KR20180071959A - Separator for energy storage device, and laminated body, roll, lithium ion secondary battery or energy storage device using the same - Google Patents

Abstract

The present invention provides a separator for a power storage device which is excellent in exfoliation strength of a substrate and a modified layer, battery winding when the separator is wound around a cylindrical battery, a thermal shock property and a low temperature cycle property among basic properties required in a conventional separator, and has balancing of each performance. The separator for a power storage device is excellent in the exfoliation strength of the substrate and the modified layer, the battery winding, the thermal shock property and the low temperature cycle property compared to the conventional separator, and has balancing of each performance. The separator for a power storage device comprises: a polyolefin multilayer microporous film including polyethylene and polypropylene; and an active layer located on at least one surface of the porous film.

Description

TECHNICAL FIELD [0001] The present invention relates to a separator for a power storage device, and a laminate, a winding, a lithium ion secondary battery or a storage device using the separator, a lithium ion secondary battery,

The present invention relates to a separator for a power storage device.

2. Description of the Related Art In recent years, development of a battery device represented by a lithium ion secondary battery has been actively conducted. Normally, a microporous membrane (separator) is provided between the government poles in the electrical storage device. The separator has a function of preventing direct contact between the positive and negative electrodes, passing the electrolyte solution held in the micropores, and transmitting ions.

The separator is deeply related to battery characteristics, battery productivity, and battery safety, and is required to have excellent permeability, mechanical characteristics, impedance characteristics, hole clogging characteristics (shutdown characteristics), and melting prevention characteristics (meltdown prevention characteristics).

In order to satisfy such demands, it has been investigated to laminate various modified porous films on a microporous substrate constituting the separator.

For example, Patent Document 1 discloses a laminate comprising a first microporous layer containing polypropylene and a second microporous layer containing ultra-high molecular weight polyethylene, and further comprising a layer (polyvinyl fluoride Discloses a polyolefin multilayer microporous membrane having a specific porosity / film thickness and a specific degree of porosity, provided with a fluorine-containing resin such as a single substance or copolymer such as polyvinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) Examples include a microporous layer having a dense pore structure having a high uniformity of the through-hole diameter, a low air permeability, a high porosity and mechanical strength even when formed into a thin film, and a balanced impedance characteristic.

Patent Document 2 discloses a polyolefin multilayer microporous membrane in which the coefficient of static friction and the hole density of the other surface of one surface of the surface layer including polyethylene and polypropylene of the polyolefin multilayer microporous membrane are within a specific range , And the multilayer microporous membrane has excellent slidability between films and high durability (withstanding voltage and electrochemical stability) due to a fine pore structure.

Patent Document 3 discloses that a modified porous layer containing a PVDF layer is laminated on a polyethylene microporous film having irregular protrusions containing a specific number of polyethylenes so that peeling of the modified porous layer does not occur even during high- A battery separator is disclosed.

Patent Document 4 discloses a composite porous film in which a porous film containing a heat resistant resin layer containing a PVDF layer is laminated on a porous film having a polypropylene resin layer having mechanical strength and compressibility as the outermost layer, In addition, since the fluorine-based resin layer is laminated, it is disclosed that the excellent adhesion of the fluorine-based resin layer and the increase in the durability of small durability can be achieved at the same time, and is particularly suitable for battery separators.

International Publication No. 2015/194667 International Publication No. 2013/146403 International Publication No. 2015/190264 Japanese Patent Laid-Open Publication No. 2012-061791

Not only is the demand for hybrid cars soaring in the recent eco-friendly boom, but also electric vehicles are being recognized in the market, and the frequency with which these cars are used all over the world has increased. Under such circumstances, performance corresponding to the place of use is naturally required in the separator, and in particular, improvement in the durability of the separator in the cold region has been demanded. On the other hand, conventional separators such as those disclosed in Patent Documents 1 to 4 do not necessarily take the above circumstances into consideration, and a separator that can be used in various parts of the world including the cold regions has been longed for.

In view of the above circumstances, it is an object of the present invention to provide a separator which is excellent in not only the peel strength of the base material and the modified layer but also the cell winding property when the separator is wound around a cylindrical battery, It is an object of the present invention to provide a separator for a power storage device which is excellent in shock characteristics and low-temperature cycle characteristics and in which each performance is balanced.

The present inventors have found out that the above problems can be solved by the following technical means, and have completed the present invention.

That is, the present invention is as follows:

[1] A polyolefin multilayer microporous membrane comprising polyethylene and polypropylene, wherein the outermost polypropylene concentration is higher than the innermost polypropylene concentration and the outermost polyethylene concentration is lower than the innermost polyethylene concentration, An active layer disposed on at least one side of the film,

Wherein the active layer comprises at least one vinyl compound having at least one fluorine atom selected from polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE) And a power storage device separator.

[2] The polyolefin multilayer microporous membrane is laminated in the order of a first microporous layer, a second microporous layer, and a first microporous layer, wherein the first microporous layer comprises a first polyolefin having polyethylene and polypropylene Wherein the second microporous layer comprises a second polyolefin resin that is different from the first polyolefin resin, the first polyolefin resin being polyethylene, the active layer being formed on at least one of the first microporous layer The separator for power storage device according to [1], wherein the separator is laminated.

[3] The separator for a power storage device according to [1] or [2], wherein the first polyolefin resin or the second polyolefin resin comprises linear low density polyethylene.

[4] The separator for a power storage device according to [1] or [2], wherein the first polyolefin resin or the second polyolefin resin further contains polypropylene having a heat of fusion of 150 J / g or less.

[5] The separator for a power storage device according to [3], wherein the linear low density polyethylene is poly (ethylene-co-1-hexene).

[6] The separator for a power storage device according to any one of [1] to [5], wherein the mass ratio of the vinyl compound having a fluorine atom to the inorganic particle is 5/95 to 80/20.

[7] The separator for a power storage device according to any one of [1] to [6], wherein the fluorine atom-containing vinyl compound has a weight average molecular weight of 0.6 × 10 ⁶ to 2.5 × 10 ⁶ .

[8] The pharmaceutical composition according to any one of [1] to [7], wherein the active layer further contains at least one selected from cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethyl cellulose and cyanoethyl sucrose. And a separator for a power storage device.

[9] The method according to [1], wherein the ratio of the weight average molecular weight of the polyethylene and the polypropylene contained in the first polyolefin resin (MwE (weight average molecular weight of polyethylene) / MwP (weight average molecular weight of polypropylene) The battery separator according to any one of claims 1 to 8,

[10] The separator for a power storage device according to any one of [1] to [9], wherein the first polyolefin resin further contains at least one selected from the group consisting of silica, alumina and titania.

[11] A laminate comprising the separator for power storage device according to any one of [1] to [10], a positive electrode, and a negative electrode.

[12] A laminate according to [11], wherein the laminate is wound.

[13] A secondary battery comprising the laminate according to the above [11] or the winding described in [12] and an electrolytic solution.

According to the present invention, it is possible to provide a battery separator for a power storage device, which is superior in peel strength of the active layer and the base material as well as in the battery winding property as well as in the conventional separator, .

Fig. 1 (A) is an explanatory view showing the entire configuration of a manual winding machine used for obtaining the peel strength of the active layer and the polyolefin multilayer microporous membrane, and Fig. 1 (B) is an explanatory view to be.
2 is a schematic view of an apparatus used to perform a crash test.

<Separator for Power Storage Device>

The separator for power storage device of the present invention is characterized in that a polyolefin multi-layered structure comprising polyethylene and polypropylene, wherein the outermost polypropylene concentration is higher than the innermost polypropylene concentration and the outermost polyethylene concentration is lower than the innermost polyethylene concentration A power storage device separator comprising a porous film and an active layer disposed on at least one surface of the microporous film. The outermost portion of the polyolefin multi-layer microporous membrane refers to the cross-section portion of the two outer membranes when the multi-layer microporous membrane is divided into three portions so as to have the same film thickness in the lamination direction. Lt; / RTI &gt;

In a preferred form of the separator for a power storage device of the present invention, the separator includes a polyolefin multi-layer microporous membrane and an active layer, the multi-layer microporous membrane includes at least a first microporous layer and a second microporous layer, 1 microporous layer comprises a first polyolefin resin containing polyethylene and polypropylene and the second microporous layer comprises a polyolefin resin different from the first polyolefin resin containing polyethylene and the multi- The microporous membrane is laminated in the order of the first microporous layer, the second microporous layer, and the first microporous layer.

A separator obtained by coating the active layer on at least one layer of a polyolefin multilayer microporous film having three layers and both outer layers being a first microporous layer and obtained by laminating the active layers on the porous film, The permeability is less likely to be deteriorated, and there is a tendency to give a battery device having a high output characteristic. In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics, and high safety tends to be obtained.

Further, by disposing a film containing polyethylene and polypropylene as the outer layer of the polyolefin multilayer microporous film, the peel strength with the active layer stacked on the outer layer is increased. When the polypropylene and the polyethylene are coexisted in this manner, the surface free energy of the surface of the layer is increased by the polarity effect of the polypropylene, compared with the case of using only polyethylene, and the adhesion with the active layer is increased. In addition, by disposing a film containing polyethylene and polypropylene in the outer layer, the low-temperature characteristics, particularly the low-temperature cycleability, which is one of the characteristics of the separator according to the present embodiment, It is considered that the transition temperature is lowered by the blend as compared with propylene alone, and brittle fracture of the material is hardly caused.

This separator for power storage device is formed by laminating at least an active layer on a polyolefin multilayer microporous film. By the active layer, the adhesive force between the active layer and the adhesive layer on the electrode side becomes stronger, and particularly the cold shock property described later becomes better.

As described above, the separator may include only the polyolefin multilayer microporous film and the active layer. However, the separator may further include a thermoplastic polymer layer in addition to the polyolefin multilayer microporous film and the active layer. When the active layer and the thermoplastic polymer layer are disposed on the polyolefin multilayer microporous film, the mutual positional relationship between them is arbitrary. However, from the viewpoint of achieving both the rate characteristic and the safety of the electrical storage device, the thermoplastic polymer layer Or may be disposed on the active layer.

Preferred embodiments of the respective members constituting the separator for power storage device and the method of manufacturing the separator for power storage device according to the present embodiment will be described in detail below.

[Polyolefin multilayer microporous membrane]

The polyolefin multilayer microporous membrane (hereinafter, referred to as a polyolefin porous substrate) used in the present embodiment is preferably a porous membrane having no electron conductivity, ionic conductivity, high resistance to organic solvents, and minute pore diameters.

