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...

There is a growing worldwide demand in developing lithium ion batteries with high energy densities and longer cycle life. In recent years, rechargeable lithium ion batteries have become important alternative...

This study covers the development of a fast, selective, sensitive, and stable method for the simultaneous determination of cephalosporins (cephalexin (CLN) and cefadroxil (CFL)) in biological fluids and tablet samples using potentiodynamic fabrication of a poly(resorcinol)-modified glassy carbon electrode (poly(reso)/GCE). The results of cyclic voltammetry and electrochemical impedance spectroscopy supported the modification of the GCE by a polymer layer that raised the electrode surface area and conductivity. At the poly(reso)/GCE, an irreversible oxidative peak with four- and fivefold current enhancement for CLN and CFL, respectively, at a substantially lower potential demonstrated the catalytic action of the modifier. Under optimized solution and parameters, the peak current response at the poly(reso)/GCE revealed a linear dependence on the concentration of CLN and CFL within the range 0.1–300 and 0.5–300 μM, respectively, with a limit of detection (LoD) of 3.12 and 8.7 nM, respectively. The levels of CLN in four selected tablet brands and CFL in two tablet brands were in the vicinity of 91.00–103.65% and 97.7–98.83%, respectively, of their nominal values. The recovery results for CLN in pharmaceutical samples were in the range of 99.00–100.67% and for CFL 97.9–99.75% and for blood serum and urine samples 99.55–100.55% and 99.33–100.34% for CLN and 97.13–100.60% and 96.73–102.50% for CFL, respectively. Interference recovery results with errors less than 4.81%, lower LoD, wider dynamic range, excellent recovery results, and good stability of the modifier compared to those for the previously reported methods validated the use of the poly(reso)/GCE for determining CLN and CFL simultaneously in various real samples.

The formation of solid electrolyte interphase (SEI) on electrodes of Lithium ion batteries (LiBs) is known to influence the electrochemical performance of LiBs. In this work, the effect of fluoroethylene carbonate (FEC) and vinylene carbonate (VC) on the SEI formation on mesocarbon microbeads (MCMB) anode is examined by in situ DRIFTS (diffuse reflectance infrared Fourier-transformed spectroscopy). Formation of SEI species on MCMB starts in the first lithiation cycle with an onset potential corresponding to the electrochemical reduction potential of the additive. However, both VC and FEC result in continuous SEI formation in subsequent cycles with no onset potential. Similar SEI species are found in the first lithiation cycle and in the subsequent cycles. This suggests the presence of an electrochemical initiation of SEI species formation with a subsequent propagation, similar with what we found previously over Si-based anode. [Y. B. Yohannes, S. D. Lin and N.-L. Wu, J. Electrochem. Soc., 164, A3641 (2017)] The contribution of the observed SEI species for the improved electrochemical impedances through cycling and its implications are discussed.