Effect Of Fluoroethylene Carbonate Research Articles

The Impact of Fluoroethylene Carbonate Additive on Charged Sodium Ion Electrodes/Electrolyte Reactivity Studied Using Accelerating Rate Calorimetry

The effects of fluoroethylene carbonate (FEC) electrolyte additive on charged sodium ion electrode/electrolyte reactivity at elevated temperatures were investigated using accelerating rate calorimetry (ARC). The beneficial effect of FEC on cell lifetime was demonstrated using Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2 (NCMFNZO)/hard carbon (HC) pouch cells first prior to ARC measurements. Electrodes from these pouch cells were utilized as sample materials and 1.0 m NaPF6 in propylene carbonate (PC):ethyl methyl carbonate (EMC) (1:1 by vol.) was chosen as control electrolyte. Adding 2wt.% or 5wt.% FEC to the electrolyte does not significantly affect the reactivity of de-sodiated NCMFNZO compared to the control electrolyte (Figure A). However, the addition of FEC obviously changed the reactivity between sodiated HC and electrolytes, especially by showing a suppression on the exothermal behavior between 160°C and 230°C (Figure B). These results give a head to head comparison of the reactivity of FEC additive containing electrolytes with charged sodium ion electrode materials at elevated temperatures and show that the use of FEC at additive levels should not compromise the cell safety when extending cell lifetime. Figure 1

(Digital Presentation) Unraveling of the Morphology and Chemistry Dynamics in the FEC-Generated Silicon Anode SEI across Delithiated and Lithiated States

The silicon solid electrolyte interphase (SEI) faces cyclical cracking and reconstruction due to the ~350% volume expansion of Si which leads to shortened cell life during electrochemical cycling. Understanding the SEI morphology/chemistry and more importantly its dynamic evolution from delithiated and lithiated states is paramount to engineering a stable Si anode. Fluoroethylene carbonate (FEC) is a preferred additive with widely demonstrated enhancement of the Si cycling. Thus, insights into the effects of FEC on the dynamics of the resulting SEI may provide hints toward engineering the Si interface. Herein, ATR-FTIR, AFM, tip IR, and XPS probing all show pronounced relative invariance of the FEC-generated SEI compared to the FEC-free SEI between adjacent lithiated and delithiated states beyond the formation cycles. The SEI of Si thin film model surfaces in the baseline 1 M LiPF6 in EC:EMC (1:1) undergoes major morphological and chemical speciation swings between half-cycles while comparatively the SEI upon addition of FEC displays far less dynamic evolution. This morphology and chemistry stability of the FEC-SEI supports the enhanced cycling stability of silicon anodes in FEC-containing electrolytes. The experimental evidence gathered suggests that the FEC-SEI invariance is enabled by an elastomeric polycarbonate matrix that preserves the SEI integrity against the expansion of silicon upon lithiation. In turn, less electrolyte-consuming reconstruction occurs which manifests as and high LiF content from one half-cycle to the next. This work provides critical insights to enhance the silicon anode stability via targeted SEI engineering, namely that LiF protected by an elastomeric protective matrix may be key to buffering the unavoidable mechanical disruption. Figure 1

Improved performance of LiMn0.8Fe0.2PO4 by addition of fluoroethylene carbonate electrolyte additive

The addition of electrolyte additives is an effective strategy for tuning the property of the electrolyte to engineer the electrode/electrolyte interface, and there exist obvious discrepancies regarding the effect of fluoroethylene carbonate (FEC) as an electrolyte additive on the performance of cathodes. Herein FEC is introduced into the electrolyte of the LiMn0.8Fe0.2PO4/Li cell and its effect on the properties of the LiMn0.8Fe0.2PO4 is investigated. It is found that the addition of FEC in the electrolyte has a positive effect on the performance of the LiMn0.8Fe0.2PO4 cathode, which can be attributed to the reduced products generated by the interfacial side-reactions on the LiMn0.8Fe0.2PO4 cathode surface and the decreased metal dissolution in the FEC-containing electrolyte, thanks to the higher oxidation resistance of FEC and the easier and stronger binding of FEC and PF6−.

