Defect‐Driven Ionic Trap Construction and Interface Modulation for Rapid Li ⁺ Kinetics in Composite Solid Electrolytes

ABSTRACT Composite solid electrolytes (CSEs) hold great promise for lithium metal batteries owing to the inherent safety and mechanical flexibility, yet their progress is impeded by sluggish Li + transport and unstable interfacial chemistry. Herein, we unveil an ionic‐trap framework to clarify the essential role of inorganic fillers in regulating ion migration. Specifically, milled carbon nitride with oxamide incorporation (MCNOI) introduces abundant nitrogen vacancies that function as a shallow ionic trap, enabling reversible Li + capture/release and constructing continuous conduction pathways. By contrast, traditional carbon nitride forms a deep ionic trap that immobilizes Li + , whereas ionic trap‐free polymer electrolytes lack effective guidance for Li + transport. Beyond intrinsic ion conduction, MCNOI facilitates the formation of a gradient organic‐inorganic interphase, redistributing interfacial charges, suppressing anion migration, and promoting uniform Li deposition. Consequently, the optimized CSE achieves a high Li + transference number (0.68), ultralong cycling stability (>3000 h), and remarkable full‐cell durability (92.3% capacity retention after 1800 cycles at 5 C). These findings highlight defect‐engineered fillers as active regulators of Li + transport, redefining design strategies for durable high‐performance solid‐state batteries.