JPH05151997A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PURPOSE:To prevent rapid temp. rise and breakage even at over-charging by furnishing a current shutoff device actuated with rise of the intra-battery pressure, and giving the carbon-distributed lithium in the positive electrode a specific surface area exceeding 0.1m<2>/g. CONSTITUTION:A positive electrode 2 has the composition LixMO2 where lithium carbonate is added to lithium composite oxides as active material for positive electrode, while a negative electrode 1 is capable of being doped with lithium or dedoped, where M represents one or more of the transfer metals and (x) is conditioned as 0.05<=x<=1.10. The negative electrode 1 prepared by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode 2 prepared by applying the positive electrode active material, to which lithium carbonate is added, to a positive electrode current collector are wound with a separator 3 interposed. Insulation 4 is arranged over and below this winding, and the resultant is housed in a battery can 5. The specific surface area of the lithium carbonate is made over 0.1m<2>/g, and a current shutting thin film is provided which is actuated with rise of the intra- battery pressure. This quickens decomposition of the lithium, and there is no risk of breakage due to quick temp. rise even at over-charging.

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 interruption means that operates during overcharge.

[0002]

2. Description of the Related Art In recent years, advances in electronic technology have led to advances in performance, miniaturization, and portability of electronic devices, and the demand for secondary batteries of high energy density used in these electronic devices is increasing. 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 with low discharge potential and high energy density. is there.

Recently, substances capable of doping and dedoping lithium ions such as lithium and lithium alloys and carbon materials have been used as negative electrodes, and lithium composite oxides such as lithium cobalt composite oxides have been used as positive electrodes. Research and development of non-aqueous electrolyte secondary batteries are being actively conducted.
This battery has a high battery voltage, a high energy density, little self-discharge, and excellent cycle characteristics.

However, in the non-aqueous electrolyte secondary battery as described above, if an electric current of a predetermined amount or more flows at the time of charging for some reason and the battery is overcharged, the battery voltage increases and the electrolyte or the like decomposes. Then, gas is generated, and the battery internal pressure and battery temperature rise. Further, if this overcharged state continues, an abnormal reaction such as rapid decomposition of the electrolyte or active material may occur, resulting in a damage state such as heat generation accompanied by temperature rise or relatively rapid damage.

As a measure against such a problem, the inventors of the present invention have provided a non-aqueous electrolyte secondary battery which is equipped with a current interrupting device which operates in response to an increase in battery internal pressure and which contains lithium carbonate as a battery internal pressure increasing agent in the positive electrode. Proposed. In this battery, as the overcharged 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 interrupt device operates to interrupt the current. As a result, the abnormal reaction of the battery is suppressed and the battery is prevented from being damaged due to the rapid increase in the battery temperature and the battery internal pressure.

[0006]

However, in recent years, the rapid charging of batteries has further progressed, and safety at a higher charging current is required. The battery with the above-mentioned current cutoff device and the structure in which lithium carbonate was added to the positive electrode was secured against the overcharge state at the conventional charging current, but was overcharged at a higher charging current. However, there are some cases in which a heat generation accompanied by a rapid temperature rise occurs before the operation of the circuit breaker, which causes a damage state such as a relatively rapid breakage.

Therefore, the present invention has been proposed in view of such conventional circumstances, and a non-aqueous electrolyte secondary battery in which temperature rise and damage do not occur even when overcharging is performed at a high charging current. The purpose is to provide.

[0008]

Means for Solving the Problems As a result of repeated studies by the present inventors in order to achieve the above-mentioned object, if lithium carbonate having a large specific surface area is used as lithium carbonate to be added to the positive electrode,
We have found that the current interruption device operates reliably even when overcharged with a high charging current, and a rapid temperature rise and damage are prevented.

The non-aqueous electrolyte secondary battery of the present invention has been proposed on the basis of such findings, and Li _X MO ₂
(However, M represents one or more kinds of transition metals, and 0.05 ≦ X
≦ 1.10) and lithium carbonate, a negative electrode capable of being doped and dedoped with lithium, a non-aqueous electrolyte solution, and a current interrupting device that operates in response to an increase in internal pressure of the battery. The specific surface area of the lithium carbonate is 0.
It is characterized by being 1 m ² / g or more.

In the present invention, the positive electrode is formed by adding lithium carbonate to a lithium composite oxide which is 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 ≦
It is 1.10. ) Lithium composite oxide represented by, for example, LiCoO ₂ , LiNiO ₂ , Li _X Ni _Y C
o _1-Y O ₂ (however, 0.05 ≦ X ≦ 1.10, 0 <Y
Examples include lithium composite oxides represented by ≦ 1.0).

