Journal of the Korean Electrochemical Society (전기화학회지)

The Korean Electrochemical Society (한국전기화학회)
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Electrochemical Behaviors of Graphite/LiNi0.6Co0.2Mn0.2O2 Cells during Overdischarge

흑연과 LiNi0.6Co0.2Mn0.2O2로 구성된 완전지의 과방전 중 전기화학적 거동분석

  • Bong Jin Kim (Depratment of Chemical Engineering and Biotechnology, Tech University of Korea) ;
  • Geonwoo Yoon (Depratment of Chemical Engineering and Biotechnology, Tech University of Korea) ;
  • Inje Song (Graduate School of Knowledge-based Technology and Energy, Tech University of Korea) ;
  • Ji Heon Ryu (Graduate School of Knowledge-based Technology and Energy, Tech University of Korea)
  • 김봉진 (한국공학대학교 생명화학공학과) ;
  • 윤건우 (한국공학대학교 생명화학공학과) ;
  • 송인제 (한국공학대학교 지식기반기술.에너지대학원) ;
  • 류지헌 (한국공학대학교 지식기반기술.에너지대학원)
  • Received : 2022.12.04
  • Accepted : 2022.12.13
  • Published : 2023.02.28
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Abstract

As the use of lithium-ion secondary batteries is rapidly increasing due to the rapid growth of the electric vehicle market, the disposal and recycling of spent batteries after use has been raised as a serious problem. Since stored energy must be removed in order to recycle the spent batteries, an effective discharging process is required. In this study, graphite and NCM622 were used as active materials to manufacture coin-type half cells and full cells, and the electrochemical behavior occurring during overdischarge was analyzed. When the positive and negative electrodes are overdischarged respectively using a half-cell, a conversion reaction in which transition metal oxide is reduced to metal occurs first in the positive electrode, and a side reaction in which Cu, the current collector, is corroded following decomposition of the SEI film occurs in the negative electrode. In addition, a side reaction during overdischarge is difficult to occur because a large polarization at the initial stage is required. When the full cell is overdischarged, the cell reaches 0 V and the overdischarge ends with almost no side reaction due to this large polarization. However, if the full cell whose capacity is degraded due to the cycle is overdischarged, corrosion of the Cu current collector occurs in the negative electrode. Therefore, cycled cell requires an appropriate treatment process because its electrochemical behavior during overdischarge is different from that of a fresh cell.

전기자동차 시장의 급속한 성장으로 이차전지의 사용이 급증함에 따라 사용 후 전지의 폐기 및 재활용이 심각한 문제로 제기되고 있다. 사용 후 리튬이온 전지를 처리하기 위해서는 저장된 에너지를 제거하기 위하여 효과적으로 방전하는 과정이 필수적이다. 본 연구에서는 흑연과 LiNi0.6Co0.2Mn0.2O2 (NCM622)을 사용하여 코인셀 형태로 반쪽전지 및 완전지를 제조하였고, 이를 과방전할 때 발생하는 전기화학적 거동에 대하여 분석하였다. 반쪽전지를 사용하여 양극과 음극을 각각 과방전시키면, 양극에서는 먼저 전이금속 산화물이 금속으로 환원되는 전환반응을 겪게 되며, 음극에서는 SEI 피막의 분해에 이어 집전체인 Cu가 용출되는 부반응이 발생하였다. 또한, 이러한 과방전의 발생 시에는 큰 분극을 필요로 하였다. 완전지의 과방전 시에는 각각의 부반응이 진행되는 시점에 존재하는 큰 분극들로 인하여 부반응의 본격적인 발생 전에 0 V에 도달하여 방전이 종료되었다. 그러나, 사이클을 통하여 용량이 퇴화된 완전지의 경우에는 과방전거동이 변화하여 음극에서 Cu 집전체의 부식이 발생됨을 확인하였다. 따라서, 사용 후 전지는 사용 전의 전지와는 과방전 시에 다른 거동을 지니고 있으므로 이러한 점들이 고려되어야 한다.

Keywords

Acknowledgement

이 연구는 환경부 및 한국환경산업기술원(KEITI) 연구비 지원에 의한 연구임(2022003500005, 미래발생 폐자원의 재활용 촉진 기술개발사업).

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