The Effects of C-Rate on the Discharge Capacities of LiNi1-yMyO2 (M=Ni, Ga, Al and/or Ti) Cathodes

( Myoung Youp Song ),( Chan Kee Park ),( Soon Do Yoon ),( Hye Ryoung Park ),( Daniel R. Mumm ) 대한금속재료학회 ( 구 대한금속학회 ) 2008 ELECTRONIC MATERIALS LETTERS Vol.4 No.4

LiNi1-yMyO2 specimens with compositions of LiNiO2, LiNi0.975Ga0.025O2, LiNi0.975Al0.025O2, LiNi0.995Ti0.005O2 and LiNi0.990Al0.005Ti0.005O2 were synthesized by wet milling and solid-state reaction method. All the synthesized samples possessed the α-NaFeO2 structure of the rhombohedral system (space group; R3m) with no evidence of any impurities. Among the LiNiO2 cathodes prepared with the weight ratios of LiNiO2:acetylene black: binder = 85:10:5, 85:12:3 and 90:7:3, the cathode with the weight ratio of 85:10:5 had the best cycling performance, with a discharge capacity degradation rate of 1.06 mAh/g/cycle and a discharge capacity at n=20 of 143.5 mAh/g. Among all the samples, LiNi0.990Al0.005Ti0.005O2 had the highest first discharge capacities at 0.1 C, 0.2 C and 0.5 C rates. That sample had the smallest R-factor value, indicating that it had the lowest degree of cation mixing. Among all the samples, LiNi0.975Al0.025O2 showed the lowest rate of decrease in the first discharge capacity with C rate. The first discharge capacities at 0.1 C, 0.2 C and 0.5 C rates were 170.5 mAh/g, 155.0 mAh/g and 124.2 mAh/g, respectively.

Synthesis of LiCo1/3Ni1/3Mn1/3O2 by a Simple Combustion Method and Electrochemical Properties

( Hun Uk Kim ),( Daniel R. Mumm ),( Hye Ryoung Park ),( Myoung Youp Song ) 대한금속재료학회 ( 구 대한금속학회 ) 2010 ELECTRONIC MATERIALS LETTERS Vol.6 No.3

LiCo1/3Ni1/3Mn1/3O2 was synthesized by a simple combustion method and its electrochemical properties were examined. The XRD patterns of the samples calcined at 900°C and 1,000°C showed sharp peaks for an R3m structure with clear splitting between the (006) and (102) peaks and between the (108) and (110) peaks. The size of the particles increased as the calcination temperature rose. The samples after combustion, and after combustion and calcinations, were analyzed by FT-IR. The samples calcined at 900°C and 1,000°C had similar a and c values, and similar first discharge capacities (176 mAh/g and 177 mAh/g, respectively, at 20 mA/g), but the sample calcined at 900°C had better cycling performance. The sample calcined at 900°C had smaller particles and more uniform particle sizes than the sample calcined at 1,000°C.

Variations in the Electrochemical Properties of Metallic Elements-Substituted LiNiO2 Cathodes with Preparation and Cathode Fabrication Conditions

송명엽,Chan Kee Park,박혜령,Daniel R. Mumm 대한금속·재료학회 2012 ELECTRONIC MATERIALS LETTERS Vol.8 No.1

Variations in the electrochemical properties of LiNiO2 with preparation and cathode fabrication conditions were studied. The LiNiO2 cathode fabricated with a weight ratio of LiNiO2 : acetylene black : binder = 85:10:5,after wet Spex milling for 60 min and drying in a shaking incubator showed the best cycling performance,with a discharge capacity degradation rate of 1.06 mAh/g/cycle between the first cycle and the 20th cycle and a discharge capacity at n = 20 of 143.5 mAh/g at 0.1 C rate. LiNi1-yMyO2 cathodes with active material compositions of LiNiO2, LiNi0.975Ga0.025O2, LiNi0.975Al0.025O2, LiNi0.995Ti0.005O2, and LiNi0.990Al0.005Ti0.005O2 were fabricated under these conditions. Among all the samples, LiNi0.990Al0.005Ti0.005O2 had the highest first discharge capacities at 0.1 C rate (196.3 mAh/g) and 0.5 C rate (147.3 mAh/g). This sample had the smallest R-factor value, indicating that it had the lowest degree of cation mixing. At 0.1 C rate LiNiO2 had the best cycling performance. At 0.5 C rate LiNi0.975Al0.025O2 had the best cycling performance and its discharge capacity deg-radation rate was 1.28 mAh/g/cycle between the first cycle and the 20th cycle.

