JP3297034B2 - Secondary battery and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a secondary battery such as a polymer secondary battery using a gelled solid electrolyte, and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, various batteries are used in the field of electronics from automobiles. Since many of these batteries contain a liquid electrolyte, a strong seal is required to prevent leakage of the liquid electrolyte. Even in lithium-ion secondary batteries, which are widely used as driving power supplies for portable devices due to their high energy density, etc., since a strong metal can is used as the outer can without exception to prevent liquid leakage, The advantage of being suitable for weight reduction cannot be fully utilized. Although it is inevitable to reduce the weight and thickness of current devices in general, devices using current lithium-ion rechargeable batteries are occupying a larger weight in the entire device,
Also, the thickness of the battery has been limiting the thickness of the device. Therefore, it is no exaggeration to say that one key to the future development of the lithium ion secondary battery lies in its light weight and thinness.

[0003] Under such circumstances, lithium polymer secondary batteries are being developed. In a lithium polymer secondary battery, a gelled solid electrolyte obtained by swelling a polymer with an electrolyte solution is used, so that there is no free liquid in the battery. Therefore, there is no fear of liquid leakage. Also, sheeting,
That it can be made thinner, that it can be made smaller by lamination,
Due to its high degree of freedom in shape selection, it is attracting attention as a next-generation battery. For example, US Pat.
Nos. 96,318 and 5,418,091 disclose a copolymer of vinylidene fluoride (VDF) and 8 to 25% by weight of propylene hexafluoride (HFP) [P (VDF
-HFP)], the solution in which the lithium salt is dissolved is 20 to 7
A gel electrolyte containing 0% by weight and a lithium intercalation battery using the same are disclosed.

[0004] As a method for producing a gelled solid electrolyte, the following two methods are known.

[0005] The first method is to dissolve the polymer in a solvent,
After mixing an electrolytic solution or the like therewith, this is applied to a substrate by various methods, and the solvent is volatilized to obtain a gelled solid electrolyte film, which is a general method. Further, a method has been proposed in which a polymer is dissolved in an electrolytic solution and applied or extruded to obtain a gelled solid electrolyte film. However, the electrolytic solution used for the electrochemical device generally dislikes water. Therefore, when industrially producing a gelled solid electrolyte using these methods, the entire process must be performed in a dry atmosphere with a dew point of about minus 30 ° C. Need to be maintained. Therefore, a large amount of capital investment and maintenance costs are required.

A second method is disclosed in, for example, the aforementioned US Pat.
No. 418,091. In this method, a plasticizer is added to a polymer solution, applied to a substrate, and then the solvent is volatilized to produce a film, from which a plasticizer is extracted to form a porous film, and a void formed by plasticizer extraction. Is impregnated with an electrolytic solution. When a battery is manufactured using this method, first, a positive electrode and a negative electrode are stacked with a porous film containing a plasticizer interposed therebetween, and a current collector is further stacked and thermocompression-bonded to form a stacked body. I do. Next, extraction of the plasticizer and impregnation of the electrolytic solution are performed to gel the porous membrane. According to this method, it is possible to work under a normal environment before the electrolyte impregnation step, so that the capital investment and the maintenance cost can be greatly reduced. Further, since the porous membrane after coating and drying or after extracting the plasticizer can be stocked in a film state, inventory management of the porous membrane becomes easy. However, in this method, since the electrolytic solution is impregnated in a state where the porous film is sandwiched in the laminate, an expanded metal through which the electrolytic solution can pass is used as the current collector serving as the outermost layer of the laminate. Must be used. The expanded metal is formed by forming a large number of holes in a metal plate. If the metal is thin, it is easily deformed by an external force. Therefore, the expanded metal needs to have a certain thickness for use in a battery. For this reason, in the lithium polymer secondary battery using the expanded metal, there is a problem that, excluding the weight of the outer can, the lithium polymer secondary battery becomes heavier than the lithium secondary battery using the liquid electrolyte. If the expanded metal is brought into direct contact with the electrode, uniform electrical contact between the two cannot be obtained. For example, as shown in US Pat. No. 5,554,459, conductive It is necessary to apply a conductive paint in which an agent is dispersed to the expanded metal in advance. In addition, the use of expanded metal causes uneven pressure distribution during thermocompression bonding,
Further, since the strength of the gelled solid electrolyte is low, many internal short circuits occur due to thermocompression bonding, which is an obstacle to mass production.

[0007]

As described above, the conventional method for manufacturing a lithium polymer secondary battery has various problems. These problems are one of the major reasons why polymer secondary batteries have been proposed but have not been practically used for a long time. Therefore, in the industrial use of lithium polymer secondary batteries, it is important to establish a rational manufacturing method in addition to various materials problems.

The present invention has been made in view of such circumstances, and a method for easily manufacturing a thin and lightweight secondary battery such as a polymer secondary battery at low cost and a secondary battery manufactured by this method have been proposed. It is intended to provide a battery.

[0009]

The above object is achieved by the following (1).
This is achieved by the present invention according to (7). (1) A positive electrode, a negative electrode, and a porous film are prepared. The positive electrode and the negative electrode are positioned with respect to the porous film, and a part of the positive electrode and a part of the negative electrode are fixed to the porous film. A method for producing a secondary battery, comprising the steps of: immersing a positive electrode and a negative electrode in an electrolytic solution; (2) The method for producing a secondary battery according to (1), wherein the porous film contains a polymer, and at least a part of the polymer is gelled by immersion in an electrolytic solution to become a solid electrolyte. (3) The above (1) or (1), wherein the positive electrode and the negative electrode contain a polymer as a binder for binding the electrode active material, and at least a part of the polymer is gelled by immersion in an electrolytic solution. 2) The method for manufacturing a secondary battery. (4) The method for producing a secondary battery according to any one of (1) to (3), wherein the positive electrode and the negative electrode contain polyvinylidene fluoride as a binder. (5) When fixing a part of the positive electrode and a part of the negative electrode to the porous film, the above (1) to (1) to which a hot melt adhesive is used.
(4) The method for manufacturing a secondary battery according to any of (4). (6) The method for manufacturing a secondary battery according to any one of (1) to (5), wherein the positive electrode and the negative electrode are integrated with a current collector made of a metal foil. (7) The method for producing a secondary battery according to any one of the above (1) to (6), which is used for producing a lithium ion secondary battery.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have utilized metal foil as a current collector for the purpose of reducing the weight and thickness of a polymer secondary battery and eliminating the step of applying a conductive paint to the current collector. An experiment was performed. In this experiment, the polymer-containing porous membrane and the polymer-containing positive and negative electrodes formed on the metal foil current collector were integrated by thermocompression bonding, and then impregnated with an electrolytic solution. As a result, the polymer could not be sufficiently gelled.

From these results, it has been found that when a metal foil current collector is used, it is necessary to impregnate the electrolytic solution before thermocompression bonding. In order to thermocompression-bond a porous membrane using a polymer, a positive electrode and a negative electrode, it is necessary to add a plasticizer to them, but as described in the above-mentioned US Pat. No. 5,418,09.
When a plasticizer that needs to be extracted after thermocompression bonding is used as in the method described in No. 1, it is necessary to perform the impregnation of the electrolytic solution after plasticizer extraction, that is, after thermocompression bonding. Therefore, thermocompression bonding was performed after the polymer was gelled by previously impregnating the electrolytic solution with the electrolytic solution as a plasticizer. Specifically, a metal foil current collector and an electrode applied thereto,
The sheet-like porous membrane before the impregnation with the electrolyte is punched out to a predetermined size, then each is impregnated with the electrolyte, and then laminated and thermocompression-bonded to obtain a polymer secondary battery having good characteristics. I knew it could be done.

However, when the porous membrane and the electrode used as a separator are individually impregnated with an electrolytic solution and then gelled, it is difficult to align them when laminating them, and the gelling results in strength. It became very difficult to handle the porous membrane having a reduced amount, and mass production was practically impossible. Here, the reason why accurate positioning is required when laminating the positive and negative electrodes will be described. In a lithium ion secondary battery, a negative electrode is usually made larger than a positive electrode, and stacked so that the positive electrode is completely covered by the negative electrode when viewed from the stacking direction. This is because if the negative electrode does not exist facing the positive electrode, the lithium ions released from the positive electrode are deposited without being taken into the negative electrode, and as a result,
This is because the battery capacity decreases. Therefore, it is necessary to accurately determine the positional relationship between the two electrodes so that the negative electrode faces the positive electrode accurately.

According to the present invention, based on the above experimental results, FIG.
Before the impregnation with the electrolytic solution, the positive electrode 3 and the negative electrode 4 are positioned with respect to the porous film 2 and a part of the positive electrode 3 and a part of the It is fixed to the membrane 2. This fixation is a temporary fixation. For example, since only the center of each of the positive electrode and the negative electrode is fixed to the porous film with the adhesive 5 or the like, the electrolytic solution is fixed between each of the positive electrode 3 and the negative electrode 4 and the porous film 2 after the fixation. Can easily penetrate. Therefore, after the temporary fixing and before the thermocompression bonding, the electrolyte can be impregnated. Therefore, the positive electrode 3
Since it is possible to use metal foil as the current collector 31 for the battery and the current collector 41 for the negative electrode 4, the weight and thickness of the battery can be reduced. In addition, the use of the metal foil current collector eliminates the need to apply a conductive paint to the current collector, thereby simplifying the process. Also, by using a metal foil current collector,
Non-uniformity of pressure distribution during thermocompression bonding is less likely to occur.
The occurrence of an internal short circuit can be suppressed. Further, it is not necessary to handle the porous membrane whose strength has been reduced by the impregnation with the electrolytic solution alone.

When the temporary fixing is performed with an adhesive, the adhesive may hinder the diffusion of lithium ions.
Since the penetration of the electrolytic solution is hindered, it is preferable that the number of places where the adhesive is applied is as small as possible, and the area where the adhesive is applied is as small as possible. Specifically, the adhesive is
Preferably, only one point at the center of the surface to be coated with the porous film or the electrode is provided. Further, the ratio of the adhesive application area to the entire application target surface may be appropriately determined according to the type of the adhesive, the area of the entire application target surface, and the like so as to obtain an adhesive strength that does not cause displacement. But usually 0.001 to
What is necessary is just to select from the range of 1 area%.

The adhesive used for the temporary fixing is preferably a hot melt adhesive. The hot-melt adhesive can be used without any particular limitation as long as it is capable of adhering the electrode and the porous membrane and has a lower melting point than the polymer which is a component of the electrode and the porous membrane. it can. As such a hot melt adhesive, for example, an ethylene-methacrylic acid copolymer can be used.

In the present invention, the temporary fixing may be performed by means other than the adhesive. For example, after the porous film and the positive electrode and the negative electrode are positioned and stacked, the porous film and the electrode can be temporarily fixed by puncturing the vicinity of the center with a fixing means such as a pin, a screw, or a bolt. . The fixing means may be removed after thermocompression bonding, but may be left as long as it does not adversely affect the characteristics of the battery.

In the present invention, the integration of the porous membrane, which is a solid electrolyte, and the positive electrode and the negative electrode is preferably performed by thermocompression as described above, but may be performed by compression without heating. .

The porous membrane used in the present invention is not particularly limited, and its production method is not particularly limited. Porous membranes obtained by various production methods including the production method described in “Microporous Polymer and Its Application Development” (Toray Research Center, issued on January 1, 1997) can be used.

For example, US Pat. No. 5,418,09 mentioned above.
As described in the specification of Japanese Patent Publication No. 1, a structure may be used in which pores are formed in a polymer using a polymer containing a plasticizer, the pores are extracted, and then the electrolyte is impregnated. In this case, the extraction of the plasticizer is preferably performed before the porous membrane and the electrode are temporarily fixed.

Further, for example, when a polymer comprising a polymer particle and a polymer binder binding the polymer particle is used as the polymer constituting the porous membrane, the electrolyte solution can be sufficiently contained in the polymer binder without using a plasticizer. Simplifies the manufacturing process and provides a sufficiently high ionic conductivity. In this case, it is preferable to use polyvinylidene fluoride (hereinafter, PVDF) for the polymer particles, and it is preferable to use a copolymer containing vinylidene fluoride units for the polymer binder.

As described above, the conventional gelled solid electrolyte is formed by forming a large number of pores in a polymer with a plasticizer and impregnating the electrolyte with the polymer to form a gel. Both the electrolyte solution absorbed by the molecules contributes to ionic conduction. On the other hand, in the gelled solid electrolyte containing the polymer particles preferably used in the present invention, unlike the conventional case, the pores are three-dimensionally formed by the polymer particles bound by the polymer binder, and the pores are formed in the pores. The electrolyte is held to form a gelled solid electrolyte. The pores in this case usually have a larger pore diameter than the conventional gelled solid electrolyte. The polymer particles and the polymer binder may or may not swell with the electrolytic solution. The gelled solid electrolyte in which pores are formed by polymer particles has the same sufficient liquid retention as a conventional gelled solid electrolyte consisting of a PVDF-based copolymer in which pores are formed using a plasticizer. Is obtained. In addition, since the battery has particularly excellent rate characteristics and a small decrease in discharge capacity even when the discharge current is increased, a battery having a discharge rate equal to or higher than that of the conventional gelled solid electrolyte is realized.

The gelled solid electrolyte using polymer particles has a higher strength than the above-mentioned conventional gelled solid electrolyte, and therefore can be formed into a thinner sheet. For example, the thickness is 60 μm or less. Furthermore, it can be set to 40 μm or less, and can be set to 15 μm or less. Further, since the positive electrode and the negative electrode are not easily deformed by an external force, a short circuit between the positive electrode and the negative electrode is difficult. Further, since both tensile strength and bending strength are high, it is advantageous in mass production. In other words, usually, a slurry in which a polymer is dissolved and dispersed is applied to a substrate (carrier film), and a solvent is evaporated to produce a polymer film. However, a polymer film containing polymer particles is hardly stretched even when pulled, and is bent. Since it is hard to break, it can be peeled off from the carrier film during production and wound into a roll.

Further, since the porous film is formed by containing polymer particles instead of inorganic particles, the weight can be further reduced as compared with the case where inorganic particles are contained.

In a gelled solid electrolyte containing polymer particles, a PVDF copolymer having poor heat resistance and chemical resistance is used only as a binder, and the amount used is very small as compared with a conventional gelled solid electrolyte. Because of high temperature (85 ℃
), The storage capacity is very small, and the occurrence of internal short circuit is small. Moreover, it has excellent charge / discharge characteristics at high temperatures.

The above US Pat. No. 5,418,091
In the specification, 20% by weight of a filler made of alumina or silica is mixed with a polymer solid electrolyte in order to improve the impregnation rate of an electrolytic solution by forming a porous film. And lower strength than the solid electrolyte containing polymer particles. Therefore, the film cannot be thinned, and a short circuit is likely to occur. In addition, since an inorganic filler is used for improving strength, there is also a problem that the weight is heavy. Further, the method for extracting a plasticizer described in the same specification has significant disadvantages in terms of productivity and mass productivity.

When a plasticizer for forming pores such as DBP is used, the electrolyte solution enters and is retained in the pores formed by the extraction of the plasticizer. After that, the volume of the polymer does not change much. On the other hand, when the plasticizer for forming pores is not used, the polymer swells relatively largely due to the impregnation with the electrolytic solution. On the other hand, the metal foil current collector does not swell even when immersed in the electrolytic solution. For this reason, in an electrode using a polymer as a binder for binding the active material and using no plasticizer for forming pores,
When an electrode is formed on only one of the metal foil current collectors, warpage occurs. In order to reduce the warpage, it is preferable to use PVDF (homopolymer) which is hardly swelled by the electrolytic solution as a binder in at least a single-sided electrode formed on only one surface of the metal foil.

