Negative electrode plate and zinc secondary battery

Abstract

The present invention provides a negative electrode plate including a negative electrode active material and a nonionic water-absorbing polymer, and comprising a nonionic water-absorbing polymer layer formed from the nonionic water-absorbing polymer on a surface of at least one of a pair of main surfaces. The present invention also provides a zinc secondary battery including a positive electrode, a negative electrode including the negative electrode plate, a separator that isolates the positive electrode and the negative electrode in a manner allowing for hydroxide ion conduction, and an electrolytic solution.

Description

Negative electrode plate and zinc secondary battery

[0001] This disclosure relates to a negative electrode plate and a zinc secondary battery. This application claims priority to Japanese Patent Application No. 2024-046600, filed on March 22, 2024, and incorporates by reference all of the contents of said Japanese Patent Application.

[0002] The structure of the negative electrode has been studied for zinc secondary batteries such as nickel-zinc secondary batteries and air-zinc secondary batteries. Patent Document 1 (JP 2014-29818 A) 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 that is a compound of elements such as B, Ba, Bi, Br, Ca, Cd, Ce, Cl, F, Ga, Hg, In, La, and Mn. Patent Document 1 also discloses mixing the negative electrode active material, the polymer, the conductive additive, and other components in a mixer or the like to obtain a slurry or paste mixture, and then coating or pressing the resulting slurry onto a current collector to form a negative electrode.

[0003] Patent Document 2 (WO 2022 / 118625) discloses a negative electrode used in a zinc secondary battery, which includes a negative electrode active material containing ZnO particles and Zn particles, and a nonionic water-absorbing polymer, and at least a portion of the ZnO particles are covered with the nonionic water-absorbing polymer.

[0004] JP 2014-29818 A International Publication No. 2022 / 118625

[0005] In zinc secondary batteries, it is believed that the morphology of zinc, which is the negative electrode active material, changes with repeated charge and discharge, and that suppressing this morphology change leads to improved durability against repeated charge and discharge, i.e., improved cycle characteristics. One of the objects of the present disclosure is to provide a negative electrode plate that can further improve the cycle characteristics of zinc secondary batteries, and a zinc secondary battery with excellent cycle characteristics.

[0006] The negative electrode plate according to the present disclosure includes a negative electrode active material and a nonionic water-absorbing polymer. The negative electrode plate has a nonionic water-absorbing polymer layer formed on at least one of a pair of main surfaces.

[0007] The zinc secondary battery according to the present disclosure includes a positive electrode, a negative electrode including the negative electrode plate, a separator that separates the positive electrode and the negative electrode in a manner that allows hydroxide ions to be conducted between them, and an electrolyte.

[0008] The negative electrode plate according to the present disclosure can further improve the cycle characteristics of the zinc secondary battery. The zinc secondary battery according to the present disclosure provides a zinc secondary battery with excellent cycle characteristics.

[0009] FIG. 1 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. FIG. 2 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. FIG. 3 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. FIG. 4 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. FIG. 5 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. FIG. 6 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. FIGS. 7(a) and 7(b) are conceptual diagrams illustrating how to determine measurement points when measuring the thickness of layers constituting the negative electrode plate, and how to determine measurement locations for the thickness of each layer in the negative electrode plate. FIGS. 8(a) and 8(b) are SEM images and binarized images of a nonionic water-absorbing polymer layer in a negative electrode plate according to the present disclosure. FIG. 9 is a schematic diagram conceptually illustrating one embodiment of a zinc secondary battery according to the present disclosure. FIG. 10 is a cross-sectional schematic diagram of 1 cm of a nonionic water-absorbing polymer used in a negative electrode plate according to the present disclosure. ３ 1 is a graph showing an example of the relationship between the amount of water absorbed and the amount of KOH collected per unit time, and the KOH concentration.

[0010] [Summary of the embodiment] First, embodiments of the present disclosure will be described. A negative electrode plate according to the present disclosure includes a negative electrode active material and a nonionic water-absorbing polymer. The negative electrode plate has a nonionic water-absorbing polymer layer on at least one of a pair of main surfaces.

[0011] Previously, studies have been conducted on the structure of the negative electrode of zinc secondary batteries with the aim of improving the cycle characteristics. Among these, studies have focused on the morphological changes of zinc, the negative electrode active material. Repeated charge and discharge cycles cause zinc dissolution and precipitation in the negative electrode of zinc secondary batteries. This repetition is known to cause morphological changes in the negative electrode, specifically, pore blockage and the formation of a metallic zinc layer. Pore blockage is thought to be a factor in the high resistance of the battery. The formation of a metallic zinc layer leads to a decrease in the charge active material.

[0012] To address this issue, a negative electrode in which at least a portion of the ZnO particles is covered with a nonionic water-absorbing polymer has been proposed (Patent Document 2). However, the need for improved cycle characteristics continues, and further research has been conducted. As a result, it has been discovered that a negative electrode plate with a surface layer composed of a nonionic water-absorbing polymer can provide a zinc secondary battery with a high short-circuit suppression effect and improved cycle characteristics.

[0013] The negative electrode plate may have a mixed layer in contact with the nonionic water-absorbing polymer layer, in which the negative electrode active material and the nonionic water-absorbing polymer are mixed. When the negative electrode plate has this configuration, the effect of improving cycle characteristics can be more reliably obtained. Without being bound by theory, it is believed that when the mixed layer is provided, the charge / discharge reaction between the negative electrode active material present in the portion closer to the surface layer and the negative electrode active material present in the inner layer (position closer to the center in the thickness direction of the negative electrode) within the negative electrode is made uniform, which leads to improved cycle characteristics.