The polyolefin multilayer microporous membrane (polyolefin porous substrate) according to the present embodiment includes at least a first polyolefin microporous layer and a second polyolefin microporous layer, wherein the first microporous layer contains polyethylene and polypropylene, The microporous layer contains polyethylene.

The polyolefin porous substrate is a separator substrate which is excellent in mechanical properties, shutdown characteristics, and meltdown characteristics and has a first microporous layer, a second microporous layer, a first microporous layer Layers are stacked in this order, and polyethylene and polypropylene are contained as the first layer and polyethylene is contained as the second layer, whereby a good balance of desired mechanical characteristics, shutdown characteristics, and meltdown characteristics is exhibited as a separator.

Examples of the polyethylene and polypropylene contained in the first microporous layer include, but not limited to, low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene (HDPE), ultra high molecular weight polyethylene (UHMwPE), isotactic poly Propylene, atactic polypropylene, ethylene-propylene random copolymer, and ethylene propylene rubber. The polymerization catalyst used in the production of these polyethylene or polypropylene is not particularly limited, and examples thereof include Ziegler · Natta catalyst, Phillips catalyst and metallocene catalyst.

It is preferable that the first polyolefin resin further contains linear low density polyethylene in addition to the polyethylene in view of the impact resistance of the electrical storage device. More preferably, the first polyolefin resin further contains linear low-density polyethylene in addition to high-density polyethylene (HDPE). The linear low density polyethylene is more preferably a poly (ethylene-co-hexene) copolymer, for example.

In addition to the above polypropylene, the first polyolefin resin has a steric structure among the polypropylenes, and any of isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene which can improve the heat resistance of the separator Is more preferable from the viewpoints of the peel strength of the active layer and the substrate.

Particularly, if polypropylene having a heat of fusion of 150 J / g or less is further contained in the first microporous layer, the amorphous portion in the polypropylene is increased and the impact resistance of the power storage device is further improved.

The ratio of polypropylene to 100% by mass of the entire polyolefin resin in the first microporous layer is not particularly limited, but is preferably 1 to 50% by mass from the viewpoints of the peel strength of the active layer and the base material, the cold-shock property, More preferably from 5 to 40% by mass, and still more preferably from 15 to 35% by mass. And particularly preferably less than 15 to 30% by mass.

Further, the ratio of the polyolefin resin to the 100 mass% of the polyolefin resin composition in the first microporous layer is not particularly limited, but is preferably 50 to 100 mass% from the viewpoint of compatibility with both the permeability and heat resistance and the good shutdown function, Is 60 to 100% by mass, and more preferably 70 to 100% by mass. The polymerization catalyst is not particularly limited, and examples thereof include a Ziegler · Natta catalyst and a metallocene catalyst. When the first microporous layer further contains at least one selected from silica, alumina and titania, it is more preferable from the viewpoint of affinity with the nonaqueous electrolyte solution of the separator, power holding performance, and low temperature cycle characteristics as described later.

The ratio of silica, alumina and titania in the first microporous layer is preferably 5% by mass or more, more preferably 10% by mass or more, and still more preferably 10% by mass or more, relative to 100% by mass of the first polyolefin resin in the first microporous layer. Is not less than 20% by mass, preferably not more than 90% by mass, more preferably not more than 80% by mass, further preferably not more than 70% by mass. This ratio is preferable from the viewpoint of obtaining good heat resistance and from the viewpoint of obtaining a porous film having a high sticking strength by improving the stretchability.

Next, the second microporous layer according to the present embodiment will be described.

The second microporous layer comprises a second polyolefin resin different from the first polyolefin resin containing polyethylene. Examples of the polyethylene include, but not particularly limited to, low density polyethylene, linear low density polyethylene (L-LDPE), medium density polyethylene, high density polyethylene (HDPE) and ultra high molecular weight polyethylene (UHMwPE). The polyethylene contained in the polyolefin resin of the second microporous layer is preferably high density polyethylene and ultrahigh molecular weight polyethylene in view of strength and heat resistance. In addition to high-density polyethylene and ultrahigh molecular weight polyethylene, it is more preferable to further include a linear low-density polyethylene in view of the impact resistance of the power storage device. The linear low density polyethylene is more preferably a poly (ethylene-co-hexene) copolymer, for example. The polyethylene may be used singly or in combination of two or more for the purpose of giving flexibility.

The content of polyethylene in the second microporous polyolefin resin is preferably 50 mass% or more, more preferably 50 mass% or less, more preferably 50 mass% or less, % To 100% by mass, more preferably 60% by mass to 100% by mass, still more preferably 70% by mass to 95% by mass.

The polyolefin resin of the second microporous layer may further comprise polypropylene. As the polypropylene, if polypropylene having a heat of fusion of 150 J / g or less is included, the amount of amorphous portions in the polypropylene is increased, which is preferable because the impact resistance of the power storage device is improved.

The above-mentioned straight-chain low-density polyethylene or polypropylene having a heat of fusion of 150 J / g or less is included in the second polyolefin resin rather than the first polyolefin resin from the viewpoint of impact resistance of the power storage device. The details of this mechanism are unclear. However, when the layer containing the linear low density polyethylene or the polypropylene having the heat of fusion of 150 J / g or less is thicker than the other layers, the straight chain low density polyethylene or the polypropylene having the heat of fusion of 150 J / When the layer is further away from the electrode (when another layer is interposed), it is presumed that the impact resistance of the power storage device is good.

The first and second microporous layers according to the present embodiment are preferably used in order to make the balance between the cold and heat impact characteristics and the low temperature cycle characteristics, the heat resistance, the impact resistance and the peel strength of the base material and the active layer better. Or a porous film layer containing a polyolefin resin composition containing a polyolefin resin. The olefin resin used for the first layer and the second layer is not particularly limited and may be any polyolefin resin used for ordinary extrusion, injection, inflation, blow molding and the like. Examples of the olefin resin include 1-butene, 4-methyl- Homopolymers and copolymers such as 1-octene, and multi-terminal polymers. The polyolefin selected from the group consisting of homopolymers and copolymers and multistage polymers may be used singly or in combination.

The weight average molecular weight of the polyethylene or polypropylene constituting the first and second microporous layers is not particularly limited, but is preferably 30,000 or more and 12,000,000 or less, more preferably 50,000 or less and 2,000,000 or less, Is less than 100,000. When the weight average molecular weight is 30,000 or more, the melt tension during melt molding becomes large, which leads to a good moldability and a high strength due to entanglement of the polymers. On the other hand, if the weight average molecular weight is not more than 12 million, it is preferable that the melt-kneading can be uniformly performed, and the moldability, particularly the thickness stability, of the sheet tends to be excellent. If the weight average molecular weight is less than 1,000,000, the hole is likely to be occluded at the time of temperature rise, and a good shutdown function tends to be obtained, which is preferable.

As described above, the polyolefin multilayer microporous membrane (polyolefin porous substrate) according to the present embodiment is formed by laminating the first microporous layer, the second microporous layer, and the first microporous layer in this order, Wherein the ratio of the weight average molecular weight (MwE) of the polyethylene contained in the first microporous layer in close contact with the active layer to the weight average molecular weight (MwP) of the polypropylene MwE / MwP) of 0.6 to 1.5 is preferable in that fluctuation of peeling strength between the first microporous layer and the active layer can be reduced. When the ratio of the MwE / MwP of the first layer is in this range, the reason why the peeling strength fluctuation is reduced is presumed as follows. When the ratio is within a predetermined range (closer to 1), the difference in molecular weight between the polyethylene and the polypropylene becomes smaller, the compatibility becomes better, and macro phase separation becomes difficult to occur. In this case, the localization of the polyethylene-rich portion or the polypropylene-enriched portion is suppressed at the bonding interface with the active layer of the first layer, whereby the ratio between the polyethylene-rich portion and the polypropylene- Further, since the adhesiveness of the polypropylene and the polyethylene is not the same, it is considered that the fluctuation in the adhesive force (peel strength) between the active layer and the substrate becomes small.

A specific production method of the porous substrate of polyolefin will be described later.

As described above, the polyolefin porous substrate including the first, second, and first three layers of the microporous layer has been described. However, the porous substrate may have a multilayer structure of more than three layers. In this case, And the outermost polyethylene concentration is lower than the innermost polyethylene concentration. As used herein, the term "outermost layer" refers to the two outer sides when the multilayered film is divided into three portions in the lamination direction so as to have the same film thickness, and the innermost portion refers to the inner portion of the film. The components of each film can be found by infrared spectroscopy or liquid chromatography (for example, GPC).

The polyolefin porous substrate in the present embodiment may contain optional additives. Such additives are not particularly limited and include, for example, polymers other than polyolefins; Inorganic particles; Antioxidants such as phenol, phosphorus, and sulfur; Metal soaps such as calcium stearate and zinc stearate; Ultraviolet absorber; Light stabilizer; An antistatic agent; Antifogging agents; And coloring pigments.

The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less based on 100 parts by mass of the polyolefin resin.

The porosity of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 20% or more, more preferably 35% or more, preferably 90% or less, more preferably 80% or less. The porosity of 20% or more is preferable from the viewpoint of securing the permeability of the separator. On the other hand, setting the porosity to 90% or less is preferable from the viewpoint of securing the stiction intensity. Here, the porosity can be calculated from the volume (cm 3), the mass (g), and the film density (g / cm 3) of the polyolefin porous base sample,

Porosity = (volume-mass / membrane density) / volume x 100

. Here, for example, in the case of a polyolefin multilayer microporous film containing polyethylene, the film density can be calculated assuming 0.95 (g / cm 3). In the case of a multilayer microporous film containing polyethylene and polypropylene, the film density can be calculated similarly from each film density. The porosity can be adjusted by changing the stretching magnification of the polyolefin multilayer microporous membrane.

The permeability of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 10 sec / 100cc or more, more preferably 50 sec / 100cc or more, preferably 1,000 sec / 100cc or less, And more preferably 500 sec / 100cc or less. It is preferable to set the air permeability to 10 sec / 100cc or more from the viewpoint of suppressing the self-discharge of the electrical storage device. On the other hand, setting the air permeability to 1,000 sec / 100 cc or less is preferable from the viewpoint of obtaining good charge / discharge characteristics. Here, the air permeability is the air permeability resistance measured in accordance with JIS P-8117. The air permeability can be controlled by changing the drawing temperature and / or the draw ratio of the porous base material.

