Biaxially oriented polyphenylene sulfide film, and film for secondary battery electrodes made therefrom.

Abstract

The present invention addresses the problem of providing a polyphenylene sulfide film which has an excellent productivity in manufacturing batteries and enables electrode materials and base materials to be thin, and with which the battery capacity is improved.　This biaxially stretched polyphenylene sulfide film comprises at least one layer, and is composed of a polyphenylene sulfide resin composition. The biaxially stretched polyphenylene sulfide film has a thickness of 0.2-30 μm, and a tensile elongation at break of 30-150% in each of MD and TD directions. The relation between the tensile elongation at break in the MD direction and the tensile elongation at break in the TD direction satisfies formula (1): 0.75≤SMD / STD≤1.25. The heat shrinkage at 180℃ for 30 minutes both in the MD and TD directions is 4% or less. In formula (1), SMD represents the tensile elongation at break in the MD direction, and STD represents the tensile elongation at break in the TD direction.

Description

Technical Field

[0001] The present invention relates to a biaxially stretched polyphenylene sulfide film, an electrode for a secondary battery, and a film used therefor. More specifically, the present invention relates to a polyphenylene sulfide film excellent in battery manufacturing productivity, capable of thinning an electrode material and a base material, and having an improved battery capacity. Further, the present invention relates to an electrode for a secondary battery and an electrode for a secondary battery that are lighter in weight than conventional products by using the film of the present invention.

Background Art

[0002] In recent years, with the miniaturization of electric and electronic devices, miniaturization of the batteries used therein has been demanded, and improvement in battery capacity and extension of battery life have been demanded with the development of portable electric and electronic devices. As a battery structure, an electrode formed by laminating an electrode material on a metal foil having a thickness of 10 to 30 μm and winding it through a sheet-like separator is used. By thinning this electrode and separator, miniaturization of the battery, improvement in battery capacity, and extension of battery life are expected.

[0003] However, there is a limit to thinning while maintaining characteristics such as process handling properties, flexural fatigue resistance, and puncture resistance of the electrode so that the electrode is not penetrated by a nail or the like and does not lead to conduction. Moreover, since the amount of metal used does not change, the battery weight cannot be reduced. No. Therefore, as a new material replacing metal, the present inventors have proposed using a material having a structure in which a conductive thin film layer such as metal is provided on the surface of a biaxially stretched polyester thin film excellent in mechanical properties and heat-resistant dimensional stability as an electrode base material having a current collector function (Patent Documents 1 and 2).

[0004] When using biaxially oriented polyester film as an electrode substrate for energy storage elements, it is necessary to provide conductive thin film layers on both sides of the film, which are often achieved by methods such as vacuum deposition, electroplating, and sputtering. For example, vacuum deposition involves solidifying and depositing a laminated material, such as heated and vaporized metal, onto a film substrate that is in close contact with a cooling roll in a vacuum chamber. However, if the film lacks sufficient slipperiness or the film surface is excessively rough, adhesion to the cooling roll is often unsuccessful. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-40919 [Patent Document 2] Japanese Patent Application Publication No. 10-40920 [Overview of the project] [Problems that the invention aims to solve]

[0006] One possible solution involves using a plastic film with a reinforced structure oriented onto a substrate, and then applying a thin metal film to its surface. However, this could lead to increased resistance due to the reduced metal film thickness, potentially causing a temperature rise. With conventional plastic films, this would likely result in poor battery durability. Furthermore, polyester films tend to have low resistance to electrolytes, which can hinder the long lifespan of batteries.

