Iron carbide allured lithium metal storage in carbon nanotube cavities

The controversies on the metallic lithium storage in the carbon nano-pores have never stopped for more than three decades since Sato speculated the formation of Li2 molecules in the porous carbon to explain its high lithium storage capacity. Herein, we successfully realized lithium metal storage in the cavities of the carbon nanotubes (CNTs) and directly observed the metallic lithium by the cryogenic transmission electron microscopy (cryo-TEM). By way of experimental characterization and theoretical calculations, we recognized that the capability of lithium-ion intercalation into the graphitic structure and the affinity of the iron carbides in the CNT cavities to lithium are critical to the formation of the metallic lithium therein. These findings will open up a new gate for metal storage in the micro/nano pores or cavities of various carbons and other materials as well as inspire new strategies for improving the metal deposition in the secondary metal batteries.