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Choi, Sinho,Kim, Jieun,Choi, Nam-Soon,Kim, Min Gyu,Park, Soojin American Chemical Society 2015 ACS NANO Vol.9 No.2
<P>Nanostructured germanium is a promising material for high-performance energy storage devices. However, synthesizing it in a cost-effective and simple manner on a large scale remains a significant challenge. Herein, we report a redox-transmetalation reaction-based route for the large-scale synthesis of mesoporous germanium particles from germanium oxide at temperatures of 420–600 °C. We could confirm that a unique redox-transmetalation reaction occurs between Zn<SUP>0</SUP> and Ge<SUP>4+</SUP> at approximately 420 °C using temperature-dependent <I>in situ</I> X-ray absorption fine structure analysis. This reaction has several advantages, which include (i) the successful synthesis of germanium particles at a low temperature (∼450 °C), (ii) the accommodation of large volume changes, owing to the mesoporous structure of the germanium particles, and (iii) the ability to synthesize the particles in a cost-effective and scalable manner, as inexpensive metal oxides are used as the starting materials. The optimized mesoporous germanium anode exhibits a reversible capacity of ∼1400 mA h g<SUP>–1</SUP> after 300 cycles at a rate of 0.5 C (corresponding to the capacity retention of 99.5%), as well as stable cycling in a full cell containing a LiCoO<SUB>2</SUB> cathode with a high energy density (charge capacity = 286.62 mA h cm<SUP>–3</SUP>).</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/ancac3/2015/ancac3.2015.9.issue-2/acsnano.5b00389/production/images/medium/nn-2015-00389h_0008.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nn5b00389'>ACS Electronic Supporting Info</A></P>
Choi, Sinho,Bok, Taesoo,Ryu, Jaegeon,Lee, Jung-In,Cho, Jaephil,Park, Soojin Elsevier 2015 Nano energy Vol.12 No.-
<P><B>Abstract</B></P> <P>We revisit the metallothermic reduction process to synthesize shape-preserving macro-/nanoporous Si particles via aluminothermic and subsequent magnesiotheric reaction of porous silica particles. This process enables us to control the specific capacity and volume expansion of shape-preserving porous Si-based anodes. Two step metallothermic reactions have several advantages including a successful synthesis of shape-preserving Si particles, tunable specific capacity of as-synthesized Si anode, accommodation of a large volume change of Si by porous nature and alumina layers, and a scalable synthesis (hundreds of gram per batch). An optimized macroporous Si/Al<SUB>2</SUB>O<SUB>3</SUB> composite anode exhibits a reversible capacity of ~1500mAhg<SUP>−1</SUP> after 100 cycles at C/5 and a volume expansion of ~34% even after 100 cycles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We revisited the metallothermic reduction to synthesize shape-preserving macro/nanoporous Si particles. </LI> <LI> Two-step reduction reaction enabled us to control the specific capacity and volume expansion of porous Si-based anodes. </LI> <LI> Macro/nanoporous Si anode showed a reversible capacity of 1500mAhg<SUP>−1</SUP> after 100 cycles and a volume expansion of 34% even after 100 cycles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Shape-reserving macroporous Si/Al<SUB>2</SUB>O<SUB>3</SUB> composite can be synthesized by two-step metallothermic reaction. This process enables us to control a reversible capacity of a volume expansion of Si-base anode materials for practical lithium-ion battery applications. Optimized Si-based composite electrodes show a reversible capacity of 1500mAhg<SUP>−1</SUP> at C/5 with minimized volume expansion (<35%) after 100 cycles.</P> <P>[DISPLAY OMISSION]</P>
Choi, Sinho,Kim, Jieun,Hwang, Dae Yeon,Park, Hyungmin,Ryu, Jaegeon,Kwak, Sang Kyu,Park, Soojin American Chemical Society 2016 NANO LETTERS Vol.16 No.2
