JP6187464B2 - Porous membrane composition for lithium ion secondary battery, separator for lithium ion secondary battery, electrode for lithium ion secondary battery, lithium ion secondary battery, method for producing separator for lithium ion secondary battery, and for lithium ion secondary battery Electrode manufacturing method - Google Patents

Description

  The present invention relates to a porous membrane composition for a lithium ion secondary battery, a separator for a lithium ion secondary battery, an electrode for a lithium ion secondary battery, a lithium ion secondary battery, a method for producing a separator for a lithium ion secondary battery, and lithium ion The present invention relates to a method for manufacturing a secondary battery electrode.

  The demand for secondary batteries such as lithium ion secondary batteries that are small and light, have high energy density, and can be repeatedly charged and discharged is expected to increase in the future from the environmental viewpoint. Lithium ion secondary batteries have a high energy density and are used in fields such as mobile phones and notebook personal computers. In addition, with the expansion and development of applications, secondary batteries have reduced resistance, increased capacity, extended life (improved cycle characteristics), improved charge / discharge capacity maintenance rate (rate characteristics) at high rates, etc. Therefore, further improvement in performance is required.

  For the purpose of improving cycle characteristics, a secondary battery composition containing a water-based binder is used as a binder when forming components such as electrodes and separators of lithium ion secondary batteries. The water-based binder does not cover the entire surface of the active material, but covers it appropriately, so that it does not hinder the lithium ion insertion / release reaction. Therefore, in the lithium ion secondary battery, the internal resistance of the battery is reduced and the cycle characteristics are improved.

  For example, Patent Document 1 describes that, when an alloy is used for the negative electrode active material, a water-based negative electrode binder with a large amount of acid is used. In Patent Document 2, in order to increase the adhesion with the current collector, The use of a fluorine-based binder is described.

  Here, as a separator normally used for a lithium ion secondary battery, for example, a microporous film made of a polyolefin resin is used. When the temperature inside the battery reaches around 130 ° C, the separator melts and closes the micropores, thereby preventing the movement of lithium ions and shutting down the current, thereby reducing the safety of the lithium ion secondary battery. Have a role to hold. However, when the battery temperature exceeds, for example, 150 ° C. due to instantaneous heat generation, the separator contracts rapidly, and the positive electrode and the negative electrode may be in direct contact with each other, thereby expanding the location where a short circuit occurs. In this case, the battery temperature may reach a state where it is abnormally overheated to several hundred degrees Celsius or higher.

  For this reason, non-aqueous separators in which a heat-resistant porous membrane layer is laminated on the surface of a separator such as a polyethylene microporous membrane have been studied. The porous membrane layer is a membrane having a large number of linked micropore structures inside, and for binding non-conductive particles, non-conductive particles to each other, and non-conductive particles to a separator or a current collector. Contains a binder. Further, the porous membrane layer can be used by being laminated on an electrode, or can be used as a separator itself.

International Publication No. 2011-037142 JP 2010-146870 A

  Here, from the viewpoint of further improving the performance of the lithium ion secondary battery, the gas generation in the lithium ion secondary battery is suppressed, the swelling of the cell is suppressed, and the porous film layer in the separator or electrode in which the porous film layer is laminated. It is required to improve the adhesion strength.

  An object of the present invention is to use a porous membrane composition for a lithium ion secondary battery, which can obtain a porous membrane layer having a low water content and excellent adhesion strength, and using this porous membrane composition for a lithium ion secondary battery. Providing a separator for a lithium ion secondary battery, an electrode for a lithium ion secondary battery, and a lithium ion secondary battery, and a lithium ion secondary battery using the porous membrane composition for a lithium ion secondary battery It is providing the manufacturing method of a separator, and the manufacturing method of the electrode for lithium ion secondary batteries.

  As a result of intensive studies, the present inventor has found that the above object can be achieved by using a composition containing a specific water-soluble thickener and a carbodiimide compound in addition to the binder, and has completed the present invention.

That is, according to the present invention,
(1) Lithium ion secondary containing non-conductive particles, a water-soluble thickener (A) containing a hydroxyl group or / and a carboxyl group, a carbodiimide compound crosslinking agent (B), and a particulate polymer (C) A porous membrane composition for a secondary battery, wherein the particulate polymer (C) has a functional group that reacts with the carbodiimide compound crosslinking agent (B),
(2) The water-soluble thickener (A) is at least one selected from the group consisting of carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, polyvinyl alcohol, polyacrylic acid or salts thereof. The porous membrane composition for a lithium ion secondary battery according to (1),
(3) The functional group that reacts with the carbodiimide compound crosslinking agent (B) in the particulate polymer (C) is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, a glycidyl ether group, and a thiol group. The porous membrane composition for a lithium ion secondary battery according to (1) or (2),
(4) The water-soluble thickener (A) is 0.2 to 15 parts by weight, the carbodiimide compound crosslinking agent (B) is 0.01 to 10 parts by weight with respect to 100 parts by weight of the non-conductive particles. The porous membrane composition for a lithium ion secondary battery according to any one of (1) to (3), containing 1 to 15 parts by weight of the particulate polymer (C),
(5) A separator for a lithium ion secondary battery obtained by applying the porous film composition for a lithium ion secondary battery according to any one of (1) to (4) on a substrate and drying,
(6) An electrode for a lithium ion secondary battery obtained by applying the porous film composition for a lithium ion secondary battery according to any one of (1) to (4) on an electrode plate and drying the composition,
(7) A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the separator is a separator for a lithium ion secondary battery according to (5),
(8) A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the positive electrode and / or the negative electrode is an electrode for a lithium ion secondary battery according to (6) battery,
(9) By the manufacturing method of the separator for lithium ion secondary batteries obtained by apply | coating the porous film composition for lithium ion secondary batteries in any one of (1)-(4) on a board | substrate, and drying. A method for producing a separator for a lithium ion secondary battery, comprising: a step of applying the porous film composition for a lithium ion secondary battery on a substrate; and a step of drying at 50 to 200 ° C.
(10) A method for producing an electrode for a lithium ion secondary battery obtained by applying the porous membrane composition for a lithium ion secondary battery according to any one of (1) to (4) on an electrode plate and drying the composition. And the manufacturing method of the electrode for lithium ion secondary batteries which has the process of apply | coating the said porous membrane composition for lithium ion secondary batteries on an electrode plate, and the process of drying at 50-200 degreeC is provided. .

  According to the porous membrane composition for a lithium ion secondary battery according to the present invention, it is possible to obtain a porous membrane layer having a low water content and excellent adhesion strength. Further, according to the present invention, a separator for a lithium ion secondary battery, an electrode for a lithium ion secondary battery and a lithium ion secondary battery, and a porous for a lithium ion secondary battery using the porous membrane composition for a lithium ion secondary battery. The manufacturing method of the separator for lithium ion secondary batteries using a membrane composition, and the manufacturing method of the electrode for lithium ion secondary batteries can be provided.

  Hereinafter, a porous membrane composition for a lithium ion secondary battery according to an embodiment of the present invention will be described. The porous membrane composition for a lithium ion secondary battery of the present invention comprises non-conductive particles, a water-soluble thickener (A) containing a hydroxyl group and / or a carboxyl group, a carbodiimide compound crosslinking agent (B), and particles. It is a porous membrane composition for lithium ion secondary batteries containing a particulate polymer (C), and the particulate polymer (C) has a functional group that reacts with the carbodiimide compound crosslinking agent (B).

(Non-conductive particles)
The material constituting the non-conductive particles used in the porous membrane composition for a lithium ion secondary battery of the present invention (hereinafter sometimes referred to as “porous membrane composition”) is the operating environment of the lithium ion secondary battery. It is desirable that it be stable and electrochemically stable. For example, various non-conductive inorganic particles and organic particles can be used.

As the material of the inorganic particles, a material that is electrochemically stable and suitable for preparing a porous film composition by mixing with other materials, for example, a viscosity adjusting agent described later is preferable. From this point of view, the inorganic particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ ), bakelite, magnesium oxide, magnesium hydroxide, iron oxide, Silicon oxide, titanium oxide (titania), oxides such as calcium oxide, nitrides such as aluminum nitride and silicon nitride, silica, barium sulfate, barium fluoride, calcium fluoride, etc. Among these, in electrolyte Oxides are preferred from the standpoint of stability and potential stability at high temperatures, and titanium oxide, alumina, boehmite, magnesium oxide and magnesium hydroxide are particularly preferred from the standpoint of low water absorption and excellent heat resistance (eg, resistance to high temperatures of 180 ° C. or higher). Alumina, boehmite, magnesium oxide and water Magnesium reduction is particularly preferred.

  As the organic particles, polymer (polymer) particles are usually used. By adjusting the type and amount of functional groups on the surface of the organic particles, the affinity for water can be controlled, and thus the amount of water contained in the porous membrane of the present invention can be controlled. Preferred examples of the organic material for the non-conductive particles include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer compound forming the particles may be a homopolymer or a copolymer. In the case of a copolymer, any of a block copolymer, a random copolymer, a graft copolymer, and an alternating copolymer is used. it can. Furthermore, it may be at least partially modified or a crosslinked product. And a mixture of these may be sufficient. In the case of a cross-linked product, the cross-linking agent includes a cross-linked product having an aromatic ring such as divinylbenzene, a polyfunctional acrylate cross-linked product such as ethylene glycol dimethacrylate, and a cross-linked product having an epoxy group such as glycidyl acrylate and glycidyl methacrylate. Can be mentioned.

  The non-conductive particles may be subjected to element substitution, surface treatment, solid solution, or the like, if necessary. Further, the non-conductive particles may include one kind of the above materials alone in one particle, or may contain two or more kinds in combination at an arbitrary ratio. . Further, the non-conductive particles may be used in combination of two or more kinds of particles formed of different materials.

  The volume average particle diameter D50 of the non-conductive particles is preferably from the viewpoint of increasing the capacity of the lithium ion secondary battery because a uniform porous film can be obtained even if the porous film is thin. It is 0.1-5 micrometers, More preferably, it is 0.2-2 micrometers or less, More preferably, it is 0.2-1 micrometers. Here, the volume average particle diameter D50 represents the particle diameter at which the cumulative volume calculated from the small particle diameter side becomes 50% in the particle size distribution measured by the laser diffraction method.

