JP7773647B2 - Negative electrode plate and zinc secondary battery - Google Patents

Description

The present invention relates to a negative electrode plate and a zinc secondary battery.

It is known that in zinc secondary batteries, such as nickel-zinc secondary batteries and air-zinc secondary batteries, metallic zinc precipitates in the form of dendrites from the negative electrode during charging, penetrates the voids in the separator, such as nonwoven fabric, and reaches the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the repeated charge-discharge life.

To address the above issues, batteries have been proposed that include a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to pass through while preventing zinc dendrites from penetrating. For example, Patent Document 1 (WO 2013/118561) discloses the placement of an LDH separator between the positive and negative electrodes in a nickel-zinc secondary battery. Patent Document 2 (WO 2016/076047) discloses a separator structure that includes an LDH separator fitted or bonded to a resin outer frame, and that the LDH separator has such high density that it is gas- and/or water-impermeable. This document also discloses that the LDH separator can be composited with a porous substrate. Patent Document 3 (WO 2016/067884) discloses various methods for forming a dense LDH membrane on the surface of a porous substrate to obtain a composite material. This method includes the steps of uniformly attaching a starting substance capable of providing a starting point for LDH crystal growth to a porous substrate, and then subjecting the porous substrate to hydrothermal treatment in a raw material aqueous solution to form a dense LDH membrane on the surface of the porous substrate.

Another factor that shortens the lifespan of zinc secondary batteries is morphological changes in the zinc, the negative electrode active material. Specifically, as zinc dissolves and precipitates during repeated charge and discharge cycles, the negative electrode undergoes morphological changes, resulting in increased resistance due to pore blockage and a decrease in the charge active material due to the accumulation of isolated zinc, making charging and discharging difficult. To address this issue, Patent Document 4 (WO 2020/049902) proposes the use of a negative electrode that combines ZnO particles with at least two selected from (i) metallic Zn particles of a specified particle size, (ii) a specified metal element, and (iii) a binder resin containing hydroxyl groups. This negative electrode is said to suppress negative electrode deterioration associated with repeated charge and discharge cycles in zinc secondary batteries, improving durability and thereby extending cycle life.

Patent document 5 (Japanese Patent Publication No. 6190101) discloses a negative electrode composite containing a negative electrode active material such as metallic Zn or ZnO, a polymer such as an aromatic group-containing polymer, an ether group-containing polymer, or a hydroxyl group-containing polymer, and a conductive additive which is a compound of elements such as B, Ba, Bi, Br, Ca, Cd, Ce, Cl, F, Ga, Hg, In, La, or Mn. It describes that this composite is suitable for forming a storage battery that exhibits high battery performance, such as high cycle characteristics, rate characteristics, and coulombic efficiency, while suppressing shape changes, dendrite-like morphological changes, dissolution, corrosion, and passivation of the electrode active material.

International Publication No. 2013/118561 International Publication No. 2016/076047 International Publication No. 2016/067884 International Publication No. 2020/049902 Patent No. 6190101

As disclosed in Patent Documents 4 and 5, various attempts have been proposed to address the decline in cycle characteristics due to morphological changes in the zinc negative electrode, but further improvement in cycle characteristics is required.

The inventors have now discovered that the cycle life of a zinc secondary battery can be extended by providing a predetermined proportion of a reaction suppression region in the negative electrode plate, where the negative electrode reaction is less likely to proceed.

Therefore, the object of the present invention is to provide a negative electrode plate that can extend the cycle life of a zinc secondary battery.

According to the present invention, the following aspects are provided.
[Aspect 1]
A negative electrode plate used in a zinc secondary battery,
a negative electrode active material containing ZnO particles and Zn particles;
A polymer;
Including,
When viewed from above, the negative electrode plate has a normal reaction region and a reaction suppression region in which the negative electrode reaction proceeds more slowly than in the normal reaction region, and the reaction suppression region accounts for 30 to 75% of the total area of the normal reaction region and the reaction suppression region;
the reaction suppression region has a polymer content C _A of 0.5 to 6 parts by weight relative to 100 parts by weight of the ZnO particles occupying the reaction suppression region;
The normal reaction region has a polymer content C _B of 0 to 3 parts by weight relative to 100 parts by weight of the ZnO particles occupying the normal reaction region, and is lower than C _A.
[Aspect 2]
2. The negative electrode plate according to claim 1, wherein the reaction-suppression region has a circular and/or polygonal shape.
[Aspect 3]
A negative electrode plate according to aspect 1 or 2, wherein a plurality of the reaction suppression regions are present, and the plurality of reaction suppression regions are spaced apart from one another.
[Aspect 4]
The negative electrode plate according to any one of aspects 1 to 3, wherein the polymer is a nonionic water-absorbing polymer.
[Aspect 5]
The nonionic water-absorbing polymer is at least one selected from the group consisting of polyalkylene oxide-based water-absorbing resins, polyvinyl acetamide-based water-absorbing resins, polyvinyl alcohol (PVA resin), and polyvinyl butyral (PVB resin). The negative electrode plate according to aspect 4.
[Aspect 6]
The negative electrode plate according to aspect 4 or 5, wherein the nonionic water-absorbing polymer is a polyalkylene oxide-based water-absorbing resin.
[Aspect 7]
The negative electrode plate according to any one of aspects 4 to 6, wherein the nonionic water-absorbing polymer has a property that its liquid absorption property changes depending on changes in pH.
[Aspect 8]
A negative electrode plate according to any one of Aspects 1 to 7, wherein the polymer is in the form of particles having a particle size of 10 to 200 μm.
[Aspect 9]
The negative electrode plate according to any one of aspects 1 to 8, wherein the Zn particles are contained in an amount of 1.0 to 87.5 parts by weight, based on 100 parts by weight of the ZnO particles.
[Aspect 10]
The negative electrode plate according to any one of aspects 1 to 9, further comprising one or more metal elements selected from In and Bi.
[Aspect 11]
The negative electrode plate according to any one of aspects 1 to 10, wherein the negative electrode plate is a sheet-shaped press-molded body.
[Aspect 12]
A positive electrode and
A negative electrode plate according to any one of aspects 1 to 11,
a separator that separates the positive electrode and the negative electrode plate in a manner that allows hydroxide ions to be conducted between them;
An electrolyte;
A zinc secondary battery comprising:
[Aspect 13]
A zinc secondary battery according to aspect 12, wherein the separator is an LDH separator comprising a layered double hydroxide (LDH) and/or an LDH-like compound.
[Aspect 14]
14. The zinc secondary battery according to claim 12, wherein the LDH separator is composited with a porous substrate.
[Aspect 15]
A zinc secondary battery according to any one of aspects 12 to 14, wherein the positive electrode comprises nickel hydroxide and/or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery.
[Aspect 16]
The zinc secondary battery according to any one of aspects 12 to 14, wherein the positive electrode is an air electrode, thereby forming the zinc secondary battery into a zinc-air secondary battery.

FIG. 1 is a schematic top view conceptually illustrating one embodiment of a negative electrode plate of the present invention, showing an example of the pattern shape of a reaction suppression region. 10 shows another example of the pattern shape of the reaction suppression region. 10 shows another example of the pattern shape of the reaction suppression region. 10 shows another example of the pattern shape of the reaction suppression region. 1 is a graph showing an example of the relationship between the amount of water absorbed and the amount of KOH collected per 1 cm ³ of nonionic water-absorbing polymer and the KOH concentration. FIG. 1 is a schematic top view showing the pattern shape of the reaction suppression region in the negative electrode plates of Examples 1 to 9 (comparison). FIG. 10 is a schematic top view showing the pattern shape of the reaction suppression region in the negative electrode plates of Examples 23 to 31 (comparison).

The negative electrode plate of the present invention is a negative electrode plate used in a zinc secondary battery. This negative electrode plate includes a negative electrode active material and a polymer such as a nonionic water-absorbing polymer. The negative electrode active material includes ZnO particles and Zn particles. FIG. 1A shows one embodiment of the negative electrode plate of the present invention, and FIGS. 1B to 1D show modified embodiments of the negative electrode plate of the present invention, respectively. As shown in FIGS. 1A to 1D, the negative electrode plate 10 according to the present invention has a reaction suppression region 10a and a normal reaction region 10b when viewed in plan. The reaction suppression region 10a is a region where the negative electrode reaction proceeds more slowly than the normal reaction region 10b. In the reaction suppression region 10a, the polymer content C _A is 0.5 to 6 parts by weight per 100 parts by weight of the ZnO particles occupying the reaction suppression region 10a. On the other hand, in the normal reaction region 10b, the polymer content C _B is 0 to 3 parts by weight per 100 parts by weight of the ZnO particles occupying the normal reaction region 10b, and is lower than the above C _A. The proportion of the reaction suppression region 10a in the total area of the normal reaction region 10b and the reaction suppression region 10a is 30 to 75%. In this way, by providing a predetermined proportion of the reaction suppression region 10a, where the negative electrode reaction is less likely to proceed, in the negative electrode plate 10, the cycle life of the zinc secondary battery can be extended.

As mentioned above, with conventional negative electrodes, repeated charge and discharge cycles cause zinc to dissolve and precipitate, which causes the morphology of the negative electrode to change, resulting in problems such as high resistance due to pore blockage and a decrease in charge active material due to the accumulation of isolated zinc, making charging and discharging difficult. These problems can be effectively suppressed or resolved by providing a predetermined proportion of reaction suppression zones 10a, which have a higher polymer concentration than the normal reaction zones 10b, in the negative electrode plate 10. While the mechanism behind this is not entirely clear, it is thought that the addition of polymer uniformly distributes the charge and discharge reactions throughout the negative electrode plate 10, thereby suppressing zinc segregation or accumulation.

That is, during the charge reaction, the reaction at the negative electrode proceeds based on ZnO + H ₂ O + 2e ⁻ → Zn + 2OH ⁻ . As the charge reaction progresses, the OH ⁻ concentration inside the negative electrode near the current collector becomes higher than the OH ⁻ concentration on the negative electrode surface near the separator. As a result, the above reaction at the negative electrode surface progresses, while the reaction inside the negative electrode slows down. On the other hand, during the discharge reaction, the reaction at the negative electrode proceeds based on Zn + 2OH ⁻ → ZnO + H ₂ O + 2e ⁻ . As the discharge reaction progresses, the OH ⁻ concentration inside the negative electrode near the current collector becomes lower than that on the negative electrode surface near the separator, and the reaction inside the negative electrode slows down. In this way, it is thought that the charge/discharge reaction becomes uneven in conventional negative electrodes, which causes zinc segregation.

