<p>The effective use of polymer electrolytes in lithium metal batteries is tied to the molecular design and topological control of the polymer to simultaneously achieve high ionic conductivity, robust mechanical modulus and low interfacial resistance at the electrode interface. Here we introduce a composite polymer electrolyte design strategy based on tailored interactions between rigid polyanion architectures and lithium-containing ionic liquids. In these composite polymer electrolytes, the lithium-ion conduction is decoupled from polymer segmental dynamics, while enabling fast interfacial charge transfer and a high modulus to effectively stabilize the interfacial area in contact with the lithium metal electrode. Using solid-state exchange nuclear magnetic resonance and discrete Markov state model analysis of nanocluster dynamics, we reveal distinct lithium-ion conduction mechanisms and quantitatively assign their contributions to the bulk lithium-ion conductivity. The various lithium-ion transport pathways in rigid polyanion architectures endow the composite polymer electrolytes with ionic conductivity up to 2.5 mS cm⁻¹ at 25 °C, mechanical modulus ranging from 250 to 530 MPa and improved interfacial kinetics. The best-performing composite polymer electrolyte also enables effective battery operation of Li||LiFePO₄ 60-mAh pouch and 80-mAh cylindrical cells.</p>