JP3578185B2 - Thin lithium battery and method of manufacturing the same - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin lithium battery and a method for producing the same, and more particularly, to an improvement of a positive electrode mixture and a negative electrode mixture of a thin lithium battery and a thin lithium battery using the improved positive electrode mixture and the negative electrode mixture. The present invention relates to a new method for manufacturing a lithium battery.
[0002]
[Prior art]
In recent years, portable devices such as mobile phones, PHSs, and small personal computers have been significantly reduced in size and weight with the development of electronics technology, and the batteries used as power sources for these devices have also become smaller and thinner. Is required.
[0003]
Lithium batteries have attracted attention as batteries that can be expected for such applications, and in addition to lithium primary batteries that have already been put into practical use, lithium ion secondary batteries that can be expected to have higher capacity and higher cycle life characteristics in addition to the practical use of lithium secondary batteries Research on batteries is ongoing.
[0004]
All of the above-mentioned various lithium batteries are mainly cylindrical, and thin types of lithium primary batteries use a solid electrolyte for the lithium primary batteries, and some of them are manufactured by diversion of printing technology. This is a technology that has not yet been achieved in secondary batteries.
[0005]
This means that, in the case of a cylindrical shape, the electrode consisting of the positive electrode, the electrolyte and the negative electrode is inserted into the cylinder and then injected, so that it is possible to easily suppress electronic isolation of the active material by swelling by pressing the electrode. Due to which high cycle life characteristics can be achieved.
[0006]
On the other hand, in the case of the thin type, the positive electrode in which the positive electrode mixture is applied on the positive electrode current collector and the negative electrode in which the negative electrode mixture is applied on the negative electrode current collector are opposed to each other via the electrolyte. It is difficult to pressurize, and instead of pressurizing, the electron conductivity and ionic conductivity of the active material are improved by preparing a binder to be compounded in the positive electrode mixture and the negative electrode mixture, and high cycle. Attempting to achieve life characteristics.
[0007]
Conventionally, fluorine-containing polymers such as ethylene tetrafluoride and hexafluoroethylene have been used as the above-mentioned binder, and these are dissolved in N-methyl-2-pyrrolidone or the like together with the positive electrode active material or the negative electrode active material and mixed. Then, a positive electrode mixture or a negative electrode mixture is formed, the positive electrode mixture is applied to a positive electrode current collector plate, and the negative electrode mixture is applied to a negative electrode current collector plate, and then dried and pressed to produce an electrode.
[0008]
[Problems to be solved by the invention]
In the above-mentioned conventional thin lithium battery, it is necessary to completely remove N-methyl-2-pyrrolidone, in which ethylene tetrafluoride or hexafluoroethylene as a binder is dissolved together with the positive electrode active material or the negative electrode active material, by drying. However, if it remains, there is a problem that the cycle life characteristic is deteriorated.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the present invention relates to a method for manufacturing a thin lithium battery in which a positive electrode mixture and a negative electrode mixture are opposed via an electrolyte ,
A step of mixing a positive electrode active material, an electrolytic solution, and a polymer precursor monomer as a binder, and performing polymerization to obtain a positive electrode mixture;
A step of mixing a negative electrode active material, an electrolytic solution, and a polymer precursor monomer as a binder, and performing polymerization to obtain a negative electrode mixture;
Has,
The method for producing a thin lithium battery, wherein the monomer has an aromatic unit and an oxyalkylene unit and the molecular chain terminal is an oligomer of an allyl unit or an acrylic unit , and the solvent is removed by having the oxyalkylene unit. The solubility in an unnecessary electrolyte solution can be improved, and the swelling property of the electrolyte solution can be suppressed by suppressing the flexibility of the molecular chain by having the aromatic unit. By using an acrylic unit, polymerization of the oligomer having the aromatic unit and the oxyalkylene unit can be easily performed.
[0010]
Further, the present invention is characterized in that in the above-mentioned production method , the oligomer is a polymer having a molecular weight of 10,000 or less, whereby the solubility in an electrolytic solution which does not require removal of the solvent can be further improved.
[0011]
Further, the present invention is characterized in that in the above-mentioned production method , the swelling of the polymer as the binder by the electrolytic solution is 120% or less by volume percentage, whereby the solvent accompanying the charge and discharge is reduced. Swelling due to migration of molecules can be minimized, and deterioration of cycle life characteristics can be prevented.
