TiO2作为钠离子电池负极材料的界面性能研究

TiO2 has been regarded as a promising anode material for Na-ion battery, due to its low cost, environmental benignity, relatively high charge/discharge voltage, and small volume change during cycling. Regarding to the fundamental research, the sodium storage mechanism in TiO2 is not clear yet, and the transport of sodium ions and electrons is slow. In addition, the passivation layer between TiO2 electrode and electrolyte is not as stable as that in lithium ion batteries. Electrode interface property is one of the key factors which determine the cycling life, rate performance and safety of batteries. In this project, based on a clear understanding of the sodium storage mechanism in TiO2 and the electrochemical kinetics, we will further enhance the electrochemical properties of TiO2 in Na-ion batteries with electrode interface decoration, such as defect introduction and protective layer coating. The relationship between interface decoration and interfacial /electrochemical properties would be discussed, in terms of interfacial/bulk sodium storage mechanisms, interfacial charge transfer, ion/electron diffusion and the stability of electrode/electrolyte interface. With the analysis aforementioned, optimized methods for synthesis and interfacial decoration of TiO2 would be proposed, which presents excellent electrochemical performance (long cycle life, good rate performance, high coulombic efficiency) as anode material in Na-ion batteries.

TiO2 由于资源丰富、价格低廉、环境友好、嵌脱钠电压平台较高、嵌钠过程体积膨胀小等优点，被认为是很有潜力的钠离子电池负极材料。目前，文献上报道TiO2的储钠机理还存在一定分歧，TiO2的离子和电子传输较慢，同时也面临着电极材料/电解液界面不稳定的问题。电极界面特性是影响电池循环寿命、倍率性能和安全性能的关键因素之一。本项目拟先对具有不同物理性质TiO2的储钠机理进行研究，系统分析材料物理性质（结晶度、颗粒尺寸）对储钠机理和电化学动力学的影响机制。在此基础上，采用引入缺陷、保护层包覆等界面修饰的方法对TiO2材料进行改性，总结各修饰方法对界面/体相储钠机理、界面电荷传质和电极材料/电解液的界面稳定性的影响因素；优化界面修饰方法，得到具有高容量、高充放电效率和良好循环、倍率性能的TiO2钠离子电池负极材料。

TiO2由于资源丰富、价格低廉、环境友好等优点，被认为是很有潜力的钠离子电池负极材料。目前已有较多相关研究，但进一步提高其储钠性质依然存在一定的挑战：TiO2首周效率较低，文献上报道的TiO2储钠机理还存在一定分歧。需要进一步认识TiO2储钠机理，对TiO2进行改性，进而提高其储钠性能。本项目在对电极的界面形式对其电化学性能影响研究的基础上，以锐钛矿TiO2纳米管（棒）/石墨烯的复合物作为研究对象，研究了TiO2中引入氧缺陷对其储钠动力学的影响，并探讨了其储钠机理。结果表明，引入氧缺陷，调控了界面和体相性质，有利于提高储钠过程动力学，得到了更好的倍率性能。同时，锐钛矿TiO2纳米管（棒）/石墨烯复合物的储钠过程是一个嵌入反应，在反应过程中，钠的嵌入没有引起Ti的价态变化，而是改变了电子分布；首周储钠引起了不可逆的晶体和电子结构变化，这种变化在第二周变得可逆。这些研究成果有利于更进一步认识TiO2的储钠过程，对进一步改善TiO2的材料设计有指导意义。本项目共发表SCI论文5篇，申请专利2项，培养学生2名。