Abstract
Formation protocols dictate the nascent cathode–electrolyte interphase (CEI) and therefore the attainable energy density and lifetime of sulfide‐based all‐solid‐state batteries (ASSBs). Yet, in contrast to liquid‐electrolyte systems, the electro‐chemo pathways activated during formation in ASSBs remain poorly defined and are rarely optimized with mechanistic intent. Herein, the formation protocol is positioned as an independent design variable that programs CEI passivation and establishes effective ion and electron transport pathways. Five distinct formation protocols are systematically evaluated to connect the initial cycling behavior with long‐term cycling performance. A conventional constant voltage holding during the initial charge fails to passivate the CEI, leading to continued resistance buildup. Counterintuitively, elevated and dynamically modulated charge/discharge rates (C‐rates) enable rapid and uniform CEI passivation. Most notably, turbo schedules that impose controlled high discharge current densities stabilize interfacial resistance and deliver durable cycling performance with substantially shortened formation time. Direct current internal resistance (DCIR) and average voltage evolution provide direct, operando‐accessible descriptors of formation quality, generating a data stream readily usable for future AI‐assisted, closed‐loop protocol optimization. These results redefine formation from a manufacturing afterthought to a scalable strategy for engineering stable cathode interfaces in next‐generation solid‐state batteries.