Further, the BET specific surface area of these non-conductive particles is specifically 0.9 to ²⁰⁰ m ² / g from the viewpoint of suppressing particle aggregation and optimizing the fluidity of the porous membrane composition. It is preferably 1.5 to 150 m ² / g. The BET specific surface area of the nonconductive particles is measured by a BET measurement method by adsorbing nitrogen gas to the nonconductive particles using a specific surface area measuring device (Gemini 2310: manufactured by Shimadzu Corporation).

  In the present invention, examples of the shape of the nonconductive particles include a spherical shape, an elliptical spherical shape, a polygonal shape, a tetrapod (registered trademark) shape, a plate shape, and a scale shape. Among these, from the viewpoint of increasing the porosity of the porous membrane and suppressing the decrease in ionic conductivity due to the porous membrane separator, a tetrapod (registered trademark) shape, a plate shape, and a scale shape are preferable.

(Water-soluble thickener (A))
The water-soluble thickener (A) used in the porous membrane composition for a lithium ion secondary battery of the present invention contains a hydroxyl group and / or a carboxyl group. The water-soluble thickener (A) used in the present invention is a thickener having an insoluble content of less than 1.0% by weight when 25 g of the thickener is dissolved in 100 g of water at 25 ° C. .

  As the water-soluble thickener (A), carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, hydroxyethyl methyl cellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof is preferably used, and carboxymethyl cellulose or polyacrylic acid is used. More preferred.

  The content ratio of the water-soluble thickener (A) in the porous film composition of the present invention is preferably 0.2 to 15 parts by weight, more preferably 0.5 to 10 parts by weight with respect to 100 parts by weight of the non-conductive particles. Part by weight, more preferably 0.5 to 8 parts by weight. If the content ratio of the water-soluble thickener (A) is too large, the drying rate when obtaining the porous membrane tends to be slow. Moreover, when the content rate of a water-soluble thickener (A) is too small, it will become the tendency for the adhesive strength of a porous film to fall.

(Carbodiimide compound crosslinking agent (B))
The carbodiimide compound crosslinking agent (B) used in the porous membrane composition for a lithium ion secondary battery of the present invention reacts with a functional group possessed by the particulate polymer (C) described later.

The carbodiimide compound has a carbodiimide group represented by the general formula (1): -N = C = N- (1) in the molecule, and the water-soluble thickener between the water-soluble thickener (A). There is no particular limitation as long as it is a crosslinkable compound capable of forming a crosslinked structure between the agent (A) and the particulate polymer (C) and between the particulate polymers (C). And as such a carbodiimide compound crosslinking agent (B), for example, a compound having two or more carbodiimide groups, specifically, a general formula (2): -N = C = N-R ^1. 2) [In General Formula (2), R ¹ represents a divalent organic group. Suitable examples include polycarbodiimides and / or modified polycarbodiimides having a repeating unit represented by the formula: In addition, in this specification, a modified polycarbodiimide means resin obtained by making the reactive compound mentioned later react with polycarbodiimide.

(Synthesis of polycarbodiimide)
The method for synthesizing the polycarbodiimide is not particularly limited. For example, the organic polyisocyanate is reacted in the presence of a catalyst for promoting the carbodiimidization reaction of the isocyanate group (hereinafter referred to as “carbodiimidization catalyst”). Polycarbodiimide can be synthesized. The polycarbodiimide having a repeating unit represented by the general formula (2) is a copolymer of an oligomer obtained by reacting an organic polyisocyanate (carbodiimide oligomer) and a monomer copolymerizable with the oligomer. Can also be synthesized. In addition, as organic polyisocyanate used for the synthesis | combination of this polycarbodiimide, organic diisocyanate is preferable.

  Examples of the organic diisocyanate used for the synthesis of polycarbodiimide include those described in JP-A-2005-49370. Among these, 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate are particularly preferable from the viewpoint of storage stability of a porous film composition containing polycarbodiimide as the carbodiimide compound crosslinking agent (B). An organic diisocyanate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  In addition to the above organic diisocyanates, organic polyisocyanates having three or more isocyanate groups (trifunctional or higher functional organic polyisocyanates), and stoichiometric excesses of trifunctional or higher organic polyisocyanates and difunctional or higher polyfunctionality. Terminal isocyanate prepolymer obtained by reaction with a reactive active hydrogen-containing compound (hereinafter, the trifunctional or higher functional organic polyisocyanate and the terminal isocyanate prepolymer are collectively referred to as “trifunctional or higher functional organic polyisocyanates”). May be used. Examples of such trifunctional or higher functional organic polyisocyanates include those described in JP-A-2005-49370. Trifunctional or higher functional organic polyisocyanates may be used alone or in combination of two or more at any ratio. The amount of the trifunctional or higher functional organic polyisocyanate used in the polycarbodiimide synthesis reaction is preferably 40 parts by weight or less, more preferably 20 parts by weight or less per 100 parts by weight of the organic diisocyanate.

  Furthermore, in the synthesis of polycarbodiimide, an organic monoisocyanate can be added as necessary. By adding an organic monoisocyanate, when the organic polyisocyanate contains organic polyisocyanates having a functionality of 3 or more, the molecular weight of the resulting polycarbodiimide can be appropriately regulated, and the organic diisocyanate is used in combination with the organic monoisocyanate. By doing so, a polycarbodiimide having a relatively small molecular weight can be obtained. Examples of such organic monoisocyanates include those described in JP-A-2005-49370. An organic monoisocyanate may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The amount of the organic monoisocyanate used in the synthesis reaction of the polycarbodiimide depends on the molecular weight required for the polycarbodiimide to be obtained and the presence or absence of the use of trifunctional or higher functional organic polyisocyanates. It is preferably 40 parts by weight or less, more preferably 20 parts by weight or less per 100 parts by weight of the functional or higher organic polyisocyanate) component.

  Examples of the carbodiimidization catalyst include phospholene compounds, metal carbonyl complexes, metal acetylacetone complexes, and phosphate esters. Specific examples of these are disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-49370. A carbodiimidization catalyst may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. The amount of the carbodiimidization catalyst used is preferably 0.001 to 30 parts by weight, more preferably 0, per 100 parts by weight of the total organic isocyanate (organic monoisocyanate, organic diisocyanate, and trifunctional or higher organic polyisocyanate) component. 0.01 to 10 parts by weight.

  The carbodiimidization reaction of the organic polyisocyanate can be carried out in the absence of a solvent or in a suitable solvent. The solvent for carrying out the synthesis reaction in the solvent is not particularly limited as long as it can dissolve the polycarbodiimide or carbodiimide oligomer generated by heating during the synthesis reaction, and is a halogenated hydrocarbon solvent, ether solvent. , Ketone solvents, aromatic hydrocarbon solvents, amide solvents, aprotic polar solvents, and acetate solvents. Specific examples of these are disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-49370. These solvents may be used alone or in combination of two or more at any ratio. The amount of the solvent used in the polycarbodiimide synthesis reaction is such that the concentration of the total organic isocyanate component is preferably 0.5 to 60% by weight, more preferably 5 to 50% by weight. If the concentration of the total organic isocyanate component in the solvent is too high, the resulting polycarbodiimide or carbodiimide oligomer may gel during the synthesis reaction. Moreover, when the density | concentration of all the organic isocyanate components in a solvent is too low, reaction rate will become slow and it will become the tendency for productivity to fall.

  The temperature of the carbodiimidization reaction of the organic polyisocyanate is appropriately selected according to the type of the organic isocyanate component and the carbodiimidization catalyst, but is preferably 20 to 200 ° C. In the carbodiimidization reaction of the organic polyisocyanate, the organic isocyanate component may be added in the whole amount before the reaction, or a part or the whole thereof may be added continuously or stepwise during the reaction. Further, in the present invention, a compound capable of reacting with an isocyanate group is added at an appropriate reaction stage from the initial stage to the late stage of the carbodiimidization reaction of the organic polyisocyanate, and the terminal isocyanate group of the polycarbodiimide is sealed. The molecular weight of the polycarbodiimide can also be adjusted. Further, the molecular weight of the resulting polycarbodiimide can be regulated to a predetermined value by adding in the latter stage of the carbodiimidization reaction of the organic polyisocyanate. Examples of such a compound that can react with an isocyanate group include alcohols such as methanol, ethanol, i-propanol, and cyclohexanol; and amines such as dimethylamine, diethylamine, and benzylamine.

  Moreover, as a monomer copolymerizable with a carbodiimide oligomer, an oligomer obtained by using a dihydric or higher alcohol, a dihydric or higher alcohol as a monomer, and an ester thereof, for example, 2 such as ethylene glycol and propylene glycol A hydric alcohol, polyalkylene oxide, polyethylene glycol monomethacrylate, polypropylene glycol monomethacrylate, polyethylene glycol monoacrylate, or polypropylene glycol monoacrylate is preferred.

  For example, polycarbodiimide having a polycarbodiimide group and a monomer unit derived from a divalent alcohol is synthesized by copolymerizing a divalent alcohol having a hydroxyl group at both ends of the molecular chain with a carbodiimide oligomer by a known method. can do. Thus, when the polycarbodiimide as the carbodiimide compound cross-linking agent (B) has a monomer unit derived from a divalent or higher alcohol, preferably a monomer unit derived from a divalent alcohol, a porous material containing the polycarbodiimide is contained. The wettability with respect to the electrolytic solution of the porous film formed from the membrane composition is improved, and the pouring property of the electrolytic solution in the production of the secondary battery including the negative electrode can be improved. In addition, when the above-mentioned alcohol is copolymerized, the water solubility of the polycarbodiimide can be increased, and the polycarbodiimide is self-micelleized in water (the hydrophobic carbodiimide group is covered with a hydrophilic ethylene glycol chain). Therefore, chemical stability can be improved.

