Borštnar Petruša, Dražić Goran, Šala Martin, Lin Che-An, Lin Shih-Kang, Spreitzer Matjaž, Daneu Nina
Advanced Materials Department, Jožef Stefan Institute, Jamova cesta 39, 1000 Ljubljana, Slovenia.
Jožef Stefan International Postgraduate School, Jamova cesta 39, 1000 Ljubljana, Slovenia.
ACS Nano. 2024 Apr 23;18(16):10850-10862. doi: 10.1021/acsnano.4c00706. Epub 2024 Apr 9.
Lithium lanthanum titanate (LLTO) perovskite is one of the most promising electrolytes for all-solid-state batteries, but its performance is limited by the presence of grain boundaries (GBs). The fraction of GBs can be significantly reduced by the preparation of coarse-grained LLTO ceramics. In this work, we describe an alternative approach to the fabrication of ceramics with large LLTO grains based on self-seeded grain growth. In compositions with the starting stoichiometry for the LiLaTiO phase and with a high excess addition of Li (Li:La:Ti = 11:15:25), microstructure development starts with the formation of the layered RP-type LiLaTiO phase. Grains with many RP-type defects initially develop into large platelets with thicknesses of up to 10 μm and lengths over 100 μm. Microstructure development continues with the crystallization of LLTO perovskite, epitaxially on the platelets and as smaller grains with thinner in-grain RP-lamellae. Theoretical calculations confirmed that the formation of RP-type sequences is energetically favored and precedes the formation of the LLTO perovskite phase. At around 1250 °C, the RP-type sequences become thermally unstable and gradually recrystallize to LLTO via the ionic exchange between the Li-rich RP-layers and the neighboring Ti and La layers as shown by quantitative HAADF-STEM. At higher sintering temperatures, LLTO grains become free of RP-type defects and the small grains recrystallize onto the large platelike seed grains via Ostwald ripening. The final microstructure is coarse-grained LLTO with total ionic conductivity in the range of 1 × 10 S/cm.
钛酸镧锂（LLTO）钙钛矿是全固态电池中最具潜力的电解质之一，但其性能受晶界（GBs）的存在限制。通过制备粗晶LLTO陶瓷可显著降低晶界比例。在本工作中，我们描述了一种基于自籽晶生长制备大晶粒LLTO陶瓷的替代方法。在具有LiLaTiO相起始化学计量比且Li过量添加量高（Li:La:Ti = 11:15:25）的组成中，微观结构发展始于层状RP型LiLaTiO相的形成。最初具有许多RP型缺陷的晶粒发展成厚度达10μm、长度超过100μm的大薄片。微观结构发展随着LLTO钙钛矿的结晶继续进行，在薄片上外延生长，并形成具有较薄晶粒内RP薄片的较小晶粒。理论计算证实，RP型序列的形成在能量上更有利，且先于LLTO钙钛矿相的形成。在约1250℃时，RP型序列变得热不稳定，并通过富含Li的RP层与相邻Ti和La层之间的离子交换逐渐重结晶为LLTO，如定量HAADF-STEM所示。在较高烧结温度下，LLTO晶粒不含RP型缺陷，小晶粒通过奥斯特瓦尔德熟化在大的板状籽晶上重结晶。最终的微观结构是粗晶LLTO，其总离子电导率在1×10 S/cm范围内。
