JP3010781B2 - 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 having a lithium composite oxide as a positive electrode and a current interrupting means which operates in response to an increase in battery internal pressure.

[0002]

2. Description of the Related Art In recent years, with the advance of electronic technology, electronic devices have been improved in performance, downsized and portable, and the demand for high energy density secondary batteries used in these electronic devices has been 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 a battery having a low discharge potential and a high energy density. It is.

In recent years, non-aqueous materials using lithium or lithium alloys or materials capable of doping and undoping lithium ions such as carbon materials as negative electrodes and using lithium composite oxides such as lithium cobalt composite oxides as positive electrodes have been used. Research and development of electrolyte secondary batteries are being conducted. 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 rapidly 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 manufactured 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 solution increases. Decompose, gas is generated, and the internal pressure of the battery rises.
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 is provided with current interrupting means that operates in response to an increase in battery internal pressure. For example, a battery provided with this current interrupting means is charged and generated by an overcharged state due to a chemical change inside the battery, and the internal pressure of the battery starts to increase due to the filling of the gas. Operates to cut off the 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. A non-aqueous electrolyte secondary battery using a lithium composite oxide such as a lithium-cobalt composite oxide was fabricated and overcharged, and exhibited a damaged state such as heat generation with a rapid temperature rise and relatively rapid damage. There is something. The present inventors have investigated the causes of heat generation and a relatively rapid damage accompanied by a rapid temperature rise of the battery due to overcharging, and found that in a non-aqueous electrolyte secondary battery, the battery internal pressure increased rapidly before the battery internal pressure increased so much. It was found that heat was generated with a rise in temperature and relatively rapid damage occurred, and the current interrupting means did not function effectively.

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

[0008]

Means for Solving the Problems The inventors of the present invention have conducted various studies in order to achieve the above object. As a result, Li _x MO ₂ (where M is one or more transition metals) Preferably, at least one of Co or Ni is represented, and 0.05 ≦ X ≦ 1.10.) And 0.5 to 15% by weight of lithium carbonate is added to ensure that the current interrupting means is provided. It has been found that it can work.

That is, the present invention relates to Lix MO2 (where M represents at least one kind of transition metal and 0.05 ≦
X ≦ 1.10. ), A negative electrode capable of doping / dedoping lithium, a non-aqueous electrolyte, and current interrupting means that operates in response to an increase in battery internal pressure. It is characterized by containing from 5% by weight to 15% by weight.

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 ,
LiNi _y Co _(1-y) O ₂ (provided that 0.05 ≦ X ≦ 1.
And a composite oxide represented by 10,0 <y <1). The composite oxide is, for example, lithium, cobalt,
Nickel carbonate is used as a starting material, and these carbonates are mixed according to the composition, and are mixed at 600 ° C. to 1000 ° C. in an atmosphere containing oxygen.
It is obtained by firing in a temperature range of ° C. Further, the starting material is not limited to carbonate, but can be similarly synthesized from hydroxide and oxide.

On the other hand, in the present invention, for example, a carbon material is used for the negative electrode. As the carbon material, any material capable of doping and undoping lithium can be used.
Coke (pitch coke, needle coke, petroleum coke, etc.), graphites, glassy carbons, organic polymer compound fired product (phenol resin, furan resin, etc. fired at appropriate temperature and carbonized), carbon fiber , Activated carbon and the like. Alternatively, in addition to carbon materials, polymers such as polyacetylene and polypyrrole can be used in addition to metallic lithium and lithium alloy (for example, lithium-aluminum alloy).

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, LiClO ₄ , LiAsF
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 current interrupting means usually provided in this type of battery can be adopted, and the current is interrupted according to the internal pressure of the battery. Anything that can be used may be used.

[0015]

[Function] When lithium carbonate is added to a positive electrode mainly composed of lithium composite oxide, heat generation accompanied by a rapid temperature rise before the internal pressure of the battery rises so much due to overcharging and relatively rapid damage do not occur, and When the internal pressure of the battery rises relatively slowly, the current cutoff means operates reliably and cuts off the charging current. Although the reason is not clear, since the lithium carbonate 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 It is considered that in order to reliably operate the current interrupting means by the gas, heat generation accompanied by a rapid temperature rise and relatively rapid damage were prevented.

