JP2008210782A - Separator for battery, manufacturing method of separator for battery, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a lithium secondary battery having high reliability and to provide a separator for a battery capable of constituting the lithium secondary battery and its manufacturing method. <P>SOLUTION: The separator is composed of at least plate-like boehmite and an organic binder, and constituted so that a ratio of peak intensity of (002) plane to the sum of peak intensities of (020) plane, (120) plane, (031) plane, and (051) plane becomes 0.80 or more, and the lithium secondary battery is constituted by assembling a positive electrode, a negatived electrode, and an organic electrolyte with the separator. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an inexpensive separator excellent in dimensional stability at high temperature, and a safe lithium secondary battery excellent in reliability using the separator.

  A lithium secondary battery, which is a type of nonaqueous electrolyte battery, is widely used as a power source for portable devices such as mobile phones and notebook personal computers because of its high energy density. As the performance of portable devices increases, the capacity of lithium secondary batteries tends to increase further, and it is important to ensure safety.

  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 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. 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, when the battery temperature reaches the shutdown temperature in the case of abnormal charging, the current must be immediately decreased 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 such a short circuit due to thermal contraction of the separator and improving the reliability of the battery, for example, it has a porous substrate with good heat resistance, filler particles, and a resin component for ensuring a shutdown function It has been proposed to configure an electrochemical element with a separator (Patent Document 1).

International Publication No. 2006/62153

  According to the technique disclosed in Patent Document 1, it is possible to provide a battery having excellent safety that is unlikely to cause thermal runaway even when abnormally heated.

  However, in the future, lithium secondary batteries will be required to ensure better battery characteristics, and when lithium dendrite is likely to precipitate in the battery, Ensuring reliability that can sufficiently suppress the occurrence of short circuits is also required.

  That is, in the separator composed of the fine particles and the binder, when the fine particle filling property is not uniform, the lithium ion permeability is not uniform. Therefore, when such a separator is used for a lithium secondary battery, minute lithium dendrite is likely to precipitate due to the non-uniformity of lithium ion permeability described above, and the deposited lithium dendrite penetrates the separator. A weak short circuit may occur and the reliability of the battery may be impaired, and the charge / discharge cycle characteristics may be deteriorated.

  In addition, when plate-like fine particles are used as the fine particles constituting the separator, the plate surface of the plate-like fine particles is oriented parallel or substantially parallel to the separator surface to increase the curvature in the separator. Thus, even if lithium dendrite is deposited, it is possible to prevent the separator from penetrating. However, in the separator having plate-like fine particles, if the orientation and filling are non-uniform, the above-mentioned action due to the plate-like fine particles is not sufficiently exhibited, and the lithium ion permeability in the separator is non-uniform. Thus, the deposited lithium dendrite penetrates the separator, and a weak short circuit may occur, thereby impairing the reliability of the battery or reducing charge / discharge cycle characteristics. The technique disclosed in Patent Document 1 is also required to solve such a problem at a higher level.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a lithium secondary battery having excellent reliability, a battery separator that can constitute the lithium secondary battery, and a method for manufacturing the same. is there.

  The battery separator of the present invention that can achieve the above object is composed of at least insulating fine particles that are stable with respect to the organic electrolyte and an organic binder, and has a glossiness of 5 or more at 60 °. It is a feature.

  Another aspect of the battery separator of the present invention is composed of at least plate-like boehmite and an organic binder, and has peak intensity of 020, 120, 031 and 051 planes in the X-ray diffraction spectrum. The ratio of the peak intensity of the 020 plane to the sum is 0.80 or more.

  Further, another aspect of the battery separator of the present invention is composed of at least plate-like boehmite and an organic binder, and among the peak intensities of the 120, 031 and 051 planes in the X-ray diffraction spectrum, The ratio between the intensity of the strongest peak and the peak intensity of the 020 plane is 0.1 or less.

  Furthermore, the present invention applies a separator-forming composition containing insulating fine particles stable to an organic electrolyte, an organic binder, and a solvent to a substrate or a sheet-like material composed of a fibrous material, A method for producing a battery separator for forming a battery separator, wherein the insulating fine particles are dispersed in a solvent to form a dispersion, the dispersion and the organic binder are mixed, and the insulating fine particles are mixed. And a step of preparing a separator-forming composition having a solid content of 10 to 80% by mass including the organic binder, and applying the separator-forming composition to a substrate or a sheet-like material composed of a fibrous material The manufacturing method of the separator for batteries which has a process to dry is provided.

  Furthermore, the lithium secondary battery of the present invention includes a positive electrode, a negative electrode, an organic electrolyte, and a separator, and has the battery separator of the present invention as the separator.

  As a result of intensive studies on the relationship between the internal structure of the separator evaluated by observation with an electron microscope, etc., and the surface characteristics of the separator, etc., the inventors have further improved the filling properties of the insulating fine particles in the separator, If the separator is formed so that the glossiness at 60 ° is 5 or more, the structure can be made denser and uniform, and a highly reliable separator can be formed, in particular, a plate shape such as plate boehmite. It has been found that when the insulating fine particles are used, the filling properties and orientation of the insulating fine particles can be further improved, and the present invention has been achieved.

  Here, when plate-like boehmite is used as the plate-like insulating fine particles, the ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 020, 120, 031 and 051 planes in the X-ray diffraction spectrum is The separator may be configured to be 0.80 or more.

  Further, by using the separator with improved filling properties and orientation of the insulating fine particles as described above, it is possible to satisfactorily prevent a short circuit due to generation of lithium dendrite during charging, and a lithium secondary battery with higher reliability. Is now available.

  The “60 ° glossiness” in the separator in the present specification is measured by a method defined in JIS Z 8741, and specifically, “micro TRI gloss” manufactured by BYK Gardner, etc. Refers to the glossiness measured at an angle of 60 ° from the membrane surface of the separator.

  ADVANTAGE OF THE INVENTION According to this invention, the lithium secondary battery which has the outstanding reliability, the battery separator which can comprise this lithium secondary battery, and the manufacturing method of this battery separator can be provided.

