JP5645473B2 - Alkaline battery - Google Patents

Description

  The present invention relates to an alkaline battery, and more particularly to a technology for improving the productivity of an alkaline battery.

  FIG. 1 shows a general structure of an alkaline dry battery that is an object of the present invention. The drawing is an LR14 type cylindrical alkaline battery 1 and is a longitudinal sectional view when the extending direction of the cylindrical shaft 10 is a longitudinal direction. The alkaline dry battery 1 includes a bottomed cylindrical metal battery can (positive electrode can) 2, a positive electrode mixture 3 formed in an annular shape, and a bottomed cylindrical separator 4 disposed inside the positive electrode mixture 3. The negative electrode gel 5 is filled with zinc alloy and filled inside the separator 4, the negative electrode current collector 6 inserted in the negative electrode gel 5, the negative electrode terminal plate 7, the sealing gasket 8, and the like. In this structure, the positive electrode mixture 3, the separator 4, and the negative electrode gel 5 form the power generation element of the alkaline dry battery 1 in the presence of the electrolytic solution.

  The positive electrode can 2 also serving as a battery case has a positive electrode terminal 9 on the bottom surface and functions as a positive electrode current collector by directly contacting the positive electrode mixture 3 on the inner surface. Therefore, the positive electrode mixture 3 in an annular shape is press-fitted into the positive electrode can 2, and the annular positive electrode mixture 3 is placed in close contact with the inner wall of the positive electrode can 2, so that the positive electrode can 2 and the positive electrode It is necessary to reduce the contact resistance with the mixture 3 as much as possible. In order to reduce the contact resistance, a conductive film is usually formed on the inner wall of the positive electrode can 2 by applying a conductive paint.

  A rod-shaped metal negative electrode current collector 6 inserted into the negative electrode gel 5 is fixed upright on the inner surface 7i of the dish-shaped metal negative electrode terminal plate 7 by welding. The negative electrode terminal plate 7, the negative electrode current collector 6, and the sealing gasket 8 are combined in advance as a sealing body, and the outer periphery of the sealing gasket 8 is formed between the opening edge of the positive electrode can 2 and the peripheral edge of the negative electrode terminal plate 7. The positive electrode can 2 is hermetically sealed by being clamped in between.

  By the way, the positive electrode mixture 3 is mixed with a positive electrode active material such as manganese dioxide, graphite, a binder, and an aqueous potassium hydroxide solution that is an electrolytic solution, and the mixture is subjected to predetermined steps by processes such as compacting, crushing, and granulating. It can be obtained by preparing a powdery granulated product (mixture granule) adjusted to the particle size of the material and making the mixture granule into an annular molded body using a mold. And as above-mentioned, the cyclic | annular positive electrode mixture 3 is press-fit in the positive electrode can 2, and it is made to adhere to the inner surface of the positive electrode can 2. FIG. Alternatively, powdery mixture particles are put into the positive electrode can 2, and the positive electrode can 2 is used as a mold to apply pressure to form an annular shape. In any case, the annular positive electrode mixture 3 is disposed in a state of being in close contact with the positive electrode can 2. However, if the molding strength of the positive electrode mixture 3 is insufficient, the positive electrode mixture 3 may be lost during the press-fitting or in the battery assembly process after being disposed in the positive electrode can 2. Therefore, conventionally, in order to ensure sufficient molding strength, the ratio of graphite and moisture contained in the positive electrode mixture 3 has been increased, or the molding pressure has been increased. Or like the technique of the following patent document 1, while using swelling type binders, such as polyacrylic acid, as a binder, the addition amount of the binder was optimized.

JP-A-10-144304

  However, in the conventional technology, the relationship between the molding strength of the positive electrode mixture and other performances (internal resistance, discharge performance, productivity, manufacturing cost, etc.) of the alkaline battery is contradictory. For example, if the graphite ratio is increased, the amount of the positive electrode active material is relatively reduced, and the battery capacity is reduced. In particular, the decrease in the positive electrode active material deteriorates the discharge performance at light load.

