生物藻类衍生N-掺杂炭材料的结构调控及用于钠离子体系负极材料储能研究

Based on the wide availability and low cost of sodium, sodium-based systems can provide an alternative option to lithium-based systems, and have been received extensive attention. Carbonaceous material is one of the most promising anodes for sodium-ion batteries. However, carbons in sodium-based systems face the problems of the low capacity, unqualified cyclability and rate performance, which makes it hard to approach the electrochemical characteristics of graphite in lithium-based systems. Development of nitrogen-doped carbons with suitable porosity is an efficient way to solve above-mentioned problems and improve the electrochemical performance. Due to the limitation of synthesis methods, how to control the type of functional groups and reduce the preparation cost still challenge the preparation of nitrogen-doped carbons. In this project, we proposed a novel "green" synthesis strategy, and nitrogen-doped carbons with controlled functional groups and structure can be obtained by using protein-rich biomass-algae as the precursors. Combined with electrochemical evaluation, the relationship among microstructure, porous structure, functional groups and sodium storage mechanisms can be clarified, which can help to find the limiting factors for enhancing capacity and rate capability. Algae-based biomass derived nitrogen-doped carbon material may become a dominate candidate as electrode material for sodium-based energy storage devices with high capacity, low cost, excellent rate capability and long cycle life. Based on the half-cell analysis, the fabrication of sodium-ion capacitor is also performed, which can be beneficial for the development of next-generation capacitors.

从资源安全角度出发，寻找锂离子体系替代品至关重要。由于钠资源丰富，基于钠离子体系的研究受到广泛重视。炭材料是最具应用潜力的钠离子体系负极材料之一，但是比容量较低、倍率性能以及循环稳定性欠佳的问题，使其无法与石墨在锂离子体系中的性能表现相媲美。制备具有一定孔隙结构的N-掺杂炭材料有望解决上述问题，提高炭材料的电化学性能。因合成方法的限制，N-掺杂炭材料普遍存在如何实现官能团可控调变、降低制备成本的问题。本项目拟引入绿色制备理念，采用富含蛋白质生物质-生物藻类为前驱体，探索制备N-掺杂炭材料的新技术，并实现对含氮官能团种类和含量的调控。结合电化学分析，揭示炭材料微结构、孔结构、官能团种类对电化学储钠机制的影响，提出限制储钠容量的关键因素。上述生物藻类衍生N-掺杂炭材料有望成为高比容量、低成本、高倍率和长寿命的新型负极材料。在此基础上，组装钠离子电容器，并为高能量钠离子电容器设计组装打下基础。

目前对储能器件的需求日益旺盛，加剧了锂资源短缺，推高了锂离子电池的价格，迫切需要开发出无资源限制的高性能储能器件。与锂相比，钠具有储量丰富、价格低廉的优势；并且钠和锂在同一主族，具有相似的物理化学性质，钠离子电池被认为是最有希望替代锂离子电池的储能体系。碳材料具有成本低、结构可控的优点，是最有潜力的一种负极材料。但是，钠离子不能自由嵌入到石墨层状结构中，并且由于钠离子尺寸远大于锂离子导致碳电极的倍率性能和循环稳定性较差。因此，开发低成本、高性能的钠离子体系碳负极材料显得至关重要。. 为了突破这一关键问题，本项目从钠离子体系碳负极的结构需求出发来设计碳材料，实现了大石墨层间距、有效官能团修饰、合适孔隙结构碳材料的制备。同时从低成本角度考虑，选取了富有地域特色的海洋藻类生物质为前驱体，实现了碳材料的宏量可控制备。在对碳材料孔结构、微晶结构以及官能团修饰进行调控的基础上，阐明了储钠机理及其性能的衍变规律，解决了碳负极在钠离子体系中容量低、倍率性能差、循环稳定差的问题。经过性能优化，碳负极的可逆容量达到300 mAhg-1以上、循环500圈容量保持在80%以上。在材料制备过程中，重点实现了含氮、含硫官能团的可控修饰，创新性发展了掺杂碳材料的制备技术，指出了官能团在提高电极性能、库伦效率中的关键影响。基于碳负极的优异性能，进一步发展了基于双碳型钠离子电容器的组装。结合正负极质量调控和电位调节，组装的钠离子电容器的能量密度达到100 Whkg-1 以上。. 本项目的实施将促进对海洋生物资源的利用，对开发高效、低成本碳电极材料打下坚实的基础，并为设计高性能混合电容器提供了必要的材料储备、理论依据和技术支持。除此以外，本项目还涉及了其它陆地生物质衍生碳材料的制备及其它水系、锂离子体系非对称混合电容器的组装应用，揭示了碳材料的结构、形貌、组成等与电化学性能之间的相互关系。本项目共发表SCI收录论文30篇，申请中国发明专利4项。