JP2011181493A - Nonaqueous electrolyte secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-aqueous electrolyte secondary battery excellent in safety at high temperature and having good productivity.
A non-aqueous electrolyte secondary comprising: a positive electrode, a negative electrode, and an electrode winding body in which two separators A and B interposed between the positive electrode and the negative electrode are overlapped and wound; and a non-aqueous electrolyte Among the two separators, the separator A is a porous layer mainly composed of a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin and a filler having a heat resistant temperature of 150 ° C. or higher. The non-aqueous electrolyte secondary battery is a multi-layered separator having a porous layer (II), and the separator B is a microporous membrane made of polyolefin.
[Selection] Figure 2

Description

  The present invention relates to a non-aqueous electrolyte secondary battery that has excellent safety at high temperatures and good productivity.

  In a nonaqueous electrolyte secondary battery, for example, a high capacity is required. For example, a positive electrode, a negative electrode, and two separators interposed between them are stacked and wound in a spiral shape. A structure in which the electrode body is housed in a battery container such as an outer can or a laminated film outer body is generally used.

  The two separators related to the wound electrode body of the non-aqueous electrolyte secondary battery are usually of the same configuration, but those having different characteristics are used to make the non-aqueous electrolyte. A technique for improving various characteristics of the electrolyte secondary battery has also been proposed (Patent Document 1).

JP 2005-93078 A

  By the way, in the current nonaqueous electrolyte secondary battery, a polyolefin microporous film having a thickness of, for example, about 20 to 30 μm is used as a separator. 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.

  For such a separator, for example, a wet and biaxially stretched film is often used to increase porosity and improve 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 secured by the stretching. However, such a stretched film has increased crystallinity, and the shutdown temperature has also increased to a temperature close to the thermal runaway temperature of the battery. For this reason, the thermal runaway region is reached before the shutdown, causing thermal contraction of the separator, which may cause a short circuit between the positive electrode and the negative electrode.

  The safety at high temperatures of conventional non-aqueous electrolyte secondary batteries is also at a level that does not cause any practical problems in many applications. However, as the application field of non-aqueous electrolyte secondary batteries expands, the safety exceeding conventional levels will increase. It may be necessary. Therefore, for example, there is a need for development of a technology that can meet such demands without significantly reducing battery productivity.

  This invention is made | formed in view of the said situation, The objective is to provide the nonaqueous electrolyte secondary battery which is excellent in safety | security at the time of high temperature, and favorable productivity.

  The non-aqueous electrolyte secondary battery of the present invention that has achieved the above object has a positive electrode, a negative electrode, and an electrode winding in which two separators A and B interposed between the positive electrode and the negative electrode are overlapped and wound A non-aqueous electrolyte secondary battery including a body and a non-aqueous electrolyte, wherein the separator A of the two separators includes a porous layer (I) made of a microporous film mainly composed of a thermoplastic resin. A separator having a multilayer structure having a porous layer (II) mainly containing a filler having a heat resistant temperature of 150 ° C. or higher, and the separator B is a microporous membrane made of polyolefin.

  ADVANTAGE OF THE INVENTION According to this invention, the nonaqueous electrolyte secondary battery excellent in the safety | security at high temperature and productivity can be provided.

It is a perspective view which represents typically an example of the electrode winding body which concerns on the nonaqueous electrolyte secondary battery of this invention. It is a cross-sectional view of the electrode winding body shown in FIG. It is a figure which shows typically an example of the nonaqueous electrolyte secondary battery of this invention, (a) is the top view, (b) is the fragmentary longitudinal cross-sectional view. FIG. 4 is a perspective view of the nonaqueous electrolyte secondary battery shown in FIG. 3.

  1 and 2 schematically show an example of an electrode winding body according to the nonaqueous electrolyte secondary battery of the present invention. FIG. 1 is a perspective view of an electrode winding body, and FIG. 2 is a cross-sectional view thereof. In FIG. 2, for the purpose of facilitating understanding of the structure of the electrode winding body, the positive electrode and the negative electrode are shown separately from the current collector and the electrode mixture layer (the positive electrode mixture layer and the negative electrode mixture layer). In addition, although a certain amount of gap is provided for each winding circumference, in an ordinary battery, the electrode winding body is formed so as to eliminate the gap between components as much as possible.

  The electrode winding body 10 according to the nonaqueous electrolyte secondary battery of the present invention includes a positive electrode 20, a negative electrode 30, and two separators interposed between them [separator A (40) and separator B (50)]. Are stacked and wound in a spiral shape. Reference numeral 21 denotes a lead part for connecting the positive electrode 20 and the external terminal of the battery, and reference numeral 31 denotes a lead part for connecting the negative electrode 30 and the external terminal of the battery.

  The electrode winding body shown in FIGS. 1 and 2 is a flat electrode winding body having a shape crushed in the vertical direction in FIG. 1 (the cross section is flat), but the electrode winding according to the present invention. The body is not limited to such a shape. For example, the body may have a circular cross section, and can have a shape corresponding to the shape of the exterior body to be used.

