Sodium Metal Anodes with Self-Correction Function Based on Fluorine-Superdoped CNTs/Cellulose Nanofibrils Composite Paper

Despite much efforts to stabilize sodium metal anodes for promoting their commercial applications, achieving a safe cycling process without intrinsic dendrite growth remains difficult owing to the unstable reaction interface and irregular sodium metal propagation. Herein, fluorine-superdoped carbon nanotubes with a fluorine content of 14.38 at% are achieved using a new oxidation-assisted plasma strategy, and then alternately assembled with cellulose nanofibrils to form periodical conductive/dielectric composite paper with outstanding mechanical properties. The superdoping of fluorine facilitates the construction of a NaF-dominated solid electrolyte interphase layer, while the periodical conductive/dielectric network re-homogenizes electric field distribution around irregular sodium protrusions, realizing a bottom-up sodium orientation deposition and the self-correction functionality during sodium plating/stripping process. Density functional theory calculations reveal that the specific oxygen species (C-O/C(sic)O) and fluorine species (semi-ionic C-F/covalent CF2) on the surface of carbon matrix, could remarkably trap active fluorine fragments and generate NaF with sodium metal, respectively, which promotes the superdoping of fluorine and forms dendrite-free sodium anodes. This delicate structure renders the sodium anodes a low nucleation overpotential of approximate to 7 mV, high Coulombic efficiency of 99.5% over 300 cycles at 3 mA cm(-2), stable operation for up to 2100 h under approximate to 16 mV, and excellent full battery performance.

Automated summary

Superdoped carbon nanotubes with high fluorine content were successfully achieved and assembled with cellulose nanofibrils to form conductive/dielectric composite paper. The superdoping of fluorine and the periodic conductive/dielectric network enable dendrite-free sodium deposition and self-correction during sodium plating/stripping process.