The average pore diameter of the polyolefin porous substrate in the present embodiment is preferably 0.15 占 퐉 or less, more preferably 0.1 占 퐉 or less and preferably 0.01 占 퐉 or more as a lower limit. The average pore diameter of 0.15 mu m or less is preferable from the viewpoint of suppressing the self-discharge of the electric storage device and suppressing the capacity decrease. The average pore diameter can be controlled by changing the draw ratio at the time of producing the polyolefin porous substrate.

The sticking strength of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 200 g / 20 m or more, more preferably 300 g / 20 m or more, preferably 2,000 g / 20 m or less Is not more than 1,000 g / 20 탆. The sticking strength of 200 g / 20 占 퐉 or more is preferable from the viewpoint of suppressing the wave film caused by the dropped active material at the time of battery winding and suppressing the risk of short circuit due to the expansion and contraction of the electrode due to charging and discharging. On the other hand, the sticking strength of 2,000 g / 20 m or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The stab intensity is measured by the method described in the following Examples.

The stab intensity can be adjusted by adjusting the draw ratio of the polyolefin porous substrate and / or the stretching temperature.

The thickness of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 2 탆 or more, more preferably 5 탆 or more, preferably 100 탆 or less, more preferably 60 탆 or less Or less. It is preferable to adjust the thickness to 2 탆 or more from the viewpoint of improving the mechanical strength. On the other hand, adjusting the film thickness to 100 탆 or less is preferable because the volume occupied by the separator in the battery is reduced, which tends to be advantageous from the viewpoint of high capacity of the battery.

&Lt; Active layer &

(Fluorine atom-containing vinyl compound)

The active layer according to the present embodiment contains a vinyl compound having fluorine atoms and inorganic particles, and is laminated on the first microporous layer.

By providing the active layer on the polyolefin multilayer microporous film as described above, the battery winding performance and the cold / thermal shock characteristics of the electrical storage device are superior to those of only the substrate.

The separator in which the active layer is coated on the first microporous layer, that is, the polyolefin porous substrate, and the active layer is stuck on the porous substrate has a tendency that the ion permeability is less likely to deteriorate, . In addition, even when the temperature rises rapidly during abnormal heat generation, it exhibits smooth shutdown characteristics, and high safety tends to be obtained.

The vinyl compound having a fluorine atom (hereinafter also referred to as a fluorine-based resin or a binder) can be obtained from polyvinylidene fluoride-hexafluoropropylene (polymer PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (polymer PVdF-CTFE) At least one selected. By copolymerizing hexafluoropropylene or chlorotrifluoroethylene with vinylidene fluoride as described above, it is possible to control the crystallinity of the fluorine resin to an appropriate range, so that it is possible to suppress the flow of the active layer during the adhesion treatment with the electrode can do. In addition, when the electrode is used as a separator for a secondary battery, the adhesive force is improved when the electrode is bonded to the electrode. Therefore, the interface deterioration does not occur, thereby improving the thermal shock resistance. The fluororesin is usually obtained by emulsion polymerization or suspension polymerization.

The weight average molecular weight of the fluororesin is preferably 0.6 x 10 ⁶ to 2.5 x 10 ⁶ . When the weight average molecular weight of the fluorine-based resin is within this range, it is preferable that the cold-shock property is good (it is considered that peeling is unlikely to occur between the active layer and the substrate due to small expansion and contraction during cold heating).

The fluorine-based resin, that is, the polymer PVdF-HFP and the polymer PVdF-CTFE preferably has a proportion of the constituent unit derived from HFP or CTFE of 2.0% by mass to 20.0% by mass. When the content of HFP or CTFE is 2.0 mass% or more, the degree of crystallization of the fluorine-based resin is suppressed, and when the content of HFP or CTFE is 20.0 mass% or less, crystallization of the fluorine resin is adequately expressed. When the content of HFP or CTFE is 20.0% by mass or less, it is preferable because it is easy to secure the cold / heat impact property.

From the above viewpoint, the proportion of the constituent unit derived from HFP or CTFE in the polymer PVdF-HFP and the polymer PVdF-CTFE is more preferably not less than 2.25 mass%, more preferably not less than 2.5 mass%, further preferably not more than 18 mass% And more preferably 15 mass% or less.

The degree of swelling of the resin contained in the separator when the separator containing the active layer is impregnated with the electrolyte differs depending on the kind of the resin and the composition of the electrolytic solution. In order to suppress the problem accompanying the swelling of the resin, It is preferable to select the above-mentioned fluorine-based resin which is difficult to obtain.

The active layer may be doped with one selected from the group consisting of a hydroxyl group (-OH), a carboxyl group (-COOH), a maleic anhydride group (-COOOC-), a sulfonic acid group (-SO ₃ H) and a pyrrolidone group , Or a polymer having two or more polar groups out of these, is preferable since the low temperature cycle characteristics of the separator are improved. Examples of such a polymer include at least one polymer selected from cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, and cyanoethyl sucrose.

The reason why the low temperature cycle characteristics of the separator is improved by including the polymer having a polar group as described above in the active layer is presumably because the resistance of the separator is lowered even at a low temperature due to the high relative dielectric constant of these polymers.

The relative dielectric constant of the polymer having a polar group may be 1 to 100 (measurement frequency = 1 kHz), and particularly preferably 10 or more.

The active layer may contain the following resins in addition to the above-described resin, so long as it does not impair various properties expressed by the separator according to the present embodiment. Polyvinylidene fluoride-trichlorethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, ethylene vinyl acetate copolymer, polyimide, polyethylene oxide, and the like, which correspond to the above- Or a mixture of two or more of them may be used, but the present invention is not limited thereto.

(Inorganic particles)

The inorganic particles to be used in the active layer are not particularly limited, but preferably have a melting point of 200 占 폚 or higher, have a high electrical insulating property, and are electrochemically stable in the range of use of the lithium ion secondary battery.

Examples of the inorganic particles include, but are not limited to, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; Nitride ceramics such as silicon nitride, titanium nitride, and boron nitride; But are not limited to, silicon carbide, silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide, potassium titanate, talc, kaolinite, diketite, nacrite, halite, pyrophyllite, montmorillonite, , Bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica and the like; Glass fibers and the like. These may be used alone or in combination.

Among these, from the viewpoint of improving the electrochemical stability and the heat resistance of the separator, aluminum oxide compounds such as alumina and aluminum hydroxide oxide; And aluminum silicate compounds having no ion exchange ability such as kaolinite, diketate, nacrite, haloisite, and pyrophyllite are preferable.

There are many crystalline forms of alumina such as? -Alumina,? -Alumina,? -Alumina and? -Alumina, but all of them can be suitably used. Among these,? -Alumina is preferable because it is thermally and chemically stable.

As the aluminum oxide compound, aluminum hydroxide (AlO (OH)) is particularly preferable. As the aluminum hydroxide, boehmite is more preferable from the viewpoint of preventing an internal short circuit due to the generation of lithium dendrites. By employing particles mainly composed of boehmite as the inorganic particles constituting the active layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and in addition, even in thinner porous layers, heat shrinkage at high temperatures And tends to exhibit excellent heat resistance. A synthetic boehmite capable of reducing ionic impurities adversely affecting the characteristics of an electrochemical device is more preferable.

As the aluminum silicate compound having no ion exchange capacity, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easy to obtain. In kaolin, wet kaolin and fired kaolin obtained by calcining it are known. In this embodiment, fired kaolin is particularly preferable. Fired kaolin is particularly preferable from the viewpoint of electrochemical stability in that crystal water is discharged at the time of firing treatment and impurities are also removed.

The average particle diameter of the inorganic particles is preferably more than 0.01 탆 and not more than 4.0 탆, more preferably not less than 0.2 탆 and not more than 3.5 탆, and more preferably not less than 0.4 탆 and not more than 3.0 탆. Adjusting the average particle size of the inorganic particles to the above range is preferable from the viewpoint of suppressing heat shrinkage at a high temperature even when the thickness of the active layer is small (for example, 7 탆 or less). As a method for adjusting the particle size and distribution of the inorganic particles, a method of pulverizing the inorganic particles using a suitable pulverizing apparatus such as a ball mill, a bead mill or a jet mill to reduce the particle size can be given.

Examples of the shape of the inorganic particles include plate-like, scaly, needle-shaped, columnar, spherical, polyhedral, and agglomerate. A plurality of inorganic fillers having these shapes may be used in combination.

The ratio of the fluorine resin to the inorganic particles in the active layer according to the present embodiment is preferably 5/95 to 80/20, more preferably 7/93 to 65/35, and still more preferably, 9/91 to 50/50. When the fluororesin / inorganic particles are in this range, it is preferable that the battery turnability to be described later becomes particularly good. For example, when the above-mentioned polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) is used for a fluororesin, since the resin is eluted on the film surface due to the tribocatalytic effect peculiar to the resin, The contact resistance with the pin is lowered, and the pin can be easily pulled out.

The thickness of the active layer is preferably 0.5 占 퐉 or more from the viewpoint of improving the heat resistance and the insulating property, and is preferably 50 占 퐉 or less from the viewpoint of improving the capacity and permeability of the battery.

The layer density of the active layer is preferably 0.5 g / cm3 to 3.0 g / cm3, more preferably 0.7 g / cm3 to 2.0 g / cm3. When the layer density of the active layer is 0.5 g / cm 3 or more, the heat shrinkage rate at high temperature tends to be good, and when 3.0 g / cm 3 or less, the toughness tends to be good.

As a method of forming the active layer, for example, a method of coating a coating liquid containing inorganic particles and a resin binder on at least one side of the substrate can be mentioned. In this case, the coating liquid may contain a solvent, a dispersant, and the like in order to improve dispersion stability and coatability.

The method of applying the coating solution onto the substrate is not particularly limited as long as it can realize the required layer thickness and coating area. For example, the particle raw material containing the resin binder and the polymer-based raw material may be laminated and extruded by coextrusion, and the base and the active film may be separately manufactured and then bonded.

[Thermoplastic polymer layer]

The separator for a power storage device may have a thermoplastic polymer layer in addition to the polyolefin porous substrate and the active layer, if desired. The thermoplastic polymer layer may be disposed on one side or both sides of the porous substrate, or on the active layer, and may be arranged so that at least a part of the active layer is exposed.

In the present embodiment, it is preferable that the area ratio of the thermoplastic polymer layer to the total area of the surface on which the thermoplastic polymer layer is disposed in the surface of the polyolefin porous substrate is 100% or less, 80% or less, 75% or less or 70% , And the area ratio is preferably 5% or more, 10% or more, or 15% or more. The coating area of the thermoplastic polymer layer is preferably 100% or less from the viewpoint of further inhibiting the clogging of the pores of the substrate by the thermoplastic polymer and further improving the permeability of the separator. On the other hand, setting the coating area to 5% or more is preferable from the viewpoint of further improving the adhesion with the electrode. This area ratio is measured by observing the thermoplastic polymer layer-formed surface of the resulting separator with an SEM.

