JP6277225B2 - Storage device separator - Google Patents

Description

  The present invention relates to an electrical storage device separator.

  In recent years, non-aqueous electrolyte batteries represented by lithium ion batteries have been actively developed. Usually, in a nonaqueous electrolyte battery, a separator including a microporous membrane is provided between positive and negative electrodes. The separator has a function of preventing direct contact between the positive and negative electrodes and allowing ions to permeate through the electrolytic solution held in the micropores.

  In general, a polyolefin microporous membrane is used as a separator. As the hole forming material, liquid paraffin, paraffin wax, or the like is used, and the amount or melting point of liquid paraffin contained in the separator is measured (Patent Documents 1 and 2).

  By the way, as a means for ensuring the safety of the battery, a CID (Current Interrupt Device) that mechanically cuts off the current path when the internal pressure of the battery increases may be used. One of the battery characteristics is initial charge / discharge efficiency. However, Patent Documents 1 and 2 do not evaluate the CID activation time and initial charge / discharge efficiency of a battery using the separator.

  In some separators, a polyolefin resin containing an inorganic filler is used to adjust the pore diameter, porosity, and the like (Patent Documents 3 and 4). However, Patent Documents 3 and 4 do not evaluate the CID start time and initial charge / discharge efficiency of a battery using the separator.

JP 2002-234963 A JP 2001-96614 A International Publication No. 09/099088 JP 2010-202829 A

  The separators described in Patent Documents 1 to 4 include the amount of liquid paraffin and silica contained in the separator, the safety (CID start-up time) and battery characteristics (initial charge / discharge efficiency) of a nonaqueous electrolyte battery including the separator. ) And the withstand voltage of the separator still have room for study.

  Therefore, the problem to be solved by the present invention is to provide a separator for an electricity storage device that can improve the electric resistance of the separator and the safety (CID start time) and battery characteristics (initial charge / discharge efficiency) of an electricity storage device including the separator. Is to provide.

The present inventors have found that the above problems can be solved by controlling the liquid paraffin content and silicon (Si) content contained in the electricity storage device separator, and have completed the present invention. That is, the present invention is as follows.
[1]
There is a separator for an electricity storage device including a polyolefin microporous film containing one or a plurality of polyethylene,
A separator for an electricity storage device, wherein the microporous film contains paraffin in an amount of 1.0 wt% to 2.0 wt%.
[2]
The separator for an electricity storage device according to [1], wherein the microporous film contains silicon atoms (Si) in an amount of 1 ppm to 1000 ppm.
[3]
The separator for an electricity storage device according to [1] or [2], wherein the microporous film contains the paraffin in an amount of 1.5 wt% to 2.0 wt%.
[4]
The separator for an electricity storage device according to [2], wherein the microporous film contains the silicon atom (Si) in an amount of 1 ppm to 500 ppm.
[5]
[1] to [4] any one of the separators for electricity storage devices according to any one of the above,
A positive electrode;
A negative electrode,
A laminate consisting of
[6]
A wound body in which the laminate according to [5] is wound.
[7]
The secondary battery containing the laminated body as described in [5], or the winding body as described in [6], and electrolyte solution.

  ADVANTAGE OF THE INVENTION According to this invention, the separator for electrical storage devices which is excellent in the electrical resistance of a separator and the safety | security (CID starting time) of an electrical storage device provided with a separator, and battery characteristics (initial charge / discharge efficiency) is provided.

  Hereinafter, a mode for carrying out the present invention (hereinafter referred to as “the present embodiment”) will be described in detail. In addition, this invention is not limited to the following embodiment, It can implement by changing variously within the range of the summary.

  The microporous membrane of this embodiment contains a polyolefin resin and is used for a separator of an electricity storage device such as a battery, a capacitor, or a capacitor.

  The microporous membrane according to this embodiment must contain 1.0% by weight or more and 2.0% by weight or less of paraffin. The microporous membrane of the present embodiment focuses on the paraffin content of the separator, and when the content is within an appropriate range, battery safety and battery characteristics are improved. When the paraffin content is within the above range, the microporous membrane can realize a power storage device separator having excellent safety (CID start time) and battery characteristics (initial charge / discharge efficiency) of the power storage device including the separator.

  In addition, the microporous membrane according to this embodiment preferably has a silicon atom (Si) content of 1 ppm or more and 1000 ppm or less. The microporous membrane of the present embodiment pays attention to the Si content of the separator, and when the content is within an appropriate range, the separator characteristics, battery safety, and battery characteristics are improved. When the Si content is in the above range, the microporous membrane is excellent in the electrical resistance of the separator and the safety (CID start time) of the electrical storage device including the separator and the battery characteristics (initial charge / discharge efficiency). Can be realized.

<Microporous membrane>
The porous film in the present invention will be described.
The porous film is preferably a porous film having low electron conductivity, ionic conductivity, high resistance to organic solvents, and a fine pore size.

  Examples of such a porous film include porous films containing polyolefin resin, polyethylene terephthalate, polycycloolefin, polyether sulfone, polyamide, polyimide, polyimide amide, polyaramid, polycycloolefin, nylon, polytetrafluoroethylene, and other resins. , A woven fabric of polyolefin fibers (woven fabric), a nonwoven fabric of polyolefin fibers, paper, and an aggregate of insulating substance particles. Among these, when a multi-layer porous film, that is, a storage device separator, is obtained through a coating process, the coating solution is excellent in coating properties, and the thickness of the separator is made thinner so that the activity in the storage device such as a battery can be reduced. From the viewpoint of increasing the material ratio and increasing the volume per volume, a porous membrane containing a polyolefin resin (hereinafter also referred to as “polyolefin resin porous membrane” or “polyolefin microporous membrane”) is preferable.

