Modulating Conductivity and Porosity of Interlayer for Long‐Cycling All‐Solid‐State Lithium Metal Batteries

Abstract Sulfide‐based all‐solid‐state lithium metal batteries (ASSLMBs) are considered promising next‐generation energy storage solutions due to their high energy density and enhanced safety. However, persistent challenges such as dendrite formation, solid electrolyte (SE) decomposition, and unstable interfaces impede the utilization of lithium metal anodes. In this study, a triple Si/Carbon nanotube (CNT) interlayer featuring meticulously engineered gradients in conductivity and porosity is introduced. Thus, the designed interlayer consists of low electronic conductivity and high ionic conductivity with a densely low‐porosity structure at the SE interface, balanced ionic‐electronic conductivity in the porous middle layer, and high electronic conductivity adjacent the current collector. This strategic configuration effectively suppresses dendrite growth, minimizes SE degradation, and promotes uniform lithium deposition. Experimental results demonstrate that the triple Si/CNT interlayer achieves an initial Coulombic efficiency of 95.1% and maintains approximately 99.9% cycling efficiency over 150 cycles in half‐cell tests. Notably, full‐cell evaluations with an Ni‐rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 cathode exhibit outstanding performance, delivering a capacity retention of 85.2% after 500 cycles and demonstrating long‐term cycling stability up to 1800 cycles, alongside superior rate capabilities (85.2% at 2C, 76.3% at 5C, and 65.2% at 10C). These results highlight the efficacy of gradient‐structured interlayers in enabling high‐energy‐density, long‐cycling ASSLMBs.