A metal foam as a current collector for high power and high capacity lithium iron phosphate batteries

Abstract

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.

Calendering effect on the electrochemical performances of the thick Li-ion battery electrodes using a three dimensional Ni alloy foam current collector

“…1. (The image of bare metal foam can be found in the previous work [18]) Due to the unique structure of the current collector, the triple junctions (the junction of metal frame, active material and electrolyte) not only exist at the surface but also exist inside of the electrodes both for the cells using the pressed and unpressed electrodes. The advantage of the triple junction is that the redox reaction occurs preferentially at that region because of the fast electron transfer [18]. However, it is expected that the electrochemical performances exhibit in different way for the two kinds of electrodes since the electronic conductivity and effective redox area could be different in the condition of different electrode density.…”

“…It shows that the effective redox area is much larger for the unpressed electrode, although the metal foam surface area and mass loading of the active material are the same for the two kinds of electrodes. The electrode densities were calculated by using the same method of in previous study [18], and as a result, each value is 1.59 and 0.79 g cm À3 respectively for the two kinds of electrodes. The electrode density increased almost two times after calendering.…”

“…Nevertheless, to be useful for electric vehicles or high power energy storage, the active material of a Li-ion battery should be coated with a foil type current collector that is much thinner, and its electrode area should be large enough to meet the high power performance with a sufficient capacity. Thus, the weight of battery becomes heavier and larger because of the increase in the use of inactive materials, such as the current collector and separator [18].…”

“…Additionally, the contact area between the active material and current collector is much larger for the threedimensional metal foam [18,26,28]. So it is possible to increase the mass loading of active material in the metal foam current collector for high power and high capacity Li-ion battery due to the better electrochemical performance and the unique structure.…”

“…Due to the unique structure of metal foam, the triple junctions of the active material, metal frame and the electrolyte are directly exposed at the electrode surface whereas the current collector exists at the back side of active material in the case where a foil type is used [18]. Additionally, the contact area between the active material and current collector is much larger for the threedimensional metal foam [18,26,28].…”