JP6349442B1 - Composite membrane and battery - Google Patents

Abstract

Disclosed are a composite film and a battery that have low electrical resistance at low temperatures and high electrical resistance at high temperatures. A composite film 10 having a plurality of conductive particles 1 and an insulating polymer material 2 and having PTC characteristics is provided. The polymer material 2 includes at least a first material 2A and a second material 2B having a melting point lower than that of the first material 2A. The melting point of the second material 2B is 54 to 58 ° C. The plurality of conductive particles 1 are arranged so that at least a part thereof forms a row from one surface 10a of the composite film 10 to the other surface 10b. [Selection] Figure 1

Description

  The present invention relates to a composite membrane and a battery.

For batteries, electronic devices, and the like, a PTC element including a PTC film having a PTC characteristic (Positive Temperature Coefficient) may be used (for example, see Patent Document 1). The PTC characteristic is a characteristic that limits the current by increasing the volume resistivity when the temperature rises.
For example, in order to prevent thermal runaway in a lithium ion battery mounted on an electric vehicle, a hybrid vehicle, etc., it is effective to cut off the current and suppress the battery reaction. When the temperature of the electrolytic solution exceeds 55 ° C., the rate of the battery reaction increases, and the thermal decomposition reaction of the electrolytic solution easily occurs. The temperature of the electrolytic solution is preferably 130 ° C. or lower in consideration of safety (ignition prevention, etc.). Therefore, in lithium ion batteries, temperature management is often performed based on 55 ° C and 130 ° C. JIS C8712 also stipulates that safety should be confirmed by the presence or absence of a short circuit at 55 ° C. and the presence or absence of ignition at 130 ° C. In addition, when contamination of metal particles occurs on the positive electrode plate or negative electrode plate, abnormal charging / discharging such as short-circuit current and overcharging occurs, the temperature of the battery rises due to Joule heating, and the battery reaction is accelerated. Charging / discharging may occur.

As means for preventing abnormal temperature rise and charging / discharging, a PTC element having a PTC characteristic (for example, a PTC thermistor) is used. A protection circuit, a protection element, or the like using a PTC element can limit a short-circuit current or an excessive current and protect a battery.
The PTC film used for the PTC element includes, for example, conductive particles and a polymer material. The PTC film exhibits high conductivity because the conductive particles form a conductive path at a low temperature, but at a high temperature, the conductive path is cut due to thermal expansion of the polymer material, resulting in a decrease in conductivity. Therefore, the current is limited at a high temperature, and abnormal heat generation can be prevented.

Japanese Unexamined Patent Publication No. 2016-44257

  In the conventional PTC film, when the content of the conductive particles is increased in order to reduce the electric resistance at low temperatures, the change in electric resistance when the temperature rises becomes small, and the current limiting effect may be reduced. Therefore, there is a demand for a PTC film that has a low electrical resistance at low temperatures and a high electrical resistance at high temperatures.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide a composite film and a battery that have low electrical resistance at low temperatures and high electrical resistance at high temperatures.

The first aspect of the present invention is a composite film having a plurality of conductive particles and an insulating polymer material and having PTC characteristics. The polymer material includes at least a first material and a second material having a melting point lower than that of the first material. The melting point of the second material is 54 to 58 ° C. The plurality of conductive particles are arranged so that at least a part thereof forms a row from one surface of the composite film to the other surface.
According to a second aspect of the present invention, in the composite film of the first aspect, the first material is a crystalline material. The second material is an amorphous material.
According to a third aspect of the present invention, in the composite film of the first or second aspect, a ratio C2 / C1 (volume basis) of the content ratio C1 of the first material and the content ratio C2 of the second material is 1/3 to 1.
According to a fourth aspect of the present invention, in the composite film of the first to third aspects, the second material is paraffin.

The 5th aspect of this invention is a battery provided with the positive electrode plate, the negative electrode plate, and electrolyte solution. The positive electrode plate includes a positive electrode current collector plate and a positive electrode active material layer provided on the inner surface side of the positive electrode current collector plate. The negative electrode plate includes a negative electrode current collector plate and a negative electrode active material layer provided on the inner surface side of the negative electrode current collector plate. Between the negative electrode current collector plate and the negative electrode active material layer, the composite film and a metal coating layer provided on the inner surface side of the composite film are formed.
According to a sixth aspect of the present invention, in the battery according to the fifth aspect, a part of the composite film is formed to extend outward from at least a part of a peripheral edge of the metal coating layer.

  According to one embodiment of the present invention, the polymer material includes the first material and the second material, and the melting point of the second material is 54 to 58 ° C. Since the second material has a low melting point and high fluidity, the conductive particles easily move in the phase made of the second material, so that the conductive particles are easily aligned according to the magnetic field. Therefore, a composite film having a low electrical resistivity in a low temperature range can be obtained. In addition, since the phase containing the first material having a high melting point has a high coefficient of thermal expansion, the conductive path of the composite film is likely to be cut due to thermal expansion in a high temperature range. Therefore, the electrical resistivity can be sufficiently increased. Therefore, it is possible to obtain a composite film having a characteristic that the electrical resistance is low at a low temperature and the electrical resistance is high at a high temperature.

It is a schematic diagram which shows the structure of the composite film of one Embodiment. It is a schematic diagram which shows the structure of the composite film of one Embodiment. It is a figure which shows typically the cross section of electroconductive particle. It is a photograph of an example of electroconductive particle. It is sectional drawing which shows a some electroconductive particle typically, and is a figure which shows the cross section along the thickness direction of a composite film. It is the photograph which expanded the cross section of the composite film of this embodiment. It is process drawing which shows an example of the manufacturing method of the composite film of this embodiment. FIG. 8 is a process diagram following FIG. 7. It is a figure which shows typically the 1st example of the apparatus which manufactures the composite film of this embodiment. It is a figure explaining the effect | action of the magnet in the manufacturing apparatus of FIG. It is a schematic diagram which shows the structure of the composite film of this embodiment. It is a schematic diagram which shows the structure of an example of the conventional composite film. It is a figure which shows typically the 2nd example of the apparatus which manufactures the composite film of this embodiment. It is a figure which shows typically the lithium ion battery using the composite film of this embodiment. It is a figure which shows typically the 3rd example of the apparatus which manufactures the composite film of this embodiment. It is a photograph of the section of the composite film of a test example. It is a photograph of the section of the composite film of a test example. It is a figure which shows the temperature dependence of an electrical resistivity about the composite film of a test example. It is a figure which shows the temperature dependence of an electrical resistivity about the composite film of a test example. It is a photograph of the surface of the composite film of a test example. It is a photograph of the surface of the composite film of a test example.

