MX2008006830A - Rechargeable alkaline manganese cell having reduced capacity fade and improved cycle life - Google Patents

Abstract

Rechargeable galvanic cells are disclosed which comprise a manganese dioxide cathode, a zinc anode and a potassium hydroxide electrolyte wherein the cathode includes additive compounds to increase the cycle life and cumulative discharge capacity of the cell. The additives comprise at least a strontium compound and optionally a barium and/or calcium compound. Cells including the additive(s) desirably have an individual discharge capacity after 50 deep discharge-charge cycles of at least 0.100 Ah/gMnO2.

Description

RECHARGEABLE MANGANESE ALKALINE PILA THAT HAS REDUCED CAPACITY WEAKNESS AND LIFE CYCLE IMPROVED FIELD OF THE INVENTION The invention relates to rechargeable alkaline batteries or batteries having a positive electrode material of manganese dioxide (Mn02), an electrolyte of potassium hydroxide (KOH) and zinc (zn) as the negative electrode material . Specifically, the invention relates to cathode formulations of such batteries comprising additives for an improved life cycle and cumulative performance.

BACKGROUND OF THE INVENTION Alkaline batteries based on manganese dioxide, primary and secondary (rechargeable), are well known and include a positive electrode having manganese dioxide as an active material, a negative electrode that uses zinc as the active material, a aqueous solution of potassium hydroxide as electrolyte, and a separator between positive and negative electrode. To overcome the problems of recharging the Mn02 in the positive electrode, the cells in the which the discharge capacity of the cell was limited by the imposition of a zinc electrode limitation. Due to problems with the recharge capacity of the Mn02 cathode, these cells experience weakening of the deep discharge capacity, which results in a successive reduction of the available discharge time after each discharge-charge cycle. End users of the batteries perceive this as a diminished utility and may be inclined to premature disposition or disposal of the battery. The appearance of weakening capacity is evidence that the manganese dioxide electrode is not completely reversible. New procedures have been taken to reduce the weakening of the capacity, experienced such as the use of various additives for the positive and negative electrodes. In this regard, reference is made to Kordesch et al. in German Patent No. 3,337,568 issued April 25, 1984. This patent describes a method for producing electrolytic manganese dioxide that is doped with titanium. Such Mn02 doped with titanium is particularly suitable for use in rechargeable manganese / zinc dioxide cells. Taucher et al., In WO 93/12551 filed on December 21, 1992, describes the improvements to the primary and rechargeable alkaline manganese dioxide cells, which contain barium compounds in an amount of 3 to 25% of the positive electrode material of Mn02. Tomantschger et al., In the Patent of the States No. 5,300,371, issued April 5, 1994, teaches an alkaline manganese dioxide cell, rechargeable with improved performance, and improved life cycle, containing organic binders, and silver and barium compounds added to the positive electrode of Mn02 . Daniel-Ivad, et al., In U.S. Patent No. 6,361,899 discloses a range of additives to the positive electrode formulation comprising a first additive selected from the group consisting of barium and strontium compounds; and a second additive selected from the group consisting of titanium, lanthanum, cerium, yttrium, zinc, calcium, tin and magnesium compounds. Daniel-Ivad in U.S. Patent Application No. 2005/0164076 teaches the use of hydrophobic additives for more efficient processing of cathode pellets or spheres comprising hygroscopic additives such as barium, strontium, hydroxide or hydrate oxides. . These hygroscopic additives desirably increase the operation of the cell, as indicated by the increases in the cumulative discharge capacity and the life cycle of the cell. While the above references describe a number of methods for improved operation and improved life cycle, rechargeable alkaline cells still show weakening of capacity and decrease in useful capacity as the number of cycles increases. Particularly at moderate speeds at low discharge at 10-15 mA / cm2, the weakening of the capacity is still very pronounced. Accordingly, there is still a need for an improved rechargeable alkaline battery cathode composition, which results in improved performance of the entire battery, and improved battery life.

BRIEF DESCRIPTION OF THE INVENTION According to one aspect of the present invention, a rechargeable electrochemical cell comprising a cathode of manganese dioxide, a separator, an anode and an aqueous alkaline electrolyte is provided, the cathode comprises a strontium compound in a amount of 4.50 to 16.10% by weight of the cathode, the cell having an individual discharge capacity after 50 deep discharge-charge cycles of at least 0.100 Ah / gMn02.

