【作者】 张运丰；

【导师】 程寒松；

【作者基本信息】 中国地质大学 ， 岩石矿物材料学， 2013， 博士

【摘要】 锂离子电池具有质量密度高,体积密度大,循环寿命长,可靠性强等优点被广泛应用于各种电子产品和动力电车等方面。电解质是锂离子电池重要的组成部分,性能良好的电解质可以大大提高锂离子电池的能量效率。锂离子迁移数是锂离子二次电池电解质的一个重要性质,锂离子迁移数越高,锂离子电池的能量效率越高,锂离子迁移数接近或者达到1时,电池的能量效率将达到最高。这是由于,在锂离子二次电池内部,一方面,阴离子的迁移会导致电池能量的消耗；另一方面,由于阴离子的迁移速度比锂离子快,在充放电过程中会导致电解质盐产生浓度梯度,产生浓差极化,从而降低锂离子电池的能量效率。对于传统的液态有机小分子电解质,增大阴离子的半径和分散负电荷在阴离子的分布是提高锂离子迁移数的重要途径。对此,基于电荷分散的sp3硼的LiBOB电解质和三氟甲基磺酰亚胺的N(SO2CF3)2-电解质得到了广泛研究,并在锂离子二次电池电解质中得到了一定的应用。但是,上述两种电解质的锂离子迁移数远低于1。要想将锂离子的迁移数增大到接近1,另一个途径就是要极大的增大阴离子的大小,使之阴离子能够完全固定。基于这一思想,近年来,一种新型的聚合物电解质材料,单离子聚合物电解质,应运而生。单离子聚合物电解质是一类新型的,同时具有较高的锂离子迁移数和传统聚合物电解质的优点的聚合物电解质。基于以上的研究思路,本文将上述具有分散电荷的两种官能团(BOB-和N(SO2CF3)2-)交联在聚合物骨架上,制备出含有以上两种大阴离子官能团的单离子聚合物电解质。本文设计并合成了两类具有高度离域化阴离子的聚合物材料：第一类是含有sp3杂化硼原子的阴离子聚合物材料。这类材料通过选择具有刚性的或者柔性的前驱体可以合成具有一维或者三维空间结构的聚合物电解质材料。通过选择可能制备出具有良好性能的前驱体,本文合成了四种基于sp3杂化硼的聚合物材料：聚对苯二酚硼酸锂(LiPHB),聚均苯三酚硼酸锂(LiPPB),聚联苯二酚硼酸锂(LiPBB)和聚1,2,3,4-丁烷四羧酸硼酸锂(LiPBAB)。采用傅里叶变换红外光谱仪(FT-IR),核磁共振硼谱("BNMR),凝胶渗透色谱分析仪(GPC),扫描电子显微镜(SEM)和x射线衍射仪(XRD)等手段对聚合物电解质的结构进行了测定。采用热重分析仪(TGA),线性扫描伏安法(LSV)和电化学交流阻抗法(EIS)分别对所合成的四种单离子聚合物电解质的热稳定性,电化学稳定性和锂离子电导率进行了测定。在所合成的四个聚合物材料中,LiPHB, LiPPB和LiPBB为三维空间结构,LiPBAB为一维和二维空间结构。另外采用溶剂热法(M1)和溶液浇铸法(M2)与PVdF聚合物交联成功制备了单离子凝胶聚合物电解质膜,并对两种方法制备的单离子凝胶聚合物电解质薄膜的性质进行研究和比较。1.所合成的聚合物电解质的数均分子量(Mn)在16,400-27,800范围内,多分散指数(Mw/Mn)在1.32-2.13范围内。傅里叶变换红外光谱在1400cm-1-1000cm-1内有很强的硼-氧键伸缩振动峰,11BNMR的峰在10ppm以内有很强的sp3杂化的硼的峰,以上测试结果表明本文成功合成了具有高分子量的基于sp3杂化硼的阴离子聚合物材料。2.SEM和XRD是测定物质结构的重要手段。本文的测试结果表明,除LiPHB外,其它三个聚合物材料的扫描电子显微镜的照片都呈规则的结构。LiPHB呈现均匀的球状结构,LiPPB呈现瓦片状结构；LiPBB呈现规则的立方体结构,LiPBAB由于采用柔性的1,2,3,4-丁烷四羧酸为前驱体而呈现线性和片状结构。LiPBB和LiPBAB的X射线衍射谱图显示了明显的尖锐的衍射峰,表明这两种单离子聚合物电解质具有规则的微观结构,而LiPPB的X射线衍射谱图仅在一个很宽的衍射峰上显示了几个很弱的衍射峰,表明此单离子聚合物电解质的规则结构含量很低。令人费解的是,LiPHB的XRD仅为一个很宽的衍射峰,说明LiPHB没有规则的微观结构,这与SEM的球状结构相吻合。3.热分析测试结果表明,以上合成的材料具有较好的热稳定性(160℃-260℃),适合锂离子电池的工作温度(<100℃),以上合成的单离子聚合物电解质材料均可满足锂电池电解质的要求。4.电化学测试结果表明,以上合成的材料的电化学稳定性在4.3V到4.7V范围内,与锂工作电压(<4.2V)相比,以上合成的单离子聚合物电解质材料均可满足锂电池电解质的要求。5.对两种方法制备的聚合物电解质膜的测试结果表明,两种膜的界面电阻呈现巨大的差别。采用溶剂热法制备的聚合物电解质薄膜由于具有粗糙的,多空的表面形貌导致其具有很高的,不稳定的界面电阻。但是,采用溶剂浇注法制备的聚合物电解质薄膜却呈现低的,稳定的界面电阻。对两种单离子聚合物电解质膜的SEM测试结果表明,后者优良的性质源于膜的平整的表面结构。而前者高界面电阻使其难以在锂电池的应用过程中得到优良的电池性能。因此,我们可以认为,采用溶液浇注法制备的薄膜性能优于溶剂热法制备的薄膜。6.EIS测试前后分别对上述两种方法制备的单离子聚合物电解质膜进行了SEM测试,测试结果表明,经过EIS测试后,由于测试过程中不锈钢电极的挤压,两种单离子聚合物电解质膜的表面形貌均相应变得平整,与其界面电阻随着测试时间延长,二者的界面电阻逐渐降低相对比可以知道,界面电阻的降低是由平整的表面形貌的逐渐形成引起的。7.另一方面,两种膜的电导率随温度的变化都符合阿伦尼乌斯公式。并且,由于具有高的孔状结构和高的溶剂吸附量,采用溶液浇铸法制备的聚合物电解质薄膜的离子电导率高达10-3S/cm,接近商业化电解质的离子电导率。相反,采用溶剂热法制备的聚合物电解质薄膜由于具有较少的孔结构和低的溶剂吸附量,使之具有比溶液浇铸法制备的聚合物薄膜低的离子电导率。第二类聚合物电解质材料是基于磺酰亚胺官能团而设计的。本文首先设计并合成了具有高的热稳定性和质子离域化的4,4’-二羧基苯磺酰亚胺作为此类聚合物电解质的前驱体,通过选择合适的配体进一步聚合制备出具有磺酰亚胺活性基团的聚合物电解质材料。在此基础上,本文设计并合成了三个不同结构的高分子聚合物电解质材料：聚双苯磺酰亚胺二酰二苯基砜二胺基锂,聚双苯磺酰亚胺二酰正辛烷二胺基锂和聚间苯二酰-1-苯磺酰亚胺-2,4-苯二胺-2,,4-二苯砜二胺锂。