Patent Application
20080085448
Hereinafter, a preferred embodiment of an alkaline dry battery of the invention will be explained with reference to
The alkaline dry battery shown in
Here, a feature of the alkaline dry battery of this embodiment is that manganese dioxide of the hollow cylindrical positive electrode mixture pellet containing manganese dioxide and graphite contains at least manganese dioxide particles having a particle diameter of 10 μm or less of 25 to 35% and manganese dioxide particles having a particle diameter of 60 to 100 μm of 15 to 25% in a particle size distribution based on volume.
The positive electrode mixture pellet 2 is made of a mixture containing a powder of manganese dioxide which is an active material, a powder of graphite which is a conductive agent and an alkaline electrolyte. A binder such as polyethylene, sodium polyacrylate and compound of stearic acid may also be added to the mixture according to the purpose as appropriate.
The above-described manganese dioxide preferably contains at least manganese dioxide particles having a large particle diameter (first manganese dioxide particles) and manganese dioxide particles having a small particle diameter (second manganese dioxide particles) in a particle size distribution based on volume.
As a combination of the first manganese dioxide particles and second manganese dioxide particles, it is preferable to use manganese dioxide containing at least manganese dioxide particles having a particle diameter of 10 μm or less of 25 to 35% and manganese dioxide particles having a particle diameter of 60 to 100 μm of 15 to 25%. Such a composition can increase a density of the positive electrode mixture pellet 2 obtained and secure a sufficient discharge capacity.
As another combination of the first manganese dioxide particles and second manganese dioxide particles, it is further preferable to use manganese dioxide containing at least manganese dioxide particles having a particle diameter of 5 μm or less of 15 to 20% and manganese dioxide particles having a particle diameter of 60 to 80 μm of 10 to 15%. Furthermore, the content of manganese dioxide particles having a particle diameter of 100 μm or more in the above described manganese dioxide is preferably 5% or less. This is based on a reason that the density of the positive electrode mixture pellet 2 can be improved more reliably and a sufficient discharge capacity can be secured more reliably.
Furthermore, the average particle diameter based on volume of the above-described manganese dioxide including the first manganese dioxide particles and second manganese dioxide particles is preferably 25 to 45 μm. Within such a range, the density of the positive electrode mixture pellet 2 can be improved more reliably and a sufficient discharge capacity can be secured more reliably.
As the above-described manganese dioxide, for example, electrolytic manganese dioxide obtained through electro-deposition may be used. More specifically, for example, “HHN” manufactured by Tosoh Corporation or the like can be used.
The graphite contained in the positive electrode mixture pellet 2 of this embodiment functions as a conductive material and graphite particles having an average particle diameter based on volume within a range of 10 to 20 μm are preferably used. This can suppress the internal resistance of the alkaline dry battery more reliably. Graphite and expanded graphite can be used as such graphite and more specifically, “SP-20” manufactured by Nippon Graphite Industry Co., Ltd. or the like can be used.
The weight ratio of manganese dioxide and graphite in the positive electrode mixture pellet 2 is preferably 90:10 to 95:5. This can secure a sufficient discharge capacity of the alkaline dry battery obtained. Furthermore, it is preferable that four or more positive electrode mixture pellets 2 construct a positive electrode. This further improves the accuracy of the height of the positive electrode when the battery is constructed.
Next, the gel negative electrode 3 of this embodiment includes, for example, an alkaline electrolyte, a gelling agent and a negative electrode active material. The negative electrode active material preferably contains zinc or a zinc alloy. An alloy containing, for example, aluminum, bismuth, indium or the like can be used as the zinc alloy. For zinc or the zinc alloy, powder including a various average particle diameters within a range not impairing the effect of the invention can be used. The negative electrode active material may contain a small amount of unavoidable impurities. As the gelling agent, conventional ones can be used. An example of this is sodium polyacrylate.