On the other hand, in the negative electrode plate 10 of the present invention, as shown in Figures 1A-1D, a reaction suppression region 10a with a higher polymer concentration than the normal reaction region 10b is provided at a predetermined ratio. In this regard, polymers such as nonionic water-absorbing polymers are not ion-permeable, so the reactive portions of the Zn particles and/or ZnO particles in the negative electrode plate 10 are limited to areas that are not in contact with the polymer. Therefore, in the reaction suppression region 10a with a high polymer concentration, the negative electrode reaction is less likely to proceed than in the normal reaction region 10b. In this way, the negative electrode reaction, which tends to proceed excessively in certain areas of the negative electrode plate 10, is effectively suppressed, thereby making the charging reaction uniform throughout the negative electrode plate 10. As a result, zinc segregation is suppressed, which is believed to extend the cycle life of zinc secondary batteries.

When viewed from above, the negative electrode plate 10 has a reaction suppression region 10a that occupies 30-75% of the total area of the normal reaction region 10b and the reaction suppression region 10a, preferably 30-70%, more preferably 30-60%, even more preferably 30-50%, and particularly preferably 30-40%. This effectively suppresses the negative electrode reaction, which tends to proceed excessively in some areas of the negative electrode plate 10, while suppressing increased resistance and worsening gas escape caused by an excessively large occupancy rate of the reaction suppression region 10a. As a result, the reaction can be made uniform throughout the negative electrode plate 10, extending the cycle life of the zinc secondary battery.

The reaction suppression region 10a has a polymer content C _A of 0.5 to 6 parts by weight, preferably 1 to 6 parts by weight, more preferably 2 to 6 parts by weight, even more preferably 4 to 6 parts by weight, and particularly preferably 4 to 5 parts by weight, per 100 parts by weight of the ZnO particles occupying the reaction suppression region 10a. This effectively suppresses the negative electrode reaction, which tends to proceed excessively in some areas of the negative electrode plate 10, while suppressing increased resistance and worsening gas leakage caused by an excessively high polymer concentration in the reaction suppression region 10a. As a result, the reaction can be made uniform throughout the negative electrode plate 10, thereby extending the cycle life of the zinc secondary battery.

The reaction inhibition region 10a preferably has a circular and/or polygonal (e.g., rectangular) shape, as shown in Figures 1A to 1D. Furthermore, as shown in Figures 1A, 1B, and 1D, it is preferable that there are multiple reaction inhibition regions 10a, and that these multiple reaction inhibition regions 10a are spaced apart from one another, from the perspective of uniforming the charging reaction across the entire negative electrode plate 10. When there are multiple reaction inhibition regions 10a, the shapes and/or sizes of the individual reaction inhibition regions 10a may be the same as or different from one another.

In the normal reaction region 10b, the polymer content C _B is 0 to 3 parts by weight, preferably 0.5 to 3 parts by weight, and more preferably 0.5 to 2 parts by weight, per 100 parts by weight of the ZnO particles occupying the normal reaction region 10b. However, the polymer content C _B in the normal reaction region 10b is lower than the polymer content C _A in the reaction suppression region 10a described above. Preferably, the difference between C _A and C _B (i.e., C _A -C _B ) is 0.5 to 6 parts by weight, more preferably 1 to 6 parts by weight, even more preferably 3 to 6 parts by weight, and particularly preferably 3 to 5 parts by weight. In this way, by providing regions with different polymer concentrations, the reaction suppression region 10a and the normal reaction region 10b, in the in-plane direction of the negative electrode plate 10, it is possible to effectively eliminate uneven charge/discharge reactions in the negative electrode plate 10. The polymer concentrations in the reaction suppression region 10 a and the normal reaction region 10 b (i.e., C _A and C _B ) may be constant across the thickness of the negative electrode plate 10 .

The polymer is not particularly limited as long as it can restrict the reactive portions of Zn particles and/or ZnO particles in the negative electrode plate 10. A preferred example of such a polymer is a nonionic water-absorbing polymer. The nonionic water-absorbing polymer can be any commercially available nonionic water-absorbing polymer, but it is preferable that its absorbency changes in response to pH fluctuations. That is, the nonionic water-absorbing polymer advantageously absorbs water during the discharge reaction that generates water, allowing the discharge reaction to continue within the negative electrode plate 10 and making the discharge reaction more uniform. As a result, zinc accumulation is suppressed, which is believed to further extend the cycle life of the zinc secondary battery. Figure 2 shows an example of the relationship between the amount of water absorbed and the amount of KOH collected per 1 ^cm3 of such a nonionic water-absorbing polymer and the KOH concentration. As shown in Figure 2, the amount of water absorbed changes with changes in the KOH concentration (i.e., changes in pH) in the electrolyte, but a polymer that does not significantly change the amount of KOH collected is preferred because it can absorb or release only water with pH fluctuations. In particular, those that exhibit a behavior in which the amount of water absorbed decreases as the pH increases are preferred. Preferred examples of such nonionic water-absorbing polymers include polyalkylene oxide-based water-absorbing resins, polyvinyl acetamide-based water-absorbing resins, polyvinyl alcohol (PVA resin), and polyvinyl butyral (PVB resin), with polyalkylene oxide-based water-absorbing resins being more preferred. Commercially available polyalkylene oxide-based water-absorbing resins can be used. The nonionic water-absorbing polymer may contain at least one selected from hydrophilic ether groups, hydroxyl groups, amide groups, and acetamide groups. The presence of these functional groups can provide water absorption and release functions that are more favorable for battery reactions.

The polymer is preferably particulate. In this case, the particle size of the polymer is preferably 10 to 200 μm, more preferably 15 to 180 μm, even more preferably 20 to 160 μm, and particularly preferably 30 to 150 μm. It is not necessary for all of the polymer particles to fall within the above numerical range; it is sufficient that the average particle size D50 falls within the above numerical range. In this specification, the average particle size D50 refers to the particle size at which the cumulative volume from the small particle size side in the particle size distribution obtained by laser diffraction/scattering method is 50%.

The method for forming the negative electrode plate 10 having the reaction suppression region 10 a and the normal reaction region 10 b is not particularly limited. For example, the negative electrode plate 10 can be preferably formed by using any of the following methods (a) to (d).
(a) A mixed powder containing ZnO particles, Zn particles, and a binder (e.g., polytetrafluoroethylene) is prepared. This mixed powder is kneaded in a kneader together with a solvent (e.g., propylene glycol, isopropyl alcohol). The kneaded material is formed into a sheet and attached to a current collector, and then dried to remove the solvent. A solvent in which a polymer (e.g., a nonionic water-absorbing polymer) is dissolved is applied to a predetermined portion of the obtained dried material by dropwise or dip coating, and then dried to coat the polymer.
(b) A solvent in which a polymer has been dissolved is applied to the dried product obtained in the same manner as in (a) above by screen printing, gravure printing, or dispenser application to coat the polymer in predetermined areas.
(c) A solvent in which a polymer is dissolved is added to a mixed powder containing ZnO particles, Zn particles, and a binder, and the mixture is kneaded. In this way, multiple kneaded materials with different polymer concentrations are prepared, and these multiple kneaded materials are layered.
(d) A mixed powder containing ZnO particles, Zn particles, a binder, and polymer particles is heated and kneaded. In this way, a plurality of kneaded materials with different polymer concentrations are prepared, and these kneaded materials are layered.

The polymer contents C _A and C _B in the reaction inhibition region 10a and the normal reaction region 10b can be calculated from the amount of polymer added in each region. Alternatively, they can also be calculated from the weight difference before and after the preparation process of the reaction inhibition region 10a and the normal reaction region 10b by the above method. Alternatively, the polymer contents C _A and C _B can be determined by analyzing the negative electrode plate 10 using a predetermined device. That is, the cross section of the negative electrode plate 10 is observed at a predetermined magnification (e.g., 50,000 times, field of view: 2.3 μm × 1.6 μm) using a field emission scanning electron microscope (FE-SEM, for example, JSM-7900M manufactured by JEOL Ltd.). The acquired FE-SEM image is then imported into image processing software (e.g., Adobe Illustrator manufactured by Adobe). The polymer contents C _A and C _B can be determined by calculating the proportion of the polymer in the field of view. Alternatively, the polymer contents C _A and C _B can be calculated by subjecting the negative electrode active material contained in the negative electrode plate 10 to thermogravimetric differential thermal analysis (TG-DTA).

The negative electrode active material includes Zn particles and ZnO particles. The Zn particles are typically metallic Zn particles, but Zn alloy or Zn compound particles may also be used. While metallic Zn particles commonly used in zinc secondary batteries can be used, the use of smaller metallic Zn particles is preferable from the perspective of extending the battery's cycle life. Specifically, the average particle size D50 of the metallic Zn particles is preferably 5 to 200 μm, more preferably 50 to 200 μm, and even more preferably 70 to 160 μm. The preferred content of Zn particles in the negative electrode plate 10 is preferably 1.0 to 87.5 parts by weight, more preferably 3.0 to 70.0 parts by weight, and even more preferably 5.0 to 55.0 parts by weight, based on 100 parts by weight of the ZnO particles. The metallic Zn particles may be doped with a dopant such as In or Bi. The ZnO particles are not particularly limited, and may be a commercially available zinc oxide powder used in zinc secondary batteries, or a zinc oxide powder obtained by growing particles from such a starting material through a solid-state reaction, etc. The average particle size D50 of the ZnO particles is preferably 0.1 to 20 μm, more preferably 0.1 to 10 μm, and even more preferably 0.1 to 5 μm.

The negative electrode plate 10 preferably further contains one or more metal elements selected from In and Bi. These metal elements can suppress the generation of undesirable hydrogen gas due to self-discharge of the negative electrode plate 10. These metal elements may be contained in the negative electrode plate 10 in any form, such as metal, oxide, hydroxide, or other compound. However, these metal elements are preferably contained in the form of oxide or hydroxide, and more preferably in the form of oxide particles. Examples of oxides of the above metal elements include In ₂ O ₃ and Bi ₂ O _3. Examples of hydroxides of the above metal elements include In(OH) ₃ and Bi(OH) _3. In any case, when the content of the ZnO particles is taken as 100 parts by weight, the content of In is preferably 0 to 2 parts by weight in terms of oxide, and the content of Bi is preferably 0 to 6 parts by weight in terms of oxide, more preferably 0 to 1.5 parts by weight in terms of oxide, and 0 to 4.5 parts by weight in terms of oxide. When In and/or Bi are contained in the negative electrode plate 10 in the form of oxides or hydroxides, it is not necessary that all of the In and/or Bi be in the form of oxides or hydroxides; some of them may be contained in the negative electrode in other forms, such as metals or other compounds. For example, the metal elements may be doped into metal Zn particles as trace elements. In this case, the In concentration in the metal Zn particles is preferably 50 to 2000 ppm by weight, more preferably 200 to 1500 ppm by weight, and the Bi concentration in the metal Zn particles is preferably 50 to 2000 ppm by weight, more preferably 100 to 1300 ppm by weight.

The negative electrode plate 10 may further contain a conductive additive. Examples of conductive additives include carbon, metal powder (tin, lead, copper, cobalt, etc.), and precious metal paste.

The negative electrode plate 10 may further contain a binder resin. The inclusion of a binder in the negative electrode plate 10 makes it easier to maintain the shape of the negative electrode. Various known binders can be used as the binder resin, but preferred examples include polyvinyl alcohol (PVA) and polytetrafluoroethylene (PTFE). It is particularly preferred to use a combination of both PVA and PTFE as the binder.

The negative electrode plate 10 is preferably a sheet-shaped pressed body. This prevents the negative electrode active material from falling off, improves electrode density, and more effectively suppresses changes in the shape of the negative electrode plate 10. Such a sheet-shaped pressed body can be produced by adding a binder to the negative electrode material and kneading it, and then pressing the resulting kneaded material into a sheet using a press such as a roll press.

A current collector is preferably provided on the negative electrode plate 10. Preferred examples of current collectors include copper punched metal and copper expanded metal. In this case, a negative electrode plate consisting of the negative electrode plate 10/current collector can be preferably produced by applying a mixture containing Zn particles, ZnO particles, an optional polymer (e.g., a nonionic water-absorbing polymer), and an optional binder resin (e.g., polytetrafluoroethylene particles) to the copper punched metal or copper expanded metal. It is also preferable to press the dried negative electrode plate (i.e., the negative electrode plate 10/current collector) to prevent the negative electrode active material from falling off and improve electrode density. Alternatively, the sheet-like pressed compact described above may be crimped onto a current collector such as copper expanded metal. Regions with different polymer concentrations (i.e., the reaction suppression region 10a and the normal reaction region 10b) can be formed by coating the dried negative electrode plate with a polymer-containing solvent using the method described above.

The negative electrode plate 10 of the present invention is preferably applied to a zinc secondary battery. Therefore, according to a preferred embodiment of the present invention, a zinc secondary battery is provided, comprising a positive electrode, a negative electrode plate 10, a separator separating the positive electrode and the negative electrode plate 10 in a manner that allows hydroxide ion conductivity, and an electrolyte. The zinc secondary battery of the present invention is not particularly limited as long as it uses the above-described negative electrode plate 10 and an electrolyte (typically an aqueous alkali metal hydroxide solution). Therefore, it can be a nickel-zinc secondary battery, a silver oxide-zinc secondary battery, a manganese oxide-zinc secondary battery, a zinc-air secondary battery, or any other type of alkaline zinc secondary battery. For example, it is preferable that the positive electrode contains nickel hydroxide and/or nickel oxyhydroxide, thereby forming a nickel-zinc secondary battery. Alternatively, the positive electrode may be an air electrode, thereby forming a zinc-air secondary battery.

The separator is preferably a layered double hydroxide (LDH) separator. As mentioned above, LDH separators are known in the fields of nickel-zinc secondary batteries and air-zinc secondary batteries (see Patent Documents 1 to 3), and these LDH separators can also be preferably used in the zinc secondary battery of the present invention. LDH separators can selectively allow hydroxide ions to pass through while preventing the penetration of zinc dendrites. Combined with the effects of the negative electrode plate of the present invention, this can further improve the durability of zinc secondary batteries. In this specification, an LDH separator is defined as a separator containing a layered double hydroxide (LDH) and/or an LDH-like compound (hereinafter collectively referred to as a hydroxide ion-conducting layered compound) that selectively passes hydroxide ions solely by utilizing the hydroxide ion conductivity of the hydroxide ion-conducting layered compound. In this specification, "LDH-like compounds" are hydroxides and/or oxides with a layered crystal structure similar to LDH, which may not be called LDH, and can be considered equivalent to LDH. However, in a broad sense, "LDH" can be interpreted as including not only LDH but also LDH-like compounds.

