MXPA98001409A - Additives for alkaline electrochemical batteries contain manio dioxide catodes - Google Patents

Abstract

The present invention relates to alkaline batteries containing an active material of the cathode, magnesium dioxide. A substance selected from the group of compounds of CaWO4, BatiO3, CatiO3, ZnMn2O4, or Bi12TiO26, or any other combination thereof, is added to the cathode of conventional alkaline batteries typically having a anode comprising zinc and a cathode comprising dioxide of manganese and an alkaline electrolyte. The additive increases the service life of the pi

Description

ADDITIVES FOR ALKALINE ELECTROCHEMICAL BATTERIES THAT HAVE MANGANESE DIOXIDE CATHODES Field of the Invention The present invention relates to alkaline electrochemical cells with manganese dioxide cathodes and to compounds selected from the group of CaW04, MgTi03, BaTi03, CaTi03, ZnMn204, or Bi? 2Ti02o, and combinations thereof, added to the cathode material to improve the operation of the batteries.

Background of the Invention The primary alkaline cells typically contain an active material of the zinc anode, alkali electrolytes, an active cathode material of manganese dioxide, and a permeable electrolyte separating film, typically of synthetic and cellulosic fibers. Conventional alkaline batteries may contain non-added or zero-added mercury in such a way that the total mercury content is less than about 50 parts of mercury per parts per million by weight of the total battery. The active material of the anode comprises zinc particles mixed with conventional gelling agents Ref.26943, such as the carboxymethylcellulose or the sodium salt of an acrylic acid copolymer, and the electrolyte. The gelling agent keeps the zinc particles in place and in contact with each other. A conductive metallic nail, known as the anode current collector, is typically inserted into the active material of the anode. 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 cathode material is typically manganese dioxide and may include small amounts of carbon or graphite to increase conductivity. Conventional alkaline batteries are encased in a steel container to retain the components of the battery and to reduce the likelihood of leakage. Since the sizes of commercial batteries are fixed, it has been desirable to try to improve the performance and / or service life of the stack by increasing the surface area of the active material of the electrode and packing larger quantities of the active material in the stack. This approach has practical limitations, since if the active material is packaged too densely in the pile, this can reduce the speed of the electrochemical reaction during discharge, reducing in turn the service life. Other detrimental effects such as polarization can occur. Polarization limits the mobility of the ions within the active material of the electrode and within the electrolyte, which in turn delays the operation and duration in service. Accordingly, it is desirable to provide a way to delay such detrimental effects, which in turn may increase the operation and / or useful service life of the stack. It has been found that adding small amounts of the specific compounds to the positive electrode of conventional zinc / Mn02 alkaline batteries can increase the service life of the battery. The compounds which have been found to increase the service life of the alkaline battery are: CaW04, MgTi03, BaTi03, CaTi03, ZnMn204, and Bi? 2Ti02o, and combinations thereof. These compounds alone or in any combination can be added mixed with the Mn02 cathode material of a primary (non-rechargeable) alkaline battery so that their total weight comprises between about 0.1 to 5 weight percent of the total cathode, preferably between about 0.3 and 3 percent by weight. The following examples illustrate the invention and the advantages derived therefrom. (All compositions are by weight unless otherwise specified).

Example 1 (Comparative Example): An alkaline, primary, conventional manganese / zinc dioxide battery (standard C battery), is prepared with an active anode and cathode material, the electrolyte and the separating membrane, conventional. The anode material may be in the form of a gelled mixture containing the powder of the mercury-free zinc alloy (mercury added zero or without mercury addition). The total mercury content of the cell is therefore less than 50 parts of mercury per parts per million of the weight of the cell. The anode mixture can typically contain the zinc alloy powder, the aqueous KOH solution, the gelling agent, for example the acrylic acid copolymer such as CARBOPOL C940 from B.F. Goodrich; and surfactants, for example the organic phosphate ester surfactant RM510 from Rhone Poulenc. The separating membrane may be a conventional electrolyte permeable membrane of rayon / polyvinyl alcohol material. The electrolyte is an aqueous solution of KOH containing approximately 40% by weight of KOH and 2% by weight of ZnO, hereinafter referred to as the "aqueous KOH solution". The active material of the cathode in the standard cell has the following composition: Electrolytic manganese dioxide (84% by weight), graphite (9.2% by weight), polyethylene powder binder (0.3% by weight) and a "KOH solution" aqueous "7 Normal (6.5% by weight). The fresh standard batteries are discharged at standard cut-off power voltages based on a continuous discharge test and intermittent discharge tests. The continuous discharge is carried out by discharging the fresh standard batteries at a constant load of 3.9 ohms at a cut-off power of 0.75 volts (Test A). (Continuous consumption of 3.9 ohms corresponds to the American National Standard Institute (ANSE) toy test.) In a first intermittent discharge test (Test B) fresh batteries are also discharged at a constant load of 3.9 ohms, but under Intermittent discharge conditions of the well-known industrial ANSI flashing test (LIF) In the LIF test (Test B) the batteries are discharged continuously for 4 minutes per hour for a period of 8 hours per day followed by a rest period of 16 hours and then the cycle is repeated at a cut-off voltage of 0.75 volts.In a second intermittent discharge test (Test C) fresh batteries are stored first for 2 weeks at 12.77777 ° C (55 ° F) and then discharged for 1 hour per day at a constant load of 3.9 ohms at a cut-off voltage of 0.8 volts (This corresponds to the toy test of the International Electrotechnical Conference (IEC)). test the service life of the battery (hours) with respect to the cut-off voltage, is recorded. Additionally, the maximum power of the fresh standard batteries is determined by subjecting the batteries to a consumption of 7 amps for 100 milliseconds. At this consumption, the maximum power is calculated by multiplying the 7 amperes by the load voltage. The fresh standard batteries exhibit a maximum power of 6.2 watts.

