多元层状氧化物Nax[NiFeMn]O2介观晶体的设计合成及电化学性能研究

Sodium-ion batteries are now actively developed as a new generation of electric energy storage technology because of their advantages of resource abundance and low cost, thus have broad application in many areas. In particular, cathode materials with high capacity, high safety and long life have always been a key in the research field of sodium-ion batteries. However, the electrochemical performances of layered oxide cathode materials for sodium-ion batteries suffer from poor structural stability and low electronic conductivity. To address this issue, the aim of this project is to develop a facile route to fabricate sodium layered oxide Nax[NiFeMn]O2 mesocrystals as cathode materials with enhanced electrochemical performances. We will focus on the development of ionic liquid-assisted synthetic route to prepare Nax[NiFeMn]O2 mesocrystals with desired phase and carbon-coated modification, and systematically study their electrochemical performance for sodium-ion batteries. By rational design of ionic liquid precursor, we will investigate the effect of reactant ratio, temperature and ionic liquid on the formation of Nax[NiFeMn]O2 mesocrystals with desired phase and morphologies. By means of electrochemical analysis and structural characterization, we will reveal the role of each component of Nax[NiFeMn]O2 mesocrystals in the charge-discharge process, and investigate the impact of mesoscopic structured Nax[NiFeMn]O2 cathode materials based on synergistic effect for high-performance sodium-ion batteries. Furthermore, we will determine the optimal ratio of Na:Ni:Fe:Mn for Nax[NiFeMn]O2 mesocrystals with high capacity and well cycling performance. It is highly expected that these findings are useful for exploring an environment-friendly route for large-scale preparation of mesocrystal-type cathode materials with high capacity and long life for sodium-ion batteries.

钠离子电池由于资源与成本等方面的明显优势，正成为新一代储能技术的发展热点，具有广阔的应用市场。其中，高性能正极材料的制备一直是钠离子电池研究领域的重点与难点问题。本项目针对目前多元层状氧化物正极材料结构稳定性较差、电子导电率较低等问题，提出物相调控、介观结构化和碳包覆改性是提升其电化学性能的有效途径。项目将以多元层状氧化物Nax[NiFeMn]O2介观晶体为研究对象，围绕电极材料物相、微观结构及碳包覆对电化学性能的影响规律等核心内容，开展离子液体体系中多元层状氧化物介观晶体及其功能化研究，阐明反应物配比、离子液体种类及反应温度等对产物物相组成、结构、形貌等影响，探索基于协同作用机制的多元正极材料Nax[NiFeMn]O2介观晶体对钠离子电池性能的影响，揭示电极材料各组分的作用及其介观结构化与充放电特性和循环性能的内在联系，为制备高性能的钠离子电池正极材料提供相应的理论基础和实验指导。

高性能多元层状氧化物正极材料的设计制备是研发先进储能器件的核心技术基础。在本项目的资助下，申请人以高性能正极材料介观微结构的可控制备及其电化学性能为研究对象，得到关于高性能电极材料设计的系列研究进展：（1）系统地提出用于制备高性能介观晶体型电极材料的液相法合成途径，并通过晶体结构相似性及拓扑转换得到成分组成复杂的多元层状氧化物正极材料Na0.67Mn0.65Fe0.2Ni0.15O2多级介观晶体结构、聚阴离子型正极材料磷酸铁锂多面体介观晶体，突破了现有合成方法只能制备简单氧化物介观晶体型电极材料的限制，具有一定的普适性；（2）系统研究了一维纳米结构和离子掺杂对多元层状氧化物正极材料电化学性能的影响，证实了微纳结构化和表介观结构改性是提升其循环稳定性和倍率性能的关键因素；并通过简单抽滤方式得到富锂层状正极材料/碳纳米管的自支撑结构，具有高比容量、高倍率和长循环寿命的特点。与现有涂覆工艺制备正极材料相比，自支撑电极总质量共减轻47%，活性物质的有效负载量可提升2倍；（3）创新性地将离子液体前驱体引入静电纺丝体系来制备自支撑电极结构，突破了目前电纺体系仅用于制备简单化合物且机械性能较差的限制。离子液体前驱体具有可设计性和溶解性良好的特性，丰富了电纺体系聚合物的可选择性，从而能够得到机械性能良好且具有复杂组分的一系列高性能正极材料，极大地提升了其电化学性能。.本项目的完成有望为多元层状氧化物正极材料微纳介观化提供新的构建方法，同时得到得到具有复杂成分组成的正极材料物相、组成、微结构与其充放电特性和循环性能的内在联系，明确提升电化学性能的关键因素，为设计高性能的多元层状氧化物正极材料提供理论依据和实验支持。