JPH10116620A - Thin type lithium battery and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thin type lithium battery which is excellent in initial capacity and a cycle life without requiring any special production process. SOLUTION: In a thin type lithium battery in which a positive electrode and a negative electrode face to each other via an electrolyte layer, a mixture forming the positive electrode and a mixture forming the negative electrode are formed by mixing at least electrode active material, electrolyte, and a monomer having a polymerizing functional group at a molecular chain end as a binding agent, and the thin type lithium battery having a binding property between the active material is obtained by the polymerization of the monomer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin lithium battery and a method for manufacturing 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 positive electrode mixture and a negative electrode mixture thereof. The present invention relates to an improvement in a method for manufacturing a thin lithium battery using the same.

[0002]

2. Description of the Related Art In recent years, portable devices such as cellular phones, PHSs, and small personal computers have been significantly reduced in size and weight with the development of electronics technology. Miniaturization and weight reduction are required.

A lithium battery is one of the batteries that can be expected for such uses. In addition to the lithium primary battery that has already been put into practical use, a lithium secondary battery has been put to practical use, has a higher capacity, and has a longer life. Research is being pursued.

[0004] The above-mentioned various lithium batteries are mainly cylindrical. On the other hand, in lithium primary batteries, thin-type ones have been put to practical use by using a solid electrolyte and a manufacturing method that applies printing technology, but such thin-type batteries are used in lithium secondary batteries and lithium-ion secondary batteries. Has not yet been put to practical use.

The reasons for this are as follows. That is, in the case of a cylindrical battery, an electrode group consisting of a positive electrode, a negative electrode, and a separator is inserted into a cylindrical battery case, and then a liquid electrolyte is injected. In the case of a thin battery, the positive electrode and the negative electrode are opposed to each other with the electrolyte interposed therebetween, which makes it difficult to pressurize the electrodes. There is a drawback that the electrical contact of the substance is broken and the cycle life is shortened.

Therefore, conventionally, in a thin lithium secondary battery, by preparing a binder mixed in a positive electrode mixture and a negative electrode mixture, the electron conductivity and the ion conductivity of the active material are maintained. Research is underway to improve cycle life. Examples of the binder include polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVD).
F) or the like, and these are used together with a positive electrode active material and a negative electrode active material in N-methyl-2-
A positive electrode and a negative electrode are manufactured by dissolving and mixing a solvent such as pyrrolidone as a positive electrode mixture and a negative electrode mixture, applying the mixture to a current collector, and then drying and pressing the mixture.

[0007]

In the above-mentioned conventional thin lithium battery, a solvent such as N-methyl-2-pyrrolidone in which a binder such as PTFE or PVDF is dissolved together with a positive electrode active material and a negative electrode active material is used. It has to be completely removed by drying, and if it remains, it becomes one of the causes of deterioration of cycle life characteristics, and there is a problem that the manufacturing process is complicated.

The present invention has been made in view of the above problems, and has as its object to provide a thin lithium battery capable of obtaining stable battery performance without requiring a special manufacturing process or the like. Things.

[0009]

Means for Solving the Problems To solve the above problems, a first aspect of the present invention is to provide a thin lithium battery in which a positive electrode and a negative electrode are opposed to each other with an electrolyte layer interposed therebetween. The mixture forming the negative electrode is a mixture of at least an electrode active material, an electrolytic solution, and a monomer having a polymerizable functional group at a molecular chain terminal as a binder, and binding between the active materials by polymerization of the monomer. It has characteristics. More preferably, the molecular weight of the monomer is 2,000 or less, the degree of swelling of the polymer obtained by polymerizing the monomer alone in an electrolyte solvent,
130% or less by weight percentage or 13% by volume percentage
0% or less, and more specifically, the structure of the monomer is at least one of the structures represented by Chemical Formulas 5 and 6.
It is desirable to select from one.

[0010]

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[0011]

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Further, the electrolyte layer is a solid or gel composed of an organic polymer, and the organic polymer for the electrolyte has a polymer having a structure different from that of the polymer as the binder or a structure of the same kind. Desirably different polymers. In addition, the solvent of the electrolytic solution may be selected from one or more having one of a cyclic ester, a chain ester, a cyclic ether, a chain ether, a cyclic amide, and a chain amide. desirable.

In order to solve the above problems, a second aspect of the present invention is to apply a positive electrode mixture obtained by mixing at least a positive electrode active material, an electrolytic solution and a binder onto a positive electrode current collector. A step of forming a positive electrode, a step of forming a negative electrode by applying a negative electrode mixture obtained by mixing at least a negative electrode active material, an electrolytic solution and a binder on a negative electrode current collector; and And a step of sealing the end portion with an adhesive while interposing an electrolyte therebetween, wherein the binder has a polymerizable functional group at a molecular chain terminal, preferably a molecular weight. It is mixed into the positive electrode mixture and the negative electrode mixture in a state of a monomer of 2,000 or less, and after coating on the positive electrode current collector and the negative electrode current collector, forming a polymer that binds the active materials by polymerization. Features More preferably, the swelling degree of the polymer obtained by polymerizing the monomer alone in the electrolyte solvent is 130% or less by weight percentage or 130% or less by volume percentage, and more specifically, the structure of the monomer is It is desirable to select from at least one of the structures shown in Chemical formula 8 below.

[0014]

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[0015]

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Further, the electrolyte layer is a solid or gel composed of an organic polymer, and the organic polymer for the electrolyte has a polymer having a different structure from the polymer as the binder or a similar structure. Desirably different polymers. In addition, the solvent of the electrolytic solution may be selected from one or more having one of a cyclic ester, a chain ester, a cyclic ether, a chain ether, a cyclic amide, and a chain amide. desirable. More preferably, the method for forming a polymer of the binder is polymerization by irradiation with ionizing radiation.

[0017]

Accordingly, the present invention provides a method of mixing a positive electrode mixture and a negative electrode mixture with a monomer having a molecular weight of 2,000 or less and having a polymerizable functional group at a molecular chain terminal as a binder, and coating the mixture on a current collector. By polymerizing, it has a binding property between active materials, and the molecular weight of the monomer and the degree of swelling of the polymer obtained by polymerizing the monomer alone in an electrolyte solvent, the structure of the monomer, and the organic polymer in the electrolyte layer By defining the structure of (1) and the structure of the electrolyte solvent, it is possible to provide a thin lithium battery which maintains the electrical contact of the active material and has excellent initial capacity and cycle life.

Furthermore, the present invention provides a method of mixing the above-mentioned binder as a monomer having a polymerizable functional group at a molecular chain terminal and having a molecular weight of 2,000 or less in a positive electrode mixture and a negative electrode mixture, on a positive electrode current collector and a negative electrode collector. After coating on the electric body, a polymer that binds the active material by polymerization is formed, and the molecular weight of the monomer and the degree of swelling of the polymer obtained by polymerizing the monomer alone in an electrolyte solvent, the structure of the monomer By defining the structure of the organic polymer in the electrolyte layer and the structure of the electrolyte solvent, it is possible to manufacture thin lithium batteries with excellent initial capacity and cycle life without the need for special manufacturing processes such as solvent removal. A method can be provided.

If the molecular weight of the monomer is 2,000 or more, the degree of swelling with respect to the electrolyte solvent becomes 130% or more by weight or 130% or more by volume, and it becomes impossible to maintain electrical contact with the active material. .

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below based on embodiments. FIG. 1 shows a cross-sectional view of the thin lithium battery of the present invention. In FIG. 1, reference numeral 1 denotes an electrolyte containing lithium cobalt oxide, which is a positive electrode active material, as a main component, 1 mol / liter of LiBF ₄ dissolved in γ-butyrolactone, and an alkyl chain and ester structure in the molecule. This is a positive electrode mixture containing a binder obtained by polymerizing an acrylate monomer having an acrylic group, and is applied on the positive electrode current collector plate 3 made of aluminum foil. Reference numeral 2 denotes a negative electrode mixture mainly containing carbon as a negative electrode active material and containing the same electrolytic solution and binder as the positive electrode mixture 1, and is coated on a negative electrode current collector plate 4 made of copper foil. It becomes. The positive electrode mixture 1 and the negative electrode mixture 2 were prepared by mixing acrylate monomers, which are raw materials for the respective electrode active materials, the electrolytic solution and the binder, and applying the mixture on the respective electrode current collectors, followed by electron beam irradiation. It is obtained by polymerizing a monomer to form a polymer as a binder. The positive electrode mixture 1 and the negative electrode mixture 2 have a structure of the electrolyte and a copolymer of polyethylene oxide and polypropylene oxide, and mainly contain a polymer obtained by polymerizing an acrylate monomer having an acrylic group at a molecular terminal. The electrodes are opposed to each other with a gel electrolyte 5 formed therebetween, and the ends are sealed with an adhesive.

The average molecular weight of the acrylate monomer represented by Chemical Formula 9, which is a raw material of the binder contained in the positive electrode mixture 1 and the negative electrode mixture 2, is about 400, and depends on the electrolytic solution of the polymer formed by polymerization. The degree of swelling is 12 by volume percentage.
5%.

