JP7445962B2 - Secondary battery positive electrode material and its manufacturing method - Google Patents

Description

The present invention relates to a positive electrode material for a secondary battery and a method for manufacturing the same, and particularly to a positive electrode material for a secondary battery that is mainly composed of nickel hydroxide particles.

Secondary batteries are often used as power sources for electronic devices such as smartphones and personal computers. In these electronic devices, batteries are required to be small and lightweight and have a large capacity for portability and long-time operation. Furthermore, they are attracting attention as large secondary batteries installed as power sources in passenger cars and the like.

Secondary batteries for transportation machines such as passenger cars are required to have higher output, higher voltage, and higher capacity battery characteristics than secondary batteries used in conventional electronic devices. Recently, nickel compounds have been attracting attention because they are expected to have better performance than lithium cobalt oxide. Therefore, electrode materials that exhibit better battery characteristics have been studied. For example, a positive electrode for a secondary battery has been proposed that includes a base layer of a primer composition of foliar graphite particles and carbon black, and a composite material layer formed on the base layer (see Patent Document 1).

However, in order to further improve the battery performance of secondary batteries, it has become clear that there is still room for improvement in kneading and compatibility between active materials and carbon materials.

Japanese Patent Application Publication No. 2014-35900

The inventors have accumulated knowledge regarding the pulverization of particulate matter. Therefore, in the preparation of the positive electrode material, by utilizing the technology of pulverizing fine particles, we have found a positive electrode material that can exhibit excellent battery characteristics for secondary batteries.

The present invention has been made in view of the above points, and provides a secondary battery that exhibits better battery characteristics than existing positive electrode materials of secondary batteries by improving the type and form of the positive electrode material of the secondary battery. The present invention provides a positive electrode material and a method for manufacturing the same.

That is, a positive electrode material for a secondary battery is a positive electrode material for a secondary battery containing nickel hydroxide, a binder, and a conductive additive, and the positive electrode material includes nickel hydroxide, a binder, and a conductive additive. are fixed to form a fixed body, and the area ratio of nickel hydroxide to the binder and conductive aid in a unit cross section of the fixed body is 92:8 to 91:9.

Furthermore, the average particle size of the nickel hydroxide is 8 to 10 μm.

Further, the aspect ratio of nickel hydroxide is in the range of 0.9 to 1.0.

Furthermore, the binder is characterized in that it is an acrylic resin.

Furthermore, the conductive aid is characterized in that it is carbon black with an average particle size of 0.02 to 0.05 μm.

In addition, a method for manufacturing a positive electrode material for a secondary battery includes a suspension step of dispersing nickel hydroxide, a binder, and a conductive agent in water to obtain a suspension, and an orifice comprising a small diameter flow path. The present invention is characterized by comprising a mixing step of promoting mixing in the suspension by supplying the suspension under pressure to a homogenizer section, and a water removal step of removing water from the suspension that has undergone the mixing step.

Furthermore, the orifice homogenizer section includes a plurality of inflow side flow path sections, a plurality of outflow side flow path sections, a gathering section that collects the plurality of inflow side flow path sections into a single unit, and a plurality of flow path sections connected downstream of the gathering section. It is characterized by comprising an orifice flow path section and a branching section connected downstream of the orifice flow path section to branch the orifice flow path section and connect to a plurality of outflow side flow path sections.

Furthermore, in the mixing step, after the suspension passes through the orifice homogenizer, the passed suspension passes through the orifice homogenizer again, which are repeated.

Furthermore, in the mixing step, the number of times the suspension passes through the orifice homogenizer section is 25 to 35 times.

According to the positive electrode material for a secondary battery of the present invention, the positive electrode material for a secondary battery contains nickel hydroxide, a binder, and a conductive additive, and the positive electrode material contains nickel hydroxide, a binder, and a conductive additive. The auxiliary agent adheres to form a fixed body, and the area ratio of nickel hydroxide to the binder and conductive aid in the unit cross section of the fixed body is 92:8 to 91:9, so It was possible to obtain a positive electrode material for secondary batteries that exhibits better battery characteristics than positive electrode materials for secondary batteries.

Further, according to the method for manufacturing a positive electrode material for a secondary battery of the present invention, a suspension step of dispersing nickel hydroxide, a binder, and a conductive additive in water to obtain a suspension, and a small diameter flow path portion are performed. The method includes a mixing step of promoting mixing in the suspension by pressurizing and supplying the suspension to an orifice homogenizer section provided, and a water removal step of removing water from the suspension after the mixing step. Through particle size control of nickel hydroxide particles, we were able to obtain a positive electrode material for secondary batteries that exhibits better battery characteristics than existing positive electrode materials for secondary batteries.

