In Situ Analysis of Solid Electrolyte Interface over Si Based Anodes Using Diffuse Reflectance Infrared Fourier Transform Spectroscopy

Abstract

In lithium ion battery (LIB), silicon is hopeful electrode having a high theoretical capacity of 3579 mAh/g, which is ten times higher than the currently used graphite anode (1). On the other hand, Si-based electrodes suffer from the poor capacity retention due to the large volume changes during the lithium lithiation and delithiation process. The consequence of the volume change will lead to continuous decomposition of the electrolyte, which results in the formation of solid electrolyte interphase (SEI). Herein, the SEI formed based on fluoroethylene carbonate (FEC) electrolyte additive on a Si-based anode was investigated using in-situ Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), which have been also used to analyze SEI species on different electrodes (2, 3). The SEI generated on Si-based anode using 1 M LiPF6 in ethylene carbonate (EC) / ethyl methyl carbonate (EMC), 1/2 (v/v)/ vinylene carbonate (VC), (2 wt%) was started to observe at the onset of 1.1 V in the potential region of 1.0 – 1.3 V due to the decomposition of VC, which preferentially reduce prior to EC and EMC (4). Formation of poly (VC), polycarbonates, and Li2CO3 were identified during first cycle discharging. The incorporation of 10 wt% FEC results with the formation of poly (FEC)/(VC), polycarbonates, Li2CO3, alkoxy species and alkyl phosphorous fluorides. Using FEC as an additive with the onset potetial of 1.4 V the SEI formation started at a higher potential region of 1.3 – 2.5 V. In the course of second discharging, incorporation of FEC also impedes the decomposition of both solvent and salt anion reduction. Notable enough, in-situ DRIFTS spectrum due to the impact of FEC additive after five cycles also show the formation of SEI-film species is in fact increase in the lithiation process. DRIFT spectrum of the SEI-film formed over Si-based anode with and without FEC electrolyte at the onset potential is shown in Fig. 1. Fig. 1 (a) The first cycle CV results of silicon-based electrodes with EC:EMC:VC/LiPF6 (black) and EC:EMC:VC + FEC/LiPF6 (blue). (b) DRIFT difference spectra obtained at the onset potential of silicon-based electrodes using (I) EC:EMC:VC/LiPF6 and (II) EC:EMC:VC + FEC/LiPF6based electrolytes.