JPH1197070A - Lithium secondary battery and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium secondary battery wherein the burst of a laminate film can be prevented in the overcharging. SOLUTION: This battery comprises a power generating element 1 comprising a positive electrode and a negative electrode storing and releasing a lithium ion, a lithium ion conductive electrolyte layer, a positive electrode lead 9 electrically connected to the positive electrode, and a negative electrode lead 10 electrically connected to the negative electrode, and a film 11 which covers the power generating element 1 in such manner that the edge parts of the positive electrode lead 9 and the negative electrode lead 10 are extended outside, and of which an opening part is sealed by the thermal fusion. At least one area 13 having a function of a safety valve, exists on the fusion part of the film 11, and the peel strength of the area 13 having the function as the safety valve, is corresponding to 30-70% of the peel strength of the fusion parts 14 of the positive electrode lead 9 and the negative electrode lead 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a lithium secondary battery having a structure in which a power generating element is housed in a film, and a method for manufacturing the same.

[0002]

2. Description of the Related Art In recent years, with the development of electronic equipment, there has been a demand for the development of a secondary battery that is small, lightweight, has a high energy density, and can be repeatedly charged and discharged. As such a secondary battery, a negative electrode using lithium or a lithium alloy as an active material, and a suspension containing an oxide, sulfide, or selenide as an active material, such as molybdenum, vanadium, titanium, or niobium, were applied. A lithium secondary battery including a positive electrode made of a current collector and a non-aqueous electrolyte is known.

In addition, a current collector coated with a suspension containing a carbonaceous material that absorbs and releases lithium ions, such as coke, graphite, carbon fiber, fired resin, and pyrolytic gas phase carbon, is coated on the negative electrode. A used lithium secondary battery has been proposed. In the secondary battery, the deterioration of the negative electrode characteristics due to dendrite deposition can be improved, so that the battery life and safety can be improved.

Incidentally, a polymer electrolyte secondary battery, which is an example of a lithium secondary battery, has a positive electrode having a structure in which a positive electrode layer containing an active material, a nonaqueous electrolyte and a polymer holding the electrolyte is supported on a current collector. A negative electrode having a structure in which a negative electrode layer containing a carbonaceous material capable of inserting and extracting lithium ions, a nonaqueous electrolyte and a polymer holding the electrolyte is supported on a current collector, and between the positive electrode and the negative electrode. A solid polymer electrolyte layer including a non-aqueous electrolyte and a polymer holding the electrolyte, a positive electrode lead electrically connected to the positive electrode, and a negative electrode lead electrically connected to the negative electrode A power generating element; a film which covers the power generating element so that an end of the positive electrode lead and an end of the negative electrode lead extend to the outside, and has an opening thermally fused; Such a lithium secondary battery (unit cell), for example, alone or
Alternatively, the battery pack is housed in a battery pack in the form of an assembled battery, and is used as a power source for an electronic device.

However, the lithium secondary battery is
When gas is generated due to overcharging or the like, the film is significantly expanded and ruptured, so that the power generation element may be scattered, the battery pack may be deformed, and the electronic device may be damaged or the human body may be adversely affected. .

[0006]

SUMMARY OF THE INVENTION According to the present invention, when the film expands due to overcharging or the like, the expansion is stopped immediately,
An object of the present invention is to provide a lithium secondary battery capable of preventing rupture and a method of manufacturing the same.

[0007]

A lithium secondary battery according to the present invention comprises a positive electrode and a negative electrode that occlude and release lithium ions, a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode, A power generating element including a positive electrode lead electrically connected to the positive electrode and a negative electrode lead electrically connected to the negative electrode; the power generating element has ends of the positive electrode lead and the negative electrode lead extending outward. And a film having an opening portion sealed by heat sealing, wherein the film has at least one region functioning as a safety valve in the fusion bonding portion, and has a peel strength in a region functioning as the safety valve. Is equivalent to 30% to 70% of the peel strength of the fused portion of each of the positive electrode lead and the negative electrode lead.