  As the two separators related to the electrode winding body, a separator composed of a microporous membrane made of polyolefin is generally used. Since such a separator is usually stretched in both the production direction (MD direction) and the direction orthogonal to the production direction (TD direction), for example, when placed under a high temperature, the separator in the MD direction and the TD direction. It contracts greatly in either direction.

  In the electrode winding body, for example, in order to prevent contact between the positive electrode and the negative electrode at both end faces (upper and lower end faces in FIG. 1), a direction perpendicular to the winding direction of the separator (the direction indicated by the arrow in FIG. 1). ) Is made longer than the positive electrode and the negative electrode so that the separator protrudes from the positive electrode and the negative electrode on both end faces of the electrode winding body (not shown in FIG. 1). However, when the inside of the nonaqueous electrolyte secondary battery becomes high temperature, for example, due to contraction in a direction perpendicular to the winding direction of the separator (usually corresponding to the TD direction), for example, both end portions of the electrode winding body There is a possibility that the positive electrode and the negative electrode are in direct contact with each other in the vicinity of the, thereby causing a short circuit.

  Therefore, in the non-aqueous electrolyte secondary battery of the present invention, one of the two separators of the electrode winding body is a porous layer (I) 41 made of a microporous film mainly composed of a thermoplastic resin, A separator A (40) having a multilayer structure having a porous layer (II) 42 mainly containing a filler having a heat resistant temperature of 150 ° C. or higher, and the other is a separator B (50) composed of a microporous membrane made of polyolefin. It was decided that.

  The separator A has a porous layer (II) mainly comprising a filler having a heat resistant temperature of 150 ° C. or more together with a porous layer (I) serving as a base material, and the inside of the non-aqueous electrolyte secondary battery is Even when the temperature of the porous layer (I) is such that the heat shrinks, the shrinkage of the entire separator is suppressed by the action of the porous layer (II). Therefore, in the location where the separator A is disposed, the contact between the positive and negative electrodes is suppressed in the vicinity of both ends of the electrode winding body.

  On the other hand, the separator B has a relatively large thermal contraction rate as compared with the separator A, but when the inside of the nonaqueous electrolyte secondary battery becomes high temperature, the separator A and the separator A Since the part which protruded from the positive / negative electrode with the separator B fuse | melts, the separator A suppresses shrinkage | contraction of the separator B in the direction orthogonal to the winding direction of an electrode winding body. Therefore, in the electrode winding body according to the battery of the present invention, not only at the place where the separator A which is hard to shrink, but also at the place where the separator B which is easy to shrink is arranged, the contact between the positive and negative electrodes is prevented and short-circuited. Can be suppressed.

  The separator B is composed of a microporous membrane made of polyolefin, and does not require the step of forming the porous layer (II) compared to the separator A having the porous layer (I) and the porous layer (II). Therefore, the manufacturing cost can be reduced. Therefore, the nonaqueous electrolyte secondary battery of the present invention can reduce the manufacturing cost and can reduce the productivity as compared to the case where both separators of the electrode winding body are the separator A. It can be suppressed as much as possible.

  According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery that is excellent in safety at high temperatures and has good productivity due to the above-described actions.

  The separator A used in the electrochemical device of the present invention is a porous porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a porous porous body mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. And a layer (II).

  As used herein, “heat-resistant temperature is 150 ° C. or higher” means that deformation such as softening is not observed at least at 150 ° C.

  In the present specification, the term “mainly comprising a thermoplastic resin” in the porous layer (I) means a solid content ratio in the porous layer (I), and the thermoplastic resin is 50% by volume or more. Means. Further, in the porous layer (II) in the present specification, “mainly including a filler having a heat resistant temperature of 150 ° C. or higher” means a solid content ratio in the layer, and 50 volume of filler having a heat resistant temperature of 150 ° C. or higher. % Or more.

  The thermoplastic resin that is the main component of the porous layer (I) of the separator A has an electrical insulation property, is electrochemically stable, and is a non-aqueous electrolyte possessed by a non-aqueous electrolyte secondary battery described in detail later. There is no particular limitation as long as it is a thermoplastic resin that is stable to an electrolyte (non-aqueous electrolyte) and a solvent (details will be described later) used in the manufacture of the separator, but polyethylene (PE), polypropylene (PP), ethylene- Polyolefin such as propylene copolymer; polyester such as polyethylene terephthalate and copolymerized polyester;

  In addition, it is preferable that the separator A has the property (namely, shutdown function) which the hole obstruct | occludes in 80 degreeC or more and 150 degrees C or less (more preferably 100 degreeC or more). Therefore, the porous layer (I) has a melting point, that is, a melting temperature measured using a differential scanning calorimeter (DSC) in accordance with JIS K 7121, of 80 ° C. or higher and 150 ° C. (more preferably 100 ° C. More preferably, it is a single layer microporous film having PE as a main component, or a laminated microporous film in which 2 to 5 layers of PE and PP are laminated. And the like.

When the porous layer (I) is constituted by using a thermoplastic resin having a melting point of 80 ° C. or more and 150 ° C. or less like PE and a thermoplastic resin having a melting point exceeding 150 ° C. like PP, for example, A microporous film formed by mixing PE and a resin having a higher melting point than PE such as PP is used as the porous layer (I), or a resin having a higher melting point than PE such as the PE layer and the PP layer. When the laminated microporous membrane constituted by laminating the layers constituted by the above is used as the porous layer (I), the melting point of the resin (A) constituting the porous layer (I) is 80 ° C. The resin (for example, PE) at 150 ° C. or lower is preferably 30% by mass or more, and more preferably 50% by mass or more.

  As the microporous membrane as described above, for example, a microporous membrane composed of the above-described exemplified thermoplastic resin used in electrochemical elements such as lithium secondary batteries known in the past, that is, solvent extraction An ion-permeable microporous membrane produced by a method, a dry method or a wet stretching method (particularly a wet biaxial stretching method or a dry uniaxial stretching method) can be used.

  Further, the porous layer (I) may contain a filler or the like in order to improve the strength and the like within a range that does not impair the action of imparting the shutdown function to the separator. Examples of the filler that can be used for the porous layer (I) include the same fillers that can be used for the porous layer (II) described later.

The particle diameter of the filler is an average particle diameter, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, preferably 10 μm or less, more preferably 1 μm or less. The average particle diameter of the filler referred to in the present specification is measured by, for example, using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA), dispersing these fine particles in a medium in which the filler is not dissolved. the same is true for the average according to the particle diameter is D _50% [described later porous layer (II) a filler. ].

  By providing the porous layer (I) having the above-described configuration, it becomes easy to provide a shutdown function to the separator, and it is easy to ensure safety when the internal temperature of the nonaqueous electrolyte secondary battery rises. Is possible.

The content of the thermoplastic resin in the porous layer (I) is preferably as follows, for example, in order to make it easier to obtain the shutdown effect. The volume of the thermoplastic resin as a main component in all the constituent components of the porous layer (I) is 50% by volume or more, more preferably 70% by volume or more, and may be 100% by volume. Furthermore, the porosity of the porous layer (II) obtained by the method described later is 20 to 60%, and the volume of the thermoplastic resin is 50% or more of the pore volume of the porous layer (II). It is preferable.

  The filler contained in the porous layer (II) according to the separator A is not particularly limited as long as the heat resistant temperature is 150 ° C. or higher, and various inorganic particles and organic particles can be mentioned.

Specific examples of the constituent material of the inorganic particles include inorganic oxides such as iron oxide, Al ₂ O ₃ (alumina), SiO ₂ (silica), TiO ₂ , BaTiO ₃ , ZrO ₂ ; aluminum nitride, silicon nitride, etc. Inorganic nitrides of the above; poorly soluble ionic crystals such as calcium fluoride, barium fluoride and barium sulfate; covalent bonds such as silicon and diamond; clays such as montmorillonite; Here, the inorganic oxide may be boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, mica, or other mineral resource-derived substances or artificial products thereof. In addition, the surface of a conductive material exemplified by metal, SnO ₂ , conductive oxide such as tin-indium oxide (ITO), carbonaceous material such as carbon black, graphite, etc., is a material having electrical insulation ( For example, the particle | grains which gave the electrical insulation property by coat | covering with the said inorganic oxide etc. may be sufficient. As the inorganic particles, when the battery is configured such that the porous layer (II) faces the positive electrode, the storage property at high temperature and the charge / discharge cycle characteristics can be improved. Therefore, the inorganic oxide particles ( Fine particles) are preferred, and among these, alumina, silica and boehmite are particularly preferred.

  Organic particles (organic powder) include crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, crosslinked styrene-divinylbenzene copolymer, polyimide, melamine resin, phenol resin, benzoguanamine-formaldehyde condensate, etc. Examples thereof include various crosslinked polymer particles and heat-resistant polymer particles such as polysulfone, polyacrylonitrile, aramid, polyacetal, and thermoplastic polyimide. The organic resin (polymer) constituting these organic particles is a mixture, modified body, derivative, or copolymer (random copolymer, alternating copolymer, block copolymer, graft copolymer) of the materials exemplified above. Polymer) or a crosslinked product (in the case of the above-mentioned heat-resistant polymer).

  Moreover, there is no restriction | limiting in particular about the shape of a filler, However, A plate shape is preferable at the point which can raise the mechanical strength of porous layer (II) more.

  As the form of the plate-like filler, the aspect ratio (ratio between the maximum length in the plate-like filler and the thickness of the plate-like filler) is preferably 5 or more, more preferably 10 or more, and preferably 100. Below, more preferably 50 or less. The aspect ratio of the plate-like filler referred to here is a gold scale certified by JIS class 1 by taking an image (5,000 to 10,000 magnifications) taken with a scanning electron microscope (SEM). The maximum length and thickness of each filler are measured and determined as an average value (number average value) for 100 fillers.

