JP6435885B2 - Coated nickel hydroxide powder for positive electrode active material of alkaline secondary battery and method for producing the same - Google Patents

Description

  The present invention relates to a nickel hydroxide powder that is a positive electrode active material for an alkaline secondary battery and a method for producing the same, and relates to a coated nickel hydroxide powder coated with a cobalt compound and a method for producing the same.

  In recent years, alkaline secondary batteries have attracted attention as power sources for high power applications such as portable devices and electric vehicles. Various alkaline secondary batteries have been proposed. Among them, nickel-hydrogen secondary batteries are already widely used as secondary batteries having high energy density and excellent reliability. A nickel metal hydride secondary battery includes a positive electrode made of an active material mainly composed of nickel hydroxide, a negative electrode mainly composed of a hydrogen storage alloy, and an alkaline electrolyte. It is produced by directly filling the active material containing nickel hydroxide in the holes.

  The nickel hydroxide used for the positive electrode is a solid solution of cobalt in nickel hydroxide powder to improve utilization at high temperatures, or a solid solution of zinc or magnesium to improve life characteristics, etc. Improvements have been made. In high power applications, not only improvement of utilization at high temperatures and improvement of life characteristics, but also improvement of output characteristics are strongly demanded. However, since nickel hydroxide powder is an electrical insulator, it has poor electrical conductivity, and since the current does not reach the nickel hydroxide sufficiently, the electrochemistry of nickel hydroxide when used as a positive electrode active material for alkaline secondary batteries. There is a problem that the utilization rate is low.

  In order to solve such a problem, a cobalt compound such as cobalt oxide or cobalt hydroxide is added as a conductive material to ensure conductivity between nickel hydroxide particles. These added cobalt compounds are dissolved in a high-concentration alkali metal hydroxide solution, which is an electrolyte for alkaline secondary batteries, and are oxidized during charging to form cobalt oxyhydroxide on the surface of the nickel hydroxide particles. By precipitating, electrical conductivity is expressed and a conductive network is formed between the nickel hydroxide particles.

  The nickel hydroxide powder-added positive electrode to which the cobalt compound is added is generally formed by mixing nickel hydroxide powder and cobalt compound powder together with a binder into a paste, which is three-dimensional such as foam metal (material is nickel metal). The metal porous body is filled and manufactured through processes such as drying and pressing. However, since the cobalt compound powder mixed with the binder is not necessarily sufficiently dispersed in the nickel hydroxide powder, there is a problem in that the utilization rate of the positive electrode is greatly reduced under use conditions during high load charging. there were.

  As means for solving this problem, a method of coating the surface of nickel hydroxide powder particles with a cobalt compound has been proposed. For example, Patent Document 1 proposes a nickel active material for a storage battery in which a thin layer of β-type cobalt hydroxide is formed on particles whose main component is nickel hydroxide. This nickel active material is obtained by precipitating nickel hydroxide powder from a nickel salt in an alkaline aqueous solution, immersing the nickel hydroxide powder in an aqueous solution of cobalt sulfate or cobalt nitrate, and then neutralizing with an alkaline aqueous solution. It is supposed to be obtained by doing.

  In addition, as a method for producing nickel hydroxide powder coated with cobalt hydroxide, Patent Document 2 discloses that an aqueous solution containing nickel hydroxide powder and adjusted to pH 11 to 13 with caustic alkali, an aqueous solution containing cobalt and ammonium ions. There has been proposed a method of continuously and quantitatively supplying a supply body simultaneously.

  Furthermore, in Patent Document 3, the nickel ion concentration is 10 to 50 mg / L and the cobalt ion concentration is 5 to 40 mg while maintaining the pH, temperature, and ammonium ion concentration of the suspension of the nickel hydroxide raw material powder at predetermined values. The aqueous solution containing cobalt ions is supplied to 1 kg of the nickel hydroxide raw material powder at a supply rate of 0.7 g / min or less in terms of cobalt, and the aqueous solution containing ammonium ions is added to the suspension so as to be / L. A supply method has been proposed.

  However, these proposals have a problem that the coating of cobalt hydroxide is unevenly formed on the surface of the nickel hydroxide particles, or the coating is peeled off in the paste manufacturing process. That is, in general, a battery positive electrode plate using nickel hydroxide powder is dispersed in a solvent such as water, kneaded with various auxiliaries, pasted into a foam metal, and dried. It is produced by. At this time, the coating of the cobalt compound formed on the particle surface in the kneading of the paste manufacturing process is peeled off, and a dense portion and a sparse portion of the coating are formed in the produced electrode plate, and between the nickel hydroxide particles The formation of the conductive network is not uniformly performed, and there is a problem that the utilization factor of the positive electrode is greatly reduced under use conditions during high load charging. Moreover, when there are many peelings, the problem that the difference arises in the nickel hydroxide powder used as a raw material and the cobalt content in a battery positive electrode plate may arise.

  In order to solve these problems, proposals have been made for the purpose of optimizing the kneading conditions in the paste manufacturing process and improving the uniformity and adhesion of the cobalt compound coating. For example, Patent Document 4 discloses that an alkali two-powder amount of a cobalt compound coating layer when 20 g of coated nickel hydroxide powder is shaken in 50 mL of water and a sealed container for 1 hour is 20% by mass or less of the total cobalt compound coating amount. A coated nickel hydroxide powder for a secondary battery positive electrode active material has been proposed. Although the technology of Patent Document 4 can improve the uniformity and adhesion of the cobalt compound coating as compared with the prior art, with the recent increase in output and capacity of alkaline secondary batteries, the uniformity and adhesion are improved. Further improvement is required.

JP-A-63-152866 JP 07-133115 A JP 2000-149941 A JP 2012-230840 A

  The present invention has been made in view of such conventional circumstances, and when forming a coating of a cobalt compound on the particle surface of nickel hydroxide powder in an aqueous solution, the uniformity and adhesion of the coating are ensured. Thus, an object of the present invention is to provide a coated nickel hydroxide powder suitable for an alkaline secondary battery positive electrode active material, in which peeling of the coating during paste formation is suppressed, and a method for producing the same.

  In order to achieve the above object, the present inventors have conducted extensive research on a method for producing a coated nickel hydroxide powder. As a result, the adhesiveness of the cobalt compound coating during paste formation includes the powder in the cylindrical cell. It was found that the slurry can be inserted and shaken, and the exfoliation matter adhering to the inner wall surface of the cell generated at that time can be evaluated by the turbidity of the dispersion obtained by dispersing in a predetermined aqueous solution. Furthermore, by obtaining the knowledge that the adhesion of the formed cobalt compound coating is improved by controlling the temperature and time of the drying process performed after the cobalt compound is formed on the particle surface of the cobalt hydroxide powder by a wet method. The present invention has been completed.

That is, the coated nickel hydroxide powder for an active material of an alkaline secondary battery according to the present invention is an alkaline secondary battery positive electrode in which the surface of core particles made of nickel hydroxide is coated with a cobalt compound having a cobalt valence of 2.5 or more. A nickel hydroxide powder for active material, in which 10 g of the coated nickel hydroxide powder and 10 to 30 mL of water are charged in a cylindrical cell made of polypropylene that can be sealed, and rolls at 200 to 280 times / min. After shaking with a shaker for 16 hours, the exfoliated material adhering to the inner wall surface of the cylindrical cell was redispersed in 20 mL of an aqueous solution containing 0.2 to 0.8% by mass of formic acid, and the resulting dispersion was cloudy. The turbidity measured by an integrating sphere turbidimeter is 30 degrees or less.

Arbitrary preferable to use a cylindrical or prismatic cell as the tubular cell. Further, the composition of the core particles have the general _{formula: Ni 1-x-y Co} x M y (OH) 2, ( wherein x is 0.005 to 0.05, y is from 0.005 to 0. And M is preferably represented by one or more elements of Ca, Mg, and Zn), and the cobalt content in the cobalt compound is 1 to 10 mass based on the entire coated nickel hydroxide powder. % Is preferred.

The method for producing a coated nickel hydroxide powder for an alkaline secondary battery positive electrode active material according to the present invention includes a coated nickel hydroxide for a positive electrode active material of an alkaline secondary battery in which the surface of core particles made of nickel hydroxide is coated with a cobalt compound. A method for producing a powder, wherein an aqueous solution of cobalt salt and an aqueous alkali solution are supplied to a slurry in which core particles made of nickel hydroxide are dispersed in water while stirring, and the surface of the core particles is neutralized and crystallized with cobalt hydroxide. A coating step for forming a coating containing cobalt hydroxide as a main component and a slurry of core particles on which the coating is formed are maintained at a pH of 12.5 or more and 13.5 or less on a 25 ° C. basis, and oxygen is supplied while stirring. after separation of the cobalt hydroxide in the coating is oxidized and the oxidation step you the cobalt valence of the cobalt compound in 2.5 above, the solid-liquid the slurry by, Covering and having a dry step of then 1.5 to 3.5 hours drying held in the range temperature of one hundred and four to one hundred and twenty ° C. of the formed core particles. In the above oxidation step, the total amount of oxygen supplied to the slurry of the core particles on which the coating is formed is 30 L / mol or more and 110 L / mol or less in a standard state with respect to the molar amount of cobalt in the coating. Is preferred.

In the coating step, while the pH of the slurry in which the core particles are dispersed in water is maintained at 8 or more based on the liquid temperature of 25 ° C., the slurry flow at the contact portion between the slurry liquid surface and the supplied cobalt salt aqueous solution Ratio of the feed rate ρ (mol / sec) of the cobalt salt in the cobalt salt solution to the product of the feed width d (cm) of the cobalt salt solution in the direction perpendicular to the direction and the flow velocity v (cm / sec) of the slurry ρ / It is preferable to control (d × v) to 3.5 × 10 ⁻⁴ mol / cm ² or less.

In the coating step, the supply position of the cobalt salt aqueous solution with respect to the ratio ρ / (d × v) of the supply rate ρ of the cobalt salt in the cobalt salt aqueous solution to the product of the supply width d of the cobalt salt aqueous solution and the flow velocity v of the slurry; It is preferable to control the ratio D / {ρ / (d × v)} of the separation distance D (cm) from the supply position of the alkaline aqueous solution to 0.5 × 10 ⁵ cm ³ / mol or more.

  According to the present invention, the cobalt compound is uniformly coated on the particle surface of the coated nickel hydroxide powder, and the coating is difficult to peel off in the process of mixing with a binder or the like to form a paste. A coated nickel hydroxide powder for a secondary battery positive electrode active material can be provided. Furthermore, the coated nickel hydroxide powder of the present invention is not only difficult to peel off as described above, but also has high conductivity, so the utilization rate is improved, and a portable device that requires high output characteristics and high capacity is required. It is suitable as a power source for power applications for electronic devices and electric vehicles.

  In addition, according to the method for producing a coated nickel hydroxide powder according to the present invention, a coated nickel hydroxide powder having a uniform and highly adhesive cobalt compound coating can be obtained easily and stably on an industrial scale. Value is extremely high.

  Conventionally, as a method of evaluating the adhesion of a coating such as cobalt hydroxide or cobalt oxyhydroxide in a coated nickel hydroxide powder, the coated nickel hydroxide powder is mixed with a solvent such as water in a sealed container and shaken for a certain period of time. A method is used in which the amount of peeling of the cobalt hydroxide coating is measured and the amount of peeling with respect to the total amount of coating is evaluated. However, the above method has a problem in that it is difficult to accurately separate and quantify the peeled coating and the remaining coating, and the measurement error becomes large. In addition, the peeled material adhering to the inner wall of the container using a transparent sealed container is also evaluated by the transmittance of the container, but the coated nickel hydroxide powder with improved coating adhesion has a large amount of peeling. Since there are few, it is hard to make a difference in evaluation and it was difficult to predict the influence at the time of paste manufacture.

  On the other hand, in the present invention, the exfoliated matter adhering to the inner wall of the sealed container is redispersed in the solution, and evaluated by the turbidity of the obtained dispersion solution. Therefore, in the coated nickel hydroxide powder with improved adhesion, In addition, it is possible to accurately evaluate the adhesion, and it is possible to accurately predict the ease of peeling at the time of manufacturing the paste.

  The coated nickel hydroxide powder for an alkaline secondary battery positive electrode active material of the present invention (hereinafter simply referred to as a coated nickel hydroxide powder) is an alkaline secondary battery positive electrode active material in which the surface of core particles made of nickel hydroxide is coated with a cobalt compound. It is a coated nickel hydroxide powder for a substance, and 10 g of coated nickel hydroxide powder and 10 to 30 mL of water are charged into a cylindrical cell that can be sealed, and 16 rolls are shaken at 200 to 280 times / min. After shaking for a period of time, the exfoliated material adhering to the inner wall surface of the cylindrical cell was redispersed in 20 mL of an aqueous solution containing 0.2 to 0.8% by mass of formic acid, and the turbidity of the obtained dispersion was integrated. The turbidity measured with a photometer is 30 degrees or less.

  More specifically, first, 10 g of coated nickel hydroxide powder and 10 to 30 mL of water are charged into a cylindrical cell that can be sealed to form a slurry. When the amount of the coated nickel hydroxide powder charged into the cylindrical cell is small, the amount of wall surface adhesion due to shaking decreases, and the measurement accuracy decreases. On the other hand, when the amount of the coated nickel hydroxide powder charged into the cylindrical cell is increased, the amount of exfoliation that cannot adhere to the inner wall of the container is increased, and the measurement accuracy is lowered.

  In addition, when the amount of water charged into the cylindrical cell together with the above-described coated nickel hydroxide powder is less than 10 mL, the amount of coated nickel hydroxide powder per unit volume of water is too large. The nickel powder cannot be sufficiently shaken, and the amount of peeling of the coating is reduced more than originally, so that the measurement accuracy is lowered. On the other hand, when the amount of water exceeds 30 mL, the amount of the coated nickel hydroxide powder with respect to the unit volume of water becomes too small.

  The reason for using the cylindrical cell for shaking is that the contact area between the coated nickel hydroxide powder and the inner wall of the cylindrical cell can be made relatively large and the contact time during shaking can be made large. The form of the cylindrical cell is not particularly limited as long as it can be sealed, but is preferably a cylindrical or square cylindrical transparent cell because it is easily available. Further, the material of the cylindrical cell is preferably one in which the charged state of the wall surface is negative in order to sufficiently adhere the peeled material to the inner wall surface, and any one of polyethylene, polypropylene, polyethylene terephthalate, and polystyrene is used. It preferably consists of seeds. In particular, a transparent cylindrical cell is preferable because it can be easily confirmed whether or not there is a peeled material remaining in the cylindrical cell when the peeled material is redispersed. The size of the cylindrical cell is preferably about 1.5 to 3 times the volume of the slurry so that the slurry obtained by mixing the coated nickel hydroxide powder and water can be sufficiently shaken.

  The cylindrical cell containing the slurry described above is shaken for 16 hours with a roll-type shaker with the number of shakes set to 200 to 280 times / minute. As a shaker, for example, a cylindrical cell is installed horizontally in a roll-type shake incubator (manufactured by Thomas Scientific Instruments, equivalent to TS-12, shake width 70 mm).

  After shaking, the slurry is carefully washed out from the cylindrical cell while paying sufficient attention not to peel off the exfoliated material adhering to the inner wall surface. Thereafter, the peeled material adhering to the inner wall surface is redispersed in 20 mL of an aqueous solution containing 0.2 to 0.8% by mass of formic acid. At this time, formic acid acts as a dispersant to peel off the peeled material from the inner wall surface and re-disperse it in the aqueous solution. The turbidity of the obtained redispersion is measured to evaluate the adhesion of the coated nickel hydroxide powder coating. Turbidity (JIS K0101) is measured with an integrating sphere turbidimeter (for example, turbidimeter PT-200 manufactured by Mitsubishi Analitech Co., Ltd.).

  In the coated nickel hydroxide powder of the present invention, the turbidity measured by the above measuring method is 30 degrees or less. That is, the cobalt compound coating of the coated nickel hydroxide powder of the present invention has high adhesion. In this way, the coated nickel hydroxide powder having a turbidity of 30 degrees or less suppresses the peeling of the cobalt compound coating in the process of mixing with a binder or the like in the paste manufacturing process of an alkaline secondary battery, and contains cobalt in the resulting paste. It has been confirmed that the amount is maintained approximately equal to the cobalt content of the coated nickel hydroxide powder prior to pasting.

In the core particles to be coated the cobalt compound, the composition _{formula: Ni 1-x-y Co} x M y (OH) 2, ( wherein x is 0.005 to 0.05, y is 0 0.005 to 0.05, and M is preferably represented by one or more elements of Ca, Mg, and Zn.

  In the above general formula, if x in the formula representing the cobalt content is less than 0.005, the effect of improving the charging efficiency achieved by the addition of cobalt cannot be obtained, and conversely if it exceeds 0.05, the discharge voltage decreases. Occurs and the battery performance decreases. In addition, regarding the content of M representing the additive element, if y in the formula is less than 0.005, the effect of reducing the volume change of nickel hydroxide at the time of charge / discharge, which is the effect of adding the element M, is not exhibited. If it exceeds 0.05, the battery capacity will be lowered more than the effect of reducing the volume change, and the battery performance will be deteriorated.

  Moreover, in the said coated nickel hydroxide powder, it is preferable that the cobalt amount contained in the cobalt compound which comprises the coating | cover is 1-10 mass% with respect to the whole coated nickel hydroxide powder, and 3-7 mass% It is more preferable that When the cobalt content in the coating is less than 1% by mass, the coating amount as a cobalt compound is insufficient, so that the electrical conductivity is not sufficiently exhibited, and the effect of forming a conductive network between nickel hydroxide particles is sufficient. It may not be demonstrated. On the other hand, even if the amount of cobalt in the coating exceeds 10% by mass, only the amount of coating of the cobalt compound increases, and no further improvement in the coating effect is observed. In addition, the coating of the cobalt compound is preferably one in which the nickel hydroxide particles that are the core particles are uniformly coated, and may be a fine island-shaped coating as long as it is uniform. What coat | covers the whole surface is preferable.

  Further, the cobalt compound constituting the coating is mainly composed of cobalt oxyhydroxide or a mixture of cobalt oxyhydroxide and cobalt hydroxide, and the cobalt content in the coating is The content is preferably 90% by mass or more, and more preferably 95% by mass or more, based on the entire metal element contained in the coating. In addition, in order to improve battery characteristics when used for the positive electrode of the battery, it is possible to add Ca, Mg, Zn or the like as an additive element to the coating, but the cobalt content is 90% by mass. If it is less than this, the conductivity may not be sufficiently improved by the coating.

  Further, the cobalt in the coating preferably has a valence of 2.5 or more. Thereby, a required amount of cobalt oxyhydroxide is generated in the coating, and better adhesion and conductivity are obtained. Usually, the upper limit of the cobalt valence is 3.

  The method for producing a coated nickel hydroxide powder of the present invention comprises supplying a cobalt salt aqueous solution and an alkaline aqueous solution to a stirred slurry in which core particles made of nickel hydroxide are dispersed in water, and neutralizing crystals on the surface of the core particles. A coating step of forming a coating mainly composed of the deposited cobalt hydroxide, and an oxidation step of oxidizing the cobalt hydroxide in the coating by supplying oxygen while stirring the slurry of the core particles on which the coating is formed And a drying step of drying the slurry for 1.5 to 3.5 hours while keeping the temperature of the core particles on which the coating is formed within a range of 104 to 120 ° C. after solid-liquid separation of the slurry. It is said.

  Here, the drying conditions in the drying step are important. The coating of the cobalt compound formed in the coating step is excellent in uniformity, but it is necessary to further improve the adhesion. By controlling the heating conditions in the drying step, the adhesion is improved and a coating with high uniformity and adhesion can be obtained. Hereafter, the manufacturing method of the covering nickel hydroxide powder of this invention is demonstrated for every process.

(Coating process)
In the coating step, while stirring a slurry in which core particles made of nickel hydroxide are dispersed in water, an aqueous cobalt salt solution and an alkaline aqueous solution are supplied to the slurry, and the cobalt hydroxide that has been neutralized and crystallized on the surface of the core particles is added. This is a step of forming a coating containing the main component.

In this way, a coating with good uniformity can be obtained by coating nickel hydroxide particles, which are core particles, with a cobalt compound by a wet method, but in order to achieve higher uniformity, the core particles are dispersed in water. Cobalt in a direction perpendicular to the flow direction of the slurry at the contact portion between the slurry liquid surface and the supplied cobalt salt aqueous solution while maintaining the pH of the slurry at 25 ° C. based on the liquid temperature of 25 ° C. or more with an alkaline aqueous solution. The ratio ρ / (d × v) of the supply rate ρ (mol / sec) of the cobalt salt in the cobalt salt aqueous solution to the product of the supply width d (cm) of the aqueous salt solution and the flow velocity v (cm / sec) of the slurry is 3. It is preferable to control to 5 × 10 ⁻⁴ mol / cm ² or less.

  As described above, a cobalt salt aqueous solution and an alkaline aqueous solution are added to a slurry in which nickel hydroxide powder is dispersed in water while stirring the slurry, and water is added to the surface of the nickel hydroxide particles by neutralization crystallization reaction. In the case of coating with cobalt oxide, cobalt is present in an ionic state in a region where the pH value of the slurry is low, but as the pH value increases, precipitation of cobalt hydroxide starts gradually. At this time, if nickel hydroxide particles are present nearby, cobalt hydroxide precipitates on the surface of the nickel hydroxide particles that are more energetically stable.

  If the cobalt ion concentration suddenly increases and exceeds the critical supersaturation degree in the pH range of the slurry in which cobalt ions are present, cobalt hydroxide alone in water, even if nickel hydroxide particles are not present nearby Precipitates. However, when the pH value of the slurry is low, specifically, when the pH is less than 8, the precipitation rate of cobalt hydroxide is slow, so even if the cobalt ion concentration exceeds the critical supersaturation level, Cobalt hydroxide does not precipitate.

  On the other hand, when the pH value of the slurry in which the cobalt ions are present is 8 or more, the critical supersaturation degree of the cobalt ion concentration is decreased, and therefore, when the cobalt ion concentration is increased, the critical supersaturation degree is easily exceeded. As a result, cobalt hydroxide that does not adhere to the surface of the nickel hydroxide particles and precipitates alone is generated. Cobalt hydroxide precipitated in this way adheres to the surface of the nickel hydroxide particles when the nickel hydroxide slurry is filtered, but it adheres sparsely, not only reducing the uniformity, but also simply by filtration. Therefore, the adhesion is low.

  Therefore, in order to uniformly form cobalt hydroxide on the surface of the nickel hydroxide particles, the pH (25 ° C. standard) of the slurry of nickel hydroxide particles is controlled to 8 or more, and cobalt ions in the liquid in the pH region are controlled. It is preferable to maintain the concentration below a concentration at which single precipitation of cobalt hydroxide does not occur. Cobalt hydroxide deposited on the surface of nickel hydroxide particles by this method is deposited according to the surface structure of nickel hydroxide, so that it is uniformly formed on the surface of the particle, and adhesion is increased by drying in a subsequent step.

  Thus, in order to ensure the precipitation of cobalt hydroxide with high adhesion, it is important to avoid the formation of a high cobalt ion concentration region. For this purpose, the ratio of the supply rate of the cobalt salt to the amount of slurry that flows into the supply unit and is mixed may be reduced in the supply unit in which the aqueous solution of cobalt salt is supplied to the slurry. That is, by reducing the supply rate of the cobalt salt aqueous solution, even when the amount of slurry to be mixed is small, the cobalt salt concentration is sufficiently lowered, or the amount of slurry mixed is increased and the cobalt salt supplied into the slurry is supplied. It is preferable to dilute the aqueous solution so that it diffuses into the slurry as fast as possible to prevent a state in which an extremely high cobalt ion concentration region appears in the slurry.

  The amount of the slurry to be mixed may be considered as the amount of slurry flowing into the portion to be mixed in contact with the supplied cobalt salt aqueous solution on the slurry surface, and the initial mixing is performed in a very short time. When the flow rate is sufficient, it can be considered as a slurry surface that contacts the cobalt salt aqueous solution per unit time. That is, the amount of slurry mixed is determined by the supply width (d) of the cobalt salt aqueous solution in the direction perpendicular to the flow direction of the slurry at the contact portion between the liquid level of the slurry and the cobalt salt aqueous solution and the flow velocity (v) of the slurry surface. ). When the contact portion between the slurry liquid surface and the cobalt salt aqueous solution is circular, the supply width (d) of the cobalt salt aqueous solution in the direction perpendicular to the flow direction of the slurry surface is equal to the diameter of the circular contact portion. Will be equal. Further, the flow velocity on the slurry surface can be easily obtained by simulation when actual measurement is difficult.

Therefore, in the present invention, at the contact portion between the liquid level of the slurry and the cobalt salt aqueous solution, the product of the supply width (d) of the cobalt salt aqueous solution and the flow velocity (v) of the slurry in a direction perpendicular to the flow direction of the slurry. The ratio of the feeding rate (ρ) of the cobalt salt in the cobalt salt aqueous solution, that is, ρ / (d × v) is decreased. Specifically, ρ / (d × v) is set to 3.5 × 10 ⁻⁴ mol / it is preferably in the cm ² or less, and more preferably set to 2.0 × ¹⁰ -4 mol / cm ² or less. When the above ρ / (d × v) exceeds 3.5 × 10 ⁻⁴ mol / cm ² , a high concentration region of cobalt ions may appear and single precipitation of cobalt hydroxide may occur. In addition, although the minimum of said (rho) / (dxv) is not specifically limited, Since productivity will fall when supply rate ((rho)) is reduced, it shall be 0.01 * 10 < ^-4 > mol / cm < ² > or more. Is preferred.

  Here, the area of the contact portion, that is, the area where the cobalt salt aqueous solution supplied from the supply port toward the liquid level of the slurry first comes into contact with the liquid level of the slurry is defined as the cobalt salt aqueous solution and the opening size of the supply port. When the supply port is small enough to be supplied as a single stable liquid flow having substantially the same cross section, it corresponds to the projected area of the supply port on the slurry surface. That is, when the supply port of the aqueous solution of cobalt salt is as small as described above, the area of the contact portion between the liquid surface of the slurry and the aqueous solution of cobalt salt may be the projected area of the supply port on the slurry surface. On the other hand, when the supply port of the cobalt salt aqueous solution is larger than the above-described level, the flow rate of the cobalt salt aqueous solution discharged from the supply port is generally slow, so the cobalt salt aqueous solution is supplied uniformly from the supply port. In other words, it may be difficult to control the area of the contact portion between the slurry liquid level and the cobalt salt aqueous solution.