A method for manufacturing a lithium secondary battery according to the present invention comprises a positive electrode and a negative electrode that occlude and release lithium ions;
A power generation element including a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode, a positive electrode lead electrically connected to the positive electrode, and a negative electrode lead electrically connected to the negative electrode is a film. In a method for manufacturing a lithium secondary battery having a structure in which the ends of the positive electrode lead and the negative electrode lead are coated so as to extend to the outside, and the opening of the film is sealed by heat sealing. At least one of the openings is heat-fused with a non-heat-fusible resin sheet interposed therebetween, and the peel strength of the fused portion where the sheet is present is the fusion strength of each of the positive electrode lead and the negative electrode lead. Characterized in that it corresponds to 30% to 70% of the peel strength of the part.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION An example of a lithium secondary battery (a polymer electrolyte secondary battery) according to the present invention will be described in detail with reference to FIGS. FIG. 1 is a cross-sectional view showing an example of a power generating element included in a lithium secondary battery according to the present invention. FIG. 2 is a partially cutaway plan view showing a lithium secondary battery according to the present invention.
FIG. 4 is a side view of the secondary battery of FIG. 2, FIG. 4 is a partially cutaway plan view showing a state in which the safety valve is operated in the secondary battery of FIG.
FIG. 5 is a side view of the secondary battery in FIG. 4.

A lithium secondary battery according to the present invention includes a power generating element 1 as shown in FIG. 1, for example. Such a power generating element 1 includes a negative electrode having a structure in which a negative electrode layer 3 is supported on both surfaces of a mesh current collector 2 such as a copper expanded metal;
Two positive electrodes having a structure in which a positive electrode layer 5 containing an active material is supported on both surfaces of a net-like current collector 4 such as an expanded metal made of aluminum are provided. Two solid polymer electrolyte layers 6 as lithium ion conductive electrolyte layers are respectively laminated on both surfaces of the negative electrode. The positive electrode is laminated on each of the solid polymer electrolyte layers 6.
The negative electrode current collector 2 has a strip-shaped terminal portion 7 made of the same material as the current collector. Further, the positive electrode current collector 4
Has a strip-shaped terminal portion 8 made of the same material as the current collector. For example, a positive electrode lead 9 made of a strip-shaped aluminum foil
Are connected to the two band-shaped terminal portions 8. For example, the negative electrode lead 10 made of a strip-shaped copper foil is
It is connected to the. Such a power generation element 1 is covered with a film 11 which is folded vertically. Openings (ends along the longitudinal direction and both ends perpendicular to the longitudinal direction) of the film 11 are sealed by heat fusion. In the heat-sealed portion 12, the vicinity of the center of the end along the longitudinal direction has a narrower fusion width than the other portions. The narrow fused portion 13 (the area surrounded by the ellipse in FIG. 2) functions as a safety valve, and the peel strength of the fused portion 14 of each of the positive electrode lead 9 and the negative electrode lead 10 (circled in FIG. 2). (Enclosed area) corresponds to 30% to 70% of the peel strength. Such a narrow fused portion can be formed, for example, by providing a portion that is not pressurized during thermal fusion.

[0011] The fusion portion 1 thus functioning as a safety valve.
The peel strength of No. 3 is set for the following reason. If the peel strength of the fusion portion 13 is less than 30% of the peel strength of the fusion portion 14, the airtightness of the film 11 is reduced, and battery characteristics such as charge / discharge cycle characteristics may be reduced. On the other hand, if the peel strength of the fused portion 13 exceeds 70% of the peel strength of the fused portion 14, when the internal pressure increases due to overcharging or the like, it may be difficult to prevent rupture beforehand. . The more preferable range of the exfoliation extreme of the fusion part 13 is 40% to 60%.

In the thus constructed lithium secondary battery, when a gas is generated due to, for example, overcharging and the internal pressure of the film 11 increases, as shown in FIGS. 13 is peeled off, and the gas in the film 11 can escape to the outside from this portion, so that the rupture of the film 11 can be avoided.

As the positive electrode, the negative electrode, and the electrolyte layer of the lithium secondary battery, for example, those described below can be used. (Positive Electrode) This positive electrode is formed of a positive electrode layer containing a positive electrode active material, a non-aqueous electrolyte, and a polymer for holding the electrolyte, supported on a current collector.

Examples of the positive electrode active material include various oxides (eg, lithium-manganese composite oxide such as LiMn ₂ O ₄ , manganese dioxide, lithium-containing nickel oxide such as LiNiO _2, and lithium-containing cobalt oxide such as LiCoO ₂ , for example). Oxide, lithium-containing nickel-cobalt oxide, lithium-containing amorphous vanadium pentoxide and the like, and chalcogen compounds (for example, titanium disulfide and molybdenum disulfide). Among them, it is preferable to use a lithium manganese composite oxide, a lithium-containing cobalt oxide, and a lithium-containing nickel oxide.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent. As the non-aqueous solvent,
Ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DE
C), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (TH
F) and 2-methyltetrahydrofuran. The non-aqueous solvents may be used alone or as a mixture of two or more.

Examples of the electrolyte include lithium perchlorate (LiClO ₄ ) and lithium hexafluorophosphate (L
iPF ₆ ), lithium borotetrafluoride (LiBF ₄ ), lithium arsenic hexafluoride (LiAsF ₆ ), lithium trifluoromethanesulfonate (LiCF ₃ SO ₃ ), lithium bistrifluoromethylsulfonylimide [LiN
(CF ₃ SO ₃ ) ₂ ].

The amount of the electrolyte dissolved in the non-aqueous solvent is desirably 0.2 mol / l to 2 mol / l. Examples of the polymer for holding the nonaqueous electrolyte include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative,
A copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP) or the like can be used. The copolymerization ratio of the HFP depends on the method of synthesizing the copolymer, but is usually at most about 20% by weight.

In FIG. 1 described above, an aluminum expanded metal is used for the current collector and the terminal of the positive electrode. However, the current collector may be, for example, aluminum foil, aluminum mesh, aluminum punched metal, or the like. May be used.

The positive electrode may include a conductive material from the viewpoint of improving conductivity. Examples of the conductive material include artificial graphite, carbon black (eg, acetylene black), nickel powder, and the like.

(Negative Electrode) The negative electrode is formed of a negative electrode active material, a non-aqueous electrolyte and a negative electrode layer containing a polymer for holding the electrolyte supported on a current collector.

Examples of the negative electrode active material include carbonaceous materials that occlude and release lithium ions. Such carbonaceous materials include, for example, those obtained by firing organic polymer compounds (eg, phenolic resin, polyacrylonitrile, cellulose, etc.), those obtained by firing coke and mesophase pitch, and those made by artificial graphite. And carbonaceous materials represented by natural graphite and the like. Among them, 500
It is preferable to use a carbonaceous material obtained by calcining the mesophase pitch at a temperature of from ℃ to 3,000 ℃ under normal pressure or reduced pressure.

As the non-aqueous electrolyte and the polymer, those similar to those described for the above-mentioned positive electrode are used. In FIG. 1 described above, a copper expanded metal was used as the current collector and terminal of the negative electrode.
For example, copper foil, copper mesh, copper punched metal, or the like may be used.

The negative electrode sheet contains conductive materials such as artificial graphite, natural graphite, carbon black, acetylene black, Ketjen black, nickel powder, and polyphenylene derivatives, and fillers such as olefin polymers and carbon fibers. Allow.

(Solid Polymer Electrolyte Layer) This electrolyte layer contains a non-aqueous electrolyte and a polymer for holding the electrolyte.

As the non-aqueous electrolyte and the polymer, those similar to those described for the positive electrode described above are used. From the viewpoint of further improving the strength, the electrolyte layer may include an inorganic filler such as silicon oxide powder.

Examples of the film used in the lithium secondary battery include a film in which a heat-sealing resin (for example, ionomer, polyethylene) layer is disposed inside. Among them, it is preferable that the sealing surface is formed of a multilayer film in which a heat-fusible resin is disposed and a metal thin film such as aluminum (Al) is interposed therebetween. Specifically, polyethylene (PE) / polyethylene terephthalate (PET) /
Al foil / PET multilayer film; PE / Nylon / Al
Foil / PET multilayer film; ionomer / Ni foil / P
A multilayer film of E / PET; a multilayer film of ethylene vinyl acetate (EVA) / PE / Al foil / PET; a multilayer film of ionomer / PET / Al foil / PET can be used. Here, the film other than PE, ionomer, and EVA on the sealing surface has moisture resistance, air resistance, and chemical resistance.

In FIG. 2 described above, a part of the fused portion is dented into a rectangular shape to reduce the width of the fused portion, thereby forming a region functioning as a safety valve. Any shape may be used as long as the above range is satisfied. For example, a shape having a rectangular non-fused region in the center can be used. Alternatively, the fusion strength of the entire region may be reduced without forming the non-fusion region.

