JP2006066243A - Method of manufacturing electrode plate for non-aqueous electrolytic liquid secondary battery, and non-aqueous electrolytic liquid secondary battery using electrode plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of manufacturing an electrode plate superior in adhesion with an active material mixture and conductivity, and a non-aqueous electrolytic liquid secondary battery superior in cycle life characteristics using the electrode plate. <P>SOLUTION: The method of manufacturing the electrode plate for a non-aqueous electrolytic liquid secondary battery is characterized in that an active material mixture paste containing a dispersant and a binder is coated on a current collector, and after drying and removing the dispersant, pressurized, and subsequently, heat-treated under the temperature of crystallization temperature or more and less than the melting point of the binder. The method of manufacturing the electrode plate for non-aqueous electrolytic liquid secondary battery is configured such that the active material mixture contains a lithium complex oxide which can store and release lithium ions or contains a carbon material which can absorb and release lithium ions. The non-aqueous electrolytic liquid secondary battery uses the electrode plate manufactured by the above manufacturing method at least for one of the positive electrode or negative electrode. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method for producing an electrode plate for a non-aqueous electrolyte secondary battery in which an active material mixture is hardly peeled off and excellent in conductivity, and a non-aqueous electrolyte secondary battery excellent in cycle life characteristics using the electrode plate About.

  Lead-acid batteries, nickel-cadmium batteries, nickel-hydrogen batteries, etc. are used for electronic devices. However, in recent years, as electronic devices become more sophisticated, more compact, and more portable, there are even higher energy density storage batteries. In response to this, negative electrode plates using metal lithium, lithium alloys, carbon materials that can occlude and release lithium ions, and lithium-containing composite oxides, chalcogen compounds, and the like as active materials Lithium secondary batteries (non-aqueous electrolyte secondary batteries) combined with the positive electrode plate used in the above have been developed and partially used. This type of secondary battery is the most expected secondary battery (storage battery) in the future because of its high battery voltage and high energy density per weight and volume.

A positive electrode plate or a negative electrode plate used for a lithium secondary battery is mixed with a binder, a conductive agent, and the like in its active material, mixed with a dispersant, applied as a paste, and then applied to the current collector. It is manufactured by applying pressure after drying and removing the agent.
The cycle life of this lithium secondary battery strongly depends on the adhesion between the active material mixture and the current collector, and the adhesion between the active material mixtures. As a method for improving the property, a method of applying a paste while applying tension to a current collector and drying it has been proposed (Patent Document 1).

JP 2002-270161 A

However, even if the electrode plate with improved adhesion was used, a sufficient cycle life could not be obtained. Accordingly, the present inventors have conducted various studies on methods for producing electrode plates for nonaqueous electrolyte secondary batteries with the aim of improving cycle life. As a result, the active material mixture paste containing the dispersant and the binder applied to the current collector is subjected to drying removal of the dispersant, pressurization, and heat treatment in this order to thereby improve the adhesion of the active material mixture and the conductivity of the electrode plate. The inventors have found that the properties and the like are improved, and have further studied and completed the present invention.
It is an object of the present invention to provide a method for producing an electrode plate excellent in adhesion and conductivity of an active material mixture, and a non-aqueous electrolyte secondary battery excellent in cycle life characteristics using the electrode plate. .

  According to the first aspect of the present invention, after applying an active material mixture paste containing a dispersant and a binder to a current collector, the dispersant is dried and removed, and then pressurized, and then at or above the crystallization temperature of the binder and below the melting point It is the manufacturing method of the electrode plate for nonaqueous electrolyte secondary batteries characterized by heat-processing at the temperature of.

  The invention according to claim 2 is the non-aqueous electrolysis according to claim 1, wherein the active material mixture contains a lithium composite oxide capable of occluding and releasing lithium ions or a carbon material capable of absorbing and releasing lithium ions. It is a manufacturing method of the electrode plate for liquid secondary batteries.

  A third aspect of the invention is a non-aqueous electrolyte secondary battery in which an electrode plate produced by the production method of the first or second aspect is used for at least one of a positive electrode and a negative electrode.