Therefore, in order to supply the cobalt salt aqueous solution from the supply port as one stable liquid flow, when the supply amount of the cobalt salt aqueous solution is about 100 to 10000 mL / min, the opening area of the supply port is set to 0.01 to It is preferable to set it as 1.0 cm ² . When the opening area is less than 0.01 cm ² , the supply rate of the cobalt salt aqueous solution becomes slow, and sufficient productivity may not be obtained. Further, when the cross-sectional area of the supply port exceeds 1.0 cm ² , it becomes difficult to uniformly supply the cobalt salt aqueous solution from the supply port, and supply of the cobalt salt aqueous solution is within the projected area onto the slurry surface of the supply port. Since the amount varies and is easily supplied in a concentrated manner, the cobalt salt aqueous solution may not be sufficiently diffused.

  When the cobalt salt aqueous solution is supplied by spraying the slurry surface from the supply port with a spray nozzle or the like, the contact area of the cobalt salt aqueous solution with the slurry surface is the area where the cobalt salt aqueous solution is sprayed on the slurry surface. can do. In addition, if the cobalt salt aqueous solution can be uniformly supplied from the supply port to the slurry surface as described above, a plurality of supply ports are provided in order to increase the total supply amount of the cobalt salt aqueous solution and increase the productivity. May be. The number of supply ports is not particularly limited, and may be determined in consideration of the supply rate of the cobalt salt aqueous solution at each supply port and the product of the supply width of the cobalt salt aqueous solution and the flow rate of the slurry.

  Further, even when the pH value suddenly increases in the supply part of the cobalt salt aqueous solution, the concentration at which the cobalt hydroxide alone does not occur within the high pH range, that is, the critical saturation concentration decreases, and the cobalt hydroxide alone Precipitation is facilitated. As a result, even if nickel hydroxide particles are not present nearby, single precipitation of cobalt hydroxide starts, and cobalt hydroxide having poor adhesion and uniformity tends to adhere to the nickel hydroxide surface particles. In order to prevent this, it is preferable that the alkaline aqueous solution supplied at the same time is also diffused at a sufficient rate to suppress the formation of a high pH region due to a rapid concentration increase of the alkaline aqueous solution.

For example, even when the flow rate of the slurry is sufficiently high, especially when the supply rate of cobalt salt per unit area to the slurry surface exceeds 0.01 mol / cm ² · min, If the distance from the supply position of the alkaline aqueous solution is short, the reaction occurs in the high pH region in contact with the cobalt salt aqueous solution before the alkaline aqueous solution is sufficiently diffused in the slurry. The possibility of precipitation of cobalt oxide may increase.

In order to avoid this, the cobalt salt aqueous solution with respect to the ratio {ρ / (d × v)} of the supply rate ρ of the cobalt salt in the cobalt salt aqueous solution to the product of the supply width d of the cobalt salt aqueous solution and the flow velocity v of the slurry. The ratio of the distance D (cm) between the supply position of the aqueous solution and the supply position of the alkaline aqueous solution, that is, D / {ρ / (d × v)} is preferably 0.5 × 10 ⁵ cm ³ / mol or more, More preferably, it is 1.0 × 10 ⁵ cm ³ / mol or more. In addition, since the upper limit of D / {ρ / (d × v)} is limited by the feed rate (ρ) and the size of the reaction tank, the upper limit in the normal range is 100 × 10 ⁵ cm ³ / mol. Degree.

  The productivity can be improved by carrying out the coating process in a continuous manner, but it is preferable to carry out in a batch manner in order to achieve uniform coating on the nickel hydroxide particles. Accordingly, the following description will be made with reference to an example of a manufacturing method using a batch method.

  First, a nickel hydroxide powder slurry, a cobalt salt aqueous solution, and an alkaline aqueous solution are prepared. Each particle constituting the nickel hydroxide powder as the core material preferably has an average particle diameter of 6 to 12 μm in order to obtain good battery characteristics when used as a positive electrode material of a battery. The concentration of the nickel hydroxide powder in the slurry is preferably 400 to 1200 g / L. When the concentration of the nickel hydroxide powder is less than 400 g / L, the active sites on the surface of the nickel hydroxide particles, where the cobalt hydroxide is deposited, are insufficient, and the cobalt hydroxide may precipitate alone in the liquid. On the other hand, when the concentration of the nickel hydroxide powder exceeds 1200 g / L, the viscosity of the slurry increases and stirring cannot be performed sufficiently, and the coating of cobalt hydroxide may become uneven.

  There is no limitation in particular in the said cobalt salt, What is necessary is just a water-soluble cobalt compound with which cobalt hydroxide is produced | generated by pH control. Specifically, cobalt sulfate and cobalt chloride are preferred, and cobalt sulfate free from halogen contamination is more preferred. Moreover, although there is no limitation in particular also to the said alkali, water-soluble sodium hydroxide, potassium hydroxide, etc. are preferable and sodium hydroxide is more preferable from a viewpoint of cost.

  The nickel hydroxide powder slurry is preferably one in which particles are dispersed in pure water or the like in order to prevent contamination of impurities. Also, the cobalt salt aqueous solution and the alkali aqueous solution are preferably those obtained by dissolving a cobalt salt or an alkali in pure water. The concentration of the cobalt salt aqueous solution and the alkali aqueous solution may be within a range that does not reprecipitate in the piping of the apparatus and can be suppressed to the extent that there is no problem even if the nickel hydroxide concentration of the slurry changes. It is preferable to adjust the concentration appropriately according to the concentration of the liquid.

  In the batch production method, a cobalt salt aqueous solution and an alkaline aqueous solution forming a coating are continuously supplied to a reaction vessel containing a nickel hydroxide powder slurry as a core material while stirring the slurry, Cobalt hydroxide-coated nickel hydroxide powder is produced by coating the surface of nickel hydroxide particles with neutralized and crystallized cobalt hydroxide. The batch-type reaction tank is not particularly limited, but a reactor having a stirring device and a liquid temperature adjusting mechanism is desirable in order to uniformly coat the surface of the nickel hydroxide particles.

  The cobalt salt aqueous solution and the alkaline aqueous solution need to be supplied separately. These may be supplied at the same time, or a part of the slurry may be put in the reaction vessel, and the aqueous cobalt salt solution and the aqueous alkali solution and the remaining slurry may be supplied to this slurry. However, when all these liquids are mixed in advance and supplied to the reaction vessel as a mixed liquid, the reaction may occur in the mixed liquid and cobalt hydroxide may be deposited alone. Further, when the cobalt salt aqueous solution and the alkaline aqueous solution are not separately supplied to the slurry, the coating amount of cobalt hydroxide formed on the nickel hydroxide particle surface may not be uniform among the particles. In addition, you may mix the metal salt aqueous solution used as an addition element with cobalt salt aqueous solution.

  The pH of the slurry when the supplied cobalt salt aqueous solution and alkaline aqueous solution are mixed to an equilibrium state is preferably maintained within the range of 8 to 11.5 on the basis of the liquid temperature of 25 ° C. More preferably, it is kept within the range of 5. When the pH value of the slurry is less than 8, the precipitation of cobalt hydroxide is too slow, so the productivity is lowered. Conversely, when the pH value exceeds 11.5, the generated cobalt hydroxide tends to be in a gel state, so that the coating is good. Can be difficult.