  Hereinafter, a composite film according to an embodiment will be described with reference to the drawings. Note that in the drawings used in the following description, in order to make the characteristics easy to understand, there are cases where the characteristic portions are enlarged for the sake of convenience, and the dimensional ratios of the respective components may differ from the actual ones. Further, the present invention is not limited to the following embodiment.

<Composite membrane>
1 and 2 are schematic views showing the structure of the composite film 10 (composite film) of this embodiment. 1 and 2 are cross-sectional views of the composite film 10 along the thickness direction. The thickness direction is a direction perpendicular to the surface of the composite film 10. FIG. 3 is a diagram schematically showing a cross section of the conductive particle 1. FIG. 4 is a photograph of an example of the conductive particles 1. FIG. 5 is a cross-sectional view schematically showing a plurality of conductive particles 1, and is a view showing a cross section along the thickness direction of the composite film 10.

As shown in FIG. 1, the composite film 10 is composed of a composite material 3 including a plurality of conductive particles 1 and a polymer material 2.
As shown in FIG. 3, the conductive particles 1 have conductive magnetic particles 4 and a carbon material coating 5 that covers the magnetic particles 4.
The magnetic particles 4 are made of a magnetic material containing one or more of nickel (Ni), cobalt (Co), and iron (Fe), for example. The magnetic material is preferably a metal. The magnetic particles 4 are preferably made of Ni or Ni alloy, which is a metal having excellent conductivity and corrosion resistance. That is, the magnetic material constituting the magnetic particles 4 may be Ni or a Ni alloy.

  As shown in FIGS. 3 and 4, the magnetic particle 4 has a shape having a plurality of protrusions 6 on the outer surface (for example, a particle main body 7 and a plurality of protrusions 6 protruding from the outer surface 7 a of the particle main body 7. Shape). It is preferable that the protrusion 6 has a tapered shape, that is, a shape (for example, a pyramid shape such as a polygonal cone shape or a cone shape) whose width (outside dimension, for example, an outside diameter) becomes narrower as the distance from the outer surface 7a increases. The protrusion 6 is integrated with the particle body 7, for example. Since the magnetic particles 4 have the protrusions 6, the number of contact points when the plurality of conductive particles 1 come into contact with each other increases, and the conductivity is improved. Particles having sharply tapered protrusions are called “spike-like particles”.

The magnetic particle 4 has, for example, a plurality of sharp protrusions 6 (usually 10 to 500) on the surface of one spherical particle body 7. The height of the protrusion 6 is approximately 1/3 to 1/500 with respect to the particle size of the particle body 7. The conductive particles 1 are obtained, for example, according to a reaction of Ni (CO) ₄ → Ni + 4CO using carbonyl metal powder (nickel carbonyl having a purity of 99.99%) as a raw material (refer to Japanese Patent Laid-Open No. 5-47503).

  The average particle diameter of the magnetic particles 4 is, for example, 0.2 to 10 μm (preferably 1 to 3 μm). If the particle size of the magnetic particles 4 is too small, even if a magnetic field is applied in the manufacturing process, for example, the force generated in the conductive particles 1 is small so that the conductive particles 1 are difficult to move. When the particle diameter is in the above range, the conductive particles 1 are easy to move in a magnetic field, and as described later, it is easy to take a row arrangement. If the particle size of the magnetic particles 4 is too large, the flow resistance in the liquid polymer material 2 is increased in the manufacturing process, for example, so that the conductive particles 1 are difficult to move even when a magnetic field is applied. However, if the average particle diameter of the magnetic particles 4 is within the above range, the conductive particles 1 can easily move in a magnetic field, and can easily be arranged in rows.

  The average particle diameter can be measured by, for example, a particle size distribution measuring apparatus based on a laser diffraction scattering method. As the average particle size, for example, 50% cumulative particle size (mass basis or volume basis), mode particle size, etc. can be adopted. As the average particle diameter, an average value of measured values for a sufficient number (for example, 100 or more) of particles based on an image obtained by observing the particles may be employed. The image of the particles is an observation image obtained using, for example, an optical microscope or an electron microscope. As the particle diameter of the non-spherical particles, for example, an average value of the longest diameter and the shortest diameter in the observation image may be adopted.

  As shown in FIG. 3, the carbon material coating 5 is made of a carbon material. Examples of the carbon material include graphene, carbon nanotube, and carbon black. As the carbon material, graphene which is a material excellent in conductivity and durability is preferable. The carbon material coating 5 is formed so as to cover the outer surface of the magnetic particles 4. The thickness of the carbon material coating 5 is, for example, 1 to 100 nm (preferably 10 to 20 nm).

  The carbon material coating 5 has a function of protecting the magnetic particles 4. Therefore, as will be described later, when the composite film 10 is applied to a battery, the magnetic particles 4 can be protected from the electrolytic solution. The carbon material coating 5 also has a function of increasing the contact area between the conductive particles 1 and reducing the electrical resistance of the composite film 10.

  The average particle diameter of the conductive particles 1 is, for example, 0.2 to 10 μm (preferably 1 to 3 μm). The average particle diameter of the conductive particles 1 is smaller than the thickness of the composite film 10. Note that the maximum particle size of the plurality of conductive particles 1 is smaller than the thickness of the composite film 10. Further, compressive strain may be applied to the conductive particles 1 in the thickness direction of the composite film 10.

  As shown in FIG. 5, since the conductive particles 1 have protrusions 6 and are easily in contact with other conductive particles 1, a conductive path is easily formed. Therefore, even if the content rate of the conductive particles 1 in the composite film 10 is low, the electrical resistivity of the composite film 10 can be lowered.

A polymer material 2 shown in FIG. 1 includes a crystalline material 2A (first material) and an amorphous material 2B (second material).
The crystalline material 2A is an insulating material. Examples of the crystalline material 2A include polyolefin resins and polyamide resins.
Examples of the polyolefin resin include high density polyethylene (melting point 120 to 140 ° C.), medium density polyethylene, low density polyethylene (melting point 95 to 130 ° C.), ethylene propylene diene copolymer (EPDM), and ethylene / vinyl acetate copolymer. Polyethylenes such as (EVA); Polypropylenes such as isotactic polypropylene and syndiotactic polypropylene (melting point: 100 to 140 ° C.); polybutene and the like. Examples of the polyamide-based resin include nylon 6, nylon 8, nylon 11, nylon 66, nylon 610, and the like. Other examples of the crystalline material 2A include polyacetal resin, polyester resin, and fluororesin. As the crystalline material 2A, one of these may be used alone, or two or more thereof may be mixed and used. The crystalline material 2A is preferably a liquid curable material (for example, a thermoplastic material).
The crystalline material 2A preferably has a higher coefficient of thermal expansion than the non-crystalline material 2B.

  As the crystalline material 2A, polyethylene is preferable. The embrittlement temperature of polyethylene is −80 to −20 ° C., and the glass transition point is −20 to −120 ° C.

  The content (volume basis) of the crystalline material 2A in the polymer material 2 is, for example, 50 to 75 Vol. %. Content rate is 50 Vol. When it is at least%, the electrical resistivity can be increased at high temperatures. Further, the mechanical strength of the composite film 10 can be increased. Content rate is 75 Vol. If it is less than or equal to%, the fluidity of the polymer material 2 becomes high and the rows of the conductive particles 1 are easily formed, so that the electrical resistivity can be lowered in a low temperature range.

  The amorphous material 2B is an insulating material. Examples of the amorphous material 2B include paraffins. As the non-crystalline material 2B, polystyrene resin or the like can be used, but paraffins are preferable. As the non-crystalline material 2B, one of these may be used alone, or two or more thereof may be mixed and used. The crystalline material 2A is preferably a liquid curable material (for example, a thermoplastic material). The amorphous material 2B preferably has a lower molecular weight than the crystalline material 2A.

  The melting point of the amorphous material 2B is lower than the melting point of the crystalline material 2A. The melting point of the amorphous material 2B is 54 to 58 ° C. When the melting point of the amorphous material 2B is 54 ° C. or higher, excessive fluidization of the amorphous material 2B can be suppressed. Therefore, it is possible to prevent the row formation of the above-described structure from being inhibited by the non-crystalline material 2B flowing out near the surface of the composite film 10. When the melting point of the non-crystalline material 2B is 58 ° C. or less, the non-crystalline material 2B can be imparted with appropriate fluidity, and the formation of the rows of the conductive particles 1 in the non-crystalline phase 9 can be promoted.

  The content (volume basis) of the amorphous material 2B in the polymer material 2 is, for example, 25 to 50 Vol. %. Content rate is 25 Vol. When it is at least%, the fluidity of the polymer material 2 becomes high and the rows of the conductive particles 1 are easily formed, so that the electrical resistivity can be lowered in a low temperature range. Content rate is 50 Vol. When it is at most%, the electrical resistivity can be increased at high temperatures.

  In the polymer material 2, the ratio C2 / C1 (volume basis) between the content C1 of the crystalline material 2A and the content C2 of the amorphous material 2B is preferably 1/3 to 1. When the ratio C2 / C1 is 1/3 or more, the fluidity of the polymer material 2 is increased, and the rows of the conductive particles 1 are easily formed, so that the electrical resistivity can be lowered in a low temperature range. When the ratio C2 / C1 is 1 or less, the electrical resistivity can be increased in a high temperature range.

The addition ratio of the conductive particles 1 to the polymer material 2 is selected so that the required electrical resistivity is obtained. The content rate of the electroconductive particle 1 in the composite film 10 is 10-20 Vol. %. That is, the volume of the plurality of conductive particles 1 included in the composite film 10 may be 10 to 20% of the volume of the composite film 10.
The thickness of the composite film 10 can be set to, for example, 20 to 100 μm.

  As shown in FIG. 1, the composite film 10 has one or more crystalline phases 8 and one or more amorphous phases 9 in a cross section along the thickness direction. In FIG. 1, a plurality of crystalline phases 8 and non-crystalline phases 9 are provided. “T” indicates the thickness direction of the composite film 10, and “t1” is the first direction from the first surface 10 a toward the second surface 10 b in the thickness direction T. “T2” is a second direction in the thickness direction T from the second surface 10b toward the first surface 10a. The second direction t2 is a direction opposite to the first direction t1. The crystalline phase 8 and the non-crystalline phase 9 may have a strip shape in a cross section along the thickness direction, and may form a striped pattern alternately arranged in the in-plane direction of the composite film 10.

  The crystalline phase 8 includes the crystalline material 2A. The amount of the conductive particles 1 contained in the crystalline phase 8 is less than the amount of the conductive particles 1 contained in the amorphous phase 9. At least a part of the plurality of crystalline phases 8 is preferably formed from one surface (for example, the first surface 10a) of the composite film 10 to the other surface (for example, the second surface 10b).

  The non-crystalline phase 9 includes the non-crystalline material 2B. At least a part of the plurality of amorphous phases 9 is preferably formed from one surface (for example, the first surface 10a) of the composite film 10 to the other surface (for example, the second surface 10b).

  In the non-crystalline phase 9, at least some of the plurality of conductive particles 1 form a line from one surface (for example, the first surface 10a) of the composite film 10 to the other surface (for example, the second surface 10b). Is arranged. That is, among the plurality of conductive particles 1 included in the composite film 10, the plurality of conductive particles 1 that are at least a part of the composite film 10 are transferred from one surface (for example, the first surface 10 a) to the other surface (for example, the first surface 10 a). They are arranged in rows up to the second surface 10b). As shown in FIG. 5, “the plurality of conductive particles 1 form a line from one surface of the composite film 10 to the other surface” means that the plurality of conductive particles 1 are, for example, at room temperature (for example, 20 ° C.). The one end 11a and the other end 11b of the row 11 are arranged so as to form one or a plurality of rows 11, respectively, and one surface (for example, the first surface 10a) and the other surface (for example, the second surface 10b) of the composite film 10, respectively. It means that it has reached.

