JP5837437B2 - Nonaqueous secondary battery separator and nonaqueous secondary battery - Google Patents

Description

  The present invention relates to a separator for a non-aqueous secondary battery and a non-aqueous secondary battery.

  Non-aqueous secondary batteries such as lithium ion secondary batteries are widely used as power sources for portable electronic devices such as notebook computers, mobile phones, digital cameras, and camcorders. Further, in recent years, these batteries have been studied for application to automobiles and the like because of their high energy density.

  With the reduction in size and weight of portable electronic devices, the exterior of non-aqueous secondary batteries has been simplified. Initially, stainless steel battery cans were used as the exterior, but aluminum can exteriors have been developed, and now soft pack exteriors made of aluminum laminate packs have also been developed. In the case of an aluminum laminate-made soft pack exterior, since the exterior is soft, a gap may be formed between the electrode and the separator along with charge and discharge, and there is a technical problem that the cycle life is deteriorated. From the viewpoint of solving this problem, a technique for bonding an electrode and a separator is important, and many technical proposals have been made.

  As one of the proposals, a technique is known that uses a separator in which a porous layer made of a polyvinylidene fluoride resin (hereinafter also referred to as an adhesive porous layer) is formed on a polyolefin microporous film, which is a conventional separator ( For example, see Patent Document 1). When the adhesive porous layer is hot-pressed over the electrode in a state containing the electrolytic solution, the electrode and the separator can be satisfactorily bonded and can function as an adhesive. Therefore, the cycle life of the soft pack battery can be improved.

  Further, when a battery is manufactured using a conventional metal can exterior, a battery element is manufactured by winding the electrode and the separator in an overlapped state, and the element is enclosed in the metal can exterior together with an electrolytic solution. Is made. On the other hand, when producing a soft pack battery using the separator as in Patent Document 1 described above, a battery element is produced in the same manner as the battery with the above metal can, and this is put together with the electrolyte in the soft pack exterior. A battery is produced by encapsulating and finally adding a hot press process. Therefore, in the case of using the separator having the adhesive porous layer as described above, a battery element can be produced in the same manner as the battery with the above metal can outer case. There is also an advantage that no change is required.

For example, Patent Document 1 proposes a technical proposal focusing on the porous structure and thickness of a polyvinylidene fluoride resin layer from the viewpoint of ensuring sufficient adhesiveness and ion permeability.
As another proposal, a technique using a separator made of a porous film made of an organic polymer that encloses a mesh-like support and swells in an electrolyte and holds the electrolyte (see Patent Documents 2 and 3) is known. . Patent Documents 4 to 6 disclose a technique for forming an adhesive porous layer by combining two types of polyvinylidene fluoride resins from the viewpoint of improving adhesion to an electrode.

JP 2003-086162 A International Publication No. 01/067536 Pamphlet International Publication No. 04/019433 Pamphlet JP 2005-019157 A JP 2004-111160 A JP 2005-056800 A

  By the way, the positive electrode or negative electrode of a general non-aqueous secondary battery is comprised from the electrical power collector and the active material layer containing the electrode active material and binder resin which were formed on this electrical power collector. And the adhesive porous layer mentioned above adhere | attaches with respect to the binder resin in an electrode, when making it join with an electrode by hot press. Therefore, in order to ensure better adhesiveness, it is preferable that the amount of the binder resin in the electrode is large.

  However, in order to further increase the energy density of the battery, it is necessary to increase the content of the active material in the electrode, and it is preferable that the content of the binder resin is small. Therefore, in order to ensure sufficient adhesion in the prior art, it is necessary to perform hot pressing under severe conditions such as higher temperature and higher pressure. And in the prior art, when it hot-presses on such severe conditions, there existed a problem that the porous structure of the adhesive porous layer which consists of a polyvinylidene fluoride resin will be crushed. For this reason, the ion permeability after the hot pressing step is insufficient, and it is difficult to obtain good battery characteristics.

  Conventionally, the binder resin used for the electrode is generally a polyvinylidene fluoride resin, but in recent years, the use of styrene-butadiene rubber has been increasing. For an electrode using such a styrene-butadiene rubber, it has been difficult to obtain sufficient battery characteristics while achieving both ion permeability and adhesiveness in a separator having a conventional adhesive porous layer.

  For example, in the configuration of Patent Document 1, the porosity of the porous layer made of polyvinylidene fluoride resin is as high as 50 to 90%. There is a problem that the mechanical properties are insufficient with respect to the severe bonding conditions of the process. Furthermore, the surface structure has a structure in which holes having a pore diameter of 0.05 to 10 μm are scattered. With such a non-uniform surface structure, compatibility with the electrode, ion permeability, and cycle characteristics of the battery are compatible. The current situation is that it is becoming difficult to make it happen.

In Patent Documents 2 and 3, there is a separator that uses a nonwoven fabric made of a heat-resistant polymer as a network support, swells in an electrolytic solution, and mainly uses polyvinylidene fluoride as an organic polymer that holds the electrolytic solution. Although described, there is no discussion of adhesion.
Moreover, in the structure of patent documents 4-6, the surface of the adhesive porous layer is a dense film | membrane, and it has what is called a finger skin structure in which the coarse pore larger than this was formed in the inside of the same layer. In the case of this structure, the surface of the adhesive porous layer is dense so that adhesion to the electrode can be ensured, but it is difficult for ions to move on the surface portion, and the entire porous layer has a non-uniform pore structure. Therefore, the movement of ions becomes non-uniform, and the battery performance may not be sufficiently obtained.