  When using a plate-like filler as the filler, only the plate-like filler may be used, or a plate-like filler and a filler having another shape (such as a sphere or an ellipsoid) may be used in combination. In the case where a plate-like filler and a filler of other shapes are used in combination, from the viewpoint of ensuring better the above-mentioned effect due to the use of the plate-like filler, in the total amount of filler contained in the porous layer (II), The plate-like filler is preferably 80% by volume or more, and more preferably 90% by volume or more.

The average particle diameter D _50% of the filler is, for example, preferably 0.01 μm or more, more preferably 0.1 μm or more, and preferably 15 μm or less, more preferably 5 μm or less. preferable. In the case where the filler is a plate-like particle, the particle size indicates the maximum plate diameter.

  The amount of filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is 50% by volume or more in the total volume of the constituent components of the porous layer (II), preferably 70% by volume or more, It is more preferably 80% by volume or more, and further preferably 90% by volume or more. By making the filler in the porous layer (II) high as described above, the mechanical strength of the separator A as a whole can be improved more favorably, and the nonaqueous electrolyte secondary battery becomes high temperature. The occurrence of a short circuit due to direct contact between the positive electrode and the negative electrode can be suppressed more favorably.

  Moreover, the porous layer (II) binds fillers having a heat resistant temperature of 150 ° C. or more, or binds the porous layer (I) and the porous layer (II) as necessary. Therefore, it is preferable to contain an organic binder. From such a viewpoint, the preferred upper limit of the filler amount having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is, for example, a constituent component of the porous layer (II) Is 99.5% by volume. If the amount of the filler having a heat resistant temperature of 150 ° C. or higher in the porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the porous layer (II). In the porous layer (II), the pores of the porous layer (II) are likely to be filled with an organic binder, and the function as a separator may be deteriorated. There exists a possibility that the space | interval may become large too much and the effect which suppresses heat shrink may fall.

  The porous layer (II) preferably contains an organic binder in order to ensure the shape stability of the separator A and to integrate the porous layer (II) and the porous layer (I). Examples of organic binders include ethylene-vinyl acetate copolymers (EVA, those having a structural unit derived from vinyl acetate of 20 to 35 mol%), ethylene-acrylic acid copolymers such as ethylene-ethyl acrylate copolymers, and fluorine-based binders. Rubber, styrene butadiene rubber (SBR), carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinyl pyrrolidone (PVP), cross-linked acrylic resin, polyurethane, epoxy resin, etc. In particular, a heat-resistant binder having a heat-resistant temperature of 150 ° C. or higher is preferably used. As the organic binder, those exemplified above may be used singly or in combination of two or more.

  Among the organic binders exemplified above, highly flexible binders such as EVA, ethylene-acrylic acid copolymer, fluorine-based rubber, and SBR are preferable. Specific examples of such highly flexible organic binders include Mitsui DuPont Polychemical's “Evaflex Series (EVA)”, Nihon Unicar's EVA, Mitsui DuPont Polychemical's “Evaflex-EAA Series (Ethylene). -Acrylic acid copolymer) ", Nippon Unicar EEA, Daikin Industries" DAI-EL Latex Series (Fluororubber) ", JSR" TRD-2001 (SBR) ", Nippon Zeon" BM-400B " (SBR) ".

  When the organic binder is used for the porous layer (II), it can be used in the form of an emulsion dissolved or dispersed in the solvent for the composition for forming the porous layer (II) described later. Good.

  In the separator A, the thickness of the porous layer (II) [when the separator A has a plurality of porous layers (II), the total thickness thereof] makes the above-mentioned actions by the porous layer (II) more effective. From the viewpoint of exhibiting, it is preferably 1 μm or more, and preferably 2 μm or more. However, if the porous layer (II) is too thick, the energy density of the battery may be lowered. Therefore, the thickness of the porous layer (II) is preferably 10 μm or less, and 8 μm or less. Is more preferable.

Further, the thickness of the porous layer (I) [when the separator A has a plurality of porous layers (I), the total thickness thereof. same as below. ] Is the effect of using the porous layer (I) (especially shutdown action)
Is more preferably 6 μm or more, and more preferably 10 μm or more from the viewpoint of more effectively exhibiting. However, if the porous layer (I) is too thick, in addition to the possibility of causing a decrease in the energy density of the battery, the force that the porous layer (I) tends to shrink by heat increases. There is a possibility that the effect of suppressing the overall thermal shrinkage may be reduced. Therefore, the thickness of the porous layer (I) is preferably 25 μm or less, more preferably 20 μm or less, and further preferably 14 μm or less.

The porosity of the separator A as a whole is preferably 30% or more in a dried state in order to ensure the amount of electrolyte retained and to improve ion permeability. On the other hand, from the viewpoint of securing the strength of the separator A and preventing internal short circuit, the porosity of the separator A is preferably 70% or less in a dry state. The porosity of the separator A: P (%) is calculated by obtaining the sum of each component i from the thickness of the separator A, the mass per area, and the density of the constituent components using the following formula (1). it can.
P = {1−m / [(t−t _m ) × (Σa _i ρ _i ) + (t _m × ρ _m )]} × 100 (1)
Here, in the above formula, a _i : ratio of component i, ρ _i : density of component i (g / cm ³ ), m: mass per unit area of separator A (g / cm ² ), t: separator A Thickness (cm), t _m : thickness (cm) of the porous layer (II), ρ _m : density of components constituting the porous layer (II) (g / cm ³ ).

In the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (I), t is the thickness (cm) of the porous layer (I), and tm = 0 ( cm), the porosity: P (%) of the porous layer (I) can also be obtained using the above formula (1). The porosity of the porous layer (I) determined by this method is preferably 30 to 70%.

Furthermore, in the formula (1), m is the mass per unit area (g / cm ² ) of the porous layer (II), and t is the thickness (cm) of the porous layer (II), The porosity: P (%) of the porous layer (II) can also be obtained using the formula (1). The porosity of the porous layer (II) obtained by this method is preferably 20 to 60%.

  The separator A is, for example, a composition for forming a porous layer (II) containing a filler having a heat resistant temperature of 150 ° C. or higher (a liquid composition such as a slurry) to form the porous layer (I). It can be produced by coating the surface of the microporous membrane and drying it at a predetermined temperature to form the porous layer (II).

  The composition for forming the porous layer (II) contains an organic binder or the like, if necessary, in addition to a filler having a heat resistant temperature of 150 ° C. or higher, and these are dispersed in a solvent (including a dispersion medium; the same applies hereinafter). It is a thing. The organic binder can be dissolved in a solvent. The solvent used in the composition for forming the porous layer (II) is not particularly limited as long as it can uniformly disperse the filler and can uniformly dissolve or disperse the organic binder. Common organic solvents such as furans such as hydrogen and tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone are preferably used. In addition, for the purpose of controlling the interfacial tension, alcohols (ethylene glycol, propylene glycol, etc.) or various propylene oxide glycol ethers such as monomethyl acetate may be appropriately added to these solvents. In addition, when the organic binder is water-soluble or used as an emulsion, water may be used as a solvent. In this case, alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) are appropriately added. It is also possible to control the interfacial tension.

  The composition for forming the porous layer (II) preferably has a solid content including a filler having an heat resistant temperature of 150 ° C. or higher and an organic binder, for example, 10 to 80% by mass.

  In addition, the porous layer (II) forming composition is applied onto a substrate such as a film or a metal foil, dried at a predetermined temperature, and then peeled off from the substrate as necessary to form the porous layer (II). It is also possible to manufacture a separator by forming a porous film, and bonding the porous film and a microporous film for forming the porous layer (I) together. In this case, in order to integrate the microporous membrane for forming the porous layer (I) and the porous membrane to be the porous layer (II), for example, the porous layer (I) and the porous layer ( It is possible to use a method of superimposing II) and pasting them together using a roll press or the like.

  In the separator A, the porous layer (I) and the porous layer (II) do not have to be one each, and a plurality of layers may be in the separator. For example, a configuration in which the porous layer (I) is disposed on both sides of the porous layer (II) or a configuration in which the porous layer (II) is disposed on both sides of the porous layer (I) may be employed. However, increasing the number of layers may increase the thickness of the separator A, leading to an increase in the internal resistance of the battery and a decrease in energy density. Therefore, it is not preferable to increase the number of layers. The total number of layers of the porous layer (I) and the porous layer (II) is preferably 5 or less.

  Among the two separators used in the electrode winding body according to the nonaqueous electrolyte secondary battery of the present invention, the separator B is constituted by a microporous membrane made of polyolefin, and specifically, for example, Those composed of polyolefins such as PE, PP, and ethylene-propylene copolymer are listed.

  In addition, the separator B may have a single layer structure made of the exemplified polyolefin, or may have a multilayer structure. Examples of the separator having a multilayer structure include, for example, a separator having a two-layer structure having a PE layer and a PP layer; a separator formed by sequentially laminating a PE layer / PP layer / PE layer, and a PP layer / PE layer / PP layer. For example, a separator having a three-layer structure in which are sequentially stacked.

  The separator B has a melting point, that is, a melting temperature measured by using a differential scanning calorimeter (DSC) of 80 according to JIS K 7121 from the viewpoint of ensuring a satisfactory shutdown function of the separator. It is preferable to contain a polyolefin having a temperature of 150 ° C. or more and 150 ° C. (more preferably 100 ° C. or more), and more specifically, it preferably contains PE.

