JP2013145693A - Separator and lithium-ion secondary battery - Google Patents

Abstract

A separator with good shutdown characteristics and a highly safe lithium ion secondary battery using the separator are provided.
A separator has a first porous layer made of polypropylene and a second porous layer made of polyethylene. Further, the separator 30 includes composite oxide particles 36 containing Ca, Na, Al, and Si between the first porous layer 31 and the second porous layer 32.
[Selection] Figure 3

Description

  The present invention relates to a separator and a lithium ion secondary battery using the separator.

  In recent years, lithium ion secondary batteries have been used as driving power sources for portable electronic devices such as hybrid vehicles, notebook computers, and video camcorders. Patent Document 1 discloses a separator having a porous resin base material (resin porous layer) in which a porous polyethylene layer and a porous polypropylene layer are laminated as a separator of a lithium ion secondary battery.

JP 2011-71009 A

  In Patent Document 1, when the above-described separator reaches a certain temperature range (typically, the melting point of the resin constituting the separator), the ion conduction path is interrupted to stop the battery reaction. And exhibiting a function to prevent thermal runaway of the battery (shutdown function).

  For example, when the temperature in the battery reaches the melting point of polyethylene (porous layer) constituting the separator, the porous layer made of polyethylene is melted, so that fine pores (ionic conductive paths) of the porous layer are formed. Block (disappear). Thereby, ion conduction between the positive and negative electrodes through the separator (resin porous layer) is blocked, and the battery reaction is stopped. As a result, thermal runaway of the battery is prevented and the safety of the battery is ensured.

  By the way, when the porous layer made of polyethylene is melted, the fine pores of the porous layer are blocked (disappeared), so that the thickness of the porous layer is reduced. At this time, the thickness of the porous layer may be reduced non-uniformly, resulting in a location where the thickness becomes extremely thin. For this reason, good shutdown characteristics may not be obtained. For example, when the battery temperature reaches the shutdown temperature (for example, the melting point of polyethylene + α) due to overcharge, ion conduction between the positive and negative electrodes may not be properly interrupted (current interrupt). The reason for this is considered to be that ions can move at a location where the thickness is extremely reduced by melting.

  This invention is made | formed in view of this problem, Comprising: It aims at providing the lithium ion secondary battery with high safety | security which used this separator and the separator with favorable shutdown characteristics.

  One aspect of the present invention is a separator having a first porous layer made of polypropylene and a second porous layer made of polyethylene, between the first porous layer and the second porous layer, The separator includes composite oxide particles containing Ca, Na, Al, and Si.

  The separator described above includes composite oxide particles containing Ca, Na, Al, and Si between the first porous layer made of polypropylene and the second porous layer made of polyethylene. By disposing the composite oxide particles between the first porous layer and the second porous layer, the shutdown characteristics of the separator can be improved.

  Specifically, by disposing the composite oxide particles between the first porous layer and the second porous layer, the second porous layer can be finely evacuated by melting the second porous layer. When the thickness of the porous layer is reduced by closing (disappearing) the pores (the pores are ion conductive paths), the thickness of the second porous layer can be reduced uniformly.

  As a result, it is possible to prevent the occurrence of an extremely thin portion in the second porous layer, and the shutdown resistance of the separator (the function of shutting down the pores of the second porous layer due to melting of the second porous layer) Can be increased). The greater the shutdown resistance, the higher the ability to prevent the movement of ions (the ability to cut off the current), so that the above separator is a separator with good shutdown characteristics.

  The separator described above may further have a third porous layer made of polypropylene in addition to the first porous layer made of polypropylene and the second porous layer made of polyethylene. In this case, the composite oxide particles may be arranged between the second porous layer and the third porous layer in addition to the interlayer between the first porous layer and the second porous layer.

  Moreover, as a form which arrange | positions the said composite oxide particle between the layers of a 1st porous layer and a 2nd porous layer, for example, the said composite oxide is provided between the layers of a 1st porous layer and a 2nd porous layer. The form which arrange | positions only particle | grains is mentioned. Further, a porous layer (a porous layer made of polyethylene or polypropylene) containing the composite oxide particles may be interposed between the first porous layer and the second porous layer.

  Furthermore, the separator is a porous layer made of polyethylene or polypropylene and containing the composite oxide particles in the layer, the first porous layer and the second porous layer, By interposing between these layers, a separator in which the composite oxide particles are arranged between the first porous layer and the second porous layer is preferable.

  The separator described above is a porous layer made of polyethylene resin or polypropylene resin, and the porous layer containing the composite oxide particles in the layer is interposed between the first porous layer and the second porous layer. I am letting. By arranging the composite oxide particles between the first porous layer and the second porous layer in such a form, the composite oxide particles are converted into the first porous layer and the second porous layer. It can arrange | position in the state disperse | distributed uniformly over the whole surface between layers. For this reason, in the above-described separator, when the thickness of the porous layer decreases while the fine pores of the second porous layer disappear (clog) due to melting of the second porous layer, The thickness can be reduced more uniformly. Therefore, the separator has a good shutdown characteristic.

  The porous layer containing the composite oxide particles in the layer is produced, for example, as follows. First, a polyethylene resin is melted, and the composite oxide particles are dispersed in the polyethylene solution to prepare a paste. By molding (curing) this paste into a sheet, a polyethylene resin layer in which the composite oxide particles are uniformly dispersed is obtained. Thereafter, the polyethylene resin layer is subjected to processing such as stretching (processing to make it porous), whereby a porous layer in which the composite oxide particles are uniformly dispersed can be obtained. Therefore, by interposing this porous layer between the first porous layer and the second porous layer, the composite oxide particles are spread over the entire surface between the first porous layer and the second porous layer. It can arrange | position in the state disperse | distributed uniformly over.

Furthermore, in any one of the separators described above, the number of the composite oxide particles is 1 × 10 ⁴ μm ² per unit area between the first porous layer and the second porous layer. A separator having a value in the range of 5 to 50 is preferable.
In other words, any one of the separators described above, wherein the composite oxide particles are placed in a unit area of 1 × 10 ⁴ μm ² between the first porous layer and the second porous layer (that is, (Per unit area of 100 μm square), it is preferable that the separator is formed by arranging a number in the range of 5 to 50.

  By disposing the composite oxide particles at the ratio as described above, the shutdown resistance of the separator (resistance when the shutdown function is exhibited by melting of the second porous layer) can be further increased. Therefore, the separator described above is a separator having excellent shutdown characteristics.

  Furthermore, in any of the separators described above, the composite oxide particles may have an average particle size of 1 to 4 μm.

  By setting the average particle size of the composite oxide particles to a value within the range of 1 to 4 μm, the shutdown resistance of the separator can be further increased. Therefore, the separator described above is a separator having excellent shutdown characteristics.

  Furthermore, any of the above separators may be a separator having a heat-resistant porous layer laminated on the surface of the first porous layer or the second porous layer.

  By providing a heat-resistant porous layer on the surface of the first porous layer or the second porous layer, even if a fine short circuit occurs between the positive and negative electrodes due to foreign substances penetrating the separator, the subsequent expansion of the short circuit is prevented. can do.

  Specifically, for example, in the case of a separator composed only of a resin porous layer (first porous layer and second porous layer) (that is, a separator having no heat-resistant porous layer), foreign matter or the like penetrates the separator. As a result, when the electrical insulation of the separator is locally broken and a fine short-circuit occurs between the positive and negative electrodes, there is a possibility that the through-holes of the resin porous layer are expanded due to heat generation at that portion. As a result, the short circuit between the positive and negative electrodes may be enlarged.

  On the other hand, by providing the heat resistant porous layer on the surface of the first porous layer or the second porous layer, it is possible to prevent the short circuit between the positive and negative electrodes from being expanded due to foreign matters or the like. The heat-resistant porous layer (specifically, the heat-resistant fine particles constituting the heat-resistant porous layer) has a melting point much higher than that of the resin porous layer, so even when a local short circuit as described above occurs. The through-holes of the heat resistant porous layer do not expand due to heat generation in the portion. Thereby, the expansion of the short circuit between positive and negative electrodes by a foreign material etc. can be prevented by the heat resistant porous layer.

  Moreover, by providing the heat resistant porous layer on the surface of the first porous layer or the second porous layer, the temperature of the separator has reached the shutdown temperature (the melting point of the second porous layer + the temperature of α, for example, 150 ° C.). Even in this case, thermal contraction in the surface direction (direction orthogonal to the stacking direction) can be suppressed for the resin porous layer (the first porous layer and the second porous layer). The heat-resistant porous layer (specifically, the heat-resistant fine particles constituting the heat-resistant porous layer) has a much higher melting point than the resin porous layer, so even when the temperature of the separator reaches the shutdown temperature, It is because it hardly heat shrinks.

  By this heat-resistant porous layer, the thermal contraction of the resin porous layer (the first porous layer and the second porous layer) in the surface direction is suppressed, thereby maintaining the electrical insulation between the positive and negative electrodes by the separator. be able to. Thereby, the reliability of the shutdown function of the separator can be improved, and as a result, the shutdown characteristics can be improved.

  Note that the shutdown temperature is a temperature at which the shutdown function of the separator is reliably exhibited. Specifically, it is a temperature at which it is determined that the pores of the second porous layer are almost completely closed by melting of the second porous layer made of polyethylene, and the melting point of the second porous layer (the melting point of polyethylene). ) + Α temperature. In the present application, the shutdown temperature is set to 150 ° C.

  The heat resistant porous layer is a porous layer having heat resistant fine particles and a binder. Examples of the heat-resistant fine particles include inorganic fillers such as alumina, boehmite, and magnesium hydroxide.

  Another aspect of the present invention is a lithium ion secondary battery having a separator interposed between a positive electrode and a negative electrode, wherein the separator is a lithium ion secondary battery that is any one of the separators.

The above-described lithium ion secondary battery includes any of the separators described above as a separator interposed between the positive electrode and the negative electrode. For this reason, when the temperature in the battery (the temperature of the separator) reaches the shutdown temperature, the ion conduction between the positive and negative electrodes can be appropriately cut off (current cut off), and as a result, the battery can be prevented from thermal runaway. be able to.
Therefore, the above-described lithium ion secondary battery is a highly safe lithium ion secondary battery.

It is a longitudinal cross-sectional view of the lithium ion secondary battery concerning Examples 1-3. It is the W section enlarged view of Drawing 1, and is equivalent to the expanded sectional view of an electrode body. 1 is an enlarged cross-sectional view of a separator according to Example 1. FIG. It is an expanded sectional view of the separator concerning Example 2. FIG. It is an expanded sectional view of the separator concerning Example 3. It is an expanded sectional view of the separator concerning a comparative example. It is the schematic of the apparatus which measures the shutdown resistance of a separator. It is sectional drawing of the sample measured with the measuring apparatus. It is a correlation diagram of the number of composite oxide particles and SD resistance value. It is a correlation diagram of the particle size of composite oxide particles and the SD resistance value.

Next, Example 1 of the present invention will be described.
The lithium ion secondary battery 1 of Example 1 is a cylindrical lithium ion secondary battery as shown in FIG. The lithium ion secondary battery 1 includes an electrode body 40 and a battery case 60 that accommodates the electrode body 40.

  The battery case 60 is a cylindrical battery case, and includes a metal battery can 61 formed by drawing a metal plate into a bottomed cylindrical shape and a metal battery lid 62 having a disk shape ( (See FIG. 1). The battery lid 62 is caulked at the opening 61 b of the battery can 61 with an annular gasket 69 made of an electrically insulating resin interposed between the battery can 61 and seals the battery can 61. . As a result, the battery can 61 and the battery lid 62 that house the electrode body 40 are integrated while the battery can 61 and the battery lid 62 are electrically insulated by the gasket 69, thereby forming the battery case 60. Yes.

  The electrode body 40 includes a positive electrode 10, a negative electrode 20, and a separator 30 interposed between the positive electrode 10 and the negative electrode 20. Specifically, the positive electrode 10, the negative electrode 20, and the separator 30 are cylindrical wound electrode bodies wound around a winding shaft 45.

  The positive electrode 10 has a positive electrode current collector foil 11 and a positive electrode mixture layer 13 coated on the surface (both sides) (see FIG. 2). Specifically, as the positive electrode mixture layer 13, the first positive electrode mixture layer 13 b applied to the first surface 11 b of the positive electrode current collector foil 11 and the second surface 11 c of the positive electrode current collector foil 11 are applied. The second positive electrode mixture layer 13c is provided.

