Realizing a highly stable sodium battery with dendrite-free sodium metal composite anodes and O3-type cathodes

Room-temperature Na metal batteries have been regarded as promising candidates for energy storage systems due to their high energy density and the widespread availability of low cost sodium. However, the practical application of metallic sodium anode is impeded by its low stripping/plating efficiency and poor cycling performance due to the poor reversibility of sodium anode caused by the formation of inhomogeneous solid electrolyte interphase, the growth of dendritic sodium, and relatively infinite volume change. Here, Na-C composite anode was fabricated by depositing nanoscale metallic sodium in graphitized carbon microspheres which were assembled from graphitized carbon nanosheets. The carbon microspheres function as a mini-nanoreservoir with high-surface-area, conductivity, and mechanical stability, which lower the local current density, ensure a homogeneous Na nucleation and high electrochemical active of Na, and restrict the volume change. As a result, metallic sodium can be reversibly nondendritic stripped/plated with a high Coulombic efficiency of 99.3% up to 4 mA cm⁻² for 4 mA h cm⁻². Building upon this dendrite-free anode, we demonstrate a full cell using O3-NaNi_0.5Mn_0.2Ti_0.3O₂ cathode to achieve a superior long lifespan of ~100 cycles at high current density of 0.5 C.