The above lithium composite oxide is prepared by using, for example, a carbonate of lithium, cobalt, or nickel as a starting material, and mixing these carbonates according to the composition in an oxygen-existing atmosphere.
It is obtained by firing in a temperature range of 0 ° C to 1000 ° C. The starting material is not limited to carbonate, and can be synthesized from hydroxide or oxide.

The above-mentioned lithium carbonate is added as a battery internal pressure increasing agent for activating the current interruption device during overcharge. That is, in the above battery, when the overcharged 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 interrupt device operates to interrupt the current.

Here, in order to promote the electrolysis of lithium carbonate more quickly, it is important that the specific surface area of lithium carbonate is 0.1 m ² / g or more.
If the specific surface area of lithium carbonate is less than 0.1 m ² / g, the progress of the decomposition reaction of lithium carbonate will be slow, and the operation of the current interrupt device will be delayed until the abnormal reaction occurs if overcharged with a high charging current. Without causing damage to the battery.

The surface area of the lithium carbonate can be adjusted by controlling the amount of lithium carbonate added to the ball mill and the crushing time when the lithium carbonate lumps are crushed by a ball mill into lithium carbonate for addition. ..

On the other hand, as the negative electrode material, any material that can be doped with lithium and dedoped can be used, and pyrolytic carbons,
Cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired bodies (carbonized by firing phenolic resin, furan resin, etc. at an appropriate temperature), carbon In addition to carbon materials such as fibers and activated carbon, metallic lithium and lithium alloys, polymers such as polyacetylene and polypyrrole can also be used.

As the electrolytic solution, for example, an electrolytic solution in which a lithium salt is used as an electrolyte and this is 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,
Tetrahydrofuran, 2-methyl-tetrahydrofuran, 1,3-dioxolane, sulfolane, acetonitrile, dimethyl carbonate, diethyl carbonate, dipropyl carbonate and the like can be used alone or in combination of two or more kinds.

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 to provide a current interrupting means, but as this current interrupting means, any current interrupting means usually provided in this type of battery can be adopted, and the current is increased in accordance with the increase in the internal pressure of the battery. Anything can be used as long as it can be cut off.

[0020]

In a non-aqueous electrolyte secondary battery having a current interrupting device that operates according to an increase in battery internal pressure and lithium carbonate as a battery internal pressure increasing agent added to the positive electrode, the surface area of lithium carbonate is 0.1 m ² / g. If a large one is used, the current interruption device operates reliably even when overcharged with a high charging current, and the rapid temperature rise and battery damage that occur subsequently are prevented.

The reason for this is not clear, but it is considered to be due to the following reason. That is, in the non-aqueous electrolyte secondary battery, when it is in an overcharged state, lithium carbonate is electrochemically decomposed to generate carbon dioxide gas, and the carbon dioxide gas is generated, and the current interrupt device operates.

At this time, when the specific surface area of lithium carbonate is small, the reaction area of lithium carbonate is small and the decomposition reaction proceeds slowly. Therefore, 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 of the lithium carbonate having a small specific surface area is increased by increasing the addition amount, the polarization inside the electrode is increased, and the decomposition reaction of lithium carbonate slows down, so that the current interrupt device 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 increases, and the polarization of lithium carbonate itself in the electrode also decreases.
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, and the heat generation associated with the rapid temperature rise of the battery and the relatively rapid damage are prevented.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described with reference to the drawings.

Structure of Battery Produced FIG. 1 shows the structure of the battery produced in each Example described later.

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

In the battery of this embodiment, the positive electrode lead 12 is attached by welding to the thin plate 8 for cutting off the battery, and is electrically connected to the battery lid 7 through the thin plate 8 for breaking off the current. There is. In the battery having such a structure, when the pressure inside the battery rises, the thin plate 8 for current interruption is pushed up and deformed. Then, the positive electrode lead 1
2 is cut off except for the portion welded to the current breaking thin plate 8 to cut off the current.

Example 1 A positive electrode was prepared as follows. First, the positive electrode active material (LiC
In order to obtain oO ₂ ) lithium carbonate and cobalt carbonate
i / Co = 1 and mixed in air at 900 ° C,
It was obtained by firing for 5 hours. As a result of X-ray diffraction measurement of this positive electrode active material, LiCoO _{2 of} JCPDS card
Was in good agreement with. Then, to obtain a LiCoO ₂ was pulverized using an automatic mortar.

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

Next, this slurry was applied on both sides of a strip-shaped aluminum foil as the positive electrode current collector 10, dried and then compression-molded by a roll press machine to form a positive electrode 2.

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

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

The strip-shaped positive electrode 2, negative electrode 1 and separator 25 made of a microporous polypropylene film having a thickness of 25 μm were laminated in this order and then spirally wound many times to form 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, in order to collect the current of the negative electrode, one end of a negative electrode lead 11 made of nickel was pressure-bonded to the negative electrode 1, and the other end was welded to a battery can. Further, one end of a positive electrode lead 12 made of aluminum was attached to the positive electrode 2 in order to collect current from the positive electrode, and the other end was electrically connected to the battery lid 7 via a thin plate 8 for cutting off current.

Then, into the battery can 5, an electrolytic solution in which 1 mol of LiPF ₆ was dissolved in a mixed solvent of 50% by volume of propylene carbonate and 50% by volume of diethyl carbonate was injected. Then, the battery lid 5 is fixed by caulking the battery can 5 via the insulating sealing gasket 6 coated with asphalt, and the 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 Cylindrical nonaqueous electrolyte secondary batteries (Example batteries) were used in the same manner as in Example 1 except that lithium carbonate having a specific surface area shown in Table 1 was used as the lithium carbonate added to the positive electrode. 2 to Example batteries 7) were prepared.

[0037]

[Table 1]

Comparative Example 1 Lithium carbonate added to the positive electrode has a specific surface area of 0.05.
A cylindrical non-aqueous electrolyte secondary battery (Comparative Example Battery 1) was produced in the same manner as in Example 1 except that 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, and the mixture was mixed with 9%.
A cylindrical non-aqueous electrolyte solution 2 was prepared in the same manner as in Example 1 except that 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 prepare a positive electrode mixture. A next battery (Comparative battery 2) was prepared.

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

Incidentally, Examples 1 to 7 and Comparative Example 1
-The specific surface area of the lithium carbonate used in Comparative Example 3 was adjusted by changing the charging amount and the crushing time of the lithium carbonate charged into the ball mill when the lithium carbonate lump was crushed by the ball mill into the lithium carbonate for addition. .. 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 shown above 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 rapid temperature rise and relatively rapid damage was investigated. The results are shown in Table 2.

[0043]

[Table 2]

As shown in Table 2, when the charging current is set to 1.5 A, the battery of Examples 1 to 7 and the batteries of Comparative 1 to 1 are not damaged. I couldn't see it. However, the charging current is 3.7A.
When the temperature was raised to 0, no damage was found in Example battery 1 to Example battery 7, but damage was found in Comparative example battery 1 to Comparative example battery 3.

Therefore, by making the specific surface area of the lithium carbonate added to the positive electrode to be 0.1 m ² / g or more, heat generation accompanied by a rapid temperature rise even when the battery is overcharged with a high charging current. It was found that a non-aqueous electrolyte secondary battery in which relatively rapid damage does not occur can be obtained. Further, especially from the results of Comparative Example Battery 2 and Comparative Example Battery 3, when the specific surface area of lithium carbonate is less than 0.1 m ² / g, the amount of lithium carbonate added was increased to increase the reaction area. However, it was also found that the abnormal reaction cannot be completely prevented.

In this example, L was used as the positive electrode active material.
iCoO ₂ was used, but other positive electrode active materials such as Li
_X Ni _Y Co _(1-Y) O ₂ (where 0.05 ≦ X ≦ 1.
Even when 10, 0 <Y ≦ 1.0) was used, the present invention exhibited the same effect.

[0047]

As is apparent from the above description, the present invention is a non-aqueous electrolytic solution that includes a current interrupting device that operates in response to an increase in battery internal pressure and has lithium carbonate added to the positive electrode as a battery internal pressure increasing agent. In the secondary battery, since the lithium carbonate having a specific surface area of 0.1 m ² / g is used, the current interrupting device operates reliably even if the battery is overcharged with a high charging current to prevent damage. It is possible.

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

[Brief description of drawings]

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

[Explanation of symbols]

 1 ... Negative electrode 2 ... Positive electrode 3 ... Separator 8 ... Current blocking thin film

Claims (1)

[Claims] 1. A positive electrode comprising Li _X MO ₂ (wherein M represents one or more kinds of transition metals and 0.05 ≦ X ≦ 1.10) and lithium carbonate, and lithium is doped and dedoped. The negative electrode to be obtained, a non-aqueous electrolytic solution, and a current interrupting device that operates in response to an increase in internal pressure of the battery, respectively, and the lithium carbonate has a specific surface area of 0.1 m ² / g or more. Water electrolyte secondary battery.