Process for producing metal foams having uniform cell structure

Abstract

A method for producing porous metal plated polymeric foam having uniform pore properties. Polymeric foam buns are horizontally cut along a longitudinal surface thereby lifting off a foam sheet. The sheet is spooled and then reticulated to remove any remaining cell walls and to round off the internal pore struts to enlarge the openings between the adjacent cells. The reticulated foam sheet is unwound and then plated. Slabs may be attached end to end and loop slitted and then reticulated. The resulting plated uniform foam provides a superior substrate for battery plaques and other applications.

Description

TECHNICAL FIELD [0001] The present invention relates to the production of foams in general, and in particular, to the production of porous metal plated foams having substantially isotropic characteristics. BACKGROUND OF THE INVENTION [0002] Porous metal plated foams are used in many industrial and commercial applications: battery electrodes, fuel cell components, filters, pollution control equipment, catalyst supports, audio components, etc. [0003] The underlying cell structure is often key to the characteristics of the foam. The three dimensional shape of the repeating cell matrix affects the performance of the foam. [0004] Foams typically come in either open cell or closed cell variants. Different manufacturing techniques are used to produce each type. [0005] Open cell nickel plated foam is predominantly used for electrodes in nickel metal hydride (“NiMH”) and nickel cadmium (“NiCd”) batteries. In addition to mass production of small consumer cell batteries, large-pack NiMH batter...

AI Technical Summary

Benefits of technology

[0022] There is provided a process for producing metal foams with substantially uniform cell structure. Polymeric foam slabs of desired length are slit with a horizontal slitting knife along the longitudinal bun surface to a desired thickness in a horizontal slitting apparatus. The resulting sheets may be attached to one another end to end to increase their effective length and in any event are typically spooled. Alternatively the horizontal slitting can be done in a loop slitting apparatus, producing a spooled long sheet similar to the long sheet produced by the joining shorter sheets made by the horizontal slitting apparatus. In either case, the rolled or spooled sheets are subject to thermal reticulation and then plated by chemical vapor deposition, by electrodeposition (preceded by a suitable treatment to make the foam sufficiently conductive) or by other metal deposition process. The resulting metal foam is substantially uniform having consistent and desirable characteristics.

Problems solved by technology

Non-uniform size, shape and orientation of foam cells lead to non-uniform thickness of nickel, foam conductivity, active mass loading and electrochemical performance of individual battery cells.

This in turn will give some of the battery cells different performance characteristics (capacity, impedance, rate of aging) and will eventually cause a premature failure of a large battery pack that often contains as many as 200 battery cells.

When such foam is used as a substrate for nickel foam production, periodic density perturbation patterns are created, adversely affecting the application performance of the material when used as battery electrodes.

However, the slitting of a large loop 24 requires sophisticated control machinery.

Unfortunately, the conventional industry standard size polymeric foam bun, typically 60 meters long, is too large to be placed into an autoclave.

It cannot be reticulated by the flame method before loop peeling.

Accordingly, the loop slitting method suggested by Japanese patent JP 9152365 does not include thermal (flame) reticulation and it is not believed to be useful for advanced batteries requiring flame reticulated plated foam substrates.

Because of the inability to properly reticulate the typical 60 meter long foam blocks destined for loop peeling, almost all of the nickel foam produced for battery applications today is rotary peeled foam.

However, as noted, rotary peeled foam suffers from disabilities: unavoidable cyclic variations in foam density, conductivity, strength and plating density across the thickness of the foam.

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