The Key Role of Grain Boundary Dynamics in Revolutionizing the Potential of Solid Electrolytes

Abstract Solid electrolytes (SEs) have the potential to enhance the safety and performance of Li‐metal batteries. However, the existence of grain boundaries in polycrystalline SEs presents a significant challenge for both ionic and electronic migration, promoting the propagation of detrimental lithium dendrites. This study compares the roles of grain boundaries in electrical properties of three distinct SEs including garnet‐type Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZO), argyrodite‐type Li₆PS₅Cl (LPSC), and NASICON‐type Li_1+x+yAl_x(Ti,Ge)_2‐xSi_yP_3‐yO₁₂ (LATP). Results demonstrate that the electronic and ionic conductivities of solid‐state electrolytes are affected differently by grain boundaries, depending on the specific type of electrolyte. For instance, LLZO and LATP experience dielectric breakdown at 3.7 and 5.3 V, respectively, while LPSC does not exhibit such behavior. Here, a new chemical modification is proposed that simultaneously alters the composition of both the surface and grain boundaries of SEs, ultimately reducing electronic conductivity for the LLZO SEs. Consequently, the proposed LLZO exhibits unprecedented dendrite‐free cycling stability, achieving a remarkable 12 000‐h lifetime at room temperature, surpassing conventional strategies such as surface coatings in dendrite mitigation. This study highlights the significance of modifying grain boundaries to design safe and durable Li‐metal batteries. It provides new insights for developing SEs that are highly resistant to dendrite formation.