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Seunghak Lee,Eunjeong Seok,Haeun Kang,Dohyub Park,Minjun Kim,Dayoung Kam,Minsu Choi,Hyung-Seok Kim,Wonchang Choi 한국공업화학회 2023 Journal of Industrial and Engineering Chemistry Vol.126 No.-
Molybdenum sulfide (MoS2) has a 2-D open framework structure and provide delocalized sodium ion diffusionand intercalation within the MoS2 structure. The structure exhibits a high theoretical capacity dueto its wide interlayer spacing (6.2 Å). Therefore, MoS2 has recently been used as an anode material insodium-ion batteries (SIBs). However, it exhibits inferior cycle performance and rate characteristicsdue to its low electronic conductivity and volume change during continuous operation, which restrictits use as an anode material in SIBs. Herein, a MoS2 surface modified with hydrophobic reduced grapheneoxide (rGO-MoS2) was dispersed in silicone oil, which is the starting material for silicon oxycarbide(SiOC), and subsequently used to prepare a MoS2 composite with a SiOC coating-layer surface modifiedwith rGO (rGO-MoS2@SiOC) via single pyrolysis reaction. rGO expands the interlayer spacing of MoS2,improving the electronic conductivity, and the SiOC layer capable of accommodating the volume expansionof MoS2 supports the insufficient buffer layer provided by rGO alone to form a conductive pathwaythat suppressed any adverse reactions at the electrode and electrolyte interface. The rGO-MoS2@SiOCcomposite exhibits a high reversible capacity of 532.5 mAh g1, no capacity fading even after 100 cycles,and superior rate characteristics.
Seunghak Han,Ji Hyung Kim,Yoon Seok Chae,Huu Luong Quach,Yong Soo Yoon,Ho Min Kim 한국초전도저온학회 2021 한국초전도저온공학회논문지 Vol.23 No.4
The low normal zone propagation velocity (NZPV) of high-temperature superconducting (HTS) tape leads to a quench protectionproblem in HTS magnet applications. To overcome this limitation, various studies were conducted on HTS coils without turn-toturn insulation (NI coils) that can achieve self-protection. On the other hand, NI coils have some disadvantages such as slowcharging and discharging time. Previously, the HTS coils with turn-to-turn insulation (INS coils) were operated in power supply(PS) driven mode, which requires physical contact with the external PS at room-temperature, not in persistent current mode. Whena quench occurs in INS coils, the low NZPV delays quench detection and protection, thereby damaging the coils. However, therotary HTS flux pump supplies the DC voltage to the superconducting circuit with INS coils in a non-contact manner, which causesthe INS coils to operate in a persistent current mode, while enabling quench protection. In this paper, a new protection characteristicof HTS coils is investigated with INS coils charging through the rotary HTS flux pump. To experimentally verify the quenchprotection characteristic of the INS coil, we investigated the current magnitude of the superconducting circuit through a quench,which was intentionally generated by thermal disturbances in the INS coil under charging or steady state. Our results confirmedthe protection characteristic of INS coils using a rotary HTS flux pump.
Seunghak Han,Ji Hyung Kim,Yoon Seok Chae,Huu Luong Quach,Yong Soo Yoon,Ho Min Kim 한국초전도저온공학회 2021 초전도와 저온공학 Vol.23 No.4
The low normal zone propagation velocity (NZPV) of high-temperature superconducting (HTS) tape leads to a quench protection problem in HTS magnet applications. To overcome this limitation, various studies were conducted on HTS coils without turn-toturn insulation (NI coils) that can achieve self-protection. On the other hand, NI coils have some disadvantages such as slow charging and discharging time. Previously, the HTS coils with turn-to-turn insulation (INS coils) were operated in power supply (PS) driven mode, which requires physical contact with the external PS at room-temperature, not in persistent current mode. When a quench occurs in INS coils, the low NZPV delays quench detection and protection, thereby damaging the coils. However, the rotary HTS flux pump supplies the DC voltage to the superconducting circuit with INS coils in a non-contact manner, which causes the INS coils to operate in a persistent current mode, while enabling quench protection. In this paper, a new protection characteristic of HTS coils is investigated with INS coils charging through the rotary HTS flux pump. To experimentally verify the quench protection characteristic of the INS coil, we investigated the current magnitude of the superconducting circuit through a quench, which was intentionally generated by thermal disturbances in the INS coil under charging or steady state. Our results confirmed the protection characteristic of INS coils using a rotary HTS flux pump.
Han, Seunghak,Nam, Seokho,Lee, Jeyull,Song, Seunghyun,Jeon, Haeryong,Baek, Geonwoo,Kang, Hyoungku,Ko, Tae Kuk The Korea Institute of Applied Superconductivity a 2017 한국초전도저온공학회논문지 Vol.19 No.3
Current lead is a device that connects the power supply and superconducting magnets. High temperature superconductor (HTS) has lower thermal conductivity and higher current density than normal metal. For these reasons, the heat load can be reduced by replacing the normal metal of the current lead with the HTS. Conventional HTS current lead has same cross-sectional area in the axial direction. However, this is over-designed at the cold-end (4.2 K) in terms of current. The heat load can be reduced by reducing this part because the heat load is proportional to the cross-sectional area. Therefore, in this paper, heat load was calculated from the heat diffusion equation of HTS current leads with uniform and non-uniform cross-sectional areas. The cross-sectional area of the warm-end (65K) is designed considering burnout time when cooling system failure occurs. In cold-end, Joule heat and heat load due to current conduction occurs at the same time, so the cross-sectional area where the sum of the two heat is minimum is obtained. As a result of simulation, current leads for KSTAR TF coils with uniform and non-uniform cross-sectional areas were designed, and it was confirmed that the non-uniform cross-sectional areas could further reduce the heat load.