Engineering Electronic Radial Effects for Fast Li ⁺ Transport in Solid‐State Electrolytes

ABSTRACT Achieving high Li + conductivity, near‐unity transference numbers, and stable interfaces in solid‐state electrolytes remains a major challenge for lithium‐metal batteries. Here we introduce a radial‐effect design principle: relativistic expansion and spin–orbit coupling of 5 d orbitals enhance s–d / p–d hybridization, weaken Li–anion interactions, and lower migration barriers. An entropy‐based descriptor, S d , trained and validated with machine learning across >10,000 oxides, sulfides, and halides captures this effect. Machine‐learning‐guided high‐throughput screening flags monoclinic HfO 2 , whose 5 d 2 radial expansion lowers migration barriers by ∼45% vs Sc 2 O 3 or Y 2 O 3 . Guided by this insight, we employ millisecond flash‐Joule heating to convert HfO 2 into nanosized single crystals, then embed them in a Li‐conductive binder to create sc‐HfO 2 @LCB, whose radial coupling yields interconnected Li + pathways (1.23 mS cm −1 , 30°C; t Li + = 0.82, 25°C) and a 4.8 V electrochemical window. Operando Raman/XANES confirms faster Li + transport. Consequently, 2 Ah LiNi 0.9 Co 0.05 Mn 0.05 O 2 ‖Li pouch cells deliver ∼472 Wh kg −1 (stack‐level), maintain superior rate capability over hundreds of cycles, and survive 150°C hot‐plate tests. These results establish radial‐effect engineering as a sophisticated strategy for high‐performance, thermally resilient solid‐state batteries.