JP2002093404A - Flat battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a flat battery with high reliability and safety for preventing occurrence of a micro short-circuit and an internal short-circuit in an electrode group wound in an elliptic shape. SOLUTION: This flat battery has the electrode group formed by winding in the elliptic shape a positive plate and a negative plate having a collector coated with a liquid containing electrode active material via a separator. The electrode group is formed by setting a range within 5 mm or less from the innermost peripheral side end of the positive plate as a non-applied part, further preferably, setting the inner surface or both surfaces of the first bending part wound in the elliptic shape in the innermost peripheral part of the positive plate as a non-applied part, and setting the inner surface of a bending part of the negative plate facing the non-applied part of the end of the positive plate as a non-applied part, and these non-applied parts of the positive plate and the negative plate are covered with an insulating tape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an electrode group in a flat battery.

[0002]

2. Description of the Related Art A non-aqueous electrolyte secondary battery such as a lithium ion battery generally has a high battery voltage and a high energy density, and is therefore used as a power source for portable equipment such as a mobile phone and a notebook personal computer which consume relatively large power. Widely used.

[0003] In such a non-aqueous electrolyte secondary battery, the ionic conductivity of the non-aqueous electrolyte used therein is lower than that of the aqueous electrolyte, so that the thickness of the electrode mixture layer formed on the current collector is reduced. It is necessary to reduce the thickness and increase the electrode area. In the non-aqueous electrolyte secondary battery, a sheet obtained by applying and drying a coating liquid containing the electrode active material on a current collector such as a metal foil to increase the filling amount of the electrode active material, and rolling the sheet. A spirally wound structure in which a cylindrical electrode plate is wound in a cylindrical or elliptical shape via an isolator, or a laminated structure in which sheet electrode plates are stacked via an isolator. A method is employed in which the group is housed in a cylindrical or square outer can or an outer body made of a laminate sheet composed of a metal foil and a resin film.

[0004]

However, in a flat type battery having an electrode group having an elliptical winding structure, the radius of curvature is small at the innermost periphery where the electrode plate is wound.
This is the same state as when the electrode plate is bent at approximately 180 degrees. At this time, if the electrode mixture layer is hard, the electrode mixture layer may break through the current collector during winding, and the electrode plate may be cut. In addition, if the adhesiveness between the electrode mixture layer and the current collector is not sufficient, the electrode mixture layer may be peeled off from the current collector during winding and fall off.

[0005] In this manner, if the cut electrode plate or the dropped electrode mixture layer piece breaks through the separator and comes into contact with another electrode plate of another polarity, an internal short circuit of the battery occurs. In some cases. Also, even when the dropped electrode mixture layer piece stays between the electrode plates via the separator, current concentration occurs at that portion to precipitate lithium metal and cause a minute internal short circuit (small short circuit). In some cases, this may cause deterioration in characteristics such as a decrease in capacity due to an increase in the amount of self-discharge in the battery.

In a conventional flat type non-aqueous secondary battery, the negative electrode mixture lacks adhesiveness to a copper foil as a current collector and may fall off during winding. As a countermeasure, a countermeasure is taken to make the inner surface of the first bent portion at the innermost periphery of the negative electrode plate an uncoated portion (Japanese Patent Laid-Open No. 2000-21452). Can be prevented to some extent.

However, in this case alone, there is no negative electrode active material that occludes lithium in the uncoated portion of the negative electrode plate, so that during charging, metallic lithium released from the innermost peripheral end of the opposing positive electrode plate is not charged. There is a possibility that a minute short circuit may occur due to deposition on the uncoated portion of the current collector. Similarly, in the first bent portion of the innermost peripheral portion of the positive electrode plate, if the innermost peripheral portion of the positive electrode mixture layer is hard, the positive electrode mixture layer breaks through the current collector or the positive electrode mixture falls off. In some cases, inconveniences such as an internal short circuit and a decrease in discharge capacity were caused.

[0008]

Accordingly, the present invention provides a sheet-like positive electrode plate and a negative electrode plate obtained by applying a coating solution containing an electrode active material to a current collector such as a metal foil. By devising the processing pattern, it prevents the electrode mixture layer from falling off and deposits of metallic lithium, does not cause a micro short circuit, and is a flat type that has both good charge / discharge cycle characteristics and high reliability and safety. The purpose is to produce batteries.

First, the first invention of the present application relates to an electrode in which a positive electrode plate and a negative electrode plate each formed by applying a coating liquid containing an electrode active material on a current collector are wound in an elliptical shape with a separator interposed therebetween. In a flat type battery including a group, an uncoated portion is provided at an innermost end of the positive electrode plate. According to the first invention of the present application, by providing an uncoated portion at the end of the innermost peripheral portion of the positive electrode plate,
It is possible to prevent the deposition of metallic lithium due to charging and discharging on the current collector in the uncoated portion of the negative electrode plate opposed thereto.

In the second invention of the present application, the dimension of the uncoated portion of the positive electrode plate in the longitudinal direction of the electrode plate is 5 mm from the innermost peripheral end.
It is assumed that: According to the second invention of the present application,
The uncoated portion of the positive electrode plate needs to have a dimension in the longitudinal direction of the electrode plate just opposite to the uncoated portion of the negative electrode plate facing the same. The amount of the positive electrode active material such as LiCoO ₂ that supplies ions is reduced, and the discharge capacity of the battery is unnecessarily reduced. Therefore, the range of the uncoated portion of the positive electrode plate at the tip of the innermost peripheral portion was determined to be sufficient if it was at most 5 mm from the end.

Next, the third invention of the present application is characterized in that, on the innermost peripheral portion of the positive electrode plate, the inner surface or both surfaces of the first bent portion wound in an elliptical shape are uncoated portions. According to the third invention of the present application, it is possible to prevent the first bent portion of the positive electrode plate from being broken at the time of winding, and to prevent the positive electrode plate from being cut or the positive electrode mixture layer from falling off.

Further, the fourth invention of the present application is characterized in that, in the electrode group, the inner surface of the first bent portion of the negative electrode plate facing the uncoated portion of the positive electrode plate is an uncoated portion. Here, the bent portion of the negative electrode plate facing the uncoated portion of the positive electrode plate refers to a portion including the bent semicircular shape portion and being close to the uncoated portion of the positive electrode plate. According to the fourth invention of the present application, it is possible to prevent the first bent portion of the negative electrode plate from being broken at the time of winding, and to prevent the negative electrode plate from being cut or the negative electrode mixture layer from falling off.

Finally, the fifth invention of the present application is characterized in that, in the electrode group, uncoated portions of the positive electrode plate and the negative electrode plate are covered with an insulating tape.

In the portion where the uncoated portion exists, the current collector is wound with the aluminum foil or copper foil exposed, and the current collectors contact each other to cause an internal short circuit. In such a case, the short-circuit current becomes larger than when the electrode mixtures come into contact with each other, and therefore, more heat is generated.

According to the fifth aspect of the present invention, since the contact between the current collectors can be prevented, it is possible to enhance the safety of the battery when a short circuit occurs.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A flat type battery is usually formed into a thin sheet or foil shape, and the cut positive electrode plate and negative electrode plate are sequentially laminated via a separator (laminated type) or a spiral shape. In the latter case, in particular, in the case of the latter, by forming the cross section into an elliptical electrode group shape, it is possible to increase the electrode surface area, Charge and discharge.

As one mode of the flat battery according to the present invention,
FIG. 1 shows a structure of a nonaqueous electrolyte secondary battery housed in an outer can made of iron (nickel plating). This flat battery has an electrode group 1 in which a sheet-like positive electrode plate 2 and a negative electrode plate 3 are wound in an oval shape via an isolator 4, and this electrode group 1 is impregnated with a non-aqueous electrolyte (not shown). The battery case 6 is housed in the battery case 6, and the battery case 6 is hermetically sealed by a lid 7 having a safety valve 8 which is opened when the battery internal pressure rises abnormally.
Then, the outermost end of the positive electrode plate forming the electrode group is not coated with the positive electrode mixture, and serves as the positive electrode current collecting lead 10 as the cover 7.
Is connected to the electrically insulated positive electrode terminal 9, and the outermost end of the negative electrode plate is connected to the lid 7 as a negative electrode current collecting lead 11 (not shown) in a state where the negative electrode mixture is not applied. ing.

The battery case 6 used in the flat battery of the present invention may be a rectangular metal case made of a metal such as stainless steel, nickel-plated iron or aluminum, or aluminum or the like. (PE) or polyethylene terephthalate (PET) for metal foil
Or an outer bag made of a laminated sheet formed by laminating resin films such as those described above.

