JP2002289259A - Flat nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat nonaqueous electrolyte secondary battery having a significantly improved heavy load discharging characteristic. SOLUTION: The flat nonaqueous electrolyte secondary battery comprises a metal battery case serving both as an electrode terminal, the other terminal disposed at an opening formed in a part of a seal plate for sealing the battery case, and a group of electrodes at least including a positive electrode, a separator and a negative electrode and a nonaqueous electrolyte which are contained inside the battery. The sum total of the opposed area of the positive and negative electrodes are made larger than the area of the seal plate, so that the flat battery has a significantly improved discharging capacity at heavy load discharging compared with a conventional battery, while maintaining the advantage of a small battery size and excellent productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a flat non-aqueous electrolyte secondary battery, and more particularly to a flat non-aqueous electrolyte secondary battery having improved heavy load discharge characteristics.

[0002]

_2. Description of the Related Art A metal oxide such as MnO ₂ or V ₂ O ₅ , an inorganic compound such as fluorinated graphite, or an organic compound such as polyaniline or a polyacene structure is used as a positive electrode active material. Lithium alloy, or an organic compound such as a polyacene structure, or a carbonaceous material capable of occluding and releasing lithium, or an oxide such as lithium titanate or lithium-containing silicon oxide, and propylene carbonate, ethylene carbonate as an electrolyte, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiBF ₄ , LiBF ₄ , LiBF ₄ , LiBF ₄ ,
CF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO
₂ ) A coin-shaped or button-shaped flat non-aqueous electrolyte secondary battery using a non-aqueous electrolyte in which a supporting salt such as ₂ is dissolved has already been commercialized, and a light load having a discharge current of about several to several tens μA has been already commercialized. It is applied to applications such as a backup power supply for SRAMs and RTCs, and a main power supply for wristwatches that do not require battery replacement.

On the other hand, the miniaturization of equipment used has been accelerated, especially for small information terminals such as mobile phones and PDAs. Accordingly, it is essential to reduce the size of secondary batteries as main power supplies. I have. Conventionally, these main power sources include lithium-containing oxides such as lithium cobalt oxide as the positive electrode active material, lithium ion secondary batteries using carbonaceous materials for the negative electrode, nickel oxyhydroxide as the positive electrode active material, and Nickel-metal hydride storage batteries using hydrogen storage alloys have been used.However, these batteries are formed by applying or filling an active substance layer on a current collector consisting of a metal foil or metal net, forming an electrode, and placing a tab terminal at the center of the electrode. After winding or laminating the electrode group, the tab terminal taken out from the center of the electrode group is bent intricately and welded to the safety element, sealing pin, battery can, etc. I was making it.

[0004]

SUMMARY OF THE INVENTION In order to obtain a small and high-power battery, the present inventors first attempted to reduce the size of a cylindrical or prismatic lithium ion secondary battery. However, when miniaturization is attempted, the tab connection taken out of the center of the electrode group as described above is complicatedly bent, and the electrode connection work for welding to a safety element, a sealing pin, a battery can, etc. is a difficult operation. Yes, required skill.

Next, the application of a battery in which the positive electrode and the negative electrode were formed into a tablet shape slightly smaller than the opening diameter of the sealing plate, such as a button shape or a coin shape, was examined. However, the characteristics of the battery when discharged with a large current were far insufficient, and were not at a satisfactory level as a main power source for a small portable device. Therefore, there has been a strong demand for further improving the heavy load discharge characteristics of a small flat non-aqueous electrolyte secondary battery to raise it to an unprecedented level. The present invention has been made in view of the above circumstances, and has as its object to provide a flat nonaqueous electrolyte secondary battery having remarkably excellent heavy load discharge characteristics.

