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Basic theory of Dielectric Relaxation Spectroscopy and Studies of Electrolyte Structure

유전체 이완 분광법의 원리 및 이를 이용한 전해액 미시구조 연구

  • 구본협 (대구경북과학기술원에너지공학전공) ;
  • 황순욱 (대구경북과학기술원에너지공학전공) ;
  • 이호춘 (대구경북과학기술원에너지공학전공)
  • Received : 2019.05.10
  • Accepted : 2019.05.21
  • Published : 2019.05.31

Abstract

To examine the solution structure of electrolytes, it is very important to understand ion-ion and ion-solvent interactions. In this review, we introduce the basic principle of dielectric relaxation spectroscopy (DRS) and studies of electrolyte structure. DRS is a type of impedance method, which measures the dielectric properties of electrolytes over a high frequency domain at levels of tens of GHz. Therefore, DRS provides information on the different polar chemical species present in the electrolyte, including the type and concentration of free solvents and ion pairs with dipole moments. The information of DRS is complementary to the information of conventional analytical techniques (Infrared/Raman spectroscopy, nuclear magnetic resonance (NMR), etc.) and thus enables a broad understanding of electrolyte structure.

전해질의 미시 구조분석을 위해서는 이온-이온 및 이온-용매 상호작용을 이해하는 것이 매우 중요하다. 이 총설은 유전체 이완 분광법(Dielectric relaxation spectroscopy)의 기본 원리와, 이를 이용한 전해질 구조 연구 사례를 소개하고자 한다. 유전체 이완 분광법은 임피던스법의 일종으로서, 수십 GHz 수준의 높은 주파수 영역에 걸쳐 전해질의 유전 특성을 측정한다. 이를 통해, 유전체 이완 분광법은 전해질 내 존재하는 다양한 극성 화학 종, 즉, 쌍극자 모멘트(Dipole moment)를 갖는 자유 용매(Free solvent) 및 이온쌍(Ion pair)의 종류와 농도에 대한 정보를 제공한다. 유전체 이완 분광법이 제공하는 정보는 기존 분석 기법(적외선 분광법(Infrared), 라만 분광법(Raman) 및 핵자기 공명 분광법(Nuclear magnetic resonance) 등)이 제공하는 정보들과 상호보완적 관계에 있으며, 이러한 종합적 분석을 통해 전해질 구조에 관한 깊은 이해가 가능하다.

Keywords

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Fig. 1. Parallel plate capacitor with direct current (DC) voltage source.

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Fig. 2. Parallel plate capacitor with alternating current(AC) voltage source.

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Fig. 3. Frequency response of dielectric mechanisms.

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Fig. 4. Dipole rotation in electric field.

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Fig. 5. Permittivity, ε′ (v) spectra and dielectric loss, ε″ (v) spectra of water at 25oC.

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Fig. 6. Total permittivity, η″ (v) , permittivity, ε′ (v) spectra, and dielectric loss, ε″ (v) spectra of 0.1 M Fe(ClO4)2 at 25oC. The slashed areas show the contributions of the ion pair (IP) and free water molecule relaxation process to ε″ (v).

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Fig. 7. Permittivity, ε′ (v) , and dielectric loss, ε″ (v) of 1 M LiBF4-PC compared with the spectrum calculated with Debye equation. The slashed areas show the contributions of the SIP, CIP and free PC solvents (PC and PC') relaxation process to ε″ (v).

Table 1. Possible ionic species in non-aqueous system, and their activity for Raman spectroscopy and DRS.

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