JP2013222510A - Separator for secondary battery and secondary battery using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lithium ion battery in which the cycle life of a battery can be extended, by preventing formation of a gap between an electrode and a separator, thereby always holding an electrolyte between a positive electrode and a negative electrode.SOLUTION: The separator for a lithium ion secondary battery has a base material layer, and a foam layer provided on one surface of the base material layer. The foam layer has an apparent density of 10-100 kg/m, and the compression residual strain of 10% or less, and is provided with communication pores communicating with the base material layer. A secondary battery using the separator for a secondary battery is also provided.

Description

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

  Lithium-ion secondary batteries have a high energy density and little deterioration due to self-discharge among secondary batteries, so they can be used for small power supplies for various portable devices, power supplies for industrial and consumer devices, and large-scale applications such as in-vehicle and power storage. The range of use is rapidly expanding to the power supply.

  The electrode portion of the lithium ion secondary battery has a structure in which the positive electrode and the negative electrode forming the battery are electrically separated by a separator and these are laminated or wound in a spiral shape. The separator is required to have a function of preventing a short circuit between the positive electrode and the negative electrode and not hindering the ionic conductivity of the electrolyte, and a polyolefin microporous film is widely used.

  Ensuring reliability and safety is indispensable for large-scale applications such as electric vehicles and power storage that are expected to grow in the future, and research on separator materials with various ideas such as heat-resistant separators that do not melt or shrink even at high temperatures (non- Patent document 1) is underway. In addition, a separator (see Patent Document 1, Patent Document 2, and Patent Document 3) having a crosslinked polymer layer having a polyester urethane skeleton supported on a porous substrate, a composite separator of polyolefin and polyurethane (see Patent Document 4), and A lithium ion battery using the same is disclosed.

  On the other hand, as a negative electrode active material of a lithium ion battery, a carbon material such as non-graphitizable carbon or graphite is generally used. Recently, a certain type of metal is electrochemically alloyed with lithium, and this is reversible. There is an attempt to suppress expansion by alloying tin and silicon as an alloy negative electrode material applying generation / decomposition and a technique for improving cycle characteristics. However, many of these alloy negative electrode materials generally have a volume change several times larger than that of carbon materials due to adsorption / desorption of lithium ions. For this reason, although it depends on charging / discharging conditions, it was influenced by the volume change at the time of charging / discharging, and there existed a tendency for the cycle life of a battery to be short.

JP 2011-060470 A JP 2009-266812 A JP 2009-266811 A JP 2006-289985 A

Sheng Shui Zhang, A review on separatours of liquid electrolyte Li-ion batteries, Journal of Power Sources 164 (2007) 351-364

  In the case of a battery whose thickness changes due to large expansion or contraction of the electrode due to charge / discharge, compressive stress or tensile stress is generated in the battery according to the amount of change in the electrode thickness, and the electrode mixture cracks as the cycle progresses. , Peeling of the electrode mixture from the current collector, crushing of the electrode mixture and the separator, and further, a gap is formed between the positive electrode or the negative electrode and the separator, causing the electrolyte solution to drain and hindering the battery reaction. there were. In Patent Documents 1 to 4, there is no description relating to a separator that prevents formation of a gap between the positive electrode or the negative electrode and the separator.

  The present invention provides a separator for a secondary battery that prevents the formation of a gap between the positive electrode or the negative electrode and the separator caused by repeated compression and restoration according to the expansion and contraction of the electrode mixture layer due to charge and discharge, and prevents the electrolyte from draining. And a secondary battery using a secondary battery separator.

The features of the present invention for solving the above problems are as follows, for example.
A separator for a lithium ion secondary battery having a base material layer and a foam layer provided on one side of the base material layer, the apparent density of the foam layer is 10 to 100 kg / m ³ , and the compressive residual strain is 10 %, And a secondary battery separator in which a foamed layer is provided with a continuous air hole communicating with a base material layer.

