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Effects of Pyrite (FeS2) Particle Sizes on Electrochemical Characteristics of Thermal Batteries

열전지의 전기화학적 특성에 미치는 황철석(FeS2) 입자크기의 영향

  • Choi, Yusong (Convergence Technology Research Directorate, Agency for Defense Development) ;
  • Yu, Hye-Ryeon (Convergence Technology Research Directorate, Agency for Defense Development) ;
  • Cheong, Haewon (Convergence Technology Research Directorate, Agency for Defense Development) ;
  • Cho, Sungbaek (Convergence Technology Research Directorate, Agency for Defense Development) ;
  • Lee, Young-Seak (Department of Applied Chemistry and Biological Engineering, Chungnam National University)
  • 최유송 (국방과학연구소 국방신기술본부) ;
  • 유혜련 (국방과학연구소 국방신기술본부) ;
  • 정해원 (국방과학연구소 국방신기술본부) ;
  • 조성백 (국방과학연구소 국방신기술본부) ;
  • 이영석 (충남대학교 바이오응용화학과)
  • Received : 2013.12.27
  • Accepted : 2014.02.07
  • Published : 2014.04.10

Abstract

In this study, effects of pyrite ($FeS_2$) particle sizes on the electrochemical characteristics of thermal batteries are investigated using unit cells made of pulverized pyrite by ball-milling. At $450^{\circ}C$ unit cell discharge test, the electrochemical capacity of $1.46{\mu}m$ pyrite-cell largely increases compared to $98.4{\mu}m$ pyrite-cell, and their internal resistances also decrease. These results are attributed to the increase in the active reaction area of pyrite by ball milling. However, at $500^{\circ}C$ unit cell discharge test, a $1.46{\mu}m$ pyrite cell shows lower internal resistance than that of $98.4{\mu}m$ pyrite cell only at Z-phase region ($FeS_2{\rightarrow}Li_3Fe_2S_4$). After that, a $1.46{\mu}m$ pyrite cell shows a decrease in the cell voltage and an rapid increase of the internal resistance in J-phase region ($Li_3Fe_2S_4{\rightarrow}LiFe_2S_4$) is observed compared to those of $98.4{\mu}m$ pyrite cell. It can be concluded that at the higher temperature, the thermally unstable pulverized pyrite is decomposed thermally as well as self discharged, simultaneously, which causes the higher resistance and lower capacity at $500^{\circ}C$ in J-phase than that of $98.4{\mu}m$ pyrite cell.

본 연구에서는 열전지용 양극활물질로 사용되는 $FeS_2$ (Pyrite) 분말을 볼밀링법으로 분쇄하여 단위전지를 제작하고, 볼밀 전, 후 입자크기변화가 열전지의 전기화학적 특성에 미치는 영향을 고찰하였다. $450^{\circ}C$ 시험결과, 분쇄된 $1.46{\mu}m$ $FeS_2$ 분말을 사용한 단위전지가 분쇄 전 $98.4{\mu}m$$FeS_2$ 분말을 사용한 단위전지에 비해서 전지용량이 크게 향상되었으며, 내부저항도 감소되었다. 이러한 결과는 볼밀로 인한 비표면적 증가의 영향으로 판단된다. 반면, $500^{\circ}C$에서 방전시 1단계의 Z-phase 반응구간($FeS_2{\rightarrow}Li_3Fe_2S_4$)에서 $1.46{\mu}m$ 분말을 사용한 단위전지 전압 및 저항특성이 우수하였지만, 2단계의 J-phase 반응($Li_3Fe_2S_4{\rightarrow}LiFe_2S_4$)에서는 볼밀된 $1.46{\mu}m$ 분말을 사용한 전지의 전압이 감소하고, 전지 내부저항도 급격하게 증가하는 경향을 보였다. 이러한 현상은 $500^{\circ}C$ 방전시 미분화된 $FeS_2$가 Z-phase 영역에서 방전반응과 동시에 열분해에 의한 자가방전($FeS_2{\rightarrow}FeS_{1.14}$ (pyrrhotite))이 일어나 볼밀 전 조대한(coarsen) $FeS_2$ 분말에 비해 용량이 감소하고 내부 저항도 증가되기 때문으로 사료된다.

Keywords

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