JPH11273738A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent short circuit between a negative can and a positive electrode even if a separator in the outermost layer is peeled off and the positive electrode is exposed when a spirally wound electrode body is inserted into the negative can. SOLUTION: In a nonaqueous electrolyte secondary battery in which a spirally wound electrode body 15 prepared by spirally winding a belt-like negative electrode 1 and a belt-like positive electrode 2 through a separator 3 is housed in negative can 5 together with an nonaqueous electrolyte, an insulated coating film 13 is formed on the inner surface of the negative can 5 to prevent the direct contact of the spirally wound electrode body 15 with the inner surface of the negative can 5. The insulated coating film 13 is preferable to be formed with an organic polymer material such as polyvinylidene fluoride, polycarbonate, polyimide, polycarboacetal, polyester, polypropylene, acrylonitrile-butadiene- styrene copolymer resin, urethane resin, styrene-butadiene rubber, butadiene rubber, ethylene-propylene rubber, isoprene rubber or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte secondary battery in which a spirally wound electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound via a separator is accommodated in a negative electrode can together with a non-aqueous electrolyte. .

[0002]

2. Description of the Related Art Conventionally, as a secondary battery for electronic equipment,
Ni.Cd batteries and lead batteries are used. However, in recent years, with the advancement of electronic technology, the performance, size, and portability of electronic devices have advanced, and the demand for higher energy density of secondary batteries for electronic devices has increased.
A lithium ion nonaqueous electrolyte secondary battery having a higher discharge voltage, less self-discharge, and a longer cycle life than batteries and lead batteries has been put to practical use.

In this type of lithium ion nonaqueous electrolyte secondary battery, a negative electrode uses a carbonaceous material capable of doping and undoping lithium ions, and a positive electrode uses a lithium composite oxide such as a lithium cobalt composite oxide. Things are used. In addition, in order to obtain good characteristics with respect to heavy load discharge, cycle life, and the like, the electrode is generally a spiral electrode body.

[0004] The spiral electrode body comprises a strip-shaped negative electrode in which a negative electrode mixture layer composed of a carbonaceous material capable of doping and undoping lithium ions and a binder is provided on both surfaces of a negative electrode current collector, and a positive electrode current collector. It is manufactured by winding a band-shaped positive electrode provided with a positive electrode mixture layer composed of a lithium composite oxide, a conductive agent and a binder on both surfaces of a body through a separator. In this case, generally, in order to prevent an internal short circuit due to deposition of lithium at the time of charging, the band-shaped negative electrode facing the band-shaped positive electrode is formed larger in width and length than the positive electrode. Therefore, in such a spiral electrode body, a portion containing an unreacted negative electrode active material which is not involved in charge / discharge is formed at the outer peripheral end and the inner peripheral end of the strip-shaped negative electrode. There was a problem that the space could not be used effectively and the energy density could not be sufficiently increased.

[0005] Therefore, as shown in FIG.
As the (strip-shaped positive electrode current collector 2b and the positive electrode mixture layers 2a and 2c), the positive electrode mixture layer is formed on one surface of the positive electrode current collector 2b at the winding start portion (inner side) and the winding end portion (outer side). A single-layer layer A formed only on the substrate is used, and the band-shaped negative electrode 1 (band-shaped negative electrode current collector 1b, negative electrode mixture layer 1a, 1) is used.
c) is wound around the separator 3, whereby the spiral electrode body 15 is configured such that the separator 3 is located at the outermost periphery and the one-area layer portion A of the strip-shaped positive electrode 2 is located immediately inside the separator 3.
It has been proposed to use (Japanese Unexamined Patent Publication No. 5-2346)
No. 20).

Accordingly, the amount of the electrode active material not involved in charge and discharge in the battery can be reduced as much as possible, and the energy density can be increased.

