Extensive Sodium Metal Plating and Stripping in a Highly Concentrated Inorganic−Organic Ionic Liquid Electrolyte through Surface Pretreatment

In the present work, the stable and extensive cycling of Na plating and stripping is demonstrated within an inorganic-organic ionic liquid electrolyte. The electrolyte is composed of liquid-state tri(isobutyl)methylphosphonium bis(fluorosulfonyl)imide when employing a high 45mol% Na concentration in the form of sodium bis(fluorosulfonyl)imide. The liquid-state electrolyte supports safe Na metal electrochemistry at 50°C and exhibits a conductivity of 10-2.5Scm-1. Through plating/stripping with 1h polarization times (12 cycles, J=0.5mAcm-2), a surface is prepared with a smooth surface devoid of dendrites and, importantly, a stable solid-electrolyte interphase, determined by using scanning electron microscopy and impedance spectroscopy. After this, a greater mass transfer can be undertaken through an increased polarization time of 5h (Q=2.5mAhcm-2) for a duration of 120h.