JPH08329956A - Current collector for battery electrode, nickel electrode using it - Google Patents

Abstract

(57) [Abstract] [Purpose] Battery electrode with excellent strength characteristics, capable of performing stable spot welding of ear terminals, improving the current collecting function of the electrode, and thus increasing the utilization rate of the active material. And a nickel electrode using the same. [Structure] In this current collector, a non-woven fabric core made of organic fibers is nickel-plated, and the nickel plating amount is 350 g / m ² or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a current collector for an electrode incorporated in an alkaline secondary battery and a nickel electrode using the same. More specifically, it has high strength and flexibility and low electric resistance. The present invention relates to a current collector for a battery electrode, which can increase the utilization rate of a filled electrode active material, and a nickel electrode using the same.

[0002]

2. Description of the Related Art For example, a nickel electrode incorporated as a positive electrode in an alkaline secondary battery such as a nickel-cadmium battery or a nickel-hydrogen battery is a positive electrode for causing a current collector that shares a current collecting function to cause a battery reaction. It is constituted by supporting an active material. In that case, a sintered nickel plate or a punched nickel sheet has been widely used as the current collector. However, recently, in order to increase the packing density of the active material in the current collector with the demand for smaller size and higher capacity of the battery, the porosity is large and therefore the packing density of the active material can be increased. Three-dimensional net-like structures have begun to be adopted as current collectors.

This current collector having a three-dimensional network structure is usually formed by subjecting a urethane resin foam sheet or a non-woven fabric of organic fibers to known nickel plating, and then firing it in a reducing atmosphere to produce the urethane resin or Pyrolytically removes organic fibers,
It is manufactured by leaving the plated nickel as a reticulated skeleton. For this current collector,
The electrode is manufactured by crushing the place where the ear terminal is attached, filling the whole void with the active material mixture paste, and spot-welding a crushed place with, for example, a nickel piece.

The above collector has a porosity of 90 to 9
Since it is as large as 8%, it is advantageous for high-density packing of the active material mixture paste. In addition, the filled active material is firmly supported and is useful for manufacturing a high capacity battery.
However, since the current collector has a too large porosity, it cannot be said that the strength characteristics are good. Therefore, when manufacturing an electrode using this as a current collector and incorporating it into a battery, Problem is caused.

First, when the active material mixture paste is filled in the current collector, a process of press-fitting the highly viscous active material mixture paste from the surface of the current collector to a space inside by a predetermined pressure. Is given. Further, after the active material mixture paste is filled, the active material mixture paste is dried, and then subjected to rolling treatment for densification or adjustment of the electrode thickness, and then cut into a predetermined size. Is processed.

In the case of the above-mentioned current collector having inferior strength characteristics, when the applied pressure is increased for the purpose of increasing the packing density of the active material mixture paste, the buckling occurs during these series of steps and during the transfer to each step. Otherwise, it may break and become a defective product. Such a problem can be avoided by reducing the applied pressure, but at that time, it becomes difficult to realize high-density filling of the active material mixture paste.

When the strength characteristics of the current collector are low, when the manufactured electrode is wound together with the negative electrode and the separator and inserted into a bottomed cylinder to assemble a cylindrical battery, the reticulated skeleton of the current collector is It often breaks to generate protrusions such as cracks and fuzz on the outer peripheral surface of the electrode. When such a state occurs, these protrusions may break through the separator and cause an internal short circuit with the negative electrode.These protrusions also increase the electrical resistance of the electrode and reduce the current collecting function of the current collector. This may deteriorate the charge / discharge characteristics of the assembled battery.

In order to solve the above problems,
It suffices to enhance the strength characteristics of the current collector having a three-dimensional network structure. In that case, the ratio of the nickel network skeleton of the current collector may be increased to improve its strength characteristics. However, if such a structure is adopted, the porosity of the current collector becomes small as a whole, so that the packing density of the active material mixture paste is inevitably low, which is inconvenient for assembling a high capacity battery.

In order to solve such a problem, the following current collectors are disclosed in JP-A-55-30180 and JP-A-3-17957. That is, as the current collector, a urethane resin foam sheet or a polyolefin fiber nonwoven fabric is nickel-plated, and only the surface of the skeleton portion exhibits conductivity without thermally decomposing and removing the skeleton portion of these organic substances. This is a possible three-dimensional network structure.

