JP2000228214A - Alkaline secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an alkaline secondary battery of which volume energy density is high in capacity, which can maintain a long cycle life even if used in a high-temperature atmosphere, and has good characteristics during high-rate discharging. SOLUTION: This alkaline secondary battery is provided with a negative electrode 4 containing hydrogen storage alloy powder, a positive electrode 2 arranged on the negative electrode 4 interposing a separator 3, an alkaline electrolytic solution, and a container 1 for receiving those members, and the features of the secondary battery is that the capacity of the secondary battery is 310 Wh/L or more, the alkaline electrolytic solution is so received in the container as to to be set to 0.7-1.3 mL/Ah, the hydrogen storage alloy in the negative electrode is a rare earth element-nickel-based one, its equilibrium pressure is 2.04.0 atm when a pressure-composition isotherm is measured at 100 deg.C, and its specific surface area by a BET method when it is hydrogenized and fractured once under the pressure of hydrogen having a predetermined gage pressure is 0.05-0.20 m2/g.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an alkaline secondary battery having an improved negative electrode containing a hydrogen storage alloy.

[0002]

2. Description of the Related Art With the rapid spread of small cordless devices in recent years, a demand for a secondary battery having a high capacity has been increased. Among such secondary batteries, an alkaline secondary battery using a negative electrode containing a hydrogen storage alloy, a positive electrode containing a metal oxide, and an alkaline electrolyte has attracted attention. The negative electrode containing the hydrogen storage alloy can increase the energy density per unit weight or unit volume as compared with cadmium, which is a conventional representative material for a negative electrode for an alkaline secondary battery, and increase the capacity of the battery. In addition to being able to perform the following, the battery has characteristics that it has not only a low risk of environmental pollution but also excellent battery characteristics.

[0003]

However, the characteristics of the alkaline secondary battery are greatly affected by the heat generated during charging and discharging. As a result, there have been problems such as a large variation in cycle life and a large variation in characteristics during high-rate discharge.

[0004] In addition, even if the heat effect is not so large per battery, the effect is significant when a large number of batteries are assembled in a container and packaged like a battery for a personal computer. Furthermore, in recent years, particularly in personal computers and the like, the amount of heat generated from the devices themselves is large, and thus the influence of heat on the characteristics tends to be even greater.

The present invention has a high volumetric energy density (310 Wh / l or more), maintains a long cycle life even when used in a high-temperature atmosphere, has a small variation in characteristics during high-rate discharge, and has a high internal pressure. An object of the present invention is to provide an alkaline secondary battery capable of suppressing an increase.

[0006]

According to the present invention, there is provided an alkaline secondary battery comprising: a negative electrode containing a hydrogen storage alloy powder; a positive electrode containing nickel hydroxide as an active material and having a separator interposed therebetween; An alkaline secondary battery including an electrolytic solution and a container for housing these members, wherein the capacity of the secondary battery is 310 Wh / L or more, and the alkaline electrolytic solution is contained in the container. 0.7 ~
The hydrogen storage alloy contained at 1.3 mL / Ah and contained in the negative electrode was a rare earth element-nickel based
The equilibrium pressure when measuring the pressure-composition isotherm at 0 ° C. is 2.
B when hydrogenated and pulverized once at 0 to 4.0 atm and under a hydrogen pressure of 2 to 30 ° C. and 5 to 10 atm (gauge pressure)
Specific surface area by the ET method is 0.05 m ^{2 /} g to 0.20 m
² / g.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an alkaline secondary battery (cylindrical nickel-metal hydride secondary battery) according to the present invention will be described with reference to FIG.

