几种有机电极材料的改性及储能机理研究

发布时间：2018-03-20 14:43

本文选题：有机电极材料　切入点：锂离子电池　出处：《电子科技大学》2017年博士论文　论文类型：学位论文

【摘要】：锂离子电池广泛应用于社会生产生活的各个方面,传统的无机锂离子电池电极材料由于价格昂贵以及不可再生的过渡金属的使用等弊端,并不能满足现代社会对于构建“清洁能源社会”的要求。而有机小分子电极材料具有绿色环保、价格低廉、分子结构多样化以及较高的理论比容量等特性而被广泛关注。但目前该类材料仍然存在许多亟需解决的基础性科学问题,主要包括其常规有机电解液中的溶解导致容量衰减较快、实际比容量较低和倍率性能较差,并且其电化学反应机制仍需要进一步探究。本论文利用理论计算结合具体实验,围绕对苯二甲酸根(TP~(2-))有机小分子负极材料,通过对其物理化学性质调控、材料改性、离子传输通道优化以及新型电极材料体系的设计旨在解决上述问题。主要内容和结果归纳如下:(1)通过简单的酸碱反应一步法制备了一系列基于有机对苯二甲酸锂(Li_2TP)衍生物锂盐,并探讨了不同取代基对电极材料的电化学行为产生的影响。研究表明该类有机共轭二羧酸锂盐均能够可逆的储锂,其中对苯二甲酸锂(Li_2TP)具有较高的理论比容量、明显的充放电平台以及可逆的储锂通道,是一类具有较大潜力的有机负极材料。对Li_2TP苯环上引入的取代基后,会对电极材料的分子结构产生诱导效应和共轭效应,从而调控材料的电化学平台。另外,以2,5-二羟基对苯二甲酸(DHTPA)和对应的二锂盐(Li_2DHTPA)为例,通过XRD、FT-IR等测试对该类材料的储锂机理进行了研究,结果表明有机羧酸DHTPA具有电化学储锂活性但循环性能较差,DHTPA首周放电过程经历了离子取代过程,其首周循环后产物为Li_2DHTPA;而化学法制备的Li_2DHPTA能够可逆的储锂,且循环稳定特性优异。创新性的提出通过电化学取代和化学取代两种不同的方式,得到同种有机电极材料的思路。(2)针对Li_2TP在常规有机电解液中的溶解性问题导致循环性能较差,通过对Li_2TP进行碱金属阳离子取代制备另一种有机对苯二甲酸钠(Na_2TP),研究了Na_2TP作为锂离子电池负极材料并提供一种简单的喷雾干燥改性研究方法。简单的水结晶法制备的Na_2TP在电解液中的溶解度较低,因而循环性能与Li_2TP相比得到明显的改善。针对有机小分子导电性差因而活性位点利用率较低,进一步设计了一种简单的喷雾干燥的技术一步原位制备该有机Na_2TP与碳纳米管复合材料(Na_2TP-SD-MCNTs),电化学测试表明:循环50周后,复合材料容量仍然保持在214 mAh g~(-1),与微米级别的Na_2TP以及未加入碳纳米管的纯材料相比,其循环可逆容量得到明显的提升,倍率性能得到明显改善。主要原因是:该方法制备的纳米复合材料能够有效缩短锂离子在电极材料中的扩散路径,MCNTs能够提供良好的导电网络并稳定电极结构,而制备的复合材料在有机的电解液中的溶解速率能够有效减缓。(3)考虑到有机电极材料的电化学性能与其锂离子传输通道有关,实验首次对Li_2TP进行碱金属阳离子取代,制备了具有空旷结构的对苯二甲酸钾(K_2TP),并对比研究了不同碱金属对苯二甲酸盐体系(Li、Na、K)的储锂特性。由于Li、Na具有较小的离子半径,Li_2TP与Na_2TP形成较短的金属-O键(1.96?/2.43?)容易造成离子堆垛拥挤现象,离子在电化学过程中的迁移比较困难。但K_2TP由于其K+半径较大,从而使得TP~(2-)与K~+形成更加匹配的离子键,具有最低的范德华排斥力和非常稳定的晶体结构。通过理论计算和实验表明,K_2TP作为锂离子电池负极材料,在0.1 C的电流密度下,经过100周循环,可逆容量达到第二周容量的77%并且倍率特性非常优异。结合三种有机对苯二甲酸盐的晶体结构可知,Li_2TP和Na_2TP为一维锂离子扩散通道,而K_2TP具有空旷的二维离子传输通道,因而K_2TP表现出最优异的储锂循环稳定性和倍率性能。此外,为提高有机材料的实际比容量,实验制备了K_2TP/石墨烯的纳米复合材料,该材料在8 C电流密度下循环500周后,比容量仍然能够保持在122 mAh g~(-1),表现出非常稳定的大倍率循环性能。主要原因是:K_2TP活性物质在电解液中十分稳定,制备的纳米级别的K_2TP能够有效缩短锂离子扩散路径,而其与石墨烯形成的复合能够构建良好的导电网络。(4)为拓展有机电极材料的应用领域,本文首次开发了两种有机小分子对位二羧酸钾盐:K_2TP及衍生物吡啶2,5-二羧酸钾(K2PC),并研究其作为新型的有机钾离子电池负极材料。K_2TP和K2PC具有十分合适的储钾平台电位,其储钾机理为有机共轭二羧酸钾盐的共轭羰基的打开和恢复过程。K_2TP和K2PC作为钾离子电池负极材料表现出优异的循环稳定性,其循环100周后可逆容量分别为181mAh g~(-1)和190 mAh g~(-1)。该类有机材料是制备“摇椅式”钾离子电池理想负极材料。(5)另一方面,考虑到有机材料丰富的结构,本论文首次设计了一类新型有机小分子共轭氰基类化合物,以对苯二腈(DCB)和9,10-二氰基蒽(DCA)为例,研究了其可逆的储能特性、电化学行为以及溶解性问题等。与DCB相比,DCA具有更优异的电子导电率;其还原态DCA~-和DCA~(2-)的稳定性优于DCB。同时,DCB作为二次电池电极材料时,经历连续可逆的两电子转移过程。
[Abstract]:The lithium ion battery is widely used in social life and production, the traditional inorganic electrode materials for lithium ion batteries because of transition metal prices and non renewable use etc, and can not meet the modern society to build a "clean energy society". While organic small molecule electrode material with the green environmental protection, low price, molecular the structure of diversification and high theoretical capacity and other characteristics was widespread concern. But the materials still exist many basic scientific problems need to be resolved, including the conventional mechanical solution in dissolved solution leads to the capacity decay faster, lower than the actual capacity and poor rate capability, and the electrochemical reaction mechanism still needs to be this paper further explored. By theoretical calculation with the experiment, around the root of terephthalic acid (TP~ (2-)) of small organic molecules through the cathode material. A regulation on the physical and chemical properties, material modification, design of ion transmission channel optimization and new electrode material system to solve the above problems. The main contents and results are summarized as follows: (1) through one step method of simple acid-base reaction to synthesize a series of organic based on benzene two lithium formate (Li_2TP) derivatives and salts. To investigate the effect of different substituted groups on the electrochemical behavior of produced electrode materials. The results indicate that this kind of organic conjugated carboxylic acid lithium salt can two reversible lithium storage, including lithium terephthalate (Li_2TP) has high theoretical capacity, obvious charge discharge and the reversible lithium storage channel, is a kind of organic cathode materials with larger the potential of Li_2TP. By introducing substituents on the benzene ring, the molecular structure of the electrode materials will produce inductive effect and conjugated effect, thereby regulating the electrochemical platform. In addition to 2,5- Two hotp (DHTPA) and the corresponding two lithium salt (Li_2DHTPA) as an example, through the XRD, FT-IR and other tests were carried out to study on the mechanism of lithium storage in this kind of materials, the results showed that organic carboxylic acid DHTPA with electrochemical lithium storage activity but poor cycle performance, DHTPA first discharge process through ion substitution process, the first cycle after the product is Li_2DHTPA; and the chemical preparation of Li_2DHPTA can reversible lithium storage, and excellent cyclic stability. Proposed by electrochemical and chemical substitution to replace the two different ways, the same material obtained electromechanical ideas. (2) aiming at the problem of Li_2TP solubility in conventional organic electrolyte. Lead to poor cycle performance, preparation of another organic terephthalic acid sodium by alkali metal cations on the substitution of Li_2TP (Na_2TP), the effects of Na_2TP as lithium ion battery cathode material and provide a simple The spray drying method. The modified simple water crystal prepared by Na_2TP solubility in the electrolyte is low, so the cycle performance compared with Li_2TP significantly improved. For small organic molecules and poor conductivity of the active site of low utilization rate, further design a simple spray drying technique in situ the preparation of organic Na_2TP and carbon nanotube composite material (Na_2TP-SD-MCNTs), electrochemical tests show that after 50 cycles, the composite capacity remained at 214 mAh g~ (-1), and the micron level Na_2TP and without adding carbon nano tube materials pure meters compared to the cycle of reversible capacity improved obviously, rate performance improved obviously. The main reason is: the diffusion path method of nanocomposites can effectively shorten the lithium ion in the electrode material, the MCNTs can provide good and stable conductive network The electrode structure, and the dissolution rate of prepared composite materials in organic electrolyte can effectively slow down. (3) considering the electrochemical properties and organic electrode materials of lithium ion transmission channel, the