氮掺杂分级多孔碳支撑过渡金属磷化物/硫复合锂-硫电池正极材料电化学性能研究

The inferior cycling stability of sulfur electrodes for electrochemical energy storage results from its own poor electronic conductivity, volumetric expansion upon lithiation and high solubility of lithium polysulfides. This project proposes a novel conductive support system, the N-doping hierarchical porous carbon modified by electrochemical-deposited transition metal phosphide nanoparticles, for sulfur loading and immobilizing, to prepare high-performance cathode electrode materials for lithium-sulfur battery with long life time. To realize the design, the following critical scientific problems should be revealed: electrochemical energy conversion of sulfur nanoparticles in lithiation process, energy transfer interactions between transition metal phosphide and sulfur nanoparticles, the space-confining effect of hole structure, charge transport mechanism between N-doing carbon materials and phosphide nanoparticles, etc. Based on the investigation of electrochemical information, especially, the charge/discharge and cycling performance, it is expected to uncover the influence of component and structure on electrochemical performance, break through the preparation and controllable assembly of composite nano electrode materials, and develop self-supporting cathode electrode materials with high rate performance and excellent cycling stability. The successful implementation of this project will provide new idea for the design and preparation of lithium-sulfur battery materials, showing significant values from theoretical view and in practical application.

单质硫的低导电性、锂化过程中的体积膨胀与多硫化锂产物的可溶性是导致其电化学储能循环性能不稳定的重要原因。本项目提出在分级结构多孔氮掺杂碳孔道表面电化学组装过渡金属磷化物纳米结构作为复合导电固硫支撑体系，组装硫纳米颗粒，实现高效长寿命锂-硫电池正极材料。通过对锂化过程中硫纳米颗粒电化学能量转换、硫纳米颗粒与磷化物纳米结构之间的能量传递和孔道空间限域、氮掺杂碳与磷化物纳米结构之间的电荷传输机制等关键科学问题的研究，实现氮掺杂分级多孔碳/过渡金属磷化物/硫纳米复合结构的设计。通过对其电化学特性特别是充放电性能和循环性能的研究，掌握氮掺杂分级多孔碳/过渡金属磷化物/硫纳米复合材料的组成-结构对电极电化学性能影响规律，突破复合纳米电极材料的制备和可控组装，研制高充放电性能、高循环性能的具有自支撑特性的锂-硫电池正极材料。本研究为锂-硫电池电极材料的设计和制备提供了新思路，具有重要理论意义和应用价值。

项目针对碱金属-硫电池和碱金属离子电池的电极材料面对的能量密度和循环寿命问题，设计三维多孔分级结构，通过构筑分级结构多孔氮掺杂碳孔道负载过渡金属、过渡金属磷化物纳米结构作为复合导电固硫支撑体系。并进一步采用微纳结构调配，功能互补的策略，提升金属锂、钠离子扩散和电子传导速率，显著提升了活性材料内部活性位置的利用率。利用单组份材料表面的电荷属性，组装发展三维多孔、核壳结构，为离子和电子的快速传输和扩散提供了有效的通道，有利于提高电极材料的反应动力学。独特的三维分级结构不仅可以减缓活性组分电极在充放电过程中的体积膨胀，并通过其化学键和复合材料间的纳米协同作用，提升电子传导效率，提高锂硫、钾硫、钠离子和锂离子电池的能量密度和循环寿命。