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 Fe 3 O 4 nanosheets (Fe 3 O 4 @CNS) with two-dimensional (2D) active sites via the oriented attachment (OA) mechanism. Ultrathin Fe 3 O 4 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 Fe 3 O 4 against electrolyte exfoliation. As a result, the Fe 3 O 4 @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@Fe 3 O 4 @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 Na 3 V 2 (PO 4 ) 3 || Na@Fe 3 O 4 @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.