JP2005243519A - Nickel hydrogen secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a nickel hydrogen secondary battery in which deterioration of its cycle characteristic is suppressed although the capacity liquid ratio is small. <P>SOLUTION: In this nickel hydrogen secondary battery, a positive electrode 24 and a negative electrode 26 piled up to each another through a separator 28 is stored in an exterior can 10 with an alkali electrolyte, and nickel hydroxide particle 40 is distributed in the positive electrode 24. In this battery, when the amount of the electrolyte is expressed by V and the battery capacity is expressed by C, capacity liquid ratio V/C is 0.8 ml/Ah or less, the nickel hydroxide particle 40 has a coating layer 42 of cobalt compound, the peak of (101) plane acquired by X-ray powder diffractometry (Cu-Kα) has the half-value width of less than 0.8 degrees, and alkali oxidation treatment is applied to a coating layer 42. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a nickel hydride secondary battery, and more particularly to a nickel hydride secondary battery suitable for increasing the capacity.

  A nickel metal hydride secondary battery has a sealable outer can, and a positive electrode and a negative electrode that are overlapped in the outer can via a separator are accommodated in an alkaline electrolyte. The positive electrode includes, for example, a metal substrate having a porous structure, and nickel hydroxide particles are distributed as a positive electrode active material on the substrate. The negative electrode has a substrate made of, for example, a punching metal, and hydrogen storage alloy particles capable of absorbing and releasing hydrogen as the negative electrode active material are distributed on the substrate. Nickel hydroxide particles and hydrogen storage alloy particles define the positive electrode capacity and negative electrode capacity, respectively, depending on their amounts. In general, oxygen gas generated at the positive electrode during battery overcharge is reduced at the negative electrode to prevent an increase in the internal pressure of the battery. Therefore, since the negative electrode capacity is set larger than the positive electrode capacity (Neumann principle), the battery capacity is defined by the positive electrode capacity.

By the way, a high capacity is strongly desired for this type of battery. However, since the volume of the outer can is limited, when the positive electrode capacity is increased, other components such as alkaline electrolysis are relatively used. The amount of liquid had to be reduced, causing various problems. Accordingly, various technical developments have been made to solve such problems (see, for example, Patent Document 1).
In the alkaline storage battery disclosed in Patent Document 1, nickel hydroxide and zinc (zinc) having a half-value width of the peak of (101) plane obtained by X-ray powder diffraction (Cu-Kα ray) of 0.8 degrees or more. A positive electrode obtained by filling a metal porous body with a paste containing a compound) and drying the paste is used. According to such a positive electrode, the ratio of the amount of alkaline electrolyte to the positive electrode capacity (capacity liquid ratio) is 0. Even if it is limited to the range of 7 ml to 2.0 ml / Ah, it is considered that the decrease in the utilization rate of the positive electrode active material is suppressed.
JP-A-10-270071

However, the battery of Patent Document 1 has a problem that the cycle characteristics are greatly deteriorated when the capacity liquid ratio is 0.8 ml / Ah or less.
The present invention has been made based on the above-described circumstances, and an object of the present invention is to provide a nickel-metal hydride secondary battery in which a decrease in cycle characteristics is suppressed despite a small capacity-liquid ratio. is there.

  In order to achieve the above object, in the invention of claim 1, a positive electrode and a negative electrode that are overlapped with each other via a separator are accommodated in an outer can together with an alkaline electrolyte, and nickel hydroxide particles are distributed on the positive electrode. In the nickel metal hydride secondary battery, when the amount of the electrolyte is V and the battery capacity is C, the capacity liquid ratio V / C is 0.8 ml / Ah or less, and the nickel hydroxide particles are cobalt compounds. A peak of (101) plane obtained by X-ray powder diffraction method (Cu-Kα) has a half width of less than 0.8 degrees, and the coating layer is subjected to an alkali oxidation treatment It is characterized by being.

  In the above-described configuration, even when the volumetric liquid ratio V / C is 0.8 ml / Ah or less, the (101) plane obtained by the X-ray powder diffraction method (Cu-Kα) while having a coating layer made of a cobalt compound. By using nickel hydroxide particles having a half width of less than 0.8 degrees as a positive electrode active material and applying an alkaline oxidation treatment to the coating layer, deterioration of cycle characteristics is suppressed.

  More specifically, when the alkaline electrolyte amount V is decreased until the capacity liquid ratio V / C is 0.8 ml / Ah or less, the battery reaction, that is, the oxidation-reduction reaction in the positive electrode and the negative electrode, is repeated while the battery is used repeatedly. The alkaline electrolyte that can contribute to the battery is depleted, the smooth battery reaction is hindered, and the battery capacity gradually decreases. However, in the battery having the above-described configuration, the strain of the nickel hydroxide particles is controlled through the control of the half width of the peak (the smaller the peak half width, the smaller the strain). It is considered that the battery reactivity is improved due to the high conductivity and the like, and thereby the decrease in the battery reactivity due to the depletion of the electrolytic solution is compensated, and the decrease in the capacity is suppressed. Therefore, according to the battery having the above-described configuration, it is considered that the deterioration of the cycle characteristics is suppressed even when the capacity liquid ratio V / C is 0.8 ml / Ah or less.

  As described above, the nickel-metal hydride secondary battery of the present invention is suitable for increasing the capacity by increasing the amount of the positive electrode active material because the deterioration of the cycle characteristics is suppressed even if the capacity-liquid ratio is small, and has industrial value. Is big.

Hereinafter, a nickel-hydrogen secondary battery according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
The battery A is an AA size cylindrical battery and includes an outer can 10 having a bottomed cylindrical shape with an open upper end as shown in FIG. 1, and the outer can 10 functions as a negative electrode terminal having conductivity. . Inside the opening of the outer can 10, a disc-shaped cover plate 14 having conductivity is arranged via a ring-shaped insulating packing 12, and the insulating packing 12 and the cover are formed by caulking the opening edge of the outer can 10. The plate 14 is fixed in the opening of the outer can 10.

  The cover plate 14 has a gas vent hole 16 in the center, and a rubber valve element 18 is disposed on the outer surface of the cover plate 14 so as to close the gas vent hole 16. Further, a flanged cylindrical positive terminal 20 covering the valve body 18 is fixed on the outer surface of the cover plate 14, and the positive terminal 20 presses the valve body 18 against the cover plate 14. Accordingly, at the normal time, the outer can 10 is airtightly closed by the cover plate 14 via the insulating packing 12 and the valve body 18. On the other hand, when gas is generated in the outer can 10 and the internal pressure increases, the valve body 18 is compressed, and the gas is released from the outer can 10 through the gas vent hole 16. That is, the cover plate 14, the valve body 18, and the positive electrode terminal 20 form a safety valve.

  A substantially cylindrical electrode group 22 is accommodated in the outer can 10. More specifically, the electrode group 22 includes a strip-like positive electrode 24, a negative electrode 26, and a separator 28. The positive electrode 24, the negative electrode 26, and the separator 28 are in a state in which the positive electrode 24 and the negative electrode 26 are overlapped with each other through the separator 28. It is wound in a spiral shape. Although the positive electrode 24 and the negative electrode 26 will be described later, as the separator 28 of the electrode group 22, for example, a polyamide fiber nonwoven fabric or a polyolefin fiber nonwoven fabric such as polyethylene or polypropylene provided with a hydrophilic functional group can be used. In this battery, the capacity of the negative electrode 26 is set larger than the capacity of the positive electrode 24 in order to reduce the oxygen gas generated at the positive electrode 24 at the time of overcharging by the negative electrode 26, and the battery capacity is defined by the capacity of the positive electrode 24. Yes. Thus, in order to make the capacity of the negative electrode 26 larger than the capacity of the positive electrode 24, the negative electrode 26 is longer than the positive electrode 24, and the outermost periphery of the electrode group 22 is formed by a part of the negative electrode 26. A part of the outer surface of the negative electrode 26 is in direct contact with the inner peripheral wall of the outer can 10, whereby the outer can 10 and the negative electrode 26 are electrically connected.

  Further, a predetermined amount of alkaline electrolyte (not shown) is accommodated in the outer can 10 together with the electrode group 22. Specifically, the amount of alkaline electrolyte in the battery is obtained by dividing the amount of alkaline electrolyte V by the battery capacity C, where V is the amount of alkaline electrolyte and C is the battery capacity (positive electrode capacity). The volume liquid ratio V / C is set to be 0.8 ml / Ah or less. In addition, as alkaline electrolyte, sodium hydroxide aqueous solution, lithium hydroxide aqueous solution, potassium hydroxide aqueous solution, the aqueous solution which mixed 2 or more types among these aqueous solutions, etc. can be used, for example.

  Further, in the outer can 10, a positive electrode lead 30 is disposed between one end of the electrode group 22 and the lid plate 14, and both ends of the positive electrode lead 30 are connected to the positive electrode 24 and the lid plate 14. Therefore, the positive electrode terminal 20 and the positive electrode 24 are electrically connected via the positive electrode lead 30 and the lid plate 14. A circular insulating member 32 is disposed 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 disposed between the electrode group 22 and the bottom of the outer can 10.

  Although not shown, the negative electrode 26 has a conductive negative electrode substrate having a strip shape, and a negative electrode mixture is held on the negative electrode substrate. The negative electrode substrate is made of a sheet-like metal material having a large number of through holes. For the negative electrode substrate, for example, a two-dimensional substrate such as a punching metal, an expanded metal, a perforated steel plate, or a nickel net can be used. Accordingly, the negative electrode mixture is filled in the through holes of the negative electrode substrate and is held in layers on both surfaces of the negative electrode substrate.

The negative electrode mixture includes hydrogen storage alloy particles capable of occluding and releasing hydrogen as a negative electrode active material, a conductive additive, and a binder. In the present specification, the hydrogen storage alloy is also referred to as a negative electrode active material for convenience of explanation.
The hydrogen storage alloy particles distributed in the negative electrode mixture can store hydrogen generated electrochemically in an alkaline electrolyte during battery charging, and can easily release the storage hydrogen during discharge. well, it is not particularly limited, AB ₅ type system, preferably particles made of TiNi system and TiFe system hydrogen absorbing alloy. Specifically, for example, LaNi ₅ , MmNi ₅ (Mm is a misch metal), LmNi ₅ (Lm is at least one selected from rare earth elements including La), and a part of Ni of these alloys are Al, Mn, Co , Ti, Cu, Zn, Zr, Cr, B, etc., can be used multi-element hydrogen storage alloy particles substituted with one or more elements selected from such elements. In particular, hydrogen storage alloy particles having a composition represented by the general formula: LmNiwCoxMnyAlz (the total value of atomic ratios w, x, y, z is 4.80 ≦ w + x + y + z ≦ 5.40) This is suitable because the pulverization associated with is suppressed and the charge / discharge cycle life is improved.

As the binder, for example, one or two or more kinds of polymers that can be used as a positive electrode binder described later can be selected and used, and as the conductive assistant, carbon black or graphite can be used. Can be used.
Although the positive electrode 24 is schematically shown in an enlarged manner in a circle in FIG. 1, the positive electrode 24 has a conductive positive electrode substrate 36 having a belt shape, and a positive electrode mixture is supported on the substrate 36. . The positive electrode substrate 36 is made of, for example, a metal plate such as nickel or stainless steel, a resin plated with nickel, or the like, and has a sponge-like, fiber-like, or felt-like porous structure. The positive electrode mixture is held in the holes of the sponge-like substrate 36.

The positive electrode mixture is composed of, for example, composite particles 38 containing nickel hydroxide as a positive electrode active material and a binder.
As the binder, one or more of hydrophobic and hydrophilic polymers can be used. Examples of the hydrophobic polymer include polytetrafluoroethylene (PTFE), polyethylene, polypropylene, and rubber-based polymers. Can be used. As the rubber polymer, for example, styrene butadiene rubber (SBR) latex, acrylonitrile butadiene rubber (NBR) latex, or ethylene propylene diene monomer (EPDM) latex can be used. Examples of hydrophilic polymers include carboxymethyl cellulose (CMC), methyl cellulose (MC), hydroxypropyl methyl cellulose (HPMC), polyacrylic acid salts such as sodium polyacrylate (SPA), polyvinyl alcohol (PVA), poly A copolymer of a monomer having at least one ethylene oxide and a COOX group and vinyl alcohol (where X is an element selected from hydrogen, an alkali metal, and an alkaline earth metal) can be used. Polyethylene, polypropylene and polytetrafluoroethylene can be used in the form of a dispersion.

  The composite particles 38 are composed of nickel hydroxide particles 40 and a coating layer 42 formed on the surfaces of the nickel hydroxide particles 40. Therefore, the positive electrode capacity (theoretical capacity), that is, the battery capacity is defined by the total amount of nickel hydroxide distributed as the composite particles 38 on the positive electrode 24. Based on this positive electrode capacity, the above-mentioned capacity liquid ratio V / C is 0.8 ml / The amount of alkaline electrolyte V is adjusted so as to be Ah or less.

  As the nickel hydroxide particles 40 of the composite particles 38, substantially pure nickel hydroxide particles or nickel hydroxide particles in which either one or both of zinc and cobalt are co-precipitated can be used. However, the peak half-value width of the nickel hydroxide particles 40 used in this battery is less than 0.8 °, and preferably falls within the range of 0.4 ° or more and 0.75 ° or less. The peak half-value width is obtained by applying an X-ray powder diffraction method using Cu—Kα rays to the nickel hydroxide particles 40 and changing the reflection intensity from the (101) plane of nickel hydroxide while changing the diffraction angle 2θ. This is the half width of the peak obtained by measurement.

On the other hand, the coating layer 42 of the composite particles 38 is made of an alkali-oxidized cobalt compound and has good conductivity. More specifically, the coating layer 42 is formed on the surface of the nickel hydroxide particles 40 with dicobalt trioxide (Co ₂ O ₃ ), cobalt metal (Co), cobalt monoxide (CoO), and cobalt hydroxide (Co (OH)). After depositing a cobalt compound such as ₂ ), it can be formed by subjecting the precipitate of the cobalt compound to an alkali oxidation treatment. Therefore, alkali cations such as Na ⁺ are distributed on the coating layer 42 from the surface to the inside by the alkali oxidation treatment.

  The above-described battery is suitable for increasing the battery capacity C, that is, increasing the capacity because the decrease in cycle characteristics is suppressed even though the capacity liquid ratio V / C is 0.8 ml / Ah or less. More specifically, in order to increase the battery capacity C, it is necessary to increase the volume of the positive electrode 24 in order to increase the amount of the positive electrode active material. However, when the volume of the positive electrode 24 is increased, the alkaline electrolyte is accommodated. Therefore, the amount of the alkaline electrolyte V must be reduced. However, if the alkaline electrolyte amount V is decreased until the capacity liquid ratio V / C becomes 0.8 ml / Ah or less, it contributes to the battery reaction, that is, the oxidation-reduction reaction in the positive electrode and the negative electrode while the battery is repeatedly used. The possible alkaline electrolyte is depleted, the smooth battery reaction is inhibited, and the battery capacity gradually decreases. For this reason, in the conventional battery, when the capacity liquid ratio V / C is 0.8 ml / Ah or less, the cycle characteristics are greatly deteriorated. On the other hand, the battery described above uses nickel hydroxide particles 40 having a peak half-value width of less than 0.8 °, and the surface of the nickel hydroxide particles has a coating layer 42 made of a cobalt compound subjected to alkali oxidation treatment. Although the mechanism is not clear by the formation, the deterioration of the cycle characteristics is suppressed, which is suitable for increasing the capacity. Probably, the distortion of the nickel hydroxide particles 40 was controlled through the control of the peak half width (the smaller the peak half width, the smaller the strain), the alkali-oxidized coating layer 42 has high conductivity, etc. Due to this, it is considered that the battery reactivity is improved in the above-described battery, and this compensates for a decrease in battery reactivity due to depletion of the electrolyte.

Although the above-described battery can be manufactured by a normal method, an example of a method for manufacturing the positive electrode 24 will be described below.
First, nickel hydroxide particles 40 having a peak half width less than 0.8 ° are prepared. Such nickel hydroxide particles are obtained as a precipitate by adding an aqueous nickel sulfate solution and aqueous ammonia to the water in the reaction vessel, adjusting the pH of the solution by adding an alkaline aqueous solution, and then stirring and mixing for a predetermined time. be able to. In addition, a peak half value width can be made small, so that pH of the liquid at the time of reaction is kept low. In order to coprecipitate zinc and cobalt, an aqueous zinc sulfate solution and an aqueous cobalt sulfate solution may be further added to the solution.

  Next, the obtained nickel hydroxide powder 40 and cobalt hydroxide powder are mixed, and an alkaline aqueous solution is added thereto, followed by heat treatment in an oxidizing atmosphere. By this alkali oxidation heat treatment, a coating layer 42 made of a cobalt compound that has been subjected to alkali oxidation treatment is formed on the surface of the nickel hydroxide particles 40, and composite particles 38 can be obtained. In forming the coating layer 42, cobalt monoxide powder or metal cobalt powder may be used instead of the cobalt hydroxide powder.

Thereafter, a paste is prepared by adding water to the obtained composite particles 38 and the binder, and the paste is filled in a porous nickel plate to be the positive electrode substrate 36, and then dried. The nickel plate can be rolled and cut to produce the positive electrode 24.
The present invention is not limited to the above-described embodiment, and can be variously modified. For example, a rectangular outer can may be used instead of the cylindrical outer can 10. However, this battery is suitable for an AA size cylindrical secondary battery.

In the above-described embodiment, the hydrogen storage alloy is used as the negative electrode active material, but the battery may be a nickel cadmium secondary battery by using a cadmium compound instead of the hydrogen storage alloy. However, a nickel-hydrogen secondary battery is suitable for improving the battery capacity.
Further, in the above-described embodiment, the positive electrode mixture is composed of composite particles and a binder, but as a conductive auxiliary agent for the positive electrode mixture, dicobalt trioxide (Co ₂ O ₃ ), cobalt metal (Co), Cobalt compounds such as cobalt monoxide (CoO) and cobalt hydroxide (Co (OH) ₂ ) may be further added.

Examples 1-6 and Comparative Examples 1-19
1. Battery assembly (1) Examples 1-6 and Comparative Examples 1-14
As Examples 1-6 and Comparative Examples 1-14, AA size cylindrical nickel-hydrogen secondary batteries having the configuration shown in FIG. 1 and having a battery capacity C of 2600 mAh were assembled.

However, during the production of the positive electrode, nickel hydroxide particles having a peak half-value width shown in Table 1 were used for each of Examples and Comparative Examples (see Table 1). The peak half-value width in Table 1 is a value measured by the X-ray powder diffraction method under the measurement conditions shown in Table 2.
Further, when the alkaline electrolyte was poured into the outer can, the amount of the alkaline electrolyte was adjusted so that the volume ratio V / C shown in Table 1 was obtained for each of the examples and the comparative examples. The battery capacity C is the theoretical capacity of the positive electrode obtained with a capacity per gram of nickel hydroxide of 289 mAh.

(2) Comparative Examples 15-19
As Comparative Examples 15 to 19, during the production of the positive electrode, the surface of the nickel hydroxide particles was not formed with a coating layer made of an alkali-oxidized cobalt compound. Instead, the positive electrode mixture (paste) was hydroxylated. Cylindrical nickel metal hydride secondary batteries were assembled in the same manner as in Examples 4 to 6 and Comparative Examples 3 and 4 except that 8 parts by weight of cobalt hydroxide was added per 100 parts by weight of nickel particles.

2. Battery Cycle Characteristic Evaluation Test Each battery of the obtained Examples and Comparative Examples was first charged and discharged. Next, these batteries were repeatedly subjected to a charge / discharge cycle in which a ΔV charging step at 1 It (2600 mA), a one-hour resting step, and a discharging step up to a final voltage of 1.0 V at 1 It (2600 mA) were performed as one cycle. It was. During this charge / discharge cycle, the discharge capacity of each battery was measured every cycle, and the number of cycles when the discharge capacity reached 60% of the initial discharge capacity was counted. The results are shown in Table 1 and FIG.

The following is clear from Table 1 and FIG.
(1) Regardless of the peak half-value width of nickel hydroxide particles, the number of cycles until the discharge capacity reaches 60% of the initial discharge capacity as the capacity liquid ratio V / C decreases (hereinafter simply referred to as cycle) Number) decreases.
(2) In particular, when nickel hydroxide particles having a peak half width of 0.8 ° or more are used (Comparative Examples 5 to 9 and Comparative Examples 10 to 14), the volume ratio V / C is 0.8 ml / Ah or less. In particular, the number of cycles is greatly reduced at 0.7 ml / Ah or less.

(3) On the other hand, when nickel hydroxide particles having a peak half-width of less than 0.8 ° are used (Examples 1 to 6 and Comparative Examples 1 to 4), the volume liquid ratio V / C is 0.8 ml. Even when the ratio is less than / Ah, the rate of decrease in the number of cycles does not increase. That is, when nickel hydroxide particles having a peak half-value width of less than 0.8 ° are used, the capacity liquid ratio V / C is 0. 0 as compared with the case of using nickel hydroxide particles of 0.8 ° or more. A decrease in cycle characteristics in the range of 8 ml / Ah or less is suppressed. As a result, in the range where the capacity liquid ratio V / C is 0.8 ml / Ah or less, the batteries of Examples 1 to 6 using nickel hydroxide particles having a peak half-value width of less than 0.8 ° Compared to the batteries of Comparative Examples 5 to 7 and Comparative Examples 10 to 12 using nickel hydroxide particles having a value width of 0.8 ° or more, the number of cycles is large.

(4) On the other hand, although nickel hydroxide particles having a peak half width of 0.75 ° were used, a comparative example in which a coating layer made of a cobalt compound and subjected to an alkali oxidation treatment was not formed on nickel hydroxide particles In 15 to 19, when the volume liquid ratio V / C is 0.8 ml / Ah or less, the number of cycles is greatly reduced.
(5) From the above results, by using nickel hydroxide particles having a peak half-value width of less than 0.8 °, the nickel hydroxide particles are formed of a cobalt compound and subjected to alkali oxidation treatment. It can be seen that, when the capacity liquid ratio V / C is 0.8 ml / Ah or less, particularly 0.7 ml / Ah or less, it is possible to suppress the deterioration of the cycle characteristics of the battery.

1 is a partially cutaway perspective view of a cylindrical nickel-metal hydride secondary battery according to an embodiment of the present invention. It is the graph which showed the cycle characteristic evaluation test result about each battery of an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exterior can 24 Positive electrode 26 Negative electrode 28 Separator 40 Nickel hydroxide particle 42 Coating layer

Claims (1)

In a nickel metal hydride secondary battery in which a positive electrode and a negative electrode overlapped with each other through a separator in an outer can are accommodated together with an alkaline electrolyte, and nickel hydroxide particles are distributed on the positive electrode,
When the amount of the electrolytic solution is V and the battery capacity is C, the capacity liquid ratio V / C is 0.8 ml / Ah or less,
The nickel hydroxide particles have a coating layer made of a cobalt compound, and the peak of the (101) plane obtained by the X-ray powder diffraction method (Cu-Kα) has a half width of less than 0.8 degrees,
A nickel-metal hydride secondary battery, wherein the coating layer is subjected to an alkali oxidation treatment.

Images