JP2001222995A - Lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion secondary battery featured in battery property at higher temperatures, especially, with high efficiency in the output. SOLUTION: The void ratio of positive electrode mixture, void volume ratio in the positive electrode mixture is made 21%-31%, with the density of 2.58 g/cm3-2.72 g/cm3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to relates to lithium ion secondary batteries, in particular, the chemical formula _{Li x Mn y O 2 (x} 0.
4 ≦ x ≦ 1.35, y is 0.65 ≦ y ≦ 1) a composite oxide capable of inserting and extracting lithium ions, and a positive electrode mixture coated on a current collector; and The present invention relates to a lithium ion secondary battery in which a negative electrode using a carbon material capable of inserting and extracting lithium ions as an active material and a nonaqueous electrolyte using a lithium salt as an electrolyte are infiltrated.

[0002]

2. Description of the Related Art Conventionally, lithium secondary batteries using metallic lithium or a lithium alloy for the negative electrode have had problems such as dendrite-like lithium depositing on the negative electrode during charging and causing an internal short circuit with the positive electrode. , Lithium cobaltate (LiCoO ₂ ), lithium nickelate (LiNi
O ₂ ), lithium manganate (LiMn ₂ O ₄ ), etc.
The development of a lithium ion secondary battery using a composite oxide of lithium and a transition metal as a positive electrode active material and using a carbon material as a negative electrode active material has been achieved. Since a lithium ion secondary battery has a high energy density,
It is widely used in portable devices such as TR-integrated cameras, notebook computers, and mobile phones.

[0003] Among the various positive electrode active materials described above, a composite oxide using manganese is superior in cost performance due to a large amount of resources as compared with a composite oxide using cobalt and the like, and is also excellent in safety. Therefore, recently, its use in lithium ion secondary batteries has attracted attention.

[0004]

[SUMMARY OF THE INVENTION However, the chemical formula _Li x _Mn y _{O 2} positive electrode and (x is 0.4 ≦ x ≦ 1.35, y is 0.65 ≦ y ≦ 1) composite oxide represented by When used as an active material, there is a problem that the charge / discharge cycle life of a lithium ion secondary battery is short and output characteristics are low. In particular, when used at a high temperature of 50 ° C. or higher, manganese elutes from the positive electrode, and a nonconductive film is formed on the negative electrode surface, so that there is a problem that cycle life characteristics and output characteristics are deteriorated.

[0005] It is an object of the present invention to solve the above problems and to provide a lithium ion secondary battery excellent in battery characteristics at high temperature, particularly excellent output characteristics.

[0006]

In order to solve the above-mentioned problems, the present invention provides a chemical compound of the formula Li _x Mny _y O ₂ (x is 0.4 ≦
x ≦ 1.35, y is 0.65 ≦ y ≦ 1) a positive electrode prepared by applying a positive electrode mixture containing a composite oxide capable of inserting and extracting lithium ions to a current collector; In a lithium ion secondary battery in which a negative electrode containing a carbon material capable of occluding and releasing hydrogen as an active material and a non-aqueous electrolyte solution using a lithium salt as an electrolyte, a porosity of the positive electrode mixture is 21%
３１31%.

In the present invention, the porosity of the positive electrode mixture is set to 21% or less.
Since it is 31%, the permeability of the electrolytic solution and the diffusivity and conductivity of ions accompanying charge / discharge are excellently performed. Therefore, a lithium ion secondary battery having excellent output characteristics can be realized. In this case, the density of the positive electrode mixture was 2.58
is preferably ^{g / cm 3 ~2.72g / cm 3} , the compounding ratio of the composite oxide contained in the positive electrode mixture, 80
It is preferable that the content be in the range of 90% by weight to 90% by weight.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments in which the present invention is applied to a cylindrical lithium ion secondary battery will be specifically described below.

