Pentafluoroethylation of Carbonyl Compounds Using HFC-125 in a Flow Microreactor System.

The protocol of micro-flow nucleophilic pentafluoroethylation using pentafluoroethane (HC2F5, HFC-125), a nontoxic, inexpensive, and commercially available greenhouse gas, is described. The micro-flow pentafluoroethylation by HFC-125 proceeded smoothly at room temperature or at -10 °C in DMF or toluene in the presence of a potassium base, namely, t-BuOK or KHMDS. A broad range of ketones, aldehydes, and chalcones with various substituted benzene rings were successfully converted to the corresponding pentafluoroethyl carbinols instantly with good to high yields.

Pentafluoroethylation of Carbonyl Compounds by HFC-125 via the Encapsulation of the K Cation with Glymes.

A simple protocol to overcome the explosive pentafluoroethylation of carbonyl compounds by HFC-125 is described. The use of potassium (K) bases with triglyme or tetraglyme as a solvent safely yields the pentafluoroethylation products in good to high yields. The experimental results suggest that an encapsulation of the K cation by glymes as K(glyme)2 inhibits the contact between the K cation and the reactive anionic pentafluoroethyl counterion, preventing their transformation into KF and explosive tetrafluoroethylene (TFE). The generation of sterically demanding [K(G3)2]+ and [K(G4)2]+ is an effective way as an unstable pentafluoroethyl anion reservoir.

Fluorinated alkyl-phosphate-based electrolytes with controlled lithium-ion coordination structure.

Herein, we propose Li-ion solvation-controlled electrolytes based on non-flammable organic solvent TFEP and an LiFSA salt [TFEP: tris(2,2,2-trifluoroethyl)phosphate, LiFSA: lithium bis(fluorosulfonyl)amide] to allow Li-ion insertion into a graphite electrode for Li-ion batteries. Comprehensive structural study based on (1) infrared (IR)/Raman spectroscopy, (2) high-energy X-ray total scattering (HEXTS), and (3) molecular dynamics (MD) simulation revealed the solvation (or coordination) structures of Li ions in TFEP-based electrolytes at the molecular level. In binary LiFSA/TFEP with a Li salt concentration (cLi) < 1.0 mol dm-3, Li ions are coordinated with both TFEP and FSA components; in detail, two TFEP molecules coordinate in an O-donating monodentate manner and one FSA in an O-donating bidentate manner to form [Li(TFEP)2(bi-FSA)] as the major species. We demonstrated that adding acetonitrile (AN) to the LiFSA/TFEP electrolytes caused structural changes in the Li-ion complexes. The bi-FSA bound to the Li ion changed its coordination mode to mono-FSA, which was induced by solvating AN molecules to Li ions. The redox reaction corresponding to insertion/deinsertion of Li ions into/from the graphite electrode successfully occurred in 1.0 mol dm-3 LiFSA/TFEP with an AN electrolyte system, while there was no or reduced Li-ion insertion in the electrolyte without AN. We discussed the relationship between the structure and electrode reaction of the Li-ion complexes based on the FSA-coordination characteristics; i.e., in LiFSA/TFEP with the AN system, the mono-FSA bound to the Li ion is easier to decoordinate due to weaker Li+mono-FSA- interactions rather than the Li+bi-FSA- interactions, which mainly contribute to charge-transfer at the electrode/electrolyte interface to allow Li-ion insertion/deinsertion in the graphite anode.

Solvation-controlled lithium-ion complexes in a nonflammable solvent containing ethylene carbonate: structural and electrochemical aspects.

The structural and electrochemical properties of lithium-ion solvation complexes in a nonflammable organic solvent, tris(2,2,2-trifluoroethyl)phosphate (TFEP) containing ethylene carbonate (EC), were investigated using vibrational spectroscopic and electrochemical measurements. Based on quantitative Raman and infrared (IR) spectral analysis of the Li bis(trifluoromethanesulfonyl)amide (TFSA) salt in TFEP + EC electrolytes, we successfully evaluated the individual solvation numbers of EC (nEC), TFEP (nTFEP), and TFSA- (nTFSA) in the first solvation sphere of the Li-ion. We found that the nEC value linearly increased with increasing EC mole fraction (xEC), whereas the nTFEP and nTFSA values gradually decreased with increasing nEC. The ionic conductivity and viscosity (Walden plots) indicated that mainly Li+TFSA- ion pairs formed in neat TFEP (xEC = 0). This ion pair gradually dissociated into positively charged Li-ion complexes as xEC increased, which was consistent with the Raman/IR spectroscopy results. The redox reaction corresponding to an insertion/desertion of Li-ion into/from the graphite electrode occurred in the LiTFSA/TFEP + EC system at xEC ≥ 0.25. The same was not observed in the lower xEC cases. We discussed the relation between Li-ion solvation and electrode reaction behaviors at the molecular level and proposed that nEC plays a crucial role in the electrode reaction, particularly in terms of solid electrolyte interphase formation on the graphite electrode.

Ion-solvation structure and battery electrode characteristics of nonflammable organic electrolytes based on tris(trifluoroethyl)phosphate dissolving lithium salts.

The structure and properties of lithium salt solutions based on tris(2,2,2-trifluoroethyl)phosphate (TFEP) solvent have been studied to design a safer electrolyte system for large-sized lithium-ion battery applications. Influences of the ionic structure on the polarization behavior of the LiCoO2 (LCO) positive electrode were investigated. The ionic conductivity and viscosity of the solution consisting of lithium salts dissolved in TFEP, LiX/TFEP (X = PF6, BF4 and TFSA) (TFSA = (CF3SO2)2N), were measured. The results suggest that the ion-solvation structure greatly depends on the anionic species in the salt. Spectroscopic measurements also support the conclusion that the Li+-solvation structure varies with the lithium salts. The differences in the ionic structure of LiX/TFEP influence the electrochemical oxidation potential of the solution and the polarization behavior of the LCO electrode. The overvoltage for Li-desertion/insertion from/into LCO in LiX/TFEP, being much higher than that observed in conventional LIB electrolyte solutions, shows the order of BF4 < PF6 < TFSA. The addition of ethylene carbonate (EC) to LiX/TFEP increases the ionic conductivity, which is probably caused by changes in the Li+-solvation structure in TFEP. The overvoltage for the Li-desertion/insertion of LCO is much lowered by the addition of EC to LiX/TFEP.

Fluorophosphate-Based Nonflammable Concentrated Electrolytes with a Designed Lithium-Ion-Ordered Structure: Relationship between the Bulk Electrolyte and Electrode Interface Structures.

We propose a molecular design for lithium (Li)-ion-ordered complex structures in nonflammable concentrated electrolytes that facilitates the Li-ion battery (LIB) electrode reaction to produce safer LIBs. The concentrated electrolyte, composed of Li bis(fluorosulfonyl)amide (FSA) salt and a nonflammable tris(2,2,2-trifluoroethyl) phosphate (TFEP) solvent, showed no electrode reaction (i.e., no Li-ion intercalation into the negative graphite electrode); however, introducing a small molecular additive (acetonitrile [AN]) into concentrated TFEP-based electrolytes is shown to improve the battery electrode reaction, leading to reversible charge/discharge behavior. Combined high-energy X-ray total scattering experiments incorporating all-atom molecular dynamics simulations were used to visualize Li-ion complexes at the molecular level and revealed that (1) Li ions form mononuclear complexes in a concentrated LiFSA/TFEP (without additives) owing to solvation steric effects arising from the molecular size of TFEP and (2) adding a small-sized additive, AN, reduces the steric effect and triggers a change in Li-ion structures, i.e., the formation of a specific Li-ion-ordered structure linked via FSA anions. These Li-ion-ordered complexes stabilize the energy of the lowest unoccupied molecular orbital (LUMO) on FSA anions, which is key to producing an anion-derived solid electrolyte interphase (SEI) at the graphite electrode. We performed in situ surface-enhanced infrared absorption spectroscopy and discussed the electrode/electrolyte interface and SEI formation mechanisms in TFEP-based concentrated electrolyte systems.