JPH0346758A - Nickel-hydrogen battery - Google Patents

Abstract

PURPOSE:To extend the service life and to improve the utilization rate of the active substance by using a nickel hydroxide powder in which the development of internal transition pores whose pore radius is more than a specific value is prevented, and the whole pore capacity is controlled less than a specific value, as a positive electrode active substance. CONSTITUTION:A nickel hydroxide active substance in which the development of internal transition pores whose pore radius is more than 30Angstrom is prevented, and the whole pore capacity is controlled less than 0.05ml/g, in a pore distribution calculated by the removal and absorption isothermal line of nitrogen, is used for a positive electrode. In case of a high density nickel hydroxide powder in which the internal pore capacity is minimized, a high order oxide gamma-NiOOH is produced plentifully, but by disposing different sort of metal ions such as zink ions in the crystals of nickel hydroxide, deformations are generated in the crystals, and thereby the freedom of proton movement is increased to improve the utilization rate, and the production of the gamma-NiOOH is reduced. Consequently, the service life is extended and the utilization rate of the active substance is improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention is directed to a nickel electrode using a Peint type nickel μ electrode.
It concerns hydrogen batteries.

Conventional technology and its problems The positive electrode of the Nikke μm hydrogen battery is conventionally known as a sintered electrode. A microporous substrate made by sintering a powdered perforated steel plate or the like and filled with nickel hydroxide has been used. In this type of electrode, the process of filling the active material must be repeated many times, making it very complicated and expensive. Moreover, since the porosity of the substrate used is limited, the packing density of the active material is low, and only electrodes with an energy density of about 400 mm/cc can be manufactured. For this reason, there was a disadvantage in further increasing the high energy density that is a characteristic of nickel-metal hydride batteries.

Therefore, non-sintered electrodes are considered to be promising as positive electrodes for nickel-metal hydride batteries. For example, paste-type nickel/L/l@ is a paste-type nickel/L/l using a gold mt & fiber substrate with a high porosity of approximately 95%. ! - It is becoming commonly used as a positive electrode for power domic batteries. This electrode is cheaper than the sintered 'vL electrode and has a high energy density of 500mmh/CC.

However, the market needs for batteries include the recent demand for higher energy density due to the weight reduction of V-Tronics equipment, and the need for clean batteries that do not contain harmful substances such as cadmium from the perspective of preventing environmental pollution. Two aspects are required: Nickel-hydrogen batteries that do not use cadmium negative electrodes are expected to be the most suitable batteries to meet these market needs. However, since conventional nickel-metal hydride batteries use conventional nickel hydroxide electrodes, they must always contain a small amount of cadmium in order to extend the life of the electrode. The current situation is that this was not possible.

In order to satisfy the above two demands, first, as a means of increasing the energy density of the battery, it is possible to further increase the energy density of the positive electrode. For this purpose, since there is a limit to the porosity of the substrate, it is necessary to increase the density of the active material powder itself. High-density nickel hydroxide μ powder is used as part of the raw material for barkaising treatment of iron plates. The manufacturing method involves dissolving didium nitrate or nickel sulfate in a weakly basic ammonia aqueous solution and stabilizing it as a didium ammine complex ion.
While adding an aqueous sodium hydroxide solution, nickel hydroxide is gradually precipitated to prevent the development of pores inside the particles.

In this method, since disordered precipitation is not performed as in the conventional neutralization method, the precipitated particles have few grain boundaries and are highly crystalline (small pore volume) high-density nickel hydroxide.

However, due to its unique physical properties, there are several problems in using this powder as it is as an active material for batteries. For example, the charge/discharge reaction of the nickel hydroxide/L' electrode occurs due to the free movement of protons within the crystals of the nickel hydroxide. However, as the density of the hydroxylated dandruff ρ increases, the crystal becomes denser, which limits the freedom of proton movement within the crystal. Moreover, the current density increases due to the decrease in specific surface area, and the higher order oxide 1-NiO
■ begins to generate a large amount, resulting in two-stage discharge and electrode B.
;Causes phenomena such as deep discharge, deterioration of life characteristics, and reduction in utilization rate. The swelling mechanism associated with the formation of γ-NiOOH in nickel/I/electrodes, which is a fatal factor for electrodes, is caused by the formation of γ-NiOOH from high-density β-NiOOH to low-density 1-Ni0O.
This is due to the density change to H. This γ-NiO
It has already been found that adding cadmium to nickel hydroxide as a solid solution is effective in preventing the formation of OH.
In hydrogen batteries, a pollution-free additive that can replace cadmium is desired. We provide nickel-metal hydride batteries that have both high energy density and clean battery properties by preventing pollution with non-polluting additives, extending their lifespan, and improving the utilization rate of active materials. The purpose is to