  Moreover, it is preferable to control the pH of the slurry with a fluctuation range of ± 0.2 so that the pH of the slurry is maintained at a substantially constant value within a range of 8 to 11.5 on the basis of 25 ° C. If the fluctuation range of the pH exceeds the above range, the coating amount with cobalt hydroxide may vary. In order to keep the pH of the slurry constant within the above fluctuation range, for example, it is preferable to continuously measure the pH with a pH controller using, for example, a glass electrode method, and continuously feedback control the flow rate of the alkaline aqueous solution with the pH controller. .

  It is preferable that the temperature of a slurry exists in the range of 30-60 degreeC before and behind addition of cobalt salt aqueous solution and alkaline aqueous solution. If the temperature is less than 30 ° C, the reaction rate decreases, so the precipitation of cobalt hydroxide is slow. Conversely, if the temperature exceeds 60 ° C, the reaction rate is too fast, so the precipitation of cobalt hydroxide on the nickel hydroxide particle surface is uneven. It is because it is easy to become. Further, the temperature of the slurry is preferably controlled with a fluctuation range of ± 1 ° C. so as to be maintained at a substantially constant value within the above temperature range. This is because if the temperature of the slurry exceeds the above fluctuation range, the impurity concentration in the precipitated cobalt hydroxide tends to fluctuate, and the characteristics may not be stable when used in a battery.

(Oxidation process)
The oxidation step is a step of oxidizing cobalt hydroxide in the coating by supplying oxygen while stirring the slurry of the core particles on which the coating is formed. Thereby, cobalt hydroxide can be oxidized into cobalt oxyhydroxide, and the conductivity of the coated nickel hydroxide powder can be further improved.

  Cobalt oxyhydroxide can also be obtained by oxidizing cobalt hydroxide using an oxidizing agent such as sodium hypochlorite or persulfate, but the nickel hydroxide powder coated with cobalt hydroxide is oxidized to these oxides. When oxidized with an agent, a part of the nickel hydroxide powder that is the core material is also oxidized to produce relatively unstable nickel oxyhydroxide, so that the adhesion of the cobalt hydroxide coating becomes unstable. Moreover, it is disadvantageous in terms of cost to use an expensive oxidizing agent such as sodium hypochlorite and persulfate.

  In the oxidation step, the presence of OH ions contained in the slurry accelerates the oxidation reaction, so that it is possible to oxidize cobalt hydroxide to cobalt oxyhydroxide without using an expensive oxidizing agent. Therefore, it is preferable to maintain the OH ion concentration contained in the slurry relatively high during the oxidation step, specifically, to maintain the pH of the slurry at 12.5 or higher on a 25 ° C. basis. Thus, by making pH into 12.5 or more, an oxidation reaction is accelerated | stimulated and cobalt hydroxide can be easily oxidized into cobalt oxyhydroxide by the oxygen supply in a slurry. On the other hand, if the pH of the slurry is less than 12.5, the oxidation reaction is not sufficiently promoted, and a long-time reaction is required to reduce industrial productivity. Oxidation of cobalt to cobalt oxyhydroxide may be insufficient.

  However, even if the pH of the slurry in the oxidation step exceeds 13.5, an improvement in the oxidation promoting effect is not recognized as compared with the case where the pH is lower than that, and only an increase in alkali cost is caused. Accordingly, the pH of the slurry in the oxidation step is more preferably maintained at 12.5 or more and 13.5 or less, more preferably 12.5 or more and 13.0 or less on a 25 ° C. basis. Further, if the OH concentration fluctuates frequently, the oxidation to cobalt oxyhydroxide varies, which may adversely affect the battery characteristics when used for the positive electrode of the battery. Therefore, it is preferable to suppress the fluctuation of pH during the oxidation step within the range of ± 0.2, and more preferably within the range of ± 0.1.

  In the oxidation step, the total amount of oxygen supplied by blowing into the slurry is preferably 30 L / mol or more in a standard state with respect to the molar amount of cobalt in the coating. When the total amount of oxygen supply is less than 30 L / mol, a portion where the oxidation reaction of cobalt hydroxide becomes insufficient may remain, and the adhesion of the coating may decrease. On the other hand, even if the total amount of oxygen supply exceeds 110 L / mol in the standard state, oxygen supply is continued even after the oxidation of cobalt hydroxide in the coating is completed, and it is a core material. May cause oxidation of nickel hydroxide.

  The slurry temperature in the oxidation step is preferably maintained within the range of 40 to 60 ° C. during the oxidation reaction. When the slurry temperature is less than 40 ° C., the reaction rate decreases, so the oxidation reaction of cobalt hydroxide to cobalt oxyhydroxide may not proceed efficiently. On the other hand, when the slurry temperature exceeds 60 ° C., the oxidation reaction tends to proceed excessively, the nickel hydroxide of the core material is oxidized and unstable nickel oxyhydroxide is generated, and the adhesion of the coating may be lowered. .

  The supply of oxygen to the slurry is not limited to supply with pure oxygen gas as long as the supply amount of oxygen in the gas supplied by blowing into the slurry satisfies the condition of the oxygen supply amount. For example, air may be used, or a mixed gas of oxygen and air mixed at a predetermined ratio or a mixed gas of oxygen and inert gas may be used. Among these, it is preferable to use air in consideration of ease of handling and cost. When a gas other than oxygen gas is used as described above, the gas is selected according to the concentration of oxygen contained in the supplied gas so that the total oxygen supply amount or the oxygen supply amount per unit time is satisfied. The total supply amount and the supply amount per unit time may be increased as appropriate.

  The apparatus used in the oxidation step is not particularly limited as long as the temperature adjustment and gas blowing can be performed while stirring the slurry. For example, an ordinary reaction tank includes a stirring apparatus, a temperature adjusting mechanism, and a gas blowing unit. Are preferred. Further, in order to stabilize the oxygen blowing amount, a reaction vessel in which the inside of the reaction vessel is blocked from outside air and the inside atmosphere can be controlled is preferable.

(Drying process)
In the drying step, the slurry treated in the oxidation step is subjected to solid-liquid separation, and then the temperature of the core particles on which the coating is formed is maintained within a range of 104 to 120 ° C. and dried for 1.5 to 3.5 hours. It is a process. Although the cobalt compound coating of the coated nickel hydroxide powder obtained through the coating step and the oxidation step is excellent in uniformity and high adhesion, further excellent adhesion can be ensured by this drying step.

  Specifically, heating is performed so that the temperature of the core particles on which the coating is formed, that is, the temperature of the powder itself is 104 to 120 ° C., and this temperature range is maintained for 1.5 to 3.5 hours. And dry. Thereby, the bonding force at the interface between the core particles and the coating can be improved, and the coating can be prevented from being peeled off when the paste is formed. When the temperature of the powder is lower than 104 ° C., the above-mentioned bonding force is not sufficiently improved and the adhesiveness is likely to be lowered, so that it is difficult to suppress the peeling of the coating when it is made into a paste. On the other hand, when the temperature of the powder exceeds 120 ° C., oxidation of the core particles and crystal growth are promoted, and physical properties such as specific surface area required as an active material of the battery are deteriorated, and the characteristics may be deteriorated when used in the battery. There is.

