MXPA97006186A - Additives for primary electrochemical cells having manganese dioxide cathodes - Google Patents

Abstract

The invention relates to alkaline cells containing manganese dioxide cathode active material. A substance selected from the group of compounds Bi2O3, PbO2, SnO2, Co3O4, CoO, Bi2O33ZrO3 and K2Cr2O7 is added to the cathode of conventional alkaline cells typically having an anode comprising zinc and cathode comprising manganese dioxide and an alkaline electrolyte. The additive increases the specific capacity (amp-hr/g) of the manganese dioxide in the cathode.

Description

ADDITIVES FOR PRIMARY ELECTROCHEMICAL CELLS THAT HAVE MANGANESE DIOXIDE CATHODES FIELD OF THE INVENTION The present invention relates to alkaline electrochemical cells with manganese dioxide cathode and compounds selected from the group Bi203, Pb02, Sn02, C03O4, CoO, Bi203"3Zr03 and K2Cr207 added or added to the cathode material to improve the specific capacity of the dioxide of manganese.

BACKGROUND OF THE INVENTION The primary alkaline cells typically contain zinc anodic active material, alkaline electrolyte, a cathodic manganese dioxide active material, and an electrolyte permeable separating film, typically cellulose. Conventional alkaline cells may contain added mercury at zero such that the total mercury content is less than about 50 parts of mercury per parts per million by weight of the total or complete cell. The anodic active material comprises zinc particles mixed with conventional gelling agents, REF: 25390 such as copolymers of carboxymethylcellulose or acrylic acid, and electrolyte. The gelling agent keeps the zinc particles in place and in contact with each other. A nail or conductive metal nail, known as the anode current collector, is typically inserted into the anodic active material. The alkaline electrolyte is typically an aqueous solution of potassium hydroxide, but other alkaline solutions of sodium or lithium hydroxide may also be employed. The cathodic material is typically manganese dioxide and may include minor amounts of carbon or graphite to increase conductivity. Conventional alkaline cells are enclosed in a steel container to retain cell components and reduce the likelihood of leakage. Since the dimensions of the commercial cells are fixed, it has been desirable to attempt to achieve useful service life and / or life of the cell by increasing the surface area of the active material of the electrode and packing large amounts of the active material in the cell. This approach has practical limitations, since if the active material is packed so densely in the cell this can reduce the electrochemical reaction rate during discharge, in turn reducing the service life. Other detrimental effects such as polarization may occur, particularly at high amperage consumption rates. Polarization limits the mobility of ions within the active material of the electrode and within the electrolyte, which in turn retards the functioning and service life. Thus, it is desirable to provide a way to retard such deleterious effects which in turn can increase the useful life and / or service life of the cell.

DESCRIPTION OF THE INVENTION One way to delay such detrimental effects is to increase the actual specific capacity of the cathode material of Mn02, typically electrolytic manganese dioxide (DME). The DME in conventional alkaline cells has a theoretical specific capacity of approximately 308 mAmp-hr per gram. The actual specific capacity of the DME material made in the discharge of a conventional alkaline cell is less theoretical because of the deficiencies caused by polarization effects and another phenomenon that affects the cathodic and efficiently electron transfer reactions. For example, the actual specific capacity of the MDE in a standard alkaline cell when discharging at a high speed (in a load of 3.9 ohms) at a potential of 0.8 volts can be approximately 195 mAmp-hr / g for a continuous discharge and 220 mAmp-hr for intermittent discharge. This could correspond to a DME efficiency of 63% and 71%, respectively. It has been found that adding small amounts of specific compounds to the cathode of conventional primary zinc / Mn02 alkaline cells increases the actual specific capacity (amp-hr / g) of the active material of the Mn02 cathode in the cell. The compounds that have been found to increase i -. The actual specific capacity of the Mn02 material in such cells are: Bi203, Pb02, Sn02, Co30, CoO, Bi203"3Zr03 and K2Cr207 and combinations thereof The inclusion of a cathodic additive selected from the foreign group of compounds advantageously improves the specific capacity of the cathodic active material of MnO2 in such cells. they can add to the cathode so that their total weight comprises between about 0.1 to 10 weight percent of the total cathode The following examples illustrate the invention and advantages derived therefrom. (All compositions are by weight unless otherwise specified. shape . ) Example 1 (Comparative Example): A conventional primary zinc / manganese dioxide alkaline (standard D cell) is prepared with conventional cathodic and anodic active material, electrolyte and separating membrane. The anodic material may be in the form of a gelled mixture containing mercury-free zinc alloy powder (mercury added at zero). The total mercury content of the cell is therefore less than 50 parts of mercury per parts per million by weight of the cell. The anodic mixture typically can contain an aqueous KOH solution, gelling agent, for example acrylic acid copolymer such as CARBOPOL C934 from B.F. Goodrich; and surfactants for example organic phosphate ester surfactant GAFAC RA600 from Rhone Poulenc. The separating membrane may be a conventional electrolyte permeable membrane of polyvinyl alcohol / rayon material. The electrolyte is an aqueous solution of KOH containing approximately 40% p-ε of KOH and 2% by weight of ZnO, later referred to as "aqueous KOH solution".

