zinc battery

Abstract

To provide a zinc battery capable of suppressing self-discharge and maintaining capacity for a long time period.SOLUTION: A battery 2 comprises an outer can 10, and an electrode group 22 accommodated in the outer can 10 together with alkali electrolyte. The electrode group 22 is configured by superposing a positive electrode 24 and a negative electrode 26 via a separator 28. The negative electrode 26 at least contains zinc powder. An average particle diameter of zinc particles configuring the zinc powder is 49 to 71 μm. When the liquid amount of the alkali electrolyte is defined as A, and a theoretical capacity of the negative electrode is defined as B, a ratio A / B of the liquid amount of the alkali electrolyte to the theoretical capacity of the negative electrode is 0.30 to 0.60 mL / Ah.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to zinc batteries. [Background technology]

[0002] Zinc batteries use zinc, zinc alloys, or zinc-containing compounds as the negative electrode active material, and are a type of battery that has long been researched and developed as batteries have become more widespread. Batteries that use zinc or other materials in the negative electrode include primary batteries and secondary batteries (storage batteries). For example, air-zinc batteries use oxygen from the air as the positive electrode active material, nickel-zinc batteries use nickel-containing compounds as the positive electrode active material, manganese-zinc batteries use manganese-containing compounds as the positive electrode active material, silver-zinc batteries use silver-containing compounds as the positive electrode active material, and zinc-ion batteries have been researched and developed. In particular, air-zinc primary batteries, manganese-zinc primary batteries, and silver-zinc primary batteries have been put to practical use and are widely used around the world.

[0003] In recent years, batteries have been used in various devices such as various portable devices and hybrid electric vehicles, and the applications of batteries are expanding. With this expansion of applications, the development and improvement of batteries has become increasingly important in many industries, and there is a demand for the development and improvement of new batteries that are superior, primarily in terms of battery performance and their application as secondary batteries. Under these circumstances, there is a demand for improved performance in zinc batteries. Here, one of the performances that should be improved in zinc batteries is the suppression of self-discharge.

[0004] Currently, various studies are being conducted to suppress the self-discharge of zinc batteries, and attempts are being made to improve the effect of suppressing the self-discharge of zinc batteries (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-133844 Summary of the Invention [Problem to be solved by the invention]

[0006] One mode of self-discharge in zinc batteries is self-discharge due to a local cell reaction at the negative electrode. Specifically, the negative electrode of a zinc battery is formed by supporting a negative electrode mixture containing zinc powder, an aggregate of zinc particles, as the negative electrode active material on a negative electrode substrate. The negative electrode substrate is typically made of a metal different from zinc. Because the negative electrode is housed together with an electrolyte in a battery, the zinc particles come into contact with dissimilar metals in the electrolyte. When zinc particles come into contact with dissimilar metals in the electrolyte, a local cell reaction occurs, causing the zinc to self-dissolve, resulting in a decrease in the charged capacity. Furthermore, other zinc particles in contact with zinc particles in contact with the negative electrode substrate may also undergo a local cell reaction and self-dissolve. Thus, zinc batteries suffer from the problem of self-discharge due to local cell reactions, resulting in a decrease in the charged capacity.

[0007] However, at present, sufficient research results have not been obtained regarding the suppression of self-discharge due to local cell reactions.

[0008] As the applications of batteries continue to expand, further improvements in self-discharge suppression are required. Therefore, it is considered important to suppress self-discharge due to local cell reactions.