[0014] The negative electrode plate may further include a negative electrode active material layer in contact with the mixed layer and composed of the negative electrode active material. When the negative electrode plate has a nonionic water-absorbing polymer layer on the surface, and includes a mixed layer in contact with the nonionic water-absorbing polymer layer and a negative electrode active material layer in contact with the mixed layer, a zinc secondary battery with excellent cycle characteristics can be reliably obtained.

[0015] In the negative electrode plate, the thickness (A) of the layer containing the negative electrode active material and the thickness (B) of the nonionic water-absorbing polymer layer may satisfy B≦A × 0.3. With this configuration, the increase in resistance of the negative electrode plate due to the presence of the nonionic water-absorbing polymer layer is small, and the effect of improving cycle characteristics can be obtained.

[0016] In the negative electrode plate, the porosity of the nonionic water-absorbing polymer layer may be 0 to 50%. With this configuration, improvement in cycle characteristics and suppression of high resistance during charging are both achieved.

[0017] In the negative electrode plate, the nonionic water-absorbing polymer may be at least one selected from the group consisting of a polyalkylene oxide-based water-absorbing resin, a polyvinyl acetamide-based water-absorbing resin, a polyvinyl alcohol resin (PVA resin), and a polyvinyl butyral resin (PVB resin). Also, in the negative electrode plate, the nonionic water-absorbing polymer may be a polyalkylene oxide-based water-absorbing resin.

[0018] In the negative electrode plate, the nonionic water-absorbing polymer may have a property that liquid absorption changes in response to a change in pH.

[0019] In the negative electrode plate, the negative electrode active material may contain ZnO particles and Zn particles, and may contain 1.0 to 87.5 parts by weight of the Zn particles when the content of the ZnO particles is 100 parts by weight.

[0020] The negative electrode plate may further contain one or more metal elements selected from In and Bi.

[0021] The negative electrode active material layer in the negative electrode plate may be a sheet-like pressed body.

[0022] The zinc secondary battery according to the present disclosure includes a positive electrode, a negative electrode including the negative electrode plate, a separator separating the positive electrode and the negative electrode in a hydroxide ion conductive manner, and an electrolyte. The zinc secondary battery including the negative electrode plate has excellent cycle characteristics.

[0023] In the zinc secondary battery, the separator may be a layered double hydroxide (LDH) separator containing an LDH or an LDH-like compound. The LDH separator may be composited with a porous substrate.

[0024] In the zinc secondary battery, the positive electrode may contain nickel hydroxide or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery.

[0025] In the zinc secondary battery, the positive electrode may be an air electrode, thereby making the zinc secondary battery a zinc-air secondary battery.

[0026] [Specific Examples of Embodiments] Next, specific examples of the negative electrode plate and zinc secondary battery according to the present disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are designated by the same reference numerals, and their description will not be repeated.

[0027] (Negative electrode plate) The negative electrode plate according to the present disclosure is a negative electrode plate used in a zinc secondary battery. The negative electrode plate includes a negative electrode active material and a nonionic water-absorbing polymer. The negative electrode plate according to the present disclosure includes a nonionic water-absorbing polymer layer formed of a nonionic water-absorbing polymer on the surface of at least one of a pair of main surfaces. The negative electrode plate according to the present disclosure is a plate-shaped molded body including a plurality of stacked layers. First, the stacking configuration will be described.

[0028] FIG. 1 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. Referring to FIG. 1, negative electrode plate 1 has a pair of main surfaces 1A and 1B. Negative electrode plate 1 includes nonionic water-absorbing polymer layers 11a and 11b, each composed of a nonionic water-absorbing polymer, on the surfaces of main surfaces 1A and 1B. Negative electrode plate 1 includes a negative electrode active material layer 50 between nonionic water-absorbing polymer layers 11a and 11b. Negative electrode active material layer 50 is disposed in contact with nonionic water-absorbing polymer layers 11a and 11b.

[0029] The nonionic water-absorbing polymer layer may be provided on only one of the main surfaces. Fig. 4 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. Referring to Fig. 4, the negative electrode plate 4 has a nonionic water-absorbing polymer layer 11a on one main surface 4A. The other main surface 4B is composed of a negative electrode active material layer 50. That is, the nonionic water-absorbing polymer layer 11a is exposed on one surface of the negative electrode plate 4, and the negative electrode active material layer 50 is exposed on the other surface. The negative electrode plate 4 is composed of the nonionic water-absorbing polymer layer 11a provided on one surface and the negative electrode active material layer 50.

[0030] FIG. 2 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. Referring to FIG. 2, the negative electrode plate 2 is a plate-shaped molded body including three layers and has a pair of main surfaces 2A and 2B. The negative electrode plate 2 has nonionic water-absorbing polymer layers 11a and 11b composed of a nonionic water-absorbing polymer on the surfaces of the main surfaces 2A and 2B, respectively. The negative electrode plate 2 also has a mixed layer 30 between the nonionic water-absorbing polymer layers 11a and 11b, which is a layer formed by mixing a negative electrode active material and a nonionic water-absorbing polymer. The mixed layer 30 is disposed in contact with the nonionic water-absorbing polymer layers 11a and 11b.

[0031] 5 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. Referring to FIG. 5, the negative electrode plate 5 has a nonionic water-absorbing polymer layer 11a on one main surface 5A. The other main surface 5B is composed of a mixed layer 30. That is, the nonionic water-absorbing polymer layer 11a is exposed on one of the main surfaces of the negative electrode plate 5, and the mixed layer 30 is exposed on the other surface. The negative electrode plate 5 is composed of the nonionic water-absorbing polymer layer 11a provided on one surface and the mixed layer 30.

