Binary Mixed Solvent Electrolytes Containing Trifluoropropylene Carbonate for Lithium Secondary Batteries

Abstract

To improve the safety of the electrolyte used for lithium secondary batteries, binary mixed solvent electrolytes containing trifluoropropylene carbonate ͑TFPC͒ as cosolvent have been studied. Chloroethylene carbonate ͑ClEC͒, ethylene carbonate, and propylene carbonate were chosen as the other component of the binary mixed solvent for the electrolytes. The solution properties of these electrolytes were characterized using conductivity and nuclear magnetic resonance ͑NMR͒ spectroscopy. The chemical shift of ClEC and TFPC did not vary with the mixing ratio due to their similar enthalpies of solvation as derived by molecular orbital simulation. The ClEC/TFPC electrolyte showed higher discharge capacities with lower irreversible capacity loss in both a graphite/Li cell and Li 1ϩx Mn 2 O 4 /Li cell than other electrolyte systems. Electrochemical impedance spectroscopy measurements were made for cells composed of each electrolyte. The surface of the graphite anode was analyzed using X-ray photoelectron spectroscopy, infrared spectroscopy, and solid 7 Li-NMR spectroscopy.

Influence of the binder types on the electrochemical characteristics of natural graphite electrode in room-temperature ionic liquid

“…6). The two XPS peaks can be ascribed to the formation of LiCl, because these binding energies almost correspond to the literature values (Cl 2p1/2 (199.5 eV) and Cl 2p3/2 (197.5 eV)) [20,21]. The main ionic species in the melt were thought to be EMI + , Li(Ⅰ), and AlCl 4…”

Nonaqueous Electrolytes with Advances in Solvents

“…As the novel fl uorinated cyclic carbonates, the Li + intercalation of a graphite and SEI formation in 4-trifl uoromethyl-1,3-dioxolan-2-one (trifl uoromethylpropylene carbonate, TFPC) in Scheme 2.5 was investigated [ 29 ] and its 1 moldm −3 LiPF 6 binary mixed electrolytes with EC, PC, and ClEC were examined in graphite/Li and LiMn 2 O 4 /Li half cells [ 30 ]. The electrochemical behavior of 4-(2,2,3,3-tetrafl uoropropoxymethyl)-1,3-dioxolan-2-one, 4-(2,3,3,3-tetrafl uoro-2-trifl uoromethylpropyl)-1,3-dioxolan-2-one, and 4,5-difl uoro-4,5-dimethyl-1,3-dioxolan-2-one in Scheme 2.5 has been studied in EC-DEC and EC-DEC-PC mixtures [ 31 , 32 ].…”

A Binary Cyclic Carbonates-Based Electrolyte Containing Propylene Carbonate and Trifluoropropylene Carbonate for 5V Lithium-Ion Batteries

“…In order to realize the application of PC into LIBs, many kinds of film-forming additives and co-solvents have been synthesized and selected to suppress the intercalation reaction of PC molecules [8][9][10][11][12][13]. Recently, several groups have proposed that after substituting three hydrogen atoms in the methyl group of PC by three fluorine atoms, the obtained fluorinated-PC (trifluoropropylene carbonate, TFPC) exhibits significantly improved solid electrolyte interphase (SEI) formation capability [14][15][16][17]. This can be attributed to the strong electron withdrawing group of CF 3 , which promotes the "ring-opening" reaction and the reduction of TFPC under the condition of high potential, and therefore resulting in a stable SEI passivation film [17].…”

“…5.01 mPaÁs) and high melting point hinders its application as an effective solvent [8,16]. More importantly, the interfacial impedance of SEI film formed from TFPC is much larger than those from commonly-used organic solvents such as EC [15].…”

“…Wang et al proposed the trend of SEI formation capability of TFPC > EC > MFPC >> PC in the DMC-based binary or ternary mixed solvents, and the graphite electrode exhibited significantly higher reversible capacities and first Coulombic efficiency in TFPC/DMC (1:1) electrolyte than that in TFPC/PC/DMC (1:4.5:4.5) electrolyte [17]. Arai et al demonstrated that the electrolytes of Cl-EC/TFPC (1:1) and EC/TFPC (1:1) show good charge-discharge capacity with small irreversible capacity loss in both the graphite/Li and the Li 1+x Mn 2 O 4 /Li half cells in spite of the relatively low reversible capacities [16]. Additionally, the authors indicated that the same positive and negative electrodes present inferior electrochemical performance in TFPC/PC (1:1) electrolyte owing to the high interfacial resistance of the passivating films formed on the electrode surfaces.…”