基于三维空心碳管/石墨烯复合结构的高比能锂硫电池的研究

Lithium-sulfur batteries have attracted an enormous amount of interest owing to their various advantages, including abundant resources, low cost, environmental friendliness and high theoretical capacity, thereby become the most potential high-energy battery system. However, the low electrical conductivity of sulfur and its intermediate polysulfide products, the shuttling of dissolved lithium polysulfide and large volumetric expansion between sulfur and the final product Li2S hamper the application of lithium-sulfur batteries. Herein, three-dimensional tube-in-tube structured carbon tubes/graphene composites are employed to encapsulate sulfur in this project. Tube-in-tube structures provide inner space to confine sulfur and alleviate the large volume change during cycling, and outer heteroatom doped carbon layer helps to alleviate the dissolution of lithium sulfides, which can effectively prevent the dissolution of sulfur cathode. Besides, the inner carbon nanotubes can ensure high electronic conductivity of hollow carbon tubes. Therefore, this can promote the utilization of sulfur cathode and greatly enhance the energy density of lithium-sulfur batteries. The synergistic effect of three-dimensional carbonaceous matrix, tube-in-tube structure and heteroatom-doped carbon layer on the encapsulation of sulfur is systematically investigated. According to this project, the rational design criterion of carbon/sulfur cathode and the mechanism of sulfur immobilization are proposed. It is anticipated to provide theoretical and technological guidance for other sulfur cathode.

锂硫电池具有资源丰富、成本低廉、环境友好、理论比容量高等优点，成为最具发展潜力的高能电池体系。然而，硫及其放电产物的电绝缘性、中间产物多硫化物的溶解，以及充放电过程中严重的体积变化等缺点极大地限制了锂硫电池的应用。本项目拟将硫负载在空心碳管/石墨烯复合三维结构中，通过管中管结构提供较大空间封装硫并缓冲电极的体积变化，利用外侧管壁的杂原子碳层吸附硫，从而防止多硫化物的溶解，并以内部碳纳米管为空心碳管提供较高的电导率，提高正极材料的利用率和电池的能量密度，阐明三维碳基集流体、管中管结构的限域效应和外壁杂原子掺杂碳层的键合作用对复合硫正极电化学性能的协同效应及作用机理，优化合成高性能的硫碳复合正极材料。基于本项目的研究，提出碳硫复合正极结构设计准则和固硫机理，可为其他硫正极的改性提供指导依据。

锂硫电池由于其能量密度高、资源丰富、成本低和无污染等优点，被视为最具潜力的新一代高能量密度储能体系。然而，硫正极及其放电产物的电绝缘性，中间产物的溶解和穿梭效应，以及充放电过程中严重的体积变化，严重影响其循环性能，极大的阻碍了锂硫电池的商业化进程。本项目拟以空心碳管/石墨烯复合三维结构作为载硫碳基底。将硫封装在管中管结构内，不但可以缓解硫正极的体积变化，而且碳管外侧的杂原子碳层有效吸附多硫化物，有效的缓解穿梭效应。三维碳基集流体、管中管结构的限域效应和外壁杂原子掺杂碳层的键合作用对复合硫正极电化学性能具有良好的协同效应，因而制备出的空心碳管/石墨烯@硫正极表现出优异的电化学性能。本项目的研究能够为其它碳硫复合正极结构设计提供准则和固硫机制，同时可以为其它硫正极的改性提供指导依据。