JP2008004439A - Separator for battery, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator capable of suppressing reduction in energy density and of constituting a lithium secondary battery superior in safety and reliability, and a lithium secondary battery having the separator. <P>SOLUTION: The separator for a battery containing at least particles with a compound shown by AlOOH or Al<SB>2</SB>O<SB>3</SB>-H<SB>2</SB>O as the main component, and the lithium secondary battery having the separator are provided. The separator preferably has an embodiment of further having the fibrous material which is not substantially deformed at 150°C and the embodiment of being integrated with the electrode as the porous layer containing the particles. Moreover, boehmite is preferable as the particles. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

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

  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. 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.

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

  However, a microporous film using a heat-resistant resin such as polyamide or polyimide is excellent in dimensional stability at high temperatures and can be thinned, but is expensive. Nonwoven fabrics using heat-resistant fibers such as polyamide and aramid fibers are also excellent in dimensional stability but are expensive. Nonwoven fabrics using PP fibers and polyester fibers are inexpensive and excellent in dimensional stability at high temperatures. However, since the pore diameter is too large with the nonwoven fabrics, for example, at a thickness of 30 μm or less, short-circuiting due to contact between positive and negative electrodes The short circuit due to the generation of lithium dendrite cannot be sufficiently prevented.

  In addition, a technique has been proposed in which a nonwoven fabric made of an inexpensive material is subjected to various processes and used as a separator. For example, Patent Document 7 discloses a method in which polyethylene (PE) fine particles are applied to a PP nonwoven fabric, Patent Document 8 discloses a method in which a polyester nonwoven fabric is coated with wax, and Patent Document 9 discloses a polyester nonwoven fabric. A method in which a PE microporous membrane is used in contact with a PP nonwoven fabric is used, and Patent Document 10 discloses a method in which inorganic fine particles and organic fine particles are mixed with a PP nonwoven fabric.

  However, when inorganic fine particles are mixed into a nonwoven fabric, it is difficult to completely prevent a short circuit due to the generation of lithium dendrite unless the inorganic fine particles are uniformly and densely filled. It is difficult to uniformly and finely fill the inorganic fine particles. In addition, when organic fine particles such as PE are used, problems similar to those when inorganic fine particles are used may occur. In addition, since PE is soft, when the separator is thinned, a gap between a hard positive electrode material and a negative electrode material. Insufficient insulation may not be maintained and a short circuit may occur.

  In addition, 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 11 and 12).

  However, if an attempt is made 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, so that a short circuit is likely to occur.

JP-A-5-335005 JP 2000-306568 A JP-A-9-259856 Japanese Patent Laid-Open No. 11-40130 JP 2001-291503 A JP 2003-123728 A JP-A-60-136161 Japanese Patent Laid-Open No. 62-283553 JP-A-1-258358 JP 2003-22843 A International Publication No. 97/8863 Pamphlet 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 form a lithium secondary battery excellent in safety and reliability, and the separator An object of the present invention is to provide a lithium secondary battery having a separator.

The battery separator of the present invention were able to achieve the above object, at least, it is characterized in that it contains particles composed mainly of a compound represented by AlOOH or _{Al 2 O 3 · H 2 O} .

  In addition, a lithium secondary battery comprising at least a negative electrode containing an active material capable of occluding and releasing Li, a positive electrode containing an active material capable of occluding and releasing Li, and a battery separator of the present invention is also included in the present invention. Is included.

  ADVANTAGE OF THE INVENTION According to this invention, the fall of energy density can be suppressed as much as possible, and the lithium secondary battery excellent in safety | security and reliability can be provided.

The battery separator of the present invention, particles composed mainly of a compound represented by AlOOH or _{Al 2 O 3 · H 2 O} (A) [ hereinafter simply "may be referred to as particles (A)] as it contains the However, specific examples thereof include the following (1) or (2).
(1) In addition to the particles, a separator containing a fibrous material (B) that does not substantially deform at 150 ° C .;
(2) A separator integrated with an electrode as a porous layer containing the particles.

  In the present invention, the term “substantially not deformed at 150 ° C.” in the fibrous material (B) means that the fibrous material (B) is in the form of a sheet material for forming a separator and is softened. In particular, the change in the length of the sheet-like material at 150 ° C. (or lower temperature), that is, the ratio of shrinkage to the length at room temperature ( (Shrinkage rate) means 5% or less.

  In this invention, the same thing can be used as particle | grains (A) in any of the aspect of (1) and the aspect of (2). In the battery separator of the present invention, in any of the aspects (1) and (2), the lithium secondary battery in which the battery separator is used can be obtained by containing the particles (A). Generation | occurrence | production of the short circuit resulting from the production | generation of can be prevented, and the reliability of this battery can be improved.

