JP2000195522A - Nonaqueous electrolyte seconday battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent collapse of an electrode main body by producing an electrode mix by a first process for mixing an active material, a polymer, and a solvent (a) and a second process for extracting the solvent (a) from a mixture with a solvent (b) compatible with the solvent (a). SOLUTION: A compound capable of storing/releasing lithium is used as a positive active material, an aluminum lithium alloy, a transition metal oxide such as WO2, or a metal lithium mixture is used as a negative active material, and an electrode for a nonaqueous electrolyte secondary battery having a porous polymer is produced. In order to produce the electrode, active material particles, a conductive auxiliary such as carbon, and a solution (a) prepared by dissolving a polymer in a solvent (a) are mixed to prepare paste, the paste is applied to a glass plate, immersed in an extraction solvent (b) to extract the solvent (a), and an electrode mix sheet having a porous polymer uniformly having pores communicating from the polymer surface to the active material surface in the pores within an active material layer or on the active material surface is produced. The electrode mix sheet peeled off from the glass plate is stuck onto an aluminum foil to form the electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an electrode for a non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery using the electrode.

[0002]

2. Description of the Related Art Conventionally, a process for manufacturing an electrode provided with a porous polymer electrolyte is as follows.

[0003] In the first step, a paste comprising an active material, a binder, a conductive additive and the like is applied on a current collector such as a metal foil and dried, so that the active material is integrated with the current collector. A molded electrode body is manufactured.

[0004] In a second step, the electrode body is treated with an organic solvent a.
Is immersed in a polymer solution a ′ in which the polymer is dissolved, and the polymer solution a ′ is uniformly penetrated into the pores in the active material layer of the electrode body.

The third step is a step of extracting a solvent a for dissolving the polymer in the polymer solution a '. When the electrode body holding the polymer solution a ′ in the pores in the active material layer is immersed in the solvent b having compatibility with the solvent a, the organic solvent a
The polymer is solidified in a state where the portion from which is removed becomes a hole. By this step, the electrode body is obtained in which the pores in the active material layer are uniformly provided with the porous polymer. Finally, by drying, the attached water and the like are removed, and the electrode is completed.

[0006]

In the conventional method of manufacturing an electrode having a porous polymer electrolyte, it is necessary to immerse the electrode body in a polymer solution in the second step so that the electrode body contains the polymer solution a '. there were. When the electrode body is immersed in the polymer solution, the electrode active material particles, and also the electrode active material particles, the conductive auxiliary and the binder bonding the current collector are dissolved by the solvent a in which the polymer is dissolved, The electrode body sometimes collapsed.

[0007]

As a result of various studies for solving the above-mentioned problems, the following invention has been made. That is, in the present invention, in the first step, at least the active material, the polymer, and the solvent a are mixed, and then the mixture prepared in the first step is applied on a smooth plate, and then the solvent a A second step of extracting the solvent a in which the polymer is dissolved by immersing the porous polymer in a soluble solvent b, wherein the porous polymer is uniformly provided between the active material layers and the active material surface. An electrode mixture is formed, and then the electrode is manufactured by integrating the electrode mixture and the current collector.

Further, the present invention is characterized in that the current collector is a metal or a conductive polymer, and the shape of the current collector is a sheet, a sheet having holes, or a three-dimensional porous body.

Further, according to the present invention, the porosity of the electrode is 50%.
It is characterized by the following. Further, in the present invention, a porous polymer electrolyte is obtained by including an organic electrolyte in the porous polymer.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for manufacturing an electrode for a lithium battery according to the present invention and an embodiment in which the electrode is used as a battery will be described. The positive electrode active material used in the present invention may be any compound as long as it is a compound capable of inserting and extracting lithium. As the inorganic compound, a composition formula Li _x MO ₂ ,
Or Li _y M ₂ O ₄ (where M is a transition metal, 0 ≦ x ≦
1,0 ≦ y ≦ 2), or _{Li x M y N 1 - y} O 2 ( wherein M
Is a transition metal, N is a metal, and a complex oxide represented by 0 ≦ x ≦ 1, 0 ≦ y ≦ 1 containing at least one element in the group consisting of P and B, and having a tunnel-like hole. Oxides and metal chalcogenides having a layered structure can be used. Specific examples thereof include LiCoO ₂ , LiNiO ₂ , and LiMn ₂
O ₄ , Li ₂ Mn ₂ O ₄ , LiNi _0.5 Co _0.5 O ₂ , LiNi
_0.8 Co _0.17 Al _0.03 O ₂ , LiNi _0.8 Co _0.17 B
_0.03 O ₂ , MnO ₂ , FeO ₂ , V ₂ O ₅ , V ₆ O ₁₃ , TiO
₂ , TiS _{2 and the} like. Examples of the organic compound include a conductive polymer such as polyaniline. Furthermore, regardless of inorganic compounds or organic compounds,
The above-mentioned various active materials may be used as a mixture.