  From such a background, the present invention is superior in adhesion to the electrode compared to the conventional one, can secure sufficient ion permeability even after being bonded to the electrode, and can sufficiently withstand heat press. It aims at providing the separator for non-aqueous secondary batteries provided with the adhesive porous layer which has a physical property and a uniform porous structure.

The present invention adopts the following configuration in order to solve the above problems.
1. A separator for a non-aqueous secondary battery, comprising: a nonwoven fabric substrate; and an adhesive porous layer formed on at least a surface of the substrate and containing a polyvinylidene fluoride resin, wherein the adhesive porous layer (1) a polyvinylidene fluoride resin A containing vinylidene fluoride and hexafluoropropylene as a copolymerization component and having a hexafluoropropylene content of 1.5 mol% or less, and (2) vinylidene fluoride and And a polyvinylidene fluoride resin B containing hexafluoropropylene as a copolymerization component and having a hexafluoropropylene content of more than 1.5 mol%, and the separator has a porosity of 50 to 70%. The non-aqueous secondary battery separator is characterized in that the adhesive porous layer has an average pore diameter of 1 to 200 nm.
2. 2. The non-aqueous secondary layer according to 1, wherein the adhesive porous layer comprises 15 to 85 parts by weight of the polyvinylidene fluoride resin A and 85 to 15 parts by weight of the polyvinylidene fluoride resin B. 3. Battery separator.
3. 1 or 2 above nonaqueous secondary battery separator according to any one, characterized in that the weight of the adhesive porous layer is 3 to 10 g / m ^2.
4). The non-aqueous secondary battery using the separator in any one of said 1-3.
5. 5. The nonaqueous secondary battery as described in 4 above, wherein the electrode and the separator are bonded to form an aluminum laminate film exterior.

  According to the present invention, the adhesion to the electrode is superior to that of the conventional one, sufficient ion permeability can be secured even after bonding with the electrode, and further, the mechanical properties and uniformity that can sufficiently withstand hot pressing. It is possible to provide a separator for a non-aqueous secondary battery including an adhesive porous layer having a simple porous structure. By using such a separator of the present invention, it is possible to provide a non-aqueous secondary battery having a high energy density and a high performance aluminum laminate pack exterior.

  A separator for a non-aqueous secondary battery of the present invention is a non-aqueous secondary battery comprising a nonwoven fabric substrate and an adhesive porous layer formed on at least the surface of the substrate and containing a polyvinylidene fluoride resin. The adhesive porous layer comprises (1) polyvinylidene fluoride containing vinylidene fluoride and hexafluoropropylene as copolymerization components, and the hexafluoropropylene content is 1.5 mol% or less. A resin A, and (2) a polyvinylidene fluoride resin B containing vinylidene fluoride and hexafluoropropylene as copolymerization components, and having a hexafluoropropylene content of more than 1.5 mol%, The separator has a porosity of 50 to 70%, and the adhesive porous layer has an average pore diameter of 1 to 200 nm. Hereinafter, the present invention will be described in detail. In addition, what was shown as "-" in the numerical range below means that it is a numerical range including an upper limit value and a lower limit value.

[Nonwoven fabric substrate]
In the present invention, the material constituting the nonwoven fabric substrate is a polyester-based material such as polyethylene terephthalate or polybutylene terephthalate, a polyolefin-based material such as polyethylene or polypropylene, polyphenylene sulfide, aromatic polyamide or polyimide, polyethersulfone, polysulfone, Heat-resistant polymers such as polyether ketone and polyether imide, or a mixture thereof can be used. In particular, the nonwoven fabric is preferably composed mainly of a polyester material. Here, the main component means that the polyester-based material occupies 50% by weight or more in the nonwoven fabric substrate, and a polyolefin-based material or the like can be mixed and included as the balance. Among these, polyethylene terephthalate or a mixture of polyethylene terephthalate and a polyolefin-based material is preferable.

  In this invention, the composite nonwoven fabric base material which laminated | stacked the functional layer on the nonwoven fabric base material can also be employ | adopted as a nonwoven fabric base material. Such a composite nonwoven fabric substrate is preferable in that a further function can be added by the functional layer. As the functional layer, for example, from the viewpoint of imparting heat resistance, a porous layer made of a heat resistant resin or a porous layer made of a heat resistant resin and an inorganic filler can be used. Examples of the heat resistant resin include one or more heat resistant polymers selected from aromatic polyamide, polyimide, polyethersulfone, polysulfone, polyetherketone, and polyetherimide. As the inorganic filler, a metal oxide such as alumina or a metal hydroxide such as magnesium hydroxide can be suitably used. Examples of the composite method include a method of coating a functional sheet on a porous sheet, a method of bonding with an adhesive, and a method of thermocompression bonding.

  In the present invention, the nonwoven fabric substrate preferably has a film thickness in the range of 5 to 30 μm, more preferably 10 to 20 μm. If the film thickness is less than 5 μm, it will be difficult to obtain sufficient mechanical properties, causing problems in handling. If the film thickness is greater than 30 μm, the internal resistance increases, which is not preferable from the viewpoint of battery performance. The Gurley value (JIS P8117), which is an index of ion permeability, is preferably in the range of 0 to 500 seconds / 100 cc. If it exceeds 500 seconds / 100 cc, the ion permeability may be insufficient and sufficient battery characteristics may not be obtained. Further, a piercing strength of 50 g or more is appropriate from the viewpoint of preventing internal short circuit and manufacturing yield.

[Polyvinylidene fluoride resin]
In the present invention, the adhesive porous layer comprises (1) a polyvinylidene fluoride resin A containing vinylidene fluoride and hexafluoropropylene as a copolymerization component, and the hexafluoropropylene content is 1.5 mol% or less. And (2) a polyvinylidene fluoride-based resin B containing vinylidene fluoride and hexafluoropropylene as a copolymerization component and having a hexafluoropropylene content of more than 1.5 mol%. . By mixing these two types of polyvinylidene fluoride resins, the adhesion to the electrodes is significantly improved compared to the case where one type of polyvinylidene fluoride resin is applied.

  In the polyvinylidene fluoride resin containing vinylidene fluoride and hexafluoropropylene as a copolymerization component, if the copolymerization ratio of hexafluoropropylene is increased, the polyvinylidene fluoride resin B is used because it easily swells in the electrolyte. It is more likely that the adhesion with the electrode is improved. However, when only the polyvinylidene fluoride resin B is applied, the adhesiveness with the electrode is not necessarily high, and when the copolymerization ratio of hexafluoropropylene is increased, the adhesiveness tends to decrease.

  Here, the adhesive porous layer present on the surface of the separator is a layer that adheres to the electrode. The surface of the adhesive porous layer includes a portion made of a polyvinylidene fluoride resin having an adhesive function, and an empty space. And a hole portion exists. When the adhesive porous layer is formed only with the polyvinylidene fluoride resin B having a high hexafluoropropylene copolymerization ratio, it is easy to obtain a morphology having a high porosity and a large pore diameter. When the porous structure has a high porosity and a large pore diameter as described above, the area of the polyvinylidene fluoride resin portion is reduced, and the bonded portions are sparse. This is considered to be a factor that only the polyvinylidene fluoride-based resin B cannot provide a sufficient adhesion function with the electrode.

  Conversely, when only a resin having a small copolymerization ratio of hexafluoropropylene such as polyvinylidene fluoride resin A is used, a porous structure having a small porosity and a small pore diameter can be obtained without impairing ion permeability. it can. With such a porous structure, it is considered that the adhesion to the electrode is enhanced from the viewpoint of surface morphology. However, in this case, since the copolymerization ratio of hexafluoropropylene is small, the swelling property with respect to the electrolytic solution is poor, and it is difficult to obtain high adhesiveness.

  Therefore, in the case of the present invention, the swellability to the electrolytic solution can be ensured by including the polyvinylidene fluoride resin B having a high copolymerization ratio containing hexafluoropropylene exceeding 1.5 mol%. And it becomes possible to obtain the surface morphology suitable for adhesion | attachment with an electrode by including the polyvinylidene fluoride resin A with a low copolymerization ratio containing 1.5 mol% or less of hexafluoropropylene. For this reason, when the above-mentioned polyvinylidene fluoride resin A and polyvinylidene fluoride resin B are used in combination, a synergistic effect is produced in the adhesion to the electrode, and the adhesion can be remarkably increased. Become.

  In the present invention, the polyvinylidene fluoride resin A needs to contain 1.5 mol% or less of hexafluoropropylene. When the copolymerization ratio of the hexafluoropropylene of the polyvinylidene fluoride resin A exceeds 1.5 mol%, it becomes difficult to make the aforementioned surface morphology suitable, and sufficient adhesion to the electrode is obtained. I can't. The polyvinylidene fluoride resin A may be a homopolymer of vinylidene fluoride alone when the content of hexafluoropropylene is 0%.

  In the present invention, the polyvinylidene fluoride resin B needs to contain more than 1.5 mol% of hexafluoropropylene. A more preferable range is 1.5 to 50.0 mol%. If the copolymerization ratio of the hexafluoropropylene of the polyvinylidene fluoride resin A is less than 1.5 mol%, the swelling property with respect to the electrolytic solution is poor, and it is difficult to obtain high adhesiveness. When hexafluoropropylene is contained in excess of 50.0 mol%, it is preferable that the mixing ratio of the polyvinylidene fluoride resin A is large in order to form a surface morphology that exhibits high adhesion.

  In the present invention, the adhesive porous layer preferably comprises 15 to 85 parts by weight of the polyvinylidene fluoride resin A and 85 to 15 parts by weight of the polyvinylidene fluoride resin B. When the amount of the polyvinylidene fluoride resin A is less than 15 parts by weight, the above-mentioned suitable surface morphology tends to be difficult to obtain, and the adhesion with the electrode may not be sufficiently obtained. On the other hand, when the amount of the polyvinylidene fluoride resin B is less than 15 parts by weight, the swellability to the above-described electrolytic solution is lowered, and sufficient adhesion to the electrode may not be obtained.

  In the present invention, as the polyvinylidene fluoride resins A and B, those having a weight average molecular weight of 200,000 to 3,000,000 can be suitably used. If the weight average molecular weight is less than 200,000, there may be a case where the mechanical strength sufficient to withstand the heat press that is the bonding process with the electrode may not be obtained. On the other hand, if the weight average molecular weight exceeds 3 million, the viscosity of the coating solution becomes too high, and the moldability is remarkably lowered.

In the present invention, it is preferable to use a copolymer consisting only of vinylidene fluoride and hexafluoropropylene as the polyvinylidene fluoride resins A and B, but a copolymer containing other monomer components other than these. Can also be used. Examples of such other monomer components include one kind or two or more kinds such as tetrafluoroethylene, trifluoroethylene, trichloroethylene, and vinyl fluoride.
The polyvinylidene fluoride resin having a relatively high molecular weight as described above can be preferably obtained by emulsion polymerization or suspension polymerization, particularly preferably suspension polymerization.

[Adhesive porous layer]
In the present invention, the porous structure of the adhesive porous layer containing the polyvinylidene fluoride resin is an important technical element, and the average pore diameter is 1 to 200 nm. Here, the adhesive porous layer means a layer composed of a polyvinylidene fluoride resin, having a large number of micropores inside, and a structure in which these micropores are connected. . Such an adhesive porous layer is formed on at least the surface of the nonwoven fabric, that is, the adhesive porous layer is formed on one or both surfaces of the nonwoven fabric, or is further included in the nonwoven fabric. You may form in the state which included the nonwoven fabric as a whole. In addition, the average pore diameter is determined by randomly selecting 20 openings from a photograph obtained by photographing the surface of the porous layer with a scanning electron microscope at a magnification of 30000 times, and obtaining an average value of the diameters. Average pore diameter. The shape of the hole is not limited to a circle, and may be an ellipse or an irregular shape. The diameter of the hole in this case is calculated as an average of the length in the major axis direction and the length in the minor axis direction of the ellipse. Further, when the shape of the hole is neither a circle nor an ellipse, the diameter is calculated by approximating a circle or an ellipse.

  The average pore size of the adhesive porous layer needs to be in the range of 1 to 200 nm, and more preferably 20 to 200 nm. When the average pore diameter is larger than 200 nm, the nonuniformity of the pores increases and the adhesion points become sparse, so that it is difficult to ensure sufficient adhesion to obtain sufficient cycle characteristics. Further, the movement of ions also tends to be non-uniform, and from this point of view, it becomes difficult to obtain sufficient cycle characteristics, and load characteristics also deteriorate. The average pore diameter is preferably as small as possible from the viewpoint of uniformity, but it is practically difficult to form a porous structure smaller than 1 nm. In addition, when the adhesive porous layer is impregnated with an electrolytic solution, the polyvinylidene fluoride resin swells, but if the average pore diameter is too small, the pores are blocked by swelling and the ion permeability is inhibited. Is also not preferable.

  Although the porous structure of the adhesive porous layer in the present invention has an appropriate porosity as a separator for a non-aqueous secondary battery, its average pore diameter is very small compared to the conventional one. It is characteristic. This means that a fine porous structure is developed and uniform. Since such a porous structure has good uniformity of ion movement at the separator electrode interface as described above, it has the effect of enabling a uniform electrode reaction and improving the load characteristics and cycle characteristics of the battery. Further, since the uniformity of the in-plane distribution of the polyvinylidene fluoride resin portion contributing to adhesion is high, good adhesion with the electrode is achieved.

  Furthermore, the separator of this invention also makes the ion movement in the interface of a nonwoven fabric base material and an adhesive porous layer favorable. In general, the ion separator at the layer interface is not preferable due to clogging, and therefore it may be difficult to obtain good battery characteristics. However, the adhesive porous layer in the present invention has a fine porous structure, is uniform, and has a large number of pores. Moreover, since the nonwoven fabric base material is used, suppression of ion migration due to clogging does not occur. Therefore, since the probability that the holes of the nonwoven fabric substrate and the holes of the adhesive porous layer can be satisfactorily connected increases, it is possible to remarkably suppress the performance degradation due to clogging.

  In addition, it is also possible to mix the filler which consists of an inorganic substance or an organic substance, and another additive in the adhesive porous layer in the range which does not inhibit the effect of this invention. By mixing such a filler, it is possible to improve the slipperiness and heat resistance of the separator. As the inorganic filler, for example, a metal oxide such as alumina or a metal hydroxide such as magnesium hydroxide can be used. As the organic filler, for example, an acrylic resin or the like can be used.

[Separator for non-aqueous secondary battery]
As described above, the non-aqueous secondary battery separator of the present invention includes a nonwoven fabric substrate and an adhesive porous layer formed on at least the surface of the substrate and containing a polyvinylidene fluoride resin. Yes. Here, since the adhesive porous layer is an adhesive layer that adheres to the electrode by hot pressing in a state containing the electrolytic solution, it needs to exist as the outermost layer of the separator. Of course, since it is preferable from the viewpoint of cycle life that both the positive electrode and the negative electrode are bonded to the separator, it is preferable to form an adhesive porous layer on both sides of the nonwoven fabric substrate, and the nonwoven fabric substrate is bonded to the adhesive porous material. It is preferable to completely enclose the layer.

  The porosity of the separator for a non-aqueous secondary battery of the present invention needs to be in the range of 50 to 70%, and more preferably in the range of 55 to 70%. When the porosity exceeds 70%, it becomes difficult to obtain mechanical properties that can withstand the pressing process for bonding to the electrode. On the other hand, if the porosity is higher than 70%, the surface porosity is increased, and the area occupied by the polyvinylidene fluoride resin having an adhesive function is reduced, so that it is difficult to secure a sufficient adhesive force, which is not preferable. When the porosity is lower than 50%, the ion permeability is remarkably lowered, and it becomes difficult to obtain sufficient battery characteristics.

