JP2006073292A - Negative electrode plate for alkaline storage battery and alkaline storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an alkaline storage battery in which rise of internal pressure at the abnormal charging is fundamentally suspended and there happens no deformation of battery and which is reliable. <P>SOLUTION: Expanded graphite is added to a negative electrode plate for the alkaline storage battery. Specifically, either expanded graphite is added into a mixture layer made of a hydrogen storage alloy, or a layer made of expanded graphite is formed on the mixture layer. By utilizing an internal short circuit occurring due to expansion of the expanded graphite accompanying temperature rise of the battery and increase in the thickness of the negative electrode plate, charging is stopped and rise of internal pressure is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an alkaline storage battery, and more particularly to a technique for improving the reliability of a device.

  Alkaline storage batteries are widely used as power sources for portable devices as rechargeable batteries. Among them, nickel-hydrogen storage batteries using hydrogen storage alloys as negative electrode active materials have high energy density and are relatively clean in terms of the environment. Therefore, they are being developed in high power fields such as power tools and HEVs. In recent years, there has been a demand for further shortening the charging time for the purpose of improving convenience.

  In order to shorten the charging time, it is necessary to increase the charging current. However, when the charging current increases, the polarization increases according to the internal resistance, and oxygen gas is easily generated at the positive electrode. Normally, hydrogen in the hydrogen storage alloy reacts with oxygen gas generated at the positive electrode and is reduced to water. However, if the gas generation reaction is accelerated due to malfunction of the charger or malfunction of the battery, the above-mentioned Since the reduction reaction is difficult to be established, the battery internal pressure increases with an increase in battery temperature.

If the increase in internal pressure is significant, it will lead to deformation of the battery and the device containing it. In order to avoid this, conventionally, a technique has been proposed in which a safety valve provided on the sealing plate is operated when the internal pressure exceeds a certain level, and the generated gas is discharged to the outside (for example, Patent Document 1).
JP-A-9-237619

  However, in the conventional technology such as Patent Document 1, when a sudden increase in internal pressure occurs due to abnormal charging that occurs when an abnormality occurs in the device, the operation of the safety valve does not follow, and the battery is likely to be deformed.

  The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to fundamentally interrupt an increase in internal pressure during abnormal charging and to improve battery reliability.

  In order to solve the problems of the prior art, the negative electrode plate for an alkaline storage battery according to the present invention adds expanded graphite to a mixture layer made of a hydrogen storage alloy or expands on a mixture layer made of a hydrogen storage alloy. A layer made of graphite is formed.

  During abnormal charging, the expanded graphite disposed on the negative electrode plate expands as the temperature rises due to overcharging of the battery, increasing the thickness of the negative electrode plate. As a result, the negative electrode penetrates the separator and comes into contact with the positive electrode plate, causing an internal short circuit. Since the charging current is converted into a short-circuit current due to an internal short circuit, the charging reaction is stopped, and an increase in internal pressure due to gas generation from the positive electrode is suppressed.

  According to the present invention, since the charging reaction that is the source of the gas generation reaction can be stopped, the increase in the internal pressure during abnormal charging can be fundamentally interrupted, and the reliability of the battery can be improved.

  Hereinafter, the best mode for carrying out the present invention will be described in detail.

  Unlike normal graphite, expanded graphite, which is the gist of the present invention, can be expanded at a predetermined temperature by inserting a volatile material between the layers. Examples of the volatile material that can be inserted between the layers include sulfuric acid. The expansion start temperature and the expansion volume can be controlled by the type and the addition amount of these volatile materials.

  The expanded graphite described above may be added to a mixture layer made of a hydrogen storage alloy in the negative electrode plate, or may be formed as an expanded graphite layer on the mixture layer. As a method of adding expanded graphite to the mixture layer, it is common to add a hydrogen storage alloy when kneading with a binder or a thickener. Examples of the method for forming the expanded graphite layer on the mixture layer include a method of directly spraying expanded graphite powder, a method of spraying in the form of a slurry, and a method of applying in the form of a paste.

  The negative electrode plate with expanded graphite intervening is composed of a hydrogen storage alloy, which is an active material, as an essential component, and is formed by applying a mixture paste to a two-dimensional current collector and a three-dimensional porous current collector. Some of them are formed by filling an agent slurry. Any of these may be selected, but particularly when expanded graphite is added to the mixture layer, from the viewpoint of effectively dispersing the expanded graphite in the mixture, it is kneaded together with a binder and a thickener. It is preferable to prepare an agent paste and apply it to a two-dimensional current collector.