As the negative electrode active material, for example, Al, Si,
Alloy of lithium with Pb, Sn, Zn, Cd, etc., LiF
Transition metal composite oxides such as e ₂ O ₃ ; transition metal oxides such as WO ₂ and MoO _2; carbonaceous materials such as graphite and carbon; lithium nitride such as Li ₅ (Li ₃ N); And mixtures thereof.

The polymer provided on the electrode is preferably a polymer having flexibility capable of changing its shape following the volume expansion and contraction of the active material due to charge and discharge, and a gel-like ionic conductive polymer obtained by swelling the polymer with an electrolytic solution. It is better to use Specifically, polyvinylidene fluoride (PVd
F) / hexafluoropropylene (HFP) copolymer,
Polyether such as polyvinylidene fluoride, hexafluoropropylene, polyvinyl chloride, polyacrylonitrile, polyethylene oxide, polypropylene oxide, polyacrylonitrile, polyvinylidene fluoride, polyvinylidene chloride, polymethyl methacrylate,
Polymethyl acrylate, polyvinyl alcohol, polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone, polyethylene imine, polybutadiene,
Polystyrene, polyisoprene, or these inducers can be used alone or as a mixture.
Further, a polymer obtained by copolymerizing various monomers constituting the above polymer can also be used.

In the present invention, a solvent extraction method is used to make the polymer provided on the electrode porous. In the solvent extraction method, two types of solvents a and b are used. The solvent a is a solvent that dissolves the polymer. Solution a 'is composed of solvent a and a polymer. The solvent b is an extraction solvent for extracting the solvent a from the solution a ′. In the solvent extraction method, a solution a ′ in which a polymer is dissolved is immersed in a solvent b compatible with the solvent a, thereby extracting the solvent a of the polymer solution a ′ and removing the solvent a of the polymer. Becomes a hole,
This is to obtain a porous polymer. In the solvent extraction method, a circular opening is formed in the polymer membrane.

Examples of the solvent a for dissolving the polymer include carbonates such as dimethylformamide, propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate;
Ethers such as dimethyl ether, diethyl ether, ethyl methyl ether and tetrahydrofuran, dimethylacetamide, 1-methyl-pyrrolidinone, n-methyl-
Solvents that dissolve polymers such as 2-pyrrolidone are exemplified.

The extraction solvent b may be compatible with the solvent a, and may be water, alcohol, acetone or the like, or a mixture thereof. Examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol and the like, or a mixture thereof.

In order to produce an electrode for a non-aqueous electrolyte secondary battery having a porous polymer in the electrode, for example, for a positive electrode,
A paste obtained by mixing the active material particles and a conductive auxiliary such as carbon, and a polymer solution a ′ obtained by dissolving the polymer described above in a solvent a is applied on a glass plate, and then immersed in an extraction solvent b. The solvent a is extracted to produce an electrode mixture sheet having a porous polymer having pores in the active material layer and holes uniformly communicating from the polymer surface to the active material surface. The electrode mixture sheet peeled from the glass plate is pasted on an electrode mixture sheet on an aluminum foil and pressed to form an electrode.

The substrate on which the paste composed of the polymer solution and the active material is applied is preferably a smooth plate such as a metal plate or glass, or a smooth sheet such as silica paper.

The current collector to which the electrode mixture is adhered may be any material having conductivity, such as metals such as aluminum, copper, zinc, and iron; conductive polymers such as polypyrrole and polyaniline; A sheet made of a mixture, a sheet having holes, or a three-dimensional porous body may be used.

As an adhesive for bonding the electrode mixture and the current collector, any adhesive can be used as long as the electrode mixture and the current collector can be bonded, and preferably, carbon or the like showing conductivity is used.

By immersing the separator between the positive electrode and the negative electrode thus obtained in a non-aqueous electrolyte, the porous polymer becomes a gel-like ionic conductive polymer, and is used for a non-aqueous electrolyte secondary battery. A battery with a porous polymer electrolyte is completed. Further, as the separator, a polypropylene microporous membrane, a polyethylene microporous membrane, or a separator composed of a polymer constituting the porous polymer electrolyte may be used.

[0021]

The preferred embodiments of the present invention will be described below.

Example 1-1 As a preferred embodiment of the present invention, Li _0.83 Ni _0.17 CoO _{2 was used for} the positive electrode, graphite was used for the negative electrode, and vinylidene fluoride / hexafluoropropylene copolymer (P) was used as the material of the porous polymer electrolyte.
(VdF / HFP)) will be described.