[0032] FIG. 3 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. Referring to FIG. 3, the negative electrode plate 3 is a plate-shaped molded body including five layers and has a pair of main surfaces 3A and 3B. The negative electrode plate 3 includes nonionic water-absorbing polymer layers 11a and 11b composed of a nonionic water-absorbing polymer on the surfaces of the main surfaces 3A and 3B, respectively. The negative electrode plate 3 includes mixed layers 31a and 31b in contact with the nonionic water-absorbing polymer layers 11a and 11b, respectively, which are layers formed by mixing a negative electrode active material and a nonionic water-absorbing polymer. The negative electrode plate 3 further includes a negative electrode active material layer 50 between the mixed layers 31a and 31b. The negative electrode active material layer 50 is disposed such that both main surfaces thereof are in contact with the mixed layers 31a and 31b. In other words, the negative electrode plate 3 has nonionic water-absorbing polymer layers 11a and 11b as the outermost layers, mixed layers 31a and 31b on the inner side in the thickness direction, and a negative electrode active material layer 50 further on the inner side.

[0033] FIG. 6 is a cross-sectional schematic diagram conceptually illustrating one embodiment of a negative electrode plate according to the present disclosure. Referring to FIG. 6, the negative electrode plate 6 includes a nonionic water-absorbing polymer layer 11a on one main surface 6A. The other main surface 6B is configured with a negative electrode active material layer 50. That is, the nonionic water-absorbing polymer layer 11a is exposed on one of the main surfaces of the negative electrode plate 6, and the negative electrode active material layer 50 is exposed on the other surface. Furthermore, a mixed layer 31a is provided between the nonionic water-absorbing polymer layer 11a and the negative electrode active material layer 50. As a modification of the negative electrode plate shown in FIG. 6, the negative electrode plate according to the present disclosure may include a nonionic water-absorbing polymer layer on one main surface and a mixed layer on the other main surface, with the negative electrode active material layer being present between the nonionic water-absorbing polymer layer and the mixed layer.

[0034] In the negative electrode plate, the water-absorbent polymer layer, the mixed layer, and the negative electrode active material layer can be distinguished, for example, by observing scanning electron microscope (SEM) images. The negative electrode active material is contained in the mixed layer and the negative electrode active material layer. In this case, it is preferable that the thickness (A) of the layer containing the negative electrode active material and the thickness (B) of the nonionic water-absorbent polymer layer satisfy B≦A×0.3. The thickness of the layer containing the negative electrode active material is the sum of the thickness of the mixed layer and the thickness of the negative electrode active material layer. When the negative electrode plate consists of a water-absorbent polymer layer and a mixed layer, the thickness (A) of the layer containing the negative electrode active material is the thickness of the mixed layer. When the negative electrode plate consists of a water-absorbent polymer layer and a negative electrode active material layer, the thickness (A) of the layer containing the negative electrode active material is the thickness of the negative electrode active material layer.

[0035] The thickness of each layer can be calculated by the following method. Fig. 7 shows a schematic diagram of the negative electrode plate 3 as viewed from above, and a conceptual diagram showing how to determine the measurement points for the thickness of each layer. Fig. 7(a) is a schematic diagram of the main surface 3A of the negative electrode plate 3 as viewed from above. When the negative electrode plate is viewed from above, a line (C ｙ１ ~C ｙ３ ) and a line (C ｘ１ ~C ｘ３ ) and draw nine intersections (p １ ~p ９ 7B, an SEM image of the cross section in the thickness direction (Z direction in FIG. 7B) of the cross section of the intersection point p ９ Schematic diagram of an SEM image of a cross section of a negative electrode plate in . When the image does not fit in one field of view, continuous images are taken and joined to obtain a cross-sectional image including all layers. In this cross-sectional image, a line (D ｘ１ ~D ｘ５ ) and divide it into 6 equal parts. This line and the line segments (L １ ~L ４ ) and calculate the thickness of each layer from the intersection point. ｘ１ ~D ｘ５ Five thickness data corresponding to each of the lines D are obtained. ｘ１ The thickness of the negative electrode active material layer 50 at the position L ２ and L３ This operation is performed at nine intersection points p １ ~p ９ The measurement is repeated for each of the 45 data points, and the average value of the obtained data points is used as the thickness of the water-absorbing polymer layer, the mixed layer, and the negative electrode active material layer.

[0036] Next, each layer constituting the negative electrode plate will be described.

[0037] (Nonionic Water-Absorbing Polymer Layer) The nonionic water-absorbing polymer layer provided in the negative electrode plate according to the present disclosure is a layer substantially composed of a nonionic water-absorbing polymer. "Substantially composed of a nonionic water-absorbing polymer" means that, in a dry state, it contains no substances other than the nonionic water-absorbing polymer, excluding substances that may be mixed in due to manufacturing reasons, etc. Specifically, the nonionic water-absorbing polymer layer is a layer that is confirmed by observation and energy dispersive X-ray spectroscopy (EDX) analysis to be composed of 90% or more of nonionic water-absorbing polymer, preferably 95% or more of nonionic water-absorbing polymer, and more preferably 99% or more of nonionic water-absorbing polymer. The nonionic water-absorbing polymer layer in the negative electrode plate can be confirmed, for example, by observing SEM images of the thickness direction cross section of the negative electrode plate and by compositional and structural analysis using, for example, ICP atomic emission spectroscopy, infrared absorption spectroscopy, or nuclear magnetic resonance spectroscopy.

[0038] In the negative electrode plate according to the present disclosure, a nonionic water-absorbing polymer layer is provided on at least one of the main surfaces of the negative electrode plate. When viewed in plan from the main surface of the negative electrode plate (e.g., main surface 1A in FIG. 1), the nonionic water-absorbing polymer layer may occupy 30 to 100% of the entire area of ​​the main surface, more preferably 50 to 100%, and even more preferably 80 to 100%. It is particularly preferable that the entire main surface (substantially 100%) is a nonionic water-absorbing polymer layer. This makes it possible to more effectively uniformize the reaction throughout the negative electrode plate and extend the cycle life of the zinc secondary battery. Note that the entire area of ​​the main surface does not include the exposed portions (slits) of the current collector on the main surface.

