Spherical sodium metal deposition and growth mechanism study in three-electrode sodium-ion full-cell system

Sodium-ion batteries (SIBs) are considered to be promising alternatives to lithium-ion batteries (LIBs) due to the greater natural abundance of sodium raw materials versus lithium raw materials. However, to date, the plating and stripping mechanism of Na metal in full SIBs, which is one of the functional reactions in SIBs, has yet to be clarified. Herein, we systematically investigate the influence of current density on the nature of Na-metal deposition in a full-cell SIB using a three-electrode system composed of a commercial NaNi1/3Fe1/3Mn1/3O2 (NFM) cathode, a hard carbon (HC) anode, and a Na-metal reference electrode. Using electrochemical methods and ex situ electron microscopy, it is found that the deposition of Na metal increases with increasing current and plates on the HC anode in a spherical shape; the above morphology is in contrast to the dendrite-like morphology of Li plated onto graphite. Using first-principles calculations, it is discovered that the suppression of dendrite growth on SIB anodes can be attributed to the homogeneous adsorption energy of Na atoms on different facets of a sodium crystal.