The LDH separator may be composited with a porous substrate, as disclosed in Patent Documents 1 to 3. The porous substrate may be composed of ceramic, metal, or polymeric materials, but is particularly preferably composed of a polymeric material. Polymeric porous substrates have the following advantages: 1) flexibility (hence, they are less likely to crack even when thinned); 2) ease of achieving high porosity; 3) ease of achieving high conductivity (because thickness can be reduced while increasing porosity); and 4) ease of manufacturing and handling. Particularly preferred polymeric materials are polyolefins such as polypropylene and polyethylene, with polypropylene being the most preferred, due to their excellent hot water resistance, acid resistance, and alkali resistance, as well as low cost. When the porous substrate is composed of a polymeric material, it is particularly preferred that the hydroxide ion-conducting layered compound be incorporated throughout the entire thickness of the porous substrate (e.g., most or almost all of the pores within the porous substrate are filled with the hydroxide ion-conducting layered compound). In this case, the preferred thickness of the polymeric porous substrate is 5 to 200 μm, more preferably 5 to 100 μm, and even more preferably 5 to 30 μm. As such a polymeric porous substrate, a microporous membrane such as those commercially available as separators for lithium batteries can be preferably used.

The electrolyte preferably contains an aqueous solution of an alkali metal hydroxide. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being more preferred. Zinc oxide, zinc hydroxide, etc. may be added to the electrolyte to suppress self-dissolution of zinc-containing materials.

According to a preferred embodiment of the present invention, the LDH separator may contain an LDH- like compound. The definition of the LDH-like compound is as described above. Preferred LDH-like compounds are:
(a) a hydroxide and/or oxide having a layered crystal structure containing Mg and one or more elements, including at least Ti, selected from the group consisting of Ti, Y, and Al, or (b) a hydroxide and/or oxide having a layered crystal structure containing (i) Ti, Y, and optionally Al and/or Mg, and (ii) an additional element M, which is at least one element selected from the group consisting of In, Bi, Ca, Sr, and Ba, or (c) a hydroxide and/or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and/or In, wherein the LDH-like compound (c) is present in the form of a mixture with In(OH) ₃ .

According to a preferred aspect (a) of the present invention, the LDH-like compound may be a hydroxide and/or oxide having a layered crystal structure containing Mg and one or more elements, including at least Ti, selected from the group consisting of Ti, Y, and Al. Therefore, a typical LDH-like compound is a composite hydroxide and/or composite oxide of Mg, Ti, optionally Y, and optionally Al. While the above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, it is preferable that the LDH-like compound does not contain Ni. For example, the LDH-like compound may further contain Zn and/or K. This can further improve the ionic conductivity of the LDH separator.

LDH-like compounds can be identified by X-ray diffraction. Specifically, when X-ray diffraction is performed on the surface of an LDH separator, peaks derived from LDH-like compounds are typically detected in the range of 5°≦2θ≦10°, more typically in the range of 7°≦2θ≦10°. As described above, LDH is a substance having an alternating layer structure in which exchangeable anions and H ₂ O exist as intermediate layers between stacked hydroxide base layers. In this regard, when LDH is measured by X-ray diffraction, a peak inherently attributable to the crystalline structure of LDH (i.e., the (003) peak of LDH) is detected at 2θ = 11 to 12°. In contrast, when an LDH-like compound is measured by X-ray diffraction, a peak is typically detected in the aforementioned range, shifted to a lower angle than the peak position of LDH. Furthermore, the interlayer distance of the layered crystalline structure can be determined by the Bragg equation using 2θ corresponding to the peak derived from the LDH-like compound in X-ray diffraction. The interlayer distance of the layered crystal structure constituting the LDH-like compound determined in this manner is typically 0.883 to 1.8 nm, more typically 0.883 to 1.3 nm.

In the LDH separator according to the above aspect (a), the atomic ratio of Mg/(Mg + Ti + Y + Al) in the LDH-like compound, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.03 to 0.25, more preferably 0.05 to 0.2. The atomic ratio of Ti/(Mg + Ti + Y + Al) in the LDH-like compound is preferably 0.40 to 0.97, more preferably 0.47 to 0.94. The atomic ratio of Y/(Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.45, more preferably 0 to 0.37. The atomic ratio of Al/(Mg + Ti + Y + Al) in the LDH-like compound is preferably 0 to 0.05, more preferably 0 to 0.03. Within the above range, the alkali resistance is even better, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively achieved. Conventionally known LDHs for LDH separators can be expressed by a basic composition represented by the general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ^n- _x/n ·mH ₂ O (wherein M ²⁺ is a divalent cation, M ³⁺ is a trivalent cation, A ^n- is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratios in LDH-like compounds generally deviate from the general formula for LDH. Therefore, it can be said that the LDH-like compound in this embodiment generally has a composition ratio (atomic ratio) different from that of conventional LDHs. The EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by: 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000; 2) performing three-point analysis in point analysis mode with an interval of about 5 μm; 3) repeating the above 1) and 2) once more; and 4) calculating the average value of the six points in total.

