“丝瓜瓤”状微纳结构硫碳复合正极材料的可控制备与构效关系研究

Lithium-sulfur battery holds great potential due to its high theoretical specific capacity of 1675 mAh/g and specific energy of 2567 Wh/kg. Meanwhile, sulfur as a cathode material has the advantages of low cost, natural abundance and non-toxicity. However, the development of lithium-sulfur battery has met several challenges for its typically low sulfur utilization, low rate capacity, and poor cycle life.This project designs Luffa-sponge-like micro-/nano-structured sulfur-carbon composite electrode materials to achieve high sulfur content,high utilization and high stability of the sulfur electrode materials. With different aspect ratios of hollow carbon fibers as raw materials, the Luffa-sponge-like hollow porous carbon fibers are obtained by using pretreated process and activation process to regulate pore structure, pore size distribution and specific surface area. The nanoscale sulfur are immobilized with high efficiency into different-structured hollow porous carbon fibers using heterogeneous sulfur nucleation and heat treatment process. Then the relationships between the composition, structure, morphology, interfacial interaction of the composite electrode materials and their electrochemical properties are investigated. The control mechanism of high-efficiency sulfur immobilization is explored. The electrode kinetics of the composite electrode materials during the charging and discharging process is studied. Finally we clarify the mechanism of the composite electrode materials during the charge-discharge process and the key factors affecting the kinetic stability of the sulfur-carbon composite materials.Based on the research, we identify and achieve the preparation of high-capacity and long-life micro-/nano-structured sulfur-carbon composite cathode materials and providing guidance for the practical application of lithium-sulfur battery.

锂硫电池具有能量密度高、原料廉价、环境友好等优点，应用前景广阔。目前锂硫电池主要存在活性物质利用率低、倍率性能差以及循环性能不理想等问题。本课题通过设计具有"丝瓜瓤"状微纳结构的硫碳复合电极材料，旨在实现硫电极材料的高载硫量、高活性物质利用率与高稳定化。拟以不同长径比的中空炭纤维为原料，采用活化工艺，对其孔隙结构、孔径分布及比表面积进行调控，获得"丝瓜瓤"状中空多孔炭纤维；在此基础上，采用真空辅助液相沉积+热处理工艺，将活性物质纳米硫高效负载到中空多孔炭纤维的多尺度孔隙中；研究复合电极材料组成、结构、形貌、界面性质与其电化学性能的相互关系，探明高效负载硫的控制机制。研究复合电极材料的电极过程动力学及其储能机理，阐明影响硫碳复合材料动力学稳定性的关键限制因素。基于以上研究，确定并实现高容量、长寿命微纳结构硫碳复合正极材料的制备，为锂硫电池的开发与应用提供支撑。

锂硫电池是最具发展前景的高能二次电池之一，其正极活性物质硫按照“溶解-转化”机制进行充放电反应，所生成中间产物—多硫离子溶解在电解液中，并在正负极之间穿梭损耗，由此导致正极活性物质利用率降低、循环寿命缩短，是锂硫电池发展亟待解决的关键问题。本项目以抑制多硫离子的穿梭效应为目标，从正极材料以及夹层和隔膜两方面开展工作，抑制多硫化物的穿梭。一方面构筑“丝瓜瓤”碳纤维@介孔δ-MnO2 (HCNF@pδ-MnO2)纳米片隔膜涂层材料和自支撑的“丝瓜瓤”状氮化钒纳米线（VN-NWs）夹层，研究了材料的结构与性能关系，阐明了夹层和改性隔膜对电池电化学性能的影响机理。另一方面，利用KOH的活化作用以及碳材料的孔径调控技术，研究了孔结构对多硫化物的穿梭抑制作用，提出并开发构建高载硫量锂硫电池的硫宿主，并研究电池失效机制：锂负极的和电解液的消耗是影响其寿命的根本原因。另外，面向长寿命高载硫量锂硫电池发展需求，开展对金属氮化物/碳复合材料催化-转化机制的基础研究，为抑制多硫化物穿梭效应开辟了新途径。论文16篇，申报发明专利10项，培养博士研究生3名、硕士研究生2名。