NH3掺杂LiBH4原位机理解析及作为高性能固态锂离子电解质的探究

LiBH4 is expected to be used as solid-state lithium ionic electrolyte instead of traditional liquid electrolyte. However, its high application temperature leads to its poor thermal stability and electrochemical stability, which is the key problem restricting its practical application. In order to improve the conductivity of LiBH4 at room temperature, improving the thermal stability and electrochemical stability, this proposed project will dope ammonia into LiBH4, through rearrangement of NH3 molecules, [BH4]- ions and lithium ions to introduce more vacancies and defects, provide more channels for lithium ion migration, and improve its electrochemical performance; at the same time, advanced TEM technique will be used to observe in situ microstructural changing process in nanoscale during ammonia absorption into LiBH4. Combining with the theoretical calculation, the proposal will clarify the lithium ion migration mechanism after doping ammonia. Finally, it aims to improve the lithium ionic conductivity of LiBH4 at room temperature by controlling the amount of ammonia, and to explore its application as a solid electrolyte in lithium ion battery.

LiBH4有望作为固态锂离子电解质替代传统液态电解质，但其电导率应用温度过高，间接导致其热稳定性和电化学稳定性差，是限制其实际应用的关键问题。为了提高LiBH4室温下电导率，改善其热稳定性和电化学稳定性，本项目拟通过氨气掺杂对LiBH4微观组织结构进行调控，通过NH3分子和[BH4]-离子与锂离子重新排列，引入空位和缺陷，为锂离子迁移提供更多的通道，进而改善其电化学性能；同时，利用先进的透射电镜技术，在纳米尺度下原位研究LiBH4吸收氨气过程中晶体结构变化过程，结合理论计算，阐明氨气掺杂后的锂离子迁移机理。最后通过控制氨气量，实现室温下调节和提高LiBH4锂离子电导率的研究目标，探索其作为固态电解质在锂电池中的应用。

开发具有高能量密度、长循环寿命、安全应用水平和合理价格的锂离子电池成为时下最迫切解决的问题。传统电池一直专注于液态电解质系统，虽然它具有高导电性和优异的电极表面润湿性，但是其不稳定的电化学性能，较低的离子选择性，不可靠的安全性始终限制了电池技术革新。因此，用新型固态电解质替代，不仅可以解决液态电解质现有的问题，而且可以为新型电池（锂离子电池、锂金属电池、锂硫电池等）开发提供可能性。锂金属硼氢化物由于其对锂稳定性高、晶界电阻低、电化学窗口稳定、机械延展性优异，被认为是具有潜力的全固态锂离子电解质材料。本项目通过分子（NH3等）掺杂改善室温条件下金属硼氢化物的锂离子电导率，在宽温域下，分别实现了20℃下电导率达到10-4S/cm、45℃下电导率达到10-3S/cm，50℃下电导率达到10-2S/cm。深入研究金属硼氢化物基复合固态电解质的晶体结构调控和离子电导率之间的构效关系。同时结合原位测试技术及第一性原理计算，阐明锂离子在复合电解质内部、界面、电极界面的传输路径与机制。