金属锂负极/石榴石结构固体电解质界面问题研究

Interfacial issues have great effects on electrochemical performance of all-solid-state lithium batteries. In all-solid-state lithium batteries using garnet-type oxides as electrolyte, the key challenges of using lithium metal anode are the high interfacial impedance between garnet electrolyte and lithium anode, lithium dendrite growth along the grain boundaries, and infinite relative volume change of Li anode. This project will explore the using of alloy wetting technique to improve the contact between lithium metal and garnet electrolyte, investigate the wetting, spreading and interface bonding mechanism of Li-alloy on garnet electrolyte surface, thus reveal the underlying mechanism of interface contact and interfacial impedance. And tune the composition and microstructure of grain-boundary via controlling the segregation of the second phase; study the effects grain-boundary properties on lithium dendrite growth, disclose the electrochemical mechanism of lithium metal penetration through garnet electrolyte. We also will construct a three-dimensional lithium anode/garnet electrolyte interface to significantly improve the low electrolyte-electrode contact area of current two-dimensional interface, and study the relationships among the interfacial structure and the interfacial impedance, lithium metal penetration through garnet electrolytes, the available areal capacity and cycling stability of lithium metal anode. Through the systematical and deep investigations of garnet electrolyte/lithium anode interfacial structure and processes, guide the construction and tuning of interface, thus enable a lithium metal/garnet electrolyte configuration with high available areal capacity, high stability, low area-specific resistance, and long cycling life, and promote the development of all solid state batteries.

项目针对制约全固态锂电池发展的电极/固体电解质界面问题，以金属锂负极/石榴石结构固体电解质界面面临的高界面阻抗、晶界锂枝晶生长与穿透和金属锂巨大的体积变化三大关键问题为研究对象，利用合金润湿技术改善界面接触，降低界面阻抗，研究锂合金在石榴石结构固体电解质表面的润湿、铺展和界面结合机理，揭示界面润湿性能与界面阻抗的内在规律；通过固体电解质晶界改性抑制锂枝晶在固体电解质中生长，研究晶界组成与性质对锂枝晶生长的影响，揭示晶界锂枝晶生长的内在机制；构筑锂负极/固体电解质三维界面最小化金属锂体积变化，研究界面结构对界面阻抗、锂枝晶生长与穿透、锂负极可用面积比容量及循环稳定性的影响；通过以上对锂负极/石榴石固体电解质界面结构和过程的系统深入研究，指导界面的构筑与调控，最终实现具有高面积比容量、高稳定、低阻抗和长循环寿命的金属锂/石榴石固体电解质界面，推动全固态电池的发展。

石榴石型固体电解质因其优异的综合性能，如较高的室温离子电导率和对金属锂稳定等特性，成为最具应用前景的固体电解质材料之一。然而，石榴石电解质在固态电池中的应用仍面临一系列挑战，包括：制备高离子电导率、高致密度的电解质；电极/电解质界面阻抗大、离子传输动力学缓慢；界面电化学-机械稳定性差；锂枝晶生长等问题。其中电极/电解质固/固界面问题尤为突出，也被认为是制约当前固态电池技术发展的最大瓶颈。解决这些关键性问题对于固态离子学的发展以及对固态电池体系中构效关系的建立具有十分重要意义。在国家自然科学基金的资助下，本项目以构筑低阻抗、高稳定金属锂负极/石榴石结构固体电解质界面为目标，针对界面浸润性及锂枝晶生长等关键科学问题，展开了高致密度、高离子电导率石榴石固体电解质的制备、金属锂负极/石榴石结构固体电解质界面锂金属沉积-溶出行为及界面构筑与调控策略等方面的研究，取得了以下重要进展：1）系统优化烧结方法及工艺，制备了具有高致密度和高锂离子电导率的Li6.5La3Zr1.5Ta0.5O12（LLZTO）电解质；2）揭示了电解质不同缺陷对锂金属沉积行为影响，阐明了多晶缺陷与成核位点和Li 局部生长方式的关系，为高稳定金属锂负极/石榴石电解质界面设计与构筑提供指导；3）发展了几种可规模化应用的高效界面构筑与调控技术，显著降低了界面阻抗，有效抑制了锂枝晶生长，实现了在较高电流密度下的长时间稳定性循环；4）基于锂负极界面改性，利用等离子放电一体化烧结技术构筑牢固稳定的LiCoO2-LLZTO/LLZTO界面，构建了具有高面容量的Li|LLZTO|LiCoO2-LLZTO全固态锂电池，获得了良好的循环性能。项目研究成果为合理设计和构筑全固态电池锂金属负极/固态电解质界面，以解决高性能全固态锂电池研发中所面临的关键挑战提供了有益借鉴。