An electrode group 5 produced by stacking a positive electrode 2, a separator 3, and a negative electrode 4 and spirally winding them is accommodated in a cylindrical container 1 having a bottom. 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 at the upper opening of the container 1.
The ring-shaped insulating gasket 8 is disposed between the peripheral edge of the sealing plate 7 and the inner surface of the upper opening of the container 1, and the container 1 is formed by caulking to reduce the diameter of the upper opening inward.
The sealing plate 7 is hermetically fixed via the gasket 8. One end of the positive electrode lead 9 is connected to the positive electrode 2,
The other end is connected to the lower surface of the sealing plate 7. The positive electrode terminal 10 having a hat shape is attached on the sealing plate 7 so as to cover the hole 6. The rubber safety valve 11
The hole 6 is disposed in a space surrounded by the sealing plate 7 and the positive electrode terminal 10 so as to close the hole 6. The circular holding plate 12 made of an insulating material having a hole in the center is
The projecting portion of the positive electrode terminal 10 is disposed on the reference numeral 0 so as to project from the hole of the holding plate 12. The outer tube 13 covers the periphery of the holding plate 12, the side surface of the container 1, and the periphery of the bottom of the container 1.

Next, the negative electrode 4, the positive electrode 2, the separator 3
And the electrolyte will be described.

1) Negative Electrode 4 The negative electrode is a rare earth element-nickel system and has an equilibrium pressure of 2.0 to 4.0 when a pressure-composition isotherm at 100 ° C. is measured.
Contains a hydrogen storage alloy of 0 atm. Further, the hydrogen storage alloy is 2 to 30 ° C., 5 to 10 atm specific surface area by the BET method when the pulverized once hydrogenated under hydrogen pressure of (gauge pressure) is 0.08m ² /g~0.20m ² / G.

The rare earth element-nickel based hydrogen storage alloy is not particularly limited.
Ni ₅ , MmNi ₅ (Mm; misch metal), LmN
i ₅ (Lm; lanthanum-enriched misch metal), or a part of these Nis is replaced with Al, Mn, Co, Fe, T
Examples thereof include multi-element materials substituted with elements such as i, Cu, Zn, Zr, Cr, and B. Above all, the general formula _{ANi v Co w Mn x Al y} ( However, A is a rare earth element consisting of La70 wt% or more, preferably Lm, atomic ratio v, w, x, y are respectively 3.30 ≦ v ≦ 4.50 ,
0.30 ≦ w ≦ 1.10, 0.05 ≦ x ≦ 0.40,
0.20 ≦ y ≦ 0.50 and the total value is 4.90
≦ v + w + x + y ≦ 5.50). More preferable values of the atomic ratios v, w, x, and y are 3.80 ≦ v ≦ 4.20, respectively.
0.60 ≦ w ≦ 0.90, 0.08 ≦ x ≦ 0.30,
0.30 ≦ y ≦ 0.40 and the total value is 5.00
≦ w + x + y ≦ 5.30.

In the rare earth-nickel hydrogen storage alloy, the "pressure-composition isotherm" means a characteristic line (PCT line) representing a change in plateau pressure with respect to temperature. The measurement of the pressure-composition isotherm can be performed according to JIS H 7003. The equilibrium pressure when measuring such a pressure-composition isotherm at 100 ° C. is 2.0 to 4.0 atm.
The rare earth-nickel-based hydrogen storage alloy having the above formula can suppress a decrease in capacity at a high temperature. The equilibrium pressure is 2.0
If the hydrogen storage alloy is less than atm, the amount of released hydrogen may decrease. On the other hand, it is difficult for the hydrogen storage alloy having an equilibrium pressure exceeding 4.0 atm to sufficiently increase the amount of hydrogen storage, causing an increase in internal pressure and leakage during charging and discharging of the battery.

The rare earth-nickel-based hydrogen storage alloy comprises:
Specific surface area by the BET method under specified conditions is 0.05 m
^By setting the ratio to ² / g to 0.20 m ² / g, it becomes possible to suppress corrosion of the hydrogen storage alloy during use at high temperatures. If the specific surface area is less than 0.05 m ² / g, the hydrogen storage alloy is less likely to be cracked, and the reactivity with the electrolytic solution is reduced, causing an increase in the internal pressure. On the other hand, when the specific surface area exceeds 0.20 m ² / g, it becomes difficult to suppress corrosion of the hydrogen storage alloy. In particular, the specific surface area by BET method is preferably 0.08m ² /g~0.14m ² / g.