  Further, when the moisture in the positive electrode mixture is increased, the frictional resistance between the molded body and the mold increases during mold molding, and it becomes difficult to take out the molded body from the mold. Therefore, the productivity of the positive electrode mixture is reduced. Further, since the frictional resistance is high, the molded body may be damaged when the molded body is taken out from the mold. Further, when the frictional resistance is large, the mold wears quickly, and the life of the mold is shortened. Of course, even if the molding pressure is increased, the life of the mold is similarly shortened.

  In addition, when the mold wears quickly, it is difficult to increase the dimensional accuracy of the positive electrode mixture that is a molded body. And since the dimension becomes larger than the design value, a larger pressure is required when press-fitting into the positive electrode can, and the possibility of breakage increases even if the molding strength is high. If the mold is frequently replaced, the productivity of the alkaline battery further deteriorates, and the cost of the mold is transferred to the product price, resulting in a large cost increase. Furthermore, when the mold is worn, iron which is the mold material is likely to be mixed into the positive electrode mixture. Iron reacts with the active material in the electrolytic solution to generate a gas and cause leakage.

  In the case where polyacrylic acid is used as the binder of the positive electrode mixture as in the alkaline dry battery described in Patent Document 1, the positive electrode mixture has an improved molding strength and is less likely to shorten the mold life. . However, the present inventors have found that there is a problem that the internal resistance increases in an alkaline battery using a positive electrode mixture using polyacrylic acid as a binder. And when the mechanism of the increase in the internal resistance was examined, polyacrylic acid developed a viscosity that was the origin of the binding force between the mixture granules granulated by being dispersed in the electrolyte. Alkaline batteries are prepared by placing a positive electrode mixture formed by impregnating the electrolyte solution into the mixture particles in the positive electrode can and then infiltrating the electrolyte solution. When the polyacrylic acid absorbs liquid after the positive electrode mixture is placed, it further swells and the positive electrode mixture itself expands. In other words, even if the molding strength is high, the conclusion is that the internal resistance may actually increase due to the mechanism that the surface of the mixture particles do not adhere to each other and the contact resistance between the mixture particles increases. It was.

  The present invention has been created in view of the problems related to the molding strength of the positive electrode mixture in the alkaline dry battery as described above, and has been created based on the consideration based on the above knowledge. An object of the present invention is to provide an alkaline dry battery which is provided with a positive electrode mixture having high strength, is excellent in productivity, and is less expensive.

The present invention for achieving the above object is an alkaline dry battery in which a positive electrode mixture formed into an annular shape containing a positive electrode active material is disposed in a bottomed cylindrical positive electrode can also serving as a positive electrode current collector. And
The positive electrode mixture includes an electrolyte solution composed of a 40 wt% potassium hydroxide aqueous solution and a binder,
The binder is made of sodium polyacrylate, and 0.1 wt% to 3.0 wt% of the sodium polyacrylate is added to the positive electrode mixture,
The sodium polyacrylate has a viscosity of 15 Pa · s or less when mixed with a 40 wt% potassium hydroxide aqueous solution at 3 wt%,
On the inner surface of the positive electrode can, a conductive film formed by applying a conductive paint is not formed,
The positive electrode core strength in the positive electrode mixture when the binder is added is not less than 1.5 times the positive electrode core strength in the positive electrode mixture when the binder is not added, and the positive electrode mixture with the binder added is used. The short circuit current in the alkaline dry battery is at least 1 time the short circuit current in the alkaline dry battery using the positive electrode mixture without adding the binder.
The alkaline dry battery is characterized by this.

  According to the alkaline dry battery of the present invention, a positive electrode mixture having a low internal resistance and a high molding strength is provided, which has sufficient performance as a battery and is excellent in productivity and can be provided at a lower cost. Other effects will be clarified in the following description.

It is a figure which shows the structure of a general alkaline battery.