[0009] The present invention has been made in light of the above circumstances, and an object of the present invention is to provide a zinc battery that can suppress self-discharge and maintain capacity for a long period of time. [Means for solving the problem]

[0010] According to the present invention, there is provided a zinc battery comprising a container and an electrode group accommodated in the container together with an alkaline electrolyte, the electrode group comprising a positive electrode and a negative electrode stacked together with a separator interposed therebetween, the negative electrode containing at least zinc powder, the zinc particles constituting the zinc powder having an average particle size of 49 μm or more and 71 μm or less, and where A is the volume of the alkaline electrolyte and B is the theoretical capacity of the negative electrode, A / B, which is the ratio of the volume of the alkaline electrolyte to the theoretical capacity of the negative electrode, is 0.30 mL / Ah or more and 0.60 mL / Ah or less. [Effects of the Invention]

[0011] The zinc battery of the present invention includes a container and an electrode group housed in the container together with an alkaline electrolyte. The electrode group comprises a positive electrode and a negative electrode stacked with a separator interposed therebetween. The negative electrode contains at least zinc powder, the zinc particles constituting the zinc powder having an average particle size of 49 μm or more and 71 μm or less. When the volume of the alkaline electrolyte is A and the theoretical capacity of the negative electrode is B, the ratio A / B of the volume of the alkaline electrolyte to the theoretical capacity of the negative electrode is 0.30 mL / Ah or more and 0.60 mL / Ah or less. This configuration allows the zinc battery of the present invention to suppress the occurrence of local battery reactions at the negative electrode and to suppress self-discharge. Therefore, the zinc battery of the present invention can maintain its charged capacity for a long period of time. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a partially cutaway perspective view of a nickel-zinc battery according to one embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0013] A nickel-zinc battery (hereinafter also referred to as battery) 2 according to one embodiment will be described below with reference to the drawings.

[0014] The battery 2 is, for example, a 4 / 3 FA cylindrical battery. Specifically, as shown in FIG. 1 , the battery 2 includes an outer can 10, which serves as a cylindrical container with a bottom and an open top. The outer can 10 is electrically conductive, and its bottom wall 35 functions as a negative electrode terminal. A sealing body 11 is fixed to the opening of the outer can 10. The sealing body 11 includes a lid plate 14 and a positive electrode terminal 20, and seals the outer can 10 while providing the positive electrode terminal 20. The lid plate 14 is a disc-shaped member that is electrically conductive. The lid plate 14 and a ring-shaped insulating gasket 12 that surrounds the lid plate 14 are disposed within the opening of the outer can 10. The insulating gasket 12 is fixed to the opening edge 37 of the outer can 10 by crimping the opening edge 37 of the outer can 10. In other words, the lid plate 14 and the insulating gasket 12 cooperate to hermetically close the opening of the outer can 10.

[0015] The cover plate 14 has a central through-hole 16 in the center, and a rubber valve body 18 that closes the central through-hole 16 is disposed on the outer surface of the cover plate 14. Furthermore, a metallic positive electrode terminal 20 that is cylindrical with a flange and covers the valve body 18 is electrically connected to the outer surface of the cover plate 14. This positive electrode terminal 20 presses the valve body 18 toward the cover plate 14. The positive electrode terminal 20 is provided with a gas vent hole (not shown).

[0016] Under normal circumstances, the central through-hole 16 is airtightly closed by the valve body 18. On the other hand, if gas is generated inside the outer can 10 and the internal pressure increases, the valve body 18 is compressed by the internal pressure and opens the central through-hole 16, causing gas to be released from inside the outer can 10 to the outside through the central through-hole 16 and a gas vent hole (not shown) in the positive terminal 20. In other words, the central through-hole 16, the valve body 18, and the positive terminal 20 form a safety valve for the battery.

[0017] The outer can 10 accommodates an electrode group 22. This electrode group 22 includes a strip-shaped positive electrode 24, a strip-shaped negative electrode 26, and a strip-shaped separator 28. More specifically, the positive electrode 24 and the strip-shaped negative electrode 26 are spirally wound with the separator 28 sandwiched therebetween. That is, the positive electrode 24 and the strip-shaped negative electrode 26 are stacked on top of each other with the separator 28 interposed therebetween. The outermost periphery of the electrode group 22 is formed by a part (outermost periphery) of the negative electrode 26, and is in contact with the inner circumferential wall of the outer can 10. That is, the negative electrode 26 and the outer can 10 are electrically connected to each other.

