JPH10208773A - Manufacture of polymer electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily manufacture a polymer electrolyte secondary battery which is small-sized and has high energy density by laminating sheet-like cells in which a solid polymer electrolyte layer including non-aqueous electrolyte is interposed between positive electrode and negative electrode which are capable of storing/releasing lithium ion by being folded along a plurality of cutting parts provided on both of the surfaces. SOLUTION: A sheet-like unit cell is formed by interposing a solid polymer electrolyte layer 2 including non-aqueous electrolyte between positive electrode 1 and negative electrode 3 which are capable of storing/releasing lithium ion. As the positive electrode, the one including oxide such as LiMn2 O4 as an active material is preferable. As the negative electrode 3, the one including a carbonaceous material as an active material is preferable. Polyethelene oxide dielectric, etc., is used in the solid polymer electrolytic layer 2 including non-aqueous electrolyte such as ethylene carbonate. On both of the surfaces of this sheet-like cell, a plurality of cutting parts which are deep on the crest sides and shallow on the trough sides are formed in the longitudinal direction so that the cutting parts may be opposed each other. By folding the cell along these cutting parts, a polymer electrolyte secondary battery 6 is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a polymer electrolyte secondary battery having a solid polymer electrolyte layer.

[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 lithium secondary battery including a negative electrode using lithium or a lithium alloy as an active material and a positive electrode using an oxide, sulfide, or selenide such as molybdenum, vanadium, titanium, or niobium as an active material is used. Secondary batteries are 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 lithium dendrites are generated in the negative electrode when charge / discharge cycles are repeated.

[0003] For this reason, the negative electrode, for example coke, graphite, carbon fiber, resin fired body, a lithium ion, such as pyrolytic vapor carbon using a carbonaceous material for absorbing and releasing, electrolytes such as LiPF ₆ A non-aqueous solvent secondary battery using an electrolytic solution comprising a non-aqueous solvent such as ethylene carbonate and propylene carbonate has been proposed.
The non-aqueous solvent secondary battery can improve the negative electrode characteristics due to the precipitation of dendrite, and thus can improve the battery life and safety.

On the other hand, US Pat. No. 5,296,318 discloses a rechargeable lithium intercalation having a hybrid polymer electrolyte which has been made flexible by adding polymers to the cathode, anode and electrolyte layers. A battery, that is, a polymer electrolyte secondary battery is disclosed. Such a polymer electrolyte secondary battery has a positive electrode in which a current collector has a positive electrode layer containing an active material, a non-aqueous electrolyte and a polymer holding the electrolyte, and a carbon capable of inserting and extracting lithium ions in the current collector. Structure in which a non-aqueous electrolyte and a solid polymer electrolyte layer containing a polymer holding the electrolytic solution are interposed between a negative electrode in which a negative electrode layer containing the electrolyte material, the non-aqueous electrolyte and the polymer holding the electrolyte is laminated Having.

When the polymer electrolyte secondary battery is mounted on a small electronic device such as a mobile phone, it is conceivable to use a battery manufactured by the following method. That is, a large number of small-area flat-plate cells each including a positive electrode and a negative electrode and a solid polymer electrolyte layer interposed between these positive and negative electrodes were produced, and after stacking these cells, the current was collected from the current collector of the positive and negative electrodes. A small-sized polymer electrolyte secondary battery is manufactured by connecting the ejected leads to each other.

However, in such a method, not only is it necessary to manufacture a large number of small-sized flat plate cells, but also the flat plate cells are inferior in shape retention and difficult to handle, thus complicating the operation and reducing the cost. There was a problem of getting high.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method capable of manufacturing a small, high energy density polymer electrolyte secondary battery by a simple process.

[0008]

A polymer electrolyte secondary battery according to the present invention comprises a solid polymer electrolyte containing a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a non-aqueous electrolyte interposed between the positive and negative electrodes. A sheet-shaped unit cell having a plurality of layers, a step of forming a plurality of cut portions on both surfaces of the unit cell so as to face each other, and to be parallel to each other over a length direction; Is folded along the cut portion and laminated. It is preferable that the cut portion is formed so as to be deep on the mountain side and shallow on the valley side when the unit cell is folded in the sheet-shaped unit cell.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for manufacturing a polymer electrolyte secondary battery according to the present invention will be described in detail with reference to FIGS. i) First, as shown in FIG. 1, the positive electrode 1, the solid polymer electrolyte layer 2, the negative electrode 3, the solid polymer electrolyte layer 2, and the positive electrode 1
Are laminated to produce a sheet-shaped unit cell 4. Subsequently, a plurality of cuts 5a are formed on both sides of the unit cell 4,
5b are formed so as to face each other and to be parallel to each other over the length direction. At this time, the notches 5a and 5b are formed in the sheet-shaped unit cell 4 so that when the unit cell is folded, the notches 5a and 5b are deeper on the hill side and shallower on the valley side. The portion 5b is formed by cutting out in a groove shape.

The sheet-shaped unit cell 4 is manufactured by the following method. (Preparation of Positive Electrode Material) First, a solution of a polymer holding a non-aqueous electrolyte is prepared, and a plasticizer such as DBP (dibutyl phthalate), an active material, and a conductive material are added to the solution, and these are mixed. Then, a positive electrode paste is prepared.
Subsequently, this positive electrode paste is applied to both surfaces of the porous current collector 11 made of Al, and then dried to produce a positive electrode material not impregnated with an electrolytic solution.

Examples of the polymer holding the non-aqueous 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 used.
In the copolymer, VdF contributes to the improvement of mechanical strength in the skeleton portion of the copolymer, and HFP is incorporated in the copolymer in an amorphous state, and the non-aqueous electrolyte is retained and the Functions as a lithium ion transmission part. The copolymerization ratio of the HFP depends on the method of synthesizing the copolymer, but is usually at most about 20% by weight.

The plasticizer is added for the purpose of improving mechanical properties such as the strength of the solid electrolyte layer and improving the impregnation amount of the electrolytic solution to improve the charge / discharge characteristics. Examples of the active material include various oxides (for example, lithium manganese composite oxide such as LiMn ₂ O ₄ , manganese dioxide such as LiN
Lithium-containing nickel oxide such as iO ₂ , for example, Li
A lithium-containing cobalt oxide such as CoO ₂ , a lithium-containing nickel cobalt oxide, an amorphous vanadium pentoxide containing lithium, and a chalcogen compound (for example,
Titanium disulfide, molybdenum disulfide, etc.). Among them, it is preferable to use a lithium manganese composite oxide, a lithium-containing cobalt oxide, and a lithium-containing nickel oxide.

Examples of the conductive material include artificial graphite, carbon black (eg, acetylene black), nickel powder, and the like. As the porous current collector 11, for example, an Al mesh, an Al expanded metal, an Al punched metal, or the like can be used.

(Preparation of Solid Electrolyte Material) A solution of a polymer holding a non-aqueous electrolyte is prepared, and this solution is mixed with, for example, DB.
A solvent-soluble plasticizer such as P (dibutyl phthalate) is added, and a film is formed and dried to prepare an electrolyte material not impregnated with an electrolyte.

As the polymer for holding the non-aqueous electrolyte, the same polymer as described in the above-described preparation of the positive electrode material is used. (Preparation of Negative Electrode Material) First, a polymer solution holding a non-aqueous electrolyte is prepared, and a plasticizer such as DBP (dibutyl phthalate) and an active material are added to the solution. Prepare a paste. This negative electrode paste is applied to a porous current collector 31 made of Cu, and then dried to produce a negative electrode material not impregnated with an electrolyte.

As the polymer holding the non-aqueous electrolyte, the same polymer as described in the above-described preparation of the positive electrode material is used. 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 pitch, artificial graphite, Examples include carbonaceous materials represented by natural graphite and the like. Above all, in an atmosphere of an inert gas such as an argon gas or a nitrogen gas, 500 ° C. to 30 ° C.
It is preferable to use a carbonaceous material obtained by firing the organic polymer compound at a temperature of 00 ° C. under normal pressure or reduced pressure.

As the porous current collector 31, for example, C
A mesh made of u, an expanded metal made of Cu, a punched metal made of Cu, or the like can be used. Next, the positive electrode material, the solid electrolyte material, the negative electrode material, the solid electrolyte material and the positive electrode material are stacked in this order, and heat-sealed and stacked, and then the plasticizer in the stacked body is extracted with a solvent such as ethanol. And then impregnated with a non-aqueous electrolyte. By this step, as shown in FIG. 1 described above, the positive electrode layer 1 containing the active material, the conductive material, the non-aqueous electrolyte and the polymer holding the non-aqueous electrolyte on both surfaces of the porous current collector 11 made of Al.
2, a positive electrode 1 carrying a non-aqueous electrolyte, and a polymer electrolyte layer 2 containing a non-aqueous electrolyte and a polymer holding the non-aqueous electrolyte.
A negative electrode layer 32 containing an active material, a non-aqueous electrolyte and a polymer holding the electrolyte on both surfaces of a porous current collector 31 made of Cu
, A polymer electrolyte layer 2 containing a non-aqueous electrolyte and a polymer holding the non-aqueous electrolyte,
active material, conductive material, on both surfaces of a porous current collector 11 made of
A sheet unit cell 4 in which a nonaqueous electrolyte and a positive electrode 1 carrying a positive electrode layer 12 containing a polymer holding the nonaqueous electrolyte are stacked in this order is produced.

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. In the production of the unit cell, the plasticizer in the laminate may not be extracted with a solvent in advance, but may be directly dissolved and replaced with a nonaqueous electrolyte.

In preparing the positive electrode material and the negative electrode material, after adding a plasticizer such as DBP (dibutyl phthalate) and the active material to a polymer solution holding a non-aqueous electrolyte instead of a coating method, These may be mixed and a film formed may be laminated on both surfaces of the porous current collector.

Ii) Next, as shown in FIG. 2, the sheet-shaped unit cell 4 is cut along the cuts 5a and 5b so that the linear cut 5a is on the hill side and the groove-like cut 5b is on the valley side. Fig. 3
The polymer electrolyte secondary battery 6 shown in FIG.

According to the method of the present invention described above, the sheet-shaped unit cell 4 is formed with the cut portions 5a and 5b and folded along the cut portions 5a and 5b, whereby the polymer electrolyte having a small size and a high energy density is obtained. A secondary battery can be manufactured by a simple process.

Further, when forming the cuts 5a and 5b in the sheet-shaped unit cell 4, the linear cuts 5a are formed on the hill side and the groove-shaped cuts 5b are formed on the valley side when folded. Since the folded surfaces are in close contact with each other, a more compact polymer electrolyte secondary battery can be manufactured.

The sheet cell is not limited to a five-layer structure in which the positive electrode 1, the solid polymer electrolyte layer 2, the negative electrode 3, the solid polymer electrolyte layer 2 and the positive electrode 1 are laminated as shown in FIG. A three-layer sheet cell having a solid polymer electrolyte layer interposed between the negative electrodes may be used.

[0026]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below in detail with reference to the drawings. (Example 1) <Preparation of positive electrode> Vinylidene fluoride-hexafluoropropylene (VdF-HFP) was previously added to 20 g of acetone.
Copolymer (trade name, manufactured by Elphatochem; KYNAR2)
801; copolymerization ratio [VdF: HFP]: 88:12) After dissolving 2.8 g of powder, 4.3 g of dibutyl phthalate (DBP) is dissolved in this acetone solution, and the composition formula is represented by LiCoO ₂ as an active material. A paste for a positive electrode was prepared by weighing 10.5 g of lithium-containing cobalt oxide (manufactured by Nippon Heavy Chemical Industry).

1. A positive electrode paste of the above composition was placed on a 30 μm-thick porous current collector made of an aluminum mesh.
A positive electrode material in which an electrolyte-unimpregnated positive electrode layer was formed on both surfaces of the porous current collector by applying a coating speed of 1 m / min using a knife coater so as to have a flow rate of 5 mAh / cm ² and drying with dry air. Produced.

<Preparation of Negative Electrode> An acetone solution was prepared by dissolving 2.0 g of a vinylidene fluoride-hexafluoropropylene copolymer similar to that used for the positive electrode in 12 g of acetone. After adding 3.12 g of dibutyl phthalate (DBP), 7.37 g of mesophase pitch-based carbon fiber (manufactured by Petka Corporation) as an active material was added and mixed to prepare a paste for a negative electrode. This negative electrode paste is 50 μm thick.
Coating speed of 1 m / cm ^{2 on a} porous current collector made of a copper mesh of 2.5 mAh / cm ² using a knife coater.
min, and dried with dry air to prepare a negative electrode material in which an electrolyte-unimpregnated negative electrode layer was formed on both surfaces of the porous current collector.

<Preparation of Solid Polymer Electrolyte Layer> A vinylidene fluoride-hexafluoropropylene copolymer (2.0 g) similar to that used for the positive electrode was mixed with acetone 1
After dissolving it in 0 g to prepare an acetone solution, 2.0 g of dibutyl phthalate (DBP) was added to the acetone solution and mixed to prepare a paste for an electrolyte layer. The paste was applied on a smooth glass plate so that the film thickness after drying became 70 μm, dried in the same manner as the positive and negative electrodes, and peeled off from the glass plate to prepare a solid polymer electrolyte material not impregnated with an electrolyte.

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

The obtained positive electrode material, solid polymer electrolyte material, negative electrode material, solid polymer electrolyte material and positive electrode material were stacked in this order, and these were laminated by heating and pressing with a rigid roll heated to 130 ° C. By immersing the laminate in the non-aqueous electrolyte for 2 hours, the electrolyte-impregnated positive electrode layer of the positive electrode material, the electrolyte-unimpregnated negative electrode layer of the negative electrode material, and the DB in the electrolyte-unimpregnated polymer electrolyte material
By substituting P and the electrolytic solution and impregnating the polymer with the electrolytic solution, the width of 200 m shown in FIG.
m sheet-shaped unit cells 4 were produced.

Next, as shown in FIG. 1, a plurality of cut portions 5a and 5b are formed on both sides of the unit cell 4 so as to face each other and to be parallel to each other in the length direction.
It was formed at 0 mm intervals. At this time, the notches 5a,
5b is cut into the sheet-shaped unit cell 4 so that the unit cell is folded deeper on the mountain side and shallower on the valley side when the cell unit is folded, and the notch 5a on the mountain side is cut out linearly and the notch 5b on the valley side is cut out like a groove. Formed.

Next, as shown in FIG. 2, the sheet-shaped unit cell 4 is bent along the cuts 5a and 5b such that the linear cut 5a is on the hill side and the groove-shaped cut 5b is on the valley side. By further folding, the laminated width 50 mm, depth 100 mm, and height 2.8 shown in FIG.
Thus, a polymer electrolyte secondary battery 6 having a four-layer structure of 4 mm was manufactured.

With respect to the obtained secondary battery of the embodiment, after charging at a constant current and a constant voltage up to 4.2 V at a charging current of 100 mA, an average current of 3.7 V and 99.5 mA was applied for 5 hours. It was possible to discharge. Also,
Even if such charge / discharge was repeated 100 times, 97% or more of the performance of the initial discharge was maintained.

[0035]

As described above in detail, according to the present invention, it is possible to easily produce a polymer electrolyte secondary battery having a small size, a high energy density, and a useful power source for a small electronic crisis such as a mobile phone. Possible manufacturing methods can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a manufacturing process of a polymer electrolyte secondary battery according to the present invention.

FIG. 2 is a schematic view showing a manufacturing process of the polymer electrolyte secondary battery according to the present invention.

FIG. 3 is a schematic view showing a manufacturing process of the polymer electrolyte secondary battery according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Positive electrode, 2 ... Solid polymer electrolyte layer, 3 ... Negative electrode, 4 ... Sheet cell, 5a, 5b ... Cut part, 6 ... Polymer electrolyte secondary battery, 11, 31 ... Porous current collector, 12 ... Positive electrode Layer 32: Negative electrode layer.

Claims (2)

[Claims] 1. A step of producing a sheet-shaped cell having a positive electrode and a negative electrode capable of inserting and extracting lithium ions, and a solid polymer electrolyte layer containing a non-aqueous electrolyte interposed between the positive and negative electrodes; A step of forming a plurality of cuts on both sides of the battery so as to face each other and to be parallel to each other over the length direction; and a step of folding and stacking the unit cells along the cuts. A method for producing a polymer electrolyte secondary battery, comprising: 2. The polymer electrolyte battery according to claim 1, wherein the cut portion is formed such that when the unit cell is folded into the sheet-shaped unit cell, the cut unit is deeper on the mountain side and shallower on the valley side. Manufacturing method of secondary battery.