JPH11176478A - Organic electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an organic electrolyte secondary battery of high safety, even with high capacity. SOLUTION: In an organic electrolyte secondary battery comprising a positive electrode 1 having active material including painted film 2b at least on one surface of a positive electrode collector 1a comprising metal foil, and a negative electrode 2 having active material including painted film on at least one surface of a negative electrode collector 2a comprising metal foil wound through a separator to form a winding structure electrode body contained in a battery can 5, a part of only the positive electrode collector 1a without having the active material including painted film 2b is provided at least at the outermost circumferential part of the negative electrode in the winding structure electrode body, and the positive electrode collector 1a and the negative electrode collector 2a are disposed via the separator at the part. The battery is suitable for a fully charged negative electrode charge/discharge capacity of 96 mAh/cm<3> or more per unit volume of the battery.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electrolyte secondary battery, and more particularly, to an organic electrolyte secondary battery having a specific structure for ensuring safety.

[0002]

2. Description of the Related Art An organic electrolyte secondary battery is a secondary battery using an organic solvent as a solvent of the electrolyte. The organic electrolyte secondary battery has a large capacity, a high voltage, a high energy density, and a high capacity. Because of the output, the demand tends to increase more and more.

[0003] As a solvent for an organic electrolytic solution of this battery (hereinafter, simply referred to as "electrolytic solution" except when the battery is referred to), a cyclic ester such as ethylene carbonate, dimethyl carbonate, methyl propionate and the like have hitherto been used. A mixture of such esters has been used.

However, according to the study of the present inventors, this organic electrolyte secondary battery may be used in a case where the capacity is further increased in the future or depending on the specifications required by the user.
It has been found that the safety may be reduced unless the battery structure is further devised. To explain this in more detail, in this type of battery, measures are usually taken to prevent an internal short circuit by preventing overcharge with a protection circuit, etc. However, when a nail penetration test was performed assuming an abnormal use, it was found that safety was sometimes lacking. That is, in the nail penetration test, the battery is surely short-circuited in a small portion compared to the crushing of the battery or external short-circuit, so that the current is concentrated on the short-circuited portion, the heat is more likely to be generated, and the battery is partially heated to a high temperature rapidly. The nail penetration test can occur under normal operating conditions because the fuse tends to fluctuate (clogging due to melting) and the heat generated by the reaction between the electrolyte and the negative electrode at the short-circuit site increases. This is a severe safety confirmation test that can find any lack of safety. Therefore, if the safety can be confirmed by this nail penetration test, it is considered that the safety is ensured even when an abnormal use is encountered.

[0005] Also, the nail piercing test is 45 times longer than performed at room temperature.
When performed at a high temperature of ℃, the battery easily rises to a higher temperature, and a thermal runaway reaction of the battery is more likely to occur. Furthermore, 1 /
(2) When the nail is stopped in the middle of the battery as in the case of nail penetration, the short-circuit portion is reduced, the current is more concentrated, and heat is easily generated. Therefore, when this nail penetration test is performed at 45 ° C. and a 1/2 nail penetration is performed, it is a very severe test as a test for confirming safety, and the safety is confirmed by a test under such severe conditions. If possible, it is considered that sufficient safety can be ensured by actual use.

[0006]

By the way, when a compound capable of deintercalating lithium such as carbon is used as a negative electrode active material, reactivity with an electrolytic solution at a high temperature is much lower than when metal lithium is used. , Battery safety is improved. However, due to the recent trend toward higher capacity, the energy density of batteries tends to be higher and higher in the future, so that it is necessary to be able to show excellent safety even in the nail penetration test which is a severe safety confirmation test. It has been found that it is necessary to change the internal structure of the battery to a structure that does not easily ignite.

Accordingly, the present invention is to improve the battery structure so that the safety can be sufficiently confirmed even in a nail penetration test, which is a severe safety confirmation test, in preparation for a future increase in capacity.
An object is to provide an organic electrolyte secondary battery having excellent safety.

[0008]

SUMMARY OF THE INVENTION The present invention provides a positive electrode current collector made of a metal foil and a positive electrode having an active material-containing coating film formed on at least one surface thereof, and at least one of a negative electrode current collector made of a metal foil. In the organic electrolytic solution secondary battery in which a negative electrode having an active material-containing coating film formed on one surface thereof is wound through a separator and an electrode body having a wound structure is housed in a battery can, At least the outermost part of the positive electrode of the positive electrode in the electrode body of the structure is provided with a portion of only the positive electrode current collector without forming an active material-containing coating film, and at least the outermost part of the negative electrode of the wound electrode body contains the active material. The object has been achieved by providing a portion of only the negative electrode current collector without forming a coating film, and disposing the positive electrode current collector and the negative electrode current collector in the above portions via a separator.