(Production of Battery) First, the procedure for producing the cylindrical lithium ion secondary battery of the present embodiment will be described in the order of the positive electrode, the negative electrode, the assembly of the battery, and the non-aqueous electrolyte.

<Positive electrode> The average particle diameter is 10 μm, and lithium
Complex of lithium and manganese that can store and release ions
As a composite oxide, that is, a lithium manganese double oxide
LiMn₂O ₄, Carbon black (hereinafter referred to as conductive assistant)
Below, abbreviated as CB. ) And graphite-based carbon material, poly as binder
Vinylidene fluoride (Kureha Chemical Industry Co., Ltd., trade name:
KF # 1120, hereinafter abbreviated as PVdF. )
Mixed at a predetermined mixing ratio (weight ratio),
Disperse in 2-pyrrolidone (hereinafter abbreviated as NMP)
To make a slurry. This slurry is 20 μm thick
Roll on both sides of aluminum foil (positive electrode current collector)
-Apply by roll method transfer. When applying slurry
Is on one side of the aluminum foil in the longitudinal direction.
An uncoated portion having a width of 50 mm was left. Drying of applied solvent
And the positive electrode mixture density is 2.58 g / c by press pressure.
m³~ 2.72 g / cm³Compression and integration until
You. Then, it is cut into a predetermined length of 82 mm in width to make a positive electrode.
Made.

Then, the width 5 formed on the aluminum foil
A part of the uncoated portion of 0 mm was removed (notch), and a rectangular portion was formed to form a current collecting lead piece (positive electrode tab). The width of the lead pieces was set to about 10 mm, and the interval between adjacent lead pieces was set to about 20 mm.

<Negative Electrode> Amorphous carbon as a carbon material having an average particle diameter of 20 μm capable of inserting and extracting lithium ions, and PVdF as a binder mixed with NM as a dispersion solvent
An appropriate amount of P is added, kneaded well, and dispersed to form a slurry. This slurry is copper foil with a thickness of 10 μm (negative electrode current collector)
Is applied on both sides by a roll-to-roll method transfer.
When the slurry was applied, an uncoated portion having a width of 50 mm was left on one of the side edges in the longitudinal direction of the copper foil. Next, after drying, it is integrated by pressing. The mixture density after pressing was 1 g / cm ³ . Then, it cut | disconnected so that width was 86 mm and length was 120 mm longer than the positive electrode plate, and the negative electrode was produced.

A portion of the uncoated portion having a width of 50 mm formed on the copper foil was removed (notched), and a rectangular portion was formed to form a current collecting lead piece (negative electrode tab). The width of the lead piece is about 10 mm, and the interval between adjacent lead pieces is about 20 mm.
mm.

<Assembly of Battery> The prepared strip-shaped positive electrode and negative electrode are spirally wound through a separator made of a porous polyethylene film having a thickness of 40 μm and a width of 90 mm to form an electrode group. After the negative electrode tab made of the copper foil of the winding group is welded to the negative electrode current collecting ring, the negative electrode current collecting ring and the negative electrode tab terminal are welded, and the other end of the negative electrode tab terminal is welded to the bottom of the battery can. The positive electrode tab made of aluminum foil derived from the other side of the winding group is welded to the positive electrode current collector ring, then the positive electrode current collector ring and the positive electrode tab terminal are welded, and the other end of the positive electrode tab terminal is welded to the positive electrode cap I do. Then, the positive electrode cap is disposed on the upper portion of the battery can via an insulating gasket, and a non-aqueous electrolyte solution (to be described in detail later) is placed in the battery can for 40 m.
1 was injected. The positive electrode cap, the insulating gasket and the battery can are caulked and sealed, and the diameter is 40 mm and the height is 108 m
At m, a cylindrical lithium ion secondary battery having a design capacity described below was assembled. In addition, a current cut-off mechanism (pressure switch) that operates according to an increase in battery internal pressure and a safety valve that operates at a pressure higher than this pressure are incorporated in the positive electrode cap.

