JPH1012243A - Lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high capacity lithium secondary battery whose positive electrode active material is hardly degraded. SOLUTION: This battery is constituted by winding a sheet-like positive electrode 1 and a sheet like negative electrode 2 in a spiral shape through a separator 3. In this case, when the sheet-like positive electrode 1 is manufactured by forming a piant film containing at least a positive electrode active material and a binder on a conductive base body, a mixture with at least one kind selected from a group composed of polytetrafluoroethylene, polyvinyl butyral, polyethylene glycol, polypropylene glycol, a polyethylene oxide, a polypropylene oxide and a propylene oxide-ethylene oxide copolymer, is used as the binder.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly, to a lithium secondary battery in which deterioration of a positive electrode active material is small.
It relates to a high-capacity lithium secondary battery.

[0002]

2. Description of the Related Art Generally, a solvent is added to a mixture containing an active material, a binder, and the like, and a mixture prepared by mixing is applied to a conductive substrate and dried to form a coating film containing the active material. To form a sheet-like electrode, and then spirally wind the sheet-like electrode together with the separator, and enclose the spirally wound electrode body together with an organic solvent-based electrolytic solution in a metal battery case. The secondary battery has a feature that the energy density per unit capacity and the energy density per unit weight are high.

[0003] The binder used for the sheet-like electrode is required to have resistance to strong oxidizing action by the active material at the time of charging and chemical stability to an organic solvent-based electrolytic solution. In particular, polytetrafluoroethylene has been found to be suitable.

[0004]

However, when the above-mentioned polytetrafluoroethylene is mixed with an active material or a solvent to prepare a coating, the viscosity characteristics of the coating do not have thixotropic properties and are poor in fluidity. It is difficult to efficiently form a coating film on a conductive substrate, and the adhesion between the coating film formed by applying the above-mentioned coating material on a conductive substrate and drying and the conductive substrate is weak. There is a problem that the above-mentioned spiral electrode body cannot be manufactured because the spiral electrode body is easily peeled off from the conductive substrate.

In producing a sheet-like electrode using polytetrafluoroethylene as a binder, Japanese Patent Application Laid-Open No. 2-158055 discloses that a powdery active material and an electron conduction aid are mixed, After adding and kneading an aqueous solution of carboxymethyl cellulose as an agent,
Further, a coating is prepared by adding and kneading a dispersion of polytetrafluoroethylene, and the coating is applied to a film-shaped conductive substrate such as a rolled aluminum foil, and dried to form a coating with the conductive substrate. It is reported that a coating film having excellent adhesive strength can be obtained.

Japanese Patent Application Laid-Open No. 4-267054 discloses that polytetrafluoroethylene and a polymerization degree of 100-17.
There has been proposed a method of using a combination of polyvinyl alcohol having a saponification degree of 93 to 96 mol%.

In the above publication, besides the above-mentioned carboxylmethylcellulose and polyvinyl alcohol, cellulose resins such as methylcellulose, hydroxyethylcellulose, hydroxypropylcellulose and hydroxypropylmethylcellulose, and sodium polyacrylate are used as the viscosity agent. It is described as possible.

However, since the paint prepared by adding the above-mentioned viscous agent uses water as a solvent, lithium elutes from the positive electrode active material and reacts with water, thereby deteriorating the active material. There was a problem. This phenomenon is more likely to occur as the positive electrode active material that provides a higher capacity is used. For example, when LiNiO ₂ is used as the positive electrode active material, the battery capacity is reduced to 1/10 or less.
In addition, even with a paint in which a viscous agent was dissolved in alcohol and added, deterioration of the positive electrode active material could not be completely prevented.

Accordingly, it is an object of the present invention to provide a high capacity lithium secondary battery which solves the above-mentioned problems of the conventional lithium secondary battery and prevents deterioration of the positive electrode active material. I do.