  The polycarbodiimide compound crosslinking agent described above is used for preparing the porous membrane composition of the present invention as a solution or as a solid separated from the solution. As a method for separating polycarbodiimide from a solution, for example, a polycarbodiimide solution is added to a non-solvent inert to the polycarbodiimide, and the resulting precipitate or oil is separated and collected by filtration or decantation. A method of separating and collecting by spray drying; a method of separating and collecting by using a change in solubility with respect to the temperature of the solvent used in the synthesis of the obtained polycarbodiimide, that is, immediately after the synthesis, the solvent is dissolved in the solvent In the case where polycarbodiimide is precipitated by lowering the temperature of the system, a method of separating and collecting from the turbid liquid by filtration or the like can be exemplified, and further, these separation and collecting methods can be appropriately combined. From the viewpoint of increasing the crosslinking rate with the water-soluble thickener (A), the polystyrene-equivalent number average molecular weight (hereinafter referred to as “Mn”) obtained by gel permeation chromatography (GPC) of polycarbodiimide in the present invention is as follows. Preferably it is 1,000-200,000, More preferably, it is 2,000-100,000 or less.

(Synthesis of modified polycarbodiimide)
Next, a method for synthesizing the modified polycarbodiimide will be described. The modified polycarbodiimide is prepared by adding at least one reactive compound to at least one polycarbodiimide having a repeating unit represented by the general formula (2) at an appropriate temperature in the presence or absence of a suitable catalyst. It can be synthesized by reaction (hereinafter referred to as “denaturation reaction”).

  The reactive compound used for the synthesis of the modified polycarbodiimide has one group having reactivity with the polycarbodiimide (hereinafter, simply referred to as “reactive group”) in the molecule, and another functional group. The compound which has. This reactive compound can be an aromatic compound, an aliphatic compound or an alicyclic compound, and the ring structure in the aromatic compound and the alicyclic compound may be a carbocyclic ring or a heterocyclic ring. The reactive group in the reactive compound may be a group having active hydrogen, and examples thereof include a carboxyl group or a primary or secondary amino group. And a reactive compound has another functional group in addition to one reactive group in the molecule | numerator. Other functional groups possessed by the reactive compound include groups having an action of promoting the crosslinking reaction of polycarbodiimide and / or modified polycarbodiimide, and the second and subsequent groups in one molecule of the reactive compound (that is, as described above). In addition to reactive groups, the above-mentioned groups having active hydrogen are also included. For example, carboxyl groups and primary groups exemplified as groups having active hydrogen in addition to carboxylic anhydride groups and tertiary amino groups. Or a secondary amino group etc. can be mentioned. As these other functional groups, two or more identical or different groups may exist in one molecule of the reactive compound.

  Examples of the reactive compound include those described in JP-A-2005-49370. Of these, trimellitic anhydride and nicotinic acid are preferable. A reactive compound may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the reactive compound used in the modification reaction for synthesizing the modified polycarbodiimide is appropriately adjusted according to the type of polycarbodiimide and reactive compound, the physical properties required of the resulting modified polycarbodiimide, etc. The ratio of the reactive group in the reactive compound to 1 mol of the repeating unit represented by the general formula (2) is preferably 0.01 mol or more, more preferably 0.02 mol or more, preferably The amount is 1 mol or less, more preferably 0.8 mol or less. There exists a possibility that the storage stability of the porous film composition containing a modified polycarbodiimide may fall that the said ratio is less than 0.01 mol. On the other hand, when the ratio exceeds 1 mol, the original properties of polycarbodiimide may be impaired.

  In the modification reaction, the reaction between the reactive group in the reactive compound and the repeating unit represented by the general formula (2) of the polycarbodiimide proceeds quantitatively, and the functionality corresponding to the amount of the reactive compound used. Groups are introduced into the modified polycarbodiimide. The modification reaction can be carried out in the absence of a solvent, but is preferably carried out in a suitable solvent. Such a solvent is not particularly limited as long as it is inactive with respect to polycarbodiimide and a reactive compound and can dissolve them. Examples thereof are used for the synthesis of the above-mentioned polycarbodiimide. And ether solvents, amide solvents, ketone solvents, aromatic hydrocarbon solvents, aprotic polar solvents, and the like. These solvents may be used alone or in combination of two or more at any ratio. Moreover, when the solvent used at the time of the synthesis | combination of polycarbodiimide can be used for modification | denaturation reaction, the polycarbodiimide solution obtained by the synthesis | combination can also be used as it is. The amount of the solvent used in the modification reaction is preferably 10 to 10,000 parts by weight, preferably 50 to 5,000 parts by weight per 100 parts by weight of the total reaction raw material.

  The temperature of the modification reaction is appropriately selected according to the type of polycarbodiimide or reactive compound, but is preferably −10 to 100 ° C. or less, more preferably −10 to 80 ° C. Mn of the modified polycarbodiimide in the present invention is preferably 1,000 to 200,000, more preferably 2,000 to 400,000 from the viewpoint of increasing the crosslinking rate with the water-soluble thickener (A).

  Here, the chemical formula amount (NCN equivalent) per mole of the carbodiimide group (—N═C═N—) of the carbodiimide compound is preferably 300 to 600, more preferably 400 to 500. When the NCN equivalent of the carbodiimide compound is too small, the storage stability of the porous membrane composition is lowered. On the other hand, if the NCN equivalent of the carbodiimide compound is too large, the crosslinking reaction will not proceed sufficiently.

The NCN equivalent of the carbodiimide compound is obtained, for example, by obtaining the polystyrene-equivalent number average molecular weight of the carbodiimide compound using GPC (gel permeation chromatography) and carbodiimide per molecule of the carbodiimide compound using IR (infrared spectroscopy). The number of groups can be quantitatively analyzed and calculated using the following formula.
NCN equivalent = (Number average molecular weight in terms of polystyrene of carbodiimide compound) / (Number of carbodiimide groups per molecule of carbodiimide compound)

(Properties of carbodiimide compound crosslinking agent (B))
Here, the viscosity of the 1% by weight aqueous solution of the carbodiimide compound crosslinking agent (B) described above is preferably 5000 mPa · s or less, more preferably 700 mPa · s, from the viewpoint that the adhesion strength of the porous film can be improved. s or less, particularly preferably 150 mPa · s or less. The viscosity of the 1% by weight aqueous solution of the carbodiimide compound crosslinking agent (B) is a value when measured at 25 ° C. and a rotation speed of 60 rpm using a B-type viscometer.

  The carbodiimide compound crosslinking agent (B) is preferably water-soluble. The water-soluble carbodiimide compound crosslinking agent (B) prevents the carbodiimide compound crosslinking agent (B) from being unevenly distributed in the aqueous porous film composition, and forms a suitable crosslinked structure in the resulting porous film. be able to. Therefore, the adhesion strength of the porous film in the obtained lithium ion secondary battery is ensured, and electrical characteristics such as initial coulomb efficiency, initial resistance, cycle characteristics are improved, and in addition, resistance increase after cycling is suppressed. Can do. Furthermore, the water resistance of the porous membrane can be improved.

  Here, in this specification, that the carbodiimide compound crosslinking agent (B) is “water-soluble” is obtained by adding 1 part by weight of the crosslinking agent (corresponding to solid content) per 100 parts by weight of ion-exchanged water and stirring. The mixture obtained is adjusted to at least one of the conditions within a temperature range of 20 ° C. to 70 ° C. and within a range of pH 3 to 12 (pH adjustment uses NaOH aqueous solution and / or HCl aqueous solution). The solid content of the residue remaining on the screen without passing through the screen when passing through a 250 mesh screen does not exceed 50% by weight with respect to the solid content of the added crosslinking agent. Even if the mixture of the carbodiimide compound crosslinking agent (B) and water is in an emulsion state that separates into two phases when allowed to stand, the carbodiimide compound crosslinking agent (B) is water-soluble as long as the above definition is satisfied. Suppose that In addition, from the viewpoint of promoting the formation reaction of the crosslinked structure and improving the adhesion strength of the porous film and the cycle characteristics of the obtained lithium ion secondary battery, the mixture of the carbodiimide compound crosslinking agent (B) and water is More preferably, the carbodiimide compound cross-linking agent (B) does not separate into two phases (in a one-phase water-soluble state), that is, the carbodiimide compound crosslinking agent (B) is one-phase water-soluble.

Further, the water content of the carbodiimide compound crosslinking agent (B) is preferably 80% by weight or more, and more preferably 90% by weight or more for the same reason as described above that the crosslinking agent is preferably water-soluble. The “water solubility” of the carbodiimide compound crosslinking agent (B) means that the mixture obtained by adding 1 part by weight of the crosslinking agent (corresponding to solid content) per 100 parts by weight of ion-exchanged water and stirring the mixture to 25 ° C. and pH 7 When the weight of the solid content of the residue remaining on the screen without passing through the screen is adjusted to be X wt% when adjusted and passed through the 250 mesh screen Is defined by the following formula.
Water solubility = (100−X) wt%

  The content ratio of the carbodiimide compound crosslinking agent (B) in the porous film composition of the present invention is preferably 0.01 to 10 parts by weight, more preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the non-conductive particles. Part, more preferably 0.01 to 1 part by weight. When the content ratio of the carbodiimide compound crosslinking agent (B) is too large, the adhesion strength of the porous film is lowered, and the cycle characteristics of the obtained lithium ion secondary battery tend to be lowered. Moreover, when the content rate of a carbodiimide compound crosslinking agent (B) is too small, it will become the tendency for the adhesive strength of a porous film to fall.

(Particulate polymer (C))
The particulate polymer (C) used in the present invention has a functional group that reacts with the carbodiimide compound crosslinking agent (B). The particulate polymer (C) preferably comprises a polymer unit of a (meth) acrylic acid ester monomer. In the present specification, “(meth) acryl” means “acryl” and “methacryl”.

  As a polymerization unit of (meth) acrylic acid ester monomer, for example, methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, pentyl acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate Alkyl acrylates such as 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, t -Butyl methacrylate, pentyl methacrylate, hexyl methacrylate , Heptyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, nonyl methacrylate, decyl methacrylate, lauryl methacrylate, n- tetradecyl methacrylate, methacrylic acid alkyl esters such as stearyl methacrylate. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Moreover, as a functional group which reacts with the carbodiimide compound crosslinking agent (B) in a particulate polymer (C), a carboxyl group, a hydroxyl group, a glycidyl ether group, and a thiol group are preferable, and it uses combining a carboxyl group and a glycidyl ether group. It is more preferable.

  As a functional group that reacts with the carbodiimide compound crosslinking agent (B), examples of the monomer that can be used in the production of the particulate polymer (C) having a carboxylic acid group include an ethylenically unsaturated carboxylic acid monomer. . Specific examples of the ethylenically unsaturated carboxylic acid monomer include monocarboxylic and dicarboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid, and anhydrides thereof. . Among these, acrylic acid, methacrylic acid and itaconic acid are preferable as the ethylenically unsaturated carboxylic acid monomer from the viewpoint of the stability of the porous film composition. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  As a functional group that reacts with the carbodiimide compound crosslinking agent (B), examples of the monomer that can be used in the production of the particulate polymer (C) having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, Hydroxypropyl acrylate, hydroxypropyl methacrylate, hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate, di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl) maleate, 2-hydroxyethyl methyl fumarate and the like can be mentioned. Among these, 2-hydroxyethyl acrylate is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of the unsaturated monomer having a glycidyl ether group that can be used in the production of the particulate polymer (C) having a glycidyl ether group as a functional group that reacts with the carbodiimide compound crosslinking agent (B) include glycidyl acrylate. And glycidyl methacrylate. Of these, glycidyl methacrylate is preferred. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of the monomer unit having a thiol group that can be used in the production of the particulate polymer (C) having a thiol group as a functional group that reacts with the carbodiimide compound crosslinking agent (B) include pentaerythritol tetrakis (3-mercapto). Butyrate), trimethylolpropane tris (3-mercaptobutyrate), trimethylolethane tris (3-mercaptobutyrate), and the like. Among these, pentaerythritol tetrakis (3-mercaptobutyrate) is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  The functional group that reacts with the carbodiimide compound cross-linking agent (B) in the particulate polymer (C) is a monomer containing a functional group that reacts with the carbodiimide compound cross-linking agent (B) as described above. For example, after polymerizing a particulate polymer that does not have a functional group that reacts with the carbodiimide compound crosslinking agent (B), the functional group in the particulate polymer is converted to a carbodiimide compound crosslinking agent ( The particulate polymer (C) may be prepared by introducing a part or all of the functional groups that react with B) by substitution. The repeating unit in the particulate polymer (C) having the “functional group that reacts with the carbodiimide compound cross-linking agent (B)” introduced in this way also has a “functionality that reacts with the carbodiimide compound cross-linking agent (B)”. It shall be included in the “monomer unit containing a group”.

  And although the content rate of the monomer unit containing the functional group which reacts with the carbodiimide compound crosslinking agent (B) in a particulate polymer (C) is not specifically limited, Mechanical of the obtained particulate polymer (C) From the viewpoint of excellent stability and chemical stability, 0.5 to 10% by weight is preferred, 1.0 to 8% by weight is more preferred, and 1.5 to 5% by weight is even more preferred.

  Further, the particulate polymer (C) may contain any repeating unit other than those described above as long as the effects of the present invention are not significantly impaired. Examples of the monomer corresponding to the arbitrary repeating unit include a vinyl cyanide monomer, an unsaturated carboxylic acid alkyl ester monomer, and an unsaturated carboxylic acid amide monomer. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Although the content rate of the monomer corresponding to the arbitrary repeating units in the particulate polymer (C) is not particularly limited, the total amount is preferably 0.5 to 10% by weight, more preferably 1.0 to 8% by weight. Preferably, 1.5 to 5% by weight is more preferable.

  Examples of the vinyl cyanide monomer include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile, α-ethylacrylonitrile and the like. Of these, acrylonitrile and methacrylonitrile are preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of unsaturated carboxylic acid alkyl ester monomers include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl itaconate, monomethyl Examples thereof include fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like. Of these, methyl methacrylate is preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Examples of the unsaturated carboxylic acid amide monomer include acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N, N-dimethylacrylamide and the like. Of these, acrylamide and methacrylamide are preferable. In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Furthermore, the particulate polymer (C) may be produced using monomers used in usual emulsion polymerization such as ethylene, propylene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, and the like. . In addition, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  In the particulate polymer (C), other monomer units other than an aliphatic conjugated diene monomer unit, an aromatic vinyl monomer unit, and a monomer unit containing a functional group that reacts with the crosslinking agent (B) The content ratio of is not particularly limited, but is preferably 0.5 to 10% by weight in total, more preferably 1.0 to 8% by weight, and still more preferably 1.5 to 5% by weight.

And the particulate polymer (C) consisting of a copolymer having an aliphatic conjugated diene monomer unit and an aromatic vinyl monomer unit is, for example, a monomer composition containing the above-mentioned monomer. It is produced by polymerization in an aqueous solvent.
Here, the content ratio of each monomer in the monomer composition is usually the same as the content ratio of the repeating unit in the desired particulate polymer (C).

  The aqueous solvent is not particularly limited as long as the particulate polymer (C) can be dispersed in a particle state, and the aqueous solvent preferably has a boiling point at normal pressure of 80 to 350 ° C, more preferably 100 to 300 ° C. Selected from solvents.

  Specifically, examples of the aqueous solvent include water; ketones such as diacetone alcohol and γ-butyrolactone; alcohols such as ethyl alcohol, isopropyl alcohol, and normal propyl alcohol; propylene glycol monomethyl ether, methyl cellosolve, and ethyl cellosolve. , Glycol ethers such as ethylene glycol tertiary butyl ether, butyl cellosolve, 3-methoxy-3methyl-1-butanol, ethylene glycol monopropyl ether, diethylene glycol monobutyl ether, triethylene glycol monobutyl ether, dipropylene glycol monomethyl ether; 1,3 -Ethers such as dioxolane, 1,4-dioxolane and tetrahydrofuran; Among these, water is particularly preferable from the viewpoint that it is not flammable and a dispersion of particles of the particulate polymer (C) can be easily obtained. In addition, you may use water as a main solvent, and mix and use aqueous solvents other than said water in the range which can ensure the dispersion state of the particle | grains of a particulate polymer (C).

The polymerization method is not particularly limited, and any method such as a solution polymerization method, a suspension polymerization method, a bulk polymerization method, and an emulsion polymerization method can be used. As the polymerization method, any method such as ionic polymerization, radical polymerization, and living radical polymerization can be used. In addition, it is easy to obtain a high molecular weight, and since the polymer is obtained in a state of being dispersed in water as it is, redispersion treatment is unnecessary, and it can be used for production of the porous membrane composition of the present invention as it is. From the viewpoint of production efficiency, the emulsion polymerization method is particularly preferable.
The emulsion polymerization can be performed according to a conventional method.

  And generally used emulsifiers, dispersants, polymerization initiators, polymerization aids and the like used for the polymerization can be used, and the amount used is also generally used. In the polymerization, seed polymerization may be performed using seed particles. The polymerization conditions can also be arbitrarily selected depending on the polymerization method and the type of polymerization initiator.

Here, the aqueous dispersion of particulate polymer (C) particles obtained by the above-described polymerization method is, for example, alkali metal (for example, Li, Na, K, Rb, Cs) hydroxide, ammonia, inorganic ammonium. Using a basic aqueous solution containing a compound (for example, NH ₄ Cl), an organic amine compound (for example, ethanolamine, diethylamine, etc.), the pH is preferably in the range of 5 to 10, more preferably 5 to 9. You may adjust. Among these, pH adjustment with an alkali metal hydroxide is preferable because it improves the adhesion strength of the porous film.

(Properties of particulate polymer (C))
Usually, the particulate polymer (C) is water-insoluble. Therefore, the particulate polymer (C) is usually in the form of particles in the aqueous porous membrane composition, and is contained in the porous membrane while maintaining the particle shape.

  The number average particle size of the particulate polymer (C) is preferably 50 to 500 nm, more preferably 70 to 400 nm. The number average particle diameter can be easily measured by a transmission electron microscope method, a Coulter counter, a laser diffraction scattering method, or the like.

  The content ratio of the particulate polymer (C) in the porous film composition of the present invention is preferably 1 to 15 parts by weight, more preferably 2 to 15 parts by weight, further preferably 100 parts by weight of non-conductive particles. Is 2 to 10 parts by weight. When the content ratio of the particulate polymer (C) is too large, the adhesion strength of the porous film is lowered, and the cycle characteristics of the obtained lithium ion secondary battery tend to be lowered. Moreover, when the content rate of a particulate polymer (C) is too small, it will become the tendency for the adhesive strength of a porous film to fall.

(Porous membrane composition)
The porous membrane composition of the present invention comprises non-conductive particles, a water-soluble thickener (A) containing a hydroxyl group or / and a carboxyl group, a carbodiimide compound crosslinking agent (B), and a particulate polymer (C). It is obtained by mixing these components and a dispersion medium.

  The mixing method is not particularly limited, and examples thereof include a method using a mixing apparatus such as a stirring type, a shaking type, and a rotary type. In addition, a method using a dispersion kneader such as a homogenizer, a ball mill, a sand mill, a roll mill, a planetary mixer, and a planetary kneader can be used.

  In the porous film composition of the present invention, it is preferable to use water as a dispersion medium. In the present invention, a dispersion medium in which a hydrophilic solvent is mixed may be used as long as the dispersion stability of the porous film composition is not impaired. Examples of the hydrophilic solvent include methanol, ethanol, N-methylpyrrolidone and the like, and it is preferably 5% by weight or less based on water.

  The solid content concentration of the porous membrane composition is preferably 10 to 65% by weight. When the solid content concentration is too high, the coating property of the porous membrane composition tends to be lowered. On the other hand, if the solid content concentration is too low, it is difficult for water to escape from the porous membrane, and thus the moisture content tends to be difficult to reduce.

  Moreover, it is preferable that the viscosity of a porous film composition is 15-500 mPa * s. The viscosity of the porous film composition is a value measured using a B-type viscometer at a temperature of 25 ° C. and a rotation speed of 60 rpm.

(Porous membrane for secondary battery)
A porous film for a secondary battery (hereinafter sometimes referred to as “porous film”) can be obtained by applying the porous film composition described above onto a substrate and drying it.

  The porous film may be used by being laminated on an organic separator or an electrode, or may be used as the organic separator itself. The porous film formed from the binder resin composition for a secondary battery separator porous film may be used by being laminated on an organic separator, or may be used as the organic separator itself. Moreover, the porous film formed with the binder resin composition for secondary battery electrode porous films can be laminated | stacked and used for an electrode.

(Method for producing porous film for secondary battery)
As a method for producing a porous membrane for a secondary battery, (I) the above non-conductive particles, water-soluble thickener (A), carbodiimide compound crosslinking agent (B), particulate polymer (C), dispersion medium A method of applying a porous film composition comprising a predetermined substrate (a positive electrode plate, a negative electrode plate or an organic separator) and then drying; A porous film composition containing a sticking agent (A), a carbodiimide compound crosslinking agent (B), a particulate polymer (C), a dispersion medium and an optional component is used as a base material (a positive electrode plate, a negative electrode plate or (III) The above non-conductive particles, water-soluble thickener (A), carbodiimide compound crosslinking agent (B), particulate polymer (C), dispersion medium And a porous film composition containing an optional component is applied to a release film and formed into a film. And the like; a porous membrane a given substrate (electrode plate for the positive electrode, the electrode plate or an organic separator for the negative electrode) method of transferring onto. Among these, (I) the method of applying a porous film composition to a substrate (a positive electrode plate, a negative electrode plate or an organic separator) and then drying is easy to control the film thickness of the porous film. Most preferred.
The porous membrane of the present invention is manufactured by the above-described methods (I) to (III), and the detailed manufacturing method will be described below.

  In the method (I), the porous film composition of the present invention is produced by applying the porous film composition onto a predetermined substrate (positive electrode plate, negative electrode plate or organic separator) and drying. The

  The method for applying the porous film composition onto the substrate is not particularly limited, and examples thereof include a doctor blade method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method. Among these, the gravure method is preferable in that a uniform porous film can be obtained.

  Examples of the drying method include drying by warm air, hot air, low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying temperature is preferably 50 to 200 ° C.

In the method (II), the porous film composition of the present invention is produced by immersing the porous film composition in a substrate (positive electrode plate, negative electrode plate or organic separator) and drying. The method for immersing the porous film composition in the substrate is not particularly limited, and for example, the porous film composition can be immersed by dip coating with a dip coater or the like.
Examples of the drying method include the same methods as the drying method in the method (I) described above.

In the method (III), the porous film composition is applied on a release film and formed into a film, thereby producing a porous film formed on the release film. Next, the obtained porous film is transferred onto a substrate (a positive electrode plate, a negative electrode plate, or an organic separator).
As the coating method, the same method as the coating method in the above-mentioned method (I) can be mentioned. The transfer method is not particularly limited.

  The porous membrane obtained by the methods (I) to (III) is then subjected to pressure treatment using a die press or a roll press, if necessary, by a base material (electrode plate for positive electrode, electrode for negative electrode). The adhesion between the plate or the organic separator) and the porous film can also be improved. However, at this time, if the pressure treatment is excessively performed, the porosity of the porous film may be impaired, so the pressure and the pressure time are controlled appropriately.

  The film thickness of the porous film is not particularly limited and is appropriately set according to the use or application field of the porous film. However, if the film is too thin, a uniform film cannot be formed. Since the capacity per volume (weight) decreases, 0.5 to 50 μm is preferable, and 0.5 to 10 μm is more preferable.

  The porous film of the present invention is formed on the surface of a substrate (a positive electrode plate, a negative electrode plate or an organic separator), and is particularly preferably used as a protective film or separator for an electrode active material layer described later. The porous film of the present invention may be formed on any surface of the secondary battery positive electrode, the secondary battery negative electrode or the organic separator, or may be formed on all of the positive electrode, the negative electrode and the organic separator.

(Base material)
(Electrode plate for positive electrode)
The positive electrode plate is composed of a positive electrode composition containing a positive electrode active material, a positive electrode binder, a solvent used for preparing the electrode plate, a conductive agent used as necessary, a thickener, and the like. It is obtained by applying to the surface and drying. That is, it can be obtained by forming a positive electrode active material layer on the surface of the current collector.

  Examples of the positive electrode active material include metal oxides capable of reversibly doping and dedoping lithium ions. Examples of the metal oxide include lithium cobaltate, lithium nickelate, lithium manganate, and lithium iron phosphate. In addition, the positive electrode active material illustrated above may be used independently according to a use, and may be used in mixture of multiple types.

  Examples of the binder for the positive electrode include polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, and polyacrylonitrile derivatives. And other resins; soft polymers such as acrylic soft polymers, diene soft polymers, olefin soft polymers, vinyl soft polymers, and the like. In addition, a binder may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  As a solvent used for producing the electrode plate, either water or an organic solvent may be used. Examples of the organic solvent include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate, butyl acetate, and γ-butyrolactone Esters such as ε-caprolactone; Acylonitriles such as acetonitrile and propionitrile; Ethers such as tetrahydrofuran and ethylene glycol diethyl ether: Alcohols such as methanol, ethanol, isopropanol, ethylene glycol, and ethylene glycol monomethyl ether; N Amides such as -methylpyrrolidone and N, N-dimethylformamide; among them, N-methylpyrrolidone (NMP) is preferred. In addition, a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Of these, water is preferably used as the solvent.

  What is necessary is just to adjust the quantity of a solvent so that the viscosity of the composition for positive electrodes may become a viscosity suitable for application | coating. Specifically, the concentration of the solid content of the positive electrode composition is preferably 30 to 90% by weight, more preferably 40 to 80% by weight, and more preferably, the amount is adjusted to an amount of .

  Specific examples of the conductive agent include conductive carbon black such as furnace black, acetylene black, and ketjen black (registered trademark of Akzo Nobel Chemicals Bethloten Fennaut Shap). Among these, acetylene black and furnace black are more preferable. These conductive agents can be used alone or in combination of two or more.

  Examples of thickeners include cellulosic polymers such as carboxymethylcellulose, methylcellulose, hydroxypropylcellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof; ) Polyvinyl alcohols such as polyvinyl alcohol, copolymers of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or copolymers of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl pyrrolidone, modified Examples include polyacrylic acid, oxidized starch, phosphoric acid starch, casein, various modified starches, acrylonitrile-butadiene copolymer hydride, and the like. In the present invention, “(modified) poly” means “unmodified poly” or “modified poly”.

  The current collector is not particularly limited as long as it is an electrically conductive and electrochemically durable material, but is preferably a metal material because of its heat resistance, for example, iron, copper, aluminum, nickel, stainless steel. Examples include steel, titanium, tantalum, gold, and platinum. Among these, aluminum is preferable. The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 to 0.5 mm is preferable. In order to increase the adhesive strength with the positive electrode active material layer, the current collector is preferably used after roughening in advance. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, an abrasive cloth paper with a fixed abrasive particle, a grindstone, an emery buff, a wire brush provided with a steel wire or the like is used. Moreover, in order to improve the adhesive strength and electroconductivity of a positive electrode active material layer, you may form intermediate | middle layers, such as a conductive adhesive layer, on the collector surface.

  The method for applying the positive electrode composition to the surface of the current collector is not particularly limited. Examples of the method include a doctor blade method, a dip method, a reverse roll method, a direct roll method, a gravure method, an extrusion method, and a brush coating method.

  Examples of the drying method include drying with warm air, hot air, and low-humidity air, vacuum drying, and drying by irradiation with (far) infrared rays or electron beams. The drying time is preferably 5 to 30 minutes, and the drying temperature is preferably 40 to 180 ° C.

Further, after applying and drying the positive electrode composition on the surface of the current collector, the positive electrode active material layer is preferably subjected to pressure treatment using, for example, a die press or a roll press as necessary. By the pressure treatment, the porosity of the positive electrode active material layer can be lowered. The porosity is preferably 5 to 30%, more preferably 7% to 20%. When the porosity is too low, it is difficult to obtain a high volume capacity, and the positive electrode active material layer tends to be peeled off from the current collector. Moreover, when the porosity is too high, it tends to be difficult to obtain sufficient charge efficiency and discharge efficiency.
Furthermore, when the positive electrode active material layer includes a curable polymer, it is preferable to cure the polymer after the positive electrode active material layer is formed.

(Electrode plate for negative electrode)
For the negative electrode plate, the negative electrode composition containing the negative electrode active material, the binder for the negative electrode, the solvent used for preparing the electrode plate, the thickener used as necessary, the conductive agent, etc. It can be obtained by applying to the surface of the body and drying. That is, it can be obtained by forming a negative electrode active material layer on the surface of the current collector.

  Examples of the negative electrode active material include graphitizable carbon, non-graphitizable carbon, pyrolytic carbon and other low crystalline carbon (amorphous carbon), graphite (natural graphite, artificial graphite), tin, silicon, and the like. Examples include alloy materials, oxides such as silicon oxide, tin oxide, and lithium titanate. In addition, the negative electrode active material illustrated above may be used independently according to a use suitably, and multiple types may be mixed and used for it.

The binder for the negative electrode is not particularly limited, and known ones can be used. For example, resins such as polyethylene, polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyacrylic acid derivatives, polyacrylonitrile derivatives, acrylic soft heavy A soft polymer such as a polymer, a diene soft polymer, an olefin soft polymer, or a vinyl soft polymer can be used. These may be used alone or in combination of two or more.
Moreover, the solvent, the thickener, and the electrically conductive agent which are used for preparation of an electrode plate can use the thing similar to what can be used for the electrode plate for positive electrodes mentioned above.
Moreover, the same thing as what can be used for the above-mentioned electrode plate for positive electrodes can also be used also about a collector.
The electrode plate for the negative electrode can be produced in the same manner as the electrode plate for the positive electrode.

(Organic separator)
As the organic separator, known ones such as a microporous film or non-woven fabric made of polyolefin such as polyethylene or polypropylene or an aromatic polyamide resin; a porous resin coat containing inorganic ceramic powder; For example, polyolefin (polyethylene, polypropylene, polybutene, polyvinyl chloride), and microporous membranes made of resins such as mixtures or copolymers thereof, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide , A microporous membrane made of a resin such as polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, or a woven polyolefin-based fiber, or a nonwoven fabric thereof, an aggregate of insulating substance particles, or the like.

(Lithium ion secondary battery)
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolytic solution, and at least one of the positive electrode, the negative electrode, and the separator includes a porous film obtained from the porous film composition.

  In addition, when using the positive electrode which does not have the said porous film, the above-mentioned electrode plate for positive electrodes can be used as a positive electrode. Moreover, when using the negative electrode which does not have the said porous film, the above-mentioned electrode plate for negative electrodes can be used as a negative electrode. Moreover, when using the separator which does not have the said porous film, the above-mentioned organic separator can be used.

(Electrolyte)
As the electrolytic solution, for example, a solution obtained by dissolving a lithium salt as a supporting electrolyte in a non-aqueous solvent can be used. Examples of the lithium salt include LiPF ₆ , LiAsF ₆ , LiBF ₄ , LiSbF ₆ , LiAlCl ₄ , LiClO ₄ , CF ₃ SO ₃ Li, C ₄ F ₉ SO ₃ Li, CF ₃ COOLi, (CF ₃ CO) ₂ NLi , (CF ₃ SO ₂ ) ₂ NLi, (C ₂ F ₅ SO ₂ ) NLi, and other lithium salts. In particular, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li that are easily soluble in a solvent and exhibit a high degree of dissociation are preferably used. One of these may be used alone, or two or more of these may be used in combination at any ratio.

  The amount of the supporting electrolyte is preferably 1 to 30% by weight, more preferably 5 to 20% by weight with respect to the electrolytic solution. If the amount of the supporting electrolyte is too small or too large, the ionic conductivity is lowered, and the charging characteristics and discharging characteristics of the secondary battery may be lowered.

  The solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. Examples of the solvent include alkyl carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), and methyl ethyl carbonate (MEC); Examples include esters such as butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like. In particular, dimethyl carbonate, ethylene carbonate, propylene carbonate, diethyl carbonate, and methyl ethyl carbonate are preferred because high ion conductivity is easily obtained and the use temperature range is wide. In addition, a solvent may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Moreover, you may make an electrolyte solution contain an additive as needed. As the additive, for example, carbonate compounds such as vinylene carbonate (VC) are preferable. In addition, an additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Examples of the electrolytic solution other than the above include a gel polymer electrolyte obtained by impregnating a polymer electrolyte such as polyethylene oxide and polyacrylonitrile with an electrolytic solution; an inorganic solid electrolyte such as lithium sulfide, LiI, and Li ₃ N; Can do.

(Method for manufacturing secondary battery)
The manufacturing method of the secondary battery of the present invention is not particularly limited. For example, the negative electrode and the positive electrode may be overlapped via a separator, and this may be wound or folded according to the shape of the battery and placed in the battery container, and the electrolyte may be injected into the battery container and sealed. Furthermore, if necessary, an expanded metal; an overcurrent prevention element such as a fuse or a PTC element; a lead plate or the like may be inserted to prevent an increase in pressure inside the battery or overcharge / discharge. The shape of the battery may be any of, for example, a laminate cell type, a coin type, a button type, a sheet type, a cylindrical type, a square type, and a flat type.

  Moreover, when forming the above-mentioned porous film on the electrode active material layer surface of a positive electrode or a negative electrode, even if it does not use a separator at the time of manufacture of a lithium ion secondary battery, a porous film fulfill | performs the function as a separator. Therefore, it is possible to manufacture a lithium ion secondary battery at low cost. Further, even when a separator is used in the manufacture of a lithium ion secondary battery, since the holes formed on the separator surface are not filled, higher rate characteristics can be expressed. Furthermore, by forming the porous film on the surface of the electrode active material layer, even if the separator is contracted by heat, a short circuit between the positive electrode and the negative electrode is not caused, and high safety can be maintained.

  According to the porous film composition of the present invention, it is possible to obtain a porous film layer having a low water content and excellent adhesion strength.

EXAMPLES Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and may be arbitrarily changed without departing from the gist and equivalent scope of the present invention. Can be implemented. In the following description, “%” and “parts” representing amounts are based on weight unless otherwise specified.
In Examples and Comparative Examples, peel strength, moisture content, low-temperature output characteristics, cell swelling, and cycle characteristics were evaluated as follows.

(Peel strength)
The separators produced in the examples and comparative examples were cut into rectangles having a length of 100 mm and a width of 10 mm to form test pieces, and an electrolyte (1.0 mol / L LiPF ₆ / EC + DEC (EC / DEC = 1/2 volume ratio)) ) And then dried at 60 ° C. for 72 hours. Cellophane tape was affixed on the surface of the porous film with the dried test piece facing down. At this time, a cellophane tape defined in JIS Z1522 was used. The cellophane tape was fixed on a horizontal test bench. Thereafter, the stress was measured when one end of the current collector was pulled vertically upward and pulled off at a pulling speed of 10 mm / min. This measurement was performed 3 times, the average value of stress was calculated | required, and the said average value was made into peel strength, and it showed in Table 1 and Table 2. It shows that the binding strength of a porous membrane and an organic separator is so large that the measured peel strength is large. That is, it shows that adhesion strength is so large that the measured peel strength is large.

(amount of water)
The separator (organic separator with a porous film) manufactured in the examples and comparative examples was cut out in a size of 10 cm wide × 10 cm long to obtain a test piece. The test piece was allowed to stand for 24 hours at a temperature of 25 ° C. and a humidity of 50%, and then the test piece was subjected to Karl Fischer method (JIS K-0068 (2001) water vaporization method, vaporization temperature 150 ° C.) using a coulometric titration moisture meter. The water content (W1) was measured.
Next, the moisture content (W2) was measured in the same manner as described above for a test piece that was allowed to stand for 24 hours at a temperature of 25 ° C., a dew point of −60 ° C., and a humidity of 0.05%.

A ratio (W1 / W2) was calculated from the measured water contents W1 and W2, and evaluated according to the following criteria. The smaller the difference between W1 and W2, the smaller the moisture content of the porous membrane. When the water content of the porous film is small, curling of the separator in the dry room where the battery is manufactured can be suppressed. Further, it is preferable that the amount of water in the porous film is small because side reactions in the secondary battery due to moisture do not occur and battery characteristics such as high-temperature cycle characteristics do not deteriorate.
A: W1 / W2 is less than 2.0 B: W1 / W2 is 2.0 or more and less than 2.5 C: W1 / W2 is 2.5 or more and less than 3.0 D: W1 / W2 is 3. 0 or more

(Low temperature output characteristics)
An 800 mAh wound type lithium ion secondary battery in Examples and Comparative Examples was prepared and allowed to stand for 24 hours in an environment at 25 ° C., and then 4.2 V, 0.1 C, 5 in an environment at 25 ° C. The time charging operation was performed, and the voltage V0 at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in a -10 ° C environment, and the voltage V1 15 seconds after the start of discharge was measured. The low temperature output characteristic is evaluated by a voltage drop represented by ΔV = V0−V1, and the smaller this value, the better the low temperature output characteristic.

(Cell bulge)
An 800 mAh wound cell lithium ion secondary battery in Examples and Comparative Examples was prepared and allowed to stand in an environment at 25 ° C. for 24 hours, and then at 4.35 V and 0.1 C in an environment at 25 ° C. Charging and discharging operations were performed by charging at 2.75 V and discharging at 0.1 C. Thereafter, the wound cell was immersed in liquid paraffin, and its volume V0 was measured. Furthermore, charging and discharging were repeated under an environment of 60 ° C., the wound cell after 1000 cycles was immersed in liquid paraffin, and its volume V1 was measured. The swelling of the cell was evaluated by the volume change rate of the cell represented by ΔV (%) = (V1−V0) / V0 × 100. It shows that it is excellent in gas generation | occurrence | production suppression, so that this value is small.

(Cycle characteristics)
An 800 mAh wound cell lithium ion secondary battery in Examples and Comparative Examples was prepared and allowed to stand in an environment at 25 ° C. for 24 hours, and then at 4.35 V and 0.1 C in an environment at 25 ° C. Charging and discharging operations were performed by charging and discharging at 2.75 V and 0.1 C, and the initial capacity C0 was measured. Furthermore, charging / discharging was repeated under an environment of 60 ° C., and the capacity C1 after 1000 cycles was measured. The high-temperature cycle characteristics were evaluated by a capacity retention rate represented by ΔC = C1 / C0 × 100 (%). It shows that it is excellent in a lifetime characteristic, so that this value is high.

Example 1
(1. Separator)
[1.1. Production of alumina particles]
Aluminum hydroxide having a volume average particle diameter of 2.8 μm obtained by the Bayer method was charged into a box-shaped mortar at a charging density of 0.61 g / cm ³ . This box-shaped mortar was placed in a furnace of a stationary electric furnace (“Siliconit Furnace” manufactured by Siliconit Takao Kogyo Co., Ltd.) and fired at a firing temperature of 1180 ° C. for 10 hours. Thereafter, the produced α-alumina particles were taken out of the furnace.

  A vibrating ball mill (“Vibrating Mill” manufactured by Chuo Kako Co., Ltd.) in which 7.8 kg of alumina balls having a diameter of 15 mm were accommodated in a 6-liter pot was prepared. The pot was filled with 1.0 kg of the above α-alumina particles and 15 g of ethanol and pulverized for 36 hours to obtain α-alumina particles having a volume average particle diameter of 0.6 μm.

[1.2. Production of water-soluble thickener (A)]
As the water-soluble thickener (A), carboxymethyl cellulose (Daicel Chemical Industries, Ltd. Daicel 1220, etherification degree 0.8-1.0, 1% aqueous solution viscosity 10-20 mPa · s, hereinafter referred to as “CMC” And sodium polyacrylate D1 (weight average molecular weight 25000, 1% aqueous solution viscosity 3000 mPa · s). It added so that solid content might be 1.5 parts and 0.1 part with respect to 50 parts of water, respectively.

[1.3. Carbodiimide compound crosslinking agent (B)]
As the carbodiimide compound crosslinking agent (B), polycarbodiimide (manufactured by Nisshinbo Chemical Co., Ltd., product name: Carbodilite (registered trademark) SV-02, NCN equivalent 429, one-phase water-soluble) was used.

[1.4. Production of particulate polymer (C)]
A particulate polymer (C) was produced as follows.
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (product name “Emal 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate, The gas phase portion was replaced with nitrogen gas, and the temperature was raised to 60 ° C.

On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, and 94 parts of butyl acrylate (hereinafter sometimes referred to as “BA”) as a polymerizable monomer. , Acrylonitrile (hereinafter sometimes referred to as “AN”) 2 parts, acrylamide (hereinafter sometimes referred to as “AAm”) 1 part, methacrylic acid (hereinafter sometimes referred to as “MMA”) 2 parts, and 1 part of allyl glycidyl ether (hereinafter sometimes referred to as “AGE”) was mixed to obtain a monomer mixture. This monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was performed at 60 ° C. After completion of the addition, the reaction was further terminated by stirring at 70 ° C. for 3 hours to produce an aqueous dispersion containing a (meth) acrylic polymer as a binder for the porous membrane.
The obtained (meth) acrylic polymer had a volume average particle diameter D50 of 0.36 μm and a glass transition temperature of −45 ° C.

[1.5. Preparation of dispersion of non-conductive particles]
100 parts of the α-alumina particles obtained in the step [1.1] and 1.6 parts of the aqueous solution of the water-soluble thickener (A) obtained in the step [1.3] are mixed, and the electric conductivity is 10 μS. A dispersion of non-conductive particles was obtained by adding / cm water to adjust the solid content concentration to 50% by weight.

[1.6. Dispersion of dispersion of non-conductive particles]
Step [1.5. The dispersion of non-conductive particles obtained in the above was dispersed for 1 hour at an energy of 4000 rpm and 5.4 Wh / kg by a medialess dispersion apparatus (manufactured by IKA, in-line type pulverizer MKO).

[1.7. Production of porous film composition]
The step [1.6. ] 0.05 parts of carbodiimide compound crosslinking agent (B) and 6 parts of particulate polymer (C) were added to the dispersion of non-conductive particles obtained in the above. Furthermore, 0.2 part of polyethylene glycol type surfactant (San Nopco SN wet 366) is mixed, solid content concentration is 40%, viscosity is 160 mPa · s (measured at a temperature of 25 ° C. and a rotation speed of 60 rpm using a B type viscometer). (The same applies below), and a porous membrane composition was produced.

[1.8. Production of secondary battery separator]
An organic separator (thickness 16 μm, Gurley value 210 s / 100 cc) made of a polyethylene porous substrate (PE substrate) was prepared. The porous membrane composition was applied to both surfaces of the prepared organic separator and dried at 50 ° C. for 3 minutes. Thereby, a separator provided with a porous film having a thickness of 3 μm on one side was obtained. About the obtained separator, the peeling strength and the moisture content were measured by the said method.

(2. Negative electrode)
[2.1. Production of binder for negative electrode]
In a 5 MPa pressure vessel with a stirrer, 33.5 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 62 parts of styrene, 1 part of 2-hydroxyethyl acrylate, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, ion exchange After adding 150 parts of water and 0.5 part of potassium persulfate as a polymerization initiator and stirring sufficiently, the mixture was heated to 50 ° C. to initiate polymerization. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing a particulate binder (SBR). After adding 5% aqueous sodium hydroxide solution to the mixture containing the particulate binder and adjusting the pH to 8, the unreacted monomer is removed by heating under reduced pressure, and then cooled to 30 ° C. or lower to obtain a desired content. An aqueous dispersion containing a particulate binder was obtained.

[2.2. Production of composition for negative electrode]
100 parts of artificial graphite (average particle size: 15.6 μm), 1 part of a 2% aqueous solution of carboxymethylcellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a thickener, solid content equivalent with ion exchange water After adjusting to 68%, the mixture was mixed at 25 ° C. for 60 minutes. Further, the solid content was adjusted to 62% with ion-exchanged water, and further mixed at 25 ° C. for 15 minutes. The above-mentioned mixed binder was mixed with 1.5 parts of the particulate binder in an amount corresponding to the solid content and ion-exchanged water, adjusted to a final solid content concentration of 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a negative electrode composition having good fluidity.

[2.3. Production of negative electrode]
The negative electrode composition obtained above was applied onto a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material before pressing. The negative electrode raw material before pressing was rolled with a roll press to obtain a negative electrode after pressing with a negative electrode active material layer having a thickness of 80 μm.

[3. Positive electrode]
[3.1. Production of composition for positive electrode]
100 parts of LiCoO ₂ having a volume average particle diameter of 12 μm as the positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as the conductive agent, PVDF (manufactured by Kureha Co., Ltd.) as the binder for the positive electrode # 7208) was mixed with 2 parts corresponding to the solid content and NMP to make the total solid content concentration 70%. These were mixed by a planetary mixer to prepare a positive electrode composition.

[3.2. Production of positive electrode]
[3.1. The composition for a positive electrode was applied on a 20 μm-thick aluminum foil as a current collector with a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Then, it heat-processed for 2 minutes at 120 degreeC, and obtained the positive electrode.

[4. Production of lithium ion secondary battery]
The pressed positive electrode was cut out to 49 × 5 cm ² . A separator cut out to 55 × 5.5 cm ² was disposed on the positive electrode active material layer of the cut out positive electrode. Furthermore, the negative electrode after pressing was cut into a square of 50 × 5.2 cm ² , and the cut negative electrode was arranged on the side opposite to the positive electrode of the separator so that the surface on the negative electrode active material layer side faced the separator. This was wound by a winding machine to obtain a wound body. The wound body was pressed at 60 ° C. and 0.5 MPa to obtain a flat body. This flat body is wrapped with an aluminum wrapping case as a battery case, and an electrolytic solution (solvent: EC / DEC / VC = 68.5 / 30 / 1.5 volume ratio, electrolyte: LiPF _{6 with a} concentration of 1 M) is air. Injected so as not to remain. Further, in order to seal the opening of the aluminum packaging material, heat sealing at 150 ° C. was performed to close the aluminum exterior. Thus, an 800 mAh wound type lithium ion secondary battery was manufactured.

  About the lithium ion secondary battery obtained in this way, the low-temperature output characteristic, cell swelling, and cycling characteristics were evaluated by the method mentioned above.

(Example 2)
Above [1.2. In the production of water-soluble thickener (A)], the same as Example 1 except that the type of sodium polyacrylate used was sodium polyacrylate D2 (weight average molecular weight 10,000, 1% aqueous solution viscosity 1200 mPa · s) In addition, a separator and a lithium ion secondary battery were manufactured.

(Example 3)
Above [1.2. In the production of water-soluble thickener (A)], the same as Example 1 except that the type of sodium polyacrylate used was sodium polyacrylate D3 (weight average molecular weight 70000, 1% aqueous solution viscosity 8400 mPa · s) In addition, a separator and a lithium ion secondary battery were manufactured.

Example 4
[1.1. Instead of production of alumina particles, nonconductive fine particles made of an organic compound were produced.

[Production of non-conductive fine particles made of organic compounds]
In a reactor equipped with a stirrer, 0.06 part of sodium dodecyl sulfate, 0.2 part of ammonium persulfate, and 100 parts of ion-exchanged water were mixed to obtain a mixture N1, and the temperature was raised to 80 ° C.

  On the other hand, in another container, 98 parts of butyl acrylate and 2.0 parts of methacrylic acid, 0.1 part of sodium dodecyl sulfate, and 100 parts of ion-exchanged water were mixed as monomers, A dispersion was prepared.

The dispersion of the monomer mixture M1 was continuously added to the mixture N1 over 4 hours to be polymerized. During continuous addition of the dispersion of the monomer mixture M1, the reaction was carried out while maintaining the temperature of the reaction system at 80 ° C. After completion of the continuous addition, the reaction was further continued at 90 ° C. for 3 hours.
Thereby, an aqueous dispersion of seed polymer particles S1 having a number average particle diameter of 360 nm was obtained.

  In a reactor equipped with a stirrer, 20 parts of the aqueous dispersion of the seed polymer particles S1 obtained above on a solid basis (that is, based on the weight of the seed polymer particles S1) and ethylene glycol dimethacrylate as a monomer (Kyoeisha) Chemical Co., Ltd. “Light Ester EG”) 99 parts, acrylic acid 1.0 parts, emulsifier sodium dodecylbenzenesulfonate 1.0 parts, polymerization initiator t-butylperoxy-2-ethylhexano 4.0 parts of Eat (Nippon Oil Corporation "Perbutyl O") and 200 parts of ion-exchanged water were added. By stirring this at 35 ° C. for 12 hours, the monomer and polymerization initiator were completely absorbed by the seed polymer particles S1. Thereafter, this was polymerized at 90 ° C. for 5 hours. Thereafter, steam was introduced to remove unreacted monomers and initiator decomposition products, and non-conductive fine particles made of an organic compound were obtained.

A separator and a lithium ion secondary battery were manufactured in the same manner as in Example 1 except that non-conductive fine particles made of the organic compound were used instead of α-alumina.
The above [1.7. The production of the porous film composition] had a solid content concentration of 25% and a viscosity of 50 mPa · s.

(Example 5)
Above [1.2. Production of water-soluble thickener (A)] In the same manner as in Example 1 except that polyvinyl alcohol (hereinafter sometimes referred to as “PVOH”) was used instead of carboxymethylcellulose, production of a separator and lithium ion A secondary battery was manufactured.
The above [1.7. The production of the porous film composition] had a solid content concentration of 42% and a viscosity of 150 mPa · s.

(Example 6)
Above [1.2. In the production of water-soluble thickener (A)], without using sodium polyacrylate, water-soluble thickener (A) was produced using 1.6 parts of carboxymethylcellulose with respect to 50 parts of water. In the same manner as in Example 1, a separator and a lithium ion secondary battery were manufactured.
The above [1.7. The production of the porous film composition] had a solid content concentration of 41% and a viscosity of 140 mPa · s.

(Example 7)
Above [1.2. Production of water-soluble thickener (A)], except that carboxymethyl cellulose and sodium polyacrylate were added to 50 parts of water so that the solid content was 0.4 parts and 0.1 parts, respectively. In the same manner as in Example 1, a separator and a lithium ion secondary battery were manufactured.
The above [1.7. The production of the porous film composition] had a solid content concentration of 47% and a viscosity of 150 mPa · s.

(Example 8)
Above [1.2. Production of water-soluble thickener (A)], except that carboxymethyl cellulose and sodium polyacrylate were added to 50 parts of water so that the solid content was 1.5 parts and 6.5 parts, respectively. In the same manner as in Example 1, a separator and a lithium ion secondary battery were manufactured.
The above [1.7. The production of the porous film composition] had a solid content concentration of 32% and a viscosity of 160 mPa · s.

Example 9
[1.3. In the carbodiimide compound crosslinking agent (B)], polycarbodiimide (manufactured by Nisshinbo Chemical Co., Ltd., product name: Carbodilite (registered trademark) V-02, NCN equivalent 600, single-phase water-soluble) was used as the carbodiimide compound crosslinking agent (B). Except for the above, separators and lithium ion secondary batteries were manufactured in the same manner as in Example 1.
The above [1.7. The production of the porous film composition] had a solid content concentration of 40% and a viscosity of 160 mPa · s.