通过傅里叶变换红外光谱仪,核磁共振氢谱,凝胶渗透色谱法(GPC)分析和扫描电子显微镜对其结构进行了表征。采用热重分析仪(TGA),线性扫描伏安法(LSV)和电化学交流阻抗法(EIS)分别对所合成的四种单离子聚合物电解质的热稳定性,电化学稳定性和锂离子电导率进行了测定。采用溶剂热法和溶液浇铸法与PVdF聚合物交联分别制备了具有不同性质的聚合物电解质薄膜,并对两种薄膜的重要性质进行了测试比较。此部分主要有以下研究结果：1.此类聚合物电解质的数均分子量(Mn)在9,500-44,600范围内,多分散指数(Mw/Mn)在1.87-3.86范围内,再加上傅里叶变换红外光谱和1HNMR测试的结果表明本文成功合成了具有高分子量聚合物材料。2.此类材料表现了较好的热稳定性,热稳定性都在170℃以上,较好的热稳定性能使之作为新一代的聚合物电解质材料用在锂离子电池上成为可能。3.此类材料同样表现了较好的电化学稳定性,电化学稳定性在4.5V以上,其中LiPDSPA的电化学稳定性高达5.5V。较好的电化学稳定性使这一类单离子聚合物电解质材料有望作为新一代的聚合物电解质材料用在锂离子电池上。4.所合成的三个聚合物电解质材料的SEM照片显示了不同的表明形貌。由于LiPDSPA是由刚性芳香结构的前驱体4,4’-二胺基二苯砜与4,4’-二羧基苯磺酰亚胺聚合形成的具有刚性结构的聚合物电解质材料,此类材料的SEM照片显示了具有一定规则的块状结构。而LiPDSOA的SEM照片呈现了丝状结构,这主要是由于此类聚合物是由具有柔性结构的前驱体1,8-辛二胺与4,4’-二羧基苯磺酰亚胺聚合形成的。另外,LiPIBPSI呈现直径约为0.5μm的球状结构。从LiPIBPSI的结构不难看出,由于悬挂在聚合物电解质骨架的苯磺酰亚胺锂基团具有很强的离子性,这些具有强极性的官能团相互吸引,使整个聚合物具有不规则的结构。5.对于LiPDSOA和LiPIBPSI聚合物电解质薄膜,两种方法制备的聚合物电解质薄膜都表现了与第一类基于sp3硼的聚合物电解质薄膜类似的性质。即采用溶剂热法制备的聚合物电解质薄膜具有很高的,不稳定的界面电阻以及粗糙多空的膜表面形貌,采用溶液浇铸法制备的聚合物电解质薄膜表现出出很低的稳定的界面电阻以及光滑的膜表面形貌。但是,LiPDSPA聚合物电解质薄膜表现出了不同的特性。两种膜的体相电阻随着测试时间的延长都表现出不同程度的降低,这与本文其他聚合物电解质薄膜的性能都相反。另外,测试结果也表明,两种聚合物电解质薄膜的界面电阻都很小。其中,溶剂热法得到的薄膜界面电阻仅为40Ω左右,而溶液浇铸法制备的薄膜的界面电阻也只有75Q。通过讨论可以得到,这种极低的界面电阻和反常的体相电阻是由于LiPDSPA聚合物电解质本身具有特殊的空结构导致的。6.E1S测试前后,分别对上述两种方法制备的单离子聚合物电解质膜进行了SEM测试,测试结果表明,经过EIS测试后,由于测试过程中不锈钢电极的挤压,两种单离子聚合物电解质膜的表面形貌均相应变得平整,采用溶剂热法制备的单离子聚合物电解质膜由于具有粗糙的,多空的表面形貌,EIS测试前后的表面形貌变化较大。与其界面电阻随着测试时间延长,二者的界面电阻逐渐降低相对比可以知道,界面电阻的降低是由表明平整的表面形貌的逐渐形成引起的。7.与第一类聚合物电解质薄膜相似,采用溶剂热法制备的此类聚合物电解质薄膜由于具有较高的孔结构和溶剂吸附量,有些材料的离子电导率接近甚至超过10-3次方,与商业化电解质的离子电导率在同一个数量级。而采用溶液浇铸法制备的聚合物电解质薄膜的电导率仅在10-4次方,较低的离子电导率是由低的孔隙率和低的溶剂吸附量导致的。值得一提的是,尽管LiPDSPA和LiPDSOA聚合物电解质中的锂离子含量高于LiPIBPSI聚合物电解质中的锂离子含量,但是采用溶液浇铸法制备的LiPIBPSI聚合物电解质薄膜的电导率明显高于LiPDSPA和LiPDSOA聚合物电解质薄膜的离子电导率。与LiPDSPA和LiPDSOA聚合物电解质的直链结构相比,LiPIBPSI聚合物电解质的活性基团是悬挂在聚合物主链上的,由此可见,这种梳状结构有利于增强锂离子在聚合物电解质膜中的迁移性,从而提高锂离子电导率。由于电荷在阴离子聚合物骨架中高度离域化,阳离子(锂离子)被充分的暴露,本文合成的聚合物电解质材料表现出较好的热稳定性和电化学稳定性,以及与商业化电解质相近的离子电导率。较高的离子电导率加上聚合物电解质薄膜好的机械性能,使之作为锂离子电池聚合物电解质成为可能。更多还原

【Abstract】 Lithium ion batteries, which take advantages of high gravimetric and volumetric energy densities, long cycle life, and improved reliability, have been widely used as power source. Electrolyte is an important component in the lithium ion battery. Among the developed electrolytes, single ion conducting polymer electrolytes, which act both as separator between anode and cathode, and medium to facilitate the flow of lithium ions between two electrodes, were rapidly developed and were further, carried out to overcome the serious safety concerns. In the present works, two classes of polymeric compounds with highly exposed lithium cations are presented. The first class of sp3boron based polymeric materials