Enhancing the Cyclability of VS4 Positive Electrode in Carbonate‐Based Electrolyte using Fluoroethylene Carbonate Additive

AbstractVanadium polysulfide (VS4) is a promising material of construction for positive electrodes of next‐generation batteries due to its high theoretical capacity and electrical conductivity compared to those of elemental sulfur. In this study, we investigated the charge and discharge behavior of a low‐crystalline VS4 positive electrode using different electrolytes and under differing charge and discharge conditions. The electrolyte composed purely of cyclic carbonate exhibited higher cycle performance than the one containing linear carbonate. Furthermore, the addition of fluoroethylene carbonate (FEC) to the electrolyte was very effective to improve the cycle performance. The effects of FEC on the VS4 positive electrode were investigated using electrochemical techniques, X‐ray photoelectron spectroscopy, and electron microscopy, the results whereof indicated that LiF‐containing components were formed on the VS4 surface, and probably contributed to the improvement of the charge and discharge behavior of the VS4 positive electrode.

The effect of electrolyte additives on the rate performance of hard carbon anode at low temperature for lithium-ion capacitor

Lithium-ion capacitor (LIC), which combines the advantages of lithium-ion battery (LIB) and electrical double layer capacitor (EDLC), has a rapid development during last decade, however, the poor low temperature performance still limits its application. In this paper, three electrolyte additives including vinylene carbonate (VC), fluoroethylene carbonate (FEC) and 1,3,2-dioxathiolane 2,2-dioxide (DTD) have been utilized and their effects on the rate performance of hard carbon (HC) anode of LIC at various temperatures ranging from 25 °C to −40 °C have been well evaluated. The cell containing FEC shows the best rate performance at various temperatures and has the charge and discharge capability even at −40 °C. For HC anode, the charge transfer impedance (RCT) increases exponentially at low temperature, while the equivalent series resistance (Rs) and the impedance of solid electrolyte interface (SEI) increase relatively few. At low temperatures, the effect of FEC may be mainly reflected in its effect on the charge transfer process.

Operando Observation of a Highly Reversible Nonporous Sodium Metal Anode with Shiny-Smooth Surface

While alkali metal anodes are considered as the promising alternatives to the ion-hosting materials due to the high energy densities, the nonuniform deposition (dendritic growth) that can lead to internal shorts remains a major obstacle of their practical applications (1,2). Here, according to the operando observation in our special capillary cells, we report a shiny-smooth nonporous sodium metal anode that can be cycled reversibly even at high areal capacities, without the formation of any whiskers, mosses, gas bubbles or disconnected metal particles observed in existing studies (3,4). The plating process follows the lateral surface-growing mechanism, which transforms into tip-growing branch-like dendrites at a critical time when applying over-limiting currents (5). The superior interfacial stability is attributed to the non-accumulative solid electrolyte interphases (SEIs) upon cycles, which is supported by the elemental depth profile analysis. As a result, a reversible high capacity sodium metal anode is achieved in coin cells within a critical penetration-related current density (6 mA cm-2). Our study demonstrates the possibility of plating shiny-smooth reactive alkali metal in liquid electrolytes and provides a reliable option applicable for the next-generation alkali metal batteries. Xu W, Wang J, Ding F, Chen X, Nasybulin E, Zhang Y, et al. Lithium metal anodes for rechargeable batteries. Energy Environ Sci. 2014;7(2):513–37.Zhao C, Lu Y, Yue J, Pan D, Qi Y, Hu YS, et al. Advanced Na metal anodes. J Energy Chem. 2018;27(6):1584–96.Rodriguez R, Loeffler KE, Nathan SS, Sheavly JK, Dolocan A, Heller A, et al. In Situ Optical Imaging of Sodium Electrodeposition: Effects of Fluoroethylene Carbonate. ACS Energy Lett. 2017;2(9):2051–7.Yui Y, Hayashi M, Nakamura J. In situ Microscopic Observation of Sodium Deposition/Dissolution on Sodium Electrode. Sci Rep. 2016;6:1–8.Bai P, Li J, Brushett FR, Bazant MZ. Transition of lithium growth mechanisms in liquid electrolytes. Energy Environ Sci. 2016;9(10):3221–9. Figure 1

