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Yim, Taeeun,Han, Young-Kyu American Chemical Society 2017 ACS APPLIED MATERIALS & INTERFACES Vol.9 No.38
<P>Tris(trimethylsilyl) phosphite (TMSP) has, received considerable attention as a functional additive for various cathode materials in lithium-ion batteries, but the effect of TMSP on the surface stability of a graphite anode has not been studied. Herein, we demonstrate that TMSP serves as an effective solid electrolyte interphase (SEI)-forming additive for graphite anodes in lithium-ion batteries (LIBs). TMSP forms SEI layers by chemical reactions between TMSP and a reductively decomposed ethylene carbonate (EC) anion, which is strikingly different from the widely known mechanism of the SET-forming additives. TMSP is stable under cathodic polarization, but it reacts chemically with radical anion intermediates derived from the electrochemical reduction of the carbonate solvents to generate a stable SEI layer. These TMSP-derived SEI layers improve the interfacial stability of the graphite anode; resulting in a retention of 96.8% and a high Coulombic efficiency of 95.2%. We suggest the use of TMSP as a functional additive that effectively stabilizes solid electrolyte interfaces of both the anode and cathode in lithium-ion batteries.</P>
Yim, Taeeun,Jang, Seol Heui,Han, Young-Kyu Elsevier Sequoia 2017 Journal of Power Sources Vol. No.
<P><B>Abstract</B></P> <P>Nickel-rich cathode material has received marked attention as an advanced cathode material, however, its inferior surface property limits the achievement of high performance in lithium-ion batteries. We propose the use of a bi-functional additive of triphenyl borate (TPB) for improvement of the safety and electrochemical performance of Ni-rich cathode materials. First, TPB removes residual lithium species from the Ni-rich cathode surface via chemical binding with anion part of residual lithium species, and effectively reduces swelling behavior of the cell. Second, TPB creates effective cathode−electrolyte interphase (CEI) layers on the electrode surface by an electrochemical reaction, and greatly enhances the surface stability of the nickel-rich cathode. This work demonstrate that a cell cycled with the TPB additive exhibits a remarkable retention of 88.6% at 60 °C after 100 cycles for an NCM721 cathode material. We suggest a working mechanism for TPB based on systematic analyses, including in-situ and ex-situ experiments.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Residual lithium species remaining on NCM cathode is removed by TPB additive. </LI> <LI> TPB additive reduces internal pressures of NCM electrode. </LI> <LI> Electrochemical reaction of TPB affords borate-based CEI layer on NCM electrode. </LI> <LI> CEI layer allows improved surface stability of NCM cathode. </LI> <LI> Borate-based CEI layer exhibits improved electrochemical performance. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Yim, Taeeun,Park, Min-Sik,Woo, Sang-Gil,Kwon, Hyuk-Kwon,Yoo, Jung-Keun,Jung, Yeon Sik,Kim, Ki Jae,Yu, Ji-Sang,Kim, Young-Jun American Chemical Society 2015 NANO LETTERS Vol.15 No.8
<P>User safety is one of the most critical issues for the successful implementation of lithium ion batteries (LIBs) in electric vehicles and their further expansion in large-scale energy storage systems. Herein, we propose a novel approach to realize self-extinguishing capability of LIBs for effective safety improvement by integrating temperature-responsive microcapsules containing a fire-extinguishing agent. The microcapsules are designed to release an extinguisher agent upon increased internal temperature of an LIB, resulting in rapid heat absorption through an in situ endothermic reaction and suppression of further temperature rise and undesirable thermal runaway. In a standard nail penetration test, the temperature rise is reduced by 74% without compromising electrochemical performances. It is anticipated that on the strengths of excellent scalability, simplicity, and cost-effectiveness, this novel strategy can be extensively applied to various high energy-density devices to ensure human safety.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/nalefd/2015/nalefd.2015.15.issue-8/acs.nanolett.5b01167/production/images/medium/nl-2015-011675_0003.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/nl5b01167'>ACS Electronic Supporting Info</A></P>
