Toward Realistic Full Cells with Protected Lithium‐Metal‐Anodes: the Effect of an Adaptive Self‐healing Artificial SEI

Abstract The application of an artificial LiBFEP‐SEI on thin 48 µm Lithium‐Metal‐Anodes (LiBFEP = Li[O 2 P(OCH 2 CF 3 ) 2 ]; SEI = solid electrolyte interphase) induces improved plating/stripping of lithium at the interphase with an almost doubling of the lifetime for Li–Li symmetrical cells. Four lithium‐fluoroalkylphosphates other than LiBFEP are tested, but all perform inferior to the control. Lithium‐metal full cells with various NMC‐cathodes and LP57 standard electrolyte are employed to confirm the superior performance of the LiBFEP artificial SEI (LP57 = 1 m Li[PF 6 ] in ethylene carbonate/ethyl methyl carbonate 3:7 wt%). A tripling of the cell lifetime is observed using realistic cell‐cycle parameters. The stabilization of the modified anodes is evidenced by SEM‐EDX, ToF‐SIMS, PEIS measurements and led to an improved anode structure. The performance of the artificial SEI is further improved with the introduction of a novel low‐concentration and low‐polarity electrolyte (0.2 m lithium perfluoroalkoxyaluminate (Li[Al(OR F ) 4 ]; R F = C(CF 3 ) 3 ) in 1,2‐difluorobenzene). Cycling is sustained over 350 cycles with realistic conditions at a current density of 1 mA cm −2 and 48 µm thin Lithium‐Metal‐Anodes. This work provides a comprehensive understanding of how the artificial LiBFEP‐SEI influences the performance of Lithium‐Metal‐Battery full cells, confirming the simplicity/effectiveness of the immersion process for the LiBFEP‐coating.