Effect of Fluoroethylene Carbonate on Solid Electrolyte Interphase Formation of the SiO/C Anode Observed by In Situ Atomic Force Microscopy

Silicon oxide-based materials are promising anode materials for the real application in lithium-ion batteries. The solid electrolyte interphase is vital for the cyclability and rate capability of t...

Effect of fluoroethylene carbonate on the transport property of electrolytes towards Ni-rich Li-ion batteries with high safety.

Transport phenomena and the solvation structure of lithium ions (Li+) and hexafluorophosphate anions (PF6-) in electrolytes with different fluoroethylene carbonate (FEC) concentrations as well as the electrochemical performance and safety of Ni-rich Li-ion battery cells at the 18650 cylindrical cell level are investigated. We have found that the electrolyte with an optimized FEC concentration (25% v/v) can effectively enhance the transport property in terms of the Li+ transference number and contact ion pair (CIP) ratio leading to high performance and safety of practical 18650 cylindrical LIBs.

Effect of fluoroethylene carbonate and vinylene carbonate additives on full-cell optimization of Li-ion capacitors

Lithium-ion capacitors (LICs) operate by two mechanisms, namely a double-layer mechanism based on a capacitor-like positive electrode and the intercalation mechanism of a battery-like negative electrode. Hence, well-designed reaction kinetics between the positive electrode and negative electrode are essential for optimizing LIC full-cell configurations. In this study, we investigated the influences of fluoroethylene carbonate (FEC) or vinylene carbonate (VC) as electrolyte additives on full-cell performance of LICs. We confirmed that the internal resistance of graphite increased with the use of FEC, which degraded the cyclability of the LIC full-cell. Conversely, LICs consisting of the VC additive had good cyclability over 4000 cycles owing to the solid electrolyte interphase (SEI) containing polymeric species. This detailed investigation into the function of SEI compounds derived from VC additives and their effect on cyclability will provide new insights into optimization of LIC full-cell configurations with appropriate electrolyte additives.

Synergistic effect of fluoroethylene carbonate and lithium difluorophosphate on electrochemical performance of SiC-based lithium-ion battery

Fluoroethylene carbonate (FEC) and lithium difluorophosphate (LiPO2F2) are evaluated as hybrid functional additives to improve the electrochemical performance of SiC-based lithium-ion batteries. When added to the electrolyte, FEC + LiPO2F2 significantly enhance the performance of SiC/Li cells. The capacity retention increases from 28.5% to 76.2% after 200 cycles. The effects of FEC + LiPO2F2 are characterized by charge–discharge testing, electrochemical impedance spectroscopy, Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. Combining the results of these analyses reveals that hybrid functional additives are beneficial for forming a uniform and thinner solid–electrolyte interface film on the SiC surface. The solid–electrolyte interface film derived from FEC + LiPO2F2 greatly inhibits particle pulverization and electrolyte decomposition, which play an important role in the performance of SiC-based cells.