Furthermore, a surfactant may also be added as an inorganic inhibiter such as indium salt or an organic inhibiter depending on the purpose as appropriate. For example, the gel negative electrode 3 may contain at least one compound (anti-corrosion agent) selected from the group consisting of tetramethylammonium compounds, tetraethylammonium compounds and tetrapropylammonium compounds.
The above-described compound is preferably hydroxide, oxide or bromide. Especially, adding the above-described compound to the battery as hydroxide can obtain a better discharge characteristics. This causes the negative electrode to contain a highly symmetrical cationic surfactant and even a small amount of addition makes it possible to form a protection film layer on the surfaces of the zinc or alloy particles. The protection film layer is formed of ions constituting the surfactant that are densely arranged and adsorbed on the surface of the zinc or alloy particles. Furthermore, since the size (molecular weight) of the ions constituting the above-described surfactant is appropriately small, in the case of an instantaneously high current discharge, dispersion and diffusion of the ions from the surfaces of the zinc or alloy particles into the electrolyte is rapid. Thus, it is unlikely that a drop of closed circuit voltage (CCV) of the battery is caused. For this reason, it is possible to obtain good discharge characteristics (especially high current discharge characteristics) while maintaining the sufficient anti-corrosion effect of the negative electrode in the alkaline dry battery.
For example, unwoven fabric composed mainly of mixed polyvinyl alcohol fiber and rayon fiber can be used for the above-described separator 4.
Furthermore, conventional alkaline electrolytes can be used for the alkaline electrolyte. For example, an aqueous solution containing potassium hydroxide may be used. In the case of an aqueous solution containing potassium hydroxide, 25 to 40 weight percent of potassium hydroxide is preferably contained in the aqueous solution. Furthermore, a small amount (e.g., approximately 2 weight percent) of zinc oxide may be contained in the electrolyte.
For other components, conventional ones can be used within a range not impairing the effect of the invention.
The positive electrode mixture pellet 2 can be manufactured using a positive electrode mixture containing manganese dioxide which is a positive electrode active material, graphite which is a conductive agent, an alkaline electrolyte and additives as required using a rotary compression molding machine. Manganese dioxide which is a positive electrode active material, graphite which is a conductive agent, alkaline electrolyte and additives as required are mixed by a mixer, formed into a predetermined granule size and a granular matter is obtained. The granular matter is compressed under pressure to produce a positive electrode mixture pellet to be used as the positive electrode.
The particle size distribution of the above-described manganese dioxide can be controlled using a pulverizer such as a ball mill and a centrifugal roll and setting the number of rotations and the pulverizing time as appropriate. To put it in a simple way, it is possible to classify a powder of manganese dioxide using sieves according to the desired particle diameter. Then, the first manganese dioxide particles having a small particle diameter and the second manganese dioxide particles having a large particle diameter are mixed as appropriate so as to meet the above condition.
Furthermore, the particle size distribution based on volume of the powder of manganese dioxide can be measured using, for example, a laser diffraction type HELOS & RODOS manufactured by SYMPATEC at a diffusion pressure of 3.0 bar and using a range of R4.
The gel negative electrode 3 is obtained by mixing a negative electrode active material powder, an alkaline electrolyte, a gelling agent and anti-corrosion agent as required and allowing the mixture to be gelled as in the case of the conventional method. Zinc alloy powder can be obtained, for example, by causing aluminum, bismuth, indium or the like to be dissolved into zinc in a molten state and granulating the molten alloy using an atomizing method.
Furthermore, an alkaline dry battery will be manufactured as follows, for example. That is, four hollow cylindrical positive electrode mixture pellets 2 are inserted into a battery case 1 first and the positive electrode mixture pellets 2 are re-pressurized in the battery case 1. This causes the positive electrode mixture pellets 2 to come into close contact with the inner surface of the battery case 1. Next, a bottomed cylindrical separator 4 is disposed on the hollow section of the positive electrode mixture pellets 2. After that, the alkaline electrolyte is injected into the hollow section so as to impregnate therewith the separator 4 and the positive electrode mixture pellets 2. After the injection of the alkaline electrolyte, the interior of the separator 4 is filled with the gel negative electrode 3.
