JP5686700B2 - Positive electrode active material for alkaline storage battery, method for producing positive electrode active material for alkaline storage battery, positive electrode for alkaline storage battery, and alkaline storage battery - Google Patents

Description

  The present invention relates to a positive electrode active material for an alkaline storage battery used in an alkaline storage battery, a method for producing the positive electrode active material for the alkaline storage battery, a positive electrode for an alkaline storage battery containing the positive electrode active material, and an alkali containing the positive electrode active material in the positive electrode. It relates to a storage battery.

  As is well known, various alkaline storage batteries (secondary batteries) are used as one of power sources for portable electronic devices and one of power sources for electric vehicles and hybrid vehicles. Among such alkaline storage batteries, there is a nickel-metal hydride storage battery as a storage battery having high energy density and excellent reliability. This nickel-metal hydride storage battery includes, for example, a plurality of positive electrodes mainly composed of nickel hydroxide and negative electrodes mainly composed of a hydrogen storage alloy via separators, and an alkaline electrolyte composed of potassium hydroxide and the like. It is a storage battery configured to be stored in a storage container.

An example of such an alkaline storage battery is described in Patent Document 1. In the alkaline storage battery described in Patent Document 1, nickel hydroxide particles whose surface is coated with a cobalt compound coating layer are used as the positive electrode active material, and the specific surface area is 8.0 [m ² / g] or more. In addition, a positive electrode active material that is 1.8 × 10 [m ² / g] or less is used. As a result, this alkaline storage battery is improved in its battery characteristics such that the polarization is suppressed and the utilization rate of the positive electrode active material is increased, the decrease in the electrolyte is suppressed, and the cycle life characteristics are improved. become.

Japanese Patent Laid-Open No. 2006-48954

  By the way, in recent years, with an increase in demand for hybrid vehicles, it has become inevitable to expand the use environment that places a higher load on hybrid vehicles, such as use in extreme heat and continuous use for a long time. Along with this, nickel-metal hydride storage batteries mounted on hybrid vehicles and the like are also required to have battery characteristics that can withstand the above-mentioned use environment such as extreme heat and long-time continuous operation. In such an environment, there is a concern that the internal pressure of the battery will rise rapidly due to the generation of oxygen gas from the positive electrode including the alkaline storage battery described in Patent Document 1 described above.

  The present invention has been made in view of such circumstances, and the object thereof is a positive electrode active material for an alkaline storage battery that has low environmental dependence and can maintain excellent battery characteristics as a storage battery, and an alkaline storage battery. It is in providing the manufacturing method of the positive electrode active material for batteries, the positive electrode for alkaline storage batteries containing this positive electrode active material, and the alkaline storage battery containing this positive electrode active material in a positive electrode.

In order to solve the above problem, the invention according to claim 1 is a positive electrode active material for alkaline storage batteries containing nickel hydroxide particles, wherein the nickel hydroxide particles are coated with a cobalt compound coating layer, the specific surface area of the cobalt compound coating layer coated with nickel hydroxide particles state, and are increasing the amount of 3 [m 2 ^{/ g]} or more with respect to the specific surface area of the nickel hydroxide particles before the coating by the cobalt compound coating layer , the specific surface area of the nickel hydroxide particles after the coating by the cobalt compound coating layer is summarized as 18~23 [m 2 / ^g] der Rukoto.

In order to solve the above problem, the invention according to claim 9 is a method for producing a positive electrode active material for an alkaline storage battery containing nickel hydroxide particles, the step of coating the nickel hydroxide particles with a cobalt compound coating layer. In the coating step, the specific surface area of the nickel hydroxide particles coated with the cobalt compound coating layer is 3 m compared to the specific surface area of the nickel hydroxide particles before coating with the cobalt compound coating layer. It is summarized that the specific surface area of the nickel hydroxide particles after coating with the cobalt compound coating layer is set to 18 to 23 [m ² / g] by coating so as to increase by ² / g] or more.

  According to such a configuration or method, variation in conductivity imparted to the nickel hydroxide particles by the cobalt compound coating layer is reduced. For this reason, the reaction with respect to charge of many nickel hydroxide particle | grains comes to be performed more uniformly between each particle | grain. This suppresses the possibility that current concentrates on some of the nickel hydroxide particles and the nickel hydroxide particles are overcharged early to promote the generation of oxygen gas. Thereby, the charge characteristic of the positive electrode containing such a positive electrode active material for an alkaline storage battery is improved, specifically, the generation of oxygen gas is suppressed, and a positive electrode containing this positive electrode active material for an alkaline storage battery is used. It is possible to prevent an increase in internal pressure of the stored battery. In other words, the positive electrode active material for alkaline storage batteries makes it possible to reduce the environmental dependency of alkaline storage batteries and maintain excellent battery characteristics as a storage battery.

The invention according to claim ² is summarized in that, in the positive electrode active material for alkaline storage battery according to claim 1, the increase amount of the specific surface area is 12 [m ² / g] or less.
According to such a configuration, the paste viscosity can be easily filled into the foamed nickel substrate.

  The invention according to claim 3 is the positive electrode active material for alkaline storage battery according to claim 1 or 2, wherein the average particle diameter of the nickel hydroxide particles is A [μm], and the cobalt with respect to the mass of the nickel hydroxide particles. When the proportion of the mass of cobalt contained in the compound coating layer is B [%], “B / A” is 0.37 [% / μm] or more and 1.12 [% / μm] or less. It is a summary.

  The invention according to claim 10 is the method for producing a positive electrode active material for an alkaline storage battery according to claim 9, wherein, in the covering step, an average particle diameter of the nickel hydroxide particles is set to A [μm], and the hydroxylation is performed. When the ratio of the mass of cobalt contained in the cobalt compound coating layer to the mass of nickel particles is B [%], “B / A” is 0.37 [% / μm] or more and 1.12 The gist is to coat the film so as to be [% / μm] or less.

  It is known that the nickel hydroxide particles are improved in conductivity and charge characteristics by the cobalt compound coating layer. However, if the average particle size becomes small, the surface area increases too much, and the surface cannot be coated properly, and the charging characteristics deteriorate. Conversely, it is also known that as the average particle size increases, the surface area decreases and the output characteristics deteriorate. Therefore, as in this configuration or method, the charge characteristics of the nickel hydroxide particles are maintained favorably by selecting the amount of cobalt that coats the nickel hydroxide particles according to the particle size of the nickel hydroxide particles. Will be able to.

The gist of the invention described in claim 4 is that, in the positive electrode active material for alkaline storage battery described in claim 3, the “B / A” is 0.48 [% / μm] or more.
According to such a configuration, the amount of cobalt that coats the nickel hydroxide particles can be made in a better range according to the particle size of the nickel hydroxide particles. The characteristics can be improved.

  The invention according to claim 5 is the positive electrode active material for an alkaline storage battery according to any one of claims 1 to 4, wherein the nickel hydroxide particles contain at least magnesium in a solid solution state. .

According to such a configuration, the output characteristics of the positive electrode can be made favorable.
The invention according to claim 6 is the positive electrode active material for alkaline storage battery according to any one of claims 1 to 5, wherein the cobalt compound coating layer is made of cobalt oxyhydroxide having a β-type crystal structure. This is the gist.

According to such a configuration, it is possible to improve the capacity characteristics, particularly the high temperature capacity characteristics, by coating with cobalt oxyhydroxide having a β-type crystal structure.
In order to solve the above problems, the invention according to claim 7 is a positive electrode for an alkaline storage battery containing a positive electrode active material for an alkaline storage battery, wherein the positive electrode active material for an alkaline storage battery is any one of claims 1 to 6. The gist is that the positive electrode active material for an alkaline storage battery according to one item is used.

  According to such a configuration, the alkaline storage battery positive electrode has low environmental dependency and can maintain excellent battery characteristics as a storage battery. Thereby, the performance of the alkaline storage battery including the alkaline storage battery positive electrode can be maintained high.

  In order to solve the above-mentioned problem, the invention described in claim 8 is an alkaline storage battery provided with a positive electrode for alkaline storage battery, and as a positive electrode active material for alkaline storage battery contained in the positive electrode for alkaline storage battery, claims 1 to 6 are provided. It is summarized that the positive electrode active material for an alkaline storage battery according to any one of the above is used.

  According to such a configuration, the alkaline storage battery has low environmental dependency and can maintain excellent battery characteristics as a storage battery. Thereby, the battery performance of this alkaline storage battery is maintained high.

  According to the present invention, a positive electrode active material for an alkaline storage battery, a method for producing a positive electrode active material for an alkaline storage battery, a positive electrode for an alkaline storage battery including the positive electrode active material, and an alkaline storage battery including the positive electrode active material as a positive electrode Thus, the environment dependency is low, and excellent battery characteristics as a storage battery can be maintained.

The graph which shows the relationship of the "endurance internal pressure" with respect to the "specific surface area increase amount" of the same positive electrode active material, and the "paste viscosity" about one Embodiment of the alkaline storage battery which contains the positive electrode active material for alkaline storage batteries of this invention in a positive electrode, respectively. The graph which shows the relationship of "25 degreeC utilization factor" with respect to "cobalt coating amount / average particle diameter" in the same embodiment.

Hereinafter, the positive electrode active material for alkaline storage batteries according to the present invention will be described. First, an alkaline storage battery including a positive electrode active material for an alkaline storage battery in the positive electrode will be described.
A nickel metal hydride storage battery as an alkaline storage battery is a sealed battery, and is a battery used as a power source for an electric vehicle or a hybrid vehicle. In this nickel-metal hydride storage battery, for example, a plurality of negative electrode plates containing a hydrogen storage alloy and a positive electrode plate containing nickel hydroxide (Ni (OH) ₂ ) are laminated via a separator made of an alkali-resistant resin nonwoven fabric. The electrode group is connected to the current collector plate and is housed in a resin battery case together with the electrolytic solution.

