JP2015173058A - Nickel hydrogen storage battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nickel hydrogen storage battery arranged so that its self discharge is suppressed even when cobalt and manganese are included in the battery.SOLUTION: A nickel hydrogen storage battery comprises: a positive electrode; a negative electrode; a separator interposed between the positive and the negative electrodes; and an alkaline electrolyte. Each or one of the positive and the negative electrodes includes Mn. Each or one of the positive and the negative electrodes includes Co. The separator includes manganese and cobalt. In dividing the separator (of which the thickness is denoted by T) into a positive side region of a thickness of 0.35T, including a surface on the side of the positive electrode, a negative side region of a thickness of 0.35T, including a surface on the side of the negative electrode, and a central region of a thickness 0.3T other than the positive side region and the negative side region, the Mn existence probability Xin the positive side region, and the Mn existence probability Xin the central region satisfy the following condition: X>X; and the Co existence probability Xin the positive side region, and the Co existence probability Xin the central region satisfy the following condition: X>X.

Description

  The present invention relates to a nickel metal hydride storage battery, and more particularly to an improvement in a nickel hydride storage battery separator.

  Nickel metal hydride storage batteries using a negative electrode containing a hydrogen storage alloy as a negative electrode active material can be used in a wide current range, and are therefore widely used as power sources for various devices. In addition, the use of nickel-metal hydride storage batteries as an emergency power source is also expected due to recent concerns about abnormal weather and increased awareness of disaster prevention. In applications such as an emergency power supply, the battery is often stored for a long time in a charged state. Therefore, it is desired that battery characteristics do not deteriorate during the storage period.

  However, if the nickel metal hydride storage battery is stored for a long period of time, an internal short circuit may occur, which may cause a decrease in capacity, heat generation, an increase in battery internal pressure, and / or leakage of the electrolyte. The occurrence of an internal short circuit due to storage is due to the metal component contained in the electrode being easily eluted in the electrolyte, and the metal is deposited on the separator or the like (for example, deposited in a dendrite shape), thereby short-circuiting between the positive electrode and the negative electrode. It is considered a thing. The elution of the metal component is particularly prominent when the nickel metal hydride storage battery is stored in a high temperature environment.

  In particular, metals such as cobalt and / or manganese tend to elute into the alkaline electrolyte. The eluted metal (particularly cobalt) is likely to precipitate in the separator and easily cause an internal short circuit. However, cobalt and / or manganese is an effective element for improving the characteristics of the hydrogen storage alloy that is the negative electrode active material. Cobalt is also used as a conductive agent in the positive electrode and the like, and manganese may be contained as an impurity in the positive electrode active material. Therefore, it is difficult to exclude these elements from the nickel metal hydride storage battery.

  From the viewpoint of suppressing the internal short circuit as described above, in Patent Document 1, an element such as iron or titanium or an oxide thereof or the like is contained in a separator at a predetermined concentration to form a crystal growth nucleus. It has been proposed to disperse the precipitates and prevent the formation of conductive paths. In Patent Document 2, a nickel-metal hydride storage battery is formed using an electrode group in which a nonwoven fabric separator is interposed between a positive electrode and a negative electrode, and stored at a predetermined temperature after initial charging, so that the Co ratio is larger than Mn inside the separator. It has been proposed to deposit Co-Mn hydroxide.

JP-A-10-233200 JP 2000-299124 A

  When cobalt is contained in the electrode of the nickel metal hydride storage battery, cobalt is eluted in the electrolytic solution, and the eluted cobalt is precipitated in the separator to form a conductive path, which easily causes an internal short circuit. If an internal short circuit occurs while storing the charged nickel metal hydride storage battery, the capacity is reduced due to self-discharge. If the internal short circuit at the time of storage can be reduced like patent document 1 or 2, it is thought that self-discharge will also decrease. However, it has been found that there are various causes of self-discharge in nickel-metal hydride storage batteries, and self-discharge cannot be sufficiently suppressed only by reducing the internal short circuit.

  In nickel-metal hydride storage batteries, nickel compounds such as nickel oxyhydroxide and nickel hydroxide are used as the positive electrode active material. In the positive electrode, nickel hydroxide is oxidized and nickel oxyhydroxide is generated during charging, and nickel oxyhydroxide is reduced and nickel hydroxide is generated during discharging.

  When manganese is contained in the electrode of the nickel metal hydride storage battery, self-discharge is accelerated. In particular, when nickel-metal hydride storage batteries are stored at high temperatures for a long period of time, the elution of manganese becomes significant, resulting in significant capacity degradation due to self-discharge. Such an increase in self-discharge is presumed to be due to the reduction of nickel oxyhydroxide in a shuttle reaction in which manganese redox is repeated, as will be described later.

  Patent Documents 1 and 2 both control or suppress the formation of conductive paths in the separator, and it is difficult to suppress the manganese shuttle reaction as described above, and the self-discharge suppressing effect is insufficient. .

  This invention is made | formed in view of such a subject, Even if it is a case where cobalt and manganese are contained in a battery, it is providing the nickel hydride storage battery by which self-discharge was suppressed.

One aspect of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte.
The negative electrode active material includes a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen,
The positive electrode active material includes a nickel compound,
At least one of the positive electrode and the negative electrode contains manganese,
At least one of the positive electrode and the negative electrode contains cobalt,
The separator has a thickness T and contains manganese and cobalt;
The separator includes a positive side region having a thickness of 0.35T including the surface on the positive electrode side, a negative side region having a thickness of 0.35T including the surface on the negative electrode side, and a thickness other than the positive side region and the negative side region. When partitioning into a central region with 0.3T,
The positive side existence probability of the manganese in the region X _MNP, and the presence of manganese probability in the central region X _Mnc satisfies X _Mnp> X _Mnc,
The cobalt existence probability X _Cop in the positive region and the cobalt existence probability X _Coc in the central region relate to a nickel metal hydride storage battery that satisfies X _Cop > X _Coc .

  According to the above aspect of the present invention, even when cobalt and manganese are contained in the electrode of the nickel-metal hydride storage battery, internal short circuit during storage and reduction of the positive electrode active material are suppressed, and self-discharge is suppressed. it can. By suppressing self-discharge, a highly reliable nickel metal hydride storage battery can be obtained.

FIG. 1 is a schematic perspective view in which a part of a cylindrical nickel-metal hydride storage battery according to an embodiment of the present invention is cut away. FIG. 2 is a graph showing the influence on capacity deterioration during storage due to the addition of cobalt or manganese to the negative electrode in a nickel-metal hydride storage battery using a negative electrode containing a hydrogen storage alloy containing no cobalt and manganese as a negative electrode active material. .

First, the mechanism of self-discharge of the nickel metal hydride storage battery will be described below with reference to FIG.
FIG. 2 is a graph showing the influence on capacity deterioration during storage due to the addition of cobalt or manganese to the negative electrode in a nickel-metal hydride storage battery using a negative electrode containing a hydrogen storage alloy containing no cobalt and manganese as a negative electrode active material. . Cobalt metal and manganese metal were added to the negative electrode as additives, respectively, so that the influence of elution of cobalt and manganese could be easily understood. The amount of cobalt metal added was 2.0 parts by mass (battery 2) and the amount of manganese metal added was 1.0 part by mass (battery 3) with respect to 100 parts by mass of the hydrogen storage alloy. In Battery 1, no additive was added to the negative electrode. As the hydrogen storage alloy, an alloy having a Ce ₂ Ni ₇ type (A ₂ B ₇ type) crystal structure was used. The batteries 1 to 3 commonly used a positive electrode containing nickel hydroxide as a positive electrode active material and cobalt oxyhydroxide as a conductive agent.

  The battery was charged at an ambient temperature of 20 ° C. with a charging current of 0.1 C for 16 hours, rested for 60 minutes, discharged to a final voltage of 0.9 V with a discharging current of 0.2 C, and the discharge capacity ( The initial discharge capacity was determined. Next, the battery was charged at an ambient temperature of 20 ° C. with a charging current of 0.1 C for 16 hours, and the charged battery was stored at an ambient temperature of 65 ° C. The discharge capacity was measured after the battery was stored for a predetermined period, and the ratio of the discharge capacity after storage to the initial discharge capacity (capacity maintenance ratio (%)) was determined. FIG. 2 is a graph showing the relationship between the storage period (days) and the capacity retention rate (%) at this time. The results for Battery 1 to Battery 3 are the average values for each of the five batteries. For batteries 2 and 3, the internal resistance of the battery after storage (7 days, 14, 21, 28, and 35 days) was measured by the AC impedance method under liquid nitrogen cooling and the frequency of the AC current. Measurement was performed at 1 kHz.