  The separator of the present invention is a porous body having at least insulating fine particles and an organic binder that are stable with respect to an organic electrolytic solution (hereinafter abbreviated as “electrolytic solution”), and a glossiness at 60 ° of 5 or more. It is. When the filling property and orientation (in the case of a plate) of insulating fine particles in the separator are increased, the amount of reflection when the light is applied to the separator increases, and the glossiness increases. That is, when the 60 ° glossiness of the separator is less than 5, the filling and orientation of the insulating fine particles in the separator are insufficient, and the effect of preventing a short circuit due to the generation of lithium dendrite during battery charging is obtained. It gets smaller. The 60 ° glossiness of the separator is preferably 50 or less.

  Another aspect of the separator of the present invention is a porous body having at least plate-like boehmite that is insulating fine particles and an organic binder, and has an 020 plane, 120 plane, 031 plane and an X-ray diffraction spectrum. The ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 051 plane is 0.80 or more.

  When the X-ray diffraction pattern of the separator having plate boehmite is measured, large peaks are observed on the 020 plane, 120 plane, 031 plane, and 051 plane. When the orientation of the plate boehmite in the separator is improved, the peak of the 020 plane increases, and it has been found by the present inventors that the plate boehmite has the 020 plane orientation. Therefore, in the separator using plate boehmite, the orientation of the plate boehmite in the separator depends on the ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 020 plane, 120 plane, 031 plane, and 051 plane in the X-ray diffraction spectrum. The degree can be evaluated.

Here, among the peak intensities of the 120, 031 and 051 planes, when the intensity of the strongest peak is 0.1 or less with respect to the peak intensity of the 020 plane, the 020, 120, 031 and 051 planes. Since the ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the plane is 0.77 or more, the intensity of the strongest peak among the peak intensities of the 120 plane, 031 plane, and 051 plane is more simply You may evaluate by ratio with the peak intensity of 020 surface. That is, the separator is configured so that the intensity of the strongest peak among the peak intensities of the 120, 031 and 051 planes in the X-ray diffraction spectrum of boehmite is 0.1 or less with respect to the peak intensity of the 020 plane. There may be.

  When the ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 020 plane, 120 plane, 031 plane, and 051 plane in the X-ray diffraction spectrum is less than about 0.8 in the separator having plate boehmite The orientation of the plate boehmite in the separator becomes insufficient, and the effect of preventing a short circuit due to the generation of lithium dendrite during battery charging is reduced. The ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 020 plane, 120 plane, 031 plane, and 051 plane in the X-ray diffraction spectrum may be 1. Of the peak intensities on the 120, 031 and 051 planes, the ratio of the strongest peak intensity to the 020 plane peak intensity may be zero.

  When the separator of the present invention has plate-like boehmite, the lower limit of the glossiness of 60 °, or the 020 plane relative to the sum of the peak intensities of the 020, 120, 031 and 051 planes in the X-ray diffraction spectrum. Any one of the lower limits of the ratio of the peak intensities may be satisfied, but it is preferable to satisfy both.

  Insulating fine particles have the effect of suppressing the occurrence of short circuits due to lithium dendrite by becoming the main component in the separator of the present invention or filling gaps formed between fibrous materials described later. is doing. The insulating fine particles have electrical insulating properties, are electrochemically stable, and are stable to an electrolyte solution described later and a solvent used in a composition for forming a separator (a composition containing a solvent). If it does not melt | dissolve in electrolyte solution in a state, there will be no restriction | limiting in particular.

  The term “insulating fine particles that are stable with respect to an organic electrolyte” as used herein refers to deformation and chemical composition change in an organic electrolyte (an organic electrolyte used as an electrolyte for a lithium secondary battery). Insulating fine particles that do not occur. In addition, the “high temperature state” in the present specification is specifically a temperature of 150 ° C. or higher, and is a stable particle that does not undergo deformation and chemical composition change in an electrolyte solution at such a temperature. Good. 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 insulating fine particles include, for example, oxide fine particles such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₂ , and ZrO; nitride fine particles such as aluminum nitride and silicon nitride; Slightly soluble ionic crystal particles such as calcium fluoride, barium fluoride and barium sulfate; Covalent crystal particles such as silicon and diamond; Clay particles such as talc and montmorillonite; 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 materials constituting the electrically insulating fine particles) may be used. These insulating fine particles may be used alone or in combination of two or more.

The form of the insulating fine particles may be any form such as a spherical shape, a particle shape, or a plate shape, but a plate shape is preferable. Examples of the plate-like particles include various commercially available products. For example, “Sun Lovely” (SiO ₂ ) manufactured by Asahi Glass S Tech Co., Ltd., “NST-B1” pulverized product (TiO ₂ ) manufactured by Ishihara Sangyo Co., Ltd., Sakai Chemical Industry Co., Ltd. Plated barium sulfate “H series”, “HL series”, Hayashi Kasei “micron white” (talc), Hayashi Kasei “bengel” (bentonite), Kawai lime “BMM” and “BMT” (boehmite), Kawai lime Co. "sera sur BMT-B" [alumina _{(Al 2 O} 3)], KINSEI MATEC Co. "Seraph" (alumina), Hikawa mining Co. "Hikawa mica Z-20" (sericite ) Etc. 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.

  In the case where the insulating fine particles are plate-like, the occurrence of a short circuit can be suppressed more satisfactorily by orienting the insulating fine particles in the separator so that the flat plate surface is substantially parallel to the surface of the separator. This is because the insulating fine particles are oriented as described above so that the insulating fine particles are arranged so as to overlap each other on a part of the flat plate surface, so that the gap (through hole) from one side of the separator to the other side is It is thought that it is formed not in a straight line but in a bent shape (that is, the curvature is increased), and this prevents the lithium dendrite from penetrating the separator, so that the occurrence of a short circuit is better suppressed. Estimated.

