Supercapacitors with Extended Operating Potential Window

Electrolytes in supercapacitors (SCs) play an important role on their energy storage capacity. The electrochemical stability of electrolytes defines the operating potential of the SCs and their viscosity defines a power density of the SCs. In the present work, a new method for composing an electrochemically stabile but high viscous ethylene glycol (EG) based electrolyte has been discussed. A viscosity of the EG then reduced by dissolving an inorganic lithium tetrafluoroborate (LiBF4) salt. The affect of the concentration of the salt on EG viscosity has been investigated. The best capacitive performance of activated carbon (AC) based electrodes with large operating potential (-1.7V to 1.7V) was found in 3M LiBF4/EG electrolyte.

Morphology, Ionic-Molecular Interaction and Ionic Conductivity Behavior of PMMA/ENR 50 Electrolytes Containing Carboxylic Acids Modified SiO2 Fillers

Carboxylic acids of various carbon chain lengths (Cn); i.e. butanoic acid (C4), octanoic acid (C8), dodecanoic acid (C12) and hexadecanoic acid (C16) have been used to organically modify silicon dioxide (SiO2). The acid modification involve replacing the hydrogen atom of the silanol group (Si-OH) of SiO2 with the RnCOO-of the acid via esterification technique. SiO2 and acid modified SiO2 (MoCn-SiO2) were used as filler in preparation of polymethyl methacrylate/50% epoxidized natural rubber electrolytes containing SiO2 (PEL-SiO2) and MoCn-SiO2 (PEL-MoCn-SiO2) via solvent casting method with lithium tetrafluoroborate (LiBF4) as dopant salt. Field-emission scanning electron microscopy (FESEM) analysis of PEL-SiO2 and PEL-MoCn-SiO2 films show LiBF4 accumulated to the fillers. Fourier-transform infrared spectroscopy (FTIR) analysis confirmed formation of hydrogen bonding between LiBF4 with fillers and polymers in the polymer electrolyte films. Interestingly, the ionic conductivity of PEL-MoCn-SiO2 films increases as the Cn of acids increased with the highest ionic conductivity of 5.56 x 10-7 Scm-1 was achieved in PEL-MoC12-SiO2 film.

Effects of Acid Modified SiO2 on Ionic Conductivity and Blend Properties of LiBF4 Doped PMMA/ENR 50 Electrolytes

Previously, it was found that the addition of SiO2 filler can improve the homogeneity and enhance the ionic conductivity of lithium tetrafluoroborate (LiBF4) doped polymethyl methacrylate/50 % epoxidized natural rubber (PMMA/ENR 50) blend from 6.21 x 10-7 Scm-1 to 5.26 x 10-6 Scm-1. Unfortunately, this SiO2 filler tend to agglomerates thus obstructing the smoothness in the transportation of lithium ion in the polymer blend matrix. This unruly phenomenon was due to the formation of hydrogen bonding between the oxygen atom of SiO2 and the hydrogen atom from the moisture. Therefore, in this study, this SiO2 filler was modified using hydrochloric acid (HCl) to reduce the formation of hydrogen bonding between SiO2 and moisture. It was found that the modification was able to reduce the hydrogen bond in SiO2 filler. The CHNS analysis shows that the percentage of hydrogen reduces as concentration of acid increased. This was further confirmed from the FT-IR analysis in which the peak corresponding to Si-OH was reduces meanwhile the peaks corresponding to Si-O-Si increases as HCl concentration increased. As a result, the homogeneity of the blends was further improved. However, the ionic conductivity of the system was found slightly reduce by few magnitudes. Temperature dependence ionic conductivity of LiBF4 doped PMMA/ENR 50 filled HCl-SiO2 electrolytes shows nonlinear trend indicates that the system not obeys Arrhenius equation.