FIG. 2 shows the structure of the innermost periphery of the electrode group 1 according to the present invention. In the innermost peripheral portion of the electrode group 1 wound in an elliptical shape, both surfaces of the portion 2A within a range of 5 mm or less from the innermost peripheral end of the positive electrode plate 2 and the innermost peripheral portion have an oval shape. The inner surface or both surfaces of the wound first bent portion 2B is an uncoated portion, and the inner surface of the bent portion 3B of the negative electrode plate facing the uncoated portion at the innermost end of the positive electrode plate is not coated. Department. And, by providing such an uncoated portion, it is possible to prevent the electrode plate from being cut or the electrode mixture layer from falling off,
This has made it possible to provide a highly reliable flat battery that does not cause a capacity reduction or the like due to an internal short circuit or a minute short circuit.

Then, in order to arrange the above-mentioned uncoated portion when the positive electrode plate and the negative electrode plate are wound to form an electrode group, a predetermined coating pattern is used in the electrode plate manufacturing process. This is realized by applying a coating liquid containing a substance. Further, after coating and drying the positive electrode plate and the negative electrode plate, and after performing the rolling process, as shown in FIG. 3, the insulating tape 5 is attached to the uncoated portions 2A, 2B and 3B, and the uncoated portions are removed. By covering with an insulator, it is possible to prevent the electrode plate from being cut or the electrode mixture layer from falling off, thereby realizing a flat battery with higher safety and reliability that does not cause internal short circuit.

The insulating tape used in the present invention includes:
It is necessary to have high heat resistance and not to be dissolved in an organic electrolyte, and a polyimide resin tape is preferable. Also, if the thickness of the insulating tape is too large, a gap is generated between the electrode and the separator in the portion where the tape is stuck, and the electrode group is likely to undulate, so that the thickness of the insulating tape is 100 μm or less,
Further, the thickness is preferably 50 μm or less.

The positive electrode active material contained in the positive electrode plate of the present invention
If it is a substance that can occlude and release lithium ions
Often, metal oxides (LiCoO_Two, LiNiO_Two, LiM
n_TwoO_Four, MnO_Two, MoO_Two, CuO, Cr_TwoO_Three, CrO
_Three, V_TwoO_Five, NiOOH, etc.), metal sulfides (FeS,
TiS_Two, MoS_TwoEtc.), metal selenides (TiSe _Two
And the like). In addition, it is selected from these
May be used as a positive electrode active material by mixing
No.

Examples of the conductive agent used for the positive electrode plate include acetylene black, Ketjen black, furnace black, and the like alone or in combination. Examples of the binder include polyvinylidene fluoride, polytetrafluoroethylene, a rubber-based polymer, a mixture of these with a cellulose-based polymer, and a copolymer mainly containing polyvinylidene fluoride.

The negative electrode active material contained in the negative electrode plate of the present invention includes lithium metal, lithium aluminum alloy, pyrolytic carbon, cokes, graphites such as natural graphite and artificial graphite, organic polymer compound fired bodies, carbon It is also possible to use a carbonaceous material such as fiber or activated carbon, which stores and releases lithium, or a polymer material such as polypyrrole and polyacetylene. Note that a plurality of substances selected from these may be mixed and used as the negative electrode active material.

Examples of the conductive agent and the binder used for the negative electrode plate include, but are not limited to, those used for the positive electrode plate.

The non-aqueous electrolyte used in the present invention includes:
Generally, a non-aqueous electrolyte in which a lithium salt as an electrolyte is dissolved in an aprotic organic solvent is used. Examples of the solvent for the non-aqueous electrolyte include ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, carbonates such as methyl ethyl carbonate, γ-butyl lactone, 1,2-dimethoxyethane,
Tetrahydrofuran, 2-methyltetrahydrofuran,
Organic solvents such as methyl propionate may be used alone or as a mixture of two or more.

The electrolyte of the non-aqueous electrolyte is LiCl
O ₄ , LiAsF ₆ , LiPF ₆ , LiBF ₄ , LiCF ₃
SO ₃ , LiN (CF ₃ SO ₂ ) _{2 and the} like can be used alone or in combination of two or more. Among them, LiPF ₆ is most desirable.

