Journal of the Korean Electrochemical Society (전기화학회지)

The Korean Electrochemical Society (한국전기화학회)
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Electrochemical Characteristics of Cu3Si as Negative Electrode for Lithium Secondary Batteries at Elevated Temperatures

리튬 이차전지 음극용 Cu3Si의 고온에서의 전기화학적 특성

  • Kwon, Ji-Y. (Department of Chemical and Biological Engineering, and Research Center for Energy Conversion & Storage, Seoul National University) ;
  • Ryu, Ji-Heon (Graduate School of Knowledge-Based Technology and Energy, Korea Polytechnic University) ;
  • Kim, Jun-Ho (Department of Chemical and Biological Engineering, and Research Center for Energy Conversion & Storage, Seoul National University) ;
  • Chae, Oh-B. (Department of Chemical and Biological Engineering, and Research Center for Energy Conversion & Storage, Seoul National University) ;
  • Oh, Seung-M. (Department of Chemical and Biological Engineering, and Research Center for Energy Conversion & Storage, Seoul National University)
  • 권지윤 (서울대학교 화학생물공학부 및 에너지 변환 저장 연구센터) ;
  • 류지헌 (한국산업기술대학교 지식기반기술.에너지대학원) ;
  • 김준호 (서울대학교 화학생물공학부 및 에너지 변환 저장 연구센터) ;
  • 채오병 (서울대학교 화학생물공학부 및 에너지 변환 저장 연구센터) ;
  • 오승모 (서울대학교 화학생물공학부 및 에너지 변환 저장 연구센터)
  • Received : 2010.03.25
  • Accepted : 2010.04.02
  • Published : 2010.05.31
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Abstract

A $Cu_3Si$ film electrode is obtained by Si deposition on a Cu foil using DC magnetron sputtering, which is followed by annealing at $800^{\circ}C$ for 10 h. The Si component in $Cu_3Si$ is inactive for lithiation at ambient temperature. The linear sweep thermammetry (LSTA) and galvano-static charge/discharge cycling, however, consistently illustrate that $Cu_3Si$ becomes active for the conversion-type lithiation reaction at elevated temperatures (> $85^{\circ}C$). The $Cu_3Si$ electrode that is short-circuited with Li metal for one week is converted to a mixture of $Li_{21}Si_5$ and metallic Cu, implying that the Li-Si alloy phase generated at 0.0 V (vs. Li/$Li^+$) at the quasi-equilibrium condition is the most Li-rich $Li_{21}Si_5$. However, the lithiation is not extended to this phase in the constant-current charging (transient or dynamic condition). Upon de-lithiation, the metallic Cu and Si react to be restored back to $Cu_3Si$. The $Cu_3Si$ electrode shows a better cycle performance than an amorphous Si electrode at $120^{\circ}C$, which can be ascribed to the favorable roles provided by the Cu component in $Cu_3Si$. The inactive element (Cu) plays as a buffer against the volume change of Si component, which can minimize the electrode failure by suppressing the detachment of Si from the Cu substrate.

DC magnetron 스퍼터링을 이용해 구리(Cu) 호일 위에 실리콘(Si)을 증착한 후 $800^{\circ}C$에서 열처리하여 $Cu_3Si$를 얻고, 이의 리튬 이차전지용 음극으로서 특성을 조사하였다. $Cu_3Si$는 Si 성분을 포함하고 있으나 상온에서 리튬과 반응하지 않았다. 선형 주사 열-전류(linear sweep thermammetry, LSTA) 실험과 고온 충방전 실험을 통하여, 상온에서 비활성인 $Cu_3Si$가 $85^{\circ}C$ 이상에서는 활성화되어 Si 성분이 전환(conversion)반응에 의해 리튬과 반응함을 확인하였다. $Cu_3Si$에서 분리된 Si는 $120^{\circ}C$에서 Li-Si 합금 중에서 리튬의 함량이 가장 많은 $Li_{21}Si_5$ 상까지 리튬과 반응함을 유사 평형 조건(quasi-equilibrium)의 실험으로부터 알 수 있었다. 그러나 정전류 조건($100\;mA\;{g_{Si}}^{-1}$)에서는 리튬 합금반응이 $Li_{21}Si_5$까지 진행되지 못하였다. 또한 $120^{\circ}C$에서 전환반응에 의해 생성된 Li-Si 합금과 금속 상태의 Cu는 충전과정에서 다시 $Cu_3Si$로 돌아감, 즉 $Cu_3Si$와 리튬은 가역적으로 반응함을 확인하였다. $120^{\circ}C$에서 $Cu_3Si$ 전극은 비정질 실리콘 전극보다 더 우수한 사이클 특성을 보여 주었다. 이는 비활성인 구리가 실리콘의 부피변화를 완충하여 집전체에서 탈리되는 현상을 완화하고 결과적으로 전극이 퇴화하는 것을 억제하기 때문인 것으로 설명할 수 있다. 실제로 비정질 실리콘 전극은 충방전 후에 실리콘 층의 균열과 탈리가 관찰되었으나, $Cu_3Si$ 전극에서는 이러한 현상이 관찰되지 않았다.

Keywords

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