JPH11273674A - Organic electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an electric current cutoff mechanism or a safety valve from being actuated even if it is stored at a high temperature in a charging state by including a phosphorous compound in a positive electrode using a lithium nickel composite oxide of a secondary battery having the safety valve housed in a sealed vessel together with a negative electrode and an organic electrolyte, as an active material. SOLUTION: 0.1 to 15 wt.% of a phosphorous compound having the average particle size not more than 30 μm is included in a positive electrode active material composed of lithium nickel composite oxide expressed by the formula: LiNixMyO2 . In the formula, (x and y) are [0.9<(x+y)<1.1], and M is a metallic element other than Ni. Lithium phosphate is desirable as the phosphorous compound, and lithium metaphosphate and cobalt phosphate are also used. An electric current cutoff mechanism actuated by an increase in battery internal pressure is provided, and is desirably actuated by battery internal pressure lower than battery internal pressure for opening/actuating a safety valve. Internal pressure of an organic electrolyte secondary battery is not increased by being decomposed/gasified when the lithium nickel composite oxide in a charged state and an organic electrolyte react with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to 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 video cameras, notebook computers, and mobile phones. Particularly in recent years, lithium ion secondary batteries using a material capable of occluding and releasing lithium such as carbon powder for the negative electrode have become widespread. The internal structure of this battery is usually of a wound type as shown in FIG. That is, an electrode obtained by applying a positive electrode active material or a negative electrode active material to a metal foil is wound with a separator interposed therebetween, housed in a cylindrical can serving as a container, injected with an electrolytic solution, covered with a cap, and sealed. ing.

As a positive electrode active material used in these batteries, LiCoO ₂ (lithium cobaltate) or LiNiO
₂ (Lithium nickelate) is commonly used. Note that it is preferable to use LiNiO ₂ as the positive electrode active material because Ni, which is a constituent material, is less expensive than Co. When the discharge capacity densities were compared, LiCoO ₂ was 145.
１５０150 mAh / g, whereas LiNiO ₂ is 180
It is as high as 200 mAh / g and has excellent characteristics. However, LiNiO ₂ has a problem that the charge / discharge cycle life is short because the crystal structure is destroyed when charge / discharge is repeated. To solve this problem, Ni in the crystal structure
LiNixCoyO in which a part of is replaced by another element such as Co
_2, and a means for substituting a part of the Li site or Ni site with one or more kinds of other metal elements has been proposed, and the effect of improving the cycle life characteristics has been obtained.

However, in a battery using the above-mentioned lithium nickel composite oxide as a positive electrode active material, when stored at a high temperature in a charged state, the internal pressure of the battery increases, and the current cutoff mechanism operates and the safety valve operates. For example, the problem that the function as a battery is lost has been recognized. As the cause, the charged lithium nickel composite oxide and the organic electrolyte react to decompose and gasify,
It is thought to increase the internal pressure of the battery

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a battery using a lithium nickel composite oxide as a positive electrode active material. Is intended to not work.

[0006]

Means for Solving the Problems In order to solve the above-mentioned problems, in the first invention, a general formula LiNixMyO ₂ (0.9 <(x
+ Y) <1.1, M is a positive electrode, a negative electrode, and an organic electrolyte capable of moving lithium ions, mainly composed of a lithium-nickel composite oxide represented by the following formula: In the organic electrolyte secondary battery which is housed and has a safety valve which operates at a battery internal pressure higher than a predetermined pressure, the positive electrode contains a phosphorus compound, and in the second invention, the content of the phosphorus compound is Is characterized by being 0.1 to 15% based on the weight of the positive electrode active material, the third invention is characterized in that the average particle diameter of the phosphorus compound is 30 μm or less, and the fourth invention is characterized by: A mechanism for interrupting a current that is activated by an increase in battery internal pressure (hereinafter abbreviated as a current interrupt mechanism) is provided, wherein the current interrupt mechanism operates at a battery internal pressure lower than the battery internal pressure at which the safety valve opens and operates. In the fifth invention, the phosphorus compound contained in the positive electrode is lithium phosphate,
The sixth invention is characterized in that the negative electrode is a carbon material capable of occluding and releasing lithium with charging and discharging, and in the seventh invention, the negative electrode is selected from lithium metal and lithium alloy. Is characterized by

[0007]

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. LiNi ₀ as manufactured lithium nickel composite oxide of the positive electrode. ₈ Co _{0. 2}
O ₂ (average particle size: about 20 μm), graphite (average particle size: about 0.5 μm), polyvinylidene fluoride (trade name: KF # 112, manufactured by Kureha Chemical Industry Co., Ltd.)
PVDF) in a weight ratio of 80:10:10,
N-methyl-2-pyrrolidone (hereinafter referred to as NMP)
Abbreviated as above) to produce a slurry. Then, various phosphorus compounds described later are added to the slurry and kneaded.
The slurry is applied to both surfaces of a 20 μm thick aluminum foil serving as the positive electrode current collector 1 by roll-to-roll transfer, dried, and then pressed to integrate. The thickness of the positive electrode was 155 to 166 μm, and the density of the positive electrode active material layer 2 was 3.2 g / cm ³ . Thereafter, the strip was cut into a width of 54 mm and a length of 450 mm to produce a strip-shaped positive electrode.

[0008] 2. Preparation of Negative Electrode A graphite powder having an average particle diameter of 20 μm and PVDF as a binder were mixed at a weight ratio of 90:10, and N was used as a dispersion solvent.
An appropriate amount of MP is added, sufficiently kneaded and dispersed to form a slurry. The slurry is applied to both surfaces of a copper foil having a thickness of 10 μm 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 179 to 19
0 μm, and the density of the negative electrode active material layer is about 1.4 g / cm.
³ Thereafter, the resultant was cut into a width of 56 mm and a length of 490 mm to produce a strip-shaped negative electrode. 3. Battery assembly and test The prepared strip-shaped positive electrode and negative electrode were separated by a separator 5 made of a polyethylene porous film having a thickness of 25 µm and a width of 58 mm.
To form an electrode group. Note that the sum of the thicknesses of the positive electrode and the negative electrode was 340 to 345 μm. 34
If it exceeds 5 μm, the diameter of the wound body becomes larger than the inner diameter of the battery can 6 and cannot be inserted. On the other hand, if it is less than 340 μm, the diameter of the wound body is smaller than the inner diameter of the battery can 6, so that sufficient capacity as a battery cannot be obtained. This 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. Ethylene carbonate, dimethyl carbonate and diethyl carbonate were mixed at a volume ratio of 30:50:20, and 1 M LiPF ₆ was dissolved to prepare an electrolyte. 5 ml of this electrolytic solution 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 one of the positive electrode tab terminals 8 is connected to the positive electrode cap 7.
To weld. 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. Here, in the positive electrode cap 7, a current cutoff mechanism (pressure switch) that operates in response to an increase in battery internal pressure and a safety valve that opens in response to a pressure higher than this pressure are incorporated. In this embodiment, the operating pressure is 9 kgf / cm
² types of current interrupt mechanism and a safety valve having an operating pressure of 20 kgf / cm ² were used. The produced organic electrolyte secondary battery was operated at an ambient temperature of 25 ° C. and a constant voltage of 4.2 V (however, the limiting current was 3
After charging at 20 mA) for 8 hours, the battery was discharged at a constant current of 1 A to a final voltage of 2.5 V to check the capacity. Thereafter, the battery was stored at 60 ° C. for 30 days while being charged again under the same conditions, and the presence or absence of the operation state of the current cutoff mechanism and the safety valve was confirmed.

[0010]

EXAMPLES (Examples 1-5, Comparative Example 1) the positive electrode active material weight _{(LiNi 0. 8 Co 0.} 2 O 2) with respect to an average particle size of 1
0 μm of lithium phosphate (Li ₃ PO ₄ ) was added to each of 0.1 μm.
Table 1 shows the results obtained by measuring the discharge capacity of the batteries containing 05, 0.1, 2, 15, and 18%, and the presence or absence of the operating state of the current cutoff mechanism and the safety valve after standing. As Comparative Example 1, a battery containing no lithium phosphate in the positive electrode active material was manufactured. By adding lithium phosphate, the safety valve does not operate and the effect is recognized. On the other hand, when the content of lithium phosphate is less than 0.1%, the current cutoff mechanism operates. However, when the content of lithium phosphate is 18%, the discharge capacity decreases, which is not preferable.

[0011]

[Table 1]

(Examples 6 to 10) Discharge capacity of a battery in which lithium phosphate was added at 2% based on the weight of the positive electrode active material and the average particle diameter of lithium phosphate was 2, 10, 20, 30, and 40 μm, respectively, was left. Table 2 shows the operating states of the current cutoff mechanism and the safety valve later. In Examples 6 to 10 containing lithium phosphate, the current cutoff mechanism and the safety valve were not operated. In addition, it is not preferable that the average particle diameter of lithium phosphate exceeds 30 μm because the discharge capacity is greatly reduced. Details are unknown,
It is considered that when an insulating material having a large average particle diameter enters, the dispersion of the positive electrode active material deteriorates.

[0013]

[Table 2]

(Examples 11 to 15) Weight of positive electrode active material (L
iNi _{0. 8} Co ₀ against. ₂ O _2), an average particle diameter of 10μ
m of lithium metaphosphate, respectively, 0.05, 0.1,
Table 3 shows the results obtained by measuring the discharge capacity of the batteries containing 2, 15, and 18%, and the presence or absence of the operating state of the current cutoff mechanism and the safety valve after standing. By adding lithium metaphosphate, the safety valve is not operated, and the effect is recognized. On the other hand, when the content of lithium metaphosphate is less than 0.1%, the current cutoff mechanism operates. However, when the content of lithium metaphosphate is 18%, the discharge capacity decreases, which is not preferable.

[0015]

[Table 3]

(Examples 16 to 20) Discharge capacity of a battery in which lithium phosphate was added at 2% based on the weight of the positive electrode active material and the average particle diameter of lithium metaphosphate was 2, 10, 20, 30, and 40 μm, respectively. Table 4 shows the operating states of the current cutoff mechanism and the safety valve after the standing. In Examples 16 to 20 including lithium metaphosphate, the current cutoff mechanism and the safety valve were not operated.
It is not preferable that the average particle diameter of lithium metaphosphate exceeds 30 μm, because the discharge capacity is greatly reduced. Although details are unknown, it is considered that when an insulating material having a large average particle diameter enters, the positive electrode active material is poorly dispersed.

[0017]

[Table 4]

(Examples 21 to 25) Weight of positive electrode active material (L
iNi _{0. 8} Co ₀ against. ₂ O _2), an average particle diameter of 10μ
m of cobalt phosphate, respectively, 0.05, 0.1, 2,
Table 5 shows the results obtained by measuring the discharge capacity of the batteries containing 15% and 18%, and the presence / absence of the operation state of the current cutoff mechanism and the safety valve after standing. With the addition of cobalt phosphate, the safety valve was not operated and the effect was recognized. On the other hand, when the content of cobalt phosphate is less than 0.1%, the current cutoff mechanism operates. However, when the content of cobalt phosphate is 18%, the discharge capacity decreases, which is not preferable.

[0019]

[Table 5]

(Examples 26 to 30) Discharge capacity of a battery in which 2% of cobalt phosphate was added to the weight of the positive electrode active material and the average particle diameter of cobalt phosphate was 2, 10, 20, 30, and 40 μm, respectively, was left. Table 6 shows the operating states of the current cut-off mechanism and the safety valve later. Examples 26-3 containing cobalt phosphate
0 indicates that the current cutoff mechanism and the safety valve are not operating. If the average particle size of cobalt phosphate exceeds 30 μm, the discharge capacity is greatly reduced, which is not preferable. Although details are unknown, it is considered that when an insulating material having a large average particle diameter enters, the positive electrode active material is poorly dispersed.

[0021]

[Table 6]

(Examples 31 to 35) Weight of positive electrode active material (L
iNi _{0. 8} Co ₀ against. ₂ O _2), an average particle diameter of 10μ
m, 0.05, 0.1, 2,
Table 7 shows the results obtained by measuring the discharge capacity of the batteries containing 15 and 18%, and the presence or absence of the operating state of the current interrupting mechanism and the safety valve after being left. By adding cobalt phosphide, there is no operation of the safety valve, and the effect is recognized. On the other hand, when the content of cobalt phosphide is less than 0.1%, the current cutoff mechanism operates. However, when the content of cobalt phosphide is 18%, the discharge capacity decreases, which is not preferable.

[0023]

[Table 7]

(Examples 36 to 40) Discharge capacity and current of a battery in which 2% of cobalt phosphide was added to the positive electrode active material and the average particle diameter of cobalt phosphide was 2, 10, 20, 30, and 40 μm. Table 8 shows the operation status of the shutoff mechanism and the safety valve. In Examples 26 to 30 containing cobalt phosphide, the current cutoff mechanism and the safety valve were not operated. If the average particle diameter of cobalt phosphide exceeds 30 μm, the discharge capacity decreases, which is not preferable.

[0025]

[Table 8]

In the examples, salts such as lithium phosphate, lithium metaphosphate, cobalt phosphate and cobalt phosphide have been shown. In addition, the same effect can be obtained with phosphorus compounds such as triphosphate and tetraphosphate. showed that.

[0027]

As described above, by including a neighboring compound in the positive electrode using the lithium nickel composite oxide as the positive electrode active material, the current cutoff mechanism can be operated even when the battery is stored at a high temperature in a charged state, or the safety valve can be operated. This is extremely effective because it can solve the problem that the function as a battery is lost due to operation.

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

Continuation of the front page (51) Int.Cl. ⁶ Identification symbol FI H01M 10/40 H01M 10/40 Z (72) Inventor Yuichi Takatsuka 2-8-7 Nihonbashi Honcho, Chuo-ku, Tokyo Shin-Kobe Electric Machinery Co., Ltd.

Claims (7)

[Claims] (1) The general formula LiNixMyO ₂ (0.9 <(x + y) <1.
1; however, M is a positive electrode, a negative electrode, and an organic electrolyte capable of moving lithium ions, which contain a lithium-nickel composite oxide represented by the following formula: An organic electrolyte secondary battery having a safety valve operated at a battery internal pressure higher than a predetermined pressure, wherein the positive electrode contains a phosphorus compound. 2. The organic electrolyte secondary battery according to claim 1, wherein the content of the phosphorus compound is 0.1 to 15% based on the weight of the positive electrode active material. 3. The organic electrolyte secondary battery according to claim 1, wherein the phosphorus compound has an average particle size of 30 μm or less. 4. A mechanism for interrupting a current activated by an increase in battery internal pressure (hereinafter abbreviated as a current interrupt mechanism), wherein the current interrupt mechanism operates at a battery internal pressure lower than the battery internal pressure at which the safety valve opens. The organic electrolyte secondary battery according to claim 1, 2, or 3. 5. The organic electrolyte secondary battery according to claim 1, wherein the phosphorus compound is lithium phosphate. 6. The organic electrolyte secondary battery according to claim 1, wherein the negative electrode is a carbon material capable of inserting and extracting lithium with charge and discharge. . 7. The method according to claim 1, wherein the negative electrode is selected from lithium metal and lithium alloy.
The organic electrolyte secondary battery according to the above item.