【作者】 王磊；

【导师】 巩桂芬；

【作者基本信息】 哈尔滨理工大学 ， 高电压与绝缘技术， 2018， 硕士

【摘要】 采用静电纺丝法制备的聚酰亚胺（PI）纤维膜既具有电纺膜孔隙率高、比表面积大、孔隙结构独特等特点,又具有聚酰亚胺热稳定性高、耐化学腐蚀等优点,将其作为锂离子电池隔膜,不仅可提高隔膜的吸液率,改善隔膜与电极的相容性,提高离子电导率,还可解决现有商用聚烯烃隔膜热尺寸稳定性差的缺点,从而满足新一代高性能锂离子电池的需求,因此具有很大的发展潜力,已经成为发展的焦点。但是由静电纺丝制备的纤维膜普遍具有机械性能较差的缺点,不能够满足锂离子电池隔膜生产过程中收卷和电池封装的要求,因此如何提高聚酰亚胺纤维膜的力学性能是其作为锂离子电池隔膜研究的关键。本文首先采用3,3’,4,4’-联苯四甲酸二酐和4,4-二氨基二苯醚为原料,采用原位聚合法在聚酰胺酸（PAA）中引入纳米Al₂O₃或TiO₂,从而合成含有Al₂O₃或TiO₂改性的联苯型聚酰胺酸纺丝液;然后通过高压静电纺丝制备Al₂O₃/PAA和Ti O₂/PAA两种复合纤维膜;最后采用梯度升温热亚胺化并在升温过程中进行单向拉伸处理得到Al₂O₃/PI和Ti O₂/PI两种复合纤维膜,并将Al₂O₃/PI和Ti O₂/PI两种复合纤维膜作为锂离子电池隔膜进行相关性能测试。通过红外光谱和微观形貌分析,证实了两种复合隔膜均具有较好的三维网状结构并且隔膜中存在相应的无机纳米粒子,综合隔膜的孔隙率、浸润性能、力学性能、热性能和阻燃性能,最终确定了两种复合隔膜中纳米Al₂O₃和TiO₂的最佳添加量分别为3 wt%和4 wt%,此时两种复合隔膜的孔隙率分别为75.2%和77.5%,吸液率分别为493%和550%,静态接触角均接近于0°,拉伸强度分别为18.63 MPa和16.74 MPa,初始热分解温度分别为566℃和591℃,并且均具有较好的热收缩性能和阻燃性能。采用纳米Al₂O₃添加量为3 wt%的Al₂O₃/PI复合隔膜和纳米Ti O₂添加量为4 wt%的Ti O₂/PI复合隔膜以及PI、PP隔膜进行纽扣测试电池的组装,以进行电化学性能和电池性能测试,分析Al₂O₃和TiO₂加入对PI隔膜性能的影响。结果表明,Al₂O₃/PI复合隔膜和Ti O₂/PI复合隔膜的电化学稳定窗口分别为5.5 V和5.7 V,界面阻抗为346.72Ω和292.85Ω,离子电导率为1.961×10^-33 S/cm和2.429×10^-33 S/cm,初始放电容量为154.75 m Ah·g^-1和157.68 m Ah·g^-1,10 C高倍率下放电容量保持率为69.5%和69.9%,在25℃、1 C倍率下进行循环充放电100次后的容量保持率为95.2%和96.7%,在120℃高温下以1 C倍率进行循环充放电100次后的容量保持率也分别高达88.3%和90.7%,不仅较PI隔膜所对应的5.2 V、451.23Ω、1.214×10^-33 S/cm、149.38 m Ah·g^-1、66.1%、86.6%和80.3%有所改善,而且远优于PP隔膜的4.5 V、553.36Ω、0.480×10^-33 S/cm、141.69 m Ah·g^-1、47.6%、75.1%以及高温下无法正常工作的情况,具有较好的应用前景。更多还原