  The basic structure of the alkaline battery according to the embodiment of the present invention is the same as that of the general alkaline battery 1 shown in FIG. However, the alkaline dry battery of this example has a composition of the positive electrode mixture 3 different from the conventional one, sodium polyacrylate (Na-PA) is added as a binder, and the viscosity of the binder It is characterized in that the addition amount is optimized. Then, in order to evaluate the characteristics of the alkaline battery in Examples of the present invention, various alkaline batteries in which various positive electrode mixtures with different binder addition conditions are incorporated into the positive electrode can are prepared as samples, and the characteristics of these samples are evaluated. did.

=== Sample creation conditions ===
A sample (hereinafter referred to as an example) corresponding to the alkaline battery of the present example and a sample for comparing characteristics with the example (hereinafter referred to as a comparative example) are an LR14 type alkaline dry battery 1 having the structure shown in FIG. In addition, the addition conditions (resin, viscosity, addition amount) of the binder contained in the positive electrode mixture 3 are different between the example and the comparative example. And the alkaline dry battery of an Example uses Na-PA for the binder of positive electrode mixture. Therefore, first, a positive electrode mixture containing no binder and a positive electrode mixture molded using a binder other than Na-PA are incorporated into a positive electrode can having a conductive film formed on the inner surface, and a conventional alkaline battery (Comparative Example). 1-5), and the optimal preparation of the positive electrode mixture by evaluating the performance of the alkaline battery using the positive electrode mixture 3 with Na-PA added to the alkaline batteries of Comparative Examples 1 to 5 The conditions were sought.

  In addition, about the positive electrode material mixture to which the binder was added, electrolytic manganese dioxide (EMD), graphite, and electrolytic solution (40% potassium hydroxide aqueous solution) were respectively in a weight ratio of 89 wt%, 7 wt%, and 4 wt%, A binder was mixed with these materials under different conditions for each sample, the mixture was rolled and granulated, and then molded by molding.

  In addition, for various binders with different types and viscosities of resins added to the positive electrode mixture of each sample, respective resin materials with different blending ratios of cross-linking agents, etc. are obtained. What was mixed with 3% by weight of 3% by weight potassium hydroxide aqueous solution was measured using a viscometer (TV-10 manufactured by Toki Sangyo Co., Ltd.) under the condition of 5 RPM.

  As for the molding strength of the positive electrode mixture, an annular (hollow cylindrical) positive electrode mixture is placed on a horizontal test stand so that its cylindrical axis is in the horizontal direction, and the upper side of the positive electrode mixture is below. The pressure at the time when the positive electrode mixture was cracked was determined by gradually applying a high pressure toward the surface.

=== Conventional alkaline battery ===
Table 1 below shows the conditions for adding the binder in the positive electrode mixture and the short-circuit current characteristics in each sample (Comparative Examples 1 to 5) corresponding to a conventional alkaline battery.

  In Table 1 above, Comparative Example 1 is a sample in which a positive electrode mixture molded without adding a binder is incorporated into a general positive electrode can having a conductive film formed on its inner surface. With the molding strength and the discharge performance as the reference value 100, the performance of other samples was evaluated as a relative value (performance value) to the reference value. In addition, regarding the pass / fail judgment with respect to the reference value, regarding the molding strength of the positive electrode mixture, a performance value of 150 or more was passed, and for the short-circuit current serving as an index of internal resistance, the performance value was 100 or more.

  From Table 1, as a binder in the positive electrode mixture, polyacrylic acid (PA), polyvinyl alcohol (PVA), and polyethylene (PE) added at a ratio of 0.5 wt% (Comparative Examples 2 to 5), It was found that the positive electrode mixtures of Comparative Examples 2 and 3 in which the binder was PA had sufficient molding strength. It was also found that the molding strength of the positive electrode mixture increased in proportion to the viscosity. However, the performance about a short circuit current was rejected and the subject that the internal resistance in the alkaline dry battery which contains PA as a binder in a positive electrode mixture became large was confirmed. Further, in Comparative Example 4 and 5 positive electrode mixture using PVA or PE as a binder, a performance value equivalent to the reference value was obtained for the short circuit current, but a sufficient viscosity could not be obtained and the molding strength was insufficient and it was rejected. It became. In addition, the viscosity of PE was below the measurement limit.

