JP4184404B2 - Electrochemical element separator and electrochemical element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrochemical element excellent in safety when temperature of a battery increases anomalously by a short circuit, overcharging, or the like. <P>SOLUTION: A separator for the electrochemical element includes a porous base body 5 having heat resistance against a temperature not less than 150&deg;C, filler particles 3, and a porous membrane including at least one kind of shutdown resin 6 selected from resin A with a melting point in a range 80-130&deg;C, and resin B to swell absorbing an electrolyte by heating and to increase in swelling degree together with temperature increase. The filler particle 3 preferably contains boehmite. The shutdown resin 6 preferably contains the resin B. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to an electrochemical element separator that is inexpensive and excellent in dimensional stability at high temperatures, and an electrochemical element that uses the separator and is safe even in a high temperature environment.

  Electrochemical elements using non-aqueous electrolytes typified by lithium secondary batteries and supercapacitors are widely used as power sources for mobile devices such as mobile phones and notebook personal computers because of their high energy density. Yes. As the performance of portable devices increases, the capacity of electrochemical devices tends to increase further, and ensuring safety is important.

  In current lithium secondary batteries, a polyolefin-based porous film having a thickness of, for example, about 20 to 30 μm is used as a separator interposed between a positive electrode and a negative electrode. In addition, as a material of the separator, the constituent resin of the separator is melted at a temperature lower than the thermal runaway (abnormal heat generation) temperature of the battery to close the pores, thereby increasing the internal resistance of the battery, and in the event of a short circuit, etc. In order to secure a so-called shutdown effect that improves safety, polyethylene (PE) having a low melting point may be applied.

  By the way, as such a separator, for example, a uniaxially stretched film or a biaxially stretched film is used for increasing the porosity and improving the strength. Since such a separator is supplied as a single film, a certain strength is required in terms of workability and the like, and this is ensured by the above stretching. However, with such a stretched film, the degree of crystallinity has increased, and the shutdown temperature has increased to a temperature close to the thermal runaway temperature of the battery. Therefore, it can be said that the margin for ensuring the safety of the battery is sufficient. hard.

  Further, the film is distorted by the stretching, and there is a problem that when this is exposed to high temperature, shrinkage occurs due to residual stress. The shrinkage temperature is very close to the melting point, ie the shutdown temperature. For this reason, when a polyolefin-based porous film separator is used, if the battery temperature reaches the shutdown temperature due to abnormal charging or the like, the current must be immediately reduced to prevent the battery temperature from rising. This is because if the holes are not sufficiently blocked and the current cannot be reduced immediately, the battery temperature easily rises to the shrinkage temperature of the separator, and there is a risk of thermal runaway due to an internal short circuit.

  In order to prevent such a short circuit due to heat shrinkage, a method using a microporous film or a nonwoven fabric using a heat-resistant resin as a separator has been proposed. For example, Patent Document 1 discloses a separator using a wholly aromatic polyamide microporous film, and Patent Document 2 discloses a separator using a polyimide porous film. Patent Document 3 discloses a separator using a polyamide non-woven fabric, Patent Document 4 discloses a separator based on a non-woven fabric using an aramid fiber, Patent Document 5 discloses a separator using a polypropylene (PP) non-woven fabric, Patent Document 6 discloses a technique relating to a separator using a polyester nonwoven fabric.

  However, a separator using the above heat-resistant resin or heat-resistant fiber is excellent in dimensional stability at high temperatures and can be thinned, but does not have a so-called shutdown characteristic that closes pores at high temperatures. The safety at the time of abnormality such as an external short circuit or an internal short circuit in which the temperature of the battery rapidly rises cannot be ensured.

  As a technique for solving such a problem, for example, Patent Document 7 discloses a separator made of a polymer in which the content of the electrolytic solution becomes high at a high temperature. Patent Document 8 proposes a separator containing thermally expandable particles such as microcapsules.

  However, the technique described in Patent Document 7 uses a polymer film containing an electrolytic solution as a separator substrate, so that the strength is likely to decrease. For example, the separator is thinned to increase the battery capacity. Difficult to do. In the first place, although there is a description about the material and function of the separator in Patent Document 7, there is no disclosure as to how the separator can be manufactured, and even what form it has. Is also unknown. Further, in the technique described in Patent Document 8, since thermal expansion of particles in the separator occurs irreversibly, in the manufacturing process of the separator or battery, it is not possible to perform processing at a temperature higher than the temperature at which thermal expansion occurs, and particularly sufficient drying is performed. In the lithium secondary battery that needs to be performed, there is a problem that temperature control in the drying process must be strictly performed.

  In addition, a method of using a gel electrolyte as described in, for example, Patent Document 9 without using a microporous membrane has been studied. However, although the gel electrolyte does not have heat shrinkability, the mechanical strength is weak, and a short circuit or the like may occur due to a decrease in mechanical strength particularly at a high temperature. Further, since the shutdown function is not provided, there is a problem that safety cannot be sufficiently ensured particularly in a battery or the like enclosed in a cylindrical or square can. Moreover, in the technique using the gel electrolyte, as described in Patent Document 10 and Patent Document 11, even when it is reinforced with particles or fibrous materials to ensure its mechanical strength, Since the shutdown function is not added, a safety problem still occurs.

  On the other hand, in Patent Document 12, a porous resin is obtained by dispersing fine particles such as cross-linked polymethyl methacrylate (PMMA) in a solution containing a resin such as polyvinylidene fluoride as a substrate, and applying and drying the fine particles. A technique for forming a separator having excellent liquid-retaining properties in which crosslinked fine particles are held in the voids of the film is shown.

  However, the porous resin film disclosed in Patent Document 12 is substantially the same as the polymer gel electrolyte film, and the electrolytic solution in the separator is absorbed and retained by the crosslinked fine particles and the porous resin film. Therefore, the reaction of the battery is not suppressed at a high temperature, and a problem occurs in safety as in the case of the gel electrolyte.

JP-A-5-335005 JP 2000-306568 A JP-A-9-259856 Japanese Patent Laid-Open No. 11-40130 JP 2001-291503 A JP 2003-123728 A JP 2000-348704 A JP 2004-111157 A JP-A-8-287949 Japanese Patent Laid-Open No. 11-185773 JP 2002-237332 A JP 2004-241135 A

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a separator capable of constituting an electrochemical element excellent in safety when abnormal heat is generated, and an electrochemical element including the separator. It is in.

The separator for an electrochemical element of the present invention is for an electrochemical element comprising a porous substrate having a heat resistant temperature of 150 ° C. or higher, boehmite particles, and a resin having a melting point in the range of 80 to 130 ° C. The separator has a boehmite particle number average particle size of 0.1 μm or more and 15 μm or less, and the boehmite particle content is 20% by volume or more in the total volume of all components of the separator. Features.

Also, an electrochemical device of the present invention includes a positive electrode, a negative electrode, characterized in that it comprises a separator for an electrochemical device of the non-aqueous electrolyte and the present invention.

  ADVANTAGE OF THE INVENTION According to this invention, the electrochemical element excellent in the safety | security when the temperature of a battery rises abnormally by a short circuit, overcharge, etc. can be provided.

  The separator for an electrochemical element of the present invention (hereinafter simply referred to as a separator) includes a porous substrate having a heat resistant temperature of 150 ° C. or higher, filler particles, a resin A having a melting point in the range of 80 to 130 ° C., and It consists of a porous film containing at least one resin (hereinafter referred to as a shutdown resin) selected from the resin B that swells by absorbing an electrolyte solution by heating and whose degree of swelling increases as the temperature rises.

  When the separator of the present invention contains the resin A, when the temperature of the lithium secondary battery in which the separator of the present invention is incorporated reaches or exceeds the melting point of the resin A, the resin A melts and the separator Shuts down and suppresses the progress of electrochemical reaction. Further, when the separator of the present invention contains the resin B, the resin B absorbs the electrolyte in the battery and swells due to an increase in battery temperature, and the swelled particles block the pores of the separator. At the same time, the flowable electrolyte present in the pores is reduced to cause a shutdown.

  In addition, the separator of the present invention includes a porous substrate having a heat resistant temperature of 150 ° C. or higher, so that the shape of the separator can be kept stable even at a high temperature exceeding the shutdown temperature, which is caused by heat shrinkage. The occurrence of a short circuit can be prevented. For this reason, the safety | security of the battery after a shutdown arises can be improved. As used herein, “heat-resistant temperature” refers to the change in length of an object, that is, in the porous substrate, the rate of shrinkage (shrinkage rate) with respect to the length at room temperature is maintained at 5% or less. The maximum temperature that can be used. Further, “heat resistance” as used in the present specification means that a substantial dimensional change due to softening or the like does not occur, and the heat resistance is evaluated based on whether the heat resistant temperature is sufficiently higher than the shutdown temperature. In order to increase safety after shutdown, the porous substrate preferably has a heat resistant temperature that is 20 ° C. higher than the shutdown temperature, and more specifically, the heat resistant temperature of the porous substrate may be 150 ° C. or higher. Desirably, it is more desirable to set it as 180 degreeC or more. The upper limit of the heat resistant temperature of the porous substrate is not particularly limited.

  Furthermore, in the separator of the present invention, filler particles are contained for preventing internal short circuit and ensuring the shape stability of the separator (particularly, the shape stability at high temperature). The filler particles may constitute at least a part of the porous substrate, or may be contained in the pores of the porous substrate. Further, as will be described later, a large number of filler particles can be integrated with a binder or the like to form a porous substrate, and at least a part of the entire porous substrate may have such a configuration. The filler particles have heat resistance and electrical insulation properties, are stable to solvents used in the production of electrolytes and separators, and are less susceptible to oxidation and reduction within the battery operating voltage range. Stable particles are used.

  More specific embodiments of the separator of the present invention include, for example, the following embodiments (I) and (II).

  The separator of the aspect (I) is a separator in which a large number of filler particles are aggregated to form a porous substrate, and a large number of filler particles are integrated with a heat-resistant resin or the like alone or with a fibrous material. It becomes a porous substrate and forms a porous film together with the shutdown resin.

  Further, the separator in the mode (II) is a porous substrate made of a fibrous material, such as a woven fabric or a nonwoven fabric (including paper), and contains filler particles in the pores, and is porous with a shutdown resin. A film is formed.

  Although the form of the shutdown resin is not particularly limited, it is preferable to use a particulate resin, and the size of the shutdown resin is only required to be smaller than the thickness of the separator when dried, and is 1/100 to 1 of the thickness of the separator. It is preferable that the average particle diameter is / 3, and specifically, the average particle diameter is preferably 0.1 to 20 μm. If it is the range of the said particle size, it will become easy to disperse | distribute shutdown resin uniformly in a porous membrane. When the particle size is too small, the gap between the particles becomes small, the ion conduction path becomes long, and the battery characteristics may deteriorate. On the other hand, if the particle size is too large, the gap becomes large and a short circuit due to lithium dendrite or the like may occur. The average particle diameter of the shutdown resin is, for example, a number measured by dispersing the fine particles in a medium that does not swell the shutdown resin, for example, water, using a laser scattering particle size distribution analyzer such as “LA-920” manufactured by HORIBA. It can be defined as the average particle size.

  Further, the shutdown resin may be used in a form other than the above, or may be used in a state where it is laminated and integrated on the surface of another constituent element, for example, a porous substrate or filler particles. When the porous substrate is composed of a fibrous material, it may be used as a fiber having a multilayer structure having a shutdown resin on the surface of the core material, and a core-shell structure having filler particles as a core and a shutdown resin as a shell It may be used as a particle. When both the resin A and the resin B are used, it is also possible to use a resin B laminated on the surface of the resin B and integrated. Furthermore, the shutdown resin is composed of fine particles, and may be disposed in the pores of the porous substrate or on the surface of the porous substrate together with the filler particles.

  The shutdown resin of the present invention is a resin A having a melting point in the range of 80 to 130 ° C., or a resin B that swells by absorbing an electrolyte solution by heating and increases its degree of swelling as the temperature rises. It can also be used. In addition, the said melting | fusing point can be prescribed | regulated by the melting temperature measured using a differential scanning calorimeter (DSC) according to the prescription | regulation of Japanese Industrial Standard (JIS) K7121, for example.

  The constituent material of the resin A is preferably an electrochemically stable material that has electrical insulation, is stable with respect to the electrolyte, and is not easily oxidized or reduced in the operating voltage range of the battery. (PE), copolymerized polyolefin, or polyolefin derivative (such as chlorinated polyethylene), polyolefin wax, petroleum wax, carnauba wax, and the like. Examples of the copolymer polyolefin include an ethylene-vinyl monomer copolymer, more specifically, an ethylene-vinyl acetate copolymer (EVA), an ethylene-methyl acrylate copolymer, an ethylene-ethyl acrylate copolymer, and the like. Examples thereof include ethylene-acrylic acid copolymers. The ethylene-derived structural unit in the copolymerized polyolefin is desirably 85 mol% or more. Moreover, polycycloolefin etc. can also be used and you may have 2 or more types of the said structural material.

  Among the above materials, PE, polyolefin wax, or EVA having a structural unit derived from ethylene of 85 mol% or more is preferably used. Further, the resin A may contain various additives added to the resin as necessary, for example, an antioxidant, in addition to the above-described constituent materials.

  On the other hand, as a constituent material of the resin B, normally, in a temperature range where the battery is used (approximately 70 ° C. or less), the electrolyte solution is not absorbed or the amount of absorption is limited. However, when heated to a temperature that requires shutdown, a resin is used that absorbs the electrolyte and swells greatly, and the degree of swelling increases as the temperature rises. On the lower temperature side than the shutdown temperature, a flowable electrolyte that is not absorbed by the resin B exists in the pores of the separator, so that the conductivity of Li ions inside the separator is increased, and the battery has good load characteristics. As used herein, “load characteristics” refers to high rate discharge characteristics. On the other hand, when heated above the temperature at which the degree of swelling increases with increasing temperature (hereinafter sometimes referred to as “thermal swelling”), the resin B absorbs the electrolyte in the battery. The swelled particles greatly block the pores of the separator, and the flowable electrolytic solution is reduced to put the battery in a dry state, thereby shutting down and ensuring the safety of the battery. Moreover, when the temperature is higher than the shutdown temperature, the liquid withering further proceeds due to the thermal swellability, and the reaction of the battery is further suppressed, so that the high-temperature safety after shutdown can be further improved.

  The temperature at which the resin B starts to exhibit thermal swellability is preferably at least 75 ° C. or higher. This is because by setting the temperature to 75 ° C. or higher, the temperature at which the Li ion conductivity is remarkably reduced and the internal resistance of the battery increases (so-called shutdown temperature) can be set to about 80 ° C. or higher. On the other hand, the higher the lower limit of the temperature showing thermal swellability, the higher the shutdown temperature of the separator. Therefore, in order to set the shutdown temperature to about 130 ° C or lower, the lower limit of the temperature showing thermal swellability is 125 ° C or lower. It is preferable to set the temperature to 115 ° C. or lower. If the temperature showing the thermal swellability is too high, the thermal runaway reaction of the active material in the battery may not be sufficiently suppressed, and the effect of improving the safety of the battery may not be sufficiently secured. Is too low, the conductivity of lithium ions in the normal battery operating temperature range (approximately 70 ° C. or lower) may be too low.

  Further, at a temperature lower than the temperature exhibiting the heat swellability, it is desirable that the resin B does not absorb the electrolyte solution as much as possible and the swelling is less. This is because, in the battery operating temperature range, for example, room temperature, the electrolytic solution is better retained in the separator pores than in the resin B, and the battery characteristics such as load characteristics are better. Because it becomes.

  The amount of the electrolyte solution absorbed by the resin B at room temperature (25 ° C.) can be evaluated by the degree of swelling defined by the following formula (1) representing the volume change of the resin B.

B _R = (V ₀ / V _i ) −1 (1)

However, in the above formula, V ₀ is the volume of the resin B after 24 hours immersion at 25 ° C. in the electrolytic solution (cm ^3), the volume of V _i is before immersion in the electrolyte resin B (cm ³⁾ Respectively.

In the separator of the present invention, the swelling degree B _R of the resin B at room temperature (25 ° C.) is desirably 2.5 or less, 1 or less is more preferable. In other words, it is desirable swelling due to absorption of the electrolyte is small, B _R is desired to be a small value close to 0 as possible. Further, it is desirable that the temperature change of the degree of swelling is as small as possible on the lower temperature side than the temperature exhibiting thermal swellability. In the separator in which the resin B is bound with the binder resin, the swelling degree of the resin B may be a small value in a state where the resin B exists together with the binder resin.

On the other hand, as the resin B, when heated above the lower limit of the temperature exhibiting thermal swellability, the amount of electrolyte absorbed increases, and in the temperature range exhibiting thermal swellability, the degree of swelling increases with temperature. Used. For example, it is measured at 120 ° C., swelling degree B _T which is defined by the following formula (2) is 1 or higher is one are preferably used, more than one is more preferable.

B _T = (V ₁ / V ₀ ) −1 (2)

However, in the above formula, V ₀ is the volume (cm ³ ) of resin B after being immersed in an electrolytic solution at 25 ° C. for 24 hours, and V ₁ is an electrolytic solution after being immersed in the electrolytic solution at 25 ° C. for 24 hours. Each represents the volume (cm ³ ) of Resin B after raising the temperature to 120 ° C. and holding at 120 ° C. for 1 hour.

  On the other hand, the swelling degree of the resin B defined by the above formula (2) is preferably 10 or less, more preferably 5 or less, because if the resin B becomes too large, the battery may be deformed.

  The degree of swelling defined by the above formula (2) is estimated by directly measuring the change in the size of the resin B by using a method such as a light scattering method or an image analysis of an image taken by a CCD camera or the like. However, it can be measured more accurately using, for example, the following method.

Using a binder resin having a known degree of swelling at 25 ° C. and 120 ° C., which is defined in the same manner as in the above formulas (1) and (2), resin B is mixed with the solution or emulsion to prepare a slurry. This is coated on a substrate such as a polyethylene terephthalate (PET) sheet or glass plate to produce a film, and its mass is measured. Next, the film was immersed in an electrolyte at 25 ° C. for 24 hours to measure the mass, and the electrolyte was heated to 120 ° C. and held at 120 ° C. for 1 hour to measure the mass. The swelling degree B _T is calculated by the following formulas (3) to (9). In addition, in following formula (3)-(9), the volume increase of components other than electrolyte solution shall be disregarded when it heats up from 25 degreeC to 120 degreeC.

V _i = M _i × W / P _A (3)
V _B = (M ₀ −M _i ) / P _B (4)
V _C = M ₁ / P _C −M ₀ / P _B (5)
V _V = M _i × (1−W) / P _V (6)
V ₀ = V _i + V _B −V _V × (B _B +1) (7)
V _D = V _V × (B _B +1) (8)
B _T = {V ₀ + V _C −V _D × (B _C +1)} / V ₀ −1 (9)

Here, in the above formulas (3) to (9),
V _i : Volume of the resin B (cm ³ ) before being immersed in the electrolyte,
V ₀ : volume (cm ³ ) of resin B after being immersed in the electrolyte at 25 ° C. for 24 hours,
V _B : volume of the electrolyte solution (cm ³ ) absorbed in the film after being immersed in the electrolyte solution at room temperature for 24 hours,
V _C : The volume of the electrolytic solution absorbed by the film (cm) during the period from when the electrolytic solution was immersed in the electrolytic solution for 24 hours at room temperature until the electrolytic solution was heated to 120 ° C. and further passed for 1 hour at 120 ° C. ³ ),
V _V : volume (cm ³ ) of the binder resin before being immersed in the electrolytic solution,
V _D : volume (cm ³ ) of binder resin after being immersed in the electrolyte at room temperature for 24 hours,
M _i : the mass (g) of the film before being immersed in the electrolytic solution,
M ₀ : mass (g) of the film after being immersed in the electrolyte at room temperature for 24 hours,
M ₁ : After immersing in the electrolyte solution at room temperature for 24 hours, the electrolyte solution was heated to 120 ° C. and further held at 120 ° C. for 1 hour, and the film mass (g),
W: Mass ratio of resin B in the film before being immersed in the electrolytic solution,
P _A : Specific gravity (g / cm ³ ) of the resin B before being immersed in the electrolytic solution,
P _B : Specific gravity of electrolyte at normal temperature (g / cm ³ ),
P _C : specific gravity of electrolyte at a predetermined temperature (g / cm ³ ),
P _V : specific gravity (g / cm ³ ) of the binder resin before being immersed in the electrolytic solution,
B _B : degree of swelling of the binder resin after being immersed in the electrolyte at room temperature for 24 hours,
B _C : Swelling degree of the binder resin at the time of temperature rise defined by the above formula (1).

  The resin B is preferably an electrochemically stable material that has heat resistance and electrical insulation, is stable to an electrolytic solution, and is not easily oxidized and reduced in the operating voltage range of the battery. Examples of such a material include a crosslinked resin. More specifically, a styrene resin (polystyrene (PS), etc.), a styrene butadiene copolymer, an acrylic resin (polymethyl methacrylate (PMMA), etc.), a polyalkylene oxide (polyethylene oxide (PEO), etc.), a fluororesin (polyfluoride, etc.). Examples thereof include a crosslinked product of at least one resin selected from the group consisting of vinylidene chloride (PVDF) and the like and derivatives thereof, urea resin, polyurethane, and the like, and two or more of these may be used. In addition to the main constituent materials as described above, the resin B may contain various additives added to the resin, such as an antioxidant, as necessary.

  Among the above constituent materials, crosslinked styrene resin, crosslinked acrylic resin and crosslinked fluororesin are preferable, and crosslinked PMMA is particularly preferably used.

  Although the mechanism by which these resin crosslinked bodies absorb and swell the electrolyte solution due to temperature rise is not clear, a correlation with the glass transition temperature is conceivable. That is, since the resin generally becomes flexible when heated to its glass transition temperature (Tg), the resin as described above can absorb a large amount of electrolyte at a temperature higher than the glass transition temperature and swell. It is estimated that. Accordingly, as the resin B, a material having a glass transition temperature in the range of about 75 to 125 ° C. is considered in consideration that the temperature at which the shutdown action actually occurs is slightly higher than the temperature at which the resin B starts to exhibit thermal swellability. It is considered desirable to use it. Even if the same resin cross-linked body, there are commercially available products with various glass transition temperatures. For example, since the glass transition temperature can be changed by controlling the degree of cross-linking of the material, the desired glass can be obtained. A material prepared to have a transition temperature may be used.

  In the above-mentioned resin crosslinked body, in a so-called dry state before containing the electrolytic solution, the volume change accompanying the temperature change is reversible to some extent so that even if it expands due to a temperature rise, it shrinks again by lowering the temperature. In addition, since it has a heat-resistant temperature that is considerably higher than the temperature that exhibits thermal swellability, even if the lower limit of the temperature that exhibits thermal swellability is about 100 ° C, a material that can be heated to 200 ° C or higher is used. You can choose. Therefore, even when heating is performed in a separator manufacturing process or the like, the resin is not dissolved or the thermal swellability of the resin is not impaired, and handling in a manufacturing process including a general heating process becomes easy. Moreover, in the separator of the present invention, unlike a separator composed of a conventional polyethylene porous film, since it can be produced without applying a strong stress, there is little or no residual stress after production, Since the heat shrinkage does not substantially occur in the porous substrate, safety can be improved at a high temperature from the viewpoint of the manufacturing method.

  The resin A and the resin B can be used alone or both can coexist. The content (volume ratio) of these shutdown resins is preferably 10% by volume or more, and preferably 20% by volume or more, in the total volume of all the constituent components of the separator in order to make it easier to obtain the shutdown effect. On the other hand, it is preferably 80% by volume or less and more preferably 40% by volume or less from the viewpoint of securing the shape stability of the separator at a high temperature.

  Further, the filler particles used in the present invention may be present as at least a part of the porous substrate constituting the separator as in the aspect (I), and as in the aspect (II). , May exist in the pores of the porous substrate.

The filler particles may be organic particles or inorganic particles, but are desirably fine particles from the viewpoint of dispersibility, and inorganic fine particles are preferably used from the viewpoint of stability. Specific examples of the constituent material of the inorganic particles include inorganic oxides such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₂ , and ZrO ₂ , inorganic nitrides such as aluminum nitride and silicon nitride, and fluorine. Examples include slightly soluble ion crystals such as calcium fluoride, barium fluoride, and barium sulfate, covalent bonds such as silicon and diamond, and clays such as montmorillonite. Furthermore, the inorganic oxide is an aluminum compound represented by AlOOH or _{Al 2 O 3 · H 2 O} ( e.g. boehmite), zeolite, apatite, kaoline, mullite, spinel, mineral resource-derived substances or their artificial materials such as olivine It may be. Among the inorganic oxides, Al ₂ O ₃ , SiO ₂ and boehmite are preferable, and boehmite having the highest effect of preventing a short circuit due to generation of lithium dendrite is particularly preferably used. Among boehmite, synthetic boehmite that can easily control the particle size and shape and can control the amount of ionic impurities that adversely affect the electrochemical device is more desirable. These filler particles can be used alone or in combination of two or more.

In addition, the filler particles are formed on the surface of a conductive material exemplified by metals, conductive oxides such as SnO ₂ and tin-indium oxide (ITO), or carbonaceous materials such as carbon black and graphite. It may be a particle having electrical insulation properties by coating with an insulating material, for example, the above inorganic oxide.

The shape of the filler particles may be, for example, a shape close to a sphere or may be a plate shape, but is preferably a plate particle from the viewpoint of preventing a short circuit. Typical examples of the plate-like particles include plate-like Al ₂ O ₃ and plate-like boehmite. The particle diameter of the filler particles is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, and preferably 5 μm or less, as the number average particle diameter measured by the measurement method. More preferably.

  When plate-like fine particles are contained in the separator, the plate surface of the fine particles can be oriented so as to be as parallel as possible to the film surface of the separator by a method described later. Thereby, it can prevent more effectively that an internal short circuit arises by the projection of the lithium dendrite deposited on the electrode surface and the active material on the electrode surface. In the case of plate-like particles, the aspect ratio (ratio of the maximum length in the plate-like particles to the thickness of the plate-like particles) is preferably 2 to 100, for example, and more preferably 10 to 50. If the aspect ratio is too small, the above-described effect due to the particles being plate-like may be reduced. If the aspect ratio is too large, the specific surface area of the particles may be too large and handling may be difficult. When the particles are plate-like, the average value of the ratio of the long axis direction length to the short axis direction length (long axis direction length / short axis direction length) of the flat plate surface is 1 or more. 3 or less, more preferably 2 or less. If the ratio of the length in the major axis direction to the length in the minor axis direction of the flat plate surface of the particles is too large, the shape of the particles may approach a needle shape, and the above-described effect due to the tabular shape of the particles may be reduced.

  Moreover, the average particle diameter of filler particles should just be smaller than the thickness of a separator, and on the other hand, it is preferable to set it as 1/100 or more of the thickness of a separator. As the plate-like fine particles, in addition to the inorganic fine particles, a resin material having a heat resistant temperature of 150 ° C. or higher can also be used. Two or more of the above exemplified materials can be used in combination.

  The porous substrate of the separator according to the embodiment (I) can be formed by integrating a large number of filler particles with a binder or the like. As the binder, EVA (a structural unit derived from vinyl acetate is 20 to 35 mol). %), Ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymer, fluorine rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA) Polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane, epoxy resin and the like are used. In particular, a heat resistant resin having a heat resistant temperature of 150 ° C. or higher is preferably used, and two or more binders may be used in combination. When these binders are used, they may be used in the form of an emulsion dissolved or dispersed in a solvent for a liquid composition for forming a separator described later.

  In addition, in order to ensure the shape stability and flexibility of the separator, a fibrous material or the like may be mixed with the filler particles. The fibrous material has a heat resistance temperature of 150 ° C. or higher and has an electrical insulating property. The material is not particularly limited as long as it is electrochemically stable and is stable with respect to the electrolyte solution described in detail below and the solvent used in the production of the separator. Moreover, the upper limit of the heat-resistant temperature of a fibrous material is not specifically limited. The “fibrous material” in the present specification means that having an aspect ratio [length in the long direction / width in the direction perpendicular to the long direction (diameter)] of 4 or more. The ratio is preferably 10 or more.

Specific examples of the constituent material of the fibrous material include, for example, cellulose and its modified products (carboxymethylcellulose (CMC), hydroxypropylcellulose (HPC), etc.), polyolefin (polypropylene (PP), propylene copolymer, etc.), Polyester (polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT), etc.), polyacrylonitrile (PAN), aramid , polyamideimide, polyimide and other resins, glass, alumina, zirconia, silica and other inorganic materials An oxide etc. can be mentioned, These constituent materials may contain 2 or more types. Further, the fibrous material may contain various additives, for example, an antioxidant in the case of a resin, as necessary.

  On the other hand, the porous substrate of the separator according to the embodiment (II) is formed by forming the fibrous material into a sheet-like material such as a woven fabric or a nonwoven fabric (including paper). Can be used as In the separator of this aspect, the filler particles are contained in the pores of the porous substrate. However, in order to bind the porous substrate and the filler particles, or to bind the shutdown resin and the porous substrate, the binder is used. Can also be used.

  Moreover, although the diameter of a fibrous material should just be below the thickness of a separator, it is preferable that it is 0.01-5 micrometers, for example. When the diameter is too large, the entanglement between the fibrous materials is insufficient, and when a sheet-like material is formed to constitute a porous membrane substrate, the strength may be reduced and handling may be difficult. On the other hand, if the diameter is too small, the gap between the separators becomes too small, and the ion permeability tends to decrease, which may decrease the load characteristics of the battery.

  The content of the fibrous material in the separator of the mode (II) is preferably, for example, 10% by volume or more, more preferably 20% by volume or more, and 90% by volume or less, in the total volume of all the constituent components of the separator. Is preferable, and 80 volume% or less is more preferable. The state of the presence of the fibrous material in the separator is, for example, that the angle of the long axis (long axis) with respect to the separator surface is preferably 30 ° or less on average, and more preferably 20 ° or less. .

  In order to improve the effect of preventing internal short circuit, the content of the filler particles is preferably 20% by volume or more, more preferably 50% by volume or more in the total volume of all the constituent components of the separator. Preferably, in order to secure the content of the shutdown resin and maintain the shutdown characteristics, the content is preferably suppressed to 80% by volume or less.

  On the other hand, in the separator of the aspect (I), the content of the filler particles and the binder is set so that the proportion of the porous substrate is 10% by volume or more and 90% by volume or less in the total volume of all the constituent components of the separator. It is desirable to adjust.

  From the viewpoint of further improving the energy density of the electrochemical element while further enhancing the short-circuit prevention effect of the electrochemical element, ensuring the strength of the separator and improving the handleability, the thickness of the separator is desirably 3 μm or more, for example. Desirably, it is 5 μm or more, and on the other hand, it is desirably 30 μm or less, and more desirably 20 μm or less.

  Further, the porosity of the separator is preferably 20% or more, and more preferably 30% or more in a dried state in order to ensure the amount of electrolyte retained and to improve ion permeability. is there. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing internal short circuit, the porosity of the separator is preferably 70% or less, and more preferably 60% or less. The porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula.

P = 100− (Σa _i / ρ _i ) × (m / t)

Here, in the above formula, a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of the separator (g / cm ² ), t: The thickness (cm) of the separator.

  In the separator containing the resin B, after the battery is assembled, the resin B absorbs the electrolyte and swells, and there is no problem even if the porosity of the separator is somewhat reduced. The separator has a porosity of 10% or more. Any is suitable.

The air permeability represented by the Gurley value of the separator of the present invention is preferably 10 to 300 seconds. Here, the Gurley value is a value of the number of seconds that 100 mL of air permeates through the membrane under a pressure of 0.879 g / mm ² , measured by a method according to JIS P 8117. If the Gurley value is too large, the ion permeability decreases, whereas if it is too small, the strength of the separator may decrease. Further, the strength of the separator is desirably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too small, a short circuit may occur due to the piercing of the separator when lithium dendrite crystals are generated.

  As a manufacturing method of the separator of the present invention, for example, the following methods (a) and (b) can be adopted. The manufacturing method (a) is a method in which a separator composition is coated or impregnated with a liquid composition (slurry or the like) containing a shutdown resin and filler particles and then dried at a predetermined temperature. Thereby, the separator of the aspect of said (II) can be manufactured. Specifically, the porous substrate in this case has a woven fabric composed of at least one kind of fibrous material containing each of the exemplified materials as a constituent component, or a structure in which these fibrous materials are entangled with each other. A porous sheet such as a nonwoven fabric is used. More specifically, non-woven fabrics such as paper, PP non-woven fabric, polyester non-woven fabric (PET non-woven fabric, PEN non-woven fabric, PBT non-woven fabric, etc.) and PAN non-woven fabric can be exemplified.

  In addition to the shutdown resin and filler particles, the liquid composition contains a binder and the like as required, and these are dispersed in a solvent (including a dispersion medium, the same shall apply hereinafter). It can also be dissolved. The solvent used in the liquid composition may be any solvent that can uniformly disperse the shutdown resin and filler particles and can uniformly dissolve or disperse the binder. For example, aromatic hydrocarbons such as toluene, tetrahydrofuran, etc. In general, organic solvents such as furans, ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, an alcohol (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) is added as appropriate to the interface. The tension can also be controlled.

  In the liquid composition, the solid content including the shutdown resin, the filler particles, and the binder is preferably 10 to 40% by mass, for example.

  When the pore diameter of the porous substrate is relatively large, for example, when it is 5 μm or more, this tends to cause a short circuit of the electrochemical element. Therefore, in this case, it is preferable to have a structure in which at least a part of the filler particles are present in the pores of the substrate. In addition, it is more preferable that at least a part of the constituents other than the filler particles such as the shutdown resin exist in the pores of the substrate together with the filler particles.

  In addition, in the case where the plate-like particles are contained in the separator, in order to enhance the orientation and to make the function work effectively, in the substrate impregnated with the liquid composition, a shear or magnetic field is applied to the liquid composition. You can use the method of calling.

  Moreover, in order to exhibit the effect which each said structure has more effectively, it is good also as a form which made the structure unevenly distributed and gathered in layers parallel to the film surface of a separator. In order to achieve such a form, for example, using two heads or rolls of a die coater or a reverse roll coater, separate paints from both the front and back sides of the substrate, for example, a liquid composition mainly composed of a shutdown resin, and a filler A method in which the liquid composition mainly composed of particles is separately applied and dried can be employed.

  The manufacturing method of (b) of the separator of this invention makes the said liquid composition contain a fibrous material further as needed, apply | coats this on board | substrates, such as a film and metal foil, and dries at predetermined | prescribed temperature. And then peeling from the substrate. By the method (b), the separator according to the embodiment (I) can be produced. The liquid composition used in the method (b) preferably has a solid content including, for example, a fibrous material of 10 to 40% by mass. Moreover, it is good also as a structure which formed the separator on the surface of at least one chosen from the positive electrode and negative electrode which comprise a battery by the method of (b), and integrated the separator and the electrode.

  In addition, the separator of this invention is not limited to each structure shown above. For example, the shutdown resin may be in the form of particles and may be present independently, or may be partially fused to each other or to a fibrous material. The electrochemical element to which the separator of the present invention can be applied is not particularly limited as long as it uses a non-aqueous electrolyte, and in addition to a lithium secondary battery, it is safe at high temperatures such as a lithium primary battery and a super capacitor. It can also be applied to any application that requires high performance.

  Hereinafter, application to a lithium secondary battery will be described in detail as an example of the electrochemical device of the present invention. Examples of the form of the lithium secondary battery include a cylindrical shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventional lithium secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing Li. For example, as a positive electrode active material, a lithium-containing transition metal oxide having a layered structure represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.) Or LiMn ₂ O ₄ or a spinel-type lithium manganese oxide in which a part of the element is substituted with another element, or an olivine type compound represented by LiMPO ₄ (M: Co, Ni, Mn, Fe, etc.) is used. It is possible. Examples of the lithium-containing transition metal oxide of the layered structure, LiCoO ₂ and _{LiNi 1-x Co xy Al y} O 2 (0.1 ≦ x ≦ 0.3,0.01 ≦ y ≦ 0.2) In addition, such , Oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ , LiMn _5/12 Ni _5/12 Co _1/6 O ₂ , LiMn _3/5 Ni _1/5 (Co _1/5 O ₂ etc.) can be specifically exemplified.

  The positive electrode active material is prepared by adding a carbon material such as carbon black as a conductive additive and a fluororesin such as polyvinylidene fluoride (PVDF) as a binder. Using this positive electrode mixture, a molded body (positive electrode mixture layer) is formed on the surface of the current collector.

  Further, as the positive electrode current collector, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used, but usually an aluminum foil having a thickness of 10 to 30 μm is preferably used.

  The lead portion on the positive electrode side is normally provided by leaving the exposed portion of the current collector without forming the positive electrode mixture layer on a part of the current collector and forming the lead portion at the time of producing the positive electrode. However, the lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting an aluminum foil or the like to the current collector later.

  The negative electrode is not particularly limited as long as it is a negative electrode used in a conventional lithium secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li. For example, as a negative electrode active material, lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers, can be occluded and released. One type or a mixture of two or more types of carbon-based materials are used. Further, elements such as Si, Sn, Ge, Bi, Sb, In and alloys thereof, compounds that can be charged and discharged at a low voltage close to lithium metal such as lithium-containing nitrides or lithium-containing oxides, or lithium metal or lithium / aluminum An alloy can also be used as the negative electrode active material.

  A negative electrode mixture is prepared by appropriately adding a carbon material such as carbon black as a conductive additive and PVDF as a binder to the negative electrode active material, and a molded body is formed on the surface of the current collector using the negative electrode mixture. (Negative electrode mixture layer) is formed. Further, when the above various alloys and lithium metal are used as the negative electrode active material, various alloy and lithium metal foils can be used alone as the negative electrode, and these can be laminated on the current collector. .

  When a current collector is used for the negative electrode, a copper or nickel foil, a punching metal, a net, an expanded metal, or the like can be used as the current collector, but a copper foil is usually used. In the negative electrode current collector, when the thickness of the entire negative electrode is reduced in order to obtain a battery having a high energy density, the upper limit of the thickness is preferably 30 μm, and the lower limit is preferably 5 μm. Further, the lead portion on the negative electrode side may be formed in the same manner as the lead portion on the positive electrode side.

  The electrode can be used in the form of a laminate in which the positive electrode and the negative electrode are laminated via the separator of the present invention, or an electrode wound body in which this is wound.

As the non-aqueous electrolyte, a solution in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and hardly causes side reactions such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (2 ≦ n ≦ 5), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group], etc. Can be used.

  The organic solvent used for the non-aqueous electrolyte is not particularly limited as long as it dissolves the lithium salt and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, vinylene carbonate, chain carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate, chain esters such as methyl propionate, cyclic esters such as γ-butyrolactone, Chain ethers such as dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme, cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran, nitriles such as acetonitrile, propionitrile and methoxypropionitrile And sulfites such as ethylene glycol sulfite. These may be used as a mixture of two or more. Kill. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexylbenzene, biphenyl, and fluorobenzene are used for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these non-aqueous electrolytes. An additive such as t-butylbenzene may be added as appropriate.

  The concentration of the lithium salt in the non-aqueous electrolyte is preferably 0.5 to 1.5 mol / L, and more preferably 0.9 to 1.25 mol / L.

Hereinafter, the present invention will be described in detail based on examples. However, the present invention is not limited to the following examples. Incidentally, degree of swelling B _R and B _T of the resin B in the present embodiment are each the formula (1) and (2) the basis of the obtained degree of swelling.

<Production of negative electrode>
A negative electrode active material-containing paste was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder with N-methyl-2-pyrrolidone (NMP) as a solvent in a uniform manner. Prepared. This negative electrode mixture-containing paste was intermittently applied on both sides of a 10 μm thick collector made of copper foil so that the active material application length was 320 mm on the front surface and 260 mm on the back surface, and dried. Thereafter, calendering was performed to adjust the thickness of the negative electrode mixture layer so that the total thickness was 142 μm, and cut to a width of 45 mm to produce a negative electrode having a length of 330 mm and a width of 45 mm. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

<Preparation of positive electrode>
The positive electrode active material LiCoO ₂ : 85 parts by mass, the conductive auxiliary agent acetylene black: 10 parts by mass, and the binder PVDF: 5 parts by mass were mixed so as to be uniform using NMP as a solvent. An agent-containing paste was prepared. This paste was intermittently applied on both sides of a current collector made of aluminum foil having a thickness of 15 μm so that the active material application length was 319 to 320 mm on the front surface and 258 to 260 mm on the back surface, and dried. Thereafter, calendering was performed to adjust the thickness of the positive electrode mixture layer so that the total thickness was 150 μm, and the cut was made to have a width of 43 mm to produce a positive electrode having a length of 330 mm and a width of 43 mm. Further, a tab was welded to the exposed portion of the aluminum foil of the positive electrode to form a lead portion.

  In addition, the said negative electrode and the said positive electrode are used for preparation of the battery mentioned later.

<Production and evaluation of separator>
(Example 1)
Aqueous dispersion of polyethylene powder (resin A) [“CHEMIPARL W-700” (trade name) manufactured by Mitsui Chemicals, Inc.]: 750 g, isopropyl alcohol (IPA): 200 g, and polyvinyl butyral (PVB) [Sekisui Chemical Co., Ltd. “S Lek KX-5” (trade name) manufactured by the company]: 375 g was put into a container and dispersed with stirring with a disper at 2800 rpm for 1 hour. To this, plate-like boehmite fine particles [“BMM” (trade name) manufactured by Kawai Lime Co., Ltd., average particle size: 1 μm, aspect ratio: 10]: 300 g were added, and stirred for 3 hours to obtain a uniform slurry. . A 15 μm thick PP non-woven fabric (manufactured by Nippon Kogyo Paper Co., Ltd.) was passed through the slurry, and the slurry was applied by pulling up and then dried to obtain a separator having a thickness of 20 μm.

(Example 2)
Cross-linked PMMA fine particles (resin B) [“Ganz Pearl 0104” (trade name) manufactured by Ganz Kasei Co., Ltd., average particle size 1 μm, Tg = about 120 ° C., B _R = 0.5, B _T = 2.3]: 1 kg, Water: 800 g, isopropyl alcohol (IPA): 200 g, and as a binder, polyvinyl butyral (PVB) [“Surek KX-5” (trade name) manufactured by Sekisui Chemical Co., Ltd.]: 375 g was put in a container, and a disperser at 2800 rpm. The mixture was stirred and dispersed for 1 hour under the conditions. In addition, as filler particles, alumina (Al ₂ O ₃ ) fine particles (“Sumiko Random AA04” (trade name) manufactured by Sumitomo Chemical Co., Ltd.), heat resistant temperature: 180 ° C. or higher, average particle size: 0.4 μm, particle size distribution: 0.00 3 to 0.7 μm]: 3 kg and the above binder (PVB): 750 g were added and stirred for 3 hours to obtain a uniform slurry. A 28 μm thick non-woven fabric made of PBT (Tapyrus Co., Ltd.) was passed through this slurry, and the slurry was applied by pulling up and then dried to obtain a separator having a thickness of 35 μm.

(Example 3)
As a binder, SBR latex [“TRD-2001” (trade name) manufactured by JSR Corporation]: 300 g and CMC [“2200” manufactured by Daicel Chemical Industries, Ltd.]: 30 g and water: 4 kg are put into a container and dissolved uniformly. Stir at room temperature. Further, an aqueous dispersion of crosslinked PMMA fine particles (resin B) [“STAPHYLOID” (trade name) manufactured by Gantz Kasei Co., Ltd., average particle size 0.3 μm, B _R = 1.2, B _T = 1.2] 0.5 kg was added and dispersed with stirring with a disper at 2800 rpm for 1 hour. To this, 3 kg of the same plate-like boehmite fine particles “BMM” as in Example 1 were added and stirred with a disper at 2800 rpm for 3 hours to obtain a uniform slurry. Using an applicator, this slurry was applied onto a 23 μm-thick PP non-woven fabric (manufactured by Nippon Vilene Co., Ltd.) with a gap of 50 μm and dried to obtain a separator having a thickness of 30 μm.

Example 4
To the same slurry as in Example 3, 1 kg of the same polyethylene powder aqueous dispersion “Chemipearl W-700” as in Example 1 is added as Resin A, and dispersed with stirring with a disperser at 2800 rpm for 1 hour. It was. Thereafter, a separator having a thickness of 30 μm was obtained in the same manner as in Example 3.

(Example 5)
In place of the alumina fine particles of Example 2, plate-like alumina fine particles [“Seraph” (trade name) manufactured by Kinsei Matec Co., Ltd.]: 3 kg was added to prepare a slurry, and this was made of PET having a thickness of 15 μm using an applicator. A separator having a thickness of 20 μm was obtained in the same manner as in Example 2 except that a non-woven fabric (manufactured by Freudenberg Co., Ltd.) was applied with a gap of 50 μm.

(Example 6)
Water dispersion of the same crosslinked PMMA fine particles (resin B) “Gantz Pearl 0104” as in Example 2: 1 kg, water: 2 kg as a solvent, and an ethylene-vinyl acetate copolymer (EVA) emulsion as a binder [from vinyl acetate The structural unit was 20 mol%, “Sumika Flex S850HQ” (trade name) manufactured by Sumika Chemtex Co., Ltd.]: 100 g was added, and the mixture was dispersed with stirring with a disper at 2800 rpm for 1 hour. To this was added 1.5 kg of alumina fiber [Denka Alsen B100 (trade name) manufactured by Denki Kagaku Kogyo Co., Ltd.] as filler particles, and the mixture was stirred at room temperature until uniform. The slurry was applied on a PET substrate with a coating thickness of 50 μm using a die coater, dried, and then peeled off from the PET substrate, whereby a porous substrate formed of alumina fibers, crosslinked PMMA fine particles, A separator having a thickness of 15 μm was obtained.

(Example 7)
As a binder, the same SBR latex “TRD-2001”: 100 g and CMC “2200”: 30 g as in Example 3 and water: 6 kg were placed in a container and stirred at room temperature until evenly dissolved. Further, 1 kg of boehmite (manufactured by Daimei Chemical Co., Ltd., average particle size 2 μm) was added, and the mixture was stirred and dispersed with a disper at 2800 rpm for 1 hour. PE emulsion [Mitsui Chemicals "W-700" (trade name)]: 1 kg (solid content) was added thereto, and the mixture was stirred with a disper at 2800 rpm for 3 hours to obtain a uniform slurry. Thereafter, a separator having a thickness of 20 μm was obtained in the same manner as in Example 1.

(Reference Example 1)
As a binder, EVA (the structural unit derived from vinyl acetate is 34 mol%, manufactured by Nihon Unicar Co., Ltd.): 100 g was placed in a container together with 6 kg of toluene as a solvent, and stirred at room temperature until evenly dissolved to obtain a binder solution. Obtained. Next, 500 g of polyethylene powder [“Flow Beads LE1080” (trade name) manufactured by Sumitomo Seika Co., Ltd.]: 500 g was added as the resin A to the above binder solution, and dispersed with stirring with a disperser at 2800 rpm for 1 hour. To this, 2 kg of the same alumina fine particle “Sumicorundum AA04” as in Example 2 was added as filler particles, and dispersed with stirring with a disperser at 2800 rpm for 3 hours to obtain a uniform liquid composition for forming a separator. It was. This slurry was applied by applying it onto the negative electrode mixture layer of the negative electrode described above through a gap of 50 μm using an applicator, and then dried to form a separator having a thickness of 15 μm integrated with the negative electrode on both sides of the negative electrode. Formed.

  A scanning electron micrograph of the cross section of the negative electrode is shown in FIG. 1, and a scanning electron micrograph in which the separator portion is enlarged is shown in FIG. In FIG. 1, 1 is a separator and 2 is a negative electrode. In FIG. 2, 3 is filler particles, 4 is a binder, 5 is a porous substrate, and 6 is a shutdown resin. 1 and 2, it can be seen that the porous substrate 5 composed of the filler particles 3 and the binder 4 and the separator 1 made of the shutdown resin 6 are formed on the negative electrode 2. In Reference Example 1, resin A (polyethylene) having a melting point in the range of 80 to 130 ° C. was used as the shutdown resin, and alumina fine particles were used as the filler particles. However, when resin B was used, boehmite was used. Similarly, the separator can be directly formed on the electrode.

(Reference Example 2)
Separators were formed on both sides of the negative electrode in the same manner as in Reference Example 1 except that the amount of polyethylene powder was changed to 1 kg.

(Example 8)
A slurry similar to that in Example 7 was applied onto the positive electrode mixture layer of the positive electrode described above in the same manner as in Reference Example 1 and dried, so that the both sides of the positive electrode had a thickness of 10 μm integrated with the positive electrode. A separator was formed.

(Comparative Example 1)
A commercially available polyethylene microporous film having a thickness of 20 μm was used as the separator of Comparative Example 1.

(Comparative Example 2)
As filler particles, alumina fine particles [“AKP-30” (trade name) manufactured by Sumitomo Chemical Co., Ltd., average particle size: 0.3 μm]: 1 kg, water: 800 g, isopropyl alcohol (IPA): 200 g, and implemented as a binder The same PVB “ESREC KX-5” as in Example 1: 375 g was put in a container, and dispersed with stirring with a disper at 2800 rpm for 1 hour to obtain a uniform slurry. A 15 μm thick PP non-woven fabric (manufactured by Nippon Kogyo Paper Co., Ltd.) was passed through the slurry, and the slurry was applied by pulling up and then dried to obtain a separator having a thickness of 20 μm.

(Comparative Example 3)
A separator having a thickness of 20 μm was obtained in the same manner as in Comparative Example 2, except that the same polyethylene powder (resin A) aqueous dispersion “Chemipearl W-700” as in Example 1 was used instead of the alumina fine particles.

(Reference Example 3)
A separator having a thickness of 20 μm was obtained in the same manner as in Comparative Example 2 except that the same plate-like boehmite fine particles “BMM” as in Example 1 were used in place of the alumina fine particles.
Table 1 shows the configurations of the separators of Examples 1 to 8, Reference Examples 1 to 3, and Comparative Examples 1 to 3.

  About each produced separator, the shrinkage rate and the shutdown temperature were measured with the following method.

  The separators of Examples 1 to 7, Reference Example 3 and Comparative Examples 1 to 3 were each cut into a size of 4 cm × 4 cm and sandwiched between two stainless plates fixed by clips, and in a thermostatic chamber at 150 ° C. Then, the length of each separator piece was measured, and the reduction rate was determined as the shrinkage rate of the separator in comparison with the length before the test.

  Moreover, about the separator of Example 8 and Reference Examples 1-2 integrated with the electrode, it was taken out after being left in a thermostatic bath at 150 ° C. for 60 minutes together with the electrode, and the length of the long side of the separator was set to before heating. The shrinkage rate was obtained by comparison. Table 2 shows the shrinkage ratio of each separator.

Moreover, the air permeability at room temperature (25 ° C.) of the separators of Examples 1 to 7 and Comparative Examples 1 to 3 was measured by a method based on JIS P 8117, and the Gurley value, that is, 0.879 g / mm ^2. The number of seconds during which 100 mL of air permeates the membrane under a pressure of (8620 Pa) was determined. Furthermore, about the separator of Example 1, Example 7, and Comparative Examples 1-3, the change of the Gurley value was measured in the range of 80 to 150 degreeC with the following method. Each separator was held for 10 minutes in a constant temperature bath at 80 ° C., then taken out and slowly cooled to room temperature (25 ° C.), and the Gurley value after the temperature was raised to 80 ° C. by the above method was measured. Thereafter, the temperature was increased to 150 ° C. in increments of 5 ° C., and the separator was held at each temperature for 10 minutes, and then the Gurley value was measured in the same manner as described above. The temperature at which the Gurley value exceeded 1 × 10 ⁴ sec / 100 mL from the change in the obtained Gurley value depending on the temperature was taken as the shutdown temperature of the separator. In the separator of Comparative Example 2 that did not contain the shutdown resin, the shutdown temperature could not be measured because the shutdown did not occur.

On the other hand, the separator of Examples 2-6 calculated | required shutdown temperature with the following method. Each separator piece cut to a size of 4cm x 4cm is sandwiched between two stainless plates with terminals, inserted into a bag of aluminum laminate film, injected with non-aqueous electrolyte, and then the tip of the terminal is put into the bag The bag was sealed in a state where it was taken out of the bag to prepare a test sample. Here, as the non-aqueous electrolyte, a solution in which LiPF ₆ was dissolved at a concentration of 1.2 mol / L in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2 was used.

  Place the above sample in a thermostat and measure the resistance value when applying a 1 kHz alternating current to the terminal with a contact resistance meter “3560 AC milliohm high tester” (trade name) manufactured by HIOKI, at room temperature (25 ° C.) The temperature was increased at a rate of 1 ° C./minute and heated, and the change in internal resistance with temperature was determined. The temperature at which the resistance value was 10 times or more the value at room temperature (25 ° C.) was taken as the shutdown temperature of the separator.

  Table 3 shows the Gurley values and shutdown temperatures of the separators of Examples 1 to 7 and Comparative Examples 1 to 3.

  In addition, about the separator integrated with the electrode, the shutdown temperature of the said separator was calculated | required by measuring the change with the temperature of the internal resistance of a battery after the assembly of a battery so that it may mention later.

<Production and evaluation of battery>
The separators of Examples 1 to 7, Reference Example 3 and Comparative Examples 1 to 3 were wound in a spiral shape together with the positive electrode and the negative electrode, respectively, to produce a wound electrode body. The wound electrode body is crushed into a flat shape, loaded into a battery container, injected with a non-aqueous electrolyte having the same structure as described above, and then sealed, and Examples 1A to 7A, Reference Example 3A and Comparative Example The lithium secondary batteries of Examples 1A to 3A were prepared.

  In addition, the separators of Example 8 and Reference Examples 1 and 2 integrated with the positive electrode or the negative electrode overlap the positive electrode or the negative electrode and the counter electrode with the separator interposed therebetween, and assemble a lithium secondary battery in the same manner as described above. The lithium secondary batteries of Example 8A and Reference Examples 1A to 2A were obtained.

  First, an example of measuring the shutdown temperature of a separator integrated with an electrode is shown below. The lithium secondary batteries of Example 8A and Reference Examples 1A to 2A were placed in a thermostatic bath, and the temperature was increased from 30 ° C. to 150 ° C. at a rate of 1 ° C. per minute in the same manner as the measurement of the internal resistance of the separator alone. The battery was heated and the change in the internal resistance of the battery with temperature was determined. The temperature at which the resistance value increased to 5 times or more of the value at 30 ° C. was taken as the shutdown temperature of the separator. Moreover, in order to compare with the method of obtaining the shutdown temperature by the change of the Gurley value, the change of the internal resistance of the battery of Comparative Example 1A due to the temperature was obtained in the same manner as described above, and the shutdown temperature of the separator of Comparative Example 1 was obtained. As a result, almost the same result as the method of obtaining the shutdown temperature by the change of the Gurley value was obtained. Further, for the battery of Comparative Example 3A, an attempt was made to measure the change in internal resistance with temperature in the same manner. However, it was found that an internal short circuit occurred during battery production, and the evaluation as a battery could not be performed. . That is, since the separator of Comparative Example 3 does not contain filler particles, the strength of the separator is weak, and it seems that an internal short circuit occurred during battery production.

  The measurement results are shown in Table 4. Further, changes in internal resistance of Reference Example 2A and Comparative Example 1A with temperature are shown in FIGS. 3 and 4, respectively.

  As shown in Table 3 and Table 4, in the separators of Examples 1 to 8 and Reference Examples 1 and 2 of the present invention, the shutdown temperature is in the range of 103 to 125 ° C., which ensures the safety of the battery at high temperatures. Shutdown occurred at an appropriate temperature range. On the other hand, in the separator of Comparative Example 1, the shutdown temperature exceeded 130 ° C., which was closer to the thermal runaway temperature of the battery. Moreover, since the separator of Comparative Example 2 did not have the shutdown resin, the shutdown did not occur.

  The separators of Example 1, Examples 7 to 8 and Reference Examples 1 to 2 are those that close the pores by causing the resin A to melt and cause shutdown, and are used in conventional lithium secondary batteries. This is due to the same mechanism as the porous membrane (Comparative Example 1). In the separators of Examples 2 to 6, the shutdown was caused by the swelling of the resin B and the electrolyte withering, but the shutdown effect similar to the conventional method could be produced. In Example 4, since not only the resin B but also the resin A is included, it is considered that shutdown is caused by both the above-described mechanisms. In the former mechanism using the resin A, a free electrolyte remains as it is, but in the latter mechanism using the resin B, the electrolyte is absorbed by the resin B and the electrolyte related to the charge / discharge reaction is depleted. From the viewpoint of safety at high temperature, it seems desirable to contain the resin B.

  In addition, as shown in Table 2, the separators of Examples 1 to 8 and Reference Examples 1 to 3 of the present invention have a slight shrinkage of the separator after being heated above the shutdown temperature, while being comparative examples. In the separator No. 1, the separator contracted greatly after exceeding the shutdown temperature. For this reason, in the battery (Reference Example 2A) including a porous substrate having a heat resistant temperature of 150 ° C. or higher, as shown in FIG. 3, the shutdown state is maintained without decreasing the internal resistance until reaching 150 ° C. Although the safety after the shutdown is maintained, in the battery of Comparative Example 1A, as shown in FIG. 4, the internal resistance rapidly decreases due to the contraction of the separator, and an internal short circuit is likely to occur.

  Next, the batteries of Examples 1A to 2A, Reference Examples 1A to 2A and Comparative Example 1A were charged and discharged under the following conditions, and the load characteristics were measured. The charging was constant current-constant voltage charging in which constant current charging was performed until the battery voltage reached 4.2 V at a current value of 0.2 C, and then constant voltage charging at 4.2 V was performed. The total charging time until the end of charging was 15 hours for the batteries of Examples 1A to 2A, and 7.5 hours for the batteries of Reference Examples 1A to 2A and Comparative Example 1A. The battery after charging is discharged at a discharge current of 0.2C and 2C until the battery voltage reaches 3.0 V, respectively, and the discharge capacities at the discharges of 0.2C and 2C are obtained, respectively. The ratio of the discharge capacity of 2C to the load characteristic was evaluated as load characteristics. The results are shown in Table 5.

  The batteries of Examples 1A to 2A and Reference Examples 1A to 2A had load characteristics equivalent to or higher than those of Comparative Example 1A using a conventional separator, and functioned without problems.

  Further, the batteries of Examples 2A to 8A, Reference Example 3A and Comparative Examples 1A to 2A were charged under the above conditions (total charging time: 15 hours), and then discharged until reaching 3.0V at 0.2C. The charge capacity and the discharge capacity were obtained, and the ratio of the discharge capacity to the charge capacity was evaluated as the charge efficiency. The results are shown in Table 6.

  In the batteries of Examples 2A to 8A and Reference Example 3A, the charging efficiency was almost 100% as in Comparative Example 1A, and the generation of lithium dendrite during charging was suppressed. In particular, in a battery including boehmite as filler particles in the separator, as shown in Example 8A (separator thickness: 10 μm), generation of lithium dendrite is suppressed even when the separator thickness is small, which is suitable for thinning the separator. Had characteristics.

  On the other hand, in the battery of Comparative Example 2A (separator thickness: 20 μm) using alumina fine particles as filler particles, charge / discharge efficiency was reduced due to internal short circuit due to generation of lithium dendrite. It seems that there is a difference in the ease of lithium dendrite formation depending on the shape and the presence or absence of shutdown resin particles.

  As described above, the porous substrate having a heat resistant temperature of 150 ° C. or higher, the filler particles, the resin A having a melting point in the range of 80 to 130 ° C., and the electrolyte swells and swells by heating. By configuring the separator with a porous film containing at least one resin selected from the resin B whose degree of swelling increases with increase, the separator has characteristics equivalent to or better than those of conventional separators and is excellent in safety at high temperatures. An electrochemical element separator and an electrochemical element using the same can be provided.

The scanning electron micrograph of the negative electrode cross section of the reference example 1 is shown. The scanning electron micrograph which expanded the separator part of FIG. 1 is shown. It is a figure which shows the temperature change of the internal resistance of the battery of the reference example 2A. It is a figure which shows the temperature change of the internal resistance of the battery of the comparative example 1A.

Explanation of symbols

1 Separator 2 Negative Electrode 3 Filler Particle 4 Binder 5 Porous Substrate 6 Shutdown Resin

Claims (17)

A separator for an electrochemical element comprising a porous substrate having a heat-resistant temperature of 150 ° C. or higher, boehmite particles, and a resin having a melting point in the range of 80 to 130 ° C.,
The boehmite particles have a number average particle size of 0.1 μm or more and 15 μm or less,
The separator for an electrochemical element, wherein the content of the boehmite particles is 20% by volume or more in the total volume of all constituent components of the separator. The separator for an electrochemical element according to claim 1 , wherein the boehmite particles are present in pores of the porous substrate. The separator for an electrochemical element according to claim 1 or 2 , wherein the resin having a melting point in the range of 80 to 130 ° C is present in the pores of the porous substrate. The separator for an electrochemical element according to any one of claims 1 to 3 , comprising plate-like particles as the filler particles. The separator for an electrochemical element according to claim 4 , wherein the plate surface of the plate-like particles is oriented in the direction of the film surface of the separator. The content of the boehmite particles, separator for an electrochemical device according to any one of claims 1 to 5, the total volume of all components of the separator is 80% by volume or less. _{SiO 2, Al 2 O 3,} TiO 2 and at least one separator for an electrochemical device according to any one of claims 1 to 5, further comprising a filler particle selected from ZrO _2. The separator for an electrochemical element according to claim 7 , wherein the content of the filler particles containing boehmite is 80% by volume or less in the total volume of all constituent components of the separator. The separator for an electrochemical element according to any one of claims 1 to 8 , wherein the resin having a melting point in the range of 80 to 130 ° C is at least one selected from polyethylene, an ethylene-vinyl monomer copolymer, and a polyolefin wax. . The separator for an electrochemical element according to any one of claims 1 to 9 , wherein the porous substrate includes a fibrous material having a heat resistant temperature of 150 ° C or higher. The fibrous material is cellulose and its modified product, polyolefins, polyesters, polyacrylonitrile, aramid, polyamideimide, according to claim 10 which is composed of at least one selected from the group consisting of polyimide and an inorganic oxide Electrochemical element separator. The separator for an electrochemical element according to any one of claims 1 to 11 , wherein the porosity is 20% or more. The separator for an electrochemical element according to any one of claims 1 to 12 , wherein the porosity is 70% or less. The separator for an electrochemical element according to any one of claims 1 to 13 , wherein an air permeability represented by a Gurley value is 10 to 300 (sec / 100 mL). The separator for an electrochemical element according to any one of claims 1 to 14 , which has a thickness of 3 µm or more and 30 µm or less. Positive electrode, a negative electrode, a nonaqueous electrolyte and an electrochemical device, which comprises a separator for an electrochemical device according to any one of claims 1 to 15. The electrochemical device according to claim 16 , wherein the separator is integrated with at least one selected from the positive electrode and the negative electrode.

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