  The invention according to claim 1 is a non-aqueous electrolyte secondary solution in which an active material mixture paste containing a dispersant and a binder is applied to a current collector, and then the dispersant is dried and removed, followed by pressurization and heat treatment in this order. This is a method for producing an electrode plate for a battery. The pressurization improves the adhesion of the active material mixture and makes it difficult for the active material mixture to be peeled off, and the heat treatment forms a conductive path by recrystallization of the binder. The conductivity of the electrode plate is improved. By the pressurization, the distance between the active material mixture (particles) is shortened, and a decrease in internal resistance can be expected.

  The invention according to claim 2 is a non-aqueous electrolyte secondary using an active material mixture containing, as the active material mixture, a lithium composite oxide capable of occluding and releasing lithium ions or a carbon material capable of absorbing and releasing lithium ions. This is a method for producing an electrode plate for a battery. Similarly to the case of the first aspect of the invention, an electrode plate is obtained in which the active material mixture is difficult to peel off and is excellent in conductivity.

  A third aspect of the present invention is a non-aqueous electrolyte secondary battery using the electrode plate of the first aspect of the present invention as at least one of a positive electrode and a negative electrode, and the secondary battery has an active material mixture of the electrode plate. Since it is difficult to peel off and the electrode plate has excellent conductivity, it has excellent cycle life characteristics.

  In particular, a lithium secondary battery using an active material mixture containing a lithium composite oxide capable of occluding and releasing lithium ions in the active material mixture has excellent cycle life characteristics, a high battery voltage, and a high weight per volume and volume. Because of its high energy density, it is advantageous for improving the performance, miniaturization, and portability of electronic devices.

  In the present invention, the active material mixture includes a positive electrode active material or a negative electrode active material, and a binder as essential components, and optionally includes other additives such as a conductive agent.

  The active material mixture paste is prepared by adding a dispersant to the active material mixture and mixing them. The paste can also be prepared by dissolving a binder in a dispersant and adding a positive electrode active material or the like thereto.

  In the present invention, the dispersant is usually removed by drying at a temperature of 60 to 130 ° C. If the temperature is less than 60 ° C., it takes a long time to remove the dispersant, resulting in poor productivity. If the temperature exceeds 130 ° C., the current collector (metal foil or the like) is oxidized and the adhesion to the active material mixture is lowered.

In the present invention, the pressurization after the drying can be performed by a conventional method using a metal roll, a heating roll, a sheet press machine or the like. When the pressure (pressing force) in the pressurization is less than 5000 N / cm ² , the adhesion, homogeneity, and conductivity of the active material mixture film are not sufficiently improved, and when it exceeds 74000 N / cm ² , the electrode plate itself ( (Including current collector) may be damaged. Therefore, the applied pressure is preferably 5000 to 74000 N / cm ² , particularly 30000 to 50000 N / cm ² .

  By the heat treatment after the pressurization, the binder is recrystallized, the conductive path cut by the pressurization is re-formed, and the conductivity of the electrode plate is improved.

  The heat treatment is performed at a temperature equal to or higher than the recrystallization temperature of the binder in order to recrystallize the binder, but the upper limit temperature is lower than the melting point of the binder. This is because the binder flows above the melting point of the binder, covers the interface between the current collector and the active material mixture, and the conductivity of the electrode plate decreases.

In the present invention, the positive electrode active material includes lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , TiO ₂ , MnO ₂ , MoO ₃ , V ₂ O ₅ , TiS ₂ , MoS _2. Any compound that can occlude and release lithium, such as a chalcogen compound, can be used. In particular, lithium-containing oxides having an α-NaCrO ₂ structure such as LiCoO ₂ , LiNiO ₂ , and LiMnO ₂ having a high discharge voltage, or LiMn ₂ O ₄ are recommended.

  In addition, the negative electrode active material includes carbon materials that can occlude and release lithium ions such as natural graphite, artificial graphite, and non-graphitizable carbon, lithium alloys such as lithium aluminum alloy, lithium lead alloy, lithium antimony alloy, and lithium wood alloy, metal Lithium, amorphous tin oxide, etc. can be used. In particular, the carbon material is preferable because the cycle life characteristics of the battery are improved.

  In the present invention, a thermoplastic resin, a thermosetting resin, an ionizing radiation curable resin, or the like is used as the binder. Examples of the thermoplastic resin include polyester resin, polyamide resin, polyimide resin, polyacrylate resin, polycarbonate resin, polyurethane resin, cellulose resin, polyolefin resin, polyvinyl resin, fluorine-based resin, polyimide resin, alkyl resin, NBR, and the like. It is used alone or in combination.