Hereinafter, the progress of completing the present invention and the reason why the above configuration can improve safety will be described in detail.

In general, a current wound electrode body of an organic electrolyte secondary battery includes a sheet-shaped positive electrode having an active material-containing coating film formed on both sides of an aluminum foil serving as a positive electrode current collector, and a negative electrode current collector. A negative electrode in the form of a sheet in which an active material-containing coating film is formed on both sides of a copper foil and two separators are stacked in the order of a negative electrode, a separator, a positive electrode, and a separator. It is wound around.

The present inventors have obtained a lithium-ion secondary battery which is most widely used as an organic electrolyte secondary battery, and conducted a nail penetration test. However, it was found that the danger increased as the energy density of the battery increased. For the negative electrode of these batteries, a compound such as a carbon material that can insert and remove lithium is usually used. However, when the negative electrode is overcharged and lithium is electrodeposited to some extent, about 10% is used.
From around 0 ° C., an exothermic reaction occurs between the electrolytic solution and electrodeposited lithium or a carbon material into which lithium is inserted.

Also, in the positive electrode, the desorption of lithium lowers the temperature at which the reaction with the electrolytic solution starts, and when the heat of reaction of the negative electrode reaches the thermal runaway temperature of the positive electrode, the battery generates abnormal heat. Due to such an exothermic phenomenon accompanied by a continuous reaction, if the chargeable / dischargeable capacity of the negative electrode of the battery under normal use conditions exceeds 96 mAh / cm ³ (at full charge) per unit volume of the battery, the battery The safety when overcharged is reduced. In other words, the greater the dischargeable capacity per unit volume of the negative electrode, the greater the amount of heat generated per unit volume of the battery if heat is generated during overcharge, and the battery temperature may rise to the thermal runaway temperature of the positive electrode The nature becomes high.
Therefore, in the present invention, in a battery having a large capacity per unit volume of the negative electrode, even when an exothermic reaction occurs between the negative electrode and the electrolytic solution, the temperature of the battery is not increased by the heat generation to a thermal runaway reaction of the positive electrode. By improving the structure of the battery, even a high-capacity battery with a large capacity per unit volume of the negative electrode,
It was made possible to ensure sufficient safety.

[0013] In the present invention, at least the outermost portion of the positive electrode in the wound electrode body is provided with only the positive electrode current collector without forming an active material-containing coating film, and the negative electrode in the wound electrode body is provided. By providing a portion of only the negative electrode current collector without forming an active material-containing coating film on at least the outermost peripheral portion, and by arranging the positive electrode current collector and the negative electrode current collector of the above portion via a separator, safety is improved. The reason why can be improved is not always clear at present, but it is considered as follows.

As described above, by using a compound capable of deintercalating lithium such as a carbon material as the negative electrode active material, the reactivity between the electrolyte and the negative electrode at a high temperature can be improved when lithium is used as the negative electrode active material. However, when the chargeable / dischargeable capacity of the negative electrode increases, the reactivity with the electrolytic solution increases, the calorific value increases, and the battery temperature easily rises. However, if the active material-containing coating film is not formed on at least the outermost peripheral portions of each of the positive electrode and the negative electrode in the wound electrode body, and only the positive electrode current collector and the negative electrode current collector are provided, the collector The heat release is accelerated by the portion of the electric body alone, the positive electrode hardly reaches the thermal runaway temperature, the battery hardly generates abnormal heat, and the safety of the battery is improved.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in the wound electrode body, only the positive electrode current collector and the negative electrode current collector provided at the outermost peripheral portions of the positive electrode and the negative electrode, respectively, are the wound electrode body. Is preferably one or more rounds, and more preferably two or less rounds. That is, by making the portion of only the positive electrode current collector and the negative electrode current collector one or more times as described above, heat radiation can be accelerated, and the safety of the battery can be sufficiently improved. By setting the portion including only the electric conductor to two or less turns, it is possible to prevent a significant decrease in the energy density of the battery.

Further, if the separator at the outermost periphery of the wound electrode body is eliminated, the negative electrode current collector comes into direct contact with the inner wall of the battery can, so that heat is released more quickly and the safety of the battery is improved. The effect of this is more remarkably exhibited.

