JPWO2019181788A1 - Compound for positive electrode - Google Patents

Abstract

An object of the present invention is to provide a positive electrode compound having an excellent capacity retention rate after being left at a high temperature and having high strength. A positive electrode which is a secondary particle in which primary particles are aggregated and has a nucleus containing a nickel compound hydroxide and a coating layer containing a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less on the surface of the nucleus. Compound for positive electrode in which the content of nickel element in the coating layer is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus, and the average crushing strength of the secondary particles is 45.0 MPa or more. ..

Description

The present invention relates to a positive electrode compound for a storage battery, and more particularly to a positive electrode compound having high strength and an excellent capacity retention rate after being left at a high temperature.

In order to improve the performance of the positive electrode compound of the storage battery, a coating layer having a metal element may be formed on the surface of the metal hydroxide which is the core. For example, as a positive electrode active material for an alkaline storage battery having a high positive electrode utilization rate and improved cycle characteristics, surface-modified nickel hydroxide in which the surface of nickel hydroxide, which is the core, is coated with cobalt oxide has been proposed (Patent Documents). 1).

However, in the positive electrode active material in which the surface of nickel hydroxide in Patent Document 1 is coated with cobalt oxide, good utilization rate and cycle characteristics can be obtained at 25 ° C., but there is room for improvement in the capacity retention rate after being left at high temperature. there were.

Further, as a method of forming a metal coating layer on the surface of nickel hydroxide, nickel hydroxide is added by adding a solution containing palladium chloride and hydrochloric acid as main components while stirring the nickel hydroxide fine particles in an electroless plating bath. It has been proposed to form a coating layer of electroless plating by carrying a palladium catalyst on the surface of fine particles and performing electroless plating at the same time (Patent Document 2). In Patent Document 2, the coating layer of electroless plating is composed of a nickel-phosphorus composite coating.

As described above, in Patent Document 2, a large amount of phosphorus element is contained in the coating layer of electroless plating. However, the phosphorus element may hinder the performance improvement of the storage battery, particularly the capacity retention rate, and in Patent Document 2, there is still room for improvement in the capacity retention rate after being left at a high temperature.

Further, the positive electrode compound of the storage battery is also required to have durability, that is, mechanical strength, in order to exhibit stable performance over a long period of time.

Japanese Unexamined Patent Publication No. 2001-52695 Japanese Unexamined Patent Publication No. 2004-315946

In view of the above circumstances, an object of the present invention is to provide a positive electrode compound having an excellent capacity retention rate and high strength after being left at a high temperature.

An aspect of the present invention is a secondary particle in which primary particles are aggregated, and a coating containing a nucleus containing a nickel compound hydroxide and a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less on the surface of the nucleus. It is a compound for a positive electrode having a layer, and the content of nickel element in the coating layer is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus, and the average crushing strength of the secondary particles is 45. It is a positive electrode compound having a pressure of 0 MPa or more. In the present specification, the average crushing strength of the positive electrode compound means a value measured by "microcompression tester MCT-510" manufactured by Shimadzu Corporation.

Aspects of the present invention are positive electrode compounds in which the nucleus contains at least one metal element selected from the group consisting of cobalt, zinc, manganese, lithium, magnesium, aluminum, zirconium, yttrium, ytterbium and tungsten.

An aspect of the present invention is a positive electrode compound in which the average primary particle size of the coating layer containing the nickel element is 10 nm or more and 100 nm or less. In the present specification, the average primary particle diameter of the nickel element in the coating layer is the above-mentioned primary particle selected by selecting 10 primary particles from an image obtained by observing the coating layer with a field emission scanning electron microscope (FE-SEM). It means the average value of the measured values of the parts with the longest diameter of.

Aspects of the present invention are positive electrode compounds further containing a palladium compound.

Aspect of the present invention is a positive electrode compound for a positive electrode active material of an alkaline storage battery.

In the embodiment of the present invention, the nucleus has the general formula (1).
Ni _(1-x) M _x (OH) _{2 + a} (1)
(In the formula: 0 <x ≦ 0.2, 0 ≦ a ≦ 0.2, M is at least one metal element selected from the group consisting of cobalt, zinc, manganese, magnesium, aluminum, yttrium and ytterbium. It is a positive electrode compound represented by (shown).

Aspect of the present invention is a positive electrode compound for a precursor of a positive electrode active material of a non-aqueous electrolyte secondary battery.

In the embodiment of the present invention, the nucleus has the general formula (3).
Ni _(1-z) P _z (OH) _{2 + c} (3)
(In the formula: 0 <z ≦ 0.7, 0 ≦ c ≦ 0.28, P is at least one selected from the group consisting of cobalt, zinc, manganese, magnesium, aluminum, zirconium, yttrium, ytterbium and tungsten. It is a compound for a positive electrode represented by (.).

An aspect of the present invention is a positive electrode active material for a non-aqueous electrolyte secondary battery using the above positive electrode compound as a precursor.

According to the aspect of the present invention, the coating layer has a nucleus containing a nickel composite hydroxide and a coating layer containing a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less on the surface of the nucleus. When the content of the nickel element is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus, a positive electrode compound having an excellent capacity retention rate after being left at a high temperature can be obtained. Further, since the average crushing strength of the secondary particles is 45.0 MPa or more, a compound for a positive electrode having high strength can be obtained.

According to the aspect of the present invention, when the average primary particle size of the nickel element in the coating layer is 10 nm or more and 100 nm or less, the surface of the coating layer is smoothed and the average crushing strength of the positive electrode compound is further improved. be able to.

The details of the positive electrode compound of the present invention will be described below. The positive electrode compound of the present invention is a secondary particle in which primary particles are aggregated, and has a nucleus containing a nickel composite hydroxide and a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less on the surface of the nucleus. It is a positive electrode compound having a coating layer containing, and the content of nickel element in the coating layer is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus, and the average crushing strength of the secondary particles is 45. It is 0 MPa or more. Therefore, the positive electrode compound of the present invention is a particle having a core-shell structure, and becomes a nickel-containing coated nickel composite hydroxide having a core of nickel-containing composite hydroxide particles and a coating layer containing nickel. ing.

The shape of the compound for the positive electrode of the present invention, which is in the form of particles, is not particularly limited, and examples thereof include a substantially spherical shape.

The positive electrode compound of the present invention is a secondary particle formed by aggregating a plurality of primary particles. The average crushing strength of the positive electrode compound of the present invention is 45.0 MPa or more. It is considered that this excellent average crushing strength is due to the smoothing of the surface of the coating layer due to the refinement of the nickel element in the coating layer. The average crushing strength of the positive electrode compound is not particularly limited as long as it is 45.0 MPa or more, and a higher average crushing strength is preferable, but for example, 50.0 MPa or more is more preferable, and 55.0 MPa or more is particularly preferable. The upper limit of the average crushing strength of the positive electrode compound is not particularly limited, but is, for example, 100 MPa in that it can be efficiently produced.

The particle size distribution of the positive electrode compound is not particularly limited, but for example, the lower limit of the secondary particle size D50 (hereinafter, may be simply referred to as “D50”) having a cumulative volume percentage of 50% by volume obtains high temperature resistance. From the point of view, 2.0 μm is preferable, 2.5 μm is more preferable, and 3.0 μm is particularly preferable. On the other hand, the upper limit of D50 of the positive electrode compound is preferably 30.0 μm, particularly preferably 25.0 μm, from the viewpoint of the balance between improving the density and securing the contact surface with the electrolytic solution. The above-mentioned lower limit value and upper limit value can be arbitrarily combined.

The composition of the core of the positive electrode compound is not particularly limited as long as it contains nickel hydroxide, but if necessary, in addition to nickel, cobalt, zinc, manganese, lithium, magnesium, aluminum, etc. It may be a hydroxide containing at least one metal element selected from the group consisting of zirconium, ytterbium, ytterbium and tungsten.

The positive electrode compound of the present invention can be used, for example, for a positive electrode active material of an alkaline storage battery, a positive electrode active material of a non-aqueous electrolyte secondary battery, and a precursor of a positive electrode active material of a non-aqueous electrolyte secondary battery.

When the positive electrode compound of the present invention is applied to the positive electrode active material of an alkaline storage battery, the composition of the nucleus is the following general formula (1).
Ni _(1-x) M _x (OH) _{2 + a} (1)
(In the formula: 0 <x ≦ 0.2, 0 ≦ a ≦ 0.2, M is at least one metal element selected from the group consisting of cobalt, zinc, manganese, magnesium, aluminum, yttrium and ytterbium. The positive electrode compound represented by (shown) can be mentioned.

When the positive electrode compound of the present invention is applied to the positive electrode active material of a non-aqueous electrolyte secondary battery, the composition of the nucleus is the following general formula (2).
Li [Li _y (Ni _(1-b) N _b ) _1-y ] O ₂ (2)
(In the formula: 0 <b ≦ 0.7, 0 ≦ y ≦ 0.50, N is at least one metal selected from the group consisting of cobalt, manganese, magnesium, aluminum, zirconium, yttrium, ytterbium and tungsten. The element is shown.), And the positive electrode compound represented by) can be mentioned.

For a positive electrode compound for a positive electrode active material of a non-aqueous electrolyte secondary battery, a nucleus (for example, a nucleus represented by the general formula (2)) is prepared by adding lithium ions to nickel composite hydroxide and firing it. The obtained nucleus is coated with a nickel element having a cobalt element of 500 ppm or less, a phosphorus element of 10 ppm or less, and a nickel element content of 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus. It can be obtained by forming a layer.

Further, when the positive electrode compound of the present invention is applied as a precursor of a positive electrode active material of a non-aqueous electrolyte secondary battery, the composition of the nucleus is described in the following general formula (3).
Ni _(1-z) P _z (OH) _{2 + c} (3)
(In the formula: 0 <z ≦ 0.7, 0 ≦ c ≦ 0.28, P is at least one selected from the group consisting of cobalt, zinc, manganese, magnesium, aluminum, zirconium, yttrium, ytterbium and tungsten. The positive electrode compound represented by) is shown.

Lithium ions are further added to the positive electrode compound of the present invention (for example, a nickel-containing coated nickel composite hydroxide having a nucleus represented by the general formula (3)), which is a nickel-containing coated nickel composite hydroxide. By firing, the positive electrode active material of the non-aqueous electrolyte secondary battery can be obtained. From the above, examples of the non-aqueous electrolyte secondary battery include a lithium ion secondary battery.

In the positive electrode compound of the present invention, the surface of the nucleus is coated with a coating layer containing a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less. The content of the cobalt element and the phosphorus element is the content in the coating layer. Since the positive electrode compound of the present invention is coated with the coating layer, the capacity retention rate is improved after being left at a high temperature (for example, about 90 ° C.). The content of the cobalt element is not particularly limited as long as it is 500 ppm or less, but 200 ppm or less is preferable, 100 ppm or less is more preferable, and 50 ppm or less is further preferable, from the viewpoint of more reliably improving the capacity retention rate after being left at a high temperature. 10 ppm or less is particularly preferable. The content of the phosphorus element is not particularly limited as long as it is 10 ppm or less, but 5 ppm or less is more preferable, and 2 ppm or less is particularly preferable, from the viewpoint of more reliably improving the capacity retention rate after being left at a high temperature. From the above, the main component of the coating layer containing the nickel element is the nickel element.

As described above, the composition of the coating layer containing the nickel element is 500 ppm or less for the cobalt element and 10 ppm or less for the phosphorus element, and is mainly composed of the nickel element. The content of nickel in the coating layer is preferably 99% by mass or more, more preferably 99.9% by mass or more, and particularly 100% by mass, for example, from the viewpoint of more reliably improving the capacity retention rate after being left at a high temperature. preferable.

