JPH11121010A - Hydride secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydride secondary battery having an increased paste nickel positive electrode capacity, and excellent in a cycle characteristic and an overdischarging characteristic. SOLUTION: This secondary battery is equipped with a positive electrode having a nickel hydroxide active material, a negative electrode comprising a hydrogen storage alloy, electrolyte comprising alkaline aqueous solution, and a separator. In the nickel powder contained in the positive electrode, primary particles are spherical, the aggregation of the primary particles has a three dimensional chain structure, the diameter of a chain column is 0.5 μm or less, a crystal size measured by powder X-ray diffraction measurement is 300 Å or less, and nickel powder of an oxygen content of 0.5 to 1.5 wt.% is contained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydride secondary battery using paste-type nickel hydroxide as an active material for a positive electrode.

[0002]

2. Description of the Related Art A hydride secondary battery using a hydrogen storage alloy has a capability of storing and releasing a large amount of hydrogen, and is capable of electrochemically storing and releasing hydrogen even in an alkaline aqueous solution. When the nickel electrode is used as the positive electrode, a battery reaction occurs as in the following equation. In the reaction formula of the negative electrode, M is LaN
i ₅ based or Ti-Ni-based hydrogen storage alloy and the like.

[0003]

[0004] In the reaction formula of the positive electrode and the negative electrode, in charging, the reaction proceeds to the right, electrolyzes water in the alkaline aqueous solution, absorbs hydrogen, and generates a hydroxyl group. Reacts with ₂ to form NiOOH, producing water. In the case of discharge, the reaction proceeds to the left, and the reaction is the reverse of the above. That is, in the negative electrode, hydrogen is absorbed by charging, and hydrogen is released by discharging.

[0005] The nickel pole is disclosed in JP-A-1-2273.
As disclosed in, for example, Japanese Patent Application Laid-Open No. 63-63, the porosity is 95% or more and the pore diameter is several μm to 100 μm for high capacity and low cost.
A so-called paste method is known in which a conductive porous base material of m is used as a current collector and an active material slurry mainly composed of nickel hydroxide is supported on the current collector.

[0006]

Since the paste type electrode has a larger hole diameter than the sintered type electrode, the distance between the active material and the current collector is long, and the utilization factor and load characteristics are inferior. "Yuasa Higashi" No. 65, page 28 (1988) proposes a method of improving the utilization factor by adding a conductive additive such as a cobalt-based material to the positive electrode. However, cobalt is generally the surface is easily oxidized, a insoluble in an alkaline aqueous solution Co ₃ O
Easy to change to ₄ .

Thus, Co ₃ O ₄ is deposited on the surface of cobalt.
Is formed, there is no change in CoO → Co (OH) ₂ → CoOOH required for a network of cobalt, which acts to hold the nickel hydroxide particles during charging in the battery, and serves as a conductive additive. Will not play. For this reason, usually, a cobalt oxide having a high cobalt content, which is difficult to be oxidized, or a cobalt oxide and a metal cobalt are used.

[0008] However, cobalt is more expensive than nickel, which is another conductive assistant, so that an increased amount of cobalt results in an increase in the material cost of the battery. Further, in the case of a battery pack, when one battery cell is deteriorated, the battery becomes overdischarged and the battery voltage is forcibly reduced to 0 V, so that the above-mentioned reverse reaction occurs in the positive electrode, the CoOOH is forcibly reduced, and
Is destroyed. Some networks return to the original state in the next charging reaction, but do not completely recover, so that the capacity is lower than the initial capacity, resulting in capacity loss.

[0009] In order to solve these problems, it is also known that it is effective to add nickel powder which is electrochemically safe in an alkali together with cobalt as a conductive aid for a paste-type nickel positive electrode. However, when nickel powder is added, the capacity degradation after overdischarge is reduced, but when the addition amount is increased, gas generation during charging is increased, and the swelling of the positive electrode is increased. As a result, cycle deterioration is caused at an early stage, and the initial discharge capacity is reduced, and in particular, a problem easily occurs in the overdischarge characteristics.

The present invention overcomes the above-mentioned problems of the prior art, and in particular, provides a hydride secondary battery which improves the capacity of a paste-type nickel positive electrode and has excellent cycle characteristics and overdischarge characteristics. It is intended to be.

