In this study, a three dimensional NiCrAl alloy foam was used as a current collector for high-power and high-capacity lithium iron phosphate batteries. A charge-discharge test revealed that at a high current rate, the electrode using a metal foam had better power performance and its capacity faded much less than in the case of a conventional foil-type current collector. The cyclic voltammetric analysis showed that the redox reaction occurred much faster in the case of the metal foam than in the case of the foil. The reason for this is that in the case of metal foam, the electrons transfer rapidly at the junction of the metal frame, the active material, and the electrolyte, but, in the case of foil, the electrons transfer relatively slowly between the foil current collector and the electrode surface of the active material. An impedance analysis showed that the charge transfer resistance was much lower for the metal foam than for the foil.

LiFePO4 electrodes using three dimensional NiCrAl alloy metal foam of different electrode thickness are prepared. In order to improve the electrochemical and cycle-life performance of lithium ion batteries, it is important to optimize the electrode thickness and mass loading of active material. As compared to those with thick electrode, the cells with thin electrode exhibit high rate performance and cycle-life behavior, due to the shorter diffusion length of lithium-ion and improved kinetic behavior. Also, cyclic voltammetry curves and electrochemical impedance spectroscopy analysis indicate that the redox reaction for the thinner electrode occurs much faster, and the charge transfer resistance is much lower. The results of same current density (mA cm-2) show that 450 μm-thickness electrode exhibits superior electrochemical and power performance. It is because the 300 μm-thickness electrode which has the lowest mass loading of active material meant that it carried the highest current rate, and thicker electrodes show higher internal resistance and much poorer kinetic property. Namely, electrode thickness and an amount of active material are difference according to the intended use.

LiFePO 4 electrodes using three-dimensional NiCrAl metal foam of different conductive carbon content were prepared. Increasing the carbon black content greatly enhanced the rate performance, with a severe capacity fade shown for lower carbon black content with increases current rate. The electrode with no addition of carbon black showed very poor electrochemical performance, due to the high charge transfer resistance (R ct ) and high diffusion limitation of Li-ion. The electrodes of increased carbon black loadings enhanced the kinetic performance and dramatically decreased the R ct , due to the large effective contact area between the conductive carbon material and the LiFePO 4 particles. However, lower carbon black loading resulted in much higher areal capacity (mAh cm −2 ) at 0.2 and 0.5 C, due to increases in the amount of LiFePO 4 particles from reducing the carbon black loading. According to the results for 8 mA cm −2 , the specific capacity of 15 wt.%-electrode was higher than 10 wt.%-electrode. However, electrode polarization of 15 wt.%-electrode was more high than for 10 wt.%-electrode, due to high over-potential by the high current rate. That is to say the optimal conductive carbon content differs according to the intended use.

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