JPH1140198A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent short circuit at the time of hot-melt and capacity evaluation and heighten the weight energy density by layering a metal layer on a thermally fusible resin layer and keeping a metal layer out of a portion of the hot-melt part to be brought into contact with a positive electrode lead and a negative electrode lead. SOLUTION: A laminate film 10 is constituted of a first layer, made of insulating resin, a second layer made of thermally fusible resin, and a metal layer sandwiched between the first and the second layers. The film 10 is formed so as not to have the metal layer exist hot-melt in the upper side which is to be brought into contact with a negative electrode lead 7 and a second positive electrode lead 9. At the time when hot-melt is carried out to seal an electric power generating element in the laminate film 1 while the hot-melt parts of the positive electrode lead and the negative electrode lead of the electric power generating element being extended to the outside, the metal layer is prevented from being exposed in the portion of the hot-melt part, which is brought into contact with the positive electrode lead and the negative electrode lead, so that short-circuiting can be avoided and airtightness can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery having a structure in which a power generation element is housed in a laminate film.

[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.

[0004] A polymer electrolyte secondary battery, which is an example of a lithium secondary battery, is manufactured by, for example, a method described below. First, 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 having a positive electrode lead, a carbonaceous material capable of inserting and extracting lithium ions, A negative electrode having a structure in which a negative electrode layer containing an aqueous electrolyte and a polymer holding the electrolyte is supported on a current collector having a negative electrode lead; and a nonaqueous electrolyte and a nonaqueous electrolyte disposed between the positive electrode and the negative electrode. A power generating element comprising a solid polymer electrolyte layer containing a polymer that holds the liquid. The obtained power generating element is covered with a laminate film which is folded in two, and the film is bonded by thermocompression bonding to thereby form the power generating element in the film so that the end of the positive electrode lead and the end of the negative electrode lead form the film. Seal while extending outside. The lithium secondary battery (unit cell) thus obtained is
For example, it is housed in a battery pack either alone or in the form of a battery pack, and is used as a power source for electronic devices.

[0005] The laminated film includes, for example, an outer layer made of an insulating resin such as polyethylene terephthalate, an inner layer made of a heat-fusible resin such as Surlyn, and a layer between the outer layer and the inner layer. A three-layer structure including a metal layer such as aluminum disposed is used. The metal layer is provided for the purpose of preventing moisture from entering the film and shielding light.

However, when the pressure applied to the film during heat fusion is increased in order to increase the airtightness in the laminated film, the metal layer in the film is exposed and the positive electrode lead and the There is a problem that a short circuit occurs due to contact with the negative electrode lead.

Further, when the metal layer is exposed at the end of the laminate film, a terminal connected to the positive electrode lead and the negative electrode lead and a terminal connected to the negative electrode lead during a capacity evaluation test performed before shipment. There is a problem that short-circuit occurs due to contact with the metal layer exposed at the end portion, and the product is determined to be a defective product although it is a good product.

In order to prevent such erroneous determination, the end of the laminate film to which the lead is fixed is folded back. However, there is a problem that such operations complicate the manufacturing process and reduce the weight energy density by providing the turn.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a lithium secondary battery having a high weight energy density, in which a short circuit is prevented during heat fusion and a capacity evaluation test.

[0010]

The lithium secondary battery according to the present invention comprises a positive electrode and a negative electrode that occlude and release lithium ions, and a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode. A power generating element including: a positive electrode lead connected to the positive electrode; a negative electrode lead connected to the negative electrode;
A laminate film in which the power generating element is housed so that the ends of the positive electrode lead and the negative electrode lead extend outward, and which is sealed by heat fusion; And a layer facing the power generation element is formed from a heat-fusible resin, and a metal layer is laminated on the heat-fusible resin layer,
The metal layer does not exist in a portion of the fusion portion that contacts the positive electrode lead and the negative electrode lead.

[0011]

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 sectional view showing an example of a power generating element included in the lithium secondary battery according to the present invention, FIG. 2 is a plan view showing the lithium secondary battery according to the present invention, and FIG.
FIG. 4 is a sectional view taken along line II-II, and FIG. 4 is a plan view showing another example of the lithium secondary battery according to the present invention.

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.
For example, a negative electrode lead 7 made of copper foil is connected to the current collector 2. For example, two first positive electrode leads 8 made of aluminum foil are connected to the current collector 4 respectively. The two positive electrode leads 8 are overlapped, and the overlapped ends are connected to a second positive electrode lead 9 (for example, made of strip-shaped aluminum foil). As shown in FIG. 2, such a power generation element 1 is housed with good airtightness in a folded portion of the laminate film 10. The ends of the folded film 10 along the longitudinal direction and both ends perpendicular to the longitudinal direction are heat-sealed. The negative electrode lead 7 and the second positive electrode lead 9 are fixed to the heat-sealed portion located on the upper side. The ends of the second positive electrode lead 9 and the negative electrode lead 7 extend to the outside. The folded film 10 is
At the upper end on the back side, an auxiliary film 11 for reinforcing the second positive electrode lead 9 and the negative electrode lead 7 is provided.

As shown in FIG. 3, for example, the laminate film 10 includes a first layer 12 made of an insulating resin, a second layer 13 made of a heat-fusible resin, the first layer 12 and the second layer 13. And a metal layer 14 disposed therebetween. In such a film 10, the metal layer 14 does not exist in a portion (a region shown by oblique lines in FIG. 2) of the upper heat-sealed portion in contact with the negative electrode lead 7 and the second positive electrode lead 9.

The first layer 12 is a laminate film 1
0 constitutes a surface exposed to the outside. The insulating resin forming the first layer preferably has high mechanical strength in order to protect the power generation element 1. As such an insulating resin, for example, polyethylene terephthalate (PE)
T), urethane resin, polyimide, polystyrene and the like. The thickness of the first layer is 3 to 50 μm
Should be within the range.

The second layer 13 forms a surface facing the power generating element 1 and forms a heat-sealed portion. Examples of the heat-sealing resin forming the second layer include an ionomer resin such as Surlyn and a polyolefin-based resin such as polyethylene, manufactured by DuPont, USA. The second layer includes, besides one composed of one kind of heat-fusible resin layer, one composed of a plurality of heat-fusible resin layers. The second layer has, for example, a two-layer structure including a heat-fusible resin layer and a heat-fusible resin (eg, polyethylene) layer having an adhesive property and laminated on the heat-fusible resin layer. Can be. When such a second layer is disposed such that the heat-fusible resin layer having the adhesive property is opposed to the metal layer, the adhesion between the second layer and the metal layer can be improved. The thickness of the second layer is 3 to 50 μm.
m.

The metal layer 14 is formed for the purpose of preventing moisture from entering the power generating element 1 and of shielding light. Examples of the metal layer include copper, nickel, and aluminum. The thickness of the metal layer,
It is good to set it in the range of 3 to 50 μm.

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) The positive electrode is formed of a positive electrode layer containing a positive electrode active material, a nonaqueous electrolyte, and a polymer holding the electrolyte supported on a current collector.

Examples of the positive electrode active material include various oxides (eg, lithium-manganese composite oxides such as LiMn ₂ O ₄ , manganese dioxide, lithium-containing nickel oxides such as LiNiO _2, and lithium-containing cobalt oxides such as LiCoO _2). 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 preferably 0.2 mol / l to 2 mol / l. Examples of the polymer holding the nonaqueous electrolyte include a polyethylene oxide derivative, a polypropylene oxide derivative, a polymer containing the derivative, and a copolymer of vinylidene fluoride (VdF) and hexafluoropropylene (HFP). Can be. 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 as the current collector of the positive electrode. For the current collector, for example, an aluminum foil, an aluminum mesh, an aluminum punched metal, or the like is used. Is also good.

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 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, the same ones as those described for the positive electrode are used. In FIG. 1 described above, a copper expanded metal is used as the current collector of the negative electrode. However, for example, a copper foil, a copper mesh, a 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, 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 holding the electrolyte. As the non-aqueous electrolyte and the polymer, the same ones as described for the positive electrode described above are used.

The electrolyte layer may contain an inorganic filler such as silicon oxide powder from the viewpoint of further improving the strength. The power generating element including the positive electrode, the negative electrode, and the electrolyte layer can be manufactured by, for example, a method described below. That is, the positive electrode active material, the polymer holding the non-aqueous electrolyte, the conductive material, and a plasticizer such as dibutyl phthalate (DBP) are mixed in an organic solvent such as acetone, and a paste is prepared. Thus, a positive electrode sheet is prepared. The obtained positive electrode sheet is adhered to the current collector by, for example, thermocompression bonding to produce a positive electrode not impregnated with a non-aqueous electrolyte. On the other hand, the negative electrode active material, the polymer holding the non-aqueous electrolyte and a plasticizer such as dibutyl phthalate (DBP) are mixed in an organic solvent such as acetone, and a paste is prepared. Make a sheet. The obtained negative electrode sheet is adhered to the current collector by, for example, thermocompression bonding to produce a non-aqueous electrolyte-unimpregnated negative electrode. In addition, the polymer holding the non-aqueous electrolyte, the inorganic filler, and a plasticizer such as dibutyl phthalate (DBP) are mixed in an organic solvent such as acetone to prepare a paste, form a film, and form a non-aqueous electrolyte. A liquid-impregnated electrolyte layer is prepared. An electrolyte layer not impregnated with the non-aqueous electrolyte is interposed between the positive electrode not impregnated with the non-aqueous electrolyte and the negative electrode not impregnated with the non-aqueous electrolyte, and are integrated by, for example, thermocompression bonding. The power generating element can be produced by removing the plasticizer from the obtained laminate and impregnating the laminate with a non-aqueous electrolyte.

As described above, the lithium secondary battery according to the present invention has a positive electrode that stores and releases lithium ions,
A power generating element including a negative electrode for storing and releasing lithium ions, and a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode; a positive electrode lead connected to the positive electrode; a negative electrode lead connected to the negative electrode A laminate film that accommodates the power generation element such that ends of the positive electrode lead and the negative electrode lead extend outward, and is sealed by heat fusion;
The outer layer is formed from an insulating resin, and the layer facing the power generating element is formed from a heat-fusible resin, and a metal layer is laminated on the heat-fusible resin layer, The metal layer does not exist in a portion in contact with the positive electrode lead and the negative electrode lead.

According to such a secondary battery, when performing heat fusion to seal the power generating element in a laminate film in a state where the ends of the positive electrode lead and the negative electrode lead are extended to the outside, heat is applied. Since it is possible to prevent the metal layer from being exposed at a portion of the fused portion in contact with the positive electrode lead and the negative electrode lead, a short circuit can be avoided and airtightness can be further improved. In addition, among the end portions of the film of the secondary battery thus obtained, the metal layer is not exposed to a portion where the positive electrode lead and the negative electrode lead are fixed, so that a capacity evaluation test is performed. In this case, it is possible to prevent a short circuit caused by contact between a terminal connected to the positive electrode lead and the negative electrode lead and an end of the film, and improve test accuracy. Further, since the operation of providing the folded portion described above is not required, the manufacturing process can be simplified, and the weight energy density of the secondary battery can be improved.

In FIG. 2 described above, only the metal layer is removed from the fused portion of the laminated film 10 in contact with the positive electrode lead 9 and the negative electrode lead 7. However, the lithium secondary battery according to the present invention does not As shown in FIG. 4, a configuration in which the metal layer of the entire fused portion of the film 10 (the region indicated by oblique lines) is removed is included. 2 and 4 described above,
Although the example using the laminated film 10 having the auxiliary film 11 has been described, the auxiliary film 11 may not be provided.