[0039] The nonionic water-absorbing polymer layer may have pores, and the porosity is preferably 0 to 50% (area %). In the negative electrode plate according to the present disclosure, a nonionic water-absorbing polymer layer is formed on at least one surface of the negative electrode plate. While the presence of the nonionic water-absorbing polymer layer contributes to improving cycle characteristics, it also tends to increase resistance during charging. In this regard, when the porosity is 0 to 50%, the OH group required for charging and discharging is not easily absorbed. － It is believed that the ions are supplied to the negative electrode active material and the formation of a metallic zinc layer on the surface of the negative electrode plate is suppressed, resulting in an improvement in cycle characteristics.

[0040] The porosity is a value obtained by the following calculation method. The following description will be given with reference to Fig. 7(a) and Fig. 8. With reference to Fig. 7(a), when the negative electrode plate is viewed from the planar direction, a line (C ｙ１ ~C ｙ４ ) and a horizontal line dividing it into four equal parts (C ｘ１ ~C ｘ４ ) and draw nine intersections of each line (p １ ~p ９ ) and obtain an SEM image of the cross section of the nonionic water-absorbing polymer layer enlarged at 20,000 times. Figure 8(a) is an example of an SEM image. The obtained image is binarized using image processing software to obtain a black and white binary image. Figure 8(b) is a black and white binary image obtained by binarizing the SEM image of Figure 8(a). The black parts in the binarized image are pores, and the white parts are bodies. The ratio of the black parts (pores) to the total area of ​​the image is calculated and is taken as the porosity. Similar operations are performed on p １ ~p ９ The measurement is carried out at nine locations, and the average of the porosities obtained is taken as the porosity (%) of the nonionic water-absorbing polymer layer.

[0041] The nonionic water-absorbing polymer can be any commercially available nonionic water-absorbing polymer. It is preferable that the nonionic water-absorbing polymer has the property of changing its absorbency in response to changes in pH. Because the nonionic water-absorbing polymer does not have ion permeability, the negative electrode reaction does not occur in the portions of the Zn particles and ZnO particles that are the negative electrode active materials that come into contact with the nonionic water-absorbing polymer, and the negative electrode reaction occurs only in the portions that do not come into contact with the nonionic water-absorbing polymer. In the negative electrode plate according to the present disclosure, by providing a nonionic water-absorbing polymer layer on the surface layer of the negative electrode plate, the negative electrode reaction that tends to proceed excessively on the surface layer of the negative electrode plate is suppressed, while the discharge reaction continues inside the negative electrode, making the discharge reaction more uniform. As a result, it is believed that zinc accumulation is suppressed, thereby extending the cycle life of the zinc secondary battery.

[0042] FIG. 10 shows a graph of 1 cm of a nonionic water-absorbing polymer, which is an example of the nonionic water-absorbing polymer used in the negative electrode plate according to the present disclosure. ３ The graph shows an example of the relationship between the amount of water absorbed and the amount of KOH trapped per unit area and the KOH concentration. As shown in FIG. 10, a polymer in which the amount of water absorbed changes with changes in the KOH concentration in the electrolyte (i.e., changes in pH) but the amount of KOH trapped does not change significantly is preferred because it can absorb or release only water with pH fluctuations. In particular, a polymer that exhibits a behavior in which the amount of water absorbed decreases with increasing pH is 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), and at least one selected from the group consisting of these may be used. Polyalkylene oxide-based water-absorbing resins are 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 provides water absorption and release functions that are more favorable for battery reactions.

[0043] (Negative Electrode Active Material Layer) The negative electrode active material layer provided in the negative electrode plate according to the present disclosure is a layer made of a negative electrode active material and other components, and does not contain a nonionic water-absorbing polymer except for components that are mixed in due to manufacturing reasons, etc.

[0044] The negative electrode active material includes Zn particles and ZnO particles. In the negative electrode active material layer 50 in FIG. 7(b), particles 55 are Zn particles, and particles 56 are ZnO particles. The Zn particles are typically metal Zn particles, but particles of a Zn alloy or Zn compound may also be used. As the metal Zn particles, metal Zn particles commonly used in zinc secondary batteries can be used, but the use of smaller metal Zn particles is more preferable from the viewpoint of extending the cycle life of the battery. Specifically, the average particle diameter D of the metal Zn particles ５０ 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 is 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 ZnO particles may be any commercially available zinc oxide powder used in zinc secondary batteries, or zinc oxide powder obtained by grain growth using such a powder as a starting material through a solid-state reaction or the like, and are not particularly limited. The average particle size D of the ZnO particles ５０ is preferably 0.1 to 20 μm, more preferably 0.1 to 10 μm, and even more preferably 0.1 to 5 μm. ５０ means the particle size at which the cumulative volume from the small particle size side becomes 50% in the particle size distribution obtained by the laser diffraction / scattering method.

[0045] The negative electrode active material layer 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. These metal elements may be contained in the negative electrode in any form, such as metal, oxide, hydroxide, or other compound, but are preferably contained in the form of oxide or hydroxide, and more preferably in the form of oxide particles. Examples of oxides of metal elements include In.２ O ３ , Bi ２ O ３ Examples of hydroxides of metal elements include In(OH) ３ , Bi(OH) ３ Examples include. In any case, when the content of ZnO particles is 100 parts by weight, the In content is preferably 0 to 2 parts by weight in terms of oxide, and the Bi content 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 the Bi content is preferably 0 to 4.5 parts by weight in terms of oxide. When In and / or Bi are contained in the negative electrode in the form of oxide or hydroxide, it is not necessary for all of the In and / or Bi to be in the form of oxide or hydroxide; some of them may be contained in the negative electrode in other forms, such as metal or other compounds. For example, the metal element may be doped into the metal Zn particles as a trace element. 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.

[0046] The negative electrode active material layer may further contain a conductive additive, examples of which include carbon, metal powder (such as tin, lead, copper, or cobalt), and noble metal paste.

[0047] The negative electrode active material layer may further contain a binder resin. The inclusion of a binder 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.

[0048] The negative electrode active material layer is preferably a sheet-shaped pressed body. This can prevent the negative electrode active material from falling off, improve electrode density, and more effectively suppress morphological changes in the negative electrode active material layer. Such a sheet-shaped pressed body can be produced by adding a binder to the negative electrode material and kneading the mixture, and then subjecting the resulting kneaded mixture to press molding such as a roll press to form it into a sheet.

[0049] A current collector is preferably provided in the negative electrode active material layer. Referring to FIG. 7( b), a current collector 51 is provided in the negative electrode active material layer 50. Preferred examples of the current collector include copper punched metal and copper expanded metal. In this case, for example, a mixture containing Zn particles, ZnO particles, a nonionic water-absorbing polymer, and, if desired, a binder resin (e.g., polytetrafluoroethylene particles) can be applied to the copper punched metal or copper expanded metal to preferably produce a negative electrode active material layer containing the current collector. In this case, it is also preferable to press the dried negative electrode plate to prevent the negative electrode active material from falling off and improve the electrode density. Alternatively, the above-described sheet-shaped pressed body may be pressure-bonded to a current collector such as copper expanded metal.

[0050] (Mixed Layer) The mixed layer provided in the negative electrode plate according to the present disclosure is a layer formed by mixing a nonionic water-absorbing polymer and a negative electrode active material. The nonionic water-absorbing polymer and the negative electrode active material may be the same as those described above. In the mixed layer, the nonionic water-absorbing polymer may be present so as to cover the surfaces of the Zn particles and ZnO particles, which are the negative electrode active material, or may be present as polymer particles separate from the Zn particles and ZnO particles. Both the polymer covering the surfaces of the Zn particles and ZnO particles and the polymer present as particles may be present together.

[0051] The ratio of the nonionic water-absorbing polymer to the negative electrode active material in the mixed layer is not particularly limited, but for example, when the content of the ZnO particles in the negative electrode active material layer is 100 parts by weight, the nonionic water-absorbing polymer may be 0.01 to 6 parts by weight. The ratio of the nonionic water-absorbing polymer to the negative electrode active material can be confirmed, for example, by observing an SEM image.

[0052] The mixed layer may contain other components in addition to the nonionic water-absorbing polymer and the negative electrode active material, such as one or more metal elements selected from In and Bi, a conductive additive, and a binder resin, and specifically, the same components as those listed for the negative electrode active material layer may be used.

[0053] When the negative electrode plate has a negative electrode active material layer and a mixed layer, the mixed layer is preferably located on the outer side of the negative electrode active material layer. The relative thicknesses of the negative electrode active material layer and the mixed layer are not limited, and the thickness of the mixed layer may be smaller than the thickness of the negative electrode active material layer, or may be larger than the thickness of the negative electrode active material layer. The negative electrode active material layer and the mixed layer may have the same thickness.

[0054] (Method for Producing Negative Electrode Plate) The method for producing the negative electrode plate according to the present disclosure is not particularly limited, but it can be produced, for example, by the following method. The following describes an example of a production method for a negative electrode plate including a nonionic water-absorbing polymer layer, a mixed layer, and a negative electrode active material layer.

[0055] (Preparation Method 1) A mixed powder containing ZnO particles, Zn particles, and a binder (e.g., polytetrafluoroethylene, carboxymethyl cellulose) is prepared. This mixed powder is kneaded with a solvent (e.g., propylene glycol, isopropyl alcohol, butyl carbitol, water) in a kneader. The resulting kneaded material is formed into a sheet and attached to a current collector, and then dried to remove the solvent. A negative electrode active material layer is obtained through these steps. A solution in which a nonionic water-absorbing polymer is dissolved in a solvent is dropped onto a predetermined portion of the obtained negative electrode active material layer, and the solution is applied to the surface of the negative electrode active material layer and then dried to form a mixed layer and a nonionic water-absorbing polymer layer. Examples of application methods that can be used include dip coating, brush coating, screen printing, gravure printing, and application with a dispenser.

[0056] (Preparation Method 2) A solution of a nonionic water-absorbing polymer dissolved in a solvent is added to a mixed powder containing ZnO particles, Zn particles, and a binder, and the mixture is kneaded. This kneaded mixture is layered on a dried body (negative electrode active material layer) obtained in the same manner as in Preparation Method 1 to form a mixed layer. A solution of a nonionic water-absorbing polymer dissolved in a solvent is coated on the mixed layer in the same manner as in Preparation Method 1 to form a nonionic water-absorbing polymer layer.

[0057] (Preparation Method 3) A mixed powder containing ZnO particles, Zn particles, a binder, and particles of a nonionic water-absorbing polymer is heated and kneaded. This kneaded mixture is layered on a dried body (negative electrode active material layer) obtained in the same manner as in Preparation Method 1 to form a mixed layer. A solution in which a nonionic water-absorbing polymer is dissolved is coated thereon in the same manner as in Preparation Method 1 to form a nonionic water-absorbing polymer layer.

[0058] (Preparation Method 4) A solution in which a nonionic water-absorbing polymer is dissolved is dropped onto a release paper, coated on the release paper, dried, and then peeled off to obtain a sheet-like nonionic water-absorbing polymer layer. Examples of the coating method include dip coating, brush coating, screen printing, gravure printing, or coating with a dispenser. A sheet-like nonionic water-absorbing polymer layer is placed on a dried product of the mixed layer or negative electrode active material layer obtained in the same manner as in Preparation Methods 1 to 3, and the mixture layer or the negative electrode active material layer is welded by pressing or heat to form a nonionic water-absorbing polymer layer.

