Photochemically-driven high-entropy oxide interphase for stable alkali-metal anodes

Interfacial instability at the anode is a key challenge for alkali metal batteries. While high-entropy oxide (HEO) nanofilms show promise for stabilizing this interface, a scalability and substrate compatibility synthesis strategy is lacking. Here, we report a vacuum-ultraviolet photochemical condensation (VPC) method for fabricating stabilizing interphases. The leverages high-energy photons (7.2 eV) to initiate the decomposition of metal-organic precursors and drive the room-temperature condensation of an ultrathin (∼8 nm), dense, and uniform high-entropy oxide (HEO) film within minutes. This method enables the combination of dissimilar metallic elements regardless of their thermodynamic solubility and is applicable to numerous HEO films. By modulating the interfacial Gibbs free energy, the VPC-derived HEO film both thermodynamically lowers the nucleation barrier and kinetically homogenizes ion flux. As a result, the HEO interface reduces the Li nucleation overpotential by over 3-fold and enables dendrite-free cycling for over 550 cycles. This rapid, energy-efficient, and scalable VPC strategy with tunable compositions provides new opportunities for designing high-entropy-based interphases for advanced metal batteries.