The cathodic active material in the standard cell has the following composition: Electrolytic manganese dioxide (84% by weight), graphite (9.5% by weight) and an "aqueous solution of KOH" 7 Normal (6.5% by weight). The new or recent standard cells are discharged at a cutoff voltage of 1.0 volt and 0.8 volts, each at the base of a continuous discharge and an intermittent discharge. The continuous discharge is performed by discharging the cell at a constant current consumption rate of approximately 410 milliamps (equivalent for an average load of approximately 2.2 ohms) throughout. Intermittent discharge is done by discharging the cell to this same constant but applied current for 1 hour followed by 5-hour reset cycles. In each case, the actual specific capacity (mAmp-hr / g) of Mn02 at the cathode is calculated by multiplying the current consumption by the time taken to reach the designated cut-off voltage divided by the weight of Mn02 at the cathode.

Example 2 (Comparative Example): The same standard cells as in Example 1 are prepared. These cells are discharged at 1.0 and 0.8 volts under continuous and intermittent discharge conditions as in Example 1 except that a constant current consumption of 274 mAmp (equivalent to a 3.9 ohm load). In each case the actual specific capacity of Mn02 at the cathode is calculated in the manner described in Example 1.

EXAMPLE 3 The alkaline cells of experimental dimension D of zinc / Mn02, identical to those mentioned in Example 1 are prepared, except that in the manufacture of the experimental cell an amount (gms) of Pb02 is added so that the total cathodic material comprises 5.0 weight percent of Pb02. The amount of Mn02 at the cathode is reduced by an equal amount (gms) so that the weight of the total cathode in the experimental cell is the same as in the standard cell of Example 1. Thus, the cathode or cathode composition of the Experimental cell is: 79% electrolytic manganese dioxide (DME), 9.5% graphite, 6.5% KOH solution and 5% Pb02. The experimental cells are discharged at 1.0 volt and 0.8 volt in the same continuous and intermittent discharge conditions as in Example 1.

During the discharge the consumption speeds remain constant at 410 milliamps (equivalent to an average load of approximately 2. 2 ohms) as in Example 1. The specific capacity (mAmp-hr / g) of the Mn02 in the experimental cells is calculated in each case from the weight of Mn02 in the cells, the current consumption, and the discharge time required to reach the designated cut-off voltage, as described in Example 1. In each case the actual specific capacity of Mn02 in the experimental cell is increased over the specific capacity of Mn02 in the standard cell, in the same discharge conditions and consumption speeds. At a constant consumption speed of 410 mAmp, the increase in the specific capacity of Mn02 in the experimental cell over that of the standard cell is 12.8% for continuous discharge at 1.0 volt and 15.2% for continuous discharge at 0.8 volts. At the same consumption rate of 410 mAmp, the increase in specific capacity of Mn02 in the experimental cell over that of the standard cell is 9.5% for intermittent discharge at 1.0 volt and 10.2% for intermittent discharge at 0.8 volts. These increases are summarized in Table 1.

Example 4 The same experimental cells as in Example 3 are prepared, except that Bi203 is added to the cathode material instead of Pb02. Thus, the cathode or cathodic composition for the experimental cells is: 79% electrolytic manganese dioxide (DME), 9.5% graphite, 6.5% KOH solution and 5% Bi203. These experimental cells are discharged at a constant current of 274 mAmp (equivalent to an average load of 3.9 ohms) in the same manner as in the discharge of the standard cell of Example 2.

The specific capacity (mAmp-hr / g) of Mn02 in the experimental cells is calculated in each case in the manner described in Example 1. In each case the specific capacity of Mn02 in the experimental cell is increased over the specific capacity of Mn02 in the standard cell (Example 2) for the corresponding discharge condition and current consumption. Thus, at a constant current consumption of 274 mAmp (load of 3.9 ohms) the increase in the specific capacity of Mn02 in the experimental cell over that of the standard cell is 9.0% for continuous discharge at 1.0 volt and 12.0% for the discharge continues at 0.8 volts. At the same consumption speed of 274 mAmp, the increase in specific capacity of Mn02 in the experimental cell over that of the standard cell is 5.9% for intermittent discharge at 1.0 volt and 6.8% for intermittent discharge at 0.8 volts. These increases are summarized in Table 1.

Example 5: The same experimental cells as in Example 3 are prepared, except that Sn02 is added to the cathode material instead of Pb02. Thus, the cathodic composition for the experimental cells is: 79% of electrolytic manganese dioxide (DME), 9.5% of graphite, 6.5% of KOH solution and 5% of Sn02. These experimental cells are discharged at a constant current of 274 mAmp (equivalent to an average load of 3.9 ohms) in the same manner as in the discharge of the standard cell of Example 2. The specific capacity (mAmp-hr / g) of Mn02 in the experimental cells it is calculated in each case in the manner described in Example 1. In each case, the specific capacity of Mn02 in the experimental cell is increased over the specific capacity of Mn02 in the standard cell (Example 2) for the condition of discharge and corresponding current consumption. Thus, at a constant current consumption of 274 mAmp (load of 3.9 ohms), the increase in the specific capacity of Mn02 in the experimental cell over that of the standard cell is 9.3% for continuous discharge at 1.0 volt and 7.9% for continuous discharge at 0.8 volts. At the same consumption speed of 274 mAmp, the increase in the specific capacity of Mn02 in the experimental cell over that of the standard cell is 4.5% for intermittent discharge at 1.0 volt and 5.3% for intermittent discharge at 0.8 volts. These increases are summarized in Table 1.

Example 6 The same experimental cells as in Example 3 are prepared, except that Co304 is added to the cathode material instead of Pb02. Thus, the cathodic composition for the experimental cells is: 79% of electrolytic manganese dioxide (DME), 9.5% of graphite, 6.5% of KOH solution and 5% of C03O4. These experimental cells are discharged at a constant current of 274 mAmp (equivalent to a load of 3.9 ohms) in the same manner as in the discharge of the standard cell of Example 2. The specific capacity (mAmp-hr / g) of Mn02 in the experimental cells are calculated in the manner described in Example 1. In each case the specific capacity of the Mn02 in the experimental cell is increased over the specific capacity of the MnOa in the standard cell (Example 2) for the current consumption and the condition of corresponding discharge. Thus, at a constant current consumption of 274 mAmp (load of 3.9 ohms), the increase in the specific capacity of the Mn02 in the experimental cell over that of the standard cell is 4.2% for continuous discharge at 1.0 volt and 5.6% for continuous discharge at 0.8 volts. These increases are summarized in Table 1.

Example 7 The same experimental cells as in Example 3 are prepared, except that CoO is added to the cathode material instead of Pb02. Thus, the cathodic composition for the experimental cells is: 79% electrolytic manganese dioxide (DME), 9.5% graphite, 6.5% KOH solution and 5% CoO. These experimental cells are discharged at a constant current of 274 mAmp (equivalent to an average load of 3.9 ohms) in the same manner as in the discharge of the standard cell of Example 2. The specific capacity (mAmp-hr / g) of Mn02 in the experimental cells it is calculated in each case in the manner described in Example 1. The specific capacity of the Mn02 in the experimental cell is increased over the specific capacity of the Mn02 in the standard cell (Example 2) for the condition of discharge and consumption of corresponding current in all cases except intermittent discharge at 1.0 volt. At a constant current consumption of 274 mAmp (equivalent to an average load of 3.9 ohms) the increase in specific capacity of Mn02 in the experimental cell over that of the standard cell is 0.7% for continuous discharge at 1.0 volt and 4.7% for continuous discharge at 0.8 volts. At the same consumption rate of 274 mAmp there is a decrease in the specific capacity of Mn02 in the experimental cell over that of the standard cell of 0.1% for the intermittent discharge at 1.0 volt and an increase of 2.5% for the intermittent discharge at 0.8 volts. These changes are summarized in table 1.

Example 8 The same experimental cells as in Example 3 are prepared, except that Bi203'3Zr02 is added to the cathode material instead of Pb02. Thus, the cathodic composition for the experimental cells is: 79% electrolytic manganese dioxide (DME), 9.5% graphite, 6.5% KOH solution and 5% Bi203'3Zr02. These experimental cells are discharged at a constant current of 274 mAmp (equivalent to a load of 3.9 ohms) in the same manner as in the discharge of the standard cell of Example 2. The specific capacity (mAmp-hr / g) of Mn02 in the experimental cells are calculated in each case in the manner described in Example 1. For the discharge at a constant current consumption of 274 mAmp (load of 3.9 ohms) there is a decrease of 0. 6% in the specific capacity of the Mn02 in the experimental cell compared with that of the standard cell (Example 2) for the continuous discharge at 1.0 volt and an increase of 6.2% for the continuous discharge at 0.8 volts. At the same consumption rate of 274 mAmp, the specific capacity of the Mn02 in the experimental cell compared to the specific capacity of the standard cell does not change for the intermittent discharge at 1.0 volt but increases 5.5% for the intermittent discharge at 0.8 volts. These changes are summarized in Table 1.

Example 9 The same experimental cells as in Example 3 are prepared, except that K2Cr207 is added to the cathode material in place of Pb02. Thus, the cathodic composition for the experimental cells is: 79% of electrolytic manganese dioxide (DME), 9.5% of graphite, 6.5% of KOH solution and 5% of K2Cr207. These experimental cells are discharged at a constant current of 274 mAmp (equivalent to an average load of 3.9 ohms) in the same manner as in the discharge of the standard cell of Example 2. The specific capacity mAmp-hr / g) of Mn02 in the experimental cells is calculated in the manner described in Example 1.

In each case, the specific capacity of Mn02 in the experimental cell is increased over the specific capacity of Mn02 in the standard cell for the corresponding discharge and current consumption condition. Thus, at a constant current consumption of 274 mAmp (load of 3.9 ohms) the increase in specific capacity of the Mn02 in the experimental cell over that of the standard cell is 9.3% for continuous discharge at 1.0 volt and 18.1% for the continuous discharge at 0.8 volts. At the same consumption speed of 274 mAmp there is no change in the specific capacity of the Mn02 in the experimental cell over that of the standard cell for the intermittent discharge at 1.0 volt and there is an increase of 5.5% in the specific capacity of the Mn02 in the experimental cell over that of the standard cell for intermittent discharge at 0.8 volts. These changes are summarized in Table 1. As seen in Table 1, the addition of any of the listed additives to the cathode of the alkaline cell results in an increase in the specific capacity of Mn02 in both continuous and intermittent discharge at 0.8 volts. If the amount of additive is adjusted, for example between 0.1% and 10%, preferably between approximately 0.1 and 5% by weight of the cathode, the service life or useful life of the cell compared with the standard cell can be increased. it has an additional (equal) amount of Mn02 instead of the additive. In fact, with the amount of 5% by weight of additive used in each of the above examples, the service life or life of the cell when discharged at 0.8 volts is increased over that of the standard cell when the additives Bi203, Pb02, Sn02 and K2Cr207. The percentage increase in service life or service life in such cases is summarized in Table 1. The drive voltage or service voltage (ie the time profile of voltage versus discharge) of the cells containing the additives Pb02 is Measures to be greater than the operating voltage or service voltage of the standard cell. In general, the increase in specific capacity of Mn02 resulting from the inclusion of any of the additives described above will tend to increase the operating voltage or operating voltage of the experimental cell containing the respective additive.

TABLE 1 EFFECT OF CATHODIC ADDITIVES 1.0-volt discharge Download at 0.8 volts ADDITIVE% Increment. % of Increm. % of Increm. % of Increm. CATHODIC "PROOF OF CAPACITY Udei of Spec. Cap. Of the Life of -, (5% in weight) DOWNLOAD Spec. Of MnO Serv. Cell of MnO", Serv. of Cell Bi.O, Continuous +9.0 +2.5 +12.0 +5.3 3 BijO, Flashing +5.9 -0.5 +6.8 +0.4 PbO, C Coonnttiinnuuoo +12, .8 +6.0 +15.2 +8.3 PbO- I Inntteerrmmiitteennttee "+9 .5 + 2.9 +10.2 +3.6 SnO, CCoonnttiinnuuoo +9, .3 +2.7 +7.9 +1.4 oo M 3 SnOj Flashing + +44. .55 -1.8 +5.3 -1.0 Co, 04 Continuous ++ 44 .. .22 -2.1 +5.6 -0.7 ++ 44 ,. .33 -2.0 +0.1 -5.9 CoO Continuous ++ 77 .. .00 +0.6 +4.7 -1.6 Intermittent CoO "-0.1 -6.1 +2.5 -3.7 Bi-033ZrO, Continuous -0.6 -6.6 +6.2 -0.2 Bi-033ZrO , Flashing "0.0 -6.0 +5.5 -0.8 K3Cra07 Continuous +9.3 +2.7 +18.1 +11.0 Notes: H 1. Additive comprises 5% cathode. 2. Copparation of the service life with the same cell with N «friO- instead of the additive. 3. Repetitive 1-hour discharge cycles followed by 5-hour reset.

Although the present invention is described with respect to the specific embodiments, it should be recognized that variations are possible, for example, in the size of the cell, without departing from the concept of the invention.

It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which refers to the manufacture of the objects to which it refers.

Having described the invention as above, the content of the following is claimed as property

Claims (7)

1. A primary electrochemical cell comprising an anode, an aqueous alkaline electrolytic solution, a separator and a cathode comprising manganese dioxide, characterized in that the cathode further includes Bi203, Pb02, Sn02, Co304, CoO, Bi2O3"3Zr03 or K2Cr207 or any combination of the same for which the capacity of the cell is increased when it is discharged at 0.8 volts.

2. A primary electrochemical cell comprising an anode, an aqueous alkaline electrolytic solution, a separator and a cathode comprising manganese dioxide, characterized in that the cathode further comprises Sn02, Co304, CoO, or K2Cr207 or any combination thereof added in admixture with manganese dioxide, and where the additive has the effect of increasing the capacity of the cell when the cell is discharged at 0.8 volts.

3. A primary electrochemical cell according to claim 1, characterized in that the cathode comprises manganese dioxide and Bi203 or Pb02 or a mixture thereof.

4. The cell according to claim 1, 2 or 3, characterized in that the anode comprises zinc and the aqueous electrolyte solution comprises potassium hydroxide.

5. The cell according to claims 1, 2 or 3, characterized in that the additive comprises between about 0.1 and 10 weight percent of the cathode.

6. The cell according to claims 1, 2 or 3, characterized in that the total mercury content in the cell is less than 50 parts per million of the total weight of the cell.

7. A primary electrochemical cell comprising an anode comprising zinc, an aqueous alkaline electrolyte solution comprising potassium hydroxide, a separator and a cathode comprising manganese dioxide, characterized in that the cathode further comprises Pb02 in admixture with manganese dioxide, and where the additive has the effect of increasing the capacity of the cell when it is discharged at 0.8 volts.