DE1950920A1 - Inorganic separator for alkaline batteries - Google Patents

Description

22,897 (32,659) / Sohli. _Dr. | _nf) . Äömann October _{7, 1969}

Duiiburg

24

Yardney International Corp., New York NoY. I00I3 / UoS.A. 4o-52 Leonard Street

Inorganic separator for alkaline batteries

The invention relates to an inorganic separator for alkaline batteries with a soluble zinc electrode and a counter electrode made of silver, nickel or an air depolarization electrode consisting of the layer an inorganic compound deposited directly on an electrode or a self-supporting, between is assigned to the electrodes arranged separator, and has a particularly expedient composition and a for this purpose Appropriate manufacturing process to the subject, which the performance and service life of the battery is essential is increased.

The known separators, including the inorganic separators, have the disadvantage that they are used in alkaline batteries and rechargeable air depolarization cells, which have rechargeable zinc electrodes, oxidize in a relatively short time. For alkaline nickel / zinc batteries or alkaline silver / zinc batteries also prepares the solubility of zinc in alkaline electrolytes (e.g. potassium hydroxide) in the form of zinc ions and the solubility of the silver difficulties. Silver oxide is known to be a strong oxidizing agent and the cause most of the separators used in the previously known batteries or accumulator cells with silver electrodes a migration of the silver to the organic separator, which is a reducing agent compared to silver oxide and silver peroxide represents. The oxidation of the on cellulose or one based on similar polymeric or semi-polymeric material organic separator led to mechanical destruction

009816/13 2 0

due to which the insulation between the cell plates was reduced, so that a short-circuit current developed early on. On the other hand, there is the problem with zinc electrodes that the zinc dissolved in the electrolyte grows dendritically when it is redeposited on the zinc electrode and leads to short circuits here too if the charge-discharge process is more frequent. Zinc electrodes also have the disadvantage that they are subject to a change in shape because, during the charge-discharge process, the active electrode material migrates from the upper plate area down to the bottom. Hierdur cn found in ο Their .bereich the electrode instead of a dilution, while the lower electrode area over · W of the time is getting thicker. Such a change in shape reduces the capacity of the battery cell in the following charge-discharge cycles quite considerably.

Numerous proposals have been made to overcome the aforementioned difficulties, but none of them have led to a satisfactory result. For example, it has been proposed to use semipermeable membranes (e.g. made of cellulose) impregnate with inorganic compounds or elemental metal. Although this increases the mechanical strength of the separator material was improved and the oxidation process was reduced, the migration could be made with this design ) of zinc and do not prevent dendrite formation. These systems give only a low level of protection against mechanical Destruction and remain very susceptible to oxidation by silver oxide or silver peroxide. About the change in shape the shape of the electrodes is to be countered during the solution process For example, it has been proposed to assign the active material to an electrode carrier in the form of a bag, through which it is held on the plate. Even the suggestion, no Using oxidizable synthetic plastics as insulators between the active electrodes proved ineffective regarding the aforementioned problems. These remarks had a lower permeability and less favorable electrical properties.

009816/1328

In contrast, the invention is based on the object of a separator for alkaline batteries with a to develop soluble zinc electrode, which is particularly resistant to oxidation without impairing the electrical properties of the accumulator and a change in shape of the electrodes as a result of a Excludes zinc wandems. At the same time, the separator should also for the purposes of dialysis, electrophoresis, osmosis, as a molecular sieve or as a milliporous or microporous filter membrane be usable.

According to the invention, this object is achieved in that the inorganic separator consists of the crystal layer of an im Electrolytes of insoluble transition metal or rare earth metal oxides or hydroxides are made, with the ionic radius of the element is greater than 0.7 A *.

Surprisingly, a separator constructed according to the invention shows a significantly lower zinc migration, so that there is hardly any change in shape of the zinc electrodes occurs, the separator also resisting oxidation in the presence of silver oxides, if the inorganic Substances are selected so that they are insoluble in alkaline electrolytes (e.g. potassium hydroxide). Another The advantage is to be seen in the fact that the separator can be produced by a simple precipitation, the Precipitant corresponds to the alkaline iS electrolyte itself. The separator can either be deposited directly on a Electrode can be applied or mixed with synthetic plastics and become a self-supporting Separator foil can be processed.

Apparently the separator composed according to the invention acts like a molecular sieve through which zinc migrates is prevented by ion exchange or mechanical processes. The inorganic separator is also not disadvantageous the electrical resistance of the cell, so that this when Recharging gives good performance and has a long lifespan.

009816/1328

- * x -

The beneficial effect extends to the oxides and. Hydroxides of transition metals and rare earth metals, which get the crystal structure of cadmium iodide (CdJ ₂ ) when they are precipitated with potassium hydroxide from a salt solution of these chemical elements with various anions, e.g. sulfate anions (SO * "") or acetate anions (CH ^ COO * ") Apparently not all transition metal oxides and hydroxides are suitable as inorganic separator material "Should be 0.8 Å, while when used in self-supporting separator films that are made by adding synthetic plastics, it can also be somewhat below, for example at or above o.7 i.

In all cases, however, it should be a question of oxides and hydroxides which are precipitated in potassium hydroxide and in this are insoluble.

The oxides or hydroxides of the following transition metals or rare earth metals have proven to be particularly suitable for the inorganic separator; Trivalent Didymin-) oxides and hydroxides, manganese (II) hydroxide, cerium (III) -Oxyd and the corresponding hydroxides and oxides of praseodymium, neodymium, samarium, europium, lanthanum, scandium, yttrium, hafnium, zirconium and thorium. With results that were not quite so good, the following were also found to be useful: Cadmium (II) hydroxide and iron (II) hydroxide.

When the inorganic separator material is deposited directly on the electrode, the aforesaid Substances or compounds also together with nickel (II) hydroxide be used. However, it should be noted that the nickel hydroxide for certain areas of application · because of its tendency is not so suitable for oxidation.

009816/1320

As has already been stated, the inorganic-e Separator material can either be applied directly to one of the electrodes or can be made into a self-supporting one Process the separator film, connecting it with a suitable plastic binder. In all cases but the inorganic separator material is made from an aqueous solution of a transition metal or rare earth metal sulfate or acetate precipitated by adding potassium hydroxide »This precipitation can occur directly on the electrode take place, the zinc electrode then immersed in a suitable salt bath and the potassium hydroxide as Precipitant is supplied; the precipitated test substance will then be deposited directly on the zinc electrode On the other hand, the inorganic separator material and the deposition product can also be obtained from the solution after rinsing apply to a zinc electrode in pasty form.Tests have shown that it is also possible Corresponding deposits on the zinc electrode through an electrolytic (cathodic) deposit from a nitrate solution to obtain.

Of course, in addition to potassium hydroxide, other water-soluble alkali metal and alkaline earth metal hydroxides can be used as precipitants.However, tests have shown that it is advantageous if the precipitant is identical to the electrolyte of the electrochemical system in which the electrode is later to be used. In the case of a silver / zinc cell or a nickel / zinc cell with potassium hydroxide as the electrolyte, potassium hydroxide is expediently used as the precipitating agent. The cause of this beneficial effect is not yet known, although it can be assumed that the crystal structures involved are quite complicated and cannot be represented by the usual oxide and hydroxide formulas.

009816/1328

It has already been pointed out that the inorganic separator material can also advantageously be used in combination with synthetic plastics 2m one self-supporting Separator film can be processed. This can be done, for example, by the precipitation product with polytetrafluoroethylene, polyethylene or polyvinyl alcohol, expediently in the form of an emulsion, mixed The pastes produced in this way can be rolled out into self-supporting foils »In Surprisingly, they show the same good semipermeable properties and are practically complete resistant to oxidation in cell systems. with strong oxidizing agents and show clearly better ones Properties than those where organic separators have been metallized. In all cases it should Separator material expediently have a thickness of about 0.1 mm, the upper limit only by the proportions of the cell. So with cells for a high current discharge or charge one becomes thin Select separator material, but for slow eating and loads correspondingly thicker

The novel inorganic separator films can advantageously be used as membranes or semipermeable separators for other purposes as well. They are suitable 'as membranes for purposes of dialysis, as molecular sieves or microporous filters as cell dividers and membranes in electrochemical systems for water desalination and electrophoresis. They can also be used in non-electrical systems where more membrane mechanical diffusion is desired.

The subject matter of the invention is based on several exemplary embodiments explained, namely Fig. 1 shows a central cross section through a re-

loadable jUckumulatortn-ztll · and Fig. 2 shows a middle cross-section through a re-

Chargeable Gaadepolarization Cell · ·

069816/1329

Figure 1 shows a cell Io with a negative zinc electrode 11, at dex · the mass of the electrochemically active material 12 with an inorganic separator 14, the one in the following examples may have the composition described. A self-supporting inorganic separator 14a (see Example II) is arranged between the electrode 11 and a counter electrode 13, which is designed as a silver or nickel electrode and provided with a thin film of an inorganic separator material 14. The electrolyte 17 of the Cell is made of potassium hydroxide.

In Figure 2 is a zinc electrode 21 of the cell 2ο provided with an inorganic separator coating 22 and is arranged opposite an air depolarization electrode 24, in which air is fed through a line 25. This system can be charged via connections 26 and 27 and uses a potassium hydroxide electrolyte 2o.

Example I.

A zinc / zinc oxide electrode for a silver-zinc or a nickel-zinc cell according to FIG. 1 or a rechargeable air depolarization cell according to FIG Room temperature produced. The electrode was then removed and immersed in a 35% aqueous KOH solution for one minute. It was then re-immersed in the nickel sulfate bath for five minutes and finally again in the KOH solution for one minute The plate was then dried in a forced-air oven for four hours at 100 ° C. The plates had a coating of nickel (II) hydroxide Ni (OH) ₀ and were pressed at about 63 kg / cm so that a continuous coating was formed about 0.5 mm thick. The zinc electrode, provided with a nickel hydroxide coating, was then placed in a zinc air cell, which is a conventional one

003816/1328

Depolarization electrode after being in a nylon fabric pouch stored una with different layers of a cellophane separator material. The cell was washed with a 3% aqueous potassium hydroxide solution filled with 80 g zinc oxide (ZnO) per liter. A comparison cell was made using untreated zinc oxide plates. The test and comparison cell was charged in an identical manner and discharged at a discharge rate of 31 mA / cm. After 24 charge-discharge cycles, the Comparison cell lost more than $ 50 of its original capacity, while at 44 cycles the with . The test cell provided with an inorganic separator would still have almost its original ampere-hour capacity This inorganic nickel hydroxide separator was not suitable for silver-zinc cells because it was oxidized by silver oxide ·

Example II

Was Ceriumhydroxyd was made of an inorganic separator by heating a saturated solution of cerous chloride (CeCl,) of about looo g per liter at a temperature of 80 to 85 ⁰ C, followed by concentrated potassium hydroxide (44jt-ig) was added to the precipitation of the hydroxide was complete. The potassium hydroxide was added to ί heating to 80 ⁰ C for a period of five minutes at constant agitation of the solution. As a result of the exothermic reaction the solution Detrug the Errbemperatur 95 ⁰ C.