[0018] A positive electrode lead 30 is disposed within the exterior can 10 between one end of the electrode group 22 and the cover plate 14. More specifically, one end of the positive electrode lead 30 is connected to the positive electrode 24, and the other end is connected to the cover plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected to each other via the positive electrode lead 30 and the cover plate 14. A circular upper insulating member 32 is disposed between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit 39 provided in the upper insulating member 32. A circular lower insulating member 34 is also disposed between the electrode group 22 and the bottom of the exterior can 10.

[0019] Furthermore, a predetermined amount of alkaline electrolyte (not shown) is poured into the outer can 10. The alkaline electrolyte is impregnated into the electrode group 22 and is mainly held in the separator 28. This alkaline electrolyte promotes an electrochemical reaction (charge / discharge reaction) between the positive electrode 24 and the negative electrode 26 during charge / discharge. As this alkaline electrolyte, an aqueous solution containing at least one of KOH, NaOH, and LiOH as a solute is preferably used. The concentration of the alkaline electrolyte is not particularly limited, and an alkaline electrolyte of 7N, for example, is used. Furthermore, since the battery 2 is a nickel-zinc battery, it is preferable to use the alkaline electrolyte described above in which zinc oxide is dissolved to a saturated concentration. This reduces the amount of zinc leaching from the negative electrode into the alkaline electrolyte.

[0020] Examples of materials that can be used for the separator 28 include polyamide fiber nonwoven fabrics to which hydrophilic functional groups have been added, and polyolefin fiber nonwoven fabrics, such as polyethylene and polypropylene, to which hydrophilic functional groups have been added. Specifically, it is preferable to use a nonwoven fabric primarily composed of polyolefin fibers that have been sulfonated to provide sulfonic groups. The sulfonic groups are added by treating the nonwoven fabric with an acid containing sulfonic groups, such as sulfuric acid or fuming sulfuric acid. Batteries using separators containing fibers with such sulfonic groups exhibit excellent self-discharge characteristics. More preferably, a dendrite-resistant separator, for example, a polyolefin microporous membrane to which hydrophilic functional groups have been added, is layered on top of the nonwoven fabric to form a double layer. This can suppress the occurrence of internal short circuits and further enhance short-circuit resistance.

[0021] The positive electrode 24 includes a conductive positive electrode core material having a porous structure and a positive electrode mixture held in the positive electrode core material. The positive electrode core material described above is, for example, a nickel metal body having a three-dimensional mesh-like skeleton. The skeleton of this metal body extends throughout the entire positive electrode core material, and the gaps in this skeleton form interconnecting pores. The interconnecting pores are filled with the positive electrode mixture. For example, nickel foam can be used as such a metal body.

[0022] The positive electrode mixture contains a positive electrode active material, a positive electrode additive, and a binder. The binder functions to bind the positive electrode active material and the positive electrode additive to each other and to bind the positive electrode active material and the positive electrode additive to the positive electrode core material. Examples of the binder include hydrophilic or hydrophobic polymers. It is also preferable to add a thickener as needed. Examples of thickeners include hydroxypropyl cellulose.

[0023] Nickel hydroxide is used as the positive electrode active material. This nickel hydroxide is used in the form of powder. That is, nickel hydroxide powder, which is an aggregate of nickel hydroxide particles, is used. It is preferable to use highly ordered nickel hydroxide particles as the nickel hydroxide particles.

[0024] The nickel hydroxide particles preferably contain Co, Zn, Cd, or the like in solid solution.

[0025] The nickel hydroxide particles are preferably coated with a surface layer containing a cobalt compound, and the surface layer is preferably a high-order cobalt compound layer containing a cobalt compound that has been made trivalent or higher.

[0026] The above-mentioned high-order cobalt compound layer has excellent conductivity and forms a conductive network. As this high-order cobalt compound layer, it is preferable to adopt a layer containing a cobalt compound such as cobalt oxyhydroxide (CoOOH) that has been made higher in order to be trivalent or higher.