[0006]

Means for Solving the Problems The present inventors have intensively studied the miniaturization of a cylindrical or prismatic lithium ion secondary battery, and as a result, have adopted a battery structure suitable for miniaturization, It has been found that heavy load discharge characteristics are dramatically improved by increasing the area in each stage as compared with the conventional flat battery. That is, a metal battery case also serving as an electrode terminal and a part of a sealing plate for sealing the battery case are opened, and another electrode terminal is arranged in the opening, and the sealing plate also serving as an electrode terminal and the other electrode terminal are disposed. In a flat nonaqueous electrolyte secondary battery that is electrically insulated by an insulator and includes at least a positive electrode, a separator, and a negative electrode therein, and a nonaqueous electrolyte, the positive and negative electrode facing areas in the electrode group It has been found that a heavy non-aqueous electrolyte secondary battery having a structure in which the sum of the above is larger than the opening area of the sealing plate dramatically improves heavy load discharge characteristics.

By the way, in order to improve the workability in reducing the size of a cylindrical or prismatic lithium ion secondary battery, a part of a sealing plate for sealing a battery case is opened, and another electrode terminal is provided in this opening. And a positive electrode or a negative electrode is electrically connected via a current collector plate electrically integrated with the other electrode terminal and a separator housed in the battery, thereby facilitating contact between the electrode and the terminal. Can be.

It is supposed that it is effective to increase the electrode area in order to improve the heavy load discharge characteristics. However, in the conventional flat nonaqueous electrolyte secondary battery, the positive and negative electrodes face each other with a separator interposed therebetween. The facing area was inevitably smaller than the opening area of the sealing plate, and it was theoretically impossible to store the electrode having the facing area exceeding the opening area of the sealing plate in the battery. .

The inventors of the present invention have made a bold shift from the prior art to a band-like positive electrode via a separator.
By arranging the electrode group wound with the negative electrode in the battery case of the flat battery, the total of the positive and negative electrode facing areas in the electrode group can accommodate the electrode group larger than the opening area of the sealing plate. . As described above, in the case of a large secondary battery such as a cylinder or a prism, there is an example in which an electrode having several tens of layers is housed.
These batteries have a complicated structure as described above,
Even if it is applied, it becomes impossible to maintain the advantages of the flat nonaqueous electrolyte secondary battery such as being small in size and excellent in productivity. For this reason, no attempt has been made in the past to store an electrode group having a positive and negative electrode facing area larger than the opening area of the sealing plate in the flat nonaqueous electrolyte secondary battery.

Hereinafter, how the present inventors have realized the present invention will be described. First, there are a number of possible configurations in which an electrode having a positive / negative electrode facing area larger than the opening area of a sealing plate is housed in a flat nonaqueous electrolyte secondary battery. It is preferable that the electrode group of the positive electrode and the negative electrode is wound to accommodate the spirally wound electrode group. Because, in order to obtain excellent heavy load characteristics, the electrode area should be as large as possible, the number of parts should be reduced as much as possible, the space in the small battery should be used effectively, and the electrode group and the necessary amount of non-aqueous The electrolyte must be stored in the battery, and this storage method can achieve the requirements required for the battery. Further, according to this storage method, the electrode can be easily manufactured, and it is excellent in practical aspects such as productivity and cost, and is preferable in mass production.

Next, a description will be given of a method of connecting the electrode group to a battery metal case which also serves as an external terminal. As described above, for a relatively large lithium ion secondary battery such as a cylinder or prism, a tab terminal is welded to the center of the electrode group or the core, bent, and welded to the safety element or sealing pin. Electricity. However, since the bending process is complicated, the productivity is inferior. In addition, it is necessary to provide a space in the battery or to insert an insulating plate between the battery and the electrode group in order to prevent an internal short circuit. Also, when stress is applied to the portion where the tab terminal is welded to the electrode, the separator breaks through, or the electrode is deformed. Could not be used effectively. Therefore, these current collecting methods cannot be applied to coin-shaped or button-shaped flat non-aqueous electrolyte secondary batteries in which the internal volume of the battery is small, and it is necessary to propose a new current collecting method.