  In the battery 1 using the negative electrode containing no cobalt and manganese, the capacity retention rate after storage for 35 days was 66%, and the decrease in the capacity retention rate during storage was moderate. In the battery 2 using the negative electrode to which cobalt metal was added, the capacity retention ratio decreased to 60% after 7 days of storage, and became 0% when the storage period was 14 days or longer. The battery 2 after storage exhibited an internal resistance value of 4 to 150 MΩ, and it was confirmed that an internal short circuit occurred during storage. This is probably because cobalt was eluted from the negative electrode during storage and deposited in the separator, thereby short-circuiting the positive electrode and the negative electrode.

  In the battery 3 using the negative electrode to which manganese metal was added, the capacity retention ratio decreased as the storage days increased, and the capacity retention ratio after storage for 35 days was 28%. As shown in FIG. 2, the battery 3 and the battery 2 clearly differ in the behavior of the capacity retention rate during storage. In the battery 3 after storage, no internal resistance value was observed, and it was confirmed that no internal short circuit occurred between the positive electrode and the negative electrode. Manganese is highly soluble in an alkaline electrolyte, so it is considered that even in the battery 3, elution of manganese occurs. However, in the battery 3, since an internal short circuit is not observed, even if the eluted manganese is precipitated in the separator, the conductivity of the precipitate is not as high as in the case of cobalt.

  From the mass of the manganese metal added to the negative electrode of the battery 3, the electric capacity per electron of the manganese metal was calculated to be 44.6 mAh. On the other hand, from FIG. 2, when the storage period is 21 days or more, the difference in capacity maintenance rate between the battery 1 and the battery 3 exceeds 10%, and when converted to the difference in capacity, it exceeds 190 mAh. That is, when the storage period is 21 days or more, a capacity drop far exceeding the electric capacity of manganese metal occurs.

  Manganese metal is likely to be eluted in the alkaline electrolyte in the form of divalent manganese ions (Mn (II)), so it is considered that manganese ions are present in the electrolyte. In the battery 3, it is presumed that the decrease in capacity is remarkable because manganese ions are catalytically involved in the reaction in which the capacity decreases. In order for manganese ions to repeatedly act catalytically, it is considered that manganese ions are repeatedly oxidized and reduced in the battery, and the valence is changed. That is, manganese ions move between the positive electrode and the negative electrode in the battery, and oxidation at the positive electrode (oxidation from Mn (II) to Mn (III)) and reduction at the negative electrode (Mn (III) to Mn ( It is considered that a shuttle reaction that repeats reduction to II) occurs. And it is estimated that the electron which the manganese ion lost in the positive electrode by oxidation is consumed for reduction | restoration (namely, discharge reaction) of the nickel oxyhydroxide which is the positive electrode active material of the oxidation state which exists in a positive electrode. This discharge reaction is repeatedly caused by the action of manganese ions as a catalyst. As a result, it is considered that self-discharge is accelerated in the battery 3 as shown in FIG.

Based on the above findings, when the improvement of the separator was examined, in the region on the positive electrode side of the separator (also referred to as the positive region), both manganese and cobalt are present more than the central region of the separator, It became clear that self-discharge can be remarkably suppressed in nickel-metal hydride storage batteries.
Hereinafter, a nickel-metal hydride storage battery according to an embodiment of the present invention will be described in more detail with reference to the drawings as appropriate.

A nickel metal hydride storage battery according to an embodiment of the present invention includes a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, a separator interposed between the positive electrode and the negative electrode, and an alkaline electrolyte. The negative electrode active material includes a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen, and the positive electrode active material includes a nickel compound. At least one of the positive electrode and the negative electrode contains manganese, and at least one of the positive electrode and the negative electrode contains cobalt. The separator has a thickness T and contains manganese and cobalt. The separator has a positive region having a thickness of 0.35T including the surface on the positive electrode side, a negative region having a thickness of 0.35T including the surface on the negative electrode side, and a thickness of 0.3T other than the positive region and the negative region. when divided into a central region, and the existence probability X _MNP manganese in the positive region, and the presence of manganese probability X _Mnc in the central region, X _Mnp> X _Mnc met, the existence probability of the cobalt in the positive region X _Cop And the existence probability X _Coc of cobalt in the central region satisfies X _Cop > X _Coc .

  When manganese is contained in the electrode of the nickel-metal hydride storage battery, it is considered that self-discharge is accelerated by a shuttle reaction in which oxidation and reduction of manganese as described above occurs repeatedly during storage of the battery. Moreover, when cobalt is contained in an electrode, cobalt elutes during preservation | save of a battery, the eluted cobalt precipitates in a separator, causes an internal short circuit, and self-discharge also arises by this.

  According to the embodiment of the present invention, the positive side region of the separator contains manganese and cobalt with a higher probability of existence than the central region, so that internal short circuit during battery storage is suppressed, and self-discharge is accelerated during storage. Increase is also suppressed. As a result, self-discharge can be suppressed even though cobalt and manganese are contained in the battery (specifically, the electrode). Therefore, the capacity | capacitance fall accompanying self-discharge can be suppressed (that is, a storage characteristic can be improved) and the reliability of a battery can be improved.

  Since the acceleration increase of self-discharge is suppressed, it is considered that the reduction reaction (that is, discharge reaction) from nickel oxyhydroxide to nickel hydroxide at the positive electrode interface during storage is suppressed. Such suppression of the discharge reaction is thought to be due to suppression of oxidation / reduction of manganese ions at the electrode interface. Therefore, in the nickel metal hydride storage battery according to the embodiment of the present invention, it is considered that manganese ions are immobilized (or trapped) in the positive region of the separator even if manganese ions are eluted from the electrodes. Such immobilization of manganese ions is considered to be due to cobalt contained in the positive region, and it is presumed that cobalt present in the positive region has an anchoring effect on manganese ions. Thus, according to the embodiment of the present invention, manganese ions can be trapped particularly in the positive region of the separator. Therefore, the shuttle reaction in which the oxidation and reduction of manganese ions is repeated at the interface between the positive electrode and the negative electrode is suppressed, and the self-discharge associated therewith can be suppressed. Such self-discharge involving manganese occurs due to reduction of nickel oxyhydroxide at the positive electrode, so it is particularly important to trap manganese ions in the positive region of the separator.

  According to the embodiment of the present invention, occurrence of an internal short circuit during battery storage is also suppressed. This is because even if cobalt is eluted from the electrode, formation of a conductive path due to deposition of cobalt in the separator is suppressed. The mechanism by which cobalt deposition is suppressed is not clear, but the positive region contains more cobalt and manganese (especially manganese) than the central region, thereby blocking the formation of a conductive path due to cobalt deposition. It is thought that there is.

  In addition, it is considered that the formation of the conductive path due to the deposition of cobalt is blocked by manganese trapped in the positive region. The details are not clear, but are thought to be due to the following mechanism. First, since manganese has higher solubility in alkaline electrolyte than cobalt, it is thought that elution of manganese ions from the electrode occurs more rapidly than elution of cobalt ions. The eluted manganese ions are trapped in the positive region as described above. At this time, the trapped manganese contains a component (especially insulating) having a conductivity lower than that of the cobalt precipitate. Precipitates etc.) are considered to exist in the positive region. It is considered that such adhesion of the manganese component occurs first, thereby suppressing the growth of cobalt precipitates, inhibiting the formation of conductive paths, and suppressing internal short circuits.

  When fine cobalt precipitates are formed in the positive region, manganese components (such as precipitates containing manganese) trapped in the positive region move through the separator and reach the negative electrode interface. This is considered to be suppressed. Therefore, it is considered that the reduction of manganese ions at the negative electrode interface can be suppressed, and as a result, the shuttle reaction that repeats the oxidation and reduction of manganese is also suppressed.

  Even if only manganese or cobalt is present in the positive region, the self-discharge suppressing effect is insufficient. Considering these things, in the present invention, the presence of manganese and cobalt in the positive region comprehensively suppresses the shuttle reaction involving manganese and the formation of a conductive path due to the precipitation of cobalt. It is considered that self-discharge is greatly suppressed.

