TWI620373B - Lithium secondary battery electrode and manufacturing method thereof - Google Patents

Abstract

The present invention relates to an electrode for a lithium secondary battery which is an ion-permeable porous layer formed of a quinone-based polymer and having a porosity of 30 to 90% by volume in a surface area other than the electrode active material layer. Form one. The electrode is produced by coating a surface of a metal foil as a current collector with a binder, a dispersion of active material fine particles and a solvent, and drying, to form an electrode active material layer on the metal foil, and then Applying a coating liquid containing a quinone-based polymer and a solvent to the surface of the electrode active material layer to form a coating film, and then removing the solvent in the coating film to form a phase separation in the coating film. The ion-permeable porous layer is simultaneously formed by laminating the electrode active material layer and the ion-permeable porous layer.

Description

Electrode for lithium secondary battery and method of manufacturing same

The present invention relates to an electrode for a lithium secondary battery which is excellent in safety and has high charge and discharge cycle characteristics with high capacitance and a method for producing the same.

The lithium secondary battery sometimes causes scratches or irregularities on the surface of the electrode to break the electrical insulation of a separator connected to the electrode. As a result, an electrical internal short circuit may occur.

In order to prevent such an internal short circuit, a protective layer composed of an insulating porous film on the surface of the electrode has been proposed. A porous film to be a protective layer has been proposed to be formed of a water-soluble polymer (a cellulose derivative, a polyacrylic acid derivative, a polyvinyl alcohol derivative, etc.), a fluorine-based resin, or a rubber-based resin, and A porous film such as alumina, ceria, zirconia or the like is prepared in a large amount to form pores (Patent Documents 1 to 4).

As for other methods for forming a protective layer, it has also been proposed to form a coating film for forming a protective layer on the surface of the electrode, and then immersing it in a coagulation bath containing a poor solvent before drying to cause phase separation of the coating film. A method of obtaining a porous protective layer (Patent Documents 5 and 6).

On the other hand, in the case of lithium secondary active materials using a high capacitance In a battery, a wound electrode body in which a positive electrode and a negative electrode are wound in a spiral shape via a separator is generally filled in a square (square tubular) outer can or a laminated film outer casing to constitute a battery. At this time, there is a case where the capacitance is lowered with repeated charge and discharge, or the thickness is greatly increased due to expansion of the battery. In order to solve such a problem, a method has been proposed in which a ruthenium imine such as a polyimine which forms pores by a large amount of fine particles such as cerium oxide or aluminum oxide is disposed on the surface of the active material layer of the electrode (negative electrode). It is a porous layer of a polymer, and the volume change or deformation of the electrode is relieved (Patent Document 7).

Patent Document 1: International Publication No. 1997/008763

Patent Document 2: Japanese Patent No. 5071056

Patent Document 3: Japanese Patent No. 5,623,323

Patent Document 4: Japanese Patent No. 5370356

Patent Document 5: Japanese Patent No. 3371839

Patent Document 6: Japanese Patent No. 3593334

Patent Document 7: Japanese Laid-Open Patent Publication No. 2011-233349

As described above, the electrode having the porous layer on the surface thereof has a low adhesion effect between the active material layer and the porous layer, and the effect of preventing the short circuit is not necessarily sufficient, and there is a need for improvement from the viewpoint of securing the safety of the battery. The ion permeability of the porous protective layer is also insufficient. In such an electrode, the stress relaxation with the volume of the active material is also insufficient, and therefore, the improvement of the cycle characteristics of the battery is not necessarily sufficient. Moreover, the electrode obtained by the method of causing phase separation by using a coagulation bath containing a poor solvent such as water or alcohol is in contact with the coagulating liquid as a whole, so that the electrode may be poorly dissolved. The agent damage and the original characteristics of the active substance. Further, in this method, since a waste liquid containing a poor solvent is generated from the coagulation bath, there is a problem even as a manufacturing method from the viewpoint of environmental suitability.

In view of the above, an object of the present invention is to provide an electrode for a lithium secondary battery which is improved by improving the adhesion between the porous layer and the active material layer, and a method for producing the same. Excellent in properties, high capacitance and good charge and discharge cycle characteristics.

The present inventors have found that an ion-permeable porous layer is formed by using a laminate having an ion-permeable porous layer on the outer surface of the electrode active material layer to form a specific porosity. The present invention has been completed by forming an imide-based polymer to solve the above problems.

The gist of the present invention is as follows.

1) An electrode for a lithium secondary battery, which is an ion-permeable porous layer formed of a quinone-based polymer and having a porosity of 30 to 90% by volume in a surface area other than the electrode active material layer (hereinafter, A porous layer formed of a quinone imine polymer may be simply referred to as a "siliary imine porous layer" to form an integral body.

(2) The electrode for a lithium secondary battery according to the above aspect, wherein the electrode active material layer and the ion-permeable porous layer have a higher strength than the electrode active material layer.

3) A method for producing an electrode for a lithium secondary battery, which is a method for producing an electrode for a lithium secondary battery according to the above 1) or 2), which is characterized in that a surface of a metal foil as a current collector is coated The electrode active material layer is formed on the metal foil by containing a binder, a dispersion of the active material fine particles and the solvent, and drying. Applying a coating liquid containing a quinone-based polymer and a solvent to the surface of the electrode active material layer to form a coating film, and then removing the solvent in the coating film to form a phase separation in the coating film to form an ion. The penetrating porous layer is formed by laminating the electrode active material layer and the ion-permeable porous layer.

