高载硫量三维多孔硫复合正极的构筑及其电化学性能研究

Since it is inexpensive and environmental friendly with ultrahigh theoretical energy density, lithium-sulfur battery becomes the frontier and hot spots in energy storage field. However, there are still several fatal shortcomings of lithium-sulfur batteries, including the insulating nature of sulfur, the solubility of intermediates into organic electrolyte and the huge volume change during the charge/discharge process. To address such issues, this proposal focuses on the high-performance three-dimensional (3D) porous and conductive sulfur composition cathode with high sulfur loading. Firstly, by means of the nanostructurization and alloying process of sulfur, its conductivity and electrochemical properties can be improved. Then, carbon nanomaterials/sulfur with 3D porous network will be constructed and their integrative and synergistic effect will be utilized, which can improve the electron and/or ion conductivity, decrease the solubility of intermediates, prevent the large volume expansion of sulfur composition cathode, thus the electrochemical properties of lithium-sulfur batteries can be greatly enhanced. And then, by designing and constructing 3D binder-free and free-standing sulfur composition cathode the effective energy density of Li-S battery will be further improved. Finally, by combining in-situ characterizations of XRD, Raman and electrochemical properties with first-principles calculations, the mechanism of the enhanced electrochemical performances can be revealed. This proposal has not only fundamental significance on deeply understanding the electrochemical mechanism of lithium-sulfur batteries, but also engineering significance on developing high-performance lithium-sulfur batteries.

锂硫电池因具有超高理论能量密度、成本低廉、环境友好等优点成为当前储能领域的研究前沿与热点。然而，锂硫电池目前还存在硫电导率极低、中间产物易溶解及充放电时体积变化巨大等致命缺点。针对这些问题，本项目以高性能的高载硫量三维多孔硫复合正极为研究对象，首先，拟通过硫的结构纳米化及成分“合金化”来提高硫自身的电导率及电化学性能；然后，通过构筑碳纳米材料/硫三维多孔导电网络结构，利用该结构的集成协同效应来提高硫复合正极的电子/离子电导率、降低多硫化物的溶解、抑制体积膨胀，从而改善其电化学性能；通过构筑无粘结剂、自支撑的三维硫复合正极，进一步提高锂硫电池的有效能量密度；最后，通过原位XRD、Raman及电化学性能表征，并结合第一性原理计算，分析揭示硫复合正极电化学性能改善的电化学机制。本项目的研究，不仅对于深入理解锂硫电池的电化学机制具有科学意义，而且对于研发高性能锂硫电池具有工程意义。

锂硫电池理论能量密度高达2600 Wh/kg，是现有锂离子电池的5-10倍，是最有前景的下一代汽车动力电池候选之一。本项目重点开展了锂硫电池正极改性及机理研究，包括硫正极的改性、三维多孔硫复合正极的构筑及电化学性能及增强机理；还增加了多功能隔膜设计、构筑及其对多硫化物跨膜穿梭效应抑制效应，增加了界面功能层设计构筑及其对锂硫电池锂金属负极枝晶生长抑制机理等研究工作。本项目取得了如下创新成果，具有重要意义。.1. 研发了高负载、高稳定的硫正极材料。提出构筑三维多孔导电载硫骨架改善正极导电性和限制体积膨胀，提出引入极性氧或硫化物来化学吸附固定多硫化物；在国际上首次发现MoS2/石墨烯异质结对多硫化物的强烈化学吸附及高效转换催化双重效应；揭示了多硫化物穿梭效应的“物理化学限 域与转换催化”协同抑制机理，建立了高负载、高稳定硫正极的设计、制备方法，推进了高比能锂硫电池产业化进程。.2. 研发了多功能复合隔膜。提出在商业Celgard隔膜上设计具有极性、导电、热稳定的功能层制备成复合隔膜，通过极性化合物与多硫化物LiPS之间强烈的化学键合及空间耦合作用；揭示了“多硫化物跨膜穿梭效应”的高效抑制机理，建立了低内阻、高稳定、高安全锂硫电池隔膜的可控制备方法，推进了高稳定、高安全隔膜的产业化进程。.3. 研发了锂枝晶高效抑制的锂金属电池：通过在锂金属负极、隔膜表面构筑锂离子流均匀分布及枝晶抑制的氮化物功能层，有效抑制了锂金属电池枝晶生长，提高了电池安全性。..在Energy Environ Sci、Adv Energy Mater等发表SCI论文18篇，申请发明专利5项，“锂硫族电池隔膜与正极设计及电化学性能增强方法与机理研究” 成果荣获2020年四川省自然科学二等奖，培养了4位博士后、8位博士生（贺加瑞获2018年中国电子教育学会优秀博士学位论文奖）、11位硕士生，超额完成了项目预期目标。