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Choi, Ji Ung,Park, Yun Ji,Jo, Jae Hyeon,Kuo, Liang-Yin,Kaghazchi, Payam,Myung, Seung-Taek American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.48
<P>Layered Na<SUB>2/3</SUB>MnO<SUB>2</SUB> suffers from capacity loss due to Jahn-Teller (J-T) distortion by Mn<SUP>3+</SUP> ions. Herein, density functional theory calculations suggest Na<SUB>2/3</SUB>[Fe<SUB><I>x</I></SUB>Mn<SUB>1-<I>x</I></SUB>]O<SUB>2</SUB> suppresses the J-T effect. The Fe substitution results in a decreased oxygen-metal-oxygen length, leading to decreases in the <I>b</I> and <I>c</I> lattice parameters but an increase in the <I>a</I> lattice constant. As a result, the capacity retention and rate capability are enhanced with an additional redox pair associated with Fe<SUP>4+/3+</SUP>. Finally, the thermal properties are improved, with the Fe substitution delaying the exothermic reaction and reducing exothermic heat.</P> [FIG OMISSION]</BR>
Impact of Na2MoO4 nanolayers autogenously formed on tunnel-type Na0.44MnO2
Choi, Ji Ung,Jo, Jae Hyeon,Jo, Chang-Heum,Cho, Min Kyoung,Park, Yun Ji,Jin, Yongcheng,Yashiro, Hitoshi,Myung, Seung-Taek The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.22
<P>We propose the coating of tunnel-type Na0.44MnO2 cathode materials with multi-functional Na2MoO4 nanolayers for use in rechargeable sodium batteries. Electro-conducting Na2MoO4 nanolayers (electrical conductivity of ∼10<SUP>3</SUP> S cm<SUP>−1</SUP>) are autogenously formed on the surface of Na0.44MnO2 particles through the reaction of (NH4)2MoO4 with surface sodium residues <I>via</I> melt impregnation at 350 °C. The Na2MoO4-modified Na0.44MnO2 electrode delivers discharge capacities of ∼120.4 mA h (g-oxide)<SUP>−1</SUP> at 0.1C (12 mA g<SUP>−1</SUP>) and 79.7 mA h g<SUP>−1</SUP> at 50C (6 A g<SUP>−1</SUP>). Moreover, with continuous cycling at a rate of 60C (7.2 A g<SUP>−1</SUP>), the Na2MoO4-coated Na0.44MnO2 electrode is able to retain a capacity of approximately 56 mA h g<SUP>−1</SUP> without notable capacity fading for 1000 cycles. This achievement is attributed to the presence of Na2MoO4 on the active materials, which facilitates electron transfer during electrochemical reaction in Na cells. More interestingly, Na2MnO4 undergoes two-step HF scavenging to finally form MoO3−xF2x layers <I>via</I> an intermediate of H2MoO4 (MoO3·H2O) layers. The surface layers protect the active materials from HF attack in the electrolyte. These multi-functional effects of the Na2MoO4 and MoO3−xF2x surface layers are responsible for the long-term cycle stability of the cathode material for ultra-high-rate sodium storage applications.</P>
Identification of quantitative trait loci related to grain filling under low temperature condition
Jong-Min Jeong,Ung-Jo Hyun,Ji-Ung Jeung,Kyung-Ho Kang,Young-Chan Cho,Bo-Kyeong Kim 한국육종학회 2015 한국육종학회 심포지엄 Vol.2015 No.07
Low temperature is a major abiotic stress that adversely affects rice production in rice cultivation regions of the world. Low temperature during the rice growing season, can inhibit growth and development at any development stage, from germination to grain filling. Among the rice growth stage, reproductive stage was known as the most sensitive to low temperature, causing sterile grain and lead yield loss. However, low temperature during the grain filling stage also, may cause delay and incomplete grain maturation. In this study QTL analysis were performed to identify the QTLs associated with percent of grain filling under low temperature condition during the grain filling stage. A 139 RIL derived from a cross between ‘Milyang23’ (Tong-il, cold susceptible) and ‘Gihobyeo’(Japonica, cold tolerance) were exposed to air and water of 17℃ at the same time for 14 days during the grain filling stage. One significant QTL associated to percent of grain filling was detected on chromosome 7. This QTL could explain 14.7% of the phenotypic variance for percent of grain filling. We have the plan to confirm the detected QTL through further study.
Rocksalt-type metal sulfide anodes for high-rate sodium storage
Jo, Chang-Heum,Choi, Ji Ung,Myung, Seung-Taek The Royal Society of Chemistry 2018 Journal of Materials Chemistry A Vol.6 No.16
<P>The low electrical conductivity of α-MnS generally impedes its use as an electrode material for sodium-ion batteries. However, in this study, an unprecedentedly high capacity and long-term cyclability were achieved for an α-MnS electrode at moderate and high rates by introducing electro-conductive carbon surfaces. A capacity of 302 mA h g<SUP>−1</SUP> was delivered in the first cycle with 85% capacity retention after 200 cycles at 100 mA g<SUP>−1</SUP>. Furthermore, the cycling performance at 10C (6.1 A g<SUP>−1</SUP>) demonstrated the feasibility of high-rate sodium storage using this anode, with 78% retention of the initial capacity after 200 cycles. This performance was reproduced in a NaCrO2/α-MnS full cell as well. X-ray diffraction, X-ray photoelectron spectroscopy, and time-of-flight secondary-ion mass spectroscopy were used to unveil the reaction mechanism, and the results provided possible explanations for the good electrode performance and rapid sodium storage capabilities.</P>
Jo, Jae Hyeon,Choi, Ji Ung,Park, Yun Ji,Zhu, Jiefang,Yashiro, Hitoshi,Myung, Seung-Taek American Chemical Society 2019 ACS APPLIED MATERIALS & INTERFACES Vol.11 No.6
<P>Sacrificing sodium supply sources is needed for sodium-deficient cathode materials to achieve commercialization of sodium-ion full cells using sodium-ion intercalation anode materials. Herein, the potential of ethylenediaminetetraacetic acid tetrasodium salt (EDTA-4Na) as a sacrificing sodium supply source was investigated by intimately blending it with sodium-deficient P2-type Na<SUB>0.67</SUB>[Al<SUB>0.05</SUB>Mn<SUB>0.95</SUB>]O<SUB>2</SUB>. The EDTA-4Na/Na<SUB>0.67</SUB>[Al<SUB>0.05</SUB>Mn<SUB>0.95</SUB>]O<SUB>2</SUB> composite electrode unexpectedly exhibited an improved charge capacity of 177 mA h (g-oxide)<SUP>−1</SUP> compared with the low charge capacity of 83 mA h (g-oxide)<SUP>−1</SUP> for bare Na<SUB>0.67</SUB>[Al<SUB>0.05</SUB>Mn<SUB>0.95</SUB>]O<SUB>2</SUB>. The reversible capacity of an EDTA-4Na/Na<SUB>0.67</SUB>[Al<SUB>0.05</SUB>Mn<SUB>0.95</SUB>]O<SUB>2</SUB>//hard carbon full-cell system increased to 152 mA h (g-oxide)<SUP>−1</SUP> at the first discharge with a Coulombic efficiency of 89%, whereas the Na<SUB>0.67</SUB>[Al<SUB>0.05</SUB>Mn<SUB>0.95</SUB>]O<SUB>2</SUB> without EDTA-4Na delivered a discharge capacity 51 mA h g<SUP>-1</SUP> because of the small charge capacity. The EDTA-4Na sacrificed itself to generate Na<SUP>+</SUP> ions via oxidative decomposition by releasing four sodium ions and producing C<SUB>3</SUB>N as a decomposition resultant on charge. It is thought that the slight increase in discharge capacity is associated with the electroconducting nature of the C<SUB>3</SUB>N deposits formed on the surface of the Na<SUB>0.67</SUB>[Al<SUB>0.05</SUB>Mn<SUB>0.95</SUB>]O<SUB>2</SUB> electrode. We elucidated the reaction mechanism and sacrificial activity of EDTA-4Na, and our findings suggest that the addition of EDTA-4Na is beneficial as an additional source of Na<SUP>+</SUP> ions that contribute to the charge capacity.</P> [FIG OMISSION]</BR>
Controllable charge capacity using a black additive for high-energy-density sodium-ion batteries
Jo, Chang-Heum,Choi, Ji Ung,Yashiro, Hitoshi,Myung, Seung-Taek The Royal Society of Chemistry 2019 Journal of Materials Chemistry A Vol.7 No.8