[0011]

Means for Solving the Problems The present inventors have conducted intensive studies in order to achieve the above-mentioned object. As a result, the primary particles of the paste type nickel positive electrode have a spherical shape, and the primary particles have a spherical shape. By using the nickel powder in which the aggregate is a three-dimensional chain-shaped nickel powder and the diameter, crystallite size and oxygen content of the chain-shaped columns are set to specific ranges, the capacity of the positive electrode is increased. It has been found that a hydride secondary battery having excellent cycle characteristics and overdischarge characteristics can be obtained, and the present invention has been completed.

That is, the present invention relates to a hydride secondary battery having a positive electrode using nickel hydroxide as an active material, a negative electrode made of a hydrogen storage alloy, an electrolytic solution made of an alkaline aqueous solution, and a separator. , The primary particles are spherical,
The aggregate of the primary particles has a three-dimensional chain structure, the diameter of the chain pillar is 0.5 μm or less, the crystal size measured by powder X-ray diffraction measurement is 300 ° or less, and the oxygen content is 0. The present invention relates to a hydride secondary battery (claim 1) containing nickel powder in an amount of 5 to 1.5% by weight. In particular, in the positive electrode, together with the nickel powder, cobalt powder or The present invention relates to a hydride secondary battery (claim 5) containing at least one of cobalt oxide powders.

Further, according to the present invention, in such a hydride secondary battery, the tap density of the nickel powder is 0.2 to 0.1.
8 g / cc (claim 2), nickel powder BE
The specific surface area measured by the T adsorption method is 4 to 8 m ² / g (Claim 3).
A configuration in which the amount is 2 to 10 parts by weight relative to 00 parts by weight (claim 4) is a particularly preferable embodiment.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION In the positive electrode of the present invention, nickel powder having a spherical primary particle and an aggregate of primary particles having a three-dimensional chain structure is used as a conductive additive. In this nickel powder, a conductive chain structure is formed between the nickel hydroxides, so that even a small amount of the nickel powder can exhibit efficient conductivity.

The diameter of the chain pillar of the nickel powder is 0.5 μm.
m, preferably 0.05 to 0.4 μm, and the crystallite size measured by powder X-ray diffraction measurement is 300 ° or less, preferably 1
00 to 250 °. By setting such a diameter and a crystallite size, good results can be obtained in the conductivity and the swelling suppressing effect. If the diameter exceeds 0.5 μm or the crystallite size exceeds 300 °, the nickel powder is non-uniformly present in the positive electrode to lower the conductivity, and the effect of suppressing swelling of the positive electrode is reduced.

The crystallite size in the present invention means a size measured by a powder X-ray diffraction method. Specifically, first, a diffraction spectrum is measured at 2 degrees / minute to determine a metal nickel. The diffraction peak was measured at a rate of 0.2 ° / min (slit: 0.15), Kα1 and Kα2 rays were separated, and the spread of the crystallite size of the diffraction line profile was identified. Is assumed to be Cauchy type, and the spread due to distortion is assumed to be Gauss type.
It means the size as determined by the integral width method. Further, the diameter of the chain-shaped column referred to in the present invention is defined as a value obtained by lightly compressing nickel powder into a green compact, and measuring the flow rate of gas passing through the green compact with a fish-subsieved sizer (MPIF32) Mean value.

The above-mentioned nickel powder has an oxygen content of 0.5 to 1.5% by weight, preferably 0.8 to 1.5% by weight, more preferably 0.8 to 1.2% by weight. is there. When the oxygen content is set to such a large value, the adsorption form of the binder in the positive electrode is reformed, the dispersibility of the nickel powder is improved even with a small amount of the binder, and the nickel powder can be uniformly dispersed in the positive electrode. Good results are obtained in improving the conductivity. On the other hand, if the oxygen content is less than 0.5% by weight, the amount of oxygen in the nickel powder is small, the dispersibility in the binder is reduced, and aggregates are generated. If the content is more than 1.5% by weight, the amount of nickel decreases, and the conductivity with nickel hydroxide as an active material is likely to be adversely affected.

That is, the nickel powder of the present invention is extremely fine and has a three-dimensional chain structure. Therefore, the nickel powder is usually easily aggregated and mixed with nickel hydroxide or a binder. Sometimes, the agglomeration of the nickel powder is not sufficiently unraveled, leaving particles of agglomerates in the paste. When this is applied to a current collector made of a conductive porous substrate, the particles adhere to the application surface. It will be in the state of having done. This is flattened by the subsequent rolling process, causing a decrease in conductivity, and a hydride secondary battery using this positive electrode is:
The discharge characteristics, especially the overdischarge characteristics, are degraded.