As the separator in the flat battery of the present invention, a microporous membrane (separator) made of an insulating and porous polyethylene resin or the like is used. The separator may be formed by laminating a plurality of microporous films having different types, properties or film characteristics of the resin. Further, in addition to such a separator, a polymer solid electrolyte, a gel electrolyte in which the non-aqueous electrolyte is contained in the polymer solid electrolyte, or the like can be used as the separator. Examples of the polymer solid electrolyte here include polyvinylidene fluoride, polyethylene oxide, polyacrylonitrile, polyethylene glycol, and modified substances thereof. Further, an insulating microporous film and a solid polymer electrolyte may be used in combination. Further, when a porous solid polymer electrolyte membrane is used as the solid polymer electrolyte, the nonaqueous electrolyte contained in the polymer and the nonaqueous electrolyte contained in the pores may be different. Therefore, the non-aqueous electrolyte used in the present invention includes such a solid polymer electrolyte and a gel electrolyte.

[0029]

EXAMPLES Hereinafter, embodiments of the present invention will be described in detail based on examples of a non-aqueous electrolyte secondary battery provided with a non-aqueous electrolyte. However, the present invention is not limited to the following examples. Needless to say, the present invention can be implemented by appropriately changing the scope without changing the gist.

Example 1 (Preparation of Positive Electrode Plate) LiCoO ₂ was used as a positive electrode active material in an amount of 95%.
% Of acetylene black as a carbon-based conductive agent, and polyvinylidene fluoride (PVd) as a binder.
F) in a proportion of 3% by weight and further add N-methyl-2.
-A mixture to which pyrrolidone (NMP) was added was kneaded to obtain a positive electrode paste (coating liquid). Next, this positive electrode paste was
Intermittent coating was performed according to a predetermined coating pattern on an electrode substrate made of an aluminum foil having a thickness of 5 μm, and after drying, pressing was performed so that the porosity of the electrode mixture layer became 30%. Then, the positive electrode plate was cut out from the long positive electrode plate sheet such that both surfaces within a range of 2 mm from the outermost end of the positive electrode terminal lead portion and the innermost end were uncoated portions.

(Preparation of Negative Electrode Plate) Mesocarbon microbeads made of mesophase microspheres having a two-layer structure having a layer of non-graphitizable carbon on the surface generated in the carbonization process of pitch were used as a negative electrode active material at 96% by weight. Polyvinylidene fluoride (PVdF) was mixed at a ratio of 4% by weight as a binder,
The mixture to which N-methyl-2-pyrrolidone (NMP) was added was kneaded to obtain a negative electrode paste (coating liquid). Next, this positive electrode paste is intermittently applied to an electrode substrate made of a copper foil having a thickness of 15 μm according to a predetermined coating pattern, and after drying, is pressed so that the porosity of the electrode mixture layer becomes 35%. did.
Then, 35 m from both sides of the outermost side negative electrode terminal lead portion and the innermost side end from this long negative electrode plate sheet.
The negative electrode plate was cut out so that one side in a range of m to 39 mm was an uncoated portion.

(Preparation of Electrode Group) The uncoated portion on one side of the negative electrode plate becomes the inner surface of the first bent portion when wound, and further the uncoated portion at the innermost peripheral tip of the positive electrode plate. The positive and negative bipolar plates and the separator were simultaneously wound so as to face each other to form an electrode group. As the separator, a polyethylene microporous membrane (separator) having a thickness of 25 μm and a porosity of 40% was used.

(Preparation of Test Battery) The above electrode group was 30 m in width.
A non-aqueous electrolyte secondary battery having a structure as shown in FIG. 1 was housed in a square battery outer can having a size of mx 48 mm in height x 5 mm in thickness, and further filled with a non-aqueous electrolyte by sealing the lid. Example 1] was produced. FIG. 2 shows the structure of the innermost periphery of the electrode group in the battery of Example 1. Non-aqueous electrolytes include ethylene carbonate (EC) and diethyl carbonate (D
A mixture of 1 mol / liter of LiPF ₆ as a lithium salt in a mixed solvent having a volume ratio of 1: 1 with EC) was used.

Example 2 The same procedure as in Example 1 was carried out except that the electrode plate was cut out so that both surfaces within a range of 5 mm from the innermost end of the positive electrode plate were uncoated. An electrolyte secondary battery [Example 2] was produced.