When the thermoplastic polymer layer is a layer mixed with inorganic particles, the total area of the thermoplastic polymer and the inorganic particles is 100%, and the area of the thermoplastic polymer is calculated.

When the thermoplastic polymer layer is disposed only on a part of the surface of the porous substrate of the polyolefin and the inorganic particle layer, the arrangement pattern of the thermoplastic polymer layer may be, for example, a dot pattern, a stripe pattern, a lattice pattern, a stripe pattern, And combinations thereof.

The thickness of the thermoplastic polymer layer disposed on the polyolefin porous substrate is preferably 0.01 탆 to 5 탆, more preferably 0.1 탆 to 3 탆, and even more preferably 0.1 to 1 탆, for each side surface of the substrate.

(Thermoplastic polymer)

The thermoplastic polymer layer comprises a thermoplastic polymer. The thermoplastic polymer layer may contain at least 60 mass%, more preferably at least 90 mass%, even more preferably at least 95 mass%, particularly preferably at least 98 mass%, of the thermoplastic polymer with respect to the total amount thereof. The thermoplastic polymer layer may contain other components in addition to the thermoplastic polymer.

As the thermoplastic polymer, for example, the following:

Polyolefin resins such as polyethylene, polypropylene, and alpha -olefin;

Fluorinated polymers such as polyvinylidene fluoride and polytetrafluoroethylene, or copolymers thereof;

A diene polymer containing a conjugated diene such as butadiene or isoprene as a monomer unit, a copolymer containing any of these, or a hydride thereof;

(Meth) acrylate or the like as a monomer unit, and further contains an acrylic polymer having no polyalkylene glycol unit, (meth) acrylate or the like as a monomer unit, and also contains one or two polyalkylene glycol units Or a copolymer containing them, or a hydride thereof;

Ethylene propylene rubber, polyvinyl alcohol, and polyvinyl acetate;

Cellulose derivatives such as ethylcellulose, methylcellulose, hydroxyethylcellulose, carboxymethylcellulose and the like;

Polyalkylene glycols having no polymerizable functional group such as polyethylene glycol and polypropylene glycol;

Resins such as polyphenylene ether, polysulfone, polyether sulfone, polyphenylene sulfide, polyether imide, polyamideimide, polyamide and polyester;

A copolymer having an ethylenically unsaturated monomer having a repeating number of 3 or more of the alkylene glycol unit as a copolymerizing unit described above as the resin binder for forming the filler porous layer; And

Combinations thereof;

.

Among these, a diene-based polymer, an acrylic polymer or a fluorine-based polymer is preferable from the viewpoints of adhesion with the electrode active material, flexibility, and ion permeability of the polymer.

The glass transition temperature (Tg) of the thermoplastic polymer is preferably -50 占 폚 or higher, more preferably -50 占 폚 to 150 占 폚, from the viewpoint of adhesion with the electrode and ion permeability.

From the viewpoint of the wettability to the polyolefin multilayer microporous membrane, the bondability between the polyolefin multilayer microporous membrane and the thermoplastic polymer layer, and the adhesiveness with the electrode, it is preferable that the thermoplastic polymer layer is blended with a polymer having a glass transition temperature lower than 20 캜 From the viewpoints of blocking resistance and ion permeability, polymers having a glass transition temperature of 20 占 폚 or higher are preferably blended.

The thermoplastic polymer having at least two glass transition temperatures may be achieved by, for example, a method of blending two or more kinds of thermoplastic polymers, a method of using a thermoplastic polymer having a core shell structure, and the like.

The core shell structure is a polymer having a double structure in which the polymer belonging to the center portion and the polymer belonging to the shell portion have different compositions.

In particular, in the polymer blend and the core shell structure, the glass transition temperature of the entire thermoplastic polymer can be controlled by combining a polymer having a high glass transition temperature and a low polymer. In addition, a plurality of functions can be imparted to the whole thermoplastic polymer.

In the present embodiment, it is preferable that the thermoplastic copolymer is in a particulate form when the glass transition temperature is, for example, 20 占 폚 or higher, 25 占 폚 or higher, or 30 占 폚 or higher, from the viewpoints of blocking inhibition property and ion permeability of the separator.

By containing the particulate thermoplastic copolymer in the thermoplastic polymer layer, the porosity of the thermoplastic polymer layer disposed on the substrate and the anti-blocking property of the separator can be secured.

The average particle diameter of the particulate thermoplastic copolymer is preferably 10 nm to 2,000 nm, more preferably 50 nm to 1,500 nm, further preferably 100 nm to 1,000 nm, particularly preferably 130 nm to 800 nm, Preferably 150 to 800 nm, and most preferably 200 to 750 nm. The average particle diameter of 10 nm or more means that when the particulate thermoplastic polymer is coated on the base material containing at least the porous film, the dimension of the particulate thermoplastic polymer to such an extent that the base material does not enter the hole of the base material is secured. Therefore, in this case, it is preferable from the viewpoint of improving the adhesiveness between the electrode and the separator and the cycle characteristics of the power storage device. The average particle diameter of 2,000 nm or less is preferable from the viewpoint of coating on the substrate a particulate thermoplastic polymer in an amount necessary for achieving compatibility between the electrode and the separator, and cycle characteristics of the power storage device. The average particle diameter of the particulate thermoplastic polymer can be measured according to the method described in the following examples.

The particulate thermoplastic polymer described above can be produced by a known polymerization method using the corresponding monomers or comonomers. As the polymerization method, suitable methods such as solution polymerization, emulsion polymerization, bulk polymerization and the like can be adopted.

In the present embodiment, since the thermoplastic polymer layer can be easily formed by coating, it is preferable to form the particulate thermoplastic polymer by emulsion polymerization, and to use the obtained thermoplastic polymer emulsion as an aqueous latex.

(Optional component)

The thermoplastic polymer layer in the present embodiment may contain only a thermoplastic polymer or may contain any other components in addition to the thermoplastic polymer. Examples of optional components include the inorganic particles described above for forming the active layer.

<Manufacturing Method of Separator for Power Storage Device>

[Method for producing polyolefin multilayer microporous membrane (polyolefin porous substrate)] [

(Method for producing first and second microporous layers)

As described above, the polyolefin multi-layer microporous membrane according to the present embodiment is formed by laminating the first microporous layer, the second microporous layer, and the first microporous layer in this order, but the first microporous membrane and the second microporous membrane The method for producing the layer is not particularly limited and a known manufacturing method may be employed. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded, molded into a sheet, optionally stretched, and then extracted with a plasticizer to make the polyolefin resin composition porous; a method in which a polyolefin resin composition is melted and kneaded, extruded at a high draw ratio, A method in which the polyolefin resin composition and the inorganic filler are melt kneaded to form a sheet and then the interface between the polyolefin and the inorganic filler is peeled off by stretching to thereby make the polyolefin resin composition porous; , A method in which the polyolefin is immersed in a poor solvent for the polyolefin to coagulate the polyolefin, and at the same time, the solvent is removed to make the polyolefin porous.

The method for producing the nonwoven fabric or the paper as the base material of the first and second microporous layers may be a publicly known method. Examples of the production method include a chemical bond method in which a web is immersed in a binder and dried to bond the fibers together; A thermal bonding method in which a heat-meltable fiber is incorporated into a web, and the fibers are partially melted to bond the fibers together; A needle punching method which repeatedly stabs needle-pricked needles on the web and mechanically binds the fibers; There is a water distillation method in which a high-pressure water stream is jetted from a nozzle to a web through a net (screen), and the fibers are bound together.

Hereinafter, as an example of a method for producing a polyolefin multilayer microporous film (polyolefin porous substrate), there is a method of melt-kneading a polyolefin resin composition and a plasticizer to form first and second microporous layers on a sheet, , And a method of laminating the first and second microporous layers will be described.

First, the polyolefin resin composition and the plasticizer are melt-kneaded. As the melt kneading method, for example, a polyolefin resin and, if necessary, other additives may be added to a resin kneading apparatus such as an extruder, a kneader, a Labo Plastomill, a kneading roll or a Banbury mixer, And a plasticizer is introduced and kneaded. At this time, it is preferable that the polyolefin resin, the other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before putting them into the resin kneading apparatus. More preferably, only a part of the plasticizer is put in the pre-kneading, and the remaining plasticizer is kneaded while side-fed into the resin kneader.

As the plasticizer, a nonvolatile solvent capable of forming a homogeneous solution at a temperature not lower than the melting point of the polyolefin can be used. Specific examples of such nonvolatile solvents include hydrocarbons such as liquid paraffin and paraffin wax; Esters such as dioctyl phthalate and dibutyl phthalate; And higher alcohols such as oleyl alcohol and stearyl alcohol. Of these, liquid paraffin is preferred.

The ratio of the polyolefin resin composition to the plasticizer is not particularly limited as long as they can be uniformly melted and kneaded and molded into a sheet form. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 30 to 80 mass%, more preferably 40 to 70 mass%. By setting the mass fraction of the plasticizer within this range, it is preferable from the viewpoint that the melt tension at the time of melt molding and the formation of a uniform and minute pore structure are compatible.

Next, the melt-kneaded product is formed into a sheet. Examples of the method for producing the sheet-shaped molded article include a method of extruding a melt-kneaded product through a T-die or the like into a sheet form and bringing the melt-kneaded product into contact with the heat conductor to cool it to a temperature sufficiently lower than the crystallization temperature of the resin component, . As the thermal conductor used for cooling and solidifying, metal, water, air, a plasticizer itself and the like can be used, but a metal roll is preferable because heat conduction efficiency is high. At this time, when the sheet is brought into contact with the metal roll, it is more preferable to sandwich it between the rolls because the efficiency of heat conduction is higher and the sheet is oriented to increase the film strength and the surface smoothness of the sheet. The die lap interval when extruded from the T die into the sheet is preferably 400 占 퐉 or more and 3,000 占 퐉 or less, more preferably 500 占 퐉 or more and 2,500 占 퐉 or less.