The precipitated Ceriumhydroxyd was then washed free of potassium hydroxide and dried at 60 ⁰ C for a period of 24 hours The dried material was pulverized and sieved through a sieve o, 74 mm mesh size, and the fine powder with a Polytetrafluoräthylenemulsion (Dupon No. · 3o TFG -Emulsion) mixed in such a ratio that the solid Polyte trafluoroethylene made up about 2o percent by weight of the total solid in the mixture. the

The putty-like mixture was dried in an air circulator at 100 ° C. for a period of four hours and then ^{pressed into a film at about 2.31 / cm 2} to a thickness of 0.8 mm. The separator film had a resistance of 0.0355 Ohm-cm in a 44% KOH solution and 0.0236 ohm-cm at 35 $ KOH. An osmosis meter showed the separator's semipermeable properties. The separator film was used to enclose the zinc electrode of a zinc air cell, in which the electrode first Epoxy was used to seal three edges of the film, which then formed an open-headed pocket.As described above, a cell with a 35% KOH solution at 80 g ZnO per Liters a * »e service life with sustained capacity of 51 cycles A check of the cell after the formation of a short circuit showed some mechanical damage and breaks, but no zinc penetration.

Example III

The method according to Example II was carried out with the difference that the cerium hydroxide precipitated at room temperature to obtain an oxy salt having the above-described crystal layer structure. Try with This separator material, which was manufactured according to Example II, showed that a zinc air cell after three Deep discharges still had 8o # of the original capacity

Example IV

Cerium hydroxide separators were manufactured according to Example II with the difference that the mass after mixing with Polytetrafluoroethylene and drying again wetted with water una then between rollers to form a uniform Foil was calendered with a thickness of about 0.28 to 0.33 mm · It had a resistance of 0.35 Ohm-cm at 4o # KOH. Comparative zinc penetration samples showed that the separator had only a low level of penetration

0098 16/1328

had after 1β38ο minutes; Battery separator material, based on cellophane, only had a period of 190 to 280 minutes before zinc penetration occurred and oömose measurements showed comparable semipermeable properties between the inorganic separator and the cellophane separator. Even after prolonged immersion in 44 $> KOH, no change in the shape of the electrodes could be determined. Pockets were made of the improved material using heat-sealed edges and the cell exhibited the same number of cycles as described in connection with Examples II and III.

Example V

Nickel (II) hydroxide was made by adding a 44 ^ KOH solution to a saturated solution (625 g / liter) of NiSO * 4 H "0 produced at room temperature over a period of five minutes with continuous stirring. The received Nickel hydroxide precipitate was washed and dried at 71 ° C. for twenty hours, pulverized and sighted to a maximum grain size of 0.074 mm. The powder was then mixed with 10% fibrous potassium titanate, which had previously been sieved to a maximum of 0.074 mm grain size, and the powder mixture then with a polytetrafluoroethylene emulsion (Dupon No. 3o GFE emulsion) mixed, see above that the ratio of the solid polytetrafluoroethylene to the total solid was Io percent by weight. After this Mixing for ten minutes, the material was dried at 100 ° C for four hours in a forced air oven. The separator sheet was then through Pressing the material in a suitable shape while pressing

of 1.5t / cm pressed to a thickness of 0.6 mm. she had a resistance of 0.12 ohm-cm in 35 # KOH. In general produced separators made without potassium titanate, resistances an order of magnitude higher than those with Io # potassium titanate

These separators were made in zinc / air and Niolcel / zinc

009816/1329

Cells tested. The separator stopped in the zinc / air lines 35 cycles out and the failure was due to a break but no penetration. In nickel / zinc cells only a mechanical destruction appeared, and here in test series over 22 cycles without that zinc penetration took place.

Example VI

Nickel hydroxide separators with Io weight percent potassium titanate and Io weight percent poly te met luoroethylene were produced according to Example V with the difference that the separator was rolled out into a continuous flexible film after mixing with water. The dry separator film had a thickness of 0.29 mm and in the swollen state of 0.4 mm. After immersion for 40 hours in 44 <fa KOH, no change in the shape of the electrodes was found. The resistance of the separator was 0.02 ohm-cm compared to 0.06 ohm-cm for a conventional cellophane separator. Zinc penetration during the charge-discharge process was practically not detectable, only a tendency to crack.

