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液流电池由于其能量和功率可以独立地输出，因此非常适合用于电网的规模储能。而锂离子浆料电池则进一步突破了液流电池对于活性材料溶解度的限制，具有更高的能量密度。本文以钛酸锂（LTO）和磷酸铁锂（LFP）为研究对象，对浆料制备方法、电化学性能进行了深入研究。LTO因其易得性、尺寸稳定性以及高安全性、极长的循环寿命和环境友好性而特别具有吸引力。而LFP具有平坦的电压平台（3.4V vs Li+/Li），固有的热安全性、环保特性，并且自然环境中含有大量的铁资源，因此被认为是电动汽车（EV）和混合电动汽车（HEV）所用电池的最佳正极材料。本文主要研究开发具有连续导电网络的高稳定性悬浮浆料电极，从而为浆料电池提供高效率和长循环性能。通过组装纽扣半电池并以静态模式和测试，使用LTO（负极）和LFP（正极）验证了悬浮浆料设计的可行性。具体研究内容如下：（1） 液流电池由于其设计、制造和控制的便利性，是大型储能设备最有前途的候选之一，但其能量密度还有待提高。锂离子悬浮电极通常由电解液、活性物质和其他添加剂组成，由于其单位体积内的活性物质含量较高，是提高液流电池能量密度的有效途径。但遗憾的是，由于普通电极材料密度大、悬浮体导电网络差等原因，很难获得稳定的悬浮电极。在本研究中，我们成功地利用聚乙烯氧化物（PEO）和碳纳米管（CNTs）制备了稳定的LTO悬浮型负极浆料，其中PEO通过分子内斥力稳定了负极浆料，CNT则构建了一个完整的导电网络。在0.5C倍率下，该负极浆料具有较高的可逆容量，大于140mAh/g，并且在200个循环中保持80%以上的初始容量，这在以前的研究工作中从未实现过。该策略也有望适用于其他悬浮电极的设计，例如石墨和LiFePO4，它们对高能量密度锂离子浆料电池的发展具有启发性。（2） 采用与上述工作类似的策略，使用PEO和科琴黑（KB）制备了高度稳定的LFP电极浆料，电池在0.5C的倍率下发挥出超过155mAh / g的容量，在循环200圈之后容量保持率可达80%。 （3） 使用三乙二醇二甲醚（G3）和四乙二醇二甲醚（G4）电解液制备了基于LFP的正极浆料。G3、G4可与等摩尔的双三氟甲基磺酰亚胺锂（LiTFSI）形成溶剂化离子液体（SIL），课题组前期的研究工作表明，将SIL采用碳酸甲乙酯（EMC）稀释后，得到锂盐浓度约为1M的电解液，其仍具有良好的电化学性能，且高、低温综合性能优于碳酸酯电解液。因此，本论文也将其用于了浆料电池的研究。在这项工作中，借助于碳纳米管（CNT）和科琴黑（KB）成功地制备了高度稳定的LFP悬浮正极浆料，它们的综合作用建立了导电网络。在0.5C的倍率下，发挥出的可逆容量超过155mAh / g，在循环200圈后容量保持率可达74.19％。总之，本论文通过导电剂、分散剂、电解液等方面的优化，制备得到了3种可用于锂离子液流电池的浆料电极，其均具有较好的物理与电化学稳定性，并在扣式电池中表现了较优的性能。本论文的工作为锂离子浆料电池的开发奠定了一定的实验与理论基础。;Flow batteries have been studied for grid-scale energy storage applications because their capacity and power delivery can be independently scaled. Lithium ion slurry flow cells (LSFCs) are expected to break through the restriction of active material solubility in electrolyte, and provide higher energy density to the flow systems. In this work, two typical electrode materials, Li4Ti5O12 (LTO) anode and LiFePO4 (LFP) cathode are selected and slurry electrode was prepared based on them. The LTO flow batteries are particularly attractive because of its ease of availability, dimensional stability, as well as high security, ultra long cycle life and environmental friendliness. LFP is considered as the best favorable cathode materials for the batteries used in electric vehicles (EVs) and hybrid electric vehicles (HEVs), due to its adequate flat voltage plateau (3.4 V versus Li/Li+), inherent thermal security, environmentally friendly, and plenty of iron resources in natural surroundings. This dissertation focuses on the research of developing highly stable suspension with continuous conductive network to deliver high efficiency and long cyclic performance. The feasibility of the suspension making design verified using LTO (anolyte) and LFP (catholyte) by assembling and testing coin-cells work in static mode. The details as the following:(1) A flow battery is one of the most promising candidates for large scale energy storage devices due to its ease of design, construction, and control, while its energy density is yet to be enhanced. The lithium ion suspension electrode, which is usually comprised of electrolyte, active material and other additives, is an effective way to enhance the energy density of flow batteries for its relatively high active material loading per unit of volume. While unfortunately, a stable suspension electrode is difficult to be obtained mainly for two reasons, the high density of common electrode materials and the poor conductive network in the suspension. In this work, a stable Li4Ti5O12 (LTO) suspension anolyte is successfully prepared with the aid of polyethylene oxide (PEO) and carbon nanotubes (CNTs), in which PEO stables the anolyte by intramolecular repulsion force, and CNT builds an integrated conductive network. The anolyte delivers a high reversible capacity of more than 140mAh/g under 0.5C rate, and it keeps more than 80% of its initial capacity in 200 cycles which was never been achieved in previous reports. This strategy is also hopefully suitable for the design of other suspension electrodes, such as graphite and LiFePO4, which shine a light on high energy density flow battery development.(2) A stable LiFePO4 (LFP) suspension catholyte is successfully prepared with the aid of polyethylene oxide (PEO) and ketjen black (KB), in which PEO stables the anolyte by intramolecular repulsion force, and KB builds an integrated conductive network. Therefore, a highly stable LFP-catholyte is efficiently prepared by using PEO together with KB, making a robust conductive network delivered the electrochemical capacity over 155mAh/g at 0.5C and kept 80% of its initial capacity at 200 cycles. (3) Herein, lithium ion slurry flow cells employing triethylene glycol dimethyl ether (Triglyme/G3) and tetraethylene glycol dimethyl ether (Tetraglyme/G4) electrolyte solutions with LiFePO4 catholyte were studied. G3 and G4 could form solvated ionic liquid (SIL) with equal molar LiTFSI, which is a very promising novel electrolyte system. Our previous work proved that when ethyl methyl carbonate (EMC) was added into the SIL, even when the lithium salt concentration decreased to about 1M, the electrolyte still deliver superior performances than the carbonate electrolyte in a wide temperature range. Therefore, we also prepared suspension electrode with this electrolyte. A highly stable LiFePO4 (LFP) suspension catholyte is successfully prepared with the aid of CNTs and KB, their combined effect builds an integrated conductive complex. The catholyte delivered a reversible capacity of more than 155mAh/g under 0.5C rate, and it keeps 74.19% of its initial capacity in 200 cycles. In conclusion, we enhanced both the physical and electrochemical stability of 3 kinds of suspension electrodes by introducing conductive agents, dispersant as well as new electrolyte, based on which the semi coin cells demonstrated satisfying electrochemical performances. This work is hoped to shed some light on the future research on lithium ion slurry flow batteries.
|MUHAMMAD NAEEM. 用于锂离子浆料电池的高稳定浆料电极[D]. 中国科学院大学,2020.|
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