JPH03102765A - Ni-h secondary battery - Google Patents

Abstract

PURPOSE:To enhance the service rate of a pos. electrode by forming a Ni pos. electrode in non-sintered type from paste of a specific active substance, and forming a neg. electrode chiefly containing hydrogen absorption alloy. CONSTITUTION:A Ni-H secondary battery concerned includes a non-sintered type Ni. pos. electrode made from paste of an active substance formed by adding 5-20wt.% Co monoxide to Ni hydroxide, which contains 2-8mol% Cd in metal conversion by means of coprecipitation method, followed by mixing thoroughly, and a neg. electrode chiefly containing hydrogen absorption alloy. This improves the charging characteristic at high temp., suppresses expansion of the pos. electrode effectively, accomplishes stable existence in the pos. electrode without involvement of oxidation in the electrode manufacturing environment, allows easy dissolution in alkali electrolytic solution, and permits dispersion of Ni hydroxide and current collector to the part to be put in electric continuity. Thereby the service rate of a non-sintered type Ni pos. electrode is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a nickel-metal hydride secondary battery having an improved non-sintered nickel positive electrode.

(Prior Art) In recent years, advances in electronic technology have led to power saving, and advancements in advanced mounting technology have made electronic devices portable, which was unimaginable in the past. Along with this, there is an increasing demand for higher capacity secondary batteries, which are the power source for these electronic devices. New batteries such as nickel-zinc batteries and lithium secondary batteries are being developed to meet this demand for higher capacity. However, it has some problems in terms of cycle life, reliability, safety, etc., so although it has started to be used in some cases, it has not yet been widely used.

For this reason, in recent years, an alkaline secondary battery using a negative electrode mainly composed of a water storage alloy has been proposed, and has been presented at academic conferences such as battery discussions and the Electrochemical Society of Japan conference, and has attracted attention. It is starting to be exposed to

The negative electrode mainly composed of the hydrogen storage alloy can have a higher energy density per unit weight or about Jll volume compared to a cadmium negative electrode, which is a typical negative electrode material for alkaline secondary batteries. In addition to making it possible to increase the capacity of batteries, it not only has less risk of environmental pollution, but also has excellent battery performance.

On the other hand, as the nickel positive electrode that determines the battery capacity in the alkaline secondary battery, a so-called sintered nickel positive electrode, which has been used in alkaline secondary batteries such as conventional nickel cadmium secondary batteries, is known. . Such a sintered nickel positive electrode is produced by immersing a microporous sintered substrate in which fine nickel powder with a diameter of several μm is sintered on a perforated steel plate in an aqueous solution containing nickel ions, and then using a chemical or electrochemical method. It is manufactured by repeating charging and discharging several times in an alkaline solution with nickel hydroxide formed in the micropores on its surface. This makes the manufacturing process complicated,
In addition to not being able to reduce manufacturing costs, the sintered substrate occupies a large volume in the electrode plate, making it extremely difficult to improve the capacitance density of the electrode.

Therefore, a so-called non-sintered nickel hydroxide active material is made into a paste and is directly filled into a conductive porous substrate with a three-dimensional structure such as a sintered metal fiber substrate or a metal plated substrate. Positive electrodes are actively being developed. However, in the non-sintered nickel positive electrode, the distance between the nickel particles, which are the active material, and the gold-flexible matrix, which constitutes the conductive porous substrate, which is the current collector, is longer than in the conventional sintered nickel positive electrode. Since the length is several times to several tens of times longer, current collection performance deteriorates. As a result, the utilization rate of the nickel hydroxide active material is as low as 50 to 60%, and the performance is significantly lower than that of conventional sintered nickel positive electrodes.

In order to solve the above-mentioned problems, non-sintered nickel positive electrode techniques with the addition of metallic cobalt or cobalt hydroxide have been studied. However, cobalt metal easily reacts with oxygen in the atmosphere to form oxides, making it difficult to stabilize electrode performance and being extremely expensive, making it difficult to apply to consumer alkaline secondary batteries. There are some difficult issues.

Cobalt hydroxide has a problem in that the utilization rate improves slowly and the utilization rate is not stable for several lO cycles after the initial charge. Furthermore, when these non-sintered nickel positive electrodes are incorporated into a secondary battery together with a negative electrode whose main component is a hydrogen storage alloy, there is a problem in that the charging and discharging performance is poor as shown below.

In other words, during the first charge of a secondary battery incorporating a non-sintered nickel positive electrode to which metallic cobalt has been added, the volume of the nickel positive electrode, which is the battery capacity limiting electrode, or the capacity of the hydrogen storage alloy negative electrode is reduced even if the battery capacity is sacrificed. If you don't overdo it,
Since the amount of electricity required for irreversible oxidation of metal cobalt is large, the discharge reserve 6ifl of the hydrogen-absorbing alloy negative electrode becomes larger than necessary, resulting in a problem that the charge reserve amount becomes too small and the battery life is shortened. During the initial charge of a secondary battery incorporating a non-sintered nickel positive electrode containing cobalt hydroxide, the amount of electricity required for irreversible oxidation is not constant due to the instability of cobalt hydroxide. If the amount becomes too large, the same rrrs g as the metal cobalt will occur, but if the amount of electricity becomes too small, the discharge reserve will decrease, and the discharge characteristics, especially the large current discharge characteristics, will deteriorate. There is.

Further, the following problem also occurs when the above-mentioned cobalt compound is added to nickel hydroxide.

In other words, attempts have been made to add cobalt metal along with nickel hydroxide into the same grains by coprecipitation, which is an effective addition method used in sintered nickel positive electrodes, but it has not been stable. The conditions under which such a coprecipitate can be obtained are limited to areas where the density of nickel hydroxide is relatively low, which not only hinders the increase in battery capacity but also makes it difficult to maintain the manufacturing conditions for a long period of time. However, considering the expansion of the supply chain, this poses a major obstacle in terms of stable supply and cost. Moreover, although the cause is unknown, it has been observed that battery voltage decreases in secondary batteries incorporating nickel positive electrodes to which cobalt has been added by co-precipitation, making it difficult to apply them to batteries. There is. Furthermore, when a secondary battery incorporating the positive electrode is charged at a high temperature, the charging efficiency of the non-sintered nickel positive electrode decreases, resulting in a decrease in discharge capacity.

(Problems to be Solved by the Invention) The present invention has been made to solve the above-mentioned conventional problems, and has achieved improved utilization of the positive electrode, longer life, and improved charging characteristics at α temperature. The aim is to provide a nickel metal hydride secondary battery.

[Structure of the Invention (Means for Solving the Problems)] The present invention is a method of adding at least 5 cobalt monoxide (CoO) to nickel hydroxide containing 2 to 8 mol% of cadmium in terms of metal by a coprecipitation method. This is a nickel-metal hydride secondary battery characterized by comprising a non-sintered nickel positive electrode made from an active material paste mixed with ~20 TIi amount, and a negative electrode whose main component is a hydrogen storage alloy.

The reason for limiting the amount of cadmium co-precipitated with the nickel hydroxide is that if the amount is less than 2 mol%, it will not be possible to improve the charging characteristics at high temperatures and suppress the expansion of the non-sintered nickel positive electrode. On the other hand, if the amount exceeds 8 mol%, not only will the amount of nickel hydroxide occupying the positive electrode decrease, resulting in a decrease in capacity, but it will also interfere with co-precipitation with nickel hydroxide, stabilizing the cadmium-co-precipitated nickel hydroxide. cannot be generated.

The above-mentioned cobalt monoxide is preferably obtained by using cobalt hydroxide as a starting material and heating it in a non-oxidizing atmosphere. In particular, it is possible to use cobalt monoxide in a form in which at least a portion of the surface, preferably 90% or more, is covered with several atomic layers of cobalt high-dimensional oxide (e.g., CO2O3, CO304, etc.). desirable.

The reason why the amount of cobalt monoxide added is limited to the above range is that if the amount is less than 2fffffi%, the utilization rate of the non-sintered nickel positive electrode will decrease, while if the amount exceeds 20% by weight, it will be added to the positive electrode. The amount of nickel hydroxide that occupies decreases, leading to a decrease in capacity, and the amount of electricity required for irreversible oxidation of cobalt monoxide increases, so that the charging and discharging 7 cycles of the hydrogen storage alloy electrode become too small. At a relatively early stage, the capacity (hydrogen storage capacity) of the negative electrode, which is mainly composed of a hydrogen storage alloy, decreases, causing the internal pressure of the battery to rise.

The above cobalt monoxide is not limited to being added alone to nickel hydroxide, but may be added to nickel hydroxide together with cobalt hydroxide. The amount of cobalt hydroxide added is
2 to 15% by weight (however, the total amount including cobalt monoxide is 20% by weight)
It is desirable not to exceed % by weight.

