Bis Trifluoromethane Sulfonimide Research Articles

LiF‐Rich Alloy‐Doped SEI Enabling Ultra‐Stable and High‐Rate Li Metal Anode

AbstractLi metal is regarded as the “Holy Grail” in the next generation of anode materials due to its high theoretical capacity and low redox potential. However, sluggish Li ions interfacial transport kinetics and uncontrollable Li dendrites growth limit practical application of the energy storage system in high‐power device. Herein, separators are modified by the addition of a coating, which spontaneously grafts onto the Li anode interface for in situ lithiation. The resultant alloy possessing of strong electron‐donating property promotes the decomposition of lithium bistrifluoromethane sulfonimide in the electrolyte to form a LiF‐rich alloy‐doped solid electrolyte interface (SEI) layer. High ionic alloy solid solution diffusivity and electric field dispersion modulation accelerate Li ions transport and uniform stripping/plating, resulting in a high‐power dendrite‐free Li metal anode interface. Surprisingly, the formulated SEI layer achieves an ultra‐long cycle life of over 8000 h (20,000 cycles) for symmetric cells at a current density of 10 mA cm−2. It also ensures that the NCM(811)//PP@Au//Li full cell at ultra‐high currents (40 C) completes the charging/discharging process in only 68 s to provide high capacity of 151 mAh g−1. The results confirm that this scalable strategy has great development potential in realizing high power dendrite‐free Li metal anode.

Hydrogen-bond-driven high ionic conductivity, Li+ transfer number, and lithium-interface stability of poly(vinylidene fluoride-hexafluoropropylene)-based solid-state electrolytes

Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP)-based solid electrolytes with wide electrochemical windows and high thermal stabilities are promising candidates for use in solid-state lithium batteries. However, the practical applications of these electrolytes are currently hindered by their low room-temperature ionic conductivity, limited Li+ transfer number, and the poor stability of the lithium/electrolyte interface. This study proposes a ‘one stone, three birds’ modification method, wherein a small amount of lithium carboxymethylcellulose (CMC-Li) containing rich hydroxyl groups is added to form abundant hydrogen bonds with numerous electronegative C–F groups in the PVDF-HFP molecular chain and lithium bistrifluoromethane sulfonimide (LiTFSI). The strong connections formed between CMC-Li and PVDF-HFP or TFSI− significantly reduced the crystallinity of PVDF-HFP, promoted the dissociation of LiTFSI, and anchored TFSI−, achieving a synchronous improvement in the ionic conductivity and Li+ transfer number. The hydrogen bonds drove the densification of the membrane surface, improving the lithium/electrolyte compatibility at the interface. The ionic conductivity of the modified electrolytes was 5.1 × 10−4 S cm−1 and the Li + transfer number was 0.72 at room temperature. A Li||Li symmetric cell demonstrated stable cycling over 1000 h at 0.2 mA cm−2, where the initial discharge capacity of an all-solid-state cell was enhanced to 165.1 mAh g−1, with steady cycling for 400 runs. Thus, this study provides a novel and effective method for promoting the practical application of solid-state electrolytes.

LiF-Rich Alloy-Doped SEI Enabling Ultra-Stable and High-Rate Li Metal Anode.

Li metal is regarded as the "Holy Grail" in the next generation of anode materials due to its high theoretical capacity and low redox potential. However, sluggish Li ions interfacial transport kinetics and uncontrollable Li dendrites growth limit practical application of the energy storage system in high-power device. Herein, separators are modified by the addition of a coating, which spontaneously grafts onto the Li anode interface for in situ lithiation. The resultant alloy possessing of strong electron-donating property promotes the decomposition of lithium bistrifluoromethane sulfonimide in the electrolyte to form a LiF-rich alloy-doped solid electrolyte interface (SEI) layer. High ionic alloy solid solution diffusivity and electric field dispersion modulation accelerate Li ions transport and uniform stripping/plating, resulting in a high-power dendrite-free Li metal anode interface. Surprisingly, the formulated SEI layer achieves an ultra-long cycle life of over 8000 h (20,000 cycles) for symmetric cells at a current density of 10 mA cm-2. It also ensures that the NCM(811)//PP@Au//Li full cell at ultra-high currents (40 C) completes the charging/discharging process in only 68 s to provide high capacity of 151 mAh g-1. The results confirm that this scalable strategy has great development potential in realizing high power dendrite-free Li metal anode.

Investigation into Anion Effects on the Bulk and Interfacial Solvation Structure for Multivalent Ion Batteries

Zinc ion batteries (ZIB) are attractive because of the relative abundance of Zn as a core earth element, a higher volumetric energy density compared to lithium metal and it is cost effective. Despite this promise, a general lack of fundamental understanding of the electrode-electrolyte interface in ZIB, and multivalent (MV) ion technologies more broadly, hinders their wide scale deployment. In particular, the solvation structure of aqueous and non-aqueous electrolytes plays a critical role in promoting the necessary intermolecular charge transfer interactions to drive reversible plating/stripping at the metal anode. Here we examine the dynamics of the bulk and interfacial solvation structure to uncover differences in the bulk vs. the interfacial speciation as a function of anion chemistry in hopes to develop new design principles for new electrolyte development in ZIB and MV technologies. Utilizing Raman spectroscopy to probe the bulk solvation structures of Zn-based electrolytes containing one anion such as SO4 2-, bis-trifluoromethane sulfonimide (TFSI-) and trifluoromethanesulfonate (triflate, OTf-), we find three solvation environments present; a main feature corresponding to the “free” anion breathing mode and, in some cases, small amounts of mono- or bidentate contact ion pairs (CIPs). In some cases, introduction of co-anions (i.e., halides, X = Cl-, Br-, I-) results in significant extra intensity on the low frequency side of the overall Raman peak envelope that does not correspond with solvation structures observed in the single anion electrolytes. First principles density functional theory (DFT) calculations indicate the additional vibrational mode corresponds to a mixed anion CIP, suggesting anion-anion interactions can induce nominally dissociated anions to coordinate the cation in ways they otherwise would not. Raman and DFT analysis of Mg-based electrolytes indicate similar mixed anion CIP structures are formed, indicating similar solvation effects are active in other MV systems. Preliminary measurements utilizing shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERs) will also be discussed as a means of developing in situ understanding of the evolution of interfacial solvation and surface chemistry during the stripping/plating process. Overall, these results point to new possibilities in controlling the multivalent cation solvation structures present in the bulk and at the interface. This will aid in the development of highly reversible electrolytes that are stable against both divalent metal anodes and high voltage cathodes.

Thermal Decomposition Characteristics of Poly((4-Vinylbenzyl) Trimethylammonium Bis (Trifluoromethanesulfonimide)) Studied by Pyrolysis-GS / MS

Over the past decades, significant advances have been made in the development and research of gas separation membranes based on ionic liquids (IL) and their polymer analogs (PIL) for membrane separation of "acid gases" such as CO2 and H2S from gas mixtures. Polymers containing various amino groups are of great interest for the selective separation of acid gases from gas mixtures, since ammonia and its derivatives are used in conventional purification. In this work, we have synthesized a monomeric ionic liquid based on 4 vinylbenzyl chloride with included triethylamine by the Menshutkin reaction. Further, on its basis, polymer ionic liquids were obtained by the method of free radical polymerization, then an anion exchange reaction was carried out to replace the Cl anion with Tf2N. To analyze the process of thermal pyrolysis of poly [VBTEA-Tf2N] a pyrolysis-gas chromatography/mass spectrometer (Py-GC/MS) was employed in this research. The obtained materials, which are high molecular weight compounds, can be used to obtain polymer membranes of various architectures by traditional methods: both non-porous symmetric membranes and microporous asymmetric membranes.

Abnormal Overcharging during Lithium-Ether Co-Intercalation in a Graphite System: Formation of Shuttling Species by the Reduction of the TFSI Anion.

Materializing an ultrafast charging system is one of the crucial technologies for next-generation Li-ion batteries (LIBs). Among many studies aimed at achieving fast charging systems, Li-ether solvent cointercalation into the graphite electrodes in LIB has been identified as a novel concept for achieving high power performance because this system does not consist of the sluggish desolvation step and a resistive solid-electrolyte interface (SEI) layer. Interestingly, while studying the Li-ether solvent cointercalation into graphite electrodes, employing lithium bis-trifluoromethane sulfonimide (LiTFSI) as the Li salt, we observed an abnormal overcharging phenomenon. Here, we screened the specific conditions, under which the abnormal overcharging occurred, and revealed that this abnormal overcharging was attributable to the shuttling mechanism. The formation of shuttling species could have been derived by the reduction of TFSI- anion. With this understanding of the underlying mechanism, we efficiently suppressed the abnormal overcharging by adding LiNO3 to the electrolyte. The shuttling and resulting overcharging could be prevented by the synergistic contributions of LiNO3 and SxOy, dissolved in the electrolyte, to the formation of a dense solid LiSxOy SEI layer on Li-metal. We expect that this work could be a great reference in analyzing many unsolved phenomena in systems utilizing TFSI-.

Effect of FSI Based Ionic Liquid on High Voltage Li-Ion Batteries

In this manuscript, a functionalized ionic liquid 1-cyanoethyl-2-methyl-3-allylimidazolium bis (trifluoromethanesulfonimide) salt (CEMAImTFSI) was synthesized and explored as an electrolyte component to improve the oxidation resistance of the electrolyte in high-voltage lithium-ion batteries. Based on the calculation by Gaussian 09, CEMAImTFSI has a higher highest occupied molecular orbital (HOMO) value than the organic solvents ethylene carbonate (EC) and dimethyl carbonate (DMC), suggesting that CEMAImTFSI is more susceptible to oxidation than EC and DMC. Moreover, a low Li+ binding energy value of –3.71 eV and the lower lowest unoccupied molecular orbital (LUMO) enable CEMAImTFSI to migrate easily to the surface of the LiNi0.5Mn1.5O4 cathode and participate in the formation of the SEI (solid electrolyte interphase) film, protecting the electrode materials. Electrochemical studies showed that the LiNi0.5Mn1.5O4/Li cell with 1.0 mol/L LiPF6-EC/DMC/10 vol% has the best cycling stability in the voltage range of 3–5 V. The initial discharge specific capacity of the cells was 131.03 mAh·g−1 at 0.2 C, and even after 50 cycles the discharge specific capacity value of 126.06 mAhg−1 was observed, with the cell showing a capacity retention as high as 96.2%. Even at the rate of 5 C, the average discharge specific capacity of the cell was still 109.30 mAh·g−1, which was 1.95 times higher than the cell without the CEMAImTFSI addition. The ionic liquid molecules adsorption on the cell electrode surface was confirmed by X-ray photoelectron spectroscopic (XPS) analysis after charge–discharge measurements.

Effect of bistrifluoromethane sulfonimide treatment on nickel/InAs contacts

In this work, the effects of bis(trifluoromethane) sulfonimide (TFSI) (a superacid) surface treatment on electrical properties of nickel/InAs contacts and InAs material are investigated with transmission line measurements (TLMs). After TFSI treatments on bare InAs TLM patterns, the contact resistance between InAs and Ni contact increased. While for InAs TLM structure passivated with a ZrO2 thin film, the total resistance of InAs decreased drastically after TFSI treatments. X-ray photoelectron spectroscopy measurements revealed that the TFSI reduced the indium oxide at the InAs/ZrO2 interface. This novel passivation method can be adopted in III–V semiconductor device fabrication process to reduce contact resistance and, therefore, enhance device performances, providing a new guidance for III–V fabrication process technology.

Selective Deprotection of N-Tosyl Alkoxyamines Using Bistrifluoromethane Sulfonimide: Formation of Oxime Ethers

The detosylation of N-tosyl alkoxyamines was realized by treatment with benzaldehyde and bistrifluoromethane sulfonimide as the catalyst to afford the corresponding oxime ethers. The reaction is chemoselective as N-tosyl amines are not deprotected. A mechanism is proposed for this deprotection.

A novel organosilicon-based ionic plastic crystal as solid-state electrolyte for lithium-ion batteries

A novel organosilicon-based ionic plastic crystal, N,N,N,-diethylmethyl-N-[(trimethylsilyl)methyl]ammonium bistrifluoromethane sulfonimide ([DTMA][TFSI]) was designed and synthesized as solid-state electrolyte for lithium-ion batteries. The chemical structure and the physical and electrochemical properties were characterized in detail. The ionic conductivity of [DTMA][TFSI] was improved significantly by doping with lithium oxalyldifluoroborate (LiODFB) and propylene carbonate (PC). An optimized plastic crystal composite ([DTMA][TFSI]:LiODFB:PC=8:1:1 in molar ratio) as a solid-state electrolyte exhibited a decent cycling stability in LiFePO4/Li half-cell, with a specific discharge capacity of 144 mA·h/g and capacity retention of 94% after 50 cycles at C/20.

Solid-state electric double layer capacitors fabricated with plastic crystal based flexible gel polymer electrolytes: Effective role of electrolyte anions

Flexible gel polymer electrolyte (GPE) thick films incorporated with solutions of lithium trifluoromethanesulfonate (Li-triflate or LiTf) and lithium bis trifluoromethane-sulfonimide (LiTFSI) in a plastic crystal succinonitrile (SN), entrapped in poly(vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP) have been prepared and characterized. The films have been used as electrolytes in the electrical double layer capacitors (EDLCs). Coconut-shell derived activated carbon with high specific surface area (∼2100 m2 g−1) and mixed (micro- and meso-) porosity has been used as EDLC electrodes. The structural, thermal, and electrochemical characterization of the GPEs have been performed using scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), impedance measurements and cyclic voltammetry. The high ionic conductivity (∼10−3 S cm−1 at 25 °C), good electrochemical stability window (>4.0 V) and flexible nature of the free-standing films of GPEs show their competence in the fabrication of EDLCs. The EDLCs have been tested using electrochemical impedance spectroscopy, cyclic voltammetry, and charge–discharge studies. The EDLCs using LiTf based electrolyte have been found to give higher values of specific capacitance, specific energy, power density (240–280 F g−1, ∼39 Wh kg−1 and ∼19 kW kg−1, respectively) than the EDLC cell with LiTFSI based gel electrolyte. EDLCs have been found to show stable performance for ∼104 charge–discharge cycles. The comparative studies indicate the effective role of electrolyte anions on the capacitive performance of the solid-state EDLCs.

Esterification of carboxylic acids with alkyl halides using imidazolium based dicationic ionic liquids containing bis-trifluoromethane sulfonimide anions at room temperature

Task-specific RTILs of symmetrical N-methylimidazolium rings linked to an oligo (ethylene glycol) chain (cationic part) and bis-trifluoromethane sulfonimide (anionic part) were synthesized, and the physicochemical properties with catalytic activity were determined.

Experimental and theoretical characterization of a new synthesized extended viologen

A new extended viologen, 4,4′-(2,2′-bithiophene-5,5′-diyl)bis(1-decylpyridinium) triflimide (DTEV2+), has been synthesized and characterized at theoretical and experimental level. Electrochemical and spectroelectrochemical characterization show that this compound undergoes a two-electron reduction mechanism. Density functional computations give insights on the conformational properties of the different reduction species and allow the assignment of the absorption spectra. The agreement between calculated and experimental spectra is quite satisfactory.

Room-Temperature Thermotropic Ionic Liquid Crystals: Viologen Bis(Triflimide) Salts

Several dicationic salts with bis(triflimide) as counterions—otherwise known as viologens—were prepared by metathesis reaction of the corresponding viologen dibromides (diiodides) with lithium triflimide in a polar solvent. They were characterized for their thermotropic liquid-crystalline properties with various experimental techniques. Two of them had low crystal-to-smectic phase transitions (Tm) at –4 and 28°C; the other two also had low Tm values, at 51 and 58°C. Each had a wide range of LC phase. Two had relatively low crystal-to-isotropic (Tm) transitions at 117 and 131°C. Each had excellent thermal stability in the temperature range of 327–396°C. They exhibited photoluminescence property in both nonpolar and polar solvents as well as in the solid state. Their emission spectra in the solid state exhibited hypsochromic shift when compared with those in solution of dimethoxyethane.

Ambient temperature thermotropic liquid crystalline viologen bis(triflimide) salts

Two dicationic salts with bis(triflimide) as counterions exhibited crystal-to-smectic liquid crystalline phase transitions (T m=41 and 37°C) and smectic-to-isotropic liquid phase transitions (T i=112, 136°C). They had a broad liquid crystalline phase range (71–99°C) and an excellent range of thermal stability (360–364°C). Their mixtures of various compositions also displayed liquid crystalline properties from r.t. to an extended range of temperatures. They exhibited fluorescence in 1, 2-dimethoxyethane and methanol.

Carbon-Carbon Bond Forming Reactions by using Bistrifluoromethanesulfonimide

Bistrifluoromethanesulfonimide has been used to catalyze C-C bond forming reactions such as Friedel-Crafts, Mukaiyama, 1,2-addition and 1,4-addition as well as C-glycosidation reactions.