In order to eliminate the aggregated particles in the paste, a large amount of a binder, a thickener, or the like may be added, or the paste may be meshed to remove particles. However, in the former case, the paste thickens, making it difficult to apply the paste to a predetermined thickness on the base material, and reducing the amount of nickel hydroxide in a unit volume, making it impossible to obtain a high-capacity positive electrode. In such a case, the manufacturing process of the positive electrode becomes complicated, and the production efficiency decreases. All of these problems and the problems of the conductivity and the overdischarge characteristics are solved by using the nickel powder having the specific oxygen content according to the present invention.

The nickel powder of the present invention has a tap density of 0.2 to reduce the volume occupied in the positive electrode.
It is preferably 0.8 g / cc. Further, in order to obtain a favorable result due to the dispersibility and conductivity in the binder,
The specific surface area by the BET adsorption method is preferably ⁴ to 8 m ² / g. When the specific surface area is less than 4 m ² / g, the dispersibility in the binder tends to decrease, and when the specific surface area exceeds 8 m ² / g, the nickel powder is prevented from being miniaturized and the surface is easily oxidized. The conductivity effect decreases.

The oxygen content referred to in the present invention is defined as inert gas melting / infrared ray absorption method (TC436 manufactured by LECO).
Means a value measured at a heating rate of 10 ° C./min up to 2,500 ° C. Further, the specific surface area by the BET adsorption method referred to in the present invention is 1 to 100 ° by a nitrogen adsorption method (Yuasa Ionics, Autosorb 1), 1 g of a sample, 1 measurement time.
27 minutes means the measured value on the adsorption side.

The nickel powder of the present invention can be obtained by a carbonyl nickel method, that is, a thermal decomposition method of tetracarbonyl nickel represented by the following formula: Ni (CO) ₄ → Ni + 4CO, By appropriately adjusting the partial pressure of tetracarbonyl nickel and oxygen in the vessel, the synthesis temperature, and the like, the primary particles are spherical, the aggregate of the primary particles has a three-dimensional chain structure, and the chain columns are formed. Having a diameter, crystallite size and oxygen content within the above ranges, and preferably having a tap density and a specific surface area by the BET adsorption method within the above ranges can be easily synthesized.

In the positive electrode of the present invention, the nickel powder used as a conductive additive is used in an amount of 2 to 10 parts by weight, preferably 3 to 10 parts by weight, based on 100 parts by weight of nickel hydroxide as an active material.
It is used in a proportion of up to 8 parts by weight. If the amount of the nickel powder used is too small, sufficient conductivity with the nickel hydroxide is not obtained, and if it is too large, the absolute amount of the nickel hydroxide is undesirably reduced.

In the present invention, the above-mentioned nickel powder may be used alone as a conductive auxiliary for the positive electrode.
When the amount of use is increased, swelling of the positive electrode cannot be suppressed, and there is a possibility that problems may occur in the cycle characteristics, overdischarge characteristics and the like. In order to avoid this, it is usually desirable to use a cobalt-based conductive additive together. As the cobalt-based conductive additive, cobalt powder or cobalt oxide powder is preferable.
As the cobalt oxide powder, it is preferable to use cobalt oxide having a high cobalt content which is hardly oxidized. The amount of the cobalt-based conductive additive to be used is generally preferably 2 to 10 parts by weight based on 100 parts by weight of nickel hydroxide as an active material.

The positive electrode of the present invention comprises nickel hydroxide as an active material, and a conductive aid comprising the above-mentioned nickel powder and the above-mentioned cobalt-based conductive aid in the presence of water as a binder. The paste-like material is kneaded with a paste, and the paste-like material is filled into a collector made of an alkali-resistant conductive porous base material such as punching metal or foamed metal. It is manufactured by cutting.

The binder includes polytetrafluoroethylene, sodium polyacrylate, polyvinyl alcohol
And a copolymer of a monomer mixture containing styrene and 2-ethylhexyl acrylate as main components. Usually used in an amount of 0.5 to 5 parts by weight based on 100 parts by weight of nickel hydroxide. Can be Also, with such a binder,
Thickeners such as carboxymethyl cellulose, methyl cellulose and hydroxypropyl cellulose may be used in combination usually in an amount of 1 to 5 parts by weight based on 100 parts by weight of nickel hydroxide.

