Artificial Solid Electrolyte Interphases for Lithium Metal Electrodes by Wet Processing: The Role of Metal Salt Concentration and Solvent Choice

Katharina Thanner; Alberto Varzi; Daniel Buchholz; Stefan J Sedlmaier; Stefano Passerini

doi:10.1021/acsami.0c08938

Artificial Solid Electrolyte Interphases for Lithium Metal Electrodes by Wet Processing: The Role of Metal Salt Concentration and Solvent Choice

ACS Appl Mater Interfaces. 2020 Jul 22;12(29):32851-32862. doi: 10.1021/acsami.0c08938. Epub 2020 Jul 13.

Authors

Katharina Thanner^{1

2

3}, Alberto Varzi^{1

2}, Daniel Buchholz³, Stefan J Sedlmaier³, Stefano Passerini^{1

2}

Affiliations

¹ Helmholtz Institute Ulm (HIU), Helmholtzstraße 11, 89081 Ulm, Germany.
² Karlsruhe Institute of Technology (KIT), P.O.Box 3640, 76021 Karlsruhe, Germany.
³ BMW Group, Petuelring 130, 80788 München, Germany.

PMID: 32600026
DOI: 10.1021/acsami.0c08938

Abstract

In this study, the artificial solid electrolyte interphase (SEI) formed on lithium metal when treated in ZnCl₂ solutions is thoroughly investigated. The artificial SEI on lithium metal electrodes substantially decreases the interfacial resistance by ca. 80% and improves cycling stability in comparison to untreated lithium. The presence of a native SEI negatively affects the morphology and interfacial resistance of the artificial SEI. Increasing the ZnCl₂ concentration in tetrahydrofuran (THF) (precursor solution) results in higher homogeneity of the surface morphology. Independent of the ZnCl₂ concentrations, the artificial SEI is composed of C_x, CO, LiCl, Li₂CO₃, ZnCl₂, and Li_xZn_y alloys. ZnCl₂ (1 M) produces the most homogenous surface and additional surface species with carbonyl side groups. Nonetheless, the ZnCl₂ concentration only has a small effect on the interfacial resistance or cycling stability. Using ethyl methyl carbonate (EMC) as the solvent significantly reduces the interfacial resistance to 7 Ω cm², in comparison to 25 Ω cm² for THF. The composition of the artificial SEIs varies depending on the solvent. Either way, the SEI consists of C_x Li_xC, LiCl, Li₂CO₃, ZnCl₂, and LiZn alloys. The THF-based SEI additionally features ether and carbonyl groups, LiZnO, and Zn metal. For the artificial SEI formed with both solvents, the atomic percentage of the LiZn alloy increases close to the Li surface.

Keywords: SEI precursor; artificial SEI; lithium alloys; lithium metal battery; precursor solvent; solid electrolyte interphase.