First, the production of the positive electrode will be described. Li
_0.83 Ni _0.17 CoO ₂ 72.7 wt%, acetylene black 1.6 wt%, P (VdF / HFP) (HFP is 5
%) A mixture of 3.1 wt% and NMP 22.6 wt% was applied on a smooth glass plate. Next, in order to extract NMP in which the polymer was dissolved, the glass plate on which the paste was applied was immersed in water to which 25 wt% of methanol was added. In this way, a positive electrode mixture having a porous polymer uniformly in the pores in the active material layer and the surface of the active material is completed. The positive electrode mixture was peeled off from the glass plate and dried at 130 ° C.

Next, a positive electrode mixture was applied to both sides of a 20 μm-thick aluminum foil and pressed to form a positive electrode. A carbon paste was applied to the surface of the aluminum foil in order to bond the electrode mixture and the aluminum foil current collector well. The porosity of the pressed electrode was 30%. The thickness of the electrode after pressing was 160 μm, and the total weight of the active material and the conductive auxiliary filled per unit area was 21 mg /
cm ² .

Next, the production of the negative electrode will be described. 51.9% by weight of graphite, P (VdF / HFP) (HF
A mixture of 5.8 wt% of P and 42.3 wt% of NMP was applied on a smooth glass plate. Next, in order to extract NMP in which the polymer was dissolved, the glass plate coated with the paste was immersed in water. Thus, a negative electrode mixture having a porous polymer uniformly in the holes in the active material layer and the active material surface is completed. After the negative electrode mixture was peeled off from the glass plate, it was dried at 100 ° C., and the negative electrode mixture was attached to both surfaces of a copper foil having a thickness of 14 μm and pressed to form a negative electrode. A carbon paste was applied to the surface of the copper foil in order to favorably bond the negative electrode mixture and the copper foil current collector. The porosity of the pressed electrode was 35%. The thickness of the electrode after pressing was 190 μm, and the total weight of the active material filled per unit area was 14 mg / cm ² .

A porous P (VdF / HFP) electrolyte membrane (manufactured by Toyo Cloth; N
-13-1, porosity 44%, film thickness 26.7 μm, HFP
(12%) was inserted and wound into a stainless steel case having a bottom surface with a radius of 6.7 mm and a height of 47.0 mm to assemble a cylindrical battery. Then 1
2.5 g of a mixed electrolyte (volume 1: 1) of ethylene carbonate containing M LiPF ₆ and diethyl carbonate was added, and finally, aging treatment was performed at 60 ° C. for 48 hours.
A battery (A) according to the present invention having a nominal capacity of 520 mAh was prepared.

Example 1-2 A positive electrode mixture prepared through the same steps as in Example 1-1 was attached to an aluminum mesh and pressed to form a positive electrode. The positive electrode mixture was cut into the mesh by pressing. The porosity of the pressed electrode was 30%. The negative electrode mixture prepared through the same steps as in Example 1-1 was attached to a copper mesh and pressed to form a negative electrode. The press cut the negative electrode mixture into the mesh. The porosity of the pressed electrode was 35%. A carbon paste was applied to the mesh surface in order to bond the electrode mixture and the mesh well.

The subsequent steps were the same as in Example 1-1, and a battery (B) according to the present invention was manufactured.

Example 1-3 A positive electrode mixture prepared through the same steps as in Example 1-1 was applied to an aluminum foam and pressed to form a positive electrode. The positive electrode active material assemblage was embedded in the foam by pressing, and the porosity of the electrode after pressing was 30%.

The negative electrode mixture prepared through the same steps as in Example 1-1 was applied to a copper foam and pressed to obtain a negative electrode. The negative electrode mixture was embedded in the foam part by pressing, and the porosity of the pressed electrode was 35%. In order to favorably bond the electrode mixture and the foam, a carbon paste was applied to the surface of the foam. The subsequent steps were the same as in Example 1-1, and the battery (C) according to the present invention was used.
Was made.

Comparative Example 1 For comparison, a conventionally known battery was prepared using Li _0.83 Ni _0.17 CoO ₂ as a positive electrode active material, graphite as a negative electrode active material, and a polypropylene microporous separator as a separator.

The production of the positive electrode will be described. Li _0.83 N
i _0.17 CoO ₂ 66.8 wt%, acetylene black 1.4 wt%, PVdF 2.8 wt%, NMP 29 wt%
% Was applied to both sides of an aluminum foil having a width of 20 mm, a length of 480 mm, and a thickness of 20 μm, dried at 90 ° C. to evaporate NMP, thereby preparing a positive electrode. The production of the negative electrode will be described. Graphite 81wt%, P
A mixture of (VdF / HFP) 9 wt% and NMP 10 wt% is applied to both sides of a copper foil having a thickness of 14 μm,
Then, the NMP was evaporated to prepare a negative electrode body.

