JP2010251078A - Organic/inorganic composite porus film and nonaqueous electrolyte secondary battery separator using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an organic/inorganic composite porus film which does not dissolve in fluorine ions, or the like, even at high temperatures at which a battery itself is dissolved and broken down, includes a structure in which a separator frame is not molten down, is highly safe, and can be used for a separator for a nonaqueous electrolyte secondary battery. <P>SOLUTION: The organic/inorganic composite porus film is formed by coating heat resistant resin material on inorganic porus material as a frame. The inorganic porus material is formed of glass fiber and/or ceramic fiber, and the heat-resistant resin preferably contains either of polyamide, polyamide acid, polyimide. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an organic / inorganic composite porous film, and more particularly to an organic / inorganic composite porous film obtained by mixing or coating a fibrous inorganic material with a resin material, which is useful for a non-aqueous electrolyte secondary battery. The present invention also relates to a separator for a non-aqueous electrolyte secondary battery comprising the organic-inorganic composite porous film.

  In recent years, non-aqueous electrolyte secondary batteries, particularly lithium secondary batteries, have been used not only for conventional mobile phone applications, but also for electric tools, electric bicycles, scooters, and automobile applications (for electric vehicle batteries and hybrid cars). Battery) and the like has been started and tends to be enlarged. Non-aqueous electrolyte secondary batteries for mobile phones generally use a polyolefin-based material having a microporous material as a separator. In this case, the electrolyte is excessively large due to a short circuit between the positive electrode and the negative electrode. In order to prevent the flow of electric current and further acceleration of the reaction, causing an explosion accident, when the normal operating temperature is exceeded, the separator's microporous material is blocked as low as possible, and excess current flows in the electrolyte. Safety measures are taken so as to have a shutdown function to prevent this.

  However, unlike mobile phones, when non-aqueous electrolyte secondary batteries, especially lithium secondary batteries, are used in high-temperature environments, such as when a secondary battery is placed near an internal combustion engine, such as in a hybrid car application. Therefore, it is required that the separator functions even when the electrolyte temperature becomes high. In large lithium secondary batteries, the positive electrode material is replaced from conventional lithium cobalt oxide to lithium manganate to prevent safety, for example, to prevent short-circuiting of the positive electrode and the negative electrode during overcharging. To improve safety by improving the electrode material. In addition, the separator is a laminated porous film in which porous aramid fibers or polyimide layers and polyolefin porous films are laminated for the purpose of preventing an accidental chemical reaction due to a short circuit between the positive and negative electrodes in a secondary battery with a large capacity. A separator having heat resistance at a higher temperature such as a quality film has been proposed.

JP 2001-342282 A JP2008-307893

  As described above, a separator for a large nonaqueous electrolyte secondary battery, particularly a lithium secondary battery, is required to have high heat resistance from the viewpoint of safety. That is, the additive material contained in the battery, such as PVDF material or casing material, has only heat resistance of 300 degrees or less, so if a short circuit occurs between the positive and negative electrodes, the battery becomes high temperature, generation of abnormal current, and further the battery configuration itself A situation may occur where the material dissolves and disintegrates. On the other hand, from the viewpoint of safety, it is essential to have a so-called shutdown function at a high temperature that keeps the skeleton as a separator even at a high temperature and also shuts off an abnormal current of the electrolyte.

  Regarding this, a separator having a structure in which an inorganic porous material and an olefinic microporous material are laminated is considered as a heat-resistant separator. However, since the olefin-based material dissolves and decomposes at a temperature close to 300 ° C., the shutdown function cannot be exhibited. That is, even if the inorganic porous material maintains its skeleton structure at a high temperature and prevents meltdown, safety cannot be ensured. Can be considered. In addition, non-aqueous electrolytes may generate a small amount of fluorine ions as impurities during the charge / discharge process, and most inorganic materials may dissolve in fluorine ions, so there is a problem from the viewpoint of preventing meltdown. It is possible.