[0007] Therefore, the object of the present invention is to provide a biaxially oriented polyphenylene sulfide film that has excellent heat resistance, allows for further thinning of metal thin films, can obtain the required battery capacity, and is suitable for manufacturing battery components with improved lifespan. Furthermore, the present invention aims to provide a secondary battery electrode and a film for use therein that are lighter than conventional products. [Means for solving the problem]

[0008] According to the present invention, a film made of polyphenylene sulfide resin, having at least one layer and a thickness of 0.2 μm or more and 30 μm or less, The tensile elongation at break in the MD direction and the TD direction is between 30% and 150%, respectively. The relationship between the tensile elongation at break in the MD direction and the tensile elongation at break in the TD direction satisfies relationship (1), This is achieved by a biaxially oriented polyphenylene sulfide film in which the heat shrinkage rate at 180°C for 30 minutes is 4% or less in both the MD and TD directions. 0.75≦SMD / STD≦1.25 (1) (In equation (1) above, SMD represents the tensile elongation at break in the MD direction, and STD represents the tensile elongation at break in the TD direction.)

[0009] Furthermore, the present invention provides the following embodiments. [2] In one embodiment, the polyphenylene sulfide resin composition further comprises inert particles, the amount of which the inert particles are present in an amount of 500 ppm to 20000 ppm based on the weight of the polyphenylene sulfide resin, The average roughness SRa of the center surface of both sides of the film is between 5 nm and 70 nm, and the average roughness SRz of ten points is between 200 nm and 950 nm. SRa and SRz satisfy relationship (2). The above biaxially oriented polyphenylene sulfide film. 10≦SRz / SRa≦50 (2) [3] In one embodiment, the Young's modulus in the MD direction and the TD direction are 3500 MPa or more and 5500 MPa or less, The relationship between Young's modulus in the MD direction and Young's modulus in the TD direction satisfies relationship (3). The above biaxially oriented polyphenylene sulfide film. 0.75≦ YMD / YTD ≦1.25 (3) In equation (3) above, YMD represents the Young's modulus in the MD direction, and YTD represents the Young's modulus in the TD direction. [4] In one embodiment, the above-mentioned biaxially oriented polyphenylene sulfide film having a density of 1,340 g / dl or more. [5] In one embodiment, the above biaxially oriented polyphenylene sulfide film having a melting peak temperature of 250°C or higher in DSC measurement. [6] In one embodiment, a film for secondary battery electrodes is characterized in that a thin metal film is further provided on at least one surface of the biaxially oriented polyphenylene sulfide film described above. [7] In one embodiment, the above-mentioned secondary battery electrode film is further characterized by having an electrode material. [Effects of the Invention]

[0010] The present invention provides a polyphenylene sulfide film that exhibits high tensile elongation and a small MD-TD difference in tensile elongation, making it less prone to breakage and perforation, and thus offering excellent productivity in, for example, battery manufacturing. [Modes for carrying out the invention]

[0011] The biaxially oriented polyphenylene sulfide film of the present invention can be used, for example, as a film for secondary battery electrodes. Secondary batteries made using the present invention have improved battery capacity due to the thinning of the electrode material substrate (electrode substrate), and the electrode material substrate has a high melting peak temperature and low thermal shrinkage. Furthermore, because a biaxially oriented film is used, short circuits due to thermal deformation of the electrode material substrate are prevented, improving battery life. Furthermore, secondary batteries made using the film of the present invention are lighter than conventional products that use metal foil as the electrode material substrate (electrode substrate), and also have a higher gravimetric energy density.

[0012] The biaxially oriented polyphenylene sulfide of the present invention is a film with a thickness of 0.2 μm to 30 μm. It has thickness. Having such film thickness improves the energy density of the energy storage element, particularly its volumetric energy density, when used as a substrate film for the electrodes of an energy storage element. It also provides resistance to bending. If a thick film exceeding the upper limit value is used as the electrode substrate, it will be thicker than the conventional metal foil, which will not lead to an improvement in the energy density of the energy storage element, especially the volume energy density. On the other hand, when the film thickness is too thin to reach the lower limit value, it becomes extremely difficult to manufacture the film. Therefore, from the perspective of improving the energy density of the energy storage element, especially the volume energy density, and the efficiency of film manufacturing, the present invention has the above thickness. A more preferable film thickness is 0.2 μm or more and 20 μm or less, more preferably 0.2 μm or more and 12 μm or less, and particularly preferably 0.5 μm or more and 10 μm or less. Even when the biaxially stretched polyphenylene sulfide film of the present invention has a laminated structure having a co-extruded layer, a coating layer, etc., it is preferable that the thickness in the laminated structure is within the above range.

