JPH0426071A - Secondary battery - Google Patents

Abstract

PURPOSE:To prevent inside short-circuitting by making the thickness of the end part of one electrode of stripe-like first and second electrodes thinner than that of the center part of the electrode. CONSTITUTION:The thickness of an end part 15 in the longitudinal direction of a stripe-like negative pole 1 is made thinner than that of the center part. Consequently, in the case of preparation of a rolled-type electrode body 10, the negative pole 1 and separators 3a, 3b are not stuck together at the end part 15 of the negative pole 1 and gaps 18 are formed between them, so that anode composing substances do not likely penetrate the separators 3a, 3b in the end part 15. Also, since electrode composing substances which are easy to be peeled and drop are lessened at the end part 15 of the anode 1, dropping and peeling off of the electrode composing substances scarcely occur at the end part 15 of the anode during preparation and use of a battery. As a result, inner short-circuitting of a battery is prevented.

Description

[Detailed description of the invention] The present invention will be explained in the following order.

A. Industrial field of application B1 Overview of the invention C1 Prior art 3 Problems to be solved by the invention E1 Means for solving the problems F6 Effects G, Examples G1. Example 1 Gz, Example 2 G3. Example 3 Ga, Example 4 H1 Effects of the invention A, Industrial field of application The present invention is characterized in that strip-shaped first and second electrodes and a strip-shaped separator are stacked and wound in a spiral shape. The present invention relates to a secondary battery including a wound electrode body configured by the following methods.

B3 Summary of the Invention The invention of claim 1 provides a first strip-shaped first electrode comprising an electrode constituent material layer.
and a second electrode and a band-shaped separator are stacked and wound spirally, so that the separator is interposed between the first electrode and the second electrode. In a secondary battery equipped with a wound electrode body, by making the thickness at the end of at least one of the strip-shaped first or second electrodes thinner than the thickness at the center of the electrode, This is intended to prevent internal short circuits in the battery by preventing electrode constituent materials from falling off, peeling off, or penetrating the separator at the ends of the electrode during manufacturing and use of the battery.

According to a second aspect of the invention, in the secondary battery including the wound electrode body, a corner of at least one of the strip-shaped first or second electrodes is missing;
This prevents the electrode constituent materials from falling off or peeling off at the corners of the electrode, or from penetrating the separator during battery manufacture and use, thereby preventing internal short circuits in the battery.

The invention according to claim 3 is provided with the above-mentioned wound electrode body, and the band-shaped first and second electrodes are provided with band-shaped first and second current collectors, and the first and second electrodes are provided with band-shaped first and second current collectors. In a secondary battery configured to include an inner circumferential layer and an outer circumferential layer on the inner circumferential surface and the outer circumferential surface of each current collector, respectively, an electrode of at least one of the first or second electrodes. The constituent material includes at least an active material or an active material support and a binder, and the binder content in the outer peripheral layer of this electrode is higher than the binder content in the inner peripheral layer of this electrode. By increasing the height, the bonding strength of the electrode constituent materials in the outer peripheral layer of the electrode is increased, and during the manufacturing and use of the battery,
This prevents the electrode constituent material from falling off or peeling off in the outer peripheral layer of the electrode, thereby preventing internal short circuits in the battery.

C0 Conventional technology In recent years, electronic devices such as video cameras and hesophone stereos have improved in performance and become smaller in size, and there is a need to improve the heavy load characteristics and increase the capacity of the secondary batteries that power these electronic devices. There is also a growing demand for change. As secondary batteries, lead secondary batteries and nickel cadmium batteries have conventionally been used.

Furthermore, recently, materials that can be doped and dedoped with lithium ions have been used as negative electrode materials, such as lithium metal, lithium alloys (negative electrode active material), or carbon materials (negative electrode active material support) such as coke and fired organic materials. Non-aqueous electrolyte secondary batteries are also being actively developed.

In such a non-aqueous electrolyte secondary battery, a spirally wound electrode body is used to improve its heavy load characteristics. Such a wound electrode body is made by stacking a strip-shaped negative electrode, a strip-shaped positive electrode, and a pair of strip-shaped separators and winding them spirally many times along the length direction, thereby separating the negative electrode and the positive electrode. A separator is interposed between the two.

Further, when the electrode includes a band-shaped current collector, the electrode in the wound electrode body includes an inner circumferential layer and an outer circumferential layer on the inner circumferential surface and outer circumferential surface of the current collector, respectively.

Note that the materials constituting the electrode include an active material or an active material carrier, a binder, a conductive agent, and the like.

According to the wound electrode body as described above, since the strip-shaped negative electrode and the strip-shaped positive electrode have a relatively large area, even if a large current is passed through the secondary battery, the current per unit area is small, and the secondary battery can be used under heavy loads.

Furthermore, the thinner the electrode in the wound electrode body is, the larger the area of the electrode can be wound, and the better the heavy load characteristics of the secondary battery will be.

Further, when a current collector is used in the electrode, it is desirable to use a thinner metal foil for the current collector, so that the discharge capacity is not impaired.

D0 Problems to be Solved by the Invention However, there is a problem in that the secondary battery equipped with the above-described wound electrode body is susceptible to internal short circuits during its manufacture and use.

This internal short circuit occurs when a strip-shaped electrode and a strip-shaped separator are wound while being brought into close contact with each other during battery manufacturing, and electrode constituent materials such as active materials at the ends and/or corners of the strip-shaped electrode may cause the separator to This is caused by penetration.

Furthermore, during battery manufacturing and use, the electrode constituent materials at the ends and/or corners of the strip-shaped electrodes tend to fall off or peel off, and this falling off or peeled electrode constituent material may penetrate the separator. Internal short circuits may occur.

In addition, the present inventors have discovered that in batteries that have internal short circuits after repeated charging and discharging, the electrode active material falls off or peels off mainly in the outer peripheral layer of the electrode. The reason for this is thought to be as follows. In other words, when a band-shaped electrode is wound, the amount of elongation (strain) in the circumferential direction is greater in the outer circumferential layer of the electrode than in the inner circumferential layer of the electrode. If this is repeated, the outer peripheral layer of the electrode of the wound electrode body is more likely to deteriorate, and the electrode constituent material is more likely to fall off or peel off in the outer peripheral layer than in the inner peripheral layer. Therefore, an internal short circuit occurs in the battery.

