JP2009043547A - Electrolytic manganese dioxide for battery, positive electrode mix, and alkaline battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve discharge performance of an alkaline battery while securing its leakage resistance performance. <P>SOLUTION: By setting pH of this electrolytic manganese dioxide included in a positive electrode mix 21 as a positive electrode active material of this alkaline battery in a range of 2-5.5, further more protons are made present in the vicinity of manganese dioxide to enhance an active material utilization factor. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to electrolytic manganese dioxide for batteries, a positive electrode mixture, and an alkaline battery, and is effective when applied to, for example, an alkaline primary battery.

  As manganese dioxide used as a positive electrode active material for an alkaline primary battery or the like, electrolytically purified manganese dioxide is used. This electrolytic manganese dioxide (EMD) for batteries is obtained by neutralizing and washing manganese dioxide electrolytically deposited in a sulfuric acid acid bath, and the pH is adjusted to be almost neutral at about 6-8. (For example, refer nonpatent literature 1).

  The electrolytic manganese dioxide is pulverized into a predetermined particle size, and a conductive agent such as graphite is added to form the electrolytic manganese dioxide into a predetermined shape, thereby producing a positive electrode mixture for a battery. In this case, the positive electrode mixture may contain nickel oxyhydroxide as an active material in addition to manganese dioxide.

The LR type cylindrical alkaline battery is manufactured using a positive electrode mixture formed in a hollow cylindrical shape. The positive electrode mixture is charged in a bottomed cylindrical metal positive electrode can in a press-fitted state, and a separator, an alkaline electrolyte, and a negative electrode material are sequentially loaded therein to form a coaxial power generation element. After loading the power generation element, an alkaline battery having a sealed structure is manufactured through the sealing of the positive electrode can (see, for example, Patent Document 1).
JP 07-282802 Battery Handbook (Third Edition / Maruzen) Manganese dioxide, 61 pages-Alkaline batteries, 74 pages, etc.

  In recent years, electronic devices such as digital cameras that require a large current have become widespread, and there has been a demand for improved discharge performance, in particular, increased electric capacity (longer battery life) for alkaline batteries serving as power sources for the devices. . In particular, in an alkaline primary battery that is basically used up only once, improving discharge performance is an important issue from the viewpoint of environmental load. There are roughly two methods for improving the discharge performance of a battery.

  One of them is to increase the amount of active material (manganese dioxide for the positive electrode or zinc for the negative electrode) filled in the battery. However, in this method, the air chamber in the battery is reduced due to the increase in the amount of the active material, which causes a problem that the leakage resistance performance is lowered.

  The other is to improve the utilization rate of the positive and negative electrode active materials during discharge. In particular, if the utilization rate of manganese dioxide, which is a positive electrode active material, can be improved, the discharge performance can be improved without causing a decrease in leakage resistance due to an increase in filling amount.

  As a method of increasing the utilization rate of manganese dioxide, for example, it is effective to increase the amount of impregnation of the electrolyte by increasing the internal porosity of the positive electrode mixture, but this substantially reduces the filling amount of the active material. Therefore, the discharge performance is not improved.

  The present invention has been made in view of the above problems, and an object thereof is to use electrolytic manganese dioxide for batteries particularly suitable for improving discharge performance while ensuring the leakage resistance performance of alkaline batteries, and to use this. It is to provide a positive electrode mixture and an alkaline battery.

  Other objects and configurations of the present invention will be clarified in the description of the present specification and the accompanying drawings.

The solution provided by the present invention is as follows.
(1) An electrolytic manganese dioxide for alkaline batteries, characterized in that the pH is in the range of 2 to 5.5.
(2) The electrolytic manganese dioxide for alkaline batteries characterized in that, in the above means (1), the specific surface area is larger than that in a state where the pH is 7.
(3) The electrolytic manganese dioxide for alkaline batteries according to the above means (1) or (2), wherein the average particle size is in the range of 20 to 60 μm.
(4) In any one of the above means (1) to (3), the electrode potential is in the range of 240 to 280 mV (vs. HgO / Hg electrode, in 10 mol KOH aqueous solution). manganese.
(5) A positive electrode mixture for alkaline batteries, comprising the electrolytic manganese dioxide of the above means (1) to (4) as an active material.
(6) A positive electrode mixture for an alkaline battery, characterized in that in the above means (5), nickel oxyhydroxide is contained as an active material.
(7) In the above means (5) or (6), a positive electrode mixture for alkaline batteries, containing graphite as a conductive agent in a range of 3 to 10% by weight.
(8) An alkaline battery using the positive electrode mixture of the above means (5) to (7).

It is possible to improve the discharge performance while ensuring the leakage resistance performance of the alkaline battery.
The operations / effects other than the above will be clarified in the description of the present specification and the accompanying drawings.

  FIG. 1 is a cross-sectional view of an essential part showing an embodiment of an alkaline battery to which the technology of the present invention is applied. The battery shown in the figure is an LR6 type alkaline primary battery, and a power generation element composed of a cylindrical positive electrode mixture 21, a cylindrical separator 22, and a gel negative electrode mixture 23 is loaded in a bottomed cylindrical positive electrode can 11. In addition, the positive electrode can 11 is closed and hermetically sealed by the negative electrode terminal plate 31 and the gasket 35.

  The positive electrode mixture 21 is obtained by adding a conductive agent to a positive electrode active material and molding it into a hollow cylinder. Manganese dioxide is used as the positive electrode active material, and graphite is used as the conductive agent. Further, gelled zinc is used for the negative electrode mixture 23.

  The positive electrode mixture 21 is inserted and loaded into the positive electrode can 11 in a press-fitted state. The positive electrode can 11 is produced by deep drawing press processing of a nickel plated steel plate. The positive electrode can 11 also serves as a battery case, and also serves as a positive electrode current collector when the positive electrode mixture 21 is in pressure contact with the inner surface thereof. A convex positive terminal portion 12 is formed on the outer bottom portion by pressing.

  The negative electrode terminal plate 31 has a rod-shaped negative electrode current collector 25 welded to its inner side surface (inside the battery), and its outer central surface forms a negative electrode terminal portion. The side barrel portion excluding the terminal portion 12 of the positive electrode can 11 is covered with an exterior material 15.

  Here, the manganese dioxide used for the positive electrode active material is electrolytically purified electrolytic manganese dioxide (EMD) for batteries, and its pH is adjusted in the range of 2 to 5.5.

  Thus, the EMD adjusted to the acidic side has a specific surface area (BET specific surface area: m2 / g) larger than that adjusted to the neutral state of pH 7. The EMD is adjusted so that the average particle size is in the range of 20 to 60 μm and the electrode potential is in the range of 240 to 280 mV (vs. HgO / Hg electrode, in 10 mol KOH aqueous solution).

  As the positive electrode active material, the EMD may be used alone, but may contain nickel oxyhydroxide. As a conductive agent, it is desirable to contain graphite in the range of 3 to 10% by weight.

The electromotive force of the alkaline battery described above is obtained by a discharge reaction due to a reduction reaction of manganese dioxide at the positive electrode and an oxidation reaction of zinc at the negative electrode. Generally, the discharge reaction at the positive electrode is represented by the following reaction formula (1). It is expressed in
MnO ₂ + H ₂ O + e ⁻ → MnOOH + OH ⁻ (1)
This reaction formula (1) is stoichiometrically equivalent to the following reaction formula (2).
MnO ₂ + H ⁺ + e ⁻ → MnOOH (2)
According to the reaction formulas (1) and (2), the positive electrode discharge reaction involves manganese dioxide (MnO ₂ ) and water (H ₂ O) or protons (H ⁺ ) as active materials. Yes.

  From this, it is considered that if there are more protons in the vicinity of manganese dioxide, the discharge reaction proceeds smoothly, and as a result, the discharge performance of the battery can be improved. The present inventors pay attention to this, and by using electrolytic manganese dioxide (EMD) whose pH is adjusted to 2 to 5.5 as a positive electrode active material, the utilization rate of the active material is increased and the discharge performance of the alkaline battery is improved. Succeeded to improve.

  By improving the utilization factor of the active material, the discharge performance can be improved without causing a decrease in leakage resistance due to an increase in the amount of the active material. Furthermore, the improvement effect of the discharge performance can be obtained far exceeding the improvement in the utilization factor of the active material.

  For example, when an alkaline battery is used for heavy load equipment such as a digital camera, the utilization factor of the active material is generally about 20 to 30%. Therefore, even if the utilization rate of the active material is increased by 2 to 3%, the battery duration (life) when an alkaline battery is used for a heavy load device can be improved by about 10%. This is very useful from the viewpoint of reducing environmental load, particularly in a primary battery that is basically used up only once.

  Manganese dioxide (EMD) for batteries is electrodeposited in a sulfuric acid acid bath, and the pH of the product (acidity = proton content) is adjusted by subsequent neutralization and washing treatment. At this time, the pH of the EMD can be adjusted to a moderately acidic (containing a lot of protons) region by appropriately controlling the neutralization / washing conditions. Thus, by using the EMD whose pH is adjusted to 2 to 5.5, it is possible to improve the discharge performance while ensuring the leakage resistance.

Examples of the present invention will be described below.
(1) A plurality of types of electrolytic manganese dioxide (EMD) having different pH, average particle diameter, and electrode potential were prepared. The pH (water method) was adjusted in the neutralization / washing step, and the average particle size (microtrack method) was adjusted in the pulverization / classification step. The electrode potential (vs. HgO / Hg electrode, in 10 mol KOH aqueous solution) was arbitrarily prepared in the electrolysis process. Other manufacturing conditions were the same for each EMD.

  (2) A positive electrode mixture for AA alkaline batteries (LR6) was prepared for each type of EMD. The positive electrode mixture was prepared by mixing EMD, graphite, a binder (polyacrylic acid) and an electrolytic solution (40 wt% KOH aqueous solution), and further through steps such as kneading, rolling, granulation, and classification. The graphite content was arbitrary, and the other production conditions were the same. Moreover, although the kind using the mixture of EMD and nickel oxyhydroxide as an active material was also produced, the weight ratio of both was also arbitrary in this case.

  (3) AA alkaline batteries (LR6) were prepared for each type of positive electrode mixture. The produced alkaline battery had the same conditions other than the types of EMD and positive electrode mixture (for example, positive electrode mixture weight and molding density, separator, electrolyte amount, negative electrode gel amount, etc.).

(Test 1)
According to the above (1) to (3), five types of alkaline batteries (Comparative Examples 1 and 2 and Examples 1 to 3) having different pH of EMD (average particle size 40 μm, electrode potential 260 mV) were prepared, and the discharge performance for each. A test was conducted to check the leakage resistance performance.

  The discharge performance test was performed under the discharge conditions of (1500 mW · 2 seconds / 650 mW · 28 seconds) × 10 cycles / 1 hour (end voltage 1.05 V, test temperature 20 ° C.). Ten average values were determined for each of Examples 1 to 3. And it evaluated by the relative value when the discharge performance of the comparative example 1 (conventional example) is set to 100.

  Regarding the leakage resistance performance, the number of days until the first leakage occurs at 90 ° C. storage (n = 50), the yield rate of the molding mixture for the positive electrode mixture cracking, and 100 for Comparative Example 1 (conventional example), respectively. Evaluation was made using relative values.

Table 1 shows the test results for each sample type (Comparative Examples 1 and 2 and Examples 1 to 3) together with the EMD specific surface area (BET method).

  As shown in Table 1, the specific surface area tended to increase when the pH was adjusted low. The discharge performance was improved by 10% or more in the region of pH 5.5 or lower, but the leakage resistance performance was lowered at a pH lower than 2. This is because the surface area of the EMD is large in the region where the pH is low (high acidity), and the protons necessary for the discharge reaction are sufficiently supplied. However, when the pH is too low, the positive electrode can (nickel-plated steel plate), etc. This is considered to be due to the progress of corrosion on the member. From the above results, the pH of EMD is particularly preferably in the range of 2 to 5.5.

(Test 2)
Five types of alkaline batteries (Comparative Examples 3, 4 and Examples 4, 2, and 5) having different average particle diameters of EMD (pH 4, electrode potential 260 mV) were produced by the above (1) to (3), and each was discharged. A test was conducted to examine the performance and occurrence of cracking of the positive electrode mixture.

  The discharge performance test was performed under the same conditions as in Test 1 above, and evaluation was performed using relative values when the Comparative Example 1 was set to 100. The test for cracking of the positive electrode mixture was for comparing the moldability of the positive electrode mixture, and the evaluation was based on the relative value when the comparative example 1 was set to 100.

The test results are shown in Table 2.

