KR20110119563A - Separator - Google Patents

Abstract

PURPOSE: A separator and a lithium ion secondary battery are provided to prevent the heat from being diffused to parts adjacent to a separator since the heat generated from the inside of a battery is dissipated to the plane direction of the separator. CONSTITUTION: In a separator(1), the thermal resistance of a plane direction is smaller than the thermal resistance of a thickness direction. The separator has a central part(2) and a surface part(3) having a void ratio bigger than the central part. The void ratio of the surface part is 90% or greater. The central part has a core part and an outer circumference having a void ratio bigger than the central part. An inorganic material is included in the central part or core part.

Description

Separator {SEPARATOR}

The present invention relates to a separator.

In recent years, in order to cope with global warming, reduction of the amount of carbon dioxide is eagerly desired. In the automobile industry, the expectation is focused on the reduction of carbon dioxide emission by the introduction of an electric vehicle (EV) or a hybrid electric vehicle (HEV), and the development of a motor-driven secondary battery which holds the key to their practical use is vigorously developed. It is done.

As the motor driving secondary battery, a lithium ion secondary battery having the highest theoretical energy among all the batteries has attracted attention, and development is currently progressing rapidly. In general, a lithium ion secondary battery has a structure in which a positive electrode and a negative electrode having an active material layer in which an active material and the like are applied to a current collector together with a binder are connected through an electrolyte layer and stored in a battery case.

As described above, nonaqueous electrolyte secondary batteries used as power sources for driving motors of automobiles and the like are required to have extremely high output characteristics as compared with public nonaqueous electrolyte secondary batteries used in mobile phones, notebook computers and the like. In order to cope with such a demand, intensive research and development is in progress.

The said lithium ion secondary battery contains a separator as a structural member. In patent document 1, the separator which impregnated the inorganic particle with high thermal conductivity is proposed, and the effect which discharge | releases the heat generate | occur | produced inside a battery to the lamination direction of a battery is aimed at by this.

Japanese Patent Application Laid-open No. Hei 8-255615

According to the separator described in Patent Document 1, heat generated inside the battery can be released in the thickness direction (lamination direction) of the battery. However, there was a fear that the heat generated by the internal short circuit would propagate to other adjacent cells.

Therefore, an object of the present invention is to provide a means for suppressing propagation of heat generated inside a battery due to an internal short circuit to adjacent parts.

MEANS TO SOLVE THE PROBLEM The present inventors earnestly researched in view of the said subject. As a result, it was found that the above-mentioned problems were solved by a separator whose thermal resistance in the plane direction was smaller than the thermal resistance in the thickness direction.

Since heat generated inside the separator moves in the plane direction of the separator to dissipate heat, it is possible to suppress the propagation of heat to components adjacent to the separator.

1 is a cross-sectional schematic diagram showing the structure of a stacked lithium ion secondary battery.
2 is a schematic cross-sectional view schematically illustrating a separator of a first embodiment.
3 is a graph showing the relationship between the porosity of the surface portion of the separator and the contact thermal resistance of the separator and the electrode.
4 is a schematic diagram illustrating a method of calculating contact thermal resistance.
5 is a graph showing the relationship between the thermal conductivity of the separator surface portion and the thermal resistance in the plane direction.
6 is a view in which the graph of FIG. 3 is compared with the graph of FIG. 5.
7 is a schematic cross-sectional view schematically illustrating a separator of a second embodiment.
8 is a schematic cross-sectional view schematically illustrating a separator of a third embodiment.
9 is a perspective view showing the appearance of a lithium ion secondary battery.

First, although the nonaqueous electrolyte lithium ion secondary battery which is preferable embodiment is demonstrated, it is not limited only to the following embodiment. In addition, in description of drawing, the same number is attached | subjected to the same element, and the overlapping description is abbreviate | omitted. In addition, the dimension ratio of drawing is exaggerated on account of description, and may differ from an actual ratio.

When distinguished by the structure and the form of a lithium ion secondary battery, it does not restrict | limit especially, a laminated type (flat type) battery, a wound type (cylindrical type) battery, etc., and can apply to any conventionally well-known structure.

