JPH10208752A - Polymer electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polymer electrolyte secondary battery whose terminal part strength is improved, whose yield is heightened, and which can easily be manufactured. SOLUTION: This polymer electrolyte secondary battery comprises a positive electrode 7 having a structure produced by depositing a positive electrode layer 8 containing an active material on at least one side of a collector 2, a negative electrode 5 having a structure produced by deposition a negative electrode layer 10 containing an active material on at least one side of a collector 4, and a solid electrolyte layer 6 installed between the positive electrode layer 8 and the negative electrode layer 10 and the collector of at least one electrode of the positive electrode 7 and the negative electrode 5 is made of a metal net and has a terminal part made of a strip-like metal plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polymer electrolyte secondary battery in which a terminal portion of a current collector of an electrode is improved.

[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.

Further, for example, coke, graphite, carbon fiber,
There has been proposed a lithium secondary battery using, as a negative electrode, a current collector coated with a suspension containing a carbonaceous material that stores and releases lithium ions, such as a resin fired body and pyrolytic gas phase carbon.

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 such as a lithium composite oxide is supported on a current collector;
A negative electrode having a structure in which a negative electrode layer containing an active material such as a carbonaceous material capable of inserting and extracting lithium ions is supported on a current collector; and a lithium ion conductive material disposed between the positive electrode layer and the negative electrode layer. A solid electrolyte layer. In such a secondary battery, in order to improve the energy density per unit weight by increasing the amount of the positive electrode layer and the negative electrode layer carried on the current collector, the positive electrode and the current collector of the negative electrode Metal nets such as expanded metal made of aluminum and expanded metal made of copper are used. As shown in FIG. 5, the current collector 21 has a band-shaped terminal portion 22, and the terminal portion 22 is formed of a metal net similarly to the current collector 21.

However, if the band-shaped terminal portion is formed of a metal net, the strength of the terminal portion is so low that the terminal portion may be cut off, entangled or tangled during manufacturing. occured.

[0006] For this reason, it has been practiced to shorten the length of the strip-shaped terminal portion made of a metal net and attach a strip-shaped metal foil as an auxiliary terminal. In order to improve the connection strength even a little, the end of the band-shaped metal foil 23 is folded into a bag shape as shown in FIG. 6, and the end of the band-shaped terminal portion 22 is inserted into the formed bag. This is performed by fixing the end of the strip-shaped terminal portion 22 in the bag-shaped metal foil 23 by ultrasonic welding.

However, attaching the auxiliary terminal to the terminal portion has a problem that the productivity is reduced because the operation becomes complicated as described above. In addition, the terminal portion may come off from the auxiliary terminal in the process of manufacturing the battery, and the yield is low.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a polymer electrolyte secondary battery in which the strength of the terminal portion is improved, the yield is improved, and the battery can be manufactured by a simple method.

[0009]

The polymer electrolyte secondary battery according to the present invention comprises a positive electrode having a structure in which a positive electrode layer containing an active material is supported on at least one surface of a current collector, and a negative electrode layer containing an active material. A negative electrode having a structure supported on at least one side of the current collector, and including a solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, the positive electrode and the negative electrode of at least one of the electrodes The current collector is characterized by having a terminal portion formed of a metal net and formed of a strip-shaped metal plate.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A polymer electrolyte secondary battery according to the present invention comprises a positive electrode, a negative electrode, and a solid electrolyte layer disposed between the positive electrode and the negative electrode. One positive electrode or a second positive electrode is used, and a first negative electrode or a second negative electrode described below is used as the negative electrode. However, the secondary battery does not have a configuration including the second positive electrode and the second negative electrode.

Hereinafter, the first positive electrode, the second positive electrode, the first negative electrode, the second negative electrode, and the electrolyte layer will be described. (First Positive Electrode) This positive electrode is formed from a positive electrode layer containing an active material, a non-aqueous electrolytic solution and a polymer holding the electrolytic solution carried on at least one surface of a current collector made of a metal net. The current collector has a terminal portion made of a band-shaped metal plate.

As the active material, various oxides (for example, lithium manganese composite oxide such as LiMn ₂ O ₄ ,
Manganese dioxide, for example, a lithium-containing nickel oxide such as LiNiO ₂ , for example, a lithium-containing cobalt oxide such as LiCoO ₂ , a lithium-containing nickel cobalt oxide, and an amorphous vanadium pentoxide containing lithium.
And chalcogen compounds (for example, titanium disulfide, molybdenum disulfide, and the like). 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 ].

It is desirable that the amount of the electrolyte dissolved in the non-aqueous solvent be 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.

[0016] The positive electrode layer may contain 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 metal net 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 current collector has a thickness of 10 μm to 100 μm.
It is preferred to be within the range of m. The strip-shaped metal plate as the terminal portion can be formed, for example, from an aluminum foil.

The thickness of the terminal is 10 μm to 100 μm.
It is preferred to be within the range of m. A current collector having such a terminal portion is, for example, cut into a central portion of a metal plate,
It can be manufactured by punching a metal plate having a net-like portion in a part by pulling both end portions of the metal plate outward to a desired shape.

(Second Positive Electrode) This positive electrode has the same structure as the above-described first positive electrode except that a metal plate such as an aluminum foil is used as a current collector.

(Negative Electrode) The negative electrode is formed from a negative electrode layer containing an active material, a non-aqueous electrolyte and a polymer holding the electrolyte supported on at least one surface of a current collector made of a metal net. The current collector has a terminal portion made of a band-shaped metal plate.

Examples of the 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. The negative electrode layer is 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 metal net as the current collector, for example, a copper expanded metal, a copper mesh, a copper punched metal, or the like can be used. The current collector preferably has a thickness in the range of 10 μm to 100 μm.

The strip-shaped metal plate as the terminal portion is, for example,
It can be formed from copper foil. The thickness of the terminal portion,
It is preferable to set it in the range of 10 μm to 100 μm. A current collector having such a terminal portion is formed, for example, by cutting a metal plate having a net-like portion in a desired shape by making a cut in the center of the metal plate and pulling both ends of the metal plate outward. It can be manufactured by punching into a hole.

(Second Negative Electrode) This negative electrode is the same as the first negative electrode except that a metal plate such as a copper foil is used as a current collector.
It has a configuration similar to that of the negative electrode.

(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 SiO ₂ powder in order to improve the compressive strength. The secondary battery including the positive electrode, the negative electrode, and the electrolyte layer can be manufactured by, for example, a method described below. That is, the active material, the polymer holding the non-aqueous electrolyte, the conductive material, and the plasticizer are mixed in an organic solvent such as acetone, a paste is prepared, and a positive electrode sheet is formed by forming a film. The obtained positive electrode sheet is adhered to one or both surfaces of the current collector by, for example, thermocompression bonding to prepare a positive electrode not impregnated with a nonaqueous electrolyte. On the other hand, the active material, the polymer holding the non-aqueous electrolyte, and a plasticizer are mixed in an organic solvent such as acetone to prepare a paste, and a negative electrode sheet is prepared by forming a film. The obtained negative electrode sheet is adhered to one or both surfaces of the current collector by, for example, thermocompression bonding to prepare 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 secondary battery can be manufactured by removing the plasticizer from the obtained laminate, impregnating with a non-aqueous electrolyte, and storing this in a container such as a laminate film.
In the case where the secondary battery is manufactured using a plurality of positive electrodes and negative electrodes, a plurality of positive terminals (negative terminals) may be used.
Is fixed to a single external lead (for example, made of a strip-shaped metal foil), and the external lead is extended outside the container.
Such connection of the external lead is preferably performed before the housing in the container.

As the plasticizer, dibutyl phthalate (DBP) or the like can be used. By adding the plasticizer, the positive and negative electrodes and the electrolyte layer can be imparted with flexibility, so that the handleability during production can be improved, and the nonaqueous electrolyte impregnation amount can be increased. Further, the positive electrode, the negative electrode, and the electrolyte layer can be bonded by thermocompression bonding.

According to the polymer electrolyte secondary battery according to the present invention as described above, the positive electrode, the negative electrode, or the current collector of both electrodes is formed of a metal net and has a terminal portion formed of a strip-shaped metal plate. Having. In such a current collector, since the band-shaped metal plate serving as the terminal portion is integrally formed instead of being attached, the terminal portion can be prevented from being broken at the time of manufacturing, and the yield can be improved. . In addition, since the operation of connecting the band-shaped metal plate as the auxiliary terminal is not required, the manufacture of the secondary battery can be simplified.

[0031]

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. Also, a current collector 2 made of expanded metal made of aluminum and having a strip-shaped aluminum foil 1 as a terminal portion as shown in FIG. 1 was prepared. The terminal has a width of 10 m.
m, length 20 mm and thickness 15 μm. The current collector has a width of 45 mm and a length of 54 mm.
And the thickness was 50 to 70 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 and 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. Further, a current collector 4 made of copper expanded metal having a strip-shaped copper foil 3 as a terminal portion as shown in FIG. 2 was prepared. The terminal portion has a width of 10 mm and a length of 20 mm
And the thickness was 15 μm. The current collector has a width of 45 mm, a length of 54 mm, and a thickness of 50 to 70 μm.
m. 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
ET film), thickness 100μm, width 200m
m, formed into a sheet, and cut into a length of 300 mm to produce a solid polymer electrolyte layer not impregnated with a non-aqueous electrolyte.

<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. Strip-shaped aluminum foil as external cathode lead (width 10mm, length 30m
m and a thickness of 30 μm) were folded into a bag. The tip of the terminal part of one positive electrode and the tip of the terminal part of the other positive electrode described above are overlapped, and these terminals are arranged in the above-described bag, and under the conditions (welding conditions I) shown in Table 1 below. Were bonded by ultrasonic welding. In addition, a strip-shaped copper foil (width 10 mm, length 30 mm,
The end portion having a thickness of 30 μm) is folded into a bag shape, and the terminal portion of one negative electrode and the terminal portion of the other negative electrode described above are arranged in the bag. conditions
Bonded by ultrasonic welding in III) to produce a polymer electrolyte secondary battery having a power generating element as shown in FIG.

That is, the solid electrolyte layers 6 are arranged on both surfaces of the negative electrode 5. On the outer surface of each solid electrolyte layer 6, a positive electrode 7 is laminated. Each of the positive electrodes 7 has a structure in which a positive electrode sheet 8 is supported on both surfaces of the current collector 2. Each of the current collectors 2 has the terminal portion 1. The two terminal portions 1 are fixed by ultrasonic welding in a bag formed at an end of the external positive electrode lead 9. The negative electrode 5
Has a structure in which a negative electrode sheet 10 is supported on both surfaces of the current collector 4. The current collector 4 has the terminal portion 3. The terminal portion 3 is fixed by ultrasonic welding in a bag formed at an end of the external negative electrode lead (not shown).

(Comparative Example) <Preparation of Positive Electrode> A current collector as shown in FIG. 5 was prepared from an aluminum expanded metal having a strip-shaped aluminum expanded metal as a terminal portion. The terminal portion has a width of 10 mm and a length of 20 mm
And the thickness was 50 to 70 μm. The current collector has a width of 45 mm, a length of 54 mm, and a thickness of 50 to 50 mm.
It was 70 μm.

A positive electrode sheet not impregnated with a non-aqueous electrolyte was prepared by pressing the positive electrode sheet obtained in the same manner as in the example on both surfaces of such a current collector by heat and pressure. <Preparation of Negative Electrode> A current collector made of a copper expanded metal having a strip-shaped copper expanded metal as a terminal portion was prepared. The terminal portion has a width of 10 mm and a length of 20 m
m and the thickness was 50 to 70 μm. The current collector has a width of 45 mm, a length of 54 mm, and a thickness of 50 mm.
７０70 μm.