The Gurley value of the separator for a non-aqueous secondary battery of the present invention is preferably in the range of 800 seconds / 100 cc or less, more preferably 100 seconds / 100 cc or less. If the Gurley value is higher than 800 seconds / 100 cc, sufficient battery performance may not be obtained.
The weight of the polyvinylidene fluoride resin is preferably in the range of 3.0 to 10.0 g / m ² . If it is less than 3.0 g / m ² , the adhesion to the electrode may be insufficient. On the other hand, if it is more than 10.0 g / m ² , the ion permeability is hindered and the load characteristics of the battery tend to be lowered.

The film thickness of the non-aqueous secondary battery separator is preferably 5 to 35 μm from the viewpoint of mechanical strength and energy density. The film thickness on one side of the adhesive porous layer is preferably in the range of 0.5 to 5 μm from the viewpoint of ensuring adhesion and good ion permeability. The fibril diameter of the polyvinylidene fluoride resin in the adhesive porous layer is preferably in the range of 10 to 1000 nm from the viewpoint of cycle characteristics. The membrane resistance of the non-aqueous secondary battery separator is preferably in the range of ¹ to 10 ohm · cm ² from the viewpoint of securing sufficient battery load characteristics. Here, the membrane resistance is a resistance value when the separator is impregnated with the electrolytic solution, and is measured by an alternating current method. Of course, although depending on the type and temperature of the electrolytic solution, the above numerical values are values measured at 20 ° C. using 1M LiBF ₄ propylene carbonate / ethylene carbonate (1/1 weight ratio) as the electrolytic solution.

[Method for producing separator for non-aqueous secondary battery]
The separator for a non-aqueous secondary battery of the present invention described above needs to form an adhesive porous layer containing a polyvinylidene fluoride-based resin, and further to combine this with a nonwoven fabric substrate. It is achieved by a method such as
Specifically, first, a polyvinylidene fluoride resin is dissolved in a solvent to prepare a coating solution. This coating solution is applied onto a nonwoven fabric substrate and immersed in an appropriate coagulation solution. This solidifies the polyvinylidene fluoride resin while inducing a phase separation phenomenon. In this step, the layer made of polyvinylidene fluoride resin has a porous structure. Thereafter, the coagulating liquid is removed by washing with water, and the adhesive porous layer can be integrally formed on the nonwoven fabric substrate by drying.

  As said coating liquid, the good solvent which melt | dissolves polyvinylidene fluoride resin can be used. As such a good solvent, for example, polar amide solvents such as N-methylpyrrolidone, dimethylacetamide, dimethylformamide, and dimethylformamide can be suitably used. From the viewpoint of forming a good porous structure, it is preferable to mix a phase separation agent that induces phase separation in addition to the good solvent. Examples of such a phase separation agent include water, methanol, ethanol, propyl alcohol, butyl alcohol, butanediol, ethylene glycol, propylene glycol, and tripropylene glycol. Such a phase separation agent is preferably added in a range that can ensure a viscosity suitable for coating. Moreover, what is necessary is just to mix or melt | dissolve in the said coating liquid, when mixing a filler and another additive in an adhesive porous layer.

  The composition of the coating liquid preferably includes a polyvinylidene fluoride resin at a concentration of 3 to 15% by weight. Although depending on the type of solvent used, it is preferable to use a mixed solvent containing 60% by weight or more of a good solvent and 10 to 40% by weight of a phase separation agent, from the viewpoint of forming an appropriate porous structure. When the amount of the phase separation agent is large, there are problems that the pores become too large or the coating liquid is gelled and loses fluidity. Moreover, when the amount of the phase separation agent is small, it is not preferable because a finger skin structure is easily obtained.

  In order to form a porous structure as in the present invention, it is preferable to apply a coagulating liquid composed of the solvent, the phase separation agent, and water. In terms of production, the mixing ratio of the solvent and the phase separation agent is preferably matched to the mixing ratio of the mixed solvent used for dissolving the polyvinylidene fluoride resin. The concentration of water is an important factor for controlling the porous structure, and depending on the type of phase separation agent and the composition of the coating liquid, it is appropriate that the concentration of water is generally 40 to 80% by weight. If the water concentration is too high, a finger skin structure is likely to be formed, which is inappropriate. On the other hand, if the water concentration is too low, solidification is delayed and pores are hardly formed.

  The temperature of the coagulation liquid is also an important factor for forming a porous structure. In the present invention, the temperature of the coagulation liquid is preferably in the range of 20 to 50 ° C. If the temperature of the coagulating liquid is too low, it tends to have a finger skin structure, and if the temperature is high, the pores tend to become large. In view of this, it is necessary to optimize the porous structure of the present invention.

  Conventional coating methods such as a Meyer bar, a die coater, a reverse roll coater, and a gravure coater can be applied to the non-woven fabric substrate. When forming an adhesive porous layer on both sides of a nonwoven fabric substrate, it is possible to solidify, wash and dry after coating the coating solution one side at a time. From the viewpoint of productivity, it is preferable to solidify, wash and dry after the work.

  In addition, the separator of this invention can be manufactured also with the dry-type coating method besides the wet coating method mentioned above. Here, the dry coating method is a method in which a coating liquid containing a polyvinylidene fluoride resin and a solvent is applied onto a nonwoven fabric substrate, and the solvent is removed by volatilization by drying, thereby obtaining a porous film. Say the method. However, in the case of the dry coating method, the coating film tends to be a dense film compared to the wet coating method, and it is almost impossible to obtain a porous layer unless a filler or the like is added to the coating liquid. Moreover, even if such fillers are added, it is difficult to obtain a good porous structure. Therefore, from such a viewpoint, it is preferable to use a wet coating method in the present invention.

  The separator of the present invention can also be produced by a method in which an adhesive porous layer and a nonwoven fabric substrate are prepared separately, and these sheets are superposed and combined by thermocompression bonding or an adhesive. As a method of obtaining the adhesive porous layer as an independent sheet, the coating liquid is applied onto the release sheet, and the adhesive porous layer is formed by using the wet coating method or the dry coating method described above. Examples include a method of peeling only the porous layer.

[Non-aqueous secondary battery]
The non-aqueous secondary battery of the present invention is characterized by using the separator of the present invention described above.
In the present invention, the non-aqueous secondary battery has a configuration in which a separator is disposed between a positive electrode and a negative electrode, and these battery elements are enclosed in an exterior together with an electrolytic solution. As the non-aqueous secondary battery, a lithium ion secondary battery is suitable.

As a positive electrode, the structure which formed the electrode layer which consists of a positive electrode active material, binder resin, and a conductive support agent on a positive electrode collector can be employ | adopted. Examples of the positive electrode active material include lithium cobaltate, lithium nickelate, spinel structure lithium manganate, and olivine structure lithium iron phosphate. In the present invention, when the adhesive porous layer of the separator is disposed on the positive electrode side, since the polyvinylidene fluoride resin has excellent oxidation resistance, LiMn _1/2 Ni _{1 1 that} can operate at a high voltage of 4.2 V or higher. There is also an advantage that a positive electrode active material such as ₂ O ₂ or LiCo _1/3 Mn _1/3 Ni _1/3 O ₂ can be easily applied. Examples of the binder resin include polyvinylidene fluoride resin. Examples of the conductive assistant include acetylene black, ketjen black, and graphite powder. Examples of the current collector include aluminum foil having a thickness of 5 to 20 μm.

  As a negative electrode, the structure which formed the negative electrode active material and the electrode layer which consists of binder resin on the negative electrode electrical power collector can be employ | adopted, and you may add a conductive support agent in an electrode layer as needed. As the negative electrode active material, for example, a carbon material that can occlude lithium electrochemically, a material that forms an alloy with lithium such as silicon or tin, and the like can be used. Examples of the binder resin include polyvinylidene fluoride resin and styrene-butadiene rubber. In the case of the separator for a non-aqueous secondary battery according to the present invention, since the adhesiveness is good, sufficient adhesiveness can be secured even when not only polyvinylidene fluoride resin but also styrene-butadiene rubber is used as the negative electrode binder. Examples of the conductive assistant include acetylene black, ketjen black, and graphite powder. Examples of the current collector include copper foil having a thickness of 5 to 20 μm. Moreover, it can replace with said negative electrode and can also use metal lithium foil as a negative electrode.

The electrolytic solution has a structure in which a lithium salt is dissolved in an appropriate solvent. Examples of the lithium salt include LiPF ₆ , LiBF ₄ , LiClO _{4, and the} like. Examples of the solvent include cyclic carbonates such as ethylene carbonate, propylene carbonate, fluoroethylene carbonate, difluoroethylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, and fluorine-substituted products thereof, γ-butyrolactone, γ -Cyclic esters such as valerolactone or a mixed solvent thereof can be suitably used. In particular, what melt | dissolved 0.5-1.5M lithium salts in the solvent of cyclic carbonate / chain carbonate = 20-40 / 80-60 weight ratio is suitable. In addition, in the separator provided with the conventional adhesive porous layer, it may be difficult to exhibit the adhesion to the electrode depending on the type of the electrolytic solution used, but according to the separator of the present invention, the type of the electrolytic solution However, there is a great advantage in that good adhesiveness can be exhibited.

  Although the separator for non-aqueous secondary batteries of the present invention can be applied to a battery with a metal can exterior, it is suitably used for a soft pack battery with an aluminum laminate film exterior because of its good adhesion to the electrode. In the method of manufacturing such a battery, the positive electrode and the negative electrode are joined via a separator, impregnated with an electrolytic solution, and enclosed in an aluminum laminate film. A non-aqueous secondary battery can be obtained by hot-pressing it. With such a configuration of the present invention, an electrode and a separator can be bonded well, and a non-aqueous secondary battery excellent in cycle life can be obtained. In addition, since the adhesion between the electrode and the separator is good, the battery is excellent in safety. There are a stack method in which the electrode and the separator are laminated, a method in which the electrode and the separator are wound together, and the present invention is applicable to any method.

  Hereinafter, the present invention will be described with reference to examples. However, the present invention is not limited to the following examples.

[Measuring method]
(Average pore diameter of porous layer made of polyvinylidene fluoride resin)
From the photograph obtained by photographing the surface of the porous layer with a scanning electron microscope (Keyence Co., Ltd .: trade name “VE8800”) at a magnification of 30000 times, randomly select 20 openings and measure the diameter. The average value of all diameters was determined and used as the average pore size.

(Film thickness)
It measured using the contact-type thickness meter (made by LITEMATIC Mitutoyo). The measurement terminal was a cylindrical one having a diameter of 5 mm, and was adjusted so that a load of 7 g was applied during the measurement.

(Weight)
A sample was cut into 10 cm × 10 cm and its weight was measured. The basis weight was determined by dividing the weight by the area.

(Weight of polyvinylidene fluoride resin)
The weight of the polyvinylidene fluoride resin was determined by subtracting the basis weight of the base material from the basis weight of the separator.

(Porosity)
The porosity of the separator for a non-aqueous secondary battery and the base material was obtained from the following formula 1.
ε = {1-Ws / (ds · t)} × 100 (Formula 1)
Here, ε: porosity (%), Ws: basis weight (g / m ² ), ds: true density (g / cm ³ ), and t: film thickness (μm).
Specifically, for example, for a composite separator in which a PET nonwoven fabric base material and a porous layer made only of a polyvinylidene fluoride resin are laminated, the porosity ε (%) of the composite separator was calculated from the following Equation 2. .
ε = {1- (Wa / 1.38 + Wb / 1.78) / t} × 100 (Formula 2)
Here, Wa is weight of the PET non-woven fabric substrate ^{(g /} m 2), Wb is weight of polyvinylidene fluoride resin (g ^{/ m} 2), t represents the thickness ([mu] m). When calculating the porosity of the porous layer made of the polyvinylidene fluoride resin, Wa = 0 (g / m ² ), and t is the thickness of the porous layer made of the polyvinylidene fluoride resin, that is, the separator A value obtained by subtracting the film thickness of the substrate from the film thickness may be used.

(Gurre value)
According to JIS P8117, measurement was performed with a Gurley type densometer (G-B2C manufactured by Toyo Seiki Co., Ltd.).

[Example 1]
As the polyvinylidene fluoride resin A, KF polymer # 9300 (vinylidene fluoride / hexafluoropropylene = 98.9 / 1.1 mol% weight average molecular weight 1.95 million) manufactured by Kureha Chemical Co., Ltd. was used. As the polyvinylidene fluoride resin B, KYNAR 2801 (vinylidene fluoride / hexafluoropropylene = 95.2 / 4.8 mol% weight average molecular weight 470,000) manufactured by ARKEM was used. Polyvinylidene fluoride-based resin A / polyvinylidene fluoride-based resin B is 80/20 weight ratio, and the polyvinylidene fluoride-based resin is dissolved in a mixed solvent having a dimethylacetamide / tripropylene glycol = 7/3 weight ratio at 5% by weight. Then, a coating solution was prepared. A non-woven sheet (average film) obtained by blending PET short fibers for fineness 0.06 dtex binder with polyethylene terephthalate (PET) short fibers whose orientation is crystallized with a fineness of 0.2 dtex, and forming and calendering rolls by wet papermaking. An equal amount was applied to both sides of a thickness of 16 μm and a basis weight of 7 g / m ² ), and solidified by immersing in a coagulating liquid (40 ° C.) of water / dimethylacetamide / tripropylene glycol = 57/30/13 weight ratio. This was washed with water and dried to obtain a separator for a non-aqueous secondary battery of the present invention. This separator had a structure in which a nonwoven fabric substrate made of polyester was encapsulated in a porous layer made of a polyvinylidene fluoride resin.
About this separator, the content of hexafluoropropylene (HFP) in the resins A and B constituting the adhesive porous layer, the mixing ratio of both resins, the film thickness and basis weight of the separator, the average pore diameter of the adhesive porous layer, Table 1 shows the measurement results of the porosity of the separator, the weight of the adhesive porous layer (PVDF resin), and the Gurley value of the separator. The separators of the following examples and comparative examples are also collectively shown in Table 1.

[Example 2]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the polyvinylidene fluoride resin A / polyvinylidene fluoride resin B was changed to a 60/40 weight ratio.

[Example 3]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the polyvinylidene fluoride resin A / polyvinylidene fluoride resin B was changed to a 40/60 weight ratio.

[Example 4]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the polyvinylidene fluoride resin A / polyvinylidene fluoride resin B was changed to a 20/80 weight ratio.

[Example 5]
Except that the polyvinylidene fluoride resin was dissolved in a mixed solvent having a dimethylacetamide / tripropylene glycol = 7/3 weight ratio at 7.5% by weight and a coating solution was prepared, A separator for a non-aqueous secondary battery of the present invention was obtained.

[Example 6]
The present invention was carried out in the same manner as in Example 4 except that the polyvinylidene fluoride resin was dissolved in a mixed solvent having a dimethylacetamide / tripropylene glycol = 7/3 weight ratio at 10% by weight to prepare a coating solution. The separator for non-aqueous secondary batteries was obtained.

[Example 7]
A separator for a non-aqueous secondary battery of the present invention was obtained in the same manner as in Example 1 except that the ratio of polyvinylidene fluoride resin A / polyvinylidene fluoride resin B was 90/10.

[Comparative Example 1]
A polyvinylidene fluoride resin having a copolymer composition of vinylidene fluoride / hexafluoropropylene = 98.0 / 2.0 mol% was prepared by suspension polymerization. A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 2 except that this was used as the polyvinylidene fluoride resin A.