[0010]

Means for Solving the Problems The present invention has been made as a result of conducting various studies to achieve the above-mentioned object, and comprises forming a coating film containing at least a positive electrode active material and a binder on a conductive substrate. When producing a sheet-shaped positive electrode by doing, as the binder, selected from the group consisting of polytetrafluoroethylene, polyvinyl butyral, and polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene oxide copolymer By using at least one of the above, a sheet-shaped positive electrode was produced without using water or alcohol as a solvent, and a high-capacity lithium secondary battery with little deterioration of the positive electrode active material was provided. .

That is, the sheet-like positive electrode of the present invention comprises polytetrafluoroethylene as a binder, polyvinyl butyral having a function as a viscous agent, and polyethylene glycol for plasticizing the polyvinyl butyral to impart flexibility to a coating film. And at least one selected from the group consisting of polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene oxide copolymer, which are dissolved and dispersed in water or an organic solvent other than alcohol to prepare a coating. So you can
The deterioration of the positive electrode active material due to the elution of lithium from the positive electrode active material can be prevented.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, polytetrafluoroethylene is a main material of a binder.
%, Preferably from 2 to 1% by weight.
0% by weight is preferred. If the addition amount of polytetrafluoroethylene is less than the above range, the occurrence of cracks in the coating film or peeling of the coating film from the conductive substrate is likely to occur, and
When the addition amount of polytetrafluoroethylene is larger than the above range, the amount of the positive electrode active material in the coating film may decrease, and the battery capacity may decrease.

However, in the present invention, since the above polytetrafluoroethylene cannot be used as an aqueous dispersion, for example, an organic solvent dispersion of polytetrafluoroethylene in which fine powder of polytetrafluoroethylene is dispersed in an organic solvent. It is suitable to be used as.

In the present invention, it is preferable that polyvinyl butyral imparts an appropriate viscosity to a paint used for forming a coating film of a sheet-like positive electrode by adding a small amount thereof.
The amount of addition is preferably from 0.3 to 5% by weight in the solid content of the paint, that is, in the positive electrode mixture. If the amount of polyvinyl butyral is less than 0.3% by weight in the positive electrode mixture, it is not possible to impart proper viscosity to the paint, and the paint may not be sufficiently applied to the conductive substrate. . When the amount of polyvinyl butyral added is more than 5% by weight in the positive electrode mixture, the amount of active material in the coating film decreases, and the battery capacity may decrease.
In order for polyvinyl butyral to impart an appropriate viscosity to the paint with the addition of a small amount as described above, and to make the dried film tough, the average degree of polymerization is 700 or more,
In particular, it is preferably 1,000 or more.

[0015] In the present invention, polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide, propylene oxide-ethylene oxide copolymer, etc. not only act as a viscous agent but also plasticize polyvinyl butyral to give a flexible coating film. Has the effect of imparting

When these polyethylene glycols, polypropylene glycols, polyethylene oxides, polypropylene oxides, propylene oxide-ethylene oxide copolymers, etc., have a small molecular weight, they melt or soften during use of the battery in a high temperature environment to improve battery performance. If the molecular weight is too large, it may be difficult to dissolve in a solvent and the coating composition may not be prepared.
00000, particularly 70,000 to 2
It is preferably 000000.

These polyethylene glycols, polypropylene glycols, polyethylene oxides, polypropylene oxides, propylene oxide-ethylene oxide copolymers, etc. all have the same effect in the present invention, so that any one of them can be used. Or two or more of them may be used in combination. As the amount of use of at least one of these polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene oxide copolymer, polyvinyl butyral is plasticized to impart appropriate flexibility to the coating film. In order to do so, it is preferable to add 1/10 or more by weight ratio to polyvinyl butyral, and it is particularly preferable to add 1/4 or more by weight ratio. However,
If the added amount of these polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide, propylene oxide-ethylene oxide copolymer and the like is too large, the strength of the coating film may be reduced. The ratio is preferably 9/10 or less.

[0018] Incidentally, polyethylene glycol and polyethylene oxide is, both the basic skeleton structure of formula _{"- (CH 2 CH 2 O n} ) - " is represented by the same advantages both in the present invention. Further, the basic skeleton of both polypropylene glycol and polypropylene oxide has the chemical structural formula “-[CH (CH ₃ ) CH ₂
O] _n − ”, and both have the same effect in the present invention. Further, the propylene oxide-ethylene oxide copolymer is also a polymer having a chemical structure similar to polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide, and the like. In the present invention, the propylene oxide-ethylene oxide copolymer is also a polyethylene. It has the same effect as glycol and the like.

In the binder composition of the present invention,
A sheet using only polytetrafluoroethylene and polyvinyl butyral as a binder without using at least one selected from the group consisting of the above polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene oxide copolymer. When a sheet-shaped positive electrode is produced, the sheet-shaped positive electrode has a hard coating film and lacks flexibility. Therefore, when this sheet-shaped positive electrode is spirally wound, cracks occur in the coating film, particularly on the inner peripheral side of the spiral electrode body having a large curvature, and the coating film is easily peeled from the conductive substrate, Therefore, the electron conductivity is reduced, and the battery capacity is reduced.

Further, in the binder composition of the present invention,
If polyvinyl butyral was not used, the coating of the coating on the conductive substrate could not be performed properly, and the adhesive strength between the coating film and the conductive substrate was low, and when the sheet-shaped positive electrode was spirally wound. In addition, cracks occur in the coating film, and peeling of the coating film from the conductive substrate occurs.

In order to plasticize the polyvinyl butyral, plasticizers such as dibutyl phthalate, di-2-ethylhexyl, dioctyl sebacate, and triclozil are generally used. These plasticizers have high volatility and an electrolytic solution. In the present invention, these are not used, and as described above, polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene The polyvinyl butyral is plasticized by at least one of the group consisting of the oxide copolymer.

In the present invention, in preparing a paint for forming a coating film of a sheet-like positive electrode, the solvent may be
For example, ketone organic solvents such as cyclohexanone, methyl ethyl ketone and methyl isobutyl ketone, and aromatic organic solvents such as toluene and xylene alone or
Used as a mixture of more than one species.

In the present invention, as the positive electrode active material, for example, lithium-containing composite metal oxides such as lithium nickel oxide, lithium cobalt oxide and lithium manganese oxide may be used alone or as a mixture of two or more kinds. It is used as a solid solution.

In preparing the positive electrode, an electron conduction aid such as flaky graphite and carbon black can be added to the positive electrode active material, if necessary.

The positive electrode contains, for example, the above-mentioned positive electrode active material,
If necessary, flake graphite, including an electron conduction aid such as carbon black, further apply a paint containing a binder to the conductive substrate, dried, containing at least the positive electrode active material and a binder on the conductive substrate It is produced through a step of forming a coating film.

In the preparation of the coating material, polytetrafluoroethylene is used as an organic solvent dispersion of polytetrafluoroethylene in which fine powder is previously dispersed in an organic solvent, and polyvinyl butyral is used as a solution previously dissolved in an organic solvent. Preferably, at least one selected from the group consisting of polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene oxide copolymer is used as a solution previously dissolved in an organic solvent, and these are preferably mixed.

In the present invention, as the negative electrode active material, for example, lithium metal or a lithium-containing compound is used. As the lithium-containing compound, there are a lithium alloy and others. Examples of the lithium alloy include lithium-aluminum, lithium-lead, lithium-bismuth, lithium-indium, and lithium-
Alloys of lithium and other metals, such as gallium and lithium-indium-gallium, may be mentioned. Examples of the lithium-containing compound other than the lithium alloy include a carbon material having a turbostratic structure, graphite, and the like. Some of them do not contain lithium at the time of manufacture, but when they act as a negative electrode active material, they are in a state containing lithium by chemical means or electrochemical means.

For the negative electrode, for example, an electron conduction aid such as flake graphite and carbon black is added to the negative electrode active material, if necessary, and further, for example, polyvinylidene fluoride, polytetrafluoroethylene, ethylene propylene A binder is prepared by adding a binder such as a dienter polymer, a solvent is further added, and mixed to prepare a coating material. The coating material is applied to a conductive substrate, and dried to form a coating film. Further, upon producing the negative electrode, the binder is selected from the group consisting of polytetrafluoroethylene, polyvinyl butyral, and polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide, and propylene oxide-ethylene oxide copolymer as in the case of the positive electrode. You may comprise with at least 1 type.

In the present invention, as the coating method for applying the above-mentioned coating material to the conductive substrate, various coating methods such as an extrusion coater, a reverse roller, a doctor blade and the like can be adopted.

In the present invention, as a conductive substrate for electrodes such as a positive electrode and a negative electrode, for example, a metal, a punched metal, a foam metal, or a plate-like conductive material made of a metal such as aluminum, stainless steel, titanium, or copper is used. A processed foil is used.

Examples of the electrolytic solution include 1,2-dimethoxyethane, 1,2-diethoxyethane, propylene carbonate, ethylene carbonate, γ-butyrolactone, tetrahydrofuran, 1,3-dioxolan, diethylene carbonate, dimethyl carbonate, ethyl In a single solvent such as methyl carbonate or a mixed solvent of two or more kinds, for example, LiCF ₃ SO ₃ , LiC ₄ F ₉ SO ₃ ,
An organic solvent-based electrolyte prepared by dissolving an electrolyte such as LiClO ₄ , LiPF ₆ , or LiBF ₄ alone or by dissolving two or more of them is used.

As the separator, for example, a thickness of 10 to
A microporous polypropylene film or a microporous polyethylene film having a pore size of 50 μm and a porosity of 30 to 70% is preferably used.

The battery is, for example, a spirally wound electrode body manufactured by spirally winding a sheet-shaped positive electrode and a sheet-shaped negative electrode manufactured as described above with a separator interposed therebetween.
It is inserted through a nickel-plated iron or stainless steel battery case, injected with an electrolyte, and sealed. Further, the battery usually incorporates an explosion-proof mechanism for discharging the gas generated inside the battery to the outside of the battery when the pressure has risen to a certain pressure, thereby preventing the battery from bursting under high pressure.

[0034]

Next, an embodiment of the present invention will be described.
However, the present invention is not limited to only these examples. In the examples below,% indicating the concentration and the like is% by weight.

Example 1 (1) Preparation of Positive Electrode The preparation of a positive electrode will be described in the order of synthesis of lithium nickel oxide used as a positive electrode active material and formation of a coating film.

Synthesis of Lithium Nickel Oxide Lithium hydroxide (LiOH.H ₂ O) and nickel oxide (III) (Ni ₂ O ₃ ) are heat-treated to produce a lithium nickel oxide (generally represented by LiNiO ₂ ). Li and Ni
Is often slightly deviated from the stoichiometric composition). The above synthesis was performed as follows.

Lithium hydroxide and nickel oxide are converted to Li /
After weighing so that Ni = 1 / 1.05 (molar ratio), the mixture was pulverized and mixed in an agate mortar. This was preheated in an oxygen (O ₂ ) stream at 500 ° C. for 2 hours, then heated to 700 ° C. at a heating rate of 50 ° C./h or less, and then heated at 700 ° C. for 20 hours and fired.
Since the synthesized lithium nickel oxide is weak against moisture, handling such as pulverization was performed in an argon gas atmosphere.

Formation of Coating Film The lithium nickel oxide synthesized above, flake graphite as an electron conduction aid, polytetrafluoroethylene as a binder, polyvinyl butyral (average degree of polymerization of 1800), and polyethylene glycol (average molecular weight of 50)
0000) at the following ratio.

Lithium nickel oxide 90 parts by weight Flake graphite 6 parts by weight Polytetrafluoroethylene 3 parts by weight Polyvinyl butyral (average degree of polymerization 1800) 0.75 parts by weight Polyethylene glycol (average molecular weight 500000) 0.25 parts by weight Cyclohexanone 20 Parts by weight toluene 20 parts by weight

The preparation of the paint was carried out as follows.
First, a mixed solvent of cyclohexanone and toluene was prepared, and a part thereof was used to prepare a 10% solution of polyvinyl butyral and polyethylene glycol, respectively. Next, a fine powder of polytetrafluoroethylene was added and dispersed in the remaining mixed solvent, and lithium nickel oxide as a positive electrode active material and flaky graphite as an electron conduction aid were added thereto, and a paint was prepared by mixing. did.

The obtained paint was applied on an aluminum foil having a thickness of 20 μm using an applicator,
It dried at -120 degreeC, and formed the coating film. Similarly, apply the above paint to the back side of the aluminum foil,
The coating was formed by vacuum drying for hours. The thickness of the coating on one side of the electrode body after drying was 110 μm. Then, the electrode body was roll-pressed, and the coating thickness on one side was 80 μm.
m, a sheet-shaped positive electrode having a total thickness of 180 μm was prepared.

(2) Preparation of Negative Electrode First, artificial graphite (synthesized at 2800 ° C.) as the negative electrode active material
And using polyvinylidene fluoride as a binder (provided that it was dissolved in N-methylpyrrolidone in advance and used as a solution having a concentration of 12%), and a coating material containing them in the following ratio was prepared.

Artificial graphite (synthesized at 2800 ° C.) 90 parts by weight Polyvinylidene fluoride 10 parts by weight

The obtained paint was applied on a copper foil having a thickness of 18 μm using an applicator, and dried at 100 to 120 ° C. to form a coating film. Similarly, the paint was applied to the back side of the copper foil and vacuum dried at 100 ° C. for 8 hours to form a coating film. The thickness of the coating on one side of the electrode body after drying is 100
μm. Then, the electrode body was roll-pressed to produce a sheet-like negative electrode having a coating thickness on one side of 80 μm and a total thickness of 178 μm. The coating density was adjusted so that the weight ratio of the active materials of the positive electrode and the negative electrode was 2: 1.

(3) Preparation of Electrolytic Solution LiPF ₆ was added to a mixed solvent of ethylene carbonate and ethyl methyl carbonate (mixing ratio was 1: 1 by volume).
The resulting solution was dissolved in mol / l to prepare an organic solvent-based electrolytic solution.

(4) Assembly of Cylindrical Battery The above sheet-shaped positive electrode was cut into a strip having a width of 28 × 220 mm and the sheet-shaped negative electrode was cut into a strip having a width of 30 × 260 mm. Then, a part of the coating film at the end of each sheet-like electrode was peeled off, and a lead made of aluminum was resistance-welded to a portion where the metal foil was exposed. A strip-shaped separator made of a porous polypropylene film is interposed between the sheet-shaped positive electrode and the sheet-shaped negative electrode, spirally wound to produce a spirally wound electrode body, and the spirally wound electrode body is made of a stainless steel battery case. Inserted in.

Then, the tip of the lead body on the negative electrode side is welded to the bottom of the battery case by penetrating the insulator, and the insulator is inserted into the opening of the battery case to form a groove. The lead body on the positive electrode side was welded. Then, after the can body manufactured through such a process is vacuum-dried at 60 ° C. for 10 hours, 2 ml of an electrolyte solution is injected in a dry atmosphere, sealed, and sealed to form a cylindrical R5 battery (FIG. 1). Outer diameter: 1
4.95 mm, height: 39.7 mm).

Referring to the battery shown in FIG. 1, reference numeral 1 denotes the positive electrode and 2 denotes the negative electrode. However, FIG. 1 does not show a metal foil or the like as a conductive substrate used for manufacturing the positive electrode 1 or the negative electrode 2 in order to avoid complication.
3 is a separator, and 4 is an electrolytic solution.

5 is a battery case made of stainless steel,
This battery case 5 also serves as a negative electrode terminal. An insulator 6 made of a polytetrafluoroethylene sheet is arranged at the bottom of the battery case 5, and an insulator 7 made of a polytetrafluoroethylene sheet is also arranged at the inner periphery of the battery case 5. The spiral electrode body composed of the negative electrode 2 and the separator 3, the electrolyte 4, and the like are accommodated in the battery case 5.

Reference numeral 8 denotes a sealing plate made of stainless steel, and a gas ventilation hole 8a is provided in the center of the sealing plate 8. Reference numeral 9 denotes an annular packing made of polypropylene, reference numeral 10 denotes a flexible thin plate made of titanium, and reference numeral 11 denotes an annular, thermally deformable member made of polypropylene.

The heat deformable member 11 changes the breaking pressure of the flexible thin plate 10 by deforming according to the temperature.

Reference numeral 12 denotes a nickel-plated rolled steel terminal plate. The terminal plate 12 is provided with a cutting blade 12a and a gas discharge hole 12b. When the internal pressure rises and the flexible thin plate 10 is deformed by the internal rise, the flexible thin plate 10 is broken by the cutting blade 12a, and gas inside the battery is discharged to the outside of the battery from the gas discharge hole 12b. In addition, the battery is designed so as to prevent the battery from being destroyed under high pressure.

Reference numeral 13 denotes an insulator, 14 denotes an aluminum lead body, and the lead body 14 comprises the positive electrode 1 and the sealing plate 8.
Are electrically connected to each other, and the terminal plate 12 functions as a positive electrode terminal by contact with the sealing plate 8. Reference numeral 15 denotes a lead body for electrically connecting the negative electrode 2 and the battery case 5.

Example 2 Polyvinyl butyral in the coating material for forming a coating film of the positive electrode in Example 1 was changed from 0.75 part by weight (however, solid content) to 0.5 part by weight (however, solid content), and polyethylene was used. An R5-type battery was produced in the same manner as in Example 1, except that 0.25 parts by weight of glycol (however, solid content) was changed to 0.5 parts by weight (however, solid content).

Example 3 Polyvinyl butyral in the coating material for forming a coating film of the positive electrode in Example 1 was changed from 0.75 parts by weight (however, solid content) to 0.25 parts by weight (however, solid content), and polyethylene was used. An R5-type battery was produced in the same manner as in Example 1, except that 0.25 parts by weight of glycol (however, solid content) was changed to 0.75 parts by weight (however, solid content).

Example 4 The procedure of Example 1 was repeated except that the polyethylene glycol in the paint for forming a coating film on the positive electrode was changed to polypropylene glycol.
An R5-type battery was manufactured in the same manner as in Example 1.

Example 5 An R5-type battery was manufactured in the same manner as in Example 1 except that the polyethylene glycol in the coating film for forming a positive electrode coating film of Example 1 was changed to a propylene oxide-ethylene oxide copolymer.

Comparative Example 1 0.75 parts by weight (solid content) of polyvinyl butyral in the coating film forming coating for the positive electrode of Example 1 was changed to 1.0 part by weight (solid content), and polyethylene glycol was added. An R5-type battery was produced in the same manner as in Example 1, except that 0.25 parts by weight (however, solid content) was changed to 0 parts by weight (that is, polyethylene glycol was not used at all).

Comparative Example 2 0.75 parts by weight (but the solid content) of polyvinyl butyral in the paint for forming a coating film of the positive electrode in Example 1 was changed to 0 part by weight (that is, polyvinyl butyral was not used at all). An R5 type battery was produced in the same manner as in Example 1 except that 0.25 parts by weight (solid content) of polyethylene glycol was changed to 1.0 part by weight (solid content).

Comparative Example 3 In place of the fine powder of polytetrafluoroethylene in the paint for forming a coating film of the positive electrode in Example 1, 5 parts by weight of a 60% dispersion of polytetrafluoroethylene (solid content of polytetrafluoroethylene was 3 parts by weight), 1 part by weight of carboxymethyl cellulose was used instead of 0.75 parts by weight of polyvinyl butyral and 25 parts by weight of polyethylene glycol, and 40 parts by weight of a mixed solvent of cyclohexanone and toluene was changed to 38 parts by weight of distilled water. Otherwise, the procedure of Example 1 was repeated to fabricate an R5 battery.

Comparative Example 4 Dibutyl phthalate was used in place of 0.25 parts by weight of polyethylene glycol in the coating material for forming a coating film of the positive electrode in Example 1 with 0.1 part by weight.
An R5-type battery was produced in the same manner as in Example 1, except that 25 parts by weight was used.

The battery capacities of the batteries of Examples 1 to 5 and Comparative Examples 1 to 4 manufactured as described above were measured. Table 1 shows the results. The method for measuring the battery capacity is as follows.

Measurement method of battery capacity: When the charge / discharge current was indicated by C, charge / discharge was performed with R5 type at 560 mA as 1C. Charging was performed at a constant voltage of 4.1 V with a 1 C current limiting circuit, and discharging was performed until the voltage between the electrodes of the battery dropped to 2.75 V. Then, the discharge capacity at this time was measured, and the ratio of the discharge capacity of the battery of Example 1 to the discharge capacity of the other batteries was determined as 100%. Table 1 shows the capacity (%) when the discharge capacity of Example 1 was set to 100%.
As shown.

[0064]

[Table 1]

* 1: PTFE = polytetrafluoroethylene * 2: PVB = polyvinyl butyral * 3: PEG = polyethylene glycol * 4: PPG = polypropylene glycol * 5: PEC = propylene oxide-ethylene oxide copolymer

[0066]

[Table 2]

* 1: PTFE = polytetrafluoroethylene * 2: PVB = polyvinyl butyral * 3: PEG = polyethylene glycol * 6: CMC = carboxymethyl cellulose * 7: DBP = dibutyl phthalate

As is clear from the comparison between the capacities (%) of Examples 1 to 5 shown in Table 1 and the capacities (%) of Comparative Examples 1 to 4 shown in Table 2, PTFE (polytetrafluoroethylene) was used as the binder. And PVB (polyvinyl butyral) and P
The batteries of Examples 1 to 5 using EG (polyethylene glycol), PPG (polypropylene glycol), or PEC (propylene oxide-ethylene oxide copolymer) had a large capacity (%) and a high capacity.

On the other hand, P as a binder for the positive electrode
The battery of Comparative Example 1 using TFE (polytetrafluoroethylene) and PVB (polyvinyl butyral) and PTFE
The batteries of Comparative Example 2 using (polytetrafluoroethylene) and PEG (polyethylene glycol)
The capacity was smaller than that of the battery of No. 5.

Further, PTFE is used as a binder for the positive electrode.
The battery of Comparative Example 3 in which (polytetrafluoroethylene) and CMC (carboxymethylcellulose) were used as a paint and water was used as a solvent, had a very small capacity, and PTFE (polytetrafluoroethylene) and DBP (phthalate) The battery of Comparative Example 4 using (dibutyl acid) also had a small capacity.

[0071]

As described above, according to the present invention,
A high-capacity lithium secondary battery with less deterioration of the positive electrode active material can be provided.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing one example of a lithium secondary battery of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Positive electrode 2 Negative electrode 3 Separator 4 Electrolyte

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location H01M 10/40 H01M 10/40 Z // C08L 71/02 LPZ C08L 71/02 LPZ C09D 171/02 PLQ C09D 171/02 PLQ

Claims (1)

[Claims] 1. A lithium secondary battery in which a sheet-shaped positive electrode and a sheet-shaped negative electrode are spirally wound with a separator interposed therebetween, wherein the sheet-shaped positive electrode has a coating containing at least a positive electrode active material and a binder on a conductive substrate. The binder of the sheet-shaped positive electrode is formed from a film, and the binder of the sheet-like positive electrode is polytetrafluoroethylene, polyvinyl butyral, and polyethylene glycol, polypropylene glycol, polyethylene oxide, polypropylene oxide and propylene oxide-ethylene oxide copolymer. A lithium secondary battery comprising at least one selected from the group consisting of: