Fluorinated Linear Carbonates

5 Properties of dimethyl carbonates and its fluoiinated derivatives, (a) relative permittivity (b) viscosity (c) electrolytic conductivity (d) oxidation potential (e) lithium cycling efficiency 

The relative permittivities and viscosities of these fluorinated linear carbonates were higher than those of EMC and DEC, respectively. The relative permittivity and viscosity were in the order DEC EMC FDEC, DFDEC TFEMC, TFDEC, FEMC DFEMC and EMC DEC TFEMC TFDEC FEMC, FDEC, 

Methyl propyl carbonate (MPC) is a structural isomer of DEC. Physical and electrochemical properties of four kinds of partially fluorinated MPC derivatives, 3-fluoro-propyl methyl carbonate (EPMC), methyl 3,3,3-trifluoropropyl carbonate (TrEPMC), methyl 2,2,3,3-tetrafluoropropyl carbonate (TeEPMC), and methyl 2,2,3,3,3-pentaflu-oropropyl carbonate (PeEPMC) in Schane 2.8 were examined [42]. 

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Section 2.2 mainly reviews the papers on novel fluorinated organic solvents, which include fluorinated lactones, fluorinated linear carboxylates, fluorinated cyclic carbonates, fluorinated linear carbonates, fluorinated monoethers, fluorinated diethers, and others. The physicochemical properties of typical fluorinated compounds are summarized in comparison with nonfluorinated counterparts. 

Compared with fluorinated cyclic carbonates, less research has been conducted on fluorinated linear carbonates due to their limited availability. The stmcture variation of the fluorinated linear carbonates are much more diverse than that of... 

Preferably, the new solvents are also expected to possess better stability or ability in interfacial chemistry on both anode and cathode materials so that the new electrolyte formulation can rely less on EC or they are expected to be less inflammable, as a major shortcoming of the linear carbonates is their low flash points (Tf) (Table 1). In the search for new solvents, fluorination has been adopted as a favorable approach to achieve improvements in these two aspects because the presence of C—F bonds in organic molecules is found to affect interfacial chemistry on carbonaceous anodes in a positive manner,and... 

Linear Solvents. For novel solvents that are intended to replace linear carbonates, the emphasis was placed on such properties as melting temperature, viscosity, and inflammability of the solvents. As Table 12 shows, these solvents can be roughly classified into four groups (1) linear esters or carbonates,(2) fluorinated esters,(3) fluorinated carbonates," and (4) fluorinated ethers." " ... 

PFCs comprise a large group of compounds characterized by a fully fluorinated hydrophobic linear carbon chain attached to one or more hydrophilic head. PFCs repel both water and oil, and are therefore ideal chemicals for surface treatments. These compounds have been used for many industrial applications including stain repellents (such as Teflon), textile, paints, waxes, polishes, electronics, adhesives, and food packaging [1]. 

Among the carbonate solvents used in practical lithium batteries, linear carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) are well-known good co-solvents (thinner) for EC and PC. The direct fluorination of DMC gave fluorinated derivatives such as mono-fluorinated one, fluo-romethyl methyl carbonate (FDMC), two di-fluorinated ones (bis(fluoromelhyl) carbonate, DFDMC, and difluormethyl methyl carbonate, gem-DFDMC), and tri-fluorinated ones (difluoromethyl fluoromethyl carbonate, TFDMC) as shown in Scheme 2.6 [33]. Three kinds of partially fluorinated DMCs except gm-DFDMC were obtained by fractional distillation of the fluorinated sample. 

Linear esters, as mentioned above, are not widely used in Li-ion batteries due to their inferior anodic stability compared to linear carbonates. Although numerous patents for electrolyte formulations claim various ester stmctures as the co-solvents, literature reports on the esters are considerably fewer. Although esters oxidize much more easily than carbonates, at least one reference reported an electrolyte formulated from a mixmre of sulfone and ethyl acetate showing better electrochemical properties than carbonate-based electrolyte in LNMO/Li half cells [108]. Due to their low viscosity and melting point, linear esters are considered to be candidates for low-temperature Li-ion batteries. Both non-lluorinated [94] and fluorinated esters [95] have been examined by scientists at the Jet Propulsion Laboratory as Li-ion battery electrolyte co-solvents for space missions. 

Fluorine-substituted carbonates have lower melting points than unsubstituted carbonates, and they have improved oxidation stability, which favors formation of a dense passivation SEl film on carbon negative electrode material. Some linear fluorine-containing carbonates are methyl 2,2,2-tri-fluoroethyl carbonate, ethyl 2,2,2-trifluoroethyl carbonate, propyl 2,2,2-tri-fluoroethyl carbonate, methyl 2,2,2-2, 2, 2 -hexafluoroisopropyl carbonate, ethyl 2,2,2-2, 2, 2 -hexafluoroisopropyl carbonate, and di-2,2,2-trifluoroethyl carbonate. Some cyclic fluorine-containing carbonates include fluoro-methyl ethylene carbonate (CH2F-EC), difluoromethyl ethylene carbonate (CHF2-EC), and trifluoromethyl ethylene carbonate (CF3-EC). They are miscible with EC, PC, and other organic solvents. The fluorinated cyclic... 

Some linear carbonates (Figure 9.17) are nonflammable and can be used in lithium-ion batteries. If the hydrogen atoms of these carboxylates are replaced with fluorine, the carbonates can be used as flame retardants, which can significantly improve the thermal stability of the electrolyte. For example, when LiPFg solution in difluoroacetyl methyl carbonate reacts with lithium or Lio.5Co02, the exothermic peak is increased to about 300°C. The cycling efficiency for lithium metal is also good. 

Net atomic charges based on the stockholder partitioning of theoretical densities for a number of linear molecules containing N, C, and H are listed in Table 6.1. For these molecules, the charge transfer between atoms is relatively small. Much larger values are obtained for more electronegative atoms, such as oxygen and fluorine bonded to carbon atoms. 

Although to-date the emphasis has been on plasma polymerized films produced from hydrocarbon based systems, this trend in more recent times has swung towards fluorocarbons in an attempt to produce polymers of similar properties to conventionally prepared linear fluoropolymers. However, it will become clear from the account to follow that in many respects plasma polymerized fluorocarbons differ significantly from their linear counterparts. It is to the plasma polymerization of organic monomers containing solely carbon and fluorine therefore that we shall devote our attention in this section with only brief references to hydrocarbon and fluorohydrocarbon polymers for comparison purposes. 

Electrochemical fluorination (ECF) is described in Section 6.4.7. for the manufacture of surface-active agents. Coproducts from the ECF of octylsulfonyl fluoride are linear perfluoro-carbons containing from three to eight carbon atoms, while octanoyl fluoride yields a mixture of perfluorocyclic ethers containing mainly perfluoro(2-butyltetrahydrofuran) and perfluoro(2-propylpyran). ECF is also used for the manufacture of specific perfluorocarbon fluids, notably perfluoro(tripropylamine) and perfluoro(tripentylamine), from the corresponding hydrocarbon analogs. 

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