氧化还原掺杂的聚合物：一类新颖的高容量二次电池正极材料

发布时间：2018-09-12 07:42

【摘要】：能源危机与环境污染是当今人类社会面对的严重问题。探索和发展先进的储能方式是解决能源问题的关键技术之一。锂离子电池由于综合性能优异,被认为是最具潜力的高比能储电体系。然而现阶段,锂离子电池的能量密度主要受限于正极材料的比容量。商品化锂离子电池的正极材料主要是过渡金属氧化物。由于无机刚性晶格的限制,理论比容量很难有所突破。以碳元素为基本骨架的导电聚合物由于导电性好,理论比容量高,氧化还原可逆性好,价格低廉,环境友好等特点,是理想的二次电池正极材料。然而由于活性物质利用率低,聚合物实际容量远远低于理论容量。本文旨在探索提高导电聚合物容量利用率的新方法,以实现最大程度地释放聚合物的潜在容量,从而开发高性能,低成本的导电聚合物二次电池材料。主要研究内容和研究结果如下： 1.以聚吡咯为研究模型,通过氧化还原固定化掺杂的方式合成了Fe (CN)64-掺杂的聚吡咯复合材料PPy/FC,并考察了该材料作为锂离子电池正极材料的电化学性能。实验结果表明,相对于未掺杂的PPy,经过Fe (CN)64-掺杂的PPy (PPy/FC)的充放电容量提高了3倍以上,接近145mAh g-1,且循环100周后容量保持率可以达到80%；以400mA g-1的电流密度充放电时,放电比容量仍然有110mAh g-1.对该聚合物复合材料充放电机理的探究表明,由于大阴离子Fe(CN)64-对PPy的固定化掺杂作用,PPy/FC的充放电机理由传统的阴离子掺杂-脱杂过程变成了体积较小的阳离子(Li+)的嵌入-脱出反应,并且Fe (CN)64-/Fe (CN)63-电对在充放电过程中也通过自身的氧化还原反应为体系提供额外的容量。同时,Fe (CN)64-/Fe (CN)63-电对的存在,也对PPy主链存在显著的活化效应。 2.为了验证氧化还原掺杂对聚合物主链活化的普适性,实验分别使用了不同的掺杂剂,不同的聚合物主链以及不同的溶液体系。首先以聚吡咯为研究模型,分别采用不同类型的氧化还原掺杂剂(金属配合物类,过渡金属含氧酸盐类,有机氧化还原基团)对PPy掺杂。掺杂后的聚合物复合材料的电化学容量呈现出显著的提高,并且具有良好的电化学性能。以二苯胺磺酸根掺杂的聚吡咯(PPy/DS)为例,在50mA g-1的电流密度下可逆放电容量达到143mAh g-1,100周后容量保持率为87%。当充放电电流密度提高到1600mA g-1时,可逆放电容量仍然可以达到50mAh g-1.。同时,我们以Fe(CN)64-为掺杂剂,分别对聚苯胺,聚二苯胺,聚(3,4-二氧乙烯噻吩)掺杂,得到聚合物复合材料PAn/FC, PDPA/FC,PEDOT/FC。相对于本征态聚合物,这些聚合物复合材料的电化学容量都呈现出显著的提高,并且循环稳定。最后,我们将氧化还原固定化掺杂所得的聚合物复合材料PPy/FC, PPy/DS用于钠离子电解液中进行充放电测试。与在锂离子电池中相同,经过掺杂后的聚合物复合材料呈现出显著的容量倍增效应。PPy/FC在钠离子电池中以50mAg-1的电流密度充放电,放电容量达到135mAhg-1,循环100周后容量保持率为82%,并且大电流充放电性能良好。PPy/DS在50mA g-1的电流密度下放电容量也可以达到135mAhg-1,并且具有良好的循环稳定性与倍率性能。 3.针对氧化还原固定化掺杂的掺杂度低,由活性掺杂剂提供的电化学容量有限这个问题,我们合成了多个氧化还原活性基团复合的导电聚合物-聚(1,5-二氨基蒽醌)(PDAQ),并将其与气相炭纤维(VGCF)复合制备了PDAQ/C,考察了其室温下在锂离子电解液中的电化学性能。实验结果表明：PDAQ/C复合材料在20mA g-1的电流密度下,首周放电容量达到285mAh g-1,循环200周后,放电容量为160mAh g-1。当电流密度提高到800mA g-1时,放电容量仍然可以达到125mAh g-1。对该聚合物复合材料充放电机理的探究表明,该材料的放电容量主要包括两个部分：一是聚苯胺主链的掺杂脱杂；另一部分是醌基(Q)的氧化还原反应。 4.对于氧化还原固定化掺杂,虽然大幅提高聚合物的电化学容量,但距其潜在的理论容量仍有差距。为了探索新的方法,我们合成了自掺杂聚合物-聚二苯胺磺酸钠(PDS),实现了聚合物主链100%掺杂,并探索了该材料作为钠离子电池正极材料的可行性。实验结果表明,以50mA g-1的电流密度充放电,放电容量接近其理论值99mAhg-1,充放电平台在3.6V左右。循环50周后,当电流密度达到400mA g-1时,放电容量为43mAh g-1。而且相对于普通的导电聚合物,该自掺杂聚合物富含钠源,为解决实用化正负极匹配问题提供方便。通过对该材料充放电机理的探究表明,PDS充放电过程对应于阳离子Na+的嵌入脱出。
[Abstract]:Energy crisis and environmental pollution are serious problems facing human society nowadays. Exploring and developing advanced energy storage methods is one of the key technologies to solve energy problems. Lithium-ion batteries are considered as the most potential high-specific energy storage system because of their excellent comprehensive performance. However, the energy density of lithium-ion batteries is mainly limited at this stage. Specific capacity of cathode materials. Transition metal oxides are the main cathode materials for commercial lithium-ion batteries. Due to the limitation of inorganic rigid lattice, theoretical specific capacity is difficult to break through. It is an ideal cathode material for secondary batteries. However, due to the low utilization of active materials, the actual capacity of the polymer is far lower than the theoretical capacity. Two battery materials. The main research contents and research results are as follows:
1. Fe(CN)64-doped PPy/FC composites were synthesized by redox immobilization doping method with polypyrrole as the research model. The electrochemical properties of the composites as cathode materials for lithium-ion batteries were investigated. The results showed that the charge-discharge capacitance of Fe(CN)64-doped PPy(PPy/FC) was higher than that of undoped PPy. The specific discharge capacity of PPy/FC was 110 mAh g-1 when the current density of 400 mA g-1 was charged and discharged. The charge-discharge mechanism of the polymer composite was studied. The results showed that the charge-discharge mechanism of PPy/FC was due to the immobilization and doping of large anion Fe(CN)64-on PPy. The traditional anion doping-dehybridization process has been changed into a small cation (Li+) intercalation-dehybridization reaction, and the Fe(CN)64-/Fe(CN)63-pair also provides additional capacity for the system through its own redox reaction during charging and discharging. At the same time, the existence of Fe(CN)64-/Fe(CN)63-pair also shows the presence of PPy main chain. The activation effect.
2. In order to verify the universality of redox doping on the activation of polymer backbone chain, different dopants, different polymer backbone chains and different solution systems were used in the experiments. The electrochemical capacity of PPy-doped polymer composites was significantly improved and the electrochemical properties of the composites were good. Taking PPy/DS doped with diphenylamine sulfonate as an example, the reversible discharge capacity reached 143 mAh g-1 at the current density of 50 mA g-1, and the capacity retention rate was 87% after 100 weeks. The reversible discharge capacity of PAn/FC, PDPA/FC and PEDOT/FC composites can still reach 50 mAh g-1 when charge-discharge current density increases to 1600 mA g-1. At the same time, we doped polyaniline, Polydiphenylamine and poly (3,4-dioxyethylene thiophene) with Fe (CN) 64 - as dopant, respectively, and obtained polymer composites PAn/FC, PDPA/FC and PEDOT/FC. At last, we used PPy/FC and PPy/DS to test the charge-discharge performance of sodium ion electrolyte. As in lithium ion batteries, the doped polymer composites showed significant capacity. The discharge capacity of PPy/FC was 135 mAhg-1, and the capacity retention rate was 82% after 100 weeks of cycling. The capacitance of PPy/DS could reach 135 mAhg-1 at the current density of 50 mAg-1. Yes.
3. In view of the low doping degree of redox immobilized dopants and the limited electrochemical capacity provided by active dopants, we synthesized poly (1,5-diaminoanthraquinone) (PDAQ) with multiple redox active groups, and prepared PDAQ/C by compounding PDAQ with vapor-phase carbon fiber (VGCF) at room temperature. The experimental results show that the discharge capacity of PDAQ/C composites reaches 285mAh g-1 in the first week at the current density of 20 mA g-1, and 160 mAh g-1 after 200 cycles. When the current density is raised to 800 mA g-1, the discharge capacity can still reach 125 mAh g-1. The charge-discharge machine for PDAQ/C Composites The results show that the discharge capacity of the material mainly consists of two parts: one is doping and dehybridization of the main chain of polyaniline, the other is redox reaction of quinone group (Q).
4. For redox immobilized doping, although the electrochemical capacity of the polymer is greatly improved, there is still a gap from its potential theoretical capacity. In order to explore new methods, we synthesized a self-doped polymer-sodium Polydiphenylamine sulfonate (PDS) and realized 100% doping of the main chain of the polymer, and explored this material as the cathode material for sodium ion batteries. The experimental results show that the discharge capacity is close to the theoretical value of 99 mAhg-1 and the plateau of charge and discharge is about 3.6 V. After 50 weeks of cycling, when the current density reaches 400 mAg-1, the discharge capacity is 43 mAhg-1. Compared with ordinary conductive polymer, the self-doped polymer is rich in sodium source, which is the solution. The charge-discharge mechanism of PDS is studied and it is shown that the charge-discharge process of PDS corresponds to the intercalation and detachment of cationic Na +.
【学位授予单位】：武汉大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM912;O631.3

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