A negative electrode for a zinc secondary battery, and a nickel-zinc secondary battery and its usage method.

Abstract

This invention provides a negative electrode for zinc secondary batteries that can extend battery life by delaying the decrease in battery capacity during trickle charging. [Solution] A negative electrode used in a zinc secondary battery, comprising ZnO particles and metallic Zn particles in an amount of 55.0 to 65.0 parts by weight per 100 parts by weight of ZnO particles.

Description

Technical Field

[0001] The present invention relates to a negative electrode for a zinc secondary battery, a nickel-zinc secondary battery, and a method of using the same.

Background Art

[0002] In general, ZnO particles and metallic Zn particles are used in combination for the negative electrode of a nickel-zinc secondary battery. Patent Document 1 (Japanese Unexamined Patent Application Publication No. 2021-57339) discloses a negative electrode for a zinc secondary battery, which includes a negative electrode active material containing Zn particles and ZnO particles, and a conductive auxiliary agent containing solder. This document describes that the amount of Zn particles in the negative electrode is preferably 1 to 50 parts by weight when the content of ZnO particles is 100 parts by weight. Patent Document 2 (WO2022 / 118625) discloses a negative electrode for a zinc secondary battery, which includes a negative electrode active material containing ZnO particles and Zn particles, and a nonionic water-absorbing polymer. This document discloses that a negative electrode was prepared by adding 5.7 parts by weight of metallic Zn powder, 1 part by weight of polytetrafluoroethylene (PTFE), and optionally a nonionic water-absorbing polymer or an ionic water-absorbing polymer to 100 parts by weight of ZnO powder.

[0003] Incidentally, in zinc secondary batteries such as nickel-zinc secondary batteries and zinc-air secondary batteries, it is known that during charging, metallic zinc deposits in the form of dendrites from the negative electrode, 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 charge-discharge life. To address this problem, batteries equipped with a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to permeate while preventing the penetration of zinc dendrites have been proposed (see, for example, Patent Documents 1 and 2, and Patent Documents 3 (WO2016 / 076047) and 4 (WO2019 / 124270)). Furthermore, Patent Documents 5 (WO2019 / 069760) and 6 (WO2019 / 077953) propose a zinc secondary battery in which the entire negative electrode active material layer is covered or enclosed by a liquid-retaining member and an LDH separator, and the positive electrode active material layer is covered or enclosed by a liquid-retaining member. Nonwoven fabric is used as the liquid-retaining member. According to this configuration, a zinc secondary battery (especially a stacked battery thereof) that can prevent zinc dendrite extension can be manufactured very simply and with high productivity, without the need for complicated sealing and bonding between the LDH separator and the battery container.

[0004] Furthermore, LDH-like compounds are known as hydroxides and / or oxides with a layered crystalline structure that are similar to LDH, although they cannot be called LDH themselves. These compounds exhibit hydroxide ion conductivity characteristics so similar to LDH that they can be collectively referred to as hydroxide ion-conducting layered compounds (see, for example, Patent Documents 1 and 2). Specifically, Patent Document 7 (WO2020 / 255856) discloses a hydroxide ion-conducting separator comprising a porous substrate and a layered double hydroxide (LDH)-like compound that seals the pores of the porous substrate, wherein the LDH-like compound is a hydroxide and / or oxide with a layered crystalline structure containing Mg and at least one element selected from the group consisting of Ti, Y, and Al, including at least Ti. Furthermore, Patent Document 8 (WO2021 / 229916) discloses an LDH separator using an LDH-like compound comprising (i) Ti, Y, and optionally Al and / or Mg, and (ii) at least one additive element M selected from the group consisting of In, Bi, Ca, Sr, and Ba. In addition, Patent Document 9 (WO2021 / 229917) discloses an LDH separator comprising a mixture of an LDH-like compound and In(OH)3, wherein the LDH-like compound is a layered crystalline hydroxide and / or oxide comprising Mg, Ti, Y, and optionally Al and / or In. According to the separators disclosed in Patent Documents 7 to 9, compared to conventional LDH separators, they are said to have superior alkali resistance and to be able to more effectively suppress short circuits caused by zinc dendrites. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2021-57339 [Patent Document 2] WO2022 / 118625 [Patent Document 3] WO2016 / 076047 [Patent Document 4] WO2019 / 124270 [Patent Document 5] WO2019 / 069760 [Patent Document 6] WO2019 / 077953 [Patent Document 7] WO2020 / 255856 [Patent Document 8] WO2021 / 229916 [Patent Document 9] WO2021 / 229917 [Overview of the project]

[0006] In addition to cycle applications involving repeated charge and discharge, nickel-zinc secondary batteries also have backup applications as emergency power sources during power outages. For backup applications, it is desirable to maintain the battery capacity near full charge to ensure the minimum guaranteed capacity. Therefore, as shown in Figure 1, trickle charging (1) is performed to compensate for the battery capacity lost due to self-discharge (2). Trickle charging allows the battery capacity to be constantly maintained near full charge. However, there is a problem in that the battery capacity decreases during trickle charging, shortening the battery life.

[0007] The present inventors have now discovered that by using a negative electrode in which a predetermined amount of metallic Zn particles are mixed with ZnO particles in a zinc secondary battery, the decrease in battery capacity during trickle charging can be delayed, thereby extending the battery life.

[0008] Therefore, an object of the present invention is to provide a negative electrode for a zinc secondary battery that can delay the decrease in battery capacity during trickle charging and extend the battery life.

[0009] The present invention provides the following embodiments. [Aspect 1] The negative electrode used in a zinc secondary battery, ZnO particles and, A quantity of 55.0 to 65.0 parts by weight of metallic Zn particles per 100 parts by weight of the ZnO particles, The negative electrode, including the negative electrode. [Aspect 2] The negative electrode according to embodiment 1, wherein the content of the metallic Zn particles is 55.0 to 58.0 parts by weight per 100 parts by weight of the ZnO particles. [Aspect 3] The negative electrode according to embodiment 1 or 2, further comprising a binder resin. [Aspect 4] A positive electrode plate containing nickel hydroxide and / or nickel oxyhydroxide, A negative electrode plate according to any one of embodiments 1 to 3, A hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate in a manner that allows hydroxide ions to conduct, Electrolyte and A battery case in which the positive electrode plate, the negative electrode plate, and the hydroxide ion conductive separator are housed vertically, A nickel-zinc rechargeable battery equipped with [specific features / features]. [Aspect 5] The nickel-zinc secondary battery according to embodiment 4, wherein the hydroxide ion conductive separator is an LDH separator containing layered double hydroxide (LDH) and / or an LDH-like compound. [Aspect 6] The nickel-zinc secondary battery according to embodiment 5, wherein the LDH separator is composited with a porous substrate. [Aspect 7] A nickel-zinc secondary battery according to any one of embodiments 4 to 6, wherein the negative electrode plate is covered with the hydroxide ion conductive separator, and the outer periphery of the negative electrode plate, excluding the upper end, is hermetically sealed, thereby preventing oxygen generated on the positive electrode plate from reaching the negative electrode plate. [Aspect 8] The nickel-zinc battery comprises stacked cells, and the stacked cells are Multiple positive electrode plates, A plurality of positive electrode tab leads extending from each end of the positive electrode plate, Multiple negative electrode plates, Multiple negative electrode tab leads extend from each end of the negative electrode plate at positions that do not overlap with the positive electrode tab leads, A plurality of hydroxide ion conductive separators that isolate the positive electrode plate and the negative electrode plate in a manner that allows hydroxide ions to conduct, the electrolytic solution, The nickel-zinc secondary battery according to any one of Aspects 4 to 7, comprising the above, in which the positive electrode plate and the negative electrode plate are alternately laminated with the hydroxide ion conductive separator interposed therebetween. [Aspect 9] A method of using a nickel-zinc secondary battery, comprising performing trickle charging so as to provide a charging capacity of 80 to 85% of the mounting capacity of the nickel-zinc secondary battery, with respect to the nickel-zinc secondary battery according to any one of Aspects 4 to 8. [Aspect 10] The method of using a nickel-zinc secondary battery according to Aspect 9, in which the charging capacity is 80% of the mounting capacity of the nickel-zinc secondary battery.

Brief Description of Drawings

[0010] [Figure 1] It is a figure which shows an example of a trickle charge profile. [Figure 2] It is a figure for explaining trickle charge from the viewpoint of battery capacity. [Figure 3] It is a schematic cross-sectional view conceptually showing the movement of oxygen generated by self-discharge in a nickel-zinc secondary battery. [Figure 4] It is a schematic cross-sectional view showing an example of a nickel-zinc secondary battery according to the present invention. [Figure 5] It is a figure which shows typically the cross section of the A-A' line of the nickel-zinc secondary battery shown in FIG. 4. [Figure 6] It is a perspective view which shows typically the laminated cell of the nickel-zinc secondary battery shown in FIG. 4. [Figure 7] It is a cross-sectional view which shows typically the laminated cell of the nickel-zinc secondary battery shown in FIG. 4. [Figure 8] It is a perspective view which shows the form covered with the hydroxide ion conductive separator or the liquid retention member of the positive electrode plate or the negative electrode plate in the nickel-zinc secondary battery shown in FIG. 4. [Figure 9A] It is a figure which shows conceptually the movement of oxygen from the positive electrode plate when the negative electrode plate is covered with a microporous membrane separator. [Figure 9B]This diagram conceptually illustrates the movement of oxygen from the positive electrode plate when the negative electrode plate is covered with a hydroxide ion conductive separator. In the diagram, the "x" marks indicate that the movement of oxygen (O2) is blocked at that point. [Figure 10A] The charging profiles from the trickle charging acceleration tests conducted in Examples A1 and A2 are shown. [Figure 10B] This figure shows the results of trickle charging acceleration tests conducted at 65°C in Examples A1 and A2. [Figure 10C] This figure shows the results of trickle charging acceleration tests conducted at 55°C in Examples A1 and A2. [Figure 11A] The charging profiles from the trickle charging acceleration tests conducted in Examples B1 and B2 are shown. [Figure 11B] This figure shows the results of trickle charging acceleration tests conducted at 65°C in examples B1 and B2. [Figure 11C] This figure shows the results of trickle charging acceleration tests conducted at 55°C in examples B1 and B2. [Figure 11D] This figure shows the results of trickle charging acceleration tests conducted at 55°C in Examples A1 and B2. [Figure 12A] The charging profiles from the trickle charging acceleration tests conducted in Examples C1 and C2 are shown. [Figure 12B] This figure shows the results of trickle charging acceleration tests conducted at 65°C in examples C1 and C2. [Figure 13] This figure shows the charging curve of an example nickel-zinc secondary battery, along with the change in oxygen concentration. [Modes for carrying out the invention]

[0011] definition The definitions of terms used in this specification are given below.

[0012] In this specification, "capacity" is defined as the theoretical capacity calculated from the mass of the positive electrode active material in the battery. The theoretical capacity Cm (Ah / g) of 1g can be calculated from the formula Cm = F × N × M (wherein F is the charge amount of 1 mole of electrons, N is the number of moles of reactive electrons per mole of electrode material, and M is the number of moles per gram of electrode material). Since the theoretical capacity per unit mass of 1g of Ni(OH)2 is 289.1mAh / g, the capacity of a battery with 345.9g of Ni(OH)2 as the positive electrode active material will be 100Ah. The reason for defining the capacity based on the positive electrode active material is that we are assuming a battery where the positive electrode capacity is smaller than the negative electrode capacity, in which case the capacity will be limited by the positive electrode capacity. Therefore, if we assume a battery where the positive electrode capacity is larger than the negative electrode capacity, we should replace "mass of positive electrode active material" in the above definition with "mass of negative electrode active material".

[0013] In this specification, "rated capacity" means the amount of electricity that can be drawn (stored) under specified conditions, more specifically, the amount of electricity that can be drawn from a fully charged state at specified temperature, discharge current, and cutoff voltage. For example, the rated capacity may be the discharge capacity at 25°C, a cutoff voltage of 1.4V, and 0.1C (10-hour rate).

[0014] In this specification, "depth" and "SOC" refer to the charge state (charge rate) of the battery relative to its rated capacity of 100%. Therefore, the depth (SOC) of a completely discharged state is 0%, and the depth (SOC) of a fully charged state is 100%.

[0015] In this specification, "utilization rate" means the ratio of the charging capacity to 100% of the installed capacity. For example, if the installed capacity is 133.3Ah and the rated capacity is 120Ah, the utilization rate at the rated capacity (i.e., 100% of the state of charge (SOC)) is 90% (= (120 / 133.3) × 100), which is the ratio of the rated capacity to 100% of the installed capacity.

[0016] In this specification, "self-discharge" refers to the phenomenon in which the amount of electricity stored by a chemical reaction gradually decreases over time without any current being drawn out to an external circuit.

[0017] In this specification, "trickle charging" refers to charging (1) performed to compensate for the battery capacity lost due to self-discharge (2) of a secondary battery, as shown in Figures 1 and 3. More specifically, as shown in Figure 2, based on a rated capacity (defined as a certain percentage of the installed capacity, this is called a state of charge (SOC) of 100%), the battery capacity lost due to self-discharge can be compensated for by trickle charging, thereby maintaining the battery capacity at or near full charge at all times. Trickle charging is widely used in emergency power supplies such as uninterruptible power supplies (UPS). When a battery is stored in a fully charged state for a long period of time and then used, it may not be able to perform at its rated capacity or may not be usable at all. To avoid this problem, trickle charging is widely used as one method of charging to compensate for self-discharge. This makes it possible to guarantee a predetermined battery capacity (80% in Figure 2) or more.

[0018] negative electrode for zinc secondary batteries The negative electrode of the present invention is a negative electrode used in a zinc secondary battery. The zinc secondary battery is not particularly limited as long as it uses zinc as the negative electrode and an alkaline 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, an air-zinc secondary battery, or various other alkali-zinc secondary batteries. The negative electrode is typically a negative electrode plate 14 including a negative electrode active material layer 14a and a negative electrode current collector 14b, as shown in Figure 3. This negative electrode or negative electrode plate 14 (especially the negative electrode active material layer 14a) contains ZnO particles and metallic Zn particles. The amount of metallic Zn particles is 55.0 to 65.0 parts by weight per 100 parts by weight of ZnO particles. By using a negative electrode with a predetermined amount of metallic Zn particles in relation to ZnO particles in a zinc secondary battery, the decrease in battery capacity during trickle charging can be delayed, extending the battery life.

[0019] In other words, as mentioned above, in backup applications of nickel-zinc secondary batteries, it is desirable to maintain the battery capacity near full charge in order to ensure the minimum guaranteed capacity of the battery. Therefore, as shown in Figure 1, trickle charging (1) is performed to compensate for the battery capacity lost due to self-discharge (2). However, there is a problem that the battery capacity decreases during trickle charging, shortening the battery life. This problem is conveniently resolved by the negative electrode of the present invention. The mechanism is thought to be as follows: In other words, the positive electrode of a nickel-zinc secondary battery undergoes the following reactions during trickle charging and self-discharge (static): (1) Charging reaction: • Positive electrode: 4OH - →O2↑+2H2O+4e - (2) Self-discharge reaction: ·Positive electrode: 2NiOOH+H2O→2Ni(OH)2+1 / 2O2↑ This generates oxygen. Then, as shown in Figure 3, the generated oxygen moves from the positive electrode plate 12 to the negative electrode plate 14, passing through the liquid retention member 17 and the separator 116, resulting in the following reaction: ·Negative electrode: Zn+1 / 2O2→ZnO As a result, the metallic Zn (active material in the charged state) contained in the negative electrode plate 14 oxidizes to ZnO (active material in the discharged state), reducing the negative electrode capacity. Consequently, the battery capacity decreases, shortening the battery life when using trickle charging. Therefore, by using a negative electrode in which the amount of metallic Zn particles is increased relative to the amount of ZnO particles in a zinc secondary battery, the decrease in battery capacity during trickle charging can be delayed, extending the battery life.

[0020] The ZnO particles are not particularly limited and can be commercially available zinc oxide powder used in zinc secondary batteries, or zinc oxide powder grown by solid-phase reaction or the like using such powders as starting materials. 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. In this specification, the average particle size D50 refers to the particle size at which the cumulative volume from the smallest particle size side accounts for 50% of the particle size distribution obtained by laser diffraction-scattering.

[0021] While metal Zn particles commonly used in zinc secondary batteries can be used, the use of smaller metal Zn particles is more preferable from the viewpoint of extending the battery's cycle life. Specifically, the average particle size D50 of the metal Zn particles is preferably 50 to 150 μm. The content of metal Zn particles in the negative electrode is preferably 55.0 to 65.0 parts by weight, more preferably 55.0 to 58.0 parts by weight, and even more preferably 56.6 to 57.6 parts by weight, per 100 parts by weight of ZnO particles. This amount is significantly higher than the amount of metal Zn particles in the negative electrode of conventional nickel-zinc secondary batteries. By using a negative electrode with an increased amount of metal Zn particles relative to ZnO particles in a zinc secondary battery, the decrease in battery capacity during trickle charging can be delayed, extending the battery's life. Furthermore, by ensuring that the amount of metal Zn particles is not too high relative to ZnO particles, the molding of the negative electrode using metal Zn particles and ZnO particles becomes easier. The metal Zn particles may be doped with dopants such as In and Bi.

[0022] The negative electrode or negative electrode plate 14 (particularly the negative electrode active material layer 14a) 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 included in the negative electrode in any form such as metal, oxide, hydroxide, or other compound, but are preferably included 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 In2O3 and Bi2O3. Examples of hydroxides of the above metal elements include In(OH)3 and Bi(OH)3. In any case, when the content of ZnO particles is 100 parts by weight, it is preferable that the In content is 0 to 2 parts by weight in terms of oxide and the Bi content is 0 to 6 parts by weight in terms of oxide, and more preferably that the In content is 0 to 1.5 parts by weight in terms of oxide and the Bi content is 0 to 4.5 parts by weight in terms of oxide. When In and / or Bi are included in the negative electrode in the form of oxides or hydroxides, not all of the In and / or Bi must be in the form of oxides or hydroxides; some of them may be included in the negative electrode in other forms, such as metals or other compounds. For example, the above metal elements may be doped into metallic Zn particles as trace elements. In this case, the concentration of In in the metallic Zn particles is preferably 50 to 2000 ppm by weight, more preferably 200 to 1500 ppm by weight, and the concentration of Bi in the metallic Zn particles is preferably 50 to 2000 ppm by weight, more preferably 100 to 1300 ppm by weight.

[0023] The negative electrode or negative electrode plate 14 (particularly the negative electrode active material layer 14a) may further contain a conductive additive. Examples of conductive additives include carbon, metal powder (tin, lead, copper, cobalt, etc.), and precious metal paste.

[0024] The negative electrode or negative electrode plate 14 (particularly the negative electrode active material layer 14a) may further contain a binder resin. The inclusion of a binder in the negative electrode makes it easier to maintain the negative electrode shape. Various known binders can be used as the binder resin, but preferred examples include polyvinyl alcohol (PVA) and polytetrafluoroethylene (PTFE). It is particularly preferable to use a combination of both PVA and PTFE as the binder.

[0025] The negative electrode or negative electrode plate 14 is preferably a sheet-shaped press-molded body. This prevents the detachment of the negative electrode active material and improves electrode density, thereby more effectively suppressing changes in the negative electrode's shape. Such a sheet-shaped press-molded body can be produced by adding a binder to the negative electrode material and kneading it, then press-molding the resulting mixture using a roll press or similar method to form it into a sheet.

[0026] The negative electrode or negative electrode plate 14 preferably includes a negative electrode current collector 14b. Preferred examples of the negative electrode current collector 14b include copper perforated metal and copper expanded metal. In this case, for example, a negative electrode plate consisting of a negative electrode / negative electrode current collector can be preferably manufactured by coating a mixture containing a Zn compound, metallic zinc and zinc oxide powder, and optionally a binder (e.g., polytetrafluoroethylene particles) onto copper perforated metal or copper expanded metal. At that time, it is also preferable to press the negative electrode plate (i.e., negative electrode / negative electrode current collector) after drying to prevent the electrode active material from falling off and to improve the electrode density. Alternatively, a sheet-like press-molded body as described above may be pressed onto a current collector such as copper expanded metal.

[0027] Nickel-zinc rechargeable battery The negative electrode according to the present invention is preferably used as the negative electrode of a nickel-zinc secondary battery. Figures 4 to 8 show a nickel-zinc secondary battery 10 and its components according to one aspect of the present invention. The nickel-zinc secondary battery 10 comprises a positive electrode plate 12, a negative electrode plate 14, a hydroxide ion conductive separator 16, an electrolyte (not shown), and a battery case 20. Typically, the positive electrode plate 12 includes a positive electrode active material layer 12a and a positive electrode current collector 12b. The positive electrode plate 12 (particularly the positive electrode active material layer 12a) contains nickel hydroxide and / or nickel oxyhydroxide. The negative electrode plate 14 (particularly the negative electrode active material layer 14a) contains ZnO particles and metallic Zn particles, as described above. The hydroxide ion conductive separator 16 isolates the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ions to conduct. The battery case 20 houses the positive electrode plate 12, the negative electrode plate 14, and the hydroxide ion conductive separator 16 in a vertical orientation (i.e., perpendicular to the ground surface).

[0028] The nickel-zinc secondary battery 10 preferably comprises a laminated cell 11. As shown in Figure 7, the laminated cell 11 comprises a plurality of positive electrode plates 12, a plurality of positive electrode tab leads 13, a plurality of negative electrode plates 14, a plurality of negative electrode tab leads 15, a plurality of hydroxide ion conductive separators 16, and an electrolyte. The plurality of positive electrode tab leads 13 extend (preferably upward) from each end of the positive electrode plate 12. The plurality of negative electrode tab leads 15 extend (preferably upward) from each end of the negative electrode plate 14 at a position that does not overlap with the positive electrode tab leads 13. The plurality of hydroxide ion conductive separators 16 isolate the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ion conduction. The laminated cell 11 is constructed by alternately stacking the positive electrode plate 12 and the negative electrode plate 14 with the hydroxide ion conductive separators 16 in between. Therefore, the laminated cell 11 can be said to be in the form of a positive-negative electrode laminate in which units of positive electrode plate 12 / separator 16 / negative electrode plate 14 are stacked in a repeating manner. In other words, it is preferable that the nickel-zinc secondary battery 10 includes a plurality of unit cells 10a, each having a pair of positive electrode plates 12 and negative electrode plates 14 together with a hydroxide ion conductive separator 16, and that the plurality of unit cells 10a as a whole form the laminated cell 11. This is a so-called battery pack or laminated battery configuration, which is advantageous in that high voltage and high current can be obtained.

[0029] The positive electrode plate 12 includes a positive electrode active material layer 12a. The positive electrode active material constituting the positive electrode active material layer 12a is not particularly limited and can be appropriately selected from known positive electrode materials depending on the type of zinc secondary battery. For example, in the case of a nickel-zinc secondary battery, a positive electrode containing nickel hydroxide and / or nickel oxyhydroxide may be used. In this case, the positive electrode active material layer 12a may also contain an additive which is at least one selected from the group consisting of silver compounds, manganese compounds, and titanium compounds, thereby promoting a positive electrode reaction that absorbs hydrogen gas generated by the self-discharge reaction. Furthermore, the positive electrode active material layer 12a may further contain cobalt. It is preferable that the cobalt is included in the positive electrode plate 12 in the form of cobalt oxyhydroxide. In the positive electrode active material layer 12a, cobalt functions as a conductive additive, thereby contributing to an improvement in charge-discharge capacity.

[0030] The positive electrode plate 12 further includes a positive electrode current collector 12b. A preferred example of the positive electrode current collector 12b is a porous nickel substrate such as a foamed nickel plate. In this case, for example, a positive electrode plate consisting of a positive electrode / positive electrode current collector can be preferably manufactured by uniformly applying a paste containing an electrode active material such as nickel hydroxide onto the porous nickel substrate and drying it. At that time, it is also preferable to press the positive electrode plate (i.e., positive electrode / positive electrode current collector) after drying to prevent the electrode active material from falling off and to improve the electrode density. If the positive electrode current collector 12b is a porous nickel substrate such as a foamed nickel plate, the uncoated area of ​​the positive electrode current collector 12b may be processed into a tab shape by pressing it.

[0031] As shown in Figure 8, the positive electrode tab lead 13 is provided so as to extend from the end of the positive electrode plate 12. The positive electrode tab lead 13 is not particularly limited and can be made from commercially available thin metal sheets. It is preferable that multiple positive electrode tab leads 13 are joined to a single positive electrode terminal 26 or a member electrically connected to it to form a positive electrode tab joint 30. This allows for a simple configuration and space-efficient current collection, and also facilitates connection to the positive electrode terminal 26. The joining of the positive electrode tab lead 13 to members such as the positive electrode current collector 12b and the positive electrode terminal 26 can be performed using known joining methods such as ultrasonic welding (ultrasonic bonding), laser welding, TIG welding, and resistance welding.

[0032] As described above, the negative electrode plate 14 (particularly the negative electrode active material layer 14a) contains ZnO particles and metallic Zn particles. The negative electrode tab lead 15 is provided to extend from the end of the negative electrode plate 14 at a position that does not overlap with the positive electrode tab lead 13 (see Figure 6), as shown in Figure 8. The negative electrode tab lead 15 is not particularly limited and can be made from commercially available metal flakes. It is preferable that multiple negative electrode tab leads 15 are joined to a single negative electrode terminal 28 or a component electrically connected to it to form a negative electrode tab joint 32. This allows for space-efficient current collection with a simple configuration and facilitates connection to the negative electrode terminal 28. The joining of the negative electrode tab lead 15 to components such as the negative electrode current collector 14b and the negative electrode terminal 28 can be performed using known joining methods such as ultrasonic welding (ultrasonic bonding), laser welding, TIG welding, and resistance welding.

[0033] The hydroxide ion conductive separator 16 is provided to isolate the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ions to conduct. For example, as shown in Figures 7 and 8, the positive electrode plate 12 and / or the negative electrode plate 14 (preferably the negative electrode plate 14) may be covered or enclosed by the hydroxide ion conductive separator 16. This eliminates the need for complicated sealing and bonding between the hydroxide ion conductive separator 16 and the battery container, making it possible to manufacture nickel-zinc secondary batteries (especially stacked batteries thereof) that can prevent zinc dendrite extension very simply and with high productivity. However, a simpler configuration in which the hydroxide ion conductive separator 16 is arranged on one side of the positive electrode plate 12 or the negative electrode plate 14 is also acceptable.

[0034] The hydroxide ion conductive separator 16 is not particularly limited as long as it is a separator capable of separating the positive electrode plate 12 and the negative electrode plate 14 in a way that allows hydroxide ions to conduct, but typically it is a separator that contains a hydroxide ion conductive solid electrolyte and selectively passes hydroxide ions by exclusively utilizing its hydroxide ion conductivity. Preferred hydroxide ion conductive solid electrolytes are layered double hydroxides (LDH) and / or LDH-like compounds. Therefore, it is preferable that the hydroxide ion conductive separator 16 is an LDH separator. In this specification, "LDH separator" is defined as a separator containing LDH and / or an LDH-like compound that selectively passes hydroxide ions by exclusively utilizing the hydroxide ion conductivity of LDH and / or an LDH-like compound. In this specification, "LDH-like compound" is a layered crystalline hydroxide and / or oxide that has hydroxide ion conductivity but may not be called LDH, and can be considered an equivalent of LDH. However, in a broader definition, "LDH" can also be interpreted to include not only LDH but also LDH-like compounds. The LDH separator is preferably compounded with a porous substrate. Therefore, the LDH separator is preferably compounded with the porous substrate in a form in which LDH and / or an LDH-like compound fills the pores of the porous substrate. That is, in a preferred LDH separator, the LDH and / or LDH-like compound fills the pores of the porous substrate so as to exhibit hydroxide ion conductivity and gas impermeability (and thus function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymer material, and it is particularly preferable that the LDH is incorporated throughout the entire thickness of the polymer porous substrate. For example, known LDH separators such as those disclosed in Patent Documents 1 to 7 can be used. The thickness of the LDH separator is preferably 5 to 100 μm, more preferably 5 to 80 μm, even more preferably 5 to 60 μm, and particularly preferably 5 to 40 μm.

[0035] It is preferable that not only a hydroxide ion conductive separator 16 but also a liquid-retaining member 17 is interposed between the positive electrode plate 12 and the negative electrode plate 14. Furthermore, as shown in Figures 7 and 8, it is preferable that the positive electrode plate 12 and / or the negative electrode plate 14 are covered or encased by the liquid-retaining member 17. However, a simpler configuration in which the liquid-retaining member 17 is placed on one side of the positive electrode plate 12 or the negative electrode plate 14 is also acceptable. In any case, by interposing the liquid-retaining member 17, the electrolyte can be evenly distributed between the positive electrode plate 12 and / or the negative electrode plate 14 and the hydroxide ion conductive separator 16, and the exchange of hydroxide ions between the positive electrode plate 12 and / or the negative electrode plate 14 and the hydroxide ion conductive separator 16 can be efficiently carried out. The liquid-retaining member 17 is not particularly limited as long as it is a member capable of holding electrolyte, but it is preferable that it is a sheet-like member. Preferred examples of the liquid-retaining member 17 include nonwoven fabric, superabsorbent resin, liquid-retaining resin, porous sheet, and various spacers, but nonwoven fabric is particularly preferred because it allows for the production of a low-cost, high-performance negative electrode structure. The liquid-retaining member 17 or nonwoven fabric preferably has a thickness of 10 to 200 μm, more preferably 20 to 200 μm, even more preferably 20 to 150 μm, particularly preferably 20 to 100 μm, and most preferably 20 to 60 μm. With a thickness within the above range, a sufficient amount of electrolyte can be retained within the liquid-retaining member 17 while keeping the overall size of the positive electrode structure and / or negative electrode structure compact and efficient.

[0036] When the positive electrode plate 12 and / or the negative electrode plate 14 are covered or enclosed by the fluid-retaining member 17 and / or separator 16, it is preferable that their outer edges are closed (except for the edges from which the positive electrode tab lead 13 and the negative electrode tab lead 15 extend). In this case, it is preferable that the closed edges of the outer edges of the fluid-retaining member 17 and / or separator 16 are achieved by bending the fluid-retaining member 17 and / or separator 16, or by sealing the fluid-retaining members 17 with each other and / or the separators 16 with each other. Preferred sealing methods include adhesives, heat welding, ultrasonic welding, adhesive tapes, sealing tapes, and combinations thereof. In particular, LDH separators containing a porous substrate made of polymer material have the advantage of being flexible and therefore easy to bend, so it is preferable to form the LDH separator in a long shape and bend it to form a closed state on one side of the outer edge. Heat welding and ultrasonic welding can be performed using commercially available heat sealers, but in the case of sealing LDH separators together, it is preferable to perform heat welding and ultrasonic welding by sandwiching the outer periphery of the liquid-retaining member 17 between the LDH separators that constitute the outer periphery, as this allows for more effective sealing. On the other hand, commercially available adhesives, adhesive tapes, and sealing tapes can be used, but it is preferable to use those containing alkali-resistant resins to prevent deterioration in alkaline electrolytes. From this viewpoint, examples of preferred adhesives include epoxy resin adhesives, natural resin adhesives, modified olefin resin adhesives, and modified silicone resin adhesives, among which epoxy resin adhesives are more preferred due to their particularly excellent alkali resistance. An example of an epoxy resin adhesive product is the epoxy adhesive Hysol® (manufactured by Henkel).

[0037] In a preferred embodiment of the present invention, as shown in Figures 7 and 8, the negative electrode plate 14 is covered with a hydroxide ion conductive separator 16, and the outer periphery of the negative electrode plate 14, excluding the upper end, is hermetically sealed. This configuration prevents oxygen generated at the positive electrode plate 12 from reaching the negative electrode plate 14. In other words, as mentioned above, in the positive electrode of a nickel-zinc secondary battery, oxygen is generated during trickle charging and self-discharge (static), leading to oxidation of the metallic Zn contained in the negative electrode and a resulting decrease in the negative electrode capacity, resulting in a shorter battery life when using trickle charging. In this regard, as shown in Figure 9A, conventional microporous membrane separators 116, which have been widely used, are gas permeable, allowing oxygen O2 generated at the positive electrode to pass through, directly reaching the adjacent negative electrode plate 14 from the positive electrode plate 12 and promoting the oxidation of metallic Zn. However, according to a preferred embodiment of this disclosure, as shown by the "x" in Figure 9B, the hydroxide ion conductive separator 16 prevents oxygen generated on the positive electrode plate 12 from reaching the negative electrode plate 14, thereby suppressing oxidation of metallic Zn caused by oxygen. This further delays the decrease in battery capacity during trickle charging, thereby extending the battery life even further. This is because the hydroxide ion conductive separator 16 is a separator that selectively allows hydroxide ions to pass through by utilizing its hydroxide ion conductivity, and therefore does not have gas permeability. In other words, by hermetically covering the negative electrode plate 14 with the hydroxide ion conductive separator 16, which does not have gas permeability, oxygen generated on the positive electrode plate 12 cannot pass through, and thus the oxidation of metallic Zn at the negative electrode can be suppressed. In this embodiment, it is not necessary for the outer periphery of the upper end of the negative electrode plate 14 to be sealed with the hydroxide ion conductive separator 16. In this case, the structure may allow oxygen to enter the negative electrode plate 14 from the upper end. However, because oxygen does not directly reach the negative electrode plate 14 from the positive electrode plate 12, that is, the effect of suppressing oxygen permeation between the opposing surfaces of the positive electrode plate 12 and the negative electrode plate 14, and the resulting effect of suppressing the oxidation of metallic Zn, the decrease in battery capacity during trickle charging can be sufficiently delayed.

[0038] Therefore, the outer edge of one side that forms the upper end of the separator 16 may be open. This open-top configuration makes it possible to address the problem of overcharging in nickel-zinc batteries and the like. That is, when nickel-zinc batteries and the like are overcharged, oxygen (O2) may be generated on the positive electrode plate 12, but the LDH separator has a high degree of density that substantially only allows hydroxide ions to pass through, and therefore does not allow O2 to pass through. In this respect, with the open-top configuration, within the battery case 20, O2 can escape to the upper part of the positive electrode plate 12 and be sent to the negative electrode plate 14 side through the open top part, thereby oxidizing the Zn of the negative electrode active material with O2 and returning it to ZnO. By going through such an oxygen reaction cycle, the overcharge resistance can be improved by using the open-top laminated cell 11 in a sealed zinc secondary battery. Even if the outer edge of one side that forms the upper end of the separator 16 or the liquid retention member 17 is closed, the same effect as the open-top configuration can be expected by providing a ventilation hole in a part of the closed outer edge. For example, the outer edge of one side that forms the upper end of the LDH separator may be sealed before creating a ventilation hole, or a portion of the outer edge may be left unsealed during sealing so that a ventilation hole is formed.

[0039] The electrolyte preferably contains an aqueous alkali metal hydroxide solution. The electrolyte is not shown in Figures 1-7 because it is distributed throughout the entire positive electrode plate 12 and negative electrode plate 14. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, but potassium hydroxide is more preferred. To suppress the self-dissolution of zinc and / or zinc oxide, zinc compounds such as zinc oxide and zinc hydroxide may be added to the electrolyte. As mentioned above, the electrolyte may be mixed with the positive electrode active material and / or negative electrode active material to exist in the form of a positive electrode composite and / or negative electrode composite. Furthermore, the electrolyte may be gelled to prevent leakage of the electrolyte. As a gelling agent, it is desirable to use a polymer that absorbs the solvent of the electrolyte and swells, and polymers such as polyethylene oxide, polyvinyl alcohol, polyacrylamide, and starch are used.

[0040] The battery case 20 is preferably made of resin. The resin constituting the battery case 20 is preferably a resin that has resistance to alkali metal hydroxides such as potassium hydroxide, more preferably a polyolefin resin, ABS resin, or modified polyphenylene ether, and even more preferably ABS resin or modified polyphenylene ether. The battery case 20 has a top cover 20a. The battery case 20 (for example, the top cover 20a) may have a pressure relief valve for releasing gas. Alternatively, a group of two or more battery cases 20 arranged in a row may be housed in an outer frame to form a battery module.

[0041] Instructions for using nickel-zinc rechargeable batteries As described above, the nickel-zinc secondary battery 10 according to the present invention is suitable for backup use as an emergency power source during power outages. In backup use, trickle charging is performed to compensate for the battery capacity that decreases due to self-discharge, as shown in Figures 1 and 2. Therefore, a preferred method of using the nickel-zinc secondary battery 10 includes performing trickle charging. In this case, it is preferable to perform trickle charging on the nickel-zinc secondary battery 10 to bring the charge capacity (utilization rate) to 80-85% of the mounted capacity of the nickel-zinc secondary battery 10 (which is considered to be 100%). Conventionally, trickle charging has generally been performed to bring the charge capacity to approximately 90% of the mounted capacity of the nickel-zinc secondary battery 10, but in this embodiment, by performing trickle charging at a lower charge capacity (utilization rate) of 80-85% of the mounted capacity of the nickel-zinc secondary battery 10 (especially the positive electrode plate 12) than conventional methods, the decrease in battery capacity during trickle charging can be further delayed, and the battery life can be further extended.

[0042] In other words, as mentioned above, in the positive electrode of a nickel-zinc secondary battery, oxygen is generated during trickle charging, leading to oxidation of the metallic Zn contained in the negative electrode and a resulting decrease in the negative electrode capacity. In this regard, Figure 13 shows the change in oxygen concentration in the charging curve of a nickel-zinc secondary battery manufactured by the applicant. As can be seen from Figure 13, the positive electrode is charged with oxygen generation in the region where the charging capacity is 90% or more of the installed capacity. Also, because the positive electrode active material expands during charging, in the case of charging that results in a charging capacity of 90% or more of the installed capacity, the positive electrode active material may detach from the positive electrode current collector or separate from the positive electrode current collector, which can increase resistance. In this respect, trickle charging that results in a charging capacity of 80-85% of the installed capacity can effectively avoid these problems. That is, oxygen generation at the positive electrode plate 12 during charging can be reduced to suppress oxidation of the negative electrode plate 14, and the increase in resistance due to the volume expansion of the positive electrode plate 12 can also be suppressed. As a result, the decrease in battery capacity can be delayed more effectively.

[0043] The ratio of the charging capacity to 100% of the installed capacity (utilization rate) during trickle charging is 80-85% of the installed capacity of the nickel-zinc secondary battery 10, more preferably 80-83%, and even more preferably 80%. By lowering the charging capacity (utilization rate) during trickle charging compared to conventional methods, but not too much, it is possible to perform trickle charging at the highest possible depth of charge (SOC) while effectively delaying the degradation of the battery capacity. [Examples]

[0044] The present invention will be further explained by the following examples.

[0045] Examples A1 and A2 (1) Fabrication of the negative electrode plate The following various raw material powders were prepared. • ZnO powder (manufactured by Seido Chemical Industry Co., Ltd., JIS standard Grade 1, average particle size D50: 0.2 μm) • Metallic zinc powder (manufactured by EverZinc Co., Ltd., average particle size D50: 100 μm)

[0046] According to the mixing ratios shown in Table 1, metallic zinc powder and polytetrafluoroethylene (PTFE) were added to ZnO powder and kneaded together with propylene glycol. The resulting mixture was rolled in a roll press to obtain a negative electrode active material sheet. The negative electrode active material sheet was pressed onto tin-plated copper expanded metal to obtain a negative electrode plate. At this time, an uncoated area where the negative electrode paste was not applied was made near one edge of the copper expanded metal. [Table 1]

[0047] (2) Manufacturing of nickel-zinc secondary batteries The following components were prepared: a positive electrode plate, a positive electrode current collector tab, a negative electrode plate, a negative electrode current collector tab, an LDH separator, a nonwoven fabric, a battery case, and an electrolyte. Two types of negative electrode plates with different compositions were prepared. • Positive electrode plate: A positive electrode paste containing nickel hydroxide and binder is filled into the pores of foamed nickel and dried (an uncoated area exists near one edge of the foamed nickel where the positive electrode paste is not applied). • Positive electrode current collector tab: The uncoated portion of the foamed nickel that makes up the positive electrode plate is compressed into a tab using a roll press, and a tab lead (made of pure nickel, thickness: 100 μm) is ultrasonically welded to this tab to extend it. • Negative electrode plate: The negative electrode plate prepared in (1) above. • Negative electrode current collector tab: A tab lead (made of copper, thickness: 100 μm) is connected to the unpainted portion of copper expanded metal by ultrasonic welding. • LDH Separator: A gas-impermeable hydroxide ion conductive separator, manufactured by hydrothermal synthesis of Ni-Al-Ti-LDH (layered double hydroxide) deposited inside and on the surface of a polyethylene microporous membrane, followed by roll pressing. Thickness: 20 μm. Nonwoven fabric: Made of polypropylene, 100 μm thick • Battery case: Box-shaped case made of modified polyphenylene ether resin (equipped with a pressure relief valve to release gas generated inside the case), internal dimensions: length 190mm, width 24mm, height 165mm, external dimensions: length 200mm, width 30mm, height 170mm (excluding the height of the positive and negative terminals) • Electrolyte: 5.4 mol / L KOH aqueous solution with 0.4 mol / L ZnO dissolved in it.

[0048] The positive electrode plate was wrapped in nonwoven fabric from both sides, so that the nonwoven fabric slightly protruded from the three sides excluding the side from which the positive electrode current collector tab extended. The excess portions of the nonwoven fabric protruding from the three sides of the positive electrode plate were heat-sealed using a heat-sealing bar to obtain a positive electrode structure. Similarly, the negative electrode plate was wrapped in LDH separator from both sides, so that the LDH separator slightly protruded from the three sides excluding the side from which the negative electrode current collector tab extended. The excess portions of the LDH separator protruding from the three sides of the negative electrode plate were hermetically sealed by heat-sealing using a heat-sealing bar to obtain a negative electrode structure. In this way, multiple positive electrode structures and multiple negative electrode structures were prepared.

[0049] 42 stacked cells of varying thicknesses were fabricated by alternately stacking 12 positive electrode structures and 13 negative electrode structures. Similar to the configuration shown in Figure 6, the multiple positive electrode tab leads 13 and multiple negative electrode tab leads 15 are designed to extend from different positions from the electrode current collector when viewed from above. As a result, multiple positive electrode tab leads 13 are stacked on top of each other, while multiple negative electrode tab leads 15 are stacked on top of each other at different positions. As shown in Figure 7, the overlapping portions of the multiple positive electrode tab leads 13 were joined together to the positive electrode terminal 26 by laser welding to form a positive electrode tab joint 30. Similarly, the overlapping portions of the multiple negative electrode tab leads 15 were joined together to the negative electrode terminal 28 by laser welding to form a negative electrode tab joint 32. In this way, a stack of electrode structures equipped with positive electrode tab leads 13 and negative electrode tab leads 15 was obtained as a stacked cell 11. As shown in Figures 4 and 5, the stacked cell 11 was placed in the battery case 20, the electrolyte was injected to impregnate the stacked cell 11, and the top cover 20a was closed to seal it. In this way, two nickel-zinc secondary batteries were fabricated in each example.

[0050] (3) Accelerated trickle charge test A trickle charge acceleration test was performed on each of the two fabricated nickel-zinc secondary batteries at a temperature of 65°C using the following procedure. Using a charge / discharge device (TOSCAT3200, manufactured by Toyo System Co., Ltd.), the fabricated nickel-zinc secondary batteries were subjected to chemical conversion by 0.1C charging and 0.2C discharging. Subsequently, 0.2C charging and 0.1C discharging were performed to measure the initial discharge capacity. Then, according to the charging profile shown in Figure 10A, the nickel-zinc secondary batteries were charged to 100% state of charge (SOC) and left in a resting state for approximately 168 hours (approximately 7 days). During the approximately 168 hours of resting, the state of charge of the nickel-zinc secondary batteries decreased due to self-discharge as shown in Figure 10A. Trickle charging was performed on the fabricated nickel-zinc secondary battery using a charge / discharge device (TOSCAT3000S, manufactured by Toyo System Co., Ltd.) at 0.025C until the State of Charge (SOC) reached 100%. This was followed by approximately 168 hours of rest (self-discharge), which was repeated three times. This process maintained a high SOC for approximately one month through intermittent trickle charging. Subsequently, as shown in Figure 10A, 0.2C charging and 0.1C discharging were performed, and the discharge capacity was measured after approximately 29 days. The discharge capacity retention rate (%) was calculated by dividing the measured discharge capacity by the initial discharge capacity and multiplying by 100. Similarly, by repeating the test for approximately 29 days (28 days of rest + 1 day due to 3 charging cycles) according to the charging profile shown in Figure 10A, the change in discharge capacity retention rate up to a maximum of approximately 145 days was measured. The results are shown in Table 2 and Figure 10B. [Table 2]

[0051] The results shown in Table 2 and Figure 10B show that Example A2, which uses a negative electrode with a significantly higher proportion of metallic Zn particles, achieves a higher capacity retention rate over the same number of days compared to Example A1, which uses a negative electrode with a lower proportion of metallic Zn particles. In other words, by compensating for the decrease in conductivity and negative electrode capacity due to metallic zinc loss caused by oxidation of the negative electrode by increasing the amount of metallic Zn particles, the capacity retention rate can be improved and the decrease in battery capacity can be delayed. Specifically, as shown in Figure 10B, when the lifespan line is set at 50%, the battery in Example A2, which has an increased proportion of metallic Zn particles, has a lifespan that is approximately 1.3 times longer than the battery in the comparative example, Example A1. This test was a trickle charge acceleration test conducted at a high temperature of 65°C, but it is generally known that the lifespan of a secondary battery is reduced by approximately half when the temperature rises by 10°C. Based on this general knowledge, the expected lifespan of the battery in Example A2, which has a lifespan of approximately 130 days in an accelerated test at 65°C, at 25°C is estimated to be approximately 5.7 years, which is an increase of approximately 1.3 years compared to the battery in Example B1.

[0052] Next, a trickle charge acceleration test was performed on a nickel-zinc secondary battery, under the same conditions as above, except that the temperature was set to 55°C. The results are shown in Table 3 and Figure 10C. [Table 3]

[0053] The results shown in Table 3 and Figure 10C show that Example A2, which uses a negative electrode with a significantly higher proportion of metallic Zn particles, achieves a higher capacity retention rate over the same number of days compared to Example A1, which uses a negative electrode with a lower proportion of metallic Zn particles. In other words, by compensating for the decrease in conductivity and negative electrode capacity due to metallic zinc loss caused by oxidation of the negative electrode by increasing the amount of metallic Zn particles, the capacity retention rate can be improved and the decrease in battery capacity can be delayed. Specifically, as shown in Figure 10C, when the lifespan line is set at 50%, the battery in Example A2, which has an increased proportion of metallic Zn particles, has a lifespan that is approximately 1.8 times longer than the battery in the comparative example, Example A1. This test was a trickle charge acceleration test conducted at a high temperature of 55°C, but it is generally known that the lifespan of a secondary battery is reduced by approximately half when the temperature rises by 10°C. Based on this general knowledge, the expected lifespan of the battery in Example A2, which has a lifespan of approximately 240 days in an accelerated test at 55°C, is estimated to be approximately 5.3 years at 25°C, representing an increase of approximately 2.4 years compared to the battery in Example A1.

[0054] Examples B1 and B2 The fabrication of nickel-zinc secondary batteries (ZnO:Zn=100:57.1wt%) and the acceleration of trickle charging tests were carried out in the same manner as in Example A2, except that the depth of charge (SOC) of 100% was set to 90% (Example B1) or 80% (Example B2) of the positive electrode's installed capacity, and trickle charging was performed up to SOC 100% (90% of installed capacity) (Example B1) or SOC 90% (80% of installed capacity) according to the charging profile shown in Figure 11A.

[0055] The results of the trickle charge acceleration test at 65°C are shown in Table 4 and Figure 11B. [Table 4]

[0056] The results shown in Table 4 and Figure 11B show that Example B2, where charging is performed to a depth of charge (SOC) of 90% (80% of the installed capacity), achieves a higher capacity retention rate over the same number of days compared to Example B1, where charging is performed to a SOC of 100% (90% of the installed capacity). In other words, by reducing the charging capacity relative to the installed capacity of the positive electrode, it is possible to suppress the decrease in negative electrode capacity due to the consumption of metallic zinc due to oxidation of the negative electrode, and the deterioration of the positive electrode (especially the shedding of positive electrode active material and the increase in resistance), thereby improving the capacity retention rate and delaying the decrease in battery capacity. Specifically, as shown in Figure 11B, when the life line is set at 50%, the battery in Example B2, which has a lower maximum SOC during charging, has a lifespan that is approximately 1.25 times longer than the battery in Example B1, which has a higher maximum SOC during charging. This test was a trickle charge acceleration test conducted at a high temperature of 65°C, but it is generally known that the lifespan of a secondary battery is reduced by approximately half when the temperature rises by 10°C. Based on this general knowledge, the expected lifespan of the battery in Example B2, which has a lifespan of approximately 150 days in an accelerated test at 65°C, at 25°C is estimated to be approximately 6.6 years, which is an increase of approximately 1.3 years compared to the battery in Example B1.

[0057] The results of the trickle charge acceleration test at 55°C are shown in Table 5 and Figure 11C.

[0058] [Table 5]

[0059] The results shown in Table 5 and Figure 11C show that Example B2, where charging is performed to a depth of charge (SOC) of 90% (80% of the installed capacity), achieves a higher capacity retention rate over the same number of days compared to Example B1, where charging is performed to a SOC of 100% (90% of the installed capacity). In other words, by reducing the charging capacity relative to the installed capacity of the positive electrode, it is possible to suppress the decrease in negative electrode capacity due to the consumption of metallic zinc due to oxidation of the negative electrode, and the deterioration of the positive electrode (especially the shedding of positive electrode active material and the increase in resistance), thereby improving the capacity retention rate and delaying the decrease in battery capacity. Specifically, as shown in Figure 11C, when the life line is set at 50%, the battery in Example B2, which has a lower maximum SOC during charging, has a lifespan that is approximately 1.2 times longer than the battery in Example B1, which has a higher maximum SOC during charging. This test was a trickle charge acceleration test conducted at a high temperature of 55°C, but it is generally known that the lifespan of a secondary battery is reduced by approximately half when the temperature rises by 10°C. Based on this general knowledge, the expected lifespan of the battery in Example B2, which has a lifespan of approximately 270 days in an accelerated test at 55°C, is approximately 5.9 years at 25°C, which is estimated to be an increase of approximately 0.9 years compared to the battery in Example B1.

[0060] To verify the advantages of Example B2 (i.e., the life-extending effect achieved by increasing the proportion of metallic Zn particles and lowering the maximum SOC during charging), the results obtained in the trickle charge acceleration test at 55°C for Examples A1 and B2 are compared and shown in Table 6 and Figure 11D.

[0061] [Table 6]

[0062] The results shown in Table 6 and Figure 11D show that Example B2, which has a high proportion of metallic Zn particles and is charged to a depth of charge (SOC) of 90% (80% of the installed capacity), achieves a particularly high capacity retention rate over the same number of days compared to Example A1, which has a low proportion of metallic Zn particles and is charged to a SOC of 100% (90% of the installed capacity). In other words, a particularly high capacity retention rate can be achieved by increasing the proportion of metallic Zn in the negative electrode and limiting trickle charging to an SOC of 90% (80% of the installed capacity). Specifically, as shown in Figure 11D, when the lifespan line is set at 50%, the battery in Example B2, which has an increased proportion of metallic Zn particles and a lower maximum SOC during charging, has a lifespan that is approximately 1.8 times longer at 55°C than the comparative example battery in Example A1. This test was an accelerated trickle charge test conducted at a high temperature of 55°C. It is generally known that the lifespan of a secondary battery is reduced by approximately half for every 10°C increase in temperature. Based on this general knowledge, the expected lifespan of battery B2, which has a lifespan of approximately 270 days in the 55°C accelerated test, at 25°C is approximately 5.9 years, which is estimated to be an increase of approximately 3.1 years compared to battery A1.

[0063] Example C1 (comparison) A nickel-zinc secondary battery (ZnO:Zn=100:57.1wt%) was fabricated in the same manner as in Example A2, except that the following polymer microporous membrane separator (product name: #3401, manufactured by Cellgard, material: polypropylene, thickness: 25μm) was used instead of the LDH separator. A trickle charge acceleration test was performed at 65°C to 100% SOC (90% of installed capacity) according to the charge profile shown in Figure 12A.

[0064] Example C2 A nickel-zinc secondary battery (ZnO:Zn=100:57.1wt%) was fabricated in the same manner as in Example C1, except that an LDH separator similar to that in Examples A1-B2 was used instead of a polymer microporous membrane separator. A trickle charge acceleration test was then performed at 65°C to reach 100% SOC (90% of the installed capacity) according to the charge profile shown in Figure 11A.

[0065] The results for Examples C1 and C2 are shown in Table 7 and Figure 12B. [Table 7]

[0066] The results shown in Table 7 and Figure 12B demonstrate that the LDH separator is impermeable to gases and also impermeable to oxygen generated from the positive electrode, thus preventing oxidation of the negative electrode, suppressing battery capacity degradation, and extending battery life. Specifically, as shown in Figure 11D, with a lifespan line of 50%, the battery in Example C2, which employs an impermeable LDH separator, has a lifespan approximately 1.4 times longer at 65°C compared to the comparative example battery in Example C1, which employs a polymer microporous membrane separator. This test was an accelerated trickle charge test conducted at a high temperature of 55°C, but it is generally known that the lifespan of a secondary battery is approximately halved for every 10°C increase in temperature. Based on this general knowledge, the expected lifespan of the battery in Example C2, which has a lifespan of approximately 150 days in the 55°C accelerated test, at 25°C is approximately 6.6 years, which is estimated to be an increase of approximately 1.8 years compared to the battery in Example C1. [Explanation of symbols]

[0067] 10. Zinc rechargeable battery 10a unit cell 11 stacked cells 12 Positive plate 12a Cathode active material layer 12b Positive electrode current collector 13 Positive Tab Lead 14 Negative plate 14a Negative electrode active material layer 14b Negative electrode current collector 15 Negative Electrode Tab Lead 16,116 separators 17 Liquid retention member 20 Battery Cases 20a Top lid 26 Positive terminal 28 Negative terminal 30 Positive electrode tab joint 32 Negative electrode tab joint

Claims

1. The negative electrode used in a zinc secondary battery, ZnO particles and, A metal Zn particle in an amount of 55.0 to 65.0 parts by weight per 100 parts by weight of the ZnO particles, The negative electrode, including the negative electrode.

2. The negative electrode according to claim 1, wherein the content of the metallic Zn particles is 55.0 to 58.0 parts by weight per 100 parts by weight of the ZnO particles.

3. The negative electrode according to claim 1, further comprising a binder resin.

4. A positive electrode plate containing nickel hydroxide and / or nickel oxyhydroxide, A negative electrode plate according to any one of claims 1 to 3, A hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate in a manner that allows hydroxide ions to conduct, Electrolyte and A battery case in which the positive electrode plate, the negative electrode plate, and the hydroxide ion conductive separator are housed vertically, A nickel-zinc rechargeable battery equipped with [specific features / features].

5. The nickel-zinc secondary battery according to claim 4, wherein the hydroxide ion conductive separator is an LDH separator containing layered double hydroxide (LDH) and / or an LDH-like compound.

6. The nickel-zinc secondary battery according to claim 5, wherein the LDH separator is composited with a porous substrate.

7. The nickel-zinc secondary battery according to claim 4, wherein the negative electrode plate is covered with the hydroxide ion conductive separator, and the outer periphery of the negative electrode plate, excluding the upper end, is hermetically sealed, thereby preventing oxygen generated on the positive electrode plate from reaching the negative electrode plate.

8. The nickel-zinc battery comprises stacked cells, and the stacked cells are Multiple positive electrode plates, A plurality of positive electrode tab leads extending from each end of the positive electrode plate, Multiple negative electrode plates, Multiple negative electrode tab leads extend from each end of the negative electrode plate at positions that do not overlap with the positive electrode tab leads, A plurality of hydroxide ion conductive separators that isolate the positive electrode plate and the negative electrode plate in a manner that allows hydroxide ions to conduct, The aforementioned electrolyte, The nickel-zinc secondary battery according to claim 4, comprising the positive electrode plate and the negative electrode plate being alternately stacked with the hydroxide ion conductive separator in between.

9. A method for using a nickel-zinc secondary battery, comprising performing trickle charging on the nickel-zinc secondary battery according to claim 4 to provide a charging capacity of 80 to 85% of the mounted capacity of the nickel-zinc secondary battery.

10. The method for using a nickel-zinc secondary battery according to claim 9, wherein the charging capacity is 80% of the installed capacity of the nickel-zinc secondary battery.

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