JPH09115511A - Manufacture of alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance positive electrode utilization rate by improving a positive electrode. SOLUTION: This battery has a positive electrode 2, a negative electrode 4, a separator 3 being inerjacent between the positive electrode 2 and the negative electrode 4, and an alkaline electrolyte. In this case, the positive electrode 2 is produced by a method having a process for filling paste contg. nickel compd. particles and a least one selected from a cobalt compd. and metallic cobalt serving as an electroconductive agent in a collector; and a process for charging the paste-filled collector in a heated aqueous alkaline soln.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing an alkaline secondary battery having a positive electrode containing a positive electrode active material made of a nickel compound and a conductive agent made of one or more selected from a cobalt compound and metallic cobalt. Is.

[0002]

2. Description of the Related Art An alkaline secondary battery has a structure in which an electrode group made by interposing a separator between a positive electrode and a negative electrode and an alkaline electrolyte are contained in a container. A paste-type positive electrode has been conventionally used as this positive electrode. The paste-type positive electrode is prepared by adding a conductive agent, a binder and water to nickel compound particles as an active material and mixing them to prepare a paste, which is three-dimensional like a sponge-like metal porous body or a metal fiber mat. It is produced by filling a conductive core body having a structure.

The conductive agent in the paste type positive electrode is added to the paste in order to activate the active material. As the conductive agent, conventionally, cobalt compounds such as cobalt hydroxide and cobalt monoxide, and metallic cobalt have been known. In particular, cobalt compounds are known to be excellent conductive agents for improving the utilization rate of the positive electrode. The above-mentioned cobalt species cannot activate the active material because it has no conductivity in this state, but after being dissolved in the alkaline solution held by the positive electrode, it is oxidized and is highly conductive. When converted to cobalt, it functions as a conductive agent. Since the cobalt oxyhydroxide coats the surfaces of the nickel compound particles, the conduction between the nickel compound particles and between these particles and the conductive core is improved, and the utilization factor of the positive electrode is improved.

Oxidation of the conductive agent to cobalt oxyhydroxide is conventionally performed by first charging after assembly of a secondary battery, or by charging the paste type positive electrode in an alkaline aqueous solution at room temperature. Done.
However, in such a method, since the conductive agent cannot be sufficiently dissolved in the alkaline solution held on the positive electrode, the distribution of the cobalt oxyhydroxide film on the surface of the nickel compound particles becomes non-uniform, It becomes difficult to sufficiently improve the electrical continuity between the particles and the conductive core. As a result, the utilization rate of the positive electrode decreases,
There is a problem that the battery capacity is lowered.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing an alkaline secondary battery in which the utilization factor of the positive electrode is improved by improving the positive electrode.

[0006]

A method of manufacturing an alkaline secondary battery according to the present invention comprises an alkali having a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. In the method for manufacturing a secondary battery, the positive electrode is filled with a paste containing nickel compound particles and one or more kinds selected from cobalt compounds and metallic cobalt as a conductive agent in a current collector; And a step of charging the current collector in a heated alkaline aqueous solution.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery manufactured by the method according to the present invention will be described with reference to FIG. A positive electrode 2, a separator 3 and a negative electrode 4 are placed in a bottomed cylindrical container 1.
An electrode group 5 manufactured by stacking and winding in a spiral shape is housed. The negative electrode 4 is arranged at the outermost periphery of the electrode group 5 and is in electrical contact with the container 1. The alkaline electrolyte is contained in the container 1. A circular sealing plate 7 having a hole 6 in the center is arranged in the upper opening of the container 1. The ring-shaped insulating gasket 8 is arranged between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the sealing plate is attached to the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is airtightly fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2, and the other end is connected to the lower surface of the sealing plate 7. Hat-shaped positive electrode terminal 1
Numeral 0 is mounted on the sealing plate 7 so as to cover the hole 6. A rubber safety valve 11 is disposed so as to close the hole 6 in a space surrounded by the sealing plate 7 and the positive electrode terminal 10. A holding plate 12 made of an insulating material and having a hole in the center is disposed on the positive electrode terminal 10 such that a projection of the positive electrode terminal 10 projects from the hole. The outer tube 13 is provided around the periphery of the holding plate 12 and the container 1.
And the periphery of the bottom of the container 1.

Next, the positive electrode 2, the negative electrode 4, the separator 3 and the alkaline electrolyte will be described. 1) Positive Electrode 2 This positive electrode 2 can be manufactured by the following method. (First step) After preparing a paste containing nickel compound particles, a conductive agent consisting of one or more kinds selected from cobalt compounds and metallic cobalt, a binder, and water, the current collector is filled with the paste. Then, this is dried and pressure-molded as required.