In the hydride secondary battery of the present invention, a negative electrode made of a hydrogen storage alloy is used for the positive electrode having the above-described structure, and the positive and negative electrodes and a separator such as a non-woven fabric of nylon for separating these are further placed in the battery can. And an alkaline aqueous solution in which an electrolyte such as LiOH is dissolved in an aqueous solution such as sodium hydroxide or potassium hydroxide as an electrolytic solution.

Here, the above-mentioned negative electrode is kneaded with a hydrogen storage alloy and, if necessary, a conductive filler or a binder in the presence of water to form a paste, which is then subjected to an alkali-resistant conductive porous substrate. It is obtained by filling a current collector made of a material, drying and rolling it, and then cutting it into a predetermined size. Mm (La, Ce, Nd, Pr)-
Ni-based, _{Ti-Ni-based, Ti-NiZr (Ti 2-} X Zr
_{X V 4-y Ni y)} 1-Z Cr 2 system (x = 0~1.5, y =
0.6-3.5, z = 0.2 or less), Ti-Mn system, Z
Various alloys such as an r-Mn-based alloy may be used.

[0029]

Next, an embodiment of the present invention will be described in more detail. In the following, “parts” means “parts by weight”.

The nickel powders A to C used as conductive assistants for the positive electrodes in Examples 1 to 7 and the nickel powders D and E used as conductive assistants for the positive electrodes in Comparative Examples 1 and 2 were all carbonyl. Primary particles are spherical, and the aggregate of the primary particles has a three-dimensional chain structure, synthesized by the Nickel method by appropriately adjusting the partial pressure of tetracarbonyl nickel and oxygen in the reaction vessel, the synthesis temperature, etc. Nickel powder having a diameter of a chain pillar, a crystal size measured by powder X-ray diffraction, an oxygen content, a tap density, and a specific surface area measured by a BET adsorption method as shown in Table 1 below. is there.

[0031]

EXAMPLE 1 100 parts of nickel hydroxide powder and 100 parts of nickel powder A were dry-blended and mixed with 10 parts of cobalt powder, 5 parts of a 2% by weight aqueous carboxymethyl cellulose solution, and 60% by weight of polytetrafluoroethylene. Five parts of an aqueous ethylene (PTFE) dispersion were mixed to give a paste. This was filled and supported on a nickel foam, dried at 80 ° C. for 2 hours, and then 1 ton / cm ²
To form a sheet. This was immersed in an alkaline aqueous solution at 80 ° C. for 2 hours, washed with warm water at 80 ° C. for 2 hours, dried at 80 ° C. for 1 hour, and compression-molded.
The sheet was cut into a predetermined size to obtain a positive electrode sheet.

Commercial Mm (La, Ce, Nd, Pr),
Ni, Co, Mn, Al and Mo (all with a purity of 9
9.9% by weight or more) of each sample as Mm (La: 0.32
Atomic ratio, Ce: 0.48 atomic ratio, Nd: 0.15 atomic ratio, Pr: 0.04 atomic ratio), Ni: 3.55 atomic ratio,
Co: 0.75 atomic ratio, Mn: 0.4 atomic ratio, Al:
The mixture was heated and melted in a high-frequency melting furnace so as to have a composition of 0.3 atomic ratio and Mo: 0.04 atomic ratio to synthesize a hydrogen storage alloy.

This hydrogen-absorbing alloy is placed in a pressure vessel at 10 ⁻³ T.
After evacuating to orr and purging three times with argon gas, the system is maintained at a hydrogen pressure of 14 kg / cm ² for 24 hours, evacuated and heated at 400 ° C. to completely release hydrogen. Thereby, an alloy powder of 20 to 100 μm was obtained. To 100 parts of the alloy powder, 1.7 parts of a copolymer (emulsion polymer) of a monomer mixture containing styrene and 2-ethylhexyl acrylate as main components was added as a binder, and a thickener was added. As a polyoxyethylene aqueous solution 20
Then, the mixture was mixed well to obtain a paste. The paste was applied to a punching metal serving as a conductive porous substrate, dried, compression molded, and then cut into a predetermined size to obtain a negative electrode sheet.

The above-mentioned negative electrode sheet and the above-mentioned positive electrode sheet are wound through a nylon nonwoven fabric separator.
Put it in a AAA size electrode can and add electrolyte (30% by weight)
An alkaline aqueous solution in which 17 g of LiOH was dissolved in 1 liter of an aqueous potassium hydroxide solution) was injected. Thereafter, the positive electrode tab was spot-welded to the resin sealing body, and the outermost peripheral portion of the negative electrode was brought into contact with the side surface of the can and then sealed. After sealing, store at 60 ° C. for 17 hours, and 0.2 C (110 mA)
7.5 hours at 0.2C (110mA)
Discharged to V. This charge / discharge cycle was repeated until the discharge capacity became constant, to produce a hydride secondary battery.