In addition, when the battery is used, for example, during charging, deposits may form on one electrode on the upper end surface, lower end surface, and free end surface (end surfaces in the width direction and length direction of the strip-shaped electrode) of the wound electrode body. When this dendrite-like precipitate penetrates the separator and reaches the other electrode,
It may also cause an internal short circuit.

The object of the present invention is to provide a secondary battery that does not develop internal short circuits during its manufacture and use.

E8 Means for Solving the Problem In order to achieve the above object, the invention of claim 1 provides a secondary battery having a wound electrode body.
The thickness at the end of at least one of the electrodes is thinner than the thickness at the center of the electrode.

Note that it is preferable that the thickness of the strip-shaped electrode be made thinner at the end portion along the length direction. Furthermore, it is more preferable to make the thickness of the strip-shaped electrode thinner not only at the end portions along the length direction but also at the end portions along the width direction.

Further, the invention of claim 2 is a secondary battery having a wound electrode body, characterized in that at least one of the strip-shaped first electrode and the second strip-shaped electrode is missing a corner. shall be. In this case, it is preferable that the four corners of the strip-shaped electrode are missing.

Further, the invention of claim 3 provides a secondary battery including a wound electrode body, in which at least one of the first and second electrodes includes band-shaped first and second current collectors, respectively. The electrode constituent materials in the inner peripheral layer and the outer peripheral layer include at least an active material or an active material support and a binder, and
Bound content Xa, Xa' in the outer peripheral layer of this electrode
is the binder content χb,X in the inner peripheral layer of this electrode
It is characterized by being higher than b'.

Note that the binder content Xa (Xa'
) and the binder content χb (xb') in the inner peripheral layer, it is preferable that the following equations (1) and (2) hold true.

1.2≦χa/Xb (1)(
1,2≦Xa'/Xb') Xa-Xb≦5(2) (χa' - Since the thickness at the end of the strip-shaped electrode is thinner than that at the center of the electrode, even if the strip-shaped electrode is wound together with a strip-shaped separator when manufacturing a wound electrode body, the electrode at the end of the electrode is thinner than the center of the electrode. and the separator, and the electrode constituent material at the end of the electrode does not penetrate the separator, and during battery manufacturing and use, the electrode constituent material may fall off and peel off at the end of the electrode. Never. Therefore, internal short circuits of the battery can be prevented.

In the secondary battery of claim 2, since the strip-shaped electrode lacks corners, the electrode constituent material does not penetrate the separator at the corners of the electrode during battery manufacturing, and the battery manufacturing process is prevented. During use and during use, electrode constituent materials do not fall off or peel off at the corners of the electrode. Therefore, internal short circuits of the battery can be prevented.

In the secondary battery according to claim 3, the outer circumferential layer of the electrode in the wound electrode body has a larger elongation (strain) in the circumferential direction than the inner circumferential layer of the electrode, and the elongation is the largest on the surface of the outer circumferential layer. However, since the binder content in this outer layer is higher, the bonding strength of the electrode constituent materials in the outer circumferential layer increases, and as a result, the bonding strength of the electrode constituent materials in the outer circumferential layer increases during battery manufacturing and use. There will be no peeling or falling off. Therefore, internal short circuits of the battery can be prevented.

G. EXAMPLE Hereinafter, an example according to the present invention will be described with reference to FIGS. 1 to 7. Note that this example is a cylindrical nonaqueous electrolyte secondary battery.

G1. Example 1 In Example 1, the thickness at the end of the strip-shaped electrode is made thinner.

FIG. 1 shows a schematic longitudinal section of the non-aqueous electrolyte secondary battery of this example, and this battery was produced as described below.

First, negative electrode 1 was created as follows.

Pitch coke that has been crushed into granules is used as a negative electrode active material carrier, and 90 parts by weight of this pitch coke and 10 parts by weight of polyvinylidene fluoride (PVDF) as a binder are added and mixed to form a negative electrode mixture (negative electrode active material carrier). constituent substances).

This negative electrode mixture was then dispersed in a solvent, N-methylpyrrolidone, to form a slurry (paste).

Next, this negative electrode mixture slurry was applied to both sides of a strip-shaped copper foil with a thickness of 10 μm as the negative electrode current collector 11, and dried.
After that, compression molding is performed using a roller press machine, and as shown in FIG. 2, the thickness at both ends 15 along the length direction is also 150 βm, and the thickness t2 of the central flat part 16 is 170 μm. A strip-shaped negative electrode 1 was made. The strip-shaped negative electrode 1 has an inner peripheral layer 1 located on the inner peripheral side when forming a wound electrode body 10, which will be described later, on both sides of the current collector 11.
2 and an outer peripheral layer 13 located on the outer peripheral side.

As shown in FIG. 2, the strip-shaped negative electrode l is substantially flat except for the vicinity of the end of the electrode, forming a central flat part 16.
It is gradually decreasing towards. When the wound electrode body 10 is configured as described later, the central flat portion 16 comes into close contact with the separators 3a and 3b, but the end portions 15 do not come into close contact.

The volume average particle size X of the beach coke used was 10μ.
m, and its standard deviation σ was 5 μm.

In addition, vinylidene nitride was completely dissolved in the solvent N-methylpyrrolidone.

Next, positive electrode 2 was created as follows.

Mix 1 mole of lithium carbonate and 1 mole of cobalt carbonate,
00''C in air for 5 hours to obtain LiCoO2, which was used as a positive electrode active material, and this LiC.

0291 parts by weight, 6 parts by weight of graphite as a conductive material, and polyvinylidene fluoride (PVDF) as a binder.
Add 3 parts by weight and mix to form a positive electrode mixture (positive electrode constituent material)
And so. This positive electrode mixture was then dispersed in a solvent, N-methylpyrrolidone, to form a slurry (paste).

Next, this positive electrode mixture slurry is uniformly applied to both sides of a strip-shaped aluminum foil with a thickness of 20 μm as the positive electrode current collector 21, dried, and then compression-molded using a roller press machine to form the strip-shaped positive electrode 2. made. The thickness of the strip-shaped positive electrode 2 at the center and at the ends were both 180 μm.