According to yet another aspect of the invention, a rechargeable electrochemical cell comprising a cathode of manganese dioxide, a separator, an anode and an aqueous alkaline electrolyte is provided, the cathode comprises a strontium compound in an amount of 4.50 to 16.10. % by weight of the cathode and a barium compound in an amount other than zero, less than or equal to 1.00% by weight of the cathode. According to still another aspect of the invention, there is provided a method for increasing the cumulative discharge capacity of an electrochemical cell having a manganese dioxide cathode, a separator, an anode and an aqueous alkaline electrolyte, the method comprising the addition of a strontium compound in an amount from 4.50 to 16.10% by weight of the cathode, strontium to increase an individual cell discharge capacity after 50 deep discharge-charge cycles. The present invention provides a rechargeable alkaline manganese-zinc dioxide cell having at least one strontium compound in the positive electrode. The cells of the present invention advantageously show a high discharge capacity over the initial discharge and a prolonged life cycle (increased number of discharge / charge cycles) with reduced capacity weakening after successive unload / load cycles. This is perceived by end users as an increase in usable battery discharge time. The batteries according to the present invention desirably and advantageously have an individual discharge capacity after 50 deep discharge / charge cycles of at least 0.100 Ah / gMn02. In one embodiment, the present invention provides a cell comprising a cathode of manganese dioxide that includes a compound based on strontium and optionally a barium-based compound. Such a barium and / or strontium compound may be in the form of oxides or hydroxides and / or hydrates thereof. The effect of the barium and / or strontium-based compound is enhanced by the subsequent addition of a calcium compound comprising oxides, hydroxides or calcium fatty acids, such as calcium stearate. The calcium compound can be provided alone or in conjunction with a compound to improve catalyst processing, for example a polyethylene compound such as Coathylene ™. The compounds may be present in a total amount from about 4.5% to about 20.0% by weight of the cathode, preferably from about 5.5% to about 17.5% by weight. cathode weight, more preferably from about 7.15% to 17.5% by weight of the cathode, still more preferably from about 7.15% to about 9.75% by weight of the cathode. The strontium compound may be present in an amount from 4.50% to about 16.10% by weight of the cathode, preferably from about 5.0% to about 13.60% by weight of the cathode, more preferably from about 5.75% to about 11.85% by weight of the cathode , still more preferably from about 5.75% to about 8.35% by weight of the cathode, even more preferably from about 5.75% to about 6.75% by weight of the cathode. The strontium compound is preferably present as strontium oxide or strontium hydroxide, including strontium oxide or strontium hydroxide hydrates. The barium compound may be present in a nonzero amount of less than 1.0% by weight of the cathode. The barium compound may be present in an amount from about 0.1% to about 1.0% by weight of the cathode. The barium compound may be present in an amount from about 0.5% to about 1.0% by weight of the cathode. The compound of barium can be present in an amount from about 0.75% to about 1.0% by weight of the cathode. The barium compound is preferably present in an amount of about 1.0% by weight of the cathode. When present, the barium compound is preferably provided as barium oxide or barium hydroxide, including hydrates of barium oxide or barium hydroxide. When present, the calcium compound may be provided as an oxide, calcium hydroxide or a calcium fatty acid. The calcium compound is preferably in a non-zero amount less than 5% by weight of the cathode, more preferably from about 0.1% to about 1.25% by weight of the cathode, still more preferably from about 0.25% to about 1.25% by weight of the cathode. cathode, still more preferably from about 0.25% to about 0.4% by weight of the cathode. In one embodiment, the calcium compound is present as calcium oxide in an amount of 0.1% up to about 0.5% by weight of the cathode, preferably from about 0.2% up to about 0.3% by weight of the cathode, more preferably about 0.25% by weight in the cathode. cathode weight. In this modality, calcium oxide is preferably accompanied by a compound for improving the processing characteristics of the cathode, which is more preferably a polyethylene compound that is more preferably Coathylene ™. This compound for improving the processing characteristics of the cathode is preferably present in an amount from about 0.1% to about 0.2% by weight of the cathode, more preferably in an amount of about 0.15% by weight of the cathode. In yet another embodiment, the calcium compound is present as calcium stearate in an amount of 0.1% to about 0.75% by weight of the cathode, preferably from about 0.25% to about 0.5% by weight of the cathode, more preferably about 0.4% by weight. cathode weight. In this embodiment, the calcium compound is preferably not accompanied by a polyethylene compound to improve the processing capacity of the cathode, since calcium stearate itself can provide this function. The manganese dioxide cathode of the cell may comprise from 0.1% to 5% of a hydrogen recombination catalyst. Such catalysts can comprise silver, silver oxides or other known compounds of silver, preferably silver compounds of group I. Alternatively, the recombination catalyst 1 of hydrogen can include metal hydrides such as Ti2Ni. The individual discharge capacity of the cell after 50 deep discharge / charge cycles may be at least 0.100 Ah / gMn02, preferably at least 0.104 Ah / gMn02, more preferably at least 0.114 Ah / gMn02) still more preferably at least 0.121 Ah / gMn02. The cumulative discharge capacity of the cell after 50 deep discharge / charge cycles can be at least 41.00 Ah, preferably at least 49.00 Ah, more preferably at least 52.00 Ah, still more preferably at least 53.00 Ah. Appropriate cell designs, which provide positive and negative electrodes respectively connected to the negative and positive terminals for the cell, and separated by an appropriate separator, can be provided in coil cells, spirally wound cells, flat plate cells, and cells of button or coin.

BRIEF DESCRIPTION OF THE FIGURES These and other features of the invention will become more apparent in the following detailed description where reference is made to the accompanying Figure 1, which is a cross-sectional view of a cell according to an embodiment of the invention.