1 is a schematic cross-sectional view of a positive electrode material of a secondary battery of the present invention. FIG. 2 is a schematic configuration diagram of a mixing device. FIG. 3 is a vertical cross-sectional view of the main part of the orifice homogenizer section. FIG. 3 is a cross-sectional view of the main part of the orifice homogenizer section. It is an electron micrograph of the positive electrode material with the number of passes through the orifice homogenizer portion being set to zero. This is an electron micrograph of a positive electrode material that has passed through an orifice homogenizer section 30 times. This is an electron micrograph of a positive electrode material that has passed through an orifice homogenizer section 100 times. It is an electron micrograph of the positive electrode material of a reference sample. It is a graph of a discharge curve showing the relationship between battery capacity and discharge voltage.

A positive electrode material for a secondary battery defined in the present invention is shown as a schematic cross-sectional view in FIG. The positive electrode material 1 of the secondary battery shown in FIG. 1 mainly contains three types: nickel hydroxide 3, a binder 4, and a conductive aid 5. In the positive electrode material 1, three types of nickel hydroxide 3, a binder 4, and a conductive additive 5 are fixed to each other due to the viscosity of the binder 4, and a fixed body 2 is formed.

Nickel hydroxide (Ni(OH) ₂ ) is in powder form, and in its original state, it cannot be said to be easy to use as an electrode for a secondary battery in terms of coating, filling, etc. Therefore, in order to facilitate coating (coating) on the electrodes, a binder is required to attract the nickel hydroxide powder to each other. Here, as described later, the binder is a resin and has poor conductivity, which lowers battery performance such as charge/discharge characteristics and battery capacity. In this case, it has also been considered to adjust the conductivity by adjusting the quantitative balance between nickel hydroxide and binder resin. However, a corresponding amount of binder is required to adhere the nickel hydroxide particles to each other, and the decrease in conductivity caused by the amount of binder cannot be resolved.

Therefore, we have come to the conclusion that a conductive aid member having conductivity is interposed in the binder that binds the nickel hydroxide particles to each other to improve the decrease in conductivity of the binder portion. Therefore, the positive electrode material of the secondary battery defined in the present invention contains three types: nickel hydroxide, a binder, and a conductive aid.

The proportion of nickel hydroxide in the positive electrode material is determined as the area ratio of nickel hydroxide to components other than nickel hydroxide in a unit cross section of the fixed body. Specifically, in the unit cross section of the fixed body 2 shown in the cross-sectional schematic diagram of FIG. The area ratio satisfies the range of 92:8 to 91:9. That is, the ratio of the total area of nickel hydroxide in a unit cross section of the fixed body is in the range of 91/100 to 92/100. To calculate the total area, an electron microscope photograph (described later) is obtained, and the areas and area ratios of the nickel hydroxide area and other areas are determined using appropriate image processing software.

The area ratio is a range derived by observing a cross section of a fixed body that exhibited good results in the examples described below using an electron microscope. If the total area of nickel hydroxide is less than 91/100 in terms of area ratio, the amount of nickel hydroxide is insufficient, resulting in insufficient performance as a secondary battery. When the total area of nickel hydroxide exceeds 92/100 in terms of area ratio, the bond between nickel hydroxides becomes weak due to lack of binder, making it difficult to form a fixed body. As a result, ease of handling such as coatability of the prepared positive electrode material is reduced. Therefore, the area ratio range described above is preferable.

Regarding the nickel hydroxide used for the positive electrode material, the average particle size of the nickel hydroxide is 8 to 10 μm. The average particle size as used herein refers to the particle size at 50% of the integrated value in the particle size distribution determined by laser diffraction/scattering method. The range of the average particle size is based on the average particle size of the positive electrode material that exhibited good results in Examples described below. When the average particle size of nickel hydroxide is in the range of 8 to 10 μm, a battery using the positive electrode material has a high battery capacity and a high voltage drop rate. That is, it is considered that the charging and discharging efficiency per unit mass is high. On the other hand, when the average particle size deviates from this range, a decrease in performance becomes clear. Therefore, the above average particle size range is preferred.