(Method for producing polyolefin multilayer microporous membrane)

The polyolefin multilayer microporous membrane (polyolefin porous substrate) according to the present embodiment is formed by laminating a first microporous layer, a second microporous layer, and a first microporous layer in this order. As a method of laminating them, As described above, the polyolefin resin composition, which is a component of the first and second microporous layers, and the plasticizer are melt-kneaded using a twin-screw extruder to prepare an olefin solution Then, each of the polyolefin solutions was supplied from each twin-screw extruder to a three-layer T-die, and the layer thickness ratio of each layer (first polyolefin solution layer / second polyolefin solution layer / first polyolefin solution layer) While cooling it to a desired range while taking it at a predetermined winding speed to form a gel three-layer sheet.

In the above, three layers are simultaneously laminated by using a three-layer T-die, but they may be three layers after forming each layer.

The sheet-shaped formed body thus obtained is preferably subsequently stretched. As the stretching treatment, both uniaxial stretching and biaxial stretching can be suitably used. From the viewpoint of the strength and the like of the resulting porous polyolefin substrate, biaxial orientation is preferable. When the sheet-like formed body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous substrate is hardly torn and has high sticking strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferable from the viewpoint of enhancement of stab intensity, uniformity of stretching, and shutdown property.

The stretching ratio is preferably in the range of 20 times to 100 times, more preferably in the range of 25 times to 50 times. The stretching ratio in each axis direction is preferably in the range of 4 to 10 times in the MD direction, 4 to 10 times in the TD direction, 5 to 8 times in the MD direction, 5 times or more in the TD direction And more preferably 8 times or less. By setting the total area ratio in this range, it is preferable that sufficient strength can be given, film breakage in the stretching process can be prevented, and high productivity can be obtained.

The sheet-shaped formed body obtained as described above may also be rolled. Rolling can be performed by a pressing method using, for example, a double belt press machine or the like. Rolling can increase the orientation of the surface layer portion in particular. The rolling surface magnification is preferably greater than 1 and less than 3, more preferably greater than 1 and less than 2. By setting the rolling magnification within this range, the film strength of the polyolefin porous substrate to be finally obtained is increased, and a uniform porous structure can be formed in the film thickness direction.

Subsequently, the plasticizer is removed from the sheet-shaped molding to obtain a porous substrate. Examples of the method for removing the plasticizer include a method in which the sheet-like molded body is immersed in an extraction solvent to extract the plasticizer and sufficiently dried. The method of extracting the plasticizer may be either a batch method or a continuous method. In order to suppress shrinkage of the porous polyolefin substrate, it is preferable to confine the end portions of the sheet-shaped formed body in a series of steps of immersion and drying. The residual amount of the plasticizer in the porous substrate is preferably less than 1% by mass.

As the extraction solvent, it is preferable to use a poor solvent for the polyolefin resin, a good solvent for the plasticizer, and a boiling point lower than the melting point of the polyolefin resin. Examples of the extraction solvent include hydrocarbons such as n-hexane and cyclohexane; Halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; Non-chlorinated halogenated solvents such as hydrofluoroether, hydrofluorocarbon and the like; Alcohols such as ethanol and isopropanol; Ethers such as diethyl ether and tetrahydrofuran; And ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation.

In order to suppress shrinkage of the polyolefin porous substrate, heat treatment such as heat fixation or thermal relaxation may be performed after the stretching process or after the porous substrate is formed. The porous substrate may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, a crosslinking treatment with ionizing radiation or the like.

When the surface of the porous substrate of the polyolefin is subjected to the surface treatment, it is preferable to coat the coating liquid thereafter and to improve the adhesiveness between the polyolefin and the active layer or the thermoplastic polymer layer. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

[Arrangement of active layer]

The active layer can be disposed on a substrate by coating a coating liquid containing at least one side of the substrate, for example, an inorganic particle, a fluorine resin, and, if desired, additional components such as a solvent (e.g., water), a dispersing agent and the like. The fluorine resin may be synthesized by emulsion polymerization, and the resulting emulsion may be used directly as a coating liquid.

As a method for forming the active layer, for example, there can be mentioned a method of coating a coating liquid containing inorganic particles and a fluorine resin on at least one side of a porous substrate of polyolefin. In this case, the coating liquid may contain a solvent, a dispersant, and the like in order to improve dispersion stability and coatability.

The method of applying the coating solution onto the substrate is not particularly limited as long as it can realize the required layer thickness and coating area. For example, the constituent materials of the active layer including the polyolefin resin and the constituent materials of the polyolefin multi-layered microporous substrate may be laminated and extruded by a co-extrusion method, and the porous substrate and the active film may be individually formed and then joined.

The method of applying the coating solution onto the substrate is not particularly limited as long as it can realize the required layer thickness and coating area. Examples of the coating method include a gravure coater method, a small diameter gravure coater method, a reverse roll coater method, a transfer roll coater method, a kiss coater method, a dip coater method, a knife coater method, an air doctor coater method, A squeeze coater method, a cast coater method, a die coater method, a screen printing method, a spray coating method, and an inkjet coating method. Among them, the gravure coater method is preferable because the degree of freedom of the coating shape is high.

Further, the inorganic particle raw material containing the fluorine resin (binder) and the polymer base material may be laminated and extruded by the co-extrusion method, or the substrate and the active layer may be separately formed and then bonded.

The method of removing the solvent from the coating film after coating is not limited as long as it does not adversely affect the substrate and the porous layer. For example, a method of drying the substrate at a temperature not higher than the melting point of the substrate while fixing the substrate, and a method of drying under reduced pressure at a low temperature.

[Arrangement of Thermoplastic Polymer Layer]

The thermoplastic polymer can be placed on a substrate by coating the substrate with a coating solution comprising, for example, a thermoplastic polymer. The thermoplastic polymer may be synthesized by emulsion polymerization, and the resulting emulsion may be used directly as a coating liquid. The coating liquid preferably contains a poor solvent such as water, a mixed solvent of water and a water-soluble organic medium (for example, methanol or ethanol), and the like.

The method of coating a coating liquid containing a thermoplastic polymer on a polyolefin porous substrate is not particularly limited as long as it is a method capable of realizing a desired coating pattern, coating thickness and coating area. For example, the coating method described above may be used to coat the inorganic particle-containing coating solution. From the viewpoint that the degree of freedom of the coating shape of the thermoplastic polymer is high and the preferable area ratio is easily obtained, the gravure coating method or the spray coating method is preferable.

The method of removing the solvent from the coating film after coating is not particularly limited as long as it does not adversely affect the polyolefin porous substrate and the polymer layer. For example, a method of drying the polyolefin porous substrate while keeping it at a temperature lower than its melting point, a method of drying under reduced pressure at a low temperature, a method of immersing the thermoplastic polymer in a poor solvent for coagulating the thermoplastic polymer, And the like.

<Physical Properties of Separator for Power Storage Device>

In the present embodiment, the air permeability of the battery device separator is preferably 10 sec / 100cc or more and 650 sec / 100cc or less, more preferably 20 sec / 100cc or more and 500 sec / 100cc or less, 100 sec or more and 450 sec / 100cc or less, particularly preferably 50 sec / 100cc or more and 400 sec / 100cc or less. This air permeability is the air permeability resistance measured in accordance with JIS P-8117 as well as the permeability of the polyolefin porous substrate.

When the air permeability is 10 sec / 100cc or more, self-discharge when used as a separator for a battery tends to decrease, and when it is 650 sec / 100cc or less, good charge / discharge characteristics tend to be obtained.

The separator for power storage device according to the present embodiment exhibits a very high permeability as described above, and thus exhibits a large ion permeability when applied to a lithium ion secondary battery.

The final thickness of the separator is preferably 2 탆 or more and 200 탆 or less, more preferably 5 탆 or more and 100 탆 or less, further preferably 7 탆 or more and 30 탆 or less. If the thickness is 2 mu m or more, the mechanical strength tends to be sufficient. When the thickness is 200 mu m or less, the occupied volume of the separator tends to be reduced, which tends to be advantageous from the viewpoint of high capacity of the battery.

<Power storage device>

The separator for power storage device according to the present embodiment can be suitably applied as a separator of a power storage device by combining it with a positive electrode, a negative electrode, and a nonaqueous electrolyte. Examples of the power storage device include a lithium ion secondary battery.

When the lithium ion secondary battery is manufactured using the separator of the present embodiment, there is no limitation to the positive electrode, negative electrode, and non-aqueous electrolyte, and known ones can be used.

As the positive electrode, a positive electrode having a positive electrode active material layer containing a positive electrode active material formed on the positive electrode collector may be suitably used. Examples of the positive electrode current collector include aluminum foil and the positive electrode active material includes lithium-containing complex oxide such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO ₄ . The positive electrode active material layer may contain, in addition to the positive electrode active material, a binder, a conductive material, and the like.

As the negative electrode, a positive electrode comprising a negative electrode active material layer containing a negative electrode active material on a negative electrode collector may be suitably used. As the negative electrode current collector, for example, copper foil may be used. As the negative electrode active material, carbon materials such as graphite, non-graphitized carbonaceous material, graphitized carbonaceous material and composite carbon material may be used. Silicon, tin, metal lithium, and various alloy materials.

The non-aqueous electrolyte is not particularly limited, but an electrolytic solution in which an electrolyte is dissolved in an organic solvent can be used. Examples of the organic solvent include propylene carbonate, ethylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and the like. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ and LiPF ₆ .

The method of manufacturing the electrical storage device using the separator for power storage device of the present embodiment is not particularly limited. For example, the following method can be exemplified.

The separator of this embodiment is manufactured as a vertically elongated separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4,000 m (preferably 1,000 to 4,000 m) , A positive electrode-separator-negative electrode-separator, or a negative electrode-separator-positive electrode-separator in this order, winding them in a circular or flat manner and winding them to obtain a winding body, storing the winding body in a battery can, By weight. Or a laminate comprising a sheet-like separator and an electrode, or a method in which an electrode and a separator are folded and formed into a wound body into a battery container (for example, an aluminum film), and an electrolyte is injected thereinto.

At this time, it is also preferable that the laminate or the winding body is pressed. Specifically, the separator for power storage device according to the present embodiment and the electrode having the current collector and the active material layer formed on at least one surface of the current collector are stacked so that the former thermoplastic polymer layer and the active material layer are opposed to each other, have. The press temperature may be 25 占 폚 or higher and 120 占 폚 or lower, or 50 占 폚 to 100 占 폚. The press can be performed by appropriately using a known press apparatus such as a roll press or a surface press.

The lithium ion secondary battery produced as described above has a coating layer excellent in heat resistance and strength and includes a separator with reduced ion resistance, and thus exhibits excellent safety and battery characteristics (particularly, rate characteristics). In addition, when the thermoplastic polymer is provided on the outermost surface of the separator, excellent adhesion with the electrode is exhibited. Therefore, peeling between the electrode and the separator during charging and discharging is suppressed and uniform charge and discharge are performed. Excellent resistance.