  The binder is a binder in which a compound (monomer, oligomer or a mixture of both) containing a functional group that reacts with an electron beam is introduced (physically mixed or chemically bonded), and the bond between the active material particles is irradiated with an electron beam. Is preferable because it can be carried out more quickly and uniformly.

  Examples of the compound containing a functional group that reacts with an electron beam include a monomer or oligomer of a compound having an acrylic group, a vinyl group, an allyl group, or the like.

  Specifically, prepolymers or oligomers such as (meth) acrylate, urethane (meth) acrylate, epoxy (meth) acrylate, polyester (meth) acrylate, (meth) acrylic phosphorus-containing compound, styrene, (meth) acrylic Methyl methacrylate, butyl (meth) acrylate, 2-hydroxyethyl acrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, hexamethylene glycol diacrylate, neopentyl glycol diacrylate, ethylene glycol diglycidyl acrylate, diethylene glycol diglycidyl ether diacrylate, Hexamethylene glycol diglycidyl ether diacrylate, neopentyl glycol diglycidyl ether diacrylate, trimer Propane triacrylate, pentaerythritol tetraacrylate, dipentaerythritol tetraacrylate, it is a combination of single or a plurality of monofunctional or polyfunctional monomers such as dipentaerythritol hexaacrylate.

  The blending ratio of the compound containing a functional group that reacts with the electron beam in the entire binder is preferably 1 to 80% by mass, that is, 1 to 80% by mass with respect to 99 to 20% by mass of the synthetic resin binder.

  The binder into which the compound containing the functional group is introduced is, for example, a product obtained by coupling a hydroxyl group or a carboxyl group in a resin and a monomer or oligomer such as an acrylate having a hydroxyl group via a diisocyanate. Alternatively, through an isocyanate such as toluidine isocyanate, 4,4′-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, xylene diisocyanate, 2-hydroxyethyl acrylate, 2-hydroxyethyl (meth) acrylate, 2-hydroxy-3-phenoxy An acrylate compound such as propyl (meth) acrylate is introduced.

  The mixing ratio of the positive electrode active material or negative electrode active material constituting the active material mixture to the binder is preferably 60 to 95% by mass of the active material and 40 to 5% by mass of the binder, particularly 70 to 90% by mass of the active material and the binder 30. 10 mass% is more preferable.

  The conductive agent added to the active material mixture as desired is a metal powder such as Ni or carbon powder. As the carbon powder, graphite, carbon black, acetylene black and the like are particularly preferable. The addition amount of the conductive agent is 0.1 to 10% by mass with respect to the active material.

  The positive electrode active material or the negative electrode active material and the binder are blended in a predetermined ratio, a dispersant is added thereto, a conductive agent is added as desired, and the mixture is evenly mixed by a homogenizer, a ball mill, a sand mill, a roll mill, or the like. Mix to prepare paste. The viscosity of the paste is usually adjusted to 5000 cp. Examples of the dispersant include aromatic solvents such as toluene, ketone solvents such as amines, solvents such as esters, ether solvents, and amides.

  When a compound containing a functional group that reacts with an electron beam is introduced into the binder, and the active material mixture is prepared to have a viscosity suitable for coating, it is not necessary to add a dispersant separately. It can be applied to an electric body.

Next, the positive electrode active material mixture paste or negative electrode active material mixture paste prepared in this manner is applied to the current collector on the gravure coat, gravure reverse coat, roll coat, Meyer bar coat, blade coat, knife coat, air Apply to uniform thickness by methods such as knife coating, comma coating, slot die coating, slide die coating, dip coating.
The coating thickness is 10 to 250 μm, preferably 50 to 200 μm, after drying.

  For the current collector, non-porous metal foil, porous metal foil (for example, punched porous foil, foamed metal foil) or the like is used. In the non-porous metal foil, a paste coating film is formed on the surface, and in the porous metal foil, the paste is applied to the surface, and the paste is filled in a large number of holes.

  The non-aqueous electrolyte secondary battery of the present invention includes, for example, a positive electrode plate and a negative electrode plate manufactured according to the first and second aspects of the present invention, laminated via a separator to form an electrode plate group, and this is a battery container. The non-aqueous electrolyte is injected, covered, and sealed.

