JP2002008725A - Lithium polymer secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium polymer secondary battery. SOLUTION: This lithium polymer secondary battery has an active material layer having such structure that an electrolyte concentration in an active material is decreased toward a current collector; a lithium ion polymer battery forms such structure that the electrolyte concentration in the active material layer is decreased toward the current collector by the diffusion process of the electrolyte into the active material layer; or the lithium ion polymer secondary battery has an adhesion layer containing conductive particles between the current collector and the active material layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates mainly to a large battery or a notebook personal computer for electric vehicles and hybrid vehicles,
The present invention relates to a secondary battery or the like for a battery or the like for a portable device such as a mobile phone.

[0002]

2. Description of the Related Art The prior art is disclosed in Japanese Patent Application Laid-Open No. Hei 9-18596.
As shown in No. 0, an active material layer composed of an active material and a binder was laminated on the current collector surface, and the composition of the active material layer was changed in the thickness direction. A non-aqueous electrolyte secondary battery including an electrode plate with a high binder concentration on the current collector side in order to increase the adhesion between the current collector and the active material layer is known.

[0003]

When a polymer battery is manufactured with the structure shown in the above-mentioned prior art, the impedance at the interface between the polymer electrolyte and the active material layer increases, and the output characteristics deteriorate. There was a problem.

[0004]

Means for Solving the Problems In order to solve the above-mentioned problems, the present inventors have made intensive research and development and found that the problems can be solved by adjusting the concentration of the electrolyte in the active material layer. .

The present invention has been made based on the above findings. (1) A lithium polymer as an active material having a structure in which the concentration of the electrolyte in the active material decreases toward the current collector. 2. The lithium ion polymer secondary according to claim 1, wherein the secondary battery has (2) a structure in which the concentration of the electrolyte in the active material layer is reduced toward the current collector by diffusion treatment of the electrolyte into the active material layer. The battery is characterized by (3) the lithium ion polymer secondary battery described in (1) or (2), which has an adhesive layer containing conductive particles between the current collector and the active material layer.

In the present invention, by making the electrolyte concentration on the polymer electrolyte layer side higher than on the active material layer side, the impedance at the interface between the polymer electrolyte layer and the active material layer is reduced, and the output characteristics of the battery are reduced. Is improved. However, depending on the type of the active material or the electrolyte, the adhesion to the current collector foil may be reduced. Therefore, by providing an adhesive layer containing conductive particles between the current collector and the active material layer, the adhesive force between the current collector and the active material layer is improved, the impact resistance is increased, and heat resistance is also reduced. , No peeling,
Reliability is improved.

[0007]

Embodiments of the present invention will be described below. As the current collector used in the lithium polymer secondary battery of the present invention, for example, a metal foil such as aluminum and copper is preferably used. As the thickness of the metal foil,
One having a thickness of about 5 to 30 μm is used. In a preferred embodiment of the present invention, first, a coating liquid comprising an active material and a binder is applied to one surface of the current collector. As the active material, a positive electrode active material and a negative electrode active material are used. It is preferable that these active materials are uniformly dispersed in the formed coating layer. Therefore, in the present invention, the active material has a particle size in the range of 1 to 100 μm and an average particle size of 5 to 2 μm.
It is preferable to use a powder of about 0 μm. Further, it is possible to add a dispersant. Next, the above-mentioned powdered active material and the binder are placed in a dispersion medium composed of an appropriate organic solvent, and a composition obtained by further mixing a conductive agent, if necessary, is added to a composition known in the art. The slurry is prepared by mixing and dispersing using a suitable dispersing machine.

[0008] In the present invention, the above-mentioned current collector is provided on one surface.
A positive electrode active material layer or a negative electrode active material layer is formed. In the present invention
As the positive electrode active material used, for example, LiCoO_Two,
LiNO_Two, LiMn_TwoO_Four, LiMnO_TwoEtc. lithium oxidation
Thing, TiS_Two, MnO_Two, MoO_Three, V_TwoO_FiveEtc. chalcogen
One of the compounds or a combination of multiple
It is. On the other hand, as the negative electrode active material, metallic lithium, lithium
Alloy, or graphite, carbon black,
Carbonaceous materials such as acetylene black or lithium ion
A material that intercalates the ON is preferably used.
You. In particular, LiCoO _TwoAs a positive electrode active material, a carbonaceous material
As a negative electrode active material, high discharge voltage
A lithium secondary battery is obtained.

Examples of the binder used for preparing the coating solution containing the active material include polyvinylidene fluoride resin, polyester resin, polyamide resin, polyacrylate resin, polycarbonate resin, and polyurethane resin. Thermoplastic resin such as cellulose resin, polyolefin resin, polyvinyl resin, fluorine resin and polyimide resin, or rubber resin, acrylate monomer
Alternatively, an ionizing radiation-curable resin comprising an oligomer or a mixture thereof, and a mixture of these various resins can be used.

The above-mentioned dispersion medium comprises an organic solvent such as toluene, methyl ethyl ketone, N-methylpyrrolidone, acetone or a mixture thereof. As the above-mentioned dispersing machine, a conventionally known homogenizer, ball mill, sand mill, roll mill and the like are used.

The coating method of the present invention includes, for example, gravure coat, gravure reverse coat, roll coat,
Myr bar coat, blade coat, knife coat,
Air knife coating, comma coating, slot die coating
, Slide coat, dip coat, doctor blade method and the like are used. The thickness of the coating layer is 1
It is in the range of 0 to 250 μm, preferably 50 to 200 μm.

In order to further improve the uniformity of the coating layer formed by coating and drying, the coating layer is coated with a metal
It is also preferable to perform a press treatment using a roll, a heating roll, a sheet press machine or the like. Pressing conditions at this time include:
If it is less than 500 kgf / cm ^2, it is difficult to obtain uniformity of the coating layer, and if it exceeds 7,500 kgf / cm ² ,
The pressing conditions are preferably in the range of 500 to 7,500 kgf / cm ² because the electrode plate itself including the current collector base material is damaged. More preferably, 3,000-5,000 Kg
f / cm ² .

The lithium salt of the solute forming the electrolytic solution of the present invention includes, for example, LiClO ₄ , LiBF ₄ , LiP
Inorganic lithium salts such as F ₆ , LiAsF ₆ , LiCl, and LiBr; and LiB (C ₆ H ₆ ) ₄ , LiN (SO ₂ CF ₃ ) ₂ ,
LiC (SO ₂ CF ₃ ) ₃ , LiOSO ₂ CF ₃ , LiOSO ₂
C ₂ F ₅ , LiOSO ₂ C ₃ F ₇ , LiOSO ₂ C ₄ F ₉ , LiO
SO ₂ C ₆ F ₁₁ , LiOSO ₂ C ₆ F ₁₃ , LiOSO ₂ C ₇ F ₁₅
And the like are used.

The organic solvent for the solute of the electrolytic solution of the present invention includes cyclic esters, chain esters, cyclic ethers, chain ethers and the like. Examples of the cyclic esters include ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, 2-methyl-γ-butyrolactone, and acetyl-γ-butyrolactone. , Γ-valerolactone and the like.

Examples of the chain esters include dimethyl carbonate, diethyl carbonate, dibutyl carbonate and the like.
Carbonate, dipropyl carbonate, methyl ethyl carbonate
Examples include carbonate, methyl butyl carbonate, methyl propyl carbonate, ethyl butyl carbonate, ethyl propyl carbonate, alkyl propionate, dialkyl malonate and alkyl acetate.

Examples of the cyclic ethers include tetrahydrofuran, alkyltetrahydrofuran, dialkylalkyltetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolan, alkyl-1,3-dioxolan, and 1,4 -Dioxolane and the like. Examples of chain ethers include 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, and tetraethylene glycol dialkyl ether. No.

Next, the polymer copolymer is dissolved in an organic solvent at a predetermined temperature, and an electrolytic solution is stirred and mixed therein to produce a gelled electrolyte slurry, which is dried under a constant temperature condition. Then, a polymer electrolyte sheet was prepared, the polymer electrolyte sheet was overlaid on the above-mentioned positive electrode sheet, hot pressed, and subjected to a diffusion treatment under predetermined conditions. Next, similarly, a polymer electrolyte sheet was overlaid on the negative electrode sheet, and diffusion treatment was performed under predetermined conditions. Next, the two sheets after the treatment are overlapped so that the electrolyte layers match, and then thermocompression-bonded at a predetermined temperature by a hot roll to form the battery of the present invention.

[0018]