[0016]

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

[0017] 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 includes a negative electrode 1 formed by applying a negative electrode active material to a negative electrode current collector 9 and a positive electrode 2 formed by applying a positive electrode active material to a positive electrode current collector 10. Are wound around the separator 3 and stored in the battery can 5 with the insulating plate 4 placed on the upper and lower sides of the wound body. 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 via a negative electrode lead 11 and a positive electrode lead 12, respectively. Alternatively, it is configured to function as a positive electrode.

In the battery of this embodiment, the positive electrode lead 12 is attached to the current interrupting thin plate 8 by welding.
Electrical connection with the battery lid 7 is achieved via the current interrupting thin plate 8. In a battery having such a configuration, when the pressure inside the battery increases, as shown in FIG.
The current interrupting thin plate 8 is pushed up and deformed. 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 A positive electrode active material (LiCoO ₂ ) was synthesized as follows. Lithium carbonate and cobalt carbonate were mixed such that Li / Co (molar ratio) = 1 and fired in air at 900 ° C. for 5 hours. As a result of X-ray diffraction measurement of this material, it was in good agreement with LiCoO _{2 of} the JCPDS card. When lithium carbonate in the positive electrode active material was quantified, it was hardly detected, and was 0%. Then, it was pulverized using an automatic mortar to obtain LiCoO ₂ .

The amount of lithium carbonate in the positive electrode active material is
CO2 produced by decomposing the sample with sulfuric acid is introduced into barium chloride and sodium hydroxide solution and absorbed, and then CO2 is quantified by titration with a hydrochloric acid standard solution.
It was determined by conversion from _two quantities. Li thus obtained
91% by weight of a mixture obtained using CoO2 as 99.5% by weight of LiCoO2 and 0.5% by weight of lithium carbonate, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder. The mixture was mixed to prepare a positive electrode material, 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 serving as the positive electrode current collector 10, dried, and compression-molded with a roller press to form the positive electrode 2.

Next, as a negative electrode active material, a petroleum pitch is used as a starting material, and 10 to 20% of a functional group containing oxygen is introduced into the material (so-called oxygen crosslinking).
A non-graphitic carbon material having properties similar to glassy carbon obtained by firing in the above step 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 the negative electrode current collector 9, dried, and compression-molded with a roller press to form the negative electrode 1.

The strip-shaped positive electrode 2, negative electrode 1, and separator 3 made of a 25 μm microporous pyripropylene film were sequentially laminated, and then spirally wound 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, and the wound body was stored. 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 and 50% by volume of diethyl carbonate was injected. Then, the battery lid 5 was fixed by caulking the battery can 5 via the insulating sealing gasket 6 coated with asphalt, thereby producing a cylindrical battery having a diameter of 14 mm and a height of 50 mm.

Example 2 Using LiCoO ₂ obtained in Example 1, LiCoO ₂
91% by weight of a mixture obtained as 99.0% by weight and 1.0% by weight of lithium carbonate, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder
To produce a positive electrode.
A cylindrical battery was produced in exactly the same manner as in Example 1.

Example 3 Using LiCoO ₂ obtained in Example 1, LiCoO ₂ 95
91% by weight of a mixture obtained as 5% by weight of lithium carbonate and 5% by weight of lithium carbonate, 6% by weight of graphite as a conductive material, and 3% by weight of polyvinylidene fluoride as a binder to prepare a positive electrode. Produced a cylindrical battery in exactly the same manner as in Example 1.

Example 4 Using LiCoO ₂ obtained in Example 1, LiCoO ₂ 90
91% by weight of a mixture obtained as 10% by weight of lithium carbonate and 10% by weight of lithium carbonate, 6% by weight of graphite as a conductive material,
A positive electrode was prepared by mixing 3% by weight of polyvinylidene fluoride as a binder to prepare a positive electrode. Except for this, a cylindrical battery was prepared in exactly the same manner as in Example 1.

Example 5 Using LiCoO ₂ obtained in Example 1, LiCoO ₂ 85
9% of lithium carbonate and 15% by weight of lithium carbonate
A positive electrode was prepared by mixing 1% 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. Created.

Example 6 The LiCoO ₂ obtained in Example 1 was used to prepare LiCoO ₂ 80
91% by weight of a mixture obtained as 20% by weight of lithium carbonate and 20% by weight of lithium carbonate, 6% by weight of graphite as a conductive material,
A positive electrode was prepared by mixing 3% by weight of polyvinylidene fluoride as a binder to prepare a positive electrode. Except for this, a cylindrical battery was prepared in exactly the same manner as in Example 1.

