Seong-Jin Park

Mo6 + -Doped Li [ Ni ( 0.5 + x ) Mn ( 1.5 − 2x ) Mo x ] O 4 Spinel Materials for 5 V Lithium Secondary Batteries Prepared by Ultrasonic Spray Pyrolysis

Molybdenum-doped spinel Li[Ni ( 0 . 5 + x ) Mn ( 1 . 5 - 2 x ) Mo x ]O 4 (0 ≤ x ≤ 0.1) materials were synthesized by an ultrasonic spray pyrolysis method. Well-ordered [111] direction (octahedron shape) morphology powders were obtained at molybdenum-doped spinel. The structural, electrochemical, morphological properties, and thermal stability of the powders were characterized by X-ray diffraction, galvanostatic charge/discharge testing, scanning electron microscopy, and differential scanning calorimetry, respectively. The molybdenum doping spinel has a high discharge capacity, excellent capacity retention, rate capability, and thermal stability.

Facile synthesis of monodisperse poly(MAA/EGDMA)/Fe3O4 hydrogel microspheres with hollow structures for drug delivery systems: the hollow structure formation mechanism and effects of various metal ions on structural changes

This study presents a facile fabrication method for monodisperse poly(methacrylic acid/ethylene glycol dimethacrylate)/Fe3O4 [poly(MAA/EGDMA)/Fe3O4] composite microcapsules with magnetic properties and hollow structures for use as a targeted drug delivery system. In aqueous solution, the iron ions diffuse into the negatively-charged spherical polymer particles by electrostatic attraction. Since the obtained polymer–metal complexes decrease the repulsive force between the negatively-charged carboxyl groups of the polymer chains, the chelating parts of the polymer particles lose their hydrophilic properties and become relatively hydrophobic. As the number of iron ions continues to increase in the polymer particles, an internal cavity begins to be formed by interaction between the hydrophobic domains and the inner polymer chains. After the reducing agent is added into the synthetic system, Fe3O4 nanoparticles formed in the shells of the polymer particles retain the hollow structure. Confocal laser scanning microscopy and zeta potential measurements are employed to confirm the formation of the hollow structure during the diffusion of the various metal ions into the polymer gel. The magnetic properties of the poly(MAA/EGDMA)/Fe3O4 composite microcapsules synthesized under diverse experimental conditions are characterized by a vibrating sample magnetometer. The controlled release behavior of the model drug doxorubicin hydrochloride from the polymer–metal hollow composite microcapsules is investigated under different pH conditions.

Structural and electrochemical characteristics of nano-structured Li0.53Na0.03MnO2 manganese oxide prepared by the sol-gel method

Li0.53Na0.03MnO2 compound was prepared by ion exchange from Na0.7MnO2 which was synthesized by the sol–gel method using glycolic acid as a chelating agent. Powder X-ray diffraction and transmission electron microscopy (TEM) confirmed the structure of the as-prepared material resembled that of spinel with a high degree of disorder in the (111) planes. The material delivered a discharge capacity of 200 mA h g−1 after 50 cycles and showed excellent cyclability without undergoing the typical capacity fading exhibited by normal spinel material. It is speculated that the stacking disorder and small particle size of the prepared Li0.53Na0.03MnO2 powder have contributed to prevent the symmetry-breaking transformation which is believed to be responsible for capacity fading.

Single-shot digital holographic microscopy with a modified lateral-shearing interferometer based on computational telecentricity

Single-shot digital holographic microscopy (SS-DHM) with a modified lateral-shearing interferometer (MLSI) based on computational telecentricity is proposed. The proposed system is composed of three-step processes such as optical recording, digital compensation and numerical reconstruction processes. In the 1st step, the object beam is optically recorded with the MLSI, where a tube lens is set to be located at the slightly shorter distance than its focal length from the objective lens. Then, another phase factor due to the deviated locating of the tube lens from its focal length is additionally generated, which is called an additional quadratic phase factor (AQPF). However, in the 2nd step, this AQPF can be balanced out with the computer-generated version of the AQPF. In the 3rd step, the three-dimensional (3-D) object can be finally reconstructed from this AQPF-compensated hologram. Thus, by combined use of the optical recording and digital compensation processes of the AQPF, the proposed system can be made virtually operate in a so-called computational telecentricity, which enables us to implement a MLSI-based SS-DHM system. Wave-optical analysis and successful experiments with actual 3-D objects confirm the feasibility of the proposed system in the practical application fields.