Similarly, there is no restriction | limiting in particular also when distinguishing in the form of electrolyte. For example, it can be applied to both a liquid electrolyte type battery in which a nonaqueous electrolyte solution is impregnated in a separator, a polymer gel electrolyte type battery also called a polymer battery, and a solid polymer electrolyte (all-solid electrolyte) type battery. Regarding the polymer gel electrolyte and the solid polymer electrolyte, these may be used alone, or these polymer gel electrolytes or solid polymer electrolytes may be impregnated in the separator and used.

[Overall Structure of Battery]

1 is a schematic diagram showing a basic configuration of an embodiment of a flat (laminated) nonaqueous electrolyte lithium ion secondary battery (hereinafter, also simply referred to as a "laminated battery"). As shown in FIG. 1, the stacked battery 10 of the present embodiment has a structure in which a substantially rectangular power generating element 21 in which a charge / discharge reaction actually proceeds is sealed inside a battery packaging material 29, which is an exterior body. Have Here, the power generation element 21 includes the positive electrode having the positive electrode active material layer 13 disposed on both surfaces of the positive electrode current collector 11, the electrolyte layer 17, and the negative electrode active material layer 15 on both sides of the negative electrode current collector 12. ) Has a structure in which a negative electrode on which is disposed is stacked. Specifically, the negative electrode, the electrolyte layer, and the positive electrode are laminated in this order so that one positive electrode active material layer 13 and the negative electrode active material layer 15 adjacent thereto face each other via the electrolyte layer 17.

As a result, the adjacent positive electrode, electrolyte layer, and negative electrode constitute one unit cell layer 19. Therefore, the laminated battery 10 of this embodiment can also be said to have a structure by which the single cell layer 19 is laminated | stacked and electrically connected in parallel. In addition, although the positive electrode active material layer 13 is arrange | positioned only to one side in the outermost layer positive electrode electrical power collector which is located in both outermost layers of the power generation element 21, the active material layer may be provided in both surfaces. In other words, the current collector having the active material layer on both sides may be used as the current collector of the outermost layer, instead of being used as the current collector for the outermost layer provided with the active material layer only on one side. In addition, as shown in FIG. 1, the arrangement of the positive electrode and the negative electrode is reversed, so that the outermost negative electrode current collector is positioned at both outermost layers of the power generation element 21, and the negative electrode active material layer is disposed on one or both surfaces of the outermost negative electrode current collector. It may be arranged.

The positive electrode current collector 11 and the negative electrode current collector 12 are each provided with a positive electrode current collector plate 25 and a negative electrode current collector plate 27, which are electrically connected to each electrode (positive electrode and negative electrode), and end portions of the battery exterior member 29. It has a structure which is led out to the exterior of the battery packaging material 29 so that it may fit in the inside. The positive electrode current collector plate 25 and the negative electrode current collector plate 27 are each ultrasonically applied to the positive electrode current collector 11 and the negative electrode current collector 12 of each electrode through a positive electrode lead and a negative electrode lead (not shown), respectively, as necessary. It may be attached by welding, resistance welding, or the like.

FIG. 2 is an enlarged cross-sectional schematic view of a separator (first embodiment) included in the electrolyte layer 17 used in the stacked lithium ion secondary battery 10. As shown in FIG. 2, the separator 1 of the present embodiment includes a central portion 2 and a surface portion 3 having a larger porosity than the porosity of the central portion 2. By setting it as such a structure, in the separator of this embodiment, the thermal resistance of a surface direction is smaller than the thermal resistance of a thickness direction (lamination direction).

Conventionally, as a countermeasure for releasing heat inside a battery, the separator has been impregnated with inorganic particles having high thermal conductivity, and the heat is released in the thickness direction (lamination direction) of the battery. However, when such a separator is used, the thermal conductivity in the thickness direction (lamination direction) of the electrode is increased, so that heat generated inside the battery due to an internal short circuit also flows to other single cell layers. As a result, the other unit cell layers adjacent also became high temperature, and there existed a problem that the suppression of the temperature rise of a battery was inadequate.

In contrast, in the separator of the present embodiment, the thermal resistance in the plane direction is smaller than the thermal resistance in the thickness direction (lamination direction). Therefore, the heat generated inside the battery (for example, the separator, etc.) due to the internal short circuit moves in the plane direction of the separator and dissipates the heat, so that heat can be prevented from propagating in the thickness direction (lamination direction). As a result, the propagation of heat to other components adjacent to the separator can be suppressed, and the temperature rise of the battery can be suppressed.

Hereinafter, the separator of this embodiment is demonstrated in detail.

(Separator)

The material of the separator is not particularly limited, and conventionally known ones can be used. For example, a porous sheet separator, a nonwoven fabric separator, etc. which consist of a polymer which absorbs, maintains, or supports an electrolyte (especially electrolyte solution) can be used.

Examples of the porous sheet made of a polymer include a polyolefin microporous membrane such as polyethylene (PE) and polypropylene (PP), a laminate having a three-layer structure of PP / PE / PP, polyethylene terephthalate (PET), and polyimide. Etc. can be mentioned. As a material of a nonwoven fabric, conventionally well-known things, such as polyolefin, polyimide, or aramid resin, such as cotton, rayon, acetate, nylon, polyester, polypropylene, and polyethylene, can be used, for example. In addition, a separator made of cellulose or ceramic may be used, and the material may be appropriately selected so that the thermal resistance in the surface direction becomes smaller than the thermal resistance in the thickness direction (lamination direction). More preferably, as shown in FIG. 2, the sheet | seat 2 of the center part is clamped and supported by the sheet | seat 3 with larger porosity than the sheet | seat 2 of the said center part. More preferably, a porous sheet made of a polymer is used as the central portion 2, and a nonwoven fabric having a larger porosity than the porous sheet made of the polymer is used for the surface portion 3. In a particularly preferred embodiment, CELGARD 2500 (manufactured by CELGARD, a polypropylene porous membrane) is used for the central portion 2, and a cellulose separator [Nippon Koshido Kogyo Co., Ltd. is used for the surface portion 3. Oh Kabuki Seiki Co., Ltd.] is used.

The sheet | seat of the center part 2 may be used individually by 1 sheet, and multiple sheets may be used. In the case of using a plurality of sheets, the same kind of sheets may be used, or different kinds of sheets may be used. Similarly, the sheet | seat of the surface part 3 may also be used individually by 1 sheet, and multiple sheets may be used. In the case of using a plurality of sheets, the same kind of sheets may be used, or different kinds of sheets may be used.

Although the porosity in particular of the surface part 3 is not restrict | limited, It is preferable to set in consideration of the effect which enlarges the thermal resistance of the thickness direction (lamination direction) of a separator.

3 is a graph showing the relationship between the porosity of the separator surface portion 3 and the contact thermal resistance of the separator and the electrode. As is apparent from this graph, the larger the porosity, the larger the contact thermal resistance. However, considering the effect of increasing the thermal resistance in the thickness direction (lamination direction) of the separator, the porosity of the surface portion 3 of the separator is preferably 70% or more, more preferably 80% or more, even more preferably. Is 90% or more. The porosity of the center part 2 of a separator should just be smaller than the porosity of the surface part 3, and is not restrict | limited at all.

The porosity described above was measured by the mercury porosimetry to determine the volume of the pores present in the separator, and was determined as a ratio to the apparent volume of the separator. In addition to this method, the porosity ε can be obtained from Equation 1 below using the bulk density ρ 'and the true density ρ of the separator.

In addition, the contact thermal resistance can be measured and calculated by the following method (refer FIG. 4). First, the heat spreading rate is measured by applying a pulsed heat amount to one end surface of the separator (surface portion) by measuring the temperature rise time of the other end surface by the laser flash method, and measuring the thermal conductivity of the separator from the heat capacity and the heat spreading rate. (λs) is calculated. Similarly, the thermal conductivity lambda e of the electrode is also calculated.

Next, the separator and the electrode are brought into contact with each other so that heat is not emitted to the side surface. A constant amount of heat Q is applied to one side, and the temperatures Tso and Teo at the end are measured.

From the above-described thermal conductivity (λs, λe), the given amount of heat (Q) and the separator (surface portion) and the temperature (Tso, Teo) of the end of the electrode, the respective temperatures (Tsi, Tei) can be obtained. Specific formulas are shown in the following formulas (2) and (3).

Tsi and Tei are calculated from the above equations (2) and (3), and the contact thermal resistance is calculated by the following equation (4) from the difference and the amount of heat Q added.

5 is a graph showing the relationship between the thermal conductivity of the separator surface portion 3 and the thermal resistance in the plane direction. As apparent from this graph, the higher the thermal conductivity of the separator surface portion 3, the smaller the thermal resistance in the plane direction. Although FIG. 6 is the figure which contrasted the graph of FIG. 3 with the graph of FIG. 5, it is preferable to set the thermal conductivity of a separator from a viewpoint of making thermal resistance of surface direction smaller than the contact thermal resistance of a thickness direction (lamination direction). . For example, when the porosity of the surface portion is 90%, the thermal conductivity of the separator is preferably 20 W / m · K or more, more preferably 50 W / m · K or more, even more preferably 75 W / m · K or more. to be.

Although the thickness in particular of the center part 2 of the said separator is not restrict | limited, It is preferable that it is 5-50 micrometers. Similarly, although the thickness of the surface part 3 of a separator is not specifically limited, It is preferable that it is 5-50 micrometers.

The manufacturing method of the separator of this embodiment is not specifically limited. For example, the method of crimping, fusion | melting, or adhering the member of a center part and the surface part may be sufficient, and the method of crimping, fusion | bonding, or adhering the member of a center part and the surface part at once may be sufficient.

The separator of 1st Embodiment demonstrated above has the following effects.

In the separator of the first embodiment, the thermal resistance in the plane direction is smaller than the thermal resistance in the thickness direction (lamination direction). Therefore, since heat generated inside the battery due to internal short circuit moves in the plane direction of the separator and radiates heat, it is possible to suppress heat propagation in the thickness direction (lamination direction). As a result, the propagation of heat to other adjacent parts can be suppressed and the temperature rise of the battery can be suppressed.

It is sectional schematic drawing which shows the separator of 2nd Embodiment. The separator of this embodiment has the center part 2 and the surface part 3 with a larger porosity than a center part like 1st Embodiment. In addition to this configuration, the central portion 2 also has a central portion 4 and an outer circumferential portion 5, the member having a small porosity is arranged in the central portion 4, and the empty portion in the outer circumferential portion 5 of the central portion 2. This large member is arranged. For this reason, the thermal conductivity of the center part 4 of the surface direction of the separator which tends to become high temperature can be improved, and the heat | fever which generate | occur | produced can be discharged | emitted to the outer peripheral part 5 of a separator more efficiently.

Although the member used for the center part 4 and the member used for the outer peripheral part 5 are not restrict | limited, The porous part which consists of a polymer is used for the center part 4, and the outer peripheral part 5 is used rather than the porous sheet which consists of the said polymer. It is preferable to use a nonwoven fabric having a large porosity. Specific examples of the porous sheet and the nonwoven fabric made of the polymer are the same as described above, and thus description thereof is omitted here. In a particularly preferred embodiment, CELGARD (registered trademark) 2500 (CELGARD Co., Ltd., polypropylene porous membrane) is used for the central portion 4, and a cellulose separator (made by Nippon Koshido Kogyo Co., Ltd.) is used for the outer circumferential portion 5. Form.

The sheet | seat of the center part 4 may be used individually by 1 sheet, and multiple sheets may be used. When using multiple sheets, the same kind of sheet may be used, and a different kind of sheet may be used. Similarly, the sheet | seat of the outer peripheral part 5 may also be used individually by 1 sheet, and may use multiple sheets. In the case of using a plurality of sheets, the same kind of sheets may be used, or different kinds of sheets may be used.

The center portion 4 may contain an inorganic substance. Examples of the inorganic substance include alumina, silica, titania, beryllia, zirconia, magnesia, aluminum nitride, boron nitride, silicon nitride, and the like, and these may be used alone or in combination of two or more thereof.

Although content in particular of the said inorganic substance is not restrict | limited, Preferably it is 5-60 mass%, More preferably, it is 10-50 mass% with respect to the mass of the center part 4 of a separator.