[0013] When the biaxially stretched film has a tensile fracture elongation of 30% or more and 150% or less in the MD direction and the TD direction, respectively, the workability of battery fabrication by laminating and winding the electrode material becomes better. If it is less than 30%, troubles such as breakage may occur during battery fabrication, which is not preferable. The tensile fracture elongations in the MD direction and the TD direction may be the same or different as long as they are within the above range. For example, the tensile fracture elongations in the MD direction and the TD direction may be 40% or more and 140% or less, respectively.

[0014] In the present invention, the relationship between the tensile fracture elongation in the MD direction and the tensile fracture elongation in the TD direction satisfies the following relationship (1). 0.75 ≦ SMD / STD ≦ 1.25 ···(1) In the above formula (1), SMD represents the tensile fracture elongation in the MD direction, and STD represents the tensile fracture elongation in the TD direction, respectively. Also, it is preferable that the tensile fracture elongation in the MD direction is in the range of 75% to 125% with respect to the tensile fracture elongation in the TD direction. More preferably, it is 80% to 120%, that is, 0.80 ≦ SMD / STD ≦ 1.20, and still more preferably, it is 85% to 119%, that is, 0.85 ≦ SMD / STD ≦ 1.19. If the difference between the tensile elongation at break in the MD direction and the tensile elongation at break in the TD direction is too large, the piercing strength is likely to decrease due to the orientation of the molecular chains in one direction, which may cause perforations and is not preferable. In the present invention, when the tensile elongation at break in the MD direction is within the above range with respect to the tensile elongation at break in the TD direction, the decrease in piercing strength can be suppressed, perforations can be suppressed, and furthermore, the resistance to the electrolyte can be enhanced, and the battery life can be maintained longer than before. Also, when the SMD / STD value is within the above range, good flex resistance can be imparted.

[0015] In the biaxially stretched film, when the Young's moduli in the MD direction and the TD direction are each 3500 or more and 5500 MPa or less, the workability of battery fabrication by laminating and winding the electrode material becomes better. When the Young's modulus is 3500 MPa or more, the occurrence of wrinkles and breaks in the battery fabrication process can be suppressed. Also, when the Young's modulus is 5500 MPa or less, the film-forming property can be improved.

[0016] For example, the Young's moduli in the MD direction and the TD direction have the relationship of the following formula (3). 0.75 ≦ YMD / YTD ≦ 1.25 ···(3) In the above formula (3), YMD represents the Young's modulus in the MD direction, and YTD represents the Young's modulus in the TD direction. The Young's modulus in the MD direction is preferably in the range of 75% to 125% with respect to the Young's modulus in the TD direction. That is, the formula (3) has the relationship of 0.75 ≦ YMD / YTD ≦ 1.25. More preferably, it is 80% to 120%, the formula (3) is 0.80 ≦ YMD / YTD ≦ 1.20, and even more preferably, it is 85% to 115%, the formula (3) is 0.85 ≦ YMD / YTD ≦ 1.15. If the difference between the Young's modulus in the MD direction and the Young's modulus in the TD direction is too large, the puncture strength is likely to decrease due to the bias of the molecular chain direction in one direction, which can lead to punctures and other problems, and is undesirable. On the other hand, in the present invention, since the Young's modulus in the MD direction and the Young's modulus in the TD direction have the above relationship, the decrease in puncture strength can be suppressed, punctures can be suppressed, and furthermore, resistance to electrolytes can be increased, making it possible to maintain a longer battery life than conventional batteries. In addition, by having the YMD / YTD value within the above range, good bending resistance can be provided.

[0017] The biaxially oriented film has a heat shrinkage rate of 4% or less in the MD and TD directions at 180°C for 30 minutes. More preferably, it is 3.5% or less, and more preferably 3% or less. If the heat shrinkage rate is too high, it is undesirable because when used as a secondary battery, the thermal deformation of the electrodes due to heat generation from internal resistance can cause a short circuit. The heat shrinkage rates in the MD and TD directions may be similar or different.