DESCRIPTION OF THE PREFERRED MODALITIES Figure 1 shows a cross-sectional elevation view of an alkaline rechargeable cell 10. The cell comprises the following main units: a steel can 12 that defines an internal cylindrical space, a cathode 14 formed by a plurality of pellets or hollow cylindrical spheres 16 pressed into the can, a zinc anode 18 made of an anode gel and accommodated in the hollow interior of the cathode 14, and a cylindrical separator 20 separating the anode 18 of the cathode 14. The ionic conductivity between and at the anode and the cathode is provided by the presence of the electrolyte of potassium hydroxide added to the cell in a predetermined amount. The can 12 is closed at the bottom, and has a central circular piece 22 that serves as the positive terminal. The upper end of the can 12 is hermetically sealed by a cell closure assembly comprising a negative cap 24 formed by a thin metal foil, a current collector 26 (sometimes known in the art as a "fingernail") coupled to the negative cap 24 and penetrating deep into the anode gel to provide electrical contact with the anode, and a plastic top 28 that electrically insulates the negative cap 24 from the can 12 and separates the gas spaces formed beyond the cathode and anode structures, respectively. A separator 20 is placed between the positive and negative electrodes. The separator 20 mechanically separates the anode from the cathode and serves as an electrolyte reservoir. The separator 20 is in general a complex flexible structure that is impermeable to zinc dendrites, but this is permeable to ions and may be permeable to the passage of gases such as hydrogen or oxygen, which are produced within the cell. after overload, wait or over-discharge conditions. The separator 20 comprises two laminated layers; an inner absorbent layer 30 made of a fibrous sheet material wettable by the electrolyte, and an external ion permeable layer 32 which is typically a membrane that is impervious to dendrites and small particles. The absorber layer 30 may be made of, for example, cellulose fibers, Rayon ™, polyamide, polypropylene or polyvinyl alcohol. A preferred material for the absorber layer 30 is a non-woven polyamide such as Freudenberg grade FS2213. The ion-permeable layer 32, made from, for example cellulose, Cellophane, polyethylene grafted by radiation, polypropylene or similar. The ion-permeable layer 32 is preferably a relatively thin Cellophane ™ membrane. The sealing of the bottom part of the cell is achieved using an insulating washer 33, as shown in Figure 1, which is butted against the bottom portion of the can 12 prior to the insertion of the cathode pellets 16 . The laminated separator 20 is inserted after this, so that its bottom edge abuts the insulating washer 33. The contact zone between the bottom of the separator 20 and the washer 33 is sealed by the application of a controlled amount of a sealant with thermoplastic properties. Suitable sealants may include epoxies, hot melt adhesives, asphalt or similar materials. The sealant is applied using an appropriate heated tool, which is inserted deep into the cylindrical cavity of the cathode and delivers a predetermined amount of sealant to the contact area. After solidification, the sealant usually has a concave profile with small height and width as shown at 34 in Figure 1. It will be appreciated that the exact configuration of the separator 20 and its bottom seal is not critical to the present invention. Other examples of sealing materials and methods are provided in U.S. Patent No. 5,272,020, which is incorporated by reference herein. Suitable active materials in the cells using manganese oxides as the cathode material comprise electrolytically or chemically synthesized manganese dioxide typically containing more than 90% tetravalent manganese and small amounts of lower-valent oxide. The manganese dioxide powder, together with any additives, can be mixed together to form the cathode material in a process as described in U.S. Patent No. 5,300,371, which is incorporated by reference herein. Depending on the nature of the cell, the positive electrode can be pelletized and inserted into the can optionally formed by recompaction. Alternatively, the positive electrode can be extruded directly into the can, or it can be laminated or cast as a flat positive electrode for use in flat plate cells and button or coin cells. The negative zinc electrode comprises zinc metal powder or zinc alloys, and optionally zinc oxide together with a suitable gelling agent such as carboxymethylcellulose, polyacrylic acid, starches and their derivatives. The mobility of the zincate within the cell can be reduced by the use of additives to the negative electrode mixture, such as 1% to 30% of the magnesium, barium and calcium compounds, typically their oxides, or their hydroxides, or mixtures thereof, as described in U.S. Patent No. 5,300,371. The electrolyte is an aqueous alkaline solution usually of 4N to 12N potassium hydroxide. The electrolyte may contain additives such as dissolved zinc oxide. ZnO, in order to reduce the gasification of the activated zinc inside the negative electrode, and thus to allow the cell to be overloaded without damaging it. Also, the ZnO can optionally be included in the cell as a reserve mass. As discussed above, it has been found that various additives to the cathode material reduce the weakening of the capacity in the rechargeable cells and increase the cycle life and thereby increase the cumulative discharge capacity. The present additives consist of barium, strontium and calcium compounds in the range from 0.1% to 20.0% by weight of the cathode. The barium, strontium and calcium compounds are present in the cell preferably in forms such as hydroxides, oxides and / or hydrates thereof. The amount of the various additive compounds will vary depending on the size of the cell. For example, a cell or stack of size "D" with thicker electrode layer will require more addition of the additive than a cell or "AA" size cell. As a general rule, the amounts of the additive must be increased as a function of the increase in the percentage of the layer thickness of the cathode electrode. For example, a cathode electrode thickness of 4 mm will require twice the additive amount of a cathode electrode thickness of 2 mm. The cells according to the present invention may include a number of other additives for purposes of improving the conductivity and structural integrity of the positive electrode of manganese dioxide, or to improve the recombination of hydrogen at the electrode. Suitable examples of these additives are provided in U.S. Patent Application No. 2005/0164076, which is incorporated by reference herein, and in U.S. Patent No. 5,300,371. For example, the manganese dioxide electrode may include at least one additive comprising graphite, carbon black, inorganic binders, organic binders (for example Coathylene ™) and at least one additive comprising silver oxide (I).

