[DESCRIPTION]

[Title of Invention]

CURRENT COLLECTOR AND METHOD OF PRODUCING THE SAME, AND MANGANESE DRY BATTERY

[Technical Field]

[1]

The present invention relates to a manganese dry-battery, and particularly relates to an improvement of a carbon rod forming a current collector in a manganese dry battery.

[Background Art]

[2]

Manganese dry batteries have been widely used as power sources for electronic devices such as portable apparatus and information equipment.

In a manganese dry battery, a positive electrode material mixture having a hollow cylindrical shape is housed in a negative electrode can having a cylindrical shape with a bottom. A separator is disposed between the positive electrode material mixture and the negative electrode can. A current collector is inserted in a hollow portion of the positive electrode material mixture. The current collector is electrically connected with a positive electrode terminalplate covering an opening portion of the battery can.

The current collector is produced, in general, through the steps of: (1) forming a mixture including a carbonaceous material and a binder; (2) compressing the mixture into a rod shape to obtain a molded body; (3) baking the molded body to obtain a carbon rod; and (4) impregnating the carbon rod with a paraffin wax.

[3]

Various studies have been made on the carbon rod.

For example, Patent Literature 1 proposes to heat the molded body at 100 to 350°C for 3 to 20 hours in an atmosphere having an oxygen concentration of 10 to 21% before the step (3) . By heating in an atmosphere including oxygen, oxidation reaction (dehydrogenation reaction) of a binder included in the molded body occurs, and cross-linking of the binder advances. Consequently, binding between particles of the carbonaceous material is strengthened. Thus, a dense carbon rod having a high bending strength and a low electric resistance can be obtained.

[4]

In contrast, Patent Literature 2 proposes to bake the molded body in an atmosphere having an oxygen concentration of 0.1% or less in order to prevent oxidation of the carbon rod during the baking.

[Citation List]

[PatentLiterature]

[5]
[PTL 1] Japanese Laid-Open Patent Publication No. Hei 4-2056

[PTL 2] Japanese Laid-Open Patent Publication No. Hei 4-2661

[Summary of Invention]

[Technical Problem]

[6]
A cylindrical tunnel furnace is generally used for baking the molded body. The molded body is baked continuously while being supplied into the tunnel furnace. However, it is difficult to maintain oxygen concentration uniformly or stably in the furnace. In particular, gradient of oxygen concentration is distinguished in the length direction in the tunnel furnace. Consequently, according to the proposition of Patent Literature 1, the degree of oxidation of the binder, that is, the properties of the carbon rod are likely to vary, and thus the reliability lowers.

According to the proposition of Patent Literature 2, since the oxygen concentration in the baking furnace is low, dehydrogenation reaction of the binder is insufficient.

[7]

Therefore, the present invention has an object to provide stably a current collector having a high bending strength, a low electric resistance, and a high reliability.

[Solution to Problem]

[8]

The present invention relates to a current collector comprising a carbon rod and a paraffin wax impregnated into the carbon rod, wherein the carbon rod includes at least one element A selected from the group consisting of Fe, Cu, Ni, Co, Bi, and V, and a content of the element A in the current collector is 0.1 to 4.0% by weight. [0009]
Also, the present invention relates to a manganese dry battery comprising: a positive electrode material mixture having a hollow cylindrical shape and including manganese dioxide; a negative electrode can including zinc; a separator between the positive electrode material mixture and the negative electrode can; the current collector inserted in a hollow portion of the positive electrode material mixture; and an electrolyte.

[10]
Further, a method of producing a current collector of the present invention comprises the steps of:

(1) forming a mixture including a carbonaceous material, a binder, and an oxidizing agent facilitating dehydrogenation reaction of the binder;

(2) compressing the mixture into a rod shape to obtain a molded body;

(3) baking the molded body to obtain a carbon rod;and

(4) impregnating the carbon rod with a paraffin wax to obtain a current collector,
wherein the oxidizing agent includes at least one element A selected from the group consisting of Fe, Cu, Ni, Co, Bi, and V, and a content of the element A in the mixture is 0.1 to 3.5% by weight.

[Advantageous Effects of Invention]

[11]
According to the present invention, since the binder and the oxidizing agent thereof are mixed in the carbonaceous material for baking, dehydrogenation reaction of the binder can be produced surely, and variation of degree of oxidation of the binder can be reduced. Consequently, it is possible to provide a current collector having a high bending strength and a low electric resistance, and also a current collector having a high reliability where properties such as the bending strength and the electric resistance are stable.

While the novel features of the invention are set forth particularly in the appended claims, the invention, both as to organization and content, will be better understood and appreciated, along with other objects and features thereof, from the following detailed description taken in conjunction with the drawings.

[Brief Description of Drawing]

[12]

[Fig. 1] A front view of an AA. size manganese dry batterywith a part cross section thereof in accordance with thepresent invention.

