Binder-less chemical grafting of SiO₂ nanoparticles onto polyethylene separators for lithium-ion batteries

Na, Wonjun,Koh, Ki Hwan,Lee, Albert S.,Cho, Sangho,Ok, Byoeri,Hwang, Suk-Won,Lee, Jin Hong,Koo, Chong Min Elsevier 2019 Journal of membrane science Vol.573 No.-

<P><B>Abstract</B></P> <P>Silica nanoparticles were chemically grafted onto a porous polyethylene separator to improve the adhesion strength, thermal stability, and electrochemical performance of a polyolefin separator. A surface activation via UVO plasma treatment, followed by silane hybridization yielded a polymeric binder-free, thin coating of SiO<SUB>2</SUB> nanoparticles onto the separator. The chemical grafting provided a much stronger adhesive strength (> 2.5 N/cm), reduced thermal shrinkage (< 5% at 120 °C), and higher ionic conductivity (0.84 mS/cm) than conventional physical coating of a ceramic particle-based polymer composite. Lithium-ion batteries fabricated with metallic lithium as the anode, a LiFePO<SUB>4</SUB> (LFP) cathode and SiO<SUB>2</SUB>-grafted separator showed an excellent rate capability (68 mAh/g at 5 C) and cycling performance (143 mAh/g after 200 cycles).</P> <P><B>Highlights</B></P> <P> <UL> <LI> Binder-free silica-grafted PE separator was fabricated for the first time. </LI> <LI> Silica grafting improved adhesion strength, mechanical property of separator. </LI> <LI> Silica-grafted separator effectively enhanced the wettability to the electrolyte. </LI> <LI> Silica-grafted separator revealed strong thermal stability and good battery performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

High Temperature Lithium Ion Capacitors Fabricated with PEO functionalized Polysilsesquioxane Ionogel Polymer Electrolytes

Wonjun Na,Albert S. Lee,Jin Hong Lee,Eunkyoung Kim,Chong Min Koo 한국고분자학회 2016 한국고분자학회 학술대회 연구논문 초록집 Vol.41 No.2

Lithium Dendrite Suppression with UV-Curable Polysilsesquioxane Separator Binders

Na, Wonjun,Lee, Albert S.,Lee, Jin Hong,Hwang, Seung Sang,Kim, Eunkyoung,Hong, Soon Man,Koo, Chong Min American Chemical Society 2016 ACS APPLIED MATERIALS & INTERFACES Vol.8 No.20

<P>For the first time, an inorganic organic hybrid polymer binder was used for the coating of hybrid composites on separators to enhance thermal stability and to prevent formation of lithium dendrite in lithium metal batteries. The fabricated hybrid-composite-coated separators exhibited minimal thermal shrinkage compared with the previous composite separators (<5% change in dimension), maintenance of porosity (Gurley number 400 s/100 cm(3)), and high ionic conductivity (0.82 mS/cm). Lithium metal battery cell examinations with our hybrid-composite -coated separators revealed excellent C-rate and cyclability performance due to the prevention of lithium dendrite growth on the lithium anode even after 200 cycles under 0.2-5C (charge discharge) conditions. The mechanism for lithium dendrite prevention was attributed to exceptional nanoscale surface mechanical properties of the hybrid composite coating layer compared with the lithium metal anode, as the elastic modulus of the hybrid-composite-coated separator far exceeded those of both the lithium metal anode and the required threshold for lithium metal dendrite prevention.</P>

Hybrid ionogel electrolytes with POSS epoxy networks for high temperature lithium ion capacitors

Na, Wonjun,Lee, Albert S.,Lee, Jin Hong,Hong, Soon Man,Kim, Eunkyoung,Koo, Chong Min North-Holland Pub. Co 2017 Solid state ionics Vol.309 No.-

<P><B>Abstract</B></P> <P>Thermally curable hybrid ionogel electrolytes consisting of epoxy-functionalized POSS, amine-terminated polypropylene glycol, and ionic liquid electrolyte, 1M LiTFSI in BMPTFSI were fabricated to give ionic conducting epoxy networks with cubic inorganic star networks crosslinked with lithium ion dissociating polypropylene glycol linkers. Characterization of these hybrid ionogels revealed high ion conduction, exceptional thermal stability, and electrochemical stability. Lithium ion capacitors fabricated with these hybrid ionogels revealed exceptional performance on par with the neat liquid ionic liquid electrolyte, and far superior over ionogels fabricated with conventional organic crosslinkers, due to the mechanical robustness and lithium ion dissociative character imparted by the POSS and PPG functionalities.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hybrid ionogel electrolytes with POSS epoxy networks were fabricated. </LI> <LI> Quasi solid state behavior was confirmed through rheological analysis. </LI> <LI> High ion conduction, good thermal and electrochemical stability were observed. </LI> <LI> Lithium ion capacitors fabricated with hybrid ionogels revealed good performance. </LI> </UL> </P>

Intelligent Vehicle Recognition using Novel Feature Extraction

Wonjun Hwang,Myoungchyl Song,Hongryeul Na,Hanseok Ko 한국정보과학회 2001 한국정보과학회 학술발표논문집 Vol.2001 No.2

Effect of Underlying Comorbidities on the Infection and Severity of COVID-19 in Korea: a Nationwide Case-Control Study

Ji Wonjun,Huh Kyungmin,Kang Minsun,Hong Jinwook,Bae Gi Hwan,이예린,Na Yewon,Choi Hyoseon,Gong Seon Yeong,Choi Yoon-Hyeong,Ko Kwang-Pil,Im Jeong-Soo,정재훈 대한의학회 2020 Journal of Korean medical science Vol.35 No.25

Background: The coronavirus disease 2019 (COVID-19) pandemic is an emerging threat worldwide. It remains unclear how comorbidities affect the risk of infection and severity of COVID-19. Methods: This is a nationwide retrospective case-control study of 219,961 individuals, aged 18 years or older, whose medical costs for COVID-19 testing were claimed until May 15, 2020. COVID-19 diagnosis and infection severity were identified from reimbursement data using diagnosis codes and on the basis of respiratory support use, respectively. Odds ratios (ORs) were estimated using multiple logistic regression, after adjusting for age, sex, region, healthcare utilization, and insurance status. Results: The COVID-19 group (7,341 of 219,961) was young and had a high proportion of female. Overall, 13.0% (954 of 7,341) of the cases were severe. The severe COVID-19 group had older patients and a proportion of male ratio than did the non-severe group. Diabetes (odds ratio range [ORR], 1.206–1.254), osteoporosis (ORR, 1.128–1.157), rheumatoid arthritis (ORR, 1.207–1.244), substance use (ORR, 1.321–1.381), and schizophrenia (ORR, 1.614–1.721) showed significant association with COVID-19. In terms of severity, diabetes (OR, 1.247; 95% confidential interval, 1.009–1.543), hypertension (ORR, 1.245–1.317), chronic lower respiratory disease (ORR, 1.216–1.233), chronic renal failure, and end-stage renal disease (ORR, 2.052–2.178) were associated with severe COVID-19. Conclusion: We identified several comorbidities associated with COVID-19. Health care workers should be more careful while diagnosing and treating COVID-19 when patients have the abovementioned comorbidities.

Design of Lightweight JavaScript Software Platform for the Internet of Things

Lee, Wonjun,Na, Yeoul,Kim, Seon Wook The Institute of Electronics and Information Engin 2014 IEIE Transactions on Smart Processing & Computing Vol.3 No.6

Recently, the internet of things (IoT) has become increasingly attractive in many areas to realize smart worlds. JavaScript has become prevalent for IoT programming because of its familiarity with web programmers. On the other hand, JavaScript does not allow the direct control of IoT hardware due to its language limitation. This paper proposes the IoT software platform for JavaScript programming to resolve the limitation. For proof of concept, the platform based on SpiderMonkey and Raspberry Pi was implemented.

저온환경에서 발생하는 인터쿨러 내부 결빙현상 예측에 관한 수치해석적 연구

윤원준(Wonjun Yoon),김성근(Seongkeun Kim),나일신(Ilsin Na),정성용(Sungyong Jung),박정수(Jungsoo Park) 한국자동차공학회 2021 한국자동차공학회 부문종합 학술대회 Vol.2021 No.6

