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随着全球经济的迅猛发展，化石燃料的快速消耗以及环境污染的日益加剧，高效、绿色、可再生的新型电化学电源受到广泛关注。锂离子电容器（LICs）具有比电池更高的功率密度，比电容器更高的能量密度成为近年来研究热点。然而传统锂离子电容器存在电解液泄露等安全问题，发展固态锂离子电容器提高储能器件的安全性成为未来储能设备研究重点。负极材料和固态电解质对电容器的性能有至关重要的作用。本文主要研究了适用于高性能固态电容器的负极材料和离子液体基电解质，结果如下：一、采用表面活性剂作为软模版剂，利用水热合成了五氧化二铌纳米复合材料。复合材料具有石墨烯和纳米无定形碳的修饰，拥有良好的孔道结构。作为负极材料，展现出优异的循环稳定性和倍率性能。随后利离子液体基凝胶电解质构筑了固态锂离子电容器。研究不同条件下的性能，器件在60 ℃时有着最佳性能：最大能量密度101.8 Wh kg-1，最大功率密度2 kW kg-1。研究了电解质组成对储能机制的影响，发现离子液体电解质具有最大的超电贡献而凝胶电解质的电容型贡献最小。探讨了温度对储能占比的影响，随着温度升高，超电占比逐渐提高并结合分子模拟结果给出解释。锂离子与离子液体阴离子形成团簇，从而抑制锂离子迁移速率，导致离子液体体系的锂电机制占比较低。二 、通过剥离法制备了Ti2Nb2O9复合多孔石墨烯纳米复合物（TNO/HrGO）。SEM和TEM 测试结果表明，TNO纳米片与石墨烯片层高度杂化形成紧密且纵横交错的纳米复合物。半电池中发现该纳米复合物呈现出优异的循环稳定性， 2000次循环后，电极材料依旧保持着207.1 mA h g-1的放电容量。在商业有机电解液中最大的能量密度为55.8 Wh kg-1。最后构建了负极为TNO/HrGO、正极为活性炭，PVDF-HFP/LiTFSI/[EMIM][BF4]为离子液体基凝胶电解质的锂离子电容器。通过对比可以发现，电容器在60℃ 时性能最优。最大能量密度为108.5 Wh kg-1，在维持最大的11.2 kW kg-1功率密度下，能量密度可达75.4 Wh kg-1。综上，本文研究从适用于离子液体基凝胶电解质的负极材料入手，合成了高性能金属氧化物复合电极并基于此构筑了离子液体基准固态锂离子电容器。准固态电容器具有较宽电压窗口、较高的温度窗口。研究了离子液体基凝胶电解质较其他电解质不同的储能机制，探讨了温度对离子液体内离子输运的影响。发现离子液体基凝胶电解质由于锂离子团簇使锂离子迁移速率降低，导致其超电储能占比较低，但是随着温度的升高超电贡献逐渐提高。高性能负极材料的结构调控和离子液体基凝胶电解质储能机制的研究为构筑具有广阔应用前景的新型准固态锂离子电容器提供了研究思路。;With the rapid development of the global economy, the rapid reduction of fossil fuels and the increasing environmental pollution, the construction of high-efficiency, green, and renewable new chemical power sources has received extensive attention. Lithium-ion capacitors have higher power density and cycle life than batteries, and higher energy density than electric double-layer capacitors. In recent years, the development of high-performance Lithium ion capacitors has become the focus of research. However, the traditional lithium-ion capacitors have the safety problem of electrolyte leakage. The development of solid-state lithium-ion capacitors to improve the safety of energy storage equipment has become the focus of future energy storage equipment research. Electrode materials, especially anode materials and solid electrolytes, play a decisive role in the performance of capacitors. The main research contents and results of this paper are as follows:1. The surfactant was used as a soft template to Nb2O5 nanocomposites by hydrothermal synthesis. The composite material has the modification of graphene and nano-amorphous carbon, and has a good pore structure. As a negative electrode material, it exhibits excellent cycle stability and rate performance. A quasi solid-state lithium-ion capacitor was constructed using the ionic liquid gel electrolyte. The performance of the device under different conditions was studied. The device has the best performance at 60 °C: maximum energy density 101.8 Wh kg-1 maximum power density 2 kW kg-1. The effect of electrolyte composition on the energy storage mechanism was studied. It was found that the ionic liquid electrolyte has the largest capacitor contribution while the gel electrolyte has the smallest capacitive contribution. The effect of temperature on the proportion of energy storage is discussed. As the temperature increases, the proportion of capacitor contribution increases gradually. Molecular simulation results show that lithium ions and ionic liquid anions form clusters, thereby inhibiting the migration rate of lithium ions, resulting in a relatively low lithium-ion battery type mechanism of the ionic liquid system.2. Ti2Nb2O9 composite porous graphene nanocomposites (TNO/HrGO) were prepared by co-flocculation. SEM and TEM results show that the TNO nanosheets and the graphene sheets are highly hybridized to form a tight and crisscross nanocomposite. The nanocomposite was found to exhibit excellent cycle stability in the half-cell, and after 2000 cycles, the electrode material still maintained a discharge capacity of 207.1 mA h g-1. The maximum energy density in commercial organic electrolyte lithium ion capacitors is 55.8 Wh kg-1. Finally, a lithium ion capacitor with negative electrode as TNO/HrGO, positive electrode as activated carbon and PVDF-HFP-LiTFSI/[EMIM][BF4] as solid electrolyte was constructed. By comparison, it can be found that the capacitor has the best performance at 60 °C. The maximum energy density is 108.5 Wh kg-1, and the energy density can reach 75.4Wh kg-1 at maximum power density of 11.2 kW kg-1.In summary, this paper studies the high-performance metal oxide composite electrode for the anode material suitable for ionic liquid gel electrolyte and builds an ionic liquid based solid-state lithium ion capacitor. Quasi-solid capacitors have a wider voltage window and a higher temperature window. The energy storage mechanism of ionic liquid electrolytes compared with other electrolytes was studied, and the effect of temperature on ions transport in ionic liquids was discussed. It is found that the ionic liquid electrolyte reduces the lithium ion migration rate due to the lithium ion cluster, resulting in its capacitor contribution being relatively low, but the capacitor contribution gradually increases with the increase of temperature. The structural regulation of high-performance anode materials and the study of ionic liquid electrolyte energy storage mechanism provide research ideas for constructing new quasi solid-state lithium-ion capacitors with broad application prospects.
|张家赫. 离子液体基准固态锂离子电容器构筑及其储能机制研究[D]. 中国科学院大学,2019.|
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