JP2018101613A - Separator for electricity storage device and laminate, wound body, lithium ion secondary battery or electricity storage device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a separator for an electric storage device with excellent balance in each performance including not only, in particular, peel strength between a substrate and a modified layer and battery winding properties when winding a separator around a cylindrical battery but also cold thermal shock characteristics and low temperature cycle characteristics among basic characteristics required for the conventional separator.SOLUTION: Provided is a separator for an electric storage device with excellent balance in each performance including not only peel strength between a substrate and a modified layer and battery winding properties but also cold thermal shock characteristics and low temperature cycle characteristics as compared with a conventional separator.SELECTED DRAWING: None

Description

  The present invention relates to an electrical storage device separator.

  In recent years, development of power storage devices represented by lithium ion secondary batteries has been actively conducted. Usually, a power storage device is provided with a microporous membrane (separator) between positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to pass through the electrolytic solution held in the micropores.

The separator is deeply involved in battery characteristics, battery productivity, and battery safety, and has excellent permeability, mechanical characteristics, impedance characteristics, pore clogging characteristics (shutdown characteristics), and melt breakage prevention characteristics (meltdown prevention characteristics). Etc. are required.
In order to satisfy such a requirement, it has been studied so far to laminate various modified porous films on a microporous substrate constituting a separator.
For example, Patent Document 1 includes a first microporous layer containing polypropylene and a second microporous layer containing ultrahigh molecular weight polyethylene, and another layer (polypropylene layer) is formed on one surface of the porous layer. Polyolefin multilayer microporous membrane having a specific porosity / film thickness and air permeability provided with a simple substance such as vinylidene fluoride (PVDF) or polytetrafluoroethylene (PTFE) and a fluorine-containing resin such as a copolymer) The disclosed embodiment has a dense pore structure with high uniformity of through-hole diameter, low air permeability, and maintains high porosity and mechanical strength in a balanced manner even when thinned. A microporous layer having excellent impedance characteristics is described.
Patent Document 2 discloses a polyolefin multilayer microporous membrane having a specific coefficient of static friction coefficient and pore density on the other surface relative to one surface of the polyolefin multilayer microporous membrane including polyethylene and polypropylene. In this example, a multi-layer microporous membrane having excellent slipperiness between membranes and high durability (withstand voltage, electrochemical stability) due to a dense pore structure is described.
In Patent Document 3, a modified porous layer made of a PVDF layer is laminated on a polyethylene microporous film having irregularly formed protrusions made of a specific number of polyethylenes, thereby improving the properties even during high-speed conveyance. A battery separator that does not cause peeling of the porous layer is disclosed.
Furthermore, Patent Document 4 discloses a composite porous membrane in which a porous membrane including a heat resistant resin layer including a PVDF layer is laminated on a porous membrane having a polypropylene resin layer having mechanical strength and compression resistance as an outermost layer. In addition, it has been disclosed that since it has an excellent shutdown function and further has a configuration in which a fluorine resin layer is laminated, it is possible to achieve both excellent adhesion of the fluorine resin layer and a small increase in air resistance resistance, particularly a battery. It is suitable for use as a separator.

International Publication No. 2015/194667 International Publication No. 2013/146403 International Publication No. 2015/190264 JP 2012-061791 A

In response to the recent eco-boom, not only is the demand for hybrid vehicles increasing rapidly, but even electric vehicles are being recognized in the market, and the frequency of these vehicles being used around the world is increasing. Under such circumstances, the separator is also required to have performance corresponding to the destination, and in particular, improvement of the durability of the separator in a cold region has been demanded. On the other hand, the conventional separators disclosed in Patent Documents 1 to 4 do not consider the above-mentioned circumstances from the beginning, and separators that can be used in various parts of the world including cold regions have long been desired. It was.
In view of the above circumstances, the present invention is a battery winding property when the separator is rubbed against a cylindrical battery, particularly the peel strength between the base material and the modified layer, among the basic characteristics required for the conventional separator. An object of the present invention is to provide a separator for an electricity storage device that is not only excellent in heat resistance but also excellent in thermal shock characteristics and low-temperature cycle characteristics, and in which each performance is balanced.

The present inventors have found 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] Polyolefin multilayer 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 the porous An active layer disposed on at least one surface of the membrane,
A vinyl compound having at least one fluorine atom, wherein the active layer is selected from polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE); and inorganic particles. An electricity 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, and the first microporous layer comprises: The second microporous layer is made of a second polyolefin resin different from the first polyolefin resin containing polyethylene, and the active layer is made of a first polyolefin resin containing polyethylene and polypropylene. The separator for an electricity storage device according to [1], which is laminated on at least one layer of the first microporous layer.
[3] The separator for an electricity storage device according to [1] or [2], wherein the first polyolefin resin or the second polyolefin resin contains linear low-density polyethylene.
[4] The electricity storage device separator 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 an electricity storage device according to [3], wherein the linear low-density polyethylene is poly (ethylene-co-1-hexene).
[6] The electricity storage device separator according to any one of [1] to [5], wherein a mass ratio of the vinyl compound having fluorine atoms to the inorganic particles is 5/95 to 80/20.
[7] The electricity storage device separator according to any one of [1] to [6], wherein the vinyl compound having a fluorine atom has a weight average molecular weight of 0.6 × 10 ^{6 to} 2.5 × 10 ⁶ .
[8] The electricity storage device separator according to any one of [1] to [7], wherein the active layer further contains at least one selected from cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose.
[9] The ratio of the weight average molecular weight of polyethylene and polypropylene contained in the first polyolefin resin (MwE (weight average molecular weight of polyethylene) / MwP (weight average molecular weight of polypropylene)) is 0.6 to 1.5. The separator for an electricity storage device according to any one of [1] to [8].
[10] The separator for an electricity 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 electricity storage device separator according to any one of [1] to [10], a positive electrode, and a negative electrode.
[12] A wound body in which the laminate according to [11] is wound.
[13] A secondary battery comprising the laminate according to [11] or the wound body according to [12] and an electrolytic solution.

  According to the present invention, as compared with the conventional separator, not only the peel strength between the active layer and the substrate and the battery winding property, but also the thermal shock characteristics and the low temperature cycle characteristics are excellent, and the performance is balanced. A separator for a device can be provided.

FIG. 1 (A) is an explanatory view showing the overall configuration of a manual winding machine used to determine the peel strength between the active layer and the polyolefin multilayer microporous membrane, and FIG. It is explanatory drawing which shows this structure. FIG. 2 is a schematic diagram of an apparatus used to perform a crash test.

<Separator for electricity storage device>
The separator for an electricity storage device of the present invention is a polyolefin multilayer microporous material 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 electricity storage device separator comprising a membrane and an active layer disposed on at least one surface of the microporous membrane. The outermost part of the polyolefin multilayer microporous membrane refers to the cross-sectional portion of the two outer membranes when the multilayer microporous membrane is divided into three so as to have the same thickness in the stacking direction. The inside refers to the cross-sectional portion of the membrane that was inside.
As a preferred embodiment of the separator for an electricity storage device of the present invention, the separator includes a polyolefin multilayer microporous membrane and an active layer, and the multilayer microporous membrane comprises at least the first microporous layer and the second microporous membrane. A polyolefin comprising a porous layer, wherein the first microporous layer comprises a first polyolefin resin containing polyethylene and polypropylene, and the second microporous layer comprises polyethylene and is different from the first polyolefin resin. The multilayer microporous membrane is made of resin, and is laminated in the order of the first microporous layer, the second microporous layer, and the first microporous layer.
The active layer is made porous through a process of coating the active layer on at least one layer of the polyolefin multilayer microporous membrane, the three outer layers being the first microporous layer in the three layers obtained in this stacking order. Separators bound on the membrane tend to provide an electricity storage device that is less likely to have reduced ion permeability and that has high output characteristics. Furthermore, even when the temperature rise during abnormal heat generation is fast, smooth shutdown characteristics are exhibited and high safety tends to be easily obtained.
Furthermore, by disposing a film containing polyethylene and polypropylene as the outer layer of the polyolefin multilayer microporous film, the peel strength from the active layer laminated on the outer layer is increased. When polypropylene and polyethylene coexist in this way, the surface free energy on the surface of the layer increases due to the polar effect of polypropylene as compared with the case of polyethylene alone, and adhesion with the active layer increases. In addition to this, by arranging a film containing polyethylene and polypropylene in the outer layer, low temperature characteristics, particularly low temperature cycle characteristics, which is one of the characteristics of the separator according to the present embodiment, is improved. Compared to polypropylene having a transition temperature of around 0 ° C. alone, the transition temperature is lowered by blending, and it is considered that brittle fracture of the material hardly occurs.

This power storage device separator is formed by laminating an active layer on at least a polyolefin multilayer microporous membrane. By the active layer, the adhesive force between the active layer and the adhesive layer on the electrode side becomes stronger, and in particular, the thermal shock characteristics described later are improved.
As described above, the separator may be composed of only the polyolefin multilayer microporous membrane and the active layer, but may further have a thermoplastic polymer layer in addition to these in order to further improve the peel strength ( Details will be described later). When the active layer and the thermoplastic polymer layer are arranged on the polyolefin multilayer microporous membrane, their mutual positional relationship is arbitrary, but at least one of the active layers is required from the viewpoint of achieving both the rate characteristics and safety of the electricity storage device. The thermoplastic polymer layer may be disposed so as to expose the portion, and is preferably disposed on the active layer layer.

  Preferred embodiments of each member constituting the electricity storage device separator of the present embodiment and a method for producing the electricity storage device separator 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 a porous membrane having a fine pore size, having no electron conductivity, ionic conductivity, high resistance to organic solvents. And preferred.
The polyolefin multilayer microporous membrane (polyolefin porous substrate) according to this embodiment includes at least a first polyolefin microporous layer and a second polyolefin microporous layer, and the first microporous layer is polyethylene. And polypropylene, and the second microporous layer contains polyethylene.
The polyolefin porous base material is excellent as a separator base material in mechanical properties, shutdown properties, meltdown properties, etc., and in order to ensure a balance among the properties, the first microporous layer and the second microporous material are used. The layer is laminated in the order of the porous layer and the first microporous layer, and further, mechanical properties desired as a separator by including polyethylene and polypropylene as the first layer and polyethylene as the second layer, shutdown characteristics, Excellent balance such as meltdown characteristics is developed.
The polyethylene and polypropylene contained in the first microporous layer are not particularly limited, and examples thereof include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene (HDPE), and ultrahigh molecular weight polyethylene. (UHMwPE), isotactic polypropylene, atactic polypropylene, ethylene-propylene random copolymer, ethylene propylene rubber and the like. The polymerization catalyst used in the production of these polyethylenes or polypropylenes is not particularly limited, and examples thereof include Ziegler-Natta catalysts, Phillips catalysts, and metallocene catalysts.
The first polyolefin resin preferably further contains linear low-density polyethylene in addition to the above polyethylene from the viewpoint of collision resistance of the electricity 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, for example, a poly (ethylene-co-hexene) copolymer.

In addition to the above polypropylene, the first polyolefin resin has a three-dimensional structure, and is an isotactic polypropylene, syndiotactic polypropylene and atactic polypropylene that can improve the heat resistance of the separator. It is more preferable to use any of the above from the viewpoint of the peel strength between the active layer and the substrate.
In particular, it is particularly preferable that the first microporous layer further contains a polypropylene having a heat of fusion of 150 J / g or less because the amorphous portion in the polypropylene increases and the impact resistance of the electricity 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 from the viewpoint of the peel strength between the active layer and the substrate, the thermal shock characteristics, the low temperature cycle characteristics, etc., 1 to 50 It is preferable that it is mass%, More preferably, it is 5-40 mass%, More preferably, it is 15-35 mass%. Especially preferably, it is less than 15-30 mass%.
Further, the ratio of the polyolefin resin to 100% by mass of the polyolefin resin composition in the first microporous layer is not particularly limited, but from the viewpoint of coexistence of air permeability, heat resistance and a good shutdown function, 50 to 100 It is preferable that it is mass%, More preferably, it is 60-100 mass%, More preferably, it is 70-100 mass%. The polymerization catalyst is not particularly limited, and examples thereof include Ziegler-Natta catalysts and metallocene catalysts. When the first microporous layer further contains at least one selected from silica, alumina, and titania, it is further from the viewpoint of the affinity of the separator with the non-aqueous electrolyte, output retention performance, and low-temperature cycle characteristics described later. preferable.

  The ratio of silica, alumina, and titania in the first microporous layer is preferably 5% by mass or more, more preferably 10% by mass with respect to 100% by mass of the first polyolefin resin in the first microporous layer. % Or more, more preferably 20% by mass or more, preferably 90% by mass or less, more preferably 80% by mass or less, and further preferably 70% by mass or less. Such a ratio is preferable from the viewpoint of obtaining good heat resistance and from the viewpoint of obtaining a porous film having high piercing strength by improving stretchability.

Next, the second microporous layer according to this embodiment will be described.
The second microporous layer is made of a second polyolefin resin containing polyethylene and different from the first polyolefin resin. The polyethylene is not particularly limited, and examples thereof include low density polyethylene, linear low density polyethylene (L-LDPE), medium density polyethylene, high density polyethylene (HDPE), and ultrahigh 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 from the viewpoint of strength and heat resistance. In addition to high-density polyethylene and ultrahigh molecular weight polyethylene, it is more preferable to further include linear low-density polyethylene from the viewpoint of collision resistance of the electricity storage device. The linear low density polyethylene is more preferably, for example, a poly (ethylene-co-hexene) copolymer. Polyethylene may be used individually by 1 type, or may be used in combination of 2 or more types for the purpose of imparting flexibility.
From the viewpoint of molding process stability, mechanical strength in the thin film, air permeability, etc., the content of polyethylene in the polyolefin resin of the second microporous layer is 100% by mass as the total mass of the second polyolefin resin. Preferably they are 50 mass%-100 mass%, More preferably, they are 60 mass%-100 mass%, More preferably, they are 70 mass%-95 mass%.
The polyolefin resin of the second microporous layer may further contain polypropylene. As the polypropylene, it is preferable to include a polypropylene having a heat of fusion of 150 J / g or less because the amorphous portion in the polypropylene increases and the collision resistance of the electricity storage device is further improved.
The linear low-density polyethylene or the polypropylene having a heat of fusion of 150 J / g or less is contained in the second polyolefin resin rather than in the first polyolefin resin in terms of collision resistance of the electricity storage device. To preferred. Although the details of this mechanism are unknown, when the layer containing linear low density polyethylene or polypropylene having a heat of fusion of 150 J / g or less is thicker than the other layers, the linear low density polyethylene or heat of fusion is When a layer containing polypropylene of 150 J / g or less is further away from the electrode (when another layer is interposed), it is estimated that the collision resistance of the electricity storage device is good.

  The first and second microporous layers according to the present embodiment have a better balance between cold shock characteristics, low temperature cycle characteristics, heat resistance, impact resistance, and peel strength between the substrate and the active layer. Therefore, a porous film layer made of a polyolefin resin composition containing a polyolefin resin other than the above-described resin may be used. The olefin resin used in the first and second layers is not particularly limited, but may be a polyolefin resin used for normal extrusion, injection, inflation, blow molding, and the like, such as 1-butene, 4-methyl-1- Homopolymers and copolymers such as pentene, 1-hexene, and 1-octene, multistage polymers, and the like can be used. In addition, polyolefins selected from the group consisting of these homopolymers and copolymers and multistage polymers can be used alone or in admixture.

The weight average molecular weight of polyethylene or polypropylene constituting the first and second microporous layers is not particularly limited, but is preferably from 30,000 to 12 million, more preferably from 50,000 to less than 2 million. More preferably, it is 100,000 or more and less than 1 million. A weight average molecular weight of 30,000 or more is preferred because the melt tension at the time of melt molding becomes large and the moldability becomes good and the strength tends to become high due to the entanglement between the polymers. On the other hand, when the weight average molecular weight is 12 million or less, uniform melt kneading is facilitated, and the sheet formability, particularly thickness stability, tends to be excellent, which is preferable. Furthermore, it is preferable that the weight average molecular weight is less than 1,000,000, since the pores are likely to be blocked when the temperature rises and a good shutdown function tends to be obtained.
As described above, the polyolefin multilayer microporous membrane (polyolefin porous substrate) according to this embodiment includes the first microporous layer, the second microporous layer, and the first microporous layer. It is formed by laminating in this order, but is further included in the first microporous layer that is in close contact with the active layer in the separator that is further coated on the polyolefin porous substrate by coating the active layer thereon. When the ratio (MwE / MwP) of the weight average molecular weight (MwE) of polyethylene and the weight average molecular weight (MwP) of polypropylene is 0.6 to 1.5, the first microporous layer and the active layer are separated. This is preferable in that the intensity variation can be reduced. The reason why the peel strength variation is reduced when the MwE / MwP ratio of the first layer is in such a range is estimated as follows. When this ratio is within a predetermined range (close to 1), the difference in molecular weight between polyethylene and polypropylene becomes small, compatibility becomes good, and macrophase separation hardly occurs. If it does so, the uneven distribution of a polyethylene rich part or a polypropylene rich part will be suppressed by the adhesion interface with the active layer of a 1st layer, and, thereby, ratio of both becomes small by an adhesion site. Furthermore, since the adhesive force is not the same between polypropylene and polyethylene, it is considered that the variation in the adhesive force (peeling strength) between the active layer and the substrate becomes small as a result.
In addition, the specific manufacturing method of a polyolefin porous base material is mentioned later.

  As described above, the polyolefin porous base material composed of the first, second, and first three microporous layers has been described. However, the porous base material may be a multilayer of more than three layers. The outermost polypropylene concentration is higher than the innermost polypropylene concentration, and the outermost polyethylene concentration is lower than the innermost polyethylene concentration. Here, as described above, the outermost portion refers to the two outer layers when the multilayer film is divided into three pieces so that each has the same film thickness in the stacking direction. I mean. The constituent components of each film can be known by infrared spectroscopy, liquid chromatography (for example, GPC) or the like.

The polyolefin porous substrate in the present embodiment can contain any additive. Such additives are not particularly limited, and include, for example, polymers other than polyolefins; inorganic particles; antioxidants such as phenolic, phosphorous, and sulfur; metal soaps such as calcium stearate and zinc stearate; Agents; light stabilizers; antistatic agents; antifogging agents; colored pigments and the like.
The total content of these additives is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and still more preferably 5 parts by mass or less with respect to 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. Setting the porosity to 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 puncture strength. Here, the porosity is calculated from the following formula, for example, from the volume (cm ³ ), mass (g), and membrane density (g / cm ³ ) of the polyolefin porous substrate sample:
Porosity = (volume−mass / film density) / volume × 100
It can ask for. Here, for example, in the case of a polyolefin multilayer microporous film made of polyethylene, the film density can be calculated assuming 0.95 (g / cm ³ ). In the case of a multilayer microporous film made of polyethylene and polypropylene, it can be similarly calculated from the respective film densities. The porosity can be adjusted by changing the draw ratio of the polyolefin multilayer microporous membrane.

  The air permeability of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 10 seconds / 100 cc or more, more preferably 50 seconds / 100 cc or more, preferably 1,000 seconds / 100 cc or less, more Preferably, it is 500 seconds / 100 cc or less. The air permeability is preferably 10 seconds / 100 cc or more from the viewpoint of suppressing self-discharge of the electricity storage device. On the other hand, setting the air permeability to 1,000 seconds / 100 cc or less is preferable from the viewpoint of obtaining good charge / discharge characteristics. Here, the air permeability is an air resistance measured in accordance with JIS P-8117. The air permeability can be adjusted by changing the stretching temperature and / or stretching ratio of the porous substrate.

  The average pore diameter of the polyolefin porous substrate in the present embodiment is preferably 0.15 μm or less, more preferably 0.1 μm or less, and the lower limit is preferably 0.01 μm or more. Setting the average pore size to 0.15 μm or less is preferable from the viewpoint of suppressing self-discharge of the electricity storage device and suppressing capacity reduction. The average pore diameter can be adjusted by changing the draw ratio when producing a polyolefin porous substrate.

The puncture strength of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 200 g / 20 μm or more, more preferably 300 g / 20 μm or more, preferably 2,000 g / 20 μm or less, more preferably 1, 000 g / 20 μm or less. It is preferable that the puncture strength is 200 g / 20 μm or more from the viewpoint of suppressing film breakage due to the dropped active material or the like during battery winding, and from the viewpoint of suppressing the concern of short-circuiting due to expansion and contraction of the electrode accompanying charge / discharge. . On the other hand, a puncture strength of 2,000 g / 20 μm or less is preferable from the viewpoint of reducing width shrinkage due to orientation relaxation during heating. The puncture strength is measured by the method described in Examples below.
The puncture strength can be adjusted by adjusting the draw ratio and / or the draw temperature of the polyolefin porous substrate.

  The thickness of the polyolefin porous substrate in the present embodiment is not particularly limited, but is preferably 2 μm or more, more preferably 5 μm or more, preferably 100 μm or less, more preferably 60 μm or less, and even more preferably 50 μm or less. . It is preferable to adjust the thickness to 2 μm or more from the viewpoint of improving the mechanical strength. On the other hand, it is preferable to adjust the film thickness to 100 μm or less because the occupied volume of the separator in the battery is reduced, and this tends to be advantageous in increasing the capacity of the battery.

<Active layer>
(Fluorine atom-containing vinyl compound)
The active layer according to this embodiment contains a vinyl compound having fluorine atoms and inorganic particles, and is laminated on the first microporous layer.
Thus, by providing an active layer on the polyolefin multilayer microporous film as a base material, the battery winding property and the thermal shock characteristics of the electricity storage device are superior to those of the base material alone.
The separator in which the active layer is bonded to the porous substrate through the process of coating the active layer on the first microporous layer, that is, the polyolefin porous substrate, has a reduced ion permeability. However, it tends to provide an electricity storage device with high output characteristics. Furthermore, even when the temperature rise during abnormal heat generation is fast, smooth shutdown characteristics are exhibited and high safety tends to be easily obtained.
Vinyl compounds having fluorine atoms (hereinafter also referred to as fluorine-based resins or binders) are polyvinylidene fluoride-hexafluoropropylene (polymer PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (polymer PVdF-CTFE). It is at least one selected. Thus, by copolymerizing hexafluoropropylene or chlorotrifluoroethylene with vinylidene fluoride, the crystallinity of the fluororesin can be controlled within an appropriate range, so that the active layer is formed during the adhesion treatment with the electrode. It can suppress flowing.
Furthermore, since the adhesive force is improved during the adhesion treatment with the electrode, the interface is not displaced when used as a separator for a secondary battery, so that the thermal shock characteristics are improved. The fluororesin is usually obtained by emulsion polymerization or suspension polymerization.
The weight average molecular weight of the fluororesin is preferably 0.6 × 10 ⁶ to 2.5 × 10 ⁶ . When the weight average molecular weight of the fluororesin is within this range, the thermal shock characteristics are good (it is considered that peeling between the active layer and the substrate hardly occurs because the expansion / contraction during cooling is small).
In the fluororesin, that is, the polymer PVdF-HFP and the polymer PVdF-CTFE, the proportion of structural units derived from HFP or CTFE is preferably 2.0% by mass to 20.0% by mass. If the HFP or CTFE content is 2.0% by mass or more, the crystallization of the fluororesin is suppressed, and if the HFP or CTFE content is 20.0% by mass or less, the fluororesin crystals It is moderately expressed. Further, it is preferable that the HFP or CTFE content is 20.0% by mass or less because it is easy to ensure the thermal shock characteristics.
In view of the above, the proportion of the structural unit derived from HFP or CTFE in the polymer PVdF-HFP and the polymer PVdF-CTFE is more preferably 2.25% by mass or more, further preferably 2.5% by mass or more, and 18% by mass. % Or less is more preferable, and 15% by mass or less is still more preferable.

In addition, when the electrolytic solution is impregnated with the separator containing the active layer, the degree of swelling of the resin contained in the separator varies depending on the type of resin and the composition of the electrolytic solution, and suppresses problems associated with swelling of the resin. For this purpose, it is preferable to select the above-mentioned fluorine-based resin which does not easily swell.
From the group consisting of hydroxyl group (—OH), carboxyl group (—COOH), maleic anhydride group (—COOOC—), sulfonic acid group (—SO ₃ H), and pyrrolidone group (—NCO—) in the active layer It is more preferable that any one selected polar group or a polymer having two or more polar groups among them is included, since the low-temperature cycle characteristics of the separator are improved. Examples of such a polymer include at least one polymer selected from cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose.
By including a polymer having a polar group as described above in the active layer, the low temperature cycle characteristics of the separator are improved because of the high relative dielectric constant of these polymers, even at low temperatures. It is presumed that the resistance is lowered.
The relative dielectric constant of the polymer having a polar group can be 1 to 100 (measurement frequency = 1 kHz), and is preferably 10 or more.

  The active layer may contain the following resins in addition to the above resins as long as the various characteristics expressed by the separator according to the present embodiment are not impaired. Examples of such resins include polyvinylidene fluoride, polyvinylidene fluoride-trichloroethylene, polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, ethylene vinyl acetate copolymer, polyimide, polyethylene oxide, etc., or a mixture of two or more of these. It is not limited to this.

(Inorganic particles)
The inorganic particles used in the active layer are not particularly limited, but those having a melting point of 200 ° C. or higher, high electrical insulation, and electrochemical stability within the use range of the lithium ion secondary battery are preferable.
The inorganic particles are not particularly limited. For example, oxide ceramics such as alumina, silica, titania, zirconia, magnesia, ceria, yttria, zinc oxide, and iron oxide; nitrides such as silicon nitride, titanium nitride, and boron nitride Ceramics: silicon carbide, calcium carbonate, magnesium sulfate, aluminum sulfate, aluminum hydroxide, aluminum hydroxide oxide, potassium titanate, talc, kaolinite, dickite, nacrite, halloysite, pyrophyllite, montmorillonite, sericite, mica, Acerite, bentonite, asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, silica sand and other ceramics; glass fiber 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 ion exchange such as kaolinite, dickite, nacrite, halloysite, and pyrophyllite. An aluminum silicate compound having no function is preferred.

  Alumina has many crystal forms such as α-alumina, β-alumina, γ-alumina, and θ-alumina, and any of them can be suitably used. Among these, α-alumina is preferable because it is thermally and chemically stable.

  As the aluminum oxide compound, aluminum hydroxide oxide (AlO (OH)) is particularly preferable. As the aluminum hydroxide oxide, boehmite is more preferable from the viewpoint of preventing internal short circuit due to generation of lithium dendrite. By adopting particles mainly composed of boehmite as inorganic particles constituting the active layer, it is possible to realize a very lightweight porous layer while maintaining high permeability, and even in a thinner porous layer, a porous membrane The thermal contraction at a high temperature is suppressed, and excellent heat resistance tends to be exhibited. Synthetic boehmite that can reduce ionic impurities that adversely affect the characteristics of the electrochemical device is more preferred.

  As the aluminum silicate compound having no ion exchange ability, kaolin mainly composed of kaolin mineral is more preferable because it is inexpensive and easily available. Known kaolins include wet kaolin and calcined kaolin obtained by calcining this. In the present embodiment, calcined kaolin is particularly preferable. The calcined kaolin is particularly preferable from the viewpoint of electrochemical stability because crystal water is released during the calcining process and impurities are also removed.

  The average particle size of the inorganic particles is preferably more than 0.01 μm and not more than 4.0 μm, more preferably more than 0.2 μm and not more than 3.5 μm, and more than 0.4 μm and 3.0 μm. More preferably, it is as follows. Adjusting the average particle size of the inorganic particles to the above range is preferable from the viewpoint of suppressing thermal shrinkage at high temperatures even when the active layer is thin (for example, 7 μm or less). Examples of the method for adjusting the particle size and distribution of the inorganic particles include a method of reducing the particle size by pulverizing the inorganic particles using an appropriate pulverizer such as a ball mill, a bead mill, or a jet mill. .

  Examples of the shape of the inorganic particles include a plate shape, a scale shape, a needle shape, a columnar shape, a spherical shape, a polyhedral shape, and a lump shape. A plurality of inorganic fillers having these shapes may be used in combination.

  The ratio of the fluorine-based resin and the inorganic particles in the active layer according to the present embodiment is preferably 5/95 to 80/20 for fluorine-based resin / inorganic particles, more preferably 7/93 to 65/35, More preferably, it is 9/91 to 50/50. When the fluorine-based resin / inorganic particles are in such a range, the battery winding property described later is particularly good, which is preferable. For example, when the above-mentioned polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) is used as a fluororesin, the resin melts on the film surface due to the tribomaterial effect peculiar to this resin. The contact resistance is lowered and the pin is easily removed.

The thickness of the active layer is preferably 0.5 μm or more from the viewpoint of improving heat resistance and insulation, and is preferably 50 μm or less from the viewpoint of increasing the capacity and permeability of the battery.
Layer density in the active layer ^is preferably ^{0.5g / cm 3 ~3.0g / cm 3} , more preferably ^{0.7g / cm 3 ~2.0g / cm 3} . When the layer density of the active layer is 0.5 g / cm ³ or more, the thermal contraction rate at high temperature tends to be good, and when it is 3.0 g / cm ³ or less, the air permeability tends to be good. It is in.

Examples of the method for forming the active layer include a method in which a coating liquid containing inorganic particles and a resin binder is applied to at least one surface of the substrate. In this case, the coating liquid may contain a solvent, a dispersing agent, and the like in order to improve dispersion stability and coating property.
The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. For example, a particle raw material containing a resin binder and a polymer base material may be laminated and extruded by a co-extrusion method, or the base material and the active film may be separately produced and then bonded.

[Thermoplastic polymer layer]
The electricity storage device separator 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 surface or both surfaces of the porous substrate or on the active layer, and it is preferable that at least a part of the active layer is disposed.

In this embodiment, 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. Setting the coating area of the thermoplastic polymer layer to 100% or less is preferable from the viewpoint of further suppressing the blockage of the pores of the base material 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 to the electrode. This area ratio is measured by observing the thermoplastic polymer layer forming surface of the obtained separator with an SEM.
When the thermoplastic polymer layer is a layer in which inorganic particles are mixed, the total area of the thermoplastic polymer and inorganic particles is taken as 100% to calculate the existing area of the thermoplastic polymer.

When the thermoplastic polymer layer is arranged only on a part of the surface of the polyolefin porous substrate and the inorganic particle layer, examples of the arrangement pattern of the thermoplastic polymer layer include a dot shape, a stripe shape, a lattice shape, a stripe shape, and a turtle shell. , Random, etc., and combinations thereof.
The thickness of the thermoplastic polymer layer disposed on the polyolefin porous substrate is preferably 0.01 μm to 5 μm, more preferably 0.1 μm to 3 μm per side of the substrate. More preferably, it is 1-1 micrometer.

