Publication date: 10th April 2024
Lithium-ion batteries (LIBs) have garnered attention for their high energy density and portability, particularly with the growing demand of electric vehicles1. However, the flammability of the electrolytes in conventional LIBs poses a significant safety hazard. To address this, solid-state batteries (SSBs) with solid electrolytes (SE) have emerged, offering enhanced safety1. Among these SE, Li6.6La3Zr1.6 Ta0.4O12 (LLZO-Ta) stands out for its stability against Li metal and high ionic conductivity2. Yet, LLZO-Ta faces challenges, including susceptibility to surface lithium hydroxide and carbonate formation, hindering lithium-ion transfer2. In this study, we investigate the ion exchange rate in LLZO-Ta with the introduction of an indium interface layer to enhance ion transfer via tracer-based experiments using SIMS analysis with isotope couples. These kinds of experiments are limited in the literature3,4. Previous studies have applied SIMS depth-profiling, and line scan analysis to understand grain boundary diffusion and determining bulk and grain diffusion coefficients3. However, the slow diffusion observed in LLZO is not solely due to the surface carbonate layer. It is also influenced by the relatively high activation energy needed for lithium-ion migration within the material4. Thus, to overcome this slow diffusion, initially, a systematic polished and annealed process is employed to remove surface carbonate layers. However, this process only yields a modest increase in the isotope exchange rate over 24 hours, which may be due to slow diffusion of lithium in this kind of systems4. Subsequently, LLZO-Ta surfaces are coated with indium (~10 nm thickness), confirmed through Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS). The indium-coated LLZO-Ta exhibits a significantly enhanced step isotope exchange rate of 29% over 24 hours, as validated by TOF-SIMS profiling (Figure 1). The observed increase in lithium-ion exchange rate with indium deposition suggests surface property modification, possibly enhancing conductivity or altering surface chemistry to facilitate faster lithium-ion diffusion. Thus, indium interlayer plays a significant role in increasing the ion conduction in LLZO-Ta, which contributes to advancing the understanding of solid-state battery interfaces, crucial for improving battery performance and safety.
The study was suppoerted by NIMS Japan.