JP5403857B2 - Battery separator, method for producing the same, and lithium secondary battery - Google Patents

Battery separator, method for producing the same, and lithium secondary battery Download PDF

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JP5403857B2
JP5403857B2 JP2006138385A JP2006138385A JP5403857B2 JP 5403857 B2 JP5403857 B2 JP 5403857B2 JP 2006138385 A JP2006138385 A JP 2006138385A JP 2006138385 A JP2006138385 A JP 2006138385A JP 5403857 B2 JP5403857 B2 JP 5403857B2
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separator
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JP2007311151A (en
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秀昭 片山
敏浩 阿部
映理 児島
吉宣 佐藤
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日立マクセル株式会社
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    • YGENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02EREDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10Energy storage
    • Y02E60/12Battery technologies with an indirect contribution to GHG emissions mitigation
    • Y02E60/122Lithium-ion batteries

Description

  The present invention relates to a separator that is inexpensive, excellent in dimensional stability at high temperature, and excellent in flexibility, and to a lithium secondary battery that uses this separator and is safe even in a high temperature environment. The separator of the present invention is particularly suitable for a battery including an electrode group having a winding structure.

  Lithium ion batteries, which are a type of non-aqueous battery, are widely used as power sources for portable devices such as mobile phones and notebook personal computers because of their high energy density. As the performance of portable devices increases, the capacity of lithium ion batteries tends to increase further, and ensuring safety is important.

  In the current lithium ion battery, as a separator interposed between a positive electrode and a negative electrode, for example, a polyolefin-based porous film having a thickness of about 20 to 30 μm is used. In addition, as separator material, the constituent resin of the separator is melted below the thermal runaway temperature of the battery to close the pores, thereby increasing the internal resistance of the battery and improving the safety of the battery in the event of a short circuit. In order to ensure the so-called shutdown effect, polyethylene 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, so it is difficult to say that the margin for ensuring the safety of the battery is sufficient. .

  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 in the case of abnormal charging or the like, the current must be immediately reduced to prevent the battery temperature from rising. This is because if the pores are not sufficiently closed and the current cannot be reduced immediately, the battery temperature easily rises to the contraction temperature of the separator, and there is a risk of ignition due to an internal short circuit.

  As a technique for preventing a short circuit of the battery due to the thermal contraction of the separator, for example, there is a method of using a microporous film or a non-woven fabric using a heat resistant resin for the separator, but such a separator has a disadvantage that it is expensive. doing.

  On the other hand, a technique has also been proposed in which various types of processing are performed on a nonwoven fabric made of an inexpensive material and this is used as a separator. For example, Patent Document 1 discloses a method in which polyethylene (PE) fine particles are applied to a PP nonwoven fabric, Patent Document 2 discloses a method in which a polyester nonwoven fabric is coated with wax, and Patent Document 3 discloses a polyester. A method of using a PE microporous membrane in contact with a non-woven fabric and a PP non-woven fabric is disclosed in Patent Document 4, in which a method of mixing inorganic fine particles and organic fine particles in a PP non-woven fabric is used, and in Patent Document 5, Methods for applying inorganic fine particles to a polyethylene terephthalate (PET) nonwoven fabric are disclosed.

  However, in the technique of mixing inorganic fine particles into a nonwoven fabric, short-circuiting due to lithium dendrite generation cannot be completely prevented unless inorganic fine particles are uniformly and densely filled in the voids of the nonwoven fabric. It is difficult to uniformly fill inorganic fine particles on a substrate having high properties. In particular, in a battery using a wound electrode group composed of a positive electrode, a negative electrode, and a separator, a curved portion in which the diameter of the electrode group is reduced even if a non-woven fabric filled with inorganic fine particles is uniformly used to some extent. However, there is a problem in that cracks and the like are generated in the separator due to bending stress, and a short circuit due to dendrite is likely to occur.

  In addition, when using organic fine particles, it is difficult to uniformly and densely fill the fine particles in the voids of the nonwoven fabric as in the case of using inorganic fine particles, and when using a soft material such as PE, In the case of a wound electrode group, the above cracks are unlikely to occur, but if the separator is made thin from the viewpoint of increasing the energy density, insulation between the hard positive electrode material and the negative electrode material cannot be sufficiently maintained. May cause a short circuit.

  Furthermore, a technique for forming a separator by applying electrochemically stable fine particles such as inorganic fine particles on electrodes has also been proposed (Patent Documents 6 and 7).

  However, if it is attempted to reduce the thickness of the separator in order to increase the energy density of the battery, the insulation between the positive electrode and the negative electrode cannot be sufficiently maintained. Then, as described above, in the bending portion, cracking due to bending stress occurs and is likely to cause a short circuit.

JP-A-60-136161 Japanese Patent Laid-Open No. 62-283553 JP-A-1-258358 JP 2003-22843 A JP 2005-536658 Gazette International Publication No. 97/8863 JP 2000-149906 A

  The present invention has been made in view of the above circumstances, and its purpose is to suppress a decrease in energy density as much as possible, and to ensure the reliability of the battery, while being excellent in safety when abnormally heated. And a lithium secondary battery having the separator.

The battery separator of the present invention capable of achieving the above object is a porous battery separator containing at least electrically insulating inorganic particles and a binder, and the binder content in the total amount of the constituent components is 0.1% by mass or more and 30% by mass or less, and the binder is water-soluble or an emulsion dispersed in water. The inorganic particles have a molar agglomeration energy of 30 kJ on the surface. Inorganic particles having a functional group smaller than / mol (hereinafter sometimes abbreviated as “functional group”). As the functional group, an amino group, an epoxy group, an acrylic group, a methacryl group, an alkyl group, a ureido group, a mercapto group, an isocyanate group, and the like are preferable.
The battery separator of the present invention comprises a step of forming a liquid composition containing electrically insulating inorganic particles, a binder, and water, and applying the liquid composition to an ion-permeable sheet or electrode. Or it can manufacture by the manufacturing method of the separator for batteries of this invention characterized by including the process to make it impregnate and dry.

  Also, a lithium secondary battery comprising at least a negative electrode containing an active material capable of occluding and releasing lithium, a positive electrode containing an active material capable of occluding and releasing lithium, and the battery separator of the present invention is also provided. Are encompassed by the present invention.

  According to the present invention, a lithium secondary battery excellent in safety when abnormally heated while suppressing a decrease in energy density as much as possible and ensuring the reliability of the battery, and the lithium secondary battery are configured. A battery separator can be provided.

  As described above, the battery separator of the present invention (hereinafter sometimes abbreviated as “separator”) has a porous structure, and at least the surface thereof has an inorganic particle having a functional group having a molar agglomeration energy of less than 30 kJ / mol [ Hereinafter, the inorganic particles having the functional group on the surface are referred to as “inorganic particles (A)”, and the inorganic particles having no functional group before surface treatment and the like are simply referred to as “inorganic particles”] And a binder (B).

  In the battery separator of the present invention, the presence of the inorganic particles (A) allows the positive electrode and the negative electrode to be satisfactorily separated even if the separator is thinned, so that a short circuit occurs while suppressing a decrease in battery energy density as much as possible. Can be prevented.

  In addition, since inorganic particles usually have OH groups on the surface thereof, they have a problem that the affinity with the binder is not so high. However, the inorganic particles (A) according to the present invention have a mole on the surface. Since the cohesive energy has a functional group smaller than 30 kJ / mol, the lipophilicity is improved, and the affinity with the binder (B) constituting the separator together with the inorganic particles (A) is high. Since the anchor effect by can also be expected, the adhesion between the inorganic particles (A) and the binder (B) is good. Therefore, when using the separator of the present invention, the positive electrode and the negative electrode to form a wound electrode group, or further crushing the electrode group to form a flat electrode group having a portion with a large curvature. However, since the occurrence of cracks and the like of the separator can be prevented, the occurrence of a fine short circuit can be suppressed and the reliability of the battery can be ensured.

  Furthermore, since the separator is composed of the inorganic particles (A), the occurrence of heat shrinkage can be suppressed. Therefore, in the battery having the separator of the present invention, even when abnormally heated, due to the heat shrinkage of the separator. Contact between the positive electrode and the negative electrode hardly occurs, and the safety is excellent.

  As the inorganic particles (A), for example, those obtained by subjecting inorganic particles to a surface treatment to have the functional groups on the surface can be used. The inorganic particles for forming the inorganic particles (A) have electrical insulating properties, are electrochemically stable, and may be further referred to as a nonaqueous electrolytic solution (hereinafter simply referred to as “electrolytic solution”). ) Or a solvent used in the liquid composition used in the production of the separator, and is not particularly limited as long as it is not soluble in the electrolytic solution at a high temperature. The “high temperature state” as used in the present specification is specifically a temperature of 150 ° C. or higher, and may be any stable particle that does not undergo deformation and chemical composition change in the electrolyte at such a temperature. Further, “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the battery.

Specific examples of such inorganic particles include, for example, oxide fine particles such as iron oxide, SiO 2 , Al 2 O 3 , TiO 2 , BaTiO 2 , ZrO, alumina-silica composite oxide; aluminum nitride, silicon nitride, etc. Nitride fine particles: Calcium fluoride, barium fluoride, barium sulfate and other poorly soluble ionic crystal fine particles; silicon, diamond and other covalently bonded crystal fine particles; talc, montmorillonite and other clay fine particles; boehmite, zeolite, apatite, kaolin , Mullite, spinel, olivine, sericite, bentonite and other mineral resource-derived substances or their artificial products. Further, the surface of conductive fine particles such as metal fine particles; oxide fine particles such as SnO 2 and tin-indium oxide (ITO); carbon fine particles such as carbon black and graphite; Fine particles imparted with electrical insulation properties by surface treatment with the above-described material constituting the electrically insulating inorganic particles) may be used.

Among the above inorganic particles, alumina (Al 2 O 3 ), silica (SiO 2 ), alumina-silica composite oxide, boehmite and the like are particularly preferable.

  The average particle size of the inorganic particles is, for example, 0.001 μm or more, more preferably 0.1 μm or more, and preferably 15 μm or less, more preferably 1 μm or less. Here, the average particle size of the inorganic particles is a number average particle size measured by dispersing in a medium (for example, water) in which the inorganic particles do not swell using a laser scattering particle size distribution meter (“LA-920” manufactured by HORIBA). Is the diameter.

  In addition, even after surface treatment is performed on the inorganic particles to obtain the inorganic particles (A) having the above functional groups, the particle diameter hardly changes. Therefore, the inorganic particles (A) also have an average particle diameter measured by the same method as described above, and are 0.001 μm or more, more preferably 0.1 μm or more, and 15 μm or less, more preferably 1 μm or less. Is desirable.

  The shape of the inorganic particles may be, for example, a so-called spherical shape, or a plate shape or a needle shape. More preferably, it is a plate-like particle. The shape of the inorganic particles is substantially maintained after the surface treatment and the inorganic particles (A) having the functional groups are provided, but in the case where the inorganic particles (A) are plate-like, The orientation of the inorganic particles (A) so that the flat plate surface thereof is substantially parallel to the surface of the separator can suppress the occurrence of a short circuit. This is because the inorganic particles (A) are oriented as described above so that the inorganic particles (A) overlap each other on a part of the flat plate surface. It is considered that the hole) is formed in a bent shape instead of a straight line, and thus it is possible to prevent the lithium dendrite from penetrating the separator.

  In order to obtain the effect obtained by orienting the plate-like inorganic particles (A) as described above, the existence form of the inorganic particles (A) in the separator is as described above. More specifically, the inorganic particles (A) in the vicinity of the surface of the separator preferably have an average angle between the flat plate surface and the separator surface of 30 degrees or less [most preferably]. The average angle is 0 degree, that is, the flat surface of the inorganic particles (A) in the vicinity of the surface of the separator is parallel to the surface of the separator. Here, “near the surface” refers to a range of 10% from the surface of the separator to the entire thickness.

  Examples of the form in which the inorganic particles [and the inorganic particles (A) having the above functional groups on the surface] are plate-like particles include, for example, an aspect ratio (ratio between the maximum length in the plate-like particles and the thickness of the plate-like particles). ) Is 5 or more, more preferably 10 or more, and is preferably 100 or less, more preferably 50 or less. The average value of the ratio of the long axis direction length to the short axis direction length of the flat plate surface of the grain is 0.3 or more, more preferably 0.5 or more, and 3 or less, more preferably 2 or less. It is desirable. When the plate-like inorganic particles [that is, the inorganic particles (A)] have the above aspect ratio or the average value of the ratio of the major axis direction length to the minor axis direction of the flat plate surface, the short circuit described above. The preventive action is more effectively exhibited.

  In addition, the average value of the ratio of the long axis direction length to the short axis direction length of the flat plate surface in the case where the inorganic particles and the inorganic particles (A) are plate-like is photographed by, for example, a scanning electron microscope (SEM). It can obtain | require by image-analyzing the done image. Further, the above aspect ratio in the case where the inorganic particles and the inorganic particles (A) are plate-like can also be obtained by image analysis of an image taken by SEM.

More specific examples of the plate-like inorganic particles include various commercially available products. For example, “Sun Lovely” (SiO 2 ) manufactured by Dokai Chemical Industries, Ltd., and “NST-B1” manufactured by Ishihara Sangyo Co., Ltd. (TiO 2 ), Sakai Chemical Industry's plate-like barium sulfate “H series”, “HL series”, Hayashi Kasei's “micron white” (talc), Hayashi Kasei's “bengel” (bentonite), Kawai lime “BMM” and “BMT” (boehmite) manufactured by Komatsu Ltd., “Cerasure BMT-B” [alumina (Al 2 O 3 )] manufactured by Kawai Lime Co., “Seraph” (alumina) manufactured by Kinsei Matec Co., Ltd. “Yodogawa Mica Z-20” (Sericite), “Micro Mica” and “Soshimafu” (Mica) manufactured by Co-op Chemical are available. In addition, SiO 2 , Al 2 O 3 , ZrO, and CeO 2 can be produced by the method disclosed in Japanese Patent Laid-Open No. 2003-206475.

Among the above, it is preferable to use plate-like particles of a compound represented by AlOOH or Al 2 O 3 · H 2 O as a main component (for example more than 80 wt%), particularly preferably used boehmite.

  In order to give the inorganic particles as described above to the inorganic particles (A) by imparting the above functional groups, the inorganic particles may be subjected to a surface treatment by a conventionally known method. That is, a method using a coupling agent, a method using a surfactant, a method using a polar resin, and the like can be mentioned. Especially, the surface treatment using various coupling agents, such as a silane coupling agent, a titanate coupling agent, an aluminate coupling agent, a zirconate coupling agent, is preferable.

  When using the various coupling agents described above, the coupling agent is preferably chemically bonded to the surface of the inorganic particles. Specifically, for example, a solution in which a coupling agent is dissolved is added to a dispersion liquid (slurry or the like) in which inorganic particles are dispersed in a dispersion medium, and a coupling reaction is performed, followed by filtration and drying. A method of chemically coupling a coupling agent to the surface of the particles can be preferably employed. In addition, the inorganic particle | grains used for surface treatment may be used individually by the said illustration, and may use 2 or more types together.

  The functional group of the inorganic particles (A) obtained by the above operation is derived from a coupling agent. Specific examples thereof include, for example, an amino group, an epoxy group, an acrylic group, a methacryl group, Examples thereof include an alkyl group, a ureido group, a mercapto group, and an isocyanate group. The molar cohesive energy of the functional group is, for example, 14.8 kJ / mol for an amino group, 17.8 kJ / mol for a mercapto group, and 7.5 kJ / mol for a methyl group. Further, the functional group may be bonded to inorganic particles through a hydrocarbon chain.

  The inorganic particles (A) may be used alone or in combination of two or more (that is, two or more types having different functional groups present on the surface, two or more types having different inorganic particles, Further, two or more of them may be used in combination.

  By using the inorganic particles (A) having the functional group on the surface as described above as the constituent material of the separator, the binding force with the binder (B) can be increased in the separator.

  In the separator of the present invention, the binder (B) is used for the purpose of binding inorganic particles (A) to each other, various added particles described later, fibrous materials for reinforcement, and the like. The binder (B) is not particularly limited as long as it is electrochemically stable and stable with respect to the electrolyte solution, and can adhere the inorganic particles (A) and the like well. For example, EVA (structural unit derived from vinyl acetate) Is an ethylene-acrylate copolymer such as ethylene-ethyl acrylate copolymer, various rubbers and derivatives thereof [styrene-butadiene rubber (SBR), fluororubber, urethane rubber, ethylene-propylene- Diene rubber (EPDM)], cellulose derivatives [carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, etc.], polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane, epoxy resin, polyfluoride Bini Den (PVDF), vinylidene fluoride - hexafluoropropylene copolymer (PVDF-HFP), and acrylic resins. Can also use these alone, it may be used in combination of two or more. Further, among the heat-meltable particles (C) and the swellable particles (D) described later, those having adhesiveness alone can be used as the binder (B). When these binders (B) are used, they can be used in the form of an emulsion dissolved or dispersed in a solvent of a liquid composition for forming a separator described later.

  Moreover, in order to give the separator a shutdown function, the heat-meltable particles (C) that melt at 80 to 130 ° C., or the swellable particles that can swell in the non-aqueous electrolyte and increase in the degree of swelling as the temperature rises It is also possible to add (D). Further, both the heat-meltable particles (C) and the swellable particles (D) may be added to the separator, and these composites may be further added.

  The above-described shutdown function relating to the separator in the case of using the hot-melt particles (C) or the swellable particles (D) can be evaluated by, for example, an increase in resistance due to the temperature of the model cell. That is, a model cell including a positive electrode, a negative electrode, a separator, and an electrolytic solution is prepared, and the model cell is held in a high-temperature bath, and the internal resistance value of the model cell is measured while the temperature is increased at a rate of 5 ° C./min. Then, by measuring the temperature at which the measured internal resistance value is 5 times or more that before heating (resistance value measured at room temperature), this temperature can be evaluated as the shutdown temperature of the separator. In a separator using hot-melt particles (C) or swellable particles (D), the shutdown temperature evaluated in this way can be set to 80 to 130 ° C., which is sufficient under normal battery use environments. When the temperature inside the battery rises, the safety of the battery can be ensured since the shutdown occurs at a relatively early stage, while ensuring good ion conductivity and improving the discharge characteristics of the battery. .

  Contains heat-meltable particles (C) that melt at 80 to 130 ° C., that is, those having a melting temperature of 80 to 130 ° C. measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121. When the separator is exposed to 80 to 130 ° C. (or higher temperature), the meltable particles (C) are melted to close the voids of the separator, so that the movement of lithium ions is hindered. And a rapid discharge reaction at a high temperature is suppressed. Therefore, in this case, the shutdown temperature of the separator evaluated by the increase in internal resistance is not less than the melting point of the heat-meltable particles (C) and not more than 130 ° C.

  Specific examples of the constituent material of the heat-meltable particles (C) include polyethylene (PE), a copolymerized polyolefin having a structural unit derived from ethylene of 85 mol% or more, polypropylene, or a polyolefin derivative (chlorinated polyethylene, chlorinated polypropylene, etc. ), 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, or an ethylene-ethyl acrylate copolymer. it can. Moreover, polycycloolefin etc. can also be used. The heat-meltable particles (C) may have only one kind of these constituent materials, or may have two or more kinds. Among these, PE, polyolefin wax, or EVA having a structural unit derived from ethylene of 85 mol% or more is preferable. The heat-meltable particles (C) contain, as a constituent component, various known additives (for example, antioxidants) that are added to the resin as necessary in addition to the constituent materials described above. It doesn't matter.

  The particle diameter of the heat-meltable particles (C) is a number average particle diameter measured by the same measurement method as the inorganic particles (A), for example, 0.001 μm or more, more preferably 0.1 μm or more, It is recommended that it is 15 μm or less, more preferably 1 μm or less.

  The swellable particles (D) that can swell in the non-aqueous electrolyte and increase in the degree of swelling with an increase in temperature are obtained when the battery equipped with the separator using the swellable particles (D) is exposed to a high temperature. Due to the property that the degree of swelling increases as the temperature rises (hereinafter sometimes referred to as “thermal swelling”), the swellable particles (D) absorb the electrolyte solution in the battery and swell. At this time, the amount of electrolyte present inside the separator gap becomes so-called “liquid withering” state, and the swollen particles also block the gap inside the separator. Since the ion conductivity is significantly reduced and the internal resistance of the battery is increased, the above-described shutdown function can be ensured.

  As the swellable particles (D), those having a heat swellability of 75 to 125 ° C. are preferable. If the temperature exhibiting thermal swellability is too high, the thermal runaway reaction of the active material in the battery may not be sufficiently suppressed, and the battery safety improvement effect may not be sufficiently ensured. Moreover, when the temperature which shows heat swelling property is too low, the conductivity of the lithium ion in the battery in a normal use temperature range will become low too much, and it may cause trouble in use of an apparatus. That is, in the separator of the present invention, when the shutdown function is provided, the temperature at which the lithium ion conductivity in the battery is remarkably reduced (so-called shutdown temperature) may be in the range of about 80 to 130 ° C. as described above. Desirably, for this reason, it is preferable that the temperature at which the swellable particles (D) begin to exhibit thermal swellability due to temperature rise is in the range of 75 to 125 ° C.

Further, as the swellable particles (D), those having a degree of swelling B defined by the following formula measured at 120 ° C. of 1.0 or more are preferable.
B = (V 1 / V 0 ) -1 (1)
[In the above formula (1), V 0 is the volume of particles (cm 3 ) 24 hours after being put into the non-aqueous electrolyte at 25 ° C., and V 1 is put into the non-aqueous electrolyte at 25 ° C. 24 hours later, the temperature of the non-aqueous electrolyte is raised to 120 ° C., and the volume of the particles (cm 3 ) after 1 hour at 120 ° C. is meant. ]

  The swellable particles (D) having the degree of swelling as described above greatly increase in degree of swelling in an environment that exceeds the above temperature (any temperature of 75 to 125 ° C.) that starts to show thermal swellability. Therefore, in a battery using a separator having swellable particles (D) having such properties, when the internal temperature exceeds a specific temperature (for example, 75 to 125 ° C.), the swellable particles (D) However, when the electrolyte in the battery further absorbs and expands greatly, the lithium ion conductivity is remarkably lowered, so that the safety of the battery can be ensured more reliably. The swelling degree of the swellable particles (D) defined by the above formula (1) may cause battery deformation if it becomes too large, and is desirably 10 or less.

  Specific measurement of the swellable particles (D) defined by the above formula (1) can be performed by the following method. Swellable particles (D) are added to a binder resin solution or emulsion in which the degree of swelling when immersed in an electrolytic solution at room temperature for 24 hours in advance and the degree of swelling defined by the above formula (1) at 120 ° C. is known. A slurry is prepared by mixing, and this is cast on a base material 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 electrolytic solution at room temperature (25 ° C.) for 24 hours, and the mass was measured. Further, the electrolytic solution was heated to 120 ° C., and the mass after 1 hour was measured at the temperature. The degree of swelling B is calculated by the formulas (2) to (8). [In the following formulas (2) to (8), the volume increase of components other than the electrolyte due to the temperature rise from room temperature to 120 ° C. can be ignored. It is said].

V i = M i × W / P A (2)
V B = (M 0 −M i ) / P B (3)
V C = M 1 / P c -M 0 / P B (4)
V V = M i × (1−W) / P V (5)
V 0 = V i + V B −V V × (B B +1) (6)
V D = V V × (B B +1) (7)
B = [{V 0 + V C −V D × (B C +1)} / V 0 ] −1 (8)

Here, in the above formulas (2) to (8),
V i : volume (cm 3 ) of the swellable particles (D) before being immersed in the electrolytic solution,
V 0 : volume (cm 3 ) of the swellable particles (D) after being immersed in the electrolyte at room temperature 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 at room temperature for 24 hours until the electrolytic solution was heated to 120 ° C. and further passed for 1 hour at the above temperature. 3 ),
V V : volume (cm 3 ) of the binder resin before being immersed in the electrolytic solution,
V D : volume of the binder resin (cm 3 ) after being immersed in the electrolytic solution at room temperature for 24 hours,
M i : mass (g) of the film before being immersed in the electrolytic solution,
M 0 : mass (g) of the film after being immersed in the electrolytic solution at room temperature for 24 hours,
M l : After immersing in the electrolyte solution at room temperature for 24 hours, the electrolyte solution was heated to 120 ° C., and the mass (g) of the film after 1 hour at the above temperature,
W: Mass ratio of the swellable particles (D) in the film before being immersed in the electrolytic solution,
P A : specific gravity (g / cm 3 ) of the swellable particles (D) before being immersed in the electrolytic solution,
P B : Specific gravity of electrolyte at room temperature (g / cm 3 ),
P C: electrolyte specific gravity at 120 ℃ (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).

Also, swellable particles (D) is the swelling degree B R at room temperature (25 ° C.) which is defined by the following equation (9) is preferably 0 or more and 1 or less.
B R = (V 0 / V i ) -1 (9)
In the above formula (9), V 0 and V i are the same as those described for the above formulas (2) to (8).

That is, the swellable particles (D) may be those that do not absorb the electrolytic solution (B R = 0) at room temperature, or those that absorb some of the electrolytic solution. In the range (for example, 70 ° C. or less), the absorption amount of the electrolytic solution does not change so much regardless of the temperature, and thus the degree of swelling does not change so much. It only needs to increase.

The swellable particles (D), and preferably has satisfied the swelling degree B or B R, also has an electrically insulating, electrochemically stable, further described below electrolyte, separator There is no particular limitation as long as it is stable to the solvent used in the liquid composition containing the inorganic particles (A) used during production and does not dissolve in the electrolytic solution at a high temperature.

  In the known lithium secondary battery, for example, a solution in which a lithium salt is dissolved in an organic solvent is used as a non-aqueous electrolyte (details of the lithium salt, the type of the organic solvent, the lithium salt concentration, etc. will be described later). ). Therefore, as the swellable particles (D), in the organic solvent solution of the lithium salt, when the temperature reaches any of 75 to 125 ° C., the above-mentioned thermal swellability starts to be exhibited. Those that can swell so that B satisfies the above values are recommended.

  In addition, even if the resin itself is soluble in an organic solvent such as an electrolyte, it is stable against the organic solvent as a result of being combined with the heat-resistant particles that form the core by chemical bonding as described below. Particles having a coating layer (shell) made of a resin that becomes can also be used as the swellable particles (D). In such a case, the degree of swelling of the swellable particles (D) can be determined by the same method as described above using the composite particles.

  Specific examples of the constituent material of the swellable particles (D) include polystyrene (PS), acrylic resin, styrene-acrylic resin, polyalkylene oxide, fluororesin, styrene butadiene rubber (SBR), and derivatives and cross-linked products thereof. Urea resin; polyurethane; and the like.

  The swellable particles (D) may contain one kind of the above-mentioned resins, or may contain two or more kinds. In addition, the swellable particles (D) may contain various known additives (for example, antioxidants) added to the resin in addition to the above-described constituent materials as necessary.

  For example, when the swellable particles (D) are composed of the above exemplified resin cross-linked bodies, they are reversible to a volume change accompanying a temperature change, such as once expanding due to a temperature rise, it shrinks again by lowering the temperature. In addition, these crosslinked resin bodies are stable up to a temperature higher than the temperature of thermal expansion in a so-called dry state containing no electrolyte solution. Therefore, in the separator using the swellable particles (D) composed of the above crosslinked resin, the swellable particles (D) are thermally swollen even through a heating process such as drying of the separator or drying of the electrode group during battery production. Therefore, the handling in such a heating process becomes easy. Furthermore, by having the above reversibility, even if the shutdown function is activated once due to the temperature rise, it can be made to function as a separator again when safety is ensured by the temperature drop in the battery. is there.

  Among the constituent materials exemplified above, crosslinked PS, crosslinked acrylic resin [for example, crosslinked polymethyl methacrylate (PMMA)] and crosslinked fluororesin [for example, crosslinked PVDF] are preferable, and crosslinked PMMA is particularly preferable.

  The details of the mechanism by which these swellable particles (D) swell due to temperature rise are not clear, but for example, in crosslinked PMMA, the glass transition point (Tg) of PMMA, which is the main component of the particles, is around 100 ° C. It is conceivable that the cross-linked PMMA particles become flexible near the Tg of PMMA, and absorb and swell more electrolytic solution. Therefore, it is considered desirable that the Tg of the swellable particles (D) is in the range of about 75 to 125 ° C.

  In addition, as described above, heat-resistant particles such as inorganic particles and organic particles are chemically bonded to a resin, specifically, inorganic particles and organic particles that are stable against an electrolyte solution are used as a core, Particles having a core-shell structure in which the above-described resin that can constitute the swellable particles (D) is combined as a shell can also be used as the swellable particles (D).

As heat-resistant particles that can be the core of swellable particles (D) with a core-shell structure, they are stable when exposed to high temperatures of 150 ° C. or higher in non-aqueous electrolytes, and are stable. Inorganic particles or organic particles that may be present in Examples of such inorganic particles include various particles exemplified above as inorganic particles capable of forming the inorganic particles (A). In addition, as organic particles, polyimide, melamine resin, phenol resin, crosslinked PMMA, crosslinked PS, polydivinylbenzene (PDVB), benzoguanamine-formaldehyde condensate [however, those that can correspond to swellable particles (D) And the like, and the like. The polymer constituting the particles is a mixture, a modified body, a derivative, a random copolymer, an alternating copolymer, a graft copolymer, a block copolymer, a crosslinked body (except for thermoplastic polyimide), and the like. May be. In the case of organic particles, the swelling degree B R as defined above (1) swelling degree B and the equation (9) is defined by the equation, as both smaller than 1 is preferred.

  Examples of the swellable particles (D) having a core-shell structure as described above include styrene and acrylic monomers [(meth) acrylate, methyl (in the presence of heat-resistant particles surface-treated with a silane coupling agent, etc.). And particles obtained by polymerizing (meth) acrylate etc.].

  The particle diameter of the swellable particles (D) is an average particle diameter obtained by the same method as that for the inorganic particles (A), and is preferably 0.1 to 20 μm.

  The separator of the present invention may be in the form of an independent film or may have a structure integrated with electrodes (positive electrode and / or negative electrode). When it is set as the form of an independent film, in order to ensure required intensity | strength, it is preferable to use a fibrous material (E) as a reinforcing material.

  The fibrous material (E) has electrical insulation, is electrochemically stable, and further contains an electrolyte solution described in detail below, and inorganic particles (A) and binders (B) used in the production of the separator. ) And the like, as long as the solvent used in the liquid composition is stable, there is no particular limitation, but those having characteristics that do not substantially deform at 150 ° C. are preferable. The “fibrous material” in the present specification means that having an aspect ratio [length in the longitudinal direction / width (diameter) in a direction perpendicular to the longitudinal direction] of 4 or more. The aspect ratio of the fibrous material (E) is preferably 10 or more.

  Specific constituent materials of the fibrous material (E) include, for example, cellulose, modified cellulose (such as carboxymethyl cellulose), polypropylene (PP), polyester [polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene. Terephthalate (PBT), etc.], polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyaramid, polyamideimide, polyimide and other resins; glass, alumina, silica and other inorganic materials (inorganic oxides); and the like. The fibrous material (E) may contain one type of these constituent materials, or may contain two or more types. In addition to the above-described constituent materials, the fibrous material (E) contains various known additives (for example, an antioxidant in the case of a resin) as necessary. It doesn't matter.

  Although the diameter of a fibrous material (E) 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 for example, the strength of the sheet-like material composed of these, and consequently the strength of the separator may be reduced, making it difficult to handle. On the other hand, if the diameter is too small, the gap of the separator becomes too small, and the ion permeability tends to be lowered, and the load characteristics of the battery may be lowered.

  The state of the presence of the fibrous material (E) in the separator (sheet-like material) is, for example, preferably that the angle of the long axis (axis in the longitudinal direction) with respect to the separator surface is 30 ° or less on average, 20 More preferably, it is not more than 0 °.

  A large number of these fibrous materials (E) are gathered together to form a sheet-like material, for example, in the form of woven fabric, non-woven fabric, paper, etc., and this sheet is inorganic. It is good also as a separator of the structure containing particle | grains (A), and good also as a separator of the structure containing the fibrous material (E) and the inorganic particle (A) disperse | distributed uniformly. Moreover, it can also be set as the structure which united both above-mentioned structures.

  In addition to the above components, the separator of the present invention includes, for example, various inorganic particles exemplified as those for forming the inorganic particles (A) and swellable particles (D) having a core-shell structure. You may contain the various organic particle etc. which were illustrated as what can be used as a core.

  The separator of the present invention is, for example, as described above, the inorganic particles (A) [further, if necessary, the heat-meltable particles (C), A porous membrane having a structure containing swellable particles (D) and the like] can be obtained. In this case, the sheet-like material composed of the fibrous material (E) is less susceptible to heat shrinkage and has good dimensional stability against heat unlike a separator made of a conventionally known porous film made of polyolefin. Even when the battery is abnormally heated, a short circuit due to thermal contraction of the separator can be prevented well.

  Moreover, the separator of this invention can also be made into the form of the porous film formed by many inorganic particle | grains (A) being bound by binder (B) other than the above forms, for example. . Also in this case, the heat-meltable particles (C), the swellable particles (D), the fibrous materials (E), and the like may be bound together with the inorganic particle particles (A) by the binder (B). In such a separator, since it is manufactured by a manufacturing method [a manufacturing method having a step of applying and drying a liquid composition containing inorganic particles (A) etc. on a base material] such that no strain remains in the separator, Since the dimensional stability against heat is good as in the case of the separator including the sheet-like material composed of the fibrous material (E), the separator is also thermally contracted even during abnormal heating of the battery. Short circuit can be prevented well.

  In the separator of the present invention having each of the above forms, for example, the thermal shrinkage rate at 150 ° C. can be less than 5%. For example, even when the inside of the battery reaches about 150 ° C., the separator shrinks almost. Therefore, a short circuit due to contact between the positive and negative electrodes can be prevented, and the safety of the battery at high temperatures can be improved. The “150 ° C. heat shrinkage rate” of the separator refers to the size of the separator before putting the separator in a thermostatic bath, raising the temperature to 150 ° C. and leaving it for 30 minutes, and then putting it in the thermostatic bath. The reduction ratio of the dimension calculated | required by this is expressed in percentage.

  The thickness of the separator is 3 μm or more, more preferably 5 μm or more, and is preferably 50 μm or less, more preferably 30 μm or less. If the separator is too thin, the short-circuit preventing effect may be reduced, and the separator may have insufficient strength and may be difficult to handle. On the other hand, if the separator is too thick, the energy density of the battery tends to be small.

Further, the porosity of the separator is desirably 20% or more, more preferably 30% or more, and 70% or less, more preferably 60% or less in a dry state. If the porosity of the separator is too small, the ion permeability (ion conductivity) may be reduced, and if the porosity is too large, the strength of the separator may be insufficient. 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 = 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 separator (g / cm 2 ), t: thickness of separator (cm).

Further, the air permeability of the separator, which is carried out by a method according to JIS P 8117 and indicated by the Gurley value indicated by the number of seconds in which 100 ml of air passes through the membrane under a pressure of 0.879 g / mm 2 , is 10 to 10. It is preferable that it is 300 sec. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. Furthermore, in the case of an independent membrane, 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 low, a short circuit may occur due to the breakthrough of the separator when lithium dendrite crystals are generated.

  In the separator of the present invention, from the viewpoint of more effectively ensuring the effect of using the inorganic particles (A), the content of the inorganic particles (A) in the total volume of the constituent components of the separator is 30% by volume or more. Preferably, 40 volume% or more is more preferable. In addition, when making a separator contain a heat-meltable particle (C) and a swellable particle (D), and also having a shutdown function, the upper limit of the volume ratio of an inorganic particle (A) is 80 volume%, for example. It is preferable. On the other hand, when it is set as the separator which does not have a shutdown function, a still higher ratio may be sufficient as the volume ratio of an inorganic particle (A), for example, it is satisfactory if it is 95 volume% or less.

The content of the binder (B) in the whole amount of the components of the separator of the present invention, 0.1 wt% or more, more preferably not less than 1 wt%, 30 wt% or less, more preferably 10 It is desirable to set it as mass% or less.

Further, by containing heat melting particles (C) and swelling particles (D), when to have a shutdown function to a separator, for example, heat-fusible particles in the total amount of the components of the separator (C) It is desirable that the content of the swellable particles (D) is 10% by mass or more, more preferably 20% by mass or more, and 80% by mass or less, more preferably 50% by mass or less.

In the case of using fibrous material and (E) is a fibrous material in the whole amount of the constituents of the separator the content of (E), 10 mass% or more, more preferably be 30 mass% or more, It is desirable that the content be 90% by mass or less, more preferably 80% by mass or less.

  As the method for producing the separator of the present invention, for example, the following methods (I), (II) and (III) can be employed. In the method (I), an ion-permeable sheet-like material is coated or impregnated with a liquid composition (slurry or the like) containing inorganic particles (A) and a binder (B), and then dried at a predetermined temperature. Is the method.

  The “sheet-like material” in the method (I) corresponds to a sheet-like material (various, woven fabric, non-woven fabric, etc.) composed of the fibrous material (E). Specifically, a porous sheet such as a non-woven fabric having a structure in which at least one of the above-exemplified materials is included as a constituent component and the fibrous materials are entangled with each other can be 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.), PAN non-woven fabric, and PVA non-woven fabric can be exemplified.

As thickness of the said sheet-like material, it is preferable that it is 20 micrometers or less, for example, and it is more preferable that it is 16 micrometers or less. The basis weight is preferably 15 g / m 2 or less, more preferably 10 g / m 2 or less. Further, the lower limit of the thickness is preferably 5 μm, and the lower limit of the basis weight is preferably 2 g / m 2 .

  As a method for producing a nonwoven fabric corresponding to the sheet-like material, conventionally known methods such as wet, dry, melt blow, spun bond, and charge melt spinning can be used.

The liquid composition for forming the separator of the present invention contains inorganic particles (A), a binder (B), and optionally, hot-melt particles (C), swellable particles (D), and the like. These are dispersed or dissolved in a solvent (including a dispersion medium, the same applies hereinafter). Liquid compositions, when the binder (B) is water-soluble, and the like when used as an emulsion, water as a solvent, this time the alcohol (methyl alcohol, ethyl alcohol, isopropyl alcohol, and ethylene glycol) and The interfacial tension can also be controlled by adding as appropriate.

  In the said liquid composition, it is preferable that solid content content containing an inorganic particle (A), a binder (B), a heat-meltable particle (C), and a swellable particle (D) shall be 10-40 mass%, for example.

  In addition, as above-mentioned, when a hot-melt particle (C) and a swellable particle (D) have adhesiveness independently, these can also serve as a binder (B).

  A sheet-like material composed of a fibrous material, such as a nonwoven fabric such as paper, PP nonwoven fabric, and polyester nonwoven fabric, with a particularly large opening diameter of the void (for example, an opening diameter of the void of 5 μm or more) In the separator having a component as a component, the voids are likely to cause a short circuit of the battery. Therefore, in this case, it is preferable to have a structure in which some or all of the inorganic particles (A) are present in the voids of the sheet-like material. Moreover, it is preferable that part or all of the heat-meltable particles (C) and the swellable particles (D) are also present in the voids of the sheet-like material. In order to make the inorganic particles (A) and the like exist in the voids of the sheet-like material, for example, after impregnating the above-mentioned liquid composition into the sheet-like material, the excess liquid composition is removed through a certain gap. Then, a process such as drying may be used. In addition, when the inorganic particle used for the inorganic particle (A) is a plate-like particle, or when a plate-like inorganic particle is contained separately from the inorganic particle (A), the orientation of these plate-like particles is increased and the In order to function effectively, a method of applying a shear or a magnetic field to the liquid composition in the substrate impregnated with the liquid composition may be used. For example, as described above, the liquid composition can be sheared by impregnating the liquid composition into a sheet and then passing through a certain gap.

  The manufacturing method of (II) of the separator of the present invention is such that the liquid composition further contains a fibrous material (E), which is coated on a substrate such as a film or a metal foil, and dried at a predetermined temperature. And then peeling from the substrate. The liquid composition used in the method (II) is the same as the liquid composition used in the method (I) except that it is essential to contain the fibrous material (E). The solid content concentration including the state (E) is preferably 10 to 40% by mass, for example. The separator obtained by the method (II) also has a structure in which some or all of the inorganic particles (A) are present in the voids of the sheet-like material formed of the fibrous material (E). Is desirable.

  The manufacturing method of (III) of the separator of the present invention includes, for example, inorganic particles (A) and a binder (B), and further, if necessary, hot-melt particles (C), swellable particles (D) or fibrous The product (E) or the like is dispersed in water or a suitable solvent to prepare a liquid composition such as a slurry, and the above-described coating apparatus such as a blade coater, a roll coater, a die coater, or a spray coater is used. In this method, a liquid composition is applied on an electrode (positive electrode or negative electrode) and dried. Thereby, the separator of the structure integrated with the electrode can be obtained. As the liquid composition, for example, the same liquid composition as described for the production method of (I) or (II) can be used.

  In addition, the separator of this invention is not limited to said structure. For example, the inorganic particles (A) may not be present independently of each other, and some of them may be fused to each other or to the fibrous material (E).

  The separator produced by the methods (I) to (III) is preferably subjected to a heat treatment after drying to remove volatile components such as moisture and solvent (dispersion medium) contained therein. By removing these volatile components, it is possible to provide a lithium secondary battery with excellent long-term reliability because deterioration of battery characteristics when charging and discharging are repeated in the lithium secondary battery can be suppressed. The residual amount of moisture and solvent is preferably 100 ppm or less with respect to the separator.

  When the heat-meltable particles (C) are contained in the separator, the temperature of the heat treatment is set to a temperature lower than the shutdown temperature of the separator. When heat treatment is performed at a temperature equal to or higher than the shutdown temperature, the pores of the separator are blocked, so that the lithium secondary battery using such a separator is inferior in characteristics. In the case where the separator does not contain the heat-meltable particles (C) and does not have shutdown characteristics, or in the case of the separator in which the shutdown characteristics are secured by the swellable particles (D), as described above, in the dry state. Even if heat treatment is performed, the properties of the separator are not affected, so the heat treatment temperature is not particularly limited as long as it is lower than the thermal decomposition temperature of the resin.

  The specific heat treatment temperature is, for example, 70 to 140 ° C., and the heat treatment time is, for example, 1 hour or more, more preferably 3 hours or more, and 72 hours or less, more preferably 24 hours or less. It is desirable to do. Such heat treatment can be performed, for example, in a warm air circulation type thermostatic bath. Moreover, you may dry under reduced pressure using a vacuum dryer as needed.

  The separator of the present invention can be widely used as a separator for nonaqueous electrolyte batteries regardless of whether it is a primary battery or a secondary battery. Hereinafter, a secondary battery, which is the main application of the separator of the present invention, will be described.

  The battery (lithium secondary battery) of the present invention is not particularly limited as long as it has the separator of the present invention, and a conventionally known configuration and structure can be adopted.

  Examples of the form of the battery include a tubular 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 conventionally known nonaqueous electrolyte battery (lithium secondary battery). For example, as an active material, lithium-containing transition metal oxide represented by Li 1 + x MO 2 (−0.1 <x <0.1, M: Co, Ni, Mn, etc.); lithium manganese such as LiMn 2 O 4 Oxide; LiMn x M (1-x) O 2 in which part of Mn of LiMn 2 O 4 is substituted with another element; olivine type LiMPO 4 (M: Co, Ni, Mn, Fe); LiMn 0.5 Ni 0.5 O 2 ; Li (1 + a) Mn x Ni y Co (1-xy) O 2 (−0.1 <a <0.1, 0 <x <0.5, 0 <y <0. 5); can be applied, and a positive electrode mixture in which a known conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these positive electrode active materials, Using a current collector as a core and finishing it into a molded body Kill.

  As the current collector of the positive electrode, a metal foil such as aluminum, a punching metal, a net, an expanded metal, or the like can be used. 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 conventionally known nonaqueous electrolyte battery (lithium secondary battery). For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and their alloys, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. A negative electrode mixture prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials and using a current collector as a core material is used. In addition, the above-described various alloys and lithium metal foils may be used alone or formed on a 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.

  Similarly to the lead portion on the positive electrode side, the negative electrode lead portion is usually exposed to the current collector without forming a negative electrode agent layer (a layer having a negative electrode active material) on a part of the current collector during negative electrode fabrication. It is provided by leaving a part and using it as a lead part. However, the negative electrode side lead portion is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.

  The electrode includes an electrode group (electrode laminate) having a laminated structure in which the positive electrode and the negative electrode are laminated via the separator of the present invention, and an electrode group having a wound structure in which this is wound (electrode winding). Body). The separator of the present invention uses inorganic particles (A) having the above functional groups on the surface as inorganic particles for ensuring insulation, and the inorganic particles (A) and inorganic particles (A) and binder ( Even if it uses it in the state where the separator was curved, such as when making it the electrode group of a winding structure, the binding property with B) can be separated well. Therefore, the separator of the present invention can be suitably used for a battery having an electrode group with a wound structure that is required to be used in a curved state as described above, and the effect is particularly effective when used for such applications. Become prominent.

As described above, a solution obtained by dissolving a lithium salt in an organic solvent is used as the nonaqueous electrolytic solution. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li + ions and does not cause a side reaction 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 (n ≧ 2), LiN (RfOSO 2 ) 2 [where Rf is a fluoroalkyl group]; it can.

  The organic solvent used in the electrolytic solution is not particularly limited as long as it dissolves the above lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and 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 ethane, 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; Sulfites such as ethylene glycol sulfite; and the like, and these may be used alone. , It may be used in combination of two or more thereof. 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, cyclohexane, biphenyl, fluorobenzene, t- for the purpose of improving safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes. Additives such as butylbenzene can also be added as appropriate.

  The concentration of the lithium salt in the electrolytic solution is preferably 0.5 to 1.5 mol / l, and more preferably 0.9 to 1.25 mol / l.

  In addition, instead of the above organic solvent, melting at room temperature such as ethyl-methylimidazolium trifluoromethylsulfonium imide, heptyl-trimethylammonium trifluoromethylsulfonium imide, pyridinium trifluoromethylsulfonium imide, guanidinium trifluoromethylsulfonium imide A salt can also be used.

  Furthermore, a polymer material that contains the above non-aqueous electrolyte and gels may be added, and the non-aqueous electrolyte may be gelled and used for a battery. Polymer materials for making the non-aqueous electrolyte into a gel include PVDF, PVDF-HFP, PAN, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, crosslink having ethylene oxide chain in the main chain or side chain Known host polymers capable of forming a gel electrolyte, such as polymers and cross-linked poly (meth) acrylates, can be mentioned.

  The lithium secondary battery of the present invention can be applied to the same uses as various uses in which conventionally known lithium secondary batteries are used.

  Hereinafter, the present invention will be described in detail based on examples. However, the following examples are not intended to limit the present invention, and all modifications made without departing from the spirit of the preceding and following descriptions are included in the technical scope of the present invention.

<Production of inorganic particles (A)>
Production Example 1
10 g of a silane coupling agent [“KBM-403 (trade name)” manufactured by Shin-Etsu Chemical Co., Ltd.] was placed in 500 g of an acetic acid aqueous solution having a concentration of 0.5% by mass and stirred to dissolve uniformly.

  The above silane coupling agent solution is added to a slurry prepared by dispersing 1000 g of inorganic particles of silica [“FS-3DC (trade name)” manufactured by Denki Kagaku Kogyo Co., Ltd., average particle size 3 μm] in 500 g of water, It processed for 60 minutes, stirring with a three-one motor. The treated inorganic particles were filtered and dried to obtain inorganic particles (A-1).

Production Example 2
Inorganic particles (A-2) were produced in the same manner as in Production Example 1 except that 1000 g of plate-like boehmite [“BMM (trade name)” manufactured by Kawai Lime Co., Ltd., average particle size of 1 μm, aspect ratio of 10] was used as the inorganic particles. Produced.

Production Example 3
10 g of a silane coupling agent [“KBE-903 (trade name)” manufactured by Shin-Etsu Chemical Co., Ltd.] was placed in 500 g of an acetic acid aqueous solution having a concentration of 0.5% by mass, and dissolved uniformly.

  Into the slurry prepared by dispersing 1000 g of plate-like alumina [Seraph 02025 (trade name) manufactured by Kinsei Matec, average particle size 2 μm, aspect ratio 25], which is inorganic particles, in 500 g of water, the above silane coupling agent solution Was added and processed for 60 minutes while stirring with a three-one motor. The treated inorganic particles were filtered off and dried to obtain inorganic particles (A-3).

Production Example 4
Inorganic particles (A-4) were produced in the same manner as in Production Example 1 except that 1000 g of alumina (Al 2 O 3 ) [“SUMIKORANDAN AA-1.5 (trade name)” manufactured by Sumitomo Chemical Co., Ltd.]] was used as the inorganic particles. Was made.

Example 1
Three-One Motor: 1000 g of inorganic particles (A-1), 800 g of water, 200 g of isopropyl alcohol (IPA), and 375 g of PVB [“SREC KX-5 (trade name)” manufactured by Sekisui Chemical Co., Ltd.] as a binder (B) The mixture was stirred and dispersed for 1 hour to obtain a uniform slurry. A non-woven fabric made of PP having a thickness of 15 μm (manufactured by Nippon Kogyo Paper Co., Ltd.) was passed through this slurry, and the slurry was applied by pulling and then dried to obtain a separator having a thickness of 20 μm.

For the separator of Example 1, the specific gravity of the inorganic particles (A-1) is 2.2 g / cm 3 , the specific gravity of the binder is 1.1 g / cm 3 , and the specific gravity of PP related to the PP nonwoven fabric is 0.9 g / cm 3. The volume content of the inorganic particles (A-1) calculated as is 51.5%.

Example 2
A separator was produced in the same manner as in Example 1 except that the inorganic particles (A-2) were used instead of the inorganic particles (A-1). For the separator of Example 2, the specific gravity of the inorganic particles (A-2) is 3.0 g / cm 3 , the specific gravity of the binder is 1.1 g / cm 3 , and the specific gravity of PP related to the PP nonwoven fabric is 0.9 g / cm 3. The volume content of the inorganic particles (A-2) calculated as is 53.6%.

Example 3
A slurry was prepared in the same manner as in Example 1 except that the inorganic particles (A-3) were used in place of the inorganic particles (A-1). To this slurry, 300 g of an emulsion containing cross-linked PMMA as a swellable particle (D) [“Staffyroid AC-3364 (trade name)” manufactured by Ganz Kasei Co., Ltd.] was added and stirred to obtain a uniform slurry. This slurry was applied to a non-woven fabric made of PET [Freudenberg, thickness: 15 μm] using a reverse coater and dried to obtain a separator having a thickness of 16 μm.

For the separator of Example 3, the specific gravity of the inorganic particles (A-3) is 4.0 g / cm 3 , the specific gravity of the binder is 1.1 g / cm 3 , the specific gravity of the crosslinked PMMA is 1.2 g / cm 3 , and the nonwoven fabric made of PET The volume content of the inorganic particles (A-3) calculated by setting the specific gravity of the PET according to 1.38 g / cm 3 to be 43.6%.

Example 4
A slurry was prepared in the same manner as in Example 1 except that the inorganic particles (A-4) were used instead of the inorganic particles (A-1). To this slurry, 300 g of an emulsion containing PE which is a heat-meltable particle (C) [“Chemical Pearl W-700 (trade name)” manufactured by Mitsui Chemicals, average particle size: 1 μm] and a slurry containing a plate-like silica [ 100 g of “Sun Lovely LFS (trade name)” manufactured by Dokai Chemical Co., Ltd. was added and stirred to obtain a uniform slurry, which was applied to a PET non-woven fabric [manufactured by Freudenberg, thickness 15 μm] using a reverse coater. And dried to obtain a separator having a thickness of 16 μm.

For the separator of Example 4, the specific gravity of the inorganic particles (A-4) is 4.0 g / cm 3 , the specific gravity of the binder is 1.1 g / cm 3 , the specific gravity of PE is 1.0 g / cm 3 , and the specific gravity of silica is The volume content of the inorganic particles (A-4) calculated as 2.2 g / cm 3 and the specific gravity of PET relating to the PET nonwoven fabric as 1.38 g / cm 3 is 40.0%.

Comparative Example 1
It replaced with the inorganic particle (A-1), and carried out similarly to Example 1 except having used the surface-treated alumina [Sumitomo Chemical Co., Ltd. "Sumicorundum AA-1.5 (brand name)"]. A separator was produced.

<Heating characteristics of separator>
The separators of Examples 1 to 4 were left in a constant temperature bath at 150 ° C. for 30 minutes, and the shrinkage rate of the separators was measured. Further, as a separator for comparison, the separator of Comparative Example 1 and a 20 μm-thick PE microporous membrane (Comparative Example 2) were also left in a thermostatic bath at 150 ° C. for 30 minutes, and were the same as the separators of Examples 1 to 4. Was measured. The results are shown in Table 1.

  The shrinkage rate was measured as follows. A separator piece cut out to 4 cm × 4 cm was sandwiched between two stainless plates fixed with clips, left in a thermostatic bath at 150 ° C. for 30 minutes, taken out, and the length of each separator piece was measured. The rate of decrease in length compared to the length was taken as the shrinkage rate.

Moreover, the shutdown temperature was calculated | required 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. The sample was placed in a thermostatic bath, and the resistance value when a 1 kHz alternating current was applied to the terminal with a contact resistance meter [3560 AC milliohm Hitester (trade name)] manufactured by HIOKI was measured from room temperature to 1 per minute. The temperature was raised at a rate of 0 ° C. and heated, and the temperature change of the internal resistance was determined. The temperature at which the resistance value was 10 times or more the value at room temperature was taken as the shutdown temperature of the separator. The results are also shown in Table 1.

  Table 1 shows the following. The separator of Comparative Example 2 corresponding to the conventional product has a large heat shrinkage rate. In the battery using this, the separator shrinks until the internal temperature reaches 150 ° C., and the positive electrode and the negative electrode are in contact with each other. There is a risk of short circuit. On the other hand, in the separators of Examples 1 to 4, almost no thermal shrinkage was observed, and substantially no deformation occurred at the visual level. Therefore, in the battery using these, even if the internal temperature reaches 150 ° C., the separator can sufficiently prevent the contact between the positive electrode and the negative electrode, thereby preventing the occurrence of a short circuit.

Example 5
<Production of negative electrode>
A negative electrode active material-containing paste is 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 to both sides of a 10 μm thick current 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, dried, and then subjected to calendar treatment. The thickness of the negative electrode mixture layer was adjusted so that the total thickness was 142 μm, and the negative electrode mixture layer was cut to have 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 are mixed uniformly using NMP as a solvent. An agent-containing paste was prepared. This paste was intermittently applied on both sides of a 15 μm thick aluminum foil serving as a current collector 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, dried, and then subjected to calendar treatment. The thickness of the positive electrode mixture layer was adjusted so that the total thickness was 150 μm, and the positive electrode mixture layer was cut to 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.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were spirally wound through the separator of Example 1 to obtain a wound electrode body. The wound electrode body is crushed into a flat shape, loaded into a laminate film outer package made by Dai Nippon Printing Co., Ltd., and electrolyte solution (LiPF 6 is added to a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2). A solution dissolved at a concentration of 1.2 mol / l) was injected and vacuum sealed to produce a lithium secondary battery.

Examples 6-8, Comparative Examples 3-4
A lithium secondary battery was produced in the same manner as in Example 5 except that the separator was changed to that in Examples 2 to 4 or Comparative Examples 1 and 2.

Example 9
The same slurry as prepared in Example 1 was applied on the same negative electrode as that prepared in Example 5 using a die coater so that the thickness when dried was 15 μm, and dried. An integrated product was obtained. The same positive electrode as that produced in Example 5 was layered on the separator side of the obtained integrated negative electrode and separator, and wound into a spiral shape to obtain a wound electrode body. A lithium secondary battery was produced in the same manner as in Example 5 except that this wound electrode body was used.

Example 10
The same slurry as that prepared in Example 3 was applied on the same positive electrode as that prepared in Example 5 using a die coater so that the thickness when dried was 10 μm, and dried. An integrated product was obtained. The obtained positive electrode-separator integrated product separator side and the negative electrode-separator integrated product separator side obtained in the same manner as in Example 9 were overlapped and wound into a spiral shape to obtain a wound electrode body. A lithium secondary battery was produced in the same manner as in Example 5 except that this wound electrode body was used.

Comparative Example 5
The same slurry as that prepared in Comparative Example 1 was applied on the same negative electrode as that prepared in Example 5 using a die coater so as to have a thickness of 15 μm when dried, and then the negative electrode and separator An integrated product was obtained. The same positive electrode as that produced in Example 5 was layered on the separator side of the obtained integrated negative electrode and separator, and wound into a spiral shape to obtain a wound electrode body. A lithium secondary battery was produced in the same manner as in Example 5 except that this wound electrode body was used.

  The lithium secondary batteries of Examples 5 to 10 and Comparative Examples 3 to 5 were subjected to electrochemical evaluation (charge / discharge efficiency) and a safety test. The results are shown in Table 2.

<Charge / discharge efficiency>
About each battery of Examples 5-10 and Comparative Examples 3-5, charging by constant current charging at 0.2 C (up to 4.2 V) and constant voltage charging at 4.2 V (constant current charging and constant voltage charging) After a total time of 15 hours, discharge was performed at 0.2 C up to 3.0 V, and charge / discharge efficiency (ratio of discharge capacity to charge capacity) was determined. In addition, charging / discharging efficiency was calculated | required as an average value of 10 batteries, respectively.

<Safety evaluation>
The batteries of Examples 5 to 10 and Comparative Examples 3 to 5 were left in a high temperature layer at 150 ° C., the time until bursting was measured, and the safety at high temperatures was evaluated.

  As can be seen from Table 2, the batteries of Examples 5 to 10 had good charge / discharge efficiency and were at a practical level. On the other hand, the batteries of Comparative Examples 3 and 5 had a low discharge capacity ratio, did not reach a practical level, and had insufficient reliability. Moreover, in the battery of Examples 5-10, it turned out that the time to rupture when left at 150 degreeC is longer than the battery of the comparative example 4 which is a conventionally well-known battery, and safety has improved.

Claims (10)

  1. A porous battery separator containing at least electrically insulating inorganic particles and a resin binder,
    The content of the resin binder in the total amount of the constituent components is 0.1% by mass or more and 30% by mass or less,
    Use a resin binder that is water-soluble or dispersed in water as an emulsion,
    Further containing particles that can swell in a non-aqueous electrolyte and have a degree of swelling B defined by the following formula of 1.0 or more,
    The inorganic separator has a functional group whose molar agglomeration energy is smaller than 30 kJ / mol on the surface.
    B = (V 1 / V 0 ) -1
    [In the above formula, V 0 is the volume of particles (cm 3 ) 24 hours after being introduced into the non-aqueous electrolyte at 25 ° C., and V 1 is 24 after being introduced into the non-aqueous electrolyte at 25 ° C. The temperature of the non-aqueous electrolyte is raised to 120 ° C. after time, and the volume (cm 3 ) of the particles after 1 hour at 120 ° C. is meant. ]
  2.   2. The battery according to claim 1, wherein the functional group having a molar cohesive energy of inorganic particles smaller than 30 kJ / mol is an amino group, an epoxy group, an acrylic group, a methacryl group, an alkyl group, a ureido group, a mercapto group, or an isocyanate group. Separator.
  3. Furthermore, the battery separator of Claim 1 or 2 containing a fibrous material.
  4. Some molar cohesive energy on the surface of the inorganic particles having small functional groups than 30 kJ / mol is, the battery separator according to claim 3 which is present in the gap of the sheet which is composed of fibrous material .
  5. The battery separator according to any one of claims 1 to 4 , further comprising particles that melt at 80 to 130 ° C.
  6. The battery separator according to any one of claims 1 to 5 , wherein the inorganic particles are plate-like particles.
  7. The battery separator according to claim 6 , wherein at least a part of the inorganic particles is boehmite.
  8. A method of manufacturing a battery separator according to any one of claims 1 to 7
    Treating electrically insulating inorganic particles with a silane coupling agent, titanate coupling agent, aluminate coupling agent or zirconate coupling agent;
    Forming a liquid composition comprising the inorganic particles and a resin binder and water,
    On SL liquid compositions, the ion permeability of a sheet or electrodes, coated, method for producing a battery separator, characterized by a step of drying.
  9. At least, characterized by having a battery separator according to any one lithium anode containing an active material capable of intercalating and deintercalating a positive electrode containing lithium capable of occluding and releasing active material, and the claims 1-7 Lithium secondary battery.
  10. The lithium secondary battery according to claim 9 , wherein the battery separator is integrated with at least one of the positive electrode and the negative electrode.
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