JPH07230808A - Positive electrode active material for nonaqueous lithium secondary battery, manufacture thereof, and lithium secondary battery - Google Patents

Abstract

PURPOSE:To provide spherical powder of LiNiO2 which is so favorable as positive electrode active material for a nonaqueous lithium secondary battery as to enable formation of a high charge/discharge capacity battery, and provide a positive electrode plate to be used as a positive electrode formed of the spherical powder of LiNiO2 obtained in a manufacturing method in which the powder can be manufactured at satisfactory reproducibility. CONSTITUTION:Nickel compound and lithium powder of an average grain size of 5-50mum are blended at a Li/Ni molar ratio of 1/1, suspension-agitated in solution including organic acid, and dried. This is then heat-treated in an oxygen gas current at 740 deg.C for 15 hours to be spherical powder of LiNiO2 of 150 mesh or less, which is kneaded with conductive agent and binding agent to be moulded, and a positive electrode plate is manufactured of this mould to be used as a positive electrode 4 in a lithium battery.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a spherical LiNiO ₂ particle which is effective as a positive electrode active material of a non-aqueous lithium secondary battery, a method for producing the same, and a positive electrode plate containing the particle as a main component, which has a high charge / discharge capacity. The present invention relates to a rechargeable lithium secondary battery.

[0002]

2. Description of the Related Art Generally, a lithium battery is used as a power source for a camera or a wrist watch, and is used by taking advantage of its small size and high energy density. However, most of these are so-called primary batteries that cannot be charged. The main reason why charging is not possible is in the positive electrode active material, which has been irreversible with lithium in the past, such as fluorocarbon, MnO ₂ , and Cu.
O and the like have been used as the positive electrode active material.

In recent years, research on a rechargeable lithium secondary battery has progressed, and it has become known that the reaction with Li ions in the negative electrode can be reversible by using the positive electrode active material V ₂ O ₅ . Further, each raw material of lithium salt and nickel salt is finely pulverized and mixed in an organic solvent, and then dried and molded.
LiNiO ₂ was synthesized by firing in an oxygen stream at about 50 ° C. for 24 hours, and a crystal structure was developed to facilitate the movement of lithium ions and increase the capacity.

As a manufacturing method, one or more powders selected from nickel hydroxide, nickel oxide and nickel oxyhydroxide, and at least one powder selected from lithium carbonate, lithium nitrate, lithium hydroxide and lithium oxide. And are mixed in an organic solvent such as lithium-insoluble acetone or alcohol while finely pulverizing using a ceramic medium, the organic solvent is volatilized to obtain a mixed powder, and then the mixed powder is granulated. Or by press-molding and crushing to obtain a dense aggregate or a compact.

Next, these agglomerated particles or compacts are fired in an oxidizing atmosphere, and pulverized and classified as required to obtain a powder for a positive electrode active material. The powder obtained by these production methods is , Squared average diameter 3
Since the particles were of the order of microns, the packing density did not increase and the battery capacity per volume could not be increased.

[0006]

Since the positive electrode active material obtained by the conventional manufacturing method as described above has a square shape, the battery capacity per volume cannot be increased, and the capacity during storage at high temperature cannot be increased. It was found that the cause of the decrease is due to the individual particle shape of the active material powder, and this has a non-negligible importance. Therefore, it has been desired to develop a material that increases the packing density by some means.

[0007]

Means for Solving the Problems The inventors of the present invention have conducted diligent research to solve such problems. As a result, it is unexpectedly expected that the particle shape of the positive electrode active material powder should be appropriately selected and controlled. It has been found that a spherical shape with no squared corners is the most preferable shape because it brings about an improvement effect.

That is, according to the present invention, firstly, the average particle diameter is 5 to 5.
A positive electrode active material for a non-aqueous lithium secondary battery, which is spherical LiNiO ₂ particles obtained by using a spherical nickel compound having a diameter of 50 μm as a raw material, and secondly, a spherical shape having an average particle diameter of 5 to 50 μm. A method for producing a positive electrode active material for a non-aqueous lithium secondary battery, comprising forming a spherical LiNiO ₂ particle by subjecting a nickel compound to a step of suspending it in a solution containing lithium ions and an organic acid. Thirdly, the present invention relates to a lithium secondary battery using spherical LiNiO ₂ particles as a positive electrode active material.

[0009]

In the present invention, the spherical shape of the raw material is used as it is to obtain a spherical active material, ideal packing characteristics as a powder are obtained, and discharge due to the shape during storage at high temperature is suppressed. To aim. Then, the spherical nickel compound powder as a starting material is focused on, and a new mixing method with a lithium compound is developed so that the characteristics thereof can be fully utilized, and a spherical LiNiO ₂ powder is produced.

Specifically, spherical nickel compound powder is suspended in a solution containing lithium ions and an organic acid, dried and solidified to form a precursor, and then the precursor is fired in an oxidizing atmosphere. Spherical LiNiO
₂ to obtain powder. In this case, the spherical nickel raw material includes not only perfect spherical bodies as shown in FIG. 4 but also approximate spherical or tertiary aggregates. The suspension solution in the present invention is mainly an aqueous solution, but it is also possible to use ethylene glycol or the like together.

As the nickel compound used in the present invention, various forms of compounds such as hydroxides, oxides, oxyhydroxides and carbonates are industrially supplied, but in the case of spherical compounds, Hydroxide is used. In this case, such a hydroxide is generally produced by using nickel sulfate, caustic soda, and ammonia, granulating by agglomeration of nickel hydroxide in an aqueous solution, and recrystallization by a nickel complex salt.

Oxides are obtained by heat-treating spherical hydroxides in the atmosphere, and oxyhydroxides are obtained by using an oxidizing agent during the synthesis of hydroxides.
Further, the carbonate is synthesized by the same method as the hydroxide, but the compound powder can be produced by other methods.

The nickel hydroxide obtained by the above-mentioned synthesis method becomes secondary or higher particles in which fine primary particles having a size of 0.1 μm or less are densely aggregated. The above-mentioned aggregate particle size (hereinafter referred to as the average size) can be controlled, but classification may be carried out in a sieve if necessary.

In the present invention, either order but also to define the particle size of the nickel compound is a starting material, this is not sufficiently absorb the lithium component to the center the particle size of the nickel compound is too large, the desired LiNiO ₂ This is because it was found that they could not be synthesized and, as a result, the battery characteristics could not be improved.

On the contrary, if the particle size of the nickel compound is too small, the density of the electrode plate is lowered during the molding of the positive electrode, so that the electric capacity of the battery of which volume is limited cannot be increased. It was confirmed that the average particle size of the nickel compound is preferably in the range of 5 to 50 μm.

In the present invention, spherical LiNiO ₂ was produced by using nickel hydroxide as a representative nickel compound.
First, the spherical nickel hydroxide powder in the range of 5 to 50 μm is suspended and dried in an aqueous solution in which lithium hydroxide and citric acid, which is a representative of carboxylic acid, are suspended. At the same time, the mixture is dried and solidified in the gaps in the nickel hydroxide particles, and the appearance of the mixture may be resin-like or mortar-like depending on the drying conditions.

The organic acid is used to prevent the segregation of lithium due to the movement of water during dryness and to prevent the secondary particles of nickel hydroxide from being crushed in the subsequent step to destroy its shape. Incidentally, in the conventional method, in order to prevent segregation of lithium and accompanying decrease in reactivity, mixing and pulverization in an organic solvent are carried out. In this case, of course, nickel hydroxide is also pulverized. Spherical Li that is the object of the present invention
No NiO ₂ powder was obtained.

The dried mixture is then mixed with 10 if necessary.
After crushing to about mm, calcination is performed in an oxidizing atmosphere, preferably in an oxygen stream, but the calcination conditions are 750 ° C as in the conventional method.
It is kept at a temperature of about 10 to 30 hours, and at this time, since the mixture becomes a lump after firing, it needs to be pulverized into fine powder. Further, after the suspension treatment step, crushing or pressurizing operation may be applied in some cases, but it is necessary to avoid breaking the spherical shape of the nickel compound.

In the above step, the spherical nickel hydroxide reacts with lithium by firing to become LiNiO ₂ , and at this time, a maximum of 20% linear shrinkage is exhibited, but the shape itself does not change. It is presumed that the reason for this is that complete sintering cannot be performed in the temperature range suitable for the formation of LiNiO ₂ , and anisotropic growth based on the crystal structure does not occur.

Generally, the synthesis of a precursor by drying a solution containing an organic acid and a metal element is called a complex polymerization or an organic acid gelling method, but the method of the present invention is fundamental in the following points. Is different. That is, (1) the conventional method cannot utilize the form of the raw material because all components are made into a solution. (2) Since the organic acid is used several times with respect to the equivalent of the metal element, the powder after firing has a low density, which is different from the purpose of increasing the capacity of the battery.

Although lithium hydroxide was used as a starting material in the examples of the present invention, lithium carbonate or organic acid lithium may also be used. However, lithium hydroxide is preferable in terms of purity and cost. Further, as the organic acid, carboxylic acid is most suitable from the viewpoint of price in terms of solubility in water, but other organic acids can be used as long as they have the same effect.

In addition, it has been considered to improve the battery characteristics by adding a predetermined amount of another component or by changing the component ratio of nickel and lithium by a small amount. For example, replacing cobalt with 15% or less, or Li: Ni = 1 ±
It may be changed within a range of 0.05: 1, but even in such a case, if the operation and effect on the shape are the same, it is within the scope of the present invention.

The capacity of the battery in the present invention was evaluated by the following method. First, a lump of LiNiO ₂ obtained by firing was mechanically crushed and classified by a 200-mesh sieve, and then the obtained powder was ketjen black as a conductive agent and polytetrafluoroethylene (PT) as a binder. .FE) was kneaded at a weight ratio of 8: 1: 1 and molded into a disk having a diameter of 37 mm at a pressure of ² ton / cm ² . This molded body was used as the positive electrode 4 shown in FIG. 1, while the negative electrode 7 was made of lithium metal (thickness 0.7 mm), and the separator 5 was made by cutting out a polypropylene film. At the same time, a mixed solution of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1 as an electrolytic solution was added with 6
Lithium fluorophosphate (LiPF ₆ ) dissolved in a concentration of 0.5 mol / l was used. In FIG. 1, 1 is a positive electrode lead wire, 2 is a cell fixing nut, 3 is a positive electrode current collector, 4 is a positive electrode, 5 is a separator, 6 is a separator fixing spacer, 7 is a negative electrode, and 8 is a negative electrode current collector. , 9 is a cell fixing screw, 10 is an electrolytic solution injection plug, and 11 is a negative electrode lead wire.

The discharge capacity was determined using the secondary battery shown in FIG. 1. The value obtained by this was the capacity per weight, and in order to consider the capacity, the tap bulk density of the active material The product was used as an index. Further, when the discharge capacity is remarkably reduced when it is repeated at room temperature, it is noted in Table 1, but the other reduction rate is about 20 to 30%.
Was in the range.

The accelerated storage test is performed by charging the test cell with
The decrease in capacity after storage at 0 ° C. for 24 hours was measured, and the amount was used as a guide. In this case, the charge and discharge capacity may not be stable in the measurement until the number of storage cycles is 2.
The difference between the discharge capacities of the third time and the discharge capacity of the third time is shown (hereinafter, this ratio is referred to as high temperature storage stability).

Hereinafter, the present invention will be described in detail with reference to Examples, but the scope of the present invention is not limited to these.

[0027]

Example 1 First, lithium hydroxide LiOH and spherical nickel hydroxide Ni (OH) ₂ consisting of average particles shown in Table 1 were weighed and added into water so that the molar ratio was Li / Ni = 1/1. After that, citric acid was added to nickel hydroxide to 60
%, And dried at 70 ° C. with stirring.

Then, the dried product is lumped to a diameter of about 2 cm,
It was fired for 15 hours at 740 ° C. in an oxygen stream, and the obtained fired product was crushed in a mortar to obtain a powder having a particle size of 150 mesh.

The obtained powder was subjected to XRD measurement, and as shown in FIG. 2, a pattern having the same shape as that of conventionally reported LiNiO ₂ was obtained. In addition, an SEM photograph showing the particle structure of Ni (OH) ₂ used as a raw material at that time is shown in FIG.
An SEM photograph of the obtained representative particles of LiNiO ₂ is shown in FIG.

The LiNiO ₂ powder obtained by the above method was used as a positive electrode active material, and Ketjen black as a conductive agent and polytetrafluoroethylene (PTFE) as a binder were mixed in a weight ratio. At a ratio of 8: 1: 1 and kneaded, and a pressure of ² ton / cm ² was applied to perform pressure molding into a disk shape having a diameter of 37 mm to obtain a positive electrode plate.

Next, the positive electrode plate was used as the positive electrode 4 of the test cell which is the lithium secondary battery shown in FIG.
A negative electrode plate was prepared by cutting out a lithium metal (thickness 0.7 mm). Further, a polypropylene film cut out is used as the separator 5, and 6% of a mixed solution of propylene carbonate (PC) and 1,2-dimethoxyethane (DME) at a volume ratio of 1: 1 is used as the electrolytic solution. Lithium fluorophosphate (LiPF ₆ ) dissolved in a concentration of 0.5 mol / l was used.

Then, these were assembled into the test cell of FIG. 1 and a charge / discharge test was conducted. As a result, as shown in FIG. 3, the discharge capacity value of 190 mAh of the most excellent secondary battery reported in the prior art was reported. A value equal to or higher than / g was obtained. Table 1 summarizes the discharge capacity, the bulk density and the product value for each average particle diameter. From these results, when the average particle diameter of the spherical nickel hydroxide as the starting material is 2 μm, repetition after 10 cycles is repeated. 52% decrease in capacity due to
In the case of 8 μm, it was found that the capacity decrease after 5 cycles was halved, which indicates that the starting material has an average particle size of 5 to 5 μm.
It has been found that the range of 50 μm is preferable.

[0033]

[Table 1] The cases of 78 μm and 2 μm are comparative examples outside the claimed range.
In the case of 78 μm, Li impurities were confirmed by XRD.

[0034]

Example 2 Lithium hydroxide - hydrate LiOH · H ₂ O
And nickel oxide NiO obtained by treating nickel hydroxide at 300 ° C. in a molar ratio of Li / Ni =
The sample was weighed so as to be 0.97 / 1 and Li / Ni = 1/1.

After each of these specimens was put into water,
Citric acid was added in an amount of 50% by weight with respect to nickel hydroxide, mixed and concentrated at 80 ° C. with stirring, and then dried at 60 ° C. to dryness.

Next, the obtained dried solid matter was crushed to 10 mm or less and calcined in an oxygen stream at 730 ° C. for 15 hours to obtain L
iNiO ₂ powder was obtained. In this case, the nickel oxide used had an average particle size of 30 μm, and the obtained LiNiO _{2 had} an average particle size of 24 μm.

XRD measurement of the obtained LiNiO ₂ powder gave the same XRD pattern as that of FIG. 2 shown in Example 1. In addition, LiNiO ₂ having the respective starting composition ratios
The powder was used to form a positive electrode molded body by the means described in Example 1, and the powder was incorporated into the test cell shown in FIG. As a result, the discharge capacity could be almost the same as or higher than that of the conventional product. Also,
It was found that the high temperature storage property was also excellent.

[0038]

[Table 2]

[0039]

Comparative Example 1 Similar to Example 1, LiOH.H ₂ O and Ni
(OH) ₂ was weighed so that the molar ratio was Li / Ni = 1/1, and these powders were crushed and mixed in ethanol for 50 hours to obtain a powder having an average particle size of about 2 μm, and then the crushed powder. The product was fired in an oxygen stream at 750 ° C. for 24 hours to obtain Li.
NiO ₂ powder was obtained.

XRD measurement of the obtained LiNiO ₂ powder showed the same results as in FIG. 2 in Example 1. However, when the powder was observed by SEM photograph, the particles were about 1 μm as shown in FIG. It was nothing more than

Using this powder, the test cell shown in FIG. 1 was prepared in the same manner as in Example 1 and the charge / discharge amount was measured. The results shown in FIG. 7 were obtained.

[0042]

[Table 3] Capacity decrease due to repetition at room temperature After 10 cycles 5
0%

[0043]

INDUSTRIAL APPLICABILITY As described above, in the non-aqueous lithium secondary battery of the present invention, by using spherical LiNiO ₂ powder in a specific range as the active material, the packing density can be increased, and as a result, a battery can be obtained. It was possible to increase the discharge capacity and the high temperature storability.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of a test cell used for a performance measurement test of a positive electrode active material or a positive electrode plate according to the present invention.

_{2 is} the XR of LiNiO ₂ prepared in Example 1. FIG.
It is D (X-ray diffraction pattern).

3 is a charge / discharge curve of the test cell manufactured in Example 1. FIG.

FIG. 4 is an SEM photograph showing a particle structure of spherical Ni (OH) ₂ used in Example 1.

5 is an SEM photograph showing the particle structure of spherical LiNiO ₂ obtained in Example 1. FIG.

6 is an SEM photograph showing the particle structure of LiNiO ₂ obtained in Comparative Example 1. FIG.

7 is a charge / discharge curve of the test cell manufactured in Comparative Example 1. FIG.

[Explanation of symbols]

 1 Positive electrode lead wire 2 Cell fixing nut 3 Positive electrode current collector 4 Positive electrode 5 Separator 6 Separator fixing spacer 7 Negative electrode 8 Negative electrode current collector 10 Cell fixing screw 11 Electrolyte injection plug 12 Negative electrode lead wire

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yukio Hiraoka 1-2-8 Marunouchi, Chiyoda-ku, Tokyo Dowa Mining Co., Ltd. (72) Inventor Norio Haga 1-2-8, Marunouchi, Chiyoda-ku, Tokyo Within Wa Mining Co., Ltd. (72) Inventor Katsuaki Okabe 1-8-2 Marunouchi, Chiyoda-ku, Tokyo Within Wa Mining Co., Ltd.

Claims (3)

[Claims] 1. A positive electrode active material for a non-aqueous lithium secondary battery, comprising spherical LiNiO ₂ particles obtained by using a spherical nickel compound having an average particle diameter of 5 to 50 μm as a raw material. 2. Non-aqueous lithium, which is formed into spherical LiNiO ₂ particles through a step of suspending and stirring a spherical nickel compound having an average particle diameter of 5 to 50 μm in a solution containing lithium ions and an organic acid. A method for producing a positive electrode active material for a secondary battery. 3. A lithium secondary battery, wherein a molded body obtained by kneading spherical LiNiO ₂ particles with a conductive agent and a binder is used as a positive electrode plate.