High-Entropy Phosphide-Polymer Nanointerfaces Enable Adaptive Li⁺ Transport for High-Performance Solid-State Li Metal Batteries

Solid polymer electrolytes (SPEs) hold broad prospects in solid-state lithium metal batteries due to their facile processability, favorable interfacial contact and flexibility, yet their practical application is severely hampered by low Li⁺ conductivity. Although introducing nanofillers in SPEs to promote Li⁺ decoupling can accelerate ion transport, interfacial heterogeneity of filler-polymer nanointerfaces causes an imbalance between their interaction forces toward Li⁺, hindering the Li⁺ transport. Herein, a high-entropy phosphide-polymer hybrid electrolyte (HEP-SPE) is developed. The HEPs provide strong Li⁺ interactions to counteract Li⁺-polymer coupling for rapid transport in site-matching nanointerfaces, while the high-entropy surface weakens electronic localization differences to reduce migration barriers, enabling adaptive rapid Li⁺ migration in site-mismatched nanointerfaces. Therefore, the HEP-SPE exhibits excellent ion transport (1.63 mS cm⁻¹ Li⁺ conductivity, 0.62 transference number) and promotes a stable electrolyte/anode interface. Symmetric batteries based on it stably cycle over 2600 and 1300 h at 0.2 and 0.5 mA cm⁻², respectively.