Embodiments of the present invention will be described below in detail. Electrodug manufactured by Acheson Japan was applied to an aluminum foil or a copper foil to a thickness of 3 μm by a doctor blade method to form an adhesive layer. First, 70 g of LiCoO ₂ powder and 4 g of Ketjen Black were dispersed and mixed in an N-methylpyrrolidone solution of polyvinylidene fluoride to prepare a slurry. In addition,
The solids weight composition in the slurry is LiCoO ₂ (89
%) And polyvinylidene fluoride (6%). The slurry is applied on an aluminum foil having an adhesive layer formed thereon by a doctor blade method, dried, and roll-rolled to form an active material film having a thickness of 80 mm.
A μm positive electrode sheet was prepared. Next, 50 g of flaky natural graphite powder was dispersed and mixed in an N-methyl bilolidone solution of polyvinylidene polyvinylidene to prepare a slurry. The weight composition of the solids in the slurry was graphite powder (90%) and polyvinylidene fluoride (10%). This slurry was applied on a copper foil having an adhesive layer formed thereon by a doctor blade method, dried and then rolled to form a negative electrode sheet having an active material film thickness of 50 μm.
Was made. Next, a solution prepared by dissolving lithium hexafluorophosphate in an equal volume of a mixed solvent of ethylene carbonate and diethyl carbonate at a concentration of 1 mol / l was used as an electrolytic solution. Subsequently, a vinylidene fluoride-hexafluoropropylene copolymer (Kynar2, manufactured by Elphatochem)
80l: product containing 12% by weight of hexafluoropropylene)
After dissolving 40 g in 200 g of dimethyl carbonate at 60 ° C., 80 g of the electrolytic solution was stirred and mixed, and an electrolyte slurry was obtained.
Was prepared. The electrolyte slurry is cast on release paper at 80 ° C., dried at 60 ° C. for 3 minutes, and polymer electrolyte
Was made. The above-mentioned polymer electrolyte sheet was similarly stacked on the above-mentioned positive electrode sheet. Thickness of the stacked sheets is 100
Using a hot press with 9 μm PET film scissors
The positive electrode-electrolyte diffusion treatment was performed at 0 ° C. × 0.5 kg / cm ² for 5 minutes. Next, a polymer electrolyte sheet was similarly scissored on a 100 μm-thick PET film on the above-mentioned negative electrode sheet, and 90 ° C. × 0.5 kg using a hot press.
/ Cm ² for 5 minutes to perform a negative electrode-electrolyte diffusion treatment. After the two kinds of sheets after the treatment were overlapped so that the electrolyte layers matched each other, thermocompression bonding was performed by a heat roll at 110 ° C.
The cross section of the battery is observed by EPMA, and the electrolyte is diffused into the negative electrode sheet, and the active material layer having a structure in which the concentration of the electrolyte in the active material decreases toward the current collector is formed. Was confirmed (Figure (a)). A charge / discharge test of this battery was performed. At 70 mA, it was 35 mAh. Even at a high rate of 700 mA, a high discharge capacity of 300 mAh was obtained.
A temperature cycle of 0 ° C x 30 minutes and 50 ° C x 30 minutes is 100
After repetition, a charge / discharge test was performed. 350 mAh at 70 mA discharge

[0019]

Comparative Example 1 For comparison, a positive electrode sheet, a polymer, an electrolyte, and a negative electrode sheet were stacked in this order, and then thermocompression-bonded by a heat roll at 110 ° C. The cross section of the battery was observed by EPMA, and it was confirmed that the electrolyte did not diffuse into the negative electrode sheet and did not constitute the present invention (FIG. (B)). The result was 350 mAh at 70 mA, but 700 mA
At a high rate, the discharge capacity was as low as 50 mAh.

[0020]

Comparative Example 2 For comparison, a battery was prepared using aluminum and copper foil without forming an adhesive layer. The manufacturing method is the same as that of the embodiment except for the formation of the adhesive layer. This battery is 0 ° C x 30
After repeating a temperature cycle of 50 ° C. × 30 minutes for 100 times, a charge / discharge test was performed. 30mAh at 70mA discharge
And low discharge capacity. As a result of observing the inside of the battery,
1 A part of the interface between the foil-positive electrode and the Cu foil-negative electrode was peeled off.

[0021]

As is clear from the above Examples and Comparative Examples, in the present invention, a lithium polymer secondary battery is
By having an active material layer having a structure in which the concentration of the electrolyte in the active material decreases toward the current collector, the impedance at the interface between the polymer electrolyte and the active material layer is reduced, and the output characteristics of the battery are reduced. The effect of improving is obtained. Current collector
By providing an adhesive layer containing conductive particles between the active material layers, the adhesive force between the current collector and the active material layer is improved, the flexibility and the adhesion are improved, the impact resistance is increased, and heat change is prevented. On the other hand, there is no peeling or the like, and the effect of improving reliability is obtained.

[Brief description of the drawings]

FIG. 1 (a) is a result of an EPMA line analysis of an example of the present invention.

FIG. 1 (b) shows the result of EPMA line analysis of a comparative example of the present invention.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Sawako Takeuchi 1-297 Kitabukurocho, Omiya City, Saitama Prefecture Inside Mitsubishi Research Institute, Inc. (72) Inventor Tadashi Kobayashi 1-297 Kitabukurocho, Omiya City, Saitama Mitsubishi Materia Al F-term in the Research Institute, Inc. (reference) CA09 CA11 CB08 CB09 CB12 DA04 DA10 DA11 EA08 FA02 FA12 FA18 HA12

Claims (3)

[Claims] 1. A lithium polymer secondary battery comprising an active material layer having a structure in which the concentration of an electrolyte in the active material decreases toward the current collector. 2. The lithium ion polymer secondary battery according to claim 1, wherein the structure for decreasing the electrolyte concentration of the active material layer toward the current collector is formed by a diffusion treatment of the electrolyte into the active material layer. . 3. The lithium ion polymer secondary battery according to claim 1, further comprising an adhesive layer containing conductive particles between the current collector and the active material.