[0018] In the present invention, the biaxially oriented film requires the addition of polymer-inert particles (inert particles) as a surface roughening agent to the extent that it does not impair the effects of the present invention, thereby roughening the film surface. Preferably, the average surface roughness SRa of the center plane of the film is 5 nm to 70 nm, and more preferably 6 nm to 65 nm. Furthermore, the ten-point average roughness SRz is preferably 200 nm to 950 nm, and more preferably 250 nm to 900 nm. If SRa is less than 5 nm and SRz is less than 200 nm, the film's transportability is significantly reduced, which is undesirable. Also, if SRa exceeds 70 nm and SRz exceeds 950 nm, proper adhesion with the cooling roll during deposition is difficult to obtain, which is undesirable. Therefore, by having the above roughness, the present invention can further improve transportability and ensure good proper adhesion with the cooling roll during deposition. Furthermore, the surface roughness must satisfy the following equation (2). Satisfying this equation improves air release during winding onto the roll, suppressing wrinkles and creases on the roll. 10 ≤ SRz / SRa ≤ 50 ···(2)

[0019] In one embodiment, formula (2) above can take the following forms. 10 ≤ SRz / SRa ≤ 40, or 12 ≤ SRz / SRa ≤ 38 By using these values, the air release during winding onto the roll is further improved, and wrinkles and folds on the roll can be suppressed more effectively.

[0020] The surface roughening agent is preferably fine particles with an average particle size of 0.05 to 5 μm. Preferably, the fine particles are inert particles. Furthermore, the amount added is preferably 500 ppm to 20,000 ppm, more preferably 1,000 ppm to 15,000 ppm, and even more preferably 1,500 ppm to 10,000 ppm.

[0021] Examples of roughening agents include calcium carbonate, magnesium carbonate, barium carbonate, barium sulfate, calcium phosphate, lithium phosphate, magnesium phosphate, lithium fluoride, aluminum oxide, silicon dioxide (silica), titanium dioxide, kaolin, talc, and carbon dioxide. Examples include lac, silicon nitride, boron nitride, and crosslinked polymer fine particles (for example, fine particles of crosslinked polystyrene, crosslinked acrylic resin, crosslinked silicone resin, etc.). These may be used alone or in combination of two or more. Preferably, the surface roughening agent is an inert particle that is inert to the polymer.

[0022] One method for incorporating such a surface roughening agent is the external particle addition method, in which inert inorganic or organic fine particles are added to the polymer during one of the following processes: polymer manufacturing, masterbatch preparation, or film formation.

[0023] The biaxially oriented polyphenylene sulfide film in the present invention has a melting peak temperature of 250°C or higher, preferably 260°C or higher, and more preferably 270°C or higher, as measured by DSC temperature rise. The melting peak temperature is, for example, 300°C or lower. Because the melting peak temperature is 250°C or higher, for example, when used in a secondary battery, thermal deformation of the electrodes can be suppressed when heat is generated due to internal resistance, and short circuits can also be prevented.

[0024] The polyphenylene sulfide resin in the present invention is preferably a homopolymer, but may also be a copolymer. Alternatively, it may be a polymer blend consisting of two or more of these homopolymers and / or copolymers.

[0025] The biaxially oriented film in this invention can be manufactured according to conventionally known methods. For example, after thoroughly drying the raw polymer under predetermined conditions, it can be extruded using a well-known melt extruder. The raw material polymer is supplied to an extruder (typically one such extruder) and heated to a temperature above the polymer melting point (Tm:°C), particularly above Tm and below (Tm+70)°C, to melt it. The mixture is melted and kneaded until it becomes uniform, and the degree of melting and kneading is adjusted.