The method of containing an inorganic substance is not specifically limited, For example, the method of inserting an inorganic substance, such as a fibrous form, a particulate form, a flaky form, directly into the cavity of a separator is mentioned. The inorganic substance can also be contained by mixing and dispersing the inorganic substance in the electrolyte or the electrolyte solution and impregnating the electrolyte or the electrolyte solution in the central portion 4.

8 is a cross-sectional schematic diagram illustrating the separator of a third embodiment. The separator of the present embodiment has the central portion 2 and the surface portion 3 having a larger porosity than the central portion 2, similarly to the first embodiment, but the central portion 2 contains the inorganic substance 6. . As a result, the thermal conductivity in the plane direction of the separator can be increased with little or no increase in the thermal conductivity in the thickness direction (lamination direction) of the separator. Therefore, the thermal resistance in the plane direction becomes smaller, and the heat generated inside the battery can be more efficiently radiated in the plane direction. Under the present circumstances, since the inorganic substance used and the method of containing inorganic substance are the same as the above, description is abbreviate | omitted here.

The lithium ion secondary battery demonstrated above has a characteristic in a separator. Hereinafter, other main structural members are demonstrated.

(Current collector)

The current collector is made of a conductive material. The size of the current collector is determined by the use of the battery. For example, a current collector having a large area is used as long as it is used for a large battery requiring high energy density. There is no restriction | limiting in particular also about the thickness of an electrical power collector. The thickness of an electrical power collector is about 1-100 micrometers normally.

There is no restriction | limiting in particular in the material which comprises a collector. For example, a metal or a resin in which a conductive filler is added to the conductive polymer material or the non-conductive polymer material may be employed. Specifically, aluminum, nickel, iron, stainless steel, titanium, copper, etc. are mentioned as a metal. In addition to these, a cladding material of nickel and aluminum, a cladding material of copper and aluminum, or a plating material of a combination of these metals can be preferably used. Moreover, the foil by which aluminum is coat | covered on the metal surface may be sufficient. Especially, aluminum, stainless steel, and copper are preferable from a viewpoint of an electron conductivity and battery operation potential.

In addition, examples of the conductive polymer material include polyaniline, polypyrrole, polythiophene, polyacetylene, polyparaphenylene, polyphenylenevinylene, polyacrylonitrile, polyoxadiazole, and the like. Such a conductive polymer material has sufficient conductivity even without adding a conductive filler, and is therefore advantageous in terms of facilitating the manufacturing process or reducing the weight of the current collector.

As a nonelectroconductive polymer material, for example, polyethylene [PE; High density polyethylene (HDPE), low density polyethylene (LDPE), etc.], polypropylene (PP), polyethylene terephthalate (PET), polyethernitrile (PEN), polyimide (PI), polyamideimide (PAI), polyamide ( PA), polytetrafluoroethylene (PTFE), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polymethylacrylate (PMA), polymethylmethacrylate (PMMA), polyvinyl chloride (PVC) ), Polyvinylidene fluoride (PVdF), polystyrene (PS), and the like. Such a nonconductive polymer material may have excellent dislocation resistance or solvent resistance.

A conductive filler may be added to the conductive polymer material or the non-conductive polymer material as required. In particular, when the resin serving as the base material of the current collector is made of only the non-conductive polymer, the conductive filler is inevitably necessary in order to impart conductivity to the resin. The conductive filler can be used without particular limitation as long as it is a substance having conductivity. For example, metal, conductive carbon, etc. are mentioned as a material excellent in electroconductivity, electric potential resistance, or lithium ion barrier property. The metal is not particularly limited, but at least one metal selected from the group consisting of Ni, Ti, Al, Cu, Pt, Fe, Cr, Sn, Zn, In, Sb, and K or an alloy containing these metals or It is preferable to include a metal oxide. The conductive carbon is not particularly limited, but includes at least one selected from the group consisting of acetylene black, vulcan, black pearl, carbon nanofibers, ketjen black, carbon nanotubes, carbon nanohorns, carbon nano balloons and fullerenes. It is desirable to. There is no restriction | limiting in particular if the addition amount of an electroconductive filler is a quantity which can provide sufficient electroconductivity to an electrical power collector, Generally, it is about 5-35 mass%.

(Active material layer)

[Positive electrode (positive electrode active material layer) and negative electrode (negative electrode active material layer)]

The active material layer 13 or 15 contains an active material and further contains other additives as necessary.

The positive electrode active material layer 13 contains a positive electrode active material. Examples of the positive electrode active material include lithium-transition metal composite oxides such as LiMn ₂ O ₄ , LiCoO ₂ , LiNiO ₂ , Li (Ni-Co-Mn) O _2, and some of these transition metals substituted by other elements. And lithium-transition metal phosphate compounds, lithium-transition metal sulfate compounds, and the like. In some cases, two or more kinds of positive electrode active materials may be used in combination. Preferably, in view of capacity and output characteristics, a lithium-transition metal composite oxide is used as the positive electrode active material. It goes without saying that a positive electrode active material other than the above may be used.

The negative electrode active material layer 15 contains a negative electrode active material. Examples of the negative electrode active material include carbon materials such as graphite (graphite), soft carbon, and hard carbon, lithium-transition metal composite oxides (for example, Li ₄ Ti ₅ O ₁₂ ), metal materials, lithium alloy negative electrode materials, and the like. Can be mentioned. In some cases, two or more types of negative electrode active materials may be used in combination. Preferably, from the viewpoint of capacity and output characteristics, a carbon material or a lithium-transition metal composite oxide is used as the negative electrode active material. It goes without saying that a negative electrode active material other than the above may be used.

Although the average particle diameter of each active material contained in each active material layer 13 and 15 is not specifically limited, From a viewpoint of high output, Preferably it is 1-20 micrometers.

The positive electrode active material layer 13 and the negative electrode active material layer 15 contain a binder.

Although it does not specifically limit as a binder used for an active material layer, For example, the following materials are mentioned. Polyethylene, polypropylene, polyethylene terephthalate (PET), polyethernitrile, polyacrylonitrile, polyimide, polyamide, cellulose, carboxymethylcellulose (CMC), ethylene-vinyl acetate copolymer, polyvinyl chloride, styrene-butadiene Rubber (SBR), isoprene rubber, butadiene rubber, ethylene propylene rubber, ethylene propylene diene copolymer, styrene butadiene styrene block copolymer and its hydrogenated substance, styrene isoprene styrene block copolymer and its hydrogenated substance Thermoplastic polymer, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), tetrafluoroethylene hexafluoropropylene copolymer (FEP), tetrafluoroethylene perfluoroalkyl vinyl ether copolymer ( PFA), ethylene tetrafluoroethylene copolymer (ETFE), polychlorotrifluoroethylene (PCTFE), fluorine resins such as ethylene / chlorotrifluoroethylene copolymer (ECTFE), polyvinyl fluoride (PVF), vinylidene fluoride-hexafluoropropylene fluorine rubber (VDF-HFP fluorine rubber), vinyl Lidenfluoride-hexafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-HFP-TFE fluorine rubber), vinylidene fluoride-pentafluoropropylene fluorine rubber (VDF-PFP fluorine rubber), vinylidene Fluoride-pentafluoropropylene-tetrafluoroethylene fluorine rubber (VDF-PFP-TFE fluorine rubber), vinylidene fluoride-perfluoromethyl vinyl ether-tetrafluoroethylene fluorine rubber (VDF-PFMVE- Vinylidene fluoride-based fluorine rubbers such as TFE-based fluorine rubber) and vinylidene fluoride-chlorotrifluoroethylene-based fluorine rubber (VDF-CTFE-based fluorine rubber); and epoxy resins. Especially, it is more preferable that they are polyvinylidene fluoride, polyimide, styrene butadiene rubber, carboxymethylcellulose, polypropylene, polytetrafluoroethylene, polyacrylonitrile, and polyamide. These suitable binders are excellent in heat resistance and have a very wide potential window so that they are stable at both the positive electrode potential and the negative electrode potential, and thus can be used for the active material layer. These binders may be used independently and may use 2 or more types together.

Although the amount of binder contained in an active material layer will not be specifically limited if it is an quantity which can bind an active material, Preferably it is 0.5-15 mass% with respect to an active material layer, More preferably, it is 1-10 mass%.

As another additive which may be contained in an active material layer, a conductive support agent, electrolyte salt (lithium salt), an ion conductive polymer, etc. are mentioned, for example.

A conductive support agent means the additive mix | blended in order to improve the electroconductivity of a positive electrode active material layer or a negative electrode active material layer. As a conductive support agent, carbon materials, such as carbon black, such as acetylene black, graphite, and vapor-grown carbon fiber, are mentioned. When the active material layer contains a conductive assistant, the electronic network in the inside of the active material layer is effectively formed, which can contribute to the improvement of the output characteristics of the battery.

Examples of the electrolyte salt (lithium salt) include Li (C ₂ F ₅ SO ₂ ) ₂ N, LiPF ₆ , LiBF ₄ , LiClO ₄ , LiAsF ₆ , LiCF ₃ SO ₃ , and the like.

As an ion conductive polymer, the polymer of a polyethylene oxide (PEO) system and a polypropylene oxide (PPO) system is mentioned, for example.

The compounding ratio of the component contained in a positive electrode active material layer and a negative electrode active material layer is not specifically limited. The blending ratio can be adjusted by appropriately referring to known knowledge about nonaqueous solvent secondary batteries. There is no restriction | limiting in particular also about the thickness of each active material layer, The conventionally well-known knowledge about a battery can be referred suitably. For example, the thickness of each active material layer is about 2-100 micrometers.

(Electrolyte layer)

As the electrolyte constituting the electrolyte layer 17, a liquid electrolyte or a polymer electrolyte can be used.

The liquid electrolyte has a form in which a lithium salt as a supporting salt is dissolved in an organic solvent as a plasticizer. As an organic solvent which can be used as a plasticizer, carbonates, such as ethylene carbonate (EC) and a propylene carbonate (PC), are illustrated, for example. Moreover, as a supporting salt (lithium salt), the compound which can be added to the active material layer of an electrode, such as LiBETI, can be employ | adopted similarly.

On the other hand, the polymer electrolyte is classified into a gel electrolyte containing an electrolyte solution and an intrinsic polymer electrolyte containing no electrolyte solution.

The gel electrolyte has a structure in which the liquid electrolyte is injected into a matrix polymer made of an ion conductive polymer. As an ion conductive polymer used as a matrix polymer, polyethylene oxide (PEO), polypropylene oxide (PPO), these copolymers, etc. are mentioned, for example. In such a polyalkylene oxide polymer, electrolyte salts such as lithium salts can be dissolved well.

The intrinsic polymer electrolyte has a structure in which a supporting salt (lithium salt) is dissolved in the matrix polymer and does not include an organic solvent which is a plasticizer. Therefore, when the electrolyte layer is made of an intrinsic polymer electrolyte, there is no fear of liquid leakage from the battery, and the reliability of the battery can be improved.

The matrix polymer of the gel electrolyte or the intrinsic polymer electrolyte can express excellent mechanical strength by forming a crosslinked structure. In order to form a crosslinked structure, a polymerization treatment such as thermal polymerization, ultraviolet polymerization, radiation polymerization, electron beam polymerization or the like may be performed on a polymerizable polymer for forming a polymer electrolyte (for example, PEO or PPO) using a suitable polymerization initiator. do.

(Tab and lead)

You may use a tab for the purpose of taking an electric current out of a battery. The tab is electrically connected to the outermost current collector and the current collector plate, and is taken out of the laminate sheet which is a battery exterior material.

The material constituting the tab is not particularly limited, and a known highly conductive material conventionally used as a tab for a lithium ion secondary battery can be used. As the constituent material of the tab, for example, metal materials such as aluminum, copper, titanium, nickel, stainless steel (SUS), and alloys thereof are preferable, and more preferably aluminum, copper from the viewpoint of light weight, corrosion resistance, and high conductivity. Etc. are preferable. In addition, the same material may be used and the other material may be used for a positive electrode tab and a negative electrode tab.

The positive electrode terminal lead and the negative electrode terminal lead are also used as necessary. As a material of a positive electrode terminal lead and a negative electrode terminal lead, the terminal lead used by a well-known lithium ion secondary battery can be used. In addition, the portion taken out from the battery packaging material 29 may be contacted with a peripheral device, a wiring, or the like to short-circuit to prevent a product (for example, an automobile part, especially an electronic device, etc.) from being affected by a heat-shrinkable heat-shrink tube or the like. It is preferable to coat.

(Battery exterior material)

As the battery packaging material 29, a well-known metal can case can be used, and the bag-shaped case using the laminated film containing aluminum which can cover a power generating element can be used. Although the laminated film etc. which consist of PP, aluminum, and nylon laminated in this order can be used for the said laminated film, For example, it is not restrict | limited to these at all. A laminate film is preferable from the viewpoint of being high in output and cooling performance and suitably used in a battery for large equipment for EV and HEV.

Moreover, said lithium ion secondary battery can be manufactured by a conventionally well-known manufacturing method.

<Appearance Configuration of the Lithium Ion Secondary Battery>

9 is a perspective view showing the appearance of a flat lithium ion secondary battery as a representative embodiment of a secondary battery.

As shown in FIG. 9, in the flat lithium ion secondary battery 50, it has a rectangular flat shape, and the positive electrode tab 58 and the negative electrode tab 59 for extracting electric power are taken out from the both sides. It is. The power generation element 57 is surrounded by the battery packaging material 52 of the lithium ion secondary battery 50, and the surroundings are heat-sealed, and the power generation element 57 includes the positive electrode tab 58 and the negative electrode tab 59. ) Is sealed in the state where it is drawn out. Here, the power generation element 57 corresponds to the power generation element 21 of the lithium ion secondary battery 10 shown in FIG. 1 described above. The power generation element 57 is formed by stacking a plurality of unit cell layers (single cells) 19 composed of the positive electrode (positive electrode active material layer) 13, the electrolyte layer 17, and the negative electrode (negative electrode active material layer) 15.

In addition, the said lithium ion secondary battery is not limited to what is a laminated flat shape. In a wound lithium ion secondary battery, it may be a cylindrical shape, it may deform | transform such cylindrical shape, and may be made into the rectangular shape flat shape, and is not specifically limited. In the said cylindrical shape, it does not restrict | limit especially, For example, a laminated film may be used for the exterior material, and a conventional cylindrical can (metal can) may be used. Preferably, the power generating element is sheathed with an aluminum laminate film. By this form, weight reduction can be achieved.

Further, the extraction of the tabs 58 and 59 shown in FIG. 9 is not particularly limited. The positive electrode tab 58 and the negative electrode tab 59 may be taken out from the same side, or the positive electrode tab 58 and the negative electrode tab 59 may be divided into a plurality, and may be taken out from each side. It is not limited to what is shown in. In the wound lithium ion battery, a terminal may be formed using, for example, a cylindrical can (metal can) instead of the tab.

The lithium ion secondary battery is a large-capacity power source for an electric vehicle, a hybrid electric vehicle, a fuel cell vehicle, a hybrid fuel cell vehicle, and the like, and is suitably used for a vehicle driving power source or an auxiliary power source requiring a solid energy density and a solid output density. It is available.

1: Separator
2: center
3: Surface part
4: center part
5: outer periphery
6: mineral
10, 50: lithium ion secondary battery
11: positive electrode current collector
12: negative electrode current collector
13: positive electrode active material layer
15: negative electrode active material layer
17: electrolyte layer
19: unit cell layer
21, 57: power generation elements
25: positive electrode collector plate
27: negative electrode collector plate
29, 52: battery exterior material
58: positive electrode tap
59: negative electrode tab

Claims (6)

A separator in which the thermal resistance in the plane direction is smaller than the thermal resistance in the thickness direction. The separator according to claim 1, wherein the separator has a central portion and a surface portion having a larger porosity than the central portion. The separator of Claim 2 whose porosity of the said surface part is 90% or more. The separator according to claim 2 or 3, wherein the central portion further has a central portion and an outer peripheral portion having a larger porosity than the central portion. The separator according to claim 4, wherein an inorganic substance is contained in the central portion or the central portion. The lithium ion secondary battery containing the separator as described in any one of Claims 1-3.

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