SEI Formation and Interfacial Stability of a Si Electrode in a LiTDI-Salt Based Electrolyte with FEC and VC Additives for Li-Ion Batteries

Fredrik Lindgren; Chao Xu; Leszek Niedzicki; Marek Marcinek; Torbjörn Gustafsson; Fredrik Björefors; Kristina Edström; Reza Younesi

doi:10.1021/acsami.6b02650

SEI Formation and Interfacial Stability of a Si Electrode in a LiTDI-Salt Based Electrolyte with FEC and VC Additives for Li-Ion Batteries

ACS Appl Mater Interfaces. 2016 Jun 22;8(24):15758-66. doi: 10.1021/acsami.6b02650. Epub 2016 Jun 9.

Authors

Fredrik Lindgren¹, Chao Xu¹, Leszek Niedzicki², Marek Marcinek², Torbjörn Gustafsson¹, Fredrik Björefors¹, Kristina Edström¹, Reza Younesi¹

Affiliations

¹ Department of Chemistry - Ångström Laboratory, Uppsala University , Box 538, 75121 Uppsala, Sweden.
² Faculty of Chemistry, Warsaw University of Technology , Noakowskiego 3, 00664 Warsaw, Poland.

PMID: 27220376
DOI: 10.1021/acsami.6b02650

Abstract

An electrolyte based on the new salt, lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide (LiTDI), is evaluated in combination with nano-Si composite electrodes for potential use in Li-ion batteries. The additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) are also added to the electrolyte to enable an efficient SEI formation. By employing hard X-ray photoelectron spectroscopy (HAXPES), the SEI formation and the development of the active material is probed during the first 100 cycles. With this electrolyte formulation, the Si electrode can cycle at 1200 mAh g(-1) for more than 100 cycles at a coulombic efficiency of 99%. With extended cycling, a decrease in Si particle size is observed as well as an increase in silicon oxide amount. As opposed to LiPF6 based electrolytes, this electrolyte or its decomposition products has no side reactions with the active Si material. The present results further acknowledge the positive effects of SEI forming additives. It is suggested that polycarbonates and a high LiF content are favorable components in the SEI over other kinds of carbonates formed by ethylene carbonate (EC) and dimethyl carbonate (DMC) decomposition. This work thus confirms that LiTDI in combination with the investigated additives is a promising salt for Si electrodes in future Li-ion batteries.

Keywords: fluoroethylene carbonate; hard X-ray photoelectron spectroscopy; lithium 4,5-dicyano-2-(trifluoromethyl)imidazolide; silicon negative electrode; solid electrolyte interphase; vinylene carbonate.