It is to be noted, however, that the positive electrode is not limited to those produced by the above-described methods, and may be produced by other methods.

When the positive electrode is a molded body of a positive electrode mixture, the thickness thereof is preferably 0.15 to 4 mm. On the other hand, when the positive electrode is formed of a positive electrode mixture layer and a current collector, the thickness of the positive electrode mixture layer (the thickness thereof per one surface of the current collector) is preferably 30 to 300 μm.

When a current collector is used for the positive electrode, the current collector may be made of, for example, a stainless steel such as SUS316, SUS430, or SUS444, aluminum, or an aluminum alloy. The current collector may be in the form of, for example, a plain-woven wire mesh, an expanded metal, a lath mesh, a perforated metal sheet, a metal foam, or a foil (plate). The thickness of the current collector is preferably 0.05 to 0.2 mm, for example. Itis also desirable to apply a conductive material in the form of a paste, such as a carbon paste or as silver paste, to a surface of the current collector.

Alkaline Battery

The alkaline battery of the present invention includes, as power generation components, a positive electrode containing silver oxide as a positive electrode active material, a negative electrode, a separator, and an alkaline electrolyte solution. The alkaline battery of the present invention encompasses a primary battery and a secondary battery.

As the above-described positive electrode, the positive electrode for alkaline batteries according to the present invention can be used.

The negative electrode of the alkaline battery uses, as an active material, zinc particles, i.e., particles made of pure zinc (containing unavoidable impurities) or a zinc alloy, or a zinc foil, for example. Examples of an alloy component in zinc alloy particles include indium, bismuth, and aluminum (the remainder is composed of zinc and unavoidable impurities). The zinc particles contained in the negative electrode may consist of one type of particles with a single composition, or may contain two or more types of particles with different compositions.

It should be noted that it is preferable to use zinc particles that do not contain mercury as an alloy component. Use of such zinc particles in batteries can reduce environmental pollution caused when discarding the batteries. Also, it is preferable to use zinc particles that do not contain lead as an alloy component for the same reason as described for mercury.

The particle size of zine particles may be as follows, for example: the proportion of particles with a particle diameter of 75 μm or less in all particles is preferably 50 mass % or less and more preferably 30 mass % or less; or the proportion of particles with a particle diameter of 100 μm to 200 μm in all particles is preferably 50 mass % or mare and more preferably 90 mass % or more. The “particle size” of zinc particles as used here is a value obtained by the same measurement method as the above-described method for measuring the average particle diameter of silver oxide.

In addition to the above-described zinc particles, the negative electrode may further contain, for example, a gelling agent (such as sodium polyacrylate or carboxymethyl cellulose) when necessary. This may be mixed with an alkaline electrolyte solution to form a negative electrode agent (gel-like negative electrode). The amount of the gelling agent in the negative electrode is preferably 0.5 to 1.5 mass %, for example.

The negative electrode may be a non-gel negative electrode that is substantially free of the above-described gelling agent (Anon-gel negative electrode may contain a gelling agent as long as the viscosity of an alkaline electrolyte solution present in the vicinity of zine particles does not increase. Thus, the phrase “substantially free of a gelling agent” means that the gelling agent may be contained to the extent that it does not affect the viscosity of the alkaline electrolyte solution.). In the case of a gel-like negative electrode, an alkaline electrolyte solution is present together with a gelling agent in the vicinity of zinc particles. However, the viscosity of the alkaline electrolyte solution increases owing to the action of the gelling agent. This hinders the movement of the alkaline electrolyte solution, which, in turn, hinders the movement of ions in the electrolyte. It is considered that this reduces the reaction rate in the negative electrode, thereby hindering the improvement in load characteristics (in particular, heavy load characteristics) of the battery. To address this problem, by using a non-gel negative electrode, an increase in the viscosity of an alkaline electrolyte solution present in the vicinity of zinc particles is not caused and the moving speed of ions in the alkaline electrolyte solution can be kept high. As a result, the reaction rate in the negative electrode can be increased, whereby the load characteristics (in particular, heavy load characteristics) can be further improved.

The alkaline electrolyte solution contained in the negative electrode may be the same as an alkaline electrolyte solution to be injected into the battery.

The content of the zinc particles in the negative electrode is, for example, preferably 60 mass % or more and more preferably 65 mass % or more, and also, preferably 75 mass % or less and more preferably 70 mass % or less.

The negative electrode preferably contains an indium compound. When the negative electrode contains an indium compound, the generation of gas due to a corrosion reaction between the zinc particles and the alkaline electrolyte can be prevented more effectively.

The above-described indium compound may be, for example, indium oxide or indium hydroxide.

The amount of the indium compound used in the negative electrode is preferably 0.003 to 1 with respect to 100 of the zinc particles in terms of mass ratio.

When tellurium or a compound thereof is contained in the negative electrode, the content thereof is preferably adjusted such that the amount of tellurium (Te) element is 0.4 parts by mass or more, more preferably 1 part by mass or more, and particularly preferably 2 parts by mass or more with respect to 100 parts by mass of the total amount of silver (Ag) element in the silver oxide as the positive electrode active material, from the viewpoint of more favorably ensuring the above-described effects brought about by using it. However, if the amount of this additive in the negative electrode is too large, the amount of zinc particles or a zinc foil as the negative electrode active material is reduced, which may result in reduced capacity and deteriorated load characteristics of the battery. Accordingly, the content of the additive in the negative electrode is preferably adjusted such that the amount of tellurium(Te) element is 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 4 parts by mass or less with respect to 100 parts by mass of the total amount of silver (Ag) element in the silver oxide.

A suitable alkaline electrolyte solution to be used in the alkaline battery is an aqueous solution containing one or more alkali metal hydroxides (such as sodium hydroxide, potassium hydroxide, and lithium hydroxide). Of these metal hydroxides, potassium hydroxide is particularly preferable. When the alkaline electrolyte solution is, for example, an aqueous solution of potassium hydroxide, the concentration of the alkaline electrolyte solution is such that the amount of the potassium hydroxide is preferably 20 mass % or more and more preferably 30 mass % or more and is preferably 40 mass % or less and more preferably 38 mass % or less. By adjusting the concentration of the aqueous solution of the potassium hydroxide to such a value, it is possible to provide an alkaline electrolyte solution with excellent conductivity.

When tellurium or a compound thereof is dissolved in the alkaline electrolyte solution, the content of this additive is preferably adjusted such that the amount of tellurium (Te) element is 0.4 parts by mass or more with respect to 100 parts by mass of the total amount of silver (Ag) element in the silver oxide as the positive electrode active material. For example, in order to allow the above-described adjustment to be performed easily the content of the additive in the electrolyte solution is preferably adjusted such that the content of the tellurium (b) element is 0.1 mass % or more, more preferably 1 mass % or more, and particularly preferably 2 mass % or more. However, if the content of the additive in the alkaline electrolyte solution is too high, the viscosity of the electrolyte solution may increase to reduce the ionic conductance, whereby the load characteristics of the battery may be deteriorated. Accordingly, the content of the additive in the alkaline electrolyte solution is preferably adjusted such that the content of tellurium(Te) element is 10 mass % or less, more preferably 8 mass % or less, and particularly preferably 6 mass % or less.

In addition to the above-described components, various known additives may be added to the alkaline electrolyte solution when necessary to the extent that the effects of the present invention are not impaired. For example, zine oxide may be added to prevent corrosion (oxidation) of the zinc particles used in the negative electrode of the alkaline battery. Note here that zine oxide may be added to the negative electrode as well.

When the alkaline battery is a secondary battery, at least one selected from the group consisting of manganese compounds, tin compounds, and indium compounds may be dissolved in the alkaline electrolyte solution.

When an alkaline secondary battery that has a positive electrode containing silver oxide as a positive electrode active material is discharged, silver is generated from the silver oxide in the positive electrode. When this battery is charged, crystals of the silver oxide are formed around the silver. As a result, the reaction area of the positive electrode active material is substantially reduced, thereby inhibiting subsequent cell reactions. However, when these compounds are dissolved in the alkaline electrolyte solution, ions derived from these compounds (manganese ions, tin ions, and indium ions) adsorb onto the positive electrode. As a result, the growth of silver oxide crystals is inhibited, whereby the silver oxide crystals to be formed are made small. This can prevent the occurrence of the problem that the silver oxide crystals formed during charging of the battery inhibit cell reactions, and thus can further improve the charge-discharge cycle characteristics when, for example, the battery is a secondary battery.

Examples of the manganese compound to be dissolved in the alkaline electrolyte solution can include manganese chloride, manganese acetate, manganese sulfide, manganese sulfate, and manganese hydroxide. Examples of the tin compound to be dissolved in the alkaline electrolyte solution can include tin chloride, tin acetate, tin sulfide, tin bromide, tin oxide, tin hydroxide, and tin sulfate. Examples of the indium compound to be dissolved in the alkaline electrolyte solution can include indium hydroxide, indium oxide, indium sulfate, indium sulfide, indium nitrate, indium bromide, and indium chloride.

The concentration of the indium compound, manganese compound, and/or tin compound in the alkaline electrolyte solution (when only one of these compounds is dissolved, the concentration refers to the concentration of this compound, and when two or more f them are dissolved, the concentration refers to the total of the concentrations of these compounds) is, on a mass basis, 50 ppm or more and more preferably 500 ppm or more, and also preferably 10000 ppm or less and more preferably 5000 ppm or less, from the viewpoint of more favorably ensuring the above-described effects.

In the alkaline batter, a separator is interposed between the positive electrode and the negative electrode. Examples of the separator that can be used in the alkaline battery can include nonwoven fabrics mainly made of vinylon and rayon, vinylon-rayon nonwoven fabrics (vinylon-rayon mixed paper), polyamide nonwoven fabrics, polyolefin-rayon nonwoven fabrics, vinylon paper, vinylon-linter pulp paper, and vinylon-mercerized pulp paper. The separator may be a laminate of a microporous polyolefin film (such as a microporous polyethylene film or a microporous polypropylene film) that has been subjected to a hydrophilic treatment, a cellophane film, and a liquid absorbing laver (electrolyte solution retaining layer) such as vinylon-rayon mixed paper. The thickness of the separator is preferably 20 to 500 μm.

When the alkaline battery is a secondary battery, it is preferable to dispose, between the positive electrode and the negative electrode, an anion conductive membrane in which a polymer is used as a matrix and particles of at least one metal compound selected from the group consisting of metal oxides, metal hydroxides, metal carbonates, metal sulfates, metal phosphates, metal borates, and metal silicates are dispersed in the matrix. The anion conductive membrane also functions as a separator.

When tellurium or a compound thereof is contained in the separator, the content thereof is preferably adjusted such that the amount of tellurium Ge) element is 0.4 parts by mass or more, more preferably 1 part by mass or more, and particularly preferably 2 parts by mass or more with respect to 100 parts by mass of the total amount of silver (Ag) element in the silver oxide as the positive electrode active material, from the viewpoint of more favorably ensuring the above-described effects brought about by using it. However, if the amount of this additive in the separator is too large, permeation of ions in the electrolyte solution may be inhibited, thereby deteriorating the load characteristics of the battery. Accordingly, the content of the additive in the separator is preferably adjusted such that the amount of tellurium (Te) element is 10 parts by mass or less, more preferably 5 parts by mass or less, and particularly preferably 4 parts by mass or less with respect to 100 parts by mass of the total amount of silver (Ag) element in the silver oxide.

Furthermore, in the alkaline battery, an additive selected from polyalkylene glycols and calcium compounds is preferably contained in at least one of the negative electrode, the alkaline electrolyte solution, and the separator In this case, polyalkylene glycols and calcium compounds can inhibit the growth of zinc dendrites in the negative electrode, thereby enabling a further improvement in the charge-discharge cycle characteristics of the alkaline battery (when the alkaline battery is a secondary battery) and in the storage characteristics of the alkaline battery.

The polyalkylene glycols are compounds in which alkylene glycols such as ethylene glycol, propylene glycol, and butylene glycol are polymerized or copolymerized. The compounds may have a cross-linked structure, a branched structure, or a structure having a substituted end. As the polyalkylene glycols, compounds with a weight-average molecular weight of approximately 200 or more are preferably used. Although the upper limit of the weight-average molecular weight is not restricted, the compounds are preferably water-soluble in order to obtain the effects of adding the compounds more easily. Typically, those having a weight-average molecular weight of 20000 or less are preferably used, and those having a weight-average molecular weight of 5000 or less are more preferably used.

More specifically, polyethylene glycols in which ethylene glycol is polymerized (such as polyethylene glycol and polyethylene oxide) and polypropylene glycols in which propylene glycol is polymerized (such as polypropylene glycol and polypropylene oxide) are preferably used, and in addition to these compounds, copolymer compounds including an ethylene oxide unit and a propylene oxide unit (such as polyoxyethylene polyoxypropylene glycol) also may be used.

When a polyalkylene glycol is used, itis preferable that 0.01 to 1.5 parts by mass of the polyalkylene glycol is present with respect to 100 parts by mass of zine particles.

The calcium compound may be a compound that reacts with Zn(OH)₄²⁻, which is generated during discharge, to produce a complex compound such as CaZn(OH)₄(examples of the compound include calcium hydroxide, calcium oxide, calcium chloride, and calcium sulfate) or the complex compound itself. Of these compounds, calcium hydroxide and calcium oxide can be used preferably.

When a calcium compound is used, the amount thereof preferably is such that to 40 parts by mass of the calcium compound is present with respect to 100 parts by mass of zinc particles.

When tellurium or a compound thereof is contained in two or more of the power generation components, the amount thereof may be adjusted in such a way that the total of the contents of tellurium element retained in the respective power generation components falls within the above-described range. Further, when a component other than the power generation components, such as, for example, an electrolyte solution absorber to be described below, is housed in the battery together with the power generation components, the total content of tellurium element retained in the components housed in the battery (including the power generation components) falls within the above-described range.

FIG. 1 is a vertical cross-sectional view schematically showing an example of the alkaline battery of the present invention. FIG. 1 shows an alkaline battery 1, which is an example where the present invention is applied to a flat-type battery. In the alkaline battery 1, a sealing plate 3 provided with a negative electrode 5 is fitted into the opening of an outer can 2 in which a positive electrode 4 and a separator 6 are placed, with an annular gasket 7 having an L-shaped cross section interposed between the sealing plate 3 and the outer can 2. As a result, the edge of the opening of the outer can 2 is tightened inward to bring the gasket 7 into contact with the sealing plate 3, whereby the opening of the outer can 2 is sealed to provide a sealed structure inside the battery. That is, the alkaline battery 1 shown in FIG. 1 is configured such that power generation components including the positive electrode 4, the negative electrode 5, and the separator 6 are placed in a space (closed space) of a battery container that is constituted by the outer can 2, the sealing plate 3, and the gasket 7, and in addition, an alkaline electrolyte solution (not shown) is contained in the space. The outer can 2 also serves as a positive electrode terminal, and the sealing plate 3 also serves as a negative electrode terminal.

Moreover, in the alkaline battery 1 shown in FIG. 1, the peripheral edge portion of the positive electrode 4 is placed between the inner bottom surface of the outer can 2 and the bottom surface of the gasket 7.

FIG. 2 is a vertical cross-sectional view schematically showing another example of the alkaline battery of the present invention. An alkaline battery 1 shown in FIG. 2 is an example where a porous electrolyte solution absorber 8 is placed between a positive electrode 4 and the inner bottom surface of an outer can 2. In a flat-type alkaline battery including an outer can and a sealing plate as shown in FIG. 2, when the amount of an electrolyte solution is large, a porous electrolyte solution absorber may be inserted between a positive electrode and the inner bottom surface of the outer can in order to prevent the leakage of the electrolyte solution during the assembly of the battery.

More specifically, since it takes some time for the separator and the positive electrode to absorb an electrolyte solution after the electrolyte solution is injected into the outer can, leakage of the electrolyte solution is likely to occur at the time of sealing when the amount of the electrolyte solution is large. However, by placing the electrolyte solution absorber on the inner bottom surface of the outer can before placing the positive electrode in the outer can in the assembly of the battery, the electrolyte solution absorber absorbs and retains a certain amount of electrolyte solution after the electrolyte solution is injected into the outer can. This can suppress the leakage of the electrolyte solution.

The electrolyte solution absorber may be a porous sheet or the like. Examples of the electrolyte solution absorber include: porous sheets made of resin (also including porous sheets made of paper), such as nonwoven fabrics mainly made of vinylon and rayon, vinylon-rayon nonwoven fabrics (vinylon-rayon mixed paper), polyamide nonwoven fabrics, polyolefin-rayon nonwoven fabrics, vinylon paper, vinylon-linter pulp paper, and vinylon-mercerized pulp paper; and porous carbon sheets made of fibrous carbon (such as carbon paper, carbon cloth, and carbon felt).

The porosity of the electrolyte solution absorber is preferably 40% or more and more preferably 60% or more, because this enhances its function of favorably absorbing and retaining the electrolyte solution. However, if the porosity of the electrolyte solution absorber is too high, the function of retaining the electrolyte solution may be deteriorated. Accordingly, the porosity of the electrolyte solution absorber is preferably 90% or less and more preferably 80% or less.

Further, from the viewpoint of allowing the electrolyte solution absorber to absorb the electrolyte solution quickly, the average pore diameter of the electrolyte solution absorber is preferably 5 μm or more and more preferably 20 μm or more. However, if the pore diameter of the electrolyte solution absorber is too large, the function of retaining the electrolyte solution may be deteriorated. Accordingly, the average pore diameter of the electrolyte solution absorber is preferably 100 μm or less and more preferably 50 μm or less. In the present specification, the average pore diameter of the electrolyte solution absorber refers to a value measured according to a bubble point method specified in JIS K 3832.

Moreover, from the viewpoint of allowing the electrolyte solution absorber to retain a somewhat large amount of electrolyte solution, the thickness of the electrolyte solution absorber is preferably 30 μm or more and more preferably 50 μm or more. However, if the electrolyte solution absorber is too thick, it becomes necessary to reduce the amount of the positive electrode and the amount of the negative electrode in the battery, and this may cause reduction in capacity. Accordingly, the thickness of the electrolyte solution absorber is preferably 150 μm or less and more preferably 100 μm or less.

When the flat-type battery employs an electrolyte solution absorber made f, for example, a conductive material such as a carbon sheet, the positive electrode and the outer can are electrically connected to each other via the electrolyte solution absorber, and thus, the use of the electrolyte solution absorber does not impair current collection from the positive electrode. However, when the flat-type battery employs an insulating electrolyte solution absorber such a resin sheet, a contact portion between the positive electrode and the inner bottom surface of the outer can is small, and thus, current collection from the positive electrode may be insufficient. Accordingly, in the flat-type battery, it is preferable that the positive electrode and the side wall of the outer can are electrically connected to each other. This allows current collection from the positive electrode to be well performed even in the case where an insulating electrolyte solution absorber is used.

Electrical connection between the positive electrode and the side wall of the outer can may be achieved, for example, through direct contact of the side surface of the positive electrode with the side wall of the outer can as shown in FIG. 2, or alternatively, by holding the positive electrode on a metal base and bringing this metal base into contact with the side wall of the outer can.

The alkaline battery of the present invention is not limited to a flat-type battery as shown in FIG. 1, and may be, for example, a tubular-type battery (including a cylindrical battery and a rectangular (rectangular tubular) battery) with a battery case constituted by joining a bottomed tubular outer can and a sealing plate by caulking via a gasket or by welding an outer can and a sealing plate to seal the joint between them.

For the outer can of the alkaline battery nickel-plated iron, stainless steel, or the like can be used, for example.

For the sealing plate of the alkaline battery, nickel-plated iron, stainless steel, or the like can be used, for example. When the zinc particles as the negative electrode active material are in direct contact with the inner surface of the sealing plate, it is preferable to form a metal layer made of copper or a copper alloy such as brass on a surface of the sealing plate on the side to be in contact with the negative electrode. Furthermore, it is more preferable to form a tin layer on the surface of the metal layer. The reason for forming the metal layer made of copper or a copper alloy on the surface of the sealing plate on the side to be in contact with the negative electrode is to prevent corrosion of zin by inhibiting the formation of a local cell with zinc. By further forming a tin layer on the surface of the metal layer, the above-described effect of preventing corrosion can be further enhanced.

The gasket of the alkaline battery may be made of a material such as nylon or polypropylene.

When the alkaline battery is a flat-type alkaline battery, the shape of the battery as viewed in a plan view may be a circular shape or a polygonal shape such as a quadrangular (square or rectangular) shape. When the battery has a polygonal shape, it may have curved corners.

EXAMPLES

In the following, the present invention will be described in detail with reference to examples. It is to be noted, however, that the following examples do not limit the present invention by any means.

Example 1

88 parts by mass of silver(I)oxide (Ag₂O) having an average particle diameter of 1.4 μm and containing 3.7% (on a mass basis) of Bi with respect to the total amount of silver, 3.8 parts by mass of graphite particles (BET specific surface area: 20 m²/g, average particle diameter: 3.7 μm), 1.2 parts by mass of carbon black (acetylene black, BET specific surface area: 68 m²/g; average particle diameter of primary particles: 35 nm), 1 part by mass of TiO₂particles (average particle diameter: 250 nm), 3 parts by mass of tellurium dioxide, and 3 parts by mass of polytetrafluoroethylene (PTFE) were mixed together to prepare a positive electrode mixture.

73 mg of this positive electrode mixture was packed into a mold at a packing density of 5.7 g/cm³and pressure-molded into a disk shape with a diameter of 5.2 mm and a height of 0.6 mm. Thus, a positive electrode mixture molded body was produced. In the positive electrode mixture used to constitute the above-described positive electrode mixture molded body, the amount of tellurium element with respect to 100 parts by mass of Ag in the silver oxide was 3.0 parts by mass. The positive electrode mixture did not contain cadmium. Thus, a positive electrode constituted by the positive electrode mixture molded body and substantially free of cadmium was obtained.

As a negative electrode active material, mercury-free zinc alloy particles that had been widely used in alkaline primary batteries and contained In (500 ppm), Bi (400 ppm), and Al(10 ppm) as additive elements were used. The particle size of the zinc alloy particles was determined by the above-described method. As a result, it was found that the average particle diameter (D₅₀) was 120 μm and the proportion of the particles with a particle diameter of 75 μm or less was 25 mass % or less.

The above-described zinc alloy particles and ZnO were mixed together at a ratio (mass ratio) of 97:3. Thus, a composition for forming a negative electrode (negative electrode composition) was obtained. 18 mg of this composition was weighed out and used to prepare the negative electrode.

An aqueous solution obtained by dissolving potassium hydroxide at a concentration of 35 mass % and then further dissolving zinc oxide at a concentration of 3 mass % was used as the alkaline electrolyte solution.

5 g of an aqueous dispersion of PTFE (solid content: 60 mass %), 2.5 g of an aqueous solution of sodium polyacrylate (concentration: 2 mass %), and 2.5 g of hydrotalcite particles (average particle diameter: 0.4 μm) were kneaded together and then subjected to rolling to form a membrane with a thickness of 100 μm. Then, a circular piece with a diameter of 5.6 mm was punched out of the membrane. Thus, an anion conductive membrane was produced.

Two graft films (thickness: 30 μm) each composed of a graft copolymer obtained through graft copolymerization of acrylic acid with a polyethylene main chain were disposed on both sides of a cellophane film (thickness: 20 μm) to form a multilayer film, and vinylon-rayon mixed paper (thickness: 100 μm) was laminated on this multilayer film. A circular piece with a diameter of 5.6 mm was punched out of the thus-obtained laminate, and the above-described anion conductive membrane was further laminated thereon, thereby obtaining a separator.

The above-described positive electrode (positive electrode mixture molded body), negative electrode (negative electrode composition), alkaline electrolyte solution, and separator were sealed in a battery container constituted by an outer can made of a steel plate and having a gold-plated inner surface, a sealing plate that was a copper-stainless steel (SUS304)-nickel clad plate, and an annular gasket made of nylon 66. Thus, an alkaline secondary battery with a structure shown in FIG. 1 and having a diameter of 5.8 mm and a thickness of 2.7 mm was produced. In the assembly of the battery, part of the alkaline electrolyte solution was added dropwise into the outer can before placing the positive electrode in the outer can, and the remainder was pre-mixed with the negative electrode composition. The separator was disposed with the anion conductive membrane facing the negative electrode.

Example 2

An alkaline secondary battery was prepared in the same manner as in Example 1, except that 90.5 parts by mass of the silver(I) oxide (Ag₂O), 3.8 parts by mass of graphite particles, 1.2 parts by mass of carbon black, 1 part by mass of TiO₂particles, 0.5 parts by mass of tellurium dioxide, and 3 parts by mass of polytetrafluoroethylene (PTFE) were mixed together to prepare a positive electrode mixture. In the positive electrode mixture used to constitute the above-described positive electrode mixture molded body, the amount of tellurium element with respect to 100 parts by mass of Ag in the silver(I) oxide was 0.5 parts by mass.

Example 3

An alkaline secondary battery was prepared in the same manner as in Example 1, except that 89.5 parts by mass of the silver(I) oxide (Ag₂O), 3.8 parts by mas of graphite particles, 1.2 parts by mass of carbon black, 1 part by mass of TiO₂particles, 1.5 parts by mass of tellurium dioxide, and 3 parts by mass of polytetrafluoroethylene (PTFE) were mixed together to prepare a positive electrode mixture. In the positive electrode mixture used to constitute the above-described positive electrode mixture molded body, the amount of tellurium element with respect to 100 parts by mass of Ag in the silver(I) oxide was 1.5 parts by mass.

Comparative Example 1

An alkaline secondary battery was prepared in the same manner as in Example 1, except that 91 parts by mass of the silver(I) oxide (Ag₂O), 3.8 parts by mass of graphite particles, 1.2 parts by mass of carbon black, 1 part by mass of TiO₂particles, and 3 parts by mass of polytetrafluoroethylene (PTFE) were mixed together to prepare a positive electrode mixture.

Measurement of Internal Resistance of Battery

Five batteries were prepared for each of Examples 1 to 3 and Comparative Example 1, and the internal resistances of these batteries at 20° C. were measured according to an alternating current impedance method at a frequency of 1 kHz. The average value of the measured values was determined as the internal resistance of the batteries.

Evaluation of Charge-Discharge Cycle Characteristics

Five batteries were prepared for each of Examples 1 to 3 and Comparative Example 1. Each battery was subjected to repeated charge-discharge cycles with each charge-discharge cycle consisting of constant current discharge in which the battery was discharged with a constant current of 2.1 mA until the voltage reached 1.2 V and constant current-constant voltage charge in which the battery was first charged with a constant current of 2.1 mA until the voltage reached 1.8V and subsequently charged with a constant voltage of 1.8V until the current value reached 0.21 mA. As the discharge capacity of each battery in each cycle, the average value of the measured values for the five batteries was determined. The charge-discharge cycle characteristics were evaluated on the basis of the ratio of the discharge capacity in the 100th cycle to the discharge capacity in the 10th cycle (i.e., the capacity retention).

The results obtained are both shown in Table 1.

TABLE 1

Internal Resistance
Capacity Retention

(mΩ)
(%)

Example 1
19.1
92.2

Example 2
22.7
94.2

Example 3
20.8
95.4

Comparative
24.1
71.4

Example 1

As shown in Table 1, the alkali secondary batteries of Examples 1 to 3 each including the positive electrode containing silver(D oxide and tellurium dioxide (compound of tellurium) exhibited a lower internal resistance, and in addition, exhibited higher capacity retention in the evaluation of charge-discharge cycle characteristics and thus had more excellent charge-discharge cycle characteristics, compared to the battery of Comparative Example 1 including the positive electrode not containing a compound of tellurium.

Example 4

90.3 parts by mass of silver(I) oxide (Ag₂O) having an average particle diameter of 1.4 μm and containing 3.7% (on a mass basis) of Bi with respect to the total amount of silver, 3.8 parts by mass of graphite particles (BET specific surface area: 20 m²/g, average particle diameter: 3.7 μm), 1.9 parts by mass of carbon black (acetylene black, BET specific surface area: 68 m²/g, average particle diameter of primary particles: 35 nm), 1 part by mass of TiO₂particles (average particle diameter: 250 nm), and 3 parts by mass of polytetrafluoroethylene (PTFE) were mixed together to prepare a positive electrode mixture substantially free of cadmium. Then, a positive electrode constituted by a positive electrode mixture molded body was produced in the same manner as in Example 1, except that this positive electrode mixture was used.

An aqueous solution was prepared by dissolving potassium hydroxide at a concentration of 35 mass % and then dissolving zinc oxide at a concentration of 3 mass %. Then, in this aqueous solution, lithium hydroxide at a concentration of 1 mass %, polyethylene glycol at a concentration of 1 mass %, and tellurium dioxide at a concentration of 9.2 mass % to prepare a mixed solution as an alkaline electrolyte solution. The tellurium element content in the above-described electrolyte solution was 7.4 mass %.

An alkaline secondary battery was produced in the same manner as in Example 1, except that the above-described positive electrode (positive electrode mixture molded body) and the above-described alkaline electrolyte solution were used. The total content of tellurium element in power generation components of this alkaline secondary battery was 3.1 parts by mass with respect to 100 parts by mass of the total amount of silver element in the positive electrode active material.

Example 5

An alkaline electrolyte solution was prepared in the same manner as in Example 4, except that sodium hydroxide was used instead of the potassium hydroxide. An alkaline secondary battery was produced in the same manner as in Example 4, except that the thus-prepared alkaline electrolyte solution was used.

Comparative Example 2

An aqueous solution was prepared by dissolving potassium hydroxide at a concentration of 35 mass % and then dissolving zinc oxide at a concentration of 3 mass %. Then, a mixed solution was prepared by further dissolving, in this aqueous solution, lithium hydroxide at a concentration of 1 mass % and polyethylene glycol at a concentration of 1 mass %. An alkaline secondary battery was produced in the same manner as Example 4, except that the thus-prepared mixed solution (aqueous solution not containing tellurium) was used as an alkaline electrolyte solution.

Comparative Example 3

An alkaline electrolyte solution was prepared in the same manner as in Comparative Example 2, except that sodium hydroxide was used instead of the potassium hydroxide. An alkaline secondary battery was produced in the same manner as in Comparative Example 1, except that the thus-prepared alkaline electrolyte solution was used.