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Adhesive Strength and Electrochemical Properties of Li(Ni0.5Co0.2Mn0.3)O2Electrodes with Lean Binder Composition

바인더 함량에 따른 Li(Ni0.5Co0.2Mn0.3)O2 전극의 접착력 및 전기화학 성능에 관한 연구

  • Roh, Youngjoon (Department of Energy Science and Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST)) ;
  • Byun, Seoungwoo (Department of Energy Science and Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST)) ;
  • Ryou, Myung-Hyun (Department of Chemical and Biological Engineering, Hanbat National University) ;
  • Lee, Yong Min (Department of Energy Science and Engineering, Daegu Gyeongbuk Institute of Science and Technology (DGIST))
  • 노영준 (대구경북과학기술원 에너지공학전공) ;
  • 변승우 (대구경북과학기술원 에너지공학전공) ;
  • 유명현 (한밭대학교 화학생명공학과) ;
  • 이용민 (대구경북과학기술원 에너지공학전공)
  • Received : 2018.07.24
  • Accepted : 2018.08.13
  • Published : 2018.08.31

Abstract

To maximize the areal capacity($mAh\;cm^{-2}$) of $LiNi_{0.5}Co_{0.2}Mn_{0.3}O_2$(NCM523) electrode with the same loading level of $15mg\;cm^{-2}$, three NCM523 electrodes with 4, 2, and 1 wt% poly(vinylidene fluoride)(PVdF) binder content are fabricated. Due to the delamination issue of electrode composite at the edge during punching process, the 1 wt% electrode is excluded for further evaluation. When the PVdF binder content decreases from 4 to 2 wt%, both adhesion strength and shear stress decrease from 0.4846 to $0.2627kN\;m^{-1}$ by -46% and from 3.847 to 2.013 MPa by -48%, respectively. Regardless of these substantial decline of mechanical properties, their initial electrochemical properties such as initial coulombic efficiency and voltage profile are almost the same. However, owing to high loading level, the 2 wt% electrode not only exhibits worse cycle performance than the 4 wt% electrode, but also cannot maintain its mechanical integrity only after 80 cycles. Therefore, if the binder content is reduced to increase the area capacity, the mechanical properties as well as the cycle performance must be carefully evaluated.

동일 전극 로딩 조건(${\sim}15mg\;cm^{-2}$)에서 면적당 용량($mAh\;cm^{-2}$)을 극대화하기 위해, 고분자 바인더의 함량을 4, 2, 1 wt%로 줄인 $LiNi_{0.5}Co_{0.2}Mn_{0.3}O_2$ 전극을 제조하였다. 바인더 함량이 1 wt%로 낮춘 경우, 압연 후 펀칭 과정에서 전극 코팅층이 부분적으로 박리되는 문제가 발생하여 추가 분석은 진행되지 않았다. 전극 내 바인더 함량을 4 wt%에서 2 wt%로 줄이면, 계면 접착력은 0.4846에서 $0.2627kN\;m^{-1}$로 약 46% 감소하고, 전극 코팅층의 강도도 3.847에서 2.013 MPa로 약 48%가 떨어졌다. 그러나, 두 전극을 리튬 전극과 반쪽 전지로 구성하여 전기화학적 특성을 살펴보면, 초기 방전 용량과 충방전 효율은 유사하였다. 하지만, 단기 수명 평가에서 2 wt% 바인더 전극은 수명 특성이 떨어질 뿐만 아니라, 전지를 분해하는 과정에서 전극 코팅층이 집전체에서 박리되는 현상이 관찰되었다. 반면, 4 wt% 바인더 전극은 높은 전극 로딩조건에서도 전극 코팅층과 집전체 계면이 잘 유지되고 있음이 확인되었다.

Keywords

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