The polyolefin resin porous membrane will be described.
The polyolefin resin porous membrane is formed from a polyolefin resin composition in which the polyolefin resin occupies 50% by mass or more and 100% by mass or less of the resin component constituting the porous membrane from the viewpoint of improving shutdown performance when used as a power storage device separator. It is preferable to be a porous film. The proportion of the polyolefin resin in the polyolefin resin composition is more preferably 60% by mass or more and 100% by mass or less, and further preferably 70% by mass or more and 100% by mass or less.

  Examples of the polyolefin resin contained in the polyolefin resin composition include a homopolymer obtained by using ethylene, propylene, 1-butene, 4-methyl-1-pentene, 1-hexene, 1-octene and the like as monomers. , A copolymer, or a multistage polymer. Moreover, these polyolefin resins may be used independently or may be used in mixture of 2 or more types.

In the present embodiment, the polyolefin microporous membrane contains one or more polyethylenes, that is, one or more types of polyethylene from the viewpoint of the shutdown characteristics of the separator, battery safety, and battery characteristics.
If desired, from the viewpoint of the shutdown characteristics of the electricity storage device separator, the polyolefin microporous membrane may contain polypropylene, a copolymer of propylene and another monomer, and a mixture thereof, in addition to polyethylene.

Specific examples of polyethylene include low density polyethylene, linear low density polyethylene, medium density polyethylene, high density polyethylene, ultra high molecular weight polyethylene, etc.
Specific examples of polypropylene include isotactic polypropylene, syndiotactic polypropylene, atactic polypropylene, etc.
Specific examples of the copolymer include an ethylene-propylene random copolymer and ethylene propylene rubber.
Among these, it is preferable to use high-density polyethylene as the polyolefin resin from the viewpoint of satisfying the required performance with a low melting point and high strength when the polyolefin microporous membrane is used as a battery separator. In the present specification, the high density polyethylene refers to polyethylene having a density of 0.942 to 0.970 g / cm ³ . The density of high density polyethylene, from the viewpoint of the strength of the porous ^{film, 0.960~0.969 (g / cm 3)} , or is preferably 0.950~0.958 (g / cm ^3). In this specification, the density of polyethylene refers to a value measured according to JIS K7112 (1999).

  Further, from the viewpoint of improving the heat resistance of the porous membrane, it is preferable to use a mixture of polyethylene and polypropylene as the polyolefin resin. In this case, the ratio of polypropylene to the total polyolefin resin in the polyolefin resin composition is preferably 1 to 35% by mass, more preferably 3 to 20% by mass from the viewpoint of achieving both heat resistance and a good shutdown function. %, More preferably 4 to 10% by mass.

  Arbitrary additives can be contained in the polyolefin resin composition. Examples of additives include polymers other than polyolefin resins; inorganic fillers; phenol-based, phosphorus-based and sulfur-based antioxidants; metal soaps such as calcium stearate and zinc stearate; ultraviolet absorbers; light stabilizers An antistatic agent, an antifogging agent, a coloring pigment, and the like.

The porous membrane has a porous structure in which a large number of very small pores are gathered to form a dense communication hole. Therefore, the porous membrane has excellent ion conductivity as well as good withstand voltage characteristics and high strength. It has the characteristics.
The porous film may be a single layer film made of the above-described material or a laminated film.

  The thickness of the porous film is preferably 0.1 μm or more and 100 μm or less, more preferably 1 μm or more and 50 μm or less, and further preferably 3 μm or more and 25 μm or less. From the viewpoint of mechanical strength, 0.1 μm or more is preferable, and from the viewpoint of increasing the capacity of the battery, 100 μm or less is preferable. The film thickness of the porous film can be adjusted by controlling the die lip interval or the stretching ratio in the stretching step. The film thickness of the porous film can be measured by a dial gauge (Ozaki Seisakusho: “PEACOCK No. 25” (trademark)).

The average pore diameter of the porous membrane is preferably 0.03 μm or more and 0.70 μm or less, more preferably 0.04 μm or more and 0.20 μm or less, further preferably 0.05 μm or more and 0.10 μm or less, and particularly preferably 0.06 μm or more and 0 or less. 0.09 μm or less. From the viewpoint of high ion conductivity and withstand voltage, 0.03 to 0.70 μm is preferable. The average pore diameter of the porous membrane can be measured by the measurement method described later.
The average pore diameter should be adjusted by controlling the composition ratio, extrusion sheet cooling rate, stretching temperature, stretching ratio, heat setting temperature, stretching ratio during heat setting, relaxation rate during heat setting, or a combination of these. Can do.

The porosity of the porous film is preferably 25% or more and 95% or less, more preferably 30% or more and 65% or less, and still more preferably 35% or more and 55% or less. 25% or more is preferable from the viewpoint of improving ion conductivity, and 95% or less is preferable from the viewpoint of withstand voltage characteristics. The porosity of the porous film is a sample of 10 cm square, and its volume and mass are given by the following formula:
Porosity (%) = {volume (cm ³ ) −mass (g) / density of polyolefin resin composition (g / cm ³ )} / volume (cm ³ ) × 100
Can be used to calculate.
The porosity of the porous film is controlled by controlling the mixing ratio of the polyolefin resin composition and the plasticizer, the stretching temperature, the stretching ratio, the heat setting temperature, the stretching ratio at the time of heat fixing, the relaxation rate at the time of heat fixing, or a combination thereof. Can be adjusted.

  When the porous membrane is a polyolefin resin porous membrane, the viscosity average molecular weight of the polyolefin resin porous membrane is preferably from 30,000 to 12,000,000, more preferably from 50,000 to less than 2,000,000. More preferably, it is 100,000 or more and less than 1,000,000. A viscosity average molecular weight of 30,000 or more is preferable because the melt tension at the time of melt molding becomes large, the moldability becomes good, and the strength tends to become high due to entanglement between polymers. On the other hand, a viscosity average molecular weight of 12,000,000 or less is preferable because uniform melt kneading is facilitated and the formability of the sheet, particularly thickness stability, tends to be excellent. Furthermore, when the polyolefin resin porous membrane is used as a battery separator, it is preferable that the viscosity average molecular weight is less than 1,000,000 because the pores are likely to be blocked when the temperature rises and a good shutdown function tends to be obtained.

<Manufacturing method>
There is no restriction | limiting in particular as a method of manufacturing a porous film, A well-known manufacturing method is employable. For example,
(1) A method in which a polyolefin resin composition and a pore-forming material are melt-kneaded and formed into a sheet shape, then stretched as necessary, and then made porous by extracting a plasticizer,
(2) A method in which a polyolefin resin composition is melt-kneaded and extruded at a high draw ratio and then made porous by peeling off the polyolefin crystal interface by heat treatment and stretching,
(3) A method in which a polyolefin resin composition and an inorganic filler are melt-kneaded and formed on a sheet, and thereafter the surface is made porous by peeling the interface between the polyolefin and the inorganic filler by stretching,
(4) After dissolving the polyolefin resin composition, it is immersed in a poor solvent for polyolefin to solidify the polyolefin, and at the same time remove the solvent to make it porous.
Etc.

  Hereinafter, as an example of a method for producing a porous film, a method for extracting a pore-forming material after melt-kneading a polyolefin resin composition and a pore-forming material to form a sheet will be described.

  First, the polyolefin resin composition and the hole forming material are melt-kneaded. As the melt-kneading method, for example, the polyolefin resin and, if necessary, other additives are put into a resin kneading apparatus such as an extruder, kneader, lab plast mill, kneading roll, Banbury mixer, etc., while the resin component is heated and melted. A method in which a plasticizer is introduced at an arbitrary ratio and kneaded is exemplified.

  Examples of the hole forming material include a plasticizer or an inorganic material.

Although it does not specifically limit as a plasticizer, It is preferable to use the non-volatile solvent which can form a uniform solution above melting | fusing point of polyolefin. Specific examples of such a non-volatile solvent include, for example, hydrocarbons such as liquid paraffin and paraffin wax; esters such as dioctyl phthalate and dibutyl phthalate; higher alcohols such as oleyl alcohol and stearyl alcohol. . Note that these plasticizers may be recovered and reused after extraction by an operation such as distillation. Preferably, the polyolefin resin, other additives, and the plasticizer are pre-kneaded in advance at a predetermined ratio using a Henschel mixer or the like before being put into the resin kneading apparatus. More preferably, in pre-kneading, only a part of the plasticizer is added, and the remaining plasticizer is kneaded while side-feeding to a resin kneading apparatus. By using such a kneading method, the dispersibility of the plasticizer is increased, and when the sheet-shaped molded body of the melt-kneaded product of the resin composition and the plasticizer is stretched in a later step, a high magnification is obtained without breaking the film. Tend to stretch.
Among the plasticizers, liquid paraffin is highly compatible with the polyolefin resin polyethylene or polypropylene, and even when the melt-kneaded product is stretched, the interface between the resin and the plasticizer is not easily peeled off. Is preferable because it tends to be easily implemented.

  The ratio of the polyolefin resin composition and the plasticizer is not particularly limited as long as they can be uniformly melt-kneaded and formed into a sheet shape. For example, the mass fraction of the plasticizer in the composition comprising the polyolefin resin composition and the plasticizer is preferably 20 to 90 mass%, more preferably 30 to 80 mass%. When the mass fraction of the plasticizer is 90% by mass or less, the melt tension at the time of melt molding is hardly insufficient and the moldability tends to be improved. On the other hand, when the mass fraction of the plasticizer is 20% by mass or more, even when the mixture of the polyolefin resin composition and the plasticizer is stretched at a high magnification, the polyolefin chain is not broken, and a uniform and fine pore structure is obtained. It is easy to form and the strength tends to increase.

  The inorganic material is not particularly limited. For example, oxide ceramics such as alumina, silica (silicon oxide), titania, zirconia, magnesia, ceria, yttria, zinc oxide, iron oxide; silicon nitride, titanium nitride, nitride Nitride ceramics such as boron; silicon carbide, calcium carbonate, aluminum sulfate, aluminum hydroxide, potassium titanate, talc, kaolin clay, kaolinite, halloysite, pyrophyllite, montmorillonite, sericite, mica, amicite, bentonite Ceramics such as asbestos, zeolite, calcium silicate, magnesium silicate, diatomaceous earth, and silica sand; glass fibers. These may be used alone or in combination of two or more. Among these, silica, alumina, and titania are preferable from the viewpoint of electrochemical stability, and silica is particularly preferable from the viewpoint of easy extraction.

  Next, the melt-kneaded product is formed into a sheet shape. As a method for producing a sheet-like molded product, for example, a melt-kneaded product is extruded into a sheet shape via a T-die or the like, and brought into contact with a heat conductor to cool to a temperature sufficiently lower than the crystallization temperature of the resin component. And then solidify. Examples of the heat conductor used for cooling and solidification include metal, water, air, and the plasticizer itself. However, since the heat conduction efficiency is high, it is preferable to use a metal roll. In addition, when the extruded kneaded product is brought into contact with a metal roll, sandwiching between the rolls further increases the efficiency of heat conduction, and the sheet is oriented to increase the film strength, and the surface smoothness of the sheet is also improved. This is more preferable. The die lip interval when the melt-kneaded product is extruded from the T die into a sheet is preferably 200 μm or more and 3,000 μm or less, and more preferably 500 μm or more and 2500 μm or less. When the die lip interval is 200 μm or more, the mess and the like are reduced, and there is little influence on the film quality such as streaks and defects, and the risk of film breakage and the like in the subsequent stretching process can be reduced. On the other hand, when the die lip interval is 3,000 μm or less, the cooling rate is fast and cooling unevenness can be prevented and the thickness stability of the sheet can be maintained.

  Moreover, you may roll a sheet-like molded object. Rolling can be performed, for example, by a pressing method using a double belt press or the like. By performing rolling, the orientation of the surface layer portion can be particularly increased. The rolling surface magnification is preferably more than 1 and 3 or less, more preferably more than 1 and 2 or less. When the rolling ratio exceeds 1, the plane orientation increases and the film strength of the finally obtained porous film tends to increase. On the other hand, when the rolling ratio is 3 times or less, the orientation difference between the surface layer portion and the center is small, and a uniform porous structure tends to be formed in the thickness direction of the film.

  Next, the hole forming material is removed from the sheet-like molded body to form a porous film. As a method for removing the hole forming material, for example, a method of extracting the hole forming material by immersing the sheet-shaped molded body in an extraction solvent and sufficiently drying it may be mentioned. The method for extracting the hole forming material may be either a batch type or a continuous type. In order to suppress the shrinkage of the porous film, it is preferable to constrain the end of the sheet-like molded body during a series of steps of immersion and drying.

  As the extraction solvent used when extracting the pore-forming material, it is preferable to use a solvent that is a poor solvent for the polyolefin resin and a good solvent for the pore-forming material and has a boiling point lower than the melting point of the polyolefin resin. . Examples of such an extraction solvent include hydrocarbons such as n-hexane and cyclohexane; halogenated hydrocarbons such as methylene chloride and 1,1,1-trichloroethane; non-chlorine such as hydrofluoroether and hydrofluorocarbon. Halogenated solvents; alcohols such as ethanol and isopropanol; ethers such as diethyl ether and tetrahydrofuran; ketones such as acetone and methyl ethyl ketone. These extraction solvents may be recovered and reused by an operation such as distillation. Moreover, when using an inorganic material as a pore formation material, aqueous solution, such as sodium hydroxide and potassium hydroxide, can be used as an extraction solvent.

  Moreover, it is preferable to extend | stretch the said sheet-like molded object or porous film. The stretching may be performed before extracting the hole forming material from the sheet-like molded body. Moreover, you may carry out with respect to the porous film which extracted the hole formation material from the said sheet-like molded object. Furthermore, it may be performed before and after extracting the hole forming material from the sheet-like molded body.

  As the stretching treatment, either uniaxial stretching or biaxial stretching can be suitably used, but biaxial stretching is preferable from the viewpoint of improving the strength and the like of the obtained porous film. When the sheet-like molded body is stretched at a high magnification in the biaxial direction, the molecules are oriented in the plane direction, and the finally obtained porous film is difficult to tear and has a high puncture strength. Examples of the stretching method include simultaneous biaxial stretching, sequential biaxial stretching, multi-stage stretching, multi-stretching, and the like, and simultaneous biaxial from the viewpoint of improvement of puncture strength, uniformity of stretching, and shutdown property Stretching is preferred.

  Here, simultaneous biaxial stretching is a stretching method in which stretching in the MD (machine direction of continuous microporous membrane) stretching and TD (in the direction crossing the MD of the microporous membrane at an angle of 90 °) are performed simultaneously. The stretching ratio in each direction may be different. Sequential biaxial stretching refers to a stretching method in which MD or TD stretching is performed independently. When MD or TD is stretched, the other direction is fixed in an unconstrained state or a constant length. State.

  The draw ratio is preferably in the range of 20 times or more and 100 times or less, more preferably in the range of 25 times or more and 50 times or less in terms of surface magnification. The draw ratio in each axial direction is preferably in the range of 4 to 10 times in MD, 4 to 10 times in TD, 5 to 8 times in MD, and 5 to 8 times in TD. More preferably, it is the range. When the total area magnification is 20 times or more, there is a tendency that sufficient strength can be imparted to the obtained porous film. On the other hand, when the total area magnification is 100 times or less, film breakage in the stretching process is prevented and high productivity is achieved. Tends to be obtained.

  In order to suppress the shrinkage of the porous film, a heat treatment can be performed for the purpose of heat setting after the stretching process or after the formation of the porous film. Further, the porous film may be subjected to a post-treatment such as a hydrophilic treatment with a surfactant or the like, or a crosslinking treatment with ionizing radiation or the like.

  It is preferable to heat-treat the porous film for the purpose of heat setting from the viewpoint of suppressing shrinkage. As a heat treatment method, a stretching operation performed at a predetermined temperature atmosphere and a predetermined stretching rate for the purpose of adjusting physical properties, and / or a relaxation operation performed at a predetermined temperature atmosphere and a predetermined relaxation rate for the purpose of stress reduction. Is mentioned. The relaxation operation may be performed after the stretching operation. These heat treatments can be performed using a tenter or a roll stretching machine.

  In the stretching operation, it is preferable to stretch the film MD and / or TD by 1.1 times or more, more preferably 1.2 times or more from the viewpoint of obtaining a porous film having higher strength and high porosity.

  The relaxation operation is an operation for reducing the film to MD and / or TD. The relaxation rate is a value obtained by dividing the dimension of the film after the relaxation operation by the dimension of the film before the relaxation operation. When both MD and TD are relaxed, it is a value obtained by multiplying the MD relaxation rate and the TD relaxation rate. The relaxation rate is preferably 1.0 or less, more preferably 0.97 or less, and even more preferably 0.95 or less. The relaxation rate is preferably 0.5 or more from the viewpoint of film quality. The relaxation operation may be performed in both the MD and TD directions, but only one of the MD and TD may be performed.

  The stretching and relaxation operations after this plasticizer extraction are preferably performed at TD. The temperature in the stretching and relaxation operation is preferably lower than the melting point of the polyolefin resin (hereinafter also referred to as “Tm”), more preferably in the range of 1 ° C. to 25 ° C. lower than Tm, and in the range of 3 ° C. to 23 ° C. lower than Tm. Is more preferable, and a range lower by 5 to 21 ° C. than Tm is particularly preferable. When the temperature in the stretching and relaxation operation is in the above range, it is preferable from the viewpoint of the balance between the reduction in thermal shrinkage and the porosity.

<CID>
A CID (Current Interrupt Device) is an element that cuts off current when a change in pressure inside a sealed battery, that is, when a pressure rise is detected and becomes a certain pressure or higher. The time from the start of charging / discharging of the battery until the CID is activated is referred to as the CID activation time. However, from the viewpoint of ensuring higher battery safety, the CID activation time is preferably shorter.

<Paraffin content of microporous membrane>
The content of paraffin contained in the polyolefin microporous membrane is 1.0% by weight or more and 2.0% by weight or less from the viewpoint of shortening the CID starting time of the cylindrical battery using the separator including the microporous membrane. It is preferably 5% by weight or more and 2.0% by weight or less. When the paraffin content is less than 1.0% by weight, the CID start-up time cannot be shortened, and when it is more than 2.0% by weight, the initial charge / discharge efficiency is deteriorated. The details of the mechanism by which the CID start-up time is shortened when the paraffin content is within the above range are unknown, but are estimated as follows. In a cylindrical battery using a separator including the microporous film, gas due to decomposition of paraffin is generated by repeating charging and discharging, and it becomes possible to start CID at an early stage and to safely insulate the battery. It is considered possible.

  The paraffin contained in the polyolefin microporous membrane may be solid or liquid as long as it contains one or more alkanes having 20 or more carbon atoms. In general, paraffins are simply referred to as “paraffin” or “paraffin wax” when solid, and “liquid paraffin” when liquid. When a plurality of types of paraffin are contained in the polyolefin microporous membrane, the total content of all paraffins is in the range of 1.0 wt% or more and 2.0 wt% or less. The paraffin content is measured according to the methods and conditions described in the examples.

  In the method for producing a microporous polyolefin membrane described above, the mixing ratio of the resin composition and paraffin, the dispersibility of the paraffin in the resin composition, the extraction conditions of the paraffin from the sheet containing the resin composition and paraffin, and the like are adjusted. Thus, it is preferable to control the paraffin content of the microporous membrane to 1.0 wt% or more and 2.0 wt% or less.

<Si content of microporous film>
The silicon atom (Si) content contained in the polyolefin microporous membrane is 1 ppm or more and 1000 ppm or less based on the weight of the microporous membrane from the viewpoint of the CID start time of the battery using the separator including the microporous membrane. Preferably, 1 ppm or more and 500 ppm or less are more preferable. The details of the mechanism by which the CID start-up time is shortened when the Si content is within the above range are unknown, but are estimated as follows. In a cylindrical battery using a separator including the microporous film, a small amount of hydrofluoric acid is generated by repeating charge and discharge, which reacts with a Si compound (for example, silica), and converts silicon fluoride (SiF ₄ ) and the like. Occur. As a result, the CID can be started at an early stage, and the battery can be safely brought into an insulating state.

  The Si content contained in the polyolefin microporous membrane is preferably 1000 ppm or less from the viewpoint of the withstand voltage of the separator. If the Si content is more than 1000 ppm, it is estimated that the moisture contained in the Si compound (for example, silica) deteriorates the voltage resistance of the separator.

(Battery separator and battery)
The microporous membrane of the present embodiment is particularly preferably used for applications as a battery separator. That is, the battery separator of the present embodiment includes the microporous film of the present embodiment. The battery of this embodiment includes the microporous film of this embodiment.

  By adhering the separator according to this embodiment to the electrode, a laminate in which the separator and the electrode are laminated can be obtained.

  The laminate is excellent not only in handling properties during winding and rate characteristics and cycle characteristics of the electricity storage device, but also in adhesion and permeability. Therefore, a laminated body can be used suitably for electrical storage devices, such as batteries, such as a nonaqueous electrolyte secondary battery, a capacitor, and a capacitor, for example.