[0033]

Embodiments of the present invention will be described below in detail with reference to the drawings. (Example) <Preparation of positive electrode> As an active material, 56% by weight of a lithium manganese composite oxide represented by a composition formula of LiMn ₂ O ₄ , 5% by weight of carbon black, and vinylidene fluoride-hexafluoropropylene (VdF- A paste was prepared by mixing 17% by weight of a copolymer powder of HFP) and 22% by weight of dibutyl phthalate (DBP) in acetone. The obtained paste was applied on a polyethylene terephthalate film (PET film) so as to have a thickness of 100 μm, formed into a sheet, and cut to prepare a positive electrode sheet. Further, a current collector made of expanded metal made of aluminum and having a strip-shaped aluminum foil was prepared as a first positive electrode lead. The positive electrode lead had a width of 10 mm, a length of 20 mm, and a thickness of 20 μm. The current collector had a width of 40 mm, a length of 70 mm, and a thickness of 40 to 60 μm. The obtained sheet was heated and pressed on both sides of the current collector with a hot roll to produce a positive electrode not impregnated with a non-aqueous electrolyte.

<Preparation of Negative Electrode> Mesophase pitch carbon fiber (58% by weight) as an active material, vinylidene fluoride-
17% by weight of hexafluoropropylene (VdF-HFP) copolymer powder and 25% of dibutyl phthalate (DBP)
% By weight in acetone to prepare a paste.
The obtained paste was applied on a polyethylene terephthalate film (PET film) so as to have a thickness of 100 μm, formed into a sheet, and cut to prepare a negative electrode sheet. In addition, a current collector made of a copper expanded metal having a strip-shaped copper foil was prepared as a first negative electrode lead. The negative electrode lead had a width of 10 mm, a length of 20 mm, and a thickness of 20 μm. The current collector has a width of 44 m.
m, the length was 74 mm, and the thickness was 40 to 60 μm. The obtained negative electrode sheet was heat-pressed on both surfaces of the current collector with hot rolls to produce a non-aqueous electrolyte-unimpregnated negative electrode.

<Preparation of Solid Electrolyte Layer> SiO ₂ Powder 3
3.3% by weight of vinylidene fluoride-hexafluoropropylene (VdF-HFP) copolymer powder
2% by weight and 44.5% by weight of dibutyl phthalate (DBP) were mixed in acetone to form a paste. The obtained paste is applied to a polyethylene terephthalate film (P
An ET film was coated on the ET film so as to have a thickness of 100 μm, formed into a sheet, and a non-aqueous electrolyte-impregnated solid polymer electrolyte layer was prepared.

<Preparation of Nonaqueous Electrolyte> LiPF ₆ as an electrolyte was added to a nonaqueous solvent in which ethylene carbonate (EC) and dimethyl carbonate (DMC) were mixed at a volume ratio of 2: 1 at a concentration of 1 mol / mol. 1 to prepare a non-aqueous electrolyte.

<Assembly of Battery> Two positive electrodes, one negative electrode, and two solid electrolyte layers were prepared, and the positive electrode and the negative electrode were alternately laminated with the solid electrolyte layer interposed therebetween. These were heat-pressed with a rigid roll heated to 130 ° C. to produce a laminate. Such a laminate was immersed in methanol, and the DBP in the laminate was extracted with methanol and removed. Subsequently, the laminate was dried, and immersed in a non-aqueous electrolyte having the above composition to impregnate the laminate with the electrolyte, thereby producing a power generating element having the structure shown in FIG. 1 described above. The end of a strip-shaped aluminum foil (width 10 mm, length 50 mm, thickness 30 μm) as a second positive electrode lead was folded into a bag shape. The tip of one of the first positive electrode leads and the tip of the other first positive electrode lead were overlapped, and these leads were placed in the bag described above and bonded by welding. Further, the end of a strip-shaped copper foil (width: 10 mm, length: 50 mm, thickness: 30 μm) as a second negative electrode lead is folded into a bag shape, and the first negative electrode lead described above is placed in the bag. And bonded by welding.

Auxiliary film (length 20 mm, width 48
mm and a thickness of 15 μm) (laminated film having a length of 114 mm, a width of 116 mm and a thickness of 15 μm).
m) was prepared. This film has a first layer (thickness: 5 μm) made of polyethylene terephthalate, a second layer (thickness: 5 μm) made of an ionomer resin manufactured by DuPont, USA and having a trade name of, and the first layer and the first layer. A metal layer of aluminum (thickness 5
μm). In the film, a metal layer does not exist in a portion corresponding to a portion in contact with the second positive electrode lead and the second negative electrode lead in a fused portion formed by thermal fusion described later. The laminate film is folded into two, and the power generating element is housed therein so that the ends of the second positive electrode lead and the external negative electrode lead extend to the outside. It has the structure shown in FIG. 2 described above by heat fusion so as to be in contact with the positive electrode lead and the negative electrode lead, and has a thickness of 630 μm.
And a 114 × 58 mm polymer electrolyte secondary battery
0 were produced. (Comparative Example) 100 polymer electrolyte secondary batteries were manufactured in the same manner as in the Example except that a laminate film having no metal layer non-formed portion was used.

With respect to the obtained secondary batteries of Examples and Comparative Examples, the internal resistance was measured to determine the number of batteries in which a short circuit occurred during thermal fusion. The results are shown in Table 1 below. Table 1 Number of batteries in which a short circuit occurred during thermal fusion (cells / 100) Example 0 Comparative Example 9 As can be seen from Table 1, a laminate in which a metal layer does not exist in a fused portion in contact with a positive electrode lead and a negative electrode lead. The secondary battery of the embodiment including the film can prevent a short circuit from occurring at the time of heat fusion. On the other hand, it can be seen that the secondary battery of the comparative example provided with the laminated film having the metal layer present on the entire fused portion causes a short circuit at the time of heat fusion. (Reference Example) A power generating element similar to that of the example was manufactured, and a second positive electrode lead and a second negative electrode lead were attached in the same manner as in the example.

An auxiliary film having the same dimensions as in the example and a laminate film having the same dimensions as the example having a folded portion having a length of 114 mm, a width of 116 mm and a thickness of 15 μm were prepared. This film is formed of a first layer, a second layer, and a metal layer made of the same material as in the embodiment. The laminated film was folded in two, and the power generating element was housed therein so that the ends of the second positive electrode lead and the external negative electrode lead extended outside, and were sealed by heat fusion. As shown in FIG. 5, the folded portion 15 of the film 10 is folded on the film side, and the end portion is an insulating tape 16 (width: 20 mm, length: 58 mm, thickness: 18 mm).
μm) to produce a polymer electrolyte secondary battery having the same dimensions as in the example.

The charge / discharge rate for each of the obtained secondary batteries of the reference example and the secondary batteries of the example was 100;
The charge / discharge evaluation was performed at 1.0 C, 4.5 V cut charge, and 3.0 V cut discharge, and the battery voltage was measured. As a result, none of the batteries had a charge voltage of 4.2 V or less. In the capacity evaluation test, a battery having no short circuit caused by heat fusion was used.

The volume energy densities of the secondary batteries of Reference Examples and Examples were measured, and the results were shown in Table 2 below.
Shown in As is clear from Table 2, the secondary batteries of the examples have a higher weight energy density than the reference example.

[0043]

As described above, according to the present invention, it is possible to provide a lithium secondary battery which prevents short circuit at the time of heat fusion and at the time of a capacity evaluation test and has a high weight energy density.

[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 plan view showing a lithium secondary battery according to the present invention.

FIG. 3 is a sectional view taken along the line II-II of FIG. 2;

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

FIG. 5 is an enlarged cross-sectional view showing a part of a polymer electrolyte secondary battery of a reference example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Power generation element 7 ... Negative electrode lead 9 ... 2nd positive electrode lead 10 ... Laminated film 11 ... Auxiliary film

Claims (1)

[Claims] A power generating element including a positive electrode and a negative electrode that occlude and release lithium ions, and a lithium ion conductive electrolyte layer disposed between the positive electrode and the negative electrode; a positive electrode lead connected to the positive electrode; A negative electrode lead connected to a negative electrode; a laminate film containing the power generating element such that ends of the positive electrode lead and the negative electrode lead extend outward, and sealed by heat fusion; The film has an outer layer formed of an insulating resin, a layer facing the power generating element formed of a heat-fusible resin, and a metal layer laminated on the heat-fusible resin layer. A lithium secondary battery, wherein the metal layer does not exist in a portion of the attachment portion that contacts the positive electrode lead and the negative electrode lead.