Further, in FIG. 2 described above, a region having a safety valve function is formed at the fusion portion along the longitudinal direction of the film, but the region may be provided anywhere except the vicinity of the positive electrode lead and the negative electrode lead. . For example, it may be formed on the side where the lead is not fixed among the end sides orthogonal to the longitudinal direction of the film.

In FIG. 2 described above, the number of regions having the safety valve function is one, but two or more regions may be formed. In FIGS. 1 to 5 described above, a power generation element having a positive electrode, a polymer electrolyte layer and a negative electrode is a multilayer film in which a heat-fusible resin film is disposed on the inner surface. A lithium battery having a structure in which the power generation element is sealed by coating so as to extend from one opening edge of the multilayer film and heat-sealing the heat-fusible resin films to each other at the opening edge of the multilayer film. Although an example in which the present invention is applied to a secondary battery has been described, a lead electrically connected to the positive electrode is a power generating element having a positive electrode, a polymer electrolyte layer, and a negative electrode in a multilayer film in which a heat-fusible resin film is disposed on the inner surface. The multilayer film extending from one opening edge of the multilayer film and being electrically connected to the negative electrode so as to extend from another opening edge of the multilayer film; Heat sealed together the heat-fusible resin film in the opening edge portion in the lithium secondary battery having a structure in which sealed the power generating element can be applied as well.

Hereinafter, an example of a method for manufacturing a lithium secondary battery according to the present invention (a method for manufacturing a polymer electrolyte secondary battery) will be described. In the manufacturing method according to the present invention, a lead in which a heat-fusible resin film is disposed on the inner surface of a positive electrode, a power generating element having a polymer electrolyte layer and a negative electrode, and a lead electrically connected to the positive and negative electrodes, respectively, is provided in the bag. A manufacturing method in which the heat-fusible resin films are housed so as to extend from the opening edge, and the heat-fusible resin films are heat-sealed to each other at the opening edge of the bag to seal the power generating element, A lead electrically connected to the positive electrode extends a power generating element having a positive electrode, a polymer electrolyte layer, and a negative electrode from a tube on which a film is disposed, and extends from one opening edge of the tube, and is electrically connected to the negative electrode. Manufacturing method for covering the formed lead so as to extend from the other opening edge of the tube, and sealing the power generating element by heat-sealing the heat-fusible resin films to each other at the opening edge of the tube. Apply to Door can be.

The heat-sealing through the non-heat-fusible resin sheet may be performed at the time of producing a tube or a bag, or may be performed at the time of sealing the opening edge portion where the lead is extended. .
The non-heat-fusible resin sheet can be formed from, for example, a water-repellent resin such as polyethylene terephthalate (PET), nylon, or polytetrafluoroethylene (PTFE).

As the film used in the method according to the present invention, the same films as described above can be mentioned.
As described above, according to the lithium secondary battery of the present invention, gas is generated from the power generation element due to overcharging or the like, and when the internal pressure of the film containing the power generation element is increased, the peel strength is equal to that of the positive electrode lead. The fused portion, which is in the range of 30 to 70% of the peel strength of the fused portion of each of the negative electrode leads, is quickly peeled off, and the gas in the film can be escaping from the peeled portion to the outside. Can be prevented beforehand.

Further, according to the method of manufacturing a lithium secondary battery according to the present invention, it is possible to manufacture a lithium secondary battery in which the peel strength of at least one of the heat-sealed portions has the specific value as described above. Can be. In other words, when such a region having a low peel strength is formed by adjusting the degree of pressurization at the time of heat fusion, heat applied to the region to be heat-fused depends on the manner of pressurization to a region where heat fusion is not performed. Transmitted,
As a result, there is a case where a region where heat fusion is not performed is fused. When a non-heat-fusible resin sheet is interposed between the films and heat-sealed as in the invention of the present application, the portion where the sheet is interposed is not heat-sealed. Can be easily performed, and a fused portion having a desired peel strength can be easily formed. As a result, a high-performance, highly safe lithium secondary battery can be manufactured by a simple method.

[0034]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Example 1) A 100 μm-thick laminated film composed of a surface layer made of polyethylene terephthalate, an intermediate layer made of aluminum, and an inner layer made of an ionomer resin was folded in two, and both ends orthogonal to the longitudinal direction were paired. And heat-sealed by sandwiching between the heat rolls to form a fused portion having a width of 5 mm at both ends orthogonal to the longitudinal direction of the film. Further, the upper heat roll is changed to one having a rectangular concave portion at one place near the center, and the end along the longitudinal direction of the film is heat-sealed, and the width is changed to the end along the longitudinal direction of the film. Formed a heat-sealed portion of 5 mm. In addition, one portion near the center of the fused portion has a narrow fused width of 1.5 mm over a length of 5 mm, and functions as a safety valve. By sealing the laminate film in this manner, a test polymer electrolyte secondary battery having a length of 76 mm and a width of 36 mm was assembled.

In the obtained secondary battery, a fused portion functioning as a safety valve was cut to a length of 20 mm in a direction perpendicular to the longitudinal direction with a width of 5 mm, and a peeling speed of 20 cm / m.
When the peeling strength was measured by performing a peeling test in, it was 0.15 kgf. The peel strength of the fused portion of the positive electrode lead (5 mm in width) and the fused portion of the negative electrode lead (5 mm in width) of the polymer electrolyte secondary battery provided with the laminate film having the above-mentioned dimensions are both 0.5 kgf. Therefore, the peel strength of the fused portion functioning as the safety valve was equivalent to 30% of the peel strength of the fused portion of the positive electrode lead and the negative electrode lead. (Example 2) A laminate film of the same type and thickness as in Example 1 was folded in two, and both ends orthogonal to the longitudinal direction were heat-sealed in the same manner as in Example 1 to obtain a laminate film with the longitudinal direction of the film. Fused portions having the same width as in Example 1 were formed at both ends orthogonal to each other. In addition, the heat roll on the upper side
Change to one having a rectangular concave portion at the place and heat-seal the end along the longitudinal direction of the film, and at the end along the longitudinal direction of the film a heat-seal part of the same width as in Example 1 Formed. In addition, in one portion near the center of the fused portion, the fused width is narrowed to 2.5 mm over a length of 5 mm,
Functions as a safety valve. By sealing the laminate film in this manner, a test polymer electrolyte secondary battery having the same dimensions as in Example 1 was assembled.

In the obtained secondary battery, when the peel strength of the fused portion functioning as a safety valve was measured in the same manner as described above, the peel strength of the fused portion of the positive electrode lead and the negative electrode lead was 0.25 kgf. Was equivalent to 50%. (Example 3) A laminate film of the same type and thickness as in Example 1 was folded in two, and both ends orthogonal to the longitudinal direction were heat-sealed in the same manner as in Example 1 to obtain a film having the same length as the longitudinal direction of the film. Fused portions having the same width as in Example 1 were formed at both ends orthogonal to each other. In addition, the heat roll on the upper side
Change to one having a rectangular concave portion at the place and heat-seal the end along the longitudinal direction of the film, and at the end along the longitudinal direction of the film a heat-seal part having the same width as in Example 1 Formed. In addition, in one portion near the center of the fused portion, the fused width is reduced to 3.5 mm over a length of 5 mm,
Functions as a safety valve. By sealing the laminate film in this manner, a test polymer electrolyte secondary battery having the same dimensions as in Example 1 was assembled.

In the obtained secondary battery, the peel strength of the fused portion functioning as a safety valve was measured in the same manner as described above. As a result, the peel strength of the fused portion of the positive electrode lead and the negative electrode lead was 0.35 kgf. It was equivalent to 70%. (Comparative Example 1) A laminate film of the same type and thickness as in Example 1 was folded in two, and both ends orthogonal to the longitudinal direction were heat-sealed in the same manner as in Example 1 to obtain a laminate film with the longitudinal direction of the film. Fused portions having the same width as in Example 1 were formed at both ends orthogonal to each other. In addition, the heat roll on the upper side
Change to one having a rectangular concave portion at the place and heat-seal the end along the longitudinal direction of the film, and at the end along the longitudinal direction of the film a heat-seal part having the same width as in Example 1 Formed. In addition, one portion near the center of the fusion portion has a fusion width of 4 mm over a length of 5 mm, and functions as a safety valve. By sealing the laminate film in this manner, a test polymer electrolyte secondary battery having the same dimensions as in Example 1 was assembled.