  Here, the temperature of the powder is a temperature measured with a thermometer installed in contact with the powder in the drying apparatus. For example, in an external heating heating type drying apparatus, a thermocouple from the inner wall of the apparatus to a position of 15 to 100 mm. Is the temperature measured by inserting and contacting with the powder. By securing the distance between the measurement position and the inner wall in this way, the particle temperature can be accurately measured while suppressing the influence from the inner wall.

  By setting the drying time to 1.5 to 3.5 hours, higher coating adhesion can be obtained while suppressing oxidation of the core particles and crystal growth. If the drying time is less than 1.5 hours, it becomes difficult to obtain high adhesion. On the other hand, if it exceeds 3.5 hours, the physical properties of the powder may deteriorate. When a continuous dryer is used, the time from the introduction of the particles into the dryer to the discharge may be 1.5 to 3.5 hours.

  The atmosphere in the drying step is not particularly limited, but is preferably a non-reducing atmosphere in order to maintain the valence of cobalt oxyhydroxide in the coating, and more preferably an air atmosphere that is easy to handle. . The apparatus used for the drying process is not particularly limited as long as the above drying conditions can be set, but a continuous dryer is preferable because the temperature and time can be easily set.

The present invention will be described in more detail with reference to the following examples and comparative examples, but the present invention is not limited to these examples. In addition, the analysis of the metal used by the Example and the comparative example, the distribution of cobalt, and the analysis of cobalt valence were each performed with the following method.
(1) Metal analysis: ICP emission analysis was performed.
(2) Cobalt distribution: It was carried out by EPMA surface analysis.
(3) Cobalt valence analysis: A method of titrating with potassium dichromate solution using ferric chloride solution and using sodium diphenylaminesulfonate as an indicator (“Cobalt metal in cobalt oxide, cobalt (divalent) And fractional determination of cobalt (trivalent) ”, Michiko Namiki, Yoshinosuke Hirokawa: Analytical Chemistry, see 30,143 (1981)), and analyzed the valence of cobalt in the cobalt oxyhydroxide-coated nickel hydroxide. The cobalt valence obtained by the analysis is the valence including the cobalt contained in the core material. Therefore, all the cobalt valences in the core material are corrected to be bivalent, and the valence of cobalt in the cobalt coat layer is corrected. Was calculated.

Example 1
Into a reaction vessel having a diameter of 190 cm and a depth of 220 cm, 2880 kg of nickel hydroxide powder (Ni _0.94 Co _0.03 Mg _0.03 (OH) ₂ ) having a spherical shape and an average particle diameter of 8 μm was placed, and the total amount was further increased. After adding water so that it might become 3000 liters, it was made to disperse | distribute by stirring at 150 rpm with a stirring propeller, and the slurry of nickel hydroxide powder was produced.

  While continuously stirring this slurry, 968.3 liters of an aqueous cobalt sulfate solution adjusted to a concentration of 1.6 mol / L was applied to two locations at a surface flow rate of 126.5 cm / sec using a roller pump. It added over 2 hours from two nozzles each having a spray area of 500 mm in diameter on the slurry liquid surface at an addition rate of 4035 mL / min. At the same time, a roller interlocked with the pH controller so that the pH of the slurry is within the range of 10.2 ± 0.2 on the basis of 25 ° C. at one place where the flow velocity on the surface of the slurry 20 cm away from these addition positions is the same as above. A 24% by mass aqueous sodium hydroxide solution was added while controlling using a pump. Thereby, cobalt hydroxide was deposited on the surface of the nickel hydroxide particles.

At this time, the supply rate ρ (mol / sec) of the cobalt salt in the cobalt salt aqueous solution with respect to the product of the supply width d (cm) of the cobalt salt aqueous solution supplied to the slurry at each addition position and the flow velocity v (cm / sec) of the slurry. ), That is, ρ / (d × v) is 1.70 × 10 ⁻⁵ mol / cm ² , and the cobalt salt in the cobalt salt aqueous solution with respect to the product of the supply width d of the cobalt salt aqueous solution and the flow velocity v of the slurry. The ratio of the distance D (cm) between the supply position of the cobalt salt aqueous solution and the supply position of the alkaline aqueous solution to the ratio of the supply speed ρ of D, that is, D / {ρ / (d × v)} is 11.8 × 10 ⁵ cm ^3. / Mol. The temperature of the slurry during this reaction was controlled at 50 ° C.

By the above operation, almost all of the supplied cobalt sulfate is precipitated as cobalt hydroxide on the particle surface of the nickel hydroxide powder, and a cobalt hydroxide-coated nickel hydroxide powder having a cobalt hydroxide coating on the particle surface is obtained. It was. After adding the total amount of cobalt sulfate aqueous solution and sodium hydroxide aqueous solution by the above operation, sodium hydroxide was added while stirring the slurry to raise the pH to 12.8 to obtain a slurry used for the oxidation step. Air was blown into the slurry at 1.68 Nm ³ / min for 4 hours to oxidize the cobalt hydroxide deposited on the nickel hydroxide particle surface to obtain cobalt oxyhydroxide. The oxygen supply amount is 52.0 L / mol in a standard state with respect to the molar amount (mol) of cobalt in the coating, and is 0.22 L / min · mol per unit time.

  Thereafter, solid-liquid separation was performed using a filter press, and the recovered cake-like powder was washed with water and filtered again. The obtained wet powder was dried using a continuous dryer to obtain a coated nickel hydroxide powder. The drying conditions were: the temperature of the powder measured with a thermocouple inserted so that the position of the tip from the inner wall of the drying apparatus was 30 mm, and the powder was supplied to the supply port of the continuous dryer and discharged from the overflow port. The time until is 2.5 hours.

  The valence of cobalt in the coating of the obtained coated nickel hydroxide powder was 2.9. Further, when the coated state of the coated nickel hydroxide powder with cobalt oxyhydroxide was observed and evaluated by SEM, it was confirmed that the particles were in a uniform coated state.

  Next, a slurry obtained by adding 25 mL of pure water to 10 g of the resulting coated nickel hydroxide powder was sealed in a polypropylene centrifuge tube (manufactured by ASONE, product number 2-5488-12). This was placed sideways in a roll-type shaking incubator (manufactured by Thomas Scientific Instruments, TS-12) and shaken at 240 times / min for 16 hours. After completion of the shaking, the sediment and water in the centrifuge tube were discarded, and the inner wall of the centrifuge tube was washed with pure water three times. Thereafter, 25 mL of a formic acid aqueous solution containing 0.5% by mass of formic acid is placed in a centrifuge tube, and the exfoliated material adhering to the inner wall of the centrifuge tube is redispersed in the aqueous solution, and the turbidity of the obtained dispersion is measured with a turbidimeter. (Measured by Mitsubishi Analytech, PT-200). As a result, the turbidity was 10 degrees, and it was confirmed that the obtained coated nickel hydroxide powder was excellent in adhesion.

(Comparative Example 1)
Example 1 except that the drying conditions of the continuous dryer were set so that the time from the introduction of the wet powder into the supply port to the discharge port through the overflow port was 3.5 hours at a temperature of 100 ° C. Similarly, coated nickel hydroxide powder was obtained and evaluated in the same manner.

  As a result, the valence of cobalt in the coating of the obtained coated nickel hydroxide powder was 2.9, and the coated state of this powder with cobalt oxyhydroxide was observed and evaluated by SEM. It was confirmed that. However, peeling of the coating was confirmed during shaking of the coated nickel hydroxide powder slurry in an incubator, and the turbidity of the dispersion obtained by redispersing the peeled material adhering to the inner wall of the centrifuge tube was 750 degrees. It was confirmed that the coating of the obtained coated nickel hydroxide powder had low adhesion.

(Example 2)
Example 1 except that the drying conditions of the continuous dryer were set so that the time from the introduction of the wet powder into the supply port to the discharge port through the overflow port was 2.5 hours at 104 ° C. Similarly, coated nickel hydroxide powder was obtained and evaluated in the same manner.

  As a result, the cobalt valence in the coating of the obtained coated nickel hydroxide powder was 2.9, and the coating state of this powder with cobalt oxyhydroxide was observed and evaluated by SEM. It was confirmed that there was. Further, the turbidity of the dispersion obtained by re-dispersing the exfoliated material adhering to the inner wall of the centrifuge tube after shaking the slurry of the coated nickel hydroxide powder in an incubator is 25 degrees. It was confirmed that the coating was excellent in adhesion.

Example 3
Example 1 except that the drying conditions of the continuous dryer were set such that the temperature of the powder was 116 ° C. and the time from the introduction of the wet powder to the supply port to the discharge from the overflow port was 2.5 hours. Similarly, coated nickel hydroxide powder was obtained and evaluated in the same manner.

  As a result, the cobalt valence in the coating of the obtained coated nickel hydroxide powder was 2.9, and the coating state of this powder with cobalt oxyhydroxide was observed and evaluated by SEM. It was confirmed that there was. Further, the turbidity of the dispersion obtained by re-dispersing the exfoliated material adhered to the inner wall of the centrifuge tube after shaking the slurry of the coated nickel hydroxide powder in an incubator is 10 degrees. It was confirmed that the coating was excellent in adhesion.

Claims (8)

Coated nickel hydroxide powder for an alkaline secondary battery positive electrode active material, wherein the surface of core particles made of nickel hydroxide is coated with a cobalt compound having a cobalt valence of 2.5 or more ,
After charging 10 g of the coated nickel hydroxide powder and 10 to 30 mL of water into a cylindrical cell made of polypropylene that can be sealed, after shaking for 16 hours with a roll-type shaker of 200 to 280 times / minute, The exfoliation matter adhered to the inner wall surface of the cylindrical cell was redispersed in 20 mL of an aqueous solution containing 0.2 to 0.8% by mass of formic acid, and the turbidity of the obtained dispersion was measured with an integrating sphere turbidimeter. Coated nickel hydroxide powder for alkaline secondary battery positive electrode active material, characterized in that the degree is 30 degrees or less.   The coated nickel hydroxide powder for an alkaline secondary battery positive electrode active material according to claim 1, wherein a cylindrical or prismatic cell is used as the cylindrical cell. The composition of the core particles, the general _{formula: Ni 1-x-y Co} x M y (OH) 2, ( wherein x is 0.005 to 0.05, y is 0.005 to 0.05 There, M is Ca, Mg, 1, characterized by being represented by more elements), alkaline secondary battery positive electrode active material for coating nickel hydroxide powder according to claim 1 or 2 of Zn. Cobalt content in the cobalt compound, characterized in that 1 to 10 wt% based on the total coating nickel hydroxide powder, an alkaline secondary battery positive electrode active material according to any one of claims 1 to 3 Coated nickel hydroxide powder. A method for producing a coated nickel hydroxide powder for a positive electrode active material of an alkaline secondary battery in which the surface of core particles made of nickel hydroxide is coated with a cobalt compound,
A cobalt salt aqueous solution and an alkaline aqueous solution are supplied to a stirred slurry in which core particles made of nickel hydroxide are dispersed in water to form a coating mainly composed of cobalt hydroxide that has been neutralized and crystallized on the surface of the core particles. A coating process to
The cobalt compound in the coating is oxidized by maintaining the slurry of the core particles on which the coating is formed at a pH of 12.5 or more and 13.5 or less on the basis of 25 ° C. and supplying oxygen while stirring . and oxidation step you of the valence of cobalt to 2.5 or more,
An alkali having a drying step of solid-liquid separating the slurry and then drying the slurry for 1.5 to 3.5 hours while keeping the temperature of the core particles on which the coating is formed within a range of 104 to 120 ° C. The manufacturing method of the covering nickel hydroxide powder for secondary battery positive electrode active materials. In the oxidation step, the total amount of oxygen supplied to the slurry of the core particles on which the coating is formed is 30 L / mol or more and 110 L / mol or less in a standard state with respect to the molar amount of cobalt in the coating. The manufacturing method of the covering nickel hydroxide powder for alkaline secondary battery positive electrode active materials of Claim 5 characterized by the above-mentioned. In the coating step, while the pH of the slurry in which the core particles are dispersed in water is maintained at 8 or more based on the liquid temperature of 25 ° C., the slurry flow at the contact portion between the slurry liquid surface and the supplied cobalt salt aqueous solution Ratio of the feed rate ρ (mol / sec) of the cobalt salt in the cobalt salt solution to the product of the feed width d (cm) of the cobalt salt solution in the direction perpendicular to the direction and the flow velocity v (cm / sec) of the slurry ρ / (Dxv) is controlled to 3.5 * 10 < ^-4 > mol / cm < ² > or less, The manufacture of the coated nickel hydroxide powder for alkaline secondary battery positive electrode active materials of Claim 5 or 6 characterized by the above-mentioned. Method. In the coating step, the supply position of the cobalt salt aqueous solution and the alkaline aqueous solution relative to the ratio ρ / (d × v) of the supply rate ρ of the cobalt salt in the cobalt salt aqueous solution to the product of the supply width d of the cobalt salt aqueous solution and the flow velocity v of the slurry The ratio D / {ρ / (d × v)} of the separation distance D (cm) from the supply position is controlled to 0.5 × 10 ⁵ cm ³ / mol or more. The manufacturing method of the covering nickel hydroxide powder for alkaline secondary battery positive electrode active materials of description.