Note that the width of the strip-shaped negative electrode 1 is slightly larger than the width of the strip-shaped positive electrode 20.

The above strip-shaped negative electrode 1, the above strip-shaped positive electrode 2, and a thickness of 25 μm
a first and a second microporous polypropylene film of
The separators 3a and 3b were stacked in the order of second separator 3b, positive electrode 2, first separator 3a, and negative electrode 1 to obtain a laminate. The wound electrode body 1
0 was created.

A schematic partial cross section of the wound electrode body 10 is shown in FIG.

In this wound electrode body 10, as shown in the figure, the negative electrode 1 has a negative electrode inner peripheral layer 12 and a negative electrode outer peripheral layer 13 made of the above-mentioned negative electrode constituent materials on the inner peripheral surface and outer peripheral surface of the negative electrode current collector 11, respectively. The positive electrode 2 includes a positive electrode inner peripheral layer 22 and a positive electrode outer peripheral layer 23 made of the above-described positive electrode constituent material layer on the inner peripheral surface and the outer peripheral surface of the positive electrode current collector 21, respectively. A first separator 3a is interposed between the negative electrode outer peripheral layer 13 and the positive electrode inner peripheral layer 22, and a second separator 3a is interposed between the positive electrode outer peripheral layer 23 and the negative electrode inner peripheral layer 12.
A separator 3b is interposed therebetween.

Further, as shown in the vertical cross-sectional view of the secondary battery in FIG.
2 or the negative electrode outer peripheral layer 13 and the second separator 3b or the first
A triangular gap 18 is formed between the surface of the negative electrode 1 and the separator 3a at the end i5b.
, 3b are not in close contact with each other.

Note that the order of stacking the negative electrode 1 and the positive electrode 2 in the above-mentioned laminate may be reversed so that the positive electrode 2 is located at the innermost periphery of the wound electrode body 10.

The wound electrode body 10 produced as described above was housed in a nickel-plated iron battery can 5, as shown in FIG. In order to collect current from the positive electrode 2, an aluminum positive electrode part 9 was attached to the positive electrode 2, led out from the positive electrode 2, and welded to the protrusion 34a of the metal safety valve 34. Further, in order to collect current from the negative electrode 1, a nickel negative electrode lead 8 was attached to the negative electrode 1, led out from the negative electrode 1, and welded to the battery can 5. A non-aqueous electrolyte obtained by mixing propylene carbonate in which 1 mol/l of lithium hexafluorophosphate was dissolved and 1,2-dimethoxyethane was injected into the battery can 5.

Next, a pair of insulating plates 4a and 4b were placed inside the battery can 5 so as to face the upper and lower surfaces of the wound electrode body 10, respectively. Further, this battery can 5, the safety valve 34 and the battery lid 7 which were in close contact with each other at their outer peripheries were caulked via an insulating sealing gasket 6 to seal the battery can 5. At this time, Gaskent 6
The lower end side in FIG. 1 is in contact with the outer peripheral surface of the insulating plate 4a, and the insulating plate 4a is in close contact with the upper surface side of the wound electrode body 10.

As described above, a cylindrical nonaqueous electrolyte secondary battery with a diameter of 14 mm and a height of 50 mm was produced. This battery is referred to as Battery A for convenience, as shown in Table 1 below.

Note that the cylindrical nonaqueous electrolyte secondary battery has a safety valve 34,
stripper 35, these safety valves 34 and strippers 36
An intermediate fitting body 35 made of an insulating material for integrating the
It is equipped with Although not shown, the safety valve 34 has a cleavage part that ruptures when the safety valve 34 is deformed.
A hole is provided in each. In the event that the battery internal pressure rises for some reason, the safety valve 34 will close its protrusion 34a.
By deforming upward in FIG. 1 around They are each configured to exhaust gas generated within the battery.

Further, the first and second separators 3a and 3b are connected to the negative electrode 1.
and slightly larger in the length and width directions than the positive electrode 2,
As shown in FIG. 1, it slightly protrudes from the respective ends of the negative electrode 1 and the positive electrode 2.

In the non-aqueous electrolyte secondary battery, lithium or lithium alloy can be used as the active material of the negative electrode 1, or a conductive polymer such as polyacetylene or a carbon material such as coke can be used as the active material carrier. Both can be doped and dedoped with lithium. On the other hand, as the active material of the positive electrode 2, transition metal compounds such as manganese dioxide and vanadium pentoxide, transition metal chalcogen compounds such as iron sulfide, and even composite compounds of transition metals and lithium can be used.

Further, as the electrolytic solution, for example, a non-aqueous electrolytic solution in which a lithium salt is used as an electrolyte and dissolved in an organic solvent (non-aqueous solvent) is used.

The organic solvent here is not particularly limited, but includes, for example, propylene carbonate, ethylene carbonate, 1,2-dimethoxyethane, 1,2-jethoxyethane, T-butyrolactone, tetrahydrofuran,
Single or mixed solvents such as 1,3-dioxolane, 4-methyl-1,3-dioxysolane, styl ether, sulfolane, methylsulfolane, acetonitrile, and propionitrile can be used.

Any conventionally known electrolytes can be used, including LiClO4, LiAsF, LiPF6, LiB
F, , LiB(C6H5)4, LjCI, LiBr
, CH35O3Li, CH35O3Li, etc.

Further, as the non-aqueous electrolyte, a conventionally known solid electrolyte can also be used.

Next, a cylindrical nonaqueous electrolyte secondary battery B was produced in the same manner as the battery A, except that the thickness at the end 15 along the length of the strip-shaped negative electrode 1 was changed to 130 μm.

In addition, as a comparative example for confirming the effects of the present invention, the thickness t at the end portion 15 along the length direction of the strip-shaped negative electrode 1 was
A cylindrical nonaqueous electrolyte secondary battery C was produced in the same manner as the battery A above, except that , was changed to 170 μm.

