TW201907603A - Battery separator, electrode laminate, electrode coil, and battery - Google Patents

Abstract

Provided are: a separator for batteries, which suppresses increase of the internal resistance and decrease of the cycle performance, and which is suitable for improving the yield of a battery production process; an electrode laminate which is provided with this separator for batteries; an electrode roll; and a battery. A separator for batteries, which comprises a film that contains a swellable resin, and wherein the swelling starting temperature T0 is from 30 DEG C to 78 DEG C (inclusive) and the maximum swelling stress Fpeak is 5 cN or more.

Description

   Battery separator, electrode laminate, electrode winding body, and battery   

The present invention relates to a battery separator, an electrode laminate including the battery separator, an electrode wound body, and a battery.

Nonaqueous electrolyte secondary batteries, especially lithium ion secondary batteries, are widely used in small electronic devices such as mobile phones or mobile information terminals. Examples of the form of the non-aqueous electrolyte secondary battery include cylindrical batteries, horn batteries, and laminated batteries. In general, these batteries have a structure in which an electrode body and a non-aqueous electrolyte are housed in an exterior body, and this electrode system is provided with a positive electrode and a negative electrode via a battery separator. The structure of the electrode body includes, for example, a laminated electrode body in which a positive electrode and a negative electrode are laminated via a separator, and a positive electrode and a negative electrode are wound into a spiral-shaped roll via a battery separator. Around the electrode body.

Conventionally, as battery separators, microporous membranes containing polyolefin resin (also called polyolefin microporous membranes) have been mainly used. Since the polyolefin microporous membrane has a so-called shut-down function, it can suppress the flow of current by blocking the pores of the separator when the battery abnormally generates heat, thereby preventing fire or the like.

In recent years, with regard to battery separators, attempts have been made to provide layers other than polyolefin resin on one or both sides of polyolefin microporous membranes to improve battery characteristics.

For example, in Patent Document 1, there is a proposal to make a separator for a battery in which a fluorine-containing resin on the battery separator is bonded to a binder resin contained in a positive electrode and / or a negative electrode, and to suppress the positive electrode And / or peeling between the negative electrode and the separator, but including a fluorine-containing resin that will be followed by the impregnation of the electrolyte; and after impregnation of the electrolyte, pressurization is performed at 70 ° C or 90 ° C and 2 MPa, so that The positive electrode and / or the negative electrode are attached to the battery separator.

Patent Document 2 describes that a battery separator containing a resin containing fluorine followed by impregnation of an electrolyte is pressurized at 79 ° C and 1 MPa after the electrolyte is impregnated, and the positive electrode and the battery are used The partition material then follows.

There is a proposal in Patent Document 3 to make a battery separator comprising a fluorine-containing resin and an acrylic resin that will be followed by impregnation of the electrolyte, and after impregnation of the electrolyte, at 98 ° C and 0.6 MPa Pressurization is performed, and the negative electrode is then adhered to the battery separator.

Prior technical literature Patent Literature

Patent Literature 1 International Publication No. 2012/137377

Patent Document 2 Japanese Patent No. 6096395

Patent Literature 3 International Publication No. 2017/026485

Compared with angle-shaped and cylindrical batteries, laminated battery systems are prone to swelling of the electrodes due to charge and discharge. Shrinkage occurs at the interface between the battery separator and the positive electrode and / or negative electrode. As a result, the battery may expand, the internal resistance of the battery may increase, and the cycle performance may decrease.

The electrolyte contained in the electrolytic solution starts to decompose when exposed to high temperature, and the resistance of the battery may increase due to the decomposition product or the like. Specifically, for example, lithium hexafluoride phosphate (LiPF ₆ ) starts to decompose at about 100 ° C., and decomposes at a lower temperature in the presence of moisture.

In addition, the pressure from the hot press for impregnating the positive electrode and / or negative electrode and the battery separator under the electrolyte impregnation may cause a foreign substance or positive electrode and / or negative electrode that comes off from the electrode active material at the time of manufacture The burrs of the current collector are pinched, etc., and an internal short circuit or the like occurs, which deteriorates the yield during manufacturing.

An object of the present invention is to provide a separator for a battery, an electrode laminate including the separator for a battery, an electrode wound body, and a battery, the separator for a battery is suitable for the aforementioned problem, that is, to suppress an increase in internal resistance and cycle performance The reduction in the yield improves the yield in the battery manufacturing process.

In order to solve the above-mentioned problems, the present inventors have repeatedly reviewed the results and found a battery separator, an electrode laminate including the battery separator, an electrode winding body, and a battery. The battery separator is borrowed The battery separator using a specific swelling start temperature T0 and a specific swelling maximum stress Fpeak exhibits adhesion in a state containing an electrolyte at a temperature capable of suppressing decomposition of the electrolyte, and yield at the time of manufacturing good.

That is, the present invention is: (1) A battery separator having a film containing a swelling resin, a swelling start temperature T0 of 30 ° C or more and 78 ° C or less, and a swelling maximum stress Fpeak of 5cN or more. The preferred aspects of the present invention are: (2) the swelling start temperature T0 is 50 ° C or more and 70 ° C or less; (3) the swelling resin contains a resin containing fluorine; (4) the swelling resin contains a resin containing a hydrophilic group; (5) The membrane containing the swellable resin contains inorganic particles; (6) The membrane containing the swellable resin is provided on at least one side of the polyolefin microporous membrane; (7) The swellable resin is a copolymer containing hexafluoropropylene, vi The content of fluoropropene is 2.5 mol% or more and 9.0 mol% or less; (8) The swelling resin is a copolymer containing chlorotrifluoroethylene, and the content of chlorotrifluoroethylene is 0.5 mol% or more and 45.0 mol% or less.