Effect of fluoroethylene carbonate as an electrolyte solvent in the LiNi0.5Mn1.5O4/Li4Ti5O12 cell

Fluoroethylene carbonate (FEC) is used as solvent for the antioxidation electrolyte system in the LiNi0.5Mn1.5O4/Li4Ti5O12 cell. We use scanning electron microscopy to analyze the solid electrolyte interphase (SEI) film covered from the surface of individual particles to the top of electrodes. The stable, uniform SEI films formed on individual Li4Ti5O12 particles with FEC solvent are responsible for the significantly improved electrochemical performance. Meanwhile, our results show that severe swelling could be observed and heavier manganese (Mn2+) deposition could be detected on top of the Li4Ti5O12 electrode surface. In this study, we adopt the metathesis reaction to illustrate the relationship between gradual changes in the SEI film and swelling problems during cycling performance. Moreover, the reduction mechanisms of FEC proposed in this study have provided a better understanding of the key issue on electrolyte system that for commercial LiNi0.5Mn1.5O4/Li4Ti5O12 cell.

SEI Grown on MCMB-Electrode with Fluoroethylene Carbonate and Vinylene Carbonate Additives as Probed by In Situ DRIFTS

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.

Fluoroethylene carbonate as an additive in a carbonates-based electrolyte for enhancing the specific capacity of room-temperature sodium-sulfur cell

Room-temperature sodium‑sulfur (RT Na-S) battery is a promising candidate for large-scale energy storage applications due to its high theoretical specific energy, low cost, and environmental benefits. Here the effect of fluoroethylene carbonate (FEC) as an additive in 1.0M NaClO4-ethylene carbonate/propylene carbonate (EC/PC, V/V=1/1) electrolyte was verified in RT Na-S battery with a high-surface-area carbon/sulfur composite (YP50F/S) as the cathode. Using 1.0M NaClO4-EC/PC electrolyte containing 5wt% FEC, the YP50F/S electrode can deliver a reversible capacity of up to 1651mAhg−1 at 0.1C. When 5wt% FEC-added electrolyte is used, X-ray photoelectron spectroscopy (XPS) analysis of the electrode surface clearly indicates a more effective solid electrolyte interface (SEI), a more thorough transformation between S and Na2S, and a more obvious redox reaction between sulfur oxides during the first discharge-charge processes. We further confirm that 5wt% FEC can also be employed for another activated carbon material (XFP01), therefore, our work may provide a new insight for the development of RT Na-S battery.

Improving the rate performance and stability of LiNi0.6Co0.2Mn0.2O2 in high voltage lithium-ion battery by using fluoroethylene carbonate as electrolyte additive

Fluoroethylene carbonate (FEC) is investigated as the electrolyte additive to improve the electrochemical performance of high voltage LiNi0.6Co0.2Mn0.2O2 cathode material. Compared to LiNi0.6Co0.2Mn0.2O2/Li cells in blank electrolyte, the capacity retention of the cells with 5 wt% FEC in electrolytes after 80 times charge-discharge cycle between 3.0 and 4.5 V significantly improve from 82.0 to 89.7%. Besides, the capacity of LiNi0.6Co0.2Mn0.2O2/Li only obtains 12.6 mAh g−1 at 5 C in base electrolyte, while the 5 wt% FEC in electrolyte can reach a high capacity of 71.3 mAh g−1 at the same rate. The oxidative stability of the electrolyte with 5 wt% FEC is evaluated by linear sweep voltammetry and potentiostatic data. The LSV results show that the oxidation potential of the electrolytes with FEC is higher than 4.5 V vs. Li/Li+, while the oxidation peaks begin to appear near 4.3 V in the electrolyte without FEC. In addition, the effect of FEC on surface of LiNi0.6Co0.2Mn0.2O2 is elucidated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The analysis result indicates that FEC facilitates the formation of a more stable surface film on the LiNi0.6Co0.2Mn0.2O2 cathode. The electrochemical impedance spectroscopy (EIS) result evidences that the stable surface film could improve cathode electrolyte interfacial resistance. These results demonstrate that the FEC can apply as an additive for 4.5 V high voltage electrolyte system in LiNi0.6Co0.2Mn0.2O2/Li cells.

