화학공학소재연구정보센터
Korean Chemical Engineering Research, Vol.55, No.2, 242-246, April, 2017
하이브리드 커패시터의 열안정성 개선을 위한 LiFePO4 복합양극 소재에 관한 연구
Study on LiFePO4 Composite Cathode Materials to Enhance Thermal Stability of Hybrid Capacitor
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초록
고온에서 Mn 이온 용출에 의한 성능저하를 보이는 스피넬 결정구조의 LiMn2O4 양극 하이브리드 커패시터의 대안으로 열안정성이 높은 올리빈 결정구조의 LiFePO4 기반 복합양극 소재의 적용가능성을 연구하였다. LiFePO4/활성탄셀을 이용한 1.0~2.3 V의 충·방전을 통한 수명평가에서 상온(25 °C) 및 고온(60 °C) 조건 모두에서 충·방전 사이클이 진행됨에 따라 음극(활성탄)의 저전압화에 따른 열화로 인한 용량저하 현상이 나타났다. 이의 해결을 위해 50:50 중량비율로 LiFePO4/LiMn2O4, LiFePO4/Activated carbon 및 LiFePO4/LiNi1/3Co1/3Mn1/3O2 복합양극을 제조하여 모노셀 충·방전 실험을 수행한 결과, 층상구조의 LiNi1/3Co1/3Mn1/3O2를 사용한 전극이 안정적인 전압거동을 보였다. 또한, 2.3 V 및 80 °C에서 1,000시간 부하를 통한 고온 안정성 실험에서도 LiFePO4/LiNi1/3Co1/3Mn1/3O2 복합양극이 상용 LiMn2O4 양극에 비해 약 2배 가량 높은 방전용량 유지율을 보였다.
The application of composite cathode materials including LiFePO4 (lithium iron phosphate) of olivine crystal structure, which has high thermal stability, were investigated as alternatives for hybrid battery-capacitors with a LiMn2O4 (spinel crystal structure) cathode, which exhibits decreased performance at high temperatures due to Mn-dissolution. However, these composite cathode materials have been shown to have a reduction in capacity by conducting life cycle experiments in which a LiFePO4/activated carbon cell was charged and discharged between 1.0 V and 2.3 V at two temperatures, 25 °C and 60 °C, which caused a degradation of the anode due to the lowered voltage in the anode. To avoid the degradation of the anode, composite cathodes of LiFePO4/LiMn2O4 (50:50 wt%), LiFePO4/activated carbon (50:50 wt%) and LiFePO4/LiNi1/3Co1/3Mn1/3O2 (50:50 wt%) were prepared and the life cycle experiments were conducted on these cells. The composite cathode including LiNi1/3Co1/3Mn1/3O2 of layered crystal structure showed stable voltage behavior. The discharge capacity retention ratio of LiFePO4/LiNi1/3Co1/3Mn1/3O2 was about twice as high as that of a LiFePO4/LiMn2O4 cell at thermal stability experiment for a duration of 1,000 hours charged at 2.3 V and a temperature of 80 °C.
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