JP2011012266A - Method of manufacturing composite porous film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a porous film comprising an organic high polymer compound including a porous support having a front-back symmetry structure.SOLUTION: This method of manufacturing a composite porous film is a method of manufacturing a composite porous film comprising an organic high polymer compound including a porous support, and a coating process in which a dope is coated on both sides of the porous support by a coating unit, a solidifying process in which the coated porous support is solidified by immersing it in a solidifying bath, and a washing and drying process are carried out. The solidifying bath is set under the coating unit, and the air gap having the predetermined spacing is set between the coating process and the solidifying process, an air gap process is carried out, and at least during the coating process, the air gap process and the solidifying process, the porous support is continuously transferred.

Description

  The present invention relates to a method for producing a composite porous membrane. The present invention also relates to a method for producing a composite porous membrane suitable for a filter, a battery separator, etc., and particularly suitable for a non-aqueous secondary battery separator.

  Other non-aqueous secondary batteries (lithium ion secondary batteries) that use lithium-containing transition metal oxides for the positive electrode, lithium-doped / dedoped carbon-based materials for the negative electrode, and non-aqueous electrolyte solutions Compared to the secondary battery, it has a feature of having a high energy density. Lithium ion secondary batteries having such characteristics meet the demands of portable electronic devices such as weight reduction and thinning, and are used as power sources for portable electronic devices such as mobile phones and laptop computers. The demand for reducing the weight and thickness of portable electronic devices has become increasingly severe. At present, the lithium-ion secondary battery used for this is also being intensively developed for higher energy in this trend.

  In the flat lithium ion secondary battery mainly used for mobile phones, technological innovation has been made in recent years to change the exterior from a conventional metal can to an aluminum laminate film in response to demands for thinning and weight reduction. Since this aluminum laminate film exterior (film exterior) is a flexible exterior unlike a metal can exterior, the external pressure is weak and it is not easy to make contact between the electrode and the separator interface. In addition, there was a problem from the viewpoint of safety due to fear of liquid leakage. For this reason, the film structure battery cannot be realized with the conventional battery configuration of positive electrode / separator / negative electrode.

  With this background, this technological innovation is made possible by the use of a separator having excellent adhesion to electrodes and electrolyte retention. By using such a separator, it is possible to achieve good interface contact between the electrode and the separator and to prevent liquid leakage. For such a separator, an organic polymer compound that swells and holds in the electrolyte is used. Although such an organic polymer compound may be used alone as a separator, it has been put to practical use in a form that is generally reinforced by a support, not suitable for continuous production, due to problems in physical properties.

  That is, a separator has been proposed in which an adhesive layer made of an organic polymer compound that swells and retains an electrolyte solution is applied to both surfaces of a porous support. Polyolefin microporous membranes that are used as separators in nonwoven fabrics and conventional lithium ion secondary batteries have been proposed as porous supports, but currently polyolefin microporous membranes are mainly used from the viewpoint of safety due to shutdown characteristics. It has been put into practical use. In addition, an organic polymer compound mainly composed of polyvinylidene fluoride (PVdF) is mainly used for the adhesive layer from the viewpoint of durability.

  In addition, the battery configuration in which the adhesive layer is disposed between the electrode and the separator as described above is not only from the viewpoint of enabling the film exterior, but also from the viewpoint of increasing the energy density of the battery in the conventional metal can exterior. ing. High energy density means that many battery elements are tightly packed in a can of a predetermined size. At this time, it is difficult to form a good electrode separator interface and the cycle characteristics and the like are problems. However, there is a possibility that this problem can be solved by disposing a flexible adhesive layer as described above.

When the adhesive layer as described above is a dense layer, it is extremely difficult to achieve both adhesion to the electrode and ion permeability, and partial coating as disclosed in JP-A-2001-118558 (Patent Document 1). There is also a proposal for the construction. However, it is considered that it is not easy to obtain good interface bonding in the partial coating due to the problem of non-uniformity of the electrode / separator interface. In order to achieve both ion permeability and adhesion to the electrode, it is considered that the adhesive layer should be made porous, and the wet film forming method is preferable from the viewpoint of ease of morphological control. it is conceivable that. From such a background, a PVdF porous film including a porous support is proposed as a separator for a non-aqueous secondary battery in JP-A-11-026025 (Patent Document 2) and the like.
A proposal of a substantial manufacturing method of such a separator is proposed in Japanese Patent No. 2992598 (Patent Document 3).

JP 2001-118558 A Japanese Patent Laid-Open No. 11-026025 Japanese Patent No. 2992598

  The method of Japanese Patent No. 2992598 is a proposal of a separator in which a nonwoven fabric and an adhesive layer are combined and integrated, and a method for producing the separator. In this description, a non-woven fabric composite PVdF porous membrane separator is manufactured by casting a solution (dope) in which PVdF is dissolved on a carrier film, pressing the non-woven fabric from the solution, and immersing the carrier film together with the coagulation bath.

  The biggest disadvantage of this production method is that the carrier film is immersed in the coagulation bath, so that a difference in coagulation speed occurs between the front and back surfaces, and both surfaces of the nonwoven fabric, that is, the front and back surfaces become asymmetric separators. Such separators for non-aqueous secondary batteries are required to have ion permeability, adhesion to electrodes, and electrolyte retention, which correlates with the surface morphology of the separator and have the same characteristics at the positive electrode interface and negative electrode interface. It is preferable to have Therefore, it is considered that a front / back symmetric structure is more preferable from the viewpoint of highly controlling these characteristics, and a manufacturing method that makes the front / back asymmetric is not preferable.

