新型Ti2Nb2xO4+5x储锂材料的制备、晶体结构修饰与结构–性能关联

The recently developed Ti2Nb2xO4+5x anode materials have large theoretical and real capacities. After modified, they may become ideal anode materials for the lithium-ion batteries (LIBs) of electric vehicles (EVs). However, very limited studies on Ti2Nb2xO4+5x compounds have been reported, their conductivities are poor and their structure–property relationships are unclear. In this project, firstly, we will systematically investigate the Ti2Nb2xO4+5x materials with various x values, fabricate several new Ti2Nb2xO4+5x compounds, and intensively study their shear ReO3 crystal structures (such as crystal symmetries, block sizes, lattice parameters, ion occupancies, defect types and defect concentrations). Secondly, we will select several Ti2Nb2xO4+5x compounds with relatively good performances, modify them using the method of crystal structure modification (including doping and ion-vacancy creation), and thus fabricate several Ti2Nb2xO4+5x-based materials having large capacities and good rate performances and fulfilling the requirements of the LIBs for EVs. Thirdly, we will clarify the bonding characteristics, band structures, density of electronic states, Li+ diffusion pathways and Li+ diffusion capabilities in the Ti2Nb2xO4+5x materials using first-principles calculations. Finally, we will clarify the relationships among material structures, electrical properties and electrochemical performances. Therefore, this project may offer new ideas and scientific basis to the anode materials for the LIBs of EVs.

最新发展的Ti2Nb2xO4+5x材料的理论和实际容量大，经过改性后有望成为电动汽车电池的理想负极材料。针对这类材料的研究少、导电性差和结构–性能关联规律不清楚的问题，本项目拟系统研究不同x值下的Ti2Nb2xO4+5x材料，制备若干新型的Ti2Nb2xO4+5x化合物，详细解析其剪切ReO3晶体结构（包括晶体对称性、结构单元、晶格参数、离子占位率、缺陷类型和缺陷浓度等）；挑选若干性能较好的Ti2Nb2xO4+5x化合物，对其采用晶体结构修饰（包括掺杂和造离子空位）进行改性，制备若干具有大容量和高倍率性能、能较好地满足电动汽车电池要求的Ti2Nb2xO4+5x材料；采用第一性原理计算探明Ti2Nb2xO4+5x材料的成键特征、能带结构、电子态密度、Li+扩散通道和Li+扩散能力；并揭示材料结构–电性能–电化学性能的关联规律。因此，本项目有望为电动汽车电池负极材料的研发提供新思路和科学依据。

Ti2Nb2xO4+5x具有高比容量、高安全性、高循环性和显著的赝电容效应，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少、导电性差和结构–性能关联规律不清楚的问题，本项目合成了Ti2Nb14O39和TiNb24O62等2种新型的Ti2Nb2xO4+5x化合物，探明了Ti2Nb2xO4+5x材料组分与晶体结构的关联规律。采用晶体结构修饰（包括掺杂和造离子空位）等改性方法对Ti2Nb2xO4+5x材料进行改性，制备出26种既具有大容量（>250 mAh g–1，0.1 C）又具有高倍率性能（>150 mAh g–1，5 C）的Ti2Nb2xO4+5x材料。揭示了Ti2Nb2xO4+5x材料的结构–电性能–电化学性能的关联规律。掺杂离子的未成对电子多和掺杂量大有利于提高电子电导率。掺杂离子的半径大有利于增大晶格参数和晶胞体积，从而增大Li+的传输通道和提高Li+扩散系数。阳离子和氧离子空位的存在都有利于增多Li+的传输通道，从而也能提高Li+扩散系数。TiNb2O7、Ti2Nb10O29和TiNb24O62中，Ti2Nb10O29晶体结构的b值（层间距的2倍）最大，因而其Li+扩散系数最大。电子电导率和Li+扩散系数的提高有利于提高电化学性能，其中Li+扩散系数的提高起主导作用。这些工作发表在ACS Nano、Journal of Materials Chemistry A和Small等期刊上，共计18篇。研究成果获2017年度海南省科技进步二等奖（排第2）。培养硕士研究生6人。本项目可以为电动汽车电池负极材料的研发提供新思路和科学依据。