In the obtained secondary battery, when the peel strength of the fused portion functioning as a safety valve was measured in the same manner as described above, the peel strength of the fused portion of the positive electrode lead and the negative electrode lead was 0.40 kgf. It was equivalent to 80%. (Comparative Example 2) A laminate film of the same type and thickness as in Example 1 was folded in two, and both ends orthogonal to the longitudinal direction and the ends along the longitudinal direction were heat-sealed with a pair of heat rolls. By sealing the film, a test polymer electrolyte secondary battery having the same dimensions as in Example 1 was assembled. The width of the fused portion was the same as that in Example 1 at both ends perpendicular to the longitudinal direction and at the ends along the longitudinal direction. No safety valve was provided.

In the obtained secondary batteries, Examples 1 to 3
And when the peel strength of the portion corresponding to the safety valve function region in Comparative Example 1 was measured in the same manner as described above,
0.7 kgf, which corresponded to 140% of the peel strength of the fused portion of the positive electrode lead and the negative electrode lead.

Next, LiCoO ₂ as a positive electrode active material,
Nonaqueous electrolyte prepared by mixing ethylene carbonate and dimethyl carbonate at a volume ratio of 2: 1 and dissolving 1 M LiPF ₆ , and a positive electrode containing a VdF-HFP copolymer as a polymer for holding the electrolyte And, a mesophase pitch-based carbonaceous material, a negative electrode containing the non-aqueous electrolyte and the polymer, and a power generation element using the non-aqueous electrolyte and a solid polymer electrolyte layer containing the polymer,
The power generating elements were each included in a laminated film having the same configuration as in Examples 1 to 3 and Comparative Examples 1 and 2 described above, to produce a polymer electrolyte secondary battery. The capacities of the obtained secondary batteries of Examples 1 to 3 and Comparative Examples 1 and 2 were all 100 mAh.

With respect to the obtained test batteries of Examples 1 to 3 and Comparative Examples 1 and 2, the maximum voltage was 1 at a constant current of 200 mA.
A 5 V overcharge test was performed to measure the time until gas was released, the location where the gas was released, and the release state. The results are shown in Table 1 below.

[0042]

[Table 1]

As is clear from Table 1, in the test batteries of Examples 1 to 3 in which a region having a peel strength of 30 to 70% was formed in the fused portion, the generated gas was released from the concave portion in a short time. It is clear that the safety is excellent. On the other hand, the test battery of Comparative Example 1 in which a region having a peel strength exceeding 70% was formed in the fused portion, and the test battery of Comparative Example 2 in which a region having a peel strength smaller than the lead fixing portion was not formed. It can be seen that the battery had a longer time to release gas than Examples 1 to 3, and the lead fusion part was peeled off and burst, resulting in poor safety.

When sealing with a laminate film similar to that of Example 1 by heat sealing, a region functioning as a safety valve mechanism was provided at a location similar to that of Example 1, and the peel strength of this region was set to 25%. However, since the obtained polymer electrolyte secondary battery had low airtightness, liquid leakage occurred during charging and discharging. Example 4 <Preparation of Positive Electrode> First, a composition formula of LiMn ₂ was used as an active material.
Lithium manganese composite oxide represented by O ₄ , carbon black, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder, and dibutyl phthalate (DBP) A paste was prepared by mixing in dimethylformamide. The obtained paste was applied on a polyethylene terephthalate film (PET film) to form a sheet, and a positive electrode sheet not impregnated with a non-aqueous electrolyte was prepared. A positive electrode not impregnated with a non-aqueous electrolyte was produced by heat-pressing the obtained positive electrode sheet on both surfaces of a current collector made of aluminum expanded metal and having a positive electrode terminal portion using a hot roll.

<Preparation of Negative Electrode> Mesophase pitch carbon fiber as an active material, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder,
A plasticizer {dibutyl phthalate (DBP)} was mixed in NN-dimethylformamide to prepare a paste.
The obtained paste was applied on a polyethylene terephthalate film (PET film) and formed into a sheet to prepare a negative electrode sheet not impregnated with an electrolyte. A negative electrode not impregnated with an electrolyte was prepared by heat-pressing the obtained negative electrode sheet on both surfaces of a current collector made of copper expanded metal and having a negative electrode terminal portion with a hot roll.

<Preparation of Solid Polymer Electrolyte Layer> Silicon oxide powder, vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder, and a plasticizer {dibutyl phthalate (DBP)} were mixed in acetone. Mix and make into a paste. The obtained paste was applied on a polyethylene terephthalate film (PET film), formed into a sheet, and an electrolyte layer not impregnated with the electrolyte was prepared.

