Sodiophilic skeleton based on the packing of hard carbon microspheres for stable sodium metal anode without dead sodium

The propensity of metallic Na dendrites from uneven electrodeposits and the low Coulombic efficiency due to the inevitable existence of “dead sodium” are crucial barriers to realizing the Na metal anode. Herein, we report a multifunctional sodiophilic skeleton based on the packing of hard carbon (HC) microspheres for stable sodium metal electrodeposition without “dead sodium”. Firstly, HC is sodiophilic substrate due to the intrinsic heteroatoms or defects which is a favor for the nucleation of Na. Secondly, silver nanoparticles electroplating on HC (Ag-HC) was adopted to boost the Na diffusion and further regulate the uniform Na metal epitaxial deposition due to well compatibility with AIMD simulation. Finally, the packing of HC microspheres provides the inner space for Na plating. Importantly, it was first found by Cryo-TEM that Na metal deposition in nanoscale is achieved by oriented attachment along [110] direction, leading to the formation of polycrystalline Na metal film on Ag-HC. Such epitaxial deposition can efficiently reduce the formation of “dead sodium” as revealed by chromatography tests, allowing the high Coulombic efficiency and good cycling stability robust kinetics. Finally, HC-Ag||Na3V2(PO4)3 full cell with a low negative/positive ratio of 0.6 is firstly achieved and displays good cycling stability. This finding provides a new practical strategy without pre-plating of Na metals and demonstrates a highly reversible polycrystalline Na metal anode toward a high-energy Na-based battery.