(4) The method for producing an electrode for a lithium secondary battery according to (3), wherein the method of causing phase separation in the coating film is a poor solvent-induced phase separation method.

(5) The method for producing an electrode for a lithium secondary battery according to (4), wherein the poor solvent-induced phase separation method is a dry phase separation method.

(6) The method for producing an electrode for a lithium secondary battery according to (5), wherein the good solvent used in the dry phase separation method is a guanamine solvent, and the poor solvent is an ether solvent.

In the electrode for a lithium secondary battery of the present invention, in order to form pores of the ion-permeable porous membrane, it is not necessary to prepare a large amount of fine particles such as alumina or cerium oxide, so that the ion-permeable porous membrane can be buffered ( The cushioning property is improved, and at the same time, the adhesion between the porous layer and the active material layer is ensured. Therefore, it can be suitably used as an electrode for a lithium secondary battery which is excellent in safety and has high capacitance and good cycle characteristics. Further, in the production method of the present invention, the electrode of the present invention can be produced by a simple process.

Fig. 1 is a cross-sectional view showing an electrode formed integrally with a porous layer of an outer surface layer of a positive electrode active material layer.

Fig. 2 is an enlarged cross-sectional view showing the electrode of Fig. 1.

Fig. 3 is a view showing the appearance of a person who peels off the positive electrode active material layer from the porous yttrium imide layer.

Fig. 4 is an enlarged view of a portion where the positive electrode active material layer of Fig. 3 is almost peeled off.

Fig. 5 is an enlarged view of a portion where the positive electrode active material layer of Fig. 3 remains.

The electrode for a lithium secondary battery of the present invention is formed by an ion-permeable porous layer formed of a surface layer of a quinone imine-based polymer other than the electrode active material layer and having a porosity of 30 to 90% by volume. Former. The electrode for a lithium secondary battery constitutes an electrode of a lithium secondary battery, and refers to a positive electrode active material layer bonded to a positive electrode of a positive electrode current collector, or a negative electrode active material layer bonded to a negative electrode of a negative electrode current collector. The electrode active material layer is a general term for the positive electrode active material layer and the negative electrode active material layer.

A metal foil such as copper foil, stainless steel foil, nickel foil, or aluminum foil can be used for the current collecting system. It is preferable to use an aluminum foil for the positive electrode and a copper foil for the negative electrode. The thickness of the metal foil is preferably from 5 to 50 μm, more preferably from 9 to 18 μm. The surface of the metal foil may also be subjected to surface roughening treatment or rustproof treatment for improving adhesion to the active material layer.

The positive electrode active material layer is a layer obtained by fixing a positive electrode active material particle with a resin binder. The material of the positive electrode active material particles can be used, and those which can adsorb and store lithium ions are preferable, and those which are generally used as a positive electrode active material of a lithium secondary battery can be mentioned. Examples thereof include an oxide system (such as LiCoO ₂ , LiNiO ₂ , and LiMn ₂ O ₄ ), a composite oxide system (LiCo _1/3 Ni _1/3 Mn _1/3 O ₂ , Li (LiaNixMnyCoz) O _{2 ,} etc.), and phosphoric acid. Active material particles such as iron (LiFePO ₄ , LiFePO ₄ F, etc.) and polymer compound (polyaniline, polythiophene, etc.). Among them, LiCoO ₂ , LiNiO ₂ , and LiFePO ₄ are preferable. In order to reduce the internal resistance of the positive electrode active material, conductive particles such as carbon (black lead, carbon black, etc.) particles or metal (silver, copper, nickel, etc.) particles may be blended in an amount of about 1 to 30% by mass.

The negative electrode active material layer is a layer obtained by fixing a negative electrode active material particle with a resin binder. The material of the negative electrode active material particles can be used, and those which can adsorb and store lithium ions are preferable, and those which are generally used as a negative electrode active material of a lithium secondary battery can be mentioned. Examples thereof include active material particles such as graphite, amorphous carbon, lanthanoid, and tin. Among them, graphite and lanthanum particles are particularly preferred. Examples of the lanthanoid particles include particles of a ruthenium monomer, a ruthenium alloy, and a ruthenium-ruthenium dioxide composite. Among these lanthanoid particles, particles of ruthenium monomer (hereinafter sometimes referred to simply as "ruthenium particles") are preferred. The oxime system refers to a crystalline or amorphous substance having a purity of 95% by mass or more. In the negative electrode active material layer, in order to reduce the internal resistance, conductive particles such as carbon (black lead, carbon black, etc.) particles or metal (silver, copper, nickel, or the like) particles may be blended in an amount of about 1 to 30% by mass.

The particle diameter of the active material particles or the conductive particles is preferably 50 μm or less for the positive electrode and the negative electrode, and more preferably 10 μm or less. If the particle diameter is too small, it may be difficult to fix with a resin binder, and therefore it is usually 0.1 μm or more, preferably 0.5 μm or more.

The porosity of the electrode active material layer is preferably 5 to 50% by volume, more preferably 10 to 40% by volume, based on the positive electrode and the negative electrode.

The thickness of the electrode active material layer is generally about 20 to 200 μm.

The resin binder for fixing the active material particles may, for example, be polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, or vinylidene fluoride-tetrafluoroethylene copolymer. A styrene/butadiene copolymer rubber, a polytetrafluoroethylene, a polypropylene, a polyethylene, a quinone imine polymer, or the like. Among them, especially polyvinylidene fluoride, styrene/butadiene copolymerized rubber, bismuth imide A polymer is preferred.

In the electrode of the present invention, the surface layer ion-permeable quinary imine porous layer is formed integrally with the electrode active material layer.

The quinone imine polymer which forms the porous yttrium layer is a polymer having a quinone bond in the main chain or a precursor thereof. Representative examples of the polymer having a quinone bond in the main chain include, for example, polyimine, polyamidimide, and polyesterimide. However, it is not limited to these.

Among the quinone imine polymers, for example, polyimine or polyamidimide can be preferably used. Polyimine can be used: poly-proline-type polyimine using poly-proline as its precursor (for polyimine, suitable for solvent-insoluble polyimine) or soluble polyfluorene Imine (solvent-soluble polyimine). From the viewpoint of ensuring excellent safety and good cycle characteristics of the electrode for a lithium secondary battery, among the quinoneimine polymers, aromatic polyimine or aromatic polyfluorene which is excellent in mechanical properties or heat resistance Amidoximine is preferred. The aromatic polyamine or the aromatic polyamidoximine may be thermoplastic or non-thermoplastic. Among them, an aromatic polyimine or an aromatic polyamidimide having a glass transition temperature of 200 ° C or higher is preferably used.

The porosity of the porous yttrium imine layer of the present invention must be 30 to 90% by volume. It is preferably 40 to 80% by volume, more preferably 45 to 80% by volume. By setting the porosity in this manner, it is possible to simultaneously ensure good mechanical properties and good cushioning properties for relieving stress accompanying volume change of the active material. Therefore, an electrode excellent in safety and having good cycle characteristics can be obtained. The porosity of the yttrium imine porous layer is a value calculated from the apparent density of the yttrium imine porous layer and the true density (specific gravity) of the quinone imine polymer constituting the yttrium imine porous layer. Specifically, when the apparent density of the yttrium imide layer is A (g/cm ³ ) and the true density of the quinone imine polymer is B (g/cm ³ ), the porosity (% by volume) depends on Calculated by the following formula: porosity (% by volume) = 100-A* (100/B).

The yttrium imine porous layer of the present invention is preferably firmly adhered to the active material layer. That is, from the viewpoint of improving the safety of the battery, the adhesion strength between the electrode active material layer and the yttrium imide porous layer is preferably higher than the strength of the electrode active material layer. Then, whether the strength is higher than the strength of the electrode active material layer, and when the electrode active material layer is peeled off from the yttrium imide porous layer, whether or not aggregation failure occurs at the interface or interfacial peeling occurs is judged. When aggregation failure occurs, it is determined that the strength of the interface is higher than the strength of the electrode active material layer. When a part of the active material layer was adhered to a part of the surface of the yttrium imide porous layer (the surface of the electrode active material layer) after peeling, it was judged that aggregation was broken. In the past, such an aggregated destruction electrode was not known, and in the electrode of the present invention, such high adhesion force is very helpful in improving the safety of the battery.

The average pore diameter of the yttrium imine porous layer of the present invention is preferably 0.1 to 10 μm, more preferably 0.5 to 5 μm. By setting the average pore diameter in this way, good ion permeability can be ensured. The degree of ion permeability can be determined by the time of penetration of the solvent from the solvent for the electrolyte constituting the battery to the surface of the electrode. The content of the determination method is detailed later. In the electrode of the present invention, the permeation time is preferably 300 seconds or less, more preferably 150 seconds or less.

The thickness of the yttrium imine porous layer of the present invention is preferably from 1 to 100 μm, more preferably from 10 to 50 μm.

The porous yttrium imide layer of the present invention may be either insulating or electrically conductive. When the porous layer of yttrium imide is insulative, this layer also functions as a separator for preventing electrical contact between the positive electrode and the negative electrode of the lithium secondary battery, so good. When the porous layer of the yttrium imide is electrically conductive, for example, carbon (black lead, carbon black, etc.) particles or metals (silver, copper, nickel, etc.) may be blended in an amount of about 5 to 50% by mass in the yttrium imine porous layer. The conductive particles may be used. The amount of the conductive particles to be added is preferably 20% by mass or less from the viewpoint of ensuring the cushioning property and the adhesion property of the yttrium imine porous layer.

Next, a method of producing the electrode for a lithium secondary battery of the present invention will be described.

For example, the electrode for a lithium secondary battery of the present invention can be produced by the following process.

(1) Applying a dispersion containing the above-mentioned binder, active material fine particles and a solvent (hereinafter sometimes referred to simply as "active material dispersion") to the surface of the metal foil as a current collector, and drying the metal foil Electrode active material layer

(2) Next, a coating liquid containing a quinone imine-based polymer and a solvent which form a porous yttrium imide layer by phase separation is applied to the surface of the electrode active material layer (hereinafter, it may be simply referred to as "醯" Imine-based coating liquid").

(3) Then, by removing the solvent in the coating film, phase separation occurs in the porous layer of yttrium imine, and pores are formed in the porous layer of yttrium imine, and the electrode active material layer and the quinone imine are laminated. The layer is formed in one piece.

When drying to form the electrode active material layer, the residual solvent content in the active material layer is preferably set to 0.5 to 50% by mass. Thereby, the strength of the interface between the electrode active material layer and the yttrium imide porous layer can be increased.

In order to form a quinone imine porous layer by phase separation using a quinone imine polymer, it is preferred to use a poor solvent-induced phase separation method. The poor solvent-induced phase separation method is a method in which a porous structure is induced by inducing phase separation by acting as a solvent for a solute as a poor solvent in a coating liquid.

From the viewpoint of the simplicity of the production process and the environmental suitability, the poor solvent-induced phase separation method is preferably a dry phase separation method. The dry phase separation method refers to the use of a poor solvent remaining in the coating film when the coating film of the quinone imide coating liquid containing a mixed solvent of a poor solvent having a different boiling point and a poor solvent is dried and dried. And the method that causes phase separation.

The quinone imine-based coating liquid used in the dry phase separation method is produced by solution polymerization when the polyamic acid, the soluble polyimine, and the polyamidimide are dissolved in a solvent. A mixed solvent obtained by dissolving a good solvent of a quinone imine polymer as a solute and a solvent having a higher boiling point than the good solvent and a solute as a poor solvent can be easily obtained. The solvent is a solvent having a solubility of 1% by mass or more for the quinone imine polymer at 25° C., and the poor solvent is a solvent having a solubility of at least 1% by mass for the quinone imine polymer at 25° C. . The difference in boiling point between the good solvent and the poor solvent is preferably 5 ° C or higher, more preferably 20 ° C or higher, and still more preferably 50 ° C or higher.

The good solvent is preferably a guanamine solvent. The guanamine-based solvent may, for example, be N-methyl-2-pyrrolidone (NMP boiling point: 202 ° C), N,N-dimethylformamide (DMF boiling point: 153 ° C), N,N-dimethyl Ethyl amide (boiling point of DMAc: 166 ° C). These may be used singly or in combination of two or more.

As the poor solvent, an ether solvent is preferably used. Examples of the ether solvent include diethylene glycol dimethyl ether (boiling point: 162 ° C), triethylene glycol dimethyl ether (boiling point: 216 ° C), tetraethylene glycol dimethyl ether (boiling point: 275 ° C), and diethyl ether. A solvent such as a diol (boiling point: 244 ° C) or triethylene glycol (boiling point: 287 ° C). These may be used singly or in combination of two or more. The blending amount of the poor solvent is preferably from 40 to 90% by mass, more preferably from 60 to 80% by mass, based on the total amount of the solvent. With such a solvent composition, The solid layer of the quinone imine and the active material layer as described above can be obtained firmly.

Examples of the quinone imide-based coating liquid are commercially available products such as U-imide varnish BP, which is sold under the trade name "U-imide varnish BP" (polyammonic acid type polyimide varnish). ), the trade name "U-imide varnish SP" (soluble polyimide varnish), and the trade name "U-imide varnish IP" (polyamide imimine varnish).

The above-mentioned commercially available product can be used as the quinone imide-based coating liquid containing the polyaminic acid solution or the soluble polyimine solution used in the dry phase separation method, but it is preferably used in a molar arrangement. As a raw material, a tetracarboxylic dianhydride and a diamine are further subjected to a polymerization reaction to obtain a polyamic acid solution or a soluble polyimine solution. Further, after a polymerization reaction is carried out in a good solvent to obtain a solution, a method of adding a poor solvent to the obtained solution, or a polymerization reaction may be carried out only in a poor solvent to obtain a suspension, and a good solvent may be added to the obtained solution. The method is to obtain a quinone imide coating liquid.

As the tetracarboxylic dianhydride, for example, pyromellitic acid, 3,3', 4,4'-biphenyltetracarboxylic acid, 3,3',4,4'-benzophenonetetracarboxylic acid, 3 can be used. , 3',4,4'-diphenylphosphonium tetracarboxylic acid, 3,3',4,4'-diphenyl ether tetracarboxylic acid, 2,3,3',4'-benzophenone IV Carboxylic acid, 2,3,6,7-naphthalenetetracarboxylic acid, 1,4,5,7-naphthalenetetracarboxylic acid, 1,2,5,6-naphthalenetetracarboxylic acid, 3,3',4,4 '-Diphenylmethanetetracarboxylic acid, 2,2-bis(3,4-dicarboxyphenyl)propane, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane, 3,4, 9,10-tetracarboxyindole, 2,2-bis[4-(3,4-dicarboxyphenoxy)phenyl]propane, 2,2-bis[4-(3,4-dicarboxyphenoxy) a dianhydride such as phenyl]hexafluoropropane. These may be used singly or in combination of two or more. Among these, pyromellitic acid and 3,3',4,4'-biphenyltetracarboxylic acid are preferred.

