Insight into the interfacial reaction mechanism of FEC and NaF on Na for high performance sodium metal batteries

Abstract

Sodium-based batteries have attracted significant attention due to their abundant resources and low cost. Sodium-metal batteries exhibit higher energy density. However, the performance of sodium metal anodes is constrained by the inevitable corrosion of organic electrolytes and uncontrolled growth of Na dendrites. Here, a NaF solid electrolyte interphase (SEI) is fabricated on the surface of sodium metal using a facile and straightforward gas–solid reaction between evaporated organic acid salt and sodium metal, to alleviate the reactivity of the sodium metal surface and prevent corrosion induced by organic electrolytes. DFT calculation verifies that the NaF artificial SEI reduces the de-solvation energy of Na⁺ and has a strong binding force with FEC to rapidly provide sources of Na⁺ and accelerate the reactions of the formation of the NaF-rich SEI layer. As a result, the side reactions from EC and DEC are limited, and the surficial Na₂CO₃ is dramatically decreased. It is verified that the synergistic effect of the NaF artificial SEI and FEC significantly improved the cycle life of the Na metal anode. By employing an electrolyte with FEC, symmetrical cells utilizing NaF@Na anodes demonstrate a remarkable cycling duration of 1500 h at a current density of 0.5 mA cm⁻² and a capacity limit of 0.5 mA h cm⁻². Furthermore, full cells incorporating NVP cathodes and NaF@Na anodes exhibit stable cycling performance for up to 4000 cycles at a rate of 20C.