纳米多孔碳电极/离子液体界面离子输运特性及选择性储能机理

Recently, electrochemical double layer capacitors (EDLCs) have attracted a great deal of interest due to their high charge and discharge rates over almost unlimited number of cycles. It is a promising candidate used as energy storage device in various applications, including smart grid, energy/transportation technologies, and so on. However, lower energy density serves as an obstacle to expand its application. Their energy density can be increased using ionic liquids and electrodes with nanometer pores which is a very promising strategy, but this tends to reduce their power density and compromise the key advantage of supercapacitors. To address this issue, selective charging scheme was proposed in this proposal. Based on molecular dynamics simulation and in situ experimental measurement methods involving nuclear magnetic resonance (NMR) method, this project aims at revealing the origin of charging mechanism and charge transport dynamics in nanoporous carbon EDLC which using ionic liquids (ILs) as electrolyte. In this project, it opens up opportunities for improving EDLC performance by fundamental understanding of charging dynamics and storage mechanisms which plays a pivotal role to select reasonable and judicious pores and ILs combination. The final objective is focused on tuning the trade-off between energy and power performance of EDLC by controlling charging mechanism, which may be determined by ion-ion interaction and ion-electrode interaction. The research achievements could provide guidelines for better pores and ILs combination design, which are potential of improving EDLC performance significantly. All of above make this present project have great significance both in academic and practical application aspects.

因超高的功率密度和超长的循环寿命，（双电层）超级电容器成为储能器件领域的一颗新星，在可再生和清洁能源利用中的地位不可或缺，但能量密度目前只有锂电池的1/20。使用离子液体和纳米多孔电极组合体系是提高能量密度最具前景的途径，但该方法折损了功率密度这一关键优点。由于严重缺乏揭示功率密度下降机理的研究，当下避免功率密度降低的方法都存在较大局限性。本项目抛弃现有方法中减小离子/离子间相互作用或减小离子/电极间相互作用的思路，以多级有序孔道和混合离子液体组合为媒介，反过来利用上述相互作用并对其进行调控，实现离子的选择性充电行为，从而实现同时提高功率和能量密度。项目主要利用MD模拟和原位实验测量研究离子在单个纳米孔中的迁移及扩散动力学、离子在多级有序孔道中的选择性充电机理、非对称离子尺寸和电极结构整体优化三部分内容。目标是在避免功率密度损失的前提下提高超级电容器能量密度，具有重要的学术意义和应用价值。

微/纳米孔和多孔电极界面及内部的离子输运特性和储能机理对改善能量存储与转换器件的性能具有重要作用。项目围绕碳基材料/离子液体界面储能机理与新材料开发、微/纳米孔及多孔电极内能量转换与储能机理展开研究。项目执行过程中，开发了离子液体电解液的力场模型，构建了石墨烯电极的MD模型，建立了离子液体/石墨烯电极体系的电容计算模型，研究了离子液体特性对双电层结构的影响，揭示了离子形状对超级电容器储能特性的影响规律，利用MD对离子液体的界面输运特性及纳米孔中的迁移和扩散动力学进行模拟，探讨了电极电荷与电极附近离子的输运特性；对受限碳纳米孔中离子液体的传输动力学进行了综述；制备了二维过渡金属碳化物电极，在水系、有机、离子液体等电解液体系下，对电容特性进行了电化学性能测试分析，制备了纽扣超级电容器，对其储能特性进行了机理揭示；制备了相变微胶囊新型复合储能材料，对其储能性能进行了研究分析，对相变微胶囊中掺杂膨胀石墨的新型复合材料储能特性进行了实验表征和机理揭示，使储能性能得到明显提升；研究了纳米孔中的离子输运情况，探索了微/纳米孔内能量转换及多孔电极内电荷传递及储能规律等。在上述研究的基础上，发现了新的研究点，拓展了新的研究思路，进一步探索了多孔材料内部及界面强化传热传质等研究内容。项目研究成果有助于理解微/纳米孔中的储能机理和能量转换机理，对提高超级电容和液流电池等储能器件性能具有一定的指导意义。