The negative electrode 4 is prepared, for example, by adding a conductive material to the hydrogen storage alloy powder, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, and drying the paste. , Manufactured by molding.

Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

As the conductive material, for example, carbon black or the like can be used.

Examples of the conductive substrate include a two-dimensional substrate such as a punched metal, an expanded metal, a perforated rigid plate, and a nickel net, and a three-dimensional substrate such as a felt-like metal porous body and a sponge-like metal substrate. be able to.

2) Positive Electrode 2 The positive electrode 2 has a structure in which a positive electrode material containing nickel hydroxide particles as an active material, a conductive material and a polymer binder is supported on a conductive substrate.

As the nickel hydroxide particles, for example, a single nickel hydroxide particle or a nickel hydroxide particle in which a metal such as zinc, cobalt, bismuth, or copper is coprecipitated with metallic nickel can be used. In particular, the latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high-temperature state.

The nickel hydroxide particles have a peak half width at (101) plane of 0.8 面 / 2θ by X-ray powder diffraction.
(Cu-Kα) or more is preferable. More preferable peak half width of the nickel hydroxide particles is 0.9 to 1.0.
゜ / 2θ (Cu-Kα).

Examples of the conductive material include metal cobalt, cobalt oxide, cobalt hydroxide and the like.

Examples of the polymer binder include carboxymethyl cellulose, methyl cellulose, sodium polyacrylate, polytetrafluoroethylene and the like.

Examples of the conductive substrate include a mesh-like, sponge-like, fiber-like, or felt-like porous metal body made of nickel, stainless steel, or nickel-plated metal.

The positive electrode 2 is prepared, for example, by adding a conductive material to nickel hydroxide particles as an active material, kneading the mixture with a polymer binder and water to prepare a paste, filling the paste into a conductive substrate, After drying, it is produced by molding.

3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of polyamide fiber, a nonwoven fabric made of polyolefin fiber such as polyethylene and polypropylene, and a nonwoven fabric provided with a hydrophilic functional group.

4) Alkaline Electrolyte As the alkaline electrolyte, for example, a mixed solution of sodium hydroxide (NaOH) and lithium hydroxide (LiOH),
A mixture of potassium hydroxide (KOH) and LiOH, KOH
And a mixed solution of LiOH and NaOH. Such an alkaline electrolyte is placed in the container at 0.7
ＭＬ1.3 mL / Ah. When the amount of the alkaline electrolyte is less than 0.7 mL / Ah, it becomes difficult to obtain a secondary battery having a sufficient charge / discharge cycle life. On the other hand, the amount of the alkaline electrolyte is 1.3 mL.
If it exceeds / Ah, it may be difficult to increase the capacity, or liquid leakage may occur due to an increase in internal pressure.

[0027] The secondary battery has a capacity of 310 Wh / L or more. This capacity C (Wh / L) [volume energy density] is defined by the following equation.

C = (C _T × Z) / V (1) where C _T (Ah) is the theoretical capacity of the secondary battery and Z (V)
Represents the voltage of the secondary battery, and V (L) represents the volume of the secondary battery (the internal volume of the container).

The above-described alkaline secondary battery according to the present invention comprises a negative electrode containing a hydrogen storage alloy powder, a positive electrode containing nickel hydroxide as an active material and having a separator interposed therebetween, and an alkaline electrolyte. And a container for accommodating these members, wherein the capacity of the secondary battery is 310 Wh / L or more, and the alkaline electrolyte is 0.7 to 1.3mL
/ Ah, and the hydrogen storage alloy in the negative electrode is a rare earth element-nickel system and has an equilibrium pressure of 2.0 to 4.0 when a pressure-composition isotherm at 100 ° C. is measured.
atm, 2-30 ° C, 5-10 atm (gauge pressure)
The specific surface area by the BET method when the pulverized once hydrogenation under a hydrogen pressure of is 0.05m ² /g~0.20m ² / g.

