DE1097499B - Process for the production of porous electrode bodies serving as carriers of the active material for alkaline batteries - Google Patents

Description

GERMAN

The electrodes of alkaline batteries should have the following properties: low weight at high capacity, chemical resistance to the electrolyte, very good electrical conductivity. this so far one has tried to achieve with the following means:

To accommodate the active material, porous electrode bodies were made from carbon; Disadvantage: not resistant to anodic oxidation (see Kurt Arndt, Künstl. Kohlen, 1922, pp. 169 to 172); porous Electrode bodies made of synthetic resins or other insulators, which are metallized or or and through Addition of conductive substances made electrically conductive; Disadvantages: conductivity too low, thin Metal layers are completely oxidized anodically, thicker metal layers close the pores; Sintered electrodes made of pure metal powder; Disadvantage: relatively heavy and expensive.

The object of the invention is to reduce these disadvantages on the basis of the following findings. It has been observed that graphite powder is not attacked by anodic oxidation when enough nickel is allowed to diffuse into the graphite. A nickel layer forms that is so thick that it is not completely oxidized. Very fine pores (approx 10 μ diameter) is necessary because this is the only way of intimate contact between the electrode framework and the active mass will be produced. In the known production of porous electrode bodies by sintering metal powder without With the addition of graphite, the pores are created by adding fillers that can be subsequently removed; because of the cheapness and chemical indifference, sodium chloride is commonly used. In the production of graphite-containing electrode bodies, however, higher temperatures are to be used at which the filler, z. B. sodium chloride, already strongly volatilized and thereby the intimate connection between metal powder and graphite powder prevented. These findings were evaluated according to the invention as follows.

To produce an electrode body from graphite and metal powder, e.g. B. nickel, cobalt, among others, is fine, metallized or non-metallized graphite powder with the metal powder and the later removable filler, z. B. sodium chloride, intimately mixed and pressed with a pressure of a few t / cm ² to form electrode bodies. The lower the metal powder content, the higher the pressing pressure. For the purpose of connecting graphite and metal, the pressed electrode bodies can be heated to just below the melting point of the metal if there is a uniform temperature, ie no temperature gradient, in the heating room. In order to prevent the fillers from escaping from the pressed body

of as a carrier of the active mass

serving porous electrode bodies

for alkaline batteries

Applicant:

ίο Friedrich Reiber,

Oberndorf near Ebersberg

Friedrich Reiber, Oberndorf near Ebersberg,
has been named as the inventor

To prevent this, a protective gas is introduced into the boiler room under pressure of up to a few atmospheres, z. B. pure nitrogen or commercial nitrogen mixed with a little hydrogen; particularly suitable are inert gases with a high atomic or molecular weight instead of nitrogen. At higher annealing temperatures the protective gas pressure must be increased. If there is a temperature gradient practically no can be avoided completely, the electrode bodies are placed in a container with small openings, the placed in the boiler room. A certain amount is also added to this container or boiler room of the fillers contained in the electrode body. This amount must be larger at a high temperature than at lower. This ensures that the boiler room is saturated with their vapors and so that Volatile fillers from the electrode body are prevented.

After the annealing, the fillers are removed in a known manner. This procedure is now there also the possibility of replacing removable additives with metal oxides, e.g. B. Nickel oxide in electrodes made of nickel and graphite. During the annealing process, the metal powder forms together with the graphite a solid framework, while the metal oxide powder is wholly or partially reduced to spongy porous metal which is embedded in the pores of the electrode body. It can then be used to manufacture the active mass can be used by converting it into oxide in a known manner. This method saves the time-consuming and costly introduction of the active material by soaking it with the appropriate Metal salt solutions and subsequent forming. When to produce the positive active mass by soaking this with a nickel salt solution

009 699/101

Silver salts are added, the latter are in normal treatment by finely divided nickel in the electrode decomposes, and the silver precipitates as a metal in a spongy form. To prevent this, become the surfaces and the pore walls of the electrodes coated with a nickel oxide layer, either directly from the nickel of the electrode Oxidation is produced or produced from this after impregnating the electrode with a nickel salt.

IO

Claims (5)

Patent claims: 1. Process for the production of porous electrode bodies serving as carriers for the active material for alkaline batteries in which graphite powder and at least 10% finely powdered Metal dust, e.g. B. nickel dust, are intimately mixed, the mixture is pressed to the body and this z. B. is heated to almost below the melting point of the metal dust, characterized in that that one introduces a protective gas under pressure up to a few atmospheres into the boiler room, with the gas pressure is kept higher at a higher annealing temperature than at a lower annealing temperature. 2. The method according to claim 1, characterized in that the graphite-metal powder mixture Metal oxide powder is added, which is formed after annealing in a manner known per se serves the active mass, e.g. B. nickel oxide powder. 3. Process according to claims 1 and 2, characterized in that the heating room is heated in this way that the temperature in the heating room is uniform when the pressed electrode body is glowing is distributed, d. H. there is no temperature gradient. 4. Process according to claims 1 to 3, characterized in that in the boiler room in which the electrode body are annealed, in addition a certain amount of the the electrode body in Removable fillers or metal oxides added in a known manner is given. 5. The method according to claims 1 to 4 when using positive active masses with Additions of silver compounds, characterized in that before the introduction of the active A metal oxide layer on the surface and on the pore walls of the porous electrode body is produced. Considered publications:
German Patent No. 920 082;
French patent specification No. 1 097 994. © 009 699/101 1.61