Next, production of this nickel metal hydride storage battery will be described.
[Production of nickel hydroxide particles]
In this embodiment, the nickel hydroxide particles contained in the positive electrode plate were produced as nickel hydroxide particles containing magnesium in a solid solution state.

  That is, a mixed solution containing nickel sulfate and magnesium sulfate, a sodium hydroxide aqueous solution, and an ammonia aqueous solution were prepared, and each was supplied into a reaction tank to prepare nickel hydroxide that solidly dissolves magnesium. As a result, the average particle diameter of nickel hydroxide powder was 10 [μm], and the ratio of magnesium to all metal elements (nickel and magnesium) contained in the nickel hydroxide powder was 3 [mol%]. The average particle diameter of the nickel hydroxide powder was measured with a laser diffraction / scattering particle size distribution analyzer.

Further, when an X-ray diffraction pattern using CuKα rays was recorded, it coincided with the XRD pattern described in the JCPDS inorganic material file number: 14-117, and consisted of a β-Ni (OH) ₂ type single layer. It was confirmed. That is, it was confirmed that magnesium was dissolved in nickel hydroxide.

[Production of positive electrode active material]
Next, oxyhydroxide having a β-type crystal structure on the surface of nickel hydroxide particles containing magnesium in a solid solution state (hereinafter also referred to as magnesium solid solution nickel hydroxide particles) obtained as described above. A cobalt coating layer (hereinafter also referred to as a cobalt compound coating layer) is formed. Thereby, a positive electrode active material composed of nickel hydroxide particles coated with a coating layer of a cobalt compound was manufactured. Specifically, first, an aqueous sodium hydroxide solution is supplied into an aqueous solution (suspension) containing magnesium-dissolved nickel hydroxide particles, a cobalt sulfate aqueous solution is supplied, and air is supplied into the reaction vessel. A coating layer made of cobalt oxyhydroxide having a β-type crystal structure was formed on the surface of the magnesium-dissolved nickel hydroxide particles in the reaction vessel.

  In addition, when the mass of nickel hydroxide particles (the mass including the solid solution when the solid solution is included) is “100”, the cobalt compound coating that coats the nickel hydroxide particles is compared with the mass corresponding to “100”. The ratio of the mass of cobalt contained in the layer, that is, the cobalt coating amount was set to 5.0 [%]. That is, the coating amount of the cobalt compound was adjusted so that the cobalt coating amount was 5.0 [%] with respect to the mass of the magnesium-dissolved nickel hydroxide particles. Moreover, the average valence of cobalt was 2.9. Furthermore, since the average particle diameter of the nickel hydroxide particles is 10 [μm], the proportion of the mass of cobalt contained in the cobalt compound coating layer (cobalt coating amount) [%] / average particle diameter [μm] is 0.5 [% / μm] (= 5.0 [%] / 10 [μm]). The amount of cobalt coating on the nickel hydroxide particles coated with the cobalt compound coating layer can be quantified by ICP analysis.

The specific surface area of the nickel hydroxide particles coated with this cobalt compound coating layer was 20 [m ² / g]. On the other hand, the specific surface area of the nickel hydroxide particles before coating with the cobalt compound coating layer was 14 [m ² / g]. From this, the specific surface area of the nickel hydroxide particles increased by the coating of the cobalt compound coating layer, that is, the “specific surface area of the nickel hydroxide particles coated by the cobalt compound coating layer” and “before coating by the cobalt compound coating layer” The increase in specific surface area was calculated from the difference from the “specific surface area of nickel hydroxide particles”. That is, the specific surface area increase amount of the nickel hydroxide particles was 6 [m ² / g] (= 20 [m ² / g] -14 [m ² / g]). The specific surface area of the nickel hydroxide particles before and after coating with the cobalt compound coating layer was measured using the BET method by nitrogen gas adsorption.

  Next, X-ray diffraction measurement using CuKα rays was performed, and the crystal structure of the cobalt compound coating layer was investigated. As a result, it was confirmed that the hexagonal rhombohedral layer structure described in JCPDS inorganic material file number: 7-169 was highly crystalline cobalt oxyhydroxide.

[Production of nickel positive electrode]
Next, the nickel positive electrode which comprises a positive electrode plate was produced. Specifically, first, a predetermined amount of an additive such as metallic cobalt, water, and a thickener such as carboxymethylcellulose (CMC) are added to the positive electrode active material powder obtained as described above, and kneaded. By doing so, it was made into a paste with a water content of about 2.6 ± 0.2 [%]. The paste viscosity can be measured with a rotary viscometer, and the measurement conditions in the rotary viscometer are, for example, a rotational speed of 50 [rpm] and a sample amount of 0.5 [ml]. Stable measurement was possible.

  The paste was filled into a foamed nickel substrate, dried, and then pressure-molded to produce a nickel positive electrode plate. Next, this nickel positive electrode plate was cut into a predetermined size, and a positive electrode plate could be obtained. The theoretical capacity of the nickel electrode (positive electrode plate) is calculated on the assumption that nickel in the active material undergoes a one-electron reaction.

[Production of alkaline storage batteries]
Next, a negative electrode containing a hydrogen storage alloy was manufactured by a known method. Specifically, by applying a predetermined amount of hydrogen storage alloy powder adjusted to a predetermined particle size to the electrode support, a negative electrode plate having a capacity larger than that of the positive electrode could be obtained.

  Next, the negative electrode plate and the positive electrode plate are laminated via a separator made of a non-woven fabric of alkali-resistant resin, connected to a current collector plate, and an electrolytic solution mainly composed of potassium hydroxide (KOH) A rectangular sealed nickel-metal hydride storage battery was produced by housing the battery in a resin battery case.

[Selection of increase in specific surface area]
Next, the relationship between the “endurance internal pressure” and “paste viscosity” and “specific surface area increase” of the manufactured nickel metal hydride storage battery will be described with reference to FIG. In FIG. 1, the measured value of “endurance internal pressure” is indicated by black diamonds, and the specific surface area increases are “0.40”, “0.40”, “1.00”, “1.60”, “ 3.20 ”,“ 5.65 ”,“ 6.25 ”,“ 7.55 ”[m ² / g], respectively. The “paste viscosity” is indicated by a white triangle, and the increase in specific surface area is “−0.20”, “0.40”, “0.40”, “0.40”, “1.00”. , “1.30”, “1.60”, “5.05”, “5.65” [m ² / g], respectively. In addition, a graph relating to “endurance internal pressure” with respect to “specific surface area increase” indicated by symbol P is obtained from the measurement value of “endurance internal pressure”, and “specific surface area increase” indicated by symbol V from the measurement value of “paste viscosity”. A graph for “paste viscosity” was obtained. The “endurance internal pressure” refers to the internal pressure measured as a result of performing a predetermined charge / discharge test on the alkaline storage battery. The lower the value, the greater the amount of oxygen gas generated by the positive electrode. This indicates that the battery characteristics as an alkaline storage battery are good because there is little or no environmental dependency.

That is, the present inventors investigated the relationship between “endurance internal pressure” and “specific surface area increase”. For this reason, nickel hydroxide particles for evaluation with different specific surface area increases after coating by the cobalt compound coating layer, for example, by changing the pH when the cobalt compound coating layer is formed, by the same method as described above Produced. And the alkaline storage battery for evaluation which contains the nickel hydroxide particle for evaluation manufactured in this way in a positive electrode was manufactured, respectively, and "durable internal pressure" of these alkaline storage batteries was measured, respectively. As a result, the present inventors have found that when the “specific surface area increase amount” is at least 3 [m ² / g] or more, a positive electrode for an alkaline storage battery in which the “endurance internal pressure” can be kept low can be produced. In addition, the specific surface area after the coating by the cobalt compound coating layer when the “specific surface area increase amount” is 3 [m ² / g] or more was 18 to 23 [m ² / g].

That is, as shown in FIG. 1, when the “specific surface area increase” is in the range of 0 to 2 [m ² / g], the “endurance internal pressure” indicates a high value such as the pressure P1 or the pressure P2. It is shown that the internal pressure is greatly increased. On the other hand, when the “specific surface area increase” is in the range of 3 [m ² / g] or more, it is indicated that the “endurance internal pressure” is maintained in the vicinity of the pressure P3 lower than the pressure P2. Incidentally, 8 [m 2 / ^g] tendency of change "durable pressure" in larger range, 3~8 [m 2 / ^g] is the inventors are continuously changing trend of "durable pressure" in the range of It is clear from their experience.

In the present embodiment, there is a difference of 0.1 [MPa] between the pressure P1 and the pressure P2, and there is a difference of 0.05 [MPa] between the pressure P2 and the pressure P3. That is, since it is clear that the amount of change in the “endurance internal pressure” in the range where the “specific surface area increase amount” is 3 to 12 [m ² / g] is at most 0.05 [MPa], The change rate of the “endurance internal pressure” is 0.0055 [MPa · g / m ² ] (≈0.05 [MPa] / 9 [m ² / g]). In order to ensure more certainty, even if the range of the “specific surface area increase” is set to a range of 3 to 8 [m ² / g], the change amount of the “endurance internal pressure” in the range is at most 0.05. Since it is [MPa], the change amount of the “endurance internal pressure” in the same range is 0.01 [MPa · g / m ² ] (= 0.05 [MPa] / 5 [m ² / g]). .

In addition, it is thought that increasing the “specific surface area increase” will form a better conductive network between the nickel hydroxide particles and the foamed nickel substrate, but the “specific surface area increase” is limited. I know. More specifically, when the “paste viscosity” is measured, it can be seen that the “paste viscosity” increases in proportion to the “specific surface area increase”. This is because the nickel hydroxide particles coated with the cobalt compound coating layer are likely to contain water, that is, moisture is dispersed and enters the surface increased by the coating, so that it remains on the surface between the nickel hydroxide particles. This is thought to be because the amount of intervening water decreases. By the way, in this embodiment, the nickel positive electrode is manufactured by filling a foamed nickel substrate with a paste. However, when the paste viscosity becomes high, it becomes difficult to fill the foamed nickel substrate with the paste. It is clear through experiments by the inventors that it is impossible to create the above. That is, in the present embodiment, when the “specific surface area increase amount” exceeds 12 [m ² / g], the “paste viscosity” becomes higher than the viscosity V1 at which it is difficult to fill the foamed nickel substrate with the paste. It has been found that a good positive electrode cannot be produced. That is, the “specific surface area increase” is preferably 12 [m ² / g] or less.

In view of the above, the inventors have determined that the range where the “specific surface area increase” is smaller than 3 [m ² / g] is not preferable because the “endurance internal pressure” becomes high, and 12 [m ² / g. g] was determined to be a range in which it was difficult to fill the foamed nickel substrate with the paste. The inventors can reduce the “endurance internal pressure” of the alkaline storage battery, and the “specific surface area increase” that can be easily filled into the foamed nickel substrate is 3 [m ² / g] or more to 12 It was found to be in the range up to [m ² / g].

  The specific surface area of the nickel hydroxide particles itself may be increased instead of increasing the specific surface area by the coating of the cobalt compound coating layer. There is a risk of changing the output characteristics of nickel hydroxide particles. Further, since nickel hydroxide particles require a coating with a cobalt compound coating layer to improve conductivity, it is considered appropriate to increase the specific surface area with the cobalt compound coating layer constituting the outer surface. Therefore, the inventors decided to increase the specific surface area by the cobalt compound coating layer.

  Here, a predetermined charge / discharge test for the alkaline storage battery, which is performed in order to measure the “endurance internal pressure”, will be described. In the charge / discharge test, the nickel-metal hydride storage battery is charged at a predetermined current under an environmental temperature of “35 ° C.” so that the SOC (State Of Charge) changes between “20% to 80%”, and This is a test in which discharge with a predetermined current is one cycle and this cycle is repeated 1000 times. At that time, after the 500th cycle, the charge / discharge cycle is temporarily stopped so that the internal pressure of the nickel-metal hydride storage battery becomes 0 [MPa]. The predetermined current to be charged is a current corresponding to three times the numerical value representing the rated capacity, that is, 3C, and the predetermined current to be discharged is a current corresponding to three times the numerical value representing the rated capacity, that is, 3C. . And the maximum value of the internal pressures measured during this charge / discharge test was obtained as the “endurance internal pressure”. By the way, this charge / discharge test is a test based on a model set by the inventors as a pattern frequently used as charge / discharge generated in a nickel-metal hydride storage battery when a hybrid vehicle is used. Further, the internal pressure of the nickel-metal hydride storage battery was measured by installing a pressure sensor in a hole provided in a sealed storage container in which the power generation element was stored so as to seal the hole.

[Cobalt coat amount / average particle size selection]
Subsequently, the relationship between the calculation of the utilization rate of the manufactured nickel metal hydride storage battery and the amount of cobalt coating with respect to the average particle diameter will be described with reference to FIG. In FIG. 2, the measured value of “25 ° C. utilization rate” is indicated by a white circle. The unit of “25 ° C. utilization rate” is [%], and the unit of “cobalt coating amount / average particle size” is [% / μm].

  That is, the inventors decided to examine the relationship between “25 ° C. utilization rate” and “cobalt coat amount / average particle size”. Therefore, nickel hydroxide particles for evaluation with different cobalt coating amounts were produced by the same method as described above. And the alkaline storage battery for evaluation which contains the nickel hydroxide particle for evaluation manufactured in this way in a positive electrode was manufactured, respectively, and "25 degreeC utilization factor" of these alkaline storage batteries for evaluation was measured, respectively. As a result, when the “cobalt coat amount / average particle size” is within a predetermined range, the “25 ° C. utilization factor” increases. Specifically, the present inventors are 95, which is optimal for electric vehicles and hybrid vehicles. It was found that a positive electrode for an alkaline storage battery having a concentration of 7% or more can be produced. The results are shown in Table 1.

図２に示されるように、「コバルトコート量／平均粒径」の異なる複数の評価用のアルカリ蓄電池は、その「２５℃利用率」の値の変化態様が「コバルトコート量／平均粒径」に対して上に凸である凸状の態様に変化することが測定された。すなわち、「コバルトコート量／平均粒径」（単に「指標」ともいう）に対する「２５℃利用率」は、「指標」が０．４８［％／μｍ］付近では約９８．０［％］であり、「指標」がそれよりも小さい０．３７［％／μｍ］付近では約９６．０［％］であり、「指標」がさらに小さい０．２８［％／μｍ］付近では約９４．２［％］である。逆に、「コバルトコート量／平均粒径」に対する「２５℃利用率」は、「指標」が０．４８［％／μｍ］よりも大きい１．１２［％／μｍ］付近では約９８．７［％］であり、「指標」がそれよりも大きい１．４０［％／μｍ］付近では約９４．６［％］である。

As shown in FIG. 2, a plurality of evaluation alkaline storage batteries having different “cobalt coat amount / average particle size” have a change mode of the “25 ° C. utilization rate” value of “cobalt coat amount / average particle size”. In contrast, it was measured to change to a convex shape that is convex upward. That is, the “25 ° C. utilization rate” relative to “cobalt coating amount / average particle size” (also simply referred to as “index”) is about 98.0 [%] when the “index” is around 0.48 [% / μm]. There is about 96.0 [%] near 0.37 [% / μm] where the “index” is smaller than that, and about 94.2 near 0.28 [% / μm] where the “index” is even smaller. [%]. On the contrary, the “25 ° C. utilization ratio” with respect to “cobalt coating amount / average particle size” is about 98.7 in the vicinity of 1.12 [% / μm] where “index” is larger than 0.48 [% / μm]. It is about 94.6 [%] in the vicinity of 1.40 [% / μm] where the “index” is larger than that.

  If the cobalt coating amount is constant, a large value of “cobalt coating amount / average particle size” indicates that the average particle size is small, and if the average particle size is too small, It is considered that the cobalt compound coating layer cannot be satisfactorily coated on the surface of the nickel particles. Conversely, a small value of “cobalt coating amount / average particle size” indicates that the average particle size is large, and it is thought that as the average particle size increases, the surface area of the nickel hydroxide particles decreases. It is done.

  Thus, the “25 ° C. utilization factor” becomes high when the “cobalt coating amount / average particle size” is 0.37 [% / μm] or more and 1.12 [% / μm] or less. It was found that the ratio was smaller in the range smaller than .37 [% / μm] and in the range larger than 1.12 [% / μm]. That is, the “25 ° C. utilization rate” increases when the “cobalt coating amount / average particle size” is 0.37 [% / μm] or more and 1.12 [% / μm] or less. It turned out to change to a convex shape. In addition, since the “cobalt coating amount / average particle size” is 0.48 [% / μm] or more and 1.12 [% / μm] or less, the “25 ° C. utilization rate” becomes extremely good. preferable.

  The “25 ° C. utilization rate” is predicted to change in value depending on the structure of the nickel-metal hydride storage battery. However, regardless of the structure of the nickel-metal hydride storage battery, The tendency that the “index” increases in the range of 0.37 to 1.12 [% / μm] and changes to a convex shape is the same. That is, even if a change occurs in elements other than “cobalt coating amount / average particle size”, the “cobalt coating amount / average particle size” is within the range of 0.37 to 1.12 [% / μm], “25 ° C. use It is the same that the “rate” tends to increase.

  By the way, the “25 ° C. utilization rate” in the present embodiment is a ratio of the capacity discharged from the nickel-metal hydride storage battery charged by a predetermined charge capacity under the environmental temperature of “25 ° C.” to the charge capacity. Calculated by equation (1).

Utilization rate [%] = discharge capacity [Ah] / charge capacity [Ah] × 100 (1)
Here, the discharge capacity is a capacity obtained by charging a nickel hydride storage battery for a predetermined charge capacity under an environmental temperature of 25 ° C., and then discharging a discharge current of 1/10 of the charge capacity from the storage battery. [Ah]. At this time, the discharge capacity is represented by the product of the measured discharge current and the measured time from the start of discharge to the end-of-discharge voltage (1 V). In general, it is judged that the storage battery is more excellent as the discharge capacity is larger. Further, SOC (State Of Charge) indicates the remaining capacity of the storage battery, and indicates a ratio excluding the amount of electricity discharged from the fully charged storage battery. That is, if the charge capacity is constant, it can be said that the battery has superior battery characteristics as the discharge capacity increases, that is, the utilization rate increases.

  From this, according to the index of “cobalt coat amount / average particle diameter”, the “25 ° C. utilization factor” is increased to 0.37 [% / μm] or more and 1.12 [% / μm] or less. If the nickel hydroxide particles are produced within the range, the battery characteristics of the nickel metal hydride storage battery using the nickel hydroxide particles can be improved. More preferably, if nickel hydroxide particles having a “cobalt coating amount / average particle size” in the range of 0.48 [% / μm] or more and 1.12 [% / μm] or less are manufactured, The battery characteristics of the nickel metal hydride storage battery using nickel hydroxide particles can be further improved.

(Function)
The nickel metal hydride storage battery is suitable when the value of “endurance internal pressure” is kept low. And it turned out that the value of "endurance internal pressure" is kept low in the range whose "specific surface area increase amount" of nickel hydroxide particle is 3-12 [m < ² > / g]. Accordingly, the nickel hydroxide particles have a specific surface area coated with the cobalt compound coating layer that increases in a range of 3 to 12 [m ² / g] with respect to the specific surface area before coating with the cobalt compound coating layer. As a result, the battery characteristics of the nickel-metal hydride storage battery using the nickel hydroxide particles for the positive electrode can be maintained high.

  In addition, the nickel-metal hydride storage battery is suitable when the value of “25 ° C. utilization factor” is maintained high. The “25 ° C. utilization factor” was found to maintain a high numerical value when “cobalt coating amount / average particle size” was in the range of 0.37 to 1.12 [% / μm]. More preferably, the “25 ° C. utilization rate” was maintained at a higher value when the “cobalt coating amount / average particle size” was in the range of 0.48 to 1.12 [% / μm]. Accordingly, the nickel hydroxide particles are coated with the cobalt compound coating layer so that the “index” is in the range of 0.37 to 1.12 [% / μm], whereby the nickel hydroxide particles are converted into the positive electrode. The battery characteristics of the nickel metal hydride storage battery used in the above can be maintained high. Furthermore, the nickel hydroxide particles are coated with a cobalt compound coating layer so that the “index” is in the range of 0.48 to 1.12 [% / μm], so that the nickel hydroxide particles are used as the positive electrode. The battery characteristics of the used nickel metal hydride storage battery can be maintained higher.

As described above, according to the positive electrode active material for an alkaline storage battery of the present embodiment, the effects listed below can be obtained.
(1) The increase amount of the specific surface area of the nickel hydroxide particles coated with the cobalt compound coating layer with respect to the specific surface area of the nickel hydroxide particles before coating with the cobalt compound coating layer is set to 3 [m ² / g] or more. This reduces the variation in conductivity imparted to the nickel hydroxide particles by the cobalt compound coating layer. For this reason, the reaction with respect to charge of many nickel hydroxide particle | grains comes to be performed more uniformly between each particle | grain. This suppresses the possibility that current concentrates on some of the nickel hydroxide particles and the nickel hydroxide particles are overcharged early to promote the generation of oxygen gas. Thereby, the charge characteristic of the positive electrode containing such a positive electrode active material for an alkaline storage battery is improved, specifically, the generation of oxygen gas is suppressed, and a positive electrode containing this positive electrode active material for an alkaline storage battery is used. It is possible to prevent an increase in the internal pressure of the battery.

Moreover, by making the increase amount of a specific surface area into 12 [m < ² > / g] or less, it can be set as the paste viscosity with easy filling to a foaming nickel board | substrate.
(2) It is known that the nickel hydroxide particles are improved in conductivity and charge characteristics by the cobalt compound coating layer. However, when the average particle diameter of the nickel hydroxide particles becomes small, the surface area increases too much, so that the cobalt compound coating layer cannot be suitably coated on the surface and the charging characteristics are deteriorated. On the other hand, it is also known that the nickel hydroxide particles have a surface area that decreases as the average particle size increases, and output characteristics deteriorate. Therefore, according to this configuration, by setting the cobalt coating amount / average particle size to 0.37 [% / μm] or more and 1.12 [% / μm], according to the particle size of the nickel hydroxide particles. Thus, by selecting the amount of cobalt that coats the nickel hydroxide particles, the charging characteristics of the nickel hydroxide particles can be maintained satisfactorily.

  (3) Further, by setting the cobalt coating amount / average particle size to 0.48 [% / μm] or more, the amount of cobalt coating the nickel hydroxide particles is further increased according to the particle size of the nickel hydroxide particles. Since it can be set as a favorable range, the charging characteristics of the nickel hydroxide particles can be further improved.

(4) Since the nickel hydroxide particles contain at least magnesium in a solid solution state, the output characteristics of the positive electrode plate can be made suitable.
(5) Also, coating with cobalt oxyhydroxide having a β-type crystal structure improves the capacity characteristics, particularly the high temperature capacity characteristics.

(Other embodiments)
In addition, the said embodiment can also be implemented with the following aspects.
In the above embodiment, the nickel hydroxide particles are exemplified for the case where magnesium is contained in a solid solution state. However, the present invention is not limited thereto, and the nickel hydroxide particles may be replaced with cadmium (Cd), cobalt (Co), Zinc (Zn) may be included in a solid solution state. As a result, the degree of freedom regarding the production and characteristics of the nickel hydroxide particles is improved.

  In the above-described embodiment, the case where metallic cobalt is used as an additive has been illustrated. However, the present invention is not limited to this, and zinc compounds such as zinc oxide, zinc chloride, and zinc hydroxide may be used as additives. Thereby, the freedom degree about preparation of an additive and a characteristic comes to improve.

  In the above embodiment, the case where the average particle diameter of the nickel hydroxide powder is 10 [μm] is exemplified, but the present invention is not limited to this, and the average particle diameter of the nickel hydroxide powder is 5 [μm] or more and 20 [μm]. It may be the following. Thereby, the freedom degree concerning a nickel hydroxide particle improves.

  In the above embodiment, the case where the average valence of cobalt is 2.9 is illustrated, but this is not limiting, and the average valence of cobalt may be 2.6 or more and 3.0 or less. . Thereby, the freedom degree concerning creation of nickel hydroxide particles improves.

  When the average valence of cobalt is larger than 3.0, the balance of charge in the crystal of cobalt oxyhydroxide is lost, and the β-type crystal structure is easily transferred to the γ-type crystal structure. Cobalt oxyhydroxide having a γ-type crystal structure has a strong oxidizing power (it is easy to reduce itself), and self-discharge increases. Thereby, there exists a possibility that an active material utilization factor may fall large. Therefore, by setting the average valence of cobalt to 3.0 or less in this way, it becomes possible to maintain the crystal structure of cobalt oxyhydroxide in β-type, and an alkali that does not cause the disadvantage of increasing self-discharge. A positive electrode for a storage battery can be obtained.

-In the said embodiment, it illustrated about the case where the specific surface area of the nickel hydroxide particle | grains coat | covered with the cobalt compound coating layer is 20 [m < ² > / g]. However, the present invention is not limited to this, and the specific surface area of the nickel hydroxide particles coated with the cobalt compound coating layer may be in the range of 18 to 23 [m ² / g] including 20 [m ² / g]. Thereby, the freedom degree of design of the positive electrode active material for alkaline storage batteries is improved.

In other words, in the above embodiment, the specific surface area of the nickel hydroxide particles before coating with the cobalt compound coating layer is exemplified as 14 [m ² / g]. However, the present invention is not limited to this, and the specific surface area of the nickel hydroxide particles coated with the cobalt compound coating layer may be in the range of 8 to 20 [m ² / g] including 14 [m ² / g]. Thereby, the freedom degree of design of the positive electrode active material for alkaline storage batteries is improved.

  In the above embodiment, the case where the “endurance internal pressure” is measured at an environmental temperature of 35 ° C. is illustrated. However, the present invention is not limited to this, and the environmental temperature at which the “endurance internal pressure” is measured may be a temperature lower than 35 ° C. or a temperature higher than 35 ° C. Thereby, the evaluation of the nickel metal hydride storage battery by the “endurance internal pressure” can be appropriately performed according to the use environment.

  In the above embodiment, the case where the utilization factor is “25 ° C. utilization factor” measured at an environmental temperature of 25 ° C. is illustrated. However, the present invention is not limited to this, and the environmental temperature at which the utilization factor is measured may be a temperature lower than 25 ° C or a temperature higher than 25 ° C. Thereby, evaluation of the nickel hydride storage battery by a utilization rate can be performed appropriately according to use environment.

  In the above embodiment, the case where the battery is a secondary battery has been illustrated, but the present invention is not limited thereto, and the battery may be a primary battery.

Claims (10)

A positive electrode active material for an alkaline storage battery containing nickel hydroxide particles,
The nickel hydroxide particles are coated with a cobalt compound coating layer,
The specific surface area of the cobalt compound coating layer coated with nickel hydroxide particles state, and are increasing the amount of 3 [m 2 ^{/ g]} or more with respect to the specific surface area of the nickel hydroxide particles before the coating by the cobalt compound coating layer the positive electrode active material for an alkaline storage battery specific surface area of the nickel hydroxide particles after the coating by the cobalt compound coating layer, wherein the Ru der 18~23 [m 2 / ^g]. The positive electrode active material for an alkaline storage battery according to claim 1, wherein an increase amount of the specific surface area is 12 [m ² / g] or less. When the average particle diameter of the nickel hydroxide particles is A [μm], and the ratio of the mass of cobalt contained in the cobalt compound coating layer to the mass of the nickel hydroxide particles is B [%]
The positive electrode active material for an alkaline storage battery according to claim 1, wherein “B / A” is 0.37 [% / μm] or more and 1.12 [% / μm] or less. The positive electrode active material for an alkaline storage battery according to claim 3, wherein the “B / A” is 0.48 [% / μm] or more. The positive electrode active material for an alkaline storage battery according to any one of claims 1 to 4, wherein the nickel hydroxide particles include at least magnesium in a solid solution state. The positive electrode active material for an alkaline storage battery according to any one of claims 1 to 5, wherein the cobalt compound coating layer is made of cobalt oxyhydroxide having a β-type crystal structure. A positive electrode for an alkaline storage battery containing a positive electrode active material for an alkaline storage battery,
The positive electrode active material for alkaline storage batteries as described in any one of Claims 1-6 is used as said positive electrode active material for alkaline storage batteries. The positive electrode for alkaline storage batteries characterized by the above-mentioned. An alkaline storage battery comprising a positive electrode for an alkaline storage battery,
The alkaline storage battery, wherein the alkaline storage battery positive electrode active material according to any one of claims 1 to 6 is used as the alkaline storage battery positive electrode active material contained in the alkaline storage battery positive electrode. A method for producing a positive electrode active material for an alkaline storage battery containing nickel hydroxide particles,
A step of coating the nickel hydroxide particles with a cobalt compound coating layer;
In the coating step, the specific surface area of the nickel hydroxide particles coated with the cobalt compound coating layer is 3 [m ² / g compared to the specific surface area of the nickel hydroxide particles before coating with the cobalt compound coating layer. ] The positive electrode active material for an alkaline storage battery , wherein the specific surface area of the nickel hydroxide particles after coating by the cobalt compound coating layer is 18-23 [m ² / g] Manufacturing method. In the coating step, the average particle diameter of the nickel hydroxide particles is A [μm], and the ratio of the mass of cobalt contained in the cobalt compound coating layer to the mass of the nickel hydroxide particles is B [%]. 10. The production of the positive electrode active material for an alkaline storage battery according to claim 9, wherein “B / A” is 0.37 [% / μm] or more and 1.12 [% / μm] or less. Method.

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