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In this study, time-dependent discharge resistance and its power capability determined by current pulse experiments (CPE) were investigated according to changes in the state-of-charge and storage temperature. Using pattern analysis of the obtained resistance, two components comprising total discharge resistance were separately obtained and compared with the best fitting results of electrochemical impedance spectroscopy (EIS). From this comparison, an initial abrupt resistance drop was found to be a major determining factor of power capability and associated with electrolyte/electric transport in the bulk/film phase. This drop was also found to be associated with a charge transfer reaction at the electrode interphase, indicative of a correlation between the initial resistance drop in CPE and semi-circle resistance in EIS. The following resistance relaxation was possibly due to a chemical diffusion process of lithium ion. After storage at high temperature, it was observed that an increase in discharge resistance was mostly attributable to larger film resistance.

Eu-doped Y2O3 particles with spherical shape and fine size were prepared by spray pyrolysis. The cathodoluminescence of Y2O3:Eu3+ powder was optimized by substituting small amount of zinc atoms in place of yttrium sites. As a result, the optimized (Y, Zn)2O3:Eu3+ phosphor showed 60% improved cathodoluminescence compared with Y2O3:Eu3+ particles. The prepared (Y, Zn)2O3:Eu3+ phosphor had spherical shape and 0.726 μm in mean size. Using these particles, the thickness of the phosphor film was controlled by varying the phosphor loading. The brightness and luminous efficiency of phosphor films prepared were monitored with varying the accelerating voltage ranges from 4 to 14 kV. The dependency of the luminous efficiency on the accelerating voltage was very sensitive to the phosphor loading. As increasing the accelerating voltage from 4 to 14 kV, the brightness of phosphor films prepared was monotonically increased from 200 to 1085 cd/cm2, but the saturation in the luminous efficiency appeared at 10 kV. The highest efficiency was achieved when the number of phosphor-particles layer was about 3. More details about the luminous efficiency and brightness were discussed with changing the phosphor loading.

Spray pyrolysis was applied to prepare CaMgSi 2 O 6 :Eu (CMS) blue phosphor particles with high luminescence intensity. The VUV characteristics of CMS particles were optimized in terms of post-treatment temperature, Eu 2+ concentration and Si content when they were prepared by spray pyrolysis. The luminescence intensity of CMS particles was gradually increased with increasing the post-treatment temperature as long as the melting does not occur. The concentration quenching was observed when the concentration of Eu 2+ was 1.0 at.%. Also, a red shift in the emission spectrum occurred at the Eu 2+ concentration of higher than 1.5 at.% due to some increase in the crystal filed around Eu 2+ . Using excess Si was not helpful to improve the photoluminescence intensity of CMS particles when they are prepared by the spray pyrolysis. It was clear that the CMS particles prepared by spray pyrolysis had better thermal stability compared with commercial BAM particles. The emission intensity of the optimized CMS particles was about 97% of BAM particles after the baking at 500 °C although the width of the spectrum was smaller.

The Mn 4+ -abundant surface of the Li- and Al-substituted spinel cathode materials is found to provide electrochemical and interfacial stabilities in the voltage region of 3.3-4.3 V vs. Li/Li + in the room temperature electrolyte of 1M LiPF 6 /EC:DEC. Surface characterization using ex situ X-ray photoelectron spectroscopy reveals that surface Mn 4+ -abundance induces the formation of a plenty of new surface components and the passivation of cathode surface before being reduced to Mn 3+ to Mn 2+ , leading to capacity retention 90% with discharge capacities 102-90 mAh/g over 50 cycles. FTIR spectroscopic analysis results and scanning electron microscopic imaging ensure that the Mn 4+ -abundant surface is better passivated by solid electrolyte interphase (SEI) layer that is composed of mixed organic and inorganic compounds, resulting in somewhat preserved particle morphology. On the contrary, the cathodes with equal amounted surface Mn 4+ /Mn 3+ and Mn 3+ -abundant surface are readily subjected to severe interfacial reaction and particle morphology change accompanied by inferior surface coverage by surface species, which are responsible for a rapid capacity fade. The data contribute to a basic understanding of importance of surface control and its impact on the cycling performance of spinel-based cathode materials for lithium-ion batteries.

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Spray pyrolysis was applied to prepare Eu 2+ -doped M 3 MgSi 2 O 8 (M = Ca, Sr, Ba) phosphor for near-ultraviolet (NUV) light-emitting diode (LED) application. The luminescence characteristics were optimized by a combinatorial screening method combined with spray pyrolysis for the Ca-Sr-Ba ternary system. The first composition library was obtained by measuring the emission spectrum under 395 NUV excitation. In this first screening, the highest luminescence intensity was obtained at (Ca 0.9 Sr 1.2 Ba 0.9 )MgSi 2 O 8 :Eu 2+ , which had 48% enhancement in the integrated emission intensity compared with Sr 3 MgSi 2 O 8 :Eu 2+ phosphor. The second screening was conducted for the potential compositions in the first library. As a result, the optimized composition was (Ca 0.9 Sr 0.45 Ba 1.65 )MgSi 2 O 8 :Eu 2+ , which showed 170% enhancement in the integrated emission intensity compared with Sr 3 MgSi 2 O 8 :Eu 2+ phosphor.

Spray pyrolysis was used to prepare high luminous Y 2 O 3 :Eu phosphor particles with spherical shape. In this work, we introduce a simple but effective preparation strategy for enhancing the photoluminescence intensity of Y 2 O 3 :Eu particles. The key idea was the solution technique used to densify the porous structure and simultaneously enhance the crystallinity of Y 2 O 3 :Eu particles. When the yttrium nitrate solution was modified using the organic additive, the nonhollow particles could be obtained but they were very porous and the luminescence intensity was not improved. To solve this drawback, we used a drying control chemical additive (DCCA) as a secondary additive. It was found that the surface area was greatly reduced and the crystallite size was increased by the use of DCCA. As a result, the densified Y 2 O 2 :Eu particles showed great improvement in the photoluminescence intensity.