WO2024195225A1 - Negative electrode for zinc secondary battery, and nickel zinc secondary battery and method of using same - Google Patents

Abstract

Provided is a negative electrode for a zinc secondary battery, the negative electrode being capable of extending the life of a battery by delaying a decrease in battery capacity during trickle charging. The negative electrode contains: ZnO particles; and metal Zn particles in an amount 55.0-65.0 parts by weight with respect to 100 parts by weight of the ZnO particles.

Description

Anode for zinc secondary battery, nickel-zinc secondary battery and method of using same

The present invention relates to a negative electrode for a zinc secondary battery, as well as a nickel-zinc secondary battery and a method for using the same.

ZnO particles and metal Zn particles are generally used in combination in the negative electrode of a nickel-zinc secondary battery. Patent Document 1 (JP 2021-57339 A) discloses a negative electrode for a zinc secondary battery, which contains a negative electrode active material containing Zn particles and ZnO particles, and a conductive assistant containing solder. This document describes that the amount of Zn particles in the negative electrode is preferably 1 to 50 parts by weight, assuming that 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 contains 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 metal 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.

Incidentally, in zinc secondary batteries such as nickel-zinc secondary batteries and air-zinc secondary batteries, it is known that metallic zinc precipitates in the form of dendrites from the negative electrode during charging, penetrating the voids in the separator such as a nonwoven fabric to reach the positive electrode, resulting in a short circuit. Such short circuits caused by zinc dendrites shorten the repeated charge/discharge life. To address this problem, batteries have been proposed that include a layered double hydroxide (LDH) separator that selectively allows hydroxide ions to pass through while preventing the penetration of zinc dendrites (see, for example, Patent Documents 1 and 2, Patent Document 3 (WO2016/076047), and Patent Document 4 (WO2019/124270)). In addition, Patent Document 5 (WO2019/069760) and Patent Document 6 (WO2019/077953) propose a zinc secondary battery in which the entire negative electrode active material layer is covered or wrapped with a liquid-retaining member and an LDH separator, and the positive electrode active material layer is covered or wrapped with a liquid-retaining member. A nonwoven fabric is used as the liquid-retaining member. With this configuration, it is said that a zinc secondary battery (especially a stacked battery thereof) capable of preventing zinc dendrite extension can be produced extremely easily and with high productivity, eliminating the need for a complicated sealing joint between the LDH separator and the battery container.

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

JP 2021-57339 A WO2022/118625 WO2016/076047 WO2019/124270 WO2019/069760 WO2019/077953 WO2020/255856 WO2021/229916 WO2021/229917

In addition to cyclic applications in which the battery is repeatedly charged and discharged, nickel-zinc secondary batteries can also be used as backup power sources in the event of a power outage. In backup applications, it is desirable to maintain the battery capacity near full charge to ensure the battery's minimum guaranteed capacity. As shown in Figure 1, trickle charging (1) is therefore performed to compensate for the loss of battery capacity due to self-discharge (2). Trickle charging makes it possible to constantly maintain the battery capacity near full charge. However, there is a problem in that the battery capacity decreases during trickle charging, shortening the battery life.

The inventors have now discovered that by using a negative electrode in which a specified amount of metallic Zn particles is mixed with ZnO particles in a zinc secondary battery, it is possible to delay the decrease in battery capacity during trickle charging and extend the battery's lifespan.

The object of the present invention is therefore 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's life.

According to the present invention, the following aspects are provided.
[Aspect 1]
A negative electrode for use in a zinc secondary battery,
ZnO particles;
Metal Zn particles in an amount of 55.0 to 65.0 parts by weight per 100 parts by weight of the ZnO particles;
a negative electrode.
[Aspect 2]
2. The negative electrode according to claim 1, wherein the content of the metal Zn particles is 55.0 to 58.0 parts by weight per 100 parts by weight of the ZnO particles.
[Aspect 3]
3. The negative electrode of any one of the preceding claims, 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 aspects 1 to 3,
a hydroxide ion conductive separator that separates the positive electrode plate and the negative electrode plate so as to be capable of conducting hydroxide ions;
An electrolyte;
a battery case in which the positive electrode plate, the negative electrode plate, and a hydroxide ion conductive separator are housed vertically;
A nickel-zinc secondary battery comprising:
[Aspect 5]
5. The nickel-zinc secondary battery of claim 4, wherein the hydroxide ion conducting separator is a layered double hydroxide (LDH) separator comprising an LDH and/or an LDH-like compound.
[Aspect 6]
The nickel-zinc secondary battery of claim 5, wherein the LDH separator is composited with a porous substrate.
[Aspect 7]
A nickel-zinc secondary battery according to any one of aspects 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 other than the upper end is hermetically sealed, thereby preventing oxygen generated at the positive electrode plate from reaching the negative electrode plate by the hydroxide ion conductive separator.
[Aspect 8]
The nickel-zinc battery comprises a stacked cell, the stacked cell comprising:
A plurality of the positive electrode plates;
a plurality of positive electrode tab leads extending from each end of the positive electrode plate;
A plurality of the negative electrode plates;
a plurality of negative electrode tab leads extending from each end of the negative electrode plate at positions not overlapping with the positive electrode tab leads;
a plurality of hydroxide ion conductive separators isolating the positive electrode plate and the negative electrode plate so as to be capable of conducting hydroxide ions;
The electrolyte;
The nickel-zinc secondary battery according to any one of aspects 4 to 7, wherein the positive electrode plate and the negative electrode plate are alternately laminated with the hydroxide ion conductive separator sandwiched therebetween.
[Aspect 9]
A method for using a nickel-zinc secondary battery, comprising trickle charging the nickel-zinc secondary battery according to any one of aspects 4 to 8 so as to provide a charge capacity of 80 to 85% of the on-board capacity of the nickel-zinc secondary battery.
[Aspect 10]
10. The method of using the nickel-zinc secondary battery according to claim 9, wherein the charging capacity is 80% of the installed capacity of the nickel-zinc secondary battery.

FIG. 4 illustrates an example of a trickle charge profile. FIG. 1 is a diagram for explaining trickle charging from the viewpoint of battery capacity. FIG. 2 is a schematic cross-sectional view conceptually showing the movement of oxygen caused by self-discharge in a nickel-zinc secondary battery. FIG. 1 is a schematic cross-sectional view showing an example of a nickel-zinc secondary battery according to the present invention. FIG. 5 is a schematic diagram showing a cross section of the nickel-zinc secondary battery shown in FIG. 4 taken along line A-A'. FIG. 5 is a perspective view showing a schematic diagram of a stacked cell of the nickel-zinc secondary battery shown in FIG. 4. FIG. 5 is a cross-sectional view showing a schematic diagram of a stacked cell of the nickel-zinc secondary battery shown in FIG. 4. FIG. 5 is a perspective view showing a state in which the positive electrode plate or the negative electrode plate in the nickel-zinc secondary battery shown in FIG. 4 is covered with a hydroxide ion conductive separator or a liquid retaining member. FIG. 2 is a diagram conceptually illustrating the transfer of oxygen from a positive electrode plate when the negative electrode plate is covered with a microporous membrane separator. FIG. 1 is a schematic diagram showing the transfer of oxygen from a positive plate when the negative plate is covered with a hydroxide ion conducting separator, where the cross marks indicate that the transfer of oxygen _O2 is blocked. 1 shows the charging profile in the trickle charge accelerated test performed in Examples A1 and A2. FIG. 1 shows the results of an accelerated trickle charge test carried out at 65° C. for Examples A1 and A2. FIG. 1 shows the results of an accelerated trickle charge test carried out at 55° C. for Examples A1 and A2. 1 shows the charging profile for the trickle charge accelerated test performed in Examples B1 and B2. FIG. 1 shows the results of an accelerated trickle charge test conducted at 65° C. for Examples B1 and B2. FIG. 1 shows the results of an accelerated trickle charge test performed at 55° C. for Examples B1 and B2. FIG. 1 shows the results of an accelerated trickle charge test carried out at 55° C. for Examples A1 and B2. 1 shows the charging profile for the trickle charge accelerated test performed on Examples C1 and C2. FIG. 1 shows the results of an accelerated trickle charge test conducted at 65° C. for Examples C1 and C2. FIG. 2 is a diagram showing a charging curve of an example of a nickel-zinc secondary battery together with changes in oxygen concentration.

Definitions The following are definitions of terms used in this specification.

In this specification, the term "loading 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 1 g of mass can be calculated from the formula Cm = F x N x M (where F is the charge amount of 1 mol of electrons, N is the number of moles of reactive electrons per mol of electrode material, and M is the number of moles per 1 g of electrode material). Since the theoretical capacity per unit mass of Ni(OH) ₂ is 289.1 mAh/g, the loading capacity of a battery loaded with 345.9 g of Ni(OH) ₂ as the positive electrode active material is 100 Ah. The reason why the loading capacity is defined based on the positive electrode active material is that a battery in which the positive electrode capacity is smaller than the negative electrode capacity is assumed, and in that case, the loading capacity is regulated by the positive electrode capacity. Therefore, if a battery in which the positive electrode capacity is greater than the negative electrode capacity is considered, the "mass of the positive electrode active material" in the above definition should be read as the "mass of the negative electrode active material".

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

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

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

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

In this specification, "trickle charging" refers to charging (1) performed to compensate for the loss of battery capacity due to self-discharge (2) of the secondary battery, as shown in Figures 1 and 3. More specifically, as shown in Figure 2, trickle charging compensates for the loss of battery capacity due to self-discharge based on a rated capacity (with 100% state of charge (SOC)) that is specified as a certain percentage of the installed capacity, so that the battery capacity can always be maintained near full charge. Trickle charging is often used in emergency power sources 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 performance or be usable. To avoid such problems, trickle charging is widely used as one method of charging to compensate for self-discharge. This ensures a specified battery capacity (80% in Figure 2) or more.

Anode for zinc secondary battery The anode of the present invention is an anode used in a zinc secondary battery. The zinc secondary battery is not particularly limited as long as it uses zinc as the anode and uses 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 any other type of alkaline zinc secondary battery. The anode 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 FIG. 3. This negative electrode or negative electrode plate 14 (particularly the negative electrode active material layer 14a) includes ZnO particles and metal Zn particles. The amount of the metal Zn particles is 55.0 to 65.0 parts by weight per 100 parts by weight of ZnO particles. By using a negative electrode in which a predetermined amount of metal Zn particles is mixed with ZnO particles in a zinc secondary battery, the decrease in battery capacity during trickle charging can be delayed, thereby extending the life of the battery.

That is, as mentioned above, in the backup use of nickel-zinc secondary batteries, it is desirable to maintain the battery capacity near full charge in order to guarantee the minimum guaranteed capacity of the battery. Therefore, as shown in FIG. 1, trickle charging (1) is performed to compensate for the battery capacity that is reduced by self-discharge (2). However, there is a problem that the battery capacity decreases during trickle charging, shortening the battery life. This problem is conveniently solved by the negative electrode of the present invention. The mechanism is considered to be as follows. That is, in the positive electrode of a nickel-zinc secondary battery, the following reaction occurs during trickle charging or self-discharge (standing):
(1) Charging reaction:
Positive electrode: ^4OH- → _O2 ↑+ _2H2O + ^4e-
(2) Self-discharge reaction:
Positive electrode: 2NiOOH + _H2O → 2Ni(OH) ₂ + 1/ _2O2 ↑
Then, when the generated oxygen moves from the positive electrode plate 12 to the negative electrode plate 14 through the liquid retaining member 17 and the separator 116 as shown in FIG. 3, the following reaction occurs:
・Negative electrode: Zn+1/2O ₂ →ZnO
As a result, the metallic Zn (active material in a charged state) contained in the negative electrode plate 14 is oxidized to ZnO (active material in a discharged state), and the negative electrode capacity is reduced. As a result, the battery capacity is reduced, and the battery life during trickle charging is shortened. 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, and the battery life can be extended.

The ZnO particles are not particularly limited and may be either commercially available zinc oxide powder used in zinc secondary batteries or zinc oxide powder obtained by growing the particles by solid-phase reaction using the commercially available zinc oxide powder as the starting material. 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 small particle size side in the particle size distribution obtained by the laser diffraction/scattering method is 50%.

The metal Zn particles can be metal Zn particles commonly used in zinc secondary batteries, but it is more preferable to use smaller metal Zn particles from the viewpoint of extending the cycle life of the battery. Specifically, the average particle size D50 of the metal Zn particles is preferably 50 to 150 μm. The content of the metal Zn particles in the negative electrode is preferably 55.0 to 65.0 parts by weight relative to 100 parts by weight of ZnO particles, more preferably 55.0 to 58.0 parts by weight, and even more preferably 56.6 to 57.6 parts by weight. Such an amount is significantly greater than the amount of metal Zn particles in a general negative electrode of a conventionally used nickel-zinc secondary battery, and by using a negative electrode in which the amount of metal Zn particles is increased relative to the amount of ZnO particles in this way for a zinc secondary battery, the decrease in battery capacity during trickle charging can be delayed and the life of the battery can be extended. In addition, by ensuring that the amount of metal Zn particles is not too large relative to the ZnO particles, it becomes easier to mold the negative electrode using the metal Zn particles and ZnO particles. The metal Zn particles may be doped with dopants such as In and Bi.

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 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 the oxides of the above metal elements include In ₂ O ₃ and Bi ₂ O _3. Examples of the hydroxides of the above metal elements include In(OH) ₃ and Bi(OH) _3. In any case, when the content of the ZnO particles is 100 parts by weight, the content of In is preferably 0 to 2 parts by weight in terms of oxide, and the content of Bi is preferably 0 to 6 parts by weight in terms of oxide, and more preferably the content of In is 0 to 1.5 parts by weight in terms of oxide, and the content of Bi 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 that all of In and/or Bi are in the form of oxide or hydroxide, and a part of them may be contained in the negative electrode in other forms such as metal or other compounds. For example, the above metal elements may be doped into the metal Zn particles as trace elements. In this case, the In concentration in the metal Zn particles is preferably 50 to 2000 ppm by weight, more preferably 200 to 1500 ppm by weight, and the Bi concentration in the metal Zn particles is preferably 50 to 2000 ppm by weight, more preferably 100 to 1300 ppm by weight.

The negative electrode 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.

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

The negative electrode or negative electrode plate 14 is preferably a sheet-like pressed body. This can prevent the negative electrode active material from falling off and improve the electrode density, and can more effectively suppress changes in the shape of the negative electrode. Such a sheet-like pressed body can be produced by adding a binder to the negative electrode material and kneading the mixture, and then applying press molding such as roll pressing to the resulting kneaded mixture to form it into a sheet.

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 punched metal and copper expanded metal. In this case, for example, a mixture containing a Zn compound, metallic zinc and zinc oxide powder, and optionally a binder (e.g., polytetrafluoroethylene particles) can be applied to the copper punched metal or copper expanded metal to preferably produce a negative electrode plate consisting of a negative electrode/negative electrode current collector. In this case, it is also preferable to press the negative electrode plate (i.e., the negative electrode/negative electrode current collector) after drying to prevent the electrode active material from falling off and improve the electrode density. Alternatively, the above-mentioned sheet-shaped press molded body may be pressed onto a current collector such as copper expanded metal.

Nickel-zinc secondary 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 according to one embodiment of the present invention and its components. The nickel-zinc secondary battery 10 includes 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) includes nickel hydroxide and/or nickel oxyhydroxide. The negative electrode plate 14 (particularly the negative electrode active material layer 14a) includes ZnO particles and metal Zn particles, as described above. The hydroxide ion conductive separator 16 separates the positive electrode plate 12 and the negative electrode plate 14 in a manner that allows hydroxide ion conduction. 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 plane).

The nickel-zinc secondary battery 10 preferably includes a stacked cell 11. As shown in FIG. 7, the stacked cell 11 includes 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 positions that do not overlap with the positive electrode tab leads 13. The plurality of hydroxide ion conductive separators 16 isolate the positive electrode plates 12 and the negative electrode plates 14 so as to be capable of conducting hydroxide ions. The stacked cell 11 includes the positive electrode plates 12 and the negative electrode plates 14 stacked alternately with the hydroxide ion conductive separators 16 sandwiched therebetween. Therefore, the stacked cell 11 can be said to be in the form of a positive and negative electrode stack in which the unit of positive electrode plate 12/separator 16/negative electrode plate 14 is repeatedly stacked. In other words, the nickel-zinc secondary battery 10 preferably includes a plurality of unit cells 10a each having a pair of positive electrode plate 12 and negative electrode plate 14 together with a hydroxide ion conductive separator 16, and the plurality of unit cells 10a as a whole form a stacked cell 11. This is the configuration of a so-called assembled battery or stacked battery, and is advantageous in that it can provide a high voltage and a large current.

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 may be appropriately selected from known positive electrode materials according to the type of zinc secondary battery, and is not particularly limited. 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 contain at least one additive selected from the group consisting of silver compounds, manganese compounds, and titanium compounds, which can promote the positive electrode reaction that absorbs hydrogen gas generated by the self-discharge reaction. The positive electrode active material layer 12a may further contain cobalt. Cobalt is preferably contained 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 assistant, thereby contributing to improving the charge/discharge capacity.

The positive electrode plate 12 further includes a positive electrode collector 12b. A preferred example of the positive electrode collector 12b is a nickel porous substrate such as a foamed nickel plate. In this case, for example, a paste containing an electrode active material such as nickel hydroxide is uniformly applied to a nickel porous substrate and then dried to preferably produce a positive electrode plate consisting of a positive electrode/positive electrode collector. In this case, it is also preferred to press the dried positive electrode plate (i.e., the positive electrode/positive electrode collector) to prevent the electrode active material from falling off and to improve the electrode density. When the positive electrode collector 12b is a nickel porous substrate such as a foamed nickel plate, the uncoated area of the positive electrode collector 12b may be pressed to form a tab.

The positive electrode tab lead 13 is provided so as to extend from the end of the positive electrode plate 12, as shown in FIG. 8. The positive electrode tab lead 13 may be a commercially available metal foil, and is not particularly limited. It is preferable that a plurality of positive electrode tab leads 13 are joined to one positive electrode terminal 26 or a member electrically connected thereto to form a positive electrode tab joint 30. This allows for efficient current collection with a simple configuration, and also makes it easier to connect to the positive electrode terminal 26. The positive electrode tab lead 13 may be joined to members such as the positive electrode current collector 12b and the positive electrode terminal 26 using a known joining method such as ultrasonic welding (ultrasonic welding), laser welding, TIG welding, or resistance welding.

The negative electrode plate 14 (particularly the negative electrode active material layer 14a) contains ZnO particles and metal Zn particles as described above. As shown in FIG. 8, the negative electrode tab lead 15 is provided so as to extend from the end of the negative electrode plate 14 at a position where it does not overlap with the positive electrode tab lead 13 (see FIG. 6). The negative electrode tab lead 15 is not particularly limited and may be a commercially available metal foil. It is preferable that a plurality of negative electrode tab leads 15 are joined to one negative electrode terminal 28 or a member electrically connected thereto to form the negative electrode tab joint 32. This allows for efficient current collection with a simple configuration and also makes it easier to connect to the negative electrode terminal 28. The negative electrode tab lead 15 may be joined to members such as the negative electrode current collector 14b and the negative electrode terminal 28 using a known joining method such as ultrasonic welding (ultrasonic joining), laser welding, TIG welding, or resistance welding.

The hydroxide ion conductive separator 16 is provided to isolate the positive electrode plate 12 and the negative electrode plate 14 so as to allow hydroxide ion conductivity. For example, as shown in Figs. 7 and 8, the positive electrode plate 12 and/or the negative electrode plate 14 (preferably the negative electrode plate 14) may be configured to be covered or wrapped with the hydroxide ion conductive separator 16. This makes it possible to manufacture a nickel-zinc secondary battery (particularly a laminated battery thereof) capable of preventing zinc dendrite extension extremely easily and with high productivity, without the need for a complicated sealing joint between the hydroxide ion conductive separator 16 and the battery container. However, a simple 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 may also be used.

The hydroxide ion conductive separator 16 is not particularly limited as long as it is a separator capable of isolating the positive electrode plate 12 and the negative electrode plate 14 in a hydroxide ion conductive manner, but is typically a separator that includes a hydroxide ion conductive solid electrolyte and selectively passes hydroxide ions solely by utilizing hydroxide ion conductivity. A preferred hydroxide ion conductive solid electrolyte is a layered double hydroxide (LDH) and/or an LDH-like compound. Thus, the hydroxide ion conductive separator 16 is preferably an LDH separator. In this specification, an "LDH separator" is defined as a separator that includes an LDH and/or an LDH-like compound and selectively passes hydroxide ions solely by utilizing the hydroxide ion conductivity of the LDH and/or the LDH-like compound. In this specification, an "LDH-like compound" is a hydroxide and/or oxide of a layered crystal structure that may not be called an LDH but has hydroxide ion conductivity, and can be considered an equivalent of an LDH. However, in a broad definition, "LDH" can be interpreted as including not only LDH but also LDH-like compounds. The LDH separator is preferably composited with a porous substrate. Therefore, the LDH separator preferably further comprises a porous substrate, and is composited with the porous substrate in a form in which the pores of the porous substrate are filled with LDH and/or LDH-like compounds. That is, in a preferred LDH separator, the pores of the porous substrate are blocked with LDH and/or LDH-like compounds so as to exhibit hydroxide ion conductivity and gas impermeability (and therefore function as an LDH separator exhibiting hydroxide ion conductivity). The porous substrate is preferably made of a polymeric material, and it is particularly preferred that the LDH is incorporated throughout the entire thickness of the porous substrate made of a polymeric material. 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.

It is preferable that not only the hydroxide ion conductive separator 16 but also the liquid retaining member 17 is interposed between the positive electrode plate 12 and the negative electrode plate 14. As shown in Figures 7 and 8, it is preferable that the positive electrode plate 12 and/or the negative electrode plate 14 is covered or wrapped with the liquid retaining member 17. However, a simple configuration in which the liquid retaining member 17 is arranged on one side of the positive electrode plate 12 or the negative electrode plate 14 may also be used. In any case, by interposing the liquid retaining member 17, the electrolyte can be evenly present between the positive electrode plate 12 and/or the negative electrode plate 14 and the hydroxide ion conductive separator 16, and hydroxide ions can be efficiently exchanged between the positive electrode plate 12 and/or the negative electrode plate 14 and the hydroxide ion conductive separator 16. The liquid retaining member 17 is not particularly limited as long as it is a material that can retain the electrolyte, but it is preferable that it is a sheet-like member. Preferred examples of the liquid-retaining member 17 include nonwoven fabric, water-absorbent resin, liquid-retaining resin, porous sheet, and various spacers, but nonwoven fabric is particularly preferred because it allows the production of a negative electrode structure with good performance at low cost. 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. If the thickness is within the above range, a sufficient amount of electrolyte can be retained in the liquid-retaining member 17 while keeping the overall size of the positive electrode structure and/or negative electrode structure compact and without waste.

When the positive electrode plate 12 and/or the negative electrode plate 14 are covered or wrapped with the liquid retaining member 17 and/or the separator 16, it is preferable that the outer edges of the plates 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 liquid retaining member 17 and/or the separator 16 are realized by folding the liquid retaining member 17 and/or the separator 16, or by sealing the liquid retaining members 17 together and/or the separators 16 together. Preferred examples of sealing methods include adhesives, heat welding, ultrasonic welding, adhesive tape, sealing tape, and combinations thereof. In particular, since the LDH separator including a porous substrate made of a polymer material has the advantage of being flexible and therefore easy to bend, it is preferable to form the LDH separator into a long shape and fold it to form a state in which one side of the outer edge is closed. Thermal welding and ultrasonic welding may be performed using a commercially available heat sealer, etc., but in the case of sealing between LDH separators, it is preferable to perform thermal welding and ultrasonic welding by sandwiching the outer peripheral portion of the liquid-retaining member 17 between the LDH separators that constitute the outer peripheral portion, since this allows for more effective sealing. On the other hand, the adhesive, adhesive tape, and sealing tape may be commercially available products, but it is preferable to use those that contain a resin that is resistant to alkali in order to prevent deterioration in an alkaline electrolyte. From this perspective, examples of preferred adhesives include epoxy resin adhesives, natural resin adhesives, modified olefin resin adhesives, and modified silicone resin adhesives, and among them, epoxy resin adhesives are more preferred because they are particularly excellent in alkali resistance. An example of an epoxy resin adhesive product is the epoxy adhesive Hysol (registered trademark) (manufactured by Henkel).

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 is airtightly sealed except for the upper end, so that the hydroxide ion conductive separator 16 prevents oxygen generated in the positive electrode plate 12 from reaching the negative electrode plate 14. That is, as described above, oxygen is generated in the positive electrode of a nickel-zinc secondary battery during trickle charging or self-discharge (standing), which causes oxidation of the metal Zn contained in the negative electrode and a resulting decrease in the negative electrode capacity, resulting in a shortened battery life when trickle charging is used. In this regard, as shown in Figure 9A, the general microporous membrane separator 116 that has been widely used in the past has gas permeability, so it allows the passage of oxygen _O2 generated at the positive electrode, which directly reaches the adjacent negative electrode plate 14 from the positive electrode plate 12, promoting the oxidation of the metal Zn. However, according to a preferred embodiment of the present disclosure, as shown by the cross in FIG. 9B, the hydroxide ion conductive separator 16 prevents oxygen generated in the positive electrode plate 12 from reaching the negative electrode plate 14, thereby suppressing the oxidation of metal Zn caused by oxygen, and thereby further delaying the decrease in battery capacity during trickle charging and further extending the life of the battery. This is because the hydroxide ion conductive separator 16 is a separator that selectively passes hydroxide ions using only hydroxide ion conductivity, and therefore does not have gas permeability. In other words, by airtightly covering the negative electrode plate 14 with the hydroxide ion conductive separator 16 that does not have gas permeability, oxygen generated in the positive electrode plate 12 is not transmitted, and therefore the oxidation of metal Zn in the negative electrode can be suppressed. In this embodiment, the outer periphery of the upper end of the negative electrode plate 14 does not need to be sealed with the hydroxide ion conductive separator 16. In this case, the structure may be such that oxygen is allowed to enter the negative electrode plate 14 from the upper end of the negative electrode plate 14. However, since the effect of preventing oxygen from reaching the negative electrode plate 14 directly from the positive electrode plate 12, i.e., the effect of inhibiting oxygen permeation between the opposing surfaces of the positive electrode plate 12 and the negative electrode plate 14 and the resulting effect of inhibiting the oxidation of metallic Zn, contribute greatly, the decrease in battery capacity during trickle charging can be sufficiently delayed.

Therefore, the outer edge of one side that is the upper end of the separator 16 may be open. This open-top type configuration makes it possible to deal with problems that occur when a nickel-zinc battery or the like is overcharged. That is, when a nickel-zinc battery or the like is overcharged, oxygen (O ₂ ) may be generated at the positive electrode plate 12, but the LDH separator has such a high density that it allows only hydroxide ions to pass through, and therefore does not allow O ₂ to pass through. In this regard, according to the open-top type configuration, in the battery case 20, O ₂ can be released above the positive electrode plate 12 and sent to the negative electrode plate 14 side through the open-top part, thereby oxidizing Zn of the negative electrode active material with O ₂ and returning it to ZnO. By going through such an oxygen reaction cycle, the open-top type stacked cell 11 can be used in a sealed zinc secondary battery to improve overcharge resistance. Note that even if the outer edge of one side that is the upper end of the separator 16 or the liquid-retaining member 17 is closed, the same effect as the open-top type configuration can be expected by providing a vent in a part of the closed outer edge. For example, the outer edge of one side of the LDH separator that will be the upper end may be sealed and then an air hole may be opened, or during sealing, part of the outer edge may be left unsealed so that an air hole can be formed.

The electrolyte preferably contains an aqueous solution of an alkali metal hydroxide. The electrolyte is not shown in Figs. 1 to 7 because it is distributed throughout the positive and negative plates 12 and 14. Examples of alkali metal hydroxides include potassium hydroxide, sodium hydroxide, lithium hydroxide, and ammonium hydroxide, with potassium hydroxide being more preferred. In order to suppress the self-dissolution of zinc and/or zinc oxide, a zinc compound such as zinc oxide or zinc hydroxide may be added to the electrolyte. As mentioned above, the electrolyte may be mixed with the positive electrode active material and/or the negative electrode active material to be present in the form of a positive electrode composite and/or a negative electrode composite. The electrolyte may also be gelled to prevent leakage of the electrolyte. As the gelling agent, it is preferable to use a polymer that absorbs the solvent of the electrolyte and swells, and starch or a polymer such as polyethylene oxide, polyvinyl alcohol, or polyacrylamide is used.

The battery case 20 is preferably made of resin. The resin constituting the battery case 20 is preferably a resin that is resistant 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 lid 20a. The battery case 20 (e.g., top lid 20a) may have a pressure relief valve for releasing gas. In addition, a group of cases in which two or more battery cases 20 are arranged may be housed within an outer frame to form a battery module.

Usage of the nickel-zinc secondary battery As described above, the nickel-zinc secondary battery 10 according to the present invention is suitable for backup use as an emergency power source in the event of a power outage. In backup use, trickle charging is performed to compensate for the battery capacity that is reduced by self-discharge, as shown in Figs. 1 and 2. Therefore, a preferred method of using the nickel-zinc secondary battery 10 includes trickle charging. In this case, it is preferable to perform trickle charging on the nickel-zinc secondary battery 10 so as to provide a charge capacity (utilization rate) of 80 to 85% of the installed capacity of the nickel-zinc secondary battery 10 (which is taken as 100%). Conventionally, trickle charging was generally performed so as to provide a charge capacity of about 90% of the installed capacity of the nickel-zinc secondary battery 10, but in this embodiment, trickle charging is performed at a charge capacity (utilization rate) that is lower than conventionally, that is, 80 to 85% of the installed capacity of the nickel-zinc secondary battery 10 (particularly the positive electrode plate 12), thereby further delaying the decrease in battery capacity during trickle charging and further extending the life of the battery.

That is, as mentioned above, oxygen is generated in the positive electrode of a nickel-zinc secondary battery during trickle charging, which causes oxidation of the metal Zn contained in the negative electrode and a resulting decrease in the negative electrode capacity. In this regard, FIG. 13 shows the change in oxygen concentration in the charging curve of a nickel-zinc secondary battery made by the applicant. As can be seen from FIG. 13, the positive electrode is charged with oxygen generation in the region where the charge capacity is 90% or more of the installed capacity. In addition, since the positive electrode active material expands due to charging, in the case of charging which results in a charge capacity of 90% or more of the installed capacity, the positive electrode active material may fall off the positive electrode collector or separate from the positive electrode collector, resulting in an increase in resistance. In this regard, trickle charging which results in a charge capacity of 80 to 85% of the installed capacity can effectively avoid these problems. In other words, it is possible to reduce oxygen generation in the positive electrode plate 12 during charging and suppress oxidation of the negative electrode plate 14, and also to suppress an increase in resistance due to the volume expansion of the positive electrode plate 12. As a result, the decrease in battery capacity can be delayed even more effectively.

The ratio (utilization rate) of the charge capacity to 100% installed capacity 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%. In this way, by lowering the charge capacity (utilization rate) during trickle charging compared to conventional methods but not lowering it too much, trickle charging can be performed at as high a depth of charge (SOC) as possible while effectively slowing down the decrease in battery capacity.

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

Examples A1 and A2
(1) Preparation of Negative Electrode Plate Various raw material powders shown below were prepared.
ZnO powder (manufactured by Seido Chemical Industry Co., Ltd., JIS standard type 1 grade, average particle size D50: 0.2 μm)
Metal Zn powder (manufactured by EverZinc Co., Ltd., average particle size D50: 100 μm)

According to the mixing ratio shown in Table 1, ZnO powder was added with metal Zn powder and polytetrafluoroethylene (PTFE), and the mixture was kneaded with propylene glycol. The kneaded product was rolled with 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 to obtain a negative electrode plate. At this time, an uncoated portion where the negative electrode paste was not coated was present near one end side of the copper expand metal.

(2) Preparation of nickel-zinc secondary battery The following positive electrode plate, positive electrode current collector tab, negative electrode plate, negative electrode current collector tab, LDH separator, nonwoven fabric, battery case, and electrolyte were prepared. Two types of negative electrode plates with different compositions were prepared.
Positive electrode plate: The pores of the nickel foam are filled with a positive electrode paste containing nickel hydroxide and a binder and then dried (there is an uncoated area near one end of the nickel foam where the positive electrode paste is not applied).
Positive electrode current collecting tab: The uncoated portion of the foamed nickel that constitutes the positive electrode plate is compressed with a roll press to form a tab, 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 collecting tab: a tab lead (made of copper, thickness: 100 μm) connected to an uncoated portion of the copper expanded metal by ultrasonic welding.
LDH separator: a hydroxide ion conductive separator having gas impermeability, which is prepared by precipitating Ni-Al-Ti-LDH (layered double hydroxide) in the pores and on the surface of a polyethylene microporous membrane by hydrothermal synthesis and then roll pressing, thickness: 20 μm;
Non-woven fabric: polypropylene, thickness 100 μm
Battery case: box-shaped case made of modified polyphenylene ether resin (equipped with a pressure relief valve that allows gas generated inside the case to be released); internal dimensions: length 190 mm, width 24 mm, height 165 mm; external dimensions: length 200 mm, width 30 mm, height 170 mm (not including the height of the positive and negative terminals)
Electrolyte: 5.4 mol/L KOH aqueous solution with 0.4 mol/L ZnO dissolved therein

The positive electrode plate was wrapped in nonwoven fabric so that it covered both sides, with the nonwoven fabric slightly protruding from the remaining three sides except for the side from which the positive electrode current collector tab extends. The excess nonwoven fabric protruding from the three sides of the positive electrode plate was heat-sealed and sealed with a heat seal bar to obtain a positive electrode structure. The negative electrode plate was wrapped in LDH separator so that it protruding slightly from the remaining three sides except for the side from which the negative electrode current collector tab extends. The excess LDH separator protruding from the three sides of the negative electrode plate was hermetically sealed by heat-sealing with a heat seal bar to obtain a negative electrode structure. In this way, multiple positive electrode structures and multiple negative electrode structures were prepared.

12 positive electrode structures and 13 negative electrode structures were alternately stacked to produce 42 stacked cells of various thicknesses. As in the configuration shown in FIG. 6, the positive electrode tab leads 13 and the negative electrode tab leads 15 are designed to extend from different positions from each other from the electrode current collector when viewed in a plan view, so that the positive electrode tab leads 13 are stacked on top of each other, while the negative electrode tab leads 15 are stacked on top of each other at a different position. As shown in FIG. 7, the overlapping portions of the 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 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 including the positive electrode tab leads 13 and the negative electrode tab leads 15 was obtained as the stacked cell 11. As shown in Figures 4 and 5, this stacked cell 11 was placed in a battery case 20, an electrolyte was injected to impregnate the stacked cell 11, and the top lid 20a was closed and sealed. In this way, two nickel-zinc secondary batteries were produced in each example.

(3) Trickle Charge Acceleration Test A trickle charge acceleration test was performed on each of the two nickel-zinc secondary batteries prepared at a temperature of 65°C according to the following procedure. Using a charge/discharge device (TOSCAT3200, manufactured by Toyo Systems Co., Ltd.), the nickel-zinc secondary batteries prepared were subjected to formation at 0.1C charge and 0.2C discharge. Then, 0.2C charge and 0.1C discharge were performed to measure the initial discharge capacity. Then, according to the charge profile shown in Figure 10A, the nickel-zinc secondary battery was charged to a depth of charge (SOC) of 100%, and then left in a rest state for about 168 hours (about 7 days). During the approximately 168 hours of leaving, the depth of the nickel-zinc secondary battery decreased due to self-discharge as shown in Figure 10A. Trickle charging was performed on the nickel-zinc secondary battery prepared using a charge/discharge device (TOSCAT3000S, manufactured by Toyo Systems Co., Ltd.) at 0.025C up to SOC100%, and then the battery was left for about 168 hours (self-discharge) three more times, so that the nickel-zinc secondary battery was kept at a high SOC while being intermittently trickle charged for about one month. Thereafter, as shown in FIG. 10A, 0.2C charging and 0.1C discharging were performed to measure the discharge capacity after about 29 days. The discharge capacity thus measured was divided by the initial discharge capacity and multiplied by 100 to calculate the discharge capacity retention rate (%). Similarly, the test for about 29 days (28 days of rest + 1 day of charging three times) according to the charging profile shown in FIG. 10A was repeated to measure the progress of the discharge capacity retention rate up to about 145 days. The results were as shown in Table 2 and FIG. 10B.

From the results shown in Table 2 and Figure 10B, it can be seen that Example A2, which uses a negative electrode with a significantly higher content of metal Zn particles, achieves a higher capacity retention rate even after the same number of days have passed, compared to Example A1, which uses a negative electrode with a lower content rate of metal Zn particles. In other words, by compensating for the decrease in conductivity and the decrease in negative electrode capacity due to the loss of metal zinc caused by the oxidation of the negative electrode with an increase in the amount of metal Zn particles, it is possible to improve the capacity retention rate and delay the decrease in battery capacity. Specifically, as shown in Figure 10B, when the life line is set to 50%, it can be seen that the battery of Example A2, which has an increased content rate of metal Zn particles, has a life that is approximately 1.3 times longer than the battery of Example A1, which is a comparative example. This test was a trickle charge accelerated test performed at a high temperature of 65°C, and it is generally known that the life of a secondary battery is approximately 1/2 when the temperature increases by 10°C. Based on this general knowledge, the expected life of the battery of Example A2, which has a life of about 130 days in an accelerated test at 65°C, at 25°C is estimated to be about 5.7 years, an increase of about 1.3 years over the battery of Example B1.

Next, an accelerated trickle charge test was performed on the nickel-zinc secondary battery in the same manner as above, except that the temperature condition was 55° C. The results are shown in Table 3 and FIG.

From the results shown in Table 3 and Figure 10C, it can be seen that Example A2, which uses a negative electrode with a significantly higher content of metal Zn particles, achieves a higher capacity retention rate even after the same number of days have passed, compared to Example A1, which uses a negative electrode with a lower content rate of metal Zn particles. In other words, by compensating for the decrease in conductivity and the decrease in negative electrode capacity due to the loss of metal zinc caused by the oxidation of the negative electrode with an increase in the amount of metal Zn particles, it is possible to improve the capacity retention rate and delay the decrease in battery capacity. Specifically, as shown in Figure 10C, when the life line is set to 50%, it can be seen that the battery of Example A2, which has an increased content rate of metal Zn particles, has a life that is approximately 1.8 times longer than the battery of Example A1, which is a comparative example. This test was a trickle charge acceleration test performed at a high temperature of 55°C, and it is generally known that the life of a secondary battery is approximately 1/2 when the temperature increases by 10°C. Based on this general knowledge, the expected life of the battery of Example A2, which has a life of about 240 days in an accelerated test at 55°C, at 25°C is estimated to be about 5.3 years, an increase of about 2.4 years over the battery of Example A1.

Examples B1 and B2
A nickel-zinc secondary battery (ZnO:Zn=100:57.1 wt%) was produced and a trickle charge accelerated test was performed in the same manner as in Example A2, except that 100% state of charge (SOC) was set to 90% (Example B1) or 80% (Example B2) of the installed capacity of the positive electrode, and trickle charging was performed up to SOC 100% (90% of the installed capacity) (Example B1) or SOC 90% (80% of the installed capacity) according to the charging profile shown in FIG. 11A.

The results of the accelerated trickle charge test at 65° C. are shown in Table 4 and FIG. 11B.

From the results shown in Table 4 and FIG. 11B, it can be seen that Example B2, in which charging is performed to a depth (SOC) of 90% (80% of the installed capacity), achieves a higher capacity retention rate even with the same number of days elapsed, compared to Example B1, in which charging is performed to an SOC of 100% (90% of the installed capacity). In other words, by lowering 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 consumption of metallic zinc caused by oxidation of the negative electrode, and the deterioration of the positive electrode (especially the loss of positive electrode active material and increased resistance), improve the capacity retention rate, and delay the decrease in battery capacity. Specifically, as shown in FIG. 11B, when the life line is set to 50%, it can be seen that the battery of Example B2, in which the maximum SOC during charging is lowered, has a life of about 1.25 times longer than the battery of Example B1, in which the maximum SOC during charging is higher. This test is a trickle charge accelerated test performed at a high temperature of 65°C, and it is generally known that the life of a secondary battery is reduced by about half when the temperature rises by 10°C. Based on this general knowledge, the expected life of the battery of Example B2, which has a life of about 150 days in an accelerated test at 65°C, at 25°C is estimated to be about 6.6 years, an increase of about 1.3 years over the battery of Example B1.

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

From the results shown in Table 5 and FIG. 11C, it can be seen that Example B2, in which charging is performed to a depth (SOC) of 90% (80% of the installed capacity), achieves a higher capacity retention rate even with the same number of days elapsed, compared to Example B1, in which charging is performed to an SOC of 100% (90% of the installed capacity). In other words, by lowering 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 consumption of metallic zinc caused by oxidation of the negative electrode, and the deterioration of the positive electrode (especially the loss of positive electrode active material and increased resistance), improve the capacity retention rate, and delay the decrease in battery capacity. Specifically, as shown in FIG. 11C, when the life line is set to 50%, it can be seen that the battery of Example B2, in which the maximum SOC during charging is lowered, has a life extended by about 1.2 times compared to the battery of Example B1, in which the maximum SOC during charging is higher. This test is a trickle charge accelerated test performed at a high temperature of 55°C, and it is generally known that the life of a secondary battery is reduced by about half when the temperature rises by 10°C. Based on this general knowledge, the expected life of the battery of Example B2, which has a life of about 270 days in an accelerated test at 55°C, at 25°C is about 5.9 years, which is an estimated increase in life of about 0.9 years compared to the battery of Example B1.

To verify the superiority of Example B2 (i.e., the life extension effect of increasing the content of metallic Zn particles and lowering the maximum SOC during charging), the results obtained in an accelerated trickle charge test at 55°C for Examples A1 and B2 are compared in Table 6 and Figure 11D.

From the results shown in Table 6 and Figure 11D, it can be seen that Example B2, in which the content of metal Zn particles is high and charging is performed to a depth (SOC) of 90% (80% of the installed capacity), achieves a particularly high capacity retention rate even with the same number of days elapsed, compared to Example A1, in which the content of metal Zn particles is low and charging is performed to an SOC of 100% (90% of the installed capacity). In other words, it can be said that a particularly high capacity retention rate can be achieved by increasing the content of metal 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 life line is set to 50%, it can be seen that the battery of Example B2, in which the content of metal Zn particles is increased and the maximum SOC during charging is lowered, has a lifespan that is approximately 1.8 times longer at 55°C than the battery of Example A1, which is a comparative example. This test was a trickle charge accelerated test carried out at a high temperature of 55°C, but it is generally known that a 10°C rise in temperature of a secondary battery reduces the battery life by approximately half. Based on this general knowledge, the expected battery life at 25°C for the battery in Example B2, which has a battery life of approximately 270 days in the accelerated test at 55°C, is approximately 5.9 years, which is an estimated increase in battery life of approximately 3.1 years compared to the battery in Example A1.

Example C1 (Comparative)
A nickel-zinc secondary battery (ZnO:Zn=100:57.1 wt %) was produced in the same manner as in Example A2, except that the following polymeric microporous membrane separator (product name: #3401, manufactured by Celgard, material: polypropylene, thickness: 25 μm) was used instead of the LDH separator, and an accelerated trickle charge test was performed at 65° C. up to SOC 100% (90% of the installed capacity) according to the charging profile shown in FIG. 12A .

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

The results of Examples C1 and C2 are shown in Table 7 and FIG. 12B.

From the results shown in Table 7 and Figure 12B, it can be seen that the LDH separator is not permeable to gases and does not allow oxygen generated from the positive electrode to pass through, so it has the effect of preventing oxidation of the negative electrode, suppressing the decrease in battery capacity, and extending the lifespan. Specifically, as shown in Figure 11D, when the lifespan line is set to 50%, the battery of Example C2, which uses a gas-permeable LDH separator, has a lifespan that is approximately 1.4 times longer at 65°C than the battery of Example C1, which is a comparative example that uses a polymer microporous membrane separator. This test is a trickle charge accelerated test performed at a high temperature of 55°C, but it is generally known that the lifespan of a secondary battery is approximately 1/2 when the temperature rises by 10°C. Based on this general knowledge, the expected lifespan of the battery of Example C2, which has a lifespan of approximately 150 days in the accelerated test at 55°C, at 25°C is approximately 6.6 years, which is estimated to be an increase of approximately 1.8 years compared to the battery of Example C1.

Claims (10)

1. A negative electrode for use in a zinc secondary battery,
   ZnO particles;
   Metal Zn particles in an amount of 55.0 to 65.0 parts by weight per 100 parts by weight of the ZnO particles;
   a negative electrode.
2. The negative electrode according to claim 1, wherein the content of the metal Zn particles is 55.0 to 58.0 parts by weight per 100 parts by weight of the ZnO particles.
3. The negative electrode of claim 1, further comprising a binder resin.
4. a positive electrode plate containing nickel hydroxide and/or nickel oxyhydroxide;
   The 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 so as to be capable of conducting hydroxide ions;
   An electrolyte;
   a battery case in which the positive electrode plate, the negative electrode plate, and a hydroxide ion conductive separator are housed vertically;
   A nickel-zinc secondary battery comprising:
5. The nickel-zinc secondary battery of claim 4, wherein the hydroxide ion conductive separator is an LDH separator containing a 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 of claim 4, wherein the negative electrode plate is covered with the hydroxide ion conductive separator, and the outer periphery of the negative electrode plate other than the upper end is hermetically sealed, so that the hydroxide ion conductive separator prevents oxygen generated in the positive electrode plate from reaching the negative electrode plate.
8. The nickel-zinc battery comprises a stacked cell, the stacked cell comprising:
   A plurality of the positive electrode plates;
   a plurality of positive electrode tab leads extending from each end of the positive electrode plate;
   A plurality of the negative electrode plates;
   a plurality of negative electrode tab leads extending from each end of the negative electrode plate at positions not overlapping with the positive electrode tab leads;
   a plurality of hydroxide ion conductive separators isolating the positive electrode plate and the negative electrode plate so as to be capable of conducting hydroxide ions;
   The electrolyte;
   5. The nickel-zinc secondary battery according to claim 4, wherein the positive electrode plate and the negative electrode plate are alternately laminated with the hydroxide ion conductive separator interposed therebetween.
9. A method of using a nickel-zinc secondary battery, comprising trickle charging the nickel-zinc secondary battery described in claim 4 to provide a charge capacity of 80 to 85% of the installed capacity of the nickel-zinc secondary battery.
10. The method for using the 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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