JPH11185714A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a nonaqueous secondary battery provided with a marking explosion proof valve surely broken by predetermined operation pressure and holding good strength against falling shock. SOLUTION: A nonaqueous secondary battery is provided with an armoring can 1 comprising a rectangular metal having an opening serving also as one polar terminal, a power generation element contained in the armoring can 1 and having a positive electrode and a negative electrode confronting as sandwiching a separator, nonaqueous electrolyte contained in the armoring can 1, and a sealing body fitted to the opening portion of the armoring can 1 and having the other polar terminal airtightly sealed by hermetic sealing. A marking explosion proof valve 18 comprising a slit-like thin film portion of 0.06 to 0.15 mm thick and having a straight line portion of 6 to 15 mm long is formed at some place of an armoring can 1 surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a non-aqueous electrolyte secondary battery having a safety valve mechanism.

[0002]

2. Description of the Related Art In recent years, as electronic devices such as mobile phones and video cameras, and computers and the like have become smaller, lighter, and more sophisticated, the weight of secondary batteries serving as power sources for these electronic devices has also been reduced. , High energy density is required.

A non-aqueous electrolyte secondary battery capable of increasing the voltage above the decomposition voltage of water is being developed as a secondary battery that replaces conventionally used lead secondary batteries and nickel-cadmium secondary batteries. And has been put to practical use. Such a non-aqueous electrolyte secondary battery has coke, graphite,
Using a carbon material capable of inserting and extracting lithium such as an organic sintered body, and using LiCoO ₂ , Li as a positive electrode active material
2. Description of the Related Art A lithium ion secondary battery using a metal oxide such as NiO ₂ capable of inserting and extracting lithium ions is known.

[0004] However, the above-mentioned non-aqueous electrolyte secondary battery has the above-mentioned advantages, but has a problem of poor reliability. One example is that an electrode body, which is a power generating element having a positive electrode and a negative electrode, housed in an outer can is chemically changed to increase the internal pressure, causing ignition and explosion. For example, when a current higher than normal is applied to a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery, the battery is put into a so-called overcharged state, or when a large current flows due to short-circuit due to misuse, the electrode body The non-aqueous electrolyte in is decomposed to generate gas. When gas fills the outer can and the internal pressure in the outer can rises, the battery eventually ruptures.

[0005] For this reason, conventionally, when the internal pressure of the outer can exceeds a certain value in order to prevent the above-described battery rupture, the generated gas is discharged to the outside of the outer can to prevent rupture. Is provided. The following structure is known as a nonaqueous electrolyte secondary battery provided with such a safety valve mechanism.

The non-aqueous electrolyte secondary battery comprises a cylindrical outer can having a bottom, an electrode body housed in the outer can and having a positive electrode, a separator, and a negative electrode spirally wound thereon; The housing includes a nonaqueous electrolyte contained therein, and a sealing body attached to an upper end opening of the outer can. A pressure release hole is opened in the sealing body, and a thin plate made of, for example, stainless steel is hermetically attached to the lower surface of the sealing body by laser welding so as to cover the hole. In addition, cut portions having V-shaped portions at both ends of the linear portion are formed on the upper surface of the thin plate. That is, the thin plate is attached to the lower surface of the sealing body such that the opening side of the cut groove faces the outside of the outer can. The cut groove is formed on the lower surface of the thin plate by etching. The pressure relief hole of the sealing body and the thin plate constitute a safety valve mechanism.

In the non-aqueous electrolyte secondary battery having such a safety valve mechanism, when the internal pressure of the outer can increases due to an overcurrent or the like, the cut groove portion is pressurized, and the thin plate is broken therefrom to form a hole. It is formed. The gas filled in the outer can is released to the outside through the hole and the pressure release hole, thereby preventing explosion.

