Journal of the Korean Electrochemical Society (전기화학회지)

The Korean Electrochemical Society (한국전기화학회)
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Effect of Acid / Heat Treatment on Electric Double Layer Performance of Needle Cokes

니들코크스의 전기이중층 거동에 미치는 산화처리/열처리 효과

  • Yang, Sun-Hye (Battery Research Center, Korea Electrotechnology Research Institute) ;
  • Kim, Ick-Jun (Battery Research Center, Korea Electrotechnology Research Institute) ;
  • Choi, In-Sik (Battery Research Center, Korea Electrotechnology Research Institute) ;
  • Kim, Hyun-Soo (Battery Research Center, Korea Electrotechnology Research Institute)
  • 양선혜 (한국전기연구원 전지연구센터) ;
  • 김익준 (한국전기연구원 전지연구센터) ;
  • 최인식 (한국전기연구원 전지연구센터) ;
  • 김현수 (한국전기연구원 전지연구센터)
  • Published : 2009.02.28
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Abstract

In this study, a needle coke was oxidized in a mixture of dilute nitric acid and sodium chlorate ($NaClO_3$) solutions and followed by heat treatment. The samples were analyzed with using XRD, FESEM, elemental analyzer, BET, and Raman spectroscopy. Double layer capacitance was measured with the charge and discharge measurements. The consisting layers of the needle coke were expanded to single phase showing only (001) diffraction peak by the acid treatment for 24 hours. The oxidized coke returned to a graphite structure appearing (002) peak after heat treatment above $200^{\circ}C$. The structure returned could be more easily accessible to the ions by the first charge, and improve the double layer capacitance at the second charge. The two-electorde cell from acid treated coke and $300^{\circ}C$ heat treatment exhibited the maximum capacitances of 32.1 F/g and 29.5 F/ml at the potential of $0{\sim}2.5\;V$.

니들 코크스의 활성화를 위해 $HNO_3$와 $NaClO_3$ 혼합용액에서의 산처리와 열처리를 행하였다. 산화처리 코크스와 열처리한 코크스의 미세구조는 XRD, FESEM, elemental analysis, BET, Raman spectroscopy를 이용하였으며, 전기이중층 거동은 충방전 분석을 행하였다. 니들 코크스는 산화처리 시간에 따라 산소의 중량 %의 증가와 함께 층간이 분리되어(001) 구조로 상변화가 일어나고, $200^{\circ}C$ 이상의 열처리에서 흑연구조 특성인(002) 구조로 되돌아갔다. 이들 산화처리 과정에서 층간에 관능기가 도입 되어 구조결함이 발생하고 1차 충전에서 전계 활성화에 의해 층간을 확장되어 2차 충전에서 전기이중층 용량을 발생 시키는 것으로 보인다. 24시간 산화처리후 $300^{\circ}C$ 열처리한 코크스의 2.5 V까지의 2 전극 기준에서 구한 활물질 중량 당 용량과 전극 부피 당 용량은 각각 32.1 F/g과 29.5 F/ml을 나타내었다.

Keywords

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