JPS638587B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] This invention relates to iron-silver storage batteries. BACKGROUND OF THE INVENTION Iron-silver storage batteries using metal fiber current collectors and negative electrodes made from Fe ₃ O ₄ paste active material are well known in the industry and are disclosed in U.S. patent application Ser.
No. 690444 (Brown). When the negative electrode is combined with a silver electrode in a 25 wt% KOH electrolyte, these batteries exhibit excellent high energy density, but the voltage regulation is insufficient due to the limited capacity of the iron electrode. There are drawbacks. Additionally, these batteries require a long formation period requiring several charge-discharge cycles before reaching their full design capacity, and active material may fall off from the iron electrode during this long formation process. Ru. [Means for Solving the Problems] The iron-silver storage battery according to the present invention comprises a container and a lid, a porous supporting electrode substrate containing silver therein, and an electrode active comprising silver dispersed thereon. at least one positive electrode with a conductive tab bonded to the material and said substrate, and porous particles of ferrous active material having an average particle size of 10 microns to 275 microns in diameter in interconnected and contacting contact with a material; at least one negative electrode comprising a fully activated electrode structure and a conductive tab bonded to the electrode plate, resistant to chemical attack by electrolytes or ions contained in the electrolyte and containing silver; consisting of a plastic material that is effective for ion diffusion but restricts the formation of a conductive film of silver on the separator;
Separator between electrodes, basically 2.5 to 65 per unit
10wt% to 5wt% containing g LiOH
It is equipped with an alkali hydroxide electrolyte consisting of an aqueous KOH solution and a device for electrically connecting to the electrodes. OPERATION This combination of the above elements provides a battery with excellent performance characteristics and which does not require lengthy and repeated formations. The negative electrode is made of 100% sintered active material and has a high degree of structural integrity.
The active material does not fall off even during long charge/discharge cycles. These batteries have a very long usable electrochemical life, at least 50 cycles or more.
78 to 78 depending on design at a 3 hour discharge rate for 500 cycles without the use of expensive iron electrode additives.
156 watts/hour/Kg (35-70 watts/hour/lb)
and an energy density of 0.16 to 0.19 watt-hour/cm ³ (2.5-3 watt-hour/cubic inch). Although the storage battery of this invention uses sintered metallic iron electrodes, the active metallic elemental iron itself constitutes the entire electrode structure. This electrode does not contain sulfur or sulfur salt activators. The active battery material is substantially pure iron particles. This material is easily manufactured from cheap and commercially available ferric oxide (Fe ₂ O ₃ ).
Fe ₂ O ₃ is thermally reduced to metallic iron at 400° C. to 1000° C. in a reducing atmosphere, preferably in hydrogen, for 15 minutes to 600 minutes. It is then ground or otherwise pulverized into a powder with an average particle size of 10 microns to 275 microns. Particle sizes greater than 275 microns cause problems in subsequent reduction and sintering steps. The sized iron is then pressed using a suitable press device such as a flat plate press to form a handleable electrode substrate structure. This structure is then heated to 700℃~
Sinter for approximately 15 min at 1000 °C in a reducing atmosphere, preferably _H2 . The iron particles are sintered at their contact points into interconnected, contacting metal structures of iron. This electrode must be very thin, i.e. approximately 0.625
Advantageously from about 25 mils to about 150 mils. It has a density of 2.5 g/cm ³ to 3.5 g/cm ³ , a porosity of 50% to 95%, and a high degree of structural integrity. Porous bonded particle structure is 100
% active material and does not require a support structure. However, nickel, nickel coated or uncoated iron expanded metal grids or other current collectors can be placed in the electrodes. Current collectors, however, are advantageous in preventing surface densification. This type of electrode does not require heavy supports, complex and time-consuming paste application to electrode substrates, or other electrode substrate filling techniques. This electrode does not shed active material and is capable of rapid discharge, providing an output of up to about 0.5 amp hours per gram of active material structure. The electrode does not require repeated charge-discharge cycles before use, does not require activator dipping or spraying steps, and is a very simple, low cost, high power iron electrode. The sintered electrode metal powder has an average particle size of 10 microns to 275 microns and is free of cracks, nodules, and molten spherules, allowing easy contact between the active material structure and the electrolyte. The positive electrode plate is a silver or silver-plated metal support,
Typically, a thin perforated silver sheet or expanded silver screen, mesh, net, or strand structure containing preferably substantially pure (at least about 98% pure) silver metal particles, preferably in powdered form, is used. [generally applied by a roll compaction method]. The filled supporting electrode substrate is then thermally sintered to form a substantially pure silver anode of 50% to 85% porosity. Although a small amount of silver is oxidized during this process, no silver oxide is intentionally added. At this point, a battery is constructed by alternately arranging iron (negative) electrodes and silver (positive) electrodes and placing a caustic-resistant separator between adjacent electrodes;
