Sodiophilic current collectors based on MOF-derived nanocomposites for anode-less Na-metal batteries

"Anode-less" sodium metal batteries (SMBs) with high energy may become the next-generation batteries due to the abundant resources. However, their cycling performance is still insufficient for practical uses. Herein, a metal organic frameworks (MOF)-derived copper-carbon (Cu@C) composite is developed as a sodiophilic layer to improve the Coulombic efficiency (CE) and cycle life. The Cu particles can provide abundant nucleation sites to spatially guide Na deposition and the carbon framework offer void volume to avoid volume changes during the plating/stripping process. As a result, Cu@C-coated copper and aluminum foils (denoted as Cu-Cu@C and Al-Cu@C foil) can be used as efficient current collectors for sodium plating/stripping, achieving, nearly 1600 and 240 h operation upon cycling at 0.5 mA cm(-2) and 1 mA h cm(-2), respectively. In situ dilatometry measurements demonstrate that Cu@C promotes the formation of dense Na deposits, thereby inhibiting side reactions, dendrite growth, and accumulation of dead Na. Such current collectors are employed in Na metal cells using carbon-coated Na3V2(PO4)(3) (NVP/C) and copper selenides (Cu2-xSe@C) cathodes, achieving outstanding rate capability and improved cycling performance. Most noticeably, "anode-less" Na batteries using Al-Cu@C as anode and NVP/C as cathode demonstrate promising CE as high as 99.5%, and long-term cycling life.