Another disadvantage is that the impregnation is performed by pressing the nonwoven fabric over the dope cast on the carrier film. In this method, the familiarity between the dope and the non-woven fabric becomes the rate-determining factor, and it is considered that impregnation failure occurs in a combination with poor compatibility, which may cause voids and the like, and may deteriorate the quality of the separator. In addition, it is extremely difficult to position the nonwoven fabric in the center, and if the film is made thinner, there may be a problem in handling properties due to curling problems. Furthermore, this method can only be used for porous supports that are essentially impregnated with the dope, such as non-woven fabric, and are essentially completely impregnated with the dope, such as a polyolefin microporous membrane. There is also a problem that it cannot be applied to such a porous support.
Furthermore, although this manufacturing method is a process using a carrier film, the use of a carrier film is not preferable in terms of production cost.

  In view of such a current situation, the present invention is basically applicable to any porous support, and includes a porous support having a symmetrical structure, particularly suitable for a separator for a non-aqueous secondary battery. A method for producing a composite porous membrane made of an organic polymer compound is provided, and the ion permeability, adhesion to the electrode, and electrolyte retention are highly controlled, and the handling is sufficient and the cost is low. It aims at providing the manufacturing method of the separator for secondary batteries.

  In order to solve the problems as described above, the present inventors have prepared a porous support coated with a dope (solution) obtained by dissolving an organic polymer compound in a water-soluble organic solvent so that a coating film can be formed on both surfaces thereof. The air-gap step is carried to a coagulation bath having water or a coagulation liquid composed of water and the organic solvent, and the coating on both sides of the porous support is directly in contact with the coagulation bath. The method of manufacturing a composite porous membrane characterized by being immersed and solidified in water, then washed with water and dried is excellent in terms of structure, dope impregnation, industrial productivity, etc. Especially, ion permeability and adhesion to electrodes The present invention has been achieved by discovering that a composite porous membrane having a high degree of control over electrolytic solution retention and sufficient handling and low cost, in particular, a separator for a non-aqueous secondary battery can be provided.

That is, the present invention employs the following configuration.
1. A method for producing a composite porous membrane comprising an organic polymer compound encapsulating a porous support, wherein a solution (dope) containing an organic polymer compound and a water-soluble organic solvent is applied to both sides of the porous support. A coating step of coating by an apparatus, and a coagulation step of solidifying the coated porous support by immersing it in a coagulation bath having a coagulation liquid comprising water or a mixture of water and the water-soluble organic solvent; And a step of washing and drying the porous support after the coagulation step, and the coagulation bath is installed below the coating device, and an outlet of the coating device and an inlet of the coagulation bath There is an air gap between the coating step and the solidification step between the coating step and the solidification step so that the porous support unloaded from the coating device is not brought into contact with another device. Transport through the gap from top to bottom A composite porous body characterized in that an air gap step for carrying into the coagulation bath is carried out and the porous support is continuously conveyed at least during the coating step, the air gap step and the coagulation step. Manufacturing method of membrane.
2. An outlet of the coating apparatus and an inlet of the coagulation bath are arranged to face each other, and in the air gap step, the coated porous support is allowed to enter perpendicularly to the coagulation bath. 2. The method for producing a composite porous membrane as described in 1 above.
3. 3. The method for producing a composite porous membrane according to 1 or 2 above, wherein the porous support has a film thickness of 5 to 45 μm and a Macmillan number of 2 to 20.
4). 4. The method for producing a composite porous membrane according to any one of 1 to 3, wherein the dope contains a phase separation agent and has a concentration of 5 to 50% by weight.
5. A method for producing a separator for a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium, wherein the separator for a non-aqueous secondary battery is a composite made of an organic polymer compound containing a porous support. A method for producing a separator for a nonaqueous secondary battery, comprising a porous membrane, wherein the composite porous membrane is produced using the method according to any one of 1 to 4 above.

  According to the present invention, it is possible to produce a composite porous membrane having a surface morphology that is front and back symmetrical, and the surface morphology can be easily controlled. This production method is particularly suitable as a method for producing a separator for a non-aqueous secondary battery, and in particular, a method for producing a separator for a non-aqueous secondary battery having good ion permeability, adhesion to electrodes, and electrolyte retention. It is suitable as. Moreover, it becomes possible to manufacture industrially the separator for non-aqueous secondary batteries which has the feature in the safety | security at the time of an overcharge by using a nonwoven fabric for a porous support body.

An example of the apparatus for implementing the separator manufacturing method for non-aqueous secondary batteries of this invention. 1 is a porous support, 2 is a dope bath, 3 is a metering / smoothing jig, 4 is a coagulation bath, and 5 is a bar. An example of the apparatus used when coating by die | dye in this invention. 1 is a porous support, 2 is a die body, 3 is a delivery outlet lip, 4 is a die discharge part, 5 is a liquid storage space, and 6 is a die lip delivery exit end. The result of the SEM observation of the separator for non-aqueous secondary batteries produced in Example 1 is shown. (A) represents a cross-sectional view, and (b) represents a surface view. The result of the SEM observation of the separator for non-aqueous secondary batteries produced in Example 2 is shown. (A) represents a cross-sectional view, and (b) represents a surface view. The result of the SEM observation of the separator for non-aqueous secondary batteries produced in Example 5 is shown. (A) represents a cross-sectional view, and (b) represents a surface view. The result of the SEM observation of the separator for non-aqueous secondary batteries produced in Example 6 is shown. (A) represents a cross-sectional view, and (b) represents a surface view. The result of the SEM observation of the separator for non-aqueous secondary batteries produced in Example 7 is shown. (A) represents a cross-sectional view, and (b) represents a surface view.

