JPH11260417A - Polymer electrolyte lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte lithium secondary battery with high productivity, high reliability, and no internal short circuit in production process and in charge/discharge. SOLUTION: This polymer electrolyte lithium secondary battery has a unit cell 1 formed by stacking a positive electrode 2 capable of absorbing/desorbing lithium ions; a lithium ion conductive polymer electrolyte layer 3; a negative electrode 4 capable of absorbing/desorbing lithium ions; the lithium ion conductive polymer electrolyte layer 3; and the positive electrode 2 capable of absorbing/desorbing lithium ions in this order, and the tips of terminal parts 5 extended from the positive electrodes 2 are connected to an outer lead. Insulating films 14 are formed on the surfaces facing the terminal parts 5 of the positive electrodes 2 located in the vicinity of the unit cell 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a polymer electrolyte lithium secondary battery.

[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 containing lithium or a lithium alloy as an active material and a suspension containing an active material containing an oxide, sulfide, or selenide of molybdenum, vanadium, titanium, or niobium were applied. A non-aqueous electrolyte secondary battery including a positive electrode made of a current collector and a non-aqueous electrolyte is known.

However, a secondary battery provided with a negative electrode using lithium or a lithium alloy as an active material has a problem that the charge / discharge cycle life is short because repetition of charge / discharge cycles generates lithium dendrites in the negative electrode. .

[0004] For this reason, a suspension containing a carbonaceous material that occludes and releases lithium ions, such as coke, graphite, carbon fiber, fired resin, and pyrolytic gas phase carbon, is applied to the negative electrode. A non-aqueous electrolyte secondary battery using a current collector 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.

On the other hand, US Pat. No. 5,429,891 discloses a rechargeable lithium intercalation having a hybrid polymer electrolyte which has been made flexible by adding a polymer to the cathode, anode and electrolyte layers. A battery, that is, a polymer electrolyte lithium secondary battery is disclosed. Such a polymer electrolyte lithium secondary battery is manufactured by the following method.

First, a plasticizer such as DBP (dibutyl phthalate) which can be removed later, vinylidene fluoride (VdF) and hexafluoropropylene (H
An FP) copolymer and a positive electrode material capable of inserting and extracting lithium are mixed in the presence of a solvent, formed into a sheet, and the obtained sheet is laminated on a current collector to form an electrolytic solution. A non-impregnated positive electrode material is produced. Also, a plasticizer and VdF
The HFP copolymer is mixed in the presence of a solvent, and the mixture is formed into a sheet to form an electrolyte-unimpregnated separator sheet. Further, a plasticizer, a copolymer of VdF-HFP, and a carbonaceous material capable of occluding and releasing lithium are mixed in the presence of a solvent, formed into a sheet, and the obtained sheet is collected with a current collector. An electrolyte-unimpregnated negative electrode material is produced by laminating on a body. Subsequently, the positive electrode material, the separator sheet, the negative electrode material, the separator sheet and the positive electrode material are laminated in this order, and thermocompression-bonded to produce an electrolyte-impregnated unit cell. The area of the negative electrode is made larger than that of the positive electrode in order to prevent lithium dendrite. Further, the separator sheet is equal to or larger in area than the negative electrode material in order to prevent an internal short circuit between the positive and negative electrodes. Subsequently, the plasticizer in the unit cell is extracted and removed with a solvent, and then impregnated with a non-aqueous electrolyte to produce a polymer electrolyte lithium secondary battery. In such a secondary battery, two positive electrode terminal portions and two negative electrode terminal portions are respectively extended from the same side surface of the unit cell for connection with an external load, and the positive electrode terminal portion and the negative electrode terminal are connected to each other. In such a conventional polymer electrolyte lithium secondary battery having a structure in which a portion is connected to an external lead at a tip end, the unit cell contains substantially no liquid component and its constituent layers are integrated. A simple exterior material such as a laminate film can be used, and it is thin, lightweight, and excellent in safety.

[0007]

As described above, the conventional polymer electrolyte lithium secondary battery has a structure in which a terminal portion of each positive electrode faces the negative electrode, and a separator sheet is disposed on the facing portion. Prevents short circuit. However, burrs at the terminal portion of the positive electrode, pressure during the manufacturing process, etc., break through the separator sheet and come into contact with the negative electrode, thereby causing an internal short circuit. Another problem is that the terminal of the positive electrode similarly breaks through the separator sheet and comes into contact with the negative electrode due to a change in the volume of the electrode during charge / discharge after battery assembly, causing an internal short circuit.

An object of the present invention is to provide a polymer electrolyte lithium secondary battery in which an internal short circuit is prevented during a manufacturing process and during charging and discharging.

[0009]

According to the present invention, there is provided a polymer electrolyte lithium secondary battery comprising: a positive electrode capable of inserting and extracting lithium ions; a lithium ion conductive polymer electrolyte layer;
A negative electrode capable of inserting and extracting lithium ions, a lithium ion conductive polymer electrolyte layer,
In a polymer electrolyte lithium secondary battery having a unit cell in which a positive electrode capable of being discharged is stacked in this order, and having a structure in which the tip of a terminal portion extended from each of the positive electrodes is connected to an external lead, An insulating film is formed on a surface of each of the positive electrodes located near the unit cell, the surface being opposed to the terminal part.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a polymer electrolyte lithium secondary battery according to the present invention will be described with reference to FIGS.

The unit cell 1 comprises a positive electrode 2 capable of occluding and releasing lithium ions, a lithium ion conductive polymer electrolyte layer 3, and a negative electrode 4 capable of occluding and releasing lithium ions.
And a lithium ion conductive polymer electrolyte layer 3 and a positive electrode 2 capable of occluding and releasing lithium ions are laminated and integrated in this order.

The negative electrode 4 has a larger area than the positive electrode 2, and the electrolyte layer 3 has a larger area than the negative electrode 4.

Each of the positive electrodes 2 has a structure in which a positive electrode layer 7 is supported on a current collector 6 having a strip-shaped terminal portion 5 extending to the outside. The negative electrode 4 has a structure in which a negative electrode layer 10 is supported on a current collector 9 having a strip-shaped terminal portion 8 extending to the outside. The strip-shaped terminal portions 5 of the positive electrode 2 and the strip-shaped terminal portions 8 of the negative electrode 4 respectively extend from the same side surface of the unit cell 1, and the strip-shaped terminal portions 5 of the respective positive electrodes 2 are mutually sandwiched with the negative electrode 4 interposed therebetween. They are arranged facing each other.

The unit cell 1 includes an exterior film 11
The film 11 is hermetically sealed by fusing the opening of the film 11. The strip-shaped terminal portions 5 of the respective positive electrodes 2 of the unit cell 1 have their tips bundled together in the exterior film 11 and connected to one end of an external lead 12. The external lead 12 extends outside through the fusion portion 13 of the exterior film 11. The strip-shaped terminal portion 8 of the negative electrode 4 of the unit cell 1 is connected to one end of an external lead (not shown) in the external film 11, and the external lead is connected to the external film 1.
It extends to the outside through one fusion part 13.

The insulating coating 14 is provided at least on the surface of the positive electrode 2 facing the unit cell 1 facing the band-like terminal 5, for example, from the base of the unit cell 1 to the connection with the external lead 12. Are formed on opposing surfaces of

Next, the positive electrode 2, the lithium ion conductive polymer electrolyte layer 3, the negative electrode 4, the insulating film 14
And the exterior film 11 will be described.

1) Positive Electrode 2 The positive electrode 2 is made of an active material for absorbing and releasing lithium ions on both surfaces of an aluminum current collector 6 having an aluminum strip terminal portion 5, a non-aqueous electrolyte, and a polymer holding the electrolyte. Has a structure in which the positive electrode layer 7 containing is supported.

Examples of the 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). Materials, lithium-containing nickel-cobalt oxide, lithium-containing amorphous vanadium pentoxide, etc.)
Chalcogen compounds (for example, titanium disulfide, molybdenum disulfide, etc.) can be exemplified. Among them, lithium manganese composite oxide, lithium-containing cobalt oxide,
It is preferable to use lithium-containing nickel oxide.

The non-aqueous electrolyte is prepared by dissolving an electrolyte in a non-aqueous solvent.

Examples of the non-aqueous solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and dimethyl carbonate (D
MC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (γ-
BL), sulfolane, acetonitrile, 1,2-dimethoxyethane, 1,3-dimethoxypropane, dimethyl ether, tetrahydrofuran (THF), 2-methyltetrahydrofuran and the like. 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 (Li
PF 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 holding the non-aqueous 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.

The positive electrode layer 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.

As the current collector, for example, expanded metal made of aluminum, mesh made of aluminum, punched metal made of aluminum, or the like can be used.

The band-like terminal portion is formed by extending the current collector as it is or by using an aluminum foil connected to the current collector.

2) Lithium-ion conductive polymer electrolyte layer 3 The electrolyte layer 3 contains a non-aqueous electrolyte and a polymer holding the electrolyte.

As the non-aqueous electrolyte and the polymer, those similar to those described for the positive electrode described above are used.

The electrolyte layer may contain an inorganic filler such as SiO ₂ powder in order to improve the compressive strength.

3) Negative Electrode 4 This negative electrode 4 is a copper current collector 9 having a copper strip terminal portion 8.
Has a structure in which a negative electrode layer 10 containing a carbonaceous material capable of inserting and extracting lithium ions, a non-aqueous electrolyte, and a polymer holding the electrolyte is supported on both surfaces.

Examples of the carbonaceous material include those obtained by firing an organic polymer compound (for example, phenol resin, polyacrylonitrile, cellulose, etc.), those obtained by firing coke or mesophase pitch. And carbonaceous materials represented by artificial graphite, natural graphite and the like.
Above all, it is preferable to use a carbonaceous material obtained by firing the mesophase pitch at a temperature of 500 ° C to 3000 ° C 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.

The negative electrode layer may be made of artificial graphite, natural graphite, carbon black, acetylene black,
It is allowed to contain conductive materials such as Ketjen black, nickel powder, and polyphenylene derivatives, and fillers such as olefin polymers and carbon fibers.

As the current collector, for example, a copper expanded metal, a copper mesh, a copper punched metal, or the like can be used.

The band-shaped terminal portion is formed by extending the current collector as it is or by using a copper foil connected to the current collector.

4) Insulating Coating 14 The insulating coating is formed, for example, by applying an insulating paint or inserting an insulating resin film to the strip-shaped terminal portion of the positive electrode. Particularly, it is preferable to use a non-aqueous electrolyte resistant insulating tape from the viewpoint of workability. As the insulating tape, for example, polyethylene terephthalate (P
ET), polyethylene (PE), polypropylene (P
P) and modified products of these resins, and tapes based on polyimide or the like.

5) Exterior film 11 The exterior film material 11 is a laminated film in which a heat-fusible resin film, a metal foil and a rigid resin film are laminated at least in this order from the inner surface side. Examples of the heat-fusible resin include polyethylene (PE),
Ionomer, ethylene vinyl acetate (EVA) and the like can be used. As the metal foil, for example, A
Although 1 foil, Ni foil and the like can be used, Al foil which can be made thinner is preferable. As the rigid resin, for example, polyethylene terephthalate (PET), nylon or the like can be used. However, the rigid resin film may be a combination of two or more films.

Next, an example of a method for producing a polymer electrolyte lithium secondary battery according to the present invention will be described below.

First, a polymer holding at least a non-aqueous electrolyte, an active material capable of inserting and extracting lithium and a plasticizer are mixed in the presence of a solvent, and the mixture is formed into a sheet.
The obtained sheet is laminated on a portion of the current collector having a strip-shaped terminal portion other than the terminal portion, to prepare a positive electrode material not impregnated with an electrolyte.

Examples of the plasticizer include dibutyl phthalate (DBP), dimethyl phthalate (DMP), and ethyl phthalyl ethyl glycolate (EPEG).

Further, at least a polymer holding a non-aqueous electrolyte and a plasticizer are mixed in the presence of a solvent, and the mixture is formed into a sheet to form an electrolyte-unimpregnated electrolyte layer.

Further, at least a polymer holding a non-aqueous electrolyte, a carbonaceous material capable of inserting and extracting lithium and a plasticizer are mixed in the presence of a solvent, and the mixture is formed into a sheet. A negative electrode material not impregnated with an electrolyte is produced by laminating the current collector having a strip-shaped terminal portion on a portion other than the terminal portion.

Next, the positive electrode material, the electrolyte layer, the negative electrode material, the electrolyte layer and the positive electrode material are laminated in this order, and thermocompression-bonded to produce an electrolyte-unimpregnated unit cell. Subsequently, after extracting and removing the plasticizer in the unit cell with a solvent, an adhesive tape is attached to a desired surface of the positive electrode material opposite to the strip-shaped terminal portion to form an insulating film. Subsequently, storing the unit cell in an exterior film,
After injecting a non-aqueous electrolyte from the opening of the exterior film and impregnating the constituent members of the unit cell with the electrolyte, the opening of the exterior film is fused and the positive electrode terminal and the negative electrode of the unit cell are removed. The polymer electrolyte lithium secondary battery is manufactured by extending the external leads respectively connected to the terminal portions to the outside through the fused portion.

The polymer electrolyte lithium secondary battery according to the present invention described above comprises a positive electrode capable of occluding and releasing lithium ions, a lithium ion conductive polymer electrolyte layer, and a negative electrode capable of occluding and releasing lithium ions. A unit cell in which a lithium ion conductive polymer electrolyte layer and a positive electrode capable of occluding and releasing lithium ions are laminated in this order, and a tip of a terminal portion extended from each of the positive electrodes is referred to as an external lead. The polymer electrolyte lithium secondary battery having a connected structure has a structure in which an insulating film is formed on at least a surface of each of the positive electrodes located near the unit cell and facing the terminal portion.

According to such a structure, the insulating film is formed on at least the surface of each of the positive electrodes located near the unit cell, opposite to the terminal of each of the positive electrodes. Even if the terminal portion breaks through the polymer electrolyte layer adjacent to the terminal portion due to a change in the volume of the electrode at the time, the insulating coating can prevent the terminal portion of the positive electrode from directly contacting the negative electrode. Therefore, it is possible to prevent the positive electrode and the negative electrode of the unit cell from coming into contact with each other through the terminal part of the positive electrode to cause an internal short circuit at the time of manufacture or charge / discharge. (High yield).

[0046]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(Example 1) <Preparation of positive electrode material not impregnated with non-aqueous electrolyte> A lithium manganese composite oxide having a composition formula of LiMn ₂ O ₄ as an active material, carbon black, and vinylidene fluoride in acetone Ride-hexafluoropropylene (VdF-HF
A paste was prepared by mixing a mixture of the copolymer powder P) and dibutyl phthalate (DBP) in acetone. The LiMn ₂ O ₄ , carbon black, VdF-
The mixing ratio of the HFP copolymer powder and DBP is 56% by weight, 5% by weight, 17% by weight, and 22% by weight. Subsequently, the paste was mixed with polyethylene terephthalate (P
ET) It was applied on a film so as to have a thickness of 100 μm and a width of 200 mm to form a sheet.

Next, the positive electrode layer was heat-pressed with a hot roll to both surfaces of a current collector made of an expanded metal made of aluminum having an aluminum band-shaped terminal portion, excluding the terminal portions, and then cut into 30 mm × 52 mm. A positive electrode material having an electrolyte-unimpregnated positive electrode layer was produced. Thereafter, an insulating paint prepared by dissolving asphalt with toluene is applied to one surface of the band-shaped terminal portion except for a connection portion with an external lead described later (the surface facing the unit cell when it is manufactured), and dried. An insulating film was formed.

<Preparation of Negative Electrode Impregnated with Non-Aqueous Electrolyte>
A paste was prepared by mixing the powder heat-treated at 0 ° C., the VdF-HFP copolymer powder, and DBP in acetone. The carbon fiber powder, VdF-HF
The mixing ratio of the P copolymer powder and DBP is 58% by weight, 17% by weight, and 25% by weight. Subsequently, the paste was applied on a polyethylene terephthalate (PET) film so as to have a thickness of 100 μm and a width of 200 mm to form a sheet. Subsequently, the negative electrode layer was heat-pressed with a hot roll to both sides of a porous current collector made of a copper expanded metal having a copper strip-shaped terminal portion except for the terminal portion, and then cut to obtain a 32 mm × 54 mm electrolyte solution. A negative electrode material having an impregnated negative electrode layer was produced.

<Preparation of polymer electrolyte material not impregnated with non-aqueous electrolyte> Silicon oxide powder 33.3 parts by weight, VdF-HFP
A paste was prepared by mixing 22.2 parts by weight of the copolymer powder and 44.5 parts by weight of DBP in acetone. Subsequently, the paste was applied on a polyethylene terephthalate (PET) film to a thickness of 100 μm and a width of 2 μm.
It was applied to a thickness of 00 mm, formed into a sheet, and then cut to prepare a 32 mm × 54 mm non-aqueous electrolyte unimpregnated polymer electrolyte material.