<Preparation of Nonaqueous Electrolyte> A nonaqueous electrolyte was prepared by dissolving LiPF ₆ as an electrolyte in a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed.

<Assembly of Battery> The positive electrode and the negative electrode were laminated with the electrolyte layer interposed therebetween,
The laminate was prepared by heat-pressing with a rigid roll heated to ℃. Such a laminate was immersed in methanol, and the DBP in the laminate was extracted with methanol and removed. This is dried and the lamination thickness is 1.0 mm and the outer diameter is 4 mm.
A laminated electrode of 0 × 60 mm was produced. The terminal part of the positive electrode has a thickness of 0.05 mm and a width of 5 mm as a positive electrode lead.
Was welded. In addition, a negative electrode lead having a thickness of 0.05 mm and a width of 5
mm copper foil was welded.

Next, a composite film (external dimensions: 113 × 90 mm, thickness: 0.1 mm) in which a PET layer, an aluminum foil layer, and an ionomer resin layer were laminated in this order was prepared as an exterior material. Fold the film vertically so that the ionomer resin layer is located inside,
A bag was formed by heat-sealing an end along the longitudinal direction and an end perpendicular to the longitudinal direction with a width of 10 mm. At this time, a non-thermally fused region was formed at a part of the end perpendicular to the longitudinal direction as an electrolyte injection port.

Next, as shown in FIG. 6, the laminated electrode is housed in a bag, and a non-heat-fusible resin sheet is placed in the bag.
Heat fusion was applied. First, the laminated electrode 21 was housed in the bag 20 so that the ends of the positive electrode lead 22 and the negative electrode lead 23 protruded outside. Then, the inside of the bag 20 has a bottom of 5 mm, a height of 8 mm, and a thickness of 0.3 mm.
A triangular sheet 24 of 02 mm made of polyethylene terephthalate was arranged. The sheet 24 was disposed at the center of a location 5 mm away from the end where the positive electrode lead 22 and the negative electrode lead 23 protruded. Next, the opening of the bag 20 from which the lead is extended has a margin of a laminated electrode dimension and a heat-fused portion so that the influence at the time of heat fusion does not appear on the laminated electrode. Heat fusion was performed. The non-aqueous electrolyte was injected from a non-thermally fused region formed as an injection port, and impregnated into the laminated electrode.
Then, the non-heat-bonded area is heat-fused with a fusion width of 10 mm, so that the thickness is 1.2 mm, the outer diameter excluding the lead portion is 55 × 90 mm, and the electric capacity is 100 mA.
h, 100 thin polymer electrolyte secondary batteries were manufactured.

In each of the obtained secondary batteries, the fused portion adjacent to the non-heat-fusible resin sheet has a width at the bottom of the resin sheet and a length of 20 mm parallel to the longitudinal direction of the battery.
Cut to width 5mm, peeling speed 20cm / min
When a peeling test was performed to measure the peel strength,
It was 0.2 kgf. Further, the fused portion of the positive electrode lead and the fused portion of the negative electrode lead were cut into a length of 20 mm and a width of 5 mm in parallel with the longitudinal direction of the battery.
When the peeling strength was measured by performing a peeling test at cm / min, each was 0.5 kgf. Therefore, the peel strength of the narrow fused portion formed by interposing the non-heat-fusible resin sheet was equivalent to 40% of the peel strength of the fused portion of the positive electrode lead and the negative electrode lead. .

Each of the obtained secondary batteries has a battery storage space of 57 × 92 × 4.0 mm and external dimensions of 60 × 95 ×
The battery was housed in a 6.0 mm polypropylene case with external connection terminals to form a battery pack. Comparative Example 3 Production of a laminated electrode and production of a bag from a composite film were performed in the same manner as in Example 4. The obtained laminated electrode was housed in the bag such that the ends of the positive electrode lead and the negative electrode lead protruded outside. The opening where the lead of the bag is extended is heat-fused at a fusion width of 10 mm so as to have a margin of the laminated electrode dimensions and the heat-fused portion so that the influence of the heat fusion does not appear on the laminated electrode. did. The non-aqueous electrolyte was injected from a non-thermally fused region formed as an injection port, and impregnated into the laminated electrode. Next, the non-heat-fused region is heat-fused with a fusion width of 10 mm so that the thickness is 1.
2mm, outer diameter of 55 x 90mm excluding lead
Thus, 100 thin polymer electrolyte secondary batteries having an electric capacity of 100 mAh were manufactured.

In each of the obtained secondary batteries, the peel strength of the fused portion at a position corresponding to the fused portion adjacent to the non-heat-fusible resin sheet in Example 4 was measured in the same manner as in Example 4. However, it was 0.7 kgf. The peel strength of the fused portion was equivalent to 140% of the peel strength of the fused portion between the positive electrode lead and the negative electrode lead.

Next, each of the obtained secondary batteries was housed in the same polypropylene case with external connection terminals as in Example 4 to obtain a pack-type battery. The battery packs of Example 4 and Comparative Example 3 were subjected to an overcharge test in which charging was performed at 2 C and 15 V for 3 hours, and the number of valve operations and the thickness of the battery pack after the overcharge test were measured. It is shown in Table 2.

[0055]

[Table 2]

As is clear from Table 2, in the secondary battery of Example 4, the thickness of the pack did not change after overcharging, and the safety valve was activated immediately after the internal pressure increased. On the other hand, it can be seen that the secondary battery of Comparative Example 3 ruptures during overcharging after the film expands enough to deform the pack.

In the fourth embodiment, the shape of the non-heat-fusible resin sheet is triangular, and the width of the fused portion adjacent to this sheet is gradually reduced. Any shape may be used as long as the peel strength of the fused portion where the sheet exists satisfies the above-described specific range. For example, the shape can be a rectangle, a circle, an ellipse, or the like.

In the fourth embodiment, the non-heat-fused resin sheet is disposed at the fusion portion to which the positive electrode lead and the negative electrode lead are fixed. It may be provided anywhere. For example, it can be formed on the side to which the lead is not fixed among the end sides orthogonal to the longitudinal direction of the film, or on the end along the longitudinal direction of the film. Further, in the above-described fourth embodiment, the position where the sheet is interposed is one, but
Two or more locations may be used.

[0059]

As described above in detail, according to the present invention, it is possible to provide a lithium secondary battery in which rupture during overcharge is avoided and safety is improved, and a method of manufacturing the same.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a power generation element included in a lithium secondary battery according to the present invention.

FIG. 2 is a partially cutaway plan view showing a lithium secondary battery according to the present invention.

FIG. 3 is a side view of the secondary battery of FIG.

FIG. 4 is a partially cutaway plan view showing a state in which a safety valve mechanism operates in the secondary battery of FIG. 2;

FIG. 5 is a side view of the secondary battery of FIG.

FIG. 6 is a plan view showing a lithium secondary battery according to Embodiment 4 of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Power generation element, 9 ... Positive electrode lead, 10 ... Negative electrode lead, 11 ... Film, 12 ... Fusion part, 13 ... Fusion part provided with a safety valve function, 14 ... Lead fusion part.

Claims (2)

[Claims] A positive electrode and a negative electrode that occlude and release lithium ions; a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode; a positive electrode lead electrically connected to the positive electrode; A power generating element including a negative electrode and a negative electrode lead electrically connected to the negative electrode; covering the power generating element such that ends of the positive electrode lead and the negative electrode lead extend outward, and an opening is sealed by heat fusion Wherein the film has one region which functions as a safety valve at the fusion spliced part.
A lithium secondary battery, wherein two or more of the regions function as the safety valve, and a peel strength of the region functioning as the safety valve corresponds to 30% to 70% of a peel strength of a fused portion of each of the positive electrode lead and the negative electrode lead. 2. A positive electrode and a negative electrode that occlude and release lithium ions, a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode, a positive electrode lead electrically connected to the positive electrode, and A power generation element including a negative electrode and a negative electrode lead electrically connected to the negative electrode is covered with a film so that ends of the positive electrode lead and the negative electrode lead extend to the outside, and an opening of the film is sealed by heat sealing. A method of manufacturing a lithium secondary battery having a stopped structure, wherein at least one of the openings is heat-fused with a non-heat-fusible resin sheet interposed therebetween, and the fusion sheet in which the sheet is present The method for manufacturing a lithium secondary battery according to claim 1, wherein the peel strength of the bonded portion corresponds to 30% to 70% of the peel strength of the fused portion of each of the positive electrode lead and the negative electrode lead.