Structure of the invention The present invention adds zinc to a nickel hydroxide μ powder active material,
The zinc is in a solid solution state in the crystal of nickel hydroxide, and in the pore size distribution calculated from the nitrogen desorption/adsorption isotherm, the development of internal transition pores with a pore radius of 50 Å or more is prevented. Furthermore, the present invention is a nickel-hydrogen battery characterized in that a hydroxide Efkel active material powder whose total pore volume is controlled to be 0.05 gt/liter or less is used as a positive electrode.

In the case of a high-density hydroxide dandruff powder with a minimum working internal pore volume, a large amount of higher order oxide γ-NiOOH is produced.

However, when dissimilar metal ions, especially zinc ions, are placed in the crystal of nickel hydroxide, the crystal becomes distorted, which increases the freedom of movement of protons, improves the utilization rate, and improves the utilization rate of γ-Ni.
It has been found that it has the effect of reducing the production of OOH.

On the other hand, outside the crystals of nickel hydroxide, a cobalt compound additive is dissolved, and the current collector and the nickel hydroxide particles are connected by the HOOO2-→β-Go(OH)2 reaction. A part of Ho2O3- may form a solid solution with nickel present on the surface of the hydroxide/%/particles, but
Most of it is in a free state as β-co(OH)2. After that, charging w, β due to gas chemical oxidation
-Go(OH)2 → Co0OH reaction changes to oxyV hydroxide with high conductivity, and the current collector Nifke tvt
& It has the effect of smoothing the flow of electrons between fibers and nickel hydroxide particles and increasing the utilization rate.

In this way, a pollution-free nickel-hydrogen battery can be obtained by using a high-performance nickel A/[electrode] without adding cadmium.

EXAMPLES The details of the present invention will be explained by examples below. ◎ Nickel hydroxide powder for parkafizing prepared using didandruff sulfate as a starting material, and an aqueous solution containing 1vIc of nickel sulfate mixed with a small amount of zinc sulfate as a starting material. , nickel hydroxide μ powder prepared in the same manner, and nickel hydroxide μ powder for pocket type nickel positive electrode prepared by a known method.
shall be. FIG. 1 shows a comparison of the internal pore size distributions of the 0 powder produced by the conventional method and the MU powder produced by the present invention.

C powder has a specific surface area of about 66 trl/9 and a pore radius of 1
It is present in large amounts ranging from 5 to 100 people. ,
Its pore volume is 0.136 d! /fi and particle volume (
0.41 dlg"), and the pores are quite large. On the other hand, the zinc-added high-density hydroxide didander powder B of the present invention has a pore volume of 0.028 dlg").
It is as small as +w//9 and is only about 0% of particles. This means that 8 particles have a density of 20 to 50% higher than that of C particles.In other words, in order for one active material particle to have a high ra, it must have a specific surface area and pore volume as small as possible. It shows that it must be. It was confirmed that the internal pore distribution of the B powder was almost the same as that of the A powder, and that it had a high density like the A powder even though it contained zinc.

A small amount of cobalt compound, Coo, α-Co(OH) 2% β-0O(OH), which dissolves in an alkaline electrolyte to form 0O(1) complex ion, is added to these nickel hydroxide μ powders.
2 or a powder such as cobalt acetate. Thereafter, an aqueous solution containing 1% VCT-1VCT-Z was added to prepare a fluid coating.

Apply this paste solution to an alkali-resistant fiber substrate 1 with a porosity of 95%.
For example, Nikkei! A predetermined amount of the solution was filled into a fiber substrate, etc., and after drying, it was made into a didander/1/' [pole.

On the other hand, predetermined amounts of Km (Mifshemetal), Ni, and MuE were weighed and melted four times in an arc melting furnace to 1MmNi4,7.
Mul Q,S hydrogen storage alloy was obtained. This was mechanically crushed to obtain a hydrogen storage alloy powder sample. This powder contains 3% P.
Added an aqueous solution of hydrogen to make a paste, filled it into a nickel fiber substrate similar to the positive electrode, and after drying, made it into a hydrogen storage electrode.
These were treated with a polyamide nonwoven fabric as a separator, and the specific gravity was 1.
．． Nominal capacity of positive electrode capacity regulation is 100100O using No. 28 potassium hydroxide aqueous solution as electrolyte.

I assembled a AA size sealed Nifuke hydrogen battery. After charging and discharging this battery under various conditions, the battery was disassembled and the following results were obtained.

Figure 2 shows the relationship between various types of nickel hydroxide μ and the active material utilization rate. The active material composition is hydroxide! Mu consisting only of
Comparing O, it can be seen that a high specific surface area is required to obtain a high active material utilization rate. However, B, which has a small amount of zinc added to the crystals of hydroxide dandruff μ, shows a high utilization rate that is as high as that of the conventional powder 0, despite its small specific surface area.

Compared to conventional powder, more high-density powder can be filled into the same volume substrate, so the energy density per unit volume of the electrode plate is 504 mAh for conventional powder 0/CC1 high-density powder B
is 620 mmh/CC, which is about 20% higher for high-density powder B than for conventional powder C. Due to the increased density of the active material, the specific surface area is reduced.As a result, the entrance and exit of reactive species protons from the electrolyte is reduced. However, by adding zinc to the nickel hydroxide crystal, it is thought that the proton movement in the solid phase becomes smoother. It is governed by two factors: specific surface area and diffusion rate inside the crystal (solid phase).If the crystals are the same, it is governed by the specific surface area, and if the crystals are folded, it is governed by internal strain. Will be considered.

In order for the active material to react, it is necessary to smoothly move electrons from the current collector to the active material particle surface, and as mentioned above, free form II (exists on the particle surface without being solidly dissolved in hydroxide dandruff). A network of conductive CooOH particles is essential. C to create this network
For the oo additive, increasing the amount of additive also increases the active material utilization. However, since the additive itself only contributes to conductivity and does not actually cause discharge, the plate energy density tends to decrease from around 15%.

In addition to Coo, cobalt compounds that can form this network include a-co(OH)2, β-Co(
Examples include compounds that generate Co(I[) complex ions such as OH)2, but the active material utilization rate when these compounds are added is C3oO>α-00(OH)2>β-Co
(OH) It becomes 2. The reason for this is thought to be due to the solubility in the electrolytic solution. That is, in the case of β-Co(OH)2, it is easily oxidized by dissolved oxygen after pouring the electrolyte to form brown, low-solubility co(on)s (or ashes with COHO2); on the other hand, Q -Co(OH)2,
(00(OH)3 is more difficult to form because it passes through 1-00(OH)2-β-Co(0■)2. In the case of Coo, s is the best because Co(OH)3 is not formed at all. It can be said that it is an additive.

More specifically, from the viewpoint of dissolution rate, β-Co(OH
) 2 as a starting material by heating at a high temperature of 200 to 800° C. in an inert atmosphere and having a low degree of crystallinity is desirable.

Cobalt hydroxide was immersed in HOOO2- ions and filled with a powdery paste with cobalt hydroxide precipitated on the surface. ) Did you mix z powder? It was about u. Furthermore, after charging and discharging an electrode in which conductive OoOOHN is formed on the surface of Oki-V nickel hydroxide/I/powder (specifically, after charging and discharging an electrode mixed with OoO powder, nickel fibers as a current collector are removed from the electrode). Electrodes that are re-filled with paste (removed) have a poor utilization rate. That is, it is essential that a conductive network (OOOOOH) between the active material powder and the current collector be formed in the produced 'WIL pole. In other words, even if it is formed on the surface of the active material particles in advance, the effect will be negligible if the connections between the particles are incomplete. Therefore,! After assembling the electrodes as a battery, it is necessary to dissolve and reprecipitate the TC coo powder. Specifically, it is necessary to add highly soluble Coo powder, or to leave it for an appropriate period of time after assembling the battery. It is to put

Charging was carried out at a high current density of 10, and the correlation between the amount of γ-NiOOH produced in the positive electrode active material at the end of charging and the type of active material powder was investigated by X-ray analysis.

As shown in Figure 6, if zinc is added as a solid solution in the crystals of nickel hydroxide, as the amount added increases, γ-NiOO
It can be seen that the amount of H produced decreases.

In the case of high-density powder containing only nickel hydroxide, which produces a large amount of γ-NiOOH, a two-stage discharge occurs as shown in Figure 4, but with zinc-added high-density powder, r-N100H generation is prevented. , this is not the case.

FIG. 5 shows the relationship among active materials, charge/discharge temperatures, and active material utilization rates. In D, in which both zinc and cobalt were added as a solid solution, the charging performance at high temperature (about 45° C.) was found to be improved compared to B in which only zinc was added.

FIG. 6 shows the cycle characteristics of this battery.

In B, the production of 1-NiOH was suppressed compared to the rubber containing no additives, so it showed stable performance without causing a long-term capacity drop.

In the above embodiments, a metal fiber sintered body is used as the substrate, but the substrate is not limited to this. In addition to the production method of the present invention, the effect of adding zinc has been similarly observed for highly crystalline nickel hydroxide particles1. A similar effect is observed in mixed addition, but
From the viewpoint of non-polluting properties, it is preferable to use zinc alone.

Effects of the Invention As described above, the present invention increases the density of nickel hydroxide ρ powder, prevents the formation of γ-NiOO11 due to the increase in density using a less toxic additive, extends the life of the active material, and By improving the utilization rate of nickel-metal hydride and using an active material for dandruff 1vvii with a high discharge potential, it is possible to provide a nickel-metal hydride battery that is both extremely high in energy density and non-polluting. Its industrial value is extremely large.

[Brief explanation of drawings]

FIG. 1 is a diagram showing pore size distribution curves of a conventional nickel hydroxide powder and a high-density nickel hydroxide powder of the present invention. FIG. 2 is a diagram showing the relationship between the specific surface area of nickel hydroxide particles and the active material utilization rate. FIG. 3 shows the relationship between the amount added and the amount of γ-NiOOH produced. FIG. 4 is a discharge curve diagram of a nickel-metal hydride battery. FIG. 5 is a diagram showing the relationship among active materials, charging/discharging temperatures, and active material utilization rates. FIG. 6 is a diagram showing the cycle characteristics of a nickel-hydrogen battery. Figure 2 Figure 1 DES Dv (Log r) vs rγ Active material utilization rate (%) 10 100PORE RA
DILtS([M) a E, T Area Total Pare V
OILITII! 1go7q ml/g C6a28 0.15 A 2a55 0.04 000 Zn addition amount (wt%) (1 capital) No. 6I21 Number of cycles (-) No. 5 Fig.

Claims (5)

[Claims] (1) In the pore size distribution calculated from the desorption side of the nitrogen adsorption isotherm, the development of internal transition pores with a pore radius of 30 Å or more is prevented, and the total pore volume is reduced to 0.05 ml/g or less. A nickel-hydrogen battery characterized by using controlled nickel hydroxide powder as a positive electrode active material. (2) The nickel-hydrogen battery according to claim 1, wherein zinc is added to the nickel hydroxide powder active material, and the additive is in a solid solution state in the nickel hydroxide crystal. (3) The nickel-hydrogen battery according to claim 2, wherein a nickel positive electrode in which cadmium is not added to the nickel hydroxide active material powder is used. (4) A cobalt compound that dissolves in an alkaline electrolyte to generate cobalt complex ions is added to a nickel hydroxide active material powder containing zinc in a solid solution state in a range of 5 to 15 wt%, and the cobalt compound powder is The nickel-hydrogen battery according to claim 2, wherein most of the nickel-hydrogen battery is in a free state with the active material powder. (5) The nickel-hydrogen battery according to claim 2, wherein a small amount of cobalt in addition to zinc coexists in solid solution in the nickel hydroxide active material powder.