can be made in the form of one or three dimensional networks with rigid or soft morphology dictated by the choice of precursors. For the sp1boron based on polymeric materials, the four of lithium poly (hydroquinone borate)(LiPHB), lithium poly (phloroglucinol borate)(LiPPB), lithium poly (4,4’-biphenol borate)(LiPBB) and lithium poly (1,2,3,4-Butanetetracarboxylic acid borate)(LiPBAB) have been successfully synthesized and further characterized by FT-IR,11BMR, GPC, FT-SEM and XRD. Some significantly properties, for example, thermal stability, electrochemical stability and ionic conductivity have also been investigated. Among them, LiPHB, LiPPB and LiPBB diplays three dimensional networks and LiPBAB exhibits one dimensional network. Furthermore, the polymer electrolyte membrane has been successfully prepared by using solvent thermal method (M1) and solution casting method (M2), and their important performances have also been compared. The results of this investigation are summarized as follows:1. The FT-IR (1400cm-1-1000cm-1), nBNMR (<10ppm) and the number-average molecular weights (Mn) were in the range of16,400-27,800and polydispersity indices (Mw/Mn) were between1.32and2.13, suggest that sp3boron compounds with high molecular weight were successfully synthesized as expected2. Beside of PHB, the other sp3boron based polymeric materials displays regular shape as shown in SEM images. The XRD patterns of PBB and PBAB display obvious sharp diffraction peaks and PPB displays several week sharp diffraction peaks on the broad peak, suggesting that these materials have a long range order.3. These materials exhibits good thermal (160℃-260℃) are well suited for applications in Li-ion batteries as electrolytes as well as separators.4. These materials also exhibits electrochemical stability (4.3V-4.7V) are well suited for applications in Li-ion batteries as electrolytes as well as separators. 5. The considerable differences of interfacial resistances between M1membrane and M2membrane were observed. The M1membrane displays high and unstable interfacial resistance duo to the coarse and porous surface morphology. However, the M2membrane exhibits low and stable interfacial resistance which was attributed from the smooth and uniform surface morphology. So it can be concluded that the quality of M2membrane was better than M1membrane due to great uniform surface structure and stable interfacial and bulk resistance.6. The two kinds of single ion conductor polymeric electrolyte membranes before and after EIS test were measured by SEM. It was indicated that the somewhat more uniform of surface morphologies of two all single ion conductor polymeric electrolyte membranes were gained as the press between the stainless steel electrodes during EIS test. By comparing the decreasing of interface resistances as a function of storage time, we can see that the decreases of interfacial resistances of them were induced by the formation of their more uniform surface morphologies.7. On the other hand, the M1membrane exhibits high ionic conductivity in the same order of magnitude as the conventional liquid electrolytes due to larger pores and high solvent uptake. The M2membrane shows much lower ionic conductivity than M1membrane, which was caused by smaller pores and low solvent uptake.The second class of sulfonimide based polymeric materials was developed by designing the bis(4-carboxyl benzene sulphonyl) imide with high thermal stability and proton delocalization. The three of sulfonimide based polymeric materials, lithium poly(diacylbenzenesulfonylimide diphenylsulfoneamide)(LiPDSPA), lithium poly(diacylphenylsulfonylimide octylamide)(LiPDSOA) and Poly(isophthaloyl benzenesulfonic acid-2,4-diamide diphenylsulfone diamide) with pended lithium sulfonimide(LiPIBPSI), were designed, synthesized and further characterized by FT-IR,1HMR, GPC and FT-SEM. Thermal stability, electrochemical stability and ionic conductivity have also been investigated. The polymer electrolyte membrane has been successfully prepared by using solvent thermal method and solution casting method, and their important performances have also been compared. The results of this investigation are summarized as follows:1. The FT-IR and1HNMR and the number-average molecular weights (Mn) were in the range of9,500-44,600g/mol and polydispersity indices (Mw/Mn) were between1.87and3.86, suggest that polymeric compounds with high molecular weight were successfully synthesized as expected.2. These material exhibits moderate good thermal (>170℃) are well suited for applications in Li-ion batteries as electrolytes as well as separators.3. These material exhibits good electrochemical stability (>4.0V) are well suited for applications in Li-ion batteries as electrolytes as well as separators.4. SEM images revealed interesting morphologies of three polymer electrolytes. LiPDSPA shows a massive structure due to the high rigidity of the aromatic precursors and the characteristics of stronger ionic bonds existed in the polymer electrolyte structure, LiPDSOA powder displays a filiform shape due to the high the flexibility of the aliphatic precursor and the uniform-sized microsphere with the size of0.5μm for LiPIBPSI powder was obviously observed which was ascribed by the force of interattraction from