Furthermore, it is desirable that the nickel hydroxide particles be close to spheres. This is to increase the packing density per unit mass and homogenize the positive electrode material. Therefore, aspect ratio is used as an index of sphericity. Aspect ratio indicates the relative ratio of the major axis to the minor axis. When the aspect ratio is 1, the particle is a sphere. Specifically, as shown in the cross-sectional schematic diagram of FIG. 1, it is calculated from the lengths of two crisscrossing arrows (vertical and horizontal) in the particles of nickel hydroxide 3. The preferred aspect ratio of the nickel hydroxide particles is in the range of 0.9 to 1.0. This is because if the aspect ratio is smaller than 0.9, the nickel hydroxide particles will have a distorted shape that is distant from the sphere, which is not preferable.

The binder used for the positive electrode material is selected from resin materials, and acrylic resin, which has excellent chemical resistance and temperature resistance, is used. Carboxymethylcellulose is also used. Acrylic resin or carboxymethyl cellulose has affinity with water and is therefore suitable for the production method described below.

The conductive aid is a component that has electrical conductivity. However, metals are avoided due to their reaction with nickel hydroxide, the electrode material of the positive electrode. Therefore, carbon-based components are preferably used. Specifically, carbon black is preferably used. Furthermore, the average particle size of carbon black is 0.02 to 0.05 μm. As carbon black, known commercially available products are used. Carbon black is kneaded into the binder resin and filled between the nickel hydroxide particles. Therefore, from the viewpoint of fluidity, the particles are sufficiently smaller than the particles of nickel hydroxide. In addition, it is also necessary to appropriately fill in the spaces between the nickel hydroxide particles. Therefore, available carbon black has an average particle size within the above-mentioned range. The average particle size of carbon black is the particle size at 50% of the integrated value in the particle size distribution determined by laser diffraction/scattering method.

Next, a method for manufacturing a positive electrode material for a secondary battery composed of the components described above will be explained using FIGS. 2 to 4. First, nickel hydroxide powder, a binder (acrylic resin), and a conductive additive (carbon black) are dispersed in water to prepare a suspension ("suspension step"). The reason why each component is dispersed in water to form a suspension is to facilitate supply to the orifice homogenizer used in the mixing step described below and mixing in the orifice homogenizer.

The suspension prepared in the suspension step is supplied under pressure to an orifice homogenizer section 10 equipped with a small-diameter flow path section shown in FIGS. 3 and 4, and mixing of each component in the suspension is promoted. (“Mixing Process”). A feature of the method for manufacturing a positive electrode material for a secondary battery according to the embodiment is that a mixing device 100 equipped with an orifice homogenizer section 10 as shown in FIG. 2 and the like is used. Then, water is removed from the suspension that has undergone the mixing process ("moisture removal process"). The method for manufacturing a positive electrode material for a secondary battery mainly consists of these three steps.

The mixing device 100 in FIG. 2 includes a raw material tank 30, a branch block 40, an orifice homogenizer section 10, and a pump section 50, and a water tank 60 is connected to the raw material tank 30. Water is supplied from a water tank 60 by a pressure pump 61. The treated suspension is collected from the drain section 90. The suspension is stored in a raw material tank 30, and the raw material tank 30 is connected to a downstream branch block 40 via a piping section 81. Further, the raw material tank 30 is provided with a stirrer 31, and the nickel hydroxide powder, binder, and conductive aid (carbon black) are mixed in the raw material tank 30 to form a suspension. A check valve 70 and a switching valve 71 are installed in the piping section 81 . Backflow from the branch block 40 side to the raw material tank 30 side is regulated by a check valve 70 and a switching valve 71.

The pump section 50 is connected to the branch block 40 by a piping section 82. Further, the orifice homogenizer section 10 is connected to the branch block 40 through a piping section 83. Further, the orifice homogenizer section 10 is connected to the raw material tank 30 through a piping section 84. The water tank 60 is connected to the raw material tank 30 through a piping section 85. A piping section 86 is provided on the drain section 90 side. Further, as shown in the figure, switching valves 72, 73, and 74 are connected to each piping section. Each switching valve regulates a fluid flow path during operation of the pump section 50. Each switching valve is a solenoid valve or a manual valve, as appropriate. The piping portions 81, 82, 83, 84, 85, and 86 are hollow tubes with excellent pressure resistance, and allow the suspension to flow therein. Although the structure of the branch block 40 is not particularly limited, it is a member made of a pressure-resistant material such as metal, and has a T-shaped flow path formed inside. Alternatively, the branch block 40 may be a known three-way valve or the like.