The present invention is suitable for manufacturing a lithium ion secondary battery.

Hereinafter, the porous membrane, the electrode, and the electrolytic solution will be described in more detail.

The porous membrane used in the present invention may be substantially composed of only a polymer which gels by impregnation with an electrolytic solution, similarly to the separator of a conventional polymer secondary battery. And preferably a polymer particle and a polymer binder for binding the polymer particle. More specifically, a polymer binder is provided at a contact point between the polymer particles and binds the polymer particles. The polymer binder may be present around each of the polymer particles, or the polymer particles may be aggregated. In the porous film, the polymer particles three-dimensionally form a large number of pores, into which the electrolyte is invaded and held.

The porous membrane is preferably prepared by the following procedure.

First, the polymer particles are dispersed and the polymer binder is dissolved in the solvent. Specifically, a mixture of a polymer binder and polymer particles is added to a solvent,
Alternatively, the polymer particles are added to a solution prepared by dissolving a polymer binder in a solvent in advance, and the mixture is heated to room temperature or if necessary, and stirred by a magnetic stirrer, a homogenizer, a pot mill, a ball mill, a super sand mill, Disperse and dissolve using a disperser such as a pressure kneader.

The solvent used at this time may be appropriately selected from various solvents in which the polymer particles are insoluble and the polymer binder is soluble, and those having a high boiling point and high safety are industrially preferable. For example, N, N-dimethylformamide (DM
It is preferable to use F), dimethylacetamide, acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone, or the like. The concentration of the polymer binder in the solution is preferably 5 to 25% by weight.

At this time, the above-mentioned solvent in which the polymer particles are insoluble and the polymer binder is soluble is used as a first solvent.
It is preferable to add a second solvent in which both the polymer particles and the polymer binder are insoluble. In such a mixed solvent, it is preferable that the second solvent has a higher boiling point than the first solvent. By setting the boiling point in such a relationship, after the first solvent evaporates, the second solvent evaporates. As a result, a higher porosity is obtained, so that the retained amount of the electrolyte is reduced. The characteristics increase due to the increase. The difference between the boiling points of the two solvents is preferably about 20 to 100 ° C.

Specific examples of the first solvent and the second solvent include, for example, PVDF as a polymer particle and a PVDF-based polymer as a polymer binder, preferably a vinylidene fluoride-hexafluoropropylene (HFP) copolymer [P ( VDF-HFP)], ketones such as acetone and methyl ethyl ketone (MEK) are preferred as the first solvent, and toluene, xylene, butanol, isopropyl alcohol, hexane and the like are preferred as the second solvent. Note that the first solvent and the second solvent preferably have high compatibility.

In the mixed solvent, the weight ratio (first solvent:
The second solvent) is preferably from 95: 5 to 60:40, more preferably from 85:15 to 75:25. When the amount of the second solvent is small, the effect of improving the characteristics is reduced.
On the other hand, when the amount of the second solvent is large, it becomes difficult for the polymer binder to be dissolved in the mixed solvent.

After obtaining a slurry in which the polymer particles are dispersed and the polymer binder is dissolved, the slurry is applied on a carrier film or formed into a film by casting or the like. The carrier film used at this time is not particularly limited as long as it is smooth, and for example, a resin film such as a polyester film or a polytetrafluoroethylene film, or a glass plate can be used. The means for applying the slurry to the carrier film is not particularly limited, and may be appropriately determined depending on the material and shape of the carrier film, for example, dip coating, spray coating, roll coating, doctor blade, A gravure coating method, a screen printing method and the like can be used. After the application, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

After the application, the solvent in the slurry is evaporated to obtain a polymer film in which the polymer particles are bound by the polymer binder. Any of vacuum drying, air drying, heat drying, and the like may be used for evaporating the solvent.

After drying, the carrier film is peeled off. However, a porous resin film may be used as the carrier film, and the carrier film may be used without peeling. That is, a gellable polymer film attached to a porous resin film can also be used as the porous film in the present invention. As the porous resin film in this case, for example, a polyolefin porous film used as a separator in a normal lithium secondary battery can be used.

Then, by impregnating the polymer film with an electrolytic solution, a porous membrane containing a gelled solid electrolyte is obtained.

The average particle size of the polymer particles used in the present invention is preferably 0.1 to 0.5 μm, particularly preferably 0.1 to 0.4 μm. By using such particles, an appropriate pore diameter and porosity can be obtained, so that the electrolyte can be sufficiently impregnated and excellent characteristics can be obtained. If the average particle size is too small, the particles are clogged too much, and the retention of the electrolyte solution tends to be insufficient. On the other hand, if the average particle size is too large, it may hinder the thinning of the polymer film. The narrower particle size distribution of the polymer particles is preferable because a uniform pore diameter can be obtained.

The polymer particles are usually preferably spherical, but the shape is not particularly limited as long as appropriate pores can be formed, and may be other shapes such as a spheroid.

The constituent material of the polymer particles is not particularly limited as long as it is insoluble in the solvent used at the time of production. Other materials are preferable, but those having excellent heat resistance and chemical resistance are preferable. For example, PVDF, phenolic resin, epoxy resin, latex, acrylonitrile-butadiene-based latex, urethane resin and the like can be used.
F homopolymers are preferred. These may be used alone or in combination of two or more. The weight average molecular weight Mw of the polymer particle constituting material is 1.0 × in terms of the strength of the material.
It is preferably about 10 ⁵ or more, especially about 3.0 × 10 ⁵ or more. The upper limit of Mw is usually 1.0 × 10
It is about ⁶ .

[0043] Such polymer particles are commercially available. PVDF particles are, for example, trade names “KynarFlex741”, “KynarFlex731”, and “KynarFlex7” of Elf Atochem.
61, FORAFLON1000, Kureha Chemical's KF Series, SOLVAY's Solef 1000 Series, Solef 60
Phenol resin particles are sold, for example, as "Unibex" of Unitika Ltd. and "ACS series" of Sumitomo Jules,
Latex particles include, for example, “Nipol LX51” from Zeon Corporation.
3 ", and the urethane resin particles are sold, for example, as" Pernock CFB "of Dainippon Ink and Chemicals, and Sekisui Plastics" Techpolymer UB ".

The polymer binder may be any as long as it can be dissolved in a solvent at the time of production, and is not particularly limited. Preferably, a fluoropolymer is used, and more preferably, a copolymer containing vinylidene fluoride units is used.

Examples of the fluoropolymer include vinylidene fluoride-hexafluoropropylene (HFP) copolymer [P (VDF-HFP)] and vinylidene fluoride
Trifluoroethylene chloride (CTFE) copolymer [P (VD
F-CTFE)], vinylidene fluoride-hexafluoropropylene fluoro rubber [P (VDF-HFP)], vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluoro rubber [P (VDF-TFE-HF)
P)], vinylidene fluoride-tetrafluoroethylene-
Perfluoroalkyl vinyl ether fluoro rubber is preferably exemplified. The composition range of vinylidene fluoride-hexafluoropropylene fluororubber, vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene fluororubber is approximately VDF-HFP binary copolymer.
DF has a composition of 50 to 85 mol%, and TFE has a composition of 0 to 85 mol%.
This is a composition region in which 35 mol% is added. As the vinylidene fluoride polymer, vinylidene fluoride is 50% by weight or more,
Especially 70% by weight or more (the upper limit is about 97% by weight)
Is preferable, and particularly, a copolymer of vinylidene fluoride and hexafluoropropylene [P (VDF-HF
P)], a copolymer of vinylidene fluoride and ethylene trifluoride [P (VDF-CTFE)], and especially [P (V
DF-HFP)]. In the present invention, a polymer having a high swelling property or a polymer having a low swelling property may be used. However, since the polymer having a low swelling property has low solubility, handling is difficult and workability is poor. On the other hand, a polymer having a high swelling property easily impregnates and retains the electrolytic solution, so that more excellent characteristics can be obtained.

Such a vinylidene fluoride-based polymer is commercially available, and a VDF-CTFE copolymer is commercially available from Central Glass Co., Ltd. under the trade name “Sefuralsoft (G
150, G180) "sold by Solvay Japan Limited under the trade name" Solef 31508 ".
In addition, VDF-HFP copolymer is trade name "KynarFlex2750 (VDF: HFP = 85: 15wt%)" from Elf Atochem,
KynarFlex2801 (VDF: HFP = 90: 10wt%), KynarFlex2
851 (VDF: HFP = 95: 5wt%) ”, etc.
From "Solef 11008", "Solef 1101"
0, "Solef 21508", "Solef 21510", and the like.

The weight average molecular weight Mw of the polymer binder
Is 1.0 × 10 ^{5 to} 1.0 × 10 ⁶ , especially 3.0 × 10
It is preferably from ^{5 to} 8.0 × 10 ⁵ .

The weight ratio between the polymer particles and the polymer binder (polymer particles: polymer binder) is preferably 70:30 to 98: 2, more preferably 75:25 to 9
5: 5, more preferably 80:20 to 93: 7. When the ratio of the polymer binder is high, it is difficult to obtain appropriate porosity and porosity, and it is difficult to obtain high characteristics. When the ratio of the polymer binder is low, it becomes difficult to sufficiently bind the polymer particles, and thus sufficient sheet strength cannot be obtained, and it becomes difficult to reduce the thickness of the sheet.

In the present invention, the porous membrane is usually in the form of a sheet. The thickness of the sheet-like porous membrane is preferably 5 to 100 μm, more preferably 5 to 100 μm before impregnation with the electrolytic solution.
６０60 μm, more preferably 10-40 μm. Since the porous membrane containing polymer particles has high strength, the sheet can be made thin. That is, it can be made thinner than a conventional gelled solid electrolyte which could not be reduced to 60 μm or less in practical use, and can be thinner than a separator (generally, about 25 μm) used in a solution-type lithium ion battery. Therefore, the use of a gelled solid electrolyte is extremely excellent in thinning and increasing the area, which is one of the advantages of using a gelled solid electrolyte.

The porosity of the porous film is preferably 35% or more when dried before impregnation with the electrolytic solution. If the porosity is too low, it will be difficult to hold the electrolyte sufficiently, and the ionic conductivity and rate characteristics will decrease. The porosity is preferably 90% or less. If the porosity is too high, the strength will be insufficient. The porosity can be measured by the Archimedes method.

The average pore diameter in the porous membrane is 0.005 to 0.5.
It is preferably 5 μm, particularly preferably 0.01 to 0.3 μm. If the average of the pore diameters is larger than this, the current is biased, and lithium dendrite may be generated on the negative electrode. On the other hand, if it is smaller than this, a problem may occur in diffusion of lithium ions. The pore diameter can be measured with a mercury porosimeter.

In the present invention, it is preferable to use a porous membrane containing polymer particles as described above, but a porous membrane containing no polymer particles may be used as in the prior art.
In this case, from the above-mentioned polymer binders, those which can be gelled by impregnation with an electrolytic solution and which can be laminated with an electrode and subjected to pressure bonding or thermocompression bonding may be appropriately selected. In this case, it is preferable to form pores in the porous film by including a plasticizer [dibutyl phthalate (DBP) or the like] as described above.

Electrodes In the present invention, the electrodes may be appropriately selected from known ones and used. Preferably, the electrodes contain an electrode active material and a polymer as a binder for binding the same, and if necessary, a conductive material. One containing an auxiliary agent is used. The polymer used as the binder is preferably a polymer that becomes a gelled solid electrolyte by impregnation with an electrolytic solution.

In the case of a lithium secondary battery, it is preferable that the negative electrode active material is appropriately selected from a carbon material, a lithium metal, a lithium alloy, an oxide material, and the like. It is preferable to use an intercalable oxide or carbon material.

The carbon material used as the electrode active material may be appropriately selected from, for example, mesocarbon microbeads (MCMB), natural or artificial graphite, resin fired carbon material, carbon black, carbon fiber and the like.

Lithium ion is intercalated day
Intercalatable oxides include lithium
Complex oxides are preferred, for example, LiCoO_Two, LiM
n_TwoO _Four, LiNiO_Two, LiV_TwoO_FourAnd the like.
The average particle size of these oxide powders is about 1 to 40 μm
It is preferred that

A conductive assistant is added to the electrode as required. Examples of the conductive auxiliary agent include preferably carbonaceous materials such as graphite, carbon black, and carbon fiber, and metals such as nickel, aluminum, copper, and silver. Particularly, graphite and carbon black are preferable.

The electrode composition of the positive electrode was as follows: active material: conductive auxiliary agent: gelled solid electrolyte = 30 to 90: 3 to 1 in weight ratio.
The range of 0:10 to 70 is preferable. In the negative electrode, the active material: conductive auxiliary agent: gelled solid electrolyte = 30 to 9 by weight ratio.
The range of 0: 0 to 10:10 to 70 is preferred. The type of polymer used as the gelled solid electrolyte is not particularly limited, and may be appropriately selected from, for example, the various polymers described in the description of the porous membrane. In order to suppress the warpage of the electrode, as described above, PVDF (homopolymer) is used. (Polymer).

In the present invention, a polymer that does not gel by the impregnation of the electrolyte may be used as a binder for the electrode.
For example, a non-gelling material such as a fluororesin or a fluororubber can be selected. In this case, the amount of the binder is preferably about 3 to 30% by weight of the whole electrode.

In manufacturing the electrode, first, an active material and a conductive additive to be added as required are dispersed in a binder solution to prepare a coating solution. Next, this coating liquid is applied to the current collector. The application means is not particularly limited, and may be appropriately determined according to the material and shape of the current collector, but generally, a metal mask printing method, an electrostatic coating method, a dip coating method, a spray coating method, a roll coating method, Doctor blade method,
A gravure coating method, a screen printing method, or the like may be used. Thereafter, if necessary, a rolling treatment is performed by a flat plate press, a calender roll, or the like.

The material and form of the current collector may be appropriately selected according to the shape of the battery, the method of disposing the current collector in the case, and the like. Generally, aluminum is used for the positive electrode and copper or nickel is used for the negative electrode. In the present invention, the effect is high when the metal foil is used as the current collector as described above, but a metal mesh may be used if necessary.

After the application, the solvent is evaporated to obtain an electrode integrated with the current collector. The thickness of the coating is 50
The thickness is preferably about 400 μm.

Electrolyte The electrolyte used in the present invention is a non-aqueous electrolyte in which an electrolyte salt is dissolved in an organic solvent. In consideration of application to a lithium ion secondary battery, the electrolyte salt needs to contain lithium. Examples of the lithium-containing electrolyte salt include LiPF ₆ , LiClO ₄ , LiBF ₄ , LiAsF ₆ , L
ISO ₃ CF ₃ , LiN (CF ₃ SO ₂ ) _{2 and the} like can be used. As the electrolyte salt, only one kind may be used alone, or a plurality of salts may be mixed and used.

The organic solvent is not particularly limited as long as it has good compatibility with the polymer contained in the porous film or the electrode or the electrolyte salt. However, considering the application to the lithium secondary battery, a high voltage is required. Those which do not decompose even when applied are preferred, for example, ethylene carbonate (E
C), carbonates such as propylene carbonate (PC), butylene carbonate, dimethyl carbonate (DMC), diethyl carbonate and ethyl methyl carbonate, cyclic ethers such as tetrahydrofuran (THF) and 2-methyltetrahydrofuran, 1,3-dioxolane, Cyclic ethers such as 4-methyldioxolane, γ-
Lactones such as butyrolactone, sulfolane, 3-methylsulfolane, dimethoxyethane, diethoxyethane, ethoxymethoxyethane, ethyldiglyme and the like can be preferably used. These may be used alone or as a mixture.

The concentration of the electrolyte salt in the electrolytic solution is preferably from 0.3 to 5 mol / l, and usually shows the highest conductivity at around 1 mol / l.

The content of the electrolyte was 30% of the gelled solid electrolyte.
It is preferably from 70 to 70% by weight, particularly preferably from 40 to 60% by weight. If the content is more than this, an excessive amount of electrolyte increases, which is disadvantageous in weight when a battery is manufactured. On the other hand, if the content is less than this, it becomes difficult to obtain sufficient ionic conductivity.

The present invention relates to the production of a polymer secondary battery, that is, a secondary battery in which a porous film contains a polymer, and at least a part of the polymer is gelled by immersion in an electrolyte to become a solid electrolyte. Effective when applied.
However, the present invention is also applicable to secondary batteries other than polymer secondary batteries. That is, a porous film that does not gel may be used, for example, a polyolefin porous film used as a separator in a normal lithium secondary battery. Even in this case, since the positive electrode, the negative electrode, and the porous film can be immersed in the electrolytic solution while being aligned and temporarily fixed, the displacement of the positive electrode and the negative electrode can be prevented, and the impregnation of the electrolytic solution can be easily performed. It becomes possible.

When the binder of the electrode contains a polymer which gels by the impregnation of the electrolyte, the electrode strength is lowered by the impregnation of the electrolyte and the positioning becomes difficult. Therefore, the positive electrode and the negative electrode can be easily and accurately positioned. Therefore, in both cases where the porous membrane gels and when it does not, using an electrode that gels,
The present invention is more effective.

[0069]

EXAMPLES Based on the steps shown in Embodiment FIG 1, to produce a polymer secondary battery by the following procedure.

First, LiCoO ₂ was used as a positive electrode active material,
Carbon black and graphite are used as conductive aids, and KynarFlex741 (PVDF homopolymer particles manufactured by Elf Atochem, weight average molecular weight Mw is used as a binder).
5.5 × 10 ⁵ , average particle size 0.2 μm, soluble in NMP) and weighed so that the weight ratio of LiCoO ₂ : carbon black: graphite: binder = 90: 3: 3: 4. , N-methyl-2-pyrrolidone (NMP)
Was added so that NMP: binder = 94: 6 (weight ratio), and these were mixed at room temperature to obtain a slurry for a positive electrode. This positive electrode slurry was applied on one side of an aluminum foil current collector having a thickness of 60 μm and dried to produce a single-sided application positive electrode integrated with the current collector. Further, the positive electrode slurry was applied on both sides of an aluminum foil current collector having a thickness of 20 μm and dried to prepare a double-sided application type positive electrode integrated with the current collector.

Also, using mesocarbon microbeads (MCMB) as the negative electrode active material, carbon black as the conductive additive, and the above-mentioned KynarFlex741 as the binder, MCMB: carbon black: binder = 87:
The sample was weighed so as to be 3:10, and NMP was further NM
P: binder = 93: 7 (weight ratio)
These were mixed at room temperature to obtain a negative electrode slurry. This negative electrode slurry was applied on both sides of a copper foil current collector having a thickness of 10 μm and dried to prepare a negative electrode integrated with the current collector.

Further, KynarFlex7 is used as polymer particles.
41 was weighed and mixed using the above-mentioned KynarFlex2851 (VDF: HFP = 95: 5 wt%, manufactured by Elf Atochem Co., Ltd.) as a binder so that the weight ratio became polymer particles: binder = 90: 10, and 1 weight of the mixture was obtained. 2.4 parts by weight of a solvent [acetone: toluene = 8.9: 1.1 (weight ratio))] was added to the parts, and these were mixed and dissolved at 30 to 40 ° C. using a homogenizer, and a slurry was obtained. Obtained. Note that acetone is the first solvent, and toluene is the second solvent.
In this slurry, only the binder polymer was dissolved, and the polymer particles composed of the PVDF homopolymer were dispersed in the solution.

The slurry was applied on a polyethylene terephthalate (PET) film by a doctor blade method, and the solvent was evaporated at a temperature in the range of room temperature to 120 ° C. to obtain a solid electrolyte sheet. The thickness (dry thickness) of this solid electrolyte sheet was 30 μm. The porosity measured by the Archimedes method was 40%.

Next, the positive electrode, the negative electrode and the porous film are cut into substantially rectangular sheets to form a sheet, and a hot melt adhesive (ethylene-
(Methacrylic acid copolymer). The adhesive applied area was 0.05 to 0.5 area% of the sheet surface. Then, as shown in FIG. 2, a positive electrode, a porous film, a negative electrode, a porous film, a positive electrode,.
The sheets were positioned and laminated in this order, and were pressed while heating to 110 ° C. and temporarily fixed with the above adhesive to obtain a laminate. The number of porous films in this laminate was set to 10.

Next, an aluminum wire was welded to the positive electrode tab and a nickel wire was welded to the negative electrode tab to take out a lead, and the laminate was immersed in an electrolytic solution for impregnation. For the electrolyte, 1M LiPF ₆ / EC + DMC [EC: DMC
= 1: 2 (volume ratio)]. Next, after removing the excessive electrolyte solution in the laminate, the laminate is sealed in an aluminum laminate pack, and pressed at 70 to 90 ° C. to thermally press the sheets in the laminate to obtain a polymer secondary battery. Was.

In this polymer secondary battery, the binder contained in the positive electrode and the negative electrode is gelled by impregnation with the electrolytic solution.

Comparative Example LiCoO ₂ was used as the positive electrode active material, acetylene black was used as the conductive additive, and the above-mentioned Kynar Flex2801 was used as the binder.
(VDF: HFP = 90: 10wt%), and a positive electrode sheet containing DBP as a plasticizer was prepared by using a doctor blade method. Also, a negative electrode sheet containing mesocarbon microbeads (MCMB) as a negative electrode active material, acetylene black as a conductive aid, the aforementioned KynarFlex2801 as a binder, and DBP as a plasticizer was prepared using a doctor blade method. . Further, a porous film containing SiO ₂ as an inorganic filler, DBP as a plasticizer, and the aforementioned KynarFlex2801 as a binder,
It was produced using a doctor blade method.

Next, the positive electrode, the negative electrode, and the porous film are cut into a substantially rectangular shape to form a sheet. The sheets are stacked so that the positive electrode, the porous film, and the negative electrode are in this order, and pressed at 130 ° C. Thermocompression bonded. After integration, thermocompression bonding was performed at 100 to 130 ° C. with both ends sandwiched between current collectors to obtain a laminate. For the current collector for the positive electrode, a material obtained by applying a slurry obtained by mixing carbon and an ethylene-acrylic acid copolymer on an aluminum expanded metal having a thickness of 80 μm,
As the current collector for the negative electrode, one obtained by applying the above slurry to a copper expanded metal having a thickness of 30 μm was used.

Next, an aluminum wire was welded to the positive electrode tab and a nickel wire was welded to the negative electrode tab, and the lead was taken out. Then, the laminate was immersed in hexane to extract DBP as a plasticizer. After drying, the laminate was immersed in the electrolytic solution used in the above example to be impregnated. Next, after removing excess electrolyte solution in the laminate, the laminate was sealed in an aluminum laminate pack to obtain a polymer secondary battery.

For each of the above Examples and Comparative Examples, 50 batteries were manufactured by the above-described procedure, and the number of batteries that were internally short-circuited was examined. The average value of the ratio between the 2C discharge capacity (capacity when discharged at a constant current of 800 mA) and the 0.2 C discharge capacity (capacity when discharged at a constant current of 80 mA) of the battery that was not short-circuited was I asked.
Table 1 shows the results. FIG. 3 shows the cycle characteristics of the manufactured battery.

[0081]

[Table 1]

Table 1 shows that the batteries of the examples have a lower short-circuit occurrence rate than the batteries of the comparative examples. Further, in the batteries of the examples, the ratio between the 2C discharge capacity and the 0.2C discharge capacity was equivalent to that of the battery of the comparative example, and it can be seen that the rate characteristics equivalent to those of the conventional battery were obtained.

When the battery was charged and discharged at 85 ° C., no deterioration in capacity was observed in the batteries of Examples, and it was found that the batteries had good reliability. On the other hand, in the battery of the comparative example,
A short circuit has occurred.

[0084]

According to the present invention, a thin and lightweight secondary battery such as a polymer secondary battery can be easily manufactured.

[Brief description of the drawings]

FIG. 1 is a flowchart for explaining a manufacturing method of the present invention.

FIG. 2 is a front view showing the structure of a polymer secondary battery manufactured according to the present invention.

FIG. 3 is a graph showing cycle characteristics of a battery in Examples and Comparative Examples.

[Explanation of symbols]

 2 Porous film 3 Positive electrode 31 Current collector for positive electrode 4 Negative electrode 41 Current collector for negative electrode 5 Adhesive

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Makoto Kobayashi 1-13-1 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-11-195433 (JP, A) JP-A-2000- 21234 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01M 10/40 H01M 2/16 H01M 4/02-4/04

Claims (7)

(57) [Claims] 1. A positive electrode, a negative electrode, and a porous film are prepared. The positive electrode and the negative electrode are positioned with respect to the porous film, and a part of the positive electrode and a part of the negative electrode are fixed to the porous film. Immerse the porous membrane in the electrolyte,
Next, a method for manufacturing a secondary battery, comprising a step of integrating a positive electrode and a negative electrode by pressure bonding to a porous membrane. 2. The method for producing a secondary battery according to claim 1, wherein the porous membrane contains a polymer, and at least a part of the polymer is gelled by immersion in an electrolytic solution to form a solid electrolyte. 3. The positive electrode and the negative electrode contain a polymer as a binder for binding an electrode active material, and at least a part of the polymer is gelled by immersion in an electrolytic solution. 2. A method for manufacturing a secondary battery. 4. The method according to claim 1, wherein the positive electrode and the negative electrode contain polyvinylidene fluoride as a binder. 5. A hot melt adhesive is used for fixing a part of the positive electrode and a part of the negative electrode to the porous film.
5. The method for manufacturing a secondary battery according to any one of items 4 to 4. 6. The method for manufacturing a secondary battery according to claim 1, wherein the positive electrode and the negative electrode are integrated with a current collector made of a metal foil. 7. The method for manufacturing a secondary battery according to claim 1, which is used for manufacturing a lithium ion secondary battery.