<P>One-dimensional metallic/semiconducting materials have demonstrated as building blocks for various potential applications. Here, we report on a unique synthesis technique for redox-responsive assembled carbon-sheathed metal/semiconducting nanowire heterostructures that does not require a metal catalyst. In our approach, germanium nanowires are grown by the reduction of germanium oxide particles and subsequent self-catalytic growth during the thermal decomposition of natural gas, and simultaneously, carbon sheath layers are uniformly coated on the nanowire surface. This process is a simple, reproducible, size-controllable, and cost-effective process whereby most metal oxides can be transformed into metallic/semiconducting nanowires. Furthermore, the germanium nanowires exhibit stable chemical/thermal stability and outstanding electrochemical performance including a capacity retention of similar to 96% after 1200 cycles at the 0.5-1C rate as lithium-ion battery anode.</P>
Patterning of electrodes for mechanically robust and bendable lithium-ion batteries
Choi, Sinho,Lee, Jung-In,Park, Soojin The Royal Society of Chemistry 2012 Journal of materials chemistry Vol.22 No.42
<P>We demonstrate a simple route for fabricating trench-type copper patterns by combining a photo-lithography with a wet etching process. Nanostructured CuO was grown on the patterned Cu current collectors <I>via</I> a simple solution immersion process. And silicon nanoparticles were filled into the patterned Cu current collectors. The strongly immobilized CuO on the patterned Cu exhibited high electrochemical performance, including a high reversible capacity and a high rate capability.</P> <P>Graphic Abstract</P><P>We demonstrate the fabrication of mechanically robust and bendable lithium-ion batteries by growth of CuO on a patterned Cu foil. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c2jm34626e'> </P>
Choi, Sinho,Song, Jianjun,Wang, Chengyin,Park, Soojin,Wang, Guoxiu Wiley (John WileySons) 2017 Chemistry, an Asian journal Vol.12 No.13
<P>Free-standing trimethylolpropane ethoxylate triacrylate gel polymer electrolyte is synthesized by a chemical cross-linking process and used as an electrolyte and separator membrane in lithium-sulfur batteries. The cross linked gel polymer electrolyte also exhibited a stable geometric size retention of 95% at the high temperature of 130 degrees C. The as-prepared gel polymer electrolyte membrane with carbon nanofibers interlayer can effectively prevent polysulfide dissolution and shuttle effect, leading to significantly enhanced electrochemical properties, including high capacity and cycling stability, with an enhanced specific capacity of 790 mAhg(-1) after 100 cycles.</P>
Development and feasibility test of sit-to-stand transfer assistive device
Ha, SinHo,Jeong, SeYeon,Hong, SoungKyun,Choi, Wonjae,Lee, Kwangkook,Park, Donghwan,Son, SangJun,Shin, HyeonHui,Lee, GyuChang Korean Physical Therapy Science 2022 대한물리치료과학회지 Vol.29 No.1
Background: The purpose of this study was to develop a sit-to-stand transfer assistive device, and to conduct a feasibility test. Design: A technical note. Methods and results: In this study, we developed a sit-to-stand transfer assistive device for the elderly and the disabled who have difficulty standing up independently from sitting positions. The sit-to-stand transfer assistive device allows the user to transfer the weight from a sitting position to a standing position while shifting the weight forward by grabbing and pulling a support stand. Ten healthy adults participated in the feasibility test of the device. Each participant used the developed sit-to-stand transfer assistive device and investigated supplementation through a brief interview. As a result of the feasibility test, the opinion was that the device could assist the sit-to-stand transfer to some extent. There were opinions that it needed a function to adjust the height of the knee protective plate in the sitting position according to the user's physical characteristics. Because of the inconvenience of operating the lock device for fixing the position and adjusting inclination, there was an opinion that the improvement for a locking device is needed. There were opinions that it would be better to reduce the size of the device due to its inconvenience of portability. Conclusion: In this study, we developed the sit-to-stand transfer assistive device for the elderly and the disabled who have difficulty standing up independently from sitting positions. In addition, it is considered that the upgrade of the device is necessary for the future since there are supplementary opinions on some points.