<P>Sodium-deficient P2 or P′2 type layered materials are known to deliver high capacity with acceptable capacity retention. However, the initial charge capacity is substantially lower than the discharge capacity because of the insufficient amount of sodium in their crystal structure, hindering practical application of these materials as cathodes in sodium-ion batteries (SIBs). This limitation can be overcome by introducing a sacrificial salt additive, which participates in the electrochemical oxidation reaction by releasing enough sodium ions to compensate for the insufficient sodium content in the cathode material. Herein, the sacrificial salt NaNO2 was blended with a high-capacity orthorhombic P′2 type Na2/3[Co0.05Mn0.95]O2 cathode material, increasing the initial charge capacity from 154 to 210 mA h g<SUP>−1</SUP>. During electrochemical oxidation, the NaNO2 was oxidatively decomposed by the following reaction: NaNO2 → NO2 + Na<SUP>+</SUP> + e<SUP>−</SUP>, where NO2 is an oxidizer that enables full desodiation to Na0[Co0.05Mn0.95]O2. The first coulombic efficiency of Na2/3[Co0.05Mn0.95]O2 was improved from 1.38 to 0.98 by virtue of the sacrificing and oxidizing roles of NaNO2. These findings demonstrate that the introduction of NaNO2 as an additional sodium source in cathodes can open new opportunities for the adoption of sodium-deficient cathode materials in practical SIBs.</P>
이지영(Ji Young Lee),김철환(Chul Hwan Kim),김은혜(Eun Hea Kim),박태웅(Tae Ung Park),조해민(Hae Min Jo) 한국펄프·종이공학회 2016 펄프.종이技術 Vol.48 No.6
Oil palm byproducts, such as EFB (empty fruit bunches), OPF (oil palm fronds), and OPT (oil palm trunks), are generated during the production of palm oil but are discarded as waste for lack of an end use. Therefore, new industrial uses for oil palm byproducts should be developed. In this study, we fabricated novel organic fillers using OPT and investigated their effects on paperboard bulk and the energy required for paperboard drying. Handsheets containing OPT fillers were prepared and their physical properties were measured. The effect of the OPT fillers on the drying energy was determined by measuring the moisture content of these handsheets and by calculating the reduction in the required drying energy. The OPT fillers increased the bulk and the decreased the strength of the handsheets. The required drying energy was reduced by adding OPT fillers to the handsheets. Therefore, OPT could be used to manufacture organic fillers for use in the paperboard industry.
펄프 종류와 기계적 처리조건에 의한 셀룰로오스 나노섬유의 특성 및 탈수성 평가
이지영(Ji Young Lee),박태웅(Tae Ung Park),김은혜(Eun Hea Kim),조해민(Hae Min Jo),김철환(Chul Hwan Kim),김태영(Tae Young Kim),허용대(Yong Dae Heo),이종현(Jong Hyun Lee),김준규(Jun Kyu Kim) 한국펄프·종이공학회 2017 펄프.종이技術 Vol.49 No.3
Many studies have shown that cellulose nanofibrils (CNFs) are powerful in improving paper strength. However, CNFs are usually manufactured as a slurry and their drainage is critical to their internal addition in the papermaking process. Therefore, the production conditions of CNF for internal addition must be established in order for its use to spread in the paper industry. In this study, various CNFs were made in a laboratory according to the functions of pulp type, freeness, and the pass number of grinding. The viscosity, average particle size, zeta-potential, and the fiber width of the CNFs were measured. After the physical properties of the CNFs were measured, the drainage rates of the CNF slurries were determined through the use of a pressure dehydration tester. An increased pass number of grinding simultaneously increased the viscosity of the CNFs and decreased their particle size and fiber widths. However, the relationship between the pass number and the zeta-potential of the CNFs was not observed. As the pass number of grinding increased, the drainage rates of the CNFs decreased linearly. Specifically, the decrease in the drainage of the CNFs made from SwBKP was lower than those made from HwBKP. Therefore, the pulp type and the pass number of the CNFs should be controlled for the purpose of their internal addition in the papermaking process.