CN108352486A - Diaphragm for non-water system secondary battery and non-aqueous secondary battery - Google Patents

Abstract

The present invention provides a separator for a non-aqueous secondary battery, comprising a porous substrate and an adhesive porous layer, wherein the adhesive porous layer is provided on one or both surfaces of the porous substrate, and The adhesive porous layer contains a vinylidene fluoride-hexafluoropropylene binary having a hexafluoropropylene monomer unit ratio of 5.1% by mass to 6.9% by mass and a weight average molecular weight of 810,000 to 3 million. Copolymer, the vinylidene fluoride-hexafluoropropylene binary copolymer accounts for more than 95% by mass of the entire resin.

Description

Separator for nonaqueous secondary battery and nonaqueous secondary battery

technical field

The present invention relates to a separator for a nonaqueous secondary battery and a nonaqueous secondary battery.

Background technique

Non-aqueous secondary batteries represented by lithium-ion secondary batteries have been widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and camcorders. With the miniaturization and weight reduction of portable electronic equipment, the simplification and weight reduction of the external packaging of non-aqueous secondary batteries have been carried out. As the external packaging material, aluminum casings have been developed instead of stainless steel casings. Aluminum laminated film packaging (pack) has been developed instead of a metal casing. However, since the package made of aluminum laminate film is soft, there are cases where the battery (so-called flexible package battery) using the package as the outer packaging material may expand due to external shocks and electrodes accompanying charging and discharging. and shrinkage to easily form a gap between the electrode and the separator, and the cycle life is reduced.

In order to solve the above-mentioned problems, a technique of improving the adhesion between electrodes and separators has been proposed. As one of such techniques, a separator obtained by providing an adhesive porous layer containing a polyvinylidene fluoride resin on a polyolefin microporous membrane is known. Since the separator adheres favorably to the electrodes via the adhesive porous layer when it is laminated on the electrodes and hot-pressed while containing the electrolyte solution, the cycle life of the flexible battery can be improved. Separators obtained by forming an adhesive porous layer containing polyvinylidene fluoride resin on a polyolefin microporous film are suitable for flexible packaging batteries, and various proposals have been made to further improve performance.

For example, Patent Document 1 discloses an adhesive porous layer containing two kinds of polyvinylidene fluoride-based resins having different ratios of hexafluoropropylene monomer units. For example, Patent Document 2 discloses a porous layer containing a polyvinylidene fluoride resin and inorganic particles. For example, Patent Document 3 discloses a porous organic polymer film containing a polyvinylidene fluoride-based resin as a terpolymer. For example, Patent Document 4 discloses an adhesive porous layer containing a polyvinylidene fluoride-based resin in a ratio of 0.1 mol % to 5 mol % of hexafluoropropylene monomer units. For example, Patent Document 5 discloses a porous layer containing a polyvinylidene fluoride resin having a weight average molecular weight of 1 million or more.

prior art literature

patent documents

Patent Document 1: International Publication No. 2013/058367

Patent Document 2: Japanese Unexamined Patent Publication No. 2012-74367

Patent Document 3: Japanese Patent No. 5171150

Patent Document 4: International Publication No. 2014/021293

Patent Document 5: International Publication No. 2016/002567

Contents of the invention

The problem to be solved by the invention

In recent years, non-aqueous secondary batteries typified by lithium ion secondary batteries have been studied for their application as batteries for power storage or electric vehicles due to their high energy density. When using a non-aqueous secondary battery as a battery for power storage or an electric vehicle, it is necessary to increase the area. With the increase in the area of the soft package battery, even if it is equipped with an adhesive containing polyvinylidene fluoride resin For separators with a porous layer, the following may sometimes occur: the adhesion between the electrodes and the separator is insufficient, resulting in a decrease in battery capacity, poor charge-discharge characteristics, and battery swelling. With the increase in the area of batteries, it is desired that the adhesiveness of the above-mentioned adhesive porous layer to electrodes be improved.

In addition, a battery provided with a separator having an adhesive porous layer containing a polyvinylidene fluoride resin is generally manufactured by manufacturing a laminate of an electrode and a separator, housing the laminate in an external packaging material, and injecting After the electrolytic solution is added, hot pressing treatment (referred to as "wet hot pressing" in this specification.) is carried out. With the increase in the area of batteries, separators with better adhesion by wet heat pressing are desired.

The embodiments of the present disclosure have been made in view of the above circumstances.

An object of an embodiment of the present disclosure is to provide a separator for a non-aqueous secondary battery that includes an adhesive porous layer containing a polyvinylidene fluoride resin and that is excellent in adhesion to an electrode by wet hot pressing .

In addition, an object of embodiments of the present disclosure is to provide a non-aqueous secondary battery excellent in cell strength and cycle characteristics.

means to solve the problem

Specific means for solving the above-mentioned problems include the following means.

[1] A separator for a non-aqueous secondary battery, comprising:

porous substrates; and

An adhesive porous layer, the adhesive porous layer is provided on one or both sides of the porous substrate, and the ratio of the adhesive porous layer containing hexafluoropropylene monomer units is 5.1 A vinylidene fluoride-hexafluoropropylene binary copolymer having a mass % to 6.9 mass % and a weight average molecular weight of 810,000 to 3 million, the vinylidene fluoride-hexafluoropropylene binary copolymer accounting for all resins More than 95% by mass.

[2] The separator for a non-aqueous secondary battery according to the above [1], wherein the adhesive porous layer has a thickness of 0.5 μm or more and 5 μm or less on one side.

[3] The separator for a non-aqueous secondary battery according to the above [1] or [2], wherein the adhesive porous layer further contains an inorganic filler.

[4] The separator for a non-aqueous secondary battery according to the above [3], wherein the inorganic filler is at least one selected from metal hydroxides and metal oxides.

[5] The separator for a non-aqueous secondary battery according to the above [3], wherein the inorganic filler is at least any one of magnesium hydroxide and magnesium oxide.

[6] The separator for a non-aqueous secondary battery according to any one of [3] to [5] above, wherein the content of the inorganic filler in the adhesive porous layer is equal to the adhesive porous layer. The total solid content of the porous layer is not less than 40% by volume and not more than 85% by volume.

[7] A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and the non-aqueous secondary battery according to any one of [1] to [6] disposed between the positive electrode and the negative electrode A separator, the non-aqueous secondary battery obtains an electromotive force through doping/dedoping of lithium.

The effect of the invention

According to the embodiments of the present disclosure, it is possible to provide a separator for a non-aqueous secondary battery that includes an adhesive porous layer containing a polyvinylidene fluoride resin and is excellent in adhesion to an electrode by wet hot pressing .

In addition, according to the embodiments of the present disclosure, it is possible to provide a non-aqueous secondary battery excellent in unit cell strength and cycle characteristics.

Detailed ways

Embodiments are described below. It should be noted that these descriptions and examples are for illustrating the implementation, and do not limit the scope of the implementation.

In this specification, the numerical range represented using "-" shows the range which includes the numerical value described before and after "-" as a minimum value and a maximum value, respectively.

In this specification, the term "process" does not only refer to an independent process, but is included in this term as long as the intended purpose of the process is achieved even when it cannot be clearly distinguished from other processes.

Regarding the separator in the present disclosure, the "longitudinal direction" refers to the longitudinal direction of the elongated porous substrate and the separator, and the "width direction" refers to the direction perpendicular to the "longitudinal direction". The "longitudinal direction" is also called "MD direction", and the "width direction" is also called "TD direction".

In the present specification, the "monomer unit" of the polyvinylidene fluoride-based resin is a structural unit of the polyvinylidene fluoride-based resin, and refers to a structural unit formed by polymerizing a monomer.

＜Separators for non-aqueous secondary batteries＞

The separator for a non-aqueous secondary battery (also simply referred to as a "separator") of the present disclosure includes a porous substrate and an adhesive porous layer provided on one or both surfaces of the porous substrate. In the separator of the present disclosure, the adhesive porous layer contains vinylidene fluoride-hexafluoropropylene in a ratio of 5.1% by mass to 6.9% by mass of hexafluoropropylene monomer units and a weight average molecular weight of 810,000 to 3 million. In the binary copolymer, the vinylidene fluoride-hexafluoropropylene binary copolymer accounts for more than 95% by mass of the entire resin.

Hereinafter, the vinylidene fluoride monomer unit is also referred to as "VDF unit", the hexafluoropropylene monomer unit is also referred to as "HFP unit", and the vinylidene fluoride-hexafluoropropylene binary copolymer is also referred to as "VDF unit". VDF-HFP binary copolymer", the VDF-HFP binary copolymer with the ratio of HFP units of 5.1 mass% to 6.9 mass% and a weight average molecular weight of 810,000 to 3 million is also called "specific VDF-HFP binary copolymer" meta-copolymer".

In the separator of the present disclosure, by having an adhesive porous layer containing a specific VDF-HFP binary copolymer in a ratio of 95% by mass or more of all resins, adhesion to electrodes by wet hot pressing is achieved. excellent. Although the mechanism is not necessarily clear, it is presumed as follows.

The higher the ratio of the HFP unit in the VDF-HFP binary copolymer, the greater the mobility of the polymer chain during heating. Therefore, in the case of hot pressing, the higher the proportion of HFP units in the VDF-HFP binary copolymer, the easier it is to adhere to the electrode. In addition, it can be bonded even under lower temperature hot pressing conditions. .

In addition, the higher the ratio of the HFP unit in the VDF-HFP binary copolymer, the easier it is to swell in the electrolyte solution. Therefore, in the case of wet hot pressing, if the ratio of HFP units in the VDF-HFP binary copolymer is increased to a certain extent, it will swell moderately and easily adhere to the electrode.

Therefore, focusing on the behavior of the VDF-HFP binary copolymer, it is advantageous for adhesion to electrodes that the ratio of the HFP unit in the VDF-HFP binary copolymer is increased to some extent.

However, when the adhesive porous layer is formed from a VDF-HFP binary copolymer having a large ratio of HFP units, the porosity tends to increase and the pore diameter tends to increase. When the porosity of the adhesive porous layer is high and the pore diameter is also large, the area of the VDF-HFP binary copolymer part that becomes the bonding position with the electrode decreases on the surface of the adhesive porous layer, and the VDF-HFP Binary copolymers are present sparsely. Therefore, there is a tendency that the higher the ratio of the HFP unit in the VDF-HFP binary copolymer constituting the adhesive porous layer, the weaker the adhesion between the adhesive porous layer and the electrode. In addition, when the porosity of the adhesive porous layer is high and the pore diameter is also large, ion migration at the electrode interface becomes uneven, which adversely affects the cycle characteristics and load characteristics of the battery.

In addition, when the ratio of the HFP unit in the VDF-HFP binary copolymer is too large, it tends to be easily dissolved in the electrolytic solution, and the adhesion to the electrode tends to be weakened.

Therefore, when focusing on the surface morphology (morphology) of the adhesive porous layer, it is advantageous when the ratio of the HFP unit in the VDF-HFP binary copolymer is small, in order not to dissolve the VDF-HFP copolymer in the electrolytic solution , it is preferable that the proportion of HFP units in the VDF-HFP binary copolymer is not too much.

Therefore, the proportion of the HFP unit in the specific VDF-HFP binary copolymer is 5.1% by mass to 6.9% by mass.

For a specific VDF-HFP binary copolymer, by setting the ratio of the HFP unit to 5.1% by mass or more, the polymer chain mobility during heating is large, and strong adhesion to the electrode can be obtained during hot pressing . On the other hand, for a specific VDF-HFP binary copolymer, by setting the ratio of the HFP unit to 6.9% by mass or less, it is possible to realize adhesive porosity with small porosity and pore diameter without inhibiting ion permeability. The texture layer realizes a surface morphology suitable for bonding with electrodes.

In addition, for a specific VDF-HFP binary copolymer, by setting the ratio of the HFP unit to 5.1% by mass to 6.9% by mass, it can be moderately swelled in the electrolyte solution, so it can adhere well to the electrode during wet hot pressing. Since it does not easily dissolve in the electrolyte and does not swell excessively, it maintains its adhesion to the electrodes.

From the above viewpoint, the lower limit of the ratio of the HFP unit in the specific VDF-HFP binary copolymer is 5.1% by mass or more, and the upper limit of the ratio of the HFP unit in the specific VDF-HFP binary copolymer is 6.9% by mass or less, More preferably, it is 6.5 mass % or less, More preferably, it is 6.0 mass % or less.

In addition, the weight average molecular weight (Mw) of the specific VDF-HFP binary copolymer is 810,000 to 3,000,000.

In the specific VDF-HFP binary copolymer, by setting the Mw to 810,000 or more, sufficient mechanical properties capable of withstanding the adhesion treatment with the electrode can be imparted to the adhesive porous layer. Therefore, the pressure of the hot-pressing condition can also be increased to make the separator more firmly bonded to the electrode.

From the above viewpoint, the Mw of the specific VDF-HFP binary copolymer is 810,000 or more, more preferably 1,000,000 or more, and still more preferably 1,100,000 or more.

On the other hand, for a VDF-HFP binary copolymer with a Mw greater than 3 million, the viscosity of the coating liquid used for coating and forming an adhesive porous layer becomes too high, making it difficult to form a porous structure. contacting porous layer.

From the above viewpoint, the Mw of the specific VDF-HFP binary copolymer is 3 million or less, more preferably 2.5 million or less, and still more preferably 2 million or less.

Furthermore, in the present embodiment, 95% by mass or more of all the resins contained in the adhesive porous layer is the specific VDF-HFP binary copolymer. This means that the adhesive porous layer does not substantially contain other resins other than the specific VDF-HFP binary copolymer, and substantially contains only the specific VDF-HFP binary copolymer as a binder resin. Thus, the adhesive porous layer of this embodiment can suppress the unevenness of the porous structure caused by the uneven mixing of various resins, make the uniformity of the porous structure excellent, and realize the adhesiveness suitable for electrodes. connected surface morphology.

The effect of the HFP unit ratio in the specific VDF-HFP binary copolymer described above, the effect of the weight average molecular weight of the specific VDF-HFP binary copolymer, and the adhesive porous layer substantially containing only the specific VDF-HFP binary The effects of the meta-polymer combine with each other, so that the separator of the present disclosure is excellent in adhesion to electrodes based on hot pressing, especially excellent in adhesion to electrodes based on wet hot pressing.

The separator of the present disclosure is not only excellent in adhesion to electrodes using a solvent-based binder (specifically, polyvinylidene fluoride-based resin), but also has excellent adhesion to electrodes using a water-based binder (specifically, styrene-butylene ethylene copolymer) electrode adhesion is also excellent.

Since the separator of the present disclosure is excellent in adhesion to electrodes, a non-aqueous secondary battery to which the separator of the present disclosure is applied has excellent cell strength.

In addition, because the uniformity of the porous structure of the adhesive porous layer in the separator of the present disclosure is excellent, and the adhesion to the electrode is excellent, therefore, the non-aqueous secondary battery to which the separator of the present disclosure is applied Excellent cycle characteristics.

According to the separator of the present disclosure, it is possible to suppress the formation of a gap between the electrode and the separator due to expansion and contraction of the electrode accompanying charging and discharging, and external impact. Therefore, the separator of the present disclosure is suitable for a soft-package battery using an aluminum laminated film package as an outer packaging material, and the separator of the present disclosure can provide a soft-package battery with high battery performance.

In one embodiment of the separator of the present disclosure, by making the adhesive porous layer contain the specific VDF-HFP binary copolymer in a ratio of 95% by mass or more of the total resin, even through relatively low pressure and low High temperature hot pressing can also be well bonded to the electrode. The higher the pressure and temperature of the hot pressing conditions, the more the porous structure of the adhesive porous layer will be destroyed. However, according to one embodiment of the separator of the present disclosure, the hot pressing conditions can be made milder. The ion permeability of the bonded separator is maintained, and the battery characteristics are excellent. In addition, according to one embodiment of the separator of the present disclosure, the temperature at the time of wet hot pressing can be set to a relatively low temperature, and therefore, gas generation due to decomposition of the electrolytic solution and the electrolyte can be suppressed.

In one embodiment of the separator of the present disclosure, by making the adhesive porous layer contain a specific VDF-HFP binary copolymer in a ratio of 95% by mass or more of the total resin, the porous substrate and the adhesiveness The adhesiveness between the porous layers is also improved, and the peeling resistance between the layers is improved.

In one embodiment of the separator of the present disclosure, by making the adhesive porous layer contain a specific VDF-HFP binary copolymer in a ratio of 95% by mass or more of the total resin, the porous substrate and the adhesiveness The ion movement at the interface between the porous layers is also excellent.

Conventionally, in a separator formed by coating an adhesive porous layer on a porous substrate, the interface between the two is prone to pore clogging, resulting in poor ion movement at the interface, and sometimes it is difficult to achieve good battery characteristics. .

On the other hand, in the adhesive porous layer in one embodiment of the present disclosure, since the fine porous structure is developed, the distribution of pores is uniform and the number of pores is large. Therefore, the probability of connecting the pores of the porous base material to the pores of the adhesive porous layer increases, and it is possible to suppress a decrease in battery performance due to pore clogging.

In one embodiment of the separator of the present disclosure, the adhesion to the electrode is good even by hot pressing without impregnating the electrolyte solution (referred to as "dry hot pressing" in this specification). . The deformation of the laminate can be suppressed if the electrode and the separator are adhered to each other by performing dry heat pressing on the laminate before wet heat pressing.

Hereinafter, the material, composition, physical properties, etc. of the separator of the present disclosure will be described in detail.

[Porous substrate]

In this disclosure, the term "porous base material" refers to a base material having pores or voids inside. As such a substrate, a microporous film; a porous sheet such as a nonwoven fabric or paper formed of a fibrous material; into a composite porous sheet; and so on. The microporous membrane refers to a membrane having a structure in which a large number of micropores are connected and a gas or a liquid can pass through from one surface facing the other.

The porous substrate contains an electrically insulating organic material and/or inorganic material.

The porous substrate preferably contains a thermoplastic resin from the viewpoint of imparting a shutdown function to the porous substrate. The shutdown function refers to a function that when the temperature of the battery rises, the material melts to block the pores of the porous substrate, thereby blocking the movement of ions and preventing thermal runaway of the battery. As the thermoplastic resin, a thermoplastic resin having a melting point lower than 200°C is preferable. Examples of thermoplastic resins include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; and the like, among which polyolefins are preferred.

As the porous substrate, a microporous film containing polyolefin (referred to as "polyolefin microporous film") is preferable. Examples of the polyolefin microporous membrane include polyolefin microporous membranes used in existing separators for non-aqueous secondary batteries, and it is preferable to select a polyolefin microporous membrane having sufficient mechanical properties and ion permeability among them. .

From the viewpoint of exhibiting a shutdown function, the polyolefin microporous membrane preferably contains polyethylene, and the polyethylene content is preferably 95% by mass or more of the mass of the entire polyolefin microporous membrane.

The polyolefin microporous membrane is preferably a polyolefin microporous membrane containing polyethylene and polypropylene from the viewpoint of imparting heat resistance to such an extent that the membrane is less prone to breakage when exposed to high temperature. Examples of such polyolefin microporous membranes include microporous membranes in which polyethylene and polypropylene are mixed in one layer. From the viewpoint of achieving both the shutdown function and heat resistance, the microporous membrane preferably contains 95% by mass or more of polyethylene and 5% by mass or less of polypropylene. In addition, from the viewpoint of simultaneously realizing the shutdown function and heat resistance, a polyolefin microporous membrane having the following structure is also preferable: the polyolefin microporous membrane has a laminated structure of two or more layers, at least one layer contains polyethylene, and at least one layer contains polyethylene. Layer 1 contains polypropylene.

The polyolefin contained in the polyolefin microporous membrane is preferably a polyolefin having a weight average molecular weight (Mw) of 100,000 to 5 million. When the Mw of the polyolefin is 100,000 or more, sufficient mechanical properties can be secured. On the other hand, when the Mw of the polyolefin is 5 million or less, the shutdown characteristics are good, and film molding is easy.

The polyolefin microporous membrane can be produced, for example, by the following method. That is, it is a method of extruding molten polyolefin resin from a T-die to form a sheet, subjecting it to crystallization treatment, stretching, and further heat treatment to form a microporous membrane. Alternatively, it is a method of extruding a polyolefin resin melted together with a plasticizer such as liquid paraffin from a T-die, cooling it to form a sheet, stretching it, extracting the plasticizer and performing heat treatment, Thus, a microporous membrane is produced.

Examples of porous sheets made of fibrous materials include polyesters such as polyethylene terephthalate; polyolefins such as polyethylene and polypropylene; aromatic polyamides, polyimides, and polyethers; Non-woven fabrics, paper, etc. made of fibrous materials such as heat-resistant resins such as sulfone, polysulfone, polyetherketone, and polyetherimide. Here, the heat-resistant resin refers to a polymer having a melting point of 200°C or higher, or a polymer having no melting point and a decomposition temperature of 200°C or higher.

Examples of the composite porous sheet include sheets in which a functional layer is laminated on a microporous membrane or a porous sheet. Such a composite porous sheet is preferable from the viewpoint that a function can be further added by using a functional layer. As the functional layer, from the viewpoint of imparting heat resistance, a porous layer containing a heat-resistant resin, or a porous layer containing a heat-resistant resin and an inorganic filler is preferable. Examples of the heat-resistant resin include aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. Examples of the inorganic filler include metal oxides such as alumina and metal hydroxides such as magnesium hydroxide. As a method of providing a functional layer on a porous membrane or a porous sheet, a method of coating a functional layer on a porous membrane or a porous sheet, bonding a porous membrane or a porous sheet with an adhesive, etc. A method of joining the functional layer, a method of thermocompression bonding the microporous membrane or the porous sheet and the functional layer, and the like.

In order to improve the wettability with the coating liquid for forming the adhesive porous layer, various surface treatments may be applied to the porous substrate within the range not impairing the properties of the porous substrate. Examples of surface treatment include corona treatment, plasma treatment, flame treatment, and ultraviolet irradiation treatment.

[Characteristics of porous substrates]

From the viewpoint of obtaining good mechanical properties and internal resistance, the thickness of the porous substrate is preferably 3 μm to 25 μm, more preferably 5 μm to 25 μm, and even more preferably 5 μm to 20 μm.

From the viewpoint of obtaining appropriate sheet resistance and shutdown function, the porosity of the porous base material is preferably 20% to 60%.

From the viewpoint of preventing battery short circuit and obtaining sufficient ion permeability, the Gurley value (JIS P8117:2009) of the porous substrate is preferably 50 seconds/100cc to 800 seconds/100cc, more preferably 50 seconds/100cc to 400 sec/100cc.

From the viewpoint of improving the production yield, the piercing strength of the porous base material is preferably 200 g or more, more preferably 250 g or more. The puncture strength of the porous substrate is measured by using the KES-G5 hand-held compression tester manufactured by Kato Tech Co., Ltd. to perform a puncture test under the conditions that the radius of curvature of the tip of the needle is 0.5 mm, and the puncture speed is 2 mm/sec. Maximum piercing load (g).

The average pore diameter of the porous substrate is preferably 20 nm to 100 nm. When the average pore diameter of the porous substrate is 20 nm or more, ions move easily, and good battery performance can be easily obtained. From the above viewpoint, the average pore diameter of the porous substrate is more preferably 30 nm or more, and still more preferably 40 nm or more. On the other hand, when the average pore diameter of the porous substrate is 100 nm or less, the peel strength between the porous substrate and the adhesive porous layer can be increased, and a good shutdown function can also be realized. From the above viewpoint, the average pore diameter of the porous substrate is more preferably 90 nm or less, and still more preferably 80 nm or less. The average pore diameter of the porous substrate is a value measured using a Perm-Porometer (pore size distribution meter), and can be measured using a Perm-Porometer (CFP-1500-A, manufactured by PMI Corporation), for example, in accordance with ASTME1294-89.

[Adhesive porous layer]

In this disclosure, the adhesive porous layer is a porous layer provided on one or both surfaces of a porous substrate and containing a specific VDF-HFP binary copolymer.

The adhesive porous layer has a large number of micropores inside and these micropores are connected so that gas or liquid can pass through the surface facing the other side.

The adhesive porous layer is a layer provided on one or both surfaces of the porous substrate as the outermost layer of the separator, and can be bonded to the electrode when the separator and the electrode are laminated and hot-pressed.

From the standpoint of excellent cell strength and cycle characteristics (capacity retention) of the battery, it is more preferable that the adhesive porous layer is present on one side of the porous substrate than the case where the adhesive porous layer is present on only one side of the porous substrate. Both sides of the porous substrate. This is because, when the adhesive porous layer is present on both surfaces of the porous substrate, both surfaces of the separator are well adhered to both electrodes via the adhesive porous layer.

The adhesive porous layer contains at least the specific VDF-HFP binary copolymer. The adhesive porous layer may further contain other resins, fillers, and the like other than the specific VDF-HFP binary copolymer.

[Specific VDF-HFP binary copolymer]

In this disclosure, a specific VDF-HFP binary copolymer is a binary copolymer having only VDF units and HFP units. Compared with multi-polymer copolymers having VDF units, HFP units and other monomer units other than them, VDF-HFP binary copolymers can be firmly bonded to electrodes at an appropriate bonding temperature. From the above point of view, it is preferred.

The ratio of the HFP unit in the specific VDF-HFP binary copolymer is 5.1% by mass to 6.9% by mass. The ratio of the HFP unit significantly affects the bonding temperature, and if it is less than 5.1% by mass, hot pressing at high temperature is required, and the hot pressing process may adversely affect the performance of the battery. When the ratio of the HFP unit exceeds 6.9% by mass, the VDF-HFP binary copolymer may not be able to maintain sufficient adhesion to the electrode in the temperature range generally assumed to be used in the battery, which is not preferable. The ratio of the HFP unit in the specific VDF-HFP binary copolymer is more preferably 6.5% by mass or less, still more preferably 6.0% by mass or less.

The weight-average molecular weight (Mw) of the specific VDF-HFP binary copolymer is 810,000 to 3 million. When the Mw of the VDF-HFP binary copolymer is less than 810,000, sufficient adhesive strength may not be exhibited and good battery performance may not be obtained, which is not preferable. When the Mw of the VDF-HFP binary copolymer exceeds 3 million, the formability of the adhesive porous layer is poor, which is not preferable. In addition, it is difficult to obtain a polymer having a weight average molecular weight of more than 3 million. The Mw of the specific VDF-HFP binary copolymer is more preferably 1 million or more, still more preferably 1.1 million or more, more preferably 2.5 million or less, still more preferably 2 million or less.

Examples of methods for producing the specific VDF-HFP binary copolymer include emulsion polymerization and suspension polymerization. In addition, a commercially available VDF-HFP binary copolymer satisfying the ratio of HFP units and the weight average molecular weight can also be selected.

The content of the specific VDF-HFP binary copolymer contained in the adhesive porous layer is 95 mass % or more of the total amount of all resins contained in the adhesive porous layer, more preferably 97 mass % or more, still more preferably It is 98 mass % or more, More preferably, it is 99 mass % or more, Especially preferably, it is 100 mass %.

[Other resins]

In the present disclosure, the adhesive porous layer may contain polyvinylidene fluoride-based resins other than the specific VDF-HFP binary copolymer, or may contain other resins other than polyvinylidene fluoride-based resins. Here, the resin other than the specific VDF-HFP binary copolymer contained in the adhesive porous layer is 5% by mass or less of the total amount of all the resins contained in the adhesive porous layer.

Examples of polyvinylidene fluoride-based resins other than specific VDF-HFP binary copolymers include VDF-HFP binary copolymers in which the proportion of HFP units is different from that of specific VDF-HFP binary copolymers; vinylidene fluoride Homopolymers of polyvinylidene fluoride (polyvinylidene fluoride); copolymers of vinylidene fluoride and at least one fluorine-containing monomer selected from tetrafluoroethylene, trifluoroethylene, trifluorochloroethylene, and vinyl fluoride; A copolymer of difluoroethylene, hexafluoropropylene, and at least one fluorine-containing monomer selected from tetrafluoroethylene, trifluoroethylene, trifluorochloroethylene, and vinyl fluoride.

Examples of resins other than polyvinylidene fluoride resins include homopolymers of fluororubbers, acrylic resins, styrene-butadiene copolymers, vinyl nitrile compounds (acrylonitrile, methacrylonitrile, etc.) Compounds or copolymers, carboxymethyl cellulose, hydroxyalkyl cellulose, polyvinyl alcohol, polyvinyl butyral, polyvinyl pyrrolidone, polyether (polyethylene oxide, polypropylene oxide, etc.), etc.

[filler]

In the present disclosure, the adhesive porous layer may contain fillers made of inorganic or organic substances in order to improve the slidability and heat resistance of the separator. In this case, it is preferable that the content and the particle size are to such an extent that the effects of the present disclosure are not hindered.

The average primary particle diameter of the filler is preferably 0.01 μm to 5 μm, the lower limit is more preferably 0.1 μm or more, and the upper limit is more preferably 1.5 μm or less, and still more preferably 1 μm or less.

The particle size distribution of the filler is preferably 0.1 μm<d90-d10<3 μm. Here, d10 represents the cumulative 10% particle diameter (μm) in the volume-based particle size distribution from the small particle side, and d90 represents the cumulative 90% particle diameter (μm) in the volume-based particle size distribution from the small particle side . The measurement of particle size distribution is carried out in the following manner: for example, using a laser diffraction particle size distribution measuring device (for example, Mastersizer 2000 manufactured by Sysmex Corporation), using water as a dispersion medium, and using a small amount of nonionic surfactant Triton X-100 as a dispersant .

[Inorganic Filler]

From the viewpoint of further improving the heat resistance of the separator, the strength of the unit cell, and securing the safety of the battery, the adhesive porous layer preferably contains an inorganic filler.

As the inorganic filler in the present disclosure, an inorganic filler that is stable to the electrolytic solution and electrochemically stable is preferable. Specifically, metal hydroxides such as magnesium hydroxide, aluminum hydroxide, calcium hydroxide, chromium hydroxide, zirconium hydroxide, cerium hydroxide, nickel hydroxide, and boron hydroxide; , titanium dioxide, silicon dioxide, zirconia, barium titanate and other metal oxides; magnesium carbonate, calcium carbonate and other carbonates; magnesium sulfate, calcium sulfate, barium sulfate and other sulfates; magnesium fluoride, calcium fluoride and other metal fluorides compounds; clay minerals such as calcium silicate and talc; etc. These inorganic fillers may be used alone or in combination of two or more. The inorganic filler may be one surface-modified with a silane coupling agent or the like.

The inorganic filler in the present disclosure is preferably at least one of metal hydroxides and metal oxides from the viewpoint of stability in the battery and ensuring battery safety. As the inorganic filler in the present disclosure, from the viewpoint of suppressing gas generation in the battery, inorganic compounds containing magnesium (for example, magnesium hydroxide, magnesium oxide, magnesium carbonate, magnesium sulfate, magnesium fluoride, etc.), more preferably Magnesium hydroxide or magnesium oxide is preferred. Hydrogen fluoride is the main component of the gas generated by the decomposition of the electrolyte or electrolyte, but it is speculated that inorganic compounds containing magnesium tend to form a coating on the surface of the particles by reacting with hydrogen fluoride, thereby limiting the reaction with hydrogen fluoride, thereby inhibiting the easy linkage. The gas-forming reaction that occurs.

The particle shape of the inorganic filler is not limited, and may be approximately spherical or plate-like. From the viewpoint of suppressing battery short circuit, plate-like particles and unaggregated primary particles are preferable.

The content of the inorganic filler contained in the adhesive porous layer is preferably 40% by volume to 85% by volume of the total solid content of the adhesive porous layer. When the content of the inorganic filler is 40% by volume or more, the heat resistance of the separator, the further improvement of the strength of the unit cell, and the securing of battery safety can be expected. On the other hand, when the content of the inorganic filler is 85% by volume or less, the formability and form of the adhesive porous layer can be maintained, and it contributes to the improvement of the strength of the unit cell. The content of the inorganic filler is more preferably 45 vol% or more, more preferably 50 vol% or more, more preferably 80 vol% or less, and still more preferably 75 vol% or less of the total solid content of the adhesive porous layer.

[Organic Filler]

Examples of the organic filler in this disclosure include cross-linked acrylic resins such as cross-linked polymethyl methacrylate, cross-linked polystyrene, and the like, preferably cross-linked polymethyl methacrylate.

[Other additives]

The adhesive porous layer in the present disclosure may contain additives such as dispersants such as surfactants, wetting agents, defoamers, and pH adjusters. The dispersant is added to the coating liquid for forming the adhesive porous layer for the purpose of improving dispersibility, coatability, and storage stability. A wetting agent, an antifoaming agent, and a pH adjuster are added to the substrate for the purpose of improving the affinity with the porous substrate, suppressing the generation of air bubbles in the coating liquid, or adjusting the pH. in the coating solution for forming the adhesive porous layer.

[Characteristics of Adhesive Porous Layer]

The thickness of the adhesive porous layer is preferably 0.5 μm to 5 μm on one side of the porous substrate. When the above-mentioned thickness is 0.5 μm or more, the adhesion to the electrodes is more excellent, and as a result, the unit cell strength of the battery is more excellent. From the above-mentioned viewpoint, the above-mentioned thickness is more preferably 1 μm or more. On the other hand, when the above-mentioned thickness is 5 μm or less, the cycle characteristics and load characteristics of the battery are more excellent. From the above viewpoint, the thickness is more preferably 4.5 μm or less, and still more preferably 4 μm or less.

When the adhesive porous layer is provided on both surfaces of the porous substrate, the difference between the coating amount on one side and the coating amount on the other side is preferably 20% by mass or less of the total coating amount on both sides. When it is 20% by mass or less, the separator is less prone to curling, the handleability is good, and the cycle characteristics of the battery are also good.

The porosity of the adhesive porous layer is preferably 30% to 80%. When the porosity is 80% or less, the mechanical properties capable of withstanding the pressurized process of bonding to the electrode can be ensured, and the surface opening ratio does not become too high, which is suitable for securing the adhesive force. On the other hand, when the porosity is 30% or more, it is preferable from the viewpoint of favorable ion permeability.

The average pore diameter of the adhesive porous layer is preferably 10 nm to 300 nm, more preferably 20 nm to 200 nm. When the average pore diameter is 10 nm or more (preferably 20 nm or more), when the adhesive porous layer is impregnated with an electrolytic solution, even if the resin contained in the adhesive porous layer swells, the pores are less likely to be blocked. On the other hand, if the average pore diameter is 300nm or less (preferably 200nm or less), then on the surface of the adhesive porous layer, the unevenness of the pores can be suppressed, and the bonding points are evenly scattered, and the bonding with respect to the electrode more excellent. In addition, when the average pore diameter is 300 nm or less (preferably 200 nm or less), the uniformity of ion migration is high, and the cycle characteristics and load characteristics of the battery are more excellent.

The average pore diameter (nm) of the adhesive porous layer is calculated by the following formula, assuming that all the pores are columnar.

d=4V/S

In the formula, d represents the average pore diameter (diameter) of the adhesive porous layer, V represents the pore volume per 1 m ² of the adhesive porous layer, and S represents the pore surface area per 1 m ² of the adhesive porous layer.

The pore volume V per 1 m ² of the adhesive porous layer was calculated from the porosity of the adhesive porous layer.

The pore surface area S per 1 m ² of the adhesive porous layer was obtained by the following method.

First, the specific surface area (m ² /g) of the porous substrate and the specific surface area (m ² /g) of the separator were calculated from the nitrogen adsorption amount by applying the BET formula using the nitrogen adsorption method. These specific surface areas (m ² /g) were multiplied by their respective weights per unit area (g/m ² ) to calculate their respective pore surface areas per 1 m ² . Then, the pore surface area per 1 m ² of the porous substrate was subtracted from the pore surface area per 1 m ² of the separator to calculate the pore surface area S per 1 m ² of the adhesive porous layer.

[Characteristics of separators for non-aqueous secondary batteries]

From the viewpoint of mechanical strength, energy density of the battery, and output characteristics, the thickness of the separator of the present disclosure is preferably 5 μm to 35 μm, more preferably 5 μm to 30 μm, still more preferably 10 μm to 25 μm, and even more preferably 10 μm to 20 μm.

From the viewpoint of mechanical strength, adhesion to electrodes, and ion permeability, the separator of the present disclosure preferably has a porosity of 30% to 60%.

From the viewpoint of good balance between mechanical strength and sheet resistance, the Gurley value (JIS P8117:2009) of the separator of the present disclosure is preferably 50 seconds/100cc to 800 seconds/100cc, more preferably 50 seconds/100cc to 400 seconds /100cc.

For the separator of the present disclosure, from the viewpoint of ion permeability, the Gurley value of the porous substrate is subtracted from the Gurley value of the separator (in a state where an adhesive porous layer is formed on the porous substrate). The resulting value (hereinafter referred to as "Gurley value difference") is preferably 300 sec/100 cc or less, more preferably 150 sec/100 cc or less, still more preferably 100 sec/100 cc or less. When the difference in Gurley value is 300 sec/100 cc or less, the adhesive porous layer does not become too dense, ion permeability remains good, and excellent battery characteristics can be obtained. On the other hand, the difference in Gurley value is preferably 0 sec/100 cc or more, and is preferably 10 sec/100 cc or more from the viewpoint of improving the adhesive force between the adhesive porous layer and the porous substrate.

From the viewpoint of the load characteristics of the battery, the sheet resistance of the separator of the present disclosure is preferably 1 ohm·cm ² to 10 ohm·cm ² . Here, the sheet resistance refers to the resistance value when the separator is impregnated with an electrolytic solution, and can be measured by an alternating current method. The value of sheet resistance varies depending on the type and temperature of the electrolyte. The above values are based on the use of a mixed solvent of 1mol/L LiBF ₄ -1,2-propylene carbonate: ethylene carbonate (mass ratio 1:1) The value measured at the temperature of 20 degreeC as an electrolytic solution.

The puncture strength of the separator of the present disclosure is preferably from 200 g to 1000 g, more preferably from 250 g to 600 g. The method of measuring the puncture strength of the separator is the same as the method of measuring the puncture strength of the porous substrate.

The heat shrinkage rate at 120° C. of the separator of the present disclosure is preferably 10% or less in both the MD direction and the TD direction from the viewpoint of a balance between shape stability and shutdown characteristics.

From the viewpoint of ion permeability, the tortuosity of the separator of the present disclosure is preferably 1.5 to 2.5.

The moisture content (based on mass) contained in the separator of the present disclosure is preferably 1000 ppm or less. The smaller the moisture content of the separator, the more the reaction between the electrolyte and water can be suppressed when the battery is formed, thereby suppressing the generation of gas in the battery and improving the cycle characteristics of the battery. From the above viewpoint, the moisture content contained in the separator of the present disclosure is more preferably 800 ppm or less, and still more preferably 500 ppm or less.

[Manufacturing method of separator for non-aqueous secondary battery]

The separator of the present disclosure can be produced, for example, by applying a coating solution containing a polyvinylidene fluoride-based resin on a porous substrate to form a coating layer, and then making the poly(vinylidene fluoride) contained in the coating layer The vinylidene fluoride resin is cured to form an adhesive porous layer on the porous substrate. Specifically, the adhesive porous layer can be formed by, for example, the following wet coating method.

The wet coating method is a film-forming method in which the following steps are sequentially performed: (i) coating liquid preparation process, dissolving or dispersing polyvinylidene fluoride resin in a solvent to prepare a coating liquid; (ii) coating process, coating the coating liquid on the porous substrate to form a coating layer; (iii) coagulation process, contacting the coating layer with the coagulation liquid, and curing the polyvinylidene fluoride-based resin while inducing phase separation , to obtain a composite membrane with an adhesive porous layer on the porous substrate; (iv) a water washing step, washing the composite membrane with water; and, (v) a drying step, removing water from the composite membrane. The details of the wet coating method applicable to the separator of the present disclosure are as follows.

As a solvent for dissolving or dispersing polyvinylidene fluoride-based resins (hereinafter also referred to as "good solvents") for preparing coating liquids, N-methyl-2-pyrrolidone (NMP), di Polar amide solvents such as methylacetamide (DMAc), dimethylformamide, and dimethylformamide.

From the viewpoint of forming an adhesive porous layer having a good porous structure, it is preferable to mix a phase separation agent that induces phase separation with a good solvent. Examples of the phase separation agent include water, methanol, ethanol, propanol, butanol, butylene glycol, ethylene glycol, propylene glycol, tripropylene glycol (TPG), and the like. Preferably, the phase separation agent is mixed with a good solvent within a range where a viscosity suitable for coating can be ensured.

As a solvent for preparing the coating liquid, from the viewpoint of forming an adhesive porous layer having a good porous structure, a mixture containing 60% by mass or more of a good solvent and 5% to 40% by mass of a phase separation agent Solvents are preferred.

Conventionally, as a coating solution for forming an adhesive porous layer, a coating solution obtained by dissolving a polyvinylidene fluoride-based resin in a mixed solvent of a good solvent such as DMAc or NMP and a poor solvent such as water or TPG has been used. liquid.

However, a coating solution containing a poor solvent tends to be gelled, depending on the environmental conditions after preparation, and when gelled, it is impossible to form an adhesive with a well-developed fine porous structure. porous layer, or streaks may be generated on the surface of the adhesive porous layer. Since the porous structure and surface morphology of the adhesive porous layer affect the adhesion to electrodes and battery characteristics, the coating liquid is required to have storage stability.

In the present embodiment, the binder resin contained in the coating solution for forming the adhesive porous layer is substantially only the specific VDF-HFP binary copolymer. Accordingly, the storage stability of the coating liquid is high, and gelation is less likely to occur (the detailed mechanism is unclear). Therefore, even if a coating liquid that is not just prepared is used, the effect that a fine porous structure is developed, an adhesive porous layer with a good surface morphology can be formed, and the cycle characteristics and load characteristics of the battery are excellent.

From the viewpoint of forming an adhesive porous layer having a good porous structure, the concentration of the polyvinylidene fluoride-based resin in the coating liquid is preferably 3% by mass to 10% by mass of the total mass of the coating liquid.

When fillers or other components are contained in the adhesive porous layer, the fillers or other components may be dissolved or dispersed in the coating liquid.

The coating liquid may contain a dispersant such as a surfactant, a wetting agent, an antifoaming agent, a pH adjuster, and the like. These additives may remain in the adhesive porous layer as long as they are electrochemically stable within the range of use of the non-aqueous secondary battery and do not inhibit reactions in the battery.

The coagulation liquid usually consists of a good solvent and a phase separation agent for preparing a coating liquid, and water. From the viewpoint of production, the mixing ratio of the good solvent and the phase separation agent is preferably consistent with the mixing ratio of the mixed solvent used to prepare the coating liquid. From the viewpoint of formation of the porous structure and productivity, the water content of the coagulation liquid is preferably 40% by mass to 90% by mass.

Coating of the coating liquid onto the porous base material can utilize a conventional coating method using a Meyer bar, a die coater, a reverse roll coater, a gravure coater, or the like. When forming the adhesive porous layer on both surfaces of the porous substrate, it is preferable to apply the coating liquid to both surfaces of the substrate simultaneously from the viewpoint of productivity.

The adhesive porous layer can also be produced by the dry coating method other than the wet coating method mentioned above. The so-called dry coating method is a method in which a coating solution containing a polyvinylidene fluoride resin and a solvent is applied to a porous substrate, the coating layer is dried, and the solvent is volatilized and removed, thereby, An adhesive porous layer was obtained. However, the dry coating method tends to make the coating layer denser than the wet coating method, and therefore, the wet coating method is preferable because a good porous structure can be obtained.

The separator of the present disclosure can also be produced by forming an adhesive porous layer in the form of an independent sheet, overlapping the adhesive porous layer with a porous substrate, and bonding the adhesive porous layer by thermocompression or bonding. Agents are compounded. As a method of producing an adhesive porous layer as an independent sheet, there may be mentioned a method of forming an adhesive porous layer on a release sheet by applying the above-mentioned wet coating method or dry coating method.

＜Non-aqueous secondary battery＞

The nonaqueous secondary battery of the present disclosure is a nonaqueous secondary battery that obtains an electromotive force by doping/dedoping lithium, and includes a positive electrode, a negative electrode, and the separator of the present disclosure. Doping refers to occlusion, loading, adsorption, or intercalation, and refers to a phenomenon in which lithium ions enter active materials in electrodes such as positive electrodes.

The non-aqueous secondary battery of the present disclosure has, for example, a structure in which a battery element in which a negative electrode and a positive electrode are opposed to each other through a separator is enclosed together with an electrolyte solution in an external packaging material. The non-aqueous secondary battery of the present disclosure is particularly preferably used for a lithium ion secondary battery. The non-aqueous secondary battery of the present disclosure can be efficiently produced by using the separator of the present disclosure having excellent adhesion to electrodes.

Since the non-aqueous secondary battery of the present disclosure is provided with the separator of the present disclosure having excellent adhesion to electrodes, it is excellent in unit cell strength.

In addition, since the non-aqueous secondary battery of the present disclosure has excellent uniformity of the porous structure of the adhesive porous layer and the separator of the present disclosure having excellent adhesion to electrodes, the cycle characteristics are excellent. .

Hereinafter, an embodiment example of the positive electrode, the negative electrode, the electrolytic solution, and the external packaging material included in the non-aqueous secondary battery of the present disclosure will be described.

The positive electrode may have a structure in which an active material layer containing a positive electrode active material and a binder resin is molded on a current collector. The active material layer may further contain a conductive additive. Examples of positive electrode active materials include lithium-containing transition metal oxides, and specifically, LiCoO ₂ , LiNiO ₂ , LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , LiMn ₂ O ₄ , LiFePO ₄ , LiCo _1/2 Ni _1/2 O ₂ , LiAl _1/4 Ni _3/4 O ₂ , etc. As a binder resin, polyvinylidene fluoride resin etc. are mentioned, for example. Examples of the conductive aid include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of the current collector include aluminum foil, titanium foil, stainless steel foil and the like having a thickness of 5 μm to 20 μm.

According to one embodiment of the separator of the present disclosure, since the adhesive porous layer has excellent oxidation resistance, it can be easily applied by disposing the adhesive porous layer on the positive electrode side of the non-aqueous secondary battery. LiMn _1/2 Ni _1/2 O ₂ , LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ , etc. working at a high voltage above V are used as positive electrode active materials.

The negative electrode may have a structure in which an active material layer containing a negative electrode active material and a binder resin is formed on a current collector. The active material layer may further contain a conductive additive. Examples of the negative electrode active material include materials capable of electrochemically occluding lithium, and specific examples thereof include carbon materials; alloys of silicon, tin, aluminum, etc., and lithium; and the like. Examples of the binder resin include polyvinylidene fluoride-based resins, styrene-butadiene copolymers, and the like. Examples of the conductive aid include carbon materials such as acetylene black, Ketjen black, and graphite powder. Examples of the current collector include copper foil, nickel foil, stainless steel foil and the like having a thickness of 5 μm to 20 μm. In addition, instead of the above-mentioned negative electrode, metal lithium foil may also be used as the negative electrode.

For the non-aqueous secondary battery of the present disclosure, by applying the separator of the present disclosure, not only the adhesion to the negative electrode using a solvent-based binder (specifically, polyvinylidene fluoride-based resin) is excellent, Furthermore, it is also excellent in adhesion to a negative electrode using a water-based binder (specifically, a styrene-butadiene copolymer).

In the electrode, it is preferable to contain a large amount of binder resin in the active material layer from the viewpoint of adhesion to the separator. On the other hand, from the viewpoint of increasing the energy density of the battery, it is preferable to contain a large amount of active material in the active material layer, and it is preferable to have a relatively small amount of binder resin. Since the separator of the present disclosure is excellent in adhesion to the electrodes, the amount of the binder resin in the active material layer can be reduced and the amount of the active material can be increased, thereby improving the energy density of the battery.

The electrolytic solution is a solution obtained by dissolving a lithium salt in a non-aqueous solvent. Examples of lithium salts include LiPF ₆ , LiBF ₄ , LiClO ₄ and the like. As the non-aqueous solvent, for example, cyclic carbonates such as ethylene carbonate, 1,2-propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, vinylene carbonate, etc.; Chain carbonates such as methyl ester, diethyl carbonate, ethyl methyl carbonate, and their fluorine substitutes; cyclic esters such as γ-butyrolactone and γ-valerolactone; etc., they can be used alone or Mixed use. As an electrolyte, mix cyclic carbonate and chain carbonate at a mass ratio of 20:80 to 40:60 (cyclic carbonate: chain carbonate) and dissolve 0.5mol/L to 1.5mol/L lithium An electrolyte solution obtained from a salt is preferred.

Examples of the external packaging material include a metal case, an aluminum laminated film package, and the like. The shape of the battery is square, cylindrical, button, etc., and the separator of the present disclosure is applicable to any shape.

The non-aqueous secondary battery of the present disclosure can be produced by manufacturing a laminate in which the separator of the present disclosure is arranged between the positive electrode and the negative electrode, and then using the laminate by using, for example, the following 1) and 2) produced by any of the methods.

1) Store the laminated body in an external packaging material (such as an aluminum laminated film package; the same below), inject an electrolyte solution into it, and heat press the laminated body from above the external packaging material (wet hot pressing) to perform electrode Adhesion to the diaphragm, and sealing of the external packaging material.

2) Hot press the laminated body (dry hot pressing), bond the electrode and the separator, store it in the outer packaging material, inject the electrolyte solution into it, and further hot press the laminated body from above the outer packaging material ( Wet hot pressing) to bond electrodes and separators and seal external packaging materials.

According to the production method of the above-mentioned 1), the specific VDF-HFP binary copolymer contained in the adhesive porous layer of the separator is hot-pressed in the state where the laminate is swollen in the electrolytic solution, so that the electrode and the separator are well adhered. Then, a non-aqueous secondary battery excellent in unit cell strength and battery characteristics can be obtained.

According to the manufacturing method of 2) above, since the electrodes and the separator are bonded before the laminate is housed in the exterior packaging material, deformation of the laminate during transportation for housing in the exterior packaging material can be suppressed.

In addition, according to the production method of the above-mentioned 2), the laminate is further hot-pressed in a state where the specific VDF-HFP binary copolymer contained in the adhesive porous layer of the separator is swollen in the electrolytic solution, so that the electrode The bond to the diaphragm becomes stronger.

In addition, the wet hot pressing in the production method of the above 2) may be carried out under mild conditions to the extent that the adhesion between the electrode and the separator, which has been slightly weakened by impregnating the electrolyte solution, can be restored, that is, the wet hot pressing can be carried out. Since the temperature of the hot pressing is set at a relatively low temperature, gas generation due to decomposition of the electrolytic solution and the electrolyte in the battery can be suppressed when the battery is produced.

As conditions for the hot pressing in the production methods of the above 1) and 2), in wet hot pressing, the pressing pressure is preferably 0.5 MPa to 2 MPa, and the temperature is preferably 70°C to 110°C. In dry hot pressing, the pressing pressure is preferably 0.5 MPa to 5 MPa, and the temperature is preferably 20°C to 100°C.

The separator of the present disclosure can be bonded to an electrode by being overlapped with the electrode. Therefore, pressurization is not an essential step in manufacturing a battery, but it is preferable to perform pressurization from the viewpoint of making the adhesion between the electrodes and the separator stronger. From the viewpoint of further strengthening the adhesion between the electrode and the separator, the pressurization is preferably pressurization (hot press) performed while heating.

When manufacturing a laminated body, the method of disposing the separator between the positive electrode and the negative electrode may be a method of sequentially stacking at least one layer of each of the positive electrode, separator, and negative electrode (so-called stacking method), or the method of stacking the positive electrode, separator, negative electrode, and separator. And in the way of winding along the length direction.

Example

Examples are given below to describe more concretely the separator and the non-aqueous secondary battery of the present disclosure. However, the separator and the non-aqueous secondary battery of the present disclosure are not limited to the following examples.

<Measurement method, evaluation method>

The measurement methods and evaluation methods applied to Examples and Comparative Examples are as follows.

[Proportion of HFP unit in polyvinylidene fluoride resin]

The ratio of the HFP unit of the polyvinylidene fluoride resin was determined from the NMR spectrum. Specifically, 20 mg of polyvinylidene fluoride resin was dissolved in 0.6 mL of deuterated dimethyl sulfoxide at 100°C, and ¹⁹ F-NMR spectrum was measured at 100°C.

[Weight average molecular weight of polyvinylidene fluoride resin]

The weight average molecular weight (Mw) of a polyvinylidene fluoride resin is measured by gel permeation chromatography (GPC). For the molecular weight measurement by GPC, the GPC device "GPC-900" manufactured by JASCO Corporation was used, two TSKgelSUPER AWM-H manufactured by Tosoh were used as columns, and dimethylformamide was used as a solvent at a temperature of 40 °C and a flow rate of 10 mL/min, the molecular weight was obtained in terms of polystyrene.

[Coating Amount of Adhesive Porous Layer]

The separator was cut out to 10 cm×10 cm, the mass was measured, and the mass was divided by the area to obtain the weight per unit area of the separator. In addition, the porous base material for producing the separator was cut out to 10 cm×10 cm, the mass was measured, and the mass was divided by the area to obtain the weight per unit area of the porous base material. Then, by subtracting the weight per unit area of the porous base material from the weight per unit area of the separator, the total coating amount of both surfaces of the adhesive porous layer was obtained.

[film thickness]

The film thicknesses of the porous substrate and the separator were measured using a contact-type thickness gauge (LITEMATIC manufactured by Mitutoyo Corporation). As for the measurement terminal, a cylindrical measurement terminal with a diameter of 5 mm was used, adjusted so that a load of 7 g was applied during the measurement, and the measurement was performed at 20 arbitrary locations within 10 cm×10 cm, and the average value was calculated.

The layer thickness of the adhesive porous layer was obtained by subtracting the film thickness of the porous substrate from the film thickness of the separator.

[Porosity]

The porosity of the porous substrate and the separator was obtained by the following calculation method.

The constituent materials are a, b, c, ..., n, the mass of each constituent material is Wa, Wb, Wc, ..., Wn (g/cm ² ), and the true density of each constituent material is da, db, dc, ..., When dn (g/cm ³ ) and the film thickness are expressed as t (cm), the porosity ε (%) can be obtained by the following formula.

ε＝{1-(Wa/da+Wb/db+Wc/dc+...+Wn/dn)/t}×100

[Gurley value]

According to JIS P8117:2009, the Gurley value of the porous substrate and the separator was measured using a Gurley-type air permeability meter (G-B2C manufactured by Toyo Seiki Co., Ltd.).

[heat resistance]

Place the diaphragm on a horizontal table, heat a soldering iron with a tip diameter of 2mm so that the temperature of the tip is 260°C, and in this state, make the tip of the soldering iron contact the surface of the diaphragm for 60 seconds, and measure the force generated on the diaphragm due to the contact. Area of the hole (mm ² ). The higher the heat resistance of the separator, the smaller the area of pores generated on the separator.

[Wet adhesion to electrodes]

91g of lithium cobalt oxide powder as positive electrode active material, 3g of acetylene black as conductive aid, and 3g of polyvinylidene fluoride as binder are dissolved in N-methylpyrrolidone so that the concentration of polyvinylidene fluoride It became 5 mass %, it stirred with the twin-arm mixer, and the slurry for positive electrodes was prepared. This positive electrode slurry was applied to one side of an aluminum foil with a thickness of 20 μm, dried, and then pressed to obtain a positive electrode (one-sided coating) having a positive electrode active material layer as an electrode for wet adhesion evaluation between a separator and an electrode.

The electrode and aluminum foil (thickness 20 μm) obtained by the above method were cut into a size of 1.5 cm in width and 7 cm in length, and each separator obtained in the following examples and comparative examples was cut into a size of 1.8 cm in width and 7 cm in length. The size of 7.5cm. Laminate in the order of electrode-separator-aluminum foil to make a laminate, and immerse the electrolyte (1mol/L LiBF ₄ -ethylene carbonate: 1,2-propylene carbonate [mass ratio 1:1]) into the laminate , Store it in an aluminum laminated film package, decompress and seal it using a vacuum sealer. Next, using a heat press machine, the laminated body was heat-pressed together with the package, and the electrodes and the separator were bonded together. The hot pressing conditions were set as follows: a pressure of 1 MPa, a temperature of 90° C., and a pressing time of 2 minutes. Then, the package was opened, the laminate was taken out, and the product obtained by removing the aluminum foil from the laminate was used as a measurement sample.

The non-coated surface of the electrode of the measurement sample was fixed to a metal plate with double-sided tape, and the metal plate was fixed to the lower chuck of Tensilon (STB-1225S manufactured by A&D). At this time, the metal plate was fixed to Tensilon so that the longitudinal direction of the measurement sample became the gravitational direction. The separator was peeled away from the electrode by about 2 cm from the lower end, and the end was fixed to the upper chuck so that the pulling angle (the angle of the separator relative to the measurement sample) was 180°. The separator was pulled at a pulling speed of 20 mm/min, and the load when the separator was peeled off from the electrode was measured. Loads from 10 mm to 40 mm from the measurement start were collected at intervals of 0.4 mm. This measurement was carried out three times, and the average value was calculated, and this average value was taken as the wet adhesive force to the electrode (N/15mm, the adhesive force between the electrode and the separator by wet hot pressing).

[Gas generation amount]

The separator was cut into a size of 600 cm ² , packed in an aluminum laminated film package, an electrolyte solution was poured into the package, the separator was impregnated with the electrolyte solution, and the package was sealed to obtain a test unit cell. As the electrolyte, 1 mol/L LiPF ₆ -ethylene carbonate:ethyl methyl carbonate (mass ratio 3:7) was used. The test unit cells were left in an environment at a temperature of 85° C. for 3 days, and the volumes of the test unit cells before and after heat treatment were measured. The volume V1 of the test unit cell before heat treatment was subtracted from the volume V2 of the test unit cell after heat treatment to obtain the amount of gas generation V (=V2−V1, unit: ml).

[Unit battery strength]

91g of lithium cobalt oxide powder as positive electrode active material, 3g of acetylene black as conductive aid, and 3g of polyvinylidene fluoride as binder are dissolved in N-methylpyrrolidone so that the concentration of polyvinylidene fluoride It became 5 mass %, it stirred with the twin-arm mixer, and the slurry for positive electrodes was prepared. This positive electrode slurry was applied to an aluminum foil having a thickness of 20 μm, dried and then pressed to obtain a positive electrode having a positive electrode active material layer.

300 g of artificial graphite as the negative electrode active material, 7.5 g of the water-soluble dispersion of the modified body containing 40% by mass of styrene-butadiene copolymer as the binder, and 7.5 g of the modified body as the thickener were utilized in a double-arm mixer. 3 g of carboxymethylcellulose and an appropriate amount of water were stirred and mixed to prepare a negative electrode slurry. This negative electrode slurry was applied to a 10 μm thick copper foil serving as a negative electrode current collector, dried and then pressed to obtain a negative electrode having a negative electrode active material layer.

The above-mentioned positive electrode and negative electrode were wound through each separator obtained in the following Examples and Comparative Examples, and tabs were welded to obtain a battery element. The battery element was housed in an aluminum laminated film package, impregnated with an electrolyte solution, and subjected to hot pressing (wet hot pressing) at a pressure of 1 MPa and a temperature of 90°C for 2 minutes to seal the outer package to obtain a test A secondary battery (length 65mm, width 35mm, thickness 2.5mm, capacity 700mAh) is used. As the electrolyte, 1 mol/L LiPF ₆ -ethylene carbonate:diethyl carbonate (mass ratio 3:7) was used.

The test secondary battery obtained as described above was subjected to a three-point bending test according to ISO178, and the unit cell strength (N) was obtained.

[Cycle characteristics]

A test secondary battery was produced by the same production method as above. In an environment of 25° C., 300 cycles of charge and discharge were performed under the conditions of 4.2 V constant current and constant voltage charging at 1 C for 2 hours and 3 V cut-off constant current discharge at 1 C. Based on the discharge capacity obtained in the first cycle, the ratio of the discharge capacity obtained after 300 cycles was calculated as a percentage, and this was used as an index of cycle characteristics.

＜Manufacture of diaphragm＞

[Example 1]

The VDF-HFP binary copolymer (the proportion of HFP units is 5.1% by mass, and the weight average molecular weight is 1.13 million) is dissolved in a mixed solvent of dimethylacetamide and tripropylene glycol (dimethylacetamide) so that the resin concentration becomes 5% by mass. Acetamide:tripropylene glycol=80:20 [mass ratio]), a coating liquid for forming an adhesive porous layer was prepared. This coating solution is equally applied to both sides of a polyethylene microporous membrane (film thickness is 9 μm, porosity is 38%, Gurley value is 160 seconds/100cc), and is immersed in a coagulation solution (water: dimethylacetamide : tripropylene glycol=62:30:8 [mass ratio], the temperature is 40° C.), and solidified. Next, this was washed with water and dried to obtain a separator in which adhesive porous layers were formed on both surfaces of the polyethylene microporous membrane.

[Embodiments 2-5]

Except that the VDF-HFP binary copolymer was changed to other VDF-HFP binary copolymers shown in Table 1, the same procedure as in Example 1 was performed to make a polyethylene microporous membrane with adhesive bonds formed on both sides. The separator of the porous layer.

[Example 6]

The VDF-HFP binary copolymer is changed to the first VDF-HFP binary copolymer (the ratio of HFP unit is 5.4% by mass, and the weight average molecular weight is 1.13 million) and the second VDF-HFP binary copolymer (the ratio of HFP unit Ratio is 2.5% by mass, weight average molecular weight is 1,500,000) mixture (mass ratio 99:1), except that, operate in the same manner as in Example 1, and make a polyethylene microporous membrane with adhesiveness formed on both sides. The separator of the porous layer.

[Comparative example 1]

The mixing ratio of the first VDF-HFP binary copolymer and the second VDF-HFP binary copolymer was changed to 90:10, except that, it was operated in the same manner as in Example 6 to make a polyethylene microporous membrane. A separator with adhesive porous layers formed on both sides.

[Comparative examples 2 to 4]

Except that the VDF-HFP binary copolymer was changed to other VDF-HFP binary copolymers shown in Table 1, the same procedure as in Example 1 was performed to make a polyethylene microporous membrane with adhesive bonds formed on both sides. The separator of the porous layer.

[Comparative Example 5]

Change the VDF-HFP binary copolymer into other VDF-HFP binary copolymers (the ratio of HFP units is 5.4% by mass, and the weight-average molecular weight is 3.1 million), operate in the same way as in Example 1, and try Adhesive porous layers were formed on both surfaces of the porous membrane, but the viscosity of the coating liquid was too high, and the adhesive porous layers could not be formed.

[Comparative Example 6]

The VDF-HFP binary copolymer was changed to a vinylidene fluoride-hexafluoropropylene-trifluorochloroethylene terpolymer (the ratio of the HFP unit was 5.2% by mass, the ratio of the CTFE unit was 3.8% by mass, and the weight average molecular weight was 600,000), except that, in the same manner as in Example 1, a separator in which an adhesive porous layer was formed on both surfaces of a polyethylene microporous membrane was produced.

[Embodiments 7-13]

Magnesium hydroxide (KISUMA 5P manufactured by Kyowa Chemical Industry Co., Ltd., average primary particle size: 0.8 μm, BET specific surface area: 6.8 m ² /g) was added as an inorganic filler to the coating solution in which the resin was dissolved, and it was shown in Table 1 The indicated content (volume ratio relative to the total solid content) was stirred until it became uniform to prepare a coating liquid, and the coating amount of the coating liquid was changed as shown in Table 1. In addition, the same as In the same manner as in Example 5, a separator in which an adhesive porous layer was formed on both surfaces of a polyethylene microporous membrane was produced.

[Example 14]

Except having changed the coating amount of the coating liquid as shown in Table 1, it carried out similarly to Example 5, and produced the separator which formed the adhesive porous layer on both surfaces of the polyethylene microporous membrane.

[Example 15]

The inorganic filler was changed to two types (magnesium hydroxide: aluminum oxide = 95:5 [volume ratio]), and in the same manner as in Example 11, a separator in which an adhesive porous layer was formed on both surfaces of a polyethylene microporous membrane was produced.

[Example 16]

The inorganic filler was changed to magnesium oxide (PUREMAGFNM-G manufactured by Tateho Chemical Industries Co., Ltd., with an average primary particle size of 0.5 μm), except that it was performed in the same manner as in Example 11 to produce a polyethylene microporous membrane. A separator with an adhesive porous layer formed on both sides.

[Example 17]

The inorganic filler was changed to alumina (AL-160SG-3 manufactured by Showa Denko Co., Ltd., with an average primary particle diameter of 0.5 μm), except that it was performed in the same manner as in Example 11, and a polyethylene microporous membrane was formed on both sides of the polyethylene microporous membrane. Separator with adhesive porous layer.

[Example 18]

Except that the VDF-HFP binary copolymer was changed to other VDF-HFP binary copolymers shown in Table 1, it was performed in the same manner as in Example 11 to make a polyethylene microporous membrane with adhesive bonds formed on both sides. The separator of the porous layer.

Table 1 shows the physical properties and evaluation results of the separators of Examples 1 to 18 and Comparative Examples 1 to 6.

[Table 1]

The entire disclosure of Japanese Application No. 2015-221570 for which it applied on November 11, 2015 is incorporated into this specification by reference. The entire disclosure of Japanese Application No. 2015-221600 for which it applied on November 11, 2015 is incorporated in this specification by reference.

All documents, patent applications, and technical standards described in this specification are incorporated by reference into this specification, and each document, patent application, and technical standard is incorporated by reference to the same extent as if it were specifically and individually described.

Claims (7)

1. diaphragm for non-water system secondary battery has：

Porous base material；With

Cementability porous layer, the cementability porous layer are arranged at the one or both sides of the Porous base material, also, The ratio that the cementability porous layer contains hexafluoropropene monomeric unit is 5.1 mass % or more, 6.9 mass % or less and again Average molecular weight is 810,000 or more 300 ten thousand vinylidene fluoride below-hexafluoropropene bipolymers, the vinylidene fluoride-six Fluoropropene bipolymer accounts for the 95 mass % or more of all resins.

2. diaphragm for non-water system secondary battery as described in claim 1, wherein thickness of the cementability porous layer in one side Degree is 0.5 μm or more 5 μm or less.

3. diaphragm for non-water system secondary battery as claimed in claim 1 or 2, wherein the cementability porous layer also contains Inorganic filler.

4. diaphragm for non-water system secondary battery as claimed in claim 3, wherein the inorganic filler is selected from metal hydroxide It is at least one kind of in object and metal oxide.

5. diaphragm for non-water system secondary battery as claimed in claim 3, wherein the inorganic filler is magnesium hydroxide and oxidation At least either in magnesium.

6. the diaphragm for non-water system secondary battery as described in any one of claim 3~5, wherein the cementability Porous The content of the inorganic filler in layer is 40 volume % or more, 85 bodies of the solid state component total amount of the cementability porous layer Product % or less.

7. non-aqueous secondary battery, the right for having positive, cathode and being configured between the anode and the cathode is wanted Seek the diaphragm for non-water system secondary battery described in any one of 1~6, the non-aqueous secondary battery is mixed by the doping of lithium/de- It is miscellaneous and obtain electromotive force.