Furthermore, the present invention is: (9) an electrode laminate including the battery separator, negative electrode, and positive electrode; (10) an electrode wound body including the battery separator, negative electrode, and positive electrode; (11) one A battery including the above battery separator.

According to the present invention, it is possible to provide a battery separator, an electrode laminate including the battery separator, an electrode winding body, and a battery, which are suitable for suppressing an increase in internal resistance and a decrease in cycle performance , To improve the yield in battery manufacturing steps.

1‧‧‧ Film containing swelling resin

2‧‧‧Polyolefin microporous membrane

10‧‧‧Single layer insulation material for battery

20‧‧‧Layered separator for battery

FIG. 1 is a diagram schematically showing a separator according to an embodiment of the present invention containing only a film containing a swelling resin.

FIG. 2 is a graph showing the swelling start temperature T0 and the swelling maximum stress Fpeak in a temperature-stress plot obtained by swelling measurement.

Fig. 3 is a diagram schematically showing a separator according to an embodiment of the present invention in which a membrane containing a swelling resin is layered on both areas of a polyolefin microporous membrane.

Forms for carrying out the invention

Hereinafter, an embodiment of the battery separator of the present invention, an electrode laminate including the battery separator, an electrode wound body, and a battery will be described. However, the present invention is not limited to the following embodiments and can be applied to the present invention. Appropriate changes are added within the scope of implementation.

Hereinafter, an embodiment of the battery separator of the present invention will be described. However, the present invention is not limited to the following embodiments at all, and can be implemented by adding appropriate changes within the scope of the present invention. In addition, the terms and vocabulary used in this specification and the scope of patent application shall not be interpreted as a general or dictionary meaning, and the inventor shall describe the invention in the best way in accordance with the so-called definition of the term. The principle of the concept is interpreted as meaning and concept consistent with the technical idea of the present invention.

    1. Film containing swelling resin    

Referring to FIG. 1, the single-layer separator for battery 10 is a film 1 containing a swellable resin.

The swelling resin-containing film 1 has a swelling start temperature T0 of 30 ° C or more and 78 ° C or less, and a swelling maximum stress Fpeak of 5cN or more.

The swelling start temperature T0 of the present invention refers to the temperature at which the film containing the swellable resin starts to swell when the battery separator is immersed in an organic solvent and heated up. It can be determined by, for example, immersing the battery separator in which 4 sheets are superimposed in an organic solvent (propylene carbonate), and using a probe (φ 1 mm) of a thermomechanical analyzer (hereinafter referred to as TMA) The tip is contacted, and the temperature at which stress is generated when the temperature is raised from room temperature at 10 ° C per minute in the fixed-length mode is measured, that is, the temperature at which the battery separator swells and the TMA probe starts to be pushed back.

The swelling maximum stress Fpeak refers to the first peak crest stress after the stress is generated in the above swelling start temperature T0 measurement method, that is, the maximum stress when the battery separator swells and the TMA probe is pushed back.

FIG. 2 shows the swelling start temperature T0 and the swelling maximum stress Fpeak in the temperature-stress graph obtained by swelling measurement.

By hot-pressing the positive electrode and / or negative electrode and the battery separator at a temperature higher than the swelling start temperature T0, the swellable resin is anchored on the electrode surface.

The upper limit of the swelling start temperature T0 is 78 ° C or lower. It is preferably 75 ° C or lower, more preferably 73 ° C or lower, and even more preferably 70 ° C or lower. If T0 exceeds 78 ° C, a pressing temperature exceeding 78 ° C is required, and the internal resistance may increase due to decomposition of the electrolyte in the electrolyte. If T0 is 78 ° C or lower, the pressing temperature can be reduced to 78 ° C or lower, the electrolyte is not decomposed, and an increase in internal resistance can be suppressed.

The lower limit of the swelling start temperature T0 is 30 ° C or higher. It is preferably 40 ° C or higher, more preferably 50 ° C or higher, and even more preferably 60 ° C or higher. If T0 is lower than 30 ° C, it will have fluidity even at room temperature, and there may be a case where adhesiveness cannot be exhibited, which may deteriorate the cycle performance. If T0 is 30 ° C. or higher, the adhesiveness can be maintained at room temperature, and the deterioration of the cycleability can be suppressed.

The lower limit value of the swelling maximum stress Fpeak is 5 cN or more. It is preferably 6 cN or more. If it is less than 5 cN, in order to anchor the swellable resin for the battery separator to the electrode surface, a high pressure is required during hot pressing, specifically, a pressure of 1 MPa or more. If the pressure at the time of hot pressing is high, foreign substances that come off from the electrode active material at the time of manufacture, or the burrs of the electrode current collector, etc., are pressed, and an internal short circuit or the like occurs, which deteriorates the yield at the time of manufacture. Even if the swellable resin of the battery separator is anchored on the electrode surface, there is no adhesiveness between the battery separator and the electrode, peeling occurs, and the cycle performance deteriorates.

In addition, if the swelling maximum stress Fpeak is less than 5 cN, the film containing the swellable resin does not flow during hot pressing, and there may be no adhesion.

If the swelling maximum stress Fpeak is 5 cN or more, the adhesion after being impregnated with the electrolyte can be sufficiently ensured. This means that the molecular chains of the swellable resin continue to entangle due to the temperature of hot pressing and swell moderately. This is due to the good gel hardness caused by the loss of fluidity and gelation after cooling after hot pressing. of.

    [Swelling resin]    

Swelling resin means a resin that swells the electrolyte. The resin that swells to the electrolyte refers to a resin that swells when the resin is impregnated with the electrolyte or the organic solvent used in the electrolyte, and the temperature is increased. The swelling resin specifically includes, for example, fluorine-containing resin, acrylonitrile-containing resin, vinyl acetate-containing resin, ethylene oxide-containing resin, propylene oxide-containing resin, and the like. Among them, from the viewpoint of oxidation resistance, fluorine-containing resins are preferred. In addition, the swelling resin preferably contains a resin containing a hydrophilic group.

For the resin containing fluorine, it is preferably polymerized using at least one polymerization unit selected from the group consisting of polymerization unit species including vinylidene fluoride, hexafluoropropylene, trifluoroethylene, tetrafluoroethylene, and chlorotrifluoroethylene Homopolymer, or copolymer. In particular, from the viewpoint of swelling to the electrolyte, a copolymer containing vinylidene fluoride and other polymerized units is preferred, and a vinylidene fluoride-hexafluoropropylene copolymer or vinylidene fluoride- Chlorotrifluoroethylene copolymer.

The fluorine-containing resin preferably contains a hydrophilic group. The swelling start temperature T0 can also be adjusted by controlling the proportion of the hydrophilic group in the fluorine-containing resin. In addition, the fluorine-containing resin becomes more firmly adhered to the active material present on the electrode surface or the binder component in the electrode by having a hydrophilic group. The reason for this is not particularly limited, and it is presumed that the adhesive force will increase due to hydrogen bonding.

Examples of the hydrophilic group include hydroxyl groups, carboxylic acid groups, and sulfonic acid groups. Among these, carboxyl groups are particularly preferred. In addition, it may be in the form of a salt such as carboxylate or sulfonate.

As a method of introducing a hydrophilic group into a fluorine-containing resin, a well-known method can be used, for example, when synthesizing a fluorine-containing resin, by using maleic anhydride, maleic acid, maleate, and male A method of introducing a main chain by copolymerizing a monomer having a hydrophilic group such as monomethyl methacrylate or a method of introducing a side chain by grafting, etc. In particular, from the viewpoint of adjusting the swelling start temperature T0 and the swelling maximum stress Fpeak, the monomer having a hydrophilic group is preferably monomethyl maleate.

The lower limit of the content of the monomer unit having a hydrophilic group in the fluorine-containing resin is preferably 0.1 mol% or more, more preferably 0.3 mol% or more, and the upper limit is preferably 5 mol% or less, It is more preferably 4 mol% or less. By setting the content of the monomer unit having a hydrophilic group within the above-mentioned preferred range, interaction between the hydrophilic group and the surface of the active material in the electrode or the hydrophilic part of the binder component in the electrode occurs, enabling the It has good adhesion to the electrode when inserted into the battery. If the content of the monomer unit having a hydrophilic group is 5 mol% or less, sufficient polymer crystallinity can be ensured, so that the swelling degree to the electrolyte can be reduced, and good compatibility with the electrode can be obtained when the battery is installed Continuity. In addition, when the porous layer contains particles, it is possible to prevent the particles from falling off by setting the content of the monomer unit having a hydrophilic group within the above-described preferred range.

The content of the monomer unit having a hydrophilic group in the vinylidene fluoride-hexafluoropropylene copolymer can be measured by FT-IR, NMR, quantitative titration, or the like. For example, in the case of a carboxylic acid group, FT-IR can be used to obtain the ratio of the absorption strength of C-H stretching vibration and C = O stretching vibration of the carboxyl group based on the homopolymer as a reference.

When the swelling resin is a copolymer, if the introduction amount of the polymerization unit of the fluorine-containing resin is increased, the swelling start temperature T0 can be lowered.

Specifically, for example, in the case where the swelling resin is a copolymer containing hexafluoropropylene, in order to easily reduce the swelling start temperature T0, the content of hexafluoropropylene is preferably 2.5 mol% or more, more preferably More than 3.0 mole%. In order to make it easier to adjust the swelling start temperature T0 of the invention, it is preferably 9.0 mol% or less, and more preferably 8.0 mol% or less.

For example, in the case where the swelling resin is a copolymer containing chlorotrifluoroethylene, in order to easily reduce the swelling start temperature T0, the content of chlorotrifluoroethylene is preferably 0.5 mol% or more, more preferably 10 mol Ear% or more. In order to make it easier to adjust the swelling start temperature T0 of the invention, it is preferably 45.0 mol% or less, and more preferably 40.0 mol% or less.

When the swelling resin is a copolymer containing vinylidene fluoride and other polymerized units, if the amount of other polymerized units introduced is increased, the swelling start temperature T0 can be lowered.

Specifically, for example, in the case of a copolymer containing vinylidene fluoride and hexafluoropropylene, if the hexafluoropropylene is 2.5 mol% or more and 9.0 mol% or less, the swelling start temperature T0 of the invention can be adjusted , Which is better. In the case of a copolymer containing vinylidene fluoride and chlorotrifluoroethylene, if the chlorotrifluoroethylene is 0.5 mol% or more and 45.0 mol% or less, the swelling start temperature T0 of the invention can be adjusted, which is preferable .

The copolymer containing vinylidene fluoride and other polymerization units can be obtained by a suspension polymerization method or the like. During the polymerization, the swelling start temperature T0 can be adjusted by changing the ratio of the head-to-head bonding (-CH ₂ -CF ₂ -CF ₂ -CH _2- ) of the vinylidene fluoride unit. The swelling start temperature T0 can be reduced by increasing the ratio of head-to-head bonding of the vinylidene fluoride unit.

The weight average molecular weight of the fluorine-containing resin is not particularly limited, but the lower limit is preferably 700,000 or more, and more preferably 1 million or more. The upper limit value is preferably 2 million or less, and more preferably 1.5 million or less. When the weight-average molecular weight of the fluorine-containing resin is within the above range, in the step of forming the film containing the swellable resin, the time for dissolving the fluorine-containing resin in the solvent can be reduced to improve production efficiency, or the cost can be adjusted. Invented swelling maximum stress Fpeak. In addition, the weight average molecular weight of the fluorine-containing resin is based on the polystyrene conversion value of gel permeation chromatography.

The resin containing acrylonitrile is preferably a resin that polymerizes acrylonitrile. In addition, a copolymer containing styrene and acrylonitrile is also preferable.

The acrylonitrile-containing resin preferably contains a hydrophilic group. As a method of introducing a hydrophilic group, a known method can be used.

The film containing the swellable resin may contain resins other than the swellable resin within a range that does not impair the swelling start temperature T0 and the swell maximum stress Fpeak of the present invention.

    [Inorganic particles]    

The film containing a swellable resin may contain inorganic particles from the viewpoint of heat resistance. When a swelling resin containing a hydrophilic group is used, the swelling maximum stress Fpeak can be increased by the interaction between the inorganic particles and the hydrophilic group of the swelling resin. The amount of the hydrophilic group is not particularly limited, but the lower limit is preferably 0.1 mol% or more, more preferably 0.3 mol% or more, and the upper limit is preferably 5 mol% or less, more preferably 4 mol% the following.

Examples of inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass particles, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, Calcium fluoride, lithium fluoride, zeolite, molybdenum sulfide, mica, diaspore, magnesium oxide, etc. In particular, from the viewpoint of affinity with the fluorine-containing resin, it is preferable to use one or more kinds selected from titanium dioxide, aluminum oxide, and diaspore.

The content of the particles is preferably 85% by mass or less, more preferably 80% by mass or less, even more preferably 75% by mass or less, and the lower limit with respect to the total amount of the swellable resin and the particles It is preferably 50% by mass or more, more preferably 60% by mass or more, and still more preferably 65% by mass or more. By setting the content of the particles within the above-mentioned preferred range, a good balance of air permeability can be easily obtained.

    2. Laminated film containing swelling resin    

The laminate film containing a swelling resin means, for example, referring to FIG. 3, a battery laminate separator 20 in which a film containing a swelling resin is laminated on both areas of the polyolefin microporous membrane 2. The polyolefin microporous membrane 2 is not particularly limited, and a polyolefin microporous membrane used for a known battery separator can be used.

In the present invention, a microporous membrane means a membrane having connected voids inside. The microporous membrane is not particularly limited, and a nonwoven fabric or microporous membrane can be used. Hereinafter, a polyolefin microporous membrane in which the resin constituting the microporous membrane is a polyolefin resin will be described in detail.

Examples of polyolefin resins include polyethylene, polypropylene, polybutene, and polypentene.

The mass average molecular weight (Mw) of the polyolefin resin is not particularly limited, but it is usually in the range of 1 × 10 ⁴ to 1 × 10 ⁷ , preferably in the range of 1 × 10 ⁴ to 15 × 10 ⁶ , and more It is preferably in the range of 1 × 10 ⁵ to 5 × 10 ⁶ .

The polyolefin resin preferably contains polyethylene. Examples of polyethylene include ultra-high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene.

In addition, the polymerization catalyst is not particularly limited, and can be cited by Ziegler. Polyethylene manufactured by polymerization catalysts such as Nata catalysts, Philips catalysts, and metallocene catalysts. These polyethylenes are not just homopolymers of ethylene, but may also be copolymers containing small amounts of other α-olefins. For α-olefins other than ethylene, it can be suitably used: propylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene, 1-octene, (methyl) Acrylic acid, (meth) acrylic acid ester, styrene, etc.

The polyethylene may be a single substance, but it is preferably a mixture containing two or more kinds of polyethylene. As for the polyethylene mixture, a mixture of two or more types of ultra-high molecular weight polyethylene with different Mw, a mixture of the same high-density polyethylene, a mixture of the same medium-density polyethylene, and a mixture of low-density polyethylene can be used. In addition, a mixture of two or more types of polyethylene selected from the group consisting of ultra-high molecular weight polyethylene, high density polyethylene, medium density polyethylene, and low density polyethylene can also be used.

Among them, regarding the mixture of polyethylene, from the viewpoint of the responsiveness of the shutdown phenomenon to temperature rise (shutdown speed), or maintaining the shape of the polyolefin porous membrane in the high temperature region above the shutdown temperature and maintaining the insulation between the electrodes, More preferably, it is a mixture containing an ultra-high molecular weight polyethylene having an Mw of 5 × 10 ⁵ or more, and a polyethylene having an Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ . The Mw of the ultra-high molecular weight polyethylene is preferably in the range of 5 × 10 ⁵ to 1 × 10 ⁷ , more preferably in the range of 1 × 10 ⁶ to 15 × 10 ⁶ , and particularly preferably in the range of 1 × 10 ⁶ ~ 5 × 10 ⁶ in the range. For polyethylene having an Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , any one of high-density polyethylene, medium-density polyethylene, and low-density polyethylene can be used, but it is particularly preferred to use high-density polyethylene . For polyethylene having an Mw of 1 × 10 ⁴ or more and less than 5 × 10 ⁵ , two or more types of polyethylenes having different Mws may be used, or two or more types of polyethylenes having different densities may be used. It is possible to easily perform melt extrusion by setting the upper limit value of Mw of the polyethylene mixture to 15 × 10 ⁶ . The content of ultra-high molecular weight polyethylene in the polyethylene mixture is preferably 1% by weight or more relative to the entire mixture of polyethylene, and more preferably in the range of 10 to 80% by weight.

For polyolefin resins, for the purpose of improving melt-down characteristics and high-temperature storage characteristics of batteries, it may also be a mixture of polyethylene and polypropylene. The Mw of polypropylene is preferably in the range of 1 × 10 ⁴ to 4 × 10 ⁶ . In the case of polypropylene, homopolymers or block copolymers and / or random copolymers containing other α-olefins can also be used. For other α-olefins, ethylene is preferred. The overall polyolefin mixture is set to 100% by weight, and the content of polypropylene is preferably set to 80% by weight or less.

In order to improve the characteristics as a battery separator, polyolefin resins may contain polyolefins that impart shutdown characteristics. For the polyolefin imparting closing characteristics, for example, low-density polyethylene can be used. For low-density polyethylene, it is preferably at least one selected from the group consisting of ethylene / α-olefin copolymers produced by branched, linear, and single-point catalysts. The total polyolefin content is 100% by weight, and the amount of low-density polyethylene added is preferably 20% by weight or less. If the amount of low-density polyethylene added exceeds 20% by weight, film breakage will easily occur during stretching, which is not good.

In the polyethylene composition containing the above ultra-high molecular weight polyethylene, poly 1-butene containing Mw in the range of 1 × 10 ⁴ to 4 × 10 ⁶ and Mw in the range of 1 × 10 ³ to 4 × may be added. polyethylene wax is in the range of ^104, Mw of ethylene and in the range of ^{1 × 10 4 ~ 4 × 10} 6 a / α- olefin copolymer group of at least one polyolefin as an optional component. The polyolefin composition is set to 100% by weight, and the addition amount of these optional components is preferably 20% by weight or less.

The polyolefin microporous membrane has a plurality of fine pores, but the porosity is preferably 20 to 80%. Since the porosity of the polyolefin microporous membrane is 20% or more, it is possible to achieve good air permeability of the separator, and it is possible to suppress an increase in resistance generated by the membrane and circulate a large current, which is preferable. In addition, the porosity of the polyolefin microporous membrane is 80% or less, and it is preferable to obtain sufficient mechanical strength of the separator. The void rate is more preferably 25 to 65%, and particularly preferably 30 to 55%. In addition, the porosity refers to the proportion (volume%) of the void portion in the porous base material.

    [Manufacturing method of battery separator]    

The battery separator can be exemplified by a single-layer separator for batteries and a laminated separator for batteries.

The manufacturing method will be described by taking the laminated separator for batteries as an example. The following steps (1) and (2) are included in sequence.

(1) Step of using a swelling resin solution in which a swelling resin has been dissolved in a solvent as a coating liquid

(2) The step of applying the coating liquid to the polyolefin microporous membrane, immersing it in the coagulation liquid, and washing and drying

In the case of forming a film containing inorganic particles and containing a swellable resin, it can be obtained by using a coating liquid in which inorganic particles are added to a swellable resin solution and mixed and dispersed.

More specifically, for example, the swelling resin is slowly added to the solvent to completely dissolve it. The solvent is not particularly limited as long as it can dissolve the swelling resin and can be mixed with the coagulating liquid. From the viewpoint of solubility and low volatility, N-methyl-2-pyrrolidone is preferred.

The method of applying the coating liquid to the polyolefin microporous membrane may be a well-known method, and examples thereof include dip coating method, reverse roll coating method, gravure coating method, kiss coating method, roll brush method, spray coating method, and air knife coating Method, Mayer bar coating method, pipe doctor method, blade coating method, bar coating method, die coating method, etc., these methods can be implemented individually or in combination.

The laminated separator for batteries may have a film containing a swelling resin on at least one side of the polyolefin microporous membrane, a film containing a swelling resin on one area of the polyolefin microporous film, or a polyolefin microporous film The two-area layer contains a film of swellable resin. In addition, the battery laminate separator may further laminate another layer between the membrane containing the swellable resin and the polyolefin microporous membrane within a range that does not hinder the swelling start temperature T0 and the swelling maximum stress Fpeak in the swelling measurement.

Next, a method of manufacturing a single-layer separator for batteries will be described. For example, in the above manufacturing method, the polyolefin microporous membrane can be replaced with a PET film, coated on the PET film, immersed in a coagulating liquid, washed, and dried, and then the PET film can be obtained.

The thickness of the single-layer separator for batteries is preferably 1 μm or more and 10 μm or less, more preferably 2 μm or more and 8 μm or less, and still more preferably 2 μm or more and 6 μm or less.

The thickness of the swellable resin layer in the battery laminate separator is preferably 0.5 μm or more and 5 μm or less, more preferably 1 μm or more and 4 μm or less, and even more preferably 1 μm or more and 3 μm or less on each side.

    [Battery separator]    

The battery separator of the present invention can be suitably used for any of batteries using aqueous electrolytes and batteries using non-aqueous electrolytes, but can be more suitably used for non-aqueous electrolyte secondary batteries. Specifically, it can be suitably used as a separator for secondary batteries such as nickel-hydrogen batteries, nickel-cadmium batteries, nickel-zinc batteries, silver-zinc batteries, lithium secondary batteries, and lithium polymer secondary batteries. Among them, it is preferably used as a separator for lithium ion secondary batteries.

In a non-aqueous electrolyte secondary battery, the positive electrode and the negative electrode are arranged with a separator in between, and the separator contains an electrolyte. The structure of the non-aqueous electrolyte electrode is not particularly limited, and a conventionally known structure can be used. For example, it can have a coin-shaped electrode structure in which a disc-shaped positive electrode and a negative electrode are opposed to each other, and a flat plate-shaped positive electrode is alternately stacked Laminated electrode structure of the negative electrode, the electrode structure of the wound positive electrode and the negative electrode of the laminated strip, etc. The battery separator according to this embodiment can have excellent adhesion between the separator and the electrode in any battery structure.

The current collector, positive electrode, positive electrode active material, negative electrode, negative electrode active material, and electrolytic solution used in a non-aqueous electrolyte secondary battery including a lithium ion secondary battery and the like are not particularly limited, and can be suitably used in combination with conventionally known materials. .

The organic solvent contained in the electrolytic solution may be a carbonate-based solvent, and it may be a single type or a mixture of two or more types. Specifically, examples thereof include ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, vinyl fluoride carbonate, and vinylene carbonate.

Examples of the electrolyte include LiPF ₆ , LiBF ₄ , LiClO ₄ , LiN (CF ₃ SO ₂ ) ₂ , Li (C ₂ F ₅ SO ₂ ) ₂ and the like.

In addition, the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications within the scope of the gist thereof.

    [Example]    

Hereinafter, the present invention will be described in further detail with examples, but the embodiments of the present invention are not limited to these examples. In addition, the evaluation methods and various analysis methods and materials used in the examples are as follows.

    (1) Film thickness    

Using a contact-type film thickness meter ("Lightomatic" (registered trademark) series 318 manufactured by Mitsutoyo Co., Ltd.), the film thickness of the polyolefin microporous membrane and the battery separator was measured. In the measurement system, a super-hard spherical probe Φ 9.5 mm was used, and 20 points were measured under a weight of 0.01 N. The average value of the obtained measurement values was used as the film thickness.

    (2) Weight average molecular weight (Mw) of swellable resin    

It was obtained by gel permeation chromatography under the following conditions. From the calibration curve obtained by using a monodisperse polystyrene standard sample, Mw is determined using a predetermined conversion factor.

Measuring device: GPC-150C manufactured by Waters Corporation

Pipe column: Shodex KF-806M made by Showa Denko Co., Ltd. 2 pieces

Column temperature: 23 ℃

Solvent (mobile phase): 0.05M N-methyl-2-pyrrolidone with lithium chloride added

Flow rate of solvent: 0.5ml / min

Sample preparation: Add 2mL of the measurement medium to 2mg of the sample and stir it steadily at room temperature (visually confirm the dissolution)

Injection volume: 0.2mL

Detector: differential refractive index detector RI (manufactured by Tosoh Corporation, RI-8020 type, sensitivity 16)

    (3) Swelling measurement: swelling start temperature T0    

This measurement system uses a thermomechanical machine equipped with a quartz penetration test rod (manufactured by NETZSCH JAPAN Co., Ltd., model T1442-010, diameter of the compression part 1 mm) and a quartz compression support tube (manufactured by NETZSCH JAPAN Co., Ltd., model T1442-03) An evaluation device (manufactured by NETZSCH JAPAN Co., Ltd., model TMA4000SE) was used for evaluation. The following sample was used as a sample: 4 pieces of the separator made in the production example were stacked, perforated to φ 5 mm, set in a quartz penetrating container (manufactured by NETZSCH JAPAN Co., Ltd., model T1162-091), and then 150 μL of propylene carbonate was dropped , Use a differential pressure gauge to perform a pressure reduction of -0.1MPa for 2 minutes, and return to atmospheric pressure to impregnate the battery separator. Next, the sample was set in the support tube of TMA4000SE. Start the measurement software, set the sample installation load to 0.5g, and set it to fixed-length stress in the program window, set to offset (offset) 0g, standby time 0 hours, amplitude 0g, cycle 0 seconds, and start manually. After that, the temperature setting system was set as follows, the measurement was started under a nitrogen flow of 200 cc / min, and the stress variation trend at the time of temperature increase was measured.

Setting temperature range: 30 ℃ to 120 ℃

Heating rate: 10 ℃ / min

In the temperature-stress graph obtained by this measurement (FIG. 2), the initial temperature at which the increase in stress at 1 ° C. rises to 0.3 cN / ° C. or higher is taken as the temperature at which swelling starts. For example, when the temperature rise is performed, when the increase in stress at 1 ° C rise is 0.3 cN / ° C or more for the first time in the range of 50 ° C to 51 ° C, 50 ° C is used as the temperature at which swelling starts. This series of measurements was performed three times in total, and the three temperature-stress plots were obtained for each to obtain the temperature at which swelling started, and the average value was taken as the swelling start temperature T0.

    (4) Swelling measurement: swelling maximum stress Fpeak    

In the measurement of the swelling start temperature T0 three times in total, the stress (cN) of the peak top is read separately, and the average value of these is taken as the swelling maximum stress Fpeak (cN).

    (5) Battery evaluation         [Production of positive electrode]    

An NMP solution containing 1.2 parts by mass of PVDF was added to 97 parts by mass of lithium cobaltate and 1.8 parts by mass of carbon black to mix, to prepare a slurry containing a positive electrode composite additive. This slurry containing the positive electrode composite additive was uniformly coated on both sides of the positive electrode current collector containing an aluminum foil with a thickness of 20 μm, dried to form a positive electrode layer, and thereafter, compression molded using a roller press so as not to include the current collector The density of the positive electrode layer was 3.6 g / cm ³ , and the positive electrode was produced.

    [Production of negative electrode]    

An aqueous solution containing 1.0 part by mass of sodium carboxymethylcellulose was added to 98 parts by mass of artificial graphite and mixed, and further 1.0 part by mass of styrene butadiene latex was added as a solid component and mixed to make a compound additive containing a negative electrode Of slurry. This slurry containing the negative electrode composite additive was uniformly coated on both sides of the negative electrode current collector including a copper foil with a thickness of 10 μm, dried to form a negative electrode layer, and then subjected to compression molding using a roller press so that The density of the negative electrode layer of the electric body was 1.45 g / cm ³ , and a negative electrode was produced.

    [Manufacture of test battery]    

A wound body was produced by using the positive electrode and the negative electrode with a tab and each microporous membrane. Next, the wound body was placed in an aluminum laminated bag, and an electrolyte solution (1.1 mol / L, LiPF ₆ , ethylene carbonate / ethyl carbonate / divinyl carbonate = 3/5/2 (volume ratio) was dropped 0.5 wt% of vinylene carbonate and 2 wt% of vinyl fluoride carbonate were added to 750 μL, and sealed in a vacuum laminator. Next, using a precision heating and pressurizing device (manufactured by Shinto Industries Co., Ltd., CYPT-10), heat and pressure treatment was performed at the temperature, pressure, and 2 minutes and 30 seconds described in Table 1, and this was used as a 300 mAh test battery.

    [Resistance test]    

The test battery was charged at a constant current and a constant voltage of 0.2C (C represents a current value that can fully charge the battery in 1 hour), 4.35V, and a cut-off current of 0.05C, and then was discharged at a constant current of 0.2C and 3V. The test battery for the discharge state after this charge and discharge was repeated 4 times was measured for resistance at 25 ° C. and 1 kHz using Battery HiTester 3561 (manufactured by Hitachi Electric Co., Ltd.). The test was carried out with three batteries, and the average value of resistance was derived.

At this time, those with a value of 75 mΩ or less are considered good and marked with ○. Those exceeding 75 mΩ are regarded as insufficient, and marked as ×.

    [Cycle performance test]    

Using the battery after the above resistance test, a cycle performance test was conducted under the following charge and discharge conditions.

Charging: 1C, 4.35V constant current and constant voltage charging, cut-off current 0.05C

Discharge: 1C, 3V constant current discharge

Measuring temperature: 25 ℃

It was implemented with three test batteries, and the ratio of the 400th charge capacity based on the 1C charge capacity of the first time, that is, the average value of the capacity maintenance rate, was derived as an index of cycle performance.

At this time, the average value of the capacity retention rate is 85% or more, which is particularly good, and is marked as ⊚. Those who are 80% or more and less than 85% are considered good, and are marked with ○. If it is less than 80%, it is regarded as insufficient and marked as ×.

    [Self-discharge test]    

1000 test batteries were produced and charged at a constant current and voltage of 0.2C, 4.35V, and a cut-off current of 0.05C. Next, in a pause state (a state where charging and discharging are not performed), the voltage after 24 hours becomes 3.5 V or less is regarded as a failure, and the number of failed test batteries is 1 or less as a good, 2 More than one is considered bad.

    (Production Example 1)    

As the swelling resin, the following copolymer was synthesized. Using vinylidene fluoride, hexafluoropropylene and monomethyl maleate as starting materials, the molar ratio of vinylidene fluoride / hexafluoropropylene / monomethyl maleate to 96.5 / 3.0 by suspension polymerization /0.5 to synthesize the copolymer. The weight average molecular weight of the obtained copolymer was 1.5 million.

After mixing 30.7 parts by mass of the copolymer obtained in the above order with 669.2 parts by mass of N-methyl-2-pyrrolidone, alumina particles (average particle diameter 1.1 μm, density) were added while stirring with a disperser 4.0g / cc) 69.3 parts by mass, further preliminarily stirred with a disperser at 2000 rpm for 1 hour. Next, using DYNO-MILL (DYNO-MILL Multi Lab (1.46L container, filling rate 80%, Φ 0.5mm alumina beads) manufactured by SHINMARU ENTERPRISES), under the conditions of a flow rate of 11 kg / hr and a peripheral speed of 10 m / s The treatment was performed three times to prepare a coating liquid (A). By the dip coating method, the obtained coating liquid (A) was equally applied to both sides of a polyethylene microporous membrane having a thickness of 7 m, a porosity of 40%, and an air permeability of 100 seconds / 100 cc. The coated film was immersed in an aqueous solution containing 10% by mass of N-methyl-2-pyrrolidone for 30 seconds, washed with pure water, and then dried at 50 ° C to obtain a battery separator. The thickness of the battery separator is 10 μm. When swelling measurement was performed, the swelling start temperature T0 was 65 ° C, and the swelling maximum stress Fpeak was 10 cN.

    (Production example 2)    

Except that it is synthesized in such a way that the molar ratio of vinylidene fluoride / chlorotrifluoroethylene / monomethyl maleate is 70.5 / 29.0 / 0.5, and the weight average molecular weight is 1.5 million, it is used as the swelling resin. The battery separator was obtained in the same manner. The swelling measurement was performed, the swelling start temperature T0 was 55 ° C, and the swelling maximum stress Fpeak was 10 cN.

    (Production Example 3)    

In addition to using a swellable resin synthesized in such a manner that the molar ratio of vinylidene fluoride / hexafluoropropylene / monomethyl maleate is 96.5 / 3.0 / 0.5 and the weight average molecular weight is 1 million, it is the same as Preparation Example 1. The battery separator was obtained in the same manner. The swelling measurement was performed, the swelling start temperature T0 was 67 ° C, and the swelling maximum stress Fpeak was 6 cN.

    (Production Example 4)    

Except that it was synthesized in such a way that the molar ratio of vinylidene fluoride / hexafluoropropylene / monomethyl maleate was 92.5 / 7.0 / 0.5 and the weight average molecular weight was 1.5 million, it was used as the swelling resin. The battery separator was obtained in the same manner. The swelling measurement was performed, the swelling start temperature T0 was 51 ° C, and the swelling maximum stress Fpeak was 9 cN.

    (Production Example 5)    

Except that it was synthesized in such a way that the molar ratio of vinylidene fluoride / hexafluoropropylene / monomethyl maleate was 98.5 / 1.0 / 0.5 and the weight average molecular weight was 1.5 million, it was used as the swelling resin. The battery separator was obtained in the same manner. The swelling measurement was performed, the swelling start temperature T0 was 83 ° C, and the swelling maximum stress Fpeak was 11 cN.

    (Production Example 6)    

Except that Kynar Flex (registered trademark) 2851-00 (manufactured by Arkema) was used as the swelling resin, the same procedure as in Production Example 1 was performed to obtain a battery separator. The swelling measurement was performed, the swelling start temperature T0 was 73 ° C, and the swelling maximum stress Fpeak was 2cN.

    (Production Example 7)    

A battery separator was obtained in the same manner as in Production Example 1, except that the vinylidene fluoride / chlorotrifluoroethylene molar ratio was 71.0 / 29.0 and the weight average molecular weight was 600,000 as the swelling resin. material. The swelling measurement was performed, the swelling start temperature T0 was 55 ° C, and the swelling maximum stress Fpeak was 4 cN.

    (Example 1)    

Using the separator obtained in Preparation Example 1, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1. A self-discharge test was conducted and the result was good.

    (Example 2)    

Using the separator obtained in Preparation Example 2, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Example 3)    

Using the separator obtained in Preparation Example 3, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Example 4)    

Using the separator obtained in Preparation Example 4, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Example 5)    

Using the separator obtained in Preparation Example 2, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Example 6)    

Using the separator obtained in Preparation Example 4, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Example 7)    

Using the separator obtained in Preparation Example 4, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Comparative example 1)    

Using the separator obtained in Preparation Example 5, an electrical resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Comparative example 2)    

Using the separator obtained in Preparation Example 6, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Comparative example 3)    

Using the separator obtained in Preparation Example 7, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Comparative example 4)    

Using the separator obtained in Preparation Example 5, an electrical resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Comparative example 5)    

Using the separator obtained in Preparation Example 6, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Comparative example 6)    

Using the separator obtained in Preparation Example 6, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Reference example 1)    

Using the separator obtained in Preparation Example 1, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Reference example 2)    

Using the separator obtained in Preparation Example 5, an electrical resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1.

    (Reference example 3)    

Using the separator obtained in Preparation Example 1, a resistance test and a cycle performance test were performed at the hot pressing temperature and hot pressing pressure described in Table 1. A self-discharge test was conducted and the result was bad.

As clearly shown in Table 1, it can be seen that the battery using the battery separator of the present invention having a swelling start temperature T0 of 30 to 78 ° C. and a swelling maximum stress Fpeak of 5 cN or more is used. Resistance test and cycle performance test are good.

In addition, as clearly shown in Example 1 and Reference Example 3, it can be seen that the yield is good by setting the hot-pressing pressure to 0.6 MPa.

Industrial availability

The battery separator of the present invention exhibits adhesiveness in a state containing an electrolyte at a temperature capable of suppressing the decomposition of an electrolyte, and has a good yield at the time of manufacture, and can be used for an electrode laminate or an electrode wound body , And batteries.

Although the present invention has been described in detail and with reference to specific embodiments, it should be understood by those skilled in the art that various changes or modifications can be added without departing from the spirit and scope of the present invention.

This application is based on the Japanese patent application filed on June 29, 2017 (Japanese Patent Application No. 2017-127165), the contents of which are incorporated herein by reference.

Claims (11)

    A battery separator having a film containing a swelling resin, a swelling start temperature T0 of 30 ° C or more and 78 ° C or less, and a swelling maximum stress Fpeak of 5cN or more.         The battery separator according to claim 1, wherein the swelling start temperature T0 is 50 ° C or higher and 70 ° C or lower.         The battery separator according to claim 1 or 2, wherein the swellable resin contains a fluorine-containing resin.         The battery separator according to any one of claims 1 to 3, wherein the swelling resin contains a resin containing a hydrophilic group.         The battery separator according to any one of claims 1 to 4, wherein the swellable resin-containing film contains inorganic particles.         The battery separator according to any one of claims 1 to 5, which has the swelling resin-containing film on at least one side of the polyolefin microporous film.         The battery separator according to any one of claims 1 to 6, wherein the swellable resin system contains a copolymer of hexafluoropropylene, and the content of hexafluoropropylene is 2.5 mol% or more and 9.0 mol% or less.         The battery separator according to any one of claims 1 to 6, wherein the swellable resin system contains a copolymer of chlorotrifluoroethylene, and the content of chlorotrifluoroethylene is 0.5 mol% or more and 45.0 mol% or less.         An electrode laminate including the battery separator according to any one of claims 1 to 8, a negative electrode, and a positive electrode.         An electrode wound body comprising the battery separator according to any one of claims 1 to 8, a negative electrode, and a positive electrode.         A battery comprising the battery separator according to any one of claims 1 to 8.