JP6901234B2 - Separator for secondary batteries and secondary batteries - Google Patents

Description

The present invention relates to a separator for a secondary battery and a secondary battery.

Recently, as various electronic devices have become smaller and lighter, secondary batteries used as power sources for these electronic devices are required to have higher capacity, smaller size, and lighter weight. Among them, lithium ion secondary batteries have advantages such as high voltage, long life, and high energy density. For this reason, active research on lithium-ion secondary batteries is being carried out, and they are being produced and sold.

The characteristics of these lithium secondary batteries are greatly influenced by the characteristics of the electrodes, electrolytes, other battery materials, etc. used. In particular, the separator of the lithium ion secondary battery affects the cycle characteristics of the lithium ion secondary battery. Specifically, a separator may be produced by applying a slurry containing inorganic particles and a binder to a porous substrate. Such a separator is also referred to as a coating separator because a coating layer composed of inorganic particles and a binder is formed on a porous substrate. The binder binds the inorganic particles to a porous polyethylene membrane. When a lithium ion secondary battery is manufactured using such a separator, the cycle characteristics of the lithium ion secondary battery are porous polyethylene (PE) and ceramic particles (a type of inorganic particles). It also depends on the characteristics of the binder that has a binding force between the ceramic particles and the ceramic particles.

In particular, when highly heat-resistant ceramic particles are used for the coating film, a high-voltage and high-capacity battery can be produced. However, in order for the highly heat-resistant ceramic particles to fully exhibit their characteristics, it is necessary for the binder to stably maintain the structure of the ceramic coating layer during charging and discharging of the lithium ion secondary battery. That is, it is necessary to stably hold the highly heat-resistant ceramic particles in the separator. Further, the binder needs to firmly bond the separator and each electrode. Therefore, there is a demand for a binder having excellent heat resistance and adhesive strength.

At present, there are not many research examples on binders for coating separators, and at present, binders for electrodes are often diverted to binders for coating separators. Specifically, a binder composition obtained by mixing a polyvinylidene fluoride (PVDF) polymer, which is a typical binder for electrodes, with an organic solvent such as N-methyl-2-pyrrolidone (NMP) (hereinafter, "PVDF"). It is often referred to as "system binder") as a binder for coating separators.

Special Table 2010-52095

However, PVDF-based binders have the problem that the amount introduced into the separator is large in order to maintain sufficient adhesive strength, and coating by impregnation of the electrolytic solution and transfer of lithium ions during charging and discharging of the lithium ion secondary battery. There was a problem that it was difficult to maintain a stable structure of the layer. As a solution to these problems, for example, a binder having a different two-phase structure including a porous PE and a chemical structure having a strong adhesive force and a silane coupling agent are used to form an inorganic oxide (a type of inorganic particles). A binder containing a lithium ion secondary battery with improved adhesive strength and an IPN (interpentrating polymer network) type resin obtained by polymerizing a PVDF polymer and a hydrophilic polymer (polymer) (unsaturated carboxylic acid). Etc. are known.

In addition to these, a separator having a porous coating layer formed of a mixture of inorganic particles and a binder polymer on the surface of a porous substrate, and a lithium secondary battery using the separator are known. (See, for example, Patent Document 1). Patent Document 1 describes that butyl acrylate or a copolymer of acrylonitrile and acrylic acid is used as the binder polymer, and BaTIO ₃ or Al ₂ O ₃ is used as the inorganic particles. Has been done.

However, although these binders are satisfied with the adhesive force to only one of the porous PE and the inorganic particles, they do not have a sufficient adhesive force to both the porous PE and the inorganic particles. Therefore, when the lithium ion secondary battery using the coating separator using such a binder is repeatedly charged and discharged, there is a problem that the structure of the coating layer is changed and the capacity of the cell is unavoidably reduced.

Therefore, the present invention has been made in view of the above problems, and an object of the present invention is a novel invention using a binder having high heat resistance and strong adhesive force and improving cycle characteristics. Another object of the present invention is to provide an improved separator for a secondary battery and a secondary battery using the same.

In order to solve the above problems, according to a certain viewpoint of the present invention, in a separator for a secondary battery including a base material and at least a coating layer formed on the surface of the base material, the coating layer is carboxylated. (Carboxyl) group-containing acrylic monomer (acryl monomer) and a binder for a secondary battery containing an acrylic resin containing an acrylic acid derivative monomer as an essential monomer, and a combination of the carboxyl group-containing acrylic monomer and the acrylic acid derivative monomer. A separator for a secondary battery is provided, characterized in that the ratio is 20/80 to 80/20 in terms of molar ratio.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance and strong adhesive force and improves the cycle life. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Here, the carboxyl group-containing acrylic monomer is acrylic acid, methacrylic acid, maleic acid, monomethylmalic acid, 2-carboxyethyl acrylate (2-carboxyethyl acrylicate), and 2-carboxylate. Any one or more of the group consisting of ethyl methacrylate (2-carboxyl methacrylate) may be used.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance and strong adhesive force and improves cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, the acrylic acid derivative monomer may be at least one selected from the group consisting of a nitrile group-containing acrylic monomer, an acrylic acid ester (ester) and acrylamide (acrylamide).

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance and strong adhesive force and improves cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, among the group in which the nitrile group-containing acrylic monomer is composed of acrylonitrile, methacrylonitrile, 2-cyanoethyl acrylate, and 2-cyanoethyl methacrylate. , Any one or more may be used.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance and strong adhesive force and improves cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, it is preferable that at least a part of the carboxyl group-containing acrylic monomer is an alkali metal salt or an ammonium salt.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance, strong adhesive strength, and improved cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, the coating layer may further contain a water-insoluble resin as the binder for the secondary battery.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance, strong adhesive strength, and improved cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, the water-insoluble resin may contain one or both of polyvinylidene fluoride and the water-insoluble acrylic resin.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance and strong adhesive force and improves cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, the coating layer may further contain polyvinyl alcohol as the binder for the secondary battery.

From this point of view, the separator for a secondary battery is manufactured by using a binder for a secondary battery which has high heat resistance and strong adhesive force and improves cycle characteristics. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

Further, the coating layer may further contain inorganic particles.

The separator for a secondary battery from this point of view contains inorganic particles. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be further improved.

Further, the inorganic particles may be one or both of alumina and boehmite.

The separator for a secondary battery from this point of view contains inorganic particles. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be further improved.

According to another aspect of the present invention, there is provided a secondary battery comprising the above separator.

From this point of view, the secondary battery has improved cycle characteristics.

As described above, the separator for a secondary battery according to the present invention contains a binder containing a carboxyl group-containing acrylic monomer having a specific compounding ratio and an acrylic acid derivative monomer as essential monomers as a binder for the coating layer. Has high heat resistance and strong adhesive strength. Further, since this binder has the above composition, the cycle characteristics of the secondary battery can be improved. Therefore, by manufacturing a secondary battery using this separator, the cycle characteristics of the secondary battery can be improved.

It is a side sectional view which shows the structure of the lithium ion secondary battery which concerns on embodiment of this invention. It is a schematic diagram which shows the sample used in the heat shrinkage evaluation of the Example of this invention.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present specification and the drawings, components having substantially the same functional configuration are designated by the same reference numerals, so that duplicate description will be omitted.

In the present invention, in a separator for a secondary battery having a coating layer on the surface of a base material, an acrylic containing a carboxyl group-containing acrylic monomer having a specific compounding ratio and an acrylic acid derivative monomer as essential monomers as a binder for forming the coating layer. By using a binder composition containing a based resin, the heat resistance of the separator and the adhesion between the base material and the coating layer are improved. Further, in the present invention, the adhesion strength between the separator and the electrode layer is improved by forming the coating layer using the acrylic resin as a binder. This improves the safety and cycle life of the secondary battery. Hereinafter, the lithium ion secondary battery according to the preferred embodiment of the present invention will be described in detail.

(First Embodiment)
(Construction of lithium-ion secondary battery)
First, the configuration of the lithium ion secondary battery 10 according to the first embodiment will be described with reference to FIG.

The lithium ion secondary battery 10 includes a positive electrode 20, a negative electrode 30, a separator 40, and a non-aqueous electrolytic solution. The charge reaching voltage (oxidation-reduction potential) of the lithium ion secondary battery 10 is, for example, 4.3 ^{V (vs. Li /} Li +) or more and 5.0 V or less, particularly 4.5 V or more and 5.0 V or less. The form of the lithium ion secondary battery 10 is not particularly limited. That is, the lithium ion secondary battery 10 may be any of a cylindrical shape, a square shape, a laminate type, a button type, and the like.
(Positive electrode 20)

The positive electrode 20 includes a current collector 21 and a positive electrode active material layer 22. The current collector 21 may be any conductor, and is made of, for example, aluminum, stainless steel, nickel-coated steel, or the like.

The positive electrode active material layer 22 contains at least the positive electrode active material, and may further contain a conductive agent and a binder. The positive electrode active material is, for example, a solid solution oxide containing lithium, but is not particularly limited as long as it is a substance capable of electrochemically storing and releasing lithium ions. Solid solution oxides, for _{example, Li a Mn x Co y Ni} z O 2 (1.150 ≦ a ≦ 1.430,0.45 ≦ x ≦ 0.6,0.10 ≦ y ≦ 0.15,0. _{20 ≦ z ≦ 0.28), LiMn} x Co y Ni z O 2 (0.3 ≦ x ≦ 0.85,0.10 ≦ y ≦ 0.3,0.10 ≦ z ≦ 0.3), LiMn It becomes _1.5 Ni _0.5 O _4.

The conductive agent is, for example, carbon black such as Ketjen black or acetylene black, natural graphite, artificial graphite, or the like, but is not particularly limited as long as it is for increasing the conductivity of the positive electrode.

The binder is, for example, polyvinylidene fluoride, ethylene propylene diene (ethylene-polyethylene-diene) ternary copolymer, styrene butadiene rubber (Stylene-butadiene rubber), acrylonitrile butadiene rubber (acryloline) rubber (acrylone). (Styrene), polyvinylidene acetate, polymethylmethacrylate, polyethylene, nitrocellulose, etc., but the positive electrode active material and conductive agent are bound onto the current collector 21. There is no particular limitation as long as it can be made to occur.

The positive electrode active material layer 22 is produced, for example, by the following production method. That is, first, a positive electrode mixture is prepared by dry-mixing the positive electrode active material, the conductive agent, and the binder. Then, a positive electrode mixture slurry is prepared by dispersing the positive electrode mixture in an appropriate organic solvent, and the positive electrode mixture slurry is applied onto the current collector 21 and dried and rolled to activate the positive electrode. A material layer is created.

(Negative electrode 30)
The negative electrode 30 includes a current collector 31 and a negative electrode active material layer 32. The current collector 31 may be any conductor, and is made of, for example, aluminum, stainless steel, nickel-plated steel, or the like. The negative electrode active material layer 32 may be any material as long as it is used as the negative electrode active material layer of the lithium ion secondary battery. For example, the negative electrode active material layer 32 contains a negative electrode active material and may further contain a binder. The negative electrode active material is, for example, graphite active material (artificial graphite, natural graphite, a mixture of artificial graphite and natural graphite, natural graphite coated with artificial graphite, etc.), fine particles of silicon or tin or their oxides, and graphite active material. , Fine particles of silicon or tin, alloys using silicon or tin as a basic material, _{titanium oxide compounds such as Li 4} Ti ₅ O ₁₂ and the like are conceivable. The oxide of silicon is represented by SiO _x (0 ≦ x ≦ 2). In addition to these, examples of the negative electrode active material include metallic lithium and the like. The binder is also the same as the binder constituting the positive electrode active material layer 22. The mass ratio of the positive electrode active material to the binder is not particularly limited, and the mass ratio adopted in the conventional lithium ion secondary battery is also applicable to this embodiment.

The negative electrode active material layer 32 is produced, for example, by the following manufacturing method. That is, first, a negative electrode mixture is prepared by dry-mixing the negative electrode active material and the binder. Then, a negative electrode mixture slurry is prepared by dispersing the negative electrode mixture in an appropriate solvent, and this negative electrode mixture slurry is applied onto the current collector 31 and dried and rolled to obtain a negative electrode active material. Layer 32 is made.

(Separator 40)
The separator 40 includes a base material 40a and a coating layer (filler layer) 40b. The base material 40a is not particularly limited, and may be any material as long as it is used as a separator for a lithium ion secondary battery. As the base material 40a, it is preferable to use a porous film (porous film), a non-woven fabric, or the like exhibiting excellent high-rate discharge performance alone or in combination. Examples of the resin constituting the base material 40a include polyolefin-based resins typified by polyethylene, polypropylene and the like, polyethylene terephthalate, polybutylene terephthalate and the like. Polyethylene resin, PVDF, vinylidene fluoride (VDF) -hexafluoropropylene (HFP) copolymer, vinylidene fluoride-perfluorovinyl ether copolymer, vinylidene fluoride-tetrafluoroethylene (Tetrafluoroethylene) copolymer, vinylidene fluoride-trifluoroethylene copolymer, vinylidene fluoride-fluoroethylene copolymer, vinylidene fluoride-hexafluoroacetone copolymer, fluoride. Vinylidene-ethylene (ethylene) copolymer, vinylidene fluoride-propylene (polyethylene) copolymer, vinylidene fluoride-trifluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene-hexafluoro Examples thereof include propylene (hexafluoropolyethylene) copolymer, vinylidene fluoride-ethylene (ethylene) -tetrafluoroethylene (terrafluoropolyethylene) copolymer and the like.

The coating layer 40b contains inorganic particles and a binder. Examples of the inorganic particles according to the present embodiment include inorganic particles having high heat resistance. Specific examples of such inorganic particles include oxides of silicon, aluminum, magnesium and titanium, and hydroxides thereof. Of these, as the inorganic particles of the present embodiment, either or both of alumina and boehmite, which have particularly high heat resistance and a low water content (water content), is particularly preferable. By including the inorganic particles having such characteristics in the separator 40, the cycle characteristics of the lithium ion secondary battery 10 are improved. The particle size of the inorganic particles is not particularly limited as long as it is the particle size of the inorganic particles used in the lithium ion secondary battery 10.

The binder holds the inorganic particles in the coating layer 40b, that is, in the separator 40. The binder of the present embodiment is an acrylic resin in which a carboxyl group-containing acrylic monomer and an acrylic acid derivative monomer are essential monomers, and these essential monomers are polymerized at a molar ratio of 20/80 to 80/20 (hereinafter, "" It is described as "copolymerized acrylic resin"). By using the copolymerized acrylic resin of the present embodiment as a binder for the coating layer 40b, the heat resistance of the separator 40 and the adhesion between the base material 40a and the coating layer 40b are improved. Further, in the present embodiment, by forming the coating layer 40b using the copolymerized acrylic resin as a binder, the adhesion strength between the separator 40 and the electrodes (positive electrode 20 and negative electrode 30) is improved. This improves the safety and cycle life of the lithium ion secondary battery 10.

From the viewpoint of further improving the heat resistance of the separator 40, the adhesion between the base material 40a and the coating layer 40b, and the adhesion strength between the separator 40 and the electrodes (positive electrode 20 and negative electrode 30), the carboxyl group is used. The compounding ratio of the contained monomer and the acrylic acid derivative monomer is preferably 30/70 to 70/30, more preferably 40/60 to 60/40, and 40/60 to 50/40 in terms of molar ratio. Most preferably, it is 50.

Further, the copolymerized acrylic resin which is the main component of the binder of the coating layer 40b of the present embodiment may be any of a block copolymer, a random copolymer, and a graft copolymer. However, in order to further greatly improve the heat resistance of the separator 40, the adhesion between the base material 40a and the coating layer 40b, and the adhesion strength between the separator 40 and the electrodes (positive electrode 20 and negative electrode 30), the carboxyl is used. A graft copolymer in which a polymer main chain on which a group-containing acrylic monomer is polymerized is grafted with a polymer side chain on which a nitrile group-containing acrylic monomer is polymerized is preferable. In this case, the amount of water contained in the separator 40 can be further reduced.

Examples of the carboxyl group-containing acrylic monomer of the present embodiment include acrylic acid, methacrylic acid, maleic acid, monomethylmaleic acid, 2-carboxyethyl acrylate, 2-carboxyethyl methacrylate and the like. These monomers can be used alone or in combination of two or more.

Further, examples of the acrylic acid derivative monomer of the present embodiment include a nitrile group-containing acrylic monomer, an acrylic acid ester, and acrylamide. These monomers can be used alone or in combination of two or more.

Examples of the nitrile group-containing acrylic monomer include acrylonitrile, methacrylonitrile, 2-cyanoethyl acrylate, and 2-cyanoethyl methacrylate. These monomers can be used alone or in combination of two or more.

Examples of the acrylic acid ester include isobornyl acrylate, 2,2,2-trifluoroethyl acrylate, methyl (meth) acrylate, butyl (meth) acrylate, ethyl (meth) acrylate, and 2-ethylhexyl (). Meta) Acrylate, hydroxyethyl acrylate, 1H, 1H-pentafluoropropyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, adamantyl acrylate, t-butyl acrylate, acryloisobutyl POSS, butyl acrylate, glycidyl methacrylate, etc. Can be mentioned. The amino group of acrylamide may be substituted with various substituents. Examples of acrylamide substituted with a substituent include 2-acrylamide-2-methylpropanesulfonic acid. These monomers can be used alone or in combination of two or more.

Further, the higher the glass transition temperature Tg of the copolymerized acrylic resin of the present embodiment, the higher the heat resistance of the binder, which is preferable. Therefore, in the present embodiment, at least one of the carboxyl group-containing acrylic monomer and the nitrile group-containing acrylic monomer has a Tg of 0 ° C. or higher, more preferably room temperature (25 ° C.) or higher. That is, it is sufficient that the glass transition point of the copolymer as a whole is high.

Further, when the copolymerized acrylic resin of the present embodiment is in a salt state, Tg increases and the heat resistance of the binder increases. Therefore, an alkali metal salt or an ammonium salt of a carboxylic acid is used as at least a part of the carboxyl group-containing acrylic monomer instead of or in combination with the method of increasing the Tg of the constituent monomer of the copolymerized acrylic resin. Is preferable. Examples of the alkali metal include sodium and the like. Further, in order to further reduce the amount of water contained in the separator 40, it is particularly preferable to use an ammonium salt of a carboxylic acid as at least a part of the carboxyl group-containing acrylic monomer.

Here, the separator 40 of the present embodiment may further contain a water-insoluble resin in addition to the above-mentioned copolymerized acrylic resin used as a main component as a binder. Examples of such a water-insoluble resin include polyvinylidene fluoride (PVDF), a water-insoluble acrylic resin, and the like. These water-insoluble resins can be used alone or in combination of two or more. The water-insoluble acrylic resin preferably has a molecular weight of 50,000 or more, and for example, methyl poly (meth) acrylate, butyl poly (meth) acrylate, ethyl poly (meth) acrylate, and poly2-ethylhexyl (meth). ) Examples thereof include polyalkyl (meth) acrylate compounds such as acrylic acid.

Further, in the present embodiment, polyvinyl alcohol (PVA) and polyvinylacrylamide (PNVA) may be further contained as the binder in addition to the above-mentioned copolymerized acrylic resin used as the main component. PVA and PNVA may be used in place of the water-insoluble resin, or may be used in combination with the water-insoluble resin.

By including the above-mentioned water-insoluble resin or PVA as a binder, the heat resistance, adhesion, and air permeability of the binder are further improved. Therefore, by using the separator 40 produced by using such a binder for the lithium ion secondary battery 10, the safety and cycle characteristics of the lithium ion secondary battery 10 can be further improved.

The separator 40 is manufactured, for example, by the following manufacturing method. That is, first, an inorganic particle dispersion liquid and a binder solution are prepared. The solvent of the inorganic particle dispersion liquid is not particularly limited as long as it can disperse the inorganic particles. The solvent of the inorganic particle dispersion is preferably the same as that of the binder solution. The solvent of the binder solution is not particularly limited as long as the binder can be dissolved. Examples of such a solvent include N-methylpyrrolidone (NMP) and the like. Then, a slurry is prepared by mixing the inorganic particle dispersion liquid and the binder solution. The concentration of the inorganic particles and the binder may be adjusted by optionally adding the same solvent as the binder solution to the slurry. Further, another type of binder, for example, a PVDF-based binder (a binder containing PVDF as a main chain) may be further added to the slurry. Then, the slurry is developed (for example, coated) on the base material 40a and dried to prepare the coating layer 40b. The base material 40a may be immersed in the slurry. The separator 40 is manufactured by these steps. In FIG. 1, the coating layer 40b is formed only on the surface of the base material 40a, but the coating layer 40b may also be formed in the pores of the base material 40a.

As the non-aqueous electrolytic solution, the same non-aqueous electrolytic solution as that conventionally used for a lithium secondary battery can be used without particular limitation. The non-aqueous electrolyte solution has a composition in which an electrolyte salt is contained in a non-aqueous solvent. Examples of the non-aqueous solvent include propylene carbonate (propylene carbonate), ethylene carbonate (ethylene carbonate), butylene carbonate (ethylene carbonate), chloroethylene carbonate (chloroethylene carbonate), vinylene carbonate (vinylene carbonate) and the like. ) Classes; cyclic esters such as γ-butyrolactone and γ-valerolactone; dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like. Classes; chain esters such as methyl formate, methyl acetate, methyl butyrate, tetrahydrofuran or derivatives thereof; 1,3-dioxane, 1,4 -Esters such as dioxane, 1,2-dimethoxyethane, 1,4-dibutoxyethane, methyl diglyme; acetonitrile (acetylene), benzonitrile (acetonoil), benzonitrile, etc. Nitriles such as bentonitol; dioxolane or a derivative thereof; ethylene sulfide (etherylene sulfide), sulfolane, sultone or a derivative thereof, etc. alone or a mixture of two or more thereof. It can, but is not limited to these.

As the electrolyte salt, for _{example, LiClO 4, LiBF 4, LiAsF} 6, LiPF 6, LiPF 6-x (C n F 2n + 1) x [ where, 1 <x <6, n = 1or2], LiSCN, LiBr, Inorganic ions containing one of lithium (Li), sodium (Na) or potassium (K) such as LiI, Li ₂ SO ₄ , Li ₂ B ₁₀ Cl ₁₀ , NaClO ₄ , NaI, NaSCN, NaBr, KClO _{4, KSCN.} Salt, LiCF ₃ SO ₃ , LiN (CF ₃ SO ₂ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiN (CF ₃ SO ₂ ) (C ₄ F ₉ SO ₂ ), LiC (CF ₃ SO ₂ ) ₃ , LiC (C ₂ F ₅ SO ₂ ) ₃ , (CH ₃ ) ₄ NBF ₄ , (CH ₃ ) ₄ NBr, (C ₂ H ₅ ) ₄ NClo ₄ , (C ₂ H ₅ ) ₄ NI, (C ₃₎ H ₇ ) ₄ NBr, (n-C ₄ H ₉ ) ₄ NClO ₄ , (n-C ₄ H ₉ ) ₄ NI, (C ₂ H ₅ ) ₄ N-malate, (C ₂ H ₅ ) ₄ N-benzoate , (C ₂ H ₅ ) ₄ N-phtalate, lithium sulphonic acid lithium, lithium octyl sulphonic acid, lithium dodecylbenzene sulfonate, etc. organic salt, etc. These ionic compounds can be used alone or in combination of two or more. The concentration of the electrolyte salt may be the same as that of the non-aqueous electrolyte solution used in the conventional lithium secondary battery, and is not particularly limited. In the present embodiment, a non-aqueous electrolytic solution containing an appropriate lithium compound (electrolyte salt) at a concentration of about 0.8 to 1.5 mol / L can be used.

Various additives may be added to the non-aqueous electrolytic solution. Examples of such additives include negative-negative action additives, positive-side action additives, ester-based additives, carbonic acid ester-based additives, sulfate ester-based additives, phosphate ester-based additives, and borate ester-based additives. Additives, acid anhydride-based additives, electrolyte-based additives and the like can be mentioned. Any one of these may be added to the non-aqueous electrolytic solution, or a plurality of types of additives may be added to the non-aqueous electrolytic solution.

(Manufacturing method of lithium ion secondary battery)
Next, a method of manufacturing the lithium ion secondary battery 10 will be described. The positive electrode 20 is manufactured as follows. First, a slurry is prepared by dispersing a mixture of a positive electrode active material, a conductive agent, and a binder in a solvent (for example, N-methyl-2-pyrrolidone). Next, the slurry is developed (for example, coated) on the current collector 21 and dried to prepare the positive electrode active material layer 22. The coating method is not particularly limited. As a coating method, for example, a knife coater method, a gravure coater method, or the like can be considered. Each of the following coating steps is also performed by the same method. Next, the positive electrode active material layer 22 is pressed by a press machine. As a result, the positive electrode 20 is produced.

The negative electrode 30 is also manufactured in the same manner as the positive electrode 20. First, a slurry is prepared by dispersing a mixture of a negative electrode active material and a binder in a solvent (for example, N-methyl-2-pyrrolidone, water). Next, the slurry is developed (for example, coated) on the current collector 31 and dried to prepare the negative electrode active material layer 32. Next, the negative electrode active material layer 32 is pressed by a press machine. As a result, the negative electrode 30 is manufactured.

The separator 40 is manufactured, for example, by the following manufacturing method. That is, first, an inorganic particle dispersion liquid and a binder solution are prepared. Then, a slurry is prepared by mixing the inorganic particle dispersion liquid and the binder solution. The concentration of the inorganic particles and the binder may be adjusted by optionally adding the same solvent as the binder solution to the slurry. Then, the slurry is developed (for example, coated) on the base material 40a and dried to prepare the coating layer 40b. The base material 40a may be immersed in the slurry. The separator 40 is produced by these steps.

Next, the electrode structure is manufactured by sandwiching the separator 40 between the positive electrode 20 and the negative electrode 30. Next, the electrode structure is processed into a desired shape (for example, cylindrical shape, square shape, laminated shape, button shape, etc.) and inserted into the container of the desired shape. Next, by injecting an electrolytic solution having the above composition into the container, each pore in the separator is impregnated with the electrolytic solution. As a result, a lithium ion secondary battery is manufactured.

<1. Binder synthesis>
Next, an example of this embodiment will be described. First, an example of binder synthesis will be described. The compounding ratio of sodium polyacrylate (PAANA) and the like described below and other monomers shall represent a molar ratio unless otherwise specified.

(Synthesis Example 1: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) = 50/50)
Add 363 g of distilled water and a 20 mass% sodium hydroxide aqueous solution (62.4 g, 0.9 equivalent to acrylic acid) in a 500 ml 4-neck separable flask equipped with a stir bar, a thermometer, and a cooling tube. After that, the operation of reducing the internal pressure to 10 mmHg with a diaphragm pump and returning the internal pressure to normal pressure with nitrogen was repeated three times. Next, acrylic acid (25 g, 0.347 mol), acrylonitrile (25 g, 0.471 mol), and ammonium persulfate (0.29 g, 0.00126 mol, 0.0015 equivalent) were added to a four-neck separable flask at 600 rpm. Stirred. While controlling the heating so that the temperature of the reaction solution was stable between 65 ° C. and 70 ° C., the temperature was further raised to 80 ° C. for 4 hours, and the reaction was carried out for 4 hours.

After cooling to room temperature, the pH of the reaction solution was adjusted to 7 to 8 using a 20 mass% sodium hydroxide aqueous solution. About 2 ml of the reaction solution was taken and the non-volatile content (NV) was measured and found to be 11.4% by mass (theoretical value of 12% by mass).

(Synthesis Example 2: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) = 40/60)
456 g of distilled water, 20 mass% sodium hydroxide aqueous solution (52.7 g, 0.95 equivalent to acrylic acid) Acrylic acid (20 g, 0.278 mol), acrylonitrile (30 g, 0.565 mol), ammonium persulfate (0. All were synthesized in the same manner as in Synthesis Example 1 except that 29 g, 0.00126 mol, 0.0015 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.3% by mass (theoretical value of 10% by mass).

(Synthesis Example 3: Synthesis example of polysodium methacrylate (PAANA) / polyacrylonitrile (PAN) = 50/50)
362 g of distilled water, 20 mass% sodium hydroxide aqueous solution (55.2 g, 0.95 equivalent to methacrylic acid) methacrylic acid (25 g, 0.290 mol), acrylonitrile (25 g, 0.471 mol), ammonium persulfate (0. All were synthesized in the same manner as in Synthesis Example 1 except that 348 g, 0.00168 mol, 0.002 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 12.0% by mass (theoretical value of 12% by mass).

(Synthesis Example 4: Synthesis Example of Polysodium Polymethacrylate (PMAANA) / Polymethacrylonitrile (PMAN) = 50/50)
362 g of distilled water, 20 mass% sodium hydroxide aqueous solution (55.2 g, 0.95 equivalent to methacrylic acid) methacrylic acid (25 g, 0.290 mol), methacrylic acid (25 g, 0.373 mol), ammonium persulfate (25 g, 0.373 mol) All were synthesized in the same manner as in Synthesis Example 1 except that 0.30 g, 0.00133 mol, 0.002 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 12.0% by mass (theoretical value of 12% by mass).

(Synthesis Example 5: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyisobornyl Acrylate (PIsobor) = 50/50)
205 g of distilled water, 20 mass% sodium hydroxide aqueous solution (39.5 g, 0.95 equivalent to acrylic acid) Acrylic acid (15 g, 0.208 mol), isobornyl acrylate (15 g, 0.072 mol), ammonium persulfate All were synthesized in the same manner as in Synthesis Example 1 except that (0.096 g, 0.00042 mol, 0.0015 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 12.4% by mass (theoretical value of 12.5% by mass).

(Synthesis Example 6: Synthesis Example of Sodium Polyacrylate (PAANA) / Poly 2,2,2-Trifluoroethyl Acrylate = 50/50)
205 g of distilled water, 20 mass% aqueous sodium hydroxide solution (39.5 g, 0.95 equivalent to acrylic acid) Acrylic acid (15 g, 0.208 mol), 2,2,2-trifluoroethyl acrylate (15 g, 0) All were synthesized in the same manner as in Synthesis Example 1 except that (0.089 mol) and ammonium persulfate (0.102 g, 0.00045 mol, 0.0015 equivalent) were used. The non-volatile content (NV) of the reaction solution was measured and found to be 12.4% by mass (theoretical value of 12.5% by mass).

(Synthesis Example 7: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyacrylamide (PAAm) = 30/70)
Distilled water 235 g, 20 mass% sodium hydroxide aqueous solution (11.9 g, 0.95 equivalent to acrylic acid) Acrylic acid (4.5 g, 0.062 mol), acrylamide (10.5 g, 0.148 mol), excess All were synthesized in the same manner as in Synthesis Example 1 except that ammonium sulfate (0.048 g, 0.00021 mol, 0.001 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 6.0% by mass (theoretical value: 6.0% by mass).

(Synthesis Example 8: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyacrylamide (PAAm) = 50/50)
Distilled water 235 g, 20 mass% sodium hydroxide aqueous solution (19.8 g, 0.95 equivalent to acrylic acid) Acrylic acid (7.5 g, 0.104 mol), acrylamide (7.5 g, 0.106 mol), excess All were synthesized in the same manner as in Synthesis Example 1 except that ammonium sulfate (0.048 g, 0.00021 mol, 0.001 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 6.0% by mass (theoretical value: 6.0% by mass).

(Synthesis Example 9: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyacrylamide (PAAm) = 70/30)
235 g of distilled water, 20 mass% sodium hydroxide aqueous solution (27.7 g, 0.95 equivalent to acrylic acid) Acrylic acid (10.5 g, 0.146 mol), acrylamide (4.5 g, 0.063 mol), excess All were synthesized in the same manner as in Synthesis Example 1 except that ammonium sulfate (0.048 g, 0.00021 mol, 0.001 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 6.0% by mass (theoretical value: 6.0% by mass).

(Synthesis Example 10: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyadamantyl Acrylate (PADМ) = 62.5 / 37.5)
89 g of distilled water, polyvinyl alcohol (0.92 g, RS2217 manufactured by Kuraray Co., Ltd.) as a dispersant, and a 20 mass% sodium hydroxide aqueous solution (in a 300 ml four-neck separable flask equipped with a stirrer, a thermometer, and a cooling tube). 8.0 g (0.9 eq with respect to acrylic acid) was added, and after stirring until all were dissolved, the internal pressure was reduced to 10 mmHg with a diaphragm pump, and the operation of returning the internal pressure to normal pressure with nitrogen was repeated three times. .. Then, in a four-neck separable flask, acrylic acid (3.2 g, 0.044 mol), adamantyl acrylate (4.8 g, 0.027 mol), ammonium persulfate (0.023 g, 0.00011 mol, 0.0015 equivalent) ) Was added, and the mixture was stirred at 600 rpm. While controlling the heating so that the temperature of the reaction solution was stable between 65 ° C. and 70 ° C., the temperature was further raised to 80 ° C. for 4 hours, and the reaction was carried out for 4 hours.

After cooling to room temperature, the pH of the reaction solution was adjusted to 7 to 8 using a 25 mass% aqueous ammonia solution. When about 2 ml of the reaction solution was taken and the non-volatile content (NV) was measured, it was 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 11: Synthesis example of sodium polyacrylate (PAANA) / polyadamantyl acrylate (PADМ) = 70/30)
93 g of distilled water, 20 mass% aqueous sodium hydroxide solution (9.7 g, 0.9 equivalent to acrylic acid) Acrylic acid (3.89 g, 0.054 mol), Adamanthyl acrylate (4.34 g, 0.024 mol), All were synthesized in the same manner as in Synthesis Example 10 except that ammonium persulfate (0.027 g, 0.00012 mol, 0.0015 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 8.9% by mass (theoretical value: 10% by mass).

(Synthesis Example 12: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyadamantyl Acrylate (PADМ) = 80/20)
86 g of distilled water, 20 mass% aqueous sodium hydroxide solution (11.2 g, 0.9 equivalent to acrylic acid) acrylic acid (4.48 g, 0.062 mol), adamantyl acrylate (2.80 g, 0.016 mol), All were synthesized in the same manner as in Synthesis Example 10 except that ammonium persulfate (0.027 g, 0.00012 mol, 0.0015 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 8.9% by mass (theoretical value: 10% by mass).

(Synthesis Example 13: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyt-Butyl Acrylate (Pt-BuA) = 70/30)
81 g of distilled water, 20 mass% sodium hydroxide aqueous solution (9.7 g, 0.9 equivalent to acrylic acid), acrylic in a 300 ml 4-neck separable flask equipped with a stir bar, a thermometer, and a cooling tube. After adding an acid (3.8 g, 0.054 mol) and stirring until all of them were uniformly dissolved, the internal pressure was reduced to 10 mmHg with a diaphragm pump, and the operation of returning the internal pressure to normal pressure with nitrogen was repeated three times. Then, t-butyl acrylate (3.08 g, 0.024 mol) and ammonium persulfate (0.027 g, 0.00012 mol, 0.0015 equivalent) were added to a four-neck separable flask, and the mixture was stirred at 600 rpm. While controlling the heating so that the temperature of the reaction solution was stabilized between 65 ° C. and 70 ° C., the temperature was further raised to 80 ° C. for 4 hours, and the reaction was carried out for 4 hours. After cooling to room temperature, the pH of the reaction solution was adjusted to 7 to 8 using a 25 mass% aqueous ammonia solution. When about 2 ml of the reaction solution was taken and the non-volatile content (NV) was measured, it was 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 14: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyt-Butyl Acrylate (Pt-BuA) = 80/20)
79 g of distilled water, 20 mass% aqueous sodium hydroxide solution (11.2 g, 0.9 equivalent to acrylic acid), acrylic acid (4.48 g, 0.062 mol), t-butyl acrylate (2.05 g, 0. All were synthesized in the same manner as in Synthesis Example 13 except that 016 mol) and ammonium persulfate (0.027 g, 0.00012 mol, 0.0015 equivalent) were used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 15: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium poly-2-acrylamide-2-methylpropanesulfonate (PAMPS) = 20/60/20)
145 g of distilled water, 20 mass% sodium hydroxide aqueous solution (9.0 g, 0.8 equivalent to the total amount of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid), acrylic acid (3.0 g, 0.042 mol) ), Ammonium persulfate (0.077 g, 0.00034 mol, 0.0015 equivalent), acrylonitrile (9.0 g, 0.170 mol) instead of t-butyl acrylate, and 2-acrylamide-2-methylpropanesulfonic acid (3). All were synthesized in the same manner as in Synthesis Example 13 except that 0.0 g, 0.014 mol) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 16: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium poly-2-acrylamide-2-methylpropanesulfonate (PAMPS) = 30/60/10)
147 g of distilled water, 20 mass% sodium hydroxide aqueous solution (11.1 g, 0.8 equivalent to the total amount of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid), acrylic acid (4.5 g, 0.062 mol) ), Acrylonitrile (9.0 g, 0.170 mol), 2-acrylamide-2-methylpropanesulfonic acid (1.5 g, 0.007 mol), ammonium persulfate (0.082 g, 0.00036 mol, 0.0015 equivalent). All of them were synthesized in the same manner as in Synthesis Example 15 except that they were used. The non-volatile content (NV) of the reaction solution was measured and found to be 8.9% by mass (theoretical value: 10% by mass).

(Synthesis Example 17: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium poly-2-acrylamide-2-methylpropanesulfonate (PAMPS) = 35/60/5)
148 g of distilled water, 20 mass% sodium hydroxide aqueous solution (12.2 g, 0.8 equivalent to the total amount of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid), acrylic acid (5.25 g, 0.073 mol) ), Acrylonitrile (9.0 g, 0.170 mol), 2-acrylamide-2-methylpropanesulfonic acid (0.75 g, 0.004 mol), ammonium persulfate (0.084 g, 0.00037 mol, 0.0015 equivalent). All of them were synthesized in the same manner as in Synthesis Example 15 except that they were used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthetic Example 18: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium poly-2-acrylamide-2-methylpropanesulfonate (PAMPS) = 25/55/20)
147 g of distilled water, 20 mass% sodium hydroxide aqueous solution (10.6 g, 0.8 equivalent to the total amount of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid), acrylic acid (3.75 g, 0.052 mol) ), Acrylonitrile (8.25 g, 0.155 mol), 2-acrylamide-2-methylpropanesulfonic acid (3.0 g, 0.014 mol), ammonium persulfate (0.076 g, 0.00033 mol, 0.0015 equivalent). All of them were synthesized in the same manner as in Synthesis Example 15 except that they were used. The non-volatile content (NV) of the reaction solution was measured and found to be 8.8% by mass (theoretical value: 10% by mass).

(Synthesis Example 19: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium poly-2-acrylamide-2-methylpropanesulfonate (PAMPS) = 35/55/10)
149 g of distilled water, 20 mass% sodium hydroxide aqueous solution (12.8 g, 0.8 equivalent to the total amount of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid), acrylic acid (5.25 g, 0.073 mol) ), Acrylonitrile (8.25 g, 0.155 mol), 2-acrylamide-2-methylpropanesulfonic acid (1.5 g, 0.007 mol), ammonium persulfate (0.081 g, 0.00035 mol, 0.0015 equivalent). All of them were synthesized in the same manner as in Synthesis Example 15 except that they were used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 20: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium poly-2-acrylamide-2-methylpropanesulfonate (PAMPS) = 40/55/5)
150 g of distilled water, 20 mass% sodium hydroxide aqueous solution (13.9 g, 0.8 equivalent to the total amount of acrylic acid and 2-acrylamide-2-methylpropanesulfonic acid), acrylic acid (6.0 g, 0.083 mol) ), Acrylonitrile (8.25 g, 0.155 mol), 2-acrylamide-2-methylpropanesulfonic acid (0.75 g, 0.004 mol), ammonium persulfate (0.083 g, 0.00036 mol, 0.0015 equivalent). All of them were synthesized in the same manner as in Synthesis Example 15 except that they were used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 21: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / sodium polymaleate (PMalNa) = 38/57/5)
143 g of distilled water, 20 mass% sodium hydroxide aqueous solution (14.2 g, 0.8 equivalent to twice the total mol of acrylic acid and maleic acid) Acrylic acid (5.40 g, 0.075 mol), acrylonitrile ( 8.10 g, 0.153 mol), maleic acid (0.69 g, 0.007 mol), ammonium persulfate (0.08 g, 0.00035 mol, 0.0015 equivalent) were all used in the same manner as in Synthesis Example 13. Was synthesized. The non-volatile content (NV) of the reaction solution was measured and found to be 8.8% by mass (theoretical value: 10% by mass).

(Synthesis Example 22: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyacrylonitrile (PAN) / Polyacryloisobutyl POSS (P-i-BuPOSS) = 40/45/15)
149 g of distilled water, 20 mass% sodium hydroxide aqueous solution (13.3 g, 0.8 equivalent with respect to acrylic acid) Acrylic acid (6.00 g, 0.083 mol), acrylonitrile (6.75 g, 0.127 mol), acrylic All were synthesized in the same manner as in Synthesis Example 15 except that loisobutyl POSS (2.25 g, 0.0024 mol) and ammonium persulfate (0.073 g, 0.00032 mol, 0.0015 equivalent) were used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 23: Synthesis example of sodium polyacrylate (PAANA) / polyacrylonitrile (PAN) / polyacryloisobutyl POSS (P-i-BuPOSS) = 40/50/10)
149 g of distilled water, 20 mass% sodium hydroxide aqueous solution (13.3 g, 0.8 equivalent with respect to acrylic acid) Acrylic acid (6.00 g, 0.083 mol), acrylonitrile (7.50 g, 0.141 mol), acrylic All were synthesized in the same manner as in Synthesis Example 15 except that loisobutyl POSS (1.50 g, 0.0016 mol) and ammonium persulfate (0.077 g, 0.00034 mol, 0.0015 equivalent) were used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 24: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyacrylonitrile (PAN) / Polyacryloisobutyl POSS (P-i-BuPOSS) = 40/55/5)
150 g of distilled water, 20 mass% sodium hydroxide aqueous solution (13.3 g, 0.8 equivalent with respect to acrylic acid) Acrylic acid (6.00 g, 0.083 mol), acrylonitrile (8.25 g, 0.155 mol), acrylic All were synthesized in the same manner as in Synthesis Example 15 except that loisobutyl POSS (0.75 g, 0.0008 mol) and ammonium persulfate (0.082 g, 0.00036 mol, 0.0015 equivalent) were used. The non-volatile content (NV) of the reaction solution was measured and found to be 8.9% by mass (theoretical value: 10% by mass).

(Synthesis Example 25: Synthesis Example of Sodium Polyacrylate (PAANA) / Polyacrylonitrile (PAN) = 80/20)
167 g of distilled water, 20 mass% aqueous sodium hydroxide solution (30.0 g, 0.9 equivalent to acrylic acid) Acrylic acid (12.0 g, 0.167 mol), acrylonitrile (3.0 g, 0.057 mol), excess All were synthesized in the same manner as in Synthesis Example 1 except that ammonium sulfate (0.076 g, 0.00033 mol, 0.0015 equivalent) was used. The non-volatile content (NV) of the reaction solution was measured and found to be 9.0% by mass (theoretical value: 10% by mass).

(Synthesis Example 26: Synthesis Example of Sodium Polyacrylate (PAANA) / Polybutyl Acrylate (Pn-Bu) / Polyglycidyl Methacrylate (PGryci) = 11/86/3)
181 g of distilled water, 20 mass% sodium hydroxide aqueous solution (5.2 g, 0.9 equivalent to acrylic acid) acrylic acid (2.10 g, 0.029 mol), butyl acrylate (16.8 g, 0.131 mol), All were synthesized in the same manner as in Synthesis Example 15 except that glycidyl methacrylate (0.6 g, 0.004 mol) and ammonium persulfate (0.056 g, 0.00036 mol, 0.0015 equivalent) were used. The non-volatile content (NV) of the reaction solution was measured and found to be 8.9% by mass (theoretical value: 10% by mass).

<2. Coating separator production>
(Comparative Example 1)
61.4 g of boehmite C20 (manufactured by Taimei Chemicals Co., Ltd.), 6.8 g of boehmite ACTILOX-200SM (manufactured by Navaltec), 164 g of distilled water, and a 10 mass% sodium polyacrylate aqueous solution (manufactured by Aldrich, 68.3 g) as a binder. Add 6.8 g in NV conversion, 10% by mass based on the total weight of boehmite), stir until it becomes a slurry, and then use a bead mill (manufactured by Zirconia beads, 0.5φ, filling rate 60% by volume, 2000 rpm, 4 times). (Pass) was dispersed to prepare a boehmite / binder mixed solution.

Then, using a gravure coater prepared so that the coating amount (loading amount) after drying was 3.0 g / m ² , a commercially available polyethylene microporous film having a thickness of 12 μm (T12-507 <manufactured by SK Innovation Co., Ltd.) >), The above-mentioned polyethylene / binder mixed solution was applied and dried to obtain a coating separator of Comparative Example 1. Further, vacuum drying (133 Pa) was performed at 60 ° C. for 12 hours to remove water, and the battery was used for manufacturing.

(Comparative Example 2)
Comparative Example 1 except that 175 g of distilled water and 27.2 g of PVDF aqueous dispersion (Solvay's Solef90000) (6.8 g in terms of NV, 10% by mass with respect to the total weight of boehmite) were used as a binder. The same procedure as above was carried out to obtain a coating separator of Comparative Example 2.

(Example 1)
Except for the use of 171 g of distilled water and the binder (59.9 g, 6.8 g in terms of NV, 10% by mass with respect to the total weight of boehmite) prepared in Synthesis Example 1, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 1. A coated separator was obtained.

(Example 2)
Except for the use of 158 g of distilled water and the binder (73.4 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 2, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 2. A coated separator was obtained.

(Example 3)
Except for the use of 175 g of distilled water and the binder (73.4 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 3, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 3. A coated separator was obtained.

(Example 4)
Except for the use of 175 g of distilled water and the binder (56.9 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 4, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 4. A coated separator was obtained.

(Example 5)
Except for the use of 177 g of distilled water and the binder prepared in Synthesis Example 5 (55.0 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite), all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 5. A coated separator was obtained.

(Example 6)
Except for the use of 177 g of distilled water and the binder prepared in Synthesis Example 6 (55.0 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite), all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 6. A coated separator was obtained.

(Example 7)
Except for using 118 g of distilled water and the binder (113.8 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 7, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 7. A coated separator was obtained.

(Example 8)
Except for using 118 g of distilled water and the binder (113.8 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 8, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 8. A coated separator was obtained.

(Example 9)
Except for using 118 g of distilled water and the binder (113.8 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 9, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 9. A coated separator was obtained.

(Example 10)
188 g of distilled water, 29.9 g of binder prepared in Synthesis Example 1, 3.4 g of NV equivalent, 5% by mass with respect to the total weight of boehmite, and 25% by mass of PVDF aqueous dispersion (Solvay's Solef90000, 13. The same procedure as in Comparative Example 1 was carried out except that 7 g, 3.4 g in terms of NV, and 5% by mass based on the total weight of boehmite) were used to obtain a coating separator of Example 10.

(Example 11)
188 g of distilled water, 36.7 g of binder prepared in Synthesis Example 2, 3.4 g of NV equivalent, 5% by mass with respect to the total weight of boehmite, and 25% by mass of PVDF aqueous dispersion (Solvay's Solef90000, 13. The same procedure as in Comparative Example 1 was carried out except that 7 g, 3.4 g in terms of NV, and 5% by mass based on the total weight of boehmite) were used to obtain a coating separator of Example 11.

(Example 12)
182 g of distilled water, 29.9 g of binder prepared in Synthesis Example 1, 3.4 g of NV equivalent, 5% by mass with respect to the total weight of boehmite, and 16.9% by mass of a water-insoluble acrylic aqueous dispersion (Hitachi Kasei). A coating separator of Example 12 was obtained in the same manner as in Comparative Example 1 except that SSE2G, 20.2 g, NV equivalent 3.4 g, 5% by mass based on the total weight of boehmite) was used.

(Example 13)
174 g of distilled water, 36.7 g of binder prepared in Synthesis Example 2, 3.4 g of NV equivalent, 5% by mass with respect to the total weight of boehmite, and 16.9% by mass of a water-insoluble acrylic aqueous dispersion (Hitachi Kasei). A coating separator of Example 13 was obtained in the same manner as in Comparative Example 1 except that SSE2G, 20.2 g, NV equivalent 3.4 g, 5% by mass based on the total weight of boehmite) was used.

(Example 14)
All was carried out in the same manner as in Comparative Example 1 except that 157 g of distilled water and the binder (75.6 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 10 were used. A coated separator was obtained.

(Example 15)
Except for the use of 156 g of distilled water and the binder (76.4 g, 6.8 g in terms of NV, 10% by mass with respect to the total weight of boehmite) prepared in Synthesis Example 11, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 15. A coated separator was obtained.

(Example 16)
All was carried out in the same manner as in Comparative Example 1 except that 156 g of distilled water and the binder (76.4 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 12 were used. A coated separator was obtained.

(Example 17)
Except for the use of 157 g of distilled water and the binder (75.6 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 13, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 17. A coated separator was obtained.

(Example 18)
All was carried out in the same manner as in Comparative Example 1 except that 157 g of distilled water and the binder (75.6 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 14 were used. A coated separator was obtained.

(Example 19)
Except for the use of 157 g of distilled water and the binder (75.6 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 15, the same procedure as in Comparative Example 1 was carried out. A coated separator was obtained.

(Example 20)
Except for the use of 156 g of distilled water and the binder (76.4 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 16, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 20. A coated separator was obtained.

(Example 21)
All was carried out in the same manner as in Comparative Example 1 except that 157 g of distilled water and the binder (75.6 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 17 were used. A coated separator was obtained.

(Example 22)
All was carried out in the same manner as in Comparative Example 1 except that 155 g of distilled water and the binder (77.3 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 18 were used. A coated separator was obtained.

(Example 23)
Except for the use of 157 g of distilled water and the binder (75.6 g, NV equivalent of 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 19, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 23. A coated separator was obtained.

(Example 24)
Except for the use of 157 g of distilled water and the binder (75.6 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 20, the same procedure as in Comparative Example 1 was carried out in the same manner as in Comparative Example 24. A coated separator was obtained.

(Example 25)
Except for the use of 155 g of distilled water and the binder (77.3 g, NV equivalent of 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 21, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 25. A coated separator was obtained.

(Example 26)
Except for the use of 157 g of distilled water and the binder (75.6 g, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 22, all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 26. A coated separator was obtained.

(Example 27)
Except for the use of 157 g of distilled water and the binder prepared in Synthesis Example 23 (75.6, 6.8 g in terms of NV, 10% by mass based on the total weight of boehmite), all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 27. A coated separator was obtained.

(Example 28)
Except for the use of 156 g of distilled water and the binder prepared in Synthesis Example 24 (76.4, 6.8 g in terms of NV, 10% by mass with respect to the total weight of boehmite), all the same operations were carried out in the same manner as in Comparative Example 1 and in Example 28. A coated separator was obtained.

(Example 29)
All was carried out in the same manner as in Comparative Example 1 except that 157 g of distilled water and the binder (75.6 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 25 were used. A coated separator was obtained.

(Comparative Example 3)
All was carried out in the same manner as in Comparative Example 1 except that 159 g of distilled water and the binder (73.1 g, NV equivalent 6.8 g, 10% by mass based on the total weight of boehmite) prepared in Synthesis Example 26 were used. A coated separator was obtained.

<3. Adhesion evaluation of coating layer>
An adhesive tape (cellotape manufactured by Nichiban Co., Ltd. (registered trademark) No. 405) having a width of 1.5 cm was attached to a coating separator fixed on a stainless steel plate. Then, the peel strength at 180 ° peeling was measured using a peeling tester (SHIMAZU EZ-S manufactured by Shimadzu Corporation). The adhesion evaluation results are summarized in Table 1.

<4. Heat shrinkage evaluation>
As shown in FIG. 2, the coating separator was cut out so that TD * MD = 60 mm * 80 mm, and marks were made in the TD / MD direction with a caliper at intervals of 50 mm. The separator was sandwiched between the folded aluminum foils and allowed to stand in a constant temperature bath at 130 ° C. for 60 minutes. After taking out the separator, the distance between the marks of TD / MD was read with a caliper, and the heat shrinkage rate was calculated according to the following formula. The heat shrinkage evaluation results are summarized in Table 1. In the following formula, the interval after heating was the interval in the TD direction.

Shrinkage rate (%) = ((50-interval after heating) / 50) * 100)

<4-1. Evaluation of air permeability ＞
The air permeability was evaluated by measuring the permeation time of 100 cc of air with a Garley type densometer manufactured by Toyo Seiki Co., Ltd. (inner cylinder weight (pressure) 567 g, permeation surface hole diameter 28.6 mm (6.45 square centimeter)). The shorter the permeation time, the higher the air permeability.

According to Table 1, it can be seen that the binders of Synthesis Examples 1 to 25 and the binders obtained by adding a water-insoluble resin to Synthesis Examples 1 and 2 are excellent in heat resistance and adhesive strength. Furthermore, it can be seen that these binders also have low air permeability.

<5. Rechargeable battery production>
(Example 30)
(Preparation of negative electrode mixture slurry)
By mixing 96% by mass of artificial graphite, 2% by mass of acetylene black, 1% by mass of styrene-butadiene copolymer (SBR) binder, and 1% by mass of carboxymethyl cellulose (CMC), water is added to the mixture to adjust the viscosity. A negative electrode mixture slurry was prepared. The non-volatile content in the negative electrode mixture slurry was 48% by mass with respect to the total mass of the slurry.

(Preparation of negative electrode)
Next, the gap of the bar coater was adjusted so that the amount of the mixture applied (area density) after drying was 9.55 mg / cm ^2, and the negative electrode mixture slurry was made into a copper foil (current collector, thickness 10 μm) by this bar coater. ) Was evenly coated. Next, the negative electrode mixture slurry was dried for 15 minutes in a blower type dryer set at 80 ° C. Then, the dried negative electrode mixture was pressed by a roll press machine so that the mixture density was 1.65 g / cm3. Then, the negative electrode mixture was vacuum dried at 150 ° C. for 6 hours to prepare a sheet-shaped negative electrode composed of a negative electrode current collector and a negative electrode active material layer.

(Preparation of positive electrode mixture slurry)
Disperse solid solution oxide Li _1.20 Mn _0.55 Co _0.10 Ni _0.15 O ₂ 96% by mass, Ketjen Black 2% by mass, and polyvinylidene fluoride 2% by mass in N-methyl-2-pyrrolidone. To form a positive electrode mixture slurry. The non-volatile content in the positive electrode mixture slurry was 50% by mass with respect to the total mass of the slurry.

(Preparation of positive electrode)
Next, the gap of the bar coater is adjusted so that the amount of the mixture applied (area density) after drying is 22.7 mg / cm ^2, and the positive electrode mixture slurry is collected on the aluminum current collector foil which is the current collector by this bar coater. Was painted on. Then, the positive electrode mixture slurry was dried for 15 minutes in a blower type dryer set at 80 ° C. Then, the dried positive electrode mixture was pressed by a roll press machine so that the mixture density was 3.9 g / cm3. Then, the positive electrode mixture was vacuum dried at 80 ° C. for 6 hours to prepare a sheet-shaped positive electrode composed of a positive electrode current collector and a positive electrode active material layer.

(Manufacturing of lithium ion secondary battery)
The negative electrode shown in the negative electrode production example was cut into a circle with a diameter of 1.55 cm, and the positive electrode shown in the positive electrode production example was cut into a circle with a diameter of 1.3 cm. Then, the coating separator prepared in Example 1 was cut into a circle having a diameter of 1.8 cm. A positive electrode cut into a circle with a diameter of 1.3 cm, a coating separator of Example 1 cut into a circle with a diameter of 1.8 cm, and a negative electrode cut into a circle with a diameter of 1.55 cm in a stainless coin outer container having a diameter of 2.0 cm. Further, as a spacer, a copper foil having a thickness of 200 μm cut into a circle having a diameter of 1.5 cm was laminated in this order. Then, 150 μL of an electrolytic solution (1.4 M LiPF ₆ ethylene carbonate / diethyl carbonate / fluoroethylene carbonate = 10/70/20 mixed solution (volume ratio)) was added to the container. Then, a stainless steel cap was put on the container via a polypropylene packing, and the container was sealed with a crimping device for making a coin battery. As a result, the lithium ion secondary battery (coin cell) according to Example 30 was produced.

(Examples 31 to 58, Comparative Examples 4 to 6)
The lithium ion secondary batteries according to Examples 31 to 58 and Comparative Examples 4 to 6 were produced by performing the same treatment as in Example 30 except that the separators shown in Table 2 were used.

<6. Evaluation of cycle life>
The lithium ion secondary batteries according to each Example and Comparative Example were charged and discharged once at 0.2 C at 25 ° C. Then, the charge / discharge cycle of charging / discharging the lithium ion secondary battery at 1.0 C was repeated 100 times. The discharge capacity retention rate (percentage) is calculated by dividing the discharge capacity at 100 cycles (100th 1.0C charge / discharge cycle) by the discharge capacity at 1 cycle (1st 1.0C charge / discharge cycle). did. The larger the capacity retention rate, the better the cycle life. The evaluation results are summarized in Table 2.

According to Table 2, it can be seen that the cycle characteristics of the lithium ion secondary battery according to this embodiment are improved. Further, it can be seen that the cycle characteristics are particularly improved when a water-insoluble resin is added as the binder. The separator of Comparative Example 1 had good peel strength and shrinkage rate, but the secondary battery using the separator of Comparative Example 1 had low cycle characteristics. It is considered that the reason for this is that the air permeability of Comparative Example 1 is high and that water remains in the separator. Therefore, it can be seen that even if an acrylic resin obtained by polymerizing only a carboxyl group-containing acrylic monomer (for example, sodium polyacrylate of Comparative Example 1) is used as a binder, the cycle characteristics cannot be improved. That is, it can be seen that in order to synthesize a binder capable of improving cycle characteristics, it is necessary to use not only the carboxyl group-containing acrylic monomer but also the acrylic acid derivative monomer as an essential monomer.

As described above, the binder according to the present embodiment can have high heat resistance and strong adhesive strength, and can improve the cycle characteristics. Therefore, by manufacturing the separator 40 using the binder according to the present embodiment and manufacturing the lithium ion secondary battery 10 using the separator 40, the cycle characteristics of the lithium ion secondary battery 10 can be improved. .. Further, since the thermal shrinkage of the separator 10 is also suppressed, the thermal runaway of the lithium ion secondary battery 10 can be suppressed, and the safety of the lithium ion secondary battery 10 is improved.

Although the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the field of technology to which the present invention belongs can come up with various modifications or modifications within the scope of the technical ideas described in the claims. , These are also naturally understood to belong to the technical scope of the present invention.

For example, in the above embodiment, the binder according to the present embodiment is used for the lithium ion secondary battery, but the binder according to the present embodiment may be used for another type of secondary battery.

10 Lithium-ion secondary battery 20 Positive electrode 30 Negative electrode 40 Separator 40a Base material 40b Coating layer

Claims (8)

In a separator for a lithium ion secondary battery comprising a base material and at least a coating layer formed on the surface of the base material.
The coating layer is composed of a binder for a secondary battery containing an acrylic resin obtained by copolymerizing a carboxyl group-containing acrylic monomer and an acrylic acid derivative monomer, and inorganic particles.
The compounding ratio of the carboxyl group-containing acrylic monomer and the acrylic acid derivative monomer is 20/80 to 80/20 in terms of molar ratio.
Ri least some alkali metal salts or ammonium salts der of the carboxyl group-containing acrylic monomer,
Wherein said derivative monomer acrylic acid, a nitrile group-containing acrylic monomer, and at least any one kind der wherein Rukoto selected from the group consisting of acrylic acid ester and acrylamide, separators for lithium ion secondary battery. The carboxyl group-containing acrylic monomer is characterized by containing at least one of the group consisting of acrylic acid, methacrylic acid, maleic acid, monomethylmaleic acid, 2-carboxyethyl acrylate, and 2-carboxyethyl methacrylate. The separator for a lithium ion secondary battery according to claim 1. Claim 1 or 2 , wherein the nitrile group-containing acrylic monomer is at least one of the group consisting of acrylonitrile, methacrylnitrile, 2-cyanoethyl acrylate, and 2-cyanoethyl methacrylate. The above-mentioned separator for a lithium ion secondary battery. The separator for a lithium ion secondary battery according to any one of claims 1 to 3 , wherein the coating layer further contains a water-insoluble resin as the binder for the secondary battery. The separator for a lithium ion secondary battery according to claim 4 , wherein the water-insoluble resin contains one or both of polyvinylidene fluoride and a water-insoluble acrylic resin. The separator for a lithium ion secondary battery according to any one of claims 1 to 5 , wherein the coating layer further contains polyvinyl alcohol as the binder for the secondary battery. The separator for a lithium ion secondary battery according to any one of claims 1 to 6 , wherein the inorganic particles are one or both of alumina and boehmite. A lithium ion secondary battery comprising the separator according to any one of claims 1 to 7.

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