  The non-aqueous electrolyte secondary battery of the present invention includes one using the positive electrode plate or the negative electrode plate of the present invention for one electrode and the conventionally known electrode plate for the other electrode.

  The material of the separator is not particularly limited as long as it is insoluble in the non-aqueous electrolyte, but a monolayer of a polyolefin-based microporous film such as polypropylene, polyethylene, or a copolymer thereof having a three-dimensional pore structure, Or a multilayer body is especially preferable.

In the present invention, the nonaqueous electrolyte includes, for example, LiClO ₄ , LiBF ₄ , LiPF ₆ , LiAsF ₆ , LiCl, LiBr, and other inorganic lithium salts such as LiB (C ₆ H ₅ ) _{4 in} the case of a lithium secondary battery. , LiN (SO ₂ CF ₃ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiOSO ₂ CF ₃ and other organic lithium salts dissolved in a solvent are used.
Examples of the solvent include propylene carbonate, ethylene carbonate, butylene carbonate, γ-butyrolactone, vinylene carbonate, cyclic esters such as 2-methyl-γ-butyrolactone, acetyl-γ-butyrolactone, and γ-valerolactone, tetrahydrofuran, alkyltetrahydrofuran, and dialkyl. Cyclic ethers such as tetrahydrofuran, alkoxytetrahydrofuran, dialkoxytetrahydrofuran, 1,3-dioxolane, alkyl-1,3-dioxolane, 1,4-dioxolane, 1,2-dimethoxyethane, 1,2-diethoxyethane, diethyl Ether, ethylene glycol dialkyl ether, diethylene glycol dialkyl ether, triethylene glycol dialkyl ether, tetraethylene glycol And at least one selected from chain ethers such as alkyl dialkyl ether, chain esters such as dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, propionic acid alkyl ester, meronic acid dialkyl ester, and acetic acid alkyl ester. .

The non-aqueous electrolyte is a mixed solvent of at least one selected from LiBF ₄ or LiPF ₆ or a mixture thereof from propylene carbonate and ethylene carbonate and at least one selected from ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate. A dissolved one is particularly preferred.

(1) Preparation of positive electrode active material mixture paste 90 parts by weight of LiCoO ₂ powder having a particle diameter of 1 to 100 μm as a positive electrode active material, 5 parts by weight of polyvinylidene fluoride resin as a binder, and 5 parts by weight of graphite powder as a conductive agent Thus, a positive electrode active material mixture paste was mixed with N-methylpyrrolidone as a dispersant, and this was stirred and mixed at 8000 rpm for 20 minutes with a disperser to prepare a positive electrode active material mixture paste.

(2) Manufacture of positive electrode plate The positive electrode active material mixture paste prepared in (1) above was continuously applied on one side of a 20 μm thick aluminum foil (current collector) using a die coater, and then a dispersant. After being removed by drying, pressure was applied, followed by heat treatment to produce a positive electrode plate. The drying, pressurization, and heat treatment were performed under various conditions. The coating thickness of the positive electrode active material mixture after drying was 180 μm.

(3) Preparation of negative electrode active material mixture paste 93 parts by weight of graphite powder as a negative electrode active material and 7 parts by weight of polyvinylidene fluoride resin as a binder were used as a negative electrode active material mixture, and N-methyl was used as a dispersant. Pyrrolidone 2 was blended, and this was stirred and mixed at 8000 rpm for 20 minutes with a disperser to prepare a negative electrode active material mixture paste.

(4) Manufacture of Negative Electrode Plate The negative electrode active material mixture paste prepared in (3) above was continuously applied on one side of a 14 μm thick copper foil (current collector) using a die coater (application width 300 mm). Then, after the dispersant was dried and removed, the pressure was applied, followed by heat treatment to produce a negative electrode plate. The drying, pressurization, and heat treatment were performed under various conditions. The coating thickness of the negative electrode active material mixture after drying was 190 μm.

Test pieces were cut out from the positive electrode plate and the negative electrode plate produced in the above (2) and (4), and each test piece was fixed with a double-sided tape to perform a tape peeling test of the active material mixture coating film. A peel strength of 50 N / cm ² or more was determined as good adhesion, and less than 50 N / cm ² was determined as poor adhesion.

