고전압 구동 Li2MnO3-LiMO2(M=Ni, Co, Mn)/graphite 시스템에서의 전지 수명 및 고온 방치 특성 향상에 효과적인 플루오로 화합물계 전해액에 대한 연구
Improved Cycle Life and Storage Performance in High-Voltage Operated Li2MnO3-LiMO2(M=Ni, Co, Mn)/Graphite Cell System by Fluorine Compounds as Main Electrolyte Solvent
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초록
Li2MnO3-LiMO2(M=Ni, Co, Mn) 나노 복합체는 높은 이론 용량을 가지고 있어 전기 자동차용 2차 전지 활물질 재료로 많은 연구가 진행되고 있다. 하지만 Li2MnO3-LiMO2(M=Ni, Co, Mn)로부터 250 mAh/g 이상의 용량을 구현하기 위해서는 4.4 V 이상의 구동전압이 필요하며, 이러한 높은 구동 전압은 전지의 수명 및 고온 방치 특성의 저해 요소로 작용하고 있다. 본 연구에서는 이러한 문제점을 개선하기 위해서 FEC (Fluoroethylene carbonate), 플루오로알킬 에테르, LiPF6가 주성분인 신규 전해액(F-based EL)을 설계하였다. F-based EL은 1.3 M LiPF6 EC/EMC/DMC (3/4/3, v/v/v) (STD) 대비 안정한 SEI를 형성하며, 산화 안정성이 뛰어나 Li2MnO3-LiMO2(M=Ni, Co, Mn)/graphite 셀의 수명 및 방치 중 가스 저감에 효과가 있음을 확인할 수 있었다.
Abstract
Li2MnO3-LiMO2(M=Ni, Co, Mn) nano-composite is a promising cathode material for xEV application due to its high theoretic capacity. However high voltage operating system of Li2MnO3-LiMO2(M=Ni, Co, Mn) has worked as a hurdle in its application because of the inherent demerits, such as cycle life degradation and gas evolution. In order to enhance cell performance of Li2MnO3-LiMO2(M=Ni, Co, Mn)/graphite cell, we examined electrolyte mainly composed of FEC, fluroalkyl ether and LiPF6 (F-based EL). F-based EL showed much better discharging retention ratio than 1.3 M LiPF6 EC/EMC/DMC (3/4/3, v/v/v) (STD). Furthermore gas evolution, especially CO and CO2 during 60oC storage for 30 days was dramatically reduced owing to thermal stable SEI formation effect of F-based EL.
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