Performance Of Package Film And Carbon-coated Al Collector For Soft-packed Lithium Iron Phosphate Cells

In recent years the rapid development of electric vehicles results in the sharpboost of power batteries in the market. Lithium iron phosphate-based batteries havebecome the first candidate due to the merits of cycle life, safety concern and evencost. The different principle from the aqueous-based secondary cells made Lithiumion cell could take the form of prismatic pouch cells at the same time. As a result,the specific energy density and safety of batteries are further improved because ofemployment of aluminum-plastic composite film as package material.But as one of the key raw materials of LiFePO4-based cells, the performance ofcomposite package film has a great influence on the batteries, like electrolyte-proof,air tightness and so on. The calorimetric analysis on the composite package film wasconducted by means of Differential Scanning Calorimetry (DSC), and then thepreferable sealing temperature was fixed down according to DSC results. Inaddition, the pinholes and exposure of metal Aluminum are the common defects, areinvisible and ignored in application. So a novel method was attempted to detect thedamages, in which the compositepackage film was served as the cathode in the Cu2+contained aqueoussolution, andCu2+would be reduced to the metal copper depositedon the pinholes and the exposure. The applied results showed the method waseffective and ease to operate.Another disadvantage of LiFePO4-based cell was the inferior performance inlow temperature, so laser particle size analyzer, specific analyzer, XRD and ICPwere employed to investigate LiFePO4by comparison, and then the effect ofLiFePO4on cell was statisticallyevaluated by comparing the charge-dischargeperformance of the commercialized cells. The results showed LiFePO4took the firstplace in the influential effectors on the prismatic pouch cells.In the end a novel positive collector-carbon-coated aluminum foil wasinvestigated, which appeared in the industry recently. The results displayed theemployment of the collector could diminish the polarization during charge-dischargeobviously, and enhance the retention of electrolyteat the same time. In addition the collector could raise the qualified rate and restrain the distribution of internalresistance effectively.