Zinc battery

Abstract

To provide a zinc battery arranged to use zinc as an anode active material, and capable of keeping a charged battery capacity over a long period of time.SOLUTION: A zinc battery comprises a cathode and an anode containing zinc as an active material, which face each other with a separator interposed therebetween, which are encased in an outer can together with a liquid electrolyte. The anode further contains an oxalic acid compound.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a zinc battery in which the negative electrode active material is zinc.

Background Art

[0002] A zinc battery is a battery that uses zinc as the negative electrode active material. Examples include alkaline dry batteries, nickel-zinc batteries, air-zinc batteries, silver-zinc batteries, etc. In particular, a nickel-zinc battery is a battery in which a hydrogen storage alloy, which is a negative electrode material, is replaced with zinc. Since it does not use an organic solvent in the electrolyte, it has high safety. In addition, zinc has high output characteristics while having a relatively high energy density in an aqueous battery and a high electromotive force due to its combination with nickel hydroxide as the positive electrode active material, and zinc is also low-cost. Therefore, zinc batteries are being considered for application to industrial uses and mobility uses.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] A problem with nickel-zinc batteries is self-discharge. Self-discharge is a phenomenon in which zinc, which is the negative electrode active material, spontaneously dissolves and oxidizes when it comes into contact with the electrolyte, resulting in a decrease in the charged capacity. Due to its principle, this self-discharge is not only a problem with nickel-zinc batteries but also with other zinc batteries having zinc as the negative electrode active material.

Means for Solving the Problems

[0005] To achieve the above object, in the zinc battery of the present invention, a positive electrode and a negative electrode facing each other through a separator are housed in an exterior can together with an electrolytic solution, and the negative electrode has zinc as an active material and further contains an oxalic acid compound.

Advantages of the Invention

[0006] According to the zinc battery of the present invention, self-discharge is suppressed, so that the battery capacity can be maintained for a longer period.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0008] A case where the zinc battery according to the embodiment is applied to a secondary battery will be described with reference to the drawings.

[0009] As shown in FIG. 1, the battery 2 includes an exterior can 10 having a bottomed cylindrical shape with an open upper end. The bottom wall 35 of the exterior can 10 has conductivity and functions as a negative electrode terminal. Inside the opening of the exterior can 10, a disc-shaped cover plate 14 having conductivity and a ring-shaped insulating packing 12 surrounding the cover plate 14 are arranged, and the insulating packing 12 is fixed to the opening edge of the exterior can 10 by caulking the opening edge of the exterior can 10. That is, the cover plate 14 and the insulating packing 12 cooperate with each other to airtightly close the opening of the exterior can 10.

[0010] The cover plate 14 has a gas vent hole 16 at the center, and on the outer surface of the cover plate 14, a rubber valve body 18 that closes the gas vent hole 16 is arranged. Further, on the outer surface of the cover plate 14, a cylindrical positive electrode terminal 20 with a flange is fixed so as to cover the valve body 18, and the positive electrode terminal 20 presses the valve body 18 toward the cover plate 14. Note that the positive electrode terminal 20 is provided with a vent hole (not shown). Normally, the gas vent hole 16 is airtightly closed by the valve body 18. However, when gas is generated inside the outer can 10 and its internal pressure increases, the valve body 18 is compressed by the internal pressure and opens the gas vent hole 16. Thereby, gas is released from the outer can 10 through the gas vent hole 16 and the vent hole of the positive electrode terminal 20. That is, the gas vent hole 16, the valve body 18, and the positive electrode terminal 20 form a safety valve for the battery.

[0011] The outer can 10 houses an electrode group 22. The electrode group 22 is composed of strip-shaped positive electrodes 24, negative electrodes 26, and separators 28, and is wound in a spiral shape with the separators 28 sandwiched between the positive electrodes 24 and the negative electrodes 26. That is, the positive electrodes 24 and the negative electrodes 26 face each other through the separators 28 and are overlapped.

[0012] Inside the outer can 10, a positive electrode lead 30 is arranged between one end of the electrode group 22 and the cover plate 14, and each end of the positive electrode lead 30 is connected to the positive electrode 24 and the cover plate 14, respectively. That is, the positive electrode terminal 20 of the cover plate 14 and the positive electrode 24 are electrically connected to each other through the positive electrode lead 30 and the cover plate 14. Note that a circular insulating member 32 is arranged between the cover plate 14 and the electrode group 22, and the positive electrode lead 30 extends through a slit provided in the insulating member 32. A circular insulating member 34 is also arranged between the electrode group 22 and the bottom of the outer can 10.

[0013] A predetermined amount of alkaline electrolytic solution (not shown) is injected into the outer can 10. The alkaline electrolytic solution is impregnated into the positive electrode 24, the negative electrode 26, and the separator 28, and causes a charge and discharge reaction between the positive electrode 24 and the negative electrode 26 to proceed. Although the alkaline electrolytic solution is not particularly limited, for example, an aqueous potassium hydroxide solution can be used, and the concentration of the alkaline electrolytic solution is not particularly limited either.

[0014] In the electrode group 22, on the outer periphery, the separator 28 is not wound, and the outermost peripheral portion of the negative electrode 26 forms the outer periphery of the electrode group 22. When the outer surface 52 comes into contact with the peripheral wall of the outer can, the negative electrode 26 and the outer can 10 are electrically connected to each other.

[0015] The separator 28 is composed of a non-woven fabric separator and a dendrite-resistant separator. As the non-woven fabric separator, for example, a non-woven fabric made of polyamide fibers, or a non-woven fabric made of polyolefin fibers such as polyethylene or polypropylene to which a hydrophilic functional group is imparted can be used. The dendrite-resistant separator is laminated on the non-woven fabric separator and used as the separator. As the dendrite-resistant separator, for example, a microporous membrane made of polyolefin such as polyethylene or polypropylene can be used.

[0016] The positive electrode 24 is composed of a conductive positive electrode substrate having a porous structure and a positive electrode mixture held in the pores of the positive electrode substrate. As the positive electrode substrate, for example, a net-like, sponge-like or fibrous metal body plated with nickel, or foamed nickel can be used.

[0017] The positive electrode mixture contains positive electrode active material particles and a thickener. The positive electrode active material particles are nickel hydroxide powder, cobalt hydroxide powder, yttrium oxide powder, zinc oxide powder, and niobium oxide powder. These positive electrode active material particles, thickener, and water are mixed to prepare a positive electrode active material slurry. The positive electrode active material slurry is filled into the positive electrode substrate, dried, rolled, and cut into a predetermined size. In the present embodiment, the nominal capacity per positive electrode plate is 1150 mAh.

[0018] The negative electrode 26 has a strip-shaped conductive negative electrode core 60, and a negative electrode mixture 62 is carried on the negative electrode core 60. The negative electrode core 60 is made of a sheet-shaped metal material with through holes distributed therein. For example, a copper punching metal sheet with a tin plating on its surface is used. When the negative electrode mixture is held by the negative electrode core 60, it forms a negative electrode mixture layer.

[0019] The negative electrode mixture 62 contains zinc oxide powder, zinc powder, and bismuth oxide powder as negative electrode active materials, a thickening agent, water, and potassium oxalate monohydrate. These negative electrode active material particles, thickening agent, water, and potassium oxalate monohydrate are mixed to prepare a negative electrode active material slurry. After the slurry is uniformly coated on the negative electrode core 60 and dried, it is rolled with a rolling roll to increase the density of the negative electrode active material and cut into a predetermined size. The negative electrode mixture 62 is not only filled in the through holes of the negative electrode core 60 but also held in layers on both surfaces of the negative electrode core 60. In this embodiment, the nominal capacity per negative electrode plate is 4500 mAh.

[0020] The positive electrode 24 and the negative electrode 26 produced in the above process are opposed to each other with a separator in between and wound in a spiral shape and housed in the exterior can 10. The electrolytic solution is prepared by saturating an aqueous solution with 30% by weight of potassium hydroxide with zinc oxide, and a predetermined amount thereof is poured into the exterior can 10 to seal the opening of the exterior can 10. In this way, a cylindrical nickel-zinc battery with a nominal capacity of 1150 mAh is produced.

[0021] In order to examine the self-discharge characteristics of the zinc secondary battery having the above configuration, five types of negative electrode active material slurries were prepared by changing the weight of potassium oxalate monohydrate with respect to the total amount of zinc composed of zinc oxide and zinc contained in the negative electrode 26. Specifically, with respect to the total amount of zinc, 0.52% by weight (Example 1), 1.05% by weight (Example 2), 2.09% by weight (Example 3), 5.23% by weight (Example 4), and 10.46% by weight (Example 5) were mixed to prepare a negative electrode active material slurry, and zinc secondary batteries using each slurry were produced. On the other hand, as a comparative example, a zinc secondary battery including a negative electrode 26 produced from a negative electrode active material slurry not containing potassium oxalate monohydrate was produced.

[0022] When converting the weight of oxalic acid monohydrate in each example to the weight of oxalate ions ((COO)2 2- ) in potassium oxalate monohydrate with respect to the total zinc amount, the following results are obtained. Specifically, multiply the weight of potassium oxalate monohydrate by the weight ratio of oxalate ions, 0.478. The ratios of oxalate ions with respect to the total zinc amount are 0.25 wt% (Example 1), 0.50 wt% (Example 2), 1.0 wt% (Example 3), 2.5 wt% (Example 4), and 5.0 wt% (Example 5).

[0023] Next, the self-discharge characteristics of Examples 1 to 5 according to this embodiment will be described below. For six types of zinc secondary batteries consisting of Examples 1 to 5 and Comparative Examples, after charging to 100% of the nominal capacity, a charge-discharge cycle of discharging to 1.1 V was performed once to activate the batteries.

[0024] Furthermore, after charging the activated zinc secondary battery to 80% of the nominal capacity, a charge-discharge cycle of discharging to 1.1 V was performed 5 times, and the battery capacity after 5 charge-discharge cycles was defined as the initial capacity A. Next, it was charged again to 80% of the nominal capacity, and after leaving the battery at rest for 2 weeks in an environment at a temperature of 35°C, it was discharged to 1.1 V, and the battery capacity at this time was defined as the remaining capacity B. From the capacities obtained by these procedures, the remaining rate and the increase amount of the remaining rate of the capacity were calculated using the following formula. The results are shown in Figure 2. Remaining rate (%) = B / A = (Remaining capacity B) / (Initial capacity A) Increase amount of remaining rate (%pt) = Remaining rate - (Remaining rate of Comparative Example 1) Note that "%pt" indicates percentage points.

[0025] Figure 2 shows the self-discharge characteristics of Examples 1 to 5 and the Comparative Example.

[0026] The initial capacity A was 906 mAh in Example 1, 903 mAh in Example 2, 903 mAh in Example 3, 906 mAh in Example 4, 902 mAh in Example 5, and 905 mAh in the comparative example. The values of Examples 1 to 5 and the comparative example were almost the same. However, the remaining capacity B was 667 mAh in Example 1, 687 mAh in Example 2, 708 mAh in Example 3, 677 mAh in Example 4, 685 mAh in Example 5, and 642 mAh in the comparative example. In the zinc secondary batteries of Examples 1 to 5 equipped with a negative electrode prepared using potassium oxalate monohydrate, the remaining rate of the battery capacity increased in all cases compared to the battery of the comparative example without the addition of potassium oxalate monohydrate. Specifically, it increased by 2.7%pt in Example 1, 5.1%pt in Example 2, 7.5%pt in Example 3, 3.8%pt in Example 4, and 5.0%pt in Example 5. Therefore, it is considered that by including oxalate ions in the negative electrode active material, the remaining capacity (remaining rate) of the zinc battery increases, that is, self-discharge is suppressed.

[0027] The reason for the improved self-discharge characteristics is presumed as follows. In a nickel-zinc battery, the zinc active material in the negative electrode is reduced from zinc oxide to zinc by charging. However, since zinc is in contact with the electrolyte, it spontaneously dissolves into the electrolyte even during battery rest, resulting in self-discharge where the remaining capacity of the battery decreases. In the comparative example where potassium oxalate monohydrate was not added to the electrolyte, it is considered that this self-discharge occurs significantly.

[0028] On the other hand, in the examples, since potassium oxalate monohydrate is added to the negative electrode, after battery fabrication, a part of the potassium oxalate monohydrate contained in the negative electrode dissolves into the electrolyte and dissociates into its cations and oxalate ions ((COO)2 2- ). It is presumed that the oxalate ions form a sparingly soluble salt with the zinc generated by charging the battery and coat the surface of the negative electrode active material. By covering the surface of the negative electrode active material with the sparingly soluble zinc oxalate as a sparingly soluble salt, the contact between the active zinc inside the negative electrode active material and the electrolyte is suppressed, and it is considered that the spontaneous dissolution of zinc into the electrolyte is suppressed. That is, the self-discharge of the battery is suppressed.

[0029] From the table shown in FIG. 2, it can generally be seen that the residual capacity tends to increase as the content of oxalate ions increases. However, for Example 5, the viscosity increased significantly during the preparation of the negative electrode active material slurry, and it was difficult to prepare a defect-free negative electrode plate.

[0030] From the above, in order to suppress the self-discharge of the zinc secondary battery, it is preferable that the negative electrode active material contains a trace amount of oxalate ions. Further, from the viewpoint of making it possible to fabricate a negative electrode containing oxalate ions and assemble it into a battery, the upper limit of the addition amount of potassium oxalate monohydrate is 10.46% by weight, that is, the upper limit of the content of oxalate ions is 5.0% by weight, based on the total amount of zinc in the negative electrode.

[0031] In the present invention, it is important that oxalate ions are present in the electrolyte of the zinc battery. Therefore, as the oxalate compound contained in the negative electrode, an appropriate oxalate compound can be used as long as it can be dissociated into cations and oxalate ions in an alkaline aqueous solution.

[0032] In the above embodiment, a nickel-zinc battery is used as the battery. However, the present invention is also applicable to an air-zinc battery, an alkaline dry battery, etc. that include zinc as a negative electrode active material, and is not limited to a nickel-zinc battery. For example, when applied to a zinc primary battery as the battery, manganese dioxide is used as the positive electrode active material, zinc is used as the negative electrode active material, and an aqueous solution of sodium hydroxide or potassium hydroxide is used as the electrolyte. Similar to the above embodiment, when preparing the negative electrode, potassium oxalate monohydrate is added to the negative electrode active material slurry to prepare the negative electrode. Thus, also in a zinc primary battery having a negative electrode containing an oxalate compound, compared with a zinc primary battery not containing an oxalate compound in the negative electrode, self-discharge is suppressed and the charged capacity can be maintained for a longer period.

Explanation of reference numerals

[0033] 2 Zinc battery 24 Positive electrode 26 Negative electrode 28 separator

Claims

1. A positive electrode and a negative electrode facing each other through a separator are accommodated in an exterior can together with an electrolytic solution, The negative electrode has at least one of zinc oxide powder and zinc powder as an active material, further contains an oxalic acid compound that dissociates into a cation and oxalate ions ((COO)22−) in the electrolytic solution, and the concentration of oxalate ions in the oxalic acid compound with respect to the total zinc amount in the negative electrode is 0.25 to 5.0% by weight. A zinc battery.

2. The positive electrode contains nickel hydroxide, and the zinc battery is a secondary battery. The zinc battery according to claim 1.

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