[Description of Embodiments]

[13]

First, the method of producing a current collector in accordance with the present invention will be described. The production method includes the steps of:

(1) forming a mixture including a carbonaceous material, a binder, and an oxidizing agent facilitating dehydrogenation reaction of the binder;

(2) compressing the mixture into a rod shape to obtain a molded body;

(3) baking the molded body to obtain a carbon rod; and

(4) impregnating the carbon rod with a paraffin wax to obtain a current collector.

[14]
In general, tar and pitch are used as the binder in the step (1) . The binders such as tar and pitch include a component facilitating dehydrogenation reaction when an oxidizing agent is added. In the step (3) , since the molded body is housed in the high-temperature baking furnace,oxidation of the binder by the oxidizing agent added in the step (1) can be facilitated effectively. That is, dehydrogenation reaction of the binder occurs and cross-linking advances. When the binder includes volatile components, the volatile components are removed. Consequently, removal of carbon atoms during the baking is suppressed, remaining ratio of carbon is increased, and binding between particles of the carbonaceous material is strengthened.

Further, minute space in the carbon rod is decreased and bulk density is increased. As a result, the bending strength of the current collector is increased and the electric resistance is reduced.

[15]
As a method of oxidizing the binder, it is considered providing the inside of the baking furnace with an atmosphere having a relatively high oxygen concentration. It is however difficult to make the oxygen concentration uniform while maintaining the oxygen concentration stably in the baking furnace. In particular, in the cylindrical tunnel furnace generally used for producing current collectors, gradient of oxygen concentration in the length direction is distinguished. In consequence, the degree of oxidation of the binder is likely to vary, and variation of properties of the current collector is increased to lower the reliability.

[16]
In contrast, in the present invention, in the step

(1), a mixture is formed by mixing a carbonaceous material with a binder and an oxidizing agent of the binder. In the mixture, the binder and the oxidizing agent are sufficiently uniformly dispersed. Thus, in the step (3) , the binder dispersed uniformly in the molded body can be oxidized efficiently by the oxidizing agent dispersed uniformly in the molded body. Consequently, the degree of oxidation of the binder in the molded body and between the molded bodies can be uniform. Further, variation in the properties of the current collector is decreased, which enables to provide a high-quality current collector having an excellent reliability.

[17]
The oxidizing agent in the step (1) includes at least one element (element A, hereinafter) selected from the group consisting of Fe, Cu, Ni, Co, Bi, and V.
When an oxidizing agent including the element A is used, according to an Ellingham diagram, oxidation and dehydrogenation reaction of the binder occurs preferentially by reductive action of the element A at baking temperatures (about 900 to 1,000°C).
Fe and Bi are preferable among the elements A. Since the oxidizing agent including Fe is reduced during the baking and is present as a baked body of Fe after the baking, the bending strength of the current corrector can be increased. Also, since Fe having an excellent electronic conductivity is present in the current collector, the electric resistance ofthe current collector can be reduced. Since the oxidizing agent including Bi has a low melting point and is present as a binder after the baking, the bending strength of the current collector can be increased.

The content of the element A in the mixture in the step (1) is 0.1 to 3.5% by weight. When the content of the element A in the mixture is less than 0.1% by weight, the effect by the element A is insufficient. When the content of the element A in the mixture is more than 3.5% by weight, elution amount of the element A from the current collector is increased during a long-term storage of the battery, and the corrosion resistance of the negative electrode can including zinc deteriorates, which may lower the storage characteristics.

[18]
Examples of the oxidizing agent including the element A include oxides including the element A. The oxides including the element A are preferably at least one compound (compound B, hereinafter) selected from the group consisting of Fe203, Cu20, NiO, Co304, Bi203, and V205. The compound B turns into a sintered body after the step (3) . Bi203 and V205 are preferable in point of acting as binders.

[19]
When the carbonaceous material and the binder include a very small amount of Fe as impurities, the very small amount of Fe included as impurities also acts as the element A. However, since the amount of Fe resulting fromimpurities included in the current colleqtor is about 0.05% by-weight at largest, the effect by the element A cannot be obtained sufficiently with only Fe included in the mixture as impurities.

[20]
The addition amount of the compound B is preferably 0.1 to 3.5 parts by weight per 100 parts by weight of the sum of the carbonaceous material and the binder. When the addition amount of the compound B is less than 0.1 parts by weight per 100 parts by weight of the sum of the carbonaceous material and the binder, the effect by adding the element A is insufficient. Even when the addition amount of the compound B is more than 3.5 parts by weight per 100 parts by weight of the sum of the carbonaceous material and the binder, the electric resistance and the bending strength of the current collector is roughly the same as in the case where the addition amount of the compound B is 3.5 parts by weight.