In view of the above, the present inventors have exposed a conductive positive electrode component at one end in a direction horizontal to the flat surface of the flat battery in the electrode group, and provided a conductive negative electrode component at the other end of the counter electrode. The present inventors have found that an electrode group having an exposed shape is prepared, and that each electrode component is brought into contact with a positive or negative electrode battery case or terminal, whereby current collection between the electrode group and the battery case can be secured. According to this method, there is no need to provide a useless space or an insulating plate between the electrode group and the battery case, and the discharge capacity can be increased. In addition, the battery case and the conventional bent tab terminal welded to the electrode and the electrode do not cause a short circuit and have excellent safety and reliability.

The exposed portion of the electrode member of the electrode group may be in direct contact with the electrode case or the terminal, or electrically indirectly via a metal foil, a metal net, a metal powder, a carbon filler, a conductive paint, or the like. You may be in contact.

Although a number of winding methods are conceivable, a method in which a strip-shaped positive electrode and a negative electrode with a separator interposed therebetween are wound while facing each other is excellent.
According to this winding method, it can be used effectively from the beginning to the end of the electrode winding. Furthermore, since there is no space at the center of the winding core of the wound electrode, when a flat spiral electrode is used, the electrode can be effectively used because the electrode at the beginning of winding is also opposed.

The wound electrode group may be a wound electrode group, but may be used as a wound electrode group. A spiral electrode is preferred. Since the internal volume of a flat non-aqueous electrolyte secondary battery such as a coin or button is small, the internal volume of the battery is limited. Many electrodes can be loaded. In addition, the adhesion between the positive and negative electrodes via the separator is improved. Regarding the improvement of adhesion, a flat spiral electrode that is wound and pressed while folding the negative electrode so as to have the positive and negative electrode facing parts in the horizontal direction with respect to the flat surface of the flat battery is more favorable, Is also less likely to occur.

Next, as for the electrodes, for the positive and negative electrodes, a conventional method of molding a granular mixture or a method of filling the mixture into a metal base such as a metal net or nickel foam may be used. From the standpoint of ease, a slurry mixture is preferably applied to a metal foil and dried, and a rolled product thereof can also be used. In the case of using an electrode in which a mixture layer containing an active substance is applied to such a metal foil, the electrode used inside the electrode group should have an active substance layer formed on both sides of the metal foil. Preferably from the top, for the electrode component exposed portion contacting the battery case at both ends of the electrode group, of the electrode component to reduce the contact resistance,
In particular, it is preferable to expose the metal foil. In this regard, an electrode having an active substance layer formed only on one side may be used only for this portion, or an active substance layer may be formed on both sides, and then the active substance layer may be removed only on one side.

The structure of the battery will be described below. The electrode group is set in a metal container and sealed using a sealing plate.
In this case, an opening is provided in a part of the sealing plate, and a terminal electrically integrated with the current collector is arranged in the opening. The current collector and the sealing plate are insulated by an insulator. The current collection of the electrodes is performed by a metal container and a current collector, and the polarity of the positive electrode and the negative electrode may be either.

Regarding the battery sealing structure, a metal negative electrode case also serving as an electrode terminal and a metal case also serving as a positive electrode terminal are fitted via an insulating gasket, and the case or the negative electrode case is caulked by crimping. The container may have a closed sealing structure, but preferably has a sealing structure in which the sealing portion of the container which does not transmit moisture in the outside air and has excellent long-term storage properties is sealed by laser welding.

The insulator may be any as long as the sealing plate and the negative electrode terminal are insulated and have excellent airtightness. Examples of the insulator include glass, olefin resins such as polypropylene and polyethylene, epoxy resins, and fluororesins. And polyphenylene sulfide resin, polyethylene terephthalate resin, polybutylene terephthalate resin, polymethylpentene resin, and those obtained by mixing a filler such as glass fiber into these resins.

The present secondary battery focuses on the structure of the battery including the electrodes, and the active material of the positive electrode is not limited. MnO ₂ , V ₂ O ₅ , Nb ₂ O ₅ , LiTi
Metal oxides such as ₂ O ₄ , Li ₄ Ti ₅ O ₁₂ , LiFe ₂ O ₄ , lithium cobaltate, lithium nickelate, lithium manganate, or inorganic compounds such as graphite fluoride, FeS ₂ , or polyaniline or polyacene structures Any substance such as an organic compound such as a body can be applied. However, lithium-containing oxides in which lithium cobalt oxide, lithium nickelate, lithium manganate, mixtures thereof, and some of these elements are replaced with other metal elements, because of their high operating potential and excellent cycle characteristics. Is more preferable, and the flat non-aqueous electrolyte secondary battery, which may be used for a long period of time, has a high capacity, a low reactivity with an electrolytic solution or moisture, and is chemically stable. Is more preferred.

Next, the negative electrode active material of the secondary battery is not limited, and may be metallic lithium or Li-A
1, Li-In, Li-Sn, Li-Si, Li-G
e, a lithium alloy such as Li-Bi, Li-Pb, an organic compound such as a polyacene structure, a carbonaceous material capable of absorbing and releasing lithium, or Nb ₂
Oxides such as O ₅ , LiTi ₂ O ₄ , Li ₄ Ti ₅ O _12, and oxides such as Li-containing silicon oxides can be applied, but they have excellent cycle characteristics, low operating potential, and high capacity. A carbonaceous material capable of occluding and releasing Li is preferable in terms of the point, and in particular, natural graphite, artificial graphite, expanded graphite, mesophase pitch fired body, mesophase pitch fiber fired body, etc. in that the operating voltage of the battery is small even at the end of discharge. carbonaceous material spacing of the d ₀₀₂ is less graphite structure 0.338mm has developed is more preferable.

[0022]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention and comparative examples will be described in detail. (Example 1) FIG. 1 is a sectional view of a battery according to Example 1 of the present invention. Hereinafter, a method for manufacturing the battery of Example 1 will be described.
First, 5 parts by mass of acetylene black and 5 parts by mass of graphite powder were added as conductive agents to 100 parts by mass of LiCoO ₂ .
5 parts by mass of polyvinylidene fluoride as a binder,
-Methylpyrrolidone was diluted and mixed to obtain a slurry-like positive electrode mixture. Next, this positive electrode mixture is applied to one surface of a 0.02 mm thick aluminum foil as a positive electrode current collector by a doctor blade method and dried, and a positive electrode active substance-containing layer (positive electrode) 2 is formed on the aluminum foil surface. Formed. Thereafter, coating until the coating thickness of the positive electrode active substance containing layer 2 is 0.15 mm on both sides,
The drying was repeated to produce a double-sided coated positive electrode. Next, the active substance-containing layer of 10 mm from the end of one side of the electrode body was removed, and the aluminum layer was exposed to form a current-carrying part.
m, a positive electrode plate cut to a length of 120 mm was prepared.

Next, styrene butadiene rubber (SBR) and carboxymethyl cellulose (CMC) were used as binders in 100 parts by mass of the graphitized mesophase pitch carbon fiber powder.
Was added and diluted with ion-exchanged water and mixed to obtain a slurry-like negative electrode mixture. The obtained negative electrode mixture is applied to a 0.02 mm-thick copper foil serving as a negative electrode current collector in the same manner as the positive electrode so that the thickness of the negative electrode active material-containing layer (negative electrode) 4 becomes 0.15 mm. And drying were repeated to produce a double-sided coated negative electrode. Next, a 10 mm portion of the active substance-containing layer was removed from one end of the electrode body, and the copper layer was exposed to form a current-carrying part.
To produce a negative electrode plate cut into a length.

Next, the surface of the current-carrying portion of the positive and negative electrodes is set as the outer peripheral winding end side, and spirally wound between the positive electrode and the negative electrode with a separator 3 made of a 25 μm-thick polyethylene microporous film interposed therebetween to form a flat battery. Pressure was applied in a certain direction so that the space at the center of the wound electrode was exhausted so as to have the positive and negative electrode facing portions in the horizontal direction with respect to the flat surface. The total area of the positive and negative electrodes facing each other via the separator of this battery is 34.5 cm ² .

The prepared electrode group was dried at 85 ° C. for 12 hours, and then subjected to insulation treatment by applying SBR to the inner surface. A positive electrode metal case (positive electrode case) having an opening diameter of 20 mm and an opening area of 3.14 cm 2 was obtained. 1 was placed so that the uncoated side of the one-side coated positive electrode plate of the electrode group was in contact with the inner bottom surface of the electrode group 1, and LiPF ₆ was used as a supporting salt in a solvent in which ethylene carbonate and methyl ethyl carbonate were mixed at a volume ratio of 1: 1.
Was dissolved at a rate of 1 mol / l, and a non-aqueous electrolyte was injected. At the center of the sealing plate (negative electrode case) 5, a negative electrode current collector 8 electrically integrated with the negative electrode terminal 6 is provided, and the uncoated side of the single-side coated negative electrode plate of the electrode group comes in contact with the negative electrode current collector 8. I have. The negative electrode terminal 6 and the negative electrode case 5 are electrically insulated by a glass seal (insulator) 7. Positive case 1
And the negative electrode case 5 are sealed by laser welding, and the total height is 5 m.
m, a flat nonaqueous electrolyte secondary battery of Example 1 having a diameter of 21.0 mm was produced.

(Example 2) A band-shaped positive electrode and a negative electrode group with a separator interposed therebetween were wound while being folded at a fixed distance so as to have a positive and negative electrode facing portion in the horizontal direction with respect to the flat surface of the flat battery. A battery was fabricated in the same manner as in Example 1 except that the electrode group was used, and the battery was defined as Example 2.

Comparative Example 1 5 parts by mass of acetylene black and 5 parts by mass of graphite powder were added as conductive agents to 100 parts by mass of LiCoO _2, and 5 parts by mass of polytetrafluoroethylene were added as a binder, and mixed. And pulverized to obtain a granular positive electrode mixture. Next, this positive electrode granule mixture was subjected to pressure molding to a diameter of 19 mm and a thickness of 1.15 mm to obtain a positive electrode tablet 2a.

Next, 2.5 parts by weight of SBR and CMC were added as binders to 100 parts by weight of the graphitized mesophase pitch carbon fiber powder, mixed, dried, and further pulverized to obtain a granular negative electrode mixture. . The obtained negative electrode granule mixture was subjected to pressure molding to a diameter of 19 mm and a thickness of 1.15 mm to obtain a negative electrode tablet 4a. 85 of these positive and negative electrode tablets
Example 1 except that the positive and negative tablets 2a and 4a were separated by a separator 3a.
A battery was prepared in the same manner as in Example 1 to obtain a battery of Comparative Example 1 in FIG.

The batteries of Examples 1 and 2 and Comparative Example 1 produced as described above were initially charged at a constant current and voltage of 4.2 V and 3 mA for 48 hours. Thereafter, discharging was performed at a constant current of 30 mA to 3.0 V to determine a heavy load discharge capacity. Table 1 shows the results. As is clear from Table 1, in the batteries of Examples 1 and 2 of the present invention, the facing areas of the positive and negative electrodes using the tablet-shaped electrodes prepared by the conventional granule mixture molding method of Comparative Example 1 were larger than the area of the sealing plate. In addition, the battery has only one opposing surface of the positive and negative electrodes of Comparative Example 1 and the battery of Comparative Example 1, and the discharge capacity at the time of heavy load discharge is significantly larger than that of the battery having a small opposing area.
Regarding the difference in the winding method, the method in which the electrode is wound while being folded as in Example 2 has better current collection between the electrode layers and has a better heavy load characteristic.

