JP2004119110A - Positive electrode active material for lithium-ion secondary battery, and its process of manufacture - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a positive electrode active material for a lithium ion secondary battery containing a compound nickel acid lithium particulate wherein low temperature output of the lithium ion secondary battery can be improved. <P>SOLUTION: A covering layer 12 of lithium carbonate is formed on the surrounding of a compound nickel acid lithium particulate 10 and the carbonate ion richness on the surface of the composite nickel acid lithium particulate is made 0.012-0.018 g<SP>2</SP>/Lm<SP>2</SP>. Then, by modulating the blowing in quantity of the oxygen gas at the manufacturing of the active material, the carbonate ion concentration is made into the above range. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement in a positive electrode active material for a lithium ion secondary battery and a method for producing the same.
[0002]
[Prior art]
In recent years, with the widespread use of portable information terminals such as mobile phones and notebook computers, there is a strong demand for the development of secondary batteries that have a high energy density and are small and light. In particular, lithium ion secondary batteries using a carbon material containing a light metal such as lithium as a mobile ion species as a negative electrode are most widely researched and developed.
[0003]
A lithium ion secondary battery can realize a high voltage and a high energy density, but the lithium cobalt composite oxide is most widely used as a positive electrode material. However, the composite lithium cobaltate uses an expensive cobalt compound as a raw material, and causes an increase in the cost of the positive electrode material, and hence the cost of the secondary battery, so that there is a high demand for a cheaper active material. Research has been conducted on lithium metal composite oxides using manganese or nickel as cathode materials that can be replaced by composite lithium cobaltate. In particular, composite lithium nickelate exhibits a high battery voltage as well as composite lithium cobaltate. In addition, since the theoretical capacity is larger than that of the composite lithium cobaltate, research and development have been widely conducted.
[0004]
However, when lithium nickelate synthesized purely with nickel is used as the positive electrode active material, the cycle characteristics are inferior to those of composite lithium cobaltate, and battery performance is relatively easily lost when used in high and low temperature environments. Has drawbacks. In order to improve this drawback, a lithium metal composite oxide in which a part of nickel is substituted with at least one metal element selected from Co, Al, Mg, Mn, Ti, Fe, Cu, Zn, and Ga is used. The surface decoration of composite lithium nickelate has been studied.
[0005]
For example, Japanese Patent Application Laid-Open No. 11-167919 discloses an example in which lithium carbonate is coated on the surface of composite lithium nickelate fine particles in order to suppress heat generation at the time of a short circuit and improve moisture resistance.
[0006]
[Patent Document 1]
Japanese Patent Laid-Open No. 11-167919 [0007]
[Problems to be solved by the invention]
However, the conventional positive electrode material for a lithium ion secondary battery has a problem that the low-temperature output of the lithium ion secondary battery cannot always be improved.
[0008]
The present invention has been made in view of the above-described conventional problems, and its object is to improve the low-temperature output of a lithium ion secondary battery, and to provide a positive electrode active for lithium ion secondary batteries containing composite lithium nickelate fine particles. It is to provide a substance and a manufacturing method thereof.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a positive electrode active material for a lithium ion secondary battery containing composite lithium nickelate fine particles, wherein at least a part of the surface of the composite lithium nickelate fine particles is coated with a weak lithium salt. The surface ion concentration which is the ion concentration of the weak acid on the surface of the composite lithium nickelate fine particles is in the range of 0.012 to 0.018 g ² / Lm ² .
[0010]
According to the above configuration, by setting the surface ion concentration on the surface of the composite lithium nickelate fine particles in the above range, lithium ions can be easily released in a low temperature region, and the low temperature output of the battery can be improved. Can do.
[0011]
Further, nickel hydroxide or nickel hydroxide containing a metal element other than nickel is added and mixed with aluminum hydroxide and lithium hydroxide, the mixture is granulated, and the granulated product contains carbon dioxide gas. A method for producing a positive electrode active material for lithium ion secondary battery containing composite lithium nickelate fine particles, which is fired while blowing oxygen gas, and pulverizes and dehydrates the fired product, wherein in the firing step, composite lithium nickelate The oxygen gas blowing amount is adjusted so that the carbonate ion concentration on the surface of the fine particles is in the range of 0.012 to 0.018 g ² / Lm ² .
[0012]
According to the said structure, the positive electrode active material containing the composite lithium nickelate microparticles | fine-particles which can improve the low temperature output of a lithium ion secondary battery can be manufactured easily.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention (hereinafter referred to as embodiments) will be described with reference to the drawings.
[0014]
FIG. 1 shows a configuration example of a positive electrode active material for a lithium ion secondary battery according to the present invention. In FIG. 1, a coating layer 12 made of a weak lithium salt, such as lithium carbonate, is formed on at least a part of the surface of a composite lithium nickelate fine particle 10 containing lithium and nickel or other metal element. The surface ion concentration that is the concentration of carbonate ions in the coating layer 12 on the surface of the composite lithium nickelate fine particles 10 is preferably in the range of 0.012 to 0.018 g ² / Lm ² .
[0015]
The unit of the surface ion concentration is g ² / Lm ² indicates that the concentration measurement was performed by extracting carbonate ions from the coating layer 12 with pure water as described below. That is, 0.1 g of a sample of composite lithium nickelate fine particles 10 having a coating layer 12 was put into a 100 mL volumetric flask, made 100 mL with pure water, shaken for 30 seconds, and filtered with a membrane filter having a pore size of 0.22 μm. To do. The filtrate is injected into ion chromatography, and the carbonate ion concentration is measured as CO ₃ ^2- . In this way, the carbonate ion concentration (g) in the sample 0.1 g is obtained, and this value is the carbonate ion concentration (g / L) extracted in 100 mL of water. Accordingly, a value obtained by multiplying the extracted carbonate ion concentration (g / L) by 10 becomes the carbonate ion concentration (g / L) in 1 g of the sample. Next, by dividing this carbonate ion concentration by the specific surface area of the composite lithium nickelate fine particles 10, the concentration of carbonate ions on the surface of each composite lithium nickelate fine particle 10, that is, the surface ion concentration can be obtained. Since the unit of the specific surface area is m ² / g, the unit of the surface ion concentration is g ² / Lm ² when the carbonate ion concentration is divided by the specific surface area. In this case, L represents the extraction result with pure water.
[0016]
By setting the surface ion concentration of the composite lithium nickelate fine particles 10 measured as described above to the range of 0.012 to 0.018 g ² / Lm ² as described above, the lithium ion 2 used as the positive electrode active material was used. The low temperature output of the secondary battery can be improved. This is because lithium ions are easily released from the lithium carbonate constituting the coating layer 12 on the surface of the composite lithium nickelate fine particles 10 at a low temperature.
[0017]
FIG. 2 shows the relationship between the surface ion concentration of the composite lithium nickelate fine particles 10 and the low-temperature output of a lithium ion secondary battery using this as a positive electrode active material. As shown in FIG. 2, the low-temperature output of the lithium ion secondary battery is improved when the surface ion concentration is in the range of 0.012 to 0.018 g ² / Lm ² . The reason for this is that lithium carbonate constituting the coating layer 12 is a salt that has a lithium equilibrium at low temperatures, and easily releases lithium ions at low temperatures as described above.
[0018]
FIG. 3 shows a process diagram of a method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention. In FIG. 3, nickel hydroxide (Ni (OH) ₂ ) is synthesized by a conventionally known method (S1), aluminum hydroxide is added to the nickel hydroxide (S2), and lithium hydroxide is further added. Mix (S3) and granulate (S4). This granulated product becomes primary particles, and becomes the composite lithium nickelate fine particles 10 having the coating layer 12 shown in FIG. 1 by the following firing process.
[0019]
The granulated product is fired by the following procedure (S5). First, it is dehydrated by heating from room temperature to 300 ° C. Next, initial synthesis is performed at a temperature of 400 to 550 ° C. or 400 ° C. or lower, and then homogenization is performed at a temperature of 650 to 800 ° C. In such a firing step, particles of composite lithium nickelate (LiNiMO ₂ ; M is a metal other than nickel) grow. The composite lithium nickelate particles contain metal elements other than nickel, such as aluminum, represented by M, and become composite lithium nickelate fine particles 10. Here, when producing the composite lithium nickelate, a metal element such as cobalt, iron, manganese, and magnesium can be coprecipitated and added as a hydroxide such as cobalt hydroxide in step S1. Further, in the step S2, other metals can be added as metals, metal oxides, metal hydroxides, sulfates, nitrates and the like in the same manner as aluminum.
[0020]
Furthermore, oxygen gas containing carbon dioxide (carbon dioxide) is supplied during the firing step. Thereby, at least a part of the surface of the composite lithium nickelate fine particles is coated with lithium carbonate, and the coating layer 12 according to the present invention is formed. In this case, the component of the coating layer 12 is not necessarily limited to lithium carbonate, and may be a weak acid salt of lithium.
[0021]
After the firing step, since the primary particles are in a state of being bonded to each other, they are pulverized and monodispersed into secondary particles having an average particle size of 5 to 15 μm (S6). After this pulverization step, sieving is performed to make the secondary particle size equal to or less than 30 μm (S7). Furthermore, this is classified and fine powder is cut (S8). As shown in FIG. 1, the secondary particles described above are in a state where a plurality of composite lithium nickelate fine particles 10 having a coating layer 12 which is a primary particle are solidified.
[0022]
The particulate positive electrode active material produced as described above is freed of moisture adsorbed in the dehydration step (S9), and becomes a positive electrode active material for a lithium ion secondary battery.
[0023]
The characteristic point in the above manufacturing process is that when supplying oxygen gas containing carbon dioxide gas in the firing step S5, the film thickness of the coating layer 12 formed around the composite lithium nickelate fine particles 10 is controlled, The oxygen gas blowing amount is adjusted so that the surface ion concentration, which is the concentration of carbonate ions on the surface of the composite lithium nickelate fine particles 10, is in the range of 0.012 to 0.018 g ² / Lm ² described above.
[0024]
【The invention's effect】
As described above, according to the present invention, the surface ion concentration, which is the carbonate ion concentration on the surface of the composite lithium nickelate fine particles, is set in the range of 0.012 to 0.018 g ² / Lm ² , thereby The low temperature output of the lithium ion secondary battery used as the material can be improved.
[0025]
Further, the composite lithium nickelate fine particles can be easily produced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration example of a positive electrode active material for a lithium ion secondary battery according to the present invention.
FIG. 2 is a graph showing the relationship between the low-temperature output of a lithium ion secondary battery using the positive electrode active material for a lithium ion secondary battery according to the present invention and the ion concentration on the surface of the active material.
FIG. 3 is a process diagram illustrating a method for producing a positive electrode active material for a lithium ion secondary battery according to the present invention.
[Explanation of symbols]
10 Composite lithium nickelate fine particles, 12 Coating layer.

Claims (2)

A positive electrode active material for a lithium ion secondary battery comprising composite lithium nickelate fine particles,
At least a part of the surface of the composite lithium nickelate fine particles is coated with a weak acid salt of lithium,
A positive electrode active material for a lithium ion secondary battery, wherein a surface ion concentration, which is an ion concentration of the weak acid, on the surface of the composite lithium nickelate fine particles is in a range of 0.012 to 0.018 g ² / Lm ² . Aluminum hydroxide and lithium hydroxide are added and mixed with nickel hydroxide or nickel hydroxide containing a metal element other than nickel,
Granulate the mixture,
The granulated product is fired while blowing oxygen gas containing carbon dioxide gas,
A method for producing a positive electrode active material for a lithium ion secondary battery containing composite lithium nickelate fine particles, wherein the fired product is pulverized and dehydrated,
In the firing step, the amount of oxygen gas blown is adjusted so that the carbonate ion concentration on the surface of the composite lithium nickelate fine particles is in the range of 0.012 to 0.018 g ² / Lm ^2. A method for producing a positive electrode active material for a secondary battery.

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