The content of the nickel element in the coating layer is in the range of 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus. When the content of the nickel element in the coating layer is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus, an excellent capacity retention rate can be obtained even after being left at a high temperature. The content of the nickel element in the coating layer is not particularly limited as long as it is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus, but the nucleus 100 is from the viewpoint of further improving the capacity retention rate after being left at a high temperature. It is particularly preferable to use 7 parts by mass or more and 15 parts by mass or less with respect to parts by mass.

The nickel element of the coating layer is in the form of particles. The surface of the nucleus containing the nickel composite hydroxide is coated with the nickel particles overlapping. The shape of each nickel element in the coating layer is not particularly limited, and is, for example, substantially spherical.

The average primary particle size of the nickel element in the coating layer is not particularly limited, but is preferably in the range of 10 nm or more and 100 nm or less. Since the average primary particle size of the nickel element in the coating layer is 10 nm or more and 100 nm or less, the nickel element is refined, so that the surface of the coating layer is smoothed and the average crushing strength of the positive electrode compound is further improved. Can be made to. The average primary particle size of the nickel element in the coating layer is more preferably 20 nm or more and 80 nm or less, and particularly preferably 30 nm or more and 70 nm or less. The coating layer containing the nickel element may cover the entire surface of the nucleus containing the nickel composite hydroxide, or may cover a part of the surface of the nucleus containing the nickel composite hydroxide.

The average thickness of the coating layer is not particularly limited, and for example, the lower limit thereof is preferably 20 nm and particularly preferably 70 nm from the viewpoint of more reliably improving the average crushing strength. On the other hand, the upper limit value is preferably 200 nm, particularly preferably 100 nm, from the viewpoint that the nucleus mainly contributes to the exertion of the battery characteristics of the positive electrode compound and the excellent battery characteristics of the positive electrode compound are surely maintained.

As will be described later, in the production of the positive electrode compound of the present invention, a palladium catalyst is used. Therefore, the positive electrode compound of the present invention contains a trace amount of palladium compound. The content of the palladium element in the positive electrode compound is, for example, 1 ppm or more and 100 ppm or less.

The BET specific surface area of the positive electrode compound of the present invention is not particularly limited, but for example, the lower limit is preferably ^{0.1 m 2 / g from the viewpoint of the balance between improving the density and securing the contact surface with the electrolytic solution.} , 0.3 m ² / g is particularly preferable. On the other hand, the upper limit is preferably ^{50.0m 2 / g, 40.0m 2 /} g is particularly preferred. The above-mentioned lower limit value and upper limit value can be arbitrarily combined.

The tap density of the positive electrode compound of the present invention is not particularly limited, for example, from the viewpoint of filling degree improve in when used as a positive electrode active material, 1.5 g / cm ³ or more preferably, 1.7 g / cm ³ The above is particularly preferable.

^{The bulk density of the positive electrode compound of the present invention is not particularly limited, but is preferably 0.8 g / cm 3} or more, preferably 1.0 g / cm ³ or more, for example, from the viewpoint of improving the filling degree when used as a positive electrode active material. Is particularly preferable.

Next, an example of a method for producing the positive electrode compound of the present invention will be described.

As the above-mentioned production method, for example, first, nickel composite hydroxide particles as a core are prepared. The method for preparing nickel composite hydroxide particles is as follows: First, a nickel salt solution (for example, a sulfate solution) or nickel and other metal elements (for example, cobalt, zinc, manganese, lithium, magnesium, aluminum) are prepared by a co-precipitation method. , Zirconium, Ittium, Itterbium and / or Tungsten) with a salt solution (eg, sulfate solution) and a complexing agent to react with nickel composite hydroxide particles (eg, nickel hydroxide particles, nickel and other metals). Hydroxide particles containing elements (eg, cobalt, zinc, manganese, lithium, magnesium, aluminum, zirconium, ittrium, itterbium and / or tungsten) are prepared to form a slurry containing nickel composite hydroxide particles. Get a suspension. As the solvent of the suspension, for example, water is used.

The complexing agent is not particularly limited as long as it can form a complex with ions of nickel and other metal elements in an aqueous solution, and is, for example, an ammonium ion feeder (ammonium sulfate, ammonium chloride, ammonium carbonate). , Ammonium fluoride, etc.), hydrazine, ethylenediamine tetraacetic acid, nitrilotriacetic acid, uracil diacetic acid, and glycine. At the time of precipitation, an alkali metal hydroxide (for example, sodium hydroxide or potassium hydroxide) may be added as needed in order to adjust the pH value of the aqueous solution.

When the complexing agent is continuously supplied to the reaction vessel in addition to the salt solution, nickel and the other metal elements react with each other to prepare nickel composite hydroxide particles. In the reaction, the temperature of the reaction vessel is controlled in the range of, for example, 10 ° C. to 80 ° C., preferably 20 to 70 ° C., and the pH value in the reaction vessel is set based on the liquid temperature of 25 ° C., for example, pH 9 to pH 13. The substances in the reaction vessel are appropriately stirred while controlling the pH in the range of 11 to 13, preferably in the range of pH 11 to 13. Examples of the reaction tank include a continuous type in which the formed nickel composite hydroxide particles are overflowed in order to separate them.

Next, a palladium-based catalyst and a surfactant are supplied to the core nickel composite hydroxide particles obtained as described above, and the palladium-based catalyst is supported on the surface of the nickel composite hydroxide particles. After that, the nickel composite hydroxide particles carrying a palladium-based catalyst are immersed in a plating solution mainly composed of nickel without containing a phosphorus element, and further, a hydrazine-based additive is added to perform electroless plating. Nickel is plated on the surface of composite hydroxide particles. In electroless plating, the film thickness and / or the composition of the plating solution is adjusted so that the content of the nickel element in the coating layer is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus. A plating film is formed on the surface of the composite hydroxide particles. As a result, a coating layer containing a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less can be formed.

In the method for forming a coating layer using electroless plating described above, the average primary particle size of the nickel element in the coating layer is in the range of 10 nm or more and 100 nm or less. If a palladium-based catalyst is not supported on the surface of the nickel composite hydroxide particles, the average primary particle diameter of the nickel element in the coating layer becomes coarser than 100 nm, and the surface of the coating layer becomes roughened to 45.0 MPa or more. The average crushing strength of is not obtained.

Next, a positive electrode using the positive electrode compound of the present invention will be described. Hereinafter, a case where the positive electrode compound of the present invention is used as the positive electrode of an alkaline storage battery such as a nickel hydrogen secondary battery will be described. The positive electrode includes a positive electrode current collector and a positive electrode active material layer containing the positive electrode compound of the present invention formed on the surface of the positive electrode current collector. The positive electrode active material layer has a positive electrode active material which is a compound for a positive electrode of the present invention, a binder (binding agent), and, if necessary, a conductive auxiliary agent. The conductive auxiliary agent is not particularly limited as long as it can be used for a livestock battery (secondary battery), but acetylene black (AB), metallic cobalt, cobalt oxide and the like can be used. The binder is not particularly limited, but is limited to polymer resins such as polyvinylidene fluoride (PVdF), butadiene rubber (BR), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), and the like. A combination of these can be mentioned. The positive electrode current collector is not particularly limited, and examples thereof include punching metal, expanded metal, wire mesh, foamed metal, for example, nickel foam, reticulated metal fiber sintered body, and metal-plated resin plate.

As a method for producing a positive electrode of an alkaline storage battery such as a nickel-metal hydride secondary battery, for example, first, a positive electrode active material slurry is prepared by mixing the positive electrode compound of the present invention, a conductive auxiliary agent, a binder, and water. Next, the positive electrode active material slurry is filled in the positive electrode current collector by a known filling method, dried, and then rolled and fixed by a press or the like to obtain a positive electrode.

When the positive electrode compound of the present invention is used as a precursor of the positive electrode active material of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, the positive electrode compound of the present invention may be composed of lithium carbonate, lithium hydroxide or the like. A lithium compound is added to obtain a mixture of the lithium compound and the positive electrode compound, and the obtained mixture is first fired (the firing temperature is, for example, 600 ° C. to 900 ° C., and the firing time is, for example, 5 hours to 20 hours). Further, by further secondary firing (firing temperature is, for example, 700 ° C. or higher and 1000 ° C. or lower, firing time is, for example, 1 to 20 hours), positive electrode activity of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery is activated. The substance can be obtained. The positive electrode of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery includes a positive electrode current collector and a positive electrode active material layer formed on the surface of the positive electrode current collector and using the positive electrode compound of the present invention as a precursor. Be prepared. The positive electrode active material layer has a positive electrode active material using the positive electrode compound of the present invention as a precursor, a binder (binding agent), and, if necessary, a conductive auxiliary agent. As the positive electrode current collector, the binder, and the conductive auxiliary agent, the same ones as described above can be used.

As a method for producing a positive electrode of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, for example, first, a positive electrode active material using the positive electrode compound of the present invention as a precursor, a conductive auxiliary agent, a binder, and N. -Mixed with methyl-2-proridone (NMP) to prepare a positive electrode active material slurry. Next, the positive electrode active material slurry is filled in the positive electrode current collector by a known filling method, dried, and then rolled and fixed by a press or the like to obtain a positive electrode.

A positive electrode using the positive electrode active material obtained as described above, a negative electrode having a negative electrode active material layer containing the negative electrode active material formed on the surface of the negative electrode current collector and the negative electrode current collector, and a predetermined electrolyte. A storage battery (for example, an alkaline storage battery, a non-aqueous electrolyte secondary battery, etc.) can be assembled by mounting the separator by a known method.

Next, examples of the present invention will be described, but the present invention is not limited to these examples as long as the gist of the present invention is not exceeded.

Method for Producing Positive Compounds of Examples 1 to 3 Preparation of Nickel Composite Hydroxide Particles Nickel sulfate, cobalt sulfate, and zinc sulfate were placed in a predetermined ratio (nickel: cobalt: zinc = 92.1:) in a reaction vessel equipped with a stirrer. An aqueous solution of ammonium sulfate and an aqueous solution of sodium hydroxide were added dropwise to an aqueous solution dissolved at a mass ratio of 1.12: 6.77), and the reaction was carried out in a reaction vessel having a reaction volume of 500 L based on a reaction temperature of 45.0 ° C. and a liquid temperature of 40 ° C. While maintaining the pH at 12.1, the mixture was continuously stirred with a propeller stirrer having a stirring blade of 250 mm at a stirring rotation speed of 520 rpm. The produced hydroxide was taken out by overflowing from the overflow pipe of the reaction vessel. The removed hydroxide was subjected to each treatment of washing with water, dehydration, and drying to obtain nickel composite hydroxide particles as nuclei. The composition of the obtained nickel composite hydroxide particles is such that the content of nickel element is 92.1 parts by mass, the content of cobalt element is 1.12 parts by mass, and the content of zinc element is 6.77 parts by mass. This was confirmed by an inductively coupled plasma emission spectrometer.

The nickel composite hydroxide particles prepared as described above are directly subjected to electroless pure nickel plating treatment to have a nickel plating film as a coating layer, that is, nickel-containing coated nickel composite hydroxide. Manufactured a thing. More specifically, a nickel composite hydroxide having a nickel plating film was produced as follows.

First, nickel composite hydroxide particles having a particle diameter of 10 μm were used as base particles, and the base particles were stirred with a cationic surfactant for 10 minutes in order to modify the surface of the base particles. Then, after washing with filtered water, the mixture was stirred with a palladium ion catalyst solution for 10 minutes to adsorb palladium ions on the surface of the substrate particles. Then, after washing with filtered water, the mixture was stirred with a reducing solution for 10 minutes to support a palladium catalyst on the surface of the substrate particles. Then, after washing with filtered water, the substrate particles having a palladium catalyst supported on the surface were pre-stirred for 1 minute in a nickel sulfate solution heated to 80 ° C. The composition of the nickel sulfate solution was 0.30 mol / L of nickel salt, 1 mol / L of citrate, and 1.7 mol / L of carbonate. Then, hydrazine monohydrate was added to the nickel sulfate solution in an amount of 0.4 mol / L. After the reaction is started, the substrate particles having a palladium catalyst supported on the surface are stirred in a nickel sulfate solution containing hydrazine monohydrate for 5 minutes or more, and a nickel plating film is formed on the surface of the nickel composite hydroxide particles. Was formed to form a coating layer containing an element of nickel. After stirring, the nickel composite hydroxide particles on which the coating layer containing the nickel element was formed were washed with filtered water and dried at 80 ° C. In this way, nickel-containing coated nickel composite hydroxide particles, which are the positive electrode compound according to the present invention, were obtained. The content of the nickel element in the coating layer with respect to 100 parts by mass of the nickel composite hydroxide particles was adjusted by adjusting the amount of the nickel sulfate liquid added.

Method for Producing Positive Electrode Compound of Comparative Example 1 Nickel composite hydroxide particles as nuclei were obtained in the same manner as in the above Examples. Then, the nickel composite hydroxide particles as nuclei were put into an alkaline aqueous solution in a reaction bath maintained at pH 9.0 with sodium hydroxide at a liquid temperature of 50 ° C. as a reference. After the addition, a cobalt sulfate aqueous solution having a concentration of 90 g / L was added dropwise while stirring the solution. During this period, an aqueous sodium hydroxide solution is appropriately added dropwise, and the reaction bath is maintained at pH 9.0 at a liquid temperature of 50 ° C. for 1 hour to obtain cobalt hydroxide on the surface of the nickel composite hydroxide particles (nucleus). Cobalt hydroxide-coated nickel composite hydroxide particles having a coating layer made of the above were obtained. The content of the coated cobalt was 2.55 parts by mass with respect to 100 parts by mass of the nickel composite hydroxide particles.

Then, 7 kg of the obtained cobalt hydroxide-coated nickel composite hydroxide particles was put into a high-speed mixer (manufactured by Fukae Powtech Co., Ltd., model FMD-25J) having a volume of 25 L. After that, air is introduced into the stirring / mixing device from the introduction port of the stirring / mixing device, and while exhausting from the exhaust port, the main stirring blade at the bottom of the stirring / mixing device is rotated at 200 rpm, and the auxiliary stirring blade on the side wall of the stirring / mixing device is operated at 1200 rpm. , Each of which was rotated to mix cobalt hydroxide coated nickel composite hydroxide particles. While continuing the mixing, the sample was heated with a heating jacket to bring the temperature of the sample in the stirring and mixing device to about 90 ° C., and then 0.4 L of 48 mass% sodium hydroxide aqueous solution was placed in the stirring and mixing device for about 2 minutes. Sprayed from a sprayer. After the spraying was completed, the temperature inside the stirring and mixing device was raised to about 120 ° C. for about 30 minutes, and the color of the surface of the particles changed from pale pink to black. Then, the temperature in the stirring and mixing device was returned to room temperature, the product particles were taken out, the taken out product particles were washed with water, and then heated and dried in air. In this way, CoOOH-coated nickel composite hydroxide particles, which are the positive electrode compound of Comparative Example 1, were obtained.

Method for Producing Positive Electrode Compounds of Comparative Examples 2 to 4 Nickel composite hydroxide particles as nuclei were obtained in the same manner as in the above Examples. Then, electroless nickel plating was applied to the nickel composite hydroxide particles having an average particle size of 10 μm. As the electroless plating bath, a bath having the following composition was used.
Nickel sulfate 22.0 g / L
Glycine 33.3 g / L
Sodium hypophosphate 23.3 g / L
Sodium hydroxide 12.3g / L
Surfactant 10 mL / L
pH 9.5

A 3 L plating bath satisfying the above conditions was built at 60 ° C., and 50 g of nickel composite hydroxide particles were directly charged. That is, no pretreatment steps such as a dipping degreasing step, a surface adjusting step, and an etching step were performed. After adding the nickel composite hydroxide particles, the propeller is stirred at a speed of 500 rpm for 10 minutes, and 20 mL of a solution containing palladium chloride and hydrochloric acid as main components (activator, palladium chloride concentration 2 g / L) is added thereto. I put it in. With this injection, foaming began instantly, and reduction of palladium ions and nickel plating began to proceed. Propeller stirring was continued at a speed of 500 rpm for about 30 minutes until the foaming was completed, and after the foaming was completed, the stirring was stopped. After filtering using a suction filter, washing with water was repeated 3 times, and then the mixture was dried at 80 ° C. for 1 hour with warm air. In this way, nickel composite hydroxide particles coated with a nickel-phosphorus composite plating film, which are compounds for positive electrodes of Comparative Examples 2 to 4, were obtained. The content of the nickel element in the coating layer with respect to 100 parts by mass of the nickel composite hydroxide particles was adjusted by adjusting the amount of the nickel sulfate liquid added.

Content of nickel element in the coating layer with respect to 100 parts by mass of nickel composite hydroxide particles of Examples 1 to 3, content of cobalt element in the coating layer with respect to 100 parts by mass of nickel composite hydroxide particles of Comparative Example 1, Comparative Example The content of the nickel element in the coating layer with respect to 100 parts by mass of the nickel composite hydroxide particles of 2 to 4 is shown in Table 1 below.

The evaluation items are as follows.
(1) Composition analysis In the composition analysis of the nickel composite hydroxide powders obtained in Examples 1 to 3 and Comparative Examples 2 to 4, inductively coupled plasma emission was performed after the obtained powder was dissolved in hydrochloric acid or aqua regia. This was performed using an analyzer (7300DV manufactured by PerkinElmer Japan Co., Ltd.).
(2) Average crush strength Measured with "Micro compression tester MCT-510" manufactured by Shimadzu Corporation.
One secondary particle arbitrarily selected from the nickel composite hydroxide powders obtained in Examples 1 to 3 and Comparative Examples 2 to 4 using a "microcompression tester MCT-510" manufactured by Shimadzu Corporation. A test pressure (load) was applied to the particles, and the displacement of the secondary particles was measured. When the test pressure is gradually increased, the pressure value at which the displacement amount is maximized while the test pressure remains almost constant is defined as the test force (P), and the formula of Hiramatsu et al. Vol.81, (1965)) was used to calculate the crushing strength (St). This operation was performed a total of 10 times, and the average crush strength was calculated from the average value of the crush strength 10 times.
St = 2.8 × P / (π × d × d) (d: secondary particle size) (A)

(3) Capacity retention rate (leave at 90 ° C for 6 days)
The nickel-metal hydride battery was discharged by performing a 0.2 C deep discharge test and then allowing it to stand naturally at 90 ° C. for 6 days in a no-load connection state. The capacity retention rate was defined as the discharge capacity when charging at 0.2 C, which is the second CY after deep discharge, with respect to the discharge capacity when charging at 0.2 C until deep discharge.
(4) Average primary particle size of the coating layer containing nickel element The average primary particle size of the coating layer containing nickel element is independent of the image obtained by observing the coating layer with an electro-emission scanning electron microscope (FE-SEM). Ten primary particles existing were randomly selected, the sites having the longest diameters of the selected primary particles were measured, and the average value was taken as the average primary particle diameter.

In Examples 1 to 3 and Comparative Examples 2 to 4, the formation of a coating layer containing a nickel element on the core nickel composite hydroxide particles means that the core nickel composite hydroxide particles and the final product are formed. The cross section of the nickel-containing coated nickel composite hydroxide particles was confirmed by composition analysis by energy dispersive X-ray analysis (EDX) at substantially equal intervals from the central portion to the surface portion. That is, as shown in Table 2 below, in the nucleus, there is no significant change in the amount of nickel between the nucleus center and the nucleus surface, whereas in the nickel-containing coated nickel composite hydroxide particles, the particle center and the particle surface. There is a large change in the amount of nickel, and the amount of nickel on the surface of the particle is significantly larger than that in the center of the particle (the amount of nickel shown by the underline in Table 2). From this, it was confirmed that a coating layer containing a nickel element was formed on the nickel composite hydroxide particles which are the nuclei.

The evaluation results are shown in Table 1 below.

In Examples 1 to 3 and Comparative Examples 2 to 4, since the cobalt element was not added in forming the coating layer, in Examples 1 to 3 and Comparative Examples 2 to 4, the coating layer contained cobalt. It can be determined that the amount is none (0 ppm).

As shown in Table 1 above, the surface of the nickel composite hydroxide particles has a coating layer containing a nickel element having 0 ppm of cobalt element and 2 ppm or less of phosphorus element, and the content of nickel element in the coating layer is nickel. In Examples 1 to 3 in which 5.0 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the composite hydroxide particles, the average crushing strength of the secondary particles was 55.3 Mpa or more, 90 ° C., on the 6th day. The capacity retention rate was 77.7% or more. Therefore, in Examples 1 to 3, it was possible to obtain a positive electrode compound having an excellent capacity retention rate after being left at a high temperature and having a high average crushing strength. In particular, in Example 1 in which the content of the nickel element in the coating layer is 10 parts by mass with respect to 100 parts by mass of the nickel composite hydroxide particles, the capacity retention rate after being left at a high temperature and the average crushing strength of the secondary particles are further increased. Improved.

Further, from Examples 1 to 3, it was confirmed that the capacity retention rate tends to improve after being left at a high temperature with the improvement of the average crushing strength of the positive electrode compound. Further, in Examples 1 to 3, the average primary particle size of the coating layer containing the nickel element was refined to 58 nm to 83 nm as compared with Comparative Examples 2 to 4.

On the other hand, in Comparative Example 1, which is a nickel composite hydroxide particle coated with CoOOH, the average crushing strength of the secondary particles was 44.7 Mpa, 90 ° C., and the capacity retention rate on the 6th day was only 70.0%. .. Therefore, in Comparative Example 1, it was not possible to obtain a good capacity retention rate and a high average crush strength after being left at a high temperature.

Further, in Comparative Examples 2 to 4 in which 1570 ppm to 2327 ppm of phosphorus element is contained in the coating layer containing nickel element, the capacity retention rate after being left at high temperature is 67.0% to 75.2%, and the average crush strength of secondary particles is 20. Both were greatly reduced from .2 Mpa to 33.9 Mpa. In particular, in Comparative Example 2 containing 2327 ppm of phosphorus element, the average crushing strength was significantly reduced.

Next, a method for producing the positive electrode compound of Examples 4, 5 and Comparative Examples 5 and 6 will be described.

Method for Producing Compound for Positive Electrode of Comparative Example 6 After putting water in a reaction vessel equipped with a stirrer and an overflow pipe, an aqueous sodium hydroxide solution was added. A nickel sulfate aqueous solution, a cobalt sulfate aqueous solution, and a manganese sulfate aqueous solution are mixed so that the atomic ratio of nickel atom, cobalt atom, and manganese atom is 0.50: 0.20: 0.30 to prepare a mixed raw material solution. Prepared. Next, the mixed raw material solution and the ammonium sulfate aqueous solution are continuously added as a complexing agent into the reaction vessel under stirring so that the pH of the solution in the reaction vessel becomes pH 11.3 based on the liquid temperature of 40 ° C. An aqueous sodium oxide solution was added dropwise at appropriate times to obtain nickel-cobalt-manganese composite hydroxide particles, which are nickel-composite hydroxide particles. The obtained nickel composite hydroxide particles were filtered, washed with water, and dried at 105 ° C. to obtain a dry powder of the nickel composite hydroxide of Comparative Example 6.

Method for Producing Positive Compound of Example 4 The nickel composite hydroxide particles of Comparative Example 6 prepared as described above are directly subjected to a non-electrolytic pure nickel plating treatment to directly apply a coating layer of Example 4. A nickel composite hydroxide having a nickel plating film (a nickel cobalt manganese composite hydroxide having a nickel plating film as a coating layer), that is, a nickel-containing coated nickel composite hydroxide was produced. More specifically, a nickel composite hydroxide having a nickel plating film was produced as follows.

First, nickel composite hydroxide particles having a particle diameter of 10 μm were used as base particles, and the base particles were stirred with a cationic surfactant for 10 minutes in order to modify the surface of the base particles. Then, after washing with filtered water, the mixture was stirred with a palladium ion catalyst solution for 10 minutes to adsorb palladium ions on the surface of the substrate particles. Then, after washing with filtered water, the mixture was stirred with a reducing solution for 10 minutes to support a palladium catalyst on the surface of the substrate particles. Then, after washing with filtered water, the substrate particles having a palladium catalyst supported on the surface were pre-stirred for 1 minute in a nickel sulfate solution heated to 80 ° C. The composition of the nickel sulfate solution was 0.30 mol / L of nickel salt, 1 mol / L of citrate, and 1.7 mol / L of carbonate. Then, hydrazine monohydrate was added to the nickel sulfate solution in an amount of 0.4 mol / L. After the reaction is started, the substrate particles having a palladium catalyst supported on the surface are stirred in a nickel sulfate solution containing hydrazine monohydrate for 5 minutes or more, and a nickel plating film is formed on the surface of the nickel composite hydroxide particles. Was formed to form a coating layer containing an element of nickel. After stirring, the nickel composite hydroxide particles on which the coating layer containing the nickel element was formed were washed with filtered water and dried at 80 ° C. In this way, nickel-containing coated nickel composite hydroxide particles, which are the positive electrode compound according to the present invention, were obtained. The content of the nickel element (10 parts by mass) in the coating layer with respect to 100 parts by mass of the nickel composite hydroxide particles was adjusted by adjusting the input amount of the nickel sulfate solution.

Method for Producing Positive Compound of Example 5 Li / (Ni + Co + Mn) = 1.03 of the dry powder of the nickel-containing coated nickel composite hydroxide of Example 4 and the lithium carbonate powder obtained as described above. After weighing and mixing as described above, primary calcining was carried out at 740 ° C. for 8.4 hours in an air atmosphere to obtain a lithium-nickel-containing coated nickel composite oxide as a primary calcined powder. Then, the primary calcined powder was pulverized and secondary calcined at 940 ° C. for 8.4 hours in an air atmosphere to obtain the lithium-nickel-containing coated nickel composite oxide of Example 5 as the secondary calcined powder.

Method for Producing Positive Compound of Comparative Example 5 After weighing and mixing the dry powder of the nickel composite hydroxide of Comparative Example 6 and the lithium carbonate powder so that Li / (Ni + Co + Mn) = 1.03, the atmosphere is atmospheric. The primary calcining was carried out at 740 ° C. for 8.4 hours to obtain a lithium-nickel composite oxide as a primary calcined powder. Then, the primary calcined powder was pulverized and secondary calcined at 940 ° C. for 8.4 hours in an air atmosphere to obtain the lithium-nickel composite oxide of Comparative Example 5 as the secondary calcined powder.

The evaluation items are as follows.
(1) Composition analysis In the composition analysis of the compound powder for the positive electrode obtained in Example 5 and Comparative Example 5, the obtained powder was dissolved in hydrochloric acid or aqua regia, and then an inductively coupled plasma emission spectrometer (Perkin Co., Ltd.) was used. This was performed using a 7300DV manufactured by Elmer Japan.
(2) Average crush strength Measured with Shimadzu microcompression tester MCT-510.
One secondary particle arbitrarily selected from the nickel composite hydroxide powders obtained in Examples 4 and 5 and Comparative Examples 5 and 6 using a "microcompression tester MCT-510" manufactured by Shimadzu Corporation. A test pressure (load) was applied to the particles, and the displacement of the secondary particles was measured. When the test pressure is gradually increased, the pressure value at which the displacement amount is maximized while the test pressure remains almost constant is defined as the test force (P), and the formula of Hiramatsu et al. (Journal of the Japan Mining Association,) shown in the following formula (A). Vol.81, (1965)) was used to calculate the crushing strength (St). This operation was performed a total of 10 times, and the average crush strength was calculated from the average value of the crush strength 10 times.
St = 2.8 × P / (π × d × d) (d: secondary particle size) (A)

(3) Self-discharge rate and capacity recovery rate when stored at 60 ° C. Using a laminated cell type battery prepared using the compound powder for the positive electrode of Example 5 and Comparative Example 5, the condition of 0.2 C at an environmental temperature of 25 ° C. After charging to 4.2 V under CV conditions, the battery was discharged to 3.0 V under 0.2 C conditions. The discharge capacity at this time is 1. And. After charging at an environmental temperature of 25 ° C. under the condition of 0.2 C to 4.2 V under the CV condition, the mixture was left to stand in the environment of 60 ° C. for 2 weeks. After leaving for 2 weeks, the temperature was returned to 25 ° C. and discharged to 3.0 V under the condition of 0.2 C. The discharge capacity at this time is 2. Next, the battery was charged to 4.2 V under the condition of 0.2 C at an environmental temperature of 25 ° C. under the condition of CV, and then discharged to 3.0 V under the condition of 0.2 C. The discharge capacity at this time is 3. After charging to 4.2 V under the condition of 0.2 C at the environmental temperature of 25 ° C., it was left to stand in the environment of 60 ° C. for another 2 weeks. After leaving for 2 weeks, the temperature was returned to 25 ° C. and discharged to 3.0 V under the condition of 0.2 C. The discharge capacity at this time is 4. Next, the battery was charged to 4.2 V under the condition of 0.2 C at an environmental temperature of 25 ° C. under the condition of CV, and then discharged to 3.0 V under the condition of 0.2 C. The discharge capacity at this time is 5.
The self-discharge rate and capacity recovery rate when stored at 60 ° C. are shown in the following equations.
(A) Self-discharge rate and capacity recovery rate after leaving for 2 weeks Self-discharge rate (%) = (1.-2.) × 100
Capacity recovery rate (%) = (3.1.) × 100
(B) Self-discharge rate and capacity recovery rate after leaving for 4 weeks Self-discharge rate (%) = (1.-4.) × 100
Capacity recovery rate (%) = (5.1.) × 100
(4) Cycle characteristics under 60 ° C. conditions Using a laminated cell type battery prepared using the positive electrode compound powders of Example 5 and Comparative Example 5, the temperature is 60 ° C. and the environmental temperature is 2C and up to 4.2V under CC conditions. After charging, it was discharged to 3.0V under the condition of 2C. This charge / discharge operation was performed for 500 cycles. The ratio of the capacity discharged in the 500th cycle to the capacity discharged in the first cycle was defined as the capacity retention rate.
Capacity retention rate (%) = 500th cycle discharge capacity (mAh / g) / 1st cycle discharge capacity (mAh / g) x 100
(5) Average Primary Particle Size of Coating Layer Containing Nickel Element The average primary particle size of the coating layer containing nickel element of the positive electrode compound powder of Example 4 is coated with an electric field emission scanning electron microscope (FE-SEM). From the image of observing the layers, 10 independently existing primary particles were randomly selected, the sites of the longest diameter of the selected primary particles were measured, and the average value was taken as the average primary particle diameter. ..

The evaluation results are shown in Table 3 below.

When the composition of the lithium-nickel-containing coated nickel composite oxide powder of Example 5 was analyzed, the molar ratio of Li: Ni: Co: Mn was 1.011: 0.575: 0.170: 0.255. there were. When the composition of the lithium-nickel cobalt-manganese composite oxide powder of Comparative Example 5 was analyzed, the molar ratio of Li: Ni: Co: Mn was 1.022: 0.499: 0.200: 0.301. It was.
As shown in Table 3 above, the average crush strength of the nickel-containing coated nickel composite hydroxide of Example 4 was 45.9 Mpa, as compared with the nickel composite hydroxide having an average crush strength of 65.0 Mpa in Comparative Example 6. The particle strength decreased. However, the lithium-nickel-containing coated nickel composite oxide of Example 5 is an oxide obtained by lithium-burning the nickel-containing coated nickel-cobalt-manganese composite hydroxide of Example 4, and has an average crushing strength of 64.3 Mpa. Compared with the lithium-nickel composite oxide of Example 5, the average crushing strength of Example 5 was 79.7 Mpa, which was an improvement in particle strength.

As shown in Table 3 above, the particles are compared with the lithium-nickel cobalt-manganese composite oxide in Comparative Example 5 in which the self-discharge rate and the capacity recovery rate after storage at 60 ° C. for 2 weeks are 32.1% and 79.1%, respectively. The lithium-nickel-containing coated nickel composite oxide of Example 5, which has high strength, has excellent properties such as self-discharge rate and capacity recovery rate of 31.2% and 80.6%, respectively, when stored at 60 ° C. for 2 weeks. It was. Further, compared to the lithium-nickel composite oxide in which the self-discharge rate and the capacity recovery rate in Comparative Example 5 storage at 60 ° C. for 4 weeks are 39.1% and 68.5%, respectively, the lithium of Example 5 has higher particle strength. -The nickel-containing coated nickel composite oxide had excellent properties such as a self-discharge rate and a capacity recovery rate of 36.6% and 70.6%, respectively, when stored at 60 ° C. for 4 weeks.

As shown in Table 3 above, the lithium-nickel content of Example 5 has a higher particle strength than the lithium-nickel composite oxide having a capacity retention rate of 66.9% for 500 cycles under the condition of 60 ° C. of Comparative Example 5. The coated nickel composite oxide had a high capacity retention rate of 70.4% for 500 cycles under the condition of 60 ° C.

Further, the average primary particle size of the coating layer containing the nickel element of Example 4 was refined to 50 nm to 90 nm.

Since the positive electrode compound of the present invention has the structure of the coating layer, it has an excellent capacity retention rate after being left at a high temperature and has high strength, so that it can be used in a wide range of storage battery fields. It has high utility value for positive electrode active materials, for positive electrode active materials of non-aqueous electrolyte secondary batteries, and for precursors of positive electrode active materials for non-aqueous electrolyte secondary batteries.

Claims (9)

A positive electrode which is a secondary particle in which primary particles are aggregated and has a nucleus containing a nickel composite hydroxide and a coating layer containing a nickel element having a cobalt element of 500 ppm or less and a phosphorus element of 10 ppm or less on the surface of the nucleus. Compound for
The content of nickel element in the coating layer is 5 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the nucleus.
A compound for a positive electrode having an average crushing strength of the secondary particles of 45.0 MPa or more. The positive electrode compound according to claim 1, wherein the nucleus contains at least one metal element selected from the group consisting of cobalt, zinc, manganese, lithium, magnesium, aluminum, zirconium, yttrium, ytterbium and tungsten. The compound for a positive electrode according to claim 1 or 2, wherein the average primary particle size of the coating layer containing a nickel element is 10 nm or more and 100 nm or less. The positive electrode compound according to any one of claims 1 to 3, further comprising a palladium compound. The compound for a positive electrode according to any one of claims 1 to 4, which is used for a positive electrode active material of an alkaline storage battery. The nucleus is the general formula (1).
Ni _(1-x) M _x (OH) _{2 + a} (1)
(In the formula: 0 <x ≦ 0.2, 0 ≦ a ≦ 0.2, M is at least one metal element selected from the group consisting of cobalt, zinc, manganese, magnesium, aluminum, yttrium and ytterbium. The positive electrode compound according to claim 5, which is represented by (shown). The compound for a positive electrode according to any one of claims 1 to 4, which is used as a precursor of a positive electrode active material of a non-aqueous electrolyte secondary battery. The nucleus is the general formula (3).
Ni _(1-z) P _z (OH) _{2 + c} (3)
(In the formula: 0 <z ≦ 0.7, 0 ≦ c ≦ 0.28, P is at least one selected from the group consisting of cobalt, zinc, manganese, magnesium, aluminum, zirconium, yttrium, ytterbium and tungsten. The positive electrode compound according to claim 7, which is represented by (.). A positive electrode active material for a non-aqueous electrolyte secondary battery using the positive electrode compound according to claim 7 or 8 as a precursor.