<Non-Aqueous Electrolyte> In the present embodiment, the aforementioned
Ethylene carbonate (EC) and dimethyl
Leucarbonate (DMC) and diethyl carbonate (D
EC) with EC: DMC: DEC = 1: 1: by volume ratio.
LiPF as the electrolyte in the mixed solvent ₆1 mole
Per liter was used.

(Example) Next, the LiMn of the above-described positive electrode was used.
₂ O ₄ : CB: graphite-based carbon: PVdF compounding ratio
It is called the positive electrode compounding ratio. ), The density of the positive electrode mixture and the porosity will be described in detail, and the batteries of Examples produced by changing them in various ways will be described. Note that a battery of a comparative example manufactured for comparison with the battery of the example is also described.

<Example 1> As shown in Table 1 below, in Example 1, the mixing ratio of the positive electrode was 80.0: 10.0: 2.0:
8.0 and a positive electrode mixture density of 2.65 g / cm ³ was produced. The porosity of this positive electrode mixture, that is, the pore volume ratio in the positive electrode mixture is 22.56%. Then, a cylindrical lithium ion secondary battery having a design capacity of 3.85 Ah (hereinafter, referred to as a battery of Example 1; the same applies to the following Examples and Comparative Examples) was assembled.

[0018]

[Table 1]

Examples 2 and 3 As shown in Table 1, the compounding ratio of the positive electrode in Example 2 was 85.0: 9.0: 2.0: 4.0.
In the third embodiment, 87.6: 7.0: 1.4: 4.0
And In Examples 2 and 3, as in Example 1, batteries were assembled using the positive electrode compressed to a positive electrode mixture density of 2.65 g / cm ³ . The porosity of the positive electrode mixture of Example 2 was 26.64%, and the battery design capacity was 3.89 Ah. The porosity of the positive electrode mixture of Example 3 was 28.62.
And the battery design capacity is 3.96 Ah.

Examples 4 and 5 As shown in Table 1, in Examples 4 and 5, the same positive electrode compounding ratio as in Example 2 was used. The positive electrode mixture density was set to 2.58 g / cm ^{3 in} Example 4.
In Example 5, the battery was assembled at 2.72 g / cm ³ . The porosity of the positive electrode mixture of Example 4 is 28.58%
In Example 5, it is 24.70%. The design capacity of each of these batteries is 3.87 Ah.

<Comparative Examples 1 and 2> In Comparative Examples 1 and 2, similarly to Examples 1 to 3, the positive electrode mixture density was 2.
A positive electrode was produced at 65 g / cm ³ . Positive electrode mixing ratio,
In Comparative Example 1, it is 77.6: 12.0: 2.4: 8.0, and in Comparative Example 2, 91.5: 3.75: 0.75: 4.
0 was set. The porosity of the positive electrode mixture of Comparative Example 1 was 20.86%
And the battery design capacity is 3.80 Ah. The porosity of the positive electrode mixture of Comparative Example 2 was 31.38%, and the battery design capacity was 4.00 Ah.

(Test) Next, each of the assembled batteries of Examples and Comparative Examples was charged as follows.
After measuring the initial discharge capacity, a charge / discharge pulse cycle test was performed in a normal temperature (room temperature) / high temperature environment, and the discharge capacity and output were measured.

<Details of Test Content> (1) Charging: The battery was charged for 5 hours at a constant temperature of 25 ° C. and a constant voltage of 4.1 V (however, a limited current of 1 CA). (2) Initial discharge capacity measurement: An initial discharge capacity was measured by discharging to a final voltage of 2.7 V at an ambient temperature of 25 ° C. and a constant current of 1 CA. (3) Charge / discharge pulse cycle test: After measuring the initial discharge capacity, in a 25 ° C or 50 ° C constant temperature bath, the current value is 10C.
The discharge at A (discharge end voltage 2.7 V) and the charging at a current value of 10 CA (charge end voltage 4.1 V) were repeated. (4) Measurement: charge / discharge capacity (Ah) and output (W) of each battery after 100,000 cycles in the charge / discharge pulse cycle test
Was measured.

(Test Results and Evaluation) Table 2 below shows the discharge capacity and output measurement results at room temperature (25 ° C.) and high temperature (50 ° C.) of each battery after 10 cycles in the charge / discharge pulse cycle test. Show.

[0025]

[Table 2]

As shown in Table 2, the batteries of Examples 1 to 5 had a higher discharge capacity and a higher capacity at room temperature and in a high temperature environment than the battery of Comparative Example 1 in which the porosity of the positive electrode mixture was 20.86%. Excellent output. On the other hand, as shown in Table 1, the battery of Comparative Example 2 had a compounding ratio of the positive electrode active material LiMn ₂ O ₄ in the positive electrode mixture of 91.5 wt%, which was higher than the batteries of Examples 1 to 5, Since the porosity of the positive electrode mixture exceeds 31%, 10%
The discharge capacity and output after 10,000 cycles have been reduced under both normal temperature and high temperature environments. Therefore, the porosity of the positive electrode mixture is 21%
It can be seen that the cycle life characteristics and the output characteristics can be improved under normal temperature and high temperature environments by setting the content to 31%. The reason why the batteries of Examples 1 to 5 are excellent in the cycle life characteristics and the output characteristics is that the permeability of the electrolytic solution and the diffusivity and conductivity of ions accompanying charge / discharge are excellent. When the test results are further examined, the battery of Example 2 shows the best cycle life characteristics and output characteristics. As shown in Table 1, the porosity of the positive electrode mixture of the battery of Example 2 was 26.64%. Therefore, it can be seen that the porosity of the positive electrode mixture is around 26%. Considering the cycle life characteristics and the output characteristics of the batteries of the other examples, the more preferable range of the porosity of the positive electrode mixture is from 25% to
Probably 27%.

Further, as shown in Table 1, Examples 1 to 5
Of the positive electrode mixture of the battery of 2.58 g / cm ^{3 to} 2.72
g / cm ³ . Therefore, the positive electrode mixture density is 2.
When it is preferred to an ^{58g / cm 3 ~2.72g / cm 3} , to compare the battery of Example 2, 4 and 5 of the same compounding ratio, since the battery of Example 2 is most preferred, the positive electrode It can be seen that it is more preferable that the agent density be around 2.65 g / cm ³ .

Further, when examining the mixing ratio of the positive electrodes of the batteries of Examples 1 to 5, the amount of the positive electrode active material contained in the positive electrode mixture was 80%.
It is also understood that it is preferable to set the content to 90 wt%.

The batteries of Examples 1 to 5 were tested at room temperature (2
The discharge capacity retention rate after 100,000 cycles (percentage obtained by dividing the discharge capacity after 100,000 cycles by the initial discharge capacity) under the environment of 5 ° C. and high temperature (50 ° C.) is equal to that of the battery of Comparative Example 1. Approximately the same, superior to the battery of Comparative Example 2, and
In the output retention ratio after the 100,000 cycles (percentage of the output after the 10th cycle divided by the initial output), Comparative Examples 1 and 2
Better than batteries.

In this embodiment, the positive electrode active material is Li
Was exemplified Mn ₂ O _4, the chemical formula _Li x _Mn y _{O 2} (x
Is 0.4 ≦ x ≦ 1.35, and y is 0.65 ≦ y ≦ 1) The same result as the above-described test result can be obtained by using another lithium manganese double oxide represented by the following formula: . Such a lithium manganese double oxide includes, for example, LiMn.
O ₂ , Li ₂ Mn ₄ O ₉ , Li ₄ Mn ₅ O ₁₂ , Li ₂
MnO ₃ , Li ₇ Mn ₅ O ₁₂ , Li ₅ Mn ₄ O _{9 and the} like can be mentioned. Li, Al, V, Cr, F
The manganese site or lithium site of the lithium-manganese double oxide may be substituted with at least one metal selected from e, Co, Ni, Mo, W, Zn, B, and Mg.

