College of Science, China Agricultural University , Beijing 100193, P. R. China.
ACS Appl Mater Interfaces. 2017 May 3;9(17):14741-14748. doi: 10.1021/acsami.6b15383. Epub 2017 Apr 18.
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. Quantitative Li 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.
采用高场多核固态 MAS NMR 研究，确定了在 1,2-二甲氧基乙烷（DME）电解液中使用双（氟磺酰基）亚胺锂（LiFSI）和双（三氟甲烷磺酰基）亚胺锂（LiTFSI）的 Cu|Li 电池中形成的固体电解质中间相（SEI）层的组成。研究发现，与在 1 M LiFSI-DME 电解液体系中形成的 SEI 层相比，在 4 M LiFSI-DME 电解液体系中形成的 SEI 层中“死”的金属 Li 被大量还原。这一发现直接关系到 Li 金属电池的安全性，因为这些电池的主要安全问题之一与长期循环后形成的“死”的金属 Li 有关。研究还发现，在高浓度的 4 M LiFSI-DME 和 3 M LiTFSI-DME 电解液体系中形成的 SEI 层中观察到大量具有优异机械强度和良好锂离子电导率的 LiF，但在稀释的 1 M LiFSI-DME 电解液体系中则没有。定量 Li MAS NMR 结果表明，与在 1 M LiFSI-DME 和 3 M LiTFSI-DME 电解液体系中形成的 SEI 相比，在 4 M LiFSI-DME 电解液体系中形成的 SEI 更致密。这些研究揭示了与高浓度 LiFSI-DME 电解液体系相关的优异电化学性能背后的基本机制。