Next, the negative electrode current collector 6 is inserted into the gel negative electrode 3. The negative electrode current collector 6 is integrated with a resin sealing plate 5, a bottom plate 7 which also serves as a negative electrode terminal and an insulating washer (not shown). The opening of the battery case 1 is sealed by swaging the opening end of the battery case 1 onto the perimeter of the bottom plate 7 via the end of the resin sealing body 5. Finally, the outer surface of the battery case 1 is covered with an outer label 8 and the alkaline dry battery is obtained in this way.
The cylindrical type alkaline dry battery has been described so far, but the effect of the invention can also be obtained with batteries having different structures such as button type, rectangular type or the like.
Examples of the invention will be explained in detail below, but the invention is not limited to the examples. In the following examples, an AA type alkaline dry battery having the structure shown in
A powder of manganese dioxide which contains manganese dioxide particles having a particle diameter of 10 μm or less and manganese dioxide particles having a particle diameter of 60 to 100 μm in a particle size distribution based on volume at a weight ratio of 25.1:21.4 was prepared. The powder of manganese dioxide and a powder of graphite including graphite particles having an average particle diameter based on volume of 15 μm were dry-mixed at a weight ratio of 93:7. The mixture obtained and an alkaline electrolyte (aqueous solution) containing 36 weight percent potassium hydroxide and 2 weight percent zinc oxide were fully wet-mixed at a weight ratio of 100:3, and the mixture obtained was then compress-molded into flakes using a roll press machine and a flake-shaped positive electrode mixture was obtained.
Next, the flake-shaped positive electrode mixture was pulverized and the pulverized matter obtained was adjusted in particle size of 10 to 100 meshes using a sieve, thus a granulated mixture was obtained. Using a powder compression molding machine furnished with a die 23 having a hole diameter of φ13.3 mm (equivalent to the outer diameter of the positive electrode mixture pellet 2) and a center pin 24 having an outer diameter φ9.2 mm (equivalent to the inner diameter of the positive electrode mixture pellet 2), the above granulated mixture was press-molded into a hollow cylindrical shape in such a way that the weight of the positive electrode mixture pellet 2 obtained became approximately 2.55 g and the height became approximately 11.0 mm, thus the positive electrode mixture pellet 2 was obtained.
The AA type alkaline dry battery (LR6) having the structure shown in
The gel negative electrode 3 was obtained by mixing sodium polyacrylate as the gelling agent, the above described alkaline electrolyte and zinc alloy powder at a weight ratio of 2:33:65. The zinc alloy powder used contained indium of 0.025 weight percent, bismuth of 0.015 weight percent and aluminum of 0.004 weight percent, had an average particle diameter based on volume of 185 μm, and included particles of 75 μm or less which accounted for 30%. Furthermore, unwoven fabric composed of mixed polyvinyl alcohol fiber and rayon fiber as main components was used as the separator 4.
Alkaline dry batteries were manufactured as in the case of Example 1 except using powders of manganese dioxide containing manganese dioxide particles having a particle diameter of 10 μm or less and manganese dioxide particles having a particle diameter of 60 to 100 μm in a particle size distribution based on volume at the weight ratios shown in Table 1.
The positive electrode mixture pellet and the alkaline dry battery manufactured in Examples 1 to 6 and Comparative Examples 1 to 4 as described above were subjected to the following evaluations and results are shown in Table 1.
(i) Evaluation on Repulsion of Positive Electrode Mixture Pellet (Evaluation on Correlation Between Weight and Height)
More specifically, twenty positive electrode mixture pellets having substantially uniform weights within a weight range of 2.4 to 2.7 g were selected from among a plurality of positive electrode mixture pellets manufactured in the respective examples and comparative examples. Weight W and height H of the selected positive electrode mixture pellets were measured. Based on the measurement results, an expression of a regression line of weight W and height H was obtained using a minimum square method as shown in
(ii) Measurement of Height Variation Coefficient of Positive Electrode Mixture Pellet
100 positive electrode mixture pellets according to the respective examples and comparative examples were manufactured and height H of each positive electrode mixture pellet was measured. Based on the measurement results, variation coefficient Cv was calculated according to Expression (1) below. The variation decreases as the variation coefficient Cv decreases and the variation coefficient Cv is preferably less than 2 at a stage of the positive electrode mixture pellet before the assembly of the alkaline dry battery.
Cv=(standard deviation(σn-1)/mean value(X))×100 (1)
(iii) Measurement of Internal Resistance of Alkaline Dry Battery and Variation Coefficient Thereof
Voltages between terminals of fifty alkaline dry batteries obtained above were measured when a 1-kHz AC current was applied to pass through the battery using “3560 ACmΩ HITESTER” manufactured by HIOKI and the internal resistance of the battery was examined. Based on the measurement results, the variation coefficient Cv was calculated according to Expression (1). Among batteries in a range of ±3σn-1, in order to suppress the variation in the internal resistance value of the battery to substantially within ±10%, the variation coefficient Cv must be less than 3.3 at the stage of the completed battery.
In the case of the positive electrode mixture pellet of Examples 1 to 6 containing manganese dioxide particles having a large particle diameter of 60 to 100 μm of 15 to 25% and manganese dioxide particles having a small particle diameter of 10 μm or less of 25 to 35%, the gradient of the regression line of weight W and height H was less than 2.5 and the height variation coefficient Cv was also less than 2. Furthermore, the variation coefficient Cv of the internal resistance of the alkaline dry battery of Examples 1 to 6 was less than 3.3.
Here,
As shown in
On the other hand, in the case of the positive electrode mixture pellet of Comparative Examples 1 to 4 in which the manganese dioxide particles 12 having a large particle diameter of 60 to 100 μm do not fall within a range of 15 to 25% and manganese dioxide particles 13 having a small particle diameter of 10 μm or less do not fall within a range of 25 to 35%, the frequency with which relatively large manganese dioxide particles 13 exist among the manganese dioxide particles 12 increases as shown in
Powders of manganese dioxide containing manganese dioxide particles having a particle diameter of 10 μm or less of approximately 30%, manganese dioxide particles having a particle diameter of 60 to 100 μm of approximately 20% in a particle size distribution based on volume where manganese dioxide particles having a particle diameter of 5 μm or less and manganese dioxide particles having a particle diameter of 60 to 80 μm were contained in various proportions as shown in Table 2 were prepared. Positive electrode mixture pellets and alkaline dry batteries were manufactured and evaluation tests were conducted in the same way as for Example 1 except using the above powders of manganese dioxide. The results of the evaluation tests are shown in Table 2.
In all positive electrode mixture pellets of Examples 7 to 10, the gradient of the regression line of weight W and height H was less than 2.5 and height variation coefficient Cv was also less than 2. Furthermore, the variation coefficient Cv of the internal resistance of those batteries was less than 3.3.
Especially, Examples 8 and 9 in which manganese dioxide particles having a particle diameter of 5 μm or less range from 15 to 20% and manganese dioxide particles having a particle diameter of 60 to 80 μm range from 10 to 15% showed lower internal resistance than Examples 7 and 10. This is believed to be attributable to the fact that the frequency with which small particles exist among large particles is especially high and that small particles form groups of aggregation in a well-balanced manner.
In these examples, the particle diameter of graphite which had an influence on the conductivity of the positive electrode mixture pellet was examined. Generally, when the particle diameter of graphite is reduced down to approximately 10 μm, the conductivity of the positive electrode mixture pellet improves, whereas the releasability deteriorates, which constitutes a drawback in practical use.
Therefore, a positive electrode mixture pellet and an alkaline dry battery were manufactured and evaluation tests were conducted in the same way as for Example 1 except using graphite having an average particle diameter based on volume of 10 μm in Examples 11 to 16 and using graphite having an average particle diameter based on volume of 20 μm in Examples 17 to 22 in combination with the manganese dioxide in each of Examples 1 to 6 where the average particle diameter based on volume of graphite was 15 μm. The results of the evaluation tests are shown in Table 3.
As is clear from the results of Examples 1 to 6 and Examples 11 to 22, when graphite having an average particle diameter based on volume of 10 to 20 μm and manganese dioxide containing at least manganese dioxide particles having a particle diameter of 10 μm or less of 25 to 35% and manganese dioxide particles having a particle diameter of 60 to 100 μm of 15 to 25% in a particle size distribution based on volume was used, the gradient of the regression line of weight W and height H was less than 2.5 and the height variation coefficient Cv was also less than 2 for the positive electrode mixture pellet. Furthermore, the variation coefficient Cv of the internal resistance of those batteries was less than 3.3. When graphite having a particle diameter of 10 μm or less was used, cracks were easily produced in the positive electrode mixture pellet when it was removed from the molding die. When graphite having a particle diameter of 20 μm or greater was used, the internal resistance increased, which was not desirable.
Moreover, the weight ratio of manganese dioxide and graphite which has an influence on the moldability of the positive electrode mixture pellet was examined. For an alkaline dry battery available on the market, the weight ratio of manganese dioxide and graphite generally ranges approximately from 90:10 to 93:7 to secure discharge capacity. A higher proportion of manganese dioxide deteriorates moldability, which will constitute a drawback in practical use.
Therefore, positive electrode mixture pellets and alkaline dry batteries were manufactured and evaluation tests were conducted in the same way as for Example 1 except in that the weight ratio of manganese dioxide and graphite was set to 90:10 in Examples 23 to 28, and the weight ratio of manganese dioxide and graphite was set to 95:5 in Examples 29 to 34 in combination with the manganese dioxide of each of Examples 1 to 6 where the weight ratio of manganese dioxide and graphite is 93:7. The results of the evaluation tests are shown in Table 4.
As is clear from the results of Examples 1 to 6 and Examples 23 to 34, when the weight ratio of manganese dioxide and graphite was 90:10 to 95:5 and a powder of manganese dioxide containing at least manganese dioxide particles having a particle diameter of 10 μm or less of 25 to 35% and manganese dioxide particles having a particle diameter of 60 to 100 μm of 15 to 25% in a particle size distribution based on volume was used, the gradient of the regression line of weight W and height H was less than 2.5 and height variation coefficient Cv was also less than 2 for the positive electrode mixture pellet. Furthermore, variation coefficient Cv of the internal resistance of those batteries was also less than 3.3. When the weight ratio of manganese dioxide to graphite was less than 90/10, the amount of manganese dioxide tends to be short and a sufficient discharge capacity cannot be obtained and when the weight ratio exceeds 95/5, the variation in the weight and height of the positive electrode mixture pellet increases, which is not desirable.
The above shows examples using four positive electrode mixture pellets for each alkaline dry battery, but constructing an alkaline dry battery using four or more positive electrode mixture pellets is preferable because variations in the weights and heights of the respective positive electrode mixture pellets are canceled out after the assembly. Using three or less positive electrode mixture pellets increases those variations, increases the height (size) of the pellet and increases the load during compression molding and tends to reduce durability of the molding die which is not desirable.
The alkaline dry battery of the invention has internal resistance with less variation and is suitable for use in all types of battery-driven devices such as a remote controller, light, toy, and electronic device.
Although the present invention has been described in terms of the presently preferred embodiments, it is to be understood that such disclosure is not to be interpreted as limiting. Various alterations and modifications will no doubt become apparent to those skilled in the art to which the present invention pertains, after having read the above disclosure. Accordingly, it is intended that the appended claims be interpreted as covering all alterations and modifications as fall within the true spirit and scope of the invention.
| Number | Date | Country | |
|---|---|---|---|
| 60850336 | Oct 2006 | US |
