JP3010783B2 - 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 having an explosion-proof sealed structure.

[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 substance capable of doping and undoping lithium ions, such as lithium, a lithium alloy or a carbonaceous material, is used as a negative electrode, and a lithium composite oxide such as a lithium cobalt composite oxide is used for a positive electrode. Research and development of non-aqueous electrolyte secondary batteries. This battery has a high battery voltage, a high energy density, low self-discharge, and excellent cycle characteristics.

In general, when a battery has a sealed structure, if the internal pressure of the battery rises for some reason, the battery is suddenly damaged, and the battery loses its function or damages peripheral devices. Sometimes. In particular, when the non-aqueous electrolyte secondary battery as described above is made in a sealed structure, for some reason, when a current of a predetermined amount or more flows during charging and the battery is overcharged, the battery voltage increases, and the electrolyte Decompose to generate gas, and the internal pressure of the battery rises. Furthermore, if the overcharge state continues, an abnormal reaction such as rapid decomposition of the electrolyte or active material occurs, and the battery temperature may rise rapidly.

As a countermeasure against such a problem, an explosion-proof sealed battery has been proposed. This explosion-proof sealed battery includes a current cutoff device that operates in response to an increase in battery internal pressure. In a battery provided with this current interrupting device, for example, when an overcharged state advances and gas is generated / filled due to a chemical change inside the battery and the internal pressure of the battery starts to rise due to the filling of the gas, the current interrupting device becomes Activates and interrupts charging current. Therefore, the progress of the abnormal reaction inside the battery can be stopped to prevent a rapid rise in battery temperature and a rise in battery internal pressure.

[0006]

However, in the structure of the explosion-proof sealed battery, a material capable of doping and undoping lithium ions, such as lithium, a lithium alloy or a carbon material, is used as a negative electrode. In addition, when a non-aqueous electrolyte secondary battery using a lithium composite oxide such as a lithium cobalt composite oxide for the positive electrode was made and overcharged, heat generation with a rapid temperature rise and relatively rapid damage Some exhibit a damaged state. The present inventors have investigated the cause of heat generation and rapid damage accompanying rapid temperature rise due to overcharging in this explosion-proof sealed battery, and found that the battery temperature was rapidly increased before the battery internal pressure increased so much. It was found that fever and relatively rapid damage occurred.

Therefore, the present invention has been proposed in view of such a conventional situation, and the current interrupting means operates reliably during overcharging, generating heat with a rapid temperature rise and relatively rapid damage. It is an object of the present invention to provide a non-aqueous electrolyte secondary battery capable of preventing the occurrence of a battery.

[0008]

Means for Solving the Problems The present inventors have made various studies to achieve the above object, and as a result, have found that Li _X MO ₂ (where M is one or more transition metals) is a positive electrode active material. Preferably, at least one of Co or Ni is represented and 0.05 ≦ X ≦ 1.10) is added with 0.1 to 15% by weight of lithium oxalate, so that the current interrupting means is reliably provided. It has been found that it can be activated.

The present invention has been proposed based on such findings, and Li _x MO ₂ (where M represents one or more transition metals and 0.05 ≦ X ≦ 1.10.) And a negative electrode capable of doping / dedoping lithium, a non-aqueous electrolyte, and a current cutoff device that operates in response to a rise in battery internal pressure.
It is characterized by containing lithium oxalate in an amount of from 15% by weight to 15% by weight.

In the non-aqueous electrolyte secondary battery of the present invention,
Lithium oxalate is added to the positive electrode to prevent damage to the battery during overcharge. The addition amount of this lithium oxalate is
The content is set to 0.1% by weight to 15% by weight from the viewpoint of obtaining a sufficient damage prevention effect and securing the battery capacity. If the amount of lithium oxalate added is less than 0.1% by weight, overcharging causes heat generation with a rapid temperature rise and relatively rapid damage to the battery. In addition, the addition amount of lithium oxalate is 15
If the amount exceeds 10% by weight, a sufficient battery capacity cannot be obtained due to reasons such as an increase in the internal resistance of the battery.

In the present invention, the positive electrode is Li _X MO
₂ (where M is one or more transition metals, preferably C
at least one of o or Ni, and 0.05 ≦
X ≦ 1.10. ) Is used.
Such active materials include LiCoO ₂ , LiNiO ₂ ,
Li _X Ni _y Co _(1-y) O ₂ (provided that 0.05 ≦ X ≦
1.10, 0 <y <1).

The above-mentioned 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 heating at 600 ° C.
It is obtained by firing in a temperature range of 1000 ° C.
In addition, the starting material is not limited to carbonate, but can be similarly synthesized from hydroxide and oxide.

On the other hand, the negative electrode may be any material which can be doped with and dedoped with lithium.
Cokes (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired products (phenol resin, furan resin, etc. fired at appropriate temperature and carbonized), carbon fiber In addition to carbonaceous materials such as activated carbon, metallic lithium, lithium alloy (for example, lithium-aluminum alloy), 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-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolan, sulfolane, acetonitrile, A single solvent such as diethyl carbonate and dipropyl carbonate or a mixture of two or more solvents can be used. As the electrolyte, LiClO4, LiAsF6, L
iPF6, LiBF4, LiB (C6 H5) 4, LiC
1, LiBr, CH3 SO3 OLi, CF3 SO3 Li
Etc. 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 device, any of the current interrupting means usually provided in this type of battery can be employed, and the current is interrupted according to the internal pressure of the battery. Anything that can be used may be used.

[0016]

[Function] When lithium oxalate is added to the positive electrode of a non-aqueous electrolyte secondary battery, overheating does not cause heat generation with a rapid temperature rise before the internal pressure of the battery rises so much, and relatively rapid damage does not occur. When the internal pressure of the battery gradually rises, the current interrupting device operates reliably and the charging current is interrupted. Although the reason for this is not clear, since the lithium oxalate at the positive electrode is electrochemically decomposed to generate carbon dioxide gas, the carbon dioxide gas suppresses an abnormal reaction during overcharging in some form, and the carbon dioxide gas is generated again. It is considered that the carbon dioxide gas reliably operated the current interrupter, thereby preventing heat generation with a rapid temperature rise and relatively rapid damage.

[0017]

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

[0018] 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, the nonaqueous electrolyte secondary battery has a negative electrode 1 formed by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode formed by applying a positive electrode active material to a positive electrode current collector 10. 2 is wound with a separator 3 interposed therebetween, and is housed in a battery can 5 with the insulator 4 placed above and below the wound body.

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 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 negative electrode or a positive electrode. In the battery of the present embodiment, the positive electrode lead 12 is welded and attached to the current interrupting thin plate 8, and an electrical connection with the battery lid 7 is achieved through the current interrupting thin plate. In the battery having such a configuration, when the pressure inside the battery rises, the current interrupting thin plate 8 is pushed up and deformed as shown in FIG. Then, the positive electrode lead 12 is cut leaving a portion welded to the current interrupting thin plate 8, and the current is interrupted.

Example 1 First, a positive electrode was prepared as follows. Positive electrode active material (L
iCoO ₂ ) converts lithium carbonate and cobalt carbonate into Li /
It was obtained by mixing at a ratio of Co (molar ratio) = 1 and firing in air at 900 ° C. for 5 hours. X-ray diffraction measurement of this positive electrode active material showed a good match with LiCoO _{2 of} the JCPDS card. Further, when lithium carbonate in this positive electrode active material was quantified, it was hardly detected, and was 0%. Thereafter, the powder was pulverized using an automatic mortar to obtain powdery LiCoO ₂ . L obtained in this way
A mixture of 99.9% by weight of iCoO ₂ and 0.1% by weight of lithium oxalate 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,
-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 then compression-molded with a roller press to form the positive electrode 2.

Next, a negative electrode was prepared as follows. As a negative electrode active material, a petroleum pitch is used as a starting material, and a functional group containing oxygen is introduced in an amount of 10 to 20% (so-called oxygen crosslinking).
Then, a non-graphitizable carbon material having properties similar to glassy carbon obtained by firing at 1000 ° C. in an inert gas was used. X-ray diffraction measurement of this material showed that the (002) plane spacing was 3.76 ° and the true specific gravity was 1.58.
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, which was dispersed in N-methyl-2-pyrrolidone to obtain a slurry. Shape. Next, this slurry was applied to both sides of a strip-shaped copper foil as a negative electrode current collector, dried, and then compression-molded with a roller press to form a negative electrode 1.

This strip-shaped positive electrode 2, negative electrode 1, and 25 μm
The separator 3 made of a microporous polypropylene film was 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 above-mentioned 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 the battery can 5 in order to collect the current of the negative electrode. Also, in order to collect the current of the positive electrode, one end of an aluminum positive electrode lead 12 is attached to the positive electrode 2 and the other end is welded to a current interrupting thin plate 8 for interrupting a current according to the internal pressure of the battery. 8 and electrically connected to the battery lid 7.

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, 49.97% by volume of diethyl carbonate and 0.03% by volume of toluene is injected. did. Then, the battery cover 5 is fixed by caulking the battery can 5 through the insulating sealing gasket 6 coated with asphalt, and has a diameter of 14 mm and a height of 5 mm.
A 0 mm cylindrical nonaqueous electrolyte battery (Example Battery 1) was prepared.

EXAMPLE 2 91% by weight of a mixture comprising 99.5% by weight of LiCoO _{2 and} 0.5% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and polyfluorinated as a binder. A cylindrical nonaqueous electrolyte battery (Example Battery 2) was prepared in exactly the same manner as in Example 1 except that the mixture was mixed at a ratio of 3% by weight of vinylidene fluoride to prepare a positive electrode mixture.

Example 3 91% by weight of a mixture composed of 99% by weight of LiCoO _{2 and} 1% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder %, And a cylindrical nonaqueous electrolyte battery (Example Battery 3) was created in exactly the same manner as in Example 1 except that a positive electrode mixture was prepared by mixing at a ratio of 1%.

Example 4 91% by weight of a mixture composed of 95% by weight of LiCoO _{2 and} 5% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder %, Except that they were mixed in a percentage of
A cylindrical nonaqueous electrolyte battery (Example Battery 4) was prepared in exactly the same manner as in Example 1.

Example 5 91% by weight of a mixture composed of 90% by weight of LiCoO _{2 and} 10% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder %, And a cylindrical nonaqueous electrolyte battery (Example Battery 5) was prepared in exactly the same manner as in Example 1 except that the positive electrode was prepared by mixing at a ratio of 0.1%.

Example 6 91% by weight of a mixture composed of 85% by weight of LiCoO _{2 and} 15% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder %, A cylindrical nonaqueous electrolyte battery (Example Battery 6) was prepared in exactly the same manner as in Example 1 except that the positive electrode was prepared by mixing at a ratio of 0.1%.

Comparative Example 1 A positive electrode was prepared by mixing 91% by weight of LiCoO ₂ obtained in Example 1, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder. A cylindrical nonaqueous electrolyte battery (Comparative Battery 1) was prepared in exactly the same manner as in Example 1.

Comparative Example 2 91% by weight of a mixture composed of 99.95% by weight of LiCoO _{2 and} 0.05% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and polyfluorinated as a binder A cylindrical non-aqueous electrolyte battery (Comparative Battery 2) was prepared in exactly the same manner as in Example 1, except that the mixture was mixed at a ratio of 3% by weight of vinylidene fluoride to form a positive electrode.

Comparative Example 3 91% by weight of a mixture composed of 80% by weight of LiCoO _{2 and} 20% by weight of lithium oxalate obtained in Example 1, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder %, And a cylindrical nonaqueous electrolyte battery (Comparative Battery 3) was prepared in exactly the same manner as in Example 1 except that the positive electrode was prepared by mixing at a ratio of%.

Each of the batteries prepared as described above is 2
The occurrence rate of battery damage products, such as heat generation accompanied by a rapid temperature rise of the battery and relatively rapid damage caused by overcharging the battery at a current of 1.5 A for each battery, was investigated. Table 1 shows the results. After charging the above-mentioned battery at 500 mA at an upper limit voltage of 4.1 V, the battery was charged at 2.7Ω with a resistance of 18Ω.
The battery capacity when discharged to 5V was investigated. The result is shown in FIG.

[Table 1]

As shown in Table 1, in the battery in which lithium oxalate was added to the positive electrode in an amount of 0.1% by weight or more, the incidence of damaged products was lower than in the battery in which lithium oxalate was not added. From this, it was found that adding lithium oxalate to the positive electrode was effective in preventing heat generation with a rapid temperature rise of the battery and relatively rapid damage.

However, as shown in FIG. 3, when the amount of lithium oxalate added to the positive electrode exceeds 15% by weight, the decrease in battery capacity increases, and the battery becomes insufficient. This is presumably because lithium oxalate is a substance having low conductivity and if added in an amount exceeding 15% by weight, the internal resistance of the battery increases and the load characteristics deteriorate.

Therefore, it was found that the amount of lithium oxalate added to the positive electrode was preferably 0.1 to 15% by weight.

In this embodiment, L is used as the positive electrode active material.
Although iCoO ₂ was used, other positive electrode active materials (for example, L
i _X Ni _y Co _(1-y) O ₂ (provided that 0.05 ≦ X ≦ 1.
A similar effect was confirmed when 10,0 <y ≦ 1)) was used.

[0038]

As is apparent from the above description, in the present invention, 0.1 to 15% by weight of lithium oxalate is added to the positive electrode of a nonaqueous electrolyte secondary battery having a current interrupting device. Therefore, even if the battery is overcharged, the above-mentioned current cutoff device operates reliably, thereby preventing an abnormal reaction inside the battery due to the overcharge.
Heat generation accompanied by a rapid temperature rise of the battery and relatively rapid damage can be prevented. Therefore, a non-aqueous electrolyte secondary battery having high energy density, excellent cycle characteristics, and high safety can be provided, 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.

FIG. 2 is a schematic cross-sectional view illustrating an operation state of a current interrupting unit.

FIG. 3 is a characteristic diagram showing a relationship between an added amount of lithium oxalate and a battery capacity.

[Explanation of symbols]

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

Continuation of the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01M 4/02-4/04 H01M 4/58 H01M 10/40

Claims (1)

(57) [Claims] 1. A positive electrode mainly composed of Li _x MO ₂ (where M represents one or more transition metals and 0.05 ≦ X ≦ 1.10), and lithium can be doped and de-doped. A negative electrode, a non-aqueous electrolyte, and a current cutoff device that operates in response to a rise in battery internal pressure, wherein the positive electrode contains 0.1% by weight to 15% by weight of lithium oxalate. Non-aqueous electrolyte secondary battery.