BDMI+ 양이온을 함유한 이온성 액체로부터 흑연으로의 전기화학적 리튬 삽입
Electrochemical Lithium Intercalation within Graphite from Ionic Liquids containing BDMI+ Cation
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흑연과 1-buthyl-2,3-dimethylimidazolium(BDMI)계 이온성 액체의 계면 반응을 이해하기 위하여lithium bis(fluorosulfonyl)imide(LiTFSI)가 용해된 BDMI-TFSI 용액 중에서 전기화학 원자간력현미경(electrochemical atomic force microscopy, ECAFM)을 이용하여 순환 전압전류법 전후에있어서의 고배향성 열분해 흑연(highly oriented pyrolytic graphite, HOPG)의 표면을 in-situ로관찰하였다. HOPG 전극에서 리튬의 가역적인 삽입과 탈리반응은 진행되지 않았으며, BDMI+양이온의 삽입에 의한 blister의 형성 및 그라펜 층의 파괴만이 관찰되었다. 한편, BDMI+ 양이온의삽입 반응은 농도가 4.90 mol/kg인 LiTFSI-propylene carbonate(PC)를 15 wt% 함유하고 있는BDMI-TFSI계에서는 일어나지 않았으며, 이 경우에는 가역적인 리튬의 삽입과 탈리반응이 진행되었다. ECAFM 결과는 고농도의 PC계 용액이 solid electrolyte interface(SEI)를 형성함으로인해 BDMI+ 양이온의 삽입을 막는 매우 효과적인 첨가제임을 나타내었다.
Abstract
In situ electrochemical atomic force microscopy (ECAFM) observations of the surface of highly oriented pyrolytic graphite (HOPG) was performed before and after cyclic voltammetry in lithium bis(fluorosulfonyl)imide (LiTFSI) dissolved in 1-buthyl-2,3-dimethylimidazolium (BDMI)-TFSI to understand the interfacial reactions between graphite and BDMI-based ionic liquids. The formation of blisters and the exfoliation of graphene layers by the intercalation of BDMI+cations within HOPG were observed instead of reversible lithium intercalation and de-intercalation. On the other hand, lithium ions are reversibly intercalated into the HOPG and de-intercalatied from the HOPG without intercalation of the BDMI+ cations in the presence of 15 wt% of 4.90 mol/kg−1 LiTFSI dissolved in propylene carbonate (PC). ECAFM results revealed that the concentrated PC-based solution is a very effective additive for preventing BDMI+ intercalation through the formation of solid electrolyte interface (SEI).
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