stronger ionic bonds existed in the side chain of polymer electrolyte structure.5. For LiPDSOA and LiPIBPSI, both M1and M2membranes show the similar performances with that of the sp3boron based polymeric materials, which the M1membrane show high and unstable interfacial resistance and coarse and porous surface morphology and M2membranes display low and stable interfacial resistance and smooth surface morphology. However, LiPDSPA gave considerable performances of interfacial resistance. The extreme low interfacial resistances of around40Ω for M1membrane and75Ω for M2membrane were obtained. As discussed below, it should be noted that the abnormal interfacial of both two method composite polymer electrolyte membranes might be due to the special porous structures in the LiPDSPA polymer electrolyte.6. The two kinds of single ion conductor polymeric electrolyte membranes before and after EIS test were measured by SEM. It was indicated that the somewhat more uniform of surface morphologies of two all single ion conductor polymeric electrolyte membranes were gained as the press between the stainless steel electrodes during EIS test. By comparing the decreasing of interface resistances as a function of storage time, we can see that the decreases of interfacial resistances of them were induced by the formation of their more uniform surface morphologies.7. The M1membrane exhibits high ionic conductivity in the same order of magnitude as the conventional liquid electrolytes due to larger pores and high solvent uptake. The M2membrane shows much lower ionic conductivity than M1membrane, which was caused by smaller pores and low solvent uptake. It’s worthy to note that LiPIBPSI polymer electrolyte shows the better ionic conductivity of M2membrane than the LiPDSPA and LiPDSOA even although the content of lithium ion in the LiPIBPSI polymer electrolyte structure was large lower than that of LiPDSPA and LiPDSOA polymer electrolyte structures. It was concluded that this comb-like structure is helpful for enhancing the movement of lithium ion in the polymer electrolyte membrane and subsequently improving its ionic conductivity.With the charges on the framework anions well delocalized and the cations in the extra framework highly exposed, the polymeric compounds are both thermally and electrochemically stable with ionic conductivity of the fabricated membranes comparable to the values of the conventional liquid electrolytes for Li-ion batteries. The high conductivity coupled with the good mechanical strength of the membranes enables the materials to be used as single ion electrolytes as well as separators in the battery cells.更多还原