JP2015028842A - Adhesive agent for lithium ion secondary batteries, lithium ion secondary battery separator, and lithium ion secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive agent for lithium ion secondary batteries which is superior in adhesiveness and enables the materialization of a lithium ion secondary battery having an excellent low-temperature output characteristic.SOLUTION: An adhesive agent for gluing members included by a lithium ion secondary battery to each other comprises polymer particles. The polymer particles each have a core-shell structure in which each polymer particle has an outermost shell part and a core part located inside the shell part. The core part is made of polymer, of which the swelling degree to an electrolytic solution is 5 to 30 times. The shell part is made of polymer, of which the swelling degree to the electrolytic solution is more than 1 to 4 times.

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 (see Patent Document 1).

  Furthermore, techniques such as Patent Documents 2 to 7 are also known.

International Publication No. 2011/040474 International Publication No. 2005/029614 International Publication No. 2011/068215 JP 2005-11822 A JP 2012-104406 A JP 2013-012357 A International Publication No. 2007-088979

  However, the conventional lithium ion secondary battery including the separator has poor adhesion between the separator and the electrode, and has a problem in low-temperature output characteristics.

  The present invention was devised in view of the above-mentioned problems, and is an adhesive for a lithium ion secondary battery capable of realizing a lithium ion secondary battery excellent in adhesiveness and excellent in low-temperature output characteristics; It aims at providing the separator for lithium ion secondary batteries which can implement | achieve the lithium ion secondary battery which is excellent in the property, and was excellent in the low temperature output characteristic; and the lithium ion secondary battery excellent in the low temperature output characteristic.

As a result of intensive studies to solve the above problems, the present inventors have found that an adhesive containing a particulate polymer having a core-shell structure formed of a polymer that can swell with a predetermined degree of swelling with respect to an electrolytic solution is bonded. The present invention has been completed by finding that a lithium ion secondary battery having excellent performance and low temperature output characteristics can be realized.
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 shell portion that is outermost in the particulate polymer and a core portion that is inside the shell portion,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
An adhesive for a lithium ion secondary battery, wherein the shell part is made of a polymer having a swelling degree with respect to an electrolytic solution of greater than 1 and 4 or less.
[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], wherein the shell portion has a thickness of 1% or more and 30% or less with respect to a volume average particle diameter of the particulate polymer. .
[4] The adhesive for lithium ion secondary batteries according to any one of [1] to [3], which is an adhesive for bonding the porous film and the electrode.
[5] A separator base, a porous film provided on the surface of the separator base, and an adhesive layer provided on the surface of the porous film,
The adhesive layer comprises a particulate polymer;
The particulate polymer has a core-shell structure including a shell portion that is outermost in the particulate polymer and a core portion that is inside the shell portion,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
A separator for a lithium ion secondary battery, wherein the shell portion is made of a polymer having a swelling degree with respect to an electrolytic solution of greater than 1 and 4 or less.
[6] The separator for a lithium ion secondary battery according to [5], wherein the porous film includes non-conductive particles.
[7] 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 [5] or [6].

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

FIG. 1 is a cross-sectional view schematically showing an example of a particulate polymer.

  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.

  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.

[1.1. (Particulate polymer)
FIG. 1 is a cross-sectional view schematically showing an example of a particulate polymer. As shown in FIG. 1, the particulate polymer 100 has a core-shell structure including a core part 110 and a shell part 120. Here, the shell portion 120 is an outermost layer portion in the particulate polymer 100 and is exposed on the surface 100 </ b> S of the particulate polymer 100. The core part 110 is a part located inside the shell part 120.

  In the particulate polymer, the core part and the shell part are each made of a polymer having a predetermined degree of swelling with respect to the electrolytic solution. The adhesive layer produced using the adhesive containing the particulate polymer includes, for example, a lithium ion secondary battery separator (hereinafter sometimes referred to as “separator” as appropriate), a member constituting the battery, such as an electrode, and the like. Excellent adhesion. Moreover, if the separator and the electrode are bonded using the adhesive of the present invention in a lithium ion secondary battery provided with a separator, the low-temperature output characteristics of the lithium ion secondary battery can be improved. Furthermore, normally, the high-temperature cycle characteristics of the lithium ion secondary battery can be improved. In addition, 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 surface causes blocking even when wound. Difficult and easy to handle. 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.

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.
Here, in order to improve the adhesiveness between the separator and the electrode, it is conceivable to provide an adhesive layer between the separator and the electrode. However, in the conventional adhesive layer, the volume of the adhesive layer may be increased due to the large swelling of the polymer component contained in the adhesive layer.
When such a phenomenon occurs, the distance between the positive electrode and the negative electrode increases, resulting in an increase in the internal resistance of the battery and a non-uniform reaction field between the lithium ions and the electrode active material. May decrease.

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.
Further, since the degree of swelling of the polymer in the shell portion with respect to the electrolytic solution is controlled to be small, the particulate polymer is unlikely to cause a large increase in volume due to swelling in the electrolytic solution. For this reason, the adhesive layer containing the particulate polymer suppresses an increase in the volume of the adhesive layer in the electrolytic solution.
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.

  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.

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.
Even when the core part is greatly swollen in the electrolytic solution, it is presumed that the core part is covered with the shell part whose degree of swelling is suppressed, so that the particulate polymer does not easily increase in volume.

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. Further, as described above, in the lithium ion secondary battery, the electrode active material may expand and contract due to charge / discharge. Therefore, when charging / discharging of the lithium ion secondary battery is repeated, a gap is formed between the separator and the electrode, the distance between the positive electrode and the negative electrode is gradually increased, and the battery capacity may be reduced.
On the other hand, since the adhesive layer formed using the adhesive according to the present invention includes the particulate polymer, it is excellent in adhesiveness with the separator and the electrode as described above. Therefore, in a lithium ion secondary battery provided with this adhesive layer, even if charging and discharging are repeated, it is difficult to form a gap between the separator and the electrode, so that the battery capacity is unlikely to decrease. Thereby, it is guessed that the outstanding high temperature cycling characteristic is implement | achieved.

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, and develops adhesiveness only after swelling 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.

[1.1.1. (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 normally improved by making the swelling degree of the polymer of a core part more than the lower limit of the said range. Furthermore, the life of the lithium ion secondary battery can be normally extended by setting it to the upper limit value or less.

Here, the electrolytic solution used for measuring the degree of swelling of the polymer in the core part 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; SP value 12.7 (cal / cm ³ ) ^1/2 ) As a supporting electrolyte, a solution in which LiPF ₆ is dissolved 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 and 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, the lifetime of a secondary battery can be lengthened by making it into an upper limit or less.

  Further, the glass transition temperature of the polymer of the core part is preferably 0 ° C. or higher, more preferably 10 ° C. or higher, further preferably 20 ° C. or higher, particularly preferably 30 ° C. or higher, preferably 100 ° C. or lower, more preferably. Is 90 ° C. or lower, particularly preferably 80 ° C. or lower. 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 enhanced. Furthermore, the lifetime of a lithium ion secondary battery can be lengthened by setting it as below an upper limit. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be normally improved by keeping the glass transition temperature of the polymer of a core part in the said range. 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. Adhesiveness with an electrode can be improved by making the diameter of a core part more than the lower limit of the said range. Moreover, ion conductivity can be raised by making it below an upper limit.

  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 portion with respect to the electrolytic solution is usually greater than 1 time, preferably 1.05 times or more, more preferably 1.1 times or more, and further preferably 1.2 times or more. In addition, it is usually 4 times or less, preferably 3.5 times or less, more preferably 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. In addition, since the degree of swelling of the shell portion with respect to the electrolytic solution is controlled to be small, an increase in volume due to swelling of the particulate polymer can be suppressed. Therefore, since the internal resistance of the lithium ion secondary battery can be reduced, battery characteristics can be maintained well. Moreover, the low temperature output characteristic of a lithium ion secondary battery can be normally 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 normally improved by making it below an upper limit.

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

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, particularly preferably 60% by weight or more, and preferably 100% by 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.

  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 setting the glass transition temperature of the polymer in 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 improved. Moreover, the adhesiveness of a contact bonding layer can further be improved by setting it as below an upper limit. In addition, by keeping the glass transition temperature of the polymer of the shell part within the above range, it is usually possible to improve the cycle characteristics of the lithium ion secondary battery.

  The shell portion preferably has a thickness that falls within a predetermined range with respect to the volume average particle diameter of the particulate polymer. Specifically, the 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% or less. More preferably, it is 25% or less, particularly preferably 20% or less. By setting the thickness of the shell part to be equal to or more than the lower limit value 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.

  Here, the thickness of the shell part is determined from the volume average particle diameter of the particulate polymer after forming the shell part, and the particulate polymer before forming the shell part obtained in the production process of the particulate polymer ( That is, it can be measured as a difference obtained by subtracting the volume average particle diameter of the particulate polymer constituting the core portion.

[1.1.3. (Optional components)
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 50% by weight or more, more preferably 55% by weight or more, particularly preferably 60% by weight or more, preferably 99.9% by weight or less, More preferably, it is 99 weight% or less, Most preferably, it is 98 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 obtained by a continuous multi-stage emulsion polymerization method and a multi-stage suspension polymerization method in which the polymer in the previous stage is sequentially coated with the polymer in 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, the particulate polymer which has a core-shell structure can be obtained by polymerizing the monomer which comprises a shell part in presence of the particulate polymer which comprises this core part. 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.

  The volume average particle diameter of the particulate polymer constituting the core part and the volume average particle diameter of the particulate polymer after forming the shell part can be adjusted, for example, by adjusting the amount of emulsifier, the amount of monomer, etc. Can be in the desired range.

[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 is usually used, and among them, a thermoplastic elastomer is preferably used. In particular, a polymer containing an amide monomer unit is preferably used as the binder for the adhesive layer. Here, the 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.

  A polymer having an amide monomer unit can capture halide ions in the electrolyte. Therefore, since decomposition | disassembly of the electrolyte solution and SEI (Solid Electrolyte Interface) caused by halide ion can be suppressed, generation | occurrence | production of the gas accompanying charging / discharging can be suppressed. Moreover, the polymer containing an amide monomer unit can capture the transition metal ion in the electrolytic solution. For example, metal ions eluted from the positive electrode can be captured by a polymer containing amide monomer units. Therefore, it is possible to suppress the precipitation of the transition metal at the negative electrode accompanying charge / discharge. Therefore, by using the polymer containing the amide monomer unit as the binder for the adhesive layer in this way, the degree of decrease in battery capacity due to charging / discharging can be reduced, so that the cycle characteristics of the lithium ion secondary battery are improved. be able to.

Moreover, if the polymer containing an amide monomer unit is used, generation | occurrence | production of the gas accompanying charging / discharging can be suppressed as mentioned above. Therefore, generation | occurrence | production of the space | gap by the gas can be suppressed. Therefore, it is possible to further improve the low temperature output characteristics of the lithium ion secondary battery.
Here, the generation amount of the gas can be evaluated by the volume change of the cell of the lithium ion secondary battery when charging and discharging are repeated.

  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, from the viewpoint of enhancing the durability of the adhesive layer, carboxylic acid amide monomers are preferable, unsaturated carboxylic acid amide compounds are more preferable, (meth) acrylamide and N-hydroxymethyl (meth). Acrylamide is particularly preferred.
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 cycle characteristic of a lithium ion secondary battery can be improved by being 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, a polymer as a binder for an 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. Even in the middle, 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, particularly preferably 15 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. solvent〕
The adhesive of the present invention usually contains a solvent. As the solvent, water is preferably used. Since the particulate polymer and the binder for the adhesive layer are usually water-insoluble, when water is used as the solvent, the particulate polymer and the binder for the adhesive layer are dispersed in the form of particles in water. .

  As the solvent, a solvent other than water may be used in combination with water. Examples of the solvent that can be used in combination with water include cycloaliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; ethyl acetate and acetic acid Esters such as butyl, γ-butyrolactone, ε-caprolactone; nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether: methanol, ethanol, isopropanol, ethylene glycol, ethylene glycol monomethyl ether, and the like Alcohols; amides such as N-methylpyrrolidone (NMP) and N, N-dimethylformamide; and the like. 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.

[1.4. Non-conductive particles
The adhesive of the present invention may further contain non-conductive particles. For example, particles selected from those described below 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.

[1.5. Water-soluble polymer)
The adhesive of the present invention can further 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 diffusivity which a particulate polymer has can fully be exhibited by making it into an upper limit or less.

[1.6. (Optional ingredients)
The adhesive of this invention can contain arbitrary components other than the particulate polymer mentioned above, the binder for contact bonding layers, a solvent, a nonelectroconductive particle, and a water-soluble polymer. 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.

[1.7. 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.

[1.8. (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.

[1.9. (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]
By applying the adhesive of the present invention on a suitable substrate and drying it as necessary, an adhesive layer can be produced as a film formed from the solid content of the adhesive. 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 of the present invention can be applied directly to the electrode surface to produce an adhesive layer as a film formed on the electrode surface.

  The adhesive layer thus obtained contains the particulate polymer according to the present invention. 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. 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 crosslinking 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 below an upper limit, it can prevent that the raise of resistance by an contact bonding layer becomes excessive and a cycle characteristic falls.

  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 making the thickness of the adhesive layer equal to or greater than the lower limit of the above range, the adhesiveness of the adhesive layer can be increased. Moreover, by making it below an upper limit, it can prevent that the raise of resistance by an contact bonding layer becomes excessive and a cycle characteristic falls.

[3. Lithium ion secondary battery separator]
The separator of this invention is equipped with the separator base material, the porous film provided in the surface of the separator base material, and the said contact bonding layer provided in 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 porous film and the electrode can be improved in the electrolytic solution. Therefore, the low-temperature output characteristics of the lithium ion secondary battery can be improved, and moreover, usually the high-temperature cycle characteristics can be improved. Further, since the adhesive layer has a low adhesive force in a state where it is not swollen in the electrolytic solution, it is difficult to cause blocking even when it is 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; Non-work cloth; aggregate 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 the material of such inorganic particles include aluminum oxide (alumina), aluminum oxide hydrate (boehmite (AlOOH), gibbsite (Al (OH) ₃ ), silicon oxide, magnesium oxide (magnesia), hydroxylation. Oxide particles such as magnesium, calcium oxide, titanium oxide (titania), BaTiO ₃ , ZrO ₂ , alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond Insoluble ion crystal particles such as barium sulfate, calcium fluoride, barium fluoride, etc., clay fine particles such as talc, montmorillonite, etc. Among these, from the viewpoint of stability in the electrolyte and potential stability Oxide particles are preferred, and especially water absorption is low and heat resistance (for example, 180 ° C. or higher). Of titanium oxide, aluminum oxide, aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferable, and aluminum oxide, aluminum oxide hydrate, magnesium oxide and magnesium hydroxide are more preferable. Aluminum oxide is particularly preferable, and one of these may be used alone, or two or more may be used in combination at any ratio.

  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 such organic particle materials include various polymer compounds such as polystyrene, polyethylene, polyimide, melamine resin, and phenol resin. The polymer compound forming the particles may 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, or the like. The organic particles may be formed of a mixture of two or more kinds of 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 compound 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, 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 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 in combination of 2 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 film state rally film. 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 thermal crosslinking 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 this invention is equipped with the contact bonding layer mentioned above on the porous film. For such a separator, for example, a laminate including a separator base material and a porous film is prepared, and this laminate is used as a base material, and the adhesive layer is formed on the porous film of the laminate by the method for manufacturing an adhesive layer described above. Can be manufactured. 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. In general, the lithium ion secondary battery of the present invention is excellent in 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 a lithium ion secondary battery, there is an adhesive layer between the electrode and the porous membrane of the separator, and the particulate polymer contained in this adhesive layer exhibits adhesiveness in the electrolyte solution, so that the electrode and the porous film are porous. It is strongly bonded to the membrane.

  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 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 or less. It is. 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 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 even more preferably 5 μm or more. Is 100 μm or less, more preferably 50 μm or less, and still more preferably 20 μm 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 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 the reinforcing material, a tough and flexible electrode can be obtained, and excellent long-term 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 cell volume change before and after high temperature cycle test]
The lithium ion secondary battery of the 800 mAh wound type cell manufactured by the Example and the comparative example was left still for 24 hours in 25 degreeC environment. 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. This wound cell 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 wound cell 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 suppression capability of gas generation, so that the value of this cell volume change rate (DELTA) X is small.

[2. (Measurement method of peel strength between porous membrane and electrode)
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 an electrolytic solution, a mixed solvent of ethylene carbonate and diethyl carbonate (volume mixing ratio EC / DEC / VC = 68.5 / 30 / 1.5; SP value 12.7 (cal / cm ³ ) ^1/2 ) Was used as a supporting electrolyte in which LiPF ₆ was dissolved in a solvent at a concentration of 1 mol / liter.
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.

[3. (Method for evaluating high-temperature cycle characteristics)
The lithium ion secondary battery of the 800 mAh wound type cell manufactured by the Example and the comparative example was left still for 24 hours in 25 degreeC environment. 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. (Evaluation method of blocking resistance)
The separators produced in the examples and comparative examples were cut into squares of 5 cm wide × 5 cm long and 4 cm wide × 4 cm long to obtain 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 separators of each sample 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.

[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, the discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., 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 low temperature output characteristics, 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. (Measurement method of core-shell ratio)
From the volume average particle diameter of the particulate polymer after forming the shell part, 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). The thickness of the shell portion was measured by subtracting the volume average particle diameter of the polymer. The core-shell ratio was calculated by dividing the measured shell thickness by the volume average particle diameter of the particulate polymer.
The volume average particle diameter is a particle whose cumulative volume calculated from the small diameter side is 50% in the particle diameter distribution measured by a laser diffraction particle size distribution measuring apparatus “SALD-3100 (manufactured by Shimadzu Corporation)”. The diameter.

[9. Method for evaluating metal deposition on negative electrode]
The lithium ion secondary battery of the 800 mAh wound type cell manufactured by the Example and the comparative example was left still for 24 hours in 25 degreeC environment. 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. Furthermore, the charge / discharge operation was repeated 1000 cycles under the same conditions as described above in a 60 ° C. environment. Thereafter, the battery was disassembled, the negative electrode was taken out, and metal deposition on the negative electrode was evaluated.
Precipitation of the metal in the negative electrode was evaluated using an ICP emission spectroscopic analyzer “SPS3000 (manufactured by SII NanoTechnology Co., Ltd.) based on the weight ratio of cobalt in the negative electrode.
It shows that the metal precipitation has occurred in the negative electrode, so that the cobalt weight in a negative electrode is large.

[Example 1]
(1-1. Production of binder for porous membrane)
In a reactor equipped with a stirrer, 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (product name “Emal 2F” manufactured by Kao Chemical Co., Ltd.) as an emulsifier, and 0.5 part of ammonium persulfate, The gas phase portion was replaced with nitrogen gas, and the temperature was raised to 60 ° C.
On the other hand, in a separate container, 50 parts of ion 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 mixture was obtained by mixing 1 part of methylolacrylamide and 1 part of acrylamide. This monomer mixture 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 further terminated by stirring at 70 ° C. for 3 hours, and an aqueous dispersion containing an acrylic polymer as a porous membrane binder was produced.
The obtained 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 (manufactured by Sumitomo Chemical Co., Ltd., product name “AKP-3000”, volume average particle diameter D50 = 0.45 μm, tetrapot-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 (manufactured by Daicel Finechem, product name “Dacel1220”) was prepared. The viscosity of a 1% aqueous solution of this water-soluble polymer was 10 Pa · s to 20 mPa · s.

  100 parts of non-conductive particles and 1.5 parts of a water-soluble polymer were mixed, and ion-exchanged water was further mixed so that the solid content concentration was 40% by mass to disperse the non-conductive particles. Furthermore, 6 parts of an aqueous dispersion containing the above acrylic polymer as a binder for the porous film is equivalent to a solid content, and 0.2 part of a polyethylene glycol type surfactant (manufactured by San Nopco, product name “SN Wet 366”) Were mixed to produce a slurry for a porous membrane.

(1-3. Production of particulate polymer)
In a 5 MPa pressure vessel with a stirrer, 75 parts of methyl methacrylate, 4 parts of methacrylic acid and 1 part of ethylene dimethacrylate as monomer composition used for the production of the core part; 1 part of sodium dodecylbenzenesulfonate as emulsifier; ion-exchanged water 150 parts; and 0.5 part of potassium persulfate as a polymerization initiator was added and stirred sufficiently. 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.

  To this aqueous dispersion, 20 parts of styrene as a monomer composition used for the production of the shell part was added all at once, and heated to 70 ° C. to continue polymerization. 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 was measured by the method mentioned above.

(1-4. Production of adhesive)
100 parts by weight of the aqueous dispersion containing the particulate polymer, 6 parts by weight of the aqueous dispersion of the acrylic polymer prepared as the binder for the porous film as the binder for the adhesive, and Mix 0.5 parts of carboxymethylcellulose having a degree of etherification of 0.8 to 1.0 (manufactured by Daicel Finechem, product name “Daicel1220”), and further mix ion-exchanged water so that the solid content is 20%. A slurry adhesive was obtained.

(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 of each other eardrum was 3 μm.
Next, the above slurry-like 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.
This separator was evaluated for blocking resistance by the method described 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 composition 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 content concentration to 68%, and the mixture was mixed at 25 ° C. for 60 minutes. Ion exchange water was added to the liquid mixture thus obtained to adjust the solid content concentration to 62%, and the mixture was further mixed at 25 ° C. for 15 minutes. To this mixed solution, 1.5 parts of the above aqueous dispersion containing the particulate binder is added in an amount corresponding to the solid content, and ion-exchanged water is further 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. Production 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 the positive electrode active material, ₂ parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., product name “HS-100”) as the conductive material, and polyvinylidene fluoride as the positive electrode binder ( 2 parts of a product name “# 7208” manufactured by Kureha Co., Ltd. were mixed in an amount 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 obtain 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 with a roll press to obtain a positive electrode.

(1-11. Production of negative electrode / separator / positive electrode laminate)
The positive electrode was cut into a circle having a diameter of 13 mm to obtain a circular positive electrode. The negative electrode was cut into a circle with 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.

  Further, only the negative electrode or the positive electrode was placed on one side of the circular separator so as to be in contact with the separator on the surface on the electrode active material layer side. Thereafter, a heat press treatment is 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 are pressure-bonded to the separator to obtain a laminate including the positive electrode and the separator, and a laminate including the negative electrode and the separator. It was. Using these laminates, the peel strength between the porous membrane and the electrode was measured by the method described above.

(1-12. Production of lithium ion secondary battery)
The pressed positive electrode was cut out to 49 × 5 cm ² . A separator cut out to 55 × 5.5 cm ² was disposed on the positive electrode active material layer of the cut out positive electrode. Furthermore, the negative electrode after pressing was cut into a square of 50 × 5.2 cm ² , and the cut negative electrode was arranged on the side opposite to the positive electrode of the separator so that the surface on the negative electrode active material layer side faced the separator. This was wound by a winding machine to obtain a wound body. The wound body was pressed at 60 ° C. and 0.5 MPa to obtain a flat body. 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, low temperature output characteristics, and metal deposition on the negative electrode before and after the high temperature cycle test by the above-described methods.

[Example 2]
In the monomer composition used for producing the core part according to the step (1-3), the amount of methyl methacrylate was changed to 75.85 parts, and the amount of ethylene dimethacrylate was changed to 0.15 parts.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 3]
In the monomer composition used for producing the core part according to the step (1-3), the amount of methyl methacrylate was changed to 71.5 parts, and the amount of ethylene dimethacrylate was changed to 4.5 parts.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 4]
In the monomer composition used for producing the core part according to the step (1-3), the amount of methyl methacrylate was changed to 75.95 parts, and the amount of ethylene dimethacrylate was changed to 0.05 parts.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 5]
In the monomer composition used for manufacturing the core part according to the step (1-3), 55 parts of methyl methacrylate and 20 parts of 2-ethylhexyl acrylate were used in combination instead of 75 parts of methyl methacrylate.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 6]
In the monomer composition used for producing the core part according to the step (1-3), 75 parts of acrylonitrile was used instead of 75 parts of methyl methacrylate.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 7]
In the monomer composition used for producing the core part according to the step (1-3), instead of 75 parts of methyl methacrylate, 65 parts of acrylonitrile and 10 parts of 2-ethylhexyl acrylate were used in combination.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 8]
In the monomer composition used for producing the core part according to the step (1-3), 72 parts of acrylonitrile was used instead of 75 parts of methyl methacrylate, and the amount of ethylene dimethacrylate was changed to 4.0 parts. .
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 9]
In the monomer composition used for manufacturing the shell part according to the step (1-3), 10 parts of styrene and 10 parts of acrylonitrile were used in combination instead of 20 parts of styrene.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 10]
In the monomer composition used for producing the shell part according to the step (1-3), 5 parts of styrene and 15 parts of acrylonitrile were used in combination instead of 20 parts of styrene.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 11]
In the monomer composition used for producing the shell part according to the step (1-3), 20 parts of sodium salt of styrenesulfonic acid was used instead of 20 parts of styrene.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 12]
In the monomer composition used for manufacturing the shell part according to the step (1-3), instead of 20 parts of styrene, 15 parts of sodium salt of styrene sulfonic acid and 5 parts of acrylonitrile were used in combination.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 13]
In the monomer composition used for producing the core part according to the step (1-3), the amount of methyl methacrylate was changed to 72.5 parts, and ethylene dimethacrylate was not used.
Moreover, in addition to 20 parts of styrene, 3.5 parts of ethylene dimethacrylate was used as a monomer composition used for manufacturing the shell part according to the step (1-3).
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 14]
In the monomer composition used for manufacturing the core part according to the step (1-3), the amount of methyl methacrylate was changed to 90 parts.
Moreover, in the monomer composition used for manufacturing the shell part according to the step (1-3), the amount of styrene was changed to 5 parts.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 15]
In the monomer composition used for producing the core part according to the step (1-3), the amount of methyl methacrylate was changed to 52.5 parts, and the amount of ethylene dimethacrylate was changed to 3.5 parts.
Moreover, in the monomer composition used for manufacturing the shell part according to the step (1-3), the amount of styrene was changed to 40 parts.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 16]
In the step (1-5), the thickness per adhesive layer was changed to 0.5 μm by changing the application amount of the slurry adhesive.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 17]
In the step (1-5), the thickness per adhesive layer was changed to 4 μm by changing the application amount of the slurry adhesive.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 18]
In the step (1-5), the separator substrate was changed to a polypropylene organic porous substrate (thickness 15 μm, Gurley value 560 s / 100 cc).
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 19]
In the step (1-5), the separator base material was changed to a non-woven cloth made of cellulose (thickness 25 μm, Gurley value 0.03 s / 100 cc).
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 20]
In the step (1-3), the amount of sodium dodecylbenzenesulfonate as an emulsifier was changed to 2 parts.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 21]
In the step (1-3), the amount of sodium dodecylbenzenesulfonate as an emulsifier was changed to 0.5 part.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 22]
In the step (1-4), 50 parts of alumina particles similar to those used in the slurry for the porous membrane of Example 1 were mixed with the slurry adhesive.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Example 23]
In the step (1-2), polystyrene particles (volume average particle diameter 0.45 μm) were used instead of alumina particles.
In the step (1-4), 50 parts of the polystyrene particles were further added to the slurry adhesive.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Comparative Example 1]
In the step (1-5), an NMP solution of polyvinylidene fluoride (concentration: 12% by weight) is used instead of the adhesive, and a polyvinylidene fluoride layer having a thickness of 2 μm per layer is formed on the porous film instead of the adhesive layer. Formed.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Comparative Example 2]
In the monomer composition used for manufacturing the core part according to the step (1-3), the amount of methyl methacrylate is changed to 70 parts, the amount of methacrylic acid is changed to 5 parts, and instead of ethylene dimethacrylate. 25 parts of acrylonitrile was used.
Moreover, in the said process (1-3), the monomer composition used for manufacture of a shell part was not added.
Further, in the step (1-4), 50 parts of alumina particles similar to those used for the slurry for the porous membrane of Example 1 were mixed with the slurry adhesive.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Comparative Example 3]
In the step (1-4), 100 parts of an aqueous dispersion containing polystyrene particles (volume average particle diameter of polystyrene particles: 45 μm) containing polystyrene particles was used instead of the aqueous dispersion of the particulate polymer.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Comparative Example 4]
In the monomer composition used for producing the core part according to the step (1-3), instead of 75 parts of methyl methacrylate, 4 parts of methacrylic acid and 1 part of ethylene dimethacrylate, 60 parts of 2-ethylhexyl acrylate, styrene 15 parts and 5 parts of methacrylic acid were used.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Comparative Example 5]
In the monomer composition used for producing the core part according to the step (1-3), instead of 75 parts of methyl methacrylate, 4 parts of methacrylic acid and 1 part of ethylene dimethacrylate, 50 parts of methyl methacrylate and 25 acrylonitrile 25 Parts and 5 parts of methacrylic acid were used.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[Comparative Example 6]
In the monomer composition used for producing the core part according to the step (1-3), instead of 75 parts of methyl methacrylate, 4 parts of methacrylic acid and 1 part of ethylene dimethacrylate, 50 parts of methyl methacrylate, 2- 25 parts of ethylhexyl acrylate and 5 parts of methacrylic acid were used.
Moreover, in the monomer composition used for manufacturing the shell part according to the step (1-3), 20 parts of acrylonitrile was used instead of 20 parts of styrene.
A lithium ion secondary battery was manufactured and evaluated in the same manner as in Example 1 except for the above items.

[result]
The results of the examples and comparative examples are shown in the table below. In the following table, the meanings of the abbreviations are as follows. In the table below, the numerical value described next to the abbreviation of the monomer in the monomer section represents the weight part of the monomer.
PE: polyethylene PP: polypropylene PST: polystyrene BA: butyl acrylate AN: acrylonitrile MAA: methacrylic acid NMA: N-methylol acrylamide AAm: acrylamide EDMA: ethylene dimethacrylate MMA: methyl methacrylate 2-EHA: 2-ethylhexyl acrylate Tg: glass Transition temperature NaSS: Sodium salt of styrene sulfonic acid Core shell ratio: Ratio of thickness of shell portion to volume average particle diameter of particulate polymer PVDF: Polyvinylidene fluoride

[Consideration]
In the examples, it was confirmed that the electrode and the porous film of the separator were strongly adhered by the adhesive layer containing the particulate polymer swollen by the electrolytic solution. Thereby, it was confirmed that the contact bonding layer manufactured with the adhesive agent which concerns on this invention has high adhesiveness with respect to the member which comprises a battery.
In the example, a voltage change ΔV lower than that of the comparative example was obtained. Thereby, it was confirmed that the lithium ion secondary battery which concerns on this invention is excellent in a low-temperature output characteristic.

  Furthermore, from the results of the examples and comparative examples described above, the adhesive layer according to the present invention is excellent in blocking resistance, the lithium ion secondary battery of the present invention generates less gas due to charge and discharge, and the present invention It was confirmed that the lithium ion secondary battery of the invention was excellent in high-temperature cycle characteristics.

100 Particulate Polymer 100S Surface of Particulate Polymer 110 Core Part 120 Shell Part

Claims (7)

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 shell portion that is outermost in the particulate polymer and a core portion that is inside the shell portion,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
An adhesive for a lithium ion secondary battery, wherein the shell part is made of a polymer having a swelling degree with respect to an electrolytic solution of greater than 1 and 4 or less. 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, wherein the shell portion has a thickness of 1% or more and 30% or less with respect to a volume average particle diameter of the particulate polymer.   The adhesive for lithium ion secondary batteries as described in any one of Claims 1-3 which is an adhesive agent for adhere | attaching a porous film and an electrode. A separator base material, a porous film provided on the surface of the separator base material, and an adhesive layer provided on the surface of the porous film,
The adhesive layer comprises a particulate polymer;
The particulate polymer has a core-shell structure including a shell portion that is outermost in the particulate polymer and a core portion that is inside the shell portion,
The core portion is made of a polymer having a swelling degree with respect to the electrolyte of 5 to 30 times,
A separator for a lithium ion secondary battery, wherein the shell portion is made of a polymer having a swelling degree with respect to an electrolytic solution of greater than 1 and 4 or less.   The separator for a lithium ion secondary battery according to claim 5, wherein the porous film contains nonconductive particles. A lithium ion secondary battery comprising a positive electrode, a negative electrode, an electrolyte and a separator,
The lithium ion secondary battery whose said separator is a separator for lithium ion secondary batteries of Claim 5 or 6.

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