[21]
As the carbonaceous material, it is preferable to use artificial graphite and at least one of carbon black and coke. As the coke, coal coke and oil coke may be used. The ratio (W1/W2) of the weight (W1 ) of artificial graphite to the weight (W2) of at least one of carbon black and coke is preferably 30/70 to 85/15. When both of carbon black and coke are used, the ratio (W3/W4) of the weight (W3) of carbon black to the weight (W4) of coke is preferably 25/75 to 75/25.

The carbonaceous material is used as a powder. In view of the strength and the current colljecting performance of the carbon rod, the bulk specific gravity of artificial graphite is preferably 1/3 to 1 g/ml. In view of the strength and the current collecting performance of the carbon rod, the bulk specific gravity of coke is preferably 1/3 to 1 g/ml. In view of the strength and the current collecting performance of the carbon rod, the bulk specific gravity of carbon black is preferably 1/6 to 1/2 g/ml.

[22]
As the binder, it is preferable to use at least one of pitch and tar. When both of pitch and tar are used, the ratio (W5/W6) of the weight (W5) of pitch to the weight (W6) of tar is preferably 40/60 to 60/40.

Tar is a black or brown oily liquid having viscosity produced by heat decomposition of coal, wood, or other organic materials. Examples of tar include coal tar and wood tar. For example, coal tar is obtained as a byproduct when coke is produced from coal.
Pitch is a carbonaceous solid residue formed when tar is distilled. Examples of pitch include coal tar pitch, wood tar pitch, rosin pitch, and petroleum pitch.

[23]
The content of the binder in the mixture is preferably 30 to 50 parts by weight per 100 parts by weight of the carbonaceous material. When the content of the binder in
the mixture is less than 30 parts by weight per 100 parts by-weight of the carbonaceous material, the binding strength between particles of the carbonaceous material may become insufficient. When the content of the binder in the mixture is more than 50 parts by weight per 100 parts by weight of the carbonaceous material, the ratio of the carbonaceous material is decreased and the current collecting characteristics may become insufficient.

[24]
In the step (2), for example, the mixture is extrusion molded into a rod shape to produce a molded body. For example, the diameter of the molded body is 4.2 to 4.4 mm in R6 size (AA size) batteries.

In the step (3) , the molded body is baked in a non-oxidizing atmosphere (e.g. inert gas atmosphere such as argon). The baking temperature is 900 to 1,000°C, for example. The baking time is 40 to 50 hours, for example.

In view of mass-productivity, the baking furnace is preferably a tunnel furnace permitting continuous baking of molded bodies. Even when the tunnel furnace is used, highly reliable current collectors can be mass-produced stably.

In the step (3) , since volatile components included in the binder vaporized during the baking, the weight of the carbon rod is decreased by about 5 to 10% by weight relative to the weight of the molded body.

[25]

In the step (4) , for example, a cylindrical carbon rod cut into a prescribed length is impregnated with a liquid paraffin wax having a prescribed temperature (e.g. a temperature higher than room temperature and higher than the melting point of the paraffin wax) . Subsequently, the paraffin wax is solidified in a room-temperature environment. The paraffin wax is composed, for example, of a hydrocarbon compound having 20 to 40 carbons and a molecular weight of about 300 to 550, and for example, 90% by weight or more of the hydrocarbon compound is normal paraffin (straight-chain hydrocarbon compound).

Thus, minute space inside the carbon rod and depressions on the surface of the carbon rod are filled with the paraffin wax to ensure sealing performance of the battery. Subsequently, the surface of the carbon rod is polished and the paraffin wax adhered to the surface of the carbon rod is removed to ensure electronic conductivity on the surface of the carbon rod. Thus, the current collector is obtained. In view of the sealing performance and the density of the carbon rod, the content of the paraffin wax in the current collector is preferably 3 to 5 parts by weight per 100 parts by weight of the carbon rod.

[26]
The present invention relates to the current collector obtained by the above production method. That is, the present invention relates to a current collector including
a carbon rod and a paraffin wax impregnated into the carbon rod, wherein the carbon rod includes an element A resulting from an oxidizing agent added in the step (1) . The element A is dispersed uniformly in the carbon rod. The content of the element A in the current collector is 0.1 to 4.0% by weight, and preferably 1.0 to 4.0% by weight.

[27]
In the current collector of the present invention, the carbonaceous material forming the carbon rod has high aggregating properties and a low electric resistance. The current collector of the present invention can reduce the electric resistance to 2.4 m Ω.cm or less, and further to 2.0 mΩ . cm or less, and can reduce the electric resistance more than conventional current collectors.

The current collector of the present invention has a high bending strength because the carbon rod has a high density. The density of the carbon rod is preferably 1.5 to 1.8 g/cm . The bending strength is a value of physical properties representing strength to bending.

[28]
When the amount of the oxidizing agent used in the production process of the current collector is decreased to an extent that the content of the element A in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. When the content of the element A in the current collector ismore than 4.0% by weight, elution amount Of the element A from the current collector is increased during a long-term storage of the battery and the corrosion resistance of the negative electrode can including zinc is reduced, which may deteriorate the storage characteristics.

[29]
When the element A includes Fe, the Fe content in the current collector is preferably 0.1 to 2.8% by weight. When the amount of the oxidizing agent used in the production process of the current collector is decreased to an extent that the Fe content in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. However, this does not apply to the case where the element A other than Fe is included. Even when the Fe content in the current collector is more than 2.8% by weight, the electric resistance and the bending strength of the current collector are roughly the same as in the case where the Fe content in the current collector is 2.8 % by weight.

The Fe content in the current collector is more preferably 0.4 to 2.8% by weight because the electric resistance can be reduced to 2.0 mQ-cm or less and the bending strength can be increased to 50 MPa or more. The Fe content in the current collector is particularly preferably 0.7 to 2.8% by weight because the electric resistance can be decreased to 1.8 mQ-cm or less. The Fe content in the currentcollector is still more preferably 1.0 tp 2.8% by weight because the electric resistance can be reduced to 1.6 mΩ. cm or less and the strong discharge characteristics can be improved greatly.

[30]
When the element A includes Bi, the Bi content in the current collector is preferably 0.1 to 3.6% by weight. In case the amount of the oxidizing agent used in the production process of the current collector is decreased to an extent that the Bi content in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. However, this does not apply to the case where the element A other than Bi is included. Even when the Bi content in the current collector is more than 3.6% by weight, the electric resistance and the bending strength of the current collector are roughly the same as in the case where the Bi content in the current collector is 3.6% by weight.

The Bi content in the current collector is more preferably 0.5 to 3.6% by weight because the electric resistance can be reduced to 2.0 mΩ. cm or less and the bending strength can be increased to 50 MPa or more. The Bi content in the current collector is particularly preferably 1.0 to 3.6% by weight because the electric resistance can be reduced to 1.8 mΩ. cm or less. The Bi content in the current collector is still more preferably 1.5 to 3.6% by weight because theelectric resistance can be reduced to 1.7 mΩ. cm or less and the strong discharge characteristics can be improved greatly.

[31]
When the element A includes V, the V content in the current collector is preferably 0.1 to 2.5% by weight.

In case the amount of the oxidizing agent used in the production process of the current collector is decreased to an extent that the V content in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. However, this does not apply to the case where the element A other than V is included. Even when the V content in the current collector is more than 2.5% by weight, the electric resistance and the bending strength of the current collector are roughly the same as in the case where the V content in the current collector is 2.5% by weight.

The V content in the current collector is more preferably 0.4 to 2.5% by weight because the electric resistance can be reduced to 2.0 mΩ -cm or less. The V content in the current collector is still more preferably 1.0 to 2.5% by weight because the electric resistance can be reduced to 1.7 mΩ- cm or less and the strong discharge characteristics can be improved greatly.

[32]
When the element A includes Cu, the Cu content in the current collector is preferably 0.1 to 3.4% by weight.

In case the amount of the oxidijzing agent used in the production process of the current collector is decreased to an extent that the Cu content in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. However, this does not apply to the case where the element A other than Cu is included. Even when the Cu content in the current collector is more than 3.4% by weight, the electric resistance and the bending strength of the current collector are roughly the same as in the case where the Cu content in the current collector is 3.4% by weight.

The Cu content in the current collector is more preferably 0.5 to 3.4% by weight because the electric resistance can be reduced to 2.0 mQ-cm or less. The Cu content in the current collector is still more preferably 1.0 to 3.4% by weight because the electric resistance can be reduced to 1.7 mQ-cm or less and the strong discharge characteristics can be improved greatly.

[33]
When the element A includes Ni, the Ni content in the current collector is preferably 0.1 to 3.2% by weight.

In case the amount of the oxidizing agent used in the production process of the current collector is decreased to an extent that the Ni content in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. However, thisdoes not apply to the case where the element A other than Ni is included. Even when the Ni content in the current collector is more than 3.2% by weight, the electric resistance and the bending strength of the current collector are roughly the same as in the case where the Ni content in the current collector is 3.2% by weight.

The Ni content in the current collector is more preferably 0.5 to 3.2% by weight because the electric resistance can be reduced to 2.0 mΩ-cm or less. The Ni content in the current collector is still more preferably 1.0 to 3.2% by weight because the electric resistance can be reduced to 1.7 mΩ-cm or less and the strong discharge characteristics can be improved greatly.

[34]
When the element A includes Co, the Co content in the current collector is preferably 0.1 to 3.0% by weight.

In case the amount of the oxidizing agent used in the production process of the current collector is decreased to an extent that the Co content in the current collector is less than 0.1% by weight, dehydrogenation reaction of the binder may not be facilitated sufficiently. However, this does not apply to the case where the element A other than Co is included. Even when the Co content in the current collector is more than 3.0% by weight, the electric resistance and the bending strength of the current collector are roughly the same as in the case where the Co content in the currentcollector is 3.0% by weight.

The Co content in the current collector is more preferably 0.4 to 3.0% by weight because the electric resistance can be reduced to 2.0 mQ-cm or less. The Co content in the current collector is still more preferably 0.9 to 3.0% by weight because the electric resistance can be reduced to 1.7 mQ-cm or less and the strong discharge characteristics can be improved greatly.

[35]
Further, the present invention relates to a manganese dry battery using the current collector described above.

In the following, an embodiment of the manganese dry battery in accordance with the present invention will be described by referring to Fig. 1. Fig. 1 is a front view of an AA size manganese dry battery (R6) with a part cross section thereof.

A positive electrode material mixture 1 having a hollow cylindrical shape is housed in a negative electrode can 4 having a cylindrical shape with a bottom and including zinc. A separator 3 is disposed between the positive electrode material mixture 1 and the negative electrode can 4. As the separator 3, Kraft paper on which a paste material prepared by dissolving a binder mainly composed of a cross-linking starch and polyvinyl acetate in an alcohol-based solvent is applied and dried is used. The separator 3 is disposed such that theface on which the paste material is applied faces the negative electrode can 4. The separator 3 includes an electrolyte. As the electrolyte, for example, an aqueous solution including zinc chloride is used. A positive electrode current collector 2 is inserted in a hollow portion of the positive electrode material mixture 1.

[36]
As the positive electrode material mixture 1, for example, a mixture of powdered manganese dioxide, a powdered conductive agent such as acetylene black, and an electrolyte is used. The content of manganese dioxide in the positive electrode material mixture 1 is preferably 40 to 60% by weight. The content of the conductive agent in the positive electrode material mixture 1 is preferably 5 to 15% by weight.

[37]
The positive electrode current collector 2 having a cylindrical shape is inserted in a hole in the center of a gasket 5 made of resin. In order to ensure the sealing performance, a sealing agent such as polybutene is applied onto the contacting portion of the positive electrode current collector 2 with the hole of the gasket 5, and the contacting portion of the groove on the lower face of the periphery of the gasket 5 with the opening end portion of the negative electrode can 4. A guard paper 9 having a circular shape with a through hole in the center is placed on top of the positive electrode material mixture 1, and the positive electrodecurrent collector 2 is inserted in the through hole of the guard paper 9.

[38]
The opening portion of the negative electrode can 4 is covered with the gasket 5 and a positive electrode terminal 11 composed of a cap-shaped tin plate having a protruding portion in the center and a flat brim portion on the periphery thereof. The top portion of the positive electrode current collector 2 is fitted in and connected electrically with a recess portion formed on the inner side of the protruding portion of the positive electrode terminal 11. An insulating ring 12 made of resin is arranged on the flat brim portion of the positive electrode terminal 11. In order to ensure the insulation performance between the bottom portion of the positive electrode material mixture 1 and the bottom portion of the negative electrode can 4, a bottom paper 13 is arranged therebetween. A seal ring 7 is disposed on the outer surface side of the flat peripheral portion of the negative electrode terminal 6.

A resin tube 8 made of a heat-shrinkable resin film is arranged on the circumference of the negative electrode can 4, the upper end portion of the resin tube 8 covers the upper surface of the peripheral portion of the gasket 5, and the lower end portion of the resin tube 8 covers the lower face of the seal ring 7.

[39]

A metal jacket 10 composed of a cylindrical tin plate is disposed on the outer side of the resin tube 8, and the lower end portion thereof is bent inward so as to cover the seal ring 7. The manganese dry battery is sealed by curling inward the upper end portion of the metal jacket 10 and caulking the tip of the upper end portion of the metal jacket 10 to the positive electrode terminal 11 with the insulating ring 12 disposed therebetween.

[40]
The current collector of the present invention is used as the positive electrode current collector 2. Since the current collector of the present invention has a low electric resistance, a battery having a low internal resistance can be obtained. Since the current collector of the present invention has a high bending strength, it is possible to suppress occurrence of cracks and ruptures of the current collector caused by the fact that an excessive force is applied to the current collector during battery assembly (e.g. at the time of inserting the current collector into the hollow portion of the positive electrode material mixture and the hole of the gasket, and at the time of fitting the current collector into the recess portion of the positive electrode terminal). Leakage of the electrolyte from the fitting portion of the top portion of the current collector with the positive electrode terminal by the presence of cracks in the top portion of the current collector is suppressed.

Consequently, reliability of the battery is improved.

[EXAMPLES]

[41]
In the following, examples of the present invention will be described in detail, but the present invention is not limited to these examples.

[42]
<> (1) Production of carbon rod
Carbonaceous materials and binders are mixed in the ratio as shown in Table 1.
As the carbonaceous materials, artificial graphite (AGP-40, manufactured by Kobayashi Shoji, K.K.), carbon black (manufactured by China Synthetic Rubber Corporation), and petroleum coke (manufactured by Liaoning Petroleum Coke Corporation) were used.

