JP6311269B2 - Adhesive for lithium ion secondary battery, separator for lithium ion secondary battery, and lithium ion secondary battery - Google Patents

Description

  The present invention relates to an adhesive for a lithium ion secondary battery, a separator for a lithium ion secondary battery using the same, and a lithium ion secondary battery.

  In recent years, portable terminals such as notebook computers, mobile phones, and PDAs (Personal Digital Assistants) have been widely used. Lithium ion secondary batteries are frequently used as secondary batteries used as power sources for these portable terminals.

  In a lithium ion secondary battery, a separator is generally provided in order to prevent a short circuit between the positive electrode and the negative electrode. Moreover, this separator may be provided with a porous film on the separator substrate as necessary. As such a porous film, for example, a film containing non-conductive particles such as alumina and a binder for adhering the non-conductive particles is known.

  Furthermore, techniques such as Patent Documents 1 to 3 are also known.

JP 2013-012357 A International Publication No. 2007/088979 JP 2003-031199 A

  However, in the conventional lithium ion secondary battery including the separator, the adhesion between the separator and the electrode is low. In order to improve the adhesion between the separator and the electrode, it is conceivable to provide an adhesive layer between the separator and the electrode. When such an adhesive layer is provided, the low temperature output characteristics of the lithium ion secondary battery are considered. Was sometimes lower.

  Moreover, in a lithium ion secondary battery, gas may be generated during use. When such a gas is generated, the high-temperature cycle characteristics of the lithium ion secondary battery are lowered, and the life tends to be shortened.

  The present invention was devised in view of the above-described problems, and is an adhesive for a lithium ion secondary battery that can realize a lithium ion secondary battery that is excellent in adhesiveness and excellent in low-temperature output characteristics and high-temperature cycle characteristics. A separator for a lithium ion secondary battery that can realize a lithium ion secondary battery having excellent adhesion to an electrode and excellent in low temperature output characteristics and high temperature cycle characteristics; and lithium excellent in low temperature output characteristics and high temperature cycle characteristics An object is to provide an ion secondary battery.

As a result of intensive studies to solve the above-mentioned problems, the present inventor is an adhesive containing a particulate polymer, the particulate polymer having a core-shell structure, and the core portion and the shell portion with respect to the electrolytic solution. A lithium ion secondary resin having a predetermined degree of swelling and having a particulate polymer containing a predetermined proportion of amide monomer units is excellent in adhesiveness and excellent in low-temperature output characteristics and high-temperature cycle characteristics. The present inventors have found that a secondary battery can be realized and completed the present invention.
That is, the present invention is as follows.

[1] An adhesive for bonding members constituting a lithium ion secondary battery,
The adhesive comprises a particulate polymer;
The particulate polymer has a core-shell structure including a core part and a shell part covering an outer surface of the core part,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
The shell part is made of a polymer having a swelling degree with respect to the electrolytic solution of greater than 1 and 4 or less,
The adhesive for lithium ion secondary batteries whose ratio of the amide monomer unit in the said particulate polymer is 0.1 to 20 weight%.
[2] The glass transition temperature of the polymer of the core part is 0 ° C. or higher and 100 ° C. or lower,
The adhesive for a lithium ion secondary battery according to [1], wherein the polymer of the shell part has a glass transition temperature of 50 ° C or higher and 200 ° C or lower.
[3] The adhesive for a lithium ion secondary battery according to [1] or [2], which is an adhesive for bonding the porous film and the electrode.
[4] A separator substrate and an adhesive layer are provided,
The adhesive layer comprises a particulate polymer;
The particulate polymer has a core-shell structure including a core part and a shell part covering an outer surface of the core part,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
The shell part is made of a polymer having a swelling degree with respect to the electrolytic solution of greater than 1 and 4 or less,
The separator for lithium ion secondary batteries whose ratio of the amide monomer unit in the said particulate polymer is 0.1 to 20 weight%.
[5] A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolytic solution and a separator,
The lithium ion secondary battery whose said separator is a separator for lithium ion secondary batteries as described in [4].

The adhesive for lithium ion secondary batteries of this invention can implement | achieve the lithium ion secondary battery excellent in adhesiveness, and excellent in the low temperature output characteristic and the high temperature cycling characteristic.
The separator for a lithium ion secondary battery of the present invention can realize a lithium ion secondary battery excellent in adhesiveness to an electrode and excellent in low temperature output characteristics and high temperature cycle characteristics.
The lithium ion secondary battery of the present invention is excellent in low temperature output characteristics and high temperature cycle characteristics.

  Hereinafter, the present invention will be described in detail with reference to embodiments and examples. However, the present invention is not limited to the embodiments and examples described below, and can be implemented with any modifications without departing from the scope of the claims of the present invention and its equivalents.

  In the following description, (meth) acrylic acid includes acrylic acid and methacrylic acid. The (meth) acrylate includes acrylate and methacrylate. Furthermore, (meth) acrylonitrile includes acrylonitrile and methacrylonitrile. (Meth) acrylamide includes acrylamide and methacrylamide.

  Furthermore, that a substance is water-soluble means that an insoluble content is less than 0.5% by weight when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C. Further, that a certain substance is water-insoluble means that an insoluble content is 90% by weight or more when 0.5 g of the substance is dissolved in 100 g of water at 25 ° C.

  In addition, in a polymer produced by copolymerizing a plurality of types of monomers, the proportion of the structural unit formed by polymerizing a certain monomer in the polymer is usually that unless otherwise specified. This coincides with the ratio (preparation ratio) of the certain monomer in the total monomers used for polymerization of the polymer.

  The “monomer composition” is used not only as a composition containing two or more monomers but also as a term indicating one monomer.

[1. Adhesive for lithium ion secondary battery]
The lithium ion secondary battery adhesive of the present invention (hereinafter sometimes referred to as “adhesive” as appropriate) is an adhesive for adhering members constituting a lithium ion secondary battery, and is in the form of particles. Including polymers. This particulate polymer has a core-shell structure including a core part and a shell part. In the particulate polymer, each of the core part and the shell part is made of a polymer having a predetermined degree of swelling with respect to the electrolytic solution. Further, the particulate polymer contains amide monomer units at a predetermined ratio.

According to the adhesive containing such a particulate polymer, the following advantages can be obtained.
i. The adhesive layer produced using the adhesive of the present invention has, for example, an adhesive property with a member constituting a battery such as a separator for a lithium ion secondary battery (hereinafter sometimes referred to as “separator” as appropriate) and an electrode. Excellent.
ii. In the lithium ion secondary battery provided with the separator, the separator and the electrode are bonded using the adhesive of the present invention, whereby the low temperature output characteristics of the lithium ion secondary battery can be improved.
iii. In the lithium ion secondary battery provided with the separator, the separator and the electrode are bonded using the adhesive of the present invention, whereby the high temperature cycle characteristics of the lithium ion secondary battery can be improved. Thereby, the lifetime of the lithium ion secondary battery can be extended.
iv. The separator may be stored and transported in a wound state, but the separator having the adhesive layer formed by using the adhesive of the present invention on the outermost surface hardly causes blocking even when wound. Excellent handling.
The reason why such an excellent effect is obtained is not necessarily clear, but according to the study of the present inventor, it is presumed as follows. However, the present invention is not limited for the reason presumed below.

i. Adhesiveness:
The polymer constituting the shell part of the particulate polymer swells in the electrolytic solution. At this time, for example, the functional group of the polymer in the swollen shell part is activated to cause a chemical or electrical interaction with the functional group on the surface of a member (for example, separator, battery, etc.) constituting the battery. Due to these factors, the shell part can be firmly bonded to the members constituting the battery. Therefore, it is presumed that the member constituting the battery can be strongly bonded by the adhesive containing the particulate polymer. For such reasons, when the adhesive layer containing the particulate polymer according to the present invention is provided between the separator and the electrode, it is possible to strongly bond the separator and the electrode. Inferred.

  By the way, some particulate polymers can exhibit high adhesive force even in a state where they do not swell in the electrolytic solution. However, a polymer that exhibits a high adhesive force even in a state where it does not swell in the electrolytic solution tends to increase the resistance of the battery, and thus it is difficult to sufficiently improve the low-temperature output characteristics and the high-temperature cycle characteristics. On the other hand, the adhesive of the present invention is not only excellent in adhesiveness but also one that is superior to the prior art in that it can improve the low-temperature output characteristics and high-temperature cycle characteristics of lithium ion secondary batteries.

ii. Low temperature output characteristics:
In a lithium ion secondary battery, a separator is generally provided between a positive electrode and a negative electrode. Here, conventionally, when a lithium ion secondary battery is charged and discharged, the electrode active material (particularly, the negative electrode active material) expands and contracts, and thus a gap may be formed between the separator and the electrode. When such a phenomenon occurs, the distance between the positive electrode and the negative electrode increases, the internal resistance of the battery increases, and the reaction field between the lithium ions and the electrode active material becomes non-uniform. There was a decline.

  On the other hand, in the adhesive layer formed using the adhesive according to the present invention, as described above, high adhesion to the separator and the electrode is obtained in the state where the shell portion of the particulate polymer is swollen in the electrolytic solution. To express. For this reason, even if it charges / discharges, it is hard to produce a space | gap between a separator and an electrode. Therefore, in the lithium ion secondary battery, the distance between the positive electrode and the negative electrode is difficult to increase, so that the internal resistance of the battery can be reduced, and the reaction field between the lithium ions and the electrode active material is unlikely to be uneven.

  Moreover, since the shell part covers the outer surface of the core part, deformation | transformation of an internal core part can be normally suppressed by the shell part with a small swelling degree with respect to electrolyte solution. Therefore, since the increase in volume due to swelling of the particulate polymer in the electrolyte can be suppressed, the distance between the positive electrode plate and the negative electrode plate can be further reduced. Therefore, it is possible to reduce the internal resistance of the battery.

  Furthermore, the polymer in the core part of the particulate polymer swells greatly in the electrolytic solution. In a state swollen greatly in the electrolytic solution, the gap between the molecules of the polymer becomes large, and ions easily pass between the molecules. Therefore, since ions easily pass through the core portion in the electrolytic solution, the particulate polymer can exhibit high ion diffusibility. Therefore, it is possible to suppress an increase in resistance due to the adhesive layer.

  In addition, since lithium ions can easily pass through the adhesive layer, lithium deposition in the electrolyte can be prevented. Therefore, an increase in resistance due to precipitated lithium can be suppressed.

  By combining these factors, it is presumed that the low-temperature output characteristics of the lithium ion secondary battery including the adhesive layer formed using the adhesive according to the present invention can be improved.

iii. High temperature cycle characteristics:
In a lithium ion secondary battery, when charging and discharging are repeated, gas may be generated, for example, due to decomposition of the electrolytic solution and the additive. It is considered that this gas is generated because halide ions are contained in the secondary battery, so that the electrolytic solution and SEI (interlayer solid electrolyte interface) are decomposed with charge and discharge. When gas is generated in this way, a gap is formed between the separator and the electrode. Therefore, when charging / discharging of the lithium ion secondary battery is repeated, the distance between the positive electrode and the negative electrode gradually increases and the battery capacity decreases.

On the other hand, the porous membrane containing the particulate polymer can trap halide ions in the electrolytic solution when the particulate polymer contains an amide monomer unit. As a result, the generation of gas due to halide ions is suppressed, so that the decrease in battery capacity associated with charge / discharge is suppressed.
Furthermore, as described above, according to the adhesive layer formed using the adhesive according to the present invention, it is possible to suppress the precipitation of lithium in the electrolytic solution, and thus it is difficult for resistance to increase due to repeated charge and discharge.
Therefore, a lithium ion secondary battery provided with an adhesive layer formed using the adhesive according to the present invention is presumed to be excellent in high-temperature cycle characteristics.

iv. Blocking resistance:
Usually, the polymer of the shell portion does not have adhesiveness in a state where it is not swollen in the electrolytic solution, but exhibits adhesiveness only when it is swollen in the electrolytic solution. Therefore, the particulate polymer does not exhibit adhesiveness in a state where it is not swollen in the electrolytic solution. For this reason, since the adhesive layer containing the particulate polymer does not exhibit adhesiveness in a state where it is not swollen in the electrolytic solution, it is presumed that the separator provided with the adhesive layer is unlikely to cause blocking even when stacked.

[1.1. (Particulate polymer)
The particulate polymer has a core-shell structure including a core part and a shell part. Here, a core part is a part which exists inside a shell part in a particulate polymer. The shell part is a part that covers the outer surface of the core part, and is usually the outermost part of the particulate polymer. Therefore, the shell part is usually exposed on the surface of the particulate polymer.

  The particulate polymer contains an amide monomer unit. An amide monomer unit is a structural unit having a structure formed by polymerizing an amide monomer. The amide monomer is a monomer having an amide group and includes not only an amide compound but also an imide compound. Since the particulate polymer contains an amide monomer unit, gas generation can be effectively prevented in the lithium ion secondary battery, so that the high-temperature cycle characteristics of the lithium ion secondary battery can be improved.

  Examples of the amide monomer include a carboxylic acid amide monomer, a sulfonic acid amide monomer, and a phosphoric acid amide monomer.

  The carboxylic acid amide monomer is a monomer having an amide group bonded to a carboxylic acid group. Examples of the carboxylic acid amide monomer include (meth) acrylamide, α-chloroacrylamide, N, N′-methylenebis (meth) acrylamide, N, N′-ethylenebis (meth) acrylamide, and N-hydroxymethyl (meta). ) Acrylamide, N-2-hydroxyethyl (meth) acrylamide, N-2-hydroxypropyl (meth) acrylamide, N-3-hydroxypropyl (meth) acrylamide, crotonic acid amide, maleic acid diamide, fumaric acid diamide, diacetone Unsaturated carboxylic acid amide compounds such as acrylamide; N-dimethylaminomethyl (meth) acrylamide, N-2-aminoethyl (meth) acrylamide, N-2-methylaminoethyl (meth) acrylamide, N-2-ethylamino Ethyl (meta Acrylamide, N-2-dimethylaminoethyl (meth) acrylamide, N-2-diethylaminoethyl (meth) acrylamide, N-3-aminopropyl (meth) acrylamide, N-3-methylaminopropyl (meth) acrylamide, N- And N-aminoalkyl derivatives of unsaturated carboxylic acid amides such as 3-dimethylaminopropyl (meth) acrylamide.

  The sulfonic acid amide monomer is a monomer having an amide group bonded to a sulfonic acid group. Examples of the sulfonic acid amide monomer include 2-acrylamido-2-methylpropanesulfonic acid and Nt-butylacrylamidesulfonic acid.

  The phosphoric acid amide monomer is a monomer having an amide group bonded to a phosphate group. Examples of the phosphoric acid amide monomer include acrylamide phosphonic acid and acrylamide phosphonic acid derivatives.

  Among these amide monomers, carboxylic acid amide monomers are preferable, unsaturated carboxylic acid amide compounds are more preferable, and (meth) acrylamide and N-hydroxymethyl (meth) acrylamide are particularly preferable. By using these amide monomers, generation of gas can be more effectively suppressed in the lithium ion secondary battery.

  An amide monomer and an amide monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the amide monomer unit in the particulate polymer is usually 0.1% by weight or more, preferably 0.2% by weight or more, more preferably 0.3% by weight or more, and usually 20% by weight or less, preferably Is 15% by weight or less, more preferably 10% by weight or less. By setting the ratio of the amide monomer unit in the particulate polymer to be equal to or higher than the lower limit of the above range, the generation of gas in the lithium ion secondary battery can be effectively suppressed, thereby improving the high temperature cycle characteristics. it can. Moreover, since the mechanical strength of a contact bonding layer can be raised by making it into an upper limit or less, durability of a contact bonding layer can be improved. Therefore, even if charging / discharging is repeated, the adhesive force of the adhesive layer can hardly be reduced, and thus the high-temperature cycle characteristics can be improved.

[1.1.1. (Core part)
A core part consists of a polymer which has predetermined | prescribed swelling degree with respect to electrolyte solution. Specifically, the swelling degree of the polymer of the core part with respect to the electrolytic solution is usually 5 times or more, preferably 6 times or more, more preferably 7 times or more, and usually 30 times or less, preferably 25 times or less, more Preferably it is 20 times or less. By keeping the degree of swelling of the polymer in the core part within the above range, the ion diffusibility of the adhesive layer can be increased, so that the low-temperature output characteristics of the lithium ion secondary battery can be improved. Moreover, the adhesiveness of a contact bonding layer can be improved by making the swelling degree of the polymer of a core part more than the lower limit of the said range. Furthermore, since the high temperature cycle characteristic of a lithium ion secondary battery can be improved by setting it as an upper limit or less, a lifetime can be lengthened.

As an electrolytic solution used for measuring the swelling degree of the polymer in the core part, a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30/1) .5; SP value 12.7 (cal / cm ³ ) ^1/2 ), a solution in which LiPF ₆ is dissolved as a supporting electrolyte at a concentration of 1 mol / liter with respect to the solvent is used.

Specifically, the swelling degree of the polymer in the core part can be measured as follows.
First, the polymer of the core part of a particulate polymer is prepared. For example, the polymer obtained by performing the same process as that performed in order to manufacture a core part in the manufacturing method of a particulate polymer is prepared.
Then, a film is produced with the prepared polymer. For example, if the polymer is solid, the polymer is dried at 25 ° C. for 48 hours, and then the polymer is formed into a film to produce a film having a thickness of 0.5 mm. For example, when the polymer is a solution or dispersion such as latex, the solution or dispersion is placed in a petri dish made of polytetrafluoroethylene and dried under the conditions of 25 ° C. and 48 hours to obtain a thickness of 0. Create a 5 mm film.
The film thus prepared is cut into 1 cm squares to obtain test pieces. The weight of this test piece is measured and set to W0.
Moreover, this test piece is immersed in electrolyte solution at 60 degreeC for 72 hours, and the test piece is taken out from electrolyte solution. The electrolyte solution on the surface of the removed test piece is wiped off, and the weight W1 of the test piece after the immersion test is measured.
Then, using these weights W0 and W1, the degree of swelling S (times) is calculated as S = W1 / W0.

  As a method for adjusting the degree of swelling of the polymer in the core part, for example, in consideration of the SP value of the electrolytic solution, the kind and amount of the monomer for producing the polymer in the core part are appropriately selected. Can be mentioned. Generally, when the SP value of a polymer is close to the SP value of an electrolytic solution, the polymer tends to swell in the electrolytic solution. On the other hand, when the SP value of the polymer is far from the SP value of the electrolytic solution, the polymer tends to hardly swell in the electrolytic solution.

Here, the SP value means a solubility parameter.
The SP value can be calculated using the method introduced in Hansen Solubility Parameters A User's Handbook, 2ndEd (CRCPless).
The SP value of an organic compound can be estimated from the molecular structure of the organic compound. Specifically, it can be calculated using simulation software (for example, “HSPiP” (http://www.hansen-solubility.com)) that can calculate the SP value from the SMILE equation. The simulation software also includes Hansen SOLUBILITY PARAMETERS A User's Handbook Second Edition, Charles M. Based on the theory described in Hansen.

  As the monomer used for producing the polymer of the core part, those having a swelling degree of the polymer in the above range can be used. Examples of such monomers include vinyl chloride monomers such as vinyl chloride and vinylidene chloride; vinyl acetate monomers such as vinyl acetate; styrene, α-methylstyrene, styrenesulfonic acid, butoxystyrene, Aromatic vinyl monomers such as vinylnaphthalene; Vinylamine monomers such as vinylamine; Vinylamide monomers such as N-vinylformamide and N-vinylacetamide; (Meth) acrylic acid such as acrylic acid and methacrylic acid (Meth) acrylic acid derivatives such as 2-hydroxyethyl methacrylate; (meth) acrylic acid ester monomers such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl acrylate; (Meth) acrylamide monomers such as acrylamide and methacrylamide; (Meth) acrylonitrile monomers such as nitrile and methacrylonitrile; fluorine-containing acrylate monomers such as 2- (perfluorohexyl) ethyl methacrylate and 2- (perfluorobutyl) ethyl acrylate; maleic acid, fumaric acid, anhydrous Unsaturated dicarboxylic acid monomers such as maleic acid; maleimide; maleimide derivatives such as phenylmaleimide; diene monomers such as 1,3-butadiene and isoprene; Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Among the above monomers, it is preferable to use a (meth) acrylic acid ester monomer or a (meth) acrylonitrile monomer. That is, the polymer of the core part preferably contains a (meth) acrylic acid ester monomer unit or a (meth) acrylonitrile monomer unit. Here, the polymer of the core part may contain only the (meth) acrylic acid ester monomer unit, may contain only the (meth) acrylonitrile monomer unit, and (meth) acrylic acid ester A monomer unit and a (meth) acrylonitrile monomer unit may be included in combination. The (meth) acrylic acid ester monomer unit means a structural unit having a structure formed by polymerizing a (meth) acrylic acid ester monomer. The (meth) acrylonitrile monomer unit means a structural unit having a structure formed by polymerizing (meth) acrylonitrile. This facilitates control of the degree of swelling of the polymer. Further, the ion diffusibility of the adhesive layer can be further enhanced.

  The total proportion of (meth) acrylic acid ester monomer units and (meth) acrylonitrile monomer units in the polymer of the core part is preferably 50% by weight or more, more preferably 55% by weight or more, and particularly preferably 60%. % By weight or more, preferably 99% by weight or less, more preferably 95% by weight or less, and particularly preferably 90% by weight or less. By keeping the ratio of the (meth) acrylic acid ester monomer unit and the (meth) acrylonitrile monomer unit within the above range, the degree of swelling can be easily controlled within the above range. In addition, the ion diffusibility of the adhesive layer can be increased. Furthermore, the low temperature output characteristics of the lithium ion secondary battery can be further improved.

  The polymer of the core part preferably contains a crosslinkable monomer unit. A crosslinkable monomer unit is a structural unit having a structure formed by polymerizing a crosslinkable monomer. The crosslinkable monomer is a monomer that can form a crosslinked structure during or after polymerization by heating or irradiation with energy rays. By including a crosslinkable monomer unit, the degree of swelling of the polymer can be easily within the above range.

  As a crosslinkable monomer, the polyfunctional monomer which has a 2 or more polymerization reactive group in the said monomer is mentioned, for example. Examples of such polyfunctional monomers include divinyl compounds such as divinylbenzene; di (meta) such as ethylene dimethacrylate, diethylene glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, and 1,3-butylene glycol diacrylate. ) Acrylic acid ester compounds; Tri (meth) acrylic acid ester compounds such as trimethylolpropane trimethacrylate and trimethylolpropane triacrylate; Ethylenically unsaturated monomers containing epoxy groups such as allyl glycidyl ether and glycidyl methacrylate; Is mentioned. Among these, from the viewpoint of easily controlling the swelling degree of the polymer of the core part, a dimethacrylic acid ester compound and an ethylenically unsaturated monomer containing an epoxy group are preferable, and a dimethacrylic acid ester compound is more preferable. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  Generally, when the proportion of the crosslinkable monomer unit in the polymer increases, the degree of swelling of the polymer with respect to the electrolyte solution tends to decrease. Accordingly, the proportion of the crosslinkable monomer unit is preferably determined in consideration of the type and amount of the monomer used. The specific ratio of the crosslinkable monomer unit in the polymer of the core part is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, Preferably it is 5 weight% or less, More preferably, it is 4 weight% or less, Most preferably, it is 3 weight% or less. By setting the ratio of the crosslinkable monomer unit to the lower limit value or more of the above range, the adhesiveness of the adhesive layer can be enhanced. Moreover, since the high temperature cycle characteristic of a secondary battery can be improved by making it below an upper limit, a lifetime can be lengthened.

  Furthermore, from the viewpoint of introducing the amide monomer unit into the particulate polymer, the polymer in the core part preferably includes the amide monomer unit described above. Since the polymer in the core part swells greatly in the electrolytic solution, the field where the polymer molecules in the core part come into contact with the electrolytic solution tends to increase. Therefore, the field where the polymer molecules of the core part can contact with the halide ions in the electrolytic solution tends to increase. Therefore, when the polymer of the core part contains an amide monomer unit, the amide monomer unit can effectively capture halide ions, and efficiently suppress the generation of gas in the lithium ion secondary battery. it can.

  The ratio of the amide monomer unit in the polymer of the core part can be set so that the ratio of the amide monomer unit in the whole particulate polymer falls within the above-described range. The specific ratio is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, particularly preferably 0.2% by weight or more, preferably 20% by weight or less, more preferably 10% by weight. Hereinafter, it is particularly preferably 5% by weight or less. Since the generation of gas in the lithium ion secondary battery can be suppressed by setting the ratio of the amide monomer unit in the polymer of the core part to be equal to or higher than the lower limit of the above range, the high temperature cycle characteristics can be enhanced. Moreover, a high temperature cycling characteristic can be improved by making it below an upper limit.

  The glass transition temperature of the polymer of the core part is preferably 0 ° C. or higher, more preferably 10 ° C. or higher, particularly preferably 20 ° C. or higher, preferably 100 ° C. or lower, more preferably 90 ° C. or lower, particularly preferably 80 ° C. It is below ℃. By setting the glass transition temperature of the polymer of the core part to be equal to or higher than the lower limit of the above range, the adhesiveness of the adhesive layer can be further improved. Furthermore, the high temperature cycling characteristic of a lithium ion secondary battery can further be improved by setting it as below an upper limit. Here, the glass transition temperature can be measured according to JIS K7121.

  The diameter of the core part is preferably 50% or more, more preferably 60% or more, particularly preferably 70% or more, preferably 99% or less, with respect to 100% of the volume average particle diameter of the particulate polymer. More preferably, it is 98.5% or less, Most preferably, it is 98% or less. By making the diameter of the core part equal to or greater than the lower limit of the above range, the ionic conductivity can be increased. Moreover, adhesiveness with an electrode can be improved by making it into an upper limit or less.

  Here, the diameter of the core part is the volume average particle diameter of the particulate polymer before forming the shell part obtained in the production process of the particulate polymer (that is, the particulate polymer constituting the core part). Can be measured as The volume average particle diameter represents a particle diameter at which the cumulative volume calculated from the small diameter side is 50% in the particle diameter distribution measured by the laser diffraction method.

[1.1.2. Shell part)
The shell part is made of a polymer having a predetermined swelling degree smaller than that of the core part with respect to the electrolytic solution. Specifically, the swelling degree of the polymer of the shell part with respect to the electrolytic solution is usually larger than 1 time, preferably 1.1 times or more, more preferably 1.2 times or more, and usually 4 times or less, Preferably it is 3.5 times or less, More preferably, it is 3 times or less. By keeping the degree of swelling of the polymer in the shell part within the above range, the adhesiveness of the adhesive layer can be enhanced. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be made favorable by making swelling degree of the polymer of a shell part more than the lower limit of the said range. Furthermore, the adhesiveness of a contact bonding layer can be improved by setting it as an upper limit or less.

  Here, as the electrolytic solution used for measuring the swelling degree of the polymer in the shell portion, the same electrolytic solution used for measuring the swelling degree of the polymer in the core portion is used.

Specifically, the swelling degree of the polymer in the shell part can be measured as follows.
First, the polymer of the shell part of a particulate polymer is prepared. For example, in the method for producing a particulate polymer, a monomer composition used for the production of the shell part is used instead of the monomer composition used for the production of the core part. A coalescence is produced.
Thereafter, a film is produced from the polymer in the shell portion by the same method as the method for measuring the degree of swelling of the polymer in the core portion, a test piece is obtained from the film, and the degree of swelling S is measured.

  As a method for adjusting the degree of swelling of the polymer of the shell part, for example, considering the SP value of the electrolytic solution, the kind and amount of the monomer for producing the polymer of the shell part are appropriately selected. Can be mentioned.

  As a monomer used for producing the polymer of the shell portion, a monomer having a swelling degree of the polymer within the above range can be used. As such a monomer, the same example as the monomer illustrated as a monomer which can be used in order to manufacture the polymer of a core part is mentioned, for example. Moreover, such a monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Among these monomers, aromatic vinyl monomers are preferable. That is, the polymer of the shell part preferably contains an aromatic vinyl monomer unit. Here, the aromatic vinyl monomer unit refers to a structural unit having a structure formed by polymerizing an aromatic vinyl monomer. Among aromatic vinyl monomers, styrene derivatives such as styrene and styrene sulfonic acid are more preferable. When an aromatic vinyl monomer is used, it is easy to control the degree of swelling of the polymer. Moreover, the adhesiveness of the adhesive layer can be further enhanced.

  The ratio of the aromatic vinyl monomer unit in the polymer of the shell part is preferably 40% by weight or more, more preferably 50% by weight or more, further preferably 60% by weight or more, and particularly preferably 80% by weight or more. Preferably it is 100 weight% or less, More preferably, it is 99.5 weight% or less, More preferably, it is 99 weight% or less, Most preferably, it is 95 weight% or less. By keeping the ratio of the aromatic vinyl monomer unit within the above range, the degree of swelling can be easily controlled within the above range. In addition, the adhesive strength of the adhesive layer can be further increased.

  Further, the polymer of the shell part may contain a crosslinkable monomer unit. As a crosslinkable monomer, the same example as what was illustrated as a crosslinkable monomer which can be used for the polymer of a core part is mentioned, for example. Moreover, a crosslinking | crosslinked monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The ratio of the crosslinkable monomer unit in the polymer of the shell part is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably 5%. % By weight or less, more preferably 4% by weight or less, particularly preferably 3% by weight or less. By setting the ratio of the crosslinkable monomer unit to the lower limit value or more of the above range, the adhesiveness of the adhesive layer can be enhanced. Moreover, since the high temperature cycle characteristic of a secondary battery can be improved by making it below an upper limit, a lifetime can be lengthened.

  Furthermore, from the viewpoint of introducing the amide monomer unit into the particulate polymer, the polymer in the shell part preferably includes the amide monomer unit described above. Since the shell portion is usually on the outermost surface of the particulate polymer, the frequency of contact of halide ions in the electrolyte with the polymer molecules in the shell portion increases. Therefore, when the polymer of the shell portion contains an amide monomer unit, the amide monomer unit can effectively capture halide ions, and efficiently suppress the generation of gas in the lithium ion secondary battery. it can.

  The ratio of the amide monomer unit in the polymer of the shell part can be set so that the ratio of the amide monomer unit in the whole particulate polymer is within the above-described range. The specific ratio is preferably 0.05% by weight or more, more preferably 0.1% by weight or more, particularly preferably 0.2% by weight or more, preferably 20% by weight or less, more preferably 10% by weight. Hereinafter, it is particularly preferably 5% by weight or less. Since the generation of gas in the lithium ion secondary battery can be suppressed by setting the ratio of the amide monomer unit in the polymer of the shell part to be equal to or higher than the lower limit of the above range, the high temperature cycle characteristics can be improved. Moreover, since the swelling degree of the polymer of a shell part can be stably made small by setting it as an upper limit or less, the adhesive force of an adhesive agent can be made high.

  In particular, in the particulate polymer, it is preferable that both the core polymer and the shell polymer contain amide monomer units. As a result, both the action of the polymer in the core part containing the amide monomer unit and the action of the polymer in the shell part containing the amide monomer unit can be expressed. The performance of the secondary battery can be effectively improved.

  The glass transition temperature of the polymer of the shell part is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, particularly preferably 70 ° C. or higher, preferably 200 ° C. or lower, more preferably 180 ° C. or lower, particularly preferably 150 ° C. It is below ℃. By making the glass transition temperature of the polymer of the shell part equal to or higher than the lower limit of the above range, the separator provided with the adhesive layer is less likely to be blocked, and further improves the low temperature output characteristics of the lithium ion secondary battery. be able to. Moreover, the adhesiveness of a contact bonding layer can further be improved by setting it as below an upper limit.

  The shell part may cover the entire outer surface of the core part, or may partially cover the outer surface of the core part. Therefore, the shell portion covers the outer surface of the core portion, but may not cover the entire outer surface of the core portion. Even if it appears that the outer surface of the core part is completely covered by the shell part, the shell part is outside the core part as long as a hole that communicates the inside and outside of the shell part is formed. Judged to partially cover the surface. Therefore, for example, the shell part having pores communicating from the outer surface of the shell part (that is, the peripheral surface of the particulate polymer) to the outer surface of the core part partially covers the outer surface of the core part.

  When the shell part partially covers the outer surface of the core part, ions are more likely to pass through the core part. Therefore, it is preferable because the ion diffusibility of the particulate polymer can be further increased, and an increase in resistance due to the adhesive layer can be particularly suppressed.

  The average ratio of the outer surface of the core part covered by the shell part is preferably 10% or more, more preferably 30% or more, still more preferably 40% or more, particularly preferably 60% or more, preferably 95% or less, More preferably, it is 90% or less, More preferably, it is 85% or less. By keeping the average ratio of the outer surface of the core portion covered by the shell portion within the above range, the balance between ion diffusibility and adhesiveness of the adhesive layer can be improved.

The average ratio at which the outer surface of the core part is covered with the shell part can be measured from the observation result of the cross-sectional structure of the particulate polymer. Specifically, it can be measured by the method described below.
First, the particulate polymer is sufficiently dispersed in a room temperature curable epoxy resin and then embedded to produce a block piece containing the particulate polymer. Next, it cuts out in the shape of a thin piece of thickness 80nm-200nm with the microtome provided with the diamond blade, and produces the sample for a measurement. Thereafter, if necessary, the measurement sample is dyed using, for example, ruthenium tetroxide or osmium tetroxide.
Next, this measurement sample is set in a transmission electron microscope (TEM), and the cross-sectional structure of the particulate polymer is photographed. The magnification of the electron microscope is preferably such that the cross section of one particulate polymer enters the field of view, specifically about 10,000 times.
In the photographed cross-sectional structure of the particulate polymer, the circumference length D1 corresponding to the outer surface of the core portion and the length D2 of the portion where the outer surface of the core portion and the shell portion abut are measured. And the ratio Rc by which the outer surface of the core part of the particulate polymer is covered with a shell part is calculated by the following formula (1) using the measured length D1 and length D2.
Covering ratio Rc (%) = D2 / D1 × 100 (1)
The coating ratio Rc is measured for 20 or more particulate polymers, and the average value is calculated to obtain the average ratio at which the outer surface of the core part is covered by the shell part.
The covering ratio Rc can be calculated manually from the cross-sectional structure, but can also be calculated using commercially available image analysis software. As commercially available image analysis software, for example, “AnalySIS Pro” (manufactured by Olympus Corporation) can be used.

  The shell part preferably has an average thickness that falls within a predetermined range with respect to the volume average particle diameter of the particulate polymer. Specifically, the average thickness of the shell part with respect to the volume average particle diameter of the particulate polymer is preferably 1% or more, more preferably 1.5% or more, particularly preferably 2% or more, preferably 30%. Below, more preferably 25% or less, particularly preferably 20% or less. By setting the average thickness of the shell portion to be equal to or higher than the lower limit of the above range, the low temperature output characteristics of the lithium ion secondary battery can be further enhanced. Moreover, the adhesive force of a contact bonding layer can further be raised by setting it as below an upper limit.

  The average thickness of the shell part is determined by observing the cross-sectional structure of the particulate polymer with a transmission electron microscope (TEM). Specifically, the maximum thickness of the shell part in the cross-sectional structure of the particulate polymer is measured, and the average value of the maximum thickness of the shell part of 20 or more arbitrarily selected particulate polymers is determined as the average thickness of the shell part. And However, the shell part is composed of polymer particles, and the particles constituting the shell part do not overlap each other in the radial direction of the particulate polymer, and the polymer particles are a single layer and the shell part. In this case, the number average particle diameter of the particles constituting the shell portion is defined as the average thickness of the shell portion.

  When the shell part partially covers the outer surface of the core part, the shell part is preferably composed of polymer particles. When the shell part is constituted by polymer particles, a plurality of particles constituting the shell part may overlap in the radial direction of the particulate polymer. However, in the radial direction of the particulate polymer, it is preferable that the particles constituting the shell portion do not overlap each other and the particles of the polymer constitute the shell portion as a single layer.

  The number average particle diameter of the particles constituting the shell part is preferably 10 nm or more, more preferably 20 nm or more, particularly preferably 30 nm, preferably 200 nm or less, more preferably 150 nm or less, particularly preferably 100 nm or less. By keeping the number average particle diameter in the above range, the balance between ion diffusibility and adhesiveness of the adhesive layer can be improved.

  The number average particle diameter of the particles constituting the shell portion is determined by observing the cross-sectional structure of the particulate polymer with a transmission electron microscope (TEM). Specifically, the longest diameter of the particles constituting the shell part in the cross-sectional structure of the particulate polymer is measured, and the average of the longest diameters of the particles constituting the shell part of 20 or more arbitrarily selected particulate polymers The value is the number average particle diameter of the particles constituting the shell portion.

[1.1.3. (Optional component)
The particulate polymer may include arbitrary constituent elements other than the above-described core part and shell part as long as the effects of the present invention are not significantly impaired.
For example, you may have the part formed with the polymer different from a core part inside a core part. As a specific example, the seed particles used when the particulate polymer is produced by the seed polymerization method may remain inside the core portion.
However, from the viewpoint of remarkably exhibiting the effects of the present invention, the particulate polymer preferably includes only a core part and a shell part.

[1.1.4. Size of particulate polymer]
The volume average particle diameter of the particulate polymer is preferably 0.01 μm or more, more preferably 0.02 μm or more, particularly preferably 0.05 μm or more, preferably 10 μm or less, more preferably 5 μm or less, particularly preferably. 1 μm or less. By making the volume average particle diameter of the particulate polymer not less than the lower limit of the above range, the dispersibility of the particulate polymer in the adhesive and the adhesive layer can be improved. Moreover, the adhesive force of a contact bonding layer can be raised by making it into an upper limit or less.

[1.1.5. Amount of particulate polymer]
The amount of the particulate polymer in the adhesive is preferably set so that the proportion of the particulate polymer in the adhesive layer is within a predetermined range. Specifically, the proportion of the particulate polymer in the adhesive layer is preferably 40% by weight or more, more preferably 50% by weight or more, particularly preferably 60% by weight or more, preferably 99.9% by weight or less, More preferably, it is 95 weight% or less, Most preferably, it is 90 weight% or less. By setting the amount of the particulate polymer in the above range, the adhesion between the porous membrane and the electrode can be enhanced, and the ion diffusibility can be enhanced.

[1.1.6. Method for producing particulate polymer]
For example, the particulate polymer may be polymerized in stages by using a monomer of the polymer of the core part and a monomer of the polymer of the shell part and changing the ratio of these monomers over time. Can be manufactured. Specifically, it can be produced by a continuous multi-stage emulsion polymerization method and a multi-stage suspension polymerization method in which the polymer of the previous stage is sequentially coated with the polymer of the subsequent stage.

An example in the case of obtaining a particulate polymer having a core-shell structure by a multistage emulsion polymerization method is shown.
In the polymerization, according to a conventional method, as an emulsifier, for example, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium dodecylsulfate, nonionic surfactants such as polyoxyethylene nonylphenyl ether and sorbitan monolaurate, or Cationic surfactants such as octadecylamine acetate can be used. Examples of the polymerization initiator include peroxides such as t-butylperoxy-2-ethylhexanoate, potassium persulfate, cumene peroxide, 2,2′-azobis (2-methyl-N- (2 An azo compound such as (hydroxyethyl) -propionamide) or 2,2′-azobis (2-amidinopropane) hydrochloride can be used.

  As a polymerization procedure, first, a particulate polymer constituting the core part is obtained by emulsion polymerization in a batch in a state where the monomer and the emulsifier forming the core part are mixed. Furthermore, a particulate polymer having a core-shell structure can be obtained by polymerizing a monomer that forms a shell portion in the presence of the particulate polymer constituting the core portion.

  At this time, from the viewpoint of completely covering the core portion with the shell portion, it is preferable to supply the polymer monomer of the shell portion all at once. By supplying the monomer of the polymer of the shell part all at once to the polymerization system, it is usually possible to form a layered shell part that covers the entire core part.

  From the viewpoint of partially covering the outer surface of the core portion with the shell portion, it is preferable that the polymer monomer in the shell portion is divided into a plurality of times or continuously supplied to the polymerization system. By dividing the polymer monomer of the shell part into a polymerization system or continuously supplying it, the polymer constituting the shell part is usually formed into particles, and these particles are bonded to the core part. By doing so, the shell part which covers a core part partially can be formed.

  In the case where the monomer of the polymer of the shell part is divided and supplied in a plurality of times, the particle diameter of the particles constituting the shell part can be controlled according to the ratio of dividing the monomer. In addition, when the polymer monomer of the shell part is continuously supplied, the particle size of the particles constituting the shell part can be controlled by adjusting the monomer supply amount per unit time. Is possible.

  The volume average particle diameter of the particulate polymer constituting the core part, the volume average particle diameter of the particulate polymer after forming the shell part, and the number average particle diameter of the particles constituting the shell part are: For example, the desired range can be achieved by adjusting the amount of emulsifier, the amount of monomer, and the like.

[1.2. Adhesive layer binder)
The adhesive of the present invention preferably further contains an adhesive layer binder in addition to the particulate polymer. By using the adhesive layer binder, the particulate polymers can be bonded to each other in both the swollen state and the unswelled state in the electrolytic solution. For this reason, it is possible to easily form the adhesive layer, and it is possible to increase the mechanical strength of the adhesive layer. Furthermore, the adhesiveness of the adhesive layer can be further improved by the adhesive layer binder.

As the binder for the adhesive layer, a water-insoluble polymer can be usually used. Among them, it is preferable to use a thermoplastic elastomer as the binder for the adhesive layer, and it is particularly preferable to use a polymer containing an amide monomer unit.
By using a polymer with an amide monomer unit as a binder for the adhesive layer, the amide monomer unit can capture halide ions in the electrolyte, effectively suppressing the generation of gas associated with charge and discharge. it can.

  Examples of the amide monomer include the same examples as those exemplified in the section of the particulate polymer. Moreover, an amide monomer and an amide monomer unit may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The ratio of the amide monomer unit in the polymer as the binder for the adhesive layer is preferably 0.1% by weight or more, more preferably 0.2% by weight or more, particularly preferably 0.5% by weight or more, preferably Is 20% by weight or less, more preferably 15% by weight or less, and particularly preferably 10% by weight or less. By setting the ratio of the amide monomer unit to be equal to or higher than the lower limit of the above range, gas generation in the lithium ion secondary battery can be effectively suppressed. Moreover, the high temperature cycling characteristic of a lithium ion secondary battery can be effectively improved by setting it as below an upper limit.

  The polymer as the binder for the adhesive layer may contain an arbitrary structural unit in addition to the amide monomer unit. For example, a polymer as a binder for an adhesive layer has a structure formed by polymerizing styrene and a structural unit (styrene unit) having a structure formed by polymerizing styrene in combination with an amide monomer unit. A structural unit (butadiene unit) may be included. For example, the polymer as the binder for the adhesive layer may contain a structural unit (acrylonitrile unit) having a structure formed by polymerizing acrylonitrile and a butadiene unit in combination with an amide monomer unit. Further, for example, the polymer as the binder for the adhesive layer may contain a (meth) acrylate monomer unit in combination with an amide monomer unit. Moreover, these arbitrary structural units may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Among them, the polymer as the binder for the adhesive layer has a high ion conductivity, can improve the rate characteristics of the secondary battery, and is electrochemically stable and can improve the high temperature cycle characteristics of the battery. It preferably contains a (meth) acrylic acid ester monomer unit.

  Examples of the (meth) acrylate monomer corresponding to the (meth) acrylate monomer unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, and pentyl. Acrylic acid alkyl esters such as acrylate, hexyl acrylate, heptyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, nonyl acrylate, decyl acrylate, lauryl acrylate, n-tetradecyl acrylate, stearyl acrylate; and methyl methacrylate, ethyl methacrylate, n-propyl Methacrylate, isopropyl methacrylate, n-butyl methacrylate, t-butyl methacrylate, pentyl methacrylate Rate, 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. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Among these, n-butyl acrylate and 2-ethylhexyl acrylate are preferable from the viewpoint of excellent flexibility.

  The proportion of the (meth) acrylic acid ester monomer unit in the polymer as the binder for the adhesive layer is preferably 50% by weight or more, more preferably 70% by weight or more, particularly preferably 90% by weight or more, preferably It is 99 weight% or less, More preferably, it is 98 weight% or less, Most preferably, it is 97 weight% or less. By setting the ratio of the (meth) acrylic acid ester monomer unit to the lower limit value or more, the flexibility of the adhesive layer can be increased and the adhesiveness of the adhesive layer can be improved. Moreover, the rigidity of an adhesive layer can be raised by making the ratio of a (meth) acrylic acid ester monomer unit below the upper limit value, and the adhesiveness of the adhesive layer can also be improved.

  Moreover, the polymer as a binder for adhesive layers may contain a (meth) acrylic acid monomer unit. Here, the (meth) acrylic acid monomer unit is a structural unit having a structure formed by polymerizing a (meth) acrylic acid monomer. As the (meth) acrylic acid monomer, acrylic acid may be used, methacrylic acid may be used, or acrylic acid and methacrylic acid may be used in combination.

  The ratio of the (meth) acrylic acid monomer unit in the polymer as the binder for the adhesive layer is preferably 0.2% by weight or more, more preferably 0.4% by weight or more, and particularly preferably 0.6% by weight or more. It is preferably 10.0% by weight or less, more preferably 6.0% by weight or less, and particularly preferably 4.0% by weight or less. By setting the ratio of the (meth) acrylic acid monomer unit within the above range, the cohesive failure of the adhesive layer can be suppressed, and the adhesive force of the adhesive layer can be improved.

  Furthermore, the polymer as the binder for the adhesive layer may contain a (meth) acrylonitrile monomer unit. At this time, as the (meth) acrylonitrile monomer corresponding to the (meth) acrylonitrile monomer unit, acrylonitrile may be used, methacrylonitrile may be used, or acrylonitrile and methacrylonitrile are used in combination. May be.

  The ratio of the (meth) acrylonitrile monomer unit in the polymer as the binder for the adhesive layer is preferably 0.2% by weight or more, more preferably 0.5% by weight or more, and particularly preferably 1.0% by weight or more. Yes, preferably 20.0% by weight or less, more preferably 10.0% by weight or less, particularly preferably 5.0% by weight or less. By making the ratio of the (meth) acrylonitrile monomer unit equal to or higher than the lower limit, the life of the secondary battery can be particularly prolonged. Moreover, the mechanical strength of a contact bonding layer can be raised by making the ratio of a (meth) acrylonitrile monomer unit below the said upper limit.

  The polymer as the binder for the adhesive layer may contain a crosslinkable monomer unit. Examples of the crosslinkable monomer corresponding to the crosslinkable monomer unit include the same examples as those exemplified in the description of the particulate polymer. Furthermore, since N-hydroxymethyl (meth) acrylamide exemplified as a carboxylic acid amide monomer can act as both an amide monomer and a crosslinkable monomer, the N-hydroxymethyl (meth) acrylamide is crosslinked. It may be used as a functional monomer. A crosslinkable monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The proportion of the crosslinkable monomer unit in the polymer as the binder for the adhesive layer is preferably 0.2% by weight or more, more preferably 0.6% by weight or more, particularly preferably 1.0% by weight or more, Preferably it is 5.0 weight% or less, More preferably, it is 4.0 weight% or less, Most preferably, it is 3.0 weight% or less. By setting the ratio of the crosslinkable monomer unit to the lower limit value or more, the mechanical strength of the adhesive layer can be increased. Moreover, by making it into the upper limit value or less, the flexibility of the adhesive layer can be prevented from becoming brittle.

  The glass transition temperature of the polymer as the binder for the adhesive layer is preferably −100 ° C. or higher, more preferably −90 ° C. or higher, particularly preferably −80 ° C. or higher, preferably 0 ° C. or lower, more preferably −5. ° C or lower, particularly preferably -10 ° C or lower. By making the glass transition temperature of the polymer as the binder for the adhesive layer equal to or higher than the lower limit of the above range, the adhesiveness of the adhesive layer can be enhanced. Moreover, the softness | flexibility of an contact bonding layer can be improved by making it into an upper limit or less.

  The form of the binder for the adhesive layer may be particulate or non-particulate. Among these, it is preferable to use a particulate binder from the viewpoint of providing pores in the adhesive layer to increase ion diffusibility.

  When the binder for the adhesive layer is in the form of particles, the volume average particle size of the binder for the adhesive layer is preferably 0.01 μm or more, more preferably 0.02 μm or more, particularly preferably 0.05 μm or more, preferably It is 1 μm or less, more preferably 0.9 μm or less, and particularly preferably 0.8 μm or less. The dispersibility of the binder for adhesive layers can be improved by setting the volume average particle diameter of the binder for adhesive layers to be equal to or greater than the lower limit of the above range. Moreover, the adhesiveness of a contact bonding layer can be improved by making it into an upper limit or less.

  Examples of the method for producing the adhesive layer binder include a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among these, the emulsion polymerization method and the suspension polymerization method are preferable because they can be polymerized in water and can be suitably used as an adhesive material as they are. Moreover, when manufacturing the polymer as a binder for contact bonding layers, it is preferable that the reaction system contains a dispersing agent. The binder for the adhesive layer is usually formed of a polymer that substantially constitutes the binder, but it may be accompanied by optional components such as additives used in the polymerization.

  The amount of the binder for the adhesive layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, preferably 30 parts by weight or less, more preferably 100 parts by weight of the particulate polymer. 20 parts by weight or less. By setting the amount of the binder for the adhesive layer to be equal to or more than the lower limit of the above range, the strength of the adhesive layer can be increased. Moreover, the ion diffusivity which a particulate polymer has can fully be exhibited by making it into an upper limit or less.

[1.3. Water-soluble polymer)
The adhesive of the present invention can contain a water-soluble polymer. In the adhesive, the water-soluble polymer usually functions as a viscosity modifier. In particular, when the adhesive contains water as a solvent, in the adhesive, some of the water-soluble polymers are free in the solvent, but another part of the water-soluble polymer is a particulate polymer. Adsorb to the surface. Thereby, since the surface of a particulate polymer is covered with the layer of a water-soluble polymer, the dispersibility in water of a particulate polymer can be improved.

  Examples of the water-soluble polymer include cellulose polymers such as carboxymethyl cellulose, methyl cellulose, hydroxypropyl cellulose, and ammonium salts and alkali metal salts thereof; (modified) poly (meth) acrylic acid and ammonium salts and alkali metal salts thereof. Polyvinyl alcohol compounds such as (modified) polyvinyl alcohol, a copolymer of acrylic acid or acrylate and vinyl alcohol, maleic anhydride or a copolymer of maleic acid or fumaric acid and vinyl alcohol; polyethylene glycol, polyethylene oxide, polyvinyl Examples include pyrrolidone, modified polyacrylic acid, oxidized starch, phosphate starch, casein, and various modified starches. Here, “(modified) poly” means “unmodified poly” and “modified poly”.

  The amount of the water-soluble polymer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the particulate polymer. The amount is preferably 15 parts by weight or less, more preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less. The dispersibility of the particulate polymer in the adhesive can be increased by setting the amount of the water-soluble polymer to be equal to or higher than the lower limit of the above range. Moreover, the ion diffusibility which a particulate polymer has can be fully exhibited by making it into an upper limit or less.

[1.4. Non-conductive fiber)
The adhesive of the present invention can include non-conductive fibers. Non-conductive fibers are fibers having non-conductivity. Non-conductive fibers do not dissolve in the adhesive and can maintain the shape of the fibers. Further, the non-conductive fiber is not dissolved in the electrolytic solution and can maintain the shape of the fiber. When the adhesive contains non-conductive fibers, the mechanical strength of the adhesive layer can be improved by entanglement between the non-conductive fibers and entanglement between the non-conductive fibers and the particulate polymer. Moreover, the swelling of the adhesive layer in the electrolytic solution can be suppressed. Therefore, an increase in the distance between the positive electrode and the negative electrode due to charge / discharge can be suppressed, and high-temperature cycle characteristics can be improved. Furthermore, when a non-conductive fiber having a high affinity with the electrolytic solution such as cellulose is used, the diffusibility of the electrolytic solution into the adhesive layer can be particularly improved. Therefore, it is possible to improve the low temperature output characteristics of the lithium ion secondary battery.

  The nonconductive fiber may be formed of an organic material, an inorganic material, or a combination of an organic material and an inorganic material. Especially, since there is no elution of a metal and acquisition is easy, the nonelectroconductive fiber formed with the organic material is preferable.

  As the material of the non-conductive fiber, a material having non-conductivity, electrochemically stable, and stable to the electrolytic solution is preferable. From this point of view, examples of suitable materials for non-conductive fibers include cellulose, cellulose modified products, polysaccharides such as chitin and chitosan, polymers such as polypropylene, polyester, polyacrylonitrile, polyaramid, polyamideimide, and polyimide. Is mentioned. Among these, since it is excellent in heat resistance and is excellent in the diffusibility of electrolyte solution, a polysaccharide is preferable and a cellulose is more preferable. Moreover, the material of a nonelectroconductive fiber may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Furthermore, the non-conductive fiber may contain an optional additive as a constituent component in addition to the above constituent materials.

  The number average fiber length of the non-conductive fibers is preferably 50 μm or more, more preferably 60 μm or more, particularly preferably 70 μm or more, preferably 1000 μm or less, more preferably 500 μm or less, and particularly preferably 200 μm or less. By setting the number average fiber length in the above range, entanglement between the nonconductive fibers and entanglement between the nonconductive fibers and the particulate polymer are likely to occur. Therefore, the effect of improving the mechanical strength of the adhesive layer or suppressing the swelling of the adhesive layer when immersed in an electrolyte increases, effectively improving the low-temperature output characteristics and high-temperature cycle characteristics of the secondary battery. be able to.

  The amount of non-conductive fibers is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, still more preferably 0.5 parts by weight or more, particularly preferably 100 parts by weight of the particulate polymer. 1 part by weight or more, preferably 100 parts by weight or less, more preferably 50 parts by weight or less, and still more preferably 40 parts by weight or less. When the amount of the nonconductive fiber is in the above range, the mechanical strength of the adhesive layer can be increased. Further, when the adhesive layer is immersed in the electrolytic solution, the particulate polymer can be prevented from swelling and the distance between the electrode plates from increasing. Therefore, the internal resistance of the secondary battery can be reduced, and the low temperature characteristics and high temperature cycle characteristics of the secondary battery can be effectively improved.

[1.5. Non-conductive particles
The adhesive of the present invention can contain non-conductive particles. For example, particles selected from a range described later may be included as non-conductive particles that can be included in the porous film. Usually, since non-conductive particles have high rigidity, the mechanical strength of the adhesive layer can be increased by including the non-conductive particles in the adhesive layer.

  The amount of the non-conductive particles is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the particulate polymer. The amount is preferably 100 parts by weight or less, more preferably 90 parts by weight or less, and particularly preferably 80 parts by weight or less.

[1.6. solvent〕
The adhesive of the present invention usually contains a solvent. As the solvent, water is preferably used. Since the particulate polymer, the adhesive layer binder and the non-conductive particles are usually water-insoluble, when water is used as the solvent, the particulate polymer and the adhesive layer binder become particulate in water. Are distributed. In addition, since non-conductive fibers are usually water-insoluble, when water is used as a solvent, the non-conductive fibers are dispersed in the form of fibers in water.

  As the solvent, a solvent other than water may be used in combination with water. Examples of solvents that can be used in combination with water include cycloaliphatic hydrocarbon compounds such as cyclopentane and cyclohexane; aromatic hydrocarbon compounds such as toluene and xylene; ketone compounds such as ethyl methyl ketone and cyclohexanone; ethyl acetate and acetic acid Ester compounds such as butyl, γ-butyrolactone, ε-caprolactone; nitrile compounds such as acetonitrile and propionitrile; ether compounds such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, and the like And alcohol compounds; amide compounds such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide; One of these may be used alone, or two or more of these may be used in combination at any ratio. However, it is preferable to use water alone as the solvent.

  The amount of the solvent in the adhesive is preferably set so that the solid content concentration of the adhesive falls within a desired range. The solid content concentration of the specific adhesive is preferably 10% by weight or more, more preferably 15% by weight or more, particularly preferably 20% by weight or more, preferably 80% by weight or less, more preferably 75% by weight or less. Particularly preferably, it is 70% by weight or less. Here, the solid content of a certain composition means a substance remaining after the composition is dried.

[1.7. (Optional ingredients)
The adhesive of the present invention may contain optional components in addition to the above-described particulate polymer, adhesive layer binder, water-soluble polymer, non-conductive fiber, non-conductive particle, and solvent. As such optional components, those which do not exert an excessively unfavorable influence on the battery reaction can be used. Arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  For example, the adhesive is an isothiazoline compound, a chelate compound, a pyrithione compound, a dispersant, a leveling agent, an antioxidant, a thickener, an antifoaming agent, a wetting agent, and an electrolyte solution having a function of inhibiting electrolyte decomposition. An agent or the like may be included.

[1.8. Adhesive properties)
The adhesive of the present invention is usually a fluid slurry composition. Moreover, in the adhesive of this invention, each component contained in the adhesive has high dispersibility. Therefore, the viscosity of the adhesive of the present invention can usually be easily lowered.

[1.9. (Adhesive production method)
The method for producing the adhesive is not particularly limited. Usually, an adhesive agent is obtained by mixing each component mentioned above.
There is no restriction | limiting in particular in the mixing order of each component. There is no particular limitation on the mixing method. Usually, in order to disperse particles quickly, mixing is performed using a disperser as a mixing device.

  The disperser is preferably an apparatus capable of uniformly dispersing and mixing the above components. Examples include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. Among them, a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix is particularly preferable because a high dispersion share can be added.

[1.10. (Use of adhesive)
The adhesive of this invention can be used for adhesion | attachment of the member which comprises a lithium ion secondary battery. The adhesive of the present invention is preferably used for bonding the separator and the electrode. At this time, the adhesive property of the present invention may be used for the purpose of bonding the separator made of the separator substrate and the electrode, but in the lithium ion secondary battery including the separator substrate and the separator provided with the porous film and the electrode. In order to adhere the membrane and the electrode, it is preferable to use the adhesive of the present invention.

[2. Adhesive layer for lithium ion secondary battery]
An adhesive layer can be produced by applying the adhesive of the present invention on a suitable substrate and drying it as necessary. For example, an adhesive layer is produced by a production method including a step of applying an adhesive on a substrate to obtain a film of the adhesive, and a step of removing a solvent such as water by drying from the film as necessary. it can.

The adhesive layer thus obtained is a film formed from the solid content of the adhesive. Therefore, the adhesive layer includes a particulate polymer, and may further optionally include an adhesive layer binder, a water-soluble polymer, non-conductive fibers, and non-conductive particles.
In the particulate polymer, the shell part swells in the electrolytic solution and develops adhesiveness. Therefore, according to the adhesive layer, the members constituting the battery can be strongly bonded in the electrolytic solution. Moreover, since the core part of a particulate polymer has high ion diffusibility, the raise of resistance by an contact bonding layer is small. Furthermore, since the particulate polymer contains amide monomer units, generation of gas due to halide ions can be suppressed. Therefore, the lithium ion secondary battery provided with this adhesive layer can have excellent battery characteristics.

  In addition, since the shell part of the particulate polymer has low adhesiveness in a state where it is not swollen in the electrolytic solution, the adhesive force of the adhesive layer is small in a state where it is not swollen in the electrolytic solution. Therefore, this adhesive layer is excellent in blocking resistance in a state where it is not swollen in the electrolytic solution.

  Examples of the method for applying the adhesive include a doctor blade method, a dip coating method, a reverse roll method, a direct roll method, a spray coating method, a gravure method, an extrusion method, and a brush coating method.

  Examples of the drying method include a drying method using warm air, hot air, low-humidity air, or the like; vacuum drying; a drying method using irradiation with energy rays such as infrared rays, far infrared rays, and electron beams. A specific drying method is preferably selected according to the type of solvent used.

Moreover, in the manufacturing method of an adhesive layer, you may perform arbitrary operations other than having mentioned above.
For example, heat treatment may be performed. The heat crosslinkable group contained in the polymer component can be crosslinked by the heat treatment.

The application amount of the adhesive is the solid content of the adhesive applied per unit area, preferably 0.1 g / m ² or more, and more preferably 1.5 g / m ² or less. Adhesiveness of the adhesive layer can be increased by setting the coating amount to be equal to or greater than the lower limit of the above range. Moreover, by making it into the upper limit value or less, it is possible to prevent the resistance increase due to the adhesive layer from becoming excessive and the high temperature cycle characteristics from being deteriorated.

  The thickness of the adhesive layer is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.5 μm or more, preferably 5 μm or less, more preferably 4 μm or less, and particularly preferably 3 μm or less. By setting the thickness of the adhesive layer to be equal to or more than the lower limit of the above range, the adhesiveness of the adhesive layer can be increased. Moreover, by making it into the upper limit value or less, it is possible to prevent the resistance increase due to the adhesive layer from becoming excessive and the high-temperature cycle characteristics from deteriorating.

[3. Lithium ion secondary battery separator]
The separator of the present invention includes a separator substrate and an adhesive layer. The adhesive layer may be provided directly on the surface of the separator base material without interposing another layer, or may be provided indirectly on the surface of the separator base material via an arbitrary layer. Among these, it is preferable that a porous film is formed on the surface of the separator substrate, and an adhesive layer is provided on the surface of the porous film. In this separator, since the adhesive layer contains the particulate polymer according to the present invention, the adhesion between the separator and the electrode can be improved in the electrolytic solution. Moreover, the low temperature output characteristic and high temperature cycling characteristic of a lithium ion secondary battery can be improved. Furthermore, since the adhesive layer has a low adhesive force in a state where it is not swollen in the electrolyte, the separator of the present invention hardly causes blocking even when rolled up, and has excellent handling properties.

[3.1. (Separator substrate)
As the separator substrate, for example, a porous substrate having fine pores can be used. By using such a separator base material, a short circuit can be prevented in the secondary battery without hindering charging / discharging of the battery. Especially, as a separator base material, it is preferable to use the porous base material formed with the organic material. A porous substrate made of an organic material melts and closes the pores when the temperature inside the battery rises, thereby preventing lithium ion movement and blocking current, so a lithium ion secondary battery Can improve the safety.

  Examples of the separator substrate include porous substrates made of a resin including polyolefin (for example, polyethylene, polypropylene, polybutene, polyvinyl chloride), a mixture thereof, and a copolymer thereof; polyethylene terephthalate, polycyclo A porous substrate made of a resin containing olefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, nylon, polytetrafluoroethylene, cellulose, etc .; woven fabric of the above resin fibers; Nonwoven fabrics; aggregates of insulating particles. Moreover, you may use the laminated body of a multilayer structure provided with two or more layers by arbitrary combinations as a separator base material.

  The thickness of the separator substrate is preferably 0.5 μm or more, more preferably 1 μm or more, preferably 40 μm or less, more preferably 30 μm or less, and particularly preferably 10 μm or less. Within this range, the increase in resistance due to the separator base material in the secondary battery is reduced, and the workability during battery production is excellent.

[3.2. (Porous membrane)
The porous film is a porous film provided on the surface of the separator substrate, and may be provided on only one surface of the separator substrate, or may be provided on both surfaces. This porous film contains non-conductive particles, and usually further contains a binder for the porous film. In such a porous film, the nonconductive particles are bonded by the binder for the porous film, and the gaps between the nonconductive particles constitute the pores of the porous film. Moreover, the binder for porous films can show the function to adhere a porous film to a separator base material.

  In general, when a porous substrate formed of an organic material is used as a separator substrate, the separator substrate may tend to contract when the battery is heated excessively. On the other hand, when a porous film is provided on the surface of the separator substrate, the porous film resists the stress that the separator substrate tends to shrink. Therefore, shrinkage of the separator substrate can be prevented. Therefore, the short circuit by shrinkage | contraction of a separator base material can be prevented, and the safety | security of a lithium ion secondary battery can be improved.

[3.2.1. Non-conductive particles
As the non-conductive particles, it is preferable to use particles formed of an electrochemically stable material, inorganic particles may be used, and organic particles may be used.

Inorganic particles are excellent in dispersion stability in a solvent, and are difficult to settle in a slurry for a porous membrane used for production of a porous membrane. Therefore, the slurry for porous films can maintain a uniform slurry state for a long time. In addition, when inorganic particles are used, the heat resistance of the porous film can usually be increased. Examples of such inorganic particle materials include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ )), silicon oxide, magnesium oxide (magnesia), water, and the like. Oxide particles such as magnesium oxide, calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO ₂ , alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystals such as silicon and diamond Particles; Insoluble ion crystal particles such as barium sulfate, calcium fluoride, and barium fluoride; Clay fine particles such as talc and montmorillonite; Among these, oxide particles are preferable from the viewpoints of stability in an electrolytic solution and potential stability, and titanium oxide and aluminum oxide are particularly preferable from the viewpoint of low water absorption and excellent heat resistance (for example, resistance to high temperature of 180 ° C. or higher). Aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferable, aluminum oxide, aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferable, and aluminum oxide is particularly preferable. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

  As the organic particles, polymer particles are usually used. The organic particles can control the affinity for water by adjusting the type and amount of the functional group on the surface of the organic particles, and thus can control the amount of water contained in the porous film. Organic particles are excellent in that they usually have less metal ion elution. Examples of the material of such organic particles include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer compound forming the particles can be used, for example, as a mixture, a modified product, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked product, and the like. The organic particles may be formed of a mixture of two or more polymer compounds.

  When organic particles are used as the non-conductive particles, the organic particles need not have a glass transition temperature. However, when the polymer forming the organic particles has a glass transition temperature, the glass transition temperature is preferably 150 ° C. or higher, more preferably 200 ° C. or higher, and particularly preferably 250 ° C. or higher.

  The non-conductive particles may be subjected to, for example, element substitution, surface treatment, solid solution treatment, or the like as 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.

  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 film and suppressing the decrease in ionic conductivity due to the porous film, a tetrapod (registered trademark) shape, a plate shape, and a scale shape are preferable.

  The volume average particle diameter D50 of the non-conductive particles is preferably 0.1 μm or more, more preferably 0.2 μm or more, preferably 5 μm or less, more preferably 2 μm or less, and particularly preferably 1 μm or less. By using such non-conductive particles having a volume average particle diameter D50, a uniform porous film can be obtained even if the thickness of the porous film is thin, so that the capacity of the battery can be increased.

The BET specific surface area of the non-conductive particles is, for example, preferably 0.9 m ² / g or more, more preferably 1.5 m ² / g or more. Further, from the viewpoint of suppressing aggregation of non-conductive particles and optimizing the fluidity of the slurry for the porous membrane, the BET specific surface area is preferably not too large, for example, 150 m ² / g or less.

  The amount of non-conductive particles in the porous membrane is preferably 70% by weight or more, more preferably 80% by weight or more, preferably 97% by weight or less, more preferably 95% by weight or less. By keeping the amount of the non-conductive particles in the above range, the gap between the non-conductive particles can be formed to such an extent that the non-conductive particles have contact portions and the movement of ions is not hindered. Therefore, the intensity | strength of a porous film can be improved and the short circuit of a secondary battery can be prevented stably by keeping the quantity of nonelectroconductive particle in the said range.

[3.2.2. Porous membrane binder)
As the binder for the porous film, for example, a binder selected from the same range as that described as the binder for the adhesive layer can be used. Among these, it is preferable to use a polymer containing an amide monomer unit because the high-temperature cycle characteristics of the lithium ion secondary battery can be further improved. Moreover, the binder for porous films may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the binder for the porous membrane is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, preferably 30 parts by weight or less, more preferably 100 parts by weight of the non-conductive particles. 20 parts by weight or less. By setting the amount of the binder for the porous film to be equal to or higher than the lower limit of the above range, the adhesion between the porous film and the separator substrate can be enhanced. Moreover, the lifetime of a lithium ion secondary battery can be lengthened by making it into an upper limit or less.

[3.2.3. Water-soluble polymer)
The porous film preferably contains a water-soluble polymer in addition to the nonconductive particles and the binder for the porous film. The water-soluble polymer usually functions as a viscosity modifier in the slurry for the porous membrane. In particular, when the porous membrane slurry contains water as a solvent, in the porous membrane slurry, a part of the water-soluble polymer is free in the solvent, but another part of the water-soluble polymer is Adsorbs on the surface of non-conductive particles. As a result, the surface of the non-conductive particles is covered with the water-soluble polymer layer, so that the dispersibility of the non-conductive particles in water can be improved, and consequently the dispersibility of the non-conductive particles in the porous film is improved. Can be made. Furthermore, the water-soluble polymer can also have a function of adhering non-conductive particles.

  As the water-soluble polymer, for example, a water-soluble polymer selected from the same range as described for the water-soluble polymer that can be contained in the adhesive may be used. Moreover, a water-soluble polymer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the water-soluble polymer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, preferably 10 parts by weight or less, more preferably 100 parts by weight of the non-conductive particles. 5 parts by weight or less. By setting the amount of the water-soluble polymer to be not less than the lower limit of the above range, the adhesion between the porous membrane and the separator substrate can be enhanced. Moreover, the lifetime of a lithium ion secondary battery can be lengthened by making it into an upper limit or less.

[3.2.4. (Optional ingredients)
The porous film may contain arbitrary components in addition to the non-conductive particles, the porous film binder, and the water-soluble polymer described above. As such optional components, those which do not exert an excessively unfavorable influence on the battery reaction can be used. As an example of arbitrary components, the same example as what was illustrated as an arbitrary component which an adhesive agent can contain is mentioned. Moreover, arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

[3.2.5. (Thickness of porous film)
The thickness of the porous membrane is preferably 0.1 μm or more, more preferably 0.2 μm or more, particularly preferably 0.3 μm or more, preferably 20 μm or less, more preferably 15 μm or less, and particularly preferably 10 μm or less. By setting the thickness of the porous film to be equal to or more than the lower limit of the above range, the heat resistance of the porous film can be increased. Moreover, the fall of the ionic conductivity by a porous film can be suppressed by setting it as an upper limit or less.

[3.2.6. Method for producing porous membrane]
As the porous membrane, for example, a porous membrane slurry containing the components of the porous membrane (that is, non-conductive particles, a binder for the porous membrane, a water-soluble polymer, and an optional component) is prepared. It can manufacture by apply | coating on an appropriate base material and drying as needed. That is, a step of preparing a slurry for a porous membrane, a step of applying the slurry for a porous membrane on a substrate to obtain a membrane of the slurry for a porous membrane, and a solvent such as water by drying from the membrane as necessary A porous film can be manufactured by a manufacturing method including a removing step.

  The slurry for a porous membrane can be produced, for example, by mixing non-conductive particles, a binder for a porous membrane, a water-soluble polymer and an optional component, and a solvent. There is no restriction | limiting in particular in the mixing order of each component. There is no particular limitation on the mixing method. Usually, in order to disperse particles quickly, mixing is performed using a disperser as a mixing device. As the disperser, for example, a disperser similar to that exemplified as a disperser that can be used for manufacturing an adhesive can be used.

  As the solvent for the slurry for the porous film, for example, a solvent selected from the same range as that described as the solvent that can be contained in the adhesive can be used. Moreover, 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.

  The amount of the solvent in the porous membrane slurry is preferably set so that the solid content concentration of the porous membrane slurry is within a desired range. The solid content concentration of the specific slurry for the porous membrane is preferably 10% by weight or more, more preferably 15% by weight or more, particularly preferably 20% by weight or more, preferably 80% by weight or less, more preferably 75% by weight. % Or less, particularly preferably 70% by weight or less.

  The porous film slurry is applied on a substrate to form a porous film slurry. The base material used here is a member to be a target for forming a porous membrane slurry. There is no restriction | limiting in a base material, For example, the film | membrane of the slurry for porous films is formed in the surface of a peeling film, A solvent is removed from the film | membrane, a porous film may be formed, and a porous film may be peeled from a peeling film. However, usually, a separator base material is used as the base material from the viewpoint of improving the manufacturing efficiency by omitting the step of peeling the porous film.

Examples of the coating method include the same examples as the coating method exemplified in the method for producing the adhesive layer. Among these, the dip method and the gravure method are preferable in that a uniform porous film can be obtained.
Moreover, as a drying method, the example similar to the drying method illustrated in the manufacturing method of an contact bonding layer is mentioned, for example.

In the method for producing a porous membrane, any operation other than those described above may be performed.
For example, the porous film may be subjected to pressure treatment by a pressing method such as a mold press and a roll press. By applying the pressure treatment, the adhesion between the substrate and the porous film can be improved. However, from the viewpoint of keeping the porosity of the porous film within a preferable range, it is preferable to appropriately control the pressure and the pressurization time so as not to become excessively large.
In order to remove residual moisture, it is preferable to dry in, for example, vacuum drying or a dry room.
Further, for example, heat treatment is also preferable, whereby the heat-crosslinkable group contained in the polymer component can be crosslinked to increase the adhesive force.

[3.3. Adhesive layer provided in the separator]
The separator of the present invention includes an adhesive layer on the separator substrate directly or via an arbitrary layer such as a porous film. Such a separator uses, for example, a separator base material as a base material, or a laminate including a separator base material and an arbitrary layer as a base material, and the above-described method for producing an adhesive layer on the base material. It can be manufactured by forming an adhesive layer. At this time, the adhesive layer may be provided only on one side of the separator, or may be provided on both sides.

[4. Lithium ion secondary battery]
The lithium ion secondary battery of the present invention includes a positive electrode, a negative electrode, an electrolytic solution, and a separator. Moreover, the lithium ion secondary battery of this invention is equipped with the separator of this invention mentioned above as said separator.
Since the lithium ion secondary battery of the present invention includes the separator of the present invention, it is excellent in low temperature output characteristics and high temperature cycle characteristics.

[4.1. electrode〕
The lithium ion secondary battery of the present invention includes a positive electrode and a negative electrode as electrodes. In the lithium ion secondary battery, there is an adhesive layer between the electrode and the separator base material, and the particulate polymer contained in the adhesive layer exhibits adhesiveness in the electrolytic solution, so that the electrode and the separator Is strongly bonded.

  In general, a lithium ion secondary battery is manufactured by stacking a positive electrode, a separator, and a negative electrode in this order, and then stacking the stacked body in a battery exterior. Here, when a separator having a conventional adhesive layer is used, the separator, the positive electrode, and the negative electrode are bonded when the positive electrode, the separator, and the negative electrode are stacked. Therefore, even if a deviation occurs when the positive electrode, the separator, and the negative electrode are stacked, it is difficult to eliminate the deviation because the positive electrode and the separator or the negative electrode and the separator are fixed. On the other hand, the adhesive layer provided in the separator of the present invention has low adhesiveness in a non-swelled state, and exhibits high adhesiveness by swelling in the electrolytic solution. Therefore, when the positive electrode, the separator, and the negative electrode are stacked, the separator, the positive electrode, and the negative electrode are not bonded to each other. Therefore, even when the positive electrode, the separator, and the negative electrode are stacked, the shift can be easily eliminated. Therefore, the yield can be improved.

  Each of the positive electrode and the negative electrode usually includes a current collector and an electrode active material layer. That is, the positive electrode includes a current collector and a positive electrode active material layer, and the negative electrode includes a current collector and a negative electrode active material layer.

[4.1.1. Current collector]
The current collector may be made of a material having electrical conductivity and electrochemical durability. Usually, a metal material is used as the material of the current collector. Examples thereof include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum and the like. Among them, the current collector used for the positive electrode is preferably aluminum, and the current collector used for the negative electrode is preferably copper. Moreover, the said material may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The shape of the current collector is not particularly limited, but a sheet shape having a thickness of about 0.001 mm to 0.5 mm is preferable.

  In order to increase the adhesive strength with the electrode active material layer, the current collector is preferably used after the surface is roughened. Examples of the roughening method include a mechanical polishing method, an electrolytic polishing method, and a chemical polishing method. In the mechanical polishing method, for example, an abrasive cloth paper to which abrasive particles are fixed, a grindstone, an emery buff, a wire brush provided with a steel wire, or the like is used. Further, an intermediate layer may be formed on the surface of the current collector in order to increase the adhesive strength and conductivity of the electrode active material layer.

[4.1.2. Electrode active material layer
The electrode active material layer is a layer provided on the current collector and includes an electrode active material.
As the electrode active material of the lithium ion secondary battery, a material capable of reversibly inserting or releasing lithium ions by applying a potential in an electrolytic solution can be used.

The positive electrode active material is roughly classified into those made of inorganic compounds and those made of organic compounds. Examples of the positive electrode active material made of an inorganic compound include transition metal oxides, composite oxides of lithium and transition metals, and transition metal sulfides. Examples of the transition metal include Fe, Co, Ni, and Mn. Specific examples of the inorganic compound used for the positive electrode active material include LiCoO ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiFeVO _{4 and} other lithium-containing composite metal oxides; TiS ₂ , TiS ₃ , non- Transition metal sulfides such as crystalline MoS ₂ ; transition metal oxides such as Cu ₂ V ₂ O ₃ , amorphous V ₂ O—P ₂ O ₅ , MoO ₃ , V ₂ O ₅ , V ₆ O _13, etc. Can be mentioned. On the other hand, examples of the positive electrode active material made of an organic compound include conductive polymers such as polyacetylene and poly-p-phenylene.

Furthermore, you may use the positive electrode active material which consists of a composite material which combined the inorganic compound and the organic compound.
Alternatively, for example, a composite material covered with a carbon material may be produced by reducing and firing an iron-based oxide in the presence of a carbon source material, and the composite material may be used as a positive electrode active material. Iron-based oxides tend to have poor electrical conductivity, but can be used as a high-performance positive electrode active material by using a composite material as described above.
Furthermore, you may use as a positive electrode active material what carried out the element substitution of the said compound partially.
These positive electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Moreover, you may use the mixture of the above-mentioned inorganic compound and organic compound as a positive electrode active material.

  The particle diameter of the positive electrode active material can be selected in consideration of other constituent elements of the lithium ion secondary battery. From the viewpoint of improving battery characteristics such as load characteristics and high-temperature cycle characteristics, the volume average particle diameter of the positive electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, preferably 50 μm or less, more preferably 20 μm. It is as follows. When the volume average particle diameter of the positive electrode active material is within this range, a battery having a large charge / discharge capacity can be obtained, and handling in producing the positive electrode slurry and the electrode is easy.

  The ratio of the positive electrode active material in the positive electrode active material layer is preferably 90% by weight or more, more preferably 95% by weight or more, and preferably 99.9% by weight or less, more preferably 99% by weight or less. By setting the amount of the positive electrode active material in the above range, the capacity of the lithium ion secondary battery can be increased, and the flexibility of the positive electrode and the adhesion between the current collector and the positive electrode active material layer can be improved.

  Examples of the negative electrode active material include carbonaceous materials such as amorphous carbon, graphite, natural graphite, mesocarbon microbeads, and pitch-based carbon fibers; and conductive polymers such as polyacene. Further, metals such as silicon, tin, zinc, manganese, iron and nickel, and alloys thereof; oxides of the metals or alloys; sulfates of the metals or alloys; Further, metallic lithium; lithium alloys such as Li—Al, Li—Bi—Cd, and Li—Sn—Cd; lithium transition metal nitride; silicon and the like may be used. Furthermore, an electrode active material having a conductive material attached to the surface by a mechanical modification method may be used. These negative electrode active materials may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The particle diameter of the negative electrode active material is appropriately selected in view of other constituent requirements of the lithium ion secondary battery. From the viewpoint of improving battery characteristics such as initial efficiency, load characteristics, and high-temperature cycle characteristics, the volume average particle diameter of the negative electrode active material is preferably 0.1 μm or more, more preferably 1 μm or more, and further preferably 5 μm or more. Preferably it is 100 micrometers or less, More preferably, it is 50 micrometers or less, More preferably, it is 20 micrometers or less.

The specific surface area of the negative electrode active material, the output from the viewpoint of improving the density, preferably ^2m 2 / g or more, more preferably ^3m 2 / g or more, more preferably ^{5 m} 2 / g or more, and preferably ^{20 m} 2 / g or less, more preferably 15 m ² / g or less, and further preferably 10 m ² / g or less. The specific surface area of the negative electrode active material can be measured by, for example, the BET method.

  The ratio of the negative electrode active material in the negative electrode active material layer is preferably 85% by weight or more, more preferably 88% by weight or more, and preferably 99% by weight or less, more preferably 97% by weight or less. By setting the amount of the negative electrode active material in the above range, it is possible to realize a negative electrode that exhibits excellent flexibility and adhesiveness while exhibiting a high capacity.

  The electrode active material layer preferably contains an electrode binder in addition to the electrode active material. By including the electrode binder, the adhesion of the electrode active material layer is improved, and the strength against the mechanical force applied in the process of winding the electrode is increased. In addition, since the electrode active material layer is difficult to peel off from the current collector, the risk of a short circuit due to the detached desorbed material is reduced.

  As the electrode binder, for example, a polymer can be used. Examples of the polymer that can be used as the electrode binder include a polymer selected from the same range as the polymer described as the adhesive layer binder.

Furthermore, you may use the particle | grains of the soft polymer illustrated below as a binder for electrodes. As a soft polymer, for example,
(I) Polybutyl acrylate, polybutyl methacrylate, polyhydroxyethyl methacrylate, polyacrylamide, polyacrylonitrile, butyl acrylate / styrene copolymer, butyl acrylate / acrylonitrile copolymer, butyl acrylate / acrylonitrile / glycidyl methacrylate copolymer, etc. An acrylic soft polymer which is a homopolymer of acrylic acid or a methacrylic acid derivative or a copolymer thereof with a monomer copolymerizable therewith;
(Ii) isobutylene-based soft polymers such as polyisobutylene, isobutylene-isoprene rubber, isobutylene-styrene copolymer;
(Iii) Polybutadiene, polyisoprene, butadiene / styrene random copolymer, isoprene / styrene random copolymer, acrylonitrile / butadiene copolymer, acrylonitrile / butadiene / styrene copolymer, butadiene / styrene / block copolymer, styrene・ Diene-based soft polymers such as butadiene, styrene, block copolymers, isoprene, styrene, block copolymers, styrene, isoprene, styrene, block copolymers;
(Iv) silicon-containing soft polymers such as dimethylpolysiloxane, diphenylpolysiloxane, dihydroxypolysiloxane;
(V) Liquid polyethylene, polypropylene, poly-1-butene, ethylene / α-olefin copolymer, propylene / α-olefin copolymer, ethylene / propylene / diene copolymer (EPDM), ethylene / propylene / styrene copolymer Olefinic soft polymers such as polymers;
(Vi) Vinyl-based soft polymers such as polyvinyl alcohol, polyvinyl acetate, polyvinyl stearate, vinyl acetate / styrene copolymer;
(Vii) epoxy-based soft polymers such as polyethylene oxide, polypropylene oxide, epichlorohydrin rubber;
(Viii) Fluorine-containing soft polymers such as vinylidene fluoride rubber and tetrafluoroethylene-propylene rubber;
(Ix) Other soft polymers such as natural rubber, polypeptide, protein, polyester thermoplastic elastomer, vinyl chloride thermoplastic elastomer, polyamide thermoplastic elastomer, and the like. Among these, a diene soft polymer and an acrylic soft polymer are preferable. In addition, these soft polymers may have a cross-linked structure or may have a functional group introduced by modification.
Moreover, the binder for electrodes may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  The amount of the binder for the electrode in the electrode active material layer is preferably 0.1 parts by weight or more, more preferably 0.2 parts by weight or more, particularly preferably 0.5 parts by weight or more with respect to 100 parts by weight of the electrode active material. It is preferably 5 parts by weight or less, more preferably 3 parts by weight or less. When the amount of the electrode binder is within the above range, it is possible to prevent the electrode active material from dropping from the electrode without inhibiting the battery reaction.

  The electrode active material layer may contain any component other than the electrode active material and the electrode binder as long as the effects of the present invention are not significantly impaired. Examples thereof include a conductive material and a reinforcing material. Moreover, arbitrary components may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

  Examples of the conductive material include conductive carbon such as acetylene black, ketjen black, carbon black, graphite, vapor-grown carbon fiber, and carbon nanotube; carbon powder such as graphite; fibers and foils of various metals; . By using a conductive material, electrical contact between electrode active materials can be improved, and battery characteristics such as high-temperature cycle characteristics can be improved.

The specific surface area of the conductive material is preferably 50 m ² / g or more, more preferably 60 m ² / g or more, particularly preferably 70 m ² / g or more, preferably 1500 m ² / g or less, more preferably 1200 m ² / g. Hereinafter, it is particularly preferably 1000 m ² / g or less. By setting the specific surface area of the conductive material to be equal to or higher than the lower limit of the above range, the low temperature output characteristics of the lithium ion secondary battery can be improved. Moreover, the adhesiveness of an electrode active material layer and a collector can be improved by setting it as below an upper limit.

  As the reinforcing material, for example, various inorganic and organic spherical, plate-like, rod-like or fibrous fillers can be used. By using a reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term high-temperature cycle characteristics can be obtained.

  The amount of the conductive material and the reinforcing agent used is usually 0 part by weight or more, preferably 1 part by weight or more, preferably 20 parts by weight or less, more preferably 10 parts by weight, with respect to 100 parts by weight of the electrode active material. It is as follows.

  The thickness of the electrode active material layer is preferably 5 μm or more, more preferably 10 μm or more, preferably 300 μm or less, more preferably 250 μm or less for both the positive electrode and the negative electrode.

  The method for producing the electrode active material layer is not particularly limited. The electrode active material layer is prepared, for example, by preparing an electrode active material, a solvent, and an electrode slurry containing an electrode binder and optional components as necessary. Can be manufactured. As the solvent, either water or an organic solvent can be used.

[4.2. Electrolyte)
As the electrolytic solution, a polymer that can swell the polymer in the core portion and the polymer in the shell portion of the particulate polymer with the degree of swelling in the predetermined range described above can be used. As such an electrolytic solution, an organic electrolytic solution containing an organic solvent and a supporting electrolyte dissolved in the organic solvent can be preferably used.

For example, a lithium salt is used as the supporting electrolyte. 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 the like. Among them, LiPF ₆ , LiClO ₄ and CF ₃ SO ₃ Li are preferable because they are easily soluble in a solvent and exhibit a high degree of dissociation. Moreover, a supporting electrolyte may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios. Since the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

  The concentration of the supporting electrolyte in the electrolytic solution is preferably 1% by weight or more, more preferably 5% by weight or more, preferably 30% by weight or less, more preferably 20% by weight or less. Further, the supporting electrolyte is preferably used at a concentration of 0.5 mol / liter to 2.5 mol / liter depending on the type of the supporting electrolyte. By keeping the amount of the supporting electrolyte within this range, the ionic conductivity can be increased, so that the charging characteristics and discharging characteristics of the lithium ion secondary battery can be improved.

  As the organic solvent used for the electrolytic solution, a solvent capable of dissolving the supporting electrolyte can be used. Examples of the organic solvent include dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), methyl ethyl carbonate (MEC), vinylene carbonate (VC), and the like. Suitable examples include carbonate compounds of the above; ester compounds such as γ-butyrolactone and methyl formate; ether compounds such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Among them, a carbonate compound is preferable because it has a high dielectric constant and a stable potential region in a wide range. Moreover, since the lithium ion conductivity tends to increase as the viscosity of the solvent used decreases, the lithium ion conductivity can be adjusted depending on the type of the solvent.

  Moreover, electrolyte solution may contain an additive as needed. An additive may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Among the electrolytes described above, from the viewpoint of easily controlling the swelling degree of the core polymer and the shell polymer of the particulate polymer, a solvent having a desired SP value is used as the solvent of the electrolyte. Is preferred. The specific SP value of the solvent of the electrolytic solution is preferably 8 (cal / cm ³ ) ^1/2 or more, more preferably 9 (cal / cm ³ ) ^1/2 or more, and preferably 15 (cal / Cm ³ ) ^1/2 or less, more preferably 14 (cal / cm ³ ) ^1/2 or less. Examples of the solvent having an SP value that falls within the above range include cyclic ester compounds such as ethylene carbonate and propylene carbonate; chain ester compounds such as ethyl methyl carbonate and diethyl carbonate; and the like.

[4.3. Method for producing lithium ion secondary battery]
The manufacturing method of the lithium ion secondary battery of the present invention is not particularly limited. For example, the above-described negative electrode and 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.

  Hereinafter, the present invention will be specifically described with reference to examples. However, the present invention is not limited to the following examples, and can be implemented with any modifications without departing from the scope of the claims of the present invention and the equivalents thereof.

  In the following description, “%” and “part” representing amounts are based on weight unless otherwise specified. In addition, the operations described below were performed under normal temperature and normal pressure conditions unless otherwise specified.

[Evaluation method]
[1. (Measurement method of peel strength between electrode and porous membrane)
The laminated body provided with the positive electrode and the separator and the laminated body provided with the negative electrode and the separator manufactured in Examples and Comparative Examples were each cut out to a width of 10 mm to obtain test pieces. This test piece was immersed in the electrolytic solution at a temperature of 60 ° C. for 3 days. At this time, as the electrolytic solution, a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio EC / DEC / VC = 68.5 / 30 / 1.5; SP value 12.7 (cal / cm ³ )) ^{In 1/2} ), a support electrolyte in which LiPF ₆ was dissolved in a solvent at a concentration of 1 mol / liter was used.
Then, the test piece was taken out and the electrolytic solution adhering to the surface was wiped off. Then, the cellophane tape was affixed on the surface of the electrode with the electrode (positive electrode or negative electrode) 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 separator was pulled vertically upward at a pulling speed of 50 mm / min and peeled off. This measurement was performed three times for each of the laminate including the positive electrode and the separator and the laminate including the negative electrode and the separator for a total of 6 times, and the average value of the stress was obtained, and the average value was defined as the peel strength.

[2. (Evaluation method of blocking resistance)
The separator is cut into squares of 5 cm wide × 5 cm long and 4 cm wide × 4 cm long to form test pieces. A sample obtained by superimposing these two sheets (a sample in an unpressed state) and a sample (pressed sample) placed under pressure of 40 g and 10 g / cm ² after superposition were produced. Each of these samples was left for 24 hours. In the sample after being left for 24 hours, the adhesion state (blocking state) between the stacked separators was visually confirmed and evaluated according to the following criteria.
A: In the pressed sample, the separators do not block each other.
B: In the pressed sample, the separators are blocked but peeled off.
C: In the pressed sample, the separators are blocked and do not peel off.
D: Separators block in the unpressed sample.

[3. (Method for evaluating high-temperature cycle characteristics)
The 800 mAh wound type lithium ion secondary battery manufactured in Examples and Comparative Examples was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, under an environment of 25 ° C., a charge / discharge operation of charging up to 4.35 V at 0.1 C and discharging to 2.75 V at 0.1 C was performed, and the initial capacity C0 was measured.

  Furthermore, charging and discharging were repeated 1000 cycles under the same conditions as described above in a 60 ° C. environment, and the capacity C1 after 1000 cycles was measured.

  The capacity retention rate ΔC was calculated by ΔC = C1 / C0 × 100 (%). The higher the capacity retention ratio ΔC, the better the high-temperature cycle characteristics of the lithium ion secondary battery, and the longer the battery life.

[4. Measurement method of cell volume change before and after high temperature cycle test]
The 800 mAh wound type lithium ion secondary battery manufactured in Examples and Comparative Examples was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, in an environment of 25 ° C., a charge / discharge operation was performed in which the battery was charged at 0.1 C to 4.35 V and discharged at 0.1 C to 2.75 V. The cell of this battery was immersed in liquid paraffin, and the volume X0 of the cell was measured.

  Furthermore, the charge / discharge operation was repeated 1000 cycles under the same conditions as described above in a 60 ° C. environment. The cell of the battery after 1000 cycles was immersed in liquid paraffin, and the volume X1 of the cell was measured.

  The cell volume change rate ΔX before and after the high-temperature cycle test in which charge and discharge were repeated 1000 cycles was calculated by ΔX (%) = (X1−X0) / X0 × 100. It shows that it is excellent in the capability to suppress generation | occurrence | production of gas, so that the value of this cell volume change rate (DELTA) X is small.

[5. (Evaluation method of low-temperature output characteristics)
The 800 mAh wound type lithium ion secondary battery manufactured in Examples and Comparative Examples was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, charging was performed for 5 hours at a charging rate of 0.1 C under an environment of 25 ° C., 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 voltage change ΔV was calculated by ΔV = V0−V1. It shows that it is excellent in a low temperature characteristic, so that the value of this voltage change (DELTA) V is small.

[6. Method for measuring degree of swelling of polymer in core portion)
The aqueous dispersion containing the polymer constituting the core part was produced in the same manner as the method for producing the aqueous dispersion containing the polymer constituting the core part in Examples and Comparative Examples. This aqueous dispersion was put into a petri dish made of polytetrafluoroethylene and dried under the conditions of 25 ° C. and 48 hours to produce a film having a thickness of 0.5 mm.

This film was cut into a 1 cm square to obtain a test piece. The weight of this test piece was measured and designated as W0.
The test piece was immersed in an electrolytic solution at 60 ° C. for 72 hours. Then, the test piece was taken out from the electrolytic solution, the electrolytic solution on the surface of the test piece was wiped off, and the weight W1 of the test piece after the immersion test was measured.
Using these weights W0 and W1, the degree of swelling S (times) was calculated as S = W1 / W0.

At this time, as the electrolytic solution, a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio EC / DEC / VC = 68.5 / 30 / 1.5; SP value 12.7 (cal / cm ³ )) ^{In 1/2} ), a support electrolyte in which LiPF ₆ was dissolved in a solvent at a concentration of 1 mol / liter was used.

[7. Method for measuring degree of swelling of polymer in shell part)
A method for producing an aqueous dispersion containing a particulate polymer in Examples and Comparative Examples except that the monomer composition used for the production of the shell part was used instead of the monomer composition used for the production of the core part. In the same manner as described above, an aqueous dispersion containing a particulate polymer composed of a polymer forming a shell portion was produced. Similar to the method for measuring the degree of swelling of the polymer in the core part, except that an aqueous dispersion containing a particulate polymer composed of the polymer forming the shell part was used as the aqueous dispersion for producing the test piece. Then, the swelling degree S of the polymer in the shell part was measured.

[8. Method for measuring volume average particle diameter of particulate polymer)
The volume average particle size of the particulate polymer is 50% of the cumulative volume calculated from the small diameter side in the particle size distribution measured by a laser diffraction particle size distribution measuring device (“SALD-3100” manufactured by Shimadzu Corporation). The particle diameter was as follows.

[9. (Measurement method of core-shell ratio)
The particulate polymer was sufficiently dispersed in a visible light curable resin (“D-800” manufactured by JEOL Ltd.) and then embedded to prepare a block piece containing the particulate polymer. Next, the sample for a measurement was produced by cutting out with a microtome provided with a diamond blade into a thin piece having a thickness of 100 nm. Thereafter, the measurement sample was dyed using ruthenium tetroxide.
Next, the dyed measurement sample was set in a transmission electron microscope (“JEM-3100F” manufactured by JEOL Ltd.), and a cross-sectional structure of the particulate polymer was photographed at an acceleration voltage of 80 kV. The magnification of the electron microscope was set so that the cross section of one particulate polymer was in the visual field.
Thereafter, the cross-sectional structure of the photographed particulate polymer was observed, and the average thickness of the shell portion of the particulate polymer was measured by the following procedure according to the observed configuration of the shell portion.

  When the shell portion is composed of polymer particles, the longest diameter of the polymer particles constituting the shell portion was measured from the cross-sectional structure of the particulate polymer. For 20 arbitrarily selected particulate polymers, the longest diameter of the polymer particles constituting the shell portion was measured, and the average value of the longest diameters was taken as the average thickness of the shell portion.

  Moreover, when the shell part had shapes other than particle | grains, the maximum thickness of the shell part was measured from the cross-sectional structure of the particulate polymer. About 20 arbitrarily selected particulate polymers, the maximum thickness of the shell portion was measured, and the average value of the maximum thickness was defined as the average thickness of the shell portion.

  And the core-shell ratio was calculated | required by dividing the measured average thickness of the shell part by the volume average particle diameter of the particulate polymer.

[10. Measuring method of average ratio of outer surface of core part of particle polymer covered by shell part)
The particulate polymer was sufficiently dispersed in a visible light curable resin (“D-800” manufactured by JEOL Ltd.) and then embedded to prepare a block piece containing the particulate polymer. Next, the sample for a measurement was produced by cutting out with a microtome provided with a diamond blade into a thin piece having a thickness of 100 nm. Thereafter, the measurement sample was dyed using ruthenium tetroxide.

  Next, the dyed measurement sample was set in a transmission electron microscope (“JEM-3100F” manufactured by JEOL Ltd.), and a cross-sectional structure of the particulate polymer was photographed at an acceleration voltage of 80 kV. The magnification of the electron microscope was set so that the cross section of one particulate polymer was in the visual field.

In the cross-sectional structure of the photographed particulate polymer, the circumference D1 of the core part and the length D2 of the part where the outer surface of the core part abuts on the shell part are measured. The ratio Rc of the outer surface of the core part of the particulate polymer covered by the shell part was calculated.
Covering ratio Rc (%) = D2 / D1 × 100 (1)
The coating ratio Rc was measured for 20 arbitrarily selected particulate polymers, and the average value was calculated as the average ratio at which the outer surface of the core part was covered with the shell part.

[Example 1]
[1-1. Production of porous membrane binder)
To a reactor equipped with a stirrer, 70 parts of ion exchange water, 0.15 part of sodium lauryl sulfate (manufactured by Kao Chemical Co., product name “Emar 2F”) as an emulsifier, and 0.5 part of ammonium persulfate were respectively supplied. 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 exchange water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94 parts of butyl acrylate, 2 parts of acrylonitrile, 2 parts of methacrylic acid, N- A monomer composition was obtained by mixing 1 part of methylolacrylamide and 1 part of acrylamide. This monomer composition was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was terminated by further stirring at 70 ° C. for 3 hours, and an aqueous dispersion containing a (meth) acrylic polymer as a porous membrane binder was produced.
The obtained (meth) acrylic polymer had a volume average particle diameter D50 of 0.36 μm and a glass transition temperature of −45 ° C.

[1-2. Production of slurry for porous membrane]
Alumina particles (“AKP-3000” manufactured by Sumitomo Chemical Co., Ltd., volume average particle diameter D50 = 0.45 μm, tetrapod-like particles) were prepared as non-conductive particles.
As the water-soluble polymer, carboxymethylcellulose having a degree of etherification of 0.8 to 1.0 (“Daicel 1220” manufactured by Daicel Finechem) was used. The viscosity of a 1% aqueous solution of the water-soluble polymer was 10 mPa · s to 20 mPa · s.

  Non-conductive particles were dispersed by mixing 100 parts of non-conductive particles and 1.5 parts of a water-soluble polymer, and further mixing ion-exchanged water so that the solid concentration was 40% by weight. Further, 6 parts of an aqueous dispersion containing the (meth) acrylic polymer as a binder for the porous film, corresponding to a solid content, and a polyethylene glycol type surfactant (“SN wet 366” manufactured by San Nopco) 0.2 Parts were mixed to produce a porous membrane slurry.

[1-3. Production of particulate polymer)
In a 5 MPa pressure vessel with a stirrer, 74.5 parts of methyl methacrylate, 4 parts of methacrylic acid, 1 part of ethylene dimethacrylate, and 0.5 part of acrylamide as a monomer composition used for producing the core part; 1 part of sodium benzenesulfonate; 150 parts of ion-exchanged water; and 0.5 part of potassium persulfate as a polymerization initiator were added and sufficiently stirred. Then, it heated to 60 degreeC and superposition | polymerization was started. By continuing the polymerization until the polymerization conversion rate reached 96%, an aqueous dispersion containing a particulate polymer constituting the core part was obtained.

  Next, 19.5 parts of styrene and 0.5 part of acrylamide were continuously added to the aqueous dispersion as a monomer composition used for the production of the shell part, and the polymerization was continued by heating to 70 ° C. When the polymerization conversion reached 96%, the reaction was stopped by cooling to produce an aqueous dispersion containing a particulate polymer. The volume average particle diameter D50 of the obtained particulate polymer was 0.45 μm. About the obtained particulate polymer, the core shell ratio and the average ratio by which the outer surface of a core part is covered with a shell part were measured by the method mentioned above.

[1-4. Production of adhesive
The aqueous dispersion of the (meth) acrylic polymer prepared as a binder for the porous film as the binder for the adhesive layer was used in an amount of 100 parts of the aqueous dispersion containing the particulate polymer, and (meth) acrylic. 6 parts by weight of the polymer, and 0.5 part of carboxymethylcellulose having a degree of etherification of 0.8 to 1.0 (“Daicel 1220” manufactured by Daicel Finechem) as a water-soluble polymer are mixed, and ion-exchanged water is further added. Were mixed so that the solid content concentration was 20% to obtain a slurry adhesive.

[1-5. (Manufacture of separator)
An organic porous substrate made of polyethylene (thickness 16 μm, Gurley value 210 s / 100 cc) was prepared as a separator substrate. The slurry for porous film was applied to both surfaces of the prepared separator base material and dried at 50 ° C. for 3 minutes to form a porous film on both surfaces of the separator base material. The thickness per layer of the porous film was 3 μm.
Next, the slurry adhesive was applied onto each porous film by a spray coating method and dried at 50 ° C. for 1 minute. As a result, an adhesive layer having a thickness of 2 μm per layer was provided on the porous film to obtain a separator. This separator was provided with an adhesive layer, a porous membrane, a separator substrate, a porous membrane, and an adhesive layer in this order.
About this separator, blocking resistance was evaluated by the method mentioned above.

[1-6. Production of particulate 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). A 5% aqueous sodium hydroxide solution was added to the mixture containing the particulate binder to adjust the pH to 8. Thereafter, unreacted monomers were removed from the mixture by heating under reduced pressure, and the mixture was cooled to 30 ° C. or lower to obtain an aqueous dispersion containing a desired particulate binder.

[1-7. Production of slurry for negative electrode)
100 parts of artificial graphite (volume average particle diameter: 15.6 μm) and 1 part of a 2% aqueous solution of carboxymethyl cellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a thickener are mixed in an amount equivalent to the solid content, and further ionized Exchange water was added to adjust the solid concentration to 68%, and the mixture was mixed at 25 ° C. for 60 minutes. After adding ion exchange water to the liquid mixture thus obtained to adjust the solid content concentration to 62%, the mixture was further mixed at 25 ° C. for 15 minutes. To this mixed solution, 1.5 parts of an aqueous dispersion containing the above-mentioned negative electrode particulate binder is added in an amount corresponding to the solid content, and ion-exchanged water is added to adjust the final solid content concentration to 52%, and further for 10 minutes. Mixed. This was defoamed under reduced pressure to obtain a negative electrode slurry having good fluidity.

[1-8. (Manufacture of negative electrode)
The negative electrode slurry was applied on a copper foil having a thickness of 20 μm, which was 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.

[1-9. Production of slurry for positive electrode)
100 parts of LiCoO ₂ having a volume average particle diameter of 12 μm as a positive electrode active material, ₂ parts of acetylene black (“HS-100” manufactured by Denki Kagaku Kogyo Co., Ltd.) as a conductive material, and polyvinylidene fluoride (manufactured by Kureha Co., Ltd.) as a positive electrode binder "# 7208") was mixed in two parts corresponding to the solid content, and N-methylpyrrolidone was added thereto to make the total solid content concentration 70%. These were mixed by a planetary mixer to prepare a positive electrode slurry.

[1-10. Production of positive electrode)
The positive electrode slurry was applied onto a 20 μm-thick aluminum foil as a current collector by a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the aluminum 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 positive electrode raw material before pressing. The positive electrode raw material before pressing was rolled by a roll press to obtain a positive electrode after pressing.

[1-11. (Manufacture of lithium ion secondary batteries)
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. The 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.
The lithium ion secondary battery thus obtained was evaluated for cell volume change, high-temperature cycle characteristics, and low-temperature output characteristics before and after the high-temperature cycle test by the method described above.

[1-12. (Manufacture of samples for peel strength measurement)
The positive electrode was cut out into a circle having a diameter of 13 mm to obtain a circular positive electrode. The negative electrode was cut into a circle having a diameter of 14 mm to obtain a circular negative electrode. Further, the separator was cut into a circle having a diameter of 18 mm to obtain a circular separator.
A positive electrode or a negative electrode was placed on one side of a circular separator so that the surface on the electrode active material layer side was in contact with the separator. Thereafter, a heat press treatment was performed at a temperature of 80 ° C. and a pressure of 0.5 MPa for 10 seconds, and the positive electrode and the negative electrode were pressure bonded to the separator to obtain a laminate including the positive electrode or the negative electrode and the separator.

  Using the sample thus obtained, the peel strength between the electrode and the porous film was measured by the method described above.

[Example 2]
In the monomer composition used for the production of the core part according to the step [1-3], the amount of methyl methacrylate was changed to 74.75 parts, and the amount of acrylamide was changed to 0.25 parts.
Moreover, in the monomer composition used for manufacturing the shell part according to the above-mentioned step [1-3], the amount of styrene was changed to 19.75 parts, and the amount of acrylamide was changed to 0.25 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 3]
In the monomer composition used for producing the core part according to the above step [1-3], the amount of methyl methacrylate was changed to 72.5 parts, and the amount of acrylamide was changed to 2.5 parts.
Moreover, in the monomer composition used for manufacturing the shell part according to the above-mentioned step [1-3], the amount of styrene was changed to 17.5 parts, and the amount of acrylamide was changed to 2.5 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 4]
In the monomer composition used for the production of the core part according to the step [1-3], the amount of methyl methacrylate was changed to 74.94 parts, and the amount of acrylamide was changed to 0.06 parts.
Moreover, in the monomer composition used for manufacturing the shell part according to the above-mentioned step [1-3], the amount of styrene was changed to 19.94 parts, and the amount of acrylamide was changed to 0.06 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 5]
In the monomer composition used for producing the core part according to the above step [1-3], the amount of methyl methacrylate was changed to 71 parts, and the amount of acrylamide was changed to 4 parts.
Moreover, the monomer composition used for manufacture of the shell part which concerns on the said process [1-3] WHEREIN: The quantity of styrene was changed into 16 parts and the quantity of acrylamide was changed into 4 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 6]
In the monomer composition used for producing the core part according to the above step [1-3], the amount of methyl methacrylate was changed to 74 parts, and the amount of acrylamide was changed to 1 part.
Moreover, in the monomer composition used for manufacture of the shell part according to the step [1-3], the amount of styrene was changed to 20 parts, and acrylamide was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 7]
In the monomer composition used for the production of the core part according to the step [1-3], the amount of methyl methacrylate was changed to 75 parts, and acrylamide was not used.
Moreover, in the monomer composition used for manufacturing the shell part according to the step [1-3], the amount of styrene was changed to 19 parts, and the amount of acrylamide was changed to 1 part.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 8]
In the monomer composition used for producing the core part according to the above step [1-3], the amount of methyl methacrylate was changed to 75.35 parts, and the amount of ethylene dimethacrylate was changed to 0.15 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 9]
In the monomer composition used for the production of the core part according to the above step [1-3], 64.5 parts of acrylonitrile and 10 parts of 2-ethylhexyl acrylate were used in combination instead of 74.5 parts of methyl methacrylate. .
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 10]
In the monomer composition used for the production of the shell part according to the step [1-3], 10 parts of styrene and 9.5 parts of acrylonitrile were used in combination instead of 19.5 parts of styrene.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 11]
In the monomer composition used for the production of the shell part according to the above step [1-3], 18.5 parts of styrene and 1 part of ethylene dimethacrylate were used in combination instead of 19.5 parts of styrene.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 12]
In the step [1-5], the thickness per adhesive layer was changed to 0.5 μm by changing the coating amount of the adhesive.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 13]
In the step [1-5], the thickness per adhesive layer was changed to 4 μm by changing the amount of adhesive applied.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 14]
In the step [1-3], the amount of sodium dodecylbenzenesulfonate was changed to 2 parts.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 15]
In the step [1-3], the amount of sodium dodecylbenzenesulfonate was changed to 0.5 part.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Example 16]
Softwood bleached kraft pulp (NBKP) was dispersed in ion-exchanged water so as to be 2% by weight, and beaten by cycling to a condition where the number average fiber length was 500 nm or less using a double risk refiner. A treatment liquid having a number average fiber length of 500 nm or less was treated with a high-pressure homogenizer (“LAB-1000” manufactured by SMT Corporation) under the condition of 1000 bar to obtain a cellulose fiber precursor dispersion. This precursor dispersion was concentrated to about 10% by weight by treating for 30 minutes under a condition of 10,000 rpm using a centrifugal separator to obtain a dispersion of cellulose fibers. The number average fiber length of the cellulose fibers in this cellulose fiber dispersion was 500 nm.

In the step [1-4], the dispersion of cellulose fiber produced in Example 16 was added to the adhesive so that the weight ratio of particulate polymer / cellulose fiber = 9/1.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 1]
An N-methylpyrrolidone solution of polyvinylidene fluoride (“Kureha“ # 9305 ”, concentration 8%) was prepared.
In the step [1-5], the polyvinylidene fluoride solution was used instead of the adhesive.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 2]
In the monomer composition used for producing the core part according to the above step [1-3], 74.5 parts of methyl methacrylate, 4 parts of methacrylic acid, 1 part of ethylene dimethacrylate, and 0.5 part of acrylamide are combined. Instead of using 70 parts of methacrylic acid, 25 parts of acrylonitrile, and 5 parts of methacrylic acid.
Moreover, in the said process [1-3], the monomer composition used for manufacture of a shell part was not added.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 3]
In a 5 MPa pressure vessel equipped with a stirrer, 99.9 parts of styrene, 0.1 part of methacrylic acid, 1 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator, After sufficiently stirring, the polymerization was started by heating to 80 ° C. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to obtain a mixture containing polystyrene particles. A 5% aqueous sodium hydroxide solution was added to the mixture containing the polystyrene particles to adjust the pH to 8. Thereafter, unreacted monomers were removed from the mixture containing polystyrene particles by distillation under reduced pressure under heating, and then cooled to 30 ° C. or lower to obtain an aqueous dispersion containing the desired polystyrene particles. The volume average particle diameter of the polystyrene particles was 0.45 μm.

In the step [1-4], an aqueous dispersion containing the polystyrene particles produced in Comparative Example 3 was used instead of the aqueous dispersion containing the particulate polymer.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 4]
In the monomer composition used for producing the core part according to the above step [1-3], 74.5 parts of methyl methacrylate, 4 parts of methacrylic acid, 1 part of ethylene dimethacrylate, and 0.5 part of acrylamide are combined. Instead of 60 parts 2-ethylhexyl acrylate, 15 parts styrene and 5 parts methacrylic acid.
Moreover, in the monomer composition used for manufacture of the shell part according to the step [1-3], the amount of styrene was changed to 20 parts, and acrylamide was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 5]
In the monomer composition used for producing the core part according to the above step [1-3], 74.5 parts of methyl methacrylate, 4 parts of methacrylic acid, 1 part of ethylene dimethacrylate, and 0.5 part of acrylamide are combined. Instead of using 50 parts of methyl methacrylate, 25 parts of acrylonitrile and 5 parts of methacrylic acid.
Moreover, in the monomer composition used for manufacture of the shell part according to the step [1-3], the amount of styrene was changed to 20 parts, and acrylamide was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[Comparative Example 6]
In the monomer composition used for producing the core part according to the above step [1-3], 74.5 parts of methyl methacrylate, 4 parts of methacrylic acid, 1 part of ethylene dimethacrylate, and 0.5 part of acrylamide are combined. In place of the above, 50 parts of methyl methacrylate, 25 parts of 2-ethylhexyl acrylate and 5 parts of methacrylic acid were used in combination.
Moreover, in the monomer composition used for manufacturing the shell part according to the above-mentioned step [1-3], 20 parts of acrylonitrile was used instead of styrene, and acrylamide was not used.
Except for the above items, the lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1.

[result]
The results of Examples and Comparative Examples are shown in Tables 1 to 5 below. In the following table, the meanings of the abbreviations are as follows.
“EDMA”: ethylene dimethacrylate “MMA”: methyl methacrylate “MAA”: methacrylic acid “AAm”: acrylamide “AN”: acrylonitrile “2-EHA”: 2-ethylhexyl acrylate “PVDF”: polyvinylidene fluoride “PST” : Polystyrene “Tg”: Glass transition temperature “ST”: Styrene “Core shell ratio”: Ratio of average thickness of shell part to volume average particle diameter of particulate polymer “MV”: Volume average particle diameter “BA”: Butyl acrylate “NMA”: N-methylolacrylamide “CMC”: Carboxymethylcellulose “Coating ratio”: Average ratio in which the outer surface of the core part is covered by the shell part. Represents the amount of monomer indicated by the abbreviation.
Furthermore, in the section of the water-soluble polymer, the numerical value next to the abbreviation for the water-soluble polymer represents the amount of the water-soluble polymer indicated by the abbreviation.

[Consideration]
From the results of Examples and Comparative Examples, it was confirmed that the adhesive of the present invention can realize a lithium ion secondary battery excellent in adhesiveness and excellent in low-temperature output characteristics and high-temperature cycle characteristics. In particular, since the cell volume change rate ΔX is significantly smaller in the examples than in the comparative example, the particulate polymer contains amide monomer units, thereby effectively suppressing the generation of gas due to charge / discharge. It was confirmed that it was possible.
In addition, in the examples, since excellent results were obtained as blocking resistance, the adhesive layer obtained from the adhesive of the present invention is excellent in blocking resistance in a state where it is not swollen in the electrolyte solution, and It was confirmed that high adhesiveness was developed only after swelling in the electrolytic solution.

Claims (5)

An adhesive for bonding members constituting a lithium ion secondary battery,
The adhesive comprises a particulate polymer;
The particulate polymer has a core-shell structure including a core part and a shell part covering an outer surface of the core part,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
The shell part is made of a polymer having a swelling degree with respect to the electrolytic solution of greater than 1 and 4 or less,
The degree of swelling with respect to the electrolytic solution is the weight W0 of a test piece prepared by drying the polymer of the core part or the polymer of the shell part under the conditions of 25 ° C. and 48 hours, and the test piece is the electrolytic solution. And the weight W1 of the test piece after being immersed at 60 ° C. for 72 hours, and the degree of swelling = W1 / W0,
The electrolyte solution is a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30 / 1.5), and LiPF ₆ with respect to the mixed solvent. A solution dissolved at a concentration of 1 mol / liter,
It said particulate fraction of the amide monomer units in the polymer is 20 wt% or less than 0.1 wt%, the adhesive for lithium ion secondary battery. The glass transition temperature of the polymer of the core part is 0 ° C. or more and 100 ° C. or less,
2. The adhesive for a lithium ion secondary battery according to claim 1, wherein a glass transition temperature of the polymer of the shell portion is 50 ° C. or higher and 200 ° C. or lower.   The adhesive for lithium ion secondary batteries according to claim 1 or 2, which is an adhesive for bonding the porous film and the electrode. A separator substrate and an adhesive layer;
The adhesive layer comprises a particulate polymer;
The particulate polymer has a core-shell structure including a core part and a shell part covering an outer surface of the core part,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
The shell part is made of a polymer having a swelling degree with respect to the electrolytic solution of greater than 1 and 4 or less,
The degree of swelling with respect to the electrolytic solution is the weight W0 of a test piece prepared by drying the polymer of the core part or the polymer of the shell part under the conditions of 25 ° C. and 48 hours, and the test piece is the electrolytic solution. And the weight W1 of the test piece after being immersed at 60 ° C. for 72 hours, and the degree of swelling = W1 / W0,
The electrolyte solution is a mixed solvent of ethylene carbonate, diethyl carbonate and vinylene carbonate (volume mixing ratio ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30 / 1.5), and 1 mol of LiPF ₆ with respect to the solvent. Is a solution dissolved at a concentration of / liter,
It said particulate fraction of the amide monomer units in the polymer is less than or equal to 20 wt% 0.1 wt%, the separator for lithium ion secondary battery. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a separator,
A lithium ion secondary battery, wherein the separator is a separator for a lithium ion secondary battery according to claim 4.