Highly stable Na metal anode enabled by a multifunctional hard carbon skeleton

Sodium (Na) metal and hard carbon are regarded as promising and competitive alternatives as anode materials for sodium-ion batteries (SIBs). Constructing a Na metal/hard carbon composite anode to exert a synergistic effect on the electrochemical performance of SIBs is highly desirable but rarely reported. In this work, we report a Na metal/N-functionalized hard carbon (NHC) composite as a high-performance anode for SIBs. The introduction of the N-functionalized groups transforms the surface chemistry of the hard carbon from sodiophobic to sodiophilic, thus significantly promoting the dispersion of the hard carbon in Na metal and facilitating the formation of an intimate interfacial contact between them. In addition, during Na stripping/plating cycling, the sodiated NHC particles homogenize the local electron distribution, while the desodiated NHC particles function as an artificial SEI film, which facilitate the bottom-up deposition of Na due to electron concentration gradient and mechanically inhibit the growth of Na dendrites. Consequently, the Na–NHC anode in the symmetric cell exhibits excellent cycling stability up to 1700 h without a short circuit, which significantly exceeds that of the bare Na anode. In the full cell with the Na–NHC anode, NaTi2(PO4)3 exhibits a significantly extended cycling life.