Example VII

Using the method according to Example I, a zinc electrode was produced with a separator coating of manganese hydroxide MN (OH) ₂ , D (OH) ₃ , D ₂ Oy Ce ₃ O ₃ , and the hydroxides of. Scandium, yttrium, lanthanium, hafnium, zirconium, praseodynium, neodymium, samarium and europium, and all showed an improvement in the resistance of the separator in silver / zinc cells as well as with regard to the zinc penetration tests and a limitation of the form retention capacity of the zinc in zinc / air cells out. The symbol D refers to commercially available mixtures of rare earth metal cations in products known as didymium salts, which consist predominantly of lanthanium salts. If these compounds were used together with 5 to 3o percent by weight of polytetrafluoroethylene, be it by direct application on the electrode or in the form

009816/1328

of a self-supporting separator, similar results were obtained and the separator material could also be used in Connection with a silver electrode can be used.

0 09816/1328

Claims (12)

Patent claims: 1. Inorganic separator for alkaline accumulator cells with a soluble Zinkelektroüe and a counter electrode Silver, nickel or an air depolarization electrode, consisting of the layer of an inorganic compound that deposited directly on an electrode or a self-supporting separator arranged between the electrodes is assigned, characterized in that the inorganic separator from the crystal layer is insoluble in the electrolyte Transition metal or rare earth metal oxide or hydroxide, where the ionic radius of the element is greater than o, 7 & 2. Inorganic separator according to claim 1, characterized in that, that the crystal layer from the oxides or hydroxides of the elements nickel, manganese, cerium, cadmium, iron, scandium, Consists of yttrium, lanthanum, hafnium, zirconium, uhorium, didymium, praseodymium, neodymium, samarium and europium. 3 · Inorganic separator according to claims 1 and 2, characterized in that the ionic radius of the chemical element is greater than 0.8 Å. 4. Inorganic separator according to Claims 1 to 3 »characterized in that the crystal layer is additionally 5 to 3o Contains percent by weight of an organic plastic such as polytetrafluoroethylene, polyethylene or polyvinyl alcohol. 5. Inorganic separator according to claims 1 to 3 »thereby characterized in that the crystal layer is deposited directly on one of the electrodes of the cell. 6. Inorganic separator according to claims 1 to A _9, characterized in that the layer forms a self-supporting film which is arranged between the electrodes 009816/1328 7. Process for the production of an inorganic separator according to claims 1 to 6, characterized in that a target electrode is immersed in a salt solution of manganese, ger, cadmium, Bisen, scandium, yttrium, lanthanum, hafnium, zirconium, Thorium, Didymium, Praseodymium, Heodymium, Samarium or Immersed europium and on the zinc electrode an oxide or hydroxide of the chemical element in question in one Cdjg-like crystal structure is precipitated. 8. The method according to claim 7, characterized in that the oxide or hydroxide from an aqueous salt solution of the chemical element in question by adding a precipitant is precipitated in the form of alkali metal or alkaline earth metal hydroxides 9 · Process according to claims 7 and 8, characterized in that the precipitated oxide or hydroxide with a plastic e.g. polytetrafluoroethylene, polyethylene, polyvinyl alcohol ο .dgl · - intimately mixed and the mixture pressed into foils will· Io · Method according to claim 9 · characterized in that the precipitate mixed with polytetravethylene to form an emulsion will. 11. The method according to claims 9 and Io, characterized in that that the mixture is applied to a zinc electrode. 12. ' Process according to Claims 7 to 11, characterized in that that for the production of a separator to be used in an alkaline electrolyte, that for precipitation used alkali or alkaline earth hydroxya de »envisaged Electrolyte corresponds 13. Process according to Claims 7 to 12, characterized in that that the electrolyte and the precipitating agent added to the solution au * Keliumliyäroxyä consists GGS816 / 1328