The newly-developed porous aluminum
The newly-developed porous aluminum
[Click to enlarge image]

Sumitomo Electric Industries Ltd has developed a porous aluminum called "Aluminum-Celmet."

By using the Aluminum-Celmet as current collectors of lithium-ion (Li-ion) rechargeable batteries and capacitors, their capacities can be increased. The company will build a small-scale production line at Osaka Works to accelerate development efforts toward mass production of the new material.

The newly-developed porous metal has a three-dimensional mesh-like structure that forms interconnected, open and spherical pores. Therefore, it is not clogged. Its maximum porosity is 98%, which is higher than those of other porous metals such as nonwoven metal fabric and foam metal. It can be formed into various shapes by cutting and stamping.

Thus far, Sumitomo Electric Industries has been manufacturing the "Celmet," a porous metal made from nickel (Ni). And it is currently used as positive electrode current collectors of nickel-metal-hydride (NiMH) rechargeable batteries for hybrid vehicles. The company applied the same production process used for the Celmet to the Aluminum-Celmet.

The specific gravity and electrical resistivity of the Aluminum-Celmet are about 1/3 and less than half, respectively, compared with those of the Celmet. Moreover, because the Aluminum-Celmet has a high corrosion resistance, it can be applied to Li-ion rechargeable batteries and capacitors, which have higher charge/discharge voltages than NiMH rechargeable batteries. The Celmet cannot be used for Li-ion rechargeable batteries or capacitors because its corrosion resistance is not high enough.

Currently, the positive electrode and negative electrode current collectors of Li-ion rechargeable batteries are often made from aluminum (Al) foil and copper (Cu) foil, respectively. By replacing the Al foil with the Aluminum-Celmet, it is possible to increase the amount of positive active material per unit area, enhancing battery capacity by 1.5 to 3 times (in the case of automotive batteries). And if the battery capacity does not change, the volume of the battery can be reduced to 1/3 to 2/3.

On the other hand, capacitors use Al foil for both of their positive and negative electrode current collectors. And by applying the Aluminum-Celmet to both of their electrodes, their capacities can be increased and their sizes can be reduced as much as those of Li-ion rechargeable batteries.