[0030]

[Table 1]

In the embodiment of the present invention, a flat non-aqueous solvent secondary battery using a non-aqueous solvent for the non-aqueous electrolyte has been described.
Naturally, it can be applied to a polymer secondary battery using a polymer electrolyte as a non-aqueous electrolyte or a solid electrolyte secondary battery using a solid electrolyte, and a polymer thin film or solid electrolyte membrane can be used instead of a resin separator. It is. Also, the positive and negative electrodes can be exchanged. Further, the shape of the battery does not need to be a perfect circle, and the present invention can be applied to a flat nonaqueous electrolyte secondary battery having a special shape such as an oval shape or a square shape.

[0032]

As described above, according to the present invention,
The flat battery has a small battery size, and while maintaining the advantages of excellent productivity, the discharge capacity at the time of heavy load discharge is significantly greater than conventional batteries, and has a very large industrial value. A flat nonaqueous electrolyte secondary battery can be provided.

[Brief description of the drawings]

FIG. 1 is a sectional view of a battery according to a first embodiment of the present invention.

FIG. 2 is a cross-sectional view of a battery of Comparative Example 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode metal case (positive electrode case), 2, 2a ... Positive electrode active substance containing layer (positive electrode), 3,3a ... Separator, 4,4
a: negative electrode active material-containing layer (negative electrode), 5: sealing plate (negative electrode case), 6: negative electrode terminal, 7: glass seal, 8: negative electrode current collector.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuo Udagawa 3-4-10 Minamishinagawa, Shinagawa-ku, Tokyo Toshiba Battery Corporation F-term (reference) 5H022 AA09 AA18 BB01 CC03 CC05 CC16 EE01 5H029 AJ02 AJ14 AK01 AK02 AK03 AK03 AK05 AK16 AL02 AL03 AL06 AL07 AL12 AL16 AM03 AM05 AM07 BJ03 BJ14 CJ03 CJ07 DJ05 DJ07 EJ01 HJ12

Claims (6)

[Claims] 1. A metal battery case also serving as an electrode terminal, and a part of a sealing plate for sealing the battery case is opened,
The other electrode terminal is disposed in the opening, the sealing plate also serving as an electrode terminal and the other electrode terminal are electrically insulated by an insulator, and an electrode group including at least a positive electrode, a separator, and a negative electrode therein, and a non-electrode terminal. A flat non-aqueous electrolyte secondary battery including a flat non-aqueous electrolyte secondary battery including a water electrolyte, wherein the sum of the positive and negative electrode facing areas is larger than the area of the sealing plate. 2. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein an electrode group formed by winding a strip-shaped positive electrode and a negative electrode via a separator is housed in a battery case. 3. An electrode group formed by winding a strip-shaped positive electrode and a negative electrode with a separator interposed therebetween is formed on a flat surface of a flat battery so as to have a positive and negative electrode facing portion in a horizontal direction with respect to the flat surface of the flat battery. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the flat spiral electrode pressed in a vertical direction is housed in a battery case. 4. An electrode group formed by winding a strip-shaped positive electrode and a negative electrode with a separator interposed therebetween is formed on the flat surface of the flat battery so as to have a positive and negative electrode facing portion in the horizontal direction with respect to the flat surface of the flat battery. A flat spiral electrode which is pressed in a vertical direction and has no space in the core portion of the wound electrode, and the opposed electrodes of the core portion are in close contact with each other via a separator, is housed in the battery case. The flat nonaqueous electrolyte secondary battery according to claim 1. 5. A flat spiral, which is a group of wound electrodes, while folding a strip-shaped positive electrode and a negative electrode via a separator so as to have a positive-negative electrode facing portion in a horizontal direction with respect to the flat surface of the flat battery. The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the electrode is housed in a battery case. 6. The positive electrode comprises a positive electrode plate having a positive electrode active material layer formed on one or both sides of a positive electrode current collector, and the negative electrode has a negative electrode plate having a negative electrode active material layer formed on one or both surfaces of a positive electrode current collector. The active material layer is formed only on one side at each end of the electrode plates, and the exposed current collector is a sealing plate,
The flat nonaqueous electrolyte secondary battery according to claim 1, wherein the flat nonaqueous electrolyte secondary battery is in contact with another terminal.