experiment of Li_2TP for the first time the alkali metal cation substituted potassium terephthalic acid with open structure was prepared (K_2TP), and contrast effects of different alkali metal salts of terephthalic acid (Li, Na, K) of the lithium storage properties. Due to Li, Na has a smaller ionic radius, Li_2TP and Na_2TP formed -O bond metal short (1.96? /2.43?) can cause ion stacking crowding, migration in the electrochemical process of ion but difficult. K_2TP K+ because of its large radius, so that the TP~ (2-) ionic bond formation, and more K~+, Fan Dehua has the lowest repulsion and very stable crystal structure. Through theoretical calculation and experimental results show that the K_2TP as lithium ion Battery cathode material, current density at 0.1 C, after 100 cycles, the reversible capacity reached second and 77% week capacity rate performance is excellent. The crystal structure of three kinds of organic combination of terephthalic acid salt, Li_2TP and Na_2TP for one-dimensional lithium ion diffusion channel, and K_2TP has a two-dimensional ion transfer channels open, so K_2TP showed the most excellent lithium storage cycle stability and rate performance. In addition, in order to improve the actual organic material than the capacity of K_2TP/ graphene nanocomposites were prepared and the material circulation of 500 weeks under the current density of 8 C, specific capacity can still keep at 122 mAh g~ (-1). Show a big circulation performance is very stable. The main reason is: the K_2TP activity is very stable in the electrolyte, the prepared nano level K_2TP can effectively shorten the diffusion path of lithium ion, and its formation and graphene The composite can build good conductive network. (4) for the expansion of the application of organic electrode materials, this paper developed two kinds of small molecule organic carboxylic acid salts: two para K_2TP and 2,5- two derivatives of pyridine carboxylic acid potassium (K2PC), and studied as a new organic potassium ion battery cathode materials.K_2TP and K2PC with storage the platform is very suitable for the potassium potential, the storage mechanism of potassium for conjugated carbonyl organic conjugated carboxylic acid salts of the two open and recovery process of.K_2TP and K2PC as anode materials for lithium ion batteries exhibit excellent cycle stability. After 100 cycles the reversible capacity was 181mAh g~ (-1) and 190 mAh g~ (-1). Type of organic materials is the preparation of "rocking chair" potassium ion battery ideal cathode material (5). On the other hand, considering the structure of organic rich materials, this is the first time to design a new class of small molecule organic conjugated cyanide base. In two, the benzene nitrile (DCB) and 9,10- (DCA) two cyano anthracene as an example, to study the reversible storage characteristics, electrochemical behavior and solubility problems. Compared with DCB, DCA has more excellent electronic conductivity; the reduced DCA~- and DCA~ (2-) is more stable than DCB. at the same time, as the DCB two battery electrode materials, through two consecutive reversible electron transfer process.

【学位授予单位】：电子科技大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TM912

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