Example 2 Experimental zinc size C alkaline / Mn02 batteries, identical to those referred to in Example 1, are prepared, except that in the manufacture of the experimental stack an amount (grams) of CaW04 is added mixed with the cathode so that the total cathode material comprises 1.5 percent by weight of Ca 04. The amount of Mn02 at the cathode is reduced by an equal amount (grams) so that the total cathode weight in the experimental stack is the same as in the standard stack of Example 1. Accordingly, the cathode composition of the experimental cell in the present example is: Electrolytic manganese dioxide (82.5% by weight), CaW04 (1.5% by weight), graphite (9.2% by weight), powder binder of polyethylene (0.3% by weight) and an "aqueous KOH solution" 7 Normal (6.5% by weight). The batteries are discharged at a constant load of 3.9 ohms using the same continuous discharge test (Test A) and the same two intermittent discharge tests (Tests B and C) described in the comparative example (Example 1) . The duration in the service obtained in each of the three tests with the additive of Ca 04 is compared with that obtained in the corresponding test of the comparative example (Example 1). Service life decreased 3.2% for Test A, increased 5.1% for Test B and increased 4.6% for Test C. These test results are summarized in Table 1. The maximum power of fresh batteries, determined as in Example 1, exhibits a reduction of 2.6% on the maximum power of the standard batteries of Example 1.

Example 3 Alkaline batteries of experimental size Z / Mn02 C, identical to those referred to in Example 1, are prepared, except that in the manufacture of the experimental stack an amount (grams) of MgTi03 is added mixed with the cathode so that the Total cathode material comprises 1.5 weight percent MgTi03. The amount of Mn02 at the cathode is reduced by an equal amount (grams) so that the weight of the total cathode in the experimental cell is the same as in the standard cell of Example 1. Accordingly, the cathode composition of the cell experimental in the present example is: Electrolytic manganese dioxide (82.5% by weight), MgTi03 (1.5% by weight), graphite (9.2% by weight), polyethylene powder binder (0.3% by weight) and a "solution of Aqueous KOH "7 Normal (6.5% weight). The batteries are discharged at a constant load of 3.9 ohms using the same continuous discharge test (Test A) and the same two intermittent discharge tests (Tests B and C) described in the comparative example (Example 1). The service life obtained in each of the three tests with the MgTi03 additive is compared with that obtained in the corresponding test of the comparative example (Example 1). Service life increased 5.1% for Test A, increased 0.9% for Test B and increased 3.7% for Test C. These test results are summarized in Table 1. The maximum power of fresh batteries, determined as in Example 1, exhibits a reduction of 0.1% over the maximum power of the standard stacks of Example 1.

Example 4 Zinc alkaline batteries of experimental zinc / Mn02 are prepared, identical to those referred to in Example 1, except that in the manufacture of the experimental stack an amount (grams) of BaTi03 is added mixed with the cathode so that the material of the Total cathode comprises 1.5 percent by weight of BaTi03. The amount of Mn02 at the cathode is reduced by an equal amount (grams) so that the weight of the total cathode in the experimental cell is the same as in the standard cell of Example 1. Accordingly, the cathode composition of the cell experimental in the present example is: Electrolytic manganese dioxide (82.5% by weight), BaTi03 (1.5% by weight), graphite (9.2% by weight), powder binder of polyethylene (0.3% by weight) and an "aqueous KOH solution" 7 Normal (6.5% by weight). The batteries are discharged at a constant load of 3.9 ohms using the same continuous discharge test (Test A) and the same two intermittent discharge tests (Tests B and C) described in the comparative example (Example 1). The service life obtained in each of the three tests with the BaTi03 additive is compared with that obtained in the corresponding test of the comparative example (Example 1). Service life increased 3.5% for Test A, 2.3% was increased for Test B and 4.8% was increased for Test C. These test results are summarized in Table 1. The maximum power of the fresh batteries, determined as in Example 1, exhibited an increase of 2.4. % on the maximum power of the standard batteries of Example 1.