  The elution of manganese and cobalt from the electrode becomes more prominent under a high temperature environment and / or as the storage period becomes longer, and the capacity reduction due to self-discharge increases. According to the embodiment of the present invention, it is possible to suppress the self-discharge and the accompanying capacity reduction even under the storage conditions in which the elution of manganese and cobalt becomes remarkable.

Below, the component of the nickel hydride storage battery which concerns on one Embodiment of this invention is demonstrated in detail.
(Separator)
The separator is divided into a positive region including a positive electrode surface, a negative region including a negative electrode surface, and a central region other than the positive region and the negative region. When the thickness of the separator is T, the thickness of the positive region is 0.35T, the thickness of the negative region is 0.35T, and the thickness of the central region is 0.3T. The separator thickness T is an average thickness.

  The separator preferably has a porous structure. The porous structure may be any structure of a microporous film and a nonwoven fabric. A well-known separator material in a nickel metal hydride storage battery can be used for the microporous membrane and the nonwoven fabric. Examples of such materials include resins such as polyolefin resins such as polyethylene, polypropylene (PP), and ethylene-propylene copolymers; polyamide resins such as aromatic polyamides; vinyl resins such as polyvinyl acetate or saponified products thereof; acrylics Resins; Cellulose or derivatives thereof (cellulose ether, cellulose ester, etc.); Fluororesin and the like. These materials can be used singly or in combination of two or more. Of these materials, polyolefin resins are preferred. From the viewpoint of easy distribution of manganese and cobalt in the positive region, the porous structure is preferably a fiber nonwoven fabric structure. The above materials can be used as the material constituting the fiber.

The average fiber diameter of the fibers constituting the nonwoven fabric structure is, for example, 0.8 to 20 μm, preferably 1 to 15 μm.
The basis weight of the nonwoven fabric constituting the separator is, for example, 30 to 75 g / m ² , preferably 30 to 60 g / m ² in a state before containing manganese and cobalt.

  The nonwoven fabric constituting the separator may be subjected to a hydrophilic treatment from the viewpoint of enhancing the wettability with respect to the alkaline electrolyte. For example, in the case of a nonwoven fabric containing a polyolefin resin, it is preferable to use it as a separator after hydrophilization. The method for hydrophilizing the nonwoven fabric is not particularly limited, and known methods such as sulfuric acid treatment, fluorine treatment, and plasma treatment can be used.

  The thickness (average thickness) T of the separator can be appropriately selected from the range of 30 to 500 μm, for example. When the separator has a microporous membrane structure, the thickness T of the separator is, for example, 30 to 150 μm, preferably 50 to 130 μm. When a separator contains a nonwoven fabric structure, the thickness T of a separator is 50-500 micrometers, for example, Preferably it is 50-200 micrometers or 70-150 micrometers.

In the nickel-metal hydride storage battery according to the embodiment of the present invention, the separator contains more manganese and cobalt in the positive region than in the central region. That is, the existence probability X _MNP manganese in the positive region, and the presence of manganese probability X _Mnc in the central region, X _MNP> meets X _Mnc, the existence probability X _Cop cobalt in the positive region, the cobalt in the central region The existence probability X _Coc satisfies X _Cop > X _Coc . Therefore, as described above, self-discharge during storage of the battery can be greatly suppressed.

Preferably, the positive region contains manganese and cobalt, while the central region contains as little manganese and cobalt as possible. The reason is not clear, but when the central region does not contain manganese and cobalt, it is considered that formation of a conductive path due to deposition of cobalt eluted from the electrode is easily suppressed. Therefore, the effect of suppressing self-discharge is further increased by reducing the existence probability of manganese and cobalt in the central region. From this point of view, the ratio of X _Mnp to X _Mnc : X _Mnc / X _Mnp is preferably X _Mnc / X _Mnp ≦ 0.2, and more preferably X _Mnc / X _Mnp ≦ 0.1 (or ≦ 0.09). Ratio of X _Cop to X _Coc : X _Coc / X _Cop is preferably X _Coc / X _Cop ≦ 0.2, more preferably X _Coc / X _Cop ≦ 0.1 (or ≦ 0.08). is there.

In the positive region, the content of manganese and cobalt may be increased on the surface side than on the inner side. By increasing the content on the surface side, the effect of suppressing self-discharge can be further enhanced. For example, among the positive region, the positive electrode side of the existence probability of the manganese in the region A having a thickness of 0.2T comprising surface X _Mnpa, the existence probability of the manganese in the region B other than the region A of the positive-side region and the X _Mnpb In this _case , it is preferable that X _Mnpa > X _Mnpb . Further, when the _Cob existence probability in the region A is X _Copa and the _Cob existence probability in the region B is X _Copb , it is preferable that X _Copa > X _Copb .

X _Mnpa to X _Mnpb ratio: X _Mnpb / X _Mnpa is preferably X _Mnpb / X _Mnpa ≦ 0.5, more preferably X _Mnpb / X _Mnpa ≦ 0.4 (or ≦ 0.3). is there. Ratio of X _Copa to X _Copb : X _Copb / X _Copa is preferably X _Copb / X _Copa ≦ 0.5, more preferably X _Copb / X _Copa ≦ 0.4 (or ≦ 0.3). is there.

  The separator may contain manganese and / or cobalt (preferably manganese and cobalt) in the negative region. In this case, the self-discharge suppressing effect can be further enhanced. This is considered to be because the growth of cobalt precipitates can be further suppressed even in the negative side region, and manganese ions can be trapped to reduce the reduction of manganese ions at the negative electrode interface.

Existence probability X _Mnn manganese in the negative-side region may be the existence probability X _Mnc comparable manganese in the central region may be greater than X _Mnc (i.e., X _Mnc ≦ X _Mnn). X _Mnn, even more than X _MNP (i.e., X _Mnn> even X _MNP) good but, X _MNP comparable to or less than (i.e., X _Mnn ≦ X _Mnp) is preferably . However, X _Mnc <X _Mnp needs to be _satisfied .

Towards the presence of cobalt probability in the negative-side region X _Con may be smaller than the existence probability X _Coc cobalt in the central region, more than X _Coc comparable or X _Coc (i.e., X _Coc ≦ X _Con) Is preferred. X _Con, even more than X _Cop (i.e., X _Con> even X _Cop) good but, X _Cop comparable to or less than (i.e., X _Con ≦ X _Cop) is preferably . However, X _Coc <X _Cop needs to be satisfied.

When manganese is contained in the negative side region, the ratio of X _Mnn to X _Mnc : X _Mnc / X _Mnn is preferably X _Mnc / X _Mnn ≦ 0.2, more preferably X _Mnc / X _Mnn ≦ 0. 1 (or ≦ 0.05). When cobalt is contained in the negative region, the ratio of X _Con to X _Coc : X _Coc / X _Con is preferably X _Coc / X _Con ≦ 0.2, and more preferably X _Coc / X _Con ≦ 0. 1.

Also in the negative region, the contents of manganese and cobalt may be increased on the surface side than on the inner side. By increasing the content on the surface side, the effect of suppressing self-discharge can be further enhanced. For example, among the negative region, the negative electrode side of the existence probability of the manganese in the region C having a thickness of 0.2T comprising surface X _Mnnc, and X _Mnnd the existence probability of the manganese in the region D other than the region C of the negative region In this _case , it is preferable that X _Mnnc > X _Mnnd . Moreover, the existence probability of the cobalt in the region C X _Conc, when the existence probability of the cobalt in the region D and X _Cond, it is preferable that X _Conc> X _Cond.

When manganese is contained in the negative region, the ratio of X _Mnnc to X _Mnnd : X _Mnnd / X _Mnnc is preferably X _Mnnd / X _Mnnc ≦ 0.5, more preferably X _Mnnd / X _Mnnc ≦ 0. 3 (or ≦ 0.2). When cobalt is contained in the negative region, the ratio of X _Conc to X _Cond : X _Cond / X _Conc is preferably X _Cond / X _Conc ≦ 0.5, and more preferably X _Cond / X _Conc ≦ 0. 4 (or ≦ 0.3).

  The existence probabilities of manganese and cobalt in the separator can be obtained, for example, based on a photographed image obtained by photographing a cross-sectional image in the thickness direction of the separator taken out by disassembling the battery with an electron beam microanalyzer (EPMA). . Specifically, in the captured image of EPMA, the area of the manganese region in which manganese is distributed and the area of the cobalt region in which cobalt is distributed are obtained, and the existence probability is obtained by calculating the ratio to the area of the entire region. it can. That is, the probability of existence of manganese and cobalt is the area ratio of the region where manganese and cobalt are distributed, respectively. For the calculation of existence probability (area ratio) by EPMA, binarization processing may be used as necessary. For example, in the EPMA analysis of the cross section in the thickness direction of the separator, the binarization process divides the region where manganese (or cobalt) is distributed and the region where manganese (or cobalt) is not distributed, and manganese (or cobalt) is separated. You may obtain | require the area ratio of the area | region to distribute.

  In the separator (particularly the positive region), it is preferable that the region in which manganese is distributed (manganese region) and the region in which cobalt is distributed (cobalt region) overlap as much as possible. When manganese and cobalt are distributed in the vicinity, the trapping effect of manganese ions and the effect of blocking the formation of the conductive path can be synergistically enhanced. In the separator (particularly, the positive region), for example, 20% or more (particularly, 25% or more or 30% or more) of the area of the manganese region preferably overlaps the cobalt region. When manganese and cobalt are contained in the negative side region, it is preferable that 20% or more (particularly, 30% or more or 40% or more) of the area of the manganese region overlaps the cobalt region in the negative side region.

  The existence probability of manganese and cobalt (or the area ratio of the distributed region) in the separator is, for example, in a battery in a charged state, and is preferably in a battery in a state of first charge after a break-in charge / discharge. The content (and distribution state) of manganese and cobalt in the separator may be measured in the battery after the initial charge after the break-in charge and discharge and after a predetermined period (for example, 3 months) has elapsed. For example, a nickel-metal hydride storage battery that is commercially available in a charged state is in a state of being charged for the first time, and therefore the content (and distribution state) of manganese and cobalt can be evaluated for the battery after purchase.

  In the separator, a part of each of manganese and cobalt may be contained in the form of a metal, but preferably contains a compound containing manganese and / or cobalt. By being contained in the form of a compound, formation of a conductive path is easily suppressed, and it is considered advantageous for suppressing an internal short circuit during storage. In the separator, it is preferable that manganese is contained in at least one form selected from the group consisting of a manganese compound and a manganese cobalt composite compound, for example. In the separator, cobalt is preferably included in at least one form selected from the group consisting of a cobalt compound and a manganese cobalt composite compound, for example.

  Examples of the manganese compound include manganese oxides, manganese hydroxides, manganese salts (such as inorganic salts of manganese), and manganese halides. Manganese oxides and / or manganese hydroxides are preferred. Examples of the cobalt compound include cobalt oxide, cobalt hydroxide, cobalt salt (such as an inorganic acid salt of cobalt), and cobalt halide, and cobalt oxide and / or cobalt hydroxide are preferable. Examples of the manganese cobalt composite compound include manganese cobalt composite oxide and manganese cobalt composite hydroxide. The valences of manganese and cobalt contained in each region of the separator (in particular, the positive region and the negative region) may be the same in each region, but may be different. The type of compound may be the same in each region, but may be different.

  Examples of the method for adding manganese and cobalt to the separator include a wet method (coating method, sol-gel method, precipitation method, etc.) or a dry method (vapor phase method such as CVD method, sputtering method, vapor deposition method, etc.). It is done. In the wet method, for example, a coating agent (such as a solution or a dispersion) containing a manganese compound and a cobalt compound or a compound containing manganese and cobalt is used as one of separators (such as a microporous film or a nonwoven fabric) having a porous structure (or Manganese and cobalt can be contained by a coating method applied to both surfaces. Alternatively, a compound containing manganese and / or cobalt may be attached to one (or both) surfaces of the separator having a porous structure by a sol-gel method or a precipitation method. In the dry method, a compound containing manganese and / or cobalt may be deposited on one (or both) surfaces of the separator by the above-described vapor phase method. In this manner, by introducing manganese and / or cobalt from one (or both) surfaces of the separator, the respective probability of existence of manganese and cobalt in the positive region (or the positive region and the negative region) is increased. Can do.

In addition, a separator (a microporous film or a non-woven fabric) having a porous structure so that a film of a compound containing manganese and / or cobalt is formed on the surface of the substrate by the wet method or the dry method, and is in contact with the film. Etc.) and applying pressure to transfer the compound to the separator. It does not restrict | limit especially as a base material, The base material sheet formed with resin or a metal may be used, and an electrode may be used. The pressure at the time of transfer is, for example, 300 to 1300 gf / cm ² (≈0.3 to 1.3 MPa), and preferably 500 to 1000 gf / cm ² (≈0.5 to 1 MPa). By adjusting the amount of the compound applied to the substrate and / or the pressure during transfer, the probability of manganese and cobalt in the separator can be adjusted.

  When the above film is formed on the surface of the electrode and laminated with a separator having a porous structure, the film formed on the surface of the electrode is transferred to the electrode side of the separator when an electrode group or a battery is manufactured. Manganese and / or cobalt is introduced into at least the surface side region of the separator. When the above film is formed on the surface of the positive electrode, manganese and cobalt are introduced into at least the positive region by transfer, and when the above film is formed on the surface of the negative electrode, manganese and / or cobalt is introduced into at least the negative region by transfer. Is done. When the positive region and the negative region are formed by such a method, the presence of manganese and cobalt in each region is adjusted by appropriately adjusting the pressure applied to the electrode and the separator when producing an electrode group or a battery. Probability can be adjusted.

(Negative electrode)
The negative electrode includes a negative electrode active material, and the negative electrode active material includes a hydrogen storage alloy (more specifically, a hydrogen storage alloy powder) capable of electrochemically storing and releasing hydrogen. The negative electrode may include a core material and a negative electrode active material (or a negative electrode mixture layer including the negative electrode active material) attached to the core material. The negative electrode mixture may be added with known components used for the negative electrode of the nickel-metal hydride storage battery, such as a binder, a conductive agent, and / or a thickener, as necessary.

  When a negative electrode contains manganese and / or cobalt, manganese and / or cobalt may be contained in said well-known component and may be contained in the negative electrode active material.

The hydrogen storage alloy is not particularly limited as long as it can store hydrogen generated electrochemically in an alkaline electrolyte during charging and can easily release the stored hydrogen during discharge, and is known in the field of nickel metal hydride storage batteries. Can be used.
As the hydrogen storage alloy, an alloy containing Mn and / or Co (particularly, Mn and Co) is preferable. Even when such a hydrogen storage alloy is used, according to the embodiment of the present invention, self-discharge can be remarkably suppressed by using the separator as described above.

The hydrogen storage alloy generally includes an element having a high hydrogen affinity and an element having a low hydrogen affinity. Examples of the hydrogen storage alloy include A ₂ B ₇ type (or Ce ₂ Ni ₇ type), AB ₅ type (CaCu ₅ type or MmNi ₅ type (Mm represents Misch metal)), AB ₃ type (or CeNi). ₃ type) and / or AB ₂ type (such as MgCu ₂ type). In these crystal structures, an element having high hydrogen affinity tends to be located at the A site, and an element having low hydrogen affinity tends to be located at the B site. Mn and Co are both elements that are easily located at the B site.

Of these crystal structures, the A ₂ B ₇ type and / or the AB ₅ type are preferred. In a hydrogen storage alloy having an AB ₅ type crystal structure, when Mn is added, the equilibrium pressure of the hydrogen storage alloy is reduced and the capacity is easily increased, and when Co is added, the cycle life is easily improved. From these viewpoints, in many cases, Mn and Co are added to the hydrogen storage alloy having an AB ₅ type crystal structure. In such a hydrogen storage alloy, self-discharge tends to be a problem. By using the above separator, self-discharge can be suppressed even when a hydrogen storage alloy having such an AB ₅ type crystal structure is used as the negative electrode active material. Note that the hydrogen storage alloy having the AB ₅ type crystal structure has a main crystal structure of the AB ₅ type crystal structure, and may include other types of crystal structures as necessary.

  The hydrogen storage alloy preferably includes the element Ln and the element M, and further preferably includes Ni. Here, the element Ln is at least one selected from the group consisting of Group 3 elements and Group 4 elements in the periodic table. The element M is an element of the 4th to 6th period of the 5th to 6th group of the periodic table, an element of the 4th period of the 7th to 9th group and the group of the 11th to 12th groups, It is at least one selected from the group consisting of elements, B, and P. Further, the hydrogen storage alloy may contain an alkaline earth metal element such as Mg as necessary. Alkaline earth metal elements are mainly located at the A site. In the hydrogen storage alloy, the molar ratio of the alkaline earth metal element to the total of the element Ln and the alkaline earth metal element is, for example, 0.01 to 0.5.

  The element Ln is preferably at least one selected from the group consisting of Y, lanthanoid elements (La, Ce, Pr, Nd, Sm, etc.), Zr, and Ti. As the element Ln, a hydrogen storage alloy using a mixture of lanthanoid elements (Misch metal Mm) may be used. From the viewpoint of reducing costs, it is advantageous to use Mm, La and / or Ce or the like as the element Ln. The element Ln is mainly located at the A site.

  Ni has a low affinity for hydrogen and has a function of releasing hydrogen stored in the hydrogen storage alloy (that is, located at the B site). The molar ratio of Ni to the element Ln (the total of the element Ln and the alkaline earth metal element when an alkaline earth metal element is included) is preferably 3.3 to 4.2, and 3.5 to More preferably, it is 4.1. When the molar ratio of Ni is in such a range, it is easy to adjust the hydrogen storage amount and to improve the cycle life.

  The element M is, for example, at least one selected from the group consisting of Mn, Co, V, Nb, Ta, Cr, Mo, Fe, Ga, Cu, Zn, Sn, B, Al, In, Si, and P Is preferred. Among these, at least one selected from the group consisting of Mn, Co, V, Cr, Fe, Cu, Zn, B, and Al is preferable. The molar ratio of the element M to the element Ln (the total of the element Ln and the alkaline earth metal element when an alkaline earth metal element is included) is, for example, 0.01 to 1.8, preferably 0.1 to 1. 6.

The element M preferably includes at least one selected from the group consisting of Mn, Co, and Al.
Mn has a function of reducing the hydrogen equilibrium pressure of the hydrogen storage alloy and increasing the capacity. The molar ratio of Mn to the element Ln (the total of the element Ln and the alkaline earth metal element when an alkaline earth metal element is included) is preferably 0.28 to 0.5, preferably 0.3 to 0.00. More preferably, it is 45. When the molar ratio of Mn is in such a range, it is easy to optimize the hydrogen equilibrium pressure and secure a high capacity, and it is easy to improve the cycle life by suppressing the deterioration of the hydrogen storage alloy.

  Co has a function of suppressing the pulverization of the hydrogen storage alloy during charging and discharging and improving the cycle life. The molar ratio of Co to the element Ln (when the alkaline earth metal element is included, the sum of the element Ln and the alkaline earth metal element) is preferably 0.38 to 1, preferably 0.4 to 0.8. More preferably it is. When the molar ratio of Co is in such a range, it is easy to ensure a high hydrogen storage amount, and it is easy to improve the cycle life.

  Al has a function of increasing the capacity of the hydrogen storage alloy and improving the cycle life. The molar ratio of Al to the element Ln (the total of the element Ln and the alkaline earth metal element when an alkaline earth metal element is included) is preferably 0.28 to 0.5, and preferably 0.28 to 0.00. 4 is more preferable. When the molar ratio of Al is in such a range, it is easy to ensure a high hydrogen storage amount, which is advantageous for increasing the capacity, and it is easy to improve the cycle life by suppressing the pulverization and deterioration of the hydrogen storage alloy.

  As the negative electrode core material, known materials can be used, and examples thereof include a conductive porous or non-porous substrate formed of iron or an iron alloy (such as stainless steel), nickel or an alloy thereof. As the porous substrate, for example, a sheet-like substrate having a plurality of through holes in the thickness direction of the substrate can be used. Specific examples thereof include punching metal, metal powder sintered body, expanded metal, metal net (nickel Net etc.). The core material (for example, an iron core material) may be plated as necessary.

  The negative electrode mixture layer can be formed on at least the surface of the core material. The negative electrode mixture layer may be formed on one surface of the sheet-like core material, or may be formed on both surfaces. When the core material is porous, the negative electrode mixture layer may be formed by filling the pores of the core material with the negative electrode mixture.

  The negative electrode mixture layer can be formed by molding or adhering the negative electrode mixture to a core material. The negative electrode mixture is used in the form of a slurry or paste containing a dispersion medium. Specifically, the negative electrode mixture layer can be formed, for example, by applying the negative electrode mixture to the core material, removing the dispersion medium by drying, and rolling.

  As the dispersion medium, known media such as water, organic media, and mixed media thereof can be used. Examples of the organic medium include alkanols such as ethanol and isopropanol; aliphatic ketones such as acetone; aliphatic nitriles such as acetonitrile; ethers such as diethyl ether and tetrahydrofuran; N-methyl-2-pyrrolidone and the like. Although depending on the types of other components contained in the negative electrode mixture such as a binder, the dispersion medium preferably contains at least water.

  The binder has a role of binding the hydrogen storage alloy powder, the conductive agent and the like to each other or binding the core material. As the binder, resin materials (thermoplastic resins, thermosetting resins, etc.), for example, rubbery materials such as styrene-butadiene copolymer rubber (SBR); polyolefin resins such as polyethylene and polypropylene; polytetrafluoroethylene ( Examples thereof include fluororesins such as PTFE), tetrafluoroethylene copolymers, and polyvinylidene fluoride; acrylic resins such as ethylene-acrylic acid copolymers and ethylene-methacrylic acid copolymers, and Na ion crosslinked products thereof. A binder can be used individually by 1 type or in combination of 2 or more types. The amount of the binder is not particularly limited, but is, for example, 0.01 to 5 parts by mass, preferably 0.05 to 2 parts by mass with respect to 100 parts by mass of the negative electrode active material (preferably hydrogen storage alloy powder). It is.

  It does not specifically limit as a electrically conductive agent, Various electron conductive materials can be used. Specifically, graphite such as natural graphite (such as flake graphite), artificial graphite and expanded graphite; carbon black such as acetylene black and ketjen black; conductive fiber such as carbon fiber and metal fiber; metal such as copper powder Examples of powders: Organic conductive materials such as polyphenylene derivatives. A electrically conductive agent can be used individually by 1 type or in combination of 2 or more types. Of these, artificial graphite, carbon black such as ketjen black, and carbon fiber are preferable. The amount of the conductive agent is not particularly limited, but is, for example, 0.01 to 5 parts by mass, preferably 0.05 to 2 parts by mass with respect to 100 parts by mass of the negative electrode active material (preferably hydrogen storage alloy powder). is there.

  The conductive agent may be added to the negative electrode mixture and mixed with other components. In addition, a conductive agent may be previously coated on the surface of the negative electrode active material (specifically, the hydrogen storage alloy powder). The conductive agent may be coated by a known method, for example, by coating the surface of the hydrogen storage alloy powder with a conductive agent, attaching a dispersion containing the conductive agent to dry, or mechanically coating by a mechanochemical method or the like. It can be done by doing.

  The thickener imparts viscosity to the negative electrode mixture (slurry or paste negative electrode mixture). The thickener can be appropriately selected according to the type of the dispersion medium and the like. For example, carboxymethylcellulose (CMC) and modified products thereof (including salts such as Na salt), cellulose derivatives such as methylcellulose; polyacrylic acid Acrylic acid units such as polymethacrylic acid or acrylic resins having methacrylic acid units or salts thereof; saponified polymers having vinyl acetate units such as polyvinyl alcohol; polyalkylene oxides such as polyethylene oxide, and the like. These thickeners can be used singly or in combination of two or more. When the dispersion medium contains water, it is preferable to use one having a hydrophilic group such as a carboxyl group (or a salt thereof), a hydroxyl group, or a polyoxyethylene unit among the above thickeners. The amount of the thickener is, for example, 0.01 to 5 parts by mass, preferably 0.05 to 1 part by mass with respect to 100 parts by mass of the negative electrode active material (preferably hydrogen storage alloy powder).

  The negative electrode mixture layer may further contain a known additive such as an oxidation inhibitor. Examples of the oxidation inhibitor include yttrium oxide and ytterbium oxide. The amount of the additive is, for example, 0.01 to 5 parts by mass, preferably 0.05 to 1 part by mass with respect to 100 parts by mass of the negative electrode active material (preferably hydrogen storage alloy powder).

(Positive electrode)
The positive electrode includes a positive electrode active material containing a nickel compound. The positive electrode contains nickel hydroxide and / or nickel oxyhydroxide as a nickel compound. For example, the charged positive electrode contains at least nickel oxyhydroxide. As such a positive electrode, a known positive electrode of a nickel metal hydride storage battery can be used.

The positive electrode may include a core material and an active material or an active material layer attached to the core material. The positive electrode may be a positive electrode obtained by sintering active material powder, or may be a non-sintered positive electrode.
The positive electrode can be formed, for example, by attaching a positive electrode mixture (slurry or paste-like positive electrode mixture) containing at least a positive electrode active material to the core material. More specifically, the positive electrode can be formed by applying the positive electrode mixture to the core material, removing the dispersion medium by drying, and rolling.

  A well-known thing can be used as a positive electrode core material, The porous board | substrate formed with nickel or nickel alloys, such as a nickel foam and a sintered nickel board, can be illustrated. When a porous substrate is used as the positive electrode core material, the positive electrode mixture is filled in the pores of the positive electrode core material.

  The slurry or paste-like positive electrode mixture usually contains a dispersion medium, and a known component used for the positive electrode, for example, a conductive agent or a binder, may be added as necessary. As a dispersion medium, it can select suitably from what was illustrated about the negative mix.

  Examples of the binder include hydrophilic or hydrophobic polymers, and the negative electrode mixture may be appropriately selected from the exemplified binders or may be selected from those exemplified as the thickener. A binder can be used individually by 1 type or in combination of 2 or more types. The amount of the binder is, for example, 0.1 to 15 parts by mass, preferably 0.5 to 10 parts by mass with respect to 100 parts by mass of the positive electrode active material.

As a conductive agent, you may select from the conductive agent illustrated about the negative electrode mixture, and you may use electroconductive cobalt oxides, such as cobalt hydroxide and gamma-type cobalt oxyhydroxide. A electrically conductive agent can be used individually by 1 type or in combination of 2 or more types. The quantity of a electrically conductive agent is 0.1-10 mass parts with respect to 100 mass parts of positive electrode active materials, Preferably it is 0.5-5 mass parts.
The positive electrode mixture may contain a known additive, for example, a metal compound (oxide, hydroxide, etc.) such as zinc oxide, zinc hydroxide, cadmium compound (cadmium oxide, etc.).

  The positive electrode may contain manganese and / or cobalt as impurities or cobalt as a conductive agent. Thus, even when manganese and / or cobalt is contained in the positive electrode, self-discharge can be remarkably suppressed by using the separator.

(Alkaline electrolyte)
As the alkaline electrolyte, for example, an aqueous solution containing an alkali is used. Examples of the alkali include alkali metal hydroxides such as lithium hydroxide, potassium hydroxide and sodium hydroxide. These can be used singly or in combination of two or more, but it is preferable to use sodium hydroxide alone in order to suppress the self-discharge characteristics.

  The alkali concentration in the alkaline electrolyte is, for example, 3 to 10 mol / L, preferably 5 to 9 mol / L. The specific gravity of the alkaline electrolyte is, for example, 1.03 to 1.55, preferably 1.11 to 1.32.

(Other)
In the nickel metal hydride storage battery, the negative electrode, the positive electrode, and the separator are overlaid with the separator disposed between the positive electrode and the negative electrode. The negative electrode, the positive electrode, and the separator interposed therebetween may form an electrode group. The electrode group may be formed by further laminating a negative electrode, a positive electrode, and a separator disposed therebetween, or may be wound in a spiral shape.

  When a film of a compound containing manganese and / or cobalt is formed on the electrode surface and the electrode group is formed by winding or stacking, when manganese and / or cobalt is introduced into the separator, the electrode is separated between the electrode and the separator. The introduction of manganese and / or cobalt may be promoted by adjusting the stress. The stress applied to the separator can be expressed by, for example, the tension applied to the separator during winding, and the tension is, for example, 0.09 to 0.6 kg / cm, preferably 0.1 to 0.5 kg / cm, More preferably, it is 0.2-0.4 kg / cm.

  A nickel metal hydride storage battery includes battery elements such as a positive electrode, a negative electrode, a separator, and an alkaline electrolyte, and these battery elements are usually housed in a battery case. A nickel-metal hydride storage battery may be formed by housing a battery element in a battery case having an opening and sealing the opening with a sealing body.

Hereinafter, the configuration of the nickel-metal hydride storage battery will be described in more detail with reference to the drawings. However, the present invention is not limited to the following embodiments.
FIG. 1 is a schematic perspective view in which a part of a cylindrical nickel-metal hydride storage battery according to an embodiment of the present invention is cut away.
The nickel metal hydride storage battery includes a bottomed cylindrical battery case (exterior can) 1 having an opening at the upper end, an electrode group 11 accommodated in the battery case 1 and an alkaline electrolyte (not shown), and an opening of the battery case 1. And a sealing body 18 for sealing.

  The electrode group 11 includes a positive electrode 12, a negative electrode 13, and a separator 14 disposed between the positive electrode 12 and the negative electrode 13, both of which are band-shaped (long sheet-like). It has been turned. The outermost periphery of the electrode group 11 is a part of the negative electrode 13 (outermost peripheral portion), and the outermost peripheral portion of the negative electrode 13 is electrically connected by contacting the inner wall of the battery case 1. That is, the battery case 1 functions as a negative electrode terminal. In the upper part of the battery case 1, a ring-shaped groove 4 formed so as to protrude inward so as to make one round of the peripheral surface of the battery case is formed.

  A sealing body 18 that seals the opening of the battery case 1 includes a conductive lid plate 3 having a circular vent hole 8 in the center, a ring-shaped insulating packing 2 attached to the periphery of the lid plate 3, a lid A cap-shaped positive electrode having a cylindrical insulating (such as rubber) valve element 9 disposed at the center of the top surface of the plate 3 so as to close the gas vent hole 8 and a protrusion covering the valve element 9. And a terminal 10. The other end portion of the positive electrode lead 15 having one end portion connected to the positive electrode 12 of the electrode group 11 is welded to the inner bottom surface (the lower surface in FIG. 1) of the lid plate 3. The conductive cover plate 3 is in contact with the positive electrode terminal 10, and the positive electrode 12 and the positive electrode terminal 10 are electrically connected via the positive electrode lead 15 and the cover plate 3.

  In the battery case 1, a circular insulating member 17 is disposed between the electrode group 11 and the inner bottom surface of the battery case 1, and a circular insulating member is provided between the electrode group 11 and the sealing body 18. 16 is arranged. A part of the insulating member 16 is provided with a slit for connecting the positive electrode lead 15 to the lid plate 3 of the sealing body 18 through the positive electrode lead 15 led out from the electrode group 11.

  The sealing body 18 is disposed inside the opening of the battery case 1, and the opening end of the battery case 1 is caulked to the peripheral edge of the sealing body 18 via the insulating packing 2, whereby a nickel metal hydride storage battery is obtained. Is hermetically sealed. A sealing agent (sealing agent) 5 is disposed at a portion where the insulating packing 2 and the inner wall of the battery case 1 are in contact with each other for the purpose of improving the sealing performance. Known sealants such as blown asphalt, polybutene, polyamide, and mixtures thereof can be used.

  After sealing the battery case 1 with the sealing body 18, the diameter of the battery case 1 is reduced by pressing the peripheral surface of the battery case from the outside along the height direction of the battery while the sealing body 18 is pressed from above. After the diameter reduction, the groove portion 4 is crimped by reducing the width (distance in the vertical direction) of the ring-shaped groove portion 4 on the outer side of the battery case to within 0.2 mm. Adjust so that

  The outer peripheral portion of the sealing body 18, the peripheral surface of the battery case 1, and the peripheral portion of the bottom surface of the battery case 1 are covered with the exterior label 6. Between the peripheral edge of the sealing body 18 and the exterior label 6, a donut-shaped insulating member 7 is disposed.

  In the sealing body 18, the positive electrode terminal 10 has a protruding portion that protrudes outward (outward of the battery) and has a top surface 10 a at the center. A valve body 9 is accommodated inside the protruding portion, and the valve body 9 is formed of an insulating material such as rubber having elasticity. Therefore, the positive electrode terminal 10 presses the valve body 9 against the lid plate 3. Therefore, at normal times, the battery case 1 is sealed by the sealing body 18. When gas is generated in the battery case 1 and the internal pressure of the battery increases, the valve body 9 is compressed, the gas vent hole 8 is opened, and the gas is released from the inside of the battery. That is, the sealing body 18 not only seals the battery case 1 but also functions as a battery safety mechanism (safety valve).

  A predetermined amount of an alkaline electrolyte is injected into the battery, and a charge / discharge reaction proceeds between the positive electrode 12 and the negative electrode 13 through the alkaline electrolyte contained in the separator 14.

  EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example and a comparative example, this invention is not limited to a following example.

Example 1
An AA cylindrical nickel-metal hydride storage battery having a capacity of 1900 mAh was produced by the following procedure.
(1) Fabrication of negative electrode Predetermined so that each of La, Ce, Ni, Co, Mn, and Al has a composition of the hydrogen storage alloy obtained is La _0.40 Ce _0.60 Ni _3.63 Co _0.76 Mn _0.42 Al _0.29 In an ingot melting furnace, an ingot was produced from the melt. The obtained ingot was heated in an argon atmosphere at 1000 ° C. for 10 hours to obtain an alloy ingot. The heated ingot was pulverized into coarse particles. The obtained coarse particles were further mechanically pulverized and classified in an inert gas atmosphere to obtain hydrogen storage alloy powder (La _0.40 Ce _0.60 Ni _3.63 Co _0.76 Mn _0.42 Al _0.29 having an average particle size of about 45 μm. ) Was produced.

  For 100 parts by mass of the obtained hydrogen storage alloy powder, 0.7 parts by mass of SBR as a binder, 0.15 parts by mass of CMC as a thickener, 0.3 parts by mass of ketjen black as a conductive agent, oxidation A negative electrode mixture slurry was prepared by adding 0.7 parts by mass of yttrium oxide as an inhibitor and adding and mixing an appropriate amount of water. SBR was used in the form of a dispersion containing 48% by mass of SBR and 52% by mass of ion-exchanged water.

  The obtained negative electrode mixture slurry was applied to both surfaces of an iron punching metal (thickness 60 μm, hole diameter 1 mm, hole area ratio 42%) having a nickel plating on the surface as a negative electrode core material. After the coating film of the negative electrode mixture slurry is dried at 95 ° C. for 10 minutes, the coating film is rolled together with the core material so that the total thickness of the core material and the negative electrode mixture layer is 0.28 to 0.32 mm. Was pressed to form a negative electrode plate. The obtained product was cut to have a width of 44.7 mm and a length of 134.0 mm.

(2) Production of positive electrode A non-sintered nickel positive electrode was produced by the following procedure.
First, nickel hydroxide powder containing 2.5% by mass of zinc and 1.0% by mass of cobalt as a coprecipitation component was added to an aqueous cobalt sulfate solution. While stirring the resulting mixture, an aqueous sodium hydroxide solution (sodium hydroxide concentration: 1 mol / L) was gradually added dropwise to adjust the pH to 11, followed by further stirring for a predetermined time. The precipitate was filtered off from the resulting mixture. The precipitate separated by filtration was washed with water and vacuum-dried to obtain a powder in which the surface of nickel hydroxide particles was coated with 5% by mass of cobalt hydroxide.

  10 parts by mass of an aqueous sodium hydroxide solution (sodium hydroxide concentration: 48% by mass) was added to 1 part by mass of the powder obtained above. The resulting mixture was heat-treated at 85 ° C. for 8 hours with stirring, then washed with water and dried at 65 ° C. By this heat treatment, in the layer containing cobalt hydroxide on the surface of the nickel hydroxide particles, a part of cobalt hydroxide is made higher-order and converted into cobalt oxyhydroxide, and sodium is introduced. In this way, composite particles in which a coating layer containing cobalt oxyhydroxide and 1% by mass of sodium was formed on the surface of the nickel hydroxide particles were obtained.

  By adding and mixing 25 parts by mass of an aqueous solution (CMC concentration: 0.2% by mass) containing CMC as a binder to 100 parts by mass of the obtained composite particles and zinc oxide mixed powder, A positive electrode mixture slurry was prepared. The mass ratio of the composite particles and zinc oxide in the mixed powder was 100: 2.

The obtained positive electrode mixture slurry was filled in pores of a nickel foam (surface density (unit weight) of about 325 g / m ² , thickness of about 1.2 mm) as a positive electrode core material and dried. The dried product was rolled to a thickness of 0.78 mm, and then cut into dimensions of 44.7 mm in width and 95.0 mm in length to obtain a positive electrode.
In addition, the exposed part of the core material which does not hold | maintain an active material was provided in one edge part along the longitudinal direction of a positive electrode core material, and the positive electrode lead was connected to this exposed part.

(3) Production of separator A dispersion liquid was prepared by mixing manganese hydroxide, cobalt hydroxide, and ethanol in a mass ratio of 2: 1: 45 using an ultrasonic homogenizer (amplitude 80 μm, frequency 20 kHz). Was prepared.
The dispersion liquid was applied to one surface of a plastic film as a substrate at a coating amount of 1 to 100 mg / cm ² and dried to form a film containing manganese hydroxide and cobalt hydroxide. This membrane and one surface of a PP nonwoven fabric (average thickness 100 μm, weight per unit area 48 g / m ² ) made hydrophilic by plasma treatment are superimposed on each other, and pressure (800 gf / cm ² (≈0.8 MPa)) is applied. Then, manganese hydroxide and cobalt hydroxide contained in the film were transferred to one surface of the nonwoven fabric, and manganese and cobalt were introduced into the separator from one surface side.

(4) Production of nickel-metal hydride storage battery The separator obtained in (3) above is disposed between the negative electrode obtained in (1) above and the positive electrode obtained in (2) above. The electrode group was produced by winding in a shape. At this time, it arrange | positioned so that the surface of the side which introduce | transduced manganese and cobalt of the separator might contact the surface of a positive electrode.

  The obtained electrode group was inserted into an AA bottomed cylindrical metal battery case (outer diameter 14.25 mm) having a ring-shaped groove on the opening side, and the outermost negative electrode was connected to the inner surface of the battery case. Contact. Moreover, the positive electrode lead connected to the positive electrode was welded to the inner bottom surface of the cover plate of the sealing body. The sealing body is arranged so as to close the gas vent hole at the center of the top plate of the lid plate having a circular vent hole at the center, the insulating packing attached to the periphery of the lid plate, and the lid plate. And a cap-like positive electrode terminal having a protrusion that covers the valve body.

  Next, an alkaline electrolyte was injected into the battery case, the opening of the battery case was covered with a sealing body, and sealed by insulating caulking. By pressing the peripheral surface of the battery case from the outside, the outer diameter was reduced to 14.00 mm. And the groove part formed in the opening part side of the battery case was crimped | bonded so that a battery total height might be set to 50.25 mm by pressing a battery case in a height direction. As the alkaline electrolyte, an aqueous solution containing sodium hydroxide at a concentration of 7.5 mol / L was used.

  On the upper part of the sealing body, a donut-shaped insulating member was disposed in a state where the protruding portion of the positive electrode terminal protruded from the central hole of the insulating member. Next, by attaching an exterior label so as to cover the peripheral part of the sealing body (peripheral part of the insulating member disposed on the sealing body), the peripheral surface of the battery case, and the peripheral part of the bottom surface of the battery case A nickel metal hydride storage battery (A1) was obtained. A total of 18 batteries A1 were produced in the same procedure.

(5) Evaluation (a) Distribution state of manganese and cobalt in the separator The battery was charged with a charging current of 0.2 C for 8 hours under an environmental temperature of 25 ° C., and 1.0 V with a discharging current of 0.7 C. The battery was discharged to the final voltage of 2 and this charge / discharge cycle was repeated three times to perform the charge-in / discharge.

  The three batteries were charged for 6.5 hours at an ambient temperature of 25 ° C. and a charging current of 0.2 C after running-in and charging. By disassembling this charged battery, taking out the separator, and analyzing the cross section in the thickness direction with EPMA, the distribution state of cobalt and manganese in each region of the separator (specifically, the presence of cobalt and manganese) Probability). Further, in the EPMA analysis, the areas of the manganese region and the cobalt region were determined in each of the positive side region and the negative side region of the separator, and the ratio (%) at which these regions overlap was determined.

(B) Self-discharge during storage For three of the remaining batteries used in (a) above, after charge-in / discharge, the batteries were charged for 16 hours at an ambient temperature of 20 ° C. and a charging current of 0.1 C. Then, after resting for 60 minutes, the battery was discharged to a final voltage of 0.9 V with a discharge current of 0.2 C, and the discharge capacity (initial discharge capacity) at this time was determined. Next, the battery was charged at an ambient temperature of 20 ° C. with a charging current of 0.1 C for 16 hours, and the charged battery was stored at an ambient temperature of 65 ° C. After storing the battery for 7 days, the discharge capacity was measured, and the ratio of the discharge capacity after storage to the initial discharge capacity (capacity maintenance ratio (%)) was determined as the average value of the three batteries. In the case where the battery storage period was changed to 14th, 21st, 28th, and 35th, respectively, the capacity retention rate was determined in the same manner as described above.

Comparative Example 1
In Example 1, (3), a dispersion was prepared by mixing cobalt hydroxide and ethanol in a mass ratio of 1:15. A separator having cobalt introduced into one surface side (positive side region) was formed in the same manner as in Example 1 except that the obtained dispersion was used. A nickel-metal hydride storage battery (B1) was produced and evaluated in the same manner as in Example 1 except that the obtained separator was used.

Comparative Example 2
In Example 1, (3), a dispersion was prepared by mixing manganese hydroxide and ethanol in a mass ratio of 1:15. A separator having manganese introduced into one surface side (positive side region) was formed in the same manner as in Example 1 except that the obtained dispersion was used. A nickel-metal hydride storage battery (B2) was produced and evaluated in the same manner as in Example 1 except that the obtained separator was used.

Comparative Example 3
A nickel-metal hydride storage battery as in Example 1 except that the separator formed in the same manner as in Example 1 (3) was placed so that the surface on which manganese and cobalt were introduced was in contact with the surface of the negative electrode. (B3) was prepared and evaluated. That is, in battery B3, manganese and cobalt are introduced into the negative region of the separator. About the negative side area | region of a separator, the same procedure as the case of the positive side area | region of Example 1 calculated | required the existence probability of manganese and cobalt, and calculated | required the area ratio (%) which a manganese area | region overlaps with a cobalt area | region.

Comparative Example 4
In Example 1 (3), the nonwoven fabric was made in the same manner as in Example 1 except that a nonwoven fabric made of PP hydrophilized by plasma treatment (first nonwoven fabric, average thickness 50 μm, basis weight 20 g / m ² ) was used. Manganese and cobalt were introduced on one surface of the film. Then, a separator is produced by superimposing a PP nonwoven fabric (second nonwoven fabric, average thickness 40 μm, basis weight 15 g / m ² ) made hydrophilic by plasma treatment on the surface of the first nonwoven fabric on which manganese and cobalt are introduced. did. In this way, a separator containing manganese and cobalt was formed in the central region. A nickel-metal hydride storage battery (B4) was produced and evaluated in the same manner as in Example 1 except that the obtained separator was used.

Example 2
In Example 1, (3), a separator was formed by introducing manganese and cobalt from the other surface side in the same manner as the one surface side of the nonwoven fabric. A nickel-metal hydride storage battery (A2) was produced and evaluated in the same manner as in Example 1 except that the obtained separator was used. The separator includes manganese and cobalt in both the positive region and the negative region. For the negative region, the probability of existence of manganese and cobalt was determined in the same procedure as for the positive region, and the area ratio of the manganese region overlapping with the cobalt region was determined.

Example 3
In Example 1 (3), after introducing manganese and cobalt on one surface side of the nonwoven fabric, on the other surface side, by introducing cobalt using cobalt hydroxide in the same manner as in Comparative Example 1, A separator was formed. A nickel-metal hydride storage battery (A3) was produced in the same manner as in Example 1 except that the obtained separator was used, and evaluated in the same manner as in Examples 1 and 2.

Example 4
In Example 1 (3), after introducing cobalt and manganese on one surface side of the nonwoven fabric, on the other surface side, by introducing manganese using manganese hydroxide in the same manner as in Comparative Example 2, A separator was formed. A nickel-metal hydride storage battery (A4) was produced in the same manner as in Example 1 except that the obtained separator was used, and evaluated in the same manner as in Examples 1 and 2.
The results of Examples and Comparative Examples are shown in Table 1.

  As shown in Table 1, compared with comparative batteries B1 and B4 using separators containing a large amount of manganese and cobalt in the negative region or the central region, implementation using separators containing manganese and cobalt in the positive region In the example battery A1, self-discharge was greatly suppressed even after storage for a long period of time (for example, 28 days or 35 days) in a high temperature environment of 65 ° C. The effect of such an example cannot be obtained even when a separator containing only manganese or cobalt in the positive region is used (batteries B2 and B3). From these results, it can be seen that it is important to contain both manganese and cobalt in the positive region of the separator in order to suppress self-discharge.

  From the results of the batteries A2 to A4 of the example, when a separator containing manganese and cobalt in the positive side region and manganese and / or cobalt in the negative side region is used, it is comparable to or more than the battery A1. It was found that self-discharge was suppressed. If the negative side region contains both manganese and cobalt, the self-discharge suppressing effect is enhanced.

  In the nickel metal hydride storage battery according to the embodiment of the present invention, self-discharge during storage can be greatly suppressed. Therefore, the nickel metal hydride storage battery is particularly suitable for use as an emergency power source, a backup power source, or the like.

DESCRIPTION OF SYMBOLS 1 Battery case 2 Insulation packing 3 Cover plate 4 Groove part 5 Sealant 6 Exterior label 6a The surface of the exterior label distribute | arranged to the peripheral part of the sealing body 7 Donut-shaped insulating member 8 Gas vent 9 Valve body 10 Positive electrode terminal 10a Positive electrode Top surface of protruding portion of terminal 11 Electrode group 12 Positive electrode 13 Negative electrode 14 Separator 15 Positive electrode lead 16 Insulating member with slit 17 Circular insulating member 18 Sealing body

Claims (9)

A positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; a separator interposed between the positive electrode and the negative electrode; and an alkaline electrolyte.
The negative electrode active material includes a hydrogen storage alloy capable of electrochemically storing and releasing hydrogen,
The positive electrode active material includes a nickel compound,
At least one of the positive electrode and the negative electrode contains manganese,
At least one of the positive electrode and the negative electrode contains cobalt,
The separator has a thickness T and contains manganese and cobalt;
The separator includes a positive side region having a thickness of 0.35T including the surface on the positive electrode side, a negative side region having a thickness of 0.35T including the surface on the negative electrode side, and a thickness other than the positive side region and the negative side region. When partitioning into a central region with 0.3T,
The positive side existence probability of the manganese in the region X _MNP, and the presence of manganese probability in the central region X _Mnc satisfies X _Mnp> X _Mnc,
The nickel hydride storage battery in which the cobalt existence probability X _Cop in the positive region and the cobalt existence probability X _Coc in the central region satisfy X _Cop > X _Coc . _Ratio of X _Mnp and X _Mnc : X _Mnc / X _Mnp satisfies X _Mnc / X _Mnp ≦ 0.2,
The ratio of the X _Cop and X _Coc: X _Coc / X _Cop satisfies X _Coc / X _Cop ≦ 0.2, nickel-metal hydride storage battery according to claim 1. Wherein among the positive-side region, said the existence probability X _Mnpa manganese in the region A having a thickness of 0.2T including the surface of the positive electrode side, the existence probability X _Mnpb manganese in the region B other than the area A of the positive-side region _Satisfies X _Mnpa > X _Mnpb ,
_3. The nickel-metal hydride storage battery according to claim 1, wherein the cobalt existence probability X _Copa in the region A and the cobalt existence probability X _Copb in the region B satisfy X _Copa > X _Copb . X _Mnpa to X _Mnpb ratio: X _Mnpb / X _Mnpa satisfies X _Mnpb / X _Mnpa ≦ 0.5,
_4. The nickel-metal hydride storage battery according to claim 3, wherein the ratio of X _Copa to X _Copb : X _Copb / X _Copa satisfies X _Copb / X _Copa ≦ 0.5.   5. The nickel-metal hydride storage battery according to claim 1, wherein, in the positive region, 20% or more of the area of the manganese region in which manganese is distributed overlaps with the cobalt region in which cobalt is distributed.   The nickel hydride storage battery according to any one of claims 1 to 5, wherein the negative region includes manganese and / or cobalt. The separator includes manganese in at least one form selected from the group consisting of a manganese compound and a manganese cobalt composite compound,
The nickel hydride storage battery according to any one of claims 1 to 6, wherein the separator includes cobalt in at least one form selected from the group consisting of a cobalt compound and a manganese cobalt composite compound.   The nickel hydrogen storage battery according to claim 1, wherein the hydrogen storage alloy includes manganese and cobalt. The nickel hydrogen storage battery according to claim 1, wherein the hydrogen storage alloy has an AB ₅ type crystal structure.

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