[0059] (Zinc Secondary Battery) The negative electrode plate of the present invention is preferably applied to a zinc secondary battery. FIG. 9 is a schematic diagram conceptually illustrating one embodiment of a zinc secondary battery according to the present disclosure. Referring to FIG. 9, a zinc secondary battery 500 includes a positive electrode 200, a negative electrode 100, a separator 300 that separates the positive electrode 200 and the negative electrode 100 in a manner that allows hydroxide ion conductivity, and an electrolyte 400. The zinc secondary battery according to the present disclosure is not particularly limited as long as it uses the above-described negative electrode plate and an electrolyte (typically an aqueous alkali metal hydroxide solution). Therefore, it may 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.

[0060] The separator 300 is preferably a layered double hydroxide (LDH) separator. LDH separators are known in the fields of nickel-zinc secondary batteries and air-zinc secondary batteries, and these LDH separators can also be preferably used in the zinc secondary battery of the present disclosure. The LDH separator 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 disclosure, this can further improve the durability of the zinc secondary battery. Note that, 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, an "LDH-like compound" refers to a hydroxide and / or oxide with a layered crystal structure similar to LDH, even if it may not be called an LDH, and can be considered an equivalent of LDH. However, in a broader sense, "LDH" can be interpreted as including not only LDH but also LDH-like compounds.

[0061] The LDH separator may be composited with a porous substrate. The porous substrate may be composed of any of ceramic, metal, and 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.

[0062] The electrolyte 400 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.

[0063] (LDH-like Compound) The LDH separator may contain an LDH-like compound. The definition of an LDH-like compound is as described above. Preferred LDH-like compounds are as follows: (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) at least one additional element M 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 in (c) is In(OH) ３ It exists in the form of a mixture with

[0064] As described in (a) above, 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.

[0065] 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 attributable to 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, LDHs are formed by stacking hydroxide base layers, with exchangeable anions and H as intermediate layers. ２O is present. In this regard, when LDH is measured by X-ray diffraction, a peak due to the crystalline structure of LDH (i.e., the (003) peak of LDH) is inherently 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 above-mentioned range, which is 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 due to the LDH-like compound in X-ray diffraction. The interlayer distance of the layered crystalline 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.

[0066] In the LDH separator according to 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 more excellent, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is a divalent cation, M ３＋ is a trivalent cation, and 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 the LDH-like compounds generally deviate from the general formula of LDH. Therefore, it can be said that the LDH-like compounds in this embodiment generally have compositional ratios (atomic ratios) different from those of conventional LDHs. Note that EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing images at an accelerating voltage of 20 kV and a magnification of 5,000x, 2) performing three-point analysis in point analysis mode with intervals 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.

[0067] As in the above-mentioned aspect (b), the LDH-like compound can 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.

[0068] In the LDH separator according to 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, more preferably 0 to 0.04. Within the above range, the alkali resistance is more excellent, and the effect of suppressing short circuits caused by zinc dendrites (i.e., dendrite resistance) can be more effectively realized. Incidentally, LDHs conventionally known for LDH separators have the general formula: M ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is a divalent cation, M ３＋ is a trivalent cation, and 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 the LDH-like compounds generally deviate from the general formula of LDH. Therefore, it can be said that the LDH-like compounds in this embodiment generally have compositional ratios (atomic ratios) different from those of conventional LDHs. Note that EDS analysis is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by 1) capturing images at an accelerating voltage of 20 kV and a magnification of 5,000x, 2) performing three-point analysis in point analysis mode with intervals 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.

[0069] As in the above aspect (c), the LDH-like compound is a hydroxide and / or oxide of a layered crystal structure containing Mg, Ti, Y, and optionally Al and / or In, and the LDH-like compound is In(OH) ３ The LDH-like compound of this embodiment 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. Note that the In that can be contained in the LDH-like compound is not only that which is intentionally added to the LDH-like compound, but also In(OH) ３ The above elements may be substituted with other elements or ions to the extent that the basic properties of the LDH-like compound are not impaired, but it is preferable that the LDH-like compound does not contain Ni. Incidentally, LDHs conventionally known for LDH separators are represented by the general formula: M ２＋ １－ｘ M ３＋ ｘ (OH) ２ A ｎ－ ｘ／ｎ ・mH ２ O (in the formula, M ２＋ is a divalent cation, M ３＋ is a trivalent cation, and 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. Therefore, it can be said that the LDH-like compounds in this embodiment generally have composition ratios (atomic ratios) different from those of conventional LDHs.

[0070] The mixture according to the above embodiment (c) contains not only LDH-like compounds but also In(OH) ３ (typically LDH-like compounds and In(OH) ３ It is composed of In(OH) ３ The inclusion of In(OH) in the mixture can effectively improve the alkali resistance and dendrite resistance of the LDH separator. ３ The content of In(OH) is preferably an amount that can improve the alkali resistance and dendrite resistance of the LDH separator without substantially impairing the hydroxide ion conductivity, and is not particularly limited. ３ may have a cubic crystal structure, and In(OH) ３ The crystal may be surrounded by an LDH-like compound. ３ can be identified by X-ray diffraction.

[0071] The negative electrode plate and zinc secondary battery according to the present disclosure will be described in more detail with reference to the following examples. Of Samples 1 to 21, Sample 1 is outside the scope of the negative electrode plate and zinc secondary battery according to the present disclosure and is a comparative example. Samples 2 to 7 and Samples 11 to 21 are negative electrode plates and zinc secondary batteries according to the present disclosure and are working examples.

[0072] <Sample preparation method> (1) Preparation of positive electrode Paste-type nickel hydroxide positive electrode (capacity density: approximately 700 mAh / cm ３ ) was prepared.