The pump section 50 includes a piston 51 within its structure and is generally referred to as a piston pump. When the piston 51 moves backward (in the direction in which the piston 51 moves away from the branch block 40), the suspension flows into the housing 52 of the pump section 50. Then, when the piston 51 moves forward (in the direction in which the piston 51 approaches the branch block 40), the suspension is discharged from the pump section 50 and flows into the orifice homogenizer section 10. The forward and backward movement of the piston 51 is controlled by hydraulic drive, a servo motor, or the like. After passing through the orifice homogenizer section 10, the suspension flows into the raw material tank 30.

After passing through the orifice homogenizer section 10, the nickel hydroxide powder in the initial suspension progresses to micronization (pulverization), and the nickel hydroxide powder, binder (acrylic resin), and conductive aid (carbon black) are mixed. The suspension that has progressed eventually flows out of the mixing device 100 from the drain section 90.

The structure of the orifice homogenizer section 10 will be explained using a vertical cross-sectional view of the main part in FIG. 2 and a cross-sectional view of the main part in FIG. The cross section taken along line AA in FIG. 2 is shown in FIG. 3(a), the cross section taken along line BB in FIG. 2 is shown in FIG. 3(b), and the cross section taken along line CC in FIG. 3(c).

The orifice homogenizer section 10 is formed by a first block 21, a second block 22, and a third block 23 interposed between the first block 21 and the second block 22. In the first block 21, a plurality of inlet flow path portions 11 and 12 are formed (see FIGS. 2 and 3(a)). Further, in the second block 22 as well, a plurality of outflow side flow passage portions 18 and 19 are formed.

A first gap 14 is intentionally formed at the joint surface between the first block 21 and the third block 23. This first cavity 14 becomes a gathering portion 13 that gathers the plurality of inflow side flow path portions 11 and 12 into a single unit (see FIGS. 2 and 3(b)). The downstream side of the gathering part 13 (first cavity part 14) is a third block 23, and the orifice passage part 15 is formed in the third block 23 (see FIGS. 2 and 3(c)).

On the downstream side of the orifice passage section 15, a second void section 16 is also intentionally formed at the joint surface between the third block 23 and the second block 22. This second cavity portion 16 serves as a branch portion 17 that branches the orifice flow path portion 15 and connects to a plurality of outflow side flow path portions 18 and 19.

The inner diameters (D1) of the inflow side flow path sections 11 and 12 and the outflow side flow path sections 18 and 19 are the same and larger than the inner diameter (D2) of the orifice flow path section 15. Specifically, the inner diameter (D1) is 5 to 7 times the inner diameter (D2). Further, the distance (D3) of the first cavity 14 is defined to be equal to the inner diameter (D1). Therefore, the orifice passage section 15 is a small diameter passage section.

Next, the operation when using the orifice homogenizer section 10 will be explained. A suspension in which nickel hydroxide powder, a binder, and a conductive agent (carbon black) are dispersed in water enters the gathering portion 13 (first void portion 14) via the inflow channel portions 11 and 12. Here, since the orifice flow path section 15 is narrower than the inflow side flow path sections 11 and 12, the flow rate of the suspension decreases. Then, a pressure change occurs in the suspension, and the nickel hydroxide powder in the suspension flowing from each inlet side flow path collides at the gathering part 13. At this time, the nickel hydroxide powders in the suspension are crushed by the energy of the collision, and the particle size is reduced from the initial size. In this way, each time the suspension fluid flows from the inlet flow path sections 11 and 12 to the orifice flow path section 15, the collisions between the nickel hydroxide powders in the suspension progress.

The illustrated inflow side flow path section and the outflow side flow path section are both two. Of course, the number of inflow side flow path sections and outflow side flow path sections formed is one or more. However, in order to promote collision of the objects to be treated in the dispersion, it is more preferable that the number of inflow-side flow path portions and inflow-side flow path portions be two or more. The illustrated orifice homogenizer section 10 has a symmetrical shape on both the inflow side and the outflow side. Therefore, for convenience of explanation, they are referred to as the inflow side and the outflow side. Since the inflow and outflow sides are symmetrical, the orifice homogenizer section 10 can function with inflow from either direction. Therefore, the dispersion may flow in from the outflow channel sections 18 and 19, pass through the orifice channel section 15, and flow out from the inflow channel sections 11 and 12.

As understood from the piping configuration of the mixing device 100 in FIG. 2, the suspension that has flowed into the orifice homogenizer section 10 flows into the raw material tank 30 through the piping section 84 after passing through the orifice homogenizer section 10. Then, the suspension supplied from the raw material tank 30 passes through the orifice homogenizer section 10 again. Thus, in the mixing process, the suspension passes through the orifice homogenizer section 10 repeatedly.

As the suspension passes through the orifice homogenizer section 10 repeatedly, the particle size of the nickel hydroxide powder in the suspension gradually decreases through wear due to collisions between the particles. Therefore, in order to adjust the particle size to a desired value, the number of times the suspension passes through the orifice homogenizer section 10 in the mixing device 100 is adjusted. Based on the examples described below, the number of cycles is in the range of 25 to 35 times, with the center being 30 cycles, in view of the balance between good battery performance such as charge/discharge characteristics and battery capacity, and the particle size of the nickel hydroxide powder.

If the number of times the suspension passes through the orifice homogenizer section 10 is less than 25 times, the particle size remains large due to insufficient collision between nickel hydroxide powders, and battery performance such as charge/discharge characteristics and battery capacity cannot be improved. Not expected. Furthermore, if the number of times the suspension passes through the orifice homogenizer section 10 exceeds 35 times, the nickel hydroxide powders collide excessively with each other, making the particle size smaller than necessary. Therefore, battery performance such as charge/discharge characteristics and battery capacity deteriorates. From this, in order to converge the particle size of the nickel hydroxide powder to the aforementioned 8 to 10 μm, the preferred range of the number of times the suspension passes through the orifice homogenizer section 10 is 25 to 35 times.

After the suspension has passed through the orifice homogenizer 10 25 to 35 times, in the mixing device 100 of FIG. It is leaked and recovered. In the water removal step, water is removed from this suspension. Moisture is removed by heating at a temperature that does not cause denaturation of the resin component of the binder. In this way, a positive electrode material for a secondary battery is prepared.

The illustrated mixing apparatus 100 used in the series of explanations is an example of an apparatus for manufacturing a positive electrode material for a secondary battery, and is not necessarily limited to the configuration, mechanism, operating method, etc. illustrated and described. Addition of equipment and changes to procedures are permitted as necessary.

[Materials/equipment]
The inventors prepared a positive electrode material for a secondary battery using the following materials and equipment.
Nickel hydroxide (positive electrode active material): Manufactured by Tanaka Kagaku Kenkyusho Co., Ltd. Binder: Manufactured by Sumitomo Seika Co., Ltd., AquaCharge (acrylic resin)
Conductive aid: Denka Co., Ltd., carbon black, FX-35
Electrolyte: Fujifilm Wako Pure Chemical Industries, Ltd., potassium hydroxide (reagent special grade)
Collector electrode: manufactured by Rikazai, nickel foil (15μm)
Mixing device: Joko Co., Ltd., wet jet mill device, NJ-100, unit diameter: φ0.2 mm, processing pressure: 60 MPa, cooling temperature: 25°C

In addition, measurements and tests were conducted using the following equipment.
Charge/discharge test: Kikusui Electronics Co., Ltd., PFX2011, PFX2121, PFX2332
Particle size distribution type: manufactured by Horiba, Ltd., LA-960
Focused ion beam processing device: Hitachi High-Technologies Corporation, FB-2100
Aberration-corrected scanning transmission electron microscope, JEOL Ltd., JEM-ARM200F

[Preparation of positive electrode material for secondary battery]
Nickel hydroxide powder, binder, and conductive aid (carbon black) were separated, and water was added and stirred to prepare a suspension. Then, using a wet jet mill, the suspension was repeatedly pumped to an orifice homogenizer section (see FIGS. 2 to 4) of the wet jet mill, and passed through the orifice homogenizer section multiple times. Then, the suspension was taken out from the same wet jet mill and water was removed to prepare a sample of a positive electrode material for a secondary battery. At this time, the sample that passed through the orifice homogenizer section 30 times was designated as "Sample 2", and the sample that passed through the orifice homogenizer section 100 times was designated as "Sample 3". In addition, a sample from which water was removed without passing through the orifice homogenizer section (0 passes) was designated as "Sample 1."

[Measurement of physical properties of secondary battery positive electrode material sample]
The average particle size (μm) of nickel hydroxide (positive electrode active material) of each sample 1, 2, and 3 was measured using the above-mentioned measuring device. The average particle size was defined as the particle size at 50% of the integrated value in the particle size distribution determined by laser diffraction/scattering method. The average layer thickness (μm) of the binder adhered to the surface of the nickel hydroxide particles was also measured. Then, the ratio of the particle diameter of nickel hydroxide to the layer thickness of the binder (particle diameter of nickel hydroxide/layer thickness of the binder) was calculated. Furthermore, a known positive electrode material (reference sample) of a nickel hydroxide secondary battery was obtained and subjected to the same measurements as each sample. The results are shown in Table 1.

For each of the prepared samples 1, 2, and 3 and the reference sample, cross-sectional images were taken using the above-mentioned device to obtain electron micrographs. FIG. 5 is a photograph of sample 1 (passed 0 times), FIG. 6 is a photograph of sample 2 (passed 30 times), and FIG. 7 is a photograph of sample 3 (passed 100 times). Moreover, FIG. 8 is a photograph of a reference sample. These are 7,000x (left image) and 35,000x (right image) enlarged photographs, respectively. At this point, the nickel hydroxide powder, binder, and conductive aid (carbon black) of each sample have been kneaded, so that it becomes a solid body.

[Consideration of physical property measurement]
From the measurement results in Table 1, the particle size of nickel hydroxide decreased as the number of passes through the orifice homogenizer increased. This can be considered to be due to the particles colliding with each other when passing through the orifice homogenizer section in the wet jet mill, resulting in abrasion of the particle surfaces and a decrease in particle size. Regarding the binder layer thickness of each sample, changes were observed depending on whether or not the sample passed through the orifice homogenizer section. However, no effect of the number of passes was observed. It can be considered that the particle size of the nickel hydroxide was small and the shape was distorted, as in sample 3, and the binder acted to fill the spaces between the particles (see FIG. 7). Regarding the reference sample, although the particle size is similar to sample 2, the binder layer thickness is clearly smaller.

From the taken electron micrographs, the area of the nickel hydroxide particle part and the area of the other part in the unit cross section were determined for each of the fixed bodies of Samples 1, 2, and 3 and the reference sample. Then, the area ratio between the area of the nickel hydroxide particle portion and the area of the other portion was calculated. Along with this, the aspect ratios of the nickel hydroxide particles of Samples 1, 2, and 3 were also calculated. When calculating the area and aspect ratio, image analysis software was used after obtaining an electron micrograph.

[Battery cell assembly]
The inventors tested and evaluated the battery performance of a total of four types of positive electrode materials for secondary batteries: Samples 1, 2, 3, and a reference sample. A total of four types of positive electrode materials for secondary batteries, Samples 1, 2, 3, and a reference sample, were applied to nickel foil using a doctor blade. Next, for the negative electrode, a mixture of the hydrogen storage alloy, the above-mentioned carbon black, and the above-mentioned binder was coated on a nickel foil using a doctor blade. After coating, the nickel foil for the positive electrode and the nickel foil for the negative electrode were both cut out to a diameter of 16 mm. A polypropylene film with a hydrophilic surface was used as a separator, and nickel as a positive electrode was placed on one side of the separator, and nickel as a negative electrode was placed on the other side, facing each other. This was immersed in an electrolytic solution of potassium hydroxide (concentration 6N) and assembled as a battery cell.

[Measurement of charging and discharging]
A charge/discharge test was conducted using the device for charge/discharge test described above. The test environment temperature was 20° C., the current was 2.6 mAh, and the charge/discharge cycle was 200 cycles. As a result, the discharge curve graph shown in FIG. 9 was obtained. The horizontal axis of the graph is capacity (mAh), and the vertical axis is discharge voltage (V).

From the results in FIG. 9, the capacities of Samples 1, 2, and 3 increased compared to the reference sample. Among them, the increase in sample 2 is remarkable. The difference between Samples 1, 2, and 3 is the difference in the particle size of the nickel hydroxide particles due to the number of passes through the orifice homogenizer section. From this result, it was found that the average particle size of the nickel hydroxide particles of Sample 2 was the best.

[Measurement of battery capacity and voltage drop rate]
The battery capacity (mAh) and voltage drop rate (V/mAh) were measured using the above-mentioned apparatus for charge/discharge tests. The test conditions were a temperature of 20° C., a current of 2.6 mA, and 200 cycles. The results are shown in Table 2.

[Consideration of battery performance]
Regarding battery capacity, Sample 1 and Sample 2 were good. Regarding the voltage drop rate, Sample 2 was good. This result also revealed that the average particle size of the nickel hydroxide particles under the conditions of sample 2 was a good example. Further, although the average particle diameters of the nickel hydroxide particles of sample 2 and the reference sample are similar, the binder layer thicknesses of both samples are different. In particular, in sample 2, a conductive additive (carbon black) is added to the binder, so even if the nickel hydroxide particles are separated by the binder, the mutual conductivity will decrease due to the conductive additive. Suppressed from influence.

Based on the results of the best sample 2 from the series of measurements, the preferred ratio of the total area of nickel hydroxide in a unit cross section is in the range of 91/100 to 92/100. The battery performance of Samples 1 and 3, which deviated from the range of Sample 2, decreased. Further, the preferred range of aspect ratio is 0.9 to 1.0. In particular, as in Sample 3, as the number of passes through the orifice homogenizer section increases, the nickel hydroxide particles disintegrate and become unable to maintain their spherical shape. Therefore, the preferred average particle size range of nickel hydroxide is 8 to 10 μm, centering on the average particle size of Sample 2. In this production, carbon black with an average particle size of 0.02 to 0.05 μm was used.

The positive electrode material for the secondary battery of the present invention exhibits superior battery performance compared to conventional products. Therefore, it is promising as a new positive electrode material for secondary batteries using nickel hydroxide as a raw material.

1 Positive electrode material of secondary battery 2 Fixed body 3 Nickel hydroxide 4 Binder 5 Conductive aid 10 Orifice homogenizer section 11, 12 Inflow side channel section 13 Gathering section 14 First cavity section 15 Orifice channel section 16 Second cavity section 17 Branch section 18, 19 Outflow side flow path section 21 First block 22 Second block 23 Third block 30 Raw material tank 35 Intermediate tank 40 Branch block 50 Pump section 51 Piston 52 Housing 60 Water tank 61 Pressure pump 70 Check valve 71 , 72, 73, 74 switching valve 81, 82, 83, 84, 85 piping section 90 drain section 100 mixing device

Claims (8)

A positive electrode material for a secondary battery containing nickel hydroxide, a binder, and a conductive additive that is carbon black with an average particle size of 0.02 to 0.05 μm ,
The positive electrode material is formed by fixing three types of the nickel hydroxide, the binder, and the conductive additive to form a fixed body,
A secondary battery characterized in that, in a unit cross section of the fixed body, the area ratio of the nickel hydroxide to the binder and the conductive aid excluding the nickel hydroxide is from 92:8 to 91:9. positive electrode material. The positive electrode material for a secondary battery according to claim 1, wherein the nickel hydroxide has an average particle size of 8 to 10 μm. The positive electrode material for a secondary battery according to claim 1 or 2, wherein the aspect ratio of the nickel hydroxide is in the range of 0.9 to 1.0. The positive electrode material for a secondary battery according to any one of claims 1 to 3, wherein the binder is an acrylic resin. A method for producing a positive electrode material for a secondary battery according to any one of claims 1 to 4 , comprising:
A suspension step of obtaining a suspension by dispersing nickel hydroxide, a binder, and a conductive aid which is carbon black with an average particle size of 0.02 to 0.05 μm in water;
a mixing step of promoting mixing in the suspension by supplying the suspension under pressure to an orifice homogenizer section comprising a small-diameter flow path;
A method for producing a positive electrode material for a secondary battery, comprising: a water removal step of removing water from the suspension that has undergone the mixing step. The orifice homogenizer section includes:
a plurality of inflow side flow path sections;
a plurality of outflow flow path sections;
a gathering part that gathers the plurality of inflow side flow path parts into a single unit;
an orifice flow path section connected downstream of the gathering section;
a branching portion connected downstream of the orifice flow path portion, branching the orifice flow path portion and connecting with the plurality of outflow side flow path portions;
The method for manufacturing a positive electrode material for a secondary battery according to claim 5 , comprising: 7. The positive electrode for a secondary battery according to claim 5, wherein in the mixing step, after the suspension passes through the orifice homogenizer section, the suspension passes through the orifice homogenizer section again. Method of manufacturing the material. 8. The method for producing a positive electrode material for a secondary battery according to claim 7 , wherein in the mixing step, the number of times the suspension passes through the orifice homogenizer section is 25 to 35 times.

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