三维大通道结构的钾钛氧化合物作为钠离子电池新型负极材料的研究

In this proposal, we extend the research focus from 2D layer structured Na-Ti-O compunds to 3D tunnel structured K-Ti-O compounds with the purpose to find new type of Ti-based anode candidates for sodium ion batteries. On the one hand, the larger size of K+ than Na+ can promise a larger cell volume to accomodate more insertion sites for sodium storage, and the larger tunnels in the structure would facilitate fast diffusion of Na+ to improve the rate capability; on the other hand, the 3D structure can reduce the insertion possibility of H2O and CO2 molecules into the crystal lattice so as to promote the air stability of the electrode materials, avoiding the seriously deterioration of conventional 2D layered materials when exposure to air or moisture; besides, the higher rigidity of 3D framework to 2D framwork can better afford the structural stress upon Na+ insertion/retraction, which can help to prolong the materials’ cycle life during charge/discharge. On the basis of our previous work, we will synthesize new potassium titanium oxides with different large [2×2] tunnel structures and different K+ contents in the tunnels through different synthesis methods and procedures with adjusting the K/Ti ratios; systematically investigate the effects of K+ content on the tunnel structure and physical-chemical properties of the materials；evaluate in details the chemical stability of this kind potassium titanium oxides in air and water；find the key factors to influence the electrochemical sodium storage performances of K-Ti-O compunds; further promote the materials by structure optimization and surface modification according to their behaviors; clarify the application perspective and development directions of this type potassium titanium oxide materials in sodium ion batteries, and finally provide in-depth knwoledge support and practical guidance for the development of new Ti-based anode materials with large capacity, high rate capability, long cycle life and good shelf stability for sodium ion batteries.

本项目将钛基钠离子电池负极材料从二维层状Na-Ti-O体系拓展到三维大通道结构的K-Ti-O体系，利用K+更大的半径使结构中的间隙变大提供更多储钠位点，而大的通道可满足Na+的快速扩散提升倍率性能；同时利用三维结构降低H2O和CO2嵌入材料晶格的可能性，提高材料空气稳定性，避免传统二维层状材料容易吸潮变质的难题；此外三维结构更强的骨架刚性可更好抵抗Na+嵌入时的结构应力提升材料循环寿命。在前期工作基础上，拟通过不同的合成路线及K/Ti配比调节制备不同结构及K+含量的[2x2]大通道钾钛氧化合物；系统研究通道内K+含量的变化对材料结构和物理化学性质的影响；考察材料在空气和水中的化学稳定性；找到影响其电化学储钠性能的关键因素；并据此进行结构优化和表面改性, 明晰钾钛氧在钠离子电池中应用的前景和方向，为开发大容量、高倍率、长寿命和良好储存稳定性的新型钛基钠电负极材料提供理论指导和技术借鉴。

本项目制备并探究了三维大通道结构的钾钛氧化合物的电化学储钠特性及水稳定性。通过水热法加碳热还原以及离子交换合成了具有不同x含量的大通道结构KxTiO2，在此基础上深入研究了三维通道结构的钾钛氧以及二维通道结构的钠钛氧体系的电性能及水稳定性的对比，表征了不同合成条件下材料的结构变化规律，明确了三维大通道结构本身具备的电化学稳定性与水稳定性优势，指出了其比容量与热处理温度尤其是材料的比表面积具有显著的正相关性。通过改变煅烧温度，开发出新相结构的超低电位钛基负极材料-三斜相Na2Ti3O7，证实了对相结构的调控可以改善二维通道结构钛基材料的循环稳定性。通过引入比K+更轻的Li+进行掺杂，开发出了具有零应变特性的、兼具结构稳定性与水稳定性的新型钛基负极材料Na0.73Li0.36Ti0.73O2，找到了影响二维层状材料水稳定性的决定性因素，即层间的原子空间占有率Rn，并以此作为提升材料空气稳定性的设计依据。针对钛基负极可逆性差的问题，开发出以Na-Naph-DME溶液作为液态钠源的普适性预钠化方法，弥补了钛基负极材料普遍表现出的首次库伦效率低的缺陷。最后，利用碳纳米管和纤维素的特殊组装设计并制备具有高孔隙率、高电导率、高机械强度的超柔性钛基电极，将钛基负极材料的应用拓展到了柔性电池。.项目的实施实现了长寿命、良好储钠稳定性且空气稳定的新型钛基钠电负极材料的开发，揭示了影响钛基材料空气稳定性的关键结构因素，开发了可有效提升钛基负极材料首次库仑效率的普适的预钠化方法。相关研究工作在国际知名杂志如Adv. Funct. Mater.（2篇）、 InfoMat（2篇）、Chem Commun上以通讯作者身份发表SCI论文15余篇，申请发明专利6项，授权5项，成果多次获得学术网站的公开推荐和报道。在项目支持下，培养1名博后，2名博士，多名硕士毕业生，申请人获得国家万人计划青年拔尖人才的支持。