  Although the manufacturing method of a laminated body is not specifically limited, For example, the separator and electrode which concern on this embodiment may be overlapped, and the process of heating and / or pressing as needed may be included. Heating and / or pressing can be performed when the electrode and the separator are stacked. It is also possible to obtain a wound body by stacking the electrode and the separator and then winding the electrode into a circular or flat spiral. You may heat and / or press with respect to a wound body.

  A vertically long separator having a width of 10 to 500 mm (preferably 80 to 500 mm) and a length of 200 to 4000 m (preferably 1000 to 4000 m) can be prepared and overlapped with the electrode.

  The laminate can also be produced by laminating in the order of positive electrode-separator-negative electrode-separator or negative electrode-separator-positive electrode-separator, and pressurizing and optionally heating.

  The pressure during pressurization is preferably 1 MPa to 30 MPa. The pressing time is preferably 5 seconds to 30 minutes. The heating temperature is preferably 40 ° C to 120 ° C. The heating time is preferably 5 seconds to 30 minutes. Furthermore, the pressure may be applied after heating, the pressure may be applied, the heat may be applied after the pressurization, or the pressurization and the heating may be performed simultaneously. Among these, it is preferable to perform pressurization and heating simultaneously.

  When the storage device is a secondary battery, the laminate is wound into a circular or flat spiral shape to obtain a wound body, and the wound body is stored in a storage body such as a can or a pouch-type case, and A secondary battery can be obtained by injecting an electrolyte and further heating and / or pressing as desired.

  When manufacturing a non-aqueous electrolyte secondary battery using the separator according to this embodiment, a known positive electrode, negative electrode, and non-aqueous electrolyte may be used.

As the cathode material is not particularly limited, for _example, LiCoO 2, LiNiO _2, spinel-type LiMnO _4, lithium-containing composite oxides such as olivine type LiFePO ₄ and the like.

  The negative electrode material is not particularly limited, and examples thereof include carbon materials such as graphite, non-graphitizable carbonaceous, graphitizable carbonaceous, and composite carbon bodies; silicon, tin, metallic lithium, various alloy materials, and the like. .

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

  As a battery using the separator according to this embodiment, a polyolefin microporous membrane (separator) containing 1.0% by weight or more and 2.0% by weight or less of paraffin in a cylindrical outer can, a positive electrode, and a negative electrode And a cylindrical lithium ion secondary battery including an electrolytic solution and a CID (disconnect element). The cylindrical secondary battery having such a configuration easily shortens the CID startup time to improve safety, and easily achieves both safety and battery characteristics (initial charge / discharge efficiency).

  As described above, the CID activation time of the battery using the separator according to the present embodiment is preferably as short as possible from the viewpoint of ensuring higher battery safety. The CID activation time of the battery using the separator is measured according to the method and conditions described in the examples. As described in detail in Examples, in order to measure the CID start-up time, an electrode assembly is manufactured by winding a separator between a positive electrode and a negative electrode. As the CID activation time is shorter, a change in the pressure inside the battery, that is, a pressure increase is sensed and the current is cut off earlier, so that higher battery safety can be ensured.

  The initial charge / discharge efficiency of the battery using the separator according to this embodiment is preferably 80% or more in order to increase the output of the battery. The initial charge / discharge efficiency of the battery using the separator is measured according to the method and conditions described in the examples.

  The withstand voltage of the separator according to the present embodiment is preferably 1.7 kV or more, and more preferably 2.3 kV or more, from the viewpoint of reducing internal short circuit using the separator. The withstand voltage of the separator is measured according to the method and conditions described in the examples.

  EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited to an Example. The measurement methods and evaluation methods for various physical properties used in the following production examples, examples and comparative examples are as follows. Unless otherwise specified, various measurements and evaluations were performed under conditions of room temperature 23 ° C., 1 atm, and relative humidity 50%.

<Measurement method and evaluation method>
<Viscosity average molecular weight>
Measured based on ASTM-D4020. A polyolefin raw material or a microporous membrane was dissolved in a decalin solution at 135 ° C., the intrinsic viscosity [η] was measured, and the viscosity average molecular weight (Mv) was calculated by the following formula.
[Η] = 6.77 × 10 ⁻⁴ Mv ^0.67
For polypropylene, Mv was calculated by the following formula.
[Η] = 1.10 × 10 ⁻⁴ Mv ^0.80

<Measurement of liquid paraffin content>
The liquid paraffin content in the separators of Examples and Comparative Examples was measured by the following method.
The separator sampled at 100 × 100 mm was discharged, and weighed using a precision balance (W ₀ (g)). Subsequently, 200 ml of methylene chloride was added to the sealed container, and the separator was immersed at room temperature for 15 minutes. Thereafter, the separator was taken out, dried at room temperature for 3 hours, neutralized in the same manner as described above, and weighed using a precision balance (W ₁ (g)). The liquid paraffin content was determined by the following formula.
Paraffin content (wt%) = (W ₀ −W ₁ ) / W ₀ × 100

<Si content measurement>
The Si content in the separators of Examples and Comparative Examples was measured by the following method.
About 0.2 g of separator is weighed in a fluororesin sealed decomposition vessel, 5 mL of high-purity nitric acid is added thereto, and a microwave decomposition apparatus (product name “ETHOS TC”, manufactured by Milestone General Co., Ltd., model number) After heating at 200 ° C. for 20 minutes according to 125571), the volume was adjusted to 50 mL with ultrapure water. Then, it measured with the ICP mass spectrometer (Thermo Fisher Scientific Co., Ltd. make, brand name "X series X7 ICP-MS", machine number X0126). The quantification method was performed by an internal standard method using four inspection dose lines with each element concentration of 0, 2, 10, and 20 μg / L. The test solution for measurement was diluted so as to be within the calibration curve range. Further, cobalt (Co) was used as an internal standard element.

<Evaluation of CID startup time>
LiCoO ₂ (positive electrode active material) 94% by weight, carbon black (conductive agent) 3% by weight, and polyvinylidene fluoride (binder) 3 wt% were mixed in N- methylpyrrolidone to prepare a positive active material slurry. This slurry was applied to an aluminum foil (current collector), dried and rolled to produce a positive electrode.

  Natural graphite and polyvinylidene fluoride (binder) were mixed at a mass ratio of 96: 4 with an N-methylpyrrolidone solvent to produce a negative electrode slurry. The negative electrode slurry was coated on a copper foil to a thickness of 14 μm to form a thin electrode plate, dried at 135 ° C. for 3 hours or more, and rolled to produce a negative electrode.

1.3M LiPF ₆ was added to a mixed solvent in which fluoroethylene carbonate, ethylene carbonate, ethylmethyl carbonate, and diethyl carbonate were mixed at a ratio of 20% by volume: 10% by volume: 20% by volume: 50% by volume. An electrolyte was produced by adding succinonitrile to this mixture in an amount of 5% by weight based on the total weight of the mixture.

  A lithium secondary battery having a capacity per volume of 730 Wh / l was manufactured using the positive electrode, the negative electrode, the electrolyte, and the separators of Examples and Comparative Examples.

  Furthermore, the CID (Current Interrupt Device) start-up time was measured while continuously charging the manufactured lithium secondary battery at 60 ° C. under a constant voltage condition of 4.35V. With the CID startup time of the battery using the separator according to Comparative Example 1 as a blank, the shortened time (min.) With respect to the startup time of Comparative Example 1 is calculated for the battery using the separator of Example and Comparative Example 2. did.

<Evaluation of initial charge / discharge efficiency>
(Production of coin battery)
As a negative electrode active material, 98 parts of graphite having a particle diameter of 20 μm and a specific surface area of 4.2 m ² / g, and 5 parts (corresponding to solid content) of PVDF (polyvinylidene fluoride) as a binder for the negative electrode active material layer were mixed, Further, N-methylpyrrolidone was added and mixed with a planetary mixer to prepare a slurry-like negative electrode composition. Using this negative electrode active material, a coin-type secondary battery was fabricated. In this secondary battery, a test electrode using a negative electrode active material is accommodated in a can 1, and a counter electrode is attached to the can 2, and then the can 1 is passed through the separators of Examples and Comparative Examples impregnated with an electrolytic solution. , 2 are laminated and then caulked through a gasket. The negative electrode composition was applied to a copper foil current collector so as to have a thickness of 60 μm after drying, dried, and punched into pellets having a diameter of 16.4 mm. As the counter electrode, a lithium cobalt oxide (LiCoO ₂ ) plate punched to a diameter of 15.2 mm was used. When preparing an electrolytic solution, after mixing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) as solvents, lithium hexafluorophosphate (LiPF ₆ ) as an electrolyte salt Was dissolved. In this case, the composition of the solvent was EC: EMC: DMC = 30: 10: 60 by mass ratio, and the concentration of the electrolyte salt was 1 mol / dm ³ (= 1 mol / l).

(Evaluation of initial charge / discharge efficiency)
The initial charge capacity was evaluated using the coin mold manufactured as described above. After constant current charging at a current of 1 mA until the battery voltage reaches 4.2 V, constant voltage charging is performed at a voltage of 4.2 V until the current reaches 100 μA. From the mass of the test electrode, a copper foil current collector and The charge capacity per unit mass excluding the mass of the binder was determined. Here, charging means a lithium insertion reaction into the negative electrode active material.

  When investigating the initial discharge capacity, after charging in the same procedure as when examining the initial charge capacity, discharge at a constant current until the battery voltage reaches 2.5 V at a current of 1 mA, and from the mass of the test electrode The charge capacity per unit mass excluding the mass of the copper foil current collector and the binder was determined. Here, the discharge means a lithium elimination reaction from the negative electrode active material.

The initial charge / discharge efficiency was calculated according to the following formula.
Initial charge / discharge efficiency (%) = (initial discharge capacity / initial charge capacity) × 100

<Withstand voltage measurement>
The withstand voltage of the separators of Examples and Comparative Examples was measured by the following method.
A 50 mm x 50 mm separator sample is sandwiched between Φ35 mm electrodes with a clean surface, the voltage is gradually increased by applying a voltage to the electrode, and a voltage value when a 0.5 mA current flows and sparks. Was measured. This measurement was made at least 20 different points in the plane of the same film sample, and the average value was recorded. At this time, the withstand voltage was evaluated based on the following evaluation criteria.
A (remarkably good): 2.3 kV or more B (good): 1.7 kV or more and less than 2.3 kV C (allowable): less than 1.7 kV

[Example 1]
45 parts by mass of homopolymer high-density polyethylene with Mv of 700,000, 45 parts by mass of homopolymer high-density polyethylene with Mv of 300,000, and Hv of homopolymer with Mv of 400,000 and Mv of 150,000 A mixture of a certain homopolymer with polypropylene (mass ratio = 4: 3) 10 parts by mass and silica “LP” having an average primary particle size of 15 nm (manufactured by Tosoh Silica Co., Ltd.) 0.0495 parts by mass (500 ppm) Were dry blended using a tumbler blender to obtain a polyolefin mixture.

