中孔碳微球的可规模制备及其在液流超级电容器中的应用

Flow supercapacitor is one of novel grid-scale electric energy storage systems, which could share the major advantages of both supercapacitors and flow batteries, providing rapid charging/discharging while enabling the decoupling of the power and energy ratings. However, some intrinsic problems including low slurry stability, slow flowability and poor cycling performance limit greatly its real-world applications. To overcome these drawbacks, the present project will take the following aspects into consideration, namely electrochemistry, colloidal science, material science, fluid mechanics, and rheology to describe ion and charge percolation, adsorption of ions, and redox charge storage processes in suspension electrodes. Firstly, mesoporous carbon microspheres will be prepared using a novel and low-cost approach based on a spray drying process. Their mesoporous structure and surface chemistry will be carefully controlled to maximize the electrochemical performance. Then, the suspension of mesoporous carbon microspheres in a liquid electrolyte as a flowable electrode will be prepared, and its rheological behavior will be systematically studied. Also, the flow cell will be designed and optimized which is critically important to facilitate the flow of the slurry and maximize system performance. Based on the rheological and electrochemical performance, the electrochemical capacitive behaviors in both static and flow configurations will be analyzed and the ions/electrons transport across the electrode via percolation networks will be discussed. Furthermore, the pseudocapacitance via the fast redox reactions will be introduced by adding redox-active electrolytes or composting transition metal oxides into mesoporous channels. These strategies should lead to a substantial increase in the energy and power densities of a suspension electrode system. The present project demonstrates a cost-effective, pragmatic, and scalable approach toward obtaining high energy and power densities by a flowable electrode systems for grid scale energy storage.

液流超级电容器是一种半固态流动储能体系，兼具超级电容器高功率和液流电池大规模储能特点。本项目针对液流超级电容器的稳定性、流动性、倍率性能不足等瓶颈问题，开展中孔碳微球电极材料的化工制备及结构调控、半固态浆料的流体力学和电化学性能提升策略研究。首先基于喷雾干燥平台，耦合液相合成和颗粒工程技术，实现“微反应器”内快速溶胶-凝胶和干燥过程，揭示颗粒内部的结构形成机制，突破孔隙结构与孔道表面化学的协同调控技术。其次系统研究高浓度、高稳定性悬浮态浆料的调配及流变行为，结合仿真模拟手段，构建高稳定性液流超级电容器体系，阐明电子/离子在流动相、微球界面、微球孔内的输运机理、适配原则。在此基础上，进一步引入氧化-还原反应提升液流超级电容器性能，揭示流动和静止状态下半固态浆料的电化学双电层形成、赝电容反应机理，建立和完善高效液流超级电容器储能技术的基础理论方法。

本项目以基于多孔炭材料实现兼具高功率密度和高能量密度的超级电容器材料和结构设计为研究主线，从材料设计角度对多孔炭材料进行结构化及复合化设计、从储能机理角度构造双电层与赝电容或电池反应的复合储能、从电解液角度适配高价阳离子或高氧化还原活性的电解液，构建高能量密度超级电容器。首先，采用喷雾干燥法规模化制备中孔炭微球 (MCM)，电化学测试下扫描速率增大50倍后容量保持率高达75%，在功率密度为1.8 kW/kg下能量密度仍能保持1 Wh/kg，与商用微孔炭球相比提升近1倍，体现了中孔材料在高倍率性能和高能量密度上的优势。而后，制备MCM/V2O5复合材料，结果表明，Al3+能够有效地在V2O5内实现嵌入和脱出，MCM/V2O5在1M Al2(SO4)3体系中的能量密度可达18 Wh/kg，是同体系下MCM能量密度的近4倍，与低价态Mg2+和Na+体系相比，高价态Al3+带有更高的离子电荷数，插层赝电容行为发生时电荷转移更多，从而能量密度提升最为明显，提供了炭基赝电容材料在水系高价阳离子体系高效储能的可行性。此外，采用MCM作为优异的正极材料，制备二维层状NiFe-LDH/rGO负极材料，基于电容双电层和电池氧化还原复合储能机理，构造不对称锂离子电容器，在正负极活性质量比为6:1下，锂离子电容器的能量密度可达133 Wh/kg，功率密度可达4016 W/kg，并能保持5000次以上的长循环稳定性。另外，采用聚丙烯腈活性碳纤维毡 (ACF-900) 作为一体化电极，电解液中正极添加K3[Fe(CN)6]和负极添加2,6-DHAQ的不对称超级电容器，其分别在正负极发生不同的氧化还原反应，使得水系工作电压窗口拓宽至2 V，全电容器的能量密度提升至39.1 Wh/kg，是空白电解液体系的10倍，比单一添加体系高3-4倍，解决了水系电容器工作电压窗口窄限制能量密度提升的难题。本项目从电极材料结构化、储能机理复合化、电解液活性化等角度出发成功构造新型炭基超级电容器，为提升炭基超级电容器的能量密度提供了思路和理论依据。在项目研究期间，发表标注受本项目资助的SCI论文共27篇，其中发表在Applied Catalysis B: Environmental、Nature Communications、Chemical Engineering Journal等杂志上的高水平论文。