[0027] As another method for forming a conductive network, it is preferable to adopt a method of adding a powder of a cobalt compound to the positive electrode mixture instead of forming a surface layer containing a cobalt compound on the surface of nickel hydroxide particles. Examples of this cobalt compound powder include cobalt hydroxide powder. The method of adding a powder of a cobalt compound has the advantage of being able to form a conductive network more easily than the method of forming a surface layer of a cobalt compound on the surface of nickel hydroxide particles.

[0028] Next, examples of the positive electrode additive include yttrium oxide. It is also preferable to use cobalt compounds such as cobalt oxide, metallic cobalt, and cobalt hydroxide, zinc compounds such as metallic zinc, zinc oxide, and zinc hydroxide, and rare earth compounds such as erbium oxide.

[0029] Next, the positive electrode 24 can be produced, for example, as follows. First, a cathode additive, a binder, water, and a thickener are added to the cathode active material powder, which is an aggregate of cathode active material particles obtained as described above, and the mixture is kneaded to prepare a cathode mixture slurry. The obtained cathode mixture slurry is filled into, for example, a nickel foam, and then dried. After the drying process, the nickel foam filled with nickel hydroxide particles and the like is rolled and then cut. This results in a cathode 24 containing the cathode mixture.

[0030] Next, the negative electrode 26 will be described. The negative electrode 26 has a strip-shaped conductive negative electrode substrate, and a negative electrode mixture is held on this negative electrode substrate.

[0031] The negative electrode substrate includes a strip-shaped metal core and a thin tin film covering the core. The core is made of a metal material having a large number of through holes, such as foamed copper, punched copper metal, or expanded copper metal. The thin tin film can be a tin-plated film or a tin-evaporated film.

[0032] The negative electrode mixture is not only filled into the through-holes of the negative electrode substrate, but also held in layers on both sides of the negative electrode substrate. This negative electrode mixture contains a negative electrode active material and a binder, and may also contain a negative electrode additive and a thickener as needed.

[0033] The negative electrode active material contains at least zinc and may further contain at least one of a zinc alloy and a zinc-containing compound. Here, in addition to zinc, bismuth, aluminum, indium, etc. are preferably used as raw materials for the zinc alloy. Examples of zinc-containing compounds include zinc oxide (type 1 / type 2 / type 3), zinc hydroxide, zinc sulfide, tetrahydroxyzinc ion salts, zinc halides, zinc carboxylate compounds such as zinc acetate, zinc tartrate, and zinc oxalate, magnesium zincate, calcium zincate, barium zincate, zinc borate, zinc silicate, zinc aluminate, zinc fluoride, zinc carbonate, zinc bicarbonate, zinc nitrate, and zinc sulfate.

[0034] The negative electrode active material is in the form of powder. That is, a negative electrode active material powder that is an aggregate of negative electrode active material particles is used. The particle diameter of zinc particles as the negative electrode active material is 49 μm or more and 71 μm or less.

[0035] The zinc alloy particles preferably have an average particle size of 10 to 1000 μm, and the zinc-containing compound particles preferably have an average particle size of 0.1 to 100 μm. In this specification, the average particle size means the average particle size corresponding to 50% of the total mass, and is determined by a laser diffraction / scattering method using a particle size distribution analyzer.

[0036] The binder functions to bind the negative electrode active material, negative electrode additive, etc. to each other and also to bind the negative electrode active material, negative electrode additive, etc. to the negative electrode substrate. Synthetic rubber is used as the binder. In particular, styrene butadiene rubber (SBR) has a high binding effect, so it is preferable to use SBR as the binder.

[0037] The negative electrode additive functions to improve the characteristics of the negative electrode, and examples of the negative electrode additive include bismuth oxide, bismuth hydroxide, indium oxide, indium hydroxide, potassium oxalate, and hydrates thereof.

[0038] The thickener is not particularly limited, and for example, hydroxypropyl cellulose is used.

[0039] Next, the negative electrode 26 can be produced, for example, as follows. First, a negative electrode mixture paste is prepared by kneading a negative electrode active material powder, which is an aggregate of particles of a negative electrode active material (e.g., zinc), a negative electrode additive, a binder, and water. The resulting negative electrode mixture paste is applied to a negative electrode substrate and then dried. After drying, the negative electrode substrate, which retains the negative electrode active material powder and binder, is entirely rolled to increase the packing density of the negative electrode active material, thereby obtaining a negative electrode intermediate product. This negative electrode intermediate product is then cut into a predetermined shape. This results in the production of a negative electrode 26.

[0040] The positive electrode 24 and negative electrode 26 manufactured as described above are spirally wound with a separator 28 interposed therebetween, thereby forming the electrode group 22.

[0041] The electrode group 22 thus obtained is housed in an outer can 10. Next, a predetermined amount of alkaline electrolyte is poured into the outer can 10.

[0042] Here, when the volume of alkaline electrolyte is A and the theoretical capacity of the negative electrode is B, a predetermined amount of alkaline electrolyte is poured into outer can 10 so that the ratio A / B of the volume of alkaline electrolyte to the theoretical capacity of the negative electrode is 0.30 mL / Ah or more and 0.60 mL / Ah or less. The theoretical capacity of the negative electrode mentioned above refers to the discharge capacity calculated from the amount of all active materials contained in the negative electrode.

[0043] Thereafter, the outer can 10 containing the electrode group 22 and the alkaline electrolyte is sealed with a sealing member 11 equipped with a positive electrode terminal 20, to obtain a battery 2. The obtained battery 2 is subjected to an initial activation process and is made ready for use.

[0044] [Example] 1. Battery manufacturing Example 1 (1) Manufacturing of the positive electrode To 100 parts by weight of nickel hydroxide powder prepared as the positive electrode active material, 25 parts by weight of cobalt hydroxide powder, 0.5 parts by weight of yttrium oxide powder, 0.5 parts by weight of zinc oxide powder, 0.3 parts by weight of niobium oxide powder, 0.2 parts by weight of a hydrophilic polymer as a binder, and 50.0 parts by weight of water containing 0.2% by weight of hydroxypropyl cellulose powder as a thickener were added and kneaded to prepare a positive electrode mixture slurry.

[0045] Next, the slurry of the positive electrode mixture was filled into a sheet-shaped foamed nickel serving as a positive electrode core material. The foamed nickel had an areal density (weight per unit area) of about 350 g / m 2 The porosity was 95% and the thickness was 1.3 mm.

[0046] Next, the foamed nickel filled with the positive electrode mixture slurry was subjected to a drying treatment. After that, the entire foamed nickel filled with the positive electrode mixture was rolled and cut to a predetermined size to obtain a positive electrode 24 for 4 / 3FA size. The positive electrode capacity of the positive electrode 24 was 2500 mAh.

[0047] (2) Manufacturing of the negative electrode 100 parts by weight of zinc oxide powder, 25 parts by weight of zinc powder, 4 parts by weight of styrene-butadiene rubber powder as a binder, 1 part by weight of hydroxypropyl cellulose powder, and 100 parts by weight of water were prepared. The zinc oxide powder, zinc powder, styrene-butadiene rubber powder, hydroxypropyl cellulose powder, and water were then kneaded in an environment of 25°C to prepare a negative electrode mixture paste.

[0048] Here, the zinc oxide particles constituting the zinc oxide powder had an average particle size of 0.75 μm, and the zinc particles constituting the zinc powder had an average particle size of 71 μm.

[0049] On the other hand, a negative electrode substrate was produced as follows. First, a copper punched metal was prepared as the core of the negative electrode substrate. This copper punched metal had a thickness of 60 μm and was perforated with a large number of round holes with a diameter of 1.5 mm in a staggered pattern. Next, this copper punched metal was electroplated with tin by a conventional method. At this time, the thickness of the tin plating film was set to 5.0 μm. In this way, a negative electrode substrate consisting of a copper punched metal having a tin plating film was obtained.