The secondary battery having such a structure has a high capacity such as a volume energy density of 310 Wh / L or more, has a small cycle life variation even when used in a high-temperature atmosphere, and has a characteristic at a high rate discharge. Is small.

That is, in an alkaline secondary battery using hydrogen as a negative electrode active material, an alloy obtained from a rare earth element represented by LaNi ₅ and another metal element is conventionally used as a hydrogen storage alloy as a main material of the negative electrode. It is heavily used. Further, instead of rare earth elements, misch metal (Mm), which is a mixture of lanthanum elements, and a metal element, or a multi-element alloy in which Mm and some metal elements are combined is also used.

However, each of the above-mentioned hydrogen storage alloys causes an exothermic reaction at the time of charging, causing an increase in the temperature of the secondary battery. In addition, the temperature of the hydrogen storage alloy itself rises due to heat generation, and the hydrogen storage amount decreases significantly. As a result, the internal pressure rises and the cycle life of the secondary battery at the time of overcharge is reduced. This phenomenon appears remarkably in a charge / discharge cycle in a high-temperature atmosphere.

On the other hand, one of the main uses of a secondary battery using a hydrogen storage alloy is a power supply for driving a personal computer. In secondary batteries for these uses, usually, a battery pack in which several secondary batteries are connected in series or in parallel and housed in a container is used. Such a battery pack generates a large amount of heat as compared with a single secondary battery, and tends to be extremely hot.
Also, secondary batteries used in devices such as personal computers
In recent years, demand for higher capacity has been increasing, and accordingly, the amount of heat generated has tended to increase further due to the higher capacity of the secondary battery itself.

From the above, as in the present invention, 10
The equilibrium pressure when measuring the pressure-composition isotherm at 0 ° C. is 2.
By using a rare earth-Ni-based hydrogen storage alloy of 0 to 4.0 atm as a negative electrode material, it is possible to suppress a decrease in capacity while maintaining a decrease in discharge efficiency and a favorable discharge property with respect to a charge amount at a high temperature.

On the other hand, when used at a high temperature, the hydrogen storage alloy itself becomes susceptible to corrosion. Further, in a secondary battery provided with a negative electrode containing a hydrogen storage alloy having a relatively low equilibrium pressure, high-rate discharge characteristics are improved by improving the reactivity of the hydrogen storage alloy, but on the other hand, they are also susceptible to corrosion. .

Accordingly, the present invention provides a hydrogen storage alloy having a specific surface area of 0.05 m ² / BET under a predetermined condition by a BET method.
By using a material having a g of 0.2 to 0.20 m ² / g, a decrease in cycle life due to corrosion of the hydrogen storage alloy itself can be suppressed.

Further, the alkaline electrolyte is placed in a container at a concentration of 0.7 to
By storing to 1.3 mL / Ah,
The capacity can be increased, and the consumption and depletion of the electrolytic solution accompanying the corrosion of the hydrogen storage alloy can be suppressed.

Therefore, the use of a specific amount of alkaline electrolyte in an alkaline secondary battery such as 310 Wh / L or more and a hydrogen storage alloy having a specific equilibrium pressure and a specific surface area can increase the volumetric energy density to a high capacity (310 Wh / L).
/ L or more), it is possible to obtain an alkaline secondary battery having a long cycle life even when used in a high-temperature atmosphere.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings.

(Examples 1 to 4, Comparative Examples 1 to 16) <Preparation of Negative Electrode> Lm, Ni, Co, Mo, Al, Zr
LmNi consisting of each element of_4.0Co _0.4Mn_0.3Al
_0.3Was prepared. 1000 ° C
Heat treatment in an argon atmosphere for 10 hours to equalize the alloy composition.
Quality. For these hydrogen storage alloys,
Equilibrium pressure when measuring pressure-composition isotherm of
Water once at 0 ° C, 5-10 atm (gauge pressure) hydrogen pressure
The specific surface area was determined by the BET method when
Eight types of hydrogen storage alloys shown in Table 1 were obtained.

Next, a part of each of the hydrogen storage alloys was mechanically pulverized. To 100 parts by weight of each of the obtained hydrogen storage alloy powders, 0.5 parts by weight of sodium polyacrylate, 0.12 parts by weight of carboxymethyl cellulose (CMC), and a dispersion of polytetrafluoroethylene (specific gravity: 1.
5, solid content of 60% by weight) in terms of solid content of 1.0 part by weight,
A paste was prepared by adding 1.0 part by weight of carbon black as a conductive material and mixing with 30 parts by weight of water. These pastes were applied to punched metal as a conductive substrate, dried, and pressed to produce eight types of negative electrodes.

<Preparation of Positive Electrode> A mixed powder consisting of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 parts of carboxymethyl cellulose (CMC).
A paste was prepared by adding 0.5 parts by weight of a polytetrafluoroethylene dispersion (specific gravity 1.5, solid content 60% by weight) in terms of solid content and mixing with 45 parts by weight of pure water. . Subsequently, the paste was filled in a foamed nickel substrate, dried, and then rolled by roller pressing to produce a positive electrode.

Next, a 0.2-mm-thick separator made of a nonwoven fabric made of polyamide fiber was interposed between each of the negative electrode and the positive electrode, and spirally wound to form an electrode group. After such an electrode group is housed in a bottomed cylindrical container, an electrolyte composed of 7N potassium hydroxide and 1N lithium hydroxide is housed, and the structure shown in FIG. And the theoretical capacity is 4000 mAh (capacity 310
(Wh / L or more), 20 kinds of 4/3 A cylindrical nickel-metal hydride secondary batteries were assembled. The electrolyte volume was 0.5 mL / Ah, 1.1 mL /
Ah, 1.8 mL / Ah.

The obtained Examples 1 to 4 and Comparative Examples 1 to 1
The secondary battery of No. 6 was charged at a current of 3 A at a high temperature of 45 ° C. for 90 minutes, and a cut-off voltage of 1.0 was applied at a current of 3 A.
Charge / discharge for discharging to V was repeated. In such charge and discharge, the number of charge and discharge cycles when the discharge capacity became 80% or less of the initial value was determined. Further, the maximum internal pressure value at that time was measured.

The results are shown in Table 1 below.

[0046]

[Table 1]

(Reference Examples 1 to 20) A capacity of 3000 mAh
As shown in Table 2 below, the same hydrogen storage alloys as in Examples 1 to 4 and Comparative Examples 1 to 16 were used and the amount of electrolyte solution was the same as that of FIG.
Twenty kinds of cylindrical nickel-metal hydride secondary batteries of A size were assembled.

The obtained secondary batteries of Reference Examples 1 to 20 were charged at a high temperature of 45 ° C. at a current of 3 A for 90 minutes at a high temperature of 45 ° C., and a cut-off voltage of 1.0 was obtained at a current of 3 A, as in Examples 1 to 4.
The charge / discharge for discharging to 0 V was repeated. In such charge and discharge, the number of charge and discharge cycles when the discharge capacity became 80% or less of the initial value was determined. Further, the maximum internal pressure value at that time was measured.

The results are shown in Table 2 below.

[0050]

[Table 2]

As is apparent from Table 1, the capacity is 310.
In a nickel hydride secondary battery of Wh / L or more, 100
The equilibrium pressure when measuring the pressure-composition isotherm at 2.0 ° C. is 2.0
BET when hydrogenated and pulverized once at a hydrogen pressure of 2 to 30 ° C. and 5 to 10 atm (gauge pressure) at −4.0 atm.
The specific surface area of law is 0.05m ² /g~0.20m ² /
g of the secondary batteries of Examples 1 to 4 provided with a negative electrode containing a hydrogen storage alloy and having an electrolyte amount of 0.7 to 1.3 mL / Ah. It can be seen that the charge / discharge cycle life is longer and the internal pressure rise is suppressed as compared with the secondary batteries of Comparative Examples 1 to 16 in which one requirement is out of the above range.

On the other hand, as shown in Table 2, in a conventional secondary battery having an energy density per capacity of less than 310 Wh / L, since the temperature rise is relatively low, the equilibrium pressure and the specific surface area are in the above range (2.0 to 4). .0atm, 0.05m ² / g~
0.20 m ² / g),
It can be seen that in a secondary battery in which the amount of the electrolytic solution is out of the above range (0.7 to 1.3 mL / Ah), no significant deterioration in characteristics has occurred.

In other words, in the conventional secondary battery having a low capacity, although the cycle life is relatively long,
It can be seen that problems such as a decrease in cycle life occur in a usage mode in which the energy density per capacity of Wh / L or more is increased.

Therefore, in a nickel-metal hydride secondary battery having a capacity of 310 Wh / L or more, 100
The equilibrium pressure when measuring the pressure-composition isotherm at 2.0 ° C. is 2.0
BET when hydrogenated and pulverized once at a hydrogen pressure of 2 to 30 ° C. and 5 to 10 atm (gauge pressure) at −4.0 atm.
The specific surface area of law is 0.05m ² /g~0.20m ² /
It is extremely effective to provide a negative electrode containing a hydrogen storage alloy, which is g, and to specify the electrolyte amount to be 0.7 to 1.3 mL / Ah in terms of improving cycle life and suppressing an increase in internal pressure. I understand.

In the above-described embodiment, the separator is interposed between the positive electrode and the negative electrode and spirally wound and accommodated in the cylindrical container 1 having a bottom. It is not limited to such a structure. For example, the present invention is similarly applicable to a square nickel-metal hydride secondary battery in which a separator is interposed between a positive electrode and a negative electrode, and a laminate of a plurality of the separators is housed in a bottomed rectangular cylindrical container.

[0056]

As explained above, according to the present invention, the volume energy density is high (310 Wh / L or more),
Even when used in a high-temperature atmosphere, it is possible to provide an alkaline secondary battery that maintains a long cycle life, has small variations in characteristics during high-rate discharge, and can suppress an increase in internal pressure.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a nickel-hydrogen secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Container, 2 ... Positive electrode, 3 ... Separator, 4 ... Negative electrode, 5 ... Electrode group, 7 ... Sealing plate, 8 ... Insulating gasket.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 5H003 AA04 BB02 BC01 BD01 BD05 5H016 AA01 AA08 BB18 EE01 HH04 HH06 HH11 HH17 5H028 AA01 AA06 BB15 CC12 EE01 HH02 HH08 HH09 HH10

Claims (1)

[Claims] 1. A negative electrode containing a hydrogen storage alloy powder, a positive electrode containing nickel hydroxide as an active material and having a separator interposed therebetween, an alkaline electrolyte, and a container for accommodating these members. Wherein the capacity of the secondary battery is 310 Wh / L or more, and the alkaline electrolyte is 0.7 to 1.3 m in the container.
L / Ah, and the hydrogen storage alloy in the negative electrode is a rare earth-nickel system, and has an equilibrium pressure of 2.0 to 4.0 when a pressure-composition isotherm at 100 ° C. is measured.
In 0 atm, and 2 to 30 ° C., a specific surface area by the BET method when the pulverized once hydrogenation under a hydrogen pressure of 5-10 atm (gauge pressure) at 0.05m ² /g~0.20m ² / g An alkaline secondary battery.