic liquids, 1- ethyl -3- methyl imidazole tetrafluorborate, EMIMBF4,1- n-butyl -3- methyl imidazole tetrafluorborate BMIMBF4., have been synthesized to study the physical and chemical properties of ionic liquids, and the ionic liquid is used as lithium. The compatibility of three positive electrode materials, lithium cobalt acid (LiCoO2), lithium iron phosphate (LiFePO4), nickel cobalt and manganese three element material LiNi1/3Co1/3Mn1/3O2, was studied. The target ionic liquid EMIMBF4, BMIMBF4 was synthesized by the traditional reflux method and microwave synthesis method. The results showed that the yield of the ionic liquid was compared. The results showed that the yield was compared. The results showed that the yield was compared. The results showed that the yield was compared. When the ratio of microwave synthesis is C4H9Br:N- methyl imidazole, KBF4=1.0:1.0:1.6, microwave power 240 W, reaction temperature 70 C, and reaction time 20 min, the maximum yield is 72%, higher than that of traditional method 60%, both are liquid at normal temperature, the viscosity is 51 mm2/s and 123 mm2/s respectively, and the conductivity is 14 x 10-3 S/cm, 3.1 * 10-3 S/cm, respectively. The results of the retest showed that the thermal decomposition temperatures of the two were 323.7 and 325.7, the EMIMBF4 electrochemical window was 4.4 V, the electrochemical window of BMIMBF4 was 5.3 V., and the lithium salt LiPF6 was dissolved in EMIMBF4, BMIMBF4, 0.5 mol/L, 0.8 mol/L, and 1 electrical conductivity at room temperature, respectively, 0.5 mol/L, 0.8 mol/L, 1 mol/L. The electrical conductivity of 9.2 mS/cm, 7.8 mS/cm, 5.8 mS/cm.0.5 mol/L, 0.8 mol/L and 1 mol/L LiPF6+BMIMBF4, respectively, is 2.52 mS/cm, 2.09 mS/cm, and 1.4 mS/cm. with lithium cobaltate as positive material, lithium is a negative electrode, and the ionic liquid with different concentration of lithium salt is added to the electrolyte to assemble the half battery and its electrochemical performance is carried out. The organic electrolyte is composed of a mixture of equal concentration of LiPF6+ ethylene carbonate EC and two ethyl carbonate DEC (volume ratio 1:1).0.8 mol/L and 1.0mol/L LiPF6+EMIMBF4 (EC+DEC) electrolyte for the first charge capacity of 98.4 mAh. G-1 and 95mAh. The specific capacity of the first charge of 110%, 96.1% and 99.8%.0.8 mol/L LiPF6+BMIMBF4 (EC+DEC) electrolyte is 113 mAh. G-1, the discharge specific capacity is 98.2 mAh. G-1, and the efficiency of Kulun's efficiency is 86.9%. cycle 50 capacity retention rate attenuation is not obvious. The ionic liquid with lithium salt concentration of 0.8 mol/L was used as the electrolyte to study the compatibility of the ionic liquid electrolyte with the cathode material lithium cobalt acid lithium LiCoO2, the lithium iron phosphate LiFePO4, the nickel cobalt manganese three positive electrode material, and the cyclic properties of each positive material under the 0.1C, 0.5C and 1C current density.LiCoO2 in these three cathode materials. The performance of the material is the worst, LiFePO4 and LiNi1/3Co1/3Mn1/3O2 have little difference in capacity and cycle performance at the current density of 0.1C and 0.5C. After the 50 cycle, the capacity is almost no attenuation and the capacity retention rate is above 95%. When the current density increases to 1C, the LiNi1/3Co1/3Mn1/3O2 three yuan material can still maintain a relatively high charge discharge ratio. Capacity after 50 cycles, the capacity retention rate is 93%, showing good cycling performance and rate charge discharge performance.

【学位授予单位】：山东理工大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM912

【共引文献】