[0012]
Further, the present invention is characterized in that, in the production method , the polymerization is performed by irradiation with radiation , and since a catalyst is not used, it is possible to avoid a risk that the catalyst acts as an impurity, The time required for polymerization can be reduced.
[0013]
Further, the present invention is the manufacturing method, the precursor monomer of the a binder polymer is characterized in that is obtained by acrylate of ethylene oxide adduct of bisphenol A, a binder The acrylated bisphenol A ethylene oxide adduct as a precursor monomer of the polymer is a crosslinkable polymer having a small molecular network and contains an aromatic unit having low affinity for a solvent. It has very low properties and is hardly affected by swelling and shrinking even when the solvent moves.
[0014]
Further, the present invention is a thin lithium battery manufactured by the manufacturing method. Thus, a thin battery with improved charge / discharge cycle characteristics can be obtained.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described based on the embodiments.
[0016]
FIG. 1 is a sectional view of a thin lithium battery according to an embodiment of the present invention.
[0017]
As shown in FIG. 1, the thin lithium battery of the present invention is characterized in that a positive electrode active material mainly composed of lithium cobaltate, an electrolytic solution obtained by dissolving LiBF in γ-butyrolactone at 1 mol / l, and bisphenol A Positive electrode mixture 1 prepared by mixing and polymerizing a polymer precursor monomer as a binder obtained by acrylated ethylene oxide adduct of the above, an anode active material mainly composed of non-graphitic carbon, the electrolytic solution and The negative electrode mixture 2 is formed by mixing and polymerizing a polymer precursor monomer as a binder, and the positive electrode mixture 1 is obtained by forming an undercoat 4 made of a carbon film on a positive electrode current collector 3 made of aluminum foil. The negative electrode mixture 2 is formed on a negative electrode current collector plate 5 made of copper foil, and the positive electrode mixture 1 and the negative electrode mixture 2 are made of polyethylene oxide and polypropylene. Are opposed to each other via the gel electrolyte 6 made mainly of 3 acrylic ester functionality in the copolymer of alkylene oxide, is that sealing the ends with an adhesive 7.
[0018]
In the acrylated bisphenol A ethylene oxide adduct, the oligomer has an aromatic unit and an ethylene oxide unit, and the molecular chain end is an allyl unit or an acrylic unit, and the average molecular weight is measured by GPC. The measured number average molecular weight in terms of styrene is about 500, and the average swelling of the polymer, which is a binder formed by polymerization, with the electrolytic solution is 120% by volume percentage.
[0019]
The method of manufacturing the thin lithium battery of the present invention is characterized by a positive electrode active material mainly composed of lithium cobaltate, an electrolytic solution obtained by dissolving LiBF in γ-butyrolactone at 1 mol / l, and ethylene oxide of bisphenol A. A step of applying a positive electrode mixture obtained by mixing and polymerizing a precursor monomer of a polymer as a binder obtained by acrylate-forming the adduct to the positive electrode current collector plate via an undercoat to form a positive electrode; A negative electrode active material mainly composed of carbon, a negative electrode mixture obtained by mixing and polymerizing a precursor monomer of the polymer as the electrolyte and the binder is coated on a negative electrode current collector plate to form a negative electrode. And a step of causing the positive electrode and the negative electrode to face each other via a gel electrolyte, and sealing the ends with an adhesive.
[0020]
The polymerization is carried out by mixing a polymer precursor monomer as a binder in the positive electrode mixture and the negative electrode mixture and irradiating them with radiation such as an electron beam or a gamma ray, so that the catalyst may act as an impurity. Properties can be avoided and the time required for polymerization can be shortened.
[0021]
Further, in the polymerization, a precursor of the polymer as the binder is made into a plurality of kinds of monomers, whereby the molecular structure can be crosslinked, and the flexibility of the polymer as the binder can be further increased.
[0022]
【Example】
(Thin lithium battery of the present invention)
Lithium cobaltate as a positive electrode active material, non-graphite-based carbon as a negative electrode active material, and LiBF dissolved at 1 mol / l in γ-butyrolactone as an electrolytic solution were used as precursors of a polymer as a binder. As the base monomer, an acrylated bisphenol A ethylene oxide adduct was prepared, and the average positive molecular weight was 500. A positive electrode was formed on a 50 μm-thick aluminum foil serving as a positive electrode current collector plate 3 by a carbon coating as an undercoat 4. And dried, and a positive electrode mixture obtained by mixing 10 g of lithium cobaltate as a positive electrode active material, 0.2 g of Ketjen black, 4.8 g of the electrolyte solution, and 1.2 g of the precursor monomer is mixed thereon. The agent 1 was applied, irradiated with an electron beam, and polymerized to have a thickness of 155 μm. m, a negative electrode mixture 2 obtained by mixing 10 g of carbon as a negative electrode active material, 4.8 g of the electrolyte solution, and 1.2 g of the precursor monomer, and irradiating an electron beam, Polymerization is performed to a thickness of 100 μm, and the electrolyte 6 is mixed with the electrolytic solution in a ratio of 3: 7 to a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide, and applied on the positive electrode and the negative electrode. And cured to form gels each having a thickness of 45 μm.
[0023]
After bonding the positive electrode-electrolyte and the electrolyte-negative electrode thus prepared and placing a hot-melt adhesive as an adhesive 7 on the end, heat-sealing three sides of the square and then applying vacuum to the other side A 10 mAh battery was manufactured by sealing.
[0024]
The equilibrium swelling of the binder polymer thus obtained was about 120%.
[0025]
(Thin lithium battery of Comparative Example 1)
The same positive electrode active material, negative electrode active material and electrolytic solution as those of the thin lithium battery of the present invention were prepared, and ethylene tetrafluoride was dissolved in N-methyl-2-pyrrolidone to form an 8% by weight solution, which was then bound. A positive electrode is prepared as a polymer, and a positive electrode is coated with a carbon coating as an undercoat 4 on an aluminum foil having a thickness of 50 μm as a positive electrode current collector 3 and dried. Of lithium cobaltate, 0.2 g of Ketjen black, and 15 g of the binder polymer solution, dried, pressed and injected with the electrolyte to have a thickness of 150 μm. The negative electrode was coated with a mixture of 10 g of carbon and 15 g of the polymer solution as the binder on a copper foil having a thickness of 35 μm as the negative electrode current collector plate 5, dried, and pressed. Previous An electrolyte was injected to a thickness of 100 μm, and the electrolyte 6 was mixed with the electrolyte at a ratio of 3: 7 of a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide to the positive electrode and the negative electrode. It was applied on top and cured to form a gel having a thickness of 45 μm.
[0026]
After bonding the positive electrode-electrolyte and the electrolyte-negative electrode thus prepared and placing a hot-melt adhesive as an adhesive 7 on the end, heat-sealing three sides of the square and then applying vacuum to the other side Sealed.
[0027]
The equilibrium swelling of the binder polymer thus obtained was about 160%.
[0028]
(Thin lithium battery of Comparative Example 2)
The same positive electrode active material, negative electrode active material and electrolyte solution as those of the thin lithium battery of the present invention were prepared, and a polymer having an average molecular weight of 11,000 in which acrylate of polyethylene glycol was prepared as a precursor monomer of a polymer as a binder was prepared. Is coated on a 50 μm-thick aluminum foil serving as the positive electrode current collector plate 3 with a carbon coating as an undercoat 4 and dried, and then 10 g of lithium cobalt oxide as a positive electrode active material and 0.2 g of Ketjen black, 4.8 g of the electrolyte solution, and 1.2 g of the precursor monomer mixed with the positive electrode mixture 1 were applied, irradiated with an electron beam, polymerized to a thickness of 155 μm, and the negative electrode was formed. A negative electrode mixture obtained by mixing 10 g of carbon as a negative electrode active material, 4.8 g of the electrolytic solution, and 1.2 g of the precursor monomer on a copper foil as the negative electrode current collector plate 5 Is applied, irradiated with an electron beam, and polymerized to have a thickness of 100 μm. The electrolyte 6 is prepared by mixing a trifunctional acrylic ester of a copolymer of polyethylene oxide and polypropylene oxide with the electrolyte at a ratio of 3: 7. The mixture was mixed, applied on the positive electrode and the negative electrode, and cured to form a gel having a thickness of 45 μm.
[0029]
After bonding the positive electrode-electrolyte and the electrolyte-negative electrode thus prepared and placing a hot-melt adhesive as an adhesive 7 on the end, heat-sealing three sides of the square and then applying vacuum to the other side A 10 mAh battery was manufactured by sealing.