A facile template-free synthesis of pH-responsive polyelectrolyte/amorphous TiO2 composite hollow microcapsules for photocatalysis

This paper presents a novel, facile method for fabricating pH-responsive inorganic/organic composite microspheres with hollow structures in the absence of a step for the removal of the core. Using polyelectrolyte (hydrogel) hollow microspheres without a need for further calcination and chemical etching, minimally cross-linked poly(methacrylic acid/ethylene glycol dimethacrylate/3-(trimethoxysilyl) propylmethacrylate), poly(MAA/EGDMA/TMSPM) [pMET] microspheres were prepared by a distillation–precipitation method. Once the pMET microspheres disperse in 2-propanol, the hollow structure is clearly observed and can be maintained more rigidly in a dry state after amorphous TiO2 (a-TiO2) is incorporated into the shell of a microsphere by a sol–gel method. The a-TiO2-incorporated pH-responsive pMET composite [pMET/TiO2] hollow microspheres were tested as a photocatalyst in acidic and neutral conditions. The photocatalytic performance of the hollow pMET/TiO2 composite microcapsules under neutral condition was better than that under acidic conditions due to their large active surface and strong adsorption ability against methylene blue (MB).

Stabilization of Lithium-Metal Batteries Based on the in Situ Formation of a Stable Solid Electrolyte Interphase Layer

Lithium (Li) metals have been considered most promising candidates as an anode to increase the energy density of Li-ion batteries because of their ultrahigh specific capacity (3860 mA h g-1) and lowest redox potential (-3.040 V vs standard hydrogen electrode). However, unstable dendritic electrodeposition, low Coulombic efficiency, and infinite volume changes severely hinder their practical uses. Herein, we report that ethyl methyl carbonate (EMC)- and fluoroethylene carbonate (FEC)-based electrolytes significantly enhance the energy density and cycling stability of Li-metal batteries (LMBs). In LMBs, using commercialized Ni-rich Li[Ni0.6Co0.2Mn0.2]O2 (NCM622) and 1 M LiPF6 in EMC/FEC = 3:1 electrolyte exhibits a high initial capacity of 1.8 mA h cm-2 with superior cycling stability and high Coulombic efficiency above 99.8% for 500 cycles while delivering a unprecedented energy density. The present work also highlights a significant improvement in scaled-up pouch-type Li/NCM622 cells. Moreover, the postmortem characterization of the cycled cathodes, separators, and Li-metal anodes collected from the pouch-type Li/NCM622 cells helped identifying the improvement or degradation mechanisms behind the observed electrochemical cycling.

Ultraviolet photodetector using pn junction formed by transferrable hollow n-TiO 2 nano-spheres monolayer

We report an ultraviolet (UV) photodetector with a universally transferable monolayer film with ordered hollow TiO2 spheres on p-GaN. After forming a TiO2 monolayer film by unidirectional rubbing of hollow TiO2 spheres on a polydimethylsiloxane (PDMS) supporting plate, we used a 5% polyvinyl alcohol (PVA) aqueous solution to transfer the film onto the target substrate. The PVA/TiO2 monolayer film was detached from the PDMS film and transferred to the p-GaN/Al2O3 substrate. To investigate the effects of crystallized phases of the TiO2 hollow spheres, anatase and rutile TiO2 sphere monolayers prepared by combining template synthesis and thermal treatment. The responsiveness of the UV photodetectors using anatase and rutile hollow n-TiO2 monolayer/p-GaN was 0.203 A/W at 312 nm and 0.093 A/W at 327 nm, respectively.