JPH10162826A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous electrolyte secondary battery which has high discharging capacity and is excellent in a cycle characteristic by regulating a particle diameter, a particle diameter distribution width or the like of positive electrode active material particles. SOLUTION: An average particle diameter of particles of a positive electrode active material using LiMn2 Oy is set to 5 to 30μm, and a particle diameter distribution width by converting a width of a minimum and maximum diameter from an average particle diameter into a numeric value by classifying the whole particles by particle diameters, is set not more than 20%, and microscopic particles on which dispersion of particle diameters is extremely reduced and which have a uniform particle diameter are formed. Therefore, filling density of a positive electrode active material is enhanced, and discharging capacity is improved, and it can be flatly and uniformly brought into close contact with a positive electrode core body, and a cycle characteristic is improved. In particles not less than 80% of the whole positive electrode active material particles, a particle diameter distribution width is also made to exist within 10%, and dispersion of particle diameters is reduced, and sufficient filling density of the positive electrode active material is obtained, and initial discharge capacity can be improved, and the deterioration of the cycle characteristic is also restrained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly, to an improvement of positive electrode active material particles for a positive electrode active material, particularly for improving cycle characteristics and increasing capacity. It is about.

[0002]

2. Description of the Related Art Conventionally, in a non-aqueous electrolyte secondary battery, titanium disulfide, vanadium pentoxide, manganese oxide and the like have been proposed as a positive electrode active material. In particular, a manganese oxide represented by LiMn ₂ O ₄ has attracted particular attention because of its ability to extract a high voltage, being rich in resources, and being inexpensive.

It is known that the LiMn ₂ O ₄ particles have a spinel structure, and that lithium ions can be doped and de-doped in the crystal, and that excellent charge / discharge characteristics can be obtained. .

[0004] However, conventionally, a non-aqueous electrolyte secondary battery using LiMn ₂ O ₄ particles has been produced by using LiMn as a positive electrode active material.
Since the filling property of n ₂ O ₄ is poor, there is a problem that the discharge capacity and the cycle characteristics are poor.

[0005]

DISCLOSURE OF THE INVENTION The present invention solves the above-mentioned problems, and an object of the present invention is to specify a particle size and a particle size distribution width of positive electrode active material particles so that a discharge capacity is high and a cycle An object of the present invention is to provide a non-aqueous electrolyte secondary battery having excellent characteristics.

[0006]

According to the present invention, there is provided a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material particles have an average particle size of 5 μm to 30 μm.
m or less, and the particle size distribution width with respect to the average particle size is ± 2.
0% or less. As described above, the particle density distribution of the positive electrode active material particles is very narrow, and by using particles having a uniform particle size, the packing density of the positive electrode active material can be increased, and the discharge capacity and cycle characteristics are improved. The effect of making it possible to obtain can be obtained.

[0007] In addition, since the particles of the positive electrode active material are arranged as described above, the positive electrode active material can be evenly and uniformly applied on the positive electrode core. This allows the entire positive electrode active material to be uniformly pressed to the positive electrode core in the rolling step of the positive electrode active material, and the positive electrode active material and the positive electrode core are more firmly adhered to each other. Therefore, it is possible to prevent the active material from falling off from the core due to charge and discharge, and it is possible to improve cycle characteristics.

The particle size distribution width referred to here is a value obtained by classifying all the particles according to the particle size and quantifying the range of the minimum particle size and the maximum particle size from the average particle size. Diameter, maximum particle size−average particle size) / average particle size × 100].

That is, even if the average particle size is the same,
It can be said that the larger the numerical value of the particle size distribution width is, the larger the particle size variation is. Therefore, it can be said that particles having a particle size distribution width of ± 20% or less as in the present invention are particles having a very small variation in particle size.

Further, in the positive electrode active material particles of the present invention, 80% or more of all the positive electrode active material particles have a particle size distribution range of ± 10%.
By being present within, these particles have mostly or average particle size,
Variations in particle size are particularly small.

In addition, the average particle size of the positive electrode active material particles is 5 μm.
m and 30 μm or less. In this case, a more sufficient filling density of the positive electrode active material can be obtained, the initial discharge capacity can be improved, and a decrease in cycle characteristics can be suppressed.

Further, the particle shape of the positive electrode active material particles is preferably spherical. This is because when the particle shape is spherical, the positive electrode can be filled into the positive electrode much more efficiently than other shapes.

Incidentally, as the positive electrode active material particles, LiCo is used.
O ₂ , LiNiO ₂ , LiMn ₂ O ₄ particles and the like are used. Particularly, LiMn is used because of its high voltage and low cost.
It is effective to use ₂ O ₄ .

Examples of the negative electrode include metallic lithium or alloys and carbon materials capable of inserting and extracting lithium. In particular, a carbon material is preferable from the viewpoint of improving cycle characteristics.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION

[Example 1] [Preparation of positive electrode] (Preparation of positive electrode active material particles) After a 0.1 mol / l aqueous solution of lithium nitrate and manganese nitrate was mist-formed, compressed air was introduced into a pyrolysis furnace as a carrier gas. By pyrolysis, spherical porous LiMn ₂ O ₄ particles were synthesized.

The flow rate of the carrier gas is set to 5.5 (L /
min), LiMn ₂ O ₄ particles having an average particle size of 5 μm were synthesized.

When the particle size distribution of the LiMn ₂ O ₄ particles was measured, it was ₄ μm to ₆ μm. Therefore, the particle size distribution width of these particles is ± 20%. FIG. 1 shows a particle size distribution diagram of the particles. The vertical axis in FIG. 1 indicates frequency (existence ratio), and the horizontal axis indicates particle size distribution. The particle size distribution = 0 on the horizontal axis represents the average particle size (5 μm). This particle size distribution is represented by [(particle size of each particle−average particle size) / average particle size × 10
0].

As apparent from FIG. 1, the particle size distribution width of all the particles is within ± 20%, and the particles existing within the particle size distribution width of ± 10% are 90% or more of all the particles. You can see that. That is, it can be seen that the LiMn ₂ O ₄ particles have a very narrow particle size distribution width and uniform particle sizes.

Next, 90 parts by weight of the above LiMn ₂ O ₄ particles,
5 parts by weight of carbon as a conductive agent and polyvinylidene fluoride (PVdF) dissolved in N-methyl-2-pyrrolidone as a binder were mixed so that the solid content was 5 parts by weight to prepare a positive electrode slurry.

The above positive electrode slurry is coated on both sides of a core of aluminum foil, dried, rolled by a roller press, and an aluminum lead is ultrasonically welded to an end portion.
A drying treatment was performed to produce a positive electrode. When the packing density of this positive electrode was measured, it was 3.1 g / cm ³ . The surface of the produced positive electrode was very smooth.

[Preparation of Negative Electrode]
A negative electrode slurry was prepared by mixing 5 parts by weight of 5 μm of natural graphite powder and 5 parts by weight of PVdF dissolved in N-methyl-2-pyrrolidone as a solid content.

This negative electrode slurry is coated on both sides of a copper foil,
After drying, the resultant was rolled by a roller press, a nickel lead was ultrasonically welded to an end portion, and then a drying treatment was performed to produce a negative electrode.

[Preparation of electrolyte solution] LiPF ₆ was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) having a volume mixing ratio of 1: 1 to a concentration of 1 mol / dm ^3. A non-aqueous electrolyte was prepared.

[Preparation of Battery] The above positive electrode and negative electrode were spirally wound through a 25-μm-thick porous polypropylene separator to produce a spiral electrode body.

After inserting this spiral electrode body into a nickel-plated iron battery can, the above-mentioned electrolytic solution was injected.

Next, a sealed cylindrical battery was manufactured by using a sealing body with a gasket interposed at the opening of the battery can. This sealed cylindrical battery is referred to as Battery A1 of the present invention.

Examples 2 to 4 By adjusting the flow rate of the carrier gas to 7 (L / min), 10 (L / min) and 12 (L / min), the average particle diameter was 10 μm, 20 μm,
Example 1 except that 30 μm LiMn ₂ O ₄ particles were synthesized.
In the same manner as in the above, a battery was produced.

The batteries thus manufactured are hereinafter referred to as batteries A2 to A4 of the present invention, respectively.

The surfaces of the positive electrodes of the batteries A2 to A4 of the present invention were also very smooth.

Comparative Examples 1 and 2 LiMn ₂ O ₄ particles having an average particle size of 2 μm and 50 μm were synthesized by adjusting the flow rate of the carrier gas to 5 (L / min) and 15 (L / min). A battery was fabricated in the same manner as in Example 1 except that the above procedure was performed.

The batteries fabricated in this manner are hereinafter referred to as comparative batteries X1 and X2, respectively.

The batteries A1 to A4 of the present invention and the comparative battery X
Table 1 shows the physical properties of the positive electrode active material particles of Nos. 1 to X2.

[0033]

[Table 1]

The term “particle ratio having a particle size distribution width of ± 10% or less” in Table 1 means “the particle size distribution width in all positive electrode active material particles is ± 10%.
Particles within 10% / all positive electrode active material particles].

(Experiment 1) Using the batteries A1 to A4 of the present invention and the comparative batteries X1 to X2, the initial discharge capacity of each battery,
The discharge capacity after 0 cycles was examined, and the results are shown in Table 2. As for the experimental conditions, the initial discharge capacity was 1
After charging until the battery voltage reaches 4.1 V at C,
The battery was fully charged by charging at a constant voltage of 1 V, and the capacity at the time of discharging at a current of 1 C to a discharge end voltage of 3.0 V was measured. The cycle conditions were the same as those described above.

[0036]

[Table 2]

As is apparent from Table 2, the battery of the present invention has a very high ratio of the capacity after 50 cycles to the initial discharge capacity, that is, less cycle deterioration, as compared with the comparative battery X1. This is because the average particle diameter of the positive electrode active material particles of the comparative battery X1 is very fine, 2 μm, and the crystallinity of the primary particles constituting the particles is not so good.
It is considered that the deterioration of the crystal structure of LiMn ₂ O ₄ due to the charge / discharge cycle caused cycle deterioration.

When the spirally wound electrode body of the comparative battery X2 was manufactured, the positive electrode active material was severely peeled off from the positive electrode core, and the initial discharge capacity and cycle characteristics could not be evaluated.

From the above results, the average particle size was 5 μm or more and 3
It can be seen that particles having a size of 0 μm or less can suppress cycle deterioration and are desirable.

[Comparative Examples 3 and 4] The carrier gas flow rate was adjusted to 5.5 (L / min) while the aqueous solution concentrations of lithium nitrate and manganese nitrate were 0.3 mol / l and 0.8 mol / l. The average particle size is 5 μm and the particle size distribution width is ±
A battery was produced in the same manner as in Example 1 except that LiMn ₂ O ₄ particles of 60% and −90% to + 200% were synthesized.

The batteries fabricated in this manner are hereinafter referred to as comparative batteries X3 and X4.

Incidentally, both the comparative batteries X3 and X4 had severe irregularities on the positive electrode surface.

[Comparative Examples 5 and 6] By adjusting the aqueous solution concentration of lithium nitrate and manganese nitrate to 0.3 mol / l and 0.8 mol / l, and adjusting the flow rate of the carrier gas to 12 (L / min), The average particle size is 30 μm and the particle size distribution width is ±
67%, - has a battery was fabricated in the same manner as in Example 1 except that 93% + 233% of LiMn ₂ O ₄ particles synthesized.

The batteries fabricated in this manner are hereinafter referred to as comparative batteries X5 and X6, respectively.

The surface of the positive electrode of each of the comparative batteries X5 and X6 was extremely uneven.

The batteries A1 and A4 of the present invention and the comparative battery X
Table 3 shows the physical properties of the positive electrode active material particles of Nos. 3 to X6.

[0047]

[Table 3]

As is clear from Table 3, the batteries A1 and A4 of the present invention have a small particle size distribution range of ± 20% and a particle size distribution range of 80% or more of all the particles. ±
It can be seen that the particles have a uniform particle size of 10% or less. On the other hand, it can be seen that the comparative batteries X3 to X6 are particles having a very wide particle size distribution width, a large particle size width, and a nonuniform particle size.

(Experiment 2) An experiment similar to (Experiment 1) was conducted using the batteries A1 and A4 of the present invention and the comparative batteries X3 to X6. Table 4 shows the results.

[0050]

[Table 4]

As is clear from Table 4, the battery of the present invention has a very high initial discharge capacity as compared with the comparative batteries X3 to X6. This is considered to be because the width of the particle size distribution of the positive electrode active material particles of the comparative batteries X3 to X6 was very large, so that the packing density of the electrodes was low and the initial discharge capacity was low.

The comparative batteries X3 to X6 all had very large capacity deterioration after 50 cycles. This is because the particles of various sizes are present in the positive electrode active material particles of the comparative batteries X3 to X6 (the particle size distribution width is large), so that the positive electrode active material is uniformly and evenly applied to the positive electrode core. Was difficult. In other words, when the positive electrode active material is applied on the positive electrode core with irregularities, the concave portions are not sufficiently rolled during rolling, so that the positive electrode active material and the positive electrode core cannot be firmly adhered. Therefore, it is considered that the positive electrode active material falls off from the positive electrode core body during repeated charge and discharge, and the capacity decreases.

From the above results, if the particle size distribution width is ± 20% or less, the packing density of the active material particles can be increased, the initial discharge capacity can be improved, and a battery having excellent cycle characteristics can be obtained. You can see that there is.

[0054]

According to the nonaqueous electrolyte secondary battery of the present invention, particles having an average particle size of 5 μm or more and 30 μm or less are used as the positive electrode active material particles, and the particle size distribution width with respect to the average particle size is set to ± 20% or less. Thereby, the packing density of the positive electrode can be improved, and the particles having a very uniform particle size are used, so that the positive electrode active material can be applied evenly on the positive electrode core. Thereby, the discharge capacity and the cycle characteristics can be improved.

[Brief description of the drawings]

FIG. 1 shows a distribution diagram of positive electrode active material particles of a battery A1 of the present invention.

Continued on the front page. (72) Inventor Ikuro Nakane 2-5-2-5 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Kazuo Terashi 2-5-2 Keihanhondori, Moriguchi-shi, Osaka No. 5 Sanyo Electric Co., Ltd.

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, wherein the positive electrode active material particles have an average particle size of 5 μm or more and 30 μm or less, and A nonaqueous electrolyte secondary battery having a particle size distribution width of ± 20% or less. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein 80% or more of the total positive electrode active material particles are present within a particle size distribution range of ± 10%. 3. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material particles are LiMn ₂ O ₄ . 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material particles are spherical particles.