Examples of the nickel compound particles include nickel hydroxide particles, nickel hydroxide particles in which zinc and cobalt are coprecipitated, nickel oxide particles and the like. Above all, it is preferable to use nickel hydroxide particles in which the zinc and cobalt are coprecipitated.

The conductive agent is made of one or more selected from cobalt compounds and metallic cobalt. Examples of the cobalt compound include cobalt hydroxide (Co (OH) ₂ ) and cobalt monoxide (CoO). In particular, it is preferable to use a conductive agent composed of cobalt hydroxide, cobalt monoxide, or both cobalt hydroxide and cobalt monoxide. A positive electrode containing such a conductive agent can increase the utilization factor. Further, since metallic cobalt has a low solubility in an alkaline aqueous solution, it is preferable to use the cobalt compound together when used as a conductive agent.

Examples of the binder include polytetrafluoroethylene (PTFE), polyethylene, rubber polymers (for example, latex of polypropylene styrene butadiene rubber (SBR), latex of acrylonitrile butadiene rubber (NBR), ethylene propylene diene). Hydrophobic polymers such as monomers (EPDM) latex); carboxymethyl cellulose (CMC),
Methylcellulose (MC), hydroxypropylmethylcellulose (HPMC), polyacrylate (eg sodium polyacrylate (SPA)), polyvinyl alcohol (PVA), polyethylene oxide, copolymer of acrylic acid and vinyl alcohol, acrylate And a hydrophilic alcohol such as a copolymer of vinyl alcohol and a copolymer of maleic acid and vinyl alcohol. The binder may be formed of one or more kinds selected from the above-mentioned types of polymers. Above all, it is preferable to use a mixed polymer composed of a hydrophobic polymer and a hydrophilic polymer. The hydrophobic polymer can improve the strength of the positive electrode. On the other hand, the hydrophilic polymer can impart fluidity to the paste. Especially,
Polytetrafluoroethylene as a hydrophobic polymer,
It is more preferable to use a mixed polymer having one or more selected from carboxymethyl cellulose, methyl cellulose and polyvinyl alcohol as the hydrophilic polymer. Carboxymethyl cellulose,
The methyl cellulose, the polyvinyl alcohol,
It is an excellent paste fluidity modifier. The polyethylene, polypropylene and polytetrafluoroethylene can be used in the form of dispersion.

The current collector is, for example, a mesh-like, sponge-like, fibrous or felt-like metal porous material formed of a metal such as nickel or stainless steel or an alkali resistant material such as a resin plated with nickel. The body etc. can be mentioned. (Second step) A current collector filled with the paste is charged in a state of being immersed in a heated alkaline aqueous solution to produce a positive electrode.

Examples of the alkaline aqueous solution include an aqueous solution of sodium hydroxide (NaOH), an aqueous solution of lithium hydroxide (LiOH), an aqueous solution of potassium hydroxide (KOH), and the like. As the alkaline aqueous solution, these types of aqueous solutions may be used alone,
For example, a mixed solution composed of two or more kinds of aqueous solutions such as a mixed solution composed of NaOH and LiOH may be used. Also,
The alkaline aqueous solution may be different in composition from the alkaline electrolyte.

The solubility of the conductive agent in the alkaline aqueous solution increases in proportion to the temperature of the alkaline aqueous solution. The alkaline aqueous solution is preferably heated to 40 ° C. or higher, and more preferably 60 ° C. or higher.
The higher the heating temperature, the more preferable. In particular, the positive electrode charged in a boiling alkaline aqueous solution can significantly improve the utilization rate. If the heating temperature is lower than 40 ° C., the dissolution of the conductive agent in the alkaline aqueous solution is not sufficiently promoted,
It may be difficult to improve the utilization rate of the positive electrode.
The upper limit of the heating temperature is the boiling point of the alkaline aqueous solution.

The solubility of the conductive agent in the alkaline aqueous solution increases in proportion to the concentration of the alkaline aqueous solution. The concentration of the alkaline aqueous solution is preferably 2N or more, and 4
More preferably, it is N or more. The higher the concentration of the alkaline aqueous solution, the more preferable. In particular, the saturated solution is preferable because it can dramatically improve the solubility of the conductive agent in the alkaline aqueous solution and can significantly improve the utilization rate of the positive electrode. If the concentration of the aqueous solution is less than 2N, the solubility of the conductive agent in the alkaline aqueous solution becomes low, which may make it difficult to improve the utilization rate of the positive electrode. Moreover, the upper limit of the concentration is the concentration of the saturated alkali solution.

As a method of charging the positive electrode in the heated alkaline aqueous solution, for example, constant current charging of 0.05 C to 2.0 C with respect to the theoretical capacity of the positive electrode can be adopted. The reason for limiting the current value in the constant current charging to the above range is as follows. If the current value is less than 0.05 C, it takes time to charge and the productivity may be reduced. On the other hand, the current value is 2.0C
If it exceeds, the positive electrode may undergo a heterogeneous reaction and the activation efficiency may decrease. The negative electrode used for this charging is not particularly limited, and the same negative electrode 4 as described later can be used. The negative electrode used for charging is
The type of the negative electrode actually incorporated in the secondary battery does not have to be the same, and may be different. 2) Negative Electrode 4 The negative electrode 4 preferably has a structure in which a negative electrode active material is carried on a conductive substrate.

For the negative electrode, for example, a paste containing a negative electrode active material, a binder, a conductive powder and water is prepared, the conductive substrate is filled with the paste, dried, and then pressure-molded if necessary. It is manufactured by

As the active material, a material directly involved in the charge / discharge reaction or a material directly involved in the charge / discharge reaction
Any substance that releases can be used. Examples of the former include powders of cadmium compounds such as cadmium metal and cadmium hydroxide. Examples of the latter include a hydrogen storage alloy that stores and releases hydrogen. Among them, the secondary battery provided with the negative electrode containing the hydrogen storage alloy is capable of discharging a large current and less likely to cause environmental pollution as compared with the secondary battery provided with the negative electrode containing the powder of the cadmium compound. Therefore, it is preferable.

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen electrochemically generated in the electrolytic solution and can easily release the stored hydrogen during discharge. . For example, LaNi ₅ , MmN
i ₅ (Mm; misch metal), LmNi ₅ (Lm; lanthanum-enriched misch metal), or Ni
A part of Al, Mn, Co, Ti, Cu, Zn, Zr,
Examples thereof include a multi-element type substituted by elements such as Cr and B, or a TiNi type, TiFe type, ZrNi type, or MgNi type. Among them, the general formula LmNi
_x Mn _y A _z (However, A is Al, shows at least one metal selected from Co, the atomic ratio x, y, z is the total value of 4.8 ≦ x + y + z ≦ 5.4) hydrogen represented by It is desirable to use an occlusion alloy. The negative electrode containing the hydrogen storage alloy having such a composition can suppress the pulverization accompanying the progress of the charge / discharge cycle, so that the charge / discharge cycle life of the secondary battery can be improved.

As the binder, the same binder as described above for the positive electrode can be used. As the conductive powder, for example, nickel powder, cobalt oxide,
Examples thereof include titanium oxide and carbon black. In particular, it is preferable to use the carbon black as the conductive powder.

As the conductive substrate, for example, a two-dimensional substrate such as punched metal, expanded metal, perforated rigid plate, nickel net, or a three-dimensional substrate such as a felt-like porous metal body or a sponge-like metal substrate. Can be mentioned. 3) Separator 3 As the separator 3, for example, a nonwoven fabric made of a polyolefin fiber, such as a nonwoven fabric made of polyethylene fiber, a nonwoven fabric made of ethylene-vinyl alcohol copolymer fiber, or a nonwoven fabric made of polypropylene fiber, provided with a hydrophilic functional group,
For example, a nonwoven fabric made of polyamide fiber such as nylon 6,6 can be used. Examples of a method for imparting a hydrophilic functional group to the polyolefin fiber nonwoven fabric include a corona discharge treatment, a sulfonation treatment, a graft copolymerization, and the application of a surfactant or a hydrophilic resin. 4) Alkaline Electrolyte Solution Examples of the alkaline electrolyte solution include an aqueous solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH).
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixture, NaOH and KOH mixture, K
Mixture of OH and LiOH, KOH, LiOH and NaOH
It is possible to use a mixed solution of the above.

The method for producing an alkaline secondary battery of the present invention is as follows:
Filling a current collector with a paste containing nickel compound particles and one or more selected from cobalt compounds and metallic cobalt as a conductive agent; and charging the current collector filled with the paste in a heated alkaline aqueous solution. A positive electrode is produced by a method including the steps of: Unlike the alkaline electrolyte contained in the secondary battery, the alkaline aqueous solution has no restrictions on the amount, concentration, composition and temperature, and enhances the solubility of the conductive agent in the alkaline aqueous solution held in the paste. It is possible to freely set the necessary conditions. Therefore, by immersing the current collector filled with the paste in a heated alkaline aqueous solution, it is possible to immerse it in a high-temperature alkaline aqueous solution having a higher concentration than the alkaline electrolytic solution in the secondary battery. Therefore, the solubility of the conductive agent can be dramatically improved. When the conductive agent dissolved in a large amount in the alkaline aqueous solution in the paste is oxidized by charging, the surface of the nickel compound particles can be uniformly coated with the cobalt oxyhydroxide film, so that the nickel compound particles and the nickel compound particles can be coated with each other. It is possible to improve the conduction between the particles and the current collector. as a result,
Since the utilization rate of the positive electrode can be improved, the discharge capacity of the secondary battery can be improved.

In the alkaline secondary battery, when the conductive agent is changed to cobalt oxyhydroxide by electrochemical oxidation such as initial charging, the conductive agent is changed to cobalt oxyhydroxide through the following reaction. In the secondary battery, after assembling, the conductive agent is dissolved in an alkaline electrolyte held in the positive electrode to form a blue complex ion (HCo).
O ₂ ^-) is changed to. The elution reaction into the electrolytic solution when the conductive agent is cobalt monoxide is shown in the following formula (1).

CoO + OH ⁻ → HCoO ₂ ⁻ (1) When this secondary battery is initially charged, the blue complex ions are deposited as cobalt hydroxide on the surface of the nickel compound particles according to the reaction formula shown in the following formula (2). The surfaces of the nickel compound particles are covered with a film made of cobalt hydroxide.

HCoO ₂ ⁻ + H ₂ O → Co (OH) ₂ + OH ⁻ (2) Then, as shown in the following formula (3), hydroxide ion (OH ⁻ ) is contacted with the surface of the cobalt hydroxide film. After that, an electron is emitted by an electrochemical reaction to change into conductive cobalt oxyhydroxide (CoOOH).

Co (OH) ₂ + OH ⁻ → CoOOH + H ₂ O + e ⁻ (3) In the reactions (1) to (3), the reaction in which the conductive agent of (1) is changed to a blue complex ion is a reversible reaction. When the solubility of the conductive agent in the alkaline solution is low as in the conventional method of initial charging or charging in an alkaline aqueous solution at room temperature, the generated blue complex ions are likely to return to the original conductive agent. As a result, it becomes difficult to shift to the precipitation reaction of (2) above, so that the reaction efficiency decreases and the distribution of the cobalt oxyhydroxide film becomes non-uniform.

When the current collector filled with the paste is charged while being immersed in a heated alkaline aqueous solution as in the method of the present invention, the solubility of the conductive agent in the alkaline aqueous solution is dramatically increased. Since the dissolution reaction of the above (1) rapidly shifts to the precipitation reaction of the above (2) and the dissolution, precipitation, and oxidation reactions proceed efficiently, a sufficient amount of cobalt oxyhydroxide film is formed on the surface of the nickel compound particles. It can be coated uniformly. Therefore, the utilization rate of the positive electrode and the discharge capacity of the secondary battery can be improved.

[0028]

Embodiments of the present invention will be described below in detail with reference to the drawings. Example 1 Lanthanum-rich misch metal Lm, Ni, Co,
LmNi _4.0 C in a high frequency furnace using Mn and Al
A hydrogen storage alloy having a composition of o _0.4 Mn _0.3 Al _0.3 was prepared. The hydrogen storage alloy is mechanically crushed to obtain 20
It was passed through a 0 mesh sieve. Obtained alloy powder 1
0.5 parts by weight of sodium polyacrylate and 0.12 of carboxymethyl cellulose (CMC) with respect to 00 parts by weight
5 parts by weight, 1.5 parts by weight of polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60 wt%) in terms of solid content and 1 part by weight of carbon powder as a conductive material are mixed with 50 parts by weight of water. To prepare a paste. This paste was applied to a punched metal as a conductive substrate, dried, and then pressure-molded to prepare a paste-type negative electrode for AA size.

To 90% by weight of nickel hydroxide powder, 10% by weight of cobalt hydroxide powder was added as a conductive agent, and 0.25% of carboxymethyl cellulose was added as a binder.
A paste was prepared by adding 3% by weight of a dispersion of sodium tetraacrylate and 0.25% by weight of sodium polyacrylate and polytetrafluoroethylene in terms of solid content and 30% by weight of water and kneading. Subsequently, this paste was filled in a nickel fiber substrate as a current collector, dried, and pressure-molded to assemble a paste type positive electrode for AA size having a theoretical capacity of about 1100 mAh.

The positive electrode and the negative electrode were immersed in 300 ml of an 8N sodium hydroxide aqueous solution heated to 40 ° C.,
In this state, constant current charging was performed at 0.3 C with respect to the theoretical capacity of the positive electrode. The charged positive electrode is incorporated into a secondary battery in the next step, but the charged negative electrode occludes hydrogen, and thus is not safe to handle. Therefore, as the negative electrode to be incorporated in the secondary battery, an uncharged negative electrode of the same type as the negative electrode was prepared.

A separator (composite fiber non-woven fabric made of polypropylene fiber and polyethylene fiber subjected to hydrophilic treatment) is interposed between the charged positive electrode and the uncharged negative electrode, and wound in a spiral shape. To prepare an electrode group. This electrode group was housed in a cylindrical container having a size AA bottom. A cylindrical alkaline secondary battery having an AA size and a theoretical capacity of 1100 mAh was assembled by accommodating an alkaline electrolyte solution made of potassium hydroxide in this container and sealing the structure. . Example 2 After assembling a positive electrode having the same configuration as in Example 1, the positive electrode and the negative electrode similar to Example 1 were immersed in 300 ml of 8N sodium hydroxide aqueous solution at 100 ° C., and in this state, the theoretical capacity of the positive electrode was increased. Was subjected to constant current charging at 0.3C.
Using the obtained positive electrode, a cylindrical alkaline secondary battery having the structure shown in FIG. 1 described above and having an AA size and a theoretical capacity of 1100 mAh was assembled by the same method as in Example 1. Comparative Example 1 After assembling a positive electrode having the same configuration as in Example 1, the positive electrode and the negative electrode similar to Example 1 were immersed in 300 ml of 8N sodium hydroxide aqueous solution at 25 ° C., and in this state, the theoretical capacity of the positive electrode was increased. Was subjected to constant current charging at 0.3C. Using the obtained positive electrode, a cylindrical alkaline secondary battery having the structure shown in FIG. 1 described above and having an AA size and a theoretical capacity of 1100 mAh was assembled by the same method as in Example 1. Comparative Example 2 Except that a positive electrode was prepared without charging in a heated alkaline aqueous solution, the positive electrode had the structure shown in FIG. 1 described above in the same manner as in Example 1, was an AA size, and had a theoretical capacity of 1100 mA.
The cylindrical alkaline secondary battery of h was assembled.

Regarding the secondary batteries of Examples 1 and 2 and Comparative Example 1, the positive electrode was discharged to 0.2 V at 1 V, charged at 0.1 C for 15 hours, and then discharged at 1.0 C to 1.0 V. Was measured and the results are shown in Table 1 below. Also,
For the secondary battery of Comparative Example 2, the utilization rate of the positive electrode was measured when the secondary battery was charged at 0.1 C for 15 hours and then discharged at 1.0 C to 1.0 V. The results are also shown in Table 1 below.

Table 1 Temperature of Alkaline Aqueous Solution Positive Electrode Utilization Example 1 40 ° C. 87 Example 2 100 ° C. 95% Comparative Example 1 25 ° C. 82% Comparative Example 2 Not Performed 80% As is apparent from Table 1, nickel hydroxide The secondary batteries of Examples 1 to 2 in which a positive electrode is manufactured by charging a current collector filled with a paste containing cobalt hydroxide in a heated alkaline aqueous solution have positive electrode utilization rates of Comparative Examples 1 to 2.
You can see that it is higher than.

In addition, in the above-mentioned embodiment, the example applied to the cylindrical alkaline secondary battery has been described, but the invention can be similarly applied to the prismatic alkaline secondary battery. Further, the electrode group housed in the battery container is not limited to the spiral shape, but may be a form in which a plurality of positive electrodes, separators, and negative electrodes are stacked in this order.

[0035]

As described in detail above, according to the method for producing an alkaline secondary battery of the present invention, remarkable effects such as an increase in the utilization rate of the positive electrode and an increase in battery capacity can be obtained.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing an alkaline secondary battery manufactured by a method according to the present invention.

[Explanation of symbols]

1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ...
Electrode group, 7 ... sealing plate.

Front Page Continuation (72) Inventor Kenichi Sugano 3-4-10 Minami-Shinagawa, Shinagawa-ku, Tokyo Inside Toshiba Battery Co., Ltd.

Claims (1)

[Claims] 1. A method of manufacturing an alkaline secondary battery comprising a positive electrode, a negative electrode, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte, wherein the positive electrode is nickel compound particles. The method comprises the steps of filling a current collector with a paste containing one or more selected from cobalt compounds and metallic cobalt as a conductive agent, and charging the current collector filled with the paste in a heated alkaline aqueous solution. A method for manufacturing an alkaline secondary battery, characterized by being manufactured by the method described above.