  As shown in Table 2, the discharge performance was improved by 10% or more in the region where the average particle size (Microtrack method) was 60 μm or less. This is because, in the region where the average particle size is small, the surface area of the EMD is large and the discharge reaction proceeds smoothly. However, if the average particle size is too small, the filling property (compressibility) of the positive electrode mixture is lowered. Conceivable. When the filling property (compressibility) of the positive electrode mixture decreases, as in Comparative Example 3, the positive electrode mixture cracks easily occur. From the above results, the average particle diameter of EMD is particularly preferably in the range of 20 to 60 μm.

(Test 3)
Five types of alkaline batteries (Comparative Examples 5, 6 and Examples 6, 2, 7) with different electrode potentials of EMD (pH 4, average particle size 40 μm) were produced by the above (1) to (3), and each was discharged Tests were conducted to investigate performance and storage performance.

  The discharge performance test was performed under the same conditions as in Test 1 above, and evaluation was performed using relative values when the Comparative Example 1 was set to 100. As for storage performance, the degree of decrease in discharge performance after storage at 60 ° C. for 20 days was evaluated as a relative value when the above Comparative Example 1 was taken as 100.

The test results are shown in Table 3.

  As shown in Table 3, the discharge performance was improved by 10% or more in the region where the electrode potential was 240 mV or more, but when it exceeded 280 mV, the storage performance was lowered. This is presumably because the voltage at the time of discharge increases in a region where the potential is high, but if the potential is too high, self-discharge during storage increases. From the above results, the EMD electrode potential is particularly preferably in the range of 240 to 280 mV.

(Test 4)
Five types of alkaline batteries with different graphite contents (Comparative Examples 7, 8 and Examples 8, 2, and 9) were prepared using EMD having a pH of 4, an average particle diameter of 40 μm, and an electrode potential of 260 mV. An examination was conducted.
The discharge performance test was performed under the same conditions as in Test 1 above, and evaluation was performed using relative values when the Comparative Example 1 was set to 100.

The test results are shown in Table 4.

  As shown in Table 4, the discharge performance improved by 10% or more in the range of 3 to 10% by weight of the graphite content. This is probably because the conductivity of the positive electrode mixture is insufficient when the graphite content is too low, and conversely, when the graphite content is too high, the absolute amount of EMD as the active material is insufficient. From the above results, the graphite content of the positive electrode mixture is particularly preferably in the range of 3 to 10% by weight.

(Test 5)
In the above examples, only EMD was used as the positive electrode active material, but the same test as in Tests 1 to 4 was performed when EMD and nickel oxyhydroxide were mixed at an arbitrary ratio (for example, 1: 1 by weight). As a result, almost the same test results were obtained as relative values. From this, it was found that the present invention is effective even when the positive electrode active material contains EMD and nickel oxyhydroxide.

  As mentioned above, although this invention was demonstrated based on the typical Example, this invention can have various aspects other than having mentioned above. For example, the present invention is applicable not only to alkaline primary batteries but also to alkaline secondary batteries.

  It is possible to improve the discharge performance while ensuring the leakage resistance performance of the alkaline battery.

It is principal part sectional drawing which shows one Embodiment of the alkaline battery to which the technique of this invention was applied.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Battery can 12 Positive electrode terminal part 15 Exterior material 21 Positive electrode mixture 22 Separator 23 Negative electrode mixture 25 Negative electrode current collector 31 Negative electrode terminal plate 35 Gasket

Claims (8)

  An electrolytic manganese dioxide for alkaline batteries, characterized in that the pH is in the range of 2 to 5.5.   2. The electrolytic manganese dioxide for alkaline batteries according to claim 1, wherein the specific surface area is larger than that in a pH of 7.   The electrolytic manganese dioxide for alkaline batteries according to claim 1 or 2, wherein the average particle size is in the range of 20 to 60 µm.   The electrolytic manganese dioxide for alkaline batteries according to any one of claims 1 to 3, wherein the electrode potential is in the range of 240 to 280 mV (vs. HgO / Hg electrode, in 10 mol KOH aqueous solution).   A positive electrode mixture for an alkaline battery, comprising the electrolytic manganese dioxide of claims 1 to 4 as an active material.   6. The positive electrode mixture for alkaline batteries according to claim 5, which contains nickel oxyhydroxide as an active material.   7. The positive electrode mixture for alkaline batteries according to claim 5, wherein graphite is contained in a range of 3 to 10% by weight as a conductive agent.   An alkaline battery using the positive electrode mixture according to claim 5.

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