Example 5 Zinc alkaline batteries of experimental zinc / Mn02 were prepared, identical to those referred to in Example 1, except that in the manufacture of the experimental battery an amount (grams) of CaTi03 is added mixed with the cathode so that the material of the Total cathode comprises 1.5 percent by weight of CaTi03. The amount of Mn02 at the cathode is reduced by an equal amount (grams) so that the weight of the total cathode in the experimental cell is the same as in the standard cell of Example 1. Accordingly, the cathode composition of the cell experimental in the present example is: Electrolytic manganese dioxide (82.5% by weight), CaTi03 (1.5% by weight), graphite (9.2% by weight), polyethylene powder binder (0.3% by weight) and a "solution of Aqueous KOH "7 Normal (6.5% by weight). The batteries are discharged at a constant load of 3.9 ohms using the same continuous discharge test (Test A) and the same two intermittent discharge tests (Tests B and C) described in the comparative example (Example 1). The duration in the service obtained in each of the three tests with the additive of CaTi03 is compared with that obtained in the corresponding test of the comparative example (Example 1). The duration in service increased 6.8% for Test A, increased 3.5% for Test B and increased 5.0% for Test C. These test results are summarized in Table 1. The maximum power of fresh batteries, determined as in Example 1, exhibits a 9.6% increase over the maximum power of the standard stacks of Example 1.

Example 6 Zinc alkaline batteries of experimental zinc / Mn02 are prepared, identical to those referred to in Example 1, except that in the manufacture the experimental cell is added an amount (grams) of ZnMn204 mixed with the cathode so that the cathode material total comprise 1.5 percent by weight of ZnMn204. The amount of Mn02 at the cathode is reduced by an equal amount (grams) so that the weight of the total cathode in the experimental cell is the same as in the standard cell of Example 1. Accordingly, the cathode composition of the cell experimental in the present example is: Electrolytic manganese dioxide (82.5% by weight), ZnMn20 (1.5% by weight), graphite (9.2% by weight), polyethylene powder binder (0.3% by weight) and a "solution of Aqueous KOH "7 Normal (6.5% by weight). The batteries are discharged at a constant load of 3.9 ohms using the same continuous discharge test (Test A) and the same two intermittent discharge tests (Tests B and C) described in the comparative example (Example 1). The duration in the service obtained in each of the three tests with the additive of ZnMn204 is compared with that obtained in the corresponding test of the comparative example (Example 1). In-service duration increased 2.2% for Test A, increased 0.8% for Test B and increased 2. 3% for Test C. These test results are summarized in Table 1. The maximum power of fresh batteries, determined as in Example 1, exhibits a 10.6% increase over the maximum power of the standard batteries of Example 1 .

Example 7 Zinc alkaline batteries of experimental zinc / Mn02 were prepared, identical to those referred to in Example 1, except that in the manufacture of the experimental battery an amount (grams) of Bi? 2TiO20 mixed with the cathode was added so that the Total cathode material comprises 1.5 weight percent of Bi12Ti02o. The amount of Mn02 at the cathode is reduced by an equal amount (grams) so that the weight of the total cathode in the experimental cell is the same as in the standard cell of Example 1. Accordingly, the cathode composition of the cell experimental is: Electrolytic manganese dioxide (82.5% by weight), Bi12Ti02o (1.5% by weight), graphite (9.2% by weight), polyethylene powder binder (0.3% by weight) and an "aqueous KOH solution" 7 Normal (6.5% by weight). The batteries are discharged at a constant load of 3.9 ohms using the same continuous discharge test (Test A) and the same two intermittent discharge tests (Tests B and C) described in the comparative example (Example 1) . The duration in the service obtained in each of the three tests with the additive of Bi? 2TiO20 is compared with that obtained in the corresponding test of the comparative example (Example 1). The duration in service increased 8.1% for the Test A, 3.9% was increased for Test B and 3.6% was increased for Test C. These test results are summarized in Table 1. The maximum power of the fresh batteries, determined as in Example 1, exhibits an increase of 10.3% on the maximum power of the standard batteries of Example 1. In summary, each of the additives described in the examples led to an improvement in the service life of the alkaline battery as shown in Table 1.