This current collector does not require thermal decomposition and removal of the skeleton portion and has excellent strength characteristics, and cracks in the outer peripheral portion are reduced when the electrode is wound using the current collector. It can be said that it is more useful than the current collector composed only of the nickel network skeleton. However, this collector also has the following problems.

First, when a nickel electrode of a nickel-hydrogen battery is manufactured using this current collector, its active material is nickel hydroxide, so that it does not exhibit a sufficient current collecting function and has a high capacity. It was difficult to assemble the battery. Also, when attaching the ear terminal to the electrode, the nickel plating on the surface may be crushed and the organic skeleton may be exposed when the attachment point is crushed, so satisfactory welding strength can be obtained during spot welding of nickel pieces. Not again,
The electric resistance of the welded part increases, and problems such as the situation where these ear terminals are peeled off in the subsequent handling process and the utilization rate of the active material carried is reduced.

[0012]

DISCLOSURE OF THE INVENTION The present invention solves the above problems in a current collector produced without thermally decomposing and removing an organic core, and has excellent strength characteristics, good flexibility, and active material. High-density filling of mixture paste is possible,
By improving the current collecting function of the manufactured electrode, the utilization rate of the active material can be increased, and further, the work of attaching the ear terminals can be easily performed, and the current collector for the battery electrode and the same are used. The purpose is to provide a nickel electrode.

[0013]

Means for Solving the Problems As a result of intensive studies conducted by the present inventors in order to achieve the above-mentioned object, the amount of nickel plated on a non-woven fabric core depends on the performance of the obtained current collector. The fact that it has a great influence was found, and the appropriate amount of the nickel plating amount was examined to develop the current collector of the present invention.

That is, the current collector for battery electrodes of the present invention is a current collector in which a non-woven fabric core made of organic fiber is nickel-plated, and the nickel plating amount is 350 g / m ^2. The above is the feature, and the nickel electrode of the present invention is characterized in that the above-mentioned current collector carries an active material mixture mainly composed of nickel hydroxide.

The current collector of the present invention comprises a non-woven fabric core described later and a nickel-plated layer that covers the surface of the skeleton portion of the organic fibers that compose it. First, the non-woven fabric core is
It is manufactured by making organic fibers. Examples of the organic fibers used include polyester fibers, polyolefin fibers, polyvinyl chloride fibers, polyacrylonitrile fibers, polyamide fibers, polyvinyl alcohol fibers,
Examples thereof include urethane type fibers and cellulosic type fibers. Of these, polyolefin-based fibers such as polypropylene fibers and polyethylene fibers, which have excellent alkali resistance, are suitable, and in particular, a core-sheath type composite in which the core part is made of polypropylene and the periphery is a polyethylene sheath part. Fibers are suitable because they can simultaneously satisfy both alkali resistance and strength characteristics.

Examples of the method for producing these organic fibers into paper include, for example, a card method or an air-laying method in which the fibers are once made into short fibers and then formed into a sheet, or a melt blow method or a spun bond in which the fibers are continuously formed into a sheet from a spinning state. A dry method such as a method; a wet method in which organic fibers are dispersed in water and the resulting paper is made; and the like. At this time, it is preferable that the paper-made nonwoven fabric has a porosity of 90% or more. If the porosity is smaller than 90%,
Although the strength characteristics of the obtained non-woven fabric are improved, the packing density of the active material mixture paste is lowered, and as a result, the performance as the electrode current collector of the high capacity battery is deteriorated. However, if the porosity is too high, the strength properties will be significantly reduced, and buckling or breakage will be caused by the applied pressure when the active material mixture paste is filled in manufacturing the electrode. Papermaking is preferably performed so that the rate is 90 to 98%.

The non-woven fabric core in the present invention may be the one after the above-mentioned paper making as it is, but it is preferably used after the strength property is enhanced by the following entanglement treatment or heat treatment. As the entanglement treatment, for example, a hydroentanglement treatment or a needle punch entanglement treatment can be adopted. When the non-woven fabric is entangled, the organic fibers are entangled with each other, increasing the number of contact points between the fibers, improving their strength characteristics, and also reducing the thickness, and further adjusting the porosity to an appropriate value. You can also do it.

