리튬 이차전지의 음극재료인 천연흑연의 충방전 속도에 따른 충방전 용량
Charge/discharge Capacity of Natural Graphite Anode According to the Charge/discharge Rate in Lithium Secondary Batteries

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류지헌; 오은영; 오승모
Issue Date
한국전기화학회 = The Korean Electrochemical Society (KECS)
J. Korean Electrochem. Soc., 7, 32 (2004)
Lithium secondary batteriesNatural graphiteRate capabilityCut-off voltage
리튬 이차전지의 음극재료로서 천연흑연의 충방전 속도에 따른 용량특성을 조사하였다 정전류 조건에서 0.0-2.0 V(vs. Li/Li+) 의 범위에서 충방전 하였을 때, 충전전류가 증가할수록 충전반응의 과전압이 증가하여 Li+이온이 충분히 삽입되지 못한 상태에서 컷오프 전압(0.0 V)에 도달하기 때문에 충전용량은 충전전류의 크기가 클수록 감소하였다. 한편, 방전전류가 증가함에 따라 방전반응의 과전압도 증가하여 0.0-0.3V범위에서 방전반응이 일어나나 방전 컷오프 전압(2.0 V)과는 격차가 커서 Li+이온이 탈리되지 못한 상태에서 방전 컷오프에 도달하는 현상은 없기 때문에 방전용량이 방전전류의 크기에 영향을 받지 않았다. 충전전류가 증가함에 따라 부반응인 리튬 전착반응의 과전압도 증가하므로 충전 컷오프 전압을 0.0V 이하로 낮출 수 있었다. 그러나 Li+ 이온의 삽입반응에 비해 전착반응의 저항이 적어 충전전류에 따른 전착반응의 과전압 증가에는 한계가 있었다. 1C조건에서 -0.04V까지 충전 컷오프 전압을 낮추었을 때 리튬의 전착반응은 없었고, 이로부터 약 11%의 방전용량을 증가시킬 수 있었다.
The charge/discharge capacity of natural graphite anode in lithium secondary batteries was examined as a function of charge/discharge rate. When the natural graphite anode was galvanostatically cycled in the range of 0.0-2.0V (vs. Li/Li+) , the charging capacity decreased with an increase in the charging rate, which is caused by an earlier approach to the charging cut-off (0.0 V) before the complete charging that is in turn caused by an ever-increasing overpotential at higher rates. Even if the overpotential of discharging reaction also increased at higher discharge rates, the discharging reaction took place in the range of 0.0-0.3 V that is far below the discharge cut-off (2.0 V).
As a result, the discharge capacity was not affected by the discharge rate because all the lithium ions once intercalated are fully discharged even at high current condition.
As the overpotential of lithium deposition reaction also increased at high current condition,
the charge capacity of natural graphite could be enlarged by lowering the charging cut-off voltage below 0.0 V,
There is, however, a limitation for the lowering of cut-off voltage because the resistance for lithium deposition is smaller than that of lithium intercalation into graphite. When the charge cut-off voltage was lowered down to -0.04 V under IC condition, lithium ions were inserted into graphite without lithium deposition such that the discharge capacity could be raised up to 11% .
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Chemical and Biological Engineering (화학생물공학부)Journal Papers (저널논문_화학생물공학부)
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