WO2020184351A1

WO2020184351A1 - Separator for nonaqueous secondary batteries, and nonaqueous secondary battery

Info

Publication number: WO2020184351A1
Application number: PCT/JP2020/009271
Authority: WO
Inventors: 裕佳子新部; 水野　直樹
Original assignee: 東レ株式会社
Priority date: 2019-03-13
Filing date: 2020-03-04
Publication date: 2020-09-17
Also published as: JPWO2020184351A1

Abstract

The present invention relates to a separator for nonaqueous secondary batteries, which is provided with a polyolefin porous membrane and a porous layer that is superposed on at least one surface of the polyolefin porous membrane, and which is configured such that: the porous layer contains a vinylidene fluoride-hexafluoropropylene copolymer and a hydrophobic ionic liquid-type antistatic agent that is soluble in a nonaqueous electrolyte solution; the vinylidene fluoride-hexafluoropropylene copolymer has from 0.3 mol% to 10 mol% (inclusive) of a hexafluoropropylene unit, while having a weight average molecular weight of from 350,000 to 2,000,000 (inclusive); the hydrophobic ionic liquid-type antistatic agent that is soluble in a nonaqueous electrolyte solution is a fluorine-containing quaternary ammonium salt which contains, as a cation, a quaternary ammonium ion that has one or more hydrocarbon groups having 4 or more carbon atoms.

Description

Separator for non-water secondary battery and non-water secondary battery

The present invention is a battery separator in which a porous layer containing a polyvinylidene fluoride resin is laminated on a porous film made of a polyolefin resin, which has excellent adhesion to an electrode material and has antistatic properties. In particular, the present invention relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery, which are useful as a separator for a lithium ion battery.

Porous membranes made of thermoplastic resins are widely used as materials for separation, selective permeation and isolation of substances. For example, various filters such as battery separators for lithium secondary batteries, nickel-hydrogen batteries, nickel-cadmium batteries, and polymer batteries, separators for electric double layer capacitors, reverse osmosis filtration membranes, ultrafiltration membranes, and precision filtration membranes. , Used in breathable waterproof clothing, medical materials, etc. In particular, polyethylene porous membranes are suitably used as separators for lithium ion secondary batteries because of their excellent electrical insulation, ion permeability due to impregnation with electrolyte, electrolyte resistance and oxidation resistance. This is because it not only has excellent properties, but also has a hole closing effect of blocking the current at a temperature of about 120 to 150 ° C. at the time of abnormal temperature rise of the battery and suppressing excessive temperature rise. However, if the temperature of the polyethylene porous membrane continues to rise even after the pores are closed for some reason, the membrane may rupture at a certain temperature due to a decrease in viscosity of the melted polyethylene constituting the membrane and shrinkage of the membrane. In addition, if left at a constant high temperature, the melted polyethylene may decrease in viscosity and the film may shrink, resulting in film rupture after a certain period of time. This phenomenon is not limited to the polyethylene porous membrane, and even when another thermoplastic resin is used, it cannot be avoided above the melting point of the resin constituting the porous membrane.

In particular, separators for lithium-ion batteries are deeply involved in battery characteristics, battery productivity, and battery safety, and have excellent ion permeability, adhesion to electrode materials, hole closure characteristics (shutdown characteristics), and melt film rupture prevention characteristics. (Meltdown prevention characteristics), antistatic properties, etc. are required. In order to impart adhesiveness to the electrode material, a method of laminating a porous layer containing a polyvinylidene fluoride-based resin is preferably used.

Adhesion with the electrode material is required for the following reasons.

The adhesiveness between the electrode material and the battery separator (hereinafter, may be referred to as wet adhesiveness) in the presence of the electrolytic solution in the battery is deeply related to the battery characteristics, and excellent adhesiveness is required. Be done.

Further, in general, the electrode material and the separator are heated at about 50 ° C. to 100 ° C. during the transport process to soften the polyvinylidene fluoride-based resin and bond them by pressure (referred to as a dry pressure bonding step).
When transporting an electrode body composed of an electrode material and a battery separator, if the members are not sufficiently adhered, the electrode and the separator will be peeled off and it will not be possible to transport the electrode body with good yield. In addition, it becomes apparent due to the increase in size of the battery, and there is a concern that the yield may be further deteriorated. Therefore, in order to prevent the separator from being peeled off during transportation, the separator is required to have adhesiveness to the electrode (hereinafter referred to as dry adhesiveness).

Antistatic properties are required for the following reasons. The polyvinylidene fluoride-based resin has a property of being easily charged, and exhibits a property of having strong static electricity due to friction or peeling. On the other hand, the battery separator is distributed as a reel-shaped winding body, and the winding body is unwound when it is inserted between the positive and negative electrodes to form an electrode group. Therefore, when the active material, which is an electrode material that easily falls off, reattaches due to the static electricity of the separator and becomes a wound body, the fallen active material agglomerates are caught between the electrode and the battery separator, and a short circuit is easily induced. May become. As the capacity of batteries increases in the future, the thickness of the polyolefin porous membrane tends to become thinner, and it is expected that this tendency of decreasing short-circuit resistance will become more remarkable. Further, static electricity makes it difficult to slip, and handleability may become a problem in the battery manufacturing process. Even if a static electricity removing step for removing static electricity from the separator is provided, it is difficult to remove static electricity throughout the battery manufacturing process. Therefore, studies have been made so far on adding various antistatic agents to the porous layer.

In Patent Document 1, a coating solution obtained by dissolving a vinylidene fluoride-hexafluoropropylene copolymer in a mixed solvent of dimethylacetamide / tripropylene glycol is applied to a polyethylene porous film, and then immersed in a coagulation solution. A separator for a non-aqueous secondary battery is obtained by solidifying with water, washing with water, and drying.

In Patent Document 2, an aramid resin is coated on the surface of a porous polyethylene film as a base material, and NNN-trimethyl-n- (2-hydroxy-3-methacryloyloxy) as an antistatic agent is applied to the aramid-porous polyethylene laminated film. An example is a separator coated with a 50% by mass aqueous solution of propyl) ammonium chloride.

In Patent Document 3, a coating liquid in which a polyvinylidene fluoride-based resin and acetylene black are mixed is applied to a polyethylene porous membrane to obtain a separator for a non-aqueous secondary battery.

Patent Document 4 contains a polyether ester amide and LiN (CF ₃ SO ₂ ) ₂ in order to impart an antistatic function to a vinylidene fluoride resin (weight average molecular weight: about 300,000, homopolymer) in a polyethylene porous film. The coating liquid to be coated is applied and immersed in a poor solvent to obtain a separator for electronic parts.

Patent Document 5 discloses a coating separation membrane using a polyvinylidene fluoride (PVDF) and a fluoroquaternary ammonium salt as an antistatic agent, using a polyethylene film having a thickness of 20 μm as the separation membrane base material. Specifically, tetraethylammonium hexafluorophosphate is exemplified as a fluorine-based quaternary ammonium salt.

The battery separator of Patent Document 1 does not have antistatic properties.

Although the generation of static electricity was suppressed in the battery separators of Patent Documents 2 to 4, none of them satisfied the dry adhesiveness, wet adhesiveness and rate characteristics with the electrode material.

Here, the rate characteristic referred to in the present specification is the ratio of the discharge capacity to the nominal battery capacity under a specific discharge condition (discharge capacity (Ah) / nominal capacity (Ah)), and represents the discharge characteristic of the battery. For example, discharging a battery with a nominal capacity of 20 Ah at a discharge rate of 1 C means discharging at a constant temperature with a discharge current of 20 A, and a rate of 1 C from the discharge capacity (Ah) until the specified voltage is reached. The characteristics can be obtained.

As for the rate characteristics, the larger this value is, the better the charge / discharge characteristics are. In addition to the active material, the rate characteristics are also affected by the voltage drop due to the internal resistance of the cell.

Japanese Patent No. 4988973 Japanese Patent Application Laid-Open No. 2008-16238 Japanese Patent No. 5873605 Japanese Patent Application Laid-Open No. 2005-190736 Japanese Patent Application Laid-Open No. 2015-079752

The present invention has been made in view of the above circumstances, and is excellent in adhesiveness to an electrode material and antistatic property, and is capable of retaining excellent rate characteristics and cycle characteristics when used in a non-aqueous secondary battery. It is an object of the present invention to provide a separator for a water secondary battery.

The present invention has the following configuration.

The separator for a non-aqueous secondary battery according to the embodiment of the present invention (hereinafter, may be simply referred to as a battery separator) is laminated on the polyolefin porous film and at least one surface of the polyolefin porous film. A separator for a non-aqueous secondary battery including a porous layer, wherein the porous layer contains a vinylidene fluoride-hexafluoropropylene copolymer and a hydrophobic ionic liquid antistatic agent that dissolves in a non-aqueous electrolytic solution. The vinylidene fluoride-hexafluoropropylene copolymer has a hexafluoropropylene unit of 0.3 mol% or more and 10 mol% or less, has a weight average molecular weight of 350,000 or more and 2 million or less, and is soluble in the non-aqueous electrolytic solution. The hydrophobic ionic liquid antistatic agent is a fluorine-based quaternary ammonium salt containing a quaternary ammonium ion having at least one hydrocarbon group having C4 or more carbon atoms as a cation.

The separator for a non-aqueous secondary battery according to the embodiment of the present invention preferably contains a fluorine-containing anion having a van der Waals volume of 0.08 nm ³ or more as an anion.

The battery separator according to the embodiment of the present invention contains a hydrophobic ionic liquid antistatic agent that dissolves in the non-aqueous electrolytic solution in an amount of 0.3 to 30% by mass based on the vinylidene fluoride-hexafluoropropylene copolymer. It is preferable to do so.

The battery separator according to the embodiment of the present invention preferably contains inorganic particles in the porous layer.

The battery separator according to the embodiment of the present invention preferably has a polyolefin porous membrane having a thickness of 16 μm or less.

The battery separator according to the embodiment of the present invention preferably has a polyolefin porous membrane having a thickness of 7 μm or less.

Further, the non-aqueous secondary battery according to the embodiment of the present invention is characterized in that the separator for the non-aqueous secondary battery of the present invention is used.

The separator for a non-aqueous secondary battery of the present invention is excellent in adhesiveness to an electrode material and antistatic property, and can be suitably used particularly when an electrode and a battery separator are superposed at a high speed to manufacture an electrode body. .. Further, a hydrophobic ionic liquid antistatic agent (hereinafter, may be abbreviated as an ionic liquid antistatic agent) that dissolves in an electrolytic solution is contained in a porous layer containing a vinylidene fluoride-hexafluoropropylene copolymer. Not only can antistatic properties be obtained, but when used in non-aqueous secondary batteries, deformation (crushing) of the porous structure of the porous layer can be minimized in the dry crimping process of the battery assembly process, resulting in this. As a result, excellent rate characteristics and cycle characteristics can be maintained after the battery is assembled.

The hydrophobicity referred to in the present invention means that it has water repellency or has a solubility in water at 23 ° C. of 1% by mass or less.

FIG. 1 is a schematic view showing a method for evaluating wet adhesiveness.

The battery separator according to the embodiment of the present invention is a porous film made of a polyolefin resin, which contains a vinylidene fluoride-hexafluoropropylene copolymer having a specific molecular weight and a copolymerization ratio and an ionic liquid antistatic agent. It is a laminated layer, and has excellent adhesion to the electrode material and antistatic properties, and is not easily charged with static electricity, so it is excellent in transportability and handleability. Furthermore, it has the feature of retaining excellent rate characteristics and cycle characteristics when used as a separator for non-aqueous secondary batteries, and in particular, a pouch manufactured by processing a battery separator and an electrode material via a dry crimping process. Effective for type batteries.

Here, excellent wet adhesiveness with the electrode material means that the wet adhesive force according to the measurement method described later is 3.0 N or more, preferably 3.5 N or more, and more preferably 4.0 N or more. .. If it is less than 3.0 N, cell deformation occurs due to expansion and contraction of the electrode during the battery cycle test, and long-term reliability is lowered. On the other hand, when the wet adhesive force is 3.0 N or more, cell deformation due to electrode expansion and contraction during the battery cycle test is less likely to occur, and long-term reliability is improved. There is no particular upper limit to the wet adhesive strength, but 30 N is sufficient for wet adhesive strength.

The separator for a non-aqueous secondary battery according to the embodiment of the present invention is soluble in an ionic liquid antistatic agent, a vinylidene fluoride-hexafluoropropylene copolymer and a vinylidene fluoride-hexafluoropropylene copolymer. A resin solution composed of a solvent miscible with water (hereinafter, may be abbreviated as a coating liquid) is applied to a predetermined porous film to form a coating layer, and then the coating layer is formed. Is made porous (formation of a three-dimensional network structure). If necessary, a phase separation aid may be added to the coating liquid. Examples of the phase separation aid include water, ethylene glycol, propylene glycol, tetramethylene glycol, neopentyl glycol and the like.

First, the polyolefin porous membrane used in the embodiment of the present invention will be described. As the resin constituting the polyolefin porous film, a polyolefin-based resin is used, and a polyethylene resin, a polypropylene resin, and a mixture thereof are particularly preferable. This is because, in addition to basic characteristics such as electrical insulation and ion permeability, it has a hole closing effect that cuts off the current and suppresses an excessive temperature rise when the battery temperature rises abnormally.

Further, the resin constituting the polyolefin porous membrane is preferably from the viewpoint of process workability and mechanical strength to withstand various external pressures generated at the time of winding with the electrode, for example, tensile strength, elastic modulus, elongation, and piercing strength. The weight average molecular weight is 300,000 or more, more preferably 400,000 or more, and most preferably 500,000 or more. When these resins are used, it is preferable that the polyolefin component having a weight average molecular weight in the above range is contained in an amount of 50% by mass or more, and more preferably 60% by mass or more. If the content is within the above range, the melt viscosity is not too low, and deterioration of mechanical properties when the temperature rises beyond the pore closing temperature can be suppressed, and winding pressure and burrs at the electrode ends can be suppressed even near the pore closing temperature. Can reduce the possibility of melt rupture.

The phase structure of the porous polyolefin membrane differs depending on the manufacturing method. As long as it is within the range that satisfies the above various characteristics, it is possible to freely have a phase structure according to the purpose by the manufacturing method.
Methods for producing a porous polyolefin membrane include a foaming method, a phase separation method, a dissolution recrystallization method, a stretch opening method, a powder sintering method, etc. Among these, the phase is considered in terms of homogenization of fine pores and cost. The separation method is preferred.

The polyolefin porous membrane preferably has a function of closing pores (pore closing function) when the charge / discharge reaction is abnormal. Therefore, the melting point (softening point) of the constituent resin is preferably 70 to 160 ° C, more preferably 80 to 140 ° C, and most preferably 100 to 130 ° C. If the temperature is 70 ° C. or higher, the possibility that the hole closing function is exhibited during normal use and the battery becomes unusable can be reduced, and if the temperature is 160 ° C. or lower, the hole closing function is developed before the abnormal reaction sufficiently progresses. Therefore, safety can be ensured.

The film thickness of the polyolefin porous membrane is preferably 16 μm or less. The upper limit is preferably 9 μm or less, more preferably 7 μm or less. The lower limit is preferably 4 μm or more, more preferably 5 μm or more. If it is 4 μm or more, it can have practical film strength and pore closing function, and if it is 16 μm or less, the area per unit volume of the battery case is not restricted, and the high capacity of the battery will be advanced in the future. Suitable for conversion.

The upper limit of the air permeability resistance (JIS-P8117) of the polyolefin porous membrane is preferably 500 seconds / 100 ccAir or less, more preferably 400 seconds / 100 ccAir or less, most preferably 300 seconds / 100 ccAir or less, and the lower limit is preferably 50. Seconds / 100ccAir or more, more preferably 70 seconds / 100ccAir or more, and most preferably 100 seconds / 100ccAir or more. Sufficient rate characteristics can be obtained when the air permeation resistance is 500 seconds / 100 ccAir or less.

The upper limit of the porosity of the polyolefin porous membrane is 70% or less, preferably 60% or less, and more preferably 55% or less. The lower limit is 30% or more, preferably 35% or more, and more preferably 40% or more. Whether the air permeation resistance is higher than 500 seconds / 100 ccAir or the porosity is lower than 30%, it is closely related to ion permeability (charge / discharge operating voltage) and battery life (holding amount of electrolyte). ) Is not sufficient, and if it exceeds these ranges, it may not be possible to fully exert its function as a battery. On the other hand, even if the air permeation resistance is lower than 50 seconds / 100 ccAir or the porosity is higher than 70%, sufficient mechanical strength and insulation cannot be obtained, and a short circuit may occur during charging / discharging. The sex becomes high.

The average pore size of the polyolefin porous membrane has a great influence on the pore closing rate, and is therefore 0.01 to 1.0 μm, preferably 0.05 to 0.5 μm, and more preferably 0.1 to 0.3 μm. When the average pore size is 0.01 μm or more, the anchor effect of the vinylidene fluoride-hexafluoropropylene copolymer can be obtained, and sufficient adhesiveness of the porous layer can be obtained. When the average pore diameter is 1.0 μm or less, it is possible to suppress the slow response of the pore closing phenomenon to the temperature and reduce the possibility that the pore closing temperature shifts to a higher temperature side due to the temperature rise rate. .. For the average pore size of the porous film, the surface of the film was measured by SEM (Scanning Electron Microscope) at an appropriate magnification, and any 10 points were selected on the obtained image, and the pore diameters of those 10 points were selected. It can be calculated from the average value of.

Next, the porous layer used in the embodiment of the present invention will be described.

The porous layer contains a vinylidene fluoride-hexafluoropropylene copolymer having a specific molecular weight and a copolymerization ratio, and plays a role of imparting wet and dry adhesiveness to the electrode material. Therefore, the melting point of the vinylidene fluoride-hexafluoropropylene copolymer constituting the porous layer is preferably 60 ° C. or higher, more preferably 80 ° C. or higher, most preferably 100 ° C. or higher, and the upper limit is preferably 160 ° C. or lower. , More preferably 155 ° C or lower, and most preferably 150 ° C or lower. Within the above range, appropriate wet adhesiveness and dry adhesiveness with the electrode material can be obtained. In particular, when the melting point is 160 ° C. or lower, wet adhesiveness and dry adhesiveness with the electrode material can be obtained.

The vinylidene fluoride-hexafluoropropylene copolymer used for the porous layer will be described in detail below.

The lower limit of the hexafluoropropylene unit content in the vinylidene fluoride-hexafluoropropylene copolymer is 0.3 mol% or more, preferably 0.8 mol% or more, more preferably 1.0 mol% or more, and the upper limit is 10 mol% or less. It is preferably 5 mol% or less, more preferably 4 mol% or less, and most preferably 3 mol% or less. The lower limit of the weight average molecular weight is 350,000 or more, preferably 500,000 or more, and more preferably 650,000 or more. On the other hand, the upper limit is 2 million or less, preferably 1.5 million or less, and more preferably 1.2 million or less.
The weight average molecular weight is a polystyrene-equivalent value obtained by gel permeation chromatography.

If the content of hexafluoropropylene units is less than 0.3 mol%, sufficient dry adhesiveness may not be obtained. If it exceeds 10 mol%, the three-dimensional network structure of the porous layer is easily deformed. If the molecular weight is less than 350,000, sufficient wet adhesiveness may not be obtained. If it exceeds 2 million, the solubility in a solvent decreases and it becomes difficult to prepare a coating solution.
When the ratio of hexafluoropropylene units and the weight average molecular weight in the vinylidene fluoride-hexafluoropropylene copolymer are within the above ranges, the porous layer is formed by interaction with an ionic liquid antistatic agent in the dry pressure bonding step. Deformation of the three-dimensional network structure is suppressed, and as a result, excellent rate characteristics can be obtained when incorporated into a battery. That is, by using an ionic liquid antistatic agent and a vinylidene fluoride-hexafluoropropylene copolymer having the ratio and weight average molecular weight of the hexafluoropropylene unit, antistatic property, dry adhesive property, and wet adhesive property are imparted. Not only can these interactions be possible, but deformation of the three-dimensional network structure of the porous layer in the dry pressure bonding step can also be suppressed. This is an unexpected effect.

Next, the ionic liquid antistatic agent will be described. It is important that the ionic liquid antistatic agent used in the embodiment of the present invention has an affinity for a solvent that dissolves the vinylidene fluoride-hexafluoropropylene copolymer, dissolves in a non-aqueous electrolytic solution, and is further hydrophobic. Is. A commonly used antistatic agent that adsorbs moisture in the air to impart antistatic properties cannot obtain the effect of retaining rate characteristics.

The ionic liquid antistatic agent used in the embodiment of the present invention is a fluorinated quaternary ammonium salt.

Specific examples of the fluorine-based quaternary ammonium salt include a quaternary ammonium ion having at least one hydrocarbon group having C4 or more carbon atoms as a cation and a van der Waals volume of 0.08 nm ³ or more as an anion. It preferably has a fluorine-containing anion. A quaternary ammonium cation having a carbon number C within the above range and van der Waals with respect to vinylidene fluoride having an electron attracting property and hexafluoropropylene having a higher electron attracting property, which are constituents of the porous layer. When an ionic liquid antistatic agent having a fluorine-containing anion having a volume in the above range is used, the charge is appropriately delocalized, the compatibility is good, and bleed-out is unlikely to occur. Therefore, dry adhesion due to bleed-out Can be suppressed.
Although the mechanism by which such cations and anions are used to improve compatibility and make bleed-out less likely to occur is not clear, the inventors think as follows. In the ionic bond compound containing a fluoroquaternary ammonium salt, the charge density decreases in proportion to the structure of the side chain (the number of carbon atoms in the side chain), and the charge is delocalized. Fluorine-based quaternary ammonium salt, vinylidene fluoride constituting the porous layer - vinylidene fluoride through interaction with CF ₂ chain in hexafluoropropylene copolymer - are considered to be compatible with hexafluoropropylene copolymer When a quaternary ammonium ion having no hydrocarbon group having C4 or more carbon atoms is used as the cation, the charge density is high and the charge is localized, so that the fluoridene-hexafluoropropylene copolymer weight is high. It is presumed that the interaction with the coalescence becomes excessive and does not uniformly dissolve, and bleed-out is likely to occur.
Further, in the ionic bonding compound containing a fluorine-based quaternary ammonium salt, the charge density decreases in proportion to the van der Waals volume of the constituent ions, and the charge is delocalized. Therefore, by using a fluorine-containing anion having a van der Waals volume of 0.08 nm ³ or more as an anion, an increase in charge density and localization of electric charge are suppressed, and compatibility is further improved, so that bleed-out is less likely to occur. It is estimated that it will be.

As specific examples of the cations constituting the fluoroquaternary ammonium salt, for example, tetrabutylammonium, tributylmethylammonium, tributylethylammonium, tetrapentylammonium and the like can be used, and tributylmethylammonium is preferable.

Specific examples of the fluorine-containing anions constituting the fluorine-based quaternary ammonium _{_{_{^{_{salt, N (SO 2 CF 3)}}}}} 2 -, N (SO 2 F) 2 -, N (SO 2 CF 3) (COCF 3) - , N (SO ₂ CF ₃ ) (SO ₂ C ₂ F ₅ ) ⁻ , and the like, and N (SO ₂ CF ₃ ) ₂ ⁻ is preferable.

By using these ionic liquid antistatic agents, not only can antistatic properties be imparted to the battery separator, but also excellent rate characteristics can be maintained when used as a non-aqueous secondary battery separator. The present inventors presume the mechanism by which the ionic liquid antistatic agent affects the rate characteristics as follows.

The porous layer is a resin solution composed of an ionic liquid antistatic agent, a vinylidene fluoride-hexafluoropropylene copolymer, and a solvent that is soluble in the vinylidene fluoride-hexafluoropropylene copolymer and is compatible with water. Is coated on the porous polyolefin film to form a coating layer, and the vinylidene fluoride-hexafluoropropylene copolymer and the solvent to be mixed with water are phase-separated. Further, the copolymer is put into a water bath (coagulation bath) to coagulate the vinylidene fluoride-hexafluoropropylene copolymer, washed with water, and dried to form a three-dimensional network structure.
Here, in the coagulation bath, the solvent dissolves from the coating layer into the coagulation bath, but the ionic liquid antistatic agent used in the embodiment of the present invention is hydrophobic and has low volatility, so that it can be used as a battery separator. Even after this, a part remains in the three-dimensional network structure of the porous layer. The ionic liquid antistatic agent remaining in the three-dimensional network structure imparts the effect of imparting elasticity to the porous layer and the effect of filling the pores, and has a specific molecular weight and a specific hexafluoropropylene copolymerization ratio. It is presumed that the effect of suppressing deformation of the porous layer in the dry pressure bonding step can be obtained by the interaction with the vinylidene fluoride-hexafluoropropylene copolymer having both electrode adhesiveness and film strength. This is an effect that cannot be obtained when the inside of the three-dimensional network structure of the porous layer is simply a cavity.
Furthermore, when used as a separator for non-aqueous secondary batteries, the vinylidene fluoride-hexafluoropropylene copolymer swells due to the injection of an electrolytic solution in the battery assembly process, and most of the three-dimensional network structure becomes gel-like. However, swelling is suppressed in the portion where the ionic liquid antistatic agent remains. Over time, the ionic liquid antistatic agent is replaced with the electrolytic solution, and the electrolytic solution partially remains in a liquid state.

Considering that the ion permeability is greater in the order of solid containing almost no electrolytic solution, gel state containing electrolytic solution, and electrolytic solution in liquid state, the porous layer is an electrolytic solution formed by an ionic liquid antistatic agent. When the pores are filled, the ionic liquid antistatic agent is not contained, and the ion permeability is improved as compared with the case where the entire porous layer is in a gel state.

In addition, since the ionic liquid antistatic agent is hydrophobic, it also has the effect of suppressing the adverse effect of moisture on the battery. When the antistatic agent is hydrophilic, the water adsorbed on the hydrophilic antistatic agent of the battery separator mounted in the battery may react with the electrolytic solution to generate gas. In addition, the presence of water consumes lithium ions, which reduces the cycle life of the entire battery.

The method for containing the ionic liquid antistatic agent in the porous layer is not particularly limited as long as the separator according to the embodiment of the present invention can be produced, but for example, it may be added to a coating liquid and mixed sufficiently evenly. Can be done. The amount of the ionic liquid antistatic agent added to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer in the coating liquid can be regarded as the content in the porous layer. The amount of the ionic liquid antistatic agent added to the total mass of the vinylidene fluoride-hexafluoropropylene copolymer is preferably 0.3 to 30% by mass, more preferably 0.5 to 20% by mass, and further preferably 1. It is 0 to 15% by mass. In the above range, the electric charge generated by the peeling or friction of the separator can be effectively dispersed. If the addition amount is 0.3% or more, a sufficient charge diffusion path can be formed to diffuse the charge generated in the separator and obtain an antistatic effect. Further, when the addition amount is 30% by mass or less, the diffusivity of electric charge can be obtained.
As the vinylidene fluoride-hexafluoropropylene copolymer, a hexafluoropropylene copolymer or two or more kinds of vinylidene fluoride-hexafluoropropylene copolymers having different weight average molecular weights may be mixed. Further, another fluororesin such as polytetrafluoroethylene may be added. Since these copolymers have high affinity with non-aqueous electrolytes and high chemical and physical stability with respect to non-aqueous electrolytes, they maintain sufficient affinity with electrolytes even when used at high temperatures. it can.

Solvents that can be used to dissolve the vinylidene fluoride-hexafluoropropylene copolymer include N, N-dimethylacetamide (DMAc), N-methyl-2-pyrrolidone (NMP), and hexamethyltriamide phosphate (HMPA). ), N, N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), γ-butyrolactone, chloroform, tetrachloroethane, dichloroethane, 3-chloronaphthalene, parachlorophenol, tetraline, acetone, acetonitrile, etc. It can be freely selected according to the solubility.

The solid content concentration of the coating liquid is not particularly limited as long as it can be coated uniformly, but is preferably 2% by mass or more and 50% by mass or less, and more preferably 4% by mass or more and 40% by mass or less. When the solid content concentration is 2% by mass or more, the obtained porous layer is less likely to become brittle. Further, if it is 50% by mass or less, the thickness of the porous layer can be easily controlled.

In order to reduce the heat shrinkage rate of the porous layer and impart slipperiness, the porous layer preferably contains inorganic particles or heat-resistant polymer particles, and preferably contains inorganic particles. In order to contain the inorganic particles or the heat-resistant polymer particles in the porous layer, the inorganic particles or the heat-resistant polymer particles may be added to the coating liquid. When particles are added, the content of particles in the porous layer is preferably 85% by volume or less, more preferably 75% by volume, with the total of vinylidene fluoride-hexafluoropropylene copolymer and particles as 100% by volume. % Or less, more preferably 70% by volume or less. The lower limit is preferably 20% by volume or more, more preferably 30% by volume or more, and further preferably 50% by volume or more. If it is 85% by volume or less, the ratio of the polyvinylidene fluoride-based resin to the total volume of the porous layer does not become too small, which not only suppresses the deterioration of the adhesiveness with the electrode material, but also with respect to the porous polyolefin membrane. Sufficient adhesiveness of the vinylidene fluoride-hexafluoropropylene copolymer can be obtained. If it is 20% by volume or more, a sufficient effect of reducing the heat shrinkage rate can be obtained.

Inorganic particles include calcium carbonate, calcium phosphate, amorphous silica, crystalline glass filler, kaolin, talc, titanium dioxide, alumina, silica-alumina composite oxide particles, barium sulfate, calcium fluoride, lithium fluoride, and zeolite. , Molybdenum sulfide, mica, zeolite and the like. Examples of the heat-resistant polymer particles include crosslinked polystyrene particles, crosslinked acrylic resin particles, crosslinked methyl methacrylate-based particles, benzoguanamine / formaldehyde condensate particles, melamine / formaldehyde condensate particles, and polytetrafluoroethylene particles. ..

In the separator for a non-aqueous secondary battery according to the embodiment of the present invention, the porous layer may be laminated on at least one surface of the polyolefin porous membrane, but it may be laminated on both sides of the polyolefin porous membrane. preferable.

The film thickness of the porous layer is preferably 0.5 to 6 μm per side, more preferably 1 to 5 μm, and even more preferably 1 to 4 μm. If the film thickness is 0.5 μm or more, sufficient adhesiveness to the electrode material can be obtained, and if it is 6 μm or less, the winding volume does not become too large, and it is suitable for increasing the capacity of batteries that will be advanced in the future. ing.

The upper limit of the total thickness of the battery separator obtained by laminating the polyolefin porous membrane and the porous layer is 25 μm or less, more preferably 20 μm or less. The lower limit is preferably 6 μm or more, more preferably 7 μm or more. If the total thickness of the battery separator is 25 μm or less, a sufficient electrode area that can be filled in the container can be sufficiently secured, and a decrease in capacity can be avoided. Further, if the total thickness of the battery separator is 6 μm or more, sufficient mechanical strength and insulating properties can be ensured.

The air permeability resistance of the battery separator is preferably 50 to 600 seconds / 100 ccAir, more preferably 100 to 500 seconds / 100 ccAir, and most preferably 100 to 400 seconds / 100 ccAir. If the air permeability resistance is 50 seconds / 100 ccAir or more, sufficient insulation can be obtained, the possibility of foreign matter clogging, short circuit, or film rupture can be reduced, and if it is 600 seconds / 100 ccAir or less, the film resistance is low. Rate characteristics and cycle characteristics within the range that can be actually used can be obtained.

The water content of the battery separator is preferably 0 to 1000 ppm, more preferably 0 to 800 ppm, and most preferably 0 to 500 ppm. Moisture contained in the electrolytic solution, the electrode, and the separator, which are battery members, causes decomposition of the electrolytic solution during charging and discharging, which causes deterioration of battery performance. It is desirable that the water content of each member is small, and if the water content of the separator is 1000 ppm or less, the battery performance is not deteriorated and cycle characteristics within a practically usable range can be obtained.

Next, a method for manufacturing the battery separator according to the embodiment of the present invention will be described.

The porous layer is formed by coating a polyolefin porous film with a coating solution composed of an ionic liquid antistatic agent, a vinylidene fluoride-hexafluoropropylene copolymer, a solvent, and if necessary, particles. A coating layer is formed, the vinylidene fluoride-hexafluoropropylene copolymer and the solvent are phase-separated, and the polymer is further put into a water bath (coagulation bath) to coagulate the vinylidene fluoride-hexafluoropropylene copolymer and washed with water. , A three-dimensional network structure is formed by drying.

Examples of the method of applying the coating liquid onto the porous polyolefin film include a reverse roll coating method, a gravure coating method, a kiss coating method, a roll brushing method, a spray coating method, an air knife coating method, a wire barber coating method, and a pipe doctor. Examples thereof include a method, a blade coating method and a die coating method, and these methods can be performed alone or in combination.

The coagulation bath preferably contains water as a main component, preferably an aqueous solution containing 1 to 20% by mass of a good solvent for the vinylidene fluoride-hexafluoropropylene copolymer, and more preferably an aqueous solution containing 5 to 15% by mass. .. Examples of a good solvent include N-methyl-2-pyrrolidone, N, N-dimethylformamide, and N, N-dimethylacetamide. The immersion time in the coagulating liquid is preferably 3 seconds or longer. The upper limit is not limited, but 10 seconds is sufficient.

Water can be used for cleaning. The drying can be performed by using hot air of, for example, 100 ° C. or lower.

Hereinafter, examples will be described in detail, but the present invention is not limited to these examples. The measured values in the examples were measured by the following method.

(1) Film thickness The film thickness was measured using a contact type film thickness meter (Digital Micrometer M-30 manufactured by Sony Manufacturing Co., Ltd.).

(2) Wet Adhesiveness Generally, when a fluororesin binder is used for the positive electrode and a porous layer containing the fluororesin is provided on the separator, the adhesiveness is easily ensured by mutual diffusion between the fluororesins. On the other hand, a binder other than the fluororesin is used for the negative electrode, and diffusion of the fluororesin is unlikely to occur, so that the negative electrode is less likely to obtain adhesiveness to the separator than the positive electrode. Therefore, in this measurement, the wet adhesive force described below was measured and evaluated as an index of the wet adhesiveness between the separator and the negative electrode.

(Preparation of negative electrode)
An aqueous solution containing 1.5 parts by mass of carboxymethyl cellulose was added to 96.5 parts by mass of artificial graphite and mixed, and 2 parts by mass of styrene-butadiene latex as a solid content was added and mixed to obtain a negative electrode mixture-containing slurry. This negative electrode mixture-containing slurry is uniformly applied to both sides of a negative electrode current collector made of copper foil having a thickness of 8 μm and dried to form a negative electrode layer, and then compression-molded by a roll press to collect current. A negative electrode was prepared by setting the density of the negative electrode layer excluding the body to 1.5 g / cm ³ .

(Preparation of test winding body)
The negative electrode 11 created above (161 mm in the mechanical direction × 30 mm in the width direction) and the prepared battery separator 10 (160 mm in the mechanical direction × 34 mm in the width direction) are overlapped with each other to form a metal plate (length 300 mm, width 25 mm, thickness 1 mm). The battery separator 10 and the negative electrode 11 were wound around the winding core so that the battery separator 10 was inside, and the metal plate was pulled out to obtain a test winding body 30. The test wound body had a length of about 34 mm and a width of about 28 mm. In addition, each of the above-mentioned reference numerals represents a reference numeral in FIG.

(Measuring method of wet adhesive strength)
Two polypropylene laminated films (length 70 mm, width 65 mm, thickness 0.07 mm) were laminated, and the test winding body 30 was placed in a bag-shaped laminated film 20 in which three of the four sides were welded. .. 500 μL of an electrolytic solution prepared by dissolving LiPF ₆ at a ratio of 1 mol / L in a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 3: 7 is injected through the opening of the laminate film 20 in a glove box, and a test roll is used. The body 30 was impregnated, and one side of the opening was sealed with a vacuum sealer.

Next, the test winding body 30 enclosed in the laminate film 20 is sandwiched between two gaskets (thickness 1 mm, 5 cm × 5 cm), and a precision heating and pressurizing device (manufactured by Shinto Kogyo Co., Ltd., CYPT-10). The pressure was increased at 98 ° C. and 0.6 MPa for 2 minutes, and the mixture was allowed to cool at room temperature (25 ° C.). The wet adhesive strength of the test winding body 30 after pressurization was measured using a universal testing machine (AGS-J, manufactured by Shimadzu Corporation) while being sealed in the laminate film 20. Details will be described below with reference to FIG.

Two aluminum L-shaped angles 40 (thickness 1 mm, 10 mm × 10 mm, length 5 cm) are arranged in parallel so that the 90 ° part faces up, with the ends aligned, and the 90 ° part is the fulcrum. It was fixed so that the distance between them was 15 mm. The aluminum L-shaped angle 40 is aligned with the midpoint of the widthwise side (about 28 mm) of the test winding body at the 7.5 mm point, which is the middle of the distance between the fulcrums of the two aluminum L-shaped angles 40. The test winding body 30 was arranged so as not to protrude from the side in the length direction of.

Next, as an indenter, the side (about 34 mm) in the length direction of the test winding body protrudes from the side in the length direction of the aluminum L-shaped angle 41 (thickness 1 mm, 10 mm × 10 mm, length 4 cm). Align the 90 ° portion of the aluminum L-shaped angle 41 with the midpoint of the widthwise side of the test winding body so that it is not and parallel, and the aluminum L-shaped angle so that the 90 ° portion is on the bottom. 41 was fixed to the load cell (load cell capacity 50N) of the universal testing machine. A total of three test winding bodies were measured at a load speed of 0.5 mm / min, and the average value of the obtained maximum test forces was taken as the wet adhesive force.

(3) Dry adhesive strength (manufacturing of negative electrode)
The same negative electrode as in the case of the wet adhesiveness evaluation was used.

(Preparation of dry adhesive strength test piece)
The negative electrode (70 mm × 15 mm) produced above and the prepared separator (mechanical direction 90 mm × width direction 20 mm) are overlapped, sandwiched between two gaskets (thickness 0.5 mm, 95 mm × 27 mm), and precision heated. It was pressurized at 60 ° C. and 7 MPa for 2 minutes with a pressurizing device (CYPT-10 manufactured by Shinto Kogyo Co., Ltd.) and allowed to cool at room temperature (25 ° C.). A double-sided tape having a width of 1 cm is attached to the negative electrode side of the laminate of the negative electrode and the separator, and the other side of the double-sided tape is placed on a SUS plate (thickness 3 mm, length 150 mm × width 50 mm) in the mechanical direction of the separator. And SUS plate length direction are parallel to each other. This was used as a test piece.

(Measuring method of dry adhesive strength)
A separator was sandwiched between load cell side chucks using a universal testing machine (AGS-J manufactured by Shimadzu Corporation), and a 180-degree peeling test was performed at a test speed of 300 mm / min. The value obtained by averaging the measured values of the strokes from 20 mm to 70 mm during the peeling test was taken as the peeling force of the peeling test piece. A total of three peeling test pieces were measured, and the value obtained by converting the average value of the peeling force into a width was defined as the peeling force during drying (N / m). The peeling force at the time of drying is preferably 2 N / m or more, more preferably 4 N / m or more, and further preferably 6 N / m or more. The upper limit is not particularly set, but if it is 50 N / m or less, it is preferable that the separator wound in a reel shape can be stored without being adhered to each other.
Judgment of the evaluation result is that the peeling force at the time of drying is less than 2 N / m and fails (x), 2 N / m or more and less than 4 N / m passes (C), and 4 N / m or more and less than 6 N / m is good (B). It was evaluated as excellent (A) at 6 N / m or more.

(4) Battery evaluation (rate characteristics, cycle characteristics)
(Preparation of positive electrode)
Lithium cobalt composite oxide LiCoO ₂ as the positive electrode active material, acetylene black as the conductive material, and polyvinylidene fluoride (PVDF) as a binder are mixed at a mass ratio of 93.5: 4.0: 2.5 to form a solvent. A slurry was prepared by mixing and dispersing in N-methylpyrrolidone (NMP). This slurry was applied to both sides of a 12 μm-thick aluminum foil serving as a positive electrode current collector, dried, and then rolled with a roll press. The rolled product was slit to a width of 30 mm to obtain a positive electrode.

(Preparation of negative electrode)
A slurry was prepared by mixing and dispersing artificial graphite as a negative electrode active material, carboxymethyl cellulose as a binder, and styrene-butadiene copolymer latex in purified water so as to have a mass ratio of 98: 1: 1. This slurry was applied to both sides of a copper foil having a thickness of 10 μm as a negative electrode current collector, dried, and then rolled by a roll press. The rolled product was slit to a width of 33 mm to form a negative electrode.

(Non-aqueous electrolyte)
LiPF ₆ as a solute was dissolved in a mixed solvent of ethylene carbonate: ethyl methyl carbonate: dimethyl carbonate = 3: 5: 2 (volume ratio) so as to have a concentration of 1.15 mol / liter. Further, 0.5% by mass of vinylene carbonate was added to 100% by mass of the non-aqueous electrolytic solution to prepare a non-aqueous electrolytic solution.

(Battery production)
After laminating the above positive electrode, the above separator, and the above negative electrode, dry pressure bonding (60 ° C., 2 MPa, 30 sec) was performed to prepare a flat wound electrode body (height 2.2 mm × width 36 mm × depth 29 mm). .. A tab with a sealant was welded to each electrode of this flat wound electrode body to form a positive electrode lead and a negative electrode lead.
The flat wound electrode body is sandwiched between aluminum laminate films, sealed with some openings left, and dried in a vacuum oven at 80 ° C. for 6 hours. After drying, the electrolytic solution is immediately injected. It was sealed with a vacuum sealer and press-molded at 80 ° C. and 1 MPa for 1 hour. Subsequently, charging and discharging were carried out. The charging / discharging condition was a current value of 300 mA, and after charging with a constant current to a battery voltage of 4.2 V, constant voltage charging was performed with a battery voltage of 4.2 V until reaching 15 mA. After a 10-minute pause, a constant current discharge was performed at a current value of 300 mA to a battery voltage of 3.0 V, followed by a 10-minute pause. The above charging and discharging were carried out for 3 cycles to prepare a test secondary battery having a battery capacity of 300 mAh.

(Rate characteristics)
For the rate characteristics, the test secondary battery prepared in the above (manufacturing of the battery) is used, and after constant current charging with a current value of 1.0C up to a battery voltage of 4.2V, the rate characteristic is 0.05C at a battery voltage of 4.2V. Constant voltage charging was performed until the current value was reached, and discharge (constant current discharge) was performed until the battery voltage reached 3.0 V at a current value of 0.2 C, and the discharge capacity was measured. Then, after charging to 4.2V again by the above procedure, discharge (constant current discharge) until the battery voltage reaches 3.0V at a current value of 5C, measure the discharge capacity, and measure the discharge capacity at 0.2C. The ratio of the discharge capacity at 5C to the discharge capacity was defined as the discharge capacity ratio.
This discharge capacity ratio is preferably 80% or more, more preferably 82% or more, still more preferably 85% or more. The upper limit is not particularly set, but it is preferably 98% or less because there is a concern that the self-discharge characteristics may deteriorate due to a decrease in strength.
Judgment of the evaluation result is rejected when the discharge capacity ratio is less than 80% (x), passed when 80% or more and less than 82% (C), good when 82% or more and less than 85% (B), and excellent when 85% or more (A). ).

(Cycle characteristics)
The cycle characteristic test was carried out by placing the produced lithium-ion battery in a constant temperature bath (Yamato Scientific Co., Ltd., DNE-610) and connecting it to a charge / discharge tester (TOSCAT-3000) manufactured by Toyo System. The test temperature of the cycle characteristic test is 30 ° C., and the charging condition is that a current of 1C is passed in the constant current (CC) mode until the voltage of the lithium ion battery reaches 4.35V, and after reaching 4.35V, the constant voltage ( Charging was performed in the CV) mode until the charging current reached 0.05 C.
As for the discharge conditions, a current of 0.5 C was passed in the constant current mode, and the cutoff voltage was set to 3 V. One charge / discharge was set as one cycle, and the charge / discharge test was repeated until a total of 500 cycles was reached.
The ratio of the discharge capacity after 500 cycles to the initial discharge capacity at 0.2C was defined as the cycle characteristic discharge capacity ratio.
The discharge capacity ratio is not particularly set, but is preferably 78% or more, more preferably 80% or more, and further preferably 82% or more.
The evaluation results are judged as rejected when the discharge capacity ratio is less than 78% (x), passed when 78% or more and less than 80% (C), good when 80% or more and less than 82% (B), and (excellent) when 82% or more. It was designated as A.

(5) Antistatic property (measurement of charge voltage)
The charging voltage of the separators produced in the following examples and comparative examples was measured using an electrostatic attenuation measuring device (Static Honestmeter H-0110-S4, manufactured by Sisid Electrostatic Co., Ltd.) under the following conditions.
Test conditions: JIS L1094-1980 compliant Charging method: Corona discharge Applied voltage: ± 10 kV
Application time: 30 seconds Distance between application part (needle electrode) and sample surface: 18 mm
Distance between the power receiving part and the sample surface: 13 mm
Sample size: 45 mm x 45 mm
For the charging voltage on the sample surface, a numerical value measured when the application time reached 30 seconds was adopted. The measurement environment was adjusted to a room temperature of 20 to 24 ° C. and a humidity of 40 to 50%.

(Evaluation of antistatic property)
When the charge voltage on the surface of the sample was 500 V or less, it was determined to be acceptable (◯) as the range in which the antistatic property was exhibited, and when the charge voltage exceeded 500 V, it was determined to be rejected (x).

(6) Moisture content The water content of the separators prepared in the following Examples and Comparative Examples was measured by using the Karl Fischer titration method.
Moisture vaporization conditions:
Equipment: Moisture vaporizer (ADP-611, manufactured by Kyoto Electronics Industry Co., Ltd.)
Atmosphere ... N2 (200mL / min)
Temperature: 150 ° C
Time ... 10 minutes Sample volume: Approximately 1.0 g
Moisture measurement conditions:
Measurement method: Coulometric titration method Device: MKC-610, manufactured by Kyoto Electronics Industry Co., Ltd. Reagent: Chemaqua anode solution AGE, Chemaqua cathode solution CGE (manufactured by Kyoto Electronics Industry Co., Ltd.).

Example 1
(Preparation of coating liquid)
5% by mass of vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, weight average molecular weight 1.2 million, ratio of hexafluoropropylene monomer unit is 0.6 mol%) with respect to N-methyl-2-pyrrolidone To obtain a fluororesin solution in which the PVDF-HFP was completely dissolved. Next, the alumina particles were added to the fluororesin solution while stirring with a mechanical stirrer so that the volume of the alumina particles having an average particle diameter of 1 μm and the volume of PVDF-HFP were 50:50, and then Dynomill (manufactured by Simmal Enterprises). It was completely dispersed using a Dynomill Multilab) to prepare an alumina particle-dispersed fluororesin solution. Next, a hydrophobic ionic liquid antistatic agent (tri-N-butylmethylammonium) was added to the alumina particle-dispersed fluororesin solution so as to be 6% by mass based on the mass of PVDF-HFP contained in the prepared alumina particle-dispersed fluororesin solution. Bistrifluoromethanesulfonimide (Bu ₃ MeNTFSA) was added while stirring with a mechanical stirrer to obtain a coating solution. At this time, the temperature of the coating liquid was adjusted so as to be in the range of 30 to 35 ° C.
The coating liquid was kept sealed so as not to come into contact with the outside air until the time of coating.

(Lamination of porous layers)
An equal amount of coating liquid is applied to both sides of a polyethylene porous membrane (polyolefin porous membrane: thickness 7 μm, air permeability resistance 100 sec / 100 ccAir) by the dip coating method, and water is applied at a temperature of 25 ° C. for about 3 seconds. After being immersed in (coagulating liquid) and washed with pure water, it was passed through a hot air drying furnace at 60 ° C. and dried to obtain a battery separator having a final thickness of 10 μm.

Example 2
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 1.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 3
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 2.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 4
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 1.2 million and a hexafluoropropylene monomer unit ratio of 3.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 5
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the ratio of hexafluoropropylene monomer units is 4.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 6
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 5.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 7
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the ratio of hexafluoropropylene monomer units is 7.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 8
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the ratio of hexafluoropropylene monomer units is 10.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 9
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 350,000 and the proportion of hexafluoropropylene monomer units is 1.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 10
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.8 million and the proportion of hexafluoropropylene monomer units is 1.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that it was replaced with.

Example 11
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 1.0 mol%. A coating solution was obtained in the same manner as in Example 1 except that alumina particles were not used, and the thickness of the porous layer was adjusted to obtain a battery separator having a final thickness of 8 μm.

Example 12
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 1.2 million and a hexafluoropropylene monomer unit ratio of 1.0 mol%. A separator for a battery was obtained in the same manner as in Example 1 except that the volume of alumina particles and the volume of PVDF-HFP were 80:20.

Example 13
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 1.2 million and a hexafluoropropylene monomer unit ratio of 1.0 mol%. A separator for a battery was obtained in the same manner as in Example 1 except that a hydrophobic ion liquid type antistatic agent was blended so as to be 3% by mass based on the mass of PVDF-HFP contained in the alumina particle-dispersed fluororesin solution. It was.

Example 14
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer is a vinylidene fluoride-hexafluoropropylene copolymer having a weight average molecular weight of 1.2 million and a hexafluoropropylene monomer unit ratio of 1.0 mol%. A battery separator was obtained in the same manner as in Example 1 except that the hydrophobic ion liquid type antistatic agent was blended so as to be 14% by mass based on the mass of PVDF-HFP contained in the alumina particle-dispersed fluororesin solution. It was.

Example 15
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 1.0 mol%. A coating liquid was obtained in the same manner as in Example 1 except that the thickness was changed to, a polyethylene porous film having a thickness of 5 μm and an air permeation resistance of 100 sec / 100 ccAir was used, and the thickness of the porous layer was adjusted to a final thickness of 9 μm. A separator for a battery was obtained in the same manner as in Example 1 except for the above.

Example 16
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 1.0 mol%. A coating liquid was obtained in the same manner as in Example 1 except that the thickness was changed to, a polyethylene porous film having a thickness of 12 μm and an air permeation resistance of 170 sec / 100 ccAir was used, and the thickness of the porous layer was adjusted to a final thickness of 15 μm. A battery separator was obtained.

Example 17
In preparation of the coating solution, except for changing the hydrophobic ionic liquid antistatic agent to tetra -N- pentyl ammonium bis trifluoromethane sulfonimide _{_{_{((C 5 H 11) 4}}} NTFSA) in the same manner as in Example 1 battery Separator was obtained.

Example 18
A battery separator was obtained in the same manner as in Example 1 except that the hydrophobic ionic liquid antistatic agent was replaced with tri-N-butylmethylammonium bisfluorosulfonylimide (Bu ₃ MeNFSA) in the preparation of the coating liquid. ..

Comparative Example 1
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and the proportion of hexafluoropropylene monomer units is 1.0 mol%. Instead, a separator for a battery was obtained in the same manner as in Example 1 except that a hydrophobic ion liquid type antistatic agent was not used and an alumina particle-dispersed fluororesin solution was used as a coating liquid.

Comparative Example 2
A battery separator was obtained in the same manner as in Example 1 except that the vinylidene fluoride-hexafluoropropylene copolymer was replaced with homopolyvinylidene fluoride in the preparation of the coating liquid.

Comparative Example 3
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 300,000 and a hexafluoropropylene monomer unit ratio of 1.0 mol% of vinylidene fluoride-hexafluoropropylene copolymer weight. A battery separator was obtained in the same manner as in Example 1 except that the mixture was replaced with a coalesced mixture.

Comparative Example 4
In the preparation of the coating liquid, the vinylidene fluoride-hexafluoropropylene copolymer has a weight average molecular weight of 1.2 million and a hexafluoropropylene monomer unit ratio of 12.0 mol% of vinylidene fluoride-hexafluoropropylene copolymer weight. A battery separator was obtained in the same manner as in Example 1 except that the mixture was replaced with a coalesced mixture.

Comparative Example 5
A battery separator was obtained in the same manner as in Example 1 except that the hydrophobic ionic liquid antistatic agent was replaced with tetrapropylammonium tetrafluoroborate (Pr ₄ NBF ₄ ) in the preparation of the coating liquid.

Comparative Example 6
A battery separator was obtained in the same manner as in Example 1 except that the hydrophobic ionic liquid antistatic agent was replaced with tri-N-butylmethylammonium hexafluorophosphorate (Bu ₃ MeNPF ₆ ) in the preparation of the coating liquid. It was.

The separator for a non-aqueous secondary battery of the present invention is excellent in adhesiveness to an electrode material and antistatic property, and can be suitably used particularly when an electrode and a battery separator are superposed at a high speed to manufacture an electrode body. .. Furthermore, by incorporating a hydrophobic ionic liquid antistatic agent that dissolves in the electrolytic solution in the porous layer containing the vinylidene fluoride-hexafluoropropylene copolymer, not only antistatic properties can be obtained, but also the dryness of the battery assembly process can be obtained. In the crimping process, deformation (crushing) of the porous structure of the porous layer can be suppressed to a minimum, and as a result, excellent rate characteristics and cycle characteristics can be maintained after battery assembly.

Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention.
This application is based on a Japanese patent application filed on March 13, 2019 (Japanese Patent Application No. 2019-046493), the contents of which are incorporated herein by reference.

10 ... Battery separator 11 ... Negative electrode (for adhesive evaluation)
20 ... Laminated film 30 ... Test winding body 40 ... Aluminum L-shaped angle (lower side)
41 ... Aluminum L-shaped angle (upper side)

Claims

A separator for a non-aqueous secondary battery including a polyolefin porous film and a porous layer laminated on at least one surface of the polyolefin porous film, wherein the porous layer is a vinylidene fluoride-hexafluoropropylene copolymer. The vinylidene fluoride-hexafluoropropylene copolymer has a hexafluoropropylene unit of 0.3 mol% or more and 10 mol% or less, and contains a hydrophobic ionic liquid type antistatic agent that dissolves in a non-aqueous electrolytic solution, and has a weight average. The hydrophobic ionic liquid antistatic agent having a molecular weight of 350,000 or more and 2 million or less and dissolved in the non-aqueous electrolytic solution is a quaternary ammonium ion having at least one hydrocarbon group having C4 or more carbon atoms as a cation. A separator for non-aqueous secondary batteries that is a fluorinated quaternary ammonium salt containing.
The separator for a non-aqueous secondary battery according to claim 1, wherein the fluorine-based quaternary ammonium salt contains a fluorine-containing anion having a van der Waals volume of 0.08 nm 3 or more as an anion.
The non-aqueous solution according to claim 1 or 2, wherein the hydrophobic ionic liquid antistatic agent that dissolves in the non-aqueous electrolytic solution is contained in an amount of 0.3 to 30% by mass based on the vinylidene fluoride-hexafluoropropylene copolymer. Separator for secondary batteries.
The separator for a non-aqueous secondary battery according to any one of claims 1 to 3, wherein the porous layer contains inorganic particles.
The separator for a non-aqueous secondary battery according to any one of claims 1 to 4, wherein the thickness of the polyolefin porous membrane is 16 μm or less.
The separator for a non-aqueous secondary battery according to any one of claims 1 to 5, wherein the thickness of the polyolefin porous membrane is 7 μm or less.
A non-aqueous secondary battery characterized in that the separator for a non-aqueous secondary battery according to any one of claims 1 to 6 is used.