Impact of Lithium Diffusivity in Active Materials on the Performance of All-Solid-State Batteries Based on Numerical Simulations and Experiments

To achieve high performance in all-solid-state batteries, it is necessary to improve lithium-ion transport in the solid electrolyte (SE) and lithium diffusion in the active material (AM) by understanding the internal reaction mechanisms. However, the lithium diffusion behavior of various AMs in all-solid-state batteries and its effects on battery performance have not been fully clarified. Herein, we performed 3D simulations that reproduce the actual cathode structures visualized by X-ray CT images, using LiCoO 2 (LCO), LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811), and LiNi 0.5 Co 0.2 Mn 0.3 O 2 (NCM523) as AMs. The 3D simulations were validated by comparing the predictions of capacity with experimental results for various C-rates. Subsequently, 3D simulations were employed to elucidate the lithium diffusion behavior within the AM structures. Results indicate that LCO can maintain a higher lithium concentration in the center of its structure (i.e., inside the particles, away from the surface) owing to its high lithium diffusivity, achieving a higher capacity under high C-rates than the other AMs. However, for NCM811 and NCM523, lithium is only present near the AM–SE interface, thereby constraining the battery performance. These findings suggest that lithium diffusivity in AMs plays a crucial role in battery performance during fast charging and discharging, highlighting LCO as a promising AM candidate.