[0008]

However, the safety valve mechanism is limited in space and size because the sealing body is attached to the upper end of the outer can. In particular, as a structure for ensuring the stability of impedance, one of the lead tabs of the positive electrode and the negative electrode is connected to an electrode terminal insulated by hermetic on the sealing body, and the other is connected to a region other than the electrode terminal of the sealing body. In the case of such a structure, the space restriction becomes more severe. In order to secure a predetermined operating pressure in such a limited space, it is necessary to increase the depth of the cut groove of the thin plate (reduce the remaining thickness). In a non-aqueous electrolyte secondary battery provided with a safety valve mechanism having a thin plate having a large depth of such a cut groove, when a drop impact, particularly a drop impact is directly received on a sealing body provided with a safety valve mechanism, the thin plate The cut groove is broken to open, causing loss of battery function and leakage of the non-aqueous electrolyte contained in the outer can to damage peripheral devices.

Further, the safety valve mechanism is composed of two parts, the sealing body and a thin plate. Further, since the thin plate is welded to the sealing body by laser welding, poor airtightness occurs due to welding conditions and the like. When the non-aqueous electrolyte secondary battery is assembled, there is a possibility that a failure that the electrolyte leaks out may occur.

An object of the present invention is to provide a non-aqueous electrolyte secondary battery provided with an imprint explosion-proof valve that is reliably broken at a predetermined operating pressure and maintains good strength against a drop impact. is there.

[0011]

In order to achieve the above object, a nonaqueous electrolyte secondary battery according to the present invention comprises a rectangular metal outer can having an opening serving also as a unipolar terminal; A power generating element having a positive electrode and a negative electrode housed in an outer can and opposed to each other with a separator interposed therebetween, a non-aqueous electrolytic solution housed in the outer can, and attached to an opening of the outer can, having another polarity The terminal was hermetically sealed by Hermetec with a sealing body, and the thickness was 0.06 to 0.1.
An imprinted explosion-proof valve comprising a grooved thin film portion having a length of 5 mm and a linear portion having a length of 6 to 15 mm is formed at any location on the surface of the outer can.

Preferably, one of the positive electrode and the negative electrode is connected to the other polarity terminal through a lead.

It is preferable that the imprint explosion-proof valve has a linear shape parallel or perpendicular to the ridge line of the outer can or a shape having V-shaped portions at both ends of the linear portion.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a sealed battery according to the present invention will be described in detail with reference to the drawings, taking a rectangular sealed battery as an example. Here, the square shape means that the shape when the outer can is cut at the surface including the power generation element is a rectangle, but allows the corner to be rounded.

FIG. 1 is a perspective view showing a nonaqueous electrolyte secondary battery according to the present invention, for example, a prismatic lithium ion secondary battery.
2 is an external perspective view of the secondary battery of FIG. 1, and FIG. 3 is a bottom sectional view of the secondary battery of FIG.

Outer can 1 in the form of a bottomed rectangular tube made of metal
Is, for example, also serving as a positive electrode terminal, and an insulating film 2 on the bottom inner surface.
Is arranged. The electrode body 3 as a power generation element is housed in the outer can 1. The electrode body 3 is manufactured by spirally winding the negative electrode 4, the separator 5, and the positive electrode 6 such that the positive electrode 6 is located at the outermost periphery, and then press-forming the flat shape. A spacer 7 made of, for example, a synthetic resin and having a lead extraction hole near the center is disposed on the electrode body 3 in the outer can 1.

The metal lid 8 is hermetically joined to the upper end opening of the outer can 1 by, for example, laser welding. In the vicinity of the center of the lid 8, a hole 9 for taking out a negative electrode terminal is opened. The negative electrode terminal 10 is hermetically sealed in the hole 9 of the lid 8 via an insulating material 11 made of glass or resin. A lead 12 is connected to the lower end surface of the negative electrode terminal 10, and the other end of the lead 12 is connected to the negative electrode 4 of the electrode body 3.