=== Optimum viscosity of sodium polyacrylate ====
Next, the characteristics of a sample prepared by incorporating a positive electrode mixture using Na-PA as a binder into a positive electrode can having a conductive film formed on the inner surface thereof were evaluated. First, in order to obtain the optimum value of the viscosity of Na-PA, the addition amount of Na-PA is set to 0.5 wt% which is the same as that of each sample corresponding to the conventional alkaline battery shown in Table 1, and the viscosity is Samples (Examples 1 to 3, Comparative Example 6, and Comparative Example 7) were prepared by incorporating various positive electrode mixtures to which different Na-PA was added into a positive electrode can.

Table 2 shows the viscosity dependency of Na-PA for the molding strength of the positive electrode mixture and the short-circuit current of the alkaline battery.

  From Table 2, it was found that the molding strength and the short-circuit current are in a trade-off relationship. In the samples of Examples 1 to 3 in which the viscosity of Na-PA is 15 Pa · s or less, both the molding strength and the short-circuit current are determined to be acceptable, and the sample has a viscosity greater than 15 Pa · s (Comparative Example 6, Comparative Example). In 7), a large short-circuit current could not be obtained, resulting in a failure determination.

  Here, looking at the characteristics of Comparative Example 2 and Comparative Example 3 in Table 1, it is estimated that if the viscosity of PA is further lowered, the performance with respect to the short-circuit current is also passed, but the results shown in Table 2 By comparison, it can be seen that when the addition amount and the molding strength are the same, the viscosity of PA is higher. For example, when Comparative Example 2 and Example 3 in which the performance value of the molding strength is the same 200 are compared, the viscosity of PA is 30% or more of the viscosity of Na-PA. Therefore, in the positive electrode mixture using PA as a binder, there is a concern that the materials are difficult to mix evenly when the materials of the mixture are mixed. In order to mix uniformly, it is necessary to lengthen the stirring time at the time of mixing, and productivity falls.

  In Example 1 and Comparative Example 4 using PVA as the binder, the viscosity of the binder is a low viscosity (1 Pa · s) close to the measurement limit, which is extremely low. In Comparative Example 4, sufficient molding strength was not obtained, but in Example 1, sufficient molding strength was obtained, and the positive electrode mixture using Na-PA as a binder is sufficient even if the viscosity is extremely low. It was confirmed that a good molding strength was obtained.

  Here, when considering the fact that Na-PA can obtain a large molding strength even at a low viscosity, the expression mechanism of the viscosity in Na-PA is dispersed in the electrolyte like PA. Contrary to the manifestation of viscosity, Na-PA absorbs the electrolyte and holds the electrolyte in its molecular structure, so that the viscosity is developed, and the binding force is fully exhibited even at low viscosity. Can do. Also, based on this consideration, Na-PA does not require an increase in viscosity in order to increase the molding strength like PA, so there is no increase in internal resistance due to the expansion of the positive electrode mixture, resulting in a large Short circuit current can be obtained. The logic is established.

  The optimum value of the viscosity of Na-PA is 15 Pa · s or less when mixed in a 40 wt% potassium hydroxide aqueous solution at a weight ratio of 3 wt%, and Na-PA having the optimum viscosity is used as a binder. In the alkaline dry battery according to the embodiment of the present invention using the positive electrode mixture, a sufficient short-circuit current is obtained, and the positive electrode mixture having sufficient molding strength is used, so that it can be damaged when pressed into the positive electrode can. It can be expected that productivity will be reduced, productivity will be improved, and it will be provided at lower cost. Moreover, since the viscosity of a binder is low, when preparing positive mix, the material of a mix is mixed uniformly and the characteristic of positive mix itself becomes uniform. As a result, the quality of the alkaline battery as the final product becomes uniform, and the productivity is further improved.