In Example 1, an aluminum foil having a thickness of 15 μm is used as the positive electrode current collector foil. The positive electrode mixture layer 13 is composed of a positive electrode active material, a conductive material, and a binder. In Example 1, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ is used as the positive electrode active material. Further, acetylene black is used as the conductive material. Moreover, PVdF is used as a binder.

  The negative electrode 20 has a negative electrode current collector foil 21 and a negative electrode mixture layer 23 coated on the surface (both sides). Specifically, as the negative electrode mixture layer 23, the first negative electrode mixture layer 23 b applied to the first surface 21 b of the negative electrode current collector foil 21 and the second surface 21 c of the negative electrode current collector foil 21 are applied. The second negative electrode mixture layer 23c is provided.

  In Example 1, a copper foil having a thickness of 10 μm is used as the negative electrode current collector foil 21. The negative electrode mixture layer 23 is composed of a negative electrode active material, a binder, and a thickener. In Example 1, amorphous coated graphite is used as the negative electrode active material. Further, SBR (styrene butadiene rubber) is used as the binder. Moreover, CMC (carboxymethylcellulose) is used as a thickener.

  As illustrated in FIG. 3, the separator 30 includes a first porous layer 31 made of polypropylene, a second porous layer 32 made of polyethylene, and a third porous layer 33 made of polypropylene. In addition, although the 1st porous layer 31, the 2nd porous layer 32, and the 3rd porous layer 33 have all the fine void | holes connected throughout the inside of a layer, FIG. However, illustration of a void | hole is abbreviate | omitted.

  In this separator 30, since the polyethylene constituting the second porous layer 32 has a lower melting point than the polypropylene constituting the first porous layer 31 and the third porous layer 33, the melting of the second porous layer 32 is performed. As a result, the fine pores of the second porous layer 32 disappear (clog), and the shutdown function is exhibited. That is, the minute pores (ionic conduction path) in the second porous layer 32 disappear (clogging), thereby blocking ion conduction between the positive and negative electrodes through the separator 30 (current interruption) and stopping the battery reaction. Let As a result, thermal runaway of the lithium ion secondary battery 1 can be prevented.

  By the way, when the porous layer made of polyethylene is melted, the fine pores of the porous layer are blocked (disappeared), so that the thickness of the porous layer is reduced. At this time, in a battery including a conventional separator, the thickness of the porous layer may be reduced non-uniformly, resulting in a location where the thickness becomes extremely thin. For this reason, good shutdown characteristics may not be obtained. For example, when the battery temperature reaches the shutdown temperature (for example, the melting point of polyethylene + α) due to overcharge, ion conduction between the positive and negative electrodes may not be properly interrupted (current interrupt). The reason is considered to be that the resistance becomes extremely small at a location where the thickness is extremely reduced by melting, and Li ions can move.

  On the other hand, as shown in FIG. 3, the separator 30 of Example 1 includes a plurality of Ca, Na, Al, and Si between the first porous layer 31 and the second porous layer 32. The composite oxide particles 36 are provided. Further, a plurality of composite oxide particles 36 are also provided between the second porous layer 32 and the third porous layer 33.

  Thus, by disposing the composite oxide particles 36 between the first porous layer 31 and the second porous layer 32, the shutdown characteristics of the separator 30 can be improved. Furthermore, by disposing the composite oxide particles 36 between the second porous layer 32 and the third porous layer 33, the shutdown characteristics of the separator 30 can be further improved.

  Specifically, by disposing the composite oxide particles 36 between the first porous layer 31 and the second porous layer 32, the second porous layer 32 is melted by the melting of the second porous layer 32. When the thickness of the porous layer decreases while the fine pores disappear (closed), the thickness of the second porous layer 32 can be reduced uniformly.

  As a result, it is possible to prevent the occurrence of a location where the thickness of the second porous layer 32 becomes extremely thin, and to prevent the shutdown resistance of the separator 30 (the separator's electricity when the shutdown function is exhibited by melting of the second porous layer 32). Resistance value) can be increased. The greater the shutdown resistance, the higher the ability to prevent the movement of Li ions (the ability to cut off the current). Therefore, the separator 30 of Example 1 is a separator with good shutdown characteristics.

  Moreover, in the separator 30 of Example 1, as shown in FIG. 3, the particle-containing porous layer 34 that is a porous layer made of polyethylene and contains the composite oxide particles 36 in the layer is used as the first porous layer. By interposing between the layer 31 and the second porous layer 32, the composite oxide particles 36 are disposed between the first porous layer 31 and the second porous layer 32.

  In such a form, the composite oxide particles 36 are disposed between the first porous layer 31 and the second porous layer 32 by disposing the composite oxide particles 36 between the first porous layer 31 and the second porous layer 32. It can arrange | position in the state disperse | distributed uniformly over the whole surface between the layers with the porous layer 32. FIG. For this reason, when the thickness of the porous layer decreases when the fine pores of the second porous layer 32 disappear (clog) due to melting of the second porous layer 32, the thickness of the second porous layer 32 is reduced. It can be reduced more uniformly. Accordingly, the shutdown characteristics of the separator 30 are improved.

  Further, in the separator 30 of Example 1, the particle-containing porous layer 35 which is a porous layer made of polyethylene and contains the composite oxide particles 36 in the layer, the second porous layer 32 and the second porous layer By interposing between the layers 33, the composite oxide particles 36 are disposed between the second porous layer 32 and the third porous layer 33 (see FIG. 3). For this reason, the shutdown characteristics of the separator 30 are further improved.

In the separator 30 of Example 1, the number of the composite oxide particles 36 is set to 1 × 10 ⁴ μm ² per unit area between the first porous layer 31 and the second porous layer 32 ( That is, it is preferable to set the value within a range of 5 to 50 per unit area of 100 μm square. In other words, between the first porous layer 31 and the second porous layer 32, the composite oxide particles 36 are per unit area of 1 × 10 ⁴ μm ² (that is, per unit area of 100 μm square), It is preferable to arrange the number in the range of 5 to 50. Specifically, in the particle-containing porous layer 34, the number of the composite oxide particles 36 per unit area of 1 × 10 ⁴ μm ² is preferably set to a value in the range of 5-50.