(Example 10)
[1.3. In the carbodiimide compound crosslinking agent (B)], polycarbodiimide (manufactured by Nisshinbo Chemical Co., Ltd., product name: Carbodilite (registered trademark) V-04, NCN equivalent 335, one-phase water-soluble) was used as the carbodiimide compound crosslinking agent (B). Except for the above, separators and lithium ion secondary batteries were manufactured in the same manner as in Example 1.
The above [1.7. The production of the porous membrane composition] had a solid content concentration of 39% and a viscosity of 165 mPa · s.

(Example 11)
[1.7. In the production of the porous film composition], the separator and the lithium ion secondary battery were produced in the same manner as in Example 1 except that the amount of the carbodiimide compound crosslinking agent (B) added was 0.01 parts. The obtained porous film composition had a solid content concentration of 40% and a viscosity of 160 mPa · s.

(Example 12)
[1.7. In production of porous film composition], a separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the amount of the carbodiimide compound crosslinking agent (B) added was 1 part. The resulting porous film composition had a solid content concentration of 38% and a viscosity of 160 mPa · s.

(Example 13)
In a 5 MPa pressure vessel equipped with a stirrer, 67.5 parts of ethyl acrylate, 30 parts of methacrylic acid, 2.5 parts of trifluoromethyl methacrylate, 1.0 part of sodium dodecylbenzenesulfonate, 150 parts of ion-exchanged water and 0. After 5 parts were added and sufficiently stirred, the polymerization was started by heating to 60 ° C. When the polymerization conversion reached 96%, the reaction was stopped by cooling to obtain an aqueous solution containing a water-soluble polymer. The aqueous solution containing the water-soluble polymer thus obtained was adjusted to pH 8 by adding 10% ammonia water to obtain an aqueous solution containing the desired water-soluble polymer. The water-soluble polymer had a weight average molecular weight of 128,000 and a 1% aqueous solution having a viscosity of 1500 mPa · s.

Above [1.2. Production of water-soluble thickener (A)] In place of carboxymethylcellulose and sodium polyacrylate, the water-soluble polymer was added to 50 parts of water so that the solid content was 1.6 parts. Except for the above, separators and lithium ion secondary batteries were manufactured in the same manner as in Example 1.
The above [1.7. The production of the porous film composition] had a solid content concentration of 39% and a viscosity of 160 mPa · s.

(Example 14)
Above [1.2. Production of water-soluble thickener (A)] In 50 parts of water, the solid content of carboxymethyl cellulose and the water-soluble polymer produced in Example 13 was 0.8 parts and 0.8 parts, respectively. A separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except for adding to the above.
The above [1.7. The production of the porous film composition] had a solid content concentration of 40% and a viscosity of 200 mPa · s.

(Example 15)
Above [1.2. Production of water-soluble thickener (A)] In 50 parts of water, the solid content of sodium polyacrylate D1 and the water-soluble polymer produced in Example 13 was 0.1 parts and 1.6 parts, respectively. A separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the addition was performed.
The above [1.7. The production of the porous film composition] had a solid content concentration of 38% and a viscosity of 160 mPa · s.

(Example 16)
Above [1.2. Production of water-soluble thickener (A)] In 50 parts of water, carboxymethylcellulose, sodium polyacrylate D1 and the solid content of the water-soluble polymer produced in Example 13 were 0.8 parts and 0 parts, respectively. A separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that the amount was 0.1 parts and 0.8 parts.
The above [1.7. The production of the porous film composition] had a solid content concentration of 39% and a viscosity of 195 mPa · s.

(Example 17)
[1.4. In the production of the particulate polymer (C)], 95 parts of butyl acrylate, 2 parts of acrylonitrile, 1 part of acrylamide, 2-hydroxyethyl acrylate (hereinafter referred to as “β-HEA”) may be described as polymerizable monomers. There was a separator manufactured and a lithium ion secondary battery manufactured in the same manner as in Example 1 except that 1 part and 1 part of allyl glycidyl ether were used.
The above [1.7. The production of the porous film composition] had a solid content concentration of 39% and a viscosity of 160 mPa · s.

(Example 18)
[1.4. Production of particulate polymer (C)], except that 94 parts of butyl acrylate, 2 parts of acrylonitrile, 1 part of acrylamide, 1 part of methacrylic acid and 2 parts of 2-ethylhexyl acrylate were used as polymerizable monomers. In the same manner as in Example 1, a separator and a lithium ion secondary battery were manufactured.
The above [1.7. The production of the porous film composition] had a solid content concentration of 39% and a viscosity of 160 mPa · s.

(Example 19)
[1.8. Production of secondary battery separator], except that an organic separator made of a polypropylene porous substrate (PP substrate) was used instead of an organic separator made of a polyethylene porous substrate. In addition, a separator and a lithium ion secondary battery were manufactured.

(Example 20)
[1.8. In the production of a separator for a secondary battery], a separator and a lithium ion secondary were produced in the same manner as in Example 1 except that a non-woven fabric organic separator was used instead of an organic separator made of a polyethylene porous substrate. The battery was manufactured.

(Example 21)
[1.8. [Manufacture of Separator for Secondary Battery] was omitted, and the porous film composition was applied to the negative electrode active material layer side surface of the negative electrode obtained in (2. Negative Electrode) and dried at 50 ° C. for 3 minutes. Thereby, a negative electrode provided with a porous film having a thickness of 3 μm was obtained.

  The above [4. Lithium ion secondary battery] in the same manner as in Example 1 except that the surface on which the negative electrode porous film was formed and the surface of the positive electrode were placed so as to face each other and wound using a winding machine. A secondary battery was manufactured.

(Comparative Example 1)
Above [1.7. Production of porous film composition] in Example 1 except that the porous film composition was produced without adding the carbodiimide compound crosslinking agent (B), and the addition amount of the particulate polymer (C) was 5 parts. The separator and the lithium ion secondary battery were manufactured in the same manner as described above.
The above [1.7. The production of the porous film composition] had a solid content concentration of 40% and a viscosity of 160 mPa · s.

(Comparative Example 2)
Above [1.2. Production of water-soluble thickener (A)] In place of carboxymethylcellulose and sodium polyacrylate, the polyethylene oxide (molecular weight 1000) is 50 parts of water so that the solid content is 1.5 parts. A separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except for the addition.
The above [1.7. The production of the porous film composition] had a solid content concentration of 40% and a viscosity of 120 mPa · s.

(Comparative Example 3)
[1.4. In the production of the particulate polymer (C)], a separator and a lithium ion secondary battery were produced in the same manner as in Example 1 except that 97 parts of butyl acrylate and 3 parts of acrylonitrile were used as the polymerizable monomers. Went.
The above [1.7. The production of the porous film composition] had a solid content concentration of 40% and a viscosity of 170 mPa · s.

  As shown in Table 1 and Table 2, non-conductive particles, a water-soluble thickener (A) containing a hydroxyl group or / and a carboxyl group, a carbodiimide compound crosslinking agent (B), and a particulate polymer (C The peel strength of the porous film obtained by using the porous film composition having a functional group that reacts with the carbodiimide compound crosslinking agent (B) is It was good and the water content was reduced. Moreover, the low-temperature output characteristics, cell swelling and cycle characteristics of the lithium ion battery obtained using this porous film composition were good.

Claims (10)

Non-conductive particles;
A water-soluble thickener (A) containing a carboxyl group;
A carbodiimide compound crosslinking agent (B);
A porous membrane composition for a lithium ion secondary battery comprising a particulate polymer (C) as a binder ,
The particulate polymer (C) has a functional group that reacts with the carbodiimide compound crosslinking agent (B),
The porous membrane composition for a lithium ion secondary battery, wherein the functional group that reacts with the carbodiimide compound crosslinking agent (B) is at least one of a carboxyl group, a hydroxyl group, a glycidyl ether group, and a thiol group.   The water-soluble thickener (A) is at least one selected from the group consisting of carboxymethylcellulose, methylcellulose, hydroxypropylmethylcellulose, hydroxyethylmethylcellulose, polyvinyl alcohol, polyacrylic acid or a salt thereof. 2. A porous membrane composition for a lithium ion secondary battery according to 1.   The functional group that reacts with the carbodiimide compound crosslinking agent (B) in the particulate polymer (C) is at least one selected from the group consisting of a carboxyl group, a hydroxyl group, a glycidyl ether group, and a thiol group. Item 3. The porous membrane composition for a lithium ion secondary battery according to Item 1 or 2.   0.2 to 15 parts by weight of the water-soluble thickener (A), 0.01 to 10 parts by weight of the carbodiimide compound crosslinking agent (B), 100 parts by weight of the non-conductive particles The porous membrane composition for a lithium ion secondary battery according to any one of claims 1 to 3, which contains 1 to 15 parts by weight of the polymer (C).   The separator for lithium ion secondary batteries obtained by apply | coating the porous film composition for lithium ion secondary batteries as described in any one of Claims 1-4 on a board | substrate, and drying.   The electrode for lithium ion secondary batteries obtained by apply | coating the porous film composition for lithium ion secondary batteries as described in any one of Claims 1-4 on an electrode plate, and drying.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the separator is the lithium ion secondary battery separator according to claim 5.   A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution, and a separator, wherein the positive electrode and / or the negative electrode is an electrode for a lithium ion secondary battery according to claim 6. It is a manufacturing method of the separator for lithium ion secondary batteries obtained by apply | coating the porous film composition for lithium ion secondary batteries as described in any one of Claims 1-4 on a board | substrate, and drying,
Applying the porous membrane composition for a lithium ion secondary battery on a substrate;
The manufacturing method of the separator for lithium ion secondary batteries which has a process dried at 50-200 degreeC. It is a manufacturing method of the electrode for lithium ion secondary batteries obtained by apply | coating the porous film composition for lithium ion secondary batteries as described in any one of Claims 1-4 on an electrode plate, and drying. ,
Applying the porous membrane composition for a lithium ion secondary battery on an electrode plate;
The manufacturing method of the electrode for lithium ion secondary batteries which has a process dried at 50-200 degreeC.