(Thermoplastic polymer)
The thermoplastic polymer layer includes a thermoplastic polymer. The thermoplastic polymer layer may contain 60% by mass or more, more preferably 90% by mass or more, still more preferably 95% by mass or more, particularly preferably 98% by mass or more of the thermoplastic polymer, based on the total amount of the thermoplastic polymer layer. . The thermoplastic polymer layer may contain other components in addition to the thermoplastic polymer.

Examples of the thermoplastic polymer include the following:
Polyolefin resins such as polyethylene, polypropylene and α-polyolefin;
Fluoropolymers such as polyvinylidene fluoride and polytetrafluoroethylene or copolymers containing these;
A diene polymer containing a conjugated diene such as butadiene or isoprene as a monomer unit, a copolymer containing these, or a hydride thereof;
Acrylic polymer containing (meth) acrylate or the like as a monomer unit and not having a polyalkylene glycol unit, (meth) acrylate or the like as a monomer unit, and one or two polyalkylene glycol units An acrylic polymer or a copolymer containing these or a hydride thereof;
Rubbers such as ethylene propylene rubber, polyvinyl alcohol, polyvinyl acetate;
Cellulose derivatives such as ethyl cellulose, methyl cellulose, hydroxyethyl cellulose, carboxymethyl cellulose;
Polyalkylene glycols having no polymerizable functional group, such as polyethylene glycol and polypropylene glycol;
Resins such as polyphenylene ether, polysulfone, polyethersulfone, polyphenylene sulfide, polyetherimide, polyamideimide, polyamide, polyester;
A copolymer having, as a copolymerization unit, an ethylenically unsaturated monomer having 3 or more repeating alkylene glycol units, as described above as a resin binder for forming a filler porous layer; and combinations thereof;
Is mentioned.
Among these, a diene polymer, an acrylic polymer, or a fluorine polymer is preferable from the viewpoints of adhesion to an electrode active material, flexibility, and ion permeability of the polymer.

  The glass transition temperature (Tg) of the thermoplastic polymer is preferably −50 ° C. or higher, more preferably in the range of −50 ° C. to 150 ° C., from the viewpoints of adhesion to the electrode and ion permeability. .

  From the viewpoint of wettability to the polyolefin multilayer microporous membrane, the binding property between the polyolefin multilayer microporous membrane and the thermoplastic polymer layer, and the adhesion to the electrode, the thermoplastic polymer layer has a glass transition temperature of 20 A polymer having a glass transition temperature of 20 ° C. or higher is preferably blended from the viewpoint of blocking resistance and ion permeability.

The thermoplastic polymer having at least two glass transition temperatures can be achieved by, for example, a method of blending two or more 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 dual structure in which the polymer belonging to the central portion and the polymer belonging to the outer shell portion are composed of different compositions.
In particular, in a polymer blend and a 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 polymer having a low glass transition temperature. Moreover, a plurality of functions can be imparted to the entire thermoplastic polymer.

In the present embodiment, from the viewpoint of blocking suppression and ion permeability of the separator, the thermoplastic copolymer is particulate when the glass transition temperature is, for example, 20 ° C. or higher, 25 ° C. or higher, or 30 ° C. or higher. It is preferable.
By including the particulate thermoplastic copolymer in the thermoplastic polymer layer, the porosity of the thermoplastic polymer layer disposed on the substrate and the blocking resistance of the separator can be ensured.

  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, still more preferably 100 nm to 1,000 nm, particularly preferably 130 nm to 800 nm, and particularly preferably 150 nm. It is -800 nm, Most preferably, it is 200-750 nm. Setting the average particle size to 10 nm or more ensures that the size of the particulate thermoplastic polymer is such that it does not enter the pores of the substrate when at least the particulate thermoplastic polymer is applied to the substrate including the porous film. Means that Therefore, in this case, it is preferable from the viewpoint of improving the adhesion between the electrode and the separator and the cycle characteristics of the electricity storage device. In addition, when the average particle diameter is 2,000 nm or less, an amount of the particulate thermoplastic polymer necessary for achieving both the adhesion between the electrode and the separator and the cycle characteristics of the electricity storage device is formed on the substrate. It is preferable from the viewpoint of coating. The average particle size 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 monomer or comonomer. As a polymerization method, for example, an appropriate method such as solution polymerization, emulsion polymerization, bulk polymerization or the like can be employed.

  In this embodiment, since the thermoplastic polymer layer can be easily formed by coating, a particulate thermoplastic polymer is formed by emulsion polymerization, and the resulting thermoplastic polymer emulsion is used as an aqueous latex. It is preferable.

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

<Method for producing separator for power storage device>
[Production method of polyolefin multilayer microporous membrane (polyolefin porous substrate)]
(Method for producing first and second microporous layers)
As described above, the polyolefin multilayer microporous membrane according to this embodiment is formed by laminating the first microporous layer, the second microporous layer, and the first microporous layer in this order. However, the method for producing the first and second microporous layers is not particularly limited, and a known production method can be employed. For example, a method in which a polyolefin resin composition and a plasticizer are melt-kneaded and formed into a sheet shape, optionally stretched and then made porous by extracting the plasticizer, and a polyolefin resin composition is melt-kneaded to obtain a high draw rate. After extruding at a ratio, the polyolefin crystal interface is peeled off by heat treatment and stretching, the polyolefin resin composition and the inorganic filler are melt-kneaded and molded on a sheet, and then the polyolefin and inorganic filler are stretched And a method of making the structure porous by removing the solvent at the same time as solidifying the polyolefin by dissolving it in a poor solvent for the polyolefin after dissolving the polyolefin resin composition.

  Moreover, the method of producing the nonwoven fabric or paper as a base material of a 1st and 2nd microporous layer may be a well-known thing. The production method includes, for example, a chemical bond method in which a web is dipped in a binder, dried, and bonded between fibers; a heat-bondable fiber is mixed into the web, and the fibers are partially melted to bond between fibers. A needle punch method in which a needle having a stab is repeatedly stabbed into the web and mechanically entangled with the fiber; a high-pressure water flow is entangled between the fibers by jetting a high-pressure water stream from the nozzle through the net (screen).

Hereinafter, as an example of a method for producing a polyolefin multilayer microporous membrane (polyolefin porous substrate), a polyolefin resin composition and a plasticizer are melt-kneaded to form sheet-like first and second microporous layers. A method of laminating the first and second microporous layers through a method of extracting a plasticizer after molding will be described.
First, a polyolefin resin composition and a plasticizer are melt-kneaded. As the melt-kneading method, for example, polyolefin resin and other additives as required may be added to a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc. A method of introducing a plasticizer at a ratio of kneading and kneading. At this time, it is preferable that the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being added to the resin kneading apparatus. More preferably, only part of the plasticizer is added in the pre-kneading, and the remaining plasticizer is kneaded while side-feeding the resin kneading apparatus.

  As the plasticizer, a non-volatile solvent capable of forming a uniform solution at a melting point or higher of the polyolefin can be used. Specific examples of such a non-volatile solvent include hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. Of these, liquid paraffin is preferred.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. 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 of achieving both melt tension during melt molding and formability of a uniform and fine pore structure.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. As the heat conductor used for cooling and solidification, metal, water, air, plasticizer itself, and the like can be used, but a metal roll is preferable because of high heat conduction efficiency. In this case, it is more preferable that the metal roll is sandwiched between the rolls, since the efficiency of heat conduction is further increased, the sheet is oriented and the film strength is increased, and the surface smoothness of the sheet is also improved. The die lip interval when extruding from a T-die into a sheet is preferably from 400 μm to 3,000 μm, and more preferably from 500 μm to 2,500 μm.

(Manufacturing method of polyolefin multilayer microporous membrane)
The polyolefin multilayer microporous membrane (polyolefin porous substrate) according to this 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 these, for example, the following three-layer laminating method is exemplified: As described above, a polyolefin resin composition that is a constituent of the first and second microporous layers; Each plasticizer is melt-kneaded separately using a twin screw extruder to form an olefin solution, and then each polyolefin solution is supplied from each twin screw extruder to a three-layer T-die, and each layer (first layer) formed from each solution 1 polyolefin solution layer / second polyolefin solution layer / first polyolefin solution layer) is adjusted to a desired range and cooled while being taken up at a predetermined winding speed, and is a gel-like three-layer sheet To be formed.
In the above, a three-layer T-die is used, and three layers are stacked and formed at the same time. However, three layers may be formed after each layer is formed separately.

  It is preferable to subsequently stretch the sheet-like molded body thus obtained. As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used. Biaxial stretching is preferred from the viewpoint of the strength and the like of the resulting polyolefin porous substrate. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the porous substrate finally obtained is difficult to tear and has a high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multistage stretching, and multiple stretching. Simultaneous biaxial stretching is preferred from the viewpoints of improvement of puncture strength, uniformity of stretching, and shutdown property.

  The draw ratio is preferably in the range of 20 times to 100 times, more preferably in the range of 25 times to 50 times in terms of surface magnification. The stretching ratio in each axial direction is preferably in the range of 4 to 10 times in the MD direction, preferably in the range of 4 to 10 times in the TD direction, 5 to 8 times in the MD direction, and 5 times in the TD direction. More preferably, it is in the range of 8 times or less. By setting the total area magnification within this range, it is preferable in that sufficient strength can be imparted, film breakage in the stretching step can be prevented, and high productivity can be obtained.

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

  Next, the plasticizer is removed from the sheet-like molded body to obtain a porous substrate. As a method for removing the plasticizer, for example, a method of extracting the plasticizer by immersing the sheet-like molded body in an extraction solvent and sufficiently drying it can be mentioned. The method for extracting the plasticizer may be either a batch type or a continuous type. In order to suppress the shrinkage of the polyolefin porous substrate, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying. Further, the residual amount of plasticizer in the porous substrate is preferably less than 1% by mass.

  As the extraction solvent, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the plasticizer and has a boiling point lower than the melting point of the polyolefin resin. Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine such as hydrofluoroether and hydrofluorocarbon. Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; 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 heat relaxation may be performed after the stretching step or after the porous substrate is formed. The porous substrate may be subjected to post-treatment such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like.

  A surface treatment is preferably performed on the surface of the polyolefin porous substrate, since it becomes easier to apply a coating solution thereafter and adhesion between the polyolefin and the active layer or the thermoplastic polymer layer is improved. Examples of the surface treatment method include a corona discharge treatment method, a plasma treatment method, a mechanical surface roughening method, a solvent treatment method, an acid treatment method, and an ultraviolet oxidation method.

[Method of arranging active layer]
The active layer is coated on at least one side of the substrate by applying a coating liquid containing inorganic particles, a fluorine-based resin, and, if desired, an additional component such as a solvent (for example, water) and a dispersant. Can be arranged. A fluororesin may be synthesized by emulsion polymerization, and the resulting emulsion may be used as it is as a coating solution.
Examples of the method for forming the active layer include a method in which a coating liquid containing inorganic particles and a fluorine-based resin is applied to at least one surface of a polyolefin porous substrate. In this case, the coating liquid may contain a solvent, a dispersing agent, and the like in order to improve dispersion stability and coating property.
The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. For example, the constituent material of the active layer containing the polyolefin resin and the constituent material of the polyolefin multilayer microporous substrate may be laminated and extruded by a co-extrusion method, or the porous substrate and the active membrane may be separately provided. You may bond together after producing.

The method for applying the coating liquid to the substrate is not particularly limited as long as the required layer thickness and coating area can be realized. Coating methods include, for example, gravure coater method, small diameter gravure coater method, reverse roll coater method, transfer roll coater method, kiss coater method, dip coater method, knife coater method, air doctor coater method, blade coater method, rod coater method Squeeze coater method, cast coater method, die coater method, screen printing method, spray coating method, ink jet coating method and the like. Among these, the gravure coater method is preferable because the degree of freedom of the coating shape is high.
Furthermore, the inorganic particle raw material containing the fluorine-based resin (binder) and the polymer base material may be laminated and extruded by a co-extrusion method, or the base material and the active layer may be separately manufactured and bonded together. Also good.

  The method for 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 at a temperature lower than the melting point of the substrate while fixing the substrate, a method of drying under reduced pressure at a low temperature, and the like can be mentioned.

[Method of arranging thermoplastic polymer layer]
A thermoplastic polymer can be arrange | positioned on a base material by applying the coating liquid containing a thermoplastic polymer to a base material, for example. A thermoplastic polymer may be synthesized by emulsion polymerization, and the resulting emulsion may be used as it is as a coating solution. 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).

  Regarding the method of applying a coating solution containing a thermoplastic polymer on a polyolefin porous substrate, there is no particular limitation as long as it can realize a desired coating pattern, coating film thickness, and coating area. Absent. For example, the coating method described above may be used to apply the inorganic particle-containing coating solution. The gravure coater method or the spray coating method is preferable from the viewpoint that the degree of freedom of the coating shape of the thermoplastic polymer is high and a preferable area ratio can be easily obtained.

  The method for 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 at a temperature below the melting point while fixing a polyolefin porous substrate, a method of drying under reduced pressure at a low temperature, and dipping in a poor solvent for a thermoplastic polymer to solidify the thermoplastic polymer into particles The method of extracting a solvent simultaneously is mentioned.

<Physical properties of separator for electricity storage device>
In the present embodiment, the air permeability of the electricity storage device separator is preferably 10 seconds / 100 cc or more and 650 seconds / 100 cc or less, more preferably 20 seconds / 100 cc or more and 500 seconds / 100 cc or less, more preferably 30 seconds. / 100 cc to 450 seconds / 100 cc, particularly preferably 50 seconds / 100 cc to 400 seconds / 100 cc. This air permeability is the air resistance measured in accordance with JIS P-8117, similar to the air permeability of the polyolefin porous substrate.
When the air permeability is 10 seconds / 100 cc or more, self-discharge tends to decrease when used as a battery separator, and when it is 650 seconds / 100 cc or less, good charge / discharge characteristics tend to be obtained.
The electricity storage device separator according to the present embodiment exhibits a very large air permeability, and thus exhibits a large ion permeability when applied to a lithium ion secondary battery.

  The final thickness of the separator is preferably 2 μm or more and 200 μm or less, more preferably 5 μm or more and 100 μm or less, and further preferably 7 μm or more and 30 μm or less. When the thickness is 2 μm or more, the mechanical strength tends to be sufficient, and when the thickness is 200 μm or less, the occupied volume of the separator is reduced, which tends to be advantageous in terms of increasing the battery capacity.

<Power storage device>
The separator for an electricity storage device of this embodiment can be suitably applied as a separator for an electricity storage device by combining this with a positive electrode, a negative electrode, and a non-aqueous electrolyte. An example of the electricity storage device is a lithium ion secondary battery.
When manufacturing a lithium ion secondary battery using the separator of this embodiment, there is no limitation in a positive electrode, a negative electrode, and a non-aqueous electrolyte, Each can use a well-known thing.
As the positive electrode, a positive electrode in which a positive electrode active material layer containing a positive electrode active material is formed on a positive electrode current collector can be suitably used. Examples of the positive electrode current collector include aluminum foil, and examples of the positive electrode active material include lithium-containing composite oxides such as LiCoO ₂ , LiNiO ₂ , spinel type LiMnO ₄ , and olivine type LiFePO _4. . In addition to the positive electrode active material, the positive electrode active material layer may include a binder, a conductive material, and the like.

  As the negative electrode, a positive electrode in which a negative electrode active material layer containing a negative electrode active material is formed on a negative electrode current collector can be suitably used. Examples of the negative electrode current collector include copper foil, and examples of the negative electrode active material include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, and metallic lithium. And various alloy materials.

The nonaqueous electrolytic solution 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, and ethyl methyl carbonate. Examples of the electrolyte include lithium salts such as LiClO ₄ , LiBF ₄ , and LiPF ₆ .

The method for producing the electricity storage device using the electricity storage device separator of the present embodiment is not particularly limited. For example, the following method can be illustrated.
The separator of this embodiment is manufactured as a vertically long 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). Laminated in the order of positive electrode-separator-negative electrode-separator, or negative electrode-separator-positive electrode-separator, wound in a circular or flat spiral shape to obtain a wound body, and the wound body is housed in a battery can, Furthermore, it can manufacture by inject | pouring electrolyte solution. Alternatively, it is manufactured by a method in which a laminate composed of a sheet-like separator and an electrode, or a wound body obtained by folding an electrode and a separator is put into a battery container (for example, an aluminum film) and an electrolyte is injected. May be.

  At this time, it is also preferable to press the laminated body or the wound body. Specifically, the separator for an electricity storage device of the present embodiment, an electrode having a current collector and an active material layer formed on at least one surface of the current collector, the former thermoplastic polymer layer and the active material layer It is possible to perform pressing in such a manner that they face each other. The pressing temperature may be 25 ° C. or higher and 120 ° C. or lower, or 50 ° C. to 100 ° C. The press can be performed using a known press device such as a roll press or a surface press as appropriate.

  The lithium ion secondary battery manufactured as described above has a coating layer with excellent heat resistance and strength and a separator with reduced ionic resistance. Therefore, it has excellent safety and battery characteristics (especially rate Characteristic). In addition, when a separator is provided with a thermoplastic polymer on the outermost surface, it exhibits excellent adhesion to the electrode, so that peeling between the electrode and the separator accompanying charging / discharging is suppressed, and uniform charging / discharging is achieved. Therefore, it has excellent long-term continuous operation resistance.

The physical properties in the following experimental examples were evaluated according to the following methods.
<Evaluation>
<Measurement method and evaluation method>
(1) Peel strength of active layer / polyolefin porous substrate For the active layer of the separator obtained in Examples and Comparative Examples (excluding Comparative Example 1), a tape having a width of 12 mm and a length of 100 mm (manufactured by 3M, Product name: Scotch 600) was attached in a direction parallel to the separator length direction. The force when peeling the tape from the sample at a speed of 50 mm / min was measured using a 90 ° peel strength measuring device (product name: IP-5N, manufactured by IMADA). Five points were measured, and the average value of the obtained peel strengths was evaluated as the peel strength between the active layer and the substrate according to the following evaluation criteria.
A: Peel strength is 60 N / m or more B: Peel strength is 40 N / m or more and less than 60 N / m C: Peel strength is less than 40 N / m

(2) Battery winding performance (Pin-out characteristics)
Using a manual winding machine manufactured by Kaito Seisakusho Co., Ltd., as shown in FIG. 1 (A) showing the overall configuration of the device, a load of 400 g is obtained by stacking two pieces of the scraped sample (13) having a length of 3 m and a width of 60 mm. Then, after winding the pin (10) so that the active layer is in contact with the pin, the pin I (11) is pulled out and the winding sample (13) is removed by hand in the winding portion configuration shown in FIG. The pull-out characteristic was evaluated according to the following criteria from the wound form of the sample that had been removed from the pulling pin II (12).
A: Ratio of the pin contact portion that is pulled by the pin and the pin contact portion is displaced by 2 mm or more with respect to before the pin is pulled out 4/100 pieces or less B: Pulled by the pin and the pin contact portion is shifted by 2 mm or more with respect to before the pin is pulled out Proportion of things 5-9 pieces / 100 pieces C: Ratio of things that are pulled by the pin and the pin contact part is displaced by 2 mm or more before the pin is pulled out 10 pieces / 100 pieces or more

(3) Thermal shock characteristics Using the separators obtained in the examples and comparative examples, the thermal shock characteristics (cold thermal cycle characteristics) of each secondary battery assembled as shown in the following a to d were evaluated.
a. Production of positive electrode 96 parts by mass of lithium cobaltate (LiCoO ₂ ) as a positive electrode active material, ₂ parts by mass of carbon black powder as a positive electrode conductive agent, 2 parts by mass of polyvinylidene fluoride as a positive electrode binder (binder), Were mixed together and dispersed in N-methylpyrrolidone (NMP) to prepare a positive electrode mixture slurry. The positive electrode mixture slurry was applied to both surfaces of a 13 μm thick aluminum foil serving as a positive electrode current collector, dried, and then rolled to produce a positive electrode. The packing density and thickness of the positive electrode active material layer at this time were 3.95 g / cc and 140 μm at the portion where the positive electrode active material layer was formed on both sides of the current collector.
b. Production of Negative Electrode 97 parts by mass of carbon-based active material (artificial graphite) and 3 parts by mass of silicon-based active material (SiOx) (x = 1.05) were mixed.
98 parts by mass of the obtained mixture and 2 parts by mass of sodium carboxymethylcellulose (CMC-Na) were mixed and dispersed in water to obtain a negative electrode mixture slurry.
This negative electrode mixture slurry was applied to both sides of a copper foil having a thickness of 8 μm serving as a negative electrode current collector, dried, and then rolled. The negative electrode was produced 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 μm at the portion where the negative electrode active material layer was formed on both sides of the current collector.

c. Preparation of Nonaqueous Electrolyte Solution A nonaqueous electrolyte solution was prepared by dissolving LiPF ₆ as a solute in a mixed solvent of ethylene carbonate: diethyl carbonate = 3: 7 (mass ratio) to a concentration of 1.2 mol / L. did.

d. Battery assembly a. A positive electrode prepared in b. Each of the negative electrode prepared in Example 1 and the separator prepared in Example or Comparative Example was cut out and overlaid, and then rolled and crushed in the longitudinal direction at room temperature to produce a flat wound battery element did. This battery element was inserted into a laminate film having a thickness of 120 μm consisting of three layers of polypropylene / aluminum / nylon (nylon) from the inside to the outside, and the electrode terminals were taken out of the packaging material by heat fusion. The non-aqueous electrolyte was poured into the exterior member containing the battery element, and the remaining one side of the exterior material was heat-sealed under reduced pressure and sealed under reduced pressure. By heating this between metal plates at 80 ° C. for 3 minutes, a battery having a thickness of 2 mm × width of 30 mm × height of 30 mm was obtained.
Next, 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 ° C., and then charged at a constant voltage to a charging current of 14 mA.
The resistance (1 kHz AC impedance: Ω) of the charged secondary battery was measured after the above constant voltage charge, and this resistance was used as the initial resistance.
Next, the temperature was raised to 70 ° C. and maintained for 4 hours using a thermal shock tester (TSA-71H-W manufactured by Espec). Thereafter, the cycle of holding the battery at 20 ° C. for 2 hours and then holding at −40 ° C. for 4 hours was repeated 50 times. The resistance (1 kHz AC impedance: Ω) of the secondary battery was measured by the same method as d above. From this result and the initial resistance measured above, the amount of resistance change before and after the cooling cycle (resistance after the cooling cycle−initial resistance) was calculated and evaluated according to the following criteria.
A: The resistance change amount before and after the thermal shock is 0Ω or more and less than 10Ω B: The resistance change amount after the thermal shock is 10Ω or more and less than 20Ω C: The resistance change amount before and after the thermal shock is 20Ω or more

(4) Low temperature cycle characteristics Using the separators obtained in the examples and comparative examples, the following a. ~ C. Each secondary battery assembled as described above was measured for low-temperature cycle characteristics.
a. Production of positive electrode plate 100 parts by weight of lithium cobaltate as an active material, 2 parts by weight of acetylene black as a conductive agent with respect to 100 parts by weight of active material, and 2 parts of polyvinylidene fluoride as a binder with respect to 100 parts by weight of active material A positive electrode mixture slurry is formed on both surfaces of an Al foil having a thickness of 20 μm after preparing a positive electrode mixture paint by stirring and kneading with an appropriate amount of N-methyl-2-pyrrolidone in a double arm kneader. Was applied and dried to form a positive electrode active material layer. The thus obtained laminate including the positive electrode active material layers on both sides of the positive electrode current collector was pressed and rolled with a pair of rollers to obtain a positive electrode plate having a total thickness of 120 μm. In addition, the exposed part of the positive electrode current collector in which the positive electrode active material layer was not formed was provided on one side in the short direction of the positive electrode current collector.
b. Production of Negative Electrode Plate As an active material of the negative electrode, 100 parts by volume of artificial graphite and as a binder, a styrene-butadiene copolymer rubber particle dispersion as a binder, and 100 parts by volume of active material, 2.3 in terms of solid content of the binder. Volume part, carboxymethyl cellulose as a thickener is stirred with a double-arm kneader together with 1.4 parts by volume with respect to 100 parts by volume of active material and a predetermined amount of water, and the volume solid content is 55%. A negative electrode mixture paint was prepared. Here, the volume solid content rate is the volume concentration of the solid content contained in the mixture paint. This negative electrode mixture paint was applied to both sides of a copper foil having a thickness of 15 μm, dried and then rolled to obtain a negative electrode plate having a total thickness of 185 μm. In addition, the exposed part of the negative electrode collector in which the negative electrode active material layer was not formed was provided in the short side of the negative electrode collector.
c. Production of Battery These positive electrode plates, separators of Examples and Comparative Examples, and negative electrode plates were wound and inserted into a cylindrical battery case, and EC (ethylene carbonate), DMC (dimethyl carbonate), MEC (methyl ethyl carbonate) ) 5.5 g of an electrolytic solution in which 3 parts by mass of 1M LiPF ₆ and VC were dissolved in a mixed solvent was sealed, and a cylindrical 18650 non-aqueous secondary battery having a design capacity of 2000 mAh was produced.
d. Measurement of low temperature cycle characteristics The capacity retention rate at the low temperature 100 cycles was measured by the following method. The battery after sealing was conditioned and discharged twice and stored for 7 days in a 45 ° C. environment, and then the following charge / discharge cycle was repeated 100 times at −30 ° C. For charging, charging is performed at a constant voltage of 4.2 V and 1400 mA. When charging current is reduced to 100 mA, charging is terminated, and discharging is performed at a constant current of 2000 mA and discharging to a final voltage of 3 V as one cycle. The discharge capacity ratio at the 100th cycle relative to the eye was measured as a 100 cycle capacity retention rate. The low temperature cycle characteristics were evaluated according to the following criteria.
A: Capacity maintenance rate at low temperature 100 cycle is 80% or more B: Capacity maintenance rate at low temperature 100 cycle is 70% or more and less than 80% C: Capacity maintenance rate at low temperature 100 cycle is less than 70%

ここで、ｘは剥離強度の平均値、ｎは測定数を示す。
（評価基準）
Ａ：活性層／基材の剥離強度のばらつきが１０％未満
Ｂ：活性層／基材の剥離強度のばらつきが１０％以上２０％未満
Ｃ：活性層／基材の剥離強度のばらつきが２０％以上 (5) Variation in peel strength of active layer / polyolefin porous substrate Similar to the above (1) “Peel strength between active layer and polyolefin porous substrate”, for the 600 mm width separators of Examples and Comparative Examples, A tape having a width of 12 mm and a length of 100 mm (manufactured by 3M, product name: Scotch 600) was pasted at an interval of 100 mm in a direction parallel to the separator length direction (5 points in the TD direction). Similarly, 5 points of the above-mentioned tapes were attached with an interval of 500 mm in the separator length direction (5 points in the MD direction). The force when peeling a total of 25 points of the tape affixed from the sample at a speed of 50 mm / min was measured using a 90 ° peel strength measuring device (product name: IP-5N, manufactured by IMADA). Then, based on the following formula, the peel strength variation [%] was calculated from the standard deviation and average value of the peel strength, and evaluated according to the following criteria.

Here, x is an average value of peel strength, and n is the number of measurements.
(Evaluation criteria)
A: Variation in peel strength of active layer / substrate is less than 10% B: Variation in peel strength of active layer / substrate is 10% or more and less than 20% C: Variation in peel strength of active layer / substrate is 20% that's all

(6) Collision resistance (collision test)
FIG. 2 is a schematic diagram of a crash test according to UL standards 1642 and / or 2054. In UL standard 1642 and / or 2054, the round bar is placed on the specimen (22) placed on the test bench so that the specimen (22) and the round bar (21) (φ = 15.8 mm) are substantially orthogonal to each other. (21) is placed, and a weight (20) of 9.1 kg (about 20 pounds) is dropped onto the upper surface of the round bar (21) from a position of 610 ± 25 mm from the round bar (21). Observe the impact of impact on
With reference to FIG. 2 and UL standards 1642 and 2054, the procedure of the collision test in the examples and comparative examples will be described below.
a. Production of positive electrode Nickel, manganese, cobalt composite oxide (NMC) (Ni: Mn: Co = 1: 1: 1 (element ratio), density 4.70 g / cm ³ , capacity density 175 mAh / g) as a positive electrode active material 90.4% by mass, graphite powder (KS6) (density 2.26 g / cm ³ , number average particle size 6.5 μm) as a conductive additive, 1.6% by mass, and acetylene black powder (AB) (density 1.95 g) / Cm ³ , number average particle diameter 48 nm) is 3.8% by mass, and polyvinylidene fluoride (PVDF) (density 1.75 g / cm ³ ) as a binder is mixed at a ratio of 4.2% by mass. -A slurry was prepared by dispersing in methylpyrrolidone (NMP). This slurry was applied to one side of a 20 μm thick aluminum foil serving as a positive electrode current collector using a die coater, dried at 130 ° C. for 3 minutes, and then rolled using a roll press. The rolled product was slit into a width of 57.0 mm to obtain a positive electrode. The coating amount of the positive electrode active material at this time was 109 g / m ² .

b. Graphite powder A as prepared negative active material of the negative electrode (density 2.23 g / cm ^3, number average particle diameter 12.7 [mu] m) 87.6% by weight and graphite powder B (density 2.27 g / cm ^3, number average particle diameter 6.5 μm) is 9.7% by mass, and the ammonium salt of carboxymethyl cellulose as a binder is 1.4% by mass (in terms of solid content) (solid content concentration is 1.83% by mass aqueous solution) and the diene rubber latex is 1.7% by mass ( (Solid content conversion) (solid content concentration 40 mass% aqueous solution) was dispersed in purified water to prepare a slurry. This slurry was applied to one side of a 12 μm thick copper foil serving as a negative electrode current collector with a die coater, dried at 120 ° C. for 3 minutes, and then rolled using a roll press. The rolled product was slit into a width of 58.5 mm to obtain a negative electrode. The coating amount of the negative electrode active material at this time was 5.2 g / m ² .

c. Preparation of non-aqueous electrolyte solution In a mixed solvent (Lithium Battery Grade manufactured by Kishida Chemical Co., Ltd.) in which ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed at a volume ratio of 1: 2, LiPF ₆ is 1 mol / L. It melt | dissolved so that it might become, and the electrolyte solution which is a nonaqueous electrolyte was obtained.

