Hideaki Katayama

Binary Mixed Solvent Electrolytes Containing Trifluoropropylene Carbonate for Lithium Secondary Batteries

To improve the safety of the electrolyte used for lithium secondary batteries, binary mixed solvent electrolytes containing trifluoropropylene carbonate (TFPC) as cosolvent have been studied. Chloroethylene carbonate (CIEC), 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 (NMR) spectroscopy. The chemical shift of CIEC 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 1+x 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.

Solvation states and properties of binary mixtures of halogenated cyclic carbonates and a linear carbonate

Abstract The solvation states and properties of organic solvent electrolytes were investigated by 13 C NMR measurements. The electrolytes were binary mixtures composed of halogenated cyclic carbonates such as chloroethylene carbonate (Cl-EC) or trifluoropropylene carbonate (TFPC) and a linear carbonate. Comparisons were made with the non-halogenated propylene carbonate (PC)/dimethyl carbonate (DMC) system. The solution structures of Cl-EC/DMC and TFPC/DMC systems, differing from those of PC/DMC system, have both cyclic and linear carbonates solvating to lithium ions. A study was also carried out on the performances of the model cells using organic electrolytes containing Cl-EC and TFPC as solvent, carbon anode, and lithium foil counter electrode. The current density dependence of the system using the pure TFPC as a solvent was much different from that of other systems. This is mainly due to the properties of interface between electrolyte and electrode of the cell.