Scalable Lithiophilic/Sodiophilic Porous Buffer Layer Fabrication Enables Uniform Nucleation and Growth for Lithium/Sodium Metal Batteries

Abstract Metallic lithium/sodium (Li/Na) is considered an attractive anode for future high‐energy‐density batteries. The root causes of preventing their applications come from uneven Li/Na nucleation and subsequent dendrite formation. Here, a cost‐efficient and scalable solid‐to‐solid transfer method for dense buffer layer construction on Li/Na anodes is proposed, and thin lithiophilic/sodiophilic buffer layers based on natural silk fibers derived carbon (SFC) and carbon nanotubes (CNTs) composites (denoted as SFC/CNTs) are adopted, which facilitate uniform Li/Na nucleation and dendrite‐free, lateral growth behavior upon recurring Li/Na plating/stripping processes. Lithiopilic/sodiophilic buffer layers enable long‐term cycling stability ( > 250 cycles) with high Coulombic efficiency (99.2% for Li and 98.8% for Na), low polarization, and flat voltage profiles. More importantly, the cycling performance of LiFePO 4 |Li pouch cells is largely enhanced with a lifespan of 390 cycles. Further, using ultra‐thin Li anodes (25 μm) also achieves stable LiNi 1/3 Mn 1/3 Co 1/3 O 2 |Li cells with 200 cycles under a low negative/positive ratio (1.67). Similar achievement is also realized in Na‐metal batteries with negligible capacity fading for over 600 cycles in Na 3 V 2 (PO 4 ) 3 |Na cells, further demonstrating that SFC/CNT buffer layer is technically viable in practical batteries. This study provides a facile strategy for fabricating dense and uniform lithiophilic/sodiophilic buffer layers for low‐cost and scale‐up energy storage devices.