The upper insulating paper 13 covers the entire outer surface of the lid 8. The lower insulating paper 15 having the slit 14 is disposed on the bottom surface of the outer can 1. The folded PTC element 16 has one surface interposed between the bottom surface of the outer can 1 and the lower insulating paper 15, and the other surface extending outside the insulating paper 15 through the slit 14. Has been issued. The outer tube 17 is arranged so as to extend from the side surface of the outer can 1 to the periphery of the insulating papers 13 and 15 on the upper and lower surfaces, and fixes the upper insulating paper 13 and the lower insulating paper 15 to the outer can 1. doing. Due to such an arrangement of the outer tube 17, the other surface of the PTC (Positive Thermal Coefficient) element 16 extended to the outside is bent toward the bottom surface of the lower insulating paper 15.

A groove-shaped thin film portion having a thickness of 0.06 to 0.15 mm and a linear portion having a length of 6 to 15 mm, for example, a groove-shaped thin film portion having V-shaped portions at both ends of the linear portion. As shown in FIGS. 2 and 3, the engraved explosion-proof valve 18 is formed, for example, at the bottom of the outer can 1 in parallel to the ridge line of the outer can 1.

The outer can is made of, for example, aluminum, stainless steel or iron.

In the case of a lithium ion secondary battery, for example, a paste containing a carbonaceous material into or out of which lithium ions can be introduced and removed, such as graphite, needle coke, mesophase pitch-based carbon fiber, and a sintered body of an organic polymer, is used as the negative electrode. It has a structure held on both sides of a current collector as described above.

For example, in the case of a lithium ion secondary battery, the positive electrode is made of lithium nickel oxide, LiCoO ₂ , L
It has a structure in which a paste containing an active material such as a complex oxide containing lithium or cobalt such as iNiO ₂ or LiMn ₂ O ₄ is held on both surfaces of a current collector such as a thin copper plate.

For example, in the case of a lithium ion secondary battery, a porous film made of a synthetic resin such as polypropylene is used as the separator.

As the electrolyte, for example, in the case of a lithium ion secondary battery, lithium perchlorate, lithium borofluoride, lithium hexafluoride, lithium hexafluoride, lithium arsenide hexafluoride, lithium trifluoromethanesulfonate, etc. The electrolyte of ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethyloxypropane, dimethyl ether, tetrahydrofuran, 2 = methyltetrahydrofuran, dimethyl carbonate, diethyl carbonate, Those dissolved in an organic solvent such as ethyl methyl carbonate are used.

It is preferable that the lid has a thickness of 0.8 mm or more, more preferably 0.9 to 1.5 mm.
If the thickness of the lid is less than 0.8 mm, the strength is reduced and it becomes difficult to sufficiently protect the electrode body 3 housed in the outer can 1.

The grooved thin film portion constituting the stamp explosion-proof valve is
For example, it is formed by press working with a mold punch. This groove-shaped thin film portion is not limited to the shape and the formation position shown in FIG. For example, the shape and formation position of the groove-shaped thin film portion may be as shown in FIGS. That is, the groove-shaped thin film portion 18 shown in FIG. 4A has a linear shape and is formed at the bottom of the outer can 1. FIG.
The groove-shaped thin film portion 18 shown in (b) has a linear shape and is formed on the side surface of the outer can 1 so as to be parallel to the ridge line. The groove-shaped thin film portion 18 shown in FIG. 4C has a linear shape and is formed on the side surface of the outer can 1 so as to be perpendicular to the ridge line. The groove-shaped thin film portion 18 shown in FIG. 4D has a shape having V-shaped portions at both ends of the linear portion, and is formed on the side surface of the outer can 1 so as to be parallel to the ridge line. The groove-shaped thin film portion 18 shown in FIG. 4E has a shape having V-shaped portions at both ends of the straight portion, and is formed on the side surface of the outer can 1 so as to be perpendicular to the ridge line.

The reason why the thickness of the groove-shaped thin film portion and the length of the linear portion constituting the imprint explosion-proof valve are specified is as follows.

