JP2008066094A - Separator for battery, and lithium secondary battery - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a separator capable of suppressing reduction of energy density and constituting a battery superior in safety at abnormal heating while securing reliability of a battery, and a lithium secondary battery having the separator. <P>SOLUTION: This is the separator for battery which contains at least a fibrous material that is not substantially deformed at 150°C and inorganic particles that are not substantially deformed at 150°C, and in which part of the inorganic particles is scale-like particles of an aspect ratio of 30 or more, and a lithium secondary battery which has a negative electrode containing an active material capable of storing and releasing lithium, a positive electrode containing the active material capable of storing and releasing lithium, and the separator for battery. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a separator that is resistant to bending, and a lithium secondary battery that uses the separator and is safe even in a high-temperature environment. The separator of the present invention is particularly suitable for a battery including an electrode group having a winding structure.

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

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

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

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

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

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

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

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

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

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

  Patent Document 8 discloses a porous structure composed of an inorganic oxide filler and a binder containing scaly silica, with the solution of the problem of heat shrinkage of a polyolefin-based porous film separator as one of the problems. There has been proposed a technique for forming a battery by forming a porous film on the surface of a positive electrode or a negative electrode, and using this in combination with a porous film separator as described above.

  However, in the technique described in Patent Document 8, since the porous film is interposed between the positive and negative electrodes together with the separator, it is difficult to reduce the distance between the positive and negative electrodes. It is difficult to avoid the decline.

  Furthermore, in Patent Document 9, a polymer containing a non-aqueous electrolyte and a separator containing a reinforcing material including a scaly filler are applied to a battery chemical device, whereby the flow of the polymer in a high-temperature environment is controlled. It is described that the occurrence of an internal short circuit can be suppressed.

  However, when the separator described in Patent Document 9 is applied to, for example, a wound electrode group, a crack occurs in the mixture layer containing the active material of the positive and negative electrodes in a curved portion where the diameter of the electrode group decreases. In addition, since the separator is easily cracked along with the crack of the mixture layer, it is difficult to sufficiently secure the reliability of the battery.

JP-A-60-136161 Japanese Patent Laid-Open No. 62-283553 JP-A-1-258358 JP 2003-22843 A JP 2005-536658 Gazette International Publication No. 97/8863 JP 2000-149906 A JP 2005-339938 A JP 2001-84987 A

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

  The battery separator of the present invention that has achieved the above object contains at least a fibrous material that does not substantially deform at 150 ° C. and inorganic particles that do not substantially deform at 150 ° C. The part is a scaly particle having an aspect ratio of 30 or more.

  Further, at least a negative electrode containing an active material capable of occluding and releasing lithium, a positive electrode containing an active material capable of occluding and releasing lithium, and a lithium secondary battery having the battery separator of the present invention are also included in the present invention. .

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

  As described above, the battery separator of the present invention (hereinafter sometimes abbreviated as “separator”) includes a fibrous material (A) that does not substantially deform at 150 ° C. and inorganic particles that do not substantially deform at 150 ° C. And a part of the inorganic particles are scaly particles having an aspect ratio of 30 or more. [Hereinafter, scaly particles having an aspect ratio of 30 or more are referred to as “flaky particles (B)” Inorganic particles that do not correspond to the shaped particles (B) are referred to as “inorganic particles (C)”.

  In the separator of the present invention, due to the presence of the fibrous material (A) and inorganic particles (C), even if the separator is thinned, the positive electrode and the negative electrode can be well separated, so that the decrease in battery energy density is suppressed as much as possible. However, it is possible to prevent the occurrence of a short circuit.

  Further, the scaly particles (B) according to the separator of the present invention can easily take a state in which a plurality of particles are laminated after the dispersion medium is removed by drying from the state of the dispersion liquid dispersed in the dispersion medium, for example. Therefore, the scale-like particles (B) are present in a state of being laminated in the separator, and when the separator is bent, the number of surface layers of the laminated scale-like particles (B) collapses and the stress is released, Since it is difficult for further destruction to proceed, the separator is unlikely to crack. Furthermore, the scale-like particles (B) have a high affinity with the inorganic particles (C), and also have an action of firmly bonding the inorganic particles (C) as a binder.

  In the separator of the present invention, the above-described action of the scale-like particles (B) and the reinforcing action of the fibrous material (A) and the inorganic particles (C) functioning as a reinforcing material are combined to form an electrode group having a wound structure. In addition, even when this is crushed to form a flat electrode group with a part with a large curvature, cracks can be prevented from occurring, thereby preventing the occurrence of micro-shorts and ensuring battery reliability. can do.

  Furthermore, since the fibrous substance (A), the scaly particles (B), and the inorganic particles (C), which are the main constituents of the separator, are not substantially deformed at 150 ° C., the occurrence of thermal contraction of the separator is prevented. Can be suppressed. Thereby, in the battery having the separator of the present invention, even when abnormally heated, contact between the positive electrode and the negative electrode due to thermal contraction of the separator hardly occurs, and the battery is excellent in safety. The “fibrous material (A) that is not substantially deformed at 150 ° C.” as used in the present specification is a sheet-like material composed of the fibrous material (A) and has substantial dimensions due to softening or the like. This means that no change occurs. Specifically, 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) is 5%. It means the following. In addition, the term “inorganic particles [scale-like particles (B) and inorganic particles (C)] that are not substantially deformed at 150 ° C.” as used herein refers to inorganic particles [scale-like particles (B) heated to 150 ° C. Or the inorganic particles (C)] are those whose deformation is not confirmed when they are visually observed.

  The fibrous material (A) has electrical insulation, is electrochemically stable, and is further described in detail below as a nonaqueous electrolytic solution (hereinafter, may be abbreviated as “electrolytic solution”), If it is stable to the solvent used for the liquid composition containing the scaly particles (B) and the inorganic particles (C) used in the production of the separator, there is no particular limitation. The “fibrous material” in the present specification means that having an aspect ratio [length in the longitudinal direction / width (diameter) in a direction perpendicular to the longitudinal direction] of 4 or more. The aspect ratio of the fibrous material (E) is preferably 10 or more. Further, “electrochemically stable” as used in the present specification means that no chemical change occurs during charging / discharging of the battery.

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

  Although the diameter of a fibrous material (A) should just be below the thickness of a separator, it is preferable that it is 0.01-5 micrometers, for example. When the diameter is too large, the entanglement between the fibrous materials is insufficient, and for example, the strength of the sheet-like material composed of these, and consequently the strength of the separator may be reduced, making it difficult to handle. On the other hand, if the diameter is too small, the gap of the separator becomes too small, and the ion permeability tends to be lowered, and the load characteristics of the battery may be lowered.

  For example, the state of the fibrous material (A) 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 order to more effectively exert the reinforcing action by the fibrous material (A), the ratio of the fibrous material in the total volume of the constituent components of the separator is, for example, 10% by volume or more, more preferably 20% by volume or more. Thus, it is desirable that the content be 90% by volume or less, more preferably 80% by volume or less.

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

  The scaly particles (B) and the inorganic particles (C) have electrical insulation properties, are electrochemically stable, and are used in an electrolyte solution described later and a liquid composition used in the production of the separator. There is no particular limitation as long as it is stable and does not dissolve in the electrolyte solution at high temperatures.

  The scaly particles (B) and the inorganic particles (C) are both inorganic particles. Among these, the scaly particles (B) have an aspect ratio (the maximum length of the scaly particles and the thickness of the scaly particles). Ratio) is 30 or more, and the inorganic particles (C) are inorganic particles other than the scaly particles (B), that is, those having an aspect ratio of less than 30. The aspect ratio of the scaly particles (B) is preferably 35 or more, and preferably 70 or less, more preferably 50 or less. Further, in the scale-like particles (B), the average value of the ratio of the long axis direction length to the short axis direction length of the flat plate surface of the particles is 1 or more, more preferably 1.2 or more, and 3 or less. Preferably it is 2 or less.

Specific examples of the scaly particles (B) and the inorganic particles (C) include fine oxide particles such as iron oxide, SiO ₂ , Al ₂ O ₃ , TiO ₂ , BaTiO ₂ , ZrO, and alumina-silica composite oxide. Nitride fine particles such as aluminum nitride and silicon nitride; sparingly soluble ion crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; covalently bonded crystal fine particles such as silicon and diamond; clay fine particles such as talc and montmorillonite; Boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, sericite, bentonite, mica, and other substances derived from mineral resources, 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); carbon fine particles such as carbon black and graphite; Fine particles imparted with electrical insulation properties by surface treatment with the above-described material constituting the electrically insulating inorganic particles) may be used.

As the scaly particles (B) and the inorganic particles (C), silica (SiO ₂ ), mica, alumina (Al ₂ O ₃ ), alumina-silica composite oxide, boehmite and the like are particularly preferable.

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

  The shape of the inorganic particles (C) may be, for example, a so-called spherical shape or any shape such as a plate shape or a needle shape, but the inorganic particles (C) in the separator From the viewpoint of increasing the overlap of the two and increasing the path length (so-called curvature) between the positive and negative electrodes, a plate shape is more preferable.

  That is, in the case where the inorganic particles (C) are plate-shaped, in the separator, the inorganic particles (C) are oriented so that the flat plate surface thereof is substantially parallel to the surface of the separator, thereby generating a short circuit. It can be better controlled. This is because the inorganic particles (C) are oriented as described above so that the inorganic particles (C) are arranged so as to overlap each other on a part of the flat plate surface. It is considered that the hole) is formed in a bent shape instead of a straight line, and thus it is possible to prevent the lithium dendrite from penetrating the separator.

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

  As the plate-like inorganic particles (C), for example, it is desirable that the aspect ratio (ratio between the maximum length in the plate-like particles and the thickness of the plate-like particles) is 5 or more, more preferably 10 or more. Since the inorganic particles (C) do not correspond to the scaly particles (B), the aspect ratio is less than 50]. In the plate-like inorganic particles (C), the average value of the ratio of the long axis direction length to the short axis direction length of the flat plate surface of the particles is 0.3 or more, more preferably 0.5 or more, It is desirable that it is 3 or less, more preferably 2 or less. When the plate-like inorganic particles (C) have the above-mentioned aspect ratio and the average value of the ratio of the long axis direction length to the short axis direction of the flat plate surface, the short circuit prevention effect is more effectively exhibited. The

  In addition, 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 in the scale-like particles (B) or the plate-like inorganic particles (C) is measured by, for example, a scanning electron microscope (SEM). It can be obtained by image analysis of the photographed image. Furthermore, the above aspect ratio of the scale-like particles (B) and the plate-like inorganic particles (C) can also be obtained by image analysis of an image taken by SEM.

  More specific examples of the scaly particles (B) include various commercially available products, such as “Sun Lovely” (silica) manufactured by Asahi Glass Co., Ltd., “Micro Mica”, “Somasif” (Mica) manufactured by Corp Chemical Co., Ltd. “Yodogawa Mica Z20” (Sericite) manufactured by Yodogawa Kogyo Co., Ltd. is available.

In addition, as a more specific example of the plate-like inorganic particles (C), various commercially available products may be mentioned. For example, “NST-B1” pulverized product (TiO ₂ ) manufactured by Ishihara Sangyo Co., Ltd., “Hayashi Kasei Co., Ltd.” Wenger "(bentonite), Kawai lime Co." BMM "(boehmite), Kawai lime Co." sera sur BMT-B "[alumina _{(Al 2 O} 3)], KINSEI MATEC Co." Seraph "(alumina), Coop “Micro Mica” (Mica) manufactured by Chemical Corporation is available. In addition, Al ₂ O ₃ , ZrO, and CeO ₂ can be produced by the method disclosed in Japanese Patent Laid-Open No. 2003-206475.

  As the scaly particles (B) and the inorganic particles (C), those exemplified above may be used alone or in combination of two or more. Moreover, the scale-like particles (B) and the inorganic particles (C) may be particles of the same material, or may be particles of different materials.

  The inorganic particles [total inorganic particles including scaly particles (B) and inorganic particles (C)] in the separator of the present invention are preferably 30% by volume or more in the total volume of the constituent components of the separator, and 40% by volume. More preferably. By making the amount of inorganic particles in the separator as described above, the action of these inorganic particles can be exhibited more effectively. In addition, it is preferable that the upper limit of the volume ratio of the inorganic particle in a separator is 80 volume%, for example. If the volume ratio of the inorganic particles is too large, for example, it may be difficult to obtain a configuration having shutdown characteristics described later. In the case where the separator of the present invention has a configuration that does not have shutdown characteristics, the inorganic particles can be made to a higher ratio, for example, 95% by volume or less.

  Further, the amount of the scaly particles (B) is preferably 0.5% by volume or more, and more preferably 2% by volume or more, in the total volume of the constituent components of the separator. By using the scaly particles (B) in the above amounts, the effect can be more reliably exhibited. In addition, when there is too much quantity of scaly particle | grains (B), since the quantity of the inorganic particle (C) in a separator will decrease and it may become difficult to ensure the effect by this, it is difficult for scaly particle | grains (B). The amount is preferably 30% by volume or less and more preferably 20% or less in the total volume of the constituent components of the separator.

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

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

  Thermally meltable particles (D) that melt at 80 to 130 ° C., that is, thermal meltability that has a melting temperature of 80 to 130 ° C. measured using a differential scanning calorimeter (DSC) according to JIS K 7121. In the separator containing the particles (D), when the separator is exposed to 80 to 130 ° C. (or higher temperature), the hot-melt particles (D) melt and the voids of the separator are closed. The movement of lithium ions is inhibited, and a rapid discharge reaction at high temperatures is suppressed. Therefore, in this case, the shutdown temperature of the separator evaluated by the increase in the internal resistance is not less than the melting point of the heat-fusible particles (D) and not more than 130 ° C.

  Specific examples of the constituent material of the heat-meltable particles (D) include polyethylene (PE), a copolymerized polyolefin having a structural unit derived from ethylene of 85 mol% or more, polypropylene, or a polyolefin derivative (chlorinated polyethylene, chlorinated polypropylene, etc. ), Polyolefin wax, petroleum wax, carnauba wax and the like. Examples of the copolymer polyolefin include an ethylene-vinyl monomer copolymer, more specifically, an ethylene-vinyl acetate copolymer (EVA), an ethylene-methyl acrylate copolymer, or an ethylene-ethyl acrylate copolymer. it can. Moreover, polycycloolefin etc. can also be used. The heat-meltable particle (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 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 particle diameter of the heat-meltable particle (D) is a number average particle diameter measured by the same measurement method as the scaly particle (B) or the inorganic particle (C), for example, 0.001 μm or more, more preferably 0. It is recommended that it is 1 μm or more and 15 μm or less, more preferably 1 μm or less.

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

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

Moreover, as swellable particle | grains (E), the thing whose swelling degree B defined by a following formula measured at 120 degreeC is 1.0 or more is preferable.
_{B = (V 1 / V 0} ) -1 (1)
[In the above formula (1), V ₀ is the volume of particles (cm ³ ) 24 hours after being put into the non-aqueous electrolyte at 25 ° C., and V ₁ is put into the non-aqueous electrolyte at 25 ° C. 24 hours later, the temperature of the non-aqueous electrolyte is raised to 120 ° C., and the volume of the particles (cm ³ ) after 1 hour at 120 ° C. is meant. ]

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

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

V _i = M _i × W / P _A (2)
V _B = (M ₀ −M _i ) / P _B (3)
_{V C = M 1 / P c} -M 0 / P B (4)
V _V = M _i × (1−W) / P _V (5)
V ₀ = V _i + V _B −V _V × (B _B +1) (6)
V _D = V _V × (B _B +1) (7)
B = [{V ₀ + V _C −V _D × (B _C +1)} / V ₀ ] −1 (8)

Here, in the above formulas (2) to (8),
V _i : volume (cm ³ ) of the swellable particles (E) before being immersed in the electrolytic solution,
V ₀ : volume (cm ³ ) of the swellable particles (E) after being immersed in the electrolyte at room temperature for 24 hours,
V _B : volume of the electrolyte solution (cm ³ ) absorbed in the film after being immersed in the electrolyte solution at room temperature for 24 hours,
V _c : The volume of the electrolytic solution absorbed by the film (cm) during the period from when the electrolytic solution was immersed in the electrolytic solution at room temperature for 24 hours until the electrolytic solution was heated to 120 ° C. and further passed for 1 hour at the above temperature. ³ ),
V _V : volume (cm ³ ) of the binder resin before being immersed in the electrolytic solution,
V _D : volume of the binder resin (cm ³ ) after being immersed in the electrolytic solution at room temperature for 24 hours,
M _i : mass (g) of the film before being immersed in the electrolytic solution,
M ₀ : mass (g) of the film after being immersed in the electrolytic solution at room temperature for 24 hours,
M _l : After immersing in the electrolyte solution at room temperature for 24 hours, the electrolyte solution was heated to 120 ° C., and the mass (g) of the film after 1 hour at the above temperature,
W: Mass ratio of the swellable particles (E) in the film before being immersed in the electrolytic solution,
P _A : Specific gravity (g / cm ³ ) of the swellable particles (E) before being immersed in the electrolytic solution,
P _B : Specific gravity of electrolyte at room temperature (g / cm ³ ),
P _C: electrolyte specific gravity at ^{120 ℃ (g / cm 3)} ,
P _V : Specific gravity (g / cm ³ ) of the binder resin before being immersed in the electrolytic solution,
B _B : degree of swelling of the binder resin after being immersed in the electrolyte at room temperature for 24 hours,
B _C : Swelling degree of the binder resin at the time of temperature rise defined by the above formula (1).

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

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

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

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

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

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

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

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

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

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

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

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

  Examples of the swellable particles (E) having a core-shell structure as described above include styrene and acrylic monomers [(meth) acrylate, methyl ( And particles obtained by polymerizing (meth) acrylate etc.].

  As the size of the swellable particles (E), 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 1/3 to 1/100 of the thickness of the separator. Specifically, it is preferably an average particle size obtained by the same method as the scaly particles (B) and the like, and is 0.1 to 20 μm.

  When the heat-meltable particles (D) and the swellable particles (E) are contained to give the separator a shutdown function, for example, the heat-meltable particles (D) and / or Or it is preferable that the quantity of swelling particle | grains (E) shall be 20 volume% or more and 80 volume% or less. If the amount of the heat-meltable particles (D) or the swellable particles (E) is too small, the shutdown effect due to the use of these particles may be reduced. If the amount is too large, the inorganic particles [scale-like particles in the separator]. Since the amount of (B) and inorganic particles (C)] is reduced, for example, the effect of preventing a short circuit due to generation of lithium dendrite may be reduced.

  In the separator of the present invention, the binder (F) is used for the purpose of binding the fibrous material (A), the scaly particles (B), the inorganic particles (C), and the above-described various additive particles to each other or to each other. Is preferably used. The binder (F) should be one that is electrochemically stable and stable with respect to the electrolyte, and that can favorably adhere the fibrous material (A), scale-like particles (B), inorganic particles (C), and the like. For example, EVA (with a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylate copolymer such as ethylene-ethyl acrylate copolymer, various rubbers and derivatives thereof [styrene-butadiene rubber (SBR), fluoro rubber, urethane rubber, ethylene-propylene-diene rubber (EPDM, etc.), cellulose derivatives [carboxymethyl cellulose (CMC), hydroxyethyl cellulose, hydroxypropyl cellulose, etc.], polyvinyl alcohol (PVA), polyvinyl butyral (PVB) , Polyvinylpyrrolidone (PVP), polyurea , Epoxy resin, polyvinylidene fluoride (PVDF), vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), acrylic resin, etc., and these can be used alone or in combination of two or more. You can also When these binders (F) are used, they can be used in the form of an emulsion dissolved or dispersed in a solvent of a liquid composition for forming a separator described later.

  In the separator of the present invention, when the binder (F) is used, the amount of the binder (F) in the total volume of the constituent components of the separator is preferably set to 1 to 20% by volume, for example.

  The separator of the present invention may be in the form of an independent film or may have a structure integrated with electrodes (positive electrode and / or negative electrode).

  In addition to the above components, the separator of the present invention may contain, for example, various organic particles exemplified as those that can be used as the core of the swellable particles (E) having a core-shell structure.

  For example, as described above, the separator of the present invention includes a scaly particle (B) and an inorganic particle (C) in a sheet-like material composed of the fibrous material (A). It can be in the form of a porous film having a structure containing meltable particles (D), swellable particles (E) and the like]. In this case, the sheet-like material composed of the fibrous material (A) hardly undergoes thermal shrinkage, such as a separator made of a conventionally known polyolefin porous film, and has good dimensional stability against heat. Therefore, even when the battery is abnormally heated, a short circuit due to thermal contraction of the separator can be prevented well.

  In addition to the above-described form, the separator of the present invention includes, for example, a fibrous material (A), scaly particles (B), and inorganic particles (C) bound together by a binder (F). It can also be set as the form of the porous membrane formed. Also in this case, the heat-meltable particles (D), the swellable particles (E), and the like may be bound together with the fibrous material (A) by the binder (F). In such a form of separator, a manufacturing method in which no strain remains in the separator [applying a liquid composition containing a fibrous material (A), a scaly particle (B), an inorganic particle (C), etc. to a substrate, etc. Since the manufacturing method includes a step of drying and drying], the dimensional stability against heat is good as in the case of the separator including the sheet-like material composed of the fibrous material (A). Even when the battery is abnormally heated, a short circuit due to thermal contraction of the separator can be prevented well.

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

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

Further, the porosity of the separator is preferably 20% or more, more preferably 30% or more, and 70% or less, more preferably 60% or less in a dry state. If the porosity of the separator is too small, the ion permeability (ion conductivity) may be decreased, and if the porosity is too large, the strength of the separator may be insufficient. The porosity of the separator: P (%) can be calculated by calculating the sum of each component i from the thickness of the separator, the mass per area, and the density of the constituent components using the following formula.
P = Σa _i ρ _i / (m / t)
Here, in the above formula, a _i : ratio of component i expressed by mass%, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of separator (g / cm ² ), t: thickness of separator (cm).

Further, the air permeability of the separator, which is carried out by a method according to JIS P 8117 and indicated by the Gurley value indicated by the number of seconds in which 100 ml of air passes through the membrane under a pressure of 0.879 g / mm ² , is 10 to 10. It is preferable that it is 300 sec. If the air permeability is too high, the ion permeability is reduced, whereas if it is too low, the strength of the separator may be reduced. In the case of an independent membrane, the strength of the separator is preferably 50 g or more in terms of piercing strength using a needle having a diameter of 1 mm. If the piercing strength is too low, a short circuit may occur due to the breakthrough of the separator when lithium dendrite crystals are generated.

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

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

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

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

  The liquid composition for forming the separator of the present invention includes scaly particles (B), inorganic particles (C), and optionally, hot-melt particles (D), swellable particles (E), binders. (F) and the like, which are dispersed or dissolved in a solvent (including a dispersion medium, the same applies hereinafter). The solvent used in the liquid composition can uniformly disperse the scaly particles (B), inorganic particles (C), hot-melt particles (D), swellable particles (E), and the binder (F). However, organic solvents such as aromatic hydrocarbons such as toluene; furans such as tetrahydrofuran; ketones such as methyl ethyl ketone and methyl isobutyl ketone; are 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 scale-like particles (B), inorganic particles (C), heat-meltable particles (D), swellable particles (E), and binder (F) is, for example, 10 to 40 mass. % Is preferable.

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

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

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

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

  In addition, the separator of this invention is not limited to said structure. For example, the inorganic particles [scale-like particles (B) and inorganic particles (C)] do not have to exist independently, and are partially fused to each other or to the fibrous material (A). It does not matter.

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

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

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

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

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

  Examples of the form of the battery include a tubular shape (such as a rectangular tube shape or a cylindrical shape) using a steel can or an aluminum can as an outer can. Moreover, it can also be set as the soft package battery which used the laminated film which vapor-deposited the metal as an exterior body.

The positive electrode is not particularly limited as long as it is a positive electrode used in a conventionally known nonaqueous electrolyte battery (lithium secondary battery). For example, as an active material, lithium-containing transition metal oxide represented by Li _{1 + x} MO ₂ (−0.1 <x <0.1, M: Co, Ni, Mn, etc.); lithium manganese such as LiMn ₂ O ₄ Oxide; LiMn _x M _(1-x) O _{2 in} which part of Mn of LiMn ₂ O ₄ is substituted with another element; olivine type LiMPO ₄ (M: Co, Ni, Mn, Fe); LiMn _0.5 Ni _0.5 O ₂ ; Li _{(1 + a)} Mn _x Ni _y Co _(1-xy) O ₂ (−0.1 <a <0.1, 0 <x <0.5, 0 <y <0. 5); can be applied, and a positive electrode mixture in which a known conductive additive (carbon material such as carbon black) or a binder such as PVDF is appropriately added to these positive electrode active materials, Using a current collector as a core and finishing it into a molded body Kill.

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

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

  The negative electrode is not particularly limited as long as it is a negative electrode used in a conventionally known nonaqueous electrolyte battery (lithium secondary battery). For example, carbon that can occlude and release lithium, such as graphite, pyrolytic carbons, cokes, glassy carbons, fired organic polymer compounds, mesocarbon microbeads (MCMB), and carbon fibers as active materials One type or a mixture of two or more types of system materials is used. In addition, elements such as Si, Sn, Ge, Bi, Sb, In and their alloys, lithium-containing nitrides, oxides and other compounds that can be charged and discharged at a low voltage close to lithium metal, or lithium metals and lithium / aluminum alloys Can also be used as a negative electrode active material. A negative electrode mixture prepared by appropriately adding a conductive additive (carbon material such as carbon black) or a binder such as PVDF to these negative electrode active materials and using a current collector as a core material is used. In addition, the above-mentioned various alloys and lithium metal foils may be used alone or formed on a current collector.

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

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

  The electrode includes an electrode group (electrode laminate) having a laminated structure in which the positive electrode and the negative electrode are laminated via the separator of the present invention, and an electrode group having a wound structure in which this is wound (electrode winding). Body). In the separator of the present invention, some of the inorganic particles are scale-like particles (B) to suppress the occurrence of cracking when the separator is bent, and the separator is curved when used as an electrode group with a wound structure. Even if it is used in such a state, the positive electrode and the negative electrode can be well separated. Therefore, the separator of the present invention can be suitably used for a battery having an electrode group with a wound structure that is required to be used in a curved state as described above, and the effect is particularly effective when used for such applications. Become prominent.

As described above, a solution obtained by dissolving a lithium salt in an organic solvent is used as the nonaqueous electrolytic solution. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, inorganic lithium salts such as LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , LiSbF ₆ ; LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , Li ₂ C ₂ F ₄ (SO ₃ ) ₂ , LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO ₃ (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group]; it can.

  The organic solvent used in the electrolytic solution is not particularly limited as long as it dissolves the above lithium salt and does not cause side reactions such as decomposition in the voltage range used as a battery. For example, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate and vinylene carbonate; chain carbonates such as dimethyl carbonate, diethyl carbonate and methyl ethyl carbonate; chain esters such as methyl propionate; cyclic esters such as γ-butyrolactone; Chain ethers such as ethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme and tetraglyme; cyclic ethers such as dioxane, tetrahydrofuran and 2-methyltetrahydrofuran; nitriles such as acetonitrile, propionitrile and methoxypropionitrile; Sulfites such as ethylene glycol sulfite; and the like, and these may be used alone. , It may be used in combination of two or more thereof. In order to obtain a battery with better characteristics, it is desirable to use a combination that can obtain high conductivity, such as a mixed solvent of ethylene carbonate and chain carbonate. In addition, 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 non-aqueous electrolyte and gels may be added, and the non-aqueous electrolyte may be gelled and used for a battery. Polymer materials for making the non-aqueous electrolyte into a gel include PVDF, PVDF-HFP, PAN, polyethylene oxide, polypropylene oxide, ethylene oxide-propylene oxide copolymer, crosslink having ethylene oxide chain in the main chain or side chain Known host polymers capable of forming a gel electrolyte, such as polymers and cross-linked poly (meth) acrylates, can be mentioned.

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

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

Example 1
Silica water slurry (solid content concentration 15% by mass, aspect ratio 50, average particle size 0.5 μm) 200 g, silica particles (average particle size 3 μm) 1000 g, binder, binder (F) 108 g of SBR latex (solid content concentration 3% by mass) and 1000 g of water were placed in a container and dispersed by stirring with a three-one motor for 1 hour to obtain a uniform slurry. A PET nonwoven fabric having a thickness of 15 μm was passed through the slurry, and the slurry was applied by pulling and then dried to obtain a separator having a thickness of 20 μm.

About the separator of Example 1, the specific gravity of silica which is scale-like particles (B) and inorganic particles (C) is 2.2 g / cm ³ , the specific gravity of the binder (F) is 1 g / cm ³ , and the PET is a PET nonwoven fabric. The volume content of the scaly particles (B) calculated with a specific gravity of 1.38 g / cm ³ was 1.0%, and the volume content of the inorganic particles (C) was 32.5%.

Example 2
A separator was produced in the same manner as in Example 1 except that the inorganic particles (C) were changed to 1000 g of mica (average particle diameter of 2 to 3 μm).

For the separator of Example 2, the specific gravity of silica as scale-like particles (B) is 2.2 g / cm ³ , the specific gravity of mica as inorganic particles (C) is 3 g / cm ³ , and the specific gravity of binder (F) is 1 g. / ^cm 3, the volume content of the scale was calculated specific gravity of the PET of the PET nonwoven fabric as a 1.38 g / cm ³ like particles (B) is 1.0%, the volume content of the inorganic particles (C) is 31.6%.

Example 3
A separator was produced in the same manner as in Example 1 except that the inorganic particles (C) were changed to 1000 g of plate-like boehmite (average particle size 1 μm).

For the separator of Example 3, the specific gravity of silica as scale-like particles (B) is 2.2 g / cm ³ , the specific gravity of plate-like boehmite as inorganic particles (C) is 3.0 g / cm ³ , and the binder (F) The volume content of the scaly particles (B) calculated with a specific gravity of 1 g / cm ³ and a specific gravity of PET relating to a PET nonwoven fabric of 1.38 g / cm ³ is 0.9%, and the inorganic particles (C) The volume content is 27.9%.

Example 4
A separator was produced in the same manner as in Example 1 except that the inorganic particles (C) were changed to 1000 g of plate-like α-alumina (average particle size 2 μm).

For the separator of Example 4, the specific gravity of silica as scale-like particles (B) is 2.2 g / cm ³ , the specific gravity of plate-like α-alumina as inorganic particles (C) is 4.0 g / cm ³ , and the binder (F The volume content of the scaly particles (B) calculated with a specific gravity of 1) g / cm ³ and a PET specific gravity of 1.38 g / cm ³ is 0.7%, and the inorganic particles (C) The volume content of is 22.6%.

Example 5
A separator was produced in the same manner as in Example 3 except that the scaly particles (B) were changed to 20 g of mica (aspect ratio: 30, average particle size: 1 to 2 μm).

For the separator of Example 5, the specific gravity of mica as the scaly particles (B) is 3.0 g / cm ³ , the specific gravity of silica as the inorganic particles (C) is 2.2 g / cm ³ , and the specific gravity of the binder (F) Was 1 g / cm ³ , and the volume content of the scaly particles (B) calculated as 1.38 g / cm ³ of the specific gravity of the PET nonwoven fabric was 0.9%, and the volume content of the inorganic particles (C) The rate is 28.1%.

Example 6
Example 1 except that 250 g of an emulsion containing “cross-linked PMMA” as a swellable particle (E) [“Staphyroid AC-3364 (trade name)” manufactured by Ganz Kasei Co., Ltd., average particle size: 0.1 μm] was further added. A slurry was prepared in the same manner as in Example 1 except that this slurry was used.

For the separator of Example 6, the specific gravity of silica that is the scaly particles (B) and the inorganic particles (C) is 2.2 g / cm ³ , and the specific gravity of the crosslinked PMMA that is the swellable particles (E) is 1.2 g / cm. ³ , the volume content of the scaly particles (B) calculated as 1 g / cm ³ of the specific gravity of the binder (F) and 1.38 g / cm ³ of the specific gravity of the PET related to the nonwoven fabric made of PET is 0.8%, The volume content of the inorganic particles (C) is 25.6%.

Example 7
Example 2 except that 250 g of an emulsion containing “cross-linked PMMA” as a swellable particle (E) [“Staphyroid AC-3364 (trade name)” manufactured by Ganz Kasei Co., Ltd., average particle size: 0.1 μm] was further added. A slurry was prepared in the same manner as in Example 1 except that this slurry was used.

For the separator of Example 7, the specific gravity of silica as the scaly particles (B) is 2.2 g / cm ³ , the specific gravity of mica as the inorganic particles (C) is 3.0 g / cm ³ , and the swellable particles (E) Scale-like particles (B) calculated with a specific gravity of the crosslinked PMMA of 1.2 g / cm ³ , a specific gravity of the binder (F) of 1 g / cm ³ , and a specific gravity of PET relating to the PET nonwoven fabric of 1.38 g / cm ³ The volume content of is 0.8%, and the volume content of the inorganic particles (C) is 24.9%.

Example 8
The same as Example 3 except that 250 g of an emulsion containing “cross-linked PMMA” as a swellable particle (E) [“Staphyroid AC-3364 (trade name)” manufactured by Ganz Kasei Co., Ltd., average particle size: 0.1 μm] was further added. A slurry was prepared in the same manner as in Example 1 except that this slurry was used.

For the separator of Example 8, the specific gravity of silica as scale-like particles (B) is 2.2 g / cm ³ , the specific gravity of plate boehmite as inorganic particles (C) is 3.0 g / cm ³ , and swellable particles ( E) Scale-like particles calculated by setting the specific gravity of crosslinked PMMA as 1.2 g / cm ³ , the specific gravity of the binder (F) as 1 g / cm ³ , and the specific gravity of PET relating to the PET nonwoven fabric as 1.38 g / cm ³ The volume content of B) is 0.7%, and the volume content of the inorganic particles (C) is 22.0%.

Example 9
Example 4 except that 250 g of an emulsion containing “cross-linked PMMA” which is a swellable particle (E) [“STAPHYLOID AC-3364 (trade name)” manufactured by Ganz Kasei Co., Ltd., average particle size: 0.1 μm] was further added. A slurry was prepared in the same manner as in Example 1 except that this slurry was used.

For the separator of Example 9, the specific gravity of silica as scale-like particles (B) is 2.2 g / cm ³ , the specific gravity of plate-like α-alumina as inorganic particles (C) is 4.0 g / cm ³ , and swellable particles (E) Scale-like particles calculated by setting the specific gravity of the crosslinked PMMA as 1.2 g / cm ³ , the specific gravity of the binder (F) as 1 g / cm ³ , and the specific gravity of the PET relating to the PET nonwoven fabric as 1.38 g / cm ^3. The volume content of (B) is 0.6%, and the volume content of the inorganic particles (C) is 17.8%.

Example 10
Same as Example 5 except that 250 g of an emulsion containing “crosslinked PMMA” as a swellable particle (E) [“Staffyroid AC-3364 (trade name)” manufactured by Ganz Kasei Co., Ltd., average particle size: 0.1 μm] was further added. A slurry was prepared in the same manner as in Example 1 except that this slurry was used.

For the separator of Example 10, the specific gravity of mica as the scaly particles (B) is 3.0 g / cm ³ , the specific gravity of silica as the inorganic particles (C) is 2.2 g / cm ³ , and the swellable particles (E) Scale-like particles (B) calculated with a specific gravity of the crosslinked PMMA of 1.2 g / cm ³ , a specific gravity of the binder (F) of 1 g / cm ³ , and a specific gravity of PET relating to the PET nonwoven fabric of 1.38 g / cm ³ The volume content of is 0.7%, and the volume content of the inorganic particles (C) is 22.1%.

Comparative Example 1
A slurry was prepared in the same manner as in Example 1 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 2
A slurry was prepared in the same manner as in Example 2 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 3
A slurry was prepared in the same manner as in Example 3 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 4
A slurry was prepared in the same manner as in Example 4 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 5
A slurry was prepared in the same manner as in Example 6 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 6
A slurry was prepared in the same manner as in Example 7 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 7
A slurry was prepared in the same manner as in Example 8 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

Comparative Example 8
A slurry was prepared in the same manner as in Example 9 except that the scaly particles (B) were not added, and a separator was prepared in the same manner as in Example 1 except that this slurry was used.

  The separators of Examples 1 to 10 and Comparative Examples 1 to 8 were subjected to the following bending strength test and shutdown characteristic evaluation. The results are shown in Table 1.

<Bending strength test>
A separator piece cut out to 4.5 cm × 4 cm was bent with a spacer in between, and the bent portion was uniformly loaded from above, and then the SEM observation of the bent portion was performed. In SEM observation, the convex part of the fold line was observed at a magnification of 100 times, and the presence or absence of cracks and missing of inorganic particles (C) was confirmed. The bending test was performed on three samples cut out from the separators of the examples and comparative examples, and the bending strength when cracks and missing of inorganic particles (C) were not confirmed at all in the visual field observed in the three tests. The bending strength of each separator was evaluated by setting the bending strength when even one crack or missing of inorganic particles (C) was confirmed as x. In this test, the thickness of the spacer sandwiching the separator piece was set to 300 μm, assuming the R portion of the innermost circumference of the electrode group when the separator was applied to an electrode group having a winding structure.

<Shutdown temperature measurement>
Each separator piece cut out to a size of 4 cm × 4 cm is sandwiched between two stainless plates with terminals, inserted into a bag of aluminum laminate film, injected with a non-aqueous electrolyte, and then the tip of the terminal is attached to the bag. The bag was sealed in the state where it was taken out, and it was set as the sample for a test. Here, as the non-aqueous electrolyte, a solution in which LiPF ₆ was dissolved at a concentration of 1.2 mol / l in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2 was used. The sample was placed in a thermostatic bath, and the resistance value when a 1 kHz alternating current was applied to the terminal with a contact resistance meter [3560 AC milliohm HiTester (trade name)] manufactured by HIOKI was measured from room temperature to 1 per minute. The temperature was increased at a rate of 0 ° C. and heating was performed, and the temperature change of the internal resistance was determined. The temperature at which the resistance value was 10 times or more the value at room temperature was taken as the shutdown temperature of the separator. In the case where the shutdown temperature was not confirmed by this test, it is indicated as “-” in Table 1.

  Table 1 shows the following. The separators of Examples 1 to 10 having the fibrous material (A) (PET nonwoven fabric), the scaly particles (B), and the inorganic particles (C) are Comparative Examples 1 to 8 that do not use the scaly particles (B). Bending strength is superior to that of the separator. Therefore, for example, in a battery having an electrode group with a wound structure configured using the separators of Examples 1 to 10, the occurrence of cracks in the separator due to the bending at the R portion of the inner periphery, which is a concern in the electrode group, and inorganic Missing of the particles (C) can be satisfactorily suppressed, and occurrence of a short circuit can be prevented.

  Moreover, in the separator of Examples 6-10 which uses bridge | crosslinking PMMA which is swellable particle | grains (E) in order to provide a shutdown function to a separator, Except not containing scaly particle | grains (B), Examples 6- 9 has substantially the same shutdown temperature as that of the separators of Comparative Examples 5 to 8 having the same configuration as 9, and it can be seen that the shutdown characteristics of the separator are not impaired even when the scaly particles (B) are used.

Example 11
<Production of negative electrode>
A negative electrode active material-containing paste was prepared by mixing 95 parts by mass of graphite as a negative electrode active material and 5 parts by mass of PVDF as a binder with N-methyl-2-pyrrolidone (NMP) as a solvent in a uniform manner. Prepared. This negative electrode mixture-containing paste was intermittently applied to both sides of a 10 μm thick current collector made of copper foil so that the active material application length was 320 mm on the front surface and 260 mm on the back surface, dried, and then subjected to calendar treatment. The thickness of the negative electrode mixture layer was adjusted so that the total thickness was 142 μm, and the negative electrode mixture layer was cut to have a width of 45 mm to produce a negative electrode having a length of 330 mm and a width of 45 mm. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

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

<Battery assembly>
The positive electrode and the negative electrode obtained as described above were spirally wound through the separator of Example 1 to obtain a wound electrode group. The electrode group crushed into a flat shape, loaded into a DNP made a laminate film casing material in electrolytic solution (ethylene carbonate and ethyl methyl carbonate 1: mixed solvent of 2 volume ratio, the LiPF ₆ 1. A solution dissolved at a concentration of 2 mol / l) was injected, and vacuum sealing was performed to manufacture a lithium secondary battery.

Examples 12-20, Comparative Examples 9-16
A lithium secondary battery was produced in the same manner as in Example 11 except that the separator was changed to that in Examples 2 to 10 or Comparative Examples 1 to 8.

Example 21
The same slurry as that prepared in Example 6 was applied on the same negative electrode as that prepared in Example 11 using a die coater so as to have a thickness of 15 μm when dried, and the negative electrode and separator were then dried. An integrated product was obtained. The same positive electrode as that produced in Example 11 was overlapped on the separator side of the obtained integrated negative electrode and separator, and wound into a spiral shape to obtain a wound electrode group. A lithium secondary battery was produced in the same manner as in Example 11 except that this electrode group was used.

Example 22
The same slurry as that prepared in Example 9 was applied on the same positive electrode as that prepared in Example 11 using a die coater so that the thickness when dried was 10 μm, and dried. An integrated product was obtained. On the separator side of the obtained positive electrode and separator integrated product, the same negative electrode as that produced in Example 11 was layered and wound in a spiral shape to obtain a wound electrode group. A lithium secondary battery was produced in the same manner as in Example 11 except that this electrode group was used.

Comparative Example 17
A lithium secondary battery was produced in the same manner as in Example 11 except that the separator was changed to a PE microporous membrane.

Comparative Example 18
The same slurry as that prepared in Comparative Example 6 was applied on the same negative electrode as that prepared in Example 11 using a die coater so as to have a dry thickness of 15 μm, and dried. An integrated product was obtained. The same positive electrode as that produced in Example 11 was overlapped on the separator side of the obtained integrated negative electrode and separator, and wound into a spiral shape to obtain a wound electrode body. A lithium secondary battery was produced in the same manner as in Example 11 except that this wound electrode body was used.

  The lithium secondary batteries of Examples 11 to 22 and Comparative Examples 9 to 18 were subjected to electrochemical evaluation (charge / discharge efficiency) and a safety test. The results are shown in Table 2.

<Charge / discharge efficiency>
About each battery of Examples 11-22 and Comparative Examples 9-18, charging by constant current charging at 0.2 C (up to 4.2 V) and constant voltage charging at 4.2 V (constant current charging and constant voltage charging) After a total time of 15 hours, discharge was performed at 0.2 C up to 3.0 V, and charge / discharge efficiency (ratio of discharge capacity to charge capacity) was determined. In addition, charging / discharging efficiency was calculated | required as an average value of 10 batteries, respectively.

<Safety evaluation>
When the batteries of Examples 11 to 22 and Comparative Examples 9 to 18 were placed in a thermostatic bath, the temperature was increased at a rate of temperature increase of 10 ° C./min, the temperature was kept constant when the temperature reached 150 ° C., and the temperature reached 150 ° C. From this, the time until battery abnormality occurred (time until the battery reached 180 ° C. or higher) was measured to evaluate safety at high temperatures.

  Table 2 shows the following. In the batteries of Examples 11 to 22 using the separator containing the fibrous material (A), the scaly particles (B), and the inorganic particles (C), a separator not containing the scaly particles (B) was used. Compared with the batteries of Comparative Examples 9 to 16 and 18, the charge / discharge efficiency is good. This corresponds to the bending strength of the separator shown in Table 1. In the batteries of Examples 11 to 22, the separator in the inner periphery of the electrode group, which is a concern with batteries using a wound electrode group, It is considered that the occurrence of a fine short circuit due to cracking or the like is well prevented.

  In addition, the batteries of Examples 11 to 22 had a longer time until an abnormality occurred when left at 150 ° C. than the battery of Comparative Example 17 using a conventionally known PE microporous membrane as a separator, and the batteries at Safety is improved.

Claims (9)

  It contains at least a fibrous material that does not substantially deform at 150 ° C. and inorganic particles that do not substantially deform at 150 ° C., and that some of the inorganic particles are scale-like particles having an aspect ratio of 30 or more. A battery separator.   The battery separator according to claim 1, wherein the inorganic particles are silica, mica, boehmite, or alumina.   The battery separator according to claim 1 or 2, wherein a part or all of the inorganic particles are present in the voids of the sheet-like material composed of the fibrous material.   The battery separator according to claim 3, wherein the sheet-like material composed of the fibrous material is a woven fabric or a non-woven fabric.   The battery separator according to any one of claims 1 to 4, further comprising particles that melt at 80 to 130 ° C.   The battery separator according to any one of claims 1 to 5, further comprising particles that can swell in a non-aqueous electrolyte and whose degree of swelling increases with an increase in temperature, and is used in a lithium secondary battery. 7. The battery separator according to claim 6, wherein the particles that can swell in the non-aqueous electrolyte and increase in the degree of swelling with an increase in temperature have a degree of swelling B defined by the following formula of 1.0 or more.
_{B = (V 1 / V 0} ) -1
[In the above formula, V ₀ is the volume of particles (cm ³ ) 24 hours after being introduced into the non-aqueous electrolyte at 25 ° C., and V ₁ is 24 after being introduced into the non-aqueous electrolyte at 25 ° C. The temperature of the non-aqueous electrolyte is raised to 120 ° C. after time, and the volume (cm ³ ) of the particles after 1 hour at 120 ° C. is meant. ]   It has the negative electrode containing the active material which can occlude / release lithium at least, the positive electrode containing the active material which can occlude / release lithium, and the battery separator in any one of Claims 1-7 characterized by the above-mentioned. Lithium secondary battery.   The lithium secondary battery according to claim 8, wherein the battery separator is integrated with at least one of the positive electrode and the negative electrode.