Deeply Cycled Sodium Metal Anodes at Low Temperature and in Lean Electrolyte Conditions.

Enabling high-performing alkali metal anodes at low temperature and in lean electrolyte conditions is critical for the advancement of next-generation batteries with high energy density and improved safety. We present an ether-ionic liquid composite electrolyte to tackle the problem of dendrite growth of metallic sodium anode at low temperatures ranging from 0 to -40 °C. This composite electrolyte enables a stable sodium metal anode to be deeply cycled at 2 mA cm-2 with an ultrahigh reversible capacity of 50 mAh cm-2 for 500 hours at -20 °C in lean electrolyte (1.0 μL mAh-1 ) conditions. Using the composite electrolyte, full cells with Na3 V2 (PO4 )3 as cathode and sodium metal as anode present a high capacity retention of 90.7 % after 1,000 cycles at 2C at -20 °C. The sodium-carbon dioxide batteries also exhibit a reversible capacity of 1,000 mAh g-1 over 50 cycles across a range of temperatures from -20 to 25 °C.