Dong Soo Kim

This study investigates the properties of various adhesives and assesses the effects of the coating and drying conditions of aluminum surface treatment agents on adhesion strength and chemical resistance. The adhesion between aluminum and the polymer film is improved through the application of a surface treatment agent to the aluminum surface. This study examines the initial adhesive strength of a manufactured pouch film with respect to the drying temperature and time and evaluates its adhesive strength in the presence of moisture. The results indicate that the residual moisture on the aluminum surface weakens the adhesive strength and significantly affects electrolyte resistance. A noticeable reduction in strength was observed after water spraying, when the drying temperature and time were relatively low during the initial strength measurement. Among the adhesives used for aluminum and CPP lamination, olefin adhesives exhibit less susceptibility to electrolyte effects and have higher adhesive strengths compared to urethane and ester adhesives. Leveraging these characteristics, flexible pouch cells were manufactured and their stability was evaluated. The results confirm that the flexible cells demonstrate excellent stability, exhibiting potential for application in wearable devices.

In this study, a room-temperature ammonia gas sensor using a ZnO and reduced graphene oxide (rGO) composite is developed. The sensor fabrication involved the innovative application of reverse offset and electrostatic spray deposition (ESD) techniques to create a ZnO/rGO sensing platform. The structural and chemical characteristics of the resulting material were comprehensively analyzed using XRD, FT-IR, FESEM, EDS, and XPS, and rGO reduction was achieved via UV–ozone treatment. Electrical properties were assessed through I–V curves, demonstrating enhanced conductivity due to UV–ozone treatment and improved charge mobility from the formation of a ZnO–rGO heterojunction. Exposure to ammonia gas resulted in increased sensor responsiveness, with longer UV–ozone treatment durations yielding superior sensitivity. Furthermore, response and recovery times were measured, with the 10 min UV–ozone-treated sensor displaying optimal responsiveness. Performance evaluation revealed linear responsiveness to ammonia concentration with a high R² value. The sensor also exhibited exceptional selectivity for ammonia compared to acetone and CO gases, making it a promising candidate for ammonia gas detection. This study shows the outstanding performance and potential applications of the ZnO/rGO-based ammonia gas sensor, promising significant contributions to the field of gas detection.

This paper reports a high-performance humidity sensor made using a novel cellulose nanofiber (CNF)–silver nanoparticle (AgNP) sensing material. The interdigital electrode pattern was printed via reverse-offset printing using Ag nano-ink, and the sensing layer on the printed interdigitated electrode (IDE) was formed by depositing the CNF-AgNP composite via inkjet printing. The structure and morphology of the CNF-AgNP layer are characterized using ultraviolet–visible spectroscopy, an X-ray diffractometer, field emission scanning electron microscopy, energy-dispersive X-ray analysis, and transmission electron microscopy. The humidity-sensing performance of the prepared sensors is evaluated by measuring the impedance changes under the relative humidity variation between 10 and 90% relative humidity. The CNF-AgNP sensor exhibited very sensitive and fast humidity-sensing responses compared to the CNF sensor. The electrode distance effect and the response and recovery times are investigated. The enhanced humidity-sensing performance is reflected in the increased conductivity of the Ag nanoparticles and the adsorption of free water molecules associated with the porous characteristics of the CNF layer. The CNF-AgNP composite enables the development of highly sensitive, fast-responding, reproducible, flexible, and inexpensive humidity sensors.

The performance, stability, and lifespan of lithium-ion batteries are influenced by variations in the flow of lithium ions with temperature. In electric vehicles, coolants are generally used to maintain the optimal temperature of the battery, leading to an increasing demand for temperature and humidity sensors that can prevent leakage and short circuits. In this study, humidity and temperature sensors were fabricated on a pouch film of a pouch-type battery. IDE electrodes were screen-printed on the pouch film and humidity- and temperature-sensing materials were printed using a dispenser process. Changes in the capacitance of the printed Ag-CNF film were used for humidity sensing, while changes in the resistance of the printed PEDOT:PSS film were used for temperature sensing. The two sensors were integrated into a single electrode for performance evaluation. The integrated sensor exhibited a response of ΔR ≈ 0.14 to temperature variations from 20 °C to 100 °C with 20% RH humidity as a reference, and a response of ΔC ≈ 2.8 to relative humidity changes from 20% RH to 80% RH at 20 °C. The fabricated integrated sensor is expected to contribute to efficient temperature and humidity monitoring applications in various pouch-type lithium-ion batteries.

In this study, pure ZnO and Al-doped ZnO(AZO) thin films were coated onto a SiO₂ wafer using the electrostatic spray deposition (ESD) process for acetone gas detection under laboratory conditions. Voltage levels were varied to determine the optimal conditions for producing thin films with the highest uniformity. The results indicate that the optimal coating voltage for achieving the highest uniformity of the coated films is 2.9 kV for ZnO and 2.6 kV for AZO. The thin films were produced under these optimal ESD conditions by adjusting the coating time, and gas sensors were fabricated by printing electrodes using a reverse offset process on top of the thin films. Analysis of the sensing response revealed that the AZO-coated gas sensor with a 200 s deposition exhibited the best acetone-sensing ability at 300 °C, with a maximum response of 13.41 at 10 ppm. Furthermore, the fabricated gas sensors effectively detected acetone gas even at a low concentration of 2 ppm, demonstrating high selectivity in comparison to other gases.

Traditional printed electronics processes have recently been utilized within 3D-printed structures where components and interconnects are introduced during manufacturing disruptions. The dielectric performance of 3D-printed materials has a low-resolution problem, and many technologies have been proposed for direct printing on a 3D curved surface or structure. This paper reports a humidity sensor fabricated with a 3D-printed electrode and cellulose nanofibers on a curved surface. The electrode part of an interdigital electrode (IDE) sensor is printed on a flat glass substrate and a 3D-curved glass substrate using a double blanket reverse offset. Subsequently, a cellulose nanofiber emulsion is coated onto the IDE pattern as a sensing layer with a dispenser. The electrical impedance of the sensor is measured with the relative humidity (RH) changes between 10% and 90% RH. The sensor demonstrates a high repeatability and sensitivity, even on a 3D curved substrate. This technology provides a promising method to integrate humidity sensors and 3D deformable surfaces.

Ceramics have excellent properties such as hardness and thermal and chemical stability. Therefore, researchers have studied the use of 3D printing to produce complex shapes in tools and structural applications. The debinding and sintering processes for ceramic composite materials manufactured using digital light processing (DLP) 3D printing technology were studied. The slurry used for DLP 3D printing requires debinding and sintering, as it contains ceramics and binders. Therefore, the debinding and sintering processes were measured by TG-DSC curves, and the changes in material characteristics were evaluated by setting the debinding holding time (4, 5, and 6 h) and sintering temperature (1100, 1200, and 1300 °C) as parameters. After debinding for 6 h, the density of the ceramic sintered at 1300 °C was 1.36 g/cm²; the linear shrinkage was 22.1%/21.6%/28.5% along the x, y, and z axes, respectively; and the bending strength was 8.58 MPa. As a result of this study, we developed an optimized process for the debinding and sintering of ceramics manufactured through the DLP 3D printing process.

The double-layer blanket (DLB) reverse offset is a newly designed printing process for patterning electronic circuits on a 3D curved surface. Unlike the existing reverse offset process, the DLB reverse offset utilizes an offset roll composed of two layers comprising polydimethylsiloxane (PDMS) and a thick, soft cushioned rubber to print microelectrode patterns and transparent electrodes on a curved surface. The optimal printing process was determined by adjusting the printing pressure and printing speed for horizontal and vertical micropatterns, based on which transparent electrodes with metal mesh and honeycomb structures with a line width of 30 μm and pitch of 600 μm with micropatterns ranging from 30 μm to 60 μm were printed on a curved surface. Ag ink was used, and the 3D curved surface indicated a print quality similar to that of the flat surface for both the vertical and horizontal patterns and transparent electrodes. The DLB reverse offset technique demonstrated the possibility of printing on a 3D curved surface and is expected to broaden the range of printed electronics to applications such as smart glasses and 3D shape sensors.

This paper presents a novel output voltage regulator in the cascade structure under the consideration of both the parameter and load uncertainties. It leads to the first-order closed-loop inner and outer loop dynamics in the low-pass filter form by the pole-zero cancellation through the active damping injection, which is the main contribution of this study. Moreover, it is proved that the active damping injection level determines the disturbance rejection capability of the closed-loop system. A 3-kW DC/DC boost converter confirms the actual advantages from these two contributions.