In this embodiment, the carbon material as the negative electrode active material is exemplified by amorphous carbon. However, as another negative electrode active material, for example, lithium ions can be doped and dedoped. A carbon material such as graphite, activated carbon, carbon fiber, carbon black, and mesocarbon microbeads may be used.

Further, in the present embodiment, an example is shown in which a mixed solvent obtained by mixing EC, DMC and DEC is used as the non-aqueous solvent of the non-aqueous electrolytic solution. Carbonic ester, cyclic ester, chain ester, cyclic ether, chain ether and the like may be used.

That is, cyclic carbonates include ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate and the like, and chain carbonates include dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate and the like. However, as the cyclic ester, γ-butyrolactone, γ-
Valerolactone, 3-methyl-γ-butyrolactone, 2-methyl-γ-butyrolactone and the like are generally used. As the chain ester, methyl formate, ethyl formate,
Methyl acetate, ethyl acetate, propyl acetate, methyl propionate, methyl butyrate, methyl valerate and the like, as cyclic ethers, 1,4-dioxane, 1,3-dioxolane,
Tetrahydrofuran, 2-methyltetrahydrofuran,
3-Methyl-1,3-dioxolan, 2-methyl-1,3-dioxolan and the like are generally used. As the chain ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, dimethyl ether, methyl ethyl ether, dipropyl ether and the like are generally used. Further, two or more of these various non-aqueous solvents may be used in combination.

In the present embodiment, LiPF ₆ is exemplified as the electrolyte, but other examples include LiBF ₄ and LiClO ₄ .
₄ , LiAsF ₆ , LiOSO ₂ CF ₃ , LiN (SO
₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) _3, or the like may be used. These electrolytes may be used in combination of two or more. These electrolytes dissociate in a non-aqueous electrolyte to generate lithium ions, and are usually 0.5 mol / l to 2 mol / l, preferably 0.7 mol / l to 1 mol / l. It is contained in the non-aqueous electrolyte within a range of 0.5 mol / liter.

[0035]

As described above, according to the present invention,
Since the porosity of the positive electrode mixture is set to 21% to 31%, the permeability of the electrolyte and the diffusivity and conductivity of the ions accompanying charge / discharge are excellent, so that the lithium ion secondary having excellent output characteristics is obtained. The effect that a battery can be realized can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Kenji Hara 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Inside Shin-Kobe Electric Co., Ltd. (72) Kensuke Hironaka 2-87 Nihonbashi Honcho, Chuo-ku, Tokyo F-term in Shin-Kobe Electric Co., Ltd. (reference) 5H029 AJ02 AK03 AL06 AM03 AM05 AM07 BJ02 BJ14 HJ01 HJ02 HJ09 5H050 AA05 BA17 CA09 CB07 DA02 HA01 HA02 HA08 HA09

Claims (3)

[Claims] The chemical formula Li _x Mn _y O ₂ (x is 0.4 ≦
x ≦ 1.35, y is 0.65 ≦ y ≦ 1) a positive electrode prepared by applying a positive electrode mixture containing a composite oxide capable of inserting and extracting lithium ions to a current collector; In a lithium ion secondary battery in which a negative electrode containing a carbon material capable of occluding and releasing hydrogen as an active material and a non-aqueous electrolyte solution using a lithium salt as an electrolyte, a porosity of the positive electrode mixture is 21%
To 31%. 2. The density of the positive electrode mixture is 2.58 g / cm.
Lithium-ion secondary battery according to claim 1, characterized in that the ^{3 ~2.72g} / cm ^3. 3. The lithium ion secondary battery according to claim 1, wherein the compounding ratio of the composite oxide contained in the positive electrode mixture is 80% by weight to 90% by weight. Next battery.