The evaluation of physical properties in the following Experimental Examples was carried out according to the following method.

<Evaluation>

&Lt; Measurement method and evaluation method >

(1) Peel strength of active layer / polyolefin porous substrate

A tape (manufactured by 3M, product name: Scotch 600) having a width of 12 mm and a length of 100 mm was attached to the active layer of the separator obtained in Examples and Comparative Examples (excluding Comparative Example 1) in a direction parallel to the separator longitudinal direction . The force at which the tape was peeled from the sample at a rate of 50 mm / min was measured using a 90 占 peel strength meter (product name: IP-5N, manufactured by IMADA). Five points were measured, and the average value of the obtained peel strength was regarded as the peel strength of the active layer and the substrate, and evaluated according to the following evaluation criteria.

A: Peel strength of 60 N / m or more

B: Peel strength of 40 N / m or more and less than 60 N / m

C: Peel strength less than 40 N / m

(2) Battery turnability (pin pulling characteristics)

Using a manual winding machine manufactured by Kaido Seisakusho Co., Ltd., two wound samples 13 each having a length of 3 m and a width of 60 mm were stacked as shown in Fig. 1 (A) The pin I was pulled out in the winding configuration shown in Fig. 1 (B), and the wound sample 13 was wound by hand Pulled out from the pin II (12), and the pin pulling property was evaluated based on the following criteria based on the winding profile of the drawn sample.

A: The ratio of the pin contact portion shifted by 2 mm or more compared to when the pin was pulled out by the pin is 4/100 or less

B: Ratio of the pin contact portion shifted by 2 mm or more compared to that before the pin was pulled out by 5 to 9/100

C: Ratio of the pin contact portion shifted by 2 mm or more compared to when the pin was pulled by the pin.

(3) Thermal shock property

Using the separators obtained in the examples and comparative examples, each secondary battery assembled as shown in the following items a to d was evaluated for cold / heat impact characteristics (resistance to heat and cold).

a. Production of positive electrode

96 parts by mass of lithium cobalt oxide (LiCoO ₂ ) as a positive electrode active material, ₂ parts by mass of carbon black powder as a positive electrode active material, and 2 parts by mass of polyvinylidene fluoride as a positive electrode binder (binder) -Methylpyrrolidone (NMP) to prepare a positive electrode mixture slurry. The positive electrode material mixture slurry was coated on both sides of an aluminum foil having a thickness of 13 mu m serving as a positive electrode current collector, dried and rolled to produce a positive electrode. The filling density and thickness of the positive electrode active material layer at this time were 3.95 g / cc and 140 m at the portions where the positive electrode active material layer was formed on both surfaces of the current collector.

b. Production of negative electrode

97 parts by mass of a carbon-based active material (artificial graphite) and 3 parts by mass of a silicon-based active material (SiO _x ) (x = 1.05) were mixed.

98 parts by mass of the obtained mixture and 2 parts by mass of carboxymethylcellulose sodium (CMC-Na) were mixed and dispersed in water to obtain a negative electrode mixture slurry.

The negative electrode mixture slurry was applied to both sides of a copper foil having a thickness of 8 mu m to be a negative electrode current collector, dried and then rolled. The negative electrode was prepared by the above process. The packing density and thickness of the negative electrode active material layer at this time were 1.75 g / cc and 137 m at the portions where the negative electrode active material layers were formed on both surfaces of the current collector.

c. Preparation of non-aqueous electrolyte

A nonaqueous electrolytic solution was prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: diethyl carbonate = 3: 7 (mass ratio) so as to have a concentration of 1.2 mol / L.

d. Battery assembly

The positive electrode prepared in a., the negative electrode prepared in b., and the separator prepared in the example or the comparative example were cut out and superimposed, respectively, and then wound in a long-side direction at room temperature to crush the flat- Respectively. The battery element was inserted into a laminate film having a thickness of 120 占 퐉 consisting of three layers of polypropylene / aluminum / nylon from the inside toward the outside, and the electrode terminals were taken out to the casing by heat welding. The nonaqueous electrolyte solution was injected into an exterior member accommodating the battery element, and the other one side of the exterior material was thermally fused under a reduced pressure, followed by vacuum sealing. This was heated between the metal plates at 80 DEG C for 3 minutes to obtain a battery having a thickness of 2 mm, a width of 30 mm and a height of 30 mm.

Subsequently, each secondary battery using the separators of Examples and Comparative Examples was charged to 4.35 V at a constant current of 56 mA at 25 DEG C, and then charged at a constant voltage up to a charging current of 14 mA.

The secondary battery resistance (1 kHz AC impedance:?) In a charged state after the constant-voltage charging was measured, and this resistance was regarded as an initial resistance.

Subsequently, the temperature was raised to 70 캜 by using a thermal impact tester (TSA-71H-W manufactured by Espec) and held for 4 hours. Thereafter, the cycle of holding the battery at 20 캜 for 2 hours and then keeping it at -40 캜 for 4 hours was repeated 50 times. The resistance (1 kHz AC impedance:?) Of the secondary battery was measured in the same manner as in d. From this result and the initial resistance measured above, the resistance change amount (resistance after cold / heat cycle-initial resistance) before and after the cooling / heating cycle was calculated and evaluated based on the following criteria.

A: The resistance change amount before and after cold shock is 0 Ω or more and less than 10 Ω

B: Resistance change after thermal shock is more than 10 Ω and less than 20 Ω

C: The resistance change amount before and after the cold shock is 20?

(4) Low temperature cycle characteristics

Using the separators obtained in Examples and Comparative Examples, the following a. Each of the assembled secondary batteries was subjected to low-temperature cycle characteristics measurement.

a. Fabrication of cathode plate

100 parts by weight of lithium cobalt oxide as an active material, 2 parts by weight of acetylene black as a conductive agent with respect to 100 parts by weight of the active material, 2 parts by weight of polyvinylidene fluoride as a binder with respect to 100 parts by weight of the active material, -Pyrrolidone in a twin-screw kneader and kneaded to prepare a positive electrode material mixture paint. Then, a positive electrode active material layer was formed by applying a positive electrode material mixture slurry to both surfaces of a 20 탆 thick Al foil and drying it. The thus obtained laminate having the positive electrode active material layers on both sides of the positive electrode collector was rolled by a pair of rollers to obtain a positive electrode plate having a total thickness of 120 占 퐉. An exposed portion of the positive electrode current collector on which the positive electrode active material layer is not formed was provided on one side of the positive electrode current collector in the short side direction.

b. Production of negative plates

100 parts of artificial graphite as an active material of the negative electrode, and 2.3 parts of a styrene-butadiene copolymer rubber particle dispersion as a binding agent in terms of solid content of 100 parts of the active material and 2.3 parts of the binder in terms of solid content. Carboxymethylcellulose as a thickener 1.4 parts by mass of water and a predetermined amount of water were stirred in a twin-kneading kneader to prepare a negative electrode material mixture paint having a volumetric solid content of 55%. Here, the volumetric solid content refers to the volumetric concentration of the solid content contained in the compound coating material. The negative electrode material mixture paint was applied to both sides of a copper foil having a thickness of 15 mu m, dried, and then rolled to obtain a negative electrode having a total thickness of 185 mu m. In addition, an exposed portion of the negative electrode collector in which the negative electrode active material layer is not formed was provided on one side in the short side direction of the negative electrode collector.

c. Manufacture of batteries

These positive electrode plates, the separators of the examples and the comparative examples and the negative electrode plates were wound and inserted into a cylindrical battery case, and mixed with EC (ethylene carbonate), DMC (dimethyl carbonate), MEC (methyl ethyl carbonate) 5.5 g of an electrolytic solution prepared by dissolving 1 M of LiPF ₆ and 3 parts by weight of VC in a solvent was sealed and a cylindrical 18650 non-aqueous secondary battery having a design capacity of 2000 mAh was prepared.

d. Measurement of low-temperature cycle characteristics

The capacity retention rate at the low temperature 100 cycle time was measured by the following method. The sealed battery was charged and discharged twice and kept at 45 캜 for 7 days. The following charge and discharge cycles were repeated 100 times at -30 캜. Charging was performed at a constant voltage of 4.2 V and at 1400 mA. Charging was terminated when the charging current dropped to 100 mA, and discharging was continued at a constant current of 2000 mA to an ending voltage of 3 V to form one cycle. The discharge capacity ratio at the 100th cycle to the 100-cycle capacity retention ratio. The low temperature cycle characteristics were evaluated based on the following criteria.

A: Capacity retention rate at a low temperature 100 cycle time is 80% or more

B: Capacity retention rate at a low temperature 100 cycle time is 70% or more and less than 80%

C: Capacity retention ratio at a low temperature 100 cycle time is less than 70%

(5) Variation of Peel Strength of Active Layer / Polyolefin Porous Substrate

A tape (manufactured by 3M, product name: Scotch 600) having a width of 12 mm and a length of 100 mm was applied to a 600 mm wide separator of the examples and comparative examples in the same manner as the above (1) "peeling strength of the active layer and the polyolefin porous substrate" With a distance of 100 mm in the direction parallel to the longitudinal direction (5 points in the TD direction). Five points of the tape were attached (five points in the MD direction) at intervals of 500 mm in the separator longitudinal direction in the same manner. The force at the time of peeling the tape attached at 25 points from the sample at a rate of 50 mm / minute was measured using a 90 ° peel strength meter (product name: IP-5N, manufactured by IMADA). Based on the following formula, the variation [%] of the peel strength was calculated from the standard deviation and the average value of the peel strength, and evaluated based on the following criteria.

Where x is the average value of the peel strength and n is the number of measurements.

(Evaluation standard)

A: Variation in peel strength of the active layer / substrate is less than 10%

B: Variation of the peel strength of the active layer / substrate is 10% or more and less than 20%

C: Variation in peel strength of the active layer / substrate is 20% or more

(6) Collision resistance (collision test)

Figure 2 is a schematic diagram of a crash test according to UL specifications 1642 and / or 2054; In the UL standards 1642 and / or 2054, the round bar 21 is placed on the sample 22 placed on the test stand so that the sample 22 and the round bar 21 (? = 15.8 mm) The influence of the impact on the sample is observed by dropping a weight 20 of about 9.1 kg (about 20 pounds) on the top surface of the round bar 21 from a position at a height of 610 25 mm from the sample.

