用高容量碳质负极与梯度硫正极构建硫-锂离子电池的研究

Lithium sulfur battery is considered as a promising candidate for energy-storage systems due to its high theoretical specific energy. However, the utilization of lithium sulfur battery is limited by the poor cycling stability and serious safety concern of lithium anode. The design of sulfur-lithium ion batteries with high performance is expected to be an effective way to solve these problems mentioned above. This work aims to mimic the gradient structure and function of animal bones to design the graded sulfur cathode. In this way, the stable interface between cathode and electrolyte would be formed during charge-discharge process to further improve the cycle ability. A porous hard carbon anode material was prepared using animal bone as raw material. With the special composition and structure of animal bone, hard carbon with highly graphitized crytallite in microscopic scales and highly ordered structure in macroscopic scales can be formed. On this basis, a specific capacity and cycling stability of carbon-based anode could be improved. We will constitute a novel “sulfur-lithium ion” battery system with high energy and high safety using the gradient sulfur cathode, carbon-based anode, combining optimal importing the lithium ions to the battery system. And based on this, the new battery structural design principle as well as the fabrication science of the novel electrode materials will be revealed. Here, the charge storage and transport mechanism during the electrochemical process will be elucidated. We will explore new method to improve the cycle ability and safety of lithium sulfur batteries, and then promote the commercialization of lithium sulfur batteries.

因具有高理论能量密度，锂硫二次电池有望成为新一代高比能电池体系。但其循环稳定性差和金属锂负极的安全隐患成为限制其实用化的瓶颈。高性能硫锂离子电池体系的构建是解决上述问题的有效途径。本项目拟仿动物骨梯度结构和功能，设计制备梯度结构硫正极，以期获得充放电过程中稳定的正极电化学活性反应界面，提高电池的循环性能；以动物骨为原料，借助其组成和结构的优势，制备具有高度石墨化微晶且宏观结构有序的多孔硬碳负极材料，提高碳质负极的比容量和循环稳定性；基于上述新型正、负极，通过优化锂源引入方式，构建高比能、高安全性的碳质负极与梯度硫正极组成的硫-锂离子电池体系。在此基础上，揭示新型电池体系结构设计原理与电极制备科学，阐明体系电化学过程中电荷存储和输运机制，探索提高锂硫电池循环性能和安全性的新途径，加快锂硫电池的实用化进程。

锂硫二次电池被认为是最有潜力的下一代高比能电池体系之一。然而，目前亟待解决的问题是其循环稳定性差且金属锂负极存在安全隐患。本研究从电极材料的设计制备出发，研究了提高锂硫电池稳定性和安全性的方法。首先从正极活性物质的制备出发，研究了以明胶为多功能助剂合成正极活性物质硫的方法及其工艺的优化，实现了对所制备硫粒径的调控，得到了制备高性能正极活性物质的合适条件：在室温搅拌下，将浓度为1M硫代硫酸钠水溶液滴加到含有20mg/mL的明胶稀盐酸溶液中，合成出表面包覆明胶保护层的亚微米硫颗粒，且分布较为均匀。得益于所设计硫的结构优势，在0.2C的电流密度下，锂硫电池初始放电比容量为1218mAh/g；100次充放电循环后，放电比容量仍有1007mAh/g，容量保持率达到83%；在0.5C的电流密度下，300次充放循环后，放电比容量依然能够达到780mAh/g，容量保持率达75%。借助天然材料的组成与结构的特点，制备了多孔碳及碳基复合材料，并且通过锂源引入制备了高性能的负极材料，改善了负极电化学性能。还研究了蟹壳碳热解过程，揭示了热解动力学规律，并在此基础上制备了高性能碳材料；以明胶为多功能助剂在碳材料中原位合成氧化锌等，将亲锂组分引入碳基框架，得到ZnO@CSC复合材料。应用ZnO@CSC的锂铜电池在电流密度为1.0mA/cm2，容量为1.0mAh/cm2的条件下可稳定循环130次，且锂金属的平均沉积/剥离效率在90%以上。研究了废弃铬革屑的热解过程，并制备得到了三氧化二铬掺杂的胶原基碳纳米纤维，为提升负极的性能奠定了基础。应用所设计制备正极和嵌锂碳质负极构建了硫-锂离子电池体系，在0.3C的电流密度下，电池容量可以达到800mAh/g，提高电池的稳定性同时实现了负极的安全性。我们将对该体系进行进一步深入研究，为其实用化奠定基础。