A negative electrode sheet not impregnated with a non-aqueous electrolyte was prepared by heat-pressing the negative electrode sheet obtained in the same manner as in the example on both surfaces of such a current collector with a hot roll. <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 stacked with the solid electrolyte layer interposed therebetween. Heat and pressure bonding was performed 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. The end of a strip-shaped aluminum foil (width: 10 mm, length: 30 mm, thickness: 30 μm) as an auxiliary terminal (also serving as an external positive electrode lead) was folded into a bag shape. The tip of the terminal part of one positive electrode and the tip of the terminal part of the other positive electrode described above are overlapped, and these terminal parts are arranged in the above-described bag, and under the conditions (welding condition II) shown in Table 1 below. Were bonded by ultrasonic welding. Also, a strip-shaped copper foil (width 10 mm, length 3
0mm, the thickness of 30μm) is folded into a bag shape,
The terminal portion of one negative electrode and the terminal portion of the other negative electrode described above are arranged in this bag, and these are bonded by ultrasonic welding under the conditions (welding conditions IV) shown in Table 1 below, and the polymer electrolyte A secondary battery was manufactured.

With respect to the obtained secondary batteries of Examples and Comparative Examples, five batteries were prepared, and the end of the external positive electrode lead was pulled at a pulling speed of 20 mm / min. kg / 10 mm), and the results are shown in Table 2 below.

Further, five secondary batteries of each of the example and the comparative example were prepared, and the end portion of the external negative electrode lead was pulled at a pulling speed of 20 mm / min. / 10 mm)
The results are shown in Table 3 below. The results of Tables 2 and 3 are summarized in a graph and shown in FIG.

[0042]

[Table 1]

[0043]

[Table 2]

[0044]

[Table 3]

As is apparent from FIG. 4, a book provided with a positive electrode current collector made of metal mesh having a strip-shaped metal foil as a positive electrode terminal portion and a negative electrode current collector made of metal mesh having a strip-shaped metal foil as a negative electrode terminal portion. It can be seen that the secondary batteries of the examples have higher tensile strength at the positive electrode terminal portion and the negative electrode terminal portion than the secondary battery of the comparative example.

On the other hand, the secondary battery of the comparative example provided with a positive electrode current collector whose positive electrode terminal portion is a band-shaped metal mesh and a negative electrode current collector whose negative electrode terminal portion is a band-shaped metal mesh, Also, it can be seen that the wire breaks off from the welding portion with the auxiliary terminal with a weaker force as compared with the embodiment.

In the above-described embodiment, the end of the external positive electrode (negative electrode) lead is folded and the terminal portion made of a band-like foil is fixed in the formed bag. May be connected to the terminal portion without folding.

[0048]

As described above in detail, according to the present invention, there is provided a polymer electrolyte secondary battery capable of improving the strength of the terminal portion, improving the yield, and being manufactured by a simple method. be able to.

[Brief description of the drawings]

FIG. 1 is a plan view showing a positive electrode current collector of a polymer electrolyte secondary battery according to an example of the present invention.

FIG. 2 is a plan view showing a negative electrode current collector of a polymer electrolyte secondary battery of an example according to the present invention.

FIG. 3 is a sectional view showing a power generating element of a polymer electrolyte secondary battery according to an embodiment of the present invention.

FIG. 4 is a characteristic diagram showing the tensile strength of the polymer electrolyte secondary battery of the example according to the present invention and the polymer electrolyte secondary battery of the comparative example.

FIG. 5 is a plan view showing a current collector of a conventional polymer electrolyte secondary battery.

FIG. 6 is a sectional view for explaining a method of connecting an auxiliary terminal to a terminal portion.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Positive electrode terminal part 2 ... Positive electrode current collector 3 ... Negative electrode terminal part 4
... negative electrode current collector, 5 ... negative electrode, 6 ... solid electrolyte layer, 7 ... positive electrode, 8 ... positive electrode layer, 10 ... negative electrode layer.

Claims (1)

[Claims] 1. A positive electrode having a structure in which a positive electrode layer containing an active material is supported on at least one surface of a current collector, and a negative electrode having a structure in which a negative electrode layer containing an active material is supported on at least one surface of a current collector A solid electrolyte layer disposed between the positive electrode layer and the negative electrode layer, wherein the current collector of at least one of the positive electrode and the negative electrode is formed of a metal net, and a strip-shaped metal plate A polymer electrolyte secondary battery having a terminal portion comprising: