JP3392700B2 - Alkaline secondary battery - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alkaline secondary battery having an improved negative electrode using hydrogen as an active material. [0002] An alkaline secondary battery, for example, a nickel hydride secondary battery, has a separator interposed between a paste-type positive electrode containing nickel hydroxide as an active material and a paste-type negative electrode containing a hydrogen storage alloy. The electrode group produced in this manner is housed in a container together with an alkaline electrolyte. Such a nickel-hydrogen secondary battery is useful because a higher capacity and a higher energy density can be achieved compared to a nickel-cadmium secondary battery using a negative electrode containing cadmium instead of the negative electrode containing the hydrogen storage alloy. It is. As a negative electrode used in the alkaline secondary battery, a paste is prepared by kneading a hydrogen storage alloy, a conductive material and a polymer binder in the presence of water, and the paste is punched metal, felt-like. A paste-type negative electrode filled in a conductive substrate such as a porous metal body is used. As the hydrogen storage alloy, LaNi _5, La, Ce, Pr,
Nd, Sm misch metal (hereinafter, referred to as Mm) which is a mixture of lanthanide such as an alloy of Ni and, namely MmNi _5, a mixture of rare earth elements including La and alloy of Ni, i.e. NmNi ₅ or Ni, A part
Rare earth-nickel-based hydrogen storage alloys such as multi-elements substituted with elements such as l, Mn, and Co are used. By the way, in the alkaline secondary battery provided with the above-mentioned paste type negative electrode, in order to further increase the capacity, it has been attempted to increase the capacity of the positive electrode and the negative electrode housed in the container as much as possible. ing. However,
Since the increase in the capacity of the positive electrode and the negative electrode inevitably reduces the amount of the alkaline electrolyte contained in the container, when the above-mentioned rare earth-nickel-based hydrogen storage alloy is used, the consumption of the alkaline electrolyte as follows: There was a problem that the cycle characteristics deteriorated. That is, an alkaline secondary battery provided with a negative electrode containing the above-described rare earth-nickel-based hydrogen storage alloy is charged and discharged, and when this is repeated, cracks occur in the hydrogen storage alloy particles in the negative electrode. When cracks occur in the hydrogen storage alloy particles, the electrolyte is consumed because the alkaline electrolyte oozes into the cracked gaps or corrosion proceeds on the highly active cracked surface of the hydrogen storage alloy. When the electrolyte is consumed in this manner, the charge / discharge cycle characteristics are significantly reduced due to the exhaustion of the electrolyte and the like because the amount of the electrolyte stored in the container is originally small. SUMMARY OF THE INVENTION An object of the present invention is to provide an alkaline secondary battery having an improved discharge capacity while maintaining a practical charge / discharge cycle life. [0007] An alkaline secondary battery according to the present invention is an alkaline secondary battery comprising a positive electrode, a negative electrode containing a rare-earth hydrogen storage alloy, and an alkaline electrolyte. The volume energy density of the secondary battery is 310 Wh
And a / l or more, the rare-earth-based hydrogen storage alloy is represented by the following
It has a composition represented by the formula (1) . LmNi _w Co _x Al _{y M} n _z (1) where Lm is a small number selected from rare earth elements including La.
At least one kind, and the atomic ratio w is 3.3 ≦ w ≦ 4.5,
The atomic ratio x is 0.5 ≦ x ≦ 1.1, and the atomic ratio y is 0.2 ≦
When y ≦ 0.5, the atomic ratio z is 0.05 ≦ z ≦ 0.13,
And the sum of the atomic ratios w, x, y, z is 4.9 ≦ w + x +
y + z ≦ 5.5. DETAILED DESCRIPTION OF THE INVENTION Hereinafter, an alkaline secondary battery (for example, a cylindrical alkaline secondary battery) according to the present invention will be described in detail with reference to FIG. An electrode group 5 produced by stacking the positive electrode 2, the separator 3, and the negative electrode 4 and winding them in a spiral shape is accommodated in the bottomed cylindrical container 1. 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 first 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 sealing plate is formed on the container 1 by caulking to reduce the diameter of the upper opening inward. 7 is hermetically 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. The positive electrode terminal 10 having a hat shape is provided with the sealing plate 7.
It is attached so as to cover the hole 6 above. 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.
Circular holding plate 12 made of an insulating material having a hole in the center
Are arranged on the positive electrode terminal 10 such that the protrusions of the positive electrode terminal 10 protrude from the holes of the holding plate 12. The outer tube 13 is provided on the periphery of the holding plate 12,
The side surface of the container 1 and the periphery of the bottom of the container 1 are covered. Hereinafter, the negative electrode 4, the positive electrode 2, the separator 3
And the alkaline electrolyte will be described in detail. (1) Negative Electrode 4 The negative electrode 4 contains a rare earth-based hydrogen storage alloy containing cobalt atoms (Co) and manganese atoms (Mn). The content of manganese atoms in this alloy is 0.6% by weight or more,
And less than 2.6% by weight. [0010] maintained by the content of manganese atoms in the alloy to the range, it is possible capacity to improve the 310 W h / l or more alkaline secondary battery cycle life, excellent high-temperature storage characteristics can do. When the content of more than 2.6 wt%, the capacity described above is 310 W h / l or more secondary battery cycle life is reduced. One of the causes is that a large amount of the manganese component in the alloy is eluted into the alkaline electrolyte with the progress of the charge / discharge cycle, and this is deposited on the positive electrode. Such manganese component elution occurs particularly remarkably when the secondary battery is used in a high-temperature environment, and therefore, the secondary battery having an alloy having a high content of the manganese component and having the capacity is used in a high-temperature environment. Capacity recovery rate when stored at low temperatures. Although it is preferable that the content is less than 0.6% by weight from the viewpoint of improving the cycle life of the secondary battery having the capacity, when the secondary battery is stored in a high-temperature (40 ° C. or higher) environment, The cobalt component in the alloy is eluted into the alkaline electrolyte, precipitates and forms a conductive path between the positive electrode and the negative electrode, and causes an internal short circuit, so that the capacity recovery rate decreases. A more preferred range for the content of manganese atoms is 1.1% by weight to 1.5% by weight. When the alloy contains cobalt atoms, it is possible to suppress the progress of pulverization accompanying the charge / discharge cycle of the alloy. The cobalt content of the alloy is 5
It is preferable that the content be in the range of 15% by weight to 15% by weight. This is due to the following reasons. If the content is less than 5% by weight, it may be difficult to sufficiently obtain the effect of suppressing the progress of pulverization. On the other hand, if the content exceeds 15% by weight, the capacity of the alloy may be reduced. Further, cobalt is expensive, so that the production cost is high. A more preferred range for the content of cobalt atoms is 10% to 12% by weight. The rare earth component of the alloy is lanthanum (L
It is good to consist of at least one kind selected from rare earth elements including a). In particular, the alloy preferably contains lanthanum (La). Preferably, the alloy contains nickel atoms (Ni). The content of nickel atoms in the alloy is preferably in the range of 45% by weight to 60% by weight. As the alloy, for example, the following general formula (1)
LmNi _w Co _x Al _{y M} n _z (where Lm is at least one selected from rare earth elements including La, the atomic ratio w is 3.30 ≦ w ≦ 4.50, and the atomic ratio x is 0.50
≦ x ≦ 1.10, atomic ratio y is 0.20 ≦ y ≦ 0.50,
The atomic ratio z is 0.05 ≦ z ≦ 0.20 and the atomic ratio w,
The sum of x, y, and z is 4.90 ≦ w + x + y + z ≦ 5.
50) can be exemplified. The rare earth-based hydrogen storage alloy represented by the general formula (1) has a small leaching of Mn, so that the cycle life can be extended and the cost is low.
In the rare earth hydrogen storage alloy represented by the general formula (1), a more preferable range of the atomic ratio w is 3.8 to 4.2.
The more preferable range of the atomic ratio x is 0.7 to 0.9,
A more preferable range of the atomic ratio y is 0.3 to 0.4, and a more preferable range of the atomic ratio z is 0.08 to 0.13.
Further, a more preferable range of the total value of the atomic ratio is 5.0 to 5.0.
5.2. For the negative electrode, for example, a paste is prepared by kneading a rare earth-based hydrogen storage alloy powder containing a cobalt atom and the above-mentioned specific amount of manganese atoms together with a conductive agent, a binder and water. It is manufactured by filling a substrate, drying it, and then press molding. Examples of the conductive agent include carbon black and graphite. Examples of the binder include polyacrylates such as sodium polyacrylate and potassium polyacrylate, fluorine-based resins such as polytetrafluoroethylene (PTFE), and carboxymethyl cellulose (CMC). As the conductive substrate, for example, a two-dimensional substrate such as a punched metal, an expanded metal, a perforated steel plate, a nickel net, a felt-like porous metal,
Examples include a three-dimensional substrate such as a sponge-like porous metal body. (2) Positive Electrode 2 The positive electrode 2 is formed of a positive electrode material containing nickel hydroxide particles and a binder supported on a current collector. As the nickel hydroxide particles, for example, single nickel hydroxide particles or nickel hydroxide particles in which zinc and / or cobalt are coprecipitated with metallic nickel can be used. The latter positive electrode containing nickel hydroxide particles can further improve the charging efficiency in a high temperature state. From the viewpoint of improving the charge / discharge efficiency of the alkaline storage battery, the peak half-value width of the (101) plane of the nickel hydroxide particles determined by X-ray powder diffraction is 0.8 ゜ / 2θ.
(Cu-Kα) or more is preferable. A more preferable nickel hydroxide powder is powder X-ray diffraction method (10
1) The half width of the surface peak is 0.9 to 1.0 ° / 2θ.
(Cu-Kα). Examples of the binder include polytetrafluoroethylene, carboxymethylcellulose, methylcellulose, polyacrylate, and polyvinyl alcohol. Examples of the current collector include those having a sponge-like, fibrous, or felt-like porous structure made of a metal such as nickel or stainless steel or a nickel-plated resin. For the positive electrode, for example, a paste containing nickel hydroxide particles, a conductive additive, a binder and water is prepared, and the paste is filled in a current collector, which is dried and pressure-formed. By cutting into a desired size, a positive electrode having a structure in which a positive electrode material containing nickel hydroxide particles and a binder is supported on a current collector is manufactured. The conductive assistant may be formed of, for example, dicobalt trioxide (Co ₂ O ₃ ), cobalt metal (Co), cobalt monoxide (CoO), or cobalt hydroxide {Co (OH) ₂ }. it can. (3) Separator 3 Examples of the separator 3 include a nonwoven fabric made of a polyamide fiber and a nonwoven fabric made of a polyolefin fiber such as polyethylene or polypropylene provided with a hydrophilic functional group. (4) Alkaline Electrolyte As the alkaline electrolyte, for example, an aqueous solution of sodium hydroxide (NaOH), lithium hydroxide (LiOH)
Aqueous solution, potassium hydroxide (KOH) aqueous solution, NaO
H and LiOH mixed solution, KOH and LiOH mixed solution, K
A mixed solution of OH, LiOH, and NaOH can be used. [0027] The capacity of the secondary battery is more than 310 W h / l. Such a secondary battery can improve the discharge capacity. The capacitance C (W h / l) (volumetric energy density) is calculated by the following formula (i). C = (C _T × Z) / V (i) where C _T (Ah) is the theoretical capacity of the secondary battery, Z
(V) indicates the voltage of the secondary battery, and V (l) indicates the volume of the secondary battery (the inner volume of the container). The ratio (the amount of the electrolyte / theoretical capacity) of the amount of the alkaline electrolyte at 25 ° C. to the theoretical capacity of the alkaline secondary battery provided with this electrolyte is 0.8 ml / Ah to 0.8 ml / Ah.
It is preferable to be in the range of 1.25 ml / Ah. This is due to the following reasons. Wherein the electrolyte volume ratio exceeds 1.25 ml / Ah, capacity 310 W h / l
It may be difficult to set the above. The smaller the ratio of the amount of the electrolyte to the theoretical capacity of the secondary battery is, the more advantageous in increasing the capacity, and the effect of improving the cycle life by setting the Mn content in the alloy to the above range tends to be remarkable. However, if it is less than 0.8 ml / Ah,
There is a possibility that the amount of electrolyte on the surface of the positive electrode or the negative electrode decreases, and the discharge capacity decreases. A more preferable electrolyte solution ratio is 0.1.
The range is from 90 ml / Ah to 1.15 ml / Ah. The capacity ratio of the negative electrode to the positive electrode (design capacity of the negative electrode when the design capacity of the positive electrode is 1) is 1.1
It is preferred to be in the range of 0 to 1.60. This is due to the following reasons. When the volume ratio exceeds 1.60, it may become difficult to set the volume to more than 310 W h / l. As the capacitance ratio is reduced,
The capacity can be easily set in the above range, and the M
When the n content is in the above range, the effect of improving the cycle life tends to be remarkable. However, when the capacity ratio is less than 1.10, the charge reserve of the negative electrode is reduced, so that the oxygen gas reduction performance of the negative electrode is reduced and the internal pressure characteristics may be reduced. A more preferable range of the capacity ratio is a range of 1.20 to 1.40. In FIG. 1 described above, the separator 3 is interposed between the negative electrode 4 and the positive electrode 2 and spirally wound and accommodated in the bottomed cylindrical container 1. The separator may be interposed therebetween to form a laminate, and the laminate may be stored in a bottomed rectangular cylindrical container. As described in detail above, the alkaline secondary battery according to the present invention contains cobalt atoms and manganese atoms, and the content of the manganese atoms is 0.6% by weight or more and less than 2.6% by weight. comprising a negative electrode containing a rare-earth hydrogen storage alloy is a range, capacity 310 W h / l or higher. Such a secondary battery can improve the cycle life while maintaining a high discharge capacity and an excellent capacity recovery rate when stored at a high temperature. The cycle life of an alkaline secondary battery having a negative electrode containing a rare earth-based hydrogen storage alloy having a manganese atom content in a specific range and having the above-described capacity is improved by (1) a charge-discharge cycle. (2) It is possible to suppress the pulverization of the alloy due to the progress of the process, so that the consumption of the electrolyte due to the pulverization can be reduced.
This is considered to be due to the fact that the manganese component of the hydrogen storage alloy can be prevented from being eluted into the alkaline electrolyte. Embodiments of the present invention will be described below in detail with reference to the drawings. (Examples 1-3 and Comparative Examples 1-2) <Preparation of Negative Electrode> Lm (Lm is 80% by weight of La, Ce
2.0% by weight, 4.1% by weight of Pr and 13% of Nd.
9% by weight), and five kinds of rare earth hydrogen storage alloys having compositions shown in Table 1 below were produced by high frequency melting using Ni, Co, Mn, and Al. Each rare earth hydrogen storage alloy was pulverized by mechanical pulverization to a fine powder of 40 μm or less. Five kinds of negative electrodes were prepared from each rare earth hydrogen storage alloy powder by the method described below. 100 parts by weight of each rare earth hydrogen storage alloy powder, 0.5 part by weight of sodium polyacrylate, 0.12 part by weight of carboxymethylcellulose (CMC), and a dispersion of polytetrafluoroethylene (specific gravity 1.
5, a solid content of 60% by weight) and 1.0 part by weight of carbon black as a conductive agent were added, and mixed with 30 parts by weight of water to prepare a paste. This paste was applied to a punched metal as a conductive substrate, dried, and pressed to produce a negative electrode. From the obtained negative electrodes, five types of nickel-metal hydride secondary batteries were assembled as described below. <Preparation of Positive Electrode> A mixture of 90 parts by weight of nickel hydroxide powder and 10 parts by weight of cobalt monoxide powder was mixed with 0.3 part by weight of carboxymethyl cellulose and a dispersion of polytetrafluoroethylene (specific gravity 1.5, solid content 60). 0.5% by weight in terms of solid content)
A paste was prepared by adding 45 parts by weight of pure water and kneading them. This paste was filled in a foamed metal substrate as a conductive substrate, dried, and then roll-pressed to form a positive electrode. Next, for each of the negative electrodes, the design capacity ratio (the design capacity of the positive electrode was 1) was set to 1.30. A separator (made by graft-polymerizing a nonwoven fabric made of polypropylene) was interposed between each of the negative electrode and the positive electrode, and these were spirally wound to form an electrode group. Such an electrode group is placed in a cylindrical container with a bottom (with an inner volume of 0.
0145l), 7N KOH and 1N LiO
H is accommodated in such a manner that the electrolyte volume ratio with respect to the theoretical capacity is 1.0 ml / Ah, and has the structure shown in FIG. 1 described above, and the theoretical capacity is 4000 mAh (4 A
In h), with 4 / 3A size, in the voltage 1.25V, the capacity obtained from the aforementioned formula (i) has assembled a cylindrical nickel-hydrogen secondary battery of 329 W h / l. (Comparative Examples 3 to 7) Five types of negative electrodes were produced in the same manner as in Examples 1 to 3 described above. From each of the obtained negative electrodes, 5
Various kinds of nickel-metal hydride secondary batteries were assembled. A positive electrode was produced in the same manner as in Examples 1 to 3. The capacity ratio of each negative electrode to the positive electrode was set to 1.70, the same separator as in Examples 1 to 3 was interposed between each negative electrode and the positive electrode, and these were spirally wound to form an electrode group. did. Such an electrode group was housed in a cylindrical container having the same bottom as in Examples 1 to 3, and an alkaline electrolyte having the same composition as in Examples 1 to 3 having an electrolyte amount ratio to theoretical capacity of 1.
It is stored at 35 ml / Ah, has the structure shown in FIG. 1 described above, and has a theoretical capacity of 3000 mAh (3 Ah).
In at 4 / 3A size, in the voltage 1.25V, the capacity obtained from the aforementioned formula (i) has assembled a cylindrical nickel-hydrogen secondary battery of 247 W h / l. The secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were charged at a current of 3000 mAh for 90 minutes.
A charge / discharge cycle of discharging to a final voltage of 1.0 V with a current of 000 mAh was repeated. 3 for each secondary battery
Table 2 shows the discharge capacity (initial capacity) and cycle life at the cycle. Here, the cycle life is the number of cycles when the discharge capacity reaches 80% or less of the initial capacity of the secondary battery. After the initial capacities of the secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were calculated as described above, these secondary batteries were stored in a discharged state at 80 ° C. for one month. Charged with 3000 mAh current for 90 minutes, 300
The charge / discharge in which the battery was discharged to a final voltage of 1.0 V with a current of 0 mAh was repeated three times, and the discharge capacity was measured.
From the obtained recovery capacity, a recovery rate {(recovery capacity / initial capacity) × 100} was determined, and the results are shown in Table 2 below. Further, the internal pressures of the secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were measured. The measurement of the battery internal pressure was performed by accommodating the secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 in a container of a pressure measuring device shown in FIG. That is, each battery internal pressure measuring device has a battery case comprising a case main body 21 and a cap 22 made of acrylic resin. At the center of the case body 21, A
A space 23 having the same inner diameter and height as the metal container of the A-size battery is formed. The secondary battery 24 is housed inside the space 23. The cap 22 is air-tightly fixed on the case body 21 by a bolt 27 and a nut 28 via a packing 25 and an O-ring 26. A pressure detector 29 is attached to the cap 22. A negative electrode lead 30 from the negative electrode and a positive electrode lead 31 from the positive electrode are led out between the packing 25 and the O-ring 26. The secondary batteries of Examples 1 to 3 and Comparative Examples 1 to 7 were measured for 3000 m with such a battery internal pressure measuring device.
The maximum battery internal pressure when charged 130% with the current A was measured, and the results are also shown in Table 2 below. [Table 1] [Table 2] As is clear from Tables 1 and 2, rare-earth hydrogen storage containing cobalt and manganese atoms and having a manganese atom content of 0.6% by weight or more and less than 2.6% by weight. comprising a negative electrode containing an alloy, and secondary batteries of examples 1 to 3 capacity is 310 W h / l or more,
It can be seen that the discharge capacity is high, the internal pressure characteristics are excellent, and the cycle characteristics and high-temperature storage characteristics can be improved. On the other hand, the secondary battery of Comparative Example 1 in which the manganese atom content is less than 0.6% by weight has excellent cycle characteristics,
It can be seen that storage under a high temperature environment of ℃ causes an internal short circuit, and the capacity recovery rate is 0%. In addition, it can be seen that the secondary battery of Comparative Example 2 in which the content of the manganese atom is 2.6% by weight or more has a short cycle life and a low capacity recovery rate when stored at a high temperature. Meanwhile, if the result of the secondary batteries of Comparative Examples 3 to 7, more rare earth hydrogen storage alloy content of manganese atoms than 2.6 wt%, the capacity is less than 310 W h / l a long cycle life, good while indicating capacity recovery rate, it can be seen that the capacity and the cycle life of is 310 W h / l or more drops. Also, it can be seen that the secondary batteries of Comparative Examples 3 to 7 have lower discharge capacities than those of Examples 1 to 3. According to the present invention, it is possible to provide an alkaline secondary battery which simultaneously satisfies a high discharge capacity, a long cycle life, and excellent high-temperature storage characteristics.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partially cutaway perspective view showing an example of an alkaline secondary battery according to the present invention. FIG. 2 is a sectional view showing a battery internal pressure measuring device used for evaluating internal pressure characteristics of the secondary batteries of Examples 1 to 5 and Comparative Examples 1 to 7 according to the present invention. [Description of Signs] 1 ... container, 2 ... positive electrode, 3 ... separator, 4 ... negative electrode, 5 ...
Electrode group, 7 ... sealing plate.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-7-97648 (JP, A) JP-A-7-268519 (JP, A) JP-A-8-180861 (JP, A) JP-A-9-96 27315 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01M 4/38 H01M 4/24 C22C 19/00 H01M 10/24

Claims (1)

(57) [Claim 1] An alkaline secondary battery comprising a positive electrode, a negative electrode containing a rare earth hydrogen storage alloy, and an alkaline electrolyte, wherein the volume energy density of the secondary battery is Is not less than 310 Wh / l, and the rare earth hydrogen storage alloy is a group represented by the following formula (1).
Alkaline secondary battery, characterized by having formed. LmNi _w Co _x Al _{y M} n _z (1) where Lm is a small amount selected from rare earth elements including La.
At least one kind, and the atomic ratio w is 3.3 ≦ w ≦ 4.5,
The atomic ratio x is 0.5 ≦ x ≦ 1.1, and the atomic ratio y is 0.2 ≦
When y ≦ 0.5, the atomic ratio z is 0.05 ≦ z ≦ 0.13,
And the sum of the atomic ratios w, x, y, z is 4.9 ≦ w + x +
y + z ≦ 5.5.