DE2842724A1 - Long service life alkaline accumulator separators - comprise inorganic particles in a polymer binder, pref., styrene!-butadiene! or acrylic! acid-olefin! copolymer - Google Patents

Abstract

A compsn. for producing alkaline accumulator separators comprises a polymer binder in which are embedded micrometric inorganic particles in amt. of 30-80 wt.% w.r.t. polymer and particles. The polymer is pref. a styrene butadiene or an acrylic acid-olefin copolymer. The particles are pref. TiO2, hydrated Ce oxide, Pb peroxide, Mg titanate, Ca zirconate, Al silicate and/or silica. Partic. suitable for Ni/Zn accumulators used in electrical vehicles. The separators can be easily produced and have relatively long service life even under conditions of high discharge, esp. when associated with other materials.

Description

Composite separator material

for alkaline storage batteries This invention relates to alkaline batteries Battery systems and in particular on new separator materials used therein.

The alkaline accumulators are particularly suitable for a large Number of applications such as generating electricity in air and underwater vehicles, transportable machines, for starting engines and, what is particularly important, for the electric drive of vehicles because of the high energy density that is achieved can be. Typical electrode connections include silver-zinc and silver-catmium and Nickel-zinc.

Nickel-zinc accumulators have particularly remarkable properties, but which have not yet been commercially exploited. Such is the usage, for example of zinc electrodes in accumulators seriously limited because of their peculiarity to repeated charging react with a loss of capacity that is irreversible is. The difficulties associated with sufficient cycle numbers are particularly acute in applications where relatively deep discharges are pre-standardized.

The capacity loss as a function of the charge / discharge cycle number is closely related to the loss of performance of the separator and to changes in the Form of the zinc electrode. Of all the technical problems which the economic Affecting commercial uses of nickel-zinc systems is the main problem the limited life due to the deterioration of the separator used.

It is well known that in nickel-zinc batteries with an aqueous Solution such as KOH as an electrolyte, the zinc during the discharge in a considerable amount Extent is dissolved in the electrolyte. So part of the active zinc goes during the discharge phase and in the discharged state into the electrolyte.

When the battery is charged, this zinc goes out of the electrolyte above.

When the battery is charged, this zinc goes out of the electrolyte back to the zinc electrode, but changes its structure. It also happens the galvanic deposition or reapplication of zinc, often in the form of a tree washed out crystals that have sharp points (dendrites) and slightly one Can form a bridge between the plates of different polarity, causing a short circuit which destroys the cell.

Accordingly, a suitable material for a separator in the nickel-zinc system must be used be able to prevent dendrites from entering and still get through of the electrolyte, it being desirable that the material from the electrolyte is wetted. In other words, the material must have sufficient properties for possess ion transport. It should also have sufficient chemical stability in the Have medium of the accumulator. It is also known that in addition to Changes in shape of the zinc electrodes during operation of the accumulator or the cell expands to a certain extent. Therefore must an adequate separator material will be capable of these changes and expansion to participate without changing its other characteristics.

To meet these various rigorous requirements, a must separator material usable for long cycle numbers is a relatively uniform, have extremely small porosity and the transport of the electrolyte is low Oppose resistance. It must also be strong and flexible possess the properties necessary to withstand the changes in shape of the zinc anode and to adapt to the enlargement of the nickel cathode. After all, you need all of these Characteristics are combined in a layer that is as thin as possible, so that the energy density In terms of the volume of the cell, it is not reduced too much.

This representation is further complicated by the fact that the commercial Usability requires the material to be thin in an economical manner Separator layer can be formed with acceptable tolerances in quality control.

Horrible efforts have been made to find suitable separator materials for alkaline batteries. Perhaps this testifies to the difficulties who occurred in search of a satisfactory material are, which has the many different characteristics necessary for efficient function are necessary as a separator. The solutions proposed range from several organic microporous films to relatively rigid layers of inorganic, mostly ceramic particles that are connected to one another in some way. One Another solution involves combining an organic material with an inorganic one Particles, which is often referred to as inorganic / organic separator material, or even easier, as an I / O separator material. Yet another suggestion relates relying on the formation of many types of layers or the use of a variety of layers of different materials in a combination.

Quite extraordinary claims have been made for special ones Solutions in which the separators have a number of cycles of up to a few thousand charge / discharge cycles are said to be. However, one must carefully review the data on which the claims are based check. For example, the shallow discharge of the cells does not correspond to the working conditions, with which even many of the commercially available separator materials were tested will. On the other hand, the operating conditions of a battery that is used in an electrically powered vehicle would be an extremely severe one Test shows the capabilities of the separator material.

At the present time the development of an economically viable Separator material for alkaline accumulator systems is the main obstacle for a widespread use of such accumulators despite considerable efforts in this area. Suitable commercial separator materials for alkaline batteries are simply not available, except at unacceptably high prices.