As the diamine, for example, p-phenylenediamine, m-phenylenediamine, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, 4,4' can be used. -diaminodiyl Phenylmethane, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 2,2-bis[4-(4-aminophenoxy)phenyl]propane, 1, 2-bis(anilino)ethane, diaminodiphenylanthracene, diaminobenzimidamide, diaminobenzoic acid ester, diaminodiphenyl sulfide, 2,2-double (pair Aminophenyl)propane, 2,2-bis(p-aminophenyl)hexafluoropropane, 1,5-diaminonaphthalene, diaminotoluene, diaminobenzotrifluoride, 1,4- Bis(p-aminophenoxy)benzene, 4,4'-bis(p-aminophenoxy)biphenyl, diaminoguanidine, 4,4'-bis(3-aminophenoxybenzene) Diphenyl hydrazine, 1,3-bis(anilino)hexafluoropropane, 1,4-bis(anilino) octafluorobutane, 1,5-bis(anilino)decafluoropentane, 1, 7-Bis(anilino)tetradecafluoroheptane. These may be used singly or in combination of two or more. Among these, especially p-phenylenediamine, 4,4'-diaminodiphenyl ether, 2,2-bis[4-(4-aminophenoxy)phenyl]propane good.

The solid concentration of the polyamic acid in the polyimide precursor solution is preferably from 1 to 50% by mass, more preferably from 5 to 25% by mass. The polylysine contained in the polyimide precursor solution may also be partially imidized. The viscosity of the polyimide precursor solution at 30 ° C is preferably from 1 to 150 Pa.s, more preferably from 5 to 100 Pa.s.

The quinone imide coating liquid composed of the polyamidoximine solution used in the dry phase separation method may be a commercially available product as described above, but it is preferably used as a raw material in about equimolar blending. The benzene trimellitic anhydride and the diisocyanate are further subjected to a polymerization reaction in the above mixed solution. Further, after a solution is obtained by merely polymerizing a reaction in a good solvent, a poor solvent may be added to the obtained solution, or a polymerization reaction may be carried out only in a poor solvent to obtain a suspension, and then a good solvent may be added to the obtained solution. The method provides a quinone imide coating liquid composed of a polyamidoximine solution.

In the case of benzene trimellitic anhydride, it is also possible to use a part of it by pyromellitic acid. An anhydride, benzophenone tetracarboxylic anhydride, or a biphenyltetracarboxylic anhydride substitute.

As the diisocyanate, for example, m-phenylene diisocyanate, p-phenylene diisocyanate, 4,4'-diphenylmethane diisocyanate, 4,4'-diphenyl ether diisocyanate, diphenylanthracene can be used. -4,4'-diisocyanate, diphenyl-4,4'-diisocyanate, o-toluidine diisocyanate, 2,4'-methylphenylene diisocyanate, 2,6-methylphenylene Isocyanate, dimethylphenylene diisocyanate, and naphthyl diisocyanate. These may be used singly or in combination of two or more. Among these, 4,4'-diphenylmethane diisocyanate is particularly preferred.

The solid content concentration of the polyamidoximine in the polyamidoximine solution is preferably from 1 to 50% by mass, more preferably from 10 to 30% by mass.

The viscosity of the polyamidoximine solution at 30 ° C is preferably from 1 to 150 Pa.s, more preferably from 5 to 100 Pa.s.

A known additive such as various surfactants or organic decane coupling agents may be added to the quinone imide coating liquid as needed within the range which does not impair the effects of the present invention. In addition, other polymers other than the quinone-based polymer may be added to the quinone imine-based coating liquid as long as the effects of the present invention are not impaired.

The quinone imide-based coating liquid is applied onto the surface of the electrode active material layer, dried at 100 to 150 ° C, and then heat-treated at 250 to 350 ° C as necessary, thereby forming a porosity of 30 to 90% by volume. The yttrium imide porous layer; and the electrode active material layer and the ruthenium imine porous layer are integrally formed, and can be simultaneously performed. At this time, the porosity and the blending amount are adjusted to 30 to 90% by volume by selecting the type and amount of the solvent (good solvent and poor solvent) in the quinone imide coating liquid. Further, the porosity can be adjusted by selecting drying conditions.

Preferably, it is required to be on the surface of the obtained porous layer of yttrium imide. Physical polishing treatment such as sandblasting or blasting, or chemical etching. As a result, the surface area of the yttrium imine porous layer is increased and the opening ratio is also increased, so that good ion permeability of the yttrium imide porous layer can be ensured.

When the active material dispersion or the quinone-based coating liquid is applied, a method of continuously applying a roll to roll or a sheet coating method may be employed, and any method may be employed. The coating device may be a die coater, a multilayer die coater, a gravure coater, a ripper coater, a reverse coater, a knife coater (doctor) Blade coater) and so on.

As described above, the electrode system of the present invention can be easily produced by a simple process.

(Example)

Hereinafter, the present invention will be described in more detail by way of examples. Further, the present invention is not limited by the embodiments.

The active material layers (for the positive electrode and the negative electrode) formed on the current collector used in the following examples and comparative examples can be obtained as follows.

(positive electrode active material layer)

86 parts by mass of LiFePO ₄ particles (average particle diameter: 0.5 μm) as a positive electrode active material, 8 parts by mass of carbon black (acetylene black) of a conductive auxiliary agent, and 6 parts by mass of polyvinylidene fluoride as a binder resin are uniformly dispersed. An active material dispersion for a positive electrode was obtained from N-methylpyrrolidone as a solvent. This dispersion was applied to an aluminum foil having a thickness of 15 μm as a positive electrode current collector, and the obtained coating film was dried at 130 ° C for 10 minutes, and then hot pressed to obtain a positive electrode active material layer having a thickness of 50 μm.

