Extended Data Fig. 4: Cryo-FIB, cryo-STEM EELS and electrochemical results comparing lithium deposition in cells using traditional and full-fluoride electrolytes.

a, b, Cryo-FIB reveals that the dendrite density is much lower for the full-fluoride fluoroethylene carbonate (FEC) electrolyte (b) than with the traditional EC:DMC electrolyte (a). In the former case, nearly no LiH dendrites are present and the lithium deposition is modified, forming broad localized depositions. c, d, Cross-sections of these deposits reveal that they are composed of many smaller ‘blocks’ in contact, separated by SEI layers. e, f, A lamella of this type of deposition was prepared by cryo-FIB lift-out (e) and cryo-STEM EELS of the Li K-edge of the material revealed that it is composed of partially oxidized lithium metal (f), as was the type I dendrite in the traditional electrolyte. g, The Coulombic efficiency measured in a lithium versus stainless steel set-up using a constant current density of 1 mA cm⁻² and capacity of 1 mAh cm⁻² was greatly improved for the full-fluoride electrolyte compared to the traditional electrolyte. h, Cycling of a full cell comprising a lean lithium anode (50 μm) and a nickel manganese cobalt oxide (NCM) cathode (2 mAh cm⁻²) with the full-fluoride electrolyte resulted in a substantial decrease in capacity fade and improved Coulombic efficiency over the traditional electrolyte. The discharge capacity is plotted on the left axis, whereas the Coulombic efficiency is on the right axis. The operating voltage range was 4.3 V to 3 V. In all figures, the red lines and symbols represent results for the EC:DMC, 1 M LiPF₆ electrolyte, whereas the black lines and symbols are for FEC, 2 M LiPF₆.