The heat treatment is performed to locally fuse the organic fibers in the non-woven fabric at the points of contact with each other to improve the overall strength characteristics. However, when the heat treatment is performed at a temperature equal to or higher than the thermal decomposition temperature of the organic fiber, the organic fiber is thermally decomposed and disappears. Therefore, the treatment temperature needs to be set to a temperature lower than the thermal decomposition temperature. is there.

Therefore, the treatment temperature is set to a temperature range lower than the thermal decomposition temperature of the organic fiber and higher than the melting point of the organic fiber, but if the temperature is too low within the temperature range,
Since the heat fusion between the organic fibers cannot be said to be sufficient, the strength (rigidity) of the obtained non-woven fabric core becomes low, and buckling or the like begins to occur when the active material mixture paste is filled. Further, if the temperature is too high, the melting of the organic fibers proceeds and the porosity decreases, which also lowers the packing density of the active material mixture paste.

When the above-mentioned core-sheath type composite fiber is used as the organic fiber, the temperature during the heat treatment is preferably 120 to 140 ° C. The entanglement treatment and the heat treatment may be performed independently, but it is preferable to perform the entanglement treatment and then the heat treatment because the strength characteristics of the obtained nonwoven fabric core are significantly improved.

The non-woven fabric core thus obtained is provided with electroconductivity on the surface of the skeleton portion of the core by electroless nickel plating or nickel vapor deposition, and electrolytic nickel plating is further applied if necessary. Then, the surface of the skeleton part of the core body is coated with the nickel plating layer to obtain the current collector of the present invention. At this time, the plating amount of nickel is 35
It is necessary to set it to 0 g / m ² or more.

The nickel plating amount here means
The value obtained by subtracting the weight of the core body before nickel plating from the weight of the current collector after nickel plating to calculate the nickel plating amount and dividing the value by the area of one surface of the current collector. When the plating amount is less than 350 g / m ² , the current collecting function of the current collector is not sufficiently exhibited, and it becomes insufficient to increase the utilization rate of the active material to be supported, and at the same time, the current collector. Is not sufficient, and further, the welding strength at the time of spot welding of the ear terminal is not sufficiently increased or varies greatly, and further, the electric resistance of the welded portion is increased.

However, if the amount of plating is excessively large, the porosity of the current collector decreases, making it difficult to fill the active material mixture paste with a high density and to obtain a high capacity battery. For this reason, the amount of nickel plating needs to be 350 g / m ² or more, but in this case, it is preferable to limit the maximum amount to about 600 g / m ² in relation to the porosity. .

By controlling the nickel plating amount to the above-mentioned value, the resulting current collector has a specific resistance of 0.6 mΩ · cm or less as a whole, and has a good current collecting function. Even when the ear terminal is spot-welded, the resistance value of the entire welded portion is 5.5 mΩ or less, which is useful.

[0025]

The current collector of the present invention is coated with nickel so that the surface of the skeleton of the non-woven fabric core is plated with 350 g / m ² or more. Functions are surely secured. Therefore, the utilization rate of the active material carried can be sufficiently increased, and spot welding of the ear terminals can be smoothly performed.

Further, since the strength characteristics are excellent, the occurrence of cracks and the like on the outer peripheral surface can be suppressed during winding when the electrode is incorporated in a cylindrical battery.

[0027]

Examples of the invention

Examples 1 to 7 and Comparative Examples 1 to 4 A polyolefin-based composite fiber (Cisso ESC, polypropylene in the core, polyethylene in the sheath) having a fiber length of 2 d (fiber diameter of about 18 μm) and a fiber length of 51 mm is used, and a cross layer of the card method is used. 40 g / m ² , basis weight 70
Two types of nonwoven webs of g / m ² were prepared.

After hydroentangling these non-woven webs, they were subsequently left in a hot air oven at a temperature of 140 ° C. for 5 minutes to be heat-treated to obtain non-woven fabric cores. Then,
Each non-woven fabric core was electrolessly nickel-plated by a conventional method and then electrolytically nickel-plated in a watt bath to produce a current collector having the plating amount shown in Table 1. With respect to these current collectors, the tensile strength, thickness, porosity, and specific resistance were measured according to the following specifications.

