基于炭/硫复合物正极的高性能锂离子电容器构筑及电化学性能调控

Lithium ion capacitors (LICs) are a novel type of electrochemical power source consisting of a capacitor-type cathode and a lithium-ion battery type anode, which exhibit high energy density and high power density. However, the discrepancy in reaction kinetics and capacities between commonly used anode and cathode materials of LICs limits the practical application of LICs due to the unsatisfactory energy density and power density. This project aims to construct high performance LICs by using porous carbon/sulfur as cathodes and amorphous carbon nanosheets as anodes materials. It is expected that the carbon/sulfur materials can increase the specific capacity of cathode by the synergistic effect of capacitor and battery materials. In order to improve the cycling stability of the carbon/sulfur cathode, a porous carbon with numerous ultramicroporous carbons and interconnected pore channels was designed to encapsulate sulfur and cut off the contact reaction between sulfur and the carbonate electrolyte. On the other hand, amorphous carbon nanosheets will be synthesized as anode materials to shorten the diffusion path of electrolyte ions and the study on adjusting the interlayer spacing of carbons will be conducted to reduce the electrolyte ions insertion energy barrier, which will together improve the rate capability of anode. The structure-function relationship between microstructures and electrochemical performance of the materials will be revealed by the combination of galvanostatic charge-discharge experiment, Trasatti method, GITT method, and in-situ XRD technique, etc. Meanwhile, it’s anticipated to enhance the power density and energy density of lithium ion capacitor by matching the capacities of anode and cathode materials and optimizing the reaction kinetics of the two electrodes. This project will offer a new application for eco-friendly and low-cost sulfur material and meanwhile provide a basis for the construction of high-performance lithium ion capacitors.

锂离子电容器是一种基于电池和电容双重储能机制的新型化学电源，具有高能量密度、高功率密度等优点。但现有正负极材料反应动力学及容量的不匹配，限制了锂离子电容器理论能量密度和功率密度的充分发挥。本项目提出以多孔炭/硫复合物为正极，构建锂离子电容器。期望借助电容与电池效应的叠加提高正极比容量，设计富含极微孔且孔道贯通的多孔炭，封装活性硫，切断与碳酸酯电解液接触反应的路径，提高炭/硫正极的循环稳定性；同时设计制备纳米薄层无定形炭负极，缩短电解液离子的扩散路径，调控无定形炭的层间距，降低锂离子嵌入能垒，提高负极的快速充放电能力；结合恒流充放电、Trasatti法、GITT法、原位XRD等表征手段揭示材料微纳结构与充放电性能间的构效关系；匹配优化正负极容量和反应动力学，提升锂离子电容器的功率密度和能量密度。本项目的开展将会为绿色价廉的活性硫提供新的应用途径，为高性能锂离子电容器的构筑提供科学依据

本项目开展了锂离子电容器中高性能正负极材料的定向设计与电化学性能的调控研究。基于合成方法的创新，制备了多孔炭正极、多孔炭/硫或磷酸铁锂复合正极、纳米片状炭负极以及三维自支撑锰基氧化物/炭复合负极等一系列材料。在高比容量正极方面，从碳质结构和孔隙结构的角度提高多孔炭材料的比电容，并复合硫及磷酸铁锂等嵌锂材料，同步提高正极的比容量和倍率性能，证明通过定制炭载体的孔结构可设计磷酸铁锂的非晶结构及嵌锂机制。在高倍率、长寿命负极方面，发现0.52 nm极微孔可同步提高炭材料的倍率性能和首次库伦效率，证明了纳米薄层形貌对嵌锂动力学及循环稳定性的提高，并通过引入高比容量的转化机制负极进一步提高负极的比容量。在实际器件层面，引入无集流体、高负载面密度的三维自支撑概念，探讨正负极搭配及预锂化对电化学性能的影响，提出可行的器件优化方案，以促进锂离子电容器的产业化应用。