Bi Nanoparticles Embedded in 2D Carbon Nanosheets as an Interfacial Layer for Advanced Sodium Metal Anodes

Sodium metal is regarded as one of the most prospective next-generation anodes material owing to its high theoretical capacity, low redox potential, low cost, and natural abundance. Its most notable problem is the dendrite growth during Na plating/striping, which causes not only the safety concern but also the generation of inactive Na. Here, it is demonstrated that 2D carbon nanosheets embedded by bismuth nanoparticles (NPs) (denoted as Bi subset of CNs) serve as a robust nucleation buffer layer to endow the sodium metal anodes (SMAs) with high Coulombic efficiencies (CEs) and dendrite-free deposition during long-term cycling. The embedded Bi nanoparticles significantly reduce the nucleation barrier through the sodiophilic Na-Bi alloy. Meanwhile, the carbon frameworks effectively circumvent the gradual failure of those Na-Bi nucleation sites. As a result, the metallic Na on the Bi subset of CNs nucleation layer is repeatedly plated/stripped for nearly 7700 h (1287 cycles) at 3 mA h cm(-2) with an average CE of 99.92%. Moreover, the Na||Na symmetric cells with the Bi subset of CNs buffer layer are stably plated/stripped for 4000 h at 1 mA cm(-2) and 1 mA h cm(-2). It is found that the cycling stability is closely related to the Na utilization of SMAs and current rate.

Automated summary

By embedding bismuth nanoparticles in 2D carbon nanosheets, a robust nucleation buffer layer is created to enable sodium metal anodes with high Coulombic efficiencies and dendrite-free deposition during long-term cycling. The cycling stability is closely related to the Na utilization of SMAs and current rate.