Enhanced cycling stability of Mg2Si anode in fluoroethylene carbonate binary solvent for Li-ion batteries

Fluoroethylene carbonate (FEC) is proposed as the co-solvent for magnesium silicide (Mg2Si) anode in Li-ion battery. Comparing with ethylene carbonate (EC)+dimethyl carbonate (DMC) solvent, FEC + DMC solvent leads to much better cycling stability, such as 400 mAh g−1 after 100 cycles. The effect of FEC is investigated in terms of XPS, SEM and electrochemical analysis, and vinylene carbonate (VC) is also studied to better understand the function of FEC. The results show that FEC adding significantly alter the solid electrolyte interface (SEI) formed on Mg2Si, it helps to build a much denser, robust and LiF-rich SEI.

Ethyl Methyl Sulfone-Based Electrolytes for Lithium Ion Battery Applications

Sulfone-based electrolytes, known for their higher oxidative stability compared to the typically used organic carbonate-based electrolytes, are considered promising electrolytes for high voltage cathode materials towards the objective of obtaining increased energy density in lithium ion batteries. Nevertheless, sulfones suffer from high viscosity as well as incompatibility with highly graphitic anode materials, which limit their application. In this paper, the effect of fluoroethylene carbonate (FEC) as an electrolyte additive for the application of ethyl methyl sulfone (EMS) electrolytes containing LiPF6 as conducting salt, is studied in graphite-based cells by means of selected electrochemical and spectroscopic methods. In addition, influence of ethylene acetate (EA) as co-solvent on the electrolyte viscosity and conductivity of the EMS-based electrolytes is discussed, revealing improved overall nickel cobalt manganese oxide (NMC)/graphite cell performance. X-ray photoelectron spectroscopy (XPS) measurements provide information about the surface chemistry of the graphite electrodes after galvanostatic cycling. The concept of EA as co-solvent is found to be applicable for other sulfones such as isopropyl methyl sulfone (MeiPrSO2) and ethyl isopropyl sulfone (EtiPrSO2).

Effect of fluoroethylene carbonate as an electrolyte additive on the cycle performance of silicon-carbon composite anode in lithium-ion battery

The cycling performance of silicon-carbon anodes in the electrolyte with different content (0, 2, 5, 10 wt%) fluorinated ethylene carbonate (FEC) was studied. Among all the electrolytes the injection of 2 wt% FEC into carbonate electrolyte, the retention capacity of silicon carbon anode enhanced from 54.81 to 83.82% after 50 cycles. The performance of SEI layer on the anode was characterized by SEM, EIS, FTIR, and XPS analysis. These studies reveal that the SEI layer formed in the FEC-containing electrolyte effectively reduced the capacity loss of the material and reduced the interfacial impedance.

Effect of Fluoroethylene Carbonate in the Electrolyte for LiNi0.5Mn1.5O4 Cathode in Lithium-ion Batteries

Effect of Fluoroethylene Carbonate in the Electrolyte for LiNi_0.5Mn_1.5O₄ Cathode in Lithium-ion Batteries

Effect of Fluoroethylene Carbonate in the Electrolyte for LiNi0.5Mn1.5O4 Cathode in Lithium-ion Batteries

Fluoroethylene carbonate (FEC) was studied as an additive for the electrolyte in lithium ion batteries with the LiNi0.5Mn1.5O4 (LNMO) spinel cathode operating at a high potential beyond 4.7 V (vs. Li/Li+). It was found that the FEC additive was electrochemically active for the 1st charge cycle on the LNMO cathode. The presence of a large amount of FEC (more than 40 vol%) in the electrolyte caused severe side reactions with abnormally long voltage plateaus. In contrast, when the electrolyte contained less than 30 vol% FEC , the surface of the LNMO cathode was stabilized by the formation of the solid-electrolyte interphase (SEI), leading to improved cyclability. However, the resistance from the SEI limited the rate capability because of sluggish lithium transportation through the SEI and electronic insulation between the particles in the electrode. Keywords: LNMO, Electrolyte, High potential electrode, FEC

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

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. Finally, possible reactions related to the reductive decomposition of FEC and VC are discussed.