Separator and zinc secondary battery

Abstract

This separator is used in a zinc secondary battery. The separator comprises: a porous resin base material; and an inorganic compound filled into the resin base material and composed of titanium and at least one element selected from the group consisting of magnesium, aluminum, and yttrium. The composition ratio of titanium to the entire inorganic compound is at least 40 atm%. When a liquid tank in which two tubes each having an inner diameter of 6 mm protrude upward, which is partitioned into two chambers by a separator having a diameter of 26 mm, and which is filled with a 6M KOH aqueous solution is used as a measurement device, the liquid permeation amount measured 168 hours after the liquid level difference of the tubes is set to 70 cm is at least 0.05 mL and at most 5 mL.

Description

Separator and Zinc Secondary Battery

[0001] The present disclosure relates to a separator and a zinc secondary battery. This application claims priority based on Japanese Patent Application No. 2024-172655 filed on October 1, 2024, and incorporates all the descriptions set forth in the above-mentioned Japanese application.

[0002] Techniques related to separators used in zinc secondary batteries are disclosed in, for example, WO2021 / 229916 (Patent Document 1) and WO2021 / 229917 (Patent Document 2).

[0003] WO2021 / 229916 WO2021 / 229917

[0004] A separator used in a zinc secondary battery is disposed in an electrolytic solution and separates the positive electrode side and the negative electrode side. During charging, discharging, or repeated charging and discharging in a zinc secondary battery, the composition of the electrolytic solution gradually changes, and the hydrogen ion exponent (pH) changes. As a result, the resistance during charge and discharge increases, and such a state is not preferable. Therefore, it is required to suppress the change in the pH of the electrolytic solution as much as possible. Further, from the viewpoint of ensuring stable use over a long period, the separator is required to have high alkali resistance. In addition, in a zinc secondary battery, metallic zinc is deposited in a dendrite shape from the negative electrode during charging, penetrates through the voids of a separator such as a non-woven fabric, and reaches the positive electrode, resulting in a short circuit. Such a short circuit caused by zinc (Zn) dendrites is also not preferable because it leads to a shortening of the charge-discharge life. Therefore, from the viewpoint of ensuring stable use over a long period, the separator is required to have high short-circuit resistance.

[0005] Therefore, one of the objectives is to provide a separator that can be stably used over a long period.

[0006] A separator according to this disclosure is used in a zinc secondary battery. The separator comprises a porous resin substrate and an inorganic compound filled in the resin substrate, which consists of at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium. The composition ratio of titanium to the total inorganic compound is 40 atm% or more. Two tubes, each with an inner diameter of 6 mm, protrude upward and are separated into two chambers by a separator with a diameter of 26 mm. A liquid tank filled with a 6 M KOH aqueous solution is used as a measuring device, and after setting the liquid level difference between each tube to 70 cm, the permeability measured after 168 hours is 0.05 mL or more and 5 mL or less.

[0007] Such separators allow for stable use over long periods of time.

[0008] Figure 1 is a schematic diagram conceptually showing a part of a zinc secondary battery including a separator in Embodiment 1. Figure 2 is a schematic diagram showing an enlarged portion of the cross-section of the separator. Figure 3 is a schematic diagram showing a part of the He permeability measurement system for measuring He permeability. Figure 4 is a schematic diagram showing a part of the He permeability measurement system for measuring He permeability. Figure 5 is a schematic diagram of a measuring device for measuring the conductivity of the separator. Figure 6 is a schematic diagram of a measuring device for measuring the permeability.

[0009] [Summary of Embodiments] The separator according to this disclosure is used in a zinc secondary battery. The separator comprises a porous resin substrate and an inorganic compound filled in the resin substrate, which consists of at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium. The composition ratio of titanium to the total inorganic compound is 40 atm% or more. Two tubes, each with an inner diameter of 6 mm, protrude upward from each other and are divided into two chambers by a separator with a diameter of 26 mm. A liquid tank filled with a 6 M KOH aqueous solution is used as a measuring device, and after setting the liquid level difference between each tube to 70 cm, the permeable volume measured after 168 hours is 0.05 mL or more and 5 mL or less.

[0010] The separator with the above configuration contains an inorganic compound composed of at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium. The composition ratio of titanium to the total inorganic compound is 40 atm% or more, and such an inorganic compound has high alkali resistance. Furthermore, because the microstructure of the inorganic compound does not change with respect to the easily deformable resin substrate, the risk of Zn dendrites penetrating the separator is greatly reduced, and high short-circuit resistance can be ensured. Short-circuit resistance refers to the ability to withstand short circuits. In addition, the permeability after 168 hours, measured using the above measuring device, is between 0.05 mL and 5 mL, so a certain amount of electrolyte permeation can be tolerated. Therefore, it is possible to suppress both the suppression of pH changes in the electrolyte and the suppression of early short circuits caused by Zn dendrites. Based on the above, the above separator can be used stably over a long period of time.

[0011] In the separator according to the above embodiment, the thickness of the separator may be 1 μm or more and 200 μm or less. A thinner separator tends to result in a higher permeability. However, a thinner separator tends to reduce short-circuit resistance. By setting the separator thickness within the above range, it becomes easier to achieve both sufficient permeability and high short-circuit resistance. It is more preferable that the separator thickness be 5 μm or more and 100 μm or less.

[0012] In any one of the above embodiments of the separator, the porosity may be 5% or more and 30% or less. The higher the porosity of the separator, the more pathways there are for the electrolyte to permeate, and therefore the greater the permeability tends to be. On the other hand, if the porosity of the separator is high, the more pathways there are for Zn dendrites to penetrate, and therefore the short-circuit resistance tends to decrease. By setting the porosity of the separator within the above range, it becomes easier to achieve both sufficient permeability and high short-circuit resistance.

[0013] In any one of the above embodiments of the separator, the average pore diameter may be 3 nm or more and 10 nm or less. The larger the average pore diameter of the separator, the wider the path for the electrolyte permeation, and therefore the greater the amount of electrolyte that permeates. On the other hand, if the average pore diameter of the separator is large, Zn dendrites tend to grow easily within the pores, which tends to reduce short-circuit resistance. By setting the average pore diameter of the separator within the above range, it becomes easier to achieve both sufficient electrolyte permeability and high short-circuit resistance.

[0014] In any one of the above embodiments of the separator, the contact angle may be 5° or more and 60° or less. In this way, a smaller contact angle of the separator results in higher wettability, allowing the electrolyte to penetrate the separator more effectively, thus tending to increase the permeability. On the other hand, a small contact angle of the separator increases the number of entry points for Zn dendrites into the separator, thus tending to reduce short-circuit resistance. By setting the separator's contact angle within the above range, it becomes easier to achieve both sufficient permeability and high short-circuit resistance.

[0015] In any one of the above embodiments of the separator, the degree of curvature may be between 1.8 and 4.5. The smaller the degree of curvature of the separator, the shorter the path through the separator's through-hole, and therefore the greater the amount of liquid permeation. On the other hand, if the degree of curvature of the separator is small, the path for Zn dendrites that enter through the through-hole to reach the positive electrode is shortened, and therefore the short-circuit resistance tends to decrease. By setting the degree of curvature of the separator within the above range, it becomes easier to achieve both sufficient liquid permeation and high short-circuit resistance.

[0016] In a separator according to any one of the above embodiments, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound, as determined by energy-dispersive X-ray analysis (EDS), may be 0.55 or more and 0.93 or less. That is, the atomic ratio of Ti / (Ti + Y + Mg + Al) determined by EDS may be 0.55 or more and 0.93 or less. Furthermore, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound may be 0 or more and 0.23 or less. That is, the atomic ratio of Y / (Ti + Y + Mg + Al) determined by EDS may be 0 or more and 0.23 or less. In addition, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound may be 0 or more and 0.19 or less. That is, the atomic ratio of Mg / (Ti + Y + Mg + Al) determined by EDS may be 0 or more and 0.19 or less. Furthermore, the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound may be between 0 and 0.09. That is, the atomic ratio of Al / (Ti + Y + Mg + Al) determined by EDS may be between 0 and 0.09. By setting the atomic ratio within the above range, the resistance at the end of charging can be reduced.

[0017] Furthermore, the zinc secondary battery of this disclosure includes a positive electrode, a negative electrode positioned at a distance from the positive electrode, an electrolyte positioned in contact with the positive electrode and the negative electrode, and the separator described above positioned to separate the positive electrode side and the negative electrode side in the electrolyte.

[0018] The zinc secondary battery with the above configuration can be used stably over a long period of time.

[0019] [Specific Examples of Embodiments] Next, specific embodiments of the separator of this disclosure will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and their descriptions will not be repeated.

[0020] (Embodiment 1) The separator in Embodiment 1 according to this disclosure is used in a zinc secondary battery. The zinc secondary battery can be repeatedly charged and discharged. Figure 1 is a schematic diagram conceptually showing a part of the zinc secondary battery including the separator in Embodiment 1.

[0021] Referring to Figure 1, the separator 15 in Embodiment 1 is used in a zinc secondary battery 11. The zinc secondary battery 11 includes a positive electrode 12, a negative electrode 13, an electrolyte 14, and a separator 15. Nickel (Ni) is used as the positive electrode active material constituting the positive electrode 12. Zinc (Zn) is used as the negative electrode active material constituting the negative electrode 13. The negative electrode 13 is positioned at a distance from the positive electrode 12. The electrolyte 14 is positioned in contact with the positive electrode 12 and the negative electrode 13, respectively. The positive electrode 12 and the negative electrode 13 are immersed in the electrolyte 14. The separator 15 is placed in the electrolyte 14 and separates the positive electrode 12 side from the negative electrode 13 side. The separator 15 is permeable to hydroxide ions. The zinc secondary battery 11 is housed in a case (not shown).

[0022] Here, the separator 15 will be explained further. Figure 2 is a schematic diagram showing an enlarged portion of the cross-section of the separator 15. Referring to Figure 2, the separator 15 includes a porous resin substrate 17 and an inorganic compound 16 filled in the resin substrate 17. The inorganic compound 16 is also arranged inside the resin substrate 17. In this embodiment, the inorganic compound 16 is also arranged on the surface layer 18 of the separator 15. The inner layer 19 of the separator 15 is composed of the inorganic compound 16 and the porous resin substrate 17. The inner layer 19 is mainly composed of the porous resin substrate 17, and the inorganic compound 16 with pores formed inside the resin substrate 17 is randomly arranged. Examples of materials for the porous resin substrate 17 include polystyrene, polyethersulfone, epoxy resin, polyphenylene sulfide, fluororesin (tetrafluorinated resin: PTFE, etc.), cellulose, nylon, polyethylene, and any combination thereof. The average pore diameter of the separator 15, including the surface layer 18 and the inner layer 19, is preferably 3 nm to 10 nm. The porosity of the separator 15, including the surface layer 18 and the inner layer 19, was calculated from the area ratio of the pores obtained by SEM observation and used as the average value. The porosity of the separator 15 is preferably 5% to 30%. Furthermore, the thickness of the separator 15 is preferably 1 μm to 200 μm, and more preferably 5 μm to 100 μm. The contact angle is preferably 5° to 60°. Furthermore, the degree of flexibility is preferably 1.8 to 4.5. The average pore diameter, porosity, thickness, contact angle, and degree of flexibility of the separator 15 may be values ​​other than those listed above. The volume of separator 15 was determined by cutting out a 5cm x 5cm section of separator 15, measuring its thickness at five points using a micrometer, and calculating the average value (average thickness of the five points). This was then used as the thickness of separator 15. For the nitrogen gas adsorption method, a BELSORP18PLUS-HT manufactured by Nippon Bell Co., Ltd. was used as the apparatus. As a pretreatment condition, degassing under reduced pressure was performed at room temperature (25°C) for approximately 24 hours. For the measurement (evaluation conditions), nitrogen was used as the adsorbate, the measurement temperature was set to 77K (liquid nitrogen temperature), and the BJH method was used to analyze the pore size distribution.

[0023] In the separator 15 described above, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, determined by ghee-dispersive X-ray analysis (EDS), is preferably 0.55 to 0.93, and more preferably 0.58 to 0.9. Furthermore, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 is preferably 0 to 0.23, and more preferably 0 to 0.2. In addition, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 is preferably 0 to 0.19, and more preferably 0 to 0.16. Finally, the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 is preferably 0 to 0.09, and more preferably 0 to 0.07. Furthermore, the atomic ratio of the separator 15 may be a value other than that mentioned above. It is preferable to perform the EDS analysis of the inorganic compound 16 using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by (1) acquiring an image with an acceleration voltage of 20 kV and a magnification of 5,000x, (2) performing a three-point analysis in point analysis mode with an interval of approximately 5 μm, (3) repeating (1) and (2) once more, and (4) calculating the average value of the total of six points.

[0024] The separator 15 described above can be manufactured, for example, by the following method: (1) Prepare a porous resin substrate; (2) Apply a solution containing titanium alkoxide (or further yttrium alkoxide and / or aluminum alkoxide) to the porous resin substrate and dry it to form a titania-containing layer; (3) Then, add urea (or further magnesium ions (Mg ２＋ ) and / or yttrium ions (Y ３＋(4) By immersing a porous resin substrate in an aqueous raw material solution containing (4) and performing hydrothermal treatment in the aqueous raw material solution, the inorganic compound and the porous resin substrate (i.e., a separator with the above configuration) can be produced. Furthermore, it is believed that the presence of urea in step (3) causes ammonia to be generated in the solution by utilizing the hydrolysis of urea, thereby increasing the pH, and the coexisting metal ions form hydroxides and / or oxides, thereby obtaining the inorganic compound.

[0025] In particular, when producing a composite material (i.e., the separator) in which a porous resin substrate is composed of a polymer material and the inorganic compound is incorporated throughout the entire thickness of the porous resin substrate, it is preferable to apply the alkoxide solution to the substrate in (2) above by a method that allows the mixed alkoxide solution to penetrate all or most of the inside of the substrate. Examples of preferred application methods include dip coating and filtration coating, with dip coating being particularly preferred. The amount of mixed alkoxide solution applied can be adjusted by adjusting the number of applications of dip coating, etc. After the substrate coated with the mixed alkoxide solution by dip coating, etc., is dried, steps (3) and (4) above can be carried out.

[0026] When the porous resin substrate is composed of a polymer material, it is preferable to subject the separator obtained by the above method to a press treatment. The pressing method may be, for example, a roll press, a uniaxial press, or CIP (cold isostatic pressing), and is not particularly limited, but a roll press is preferred. This pressing is performed while heating the porous resin substrate. As a temperature at which it softens sufficiently, for example, in the case of polypropylene or polyethylene, it is preferable to heat it to 60°C to 200°C. By performing a press such as a roll press in such a temperature range, the microstructure of the resin substrate and the inorganic compound can be strengthened. As a result, the fracture strength of the separator microstructure can be increased, and therefore short circuits caused by Zn dendrites can be suppressed more effectively.

[0027] The separator 15 with the above configuration contains an inorganic compound 16 composed of at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium. The composition ratio of titanium to the total inorganic compound 16 is 40 atm% or more, and such an inorganic compound 16 has high alkali resistance. Furthermore, since the microstructure of the inorganic compound 16 does not change with respect to the easily deformable resin substrate 17, the risk of Zn dendrites penetrating the separator 15 is greatly reduced, and high short-circuit resistance can be ensured. In addition, the permeability after 168 hours, measured using the above measuring device, is between 0.05 mL and 5 mL, so a certain amount of permeation of the electrolyte 14 can be tolerated. Therefore, it is possible to suppress both the suppression of pH changes in the electrolyte 14 and the suppression of early short circuits caused by Zn dendrites. As a result, the above separator 15 can be used stably over a long period of time.

[0028] In the separator 15 of the above embodiment, the porosity of the separator 15 may be 5% or more and 30% or less. The higher the porosity of the separator 15, the more pathways there are for the electrolyte to permeate, and therefore the greater the amount of permeable fluid tends to be. On the other hand, if the porosity of the separator 15 is high, the number of pathways for Zn dendrites to penetrate increases, and therefore the short-circuit resistance tends to decrease. By setting the porosity of the separator 15 within the above range, it becomes easier to achieve both sufficient permeability and high short-circuit resistance.

[0029] In the separator 15 of the above embodiment, the average pore diameter of the separator 15 may be 3 nm or more and 10 nm or less. The larger the average pore diameter of the separator 15, the wider the path for the electrolyte permeation, and therefore the greater the amount of electrolyte that permeates. On the other hand, if the average pore diameter of the separator 15 is large, Zn dendrites tend to grow easily within the pores, which tends to reduce short-circuit resistance. By setting the average pore diameter of the separator 15 within the above range, it becomes easy to achieve both sufficient electrolyte permeation and high short-circuit resistance.

[0030] In the separator 15 of the above embodiment, the contact angle of the separator 15 may be 5° or more and 60° or less. The smaller the contact angle of the separator 15, the higher the wettability and the better the electrolyte penetrates into the separator, so the amount of liquid permeation tends to increase. On the other hand, if the contact angle of the separator 15 is small, the number of entry points for Zn dendrites into the separator 15 increases, so the short-circuit resistance tends to decrease. By setting the contact angle of the separator 15 within the above range, it becomes easy to achieve both sufficient liquid permeation and high short-circuit resistance.

[0031] In the separator 15 of the above embodiment, the degree of curvature of the separator 15 may be between 1.8 and 4.5. The smaller the degree of curvature of the separator 15, the shorter the path through the separator 15, and therefore the greater the amount of liquid permeation. On the other hand, if the degree of curvature of the separator 15 is small, the path for the Zn dendrite that enters through the through hole to reach the positive electrode is shortened, and therefore the short-circuit resistance tends to decrease. By setting the degree of curvature of the separator 15 within the above range, it becomes easy to achieve both sufficient liquid permeation and high short-circuit resistance.

[0032] In the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by energy-dispersive X-ray analysis (EDS), may be 0.55 or more and 0.93 or less. Furthermore, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.23 or less. In addition, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less. And the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less. By setting the atomic ratios within the above ranges, the resistance at the end of charging can be reduced.

[0033] Furthermore, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, and the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.23 or less. Also, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, and the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0 or more and 0.23 or less, and the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0 or more and 0.23 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0 or more and 0.19 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less.

[0034] Furthermore, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.23 or less, and the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.23 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less. Furthermore, in the separator 15 of the above embodiment, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0 or more and 0.23 or less, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less.Furthermore, in the separator 15 of the above embodiment, the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16, as determined by EDS, may be 0.55 or more and 0.93 or less, the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.23 or less, the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.19 or less, and the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound 16 may be 0 or more and 0.09 or less.

[0035] Furthermore, the zinc secondary battery 11 of this disclosure includes a positive electrode 12, a negative electrode 13 positioned at a distance from the positive electrode 12, an electrolyte 14 positioned in contact with the positive electrode 12 and the negative electrode 13 respectively, and the separator 15 described above positioned in the electrolyte 14 to separate the positive electrode 12 side from the negative electrode 13 side.

[0036] The zinc secondary battery 11 with the above configuration can be used stably over a long period of time.

[0037] Forty-one samples were prepared by changing the composition ratio of the inorganic compound and the roll press conditions, and each was evaluated. The results are shown in Tables 1 to 7. The composition ratio of the inorganic compound is as described in Tables 2 and 3. The evaluation method for each evaluation item was as follows. In Tables 1, etc., "100th cycle" refers to the timing of the 100th charge-discharge cycle after 100 charge-discharge cycles. Furthermore, the resistance at the end of charging, described later, was calculated using Sample 7 as the reference.

[0038] For elemental analysis, it is preferable to perform energy-dispersive X-ray spectroscopy (EDS) using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) by (1) acquiring an image with an acceleration voltage of 20 kV and a magnification of 5000x, (2) performing three-point analysis in point analysis mode with an interval of about 5 μm, (3) repeating (1) and (2) once more, and (4) calculating the average value of the total of six points.

[0039] Figures 3 and 4 are schematic diagrams showing parts of a He (helium) permeability measurement system, respectively. For He (helium) permeability measurement, the He permeability measurement system 310 shown in Figures 3 and 4 is configured such that He gas from a gas cylinder filled with He gas is supplied to a sample holder 316 via a pressure gauge 312 and a flow meter 314 (digital flow meter), and is discharged by permeating from one side to the other side of a separator 318 held in the sample holder 316.

[0040] The sample holder 316 has a structure equipped with a gas supply port 316a, a sealed space 316b, and a gas outlet 316c, and was assembled as follows. First, adhesive 322 was applied along the outer circumference of the separator 318 and attached to a jig 324 (ABS resin) having an opening in the center. Butyl rubber packings were placed at the upper and lower ends of the jig 324 as sealing members 326a and 326b, and further, support members 328a and 328b (made of PTFE) having flange openings were sandwiched from the outside of the sealing members 326a and 326b. In this way, the sealed space 316b was partitioned by the separator 318, jig 324, sealing member 326a, and support member 328a. The support members 328a and 328b were tightly fastened to each other with screw fastening means 330 to prevent leakage of He gas from parts other than the gas outlet 316c. A gas supply pipe 334 was connected to the gas supply port 316a of the assembled sample holder 316 via a fitting 332.

[0041] Next, He gas was supplied to the He permeability measurement system 310 through the gas supply pipe 334 and permeated through the separator 318 held in the sample holder 316. At this time, the gas supply pressure and flow rate were monitored by the pressure gauge 312 and the flow meter 314. After allowing the He gas to permeate for 1 to 30 minutes, the He permeability was calculated. The calculation of the He permeability was based on the permeation rate F (cm ３ / min) of the He gas per unit time, the differential pressure P (atm) applied to the separator 318 during He gas permeation, and the membrane area S (cm ２ ) through which the He gas permeated, and was calculated using the formula F / (P × S). The permeation rate F (cm ３ / min) of the He gas was directly read from the flow meter 314. Also, the differential pressure P was the gauge pressure read from the pressure gauge 312. The He gas was supplied such that the differential pressure P was within the range of 0.05 to 0.90 atm.

[0042] The ionic conductivity was measured in the electrolyte using the electrochemical measurement cell shown in Figure 5 as follows. Figure 5 is a schematic diagram of the measuring device 410 for measuring the conductivity of the separator. First, adhesive 449 was applied along the outer circumference of the separator 448 and attached to a jig 450 (ABS resin) having an opening in the center. Referring to Figure 5, this jig 450 was sandwiched on both sides with 1 mm thick silicone packing 440 and assembled into a PTFE flange-type cell 442 with an inner diameter of 6 mm. As electrodes 446, #100 mesh nickel wire mesh was assembled into the cell 442 in a cylindrical shape with a diameter of 6 mm, so that the distance between electrodes was 2.2 mm. To prevent leakage of the electrolyte from the cell 442, the cells were tightly fastened together with screw fastening means 447. As the electrolyte 444, a 6 M KOH (potassium hydroxide) aqueous solution was filled into the cell 442. Using an electrochemical measurement system (potentiometer / galvanostat-frequency response analyzer, Solartron models 1287A and 1255B), measurements were performed under conditions of a frequency range of 1 MHz to 0.1 Hz and a potential amplitude of 10 mV. The intercept of the real axis was defined as the combined resistance T of the separator 448 and the electrolyte 444. The same measurement was performed with a setup without separator 448 to determine the blank resistance B (resistance of electrolyte 444). The difference between the combined resistance T and the blank resistance B was defined as the resistance of separator 448. The ionic conductivity was determined using the obtained resistance of separator 448 and the area of ​​separator 448.

[0043] For the measurement of the liquid permeation amount, the measuring device shown in Fig. 6 was used. Fig. 6 is a schematic diagram of the measuring device 510 for measuring the liquid permeation amount. Referring to Fig. 6, the measuring device 510 has a two-chamber structure in which two tubes 511 and 512 are erected using two perforated rubber stoppers 520. An opening hole 516 is provided between the two chambers 514 and 515. A separator 513 is arranged to block the opening hole 516, and a mesh material 518 for preventing deformation of the separator 513 is installed on the tube 512 side of the separator 513. Butyl rubber packings are installed as sealing members 517 on both sides of the separator 513 and the mesh material 518. The inner diameters of the tubes 511 and 512 are 6 mm. Also, the diameter of the opening hole 516 is 26 mm. The measuring device 510 was firmly tightened together using fastening means 521 with screws so that no leakage of the electrolytic solution occurred. Then, a 6M KOH aqueous solution was filled into the two tubes 511 and 512 as the electrolytic solution 519. The electrolytic solution 519 was poured so that the liquid level on the tube 511 side was 70 cm higher than the liquid level on the tube 512 side. The liquid temperature was set at 25°C and the atmospheric pressure was set at 1 atm. That is, as shown in Fig. 6, a liquid tank in which two tubes each with an inner diameter of 6 mm protrude upward and are partitioned into two chambers by a separator with a diameter of 26 mm and filled with a 6M KOH aqueous solution was used as the measuring device 510. The liquid permeation amount was measured from the change in the liquid level height after a certain period of time, specifically 168 hours had elapsed.

[0044] For the measurement of the porosity, it was calculated as follows. The cross-sectional microstructure of the separator 15 was observed using a scanning electron microscope (SEM, JSM-6610LV, manufactured by JEOL Ltd.) at an acceleration voltage of 10 - 20 kV and a magnification of 10,000 times, and the area ratio of the pores was calculated, and its average value (the average area ratio at 5 locations) was derived. When the inorganic compound and the pores cannot be distinguished, it may be regarded as the area of the inorganic compound.

[0045] The average pore size was measured using the nitrogen gas adsorption method. For the nitrogen gas adsorption method, a BELSORP18PLUS-HT manufactured by Nippon Bell Co., Ltd. was used as the apparatus. As a pretreatment condition, degassing under reduced pressure was performed at room temperature (25°C) for approximately 24 hours. For the measurement (evaluation conditions), nitrogen was used as the adsorbate, the measurement temperature was set to 77K (liquid nitrogen temperature), and the BJH method was used to analyze the pore size distribution.

[0046] To evaluate the wettability of the separator 15, the contact angle with the electrolyte (a 6 M KOH aqueous solution containing 0.5 M Zn ions) was measured as follows. Specifically, at room temperature (25°C), 4 μL of the electrolyte was dropped onto the surface of the separator 15, and the contact angle of the resulting droplet after 1 second was evaluated using a portable contact angle meter PCA-11 manufactured by Kyowa Interface Science Co., Ltd.

[0047] The degree of curvature τ was calculated using the porosity ε of the separator 15 from the following equation (Bruggeman model where pores are considered as gaps between spherical particles).

[0048] τ = ε －１／２

[0049] Regarding the Bruggeman model, we referred to the following non-patent document: "On the origin and application of the Bruggeman correlation for analyzing transport phenomena in electrochemical systems" by Bernhard Tjaden et al., Current Opinion in Chemical Engineering, 2016, Vol. 12, pp. 44-51.

[0050] Porosity ε was calculated using the formula ε = V1 / V2, where V1 is the pore volume per unit weight of separator 15 and V2 is the volume per unit weight of separator 15. Pore volume V1 was measured by nitrogen gas adsorption. The nitrogen gas adsorption method was performed using the same apparatus, pretreatment conditions, and analysis method as described above. Volume V2 was calculated by measuring the thickness at five points on a 5 cm x 5 cm section of separator 15 using a micrometer, and taking the average value (average thickness of five points).

[0051] The EDS analysis of the inorganic compound 16 is preferably performed using an EDS analyzer (e.g., X-act, manufactured by Oxford Instruments) as described above, by (1) acquiring an image with an acceleration voltage of 20 kV and a magnification of 5,000x, (2) performing three point analyses with an interval of about 5 μm in point analysis mode, (3) repeating (1) and (2) once more, and (4) calculating the average value of the total of six points.

[0052] The presence or absence of short circuits was confirmed by repeatedly performing charge-discharge tests. First, the positive electrode (containing nickel hydroxide and / or nickel oxyhydroxide) and the negative electrode (containing zinc and / or zinc oxide) were each wrapped in nonwoven fabric, and current extraction terminals were welded to them. The prepared positive and negative electrodes were placed opposite each other with a separator in between, sandwiched between laminate films with current extraction ports, and three sides of the laminate film were heat-sealed. An electrolyte (containing 0.5 M Zn ions in a 6 M KOH aqueous solution) was added to the resulting open-top cell container, and the electrolyte was thoroughly permeated into the positive and negative electrodes by vacuuming, etc. Then, the remaining side of the laminate film was also heat-sealed to create a simple sealed cell. Using a charge-discharge device (Toyo System Co., Ltd., TOSCAT3100), chemical conversion was performed on the simple sealed cell with 0.1 C charge and 0.2 C discharge. Subsequently, a 0.5 C charge-discharge cycle was performed. While repeatedly performing charge-discharge cycles under the same conditions, the voltage between the positive and negative electrodes was monitored with a voltmeter to check for the presence of a sudden voltage drop (specifically, a voltage drop of 5 mV or more compared to the immediately preceding plotted voltage) due to a short circuit caused by Zn dendrites between the positive and negative electrodes. This was evaluated according to the following criteria: If the above-mentioned sudden voltage drop was not observed during charging even after 100 cycles, it was considered "no short circuit," and if the above-mentioned sudden voltage drop was observed during charging in less than 100 cycles, it was considered "short circuit present."

[0053] For the resistance at the end of charging, the "current value I" measured at the end of a predetermined number of 0.5C charge-discharge cycles and the "cell voltage V" 5 minutes after the end of charging were used, and the resistance at the end of charging was calculated as (1.9 - V) / I. The resistance at the end of charging of each sample after 100 cycles was calculated as a relative ratio with the resistance at the end of charging of sample 7 set to 1.0.

[0054]

[0055]

[0056]

[0057] Referring to Table 1, samples 1 to 10 comprise an inorganic compound composed of at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium. Specifically, for samples 1 to 10, the composition ratio is such that the total composition is 100, with Ti at 70 atm% to 75 atm%, Mg at 5 atm% to 8 atm%, Al at 3 atm% to 6 atm%, and Y at 15 atm% to 20 atm%. That is, for all samples 1 to 10, the composition ratio of titanium to the total inorganic compound is 40 atm% or more. For samples 1 to 6, the permeability after 168 hours is 0.05 mL to 5 mL, and more specifically, the permeability is 0.08 mL to 4.72 mL. Furthermore, there were no short circuits up to the 100th cycle, and the resistance at the end of charging at the 100th cycle was lower compared to the reference (sample 7) and sample 8, which had a permeability of less than 0.05 mL. Furthermore, the He transmittance was 0 (cm / min·atm), and the ionic conductivity was 2.8 (S / cm). ２ That's all.

[0058] In contrast, for samples 9-10, the permeability was 6.33 mL or more, which is greater than 5 mL. Furthermore, a short circuit occurred by the 100th cycle. In addition, the initial He permeability was 480 cm / min atm or more. This is thought to be because He gas easily permeated, making it easy for Zn dendrites to penetrate the separator, resulting in low short-circuit resistance.

[0059] The samples in Tables 2 and 3 were prepared under roll press conditions of 70°C and a load of 2 tons. For samples 11 to 20 shown in Tables 2 and 3, the permeability after 168 hours was between 0.05 mL and 5 mL. Furthermore, no short circuits occurred up to the 100th cycle, and the resistance at the end of charging at the 100th cycle was lower than that of sample 7. For sample 21, the permeability was 5 mL or more, and a short circuit occurred up to the 100th cycle. This is thought to be due to the fact that, although it contains titanium, its composition ratio is less than 40 atm%, resulting in low alkali resistance, degradation of the inorganic compound by the 100th cycle, and a decrease in short-circuit resistance.

[0060] Furthermore, in the above embodiment, as shown in Sample 14, the inorganic compound may be composed of titanium and magnesium; as shown in Sample 15, the inorganic compound may be composed of titanium and aluminum; or as shown in Sample 16, the inorganic compound may be composed of titanium and yttrium.

[0061]

[0062]

[0063]

[0064]

[0065] Samples 22-41 in Tables 4-7 comprise an inorganic compound composed of at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium. Specifically, for samples 22-41, the composition ratio is such that the total composition is 100, with Ti at 70 atm% to 75 atm%, Mg at 5 atm% to 8 atm%, Al at 3 atm% to 6 atm%, and Y at 15 atm% to 20 atm%. In other words, for all samples 22-41, the composition ratio of titanium to the total inorganic compound is 40 atm% or more. The roll press conditions were set to a temperature of 70°C and a load of 2 tons.

[0066] Samples 22-26 in Table 4 are samples relating to porosity and were prepared using resin substrates with different contact angles with water. The method used to change the porosity of the sample is not particularly limited, and the method used in this embodiment is just one example. The others were prepared using the same method as described above. For samples 23-25 ​​shown in Table 4, the permeability after 168 hours was between 0.05 mL and 5 mL. Furthermore, no short circuits occurred up to the 100th cycle, and the resistance at the end of charging at the 100th cycle was also smaller compared to the reference (sample 7) and sample 22, which had permeability of less than 0.05 mL. In contrast, for sample 26, the permeability was greater than 5 mL, and a short circuit occurred up to the 100th cycle. This is thought to be due to the increase in the porosity of the separator 15, which increased the number of pathways for Zn dendrites to penetrate and reduced short-circuit resistance.

[0067] Samples 27-31 in Table 5 are samples relating to average pore diameter and were prepared by changing the temperature during hydrothermal treatment. The method is not particularly limited as long as it can change the average pore diameter of the sample, and the method used in this embodiment is just one example. The others were prepared using the same method as described above. For samples 28-30 shown in Table 5, the permeability after 168 hours was between 0.05 mL and 5 mL. Furthermore, no short circuits occurred up to the 100th cycle, and the resistance at the end of charging at the 100th cycle was also smaller compared to the reference (sample 7) and sample 27, which had permeability of less than 0.05 mL. In contrast, for sample 31, the permeability was greater than 5 mL, and a short circuit occurred up to the 100th cycle. This is thought to be due to the fact that as the average pore diameter of the separator 15 increased, Zn dendrites grew more easily within the pores, reducing the short-circuit resistance.

[0068] Samples 32-36 in Table 6 are samples related to the contact angle and were prepared by changing the time during hydrothermal treatment. The method is not particularly limited as long as it can change the contact angle of the sample, and the method used in this embodiment is just one example. The others were prepared using the same method as described above. For samples 33-35 shown in Table 6, the permeability after 168 hours was between 0.05 mL and 5 mL. Furthermore, no short circuits occurred up to the 100th cycle, and the resistance at the end of charging at the 100th cycle was also smaller compared to the reference (sample 7) and sample 32, which had permeability of less than 0.05 mL. In contrast, for sample 36, the permeability was greater than 5 mL, and a short circuit occurred up to the 100th cycle. This is thought to be due to the fact that as the contact angle of the separator 15 decreased, the permeability of the electrolyte improved, increasing the number of entry points for Zn dendrites and reducing short-circuit resistance.

[0069] Samples 37-41 in Table 7 are samples relating to the degree of flexibility and were prepared using resin substrates with different porosity. The method used to change the degree of flexibility of the sample is not particularly limited, and the method used in this embodiment is just one example. The others were prepared using the same method as described above. For samples 38-40 shown in Table 7, the permeability after 168 hours was between 0.05 mL and 5 mL. Furthermore, no short circuits occurred up to the 100th cycle, and the resistance at the end of charging at the 100th cycle was also smaller compared to the reference (sample 7) and sample 37, which had a permeability of less than 0.05 mL. In contrast, for sample 41, the permeability was greater than 5 mL, and a short circuit occurred up to the 100th cycle. This is thought to be due to the fact that as the degree of flexibility of the separator 15 decreases, the path for the Zn dendrites that have entered the separator 15 to reach the positive electrode becomes shorter, resulting in a decrease in short-circuit resistance.

[0070] The embodiments disclosed herein should be understood to be illustrative in all respects and not restrictive in any way. The scope of the invention is defined by the claims and not by the foregoing description, and all modifications within the meaning and scope of the claims are intended to be included.

[0071] 11 Zinc secondary battery, 12 Positive electrode, 13 Negative electrode, 14 Electrolyte, 15 Separator, 16 Inorganic compound, 17 Resin substrate, 18 Surface layer, 19 Inner layer, 310 He permeability measurement system, 312 Pressure gauge, 314 Flow meter, 316 Sample holder, 316a Gas supply port, 316b Sealed space, 316c Gas outlet, 318 Separator, 322 Adhesive, 324 Jig, 326a, 326b Sealing member, 328a, 328b Support member, 330 Fastening means, 332 Joint, 334 Gas supply pipe, 440 Silicone packing, 442 Cell (PTFE type flange cell), 444 Electrolyte, 446 Electrode, 447 Fastening means, 448 Separator, 449 Adhesive, 450 Jig, 510 measuring device, 511, 512 pipe, 513 separator, 514, 515 chamber, 516 opening, 517 sealing member, 518 mesh material, 519 electrolyte, 520 perforated rubber stopper, 521 fastening means.

Claims

1. A separator for use in a zinc secondary battery, comprising: a porous resin substrate; an inorganic compound filled in the resin substrate, comprising at least one element selected from the group consisting of magnesium, aluminum, and yttrium, and titanium, wherein the composition ratio of titanium to the total inorganic compound is 40 atm% or more; and the liquid permeability measured after 168 hours using a liquid tank filled with a 6M KOH aqueous solution, with two tubes each having an inner diameter of 6 mm protruding upward and divided into two chambers by the separator with a diameter of 26 mm, and with the liquid level difference in each tube set to 70 cm, is 0.05 mL or more and 5 mL or less.

2. The separator according to claim 1, wherein the porosity is 5% or more and 30% or less.

3. The separator according to claim 1, wherein the average pore size is 3 nm or more and 10 nm or less.

4. The separator according to claim 1, wherein the contact angle is 5° or more and 60° or less.

5. The separator according to claim 1, wherein the degree of flexibility is 1.8 or more and 4.5 or less.

6. The separator according to any one of claims 1 to 5, wherein the atomic ratio of titanium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound, as determined by energy-dispersive X-ray analysis, is 0.55 or more and 0.93 or less.

7. The separator according to any one of claims 1 to 5, wherein the atomic ratio of yttrium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound, as determined by energy-dispersive X-ray analysis, is 0 or more and 0.23 or less.

8. The separator according to any one of claims 1 to 5, wherein the atomic ratio of magnesium / (titanium + yttrium + magnesium + aluminum) in the inorganic compound, as determined by energy-dispersive X-ray analysis, is 0 or more and 0.19 or less.

9. The separator according to any one of claims 1 to 5, wherein the atomic ratio of aluminum / (titanium + yttrium + magnesium + aluminum) in the inorganic compound, as determined by energy-dispersive X-ray analysis, is 0 or more and 0.09 or less.

10. A zinc secondary battery comprising: a positive electrode; a negative electrode disposed at a distance from the positive electrode; an electrolyte disposed in contact with the positive electrode and the negative electrode, respectively; and a separator according to any one of claims 1 to 5 disposed in the electrolyte to separate the positive electrode side from the negative electrode side.

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