In Jae Chung

Preparation and electrochemical properties of lithium-sulfur polymer batteries

Abstract The lithium/sulfur (Li–S) batteries consist of a composite cathode, a polymer electrolyte, and a lithium anode. The composite cathode is made from elemental sulfur (or lithium sulfide), carbon black, PEO, LiClO4, and acetonitrile. The polymer electrolyte is made of gel-type linear poly(ethylene oxide) (PEO) with tetra ethylene glycol dimethyl ether. Cells based on Li2S or sulfur have open-circuit voltages of about 2.2 and 2.5xa0V, respectively. The former cell shows two reduction peaks and one oxidation peak. It is suggested that the first reduction peak is caused by the change from polysulfide to short lithium polysulfide, and the second reduction peak by the change from short lithium polysulfide to lithium sulfide (Li2S, Li2S2). The cell based on sulfur has the same reduction mechanism as that of Li2S, which is caused by the multi process (first and second reduction) of lithium polysulfide. On charge–discharge cycling, the first discharge has a higher capacity than subsequent discharges and the flat discharge voltage is about 2.0xa0V. As the current load is increased, the discharge capacity decreases. One reason for this fading capacity and low sulfur utilization is the aggregation of sulfur (or polysulfide) with cycling.

Synthesis and characterization of polyaniline–polycarbonate composites prepared by an emulsion polymerization

Abstract Electrically conductive polymer composite, polyaniline (PANI)–dodecylbenzene sulfonic acid (DBSA)/polycarbonate (PC), was prepared by an inverted emulsion polymerization in which DBSA played both roles of surfactant and dopant. Fourier transform infrared (FT-IR) spectroscopy for the composite showed the existence of hydrogen bonding between PANI and PC which caused the increase of glass transition temperature with PANI content. Moreover, the electrical conductivity increased around the glass transition temperature because the PANI chains contacted more frequently and facilitated the electron transfer through the hydrogen bonding between PANI and PC. In addition, it was proved by mechanical property that tensile strength of the composite decreased with PANI content because PANI functioned as a defect in PC matrix and the tensile modulus continuously increased because PANI had a higher rigidity of molecules.

Preparation and electrical properties of lithium–sulfur-composite polymer batteries

Abstract The lithium/sulfur batteries consisted of a composite cathode, a polymer electrolyte, and lithium anode. The composite cathode was made from active sulfur (or lithium sulfide), carbon black, poly(ethylene oxide) (PEO), LiClO4, and acetonitrile. And the polymer electrolyte (PE) was made of gel-type linear PEO with tetra(ethylene glycol dimethyl ether). The open circuit voltage (OCV) of the Li–S battery was about 2.5xa0V. The Li–S battery showed two reduction peaks and one oxidation peak, which correspond to those of the cell made of lithium sulfide as active material and it had an irreversible kinetic mechanism, which was supported by the charge–discharge and cyclic voltammetry (CV) experiments as a function of current load and sweep rate. When iron (Fe) powder was added to the composite cathode, its effect on the electrochemical property of the cell was investigated. This cell showed higher specific capacity and longer cycle life than the Li–S battery, and several possible explanations for the effect of Fe in Li–S battery has been presented.

Electrical conductivity change of polyaniline–dodecyl benzene sulfonic acid complex with temperature

Polyaniline–dodecylbenzene sulfonic acid (PAn–DBSA) complex was thermally treated and its conductivity and structure change were investigated. The conductivity increased linearly from 1.1 × 10−4 to 3.0 × 10−1 S/cm on thermal heating until 140°C, but decayed above 200°C. The increase was caused by an additional thermal doping resulting from an increasing mobility of undoped dopants. After the thermal doping, the formation of the layered structure of PAn–DBSA is made. The decrease was caused by the thermal decomposition of dopants. The conductivity changes at a high temperature was strongly dependent on the nature of the dopant. The results were confirmed by means of X-ray patterns and Fourier transform infrared spectra obtained in the heating and cooling processes of polyaniline.

