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.