A 26 μm-thick polypropylene microporous separator was interposed between the positive electrode and the negative electrode, and the resultant was rolled up and wound, having a bottom radius of 6.7 mm, a height of 47.0 mm, and a height of 47.0 mm.
To assemble a cylindrical battery. Thereafter, a mixture of ethylene carbonate containing 1 M LiPF ₆ and diethyl carbonate (volume 1: 1)
2.5 g of the electrolytic solution was added, and finally, aging treatment was performed at 60 ° C. for 48 hours to prepare a conventionally known battery (D) having a nominal capacity of 520 mAh.

[Discharge Characteristics] The battery (A) according to the present invention,
(B), (C) and a conventionally known battery (D) were charged at room temperature to 4.1 V at a current of 1 CA, then charged at a constant voltage of 4.1 V for 2 hours, and then charged at a current of 1 CA to 2 V. Discharged to .75V. Table 1 shows the results of the discharge test. According to the results, the batteries (A) to (C) according to the present invention were obtained.
It can be seen that the sample shows better discharge performance than the conventionally known battery (D).

In the embodiment, as the current collector, aluminum was used for the positive electrode and copper was used for the negative electrode. However, any material having electrical conductivity may be used, and a metal such as iron or zinc, or a conductive polymer such as polyaniline may be used. Is also good. In addition, although an expanded metal or the like was used as the current collector, the same performance as the battery according to the present invention was exhibited.

In the embodiment, 1 M of L is used as the electrolytic solution.
A mixed (volume 1: 1) electrolytic solution of ethylene carbonate and diethyl carbonate containing iPF ₆ is used, but is not limited thereto. For example, ethylene carbonate, propylene carbonate, dimethyl carbonate,
Polar solvents such as diethyl carbonate, γ-butyrolactone, sulfolane, dimethylsulfoxide, acetonitrile, dimethylformamide, dimethylacetamide, 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, dioxolane, and methyl acetate Alternatively, a mixture thereof may be used. Further, in the examples,
LiPF ₆ is used as a salt to be contained in the electrolytic solution. In addition, for example, LiBF ₄ , LiAsF ₆ , LiC
10 ₄ , LiSCN, LiI, LiCF ₃ SO ₃ , LiC
1, a lithium salt such as LiBr, LiCF ₃ CO ₂ , or a mixture thereof may be used.

[0037]

According to the present invention, when producing an electrode holding a porous polymer electrolyte, a paste comprising an active material, a conductive auxiliary agent, a polymer and a solvent for dissolving the polymer is applied to a smooth plate such as a glass plate. After coating on the top, the solvent that dissolves the polymer is extracted by the solvent extraction method, and pores between the active material layers, and an electrode mixture having a porous polymer electrolyte uniformly on the active material surface are manufactured. When the electrode body is immersed in a polymer solution, the active material particles and the binder that bonds the active material and the current collector dissolve the polymer. The electrode body is surely prevented from disintegrating by dissolving the solvent and collapsing the electrode body.

Further, by providing a porous polymer electrolyte in the electrode, the electrolyte can be uniformly distributed in the positive and negative electrodes, so that the current distribution in the positive and negative electrodes during charge and discharge is uniform. This makes it possible to perform charging and discharging at a high rate, prevent the deposition of alkali metal dendrite on the negative electrode during charging, and provide a safer battery.

[0039]

[Brief description of the drawings]

FIG. 1 shows batteries (A) to (C) using electrodes according to the present invention.
FIG. 7 is a diagram showing the discharge characteristics after 4.1 V charging of a battery (D) using conventional electrodes.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01M 10/40 H01M 10/40 BF Term (Reference) 5H003 AA01 AA04 BA02 BA03 BB05 BB11 BB32 BB41 BC04 BD05 5H014 AA02 AA04 AA06 BB03 BB06 CC01 CC04 EE01 EE05 HH02 5H017 AA03 AS02 AS05 AS10 CC01 CC25 DD01 DD05 EE01 EE06 EE07 EE10 HH02 5H029 AJ02 AJ03 AJ05 AJ12 AK01 AK02 AK03 AK05 AM04 AM03 AL06 AL01 AL02 AL03 CJ12 DJ06 DJ07 DJ13 DJ14 EJ01 EJ03 EJ04 HJ09

Claims (5)

[Claims] 1. A first step of mixing at least an active material, a polymer and a solvent a, and a second step of extracting the mixture prepared in the first step with a solvent b compatible with the solvent a. A method for producing an electrode mixture for a non-aqueous electrolyte secondary battery, comprising: 2. An electrode for a non-aqueous electrolyte secondary battery, comprising the electrode mixture according to claim 1 and a current collector. 3. The electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the current collector is a sheet made of a metal or a conductive polymer, a sheet having holes, or a three-dimensional porous body. 4. The electrode for a non-aqueous electrolyte secondary battery according to claim 2, wherein the porosity of the electrode is 50% or less. 5. A non-aqueous electrolyte secondary battery comprising the positive electrode and / or the negative electrode according to claim 2, 3, or 4.