Example 3 Both sides within a range of 2 mm from the innermost end of the positive electrode plate and both sides within a range of 35 mm to 39 mm from the innermost end of the positive electrode plate are uncoated portions. A non-aqueous electrolyte secondary battery [Example 3] was produced in the same manner as in Example 1, except that the electrode plate was cut out as described above.

Example 4 Both surfaces within a range of 2 mm from the innermost end of the positive electrode plate and 35 m from the innermost end.
The electrode plate was cut out so that one side in the range of m to 39 mm was an uncoated portion. Then, an electrode group was formed using the same negative electrode plate and separator as in Example 1 so that the latter single-side uncoated portion was located on the inner surface of the innermost peripheral bent portion in the wound electrode group. In the same manner as in Example 1, a nonaqueous electrolyte battery [Example 4] was produced.

Example 5 A 30 μm-thick polyimide tape was applied to the positive electrode plate and the negative electrode plate cut out in the same manner as in Example 3 so as to completely cover the uncoated portions other than the lead joints. Then, the positive and negative bipolar plates and the same separator as in Example 1 were simultaneously wound to form an electrode group, and a nonaqueous electrolyte battery [Example 5] in the same manner as in Example 1.
Was prepared. FIG. 3 shows the structure of the innermost periphery of the electrode group in the battery of Example 5.

[Comparative Example 1] A non-aqueous electrolyte was cut out in the same manner as in Example 1 except that no uncoated portion was provided near the innermost end of both the positive and negative electrode plates. A battery [Comparative Example 1] was produced. FIG. 4 shows the structure of the innermost periphery of the electrode group in the battery of Comparative Example 1.

Comparative Example 2 A non-aqueous electrolyte battery was cut in the same manner as in Example 1 except that the electrode plate was cut out without providing an uncoated portion near the innermost end of the positive electrode plate. [Comparative Example 2] was produced.

[Comparative Example 3] 8 minutes from the innermost end of the positive electrode plate
A non-aqueous electrolyte battery [Comparative Example 3] was produced in the same manner as in Example 1, except that the electrode plate was cut out such that both sides in the range of mm were uncoated portions.

[Comparative Example 4] 1 point from the innermost end of the positive electrode plate
A non-aqueous electrolyte battery [Comparative Example 4] was produced in the same manner as in Example 1, except that the electrode plate was cut out so that both sides in a range of 1 mm were uncoated portions.

[Initial Capacity Test Method] Ten batteries of each of the above Examples and Comparative Examples were placed in a constant temperature room at an ambient temperature of 25 ° C., and a charge / discharge test was performed under the following charge / discharge conditions to measure the initial capacity of the batteries. Charging condition: 570 mA constant current, 4.2 V constant voltage × 5 h Discharging condition: 570 mA constant current, final voltage 3.0 V [Charge / discharge cycle test method] Ten batteries of the above example and comparative example were each subjected to an ambient temperature of 25 ° C. The sample was placed in a constant temperature room, and a charge / discharge cycle test was performed under the following charge / discharge conditions. Charging conditions: 570 mA constant current, 4.2 V constant voltage × 5 h Discharging conditions: 570 mA constant current, final voltage 3.0 V The charge / discharge cycle test was continued until the discharge capacity of each test battery dropped to 80% of the initial capacity. .

[Results of Initial Capacity Test and Charge / Discharge Cycle Test] The initial capacity of each battery in the batteries of the above Examples and Comparative Examples and the number of cycles when the capacity retention rate of the battery reached 80% of the initial capacity were as follows. Is shown in Table 1. Table 1
Are the average values of 10 test batteries.

[0044]

[Table 1] Note: In Example 5, the insulating tape was attached to the uncoated part of the positive and negative bipolar plates of Example 3.

From the test results in Table 1, it can be seen that the cycle characteristics of the batteries of Comparative Examples 1 and 2 were significantly inferior. In Comparative Example 1, since the negative electrode mixture on the inner surface was detached at the first bent portion in the innermost peripheral portion of the negative electrode plate by winding, the detached mixture was formed between the positive electrode plate and the negative electrode plate. It is considered that a minute short circuit was generated while charging and discharging were interposed in between, and the capacity deterioration was increased early. Further, in Comparative Example 2, the positive electrode mixture layer was present on the positive electrode plate facing the uncoated portion of the negative electrode plate, and the carbon material that occludes lithium ions released from the positive electrode active material during charging was used as the negative electrode plate. Because it does not exist, metal lithium is deposited on the copper foil, which is the current collector, and the amount of deposition increases as the charge / discharge cycle elapses, causing a minute short circuit with the positive electrode plate. It is considered that the capacity decrease was large.