Annealing effect on the electrochemical property of polyaniline complexed with various acids

The annealing effect on the electroactivity of polyaniline (PAn) complexed with various acids has been investigated. The polyaniline—p-toluene sulfonic acid complex (PAn—pTSA) and polyaniline—hydrochloric acid complex (PAn—HCl) show decreased electroactivities with annealing temperature, but the polyaniline—dodecylbenzene sulfonic acid complex (PAn—DBSA) shows an increase in electroactivity up to an annealing process of 150°C, and then a decrease at an annealing process of 180°C. The increase of the electroactivity for PAn—DBSA can be explained by an additional thermal doping of undoped DBSA with annealing. The electrical conductivities at a high temperature of 230°C are in the order of PAn—pTSA > PAn—DBSA > PAn—HCl. PAn—pTSA shows the highest conductivity because pTSA shows the most thermal stability. Decreased conductivity at a high temperature may be due to the dedoping and structural change that cannot be recovered by redoping.

Electrochemical characteristics of dodecylbenzene sulfonic acid-doped polyaniline in aqueous solutions

The electrochemical characteristics of the polyaniline (PAn) films doped with dodecylbenzene sulfonic acid (DBSA) were investigated in aqueous solutions by means of cyclic voltammetry. The PAn-DBSAs film showed a good electrochemical activity in a weak acid solution as well as in a strong acid solution due to the incorporation of small cation instead of DBSA trapped in the film for charge neutralization of polymer matrix.

Electrochemical properties of dodecylsulfate-doped polypyrrole films in aqueous solution containing NH4Cl and ZnCl2

Abstract Dodecylsulfate-doped polypyrrole (PPy) films were electrochemically synthesized in aqueous solution containing sodium dodecylsulfate. In order to examine the applicability of the films to electrode materials, the electrochemical properties and charge-discharge properties were investigated in the aqueous solution containing 0.4 M NH 4 Cl and 0.1 M ZnCl 2 . From cyclic voltammetric and chronoamperometric results, it was concluded that the good electrochemical reversibility was due to the fast mobilities of NH 4 + and Cl − instead of the dodecylsulfate trapped in the polymer matrix. The charge-discharge tests of the Zn/(NH 4 Cl, ZnCl 2 )/PPy cell showed an open-circuit voltage of 1.3 V after 80 min, specific capacity of 59 Ah kg −1 and energy density of 77 Wh kg −1 .

Electrical conductivity of stretched polypyrrole film

Abstract Polypyrrole films with high conductivity and strechability were synthesized by an electrochemical method in acetonitrile solution at low temperature and low current density. The films were stretched to over twice their original length. The variation of stretching direction conductivity ( σ 1 ) for a stretched film was evaluated directly by in situ measurements of resistance and strain during the stretching of the polypyrrole film. The calculated values of σ 1 agreed very well with experimental conductivity data measured by the four-probe technique after drying in air.

Electrochemical behavior of dodecylbenzenesulfonic acid-doped polyaniline in organic electrolyte solution

Abstract Electrochemical properties of dodecylbenzenesulfonic acid-doped polyaniline film (PAn-DBSA) were investigated by cyclic voltammetry in an organic mixture solution of propylene carbonate—1,2-dimethoxyethane containing 1 M LiClO 4 . The PAn-DBSA film showed reversibility and electrochemical stability over 500 cycles in the redox process. Its electrochemical stability was explained by the ionic replacement of DBSA anions with ClO 4 − anions and by the deprotonation during the redox process. This behavior was confirmed from the results obtained using cyclic voltammetry and energy-dispersive X-ray spectroscopy (EDXS).

pH effect on the electrochemical redox reaction of disulfide with polyaniline film electrode in organic solution

Abstract 2,5-Dimercapto-1,3,4-thiadiazole/polyaniline (DMcT/PAn) composite electrode is prepared by DMcT electrochemical oxidation on PAn film electrode in DMcT solution with a different pH. The electroactivity, DMcT concentration profile in the PAn film and the in situ resistivity of the composite are investigated in the electrolyte solution with or without DMcT. The composite film prepared in acidic condition shows higher current density and better electroactivity than those prepared under neutral and basic conditions because the protons may contribute to the protonation of PAn film. When DMcT/PAn composite is transferred into the solution without DMcT, it has enhanced electroactivity such as an anodic peak shift to a lower potential and increased cathodic current. The enhancement of electroactivity is considered to be caused by the increase of ion diffusion coefficient and the decrease of electrical resistivity. The ion diffusivity increases due to the detachment of excess DMcT from the film and the resistivity decreases by the dissociation of DMcT from the imine group of PAn.