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Effect of Lithium Bis(Oxalato)Borate Additive on Thermal Stability of Si Nanoparticle-based Anode

리튬 이차 전지용 실리콘 나노입자 음극의 고온 열안정성에 대한 Lithium bis(oxalato)borate첨가제의 효과

  • Kim, Min-Jeong (Graduate School of Energy Science and Technology, Chungnam National University) ;
  • Choi, Nam-Soon (School of Green Energy, Ulsan National Institute of Science and Technology (UNIST)) ;
  • Kim, Sung-Soo (Graduate School of Energy Science and Technology, Chungnam National University)
  • 김민정 (충남대학교 에너지과학기술대학원) ;
  • 최남순 (울산과학기술대학교, 에너지 및 화학공학부) ;
  • 김성수 (충남대학교 에너지과학기술대학원)
  • Received : 2013.12.30
  • Accepted : 2014.02.28
  • Published : 2014.05.31

Abstract

Silicon (Si) has been investigated as promising negative-electrode (anode) materials because its theoretical specific capacity of 4200 mAh/g for $Li_{4.4}Si$ is far higher than that of carbonaceous anodes in current commercial products. However, in practice, the application of Si to Li-ion batteries is still quite challenging because Si suffers from severe volume expansion and contraction and lead to a continuous solid electrolyte interphase (SEI)-filming process by cracking of Si. This process consumes the limited $Li^+$ source, builds up thick and unstable SEI layer on the Si active materials, and will eventually disable the cell. Since unstable SEI reduces electrochemical performance and thermal stability of the Si anode, the surface chemistry of the anode should be modified by using a functional additive. It is found that lithium bis(oxalato)borate (LiBOB) as an additive effectively protected the Si anode surface, improved capacity retention when stored at $60^{\circ}C$, and alleviated exothermic thermal reactions of fully lithiated Si anode.

리튬2차전지용 음극활물질로 연구되고 있는 실리콘은 흑연에 비하여 높은 이론용량 (4200mAh/g for $Li_{4.4}Si$)을 가지기 때문에 고용량 음극소재로 각광받고 있다. 이러한 실리콘 음극은 반복적인 충방전에 의해 활물질 입자의 심각한 부피변화와 균열에 의한 새로운 표면이 전해액에 계속적으로 노출되는 문제로 인하여 두껍고 불안정한 피막생성을 유도한다. 불안정한 구조의 피막은 실리콘 음극의 전기화학적 성능뿐만 아니라 고온 열안정성을 저해할 수 있기 때문에 본 연구에서는 실리콘의 열안정성 향상을 위해 전해액 첨가제를 도입하여 피막구조를 변경하고자 한다. 전해액 첨가제인 lithium bis(oxalato)borate (LiBOB)가 실리콘 음극표면에 피막을 효과적으로 형성하였으며, 만충전 상태의 실리콘 음극의 $60^{\circ}C$ 저장시 용량유지 특성을 개선하였으며 고온에서의 열안정성 크게 향상시켰다.

Keywords

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