基于二氟草酸硼酸钠的钠离子电池非水电解液的电化学性能和电极/电解液界面钝化特性研究

The sodium ion battery has attracted extensive attention right now. The electrolyte is in large responsible of the capacity, rate capacity and thermal stability for battery system. The current nonaqueous electrolytes for sodium ion batteries needs a further enhancement on electrochemical performance to support cathode, as well as an insight investigation to the electrode/electrolyte interface passivation .mechanism. Our preliminary research of 0.8 M NaBF2C2O4/PC/DMC electrolyte has shown more stable, higher coulombic efficiency and better rate performanc over the classic electrolyte formula 1 M NaClO4/EC/PC. The in-progress work of this program is expected to carry out in terms of the following design. . The strategy of mixing different sodium salts, as well as optimization of solvents formula, will be adopted to prepare nonaqueous .electrolytes, which will be evaluated by the comprehensive performance of ionic conductivity, electrochemical stability window and the reversible capacity and coulombic efficiency for the cell at room temperature and at 60 ℃. After that electrochemical impedance spectra(EIS) will be used to confirm the interface charge transfer resistance, while ATR-FTIR and XPS technique will be used to analyze the chemical formula of passivating product. Thus the passivating mechanism, at different temperature, on the surface of typical cathode NaNi0.5Mn0.5O2 and typical anode hard carbon will be confirmed. In addition, the polarization curves of electrodes in special electrolytes will be measured, and the diffusion rate of sodium ion on different state of charge for the electrode will be also analyzed in experimental cells . . The program aims to obtain better non-aqueous electrolyte to realize the construction of full cell by practical cathode and anode, and enhance the knowledge on the passivating mechanism of electrolyte/electrode interface and the electrode kinetics.

当前对于钠离子电池的研究方兴未艾。电解质材料与电池体系的可逆容量、倍率特性、热稳定性等都有密切联系。当前的钠离子电池非水电解液对于正极材料相容性有所不足，且在电极/界面钝化机理方面缺乏深入研究。前期制备的0.8 M NaBF2C2O4/PC/DMC电解液较经典的1 M NaClO4/EC/PC电解液在电池中表现出更稳定的放电容量，更高的库伦效率和倍率性能。本项目拟利用不同钠盐联用，溶剂组成优化等方法，并考察室温和60℃时电解液的离子电导率，电化学稳定窗口和电池可逆容量和库伦效率等参数获得稳定的无水电解液；利用电化学阻抗谱并结合反射红外，X光电子能谱等技术考察界面钝化膜的组成与性能，确定电解液不同温度下在正极材料镍锰酸钠和负极材料硬碳电极表面的钝化机制；测定电极的极化曲线，并分析钠离子在电极不同荷电态的扩散系数。期望制备适用于全电池的非水电解液，加深对于电解液/电极钝化机理和电极过程的认识。

自从2012年以后，钠离子电池作为一种复兴的电池体系，在国际学术界得到了极大的关注。相当多的研究和开发工作集中于电极的活性材料，对于电解质材料的关注相对比较少。已商用的锂离子电池的研发历史证实电解质材料在充分发挥电极材料的容量和循环寿命上有重要作用，因此本项目要通过发展更高性能的有机电解液推动钠离子电池技术的发展。通过考察电解液的离子电导率，电化学稳定窗口和电池可逆容量和库伦效率等参数获得稳定的无水电解液；利用电化学阻抗谱并结合反射红外，X光电子能谱等技术考察界面钝化膜的组成与性能，确定电解液不同温度下在正极材料镍锰酸钠和负极材料硬碳等电极表面的钝化机制；测定电极的极化曲线，并分析钠离子在电极不同荷电态的扩散系数。项目执行基本上是按照项目研究计划进行的。重要成果主要是在钠离子电池材料研究领域发表学术论文8篇，其中1区SCI论文一篇，3区SCI论文两篇，EI论文2篇，申报并获批国家技术发明专利3项。培养研究生2名，本科生15名。利用专利技术制备的二氟草酸硼酸钠已经作为钠离子电池有机电解液添加剂应用到实验中，对于层状NaNi0.5Mn0.5O2材料获得200-300周稳定的充放电性能。基于电解液组分的优化，进一步考察了正极材料制备方法的影响，利用草酸前驱体法制备的隧道型Na0.44MnO2材料已经实现500周稳定工作，而这样的循环稳定性已经在近期的实验结果中证实可以再提升一倍。本项目实际获得了可用于发展高性能钠离子电池的电解液配方，以及基于电解液优化基础上的电极材料的性能的提升，加深对于钠离子电池电解液/电极钝化机理和电极过程的认识。