In-situ constructing a supersodiophilic fluffy surface layer on a Cu foam host for stable Na metal anodes

Commercial Cu foam can be employed as a 3D current collector to accommodate Na metal for stable sodium metal batteries (SMBs). However, few studies focus on regulating the interphase structure and properties of Cu foam to achieve fast and uniform Na impregnation. Herein, a facile and controllable oxidation treatment strategy is used to in-situ construct a fluffy CuO/Cu 2 O surface layer on the skeleton of Cu foam (SF–Cu-3.6). The oxidation degree and interphase structure of Cu foam can be rationally designed by adjusting the concentration of (NH 4 ) 2 S 2 O 8 oxidant, which is directly related to the driving force of Na infusion. With an optimized interface, Na metal can be rapidly infused into SF-Cu-3.6 within 5 s and a structurally complete Na/SF-Cu-3.6 composite electrode with a flat surface and no visible void can be obtained. The SF-Cu-3.6 with a large surface area can be used as a 3D host for Na metal to lower the local current density during cycling, resulting in uniform Na deposition without dendrite formation and growth. In virtue of the structural advantages, the symmetric Na/SF-Cu-3.6 cell exhibits flat charge/discharge plateaus with a low overpotential of 12 mV and stable cycling up to 1000 h at 0.5 mA cm −2 . When paired with NaTi 2 (PO 4 ) 3 , the rate performance of the full cell using the Na/SF-Cu-3.6 composite anode is significantly better than that of the full cell using a bare Na anode.