煤基高导电性多级孔炭的构筑及超电性能研究

Coal tar pich in Shanxi is abundant and cheap. How to fabricate coal pitch-based porous carbon in large scale with both hierarchical porosity and high electrical conductivity for high-performance supercapacitor remains a big challenge. This proposal aims to develop a new method for the synthesis of hierarchically porous carbon using coal pitch as the carbon source and biological CaCO3 as both the template and the activating agent with the assistance of CO2/H2O. The effects of the physical and chemical properties of raw materials, the conversion of template and activating agent during the pyrolysis, as well as the progress of porous structure will be studied. The electrical conductivity of the obtained carbon will be modified by sp2 carbon using the coal-based polycyclic aromatic hydrocarbon (PAH) as the molecular dopant. The effects of the structure, size and content of the PAH on the electrical conductivity of the carbons as well as the involved mechanism will be investigated. The synergistic mechanisms of the hierarchically porous structure, the electrical conductivity and the surface properties of the resultant materials for the energy storage need to be well proposed to figure out the relationship between the performance-structure-synthesis. The aim of this work is to integrate the advantages of hierarchical porosity and high electrical conductivity of the as-made carbon for high performance of supercapacitor. This project will shed some lights on the low-cost production of high performance functional carbon materials in the fields of coal chemical industry and realize the high added-value utilization of coal tar pitch. The results will provide important data and new strategies for the design of coal-based carbon materials used in the field of electrochemical energy storage.

山西煤炭资源丰富，以廉价的煤沥青制备兼具高导电性和多级孔结构的超级电容器用炭材料是一个富有挑战性的课题。项目精选易石墨化的煤沥青为碳源，采用生物碳酸钙“模板和活化剂”一体化造孔策略，辅以CO2/H2O物理活化，创制多级孔结构可控的煤基炭，研究生物碳酸钙“模板和活化剂”自转化对炭材料多级孔结构的调变机制；采用煤基稠环芳烃“分子自组装”补强碳骨架sp2杂化结构以提高多孔炭的电导率，揭示稠环芳烃的分子构型、分子尺寸、用量等参数对炭材料电导率的调变规律和内在机制；诠释煤基炭多级孔结构、sp2杂化率和表面官能团等结构特征对其超级电容器性能的影响规律和储能机制。课题旨在通过集成孔炭的高导电性和多级孔隙输运优势提升超级电容器能量密度。项目的实施为煤炭资源的高附加值利用开辟一条新途径，为进一步提升超级电容器性能奠定坚实的科学基础。

煤沥青基多孔炭材料的环境友好制备及研究其孔结构、表面性质调控与超电/锂电电化学性能构效关系具有重要意义。项目选取具有热塑性、碳产率高、灰分低等特点的山西煤沥青作为炭前驱体，虾壳（含碳氧氮和CaCO3）和牡蛎壳（>96% CaCO3和二维片层结构）兼做碳源/氮源、模板剂、活化剂，制备了比表面积（117.6~1371 m2 g-1）、孔尺寸（0.5-6nm）、氮含量（3.26~4.2 wt.%）和电阻（0.95~6.27 Ω）可调的系列多孔炭。结果表明，所得多孔炭的比表面积、导电性、氮掺杂协同影响产物的电化学性能，其中比表面积与导电性通常成反比关系，而氮掺杂有助于改善材料的亲水性，但含量过高会降低材料的导电性。具有分级孔结构（微孔、介孔、大孔）的孔炭表现出更优的电化学性能，其中兼具小孔和大孔结构的微-介孔炭因具有适宜的孔体积和比表面积可提高材料的比容量值；兼具大孔和高氮含量的介孔炭有利于提高材料的循环稳定性。所得炭材料用做超电时，具有微、介孔和氮含量适宜的分级孔炭循环5000次电容值仍可达266 F g-1，可以保持96.0%的电化学性能，最高能量密度和功率密度分别为30.6 Wh kg-1和1470.9 W kg-1。分级孔炭用作锂电时，在电流密度为0.1 A g-1的条件下比电容值可达1251 mA h g-1，归因于其微孔、介孔和大孔相互交联的网络结构有利于离子快速运输；其在电流密度为1.0 A g-1的条件下循环450次，仍保持94%电容性，这是源于样品2D片层结构堆叠构成的限域空间，有效缓解样品在充放电过程中的体积膨胀，延长了电池的使用寿命。项目提出了生物质基“自活化剂和自模板” 制备多孔炭的新概念，降低了原料成本，减少了环境污染，开辟了廉价煤沥青和废弃海洋生物质（虾壳和贝壳）构筑兼具导电性和可控孔结构炭材料的新方法，为提升超级/锂电性能奠定坚实的科学基础。