【Abstract】 The polyimide（PI）fiber membrane prepared by electrospinning exhibits the excellent properties of high porosity,large specific surface area and unique porous structure,along with high thermal stability,chemical resistance and other advantages of polyimide.Therefore,the polyimide fiber membrane using as lithium-ion battery separator can not only improve the liquid absorption rate of the separator and the ionic conductivity,enhance the compatibility between the separator and the electrode,but also solve the shortcomings of the poor thermal dimensional stability existing in the current commercial polyolefin separator,thus it can meet the need of new generation of high-performance lithium-ion battery.It has great potentials for developmen and has become the focus of research.However,the fiber membranes prepared by electrospinning generally have the disadvantage of poor mechanical properties and couldn’t satisfy the requirements of winding and battery packaging during the production of lithium ion battery separators,consequently,improving the mechanical properties of polyimide fiber membrane is the key to the study of lithium ion battery separator.In this paper,firstly,3,3’,4,4’-biphenyl tetracarboxylic dianhydride and 4,4-diaminodiphenyl ether were used as raw materials,in-situ polymerization were adopted to introduce nano-Al₂O₃ or Ti O₂ into polyamic acid（PAA）,thus biphenyl polyamic acid spinning solution containing Al₂O₃ or TiO₂ was obtained;Then two kinds of composite fiber membranes,Al₂O₃/PAA and TiO₂/PAA,were both prepared by high-pressure electrospinning;Finally,the mixture of Al₂O₃/PI and Ti O₂/PI were obtained by thermal imidization with gradient heating and uniaxial stretching fiber membrane,the related properties of Al₂O₃/PI and TiO₂/PI composite membranes were tested as lithium ion battery separators.The infrared spectroscopy and micro-morphology analysis confirmed the presence of the corresponding inorganic nanoparticles in the membrane and the two composite membranes had good three-dimensional network microstructure.Refering to the their porosity of the separator,the infiltration performance,mechanical properties,thermal properties and flame retardance,it can be concluded that the optimal content of nano-Al₂O₃ and TiO₂ in the two composite membranes were 3 wt%and 4 wt%,respectively.Moreover,the porosities of the two composite membranes were 75.2%and 77.5%,and the liquid absorption rates were 493%and 550%,the static contact angles were close to 0°and the tensile strengths were 18.63 MPa and 16.74 MPa.The decomposition temperatures were 566℃and 591℃,and both had excellent thermal shrinkage rates and flame retardance.The button-test batteries were assembled by using Al₂O₃/PI composite membrane with nano-Al₂O₃ content of 3 wt%and Ti O₂/PI composite membrane with nano-Ti O₂ content of 4 wt%as well as PI and PP separator,respectively,for electrochemical performance and battery performance testing,analysis of the impact of the addition of Al₂O₃ and TiO₂ on the performance of PI membranes.The results showed that the electrochemical stability windows of Al₂O₃/PI composite membrane and TiO₂/PI composite membrane were 5.5 V and 5.7 V,and the interfacial impedances were 346.72Ωand 292.85Ω,and the ionic conductivities were 1.961×10^-33 S/cm and 2.429×10^-33 S/cm,and initial discharge capacities were 154.75 m Ah·g^-11 and 157.68 mAh·g^-1,and their discharge capacity retentions at 10 C rate were 69.5%and 69.9%,and their capacity retentions rates were 95.2%and 96.7%after 100 cycles at 25℃and 1 C rate,their capacity retentions rates were 95.2%and 96.7%after 100 cycles at 120℃and 1C rate,those had differfnt degrees of increase than PI which were 5.2 V,451.23Ω,1.214×10^-33 S/cm,149.38 mAh·g^-1,66.1%,86.6%and 80.3%,so it had good application prospects,better than those of PP membrane which were 4.5 V,553.36Ω,0.480×10^-33 S/cm,141.69 m Ah·g^-1,47.6%,75.1%and could not be used at high temperatures,and had a good application prospect.更多还原