As the binders, coal tar pitch (manufactured by China Steel Chemical Corporation) and coal tar (manufactured by China Steel Chemical Corporation) were used. The Fe amount included as impurities in each material was determined by atomic absorption spectrometry. The results are shown in Table 1

. [43]


[44]
Further, mixtures were obtained by adding powdered Fe203 (manufactured by Kanto Chemical Co., Inc, superfine quality, average particle diameter: 3 urn) to 100 parts by weight of the sum of the carbonaceous materials and the binders in the ratios as shown in Table 2.

These mixtures were kneaded by a Z type kneader for 90 minutes. Fe contents in the mixtures are shown in Table 2. Fe in the mixture of Comparative Example 1 in Table 2 is Fe included as impurities-in the materials in Table 1. Fe in the mixtures of Examples 1 to 6 in Table 2 is the sum of Fe include as impurities in the materials of Table 1 and Fe in the oxidizing agent.

[45]


The mixtures were molded by an extruder and cylindrical molded bodies (diameter: 4 mm, length: 700 mm) were obtained.

The molded bodies were baked in the tunnel furnace to produce carbon rods. The atmosphere was a non-oxidizing atmosphere, the baking temperature was 1,000°C, and the baking time was 48 hours. At this time, the binder caused dehydrogenation reaction by the oxidizing agent and cross-linking of the binder advanced. Since volatile components vaporized from the molded bodies during the baking, the weight of the carbon rods were about 90% of the weight of the molded bodies. The volatile components were low-molecular components included in tar or pitch. The density of the carbon rods was 1.72 g/cm3.

[47]
The carbon rods were cut into a length of 50 mm. The carbon rods were immersed in a 120˚C liquid paraffin wax (manufactured by Taiwan Wax Company) for two hours. The paraffin wax included in the carbon rods was solidified in a room temperature environment. The surface of the carbon rods including the paraffin wax was polished to produce cylindrical current collectors (diameter: 4 mm, length: 47.2 mm) . The content of paraffin in the current collectors was about 5 parts by weight per 100 parts by weight of the carbon rods.

Fe contents in the current collectors are shown in Table 3.

[48]

[49]

[Evaluation of current collector]

(a) Measurement of electric resistance

A pair of terminals of a voltmeter was attached to predetermined portions of a current collector with a predetermined distance L from each other along the length direction of the current collector. The diameter D of the current collector was 4 mm and the distance L was 30 mm. A power source for supplying electric current to the current
collector was prepared, and a pair of terminals thereof was attached to both ends of the current collector. An ammeter for measuring the electric current supplied from the power source was attached between the current collector and the power source. Electric current I (1.0 A) was passed through in the current collector, and voltage E at that time was measured.

By using electric current I, voltage E, diameter D of the current collector, and distance L between the pair of terminals of the voltmeter, electric resistance R was determined by the following formula(1).

R = (nD2/4) x (E/LI) (1) [0050] (2) Measurement of bending strength
The current collector was disposed such that the length direction of the current collector was horizontal, and the current collector was supported with a pair of fulcrums. The pair of fulcrums was placed symmetrically with a predetermined distance L from each other along the length direction of the current collector. A load was applied from the opposite side (upper side) of the pair of fulcrums, and load W with which the current collector was broken was determined.

By using diameter D of the current collector, distance L between the pair of fulcrums, and load W, bending strength F was determined by the following formula (2).

,
Distance L was set to 30 ram:
F = (8L/nD3) x W (2)

[51]
The current collectors of Examples 1 to 6 had a lower electric resistance and a higher bending strength than the current collector of Comparative Example 1.

[52]

<>

Mixtures were obtained by adding powdered Bi203 (manufactured by Kanto Chemical Co., Inc, superfine quality) to 100 parts by weight of the sum of the carbonaceous materials and the binders in the ratios as shown in Table 4.
Fe contents in the mixtures are shown in Table 4. Fe in the mixtures of Table 4 is Fe included as impurities in the materials of Table 1.

[53]

[54]
By using the above mixtures, current collectors were produced in the same manner as in Example 1. Bi contents and Fe contents in the current collectors are shown in Table 5.


[56]
The current collectors of Examples 7 to 10 were evaluated in the same manner as above. The results are shown in Table 5.

The current collectors of Examples 7 to 10 had a lower electric resistance and a higher bending strength than the current collector of Comparative Example 1.

[57]

<>

Mixtures were obtained by adding powdered V205 (manufactured by Kanto Chemical Co., Inc, superfine quality) in the ratios as shown in Table 6 to 100 parts by weight of the sum of the carbonaceous materials and the binders.

Fe contents in the mixtures are shown in Table 6. Fe in the mixtures of Table 6 is Fe included as impurities in the materials of Table 1.

[58]


[59]
By using the above mixtures, the current collectors were produced in the same manner as in Example 1. V contents and Fe contents in the current collectors are shown in Table 7.

[60]

[Table 7]

[61]
The current collectors of Examples 11 to 14 were evaluated in the same manner as above. The results are shown in Table 7. The current collectors of Examples 11 to 14 had a lower electric resistance and a higher bending strength than the current collector of Comparative Example 1.

[62] <>

Mixtures were obtained by adding powdered Cu20(manufactured by Kanto Chemical Co., Inc, superfine quality) in the ratios as shown in Table 8 to 100 parts by weight of the sum of the carbonaceous materials and the binders.

Fe contents in the mixtures are shown in Table 8. Fe in the mixtures of Table 8 is Fe included as impurities in the materials of Table .

[63]

[Table 8]

By using the above mixtures, current collectors were produced in the same manner as in Example 1. Cu contents and Fe contents in the current collectors are shown in Table 9.

[65]

[Table 9]

[66]
The current collectors of Examples 15 to 18 wereevaluated by the same method as above. The results are shown in Table 9. The current collectors of Examples 15 to 18 had a lower electric resistance and a higher bending strength than the current collector of Comparative Example 1.

[67]

<>

Mixtures were obtained by adding powdered NiO
(manufactured by Kanto Chemical Co., Inc, superfine quality) in the ratios as shown in Table 10 to 100 parts by weight of the sum of the carbonaceous materials and the binders.

Fe contents in the mixtures are shown in Table 10. Fe in the mixtures of Table 10 is Fe included as impurities in the materials of Table 1.

[68]

By using the above mixtures, current collectors were produced in the same manner as in Example 1. Ni contents and Fe contents in the current collectors are shown in Table 11.

[70]


The current collectors of Examples 19 to 22 were evaluated by the same method as above. The results are shown in Table 11. The current collectors of Examples 19 to 22 had a lower electric resistance and a higher bending strength than the current collector of Comparative Example 1.

[72]

<>
Mixtures were obtained by adding powdered Co304 (manufactured by Kanto Chemical Co., Inc, superfine quality) in the ratios as shown in Table 12 to 100 parts, by weight of the sum of the carbonaceous materials and the binders.
Fe contents in the mixtures are shown in Table 12. Fe in the mixtures of Table 12 is Fe included as impurities in the materials of Table 1.

[73]


[74]
By using the above mixtures, current collectors were produced in the same manner as in Example 1. V contents and Fe contents in the current collectors are shown in Table 13.

[75]

[76]
The current collectors of Examples 23 to 26 were evaluated by the same method as above. The results are shown in Table 13. The current collectors of Examples 23 to 26 had a lower electric resistance and a higher bending strength than the current collector of Comparative Example 1.

[77] [Evaluation of battery]

The AA size manganese dry battery (R6) as shown in

Fig. 1 was produced through the following procedures.

The positive electrode material mixture 1 having a cylindrical shape was housed in the negative electrode can 4 having a cylindrical shape with a bottom composed of a zinc alloy including 0.4% by weight of lead. The separator 3 was disposed between the positive electrode material mixture 1 and the negative electrode can 4. As the separator 3, Kraft paper on which a paste material prepared by dissolving a binder mainly composed of a cross-linking starch and polyvinyl acetate in an alcohol-based solvent was applied and dried was used. Then, the separator 3 was disposed such that the face onto which the paste material was applied faced the negative electrode can 4.
Next, the guard paper 9 having a circular shape with an opening portion was arranged on top of the positive electrode material mixture 1. Subsequently, the current collector 2 was disposed in the hollow portion of the positive electrode material mixture 1. As the positive electrode material mixture 1, a mixture of manganese dioxide, acetylene black, and an electrolyte mixed in a weight ratio of 45:10:45 was used. As the electrolyte, an aqueous solution-including 30% by weight of zinc chloride was used.

[78]
The gasket 5 composed of a polyolefin-based resin and having a hole in the center was prepared. The positive electrode current collector 2 was fitted in the hole in the
center. When the positive electrode current collector 2 was fitted in the hole of the gasket 5, polybutene was disposed as a sealing agent in the fitting portion of the gasket 5 with the positive electrode current collector 2.

The cap-shaped positive electrode terminal 11 composed of a tin plate having a protruding portion in the center and a flat brim portion on the periphery thereof was prepared. The upper portion of the positive electrode current collector 2 was fitted in the recess portion in the center of the positive electrode terminal 11, and the insulating ring 12 made of resin was arranged on the flat brim portion of the positive electrode terminal 11. The bottom paper 13 was disposed between the bottom portion of the positive electrode material mixture 1 and the negative electrode can 4 so as to ensure insulation state therebetween. The seal ring 7 was arranged on the outer surface side of the flat peripheral portion of the negative electrode terminal 6.

