GB2329179A

GB2329179A - Double layered nickel hydroxide containing additives

Info

Publication number: GB2329179A
Application number: GB9812053A
Authority: GB
Inventors: Dong-Yup Shin; Yeong-Chan Eun; Jin-Kyung Kim
Original assignee: Samsung Display Devices Co Ltd
Current assignee: Samsung SDI Co Ltd
Priority date: 1997-09-11
Filing date: 1998-06-04
Publication date: 1999-03-17
Also published as: DE19823128A1; KR100241594B1; KR19990025183A; GB9812053D0; JPH11111284A

Abstract

A double layered nickel hydroxide active material includes a core of nickel hydroxide including a first additive agent of low concentration (eg 0.5-4 wt%) and an outer layer of nickel hydroxide including a second additive agent of high concentration (eg 10-80 wt%), formed on the core. The first and second additive agents may be the same or different and are selected from cobalt, cadmium, zinc, calcium, magnesium and boron, preferably, cobalt. The nickel hydroxide material may be used on a collector in a nickel hydroxide positive electrode.

Description

2329179 A DOUBLE LAYERED NICKEL HYDROXIDE ACTIVE MATERIAL AND A NICKEL

POSITIVE ELECTRODE PREPARED BY USING THE SAME

CROSS REFERENCE TO RELATED APPLICATION

This application is based on application No. 97-46715 filed in the Korean Industrial Property Office on September 11, 1997, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION (a) Field of the Invention

The present invention relates to a nickel hydroxide active material for an alkali cell and a nickel positive electrode prepared from the same. More particularly, the present invention relates to a double-layered nickel hydroxide active material with a core and outer layer having different physical properties and additive agents, such as cobalt and zinc.

(b) Description of the Related Art

Recently, according to the increased use of portable electronic devices, such as camera, camcorder, portable CD player, portable radiolaudio, notebook computer or portable phones, there is a need for a secondary cell having high cell performance characteristics. Furthermore, it is particularly required to increase the energy density of the secondary cell.

As the secondary cell, nickel based batteries, such as a nickelcadmium battery, a nickel-metal hydride battery, a nickel-iron battery and a nickel-zinc battery et al are developed. The nickel-based batteries use cadmium, metal hydride, iron or zinc as their negative active material, and use nickel-hydroxide as their positive active material. Therefore, it is necessary to increase the capacity of the nickel positive active material.

The physical properties of the nickel hydroxides are remarkably different from each other according to their preparation method. Generally, the nickel hydroxide is prepared by the neutralization method comprising the steps of mixing a nickel salt and a hydroxide salt and adding a trace of water to the mixture. However, the nickel hydroxide active material prepared by the neutralization method is a coarse particle having a diameter of 1 to several hundred pm, thus the particle should be ground to be used as an active material for a cell. Furthermore, the shapes of the ground particle are irregular, and the densities thereof is low. Thus, it is undesirable to use the particle as an active material for a cell.

Meanwhile, if the nickel salt and hydroxide salt are neutralized in an aqueous solution, the reaction rate is very rapid. Thus, the density of the resulting particles is very low, and the sizes thereof are too minute. Therefore, it takes long time to filtrate and wash the particles. In addition, since there are large amount of water on the surface of the particles, it is difficult to paste the particle on a current collector densely and the particle is likely separated from the paste.

The nickel hydroxide for the pasted nickel positive electrode should have high density, globular shapes and uniform particle diameters. Generally, that nickel hydroxide for a cell has an apparent density of 1.6 to 1. 8glcd, tapping density of 2.0 to 2,191& and a particle diameter of 5 to 40 um.

When the nickel hydroxide having the above characteristics is used as 2 the positive active material, the resulting paste shows a good fluidity and good charging characteristics. In order to prepare the nickel hydroxide and to control to the reaction rate, conventionally a nickelammonium complex is prepared, and then the complex is neutralized. As an alternative method, in order to produce the nickel hydroxide, the nickelammonium complex is decomposed by increasing the solution temperature.

The nickel hydroxide prepared by the above described method has a high density, but it is difficult to control the reaction rate and particle size and continuously prepare the nickel hydroxide because the composition of the nickel-ammonium complex solution and pH of the solution are severely changed during the reaction.

In a pasted positive electrode of a nickel based cell, the positive electrode is deteriorated due to the expansion of the electrode, which happens when the nickel hydroxide changes its form from 0-NiOOH to 7-MOOH of low density. The expansion of the electrode causes separation of the active material, and decreases conductivity, lifetime and efficiency of the electrode. The 7 -NiOOH of low density is formed due to the compact crystalline structure of P- MOOH of high density. The compact crystalline structure results in the small number of internal micro-pores, thus hydrogen ions can not move smoothly in the crystalline structure. When charging the cell, a high overvoltage is required for complete charging, thus the charged B-NiOOH is continuously oxidized and is changed to 7 NiOOH of low density. When the 7-MOOH is formed, the volume of the active material is expanded. Furthermore, as charge-discharge is repeated, separation of the active material 3 from a current collector occurs and conductivity of the electrode decreases severely, thus capacity of the cell is remarkably decreased. This phenomenon happens more seriously when charging-discharging a cell with high-rate.

In order to prevent the electrode expansion, additives such as cobalt, cadmium, zinc, et at., are added to nickel hydroxide. The additive substitutes nickel in the nickel hydroxide lattice, thereby distorting the lattice and facilitating the transfer of hydrogen ions. Therefore, by adding the additives, the change of 9 -NiOOH to:r -NiOOH can be prevented, and high rate charge-discharge characteristic of the nickel hydroxide is achieved.

However, the method has a disadvantage in that due to the substitution of nickel of the nickel hydroxide with the additive such as cobalt or zinc, the content of nickel in the nickel hydroxide is decreased, thereby the theoretical capacity of the active material is decreased. ' SUMMARY OF THE INVENTION

An object of the present invention is to provide a nickel hydroxide active material including small amount of an additive agent. The conductivity of the active material and a cell voltage of a cell using the active material increase, but the theoretical capacity of the active material do not seriously decrease.

In order to achieve the objects, the present invention provides a double layered nickel hydroxide active material comprising a core of nickel hydroxide including a first additive agent of low concentration; an outer layer of nickel hydroxide including a second additive agent of high concentration, formed on the core. The present invention also provides a nickel positive electrode comprising a collector; the double layered nickel hydroxide active material 4 coated on at least one surface of the collector.

Additional objects, advantages and novel features of the invention will set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following drawing, detailed description and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing an apparatus for preparing a double layered nickel hydroxide active material of the present invention.

In the following detailed description, only the preferred embodiment of the invention has been shown and described, simply by way of illustration of the best mode contemplated by the inventors. As will be realized, the invention is capable of modification in various obvious respects, all without departing from the scope of the invention. Accordingly, the drawing and description are to be regarded as illustrative in nature, and not as restrictive.

DETAILED DESCRIPTION OF THE PREFERRED EMBODMENTS

The present invention provides a double layered nickel hydroxide active material comprising a core of nickel hydroxide including a first additive agent of low concentration; and an outer layer of nickel hydroxide including a second additive agent of high concentration, formed on the core.

The first and second additive agents are selected from the group consisting of cobalt, cadmium, zinc, calcium, magnesium and boron, and the most preferable additive is cobalt. The amount of the additive in the core is preferably 0.5 to 4.0 wt %, and more preferably, 0.5 to 2.0 wt %. The amount of the additive in the outer layer is preferably 10 to 80 wt %, and more preferably 10 to 50 wt %. The amount of the additives in the outer layer is from five times to one hundred times than that in the core. Furthermore, an apparent density, a tapping density of the outer layer is higher than that of the core. The diameter of core of nickel hydroxide is 1 to 30 ^ and more preferably 1 to 15 #m. The thickness of the outer layer is less than 10 im, and more preferable thickness of the outer layer is 1 to 8 gn. The total amount of the additive in the nickel hydroxide active material is preferably 1.0-5. 0 wt %.

The method of preparing the double layered nickel hydroxide of this invention is illustrated with reference to Fig. 1.

The first step for preparing a nickel hydroxide core is as follows. While nickel sulfate solution 1 and aqueous ammonia 2 are added to a spraying tube 3 which is maintained to a constant temperature by a temperature controller 8 and mixed, at the same time the mixture 4 is sprayed into the first reaction bath 9 which is maintained at the same temperature with that of the spraying tube 3.

Sodium hydroxide solution 6 is then added to the first reaction bath 9 and stirred by a shaker 5. The sodium hydroxide solution 6 reacts with the mixture 4 to produce a core of nickel hydroxide 10.

In the manufacturing process, the amount of sodium hydroxide solution 6 in the first reaction bath 9 is automatically controlled by using a pH controller 7 so as to maintain the pH of the solution in the first reaction bath 9 at a constant value in the range 11 to 13.

The second step for preparing the nickel hydroxide of the present 6 invention is as follows. After the first step, a solution including the core of nickel hydroxide 10 is automatically injected into a second reaction bath 19. While nickel sulfate solution 11 and aqueous ammonia 12 are injected into a spraying tube 13 which is maintained at a constant temperature by the temperature controller 18 and are mixed, at the same time the mixture 14 is sprayed into the second reaction bath 19 which is maintained at the same temperature with that of the spraying tube by the temperature controller 18. Sodium hydroxide solution 16 is added to the second reaction bath 19 and stirred by the shaker 15. The sodium hydroxide solution 16 reacts with the sprayed mixture 14 to produce an outer layer of nickel hydroxide on the core of nickel hydroxide 10. The outer layer has a different physical property from the core of nickel hydroxide 10, thus the double layered nickel hydroxide is produced. The amount of sodium hydroxide solution 16 in the second reaction bath 19 is automatically controlled by using a pH controller 17 so as to maintain the pH of the solution in the second reaction bath 19 at a constant value in the range 11 to 13.

The aqueous solution of nickel sulfate 1 in the first step and nickel sulfate solution 11 in the second step include nickel sulfate as a main component and at least one additive selected from the group consisting of bivalent metals, such as cobalt, cadmium, zinc, calcium and magnesium, and non-metals, such as boron. The amount of the additives to be added in the first and second steps are preferably different from each other.

The preferred concentration of nickel in the nickel sulfate solution 1, 11 is 2.0 to 2.8 M. When the concentration of nickel sulfate is less than 2.0M, large amount of the solution should be used. In addition, when the 7 1 concentration of nickel hydroxide is more than 2.8M, nickel sulfate salt is likely to be precipitated. Preferably, the nickel sulfate solution 1 used in the first step includes 0.02 to 0.2 moles of at least one additive which is selected from the group of cobalt, cadmium, zinc, calcium, magnesium and boron, and the nickel sulfate solution 11 used in the second process includes 0.02 to 2.8 moles of the at least one additive which is selected from the group of cobalt, cadmium, zinc, calcium, magnesium and boron. The amount of the additive in the nickel sulfate solution 11 used in the second process is preferably larger than that in the nickel sulfate solution 1 used in the first process. When an amount of the additives is out of the range, the nickel hydroxide having high rate charge- discharge characteristic and high capacity can not be prepared.

Nickel hydroxide prepared by the method of this invention has an apparent density of from 1.55 to 1.8g/crr? and a tapping density of from 2.0 to 2.3g/cd. By preparing the nickel hydroxide active material according to this invention, the packing amount of the active material can be increased, and fluidity and packing characteristics thereof can be improved due to a globular particle shape of the active material. Furthermore, by adding proper amount of additives to the nickel hydroxide, the capacity, the high-temperature performance and the high-rate cha rge-discharge characteristic of the nickel hydroxide active material are improved. The active material of the present invention is applicable to all nickel based cells such as a nickel-metal hydride battery, a nickel-cadmium battery, a nickel-iron battery and a nickel-zinc battery.

The present invention is further explained in more details with reference to the following examples, which are within the scope of this invention.

8 [Example 1]

First step: A 2.3 M nickel sulfate solution containing cobalt at a concentration of 0.05 M and zinc at a concentration of 0.05 M and a 15 M aqueous ammonia solution were injected into a spraying tube maintained at a temperature of 500C. The aqueous ammonia was injected so that 0.55 motes of ammonia were supplied per 1 mole of nickel, cobalt and zinc. While the mixture was sprayed into the first reaction bath, maintained at a temperature of 500C, a 6.0 M sodium hydroxide solution was automatically added to the first reaction bath so as to maintain the pH at 11.5, resulting in the preparation of a core of nickel hydroxide.

Second step: The resulting product including the core of nickel hydroxide was injected into the second reaction bath. Thereafter, a 15 M aqueous ammonia solution and a 2.3 M nickel sulfate solution including cobalt at a concentration of 0.36 M and zinc at a concentration of 0.05 M were injected into a spraying tube. The aqueous ammonia was injected so that 0. 75 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. The mixture was sprayed into the second reaction bath while a 6.0 M sodium hydroxide solution was automatically added so as to maintain the pH at 11.5, to produce a double layered nickel hydroxide having higher cobalt content in its outer layer.

The reaction times for the first step and the second step were 3 hours and 10 minutes, respectively.

The physical properties of the double layered nickel hydroxide prepared by this example were determined and the results thereof are shown in the following Table 1.

[Example 21

First step: A 2.3 M nickel sulfate solution containing cobalt at a concentration of 0.05 M and zinc at a concentration of 0.05 M, and a 15 M aqueous ammonia solution were injected into a spraying tube maintained at a temperature of 5M. The aqueous 9 ammonia was injected so that 0.55 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. While the mixture was sprayed into the first reaction bath, maintained at a temperature of 500C, a 6.0 M sodium hydroxide solution was automatically added to the first reaction bath so as to maintain the pH at 11.5, to prepare a core of nickel hydroxide.

Second step: The resulting product including the core of nickel hydroxide was injected into the second reaction bath. Thereafter, a 15 M aqueous ammonia solution and a 2.3 M nickel sulfate solution including cobalt at a concentration of 1.1 M and zinc at a concentration of 0.05 M were injected into a spraying tube. The aqueous ammonia was injected so that 0. 75 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. The mixture was sprayed into the second reaction bath, while a 6.0 M sodium hydroxide solution was automatically added so as to maintain the pH at 11.5, to produce a double layered nickel hydroxide having higher cobalt content in its outer layer.

[Example 3]

First step: A 2.5 M nickel sulfate solution containing cobalt at a concentration of 0.04 M and zinc at a concentration of 0.04 M, and a 15 M aqueous ammonia solution were injected into a spraying tube maintained at a temperature of 5WC. The aqueous ammonia was injected so that 0.55 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. While the mixture was sprayed into the first reaction bath, maintained at a temperature of 500C, a 6.0 M sodium hydroxide solution was 1 automatically added to the first reaction bath so as to maintain the pH at 11.5, to prepare a core of nickel hydroxide.

Second step: The resulting product including the core of nickel hydroxide was injected into the second reaction bath. Thereafter, a 15 M aqueous ammonia solution and a 2.5 M nickel sulfate solution including cobalt at a concentration of 1. 18 M and zinc at a concentration of 0.04 M were injected into a spraying tube. The aqueous ammonia was injected so that 0. 8 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. The mixture was sprayed into the second reaction bath, while a 6.0 M solution of sodium hydroxide was automatically added so as to, maintain the pH at 11.5, to produce a double layered nickel hydroxide having higher cobalt content in its outer layer.

[Example 4]

First step: A 2.5 M nickel sulfate solution containing cobalt at a concentration of 0.04 M and zinc at a concentration of 0.04 M and a 15 M aqueous ammonia solution were injected into a spraying tube maintained at a temperature of 500C. The aqueous ammonia was injected so that 0.6 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. While the mixture was sprayed into the first reaction bath, maintained at a temperature of 500C, a 6.0 M sodium hydroxide solution was automatically added to the first reaction bath, so as to maintain the pH at 11.5, to prepare a core of nickel hydroxide.

Second step: The resulting product including the core of nickel hydroxide was injected into the second reaction bath. Thereafter, a 15 M aqueous ammonia solution 11 1 and a 2.5 M nickel sulfate including cobalt at a concentration of 2.0 M and zinc at a concentration of 0.04 M were injected into a spraying tube. The aqueous ammonia was injected so that 0.8 moles of ammonia were supplied per 1 mole of nickel, cobalt and zinc. The mixture was sprayed into the second reaction bath, while a 6.0 M sodium hydroxide solution was automatically added so as to maintain the pH at 11.5, to produce a double layered nickel hydroxide having higher cobalt content on its outer layer.

12 1 [Table 11

Apparent Tapping Average Composition density density diameter (wt %) (g/ce) (g/ce) Example Core 1.72 2.20 2 - 25 Co 1.4 1 Zn 1.5 Outer - - Co 10.5 layer Zn 1.5 Total 1.65 2.12 2 - 45 Co 1.9 Zn 1.5 Example Core 1.72 2.20 2 - 25 Co 1.4 2 Zn 1.5 Outer - - Co 28.7 layer Zn 1.6 Total 1.60 2.08 2-45 Co 2.9 Zn 1.5 Example Core 1.75 2,26 2 - 30 Co 0.9 3 Zn 1.0 Outer - Co 31.2 layer Zn 1.1 Total 1.65 2.14 2-40 Co 2.6 Zn 1.0 Example Core 1.75 2.26 2 - 30 Co 0.9 4 Zn 1.0 Outer - - Co 47.5 layer Zn 0.9 Total 1.58 2.04 2 - 50 Co 3.6 Zn 1.0 The double layered nickel hydroxide prepared by the examples has an 13 apparent density of 1.6 to 1.8g/cd and a tapping density of 2.0 to 2. 3g/cd.

When the nickel positive electrode is prepared by using the double layered nickel hydroxide, fluidity and packing property of the active material is improved so that the positive electrode for a nickel-based cell having high capacity can be prepared. Furthermore, the nickel positive electrode having a high capacity, a high-temperature performance and an improved high-rate charge-discharge characteristic can be prepared. Therefore, this invention is applicable to all nickel-based cell such as a nickel-metal hydride battery, a nickel-cadmium battery, a nickel-iron battery and a nickel-zinc battery.

14 1

Claims

WRAT IS CLAIMED IS:

1. A double layered nickel hydroxide active material comprising:

a core of nickel hydroxide including a first additive agent of low concentration; and an outer layer of nickel hydroxide including a second additive agent of high concentration, formed on the core.

2. The double layered nickel hydroxide active material as claimed in claim 1, wherein the first and second additive agents are selected from the group consisting of cobalt, cadmium, zinc, calcium, magnesium and boron.

3. The double layered nickel hydroxide active material as claimed in claim 2, wherein thefi-rst and second additive agents are cobalt.

4.

The double layered nickel hydroxide active material as claimed in claim 3, wherein the content of cobalt in the core is 0.5 to 2 0 wt.% and the content of cobalt in the outer layer is 10 to 15 wt.% relative to the total amount of nickel hydroxide in material.

5. The double layered nickel hydroxide active material as claimed in any one of claims 1 to 4, wherein the total amount of the first and second additive agents in the double layered nickel hydroxide is 1.0 to 5.0 wt.% based on the total nickel hydroxide.

Document k 271080 - amended claims 316M - 230P78952 1

6. The double layered nickel hydroxide active material as claimed in any one of claims 1 to 5, wherein the apparent density of the core is higher than that of the outer layer.

7 The double layered nickel hydroxide active material as claimed in any one of claims 1 to 6,, wherein the tapping density of the core is higher than that of the outer layer.

8. The double layered nickel hydroxide active material as claimed in any one of claims 1 to 7, wherein the diameter of the core particles is 1 to 15 pum.

9. The double layered nickel hydroxide active material as claimed in any one of claims 1 to 8, wherein the thickness of the outer layer is less than pm.

10. A nickel hydroxide positive electrode comprising:

a collector; and a double layered nickel hydroxide active material coated on at least one surface of the collector,- wherein the double layered nickel hydroxide active material is as defined in any one of claims 1 to 9.

A double layered nickel hydroxide active material according to any one of claims 1 to 9 substantially as described herein with reference to examples 1 to 4.

16 Document #: 271080 - amended claims 316198 - 230P79952