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Development of High Capacity Lithium Ion Battery Anode Material by Controlling Si Particle Size with Dry Milling Process

건식 분쇄 공정으로 Si 입도 제어를 통한 고용량 리튬이온전지 음극 소재의 개발

  • Jeon, Do-Man (Department of Chemical Engineering and Applied Chemistry, Chungnam National University) ;
  • Na, Byung-Ki (Department of Chemical Engineering, Chungbuk National University) ;
  • Rhee, Young-Woo (Department of Chemical Engineering and Applied Chemistry, Chungnam National University)
  • 전도만 (충남대학교 응용화학공학과) ;
  • 나병기 (충북대학교 화학공학과) ;
  • 이영우 (충남대학교 응용화학공학과)
  • Received : 2018.07.25
  • Accepted : 2018.08.28
  • Published : 2018.12.31

Abstract

Currently graphite is used as an anode active material for lithium ion battery. However, since the maximum theoretical capacity of graphite is limited to $372mA\;h\;g^{-1}$, a new anode active material is required for the development of next generation high capacity and high energy density lithium ion battery. The maximum theoretical capacity of Si is $4200mA\;h\;g^{-1}$, which is about 10 times higher than the maximum theoretical capacity of graphite. However, since the volume expansion rate is almost 400%, the irreversible capacity increases as the cycle progresses and the discharge capacity relative to the charge is remarkably reduced. In order to solve these problems, it is possible to control the particle size of the Si anode active material to reduce the mechanical stress and the volume change of the reaction phase, thereby improving the cycle characteristics. Therefore, in order to minimize the decrease of the charge / discharge capacity according to the volume expansion rate of the Si particles, the improvement of the cycle characteristics was carried out by pulverizing Si by a dry method with excellent processing time and cost. In this paper, Si is controlled to nano size using vibrating mill and the physicochemical and electrochemical characteristics of the material are measured according to experimental variables.

현재 리튬이온전지의 음극 소재 활물질로는 흑연이 주로 사용되고 있다. 그러나 흑연의 최대 이론 용량이 $372mA\;h\;g^{-1}$으로 제한되기 때문에 차세대 고용량 및 고에너지 밀도의 리튬이온전지 개발을 위해서는 새로운 음극 소재 활물질이 필요하다. 여러 음극 소재 활물질 중에서 Si의 최대 이론 용량은 $4200mA\;h\;g^{-1}$으로 흑연의 최대 이론 용량보다 약 10배 이상 높은 값을 나타내고 있지만 부피 팽창율이 거의 400%로 크기 때문에 사이클이 진행될수록 비가역 용량이 증가하여 충전 대비 방전 용량이 현저히 감소하는 현상을 나타내고 있다. 이러한 문제점을 해결하기 위한 방법으로 Si 음극 소재 활물질의 입자 크기를 조절하여 기계적 응력 및 반응상의 체적 변화를 감소시켜 사이클 특성을 다소 향상시킬 수 있다. 따라서 Si 입자의 부피 팽창율에 따른 충전 및 방전 용량의 감소를 최소화하기 위해 공정 시간 및 원가 절감이 우수한 건식 방법으로 Si을 분쇄하여 사이클 특성 향상에 관한 연구를 진행 하였다. 본 논문에서는 진동밀을 이용하여 Si을 나노 크기로 제어하고 실험 변수에 따른 재료들의 물리화학적 특성과 전기화학적 특성을 측정하였다.

Keywords

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Figure 1. Particle size change of Si after milling and classification process.

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Figure 2. Particle size distribution of Si after ball milling with different material ratios: (a) Si 50 g / steel ball 3 kg / 8 h, (b) Si 100 g / steel ball 3 kg / 8 h, (c) Si 110 g / steel ball 3 kg / 8 h, (d) Si 250 g / steel ball 4.5 kg / 12 h.

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Figure 3. Analysis of Si particle after ball milling, (a) XRD pattern, (b) SEM image.

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Figure 4. Particle size distribution of Si after (a) 1st pulverization, (b) 2nd pulverization, (c) classification.

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Figure 5. SEM images of Si particles: (a) before and (b) after classification process.

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Figure 6. Electrochemical capacity and coulomb efficiency characteristics of secondary pulverized Si up to 10 cycles.

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Figure 7. Charge/discharge curves of Si anodes with particle size of (a) D50 = 0.230 μm, (b) D50 = 0.297 μm, (c) D50 = 0.300 μm.

Table 1. Average particle size and BET analysis after ball milling of Si

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Table 2. Comparison of Si particle size before and after classification

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Table 3. Electrochemical properties of second pulverized Si and commercialized Si

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