  To 99 parts by mass of the obtained polyolefin mixture, 1 part by mass of tetrakis- [methylene- (3 ′, 5′-di-t-butyl-4′-hydroxyphenyl) propionate] methane as an antioxidant was added, and the tumbler was added again. The mixture was obtained by dry blending using a blender.

The obtained mixture was supplied to the twin screw extruder by a feeder under a nitrogen atmosphere. Further, liquid paraffin (kinematic viscosity at 37.78 ° C .: 7.59 × 10 ⁻⁵ m ² / s) was injected into the extruder cylinder by a plunger pump. The operating conditions of the feeder and the pump were adjusted so that the ratio of liquid paraffin in the total mixture to be extruded was 65 parts by mass, that is, the polymer concentration was 35 parts by mass.

  Next, they are melt-kneaded while being heated to 230 ° C. in a twin-screw extruder, and the obtained melt-kneaded product is extruded through a T-die onto a cooling roll controlled at a surface temperature of 80 ° C. A sheet-like molded product was obtained by bringing into contact with a cooling roll and molding by cooling.

  The sheet was stretched by a simultaneous biaxial stretching machine under the conditions of a magnification of 7 × 6.4 times and a temperature of 112 ° C., then immersed in methylene chloride, extracted from liquid paraffin, dried, and then stretched by a tenter stretching machine. The film was stretched twice in the transverse direction at a temperature of 130 ° C. Thereafter, the stretched sheet was relaxed by about 10% in the width direction and subjected to heat treatment to obtain a polyolefin microporous membrane. At this time, the extraction conditions were adjusted so that the paraffin content of the microporous membrane by the measurement method was 1.0 wt%. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Example 2]
A polyolefin microporous membrane was obtained in the same manner as in Example 1 except that the extraction conditions of Example 1 were adjusted so that the paraffin content of the microporous membrane by the above measurement method was 1.5 wt%. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Example 3]
A polyolefin microporous membrane was obtained in the same manner as in Example 1 except that the extraction conditions of Example 1 were adjusted so that the paraffin content of the microporous membrane by the above measurement method was 2.0 wt%. Various physical properties of the obtained microporous membrane were measured by the above methods.

[ Reference Example 4]
In Example 2, a polyolefin microporous membrane was obtained in the same manner as in Example 2 except that silica “LP” (manufactured by Tosoh Silica Co., Ltd.) having an average primary particle size of 15 nm was not added. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Example 5]
In Example 2, the same procedure as in Example 2 was performed except that the amount of silica “LP” (manufactured by Tosoh Silica Co., Ltd.) having an average primary particle size of 15 nm was changed to 0.000099 parts by mass (1 ppm). A polyolefin microporous membrane was obtained. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Example 6]
In Example 2, the same procedure as in Example 2 was performed except that the amount of silica “LP” (manufactured by Tosoh Silica Corporation) having an average primary particle size of 15 nm was changed to 0.099 parts by mass (1000 ppm). A polyolefin microporous membrane was obtained. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Example 7]
In Example 2, the same procedure as in Example 2 was performed except that the amount of silica “LP” (manufactured by Tosoh Silica Corporation) having an average primary particle size of 15 nm was changed to 0.198 parts by mass (2000 ppm). A polyolefin microporous membrane was obtained. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Comparative Example 1]
A polyolefin microporous membrane was obtained in the same manner as in Example 1 except that the extraction conditions of Example 1 were adjusted so that the paraffin content of the microporous membrane by the above measurement method was 0.2 wt%. Various physical properties of the obtained microporous membrane were measured by the above methods.

[Comparative Example 2]
A polyolefin microporous membrane was obtained in the same manner as in Example 1 except that the extraction conditions of Example 1 were adjusted so that the paraffin content of the microporous membrane by the measurement method was 3.0 wt%. Various physical properties of the obtained microporous membrane were measured by the above methods.

The measurement results of physical properties of the microporous membranes obtained in Examples 1 to 3 and 5 to 7 , Reference Example 4 and Comparative Examples 1 and 2 are shown in Table 1 below.

Claims (7)

There is a separator for an electricity storage device including a polyolefin microporous film containing one or a plurality of polyethylene,
The microporous membrane contains 1.0% by weight to 2.0% by weight of paraffin , and
The microporous membrane contains silicon atoms (Si) in an amount of 1 ppm to 2000 ppm .   The separator for an electricity storage device according to claim 1, wherein the microporous film contains silicon atoms (Si) in an amount of 1 ppm to 1000 ppm.   The electrical storage device separator according to claim 1 or 2, wherein the microporous membrane contains the paraffin in an amount of 1.5 wt% to 2.0 wt%.   The separator for an electricity storage device according to claim 2, wherein the microporous film contains the silicon atom (Si) in an amount of 1 ppm to 500 ppm. The electricity storage device separator according to any one of claims 1 to 4,
A positive electrode;
A negative electrode,
A laminate consisting of   A wound body in which the laminate according to claim 5 is wound.   The secondary battery containing the laminated body of Claim 5, or the winding body of Claim 6, and electrolyte solution.