(negative electrode active material layer)

Antimony particles (average particle diameter: 0.7 μm) as a negative electrode active material, black lead particles (average particle diameter: 0.7 μm) of a conductive auxiliary agent, and a polyglycine solution of a binder resin (manufactured by Uniliga) The name "U-imide varnish CR" (solid content: 18% by mass) was uniformly dispersed in N-methylpyrrolidone (NMP) to obtain a negative electrode active material dispersion having a solid content of 25% by mass. The mass ratio of the cerium particles, the black lead particles, and the polyaminic acid solution is 70:10:20. This dispersion was applied to a copper foil having a thickness of 18 μm as a negative electrode current collector, and the obtained coating film was dried at 120 ° C for 10 minutes to obtain a negative electrode active material layer having a thickness of 40 μm. NMP 22% by mass remained in the active material layer.

The characteristics and the like of the electrodes obtained in the following examples and comparative examples were evaluated in the following manner.

(1) Ion penetration

5 μL of a mixed solvent of ethylene methyl carbonate and dimethyl carbonate (volume ratio 1:1:1) set at 30 ° C was dropped on the surface of the electrode, and the permeation time was measured by visual observation of complete permeation. The ion penetration was evaluated by the soaking time.

(2) Adhesiveness

The electrode active material layer was forcibly peeled off in the opposite direction of 180 degrees from the integrated material of the electrode active material layer and the yttrium imide porous layer. At this time, whether or not the adhesion is good or not is determined whether or not a portion of the electrode active material layer is adhered to one of the surface of the porous yttrium imide layer (the surface of the electrode active material layer) after peeling. In other words, when the chips are adhered, the interface between the electrode active material layer and the yttrium imide porous layer is less likely to be peeled off and is agglomerated, so that the adhesion between the electrode active material layer and the yttrium imide porous layer is judged to be "good". Further, when no debris was attached, peeling occurred at the interface, and it was determined that the adhesion was "defective".

<Example 1>

About 30 parts by mass of N-methyl-2-pyrrolidone (NMP) as a good solvent, such as about methicylic acid anhydride (TMA) and 4,4'-diphenylmethane diisocyanate (DMI) The solvent was reacted in a mixed solvent of 70 parts by mass of a poor solvent of tetraethylene glycol dimethyl ether to obtain a uniform polyamidoquinone imide solution (P-1) having a solid content concentration of 15% by mass. This solution was applied to the outer surface of the positive electrode active material layer, and dried at 130 ° C for 10 minutes, and then the surface was subjected to a rubbing treatment to obtain a ruthenium-containing porous material having a surface layer thickness of 23 μm outside the positive electrode active material layer. An integrated electrode (positive electrode) "C-1" is formed in layers. The evaluation results of the obtained electrodes are shown in Table 1.

The SEM image of the cross section of the positive electrode "C-1" is shown in Figs. 1 to 2 . Figure 1 shows the top three layers. The lowermost layer is a positive electrode current collector, the intermediate layer is a positive electrode active material layer, and the uppermost layer is a quinone imine porous layer. Figure 2 shows the positive electrode The interface between the active material layer and the yttrium imide porous layer and the vicinity of the interface. It can be seen from these figures that the average pore diameter of the porous layer of ruthenium is about 3 μm.

When the active material layer of the positive electrode "C-1" is forcibly peeled off in the opposite direction by 180 degrees, the SEM image of the surface of the yttrium imide porous layer contacting the side of the active material layer is shown in Figs. 3 to 5 . As is clear from Fig. 3, after the peeling, the portion where the active material layer is almost peeled off and the portion where the active material layer remains are present. Fig. 4 is an enlarged SEM image showing a portion of the numeral "1" in Fig. 3 (where the active material layer is almost peeled off). From the SEM image, it is understood that many pores exist on the surface of the yttrium imide porous layer at the interface. Fig. 5 is an enlarged SEM image showing a portion of the numeral "2" in Fig. 3 (where the fragments of the active material layer remain). From the SEM image, it is known that many pores exist in the active material layer at the interface. It is considered that the pores existing at the interfaces shown in Figs. 4 and 5 contribute to the good ion permeability of the positive electrode "C-1".

<Example 2>

The reaction of about 10 parts by weight of tetral anhydride with 4,4'-diphenylmethane diisocyanate in a mixed solvent of 25 parts by mass of NMP and 75 parts by mass of tetraethylene glycol dimethyl ether gives a solid concentration of 10 A mass% of a homogeneous polyamidoquinone solution (P-2). This solution was applied to the outer surface of the positive electrode active material layer, and dried at 130 ° C for 10 minutes, and then the surface was polished to obtain a porous yttrium imide layer having a surface layer thickness of 20 μm outside the positive electrode active material layer. An integrated electrode (positive electrode) "C-2" is formed. The evaluation results of the obtained electrodes are shown in Table 1.

