The Effect of Ethylene Carbonate and Salt Concentration on the Conductivity of Propylene Carbonate∣Lithium Perchlorate Electrolytes

Abstract

Propylene carbonate (PC) is the most common organic solvent used in lithium batteries due to its high dielectric constant and high chemical stability with lithium metal. The favorable conductivity of PC |LiClO 4 (lithium perchlorate) electrolytes, with values of about 10 Ϫ3 S cm Ϫ1 , has been reported. [1][2][3][4] Several vibrational spectroscopy studies 1,4,5 revealed that a strong interaction between Li ϩ and PC occurs for the ring deformation of PC molecules at 712 cm Ϫ1 .The conductivity of PC |LiClO 4 electrolytes is about 10 Ϫ3 S cm Ϫ1 which is lower than the conductivity of aqueous electrolytes (about 10 Ϫ2 S cm Ϫ1 ). Therefore, mixed-solvent electrolytes with conductivities as high as 10 Ϫ2 S cm Ϫ1 have been developed by adding ethylene carbonate (EC) as a co-solvent. Recently, Li ϩ -solvent interactions in PC-EC solutions have been studied using both Raman 6 and IR 7 spectroscopies and nuclear magnetic resonance (NMR). 8 Strong Li ϩ -EC interactions 6-8 were observed at the peak bands 726 and 903 cm Ϫ1 due to ring breathing and ring bending modes, respectively.The conductivities of mixed-solvent electrolytes depend on the concentration of salt and the relative amounts of the two solvents. In this work, the conductivities of electrolytes with different compositions were studied using the ac impedance technique. Also, the interactions between Li ϩ and EC were characterized by Raman spectroscopy, and these results were used to determine the solvation number of Li ϩ . ExperimentalLiClO 4 (Aldrich) was dried in a vacuum oven at 120ЊC before being added to the solvent. Both PC and EC (Aldrich) were purified by reduced-pressure distillation, and K 2 MnO 4 was added to these solvents during distillation to eliminate impurities in the solvents. Both solvents were weighted separately before mixing. Different concentrations of LiClO 4 were added to the mixed solvents containing various molar ratios of EC/PC to form the electrolytes. The electrolyte compositions are listed in Table I. The electrolytes were stored in a dessicator with 4 Å molecule sieves before testing. The same volume of liquid electrolyte was used in each measurement with the identical quartz container.The Raman spectra were recorded with a IFS66 ϩ FRA 106/S type of Fourier transform IR-Raman spectrometer (Bruker Instruments Corporation, Germany). The laser power used in the test was 475 mW with an excitation line of about 1.064 m. The angle between the scattered light and the incident light was 180Њ. Each Raman spectrum included 128 scans, each with a resolution of 2 cm Ϫ1 . All Raman spectra were collected from liquid samples.The ionic conductivities of the electrolytes were measured by ac impedance spectroscopy using a frequency response analyzer (FRA S1260) and an IBM PC. A frequency range between 30 MHz and 100 mHz was used during the test. The real resistance of the liquid electrolytes was estimated from the resistance ZЈ at which the reactance ZЉ reached its minimum value. 9 The electrodes used in the measurements were stainless steel plate...

Intrinsically Stretchable Supercapacitors Composed of Polypyrrole Electrodes and Highly Stretchable Gel Electrolyte

“…When the molecular weight increased, the longer polymer chains begun to overlap and entangle with each other, leading to stretchable film. 37 The effect of the weight ratio H 3 PO 4 /PVA was also investigated over the range 0.5:1, 1:1, 40 The H 3 PO 4 -PVA (1.5:1) polymer electrolyte was selected for further tests due to its higher elasticity and conductivity. The conductivity increased as the temperature went up in the range of 30 ℃ to 70 ℃ (Figure 2a-b), indicating an Arrhenius type thermally activated process.…”

Conductivity and Viscosity of PC-DEC and PC-EC Solutions of LiBOB

“…The most conspicuous feature emerging from these plots is the ''dome'' shape of the surfaces, as a result of peaking in both m and w. Peaking of in m is a common feature for liquid electrolytes, reflecting the process of first increasing with the number of dissociated ions as m increases and then falling as the rise in and in ion association become dominant; this has been observed for many electrolytes of lithium salts. 1,2,[5][6][7]14,15,22,[31][32][33] Peaking of in w, on the other hand, seems to be the result of the and of DEC both being much lower than those of PC and both being monotonic functions of w. As such, as w rises from zero, the change of is first dominated by the fall of of the electrolyte causing to rise and then by the fall of of the solvent which by allowing stronger ion association causes to fall. The same behavior has been observed in LiPF 6 -(PC-DEC), 1 LiBF 4 -(PC-DEC), 2 and LiPF 6 -(EC-EMC), 7 where the linear carbonates DEC and EMC have much lower and than their cyclic counterparts PC and EC, and in LiClO 4 -(PC-DME) 8 and NaClO 4 -(PC-DME), 9 where DME ͑dimethoxyethane͒ has a much lower and than PC.…”

Conductivity and Viscosity of PC-DEC and PC-EC Solutions of LiBF[sub 4]

“…5 for from 60 to Ϫ40°C in 20°decrement, once as a surface plot and once as a contour plot for each. 1,4,5,12,13,23,[26][27][28] Peaking of in w, on the other hand, seems to be the result of the and of DEC both being much lower than those of PC and both being monotonic functions of w. As such, as w rises from zero, the change of is first dominated by the fall of for m and 0 to 0.6 weight fraction of EC for w, and e f as the fitting error in percent of the range of the fitting data. 1,4,5,12,13,23,[26][27][28] Peaking of in w, on the other hand, seems to be the result of the and of DEC both being much lower than those of PC and both being monotonic functions of w. As such, as w rises from zero, the change of is first dominated by the fall of for m and 0 to 0.6 weight fraction of EC for w, and e f as the fitting error in percent of the range of the fitting data.…”