According to another preferred aspect (b) of the present invention, the LDH-like compound may be a hydroxide and/or oxide having a layered crystal structure containing (i) Ti, Y, and optionally Al and/or Mg, and (ii) an additional element M. Thus, a typical LDH-like compound is a composite hydroxide and/or composite oxide of Ti, Y, the additional element M, optionally Al, and optionally Mg. The additional element M is In, Bi, Ca, Sr, Ba, or a combination thereof. While the above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, it is preferred that the LDH-like compound does not contain Ni.

In the LDH separator according to the above aspect (b), the atomic ratio of Ti/(Mg+Al+Ti+Y+M) in the LDH-like compound, as determined by energy dispersive X-ray analysis (EDS), is preferably 0.50 to 0.85, more preferably 0.56 to 0.81. The atomic ratio of Y/(Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0.03 to 0.20, more preferably 0.07 to 0.15. The atomic ratio of M/(Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0.03 to 0.35, more preferably 0.03 to 0.32. The atomic ratio of Mg/(Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0 to 0.10, more preferably 0 to 0.02. The atomic ratio of Al/(Mg+Al+Ti+Y+M) in the LDH-like compound is preferably 0 to 0.05, and more preferably 0 to 0.04. Within this range, the alkali resistance is even better, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively achieved. Meanwhile, LDH, a conventionally known LDH separator, can be expressed by a basic composition represented by the general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ^n- _x/n ·mH ₂ O (wherein M ²⁺ is a divalent cation, M ³⁺ is a trivalent cation, A ^n- is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratio in the LDH-like compound generally deviates from the general formula of LDH. Therefore, it can be said that the LDH-like compound in this embodiment generally has a composition ratio (atomic ratio) different from that of conventional LDH. Note that the EDS analysis is preferably performed by using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing an image at an accelerating voltage of 20 kV and a magnification of 5,000 times, 2) performing three-point analysis in point analysis mode with an interval of about 5 μm, 3) repeating the above 1) and 2) once more, and 4) calculating the average value of the six points in total.

According to yet another preferred aspect (c) of the present invention, the LDH-like compound is a hydroxide and/or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and/or In, and the LDH-like compound may exist in the form of a mixture with In(OH) _3. The LDH-like compound of this aspect is a hydroxide and/or oxide having a layered crystal structure containing Mg, Ti, Y, and optionally Al and/or In. Therefore, a typical LDH-like compound is a composite hydroxide and/or composite oxide of Mg, Ti, Y, optionally Al, and optionally In. The In contained in the LDH-like compound may not only be intentionally added to the LDH-like compound, but may also be unavoidably mixed into the LDH-like compound due to the formation of In(OH) ₃ , etc. While the above elements may be replaced with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, it is preferable that the LDH-like compound does not contain Ni. Incidentally, conventionally known LDHs for LDH separators can be represented by a basic composition represented by the general formula: M ²⁺ _1-x M ³⁺ _x (OH) ₂ A ^n- _x/n ·mH ₂ O (wherein M ²⁺ is a divalent cation, M ³⁺ is a trivalent cation, A ^n- is an n-valent anion, n is an integer of 1 or more, x is 0.1 to 0.4, and m is 0 or more). In contrast, the atomic ratios in LDH-like compounds generally deviate from the above general formula of LDH. For this reason, it can be said that the LDH-like compound in this embodiment generally has a composition ratio (atomic ratio) different from that of conventional LDHs.

The mixture according to the above aspect (c) contains not only an LDH-like compound but also In(OH) ₃ (typically composed of an LDH-like compound and In(OH) ₃ ). The inclusion of In(OH) ₃ can effectively improve the alkali resistance and dendrite resistance of the LDH separator. The content of In(OH) ₃ in the mixture is preferably an amount that can improve the alkali resistance and dendrite resistance without substantially impairing the hydroxide ion conductivity of the LDH separator, and is not particularly limited. In(OH) ₃ may have a cubic crystal structure, or may have a structure in which In(OH) ₃ crystals are surrounded by the LDH-like compound. In(OH) ₃ can be identified by X-ray diffraction.

The present invention will be further illustrated by the following examples.

Examples 1 to 31
(1) Preparation of Positive Electrode A paste-type nickel hydroxide positive electrode (capacity density: approximately 700 mAh/cm ³ ) was prepared.

(2) Preparation of Negative Electrode Plate The following raw material powders were prepared.
ZnO powder (manufactured by Seido Chemical Industry Co., Ltd., JIS standard type 1 grade, average particle size D50: 0.2 μm)
Metallic Zn powder (manufactured by DOWA Electronics Co., Ltd., doped with Bi and In, Bi: 70 ppm by weight, In: 200 ppm by weight, average particle size D50: 120 μm)
Nonionic water-absorbing polymer (polyalkylene oxide-based water-absorbing resin, manufactured by Sumitomo Seika Chemicals Co., Ltd., Aquacoke, grade: TWB-P, product form: powder, average particle size D50: 50 μm)

100 parts by weight of ZnO powder was mixed with 5.7 parts by weight of metallic Zn powder and 1 part by weight of polytetrafluoroethylene (PTFE), and then kneaded with propylene glycol. The resulting mixture was rolled using a roll press to obtain a negative electrode active material sheet. The negative electrode active material sheet was then pressed onto a tin-plated copper expand metal and dried. The dried negative electrode active material sheet was then coated with a nonionic water-absorbing polymer by dripping or dip-coating with propylene glycol dissolved in a nonionic water-absorbing polymer and drying. The amount and region of the nonionic water-absorbing polymer added were appropriately adjusted as shown in Tables 1 and 2, and Figures 1A-1D, 3A, and 3B, to obtain a negative electrode plate 10 having a reaction-suppressed region 10a and a normal reaction region 10b.

(3) Preparation of Electrolyte Solution Ion-exchanged water was added to a 48% aqueous potassium hydroxide solution (special grade, manufactured by Kanto Chemical Co., Inc.) to adjust the KOH concentration to 5.4 mol%, and zinc oxide was then dissolved in the solution by heating and stirring to a concentration of 0.42 mol/L, thereby obtaining an electrolyte solution.

(4) Preparation of Evaluation Cell The positive and negative electrode plates were each wrapped in nonwoven fabric, and a current extraction terminal was welded. The positive and negative electrode plates thus prepared were placed opposite each other with an LDH separator interposed therebetween, sandwiched between laminate films with current extraction ports, and three sides of the laminate film were heat-sealed. An electrolyte solution was added to the resulting open-top cell container, and the electrolyte solution was thoroughly permeated into the positive and negative electrode plates by evacuation or the like. The remaining side of the laminate film was then heat-sealed to form a simple sealed cell.

(5) Evaluation <Cycle characteristics>
Using a charge/discharge device (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.), the simple sealed cell was subjected to chemical formation with a 0.1C charge and a 0.2C discharge. A 1C charge/discharge cycle was then performed. Repeated charge/discharge cycles were performed under the same conditions, and the number of charge/discharge cycles was recorded until the discharge capacity of the prototype battery decreased to 70% of the discharge capacity of the first cycle. The number of charge/discharge cycles for each example was calculated as a relative value when the number of charge/discharge cycles in Example 13 was set to 1.00, and this was used as an index of cycle characteristics (cycle characteristic ratio). The results are shown in Tables 1 and 2. It was confirmed that the cycle characteristics were improved by providing the negative electrode plate 10 with a reaction suppression region 10a containing a predetermined amount of nonionic water-absorbing polymer and a normal reaction region 10b.

Claims (16)

A negative electrode plate used in a zinc secondary battery,
a negative electrode active material containing ZnO particles and Zn particles;
a polymer that is not ion-permeable ;
Including,
When viewed from above, the negative electrode plate has a normal reaction region and a reaction suppression region in which the negative electrode reaction proceeds more slowly than in the normal reaction region, and the reaction suppression region accounts for 30 to 75% of the total area of the normal reaction region and the reaction suppression region;
the reaction suppression region has a polymer content C _A of 0.5 to 6 parts by weight relative to 100 parts by weight of the ZnO particles occupying the reaction suppression region;
The normal reaction region has a polymer content C _B of 0 to 3 parts by weight relative to 100 parts by weight of the ZnO particles occupying the normal reaction region, and is lower than C _A. The negative electrode plate according to claim 1, wherein the reaction suppression region has a circular and/or polygonal shape. The negative electrode plate according to claim 1 or 2, wherein there are multiple reaction suppression regions, and the multiple reaction suppression regions are spaced apart from one another. The negative electrode plate according to claim 1 or 2, wherein the polymer is a nonionic water-absorbing polymer. The negative electrode plate according to claim 4, wherein the nonionic water-absorbing polymer is at least one selected from the group consisting of polyalkylene oxide-based water-absorbing resins, polyvinyl acetamide-based water-absorbing resins, polyvinyl alcohol (PVA resin), and polyvinyl butyral (PVB resin). The negative electrode plate according to claim 4, wherein the nonionic water-absorbing polymer is a polyalkylene oxide-based water-absorbing resin. The negative electrode plate according to claim 4, wherein the nonionic water-absorbing polymer has a property in which its liquid absorption property changes in response to changes in pH. The negative electrode plate according to claim 1 or 2, wherein the polymer is in the form of particles having a particle size of 10 to 200 μm. The negative electrode plate according to claim 1 or 2, wherein the Zn particles are contained in an amount of 1.0 to 87.5 parts by weight, based on 100 parts by weight of the ZnO particles. The negative electrode plate according to claim 1 or 2, further containing one or more metal elements selected from In and Bi. The negative electrode plate according to claim 1 or 2, wherein the negative electrode plate is a sheet-like pressed body. A positive electrode and
The negative electrode plate according to claim 1 or 2,
a separator that separates the positive electrode and the negative electrode plate in a manner that allows hydroxide ions to be conducted between them;
An electrolyte;
A zinc secondary battery comprising: The zinc secondary battery of claim 12, wherein the separator is an LDH separator containing a layered double hydroxide (LDH) and/or an LDH-like compound. The zinc secondary battery described in claim 12, wherein the LDH separator is composited with a porous substrate. The zinc secondary battery according to claim 12, wherein the positive electrode contains nickel hydroxide and/or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery. 13. The zinc secondary battery according to claim 12, wherein the positive electrode is an air electrode, thereby making the zinc secondary battery a zinc-air secondary battery.