=== Optimization of addition amount ===
As described above, the positive electrode mixture using Na-PA as a binder can obtain a large molding strength even at a low viscosity, and the short-circuit current characteristics are alkaline dry batteries using a positive electrode mixture containing no binder (Comparative Example 1). ) And an alkaline dry battery with low internal resistance can be achieved while improving productivity.

  Next, a positive electrode mixture having a different amount of Na-PA added is incorporated into a positive electrode can having a conductive film formed on the inner surface, and various samples (Examples 4 to 6, Comparative Example 1, Comparative Example 8, Comparative Example 9). In Example 5, the same conditions as in Example 2 were prepared, and the discharge performance serving as an index of the positive electrode capacity was evaluated for each sample. As is well known, if the amount of the binder added in the positive electrode mixture increases, the amount of the positive electrode active material decreases relatively, and the positive electrode capacity decreases. Moreover, if the addition amount is reduced, the molding strength of the positive electrode mixture is lowered. Therefore, in an alkaline dry battery using a positive electrode mixture containing Na-PA as a binder, the conditions under which the molding strength of the positive electrode mixture and sufficient discharge performance were obtained were studied.

  Regarding the discharge performance, a cycle was repeated for each sample in which the end voltage was 0.9 V, the battery was discharged for 4 hours a day with a load of 10Ω, and the remaining 20 hours were left unloaded. Evaluation was sometimes made by measuring the discharge time to reach the end voltage. In addition, the evaluation result is that a sample having a performance value of 95 or more is passed when the discharge time of the sample of Comparative Example 1 in which the positive electrode mixture contains no binder and theoretically has the largest positive electrode capacity is 100. It was. The viscosity was 5 Pa · s, the same as in Comparative Example 1.

Table 3 below shows the relationship between the amount of Na-PA added and the discharge performance.

  From the results of Table 3, it was found that when the amount of Na-PA added was 0.1 wt% or more and 3% or less, the molding strength of the positive electrode mixture was sufficiently high and sufficient discharge performance was obtained.

  In addition, in the Na-PA addition amount dependence of the discharge performance shown in Table 3, the viscosity is 5 Pa · s. However, as shown in Table 2, at 0.5% addition amount, at least 1 Pa · s. It has been found that the viscosity can be adjusted to ˜30 Pa · s, and if the addition amount is 0.1 wt% to 3 wt%, the viscosity is adjusted to 1 Pa · s to 15 Pa · s which is the optimum value range. It is easy. Therefore, in an alkaline battery using a positive electrode mixture containing Na-PA as a binder, the viscosity of Na-Pa is set to 15 Pa · s or less in order to improve productivity after obtaining a sufficient short-circuit current. In order to obtain more sufficient discharge performance, the addition amount may be 0.1 wt% to 3 wt%.

=== About the conductive film on the inner surface of the positive electrode can ===
As described above, an alkaline dry battery using a positive electrode mixture with Na-PA as a binder can be provided at low cost due to high productivity, and the positive electrode mixture has high molding strength, low internal resistance, and sufficient short-circuit current. Can be obtained. Here, if the internal resistance is sufficiently low, the present inventor achieves a practical alkaline dry battery even if the conductive film previously formed on the inner surface of the positive electrode can in order to suppress the increase in internal resistance is omitted. I thought it could be done. And if a conductive film is unnecessary, the cost concerning the conductive paint used as the conductive film and the coating process of the conductive paint can be reduced, and further cost reduction of the alkaline battery can be achieved.

