Regulating Li deposition at artificial solid electrolyte interphases

Abstract

Developing high-energy lithium-metal batteries (LMBs) as a high priority for next-generation electrochemical energy storage. The unstable solid electrolyte interphase (SEI) formed on the anode and the subsequent nucleation of uneven lithium electrodeposits are now known to be the key limitations to progress in the field. These challenges are shared with multiple other metal anodes, implying that fundamentally-based solutions are broadly interesting. Here, we report a novel strategy of promoting uniform lithium electrodeposition by establishing an artificial SEI layer on the lithium anode via magnetron sputtering deposition. We show by means of density functional theory (DFT) simulations that an artificial SEI enriched in lithium fluoride (LiF) salt provides a low energy barrier (E_b = 0.19 eV in vacuum) for the diffusion of lithium ions, in comparison to SEI components formed spontaneously at the interface by Li reaction with electrolyte components. We also compute the electron localization function (ELF) for Li adsorbates on LiF and show for the first time that degeneracy in the adsorption energy is responsible for the low in-plane diffusion barriers experienced by Li ad atoms on LiF. On this basis we create artificial SEIs based on LiF on Li electrodes and find that the electrodes exhibit exceptional ability to promote smooth Li deposition during charging at a high current density of 1 mA cm⁻². Through post-mortem SEM analysis of patterned lithium electrodes, we find visual support for the effectiveness of the artificial SEI. By means of impedance and XPS analyses, we further show that the artificial SEI retains its integrity upon repeated cycles.