  An object of the present invention is to provide an organic-inorganic composite porous film material obtained by coating an inorganic porous material with an electrochemically stable heat-resistant resin material using the inorganic porous material as a skeleton. In addition, the surface is covered with an electrochemically stable heat-resistant resin, has a shutdown effect even at high temperatures, and has a structure in which the separator skeleton does not melt down without dissolving in fluorine ions etc. even at the temperature at which the battery itself dissolves and collapses. The nonaqueous electrolyte secondary battery separator is provided.

  The present invention is a material that is preferably used as a separator for a non-aqueous electrolyte secondary battery, and is an organic-inorganic material obtained by coating an inorganic porous material with an electrochemically stable heat-resistant resin material using an inorganic porous material as a skeleton. The gist is a composite porous film material.

  That is, the present invention is an organic-inorganic composite porous film in which an inorganic porous material is used as a skeleton and a heat-resistant resin material is coated thereon.

  Moreover, this invention is the said organic inorganic composite porous film with which the said inorganic porous material is comprised with glass fiber and / or ceramic fiber.

  Moreover, this invention is the said organic inorganic composite porous film characterized by the said inorganic porous material consisting of glass fiber.

  The present invention also provides the organic-inorganic composite porous film, wherein the inorganic porous material is a nonwoven fabric made of glass fiber.

  The present invention also provides the organic-inorganic composite porous film, wherein the inorganic porous material is a woven fabric made of glass fibers.

  Moreover, this invention is the said organic inorganic composite porous film in which the said heat resistant resin contains either polyamide, polyamic acid, or a polyimide.

  Further, the present invention is the organic-inorganic composite porous film, wherein the coated heat-resistant resin is a ratio of 10 to 500% by mass with respect to the inorganic porous material.

  Moreover, this invention is the said organic inorganic composite porous film by which the said glass fiber was surface-treated with the silane coupling agent.

  Moreover, this invention is a separator which consists of said organic-inorganic composite porous film.

  Moreover, this invention is a battery which has the said separator.

  Moreover, this invention is a capacitor which has the said separator.

  The organic-inorganic composite porous film of the present invention is formed by coating an inorganic porous material with an electrochemically stable heat-resistant resin material using an inorganic porous material as a skeleton, thereby making the surface an electrochemically stable heat-resistant resin. It has a structure that is covered and has a shutdown effect at high temperatures, and does not dissolve in fluorine ions etc. even at a temperature at which the battery itself dissolves and collapses. An electrolyte secondary battery separator can be provided.

Short resistance measuring device

  Hereinafter, embodiments of the present invention will be described in detail. The present invention is an organic-inorganic porous film in which an inorganic porous material is used as a skeleton and a heat-resistant resin material is coated thereon. As the inorganic porous material, a porous material made of glass fiber and / or ceramic fiber is preferable, and glass fiber is particularly preferable. Furthermore, since it is easy to handle if it has the form of a woven fabric or a nonwoven fabric, it is more preferable.

  Examples of the heat resistant resin in the present invention include wholly aromatic polyamide, polyimide, polyamideimide, polysulfone, and polyethersulfone. Among these, polyamide, polyamic acid, and polyimide that are electrochemically stable are preferable.

  The composition of the glass fiber in this invention is not specifically limited, The C glass composition and E glass composition which are generally known as a composition for glass fibers can be utilized. Table 1 shows an example of the composition.

The amount of the glass fiber used in the organic-inorganic composite porous film of the present invention is preferably ² to 50 g / m ² , more preferably 3 to 25 g / m ² as a basis weight. When the basis weight of the glass fiber is 2 g / m ² or less, the strength when used as a skeleton material of the separator is reduced. On the other hand, when it exceeds 50 g / m ² , the thickness of the separator is increased, which is inconvenient. Here, the basis weight is the mass per unit area.

  Moreover, it is preferable that the quantity of the heat resistant resin to coat | cover is a ratio of 10-500 mass% with respect to the quantity of glass fiber. When this ratio is 10% by mass or less, the gap of the separator becomes large, the penetrating strength is lowered, and problems such as a short circuit occur. On the other hand, when it is 300% or more, the porosity is lowered and the ionic conductivity is lowered. A more preferable coating amount of the heat resistant resin is 10 to 300% by mass, more preferably 50 to 200% by mass with respect to the glass fiber mass.

The porosity of the organic / inorganic porous film is preferably 45 to 95% by volume. When the porosity exceeds 95% by volume, the penetrating strength is lowered and problems such as short circuit are likely to occur. On the other hand, if the porosity is less than 40% by volume, the ionic conductivity decreases. A more preferable porosity is 65 to 95% by volume, and a more preferable porosity is 75 to 90% by volume. The value of the porosity V is determined by pressing an inorganic porous material such as a nonwoven fabric at 20 kPa and measuring the thickness t with a dial gauge, the mass W per unit area of the inorganic porous material, and the density of fibers such as glass. ρG (in the case of glass fiber, about 2.5 × 10 ³ kg / m ³ (= 2.5 g / cm ³ )) and true density ρI of a heat-resistant resin material such as polyimide (not including voids, occupied by the substance itself) From the value of the mass ratio cI of the solid content of the heat resistant resin, it can be obtained by the following formula.

[Equation 1]
V (%) = [1-W / t × {(1-cI) / ρG + cI / ρI}] × 100

  Furthermore, in order to improve the adhesiveness between the heat resistant resin and the glass fiber in the present invention, an appropriate surface treatment may be performed. Specifically, silane coupling agent treatment is effective. Examples of the silane coupling agent include amino silane, methacryl silane, and epoxy silane.

In addition, it is preferable that the adhesion amount of a silane coupling agent is 0.5-200 mg / m < ² > with respect to a glass fiber surface area. If the adhesion amount is less than 0.5 mg / m ² , the silane coupling agent cannot sufficiently cover the glass fiber surface, and the effect of improving the adhesion between the glass fiber and the heat-resistant resin is lowered. Further, if the adhesion amount exceeds 200 mg / m ² , a low-strength layer consisting only of silane is formed between the glass fiber and the heat-resistant resin, and breakage within the layer is likely to occur. The effect of improving the adhesive strength with the heat resistant resin is reduced.

  Moreover, you may perform surface treatments, such as forming a film, such as a silica, in glass fiber. The surface treatment method is not particularly limited as long as the heat resistance of the glass fiber is not impaired.

  In order to ensure the functions required as a separator of a lithium ion battery, the thickness of the separator is preferably 100 μm or less, more preferably 20 μm or less. In order to obtain such a thickness, the average diameter of the glass fibers used is preferably 0.1 to 10 μm. If the average diameter is less than 0.1 μm, the manufacturing cost becomes extremely high and it is not practical. On the other hand, if it exceeds 10 μm, it is difficult to form a uniform nonwoven fabric with a thickness of 100 μm or less.

  Furthermore, it is preferable that the average fiber length of the glass fiber which comprises a glass fiber nonwoven fabric exists in the range of 0.1-20 mm. When the average fiber length of the glass fiber is less than 0.1 mm, it becomes difficult to isolate the electrode at the high temperature or burning required for the separator, and when it is made of a non-woven fabric, its mechanical strength is remarkably lowered, and the electrode at the high temperature or burning. This is because isolation becomes difficult. On the other hand, when the average fiber length of the glass fibers is 20 mm or more, mixing with the heat-resistant resin becomes difficult, and even when a nonwoven fabric is used, it becomes difficult to disperse and a uniform nonwoven fabric cannot be formed.

  The organic-inorganic composite porous film of the present invention can be used as a separator for non-aqueous electrolyte secondary batteries and capacitors using known means. The nonaqueous electrolyte secondary battery and capacitor of the present invention may have any configuration as long as it is a battery or capacitor using a separator.

  Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples. In addition, unless it exceeds the gist of the present invention, it is not limited to the following examples.

Glass short fibers having the composition of C glass shown in Table 2 and having an average diameter of 0.7 μm and an average length of about 3 mm were introduced into a pulper for unraveling the fibers, and sulfuric acid was added to adjust the pH to 2.5. It was sufficiently dissociated and dispersed in an aqueous solution to prepare a papermaking slurry (glass fiber dispersion). Using this slurry as a raw material, a glass fiber nonwoven fabric was obtained using a wet papermaking machine. The obtained glass fiber nonwoven fabric had a thickness of 20 μm and a basis weight of 5 g / m ² .

  2.5% by weight of polyimide resin varnish “Rika Coat PN-20” (solid content: 20% by weight) manufactured by Shin Nippon Rika Co., Ltd., 97% by weight of dehydrated N-methyl-2-pyrrolidone, and 0.5% by weight of polyethylene glycol After the polyimide resin varnish was dissolved in N-methyl-2-pyrrolidone at 60 ° C., polyethylene glycol was added to obtain a heat-resistant resin solution that was completely and completely compatible.

  The glass fiber nonwoven fabric was cut into a size of 10 cm × 10 cm, placed on a PET (polyethylene terephthalate) film, and impregnated with 10 g of the heat resistant resin solution from above. The glass nonwoven fabric impregnated with the heat-resistant resin solution is treated for 10 minutes in humidity-conditioned air (relative humidity 75% RH, temperature 30 ° C.), then peeled off from the PET film, and then in a 60 ° C. water bath for 2 minutes. Impurities were extracted and heat treatment was further performed at 280 ° C. for 2 minutes. The obtained glass fiber nonwoven fabric impregnated with the heat resistant resin, that is, the organic-inorganic composite porous film, had a thickness of about 20 μm and a porosity of about 85% by volume.

  0.5 g of short glass fibers having an average diameter of 0.7 μm and an average length of about 3 mm used in Example 1 were prepared. As in Example 1, 10% by weight of polyimide resin varnish “Rika Coat PN-20” (solid content: 20 wt%) manufactured by Shin Nippon Chemical Co., Ltd., 88% by weight of dehydrated N-methyl-2-pyrrolidone, and polyethylene glycol After weighing out to 2% by weight and dissolving the polyimide resin varnish in N-methyl-2-pyrrolidone at 60 ° C., polyethylene glycol was added to obtain a heat-resistant resin solution that was completely and completely compatible. Add 0.5 g of the short glass fiber prepared to 25 g of this heat-resistant resin solution, stir well to make it uniform, cast it into a film with a thickness of about 200 μm on a PET (polyethylene terephthalate) film, (Humidity 75% RH, temperature 30 ° C.) for 10 minutes. Thereafter, the film was peeled off from the PET film, followed by extraction of solvent and impurities in a 60 ° C. water bath for 2 minutes, and further heat treatment at 280 ° C. for 2 minutes. The obtained glass fiber nonwoven fabric impregnated with the heat resistant resin, that is, the organic-inorganic composite porous film, had a thickness of about 20 μm and a porosity of about 85% by volume.

(Comparative Example 1)
Complete phase of polyimide resin varnish “Rika Coat PN-20” (solid content 20 wt%) 10% by weight, N-methyl-2-pyrrolidone 88% by weight, polyethylene glycol 2% by weight manufactured by Shin Nippon Rika Co., Ltd. used in Example 2 The dissolved heat-resistant resin solution was cast into a film having a thickness of about 400 μm on a PET (polyethylene terephthalate) film and treated for 10 minutes in humidity-conditioned air (relative humidity 75% RH, temperature 30 ° C.). Thereafter, the film was peeled off from the PET film, followed by extraction of solvent and impurities in a 60 ° C. water bath for 2 minutes, and further heat treatment at 280 ° C. for 2 minutes. The resulting heat resistant resin porous film had a thickness of about 20 μm and a porosity of about 50% by volume.

(Comparative Example 2)
Α-alumina (Iwatani Chemical Industries, Ltd .; SA-1) having an average particle diameter of 0.8 μm was prepared as inorganic fine particles. In addition, the polyimide resin varnish “Rika Coat PN-20” (solid content 20 wt%) manufactured by Shin Nippon Rika Co., Ltd. used in Example 2 was 10% by weight, N-methyl-2-pyrrolidone 88% by weight, and polyethylene glycol 2% by weight. A compatible heat-resistant resin solution was prepared. Add 0.5 g of the inorganic fine particles to 25 g of this heat-resistant resin solution, stir well to make it uniform, cast it into a film having a thickness of about 400 μm on a PET (polyethylene terephthalate) film, and in humidity-conditioned air (relative humidity 75 % RH, temperature 30 ° C.) for 10 minutes. Thereafter, the film was peeled off from the PET film, followed by extraction of solvent and impurities in a 60 ° C. water bath for 2 minutes, and further heat treatment at 280 ° C. for 2 minutes. The resulting silica particle composite porous resin porous film had a thickness of about 20 μm and a porosity of about 45% by volume.

    The following test was done about the film sample produced in Examples 1-2 and Comparative Examples 1-2. The results of the test are shown in Table 3.

(Tensile strength measurement)
Each film sample was cut into a width of 20 mm and a length of 80 mm to prepare a test piece, and pulled at a rate of 10 mm / min with a chuck interval of 30 mm, and a load (N) at break was measured. The tensile strength (MPa) was calculated by dividing this by the cross-sectional area calculated from the measured values of the thickness and width of the sample. The thickness of the film sample was measured using a micrometer.

(Short resistance measurement)
A schematic diagram of the apparatus used for measuring the short-circuit resistance is shown in FIG. The film sample 1 was sandwiched from above and below by a stainless steel cylinder 2 having a diameter of 50 mm, and a load of 0.14 kg / cm ² was applied using a spring 3. Here, the upper and lower stainless steel cylinders 2 are electrically insulated by a heat-resistant insulating plate 4. Further, the lower end of the upper stainless steel cylinder 2 has a curvature so that the separator can be removed when pressurized. In a state where a voltage of 3.0 V was applied between the upper and lower stainless steel cylinders, it was placed in a programmed high temperature bath and heated from room temperature to 400 ° C. over 10 hours. When the film sample reaches a high temperature at which it melts or burns, a load is applied between the upper and lower stainless steel cylinders, so that the heat-resistant resin material constituting the film sample flows or is discharged, and both electrodes are short-circuited. Whether or not a short circuit occurred was judged from the value indicated by the resistance measuring instrument 5, and as shown in Table 3, the temperature at which the short circuit occurred was defined as a short circuit temperature and used as a short circuit resistance index.

  As is clear from the results of the above examples and comparative examples, the samples of Examples 1 and 2 of the present invention have the same strength but the short-circuit temperature is improved as compared with the samples of Comparative Examples 1 and 2. I understand that. In particular, although the sample of Comparative Example 2 contains inorganic fine particles, it exhibits a short temperature equivalent to that of Comparative Example 1 that is not so, that is, the inorganic fine particles move near the heat deformation temperature of the resin and the separator is rejected. Thus, it can be seen that the short-circuit occurred, and the organic-inorganic composite porous film of the present invention has excellent short-circuit resistance.

DESCRIPTION OF SYMBOLS 1 Film sample 2 Stainless steel cylinder 3 Spring 4 Heat-resistant insulating board 5 Resistance measuring device

Claims (11)

  An organic-inorganic composite porous film obtained by coating an inorganic porous material with a heat-resistant resin material.   The organic-inorganic composite porous film according to claim 1, wherein the inorganic porous material is composed of glass fiber, ceramic fiber, or a mixture thereof.   The organic-inorganic composite porous film according to claim 2, wherein the inorganic porous material is made of glass fiber.   The organic-inorganic composite porous film according to claim 2, wherein the inorganic porous material is a nonwoven fabric made of glass fiber.   The organic-inorganic composite porous film according to claim 2, wherein the inorganic porous material is a woven fabric made of glass fiber.   6. The organic-inorganic composite porous film according to claim 1, wherein the heat-resistant resin contains any one of polyamide, polyamic acid, and polyimide.   The organic-inorganic composite porous film according to claim 1, wherein the heat-resistant resin is coated at a ratio of 10 to 500 mass% with respect to the inorganic porous material.   The organic-inorganic composite porous film according to claim 2, wherein the glass fiber is surface-treated with a silane coupling agent.   The separator which consists of an organic inorganic composite porous film in any one of Claims 1-8.   A battery comprising the separator according to claim 9.   A capacitor comprising the separator according to claim 9.

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