Influence of Free Space on Lithium Growth Behavior at Open Surfaces and Internal Cracks of Sulfide‐Based Solid Electrolyte

Abstract Lithium dendrite penetration through solid electrolyte has been the major obstacle for practical sulfide‐based all‐solid‐state lithium metal batteries (ASSLMBs). Herein, a series of tailored model solid cells are designed to investigate the intrinsic lithium growth behavior at open surfaces and internal cracks of sulfide solid electrolyte. It is shown that when plating lithium on the open surface of electrolyte (free space), the lithium exhibits an intrinsic columnar growth behavior perpendicular to the electrolyte surface, preferentially along the (110) crystal axis. When plating lithium within the internal cracks (confined free space), the growth of lithium follows two major modes: 1) Diffusion creep enabled infiltration along the crack side‐wall surface toward the counter electrode, allowing the deposited lithium to cause short circuit without fully filling the crack; 2) Columnar growth perpendicular to the crack side‐wall surface toward the confined free space inside the crack. The extent of lithium ingress into electrolyte under external pressure in the initial state is found to determine the rate of lithium infiltration after applying the current. As a further validation, intact sintered electrolytes with 99% relative density minimize initial lithium ingress, enabling lithium plating at 6.37 mA cm−2 with an areal capacity exceeding 76 mAh cm−2 without short circuit.