Unveiling the Role of Hidden Internal Stresses in Lithium Heterogeneity for High-Performance All-Solid State Batteries

All-solid-state batteries (ASSBs) offer enhanced safety and higher energy densities compared to lithium-ion batteries (LIBs) due to the use of solid electrolytes. However, mechanical challenges arise from interactions between the cathode and rigid solid electrolytes during cycling, creating internal stresses that degrade performance. While visible mechanical failures such as cracks are well understood, latent internal stresses that are not visibly manifested have yet to be fully identified, and their effects on charge-discharge mechanisms remain unclear.
This study investigates the impact of latent internal stresses on lithium distribution in ASSBs during cycling. We aim to understand how these internal stresses evolve and influence electrochemical performance. Additionally, we explore strategies for mitigating these stresses by focusing on the effect of electrolyte ductility, analyzing stress behavior at 25°C and 55°C through operando transmission X-ray microscopy coupled with X-ray absorption near edge structure (TXM-XANES), X-ray tomography, Transmission electron microscopy (TEM) and theoretical modeling.
Our results reveal that lithium heterogeneity within LiNi_xCo_yMn_zO₂ (NCM) cathode particles is primarily governed by latent internal stress evolution rather than charge transfer limitations from solid-solid contact between the electrolyte and cathode. This chemical heterogeneity persisted even after extended relaxation, indicating that internal stresses are not easily dissipated. However, increasing the electrolyte's ductility by elevating the temperature to 55°C led to more homogeneous lithium distribution, suggesting that NCM particles can dissipate internal stresses more effectively under these conditions. Theoretical modeling supported these findings, demonstrating that the mechanical properties of the electrolyte are critical in minimizing stress accumulation. Long-term cycling tests showed that ASSBs cycled at 55°C retained up to 96.7% of their capacity after 500 cycles, indicating improved stress accommodation and enhanced cycling performance.
The study demonstrates that latent internal stresses significantly influence lithium distribution and electrochemical performance in ASSBs. Internal stress can be better accommodated by increasing the electrolyte’s ductility, leading to more uniform lithium distribution and improved battery performance. These findings underscore the importance of managing internal stresses to enhance the longevity and cycling efficiency of ASSBs, supporting their potential for advanced energy storage applications.