In addition, the conductive paint applied to the inner surface of the positive electrode can to form a conductive film is obtained by dispersing or dissolving a conductive material in a volatile organic solvent (VOC) whose emission is being regulated in recent years. From the viewpoint of problems, it is desirable to omit the coating process of the conductive paint. In view of the VOC problem, it is possible to replace the conductive paint using water as a solvent, but in this case, since the solvent water does not volatilize naturally, the solvent is used after the conductive paint application process. A drying step is required to remove the water. And in this drying process, excess energy and time will be consumed, and the productivity of an alkaline battery will fall. Also, the increase in energy consumption is not desirable from the viewpoint of environmental problems, contrary to the global demand for CO ₂ reduction. In any case, improvement of productivity is an important issue not only from the manufacturing cost but also from the viewpoint of environmental problems. Therefore, samples were prepared by incorporating various positive electrode mixtures with different binders into a positive electrode can with no conductive film formed on the inner surface, and the short circuit current characteristics of each sample were evaluated.

Table 4 shows the evaluation results.

  In Table 4, Comparative Example 10, Comparative Example 11, and Comparative Example 12 have the same positive electrode mixture as Comparative Example 1, Comparative Example 2, and Comparative Example 5 in Table 1, respectively, and a conductive film formed on the inner surface. Example 7 is a sample prepared by incorporating in a positive electrode can having no “conductive film”, and Example 7 is a positive electrode having no conductive film and the same positive electrode mixture as Example 2 in Table 2 (Example 5 in Table 3) It is a sample created by incorporating it into a can.

  From Table 4, in the sample of Example 7 containing Na-PA as a binder in the positive electrode mixture, Comparative Example 1 serving as a reference for evaluation, that is, the positive electrode mixture containing no binder was used as the positive electrode can with “conductive film”. A short-circuit current equivalent to that of the alkaline battery incorporated in the battery was obtained, and the result was a pass judgment. In the samples in which the positive electrode mixture in which the binder other than Na-PA was added to the positive electrode can without the conductive film, the short-circuit current did not reach the reference value 100 in all the samples, and the determination was rejected. Specifically, each sample shown in Table 4 is a sample in which the positive electrode mixture is press-fitted into the positive electrode can at the same pressure, but a sample incorporating a conventional positive electrode mixture (Comparative Examples 10 to 12) Then, the performance value was 70 at the maximum, and the short-circuit current was reduced by 30% compared to Comparative Example 1. On the other hand, in the sample of Example 7, which is an example of the present invention, a performance value of 100, which is a reference value and also a pass standard, was achieved.

  Further, in the alkaline dry battery of this example, as described above, since the molding strength of the positive electrode mixture is high, the pressure at the time of press-fitting into the positive electrode can can be further increased while maintaining the productivity. . Therefore, it is expected that the short-circuit current characteristics can be further improved by further bringing the positive electrode can inner surface and the positive electrode mixture into close contact with each other.

1 alkaline dry battery, 2 battery can (positive electrode can), 3 positive electrode mixture, 4 separator,
5 Negative gel, 6 Negative current collector, 7 Negative terminal plate, 8 Gasket, 9 Positive terminal

Claims (1)

An alkaline dry battery in which a positive electrode mixture formed in an annular shape containing a positive electrode active material is disposed in a bottomed cylindrical positive electrode can also serving as a positive electrode current collector,
The positive electrode mixture includes an electrolyte solution composed of a 40 wt% potassium hydroxide aqueous solution and a binder,
The binder is made of sodium polyacrylate, and 0.1 wt% to 3.0 wt% of the sodium polyacrylate is added to the positive electrode mixture,
The sodium polyacrylate has a viscosity of 15 Pa · s or less when mixed with a 40 wt% potassium hydroxide aqueous solution at 3 wt%,
On the inner surface of the positive electrode can, a conductive film formed by applying a conductive paint is not formed,
The positive electrode core strength in the positive electrode mixture when the binder is added is not less than 1.5 times the positive electrode core strength in the positive electrode mixture when the binder is not added, and the positive electrode mixture added with the binder is used. The short circuit current in the alkaline dry battery is at least 1 time the short circuit current in the alkaline dry battery using the positive electrode mixture without adding the binder.
An alkaline battery characterized by that.

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