[0007]

However, in the spiral electrode body described in Japanese Patent Application Laid-Open No. Hei 5-234620, although the separator is located on the outside, the outermost electrode is a positive electrode. If the separator is slightly turned up when the body is inserted into the negative electrode can, there is a problem that the negative electrode can and the positive electrode come into contact and short-circuit. This problem is a problem that must be taken into consideration even when the outermost electrode is a negative electrode, depending on the degree of trouble that occurs when the spiral electrode body is inserted into the negative electrode can.

An object of the present invention is to solve the above-mentioned problems of the prior art and to prevent a short circuit from occurring between the negative electrode can and the positive electrode constituting the spiral electrode body. .

[0009]

Means for Solving the Problems The present inventor formed a spiral electrode body in which the outermost layer electrode is a positive electrode by forming an insulating paint film on the inner surface of the negative electrode can in contact with the spiral electrode body. The inventors have found that even if the separator is turned up when inserted into the negative electrode can, it is possible to reliably prevent a short circuit between the negative electrode can and the positive electrode, and have completed the present invention.

That is, the present invention provides a non-aqueous electrolyte secondary battery in which a spiral electrode body formed by winding a strip-shaped negative electrode and a strip-shaped positive electrode via a separator is accommodated in a negative electrode can together with a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery characterized in that an insulating paint film is formed on the inner surface of the negative electrode can so that the spiral electrode body does not directly contact the inner surface of the negative electrode can.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail.

FIG. 1 is a schematic sectional view of a non-aqueous electrolyte secondary battery according to the present invention.

This battery has a strip-shaped negative electrode 1 having negative electrode mixture layers 1a and 1c formed on both surfaces of a negative electrode current collector 1b, and positive electrode mixture layers 2a and 2b formed on both surfaces of a positive electrode current collector 2b. A spiral electrode body 15 produced by winding the strip-shaped positive electrode 2 around the center pin 12 with the separator 3 interposed therebetween is accommodated in a cylindrical negative electrode can 5 together with a non-aqueous electrolytic solution. It has a structure in which insulating plates 4 are provided on both sides. Further, a negative electrode lead 10 for electrically connecting the strip-shaped negative electrode 1 and the negative electrode can 5 is led out from the negative electrode current collector 1b and welded to the bottom of the negative electrode can 5, and the strip-shaped positive electrode 2 and the battery cover 7 are formed. And a positive electrode lead 11 for electrical connection between the positive electrode current collector 2b and the electrode lead 11 are welded to the battery cover 7. Further, the battery cover 7 is fixed to the negative electrode can 5 by caulking via the insulating sealing gasket 6 to fix the safety valve device 8 having the current cutoff mechanism and the PCT element 9.

In this non-aqueous electrolyte secondary battery, an insulating paint film 13 is formed on the inner surface of the negative electrode can 5 with which the spiral electrode body 15 contacts. For this reason, even when the outermost layer of the separator 3 is turned up and the positive electrode is exposed when the spiral electrode body 15 is inserted into the negative electrode can 5, a short circuit between the negative electrode can and the positive electrode can be reliably prevented.

When the inner surface of the negative electrode can 5 is to be insulated, an insulating sheet prepared in advance may be inserted along the inner surface of the negative electrode can 5. However, when the insulating sheet is inserted as described above, a certain thickness is required in consideration of the rigidity of the insulating sheet. Also, a relatively large clearance needs to be set between such an insulating sheet and the spiral electrode body 15 in order for the insertion operation to proceed smoothly. For this reason, the problem that battery capacity becomes small arises. Further, the spiral electrode body 15 is connected to the negative electrode can 5.
When it is inserted into the insulating sheet, the sheet may be caught on the insulating sheet, and the insulating sheet may be easily deformed or the separator 3 may be turned up.

On the other hand, the insulating paint film 13 of the present invention
Is a film obtained by forming an insulating coating on the inner surface of the negative electrode can 5, so that the insulating sheet does not rise from the inner surface of the negative electrode can 5 as compared with a case where an insulating sheet is separately inserted into the negative electrode can 5.
A thin film can be formed exactly. Therefore, the battery capacity is hardly reduced. In addition, when the spiral electrode body 15 is inserted into the negative electrode can 5, the spiral electrode body 15
Can be prevented from being caught by the insulating paint film 13.