The above active material paste contains carboxymethyl cellulose (CMC) and polyacrylic in addition to the components of nickel hydroxide containing cadmium by coprecipitation method and cobalt monoxide (or cobalt monoxide and cobalt hydroxide) added thereto. It is desirable to use a composition containing a polyacrylate such as sodium chloride in a range of 0.1 to 1% by weight. The reason for limiting the blending ratio of CMC and polyacrylate is that if it is less than their lower limit, it becomes difficult to obtain a paste that can stably produce a non-sintered nickel positive electrode with sufficient capacity. This is because if the upper limit of is exceeded, not only will it have a negative effect on battery performance, but also the amount of water required to form a paste will increase, making it difficult to produce a high-capacity positive electrode. A non-sintered nickel positive electrode is produced by applying and filling a conductive substrate, which is a current collector, with this active material paste and drying it. Examples of the conductive substrate include those with a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and those with a three-dimensional structure such as foamed metal and reticulated sintered metal fiber.

The above negative electrode is made by coating and fixing a mixture of hydrogen-absorbing alloy powder, polymer adhesive, and conductive powder as needed on a conductive substrate, which is a current collector. .

As a hydrogen storage alloy that is blended into the above mixture,
, IJ, which is not limited to, can absorb hydrogen electrochemically generated in the electrolyte, and discharge lI! Any material that can easily release its occluded hydrogen to i may be used, for example, L
a N i 5 , M m N i ,, L m N
i 5 (Lm; lanthanum-enriched mish metal)
, and some of these Ni are AISMn, Fe, Co,
T is C u % Z n SZ r % C r
Multi-element type substituted with elements such as SB, or T
Examples include iNj-based and TiFe-based materials.

Examples of polymer adhesives to be added to the above mixture include polysodium acrylate, polytetrafluoroethylene (P
TFE), carboxymethylcellulose (CMC
) etc. can also be called half-gerro. The blending ratio of the polymer binder is 0.00 parts by weight per 100 parts by weight of the hydrogen storage alloy powder.
It is desirable that the amount is in the range of 5 to 5 parts by weight.

Examples of the conductive powder to be mixed in the mixture include carbon black and graphite. The blending ratio of the conductive powder is 100% of the water cable storage alloy powder.
It is desirable that the amount is 0.1 to 4 parts by weight based on the amount of ffi.

Examples of the conductive substrate that is the current collector include those with a two-dimensional structure such as punched metal, expanded metal, and wire mesh, and those with a three-dimensional structure such as foamed metal and reticulated sintered metal fiber. can.

(Function) As mentioned above, when conventional non-sintered nickel positive electrodes are charged with low current at high temperatures, the oxygen gas generation reaction, which is a competitive reaction for charging, progresses, and as a result, charging is difficult. Become. In addition, the non-sintered nickel positive electrode expands during repeated charging and discharging, absorbs electrolyte and causes liquid depletion, and presses the negative electrode, which is mainly made of hydrogen storage alloy, as a counter electrode, reducing battery performance. .

For this reason, the present inventors developed a non-sintering active material paste containing nickel hydroxide mixed with a cadmium compound, which is used as a so-called antibolar agent to prevent an increase in battery internal pressure during battery polarity reversal. An attempt was made to fabricate a bonded nickel positive electrode. A non-sintered nickel positive electrode to which such a cadmium compound is added can improve the charging characteristics and expansion suppression at high temperatures to some extent, but as it is repeatedly charged and discharged, the cadmium compound added to the positive electrode becomes a hydrogen storage alloy as a main component. There was a problem that it diffused into the negative electrode and poisoned the negative electrode.

Therefore, the present inventors conducted intensive research on the method and amount of cadmium added, and found that by adding cadmium to nickel hydroxide using a coprecipitation method, cadmium with a large cation radius can be added to the crystal lattice of nickel hydroxide. Since cadmium can be immobilized within the nickel to make it difficult to move, it is possible to suppress the diffusion of cadmium into the negative electrode, which is mainly composed of a water cable storage alloy, to a practically sufficient level, and the expansion of the non-sintered nickel positive electrode due to the cadmium can be effectively suppressed. We found that it is possible to suppress the At this time, by regulating the amount of cadmium coprecipitated within the range of 2 to 8 mol%, it is possible to effectively improve the charging characteristics at high temperatures and suppress the expansion of the positive electrode as described above, and also to prevent cadmium coprecipitation from hydroxide. It was discovered that nickel can be produced stably. Furthermore, it has been found that by adding cobalt monoxide (C O ) separately from cadmium added by the coprecipitation method, diffusion of cadmium in the positive electrode can be suppressed even better. Although such effects have not been fully elucidated, they are thought to be due to the fact that when cobalt monoxide is added, the surface of nickel hydroxide is covered with a dense cobalt oxyhydroxide film.

In addition, the present inventors added cobalt monoxide to 5 to 20
By adding nickel hydroxide in a range of 7j% by weight, it can stably exist in the positive electrode without oxidation in a normal electrode manufacturing environment, and can be easily dissolved in an alkaline electrolyte to dissolve in water. It has been discovered that the utilization rate of the non-sintered nickel positive electrode can be significantly improved because the nickel oxide diffuses into the region where conduction occurs between the nickel oxide and the current collector. At this time, cobalt hydroxide is added to nickel hydroxide together with the cobalt monoxide in an amount of 2 to 15
Although the utilization rate is slightly lower than when cobalt monoxide is added alone by adding cobalt monoxide within the range of 20fff% by weight (however, the total amount with cobalt monoxide does not exceed 20fff%), The addition of cobalt hydroxide, which is lower in cost than cobalt monoxide, has the effect of reducing the manufacturing cost of the nickel positive electrode.

The above-mentioned addition of cadmium to nickel hydroxide by the coprecipitation method and addition of cobalt monoxide provide good charging characteristics at high temperatures, and suppress expansion of the non-sintered nickel positive electrode during charging and discharging.
; Li, it is possible to obtain a nickel-metal hydride secondary battery that has a longer lifespan due to improved utilization of the positive electrode.

Historically, the present inventors added carboxymethylcellulose (CMC) and polyacrylate in the range of 0.1 to 1% by weight each when preparing an active material paste, and investigated the solvent retention properties of CMC. It has been discovered that a non-sintered nickel positive electrode that has sufficient capacity, high strength, and is easy to handle can be obtained by having polyacrylate take over the role of structural stability.

(Example) Examples of the present invention will be described in detail below.

Example 1 First: pH of mixed solution of nickel sulfate and cadmium sulfate
By adjusting , nickel hydroxide grains containing 4 mol% of cadmium and having an average particle diameter of 50 μm and having a spherical or nearly spherical shape are precipitated, dried and then subjected to classification treatment to produce cadmium co-precipitated nickel hydroxide grains. did. Subsequently, cobalt monoxide whose surface was covered with a thin cobalt high-dimensional oxide film was added to the cadmium co-precipitated nickel hydroxide grains in amounts of 2TfX, 5% by weight, loIIlr, 20% by weight, 30% by weight, and 40ffl. % respectively, and CMCO. After adding and mixing 25% by weight/fl and 0.25% by weight/ffi% of sodium polyacrylate, water was added to prepare a type c base. Subsequently, each of these pastes was filled into a sintered nickel fiber substrate with a basis weight of m 700 g/m 2 and then dried at 120° C. to produce an active material-filled substrate. Thereafter, these active material-filled substrates were rolled using a roller press to adjust the thickness to 0.8 ms and to adjust the capacity density to 60 per lee.
It was made to have a capacity of 0 mAh or more, and further cut to form six types of non-sintered nickel positive electrodes.

Moreover, LmN i 4.2 Mno. i AN O. 3
C 00.2 (Lm is lanthanum enriched misch metal)
After mechanically crushing the ingot of 200
Relatively fine hydrogen storage alloy powder was obtained by classifying with a mesh sieve to remove large diameter particles. Next, 1% by weight of carbon black as a conductive powder and appropriate amounts of CMC and sodium polyacrylate as organic binders were added to this hydrogen storage alloy powder, and after pulverizing and mixing, water was added and kneaded. A paste was prepared. Continue to apply this paste to a thickness of 0. After coating on a perforated steel plate (■), drying and rolling, it was cut to produce a water cable occlusion alloy negative electrode.

Next, a test cell shown in FIG. 1 was assembled using an electrode group prepared by winding the negative electrode and non-sintered nickel positive electrode through a 0.2 lm thick separator made of polyamide nonwoven fabric. In FIG. 1, the battery case consists of a case body l made of acrylic resin and a cap 2 that serves as a sealing plate. A space 3 having the same inner diameter and height as an AA size metal container is formed in the center of the case body 1, and the electrode group 4 having the above structure is housed in this space 3. A pressure detector 5 is attached to the cap 2 so that the pressure inside the cell can be monitored. The case body l and the cap 2 are arranged in a space 3 in which the electrode group 4 is housed.
After injecting 2.4 ml of alkaline electromagnetic q solution prepared so that OH and LiOH were 7N and 1N, respectively,
assembled via a rubber sheet 6 and an O-ring 7,
It is sealed with bolts 8 and nuts 9. Further, the lead IO connected to the negative electrode of the electrode group 4 and the lead 11 connected to the positive electrode are connected to the rubber seats 6 and 0, respectively.
It passes between the rings 7 and extends to the outside. Such a test cell has a capacity per Ig of nickel hydroxide of 289
The capacity calculated as mA h was 1000mA h. However, in the case of a nickel positive electrode with a composition in which a large amount of cobalt monoxide is added, the nickel hydroxide content decreases, and if the size is the same, the capacity will be insufficient. Therefore, by adjusting the size of the nickel positive electrode, the above capacity value can be achieved. did.

Each test cell obtained was left at a temperature of 45° C. for 10 hours, charged with a current of 100 mA for 15 hours, and then discharged with IA until the battery voltage reached 0.8 V.

From the second cycle onwards, charge at 300mA for 5 hours,
IA discharge was repeated. The results of comparing the discharge capacity of the 20th cycle with the theoretical discharge capacity calculated from the amount of nickel hydroxide afi in the nickel positive electrode are shown in Table 1 below.

Table 1 As is clear from Table 1 above, 5% by weight of cobalt monoxide
It can be seen that by adding the above, the discharge capacity relative to the theoretical discharge capacity, that is, the utilization rate can be increased. However, as the amount of cobalt monoxide added increases, the volume occupied in the nickel positive electrode increases, which not only reduces the theoretical discharge capacity per unit volume of the electrode, but also causes irreversible oxidation of cobalt monoxide as described above. As a result, the reserve charge of the hydrogen storage alloy electrode becomes too small, resulting in a shortened battery life. Moreover, since cobalt monoxide is more expensive than nickel hydroxide, it is not preferable to increase the amount added unnecessarily. Therefore, the amount of cobalt monoxide added is 5~
A range of 20% by weight is desirable.

Example 2 The same procedure as in Example 1 was used except that a non-sintered nickel positive electrode was prepared in the same manner as in Example 1 using a paste containing cobalt monoxide and cobalt hydroxide in the proportions shown in Table 2 below. Seven test cells were assembled.

For each test cell obtained, charging and discharging were repeated in the same manner as in Example 1, and the utilization rate was investigated by comparing the discharge capacity at the 20th cycle with the theoretical discharge capacity calculated from the nickel hydroxide content in the nickel positive electrode. The results are also listed in Table 2.

Table 2 As is clear from Table 2 above, the No. 2 test cell incorporating a nickel positive electrode to which a small amount of cobalt monoxide was added was compared to the No. 1 test cell incorporating a nickel positive electrode to which only cobalt hydroxide was added. It can be seen that the utilization rate can be increased by about 15%. In addition, although not shown in Table 2, in a test cell incorporating a nickel positive electrode with cobalt hydroxide + 11% added, it took 10 to 20 hours before utilization started.
The test cell, which incorporated a nickel positive electrode with a small amount of cobalt monoxide, could be shortened to just a few cycles.

Furthermore, the lit of cobalt monoxide shown in Table 1 above
Comparing the No. 3 test cell incorporating a nickel positive electrode with the same amount of cobalt hydroxide and cobalt monoxide added (addition amount: 20 wt. 96%), the latter test cell Since the decrease in the utilization rate of nickel is only a few percent, it is effective to add cobalt hydroxide, which is relatively cheap, in combination to reduce the cost of the nickel positive electrode. However, if the total amount of both cobalt compounds exceeds 20% by weight, as explained in Example 1, the volume occupied in the nickel positive electrode becomes large and the theoretical discharge capacity per unit volume of the electrode decreases, which is not preferable.

〔Effect of the invention〕

As detailed above, according to the present invention, it is possible to provide a nickel-metal hydride secondary battery that achieves improved utilization of the positive electrode, extended life, and improved charging characteristics at high temperatures.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a test sensor used in an embodiment of the present invention. l...Battery case, 2...Kya knob, 4.
...Electrode I! 1, 5...Pressure detector.

Claims (1)

[Claims] At least cobalt monoxide (C
1. A nickel-hydrogen secondary battery comprising: a non-sintered nickel positive electrode made from an active material paste containing 5 to 20% by weight of oO); and a negative electrode mainly composed of a hydrogen storage alloy.