  As a form in the case where the insulating fine particles are plate-like particles, for example, the aspect ratio (ratio of the maximum length in the plate-like particles to the thickness of the plate-like particles) is 5 or more, more preferably 10 or more. , 100 or less, more preferably 50 or less. Further, the average value of the ratio of the major axis direction length to the minor axis direction length of the flat plate surface of the grains is preferably 0.3 or more, more preferably 0.5 or more (ie, the major axis length). And the length in the minor axis direction may be the same). When the plate-like insulating fine particles have the above-mentioned aspect ratio and the average value of the ratio of the major axis direction length to the minor axis direction of the flat plate surface, the above-mentioned short-circuit prevention effect is more effectively exhibited. The

  In addition, when the insulating fine particles are plate-like, the average value of the ratio of the long axis direction length to the short axis direction length of the flat plate surface is, for example, image analysis of an image taken with a scanning electron microscope (SEM) Can be obtained. Further, the above aspect ratio in the case where the insulating fine particles are plate-like can also be obtained by image analysis of an image taken by SEM.

  The insulating fine particles may be particles containing two or more materials constituting the various insulating fine particles exemplified above.

  In order to constitute a separator having a 60 ° gloss of 5 or more, it is more preferable to use plate-like boehmite as insulating fine particles. On the other hand, in the case where the ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 020 plane, 120 plane, 031 plane, and 051 plane in the X-ray diffraction spectrum is 0.80 or more, as described above, Use plate boehmite.

  The average particle size of the insulating fine particles is preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, more preferably 5 μm or less. In addition, the average particle diameter of the insulating fine particles referred to in this specification is obtained by, for example, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA) to dissolve the insulating fine particles, It can be defined as the number average particle diameter measured by dispersing insulating fine particles in a medium that does not swell.

  The content of the insulating fine particles in the separator is preferably 30% by volume or more in the total volume of the constituent components of the separator from the viewpoint of more effectively exerting the action by using the insulating fine particles, and 40 volumes. % Or more is more preferable. In addition, when the separator contains heat-meltable fine particles and swellable fine particles described later and also has a shutdown function, the upper limit of the volume ratio of the insulating fine particles is preferably 80% by volume, for example. On the other hand, when a separator having no shutdown function is used, the volume ratio of the insulating fine particles may be a higher ratio. For example, there is no problem as long as it is 95% by volume or less.

In the separator of the present invention, when the insulating fine particles are bound to each other, or when the fibrous material described later is contained, the fibrous materials are bound to form a sheet, or the fibrous material is configured. An organic binder is used for the purpose of binding the sheet-like material to insulating fine particles and other particles (such as heat-meltable fine particles and swellable fine particles described later).

  Any organic binder may be used as long as it is electrochemically stable and stable with respect to the electrolytic solution, and can adhere well to insulating fine particles, fibrous materials, and other particles. Vinyl-derived structural units of 20 to 35 mol%), ethylene-acrylate copolymers such as ethylene-ethyl acrylate copolymers, fluorine-based 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. These may be used alone or in combination of two or more. Absent. In addition, when using these organic binders, they can be used in the form of an emulsion dissolved or dispersed in a solvent of a composition for forming a separator described later.

  For example, when the heat-meltable fine particles and swellable fine particles described later have adhesiveness alone, they can also serve as an organic binder. Therefore, the organic binder includes those having adhesiveness alone among the heat-meltable fine particles and the swellable fine particles described later.

  The content of the organic binder in the separator is preferably 0.5 to 10% by volume in the total volume of the constituent components of the separator.

  The separator of the present invention desirably contains a fibrous material for reinforcement, and the heat resistant temperature is preferably 150 ° C. or higher. For example, when a part of the constituent material of the separator is melted at a temperature of 130 ° C. or less to block the gap of the separator to block the movement of ions in the separator (so-called shutdown function) (details are given) If the separator is made of a fibrous material having a heat resistant temperature of 150 ° C. or higher, the temperature of the separator further increases by 20 ° C. or higher after shutdown due to heat generation in the battery. However, the shape is kept stable. On the other hand, even when the shutdown function is not provided, a separator configured using a fibrous material having a heat resistant temperature of 150 ° C. or higher is not substantially deformed even at a temperature of 150 ° C., and the shape is maintained. Therefore, for example, it is possible to prevent occurrence of a short circuit due to heat shrinkage that has occurred in a separator composed of a conventional PE porous film, and thus it is possible to ensure reliability and safety when the inside of the battery is abnormally heated.

  In addition, the separator of this invention becomes the thing excellent in the dimensional stability at the time of high temperature by giving insulating fine particle sufficient heat-resistant temperature of 150 degreeC or more, even when a fibrous material is not included.

  As described above, according to the present invention, prevention of a short circuit due to thermal contraction of the separator at a high temperature can be achieved by, for example, a configuration other than increasing the thickness of the separator. Therefore, in the separator of the present invention, the thickness is made relatively thin. It is possible to reduce the energy density of a battery using the same as much as possible.

  As used herein, “heat-resistant temperature of 150 ° C. or higher” means that there is substantially no deformation at 150 ° C., more specifically, when a fibrous material or insulating fine particles heated to 150 ° C. are visually observed. This means that heat shrinkage cannot be confirmed.

  The fibrous material has a heat-resistant temperature of 150 ° C. or higher, is electrically insulating, is electrochemically stable, and further contains an electrolytic solution, insulating fine particles, and the like described in detail below. There is no particular limitation as long as the solvent used in the forming composition is stable. 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 is preferably 10 or more.

  Specific constituent materials of the fibrous material include, for example, cellulose, modified cellulose (such as carboxymethyl cellulose), polypropylene (PP), polyester [polyethylene terephthalate (PET), polyethylene naphthalate (PEN), polybutylene terephthalate (PBT). And the like], resins such as polyacrylonitrile (PAN), polyaramid, polyamideimide, and polyimide; inorganic materials (inorganic oxides) such as glass, alumina, and silica; and the like. The fibrous material may contain one kind of these constituent materials, or may contain two or more kinds. In addition to the above-described constituent materials, the fibrous material may contain various known additives (for example, an antioxidant in the case of a resin) as a constituent component. Absent.

  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. If the diameter is too large, the entanglement between the fibrous materials may be insufficient, and the strength of the sheet-like material constituted by these, and consequently the strength of the separator may be reduced, making handling difficult. 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 content of the fibrous material in the separator of the present invention is, for example, 10% by volume or more, more preferably 30% by volume or more and 90% by volume or less, more preferably 70% by volume in the total volume of the constituent components of the separator. % Or less is desirable. The state of the fibrous material in the separator (sheet-like material) is, for example, preferably that the angle of the major axis (long axis) with respect to the separator surface is 30 ° or less on average, and 20 ° or less. More preferably.

  Moreover, in order to give a shutdown function to the separator, it swells in heat-meltable fine particles that melt at 80 to 140 ° C., more preferably 130 ° C. or less, or in an electrolyte, and the degree of swelling increases with an increase in temperature. It is also possible to add swellable fine particles, both of them may be added, and these composites may be added. The shutdown function may be imparted by a microporous film in addition to the heat-meltable fine particles and the swellable fine particles, and the separator may be replaced with the heat-meltable fine particles or the swellable fine particles, or the heat-meltable fine particles. Or a microporous film that melts at 80 to 140 ° C., more preferably 130 ° C. or less, and causes a shutdown, together with the swellable fine particles.

  The above-described shutdown function related to the separator when using hot-melt fine particles, swellable fine particles, or the like 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. Further, the shutdown temperature of the microporous film can be measured in the same manner.

  Heat-melting fine particles or microporous film that melts at 80 to 140 ° C., that is, those having a melting temperature of 80 to 140 ° C. measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121 When the separator is exposed to 80 to 140 ° C. (or higher temperature), the hot-melt fine particles or the microporous film is melted to close the voids of the separator. Is inhibited, 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 fine particles and not more than 140 ° C.

  Specific examples of the constituent material of the heat-meltable fine particles include polyethylene (PE), copolymerized polyolefin, polypropylene, or polyolefin derivative (chlorinated polyethylene, chlorinated polypropylene, etc.) having a structural unit derived from ethylene of 85 mol% or more, polyolefin Examples thereof include 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 fine particles 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. Further, the heat-meltable fine particles may contain various known additives (for example, antioxidants) added to the resin as necessary, in addition to the above-described constituent materials. Absent.

Further, as the microporous film, for example, a film made of a polyolefin-based material such as polyethylene, a copolymerized polyolefin having a structural unit derived from ethylene of 85 mol% or more, or a PE / PP / PE laminate is preferably used. It is done. In addition, as a microporous film, the film comprised with PP, polyester, a polyimide, etc. with high heat resistance can also be used, and the heat resistance of a separator can also be improved by using this as a board | substrate.

  The particle diameter of the heat-meltable fine particles is, for example, 0.001 μm or more, more preferably 0.1 μm or more and 15 μm or less, more preferably a number average particle diameter measured by the same measurement method as that for the insulating fine particles. Is recommended to be 1 μm or less.

  If the separator has swellable fine particles that can swell in the electrolyte and increase in degree of swelling as the temperature rises, the electrolyte is absorbed by the swelling of the swellable fine particles when exposed to high temperatures in the battery. (Hereinafter referred to as “thermal swelling”), the conductivity of Li ions in the separator is significantly reduced. The internal resistance is increased, and the above-described shutdown function can be reliably ensured. As the swellable fine particles, those having a temperature of 75 to 125 ° C. exhibiting the above heat swellability are preferable.

  Examples of such swellable fine particles having thermal swellability include crosslinked polystyrene (PS), crosslinked acrylic resin [for example, crosslinked polymethyl methacrylate (PMMA)], and crosslinked fluororesin [for example, crosslinked polyvinylidene fluoride (PVDF). ] Is preferred, and cross-linked PMMA is particularly preferred.

  The particle size of the swellable fine particles is a number average particle size measured by dispersing the fine particles in a non-swelling medium (for example, water) using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA). It is preferable that it is 1-20 micrometers.

  Examples of commercially available swellable fine particles include cross-linked PMMA “Gantz Pearl (product name)” manufactured by Gantz Kasei Co., Ltd. and cross-linked PMMA “RSP1079 (product name)” manufactured by Toyo Ink Co., Ltd. are available.

  From the viewpoint of ensuring a good shutdown function, the content of the heat-meltable fine particles and / or swellable fine particles in the separator is preferably 5 to 70% by volume in the total volume of the constituent components of the separator. . If the content of these fine particles is too small, the shutdown effect due to the inclusion of these may be reduced, and if too large, the content of insulating fine particles and fibrous materials in the separator will be reduced. The effect secured by these may be reduced.

  More specific embodiments of the separator of the present invention include, for example, the following embodiments (1), (2), (3) and (4).

  In the separator according to the aspect (1), insulating fine particles are bound to each other by an organic binder. The separator according to the aspect (2) is a separator in which a large number of fibrous materials are gathered to form a sheet-like material only, for example, a woven fabric or a nonwoven fabric (including paper). Insulating fine particles and other fine particles as required are contained in the sheet-like material, and fibrous materials or insulating fine particles related to the sheet-like material are bound by an organic binder.

In the separator according to the aspect (3), the insulating fine particles and the fibrous material (further, if necessary, other fine particles) are uniformly dispersed, and these are bound by an organic binder to form a sheet. It is what.
The separator according to the aspect (4) is a separator in which insulating fine particles and, if necessary, fibrous materials or the like are bound by an organic binder on a microporous film as a substrate to form a sheet. is there.

  In addition, in the form which combined the aspect of (2) and the aspect of (3), ie, the independent sheet-like thing comprised with a fibrous material, insulating fine particles and a fibrous material (further, as needed Other fine particles) may be dispersed and bound by an organic binder. The separator of the present invention is not necessarily an independent film, and may be integrated with at least one of the positive electrode and the negative electrode.

  The thickness of the separator is preferably 3 μm or more, and more preferably 5 μm or more, from the viewpoint of further enhancing the effect of preventing short-circuiting of the battery, ensuring the strength of the separator, and improving its handleability. . On the other hand, from the viewpoint of further increasing the energy density of the battery, the thickness of the separator is preferably 50 μm or less, more preferably 30 μm or less, and particularly preferably 20 μm or less. These thicknesses indicate the total thickness including the thickness of the substrate when the substrate is used as in the above-described aspect (4). In the case of using a substrate, the ratio of the thickness of the substrate to the layer composed of insulating fine particles is A / B when the thickness of the substrate is A and the thickness of the insulating fine particle layer is B. Is preferably 1 or more and 10 or less.

In any of the above embodiments, the separator has a dry porosity of, for example, 20% or more, more preferably 30% or more, and 70% or less, more preferably 60% or less. It is desirable to be. If the porosity of the separator is too small, the ion permeability 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).

  Furthermore, in any of the above embodiments, 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 piercing of the separator when lithium dendrite crystals are generated.

  Further, the air permeability of the separator indicated by the Gurley value is desirably 10 to 300 sec. If the air permeability is too high, the ion permeability is reduced, and if it is too low, the strength of the separator may be reduced.

  As a method for producing the separator of the present invention, for example, the following methods (I) and (II) can be employed. The method (I) is a production method in which a separator-forming composition (slurry or the like) containing insulating fine particles and an organic binder is applied to or impregnated into an ion-permeable sheet material and then dried at a predetermined temperature. is there. By the method of (I), the separator of the aspect of (2) or the aspect of (4) can be manufactured.

  That is, the “sheet-like product” in the method (I) corresponds to a sheet-like product (various woven fabrics, non-woven fabrics, etc.) composed of fibrous materials or a microporous film. Specifically, a woven fabric composed of at least one type of fibrous material containing each of the exemplified materials as a constituent component, a porous sheet such as a nonwoven fabric having a structure in which these fibrous materials are entangled with each other, and the like. It is done. 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. Examples of the microporous film include a microporous film having an ion permeable pore structure. More specifically, polymer films such as polyethylene (PE), PP, polyester, and polyimide can be exemplified. In particular, a microporous film that causes shutdown, such as a microporous film made of PE and a multilayer film including a PE microporous film such as a PE / PP / PE laminate, is preferably used.

  The above-mentioned composition for forming a separator contains insulating fine particles and an organic binder, and further contains hot-melt fine particles, swellable fine particles, etc., if necessary, and these are dispersed in a solvent (including a dispersion medium, the same applies hereinafter). (The organic binder may be dissolved in a solvent). The solvent used in the composition for forming a separator may be any solvent that can uniformly disperse insulating fine particles, heat-meltable fine particles, and swellable fine particles, and can uniformly dissolve or disperse the organic binder. An organic solvent such as an aromatic hydrocarbon such as tetrahydrofuran; a furan such as tetrahydrofuran; a ketone such as methyl ethyl ketone and methyl isobutyl ketone; 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 organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  When the sheet-like material is composed of a fibrous material such as paper, PP nonwoven fabric, polyester nonwoven fabric or the like, and the opening diameter of the gap is relatively large (for example, the opening diameter of the gap) This is 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 insulating fine particles are present in the voids of the sheet-like material. Further, it is more preferable that a part or all of fine particles (such as heat-meltable fine particles and swellable fine particles) other than the insulating fine particles exist in the voids of the sheet-like material. By adopting such a structure, the effect of using fine particles other than insulating fine particles (shutdown function in the case of hot-melt fine particles or swellable fine particles) is more effectively exhibited. In order to make insulating fine particles, heat-meltable fine particles, swellable fine particles, etc. exist in the voids of the sheet-like material, for example, after impregnating the above-mentioned separator-forming composition into the sheet-like material, a certain gap is passed through. The excess separator forming composition may be removed and then dried.

  In the separator (II) production method of the present invention, the separator-forming composition further contains a fibrous material as required, and this is applied onto a substrate such as a film or a metal foil, In this method, the substrate is dried at a temperature of 1, and then peeled off from the substrate. By the method of (II), the separator of the aspect of (1) or (3) can be manufactured. Moreover, the separator of the aspect of (1) or (3) which is an independent film | membrane can be manufactured by apply | coating the composition for separator formation on base materials, such as a film and metal foil, By using a positive electrode or a negative electrode instead of the metal foil, the separator of the aspect (1) or (3) integrated with the electrode can be produced.

  The composition for forming a separator used in the method (II) is the same as the composition for forming a separator used in the method (I) except that a fibrous material is contained as necessary. Further, in the separator obtained by the method (II), when the fibrous material is contained, a structure in which part or all of the insulating fine particles are present in the voids of the sheet material formed of the fibrous material and It is desirable to do.

  In either of the methods (I) and (II), the 60 ° gloss of the separator is set to 5 or more, or in the separator having plate boehmite, the 020 plane and 120 plane in the X-ray diffraction spectrum. In order to set the ratio of the peak intensity of the 020 plane to the sum of the peak intensities of the 031 plane and the 051 plane to 0.80 or more, the filling properties and orientation of the insulating fine particles in the separator (the plate-like insulating fine particles In order to increase the case), any of the following methods can be employed.

  Insulating fine particles as a solvent, dispersers, agitators, homogenizers, ball mills, attritors, jet mills, sand mills and other various mixing / stirring devices, dispersion devices, etc. (preferably high-pressure homogenizers, ball mills, jet mills, sand mills, etc. Dispersion using a dispersion apparatus), and an organic binder (further, if necessary, fibrous material, heat-meltable fine particles, swellable fine particles, etc.) is added to and mixed with the resulting dispersion. Forming a separator having a high dispersibility and a solid content concentration of 45 to 80% by mass including insulating fine particles and an organic binder (in addition, fibrous materials, heat-melting fine particles, swellable fine particles, etc. added as necessary) By preparing a composition for use in coating and impregnation of the sheet-like material and application on a substrate, the insulating fine particles are filled. It is possible to increase sex and orientation (for a plate-like).

  It is possible to improve the filling and orientation of insulating fine particles to some extent by removing the solvent by drying after application / impregnation of the separator-forming composition, but when the solid content concentration of the separator-forming composition is low In this case, disorder of the insulating fine particles in the separator-forming composition occurs during drying, and the improvement of the filling property and orientation is limited to some extent. On the other hand, as described above, when a separator-forming composition having a high solid content concentration is used, disorder of the insulating fine particles hardly occurs during drying after application / impregnation of the separator-forming composition. Therefore, the filling property / orientation property can be enhanced as compared with the case where a composition for forming a separator having a low solid content concentration is used. Then, by increasing the dispersibility of the insulating fine particles in the separator-forming composition, the filling properties and orientation of the insulating fine particles can be further improved.

  In addition, after the above-described sheet-form material is coated / impregnated with the high solid content separator-forming composition with improved dispersibility of the insulating fine particles as described above, and before being dried on the substrate, In addition, it is preferable to apply a share to the composition for forming a separator. In this case, the filling property and orientation of the insulating fine particles can be further improved. As a method for applying a share to the composition for forming a separator, for example, after the separator-forming composition is applied to or impregnated into the above-mentioned sheet-like material or applied onto a substrate, an extra separator is formed through a certain gap. And a method for removing the composition.

  In addition to the above method, a composition for forming a separator prepared using insulating fine particles whose surface is modified by the action of a dispersing agent such as fats and oils, a surfactant, and a silane coupling agent on the surface. A method of using a separator-forming composition prepared by combining insulating fine particles having different shapes, diameters, or aspect ratios; a sheet-like composition is coated and impregnated, or a substrate Method of controlling drying conditions after being applied on top; Method of pressing or heating and pressing a separator after drying, for example, at a pressure of 1 to 100 MPa; Application and impregnation of a composition for forming a separator on a sheet By applying a method of applying a magnetic field before drying after applying or coating on a substrate, etc., it is possible to increase the filling and orientation (in the case of a plate) of insulating fine particles in the separator. Rukoto can. When these methods are employed, the solid content concentration of the separator forming composition is preferably 10 to 80% by mass, and even if a relatively low solid content separator forming composition is used, the separator It is possible to enhance the filling and orientation (in the case of a plate shape) of insulating fine particles inside.

  Each of the above-described methods for improving the filling property / orientation property (in the case of a plate shape) of insulating fine particles in the separator may be carried out by one or a combination of two or more. .

  The separator of the present invention is not limited to each structure shown above. For example, the insulating fine particles may not be present independently of each other. The parts may be fused.

  The lithium secondary battery of the present invention is not particularly limited as long as it has the separator of the present invention, and conventionally known configurations and structures can be adopted for other configurations and structures.

  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 conventionally known lithium secondary battery, that is, a positive electrode containing an active material capable of occluding and releasing Li ions. 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 such as LiMn ₂ O ₄ Manganese 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 known conductive additive (carbon material such as carbon black) or a binder such as polyvinylidene fluoride (PVDF) is appropriately added to these positive electrode active materials. The positive electrode mixture is formed into a molded body (ie, a current collector as a core material). Can be used such as those finished positive electrode mixture layer).

  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 lithium secondary battery, that is, a negative electrode containing an active material capable of occluding and releasing Li ions. For example, it can occlude and release lithium ions 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 carbon-based materials are 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 obtained 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 a molded body (negative electrode mixture layer) using a current collector as a core material And those having a negative electrode agent layer such as those made of the above-mentioned various alloys and lithium metal foils 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.

  As with the lead portion on the negative electrode side, the negative electrode layer (including a layer having a negative electrode active material and a negative electrode mixture layer) is usually formed on a part of the current collector during the preparation of the negative electrode. Without leaving the exposed portion of the current collector, it is provided as a lead portion. However, the lead portion on the negative electrode side 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 can be used in the form of a laminate in which the above positive electrode and the above negative electrode are laminated via the separator of the present invention, or an electrode wound body in which this is wound.

As the electrolytic solution (organic electrolytic solution), as described above, 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 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. , They 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, for the purpose of improving the safety, charge / discharge cycleability, and high-temperature storage properties of these electrolytes, vinylene carbonates, 1,3-propane sultone, diphenyl disulfide, cyclohexane, biphenyl, fluorobenzene, t- 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 electrolytic solution and gels may be added, and the electrolytic solution may be gelled for use in a battery. Polymer materials for making the electrolyte into a gel include PVDF, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), PAN, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, main Examples of the host polymer capable of forming a known gel electrolyte, such as a crosslinked polymer having an ethylene oxide chain in the chain or side chain, and a crosslinked poly (meth) acrylate.

  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 do not limit the present invention, and all modifications made without departing from the preceding and following descriptions are included in the technical scope of the present invention.

Example 1
<Preparation of separator>
A slurry of 1000 g of plate-like boehmite (average particle size: 1 μm, aspect ratio: 10), which is an insulating fine particle, and water (1000 g) is dispersed for 6 days in a table-top ball mill, and then an acrylic latex (solid content as an insulating material) is used as an organic binder. 3 parts by mass with respect to 100 parts by mass of fine particles) was added and dispersed by stirring with a three-one motor for 1 hour to obtain a uniform slurry (separator forming composition). The solid content concentration of the obtained slurry was 48% by mass.

  A non-woven fabric made of PET having a thickness of 15 μm is passed through the slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried under reduced pressure at 60 ° C. for 15 hours, and the thickness is 20 μm. A separator was obtained.

For the separator of Example 1, the volume of the insulating fine particles calculated with the specific gravity of the insulating fine particles being 3 g / cm ³ , the specific gravity of the binder being 1 g / cm ³ , and the specific gravity of the PET relating to the PET nonwoven fabric being 1.38 g / cm ³ The content is 43.5%.

<Preparation of positive electrode>
85 parts by mass of LiCoO _{2 as a} positive electrode active material, 10 parts by mass of acetylene black as a conductive additive, and 5 parts by mass of PVDF as a binder are uniformly mixed with N-methyl-2-pyrrolidone (NMP) as a solvent. It mixed so that positive electrode mixture containing paste might be prepared. This paste was intermittently applied to both sides of a 15 μm thick aluminum foil serving as a current collector so that the active material application length was 320 mm on the front surface and 250 m on the back surface, dried, and then subjected to a calendering treatment to obtain a total thickness. The thickness of the positive electrode mixture layer was adjusted to 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 340 mm and a width of 43 mm. Further, the exposed portion of the aluminum foil of the positive electrode was tabbed.

<Production of negative electrode>
A negative electrode mixture-containing paste was prepared by mixing 90 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste is intermittently applied on both sides of a 10 μm thick collector made of copper foil so that the active material application length is 320 mm on the front surface and 260 mm on the back surface, dried, and then calendered. 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 attached to the exposed portion of the copper foil of the negative electrode.

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were overlapped with each other through the separator to prepare an electrode separator laminate. The electrode separator laminate is inserted into a bag made of aluminum laminate, and LiPF ₆ is dissolved at a concentration of 1.2 mol / l in an electrolyte solution (a solvent in which ethylene carbonate and ethyl methyl carbonate are mixed at a volume ratio of 1: 2). And the opening was sealed according to a conventional method to produce a lithium secondary battery. In the pre-charging after battery assembly (charging at the time of chemical formation), constant current charging up to 4.2V at 150mA and then constant voltage at 4.2V so that the amount of electricity is 20% of the rated capacity of 750mAh. Voltage charging was performed for a total of 6 hours, and then a constant current discharge was performed up to 3 V at 150 mA.

Example 2
A slurry (separator forming composition) was prepared in the same manner as in Example 1 except that the dispersion in a table-top ball mill was performed for 3 days. A separator was prepared in the same manner as in Example 1 except that this slurry was used.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the above separator was used.

Example 3
A separator was prepared in the same manner as in Example 1 except that a slurry of 1000 g of plate boehmite (average particle size 1 μm, aspect ratio 10) and 430 g of water was prepared, and this slurry was subjected to dispersion with a table-top ball mill. The solid content concentration of the slurry (separator forming composition) used in Example 3 is 66% by mass.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the above separator was used.

Example 4
A slurry of 1000 g of plate-like boehmite (average particle size: 1 μm, aspect ratio: 10) as an insulating fine particle and 2750 g of water was dispersed in a table ball mill for 3 days, and then an acrylic latex (as a solid content, insulating property) as an organic binder. 3 parts by mass with respect to 100 parts by mass of fine particles) was added and dispersed by stirring with a three-one motor for 1 hour to obtain a uniform slurry (separator forming composition). The solid content concentration of the obtained slurry was 28% by mass.

  A non-woven fabric made of PET having a thickness of 15 μm is passed through the slurry, and after applying the slurry by pulling up, it is passed through a gap having a predetermined interval, and then dried under reduced pressure at 60 ° C. for 15 hours, and the thickness is 20 μm. A separator was obtained. The obtained separator was calendered at a press pressure of 9.8 MPa.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the above separator was used.

Example 5
A negative electrode mixture-containing paste was prepared by mixing 90 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste was applied to both sides of a 10 μm-thick current collector made of copper foil, dried, and then calendered to adjust the thickness of the negative electrode mixture layer so that the total thickness was 142 μm. . The slurry of Example 1 was applied on the obtained negative electrode with an applicator, and then dried under reduced pressure at 60 ° C. for 15 hours to obtain a negative electrode integrated separator having a separator part thickness of 20 μm.

  The separator surface of the negative electrode integrated separator and the positive electrode produced in the same manner as in Example 1 were overlapped to produce an electrode separator laminate, and the same procedure as in Example 1 was conducted except that this electrode separator laminate was used. Thus, a lithium secondary battery was produced.

Example 6
A separator was produced in the same manner as in Example 1 except that the plate boehmite was changed to one having an average particle diameter of 0.8 μm and an aspect ratio of 20. A lithium secondary battery was produced in the same manner as in Example 1 except that the above separator was used.

Example 7
A slurry of 1000 g of plate-like boehmite (average particle size: 1 μm, aspect ratio: 10), which is an insulating fine particle, and water (1000 g) is dispersed for 6 days in a table-top ball mill, and then an acrylic latex (solid content as an insulating material) is used as an organic binder. 3 parts by mass with respect to 100 parts by mass of fine particles) was added and dispersed by stirring with a three-one motor for 1 hour to obtain a uniform slurry (separator forming composition). The solid content concentration of the obtained slurry was 48% by mass.

  The obtained slurry was applied on a PE microporous film (thickness 16 μm, porosity 40%) using a die coater and dried to obtain a separator having a thickness of 20 μm. A lithium secondary battery was produced in the same manner as in Example 1 except that the separator was used.

Comparative Example 1
A slurry (separator forming composition) was prepared in the same manner as in Example 1 except that the dispersion with a table-top ball mill was not performed. A separator was prepared in the same manner as in Example 1 except that this slurry was used.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the above separator was used.

Comparative Example 2
A separator was prepared in the same manner as in Example 4 except that the calendar treatment was not performed, and a lithium secondary battery was prepared in the same manner as in Example 1 except that this separator was used.

Comparative Example 3
A slurry (a composition for forming a separator) was prepared in the same manner as in Example 1 except that spherical alumina (average particle size: 1 μm) was used as the insulating fine particles, and the dispersion was not performed with a table-top ball mill. A separator was produced in the same manner as in Example 1 except that.

  A lithium secondary battery was produced in the same manner as in Example 1 except that the above separator was used.