The following examples will help those skilled in the art to better understand the invention and its principles and advantages. It is intended that these examples be illustrative of the invention and not limit the scope thereof.

EXAMPLE 1 AA-size rechargeable alkaline cells or cells were prepared as described in U.S. Patent No. 5,300,371 and the foregoing description, except that various additives were combined with the positive electrode material. In this example, four cathode formulations of the prior art were compared to five comparative test groups according to the present invention. The additives of the test cells of the prior art comprised BaSO4 and combinations of BaSO4 / CaO as indicated in the Table below. The prior art 1 was selected as the typical formulation for rechargeable alkaline batteries most commonly sold in the market today, and is based on the prior art of Taucher et al. WO 93/12551. The best total AA formula, as shown in Table 3 of this patent, is 5% BaS0, which was chosen for the prior art 1. Examples of prior art 2 and 3 are based on the prior art by Daniel-Ivad et al. U.S. Patent No. 6,361,899, which teaches a two-additive process for better performance. The formulation of the prior art example 2 was modeled from Example 3 of the '899 patent using BaS04 as the first additive and CaO as the second additive. To express all the formulation examples in a manner consistent with this present specification, the expression "% by weight added to EMD" of Example 3 in the '899 patent was converted to "% by weight added to the cathode". To do this, the EMD content of the formulation of Example 3 must be determined mathematically. The determination of the EMD content is known to the person skilled in the art and was calculated in Example 3 at 79.5%. With this EMD content, the% by weight added to the cathode can be calculated as follows:% by weight added to the cathode =% by weight added to EMD * 0.795 Therefore, the% by weight added to the cathode in Example 3 of the '899 patent was 5% by weight of BaSO4 and 1% by weight of CaO. These additive levels were used for the prior art 2. The example of the prior art 3 uses a lower amount of BaS0 and a smaller amount of CaO to mimic the same total additive levels as tests # 4, # 5 and # 9 of this invention. The Prior art 4 is based again on Taucher et al. WO 93/12251. The best results of 10 ohms for the AA cell size were achieved with an addition of BaS04 at 15% in a 30 cycle test. Thus, the 15% level of BaS04 was chosen for the prior art 4. The comparative test groups comprise a mixture of barium hydrate (Ba (OH) 2 * 8H20), strontium hydrate (Sr (OH) 2 * 8H20) , and calcium oxide (CaO) in the amounts shown in the Table below. Comparative test groups containing the barium or strontium hydrate additive also had 0.15% Coathylene® HA1681 additive for the improved pressing characteristic of the cathode pellets as described in US Pat. 2005/0164076. In all cases the additives replaced part of the manganese dioxide active electrolytic material (EMD) in such a way that the volume of the total cell materials was maintained at a constant level, and the anode capacity was also maintained at a level constant. As a result, the theoretical capacity of the "one electron" cathode (308 mAh / gMn02) is reduced with the increasing content of the additive and the balance of the anode capacity to the cathode capacity (balance = Ah anode / Ah of the cathode) is increased accordingly as shown in Table la.

The various groups of test cells from each of the groups wtested in cycles by continuously discharging the cell in a 10-ohm load resistor at a cut-off voltage of 0.9 volts, followed by a 12-hour recharge at 1.75 volts , which completes a complete deep discharge / charge cycle. The 10-ohm load represents an average discharge velocity of 90-150 mA, or approximately 10-15 mA / cm2, and is closer to the weakening of the capacity in rechargeable alkaline batteries. Note that this 12-hour to 1.75 V discharge regime simulates approximately the performance that can be achieved with the new loading algorithm described in U.S. Patent Application No. 2005/0164076. Test stacks wtested in 50 such deep discharge / charge cycles. The Table contains the additive composition of the cathodes of Example 1 and Table Ib shows the average discharge capacity of the test cells on the 25th and 50th discharge, as well as the cumulative capacity obtained in 25 and 50 cycles. The term cumulative capacity means the sum of all individual discharge capacities over the proven number of cycles. The data represents the average of 4 cells per test in each group.

Table la: Composition of the additive for the cathodes in Example 1 Cathode Anode Balance Additive Composition Group # Ah Ah BaSÜ4 B8W S8W CaO CoA CaSt Total Tec. Ant.1 2.43 7.88 2.31 95% 5.00% 0% 0% 0% 0% 0% 5.00% Tec. Ant.2 .88 1.00 2.43 7 2.31 95% 5.00% 0% 0%% 0% 0% 6.00% 2.31 0.25 Tec. Ant.3 2.36 7.66 98% 7.15% 0% 0%% 0% 0% 7.40% Tec. Ant.4 2.19 7.10 2.31 106% 15.00% 0% 15.00 0% 0% 0% 0%% Test # 1 0.25 0.15 2.33 7.58 2.31 99% 0% 6.75% 0%%% 0% 7.15% Test # 2 2.34 7.58 1.00 2.31 99% 0% 5.75 0.25 0.15%%%% 0% 7.15% Test # 3 2.29 7.42 2.31 101% 0% 0% 7.15% 0% 0.15% 0% 7.30% Test # 4 2.29 7.44 2.31 0.25 101% 0% 1.00 6.00 0.15%%%% 0% 7.40% Test # 5 2.29 7.42 1.00 2.31 101% 0% 6.25% 0% 0.15%% 0% 7.40% Legend BaS04 = barium sulfate; B8W = barium hydrate (Ba (OH2) * 8H20); S8W = strontium hydrate (Sr (OH2) * 8H20); CaO = calcium oxide; CoA = Coathylene® HA1681; CaSt = calcium stearate (Ca [CH3 (CH2) i8C02] 2 Table Ib: Cycle operation in 50 deep discharge / charge cycles Capacities in Ah% Change vs. Tec. Ant. 1 Group # cyd cyc25 cyc25cum cyc50 cyc50cum cyd cyc25 cyc25cum cyc50 cyc50cum Tec.Ant.1 1.76 0.63 23.71 0.42 35.62 0% 0% 0% 0% 0% Tec.Ant.2 1.65 0.68 22.43 0.61 38.18 -7% 8% -5% 44% 7% Tec.Ant.3 1.72 0.76 25.01 0.47 40.36 -3% 22% 5% 10% 13% Tec. Ant. 4 1.62 0.67 23.39 0.60 38.90 |8% 8% |1% 43% 9% Test # 1 1.78 0.86 30.34 0.75 49.62 1% 38% 28% 77% 39% Test # 2 1.76 1.05 30.05 0.89 53.63 0% 68% 27% 110% 51% Test # 3 1.71 1.05 30.60 0.73 52.27 -3% 67% 29% 72% 47% Test # 4 1.68 1.00 30.78 0.91 53.71 -5% 59% 30% 115% 51% Test # 5 1.70 1.04 29.87 0.85 53.50 -3% 67% 26% 101% 50% Legend: cycl = cycle 1; cyc25 = cycle 25; cyc50 = cycle 50; cyc25cum = 25 cumulative cycles; cyc50cum = 50 cumulative cycles As can be seen from Tables la and Ib, the cells of comparative tests # 1-5 outperformed the cells or stacks made according to the prior art by a significant margin. The discharge capacity of 25 individual cycles was up to 68% better than the control of the prior art 1 and 46% better than the previous best technique. Cumulative over 25 cycles, the capacity Total service was up to 30% better than prior art control 1 and 25% better than the previous best technique. The discharge capacity of 50 individual cycles was up to 115% better than the control of the prior art 1 and 71% better than the best prior art. Over 50 cumulative cycles, the total service capacity was up to 51% better than prior art control 1 and 38% better than the previous best technique. The test cathode # 3, which contained only strontium compounds (without barium or calcium compounds in the formulation) worked much better over the prior art groups # 2 and # 3 as well, despite the teachings of the United States Patent No 6,361,899, which requires the use of a second additive selected from the group consisting of titanium, lanthanum, cerium, yttrium, zinc, calcium, tin and magnesium compounds for improved performance. Test cathode # 5, which contained only a mixture of strontium and barium compound, no calcium compound in the formulation, had a slightly lower performance than test # 4 with the calcium compound in the formulation, but it worked better than test # 1 with the mixture of the barium and calcium compound that did not have the strontium compound at all. The test cathode # 2, the which contained a mixture of barium, strontium and calcium compound, showed better performance than test # 1 with the barium and calcium compound alone. Therefore, the presence of strontium is more important for better performance than barium or calcium compounds or a mixture thereof.

EXAMPLE 2 AA size rechargeable alkaline batteries were prepared and tested similarly to Example 1, except that the total additive range was increased to 7.9% and 9.75% as shown in Table 2a. Table 2b shows the average discharge capacity of the test cells or cells in the 25th and 50th discharge, as well as the cumulative capacity obtained in 25 and 50 cycles. The term cumulative capacity means the sum of all individual discharge capacities over the number of cycles tested. The data given represent the average of 4 cells per test in each group.

Table 2a: Additive composition for cathodes in the Example Cathode Anode Balance Additive Composition Group # Ah Ah BaS04 B8W S8W CaO CoA CaSt Total Tec. Ant.1 2.43 7.88 2.31 95% 5.00% 0% 0% 0% 0% 0% 5.00% 1.00 Tec. Ant.2 2.43 7.88 2.31 95% 5.00% 0% 0% 0% 0% 6.00%% 0.25 Tec Ant.3 2.36 7.66 2.31 98% 7.15% 0% 0% 0% 0% 7.40%% 15.00 Tec. Ant.4 2.19 7.10 2.31 106% 15.00% 0% 0% 0% 0% 0%% 1.00 6.50 0.25 0.15 Test # 6 2.27 7.36 2.31 102% 0% 0% 7.90%%%%% 1.00 6.75 0.15 Test # 7 2.26 7.34 2.31 102% 0% 0% 0% 7.90%%%% 9.50 0.25 Test # 8 2.27 7.37 2.31 102% 0% 0% 0% 0% 9.75%%% Legend BaS04 - barium sulfate; B8W = barium hydrate (Ba (OH2) * 8H20); S8W = strontium hydrate (Sr (OH2) * 8H20); CaO = calcium oxide; CoA = Coathylene® HA1681; CaSt = calcium stearate (Ca [CH3 (CH2) i8C02] 2 Table 2b: Cycle operation over 50 deep discharge / load cycles Capacities in Ah% Change vs. Tec, Ant. 1 Group # cyd cyc25 cyc25cum cyc50 cyc50cum cyd cyc25 cyc25cum cyc50 cyc50cum Tec. Ant. 1 1.76 0.63 23.71 0.42 35.62 0% 0% 0% 0% 0% Tec. Ant.2 1.65 0.68 22.43 0.61 38.18 -7% 8% -5% 44% 7% Tec. Ant.3 1.72 0.76 25.01 0.47 40.36 -3% 22% 5% 10% 13% Tec. Ant.4 1.62 0.67 23.39 0.60 38.90 |8% 8% -1% 43% 9% Test # 6 1.70 1.11 29.75 0.88 54.29 -4% 77% 25% 109% 52% Test # 7 1.71 1.03 31.24 0.80 53.21 -3% 64% 32% 88% 49% Test # 8 1.58 1.08 31.63 0.76 53.29 -10% 73% 33% 79% 50% Legend: cycl = cycle 1; cyc25 = cycle 25; cyc50 = cycle 50; cyc25cum = 25 cumulative cycles; cyc50cum = 50 cumulative cycles As can be seen from Tables 2a and 2b, even though the level of additive is increased, the stacks of comparative test # 6-8 still outperform batteries made according to the prior art by a significant margin. The discharge capacity of 25 individual cycles was up to 77% better than the control of the prior art 1 and 55% better than the previous best technique. Cumulative over 25 cycles, the total serviceability was up to 33% better than the control of the prior art 1 and 28% better than the previous best technique. The individual discharge capacity of 50 cycles was up to 109% better than the control of the prior art 1 and 65% better than the best prior art. Cumulative over 50 cycles, the total service capacity was up to 52% better than the control of the prior art 1 and 39% better than the previous best technique.

EXAMPLE 3 Since all additive levels in Example 1 and 2 showed improved performance over the prior art, rechargeable alkaline batteries of size AA were prepared and tested in a manner similar to Example 1, except that the total additive range was further increased from 7. 4% up to 2 0% as shown in Table 3a. In this series of tests, calcium stearate was used instead of Coathylene ™ for the improved pressing characteristics of the cathode pellets as described in U.S. Patent Application No. 2005/016407 6.

Table 3a: Composition of the additive for the cathodes in Example 3 Cathode Anode Balance Composition of Additive Group # Ah g MnOi Ah BaS04 B8W S8W CaO CoA CaSt Total Tec. Ant. 1 2.43 7.88 2.31 95% 5.00% 0% 0% 0% 0% 0% 5.00% Tec. Ant.2 2.43 7.88 2.31 95% 5.00% 0% 0% 1.00% 0% 0% 6.00% Tec. Ant.3 2.36 7.66 2.31 98% 7.15% 0% 0% 0.25% 0% 0% 7.40% Tec. Ant.4 2.19 7.10 2.31 106% 15.00% 0% 0% 0% 0% 0% 15.00% Test # 9 2.28 7.39 2.31 101% 0% 1.00% 6.00% 0% 0% 0.40% 7.40% Test 10 2.25 7.31 2.31 103% 0% 1.00% 6.50% 0% 0% 0.40% 7.90% Test 11 2.16 7.01 2.31 107% 0% 1.00% 8.35% 0% 0% 0.40% 9.75% Test # 12 2.04 6.62 2.31 113% 0% 1.00% 10.85% 0% 0% 0.40% 12.25% Test # 13 2.04 6.61 2.31 114% 0% 0% 11.85% 0% 0% 0.40% 12.25% Test # 14 1.92 6.22 2.31 121% 0% 1.00% 13.60% 0% 0% 0.40% 15.00% Test # 15 1.81 5.87 2.31 128% 0% 1.00% 16.10% 0% 0% 0.40% 17.50% Test # 16 1.71 5.54 2.31 135% 0% 1.00% 18.60% 0% 0% 0.40% 20.00% Legend BaS04 = barium sulfate; B8W = barium hydrate (Ba (OH2) * 8H20); S8W = strontium hydrate (Sr (OH2) * 8H20); CaO = calcium oxide; CoA = Coathylene® HA1681; CaSt = stearate of calcium (Ca [CH3 (CH2) i8C02] 2 As can be seen from Table 3a, as the levels of the additive increase, the capacity of the cathode decreases accordingly, while the capacity of the anode is kept constant. This results in an increased battery balance. Compared to prior art batteries 1, test # 9 has 6% less capacity, test # 10 has 75 less, test # 11 has 11% less, tests # 12 and 13 have 16% less, test # 14 has 21% less, test # 15 has 26% less and test # 16 has 30% less capacity than the cathode. Table 3b shows the average discharge capacity of the test stacks on the Ia, 25a and 50a discharge, as well as the cumulative capacity obtained in 25 and 50 cycles. The term cumulative capacity means the sum of all individual discharge capacities over the number of cycles tested. The data given represent the average of 4 cells per test in each group. As can be seen from Table 3b, the discharge capacity of the first cycle follows more or less the trend of the theoretical capacities of the cathode. The lower theoretical capacities of the cathode also result in lower first discharge capacities.

