Facile Formation of Oxygen‐Vacancy Gradient Enables In Situ Uniform Prelithiation in Vanadium Oxide Thin‐Film Batteries

ABSTRACT Vanadium oxide (VO x ) is a promising cathode material for thin‐film all‐solid‐state lithium‐ion batteries (TF‐ASSLIBs) owing to its high theoretical capacity and compatibility with microelectronic fabrication. However, its lithium‐free nature results in low initial Coulombic efficiency and poor cycling stability, necessitating an effective prelithiation strategy. Conventional methods are limited by sluggish lithium diffusion kinetics, causing inhomogeneous lithium distribution with surface accumulation and insufficient bulk penetration. Herein, we engineer an oxygen vacancy (O V ) gradient in VO x , with O V concentration increasing from surface to interior, to homogenize lithium distribution through two synergistic effects: (i) O V creates additional Li + diffusion pathways, accelerating prelithiation kinetics; (ii) O V gradient progressively lowers diffusion barriers, enabling deep Li + penetration and uniform distribution. Notably, this O V gradient forms spontaneously during VO x deposition on Pt current collectors via moderate oxygen adsorption of Pt, which generates a higher O V concentration near the Pt interface, thereby facilitating uniform and efficient prelithiation during subsequent in situ electrolyte deposition. TF‐ASSLIBs comprising an O V ‐gradient VO x cathode|LiPON electrolyte|NiO anode exhibit substantially enhanced electrochemical performance over control devices, delivering higher initial Coulombic efficiency (76.5% vs. 43.5%), superior areal capacity (37.5 vs. 6.5 µAh cm −2 ), and better cycling stability (91.5% vs. 73.4% capacity retention@2000 cycles). This work provides a facile and scalable strategy for developing high‐performance cathodes and TF‐ASSLIBs.