Precursor-first fabrication of ultrathin lithium-metal anodes with integrated Mg-Li scaffolds

Manufacturing ultrathin lithium (Li)-metal anodes remains challenging because metallic Li is adhesive and creep-prone, making it difficult to process into mechanically stable freestanding foils. In the present work, we report an indirect metallurgical route that transfers the critical thinning step from Li metal to a processable Mg-Li precursor. Room-temperature high-ratio differential-speed rolling produces an approximately 8-µm-thick freestanding Mg-Li foil with an ultrafine-grained microstructure. Subsequent controlled prelithiation converts the foil into a compositionally graded Li-rich electrode consisting of an approximately 18-µm-thick active Li-Mg region and a 5-µm-thick residual Mg-Li scaffold. The residual scaffold preserves structural and electronic continuity, enabling full-cell cycling without a separate Cu current collector. When paired with LiFePO₄ cathodes, the electrode delivers 1.05 and 1.52 mAh cm^-2 after 200 cycles at nominal N/P ratios of 3.04 and 1.52, respectively. Post-cycling analyses indicate greater structural continuity and distinct evolution of N- and F-containing interphase species compared with a Cu-supported Li reference. Total-negative-electrode benchmarking further shows that the low-density integrated scaffold reduces the mass and volume penalties associated with conventional Cu-supported configurations. Collectively, this work establishes a precursor-first route for fabricating ultrathin Cu-current-collector-free Li-metal anodes with integrated mechanical-support and current-collecting functions.