[0026] Next, the molten and kneaded polymer is extruded into a sheet through a slit-shaped die lip and rapidly cooled and solidified on a rotating cooling drum to obtain an unstretched sheet in a substantially amorphous state. In this case, to improve adhesion with the rotating cooling drum and to improve the surface flatness (planarity, smoothness) of the sheet, In this case, the electrostatic charge application method and / or the liquid coating method are preferably employed. The contact method involves applying a DC voltage to a linear electrode stretched perpendicular to the flow of the sheet extruded from the die, thereby placing an electrostatic charge on the surface of the sheet (non-drum side), and rotating the sheet with this action. This is a method to improve adhesion with the rotating cooling drum. The liquid coating adhesion method involves uniformly applying a liquid to all or part of the surface of the rotating cooling drum (for example, the parts that come into contact with both ends of the sheet). This method improves the adhesion between the sheet and the rotating cooling drum. In this invention, both methods may be used in combination as needed. Furthermore, inflation casting or casting methods can also be employed as methods for producing an undrawn sheet that is substantially amorphous.

[0027] The resulting unstretched sheet is then stretched biaxially to form a biaxially oriented film. This stretching method can be sequential biaxial stretching (Tenter method) or simultaneous biaxial stretching (Tenter method). Alternatively, the tube method can be used. The stretching conditions for the sequential biaxial stretching method are as follows: the unstretched sheet is stretched at a temperature of (Tg-10) to (Tg+70)°C (where Tg is the highest temperature). The material is stretched 2 to 6 times, preferably 2.5 to 5.5 times, in one direction (longitudinal or transverse) at the glass transition temperature, and then stretched 2 to 6 times, preferably 2.5 to 5.5 times, in a direction perpendicular to the first stage (if the first stage stretching is longitudinal, the second stage stretching will be transverse) at a temperature of Tg or above (Tg+70)°C or below. Note that the unidirectional stretching can also be performed in multiple stages of two or more steps. It is possible, but even in that case, it is desirable that the final stretch ratio be within the range mentioned above. Also, after the second stage of stretching, intermediate heat treatment is performed, and then again in the same direction as the first stage and / or the same as the second stage. The sheet may be stretched in one direction. Alternatively, the unstretched sheet can be simultaneously biaxially stretched to an area ratio of 6 to 30 times, preferably 8 to 25 times.

[0028] A small difference in the stretch ratio between the MD and TD directions is preferable. If the difference in stretch ratio between the MD and TD directions becomes too large, the difference in Young's modulus between the MD and TD directions becomes too large, which is undesirable. The stretch ratio in the TD direction should be 0.7 to 1.5 times that of the stretch ratio in the MD direction. It is preferable to set it within a range.

[0029] The biaxially oriented film thus obtained is heat-treated as necessary, preferably at a temperature of 200°C to 280°C for 1 second to 10 minutes. It can be performed under restricted contraction or extension within the body, or under constant length, and may also be performed in two or more stages.

[0030] In one embodiment, the biaxially oriented film of the present invention has a density of 1.340 g / dl or more, for example, a density of 1.40 g / dl or less. By keeping the density within this range, crystallization is sufficiently promoted, and the effect of suppressing thermal shrinkage can be achieved.

[0031] The biaxially oriented film of the present invention may be surface-treated to improve adhesion to a thin metal film. The surface treatment method is not particularly limited, but preferred examples include coating an adhesive layer, corona treatment, plasma treatment, etc. These surface treatments may be performed during the film-forming process of the biaxially oriented film, or in a separate process. Of these, it is preferable to perform them during the film-forming process.

[0032] The biaxially oriented film in this invention may have a thin metal film on at least one of its surfaces, as it is used as a film for secondary battery electrodes. Examples of metals used to form the thin film include aluminum, nickel, gold, silver, copper, and cadmium, but are not particularly limited as long as they are conductive, for the purposes of this invention. The thickness of the thin metal film is typically 1 to 1000 nm. The range is 10 to 1000 nm, in order to suppress internal resistance and heat generation in the battery. This is preferable. Preferred methods for creating metal thin films include vacuum deposition, electroplating, and sputtering.

[0033] The secondary battery electrode film of the present invention can be used as a secondary battery electrode by further laminating an electrode material onto its metal thin film surface. Conventional electrode materials such as lithium cobalt oxide and graphite can be used. Furthermore, a secondary battery can be manufactured using this secondary battery electrode by conventionally known methods. For example, when manufacturing a lithium-ion secondary battery, a secondary battery electrode film having a copper sputtered film coated with lithium cobalt oxide can be used as the positive electrode, and a secondary battery electrode film having an aluminum vapor-deposited film coated with graphite can be used as the negative electrode. A separator made of polyethylene microporous film is interposed between the two, and the films are wound together. A secondary battery can then be formed using an organic solvent containing a dissolved lithium salt as the electrolyte. [Examples]

[0034] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to the following examples unless it exceeds the gist of the invention. The various physical properties and characteristics in the present invention were measured and defined as follows.

[0035] (1) Film thickness The film sample was placed in a spindle detector (K107C, manufactured by Anritsu Electric Co., Ltd.), and its thickness was measured at 10 different points using a digital differential electronic micrometer (K351, manufactured by Anritsu Electric Co., Ltd.). The average value was then calculated to determine the film thickness.

[0036] (2) Tensile elongation at fracture, Young's modulus The tensile elongation at break was measured by sampling the film in sections 10 mm wide and 150 mm long, and using a well-known tensile strength. Using a tension testing machine, the material is pulled at a speed of 10 mm / min with a chuck spacing of 100 mm, and the strain (%) at the point of fracture is read. (Unit: %) The Young's modulus was measured by sampling the film to a width of 10 mm and a length of 150 mm, and using the well-known tensile strength. The material was pulled using a testing machine with a chuck spacing of 100 mm and a speed of 10 mm / min. The tensile strength was determined from the tangent line at the rising portion of the resulting load-elongation curve (unit: MPa).

[0037] (3) Heat shrinkage rate at 180°C In accordance with JIS C 2318-1997 5.3.4 (Dimensional Change), the dimensional change rate (%) in the longitudinal and width directions was measured.

[0038] (4) Surface roughness The outermost surface of a biaxially oriented film was measured using a stylus-type three-dimensional roughness meter (SE-3AK, manufactured by Kosaka Research Institute Co., Ltd.) under the conditions of a needle radius of 2 μm and a load of 30 mg. The measurement was performed in the longitudinal direction of the film with a cutoff value of 0.25 mm over a measurement length of 1 mm, at a needle feed speed of 0.1 mm / second. The measurement was divided into 500 points at 2 μm intervals, and the height of each point was input into a three-dimensional roughness analyzer (SPA-11). The same procedure was performed continuously 150 times in the width direction of the film at 2 μm intervals, i.e., over a width of 0.3 mm, and the data was input into the analyzer. Next, the average roughness of the center surface (SRa) and the average roughness of ten points (SRz) were determined using the analyzer. (5) Average particle size of the surface roughening agent The surface roughening agent was observed using a scanning electron microscope (Hitachi, Ltd., S-51O model). The magnification was adjusted appropriately according to the particle size, and photographs were taken and enlarged copies were made. Next, the outer circumference of at least 200 randomly selected particles was traced, and the equivalent circular diameter of the particles was measured from these traced images using an image analysis device. The average of these measurements was taken as the average particle diameter.

[0039] (6) Melting peak temperature (Tm) A 10 mg film sample is placed in a Seiko Electronics Industries, Ltd. thermal analysis system SSC / 5200 or DSC5200 and heated in a nitrogen gas stream at a heating rate of 20°C / min. The endothermic behavior associated with the melting of the film is analyzed using first and second derivatives to determine the temperature at which a peak or shoulder appears. This temperature is defined as the melting peak temperature (unit: °C).

[0040] (7) Density The density was measured according to the method compliant with JIS K 7112:1999 (density gradient pipe method). (Unit: g / cm³) 3 ).

[0041] (8)Battery capacity A lithium-ion secondary battery is created using film, and a continuous discharge is performed. A battery with a discharge capacity of 2000mAh or more at which the discharge voltage drops to 80% is considered good.

[0042] (9) Productivity of battery manufacturing In the series of operations involving electrode coating and winding, a reduction in productivity due to breakage or other issues of less than 10% is considered satisfactory.

[0043] (10) Battery life The created batteries are subjected to repeated charge / discharge tests under 100°C conditions, and batteries are considered good if they undergo more than 500 degradation cycles before a short circuit occurs in 10% of the total number of batteries.

[0044] [Example 1] A masterbatch with a calcium carbonate particle concentration of 4000 ppm was prepared by melt-mixing a polyphenylene sulfide resin with a Tg of 95°C and a Tm of 285°C with calcium carbonate particles having an average particle size of 0.6 μm using a twin-screw extruder. After drying and crystallizing this masterbatch, it was melt-extruded through a slit-shaped die and rotate-collapsed at a surface temperature of 30°C using the electrostatic application adhesion method. The sheets were rapidly cooled and solidified on a cooling drum to obtain an unstretched sheet.

[0045] The unstretched sheet was sequentially biaxially stretched at a stretching temperature of 100°C with a stretching ratio of 3.3 times in the longitudinal direction and 3.8 times in the transverse direction. After cooling, it was subjected to a constant-length heat treatment at 250°C for 30 seconds to obtain a biaxially oriented film with a thickness of 5.0 μm. The tensile elongation at break of the obtained biaxially oriented film is shown in Table 1.

[0046] Copper sputtering was applied to both sides of this biaxially oriented film, and lithium cobalt oxide was coated on top to form the positive electrode material. Aluminum vapor deposition was applied to both sides of the same biaxially oriented film, and graphite was coated on top to form the negative electrode material. A separator made of polyethylene microporous membrane was interposed between these materials during winding, and a lithium-ion secondary battery was fabricated using a solution of lithium hexafluoride phosphate dissolved in a mixed solvent of ethylene carbonate / diethyl carbonate / ethyl acetate as the electrolyte. The capacity of the resulting battery and the productivity during the entire process are shown in Table 1.

[0047] [Examples 2 and 3] Film deposition and battery fabrication were carried out in the same manner as in Example 1, except that the thickness was changed as shown in Table 1.

[0048] [Example 4] Film formation and battery fabrication were carried out in the same manner as in Example 1, except that the heat treatment after biaxial stretching was changed to 260°C.

[0049] [Example 5] Film formation and battery fabrication were carried out in the same manner as in Example 2, except that the heat treatment after biaxial stretching was changed to 240°C for 60 seconds.

[0050] [Examples 6, 7] Film deposition and battery fabrication were carried out in the same manner as in Example 1, except that the calcium carbonate content was changed as shown in Table 1.

[0051] [Example 8] Film deposition and battery fabrication were carried out in the same manner as in Example 1, except that calcium carbonate was replaced with 0.5 μm silica.

[0052] [Example 9] Film deposition and battery fabrication were carried out in the same manner as in Example 1, except that the MD stretching ratio was changed to 2.3 times and the TD stretching ratio to 2.8 times.

[0053] [Comparative Example 1] Film formation was carried out in the same manner as in Example 1, except that the tensile strength ratio (SMD / STD) was 0.39, by sequential biaxial stretching with a stretching ratio of 2.0 times in the longitudinal direction and 3.5 times in the transverse direction.

[0054] [Comparative Example 2] The film is formed by sequentially performing biaxial stretching in the lateral direction at a stretching ratio of 4.5 times. Except for the tensile strength ratio (SMD / STD) being 5.67, film deposition and battery fabrication were carried out in the same manner as in Example 1.

[0055] [Comparative Example 3] Film formation was carried out in the same manner as in Example 1, except that the film was fabricated by sequential biaxial stretching in the longitudinal direction at a stretching ratio of 2.5 times, and the ratio of tensile elongation at break (SMD / STD) was 1.51.

[0056] Table 1 shows the battery capacity and productivity during the series of processes obtained in Comparative Examples 1, 2, and 3. In Comparative Examples 1 and 2, the elongation at break in the longitudinal and transverse directions of the base film was too low, resulting in a tensile elongation at break ratio (SMD / STD) outside the range of the present invention. This led to problems with film breakage during battery manufacturing, resulting in low battery productivity. In Comparative Example 3, the difference in elongation at break between the MD and TD directions was too large, resulting in a tensile elongation at break ratio (SMD / STD) outside the range of the present invention. This led to wrinkles and folds during winding, resulting in low battery productivity.

[0057] [Comparative Example 4] Film fabrication and battery preparation were carried out in the same manner as in Example 1, except that the heat shrinkage rate of the biaxially oriented film at 180°C for 30 minutes was set to 12% for both MD and TD.

[0058] The capacity of the obtained lithium-ion secondary battery and the productivity during the series of processes are shown in Table 1. This battery had an excessively high thermal shrinkage rate, which caused short circuits due to thermal deformation of the electrodes when heat was generated due to internal resistance, resulting in an insufficient battery life.

[0059] [Comparative Example 5] Film fabrication and battery preparation were carried out in the same manner as in Example 1, except that the thickness of the biaxially oriented film was set to 40 μm.

[0060] The capacity of the obtained lithium-ion secondary battery and the productivity during the series of processes are shown in Table 2. This battery had insufficient capacity because the film used as the electrode material substrate was too thick.

[0061] [Comparative Example 6] Except for replacing polyphenylene sulfide with polyethylene terephthalate, film deposition and battery fabrication were carried out in the same manner as in Example 1.

[0062] The capacity, productivity during the series of processes, and battery life of this battery are shown in Table 1. This battery was prone to short circuits and had a short battery life because polyethylene terephthalate dissolved in the electrolyte.

[0063] [Table 1]

[0064] [Table 2] [Industrial applicability]

[0065] The present invention provides a secondary battery electrode and film that offer excellent heat resistance, allow for further thinning of the metal thin film, achieve the required battery capacity, improve lifespan, and are lighter than conventional products due to the use of a film as the substrate.

Claims

1. A film of at least one layer made of a polyphenylene sulfide resin composition containing inert particles in an amount of 500 ppm or more and 20,000 ppm or less based on the weight of the polyphenylene sulfide resin, The thickness is 0.2 μm or more and 20 μm or less. The tensile elongation at break in the MD direction and the TD direction is 30% or more and 150% or less, The relationship between the tensile elongation at break in the MD direction and the tensile elongation at break in the TD direction satisfies relationship (1), The heat shrinkage rate at 180°C for 30 minutes is 4% or less in both the medium-distance (MD) and tectonic (TD) directions. Biaxially oriented polyphenylene sulfide film and The biaxially oriented polyphenylene sulfide film comprises a metal thin film provided on at least one surface of the biaxially oriented polyphenylene sulfide film, The above biaxially oriented polyphenylene sulfide film has a center plane average roughness SRa of 5 nm or more and 70 nm or less on both sides, and a ten-point average roughness SRz of 200 nm or more and 950 nm or less. A film for secondary battery electrodes in which SRa and SRz satisfy relationship (2). 0.75≦SMD / STD≦1.25...(1) In equation (1) above, SMD represents the tensile elongation at break in the MD direction, and STD represents the tensile elongation at break in the TD direction. 10≦SRz / SRa≦50...(2)

2. The Young's modulus of the biaxially oriented polyphenylene sulfide film in the MD direction and the TD direction is 3500 MPa or more and 5500 MPa or less, respectively. The secondary battery electrode film according to claim 1, wherein the relationship between the Young's modulus in the MD direction and the Young's modulus in the TD direction satisfies relationship (3). 0.75≦YMD / YTD≦1.25...(3) In equation (3) above, YMD represents the Young's modulus in the MD direction, and YTD represents the Young's modulus in the TD direction.

3. The secondary battery electrode film according to claim 1, wherein the density of the biaxially oriented polyphenylene sulfide film is 1,340 g / cm³ or more.

4. The secondary battery electrode film according to claim 1, wherein the melting peak temperature of the biaxially oriented polyphenylene sulfide film in DSC measurement is 250°C or higher.

5. A secondary battery electrode comprising a secondary battery electrode film according to any one of claims 1 to 4, further having an electrode material.

6. A secondary battery having electrodes for a secondary battery as described in claim 5.

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