Yeon Uk Jeong

Conductive polymer composites offer a scalable route to self-supporting electrochemical electrodes, but electrical performance must be balanced against processability at high filler loadings. Fifteen polypropylene (PP)-based carbon-filler formulations were melt-compounded and injection-molded, and their electrical resistivity and moldability were evaluated. PP/CF20/CNT20 was selected, exhibiting a mean volume resistivity of 0.1409 Ω·cm with complete mold filling, no visible surface defects, and good moldability. SEM and synchrotron X-ray CT revealed multiscale carbon-filler morphology and spatially heterogeneous CF organization. Perforated PP/CF20/CNT20 disks were assembled into a ten-electrode parallel stack. At 12 V, the voltage sweep reached approximately 7.1 A in 1 M KOH and 2.1 A in tap water; during 20 h fixed-voltage operation, currents stabilized at approximately 5.2–5.5 A and 2.1 A, respectively. In 1 M KOH, estimated H₂ flow reached approximately 42.9 sccm at 7 A. Prolonged tap-water electrolysis produced Ca-dominated surface scale. At 12 V in 0.3 wt.% NaCl, no Escherichia coli colonies were detected under the applied plating conditions from 15 min onward. These results demonstrate the feasibility of injection-molded PP/CF/CNT composites as functional electrodes for aqueous electrochemical applications.

In this study, O3-type layered Na(Ni1-2xFexMnx)O2 (x = 0.3, 1/3, and 0.4) cathode materials for sodium-ion batteries are investigated to clarify the effects of Ni content and temperature-dependent phase-transition behavior. Charge–discharge tests are performed at 20–50 °C, and ex situ X-ray diffraction (XRD) analysis with Rietveld refinement is carried out at selected potentials to quantify temperature-dependent phase transitions and structural parameters. All samples are obtained as single-phase O3-type layered materials with the R-3m space group. The c-axis parameter, slab thickness, and inter-slab distance decrease with increasing Ni content. Analysis of the temperature-dependent phase transitions confirms that the O3/P3/P′3/P3″ transitions are accelerated at higher temperatures and higher Ni contents. Formation of the P′3 and P3″ phases is accompanied by stepwise changes in slab thickness and inter-slab distance, indicating substantial volume expansion. The O3/P3 transition in the Na-rich region exhibits a higher apparent activation-energy barrier, whereas the P3/P′3/P3″ transitions at lower Na contents show lower apparent activation energies and proceed more rapidly. These results demonstrate that Ni content and operating temperature strongly affect the phase-transition behavior and structural stability of O3-type Na(Ni, Fe, Mn)O2 cathode materials.

High ionic conductivity and good stability are major factors that influence the use of polymer electrolytes in electrochemical storage and conversion devices. In this study, we present polyurethane acrylate (PUA) membranes having enhanced ionic conductivity and swelling stability by double crosslinking the polyurethane (PU) and polyacrylate (PA) compartments. The crosslinking agent concentration was varied to control their mechanical properties, swelling stability, and ionic conductivity. Under optimum conditions, the electrolyte uptake of the double-crosslinked PUA membranes without notable defects was 245%. The maximum ionic conductivity of these membranes reached 9.6 mS/cm, which was higher than those with respect to most of the previously reported PUA- or PU-based polymer electrolytes.

In an attempt to achieve a higher energy density of secondary lithium batteries, cathode materials with higher potentials are investigated. LiMn_2−xNi_xO₄ samples are synthesized by a solid‐state reaction in a controlled atmosphere. While the energy density and cycle life have improved with higher Ni contents in the phase, the electrical conductivity has decreased. In order to improve the rate capability of cells, surface modifications of the cathode material are carried out by a wet chemical method. Surface modified samples show improved rate capability and cyclability compared to the unmodified samples.