The conductive particles 1 reaching one surface (for example, the first surface 10 a) of the composite film 10 are exposed to the outside of the composite film 10 on this one surface, and are electrically connected to the outside of the composite film 10. Can be conducted. In addition, the conductive particles 1 reaching the other surface (for example, the second surface 10b) of the composite film 10 are exposed to the outside of the composite film 10 on the other surface, and to the outside of the composite film 10 Electrical conduction is possible.
Of the plurality of conductive particles 1 constituting the row 11, the adjacent conductive particles 1, 1 are in contact with each other and are electrically connected. The column 11 may be branched on the way.
As shown in FIG. 1, the width of the amorphous phase 9 may be constant in the thickness direction T, but may not be constant. The amorphous phase 9 may be branched.

  FIG. 6 is an enlarged photograph of the cross section of the composite film 10 of the embodiment. In FIG. 6, some of the plurality of conductive particles 1 are arranged in a row from the first surface 10 a to the second surface 10 b of the composite film 10.

  In the cross section along the thickness direction of the composite film 10, the conductive particles 1 constituting the row 11 (see FIG. 5) are from one surface (for example, the first surface 10 a) of the composite film 10 to the other surface (for example, the second surface). It is preferable that the arrangement is carried out without going backwards over the surface 10b). As shown in FIG. 5, “arrange without backtracking” means, for example, that the direction of arrangement of the conductive particles 1 in the row 11 is from one end 11 a (first surface 10 a) to the other end 11 b (second surface 10 b). , The straight line 1b connecting the centroids 1a, 1a of the adjacent conductive particles 1, 1 among the conductive particles 1 constituting the row 11 is a component in the second direction t2 (upward in FIG. 1). Is not included.

  When the temperature of the composite film 10 is low, a conductive path is formed by contact between the conductive particles 1, and the electrical resistance of the composite film 10 (the electrical resistance between the first surface 10a and the second surface 10b) is low. Kept. Since the conductive particles 1 are arranged so as to form a line from one surface of the composite film 10 to the other surface, even if the content of the conductive particles 1 in the composite film 10 is small, A conductive path from one surface to the other surface is ensured, and the electrical resistance of the composite film 10 is lowered. When the temperature of the composite film 10 rises, the polymer material 2 expands, and along with this, the conductive particles 1 that have been in contact with each other are separated from each other. Therefore, a part of the conductive path is cut and the electrical resistance of the composite film 10 is increased. As a result, the current flowing through the composite film 10 is reduced. Since the electrical resistance increases as the temperature rises, the composite film 10 has a PTC (Positive Temperature Coefficient) characteristic.

<Production Method of Composite Film> (First Example)
Next, the manufacturing method of the composite film of the first example will be described.

(Preparation of conductive particles)
As shown in FIG. 3, a carbon material coating 5 is formed on the surface of the magnetic particles 4 by a vapor phase deposition method such as CVD, a liquid phase growth method such as an alcohol liquid phase method, a liquid phase discharge method, or the like. Thereby, the conductive particles 1 are obtained.

(Preparation of composite material)
As shown in FIG. 7, the conductive particles 1 and the polymer material 2 are kneaded to obtain a composite material 3A. For example, particles composed of the crystalline material 2A, particles composed of the non-crystalline material 2B, and the conductive particles 1 are mixed, and the composite material 3A is formed into an uncured sheet by an extruder or the like. (This is referred to as a sheet 20 (see FIG. 9)). At this point, the conductive particles 1 of the composite material 3A are uniformly dispersed in the polymer material 2, for example.
The crystalline material 2A and the amorphous material 2B are melted by heating. Although the crystalline material 2A has a high viscosity, the polymer material 2 contains the non-crystalline material 2B, so that the viscosity of the polymer material 2 can be kept low.

(Membrane of composite material)
FIG. 9 is a diagram schematically showing a manufacturing apparatus 30 which is a first example of an apparatus for manufacturing the composite film 10. As shown in FIG. 9, the manufacturing apparatus 30 includes a pair of calendar rolls 21 and 22 (a first calendar roll 21 and a second calendar roll 22). The first calendar roll 21 and the second calendar roll 22 have, for example, the same outer diameter. The calendar rolls 21 and 22 are arranged in parallel at regular intervals. In FIG. 9, the first calendar roll 21 is located above the second calendar roll 22.

  A plurality of first magnets 23 are provided on the outer peripheral surface 21 b of the first calendar roll 21. The plurality of first magnets 23 are arranged on the outer peripheral surface 21b of the first calendar roll 21 at intervals in the circumferential direction (direction around the central axis 21a). The first magnet 23 may be formed so as to be exposed on the outer peripheral surface 21 b of the first calendar roll 21. The plurality of first magnets 23 may be arranged not only in the circumferential direction but also in the central axis 21a direction (depth direction in FIG. 9), for example, in a matrix.

  A plurality of second magnets 24 having a different polarity from the first magnet 23 of the first calendar roll 21 are provided on the outer peripheral surface 22 b of the second calendar roll 22. That is, when the first magnet 23 is one of the S pole and the N pole, the second magnet 24 is the other pole. The plurality of second magnets 24 are arranged on the outer peripheral surface 22b of the second calendar roll 22 at intervals in the circumferential direction (direction around the central axis 22a). The second magnet 24 may be formed so as to be exposed on the outer peripheral surface 22 b of the second calendar roll 22. The plurality of second magnets 24 may be arranged not only in the circumferential direction but also in the center axis 22a direction (depth direction in FIG. 9), for example, in a matrix. The arrangement of the second magnets 24 on the outer peripheral surface 22b is determined so that the first magnet rolls 21 and the second calendar rolls 22 can be arranged to face the first magnets 23 at the closest position (closest position P1). .

  As the 1st magnet 23 and the 2nd magnet 24, a permanent magnet and an electromagnet can be used, for example. As the permanent magnet, for example, a neodymium magnet, a ferrite magnet, a samarium cobalt magnet, or the like can be used.

  The sheet 20 composed of the uncured composite material 3A is introduced between the first calender roll 21 and the second calender roll 22, and in the thickness direction (thickness direction of the sheet 20) by the calender rolls 21 and 22. Apply compression force. The calendar rolls 21 and 22 rotate in a direction in which the sheet 20 is sent out in the downstream direction (right direction in FIG. 9). In FIG. 9, the first calendar roll 21 rotates counterclockwise around the central axis 21a, and the second calendar roll 22 rotates clockwise around the central axis 22a.

  The calendar rolls 21 and 22 operate so that the first magnet 23 and the second magnet 24 face each other at the closest position P1. Therefore, the sheet 20 is pressed by the calendar rolls 21 and 22 to form a film, and at that time, a magnetic field is applied by the first magnet 23 and the second magnet 24 as shown in FIG. Reference numeral 25 in FIG. 10 is a line of magnetic force generated between the first magnet 23 and the second magnet 24.

As shown in FIG. 7, the conductive particles 1 can move in the polymer material 2 fluidized by heating.
As shown in FIG. 8, since the melting point of the crystalline material 2A is higher than the melting point of the amorphous material 2B, the crystalline material 2A is fluid before the amorphous material 2B in the process of curing the polymer material 2. Decreases and aggregates to form a crystalline phase. Therefore, the conductive particles 1 are stably present in the amorphous material 2B. This is because the movement of the molecular chain is not constrained in the non-crystalline material 2B and the conductive particles 1 are easily transferred, but the crystalline material 2A has a strong attractive force acting between the molecular chains and is difficult to transfer. is there.

  As shown in FIG. 9, at least some of the conductive particles 1 are arranged in a row from one surface of the composite film 10 to the other surface by the magnetic field. Since the polymer material 2 includes the low melting point amorphous material 2B and has high fluidity, the conductive particles 1 are easily arranged as described above. The sheet 20 is formed into a film by being compressed in the thickness direction by the calendar rolls 21 and 22. The obtained film is cured by cooling or the like to obtain the composite film 10 shown in FIG. 1 or the like (film forming step).

  As shown in FIG. 1, since the conductive particles 1 are arranged from one surface of the composite film 10 to the other surface, the amorphous phase 9 including the non-crystalline material 2 </ b> B forms a row of the conductive particles 1. The composite film 10 is formed so as to cover from one surface to the other surface.

  As shown in FIG. 2, in the composite film 10, when the temperature rises, the polymer material 2 expands. Since the polymer material 2 includes the crystalline material 2A, the volume tends to increase in a high temperature range. As the polymer material 2 expands, some of the conductive particles 1 are separated from each other. Therefore, a part of the conductive path is cut and the electrical resistance of the composite film 10 is increased. As a result, the current flowing through the composite film 10 is reduced.

  In the composite film 10, the polymer material 2 includes a crystalline material 2A and an amorphous material 2B, and the melting point of the amorphous material 2B is 54 to 58 ° C. Since the non-crystalline material 2B has a low melting point and high fluidity, the conductive particles 1 are likely to move in the non-crystalline phase 9, so that the conductive particles 1 are easily aligned according to the magnetic field. Therefore, the composite film 10 having a low electrical resistivity in the low temperature range can be obtained. In addition, since the crystalline phase 8 including the crystalline material 2A having a high melting point has a high coefficient of thermal expansion, the conductive path of the composite film 10 is likely to be cut due to thermal expansion in a high temperature range. Therefore, the electrical resistivity can be sufficiently increased. Therefore, it is possible to obtain the composite film 10 having a characteristic that the electrical resistance is low at a low temperature and the electrical resistance is high at a high temperature.

  The composite film 10 is arranged such that a part of the conductive particles 1 forms a line from one surface of the composite film 10 to the other surface (see FIG. 11). Therefore, even when the content of the conductive particles 1 in the composite film 10 is smaller than that of the composite film 110 (see FIG. 12) in which the conductive particles 101 are randomly arranged in the polymer material 102, A conductive path from one surface to the other surface is ensured, and the electrical resistance of the composite film 10 at a low temperature is lowered. In addition, since the content of the conductive particles 1 can be reduced, the conductive path can be appropriately cut by the thermal expansion of the polymer material 2 at a high temperature, and the electrical resistance can be sufficiently increased.

  As shown in FIG. 2 and the like, the conductive film 1 has the carbon material coating 5, but the composite film 10 may use conductive particles without the carbon material coating. In the composite film, since the row structure of the conductive particles described above can be appropriately configured, even when conductive particles having no carbon material coating are used, even when conductive particles having no carbon material coating are used, The electrical resistance is low and the electrical resistance is high at high temperatures. Therefore, manufacturing cost can be reduced.

  In the manufacturing method of the first example, the conductive particles 1 can be easily arranged in rows by applying a magnetic field to the composite material 3A. In the manufacturing method of this example, since the composite material 3A can be formed into a film and a magnetic field can be applied, a strong magnetic force is applied to the composite material 3 at the closest position P1 to ensure that the conductive particles 1 are as described above. Can be placed. In this manufacturing method, since the composite material 3A is formed into a film and a magnetic field is applied at the same time, disorder of the arrangement of the conductive particles 1 due to deformation of the sheet 20 hardly occurs.

<Production Method of Composite Film> (Second Example)
Next, a method for manufacturing the composite film of the second example will be described.
In the manufacturing method of this example, the composite material 3A obtained in the same manner as the manufacturing method of the first example can be used.

(Application of magnetic field)
FIG. 13 is a diagram schematically showing a manufacturing apparatus 40 which is a second example of an apparatus for manufacturing the composite film 10. As shown in FIG. 13, the manufacturing apparatus 40 is first in a point where the magnets are not provided in the calendar rolls 41 and 42, and in the front stage of the calendar rolls 41 and 42 (position on the upstream side in the feeding direction of the sheet 20). It differs from the manufacturing apparatus 30 shown in FIG. 10 in that the magnet 33 and the second magnet 34 are provided. Reference numerals 41 a and 42 a are the central axes of the calendar rolls 41 and 42. The first magnet 33 and the second magnet 34 have different polarities. That is, when the first magnet 33 is one of the S pole and the N pole, the second magnet 34 is the other pole. The first magnet 33 and the second magnet 34 are arranged facing each other. As the 1st magnet 33 and the 2nd magnet 34, a permanent magnet (neodymium magnet etc.) and an electromagnet can be used, for example.

  As shown in FIG. 13, the sheet 20 made of the uncured composite material 3 </ b> A is introduced between the first magnet 33 and the second magnet 34. The introduction direction of the sheet 20 is, for example, a direction orthogonal (or intersecting) to the arrangement direction of the first magnet 33 and the second magnet 34. A magnetic field is applied to the sheet 20 by the first magnet 33 and the second magnet 34. Due to the magnetic field, at least some of the conductive particles 1 are arranged in a row from one surface of the sheet 20 to the other surface.