[79]
The resin tube 8 composed of a heat-shrinkable resin film for ensuring insulation was arranged on the circumference of the negative electrode can 4, and the resin tube 8 was heat-shrunk such that the upper end portion thereof covered peripheral upper surface of the gasket 5 and the lower end portion thereof covered the lower surface of the seal ring 7. The metal jacket 10 composed of a cylindrical tin plate was disposed on the outside of the resin tube 8, the lower endportion of the metal jacket 10 was bent inward, the upper end portion thereof was curled inward, and the tip of the upper end portion thereof was caulked to the insulating ring 12.

[80]
At the time of above battery production, by using the current collectors of Examples 1 to 26 and Comparative Example 1, batteries Al to A26 of Examples 1 to 26 and battery Bl of Comparative Example 1 were produced.

For evaluating the strong discharge characteristics, with each battery, a step of discharging at 1.8 Q for 15 seconds and resting for 45 seconds was repeated until the discharge voltage reached 0.9V. At this time, the number of repetition (cycles) was determined. The results are shown in Tables 14 to 18.

[81] Table 14

[82] Table 15

[83] Table 16

[84] Table 17

[85] Table 18

[86]
As a result, as shown in Table 14, the batteries Al to A10 of Examples 1 to 10 had more cycles than the battery Bl of Comparative Example 1. Batteries A4 to A6 and A8 to A10 of Examples 4 to 6 and 8 to 10 had about 180 cycles or more, and had excellent strong discharge characteristics. In particular, batteries A6 and A10 of Examples 6 and 10 had about 190 cycles, exhibiting greatly improved strong discharge characteristics.

[87]
As shown in Tables 15 to 18, batteries All to A26 of Examples 11 to 26 had more cycles than battery Bl of Comparative Example 1. Batteries A12 to A14, A16 to A18, A20 to A22, and A24 to A26 of Examples 13 to 14, 16 to 18, 20 to 22, and 24 to 26 had about 180 cycles or more, exhibiting excellent strong discharge characteristics. In particular, batteries A14, A17, A18, A21, A22, A25, and A26 of Examples 14, 17, 18, 21, 22, 25, and 26 had about 190 cycles or more, exhibiting greatly improved strong discharge characteristics. Among these batteries, battery A18 of Example 18 had the best strong discharge characteristics.

[88]
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.

[Industrial Applicability]

[89]
The manganese dry battery of the present invention is used suitably as a power source for electronic devices such as portable apparatus.

CLAIMS

[Claim 1]

A current collector comprising a carbon rod and a paraffin wax impregnated into said carbon rod,

wherein said carbon rod includes at least one element A selected from the group consisting of Fe, Cu, Ni, Co, Bi, and V, and

a content of said element A in said current collector is 0.1 to 4.0% by weight.

[Claim 2]

The current collector in accordance with claim 1, wherein said element A is at least one selected from the group consisting of Fe and Bi.

[Claim 3]

The current collector in accordance with claim 1, wherein said element A includes at least Fe, and an Fe content in said current collector is 0.1 to2.8% by weight.

[Claim 4]

The current collector in accordance with claim 1, wherein said element A includes at least Bi, and a Bi content in said current collector is 0.1 to3.6% by weight.

[Claim 5]

The current collector in accordance with claim 1, wherein said element A includes at least Bi and Fe, the Bi. content in said current collector is 0.1 to3.6% by weight, and
the Fe content in said current collector is 0.05% byweight or less.

[Claim 6]

The current collector in accordance with claim 1, wherein an electric resistance of said currentcollector is 2.4 m cm or less.

[Claim 7]

A manganese dry battery comprising:

a positive electrode material mixture having a hollow cylindrical shape and including manganese dioxide;

a negative electrode can including zinc;

a separator between said positive electrode material mixture and said negative electrode can;

a positive electrode current collector inserted in a hollow portion of said positive electrode material mixture; and

an electrolyte,

wherein said positive electrode; current collector is the current collector in accordance with claim 1.

[Claim 8]

A method of producing a current collector comprising the steps of:

(1) forming a mixture comprising a carbonaceous material, a binder, and an oxidizing agent facilitating dehydrogenation reaction of said binder;

(2) compressing said mixture into a rod shape to obtain a molded body;

(3) baking said molded body to obtain a carbon rod; and

(4) impregnating said carbon rod with a paraffin wax to obtain a current collector,

wherein said oxidizing agent includes at least one element A selected from the group consisting of Fe, Cu, Ni, Co, Bi, and V, and

a content of said element A in said mixture is 0.1 to 3.5% by weight.

[Claim 9]

The method of producing a current collector in accordance with claim 8, wherein said carbonaceous material includes artificial graphite and at least one of carbon black and coke.

[Claim 10]

The method of producing a current collector in accordance with claim 8, wherein said oxidizing agent is at least one compound selected from the group consisting of Fe203, Cu20, NiO, C03O4, Bi203/ and V205.

[Claim 11]
The method of producing a current collector in accordance with claim 8, wherein said binder includes at least one of tar and pitch.