Referring to FIG. 2 and UL standards 1642 and 2054, the procedure of the collision test in the examples and the comparative examples will be described below.

a. Production of positive electrode

90.4 mass% of nickel, manganese and cobalt composite oxide (Ni: Mn: Co = 1: 1: 1 (raw consumption), density 4.70 g / cm3, capacity density 175 mAh / g) , 3.8 mass% of 1.6 mass% of graphite powder (KS6) (density 2.26 g / cm3, number average particle diameter 6.5 mu m) and acetylene black powder AB (density 1.95 g / cm3, number average particle diameter 48 nm) , And polyvinylidene fluoride (PVDF) (density 1.75 g / cm3) as a binder were mixed in a ratio of 4.2 mass%, and these were dispersed in N-methylpyrrolidone (NMP) to prepare a slurry. This slurry was applied to one surface of an aluminum foil having a thickness of 20 mu m serving as a positive electrode current collector using a die coater and dried at 130 DEG C for 3 minutes and then rolled using a roll press machine. The sheet after the rolling was slit with a width of 57.0 mm to obtain a positive electrode. The amount of the positive electrode active material applied was 109 g / m 2.

b. Production of negative electrode

87.6% by mass of graphite powder A (density 2.23 g / cm3, number average particle diameter 12.7 占 퐉) and 9.7% by mass of graphite powder B (density 2.27 g / cm3, number average particle diameter 6.5 占 퐉) A slurry was prepared by dispersing 1.4 mass% of ammonium salt of carboxymethylcellulose (in terms of solid content) (solid content concentration 1.83 mass% aqueous solution) and diene rubber latex 1.7 mass% (solid content conversion) (solid content concentration 40 mass% aqueous solution). This slurry was applied to one surface of a copper foil having a thickness of 12 mu m serving as a negative electrode current collector with a die coater and dried at 120 DEG C for 3 minutes and then rolled using a roll press machine. The rolled material was slit to a width of 58.5 mm to obtain a negative electrode. At this time, the application amount of the negative electrode active material was 5.2 g / m 2.

c. Preparation of non-aqueous electrolyte

A mixed solvent (Lithium Battery Grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a volume ratio of 1: 2 was charged with LiPF ₆ at 1 mol / L So as to obtain an electrolytic solution which is a non-aqueous electrolyte.

d. Battery assembly

The positive electrode and negative electrode thus prepared were superimposed on both sides of the separator in the examples, and the wound cylindrical body was inserted into a stainless steel cylindrical battery case (outer case). Subsequently, 5 mL of the above electrolytic solution was poured therein, the current was immersed in the electrolytic solution, and the battery case was sealed to prepare a nonaqueous electrolyte secondary battery.

e. Heat treatment

The nonaqueous electrolyte secondary battery obtained in d. was stored for 48 hours under an environment of 60 캜.

f. Initial charge / discharge

The non-aqueous electrolyte secondary battery obtained in e. was charged at a constant current of 0.3 C under an environment of 25 캜, and after reaching 4.2 V, charged at a constant voltage of 4.2 V and discharged to 3.0 V at a constant current of 0.3 C. And the charging time at the constant current and the charging time at the constant voltage were 8 hours. Also, 1C is a current value at which the battery is discharged in one hour.

Next, the battery was charged with a constant current of 1 C, and after reaching 4.2 V, charged at a constant voltage of 4.2 V and discharged to 3.0 V with a constant current of 1C. And the charging time at the constant current and the charging time at the constant voltage were set to 3 hours. The capacity at the time of discharging at a constant current of 1 C was defined as 1 C discharge capacity (mAh). The nonaqueous electrolyte secondary battery 22 obtained in e. Was charged at a constant current of 1 C under the environment of 25 캜, and after reaching 4.2 V, charged at a constant voltage of 4.2 V for 3 hours in total.

Next, a round bar 21 made of stainless steel having a diameter of 15.8 mm was disposed at the center of the battery 22 so as to cross the battery in a transverse direction on a flat surface in an environment of 25 캜. A weight 20 of 9.1 kg was dropped at a height of 61 +/- 2.5 cm so that impact was applied perpendicularly to the longitudinal axis of the battery from the round bar 21 disposed at the center of the battery 22. [ Thereafter, the external temperature of the battery was measured, and the presence or absence of gas discharge from the battery and the ignition of the battery were observed. The external temperature of the battery is a temperature measured by a thermocouple (K-type seal type) at a position 1 cm from the bottom of the external body of the battery.

The crash test was evaluated based on the following criteria.

A: Battery external temperature less than 60 ℃

B: Battery external temperature 60 캜 or more and less than 80 캜

C: Battery external temperature 80 ℃ or higher, and gas spouting, no ignition

D: with gas spouting or ignition

(7) Weight average molecular weight

The weight average molecular weight of the polyolefin of the present embodiment was determined by gel permeation chromatography (GPC) and measured by the following method. The apparatus used was an ALC / GPC-150-C-plus type (trademark) manufactured by Waters Corporation, two 30 cm columns of GMH6-HT (trademark) Cm was connected in series and measurement was carried out at 140 캜 at a sample concentration of 0.05 wt% using orthodichlorobenzene as a mobile phase solvent. Further, a calibration curve was prepared using commercially available monodisperse polystyrene based on a commercially available molecular weight, and 0.43 (Q factor of polyethylene / Q polystyrene = 17.7 / 41.3) was added to the molecular weight distribution data of the obtained samples in polystyrene conversion , And the weight average molecular weight of the polyolefin was obtained.

The weight average molecular weight of the vinyl compound having fluorine atoms was determined by GPC and measured by the following method. The apparatus used was Alliance GPC 2000 (trademark) manufactured by Waters Corporation, two columns of GMH6-HT (trademark) made by Tosoh Corporation, and two columns of GMH6-HTL (trademark) Dichlorobenzene was used as a mobile phase solvent and measurement was carried out at a column temperature of 140 캜. In addition, monodisperse polystyrene (manufactured by Tosoh Corporation) having a molecular weight based on a molecular weight calibration standard material was used. From the above, the weight average molecular weight of the vinyl compound having fluorine atoms was calculated.

Example

(Example 1)

(1) Preparation of the first polyolefin solution

Mw (hereinafter referred to as weight average molecular weight) is 1.2 × 10 ⁶ of polypropylene (PP: melting point 162 ℃) is 0.74 20% by weight and Mw × 10 ⁶ High density polyethylene (HDPE: density 0.955g / ㎤, melting point 135 ℃ ) Was added to 100 parts by mass of a first polyolefin resin containing 80 mass% of an antioxidant tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) And the mixture was prepared.

25 parts by mass of the obtained mixture was fed into a twin-screw extruder (inner diameter: 58 mm, L / D = 42) of a strong kneading type and 75 parts by mass of liquid paraffin [35 cst (40 ° C)] was fed from the side feeder of the twin screw extruder, And melt-kneaded at 210 DEG C and 250 rpm to prepare a first polyolefin solution.

(2) Preparation of the second polyolefin solution

A second polyolefin resin containing 100 parts by mass of a 60% by mass,: Mw of 2.0 × 10 ⁶ of ultra high molecular weight polyethylene (UHMwPE) 40% by weight and a Mw of 5.6 × 10 ⁵ High density polyethylene (density 0.955g / ㎤ HDPE) And 0.2 parts by mass of an antioxidant tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane were mixed to prepare a mixture.

25 parts by mass of the resulting mixture was fed into another twin-screw extruder of the same type as that described above, and 75 parts by mass of liquid paraffin [35 cSt (40 占 폚)] was fed from the side feeder of the twin-screw extruder. A second polyolefin solution was prepared.

(3) Extrusion

The first and second polyolefin solutions were fed from each twin-screw extruder to a three-layer T die, and extruded so that the layer thickness ratio of the first polyolefin solution / the second polyolefin solution / the first polyolefin solution was 10/80/10. The extruded body was cooled while being pulled at a take-off speed of 2 m / min on a cooling roll adjusted to 30 캜 to form a three-layer gel sheet.

(4) First stretching, removal of film forming solvent, drying

The gel-like three-layer sheet was subjected to simultaneous biaxial stretching (first stretching) at a temperature of 116 DEG C in the MD direction and the TD direction at five times by a tenter stretching machine. The stretched gel-like three-layer sheet was fixed on an aluminum frame plate of 20 cm x 20 cm, immersed in a methylene chloride bath controlled at 25 캜, swirled at 100 rpm for 3 minutes to remove liquid paraffin, and air dried at room temperature.

(5) Second elongation, heat fixing

The dried film was stretched 1.4 times (second stretching) in the TD direction at 126 DEG C by using a batch type stretching machine. Next, this film was heat-settled at 126 DEG C by the tenter method.

(6) Formation of active layer

Polymer PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80:20 (mass ratio), weight average molecular weight: 1.510 ⁶ ) was added to acetone and dissolved at 50 ° C for about 12 hours or longer To prepare a polymer solution. The slurry was prepared by adding Al ₂ O ₃ powder as inorganic particles to a polymer solution prepared so as to have a weight ratio of polymer: inorganic particles = 17: 83, and crushing and dispersing the inorganic particles using a ball mill method for 12 hours or more. The average particle diameter of the inorganic particles of the thus-prepared slurry was 600 nm on average.

The three-layer microporous membrane prepared in (5) was immersed and dip-coated on the thus-prepared slurry, and then the thickness of the slurry coating layer applied on both sides was adjusted using a wire bar having a wire size of 0.5 mm, Lt; / RTI &gt; The thickness of the active layer formed on both surfaces of the polyolefin porous substrate was 5.0 mu m. The mixing ratios of respective components, the production conditions, the evaluation results, and the like of the polyolefin three-layered microporous membrane having the active layer formed as described above are shown in Tables 1 and 3.

(Example 2)

(2) The second polyolefin solution of Example 1 was prepared in the same manner as in Example 1 except that 17.5 mass% of ultrahigh molecular weight polyethylene (UHMwPE) having Mw of 2.0 x 10 ⁶ and high density polyethylene having Mw of 3.0 x 10 ⁵ ( 100 parts by mass of a second polyolefin resin containing 25% by weight of a poly (ethylene-co-hexene) copolymer having 57.5% by mass of HDPE, density of 0.955 g / cm3, MFR of 135 g / 10 min and a melting point of 124 占 폚, , 0.2 part by mass of an antioxidant tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane was added to the mixture to prepare a mixture.

The mixing ratios of respective components, the production conditions, the evaluation results, and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 1 except that the active layer was formed were described in Tables 1, 2 and 3.

