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

Adhesive Strength and Electrochemical Properties of Li(Ni0.5Co0.2Mn0.3)O2 Electrodes with Lean Binder Composition

유명현|이용민|노영준|변승우
한국전기화학회 (The Korean Electrochemical Society)|2018.08|전기화학회지 (Journal of the Korean Electrochemical Society)|제21권 제3호|pp. 47-54|DOI 10.5229/JKES.2018.21.3.47

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Lithium secondary batteryElectrode binderElectrochemical propertyAdhesion strengthSAICAS
주제분류화학

초록

동일 전극 로딩 조건(~15 mg cm-2)에서 면적당 용량(mAh cm-2)을 극대화하기 위해, 고분자 바인더의 함량을 4, 2, 1 wt%로 줄인 LiNi0.5Co0.2Mn0.3O2 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 0.2627 kN m-1로 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.

Abstract

To maximize the areal capacity(mAh cm-2) of LiNi0.5Co0.2Mn0.3O2(NCM523) electrode with the same loading level of 15 mg 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 0.2627 kN 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.

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