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유연 리튬 폴리머 이차전지의 기계적 변형에 따른 성능 및 안전성 평가
조장훈(Jang-Hun Jo),김진영(Jin-Yeong Kim),유기태(Ki-Tae You),엄정원(Joung-Won Eom),김유진(Yu-Jin Kim),김동오(Dong-O Kim),박민혁(Min-Hyeok Park),박재원(Jae-Won Park),이명훈(Myeong-Hun Lee),변재원(Jai-Won Byeon) 한국신뢰성학회 2021 신뢰성응용연구 Vol.21 No.3
Purpose: Flexible lithium-ion batteries have been used as energy sources for wearable and flexible devices. However, their reliability in mechanical stress environments must be guaranteed for them to be stably used in these applications. In this study, the effect of mechanical fatigue on the performance and safety of a lithium polymer battery, which is a flexible lithium-ion battery, was investigated. Methods: Mechanical fatigue tests were conducted under bending, torsion, and wrinkling (i.e., a combination of bending and torsion) modes at various fatigue rates and strains. The capacity degradation of these fatigued flexible lithium-ion batteries was evaluated using the charge–discharge test. Their safety was assessed using various environmental and electrical misuse tests in accordance with existing standards. Results: The capacity degradation of all fatigued batteries was greater than that of the undeformed battery. In particular, the torsion and wrinkling stress had a greater effect on capacity degradation. The environmental and electrical misuse tests revealed that leakage, explosion, and ignition phenomena were not caused by mechanical fatigue. Conclusion: Mechanical fatigue stress can be concluded to be the main factor affecting the performance degradation of flexible lithium-ion batteries. Furthermore, further studies are required to determine the root causes of this significant performance degradation.
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정밀금형용 SKD61 강의 복합표면처리에 의한 표면신뢰성 향상
박민혁(Min-Hyeok Park),김동오(Dong-O Kim),엄정원(Joung-Won Eom),김진영(Jin-Yeong Kim),김유진(Yu-Jin Kim),김은우(Eun-Woo Kim),양원존(Won-Jon Yang),심동하(Dongha Shim),변재원(Jai-Won Byeon) 한국신뢰성학회 2022 신뢰성응용연구 Vol.22 No.2
Purpose: The lifespan of a die-casting steel mold depends on its surface hardness and wear resistance. Gas nitriding treatments for forming surface hardening layers have been widely applied to fabricate reliable die-casting molds. In the present study, we propose a complex surface treatment consisting of a micro-shot peening process and a sulfo-nitriding treatment to improve the surface hardness of SKD61 mold steel. Methods: The cross-sectional microstructure of the complex surface-treated SKD61 mold steel was observed using an optical microscope and a scanning electron microscope. The phase of the surface hardening layer was analyzed using an X-ray diffractometer. The micro-hardness and residual stress of the complex surface-treated SKD61 mold steel were evaluated as well. Results: The surface hardening layer consisted of the top-most compound layer and a diffusion layer. The micro-shot peening pretreatment increased the thickness of the compound layer. The general nitriding (GN) treatment led to the formation of the FexN compound layer, while the sulfo-nitriding (SN) treatment led to the formation of the FexN and FeS composite compound layer, which was thicker than the compound layer of the GN specimen. The hardness of GN and SN hardening layers improved by 125% and 135%, respectively, relative to that of the as-received SKD61 mold steel with a hardness of 450 HV. Conclusion: The SN treatment formed a reliable hardening layer with superior hardness than the GN treatment. Furthermore, the thicker sulfo-nitride compound layer produced by the SN treatment can further improve the lifespan of SKD61 steel molds.
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