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

Next, the obtained positive electrode material, polymer electrolyte material, negative electrode material, polymer electrolyte material and positive electrode material are stacked in this order, and these are heated and pressed by a rigid roll heated to 125 ° C. to obtain a non-aqueous solution. An electrolyte-unimpregnated unit cell was prepared.

Next, the unit cell was immersed in a container containing n-decane, and allowed to stand for 15 minutes while stirring with a magnetic stirrer placed in the container. This operation was repeated until the concentration of the plasticizer (DBP) in n-decane by gas chromatography became 20 ppm or less, thereby removing the plasticizer from each component of the non-aqueous electrolyte non-impregnated unit cell.

Then, an aluminum external lead was connected to the strip terminal of each positive electrode of the unit cell after removing the plasticizer, and a copper external lead was connected to the negative electrode terminal.
Subsequently, these are stored in an exterior film having one side opened, and the non-aqueous electrolyte is injected into the exterior film,
After impregnating the constituent members of the unit cell with the electrolytic solution, the openings of the exterior film are fused, and the external leads connected to the terminal portions of each positive electrode and the negative electrode of the unit cell are fused. By extending to the outside through the portion, 50 polymer electrolyte lithium secondary batteries (theoretical capacity was 85 mAh) having the structure shown in FIGS. 1 and 2 described above were manufactured.

(Example 2) An insulating tape using polyimide as a base material was adhered to one surface of the positive electrode strip-shaped terminal portion except for the connection portion with the external lead (the surface facing when the unit cell was manufactured). Fifty polymer electrolyte lithium secondary batteries similar to those in Example 1 were manufactured.

Comparative Example 1 Fifty polymer electrolyte lithium secondary batteries were manufactured in the same manner as in Example 1, except that a positive electrode having a strip-shaped terminal portion without an insulating film was used.

With respect to the obtained secondary batteries of Examples 1 and 2 and Comparative Example 1, the number of internal short-circuit defects during the manufacturing process was examined. The results are shown in Table 1 below.

In the obtained secondary batteries of Examples 1 and 2 and Comparative Example 1, the number of internal short-circuit defects after repetition of charge / discharge 100 times was examined for 20 batteries which were determined to be good after production. Was. The results are shown in Table 1 below.

[0059]

[Table 1]

As is apparent from Table 1, the secondary batteries of Examples 1 and 2 in which an insulating film was formed on the opposing surfaces of the band-shaped terminal portions extending from the two positive electrodes, did not have the insulating film. It can be seen that the internal short circuit failure during the manufacturing process can be significantly reduced and the productivity (yield) can be significantly improved, as compared with the secondary battery of Comparative Example 1 using the positive electrode having a portion.

Further, it can be seen that the secondary batteries of Examples 1 and 2 can reduce the internal short circuit failure in the charge / discharge test as compared with the secondary battery of Comparative Example 1, and have high reliability.

[0062]

As described in detail above, according to the present invention, it is possible to provide a highly productive and highly reliable polymer electrolyte lithium secondary battery in which an internal short circuit is prevented during the manufacturing process and during charging and discharging. .

[Brief description of the drawings]

FIG. 1 is a sectional view showing a polymer electrolyte lithium secondary battery according to the present invention.

FIG. 2 is a perspective view showing a unit cell part of FIG. 1;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Unit cell, 2 ... Positive electrode, 3 ... Lithium ion conductive polymer electrolyte layer, 4 ... Negative electrode, 5 ... Strip terminal part of positive electrode, 11 ... Outer film, 14 ... Insulating coating

Claims (1)

[Claims] 1. A positive electrode capable of storing and releasing lithium ions, a lithium ion conductive polymer electrolyte layer, a negative electrode capable of storing and releasing lithium ions, a lithium ion conductive polymer electrolyte layer, and a lithium ion conductive polymer electrolyte layer. In a polymer electrolyte lithium secondary battery having a unit cell in which a positive electrode capable of insertion and extraction can be stacked in this order, and having a structure in which the tip of a terminal portion extended from each positive electrode is connected to an external lead, A polymer electrolyte lithium secondary battery characterized in that an insulating coating is formed on at least a surface of each of the positive electrodes located near the unit cell and facing the terminal portion.