Tensile strength (kg / mm ² ): Length 100
mm and width of 20 mm, both ends of a strip-shaped sample were chucked by a tensile tester, and the sample was cut when the sample was cut by pulling in the longitudinal direction at a speed of 5 mm / min. Thickness (mm): The thickness at 5 positions of the current collector is measured, and the average value thereof is calculated.

Porosity (%): The apparent volume (υml) is calculated from the size and shape of the current collector. On the other hand, the volume occupied by nickel (υ ₁ ml) is calculated from the amount of nickel plating and the specific gravity of nickel described above, and the volume occupied by fibers (υ ₂ ml) is calculated from the amount of fibers constituting the core and its specific gravity. Then, it is calculated based on the following formula: (υ−υ ₁ −υ ₂ ) × 100 / υ (%).

Specific resistance (mΩ · cm): Measured by the two-end needle method.
In this method, a current having a current value (I) is applied to both ends of a sample having a length (L), a width (W), and a thickness (t), and two samples are provided on the surface of the central part of the sample at intervals (1). When the platinum needle is touched. The voltage (V) between platinum needles is measured.

The specific resistance (ρ) of the sample at this time is calculated based on the following equation: ρ = VWt / Il In the present invention, L: 30 mm,
W: 10 mm, t: measured value described above, I: 50 μA,
l: Each value was set to 10 mm, V was measured, and the ρ value was calculated for each of the L and W directions of the current collector based on the above formula.

The above results are shown in Table 1. Next, each current collector was cut into a length of 75 mm and a width of 45 mm, and the ear attachment portion (length 6 mm, width 6 mm portion) of each cut piece was crushed in the thickness direction until the thickness became 0.15 mm, As a whole, the active material mixture paste density consisting of 92.5 parts by weight of nickel hydroxide, 7.5 parts by weight of cobalt oxide, and 36 parts by weight of 1.0% carboxymethylcellulose aqueous solution had a density of 2.1 to 2.2 g.
/ Cm ³ so that the roll diameter is 30
Using a rolling roll of mm, roll rolling was performed so that a pressure of 2 ton / cm was applied in the width direction to obtain an electrode plate.

Nickel pieces (length 17.5 mm, width 4 mm, thickness 0.09 m) were attached at the ear terminal attachment points of the obtained electrode plates.
m) and place NRW-15T (Nippon Avionics Co., Ltd.)
Spot welder manufactured by
Under the condition of weld time 3, spot welding was performed at 5 positions to obtain nickel electrodes. With respect to these nickel electrodes, the resistance of the welded portion and the resistance of the active material were measured according to the following specifications.

Resistance of welded part (R: mΩ): I (= 50 μA) current is applied between both electrodes with the negative electrode of the ammeter connected to the ear terminal and the positive electrode connected to the end of the nickel electrode. To do. Then, fix one terminal of the voltmeter to the ear terminal, and in this state, connect the other terminal to the spot weld (5
The voltage (V _S1 , V _S2 ,
V _S3 , V _S4 , V _S5 ) is measured, and the other side of the voltmeter is also contacted with the other side of the spot weld (5 points) (which is the surface of the nickel electrode) (the voltage at that time). V _R1 ,
V _R2 , V _R3 , V _R4 , and V _R5 ) are respectively measured, and the value calculated by the following equation is defined as the weld resistance (R).

[0036] _{R = {(V R1 -V S1} ) + (V R2 -V S2) +
_{(V R3 -V S3) + (} V R4 -V S4) + (V R5 -V S5)} /
Resistance of 5 × I active material (Ra: mΩ · cm ² ): Complies with the current interrupter method. In this method, K with a concentration of 30% by weight is used.
The nickel electrode and the reference electrode (H
g / HgO) and a counter electrode made of Pt are immersed and a direct current I (= 0.7 A) is applied between the nickel electrode and the counter electrode so that the nickel electrode has a positive potential. Then, the potential fluctuations of the nickel electrode and the reference electrode are measured with an oscilloscope, the potential drop (ΔV) displayed on the oscilloscope immediately after the current I is cut off is measured, and the resistance of the active material (Ra ) Is calculated.

Ra = ΔV · S / I (where S represents the area of one surface of the nickel electrode. In the present invention, it is 4.1 × 7.2 cm ² ) The above results are shown in Table 1. Then, a hydrogen storage alloy electrode is overlaid on each nickel electrode via a separator and wound so that the nickel electrode is on the inside, and the rated capacity is 1100 m.
An Ah nickel-hydrogen secondary battery was assembled.

At this time, no crack or the like was generated on the nickel electrode. Temperature 2 for each battery obtained
After the initial activation treatment at 0 ° C., the utilization rate of the active material after 10 cycles at 1 C was measured. Utilization rate (%): Temperature of 20 after initial activation treatment
Charging 15 hours at 110mAh and 220m at ℃
A charging / discharging test in which discharging was performed until the battery voltage reached 1 V with Ah as one cycle was performed, and the discharge capacity (mAh) at the 10th cycle was measured and calculated based on the following equation.

R (%) = C × 100 / g · 289 (where C is the measured discharge capacity (mAh), g is the weight of nickel hydroxide supported on the nickel electrode (g), and 289 is water) Theoretical capacity of nickel oxide (mAh /
The above results are shown in Table 1.

[0040]

[Table 1]

As is clear from Table 1, regardless of the basis weight of the non-woven fabric core, when the nickel plating amount was 350 g / m ² , the current collector had a large tensile strength and a large specific resistance. And its conductivity is improved. For example, comparing Example 1 and Comparative Example 2, the specific resistance of the current collector of Example 1 is about 20% lower than that of Comparative Example 1. As for the resistance of the manufactured nickel electrode at the welded portion of the ear terminal, the nickel plating amount of the current collector was 35%.
When it is less than 0 g / m ² , the resistance increases extremely and the measured resistance of the supported active material also increases. That is,
When the plating amount is 350 g / m ² or more, the strength characteristics of the current collector are improved, and the specific resistance is very small, so the current collecting function is improved, and the active material of the obtained nickel electrode is The utilization rate can be increased.

[0042]

As is apparent from the above description, the current collector for a battery electrode of the present invention has excellent strength characteristics and small specific resistance even though the porosity is about 90%. Good function. Then, when the ear terminal is spot-welded, the resistance of the welded portion becomes low. Therefore, the electrode (nickel electrode) manufactured using this current collector has an excellent current collecting function, and the utilization rate of the active material is improved.

These are the effects brought about by plating the surface of the skeleton part of the nonwoven fabric core with nickel so that the plating amount is 350 g / m ² or more.

Front Page Continuation (72) Inventor Masatoshi Ito Hakusaku, Joban Shimo-Funao, Iwaki City, Fukushima Prefecture 23-6 Furukawa Battery Co., Ltd. Iwaki Plant (72) Takahiro Imai Hakusawa, Joban Shimo-Funao, Iwaki City, Fukushima Prefecture 23-6 Furukawa Battery Co., Ltd. Iwaki Plant (72) Inventor Isao Ebihara 3-4-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Paper Co., Ltd. (72) Shun Yamada 3--4 Marunouchi, Chiyoda-ku, Tokyo No. 2 Sanryo Paper Co., Ltd. (72) Inventor Kenji Hyodo 3-4-2 Marunouchi, Chiyoda-ku, Tokyo Sanryo Paper Co., Ltd. (72) Toshio Horie 2-6-1 Marunouchi, Chiyoda-ku, Tokyo Furukawa Electric Co., Ltd.

Claims (4)

[Claims] 1. A current collector in which a non-woven fabric core made of organic fiber is nickel-plated, wherein the nickel plating amount is 350 g / m ² or more. Current collector. 2. The current collector for a battery electrode according to claim 1, wherein the total specific resistance is 0.6 mΩ · cm or less. 3. The current collector for a battery electrode according to claim 1, wherein when the ear terminal is spot-welded, a resistance value of the welded portion is 5.5 mΩ or less. 4. A nickel electrode, wherein the current collector according to claim 1 carries an active material mixture mainly composed of nickel hydroxide.