[0050] The negative electrode mixture paste obtained as described above was applied evenly to both sides of the negative electrode substrate so as to have a uniform thickness.

[0051] After the negative electrode mixture paste was dried, the negative electrode substrate holding the negative electrode mixture was rolled and then cut to a predetermined size to obtain a 4 / 3FA size negative electrode 26. At this time, the weight of zinc oxide in the negative electrode mixture of the negative electrode 26 was 6.54 g, and the weight of zinc was 1.64 g.

[0052] In the negative electrode of a nickel-zinc battery, the active material zinc undergoes a charge-discharge reaction involving a two-electron reaction as follows: Discharge: Zn+2OH - →ZnO+H2O+2e - Charging: Zn+2OH - ←ZnO+H2O+2e - The theoretical capacity per weight of each of zinc (Zn) and zinc oxide (ZnO) contained as active materials in the negative electrode composite of the negative electrode 26 can be calculated as follows, assuming that the atomic weight of zinc is 65.4, the atomic weight of oxygen is 16.0, and the Faraday constant F=96,500 C / mol.

[0053]

number

[0054]

number

[0055] Therefore, the theoretical capacity of the negative electrode 26 is the sum of the theoretical capacities of the active materials zinc (Zn) and zinc oxide (ZnO), and can be calculated as follows. Theoretical capacity of negative electrode = 820 x 1.64 + 659 x 6.54 = 5655 [mAh]

[0056] (3) Nickel-zinc battery assembly The positive electrode 24 and negative electrode 26 obtained as described above were spirally wound with a separator 28 sandwiched between them to produce an electrode group 22. The separator 28 used in producing the electrode group 22 here had a double structure in which a dendrite-resistant separator made of a microporous membrane made of hydrophilized polypropylene was layered on a base fabric of sulfonated polyolefin fiber nonwoven fabric, and its thickness was 0.16 mm (basis weight 74 g / m 2 ) was.

[0057] On the other hand, an alkaline electrolyte solution was prepared, which was an aqueous solution containing an alkali metal hydroxide as a solute and saturated with zinc oxide. This alkaline electrolyte contained 30 wt % potassium hydroxide as the alkali metal hydroxide.

[0058] Next, the electrode group 22 was placed in a cylindrical outer can 10 with a bottom, and 3.41 mL of the prepared alkaline electrolyte was poured into the can 10. Thereafter, the opening of the outer can 10 was sealed with a sealing member 11, and a 4 / 3FA size battery 2 with a nominal capacity of 2000 mAh was assembled.

[0059] Here, in the obtained battery 2, when the volume of alkaline electrolyte is A and the theoretical capacity of the negative electrode is B, the ratio A / B of the volume of alkaline electrolyte to the theoretical capacity of the negative electrode was A / B = 3.41 / 5.655 = 0.60 mL / Ah.

[0060] (4) Initial activation process The obtained battery 2 was subjected to one charge-discharge cycle in an environment at a temperature of 25°C, in which it was charged to 100% of its nominal capacity at a charge current of 0.1 It, and then discharged at a discharge current of 0.2 It until the battery voltage reached 1.3 V. This initial activation process allowed the battery 2 to be ready for use.

[0061] Example 2 A nickel-zinc battery was produced in the same manner as in Example 1, except that in the production of the negative electrode, the average particle size of the zinc particles constituting the zinc powder was set to 49 μm.

[0062] (Comparative Example 1) A nickel-zinc battery was manufactured in the same manner as in Example 1, except that in the production of the negative electrode, the average particle size of the zinc particles constituting the zinc powder was set to 85 μm, and in the assembly of the nickel-zinc battery, the amount of alkaline electrolyte injected was set to 4.83 mL. Here, A / B, which is the ratio of the amount of alkaline electrolyte to the theoretical capacity of the negative electrode, was A / B = 4.83 / 5.655 = 0.85 mL / Ah.

[0063] (Comparative Example 2) A nickel-zinc battery was produced in the same manner as in Example 1, except that in the production of the negative electrode, the average particle size of the zinc particles constituting the zinc powder was set to 85 μm.

[0064] (Comparative Example 3) A nickel-zinc battery was manufactured in the same manner as in Example 1, except that the amount of alkaline electrolyte injected was 4.83 mL in the assembly of the nickel-zinc battery. Here, A / B, which is the ratio of the amount of alkaline electrolyte to the theoretical capacity of the negative electrode, was A / B = 4.83 / 5.655 = 0.85 mL / Ah.

[0065] Comparative Example 4 A nickel-zinc battery was manufactured in the same manner as in Example 1, except that in the production of the negative electrode, the average particle size of the particles constituting the zinc powder was set to 49 μm, and in the assembly of the nickel-zinc battery, the amount of alkaline electrolyte injected was set to 4.83 mL. Here, A / B, which is the ratio of the amount of alkaline electrolyte to the theoretical capacity of the negative electrode, was A / B = 4.83 / 5.655 = 0.85 mL / Ah.

[0066] (Comparative Example 5) A nickel-zinc battery was manufactured in the same manner as in Example 1, except that in the manufacture of the negative electrode, an equal amount of polytetrafluoroethylene (PTFE) was used instead of SBR to prepare a negative electrode mixture paste. However, in the case of Comparative Example 5, the amount of negative electrode active material falling off from the negative electrode substrate increased, and sufficient battery capacity could not be obtained.

[0067] 2. Evaluation of nickel-zinc batteries (1) Self-discharge evaluation The batteries of Examples 1 and 2 and Comparative Examples 1 to 4 that had undergone the initial activation treatment were subjected to three charge-discharge cycles in an environment of 25°C, in which the batteries were charged to 100% of their nominal capacity at a charge current of 0.1 It, and then discharged at a discharge current of 0.2 It until the battery voltage reached 1.3 V. The discharge capacity at the third discharge was determined. This discharge capacity was designated as the initial capacity C.

[0068] Next, after determining the initial capacity C, the battery was charged to 100% of its nominal capacity at a charging current of 0.1 It in an environment of 25°C, and then left at an environment of 35°C for one month. After leaving the battery for one month, it was again placed in a room temperature environment of 25°C and discharged at a discharge current of 0.2 It until the battery voltage reached 1.3 V, and the discharge capacity at this time was determined. This discharge capacity was defined as the remaining capacity D.

[0069] The residual rate R was calculated using the following formula (I). The results are shown in Table 1. R [%] = (D / C) × 100 (I) Here, the larger the value of the remaining rate R, the more capacity remains in the battery and the more self-discharge is suppressed.

[0070] [Table 1]

[0071] (2) Consideration Comparative Example 1 and Comparative Example 2 differ in A / B, which is the ratio of the volume of alkaline electrolyte to the theoretical capacity of the negative electrode, and the value of A / B is lower in Comparative Example 2 than in Comparative Example 1. The survival rate R of Comparative Example 2 is improved by 1.8% compared to the survival rate R of Comparative Example 1. In other words, the lower the value of A / B, the higher the survival rate R.

[0072] Comparative Examples 1, 3, and 4 differ in the average particle size of the zinc particles, and Comparative Example 3, which has a smaller average particle size than Comparative Example 1, has a residual rate R that is 2.0% higher than Comparative Example 1, and Comparative Example 4, which has an average particle size even smaller than Comparative Example 3, has a residual rate R that is 3.1% higher than Comparative Example 1. In other words, the smaller the average particle size of the zinc particles, which are the negative electrode active material, the higher the residual rate R.

[0073] Example 1 is an embodiment in which the A / B value is smaller and the average particle size of the zinc particles is smaller than that of Comparative Example 1. The residual rate R of Example 1 is improved by 7.6% compared to that of Comparative Example 1. Example 1 is an embodiment in which the conditions of Comparative Examples 2 and 3 are combined, and the residual rate R of Example 1 is significantly improved by 3.8% (1.8% for Comparative Example 2 + 2.0% for Comparative Example 3), which is the total increase in residual rate R of Comparative Examples 2 and 3 over Comparative Example 1.