[0022]

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On the other hand, the average molecular weight of the acrylate monomer which is a raw material of the polymer contained in the electrolyte 5 is about 800
0, and the degree of swelling of the polymer formed by the polymerization with the electrolytic solution is 350% by volume percentage.

A thin lithium battery having a capacity of 10 mAh was manufactured by the above-described raw materials and manufacturing method, and the battery A of the present invention was manufactured.
And

Similarly, the binder contained in the positive electrode mixture 1 and the negative electrode mixture 2 has a structure of polyethylene oxide having a smaller molecular weight than that used for the electrolyte 5 and has an acrylic group at the molecular terminal. A thin-film lithium battery having a capacity of 10 mAh was prepared using a polymer obtained by polymerizing an acrylate monomer and using the same raw materials and manufacturing method under the other conditions. The average molecular weight of the acrylate monomer, which is the raw material of the binder used for the comparative battery B, was about 2000, and the degree of swelling of the polymer formed by polymerization with the electrolytic solution was 200% by volume percentage.
It is.

As a binder contained in the positive electrode mixture 1 and the negative electrode mixture 2, an acrylate monomer having the same copolymer structure of polyethylene oxide and polypropylene oxide as the electrolyte 5 and having an acrylic group at the molecular terminal is used. A thin-film lithium battery having a capacity of 10 mAh was produced using the polymer obtained by polymerizing the above and using the same raw materials and the same manufacturing method as the other conditions, to obtain Comparative Battery C.

Further, PVDF is used as a binder to be contained in the positive electrode mixture 1 and the negative electrode mixture 2, and the positive electrode mixture 1 and the negative electrode mixture 2 are raw materials of the respective positive electrode active materials and the binder. A solution obtained by dissolving a certain PVDF in N-methyl-2-pyrrolidone is mixed, applied on each current collector, dried, pressed, and then injected with an electrolytic solution. The following conditions were used to produce a thin lithium battery with a capacity of 10 mAh using the same raw materials and manufacturing method.
Conventional battery D was used. The degree of swelling of the PVDF with the electrolytic solution is 160% by volume.

Next, a charge / discharge cycle test was performed on the battery A of the present invention, the comparative batteries B and C, and the conventional battery C, and the relationship between the number of cycles and the discharge capacity obtained as a result is shown in FIG. The test conditions were as follows: charge at a current of 1 mA at a temperature of 20 ° C. to a final voltage of 4.2 V;
The battery was discharged to a final voltage of 2.7 V by the current A.
From FIG. 2, the initial capacity of the conventional battery D is approximately 80 times the design capacity.
%, But it was found that the capacity rapidly decreased after the lapse of the cycle, and fell below 50% of the designed capacity in the fifth cycle. The reason for this is that PV
It is considered that the swelling of the DF electronically isolates the active material in the electrode. In addition, movement of lithium ions during charge and discharge causes movement of the electrolytic solution and expansion and contraction of the active material. However, it is difficult to suppress expansion and contraction of the active material by PVDF. It is thought to occur.

On the other hand, although the initial capacity of the comparative battery B is about 90% of the designed capacity, the capacity rapidly drops after the cycle, and falls below 50% of the designed capacity at the tenth cycle. I understood that. For the comparative battery C, this tendency was further increased, and only 20% of the designed capacity was obtained from the initial capacity, and it was found that the capacity was less than 10% of the designed capacity in the third cycle. The reason for this is that the polymer used as the binder used in the comparative batteries B and C has polyethylene oxide having high affinity for the electrolytic solution in the molecule, so that the degree of swelling with respect to the electrolytic solution is large, and the polymer is mixed by the electrolytic solution during initial charging. It is considered that the agent swells and the active material in the electrode is electronically isolated. In addition, it is considered that the mixture further swells due to the movement of the electrolyte due to the movement of lithium ions and the expansion and contraction of the active material during charge and discharge, and a rapid decrease in capacity occurs as the cycle proceeds.

On the other hand, in the battery A of the present invention, almost 100% of the designed capacity was obtained from the initial stage of charge and discharge, and it was found that the capacity was hardly reduced even after 100 cycles. The reason for this is that the polymer used as the binder in the battery A of the present invention is a crosslinkable polymer having a small molecular network, and has an alkyl chain having a low affinity for the electrolytic solution in the molecule. It is considered that the degree is small, the mixture does not swell at the time of initial charging, and the active material in the electrode is not electronically isolated. In addition, the movement of the electrolyte due to the movement of lithium ions during charge and discharge and the expansion and contraction of the active material also suppress the expansion of the mixture due to the small molecular network of the polymer, and also suppress the decrease in capacity due to cycle progress. it is conceivable that.

Further, the same results as described above were obtained in a system using the monomer shown in Chemical formula 10.

[0032]

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[0033]

As described above, the thin lithium battery and the method for producing the same according to the present invention can be used as a binder in the positive electrode mixture and the negative electrode mixture as a binder having a polymerizable functional group at a molecular chain terminal and having a molecular weight of 2000 or less. By mixing the monomers and polymerizing them after coating on the current collector, it is necessary to have a binding property between the active materials, and to the molecular weight of the monomers and the electrolyte solution solvent of the polymer obtained by polymerizing the monomers alone. By defining the degree of swelling, the structure of the monomer, the structure of the organic polymer of the electrolyte layer, and the structure of the electrolyte solvent, to maintain the electrical contact of the active material in the electrode and to suppress the expansion of the mixture, A thin lithium battery excellent in initial capacity and cycle life can be provided without requiring a special manufacturing process.

[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 number of cycles and the discharge capacity when a charge / discharge cycle test is performed on a battery A of the present invention, comparative batteries B and C, and a conventional battery C.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode mixture 2 Negative electrode mixture 3 Positive electrode current collector 4 Negative electrode current collector 5 Electrolyte 6 Adhesive

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01M 10/40 H01M 10/40 Z

Claims (13)

[Claims] In a thin lithium battery in which a positive electrode and a negative electrode are opposed to each other with an electrolyte layer interposed therebetween, a mixture forming the positive electrode and a mixture forming the negative electrode include at least an electrode active material, an electrolytic solution, and a binder. A thin lithium battery comprising a mixture of a monomer having a polymerizable functional group at a molecular chain terminal as an adhesive, and having a binding property between active materials by polymerization of the monomer. 2. The thin lithium battery according to claim 1, wherein the monomer has a molecular weight of 2000 or less. 3. The polymer obtained by polymerizing the monomer alone has a degree of swelling in an electrolyte solvent of 130% by weight percentage.
2. The thin lithium battery according to claim 1, wherein the lithium battery has a volume percentage of 130% or less. 4. The structure of said monomer is
The thin lithium battery according to claim 1, wherein the lithium battery is selected from at least one of the following structures: Embedded image Embedded image 5. The electrolyte layer is a solid or gel composed of an organic polymer, and the organic polymer for the electrolyte is a polymer having a different structure from the polymer as the binder according to claim 1 or the same. The thin lithium battery according to claim 1, which is a different polymer having the following structure: 6. The solvent for the electrolytic solution is one or two of a cyclic ester, a chain ester, a cyclic ether, a chain ether, a cyclic amide, and a chain amide.
The thin lithium battery according to claim 1, wherein the lithium battery is selected from at least one species. 7. A step of forming a positive electrode by applying a positive electrode mixture obtained by mixing at least a positive electrode active material, an electrolytic solution and a binder onto a positive electrode current collector; A step of forming a negative electrode by applying a negative electrode mixture obtained by mixing the binder and a negative electrode current collector,
A step of causing the positive electrode and the negative electrode to face each other via an electrolyte and sealing the ends thereof with an adhesive, wherein the binder has a polymerizable functional group at a molecular chain terminal. It is mixed with the positive electrode mixture and the negative electrode mixture in the state of a monomer having the following formula, is applied on the positive electrode current collector and the negative electrode current collector, and then forms a polymer that binds the active materials by polymerization. Of manufacturing a thin lithium battery. 8. The thin lithium battery according to claim 7, wherein the monomer has a molecular weight of 2000 or less. 9. The polymer obtained by polymerizing the monomer alone has a degree of swelling in an electrolyte solvent of 130% by weight.
The method for producing a thin lithium battery according to claim 7, wherein the volume percentage is 130% or less. 10. The method for producing a thin lithium battery according to claim 7, wherein the structure of the monomer is selected from at least one of the structures shown in Chemical formulas 3 and 4. Embedded image Embedded image 11. The electrolyte layer is a solid or gel composed of an organic polymer, and the organic polymer for electrolyte is a polymer having a structure different from that of the polymer as a binder according to claim 7, or the same. The method for producing a thin lithium battery according to claim 7, wherein the polymer is a different polymer having the following structure. 12. The solvent for the electrolytic solution is a cyclic ester,
1 or 2 having any structure of a chain ester, a cyclic ether, a chain ether, a cyclic amide, and a chain amide
The method for producing a thin lithium battery according to claim 7, which is selected from at least one kind. 13. The method for producing a thin lithium battery according to claim 7, wherein the method of forming the polymer of the binder is polymerization by irradiation with ionizing radiation.