Varta Batterie Aktiengesellschaft

Varta Batterie Aktiengellschaft

Gunter Hofmann

Uwe Kohler

Frank Lichtenberg

Klaus Kleinsorgen

Gerhard Simon

Christoph Klaus

A Ni/Cd or Ni/hydride storage battery of the button cell type has a positive electrode tablet based on a nickel hydroxide powder having an active mass comprised of spherical particles with a high pycnometric density (d&gt;3.5 g/cm.sup.3). In contrast to conventional nickel hydroxide powders having irregular particles, a better space utilization is achieved during dry pressing due to a narrow particle-size distribution having a maximum in a range of from 5 to 20 .mu.m, and due to the rounded particle surfaces. The specific volumetric capacity of the resulting button cell electrode is consequently approximately 25% higher than that of a conventional positive button cell electrode. A microporous separator having pore sizes smaller than the mean diameter of the spherical particles prevents the danger of short circuits.

Gastight, sealed alkaline storage battery in the form of a button cell

The positive electrode of a Ni/metal hydride accumulator is formed from a mass mixture of Ni(OH).sub.2 and an oxidation-resistant graphite. The stable graphite is notable for a high degree of crystallinity and a low ash content. In conventional Ni/metal hydride accumulators, cobalt compounds play an essential part in developing a conductive matrix within their positive nickel hydroxide electrodes, leading to reductive destruction of the matrix by severe high temperature short circuit testing. In contrast, the same accumulators, with positive electrodes produced according to the present invention, survive the test with only a temporary and slight decline in capacity.

Ni/metal hydride accumulator

In a metal oxide/hydrogen storage battery, preferably formed as a coiled cell or as a button cell, having a negative electrode, a positive electrode, and an intermediate separator, the oxidation-sensitive negative electrode is protected against diffusing oxygen by a metallic covering of the electrode's metal hydride particles, and the oxygen reduction necessary for gas-tight operation is transferred to an auxiliary electrode which is arranged outside of the ionic path between the positive and negative electrodes. Metals with high solubility for hydrogen, such as Pd, Ni and Cu, are suitable as the covering material. The auxiliary electrode is formed as a film based on a mixture of activated carbon, a PTFE binder and conducting graphite, and is either laminated onto the negative metal hydride electrode or is spatially separated from the main electrodes, depending upon the cell's overall construction.

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Hofheim, Germany

Gunter Hofmann