Thermal diffusivity and conductivity of sulfide and oxide solid electrolytes: Effects of densification and microstructural evolution

Solid electrolytes (SEs), essential for all-solid-state batteries, exhibit high thermal resistance and can reduce the cooling system requirements. However, limited cooling under high-rate charging and discharging can cause thermal issues, constraining battery performance. To address these challenges, it is important to clarify the thermal transport characteristics of SEs, which remain underexplored. In sulfide SEs, structure varies with molding pressure during fabrication, while in oxide SEs, it changes with sintering temperature. This study investigates how such structural changes affect the thermal transport properties of three sulfide SEs (LPS glass, Li 3 PS 4 glass ceramic and Li 6 PS 5 Cl) and an oxide SE (Li 6.25 Ga 0.25 La 3 Zr 2 O 12 ). For sulfide SE, thermal transport characteristics were also compared with ionic conductivity. Structural analyses confirmed that increasing molding pressure or sintering temperature enhanced particle integration and densification. Thermal conductivity increased significantly with densification due to improved transport pathways and reduced tortuosity, consistent with trends in ionic conductivity. In contrast, thermal diffusivity increased only slightly, as higher density raised both thermal conductivity and volumetric heat capacity, the latter suppressing thermal diffusivity. • Thermal transport was analyzed in solid electrolytes after structural changes. • Sulfide solid electrolytes became denser with increasing molding pressure. • Oxide solid electrolytes became denser with increasing sintering temperature. • Densification significantly increases ionic and thermal conductivity. • Thermal diffusivity increases only slightly, despite densification.