SE447432B - JERN-SILVER BATTERY - Google Patents

Description

447 432 electrode, where the active, metallic element iron sjähnz constitutes the entire electrode device. This electrode does not contain any sulfur or sulphate activators. The active battery material consists of essentially pure iron particles. This material can be easily produced from ferric oxide (Fe 2 O 3), which is a cheap, commercially available material. Fe 2 O 3 can be thermally reduced to metallic iron, Fe, at from 400 ° C to 1,000 ° C, in a reducing atmosphere, preferably H 2, for 15 minutes to 600 minutes. It can then be ground or otherwise pulverized to a powder having an average particle size of from 10 microns to 275 microns. over 275 microns and problems can arise in later editing and sintering steps.

The sized iron is then pressed through a suitable pressing device, such as a flatbed press, to provide a handle that can be handled. The device is then sintered at from 700 ° C to 1,000 ° C in a reducing atmosphere, preferably H 2, for about 15 minutes. The particles are sintered at their contact points to give an interconnected, contacting metallic device consisting of iron.

I This electrode device can suitably be made very thin, i.e. from about 0.6 to about 3.7 mm. It must have a density of from 2.5 g / cm3 to 3.5 g / cm3, a porosity of between 50% and 95% and a high structural integrity. The porous bonded particle structure contains 100% active material and need not have a support device, although nickel, or nickel-plated iron expansion metal grids, or other type of current collector can be incorporated into the electrode. However, the current collector is suitable for preventing an increase in surface density. This type of electrode can eliminate the use of heavy carriers and the need for intricate and time consuming plate fitting or other plate filling techniques.

The electrode will not precipitate active material, and can be discharged immediately, giving an output of up to about 0.50 Ah / g of active material substance. The electrode eliminates the need for repeated charge-discharge period operation before use, eliminating the need for any activating dipping or spraying step, and provides a very simple, inexpensive, high-output iron electrode. The metal powder of the sintered electrode has an average particle size of from 10 microns to 275 microns, and is free from cracks and protrusions and melting spheres, and allows the electrolyte to make contact with the active material device.

The positive plate may be made of a silver or a silver-plated metal support, generally a thin perforated silver sheet, or an expanded silver mesh, grid or wire device, to which suitably substantially pure (at least about 98% pure) silver metal particles, preferably in powder form, is generally applied by a roller press method. The filled support plate is then heat sintered, to form a substantially pure silver anode with from 50% to 85% porosity. A small amount of silver can be oxidized during this process but no silver oxide as such is intentionally added. at this time, iron plates (negative) and silver plates (positive) are alternately stacked, kustic resistant separators are placed between adjacent plates to form cells, and the cells are assembled to form an Fe-Ag battery. The separator must have a graded porosity of from 60% to 90% porosity near the silver plate, to a microporous structure away from the silver plate. The separator layer suitably comprises a plurality of alternating polypropylene sheets. A sheet is from 0.006 to 0.05 thick, and is in microporous form and has average pores from 0.05 microns to 5 microns. micron in diameter- The second sheet is from 0.07 to 0.2 mm thick, 60% to 90% pile east, polypropylene sheet, which is suitably in fibrous fabric and has medium pores from 3 micron to 50 micron in diameter- The silver plate must be placed between and contact the 60% to 90% porous separators. This combination of plate and separators is then placed between the microporous separators- Conveniently and to ensure that no short circuit occurs, 2 layers of separators would be used, i.e.- a combination of microporous, porous, micro-porous, porous, flat, porous, microporous , porous, microporous, separator This microporous felted porous combination multilayer lamination is critical to the battery and is particularly effective in preventing short circuits from forming a conductive silver film on the separators while still allowing silver ion diffusion. The total thickness of the multilayer separator would be from 0.25 to 1.5 mm.

This polypropylene laminate separator is stable in the electrochemical environment of the battery cell, unaffected by the electrolyte and hydroxyl ions in the solution and not oxidized by the silver.

The raw fabric structure of the porous laminate is effective in preventing a continuous or solid accumulation of silver. After 100 cycles, from 0.75 weight to 1.5 weight of the silver is lost by migration. While polypropylene does not prevent such migration, the particular one described above is the design is uniquely effective in regulating it without harmful results for the operation of the battery. It is the combination of the pure sintered iron electrode, a useful and inefficient separator system, and a lithium alkali hydroxide electrolyte, which gives the unique advantage of this battery. Finally, electrolyte is added to the battery. The electrolyte, which we found would give outstanding activity to the iron-silver battery according to the invention, is a lithiated alkali hydroxide electrolyte, consisting essentially of a 10% to 50% by weight aqueous solution of KOH, containing from 2.5 grams to 65 grams. LiOH of the alkali hydroxide solution. 4,447,432 The preferred electrolyte is 5 grams to 30 grams of LiOH per liter of 20 parts by weight of aqueous KOH solution to 35% by weight.

Unexpectedly, we have found, in this battery system, that electrolytes of Naø fl or KOH alone, do not provide acceptable battery capacity or longevity properties. use expensive activators in the iron plate- It is believed that LiOH forms an intermediate reaction product on the iron particle surface, which appears to include Li-Fe-O inclusion compounds.

Although not fully understood, these compounds obviously increase the utilization of the active battery material and increase the conductivity of the active mass and allow better contact between the charging current and the active material. The invention will now be illustrated by reference to the following examples: EXAMPLE 1 An Iron silver battery, similar to that shown in the perspective view in Fig. 1 of the accompanying drawing, was constructed. In Fig. 1, the battery has a plurality of negative sintered Fe particle electrode plates 11, a plurality of positive Ag electrode plates 12, plate separators 13 between the positive and negative plates. , all housed in the sensor 14, which has a lid 15, ventilation 16, positive terminal 17, and negative terminal 18. Positive conductor tabs 19 are shown attached to the intermediate cell connecting rail 20 and negative conductor tabs 21, arranged 1800 away from the positive tabs, are shown attached interconnect tab122- These conductor tabs are a device for making electrical connections with the resp. the plates.

The alkali electrolyte, consisting of lithiated aqueous KOH, contacts the electrode plates and separators within the vessel. The plate separators, which are suitably of a multilayer construction of porous and microporous polypropylene, are generally shown at 13, not surrounding the plates p for clarity of illustration. The plates suitably slide into the separators, which are of an envelope type construction, have the porous layer construction in contact with the plates- Iron plates were made from commercially available Fe 2 O 3 powder with an average particle size of between about 150 and 25Q microns.

This powder was placed in a nickel tray, thermally reduced at 75006 in a hydrogen atmosphere for 51 minutes, and allowed to cool for 51 minutes in hydrogen gas. This material is converted to size so that the average particle size is below 250 microns, and then heated, as above, to form a material comprising the element Fe- A number of plates were made, each containing about 200 g of iron particles. The iron particles were placed between two sheets of 200 x 200 x 5,447,432 0.30 mm thick expanded nickel cloth current collectors, with two 1.0 mm nickel made rods attached to the ends, to establish a high density exhibit avets region for the conductor flaps. This composition was then flatbed pressed at about 0.625 tons / 6.25 meters and higher pressure to produce two batches of 400 cm 2 plates. One batch had a thickness of from 0.2 to 0.225 cm and the other batch had a thickness of about 0.2 cm. These solid pressed plate devices were easily treated at this time. After pre-pressing, the plates were sintered at 90,000 for 11 minutes in hydrogen gas, then cooled in hydrogen gas for 11 minutes.

The iron particle electrodes were produced and contained interconnected contacting active iron material particles, sintered together without significant melting. The electrodes were solid and very strong in structure. The electrodes had a density of about 2.7 to 3.5 / / cm 2 and a porosity of from 70%. to 90% and contained no activators- The iron plates were fully reduced and capable of being discharged immediately- These plates were scrubbed to a size of 8.7 cm.x 15.6 cm, and had an active weight of 58 spruce each and a total weight of Bl grams, including the nickel embossing rods, for the 0.2 cm thick plates, and an active weight of 35 grams each and a total weight of 58 grams, including the nickel embossing rods, for the 1.25 cm thick plates- Silver electrodes 8.45 x 15 x 0 , 12 cm, each weighing about 75 grams and having a porosity of about 60% were used as the positive electrodes. These plates consisted of substantially pure silver particles, rolled pressed into a silver cloth support. plate.

The iron and silver electrodes had conductor tabs attached and were stacked, with the negative conductor tabs located 180 ° away from the positive tabs. The battery, shown in Fig. 1, consisted of five internal bagged iron electrodes 0.2 cm thick and two outer bagged iron electrodes 0.12 cm thick alternating with six silver electrodes. The electrodes were insulated from each other by bags of polypropylene laminate separator material. of three alternating layers of 0.0025 mm microporous polypropylene sheet, with pores from 0.1 to 2 microns average diameter, and four alternating layers of 0.15 mm coarse nonwoven fabric 80% porous polypropylene sheet with pores from 4 to 30 microns average diameter. t The stack of multilayer separated iron and silver electrodes was placed in a 6.25 mm thick plexiglass battery vessel measuring 9.5 x 3 x 22.5 cm. The conductor flaps were trimmed to project 1.2 cm through the top of the vessel to easily provide battery connection and to allow a 0.45 um electrolyte reservoir at the bottom of the vessel. The vessel was sealed at the top with epoxy resin, vacuum tested and vacuum filled with the electrolyte electrolyte 366 ml 25% Hydrogen-containing KOH with 15 g LiOH added per liter KOH- The total weight of the battery was 1,750 g 2 The assembled battery was bench tested through a series of 12 to 15 hour charge and discharge test cycles, to establish the capacity and the energy density- A 10 A load was used for a cut-off voltage of 0.9 V- The results are given in Table 1 below.

Table l Cycle Charging Discharge Ah Wh Wh Per (hours) (hours) 0.45 kg 3 13 1ä 136.5 158.3 ä1.0 - 5 lä lä 1ää.5 167.6 ä3.ä 10 lä 15 1ä7.3 170.9 ää.3 lä 1ä 15 1ä7.0 171.0 ää.7 16 lä lä 139.5 161.8 ä1.9 20 lä lä 135.6 157.3 äo.7 30 1ä 1ä 130.0 150.8 39.1 60 1ä 12 117.5 136.3 35.3 70 1ä 12 121.8 1ä1.3 36.6 80 5 1ä 12 123.1 1ä2.0 36.8 90 lä 12 118.7 137.7 35.7, These capacity and energy density values show that the battery system, containing the sintered, inactivated Fe electrode, the silver electrode, the multilayer separator system, and the lithiated KOH electrolyte, provides a high-efficiency battery life that does not exhibit of the electrodes through the separators. This battery shows outstanding voltage characteristics, (regulation), high charge acceptance, high energy storage per unit weight, and long service life with stable operation- No cyclic formation is required.

The battery can be charged with several times from 60 hours to up to 3 hours with almost constant capacity- An exactly similar battery was tested to show the stable capacity under different discharge values during cyclic operation. Fig. 2 shows voltage as a function of Ah for a similar battery. The periodic operation was maintained for 27 cycles at a constant charging and discharging current, where the cell capacity remained substantially constant.

This battery also shows high charge acceptance, ie. greater - than 90% for long cycles without loss of capacity- Other favorable properties are low hyil discharge, ie. less than 1% per day, the ability to charge 7,447,432 for more than 30 days, the ability to maintain cell reversal without loss of cell capacity, and wide thermal working ranges of 0 ° C to 95 ° C-An exact similar battery has Provets at a 3 hour discharge level for 100 cycles, with a cut-off voltage of 0.9 V and showed an energy storage density of about 40 Wh / 0.45 38 and 2.5 wn / 16 emï cell.

This battery can be built in different sizes and shapes by simply varying the dimensions of the individual electrodes, depending on the purpose and the bettering system for which it is intended.

This battery is extremely stable and reliable and has wide working temperature grasses and would be especially useful in underwater and space applications.

Example Gel 2 As a comparative example, an iron-silver battery was constructed exactly the same as those described in Example 1 above, except that the electrolyte contained 25% by weight of aqueous KOH-excipient LiOH.

The assembled battery was bench tested through a series of 8-hour long and 3-hour discharge test cycles, to establish the capacity and energy density values. A 50 A bracket was used for a 0.9 V cutting voltage. The results are given below in Table 2: Table 2 Cycle Charging Discharge Ah Wh Wh per Ltimmarš (hours) 0.45 kg 1 8 2.8 1u1.6 1U9.9 '41.9 5 h 1.8 89.1 93-4 26-1 18 8 1.6 78.9 82.8 23.1 114 8 0.8 112.2 141m) 12.6 20. interrupted These capacity and energy density values show dramatic and favorable results en Li0H addition to the electrolyte in this battery system- Experiments on other iron electrode battery systems would indicate that each sodium addition in the electrolyte would be expected to give similar results

Claims (7)

447 452 5 _ PATPINTKRAV: An iron-silver battery comprising a vessel and a lid, within which are arranged at least one positive electrode plate, at least one negative electrode plate, a separator between the plates comprising a plastic material resistant to chemical attack of the electrolyte or ions in the electrolyte and operative to allow silver ion diffusion while limiting the formation of a conductive silver film on the separator, and an alkali hydroxide electrolyte, characterized in that at least one positive plate comprises a porous support plate comprising silver and has active electrode material comprising silver distributed thereon, that the negative plate comprises a 50-95% porous, fully activated electrode device consisting of sintered, elementary, active, iron particles having an average particle size of between 10 and 275 microns in diameter and the electrolyte consists of a 10% to 50% by weight aqueous solution of KOH, containing from 2, 5 g to 65 g LiOH per liter KOH. Battery according to claim 1, characterized in that the negative electrode is from 0.625 to 3.75 mm thick, has a metal grid current collector, and the iron particles consist of the element Fe produced by thermal reduction of Fe 2 O 3. 3. A battery according to claim 1 or 2, characterized in that the negative electrode is free of sulfur-containing activators and is free of cracks and protrusions and melting spheres. Battery according to claim 1, 2 or 3, characterized in that the separators are a multilayer polypropylene material, comprising at least one microporous polypropylene sheet with an average pore diameter of 0.05 to 3 microns and at least one 60% to 90% porous polypropylene sheet with one agent. pore diameter of 3 to 40 microns. Battery according to claim 4, characterized in that the microporous separator sheet is from 0.00625 mm to 0.05 mm thick, the 60% to 90% porous separator sheet is from 0.075 to 0.2 mm thick, and a a plurality of each sheet is alternated to form the separators, with the silver plate disposed between and contacting the 60% to 90% porous separator sheet. 6. A battery according to claim 4 or 5, characterized in that, .., ¿. 447 432 the active silver electrode material consists of at least 98% pure silver, the microporous separator sheet has an average pore size from 0.05 to 3 microns in diameter. Battery according to any one of claims 1-6, characterized in that the electrolyte consists of a 20% to 35% by weight aqueous solution of KOH containing from about 10 g to about 30 g of LiOH per liter of KOH. y: