Interface Design Considering Intrinsic Properties of Dielectric Materials to Minimize Space‐Charge Layer Effect between Oxide Cathode and Sulfide Solid Electrolyte in All‐Solid‐State Batteries

Abstract Introducing dielectric materials is a promising approach to mitigate space‐charge‐layer (SCL) formation, which negatively affects the electrochemical performance of sulfide‐based all‐solid‐state batteries (ASSBs). Most previous studies have focused on mitigating SCL formation by introducing dielectric materials, overlooking the fact that significant dielectric properties such as the dipole moment direction and the magnitude of the dielectric constant can influence SCL formation. To clarify the unclear mechanism of dielectric materials mitigating SCL formation, paraelectricity, ferroelectricity, and the magnitude of the dielectric constant are investigated to determine their effect on SCL formation. Paraelectric materials possessing no permanent dipole moment can effectively mitigate the SCL formation better than ferroelectric material with strong permanent dipole moment because of the intrinsic characteristics of the paraelectric material, in which the dipole moment can be aligned along the direction of the electric field applied inside of ASSB. Furthermore, paraelectric materials with a larger dielectric constant have a greater effect in mitigating SCL effect than paraelectric materials with a smaller dielectric constant. Thus, these properties should be considered in cathode‐solid‐electrolyte interface design. This study considers relevant dielectric material characteristics that had not been considered previously, suggesting a new paradigm for optimizing the interfacial resistance of sulfide‐based ASSBs originating from SCL formation.