Example 2 A hydride secondary battery was manufactured in the same manner as in Example 1 except that the amount of nickel powder A, which was a conductive auxiliary for the positive electrode, was changed to 4 parts.

Example 3 A hydride secondary battery was manufactured in the same manner as in Example 1 except that the amount of nickel powder A, which was a conductive auxiliary for the positive electrode, was changed to 6 parts.

Example 4 A hydride secondary battery was produced in the same manner as in Example 1 except that the amount of nickel powder A, which was a conductive auxiliary for the positive electrode, was changed to 8 parts.

Example 5 A hydride secondary battery was manufactured in the same manner as in Example 1 except that the amount of nickel powder A, which was a conductive auxiliary for the positive electrode, was changed to 10 parts.

Example 6 A hydride secondary battery was manufactured in the same manner as in Example 1, except that 6 parts of nickel powder B was used instead of 2 parts of nickel powder A as a conductive assistant for the positive electrode.

Example 7 A hydride secondary battery was manufactured in the same manner as in Example 1, except that 6 parts of nickel powder C was used instead of 2 parts of nickel powder A as a conductive auxiliary for the positive electrode.

Comparative Example 1 A hydride secondary battery was produced in the same manner as in Example 1, except that 2 parts of nickel powder A was used instead of 2 parts of nickel powder as a conductive assistant for the positive electrode.

Comparative Example 2 A hydride secondary battery was produced in the same manner as in Example 1 except that nickel powder E2 part was used instead of nickel powder A2 part as a conductive assistant for the positive electrode.

With respect to each of the hydride secondary batteries of Examples 1 to 7 and Comparative Examples 1 and 2, the initial discharge capacity, cycle characteristics and overdischarge characteristics were examined. These results were as shown in Table 2 below. The cycle characteristics were 0.58 A (−ΔV = 5 mV) charge, 0.58 A
(1.0 V cut), the cycle of discharging was repeated, and the number of cycles at which a 60% discharge capacity with respect to the initial capacity was obtained. The over-discharge characteristics are as follows.
C. for 3 days (battery voltage: 0 V), charging and discharging at 0.2 C, and the capacity recovery rate was determined by the following equation. Capacity recovery rate (%) = (capacity after storage / capacity before storage) x
100

[0045]

As is evident from the results in Table 2, each of the hydride secondary batteries of Examples 1 to 7 has a high discharge capacity and the hydride secondary batteries of Comparative Examples 1 and 2. In comparison, it can be seen that the number of cycles is large and the capacity recovery rate is also high.

[0047]

As described above, according to the present invention, the specific nickel powder is used as the conductive aid of the paste-type nickel positive electrode, so that the positive electrode has a high capacity and has excellent cycle characteristics and over-discharge characteristics. An excellent hydride secondary battery can be provided.

Claims (5)

[Claims] 1. A hydride secondary battery having a positive electrode using nickel hydroxide as an active material, a negative electrode made of a hydrogen storage alloy, an electrolyte solution made of an alkaline aqueous solution, and a separator, wherein primary particles are contained in the positive electrode. Spherical, an aggregate of primary particles has a three-dimensional chain structure, and the diameter of the chain pillar is 0.5
When the crystal size is 300 μm or less, the crystal size measured by powder X-ray diffraction
Å or less, and the oxygen content is 0.5 to 1.5% by weight
A hydride secondary battery comprising the nickel powder as described above. 2. The nickel powder having a tap density of 0.2 to 0.1.
The hydride secondary battery according to claim 1, which is 8 g / cc. 3. The hydride secondary battery according to claim 1, wherein the specific surface area of the nickel powder measured by a BET adsorption method is 4 to 8 m ² / g. 4. The content of the nickel powder is 2 to 10 parts by weight based on 100 parts by weight of the nickel hydroxide.
4. The hydride secondary battery according to any one of 3. 5. A positive electrode comprising nickel hydroxide as an active material, wherein the positive electrode contains at least one of a cobalt powder and a cobalt oxide powder together with the nickel powder.
5. The hydride secondary battery according to any one of claims 4 to 4.