Table 3b: Cycle operation over 50 deep discharge / charge cycles Capacities in Ah% Change vs. Tec. Ant. 1 Gpo # cyd cyc25 cyc25cum cyc50 cyc50cum cyd cyc25 cyc25cum cyc50 cyc50cum Tec. Ant. 1 1.76 0.63 23.71 0.42 35.62 0% 0% 0% 0% 0% Tec. Ant. 2 1.65 0.68 22.43 0.61 38.18 -7% 8% -5% 44% 7% Tec. Ant. 3 1.72 0.76 25.01 0.47 40.36 -3% 22% 5% 10% 13% PriorArt4 1.62 0.67 23.39 0.60 38.90 -8% 8% -1% 43% 9% Test # 9 1.73 1.06 30.92 0.84 54.97 -2% 69% 30% 99% 54% Test # 10 1.67 1.08 31.06 0.88 55.31 -5% 72% 31% 109% 55% Test # 11 1.62 1.01 27.70 0.89 49.09 -8% 61% 17% 111% 38% Test # 12 1.51 0.83 23.67 0.72 42.99 -14% 33% 0% 70% 21% Test # 13 1.49 0.87 24.45 0.76 44.81 |16% 40% 3% 80% 26% Test # 14 1.42 0.76 22.16 0.66 40.22 -19% 22% -7% 57% 13% Test # 15 1.33 0.70 19.97 0.61 36.20 -25% 12% -16% 45% 2% Test # 16 1.23 0.63 18.23 0.56 32.85 -30% 0% -23% 33% -8% Legend: cycl = cycle 1; cyc25 = cycle 25; cyc50 = cycle 50; cyc25cum = 25 cumulative cycles; cyc50cum = 50 cumulative cycles However, as cycle numbers increase, test groups with lower initial capacity reach and provide increased performance. For example, compared to the prior art 1, the control test # 14 showed 19% lower capacity in cycle 1, but already 22% better capacity in cycle 25 and was 57% better in the cycle 50. Cumulatively, this test # 14 was still 7% less than the previous technique 1 control over 25 cycles, but 13% better over 50 cycles. Given the fact that capacities are reached with approximately 20% less theoretical cathode capacity, the efficiency utilization of these cathodes is much better and the weakening of the capacity is much lower. This feature of lower weakening of the higher additive levels can be advantageously applied in pile designs, where the high initial capacity is not required, but the least weakening of the capacity is preferred. While the weakening characteristics of the capacity are still very good for the test # 15 and # 16 and the capacity of the cycle 50 was better than the control of the prior art 1, over 50 cumulative cycles no advantage was found in the capacity of total service. Therefore, the upper limit for the total additive was found at 17.5%. Table 3c illustrates the lower weakening of the capacity of the test groups with higher levels of additive. The discharge capacities were converted in terms of capacity for each gram of active Mn02 (Ah / gMn02). This representation takes into account that the different test groups have different capacities of n02, therefore it can be seen that the discharge capacity of the first cycle is more or less equivalent. However, as the cycles progress, the standardized capacity per gram unit of the active Mn02 of all the test groups becomes much better than any control of the prior art.

Table 3c: Normalized cycle operation over 50 deep discharge / charge cycles Capacities in Ah / gMnÜ2% Change vs. Tec. Ant. 1 Group # cyd cyc25 cyc25cum cyc50 cyc50cum cyd cyc25 cyc25cum cyc50 cyc50cum Tec. Ant 1 0.224 0.079 3.01 0.054 4.52 0% 0% 0% 0% 0% Tec. Ant 2 0.209 0.086 2.85 0.077 4.84 | 7% 8% | 5% 44% 7% Tec. Ant 3 0.224 0.100 3.27 0.061 5.27 0% 26% 9% 14% 17% Tec. Ant 4 0.228 0.095 3.29 0.085 5.48 2% 19% 9% 58% 21% Test # 9 0.233 0.143 4.18 0.114 7.43 4% 80% 39% 112% 65% Test # 10 0.229 0.148 4.25 0.121 7.57 2% 86% 41% 125% 67% Test # 11 0.230 0.144 3.95 0.127 7.00 3% 81% 31% 137% 55% Test # 12 0.228 0.125 3.57 0.109 6.49 2% 58% 19% 102% 44% Test # 13 0.226 0.132 3.70 0.116 6.78 1% 67% 23% 115% 50% Test # 14 0.229 0.123 3.56 0.107 6.47 2% 55% 18% 99% 43% Test # 15 0.226 0.119 3.40 0.104 6.17 1% 50% 13% 95% 37% Test # 16 0.222 0.114 3.29 0.101 5.93 -1% 43% 9% 89% 31% Legend: cycl = cycle 1; cyc25 = cycle 25; cyc50 = cycle 50; cyc25cum cumulative cycles; cyc50cum = 50 cumulative cycles cathodes of test # 12 and # 13 compare mixture of strontium, barium and calcium compounds with a mixture of strontium and calcium compounds that do not contain barium compound at a total additive level of 12.25%. At this high level of additive, test # 13 without barium in the formulation showed better performance over 50 cycles than test # 14 with the barium compound. This shows that at high levels of additives, no additional barium compound is necessary for the best performance. Although table 3c illustrates very clearly that all formulations from tests # 9 to # 16 show highly improved efficiency at a specific Mn02 mass basis, starting at total additive levels of 20%, absolute capacity values (provided in Table 3b) are less than the best formulations of the prior art). The addition of the additive therefore does not provide any practical benefit beyond this point. From the foregoing, it will be noted that this invention is a well adapted to achieve all the purposes and objectives described hereinbefore, together with other advantages that are obvious and that are inherent to the structure. It will be understood that certain characteristics and subcombinations are useful and can be used without reference to other characteristics and subcombinations. This is contemplated by and is within the scope of the claims. Since many possible embodiments of the invention can be made without departing from the scope thereof, it should be understood that all of the subject matter described herein or shown in the appended figures has to be interpreted as illustrative and not in a limiting sense. Variations of the above embodiments will be apparent to a person of ordinary skill in the art and the inventor intends that they be encompassed by the following claims.