If the thickness of the groove-shaped thin film portion is less than 0.06 mm, there is a possibility that the explosion-proof valve is opened and the electrolyte contained therein leaks due to an impact due to a drop of the battery or the like. On the other hand, if the thickness of the groove-shaped thin film portion exceeds 0.15 mm, the explosion-proof valve may not operate even if the internal pressure in the outer can increases. More preferably, the thickness of the groove-shaped thin film portion is 0.075 to 0.08.
5 mm.

If the length of the grooved thin film portion is less than 6 mm, the explosion-proof valve may not operate even if the internal pressure in the outer can increases. On the other hand, the length of the groove-shaped thin film portion is 15 m.
If it exceeds m, the explosion-proof valve may be opened by an impact due to a drop of the battery or the like, and the electrolyte therein may leak. More preferably, the length of the groove-shaped thin film portion is 8 to 10 mm.

The non-aqueous electrolytic secondary battery according to the present invention described above has a stamped explosion-proof valve comprising a grooved thin film portion having a thickness of 0.06 to 0.15 mm and a linear portion having a length of 6 to 15 mm. Is formed at any place on the surface of the outer can. By forming the engraved explosion-proof valve having the above-described shape on the outer can, an operation area having a larger area can be secured as compared with a secondary battery in which a safety valve mechanism is attached to a conventional sealing body. Therefore, when the outer can is deformed due to an increase in internal pressure due to gas generation in the outer can, the engraved explosion-proof valve is broken and the generated gas can escape to the outside. As a result, rupture of the battery can be prevented.

For example, when the engraved explosion-proof valve is arranged at the location of the minimum area of the outer can, the surface responsibilities received when the inner pressure of the outer can is abnormal are minimized, so that the explosion-proof valve is deformed inside the can. Explosion-proof valve is broken. In this case, it is possible to prevent the contents in the outer can from jumping out, thereby ensuring high safety. On the other hand, when the engraved explosion-proof valve is arranged at the location of the maximum area of the outer can, the surface responsibilities for receiving the internal pressure are maximum, so that the deformation easily occurs and the remaining wall thickness for obtaining a predetermined operating pressure can be increased. . As a result, workability and drop resistance can be improved.

Further, in a structure in which both the positive and negative electrodes are connected to the sealing body through the lead tab, the explosion-proof valve structure of the present invention is effective for arranging the rupture on the cap body which is strict in space.

Further, since the groove-shaped thin film portion constituting the engraved explosion-proof valve is relatively thick and is formed at the location of the outer can which is hardly subjected to a drop impact, it is superior to the conventional safety valve mechanism. Has drop impact resistance.

Further, since the stamp explosion-proof valve does not need to hermetically weld components such as a conventional safety valve mechanism to the sealing body, a non-aqueous electrolytic secondary battery having a highly reliable airtight structure can be realized.

[0035]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will now be described with reference to FIGS.
This will be described in detail with reference to a square sealed battery as shown in FIG.

Example 1 <Preparation of Positive Electrode> First, lithium carbonate and cobalt carbonate were mixed so that the molar ratio of Li / Co became 1, and calcined in air at 900 ° C. for 5 hours to produce LiCoO ₂ . After the synthesis, the powder was pulverized with an automatic mortar to prepare LiCoO ₂ powder (positive electrode active material).

Next, 95 parts by weight of the LiCoO ₂ powder and 5 parts by weight of lithium carbonate were mixed.
By weight, 6 parts by weight of graphite powder as a conductive material and 6 parts by weight of polyvinylidene fluoride resin as a binder were mixed to prepare a positive electrode mixture. Subsequently, this positive electrode mixture was dispersed in N-methyl-2-pyrrolidone to form a slurry. This slurry was applied to both sides of a belt-shaped aluminum foil as a positive electrode current collector, dried, and then compression-molded with a roll press to produce a positive electrode.