d. Battery assembly A wound body in which the produced positive electrode and negative electrode were wound on each side of the separator in a cylindrical shape and inserted into a cylindrical shape was inserted into a stainless steel cylindrical battery case (exterior body). Next, 5 mL of the above electrolytic solution was injected therein, and the wound body was immersed in the electrolytic solution, and then the battery case was sealed to prepare a nonaqueous electrolyte secondary battery.

e. Heat treatment d. The nonaqueous electrolyte secondary battery obtained in the above was stored for 48 hours in an environment of 60 ° C.

f. Initial charge / discharge e. The non-aqueous electrolyte secondary battery obtained in (1) was charged at a constant current of 0.3 C in an environment of 25 ° C., reached 4.2 V, and then charged at a constant voltage of 4.2 V. The battery was discharged at a constant current to 3.0V. The total charging time at constant current and charging at constant voltage was 8 hours. 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, reached 4.2 V, charged with a constant voltage of 4.2 V, and discharged to 3.0 V with a constant current of 1 C. The total charging time at constant current and charging at constant voltage was 3 hours. Further, the capacity when discharged at a constant current of 1 C was defined as 1 C discharge capacity (mAh). In an environment of 25 ° C., e. The non-aqueous electrolyte secondary battery (22) obtained in 1 was charged with a constant current of 1 C, reached 4.2 V, and then charged with a constant voltage of 4.2 V for a total of 3 hours.
Next, in an environment of 25 ° C., the battery was placed sideways on a flat surface, and a stainless steel round bar (21) having a diameter of 15.8 mm was placed at the center of the battery (22) so as to cross the battery. From a height of 61 ± 2.5 cm, a weight (20) of 9.1 kg is applied so that an impact is applied at right angles to the vertical axis direction of the battery from the round bar (21) arranged at the center of the battery (22). I dropped it. Then, the battery exterior temperature was measured, and the presence or absence of gas ejection from the battery and the presence or absence of ignition of the battery were observed. The battery exterior temperature is a temperature measured at 1 cm from the bottom side of the battery exterior body with a thermocouple (K-type seal type).
The crash test was evaluated according to the following criteria.
A: Battery exterior temperature of less than 60 ° C. B: Battery exterior temperature of 60 ° C. or more and less than 80 ° C. C: Battery exterior temperature of 80 ° C. or more and no gas ejection or ignition D: Gas ejection or ignition (7) Weight average molecular weight The weight average molecular weight of the polyolefin of the embodiment was measured by gel permeation chromatography (GPC) and determined by the following method. The apparatus uses ALC / GPC-150-C-plus type (trademark) manufactured by Waters, two 30 cm columns of GMH6-HT (trademark) manufactured by Tosoh Corporation and 30 cm of GMH6-HTL (trademark). Two columns were used in series, and measurement was performed at 140 ° C. with a sample concentration of 0.05 wt% using orthodichlorobenzene as a mobile phase solvent. A calibration curve was prepared using a commercially available monodisperse polystyrene having a known molecular weight as a standard substance, and the obtained molecular weight distribution data in terms of polystyrene for each sample was 0.43 (polyethylene Q factor / polystyrene Q factor = The weight average molecular weight of the polyolefin was obtained by multiplying by 17.7 / 41.3).
And the weight average molecular weight of the vinyl compound which has a fluorine atom measured GPC, and calculated | required with the following method. The apparatus uses an Alliance GPC2000 type (trademark) manufactured by Waters, using two columns of GMH6-HT (trademark) manufactured by Tosoh Corporation and two columns of GMH6-HTL (trademark) in series, Measurement was carried out at a column temperature of 140 ° C. using orthodichlorobenzene as a mobile phase solvent. In addition, monodisperse polystyrene (manufactured by Tosoh Corporation) with a known molecular weight was used as a standard substance for molecular weight calibration. From the above, the weight average molecular weight of the vinyl compound having a fluorine atom was calculated.

Example 1
(1) Preparation of first polyolefin solution 20% by mass of polypropylene (PP: melting point 162 ° C.) having a Mw (hereinafter referred to as a weight average molecular weight) of 1.2 × 10 ⁶ and a high Mw of 0.74 × 10 ⁶ To 100 parts by mass of a first polyolefin resin comprising 80% by mass of density polyethylene (HDPE: density 0.955 g / cm ³ , melting point 135 ° C.), an antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl- 4-hydroxyphenyl) -propionate] 0.2 parts by mass of methane was blended to prepare a mixture.
25 parts by mass of the obtained mixture was put into a strong kneading type twin screw extruder (inner diameter 58 mm, L / D = 42), and liquid paraffin [35 cst (40 ° C.)] 75 mass from the side feeder of the twin screw extruder. The first polyolefin solution was prepared by feeding and melting and kneading at 210 ° C. and 250 rpm.
(2) Preparation of Second Polyolefin Solution 40% by mass of ultra high molecular weight polyethylene (UHMwPE) having Mw of 2.0 × 10 ⁶ and high density polyethylene (HDPE: density of 0.955 g / Mw of 5.6 × 10 ⁵ ) cm ³ ) To 100 parts by mass of the second polyolefin resin comprising 60% by mass, 0.2 parts by mass of the antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane. Were blended to prepare a mixture.
25 parts by mass of the obtained mixture was charged into another twin screw extruder of the same type as described above, and 75 parts by mass of liquid paraffin [35 cSt (40 ° C.)] was supplied from the side feeder of the twin screw extruder. A second polyolefin solution was prepared by melt-kneading under the same conditions.
(3) Extrusion The first and second polyolefin solutions are fed from each twin-screw extruder to a three-layer T-die, and the layer thickness ratio of the first polyolefin solution / second polyolefin solution / first polyolefin solution Was extruded to 10/80/10. The extruded molded body was cooled while being drawn with a cooling roll adjusted to 30 ° C. at a take-up speed of 2 m / min, to form a gel-like three-layer sheet.
(4) First Stretching, Removal of Film Forming Solvent, and Drying The gel-like three-layer sheet was simultaneously biaxially stretched (first stretching) five times in the MD direction and the TD direction at 116 ° C. by a tenter stretching machine. The stretched gel-like three-layer sheet was fixed to a 20 cm × 20 cm aluminum frame plate, immersed in a methylene chloride bath adjusted to 25 ° C., removed from liquid paraffin while shaking at 100 rpm for 3 minutes, and air-dried at room temperature. .
(5) Second stretching and heat setting The dried film was stretched 1.4 times (second stretching) in the TD direction at 126 ° C using a batch-type stretching machine. Next, this film was heat set at 126 ° C. by a tenter method.
(6) Formation of active layer Polymer PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight 1.5 × 10 ⁶ ) added to acetone The polymer solution was prepared by dissolving at 50 ° C. for about 12 hours or more. Al ₂ O ₃ powder is added as inorganic particles to a polymer solution prepared so as to have a mass ratio of polymer: inorganic particles = 17: 83, and the inorganic particles are crushed using a ball mill method for 12 hours or more. A slurry was produced by dispersing. The average particle size of the inorganic particles in the slurry thus produced was 600 nm.
The three-layer microporous membrane produced in (5) is dipped in the slurry thus produced and dip-coated, and then a slurry coating layer applied to both sides using a wire bar having a wire size of 0.5 mm. The thickness of each was adjusted and the solvent was dried. The thickness of the active layer formed on both surfaces of the polyolefin porous substrate was 5.0 μm.
Tables 1 and 3 show the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane having the active layer formed as described above.

(Example 2)
In the preparation of the second polyolefin solution of Example 1 (2), instead of the mixture of Example 1, 17.5% by mass of Mw of 2.0 × 10 ⁶ ultrahigh molecular weight polyethylene (UHMwPE) and Mw of 3 .0 × 10 ⁵ high density polyethylene (HDPE: density 0.955g ^/ cm 3) 57.5 wt%, with an MFR of 135 g / 10min, a linear low density polyethylene having a melting point of 124 ° C. poly (ethylene - 100 parts by mass of a second polyolefin resin comprising 25% by mass of a (co-hexene) copolymer was added to the antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0. 2 parts by mass were blended to prepare a mixture.
Tables 1, 2 and 3 show the blending ratios, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 1 except that the active layer was formed.

(Example 3)
In the preparation of the second polyolefin solution of Example 1 (2), instead of the mixture of Example 1, 16% by mass of ultra high molecular weight polyethylene (UHMwPE) having an Mw of 2.0 × 10 ⁶ and an Mw of 3.0 The antioxidant tetrakis [100 mass parts of second polyolefin resin consisting of 66 mass% of high density polyethylene (HDPE: density 0.955 g / cm ³ ) of × 10 ⁵ and 18 mass% of polypropylene with a heat of fusion of 96 J / g was added to Methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0.2 parts by mass was blended to prepare a mixture.
Tables 1 and 3 show the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as Example 1 except that the active layer was formed.

Example 4
In the formation of the active layer of Example 2, instead of the polymer PVdF-HFP, a polymer PVdF-CTFE (polyvinylidene fluoride-chlorotrifluoroethylene copolymer, PVdF: CTFE = 96: 4 (molar ratio), weight average) A molecular weight of 1.2 × 10 ⁶ ) was used.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 5)
In the formation of the active layer of Example 2, the mass ratio of polymer: inorganic particles was adjusted to 9:91.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 6)
In the formation of the active layer of Example 2, as a polymer, polymer PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight 1.5 × 10 ⁶ ) and cyanoethyl pullulan were added to acetone in a mass ratio of 10: 2.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 7)
In the formation of the active layer of Example 2, as a polymer, PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight 1.5 × 10 ⁶ ) And cyanoethyl polyvinyl alcohol were added to acetone in a mass ratio of 10: 2.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 8)
In the formation of the active layer of Example 2, the polymer PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight 1.5 × 10 ⁶ ) Instead, polymer PVdF-HFP (polyvinylidene fluoride-hexafluoropropylene copolymer, PVdF: HFP = 80: 20 (mass ratio), weight average molecular weight 0.5 × 10 ⁶ ) was used.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

Example 9
In the formation of the active layer of Example 2, AlO (OH) powder (boehmite, average particle size: 1.0 μm) was used as inorganic particles instead of Al ₂ O ₃ powder.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 10)
In the formation of the active layer of Example 2, BaTiO ₃ powder (barium titanate, average particle size: 0.6 μm) was used as inorganic particles instead of Al ₂ O ₃ powder.
Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 11)
In the preparation of the first polyolefin solution of Example 2 (1), as a mixture, 16% by mass of polypropylene having a Mw of 1.2 × 10 ⁶ (PP: melting point 162 ° C.) and a high Mw of 0.74 × 10 ⁶ was obtained. To 100 parts by mass of a first polyolefin resin composed of 64% by mass of density polyethylene (HDPE: density 0.955 g / cm ³ , melting point 135 ° C.) and 20% by mass of silica powder (average particle size: 15 nm), an antioxidant tetrakis [ Methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0.2 parts by mass was blended and used. Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Comparative Example 1)
In Example 1, except that the active layer is not formed, it is manufactured in the same manner as in Example 1, and the blending ratio, manufacturing conditions, evaluation results, etc. of each component of the polyolefin three-layer microporous membrane are shown in Table 1. Described.

(Comparative Example 2)
In the preparation of the first polyolefin solution in Example 1 (1), 20% by mass of polypropylene (PP: melting point 162 ° C.) having an Mw of 1.2 × 10 ⁶ and high density polyethylene having an Mw of 0.74 × 10 ⁶ ( Instead of 100 parts by mass of the first polyolefin resin comprising 80% by mass of HDPE: density 0.955 g / cm ³ and melting point 135 ° C., high-density polyethylene having a Mw of 0.74 × 10 ⁶ (HDPE: density 0.955 g) / Cm ³ , melting point 135 ° C.) except that 100 parts by mass of the first polyolefin resin was used, the production was carried out in the same manner as in Example 1, and the blending ratio of each component of the polyolefin three-layer microporous membrane, production Conditions and evaluation results are shown in Table 1.
(Comparative Example 3)
In the preparation of the first polyolefin solution in Example 1 (1), 20% by mass of polypropylene (PP: melting point 162 ° C.) having an Mw of 1.2 × 10 ⁶ and high density polyethylene having an Mw of 0.74 × 10 ⁶ ( HDPE: Density 0.955 g / cm ³ , melting point 135 ° C.) Instead of 100 parts by mass of the first polyolefin resin consisting of 80% by mass, Mw is made of polypropylene (PP: melting point 162 ° C.) of 1.2 × 10 ⁶ Except having used 100 mass parts of 1st polyolefin resin, it manufactures similarly to Example 1, and the compounding ratio of each component of polyolefin three-layer microporous membrane, manufacturing conditions, an evaluation result, etc. are described in Table 1. did.
(Comparative Example 4)
Manufactured in the same manner as in Example 1 except that PVdF (polyvinylidene fluoride, weight average molecular weight 0.35 × 10 ⁶ ) was used in place of PVdF-HFP in the formation of the active layer in Example 1 (6). Table 1 shows the blending ratio of each component of the polyolefin three-layer microporous membrane, production conditions, evaluation results, and the like.

(Example 12)
In the preparation of the first polyolefin solution of Example 2, 20% by mass of polypropylene (PP: melting point 162 ° C.) having an Mw of 2.0 × 10 ⁶ and high density polyethylene (HDPE: density) having an Mw of 0.56 × 10 ⁶ 0.955 g / cm ³ , melting point 135 ° C.) To 100 parts by mass of the first polyolefin resin comprising 80% by mass, an antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl)- Propionate] 0.2 parts by mass of methane was blended to prepare a mixture.
Table 2 shows the blending ratios, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 13)
In the preparation of the first polyolefin solution of Example 2, 20% by mass of polypropylene (PP: melting point 162 ° C.) having an Mw of 0.6 × 10 ⁶ and high density polyethylene (HDPE: density) having an Mw of 0.86 × 10 ⁶ 0.955 g / cm ³ , melting point 135 ° C.) To 100 parts by mass of the first polyolefin resin comprising 80% by mass, an antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl)- Propionate] 0.2 parts by mass of methane was blended to prepare a mixture.
Table 2 shows the blending ratios, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 2 except that the active layer was formed.

(Example 14)
In the preparation of the first polyolefin solution in Example 1 (1), 20% by mass of polypropylene (PP: melting point 162 ° C.) having an Mw of 1.2 × 10 ⁶ and high density polyethylene having an Mw of 0.74 × 10 ⁶ ( HDPE: Density 0.955 g / cm ³ , melting point 135 ° C.) 55 mass%, MFR 135 g / 10 min, melting point 124 ° C., poly (ethylene-co-hexene) copolymer 25, which is a linear low density polyethylene Into 100 parts by mass of the first polyolefin resin composed of% by weight, 0.2 parts by mass of the antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane is blended, A mixture was prepared.
Table 3 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as Example 1 except that the active layer was formed.

(Example 15)
In the preparation of the first polyolefin solution of Example 1 (1), Mw was 0.74 × 10 ⁶ high-density polyethylene (HDPE: density 0.955 g / cm ³ , melting point 135 ° C.) 82% by mass, and the heat of fusion was To 100 parts by mass of a first polyolefin resin composed of 18% by mass of 96 J / g polypropylene, an antioxidant tetrakis [methylene-3- (3,5-ditertiarybutyl-4-hydroxyphenyl) -propionate] methane 0.2 Part by mass was blended to prepare a mixture.
Table 3 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as Example 1 except that the active layer was formed.

(Example 16)
In the preparation of the first polyolefin solution in Example 1 (1), 35% by mass of polypropylene (PP: melting point 162 ° C.) having an Mw of 1.2 × 10 ⁶ and high density polyethylene having an Mw of 0.74 × 10 ⁶ ( HDPE: Density 0.955 g / cm ³ , melting point 135 ° C.) 100 mass parts of the first polyolefin resin composed of 65 mass%. Table 1 shows the blending ratio, production conditions, evaluation results, and the like of each component of the polyolefin three-layer microporous membrane produced in the same manner as in Example 1 except that the active layer was formed.

10 pin 11 pin I
12 pin II
13 Sampling sample 20 Weight 21 Round bar 22 Sample

The present inventors have found 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] Polyolefin multilayer 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 the porous An active layer disposed on at least one surface of the membrane,
A vinyl compound having at least one fluorine atom, wherein the active layer is selected from polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE); and inorganic particles. A separator for an electricity storage device.
[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, and the first microporous layer comprises: The second microporous layer is made of a second polyolefin resin different from the first polyolefin resin containing polyethylene, and the active layer is made of a first polyolefin resin containing polyethylene and polypropylene. The separator for an electricity storage device according to [1], which is laminated on at least one layer of the first microporous layer.
[3] The first polyolefin resin or the second polyolefin resin comprises a linear low density polyethylene, an electric storage device separator according to [2].
[4] The first polyolefin resin or the second polyolefin resin, heat of fusion further comprises the following polypropylene 150 J / g, an electric storage device separator according to [2].
[5] The electricity storage device separator according to claim 3, wherein the linear low-density polyethylene is poly (ethylene-co-1-hexene).
[ 6 ] The ratio of the weight average molecular weight of polyethylene and polypropylene contained in the first polyolefin resin (MwE (weight average molecular weight of polyethylene) / MwP (weight average molecular weight of polypropylene)) is 0.6 to 1.5. The separator for an electricity storage device according to any one of [2] to [5] .
[ 7 ] The electricity storage device separator according to any one of [2] to [6] , wherein the first polyolefin resin further contains at least one selected from the group consisting of silica, alumina, and titania.
[ 8 ] The separator for an electricity storage device according to any one of [1] to [7] , wherein a mass ratio between the vinyl compound having a fluorine atom and the inorganic particles is 5/95 to 80/20.
[ 9 ] The separator for an electricity storage device according to any one of [1] to [8] , wherein the vinyl compound having a fluorine atom has a weight average molecular weight of 0.6 × 10 ^{6 to} 2.5 × 10 ⁶ .
[ 10 ] The power storage device according to any one of [1] to [9] , wherein the active layer further contains at least one selected from cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose. Separator.
[11] A laminate comprising the electricity storage device separator according to any one of [1] to [10], a positive electrode, and a negative electrode.
[12] A wound body in which the laminate according to [11] is wound.
[13] A secondary battery comprising the laminate according to [11] or the wound body according to [12] and an electrolytic solution.

Claims (13)

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; and An active layer disposed on at least one surface,
A vinyl compound having at least one fluorine atom, wherein the active layer is selected from polyvinylidene fluoride-hexafluoropropylene (PVdF-HFP) and polyvinylidene fluoride-chlorotrifluoroethylene (PVdF-CTFE); and inorganic particles. An electricity storage device separator.   The polyolefin multilayer microporous membrane is laminated in the order of a first microporous layer, a second microporous layer, and a first microporous layer, and the first microporous layer comprises polyethylene and polypropylene. The second microporous layer is made of a second polyolefin resin different from the first polyolefin resin containing polyethylene, and the active layer is the first polyolefin resin. The separator for an electricity storage device according to claim 1, wherein the separator is laminated on at least one of the microporous layers.   The electrical storage device separator according to claim 1 or 2, wherein the first polyolefin resin or the second polyolefin resin contains linear low-density polyethylene.   The electrical storage device separator according to claim 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.   The separator for an electricity storage device according to claim 3, wherein the linear low-density polyethylene is poly (ethylene-co-1-hexene).   The power storage device separator according to any one of claims 1 to 5, wherein a mass ratio of the vinyl compound having fluorine atoms to the inorganic particles is 5/95 to 80/20. The electrical storage device separator according to any one of claims 1 to 6, wherein the vinyl compound having a fluorine atom has a weight average molecular weight of 0.6 x 10 ^{6 to} 2.5 x 10 ⁶ .   The electricity storage device separator according to any one of claims 1 to 7, wherein the active layer further contains at least one selected from cyanoethyl pullulan, cyanoethyl polyvinyl alcohol, cyanoethyl cellulose, and cyanoethyl sucrose.   The ratio of the weight average molecular weight of polyethylene and polypropylene contained in the first polyolefin resin (MwE (weight average molecular weight of polyethylene) / MwP (weight average molecular weight of polypropylene)) is 0.6 to 1.5. Item 10. The electricity storage device separator according to any one of Items 1 to 8.   The electricity storage device separator according to any one of claims 1 to 9, wherein the first polyolefin resin further contains at least one selected from the group consisting of silica, alumina, and titania.   The laminated body which consists of a separator for electrical storage devices of any one of Claims 1-10, a positive electrode, and a negative electrode.   A wound body in which the laminate according to claim 11 is wound.   The secondary battery containing the laminated body of Claim 11, or the winding body of Claim 12, and electrolyte solution.

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