For the above three types of batteries A, B, and C, 100 pieces each were produced, and the order rate of internal short circuit holes in uncharged secondary batteries (uncharged holes) at the time of assembly was investigated. Furthermore, these batteries have an upper limit voltage of 4.1■ at a current of 460mA.
We investigated the ordering rate for internal short-circuit holes in rechargeable batteries (charged products) that had been charged for 2 hours.

The results are shown in Table 1 below.

- Margin below - As can be seen from Table 1 above, in Battery C of Comparative Example, internal short circuits occurred when the battery was assembled, and the number of internal short circuits increased after charging.

Further, in battery A, no internal short circuits were observed when the battery was assembled, but a small number of internal short circuits occurred after charging.

In battery B, no internal short circuit occurred even after charging.

As described above, in this Example 1, the thickness of the strip-shaped negative electrode 1 at the end portion 15 along the length direction is thinner than that of the central portion 16, so when the wound electrode body 10 is manufactured, the thickness of the negative electrode 1 is Since the negative electrode 1 and the separators 3a, 3b do not come into close contact with each other at the end portion 15, and a gap 18 is formed between them, there is a risk that the negative electrode constituent material may penetrate the separators 3a, 3b at the end portion 15. do not have. In addition, since the amount of electrode constituent materials that are likely to peel or fall off has already decreased at the end 15 of the negative electrode 1, the electrode constituent materials may fall off at the end 15 of the negative electrode 1 during battery manufacturing and use. There is very little risk of it peeling off. As a result, internal short circuits in the battery are effectively prevented.

In Example 1, the thickness at the end 15 along the length of the strip-shaped negative electrode 1 was made thin, but in addition, the thickness at the end 17 along the width direction of the negative electrode 10 was made thinner. As a result, at the ends 17 of the negative electrode 1 located at the innermost and outermost peripheries of the wound electrode body 10,
A similar effect can be obtained.

Further, it is more effective if the thickness at the end of the positive electrode 2 is made thin as in the case of the negative electrode 1.

Further, according to further research by the present inventors, when at least one kind of electrode constituent materials consisting of multiple kinds of materials is present in the electrode as particulates, the average particle size of the particulate material is defined as X; If the standard deviation is σ, then the difference in thickness between the central flat part 16 of the electrode and the end part 15 of the electrode (t2
-LI) is 12 (, r ≧X+5 σ
It is preferable to satisfy (3) in order to prevent internal short circuits in the battery. In addition, when a plurality of types of granular substances are present in the electrode, the above formula (3) may be satisfied for the one with the largest particle size.

Considering the internal short circuit occurrence rate in Table 1 above from equation (3) above, the difference in thickness for battery A does not satisfy equation (3) above, but the difference in thickness for battery B, which has a better effect, It can be seen that the difference in height satisfies equation (3). Therefore, when thinning the ends of an electrode that includes particulate electrode constituent materials, the difference in thickness between the center and the ends (t
2 t+ ) is determined to satisfy equation (3), which is more effective in preventing internal short circuits in the battery.

G2. Example 2 In Example 2, the corners of the electrode are missing by applying force to the four corners of the strip-shaped electrode.

FIG. 4 shows a schematic vertical cross-sectional view of the non-aqueous electrolyte secondary battery of this example, which was manufactured as described below.

In order to make the strip-shaped negative electrode 1a, a slurry of the same negative electrode mixture (negative electrode constituent material) as in Example 1 was applied to both sides of a strip-shaped copper foil with a thickness of 10 μm as the negative electrode current collector 11, and dried. , and then compression molded using a roller press machine. and,
By tightening the four corners, a strip-shaped negative electrode 1a was obtained.

A plan view of this strip-shaped negative electrode 1a is shown in FIG. 5A, and the four corners of the strip-shaped negative electrode 1a are cuffed in a straight line, and the corners 19 shown by broken lines that existed at the four corners have been removed to form an almost triangular shape. lacking.

Next, in order to make a strip-shaped positive electrode 2a, a slurry of the same positive electrode mixture (positive electrode constituent material) as in Example 1 was applied to the positive electrode current collector 2a.
It was coated on both sides of a strip-shaped aluminum foil with a thickness of 20 μm, dried, and then compression-molded using a roller press. Then, by cutting the four corners, a strip-shaped positive electrode 2a was obtained.

This strip-shaped positive electrode 2a is a strip-shaped negative electrode 1a shown in FIG. 5A.
It has a substantially similar shape, with the corners that existed at the four corners being removed and missing in a roughly triangular shape.

The above-mentioned band-shaped negative electrode 1a, the above-mentioned band-shaped positive electrode 2a, and the thickness 25
In Example 1, strip-shaped first and second separators 3a and 3b made of microporous polypropylene films of μm were laminated.
Similarly, a wound electrode body 10a was created by spirally winding the electrode body 10a many times.

The cross-sectional structure of this wound electrode body 10a is substantially the same as the wound electrode body 10 shown in FIG. 3, and the negative electrode 1a includes an inner peripheral layer 12 and an outer peripheral layer 13 made of negative electrode constituent materials, The positive electrode 2a includes an inner peripheral layer 22 and an outer peripheral layer 2 made of positive electrode constituent materials.
It has 3.

A cylindrical non-aqueous electrolyte secondary battery having a diameter of 14 mm and a height of 50 cm as shown in FIG. 4 was fabricated using the above-described wound electrode body 10a in the same manner as in Example 1.

This battery will be referred to as a battery for convenience as shown in Table 2 below.

Next, a strip-shaped negative electrode 1a having a circular shape after canting its four corners as shown in FIG. 5B was obtained in the same manner as in the case of the battery. In this strip-shaped negative electrode 1a, the corner portions 19 shown by broken lines, which were present at the four corners, have been removed and are missing as shown in the figure.

Further, a strip-shaped positive electrode 2a was obtained in the same manner as in the case of the battery cell described above, but this strip-shaped positive electrode 2a has a shape substantially similar to that in FIG. 5B, and the four corners of the strip-shaped positive electrode 2a are the same. It has been removed and is missing as shown.

A cylindrical non-aqueous electrolyte secondary battery E was produced in the same manner as the battery described above, except that the strip-shaped negative electrode 1a and strip-shaped positive electrode 2a as described above were used.

Next, as a comparative example for confirming the effects of the present invention, a cylindrical non-aqueous electrolyte secondary battery was prepared in the same manner as the above battery except that a strip-shaped negative electrode and a strip-shaped positive electrode were used with the four corners of the electrodes not removed. Battery F was produced.

Fifty pieces each of the above three types of batteries F and F were manufactured, and the incidence of internal short circuits in uncharged secondary batteries at the time of assembly was investigated.

This result is shown in the second display below.

Table 2 As shown in Table 2 above, the occurrence of internal short circuits was observed in Battery F of Comparative Example, but battery F of Example 2 and E
No internal short circuits were observed.

As described above, in Example 2, the corner portions 19 are missing at the four corners of the strip-shaped picture electrode, so that the electrode constituent material does not penetrate the separator at the four corners of the electrode when manufacturing the wound electrode body 10a. do not have.

Further, the electrode active material does not fall off or peel off at the four corners of the electrode during manufacture and use of the battery. As a result, internal short circuits in the battery are effectively prevented.

In addition, when making the strip-shaped negative electrode 1a and the strip-shaped positive electrode 2a,
The current collector 11.21 may be shaped in advance as shown in FIG. 5A or 5B.

Further, in Example 2, the corners are removed from the four corners of the picture electrode, but the corners may be removed only from either the negative electrode or the positive electrode.

G3. Example 3 In Example 3, the binder content in the outer circumferential layer of the electrode was higher than that in the inner circumferential layer of the electrode.

The longitudinal section of the non-aqueous electrolyte secondary battery of Example 3 is the same as that shown in FIG.
It is similar to that shown in the figure.

First, the binder content in the negative electrode outer circumferential layer 13 was made higher than that in the negative electrode inner circumferential layer 12, and in the case of the positive electrode, the binder content in the outer circumferential layer 23 and the inner circumferential layer 22 were made equal. It was made as follows.

A strip-shaped negative electrode 1b was obtained as follows.

Using pulverized pitch coke as a negative electrode active material carrier, 88 parts by weight of this pitch coke and 12 parts by weight of polyvinylidene fluoride (PVDF) as a binder were added and mixed to form the first negative electrode mixture (negative electrode constituent material). ).

Further, 90 parts by weight of pitch coke and 10 parts by weight of PVDF were similarly mixed to form a second negative electrode mixture (negative electrode constituent material).

Slurries of first and second negative electrode mixtures were obtained from the above-mentioned first and second negative electrode mixtures in the same manner as in Example 1, respectively.

Next, the slurry of the first negative electrode mixture is applied to one surface of the negative electrode current collector 11 (the side corresponding to the negative electrode outer peripheral layer 13 in the wound electrode body 10b shown in FIG. 3), and the other surface is coated with the slurry of the first negative electrode mixture. (
A slurry of the second negative electrode mixture was coated on the side corresponding to the negative electrode inner circumferential layer 12) and dried, and then compression molded using a roller press machine to obtain a strip-shaped negative electrode 1b.

At this time, the thicknesses of the negative electrode outer circumferential layer 13 side and the negative electrode inner circumferential layer 12 examples are the same, 80 μm, respectively, and the width of the strip-shaped negative electrode 1 is 4 μm.
It was 1.5 mm and 270 mm long.

The content rates Xa and xb of PVDF as a binder in the outer peripheral layer 13 and inner peripheral layer 12 of this strip-shaped negative electrode 1b are
Since the mixing ratio (blending ratio) of PVDF in the and second negative electrode mixture is as described above, 12% by weight and 1% by weight, respectively.
It is 0% by weight.

Next, a strip-shaped positive electrode 2b was obtained in the same manner as in Example 1 using the same positive electrode mixture. At this time, the positive electrode outer peripheral layer 23
The thickness of the side and the positive electrode inner circumferential layer 22 side are the same, 80 μm, respectively, and the width of the band-shaped positive electrode 2b is 40.5 mm, and the length is 23 mm.
It was 0 mm.

The content XaXb' of PVDF as a binder in the outer circumferential layer 23 and inner circumferential layer 22 of this strip-shaped positive electrode 2b is the same, 3% by weight, respectively. In addition, LiC as a positive electrode active material
The content of o0□ and graphite as a conductive agent is 9
1% by weight and 6% by weight.

The strip-shaped negative electrode 1b, the strip-shaped positive electrode 2b, and the thickness 25
Example 1 Using band-shaped first and second separators 3a and 3b made of microporous polypropylene film of μm,
In the same manner as above, a wound electrode body 10b having a structure similar to that shown in FIG. 3 was created.

Using the above-mentioned wound electrode body 10b, a diameter of 14IIIIIIl and a height of 50mm was obtained in the same manner as in Example I as shown in FIG.
A cylindrical nonaqueous electrolyte secondary battery of InI11 was produced.

For convenience, this battery is designated as Battery G as shown in Table 3 below.
shall be.

Next, by changing the blending ratio of PVDF in the first and second negative electrode mixtures, the PVDF contents Xa, Cylindrical non-aqueous electrolyte secondary batteries H and I were respectively produced in the same manner as Battery G, except that the battery was changed.

In addition, as a comparative example for confirming the effects of the present invention, as shown in Table 3, except that the PVDF contents Xa and Xb in the negative electrode outer circumferential layer 13 and the negative electrode inner circumferential layer 12 were made equal to two, Cylindrical nonaqueous electrolyte secondary batteries J and K were produced in the same manner as Battery G above, respectively.

The following margin - 50 pieces of each of the above five types of batteries G-K were manufactured, each with a current of 460 mA and an upper limit voltage of 4°1■.
A charge/discharge cycle of charging for an hour and then discharging at 18Ω to a discharge end voltage of 2.75V was performed 100 times. Then, the average discharge capacity of the battery at the 10th time when the discharge capacity became stable and the incidence of internal short circuit holes in the battery at the 100th time were investigated.

The results are shown in Table 4.

Table 4 As shown in Tables 3 and 4 above, a battery G in which the content Xa of PVDF as a binder in the negative electrode outer peripheral layer 13 is higher than the PVDF content Xb in the negative electrode inner peripheral layer 12;
In H and I, the rate of occurrence of internal short circuit holes is lower than in the battery K of the comparative example (PVDF contents Xa and Xb of the negative electrode outer circumferential layer 13 and the negative electrode inner circumferential layer 12 are equal and lowest). However, in the battery 1, the PVDF content Xa of the negative electrode outer peripheral layer 13 was made considerably high, resulting in a decrease in discharge capacity. Further, in the battery J of the comparative example, the PVDF content χ in the negative electrode outer peripheral layer 13 was
Since a is higher than that of the battery, the incidence of internal short circuit holes is low.

Also, when comparing battery J and battery H, the negative electrode outer circumference N of both
Although the PVDF content Xa in No. 13 is the same, the PVDF content xb in the negative electrode inner peripheral layer 12 of Battery J is higher than that of Battery H (the content of pinch coke is lower).
The discharge capacity of battery J is low.

Looking at the results of Table 3 and Table 4 above from the above formulas (1) and (2) showing the preferable ranges of the binder contents Xa and Xb, in the case of batteries G and H, formula (1) and (2), while battery I satisfies equation (1) but does not satisfy equation (2). Therefore, when the binder content Xa in the outer circumferential layer of an electrode is made higher than the binder content xb in the inner circumferential layer of the electrode, the binder is Agent content X
It can be seen that by determining a and xb, it is effective in preventing internal short circuits in the battery without significantly reducing the battery capacity.

Next, in not only the negative electrode 1b but also the positive electrode 2b, the binder content Xa' in the positive electrode outer peripheral layer 23 is set to the positive electrode inner circumference J! 22
A battery in which the binder content was higher than Xb' was produced as follows.

The PVDF content Xa in the outer peripheral layer 13 of the negative electrode 1b is 1
4%, and the PVDF content xb in the negative electrode inner peripheral layer 12
A strip-shaped negative electrode 1b was obtained in the same manner as in Battery G, except that the negative electrode 1b was changed to 10%.

A strip-shaped positive electrode 2b was obtained as follows.

Using the positive electrode active material (lico, o□), conductive agent [graphite], and binder (PVDF) in the above Battery G, 6 parts by weight of graphite and 4 parts by weight of pVDF were added to 90 parts by weight of LiCoz0□ and mixed. , a first positive electrode mixture (positive electrode constituent material).

Next, the positive electrode mixture used in the battery G was used as a second positive electrode mixture.

First and second positive electrode mixture slurries were obtained from the first and second positive electrode mixtures in the same manner as in Example 1, respectively.

Next, a slurry of the first positive electrode mixture is applied to one surface of the positive electrode current collector 21 (the side corresponding to the positive electrode outer peripheral layer 23 in the wound electrode body 10b shown in FIG. 3), and the other surface is coated with the slurry of the first positive electrode mixture. (
A slurry of the second positive electrode mixture was applied to the side corresponding to the positive electrode inner peripheral layer 22, and then a battery G was prepared in the same manner as in Example 1.
A strip-shaped positive electrode 2b similar to the above was obtained.

In the outer peripheral layer 23 of this strip-shaped positive electrode 2b, the P■DF content Xa' is 4% by weight, the LiCo20□ content is 90% by weight, and the graphite content is 6% by weight. Further, the PVDF content Xb' in the positive electrode inner peripheral layer 22 is 3% by weight.

Using the above-mentioned strip-shaped negative electrode 1b and strip-shaped cathode 2b, a wound electrode body 10b was obtained in the same manner as in the above-mentioned battery G, and then a cylindrical non-aqueous electrolyte secondary battery similar to the above-mentioned battery G was produced. For convenience, this battery is referred to as a battery as shown in Table 5 below.

Next, PVDF and LiC in the first positive electrode mixture
By changing the blending ratio of 0Jz, the positive electrode outer peripheral layer 23
Cylindrical non-aqueous electrolyte secondary batteries M, N, 0, and P were produced in the same manner as in Battery G, except that the PVDF content Xa' was changed several times as shown in Table 5.

- Margin below 50 of each of the above five types of batteries L-P were manufactured and the same charge/discharge cycles as described above were performed 100 times. We investigated the incidence of internally shorted products. The results are shown in Table 6.

Table 6 As shown in Tables 5 and 6 above, the PVDF content Xa in each outer peripheral layer 13.23 of the negative electrode 1b and the positive electrode 2b
, Xa' was higher than the PVDF content xb, xb' in each inner peripheral layer 12.22, and no internal short circuit was observed in any of the batteries LP. Furthermore, the decrease in discharge capacity was within an acceptable range. In addition, the above battery L
In the case of -P, both satisfy the above formulas (1) and (2).

Battery G-P in Example 3 and Comparative Example as described above
From the results, even if the binder content Xa of the negative electrode outer circumferential layer 13 is made higher than the binder content χb of the negative electrode inner circumferential layer 12 only in the negative electrode 1b, the effect of preventing internal short circuits of the battery can be obtained, and Also in the positive electrode 2b, if the binder content χa' of the positive electrode outer circumferential layer 23 is made higher than the binder content Xb' of the positive electrode inner circumferential layer, the effect of preventing internal short circuits in the battery will further increase, and the battery capacity will decrease. It can be seen that there are few If each of the contents Xa, Xb, and Xa'χb' of the PVDF satisfies the above formulas (1) and (2), a satisfactory result can be obtained regarding prevention of internal short circuit of the battery and prevention of decrease in battery capacity. Obtainable.

As explained above, in this Example 3, since the binder content in the outer peripheral layer of the electrode was higher than that in the inner peripheral layer of the electrode, the bonding strength of the electrode constituent materials in the outer peripheral layer increased, and As a result, it is possible to prevent the electrode constituent material from falling off or peeling off, particularly during use of the battery, in the outer circumferential layer where the electrode constituent material tends to fall off or peel off because the amount of elongation that occurs during winding of the electrode is greater than that of the inner circumferential layer. Therefore, it is effective to prevent internal short circuits of the battery and the charge/discharge cycle characteristics are improved.

G4. Example 4 In this Example 4, the negative electrode used in Examples 1 to 3 described above was used in order to prevent an internal short circuit of the battery due to dendrite-like precipitates and a decrease in battery capacity during use of the battery. This is an improved current collector 11, and is substantially the same as the non-aqueous electrolyte secondary battery shown in FIGS. 3 and 4.

First, the findings obtained by the present inventors regarding improvements to the current collector will be explained.

That is, in the wound electrode body 10 having the structure shown in FIG. 3, since the current collector 11 exists almost at the center of the negative electrode 1, there is no movement of ions between the outer circumferential layer 13 and the inner circumferential layer 12.
The negative electrode inner peripheral layer 27 at the innermost periphery of the negative electrode 1 (one same opening) and the negative electrode outer peripheral layer 32 at the outermost periphery of the negative electrode 1 do not contribute to the actual charging/discharging reaction of the battery. Furthermore, for example, the outer peripheral layer 28 at the innermost circumference of the negative electrode 1 has a relatively heavy load, especially in the charging reaction (because the amount of active material carrier is smaller compared to the inner peripheral layer 29 at the 102nd turn of the negative electrode). , lithium precipitates unevenly on the electrode surface and tends to grow in the form of dendrites. This dendrite-like precipitate is likely to penetrate the separator and cause an internal short circuit, impairing reliability.

The negative electrode inner circumferential layer 27 and the negative electrode outer circumferential layer 32 are useless because they do not contribute to the charge/discharge reaction, and furthermore, since the internal volume of the battery is limited, the effective volume within the battery decreases, and as a result,
Battery capacity will decrease.

In order to eliminate these drawbacks, a strip-shaped current collector is used in the innermost length of the electrode in the wound electrode body, or in the length of the innermost electrode and the outermost length of the electrode. It has been found that providing a large number of holes is effective.

Furthermore, it has been found that when a large number of holes are provided in each of the above portions, the porosity of the holes is preferably within the range of 3 to 30%. If the porosity is less than 3%, ions will not move sufficiently, and if it is more than 30%, the electrode constituent material will easily fall off, which is undesirable.

As a result, for example, in the wound electrode body shown in FIG. in,
Lithium transfer becomes possible. Therefore, the negative electrode outer peripheral layer 28
Since the load during charging is reduced and dendrite-like precipitates are less likely to occur, it is effective in preventing short circuits inside the battery. Then, the negative electrode inner peripheral layer 27 and the negative electrode outer peripheral layer 3
2 contributes to the discharging and charging reaction, and since they are not wasted and the effective volume within the battery does not decrease, it is effective in preventing a decrease in battery capacity.

Based on the above findings, in Example 4, the strip-shaped negative electrode current collector 11a was configured as follows.

FIG. 6A is a plan view of the strip-shaped negative electrode current collector 11a.

In the strip-shaped copper foil, a large number of circular holes 41 are inserted into the negative electrode 1b.
A hole 38 was formed by providing a porosity of 3% within a length 11 on the innermost circumferential side of the electrode, thereby obtaining a strip-shaped negative electrode current collector 11a. At this time, the negative electrode current collector 1
It is desirable that holes 41 are not provided in the end portion 45 along the width direction and the end portion 46 along the length direction of 1a in order to prevent the negative electrode constituent material from falling off when the negative electrode constituent material is provided. Note that the above β1 was approximately 20 mm.

A cylindrical nonaqueous electrolyte secondary battery similar to the battery in Example 3 was produced except that the negative electrode current collector 11a as described above was used. For convenience, this battery will be referred to as battery B' as shown in Table 7 below.

Next, the porosity of the pores 38 of the negative electrode current collector 11a is adjusted to the seventh level.
Cylindrical non-aqueous electrolyte secondary batteries A', C', and D' are similar to the above battery B' except that the changes were made in five ways as shown in the table.
, E' and F' were produced.

Note that the hole 38 of the negative electrode current collector 11a in the battery F' consists of a large number of square holes 42, as shown in FIG. 6B.

Further, the outer diameter of the wound electrode body 10b was 13 m, and the inner diameter of the hollow part at the center was 3.5 m.

In addition, as a comparative example to confirm the effect of Example 4, a cylindrical nonaqueous electrolyte secondary battery G' similar to the above battery B' was obtained except that a negative electrode current collector without holes was used. Ta.

What about the above seven types of batteries A' to G'? Ten batteries were produced at a time, and the same charge/discharge cycles as in Example 3 were performed to determine the average charge/discharge capacity of the batteries at the 10th cycle. The results are shown in Table 7.

Table 7 As shown in the above Table 7, the batteries A' to F' using the negative electrode current collector 11a having the holes 38 have higher discharge capacities than the battery G' of the comparative example.

Among them, in batteries B', C', D' and F', the porosity Y
is within 3% to 30%, so the capacity is 400mA, H
This shows good results.

In addition, when the batteries A' to G', which had been repeatedly charged and discharged, were disassembled and investigated, it was found that in batteries B', C', D', and F', the length 11 of the hole 38 of the negative electrode current collector 11a The corresponding portion of the negative electrode 1b underwent a battery reaction, and no dendrite-like lithium was observed. In addition, battery G′ of the comparative example
In this case, the innermost portion of the negative electrode 1b corresponding to the inner peripheral layer 27 does not undergo a battery reaction, and in the battery E', the negative electrode constituent material falls off at the hole 41 in the hole 38 of the negative electrode 1b. was observed.

Next, an example using a negative electrode current collector 11b in which holes 39 are provided not only at the innermost circumferential side of the current collector but also at the outermost circumferential side in the electrode of the wound electrode body will be described.

As shown in FIG. 7A, in the strip-shaped copper foil, a large number of circular holes 41 are provided in the outermost portion of the negative electrode 1b within a length 12 so that the porosity is 3%. □ holes 39 were formed, and a strip-shaped negative electrode current collector 11b was obtained. A cylindrical non-aqueous electrolyte secondary battery I' was produced in the same manner as the battery B', except that such a negative electrode current collector 11b was used.

In addition, the above! ! , 2 was about 50 mm, and the porosity in the holes 38 was the same as that in the holes 39.

Next, a cylindrical, non-aqueous electrolyte similar to that of the battery B was used, except that the porosity in the holes 38 and 39 of the negative electrode current collector 11b was changed as shown in Table 8 below. Secondary batteries H'J',K' and L' were produced.

Ten batteries were prepared for each of the five types of batteries H' to L', and the same charge/discharge cycles as described above were performed to determine the average discharge capacity of the batteries at the 10th cycle. This result is the 8th
Shown in the table.

Margin Table 8 Below: As shown in Table 8 above, the hole 38 of the negative electrode current collector 11b
Batteries I'J' and Ni' in which the porosity in the pores 391 was within the range of 3% to 30% had a capacity of 400 mAH or more, showing good results. Furthermore, when comparing the results in Table 8 with Table 7, all of the batteries in Table 8 have negative electrode current collectors 1 which are provided with holes 39 in addition to holes 38.
It can be seen that the capacity is large because b is used.

From the above results, by providing the holes 38 with a porosity of 3 to 30% in the current collector on the innermost side of the wound electrode body, it is possible to prevent dendrite-like lithium precipitates from forming on the negative electrode surface. This makes it possible to prevent internal short circuits in the battery and improve battery capacity. Preferably, by providing the current collector with holes 39 having a porosity of 3 to 30% on the outermost circumferential side as well, it is possible to further improve the battery capacity.

As a result, a high capacity and reliable cylindrical nonaqueous electrolyte secondary battery using metal foil as a current collector can be obtained.

Note that in the battery of Example 4, the electrodes located at the innermost and outermost peripheries of the wound electrode body were negative electrodes, but when the positive electrodes were located at the innermost and outermost peripheries, the positive electrode current collector A similar effect can be obtained by providing a hole in the hole. Further, the material of the metal foil current collector is not particularly limited, but aluminum, copper, iron, stainless steel, and titanium are preferable. Among these, aluminum and copper are more preferred. The thickness of the metal foil is preferably 200 μm or less. The shape of the hole also
Although circular or square holes can be used, circular holes are preferable because they have stronger mechanical strength. Further, in order to prevent the electrode constituent material from falling off from the electrode, it is desirable that no hole be provided at the end of the electrode.

H6 Effects of the Invention Since the present invention is configured as described above, it has the following effects.

In the secondary battery of claim 1, it is possible to prevent the electrode constituent materials from falling off, peeling off, and penetrating the separator at the ends of the band-shaped electrode, and in the secondary battery of claim 2, at the corners of the band-shaped electrode. Therefore, internal short circuits can be prevented during battery manufacture and use.

In the secondary battery according to claim 3, the bonding force of the electrode constituent material in the outer peripheral layer of the electrode of the wound electrode body is increased, and it is possible to prevent the electrode constituent material from falling off and peeling off in the second outer peripheral layer. Internal short circuits can be prevented during manufacturing and use.

Therefore, a secondary battery with high reliability and excellent heavy load characteristics can be provided.

[Brief explanation of the drawing]

1 to 7 show examples according to the present invention, in which FIG. 1 is a schematic vertical cross-sectional view of a cylindrical nonaqueous electrolyte secondary battery of Example 1, and FIG. Figure 3 is a perspective view of a strip-shaped negative electrode used in the secondary battery shown in Figure 3; Figure 4 is a schematic longitudinal sectional view of the cylindrical non-aqueous electrolyte secondary batteries of Examples 2.3 and 4, and Figures 5A and 5B are the batteries used in the secondary battery shown in Figure 4 of Example 2. FIG. 6A, FIG. 6B, and FIG. 7 are plan views of the strip-shaped negative electrode current collector used in the secondary battery shown in FIG. 4 of Example 3. In the symbols used in the drawings, the following symbols are used: Band-shaped negative electrode Band-shaped positive electrode b - First and second separator wound electrode body Negative current collector Negative inner circumferential layer (negative electrode constituent material layer) Negative electrode outer circumferential layer (negative electrode structure) Material layer) Ends along the length direction of the negative electrode (ends) Central flat part (center) of the negative electrode ・-1111 Corners of the negative electrode ・-Positive electrode current collector Positive electrode inner peripheral layer (positive electrode constituent material layer) Positive electrode outer peripheral layer (positive electrode constituent material layer)

Claims (1)

[Claims] 1. A strip-shaped first electrode including a negative electrode constituent material layer or a positive electrode constituent material layer, a strip-shaped second electrode including a positive electrode constituent material layer or a negative electrode constituent material layer, and a strip-shaped separator. are stacked and spirally wound along their length,
In a secondary battery comprising a wound electrode body configured such that the separator is interposed between the first electrode and the second electrode, one of the strip-shaped first or second electrodes A secondary battery characterized in that the thickness of at least one electrode at an end is thinner than the thickness at the center of this electrode. 2. In a state in which a strip-shaped first electrode comprising a negative electrode constituent material layer or a positive electrode constituent material layer, a strip-shaped second electrode comprising a positive electrode constituent material layer or a negative electrode constituent material layer, and a strip-shaped separator are laminated. It is wound in a spiral along its length,
In a secondary battery comprising a wound electrode body configured such that the separator is interposed between the first electrode and the second electrode, one of the strip-shaped first or second electrodes A secondary battery characterized in that at least one strip-shaped electrode lacks a corner. 3. A strip-shaped first electrode comprising a negative electrode constituent material layer or a positive electrode constituent material layer, a strip-shaped second electrode comprising a positive electrode constituent material layer or a negative electrode constituent material layer, and a strip-shaped separator are laminated. It is wound in a spiral along its length,
a wound electrode body configured such that the separator is interposed between the first electrode and the second electrode; The electric body is provided with an inner layer and an outer layer made of the negative electrode or positive electrode constituent material on the inner and outer surfaces of the second current collector, respectively, and the second electrode is provided with the inner and outer layers on the inner and outer surfaces of the second current collector. In a secondary battery in which the wound electrode body is configured to include an inner circumferential layer and an outer circumferential layer each comprising a positive electrode or a negative electrode constituent material, an electrode of at least one of the first or second electrodes. The constituent material includes at least an active material or an active material support and a binder, and the binder content in the outer peripheral layer of this electrode is higher than the binder content in the inner peripheral layer of this electrode. A secondary battery characterized by its high price.