JP2005235494A - Positive pole for nickel-hydrogen storage battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To attain high output and to suppress reduction of storage characteristics involved in a charge-and-discharge cycle, in a positive pole for a nickel-hydrogen storage battery in which a positive pole active material is held by a positive pole supporter. <P>SOLUTION: In the positive pole for the nickel-hydrogen storage battery in which the positive pole active material is held by the positive pole supporter, a densified metal portion 3 is formed by a process such as welding a metal plate to an outer peripheral edge of the positive pole supporter 1. The densified metal portion 3 may be provided so that it may form a lattice shape inside the outer peripheral edge of the positive pole supporter 1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a positive electrode used for a nickel-hydrogen storage battery.

  As a nickel electrode used for a nickel-hydrogen storage battery, a so-called sintered electrode and a non-sintered electrode are known. The sintered electrode is an electrode obtained by impregnating a sintered substrate formed by sintering nickel powder on a core body such as a punching metal and impregnating a nickel salt solution into an active material by alkali treatment. The non-sintered electrode is an electrode in which an active material slurry is directly filled in a porous metal body having a three-dimensional network structure such as foamed nickel (nickel sponge). In these electrodes, it is desired to increase the output. In Patent Document 1, a band-shaped metal plate is attached to the current collecting tab attachment portion of the sintered electrode, or the core of the non-sintered electrode. It describes that metal alkoxide is adhered to the current collector tab mounting portion of the porous metal body to form a high-density metal portion.

However, in recent years, nickel-hydrogen storage batteries for hybrid electric vehicles, which are rapidly spreading, are desired to have higher output, and it is hoped to suppress the deterioration of storage characteristics due to cycles. It is rare.
JP 2001-283863 A

  The objective of this invention is providing the positive electrode for nickel hydrogen storage batteries which can aim at high output and can suppress the fall of the storage characteristic accompanying a charging / discharging cycle.

  The present invention is a nickel-hydrogen storage battery positive electrode in which a positive electrode active material is held on a positive electrode support, and the outer peripheral edge of the positive electrode support has a high metal density.

  As a result of investigating the cause of deterioration in storage characteristics after progress of a cycle at a high current density in a nickel-hydrogen storage battery, the present inventors found that only the part of the separator close to the positive electrode current collector had cobalt eluted from the electrode. It has been found that the cause is that the compound is deposited in a large amount locally and the insulation of the separator is lowered. This precipitation of cobalt or the like is presumably due to the fact that the electrode reaction concentrates in the vicinity of the current collector during charge and discharge at a high current density because the conductivity of the positive electrode current collector is low. Moreover, it seems that heat is accumulated in the vicinity of the current collector because the positive electrode current collector has low thermal conductivity.

  In accordance with the present invention, by increasing the metal density at the outer peripheral edge of the positive electrode support (positive electrode current collector), the electrode reaction can be performed uniformly in the electrode, and the precipitation of compounds such as cobalt is suppressed. Can do. For this reason, high output can be achieved and the storage characteristics after the charge / discharge cycle can be improved.

  Moreover, in this invention, it is preferable to provide so that a high metal density-density part may also become a grid | lattice also inside the outer periphery part of a positive electrode electrical power collector. In particular, when the area of the positive electrode support is large, it is preferable that the high-density metal density portions are provided in a lattice shape. The specific aspect of providing the high metal density portion in a grid pattern is to increase the metal density so that the upper and lower sides and / or the left side and the right side of the high metal density portion provided on the outer peripheral edge are opposed to each other. The aspect which provides a part in linear form is mentioned.

  In the present invention, when the area of the high metal density portion is A and the area of the whole positive electrode support is B, the high metal density portion is formed so as to satisfy the condition of A ≦ 0.4B. It is preferable. By forming the high metal density portion so as to satisfy this condition, a storage battery having both output and battery capacity can be obtained.

  The positive electrode for nickel-hydrogen storage battery of the present invention may be a so-called sintered positive electrode or a non-sintered positive electrode.

