Analysis and Application on the Functions of Oxide/Carbon Hetero-Junctions during Electrochemical Insertion/Extraction

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Aluminum current collector of lithium secondary batteries forms compact passivated film according to the high field model in the organic electrolyte solutions including fluorine element. However, the corrosion of this passivated film and aluminum substrate increases the leak current and reduces the battery performance. Based on these points of view, the controlling of passivated film at aluminum current collector has been investigated as functions of aluminum foil purity, surface treatment, composite cathode pressing condition, electrolyte composition, and formation in the battery fabrication processes. It was clear that the charging/discharging cycle performance was improved by reducing leak current of passivated film by adding some additional metal impurities to the aluminum current collector, by applying surface heating of aluminum, by adding small amount of water to the cathode composite, and by adding oxygen donor such as water and / or LiNO_3 to the electrolyte solution.Research on cathode materials for 5 V class lithium secondary batteries is a trend in recent researches. However, the passivated film characteristic of a cathode current collector is still not well known. We investigated the anodic passivation behavior of some valve metals at such high anodic potentials in organic electrolytes for lithium secondary batteries. As a conclusion, we should use aluminum as a cathode current collector for 5 V class lithium secondary batteries since it formed a high insulating film with high tolerant voltage at the metal surface.In conclusions, Hetero-contact of passivated film on the current collector/carbon conductive additives controls the contacting resistance of the positive electrode, and this controls the total charging/discharging rate of lithium insertion/deinsertion of lithium secondary batteries.