In the present invention, the cathode active material is not particularly limited. For example, lithium cobalt oxide such as LiCoO ₂ , lithium manganese oxide such as LiMn ₂ O _4, and lithium nickel oxide such as LiNiO ₂ Oxides, metal oxides such as manganese dioxide, vanadium pentoxide, and chromium oxide; and metal sulfides such as titanium disulfide and molybdenum disulfide.

Particularly, as the positive electrode active material, LiNiO ₂ , Li
The open circuit voltage during charging of CoO ₂ , LiMn ₂ O _4, etc. is L
It is preferable to use a lithium composite oxide exhibiting 4 V or more on the basis of i because a high energy density can be obtained. Moreover, LiCoO ₂ and LiNiO ₂ was charged reaction starting temperature of the electrolyte is lower than such LiMn ₂ O _4, since easily reached thermal runaway temperature of the positive electrode due to heat generation of the negative electrode, a LiCoO ₂ and LiNiO ₂ as a positive electrode active material When used, the effects of the present invention are particularly pronounced.

For the positive electrode, for example, a conductive additive such as flake graphite or carbon black, or a binder such as polyvinylidene fluoride or polytetrafluoroethylene is appropriately added to the above-mentioned positive electrode active material, for example. The active material-containing coating material formed into a coating material with a solvent is applied to a positive electrode current collector made of a metal foil such as an aluminum foil and dried to form an active material-containing coating film. However, in the present invention, the active material-containing coating film is not formed on at least the outermost portion of the positive electrode in the wound electrode body as described above, and only the positive electrode current collector is left.

In the present invention, the material used for the negative electrode may be any material capable of doping and undoping lithium ions. In the present invention, such a material capable of doping and undoping lithium ions is referred to as a negative electrode active material. .
The negative electrode active material is not particularly limited. For example, graphite, pyrolytic carbons, cokes, glassy carbons, fired bodies of organic polymer compounds, mesocarbon microbeads, carbon fibers It is preferable to use a carbon material such as activated carbon, an alloy such as Si, Sn, or In, or an oxide such as Si, Sn, or In that can be charged and discharged at a low potential close to Li.

When a carbon material is used as the negative electrode active material,
The carbon material preferably has the following characteristics.
That is, the interlayer distance d ₀₀₂ of the (002) plane is 3.
5 ° or less, more preferably 3.45 ° or less,
More preferably, it is 3.4 ° or less. Further, the crystallite size Lc in the c-axis direction is preferably 30 ° or more, more preferably 80 ° or more, and further preferably 250 ° or more. The average particle size is 8 to 15 μm, especially 10 to 10 μm.
13 μm is preferable, and the purity is preferably 99.9% or more.

For the negative electrode, for example, a binder such as polyvinylidene fluoride or polytetrafluoroethylene is appropriately added to the above-mentioned negative electrode active material, and if necessary, a conductive additive is appropriately added. The active material-containing coating material is applied to a negative electrode current collector made of copper foil or the like, and dried to form an active material-containing coating film. However, in the present invention, the active material-containing coating film is not formed on the outermost portion of the negative electrode in the wound electrode body as described above, and only the negative electrode current collector is left.

Examples of the metal foil serving as a current collector for the positive electrode and the negative electrode include aluminum foil, copper foil, nickel foil, and the like.
Although a stainless steel foil or the like is used, an aluminum foil is particularly preferable as a metal foil serving as a positive electrode current collector, and a copper foil is particularly preferable as a metal foil serving as a negative electrode current collector.

In the present invention, the electrolytic solution is not particularly limited as long as it is of an organic solvent type. However, when a chain ester is used as a main solvent, the viscosity of the electrolytic solution is reduced and the ionic conductivity is increased. This is preferred. Examples of such a chain ester include organic solvents having a chain COO-bond such as dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, and methyl propionate. The main solvent means that the chain ester exceeds 50% by volume in the total electrolyte solvent containing these chain esters. If the chain ester exceeds 65% by volume, the safety of the battery in the nail penetration test after 4.4 V charging is reduced in the prior art, but according to the present invention, the chain ester is 65% by volume as such. Is exceeded, safety can be ensured, and the effect of the present invention is remarkably exhibited.

If the amount of the chain ester exceeds 70% by volume, the safety of the battery is more likely to be reduced in the prior art, so that the effect of the present invention is more remarkably exhibited, and If the content exceeds 75% by volume, the safety of the battery is more likely to be reduced in the conventional technique, so that the effects of the present invention are more remarkably exhibited. Also, in the case where the chain ester has a methyl group, the safety of the battery is apt to be reduced in the prior art, so that the effects of the present invention are more remarkably exhibited.

