WO2016110894A1

WO2016110894A1 - Separator for non-aqueous secondary battery, manufacturing method therefor, and non-aqueous secondary battery

Info

Publication number: WO2016110894A1
Application number: PCT/JP2015/006032
Authority: WO
Inventors: 純之介秋池; 慶大浦; 一輝浅井
Original assignee: 日本ゼオン株式会社
Priority date: 2015-01-09
Filing date: 2015-12-04
Publication date: 2016-07-14
Also published as: JP6750506B2; JPWO2016110894A1; KR20170102876A; CN107112480A; CN107112480B; KR102477891B1

Abstract

The present invention provides a separator that is excellent in terms of adhesiveness and ion conductivity in an electrolyte solution. This separator for a non-aqueous secondary battery comprises: a separator substrate; and a functional layer that is formed on at least one surface of the separator substrate. The functional layer has a configuration in which an organic particle phase exists in an irregular shape, the organic particles each having a core-shell structure that includes a core part and a shell part that partially covers an outer surface of the core part. The core part is composed of a polymer that has a degree of swelling in an electrolyte solution of 5-30 times. The shell part is composed of a polymer that has a degree of swelling in an electrolyte solution of 1-4 times. The ratio of the area of the part where the organic particle phase exists to the area of the surface of the separator substrate on which the functional layer is formed is 20-80%.

Description

Nonaqueous secondary battery separator, method for producing the same, and nonaqueous secondary battery

The present invention relates to a separator for a non-aqueous secondary battery, a method for producing a separator for a non-aqueous secondary battery, and a non-aqueous secondary battery.

Non-aqueous secondary batteries such as lithium ion secondary batteries (hereinafter sometimes simply referred to as “secondary batteries”) have the characteristics of being small and light, having high energy density, and capable of repeated charge and discharge. Yes, it is used for a wide range of purposes. The non-aqueous secondary battery generally includes a battery member such as a positive electrode, a negative electrode, and a separator that separates the positive electrode and the negative electrode and prevents a short circuit between the positive electrode and the negative electrode.

Here, in recent years, in secondary batteries, a porous film layer for improving heat resistance and strength, an adhesive layer for bonding battery members, and the like (hereinafter, these are collectively referred to as “functional layer”). In some cases, battery members are used. Specifically, for example, a separator formed by forming a functional layer on a separator base material is used as a battery member.

And the improvement of the separator which has a functional layer is performed actively for the purpose of the further performance enhancement of a secondary battery (for example, refer patent document 1).
Specifically, for example, in Patent Document 1, a thermoplastic polymer having a predetermined glass transition temperature is used for a separator formed by forming an adhesive layer made of a thermoplastic polymer coating layer on a separator substrate made of a polyolefin microporous film. A technique for improving adhesiveness and ionic conductivity has been proposed by adopting a thermoplastic polymer coating layer having a configuration in which a portion including a portion and a portion not including a thermoplastic polymer are present in a sea-island shape. According to the separator described in Patent Document 1, adhesion to an electrode can be improved by using a thermoplastic polymer having a predetermined glass transition temperature, and a portion containing the thermoplastic polymer and the thermoplastic polymer Ion conductivity can be improved by making the part which does not contain be present in the shape of a sea island.

International Publication No. 2014/017651

However, the conventional separator described above did not have sufficient adhesion of the adhesive layer (functional layer) in the electrolytic solution. Therefore, the above conventional separator further improves the adhesion of the functional layer in the electrolyte while ensuring ionic conductivity, and the battery characteristics (high temperature cycle characteristics and low temperature output characteristics) of the nonaqueous secondary battery including the separator. There was room for improvement in terms of further improvement.

Then, an object of this invention is to provide the separator excellent in the adhesiveness and ionic conductivity in electrolyte solution.
Another object of the present invention is to provide a non-aqueous secondary battery that is excellent in high-temperature cycle characteristics and low-temperature output characteristics.

The present inventor has intensively studied to achieve the above object. And about this separator which forms this functional layer on a separator base material, this inventor has the specific core shell structure provided with the core part and shell part which have the specific electrolyte solution swelling degree about the structure of a functional layer, respectively. By having a configuration in which the phase composed of organic particles is present in an irregular shape, and the ratio of the area occupied by the phase of the organic particles is within a specific range, the ionic conductivity is ensured in the electrolyte solution. It has been found that the adhesion can be further improved. In addition, the present inventor applied the functional layer composition containing the organic particles on the separator substrate, and when the functional layer composition was dried to form the functional layer on the separator substrate, By setting the water droplet contact angle on the surface of the separator substrate on which the functional layer is formed and the surface tension of the composition for the functional layer within a specific range, a functional layer having the specific configuration described above can be easily formed. Found to get. And this inventor completed this invention based on the new knowledge mentioned above.

That is, this invention aims at solving the said subject advantageously, The separator for non-aqueous secondary batteries of this invention is on a separator base material and at least one surface of the said separator base material. A functional layer formed, and the functional layer has a structure in which a phase of an organic particle having a core-shell structure including a core portion and a shell portion that partially covers an outer surface of the core portion is present in an irregular shape. The core part is made of a polymer having an electrolyte solution swelling degree of 5 times or more and 30 times or less, and the shell part is made of a polymer having an electrolyte solution swelling degree of more than 1 time and 4 times or less. The ratio of the area of the portion where the organic particle phase is present to the area of the functional layer forming surface of the material is 20% or more and 80% or less. Thus, the functional layer including the organic particle phase having the predetermined core-shell structure and properties described above is provided, and the area ratio of the portion where the organic particle phase exists in the functional layer forming surface is 20% or more. Then, the adhesiveness of the functional layer in electrolyte solution can be improved, and the separator excellent in adhesiveness can be provided. Further, the organic particle phase having the predetermined core-shell structure and properties described above is present in an irregular shape, and the area ratio of the portion where the organic particle phase is present in the functional layer forming surface is 80% or less. Then, the separator excellent in ion conductivity can be provided, improving the adhesiveness of the functional layer in electrolyte solution.
In the present invention, the “electrolyte swelling degree” of the polymer constituting the core part of the organic particles and the polymer constituting the shell part should be measured using the measuring method described in the examples of the present specification. Can do. Further, in the present invention, “the ratio of the area of the portion where the organic particle phase is present” is determined by observing the functional layer of the separator using a scanning electron microscope (SEM) and in the observation field of view using image analysis software. Can be obtained by calculating the ratio of the area of the portion where the organic particle phase exists.

In the separator for a non-aqueous secondary battery of the present invention, the glass transition temperature of the polymer of the core part is −50 ° C. or more and 150 ° C. or less, and the glass transition temperature of the polymer of the shell part is 50 ° C. The temperature is preferably 200 ° C. or lower. If the glass transition temperature of the polymer constituting the core part of the organic particle and the polymer constituting the shell part are within the above-mentioned ranges, respectively, the strength of the organic particle in the electrolytic solution and the adhesion of the functional layer are improved. This is because the handling properties of the separator can be improved.
In the present invention, the “glass transition temperature” of the polymer constituting the core part of the organic particles and the polymer constituting the shell part can be measured using the measuring method described in the examples of the present specification. it can.

Moreover, this invention aims at solving the said subject advantageously, The manufacturing method of the separator for non-aqueous secondary batteries of this invention is the manufacturing method of the separator for non-aqueous secondary batteries mentioned above. A step of preparing a separator base material having a water droplet contact angle of at least 80 ° or more and 130 ° or less on the surface, the organic particles and the dispersion medium, and a surface tension of 33 mN / m or more and 39 mN. A step of preparing a composition for a non-aqueous secondary battery functional layer that is less than or equal to / m, and applying the non-aqueous secondary battery functional layer composition onto the surface of the separator substrate and applying the non-aqueous secondary battery functional layer composition And a step of drying the composition for a secondary battery functional layer to form a functional layer on a separator substrate. Thus, if a composition for a non-aqueous secondary battery functional layer having a predetermined surface tension is applied on the surface of a separator substrate having a predetermined water droplet contact angle, a non-aqueous secondary battery function containing organic particles can be obtained. Since the layer composition is moderately repelled on the surface of the separator substrate, a functional layer having a configuration in which the phase of the organic particles exists in an irregular shape can be easily formed. Therefore, the above-described separator having excellent adhesion and ionic conductivity in the electrolytic solution can be easily produced.
In the present invention, the “water droplet contact angle” can be determined by dropping 1 μL of ion-exchanged water on the separator substrate and measuring the contact angle 60 seconds after landing. In the present invention, the “surface tension” of the composition for a non-aqueous secondary battery functional layer can be measured using a plate method.

And this invention aims at solving the said subject advantageously, The non-aqueous secondary battery of this invention is equipped with either of the separators for non-aqueous secondary batteries mentioned above, It is characterized by the above-mentioned. To do. As described above, when the above-described separator for non-aqueous secondary battery having excellent adhesion and ionic conductivity in the electrolytic solution is used, a non-aqueous secondary battery having excellent high-temperature cycle characteristics and low-temperature output characteristics can be obtained.

ADVANTAGE OF THE INVENTION According to this invention, the separator excellent in the adhesiveness and ionic conductivity in electrolyte solution can be provided.
In addition, according to the present invention, it is possible to provide a non-aqueous secondary battery excellent in high temperature cycle characteristics and low temperature output characteristics.

It is a SEM image of the functional layer of the separator for nonaqueous system rechargeable batteries of the present invention. It is sectional drawing which shows typically the structure of an example of the organic particle contained in the functional layer of the separator for non-aqueous secondary batteries of this invention.

Hereinafter, embodiments of the present invention will be described in detail.
Here, the separator for a non-aqueous secondary battery of the present invention is used as a separator for a non-aqueous secondary battery such as a lithium ion secondary battery. For example, the separator for a non-aqueous secondary battery of the present invention is used. Can be manufactured. And the non-aqueous secondary battery of this invention is equipped with the separator for non-aqueous secondary batteries of this invention.

(Separator for non-aqueous secondary battery)
The separator for non-aqueous secondary batteries of this invention is equipped with the separator base material and the functional layer formed on the at least one surface (functional layer formation surface) of a separator base material. And the functional layer of the separator for non-aqueous secondary batteries of this invention contains the organic particle which has a specific core-shell structure provided with the core part and shell part which have specific electrolyte solution swelling degree. In addition, the organic particles form a phase of organic particles singly or in combination in the functional layer. Furthermore, the phase of the organic particles exists in an irregular shape as shown in, for example, an SEM image of an example of the functional layer in FIG. 1, and exists in a specific area ratio in the functional layer forming surface. . In the SEM image as shown in FIG. 1, the organic particles are observed as spherical dots having a diameter of about 0.3 to 0.7 μm.

And in the separator for non-aqueous secondary batteries of this invention, since the functional layer containing a specific organic particle is provided, the adhesiveness of the functional layer in electrolyte solution can be improved. Therefore, the separator for non-aqueous secondary batteries of the present invention can exhibit excellent adhesiveness in the electrolytic solution. In the non-aqueous secondary battery separator of the present invention, the organic particle phase is present in an irregular shape, and the ratio of the area of the portion where the organic particle phase exists in the functional layer forming surface is specified. Since it is within the range, good ion conductivity can be ensured while sufficiently enhancing the adhesion of the functional layer in the electrolytic solution.

<Separator substrate>
Here, the separator base material on which the functional layer is formed on at least one surface (functional layer forming surface) is not particularly limited, and is a known one such as a microporous film described in JP2012-204303A. A separator substrate can be used. Among these, the film thickness of the entire separator can be reduced, thereby increasing the ratio of the electrode active material in the secondary battery and increasing the capacity per volume. A microporous membrane (organic separator substrate) made of a resin of polyethylene, polypropylene, polybutene, or polyvinyl chloride is preferable. And the thickness of a separator base material can be made into arbitrary thickness, Usually, 0.5 micrometer or more, Preferably it is 5 micrometers or more, Usually, 40 micrometers or less, Preferably it is 30 micrometers or less, More preferably, it is 20 micrometers or less.
In addition, the separator base material may contain an arbitrary layer that can exhibit an intended function other than the functional layer.

Moreover, when manufacturing a separator using the manufacturing method of the separator for nonaqueous secondary batteries of this invention demonstrated in detail later, as a separator base material, the surface on the side which forms a functional layer (functional layer formation surface) ) Is preferably 80 ° or more, more preferably 85 ° or more, still more preferably 90 ° or more, and preferably 130 ° or less, more preferably 120 ° or less, still more preferably 110 ° or less. It is preferable to use a microporous membrane. This is because if a separator substrate having a surface with a water droplet contact angle of 80 ° to 130 ° is used, an organic particle phase having an irregular shape and a specific area ratio can be easily formed.

Here, the water droplet contact angle on the surface of the separator substrate can be adjusted by using a known method such as, for example, changing the composition of the resin used for forming the microporous film or treating the surface of the microporous film. In particular, from the viewpoint of easily adjusting the size of the water droplet contact angle while using a resin (for example, polyethylene, polypropylene, etc.) that can ensure performance such as heat resistance, strength, and ion conductivity, The contact angle is preferably adjusted by surface treatment of the microporous membrane. Furthermore, from the viewpoint of easily adjusting the size of the water droplet contact angle while ensuring the porosity of the microporous membrane, the microporous membrane is subjected to surface treatment using dry treatment such as plasma treatment, corona discharge treatment, and UV treatment. It is preferable to perform surface treatment using corona discharge treatment.

In the case of using a corona discharge treatment, the treatment strength can be preferably 20 W · min / m ² or more, more preferably 30 W · min / m ² or more, still more preferably 40 W · min / m ² or more, further, preferably 80W · min / ^{m 2} or less, more preferably 70W · min / ^{m 2} or less, more preferably be a 60W · min / ^{m 2} or less. This is because if the treatment strength is too high, the water droplet contact angle may be too low. Moreover, it is because there exists a possibility that a water droplet contact angle may not fall to a desired magnitude | size when process intensity | strength is too small.

<Functional layer>
In the separator for a non-aqueous secondary battery of the present invention, the functional layer formed on the separator substrate may be a porous film layer for improving the heat resistance and strength of the separator, or the separator and the electrode are bonded. The adhesive layer may be a layer that exhibits both functions of the porous membrane layer and the adhesive layer.

Here, the functional layer of the separator for a non-aqueous secondary battery according to the present invention includes a core portion made of a polymer having an electrolyte solution swelling degree of 5 times or more and 30 times or less, and an electrolyte solution swelling degree of more than 1 time and less than 4 times. It has a configuration in which a phase of organic particles having a core-shell structure, which is made of a polymer and has a shell part partially covering the outer surface of the core part, exists in an irregular shape. In the functional layer, the ratio of the area where the organic particle phase is present is 20% or more and 80% or less with respect to the area of the functional layer forming surface. The functional layer exhibits excellent adhesiveness in the electrolyte and has good ionic conductivity.
In addition, the functional layer may be formed only on one surface of the separator base material, or may be formed on both surfaces. The separator for a non-aqueous secondary battery of the present invention includes a functional layer having the above-described configuration on one surface and a functional layer having no above-described configuration on the other surface (for example, a function not containing organic particles). Layer or a functional layer in which the area ratio of the phase of the organic particles does not satisfy the above range).

In addition to the organic particles, the functional layer optionally contains a functional layer binder, non-conductive particles (except those corresponding to organic particles and functional layer binders), and other components. May be.
In addition, the content of the organic particles in the functional layer is preferably 50% by mass or more, more preferably 60% by mass or more, still more preferably 70% by mass or more, and particularly preferably 80% by mass or more.

[Organic particles]
The organic particles contained in the functional layer have a function of exhibiting excellent adhesiveness in the functional layer in the electrolytic solution.
The organic particles have a core-shell structure including a core portion and a shell portion that partially covers the outer surface of the core portion. The core portion has an electrolyte swelling degree of 5 times or more and 30 times or less. It is made of a polymer, and the shell part is made of a polymer having an electrolyte solution swelling degree of more than 1 time and 4 times or less.

Here, the organic particles having the above structure and properties exhibit excellent adhesiveness in the electrolytic solution, and further, the elution of components into the electrolytic solution is small, and excellent adhesiveness can be maintained for a long time. And the functional layer containing an organic particle can improve the battery characteristic of a secondary battery favorably. In addition, since the organic particles do not exhibit a large adhesive force before being immersed in the electrolytic solution, a separator having a functional layer containing organic particles is less likely to cause blocking (separation between separators via the functional layer). Also, handling is excellent.

The reason why the above-described excellent effect can be obtained by using the organic particles is not clear, but is presumed to be as follows.
That is, the polymer constituting the shell portion of the organic particles swells to some extent with respect to the electrolytic solution. At this time, for example, the functional group of the polymer in the swollen shell part is activated, and the functional group is formed on the surface of the separator substrate on which the functional layer is formed or on the surface of the electrode or the like bonded to the separator having the functional layer. Due to factors such as causing chemical or electrical interaction with the group, the shell portion can be firmly bonded to the separator substrate, electrodes, and the like. On the other hand, the shell portion does not exhibit a large adhesive force before it swells in the electrolytic solution. Therefore, it is assumed that the functional layer containing the organic particles can strongly bond the separator and the electrode in the electrolytic solution while suppressing the occurrence of blocking.
Moreover, the polymer of the shell part and the polymer of the core part both have an electrolyte solution swelling degree set to a predetermined value or less, and do not swell excessively with respect to the electrolyte solution. Therefore, for example, it is speculated that the excellent adhesiveness described above can be sufficiently exhibited even after the secondary battery is operated for a long time.
And when the functional layer containing the organic particles is used, since the functional layer can exert a strong adhesive force in the electrolyte solution as described above, in the secondary battery including the functional layer, the functional layer is It is difficult to generate a gap between the separator and the electrode bonded via the electrode. Therefore, in a secondary battery using a separator having a functional layer containing the organic particles, the distance between the positive electrode and the negative electrode is difficult to increase in the secondary battery, the internal resistance of the secondary battery can be reduced, and the electric power in the electrode can be reduced. The reaction field for chemical reactions is unlikely to be uneven. Furthermore, in the secondary battery, even if charging and discharging are repeated, it is difficult to form a gap between the separator and the electrode, and the battery capacity is unlikely to decrease. Thereby, it is guessed that the secondary battery which is excellent in high temperature cycling characteristics etc. can be provided.
Furthermore, the polymer constituting the core part of the organic particles swells greatly with respect to the electrolytic solution. When the polymer is greatly swollen in the electrolytic solution, the gap between the molecules of the polymer becomes large, and ions easily pass between the molecules. In addition, the polymer in the core part of the organic particles is not completely covered by the shell part. Therefore, ions easily pass through the core portion in the electrolytic solution, so that the organic particles can exhibit high ion diffusibility. Therefore, if the organic particles are used, it is possible to suppress an increase in resistance due to the functional layer and to suppress a decrease in battery characteristics such as low-temperature output characteristics.
In addition, as above-mentioned, an organic particle exhibits the outstanding adhesiveness by swelling to electrolyte solution, and does not exhibit big adhesive force before being immersed in electrolyte solution. However, the organic particles do not exhibit adhesiveness unless they are swollen in the electrolytic solution, and are heated to a certain temperature or higher (for example, 50 ° C. or higher) even if they are not swollen in the electrolytic solution. Therefore, adhesiveness can be expressed.

[[Structure of organic particles]]
Here, the organic particles have a core-shell structure including a core part and a shell part that covers the outer surface of the core part. The shell portion partially covers the outer surface of the core portion. That is, the shell part of the organic particles covers the outer surface of the core part, but does not cover the entire outer surface of the core part. Even if it appears that the outer surface of the core part is completely covered by the shell part, the shell part is outside the core part as long as a hole that communicates the inside and outside of the shell part is formed. A shell part that partially covers the surface. Therefore, for example, organic particles including a shell portion having pores communicating from the outer surface of the shell portion (that is, the peripheral surface of the organic particle) to the outer surface of the core portion are included in the organic particles.

Specifically, the organic particle 100 has a core-shell structure including a core part 110 and a shell part 120, as shown in FIG. Here, the core part 110 is a part which is inside the shell part 120 in the organic particle 100. The shell part 120 is a part that covers the outer surface 110 </ b> S of the core part 110, and is usually the outermost part of the organic particles 100. The shell portion 120 does not cover the entire outer surface 110S of the core portion 110, but partially covers the outer surface 110S of the core portion 110.

-Coverage-
Here, in the organic particles, the average ratio (coverage) at which the outer surface of the core part is covered by the shell part is preferably 10% or more, more preferably 30% or more, and even more preferably 50% or more, preferably It is 95% or less, more preferably 90% or less, and still more preferably 80% or less. By setting the coverage to be equal to or higher than the lower limit of the above range, it is possible to suppress the occurrence of blocking, increase the adhesion in the electrolytic solution, and improve the high-temperature cycle characteristics of the secondary battery. In addition, by setting the coverage to be equal to or less than the upper limit of the above range, it is possible to improve the low temperature output characteristics of the secondary battery by expressing high ion diffusibility in the functional layer.
In addition, in this invention, "the average ratio (coverage) by which the outer surface of a core part is covered with a shell part" can be measured using the measuring method as described in the Example of this specification.

-Volume average particle diameter D50-
Further, the volume average particle diameter D50 of the organic particles is preferably 0.01 μm or more, more preferably 0.1 μm or more, further preferably 0.2 μm or more, preferably 10 μm or less, more preferably 5 μm or less, and further preferably Is 1 μm or less. By setting the volume average particle diameter D50 of the organic particles to be equal to or greater than the lower limit of the above range, it is possible to suppress the increase in internal resistance of the functional layer and improve the low-temperature output characteristics of the secondary battery. Moreover, the adhesiveness in electrolyte solution can be improved and the high temperature cycling characteristic of a secondary battery can be improved by making the volume average particle diameter D50 of an organic particle below the upper limit of the said range.
In the present invention, the “volume average particle diameter D50” of the organic particles can be measured using the measuring method described in the examples of the present specification.

-Core shell ratio-
Furthermore, the shell part preferably has an average thickness that falls within a predetermined range with respect to the volume average particle diameter D50 of the organic particles. Specifically, the average thickness (core-shell ratio) of the shell part with respect to the volume average particle diameter D50 of the organic particles is preferably 1.5% or more, more preferably 3% or more, and even more preferably 5% or more. Is 30% or less, more preferably 25% or less, and still more preferably 20% or less. By setting the core-shell ratio to be equal to or higher than the lower limit of the above range, the adhesion of the functional layer in the electrolytic solution can be further improved and the high-temperature cycle characteristics of the secondary battery can be improved. Moreover, the low temperature output characteristic of a secondary battery can further be improved by making a core-shell ratio below the upper limit of the said range.
In the present invention, the “core-shell ratio” can be measured using the measurement method described in the examples of the present specification.

Note that the organic particles may include arbitrary constituent elements other than the above-described core part and shell part as long as the intended effect is not significantly impaired. Specifically, for example, the organic particles may have a portion formed of a polymer different from the core portion inside the core portion. As a specific example, the seed particles used when the organic particles are produced by the seed polymerization method may remain inside the core portion. However, it is preferable that the organic particles include only the core part and the shell part from the viewpoint of remarkably exhibiting the intended effect.

[[Core]]
-Swelling degree of electrolyte in core polymer-
The core part of the organic particle is made of a polymer having a predetermined degree of swelling with respect to the electrolytic solution. Specifically, the electrolyte swelling degree of the polymer of the core part needs to be 5 times or more, preferably 7 times or more, more preferably 8 times or more, and 30 It is necessary that it is not more than twice, preferably not more than 28 times, and more preferably not more than 25 times. By setting the electrolyte swelling degree of the polymer in the core part to be equal to or higher than the lower limit of the above range, the functional layer can exhibit high ion diffusibility and the low-temperature output characteristics of the secondary battery can be improved. Moreover, the adhesiveness of the functional layer in electrolyte solution can be improved, and the high temperature cycling characteristic of a secondary battery can be improved by making electrolyte solution swelling degree of the polymer of a core part below the upper limit of the said range.
In the present invention, the “electrolyte swelling degree” of the polymer of the core part can be measured using the measuring method described in the examples of the present specification.

In addition, as a method of adjusting the electrolyte swelling degree of the polymer of the core part, for example, considering the SP value of the electrolyte solution, the kind and amount of the monomer used for preparing the polymer of the core part Is appropriately selected. 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, 2nd Ed (CRCPless).
Further, the SP value of an organic compound can be estimated from the molecular structure of the organic compound. Specifically, it can be calculated by using simulation software (for example, “HSPiP” (http://www.hansen-solution.com)) that can calculate the SP value from the SMILE equation. In this simulation software, Hansen SOLUBILITY PARAMETERS A User's Handbook Second Edition, Charles M. et al. The SP value is obtained based on the theory described in Hansen.

-Glass transition temperature of core polymer-
Further, the glass transition temperature of the polymer constituting the core part of the organic particles is preferably −50 ° C. or higher, more preferably 0 ° C. or higher, further preferably 20 ° C. or higher, It is preferable that it is 150 degrees C or less, It is more preferable that it is 120 degrees C or less, It is more preferable that it is 100 degrees C or less. By setting the glass transition temperature of the polymer in the core part to be equal to or higher than the lower limit of the above range, the strength and blocking resistance of the functional layer can be further improved. Moreover, the adhesiveness in the electrolyte solution of a functional layer and the high temperature cycling characteristic of a secondary battery can be improved by making the glass transition temperature of the polymer of a core part below into the upper limit of the said range.

In addition, as a method of adjusting the glass transition temperature of the polymer of the core part, for example, the type and amount of the monomer used for preparing the polymer of the core part are the same as the homopolymer glass of the monomer. Appropriate selection is considered in consideration of the transition temperature. For example, when a (meth) acrylic acid ester monomer is used for the preparation of the polymer of the core part, the polymer obtained as the carbon number of the part derived from the alcohol of the (meth) acrylic acid ester monomer increases. The glass transition temperature of the glass tends to be low.
Here, in the present invention, (meth) acryl means acryl and / or methacryl.

-Polymer composition of the core-
As a monomer used for preparing the polymer of the core part, a monomer having an electrolyte solution swelling degree within the above range can be appropriately selected and 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; methyl acrylate, ethyl acrylate, butyl acrylate, methacryl (Meth) acrylic acid ester monomers such as methyl acrylate, ethyl methacrylate and 2-ethylhexyl acrylate; (meth) acrylamide monomers such as acrylamide and methacrylamide; (meth) acrylonitrile single quantities such as acrylonitrile and methacrylonitrile Body; 2- (perfluorohexyl) ester Fluorine-containing (meth) acrylate monomers such as 2-methacrylate and 2- (perfluorobutyl) ethyl acrylate; maleimide; maleimide derivatives such as phenylmaleimide; and diene monomers such as 1,3-butadiene and isoprene; Can be mentioned. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.
In the present invention, (meth) acrylate means acrylate and / or methacrylate, and (meth) acrylonitrile means acrylonitrile and / or methacrylonitrile.

Among these monomers, it is preferable to use a (meth) acrylic acid ester monomer, and methyl methacrylate and / or butyl acrylate are used as the monomer used for preparing the core polymer. It is more preferable. That is, the polymer of the core part preferably contains a (meth) acrylate monomer unit, and more preferably contains a monomer unit derived from methyl methacrylate and / or butyl acrylate. By using the above-mentioned monomer, it is easy to control the degree of electrolyte swelling of the polymer in the core part and the glass transition temperature of the polymer in the core part, and the functional layer ion using organic particles. The diffusibility can be further enhanced.

Further, the polymer of the core part may include an acid group-containing monomer unit. Here, as the acid group-containing monomer, a monomer having an acid group, for example, a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and And monomers having a hydroxyl group.

Examples of the monomer having a carboxylic acid group include monocarboxylic acid and dicarboxylic acid. Examples of the monocarboxylic acid include acrylic acid, methacrylic acid, and crotonic acid. Examples of the dicarboxylic acid include maleic acid, fumaric acid, itaconic acid and the like.
Examples of the monomer having a sulfonic acid group include vinyl sulfonic acid, methyl vinyl sulfonic acid, (meth) allyl sulfonic acid, (meth) acrylic acid-2-ethyl sulfonate, 2-acrylamido-2-methyl. Examples thereof include propanesulfonic acid and 3-allyloxy-2-hydroxypropanesulfonic acid.
Further, examples of the monomer having a phosphoric acid group include phosphoric acid-2- (meth) acryloyloxyethyl phosphate, methyl-2- (meth) acryloyloxyethyl phosphate, and ethyl phosphate- (meth) acryloyloxyethyl phosphate. Etc.
Examples of the monomer having a hydroxyl group include 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethyl methacrylate, and 2-hydroxypropyl methacrylate.
In the present invention, (meth) allyl means allyl and / or methallyl, and (meth) acryloyl means acryloyl and / or methacryloyl.

Among these, as the acid group-containing monomer, a monomer having a carboxylic acid group is preferable, among which monocarboxylic acid is preferable, and (meth) acrylic acid is more preferable.
Moreover, an acid group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

Moreover, the ratio of the acid group content body unit in the polymer of the core part is preferably 0.1% by mass or more, more preferably 1% by mass or more, preferably 20% by mass or less, more preferably 10% by mass. Hereinafter, it is more preferably 7% by mass or less. By keeping the ratio of the acid group-containing body unit within the above range, when preparing the organic particles, the dispersibility of the polymer in the core part is improved, and the outer surface of the core part is made to be more than the outer surface of the polymer in the core part. A shell portion that partially covers can be easily formed.

Further, the polymer of the core part preferably contains a crosslinkable monomer unit in addition to the monomer unit. A 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 electrolyte solution swelling degree of the polymer can be easily kept within the above range.

Examples of the crosslinkable monomer include polyfunctional monomers having two or more polymerization reactive groups in the monomer. 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 degree of swelling of the electrolyte in the polymer of the core part, an ethylenically unsaturated monomer containing a dimethacrylic acid ester compound and an epoxy group is preferred, and a dimethacrylic acid ester compound is more preferred. preferable. Moreover, these may be used individually by 1 type and may be used combining two or more types by arbitrary ratios.

Here, generally, when the proportion of the crosslinkable monomer unit in the polymer increases, the degree of swelling of the polymer with respect to the electrolytic solution tends to decrease. Therefore, the ratio 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 mass or more, more preferably 0.2% by mass or more, and further preferably 0.5% by mass or more. Preferably it is 10 mass% or less, More preferably, it is 8 mass% or less, More preferably, it is 6 mass% 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 functional layer can be enhanced. Moreover, the cycle characteristic of a non-aqueous secondary battery can be improved by making the ratio of a crosslinkable monomer unit below the upper limit of the said range.

[[Shell]]
-Swelling degree of electrolyte in shell polymer-
The shell part of the organic particle is made of a polymer having a predetermined electrolyte solution swelling degree smaller than the electrolyte solution swelling degree of the core part. Specifically, the electrolyte solution swelling degree of the polymer of the shell portion needs to be more than 1 time, preferably 1.1 times or more, more preferably 1.2 times or more. In addition, it is necessary to be 4 times or less, 3.5 times or less is preferable, and 3 times or less is more preferable. By making the electrolyte solution swelling degree of the polymer of the shell part exceed the lower limit value of the above range, the low-temperature output characteristics of the secondary battery can be improved by expressing high ion diffusibility in the functional layer. Moreover, by making the electrolyte swelling degree of the polymer of the shell part below the upper limit of the above range, it is possible to improve the adhesion of the functional layer in the electrolyte and improve the high-temperature cycle characteristics of the secondary battery. .
Here, in this invention, the "electrolyte swelling degree" of the polymer of a shell part can be measured using the measuring method as described in the Example of this specification.

In addition, as a method for adjusting the electrolyte solution swelling degree of the polymer of the shell part, for example, considering the SP value of the electrolyte solution, the kind and amount of the monomer for producing the polymer of the shell part are determined. Appropriate selection can be mentioned.

-Glass transition temperature of polymer in shell-
The glass transition temperature of the polymer constituting the shell part of the organic particles is preferably 50 ° C. or higher, more preferably 60 ° C. or higher, still more preferably 70 ° C. or higher, and 200 It is preferably not higher than ° C., more preferably not higher than 180 ° C., and further preferably not higher than 150 ° C. By setting the glass transition temperature of the polymer of the shell part to 50 ° C. or higher, it is possible to improve the low temperature output characteristics of the secondary battery in addition to suppressing the occurrence of blocking. Moreover, the adhesiveness of a functional layer can further be improved by making the glass transition temperature of the polymer of a shell part into 200 degrees C or less.

In addition, as a method of adjusting the glass transition temperature of the polymer of the shell part, for example, the type and amount of the monomer used for preparing the polymer of the shell part are the same as the homopolymer glass of the monomer. Appropriate selection is considered in consideration of the transition temperature.

-Polymer composition of shell-
As a monomer used for preparing the polymer of the shell portion, a monomer having an electrolyte solution swelling degree within the above range can be appropriately selected and used. Examples of such a monomer include the same monomers as those exemplified as monomers that can be used to produce the core polymer. 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, it is preferable to use an aromatic vinyl monomer as a monomer used for the preparation of the shell polymer. That is, the polymer of the shell part preferably includes an aromatic vinyl monomer unit. Among aromatic vinyl monomers, styrene derivatives such as styrene and styrene sulfonic acid are more preferable. If an aromatic vinyl monomer is used, it is easy to control the degree of electrolyte swelling of the polymer. Moreover, the adhesiveness of the functional layer can be further enhanced.

And the ratio of the aromatic vinyl monomer unit in the polymer of the shell part is preferably 20% by mass or more, more preferably 40% by mass or more, further preferably 50% by mass or more, and still more preferably 60% by mass or more. Especially preferably, it is 80 mass% or more, Preferably it is 100 mass% or less, More preferably, it is 99.5 mass% or less, More preferably, it is 99 mass% or less. By keeping the ratio of the aromatic vinyl monomer unit in the above range, the degree of swelling of the electrolyte solution and the glass transition temperature of the polymer in the shell part can be easily controlled to a desired range. Moreover, the adhesiveness of the functional layer in electrolyte solution can be improved more.

Further, the polymer of the shell part may contain an acid group-containing monomer unit in addition to the aromatic vinyl monomer unit. Here, as the acid group-containing monomer, a monomer having an acid group, for example, a monomer having a carboxylic acid group, a monomer having a sulfonic acid group, a monomer having a phosphoric acid group, and And monomers having a hydroxyl group. Specifically, examples of the acid group-containing monomer include monomers similar to the acid group-containing monomer that can be contained in the core portion.

Among these, the acid group-containing monomer is preferably a monomer having a carboxylic acid group, more preferably a monocarboxylic acid, and even more preferably (meth) acrylic acid.
Moreover, an acid group containing monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

The ratio of the acid group-containing monomer unit in the polymer of the shell part is preferably 0.1% by mass or more, more preferably 1% by mass or more, still more preferably 3% by mass or more, and preferably 20% by mass. Hereinafter, it is more preferably 10% by mass or less, and further preferably 7% by mass or less. By keeping the ratio of the acid group-containing monomer unit within the above range, the dispersibility of the organic particles in the functional layer can be improved.

Further, the polymer of the shell part may contain a crosslinkable monomer unit. Examples of the crosslinkable monomer include monomers similar to those exemplified as the crosslinkable monomer that can be used in the core polymer. Moreover, a crosslinking | crosslinked monomer may be used individually by 1 type, and may be used combining two or more types by arbitrary ratios.

And the ratio of the crosslinkable monomer unit in the polymer of the shell part is preferably 0.1% by mass or more, more preferably 0.2% by mass or more, further preferably 0.5% by mass or more, preferably Is 5% by mass or less, more preferably 4% by mass or less, and still more preferably 3% by mass or less.

-Shell configuration-
The form of the shell part is not particularly limited, but the shell part is preferably composed of polymer particles. When the shell part is composed of polymer particles, a plurality of particles constituting the shell part may overlap in the radial direction of the organic particles. However, in the radial direction of the organic particles, it is preferable that the particles constituting the shell portion do not overlap each other, and those polymer particles constitute the shell portion as a single layer.

[[Preparation method of organic particles]]
The organic particles having the core-shell structure described above use, for example, a polymer monomer in the core part and a polymer monomer in the shell part, and change the ratio of these monomers over time. Can be prepared by stepwise polymerization. Specifically, the organic particles can be prepared by a continuous multi-stage emulsion polymerization method and a multi-stage suspension polymerization method in which the polymer of the previous stage is sequentially coated with the polymer of the subsequent stage.

Therefore, an example of obtaining organic particles having the above core-shell structure by a multi-stage emulsion polymerization method is shown below.

In the polymerization, according to a conventional method, as an emulsifier, for example, an anionic surfactant such as sodium dodecylbenzenesulfonate and sodium dodecylsulfate, a nonionic surfactant 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 monomer and an emulsifier that form a core part are mixed, and emulsion polymerization is performed at once to obtain a particulate polymer constituting the core part. Furthermore, the organic particle which has the core shell structure mentioned above can be obtained by superposing | polymerizing the monomer which forms a shell part in presence of the particulate polymer which comprises this core part.

At this time, from the viewpoint of partially covering the outer surface of the core portion with the shell portion, the monomer that forms the polymer of the shell portion is divided into a plurality of times or continuously supplied to the polymerization system. Is preferred. The monomer that forms the polymer of the shell part is divided into a polymerization system or continuously supplied, whereby the polymer constituting the shell part is formed into particles, and these particles are bonded to the core part. Thereby, the shell part which covers a core part partially can be formed.

In addition, when the monomer for forming the polymer of the shell part is divided and supplied in a plurality of times, it is possible to control the average thickness of the shell part according to the ratio of dividing the monomer. In addition, when continuously supplying the monomer that forms the polymer of the shell part, it is possible to control the average thickness of the shell part by adjusting the monomer supply amount per unit time. is there.

Further, the volume average particle diameter D50 of the organic particles after forming the shell portion can be set to a desired range by adjusting the amount of the emulsifier, the amount of the monomer, and the like. Furthermore, the average ratio (coverage) by which the outer surface of the core part is covered by the shell part is adjusted by, for example, adjusting the amount of the emulsifier and the amount of the monomer that forms the polymer of the shell part. Can range.

[Binder for functional layer]
Here, as described above, the organic particles usually do not swell in the electrolytic solution and do not exhibit great adhesion in a state where they are not heated. Therefore, from the viewpoint of suppressing the organic particles from dropping off from the functional layer immediately after the formation of the functional layer (before heating or immersion in the electrolytic solution), the functional layer is not swollen in the electrolytic solution, and It is preferable that the binder for functional layers which exhibits adhesiveness also in the state which is not heated is included. By using the functional layer binder, components such as organic particles can be prevented from falling off from the functional layer even in a state where the electrolyte is not swollen and heated.

And as a binder for functional layers which can be used together with the said organic particle, a known binder, for example, a thermoplastic elastomer, is mentioned. And as a thermoplastic elastomer, a conjugated diene polymer and an acrylic polymer are preferable, and an acrylic polymer is more preferable.
Here, the conjugated diene polymer refers to a polymer containing a conjugated diene monomer unit. Specific examples of the conjugated diene polymer include aromatic vinyl such as styrene-butadiene copolymer (SBR). Examples thereof include a polymer containing a monomer unit and an aliphatic conjugated diene monomer unit, and an acrylic rubber (NBR) (a polymer containing an acrylonitrile unit and a butadiene unit). Moreover, an acrylic polymer refers to the polymer containing a (meth) acrylic acid ester monomer unit. Here, the (meth) acrylate monomer that can form a (meth) acrylate monomer unit is the same as the monomer used to prepare the polymer of the core part of the organic particles. Can be used.
These functional layer binders may be used alone or in combination of two or more. However, in the case of using a functional layer binding material in which two or more kinds of polymers are combined, the polymer as the functional layer binding material is an organic particle having a core-shell structure made of the predetermined polymer described above. Be different.

Furthermore, it is more preferable that the acrylic polymer as the binder for the functional layer includes a (meth) acrylonitrile monomer unit. Thereby, the intensity | strength of a functional layer can be raised.

Here, in the acrylic polymer as the binder for the functional layer, the amount of the (meth) acrylonitrile monomer unit relative to the total amount of the (meth) acrylonitrile monomer unit and the (meth) acrylic acid ester monomer unit The ratio is preferably 1% by mass or more, more preferably 2% by mass or more, preferably 30% by mass or less, more preferably 25% by mass or less. By setting the ratio to be equal to or higher than the lower limit of the range, the strength of the acrylic polymer as the binder for the functional layer can be increased, and the strength of the functional layer using the acrylic polymer can be further increased. . Moreover, since the acrylic polymer as the binder for the functional layer is appropriately swollen with respect to the electrolytic solution by setting the ratio to be not more than the upper limit of the above range, the ion conductivity of the functional layer is reduced. A decrease in the low-temperature output characteristics of the secondary battery can be suppressed.

Further, the glass transition temperature of the binder for the functional layer is usually lower than the glass transition temperature of the polymer of the core part of the organic particles and the glass transition temperature of the polymer of the shell part, and preferably −100 ° C. or higher. More preferably, it is −90 ° C. or more, more preferably −80 ° C. or more, preferably 0 ° C. or less, more preferably −5 ° C. or less, and further preferably −10 ° C. or less. . By making the glass transition temperature of the functional layer binder higher than the lower limit of the above range, the adhesiveness and strength of the functional layer binder can be enhanced. Moreover, the softness | flexibility of a functional layer can be improved by making the glass transition temperature of the binder for functional layers below into the upper limit of the said range.

In addition, since the binder for the functional layer having a low glass transition temperature is usually fluidized by heating at the time of forming the functional layer, for example, it is widely dispersed in the functional layer so that it is difficult to grasp the shape by SEM or the like. To do.

The content of the functional layer binder in the functional layer is preferably 1 part by mass or more, more preferably 3 parts by mass or more, with respect to 100 parts by mass of the organic particles described above. The amount is more preferably at least part by mass, more preferably at most 30 parts by mass, even more preferably at most 25 parts by mass, even more preferably at most 20 parts by mass. By making the content of the binder for the functional layer more than the lower limit of the above range, the binding property of the functional layer is improved, and the organic particles fall off from the functional layer before heating or immersion in the electrolytic solution. Can be sufficiently prevented. Moreover, the fall of the ion conductivity of a functional layer and the low-temperature output characteristic of a secondary battery can be suppressed by making content of the binder for functional layers into below the upper limit of the said range.

Examples of the method for producing the functional layer binder include a solution polymerization method, a suspension polymerization method, and an emulsion polymerization method. Among them, the emulsion polymerization method and the suspension polymerization method are preferable because the polymerization can be performed in water and the aqueous dispersion containing the particulate functional layer binder can be suitably used for forming the functional layer as it is. Moreover, when manufacturing the polymer as a binder for functional layers, it is preferable that the reaction system contains a dispersing agent. The functional layer binder is usually formed of a polymer substantially constituting the functional layer binder, but may be accompanied by optional components such as additives used in the polymerization.

[Non-conductive particles]
Furthermore, when the functional layer also functions as a porous membrane layer, the functional layer may contain non-conductive particles. The non-conductive particles to be blended in the functional layer are not particularly limited, and known non-conductive particles used for non-aqueous secondary batteries can be exemplified.
Specifically, as the non-conductive particles, both inorganic fine particles and organic fine particles other than the organic particles and the functional layer binder described above can be used, but inorganic fine particles are usually used. Especially, as a material of nonelectroconductive particle, the material which exists stably in the use environment of a non-aqueous secondary battery and is electrochemically stable is preferable. From this point of view, preferable examples of the non-conductive particle material include aluminum oxide (alumina), hydrated aluminum oxide (boehmite), silicon oxide, magnesium oxide (magnesia), calcium oxide, titanium oxide (titania). Oxide particles such as BaTiO ₃ , ZrO, alumina-silica composite oxide; nitride particles such as aluminum nitride and boron nitride; covalently bonded crystal particles such as silicon and diamond; barium sulfate, calcium fluoride, barium fluoride Insoluble ion crystal particles such as; clay fine particles such as talc and montmorillonite; In addition, these particles may be subjected to element substitution, surface treatment, solid solution, and the like as necessary.
In addition, the nonelectroconductive particle mentioned above may be used individually by 1 type, and may be used in combination of 2 or more types.

[Other ingredients]
And the functional layer may contain arbitrary other components besides the component mentioned above. The other components are not particularly limited as long as they do not affect the battery reaction, and known components can be used. Moreover, these other components may be used individually by 1 type, and may be used in combination of 2 or more types.
Examples of the other components include known additives used at the time of forming a functional layer, such as a wetting agent such as an ethylene oxide-propylene oxide copolymer, a viscosity modifier, and an electrolytic solution additive.

[Function layer configuration]
The functional layer formed on the functional layer forming surface of the separator substrate is composed of a single organic particle or a plurality of assembled organic particles, as shown in FIG. The organic particle phase (that is, the portion where the organic particles are present) and the portion where the organic particles are not present (for example, the portion where only components other than the organic particles such as the binder for the functional layer are present) are mixed. Yes. In addition, on the functional layer forming surface of the separator substrate, there may be a portion where components constituting the functional layer such as organic particles and a functional layer binder are not present.

[[Phase of organic particles]]
Here, the phase of the organic particles needs to be present in a ratio of 20% to 80% with respect to the area of the functional layer forming surface without covering the entire functional layer forming surface. Ratio of the area of the organic particle phase existing on the functional layer forming surface to the area of the functional layer forming surface (= (area of the portion where the organic particle phase exists / area of the functional layer forming surface) × 100%) Is less than 20%, the amount of organic particles exhibiting excellent adhesive strength in the electrolytic solution becomes too small, and the adhesiveness of the functional layer in the electrolytic solution decreases, and a secondary battery using a separator This is because the high-temperature cycle characteristics of are deteriorated. Further, although the organic particles exhibit a certain degree of high ionic conductivity, the portion where the organic particles are present has a lower ionic conductivity than the portion where the organic particles are not present. Therefore, from the viewpoint of improving the ion conductivity of the functional layer in the electrolyte and enhancing the low-temperature output characteristics of the secondary battery using the separator, it exists on the functional layer forming surface with respect to the area of the functional layer forming surface. The ratio of the area of the phase of the organic particles to be performed needs to be 80% or less.
And, from the viewpoint of improving the high-temperature cycle characteristics of the secondary battery by sufficiently securing the adhesion of the functional layer in the electrolyte, the area of the portion where the organic particle phase is present relative to the area of the functional layer forming surface The ratio is preferably 25% or more, more preferably 30% or more, and further preferably 35% or more. Further, from the viewpoint of further improving the ion conductivity of the functional layer in the electrolyte and further improving the low-temperature output characteristics of the secondary battery using the separator, there is a phase of organic particles with respect to the area of the functional layer forming surface. The proportion of the area of the part is preferably 70% or less, more preferably 60% or less, and further preferably 45% or less.

In addition, the phase of the organic particles exists in an irregular shape. Specifically, in the functional layer, a plurality of phases composed of single organic particles or aggregated organic particles are present in an irregular shape rather than a fixed repetitive pattern shape (for example, a stripe shape or a lattice shape). is doing. And in a functional layer, the adhesiveness in electrolyte solution can be improved because the phase of an organic particle exists in an irregular shape.
Here, the configuration in which the phase of the organic particles is present in an irregular shape is not particularly limited, and for example, an island-like phase composed of a single organic particle or an aggregate of 10 or less organic particles A configuration in which a continental phase composed of an aggregate of 11 or more organic particles is mixed with a portion where no organic particles exist is included.

In addition, the area of the part in which the phase of the organic particles exists and the shape of the phase of the organic particles are, for example, the type of the material used for forming the separator base material and the functional layer (composition for the non-aqueous secondary battery functional layer), and It can be adjusted by changing the method of forming the functional layer.

(Method for producing separator for non-aqueous secondary battery)
And the separator for non-aqueous secondary batteries of this invention which has a functional layer of the structure mentioned above can be easily produced, for example using the manufacturing method of the separator for non-aqueous secondary batteries of this invention.

Here, the method for producing a separator for a non-aqueous secondary battery according to the present invention includes a step of preparing a separator base material having a water droplet contact angle of 80 ° to 130 ° on the functional layer forming surface (base material preparation step), A step of preparing a composition for a non-aqueous secondary battery functional layer containing a component constituting the functional layer and a dispersion medium such as water and having a surface tension of 33 mN / m to 39 mN / m (composition preparation) Step) and a non-aqueous secondary battery functional layer composition applied on the functional layer-forming surface of the separator base material, and the applied non-aqueous secondary battery functional layer composition is dried to function on the separator base material. And a step of forming a layer (functional layer forming step). And in the manufacturing method of the separator for non-aqueous secondary batteries of this invention, the composition for non-aqueous secondary battery functional layers was apply | coated on the functional layer formation surface of a separator base material, and the apply | coated non-aqueous secondary battery functional layer When forming the functional layer on the separator substrate by drying the composition for use, a separator substrate having a water droplet contact angle of 80 ° to 130 ° on the functional layer forming surface is used, and the surface tension is 33 mN / By using a composition for a non-aqueous secondary battery functional layer that is not less than m and not more than 39 mN / m, the functional layer having the above-described configuration can be easily formed.

<Base material preparation process>
In the base material preparation step, a separator base material having a water droplet contact angle on at least one surface (functional layer forming surface) of 80 ° or more and 130 ° or less is prepared.
Here, when the water droplet contact angle on the functional layer forming surface is less than 80 °, the ratio of the area of the portion where the organic particle phase exists in the formed functional layer becomes too large. Further, when the water droplet contact angle on the functional layer forming surface is more than 130 °, the ratio of the area of the formed functional layer where the organic particle phase exists is too small. And from the viewpoint of making the ratio of the area of the part where the organic particle phase exists to an appropriate size, the water droplet contact angle of the functional layer forming surface is preferably 85 ° or more, and preferably 90 ° or more. More preferably, it is preferably 120 ° or less, and more preferably 110 ° or less.

The separator substrate having a water droplet contact angle of 80 ° to 130 ° is not particularly limited, and may be prepared by purchasing a commercially available separator substrate having a surface with a water droplet contact angle within the above range. It is good to adjust the size of the contact angle of water droplets on the surface of the microporous membrane that can be used as a separator substrate by using a surface treatment such as corona discharge treatment as described in the section <Separator substrate>. You may prepare by.

<Composition preparation step>
In the composition preparation step, it is a slurry composition containing at least the organic particles described above, optionally containing a binder for functional layers, non-conductive particles, and other components, using water as a dispersion medium, And the composition for non-aqueous secondary battery functional layers whose surface tension is 33 mN / m or more and 39 mN / m or less is prepared.
Here, when the surface tension of the functional layer composition is less than 33 mN / m, the ratio of the area of the portion where the organic particle phase is present in the formed functional layer becomes too large. Moreover, when the surface tension of the composition for functional layers exceeds 39 mN / m, the ratio of the area of the part in which the organic particle phase exists in the formed functional layer becomes too small. And from the viewpoint of setting the ratio of the area of the portion where the organic particle phase is present to an appropriate size, the surface tension of the functional layer composition is preferably 34 mN / m or more, and more preferably 35 mN / m or more. More preferably, it is preferably 38 mN / m or less, and more preferably 37 mN / m or less.

The method for preparing the functional layer composition is not particularly limited, but usually, organic particles, water as a dispersion medium, and functional layer binder, non-conductive particles and A functional layer composition is prepared by mixing with other components. Although the mixing method is not particularly limited, in order to disperse each component efficiently, mixing is usually performed using a disperser as a mixing device.
As the disperser, it is preferable to use an apparatus capable of uniformly dispersing and mixing the above components. Examples of the disperser include a ball mill, a sand mill, a pigment disperser, a crusher, an ultrasonic disperser, a homogenizer, and a planetary mixer. From the viewpoint that a high dispersion share can be added, it is also preferable to use a high dispersion apparatus such as a bead mill, a roll mill, or a fill mix.

Moreover, the magnitude | size of the surface tension of the composition for functional layers is not specifically limited, It can adjust by adding a wetting agent to the composition for functional layers, for example, increasing the addition amount of a wetting agent. Thereby, the surface tension of the composition for functional layers can be made small.
Here, the wetting agent is not particularly limited, and a known surfactant such as a nonionic surfactant or an ionic surfactant can be used. Among these, as the wetting agent, a nonionic surfactant is preferably used, a polyether copolymer is more preferably used, and an ethylene oxide-propylene oxide copolymer is further preferably used. And the compounding quantity of a wetting agent will not be specifically limited if the surface tension of the composition for functional layers can be made into the range mentioned above, for example, shall be 0.1 mass part or more per 100 mass parts of organic particles. It is preferably 0.5 parts by mass or more, more preferably 1.0 part by mass or more, particularly preferably 1.5 parts by mass or more, and 5.0 parts by mass or less. Preferably, it is 3.0 mass parts or less, More preferably, it is 2.5 mass parts or less, It is especially preferable to set it as 2.2 mass parts or less. When the amount of the wetting agent is too small, the surface tension of the functional layer composition may not be sufficiently reduced. On the other hand, when the amount of the wetting agent is too large, the surface tension of the functional layer composition may be too small. Moreover, when there are too many compounding quantities of a wetting agent, there exists a possibility that the adhesiveness of a functional layer may fall or the high temperature cycling characteristic of a secondary battery may fall.

<Functional layer formation process>
The functional layer forming step includes a step of applying the functional layer composition to the functional layer forming surface of the separator base material (application step), and drying the functional layer composition applied on the separator base material to form a functional layer. A process of forming (drying process) is included. In the functional layer forming step, when the functional layer composition having the surface tension described above is applied onto the functional layer forming surface having the water droplet contact angle, the functional layer composition is appropriately repelled and functions. Disperse non-uniformly without covering the entire surface of the layer formation. As a result, the functional layer formed by drying the composition for the functional layer has the above-described specific shape and phase of organic particles having a specific area ratio.

Here, in the coating process, the method for coating the functional layer composition on the separator substrate is not particularly limited. For example, the spray coating method, the doctor blade method, the reverse roll method, the direct roll method, the gravure method, the extensible method. Examples include the rouge method and the brush painting method. Of these, the gravure method and the spray coating method are preferable from the viewpoint of forming a thinner functional layer.
In the drying step, the method for drying the composition for the functional layer on the separator substrate is not particularly limited, and a known method can be used. For example, a drying method using hot air, hot air, low-humidity air, or a vacuum drying method. And a drying method by irradiation with infrared rays or electron beams. The drying conditions are not particularly limited, but the drying temperature is preferably 30 to 80 ° C., and the drying time is preferably 30 seconds to 10 minutes.
In addition, after drying the composition for functional layers, you may perform a pressurization process to a functional layer using a die press or a roll press. By the pressure treatment, the adhesion between the functional layer and the substrate can be improved.

The thickness of the functional layer formed on the separator substrate is preferably 0.01 μm or more, more preferably 0.1 μm or more, further preferably 0.5 μm or more, preferably 20 μm or less, more preferably 10 μm or less. More preferably, it is 5 μm or less. When the thickness of the functional layer is not less than the lower limit of the above range, the strength of the functional layer can be sufficiently secured. Moreover, when the thickness of the functional layer is less than or equal to the upper limit of the above range, the ion diffusibility of the functional layer can be secured and the low-temperature output characteristics of the secondary battery can be further improved.

(Non-aqueous secondary battery)
The non-aqueous secondary battery of the present invention includes a positive electrode, a negative electrode, a separator, and an electrolyte, and uses a separator for a non-aqueous secondary battery including the functional layer described above as a separator. And in the non-aqueous secondary battery of this invention, when the said functional layer functions as an adhesive layer, a positive electrode and a separator and / or a negative electrode and a separator are adhere | attached favorably through a functional layer. In addition, since the non-aqueous secondary battery of the present invention includes the separator of the present invention having a functional layer that is excellent in both adhesion and ionic conductivity in an electrolytic solution, high temperature cycle characteristics, low temperature output characteristics, etc. Excellent battery characteristics.

In the nonaqueous secondary battery, known positive electrodes and negative electrodes used in nonaqueous secondary batteries can be used as the positive electrode and the negative electrode. As the electrolytic solution, a known electrolytic solution used in a non-aqueous secondary battery can be used.

Specifically, the electrode (positive electrode and negative electrode) is not particularly limited, and an electrode in which an electrode mixture layer is formed on a current collector can be used. Here, the current collector, the components in the electrode mixture layer (for example, the electrode active material (positive electrode active material, negative electrode active material) and the electrode mixture layer binder (positive electrode mixture layer binder, negative electrode composite) As a method for forming the electrode mixture layer on the current collector, and the like, a known material can be used. Specifically, for example, those described in JP2013-145663A can be used.

As the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, when the non-aqueous secondary battery is a lithium ion secondary battery, 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 these, LiPF ₆ , LiClO ₄ , and CF ₃ SO ₃ Li are preferable, and LiPF ₆ is particularly preferable because it is easily soluble in a solvent and exhibits a high degree of dissociation. In addition, electrolyte may be used individually by 1 type and may be used combining two or more types by arbitrary ratios. Usually, the lithium ion conductivity tends to increase as the supporting electrolyte having a higher degree of dissociation is used, so that the lithium ion conductivity can be adjusted depending on the type of the supporting electrolyte.

Furthermore, the organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. For example, dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC) ), Carbonates such as butylene carbonate (BC) and ethyl methyl carbonate (EMC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; Sulfur compounds; etc. are preferably used. Moreover, you may use the liquid mixture of these solvents. Among them, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential region, and it is more preferable to use a mixture of ethylene carbonate and ethyl methyl carbonate.
The concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. For example, the concentration is preferably 0.5 to 15% by mass, more preferably 2 to 13% by mass, and more preferably 5 to 10% by mass. More preferably. Further, known additives such as fluoroethylene carbonate and ethyl methyl sulfone may be added to the electrolytic solution.

<Method for producing non-aqueous secondary battery>
A non-aqueous secondary battery is, for example, a stack of a positive electrode and a negative electrode sandwiched between separators, wound in accordance with the battery shape as needed, folded into a battery container, and an electrolyte solution in the battery container. It can be manufactured by pouring and sealing. In order to prevent the occurrence of pressure rise inside the non-aqueous secondary battery, overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expanded metal, a lead plate, etc. may be provided as necessary. . The shape of the non-aqueous secondary battery may be any of a coin shape, a button shape, a sheet shape, a cylindrical shape, a square shape, a flat shape, and the like, for example.

EXAMPLES Hereinafter, although this invention is demonstrated concretely based on an Example, this invention is not limited to these Examples. In the following description, “%” and “part” representing amounts are based on mass unless otherwise specified.
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.
In Examples and Comparative Examples, the electrolyte swelling degree and glass transition temperature of the polymer of the core part and the polymer of the shell part, the glass transition temperature of the binder for the functional layer, the volume average particle diameter D50 of the organic particles, the organic particles Core-shell ratio and coverage ratio, surface tension of the composition for the non-aqueous secondary battery functional layer, water droplet contact angle of the separator base material, ratio of the area where the organic particle phase is present, electrode and separator after immersion in the electrolyte The high-temperature cycle characteristics and low-temperature output characteristics of the secondary battery were measured and evaluated by the following methods.

<Swelling degree of electrolyte solution of polymer of core part and polymer of shell part>
Using the monomers and various additives used for the formation of the core part and shell part of the organic particles, under the same polymerization conditions as the polymerization conditions for the core part and shell part, the polymer of the core part and the shell part An aqueous dispersion containing the polymer was prepared. This aqueous dispersion was put in a petri dish made of polytetrafluoroethylene and dried under conditions of 110 ° C. and 10 hours to obtain a film having a thickness of 0.5 mm. And the obtained film was cut | judged to 1 square cm, and the test piece was obtained. The mass W0 of this test piece was measured. Further, 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 mass W1 of the test piece after the immersion test was measured. And using these mass W0 and W1, electrolyte solution swelling degree S (times) was calculated | required by S = W1 / W0.
As the electrolytic solution, a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC) and vinylene carbonate (VC) (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 / L.
<Glass transition temperature of core polymer, shell polymer and functional layer binder>
A polymer (core part) to be a measurement sample under the same polymerization conditions as the polymerization conditions of the core part and the shell part using the monomers and various additives used for forming the core part and shell part of the organic particles Water dispersions containing the polymer and the shell polymer). The prepared aqueous dispersion was used as a measurement sample. Moreover, the aqueous dispersion containing the binder for functional layers was prepared, and it was set as the measurement sample.
Next, using a differential thermal analyzer (“EXSTAR DSC6220” manufactured by SII Nano Technology), 10 mg of the dried measurement sample was weighed into an aluminum pan, an empty aluminum pan was used as a reference, and a measurement temperature range− The DSC curve was measured between 100 ° C. and 500 ° C. at a rate of temperature increase of 10 ° C./min and at normal temperature and humidity. During this temperature rising process, the baseline immediately before the endothermic peak of the DSC curve where the differential signal (DDSC) becomes 0.05 mW / min / mg or more and the tangent line of the DSC curve at the first inflection point after the endothermic peak The glass transition temperature was determined from the intersection with.
<Volume average particle diameter D50 of organic particles>
The volume average particle size D50 of the organic particles is 50% of the cumulative volume calculated from the small diameter side in the particle size distribution measured by a laser diffraction type particle size distribution measuring device (“SALD-3100” manufactured by Shimadzu Corporation). The particle diameter was taken.
<Core shell ratio of organic particles>
The core-shell ratio of the organic particles was measured by the following procedure.
The prepared organic particles were sufficiently dispersed in a visible light curable resin (“D-800” manufactured by JEOL Ltd.) and then embedded to obtain a block piece containing organic particles. Next, the obtained block piece was cut into a thin piece having a thickness of 100 nm with a microtome equipped with a diamond blade to prepare a measurement sample. Thereafter, the measurement sample was dyed using ruthenium tetroxide.
Next, the dyed measurement sample was set in a transmission electron microscope (“JEM-3100F” manufactured by JEOL Ltd.), and a cross-sectional structure of organic particles was photographed at an acceleration voltage of 80 kV. The magnification of the electron microscope was set so that the cross section of one organic particle was in the visual field. Thereafter, the cross-sectional structure of the photographed organic particles was observed, and the average thickness of the shell portion of the organic particles was measured by the following procedure according to the observed configuration of the shell portion. And the core-shell ratio was calculated | required by dividing the measured average thickness of the shell part by the volume average particle diameter D50 of organic particles.
<< When the shell part is composed of polymer particles >>
From the cross-sectional structure of the organic particles, the longest diameter of the polymer particles constituting the shell portion was measured. The longest diameter of the polymer particles constituting the shell part was measured for 20 arbitrarily selected organic particles, and the average value of the longest diameters was taken as the average thickness of the shell part.
<< When the shell has a shape other than particles >>
From the cross-sectional structure of the organic particles, the maximum thickness of the shell portion was measured. The maximum thickness of the shell portion was measured for 20 arbitrarily selected organic particles, and the average value of the maximum thickness was taken as the average thickness of the shell portion.
<Coverage of organic particles>
The organic particle coverage was measured by the following procedure.
In the same manner as the method for measuring the core-shell ratio of the organic particles, the cross-sectional structure of the organic particles is photographed. In the cross-sectional structure of the captured organic particles, the circumference D1 of the core portion and the outer surface of the core portion The length D2 of the part where the shell part abuts is measured, and the ratio (covering ratio) Rc (%) = (D2 / D1) × 100 where the outer surface of the core part of the organic particle is covered by the shell part is calculated. did. For the calculation of the covering ratio Rc, “AnalySIS Pro” (manufactured by Olympus Corporation) which is image analysis software was used.
The covering ratio Rc was measured for 20 arbitrarily selected organic particles, and the average value was defined as the average ratio (covering ratio) at which the outer surface of the core portion of the organic particles was covered by the shell portion.
<Surface tension of composition for non-aqueous secondary battery functional layer>
The prepared composition for a non-aqueous secondary battery functional layer was poured onto a glass petri dish. And the surface tension was measured by the plate method using the platinum plate. The measurement is performed twice using a fully automatic surface tension meter “CBVP-Z” manufactured by Kyowa Interface Science. The average value of the surface tension is obtained from the measured value, and the average value is used for the non-aqueous secondary battery functional layer. The surface tension of the composition was used.
<Water droplet contact angle of separator substrate>
The separator substrate was fixed on a flat plate. Then, 1 μL of ion exchange water (surface tension 72 mN / m) was dropped on the separator substrate, and the contact angle 60 seconds after the landing was measured. The measurement was performed twice using a contact angle meter “DM-901” manufactured by Kyowa Interface Science, and the average value of the water droplet contact angles was determined from the measured values, and the average value was used as the water droplet contact angle of the separator substrate. It was.
<Ratio of the area of the part where the phase of organic particles exists>
The surface of the functional layer of the separator was observed at a magnification of 5000 using a scanning electron microscope (SEM) “Hitachi S-4700” to obtain 10 SEM images. About the obtained image, the ratio of the area of the part in which the phase of an organic particle exists was computed with the following formula using image analysis software ("analysis PRO" by Olympus). And the average value of the calculated value was made into the ratio of the area of the part in which the phase of an organic particle exists with respect to the area of a functional layer formation surface. However, for the functional layer of the separator of Comparative Example 5, the ratio of the area of the portion where the organic particle phase was present to the area of the functional layer forming surface was calculated from the width of the functional layer and the functional layer formation interval.
Ratio (%) of the area where the organic particle phase exists = (area of the area where the organic particle phase exists / viewing area) × 100
<Adhesiveness between separator and electrode after immersion in electrolyte>
The prepared laminate including the positive electrode and the separator and the laminate including the negative electrode and the separator were each cut into 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. Here, as an electrolytic solution, a mixed solvent of ethylene carbonate (EC), diethyl carbonate (DEC), and vinylene carbonate (VC) (volume mixing ratio: EC / DEC / VC = 68.5 / 30 / 1.5, SP value: 12.7 (cal / cm ³ ) ^1/2 ) was used in which LiPF ₆ was dissolved in a solvent at a concentration of 1 mol / L as a supporting electrolyte.
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 of this test piece with the current collector side of 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. And the stress when one end of the separator base material was pulled vertically upward at a pulling speed of 50 mm / min and peeled was measured. 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 as the peel strength. The adhesiveness was evaluated according to the following criteria. It shows that adhesiveness is so high that peel strength is large.
A: Peel strength is 6.0 N / m or more B: Peel strength is 4.0 N / m or more and less than 6.0 N / m C: Peel strength is 1.0 N / m or more and less than 4.0 N / m D: Peel strength is <1.0 N / m <High-temperature cycle characteristics>
The manufactured lithium ion secondary battery of a wound type cell having a discharge capacity of 800 mAh was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, under an environment of 25 ° C., a charge / discharge operation of charging up to 4.35 V at 0.1 C and discharging to 2.75 V at 0.1 C was performed, and the initial capacity C0 was measured. Thereafter, charging and discharging were further repeated under the same conditions as described above under an environment of 60 ° C., and the capacity C1 after 1000 cycles was measured. Then, the capacity retention ratio ΔC (%) = (C1 / C0) × 100 before and after the cycle was calculated, and the high temperature cycle characteristics were evaluated according to the following criteria. The larger the value of the capacity retention ratio ΔC, the better the high-temperature cycle characteristics and the longer the battery life.
A: Capacity maintenance ratio ΔC is 88% or more B: Capacity maintenance ratio ΔC is 84% or more and less than 88% C: Capacity maintenance ratio ΔC is 80% or more and less than 84% D: Capacity maintenance ratio ΔC is less than 80% <low temperature output characteristics >
The manufactured lithium ion secondary battery of a wound type cell having a discharge capacity of 800 mAh was allowed to stand in an environment of 25 ° C. for 24 hours. Thereafter, charging was performed for 5 hours at a charging rate of 0.1 C under an environment of 25 ° C., and the voltage V0 at that time was measured. Thereafter, a discharge operation was performed at a discharge rate of 1 C in an environment of −10 ° C., and the voltage V1 15 seconds after the start of discharge was measured. Then, the voltage change ΔV = V0−V1 was calculated, and the low temperature output characteristics were evaluated according to the following criteria. It shows that it is excellent in low temperature output characteristics, so that the value of this voltage change (DELTA) V is small.
A: Voltage change ΔV is less than 300 mV B: Voltage change ΔV is 300 mV or more and less than 350 mV C: Voltage change ΔV is 350 mV or more

(Example 1)
<Preparation of organic particles having a core-shell structure>
In a 5 MPa pressure vessel with a stirrer, 75 parts of methyl methacrylate as a (meth) acrylic acid ester monomer, 4 parts of methacrylic acid as an acid group-containing monomer, 1 part of ethylene glycol dimethacrylate; 1 part of sodium dodecylbenzenesulfonate as an emulsifier; 150 parts of ion-exchanged water and 0.5 part of potassium persulfate as a polymerization initiator were added and sufficiently stirred. Then, it heated to 60 degreeC and superposition | polymerization was started. Polymerization was continued until the polymerization conversion rate reached 96% to obtain an aqueous dispersion containing a particulate polymer constituting the core portion.
To this aqueous dispersion, a mixture of 19 parts of styrene as an aromatic vinyl monomer and 1 part of methacrylic acid as an acid group-containing monomer was continuously added to form a shell part, and heated to 70 ° C. Polymerization was continued. When the polymerization conversion rate reached 96%, the reaction was stopped by cooling to prepare an aqueous dispersion containing organic particles having a core-shell structure in which the outer surface of the core part was partially covered with the shell part. .
The obtained organic particles had a volume average particle diameter D50 of 0.45 μm.
Then, the core-shell ratio and the coverage of the obtained organic particles were evaluated. The results are shown in Table 1.
<Preparation of functional layer binder>
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, Each was supplied, the gas phase was replaced with nitrogen gas, and the temperature was raised to 60 ° C.
On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as a dispersant, 94 parts of butyl acrylate as a (meth) acrylate monomer, 2 parts of acrylonitrile, 2 parts of methacrylic acid, 1 part of N-methylolacrylamide and 1 part of acrylamide were mixed to obtain a monomer mixture. This monomer mixture was continuously added to the reactor over 4 hours for polymerization. During the addition, the reaction was carried out at 60 ° C. After completion of the addition, the reaction was terminated by further stirring at 70 ° C. for 3 hours to prepare an aqueous dispersion containing a particulate functional layer binder (acrylic polymer).
The functional layer binder obtained had a glass transition temperature of −40 ° C.
<Preparation of non-aqueous secondary battery functional layer composition>
The aqueous dispersion containing the organic particles having the core-shell structure is 100 parts in terms of solid content, and the aqueous dispersion containing the functional layer binder is 15 parts in terms of solid content. Ethylene oxide as a wetting agent -Propylene oxide copolymer (solid content concentration 70% by mass, polymerization ratio: 5/5 (mass ratio)) is mixed with 1.9 parts in solid content, and ion-exchanged water is added to a solid content concentration of 15% by mass. Thus, a slurry-like composition for a nonaqueous secondary battery functional layer was prepared (composition preparation step). And the surface tension of the obtained composition for non-aqueous secondary battery functional layers was measured. The results are shown in Table 1.
<Preparation of separator substrate>
A polyethylene microporous film (thickness 16 μm, Gurley value 210 s / 100 cc) was prepared. The prepared microporous membrane was subjected to corona discharge treatment at a treatment strength of 50 W · min / m ² using “Air Plasma APW-602f” manufactured by Kasuga Denki, and used as a separator base material (base material preparation step). And the water droplet contact angle of the separator base material was measured. The results are shown in Table 1.
<Preparation of separator>
A slurry-like composition for a non-aqueous secondary battery functional layer was applied to both surfaces of the separator substrate by a gravure coating method (number of lines: 300) and dried at 50 ° C. for 1 minute (functional layer forming step). Thus, a functional layer having a thickness of 0.8 μm per layer was formed on the separator base material, and a separator formed by forming the functional layers on both surfaces of the separator base material was obtained. This separator includes a functional layer, a separator base material, and a functional layer in this order. And the functional layer of the separator was observed with SEM, and the ratio of the area of the part in which the phase of an organic particle exists was calculated | required. The obtained SEM image is shown in FIG. 1 and the results are shown in Table 1. In the functional layer, the phase of organic particles was present in an irregular shape. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.
<Manufacture 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, ions After adding 150 parts of exchange 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 are removed from the mixture by heating under reduced pressure, and the mixture is cooled to 30 ° C. or lower to obtain an aqueous dispersion containing a desired particulate binder (binder for negative electrode mixture layer). It was.
<Manufacture of slurry composition for negative electrode>
100 parts of artificial graphite (volume average particle size: 15.6 μm) as a negative electrode active material and 1 part of a 2% aqueous solution of carboxymethylcellulose sodium salt (“MAC350HC” manufactured by Nippon Paper Industries Co., Ltd.) as a thickener are mixed in an amount equivalent to the solid content. Further, ion 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 composition having good fluidity.
<Manufacture of negative electrode>
The slurry composition for negative electrode was applied on a copper foil having a thickness of 20 μm, which is a current collector, with a comma coater so that the film thickness after drying was about 150 μm and dried. This drying was performed by conveying the copper foil in an oven at 60 ° C. at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120 ° C. for 2 minutes to obtain a negative electrode raw material before pressing. The negative electrode raw material before pressing was rolled with a roll press to obtain a negative electrode after pressing with a negative electrode mixture layer thickness of 80 μm.
<Production of positive electrode slurry composition>
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 binder for positive electrode (positive electrode mixture layer) Polyvinylidene fluoride (manufactured by Kureha Co., Ltd., product name “# 7208”) was mixed in an amount equivalent 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 composition.
<Production of positive electrode>
The positive electrode slurry composition 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.
<Manufacture of laminate of negative electrode or positive electrode and separator>
The positive electrode after pressing was cut into a circle having a diameter of 13 mm to obtain a circular positive electrode. Further, the negative electrode after pressing was cut out into a circle having a diameter of 14 mm to obtain a circular negative electrode. Further, the separator was cut into a circle having a diameter of 18 mm to obtain a circular separator.
Then, 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 mixture layer side. Thereafter, a heat press treatment was performed at a temperature of 80 ° C. and a pressure of 0.5 MPa for 10 seconds, and the positive electrode or the negative electrode was 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. . And the adhesiveness of the separator and electrode after electrolyte solution immersion was evaluated using the produced laminated body. The results are shown in Table 1.
<Manufacture of lithium ion secondary batteries>
The pressed positive electrode was cut out to 49 cm × 5 cm. A separator cut out to 55 cm × 5.5 cm was disposed on the positive electrode mixture layer of the cut out positive electrode. Furthermore, the negative electrode after pressing was cut into 50 cm × 5.2 cm, 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 mixture layer side faced the separator. Furthermore, the separator cut out to 55 cm x 5.5 cm was arrange | positioned on the negative electrode. This was wound by a winding machine to obtain a wound body. The wound body was pressed at 60 ° C. and 0.5 MPa to obtain a flat body. This flat body is wrapped with an aluminum packaging exterior as a battery exterior, and an electrolytic solution (solvent: ethylene carbonate (EC) / diethyl carbonate (DEC) / vinylene carbonate (VC) = 68.5 / 30 / 1.5 ( Volume ratio), electrolyte: LiPF ₆ ) having a concentration of 1M was injected so that no air remained. Furthermore, in order to seal the opening of the aluminum packaging material exterior, heat sealing at 150 ° C. was performed to close the aluminum packaging material exterior. Thus, an 800 mAh wound type lithium ion secondary battery was manufactured.
And about the obtained lithium ion secondary battery, the high temperature cycling characteristic and the low temperature output characteristic were evaluated. The results are shown in Table 1.

(Examples 2 to 4)
For the preparation of organic particles and functional layers in the same manner as in Example 1 except that the amounts of methyl methacrylate, methacrylic acid and ethylene glycol dimethacrylate used for the production of the core portion were changed as shown in Table 1 when the organic particles were prepared. A binder, a composition for a non-aqueous secondary battery functional layer, a separator base material, a separator, a negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Example 5)
When preparing the organic particles, the amount of methyl methacrylate is changed to 43 parts and the amount of methacrylic acid is changed to 1 part for the monomer composition used for the production of the core part. Except for adding 35 parts of butyl acrylate as a body, in the same manner as in Example 1, organic particles, functional layer binder, non-aqueous secondary battery functional layer composition, separator substrate, separator, negative electrode, A positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Example 6)
At the time of preparing the organic particles, the amount of styrene was changed to 18 parts for the monomer composition used for the production of the shell part, and 1.7 parts of acrylonitrile as a (meth) acrylonitrile monomer and a crosslinkable monomer Organic particles, binder for functional layer, functional layer for non-aqueous secondary battery, except that 0.3 part of ethylene glycol dimethacrylate as a body was added and methacrylic acid was not added Composition, separator substrate, separator, negative electrode, positive electrode, laminate, and lithium ion secondary battery were prepared. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Example 7)
When preparing organic particles, the amount of styrene is changed to 15 parts for the monomer composition used in the production of the shell part, and 4.5 parts of acrylonitrile as a (meth) acrylonitrile monomer and a crosslinkable monomer Organic particles, functional layer binder, non-aqueous secondary battery functional layer in the same manner as in Example 1 except that 0.5 part of ethylene glycol dimethacrylate as a body was added and methacrylic acid was not added. Composition, separator substrate, separator, negative electrode, positive electrode, laminate, and lithium ion secondary battery were prepared. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Examples 8 to 9)
In the same manner as in Example 1, except that the blending amount of the ethylene oxide-propylene oxide copolymer as the wetting agent was changed as shown in Table 1 when preparing the composition for the non-aqueous secondary battery functional layer, the organic particles Then, a functional layer binder, a non-aqueous secondary battery functional layer composition, a separator substrate, a separator, a negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Examples 10 to 11)
When preparing the separator base material, the organic particles and the binder for functional layers were prepared in the same manner as in Example 1 except that the treatment strength of the corona discharge treatment for the polyethylene microporous membrane was changed as shown in Table 1. Then, a composition for a non-aqueous secondary battery functional layer, a separator substrate, a separator, a negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Comparative Example 1)
In the same manner as in Example 1 except that an ethylene oxide-propylene oxide copolymer as a wetting agent was not blended when preparing the composition for the functional layer of the non-aqueous secondary battery, the binder for organic particles and the functional layer was used. Then, a composition for a non-aqueous secondary battery functional layer, a separator substrate, a separator, a negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Comparative Example 2)
In the same manner as in Example 1, except that the blending amount of the ethylene oxide-propylene oxide copolymer as the wetting agent was changed as shown in Table 1 when preparing the composition for the non-aqueous secondary battery functional layer, the organic particles Then, a functional layer binder, a non-aqueous secondary battery functional layer composition, a separator substrate, a separator, a negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, organic particles were present uniformly over the entire surface of the separator substrate. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Comparative Example 3)
At the time of preparing the organic particles, for the monomer composition used for the production of the core part, the amount of methyl methacrylate was changed to 99 parts, the amount of methacrylic acid was changed to 1 part, and ethylene glycol dimethacrylate was not added. In addition, organic particles not having a core-shell structure, a binder for a functional layer, a composition for a functional layer of a non-aqueous secondary battery, a separator base material, and a separator in the same manner as in Example 1 except that the shell portion was not formed A negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation with SEM, the phase of organic particles having no core-shell structure was present in an irregular shape in the functional layer. Further, only organic particles having no core-shell structure were observed as particles, and the functional layer binder was not observed as particles by SEM.

(Comparative Example 4)
At the time of preparing the organic particles, the monomer composition used for the production of the shell part was changed to 1 part of styrene, methacrylic acid was not added, and methacrylic acid as a (meth) acrylic acid ester monomer was newly added. Except for adding 19 parts of methyl acid, the organic particles, the functional layer binder, the non-aqueous secondary battery functional layer composition, the separator base material, the separator, the negative electrode, the positive electrode, the laminate, and the like A lithium ion secondary battery was produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, the organic particle phase was present in an irregular shape in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

(Comparative Example 5)
At the time of preparing the composition for the non-aqueous secondary battery functional layer, the blending amount of the ethylene oxide-propylene oxide copolymer as a wetting agent was changed as shown in Table 1, and the gravure coating method was used at the time of preparing the separator. In the same manner as in Example 1 except that the composition for the non-aqueous secondary battery functional layer was applied to the separator substrate using the wire bar coating method, the organic particles, the binder for the functional layer, and the non-aqueous system were used. A composition for a secondary battery functional layer, a separator base material, a separator, a negative electrode, a positive electrode, a laminate, and a lithium ion secondary battery were produced. Various measurements and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.
As a result of observation by SEM, functional layers having a width of 100 μm were regularly formed on the separator substrate at intervals of 150 μm, and organic particles were uniformly present in the functional layer. Moreover, only organic particles were observed as particles, and the binder for functional layers was not observed as particles by SEM.

In Table 1 shown below,
“MMA” indicates methyl methacrylate;
“BA” indicates butyl acrylate,
“MAA” indicates methacrylic acid,
“EDMA” refers to ethylene glycol dimethacrylate,
“ST” indicates styrene,
“AN” indicates acrylonitrile,
“NMA” stands for N-methylolacrylamide,
“AAm” indicates acrylamide.

From Table 1, a functional layer in which the phase of organic particles having a predetermined core-shell structure and properties exists in an irregular shape and the area ratio of the portion where the phase of organic particles exists is 20% or more and 80% or less In Examples 1 to 11 using the separator having the above, it is possible to obtain a secondary battery excellent in the adhesiveness between the separator and the electrode after immersion in the electrolyte, and having good battery characteristics such as high temperature cycle characteristics and low temperature output characteristics. I understand that I can do it.
Further, from Table 1, in Comparative Example 1 using a separator in which the proportion of the area where the organic particle phase is present is less than 20%, the adhesion between the separator and the electrode after immersion in the electrolyte and the high-temperature cycle characteristics are It turns out that it falls.
Furthermore, it can be seen from Table 1 that the low-temperature output characteristics are deteriorated in Comparative Example 2 using a separator in which the proportion of the area where the organic particle phase is present is more than 80%. Table 1 also shows that in Comparative Example 2 where the amount of wetting agent used is large, the adhesion between the separator and the electrode after immersion in the electrolyte and the high-temperature cycle characteristics deteriorate.
Further, from Table 1, in Comparative Examples 3 and 4 using a separator that does not contain organic particles having a predetermined core-shell structure and properties, the adhesion between the separator and the electrode after immersion in the electrolyte and the high-temperature cycle characteristics are reduced. I understand that.
Furthermore, from Table 1, in Comparative Example 5 using a separator in which the phase of the organic particles does not exist in an irregular shape, the adhesion between the separator and the electrode after immersion in the electrolyte and the high temperature cycle characteristics may be deteriorated. I understand.

100 Organic particle 110 Core part 110S Outer surface of core part 120 Shell part

Claims

A separator for a non-aqueous secondary battery comprising a separator substrate and a functional layer formed on at least one surface of the separator substrate,
The functional layer has a configuration in which a phase of an organic particle having a core-shell structure including a core part and a shell part partially covering an outer surface of the core part exists in an irregular shape,
The core portion is made of a polymer having an electrolyte solution swelling degree of 5 times or more and 30 times or less,
The shell portion is made of a polymer having an electrolyte solution swelling degree of more than 1 time and 4 times or less,
The separator for non-aqueous secondary batteries whose ratio of the area of the part in which the phase of the said organic particle exists with respect to the area of the functional layer formation surface of the said separator base material is 20% or more and 80% or less.
The glass transition temperature of the polymer of the core part is −50 ° C. or higher and 150 ° C. or lower,
The separator for a non-aqueous 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.
A method for producing a separator for a non-aqueous secondary battery according to claim 1 or 2,
Preparing a separator substrate having a water droplet contact angle of at least one surface of not less than 80 ° and not more than 130 °;
A step of preparing a composition for a nonaqueous secondary battery functional layer containing the organic particles and a dispersion medium and having a surface tension of 33 mN / m or more and 39 mN / m or less;
The composition for a non-aqueous secondary battery functional layer is applied onto the surface of the separator base material, and the applied non-aqueous secondary battery functional layer composition is dried to form a functional layer on the separator base material. Process,
A method for producing a separator for a non-aqueous secondary battery.
A non-aqueous secondary battery comprising the non-aqueous secondary battery separator according to claim 1 or 2.