石榴石型固体电解质支撑的固态锂氧电池设计及固固界面锂氧反应机制研究

The aprotic lithium-oxygen batteries (ALOB) are deemed as the potential candidates for the next-generation high performance batteries as their high theoretical energy density. However, the problems related to the organic electrolytes like the instability, the flammability as well as the incapacity on blocking the penetration of non-oxygen components from air retard their development. Replacing organic electrolyte with solid state electrolyte can fundamentally address the above mentioned issues, and such resulted solid state lithium-oxygen batteries (SSLOB) have attracted a great deal of attention. Improving their energy density, reversibility and cycle life are the hot and knotty issues for the development of SSLOB. With the idea of constructing solid electrolyte thin membrane and porous oxygen cathode, this project aims to construct high-performance SSLOB based on the garnet-type solid electrolyte which holds excellent chemical/electrochemical stability. Decreasing the thickness of the solid electrolyte can reduce the amount of the inorganic electrolyte used in the SSLOB, and designing porous oxygen cathode can significantly increase the reactive sites for Li/O2 reaction. Resorting to the improvements on these two aspects, the energy density of SSLOB will be greatly improved. By drawing support from the ambient X-ray photoelectron spectroscopy, the Li/O2 reaction occurred on the solid-solid interface can be monitored in situ. With the incorporation of the analyses of structure and morphology of the reaction products as well as the electrochemical performance of the batteries, the involved mechanism can be systemically clarified. Thereby, the obtained mechanism will further guide the construction of high performance air cathodes, thus enabling the realization of the high reversibility for Li/O2 reaction and the construction of high-performance SSLOB. The implementation of this project will lay experimental and theoretical foundations for the application of the solid state lithium-oxygen batteries.

非水系锂氧电池以其超高的理论能量密度成为新一代高比能电池研发的重要体系，但液体电解液易分解、易挥发、易燃和无法阻挡空气中非氧组分侵入等问题制约了它的发展。采用无机材料构成的固体电解质替代液体电解液构筑固态锂氧电池，可从根本上解决这些问题而备受关注。提高电池的能量密度、可逆性和寿命是当前固态锂氧电池研究的热点和难点。本项目提出电解质薄膜化、氧正极多孔化思路，以化学/电化学性质稳定的石榴石型固体电解质为基础开展高性能固态锂氧电池的构筑研究。通过电解质薄膜化实现电池中固体电解质含量的降低和氧正极多孔化实现锂氧反应位点的增加，提高电池的能量密度；借助常压X射线光电子能谱原位监控锂氧反应过程，结合对反应产物结构、形貌分析和电池性能表征，揭示固固界面锂氧反应机制，并由此指导高效氧正极设计，实现锂氧反应的高效可逆和高性能固态锂氧电池的构筑。本项目的实施将可为固态锂氧电池实用化发展提供实验和理论基础。

交通工具电动化已成为各国应对环境和能源危机的共识，这对作为能量供给单元的电池提出了更高的要求。相比目前广泛使用的锂离子电池，锂空气电池具有数倍于其的理论能量密度而受到了广泛关注。但液体电解液易分解、易挥发、易燃和无法阻挡空气中非氧组分侵入等问题制约了它的发展。采用无机材料构成的固体电解质替代液体电解液构筑固态锂氧电池，有望从根本上解决这些问题而备受关注。本项目通过固体电解质的薄膜化和氧正极多孔化思路，以化学/电化学性质稳定的石榴石型固体电解质为基础开展了高性能固态锂氧电池的构筑和固固界面特性研究。项目执行期间，建立了流延法制备高性能LLZTO固体电解质膜的方法，所获得的~200 nm厚度的LLZTO电解质膜电导率可以达到5.2*10-4 S/cm。以LLZTO电解质为基础，解析了Li2CO3的分解路径，证实了在4.3 V以上充电Li2CO3的分解会形成CO2和O2。针对电解质-电极界面问题，首先分析建立了高效电解质-电极界面的设计原则，并通过在LLZTO电解质表面引入纳米Sn过渡层验证了该原则的有效性。在固态锂氧电池中同样面临反应可逆性差的问题，从设计增加氧含量的添加剂、改善正极载体和改善正极载体表面特性等方面进行了探索，结果表明改变锂氧反应要素，促使高纯度或纳米化Li2O2的形成，可以大幅提升锂氧反应的可逆性。固体电解质膜虽可解决液体电解液所面临的难题，但其自身的脆性制约了其实际应用，本项目基于氧化物电解质颗粒与离子液体间的相互作用，探索设计了柔性固态锂氧软包电池，为实用化电池开发提供了有益的实验支持。氧化物电解质膜平台，也为探索高容量负极如Si材料在固态电池中应用提供了基础，发现在固态电池中，使用~180 nm厚度的Si薄膜负极，由LLZTO固体电解质构筑的模型电池仍可获得优异的循环稳定性，一定程度上表明固态电池中有望使用更高含量的硅负极，实现更高的负极容量。