NMR Study of the Solid Electrolyte Interface on a High Performance Lithium Metal Anode

Introduction: Li metal is an ideal anode material due to its low density (0.534 g cm -3 ), the lowest negative electrochemical potential (-3.040 V vs. standard hydrogen electrode) and extremely high theoretical special capacity (3860 mAh g -1 ), which is ten times as high as that of carbonaceous materials. However, several seemingly insurmountable barriers, including limited Columbic efficiency (CE) and dendritic Li growth during repeated Li deposition/stripping processes, have hindered the applications of using Li-metal as anode. It has been reported recently [1] that high concentrated electrolyte consisting of 4 M lithium bis(fluorosulfonyl)imide (LiFSI) in glyme solvent (1,2-dimethoxyethane (DME or monoglyme)) can limit dendrite growth and largely increase CE to more than 99% during Li cycling process. Herein, a multinuclear NMR approach, consisting of 6 Li, 19 F and 1 H MAS NMR at high magnetic field of 19.97 T, was used to understand the structure/compositions of the solid electrolyte interface (SEI) associated with this high performance lithium metal anode.