The hydrogen storage alloy is not particularly limited, general formula _{MmNi 5-x} M _X (Mm is a mixture of light rare earth elements, M = Co, Mn, Al , Fe, Cu , etc.) having composition represented by are preferred. The hydrogen storage alloy powder is preferably in the range of 20 to 30 μm in view of characteristics. In addition, from the viewpoint of stabilizing paste properties and battery characteristics and ensuring structural strength as an electrode plate, it is also possible to add appropriate amounts of a conductive agent, a binder and a thickener to the hydrogen storage alloy powder. As the conductive agent, it is desirable to add hard carbon such as acetylene black and ketjen black (hereinafter abbreviated as KB). As the binder, it is desirable to add a styrene-butadiene rubber copolymer (hereinafter abbreviated as SBR), polyvinyl alcohol or the like. Furthermore, it is desirable to use a cellulose derivative such as carboxymethylcellulose (hereinafter abbreviated as CMC) as a thickener.

  When an alkaline storage battery is configured using the above-described negative electrode, an electrode group is configured by facing a positive electrode plate made of a metal oxide via a separator. The positive electrode plate includes a two-dimensional current collector formed by sintering a mixture, and a positive electrode plate formed by filling a three-dimensional porous collector with a mixture slurry. Nickel hydroxide is mainly used as the metal oxide, and a conductive agent such as cobalt oxyhydroxide can be added as necessary. Moreover, a nonwoven fabric is generally used as the separator, and the material can be selected from polypropylene (hereinafter abbreviated as PP) that is stable in a battery environment.

Hereinafter, examples of the negative electrode plate of the present invention will be described.
Example 1
As a negative electrode material was used AB ₅ type hydrogen-absorbing alloy based on a rare earth element and nickel. The specific composition was MmNi _3.55 Mn _0.40 Al _0.30 Co _0.75 , which was synthesized by a melting method and then heat-treated at 1000 ° C. for 1 hour in an inert atmosphere. The alloy lump was mechanically pulverized to adjust the average particle size to about 25 μm, and then the alloy powder was immersed and stirred in a KOH aqueous solution at a specific gravity of 1.30 at 80 ° C. for 60 minutes. For 100 parts by weight of this hydrogen storage alloy powder, 0.2 part by weight of CMC as a thickener, 0.5 part by weight of KB as a conductive agent, 1.0 part by weight of SBR as a binder, and the present invention Expanded graphite (manufactured by Hebei Shigeru Chemical Co., Ltd., volatile material: sulfuric acid) was added and kneaded with water to prepare a negative electrode mixture paste.

  This negative electrode mixture paste was applied to both surfaces of a core material having a thickness of 0.03 mm obtained by plating nickel on an iron punching foil, and a negative electrode plate having a mixture layer was produced through a drying and pressing process.

The dimensions of the negative electrode plate are 35 mm in length and 320 mm in length, and the end on one side with a width of 2 mm extending in the longitudinal direction is a plain part of the core material to which no mixture layer is applied. The width was 1 mm and the thickness was 0.06 mm. This is the negative electrode plate of Example 1.
(Example 2)
For Example 1, without adding expanded graphite to the negative electrode mixture paste, 1.0 part by weight of SBR as a binder and 0.2 part by weight of CMC as a thickener were added to 100 parts by weight of the expanded graphite. Thus, a paste was prepared, and a negative electrode plate was prepared in the same manner as in Example 1 except that expanded graphite was coated on the negative electrode mixture layer. This is the negative electrode plate of Example 2.
(Comparative Example 1)
A negative electrode plate was produced in the same manner as in Example 1, except that expanded graphite was not added to the negative electrode mixture paste. This is the negative electrode plate of Comparative Example 1.

Using the negative electrode plate of each example described above, a nickel-hydrogen storage battery was fabricated according to the following procedure.
(Preparation of positive electrode plate)
As the positive electrode material, spherical nickel hydroxide powder whose surface was coated with cobalt oxyhydroxide was used. The cobalt oxyhydroxide was 10 parts by weight per 100 parts by weight of nickel hydroxide. To 100 parts by weight of the powder, 0.3 part by weight of PTFE as a binder and 0.2 part by weight of CMC as a thickener were added and kneaded with water to prepare a positive electrode mixture paste.