Such an insulating paint film 13 is preferably formed from an insulating organic polymer material. Examples of such an organic polymer material include polyvinylidene fluoride, polycarbonate, polyimide, polycarbonate acetal, polyester, polypropylene, acrylonitrile-butadiene-styrene copolymer resin, urethane resin, styrene-butadiene rubber, butadiene rubber, ethylene. Examples include propylene rubber and isoprene rubber.

If the thickness of the insulating paint film 13 is too small, coating unevenness is likely to occur. If the thickness is too large, the capacity of the non-aqueous electrolyte secondary battery is reduced.
m, more preferably 10 to 80 μm, particularly preferably 1 to 80 μm.
0 to 60 μm.

The formation of the insulating coating film can be performed by using a known technique.

The non-aqueous electrolyte secondary battery of the present invention differs from the conventional non-aqueous electrolyte secondary battery having a spiral electrode body except that an insulating paint film is formed on the inner surface of the negative electrode can as described above. A similar configuration can be adopted.

For example, as the negative electrode active material of the cylindrical non-aqueous electrolyte secondary battery of the present invention, an alkali metal, an alkali metal alloy, or an alkali metal ion such as lithium which can be doped or undoped with the charge / discharge reaction can be used. Carbonaceous materials, organic polymer materials, metal oxides, metal sulfides, lithium-containing transition metal nitrides, and the like can be used. For example, lithium, lithium-aluminum alloy, graphite, pyrolytic carbons, cokes (petroleum coke, pitch coke, lime coke, etc.), carbon black (acetylene black, etc.), glassy carbon, fired organic polymer material (organic Polymer material fired in an inert gas stream or vacuum at an appropriate temperature of 500 ° C. or more), carbon fiber, polyacetylene, polyacene, polyparaphenylene, MoO ₂ , Ti
S ₂ , LiCo _0.5 N or the like can be used. In addition, these materials can be used alone or as a composite or a mixture.

Particularly preferable materials for the negative electrode active material are those having a (002) plane spacing of 3.7 ° or more and a true specific gravity of 1.0.
A carbonaceous material which is less than 70 g / cm ³ and does not have an exothermic peak at 700 ° C. or more in differential thermal analysis in an air stream.

Examples of such a carbonaceous material include carbonaceous materials obtained by carbonizing an organic material by a method such as firing. As the organic material as a starting material for carbonization, furfuryl alcohol or furfural made of a homopolymer or copolymer of furfural is preferable. Specifically, a copolymer consisting of furfural and phenol, a copolymer consisting of furfuryl alcohol and dimethylol urea, a copolymer consisting of furfuryl alcohol and formaldehyde, a copolymer consisting of furfuryl alcohol and furfural, and furfural and ketones And the like.

As a negative electrode active material, a functional group containing oxygen is contained in a petroleum pitch having a hydrogen / carbon element ratio of 0.6 to 0.8.
A carbonaceous material obtained by firing a material (precursor) introduced so as to have an oxygen content of 10 to 20% by weight can also be preferably used.

Further, when carbonizing the above-mentioned furan resin, petroleum pitch or the like, a carbonaceous material having a large amount of lithium that can be doped or undoped by adding a phosphorus compound or a boron compound is also used. be able to.

As the positive electrode active material of the cylindrical non-aqueous electrolyte secondary battery of the present invention, Li _X MO ₂ (M represents one or more transition metals, preferably at least one of Co or Ni,
0.05 ≦ x ≦ 1.10.). Specifically, Li
CoO ₂ , LiNiO ₂ , and a composite oxide represented by LiNi _y Co _1-y O ₂ (where 0 <y <1) are preferable.

These composite oxides can be obtained, for example, by mixing carbonates such as lithium, cobalt, nickel and the like according to the composition and calcining the mixture in a temperature range of 600 to 1000 ° C. in an oxygen-containing atmosphere. The starting materials are not limited to carbonates, and can be synthesized from hydroxides and oxides.

The separator 3 interposed between the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 is preferably a microporous polypropylene film.

As the electrolytic solution of the cylindrical nonaqueous electrolyte secondary battery of the present invention, a solution in which an electrolyte such as a lithium salt is dissolved in an organic solvent can be used. Here, the organic solvent is not particularly limited. For example, propylene carbonate, ethylene carbonate, diethyl carbonate, 1,2-dimethoxyethane, 1,2-diethoxyethane, γ-butyllactone, tetrahydrofuran, , 3-dioxolane, diethyl ether, sulfolane, methylsulfolane, acetonitrile, propionitrile, etc., alone or in combination of two or more.

As the electrolyte, any of conventionally known electrolytes can be used, and LiClO ₄ , LiAsF ₆ , LiPF
₆ , LiBF ₄ , Li (C ₆ H ₅ ) ₄ , LiCl, LiB
r, CH ₃ SO ₃ Li, CF ₃ SO ₃ Li and the like.

Other components of the non-aqueous electrolyte secondary battery of the present invention, such as a cylindrical negative electrode can, a negative electrode or a positive electrode current collector, a battery cover, and a gasket, are the same as those of the conventional non-aqueous electrolyte secondary battery. Configuration.

The non-aqueous electrolyte secondary battery of the present invention can be manufactured, for example, as described below.

First, four layers of a strip-shaped negative electrode, a separator, a strip-shaped positive electrode, and a separator are laminated in this order, and the laminated body is wound so that the end of the strip-shaped positive electrode on one side coated with the positive electrode mixture is finished. The spiral electrode body is manufactured by spirally winding the belt-shaped positive electrode many times along the length direction such that the one-area layer portion of the belt-shaped positive electrode is outside the belt-shaped negative electrode. Then, an adhesive tape is applied to the winding end portion of the spiral electrode body. Thus, a spiral electrode body as shown in FIG. 2 is manufactured.

Next, the spirally wound electrode body thus manufactured is housed in a cylindrical negative electrode can having an insulating paint film formed on the inner surface in advance. At this time, insulating plates are provided on both upper and lower surfaces of the spiral electrode body. Further, a negative electrode lead for electrically connecting the strip-shaped negative electrode and the negative electrode can is led out from the negative electrode current collector and welded to the negative electrode can.

Next, after injecting the electrolytic solution into the negative electrode can,
A positive electrode lead for electrically connecting the belt-shaped positive electrode and the battery lid is led out from the positive electrode current collector and welded to the battery lid. Then, the negative electrode can containing the spirally wound electrode body and the electrolytic solution is caulked via an insulating sealing gasket, thereby fixing the safety valve device having the current cutoff mechanism and the battery lid. Thus, a cylindrical non-aqueous electrolyte secondary battery can be manufactured.

[0036]

The present invention will be described below in more detail with reference to examples.

Example 1 (Preparation of strip-shaped negative electrode) Using petroleum pitch as a starting material,
After oxygen cross-linking, 1000 g
A carbonaceous material having properties close to glassy carbon was fired at ℃, and a carbonaceous material powder having an average particle diameter of 20 μm obtained by pulverizing the powder was used as a negative electrode active material. X-ray diffraction measurement of this material showed that the (002) plane spacing was 3.8 °. The true specific gravity measured by the Pycnometer method was 1.54 g / cm ³ . 90 parts by weight of the thus obtained negative electrode active material and 10 parts by weight of vinylidene fluoride resin as a binder were mixed to prepare a negative electrode mixture. This negative electrode mixture was dispersed using N-methylpyrrolidone as a solvent to form a slurry (paste). A 15 μm thick strip-shaped copper foil was used for the negative electrode current collector,
A negative electrode mixture slurry was applied to both surfaces of the current collector, the solvent was removed by drying, and compression molding was performed to produce a belt-shaped negative electrode 1.
The thickness of the mixture after molding was 80 μm on both sides and the same, and the width of the electrode was 54.5 mm and the length was 520 mm.

(Preparation of belt-shaped positive electrode) Lithium carbonate 0.05
The mixture was mixed with 1 mol of cobalt carbonate and calcined in air at 900 ° C. for 5 hours, and then pulverized to obtain a LiCoO ₂ powder, which was used as a positive electrode active material.

A positive electrode mixture was prepared by mixing 91 parts by weight of this positive electrode active material, 6 parts by weight of graphite as a conductive agent, and 3 parts by weight of vinylidene fluoride resin as a binder, and dispersed in N-methylpyrrolidone to obtain a slurry ( (Paste).

Next, the obtained positive electrode mixture slurry was applied on one side of a 20 μm-thick strip-shaped aluminum foil serving as a positive electrode current collector to a length of 500 mm, dried, and then applied to the back surface thereof. The positive electrode mixture slurry was applied in a length of 446 mm while the application was started at the same position. This was dried and compression molded to a width of 53 mm and a length of one area layer portion of 5 mm.
A belt-like positive electrode 2 having a thickness of 4 mm and a thickness of the positive electrode mixture layer of 80 μm on both sides was produced.

(Preparation of Electrolyte Solution) In a mixed solvent of propylene carbonate and diethyl carbonate in equal volumes, Li
A solution of PF ₆ at a rate of 1 mol / 1 was adjusted as the electrolyte.

(Manufacture of spiral electrode body) The separator 3 interposed between the strip-shaped negative electrode 1 and the strip-shaped positive electrode 2 thus manufactured is 25 μm thick, 59 mm wide and 60 mm long.
Using a microporous polypropylene film of 0 mm, four layers of a band-shaped negative electrode 1, a separator 3, a band-shaped positive electrode 2, and a separator 3 were laminated in this order. Then, this laminate is connected to the belt-shaped positive electrode 2.
And the band-shaped negative electrode 1 such that the one-area layer portion of
Was wound a number of times in a spiral shape along the length direction such that the inside was inside, and the final end of the outermost peripheral separator 3 was fixed with tape. As a result, a spiral electrode body 15 (outer diameter 17.0 mm, inner diameter 3.5 mm in the center of the spiral electrode body) having the structure shown in FIG. 2 was produced.

(Assembly of Battery) As shown in FIG. 1, a spirally wound electrode body manufactured as described above was connected to a nickel-plated iron negative electrode can 5 (an inner surface of polyvinylidene fluoride N-
Methylpyrrolidone solution was applied with a brush and dried to form a film 5
(An insulating paint film 13 having a thickness of 0 μm is formed). Insulating plates 4 are provided on the upper and lower surfaces of the spiral electrode body 15, and a nickel negative electrode lead 10 is drawn out from the negative electrode current collector 1 b to electrically connect the strip-shaped negative electrode 1 to the negative electrode can 5. Welded to can 5.

After injecting the above-mentioned electrolytic solution into the negative electrode can 5, an aluminum positive electrode lead 11 is drawn out from the positive electrode current collector 2b to electrically connect the belt-shaped positive electrode 2 and the battery cover 7. It was welded to the battery lid 7. And the spiral electrode body 1
5 and a negative electrode can 5 containing an electrolytic solution are caulked through an insulating sealing gasket 6 coated with asphalt on the surface thereof, whereby a safety valve device 8 having a current cutoff mechanism, PC
The T element 9 and the battery cover 7 were fixed. As a result, FIG.
A non-aqueous electrolyte secondary battery having a diameter of 17.9 mm and a height of 64 mm as shown in FIG.

Example 2 Example 1 was repeated except that a solution prepared by dissolving polyvinylidene fluoride in a solvent was applied to the inner surface of the negative electrode can with a brush equivalent to the electrode width in a thickness of 10 μm or less and dried with hot air. In the same manner as in the above, a non-aqueous electrolyte secondary battery was produced.

Example 3 Example 1 was repeated except that a solution obtained by dissolving polyvinylidene fluoride in an NMP solvent was applied to the inner surface of the negative electrode can by a brush at a thickness of 100 μm or more corresponding to the electrode width and dried with hot air. In the same manner as in the above, a non-aqueous electrolyte secondary battery was produced.