  About the separator of Examples 1-7 and Comparative Examples 1-3, the following filling property and orientation measurement were performed. The results are shown in Table 1.

<Measurement of separator filling and orientation>
The glossiness at 60 ° of the separators of Examples 1 to 7 and Comparative Examples 1 to 3 was measured using a gloss meter “micro TRI gloss” manufactured by BYK Gardner according to the method defined in JIS Z 8741.

  Moreover, about the separator of Examples 1-7 and Comparative Examples 1-2, it measured by the X-ray-diffraction method ("RINT2500V" (CuK alpha ray) by a Rigaku Denki Co., Ltd.), and calculated | required the orientation degree. 020) Diffraction line intensity (020 plane peak intensity) Ia, (120) Diffraction line intensity (120 plane peak intensity) Ib, (031) Diffraction line intensity (031 plane peak intensity) Ic and (051) The diffraction line intensity (051 plane peak intensity) Id was determined and determined from the ratio of Ia to the sum of Ia, Ib, Ic, and Id, Ia / (Ia + Ib + Ic + Id), which is the X-ray diffraction of the separator of Example 3. The spectrum is shown in FIG. 1, and the X-ray diffraction spectrum of the separator of Comparative Example 1 is shown in FIG.

  As can be seen from Table 1, in the separators of Examples 1 to 7, the glossiness of 60 ° and Ia / (Ia + Ib + Ic + Id) are both high, and the orientation of the insulating fine particles is good. The separator of Comparative Example 1 prepared by using the separator-forming composition prepared without dispersing the above and the separator of Comparative Example 2 which was not subjected to calendaring treatment using the separator-forming composition having a low solid content concentration The glossiness at 60 ° and Ia / (Ia + Ib + Ic + Id) are both low, and the orientation of the insulating fine particles is poor. Further, the separator of Comparative Example 3 produced using a separator-forming composition prepared by using spherical alumina as the insulating fine particles and not being dispersed in a table-top ball mill has a low gloss of 60 °, and the insulating fine particles (The separator of Comparative Example 3 does not use plate boehmite, so X-ray diffraction measurement is not performed).

  Moreover, although the SEM photograph of the cross section of the separator of Example 6 is shown in FIG. 3, the SEM photograph of the cross section of the separator of Comparative Example 2 is shown in FIG. It can be seen that the plate-like boehmite is oriented better than the separator of Comparative Example 2.

  Furthermore, about the lithium secondary battery of Examples 1-7 and Comparative Examples 1-3, the short circuit current measurement of the separator was performed as follows. The results are shown in Table 2.

<Short-circuit current measurement of separator>
The batteries of Examples 1 to 7 or Comparative Examples 1 to 3 were subjected to constant current charging up to 4.2 V at 0.2 C, and then constant voltage charging at 4.2 V, and charging current and charging time during constant current charging The battery was charged until the product reached 1.2C. Then, constant current discharge was performed to 3V at 150 mA. Subsequently, the same charging / discharging is repeated while increasing the charging current every 0.1 C, and the charging current value when the voltage does not reach 4.2 V during charging or when the charging current does not decay even after reaching 4.2 V, The short-circuit current value of the separator was evaluated.

  As is clear from Table 2, in the lithium secondary batteries of Examples 1 to 7 using the separator with good orientation of the insulating fine particles, the short-circuit current value of the separator is improved, and between the fibrous materials of the separator By improving the orientation of the insulating fine particles that fill the voids formed in the separator, the number of through-holes and structural defects inside the separator is reduced, and the occurrence of short-circuiting is suppressed by suppressing the partial precipitation of lithium dendrite that occurs during charging. It is presumed that this can be suppressed.

3 is an X-ray diffraction spectrum of a battery separator of Example 3. FIG. 4 is an X-ray diffraction spectrum of a battery separator of Comparative Example 1. 6 is a scanning electron micrograph of the cross section of the battery separator of Example 6. FIG. 4 is a scanning electron micrograph of a cross section of a battery separator of Comparative Example 2.

Claims (11)

  A battery separator comprising at least insulating fine particles stable to an organic electrolyte and an organic binder, and having a glossiness of 60 or more of 5 or more.   The battery separator according to claim 1, wherein the insulating fine particles are plate boehmite.   It is composed of at least plate-like boehmite and an organic binder, and the ratio of the peak intensity of the 020 plane to the sum of the peak intensity of the 020 plane, 120 plane, 031 plane and 051 plane in the X-ray diffraction spectrum is 0.80. A battery separator characterized by the above.   It is composed of at least plate-like boehmite and an organic binder, and the ratio of the intensity of the strongest peak to the peak intensity of the 020 plane among the 120, 031 and 051 plane peak intensities in the X-ray diffraction spectrum is , 0.1 or less, a battery separator.   The battery separator according to any one of claims 1 to 4, further comprising a fibrous material that does not substantially deform at 150 ° C.   The battery separator according to any one of claims 1 to 5, further comprising a microporous film. The battery separator according to claim 6, wherein the microporous film is a polyolefin film. A separator for a battery is formed through a step of applying a separator-forming composition containing insulating fine particles, an organic binder, and a solvent, which are stable with respect to an organic electrolyte, to a substrate or a sheet-like material composed of a fibrous material. A method for manufacturing a battery separator,
A step of dispersing the insulating fine particles in a solvent to form a dispersion;
Mixing the dispersion and the organic binder to prepare a separator-forming composition having a solid content concentration of 10 to 80% by mass including the insulating fine particles and the organic binder;
And a step of applying the separator-forming composition to a substrate or a sheet-like material composed of a fibrous material, followed by drying.   The manufacturing method of the battery separator of Claim 8 which has the process of performing a press process with the pressure of 1-100 Mpa after drying.   A lithium secondary battery comprising a positive electrode, a negative electrode, an organic electrolyte, and a separator, wherein the separator for a battery according to claim 1 is used as the separator.   The lithium secondary battery according to claim 10, wherein the separator is integrated with at least one of a positive electrode and a negative electrode.

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