高导电M–Nb–O储锂材料的制备、结构–性能关联与电化学反应机理

The recently explored highly-conductive M–Nb–O materials have large specific capacities as well as high safety performances, rate capabilities and cyclic stability, thereby becoming ideal anode materials of lithium-ion batteries for electric vehicles. However, the studies on this type of materials are extremely limited, and their structure–property relationships and electrochemical-reaction mechanisms are not clear. In this project, firstly, we will systematically investigate M–Nb–O materials with various conductive M ions and stoichiometry, and fabricate several new M–Nb–O materials with high performances. Secondly, we will carefully clarify their shear ReO3 crystal structures using Rietveld refinements. Thirdly, we will characterize their microscopic morphologies, electrical properties (electronic conductivities and Li+ diffusion coefficients) and electrochemical performances. Fourthly, we will employ the first-principles calculations to obtain their density of electronic states, band structures and bonding characteristics, and to analyze their Li+ storage sites, diffusion pathways and capabilities, thereby revealing the relationships among their material structures, electrical properties and electrochemical performances. Finally, we will use in-situ X-ray diffraction together with other characterizations to clarify their electrochemical-reaction mechanisms, including the redox couples, one/two-phase reactions, crystal-structure/lattice-parameter variations and lithiation kinetics. Therefore, this project has significant practical and theoretical values.

申请人最近开发的高导电M–Nb–O（M为导电离子）具有高比容量、安全性能、倍率性能和循环性能，是电动汽车锂离子电池的理想负极材料。然而，目前这类材料的研究还极少，而且其结构–性能的关联规律和电化学反应机理还不清晰。对此，本项目拟系统研究不同导电M离子和化学计量比的M–Nb–O，制备若干高性能的M–Nb–O；采用Rietveld精修详细解析M–Nb–O的剪切ReO3晶体结构；表征M–Nb–O的微观形貌、电性能（电子电导率和Li+扩散系数）和电化学性能；采用第一性原理计算获取M–Nb–O的电子态密度、能带结构和成键特征，分析M–Nb–O的Li+嵌入位置、扩散通道和扩散能力，从而揭示M–Nb–O结构–电性能–电化学性能的关联规律；采用原位X光衍射等多种表征技术探索M–Nb–O的氧化还原电对、单/两相反应、晶体结构/晶格参数变化和嵌锂动力学等电化学反应机理。因此，本项目具有重要的实用和理论价值。

高导电M–Nb–O（M为导电离子）具有高比容量、安全性能、倍率性能和循环性能，是电动汽车动力锂离子电池的理想负极材料。针对之前这类材料的研究极少而且其结构–性能的关联规律和电化学反应机理还不清晰的问题，本项目合成了5种新型的高导电M–Nb–O化合物，分别为CrNb11O29、Nb25O62（NbIVNbV24O62）、Cu2Nb34O87、具有Ti2Nb10O29型晶体结构的TiNb24O62、Ni2Nb34O87，其在宽温域下具有良好的综合电化学性能。揭示了高导电M–Nb–O的结构–电性能–电化学性能的关联规律。M离子的未成对电子多和含量大有利于提高电子电导率。M离子的半径大有利于增大晶格参数、晶胞体积和层间距，从而增大Li+的传输通道和提高Li+扩散系数。电子电导率和Li+扩散系数的提高有利于提高电化学性能。揭示了高导电M–Nb–O的电化学反应机理。确定了所开发的5种高导电M–Nb–O化合物均为脱嵌型负极材料，反应过程中存在一小段两相反应，存在Nb5+↔Nb3+的两电子反应，嵌锂后晶胞体积的变化主要取决于层间距（b值）的变化，层间距的大小对Li+的嵌入和扩散具有重大影响。这些工作发表在Advanced Energy Materials、Advanced Science和Energy Storage Materials等期刊上，共21篇。授权发明专利2项。培养硕士研究生9人。本项目可为电动汽车动力电池负极材料的研发提供新思路和科学依据。