  In the case where the separator A or the separator B is configured by using a polyolefin having a melting point of 80 ° C. or more and 150 ° C. or less like PE and a polyolefin having a melting point exceeding 150 ° C. like PP, for example, PE and When a separator A or separator B is formed by mixing a resin having a higher melting point than PE such as PP, or a layer composed of a PE layer and a layer made of a resin having a higher melting point than PE such as a PP layer is laminated. In the case of constituting the separator B having a multilayer structure, the polyolefin (for example, PE) having a melting point of 80 ° C. or more and 150 ° C. or less is preferably 30% by mass or more and 50% by mass in the polyolefin constituting the separator B. % Or more is more preferable.

  As the separator B, one produced by the same method as the porous layer (I) according to the separator A can be used.

  The thickness of the separator B is preferably 5 μm or more and more preferably 10 μm or more from the viewpoint of better separating the positive electrode and the negative electrode. On the other hand, if the separator B is too thick, the energy density of the battery may be lowered. Therefore, the thickness is preferably 30 μm or less, and more preferably 25 μm or less.

As the positive electrode according to the battery of the present invention, a positive electrode used in a conventionally known non-aqueous electrolyte secondary battery, for example, a positive electrode containing an active material capable of occluding and releasing Li ions can be used. . 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); and the like, and these positive electrode active materials include known conductive assistants (carbon materials such as carbon black) For example, a positive electrode mixture to which a binder such as polyvinylidene fluoride (PVDF) is appropriately added and finished into a molded body (that is, a positive electrode mixture layer) using a current collector as a core material 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.

  For the negative electrode according to the battery of the present invention, a negative electrode used in a conventionally known non-aqueous electrolyte secondary battery, for example, a negative electrode containing an active material capable of occluding and releasing Li ions can be used. . 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 and In and alloys thereof, 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 obtained by using the above-mentioned various alloys and lithium metal foils alone or those obtained by forming the alloy or lithium metal layer on a current collector.

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

  As with the lead portion on the negative electrode side, the negative electrode layer (including a layer having a negative electrode active material and a negative electrode mixture layer) is usually formed on a part of the current collector during the preparation of the negative electrode. Without leaving the exposed portion of the current collector, it is provided as a lead portion. However, the lead portion on the negative electrode side is not necessarily integrated with the current collector from the beginning, and may be provided by connecting a copper foil or the like to the current collector later.

  In addition, in the electrode winding body according to the battery of the present invention, as shown in FIG. 2, the separator A (40), which is less likely to heat shrink, out of the separator A (40) and the separator B (50) It is preferable to arrange on the side. When the non-aqueous electrolyte secondary battery is exposed to a high temperature, the temperature becomes higher on the outer side of the electrode winding body, and the separator tends to shrink. Therefore, by making the separator A, which is more difficult to heat-shrink, to be a separator on the outer peripheral side of the electrode winding body, the heat shrinkage of the separator on the outside of the electrode winding body can be better suppressed, and the safety can be further improved. A high battery can be obtained.

  Moreover, in the electrode winding body which concerns on the battery of this invention, the length of the direction orthogonal to the winding direction in the electrode winding body of the separator A and the separator B is set in an electrode winding body among a positive electrode and a negative electrode. The length in the direction orthogonal to the winding direction is preferably longer by 0.5 mm or more and more preferably by 1.0 mm or more than the length of the longer one (usually the negative electrode). By doing in this way, when the inside of a battery becomes high temperature, the separator A and the separator B are fuse | melted favorably in the vicinity of the both end surfaces of an electrode winding body, and the shrinkage | contraction of the separator B is suppressed more favorably can do. However, it is preferable that the length of the separator A and the separator B in the direction orthogonal to the winding direction in the electrode winding body is not too long. Specifically, of the positive electrode and the negative electrode, the electrode winding body It is preferable that the difference from the longer length in the direction orthogonal to the winding direction is 3.0 mm or less.

  The non-aqueous electrolyte secondary battery of the present invention is only required to use the above-described electrode winding body, and there are no particular restrictions on other configurations and structures, and conventionally known non-aqueous electrolyte secondary batteries and Similar configurations and structures can be employed.

  Examples of the form of the non-aqueous electrolyte secondary battery of the present invention include a tubular shape (such as a square tubular 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.

As the non-aqueous electrolyte according to the battery of the present invention, for example, a solution (non-aqueous electrolyte) in which a lithium salt is dissolved in an organic solvent is used. The lithium salt is not particularly limited as long as it dissociates in a solvent to form Li ⁺ ions and does not cause a side reaction such as decomposition in a voltage range used as a battery. For example, LiClO ₄ , LiPF ₆ , LiBF ₄ , LiAsF ₆ , Li
Inorganic lithium salts such as SbF 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 fluoroalkyl Organolithium salts such as a group] and the like can be used.

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

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

  Also, instead of the 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.

  Further, a polymer material that contains the 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, vinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyacrylonitrile (PAN), polyethylene oxide, polypropylene oxide, ethylene oxide-propylene Examples of the host polymer capable of forming a gel electrolyte such as an oxide copolymer, a crosslinked polymer having an ethylene oxide chain in the main chain or a side chain, and a crosslinked poly (meth) acrylic acid ester can be given.