  By arranging the composite oxide particles 36 between the first porous layer 31 and the second porous layer 32 at the ratio as described above, the shutdown resistance of the separator 30 (due to melting of the second porous layer 32). This is because the resistance when the shutdown function is exhibited can be further increased.

Further, even between the second porous layer 32 and the third porous layer 33, the number of the composite oxide particles 36 per unit area of 1 × 10 ⁴ μm ² (that is, per unit area of 100 μm square). ), Preferably in the range of 5-50. This is because the shutdown resistance of the separator 30 can be further increased.

  Furthermore, in the separator 30 of the first embodiment, the average particle diameter of the composite oxide particles 36 is preferably set to a value in the range of 1 to 4 μm. This is because the shutdown resistance of the separator 30 can be further increased.

  As described above, the lithium ion secondary battery 1 of Example 1 appropriately cuts off the ion conduction between the positive and negative electrodes (current cut-off) when the temperature in the battery (the temperature of the separator 30) reaches the shutdown temperature. As a result, thermal runaway of the battery 1 can be prevented. Therefore, the lithium ion secondary battery 1 of Example 1 is a highly safe lithium ion secondary battery.

  In addition, the value of D50 by the laser diffraction / scattering type particle size distribution measurement method is adopted as the value of the average particle size of the composite oxide particles 36. A microtrack manufactured by Nikkiso Co., Ltd. is used as a measuring device.

  Furthermore, in the separator 30 of the first embodiment, as shown in FIG. 3, a heat resistant porous layer 38 is provided on the surface of the first porous layer 31. The heat resistant porous layer 38 is composed of heat resistant fine particles (inorganic filler), a binder, and a thickener. As the heat-resistant fine particles, alumina or boehmite can be used. As the binder, an acrylic binder, SBR, polyolefin binder, or PTFE (polytetrafluoroethylene) can be used. As the thickener, CMC, MC (methyl cellulose), or NMP (N-methyl-2-pyrrolidone) can be used.

By providing the heat-resistant porous layer 38, even if a fine short circuit occurs between the positive and negative electrodes due to foreign substances penetrating the separator, it is possible to prevent the subsequent expansion of the short circuit.
Specifically, for example, in the case of a separator that does not have a heat-resistant porous layer, when a metal foreign object penetrates the separator, the electrical insulation of the separator is locally broken, and a fine short circuit occurs between the positive and negative electrodes There is a possibility that the through-holes of the porous layer made of resin may expand due to heat generation in the portion. As a result, the short circuit between the positive and negative electrodes may be enlarged.

  On the other hand, by providing the heat resistant porous layer 38 on the surface of the first porous layer 31, it is possible to prevent the short circuit between the positive and negative electrodes from being expanded due to a metal foreign matter or the like. The heat-resistant porous layer 38 (specifically, the heat-resistant fine particles constituting the heat-resistant porous layer) is formed on the resin porous layer (the first porous layer 31, the second porous layer 32, and the third porous layer 33). In comparison, since the melting point is much higher, even when the above-described local short circuit occurs, the through-holes of the heat-resistant porous layer 38 do not expand due to heat generation in that portion. Thereby, the heat resistant porous layer 38 can prevent the expansion of the short circuit between the positive electrode and the negative electrode due to a metal foreign object or the like. If the foreign matter is melted by the heat generated after the occurrence of the fine short circuit, the electrical insulation between the positive and negative electrodes is restored again.

  Further, by providing the heat-resistant porous layer 38 on the surface of the first porous layer 31, even when the temperature of the separator 30 reaches the shutdown temperature (the temperature of the melting point of the second porous layer + α, for example, 150 ° C.) About the porous layers (the 1st porous layer 31 and the 2nd porous layer 32) which consist of resin, the thermal contraction to a surface direction (direction orthogonal to a lamination direction, the left-right direction in FIG. 3) can be suppressed. Since the heat-resistant porous layer 38 (specifically, the heat-resistant fine particles constituting the heat-resistant porous layer 38) has a melting point much higher than that of the resin-made porous layer, the temperature of the separator 30 is set to the shutdown temperature. This is because even if it reaches, it hardly heat shrinks.

  The heat-resistant porous layer 38 suppresses thermal shrinkage in the surface direction of the porous layers made of resin (the first porous layer 31 and the second porous layer 32), so that the separator 30 can have a positive electrode and a negative electrode. Electrical insulation can be maintained. Thereby, the reliability of the shutdown function of the separator 30 can be improved, and as a result, the shutdown characteristics can be improved.

In Example 1, as an electrolytic solution, a mixed organic solvent in which ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were adjusted to a volume ratio of 3: 4: 3 was used as a solute. A nonaqueous electrolytic solution to which LiPF ₆ is added is used. The concentration of LiPF ₆ in the electrolytic solution is a 1.1 mol / L.

  Further, the positive electrode mixture layer uncoated portion of the electrode body 40 (the portion of the positive electrode 10 where the positive electrode mixture layer 13 is not applied) is a positive electrode current collecting member made of a substantially cross-shaped metal plate at the end face. 71 (see FIG. 1). Further, the positive electrode current collecting member 71 is electrically connected to the battery lid 62 through the connecting member 53 made of a strip-shaped metal thin plate. Thereby, in the battery 1 of the first embodiment, the battery lid 62 serves as a positive electrode external terminal. An electrically insulating resin plate 16 is interposed between the battery lid 62 and the positive electrode current collecting member 71.

  Further, the negative electrode mixture layer uncoated portion of the electrode body 40 (the portion of the negative electrode 20 where the negative electrode mixture layer 23 is not applied) is a negative electrode current collecting member made of a disk-shaped metal plate at the end face. 72 is welded. Further, the negative electrode current collecting member 72 is welded to the bottom 61 k of the battery can 61. Thereby, in the battery 1 of the first embodiment, the bottom 61k of the battery can 61 serves as a negative external terminal.

Next, a method for manufacturing the battery 1 according to Example 1 will be described.
First, the positive electrode 10 was produced. Specifically, a positive electrode active material (LiNi _1/3 Co _1/3 Mn _1/3 O ₂ ), a conductive material (acetylene black), a binder (PVdF), and a solvent (N-methyl-2-pyrrolidone) are mixed. Thus, a slurry-like positive electrode mixture was obtained. Next, this positive electrode mixture slurry is applied to both surfaces (first surface 11b and second surface 11c) of a positive electrode current collector foil 11 (aluminum foil) having a thickness of 15 μm, and dried to form a positive electrode mixture layer 13 (first The positive electrode mixture layer 13b and the second positive electrode mixture layer 13c) were used. Then, it rolled with the roll press and the positive electrode 10 was obtained.

  Moreover, the negative electrode 20 was produced. Specifically, a negative electrode active material (amorphous coated graphite), a binder (SBR), a thickener (CMC), and a solvent (N-methyl-2-pyrrolidone) are mixed to obtain a slurry-like negative electrode mixture. It was. Next, the negative electrode mixture slurry is applied to both surfaces (first surface 21b and second surface 21c) of a negative electrode current collector foil 21 (copper foil) having a thickness of 10 μm, and dried to form a negative electrode mixture layer 23 (first The negative electrode mixture layer 23b and the second negative electrode mixture layer 23c) were used. Then, it rolled with the roll press and the negative electrode 20 was obtained.

  Moreover, the separator 30 was produced. First, one resin sheet made of polyethylene, two resin sheets made of polypropylene, and two particle-containing sheets made of polyethylene and containing the composite oxide particles 36 therein are prepared.

  The particle-containing sheet is produced as follows. First, a polyethylene resin is melted, and a plurality of composite oxide particles 36 are uniformly dispersed in the polyethylene solution to prepare a paste. By molding (curing) this paste into a sheet shape, a particle-containing sheet in which the composite oxide particles 36 are uniformly dispersed can be obtained.

  Next, a resin sheet made of polypropylene, a particle-containing sheet, a resin sheet made of polyethylene, a particle-containing sheet, and a resin sheet made of polypropylene are laminated in this order, and are then integrated by heating (sheet) A laminate).

  Thereafter, the integrated sheet laminate is subjected to processing such as stretching (processing to make it porous). Thereby, each sheet | seat which comprises a sheet laminated body changes in quality to a porous layer. Specifically, a resin sheet made of polypropylene becomes the first porous layer 31 and the third porous layer 33, a resin sheet made of polyethylene becomes the second porous layer 32, and the particle-containing sheet becomes a particle-containing porous material. It becomes the quality layers 34 and 35 (refer FIG. 3).

  In Example 1, the thickness of the first porous layer 31 is 3 μm, the thickness of the particle-containing porous layers 34 and 35 is 3.5 μm, the thickness of the second porous layer 32 is 7 μm, and the third porous layer is used. The thickness of the layer 33 is 3 μm.

Next, the heat resistant porous layer 38 is formed on the surface of the first porous layer 31.
Specifically, first, a paste for forming the heat resistant porous layer 38 is prepared. Specifically, boehmite is prepared as heat-resistant fine particles. In addition, an acrylic binder (manufactured by Zeon Corporation) is prepared as a binder. Moreover, CMC (the 1st industrial pharmaceutical company make, BSH6) is prepared as a thickener.

  Next, using the kneader, the above boehmite, binder and thickener were mixed with water as a solvent to obtain a paste. In Example 1, an ultrasonic disperser (manufactured by M Technique Co., Ltd., CLEARMIX) is used as a kneader. As kneading conditions, preliminary dispersion for 5 minutes at a rotational speed of 15000 rpm and main dispersion for 15 minutes at a rotational speed of 20000 rpm are performed.

  Next, the above-described paste was applied to the surface of the first porous layer 31 using a known gravure coating machine. Thereafter, the heat-resistant porous layer 38 having a thickness of 4 μm could be formed on the surface of the first porous layer 31 by drying the paste. In this way, the separator 30 of Example 1 was obtained.

  Next, the separator 30, the negative electrode 20, the separator 30, and the positive electrode 10 are wound around the cylindrical winding shaft 45 in this order. In Example 1, the positive electrode 10, the negative electrode 20, and the separator 30 are arranged and wound in such a direction that the heat-resistant porous layer 38 of the separator 30 faces the positive electrode mixture layer 13. In this way, a substantially cylindrical electrode body 40 is formed. Thereafter, the outer periphery of the electrode body 40 is covered with an electrically insulating resin film 68.

  Thereafter, the positive electrode current collecting member 71 made of a substantially cross-shaped metal plate is provided on the end face of the positive electrode mixture layer uncoated portion of the electrode body 40 (the portion of the positive electrode 10 where the positive electrode mixture layer 13 is not applied). Weld (see FIG. 1). Furthermore, the negative electrode current collecting member 72 made of a disk-shaped metal plate is provided on the end face of the negative electrode mixture layer uncoated portion of the electrode body 40 (the portion of the negative electrode 20 where the negative electrode mixture layer 23 is not coated). Weld. Further, the connection member 53 is welded to the positive electrode current collecting member 71.

  Next, the electrode body 40 in which the positive electrode current collecting member 71 and the negative electrode current collecting member 72 are welded is accommodated (inserted) into the battery can 61 through the opening 61 b of the battery can 61. Thereafter, the negative electrode current collecting member 72 is welded to the bottom 61 k of the battery can 61. Thereby, the bottom part 61k of the battery can 61 becomes a negative electrode external terminal. Next, a bead 61 g is formed over the entire circumference of the battery can 61, and then an electrolytic solution is injected into the battery can 61.

  Next, the battery lid 62 is assembled to the opening 61 b of the battery can 61 via the gasket 69. When the battery lid 62 is assembled in the opening 61 b of the battery can 61, the connection member 53 is welded to the battery lid 62. Thereby, the positive electrode current collecting member 71 and the battery lid 62 are electrically connected through the connection member 53, so that the battery lid 62 becomes a positive electrode external terminal.

  Thereafter, crimping is performed on the opening 61 b of the battery can 61, and the battery can 61 is sealed with the battery lid 62. At this time, a battery case 60 is formed in which the battery can 61 and the battery lid 62 are integrated while the battery can 61 and the battery lid 62 are electrically insulated by the gasket 69. Thereafter, the battery assembled as described above is subjected to treatments such as charging / discharging and aging, whereby the battery 1 of Example 1 is completed.

(Example 2)
Next, a second embodiment of the present invention will be described.
The lithium ion secondary battery 100 of Example 2 is different from the lithium ion secondary battery 1 of Example 1 only in the separator, and the other is the same (see FIG. 1). Therefore, here, the separator will be described with a focus on differences from the first embodiment, and description of similar points will be omitted or simplified.

  As shown in FIG. 4, the separator 130 according to the second embodiment includes a first porous layer 131 made of polypropylene and a second porous layer 132 made of polyethylene. Unlike Example 1, it does not have a third porous layer made of polypropylene. Note that the first porous layer 131 and the second porous layer 132 both have fine pores communicating with the entire layer, but the illustration of the pores is omitted in FIG. Yes.

  Furthermore, the separator 130 of the second embodiment includes a plurality of composite oxide particles 36 between the first porous layer 131 and the second porous layer 132. Thus, by disposing the composite oxide particles 36 between the first porous layer 131 and the second porous layer 132, the shutdown characteristics of the separator 130 can be improved.

  Specifically, by disposing the composite oxide particles 36 between the first porous layer 131 and the second porous layer 132, the second porous layer 132 is melted by the melting of the second porous layer 132. When the thickness of the porous layer decreases while the fine pores disappear (closed), the thickness of the second porous layer 132 can be reduced uniformly.

  As a result, it is possible to prevent the occurrence of a location where the thickness of the second porous layer 132 becomes extremely thin, and the shutdown resistance of the separator 130 (electricity of the separator when the shutdown function is exhibited by melting of the second porous layer 132). Resistance) can be increased. The greater the shutdown resistance, the higher the ability to prevent the movement of Li ions (the ability to cut off the current), so the separator 130 of Example 2 is a separator with good shutdown characteristics.

  Moreover, in the separator 130 of Example 2, the particle-containing porous layer 134 that is a porous layer made of polyethylene and contains the composite oxide particles 36 in the layer, the first porous layer 131 and the second porous layer By interposing between the layers 132, the composite oxide particles 36 are arranged between the first porous layer 131 and the second porous layer 132 (see FIG. 4).

  In such a form, the composite oxide particles 36 are arranged between the first porous layer 131 and the second porous layer 132 by disposing the composite oxide particles 36 between the first porous layer 131 and the second porous layer 132. They can be arranged in a state of being uniformly dispersed over the entire surface between the layers with the porous layer 132. For this reason, when the thickness of the porous layer decreases when the fine pores of the second porous layer 132 are blocked (disappeared) by melting of the second porous layer 132, the thickness of the second porous layer 132 is reduced. Can be reduced more uniformly. Accordingly, the shutdown characteristics of the separator 130 are improved.

  Furthermore, in the separator 130 of the second embodiment, as shown in FIG. 4, the heat-resistant porous layer 38 is provided on the surface of the second porous layer 132. By providing the heat-resistant porous layer 38, as in the case of the separator 30 of the first embodiment, even if a foreign material or the like penetrates the separator and a slight short circuit occurs between the positive and negative electrodes, it is possible to prevent the subsequent expansion of the short circuit. it can. Furthermore, the thermal insulation in the surface direction of the porous layers made of resin (the first porous layer 131 and the second porous layer 132) is suppressed, so that the electrical insulation between the positive and negative electrodes by the separator 130 is maintained. can do. Thereby, the reliability of the shutdown function of the separator 130 can be improved, and as a result, the shutdown characteristics can be improved.

(Example 3)
Next, Embodiment 3 of the present invention will be described.
The lithium ion secondary battery 200 of the third embodiment is different from the lithium ion secondary battery 1 of the first embodiment only in the separator, and the other is the same (see FIG. 1). Therefore, here, the separator will be described with a focus on differences from the first and second embodiments, and description of similar points will be omitted or simplified.

  As shown in FIG. 5, the separator 230 according to the third embodiment includes a first porous layer 231 made of polypropylene and a second porous layer 232 made of polyethylene. Unlike Example 1, it does not have a third porous layer made of polypropylene. Note that the first porous layer 231 and the second porous layer 232 both have fine pores communicating throughout the layer, but the illustration of the pores is omitted in FIG. Yes.

  Further, the separator 230 according to the third embodiment includes a plurality of composite oxide particles 36 between the first porous layer 231 and the second porous layer 232. Thus, by disposing the composite oxide particles 36 between the first porous layer 231 and the second porous layer 232, the shutdown characteristics of the separator 230 can be improved.

  In the third embodiment, unlike the first and second embodiments, only the composite oxide particles 36 are disposed between the first porous layer 231 and the second porous layer 232 (see FIG. 5). That is, instead of interposing a particle-containing porous layer containing the composite oxide particles 36 between the first porous layer 231 and the second porous layer 232, only the composite oxide particles 36 are arranged. Yes.

  Further, in the separator 230 of the third embodiment, the heat resistant porous layer 38 is provided on the surface of the second porous layer 232 as in the second embodiment. The effect obtained by providing the heat-resistant porous layer 38 is the same as in the first and second embodiments.

(Measurement of shutdown resistance)
First, the shutdown resistance of the separator 30 of Example 1 was measured. The shutdown resistance is an electrical resistance of the separator 30 when the shutdown function is exhibited by melting the second porous layer 32. In other words, the electrical resistance value of the separator 30 when the temperature of the separator 30 (second porous layer 32) reaches the shutdown temperature.

  The shutdown temperature is a temperature at which the shutdown function of the separator 30 is reliably exhibited. Specifically, it is a temperature at which it is determined that the pores of the second porous layer 32 are almost completely closed by the melting of the second porous layer 32 made of polyethylene. From experiments conducted in advance, it has been found that the shutdown temperature of the separator 30 is about 150 ° C. Therefore, in the present application, the shutdown temperature of the separator 30 is set to 150 ° C. The same applies to the separators 130 and 230 of the second and third embodiments.

Moreover, the shutdown resistance value of the separator 30 was calculated | required by well-known alternating current impedance measurement using the measuring apparatus shown in FIG.
Specifically, first, a separator 30 cut into 15 mm squares (15 mm × 15 mm) was prepared, and the separator 30 was impregnated with 100 μl of an electrolytic solution. As an electrolytic solution, a non-aqueous electrolytic solution in which LiPF ₆ is added as a solute to an organic solvent in which EC (ethylene carbonate), EMC (ethyl methyl carbonate), and DMC (dimethyl carbonate) are mixed with GBL (gamma butyrolactone) is used. ing. The concentration of LiPF ₆ in the electrolytic solution is a 0.5 mol / L.

  Further, as shown in FIG. 8, a separator 30 impregnated with an electrolytic solution is sandwiched between an aluminum foil 9c and an aluminum foil 9b having heat-resistant electrical insulating tapes 2b and 2c bonded to both surfaces, and these are further made of glass. The plate 8b and the glass plate 8c were sandwiched and fixed. The electrical insulating tape 2c has a rectangular ring shape with a 15 mm square (15 mm × 15 mm) through hole in the center, and the separator 30 is disposed in the through hole of the electrical insulating tape 2c. Thereby, the separator 30 contacts the aluminum foil 9c and the aluminum foil 9b without the aluminum foil 9c and the aluminum foil 9b contacting. Moreover, in order to detect the temperature of the separator 30, the thermocouple 7 is fixed to the glass plate 8c.

  Further, the measurement sample shown in FIG. 8 is placed in the hot air dryer 6. Further, the thermocouple 7 is connected to the data logger 3 so that the temperature of the separator 30 detected by the thermocouple 7 can be read. Further, the resistance of the separator 30 can be measured by electrically connecting the aluminum foil 9 c and the aluminum foil 9 b to the potentio / galvanostat 4. Note that a Solartron 1255B type is used as the FRA 5 (frequency response analyzer 5), and a Solartron 1287A type is used as the potentio / galvanostat 4.

  Then, the temperature in the hot air dryer 6 was gradually increased (temperature increase rate of 5 ° C./min), and the temperature of the separator 30 (measured temperature by the thermocouple 7) reached the shutdown temperature (150 ° C.). The resistance value at that time was calculated as the shutdown resistance value. The measurement range of FRA 5 (frequency response analyzer 5) is set to 300 kHz.

  In this measurement, sample separators (samples A to G) having different numbers of composite oxide particles 36 are prepared as the separators 30 of Example 1, and the shutdown resistance is measured for each sample ( (See Table 1).

Specifically, in the sample A, the number X of the composite oxide particles 36 per unit area of 1 × 10 ⁴ μm ² between the first porous layer 31 and the second porous layer 32 is two. It is said. That is, in the particle-containing porous layer 34, the number X of the composite oxide particles 36 per unit area of 1 × 10 ⁴ μm ² is set to two. In Sample B, the existence number X of composite oxide particles 36 (pieces / 1 × 10 ⁴ μm ² ) = 5. In sample C, X = 10, in sample D, X = 20, in sample E, X = 30, in sample F, X = 50, and in sample G, X = 100. The same applies to the number X of the composite oxide particles 36 per unit area of 1 × 10 ⁴ μm ² between the second porous layer 32 and the third porous layer 33.
In Samples A to G, the average particle diameter of the composite oxide particles 36 is 3 μm (see Table 1).

  Further, as a comparative example, a separator 430 (referred to as sample H) that differs from the separator 30 only in that it does not have the composite oxide particles 36 was prepared (see FIG. 6). That is, as a comparative example, the first porous layer 431 made of polypropylene, the second porous layer 432 made of polyethylene, the third porous layer 433 made of polypropylene, and the first porous layer 34, 35 without the particle-containing porous layers 34, 35. A separator 430 (sample H) comprising a heat-resistant porous layer 38 laminated on the surface of one porous layer 431 was prepared (see FIG. 6). Note that the thickness of the entire separator is the same as in Example 1.

Table 1 shows the measurement results of Samples A to H. Further, based on the results of Table 1, the number X of the composite oxide particles 36 per unit area between the first porous layer and the second porous layer (number / 1 × 10 ⁴ μm ² ) and shutdown A correlation diagram with the resistance value (Ω) was prepared. This correlation diagram is shown in FIG. In FIG. 9, the shutdown resistance is expressed as SD resistance.

  As shown in Table 1, in the sample H of the comparative example, the shutdown resistance value was 400Ω. On the other hand, in each of samples A to G according to Example 1, the shutdown resistance value was larger than that of sample H of the comparative example. The greater the shutdown resistance, the higher the ability to prevent Li ion migration (the ability to cut off current), so the separator 30 of Example 1 can be said to have better shutdown characteristics than the separator 430 of the comparative example. . From this result, it can be said that the shutdown characteristics of the separator 30 can be improved by arranging the composite oxide particles 36 between the first porous layer 31 and the second porous layer 32.

  In particular, in Samples A to G according to Example 1, the first porous layer and the first porous layer are arranged by disposing a porous layer containing composite oxide particles between the first porous layer and the second porous layer. Since the composite oxide particles are arranged between the second porous layer and the second porous layer, the shutdown characteristics of the separator are further improved.

Further, as shown in FIG. 9, the number X (number / 1 × 10 ⁴ μm ² ) of the composite oxide particles 36 per unit area between the first porous layer and the second porous layer is 5 By setting the value in the range of ˜50, the shutdown resistance of the separator can be extremely increased. From this result, the number of the composite oxide particles is a value in the range of 5 to 50 per unit area of 1 × 10 ⁴ μm ² between the first porous layer and the second porous layer. It is preferable to do this. By arranging the composite oxide particles at such a ratio, it can be said that the shutdown resistance of the separator can be further increased and the separator has excellent shutdown characteristics.

Next, the shutdown resistance of the separator 130 of Example 2 was measured. The shutdown resistance is a resistance value of the separator 130 when the shutdown function is exhibited by melting the second porous layer 132. Specifically, like the separator 30 of Example 1, the resistance value of the separator 130 when the temperature of the separator 130 reaches 150 ° C. (shutdown temperature).
In addition, the measuring method is the same as that of the separator 30 (samples A to G) of the first embodiment.

  In this measurement, sample separators (samples I to L) having different average particle diameters (values of D50) of the composite oxide particles 36 are prepared as the separators 130 of Example 2, and the shutdown resistance is set for each sample. (See Table 2).

Specifically, in Sample I, the average particle diameter of the composite oxide particles 36 is 0.5 μm. In Sample J, the average particle diameter of the composite oxide particles 36 is 1 μm. In sample K, the average particle diameter of the composite oxide particles 36 is 2 μm. In the sample L, the average particle diameter of the composite oxide particles 36 is 4 μm. In Sample M, the average particle diameter of the composite oxide particles 36 is 5 μm.
In all of samples I to M, the existence number X of the composite oxide particles 36 is 40 (pieces / 1 × 10 ⁴ μm ² ).

  In addition, as a comparative example, a sample separator (referred to as sample N) that differs from the separator 130 only in that it does not have the composite oxide particles 36 was prepared. That is, as a comparative example, without having the particle-containing porous layer 134, the first porous layer made of polypropylene, the second porous layer made of polyethylene, and the heat-resistant porous layer laminated on the surface of the first porous layer A sample separator (Sample N) was prepared. Note that the thickness of the entire separator is the same as in Example 2.

  Table 2 shows the measurement results of Samples I to N. Further, based on the results in Table 2, a correlation diagram between the average particle diameter (μm) of the composite oxide particles 36 and the shutdown resistance value (Ω) was created. This correlation diagram is shown in FIG. In FIG. 10, the shutdown resistance is described as SD resistance.

  As shown in Table 2, in the sample N of the comparative example, the shutdown resistance value was 600Ω. On the other hand, in all of the samples I to M according to the example 2, the shutdown resistance value was larger than that of the sample N of the comparative example. The greater the shutdown resistance, the higher the ability to prevent Li ion migration (the ability to cut off the current), so the separator 30 of Example 2 can be said to be a separator with better shutdown characteristics than the separator of the comparative example. From this result, it can be said that the shutdown characteristics of the separator can be improved by disposing the composite oxide particles between the first porous layer and the second porous layer.

  In particular, in Samples I to M according to Example 2, the first porous layer and the first porous layer are arranged by disposing a porous layer containing composite oxide particles between the first porous layer and the second porous layer. Since the composite oxide particles are arranged between the second porous layer and the second porous layer, the shutdown characteristics of the separator are further improved.

  Furthermore, as shown in FIG. 10, the shutdown resistance of the separator can be extremely increased by setting the average particle size of the composite oxide particles 36 to a value within the range of 1 to 4 μm. From this result, it can be said that the average particle diameter of the composite oxide particles is preferably set to a value in the range of 1 to 4 μm. By setting the average particle size of the composite oxide particles to a value within the range of 1 to 4 μm, it can be said that the shutdown resistance of the separator can be further increased and the separator has excellent shutdown characteristics.

Next, the shutdown resistance of the separator 230 of Example 3 was measured. The shutdown resistance is a resistance value of the separator 230 when the shutdown function is exhibited by melting the second porous layer 232. Specifically, like the separator 30 of the first embodiment, the resistance value of the separator 230 when the temperature of the separator 230 reaches 150 ° C. (shutdown temperature).
In addition, the measuring method is the same as that of the separator 30 (samples A to G) of the first embodiment.

  In this measurement, sample separators (samples O and P) having different numbers of composite oxide particles 36 were prepared as the separator 230 of Example 3, and the shutdown resistance was measured for each sample ( (See Table 3).

Specifically, in the sample O, the number X (number of particles / 1) of the composite oxide particles 36 per unit area of 1 × 10 ⁴ μm ² between the first porous layer 231 and the second porous layer 232. X10 ⁴ μm ² ) is 45. In the sample P, the existence number X (number / 1 × 10 ⁴ μm ² ) = 5 of the composite oxide particles 36 is set.
In both samples O and P, the average particle diameter of the composite oxide particles 36 is 4 μm (see Table 3).

  Table 3 shows the measurement results of Samples O and P. In Table 3, the result of the above-mentioned sample N is described as a comparative example. The sample N of the comparative example is different from the samples O and P (separator 230) only in that the composite oxide particles 36 are not provided.

  As shown in Table 3, in the sample N of the comparative example, the shutdown resistance value was 600Ω. On the other hand, in samples O and P according to Example 3, the shutdown resistance value was larger than that of sample N of the comparative example. The greater the shutdown resistance, the higher the ability to prevent Li ion migration (the ability to cut off the current), so the separator 30 of Example 3 can be said to be a separator with better shutdown characteristics than the separator of the comparative example. From this result, it can be said that the shutdown characteristics of the separator can be improved by disposing the composite oxide particles between the first porous layer and the second porous layer.

  While the present invention has been described with reference to the first to third embodiments, it is needless to say that the present invention is not limited to the above-described embodiments, and can be appropriately modified and applied without departing from the scope of the present invention. .

1,100,200 Lithium ion secondary battery 10 Positive electrode 20 Negative electrode 30, 130, 230 Separator 31, 131, 231 First porous layer 32, 132, 232 Second porous layer 33 Third porous layer 34, 35, 134 Particle-containing porous layer (porous layer containing composite oxide particles in the layer)
36 composite oxide particles 38 heat resistant porous layer

Claims (6)

A separator having a first porous layer made of polypropylene and a second porous layer made of polyethylene,
A separator comprising composite oxide particles containing Ca, Na, Al, and Si between the first porous layer and the second porous layer. The separator according to claim 1,
By interposing a porous layer made of polyethylene or polypropylene and containing the composite oxide particles in the layer between the first porous layer and the second porous layer, A separator comprising the composite oxide particles disposed between the first porous layer and the second porous layer. The separator according to claim 1 or 2,
The number of the composite oxide particles present is a value within a range of 5 to 50 per unit area of 1 × 10 ⁴ μm ² between the first porous layer and the second porous layer. Separator. It is a separator as described in any one of Claims 1-3,
The average particle size of the composite oxide particles is a separator having a value in the range of 1 to 4 μm. It is a separator as described in any one of Claims 1-4, Comprising:
A separator having a heat-resistant porous layer laminated on a surface of the first porous layer or the second porous layer. A lithium ion secondary battery having a separator interposed between a positive electrode and a negative electrode,
The said separator is a lithium ion secondary battery which is a separator as described in any one of Claims 1-5.