내연기관 자동차는 출력을 높이면서 배기가스를 감소시키는 방향으로 많은 연구와 기술개발이 발전해왔다. 출력을 높이기 위한 방법으로 연소 후 배출되는 고압가스를 이용하여 Turbo charge(TC)의 터빈을 회전시켜 얻는 회전력을 압축기에 사용하여 흡입 공기를 대기압보다 높은 압력으로 형성하여 엔진 출력을 증가시키는 방법이 있다. 하지만 흡입공기를 압축하는 과정에서 온도가 상승하고 팽창하기 때문에 공기 밀도가 감소하여 오히려 엔진 출력 효율을 감소시킬 우려가 있다. 따라서 압축된 공기를 냉각시키기 위해 Intercooler(IC)가 필요하다. IC는 압축된 공기 온도를 낮춤으로써 공기 밀도를 증가시켜 더 많은 공기 유입으로 인해 엔진 출력을 높이는데 도움을 준다. 게다가 내연기관 트렌드는 연비 향상을 위해 엔진을 다운사이징화하고 있는 추세이며 이를 보완하기위해 TC를 장작하고 있다. 배기가스를 감소시키는 방법으로는 후처리장치 및 EGR 사용이 있다. 다양한 후처리장치 추가는 차량 비용과 무게증가로 인한 연비감소로 이어져 사용자의 부담이 증가함으로 EGR 기술을 적용하여 배기가스를 감소시킬 수 있다. EGR은 HP, LP EGR로 나뉘며 HP EGR은 TC 전단에서 추출하여 intake manifold에서 압축공기와 혼합되어 응답성이 빠른 장점이 있지만 TC의 터빈을 회전시켜야 할 배기가스 일부를 사용함으로써 압축 효율이 감소되는 특징이 있다. LP EGR은 TC와 후처리장치를 거쳐 외부로 배출되는 가스를 활용하는 기술로 HP EGR에 비해 응답성은 늦고 온도차이로 인하여 응축수가 생성될 수 있지만 신기와 혼합이 잘되며, 터빈 회전력을 유지할 수 있어 압축효율이 증가한다. 따라서 각 운전영역에 따라 HP, LP EGR을 함께 사용하는 Duel loop EGR을 적용하고 있다. 최근 들어 과거에 비해 기후 변동의 폭이 커짐에 따라 전세계적으로 이상기후가 관측되고 있고 자동차의 주행조건 역시 가혹한 환경에서 운전된다. 따라서 자동차는 시중에 판매되기 전 극한의 상황을 고려하여 많은 테스트를 진행하며 특히, 영하 조건에서 초기시동부터 운전 테스트를 진행한다. 영하의 공기가 LP EGR과 압축기를 지나 혼합되면서 응축수가 생성되고 IC를 지나면서 IC 내부에 결빙이 성장하게 된다. IC 내부에서 결빙 성장의 경우 유동 흐름을 방해함과 동시에 엔진 성능에 영향을 미친다. 본 연구는 영하 온도에서 흡입되는 공기와 LP EGR이 만나 혼합되어 압축기를 통과하면서 혼합기체 온도가 상승한 상태로 IC 열교환의 영향으로 결빙이 생성된다는 것에 착안하여 연구를 진행하였다. 해석 형상은 현대자동차에서 개발한 모델로 IC전단 by pass valve를 이용하여 저온일 때는 100% by pass하고 고온일 때는 IC로 유동을 분배하는 시스템이다. 해석은 100% by pass 조건에서 수행하여 ansys fluent로 유동해석을 진행하였으며 이후 FENSAP-ICE tool을 사용하여 droplet과 icing 해석을 순차적으로 진행하였다. 해석 모델 신뢰도는 실차 실험 데이터 값과 해석모델 데이터 값을 비교하였으며 외기온도에 따른 결빙량을 예측하였다. Fluent 유동해석 결과 rpm-load가 증가할수록 압축된 혼합기체 속도가 증가하였고 형상적인 요인에 의해 swirl이 발생하는 것을 확인하였다. Swirl과 by pass pipe 형상으로 인하여 IC 하단 chamber부분으로 유입되어 체류시간이 증가하면서 결빙이 발생하였고, 결빙량에 영향을 미치는 인자로는 체류시간과 외기온도가 있다. 저속 영역보다 중속 영역에서 결빙량이 감소하는 경향성을 보였으며 이는 흡입속도가 증가하여 IC 하단 chamber부분에서 체류하는 시간이 감소하여 결빙량이 줄어든 것으로 판단된다.

ISO 13849-1 기반 엔진제어시스템 개발 방법론

최원준(Wonjun Choi),신태범(Taebeom Shin),나종성(Jongseong Na) 한국자동차공학회 2013 한국자동차공학회 학술대회 및 전시회 Vol.2013 No.11

A-NVM: 운전자 적응적 NVRAM 제어

최원준(Wonjun Choi),신태범(Taebeom Shin),나종성(Jongseong Na) 한국자동차공학회 2011 한국자동차공학회 부문종합 학술대회 Vol.2011 No.5

Non-volatile byte addressable memories in Engine Management Systems are becoming more common, and are increasingly used for user specific data that must not be lost. The NVRAM strategy how to keep and update the user-specific data need to be concerned in case of Heavy Duty and Medium Duty since many drivers can be changed on a vehicle. Existing NVRAM management system in Heavy duty/Medium duty do not include features that manage each pages according to each users. It means EMS could not save and update the user specific data. A-NVM has been designed to address these problems by providing software function in order to monitor and manage multiple users by memory page management. A-NVM uses a special user identification procedure by UDS to identify drivers, making it possible to periodically send the user identification message when driver identified by the display interface on vehicles. A-NVM will get the user specified message and do memory page loading by the identification from driver. It also checks integrity on every operation to ensure that the file system is consistent.