[0073] (2) Preparation of negative electrode The following raw material powders were prepared: ZnO powder (manufactured by Seido Chemical Industry Co., Ltd., JIS Class 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)

[0074] 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 pressed onto a tin-plated copper expand metal and dried. The dried negative electrode active material sheet was the negative electrode active material layer. A nonionic water-absorbing polymer and mixed layer were formed by brushing propylene glycol in which 3 to 7 parts by weight of a nonionic water-absorbing polymer had been dissolved onto the surface of the negative electrode active material layer and drying.

[0075] (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 then zinc oxide was dissolved therein at 0.42 mol / L by heating and stirring to obtain an electrolyte solution.

[0076] (4) Preparation of Evaluation Cell The positive and negative electrodes were each wrapped in a nonwoven fabric, and a current extraction terminal was welded. The positive and negative electrodes thus prepared were placed opposite each other via an LDH separator, 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 electrodes by evacuation or the like. The remaining side of the laminate film was then heat-sealed to form a simple sealed cell.

[0077] (5) Evaluation of Battery Characteristics Using a charge / discharge device (TOSCAT3100, manufactured by Toyo Systems Co., Ltd.), the simple sealed cell was subjected to formation by charging at 0.1 C and discharging at 0.2 C. Thereafter, a 0.5 C charge / discharge cycle was performed.

[0078] <Evaluation 1: Resistance at End of Charge in First Cycle> The resistance at end of charge in the first cycle was calculated using the following formula (1), where I is the current value measured at the end of the first 0.5 C charge-discharge cycle, and V is the cell voltage 5 minutes after the end of charge. The resistance at end of charge in the first cycle for each example was calculated as a relative value when the resistance at end of charge in the first cycle for Sample 1 was set to 1.0.

[0079]

[0080] <Evaluation 2: Cycle Characteristics> 0.5C charge / discharge cycles were repeatedly performed, and the number of charge / discharge cycles until the discharge capacity decreased to 70% of the discharge capacity at the first cycle was recorded. The number of charge / discharge cycles for each example was calculated as a relative value when the number of charge / discharge cycles in Comparative Example 1 was set to 1.0, and this was used as an index showing the cycle characteristics (cycle characteristic ratio).

[0081] [Samples 1, 2, and 11-14] Sample 1 was prepared using a negative electrode plate consisting only of a negative electrode active material layer, without a nonionic water-absorbing polymer layer or mixed layer, and an evaluation cell was fabricated using the resulting negative electrode plate. Sample 1 was fabricated using the same sample fabrication method as described above, except that the nonionic water-absorbing polymer was not applied to the surface of the negative electrode active material layer. For Samples 2, 11-14, a three-layer negative electrode plate shown in FIG. 1 was fabricated using the same sample fabrication method, and an evaluation cell was fabricated using the resulting negative electrode plate. Table 1 shows the thickness of each layer in the negative electrode plates of Samples 1, 2, and 11-14, the porosity of the nonionic water-absorbing polymer layer, and the evaluation results of the evaluation cells. The thickness of each layer shown in Table 1 is a relative value when the sum of the thicknesses of the mixed layer and the negative electrode active material layer is taken as 100. The values ​​of "resistance at end of charge in the first cycle" and "cycle characteristics" shown in Table 1 are relative values ​​when the values ​​of "resistance at end of charge in the first cycle" and "cycle characteristics" of Sample 1 are set to 1.0.

[0082]

[0083] Referring to Table 1, the inclusion of a nonionic water-absorbing polymer layer improved the cycle characteristics. This was thought to be because the nonionic water-absorbing polymer layer prevented the metal Zn layer formed on the surface of the negative electrode active material from progressing toward the separator, thereby suppressing short circuits. As shown in Samples 2 and 11 to 13, when the thickness of the nonionic water-absorbing polymer layer was 0.3 times or less the total thickness of the mixed layer and the negative electrode active material layer (i.e., when the thickness of the nonionic water-absorbing polymer layer in Table 1 was 30 or less), the cycle characteristics were improved. As shown in Sample 14, when a nonionic water-absorbing polymer layer was present on at least one surface, the cycle characteristics were improved.

[0084] [Samples 3-6 and Samples 15-20] For Samples 3-6 and 15-20, negative electrode plates with the five-layer structure shown in FIG. 3 were prepared according to the negative electrode preparation method described above, and evaluation cells containing the prepared negative electrode plates were fabricated. Additionally, for Sample 1, a negative electrode plate composed only of a negative electrode active material layer, without a nonionic water-absorbing polymer layer or mixed layer, was fabricated, and an evaluation cell containing the prepared negative electrode plate was fabricated. [Table 2] shows the layer thicknesses, polymer layer porosity, and evaluation results of the evaluation cells for Samples 1, 3-6, and 15-20. Note that the thicknesses of each layer shown in [Table 2] are relative values ​​when the sum of the thicknesses of the mixed layer and the negative electrode active material layer is set to 100. The values ​​for "resistance at end of charge at first cycle" and "cycle characteristics" shown in [Table 2] are relative values ​​when the values ​​for "resistance at end of charge at first cycle" and "cycle characteristics" of Sample 1 are set to 1.0, respectively.

[0085]

[0086] Referring to Table 2, as shown in Samples 3 to 6, the inclusion of a nonionic water-absorbing polymer layer and a mixed layer improved the cycle characteristics. As with Sample 2, the nonionic water-absorbing polymer layer suppressed short circuits, and the presence of the mixed layer likely contributed to uniformity of the reaction of the negative electrode active material. This uniformity of the reaction of the negative electrode active material is believed to be due to the following reason: Hydroxide ions must be supplied from the positive electrode to continue the charge-discharge reaction of the negative electrode active material. Therefore, with typical negative electrode active materials, the reaction in the surface layer close to the positive electrode prevails. In contrast, the formation of a mixed layer likely facilitates the charge-discharge reaction of the negative electrode active material located further inside, since a portion of the negative electrode active material in the mixed layer is covered by the water-absorbing polymer, making it difficult for the charge-discharge reaction to occur. As shown in Samples 3 to 6 and Samples 15 to 20, the cycle characteristics were improved when the thickness of the nonionic water-absorbing polymer layer was 0.3 times or less the sum of the thicknesses of the mixed layer and the negative electrode active material layer (i.e., when the thickness of the nonionic water-absorbing polymer layer in Table 2 was 30 or less). As shown in Sample 20, when a nonionic water-absorbing polymer layer was present on at least one surface, the cycle characteristics were improved.

[0087] [Sample 7 and Sample 21] For Samples 7 and 21, negative electrode plates with a five-layer structure as shown in FIG. 3 were prepared according to the negative electrode preparation method described above, and evaluation cells containing the prepared negative electrode plates were fabricated. Additionally, for Sample 1, a negative electrode plate consisting only of a negative electrode active material layer, without a nonionic water-absorbing polymer layer or mixed layer, was fabricated, and an evaluation cell containing the prepared negative electrode plate was fabricated. [Table 3] shows the thickness of each layer of the negative electrode plates of Samples 2, 3, 5 (listed again), and Samples 1, 7, and 21, the porosity of the polymer layer, and the evaluation results of the evaluation cells. The thickness of each layer shown in [Table 3] is a relative value when the sum of the thicknesses of the mixed layer and the negative electrode active material layer is set to 100. The values ​​of "resistance at end of charge at first cycle" and "cycle characteristics" shown in [Table 3] are relative values ​​when the values ​​of "resistance at end of charge at first cycle" and "cycle characteristics" of Sample 1 are set to 1.0, respectively.

[0088]

[0089] Referring to Table 3, as shown in Samples 2, 3, 5, and 7, it was confirmed that the cycle characteristics were improved when the porosity of the nonionic water-absorbing polymer layer was at least in the range of 0 to 50%. Although Samples 7 and 5 differ slightly in the thickness of the nonionic water-absorbing polymer layer and the mixed layer, this suggests that a higher porosity of the nonionic water-absorbing polymer layer improves the cycle characteristics. Sample 5, which has a higher porosity of the nonionic water-absorbing polymer layer, showed a lower resistance at the end of the first cycle charge than Sample 7, which has a lower porosity, suggesting that this is due to the easier supply of hydroxide ions necessary for the charge-discharge reaction to the negative electrode active material. Furthermore, as shown in Samples 5 and 21, which are samples having a nonionic water-absorbing polymer layer and a mixed layer of the same thickness, the cycle characteristics were improved when the porosity of the nonionic water-absorbing polymer layer was 0 to 50%.

[0090] It should be understood that the embodiments disclosed herein are illustrative in all respects and are not limiting in any respect. The scope of the present invention is defined not by the above description but by the claims, and it is intended to include all modifications within the meaning and scope of the claims.

[0091] 1, 2, 3, 4, 5, 6 negative electrode plate, 11a, 11b nonionic water-absorbing polymer layer, 30, 31a, 31b mixed layer, 50 negative electrode active material layer, 100 negative electrode, 200 positive electrode, 300 separator, 400 electrolyte, 500 zinc secondary battery.

Claims

1. A negative electrode plate comprising a negative electrode active material and a nonionic water-absorbing polymer, and having a nonionic water-absorbing polymer layer formed on the surface of at least one of a pair of main surfaces.

2. The negative electrode plate according to claim 1, further comprising a mixed layer in contact with the layer of nonionic water-absorbing polymer, the mixed layer being a mixture of the negative electrode active material and the nonionic water-absorbing polymer.

3. The negative electrode plate according to claim 2, further comprising a negative electrode active material layer made of the negative electrode active material and in contact with the mixed layer.

4. The negative electrode plate according to claim 1 or 2, wherein the thickness (A) of the layer containing the negative electrode active material and the thickness (B) of the nonionic water-absorbing polymer layer satisfy the relationship B≦A×0.

3.

5. The negative electrode plate according to claim 1 or 2, wherein the porosity of the nonionic water-absorbing polymer layer is 0 to 50%.

6. The negative electrode plate according to claim 1 or 2, 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 resins (PVA resins), and polyvinyl butyral resins (PVB resins).

7. The negative electrode plate according to claim 1 or 2, wherein the nonionic water-absorbing polymer is a polyalkylene oxide-based water-absorbing resin.

8. The negative electrode plate according to claim 1 or 2, wherein the nonionic water-absorbing polymer has a property that its liquid absorption property changes in response to changes in pH.

9. The negative electrode plate according to claim 1 or 2, wherein the negative electrode active material contains ZnO particles and Zn particles, and the content of the Zn particles is 1.0 to 87.5 parts by weight when the content of the ZnO particles is 100 parts by weight.

10. The negative electrode plate according to claim 1 or 2, further comprising one or more metal elements selected from In and Bi.

11. The negative electrode plate according to claim 3, wherein the negative electrode active material layer in the negative electrode plate is a sheet-like pressed body.

12. A zinc secondary battery comprising: a positive electrode; a negative electrode including the negative electrode plate according to claim 1 or 2; a separator separating the positive electrode and the negative electrode in a manner that allows hydroxide ions to be conducted therebetween; and an electrolyte.

13. The zinc secondary battery according to claim 12, wherein the separator is an LDH separator containing a layered double hydroxide (LDH) or an LDH-like compound.

14. The zinc secondary battery according to claim 13, wherein the LDH separator is composited with a porous substrate.

15. The zinc secondary battery according to claim 12, wherein the positive electrode comprises nickel hydroxide or nickel oxyhydroxide, thereby making the zinc secondary battery a nickel-zinc secondary battery.

16. 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.

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