[0074] Example 2 is an embodiment in which the A / B value is smaller and the average particle size of the zinc particles is smaller than that of Comparative Example 1. Specifically, the A / B value is equivalent to that of Example 1, and the average particle size of the zinc particles is even smaller than that of Example 1. The residual rate R of Example 2 is improved by 9.1% compared to the residual rate R of Comparative Example 1. Example 2 is an embodiment in which the conditions of Comparative Examples 2 and 4 are combined, and the residual rate of Example 2 is significantly improved over the total increase in residual rate R of 4.9% (1.8% for Comparative Example 2 + 3.1% for Comparative Example 4) achieved by Comparative Example 2 and Comparative Example 4.

[0075] From the above, we have found that optimizing the average particle size of zinc particles and optimizing the ratio A / B (the ratio of the volume of alkaline electrolyte to the theoretical capacity of the negative electrode) can reduce self-discharge and significantly improve the battery's survival rate. Based on this finding, we conclude that in order to suppress self-discharge and improve the battery's survival rate (R), it is effective to set the average particle size of zinc particles (the negative electrode active material) to 71 μm or less and the A / B value to 0.60 mL / Ah or less. The smaller the average particle size and A / B values ​​of zinc particles, the more likely the battery will improve its survival rate (R). However, because a mean particle size of zinc particles below 49 μm increases the likelihood of hydrogen gas generation at the negative electrode, resulting in increased self-discharge, we believe the lower limit of the average particle size of zinc particles should be 49 μm or greater. Furthermore, because a value of A / B below 0.3 mL / Ah results in insufficient electrolyte volume, preventing sufficient charging and discharging, we believe the lower limit of A / B should be 0.3 mL / Ah.

[0076] Therefore, by setting the average particle size of zinc particles to 49 μm or more and 71 μm or less, and by setting A / B, which is the ratio of the volume of alkaline electrolyte to the theoretical capacity of the negative electrode, to 0.30 mL / Ah or more and 0.60 mL / Ah or less, it is believed that the resulting zinc battery will exhibit an excellent self-discharge suppression effect and improve the capacity retention rate.

[0077] Furthermore, the results of Comparative Example 5 show that if SBR is not used as a binder when manufacturing a negative electrode, the amount of negative electrode active material that falls off from the negative electrode substrate increases, making it difficult to obtain sufficient battery capacity. Therefore, in zinc batteries, it is preferable to use SBR as a binder to enable high capacity to be maintained for a long period of time.

[0078] The present invention is not limited to the above-described embodiments and examples, and various modifications are possible. For example, the present invention is not limited to nickel-zinc batteries, as long as the negative electrode mixture contains zinc. The present invention can also be applied to other zinc batteries that do not use nickel in the positive electrode, such as air-zinc batteries. Furthermore, the present invention is not limited to secondary batteries, and the same self-discharge suppression effect can be obtained when used in primary batteries. [Explanation of symbols]

[0079] 2 Nickel-zinc batteries 22 electrode groups 24 Positive electrode 26 negative electrode 28 Separator

Claims

1. a container; and an electrode group accommodated in the container together with an alkaline electrolyte; the electrode group is formed by stacking a positive electrode and a negative electrode with a separator interposed therebetween, the negative electrode contains at least zinc powder, The zinc particles constituting the zinc powder have an average particle size of 49 μm or more and 71 μm or less, A zinc battery, wherein A / B, which is the ratio of the volume of the alkaline electrolyte to the theoretical capacity of the negative electrode, is 0.30 mL / Ah or more and 0.60 mL / Ah or less, where A is the volume of the alkaline electrolyte and B is the theoretical capacity of the negative electrode.

2. The zinc battery according to claim 1 , wherein the negative electrode contains styrene butadiene rubber as a binder.

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