Non-collapsing 3D solid-electrolyte interphase for high-rate rechargeable sodium metal batteries

Abstract

Rechargeable sodium (Na) batteries based on a Na metal anode are considered a promising, inexpensive alternative to their lithium (Li) counterparts, able to offer a high energy density for stationary and mobile energy storage. However, major challenges arising from dendrite growth, unstable solid-electrolyte interphase (SEI) and high reactivity of Na have severely hindered the practical implementation of Na metal anodes. Here, we report a novel strategy that allows easy preparation of nanostructured Na metal anodes with a three-dimensional non-collapsing artificial SEI, by simply grinding Na-rich sodium-potassium (Na57K) alloy with polytetrafluoroethylene (PTFE) nanoparticles, followed by casting the resultant mixture (PTFE@NaNR) onto a current collector. The high surface area of nanorod-like Na57K triggers defluorination of PTFE, resulting in a cross-linked artificial SEI layer containing inorganic NaF and KF. The in-situ spontaneously formed, cross-linked PTFE derivative remarkably enhances the stability of SEI, suppresses formation and growth of Na dendrites, and prevents over-consumption of electrolyte. Consequently, stable plating/stripping is accomplished in the PTFE@NaNR//PTFE@NaNR symmetric cells. When PTFE@NaNR is coupled with the sodium vanadium phosphate (Na3V2(PO4)3) cathode in a full cell, substantially improved cycling performance is achieved at high rates, even in a lean electrolyte. The PTFE@NaNR shows great promise for use as high-performance anode in fast-charging Na metal batteries.