When the following ester having a high dielectric constant (dielectric constant of 30 or more) is mixed with the above chain ester and used,
Since the cycle characteristics and the load characteristics of the battery are improved as compared with the case where only the chain ester is used, the battery is more preferable. Examples of such an ester having a high dielectric constant include propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), gamma-butyrolactone (γ-BL), and ethylene glycol sulfite (EGS). In particular, those having a cyclic structure are preferred, and cyclic carbonates are particularly preferred. Ethylene carbonate (EC)
Is most preferred.

The ester having a high dielectric constant is preferably less than 40% by volume of the total solvent of the electrolytic solution, more preferably 30% by volume.
% By volume or less, more preferably 25% by volume or less.
The improvement of the safety by these esters having a high dielectric constant becomes remarkable when the ester having a high dielectric constant becomes 10% by volume or more in the entire solvent of the electrolytic solution, and becomes further remarkable when it reaches 20% by volume. .

Examples of the solvent that can be used in combination with the ester having a high dielectric constant include 1,2-dimethoxyethane (DME), 1,3-dioxolan (DO), tetrahydrofuran (THF), and 2-methyl-tetrahydrofuran (2Me). -THF), diethyl ether (DEE) and the like. In addition, an amine imide-based organic solvent, a sulfur-containing or fluorine-containing organic solvent, and the like can also be used.

As an electrolyte of the electrolytic solution, for example, LiC
10 ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li
SbF ₆ , LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ , L
iCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN
(CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , Li
C _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (Rf ₃ OS
O ₂ ) ₂ (where Rf is a fluoroalkyl group) or the like is used alone or as a mixture of two or more.
PF ₆ and LiC ₄ F ₉ SO ₃ are preferable because of good charge / discharge characteristics. The concentration of the electrolyte in the electrolyte is
Although not particularly limited, a concentration of 1 mol / l or more is preferable because safety is improved, and is preferably 1.2 mol / l.
1 / l or more is more preferable. Further, it is preferable that the concentration of the electrolyte in the electrolytic solution be 1.7 mol / l or less, since good electrical characteristics are maintained, and it is more preferable that the concentration be 1.5 mol / l or less.

The present invention can be applied regardless of the shape of the battery, and can be applied to batteries of any shape. In particular, the present invention is applied to cylindrical batteries such as cylindrical, elliptical and rectangular cylinders. Suitable to do. When the wound electrode body is formed into a cylindrical shape or an elliptical cylindrical shape so as to be suitable for the cylindrical battery or the elliptical cylindrical battery as described above, the minimum value of the wound outer diameter is a battery can in a discharged state. 0.4-0.7mm from the inner diameter of
Preferably, it is small. That is, by making the minimum value of the winding outer diameter of the wound electrode body smaller than the inner diameter of the battery can by 0.4 mm or more in the discharged state, the safety in the nail penetration test is improved even when the battery capacity is increased. Can be secured,
By making the minimum value of the winding outer diameter of the wound electrode body smaller than the inner diameter of the battery can in the discharged state by 0.7 mm or less, it is possible to prevent a large decrease in the capacity of the battery.

[0031]

Next, the present invention will be described more specifically with reference to examples. However, the present invention is not limited to only these examples.

Example 1 Methyl ethyl carbonate and ethylene carbonate were mixed at a volume ratio of 3: 1.
₆ was dissolved at 1.0 mol / l to give a composition of 1.0 mol.
An electrolytic solution represented by / lLiPF ₆ / EC: MEC (1: 3 volume ratio) was prepared. EC in the above electrolyte is an abbreviation for ethylene carbonate, and MEC is an abbreviation for methyl ethyl carbonate. Therefore, 1.0 mol / l LiPF ₆ / EC: MEC (1: 3) indicating the above electrolyte solution was used.
Volume ratio) is LiF in a mixed solvent of methyl ethyl carbonate 3 and ethylene carbonate 1 in volume ratio.
It indicates that the P ₆ is obtained by corresponding dissolving 1.0 mol / l.

Separately, LiN as a positive electrode active material
Scalable graphite is used as a conductive additive with respect to iO ₂ in a weight ratio of 10
The mixture was added and mixed at 0: 7, and this mixture and a solution of polyvinylidene fluoride dissolved in N-methylpyrrolidone were mixed to obtain a slurry-like coating material. After the positive electrode active material-containing coating material was passed through a 70-mesh net to remove large ones, it was uniformly applied to both surfaces of a positive electrode current collector made of an aluminum foil having a thickness of 20 μm, heated and dried. However, when the positive electrode produced therefrom is formed into a wound electrode body together with a negative electrode, a separator, and the like, the outermost peripheral portion of the positive electrode is not coated with the active material-containing coating material, and the uncoated portion,
That is, the portion including only the positive electrode current collector was set to 50 mm. This sheet-shaped electrode body is compression-molded, cut, and 3 mm in width.
Were welded to produce a sheet-shaped positive electrode.