The contents of the present invention will be described below.
[Production method of composite porous membrane]
The method for producing a composite porous membrane of the present invention is a method for producing a composite porous membrane comprising an organic polymer compound encapsulating a porous support, and the organic polymer compound and the water-soluble compound are formed on both sides of the porous support. A coating process in which a solution (dope) containing an organic solvent is applied by a coating apparatus, and the coated porous support is coagulated with water or a coagulating liquid composed of water and the water-soluble organic solvent. A coagulation step for immersing and solidifying in a bath; and a step of washing and drying the porous support after the coagulation step, wherein the coagulation bath is installed below the coating device, and the coating An air gap having a predetermined interval is provided between the outlet of the apparatus and the inlet of the coagulation bath, and the porous support carried out of the coating apparatus between the coating process and the coagulation process is The air gap without contacting other devices An air gap process is carried out from above to below and carried into the coagulation bath, and the porous support is continued at least during the coating process, the air gap process and the coagulation process. It is characterized by being conveyed.

  The greatest feature of the method for producing a composite porous membrane of the present invention is that the dope-coated porous support is immersed in a coagulation bath so that both surfaces thereof are in direct contact with the coagulation liquid, and is formed as a coating film. It is a point to solidify. For this reason, the composite porous membrane obtained by the production method of the present invention has a symmetric morphology when the support is used as an axis of symmetry, and the surface morphology is the same on both sides. Its morphology can be controlled by the dope composition and coagulation bath composition. For this reason, it is possible to make the characteristics such as adhesiveness, permeability, and liquid retention, which are important for the surface morphology, the same on both sides, and these characteristics can be controlled to a high degree. The method for producing a composite porous membrane of the present invention is very effective when producing a composite porous membrane that requires the same properties on the front and back in relation to its use.

  The method for producing a composite porous membrane of the present invention is also characterized in that a porous support coated with a dope on both sides thereof by a coating apparatus is conveyed to a coagulation bath through an air gap process. Specifically, the air gap process is not a process for directly connecting the coating apparatus and the coagulation bath, such as a measuring / smoothing jig and a die lip, as described in the examples below. It means to be a continuous process through distance.

  The first advantage of providing an air gap process is from the viewpoint of temperature control. For example, when the dope temperature and the coagulation bath temperature are different, if the air gap process is not performed, temperature management becomes extremely difficult. The second advantage is from the viewpoint of morphological management of the composite porous membrane. The air gap process has a leveling effect, and when the dope is uniformly coated on both surfaces of the porous support, it is possible to stably manufacture by providing this process. In addition, by providing an air gap step between the coating apparatus and the coagulation bath and providing a distance, there is an effect of preventing gelation of the dope at the time of coating due to the entrance of the coagulation bath or its vapor, and there is an advantage that the process is stabilized. 1-100 cm is suitable for this air gap process, More preferably, 5-50 cm is more suitable. If the air gap process is too short, the above effects cannot be obtained. On the other hand, if the length is too long, depending on the compatibility between the porous support and the dope, pinholes may be generated, or it may be difficult to control the conveyance.

  In the method for producing a composite porous membrane of the present invention, the arrangement of the apparatus and the transport direction of the porous support can also be important factors. It is not preferable in terms of the process to change the transport direction by biting a bar or the like in the air gap process as described above. If the bar is bitten, the dope is scraped off by the bar, so that it is difficult to measure the dope applied to the porous support by the coating apparatus, and it is difficult to produce a uniform composite porous membrane. In particular, there is a problem when the thickness and weight are highly controlled or when a thin film is produced. In order not to change the conveying direction without biting the bar or the like, it is necessary to install a coagulation bath below the coating apparatus through an air gap process and convey it from top to bottom. That is, the method for producing a composite porous membrane of the present invention is preferably to install a coagulation bath below the coating device, more uniformly applying the dope on both sides by conveying the porous support from top to bottom, It is possible to enter the coagulation bath as it is without changing the transport direction after coating. In this case, setting the coagulation bath below the coating device means that the dope impregnated so that the porous support is located in the central part with a uniform front and back structure on both sides of the porous support is held. It does not necessarily mean a vertical relationship. After the solidification, a composite porous membrane can be produced by installing a bar or the like in the coagulation bath, pulling up the porous support that has been solidified, and washing and drying.

  As a method of coating the dope on both sides of a porous support (hereinafter also referred to as a support), for example, a dip coating in which the support is dipped in the dope and then lifted and measured using a bar or a blade is used. Known coating methods such as a construction method (for example, JP-A-7-289964) and a transfer-type coating method (for example, JP-A-62-42764) for transferring a dope measured by a die or a coating roll to a support. Etc. are preferably used.

  Among these, preferably, a support holding an excessive amount of dope is passed between two Meyer bars facing each other with a predetermined clearance via a transport path of the support. In this method, the thickness of the coating film can be controlled by changing the diameter and / or clearance of the two Meyer bars and / or the winding diameter of the Meyer bar. A method for retaining the dope is not particularly limited, for example, an impregnation method or a spray method, but a method of immersing and passing the support in a dope bath is particularly preferable. The amount of liquid to be retained is the amount of dope impregnated inside the support, the thickness of the film containing the organic polymer compound to be uniformly formed on the front and back of the support, the physical properties of the dope, and the retention of the dope on the support It can be appropriately adjusted according to the properties. Moreover, it is preferable to hold | maintain dope on both the front and back of a support body, and forming a uniform coating film simultaneously.

  When a dope bath is used, a film forming apparatus as shown in FIG. 1 can be considered. In the case of this production method, the conveying direction from the coating apparatus (dope bath and metering / smoothing jig) to the coagulation bath has a suitable direction, and is preferably downward. The positional relationship of the weighing / smoothing jig is important. Designed so that the porous support enters from the top of the dope bath and exits downward, and then passes the weighing / smoothing jig when the transport direction from the coating device to the coagulation bath is downward. It is preferable to do this. That is, it is preferable to install a weighing / smoothing jig below the dope bath. From the standpoint of ease of dope weighing, it is particularly preferable that two weighing / smoothing jigs are installed horizontally so that the support passes vertically or substantially vertically between them. By adopting such a method, it becomes possible to easily produce the composite porous membrane having the porous layer made of the organic polymer having the same thickness and the same weight on both the front and back surfaces of the porous support. By integrating the dope bath and two weighing / smoothing jigs and sealing the lower surface of the dope bath at the top of the two weighing / smoothing jigs, the support can be immersed in the coagulation bath immediately after weighing. In addition, it is not necessary to collect excess dope scraped off by the weighing / smoothing jig, which is preferable.

  In addition, there is a method in which a necessary amount of dope is passed between two dies facing each other with a predetermined clearance through a conveyance path of the support. As shown in FIG. 2, this system is formed by reducing the clearance between the die lip conveyance exit end of the support conveyance exit lip and the support from the die discharge part, and arranging it so as to face the support. The dope supplied quantitatively in the width direction is stored in the liquid storage space, and the dope is continuously immersed and measured in the support. In this system, the thickness of the coating film can be controlled by changing the clearance between the die lip conveyance exit end of the lip tip on the support exit side and the support. The application width can be controlled by changing the discharge width and the supply amount for discharging the dope from the die, and it is preferable that the dope is applied at a width similar to or smaller than the support width so that excessive dope does not occur. In the case of producing the composite porous membrane having a porous layer composed of the organic polymer having the same thickness and the same weight on both surfaces of the support by this method, the dope discharge amount on both surfaces of the support is the same. Good.

  In the case of the production method of the present invention, since the dope is applied on both sides, voids due to poor impregnation do not occur even if the combination of the support and the dope is somewhat poor and difficult to impregnate. In addition, it is easy to position the support substantially at the center by applying an equal amount of dope on both sides, and handling problems such as curling do not occur even if the film thickness is reduced.

[Usage]
The composite porous membrane obtained by the method for producing a composite porous membrane of the present invention can be used for filters, battery separators and the like. Considering the characteristics of the composite porous membrane obtained by the production method of the present invention, this production method is particularly suitable as a method for producing a separator for a non-aqueous secondary battery. This is because non-aqueous secondary battery separators have important properties that require surface morphology, such as ion permeability, adhesion to electrodes, and liquid retention. Basically, these properties are highly controlled. This is because it is preferable that the surface morphology is the same on both sides.

[Method of manufacturing separator for non-aqueous secondary battery]
In the case of a separator for a non-aqueous secondary battery, the organic polymer compound is polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyethylene oxide (PEO) or polymethyl methacrylate (PMMA), a copolymer thereof, or Organic polymer compounds that swell and retain electrolyte solutions such as organic polymer compounds mainly composed of these are preferably used. These organic polymer compounds may be used in combination.

Particularly considering durability and film-forming property, PVdF, PVdF copolymer, or an organic polymer compound mainly composed of PVdF is preferably used. Among these, in particular, terpolymers of vinylidene fluoride (VdF), hexafluoropropylene (HFP), and chlorotrifluoroethylene (CTFE) have swelling / holding properties, heat resistance and adhesion to electrodes with respect to the electrolyte. It is excellent and suitable, and as a suitable composition of these terpolymers,
VdF / HFP (a) / CTFE (b)
(A) = 2-8% by weight
(B) = 1-6% by weight
Is mentioned. The molecular weight of the organic polymer compound is preferably 100,000 to 800,000, particularly 200,000 to 600,000 in terms of weight average molecular weight (Mw). These PVdF polymers can be synthesized by a known method. In general, it can be synthesized by a radical polymerization method, and specifically, it is prepared by a method such as solution polymerization, suspension polymerization, emulsion polymerization, or bulk polymerization.

  In the production method of the present invention, the morphology of the porous film obtained can be controlled by the composition of the dope and the composition of the coagulation liquid. In the separator for a non-aqueous secondary battery, characteristics such as ion permeability, electrolyte solution retention, and adhesion to electrodes are important. Therefore, it is preferable to adjust the dope and the coagulating liquid so as to obtain a morphology that sufficiently satisfies these conditions. The dope is obtained by dissolving an organic polymer compound in a water-soluble organic solvent, and it is preferable to add an appropriate amount of a phase separation agent corresponding to a poor solvent for the organic polymer compound as necessary. When a phase separation agent is added, the water-soluble organic solvent shall also contain a phase separation agent. As the coagulation liquid, water or a mixed liquid of water and a water-soluble organic solvent used for the dope (a phase separation agent may be added) is used.

  The water-soluble organic solvent used for the dope is preferably used as long as it can dissolve the organic polymer compound. When the organic polymer compound is a PVdF-based polymer, those having high polarity are preferred, and N-methylpyrrolidone (NMP), N, N-dimethylacetamide (DMAc), N, N-dimethylformamide (DMF), dimethyl sulfoxide ( DMSO), acetonitrile and the like are preferably selected, and these may be used in combination. The concentration of the organic polymer compound in the dope varies depending on the film forming conditions, but approximately 5 to 18% by weight is preferably selected.

  The phase separation agent can be used as long as it corresponds to a poor solvent for the organic polymer compound. When the organic polymer compound is a PVdF polymer, for example, water and alcohols are preferably selected. In particular, polypropylene glycol (PPG), ethylene glycol, tripropylene glycol (TPG), 1,3-butanediol containing a polymer, Polyhydric alcohols such as 1,4-butanediol, polyethylene glycol monoethyl ether, methanol, ethanol and glycerin are preferably selected. The suitable concentration of the phase separation agent in the dope varies depending on the film forming conditions, but is generally preferably selected in the range of 0 to 60% by weight in the mixed liquid medium of the water-soluble organic solvent and the phase separation agent, particularly 5 to 50. Weight percent is preferred. In order to obtain sufficient ion permeability as a non-aqueous secondary battery separator, it is preferable that not only the support but also the layer made of the organic polymer is sufficiently porous so that there are sufficient pores on the surface. . When the concentration of the phase separation agent is low, it is difficult to obtain such a morphology. On the other hand, if the concentration of the phase separation agent is too high, the dope tends to gel and film formation tends to be difficult.

  As the coagulation liquid, a mixed liquid of water, a water-soluble organic solvent used for the dope, and a phase separation agent is preferably used. The ratio of water is suitably selected in the range of 30 to 100% by weight, and particularly preferably in the range of 30 to 70% by weight. If the ratio of water is too high, it tends to be difficult to obtain a non-aqueous secondary battery separator having a dense surface and sufficient ion permeability. Moreover, when the ratio of water is too high, coagulation is delayed and productivity is deteriorated, and a sufficient film may not be obtained. Furthermore, it is preferable in production that the weight ratio of the water-soluble organic solvent and the phase separation agent is combined with these weight ratios in the dope.

  As the support applicable to this production method, a conventionally known one having sufficient physical properties and ion permeability as a separator support for a non-aqueous secondary battery can be suitably used. It is not limited.

  The film thickness of the non-aqueous secondary battery separator is preferably about 10 to 50 μm. The thickness of the support is preferably about 5 to 45 μm. More preferably, it is 5-25 micrometers. The non-aqueous secondary battery separator is preferably thin in terms of energy density and ion permeability. Since the composite porous membrane can be produced with high accuracy from the viewpoint of film thickness, basis weight, and morphology control as described above even if the production method of the present invention is thinned, such a separator for non-aqueous secondary batteries is used. The production method is suitable.

  From the viewpoint of ion permeability, a support having a Macmillan number in the range of 2 to 20 is preferable, and a support having a range of 2 to 15 is particularly preferable. The Macmillan number is an index of ion permeability, and is a value obtained by dividing the conductivity of the electrolyte only by the conductivity when the support is impregnated with the electrolyte. That is, if this value is too large, the ion permeability is insufficient.

  In the production method of the present invention, since the dope is applied to both surfaces of the support, even if the dope such as a polyolefin microporous membrane is considered to be hardly impregnated inside, it is formed of fibers such as nonwoven fabric. Even a dope such as a two-dimensional sheet that is sufficiently impregnated inside is applicable.

  In particular, when the support is a non-woven fabric, it is effective as a method for producing a separator for a nonaqueous secondary battery that suitably exhibits the overcharge prevention function described in the specification of WO01 / 67536 found by the present inventors. A lithium ion secondary battery using a separator obtained by a simple manufacturing method is significant from the viewpoint of safety during overcharge.

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

(Measurement of Macmillan number)
The obtained support and composite porous membrane were cut into 20 mmφ, sandwiched between two SUS electrodes, and the Macmillan number was calculated by dividing the ionic conductivity of the electrolyte by the conductivity calculated from the AC impedance at 10 kHz. At this time, the measurement temperature was 25 ° C. For the measurement, 1M LiBF4 EC / PC (1/1 weight ratio) was used as an electrolytic solution.

(Production of composite porous membrane)
[Example 1]
As the organic polymer compound, a PVdF copolymer having a copolymer composition of VdF / HFP / CTFE = 92.0 / 4.5 / 3.5 (weight ratio) and Mw = 410,000 was used. The dope was prepared by dissolving the PVdF copolymer in a mixed solvent of DMAc (organic solvent): TPG (phase separation agent) = 6: 4 (weight ratio) to 12 wt%. A polypropylene microporous membrane (Celguard # 2400 manufactured by Celgard) having a film thickness of 25.6 μm and a weight per unit area of 14.8 g / m ² was used as the porous support. The Macmillan number of this porous support was 9.8. The coagulation liquid was a mixture of water: DMAc: TPG = 5: 3: 2.

  The apparatus shown in FIG. 1 was used for film formation, and a Mayer bar (No. 8 diameter 20 mm, manufactured by Yoshimitsu Seiki Co., Ltd.) was used as a weighing / smoothing jig. The air gap between the two Meyer bars and the coagulation bath was 7 cm. The clearance between the two Meyer bars was set to 40 μm, and the polypropylene microporous film was installed so as to be approximately at the center between the two Meyer bars. Thereafter, the prepared dope (temperature: 30 ° C.) and coagulation liquid (temperature: 40 ° C.) were put in a predetermined container to prepare for film formation.

A polypropylene microporous membrane was moved at a speed of 3 m / min, coated and solidified, then washed with water and dried to obtain a composite porous membrane. Under this film forming condition, the coagulation time was 30 seconds. The obtained composite porous membrane had a thickness of 39.5 μm and a basis weight of 22.9 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. The results of observation by SEM are shown in FIG. From the cross section (FIG. 3 (a)), it is observed that the polypropylene microporous membrane is in the center, the surface (FIG. 3 (b)) is the same on the front and back sides, and pores with a pore diameter of 0.1 to 0.5 μm are dotted. The presence was observed.

[Example 2]
A PET short fiber for binder having a fineness of 0.22 dtex (average fiber diameter of about 4.5 μm) is 1/1 to a polyethylene terephthalate (PET) short fiber having a fineness of 0.33 dtex (average fiber diameter of about 5.5 μm). After blending at a weight ratio of 10 and forming a film with a basis weight of 10 g / m ² by a wet papermaking method, this was calendered at 170 ° C. to obtain a nonwoven fabric. This nonwoven fabric had a film thickness of 15.1 μm. The Macmillan number was 4.5.

A composite porous membrane was obtained in the same manner as in Example 1 except that this nonwoven fabric was used as a porous support. The obtained composite porous membrane had a thickness of 22.8 μm and a basis weight of 15.4 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. The result of observation by SEM is shown in FIG. From the cross-section (FIG. 4 (a)), it is observed that the nonwoven fabric is in the center, the surface (FIG. 4 (b)) is the same on the front and back, and pores with a pore diameter of 0.1 to 0.5 μm are scattered. I was observed.

[Example 3]
A reverse roll was used for the weighing / smoothing jig shown in FIG. A reverse roll having a diameter of 50 mm, a surface material of stainless steel and a surface roughness of 1.6 S is used. The clearance L between the roll 1 and the roll 2 is 120 μm, and the speed of the nonwoven fabric of the roll 1 and the roll 2 is The rotational peripheral speed ratio was 0.3. As a result of film formation under the same conditions as in Example 2, the film thickness was 23.0 μm and the basis weight was 15.6 g / m ² , as in Example 2. In SEM observation, the cross-section was the center of the nonwoven fabric. Thus, a composite porous membrane was obtained in which the surface was the same on the front and back surfaces, and the appearance of pores having a pore diameter of 0.1 to 0.5 μm was observed.

[Example 4]
A film was formed using a die as shown in FIG. 2 as a coating apparatus instead of the dope bath and the metering / smoothing jig. The clearance between the two die lip tips was 40 μm, and the two die lip surface holding angles were 10 °. Further, the die mouth discharge amount was adjusted to 0.02 cc / min · mm per die. The film forming speed was 2 m / min and the coagulation time was 45 seconds. The air gap between the two die lips and the coagulation bath was 7 cm. As a result of film formation under the same conditions as in Example 2, the film thickness was 22.5 μm and the basis weight was 15.3 g / m ² as in Example 2. In SEM observation, the cross-section is the center of the nonwoven fabric A composite porous membrane was observed in which the appearance was observed, the surfaces were the same on the front and back sides, and the appearance of pores with pore diameters of 0.1 to 0.5 μm being observed.

[Example 5]
Using a crystallized m-aramid short fiber having a fineness of 0.9 dtex (fiber diameter of about 10 μm), a nonwoven fabric was obtained by calendering at 320 ° C. after forming a film at a basis weight of 20 g / m ² by a dry papermaking method. This nonwoven fabric had a film thickness of 35.1 μm. The Macmillan number was 5.5.
As the organic polymer compound, a PVdF copolymer having a copolymer composition of VdF / HFP / CTFE = 89.5 / 8.8 / 1.7 (weight ratio) and Mw = 680,000 was used. The dope was prepared by dissolving the PVdF copolymer in a mixed solvent of DMAc (organic solvent): 1,3-butanediol (phase separation agent) = 7: 3 (weight ratio) to 15% by weight. The m-aramid nonwoven fabric produced above was used for the porous support. The coagulation solution was a mixture of water: DMAc: 1,3-butanediol = 6: 2.4: 1.6.
The same apparatus as in Example 1 was used for film formation, and the clearance between the two Meyer bars was 60 μm and the dope temperature was 60 ° C. Using the above nonwoven fabric as a porous support, preparation for film formation was prepared in the same manner as in Example 1 using the above dope and coagulating liquid.

The m-aramid nonwoven fabric was moved at a speed of 3 m / min, coated and solidified, then washed with water and dried to obtain a composite porous membrane. Here, the coagulation is completed from the time of entering the coagulation bath until the bar, but the coagulation time is 30 seconds under the present film forming conditions. The obtained composite porous membrane had a thickness of 40.5 μm and a basis weight of 32.5 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. The result of observation by SEM is shown in FIG. From the cross section (FIG. 5 (a)), it is observed that the m-aramid non-woven fabric is in the center, the surface (FIG. 5 (b)) is the same on the front and back, and pores having a pore diameter of 1 to 2 [mu] m are observed. The situation was observed.

[Example 6]
Using a crystallized m-aramid short fiber having a fineness of 0.9 dtex (fiber diameter of about 10 μm), a nonwoven fabric was obtained by calendering at 320 ° C. after forming a film at a basis weight of 15 g / m ² by a dry papermaking method. This nonwoven fabric had a film thickness of 30 μm. The Macmillan number was 5.8.
As the organic polymer compound, a PVdF copolymer having a copolymer composition of VdF / HFP / CTFE = 88.7 / 4.4 / 6.9 (weight ratio) and Mw = 530,000 was used. The PVdF copolymer was dissolved in a mixed solvent of DMAc (organic solvent): polypropylene glycol having an average molecular weight of 400 (PPG-400: phase separation agent) = 6: 4 (weight ratio) to 13.5% by weight. The dope was adjusted. The m-aramid nonwoven fabric produced above was used for the porous support. The coagulation liquid was a mixture of water: DMAc: PPG-400 = 6: 2: 2.
Using the above nonwoven fabric as a porous support, preparation for film formation was prepared in the same manner as in Example 5 using the above dope and coagulating liquid.

The m-aramid nonwoven fabric was moved at a speed of 1.5 m / min, coated and solidified, then washed with water and dried to obtain a composite porous membrane. Under this film forming condition, the coagulation time was 60 seconds. The obtained composite porous membrane had a thickness of 35.0 μm and a basis weight of 22.7 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. The result of observation by SEM is shown in FIG. From the cross section (FIG. 6A), it was observed that the m-aramid nonwoven fabric was in the center, and the layer made of the PVdF copolymer was completely sponge-like. The surface (FIG. 6 (b)) was the same on the front and back, and it was observed that pores having a pore diameter of 0.1 to 0.5 μm were scattered.

[Example 7]
As the organic polymer compound, a PVdF copolymer having a copolymer composition of VdF / perfluoromethyl vinyl ether / CTFE = 91.3 / 5.2 / 3.5 (weight ratio) and Mw = 1,010,000 was used. The dope was prepared by dissolving the PVdF copolymer in a mixed solvent of DMAc (organic solvent): PPG-400 (phase separation agent) = 5: 5 (weight ratio) to 15% by weight. The m-aramid nonwoven fabric produced in Example 5 was used for the porous support. The coagulation liquid was a mixture of water: DMAc: PPG-400 = 6: 2: 2.
Using the above nonwoven fabric as a porous support, preparation for film formation was prepared in the same manner as in Example 5 using the above dope and coagulating liquid.

The composite porous membrane was obtained by moving the m-aramid nonwoven fabric at a speed of 2 m / min, coating and solidifying, and washing and drying. Under this film forming condition, the coagulation time was 45 seconds. The obtained composite porous membrane had a thickness of 40.0 μm and a basis weight of 27.4 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. The result of observation by SEM is shown in FIG. From the cross section (FIG. 7 (a)), it was observed that the m-aramid nonwoven fabric was in the center, and the layer made of the PVdF copolymer had a very developed finger skin layer. The surface (FIG. 7 (b)) was the same on the front and back sides, and it was observed that pores having a pore diameter of 0.1 to 0.5 μm were scattered.

[Example 8]
A PET short fiber for binder having a fineness of 0.22 dtex (average fiber diameter of about 4.5 μm) is 1/1 to a polyethylene terephthalate (PET) short fiber having a fineness of 0.33 dtex (average fiber diameter of about 5.5 μm). A nonwoven fabric was obtained by calendering at 190 ° C. after forming a film with a basis weight of 12 g / m ² by a wet papermaking method. This nonwoven fabric had a film thickness of 18.2 μm. The Macmillan number was 6.7.
As the organic polymer compound, a PVdF copolymer having a copolymer composition of VdF / HFP / CTFE = 88.7 / 4.4 / 6.9 (weight ratio) and Mw = 530,000 was used. The dope was prepared by dissolving the PVdF copolymer in a mixed solvent of DMAc (organic solvent): PPG-400 (phase separation agent) = 6: 4 (weight ratio) to 8 wt%. The PET nonwoven fabric produced above was used for the porous support. The coagulation liquid was a mixture of water: DMAc: PPG-400 = 6: 2: 2.
Using the above nonwoven fabric as a porous support, preparation for film formation was prepared in the same manner as in Example 1 using the above dope and coagulating liquid.

A PET nonwoven fabric was moved at a speed of 3 m / min, coated and solidified, then washed with water and dried to obtain a composite porous membrane. Under this film forming condition, the coagulation time was 30 seconds. The obtained composite porous membrane had a thickness of 23.4 μm and a basis weight of 16.5 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. As a result of observation by SEM, it is observed that the PET nonwoven fabric is in the center from the cross section, the surface is the same on the front and back, and the pores with pore diameters of 0.1 to 0.5 μm are scattered. It was.

[Example 9]
As the organic polymer compound, a PVdF copolymer having a copolymer composition of VdF / HFP / CTFE = 92.0 / 4.5 / 3.5 (weight ratio) and Mw = 410,000 was used. The PVdF copolymer was dissolved in DMAc so as to be 15% by weight to prepare a dope. The PET nonwoven fabric produced in Example 2 was used for the porous support. The coagulation liquid was water.
Using the above nonwoven fabric as a porous support, preparation for film formation was prepared in the same manner as in Example 5 using the above dope and coagulating liquid.

A PET nonwoven fabric was moved at a speed of 2 m / min, coated and solidified, then washed with water and dried to obtain a composite porous membrane. Under this film forming condition, the coagulation time was 45 seconds. The obtained composite porous membrane had a thickness of 26.8 μm and a basis weight of 17.9 g / m ² . Further, there was no peeling of the PVdF copolymer, and there was no problem in handling without curling. When morphological observation was performed with SEM, no holes were observed on both the front and back surfaces. It was observed that the cross-section of the PET nonwoven fabric was almost in the center.

(Measurement of Macmillan number of composite porous membrane)
[Example 10]
The Macmillan number of the composite porous membrane produced in Examples 2 and 9 was measured. As a result, the Macmillan number of Example 2 was 3.7. The product of Example 9 had a Macmillan number of 17.
From this result, a composite porous membrane with pores on the surface can be produced by adding a phase separation agent to the dope and using a coagulation bath as a mixed solution of a water-soluble organic solvent and a phase separation agent and water. It can be seen that it is suitable as a separator for a non-aqueous secondary battery because of its excellent ion permeability.

(Characteristics of composite porous membrane as a separator for non-aqueous secondary batteries)
[Example 11]
"Positive electrode"
6% by weight NMP solution of PVdF so that the dry weight of lithium cobaltate (LiCoO 2, Nippon Chemical Industry Co., Ltd.) powder 89.5 parts by weight, acetylene black 4.5 parts by weight and PVdF 6 parts by weight. Was used to prepare a positive electrode paste. The obtained paste was applied onto an aluminum foil having a thickness of 20 μm, dried and pressed to obtain a positive electrode having a thickness of 97 μm.

"Negative electrode"
As a negative electrode active material, mesophase carbon microbeads (MCMB, manufactured by Osaka Gas Chemical Co., Ltd.) powder 87 parts by weight, 3 parts by weight of acetylene black, and 6% by weight of PVdF so that the dry weight of PVdF is 10 parts by weight. An NMP solution was used to produce a negative electrode agent paste. The obtained paste was applied onto a copper foil with a thickness of 18 μm, dried and pressed to prepare a negative electrode with a thickness of 90 μm.

"Production of button batteries"
A button battery (CR2032) having a capacity of about 4.5 mAh was produced using the composite porous membrane produced in Examples 1 to 8 as a separator and using the above positive electrode and negative electrode. As the electrolytic solution, 1M LiPF6 EC / DEC / MEC (1/2/1 weight ratio) was used. The manufactured button battery could be charged and discharged without any problem. The button battery was measured for a discharge capacity ratio of 2 C discharge to 0.2 C discharge in 4.2 V constant current / constant voltage charge and 2.75 V constant current discharge. The results are shown in Table 1.

[Comparative Example 1]
A button battery was produced in the same manner as in Example 11 using a polypropylene microporous membrane (Celguard # 2400 manufactured by Celgard) as the separator, and the same measurement was performed. The results are shown in Table 1.
From the results of the button battery using the composite porous membrane of Example 1 and Comparative Example 1, it can be seen that when the production method of the present invention is applied, the layer of the PVdF copolymer is hardly in resistance. Moreover, from the result of the button battery using the composite porous membranes of Examples 2 to 8, it is possible to produce a separator having characteristics higher than those of the conventional polyolefin microporous membrane by the production method of the present invention. I understand.

[Example 12]
Using the electrode produced in Example 11 and the composite porous membrane produced in Examples 1 to 8 as a separator, a film-clad battery in which an aluminum laminate film having a capacity of about 660 mAh was packaged was produced. The size of the battery was 62 mm × 35 mm × 3.6 mm. All of these batteries were chargeable / dischargeable. The liquid did not leak even when pressed further. As a result of disassembling the battery after charging and discharging, the electrode and these composite porous membranes were very well bonded.

[Example 13]
The film-clad battery produced in Example 12 was subjected to an overcharge test with a charge rate of 500% at 1C. The results are shown in Table 2.
The result of Example 13 shows that in the composite porous membrane in which the porous support is a non-woven fabric, the overcharge prevention function described in the specification of WO01 / 67536 found by the present inventors was exhibited, so that safety during overcharge was exhibited. It shows that sex is secured. When a nonwoven fabric is used for the porous support in this production method, a separator that suitably exhibits the overcharge prevention function can be obtained.

Claims (5)

A method for producing a composite porous membrane comprising an organic polymer compound encapsulating a porous support,
A coating step in which a solution (dope) containing an organic polymer compound and a water-soluble organic solvent is applied to both surfaces of the porous support by a coating device;
A solidification step in which the coated porous support is solidified by dipping in a coagulation bath having a coagulation liquid comprising water or a mixture of water and the water-soluble organic solvent;
The step of washing and drying the porous support after the coagulation step is carried out,
The coagulation bath is installed below the coating apparatus, and an air gap of a predetermined interval is provided between the outlet of the coating apparatus and the inlet of the coagulation bath,
Between the coating process and the solidification process, the porous support carried out from the coating apparatus is conveyed from above to below without contacting the other apparatus. , Carry out an air gap process to carry into the coagulation bath,
A method for producing a composite porous membrane, comprising transporting the porous support continuously during at least the coating step, the air gap step, and the coagulation step. The outlet of the coating device and the inlet of the coagulation bath are arranged opposite to each other,
The method for producing a composite porous membrane according to claim 1, wherein in the air gap step, the coated porous support is allowed to enter perpendicularly to the coagulation bath.   The method for producing a composite porous membrane according to claim 1 or 2, wherein the porous support has a film thickness of 5 to 45 µm and a Macmillan number of 2 to 20.   The method for producing a composite porous membrane according to any one of claims 1 to 3, wherein the dope contains a phase separation agent and has a concentration of 5 to 50% by weight. A method for producing a separator for a non-aqueous secondary battery that obtains an electromotive force by doping or dedoping lithium,
The non-aqueous secondary battery separator is composed of a composite porous membrane made of an organic polymer compound containing a porous support,
A method for producing a separator for a non-aqueous secondary battery, wherein the composite porous membrane is produced by using the method according to claim 1.