  As the positive electrode core material, a nickel foam substrate, which is a three-dimensional porous collector, was used. After filling the substrate with the positive electrode mixture paste, a positive electrode plate having an active material layer was produced through drying and pressing processes.

The positive electrode plate had a length of 35 mm and a length of 260 mm, and a one-side end portion with a width of 3 mm extending in the longitudinal direction formed a core material uncoated portion with a thickness of 0.5 mm to which no active material was applied. This plain portion was made to have a width of 1 mm and a thickness of 0.3 mm by further compressing it twice in order to give strength during current collector plate welding.
(Production of battery)
The above-mentioned positive electrode plate was spirally wound together with the negative electrode plate via a PP nonwoven fabric having a thickness of 150 μm and a basis weight of 60 g / m 2 as a separator to constitute an electrode group. The negative electrode is exposed on the outermost periphery of this electrode group, and the end portions formed thick by folding the plain portion of the positive electrode core material and the negative electrode core material are exposed on both surfaces of the electrode group, respectively. A spiral positive electrode lead and a negative electrode lead are formed. The spiral positive and negative electrode leads were connected to a nickel current collector plate by known resistance welding, respectively, so that current could be collected from the positive electrode plate and the entire end in the longitudinal direction of the negative electrode plate.

  After this electrode group is inserted into a metal case, each current collector plate is connected to the positive electrode terminal and the negative electrode terminal with leads, and a predetermined amount of an electrolytic solution in which 40 g / L LiOH is dissolved in a KOH aqueous solution having a specific gravity of 1.30 is injected. did. Thereafter, a sealing plate with a safety valve was placed on the upper part of the case and sealed by caulking to produce a cylindrical sealed nickel-hydrogen storage battery having an outer diameter of 23 mm, a height of 43 mm, and a nominal capacity of 3 Ah. The battery was charged at 0.1 C (1 C = 300 mA) for 15 hours and then discharged and charged at 0.2 C for 6 hours twice, then aging at 45 ° C. for 3 days (promoting activation of the negative electrode alloy) Went.

The batteries of the above-described examples were evaluated by the following methods.
(Abnormal charge test)
Twenty batteries in each example were continuously charged at 7C. Table 1 shows the average value of the short circuit start time when the drop of the closed circuit voltage was observed. In addition, Table 1 shows the number of batteries in which the above-described expansion of the battery is observed as a modified battery.

従来電池である比較例１は、異常充電試験において連続的に充電された結果、電池内圧の急激な上昇のため安全弁が追従できず、電池が全数変形する結果となった。これに対し膨張黒鉛を負極に配置した実施例１および２は、電池変形の回避が可能となった。この理由として、異常充電時の発熱に伴って膨張黒鉛を含む負極板が膨張し、セパレータを貫通して正極板と接触して内部短絡が起こることにより充電反応が停止し、正極からのガス発生が抑止されたものと考えられる。

Comparative Example 1, which is a conventional battery, was continuously charged in the abnormal charging test, and as a result, the safety valve could not follow due to a sudden rise in the internal pressure of the battery, resulting in a total deformation of the battery. On the other hand, Examples 1 and 2 in which expanded graphite was arranged on the negative electrode made it possible to avoid battery deformation. The reason for this is that the negative electrode plate containing expanded graphite expands due to heat generation during abnormal charging, contacts the positive electrode plate through the separator, and the charging reaction stops, causing gas generation from the positive electrode. Is thought to have been suppressed.

  Since the alkaline storage battery using the negative electrode plate of the present invention does not deform the battery even if abnormal charging occurs when the device has an abnormality, it is very useful as a power source for portable devices that require rapid charging. It is valid.

Claims (3)

  A negative electrode plate for an alkaline storage battery having a mixture layer made of a hydrogen storage alloy, wherein expanded graphite is added to the mixture layer.   A negative electrode plate for an alkaline storage battery having a mixture layer made of a hydrogen storage alloy, wherein a layer made of expanded graphite is formed on the mixture layer.   An alkaline storage battery having an electrode group composed of a positive electrode plate made of a metal oxide, a negative electrode plate made of a hydrogen storage alloy, and a separator, wherein the negative electrode plate according to claim 1 is used as the negative electrode plate. An alkaline storage battery.