  The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as those in which conventionally known non-aqueous electrolyte 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.

Example 1
<Preparation of positive electrode>
85 parts by mass of LiCoO _{2 as a} positive electrode active material, 10 parts by mass of acetylene black as a conductive additive, and 5 parts by mass of PVDF as a binder are uniformly mixed with N-methyl-2-pyrrolidone (NMP) as a solvent. It mixed so that positive electrode mixture containing paste might be prepared. This paste is intermittently applied on both sides of a 15 μm thick aluminum foil serving as a current collector so that the coating length is 320 mm on the front surface and 250 mm on the back surface, dried, and then calendered to a total thickness of 150 μm. Thus, the thickness of the positive electrode material mixture layer was adjusted and cut so as to have a width of 43 mm to produce a positive electrode having a length of 340 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.

<Production of negative electrode>
Moreover, the 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 so as to be uniform using NMP as a solvent. This negative electrode mixture-containing paste is intermittently applied to both sides of a 10 μm-thick current collector made of copper foil, dried, and then calendered to adjust the thickness of the negative electrode mixture layer so that the total thickness is 142 μm. And it cut | disconnected so that it might become width 45mm, and produced the negative electrode. Further, a tab was welded to the exposed portion of the copper foil of the negative electrode to form a lead portion.

<Preparation of separator A>
An organic binder SBR emulsion (solid content ratio 40% by mass): 150 g and water: 6000 g were placed in a container and stirred at room temperature until evenly dispersed. Boehmite powder (plate shape, average particle size 1 μm, aspect ratio 10): 2000 g, which is a filler having a heat resistance temperature of 150 ° C. or higher, was added to this dispersion in 3 portions, and the mixture was uniformly stirred at 2800 rpm for 5 hours with a disper. A slurry [a slurry for forming a porous layer (II), a solid content ratio of 49.9% by mass] was prepared. While taking a PE microporous membrane [porous layer (I): thickness 12 μm, porosity 40%, puncture strength 400 gf, PE melting point 135 ° C.] produced by a wet biaxial stretching method, The slurry A was applied by a micro gravure coater and dried to form a porous layer (II) having a thickness of 4.0 μm, thereby preparing a separator A.

The porous layer (II) in the obtained separator A had a mass per unit area of 5.2 g / m ² . Further, the volume content of the plate boehmite in the porous layer (II) of this separator was 88% by volume, and the porosity of the porous layer (II) was 55%.

<Production of wound electrode body>
As the separator B, a microporous membrane made of PE (thickness 16 μm, porosity 40%) prepared by a wet biaxial stretching method was prepared.

The positive electrode, the negative electrode, and the separator A and the separator B are wound in a flat shape by overlapping and winding in the order shown in FIG. 2 (that is, in the order in which the separator A is on the outer peripheral side of the separator B). The electrode winding body was produced by crushing.

<Battery assembly>
The electrode winding body was put in an aluminum outer can having a thickness of 6 mm, a height of 50 mm, and a width of 34 mm, and a nonaqueous electrolyte (LiPF ₆ in a solvent in which ethylene carbonate and ethyl methyl carbonate were mixed at a volume ratio of 1: 2). Was injected at a concentration of 1.2 mol / l) and sealing was performed to obtain a nonaqueous electrolyte secondary battery having the structure shown in FIG. 3 and the appearance shown in FIG.

  Here, the battery shown in FIGS. 3 and 4 will be described. FIG. 3A is a plan view, and FIG. 3B is a partial cross-sectional view thereof. As shown in FIG. 102 is spirally wound through the separator 103 as described above, and then pressed so as to be flattened to form a flat electrode winding body 106, and the non-aqueous electrolyte is applied to the rectangular tube-shaped outer can 104. Is housed together. However, in FIG. 3, in order to avoid complication, a metal foil, a non-aqueous electrolyte, and the like as a current collector used for manufacturing the positive electrode 101 and the negative electrode 102 are not illustrated. Also, the separator layers are not shown separately.

  The outer can 104 is made of an aluminum alloy and constitutes an outer casing of the battery, and the outer can 104 also serves as a positive electrode terminal. An insulator 5 made of a PE sheet is disposed at the bottom of the outer can 104. From the flat electrode winding body 106 made of the positive electrode 101, the negative electrode 102, and the separator 103 (separator A and separator B), the positive electrode 101 and A positive electrode lead body 107 and a negative electrode lead body 108 connected to one end of the negative electrode 102 are drawn out. A stainless steel terminal 111 is attached to a sealing lid plate 109 made of aluminum alloy for sealing the opening of the outer can 104 via a PP insulating packing 110, and an insulator 112 is attached to the terminal 111. A stainless steel lead plate 113 is attached.

