Designing and preparing a 3D “overpass” hierarchical porous carbon membranes free-standing anode for sodium ion battery

Hard carbon (HC) is considered the most promising anode material for sodium ion batteries (SIBs), but still faces urgent challenges such as poor rate capability and low initial Coulombic efficiency (ICE). To improve these issues, herein, we creatively combine membrane science with electrode technology, using phase inversion methods to produce a carbon membrane with a 3D “overpass” hierarchical porous carbon structure as the free-standing anode for SIBs. Such an efficient and controllable strategy forms a channel-skeleton coupling structure in the carbon membrane that promotes electron/ion transport, improves the wettability of electrolytes, and boosts the Na storage performance comprehensively. In particular, the optimal sample (PMP-5) shows a superior rate capability of 257.6 mAh g-1 at 5 C and excellent cycling stability (91% retention rate after 300 cycles at 0.5 C). Meanwhile, since without any binder, the free-standing carbon membrane electrode shows an astonishing ICE of 90.5%. More importantly, when matched with a layered O3-Na(NiFeMn)1/3O2 cathode, the full-cell shows a high energy density of 287 Wh kg-1, excellent rate capability and cycling stability. Our work provides a feasible strategy to boost the Na storage capability of HC anodes by membrane science and pore engineering and serves as a theory guide for designing other superb electrode materials.