In Situ DRIFTS Analysis of Solid Electrolyte Interphase of Si-Based Anode with and without Fluoroethylene Carbonate Additive

Abstract

The effect of fluoroethylene carbonate (FEC) additive has been studied in the formation of solid electrolyte interphase (SEI) over Si-based anode using in-situ DRIFTS (diffuse reflectance infrared Fourier transform spectroscopy). SEI species were observed in the first lithiation cycle at an onset potential of 1.4 V in electrolyte containing 2 wt% vinylene carbonate (VC) + 10 wt% FEC and at 1.1 V in electrolyte without FEC additive. With blended VC and FEC, high carbon containing species including poly (FEC), poly (VC), and polycarbonates were identified, while poly (VC) and polycarbonates formed in the absence of FEC. The FEC additive also led to a higher content of organic phosphorous fluorides as compared to the electrolyte containing no FEC. Electrochemical analyses indicated that the combination of 2 wt% VC and 10 wt% FEC resulted in lower impedances and improved the stability of the Si-electrode through cycling as compared to that without FEC. DRIFTS provided evidence that similar SEI species formed after the initiation in the first cycle, and this formation was recorded for five cycles. With the increasing demand for battery systems with high energy density and high power for applications such as hybrid and electric vehicles, the development of Li-ion batteries has attracted much attention in recent years.1,2 This self-supporting energy storage system 3 works based on the principle of redox reactions that can reversibly convert chemical energy into electrical energy. In Li-ion battery operation, the negative electrodes function at low potentials close to the potential of metallic lithium, where electrolytes are not stable thermodynamically. As a result, the reduction of solvents and salts of the electrolyte will result in the formation of a surface film on the electrode. Typically, this surface film is composed of organic reduction products (closer to the electrolyte) and inorganic species (closer to the electrode). 4 This film, called the solid electrolyte interphase (SEI), is known to be an important feature of graphite anodes that can allow for reversible cycling and long-term stability due to surface passivation. 5,6 Numerous replacements for the graphite anode have been investigated, with silicon 7,8 being one of the most attractive for its high theoretical specific capacity of 4200 mAhg −1 , which is more than ten times larger than that of graphite (372 mAhg −1 ). 9 However, Si undergoes large volume changes during lithiation and delithiation cycling, which cause capacity fading.10 Many studies have tried to improve the capacity retention of Si anodes by using nano-structured silicon, [11][12][13] silicon composite electrodes, 14,15 carbon coated silicon, 16 thin film silicon, [17][18][19] and new binders. [20][21][22] The formation of a stable surface layer for Si-based anodes would have an impact on achieving a long cycle life. One way to address this issue is to use a new electrolyte and/or to add a small amount (< 10 wt%) of electrolyte additives. Different types of electrolyte additives, such as...

The solvation structure, transport properties and reduction behavior of carbonate-based electrolytes of lithium-ion batteries

“…Thus, FEC will be preferentially reduced in the early SEI formation using ECF and GenF in full cells, setting the stage for further SEI formation reactions, aging and anode passivation. 79 Moreover, FEC is expected to improve the SEI composition, through increased production of LiF and oligomeric components derived by FEC reduction. 80,81 Even though the additive may slightly affect the conductivity as discussed above, the overall effect of FEC additive is beneficial for the cycling performance and capacity retention, especially for Li metal anode 35 and Si anode applications.…”

Si/Cu-Zn(ox)/C composite as anode material for Li-ion batteries

“…The SEI also contains other organic species, such as oxygen-free polymeric species [69] and polycarbonates [66,70] that stabilize the SEI and prevent the continuous degradation of the electrolyte [68]. This gives more stable, homogeneous and conductive SEI, which explains the rather low and almost constant values of the resistances after the formation process and the good capacity retention [67,68,[71][72][73]. The SEI formation process during the ten first cycles is due to the gradual nanostructuration of electrode material.…”

Interfacing Si‐Based Electrodes: Impact of Liquid Electrolyte and Its Components

“…For the sake of completeness, reports where FEC is utilized as an electrolyte additive can be found in references [ 45–47,51–55,60–62,67,69,73,75–77,92–125 ] and reports utilizing VC as electrolyte additive can be found in references. [ 40,45,47–49,69,71,73,75–77,98,99,102–104,106,115,119,122,123,126–132 ]…”