Next, a graphite-based carbon material (however, 002
Interlayer distance d ₀₀₂ = 3.37 °, crystallite size Lc in the c-axis direction Lc = 950 °, average particle size 10 μm, purity 99.
9%) is mixed with a solution of polyvinylidene fluoride in N-methylpyrrolidone to form a slurry-like coating material, and the negative electrode active material-containing coating material is strip-shaped copper having a thickness of 10 μm. The foil was uniformly coated on both sides of the negative electrode current collector and dried. However, when the negative electrode produced therefrom is formed into a wound electrode body together with the positive electrode, the separator, and the like, the outermost peripheral portion of the negative electrode is not coated with the negative electrode active material-containing coating material, and the uncoated portion, That is, the portion including only the negative electrode current collector was set to 50 mm. This sheet-shaped electrode body was compression molded, cut, and then welded with a lead body having a width of 3 mm to produce a sheet-shaped negative electrode.

The sheet-shaped positive electrode is stacked on the sheet-shaped negative electrode through a separator made of a microporous polyethylene film having a thickness of 25 μm to form an electrode plate laminate. The spirally wound electrode structure was obtained by spirally winding the electrode. However, no separator was arranged on the outermost peripheral portion of the wound electrode body. Accordingly, the outermost peripheral portion of the wound electrode body is formed of the copper foil of the negative electrode current collector. The wound electrode body was filled in a cylindrical battery can having an outer diameter of 18 mm and having a bottom, and the positive and negative electrode lead bodies were welded. Next, the electrolytic solution is injected into the battery case, and after the electrolytic solution has sufficiently penetrated into the separator and the like, sealing, preliminary charging and aging are performed, and a cylindrical organic electrolytic solution secondary battery whose structure is schematically shown in FIG. Was prepared. FIG. 2 shows details of the outermost peripheral portion of the electrode body having the wound structure of the battery and the vicinity thereof.

The charge / discharge capacity of the negative electrode of this battery was measured under the normal charge conditions of this battery (4.2 V when charged at 1600 mA).
After that, the operation of charging at a constant voltage of 4.2 V was performed for 2 hours and 30 minutes), which was 96 mAh / cm ³ . Further, after discharging the battery at 1600 mA to 2.75 V, the battery was disassembled and the winding outer diameter of the wound electrode body was examined. As a result, the minimum value was 16.4 mm. The difference from the inner diameter was 0.5 mm.

Here, the schematic structure of this battery will be described with reference to FIG. 1. Reference numeral 1 denotes the above-mentioned sheet-shaped positive electrode, and 2 denotes the sheet-shaped negative electrode. However, FIG. 1 does not show a metal foil or the like as a current collector used in manufacturing the positive electrode 1 or the negative electrode 2 in order to avoid complication. The positive electrode 1 and the negative electrode 2 are spirally wound with a separator 3 interposed therebetween, and housed in a battery can 5 together with the electrolytic solution 4 as an electrode body having a spirally wound structure.

The battery can 5 is made of stainless steel and also serves as a negative electrode terminal. An insulator 6 made of polypropylene is arranged at the bottom of the battery can 5 before inserting the spirally wound electrode body. Have been. The sealing plate 7 is made of aluminum and is in the shape of a disk. A thin portion 7a is provided at the center on the inner side from both end surfaces in the thickness direction, and the internal pressure of the battery acts on the explosion-proof valve 9 around the thin portion 7a. Pressure inlet 7
A hole as b is provided. And this thin part 7
The projection 9a of the explosion-proof valve 9 is welded to the upper surface of a to form a welded portion 11. In addition, the thin portion 7a provided on the sealing plate 7 and the protruding portion 9a of the explosion-proof valve 9 are illustrated only in a cut plane so as to be easily understood in the drawings, and a contour line behind the cut plane is shown. Is not shown. Also, sealing plate 7
Welded portion 11 between thin portion 7a of protrusion and protrusion 9a of explosion-proof valve 9
Also, for ease of understanding in the drawings, the drawings are shown in an exaggerated state.

The terminal plate 8 is made of rolled steel, nickel-plated on its surface, and has a hat-like shape with a peripheral edge formed in a flange shape. The terminal plate 8 is provided with a gas discharge hole 8a. . The explosion-proof valve 9 is made of aluminum and is in the shape of a disk, and a central portion is provided with a projecting portion 9a having a tip on the power generation element side (the lower side in FIG. 1). As described above, the lower surface is welded to the upper surface of the thin portion 7a of the sealing plate 7 to form a welded portion 11. The insulating packing 10 is made of polypropylene and has an annular shape. The insulating packing 10 is disposed above the peripheral edge of the sealing plate 7 and has an explosion-proof valve 9
Are arranged to insulate the sealing plate 7 from the explosion-proof valve 9 and seal the gap between the two so that the electrolyte does not leak from between them. The annular gasket 12 is made of polypropylene, and the lead body 13 is made of aluminum.
And the positive electrode 1, and an insulator 1 is provided above the spiral electrode body.
The negative electrode 2 and the bottom of the battery can 5 are connected by a nickel lead body 15.

As described above, the insulator 6 is disposed at the bottom of the battery can 5, and the positive electrode 1, the negative electrode 2 and the separator 3
The spirally wound electrode body, the electrolyte solution 4, the insulator 14 above the electrode body, and the like are housed in the battery can 5 and, after being housed, are placed near the opening end of the battery can 5. An annular groove whose bottom protrudes inward is formed. A sealing plate 7, an insulating packing 10,
The annular gasket 12 into which the explosion-proof valve 9 is inserted is inserted, the terminal plate 8 is further inserted from above, and the portion of the battery can 5 that is beyond the groove is tightened inward, whereby the opening of the battery can 5 is sealed. ing. However, in assembling the battery as described above, it is preferable that the negative electrode 2 and the battery can 5 are connected in advance with the lead body 15 and the positive electrode 1 and the sealing plate 7 are connected with the lead body 13 in advance.

In the battery assembled as described above, the thin portion 7a of the sealing plate 7 and the projection 9a of the explosion-proof valve 9 are provided.
Contact at the welded portion 11, the peripheral portion of the explosion-proof valve 9 and the peripheral portion of the terminal plate 8 come into contact, and the positive electrode 1 and the sealing plate 7 are connected by the lead 13 on the positive electrode side. And terminal plate 8
The electrical connection is obtained by the lead body 13, the sealing plate 7, the explosion-proof valve 9 and the welded portion 11 thereof, and the lead body normally functions as an electric circuit.

When an abnormal situation occurs in the battery and gas is generated inside the battery and the internal pressure of the battery rises, the internal pressure rises and the central part of the explosion-proof valve 9 moves in the direction of the internal pressure (FIG. 1).
Then, it is deformed in the upper direction)
The shearing force acts on the thin portion 7a integrated at 1 and the thin portion 7a is broken or the projection 9a of the explosion-proof valve 9 is formed.
The welding portion 11 between the sealing plate 7 and the thin portion 7a of the sealing plate 7 is peeled off, whereby the electrical connection between the positive electrode 1 and the terminal plate 8 is lost, and the current is cut off.

The explosion-proof valve 9 is provided with a thin portion 9b. For example, when charging proceeds extremely and power generation elements such as an electrolyte and an active material are decomposed and a large amount of gas is generated, After the explosion-proof valve 9 is deformed and the welding portion 11 between the projection 9a of the explosion-proof valve 9 and the thin portion 7a of the sealing plate 7 is peeled off,
The thin portion 9b provided on the explosion-proof valve 9 is designed to be opened so that gas is discharged from the gas discharge holes 8a of the terminal plate 8 to the outside of the battery to prevent the battery from being ruptured.

Next, the outermost peripheral portion of the electrode body of the wound structure of the battery and its vicinity (that is, a portion corresponding to the vicinity of A in FIG. 1) will be described with reference to FIG. Is formed by forming an active material-containing coating film 1b on both surfaces of a positive electrode current collector 1a made of
At the outermost portion, only the positive electrode current collector 1a is provided without forming the active material-containing coating film 1b. The negative electrode 2 has an active material-containing coating film 2 on both surfaces of a negative electrode current collector 2a made of copper foil.
The negative electrode current collector 2a is formed without forming the active material-containing coating film 2b at the outermost periphery thereof.
Only a portion is provided.

The separator 3 is disposed between the positive electrode 1 and the negative electrode 2 and between the positive electrode current collector 2a and the negative electrode current collector 2b at the outermost periphery of the positive electrode 1 and the negative electrode 2. The negative electrode current collector 2 a is not directly disposed on the outermost peripheral portion of the electrode body, but directly contacts the inner wall of the battery can 5. As described above, in the discharge state, there is a difference of 0.5 mm between the minimum value of the winding outer diameter of the wound electrode body and the inner diameter of the battery can. In addition, the negative electrode current collector 2 a at the outermost periphery of the electrode body is in direct contact with the inner wall of the battery can 5 because the electrode body having the spirally wound structure is not a true circle.

In the battery of Example 1, the portion of only the positive electrode current collector 1a without forming the active material-containing coating film 1b on the outermost peripheral portion of the positive electrode 1 is formed around one round in the outer peripheral portion of the wound electrode body. In addition, the portion of the negative electrode 2 on which only the negative electrode current collector 2a is not formed on the outermost peripheral portion of the negative electrode 2 corresponds to about one round in the outer peripheral portion of the wound electrode body.

Example 2 A portion of the outermost periphery of the positive electrode 1 where the active material-containing coating 1b was not formed was located on the outer surface of the positive electrode current collector 1a, and the active material-containing coating 1b was formed on the inner surface thereof. Then, a cylindrical organic electrolyte secondary battery was manufactured in the same manner as in Example 1.

The outermost peripheral portion of the wound electrode structure of the battery according to the second embodiment and the vicinity thereof will be described with reference to FIG.
At the outermost peripheral portion of the positive electrode 1, only the outer surface side does not form the active material-containing coating film 1b, but only the positive electrode current collector 1a, and the active material-containing coating film 1b is formed on the inner surface side. Otherwise, the configuration is the same as that shown in FIG.

The battery of Example 2 was used up to 2.75 V
After discharging at 00 mA, the battery was disassembled and the wound outer diameter of the wound electrode body was examined. The minimum value was 16.4 mm. The difference between the minimum value and the inner diameter of the battery can 5 was 0.1 mm. 5m
m.

Example 3 A cylindrical organic electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the separator 3 was arranged at the outermost periphery of the wound electrode body.

The outermost periphery of the wound electrode body of the battery can of Embodiment 3 and its vicinity will be described with reference to FIG. 4. The separator 3 is arranged at the outermost periphery of the wound electrode body. Thus, the separator 3 is interposed between the negative electrode current collector 2a and the inner wall of the battery can 5. Otherwise, the configuration is the same as that shown in FIG.

Example 4 The structure was the same as that of Example 3, except that the portion of the positive electrode 1 where the active material-containing coating film 1b was formed was shortened by 20 mm, and the portion of the negative electrode 2 where the active material-containing coating film 2b was formed was 20 mm. A cylindrical organic electrolyte secondary battery was fabricated in the same manner as in Example 3, except that the battery was shortened.

The battery of this Example 4 was changed to
After discharge at 00 mA, the battery was disassembled and the winding outer diameter of the wound electrode body was examined. The minimum value was 16.2 mm. The difference between the minimum value and the inner diameter of the battery can 5 was 0.7 mm. Met.

COMPARATIVE EXAMPLE 1 An active material-containing coating 1b was formed on the positive electrode current collector 1a except for a portion 2 mm where the active material-containing coating 1b was not formed. The active material-containing coating film 2b is formed on the negative electrode current collector 2a while leaving a portion where the active material-containing coating film 2b is not formed at the outermost peripheral portion of the electrode collector 2a. A cylindrical organic electrolyte secondary battery was produced in the same manner as in Example 1, except that 3 was arranged.

The outermost peripheral portion of the wound electrode structure of the battery of Comparative Example 1 and its vicinity will be described with reference to FIG.
The outermost peripheral portion of the positive electrode 1 is also formed with the active material-containing coating film 1b as described above, and the outermost peripheral portion of the negative electrode 2 is also formed with the active material-containing coating film 2b except for a portion to be in contact with the lead body 15, Further, the separator 3 is disposed at the outermost periphery of the wound electrode body, and the separator 3 is interposed between the battery can 5 and the outermost periphery of the negative electrode 2.

The battery of Comparative Example 1 was charged to 2.75 V
After discharging at 00 mA, the battery was disassembled and the winding outer diameter of the wound electrode body was examined. The minimum value was 16.4 mm. The difference between the minimum value and the inner diameter of the battery can 5 was 0.5 mm. Met.

COMPARATIVE EXAMPLE 2 The structure was the same as that of Comparative Example 1, except that the portion of the positive electrode 1 where the active material containing coating 1b was formed was shortened by 20 mm, and the portion of the negative electrode 2 where the active material containing coating 2b was formed was 20 mm. A cylindrical organic electrolyte secondary battery was produced in the same manner as in Comparative Example 1 except that the length was shortened.

The battery of Comparative Example 2 was changed to 16
After discharge at 00 mA, the battery was disassembled and the winding outer diameter of the wound electrode body was examined. The minimum value was 16.2 mm. The difference between the minimum value and the inner diameter of the battery can 5 was 0.7 mm. Met.

After discharging the batteries of Examples 1-4 and Comparative Examples 1-2 to 2.75 V at 1600 mA,
The battery was charged at 0 mA, and after reaching 4.4 V, the battery was charged for 2 hours and 30 minutes under the condition of maintaining a constant voltage of 4.4 V. Thereafter, the battery was placed in a 45 ° C. constant temperature bath, taken out 2 hours later, placed on a battery holder, and subjected to a 釘 nail penetration test. That is, a stainless steel nail having a diameter of 3 mm was pierced from the side of the battery to half the diameter of the battery, and the number of abnormally heated batteries among the 20 batteries was examined. Table 1 shows the results. In Table 1, the denominator of the numerical value indicating the result is the number of batteries subjected to the test, and the numerator is the number of batteries that abnormally generate heat. The above abnormal heat generation means that the battery surface temperature is 150 ° C.
This is the case when it is over.

[0060]

[Table 1]

As shown in Table 1, Examples 1 to 4 had much less abnormal heat generation than Comparative Examples 1 and 2 and had high safety. In other words, in the nail penetration test under the severe conditions of leaving at 45 ° C. for 2 hours and performing a 1/2 nail penetration as described above, the number of abnormally heated batteries is 1/5 or less (as described above, 20 batteries were tested). If the number of batteries that generate abnormal heat is 4 or less), it is determined that the battery has sufficiently high safety. However, in Examples 1 to 4, the number of batteries that generate abnormal heat is It was below, and had sufficiently high safety.

In the above embodiment, the safety of a cylindrical organic electrolyte secondary battery was examined. However, batteries having a shape other than the cylindrical shape, such as a prismatic organic electrolyte secondary battery, are also included in the present invention. According to this, the same high safety as that of the cylindrical organic electrolyte secondary battery can be obtained.

[0063]

As described above, according to the present invention, a highly safe organic electrolyte secondary battery can be provided even when the capacity is increased.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing an example of an organic electrolyte secondary battery according to the present invention.

FIG. 2 is an enlarged cross-sectional view showing the outermost peripheral portion of the electrode body of the wound structure of the battery of Example 1 and its vicinity.

FIG. 3 is an enlarged cross-sectional view showing the outermost peripheral portion of the electrode body of the wound structure of the battery of Example 2 and its vicinity.

FIG. 4 is an enlarged cross-sectional view showing the outermost peripheral portion of the electrode body of the wound structure of the battery of Example 3 and its vicinity.

FIG. 5 is an enlarged cross-sectional view showing the outermost peripheral portion of the electrode body of the wound structure of the battery of Comparative Example 1 and its vicinity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 1a Positive electrode current collector 1b Active material containing coating film 2 Negative electrode 2a Negative electrode current collector 2b Active material containing coating film 3 Separator 4 Electrolyte 5 Battery can

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kazunobu Matsumoto 1-88 Ushitora 1-chome, Ibaraki-shi, Osaka Hitachi Maxell Co., Ltd.

Claims (3)

[Claims] A positive electrode comprising an active material-containing coating film formed on at least one surface of a positive electrode current collector made of a metal foil, and an active material-containing coating film formed on at least one surface of a negative electrode current collector made of a metal foil. A negative electrode formed with a film, an organic electrolyte secondary battery containing a wound electrode body wound in a battery can with a separator interposed therebetween, at least the positive electrode in the wound electrode body. A portion of the positive electrode current collector alone is provided without forming an active material-containing coating on the outermost peripheral portion, and the negative electrode collector is formed without forming an active material-containing coating on at least the outermost peripheral portion of the negative electrode in the wound electrode body. An organic electrolyte secondary battery comprising: a portion including only a current collector; and the positive electrode current collector and the negative electrode current collector in the above-described portions are disposed via a separator. 2. The positive electrode current collector, wherein the chargeable / dischargeable capacity of the negative electrode at full charge is 96 mAh / cm ³ or more per unit volume of the battery, and the active material containing the active material-containing coating film is not formed. 2. The organic electrolyte secondary battery according to claim 1, wherein the negative electrode current collector having no formed coating film is present at least once in each of the wound electrode bodies. 3. An electrode body having a wound structure having a cylindrical or elliptical cylindrical shape, wherein the minimum value of the wound outer diameter is 0.4 to 0.7 mm smaller than the inner diameter of the battery can in a discharged state. Or the organic electrolyte secondary battery according to 2.