基于锂镧锆氧电解质的固态金属锂二次电池关键界面科学问题与性能优化

Solid state lithium batteries are deemed to be the potential candidate for achieve the breakthrough of the energy density in the field of lithium ion batteries. The solid batteries based on the garnet-type Li-La-Zr-O have attracted a great deal of attention, owing to the satisfied ionic conductivity, stability against Li metal, large electrochemical window, and relative stability against air of the electrolytes. However, there exists critical interfacial issues in this system, which needs to be solved. This project first of all will carry out on analysis of the crystal structure and surface chemistry, clarification of key factors influencing the ionic conductivity of the bulk phase and surface, thus succeeding in preparation of highly conductive as well as surface stable electrolyte powders. Then through study of interfacial structure and composition and their influence on the ion transport, the solid state electrolyte layers with high conductivity and stably electrochemical property will be designed and fabricated. With the idea of interfacail structure match and composition combination, the interfaces with good conduction as well as stability will be constructed. By studying the solid/solid interfaces between the electrolyte layer and the electrode, the interfaces with good kinetics and stability will be constructed. Consequently, with integretion of optimized materials and interfaces in the batteries, analysis of the changing microstructure and composition during operation, the high energy density and high-performance solid state lithium batteries will be obtained.

为实现电池能量密度的根本性突破，研究固态金属锂二次电池已成为共识。以锂镧锆氧为代表的石榴石型氧化物固体电解质具有满足应用的离子电导率、对金属锂稳定、电化学窗口宽、可在大气环境中处理等优势，因而成为受人关注的电解质材料。但是基于该材料的电池体系在界面方面存在很多关键科学问题急需解决，本项目将首先通过对电解质材料晶体结构的剖析、表面化学的精确分析，揭示影响电解质材料体相和表面电导率的关键因素，获得表面稳定且具有高离子电导率的电解质粉体材料。在高性能粉体材料的基础之上，以离子导电界面增强的思想，设计制备出具有高离子电导率的电解质层。进而研究电解质层和电极材料之间固固界面的融合与协同机制，构筑具有优异动力学和稳定性的界面。最终通过材料和界面的集成，优化性能，获得具有高能量密度、动力学和循环性能优异的固态金属锂二次电池。

与目前采用有机电解液的商业化锂离子电池相比，引入固态电解质的固态锂电池在同时提升电池能量密度和安全性方面具有巨大潜力，成为开发下一代锂电池的重点。在众多固体电解质材料中，石榴石型的锂镧锆氧（Li7La3Zr2O12，LLZO）凭借高锂离子电导率、优异的对锂稳定性和宽电化学窗口等优点受到广泛关注。然而，LLZO的引入带来诸多界面之间的突出问题，例如固固界面的物理接触、应力应变、电荷重新排布以及电化学稳定性等。这些问题不仅是影响电池性能的关键因素，而且带来了很多新的物理化学现象需要深入研究。因此，本文从LLZO基固体电解质与电极之间的外部界面和固体电解质及复合电极内部界面两个角度入手，依据本课题组多年的研究积累，结合领域内最新研究动态，详细讨论了：（1）LLZO基固体电解质粉体材料表面碳酸锂（Li2CO3）的形成原因、对电化学性能的影响以及克服这一问题的手段；（2）LLZO基固体电解质层内部界面调控对锂离子电导率及电池电化学性能的影响；（3）LLZO/Li界面特性及Li在LLZO基陶瓷电解质中贯穿生长，深入探讨了诱导Li析出和生长的电场、电荷、应力应变等作用机制；（4）复合正极内部界面问题及其与电解质层外部接触界面的一体化构筑方法。希望通过本项目对LLZO固态锂电池界面问题的关键科学和技术的分析总结，为构筑高导通高稳定界面，推动高性能固态锂电池发展提供解决方案。