Yim, Taeeun,Choi, Soo Jung,Park, Jeong-Han,Cho, Woosuk,Jo, Yong Nam,Kim, Tae-Hyun,Kim, Young-Jun The Royal Society of Chemistry 2015 Physical chemistry chemical physics Vol.17 No.4
<P>As a means of enhancing the electrochemical performance of silicon–graphite composites, we propose a novel binder candidate that is modified by a combination of rigid and elastic functional groups on its binder framework. To provide an efficient binder that is also capable of rapid volume changes, a co-polymer binder (PAA–PAA/PMA) is synthesized by employing poly(acrylic acid) (PAA) as the main binder framework and poly(acrylic acid)-<I>co</I>-poly(maleic acid) (PAA/PMA) as an additional elastic polymer auxiliary. This co-polymer binder (PAA–PAA/PMA) affords a good balance of adhesive and mechanical (rigidity and elasticity) properties, which creates an excellent cycle performance with a high specific capacity (751.1 mA h g<SUP>−1</SUP>) and considerable capacity retention (64.9%) after 300 cycles. This is attributed to the ability of the added elastic functional group to respond flexibly to volume changes, thereby enhancing the overall uniformity of the electrode and ensuring a consistent electronic network. On the basis of these findings, it is considered that embedding an elastic functional group into the binder framework is an effective approach to improve the overall performance of Si–graphite composite electrodes.</P> <P>Graphic Abstract</P><P>A binder which is modified by embedding an additional elastic functional group into a rigid binder framework is investigated to enhance the electrochemical performance of Si–graphite composites. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c4cp04723k'> </P>
상온 이온성 액체로 활성화시킨 고온 작동 가능한 Nafion 고분자 전해질
이수현(Suhyun Lee),임태은(Taeeun Yim),박영돈(Yeong Don Park),문준영(Junyoung Mun) 한국고분자학회 2018 폴리머 Vol.42 No.4
고분자 연료전지의 핵심 소재 중 하나인 Nafion 고분자 전해질은 전도성을 부여하기 위해 물을 이용하여 활성화하여 사용한다. 그러나 수용액은 상온에서도 휘발성이 있고, 끓는점이 100 oC로 제한되어 고분자 연료 전지의 작동 온도 범위를 제한하는 가장 큰 이유로 지적되고 있다. 이를 극복하기 위하여, 상온에서 휘발성이 없으면서도 전도성을 띠는 상온 이온성 액체를 이용하여 Nafion 고분자 전해질을 활성화하고자 하였다. 상온 이온성 액체의 구조가 전도도에 미치는 영향성을 파악하기 위해, 상온 이온성 액체의 alkyl-methylimidazolium 양이온을 기준으로 alkyl기에 ethyl, butyl, iso-butyl 기를 각각 도입하고, 음이온을 tetrafluoroborate, bis[(trifluoromethyl)sulfonyl]imide)로 제어하여, Nafion 고분자 전해질을 활성화하였다. 또한 Nafion 고분자 전해액 내에 높은 상온 이온성 액체 함침(impregnation)을 통한 높은 전도성 구현을 위하여, Nafion 용액의 casting 시 60-120 wt%의 상온 이온성 액체를 혼합하여, 높은 전도도와 고온 작동성을 갖는 Nafion 고분자 전해질을 연구하였다. Nafion polymer electrolyte, which is essential material of polymer fuel cells, is activated by water and shows conductivity. However, such aqueous electrolyte is volatile at room temperature, and the operating temperature is limited to 100 oC. In order to overcome this problem, we tried to activate Nafion polymer electrolyte by using room temperature ionic liquids. The influence of the molecular structure of room temperature ionic liquid on conductivity is evaluated by controlling ethyl, butyl, and iso-butyl groups into an alkyl group of alkylmethylimidazolium cation. Also their anion structure is controlled with tetrafluoroborate and bis[(trifluoromethyl)sulfonyl]imide. For the high conductivity of Nafion polymer electrolytes, Nafion polymer electrolytes with high conductivity and high temperature operation are studied by mixing 60-120 wt% of room temperature ionic liquids during casting of Nafion solution.
Jeon Ye Jin,Yim Taeeun 한국물리학회 2023 Current Applied Physics Vol.46 No.-
SiOx anodes and Ni-rich LiNixCoyMnzO2 (LNMC) cathodes are considered practical electrodes for electric vehicles; however, these advanced electrode materials suffer from poor prolonged cycling. In this study, N-(4-fluorophenyl)maleimide (FPMI) is used as an electrolyte additive that simultaneously enhances the interfacial stability of each electrode through the formation of solid electrolyte interphase (SEI) or cathode electrolyte interphase (CEI) layers. The electrochemical reduction and oxidation of FPMI promote the formation of SEI and CEI layers on the SiOx anode and Ni-rich LNMC cathode, respectively. FPMI addition also considerably increases the cycling retention because the FPMI-derived SEI and CEI layers effectively inhibit electrolyte decomposition during cycling, thereby increasing the cell lifespan. Additional spectroscopic analyses indicate that the SEI and CEI layers developed on each electrode effectively prevent parasitic reactions, such as electrolyte decomposition with transition metal dissolution in the cell; thus, the surface stability of the cell is also improved.