Suk-Gi Hong

Enhancement in the electrochemical performance of zirconium/phosphate bi-functional coatings on LiNi0.8Co0.15Mn0.05O2 by the removal of Li residuals

The effect of bi-functional coatings consisting of Zr and phosphate (P) on the electrochemical performance of Li1.0Ni0.8Co0.15Mn0.05O2 (NCM) has been investigated. The presence of various types of Zr and P compounds such as oxides (ZrO2 and Li2ZrO3) and phosphates (Zr2P2O9, ZrP2O7 and LiZr2(PO4)3) in the coating was confirmed by experiments as well as density functional theory (DFT) calculations. When the NCM samples were coated with the Zr/P hybrid material, the cycle retention and the amount of removed Li residuals (LiOH, Li2CO3) were enhanced by the synergistic effect from Zr and P. The NCM sample coated with a Zr/P layer with a Zr/P ratio of 1 : 1 exhibited an increase in the initial capacity (209.3 mA h g-1) compared to the pristine sample (207.4 mA h g-1) at 0.1C, owing to the formation of the coating layer. The capacity retention of the Zr/P coated sample (92.4% at the 50th cycle) was also improved compared to that of the pristine NCM sample (90.6% at the 50th cycle). Moreover, the amount of Li residuals in the Zr/P coated NCM sample was greatly reduced from 3693 ppm (pristine NCM) to 2525 ppm (Zr/P = 5 : 5).

Multiuser Two Way Relaying Schemes in the Future Cellular Network

We propose a set of multiuser two-way relay beam-forming schemes in the cellular network. While the previous schemes are applicable only when there exist a single base station (BS) and a single relay station (RS) with the same number of antennas, multiple BSs or multiple RSs can exist in the proposed scheme without such restriction on the numbers of antennas. The degree of freedoms (DoF) achievable are analyzed and conditions to achieve these DoF values are presented. Both the decode-and-forward (DaF) protocol and amplify-and-forward (AaF) protocol are considered. It turns out that the channel alignment and the interference alignment in the multi-cell environment act the key roles in the development. We also provide an interference alignment scheme in the multi-cell environment that improves the achievable DoF values upon those of the previous schemes. The simulation results corroborate that the proposed beam-forming works as analyzed.

Re-construction layer effect of LiNi 0.8 Co 0.15 Mn 0.05 O 2 with solvent evaporation process

The solvent evaporation method on the structural changes and surface chemistry of the cathode and the effect of electrochemical performance of Li1.0Ni0.8Co0.15Mn0.05O2 (NCM) has been investigated. After dissolving of Li residuals using minimum content of solvent in order to minimize the damage of pristine material and the evaporation time, the solvent was evaporated without filtering and remaining powder was re-heated at 700 °C in oxygen environment. Two kinds of solvent, de-ionized water and diluted nitric acid, were used as a solvent. The almost 40% of Li residuals were removed using solvent evaporation method. The NCM sample after solvent evaporation process exhibited an increase in the initial capacity (214.3 mAh/g) compared to the pristine sample (207.4 mAh/g) at 0.1C because of enhancement of electric conductivity caused by decline of Li residuals. The capacity retention of NCM sample after solvent evaporation process (96.0% at the 50th cycle) was also improved compared to that of the pristine NCM sample (90.6% at the 50th cycle). The uniform Li residual layer after solvent treated and heat treatment acted like a coating layer, leading to enhance the cycle performance. The NCM sample using diluted nitric acid showed better performance than that using de-ionized water.

Resource Allocation Method Using Channel Sensing and Resource Reuse for Cognitive Femtocells

A cognitive femtocell is a new small cell based on a smart home base station to solve the spectrum-scarcity problem. Recently, dedicated resource allocation for cognitive femtocells is extensively researched to mitigate the co-channel interference. However, the cognitive femtocell may suffer from the lack of frequency resource for its users due to high data traffic load of the macrocell. In this paper, we propose a novel resource allocation scheme based on the channel sensing and the spatial radio resource reuse mechanism, which enables femto users in the cognitive femtocell to obtain more feasible radio resource. The simulation results show that the capacity of the cognitive femtocell can be improved under high data traffic load of the macrocell compared to that of the conventional scheme.

Design and Optimization of HT-PEMFC MEAs

The HT-PEMFC systems are mostly developed for the combined heat and power (CHP) and auxiliary power unit (APU) generation applications because of their relatively simple system configuration and tolerance to a wide choice of fuels. To achieve the cost and durability targets that are needed for the commercialization of the HT-PEMFC systems, many developments have been made to enhance the performance of the HT-PEMFC MEAs. The efforts to enhance the cell voltage include using catalysts with high ORR activity, controlling properties of binders and optimizing amount of acid to increase the electrochemically active surface area in the catalyst layer. The lifetime of the MEA is reported to depend on the catalyst degradation and acid loss, and notable improvements on the durability of MEAs were achieved by using oxidation-resistant catalysts. In this chapter, the factors that determine the cell voltage and durability of MEAs for HT-PEMFC are discussed, and the design of low-cost durable MEAs for HT-PEMFC is suggested.

Effects of amphiphilic surfactants on electrolyte distribution in polymer electrolyte fuel-cell electrode

To enhance Pt utilization in the fuel-cell electrode by microscopically controlling the distribution of liquid electrolytes around Pt catalysts, the amphiphilic surfactant tergitol phosphate was synthesized and introduced into the fuel-cell electrode. The chemical structure of the surfactant was determined by 1 H-nuclear magnetic resonance, and its adsorption property on Pt–C catalyst was ascertained by Fourier transform infrared analysis. The electrode into which the amphiphilic surfactants were incorporated showed improved performance, and especially the amphiphilic surfactant with polyethylene oxide, NPE10-OPO(OH) 2 , produced higher cell performance.

Resource Allocation Based on Channel Sensing and Spatial Spectrum Reuse for Cognitive Femtocells

A cognitive femtocell is a new small cell based on a smart home base station to solve the spectrum-scarcity problem. Recently, dedicated resource allocation for cognitive femtocell to mitigate co-channel interference is extensively researched. However, the cognitive femtocell may suffer from the lack of frequency resource for its users due to high data traffic load of the macrocell. We propose a novel resource allocation and power control mechanism using spatial frequency reuse and spectrum sensing, which enables femto users in the cognitive femtocell to obtain more feasible resource. We analyze and evaluate the performance gain of the proposed scheme. Although data traffic load of the macrocell increases, the capacity of the cognitive femtocell can be maintained appropriately by the proposed resource allocation and power control scheme and it is shown that the performance is improved compared to that of the conventional scheme.