These batteries are combined to create a Fe-Ag storage battery. The separator must have a porosity structure with a gradient from 60% to 90% porosity near the silver electrode to a microporous structure as it moves away from the silver electrode. Preferably, the separator layers are alternating polypropylene sheets as described below. The thickness of one sheet is 0.00625 mm (0.25 mil) to 0.05 mm (2
The sheets are microporous with average pore sizes ranging from 0.05 microns to 3 microns in diameter. Other sheets are 0.075mm (3 mil) thick
~0.2 mm (8 mil), 60% to 90 porosity polypropylene sheet, which is preferably a nonwoven fabric with an average pore size of 3 microns to 50 microns in diameter. Silver electrode plates are placed between and in contact with the 60%-90% porosity separators. This combination of electrode plates and separators is then placed between microporous separators. In order to avoid short circuits, preferably two layers of separators are used, namely microporous, porous, microporous, porous, electrode plates, porous, microporous, porous, microporous separators. A combination should be used. This multilayer laminate consisting of a combination of microporous and felt-like porous separators is essential for storage batteries, preventing short circuits due to the formation of a silver conductive film on the separator and allowing silver ions to diffuse. It is particularly effective for Multilayer separator total thickness is 0.25mm (10 mil) ~ 1.5mm (60 mil)
This polypropylene laminate separator is stable in the electrochemical environment of a storage battery because it is not affected by the electrolyte and hydroxyl ions in the electrolyte and is not oxidized by silver. The rough textured structure of the porous layer is effective in preventing continuous or bulk silver buildup. After 100 cycles, 0.75% to 1.5% silver is lost to migration. Although polypropylene does not inhibit such migration, the particular structure described above is particularly effective in inhibiting such migration without deleterious consequences to battery performance. The unique advantage of this battery is the pure sintered iron electrode,
Due to the combination of a useful and effective separator system and a lithiated alkaline hydroxide electrolyte. Finally, add the electrolyte to the battery. The electrolyte which has been found to impart excellent activity to the iron-silver storage battery of this invention contains 10% to 50% by weight of LiOH containing 2.5 to 65 grams of LiOH per alkaline hydroxide solution.
It is a lithium-containing alkaline hydroxide electrolyte consisting essentially of an aqueous solution of % by weight KOH. A suitable electrolyte is 20% to 35% by weight KOH aqueous solution per 5
Contains ~30 grams of LiOH. It has surprisingly been found in this battery system that electrolytes consisting of NaOH or KOH alone do not provide acceptable battery capacity or life characteristics. It is only the above-mentioned lithium-containing KOH that provides the iron electrode plates with the ultrahigh performance that makes this battery system commercially viable without the use of expensive activators.
LiOH appears to generate intermediate reaction products on the iron particle surface that appear to include Li-Fe-O clathrates. Although not completely understood, these compounds apparently increase the potency of active battery materials and
It increases the conductivity of the active material, allowing better contact between the charging current and the active material. [Example] The present invention will be described below with reference to examples. Example 1 An iron-silver storage battery as shown in the perspective view of Figure 1 was assembled. Referring to FIG. 1, the battery comprises a number of sintered Fe particle negative electrode plates 11, a number of silver positive electrode plates 12, and a plate-like separator 13 between the positive and negative electrode plates. These are all lid 1
5. It is housed in a container 14 equipped with a vent device 16, a positive electrode terminal 17, and a negative electrode terminal 18. Positive electrode conductive tab 19 is shown coupled to inter-battery connection ear 20, and negative electrode conductive tab 21 is positioned 180° from the positive electrode conductive tab and coupled to inter-battery connection ear 22. There is. These conductive tabs provide a means for making electrical connections to the respective electrode plates. An alkaline electrolyte consisting of a lithium-containing KOH aqueous solution comes into contact with the electrode plates and separator inside the container. A plate separator, preferably having a multilayer structure of porous polypropylene and microporous polypropylene, is indicated generally at 13 and does not surround the electrode plates for clarity of illustration. The electrode plate is slid into contact with the electrode plate by sliding it into a separator with an envelope-type structure made of porous laminate (PLY). The iron electrode plate is made from commercially available _Fe2O3 powder with _an average particle size of about 150-250 microns. This powder is placed in a shallow nickel dish, thermally reduced at 750°C for 51 minutes in a hydrogen atmosphere, and allowed to cool in hydrogen gas for 51 minutes. The resulting material is resized to an average particle size of less than 250 microns and then heated as described above for a second reduction to form a material consisting of elemental Fe. A number of electrode plates were made, each containing about 200 grams of iron particles. Two 1.0 mm (0.040 inch) nickel coined rods were joined at each end to create a dense section for welding to the conductive tab.
200mm x 200mm x 0.3mm (8 inches x 8 inches x
The iron particles were placed between two sheets of a 0.012 inch (0.012 inch) thick extracted-banded nickel mesh current collector. The resulting composite was compression molded in a flat plate press at pressures of 100 Kg/cm ² (0.625 ton/in 2 ) and above, and two sets of 400 cm ² (64 ton/in 2 )
I made a board. One set of boards has a thickness of 2 mm to 2.3 mm (0.08 inch to 0.09 inch), and the other set has a thickness of approx.
It has a thickness of 1.3 mm (0.05 inch). The combined compacted plate structure is now easy to handle. After compression, sintering in hydrogen gas at 900℃ for 11 minutes,
It was then cooled in hydrogen gas for 11 minutes. The iron particle electrodes prepared above containing interconnected and contacting iron active materials were sintered so as to be substantially unmelted. The resulting electrode is structurally rigid;
It was very durable. Electrode is approximately 2.7 g/cm ³ ~
It has a density of 3.5 grams/cm ³ and a porosity of 70% to 90% and contains no activator. The iron electrode plate is fully reduced and ready for discharge. If these electrode plates are 2.0 mm (0.08 inch) thick, each has an active material weight of 58 grams and a total weight of 81 grams including the nickel coin bar, and a thickness of 1.3 mm.
(0.05 inch) electrode plates, each with an active material weight of 35 grams and a total weight of 58 grams including the Nickel coin rod, 87.5 mm x 156.3 mm (3.5 inch x
6.25 inches). As positive electrodes, each weighs approximately 75 grams and has a porosity of approximately 60%, 84.38mm×
A 150 mm x 1.2 mm (3.375 inch x 6 inch x 0.048 inch) silver electrode plate was used. These electrode plates consisted of essentially pure silver powder roller pressed into a silver mesh screen support substrate. Conductive tabs were bonded to the iron electrode plate and the silver electrode plate, and these were layered, with the negative electrode conductive tab being placed 180° apart from the positive electrode conductive tab. The storage battery shown in Figure 1 has six silver electrodes arranged alternately with a thickness of 2 mm.
(0.08 inch) inner bag of 5 iron electrodes and 1.3 mm (0.05 inch) thick bag of 2 outer iron electrodes. These electrodes are insulated from each other by a polypropylene laminated separator bag. The laminated separator consists of three alternating 0.025 mm (1 mil) thick microporous polypropylene sheets with 0.1 to 2 micron average diameter pores and four alternating 0.025 mm (1 mil) thick microporous polypropylene sheets with 4 to 30 micron average diameter pores. and a layer of coarse, 80% porous, nonwoven polypropylene sheet 0.15 mm (6 mil) thick with average diameter pores. The laminated structure of iron electrode and silver electrode separated by a laminated separator is 93.8 mm x 30 mm x 225 mm (3.75 inch x
Thickness 6.2mm (1/20" x 9.00") dimensions
It was housed in a 4-inch plastic glass storage battery container. A cut was made to allow 1/2 inch (12.5 mm) to exit through the top of the container to facilitate connection to the battery terminals, and to provide a 4.7 mm deep electrolyte reservoir at the bottom of the container. The container was sealed at the top with epoxy resin, vacuum tested, and filled with electrolyte under vacuum. The electrolyte was 366 ml of a 25% by weight KOH aqueous solution to which 15 grams of LiOH was added per 1 KOH.
The total weight of the battery was 1750 grams (3.86 pounds). The assembled batteries were then tested through a series of charge-discharge cycles for 12-15 hour periods to determine capacity and energy density ratings. A drain rate of 10 amps was used to a cutoff voltage of 0.9 volts. Submit the results in the first section below.
Listed in the table.

[Table] These capacity and energy density values indicate that a battery containing a sintered, activator-free Fe electrode; a silver electrode; a multilayer separator; and a lithium-containing KOH electrolyte is a high-performance, long-life battery. , indicating that the electrodes are not shorted through the separator. This battery exhibits excellent voltage characteristics (rate of fluctuation), high charge tolerance, high energy storage per unit weight, and long life with stable performance characteristics. Does not require cycle conversion. This battery can be charged at very different rates ranging from a 60 hour rate to a 3 hour rate and can be made to a nearly constant capacity. Identical batteries were tested and showed safe capacity at various discharge rates during full cycle operation. FIG. 2 shows the voltage:amp-hour curve for a similar type of storage battery.
Cycling maintained constant charge current (8 hour charge at 25 amps) and discharge current for 27 cycles, but the capacity of the battery remained essentially constant. This battery exhibits high charge tolerance, ie, more than 90% charge tolerance over extended cycles without loss of capacity. Other advantageous properties include low shelf life of less than 1% per day, the ability to float charge for over 30 days, the ability to invert the battery without loss of capacity, and wide thermal stability from 0°C to 95°C. It has a range of motion. An identical battery tested for 100 cycles at a 3 hour discharge rate to a termination voltage of 0.9 volts yielded approximately 89 watts/kg (40 watts/kg).
energy storage density of 1 cm 3 (1 lb) and battery 1 cm ³ (1
gave an energy storage density of 0.16 (2.5) watt-hours per cubic inch. Depending on the intended purpose and the storage battery arrangement, this accumulator can be constructed in various sizes and shapes simply by varying the dimensions of the individual electrodes. This storage battery is very stable and reliable.
It has a wide operating temperature range, making it particularly useful in underwater and space environments. Example 2 As a comparative example, an iron-silver storage battery was made which was exactly the same as in Example 1 above, except that the electrolyte was a 25% by weight KOH aqueous solution and did not contain LiOH. The assembled battery was then tested through a series of 8 hour continuous charge and 3 hour continuous discharge test cycles to determine the capacity and energy density of the battery.
A discharge rate of 50 amps was used to a cut-off voltage of 0.9 volts. The results are listed in Table 2.

Table: These capacity and energy density values demonstrate the significant and highly beneficial results of adding LiOH to the electrolyte in the storage battery of this invention. Experiments with other iron electrode storage battery systems have shown that similar results are expected to be obtained when sodium is included in the electrolyte. [Effects of the Invention] The storage battery according to the present invention has excellent voltage characteristics (rate of fluctuation), high charge tolerance, high energy storage per unit weight, stable performance characteristics, and has a long life. Moreover, no cycle chemical conversion is required. Moreover, this storage battery is very stable and reliable.
It has a wide operating temperature range, making it particularly useful in underwater and space environments.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a battery according to the present invention, and FIG. 2 is a diagram showing a voltage versus ampere-time curve of a storage battery of a similar type to the present invention. In the figure: 11...Negative electrode plate, 12...Positive electrode plate, 13...Separator, 14...Container, 15...Lid, 16...Vent hole device, 17...Positive electrode terminal, 18...Negative electrode terminal, 19
...Positive electrode conductive tab, 20...Battery connection ear, 21
...Negative conductive tab, 22...Battery connection ear.

Claims (1)

[Scope of Claims] 1. A container and a lid, in which at least one positive electrode plate, at least one negative electrode plate, a separator disposed between the electrode plates, and an alkaline hydroxide electrolyte are housed; The separator is made from plastic materials that can resist chemical attack by electrolytes or ions contained in the electrolyte and are effective at diffusing silver ions but limit the formation of a conductive film of silver on the separator. In the iron-silver storage battery, the at least one positive electrode plate comprises a porous supporting electrode substrate containing silver and an electrode active material consisting of silver dispersed on the substrate, and the at least one negative electrode plate comprises: A porous, fully activated electrode structure with a porosity of 50-95% consisting of sintered elemental iron active material particles with an average particle size of 10-275 microns in diameter; An iron-silver storage battery, characterized in that it consists of a 10% to 50% by weight KOH aqueous solution containing 2.5 to 65 grams of LiOH per KOH. 2. The negative electrode plate has a thickness of 0.625 mm to 3.75 mm,
Contains a metal lattice current collector, with elemental iron particles
The iron-silver storage battery according to claim 1, which is produced by thermal reduction of Fe ₂ O ₃ . 3. The iron-silver storage battery according to claim 1 or 2, wherein the negative electrode plate does not contain a sulfur-containing activator and does not contain cracks, nodules, or molten spherules. 4 The separator has at least one layer of microporous separator polypropylene sheet with pores having an average diameter of 0.05 microns to 3 microns and at least one layer of 60% to 90% porosity having pores having an average diameter of 3 microns to 50 microns. The iron-silver storage battery according to claim 1, 2, or 3, comprising a polypropylene separator sheet. 5 Microporous separator polypropylene sheet
0.00625mm~0.050mm thickness and 60%~90% porosity polypropylene separator sheet from 0.075mm
4. Iron according to claim 4, with a thickness of 0.20 mm, in which separators are constructed by combining a large number of each sheet in an alternating manner, and silver electrode plates are arranged between and in contact with the separators. -Silver storage battery. 6. The iron-silver storage battery according to claim 4 or 5, wherein the silver electrode active material consists of at least 98% pure silver. 7 The electrolyte contains about 10 grams to about 30 grams of LiOH per KOH of 20% to 35% by weight.
The iron-silver storage battery according to any one of claims 1 to 6, comprising a KOH aqueous solution.