Carbon-Confined Two-Dimensional Sodiophilic Sites Boosted Dendrite-Free Sodium Metal Anodes

Carbon-supported sodium metal anodes (SMAs) have attracted growing interest in next-generation energy storage applications. Sodiophilic sites on carbon hosts such as foreign metal/metal compounds are critical for suppressing Na dendrite growth. However, the foreign active materials are mostly restricted to nanoparticle-like structures, which suffer from severe agglomeration and low metal utilization. Here, we develop the carbon-encapsulated mosaic Fe₃O₄ nanosheets (Fe₃O₄@CNS) with two-dimensional (2D) active sites via the oriented attachment (OA) mechanism. Ultrathin Fe₃O₄ nanosheets not only endow the carbon hosts with a continuous 2D nucleation region and high metal utilization but also catalyze the formation of a stable solid electrolyte interphase (SEI) film. Additionally, carbon shells can protect the Fe₃O₄ against electrolyte exfoliation. As a result, the Fe₃O₄@CNS half cells achieve a cycle of up to 1800 h with an average Coulombic efficiency (CE) of 99.6% at 1.0 mA cm^-2 and 1.0 mA h cm^-2 and still stably cycle for 800 h with a high CE of 99.2% even at 3.0 mA cm^-2 and 3.0 mA h cm^-2. The Na@Fe₃O₄@CNS symmetric cells can last for more than 2200 h at 1.0 mA cm^-2 and 1.0 mA h cm^-2. And the Na₃V₂(PO₄)₃ || Na@Fe₃O₄@CNS full cells can attain a specific capacity of 86.6 mA h g^-1 after 350 cycles at 1.0 A g^-1 (∼8C), showing excellent cycle stability for practical applications. This work provides a new method to establish efficient 2D nucleation sites in the Na hosts.