The sp Hybridization of Tin Single Atoms for Dendrite-Free Sodium Metal Batteries

Restricting the growth of sodium (Na) dendrites at the atomic level is the premise to enable both the stability and safety of sodium metal batteries (SMBs). Here, the universal synthesis of the fourth main group element (Sn, Ge, Pb) as single metal atoms anchored on graphene (Sn, Ge, Pb SAs/G) with sp hybridization for dendrite-free sodium metal anode is reported. The in situ real-time observation of Na growth on Sn SAs/G uncoils a kinetically uniform planar deposition at the atomic level for substantially suppressing the dendrite growth. The symmetrical Sn SAs/G-Na battery exhibits high Coulombic efficiency of 99.8% for 200 cycles, long-term cyclability with 600 h at 4 mA cm^-2, and ultralow overpotential of 40 mV at 8 mA cm^-2. Further, the full batteries Na₃V₂(PO₄)₃||Sn SAs/G-Na show unprecedented rate capability of 67 mAh g^-1 at 20 C and a capacity retention as high as 91% after 500 cycles. The theoretical calculations of Na deposition on different M SAs/G (M═Sn, Ni, Zn, Fe, Co) reveal that the 5s ²5p ² electron configuration of Sn SAs/G realizes the planar deposition mechanism of Na clusters along the graphene plane. Therefore, this work provides an atom-level accurate miniaturization strategy for constructing dendrite-free SMBs.