Example 7 Li / Co (molar ratio) of lithium carbonate and cobalt carbonate =
It mixed so that it might be 1.10, and baked at 900 degreeC in air for 5 hours. The positive electrode active material was subjected to X-ray diffraction measurement, and as a result, was found to be a mixture of LiCoO2 and lithium carbonate. When the amount of lithium carbonate in this positive electrode active material was quantified, it contained 3.5% by weight of lithium carbonate. Thereafter, the mixture was ground using an automatic mortar, and 91% by weight of the positive electrode active material, 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. Produced a cylindrical battery in exactly the same manner as in Example 1.

[0030] Using the LiCoO ₂ obtained in Comparative Example 1 Example 1, LiCoO ₂ 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. Except for this, a cylindrical battery was prepared in exactly the same manner as in Example 1. did.

The resulting LiCoO ₂ is used in Comparative Example 2 Example 1, LiCoO ₂ 9
91% by weight of a mixture obtained as 9.8% by weight and 0.2% by weight of lithium carbonate, and 6 parts of graphite as a conductive material.
A positive electrode was prepared by mixing at a ratio of 3% by weight of polyvinylidene fluoride as a binder by weight, and a cylindrical battery was prepared in exactly the same manner as in Example 1 except for this.

Each of the above-mentioned 20 batteries, each having a current of 1.5
The occurrence rate of a damaged battery, such as heat generation accompanied by a rapid temperature rise of the battery and relatively rapid damage caused by the overcharged state at A, was investigated. Table 1 shows the results.

[Table 1]

Further, the battery capacity when the above-mentioned battery was charged at 500 mA at an upper limit voltage of 4.1 V and then discharged to 2.75 V with a resistance of 18Ω was examined. The result is shown in FIG.
Shown in

As shown in Table 1, by adding lithium carbonate to LiCoO ₂ in an amount of 0.5% by weight or more, heat generation accompanying a rapid temperature rise of the battery and relatively rapid damage were eliminated. However, as shown in FIG.
If it exceeds 5% by weight, the decrease in battery capacity increases. This is considered to be due to the fact that lithium carbonate has a low conductivity, so that if added over 15%, the internal resistance of the battery increases and the load characteristics deteriorate. Therefore, the addition amount of lithium carbonate is desirably 0.5 to 15% by weight.

Further, from the results of Example 7, it was found that LiCoO ₂
Example 1 was obtained even when lithium carbonate was left during the synthesis.
As in the case of adding lithium carbonate later to the synthesized LiCoO ₂ in Nos. 6 to 6, it was possible to prevent heat generation with a rapid temperature rise of the battery due to overcharging and relatively rapid damage. Therefore, in either the method of adding lithium carbonate to the positive electrode, the method of remaining in the positive electrode active material during the synthesis of the positive electrode active material, or the method of adding lithium carbonate to the positive electrode, the effect of overcharging can be obtained. Seems promising.

In the examples of the positive electrode active material, L
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 also confirmed with 10,0 <y ≦ 1)). From the above experiments, it was found that by adding 0.5 to 15% by weight of lithium carbonate to the positive electrode, in a non-aqueous electrolyte secondary battery provided with a current interrupting device, the current interrupting device reliably operates even if overcharged. As a result, it was confirmed that an abnormal reaction inside the battery due to overcharging can be prevented, and heat generation accompanied by a rapid temperature rise of the battery and relatively rapid damage can be prevented.

The embodiments to which the present invention is applied have been described above. However, the present invention is not limited to these embodiments, and the structure, shape, size, material, etc. of the battery do not depart from the gist of the present invention. Is optional.

[0038]

As is clear from the above description, in the present invention, lithium carbonate is added to the positive electrode at a predetermined ratio, so that a non-aqueous electrolyte When the battery is charged, the current interrupting device operates reliably, so that an abnormal reaction inside the battery due to overcharging can be prevented, and 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 carbonate and a battery capacity.

[Explanation of symbols]

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

Claims (1)

(57) [Claims] 1. A positive electrode mainly composed of Li _x MO ₂ (where M represents at least one kind of transition metal and 0.05 ≦ X ≦ 1.10), and a lithium-doped and de-doped lithium. A negative electrode, a non-aqueous electrolyte, and a current cutoff device that operates in response to an increase in the internal pressure of the battery, wherein the positive electrode contains 0.5% to 15% by weight of lithium carbonate. Water electrolyte secondary battery.