  When the positive electrode of the present invention is a sintered positive electrode, punching metal can be used as the positive electrode support. One method for forming the high metal density portion on the punching metal is to weld a metal plate to the punching metal. As another method, in the punching metal, there is a method of forming the high metal density portion by not forming the punching portion. Therefore, for example, by using a punching metal in which no punching portion is formed on the outer peripheral edge portion, a high metal density portion can be formed on the outer peripheral edge portion. As still another method, the metal-enriched portion may be formed by increasing the thickness of the outer peripheral edge of the punching metal.

  When the positive electrode of the present invention is a non-sintered positive electrode, a porous metal body having a three-dimensional network structure such as foamed nickel (nickel sponge) can be used as the positive electrode support. One method for forming the highly metal densified portion in the porous metal body is to weld a metal plate to the porous metal body. As another method, a method of forming a high metal density portion by increasing the basis weight of a part of the metal porous body can be mentioned. Still other methods include a method disclosed in Patent Document 1 in which a metal alkoxide is deposited and then this portion is heat-treated.

  In accordance with the present invention, the reaction in the electrode can be made uniform by forming the high metal density portion on the outer peripheral edge of the positive electrode support. In addition, the thermal conductivity of the positive electrode support can be increased. For this reason, elution of cobalt or the like due to partial overdischarge of the positive electrode can be suppressed, high output can be obtained, and storage characteristics after the charge / discharge cycle can be improved.

  Hereinafter, an experiment that has been found about the cause of the deterioration of the storage characteristics after the cycle progresses will be described.

(Reference experiment)
(Production of negative electrode)
Hydrogen storage alloy particles represented by a composition formula MmNi _3.2 Co _1.0 Al _0.7 Mn _0.1 (where Mm is a misch metal composed of La: Ce: Pr: Nd = 25: 50: 6: 19 (weight ratio)) (average Punching metal in which 1.0 part by weight of PEO (polyethylene oxide) as a binder and a small amount of water are added to 100 parts by weight of a particle size of 50 μm and mixed uniformly to prepare a paste. A hydrogen storage alloy electrode was produced by uniformly applying to both sides of the (current collector), drying, and rolling.

[Production of positive electrode]
First, a nickel sintered substrate having a porosity of 85% was impregnated with a nickel nitrate aqueous solution containing cobalt nitrate and zinc nitrate by a chemical impregnation method, and filled with a positive electrode active material. Then, after impregnating it in a 3% by weight yttrium nitrate aqueous solution, it was immersed in a 25% NaO aqueous solution at 80 ° C. and coated with yttrium hydroxide on the active material filled on the nickel sintered substrate. A layer was formed to prepare a nickel positive electrode. The amount of yttrium hydroxide at this time was about 3% with respect to the total filling amount combined with the active material.

[Production of nickel-hydrogen storage battery]
Using the above-described negative electrode and positive electrode and using a polyolefin resin nonwoven fabric as a separator, a spiral electrode body in which the positive electrode, the separator, and the negative electrode are spirally wound is prepared, and this spiral electrode body is placed in the battery can. Then, a 30 wt% potassium hydroxide aqueous solution was poured into the battery can, and then sealed to produce a cylindrical sealed nickel-hydrogen storage battery having a capacity of about 1000 mAh.

[Activation of nickel-hydrogen storage batteries]
The above nickel-hydrogen storage battery was charged at 100 mA for 15 hours under a temperature condition of 25 ° C., then discharged to 1.0 V at 1000 mA, and this was regarded as one cycle, and 5 cycles of charge / discharge were repeated, Activated.

  The nickel-hydrogen storage battery obtained as described above was measured for storage characteristics immediately after activation and after 10,000 cycles. Cycle conditions and measurement conditions for storage characteristics are as follows.

(Cycle test conditions)
The battery was charged at 1000 mA up to 400 mAh (charge depth 40%). Then, 200 mAh charge and 200 mAh discharge were performed at 10 A, and the cycle was repeated with the charge and discharge at 10 A as one cycle. However, since the charging efficiency is lower than the discharging efficiency, the charging depth reached in the first charging decreases with the cycle. Then, after performing the charge depth adjustment of discharging until the battery voltage became 1.0 V every 1000 cycles and charging again to 400 mAh (charge depth 40%), the cycle at 10 A was repeated again.

(Measurement conditions for storage characteristics)
The storage characteristics of each battery before and after the cycle test were measured as follows.

  After being charged at 500 mA for 1.6 hours at 25 ° C., it was discharged to 1.0 V at 500 mA. Thereafter, the battery was again charged at 500 mA at 25 ° C. for 1.6 hours, then left in a 45 ° C. atmosphere for 7 days, and then discharged at 25 ° C. and 500 mA to 1.0 V. For the discharge capacity before and after discharge in a 45 ° C. atmosphere, the capacity retention rate was defined as in the following equation, and the storage characteristics of each battery were evaluated by comparing the capacity retention rates.

Capacity retention rate = (discharge capacity after standing in 45 ° C. atmosphere) / (discharge capacity before standing in 45 ° C. atmosphere)
Table 1 shows the storage characteristics (capacity maintenance ratio) of each battery before and after the cycle.

表１に示す結果から明らかなように、サイクル後の容量維持率は、サイクル前と比べ急激に低下している。従って、サイクルの進行により、保存特性が著しく悪くなることがわかる。

As is clear from the results shown in Table 1, the capacity retention rate after the cycle is drastically decreased as compared to before the cycle. Therefore, it can be seen that the storage characteristics are remarkably deteriorated as the cycle progresses.

  In order to investigate the cause, the separators before and after the cycle were observed, and the presence of black-brown precipitates was confirmed in both the separators before and after the cycle. However, before the cycle, the precipitate was present almost uniformly throughout the separator, but after the cycle, a large amount of precipitate was concentrated in the portion near the positive electrode current collector of the separator. It was confirmed that FIG. 5 is a photograph showing this separator. As shown in FIG. 5, a large amount of precipitates exist in the vicinity of the upper end.

  Next, the amount of cobalt was measured by fluorescent X-ray measurement for the following portions of the separator before and after the cycle.

・ Before cycle: A part close to the positive electrode current collector (3 mm from the current collector)
Before cycle: Intermediate part between the positive electrode current collector and the negative electrode current collector (a part 20 mm from the positive electrode current collector and the negative electrode current collector)
-After cycle: Part close to the positive electrode current collector (3 mm from the current collector)
-After cycle: Intermediate part between the positive electrode current collector and the negative electrode current collector (a part 20 mm from the positive electrode current collector and the negative electrode current collector)
The measurement results are shown in Table 2. In this measurement, the higher the numerical value, the more cobalt is present.

表２に示す結果から明らかなように、サイクル後のセパレータの正極集電体に近い部分において、多量のコバルトが析出していることが確認された。このコバルトは、高電流でのサイクル進行に伴い、正極の部分的な過放電により還元されたコバルト、及びアルカリ電解液によって負極の合金が酸化され、合金から溶出したものであると考えられる。この溶出したコバルトが、セパレータ上に析出することにより、セパレータの絶縁性が低下することによって、保存特性が悪くなっていたものと考えられる。

As is clear from the results shown in Table 2, it was confirmed that a large amount of cobalt was deposited in a portion near the positive electrode current collector of the separator after the cycle. It is considered that this cobalt is eluted from the alloy by oxidation of the alloy of the negative electrode by cobalt reduced by partial overdischarge of the positive electrode and the alkaline electrolyte as the cycle progresses at a high current. It is considered that the storage characteristics were deteriorated due to a decrease in the insulating properties of the separator due to precipitation of the eluted cobalt on the separator.

  The reason why cobalt concentrates and precipitates in this part is that partial overdischarge of the positive electrode due to reaction concentration in the vicinity of the current collector, and further the temperature in the vicinity of the current collector becomes high, and the oxidation deterioration rate of the negative electrode alloy This is considered to be because a large amount of cobalt is eluted and a large amount of cobalt precipitates locally in this portion.

  Such disproportionation of the reaction is considered to be caused by the concentration of the reaction in the vicinity of the current collector of the electrode because the conductive resistance in the positive electrode current collector (positive electrode support) is large.

  In the present invention, by forming a metal-enriched portion at the outer peripheral edge of the positive electrode current collector (positive electrode support), the reaction in the electrode is made uniform, and such local precipitation of cobalt is prevented. Can be suppressed. For this reason, high output can be achieved and the storage characteristics after the cycle can be improved. In addition, since the heat conductivity is improved by forming the high metal density portion, the heat diffusion rate in the battery can be increased without accumulating heat in the vicinity of the current collector, and the elution of cobalt. Can be suppressed. Therefore, this also increases the output and improves the storage characteristics after the cycle.

(Example)
FIG. 1 is a front view showing a positive electrode support (positive electrode current collector) of one embodiment according to the present invention. The positive electrode in this example is a sintered positive electrode, and the punching metal 1 is used as the positive electrode support. A punching portion 2 is formed on the punching metal 1. As the punching metal 1, a punching metal made of nickel (Ni) is used. The punching metal 1 has a thickness of 0.10 mm, and the punching portion 2 has a hole area ratio of 30%. Moreover, the vertical dimension of the punching metal 1 is 42 mm, and the horizontal dimension is 130 mm. The volume of the punching metal 1 is 0.38 cm ³ .

In this embodiment, a nickel (Ni) plate is spot-welded to the outer peripheral edge of the punching metal 1 to form the high metal density portion 3. The highly metal densified portion 3 is preferably formed continuously as shown in FIG. The welded nickel plate has a thickness of 0.20 mm and a width of 3 mm. The area of the highly metal densified portion 3 is 9.96 cm ² , its thickness is 0.40 mm, and its volume is 0.3984 cm ³ .

  The volume of the metal at the outer peripheral edge of the positive electrode support in the case where the high metal density portion is formed and in the case where the high metal density portion is not formed is as follows.

When a high metal density portion is formed: 9.96 (cm ² ) × 0.040 (cm) +9.96 (cm ² ) × 0.010 (cm) × 0.70 = 0.468 (cm ³⁾ )
When not forming a high metal density portion: 9.96 (cm ² ) × 0.010 (cm) × 0.70 = 0.070 (cm ³ )
Therefore, by forming the high metal density portion, the metal volume becomes about 7 times and the electric resistance becomes about 1/7 at the outer peripheral edge of the positive electrode support. Moreover, the volume of the metal in the outer periphery part of a positive electrode support body is about 0.47 cm < ³ > as mentioned above, and exceeds the volume (0.38 cm < ² >) of the whole punching metal. Therefore, more than half of the current flowing from the upper part of the electrode to the lower part in the conventional case in which the high metal density part is not formed passes through the outer peripheral edge of the electrode due to the formation of the high metal density part. It is possible to promote the reaction at the lower part of the electrode where the reaction hardly occurs during charging and discharging.

  The Joule heat generated by the resistance of the positive electrode support is defined by the following equation.

Joule heat (P) = current (I) x current (I) x resistance (R)
The resistance in this case is determined by the volume of the metal if the same kind of metal is used. Therefore, the total amount of heat generated can be reduced to half or less by forming a high metal density portion at the outer peripheral edge. Furthermore, since most of the heat generated is generated at the outer peripheral edge of the electrode that easily dissipates heat to the outside of the battery, it is possible to prevent heat from being accumulated inside the electrode and to suppress the temperature rise of the battery. .

  As the area of the high metal density portion increases, the conductivity improves, but the active material capacity decreases. Here, the reactivity (output) of the electrode depends on the conductivity of the positive electrode support and the reactivity of the active material (= active material amount). A / B (high metal density ratio) when the area of the high metal density portion is A and B is the area of the entire positive electrode support, and the output (output when A / B = 0) is 1. The relative output value) is as shown in Table 3 and FIG.

出力と電池容量を共に兼ね備えた設計とするためには、表３及び図４に示すように、高金属密度化部分の面積Ａと正極支持体全体の面積Ｂの関係は、Ａ≦０．４Ｂであることが好ましく、さらに好ましくは０．１Ｂ≦Ａ≦０．３Ｂである。

In order to achieve a design that combines both output and battery capacity, as shown in Table 3 and FIG. 4, the relationship between the area A of the high metal density portion and the area B of the entire positive electrode support is A ≦ 0.4B. It is preferable that 0.1B ≦ A ≦ 0.3B.

  In the above embodiment, the nickel metal plate is welded to form the high metal density portion, but instead of Ni, other metals that are stable in an alkaline aqueous solution such as Ag, Au, Pt, and Fe are used. May be used. Moreover, you may use the metal which gave Ni plating etc. on the surface.

  FIG. 2 is a front view showing a positive electrode support in another embodiment according to the present invention. In the present embodiment, the high metal density portion 3 is formed on the outer peripheral edge of the punching metal 1, and the high metal density portion 4 is formed in the vertical direction so as to connect the upper end and the lower end of the punching metal 1, The high metal density portions 3 and 4 are provided in a lattice shape.

  FIG. 3 is a front view showing a positive electrode support in yet another embodiment according to the present invention. In the present embodiment, the highly metal-enriched portion 4 is formed in the vertical direction, and a linear metal-enriched portion 5 that connects the opposing side ends of the punching metal 1 is further formed.

  As shown in FIGS. 2 and 3, by providing the high metal density portion in a lattice shape, the reaction in the electrode can be made more uniform, and the storage characteristics can be further improved.

The front view which shows the positive electrode support body of one Example according to this invention. The front view which shows the positive electrode support body of the other Example according to this invention. The front view which shows the positive electrode support body of the further another Example according to this invention. The figure which shows the relationship between high metal density ratio (A / B) and an output. The front view which shows the state of the separator which cobalt precipitated.

Explanation of symbols

1 ... Punching metal 2 ... Punching part 3, 4, 5 ... High metal density part

Claims (9)

  A positive electrode for a nickel / hydrogen storage battery, wherein the positive edge support has a high metal density in the outer peripheral edge of the positive electrode for a nickel / hydrogen storage battery in which a positive electrode active material is held on the positive electrode support.   2. The nickel-hydrogen storage battery positive electrode according to claim 1, wherein high-density metal density portions are also provided inside the outer peripheral edge of the positive electrode support so as to form a lattice pattern.   When the area of the high metal density portion is A and the area of the whole positive electrode support is B, the high metal density portion is formed so as to satisfy the condition of A ≦ 0.4B. The positive electrode for a nickel-hydrogen storage battery according to claim 1 or 2.   The positive electrode for nickel-hydrogen storage battery according to any one of claims 1 to 3, wherein the positive electrode support is a punching metal used for a sintered positive electrode.   5. The nickel-hydrogen storage battery positive electrode according to claim 4, wherein the metal-enriched portion is formed by welding a metal plate to a punching metal.   5. The positive electrode for a nickel-hydrogen storage battery according to claim 4, wherein the high metal density portion is formed by not forming a punching portion in the punching metal.   The positive electrode for nickel-hydrogen storage battery according to any one of claims 1 to 3, wherein the positive electrode support is a porous metal body having a three-dimensional network structure used for a non-sintered positive electrode. .   The positive electrode for nickel-hydrogen storage battery according to claim 7, wherein the high-metal density portion is formed by welding a metal plate to a metal porous body. The positive electrode for a nickel-hydrogen storage battery according to claim 7, wherein the high metal density portion is formed by increasing the basis weight of a part of the metal porous body.

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