JP3303319B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery, and more particularly to a non-aqueous electrolyte secondary battery provided with a current cut-off means that operates when overcharged.

[0002]

2. Description of the Related Art In recent years, with the advance of electronic technology, the performance, size, and portability of electronic devices have been advanced, and the demand for high energy density secondary batteries used in these electronic devices has increased. Conventionally, secondary batteries used in these electronic devices include nickel-cadmium batteries and lead batteries, but these batteries are still insufficient in terms of obtaining batteries having a low discharge potential and a high energy density. is there.

Recently, a material capable of doping and undoping lithium ions such as lithium, a lithium alloy, and a carbon material is used as a negative electrode, and a lithium composite oxide such as a lithium cobalt composite oxide is used as a positive electrode. Research and development of non-aqueous electrolyte secondary batteries have been actively conducted.
This battery has a high battery voltage, a high energy density, low self-discharge, and excellent cycle characteristics.

However, in the above-described non-aqueous electrolyte secondary battery, when a current of a predetermined amount or more flows during charging for some reason and the battery is overcharged, the battery voltage increases and the electrolyte or the like is decomposed. As a result, gas is generated, and the battery internal pressure and battery temperature rise. Further, if the overcharge state continues, an abnormal reaction such as rapid decomposition of the electrolyte or the active material occurs, which may cause a damage state such as heat generation with a rise in temperature or relatively rapid breakage.

As a countermeasure against such a problem, the present inventors have provided a non-aqueous electrolyte secondary battery having a current interrupting device that operates in response to an increase in battery internal pressure and having a positive electrode containing lithium carbonate as a battery internal pressure increasing agent. Proposed. In this battery, as the overcharge state progresses, lithium carbonate in the positive electrode is electrolyzed to generate carbon dioxide gas. Due to this gas generation, the internal pressure of the battery rises, and the current cutoff device operates to cut off the current. As a result, the abnormal reaction of the battery is suppressed, and the battery is prevented from being damaged due to a rapid increase in the battery temperature or the battery internal pressure.

[0006]

However, in recent years, rapid charging of batteries has been progressing, and safety at a higher charging current has been required. The battery equipped with the above-described current interrupting device and having a configuration in which lithium carbonate is added to the positive electrode was secured against overcharging with the conventional charging current, but was overcharged with a higher charging current. However, heat generation accompanied by a rapid temperature rise occurs before the operation of the shut-off device, and there is a case in which a damage state such as relatively rapid breakage is exhibited.

Accordingly, the present invention has been proposed in view of such a conventional situation, and a non-aqueous electrolyte secondary battery which does not cause temperature rise or breakage even when overcharged with a high charging current. The purpose is to provide.

[0008]

As a result of repeated studies by the present inventors to achieve the above-mentioned object, if lithium carbonate having a large specific surface area is used as lithium carbonate added to the positive electrode,
The present inventors have found that even when overcharged with a high charging current, the current cutoff device operates reliably and prevents rapid temperature rise and damage.

[0009] The non-aqueous electrolyte secondary battery of the present invention has been proposed based on such knowledge, and Li _X MO ₂
(Where M represents one or more transition metals, and 0.05 ≦ X
≦ 1.10), a positive electrode made of lithium carbonate, a negative electrode capable of doping and undoping lithium, a non-aqueous electrolyte, and a current cutoff device that operates according to an increase in battery internal pressure. The specific surface area of the lithium carbonate is 0.
It is not less than 1 m ² / g.

In the present invention, the positive electrode is obtained by adding lithium carbonate to a lithium composite oxide serving as a positive electrode active material.

As the lithium composite oxide, Li _x
MO ₂ (where M is one or more transition metals, preferably C
represents at least one of o and Ni, and 0.05 ≦ x ≦
1.10. ), For example, LiCoO ₂ , LiNiO ₂ , Li _X Ni _Y C
o _1-Y O ₂ (however, 0.05 ≦ X ≦ 1.10, 0 <Y
.Ltoreq.1.0).

The above-mentioned lithium composite oxide is prepared, for example, by using carbonates of lithium, cobalt and nickel as starting materials, mixing these carbonates according to the composition, and mixing them under an oxygen-containing atmosphere.
It is obtained by firing in a temperature range of 0 ° C to 1000 ° C. The starting materials are not limited to carbonates, but can also be synthesized from hydroxides and oxides.

The above-mentioned lithium carbonate is added as a battery internal pressure increasing agent for activating a current interrupt device at the time of overcharging. That is, in the above battery, when the overcharge state proceeds, lithium carbonate in the positive electrode is electrolyzed to generate carbon dioxide gas. Due to this gas generation, the internal pressure of the battery rises, and the current cutoff device operates to cut off the current.

Here, it is important that the specific surface area of the lithium carbonate is 0.1 m ² / g or more in order to promote the electrolysis of the lithium carbonate more quickly.
When the specific surface area of the lithium carbonate is less than 0.1 m ² / g, the progress of the decomposition reaction of the lithium carbonate is slowed down, and when the battery is overcharged with a high charging current, the operation of the current interrupting device is delayed in time for the occurrence of the abnormal reaction. Battery damage.

The surface area of lithium carbonate can be adjusted by controlling the amount of lithium carbonate charged into the ball mill and the grinding time when the lithium carbonate mass is pulverized by a ball mill into lithium carbonate for addition. .

On the other hand, any negative electrode material may be used as long as it can be doped with and dedoped with lithium.
Coke (pitch coke, needle coke, petroleum coke, etc.), graphite, glassy carbons, organic polymer compound fired product (carbonized by firing phenol resin, furan resin, etc. at appropriate temperature), carbon Fibers, carbon materials such as activated carbon, or metallic lithium and lithium alloys, as well as polymers such as polyacetylene and polypyrrole can be used.

As the electrolytic solution, for example, an electrolytic solution in which a lithium salt is used as an electrolyte and dissolved in an organic solvent is used. Here, the organic solvent is not particularly limited, but propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, γ-butyl lactone,
A single solvent such as tetrahydrofuran, 2-methyl-tetrahydrofuran, 1,3-dioxolan, sulfolane, acetonitrile, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, or a mixed solvent of two or more types can be used.

As the electrolyte, LiClO ₄ , LiAs
F ₆ , LiPF ₆ , LiBF ₄ , LiB (C
_{6 H 5) 4, LiCl,} LiBr, CH 3 SO 3 Li,
CF ₃ SO ₃ Li or the like can be used.

In the non-aqueous electrolyte secondary battery of the present invention,
It is necessary that a current interrupting means is provided. As the current interrupting means, any of the current interrupting means usually provided in this type of battery can be adopted, and the current is reduced in accordance with an increase in the internal pressure of the battery. Any device that can be shut off may be used.

[0020]

In a non-aqueous electrolyte secondary battery having a current interrupting device that operates in response to a rise in battery internal pressure and having a positive electrode to which lithium carbonate is added as a battery internal pressure increasing agent, the surface area of lithium carbonate is 0.1 m ² / g. When a battery having a large value is used, even when overcharged with a high charging current, the current cutoff device is reliably operated, and the subsequent rapid temperature rise and battery damage are prevented.

Although the reason for this is not clear, it is considered to be due to the following reason. That is, in the non-aqueous electrolyte secondary battery, when the battery is overcharged, lithium carbonate is electrochemically decomposed to generate carbon dioxide gas, and the generation of the carbon dioxide gas activates the current interrupting device.

At this time, if the specific surface area of lithium carbonate is small, the decomposition reaction proceeds slowly because lithium carbonate has a small reaction area. For this reason, when overcharged with a high charging current, the decomposition reaction of lithium carbonate does not catch up with the occurrence of the abnormal reaction, and the abnormal reaction occurs before the current interrupting device operates. In addition, when the reaction area is increased by increasing the amount of lithium carbonate having a small specific surface area, the polarization in the electrode is increased, and the decomposition reaction of lithium carbonate is also slow. Operation does not catch up with the occurrence of abnormal reaction.

On the other hand, when the specific surface area of lithium carbonate is increased, the reaction area of lithium carbonate is increased, and the polarization of lithium carbonate itself in the electrode is also reduced.
Therefore, even if the battery is overcharged with a high charging current, the decomposition of lithium carbonate occurs promptly, and the current interrupting device operates reliably, thereby preventing heat generation with a rapid temperature rise of the battery and relatively rapid damage.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the drawings.

[0025] The structure of the battery produced in each example of the structure below the battery prepared is shown in Figure 1.

As shown in FIG. 1, this non-aqueous electrolyte secondary battery has a negative electrode 1 formed by coating a negative electrode current collector 9 with a negative electrode active material.
And a positive electrode 2 obtained by applying a positive electrode active material to which lithium carbonate has been added to a positive electrode current collector 10, with a separator 3 wound therebetween, and an insulator 4 placed above and below the wound body In the battery can 5. A battery lid 7 is attached to the battery can 5 by caulking via a sealing gasket 6, and is electrically connected to the negative electrode 1 or the positive electrode 2 via a negative electrode lead 11 and a positive electrode lead 12, respectively. It is configured to function as a positive electrode.

In the battery of this embodiment, the positive electrode lead 12 is welded and attached to the battery cut-off thin plate 8, and an electrical connection with the battery lid 7 is made through the current cut-off thin plate 8. I have. In the battery having such a configuration, when the pressure inside the battery increases, the thin plate 8 such as the current interruption is pushed up and deformed. Then, the positive electrode lead 1
2 is cut off leaving a portion welded to the current interrupting thin plate 8, and the current is interrupted.

Example 1 A positive electrode was produced as follows. First, a positive electrode active material (LiC
oO ₂ ) is obtained by adding lithium carbonate and cobalt carbonate to L
i / Co = 1, 900 ° C. in air,
It was obtained by firing for 5 hours. X-ray diffraction measurement of this positive electrode active material showed that LiCoO _{2 of} the JCPDS card was used.
Well matched. Then, it was pulverized using an automatic mortar to obtain LiCoO ₂ .

LiCoO ₂ having a specific surface area of 5.10 m ² / g was added to the thus obtained LiCoO ₂ ,
A mixture of 95.0% by weight of LiCoO _{2 and} 5.0% by weight of lithium carbonate was mixed to prepare 91% by weight of the mixture of LiCoO ₂ and lithium carbonate, 6% by weight of graphite as a conductive agent, and polyvinylidene fluoride as a binder. The mixture was mixed at a ratio of 3% by weight to prepare a positive electrode mixture, which was dispersed in N-methyl-2-pyrrolidone to form a slurry.

Next, this slurry was applied to both sides of a belt-shaped aluminum foil as the positive electrode current collector 10, dried, and compression-molded with a roll press to prepare a positive electrode 2.

Next, a negative electrode was manufactured as follows. Glass obtained by using petroleum pitch as a starting material for the negative electrode active material, introducing a functional group containing oxygen in an amount of 10 to 20% by weight (so-called oxygen cross-linking), and then firing at 1000 ° C. in an inert gas stream. A soft graphite carbon material having properties similar to that of dendritic carbon was used.
When an X-ray diffraction measurement was performed on this material, (00
2) The face-to-face spacing is 3.76 ° and the true specific gravity is 1.58 g /
cm ² .

The carbon material thus obtained was mixed at a ratio of 90% by weight and polyvinylidene fluoride as a binder at a ratio of 10% by weight to prepare a negative electrode mixture.
It was dispersed in 2-pyrrolidone to form a slurry. next,
This slurry was applied to both sides of a strip-shaped copper foil as the negative electrode current collector 9, dried, and then compression-molded with a roll press to form a negative electrode 1.

The strip-shaped positive electrode 2, negative electrode 1, and separator 3 made of a 25 μm microporous polypropylene film were sequentially laminated, and then wound in a spiral form many times to produce a wound body.

Next, the insulating plate 4 was inserted into the bottom of the nickel-plated iron battery can 5 to house the wound body. Then, one end of a nickel-made negative electrode lead 11 was pressed against the negative electrode 1 and the other end was welded to a battery can in order to collect the current of the negative electrode. In addition, one end of an aluminum positive electrode lead 12 was attached to the positive electrode 2 to collect current from the positive electrode, and the other end was electrically connected to the battery lid 7 via a current interrupting thin plate 8.

Then, into the battery can 5, an electrolyte obtained by dissolving 1 mol of LiPF _{6 in} a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate was injected. The battery lid 5 is fixed by caulking the battery can 5 through an insulating sealing gasket 6 coated with asphalt, and a cylindrical non-aqueous electrolyte secondary battery having a diameter of 14 mm and a height of 50 mm (Example Battery 1) It was created.

Examples 2 to 7 A cylindrical nonaqueous electrolyte secondary battery (Example battery) was prepared in the same manner as in Example 1 except that lithium carbonate having a specific surface area shown in Table 1 was used as lithium carbonate added to the positive electrode. 2 to Example Battery 7) were prepared.

[0037]

[Table 1]

Comparative Example 1 The specific surface area of lithium carbonate added to the positive electrode was 0.05.
A cylindrical non-aqueous electrolyte secondary battery (Comparative Battery 1) was prepared in the same manner as in Example 1 except that a battery of m ² / g was used.

Comparative Example 2 The specific surface area of lithium carbonate added to the positive electrode was 0.05.
A mixture of 90% by weight of LiCoO ₂ and 10% by weight of lithium carbonate was prepared using m ² / g.
1% by weight, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder were mixed to form a positive electrode mixture. A secondary battery (Comparative Battery 2) was prepared.

Comparative Example 3 The specific surface area of lithium carbonate added to the positive electrode was 0.05.
m ² / g, LiCoO ₂ 85% by weight
A mixture was prepared except that a mixture of 15% by weight of lithium carbonate was prepared and 91% by weight of this mixture, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder were used to prepare a positive electrode mixture. A cylindrical non-aqueous electrolyte secondary battery (Comparative Battery 2) was prepared in the same manner as in Example 1.

Examples 1 to 7 and Comparative Example 1
The specific surface area of lithium carbonate used in Comparative Example 3 was adjusted by changing the amount of lithium carbonate charged into the ball mill and the pulverizing time when the lithium carbonate mass was pulverized with a ball mill to obtain lithium carbonate for addition. . Further, the specific surface area of lithium carbonate was measured according to the BET one-point method.

Each of the 20 batteries prepared in Examples 1 to 7 and Comparative Examples 1 to 3 was overcharged with a charging current of 1.5 A and 3.7 A, and The incidence of battery damage, such as heat generation with a rapid temperature rise and relatively rapid damage, was investigated. Table 2 shows the results.

[0043]

[Table 2]

As shown in Table 2, when the charging current was set to 1.5 A, the batteries of Example 1 to Example 7 and the batteries of Comparative Example 1 to Comparative Example 3 did not cause any battery damage. I couldn't see it. However, the charging current was further increased by 3.7A.
When it was raised to a higher value, no damage was observed in Example Battery 1 to Example Battery 7, but damage was observed in Comparative Battery 1 to Comparative Battery 3.

Therefore, from this fact, by setting the specific surface area of the lithium carbonate added to the positive electrode to 0.1 m ² / g or more, even when the battery is overcharged with a high charging current, heat generation accompanied by a rapid temperature rise and It was found that a non-aqueous electrolyte secondary battery free from relatively rapid damage was obtained. In particular, from the results of Comparative Battery 2 and Comparative Battery 3, when the specific surface area of lithium carbonate is less than 0.1 m ² / g, the amount of lithium carbonate added is increased to increase the reaction area. However, it was also found that abnormal reactions could not be completely prevented.

In this embodiment, L is used as the positive electrode active material.
Although iCoO ₂ was used, other positive electrode active materials such as Li
_X Ni _Y Co _(1-Y) O ₂ (provided that 0.05 ≦ X ≦ 1.
The present invention exhibited the same effect even when (10, 0 <Y ≦ 1.0) was used.

[0047]

As is apparent from the above description, the present invention comprises a non-aqueous electrolyte having a current interrupting device which operates in response to an increase in battery internal pressure and having a positive electrode to which lithium carbonate is added as a battery internal pressure increasing agent. In the secondary battery, the lithium carbonate having a specific surface area of 0.1 m ² / g is used. Therefore, even when the battery is in an overcharged state with a high charging current, the current cutoff device operates reliably to prevent breakage. It is possible.

Therefore, the present invention can provide a non-aqueous electrolyte secondary battery having high energy density, excellent cycle characteristics, and high safety, and its industrial and commercial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a configuration example of a non-aqueous electrolyte secondary battery.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 8 ... Thin film for current interruption

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/58 H01M 4/02-4/04

Claims (3)

(57) [Claims] 1. A positive electrode comprising Li _x MO ₂ (where M represents one or more transition metals and 0.05 ≦ x ≦ 1.10) and lithium carbonate, and lithium doped and undoped. A non-aqueous electrolyte, comprising: a negative electrode to be obtained; a non-aqueous electrolyte; and a current cutoff means that operates in response to a rise in pressure in the battery, wherein the specific surface area of the lithium carbonate is 0.1 m ² / g or more. Liquid secondary battery. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode is one of a carbon material, metallic lithium, and a lithium alloy. 3. The method according to claim 1, wherein Li _x MO ₂ is LiCoO ₂ , LiNi.
O ₂ , Li _x NiyCo _1-y O ₂ (0 <y ≦ 1.0)
The non-aqueous electrolyte secondary battery according to claim 1, wherein: