AbstractAll‐solid‐state lithium metal batteries are prominent candidates for next‐generation batteries with high energy density and low safety risks. However, the traditional planar contact between Li metal and solid‐state electrolytes (SSEs) exhibits substantive void formation and large interfacial morphological fluctuation, causing poor interfacial stability. Here, an interdigitated Li‐solid polymer electrolyte framework (I‐Li@SPE), a pioneering demonstration of 3D interface in polymer‐based all‐solid‐state batteries, is designed, transferring the Li‐SSE interfacial contact from planar to 3D for enhanced interfacial integrity. A smooth and intact 3D Li‐SSE interfacial contact after repeated cycling that precedes planar Li‐SSE contact, is shown. COMSOL simulation indicates I‐Li@SPE reduces local current densities by more than 40% and moderates interfacial variation by more than 50%. As a result, I‐Li@SPE achieves high critical current density of 1 mA cm⁻², as well as promising high areal capacity cycling of 4 mAh cm⁻² at 0.4 mA cm⁻². This work provides a new structure for Li‐SSE composite fabrication and high‐capacity solid‐state Li batteries.