[Comparative Example 2]
A coating solution was prepared with a polyvinylidene fluoride resin A / polyvinylidene fluoride resin B at a 100/0 weight ratio. The resulting coating solution was left at 20 ° C. for 24 hours. When the viscosity of the coating solution was measured with a B-type viscometer before and after standing, the ratio of the viscosity after standing to the viscosity before standing was 2.24. Here, the measurement temperature was 20 ° C., and the shear rate was 2.64 s ⁻¹ . This coating solution was used. Other than that was carried out similarly to Example 1, and obtained the separator for non-aqueous secondary batteries. In addition, the storage stability of the used coating liquid was bad, and it was difficult to apply uniformly.

[Comparative Example 3]
A separator for a non-aqueous secondary battery was obtained in the same manner as in Example 1 except that the polyvinylidene fluoride resin A / polyvinylidene fluoride resin B was changed to a 0/100 weight ratio.

[Production of non-aqueous secondary battery]
(Preparation of negative electrode)
300 g of artificial graphite as negative electrode active material, 7.5 g of water-soluble dispersion containing 40% by weight of modified styrene-butadiene copolymer as binder, 3 g of carboxymethyl cellulose as thickener, and a suitable amount of water The mixture was stirred with a mixer to prepare a negative electrode slurry. This negative electrode slurry was applied to a 10 μm thick copper foil as a negative electrode current collector, and the obtained coating film was dried and pressed to prepare a negative electrode having a negative electrode active material layer.

(Preparation of positive electrode)
NMP so that 89.5 g of lithium cobaltate powder as a positive electrode active material, 4.5 g of acetylene black as a conductive additive, and polyvinylidene fluoride as a binder (KF polymer W # 1100, manufactured by Kureha Chemical Co., Ltd.) are 6 wt%. The solution dissolved in 1 was stirred with a double-arm mixer so that the weight of polyvinylidene fluoride was 6% by weight, and a positive electrode slurry was prepared. This positive electrode slurry was applied to a 20 μm thick aluminum foil as a positive electrode current collector, and the resulting coating film was dried and pressed to produce a positive electrode having a positive electrode active material layer.

(Production of battery)
A lead tab is welded to the positive electrode and negative electrode produced as described above, the separators produced in the above examples and comparative examples are joined via the positive and negative electrodes, and the electrolyte solution is impregnated into the vacuum sealer in the aluminum pack. It was enclosed using. Here, 1 M LiPF ₆ ethylene carbonate / ethyl methyl carbonate (3/7 weight ratio) was used as the electrolytic solution. A battery was produced by applying a load of 20 kg per 1 cm ² of electrode with a hot press machine and performing hot pressing at 90 ° C. for 2 minutes.

[Measurement of resistance of separator when impregnated with electrolyte]
1 M LiBF ₄ propylene carbonate / ethylene carbonate = 1/1 weight ratio was used as the electrolyte solution, and the electrolyte solution was impregnated in the separators prepared in the above-described Examples and Comparative Examples. This was sandwiched between aluminum foil electrodes with lead tabs and enclosed in an aluminum pack to produce a test cell. The resistance of this test cell was measured at 20 ° C. by the AC impedance method (measurement frequency: 100 kHz). The results are summarized in Table 2.

[Adhesion test with electrode]
About the non-aqueous secondary battery produced as mentioned above, the adhesiveness was evaluated by disassembling the battery after hot pressing and measuring the peel strength. The results are summarized in Table 2. In Table 2, the average value of the peel strength for the positive electrode and the negative electrode for the separator of Example 1 was set as 100, and the average value of the peel strength for the positive electrode and the negative electrode for each separator was relatively evaluated.

[Battery cycle test]
About the non-aqueous secondary battery produced as mentioned above, the cycle test was implemented at 25 degreeC. The charging conditions were 1C and 4.2V constant current constant voltage charging, and the discharging conditions were 1C and 2.75V cut-off constant current discharging. Here, the index of the cycle characteristics was the capacity retention rate after 100 cycles. The results are summarized in Table 2.

[Battery load characteristics test]
With respect to the non-aqueous secondary battery produced as described above, a relative discharge capacity of 2C was measured at 25 ° C. based on a discharge capacity of 0.2C. The results are summarized in Table 2. In addition, the result of the load characteristic test of the battery also serves as an index of ion permeability after adhesion.

  The non-aqueous secondary battery separator of the present invention can be suitably used for a non-aqueous secondary battery, and is particularly suitable for a non-aqueous secondary battery having an aluminum laminate exterior, which is important for bonding with an electrode.

Claims (4)

A separator for a non-aqueous secondary battery comprising a nonwoven fabric substrate and an adhesive porous layer formed on at least the surface of the substrate and containing a polyvinylidene fluoride resin,
The adhesive porous layer is
(1) a polyvinylidene fluoride resin A containing vinylidene fluoride and hexafluoropropylene as a copolymerization component and having a hexafluoropropylene content of 1.5 mol% or less;
(2) a polyvinylidene fluoride-based resin B containing vinylidene fluoride and hexafluoropropylene as a copolymerization component and having a hexafluoropropylene content of more than 1.5 mol%,
The adhesive porous layer contains 15 to 85 parts by weight of polyvinylidene fluoride resin A, 85 to 15 parts by weight of polyvinylidene fluoride resin B,
The separator has a porosity of 50 to 70%, and the adhesive porous layer has an average pore diameter of 47 to 150 nm.   The weight of the adhesive porous layer is 3 to 10 g / m ² The separator for a non-aqueous secondary battery according to claim 1.   A non-aqueous secondary battery using the separator according to claim 1.   The non-aqueous secondary battery according to claim 3, wherein the electrode and the separator are bonded to form an aluminum laminate film exterior.