Comparative Example 1 A non-aqueous electrolyte secondary battery was manufactured in the same manner as in Example 1 except that the insulating paint was not applied to the inner surface of the negative electrode can.

(Evaluation) 1000 batteries were prepared for each of the examples and comparative examples, and each battery was charged at a charge voltage of 4.2.
The battery was charged for 8 hours at 300 V and a charging current of 300 mA, and then discharged to 2.75 V with a load of 1 A, and the capacity was measured. From the obtained measured values, the energy density ratio of each battery when Comparative Example 1 was set to 100 was determined, and the results are shown in Table 1. In addition, the number of short circuits and the ratio of short circuits in the measurement of the capacitance were obtained. The results are also shown in Table 1.

[0049]

[Table 1] Paint thickness Positive electrode coating length Element winding diameter Energy short circuit Number of short circuits (μm) (mm) Density ratio% Example 1 50 520 17.00 100 2 0.2 Example 2 10 or less 520 17.00 100 12 1.2 Example 3 100 or more 510 16.90 98 2 0.2 Comparative Example 1 None 520 17.00 100 25 2.5

As can be seen from Table 1, the insulating paint film was 5
In Example 1 having a thickness of 0 μm, the short-circuit rate was reduced to 1/10 or less as compared with Comparative Example 1 without changing the energy density. In the case of Example 2 in which the insulating paint film was 10 μm or less, the short-circuit rate was reduced to about half of Comparative Example 1 without changing the energy density as compared with Comparative Example 1. In Example 3 in which the thickness of the insulating paint film was 100 μm, the energy density was slightly reduced as compared with Comparative Example 1, but the short-circuit rate was reduced to 1/10 or less.

As described above, by forming an insulating paint film on the inner surface of the negative electrode can, when inserting the spiral electrode body into the negative electrode can, the separator is turned up and the outermost positive electrode portion is exposed. Also, it can be seen that an internal short-circuit occurring between the negative electrode can and the positive electrode is prevented, and the short-circuit rate is effectively reduced.

[0052]

According to the present invention, since the insulating paint film is formed on the inner surface of the negative electrode can in contact with the spiral electrode body, the outermost layer is formed when the spiral electrode body is inserted into the negative electrode can. Even if the separator is turned up and the positive electrode is exposed, a short circuit between the negative electrode can and the positive electrode can be reliably prevented.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a non-aqueous electrolyte secondary battery of the present invention.

FIG. 2 is a sectional view in a winding direction of a spiral electrode body applicable to the nonaqueous electrolyte secondary battery of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Strip negative electrode, 1a, 1c ... Negative electrode mixture layer, 1b ... Negative electrode collector, 2 ... Strip positive electrode, 2a, 2c ... Positive electrode mixture layer, 2b ... Positive electrode current collector, A ... Single area layer part

Claims (4)

[Claims] 1. A non-aqueous electrolyte secondary battery in which a spiral electrode body formed by winding a strip-shaped negative electrode and a strip-shaped positive electrode via a separator is accommodated in a negative electrode can together with a non-aqueous electrolyte.
A non-aqueous electrolyte secondary battery, wherein an insulating paint film is formed on the inner surface of the negative electrode can so that the spiral electrode body does not directly contact the inner surface of the negative electrode can. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein the insulating coating film is formed from an organic polymer material. 3. The organic polymer material is polyvinylidene fluoride, polycarbonate, polyimide, polycarbonate acetal, polyester, polypropylene, acrylonitrile / butadiene / styrene copolymer resin, urethane resin, styrene / butadiene rubber, butadiene rubber, ethylene / propylene 3. The non-aqueous electrolyte secondary battery according to claim 2, which is rubber or isoprene rubber. 4. A positive electrode mixture layer is formed only on one surface of a strip-shaped positive electrode current collector at a winding start portion and a winding end portion of the strip-shaped positive electrode. 2. The non-aqueous electrolyte secondary battery according to claim 1, wherein a winding end portion of the belt-shaped positive electrode is located inside.