A three-electrode plate-type cell was constructed using the positive electrode plate and negative electrode plate obtained in Example 1, and a charge / discharge cycle test was performed at a temperature of 25 ° C. using a charge / discharge measuring device.
The cell was constructed by interposing a separator wider than the positive electrode plate and the counter electrode plate between the positive electrode plate and the counter electrode plate (Li metal plate). A polypropylene microporous film was used as the separator. As the electrolytic solution, an organic solvent in which lithium hexafluorophosphate was dissolved to 1.3 mol / l in a mixed solvent mainly composed of ethylene carbonate was used.

  The charge / discharge cycle test of the positive electrode plate was charged until the potential of the test electrode reached 4.15 V with respect to the equilibrium potential of Li at a current value of a maximum charge current of 0.5 CA. The battery was discharged until it reached 75 V, and after charging for 10 minutes, 30 charge / discharge cycles were performed to perform the charge again. The battery capacities of the first cycle and the 30th cycle were measured.

  The charge / discharge cycle test of the negative electrode plate was charged until the potential of the test electrode reached 0 V with respect to the equilibrium potential of Li at a current value of a maximum charging current of 0.5 CA. Then, the battery was discharged for 10 minutes, and after a 10-minute pause, 30 charging / discharging cycles were performed to perform the charging again. The battery capacities of the first cycle and the 30th cycle were measured.

  In the charge / discharge cycle test of the positive electrode plate and the negative electrode plate, it was determined that the cycle life characteristics were good when the capacity at the 30th cycle was 95% or more of the capacity (initial capacity) at the first cycle, and poor when it was less than 95%.

  Comparative Example 1: A positive electrode plate and a negative electrode plate were produced by the same method as in Example 1 except that the pressurization was performed after the heat treatment in Example 1, and the peeling test and the charge / discharge cycle test were conducted by the same method as in Example 1. went.

  Comparative Example 2: A positive electrode plate and a negative electrode plate were produced by the same method as in Example 1 except that no heat treatment was performed in Example 1, and a peel test and a charge / discharge cycle test were conducted by the same method as in Example 1. .

Comparative Example 3 (conventional method): A positive electrode plate and a negative electrode plate were produced by the same method as in Example 1 except that no pressurization was performed in Example 1, and the peel test and charge / discharge were conducted by the same method as in Example 1. A cycle test was conducted. The paste was applied and dried while applying a tension of 800 N / cm ² to the current collector.

In Comparative Examples 1 and 2, the dispersant was removed by drying at 100 ° C. for 10 minutes, the heat treatment was performed at 145 ° C. for 10 minutes, and the pressurization was performed at a pressure of 60000 N / cm ² .
The test results of Example 1 and Comparative Examples 1 and 2 are shown in Table 1.

  As is clear from Table 1, the positive electrode plate and the negative electrode plate of Example 1 (invention example) had good peel strength and cycle life characteristics of the active material mixture (coating film). This is because the adhesion of the active material is improved by pressurization to prevent the active material mixture from being peeled off, and the conductive path is formed by heat treatment after pressurization to improve the conductivity of the electrode plate. In order to improve the electrical conductivity of the electrode plate, the distance between the active material mixtures (particles) is reduced by pressurization and the internal resistance is reduced.

On the other hand, since the electrode plate of Comparative Example 1 was pressurized after the heat treatment, the conductive path formed by the heat treatment was broken, the conductivity of the electrode plate was lowered, and the cycle life characteristics were inferior. Since the electrode plate of Comparative Example 2 was not subjected to heat treatment, the conductivity of the electrode plate was low and the cycle life characteristics were inferior. Since the electrode plate of Comparative Example 3 was not pressurized, the active material adhesion deteriorated and the cycle life characteristics deteriorated. In the negative electrode, the active material mixture dropped and the charge / discharge cycle test was interrupted.

Claims (3)

  After applying an active material mixture paste containing a dispersant and a binder to a current collector, the dispersant is dried and removed, then pressurized, and then heat treated at a temperature above the binder crystallization temperature and below the melting point. A method for producing an electrode plate for a non-aqueous electrolyte secondary battery.   2. The electrode plate for a non-aqueous electrolyte secondary battery according to claim 1, wherein the active material mixture includes a lithium composite oxide capable of inserting and extracting lithium ions or a carbon material capable of absorbing and releasing lithium ions. Manufacturing method. 3. A non-aqueous electrolyte secondary battery, wherein an electrode plate produced by the production method according to claim 1 or 2 is used for at least one of a positive electrode and a negative electrode.