Polymer–Inorganic\nComposite Protective Layer\nfor Stable Na Metal Anodes

Abstract

Na metal anodes have\nattracted great interest because of their\nlow electrochemical potential, high theoretical specific capacity,\nand natural abundance. However, nonuniform Na ion flux induced by\nan inhomogeneous solid electrolyte interphase (SEI) usually leads\nto the formation of mossy or dendritic Na, resulting in a low Coulombic\nefficiency (CE) and potential safety hazards. Herein, a well-designed\nartificial protective layer consisting of poly­(vinylidene fluoride)\n(PVDF) and Sn nanoparticles was successfully constructed on a Cu current\ncollector (PSN@Cu current collector) by a scalable and facile doctor\nblade coating technology. The flexible PVDF matrix in the protective\nlayer can accommodate interface fluctuations, whereas the sodiophilic\nSn nanoparticles can provide sufficient ionic conductivity for uniform\ndeposition/stripping and a high mechanical modulus against potential\ndendrite growth. As a result, a high average CE of 99.73% can be achieved\nfor 2800 h at 2 mA cm^–2 with the PSN@Cu current\ncollector. Furthermore, the PSN@Cu current collector has a stable\ncycling lifetime of 2300 h at 1 mAh cm^–2, which\nis more than 10 times higher than that of bare Cu current collector\n(∼220 h). In addition, the unique structure and composition\nof the PSN-derived SEI are carefully investigated and can explain\nthe much improved stability and electrochemical performance of Na\nmetal anodes. This approach highlights the significance of a hybrid\nprotective layer with synergistic properties and presents a new opportunity\nfor stabilizing Na metal anodes.