JP2001338639A - Non-aqueous electrolyte battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte battery that has an excellent stability even when the battery has fallen in an unforeseen state of short- circuiting by being used in such an abnormal condition as causes deformation in the electrode. SOLUTION: The battery comprises a positive electrode having plural layers of positive electrode active material layers 2 containing positive electrode active material on the positive electrode current collector 1, a negative electrode containing negative electrode active material and a non-aqueous electrolyte. The composition of the positive electrode active material contained in the positive electrode active material layers 2 is different in the thickness direction of the layers.

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 battery including a positive electrode having a positive electrode active material layer containing a positive electrode active material, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte.

[0002]

2. Description of the Related Art In recent years, portable electronic devices and communication devices such as a camera-integrated VTR, a mobile phone, and a laptop computer have been reduced in size and weight, and are used as power sources for driving these devices. There is also a demand for smaller and lighter batteries. Along with this, research and development aimed at improving the energy density of batteries are being actively conducted.

Conventionally, nickel cadmium batteries, lead batteries, and the like have been used as power sources for driving portable electronic devices and communication devices, but their energy density is lower than those of aqueous electrolyte secondary batteries. Attention has been paid to lithium ion secondary batteries, which are larger batteries.

[0004] Lithium ion secondary batteries have excellent features of high discharge voltage, low self-discharge, good cycle characteristics, and high energy density, so that they can be used as power sources for various electronic devices. The batteries are being used and are expected to be applicable to a wide range of fields.

[0005]

The use conditions of lithium ion secondary batteries have been diversified as their uses have been diversified, and the possibility of use under abnormal conditions has increased. For example, the battery may be crushed to deform the electrodes, or a metal object may be stabbed in the battery. In such a case, the electrodes are short-circuited inside the battery.

The positive electrode active material of a lithium ion secondary battery is
When heated due to short-circuiting of the electrodes during charging when Li is desorbed, Solid State Ionics69 (1994) may cause heat generation due to a chemical reaction with the organic electrolyte.
265 Known widely by reports by JR Dahn et al. In other words, when the electrodes are short-circuited inside the battery and the electrodes are heated, the battery may generate high heat.

Therefore, the electrodes are housed in a metal container so that the electrodes are not easily deformed even if the battery is crushed. In addition, thermal fuse, PT
The safety is ensured by disposing a C element, a current fuse and the like inside the battery.

On the other hand, in order to further secure safety, non-aqueous electrolyte batteries are required to further improve the stability of the batteries under various conditions.

The present invention has been proposed in view of such a conventional situation. Even when the electrode is used under an abnormal situation where the electrode is deformed, an unexpected situation such as a short circuit occurs. It is an object of the present invention to provide a non-aqueous electrolyte battery having excellent stability.

[0010]

In order to achieve the above object, a nonaqueous electrolyte battery according to the present invention has a plurality of positive electrode active material layers containing a positive electrode active material laminated on a positive electrode current collector. A positive electrode, a negative electrode containing a negative electrode active material, and a nonaqueous electrolyte are provided, and the composition of the positive electrode active material contained in the positive electrode active material layer is different in the thickness direction.

[0011] The nonaqueous electrolyte battery according to the present invention having the above-described structure includes a positive electrode in which a plurality of positive electrode active material layers having different compositions in the thickness direction of the positive electrode active material are laminated on the positive electrode current collector. Even when an unexpected situation such as a short circuit occurs, the temporal and spatial concentration of heat generation due to the chemical reaction between the positive electrode active and the non-aqueous electrolyte is prevented.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a non-aqueous electrolyte battery according to the present invention will be described in detail with reference to the drawings. A nonaqueous electrolyte secondary battery to which the present invention is applied is a so-called lithium ion secondary battery, and a positive electrode in which a plurality of positive electrode active material layers containing a positive electrode active material and a binder are stacked on a positive electrode current collector, A negative electrode in which a negative electrode active material layer containing a negative electrode active material and a binder is formed on a negative electrode current collector, and a liquid nonaqueous electrolyte as a nonaqueous electrolyte.

The positive electrode is, as shown in FIG.
A positive electrode active material layer 2 is formed on a positive electrode current collector 1, and a positive electrode active material layer adjacent to the positive electrode current collector 1 (hereinafter, referred to as a positive electrode active material lower layer 2 a) and a positive electrode current collector 1 are provided. , A positive electrode active material layer (hereinafter, referred to as a positive electrode active material upper layer 2b) formed on the positive electrode active material lower layer 2a. The composition of the positive electrode active material contained in the positive electrode active material layer 2 differs in the thickness direction. That is, the cathode active material contained in the cathode active material lower layer 2a,
The positive electrode active material contained in the positive electrode active material upper layer 2b is a material having a different composition.

Generally, when a short circuit occurs in a lithium ion secondary battery, Joule heat is generated due to the short current. This Joule heat diffuses into the battery through the positive electrode current collector, which is a good heat conductor, and further diffuses from the positive electrode current collector into the positive electrode active material layer to heat the positive electrode active material. Since the positive electrode active material heated by Joule heat causes a chemical reaction with the nonaqueous electrolyte, high-temperature heat generated by the chemical reaction may be generated inside the battery.

By the way, it is known that, when the composition of the positive electrode active material is different, the temperature at which a chemical reaction occurs with the nonaqueous electrolyte is also different. That is, in this non-aqueous electrolyte secondary battery, the positive electrode active material lower layer 2a and the positive electrode active material upper layer 2b have different compositions of the positive electrode active material, and therefore have different temperatures at which a chemical reaction occurs with the non-aqueous electrolyte.

Therefore, in this non-aqueous electrolyte secondary battery, even if a short-circuit or the like occurs inside the battery and the positive electrode is heated, the time and space of heat generation due to the chemical reaction between the positive electrode active material and the non-aqueous electrolyte are increased. Concentration is prevented.

The number of the positive electrode active material layers 2 is preferably two or more and four or less. In other words, it is preferable that the number of the positive electrode active material upper layer 2b is one or more and three or less. When the number of the positive electrode active material layers 2 exceeds four, there is a possibility that the manufacturing cost for manufacturing the electrode is increased.

The thickness of the positive electrode active material lower layer 2a and the thickness of the positive electrode active material upper layer 2b is 0.1 to 0.1 when the thickness of the positive electrode active material lower layer 2a is 1.
Preferably, the ratio is 20.

As the positive electrode active material, a general formula Li _x MO
₂ (wherein, in the range of 0.05 ≦ x ≦ 1.10, and M is at least one of various transition metal elements), etc., can be used. .

The cathode active material contained in the cathode active material lower layer 2a is preferably a Li-containing transition metal oxide containing at least one of Mn and Fe, specifically, LiMn ₂ O ₄ , LiFePO ₄ , LiF
e _1-x MPO ₄ (where 0 <x ≦ 1 and M is Co, N
At least one of i and Mn. It is preferable to contain any one or more of the compounds represented by the formula (1).

The cathode active material contained in the cathode active material upper layer 2b is preferably a Li-containing transition metal oxide containing at least one of Ni and Co, and specifically, LiCoO ₂ , LiNiO ₂ , LiN
_{i x Co 1-x O 2} , LiNi x Co 1-xy Al y O 2 ( wherein,
0 <x <1, 0 <y <1. It is preferable to contain any one or more of the compounds represented by the formula (1).

As the binder contained in the positive electrode active material layer 2, any resin conventionally known as a binder for this type of battery can be used. The positive electrode active material layer 2 may contain a conventionally known conductive material, various additives, and the like.

The negative electrode is formed by adding Li-doped /
A negative electrode active material layer formed by applying a negative electrode mixture containing a undoped negative electrode active material and a binder is formed. As the negative electrode current collector, for example, a copper foil or the like is used.

As the negative electrode active material, a carbon material capable of doping / dedoping Li, a non-graphitizable carbon-based material and a graphite-based material can be used. More specific carbon materials include pyrolytic carbons, cokes, (pitch coke, needle coke, petroleum coke, etc.),
Graphites, glassy carbons, organic polymer compound fired bodies (phenol resins, furan resins, etc. fired at an appropriate temperature and carbonized), carbon fibers, activated carbon, and the like can be used.

As the binder to be mixed with the negative electrode active material when preparing the negative electrode mixture, any resin conventionally known as a binder for this type of battery can be used.

The non-aqueous electrolyte is a so-called liquid electrolyte prepared by dissolving an electrolyte salt in a non-aqueous solvent.

