Visualization and evaluation of lithium diffusion at grain boundaries in Li0.29La0.57TiO3 solid electrolytes using secondary ion mass spectrometry

Abstract

Understanding Li diffusion at interfaces in solid-state Li batteries is essential to improving their performance (e.g., rate capabilities and energy densities). However, the visualization of Li diffusion at grain boundaries has been impossible due to the lack of experimental techniques. In this study, we visualize Li-ion diffusion at grain boundaries via secondary ion mass spectrometry at low temperatures (≈−110 °C) using an isotope exchange technique for perovskite-type Li_0.29La_0.57TiO₃ as a model solid electrolyte. The grain boundary diffusion coefficient obtained in this study is 1.4 × 10⁻¹³ cm² s⁻¹ at 25 °C, which is much smaller than the bulk diffusion coefficient of 2.6 × 10⁻⁸ cm² s⁻¹. The long-range effective diffusion coefficients can be explained well by a 1D model based on a series of bulk and grain boundaries. The Haven ratio of grain boundary diffusion suggests that correlation between the Li⁺ ions is crucial for grain boundary diffusion.