3DOM POM@MOF‐Enhanced Polymer Electrolytes Enabling Dendrite‐Suppressed, High‐Performance All‐Solid‐State Lithium‐Metal Battery

All‐solid‐state lithium batteries (ASSLBs) provide high energy density and improved safety but remain limited by lithium dendrite formation and low ionic conductivity at room temperature. This work reports an effective strategy to address these issues by incorporating hierarchically ordered macro/microporous polyoxometalate‐based metal–organic frameworks (3DOM POM@MOFs), specifically 3DOM NENU‐3a, into a polyethylene oxide (PEO) matrix to form a composite solid electrolyte (CSE). The three‐dimensionally ordered macroporous structure, prepared via a hard‐template method, preserves the advantages of microporous POM@MOFs while introducing interconnected macropores that enhance ion transport. With only 1 wt.% 3DOM NENU‐3a added to a PEO/lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) system, the resulting CSE exhibits high ionic conductivity (1.32 × 10 −4 S cm −1 at room temperature), high apparent lithium‐ion transference numbers (0.76 at room temperature and 0.89 at 60°C), and an expanded apparent electrochemical stability window up to 6.3 V at 60°C. These properties enable uniform lithium deposition and effectively suppress lithium dendrite growth during long‐term cycling by promoting uniform Li deposition. ASSLBs using LiFePO 4 cathodes show excellent long‐term cycling stability and rate performance, while cells paired with LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622) cathodes demonstrate robust cycling at elevated temperatures. This study highlights the potential of 3DOM POM@MOF fillers for developing high‐performance, dendrite‐resistant ASSLBs.