  The lid plate 109 is inserted into the opening of the outer can 104, and the joint of the two is welded to seal the opening of the outer can 104, thereby sealing the inside of the battery. Further, in the battery of FIG. 3, a non-aqueous electrolyte injection port 114 is provided in the lid plate 109, and a sealing member is inserted into the non-aqueous electrolyte injection port 114, for example, laser welding or the like. (See FIG. 3 and FIG. 4, in practice, the non-aqueous electrolyte inlet 114 is actually sealed with the non-aqueous electrolyte inlet.) Although it is a member, for ease of explanation, it is shown as a non-aqueous electrolyte inlet 114). Further, the lid plate 109 is provided with a cleavage vent 115 as a mechanism for discharging the internal gas to the outside when the temperature of the battery rises.

  In the battery of Example 1, the outer can 104 and the lid plate 109 function as positive terminals by directly welding the positive electrode lead body 107 to the lid plate 109, and the negative electrode lead body 108 is welded to the lead plate 113. When the negative electrode lead body 108 and the terminal 111 are electrically connected via the lead plate 113, the terminal 111 functions as a negative electrode terminal. However, depending on the material of the outer can 4 or the like, the sign may be reversed. There is also.

  4 is a perspective view schematically showing the external appearance of the battery shown in FIG. 3. FIG. 4 is shown for the purpose of showing that the battery is a square battery, and FIG. FIG. 1 schematically shows a battery, and only specific members of the battery are shown. Also in FIG. 3, the inner peripheral portion of the electrode body is not cross-sectional.

Example 2
Except that the separator B is positioned on the outer peripheral side of the separator A, an electrode winding body is prepared in the same manner as in Example 1, and the same procedure as in Example 1 is performed except that this electrode winding body is used. A non-aqueous electrolyte secondary battery was produced.

Example 3
Example 1 except that a microporous membrane made of PE produced by a dry uniaxial stretching method [porous layer (I): thickness 12 μm, porosity 40%, puncture strength 250 gf, PE melting point 135 ° C.] A separator A was produced in the same manner. Thereafter, a nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

Example 4
An organic binder SBR emulsion (solid content ratio 40% by mass): 150 g and water: 6000 g were placed in a container and stirred at room temperature until evenly dispersed. Alumina powder (granular, average particle size 2 μm), which is a filler having a heat resistant temperature of 150 ° C. or higher, was added to this dispersion in 3 portions, and the mixture was stirred with a disper at 2800 rpm for 5 hours to obtain a uniform slurry [porous layer (II) slurry for formation, solid content ratio 56.3 mass%] was prepared. Thereafter, a separator A was produced in the same manner as in Example 1.

The porous layer (II) in the obtained separator A had a mass per unit area of 6.8 g / m ² . Further, the volume content of the plate boehmite in the porous layer (II) of this separator was 88% by volume, and the porosity of the porous layer (II) was 55%. A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this separator A was used.

Comparative Example 1
Except that the two separators were the same separator B as that used in Example 1, an electrode winding body was prepared in the same manner as in Example 1, and this electrode winding body was used except that A nonaqueous electrolyte secondary battery was produced in the same manner as in Example 1.

  The heating test which puts the nonaqueous electrolyte secondary battery of Examples 1-4 and the comparative example 1 in a thermostat, heats up at a speed | rate of 5 degree-C / min from 25 degreeC to 150 degreeC, and hold | maintains at 150 degreeC for 3 hours after that. The maximum temperature reached on the surface of each battery was measured. These results are shown in Table 1 together with the configuration of the separator in the electrode winding body according to the battery.

  As is clear from Table 1, the nonaqueous electrolyte secondary batteries of Examples 1 to 4 each having the electrode winding body using the separator A and the separator B in combination have two separators related to the electrode winding body. Compared with the battery of Comparative Example 1 which is the separator B, the maximum temperature reached on the battery surface in the heating test is low, and the safety is high. Further, in the batteries of Examples 1, 3, and 4 in which the higher heat-resistant separator A was arranged on the outer peripheral side of the electrode winding body, this separator A was arranged on the inner peripheral side of the electrode winding body. Compared with the battery of Example 2, the maximum temperature reached on the surface of the battery in the heating test is lower, and the safety is better.

10, 106 Electrode wound body 20, 101 Positive electrode 30, 102 Negative electrode 40 Separator A
50 Separator B
51 Porous layer (I)
52 Porous layer (II)

Claims (2)

A non-aqueous electrolyte secondary battery comprising: a positive electrode, a negative electrode, and an electrode winding body in which two separators A and B interposed between the positive electrode and the negative electrode are overlapped and wound; and a non-aqueous electrolyte. ,
Of the two separators, the separator A includes a porous layer (I) composed of a microporous film mainly composed of a thermoplastic resin, and a porous layer (II) mainly composed of a filler having a heat resistant temperature of 150 ° C. or higher. A non-aqueous electrolyte secondary battery, wherein the separator B is a microporous membrane made of polyolefin.   The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the separator A is disposed on the outer peripheral side of the electrode winding body with respect to the separator B.

Images