(Example 3)

Example 1 (2) 2 in the preparation of the polyolefin solution in Example 1, a mixture Instead, the Mw was 2.0 × 10 ⁶ of ultra high molecular weight polyethylene (UHMwPE) 16% by weight and a Mw of 3.0 × 10 ⁵ High density polyethylene of ( (Methylene-3- (3,5-di (tert-butoxycarbonyl) methylene) -thiadiazole was added to 100 parts by mass of a second polyolefin resin containing 18% by mass of a polypropylene having a melting heat of 96 J / -tert butyl-4-hydroxyphenyl) -propionate] methane were mixed to prepare a mixture.

The mixing ratios of respective components of the polyolefin three-layered microporous membrane prepared in the same manner as in Example 1 except that the active layer was formed and the production conditions and the evaluation results are shown in Tables 1 and 3.

(Example 4)

(Polyvinylidene fluoride-chlorotrifluoroethylene copolymer, PVdF: CTFE = 96: 4 (molar ratio)) and a weight average molecular weight of 1.2 x 10 &lt; ⁶ &gt; ) Was used.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 5)

In the formation of the active layer in Example 2, the weight ratio of polymer: inorganic particles was adjusted to be 9:91.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 6)

(Polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight: 1.5 x 10 &lt; ⁶ &gt;) as a polymer in the active layer formation of Example 2, No ethyltoluene was added to acetone at a weight ratio of 10: 2.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 7)

(Polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight: 1.5 x 10 &lt; ⁶ &gt;) and cyano Ethyl polyvinyl alcohol was added to acetone at a weight ratio of 10: 2.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 8)

A polymer PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80:20 (mass ratio), weight average molecular weight 1.5 x 10 ⁶ ) was used instead of the polymer PVdF- HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight: 0.510 ⁶ ) was used.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 9)

In forming the active layer of Example 2, AlO (OH) powder (boehmite, average particle diameter: 1.0 탆) was used as inorganic particles in place of Al ₂ O ₃ powder.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 10)

In forming the active layer of Example 2, BaTiO ₃ powder (barium titanate, average particle size: 0.6 탆) was used as inorganic particles in place of Al ₂ O ₃ powder.

The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Example 11)

(1) In the preparation of the first polyolefin solution of Example 2, 16 mass% of polypropylene (PP: melting point 162 캜) having Mw of 1.2 × 10 ⁶ and 0.74 × 10 ⁶ high-density polyethylene (HDPE Methylene-3- (3 (tert-butoxycarbonyl) methyl) propane was added to 100 parts by mass of a first polyolefin resin containing 64 mass% of a silica powder , 5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane were used in combination. The mixing ratios of respective components, production conditions, evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 2 except that the active layer was formed are shown in Table 1.

(Comparative Example 1)

Table 1 shows the mixing ratios of the respective components of the polyolefin three-layered microporous film, the production conditions, the evaluation results, and the like in the same manner as in Example 1, except that the active layer was not formed.

(Comparative Example 2)

(1) In the preparation of the first polyolefin solution of Example 1, 20 mass% of polypropylene (PP: melting point 162 占 폚) having Mw of 1.2 占⁰⁶ and high density polyethylene having an Mw of 0.74 占⁰⁶ (HDPE: density 0.955 (HDPE: density 0.955 g / cm3, melting point 135 占 폚) having Mw of 0.74 占⁰⁶ instead of 100 parts by mass of the first polyolefin resin containing 80 mass% And 100 parts by mass of a polyolefin resin were used in place of 100 parts by mass of the polyolefin resin. The mixing ratios of the respective components of the polyolefin three-layer microporous membrane, the production conditions, and the evaluation results are shown in Table 1.

(Comparative Example 3)

(1) In the preparation of the first polyolefin solution of Example 1, 20 mass% of polypropylene (PP: melting point 162 占 폚) having Mw of 1.2 占⁰⁶ and high density polyethylene having an Mw of 0.74 占⁰⁶ (HDPE: density 0.955 100 parts by mass of a first polyolefin resin containing polypropylene (PP: melting point: 162 占 폚) having Mw of 1.2 占⁰⁶ was used instead of 100 parts by mass of the first polyolefin resin containing 80 mass% , The mixing ratios of respective components of the polyolefin three-layered microporous membrane, the production conditions, the evaluation results, and the like are shown in Table 1.

(Comparative Example 4)

Except that PVdF (polyvinylidene fluoride, weight average molecular weight: 0.35 x 10 ⁶ ) was used in place of PVdF-HFP in the formation of the active layer (6) in Example 1, and 3 polyolefin The compounding ratio of each component of the film, the production conditions, the evaluation results, and the like are shown in Table 1.

(Example 12)

In Example 2 the preparation of the first polyolefin solution, Mw 2.0 × 10 ⁶ is of polypropylene (PP: melting point 162 ℃) is 0.56 20% by weight and Mw × 10 ⁶ High density polyethylene (HDPE: density 0.955g / ㎤ Methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] was added to 100 parts by mass of a first polyolefin resin, And 0.2 parts by mass of methane were mixed to prepare a mixture.

The mixing ratios of respective components, the production conditions, the evaluation results and the like of the polyolefin three-layered microporous membrane prepared in the same manner as in Example 2 except for the above-mentioned operation and formed with the active layer were shown in Table 2.

(Example 13)

In Example 2 the preparation of the first polyolefin solution, Mw 0.6 × 10 ⁶ is of polypropylene (PP: melting point 162 ℃) is 20% by weight and 0.86 × 10 ⁶ Mw of high density polyethylene (HDPE: density 0.955g / ㎤ Methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] was added to 100 parts by mass of a first polyolefin resin, And 0.2 parts by mass of methane were mixed to prepare a mixture.

The mixing ratios of respective components, the production conditions, the evaluation results and the like of the polyolefin three-layered microporous membrane prepared in the same manner as in Example 2 except for the above-mentioned operation and formed with the active layer were shown in Table 2.

(Example 14)

(1) In the preparation of the first polyolefin solution of Example 1, 20 mass% of polypropylene (PP: melting point 162 占 폚) having Mw of 1.2 占⁰⁶ and high density polyethylene having an Mw of 0.74 占⁰⁶ (HDPE: density 0.955 100 parts by mass of the first polyolefin resin containing 25% by weight of a poly (ethylene-co-hexene) copolymer of 55% by mass of a polyolefin resin (a) having a melting point of 130 占 폚 / g and a melting point of 135 占 폚) having an MFR of 135 g / 10 min and a melting point of 124 占 폚 , 0.2 part by mass of an antioxidant tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane was added to the mixture to prepare a mixture.

The mixing ratios of respective components, the production conditions, the evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 1 except that the active layer was formed are shown in Table 3.

(Example 15)

(1) The first polyolefin solution of Example 1 was prepared by mixing 82 mass% of high density polyethylene having an Mw of 0.74x10 ⁶ (HDPE: density 0.955 g / cm3, melting point 135 占 폚), polypropylene having a heat of fusion of 96 J / g 0.2 parts by mass of an antioxidant tetrakis [methylene-3- (3,5-di-tert-butyl-4-hydroxyphenyl) -propionate] methane was added to 100 parts by mass of a first polyolefin resin containing 18% To prepare a mixture.

The mixing ratios of respective components, the production conditions, the evaluation results and the like of the polyolefin three-layered microporous membrane produced in the same manner as in Example 1 except that the active layer was formed are shown in Table 3.

(Example 16)

(1) In the preparation of the first polyolefin solution of Example 1, 35 mass% of polypropylene (PP: melting point 162 占 폚) having Mw of 1.2 占⁰⁶ and high density polyethylene having an Mw of 0.74 占⁰⁶ (HDPE: density 0.955 g / cm &lt; 3 &gt;, melting point: 135 DEG C). The mixing ratios of the respective components of the polyolefin three-layered microporous membrane, prepared in the same manner as in Example 1, except for the above, and the production conditions and evaluation results are shown in Table 1.

10: pin
11: Pin I
12: Pin II
13: Winding sample
20: Chu
21: Round bar
22: Sample

Claims (13)

A polyolefin multi-layer microporous membrane containing polyethylene and polypropylene, wherein the outermost polypropylene concentration is higher than the innermost polypropylene concentration and the outermost polyethylene concentration is lower than the innermost polyethylene concentration; and at least one And an active layer disposed on a surface of the substrate,
Wherein the active layer comprises at least one vinyl compound having at least one fluorine atom selected from polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE) And a separator for a power storage device. The polyolefin multilayer microporous membrane according to claim 1, wherein the polyolefin multilayer microporous membrane is laminated in the order of a first microporous layer, a second microporous layer, and a first microporous layer, wherein the first microporous layer comprises polyethylene and polypropylene Wherein the first microporous layer comprises a first polyolefin resin and the second microporous layer comprises a second polyolefin resin different from the first polyolefin resin containing polyethylene and the active layer comprises at least one of the first microporous layer Wherein the separator is laminated on the layer. The separator for a power storage device according to claim 2, wherein the first polyolefin resin or the second polyolefin resin comprises a linear low density polyethylene. The separator for power storage device according to claim 2, wherein the first polyolefin resin or the second polyolefin resin further contains polypropylene having a heat of fusion of 150 J / g or less. The separator for power storage device according to claim 3, wherein said linear low density polyethylene is poly (ethylene-co-1-hexene). The separator for a power storage device according to any one of claims 1 to 5, wherein the mass ratio of the vinyl compound having a fluorine atom to the inorganic particle is 5/95 to 80/20. The separator for a power storage device according to any one of claims 1 to 5, wherein the fluorine atom-containing vinyl compound has a weight average molecular weight of 0.6 x 10 ⁶ to 2.5 x 10 ⁶ . 6. The organic electroluminescent device according to any one of claims 1 to 5, wherein the active layer further comprises at least one selected from cyanoethylpullulan, cyanoethylpolyvinyl alcohol, cyanoethylcellulose, cyanoethylstarch, Separator for power storage device. 6. The polypropylene resin composition according to any one of claims 2 to 5, wherein a ratio of a weight average molecular weight of polyethylene and polypropylene contained in the first polyolefin resin (MwE (weight average molecular weight of polyethylene) / MwP ) Is 0.6 to 1.5. The separator for a power storage device according to any one of claims 2 to 5, wherein the first polyolefin resin further contains at least one selected from the group consisting of silica, alumina and titania. A laminate comprising the separator for power storage device according to any one of claims 1 to 5, a positive electrode, and a negative electrode. A laminated body according to claim 11, wherein the laminated body is wound. 12. A secondary battery comprising the laminate according to claim 11, or a winding in which the laminate is wound, and an electrolyte.

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