JP2000106210A - Organic electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent igniting and to enhance safety by housing a positive elec trode, using a lithium nickel composite oxide as an active material and a lithium ion movable organic electrolyte in a sealed container, and including a specified range at weight percent of vinylene carbonate in the organic electrolyte. SOLUTION: An electrode group, prepared by winding strip-shaped positive electrode and negative electrode via a separator 5, is put in a battery can 6, the terminal of a negative electrode current collector 3 is welded to the bottom, and an electrolyte is poured into the battery can 6. A positive tab terminal 8 is welded to a positive electrode current collector 1 and a positive electrode cap 7. The battery can 6 is sealed with the positive electrode cap 7 via an insulating gasket 9. A lithium nickel composite oxide represented by the general formula LiNixCoyOz (0.7<=x<=0.9, 0.1<=y<=0.3, x+y=1, 0.001<=z<=0.02) is used as a positive active material 2. In the electrolyte, as a solute 0.75-2.5 mol/1 LiPF6 is contained, and in addition, 1-20 wt.% vinylene carbonate is contained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to improving the safety of an organic electrolyte secondary battery.

[0002]

2. Description of the Related Art Organic electrolyte secondary batteries typified by lithium secondary batteries have a high energy density and are therefore used in portable devices such as VTR-integrated cameras, notebook computers and mobile phones. Note that a lithium secondary battery using metal lithium for the negative electrode has problems such as precipitation of dendritic lithium ions on the negative electrode during charging, causing an internal short circuit with the positive electrode. Therefore, lithium ion secondary batteries using a carbon material capable of occluding and releasing lithium ions for a negative electrode have become widespread.

Recently, there has been a strong demand for higher capacity lithium ion secondary batteries. In order to meet the demand, the capacity of the positive electrode active material and the negative electrode active material has been rapidly increased. Then, as the capacity of the positive electrode active material, instead of lithium cobalt oxide of about 145~150mAh / g which has been used conventionally (LiCoO _2), 180~200mAh / g
The development of lithium nickelate (LiNiO ₂ ) has been actively pursued. Note that LiNiO ₂ has a problem that the cycle life is short because the crystal structure is likely to collapse when charge and discharge are repeated. In order to solve this problem, a method has been proposed in which part of the Li site or Ni site in the crystal structure is replaced with one or more other metal elements, which is effective in improving the cycle life characteristics. Have been. For example, JP-A-9-17430
JP-A-10-27610 and JP-A-8-185863 disclose, as a first substitution element, an alkaline earth metal such as Sr, Mg, and Ba, and Co as a second substitution element. It is disclosed that charge / discharge cycle characteristics are improved by substitution with a transition metal element other than Ni, as typified by Ni.

On the other hand, for the purpose of improving the discharge characteristics, storage characteristics, charge / discharge cycle life characteristics, etc., JP-A-4-95362, JP-A-4-69075, JP-A-6-84542, and JP-A-8-84542 JP-96852 discloses the addition of vinylene carbonate (hereinafter abbreviated as VC) to an electrolytic solution, and its effect has been recognized.

[0005] However, the organic electrolyte secondary battery using LiNiO ₂ for the positive electrode has a larger size than that using LiCoO ₂ .
There is a problem that fire is likely to occur in a severe heating test such as when a charged battery is thrown into a fire, a nail penetration test, and the like, and safety is poor.

[0006]

DISCLOSURE OF THE INVENTION The present invention relates to the use of a lithium nickel composite oxide as a positive electrode active material,
An object of the present invention is to provide a highly safe organic electrolyte secondary battery that does not easily ignite.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, in the first invention, a general formula LiNi _x Co _y Sr _z O ₂ (0.7 ≦ x
≤ 0.9, 0.1 ≤ y ≤ 0.3, x + y ≒ 1, 0.001 ≤ z ≤ 0.02) A positive electrode using a lithium nickel composite oxide capable of occluding and releasing lithium ions as an active material, and occluding and releasing lithium ions And a negative electrode capable of moving lithium ions, and an organic electrolytic solution capable of moving lithium ions are housed in a closed container, and the closed container has an organic electrolytic solution having a valve mechanism that operates at an internal pressure higher than a predetermined pressure. In the secondary battery, the organic electrolyte contains vinylene carbonate in an amount of 1 to 20% by weight.
It is characterized by containing.

The second invention is characterized in that the organic electrolyte contains 0.75-2.5 mol / l of LiPF ₆ as a solute.

