功能化介孔空心碳球结构设计及其与锂硫电池性能的构效关系研究

There are many inevitable disadvantages of lithium-sulfur batteries: (1) sulfur and its reduced products are electron insulating at room temperature; (2) the “shuttling effect” due to intermediate products such as lithium polysulfides in organic liquid electrolytes during charge/discharge process; (3) significant volume expansion of sulfur cathode is more than 80%, during charge/discharge process. Keeping these disadvantages in mind the proposed project will focus on synthesis of functional carbon spheres with precisely controlled mesoporous hollow structures having microstructures. Controlled chemical composition of carbon spheres will cause a synergies effect which will be favorable for sulfur anode materials for lithium sulfur batteries. Proposed methodology is as followed: (1) synthesis of hollow carbon spheres structures with interconnected mesoporous shells, with precise control of mesoporous size and shell thickness; (2) preparation of mesoporous hollow carbon spheres with hierarchical structures;(3) finding the structural activity relationship between electrochemical properties, microstructures and composition of materials; (4)developing in-situ methods for study of electrochemical process of carbon/sulfur composites materials of interface and obtaining the micro-functions mechanism in electrochemical processes. It will establish a new method to synthesize functional carbon spheres with mesoporous hollow structure with precise control. Between microstructure, chemical composition and the electrochemical performance of the structure-activity relationship is established. Through test and analysis, reveal the composition change of carbon/sulfur interface and their interaction principle in the process of charging and discharging, sulfur and reduction products of the migration mechanism in the electrode material, electrolyte and in the lithium battery system. Eventually developed with large specific capacity, high power, excellent cycle performance of lithium battery, also for its practical application to lay the theoretical foundation.

针对锂-硫电池中硫及还原产物导电性差、过硫化物易产生“穿梭效应”和硫在充放电循环中的体积膨胀等必须解决的关键性问题，本项目提出了功能化空心介孔碳球微观结构的可调控制备及其能充分发挥微观结构与体相及表层化学组成间协同效应的碳/硫复合正极材料的新构想。拟开展1)具有贯穿介孔空心碳球的合成及对其尺寸、壳厚、孔径的精确调控；2)借助于元素掺杂或表面修饰进一步获得功能化碳球的可控制备；3) 研究材料的化学组成、微观结构与电化学性能的构效关系；4)利用原位技术探究碳/硫界面的电化学反应机理等工作。建立一种微观结构可调的功能化碳球的制备新方法，阐明微观结构、化学组成与电化学性能间的构效关系，揭示充放电过程中碳/硫界面的组成变化及相互作用机制，以及硫与还原产物在电极材料、电解液和锂硫电池系统中的迁移机制。最终研发出具有超大比容量、高功率和优异循环性能的锂硫电池，为其实际应用奠定坚实的理论基础和实验数据。

针对锂-硫电池中硫及还原产物导电性差、硫在充放电循环中的体积膨胀以及还原产物产生“穿梭效应”等阻碍了锂-硫电池的实际应用，针对以上问题，本项目研究了功能化空心介孔碳球微观结构的可调控制备及其利用微观结构与化学组成间协同效应的碳/硫复合正极材料。主要完成内容1)实现了贯穿介孔空心碳球的合成及对其尺寸、壳厚、孔径的调控；2)通过杂原子掺杂或表面修饰进一步地制备出具有分级结构的功能化介孔空心碳球；3) 研究了功能化介孔空心碳球的化学组成、微观结构与电化学性能的构效关系；4)探究碳/硫界面作用和电化学反应机理等工作。重要结果、关键数据及其科学意义如下：通过一步的“溶胶-凝胶”法，合成了具有“贯穿孪晶”结构的介孔纳米空心球。其中，二氧化硅为空心球提供了稳定的骨架结构及限制性的纳米空间，有效阻碍了高温碳化过程中结构的收缩和坍塌。获得了具有开放骨架结构的单分散介孔碳空心球，且直径（10~1000 nm）、孔体积和比表面积可调控。概况为以下几点：①建立溶质溶度与介孔空心碳球的构效关系，② 系列core-shell分级结构介孔空心碳球的制备与参数控制，③建立了介孔空心碳球的微观结构（尺寸、壳厚、孔径、分级结构等）与参数控制的构效关系。将硫(90.4％)浸入到介孔孔体积为4.75 cm3/g的空心碳球中，经过 3100 次循环后，锂硫电池容量衰减低至0.023%。进一步采用分步添加二氧化硅作为“一石三鸟”策略，获得具有超高比表面积 (2615 m2/g)和开放的介孔的氮掺杂蛋黄-双壳碳纳米球。单质硫分散在双壳之间，或者空心内核之中，能高效的缓释体积膨胀和多硫化物穿梭效应。这些结果初步验证了分级介孔空心碳球的微观结构和化学组成性质二者共同对作用与锂硫电池性能的有良好的构效关系。最后初步探索了碳/硫界面的组成变化及相互作用。这些研究成果对高性能的锂硫电池储能器件提供了一定的理论基础和实际应用的参考价值，且在国内外学术刊物上发表了系列成果。