TABLE 1 % Additive% Increase in Duration of% Increment in Cathode Service at 3.9 Ohms to Power Test A1 Test B2 Test C3 Maximum CaW04 1.5 -3.2 +5.1 +4.6 -2.6 MgTi03 1.5 + 5.1 +0.9 +3.7 -0.1 BaTi03 1.5 + 3.5 +2.3 +4.8 +2.4 CaTi03 1.5 + 6.8 + 3.5 + 5.0 + 9.6 ZnMn204 1.5 +2.2 +0.8 +2.3 + 10.6 Bi? 2Ti02o 1.5 + 8.1 + 3.9 +3.6 + 10.3 Notes: Continuous discharge of fresh batteries at 0.75 volts. Intermittent Discharge (Industrial Flashing Light Test) 4 minutes per hour for 8 hours followed by 16 hours of rest and the cycle is repeated at a cut-off voltage of 0.75 volts. The batteries are stored 2 weeks at 12.7777 ° C (55 ° F) followed by intermittent discharge for 1 hour per day at the cut-off voltage of 0.8 volts.

Additionally, the maximum power is improved in the case of the addition of the cathode additives of BaTi03, CaTi03 ZnMn204 or Bi? 2Ti026. Essentially there is no change in maximum power when the MgTi03 additive is used. The reduction of 2.6% in the maximum power observed with the use of CaW04 cathode additive is greater than the mismatch by the significant increase in the service life of the battery which can be obtained when such a compound is used. The increase in the service life of the primary alkaline (non-rechargeable) zinc / Mn02 battery can also be obtained by mixing the additives described above in any combination and adding the combined mixture to the Mn02 cathode during the preparation of the cathode mixture. The above additive or any combination thereof is advantageously added to the Mn02 cathode of the primary alkaline batteries so that the total weight of the additive comprises between about 0.1 and 5 weight percent of the total cathode, preferably between about 0.3 and 3 per cent. cent in weight. Although the present invention was described with respect to the specific embodiments, it should be recognized that variations are possible without departing from the concept of the invention. Accordingly, the invention is not intended to be limited to the specific embodiments, but rather so that its scope is reflected by the claims and equivalents thereof.

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

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

Claims (14)

1. An electrochemical cell, characterized in that it comprises an anode, an alkaline, aqueous electrolyte solution, a separator and a cathode comprising manganese dioxide, the cathode further comprises an additive selected from the group of compounds comprising CaW0, MgTi03, BaTi03, CaTi03 , ZnMn20, or Bii2TiO20, or any combination thereof.

2. An electrochemical cell characterized in that it comprises an anode, an alkaline, aqueous electrolyte solution, a separator and a cathode comprising manganese dioxide, the cathode further comprises an additive selected from the group of compounds comprising MgTi03 / BaTi.03 or CaTi03, or any combination of them.

3. An electrochemical cell characterized in that it comprises an anode, an alkaline, aqueous electrolyte solution, a separator and a cathode comprising manganese dioxide, the cathode further comprises CaTi034.

An electrochemical cell characterized in that it comprises an anode, an alkaline, aqueous electrolyte solution, a separator and a cathode comprising manganese dioxide, the cathode further comprises ZnMn20.

5. An electrochemical cell, characterized in that it comprises an anode, an alkaline, aqueous electrolyte solution, a separator and a cathode comprising manganese dioxide, the cathode further comprises Bi? 2TiO20.

6. The electrochemical cell according to claim 1, characterized in that the cell is a primary (non-rechargeable) alkaline cell having an anode comprising zinc.

7. The electrochemical cell according to claim 2, characterized in that the cell is a primary (non-rechargeable) alkaline cell having an anode comprising zinc.

8. The electrochemical cell according to claim 3, characterized in that the cell is a primary (non-rechargeable) alkaline cell having an anode comprising zinc.

9. The electrochemical cell according to claim 4, characterized in that the cell is a primary (non-rechargeable) alkaline cell having an anode comprising zinc.

10. The electrochemical cell according to claim 5, characterized in that the cell is a primary (non-rechargeable) alkaline cell having an anode comprising zinc.

11. The electrochemical cell according to claim 1, characterized in that the additive comprises between about 0.1 and 5 weight percent of the cathode.

12. The electrochemical cell according to claim 1, characterized in that the aqueous electrolyte solution comprises potassium hydroxide.

13. The electrochemical cell according to claim 1, characterized in that the total mercury content in the cell is less than 50 parts per million of the weight of the total cell.

14. The battery according to claim 1, characterized in that the additive has the effect of increasing the service life of the battery when the battery is discharged to approximately 0.8 volts with a load of 3.9 ohms.