It is therefore a primary purpose of the present invention to provide separator materials for alkaline accumulators to describe, which also under the conditions deeper Discharge relatively large numbers of charge / discharge cycles, especially if they can be used with other separator materials. Another purpose Is to describe separator materials for such accumulators that also in the dimensions as they are for use in electrically powered vehicles are common to have suitable properties.

Another purpose of the present invention is illustration a separator material that has the required properties in a relatively thin Layer owns.

Another purpose of this invention is economic Manufacture of separator materials. Connected with that and even more special is that Process to produce separator material all with acceptable manufacturing tolerances.

Other objects and advantages of the present invention will become evidently from the following description.

While the invention is susceptible of many modifications and alternatives only certain details are described here. However, it should be noted that there is no intention to limit the invention to the kind described. On the contrary, it is intended to include all modifications, extras, and alternatives Include within the spirit and scope of the invention as set out in the appended claims fall. So while the present invention is described in principle, for example in connection with a rechargeable Nlckel-Zlnk-accumulator, should be recognized It will be appreciated that the present invention can be used in the same manner alone or in combination with other separator materials or with other combinations of accumulator electrodes, which are a separator material that has some or all of the properties described.

The present invention is generally based on the development of a I / O separator material that contains micron-sized inorganic particles.

Such inorganic particles can for example consist of titanium dioxide, that is embedded in a polymer matrix such as a styrene-butadiene blend polymer (SBR). Preferably two different types of inorganic particles are used, one of which is leached out of the separator material by the electrolyte will, and the other will not. Films of the desired thickness, typically 2-5 mils (1 mil = 1/1000 inch) can easily be poured after the inorganic particles have been added to a dispersion of the polymer used. To more stability in terms of the shape of the film, and because of the ease of manufacture, a substrate in the form of fibers can be used. The manufactured in this way Separator materials can be used in nickel-zinc batteries and have properties that under deep discharge conditions with these batteries allow relatively large numbers of charge / discharge cycles. This also applies to accumulators with dimensions as required for electrically powered vehicles, and especially in combination with other separator materials.

As for the polymeric component used, all of the various commercially available materials can be taken. The main claim is that the polymer is available as a dispersion or aqueous emulsion and is chemical relative is stable in the presence of the alkaline electrolyte used.

Ethylene-acrylic acid copolymers, Styrene-butadlene-Mi schpolpolymers and copolymers of acrylic acid with other olefins that are suitable and commercially available. It has proven to be useful, for example proven to use a mixed polymer in which the styrene content is in the range of approx. 50-60 and the butadiene content is in the range of 40-50 percent by weight. An important point is that such polymers can be processed quickly because no organic solvent is used.

To improve the stability of an SBR latex suspension, you can commercially available materials with carboxyl groups can be used.

As for the inorganic component, a variety of materials can be used can be used. The main requirement here is that the material should be small particles on the order of 1 micron or less are present and sufficient is wettable as opposed to the resistance of the I / O material made from it the transport of the electrolyte to the desired level.

Representative examples of such suitable inorganic materials are T102, cerium hydrate (CeO2 xH20), cerium oxide, lead peroxide, magnesium titanate and calcium carbonate. Under certain circumstances, naturally occurring minerals such as kaolin can also be used (Aluminum silicate) can be used.

From a functional point of view, the inorganic component should are present in an amount that is at least sufficient for the adhesion of the resulting Reduce mixture to such an extent that the material immediately when assembling cells can be used and the desired low resistance to to the Transport of the electrolyte, the mechanical stability of the pores and thermal Has stability of the system. On the other hand, the maximum amount of inorganic æ hen limited by the amount of polymer needed to make the component assemble inorganic particles into a mechanically stable mixture. if If too little polymer is used, handling the mixture shows that it is inorganic Particles are lost, making the material feel like chalk. It has proved to be sufficient, the inorganic component in the order of magnitude of approx. 30-80% to be used, depending on the total weight of the inorganic and organic Materials.

Of the inorganic components used, at least one should cannot be leached out of the separator by the alkaline electrolyte. The particle size of the non-leachable component or components should be less than 1 micron, and preferably much smaller. Particles of this minor Size result in uniform resistance to the transport of the electrolyte (in the case of leachable species) and adequately prevent intrusion of dendrites (in the case of non-leachable species). In both cases results an increased transport of the ions of the electrolyte. It can also be seen that within this order of magnitude the particles of about 1 micron less polymer is needed for the mixture than with smaller particles because the larger particles Overall, have a smaller total surface.

At least one inorganic component is preferably used, which is relatively insoluble in the alkaline medium. By getting the I / O stuff exposed to an alkaline electrolyte for up to 24 hours at higher temperatures, one can determine whether there is sufficient stability.

This is checked, for example, by treatment in 31% KOH at 800C during 24 hours. If only a single inorganic component is used, it is preferable to use a non-leachable type, because the formed material typical microporosity has a sufficiently low resistance to it the ions of the electrolyte is given and because it prevents that through leaching out the inorganic particles, the mechanical stability and the porosity lower and thus the resistance to the ions is greater.

According to this invention, one preferably uses for the I / O material both a leachable and a non-leachable inorganic component, because the latter improves the mechanical stability of the mixture and the former improves leaching out of the material, the properties with regard to ion transport improved. The previously discussed criteria for the inorganic component are generally valid. However, it is desirable that the particle size of the leachable Component in the range of 70-500 Å and preferably 70-.00 i. Besides is it is important that the leachable inorganic component is as large as possible of 0.25-4.0%, based on the total weight of the inorganic components, thus an optimal combination of mechanical stability and low resistance compared to the ion transport is achieved. In this context is the maximum Amount of leachable component also depends on the ratio of the inorganic Materials to the polymer. If the proportion of the polymer is increased, so can the proportion the leachable inorganic component can generally be increased somewhat.

Preferred inorganic components are TiO2 (is not leached out), which is available as an aqueous dispersion from Gulf and Western New Jersey ZMC as well SiO2 (is leached out), e.g. as Ludox from DuPont. Suitable materials with Particle sizes on the order of microns or less are commercially available. A The clear advantage of these above-mentioned preferred components is their availability as aqueous suspension, which produces homogeneous mixtures with polymer latex can be. This in turn simplifies the task of creating a homogeneous I / O material to form with little likelihood of contiguous or glued inorganic particles.

An I / O blend according to the present invention can be made by adding the inorganic component with a particle size in the micron range appropriately diluted with a dispersive medium, preferably water and an SBR or other polymer latex is added, whereby a more fluid Forms sludge, which is stirred appropriately to ensure homogeneity. If desired, small amounts of conventional additives can also be used be added, such as antioxidants, antifoam agents, etc. Sludge needs to be concentrated enough to get a flawless pouring Film receives. It has been shown that a concentration of 30-60 percent by volume Is suitable for it.

The specific concentration for a particular polymer will depend on the flow properties of the system (viscosity, thixotropy) and the useful ones Under certain circumstances, values for the polymer can be outside of the above

Frame. The separator material can then then be produced by placing a film of the desired thickness on a suitable surface pours, typically about 2-5 mils, and then the water using appropriate drying methods removed from the system.

An even simpler manufacture is possible by digging into the I / O separator material incorporates a fibrous substrate which is coated with the mixture. This will also improves the mechanical stability, especially in cases where the used Polymer is prone to cold flow. With this manufacturing process, you just dip that Substrate in a stirred, low viscosity slurry of the mixture. Alternatively to this The separator reinforced by the substrate can also be used in a continuous manner getting produced. Here, as an example, the fibrous substrate material is from a Roll and pulled through the thin mud. The homogeneity of the mud can be ensured in a suitable manner by an external reservoir. the The concentration of the sludge must of course be large enough to ensure that it is free from defects To provide surfaces, but not so large that uneven coatings occur.

The manner coated in this way can then be a conventional one Pass through the furnace, with a corresponding dwell time ensuring that the coating has dried sufficiently. The resulting material can then be rolled up. It can also go through this process multiple times to create a to achieve certain desired thickness of the coating.

A wide variety of substrates can be used with success. Examples include nonwovens made of nylon, polypropylene and polypropylene-polyethylene material ien that are commercially available. In addition, many materials can be made from Cellulose can be used, but preferably not alone because of a certain tendency to swell. The substrate must be thin enough so that there is a mixture in the desired thickness can be produced. About the evenness To ensure the reinforced separator material, the fabric backing must be so be as homogeneous as possible. In addition, one should choose fabrics that are not through the alkaline electrolytes are dissolved out of the mixture.

The produced I / O separator material according to the present invention has a typical mean pore size of approx. 0.010-0.013 microns (determined by means of Passage of water) and has a specific electrical resistance (O # rcm ) in the range of 20-60 with a thickness of 2-5 mils.

The following examples are intended for illustration purposes only present invention and in no way limit it.

Example 1 This example illustrates the use of a kaolin / SBR I / O separator material made in accordance with the present invention as well as its properties when used in relatively large accumulators Deep discharge conditions.

An initial coating was made by adding 645 grams of kaolin Triturated with 1000 ml of water for about 1 hour in a ball mill. The resulting Kaolin-water mixture was 500 ml of a mixed polymer of 55% styrene with carbonyl groups and 45% butadiene were added, and this mixture was again in the ball mill for 5 minutes mixed, stopping before the latex clumped together. This thin liquid Sludge was 50 ml of a polyoxyethylene (20) sorbitol monolaurate using a magnetic stirrer added. The resulting sludge contained based on the total volume, 50% kaolin and 50% SBR.

A second coating was then prepared in the same way however, the amount of the individual parts was changed to a sludge of 45 tons Kaolin and 55% SBR, based on the total volume.

The first coating was made on a "Lyonel" nylon nonwoven fabric Howard Textile Milis applied by moving the material at a speed of approx.

6 inches / minute and then immersed at a temperature of about 600C was dried. The second coating was done the same way performed.

Two nickel-zinc accumulators were constructed, one nominal Had a capacity of 300 ampere hours and had 8 nickel cathodes and 9 zinc anodes.

The active zinc to nickel ratio used was 8: 1. the Anodes were filled with conventional 'fCelgard' polypropylene separator material (Celanese Corp.). The cathode was encased as follows: (1). a conventional one "Pellon" separator material made of polypropylene, (2). over it a layer of "Celgard", (3). the previously described I / O separator material and (4). a second layer "Celgard". The electrolytes used were aqueous KOH solutions with minor different composition.

The accumulators were then discharged to different degrees, and determines the capacity. One cell was 100% discharged at 60 amps and one Speed of 1 cycle per day. The other cell was also powered by 60 amps. discharged to 75% at a rate of 2 cycles per day.

The first accumulator retained over 85% of the nominal capacity for approx.

170 cycles despite the 100% discharge. The other accumulator with the lower but still significant discharge retained over 90% of its nominal Capacity for approx. 190 cycles.

Example 2 This example represents the manufacture of another I / O separator material according to the present invention.

A coating was prepared according to that described in Example 1 Process containing 28.6% SBR, 71% TiO2 and 0.4% SiO2 (percentages by weight).

A cellulose nonwoven fabric was made by dipping at one speed coated with the mixture at about 7 inches per minute, and then the water removed therefrom by drying with infrared.

A sample of the dried material was applied for approximately 30 minutes Soaked at 1000C in a 30% aqueous KOH solution. After soaking it was the electrical resistivity was 45 ohm cm, and the pore size was 0.03 Microns, determined by the passage of water.

It can thus be seen that according to the present invention Separator materials are available which are easy to manufacture and which in alkaline accumulators under the conditions of deep discharge relatively high Allow cycle numbers, especially when used in conjunction with other separator materials be used. In a preferred representation, the use of two different types of inorganic components the production "Tailor-made" separator materials with optimal properties. It can multiple layers of the separator materials are used, and the separator materials According to the present invention, in conjunction with other separator materials can be used to achieve the desired properties.

Claims (13)

PATENT CLAIMS 1. 1. A composite separator material for alkaline Accumulators that have a polymer as matrix from the group of styrene-butadiene copolymers and the interpolymer of acrylic acid with olefins is selected and in the inorganic Particles on the order of microns are embedded. The proportion of inorganic Particle is approx. 30-80% depending on the total weight of the particles and the polymer matrix. 2. The separator material according to claim 1, wherein the inorganic Particles are selected from the group of titanium dioxide, cerium hydrate, cerium oxide, lead peroxide, Magnesium titanate, calcitin zirconate, aluminum silicate, silicon dioxide as well as from Mixtures of the substances mentioned. 3. The separator material of claim 1, wherein two different Types of inorganic particles are present, one type of which is through one alkaline electrolyte is leached out of the material and the other is not. 4. The separator material of claim 3, wherein said leachable inorganic particles are present in a proportion of approx. 0.25 - 4% based on the total weight of the inorganic particles. 5. The separator material of claim 3, wherein the leachable inorganic particles consist of silicon dioxide and the non-leachable Particles of titanium dioxide. 6. The separator material of claim 3, wherein the leachable inorganic particles have an average particle size of less than approx. 100 Å. 7. The separator material according to claim 1, wherein the material is a Film is about 2-5 mils (1 mil = 1/1000 inch) thick. 8. The separator material according to claim 1, wherein the polymer is a Styrene-butadiene mixed polymer has a styrene content of approx. 50-60% based on the total weight of the polymer. 9. The separator material according to claim 8, wherein the interpolymer Has carboxyl groups. 10. A composite separator material for use in alkaline storage batteries, containing a substrate made of fibers. This substrate is coated with a polymer, that from the group of styrene-butadiene copolymers and the copolymers of Acrylic acid is selected with olefins, and in which inorganic particles in on the order of microns are embedded. The said inorganic particles are available with a proportion of approx. 30-80%, based on the total weight of the Particles and the polymer matrix. 11. The separator material according to any one of claims 1-10. 12. The separator material according to claim 1 and essentially as described here. 13. Use the separator material essentially as described here Reference to each of the examples.