<Preparation of Negative Electrode> First, petroleum pitch was used as a starting material, and oxygen-containing functional groups were added in an amount of 10 to 20%.
After the introduction (oxygen crosslinking), the mixture was calcined at 1000 ° C. in an inert gas to obtain a non-graphite carbon material having properties similar to glassy carbon. 90 parts by weight of this non-graphite carbon material and 10 parts by weight of polyvinylidene fluoride resin as a binder were mixed to prepare a negative electrode mixture.

Next, the negative electrode mixture was mixed with N-methyl-2-
The slurry was dispersed in pyrrolidone to form a slurry. After applying this slurry to both sides of a strip-shaped copper foil as a negative electrode current collector,
After drying and compression molding with a roll press, a negative electrode was produced.

Next, the positive electrode, the separator made of a microporous polypropylene film having a thickness of 25 μm, and the negative electrode were stacked in this order and spirally wound to form a cylindrical body. Subsequently, the cylindrical material was compressed at a pressure of 10 kg / cm ² to produce a flat electrode body (power generation element). Subsequently, as shown in FIG. 2, the flat electrode body was inserted into an outer can having an engraved explosion-proof valve formed of a groove-like thin film portion having a V-shaped portion at both ends of a straight portion on the bottom surface, and hexafluoride. After injecting a non-aqueous electrolyte solution of lithium phosphate electrolyte dissolved in ethylene carbonate and methyl ethyl carbonate,
A nonaqueous electrolyte secondary battery (lithium ion secondary battery) having the structure shown in FIGS. 1 to 3 was assembled by laser welding a sealing body to the opening of the outer can. The explosion-proof valve has a remaining wall thickness of 0.08 mm and a length of a straight portion of 8 mm.
Of the groove-shaped thin film portion.

(Comparative Example 1) The same procedure as in Example 1 was carried out except that an outer can having an engraved explosion-proof valve formed of a grooved thin film portion having a residual thickness of 0.05 mm and a linear portion having a length of 8 mm at the bottom was used. A similar lithium ion secondary battery was assembled.

(Comparative Example 2) The same procedure as in Example 1 was carried out except that an outer can having an engraved explosion-proof valve formed of a groove-like thin film portion having a residual wall thickness of 0.20 mm and a linear portion having a length of 8 mm at the bottom was used. A similar lithium ion secondary battery was assembled.

(Comparative Example 3) The same procedure as in Example 1 was carried out except that an outer can having an engraved explosion-proof valve formed of a groove-like thin film portion having a remaining thickness of 0.08 mm and a linear portion having a length of 5 mm at the bottom was used. A similar lithium ion secondary battery was assembled.

(Comparative Example 4) The same procedure as in Example 1 was carried out except that an outer can having an engraved explosion-proof valve formed of a groove-shaped thin film portion having a residual thickness of 0.08 mm and a linear portion having a length of 20 mm at the bottom was used. A similar lithium ion secondary battery was assembled.

The obtained secondary batteries of Example 1 and Comparative Examples 1 to 4 were prepared, and the current was set to 2.0 A, the power supply voltage was set to 15 V, and the condition that the explosion-proof valve was always operated was prepared. The battery was overcharged, and the number of secondary batteries in which the explosion-proof valve was activated and the number of ruptured secondary batteries were examined. The results are shown in Table 1 below.

The obtained Example 1 and Comparative Examples 1 to
100 secondary batteries of No. 4 were prepared, these secondary batteries were charged under the conditions of a current of 1.0 A, a voltage of 4.4 V, and 3 hours, placed on a hot plate set at 250 ° C., and an explosion-proof valve was operated. The number of secondary batteries and the number of ruptured secondary batteries were examined. The results are shown in Table 2 below.

Further, the obtained Example 1 and Comparative Example 1
To 100 secondary batteries were prepared, and the secondary batteries were charged under the conditions of a current of 1.0 A, a voltage of 4.4 V, and three hours. Each was dropped 10 times so that the bottom surface on which the explosion-proof valve was formed directly hit the tree. After such a drop test, the state of leakage of the nonaqueous electrolyte due to the opening of the explosion-proof valve was examined. The results are shown in Table 3 below.

[0048]

[Table 1]

[0049]

[Table 2]

[0050]

[Table 3]

As is clear from Tables 1 to 3, the remaining thickness is 0.06 to 0.15 mm and the length of the straight portion is 6 to 15 mm.
The secondary battery of Example 1 provided with an outer can having an explosion-proof valve consisting of a groove-shaped thin film portion of 0.2 mm, the explosion-proof valve operated well during overcharge and abnormal heat generation, and the explosion-proof valve was broken in a drop test. It turns out that it is extremely reliable and does not occur.

On the other hand, the secondary battery of Comparative Example 1 provided with an outer can having an explosion-proof valve having a remaining wall thickness smaller than the above range operates well during overcharge and abnormal heat generation, In the test, the explosion-proof valve breaks, causing electrolyte leakage.

The secondary battery of Comparative Example 2 provided with an outer can having an explosion-proof valve having a remaining wall thickness larger than the above range does not break the explosion-proof valve in a drop test, but does not explode during overcharge and abnormal heat generation. Valve does not work well.

The secondary battery of Comparative Example 3 provided with an outer can having an explosion-proof valve having a length of the linear portion smaller than the above-mentioned range did not break the explosion-proof valve in the drop test, but did not undergo overcharge and abnormal heat generation. Explosion-proof valve does not work well.

The secondary battery of Comparative Example 4 provided with an outer can having an explosion-proof valve having a linear portion having a length larger than the above range did not break the explosion-proof valve in the drop test, but did not exhibit any overcharge and abnormal heat generation. Explosion-proof valve does not work well.

In the above embodiment, the prismatic non-aqueous electrolyte secondary battery has been described as an example, but the present invention is not limited to this. For example, a configuration in which power generating elements are stacked in a flat plate shape instead of a wound type may be employed.

[0057]

As described above in detail, according to the present invention, a non-aqueous electrolyte provided with a stamped explosion-proof valve which is reliably broken at a predetermined operating pressure and has good strength against a drop impact. A secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a partially cutaway perspective view showing a prismatic lithium ion secondary battery as an example of a nonaqueous electrolyte secondary battery according to the present invention.

FIG. 2 is an external perspective view of the secondary battery of FIG.

FIG. 3 is a bottom sectional view of the secondary battery in FIG. 2;

FIG. 4 is an external perspective view showing another embodiment of the nonaqueous electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Outer can, 3 ... Electrode body, 4 ... Negative electrode, 5 ... Separator, 6 ... Positive electrode 8 ... Lid, 18 ... Stamped explosion-proof valve.

Continuing on the front page (72) Inventor Katsuhisa Homma 72, Horikawa-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside A / T Battery Co., Ltd.・ In the tea battery

Claims (5)

[Claims] An outer case made of a metal having a rectangular shape having an opening serving also as a unipolar terminal, a power generating element housed in the outer case and having a positive electrode and a negative electrode opposed to each other with a separator interposed therebetween; A non-aqueous electrolyte contained in the outer can and a sealing body attached to the opening of the outer can and hermetically sealed with the other polarity terminal hermetically, and having a thickness of 0. A stamped explosion-proof valve comprising a groove-shaped thin film portion having a length of 6 to 0.15 mm and a linear portion of 6 to 15 mm is formed at any position on the surface of the outer can. Electrolyte secondary battery. 2. One of the positive electrode and the negative electrode,
2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the non-aqueous electrolyte secondary battery is connected to the other polarity terminal through a lead. 3. The non-aqueous electrolysis device according to claim 1, wherein the engraved explosion-proof valve has a linear shape parallel or perpendicular to a ridgeline of the outer can or a shape having V-shaped portions at both ends of the linear portion. Liquid secondary battery. 4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the imprint explosion-proof valve is formed in a portion having a minimum area of the outer can. 5. The non-aqueous electrolyte secondary battery according to claim 1, wherein the engraved explosion-proof valve is formed in a portion having a maximum area of the outer can.