碳纳米管CNT和KB混合空气正极的制备及其在锂空气电池中的性能研究

发布时间：2018-05-03 23:20

本文选题：锂空气电池 + KB　；参考：《深圳大学》2015年硕士论文

【摘要】：锂空气电池理论能量密度高达11425 Wh/kg(不包括氧气),与锂离子电池、燃料电池、空气电池相比,是迄今为止能量密度最大的储能体系,吸引了全世界研究人员的关注。研究开发高能锂空气电池,有望解决全球所面临的能源短缺、环境污染、油价飙升及能源争夺战争等问题,特别是为电动汽车的长距离行驶,提供了新的实现途径。在锂空气电池中,空气正极作为发生氧化还原反应和容纳放电产物的主要场所,不仅要为放电产物提供足够的存储空间,还要为氧气、电子、锂离子提供正常传输的通道。孔堵塞、正极极化导致电池容量降低、循环性能下降。为了改善锂空气电池放电产物堵塞空气正极,提高锂空气电池循环性能。本文提出将碳纳米管CNT和KB混合制备锂空气电池正极。通过改变碳纳米管CNT和KB混合质量比,制备一系列碳纳米管CNT和Ketjen Black carbon(KB)混合空气正极,对相应的锂空气电池进行电化学性能测试,探究电池的循环性,并对充放电产物及反应机理进行初步的探索。1、CNT、N-CNT及KB材料具有高的电导率、平均孔径在3.5 nm左右,与锂空气电池放电产物沉积位置的孔径相当,除此KB碳多孔材料含有大量的中孔,总的孔体积高达2.79 m3/g,比表面积也高达1589.92 m2/g。碳纳米管的加入可以有效增加反应的活性位点,提高氧气和离子的传输效率。采用合适的比例将KB与碳纳米管材料混合可以制备得到具有较大比表面积和孔体积的空气正极,为锂空气电池提供更多放电产物存储场所以及最佳的气液扩散通道,从而提高电池的电化学性能和循环性能。2、在干燥的空气环境中,以1:1比例CNT/KB(KB:CNT:PTFE为4.5:4.5:1)混合的空气正极,对锂空气电池的能量效率最有利,且循环性能最好。碳纳米管CNT与KB按1:1混合,充分发挥了各自的优势,形成了适应于锂空气电池的正极结构,为放电产物提供了足够的存储空间,保障了氧气和离子在正极内部的传输,提高了电池的电化学稳定性。最终本实验获得了在0.3 m A/cm2条件下,容量高达0.4 m Ah,比容量为1000m Ah/g,稳定循环186圈的大电流,高容量和高循环性能的锂空气电池。3、本文制备的锂空气电池均以1M Li TFSI/Sulfolane作为电解液,大部分电池在0.3 m A/cm2,甚至在0.5 m A/cm2的电流密度下均可以循环上百圈,说明环丁砜体系的电解液是一种较为稳定的电解液,可以抵御电池较高的过电势,真正建立锂空气电池可逆循环,是一种适用于锂空气电池的电解液。4、环丁砜体系的锂空气电池放电时,正极表面覆盖很多的薄片状的过氧化锂产物,充电过程中过氧化锂又随之分解。但是由于过氧化锂导电性较差,分解电压较高,放电产物并不会完全分解。随着放电产物逐渐的积累,正极孔道被堵塞,造成正极钝化电池衰竭。因此深入正极研究,构造合适的多孔结构,降低空气正极极化是提高锂空气电池性能的重要途径。
[Abstract]:The theoretical energy density of lithium-air batteries is as high as 11425 Wha / kg (excluding oxygen. Compared with lithium-ion batteries, fuel cells and air batteries, it is the largest energy storage system so far and has attracted the attention of researchers all over the world. The research and development of high-energy lithium-air batteries is expected to solve the global energy shortages, environmental pollution, soaring oil prices and energy wars, especially for the long distance driving of electric vehicles, providing a new way to achieve. In lithium-air batteries, the air cathode is the main place for redox reaction and for the discharge products. It not only provides enough storage space for the discharge products, but also provides the normal transmission channels for oxygen, electrons and lithium ions. The cell capacity is reduced and the cycle performance is decreased due to the hole blockage and positive polarization. In order to improve the performance of lithium-air battery, the discharge product can block the positive electrode of air and improve the performance of lithium air battery. In this paper, carbon nanotube (CNT) and KB were mixed to prepare the cathode of lithium air battery. A series of carbon nanotube (CNT) and Ketjen Black carbonated air positive electrodes were prepared by changing the mixing mass ratio of carbon nanotubes (CNT) and KB. The electrochemical properties of the corresponding lithium air batteries were tested to explore the recirculation of the batteries. The charge-discharge products and reaction mechanism were preliminarily explored. The CNTN-CNT and KB materials had high electrical conductivity and the average pore size was about 3.5 nm, which was equivalent to the pore size of the deposition position of the discharge products of the lithium air battery. In addition, this KB carbon porous material contains a large number of mesoporous materials, the total pore volume is up to 2.79m3 / g, and the specific surface area is up to 1589.92 m2 / g. The addition of carbon nanotubes can effectively increase the active sites of the reaction and improve the transport efficiency of oxygen and ions. Air positive electrodes with large specific surface area and pore volume can be prepared by mixing KB with carbon nanotube materials in a suitable proportion, which provides more storage places for discharge products and the best gas-liquid diffusion channel for lithium air batteries. Therefore, the electrochemical performance and cycle performance of the battery are improved. In the dry air environment, the air positive electrode mixed with CNT/KB(KB:CNT:PTFE at 1:1 ratio is the most favorable to the energy efficiency of the lithium air battery, and its cycling performance is the best. The carbon nanotubes (CNT) and KB are mixed at 1:1 to give full play to their respective advantages and form a positive electrode structure suitable for lithium air batteries, which provides sufficient storage space for the discharge products and ensures the transport of oxygen and ions in the positive electrode. The electrochemical stability of the battery is improved. Finally, under the condition of 0.3 m A/cm2, the lithium air battery with a capacity of up to 0.4 m Ahh, a specific capacity of 1000m Ah/ g, a large current with a steady cycle of 186 cycles, a high capacity and high cycling performance is obtained. The lithium air battery prepared in this paper uses 1 M Li TFSI/Sulfolane as the electrolyte. Most batteries can cycle hundreds of cycles at a current density of 0. 3 Ma / cm ~ 2, or even 0. 5 m A/cm2, indicating that the electrolyte in the sulfolane system is a relatively stable electrolyte that can withstand the higher overpotential of the battery. The real establishment of a reversible cycle for lithium-air batteries is a product of lithium oxide, a thin sheet of lithium oxide coated on the surface of the positive electrode, which is suitable for lithium air batteries in the system of sulfolane. Lithium oxide decomposes again during charging. However, due to the poor conductivity of lithium oxide and high decomposition voltage, the discharge products will not be completely decomposed. With the gradual accumulation of discharge products, the positive electrode channel is blocked, resulting in positive passivation battery failure. Therefore, it is an important way to improve the performance of lithium-air battery by studying the positive electrode, constructing the appropriate porous structure and reducing the polarization of the air positive electrode.
【学位授予单位】：深圳大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TM911.41;O646.541

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