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 agglom-eration 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 (similar to 8C), showing excellent cycle stability for practical applications. This work provides a new method to establish efficient 2D nucleation sites in the Na hosts.

Automated summary

In this study, carbon-encapsulated mosaic Fe3O4 nanosheets were developed by the oriented attachment mechanism, providing continuous 2D nucleation regions and high metal utilization. The Fe3O4@CNS material exhibited stable solid electrolyte interphase (SEI) film formation and excellent cycle stability, demonstrating promising electrochemical performance for sodium metal anodes.