Ju-Sik Kim

The High Performance of Crystal Water Containing Manganese Birnessite Cathodes for Magnesium Batteries.

Rechargeable magnesium batteries have lately received great attention for large-scale energy storage systems due to their high volumetric capacities, low materials cost, and safe characteristic. However, the bivalency of Mg(2+) ions has made it challenging to find cathode materials operating at high voltages with decent (de)intercalation kinetics. In an effort to overcome this challenge, we adopt an unconventional approach of engaging crystal water in the layered structure of Birnessite MnO2 because the crystal water can effectively screen electrostatic interactions between Mg(2+) ions and the host anions. The crucial role of the crystal water was revealed by directly visualizing its presence and dynamic rearrangement using scanning transmission electron microscopy (STEM). Moreover, the importance of lowering desolvation energy penalty at the cathode-electrolyte interface was elucidated by working with water containing nonaqueous electrolytes. In aqueous electrolytes, the decreased interfacial energy penalty by hydration of Mg(2+) allows Birnessite MnO2 to achieve a large reversible capacity (231.1 mAh g(-1)) at high operating voltage (2.8 V vs Mg/Mg(2+)) with excellent cycle life (62.5% retention after 10000 cycles), unveiling the importance of effective charge shielding in the host and facile Mg(2+) ions transfer through the cathodes interface.

Adaptive Step Length Estimation Algorithm Using Low-Cost MEMS Inertial Sensors

In this paper we introduce a MEMS based pedestrian navigation system (PNS) which consists of the low cost MEMS inertial sensor. An adaptive step length estimation algorithm using the awareness of the walk or run status is presented. Future u-Health monitoring systems will be essential equipment for mobile users under the ubiquitous computing environment. It is well known that the cost of energy expenditure in human walk or run changes with the speed of movement. Also the accurate walking distance is an important factor in calculating energy expenditure in human daily life. In order to compute the walking distance precisely, the number of occurred steps has to be counted exactly and the step length should be exactly estimated as well. However the step length varies considerably with the movements speed and status. Therefore, we recognize the movement status such as walk or run of a pedestrian using the small-sized MEMS inertial sensors. Based on the result, a step length is estimated adaptively. The developed method can be applied to PNS and health monitoring mobile system.

Direct Observation of an Anomalous Spinel-to-Layered Phase Transition Mediated by Crystal Water Intercalation

The phase transition of layered manganese oxides to spinel phases is a well-known phenomenon in rechargeable batteries and is the main origin of the capacity fading in these materials. This spontaneous phase transition is associated with the intrinsic properties of manganese, such as its size, preferred crystal positions, and reaction characteristics, and it is therefore very difficult to avoid. The introduction of crystal water by an electrochemical process enables the inverse phase transition from spinel to a layered Birnessite structure. Scanning transmission electron microscopy can be used to directly visualize the rearrangement of lattice atoms, the simultaneous insertion of crystal water, the formation of a transient structure at the phase boundary, and layer-by-layer progression of the phase transition from the edge. This research indicates that crystal water intercalation can reverse phase transformation with thermodynamically favored directionality.

Highly reduced VOx nanotube cathode materials with ultra-high capacity for magnesium ion batteries

Here, we describe novel VOx nanotubes with vanadium at various oxidation states (V3+/V4+/V5+) as cathode materials for magnesium ion batteries. The VOx nanotubes synthesized by a microwave-assisted hydrothermal process using an amine as an organic template show a high initial discharge capacity (∼218 mA h g−1) of more than 200 mA h g−1 and an outstanding cycling performance, which have not been previously reported for magnesium ion batteries. These improvements in the electrochemical performance of our VOx nanotubes originate from the trivalent vanadium ions generated in the highly reduced VOx nanotubes. The VOx nanotubes with trivalent vanadium ions exhibit a lower charge transfer resistance at the electrode/electrolyte interfaces and superior cycling performance than the VOx nanotubes containing vanadium ions of a higher oxidation state. We first suggest that the pristine oxidation state of the vanadium ions and the maintenance of a bonding structure on the surface of the VOx nanotubes are the most important factors determining the magnesium insertion/extraction kinetics into/out of the VOx nanotubes. Our findings offer a breakthrough strategy for achieving high-energy-density magnesium rechargeable batteries using VOx nanotube cathode materials in combination with nanoarchitecture tailoring.

9.3: High‐Resolution 5‐in. Full‐Color FEDs with New Aging Technique

High resolution field emission display (FED) devices of 5 inch developed. Under scheme, electron diagonal in size are the gate-switching trajectory profiles fully drive are simulated and tested. Uniquely-printed spacer with high aspect ratio are fabricated on ITO coated glass for high vacuum packaging. In addition, new gas aging scheme of stabilizing field emitting array are extensively investigated during the sealing and exhausting process in order to prevent oxidation effects on the micro tip. Finally, full color images of 64 gray scale will be demonstrated.

Field emission of PECVD diamond like carbon thin film flat cathode on microstructured silicon pedestal

It has been demonstrated that patterned diamond like carbon (DLC) thin film flat cathode deposited by Plasma Enhanced Chemical Vapor Deposition (PECVD) shows good field emission characteristics on microstructured silicon pedestal. This device is tested at the chamber pressure of 3.7/spl times/10/sup -6/ torr. At the anode bias of 450 volt, the emission current of 1 /spl mu/A per cathode is observed with bright phosphor flow at the electrical field intensity of 3.5 V//spl mu/m. Simulation and fabrication step show the feasibility of DLC flat cathode for the gated structure applications.

Driving method to improve display quality as current control with external circuitry

Image quality of FED (Field Emission Display) depends on uniformity of each pixel quality, because current FEDs have a passive matrix structure. If a pixel has a leakage path between gate and cathode, this affects neighboring pixels. The panel is activated by general flat panel driving scheme (push-pull method), image distortion such as a dark line pattern is observed according to the driving method. In this paper, this is simulated and cured by a new driving method for better image quality. The results from simulation and experiment are compared.

Cycling stability of Li metal in a mixed carbonate–ionic liquid electrolyte for lithium secondary batteries

Polymeric ionic liquids (PILs) containing a poly(ethylene glycol) methacrylate (POEM) coating layer significantly suppresses the reduction of the ionic liquid and of solvent molecules on Li metal anode in the Pyr14TFSI/carbonate electrolyte. Therefore, when Li metal was coated with the PILs–POEM, a cycling test performed with the electrolyte highlights an improved cycling stability.