  In the above, the separator for secondary batteries in which the foam layer is provided with open cells that allow the gas outside the foam layer and the gas inside the foam layer to communicate with each other.

  In the above, the separator for secondary batteries in which a base material layer is formed as a secondary battery separator, and a foamed layer is formed between the two base material layers.

  In the above, the secondary battery separator in which 100 cc of air passes through the secondary battery separator according to the Gurley test method defined in JlS P8117 is 50 to 800 seconds.

  In the above, the foam layer is a separator for a secondary battery formed of polyurethane.

  An electrode group having a positive electrode including a positive electrode active material, a negative electrode including a negative electrode active material, and the above-described secondary battery separator formed between the positive electrode and the negative electrode, and a laminate film covering the electrode group A secondary battery in which a positive electrode, a negative electrode, and a separator for a secondary battery are stacked.

  In the above, the secondary battery separator is a secondary battery that is disposed only in the central portion of the electrode group in the stacking direction.

  An electrode group comprising: a positive electrode including a positive electrode active material; a negative electrode including a negative electrode active material; and the above-described secondary battery separator formed between the positive electrode and the negative electrode. Is a secondary battery that is wound up.

  When the separator of the present invention is applied to a lithium ion battery, the separator repeatedly compresses and restores following the expansion and contraction of the electrode that occurs in the charge / discharge cycle, and the formation of a gap between the electrode and the separator can be prevented. In addition, there is an effect that the electrolytic solution can be always held between the positive electrode and the negative electrode to extend the cycle life of the battery. The effects of the present invention other than those described above will become apparent from the following description of embodiments.

The electrode group deformation | transformation model diagram at the time of using the conventional separator for a lithium ion secondary battery. The cross-sectional schematic diagram of the separator for lithium ion secondary batteries which concerns on one Embodiment of this invention. The figure which shows the modification of the separator for lithium ion secondary batteries of FIG. The figure which shows the other modification of the separator for lithium ion secondary batteries of FIG. The figure which shows an example in the case of loading the separator which concerns on one Embodiment of this invention in a lithium ion secondary battery. The electrode group deformation | transformation model diagram at the time of using the separator which concerns on one Embodiment of this invention for a lithium ion secondary battery. The electrode group deformation | transformation model diagram at the time of using the separator which concerns on one Embodiment of this invention for a lithium ion secondary battery. Foam layer forming process. The enlarged view of a foam layer.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The following description shows specific examples of the contents of the present invention, and the present invention is not limited to these descriptions. Various modifications by those skilled in the art are within the scope of the technical idea disclosed in this specification. Changes and modifications are possible. In all the drawings for explaining the present invention, the same reference numerals are given to those having the same function, and the repeated description thereof may be omitted.

  In the specification, numerical ranges indicated using “to” indicate ranges including numerical values described before and after “to” as the minimum value and the maximum value, respectively.

  The functions of the separator required for lithium ion batteries are (a) being chemically stable with respect to the organic electrolyte, (b) having a withstand voltage and oxidation resistance capable of withstanding the charge / discharge of the battery, (C) To retain organic electrolyte and ensure high lithium ion conductivity, it is possible to reduce the film thickness with a highly porous structure. (D) Mechanical that does not break with tensile or compressive force during battery assembly. In order to ensure strength and to ensure safety, (e) a short-circuit can be prevented even if dendritic lithium is generated on the negative electrode side by charging, and (f) a temporary short-circuit occurs and the temperature rises. However, the communication hole is closed (shut down), and the movement of ions can be stopped.

  Separator materials that almost satisfy these required functions include polyolefin resins such as polypropylene and polyethylene, polyester resins such as polyethylene terephthalate and polybutylene terephthalate, polyimide resins, nylon resins, and silicon resins as porous films. Can be mentioned. Moreover, as a raw material of a nonwoven fabric, a polypropylene, polyethylene, a polyethylene terephthalate, glass fiber, and polyacrylonitrile are mentioned, Especially the nonwoven fabric which consists of a polyacrylonitrile nanofiber is suitable for the separator for lithium ion batteries. Examples of the material of the woven fabric include a material in which the same fibers as the nonwoven fabric material are knitted in a yarn shape. As the material for the separator, the above materials may be used alone or in combination.

  FIG. 1 shows an electrode group deformation schematic diagram when a conventional separator is used in a lithium ion battery. A structure in which the positive electrode and the negative electrode are electrically separated by a separator and these are laminated or spirally wound is referred to as an electrode group. As shown in FIG. 1, when a separator 20 having low elasticity is used between the positive electrode 21 and the negative electrode 22, the negative electrode 22 expands during charging, the electrode thickness of the negative electrode 22 increases greatly, and plastic deformation occurs. Even if the negative electrode 22 contracts and the electrode thickness of the negative electrode 22 decreases, the plastically deformed electrode group does not return to the original state, and a gap 33 may be formed between the separator 20 and the negative electrode 22. In some cases, the electrolyte solution was drained in the electrode group, and the battery output was impaired.

  Therefore, in one embodiment of the present invention, as shown in FIGS. 2 to 4, as the multilayer separator 1, the multilayer separator 2, and the multilayer separator 3 of the base layer 10 and the foamed layer 11, at least one of the base layers 10 described above. An elastic foam layer 11 having continuous air holes 12 is provided on one side. The film thickness of the foamed layer 11 is larger than the film thickness of the base material layer 10 for ensuring elasticity and retaining the liquid. By setting it as the multilayer separator 1, the chemical stability, electrical insulation, and safety at the time of an abnormality requested | required of a separator are ensured. Also, by providing the foam layer 11, even if the gap between the electrodes changes, the thickness of the foam layer 11 changes due to compression deformation due to external compressive force and expansion deformation due to restoring force, thereby preventing gap formation. It becomes possible. Further, when the foam layer 11 contracts, a part of the electrolytic solution is discharged, and when the foamed layer 11 expands, the electrolytic solution is sucked up by the surface tension, so that the electrolytic solution can always be held in the entire separator.

  Further, a large external compressive stress acts on the foam layer 11, and even if the thickness is reduced, the foam layer 11 has open cells 13 and open cells in order to ensure communication of the electrolyte between the positive electrode 21 and the negative electrode 22. A continuous vent 12 larger than the diameter of 13 is provided. As shown in FIGS. 2 to 4, open cells 13 are provided between the continuous air holes 12 in the in-plane direction of the foam layer 11. The open cell 13 is a bubble formed so that the bubbles are connected to each other so that the external gas can communicate with the gas in the foam. The continuous air holes 12 are those in which a foam made of open cells 13 is mechanically opened or thermally melted and opened so that the external gas and the gas in the foam can communicate with each other. The foam of the open cell 13 is made in the mold for forming, and the mold is removed to form the continuous air vent 12. FIG. 9 is an enlarged view of the foamed layer 11 of FIGS.

  Examples of the material suitable for forming the foamed layer 11 in one embodiment of the present invention include polyurethane, polyethylene, polyamide, and the like. As the material of the foam layer 11, the above materials may be used alone or in combination. Among them, polyurethane foam is foamed with a polyol and polyisocyanate as main components and foamed while mixing with a foaming agent, a foam stabilizer, a catalyst and the like, and has air permeability and elasticity due to the open cells 13. Depending on the type of polyol used, it can be roughly divided into polyether foam and polyester foam. In general, polyether foams with a wide range of raw material blends can provide a wide range of performance such as elastic modulus and elasticity, depending on the battery structure. Polyester foam, on the other hand, has properties such as higher mechanical strength such as tensile strength, tear strength, elongation rate, and wear resistance than polyether foam, and can be made thinner. .

  1-50 micrometers is preferable, as for the film thickness of the base material layer 10 of the multilayer separator 1 in one Embodiment of this invention, More preferably, it is 5-40 micrometers, More preferably, it is 10-30 micrometers. If the film thickness is 1 μm or less, the handleability and strength at the time of electrode group production are weak, and if it is 50 μm or more, if the foamed layer 11 provided on the film surface is taken into account, the positive electrode 21 and the negative electrode 22 are too far apart and the resistance value becomes high, and the battery performance is high. descend.

  On the other hand, the average cell diameter of the continuous air holes 12 in the foam layer 11 is preferably 100 μm or less, more preferably 20 μm or less, and most preferably a microcell plastic of 10 μm or less. If the average cell diameter is 100 μm or more, the thickness of the foamed layer 11 is physically too thick. Conversely, if the average cell size is 10 μm or less, it is difficult to disperse the foaming agent. The average cell diameter is measured by observing the cross section of the foamed layer 11 with a scanning electron microscope.

  The film thickness of the foamed layer 11 is represented by a relative displacement with the maximum expansion amount X in the electrode mixture layer thickness direction, and the initial thickness is preferably X / 0.75 or more, more preferably X / 0.65 or more, Most preferably, it is X / 0.25 or more. As the film thickness of the foam layer 11 increases, the direct current resistance increases, so it is desirable to increase the thickness within an allowable range as battery characteristics.

The apparent density of the foam layer 11 is preferably about 10 to 100 kg / m ³ , and the compressive residual strain (JIS K6401) when a predetermined compressive displacement is applied with a predetermined compressive stress is 10% or less, preferably 5% or less. More preferably, it is 2% or less. When the apparent density of the foamed layer 11 is about 10 to 100 kg / m ³ , elasticity is obtained, and when the compressive residual strain is 10% or less, good resilience is obtained. In the present invention, in the foamed layer 11, a state in which the foamed layer 11 is tightly packed without containing bubbles (only the resin) is set as a true density, and a substance containing bubbles (becomes lighter than only the resin even in the same volume) is set as an apparent density. The apparent density of the foam layer 11 is evaluated by cutting the foam layer 11 with a width and length that can be measured with a constant thickness, measuring its weight, and dividing by the volume obtained by calculation.

  The total thickness of the multilayer separator 1 comprising the base material layer 10 and the foamed layer 11 is 2000 μm or less, preferably 1000 μm or less, more preferably 500 μm or less, and desirably 100 μm or less. The air permeability of the multilayer separator 1 measured according to the JIS P8117 Gurley test method is 50 to 800 seconds, more preferably 50 to 200 seconds, and most preferably 50 to 150 seconds for 100 cc air. 1 is preferably passed. If it is 50 seconds or less, the opening degree of the multi-layer separator 1 is large, and there is a possibility of causing a micro short circuit due to foreign matter or the like.

  FIG. 2 is a cross-sectional configuration diagram of a multilayer separator 1 according to an embodiment of the present invention. The multilayer separator 1 is provided with an elastic foam layer 11 made of open cells on both sides of a base material layer 10, and the open air holes 12 are provided in the foam layer 11 in addition to the open cells 13.

  The modification of the multilayer separator 1 which concerns on one Embodiment of this invention is shown in FIG. 3 and FIG. 3 is a separator for a lithium ion secondary battery in which a foam layer 11 of a flexible polyurethane foam having open cells 13 and continuous air holes 12 is laminated on one side of a base layer 10 of a porous polypropylene film. In addition, since the thickness can be reduced compared to the multilayer separator 1, the internal resistance can be reduced. For this reason, it is suitable for application to a battery having a relatively small amount of electrode expansion and contraction.

  On the other hand, the multilayer separator 3 in FIG. 4 is obtained by disposing a foamed layer 11 between the base material layer 10 and the base material layer 10. Since the sliding of the layer 10 is good, there is a feature that it is easy to handle without being caught in handling.

  In addition to the flexible polyurethane foam composed of the continuous air holes 12 as the foam layer 11, the foam layer 11 of foam having closed cells 14 is formed on the base material layer 10 as shown in FIG. By doing so, although the compression residual strain is somewhat increased, elasticity is obtained, so that it is possible to provide a separator for absorbing the expansion and contraction of the electrode group during charging and discharging for a lithium battery.

  The multi-layer separator 1 according to an embodiment of the present invention is used, for example, for a lithium-ion battery of a laminated laminate type, a wound cylinder or a square type made of a lithium cobaltate positive electrode, a graphite or alloy negative electrode, an organic electrolyte, or the like. The multilayer separator 1 according to an embodiment of the present invention can be used for a large-capacity lithium ion secondary battery or a large-capacity lithium ion battery using a negative electrode active material using an active material having a large expansion and contraction, such as graphite. As the positive electrode active material and the negative electrode active material, those that repeatedly expand and contract by absorbing and releasing magnesium ions and sodium ions may be used in addition to those that repeatedly expand and contract by absorbing and releasing lithium ions. .

  The use of the lithium ion secondary battery in one embodiment of the present invention is not particularly limited. For example, it can be used as a power source for portable information communication devices such as a personal computer, a word processor, a cordless telephone cordless handset, an electronic book player, a cellular phone, a car phone, a handy terminal, a transceiver, and a portable wireless device. Also, as a power source for various portable devices such as portable copiers, electronic notebooks, calculators, LCD TVs, radios, tape recorders, headphone stereos, portable CD players, video movies, electric shavers, electronic translators, voice input devices, memory cards, etc. Can be used. In addition, it can be used as household electric appliances such as refrigerators, air conditioners, TVs, stereos, water heaters, oven microwaves, dishwashers, dryers, washing machines, lighting fixtures, toys and the like. In addition, it can be used as a battery for electric tools and nursing equipment (electric wheelchairs, electric beds, electric bathing facilities, etc.) regardless of whether they are for home use or business use. Furthermore, as industrial applications, as power sources for medical equipment, construction machinery, power storage systems, elevators, unmanned mobile vehicles, and mobiles such as electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, golf carts, turret vehicles, etc. The present invention can be applied as a power source. Furthermore, it is also possible to charge the battery module of the present invention with electric power generated from a solar cell or a fuel cell and use it as a power storage system that can be used outside the ground, such as a space station, spacecraft, or space base.

  FIG. 5 is a diagram showing application to a stacked lithium battery as an example suitable for applying the separator of the present invention to a lithium ion secondary battery.

  In the laminated lithium ion secondary battery 100, the positive electrode 21 and the negative electrode 22 are partitioned and laminated by the base material layer 10, and the multilayer separator 1 is disposed in almost the middle stage of the lamination. And the inside of the aluminum laminate film 23 is sealed by thermocompression bonding in a reduced pressure atmosphere. In this embodiment, the multilayer separator 1 is provided only in the middle stage (only in the center) of the multilayer electrode group. However, all the separators stacked as shown in FIG. The multilayer separator 1 increases the thickness of the laminated electrode group, which may slightly deteriorate the heat transfer characteristics. Further, when the multilayer separator 1 is installed at the upper and lower end portions of the multilayer electrode group, the heat radiation characteristic to the outside may be deteriorated (temperature rise in the cell shortens the life). Therefore, by installing the multilayer separator 1 only in the middle stage of the laminated electrode group, the heat generated by the charge / discharge can be dissipated to the upper and lower layers. On the other hand, when the expansion / contraction amount is very large and cannot be absorbed by only one layer of the multilayer separator 1, it is desirable that all the laminated separators be the multilayer separator 1.

  Specifically, the positive electrode 21 is obtained by applying a positive electrode mixture containing a lithium transition metal composite oxide as a positive electrode active material on both surfaces of an aluminum foil current collector having a thickness of about 15 μm, and having a width of about 40 mm. The sample was cut into a strip having a length of about 70 mm.

  On the other hand, the negative electrode 22 has a substantially uniform negative electrode mixture containing a carbon powder material made of graphite or the like capable of reversibly occluding and releasing lithium ions as a negative electrode active material on both sides of a copper foil current collector having a thickness of about 10 μm. This was coated and cut into strips like the positive electrode 21 and used.

The base material layer 10 was a film made of porous polypropylene and had a thickness of about 15 μm. The foam layer 11 was a flexible polyurethane foam composed of open cells 13 and was attached to both surfaces of the base material layer 10. The foam layer 11 was provided with about 100/225 mm ² continuous vent holes 12 having a diameter of about 0.5 mm. The multilayer separator 1 including the base material layer 10 and the foamed layer 11 has a thickness of about 1.6 mm and an air permeability of about 100 seconds / 100 cc, but is not limited thereto. The average bubble diameter of the continuous air holes 12 in the foamed layer 11 is 20 μm, the apparent density of the foamed layer 11 is 20 kg / m ³ , and the compressive residual strain (JIS K6401) when a predetermined compressive displacement is applied with a predetermined compressive stress is 6. %Met.

  In the electrode group, a positive electrode 21 whose upper and lower surfaces are covered with a separator 20 having a thickness of 30 μm is placed on a strip-shaped negative electrode 22, stacked in this order up to the third stage, and a multilayer separator 1 on the upper surface of the third stage positive electrode 21. After that, the negative electrode 22, the separator 20, and the positive electrode 21 are further stacked in this order, and finally the negative electrode 22 is disposed on the separator 20. After producing the electrode group, it was inserted into a bag of an aluminum laminate film 23 with one end open, an electrolyte was injected to impregnate the electrode group, and the open end was thermocompression bonded in a reduced pressure atmosphere. A predetermined amount of lithium hexafluorophosphate dissolved at a concentration of 1 mol / L in a mixed solvent such as ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate was injected into the electrolytic solution. Although omitted in the figure, the current collectors of the positive electrode 21 and the current collectors of the negative electrode 22 laminated in the aluminum laminate film 23 are joined to each other, and the terminals are taken out of the aluminum laminate film 23. It can be connected to an external charging / discharging device.

  The expansion / contraction behavior during charging / discharging in the stacked lithium ion secondary battery 100 shown in FIG. 5 will be described in the middle position where the separator of the present invention is loaded as shown in FIG. In the figure, the battery production time point shown on the left was used as a reference. When all the laminated separators are used as the multilayer separator 1, the shrinkage behavior is as shown in FIG.

  In charging, lithium in the electrolytic solution and the positive electrode active material is ionized and moves to the negative electrode active material. At this time, as shown in the center of the figure, the active material of the positive electrode 21 hardly changes because there is almost no change in the crystal lattice even when lithium ions are released, but the negative electrode active material that occludes lithium ions has a crystal lattice. Since a part is extended, the negative electrode 22 expands. The expansion of the negative electrode 22 is absorbed by the foam layer 11 of the multilayer separator 1 disposed in the middle stage contracting. The electrolytic solution impregnated in the multi-layer separator 1 is discharged into the space surrounded by the aluminum laminate film 23 as the shrinkage occurs. Even if the thickness of the foam layer 11 bottoms on the base material layer 10, since the communication air holes 12 larger than the diameter of the open cell 13 are provided, the communication of the electrolyte solution between the positive electrode 21 and the negative electrode 22 is ensured. On the other hand, in the discharge shown on the right side of the drawing, lithium ions are released from the negative electrode active material and the negative electrode 22 contracts, but the thickness of the positive electrode 21 hardly changes even when lithium ions are occluded. The shrinkage of the negative electrode 22 is absorbed by restoring the thickness of the foamed layer 11 of the multilayer separator 1 arranged in the middle stage. The electrolyte discharged together with the restoration of the foam layer 11 is sucked up by the surface tension, and the electrolyte is secured.

[Comparative Example 1]
As a comparative example, the same material was used for the positive electrode 21 and the negative electrode 22, and a laminated lithium ion secondary battery 100 composed of a microporous film of polypropylene and polyethylene was prepared as the separator 20, and the charge / discharge characteristics of both were compared.

  As the initial characteristics of the charge / discharge cycle, the total thickness of the battery at the time of full charge and full discharge of the comparative battery was compared. As a result, the battery expanded approximately 1.2% and contracted approximately 0.8%. The laminated lithium ion secondary battery 100 gradually swelled. Also, the capacity retention rate of the battery tended to decrease as the swelling increased. Compared with the comparative battery, the laminated lithium ion secondary battery 100 according to one embodiment of the present invention showed no expansion tendency and the cycle characteristics were greatly improved. This is considered to be because the multilayer separator 1 provided with the foamed layer 11 repeatedly compressed and restored following the expansion and contraction behavior of the negative electrode 22, and the electrolyte solution was always maintained.

  Although the example of the stacked lithium ion secondary battery 100 is taken up in Embodiment 1, the present invention can also be applied to a wound lithium ion secondary battery. In this case, it is necessary to select the apparent density of the foam layer 11 to an appropriate value in consideration of the tension of the electrode during winding and the tension of the separator. When the winding type lithium ion secondary battery is not provided with a shaft core, it is desirable to wind a plurality of separators 20 that do not include the foam layer 11 first. When the multi-layer separator 1 provided with the foam layer 11 is wound first, there is a possibility that the electrode will be rolled after that and may become unstable due to the balance with the tension.

  Generally, since the stress in the radial direction of the wound body is estimated to be about 200 kPa, a foam having continuous pores of about 500 kPa as the rebound resilience at the time of 50% compression of the foam layer 11 of the multilayer separator 1 is used. Apply it. The wound electrode group is spirally wound in the order of the separator 20, the negative electrode 22, the separator 20, and the positive electrode 21, but at least one of the two is a multilayer separator 1 with a foam layer 11. It is possible to absorb the expansion and contraction of the electrode during charging and discharging. Furthermore, this separator can be applied to large capacity, large lithium ion batteries that are expected to become popular in the future, and batteries to which an alloy negative electrode with high energy density and high expansion and contraction is applied, and good cycle characteristics can be obtained. it can.

1, 2, 3 Multi-layer separator 10 Base layer 11 Foam layer 12 Continuous vent 13 Open cell 14 Closed cell 20 Separator 21 Positive electrode 22 Negative electrode 23 Aluminum laminate film 33 Gap 100 Multilayer lithium ion secondary battery

Claims (8)

A base material layer;
A foam layer provided on one side of the base material layer, and a lithium ion secondary battery separator,
The apparent density of the foamed layer is 10 to 100 kg / m ³ , the compressive residual strain is 10% or less,
A separator for a secondary battery, wherein the foam layer is provided with a continuous air hole communicating with the base material layer. In claim 1,
A separator for a secondary battery, wherein the foam layer is provided with open cells that allow gas outside the foam layer and gas inside the foam layer to communicate with each other. In claim 1 or 2,
The base material layer is formed in two layers as the secondary battery separator,
A separator for a secondary battery in which the foamed layer is formed between the two base material layers. In any one of Claims 1 thru | or 3,
A secondary battery separator in which 100 cc of air passes through the secondary battery separator according to the Gurley test method specified in JlS P8117, and is 50 to 800 seconds. In any one of Claims 1 thru | or 4,
The foam layer is a secondary battery separator formed of polyurethane. A positive electrode including a positive electrode active material;
A negative electrode containing a negative electrode active material;
An electrode group comprising: a separator for a secondary battery according to any one of claims 1 to 5 formed between the positive electrode and the negative electrode;
A secondary battery having a laminate film covering the electrode group,
The positive electrode, the negative electrode, and the secondary battery separator are laminated secondary batteries. In claim 6,
The secondary battery separator is a secondary battery disposed only in a central portion of the electrode group in the stacking direction. A positive electrode including a positive electrode active material;
A negative electrode containing a negative electrode active material;
A secondary battery comprising an electrode group having a separator for a secondary battery according to any one of claims 1 to 5 formed between the positive electrode and the negative electrode,
A secondary battery in which the electrode group is wound.