[0030]
The equilibrium swelling of the binder polymer thus obtained was 210%.
[0031]
Next, with respect to the battery of the present invention and the batteries of Comparative Example 1 and Comparative Example 2, a 10-hour constant-current charge / discharge was performed at a charge end voltage of 4.2 V and a discharge end voltage of 2.7 V. FIG. 2 shows the relationship with the number of charge / discharge cycles.
[0032]
From FIG. 2, the battery of Comparative Example 1 has an initial capacity of 80% of the battery of the present invention at the 5th cycle, which is lower than 50% of the capacity of the battery of the present invention, and the capacity of the battery of the present invention at the 10th cycle is 35%. %.
[0033]
It is considered that this is because the mixture is not pressurized at the time of injection and the mixture swells due to the electrolytic solution, and the active material in the electrode is electronically isolated. In addition, when lithium ions are taken into the solvent of the electrolyte during charge and discharge and move, the mixture is expanded and contracted by doping and undoping of lithium, whereas the polymer used as the binder is used. This is probably because ethylene tetrafluoride dissolved in N-methyl-2-pyrrolidone is linear, and cannot prevent the mixture from expanding and contracting.
[0034]
From FIG. 2, it was found that the battery of Comparative Example 2 had an initial capacity of 20% of the battery of the present invention and 10% of the capacity of the battery of the present invention after the third cycle.
[0035]
This is considered to be due to the fact that the negative electrode mixture swells at the time of the initial charge, the active material is isolated electronically, and the swelling of the crosslinked polyethylene oxide of the polymer used as the binder is large.
[0036]
Compared with Comparative Examples 1 and 2 described above, it was found that the capacity of the battery of the present invention did not decrease at all even after 100 cycles.
[0037]
This implies that the acrylated bisphenol A ethylene oxide adduct as a precursor monomer of the polymer as the binder is a crosslinkable polymer having a small molecular network and contains aromatic units having low affinity for the solvent. Therefore, it is considered that the swelling property is very low and the swelling and shrinkage are hardly affected by the movement of the solvent.
[0038]
【The invention's effect】
As described above, the thin lithium battery of the present invention can improve the charge / discharge cycle characteristics, and its production method is to dissolve a precursor monomer, which is a binder polymer, in an electrolytic solution and then polymerize it in an electrode. Therefore, steps such as removing unnecessary solvent of the electrode, pressing the electrode, and pouring the battery into the battery can be omitted at the time of fabrication, so that the man-hour required for fabricating the battery can be reduced.
[Brief description of the drawings]
FIG. 1 is a sectional view of a thin lithium battery of the present invention.
FIG. 2 is a diagram showing the relationship between the discharge time and the number of charge / discharge cycles when the battery of the present invention, the thin lithium batteries of Comparative Examples 1 and 2, were discharged at a constant current.
REFERENCE SIGNS LIST 1 positive electrode mixture 2 negative electrode mixture 3 positive electrode current collector 4 undercoat 5 negative electrode current collector 6 electrolyte 7 adhesive

Claims (6)

In a method for manufacturing a thin lithium battery in which a positive electrode mixture and a negative electrode mixture are opposed via an electrolyte ,
A step of mixing a positive electrode active material, an electrolytic solution, and a polymer precursor monomer as a binder, and performing polymerization to obtain a positive electrode mixture;
A step of mixing a negative electrode active material, an electrolytic solution, and a polymer precursor monomer as a binder, and performing polymerization to obtain a negative electrode mixture;
Has,
The method for producing a thin lithium battery, wherein the monomer has an aromatic unit and an oxyalkylene unit, and the terminal of the molecular chain is an oligomer of an allyl unit or an acrylic unit. The method according to claim 1 , wherein the oligomer is a polymer having a molecular weight of 10,000 or less . 3. The method for manufacturing a thin lithium battery according to claim 1, wherein the swelling of the polymer as the binder by the electrolytic solution is 120% or less by volume percentage . The method for producing a thin lithium battery according to claim 1, wherein the polymerization is performed by irradiation with radiation. The method for producing a thin lithium battery according to any one of claims 1 to 4, wherein the polymer precursor monomer as the binder is obtained by acrylate-forming an ethylene oxide adduct of bisphenol A. A thin lithium battery manufactured by the method for manufacturing a thin lithium battery according to claim 1.

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