Claims (20)

1. A rechargeable electrochemical cell or cell comprising a cathode of manganese dioxide, a separator, an anode and an aqueous alkaline electrolyte, the cathode comprises a strontium compound in an amount of 4.50 to 16.10% by weight of the cathode, the cell has a individual discharge capacity after 50 deep discharge-charge cycles of at least 0.100 Ah / gMn02.

2. The electrochemical cell according to claim 1, characterized in that the strontium compound consists of strontium oxide or strontium hydroxide and hydrates thereof.

3. The electrochemical cell according to claim 1, characterized in that the cathode further comprises a barium compound.

4. The electrochemical cell according to claim 3, characterized in that the barium compound is present in an amount different from zero, less than or equal to 1.00% by weight of the cathode. 5. The electrochemical cell according to claim 3, characterized in that the barium compound consists of barium oxide or barium hydroxide and hydrates thereof.

5

6. The electrochemical cell according to claim 1, characterized in that the cathode further comprises a calcium compound.

7. The electrochemical cell according to claim 6, characterized in that the calcium compound is present in an amount of 0.25 to 1.25% by weight of the cathode.

8. The electrochemical cell according to claim 6, characterized in that the calcium compound is selected from the group consisting of calcium oxide, calcium hydroxide and calcium stearate.

9. The electrochemical cell according to claim 1, characterized in that the strontium compound is present in an amount of 5.75 to 11.85% by weight of the cathode. The electrochemical cell according to claim 1, characterized in that the strontium compound is present in an amount of 5.75 to 8.35% by weight of the cathode and wherein the cathode further comprises a barium compound present in a non-zero amount less than or equal to 1.00% by weight of the cathode, and a calcium compound present in an amount of 0.25 to 0.40% by weight of the cathode. 11. A rechargeable electrochemical cell, characterized in that it comprises a cathode of manganese dioxide, a separator an anode and an aqueous alkaline electrolyte, the cathode comprises a strontium compound in an amount of 4.50 to 16.10% by weight of the cathode and a barium compound in an amount other than zero less than or equal to 1.00% by weight of the cathode. The electrochemical cell according to claim 11, characterized in that the cell has an individual discharge capacity after 50 deep discharge-charge cycles of at least 0.100 Ah / g n02. 13. The electrochemical cell according to claim 11, characterized in that the strontium compound consists of strontium oxide or strontium hydroxide and hydrates thereof. 14. The electrochemical cell according to claim 11, characterized in that the barium compound consists of barium oxide or barium hydroxide and hydrates thereof. 15. The electrochemical cell according to claim 11, characterized in that the cathode further comprises a calcium compound in an amount of 0.25 to 1.25% by weight of the cathode. 16. The electrochemical cell according to claim 15, characterized in that the compound of Calcium is selected from the group consisting of calcium oxide, calcium hydroxide and calcium stearate. 17. A method for increasing the cumulative discharge capacity of an electrochemical cell having a manganese dioxide cathode, a separator, an anode and an aqueous alkaline electrolyte, the method is characterized in that it comprises the addition of a strontium compound in a amount of 4.50 to 16.10% by weight of the cathode, the strontium to increase an individual discharge capacity of the cell after 50 deep discharge-charge cycles. 18. The method of compliance with the claim 17, characterized in that the method further comprises adding a barium compound to the cathode in an amount other than zero less than or equal to 1.00% by weight of the cathode. 19. The method according to the claim 18, characterized in that the method further comprises adding a calcium compound to the cathode in an amount of 0.25 to 1.25% by weight of the cathode. 20. The method of compliance with the claim 19, characterized in that the cell has an individual discharge capacity after 50 deep discharge-charge cycles of at least 0.100 Ah / gMn02.