Variation of Microstructure and Area Specific Resistance with Surface Roughness of a Ferritic Stainless Steel after Long-Term Oxygen Exposure

( Daniel R. Mumm ),( Myoung Youp Song ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.4

One of the candidates for metallic interconnects of solid oxide fuel cells is a ferritic stainless steel, Crofer 22 APU. By grinding with different grit SiC grinding paper, Crofer 22 APU specimens with various surface roughness were prepared. The specimens were then thermally cycled by heating them to 1,073 K at a rate of 10 K min-1, holding at 1,073 K for 25 h, and cooling to 298 K at a rate of 10 K min-1. Examinations of the resulting microstructures, measurements of the area specific resistances (ASRs), and analyses of the atomic percentages of elements via energy dispersive X-ray (EDX) spectroscopy were performed. The particle size decreased as the grit number of the grinding paper used to grind the sample surfaces increased. A polished sample exhibited the smallest particle size. Plots of ln (ASR/ T) vs. 1/ T for the samples ground with grit 80 and grit 400 and the polished sample after 40 thermal cycles exhibited good linearity. At the same measuring temperature, the ASR increased as the surface of the sample became rougher. This suggests that the polished Crofer 22 APU is better than those with rougher surfaces for application as interconnect of SOFC. (Received May 9, 2014)

Effects of Milling and Hydriding-Dehydriding Cycling on the Hydriding-Storage Behaviors of a Magnesium-Nickel-Tantalum Fluoride Alloy

( Daniel R. Mumm ),( Young Jun Kwak ),( Hye Ryoung Park ),( Myoung Youp Song ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.12

In this study, Ni and TaF5 were picked as additives to enhance the hydriding and dehydriding rates of Mg. A sample with a composition of 80 wt% Mg+14 wt% Ni+6 wt% TaF5 (named Mg-14Ni-6TaF5) was prepared by reactive mechanical grinding. Its hydriding and dehydriding properties were then examined and the effects of milling and hydriding-dehydriding cycling were investigated. To activate the prepared sample, two hydriding-dehydriding cycles were required at 573 K and 593 K. At the second cycle, the sample absorbed 5.74 wt% H for 60 min under 12 bar H2 at 573 K. At 623 K, the activated Mg-14Ni-6TaF5 absorbed 2.53 wt% H for 2.5 min, 4.20 wt% H for 10 min, and 5.31wt% H for 60 min under 12 bar H2, and desorbed 2.01 wt% H for 2.5 min, 4.76 wt% H for 15 min, and 4.83 wt% H for 60 min under 1.0 bar H2. The initial hydriding rate increased as the temperature increased from 423 K to 573 K (due to the predominance of the acceleration of the thermally activated process) and then decreased from 573 K to 623 K due to the predominance of the decrease in the driving force for the hydriding reactionunder 12 bar H2.

Cycling Behavior of Transition Metals and Sodium Alanate-Added MgH2 Kept in a Glove Box

( Daniel R. Mumm ),( Seong Ho Lee ),( Myoung Youp Song ) 대한금속재료학회(구 대한금속학회) 2015 대한금속·재료학회지 Vol.53 No.8

Used was a sample with a composition of 86 wt% MgH2+10 wt% Ni+2 wt% NaAlH4+2 wt% Ti prepared by milling under H2 (reactive mechanical grinding) and then kept in a glove box for two months. The variations of its hydrogen-storage characteristics with hydriding-dehydriding cycling were investigated and compared with those of a sample just after reactive mechanical grinding. The hydriding-dehydriding cycling was performed between hydriding (at 593 K under 12 bar H2) and dehydriding (at 623 K in vacuum). The quantities of hydrogen absorbed for 2.5, 5, 10, and 60 min increased rapidly as the number of cycles, n, increased from n=1 to n=3. This is believed to be due to the predominance of the removal of the adsorbed gases and the destruction of oxide layers among the effects of hydriding-dehydriding cycling. From n=3 to n=15, Ha (2.5 min) and Ha (5 min) increased slowly and Ha (10 min) and Ha (60 min) decreased slowly. (Received July 15, 2014)

Synthesis of LiCo⅓Ni⅓Mn⅓O₂ by a Simple Combustion Method and Electrochemical Properties

김훈욱,Daniel R. Mumm,박혜령,송명엽 대한금속·재료학회 2010 ELECTRONIC MATERIALS LETTERS Vol.6 No.3

LiCo⅓Ni⅓Mn⅓O₂ was synthesized by a simple combustion method and its electrochemical properties were examined. The XRD patterns of the samples calcined at 900°C and 1,000°C showed sharp peaks for an R m structure with clear splitting between the (006) and (102) peaks and between the (108) and (110) peaks. The size of the particles increased as the calcination temperature rose. The samples after combustion, and after combustion and calcinations, were analyzed by FT-IR. The samples calcined at 900°C and 1,000°C had similar a and c values, and similar first discharge capacities (176 and 177 mAh/g, respectively, at 20mA/g), but the sample calcined at 900°C had better cycling performance. The sample calcined at 900°C had smaller particles and more uniform particle sizes than the sample calcined at 1,000°C.

Variation with Thermal Cycling in Microstructure and Area Specific Resistance of a Ferritic Stainless Steel Having Rough Surfaces

송명엽,Daniel R. Mumm,Jiunn Song 대한금속·재료학회 2013 ELECTRONIC MATERIALS LETTERS Vol.9 No.2

Crofer22 APU specimens were prepared by grinding with grit 120 and 400 SiC grinding papers, and were then thermally cycled. The variation in oxidation behavior with thermal cycling was then investigated. Observation of microstructures, measurement of area-specific resistance (ASR), analysis of the atomic percentages of the elements by EDX, and XRD analysis were performed. XRD patterns showed that the (Cr, Mn)3O4spinel phase grew on the surface of the Crofer22 APU samples ground using grit 120. For the samples ground with grit 400, ASR increased as the number of thermal cycles (n) increased. Plots of ln (ASR/T)vs. 1/T for the samples ground with grit 400 after n = 4, 20, and 40 exhibited good linearity, and the apparent activation energies were between 73.4 kJ/mole and 82.5 kJ/mole.

Cycling Performance of LiNi1-y M yO2 (M=Ni, Ga, Al and/or Ti) Synthesized by Wet Milling and Solid-State Method

송명엽,Daniel R. Mumm,Chan Kee Park,박혜령 대한금속·재료학회 2012 METALS AND MATERIALS International Vol.18 No.3

The LiNi1-y MyO2 specimens with compositions of LiNiO2, LiNi0.975Ga0.025O2, LiNi0.975Al0.025O2, LiNi0.995Ti0.005O2, and LiNi0.990Al0.005Ti0.005O2 were synthesized by wet milling and a solid-state reaction method. Among all the specimens, LiNi0.990Al0.005Ti0.005O2 has the largest first discharge capacity of 196.3 mAh/g at a rate of 0.1 C. At n=50, LiNiO2 has the largest discharge capacity of 126.7 mAh/g. LiNiO2 has the best cycling performance, its degradation rate of discharge capacity being 0.73 mAh/g/cycle. LiNi0.975Al0.025O2shows the lowest decrease rate of the first discharge capacity with C rate. An equation describing the vari-ation of the discharge capacity with the number of charge-discharge cycles, n, is obtained. The William-son-Hall method is applied to calculate the crystallite size and the strain of the samples before and after charge-discharge cycling.

Phase transitions during charging and discharging and electrochemical performances of LiNiO2 doped with gallium

권성남,Daniel R. Mumm,박혜령,송명엽 한양대학교 세라믹연구소 2016 Journal of Ceramic Processing Research Vol.17 No.6

LiNiO2 and LiNi0.975Ga0.025O2 samples were synthesized by the combustion method. The starting materials, in desiredproportions, were dissolved in distilled water and mixed with urea by a magnetic stirrer. The mixture was calcined at 750 oCfor 36 h in an O2 stream after preheating at 400 oC for 30 min in air. The phase transitions during charging and dischargingand electrochemical performances of the synthesized samples were then investigated. The dQ/|dV| vs. voltage curves, whereQ is the charge capacity and V is the voltage, for the charge and discharge of LiNiO2 and LiNi0.975Ga0.025O2 at n (number ofcycles) = 1 and n = 2 exhibit four peaks, respectively, indicating four phase transitions from a hexagonal structure (H1) to amonoclinic structure (M), from the M to a second hexagonal structure (H2), from the H2 to H2 and a third hexagonal structure(H3), and from the H2 + H3 to H3 or vice versa. LiNi0.975Ga0.025O2 had a larger first discharge capacity of 166 mA h/g thanLiNiO2. It showed a cycling performance, which is not bad, with a discharge capacity degradation rate of 0.76 mA h/g/cyclefrom n = 1 to n = 50. LiNiO2 had a smaller first discharge capacity of 158 mA h/g but a better cycling performance thanLiNi0.975Ga0.025O2 with a discharge capacity degradation rate of 0.45 mA h/g/cycle from n = 1 to n = 50. The electrochemicalproperties of LiNi0.975Ga0.025O2 prepared by the combustion method were compared with those of the sample prepared by thesolid-state reaction method.