石墨烯基高性能柔性锂硫电池的构建及性能研究

This project is dedicated to constructing the flexible lithium sulfur batteries with high energy density and long cycle life from the perspective of the configurations of the device. Firstly, this project develops the fabrication method for low-cost graphene with controllable macro- and micro- structures and the controllable technology for functionalization of graphene. The influences of different preparation technologies for graphene-based flexible sulfur cathode and silicon anode on their structures and electrochemical performances will be investigated. Then this project will further study the influences of the sandwich structures of graphene-based flexible sulfur cathode, silicon anode and different electrolyte systems on the electrochemical performance of lithium sulfur batteries, especially on the cycle stability, discussing the interaction mechanisms of these factors with polysulfides. The pre-lithiation process of the silicon anode will be optimized and the impacts of different pre-lithiation processes on its structure and electrochemical performance will also be studied. Finally, the flexible lithium sulfur batteries are assembled and the assemble process is further explored and optimized to obtain high energy density and long cycle life. The implementation of this project will provide an idea and the necessary scientific basis for the functionalization of graphene based materials, the design of composite materials, preparation and controlled assembly. At the same time, on the basis of ensuring extremely performance of high rate and long cycle, this project will optimize each section of the flexible lithium sulfur batteries, eventually promote the wide use of flexible lithium sulfur batteries, and further boost the industrialization and scale of the lithium sulfur batteries.

本项目致力于从器件角度出发构建具有高能量密度、长循环寿命的柔性锂硫电池。项目首先发展了微观和宏观织构可控的低成本石墨烯制备及功能化调控技术，研究了三明治结构柔性硫正极、石墨烯基硅负极的不同制备工艺对电极结构和电化学性能的影响；深入研究了柔性硫正极、石墨烯基硅负极以及不同电解液体系对锂硫电池电化学性能特别是循环稳定性的影响，探讨了硫正极、硅负极及电解液与多硫化物之间的作用机制；优化石墨烯基柔性硅负极的预锂化工艺以及研究了不同工艺对硅负极结构及电化学性能的影响；最终设计和组装了柔性锂硫电池，探索并优化器件组装和制备工艺，得到具有高能量密度、长循环寿命的新型柔性锂硫电池。项目的实施将为石墨烯基材料的功能化设计、电极的可控构建提供思路和必要的科学基础；同时本项目将在保证正负极高倍率、长循环性能的基础上，优化锂硫电池各部分的匹配关系，最终促进柔性锂硫电池的广泛应用，推动锂硫电池的产业化和规模化。

锂硫电池具有理论能量密度高、环境友好、成本低廉等优点，但仍存在活性物质利用率低、循环稳定性和安全性差等问题，成为制约其实用化的瓶颈。本项目发展了新的锂离子-硫全电池体系，其中采用具有三明治和钢筋混凝土结构的硫电极作为正极，具有自支撑结构的预锂化石墨烯包覆硅-碳薄膜为负极。对于硫正极，纸团状石墨烯-硫杂化材料被PVP修饰的碳纳米管缠绕，并夹在两层由石墨烯构成的片层之间，构成具有三明治结构的硫正极。这种独特的结构不仅能够提供锂离子和电子的快速传输通道，并能有效的抑制多硫化物的穿梭效应和容纳充放电过程中硫的体积膨胀。对于负极，石墨烯紧密的包裹住由无定型碳包覆的硅颗粒，这可以有效的容纳硅充放电过程中的体积膨胀，并能提供良好的电子传输网络。当组装成硅-硫全电池时，在1C倍率下循环时，首次容量可达905 mAh g-1，经过800周循环后容量仍保持在650 mAh g-1，每周的容量损失率仅为0.035%，表现出良好的循环稳定性。此外，采用水热处理和离子交换方法制备得到还原石墨烯-双金属硫化物杂化材料，其中纳米双金属硫化物颗粒均匀的分散到石墨烯的片层上，确保良好的电接触。在这种杂化材料中，双金属硫化物纳米颗粒不仅能够通过化学键合作用来限制多硫化物的穿梭，更重要的是能在充放电过程中通过催化转化来促进多硫化物向不溶硫化物的转变。此外，还原石墨烯具有相对较高的比表面积可以提供良好的导电网络和结构稳定性。由于这种独特的结构设计和组分组成，该G-NCS杂化材料在负载81.5 wt%的硫作为活性物质，仍能展现出高的面积比容量、良好的倍率性能和增强的循环稳定性，高的活性物质利用率。这些为研究高安全性、长循环性能锂硫电池储能器件，提供了新思路和理论依据。