title: Multinuclear NMR Study of the Solid Electrolyte Interface Formed in Lithium Metal Batteries.
abstract: The composition of the solid electrolyte interphase (SEI) layers formed in Cu|Li cells using lithium bis(fluorosulfonyi)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) in 1,2-dimethoxyethane (DME) electrolytes is determined by a multinuclear solid-state MAS NMR study at high magnetic field. It is found that the "dead" metallic Li is largely reduced in the SEI layers formed in a 4 M LiFSI-DME electrolyte system compared with those formed in a 1 M LiFSI-DME electrolyte system. This finding relates directly to the safety of Li metal batteries, as one of the main safety concerns for these batteries is associated with the "dead" metallic Li formed after long-term cycling. It is also found that a large amount of LiF, which exhibits superior mechanical strength and good Li+ionic conductivity, is observed in the SEI layer formed in the concentrated 4 M LiFSI-DME and 3 M LiTFSI-DME systems but not in the diluted 1 M LiFSI-DME system. Quantitative6Li MAS NMR results indicate that the SEI associated with the 4 M LiFSI-DME electrolyte is denser than those formed in the 1 M LiFSI-DME and 3 M LiTFSI-DME systems. These studies reveal the fundamental mechanisms behind the excellent electrochemical performance associated with higher concentration LiFSI-DME electrolyte systems.
authors.affiliation: College of Science, China Agricultural University , Beijing 100193, P. R. China.
authors.forename: Chuan
authors.initials: C
authors.lastname: Wan
authors.forename: Suochang
authors.initials: S
authors.lastname: Xu
authors.forename: Mary Y
authors.initials: MY
authors.lastname: Hu
authors.forename: Ruiguo
authors.initials: R
authors.lastname: Cao
authors.forename: Jiangfeng
authors.initials: J
authors.lastname: Qian
authors.affiliation: College of Science, China Agricultural University , Beijing 100193, P. R. China.
authors.forename: Zhaohai
authors.initials: Z
authors.lastname: Qin
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Karl T
authors.identifier: http://orcid.org/0000-0001-9609-9516
authors.initials: KT
authors.lastname: Mueller
authors.forename: Ji-Guang
authors.identifier: http://orcid.org/0000-0001-7343-4609
authors.initials: JG
authors.lastname: Zhang
authors.forename: Jian Zhi
authors.identifier: http://orcid.org/0000-0001-8879-747X
authors.initials: JZ
authors.lastname: Hu
keywords: 6Li MAS NMR; Li metal batteries; high concentration electrolytes; high magnetic field; solid electrolyte interphase layer