<Example 3>

The reaction of about 10 parts of benzene trimellitic anhydride with 4,4'-diphenylmethane diisocyanate in a mixed solvent of 35 parts by mass of NMP and 65 parts by mass of tetraethylene glycol dimethyl ether gives a solid content concentration of 17 A mass% of a homogeneous polyamidoquinone solution (P-3). will The solution was applied to the outer surface of the positive electrode active material layer, dried at 130 ° C for 10 minutes, and then the surface was polished to obtain a porous layer of yttrium imine having a surface layer thickness of 25 μm outside the positive electrode active material layer. An integrated electrode (positive electrode) "C-3" is formed. The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 1>

The reaction product is reacted in a mixed solvent of 65 parts by mass of NMP and 35 parts by mass of tetraethylene glycol dimethyl ether to obtain a solid content concentration of about 17 parts by weight of benzyl trimellitic anhydride and 4,4'-diphenylmethane diisocyanate. A mass% of a homogeneous polyamidoquinone solution (P-4). This solution was applied to the outer surface of the positive electrode active material layer, and dried at 130 ° C for 10 minutes, and then the surface was polished to obtain a porous yttrium imide layer having a surface layer thickness of 25 μm outside the positive electrode active material layer. An integrated electrode (positive electrode) "C-4" is formed. The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 2>

Approximately a molar amount of the phthalic acid and the 4,4'-diphenylmethane diisocyanate were reacted in NMP to obtain a uniform polyamidoquinone solution (P-5) having a solid concentration of 19% by mass. . This solution was applied to the outer surface of the positive electrode active material layer, and dried at 130 ° C for 10 minutes, and then the surface was polished to obtain a porous yttrium imide layer having a surface layer thickness of 25 μm outside the positive electrode active material layer. An integrated electrode (positive electrode) "C-5" is formed. The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 3>

The alumina particles having an average particle diameter of 0.5 μm were uniformly mixed and dispersed in the polyamidoximine solution (P-5) obtained in Comparative Example 2 to obtain an alumina filler dispersion having a solid content concentration of 25% by mass ( P-6). The mass ratio of polyamidoximine to alumina particles was 5:95 (polyamidolimine: alumina particles). Applying the dispersion to the foregoing The outer surface of the positive electrode active material layer was dried at 130 ° C for 10 minutes to obtain an electrode (positive electrode) "C-6" in which a porous layer of a quinone imine having a surface layer thickness of 25 μm outside the positive electrode active material layer was formed. . The evaluation results of the obtained electrodes are shown in Table 1.

<Example 4>

Approximately 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) and 4,4'-oxydiphenylamine (ODA) are used as N,N-dimethyl as a good solvent. 20 parts by mass of acetamidine (DMAc) was reacted with a mixed solvent of 80 parts by mass of tetraethylene glycol dimethyl ether as a poor solvent to obtain a uniform polyaminic acid solution having a solid content concentration of 15% by mass (P- 7). The solution was applied to the outer surface of the negative electrode active material layer, dried at 130 ° C for 10 minutes, and further heat treated at 300 ° C for 120 minutes to convert the polyamidamine into polyimine, and then the surface was polished. An electrode (negative electrode) "A-1" having an integrated surface layer having a surface layer thickness of 23 μm and having a thickness of 23 μm was obtained. The evaluation results of the obtained electrodes are shown in Table 1.

Next, the battery characteristics of the negative electrode "A-1" were evaluated. Specifically, the negative electrode was die-cut into a circular shape having a diameter of 14 mm, and a separator made of a porous film made of polypropylene and a lithium foil were sequentially laminated on the porous surface of the yttrium imide, and then stored in a stainless steel coin. In the outer container. An electrolyte solution is injected into the outer container (solvent: a mixed solvent obtained by mixing ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a ratio of 1:1:1 by volume, electrolyte: 1 M LiPF ₆ ) The outer container was covered with a stainless steel cap having a thickness of 0.2 mm through a polypropylene pad, and the battery can was sealed to obtain a battery for evaluation of discharge capacitance and cycle characteristics of a diameter of 20 mm and a thickness of about 3.2 mm. Using the obtained battery, charging was carried out at 30 ° C with a constant current of 0.05 C to 2 V, and discharging was performed at a constant current of 0.05 C to a charge-discharge cycle of 0.02 V. As a result, the initial discharge capacity of the negative electrode "A-1" was 2,200 "mAh/g-active material layer", and the discharge capacity after 10 cycles became 2050 "mAh/g-active material layer", and a high initial discharge was confirmed. Capacitance and good cycle characteristics.

<Example 5>

3 parts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphenylamine in 30 parts by mass of DMAc and 70 parts by mass of triethylene glycol dimethyl ether The reaction was carried out in a mixed solvent to obtain a homogeneous polyamic acid solution (P-8) having a solid concentration of 15% by mass. The solution was applied to the outer surface of the negative electrode active material layer, dried at 130 ° C for 10 minutes, and further heat-treated at 300 ° C for 120 minutes to convert polylysine into polyimine, and then the surface was polished. An electrode (negative electrode) "A-2" having an integrated surface layer having a surface layer thickness of 23 μm and having a thickness of 23 μm was obtained. The evaluation results of the obtained electrodes are shown in Table 1.

<Example 6>

A polyimine precursor varnish for forming a porous film of a commercially available porous film containing polyamic acid obtained by reacting pyromellitic dianhydride with 4,4'-oxydiphenylamine (manufactured by Uniliga) U-imide varnish BP": P-9) was applied to the outer surface of the foregoing negative electrode active material layer, dried at 130 ° C for 10 minutes, and further heat treated at 300 ° C for 120 minutes to convert polylysine to polyimine. After that, the surface of the surface of the negative electrode active material layer having a thickness of 25 μm outside the negative electrode active material layer was obtained to form an integrated electrode (negative electrode) "A-3". The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 4>

Approximately 3 parts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphenylamine in 70 parts by mass of DMAc and 30 parts by mass of tetraethylene glycol dimethyl ether The reaction was carried out in a mixed solvent to obtain a homogeneous polyaminic acid solution (P-10) having a solid concentration of 15% by mass. This solution was applied to the outer surface of the foregoing negative electrode active material layer, and dried at 130 ° C. In a minute, heat treatment was carried out at 300 ° C for 120 minutes to convert the poly-proline to polyimine, and then the surface was polished to obtain a porous layer of yttrium having a surface layer thickness of 20 μm outside the negative electrode active material layer. The integrated electrode (negative electrode) "A-4" is formed. The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 5>

Approximately 3 parts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphenylamine are reacted in DMAc 70 to obtain a uniform solid concentration of 15% by mass. Polylysine solution (P-11). The solution was applied to the outer surface of the negative electrode active material layer, dried at 130 ° C for 10 minutes, and further heat treated at 300 ° C for 120 minutes to convert the polyamidamine into polyimine, and then the surface was polished. An electrode (negative electrode) "A-5" having an integrated surface layer having a surface layer thickness of 18 μm and having a thickness of 18 μm was obtained. The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 6>

The alumina particles having an average particle diameter of 0.5 μm were uniformly mixed and mixed in the polyaminic acid solution (P-10) obtained in Comparative Example 4 to obtain an alumina filler dispersion having a solid content concentration of 25% by mass (P-12). ). The mass ratio of polyamidoximine to alumina particles was 5:95 (polyamidolimine: alumina particles). The dispersion was applied to the outer surface of the negative electrode active material layer, dried at 130 ° C for 10 minutes, and further heat treated at 300 ° C for 120 minutes, thereby obtaining a bismuth imine having a surface layer thickness of 25 μm outside the negative electrode active material layer. The porous layer forms an integrated electrode (negative electrode) "A-6". The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 7>

a mixed solvent of about 3 parts by weight of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphenylamine in NMP 30 parts by mass and γ-butyrolactone 70 parts by mass Reaction, get A homogeneous polyamic acid solution (P-13) having a solid concentration of 15% by mass. The solution was applied to the outer surface of the negative electrode active material layer, dried at 130 ° C for 10 minutes, and further heat-treated at 300 ° C for 120 minutes to convert the polyamidamine into polyimine, and then the surface was polished. An electrode (negative electrode) "A-7" having an integrated surface layer having a surface layer thickness of 20 μm and having a thickness of 20 μm was obtained. The evaluation results of the obtained electrodes are shown in Table 1.

<Comparative Example 8>

Approximately 3 parts of 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydiphenylamine are reacted in diethylene glycol dimethyl ether to obtain a solid concentration It is a 15% by mass homogeneous polyamine solution (P-14). However, a homogeneous solution could not be obtained.

As shown in the above examples and comparative examples, the electrode for a lithium secondary battery of the present invention is one which uses a guanamine-based solvent which is a good solvent for the quinone-based polymer, and a boiling point as a poor solvent. The dry phase separation method of the higher ether solvent ensures good ion permeability. Further, in order to form the pores of the ion-permeable porous membrane, the electrode for a lithium secondary battery of the present invention does not require a large amount of fine particles such as alumina or cerium oxide particles, so that the ion-permeable porous layer can be ensured. Good adhesion of the active material layer. Therefore, it can be suitably used as an electrode for a lithium secondary battery which is excellent in safety and has high discharge capacity and good cycle characteristics. Moreover, according to the manufacturing method of the present invention, it is possible to manufacture the electrode with high environmental suitability and easy to manufacture in a simple process.

Claims (4)

An electrode for a lithium secondary battery which is formed by an yttrium imide polymer having a surface area other than the electrode active material layer and having a porosity of 30 to 90% by volume and an average porosity of 0.1 to 10 μm. The porous layer is integrated into one. The electrode for a lithium secondary battery according to the first aspect of the invention, wherein the electrode active material layer and the ion-permeable porous layer have a higher strength than the electrode active material layer. A method for producing an electrode for a lithium secondary battery, which is a method for producing an electrode for a lithium secondary battery according to the first or second aspect of the invention, which is characterized in that it is a surface of a metal foil as a current collector And coating a dispersion containing a binder, an active material fine particle and a solvent, and drying to form an electrode active material layer on the metal foil, and then coating the surface of the electrode active material layer with a quinone-based polymer a good solvent and a coating liquid having a higher boiling point than the above-mentioned good solvent to form a coating film, and then a phase separation method is induced by a poor solvent belonging to the dry phase separation method to cause phase separation in the coating film. Forming the ion-permeable porous layer and integrating the electrode active material layer with the ion-permeable porous layer, wherein the poor solvent-induced phase separation method comprises drying the coating film to remove the coating The process of the solvent in the film. The method for producing an electrode for a lithium secondary battery according to the third aspect of the invention, wherein the good solvent used in the dry phase separation method is a guanamine solvent, and the poor solvent is an ether solvent.