Examples of the non-aqueous solvent include cyclic carbonates such as propylene carbonate and ethylene carbonate, chain carbonates such as dimethyl carbonate and diethyl carbonate, carboxylate esters such as methyl propionate and methyl butyrate, γ-butyrolactone, Sulfolane, 2-methyltetrahydrofuran,
Ethers such as dimethoxyethane can be used. From the viewpoint of oxidation stability, it is particularly preferable to include a carbonate ester. One of these nonaqueous solvents may be used alone, or two or more of them may be used in combination.

As the electrolyte salt, for example, LiPF ₆ , L
iBF ₄ , LiAsF ₆ , LiClO ₄ , LiCF ₃ S
O ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ C
Lithium salts such as F ₃ ) ₃ , LiAlCl ₄ and LiSiF ₆ can be used. From the viewpoint of stability against oxidation, it is particularly preferable to use LiPF ₆ or LiBF ₄ among these lithium salts. The concentration at which these electrolyte salts are dissolved in the non-aqueous solvent is 0.1 mol / l or more and 5.0 mol / l.
1 mol or less, preferably 0.5 mol / l
More preferably, the range is 3.0 mol / l or less. In addition, a fluorine-based polymer compound may be added to the non-aqueous solvent.

The non-aqueous electrolyte secondary battery includes, as shown in FIG. 2, for example, a strip-shaped positive electrode 3 in which a plurality of positive electrode active material layers 2 containing a positive electrode active material are laminated on a positive electrode current collector 1; A strip-shaped negative electrode 5 in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector 4 is laminated with a separator 6 interposed therebetween, and a spiral electrode body formed by being wound in the longitudinal direction is formed. A liquid non-aqueous electrolyte is charged into the battery can 7 as a non-aqueous electrolyte. Then, the battery cover 8 is fixed by caulking to the battery can 7 via the insulating sealing gasket 9. The nonaqueous electrolyte secondary battery has a center pin 1 connected to a negative electrode lead 10 and a positive electrode lead 11.
2 and a safety valve device 13 for releasing gas inside the battery when the pressure inside the battery becomes higher than a predetermined value, and a PT for preventing a rise in temperature inside the battery.
A C element 14 is provided. The shape of the non-aqueous electrolyte secondary battery to which the present invention is applied may be any of a square shape, a coin shape, a button shape, a sheet shape, and the like, and the size is not limited.

The non-aqueous electrolyte secondary battery constructed as described above is used under an abnormal situation where the electrode is deformed, and even when an unexpected situation such as a short circuit occurs, the stability is maintained. Excellent.

[0031]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on specific experimental results. Unless it goes beyond the gist of the invention,
The present invention is not limited to the embodiments.

[Preparation of Positive Electrode] First, a plurality of positive electrode mixtures having different compositions of the positive electrode active material were prepared.

Positive electrode mixture A 91 parts by weight of LiNiO ₂ as a positive electrode active material, 6 parts by weight of graphite as a conductive material, and 3 parts by weight of polyvinylidene fluoride as a binder were mixed to prepare a positive electrode mixture A. . Then, this was dispersed in N-methyl-2-pyrrolidone to obtain a positive electrode mixture A in a slurry state.

Positive electrode mixture B A positive electrode mixture B was prepared in the same manner as the positive electrode mixture A except that LiCoO ₂ was mixed as the positive electrode active material.

Positive electrode mixture C A positive electrode mixture C was prepared in the same manner as the positive electrode mixture A except that LiNi _0.8 Co _0.2 O ₂ was mixed as the positive electrode active material.

Positive electrode mixture D A positive electrode mixture D was prepared in the same manner as the positive electrode mixture A except that LiMn ₂ O ₄ was mixed as the positive electrode active material.

Positive electrode mixture E A positive electrode mixture E was prepared in the same manner as the positive electrode mixture A except that LiFePO ₄ was mixed as a positive electrode active material.

Positive electrode mixture F : 45 parts by weight of LiNiO ₂ as a positive electrode active material;
positive electrode mixture A except that n ₂ O ₄ was mixed with 46 parts by weight.
In the same manner as in the above, a positive electrode mixture F was prepared.

Next, the various positive electrode mixtures in the form of slurry prepared as described above were used as combinations and coating thicknesses shown in Table 1 on both sides of a strip-shaped aluminum foil having a thickness of 20 μm on the positive electrode current collector. A positive electrode active material layer was formed.

[0040]

[Table 1]

The positive electrodes of Examples 1 to 6 were produced as described below. First, the positive electrode mixture forming the lower layer of the positive electrode active material was uniformly applied on both surfaces of the positive electrode current collector and dried. Next, the positive electrode mixture forming the positive electrode active material upper layer was uniformly applied on the dried positive electrode active material lower layer, and dried.
Then, a band-shaped positive electrode was obtained by slitting after compression molding using a roll press machine. The positive electrodes of Comparative Examples 1 to 4 were uniformly coated with the positive electrode mixture shown in Table 1 above on both sides of the positive electrode current collector, dried, compression-molded at a constant pressure, and then slit. I got In addition, the coating thickness of the lower layer of the positive electrode active material and the upper layer of the positive electrode active material was measured using an electron microscope on the cross section of each positive electrode after compression molding of each positive electrode.

[Preparation of Negative Electrode] 96 parts by weight of artificial graphite (trade name: KS-6, manufactured by Lonza) as a negative electrode active material, 3 parts by weight of styrene butadiene rubber and 1 part by weight of carboxymethyl cellulose as a binder. Was mixed in water to prepare a slurry-like negative electrode mixture.

The thickness of the negative electrode current collector is 10 μm.
A slurry-like negative electrode mixture was uniformly applied to both sides of the strip-shaped copper foil, dried, compression-molded using a roll press, and then slit to produce a strip-shaped negative electrode.

[Preparation of Nonaqueous Electrolyte] As a nonaqueous solvent, 40% by volume of ethylene carbonate and 60% by volume of methyl ethyl carbonate were used.
LiPF as an electrolyte salt in a mixed solvent mixed as
₆ was dissolved at a rate of 1.0 mol / l to prepare a non-aqueous electrolyte.

[Preparation of Nonaqueous Electrolyte Secondary Battery] The band-shaped positive electrode and the band-shaped negative electrode of Examples 1 to 6 and Comparative Examples 1 to 4 prepared as described above were A negative electrode, a separator, a positive electrode, and a separator were laminated in this order via a separator made of a microporous polypropylene film having a thickness of 25 μm, and then wound many times to produce a plurality of spiral electrode bodies.

Next, after inserting the insulating plate into the bottom of the nickel-plated iron battery can, the electrode body was housed. Then, in order to collect the current of the negative electrode, one end of a nickel negative electrode lead was pressed against the negative electrode, and the other end was welded to the battery can. Further, in order to collect the current of the positive electrode, one end of an aluminum positive electrode lead was crimped to the positive electrode, and the other end was welded to the battery lid via a current interrupting thin plate for interrupting current according to the internal pressure of the battery. Then, after injecting the non-aqueous electrolyte prepared as described above into the battery can, the battery can is caulked through an insulating sealing gasket coated with asphalt to fix the battery lid, thereby obtaining a cylindrical battery. And has a diameter of 1
Non-aqueous electrolyte secondary batteries of Examples 1 to 6 and Comparative Examples 1 to 4 having a height of 8 mm and a height of 65 mm were produced.

The non-aqueous electrolyte secondary battery produced as described above was first charged at a constant current of 1.0 A and a constant voltage of 4.2 V for three hours at a constant current and a constant voltage. And, in order to evaluate the discharge characteristics of these batteries,
A constant current discharge was performed at a discharge current of 700 mA and a final voltage of 2.5 V, and the initial capacity was measured.

Next, in order to evaluate the stability of these batteries when a short circuit occurs inside the batteries, the charging current was set to 1.0 A, the final voltage was set to 4.4 V, and the constant current and constant voltage charging was performed for 3 hours. After that, an iron nail with a diameter of 5 mm
Using a press machine, the battery was stabbed until it penetrated the center of the battery, thereby causing a short circuit inside the battery. At this time, the temperature change of the battery can wall was observed, and the maximum temperature was measured. In addition, in any of the batteries, no gas ejection or rupture occurred, and the various fillers filled in the battery can did not flow out of the battery can. These series of measurements were performed in a 23 ° C. environment.

Table 2 shows the initial capacities of the nonaqueous electrolyte secondary batteries of Examples 1 to 8 and Comparative Examples 1 to 8 measured as described above, and the maximum temperature at the time of electrode short-circuit.

[0050]

[Table 2]

As is clear from Table 2, a plurality of positive electrode active material layers are stacked on the positive electrode current collector, and a positive electrode in which the composition of the positive electrode active material contained in the positive electrode active material layer differs in the thickness direction is provided. In the non-aqueous electrolyte secondary batteries of Examples 1 to 6, since the generated heat is diffused inside the battery even when the electrode generates heat due to the electrode short, the maximum temperature at the time of electrode short is 90 ° C. or less. It was found that the temperature rise was suppressed.

On the other hand, in the nonaqueous electrolyte secondary batteries of Comparative Examples 1 to 4 including the positive electrode in which the positive electrode active material layer is a single layer, the maximum temperature at the time of electrode short-circuit exceeds 100 ° C. I understand.

The non-aqueous electrolyte secondary batteries of Examples 1 to 6 have a positive electrode active material layer having a positive electrode current collector when compared with the non-aqueous electrolyte secondary batteries of Comparative Examples 1 to 4. It was found that the batteries had the same initial capacity even when a plurality of positive electrodes were stacked thereon, and thus satisfied the desired discharge characteristics.

Therefore, in the nonaqueous electrolyte secondary battery, a plurality of positive electrode active material layers are laminated on the positive electrode current collector, and the composition of the positive electrode active material contained in the positive electrode active material layer differs in the thickness direction. It was found that the provision of the positive electrode was excellent in stability.

[0055]

As is apparent from the above description, in the nonaqueous electrolyte battery, a plurality of positive electrode active material layers are stacked on the positive electrode current collector, and the positive electrode active material layer contained in the positive electrode active material layer is By providing a positive electrode whose composition is different in its thickness direction, it is used under abnormal conditions such as deformation of the electrode, even if an unexpected situation such as short circuit occurs,
Excellent stability.

[Brief description of the drawings]

FIG. 1 is a sectional view of a main part of a positive electrode provided in a nonaqueous electrolyte secondary battery to which the present invention is applied.

FIG. 2 is a cross-sectional view illustrating a configuration example of a non-aqueous electrolyte secondary battery.

[Description of Signs] 1 positive electrode current collector, 2 positive electrode active material layer, 2a lower layer of positive electrode active material, 2b upper layer of positive electrode active material

Claims (6)

[Claims] 1. A positive electrode comprising a positive electrode in which a plurality of positive electrode active material layers containing a positive electrode active material are laminated on a positive electrode current collector, a negative electrode containing a negative electrode active material, and a non-aqueous electrolyte. A non-aqueous electrolyte battery, wherein the composition of the positive electrode active material contained in the layer differs in the thickness direction. 2. When the cathode active material layer adjacent to the cathode current collector is used as a cathode active material lower layer, the cathode active material contained in the cathode active material lower layer contains at least one of Mn and Fe.
The non-aqueous electrolyte battery according to claim 1, further comprising a Li-containing transition metal oxide containing at least one kind. 3. When a positive electrode active material layer not adjacent to the positive electrode current collector is used as a positive electrode active material upper layer, the positive electrode active material contained in the positive electrode active material upper layer contains at least one kind of Ni or Co. The non-aqueous electrolyte battery according to claim 1, which is a Li-containing transition metal oxide. 4. The non-aqueous electrolyte battery according to claim 1, wherein the negative electrode active material is a carbon material. 5. The positive electrode active material contained in the lower layer of the positive electrode active material includes LiMn ₂ O ₄ , LiFePO ₄ , and LiFe _1-x MP.
O ₄ (where 0 <x ≦ 1, and M is Co, Ni, Mn
At least one of them. 3. The non-aqueous electrolyte battery according to claim 2, wherein the non-aqueous electrolyte battery contains at least one compound selected from the group consisting of: 6. The positive electrode active material contained in the upper layer of the positive electrode active material is LiCoO ₂ , LiNiO ₂ , LiNi _x Co _1-x O
₂ , LiNi _x Co _1-xy Al _y O ₂ (where 0 <x <1,
0 <y <1. Any one of the compounds represented by
4. The non-aqueous electrolyte battery according to claim 3, comprising at least one.