  For example, as described in Patent Documents 7, 8, and 10, it is difficult to uniformly and densely fill fine particles in the voids of the nonwoven fabric as described above in the technology of composing the separator by combining the nonwoven fabric and various fine particles. Therefore, it is not easy to prevent short circuit caused by lithium dendrite. On the other hand, in the aspect (1) of the present invention, the reason is unknown, but, for example, in the gap of the sheet-like material (woven fabric, non-woven fabric, etc.) composed of the aggregate of the fibrous material (B). Even if a special operation for filling the particles (A) uniformly and densely is not adopted, a short circuit due to lithium dendrite can be prevented well.

  In addition, for example, as in Patent Documents 11 and 12, in the technique of forming a separator by applying various fine particles on an electrode, especially when the thickness is reduced in order to improve the energy density of the battery, the separation between the positive and negative electrodes is insufficient. In addition to the possibility of a short circuit, the short circuit caused by the lithium dendrite is insufficiently prevented. On the other hand, in the aspect of (2) of the present invention, the reason is unknown, but for example, by configuring the separator as a porous layer integrated with the electrode using a binder or the like together with the particles (A), a comparison is made. Even if the thickness is reduced, separation between the positive and negative electrodes can be satisfactorily achieved, and a short circuit caused by lithium dendrite can be prevented well.

  Furthermore, since the fibrous substance (B) which forms the main body of the separator in the aspect (1) does not substantially deform even at 150 ° C., for example, a part of the constituent material of the separator melts at a temperature of 130 ° C. or lower. In the case where a function of blocking the movement of ions in the separator (so-called shutdown function) is given (details will be described later), after the shutdown occurs due to heat generation in the battery, 20 Even if the temperature of the separator rises by more than ° C., the shape is kept stable. On the other hand, even when the shutdown function is not provided, the shape is not substantially deformed even at a temperature of 150 ° C., and the shape is maintained. Therefore, for example, it is possible to prevent the occurrence of a short circuit due to thermal shrinkage that has occurred in a separator composed of a conventional PE porous film, and thus it is possible to ensure safety when the inside of the battery is abnormally heated.

  Also in the aspect (2), the separator containing the particles (A) is adhered to and fixed to the electrode as a porous layer, and thus, for example, occurs in a separator composed of a conventional PE porous film. Since it is possible to prevent the occurrence of a short circuit due to the thermal contraction, the safety when the inside of the battery is abnormally heated can be ensured.

  As described above, in both the aspect (1) and the aspect (2), the prevention of a short circuit due to the generation of lithium dendrite and the prevention of a short circuit due to the thermal contraction of the separator at a high temperature can be achieved. Since it can be achieved by a configuration other than increasing the thickness, the thickness of the separator of the present invention can be relatively reduced, and a decrease in energy density of a battery using the separator can be suppressed as much as possible.

The particles according to the present invention (A) is not particularly limited as long as particles of the compound represented by AlOOH or _{Al 2 O} 3 · _H 2 _O as a main component (for example more than 80 wt%), a boehmite Is preferred, and synthetic boehmite is particularly preferred.

  As the size of the particles (A), the particle size at the time of drying may be smaller than the thickness of the separator, but preferably has an average particle size of 4/3 to 1/100 of the thickness of the separator. Has an average particle diameter of 0.01 μm or more, more preferably 0.1 μm or more, and preferably 10 μm or less, more preferably 5 μm or less. If the average particle size of the particles (A) is too small, the gap between the particles (A) may be reduced, resulting in a longer ion conduction path in the separator, which may deteriorate battery characteristics. (A) The clearance gap between them may become large and the effect which prevents the short circuit resulting from generation | occurrence | production of lithium dendrite may become small.

  There is no restriction | limiting in particular about the shape of particle | grains (A), Granularity, such as substantially spherical shape and rugby ball shape, needle shape, plate shape, etc. may be sufficient. Among these, the case where the particles (A) are plate-like is particularly preferable because a further improvement in the effect of preventing a short circuit caused by lithium dendrite can be expected. FIG. 1 shows a photograph of a cross section processed with FIB (focused ion beam) of a separator of the present invention containing plate-like particles (A), using a scanning electron microscope (SEM). In FIG. 1, voids of a sheet-like material composed of plate-like particles (A), fibrous materials (B), and fibrous materials (B) are shown, but the particles (A) are representative. Only the part is shown, and all visible particles other than the fibrous material (B) and voids are particles (A). In addition, although tungsten exists in the upper part of FIG. 1, this is provided as a protective film at the time of measurement. In the separator of FIG. 1, plate-like particles (A) are present in the voids of the fibrous material (B), and the flat plate surface is oriented so as to be substantially parallel to the surface of the separator. In this way, in the separator, the plate-like particles (A) are oriented so that the flat plate surface is substantially parallel to the surface of the separator, so that the particles (A) overlap with each other on a part of the flat plate surface. Are arranged as follows. Therefore, it is considered that the gap (through hole) from one side of the separator to the other side is formed in a bent shape instead of a straight line, and this can better prevent lithium dendrite from penetrating the separator. The occurrence of a short circuit is further prevented.

  When the particles (A) are plate-like, the aspect ratio (the 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, and 100 or less. Preferably it is 50 or less. If the aspect ratio is too small, the above-mentioned effect due to the particles (A) being plate-like may be reduced. If the aspect ratio is too large, the specific surface area of the particles (A) becomes too large, making handling difficult. There is.

  When the particles (A) are plate-like, the average value of the ratio of the major axis direction length to the minor axis direction length of the flat plate surface is 1 or more, 3 or less, more preferably 2 or less. It is desirable to be. When the ratio between the length in the major axis direction and the length in the minor axis direction of the flat surface of the particle (A) is too large, the shape of the particle (A) approaches a needle shape, and the above-described effect due to the particle (A) having a plate shape. May become smaller.

  In addition, the average particle diameter of the particles (A) was measured by using a laser scattering particle size distribution meter (“LA-920” manufactured by HORIBA) and dispersing the particles (A) in a medium (for example, water) in which the particles (A) do not swell. Number average particle size. The average value of the ratio of the length in the major axis direction to the length in the minor axis direction of the flat plate surface when the particles (A) are plate-like is, for example, an image taken by a scanning electron microscope (SEM). It can be obtained by analysis. Furthermore, the above aspect ratio in the case where the particles (A) are plate-like can also be obtained by image analysis of an image taken by SEM.

  Further, as described above, the presence form when the particles (A) in the separator are plate-like is preferably such that the flat plate surface is substantially parallel to the surface of the separator, and the average angle near the surface of the separator is It is preferable that it is 30 degrees or less. Here, “near the surface” means a region within 10% of the total thickness from the surface of the separator. In the case where the presence form of the plate-like particles (A) in the separator is as described above, the particles (A) are arranged substantially in parallel in the battery, and as described above, the positive electrode Therefore, it is possible to prevent a short circuit caused by lithium dendrite more effectively.

  Commercially available products can be used as the particles (A) as described above, and, for example, granular boehmite from Daimei Chemical Co., Ltd., plate-type boehmite (Cerasur BMM, BMT) from Kawai Lime Co., etc. are available.

  In both the aspect of (1) and the aspect of (2), the particle (A) is 30% by volume or more, more preferably 40% by volume or more, in the total volume of the constituent components (total solid content) of the separator. It is desirable. By making the volume ratio of the plate-like particles (A) in this way, the short-circuit prevention function can be made more reliable. In addition, it is preferable that the upper limit of the volume ratio of particle | grains (A) is 80 volume%, for example.

  More specific embodiments of the embodiment (1) of the separator of the present invention include the following embodiments (1-1) and (1-2).

  The separator according to the embodiment (1-1) has a configuration in which a large number of fibrous materials (B) are aggregated to form a sheet-like material, for example, a woven fabric or a nonwoven fabric (including paper). In this sheet-like material, particles (A) are contained.

  Moreover, the separator which concerns on the aspect of (1-2) forms the sheet | seat in the form by which the fibrous material (B) and particle | grains (A) were disperse | distributed uniformly.

  In addition, in the form which combined the aspect of (1-1) and the aspect of (1-2), ie, the independent sheet-like object comprised with a fibrous substance (B), a fibrous substance (B) and particle | grains (A) may have a dispersed form.

  The fibrous material (B) according to the embodiment of (1) is not substantially deformed at 150 ° C., has an electrical insulating property, is electrochemically stable, and further contains an electrolyte solution described in detail below. If it is stable to the solvent used for the liquid composition containing the particles (A) used in the production of the separator, there is no particular limitation. The “fibrous material” referred to in the present invention 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 (B) according to the present invention is preferably 10 or more.

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

  Although the diameter of a fibrous material (B) 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 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 content of the fibrous material (B) in the aspect (1) of the separator is, for example, 10% by volume or more, more preferably 30% by volume or more, and preferably 90% by volume or less, more preferably, in all the constituent components. It is desirable that it is 70 volume% or less. For example, the state of the fibrous material (B) in the separator (sheet-like material) is preferably such 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 °.

  In addition, the separator according to the embodiment (2) is formed on the electrode surface as a porous layer composed of the particles (A) and other materials used as necessary (details will be described later), It is integrated with the electrode. Examples of the material that can be used together with the particles (A) include the fibrous material (B) exemplified above in the embodiment of (1).

  Among the separators according to the aspect (2), as the one containing the fibrous substance (B), for example, an aspect in which the aspect (1-1) and the aspect (2) are combined, that is, the fibrous substance ( A mode in which the particles (A) are dispersed in an independent sheet-like material constituted by B), and this is integrated with the electrode as a porous layer; a mode of (1-2) and a mode of (2) In other words, the separator composed of a sheet formed in a state where the fibrous material (B) and the particles (A) are uniformly dispersed is integrated with the electrode as a porous layer; In the aspect which combined the aspect of 1), the aspect of (1-2), and the aspect of (2), ie, the independent sheet-like material comprised by the fibrous material (B), particle | grains (A) and fibrous form The product (B) is contained in a uniformly dispersed state, and the sheet-like product is Embodiment is integrated with the electrode as a porous layer; and the like.

  Moreover, regardless of the aspect of (1) and (2), in the separator of the present invention, in addition to the particles (A) and the fibrous material (B), fine particles (C) other than the particles (A) and heat It may contain meltable fine particles (D). Such fine particles (C) and heat-meltable fine particles (D) have electrical insulating properties, are electrochemically stable, and are further used in the production of electrolytes and separators (A). As long as the fine particles are stable in the solvent used in the liquid composition containing, and do not undergo side reactions such as oxidation-reduction in the operating voltage range of the battery.

Specific examples of the fine particles (C) include the following inorganic fine particles and organic fine particles, and these may be used alone or in combination of two or more. Examples of the inorganic fine particles (inorganic powder) include 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; calcium fluoride, Slightly soluble ionic crystal particles such as barium fluoride and barium sulfate; Covalent crystal particles such as silicon and diamond; Clay particles such as montmorillonite; Mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine Substances or artificial products thereof. Further, the surface of conductive fine particles such as metal fine particles; oxide fine particles such as SnO ₂ and tin-indium oxide (ITO); carbonaceous fine particles such as carbon black and graphite; Surface treatment with a non-electrically conductive material that can constitute the fine particles (C), a material that forms cross-linked polymer fine particles or heat-resistant polymer fine particles described later, etc. has electrical insulation. Fine particles may be used. As organic fine particles (organic powder), various cross-links such as cross-linked polymethyl methacrylate, cross-linked polystyrene, cross-linked polydivinylbenzene, styrene-divinylbenzene copolymer cross-linked product, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include polymer fine particles and heat-resistant polymer fine particles such as polypropylene (PP), polysulfone, polyether sulfone, polyphenylene sulfide, polytetrafluoroethylene, polyacrylonitrile, polyaramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic fine particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. It may be a polymer or a crosslinked product (in the case of the above heat-resistant polymer).

  Further, as the heat-meltable fine particles (D), those that melt at 80 to 130 ° C., that is, the melting temperature measured by using a differential scanning calorimeter (DSC) according to the provisions of JIS K 7121 is 80 to 130 ° C. A temperature of 130 ° C. is preferred. Specific constituent materials of the heat-meltable fine particles (D) include polyethylene (PE), a copolymerized polyolefin having a structural unit derived from ethylene of 85 mol% or more, or a polyolefin derivative (such as chlorinated polyethylene), polyolefin wax, petroleum Examples thereof include wax and carnauba wax. 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 (D) 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 (D) 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 separator of the present invention is a resin that can form the above-described heat-meltable fine particles (D) with the fine particles (C) exemplified above as the core in both the aspects (1) and (2). The composite fine particles (E) having a core-shell structure obtained by compounding as a shell may be contained.

  When the fine particles (C) are contained in the separator, they can contribute to improving the shape stability (particularly, shape stability at high temperatures) of the separator. Further, when the separator contains the heat-meltable fine particles (D) and the core-shell structure composite fine particles (E), when the internal temperature rises in the battery having the separator, the heat-meltable fine particles (D) itself In addition, the shell portion of the composite fine particles (E) is melted to block the gaps in the separator, and a shutdown function for blocking the movement of ions can be secured.

The above-mentioned void blocking phenomenon in the separator can be evaluated by, for example, a Gurley value representing the air permeability of the separator. Specifically, in a separator having a shutdown function, the Gurley value measured at the time of heating by the following measurement method is preferably 3 times or more, more preferably 10 times that before heating (Gurley value measured at room temperature). That's it. As a specific measuring method, the separator is held at a predetermined temperature for 10 minutes in a thermostatic bath, taken out, slowly cooled, and the Gurley value when the temperature is raised to the predetermined temperature is measured. Thereafter, the temperature is increased in increments of 5 ° C., the separator is held for 10 minutes at each temperature, and then the Gurley value is measured in the same manner. The Gurley value is measured by a method according to JIS P 8117, and is indicated by the number of seconds that 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ² . In addition, when the shutdown completely occurs and the air does not permeate, the Gurley value becomes infinite.

  In the case of the separator containing the heat-meltable fine particles (D) that melt at 80 to 130 ° C. or the composite fine particles (E) whose shell portion is made of a resin that melts at 80 to 130 ° C., 80 to 130 ° C. When exposed to (or higher temperature), the temperature at which the void clogging phenomenon evaluated by the Gurley value (the temperature at which the Gurley value is three times or more before heating) is expressed by the heat-meltable fine particles ( D) or higher than the melting temperature of the resin constituting the shell portion and 130 ° C. or lower.

  In the separator according to the embodiment of (1) and the embodiment of (2), the content of the heat-meltable fine particles (D) and / or composite fine particles (E) in the separator is from the viewpoint of ensuring a good shutdown function. It is preferable that it is 30-70 volume% in all the structural components of a separator. If the content of these fine particles is too small, the shutdown effect due to the inclusion of these may be reduced. If the content is too large, the content of the particles (A) in the separator will be reduced. The effect of preventing a short circuit due to occurrence may be reduced. In addition, the content of the fine particles (C) in the separator according to the aspect (1) and the aspect (2) is not particularly limited, but is preferably 5 to 30% by volume in all the constituent components.

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

  Moreover, in the aspect of (1), in order to make fibrous material (B) into a sheet-like thing, the sheet-like thing comprised by fibrous material (B), particle | grains (A), and others For the purpose of binding the particles [fine particles (C), heat-meltable fine particles (D), composite fine particles (E)], etc., and also in the aspect (2), For the purpose of binding materials [fibrous matter (B), fine particles (C), hot-melt fine particles (D), composite fine particles (E), etc.], the separator may contain a binder (F). .

  The binder (F) is electrochemically stable and stable with respect to the electrolytic solution, and further includes particles (A), fibrous materials (B), fine particles (C), hot melt fine particles (D), composite fine particles ( E) and the like may be used as long as they can adhere well. For example, EVA (ethylene acetate-derived structural unit is 20 to 35 mol%), ethylene-acrylate copolymer such as ethylene-ethyl acrylate copolymer, etc. , Fluorine rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), polyurethane, epoxy resin and the like. These may be used alone or in combination of two or more. When these binders (F) are used, they can be used in the form of an emulsion or plastisol dissolved or dispersed in a solvent of a liquid composition for forming a separator described later.

  For example, when the heat-meltable fine particles (D) and the composite fine particles (E) have adhesiveness alone, they can also serve as the binder (F).

  From the viewpoint of further improving the battery's energy density while further improving the effect of preventing short-circuiting of the battery, ensuring the strength of the separator and improving the handleability, the separator in both the aspects (1) and (2) The thickness is preferably, for example, 3 μm or more, more preferably 5 μm or more, and 50 μm or less, more preferably 30 μm or less.

In either of the embodiments (1) and (2), the porosity of the separator is, for example, 20% or more, more preferably 30% or more, and 70% or less, more preferably 60%. The following is desirable. 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 = Σ a 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 the separator of the aspect of (1-1) in the aspect of (1), and the separator of the aspect of (1-2), it is desirable that the air permeability of the separator shown by a Gurley value is 10 to 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. Moreover, as for the intensity | strength of a separator in any of the aspect of (1) and (2), it is desirable that it is 50 g or more by the puncture intensity | strength using a needle with 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.

  As a 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), a liquid composition (slurry or the like) containing particles (A) is applied to or impregnated into an ion-permeable sheet that does not substantially deform at 150 ° C., and then dried at a predetermined temperature. Manufacturing method. By the method of (I), the separator of the aspect of (1-1) can be manufactured.

  That is, the “sheet-like material” referred to in the method (I) corresponds to a sheet-like material (various woven fabrics, non-woven fabrics, etc.) composed of the fibrous material (B). 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.

  The liquid composition for forming the separator of the present invention includes particles (A), and if necessary, fine particles (C), hot-melt fine particles (D), composite fine particles (E), binders (F), and the like. And these are dispersed in a solvent (including a dispersion medium, hereinafter the same) [the binder (F) may be dissolved]. The solvent used in the liquid composition can uniformly disperse particles (A), fine particles (C), heat-meltable fine particles (D), and composite fine particles (E), and can also dissolve or disperse binder (F) uniformly. An organic solvent such as aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; is preferable. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the binder (F) 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 used. In addition, the interfacial tension can be controlled.

  In the liquid composition, the solid content including particles (A), fine particles (C), hot-melt fine particles (D), composite fine particles (E), and binder (F) is, for example, 10 to 40% by mass. Is preferred.

  When the sheet-like material is composed of a fibrous material (B), such as a nonwoven fabric such as paper, PP nonwoven fabric, and polyester nonwoven fabric, and the opening diameter of the void is relatively large (for example, void This is likely to cause a short circuit of the battery. Therefore, in this case, it is preferable to have a structure in which part or all of the particles (A) are present in the voids of the sheet-like material. Further, a part or all of the fine particles other than the particles (A) [fine particles (C), heat-meltable fine particles (D), composite fine particles (E)] may be present in the voids of the sheet-like material. More preferred. By using such a structure, the effect of using fine particles other than the particles (A) [If fine particles (C), the effect of improving the shape stability of the separator, the hot-melt fine particles (D) and the composite fine particles ( If E), the shutdown effect] is more effectively exhibited. In order to allow the particles (A), fine particles (C), hot-melt fine particles (D), and composite fine particles (E) to exist in the voids of the sheet-like material, for example, the above-mentioned liquid composition is impregnated into the sheet-like material. Then, a process such as drying after removing a surplus liquid composition through a certain gap may be used.

  In the separator, in the case where the particles (A) are plate-like, the liquid composition is used in order to enhance the orientation and more effectively exert the above-described effects by using the plate-like particles (A). What is necessary is just to give a share to this liquid composition in the sheet-like material which impregnated the thing. For example, in the production method of (I), by impregnating the liquid composition described above as a method for causing the particles (A) and the like to exist in the voids of the sheet-like material, a method of passing a certain gap is used. Further, it is possible to share the liquid composition, and the orientation of the particles (A) can be improved.

  In the method for producing the separator (II) of the present invention, the liquid composition further contains a fibrous material (B), 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. That is, it is a method of simultaneously performing the operation of making the fibrous material (B) into a sheet and containing the particles (A) and the like. By the method of (II), the separator of the aspect of (1-2) can be manufactured. 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 (B). The solid content including the product (B) is preferably 10 to 40% by mass, for example. In the separator obtained by the method (II), it is desirable to have a structure in which some or all of the particles (A) are present in the voids of the sheet-like material formed of the fibrous material (B). .

  In addition, in the manufacturing method of (II), in order to improve the orientation by using a plate-like particle (A), when the liquid composition is applied on a substrate, a share is given to the liquid composition. A coating method that can be applied may be employed. Specifically, a coating method using a coating device such as a die coater or a blade coater can be used.

  The separator (III) production method of the present invention comprises particles (A) and, if necessary, fibrous materials (B), fine particles (C), hot-melt fine particles (D), composite fine particles (E), binders Apply a liquid composition (slurry or the like) in which (F) or the like is dispersed in water or a suitable solvent to the electrode surface, and dry to remove the solvent, thereby removing the separator as a porous layer integrated with the electrode. It is a method of forming. By the method (III), the separator of the aspect (2) can be produced.

  Examples of the liquid composition for forming a separator used in the production method (III) are the same as the liquid composition in the production method (I) and the same liquid composition in the production method (II) [ Liquid composition containing fibrous material (B)] can be used. As a method for applying the liquid composition to the electrode surface, for example, a coating method using a conventionally known coating apparatus such as a blade coater, a roll coater, a die coater, or a spray coater can be employed.

  In addition, in the manufacturing method of (III), in order to improve the orientation of the particles (A) in the separator using a plate-like particle (A), among the above-described coating apparatuses, a blade coater, a die coater, etc. It is preferable to use a coating apparatus capable of applying a share to the liquid composition during coating. Moreover, you may employ | adopt the application | coating method that a liquid composition passes a gap after application | coating of a liquid composition.

  The separator of the present invention is not limited to the structures shown above. For example, the particles (A) may not be present independently of each other, and may be mutually or fibrous. Part of (B) may be fused.

  If the lithium secondary battery of this invention has the separator of this invention, there is no restriction | limiting in particular about another structure and structure, A conventionally well-known structure and structure can be employ | adopted.

  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. 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). In other words, a positive electrode mixture layer) or the like can be used.

  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. 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 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 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 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. In the case of the aspect of (2) in which the separator of the present invention is integrated with the electrode, the surface of either the positive electrode or the negative electrode (that is, the positive electrode mixture layer surface, the negative electrode in the case of the positive electrode) If it exists, it should just be formed in the negative electrode agent layer surface), and may be formed in both the positive and negative electrodes. Furthermore, using the positive electrode and / or the negative electrode having the separator of the aspect of (2), the separator of the aspect of [1] [the separator of the aspect of (1-1) and the separator of the aspect of (1-2)] is also used. And you may comprise an electrode laminated body and an electrode winding body.

Examples of the electrolyte include dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, methyl propionate, ethylene carbonate, propylene carbonate, butylene carbonate, γ-butyrolactone, ethylene glycol sulfite, 1,2-dimethoxyethane, 1,3- dioxolane, tetrahydrofuran, 2-methyl - tetrahydrofuran, organic solvent consists of only one type, such as diethyl ether or a mixture of two or more solvents, for _{example, 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} [wherein Rf is a fluoroalkyl group] which was prepared by dissolving at least one selected from lithium salts such as are used. 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.

  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
Plate-like boehmite (average particle size: 1 μm, aspect ratio: 10): 1000 g, water: 800 g, isopropyl alcohol (IPA) 200 g, and PVB: 375 g as a binder (F) are put in a container as a particle (A). And stirred for 1 hour to make a uniform slurry. A PP meltblown nonwoven fabric with a thickness of 15 μm was passed through this slurry, and the slurry was applied by pulling up, then passed through a gap having a predetermined interval, and then dried to obtain a separator with a thickness of 20 μm. In addition, when the cross section of this separator was observed by SEM, it has confirmed that particle | grains (A) existed in the space | gap of a nonwoven fabric. Moreover, it was confirmed by SEM observation of the cross section that the flat surface of the particles (A) in the vicinity of the surface was oriented within an average of 30 ° with respect to the separator surface. An observation photograph of the cross section is shown in FIG.

Example 2
To the same slurry as in Example 1, alumina (Al ₂ O ₃ ) fine particles (average particle size: 0.4 μm): 250 g was added as fine particles (C), and the mixture was stirred and dispersed with a three-one motor for 3 hours. A slurry was obtained. A PBT meltblown nonwoven fabric having a thickness of 28 μm was passed through this slurry, and after applying the slurry by pulling up, it was passed through a gap having a predetermined interval and then dried to obtain a separator having a thickness of 35 μm. In addition, when the cross section of this separator was observed by SEM, it has confirmed that particle | grains (A) and microparticles | fine-particles (C) exist in the space | gap of a nonwoven fabric.

Example 3
As a binder (F), 100 g of SBR latex and 30 g of CMC and 6000 g of water were put in a container and stirred at room temperature until evenly dissolved. Further, boehmite (average particle diameter: 2 μm): 1000 g was added as particles (A), and the mixture was dispersed with stirring with a disper at 2800 rpm for 1 hour. To this, 1000 g of PE emulsion (average particle diameter: 1 μm, melting point: 125 ° C.) was added as hot-melt fine particles (D), and the mixture was stirred with a disper at 2800 rpm for 3 hours to obtain a uniform slurry. Using an applicator, this slurry was applied by sliding onto a paper having a thickness of 25 μm with a gap of 50 μm and dried to obtain a separator having a thickness of 40 μm.

Example 4
EVA emulsion (20 mol% structural unit derived from vinyl acetate) as binder (F): 100 g, plate-like boehmite (average particle diameter: 1 μm, aspect ratio: 10): 1000 g, water: 2000 g as particles (A) The mixture was stirred and dispersed with a disper at 2800 rpm for 1 hour to obtain a uniform slurry. To this slurry, alumina fiber (average fiber diameter: 3 μm, aspect ratio: 30000): 1000 g was added as a fibrous material (B) and stirred at room temperature until uniform. The slurry thus obtained was applied onto a PET substrate at a coating thickness of 50 μm using a die coater, dried, and then peeled from the PET substrate to obtain a separator having a thickness of 15 μm. When the cross section of the separator was observed with an SEM, the aspect ratio of the alumina fibers was 10 or more, and the average angle with respect to the separator surface was 30 ° or less.

Comparative Example 1
A separator was produced in the same manner as in Example 1 except that granular alumina (average particle size: 0.3 μm) was used instead of the plate-like boehmite which is the particles (A).

Comparative Example 2
A separator was produced in the same manner as in Example 1 except that PE emulsion (average particle size: 1 μm, melting point: 125 ° C.) was used instead of the plate-like boehmite as the particles (A).

<Heating characteristics of separator>
The separators of Examples 1 to 4 and Comparative Examples 1 to 2 and the PE microporous film having a thickness of 20 μm, which is a conventionally known separator as Comparative Example 3, are allowed to stand in a thermostatic bath at 150 ° C. for 30 minutes. The shrinkage ratio was measured to evaluate the heating characteristics. 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. The results are shown in Table 1.

<Shutdown characteristics>
For the separators of Example 3 and Comparative Example 3, the change in Gurley value accompanying the temperature increase was measured under the following conditions. After measuring the Gurley value at room temperature by the above-described measurement method, the separator was held at 80 ° C. for 10 minutes in a thermostatic bath, taken out, slowly cooled, and the Gurley value was measured when the temperature was raised to 80 ° C. . Thereafter, the temperature was increased to 150 ° C. in increments of 5 ° C., and the separator was held at each temperature for 10 minutes, and then the Gurley value was measured in the same manner. From the above measurement, the Gurley value before heating (room temperature) and after heating (150 ° C.) and the ratio thereof, and the temperature (rising temperature) at which the Gurley value became three times or more that before heating were obtained. The change in the Gurley value of the separator of Example 3 was 10 to 50. Further, the temperature at which the Gurley value became three times or more before heating was defined as the “shutdown temperature”. The obtained shutdown temperature is also shown in Table 1.

  Table 1 shows the following. The separator of Comparative Example 3 corresponding to the conventional product has a large heat shrinkage rate. When this is used for a battery, 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. Furthermore, in the separator of Example 3, the Gurley value (air permeability) after heating is increased by a factor of 3 or more in the temperature range of 100 to 130 ° C. before heating in the thermostatic bath. Therefore, in the battery using these, in the process of increasing the internal temperature, the shutdown function that hinders the flow of current due to the decrease in the ion permeability of the separator effectively operates, so that better safety is ensured. obtain.

Example 5
<Preparation of positive electrode>
LiCoO _{2 as a} positive electrode active material: 80 parts by mass, acetylene black as a conductive additive: 10 parts by mass, and PVDF as a binder: 5 parts by mass uniformly using 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 an aluminum foil having a thickness of 15 μm as a current collector so that the active material application length was 280 mm on the front surface and 210 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 280 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 was intermittently applied on both sides of a 10 μm-thick current collector made of copper foil so that the active material application length was 290 mm on the front surface and 230 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 290 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 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 4-6
A lithium secondary battery was fabricated 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 to 3.

Example 9
The slurry prepared in the same manner as in Example 1 was applied to the surface of the negative electrode mixture layer of the negative electrode prepared in the same manner as in Example 5 using a die coater so that the thickness when dried was 15 μm and dried. Thus, a separator composed of a porous layer integrated with the negative electrode was formed. The obtained negative electrode and the positive electrode produced in the same manner as in Example 5 were overlapped with the separator on the negative electrode surface in between 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 slurry prepared in the same manner as in Example 3 was applied to the surface of the positive electrode mixture layer of the positive electrode prepared in the same manner as in Example 5 using a die coater so that the thickness when dried was 10 μm and dried. Thus, a separator composed of a porous layer integrated with the positive electrode was formed. The separator on the surface of the positive electrode was sandwiched between the obtained positive electrode, the separator produced in the same manner as in Example 1, and the negative electrode produced in the same manner as in Example 5 and in the same manner as in Example 1. They were stacked so as to be on the negative electrode side 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 batteries of Examples 5 to 10 and Comparative Examples 4 and 6 were subjected to the following electrochemical evaluation (measurement of discharge capacity ratio) and safety test. The results are shown in Table 2. In addition, about the battery of the comparative example 5, since the internal short circuit had generate | occur | produced in the stage which produced the battery, subsequent tests were stopped.

<Discharge capacity ratio>
About the batteries of Examples 5 to 10 and Comparative Examples 4 and 6, constant current charging at 0.2 C (up to 4.2 V) and charging by constant voltage charging at 4.2 V (total of constant current charging and constant voltage charging) After 15 hours, discharge was performed at 0.2 C up to 3.0 V, and the ratio of the obtained discharge capacity to the charge capacity, that is, the discharge capacity ratio (%) was determined. The discharge capacity ratio was determined as an average value of 10 batteries.

<Reliability test>
The batteries of Examples 6 to 12 and Comparative Examples 4 and 6 were left in a high-temperature layer at 150 ° C., the time until the function of the battery was lost was measured, and a reliability test at a high temperature was performed.

  As can be seen from Table 2, in the lithium secondary batteries of Examples 5 to 10, the discharge capacity ratio is good and at a practical level, the occurrence of short circuits due to lithium dendrite is suppressed, and the lithium secondary batteries are left at 150 ° C. In this case, the time until the battery function is lost is longer than that of Comparative Example 6 corresponding to the conventional battery, and the battery is excellent in safety and reliability. On the other hand, the battery of Comparative Example 4 has a low discharge capacity ratio and has not reached the practical level, and the battery of Comparative Example 5 has problems such as an internal short circuit occurring at the stage of manufacturing the battery as described above. It was happening.

3 is a scanning electron micrograph of the cross section of the separator of Example 1. FIG.

Claims (9)

At least, battery separator characterized by containing particles composed mainly of a compound represented by AlOOH or _{Al 2 O 3 · H 2 O} .   The battery separator according to claim 1, further comprising a fibrous material that does not substantially deform at 150 ° C.   The battery separator according to claim 2, wherein the fibrous material forms a sheet-like material.   The battery separator according to claim 3, wherein the sheet-like material is a woven fabric or a non-woven fabric.   The battery separator according to claim 3 or 4, wherein a part or all of the particles are present in the voids of the sheet-like material.   The battery separator according to claim 1, wherein the porous layer containing the particles is integrated with an electrode.   The battery separator according to any one of claims 1 to 6, wherein the particles are boehmite.   The battery separator according to any one of claims 1 to 7, further comprising particles that melt at 80 to 130 ° C. It comprises at least a negative electrode containing an active material capable of occluding and releasing Li, a positive electrode containing an active material capable of occluding and releasing Li, and the battery separator according to claim 1. A featured lithium secondary battery.

Images