Poly(vinylidene difluoride) coating on Cu current collector for high-performance Na metal anode

Direct utilization of Na metal anode, instead of carbon or alloy-based anode, is highly desired in Na-ion batteries mainly because of its lowest operating potential and high capacity. Nevertheless, unstable solid electrolyte interphase and uncontrollable Na dendrite growth during the repetitive Na deposition/stripping process usually lead to the low Coulombic efficiency and safety hazards. Herein, dendrite-free Na deposition/stripping can be achieved via constructing a protective PVDF layer on Cu current collector through a facile and scalable doctor blade coating technique. As a result, PVDF@Cu current collector exhibits a stable cycling lifetime for 1200 h with a small overpotential (similar to 35 mV) at 1 mA cm(-2), which is 6 times longer than the bare Cu current collector (similar to 200 h). Furthermore, PVDF@Cu current collector delivers a high average CE of 99.91% for 2000 h at 1 mA cm(-2). The excellent electrochemical performances of PVDF@Cu current collectors are found to arise from the formation of a stable solid electrolyte interphase consisted of Na2O2 with a high shear modulus and rich NaF with a fast Na ion migration based on the defluorination reaction between PVDF and Na metal anode, which synergistically suppresses Na dendrite growth. This approach provides a new opportunity to stabilize Na metal anode.