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Dissolution of Spinel Oxides and Capecity Losses in 4 V Lithium Rechargeable Cells

Applied Chemistry for Engineering
The Korean Society of Industrial and Engineering Chemistry
Publication Date
  • Li Secondary Batteries
  • Spinel Lithium Manganese Oxide
  • Spinel Dissolution
  • Capacity Losses
  • Doped Spinel Lithium Manganese Oxide


리튬 2차 전지의 양극재료로 사용되는 스피넬 망간산화물(Li(x)Mn2O4)은 충방전이 거듭됨에 따라 점차 용량이 감소한다. 본 논문에서는 이러한 용량감소의 원인을 규명하였고 이를 억제할 수 있는 방안을 제시하였다. 결과를 요약하면 아래와 같다. (1) 양극의 충전 말기(at > 4.1 V vs. Li/Li(+))에서 카본 도전재의 표면에서 전해질에 포함된 유기용매가 전기화학적으로 산화되며 산(acid)을 발생시키는데, 이 산이 스피넬을 용해시키기 때문에 용량이 감소한다. (2) 액체전해질로 carbonate 계열의 유기용매에 fluorine을 포함하고 있는 리튬염을 사용할 경우에 전해액의 산화와 스피넬의 용해 정도가 적어 양극의 용량감소가 적다. (3) 스피넬의 용량 감소는 스피넬 용해에 의한 활물질 손실과 전극 저항 증가에 의한 분극손실의 2가지 요인에 의해서 발생한다. 표면적이 큰 카본 도전재를 사용하면 스피넬 망간산화물(Li(x)M(y)Mn(2-y)O4, M=Mn, Li, Al, Co, Ni, or B)의 용량감소 원인에 대한 연구 결과, 스피넬의 용량감소에 영향을 주는 가장 큰 요인은 충방전에 따른 스피넬 격자의 부피변화에 따른 구조적인 붕괴이며, 스피넬 용해는 두 번째로 주요한 요인임을 확인하였다. It is well known that spinel lithium manganese oxide cathode materials lose their charging capacity with repeated cycling in Li secondary batteries. In this paper, we attempt to clarify the origin of capacity losses and suggested a method th overcome this problem. The major findings fall into three categories: (1) the capacity loss stems from the spinel dissolution, which is promoted by acids generated from electrochemical oxidation of solvent molecules on the carbon surface at the charged state (at > 4.1 V vs. Li/Li(+)) of the cathode. (2) the cathodic capacity loss, arising from the solvent oxidation and spinel dissolution can by minimized by using the electrolytes composed of carbonates and/or fluorine-containing lithium salts. (3) the spinel capacity loss is accounted by two factors: material loss arising from the spinel dissolution and the polarization loss caused by an increment in the cell resistances. The relative importance between the two, the spinel and polarization, seems to be determined by the carbon surface area. The material loss is dominant for a large surface area of carbon, where the spinel dissolution is severe. Whereas for the polarization loss, it is more of a problem for a small carbon surface area. In the case of doped spinel lithium manganese oxides with the nominal composition of LiM0.05Mn1.95O4 (M=Mn, Li, Al, Co, Ni, or B), the structural breakdown, due to the repeated change in lattice volume, is the most important failure mode, and the second major role is played by the spinel dissolution.

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