(Membrane of composite material)
The sheet 20 is introduced between the first calendar roll 41 and the second calendar roll 42, and a force for compressing the sheet 20 in the thickness direction by the calendar rolls 41 and 42 is applied. That is, a compressive force is applied to the sheet 20 (composite material 3A) by the calendar rolls 41 and 42 along the direction in which the magnetic field is applied by the first magnet 33 and the second magnet 34. The sheet 20 is pressed into a film by the calender rolls 41 and 42 while the conductive particles 1 are arranged in rows. The composite film 10 shown in FIG. 1 and the like is obtained by curing the obtained film (film forming step).

  In the manufacturing method of the second example, unlike the manufacturing method of the first example, no other force is applied to the conductive particles 1 when aligning the conductive particles 1 by magnetic force. It can be arranged accurately. Further, since the conductive particles 1 are already aligned when the sheet 20 is molded, the compression strain (described later) of the conductive particles 1 by the calendar rolls 41 and 42 can be adjusted with high accuracy. Therefore, the composite film 10 having excellent PTC characteristics (that is, characteristics having low electrical resistance at low temperatures and high electrical resistance at high temperatures) can be easily manufactured.

  In this manufacturing method, the magnets 33 and 34 provided separately from the calendar rolls 41 and 42 are used. Therefore, compared with the manufacturing method of the first example using the magnets 23 and 24 provided on the calendar rolls 21 and 22, the magnets. There are few restrictions on the apparatus regarding 33,34. Therefore, for example, if the large magnets 33 and 34 are used, a magnetic field can be applied to the sheet 20 in a wide range in the feeding direction of the sheet 20. Therefore, even when the magnets 33 and 34 having a weak magnetic force are used, the conductive particles 1 can be reliably arranged as described above. Further, the conductive particles 1 can be arranged with high precision even under a low temperature condition where the viscosity of the composite material 3A is low. Therefore, it is advantageous in terms of manufacturing ease and cost.

  In the manufacturing method of the second example, a magnetic field can be applied prior to film formation of the composite material 3A. That is, since it is possible to apply a magnetic field to the composite material 3A while the curing of the composite material 3A is not progressing so much in the early stage of the manufacturing process, the conductive particles 1 are easily displaced in the magnetic field. 1 can be reliably placed as described above.

<Battery>
FIG. 14 is a diagram schematically showing a lithium ion battery 50 using the composite film 10. The lithium ion battery 50 includes a positive electrode plate 51, a negative electrode plate 52, a separator 53, an exterior container 54, and an electrolytic solution 55. In FIG. 14, the left is the front and the right is the rear. The front-rear direction is a direction along the negative electrode plate 52.

The positive electrode plate 51 includes a positive electrode current collector plate 56 and a positive electrode active material layer 57. The positive electrode current collector plate 56 is made of, for example, an aluminum foil. The positive electrode current collector plate 56 extends further rearward than the rear end of the positive electrode active material layer 57.
The positive electrode active material layer 57 includes a positive electrode active material such as a lithium-based material. The positive electrode active material layer 57 is provided on the inner surface 56 a side of the positive electrode current collector plate 56.

  The negative electrode plate 52 includes a negative electrode current collector plate 58, a composite film 10, a metal coating layer 60, and a negative electrode active material layer 59. The negative electrode current collector plate 58 is made of, for example, copper foil. The negative electrode current collector plate 58 extends further rearward than the rear end of the negative electrode active material layer 59. The negative electrode active material layer 59 includes a negative electrode active material such as a carbon-based material.

The composite film 10 and the metal coating layer 60 are formed between the negative electrode current collector plate 58 and the negative electrode active material layer 59.
The composite film 10 is formed on the inner surface 58 a of the negative electrode current collector plate 58. The composite film 10 is interposed between the negative electrode current collector plate 58 and the metal coating layer 60, and separates the negative electrode current collector plate 58 and the metal coating layer 60.

A part of the composite film 10 is formed to extend outward from at least a part of the peripheral edge 60 a of the metal coating layer 60. The portion including the front edge of the composite film 10 extends forward compared to the front edge 60a1 which is a part of the peripheral edge 60a of the metal coating layer 60. A portion of the composite film 10 that extends forward from the front edge 60a1 of the metal coating layer 60 is referred to as a front extension portion 10A. The front extension portion 10 </ b> A can prevent contact between the front edges of the metal coating layer 60 and the negative electrode current collector plate 58.
In the front extension portion 10A, it is preferable that the conductive particles 1 do not have the above-described row structure. If there is no row structure of the conductive particles 1 in the front extension portion 10A, the electrical resistance of the front extension portion 10A is increased, so that a short circuit between the metal coating layer 60 and the negative electrode current collector plate 58 is less likely to occur.

The portion including the rear edge of the composite film 10 extends rearward as compared with the rear edge 60a2 which is a part of the peripheral edge 60a of the metal coating layer 60. A portion of the composite film 10 that extends rearward from the rear edge 60a2 of the metal coating layer 60 is referred to as a rear extension portion 10B. The rear extension portion 10B can prevent the rear edges of the metal coating layer 60 and the negative electrode current collector plate 58 from contacting each other.
In the rear extension portion 10B, it is preferable that the conductive particles 1 do not have the above-described row structure. If there is no row structure of the conductive particles 1 in the rear extension portion 10B, the electrical resistance of the rear extension portion 10B is increased, so that the short circuit between the metal coating layer 60 and the negative electrode current collector plate 58 is less likely to occur.
In the composite film 10, a portion including the peripheral edge may protrude outward from the peripheral edge of the metal coating layer 60 over the entire periphery. This structure is advantageous in that contact between the peripheral edges of the metal coating layer 60 and the negative electrode current collector plate 58 is prevented.

  The metal coating layer 60 is formed on the inner surface 10 c of the composite film 10. The metal coating layer 60 has, for example, the same shape as the outer surface 59 a of the negative electrode active material layer 59 when viewed from the thickness direction of the metal coating layer 60, and is laminated on the negative electrode active material layer 59.

The separator 53 is provided between the positive electrode plate 51 and the negative electrode plate 52.
The electrolytic solution 55 is accommodated in the outer container 54 together with the positive electrode plate 51 and the negative electrode plate 52. As the electrolytic solution 55, for example, propylene carbonate (PC), diethyl carbonate (DEC), ethylene carbonate (EC), or the like can be used.

In the lithium ion battery 50, since the composite film 10 is used for the negative electrode plate 52, current can be limited at high temperatures to prevent abnormal heat generation.
Since the composite film 10 is provided on the negative electrode plate 52 having a lower potential than the positive electrode plate 51, the metal of the conductive particles 1 is less likely to elute into the electrolyte solution 55.

  Since the composite film 10 is formed such that a part (the front extension portion 10A and the rear extension portion 10B) extends from the peripheral edge 60a of the metal coating layer 60, the metal coating layer 60 and the negative electrode current collector plate 58 are Contact can be prevented, and a short circuit between the metal coating layer 60 and the negative electrode current collector plate 58 can be prevented.

The embodiment of the present invention has been described above. However, the configuration in the embodiment is an example, and the addition, omission, replacement, and other modifications of the configuration can be made without departing from the spirit of the present invention.
For example, the magnetic particles 4 of the conductive particles 1 shown in FIG. 2 and the like have a shape having protrusions 6, but the shape of the magnetic particles 4 is not limited to this and may be a shape without the protrusions 6.
The polymer material 2 may contain components other than the crystalline material 2A and the amorphous material 2B.
The PTC characteristic is a characteristic in which the electrical resistance increases as the temperature rises within a predetermined temperature range.

(Test Example 1)
A composite film 10 shown in FIG. 1 and the like was produced as follows.
As conductive particles, Ni particles (manufactured by New Metals End Chemical Corporation, average particle size of 1 to 2 μm), which are spike-like particles, were used.
Crystalline polyethylene (melting point: 100 ° C. or higher) was used as the crystalline material, and paraffin (melting point: 54 ° C.) was used as the non-crystalline material. The same amount (volume basis) was used for the crystalline material and the non-crystalline material. The content (volume basis) of the conductive particles in the composite material is 20 Vol. %. The content ratio (volume basis) of the conductive particles, the crystalline material, and the amorphous material is 20:40:40. The conductive particles and the polymer material were kneaded at a temperature of 180 ° C. to obtain an uncured composite material. A sheet 20 (see FIG. 15) having a thickness of 200 μm was produced from this composite material.

  A manufacturing apparatus 31 shown in FIG. 15 was prepared. 15 shows a cross-sectional view of the manufacturing apparatus 31 in the thickness direction of the sheet 20 (up and down direction in FIG. 15). As the first magnet 33 and the second magnet 34, neodymium magnets having an attractive force of 35N (magnetic flux density of 0.42T) were used. The sheet 20 was introduced between the first magnet 33 and the second magnet 34. A Teflon (registered trademark) plate 45 was provided between the first magnet 33 and the sheet 20, and a Teflon plate 46 was provided between the second magnet 34 and the sheet 20. That is, the sheet 20 is disposed between the plate surfaces of the Teflon plates 45 and 46. The thickness of each of the Teflon plates 45 and 46 is 1 mm. Spacers 60 made of polyimide and having a film thickness of 200 μm (that is, a thickness in the opposing direction of the Teflon plates 45 and 46) are provided on both sides of the sheet 20 (both sides in the left-right direction in FIG. 15). The pair of spacers 60 are sandwiched between Teflon plates 45 and 46. These spacers 60 are provided so that both Teflon plates 45 and 46 are parallel to each other, the distance between the first magnet 33 and the second magnet 34 is constant, and the magnetic field applied in the sheet 20 is constant. It has been. A magnetic field was applied to the sheet 20 by the first magnet 33 and the second magnet 34 at a temperature of 120 ° C. for 10 minutes, and then gradually cooled to room temperature while applying the magnetic field to obtain a composite film (thickness: about 200 μm).

  FIG. 16 shows a photograph of a cross section of the composite film 10. The thickness direction T of the composite film 10 is indicated by an arrow. Some of the plurality of conductive particles 1 of the composite film 10 are arranged in a row from one surface to the other surface.

(Test Example 2)
A composite film was produced in the same manner as in Test Example 1 except that no magnetic field was applied.
FIG. 17 shows a photograph of a cross section of the composite film. In this composite film, the conductive particles 1A are randomly arranged in the polymer material 2A. This composite film had a higher electrical resistivity at a low temperature (40 ° C.) than the composite film 10 of Test Example 1.

(Test Examples 3 to 5)
The content ratio (volume basis) of the conductive particles, the crystalline material, and the amorphous material in the composite material is 20:60:20 (Test Example 3), 20:20:60 (Test Example 4), and 20 respectively. : 0:80 (Test Example 5), a composite film was produced. Conditions other than the component ratio of the composite material were determined according to Test Example 1.

  FIG. 18 is a diagram showing the temperature dependence of the electrical resistivity for Test Examples 1 and 3-5. The horizontal axis is temperature, and the vertical axis is electrical resistivity. The electrical resistivity was measured using a two-terminal method. The temperature of the sample was measured with a thermocouple by placing the sample on a hot plate.

As shown in FIG. 18, in Test Examples 1, 3, and 4, PTC characteristics (characteristics in which the electrical resistance is low at low temperatures but the electrical resistance greatly increases as the temperature rises) were developed.
In Test Example 3 in which the ratio of the crystalline material to the amorphous material was 60:20, the electrical resistivity at 40 ° C. was about 2.4 Ω · cm. The electrical resistivity at 100 ° C. was about 1.0 × 10 ⁵ Ω · cm.
In Test Example 1 in which the ratio of the crystalline material to the amorphous material is 40:40, the electrical resistivity at 40 ° C. is about 0.8 Ω · cm, and the electrical resistivity at 100 ° C. is about 1.0 × It was 10 ⁴ Ω · cm.
In Test Example 4 in which the ratio of the crystalline material to the amorphous material is 20:60, the electrical resistivity at 40 ° C. is about 1.7 Ω · cm, and the electrical resistivity at 100 ° C. is about 1.0 ×. 10 ² Ω · cm.
In Test Example 5 in which the ratio of crystalline material to amorphous material was 0:80, the electrical resistivity at 40 ° C. was about 5.3 Ω · cm. In Test Example 5, the composite film could not maintain its shape when the temperature exceeded 60 ° C.

  In Test Examples 1 and 3 in which the ratio of the crystalline material to the amorphous material is 60:20 to 40:40 (noncrystalline material / crystalline material = 1/3 to 1), the electrical resistivity at 40 ° C. And the electrical resistivity at 100 ° C. was high, the PTC characteristics were good. In particular, in Test Example 1 in which the ratio of the crystalline material to the amorphous material was 40:40 (noncrystalline material / crystalline material = 1), the electrical resistivity at 40 ° C. was low, so the PTC characteristics were excellent. It was.

(Test Examples 6 to 8)
As the amorphous material in the composite material, low melting point paraffin (melting point 48 ° C., Test Example 6), medium melting point paraffin (melting point 54 ° C., Test Example 7), and high melting point paraffin (melting point 58 ° C., Test Example 8) are used. Thus, a composite film was produced.
The same amount (volume basis) was used for the crystalline material and the non-crystalline material. The content (volume basis) of the conductive particles in the composite material is 5 Vol. %. Other conditions were determined according to Test Example 1.

FIG. 19 is a diagram illustrating the temperature dependence of the electrical resistivity for Test Examples 6 to 8. The horizontal axis is temperature, and the vertical axis is electrical resistivity.
As shown in FIG. 19, in Test Example 7 using a medium melting point paraffin (melting point 54 ° C.) as a non-crystalline material and Test Example 8 using a high melting point paraffin (melting point 58 ° C.), a low temperature (for example, 40 ° C.). PTC characteristics were good because the electrical resistivity was low and the electrical resistivity was high at high temperatures (for example, 70 to 80 ° C.).

In Test Examples 7 and 8, the electrical resistivity was higher in the high temperature region than in Test Example 6. The following guess is possible for this.
In Test Examples 7 and 8, since the melting point of the amorphous material is in an appropriate range, the amorphous material is not excessively fluidized. Therefore, it is appropriate to form a row of conductive particles having the structure described above. Was made. FIG. 20 is a photograph showing the surface of the composite film of Test Example 7.

In contrast, in Test Example 6 using an amorphous material having a low melting point, the following assumption can be made about the decrease in electrical resistivity in the high temperature range. That is, in Test Example 6, since the excessively fluidized amorphous material flowed out to the surface of the composite film, the conductive particles can stably exist in the amorphous material when the conductive particles are formed by magnetic alignment. First, it is possible that the formation of the conductive particles having the above-described structure is hindered, and as a result, the PTC characteristic (increase in electric resistivity) is reduced.
In addition, regarding the low electrical resistivity in the high temperature region in Test Example 6, the non-crystalline material decreased in the film because the excessively fluidized non-crystalline material flowed out to the film surface. It can also be assumed that the electrical resistivity has decreased due to an increase in the apparent volume ratio of the conductive particles.
FIG. 21 is a photograph showing the surface of the composite film of Test Example 6. From FIG. 21, it can be seen that the composite membrane of Test Example 6 has a white paraffin layer formed on the surface more widely than the composite membrane of Test Example 7 (see FIG. 20).

  In addition, the content rate of the electroconductive particle in a composite film is Vol. % And mass%, but from the mass and density of the conductive particles and polymer material contained in the composite film, using the formula (1), Vol. % Can be calculated, and mass% can be calculated from the volume and density of the conductive particles and the polymer material contained in the composite film using Equation (2). In other words, Vol. % And mass% can be converted into each other using the formulas (1) and (2).

Incidentally, V _particle shows a volume of the conductive particles contained in the composite film (cm _^3), V polymer represents the volume of polymeric material contained in the composite film (cm ^3), W _particle is a composite film W _polymer represents the mass (g) of the polymer material contained in the composite film, and ρ _particle represents the density (g / cm ³ ) of the conductive particles. Ρ _polymer indicates the density (g / cm ³ ) of the polymer material.

DESCRIPTION OF SYMBOLS 1 ... Conductive particle, 2 ... Polymer material, 2A ... Crystalline material (1st material), 2B ... Amorphous material (2nd material), 10 ... Composite film, 10A ... Front extension part, 10B ... Back Extension part, 11 ... row, 50 ... lithium ion battery (battery), 51 ... positive electrode plate, 52 ... negative electrode plate, 55 ... electrolyte, 56 ... positive electrode current collector plate, 57 ... positive electrode active material layer, 58 ... negative electrode collector Electroplate, 59 ... negative electrode active material layer, 60 ... metal coating layer.

Claims (6)

A composite film comprising a plurality of conductive particles and an insulating polymer material, and having PTC characteristics,
The polymer material includes at least a first material and a second material having a melting point lower than that of the first material,
The melting point of the second material is 54-58 ° C.
The plurality of conductive particles have magnetism, and are arranged so that at least a part thereof is arranged in a row in the second material from one surface of the composite film to the other surface ,
The first material is a crystalline material;
The second material is a composite film, which is an amorphous material . A composite film comprising a plurality of conductive particles and an insulating polymer material, and having PTC characteristics,
The polymer material includes at least a first material and a second material having a melting point lower than that of the first material,
The melting point of the second material is 54-58 ° C.
The second material constitutes a second material phase having a band shape in a cross section along the thickness direction of the composite film,
The composite film, wherein the plurality of conductive particles have magnetism, and at least a part thereof is arranged in a row in the second material from one surface to the other surface of the composite film.   The composite film according to claim 1 or 2, wherein a ratio C2 / C1 (volume basis) of the content C1 of the first material and the content C2 of the second material is 1/3 to 1.   The composite film according to claim 1, wherein the second material is paraffin. A positive electrode plate, a negative electrode plate, and an electrolyte solution,
The positive electrode plate has a positive electrode current collector plate, and a positive electrode active material layer provided on the inner surface side of the positive electrode current collector plate,
The negative electrode plate has a negative electrode current collector plate and a negative electrode active material layer provided on the inner surface side of the negative electrode current collector plate,
The composite film according to any one of claims 1 to 4 and a metal coating layer provided on an inner surface side of the composite film are formed between the negative electrode current collector plate and the negative electrode active material layer. Being a battery.   The battery according to claim 5, wherein a part of the composite film is formed to extend outward from at least a part of a peripheral edge of the metal coating layer.