A third invention is characterized in that the positive electrode contains 0.5 to 5% by weight of lithium phosphate.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view of a cylindrical lithium secondary battery embodying the present invention. 1. Preparation of lithium nickel composite oxide In the following, a commercially available high-purity reagent was used as a raw material. Lithium hydroxide (LiOH), nickel hydroxide (Ni
(OH) ₂ ) and cobalt hydroxide (Co (OH) ₂ ). Strontium hydroxide octahydrate to the mixture _{(Sr (OH) 2 · 8H} 2
After mixing either O) or magnesium hydroxide (Mg (OH) ₂ ), the mixture is filled in an alumina dish, and is pre-baked by keeping it in an oxygen gas stream at 600 ° C. for 10 hours. Then, after cooling to room temperature, the mixture was pulverized in an automatic mortar to disaggregate the secondary particles. This powder is filled in an alumina dish used for preliminary firing, and is main-baked while being kept in an oxygen stream at 750 ° C. for 12 hours, and cooled to room temperature. Then, the mixture was pulverized in an automatic mortar and sieved to remove particles having a particle size of 70 μm or more. By changing the mixing ratio of the above-mentioned raw materials, lithium nickel composite oxides having the following 12 different compositions were obtained. The composition ratio of the prepared lithium nickel composite oxide was I
By CP analysis, it was confirmed that the desired composition ratio was obtained.

(Positive electrode active material A) LiNi _0.65 Co _0.35 Sr _0.002 O
₂ (Positive electrode active material B) LiNi _0.7 Co _0.3 Sr _0.002 O ₂ (Positive electrode active material C) LiNi _0.8 Co _0.2 Sr _0.002 O ₂ (Positive electrode active material D) LiNi _0.9 Co _0.1 Sr _0.002 O ₂ (Positive electrode active material E) LiNi _0.95 Co _0.05 Sr _0.002 O ₂ (Positive electrode active material F) LiNi _0.9 Co _0.1 Sr _0.0005 O ₂ (Positive electrode active material G) LiNi _0.9 Co _0.1 Sr _0.001 O ₂ (Positive electrode active material H) LiNi _0.9 Co _0.1 Sr _0.005 O ₂ ( Positive active material I) LiNi _0.9 Co _0.1 Sr _0.01 O ₂ (Positive active material J) LiNi _0.9 Co _0.1 Sr _0.02 O ₂ (Positive active material K) LiNi _0.9 Co _0.1 Sr _0.03 O ₂ (Positive active material L) LiNi _0.9 Co _0.1 Mg _0.002 O ₂ 2. Preparation of Positive Electrode Various lithium nickel composite oxides as the positive electrode active material, graphite having an average particle size of about 0.5 μm as a conductive agent, and polyvinylidene fluoride as a binder (trade name: K
After mixing F # 112 with Kureha Chemical Industry Co., Ltd., hereinafter abbreviated as PVdF), a predetermined amount of Li ₃ PO ₄ described below is added, and N-methyl-2-pyrrolidone (hereinafter, N
(Abbreviated as MP) to prepare a slurry. This slurry is applied to both sides of a 20 μm thick aluminum foil serving as the positive electrode current collector 1 by a roll-to-roll method transfer, dried, and then pressed to be integrated. The thickness of the positive electrode is 144 ± 4μm
The density of the positive electrode active material layer 2 was set to about 3.2 g / cm ³ . Thereafter, the resultant was cut into a width of 55 mm and a length of 450 mm to produce a strip-shaped positive electrode. Hereinafter, a mixture of the positive electrode active material, graphite, lithium phosphate, and PVdF is referred to as a positive electrode mixture. This time, the following seven types of positive electrode mixtures were used.

(Positive electrode mixture A) Positive electrode active material: graphite: lithium phosphate: PVdF = 83: 10: 0: 7 (Positive electrode mixture B) Positive electrode active material: graphite: lithium phosphate: PV
dF = 82.7: 10: 0.3: 7 (Positive electrode mixture C) Positive electrode active material: graphite: lithium phosphate: PV
dF = 82.5: 10: 0.5: 7 (Positive electrode mixture D) Positive electrode active material: graphite: lithium phosphate: PV
dF = 82: 10: 1: 7 (Positive electrode mixture E) Positive electrode active material: graphite: lithium phosphate: PV
dF = 80: 10: 3: 7 (Positive electrode mixture F) Positive electrode active material: graphite: lithium phosphate: PV
dF = 78: 10: 5: 7 (Positive electrode mixture G) Positive electrode active material: graphite: lithium phosphate: PV
dF = 77: 10: 6: 7 3. Fabrication of Negative Electrode A graphite powder having an average particle diameter of 20 μm capable of inserting and extracting lithium ions and PVdF as a binder in a weight ratio of 90:
After mixing at 10, an appropriate amount of NMP as a solvent is added and kneaded well to form a slurry. This slurry is applied to both surfaces of a 10 μm thick copper foil used as the negative electrode current collector 3 by a roll-to-roll method transfer, dried, and then pressed to be integrated.
The thickness of the negative electrode is 190 to 200 μm, and the density of the negative electrode active material layer is about 1.4 g / cm ³ . After that, width 56mm, length 490mm
To obtain a strip-shaped negative electrode. Note that the balance between the amount of the positive electrode active material and the amount of the negative electrode active material was adjusted such that the capacity of the negative electrode active material during discharge was 280 mAh / g.

4. Preparation of electrolyte solution Ethylene carbonate (EC), dimethyl carbonate (DMC) and diethyl carbonate (DEC) were mixed with 30:
After mixing at a volume ratio of 50:20, 1 Mol / l as solute
(Hereinafter, the mol / l which is a unit of concentration abbreviated as M) LiPF ₆
Is dissolved to form an electrolytic solution. To this electrolyte solution, vinylene carbonate (VC) in an amount described below is added. This time, the following 13 kinds of electrolyte solutions having different compositions were used.

(Electrolyte A) EC: DMC = 1: 1, VC
No addition, 1M LiPF ₆ (electrolyte B) EC: DMC = 1: 1, VC: 0.5% by weight, 1M LiPF ₆ (electrolyte C) EC: DMC = 1: 1, VC: 1% by weight,
1M LiPF ₆ (Electrolyte D) EC: DMC = 1: 1, VC: 5% by weight,
1M LiPF ₆ (Electrolyte E) EC: DMC = 1: 1, VC: 10% by weight, 1M LiPF ₆ (Electrolyte F) EC: DMC = 1: 1, VC: 20% by weight, 1M LiPF ₆ (Electrolyte) G) EC: DMC = 1: 1, VC: 25% by weight, 1M LiPF ₆ (electrolyte H) EC: DMC = 1: 1, VC: 5% by weight,
0.5M LiPF ₆ (Electrolyte I) EC: DMC = 1: 1, VC: 5% by weight,
0.75M LiPF ₆ (Electrolyte J) EC: DMC = 1: 1, VC: 5% by weight,
1.5M LiPF ₆ (electrolyte K) EC: DMC = 1: 1, VC: 5% by weight,
2M LiPF ₆ (Electrolyte L) EC: DMC = 1: 1, VC: 5% by weight,
2.5M LiPF ₆ (Electrolyte M) EC: DMC = 1: 1, VC: 5% by weight,
1M LiBF ₄ 5. Assembling the battery The strip-shaped positive electrode and the negative electrode thus prepared were put together with a thickness of 25 μm and a width of 5 μm.
An electrode group is formed by spirally winding the film through a separator 5 made of an 8 mm polyethylene porous film. The sum of the thicknesses of the positive electrode and the negative electrode was 345 ± 5 μm. The sum of the thicknesses of the positive and negative electrodes is 350
If it exceeds μm, the diameter of the wound body becomes too large to insert into the negative electrode can 6. On the other hand, if the sum of the thicknesses of the positive electrode and the negative electrode is less than 340 μm, the diameter of the wound body becomes smaller than the inner diameter of the negative electrode can 6, and a sufficient capacity as a battery cannot be obtained. In producing various batteries described below, the charge capacities of a lithium nickel composite oxide serving as a positive electrode active material and graphite serving as a negative electrode active material were measured in advance using an experimental cell. Then, the charge capacity per 1 g of the negative electrode active material and 1 g of the positive electrode active material
The amount of the positive electrode active material and the amount of the negative electrode active material were adjusted such that the charge capacity ratio per unit became 1.1.

The electrode group was inserted into the battery can 6, and the terminal of the negative electrode current collector 3 was welded to the bottom of the battery can 6. 5 ml of any of the above-mentioned electrolytes was injected into the battery can 6. After welding one of the positive electrode tab terminals 8 to the positive electrode current collector 1, the other is welded to the positive electrode cap 7. The positive electrode cap 7 is arranged on the upper part of the battery can 6 via the insulating gasket 9, and this portion is caulked and sealed. In the positive electrode cap 7, a current cutoff mechanism (pressure switch) that operates according to an increase in the internal pressure of the battery and a safety valve that opens and operates at a pressure higher than this pressure are incorporated. In this embodiment, the operating pressure is 9 kgf
/ cm and ² of the current interrupting mechanism, operating pressure using two kinds of safety valve 20 kgf / cm ^2.

6. Battery test The fabricated organic electrolyte secondary battery was charged at an ambient temperature of 25 ° C and a constant voltage of 4.2V (limited current of 320mA) for 8 hours.
Discharge was performed at a constant current of 1 A to a final voltage of 2.5 V, and the initial discharge capacity was confirmed. The charge / discharge cycle life characteristic test was performed under the above-described conditions with a pause time of 10 minutes between discharge and charge.

After recharging the battery under the above-mentioned conditions, a pass / fail judgment was made by a heating test using a burner in accordance with the projectile test shown in the UL1642 standard. That is, the battery was heated with a burner, and even if the battery ignited, a state in which components such as battery components did not protrude from the aluminum net was regarded as acceptable. When a battery with poor safety is subjected to a heating test using a burner, there is a high possibility that the battery will burst and the positive electrode cap 7 and the negative electrode can will break through the net. Therefore, in this case, not only the pass / fail was determined under the above-mentioned conditions, but also the sound volume at the time of ignition at a place 1 m away from the battery as the test body was measured. That is, it is considered that a battery having a higher volume at the time of ignition has a higher possibility of breaking through the net, and thus it is determined that the battery is inferior in safety.

[0018]

EXAMPLES (Examples 1 to 7 and Comparative Examples 1 to 5) The above-mentioned lithium-nickel composite oxides (positive electrode active materials A to L) were used.
To prepare a positive electrode having a positive electrode mixture mixture ratio A (positive electrode active material: graphite: lithium phosphate: PVdF = 83: 10: 0: 7, that is, a positive electrode active material layer containing no lithium phosphate). As the composition of the electrolytic solution, electrolytic solution D (EC: DM
C = 1: 1, VC: 5% by weight, 1M LiPF ₆ ).
Then, batteries having the specifications shown in Table 1 were prepared, and the initial discharge capacity and the capacity retention at the 100th cycle (percentage of the discharge capacity at the 100th cycle with respect to the initial discharge capacity) were measured and a burner heating test was performed. The initial discharge capacity was shown by comparison when the discharge capacity of the battery of Example 3 was set to 100.

The batteries of Examples 1 to 7 all passed the burner heating test, and had a high initial discharge capacity and a high capacity retention at the 100th cycle. The battery of (Comparative Example 1)
Despite passing the burner heating test, the initial discharge capacity is 20% lower than the battery of Example 3. Therefore, it shows that when the composition ratio of Ni of the positive electrode active material is less than 0.7, the initial discharge capacity decreases. The batteries of (Comparative Examples 2 and 3) failed the burner heating test (x),
The capacity retention at the 00th cycle is low. Although the battery of Comparative Example 4 passed the burner heating test, the initial discharge capacity was 18% lower. This is presumed to be due to the large amount of Sr substitution, which hindered the discharge reaction. In the battery of (Comparative Example 5), it is shown that the burner heating test does not pass if the alkaline earth metal such as Mg other than Sr is substituted. From the above results, the general formula LiNi _x Co _y Sr _z O ₂ (0.7 ≦ x ≦
When a lithium nickel composite oxide represented by 0.9, 0.1 ≦ y ≦ 0.3, x + y ≒ 1, 0.001 ≦ z ≦ 0.02) is used as a positive electrode active material, a highly safe battery can be obtained.

[0020]

[Table 1]

：: passed, ×: failed (Examples 3, 8 to 10, Comparative Examples 6 to 8) Positive electrode active material D (LiNi _0.9 Co _0.1 Sr _0.002 O) as a lithium nickel composite oxide used as a positive electrode active material ₂ ) was used. As the active material layer of the positive electrode, a positive electrode mixture mixture ratio A (positive electrode active material: graphite: lithium phosphate: PVdF = 83: 10: 0: 7, that is, a positive electrode active material layer containing no lithium phosphate) was used. . Then, the amount of LiPF ₆ in the electrolytic solution was set to 1M, and as shown in Table 2, V
Batteries having different C contents were prepared. Other test conditions
It is as described above.

The batteries of Examples 8, 3, 9, and 10 passed the burner heating test and had high initial discharge capacity and high capacity retention at the 100th cycle. The batteries of (Comparative Examples 6 and 7)
Failed in burner heating test. It is considered that the reason for this is that there is no addition of VC in the electrolyte and that the amount of addition is too small. The battery of Comparative Example 8 passed the burner heating test, but had a low initial discharge capacity.
It is considered that the reason for this is that the conductivity of the electrolytic solution was lowered by excessive addition of VC.

[0023]

[Table 2]

：: passed, ×: failed (Examples 3, 11 to 16) The positive electrode active material D (LiNi _0.9
Co _0.1 Sr _0.002 O ₂ ) was used. Positive electrode mixture forming ratio A for forming the positive electrode active material layer (positive electrode active material: graphite: lithium phosphate: P
VdF = 83: 10: 0: 7, that is, a material containing no lithium phosphate in the positive electrode active material layer). Then, as shown in Table 3, the amount of VC in the electrolytic solution was set to 5% by weight, and electrolytic solutions having different LiPF ₆ amounts were used. Other test conditions are as described above.

Although omitted in Table 3, all of these batteries passed the burner heating test. (Example 12,3,13,14,15), i.e. the solute of the electrolyte solution with LiPF _6, and the concentration of LiPF ₆ 0.75 to
In the range of 2.5M, the volume at the time of ignition is low, and the initial discharge capacity and the capacity retention are high. In the battery of Example 16 using LiBF ₄ as the solute of the electrolyte, the initial discharge capacity was slightly lower and the capacity retention at the 100th cycle was lower than that of Example 3 using LiPF ₆ of the same concentration. Large and undesirable.

[0026]

[Table 3]

(Example 3, 17 to 22) A positive electrode active material D (LiNi _0.9 Co _0.1 Sr _0.002 O ₂ ) was used as a lithium nickel composite oxide used as a positive electrode active material. Batteries of seven kinds of specifications having different mixing ratios as shown in Table 4 were prepared. The electrolyte D (EC: DM
C = 1: 1, VC: 5% by weight, 1M LiPF ₆ ) was used. Other test conditions are as described above.

All the batteries of (Examples 3, 17 to 22) passed the burner heating test. (Examples 18 to 2)
In the battery of 1), that is, a battery in which the amount of lithium phosphate in the positive electrode mixture is 0.5 to 5% by weight, the decrease in the initial discharge capacity is small and the volume at the time of ignition is small, which is preferable. On the other hand, when the amount of lithium phosphate was 6% by weight (Example 22), reductions in the initial discharge capacity and the capacity retention at the 100th cycle were observed.

[0029]

[Table 4]

In the present invention, examples have been shown in which graphite is used as the conductive agent in the positive electrode mixture and graphite is used as the carbon material of the negative electrode active material, but the materials are not limited to these.

[0031]

The battery according to the present invention has a high initial discharge capacity and a high capacity retention rate at the 100th cycle, and can provide a highly safe organic electrolyte secondary battery at the time of heating such as dropping into a fire. Are better.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a cylindrical organic electrolyte secondary battery embodying the present invention.

[Explanation of symbols]

1: positive electrode current collector, 2: positive electrode active material, 3: negative electrode current collector,
4: negative electrode active material, 5: separator, 6: battery can,
7: positive electrode cap, 8: positive electrode tab terminal, 9: gasket.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Yasushi Uraoka 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo F-term in Shin-Kobe Electric Co., Ltd. 5H012 AA01 BB02 5H029 AJ05 AJ12 AK03 AL07 AM03 AM05 AM07 BJ02 BJ14 BJ27 DJ02 DJ08 EJ03 HJ01 HJ02 HJ15

Claims (3)

[Claims] (1) The general formula LiNi _x Co _y Sr _z O ₂ (0.7 ≦ x ≦ 0.9, 0.1
≤ y ≤ 0.3, x + y ≒ 1, 0.001 ≤ z ≤ 0.02) A positive electrode using a lithium nickel composite oxide capable of occluding and releasing lithium ions as an active material, and a negative electrode capable of occluding and releasing lithium ions An organic electrolyte solution capable of moving lithium ions is contained in a sealed container, and the sealed container has an organic electrolyte secondary battery having a valve mechanism that operates at an internal pressure higher than a predetermined pressure. An organic electrolyte secondary battery comprising 1 to 20% by weight of vinylene carbonate in the organic electrolyte. 2. The method according to claim 1, wherein the solute of the organic electrolyte is 0.75 to 2.5 m.
The organic electrolyte secondary battery according to claim 1, characterized in that it contains LiPF ₆ in ol / l. 3. The organic electrolyte secondary battery according to claim 1, wherein the positive electrode contains 0.5 to 5% by weight of lithium phosphate.