Further, as can be seen from the test results of Comparative Examples 3 and 4, increasing the uncoated portion of the positive electrode plate reduces the amount of the positive electrode active material in the battery, that is, the amount of lithium ions involved in charge and discharge. It is merely a matter of decreasing, and increasing the uncoated portion more than necessary will decrease the initial capacity of the battery itself. For this reason, the uncoated portion of the positive electrode plate may have a size sufficient to prevent the occurrence of the micro short circuit due to the deposition of metallic lithium, and the longest is 5 mm from the end.
That is enough.

Next, regarding the cycle life characteristics, the batteries of Examples 3, 4 and 5 are particularly excellent. In the batteries of Examples 1 and 2 and Comparative Examples 1 to 4, as compared with the portion where the positive electrode plate and the negative electrode plate face in parallel, the innermost peripheral portion of the first bent portion at the inner side of the positive electrode plate has The amount of the mixture is excessive with respect to the amount of the mixture at the innermost peripheral tip portion of the negative electrode plate opposed thereto. For this reason, at the tip of the innermost periphery of the negative electrode plate, during charging, lithium ions exceeding the occlusion capacity of the negative electrode are released from the positive electrode, and the discharge capacity is increased due to an increase in the deposition amount of metallic lithium as the charge-discharge cycle progresses. Is thought to have decreased gradually. On the other hand, in Example 3, Example 4 and Example 5, since the mixture layer containing the active material does not exist on the inner surface of the first bent portion from the innermost circumference of the positive electrode plate, as described above, It is possible to prevent an increase in the precipitation of metallic lithium due to the progress of the cycle. Therefore, it is considered that the cycle life characteristics were further improved.

Next, in an electrode group in which a positive electrode plate and a negative electrode plate are wound in an oval shape with a separator interposed therebetween, an electrode group in which uncoated portions existing on the positive electrode plate and the negative electrode plate are covered with insulating tape is used. We examined the effect that it had on battery safety.

[Insulation Test] Each of the batteries of Examples 3 and 5 and Comparative Example 1 was manufactured in 1000 pieces, and 250 cells were placed between the positive electrode terminal and the negative electrode (bottom of the battery case) before injecting the electrolyte.
A voltage of V was applied and the insulation resistance was measured. A battery having an insulation resistance of 80 MΩ or less was regarded as a poorly-insulated battery. In such a battery, the electrode mixture dropped from the electrode was interposed between the positive and negative electrode plates and pressed the separator, thereby narrowing the gap between the electrode plates and damaging the separator when a high voltage was applied. Is determined.

[Drop test] Of the 1000 batteries of each of Examples 3, 5 and Comparative example 1, a test battery in which insulation failure was not found in the insulation test was used.
The battery was overcharged at an ambient temperature of 25 ° C. under the following conditions, the battery voltage was measured, and a drop test was performed. Charging conditions: 600 mA constant current, 4.3 V constant voltage × 5 h Drop test condition: 6 times each on a concrete surface from a height of 1.5 m × 10 times. After being left for 48 hours, the battery voltage was measured, and a battery having a voltage drop of 20 mV or more from before the drop test was confirmed. Here, a voltage difference of 20 mV or more occurs before and after the drop test because the electrode mixture falling pieces interposed between the positive and negative electrode plates press the separator due to the impact at the time of dropping,
It is determined that a micro short circuit occurred and caused an increase in the amount of self-discharge during the idle period.

[Insulation Test and Drop Test Results] Table 2 shows the results of the insulation test and the drop test.

[0052]

[Table 2]

In the battery of Comparative Example 1, four defective batteries were found during the battery fabrication process, and a continuous drop test after overcharging confirmed that one of the remaining 996 batteries had a voltage drop. Was done. On the other hand, in the batteries of Example 3 and Example 5, there was not found any battery in which such insulation failure or voltage drop occurred. As a result of disassembling and examining the poorly-insulated battery of Comparative Example 1, traces of sparks on the separator were found, and the electrode mixture dropped from the electrode plate was interposed between the positive and negative electrode plates and pressed the separator. It is assumed that In addition, as a result of disassembling and examining the voltage drop battery of Comparative Example 1, there was a slight shift between the electrode plates in the electrode group, and pieces of the electrode mixture dropped from the electrode plates could not be confirmed. Inferring from the fact that such a phenomenon did not occur in the batteries of Example 3 and Example 5,
It is considered that the electrode mixture flakes are involved.

In the above test, no remarkable difference was found in the test results between the battery of Example 3 and the battery of Example 5. However, when the insulating tape was applied to the uncoated portion, In addition to preventing the electrode mixture from falling off even at the edges, even if the electrode mixture pieces that have fallen off in other parts adhere to the current collector, or if there is a gap between the electrode plates in the electrode group, a tape is used. Since the current collector is insulated and the current collector is not exposed, it is considered that the effect of preventing the occurrence of a micro short circuit or an internal short circuit is large.

[0055]

As described above, according to the present invention, in a flat type battery, a coating portion is formed on the innermost peripheral edge of the positive electrode plate and the bent portion of the innermost peripheral portion of the positive and negative electrode plates. By providing this, it is possible to prevent the electrode mixture layer from falling off and to prevent the deposition of lithium metal, and to provide a battery having both good charge / discharge cycle characteristics and high reliability and safety without causing a micro short circuit. it can. Furthermore, by attaching and covering the uncoated portion with an insulating tape, it is possible to realize a battery that does not cause an internal short circuit even under severe use conditions and that is more excellent in safety. .

[Brief description of the drawings]

FIG. 1 is a diagram showing a structure of a flat battery housing a battery group of the present invention.

FIG. 2 is a diagram showing a structure of an innermost peripheral portion of an electrode group according to the present invention.

FIG. 3 is a diagram showing a structure of an innermost peripheral portion of the electrode group (with an insulating tape attached) according to the present invention.

FIG. 4 is a diagram showing a structure of a conventional innermost peripheral portion of an electrode group.

[Explanation of symbols]

Reference Signs List 1 electrode group 2 positive electrode plate 2a positive electrode current collector (aluminum foil) 2b positive electrode mixture 2c positive electrode lead portion 3 negative electrode plate 3a negative electrode current collector (copper foil) 3b negative electrode mixture 3c negative electrode lead portion 4 separator (separator) 5 Insulation tape 6 Battery case 7 Lid 8 Safety valve 9 Positive electrode terminal 10 Positive electrode current collecting lead 11 Negative electrode current collecting lead 2A Uncoated portion at innermost peripheral edge of positive electrode plate 2B Not applied at first bent portion of innermost peripheral portion of positive electrode plate Coated part 3B Uncoated part in the first bent part of the innermost part of the negative electrode plate

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01M 10/40 H01M 10/40 Z F-term (Reference) 5H022 AA09 AA18 BB03 EE06 KK03 5H028 AA01 AA05 BB07 CC02 CC08 CC13 CC15 EE10 HH06 5H029 AJ12 AK02 AK03 AK05 AK18 AL06 AL07 AL08 AL12 AL16 AM02 AM03 AM04 AM05 AM07 BJ03 BJ13 BJ14 DJ04 DJ07 DJ12 EJ12 HJ04 HJ12 5H050 AA15 BA17 CA02 CA03 CA05 CA08 CA09 CA11 CA29 CB07 CB07 CB07 CB07 GA22 HA04 HA12

Claims (5)

[Claims] 1. A flat battery comprising an electrode group in which a positive electrode plate and a negative electrode plate each formed by applying a coating liquid containing an electrode active material on a current collector are wound in an oval shape with an isolator interposed therebetween. 3. The flat battery according to claim 1, wherein an uncoated portion is provided at an innermost end of the positive electrode plate. 2. The flat battery according to claim 1, wherein an uncoated portion of the positive electrode plate is within a range of 5 mm or less from an innermost end. 3. The electrode group, wherein the inner surface or both surfaces of the first bent portion wound in an oval shape at the innermost peripheral portion of the positive electrode plate is an uncoated portion. 4. The flat battery according to claim 1. 4. The flat battery according to claim 1, wherein the inner surface of the bent portion of the negative electrode plate facing the uncoated portion of the positive electrode plate is an uncoated portion. 5. The flat battery according to claim 1, wherein uncoated portions of the positive electrode plate and the negative electrode plate are covered with an insulating tape.