JP6974930B2 - Non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a non-aqueous electrolyte secondary battery having a flat wound electrode body, which has good swelling and productivity after a charge / discharge cycle.

In recent years, with the development of portable electronic devices such as mobile phones and notebook computers and the practical application of electric vehicles, a compact, lightweight, and high-capacity non-aqueous electrolyte secondary battery has been required. ..

As a non-aqueous electrolyte secondary battery that has been made smaller and lighter, for example, the positive electrode and the negative electrode are overlapped with each other and wound in a spiral shape so that the cross section becomes flat. A structure in which the molded flat wound electrode body is housed in a thin outer body (battery case) such as a square outer can or a laminated film outer body composed of a metal laminated film. Can be mentioned.

In the flat wound electrode body as described above, a decrease in productivity due to tearing of the current collector has become a problem. For example, by using a current collector having a specific tensile strength, this can be achieved. Techniques for prevention have been proposed (for example, Patent Document 1).

Further, in Patent Document 2, a fluorine atom-containing polymer material formed from a monomer such as vinylidene fluoride or chlorotrifluoroethylene is used as a binder for the mixture layer, and the elastic modulus of the mixture layer is set to a specific value. At the same time, a technique for increasing the flexibility of the positive electrode by setting the tensile strength of the current collector to a specific value has been proposed.

Japanese Unexamined Patent Publication No. 2012-28158 Japanese Unexamined Patent Publication No. 2005-56743

By the way, with the miniaturization and diversification of equipment, improvement of the energy density per volume of the non-aqueous electrolyte secondary battery is required more than ever. When the electrode body is flat as described above, repeated charging and discharging of the battery causes gas generation and opening of the flat wound electrode body, particularly the bent portion, and the thickness of the flat wound electrode body increases. In addition, there was room for improvement in the distortion of the flat wound electrode body caused by expansion and contraction due to charge and discharge.

The present invention has been made in view of the above circumstances, and an object thereof is a non-aqueous electrolyte secondary having a flat wound electrode body, suppressing swelling after a charge / discharge cycle, and having good productivity. It is to provide batteries.

The non-aqueous electrolyte secondary battery of the present invention, which has achieved the above object, has a wound electrode body in which a positive electrode, a negative electrode and a separator are stacked and wound in a spiral shape to have a flat cross section, and a non-aqueous electrolyte. A non-aqueous electrolyte secondary battery housed inside the exterior body, the positive electrode has a metal current collector and positive electrode mixture layers on both sides of the current collector, and the positive electrode is provided. The current collector has a tensile strength of 3.6 N / mm or less, and an adhesive layer containing an adhesive resin is provided between the positive electrode and the separator and between the negative electrode and the separator, or both. It is characterized by being prepared.

According to the present invention, it is possible to provide a non-aqueous electrolyte secondary battery having a flat wound electrode body, suppressing swelling after a charge / discharge cycle, and having good productivity.

It is a perspective view schematically showing an example of the non-aqueous electrolyte secondary battery of this invention. It is a side view of the non-aqueous electrolyte secondary battery of FIG. It is a partial vertical sectional view schematically showing an example of the non-aqueous electrolyte secondary battery of this invention. It is a side view which shows an example of the non-aqueous electrolyte secondary battery of this invention.

The non-aqueous electrolyte secondary battery of the present invention includes a wound electrode body (hereinafter referred to as “flat wound electrode body”) in which a positive electrode, a negative electrode and a separator are stacked and wound in a spiral shape to have a flat cross section. , Non-aqueous electrolyte is contained in the exterior body. The positive electrode according to the non-aqueous electrolyte secondary battery of the present invention has a metal current collector and a positive electrode mixture layer formed on both sides of the current collector. The positive electrode current collector has a tensile strength of 3.6 N / mm or less.

When the non-aqueous electrolyte secondary battery is repeatedly charged and discharged, it is difficult to maintain the thickness of the flat wound electrode body. For example, if gas is generated on the surface of the electrode during repeated charging and discharging, the gas accumulates in the gap between the electrodes and the flat wound electrode body itself becomes swollen from the initial winding shape. .. In addition, when the tensile strength of the positive electrode current collector is high, the current collector has a strong force to return to its original state, so that the bent portion of the flat wound electrode body opens and the force acts in the direction of swelling, resulting in further swelling. To encourage.

In recent years, devices equipped with non-aqueous electrolyte secondary batteries have become smaller, so the space for storing batteries in the devices is limited. When the occupied volume of the electrode body in the battery increases in this way, the device may be adversely affected when the easily deformable exterior body is used.

However, the positive electrode according to the non-aqueous electrolyte secondary battery of the present invention is provided with a relatively low-strength current collector having a tensile strength of 3.6 N / mm or less, whereby the positive electrode is restored to the original state of the positive electrode current collector. The force to try can be suppressed, and the swelling of the flat wound electrode body can be suppressed.

On the other hand, when the tensile strength of the positive electrode current collector is lowered, the flat wound electrode body is distorted due to the expansion and contraction of the electrode body due to charging and discharging, and the positive electrode is easily broken. When a separator having an adhesive layer is used, the distortion of the flat wound electrode body is suppressed, so that the breakage of the positive electrode can also be suppressed.

Further, as will be described in detail later, the flat wound electrode body is flattened by providing an adhesive layer containing an adhesive resin between the positive electrode and the separator and one or both between the negative electrode and the separator. The thickness of the wound electrode body can be maintained, and in addition, by using a positive electrode current collector having a small tensile strength, the force of the current collector to return to its original state is suppressed, so that the flat wound electrode body can be used. The thickness can be maintained, and by satisfying these two configurations at the same time, the effect of preventing swelling of the flat wound electrode body can be obtained synergistically. As a result, even when a laminated film or an outer can having a thin can is used for the outer body, it is possible to prevent adverse effects on the device on which the battery is mounted, and it is possible to increase productivity from this viewpoint as well.

As the positive electrode according to the non-aqueous electrolyte secondary battery of the present invention, for example, a positive electrode having a positive electrode mixture layer containing a positive electrode active material, a conductive auxiliary agent, a binder, etc. on one or both sides of a current collector is used. can.

As the positive electrode active material of the positive electrode, a conventionally known positive electrode active material for a non-aqueous electrolyte secondary battery, for example, an active material capable of storing and releasing lithium ions is used. As a specific example of such a positive electrode active material, for example, _{a layered structure represented by Li 1 + x} MO ₂ (-0.1 <x <0.1, M: Co, Ni, Mn, Al, Mg, etc.) lithium-containing transition metal oxide, lithium manganese oxide substituted spinel structure part of LiMn ₂ O ₄ and the element with another _{element, LiMPO 4 (M: Co,} Ni, Mn, Fe , etc.) represented by the olivine Examples include type compounds. Specific examples of the lithium-containing transition metal oxide having a layered structure include LiCoO ₂ and other oxides containing at least Co, Ni and Mn (LiMn _1/3 Ni _1/3 Co _1/3 O ₂ and LiMn _{5). / 12} Ni _5/12 Co _1/6 O ₂ etc.) can be exemplified. In particular, when a non-aqueous electrolyte secondary battery is charged with a higher final voltage than usual prior to its use, in order to improve the stability of the positive electrode active material in a state of being charged to a high voltage. It is preferable that the various active materials exemplified above further contain a stabilizing element. Examples of such stabilizing elements include Mg, Al, Ti, Zr, Mo, Sn and the like.

The content of the positive electrode active material in the positive electrode mixture layer is preferably 94 to 98% by mass.

Examples of the conductive auxiliary agent for the positive electrode include graphites such as natural graphite (scaly graphite, etc.) and artificial graphite; carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black. It is preferable to use a carbon material such as carbon fiber; and conductive fiber such as metal fiber; carbon fluoride; metal powder such as aluminum; zinc oxide; conductive whiskers such as potassium titanate; Conductive metal oxides such as titanium oxide; organic conductive materials such as polyphenylene derivatives; and the like can also be used.

The content of the conductive auxiliary agent in the positive electrode mixture layer is preferably 1 to 5% by mass.

Examples of the binder for the positive electrode include acrylonitrile, acrylic acid ester (methyl acrylate, ethyl acrylate, butyl acrylate, diethylhexyl acrylate, etc.) and methacrylic acid ester (methyl methacrylate, ethyl methacrylate, butyl methacrylate, etc.). Copolymers formed by two or more monomers containing at least one monomer selected from the group consisting of; PVDF; vinylidene fluoride-tetrafluoroethylene copolymer (VDF-TFE); fluoride Vinylidene-hexafluoropropylene-tetrafluoroethylene copolymer (VDF-HFP-TFE); vinylidene fluoride-chlorotrifluoroethylene copolymer (VDF-CTFE); etc. may be mentioned, and even if only one of these is used. Often, two or more types may be used in combination.

The content of the binder in the positive electrode mixture layer enables good binding of the positive electrode active material and the conductive auxiliary agent in the positive electrode mixture layer, and prevents desorption from these positive electrode mixture layers. From the viewpoint of better improving the reliability of the battery in which the positive electrode is used, it is preferably 1% by mass or more. However, if the amount of the binder in the positive electrode mixture layer is too large, the amount of the positive electrode active material and the amount of the conductive auxiliary agent may be small, and the effect of increasing the capacity may be reduced. Therefore, the content of the binder in the positive electrode mixture layer is preferably 1.6% by mass or less.

In producing the positive electrode, a paste in which the positive electrode mixture containing the positive electrode active material, the conductive auxiliary agent, the binder and the like is uniformly dispersed using a solvent such as N-methyl-2-pyrrolidone (NMP). A composition in the form of a slurry or a slurry is prepared (the binder may be dissolved in a solvent), this composition is applied to the surface of the positive electrode current collector, dried, and if necessary, pressed to form a positive electrode. A method of adjusting the thickness and density of the agent layer can be adopted. However, the method for producing the positive electrode of the present invention is not limited to the above method, and other methods may be adopted.

In the present invention, an adhesive layer containing an adhesive resin may be provided on the positive electrode mixture layer. As the adhesive resin, the adhesive resin (C) described later can be adopted. The adhesive layer can be obtained by pressing the positive electrode mixture layer, applying a slurry containing the adhesive resin (C), and drying the layer.

The tensile strength of the positive electrode current collector of the present invention is 3.6 N / mm or less. By using a material having a relatively low tensile strength as described above, the force for the flat wound electrode body to return to its original state is reduced, and it is possible to suppress the opening of the bent portion. It is preferably 3.2 N / mm or less, more preferably 2.5 N / mm or less.

On the other hand, 1.2 N / mm or more and 1.8 N / mm are preferable. Within this range, it can be manufactured without breaking the positive electrode current collector.

As for the tensile strength of the current collector as used in the present specification, as a pretreatment, the current collector is cut into a rectangle of 15 mm × 250 mm to form a test piece, and this test piece is set to a chuck distance of 100 mm and is a tensile tester (manufactured by Imada Seisakusho Co., Ltd.). It is a value obtained by conducting a test at a crosshead speed of 10 mm / min using "SDT-52 type").

Examples of the current collector having the tensile strength as described above include the following.

As the material of the positive electrode current collector, an aluminum alloy containing aluminum as the main component is desirable. The aluminum alloy has an aluminum purity of 99.0% by mass or more, and other additive components include, for example, Si ≤ 0.6% by mass, Fe ≤ 0.7% by mass, Cu ≤ 0.25% by mass, and Mn ≤ 1. It is desirable to contain 5% by mass, Mg ≦ 1.3% by mass, and Zn ≦ 0.25% by mass. A foil or film made of such a material can be used as a current collector.

The thickness of the positive electrode current collector is not particularly limited as long as the tensile strength is in the above range, but is preferably 15 μm or less, and more preferably 12 μm or less. By adopting such a thin current collector, the volumetric energy density of the battery can be increased, which is preferable.

It is preferably 4 μm or more. Within this range, it can be manufactured without breaking the positive electrode current collector.

Examples of the negative electrode according to the non-aqueous electrolyte secondary battery of the present invention include those in which a negative electrode mixture layer containing a negative electrode active material is formed on one side or both sides of a current collector.

Examples of the negative electrode active material include graphite materials such as natural graphite (scaly graphite), artificial graphite, and expanded graphite; easily graphitizable carbonaceous materials such as coke obtained by burning pitch; furfuryl alcohol resin (flufuryl alcohol resin). Non-graphitizable carbonaceous materials such as PFA), polyparaphenylene (PPP), and amorphous carbon obtained by low-temperature firing; an amorphous carbon or resin is supported on the surface of the graphite material. Surface-treated carbon materials; carbon materials such as. In addition to the carbon material, lithium or a lithium-containing compound can also be used as the negative electrode active material. Examples of the lithium-containing compound include lithium alloys such as Li—Al and alloys containing elements that can be alloyed with lithium such as Si and Sn. Further, oxide-based materials such as Sn oxide and Si oxide can also be used. The content of the negative electrode active material in the negative electrode mixture layer is preferably, for example, 97 to 99% by mass.

It is preferable to use a surface-treated carbon material as the negative electrode active material because it can prevent an excessive reaction with the non-aqueous electrolyte.

As the negative electrode active material, particularly when a carbon material having an average particle diameter of 8 to 18 μm and relatively small particles, in which amorphous carbon is supported on the surface of the graphite material, is used, the permeability of the non-aqueous electrolyte into the negative electrode mixture layer is used. Is preferable because it improves. The reason is not clear, but if the carbon material has relatively small particles, the size of the pores formed in the negative electrode mixture layer will be uniform when the negative electrode is pressed, so it is non-water. It is considered that the electrolyte easily penetrates. In addition, this type of graphite has high lithium ion acceptability (ratio of constant current charge capacity to total charge capacity), and by using this graphite as the negative electrode active material, it is a non-aqueous electrolyte with better charge / discharge cycle characteristics. A secondary battery can be provided.

The average particle size of the carbon material referred to in the present specification may be determined by, for example, using a laser scattering particle size distribution meter (for example, a microtrack particle size distribution measuring device “HRA9320” manufactured by Nikkiso Co., Ltd.) to melt the carbon material. _{It is a value (d 50} ) median diameter of 50% diameter in a volume-based integrated fraction when the integrated volume is obtained from particles having a small particle size distribution measured by dispersing the carbon material in a medium that does not swell.

The conductive auxiliary agent is not particularly limited as long as it is an electronically conductive material, and may not be used. Specific examples of conductive auxiliary agents include acetylene black; Ketjen black; carbon blacks such as channel black, furnace black, lamp black, and thermal black; carbon fibers; and conductive fibers such as metal fibers. Kind; carbon fluoride; metal powders such as copper and nickel; organic conductive materials such as polyphenylene derivatives; etc., and these may be used alone or in combination of two or more. .. Among these, acetylene black, ketjen black and carbon fiber are particularly preferable. However, when a conductive auxiliary agent is used for the negative electrode, the content of the conductive auxiliary agent in the negative electrode mixture layer is preferably 10% by mass or less in order to increase the capacity.

The binder for the negative electrode mixture layer may be either a thermoplastic resin or a thermosetting resin. Specifically, for example, the same material as the binder according to the positive electrode of the present invention, styrene butadiene rubber (SBR), ethylene-acrylic acid copolymer or Na ⁺ ion cross-linked polymer of the copolymer, ethylene-methacryl. Of an acid copolymer or a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methyl acrylate copolymer or a Na ⁺ ion crosslinked product of the copolymer, an ethylene-methyl methacrylate copolymer or the copolymer. Na ⁺ ion-crosslinked products and the like can be used, and those materials may be used alone or in combination of two or more.

Among the above, PVDF, SBR, ethylene-acrylic acid copolymer or Na ⁺ ion cross-linking product of the copolymer, ethylene-methacrylic acid copolymer or Na ⁺ ion cross-linking product of the copolymer, ethylene-acrylic acid. Methyl copolymers or Na ⁺ ion cross-links of the copolymers, ethylene-methyl methacrylate copolymers or Na ⁺ ion cross-links of the copolymers are particularly preferred. The content of the binder in the negative electrode mixture layer is preferably, for example, 1 to 5% by mass.

In producing the negative electrode, the positive electrode mixture containing the negative electrode active material, the conductive auxiliary agent, the binder and the like is uniformly dispersed using water or a solvent such as N-methyl-2-pyrrolidone (NMP). A paste-like or slurry-like composition is prepared (the binder may be dissolved in a solvent), this composition is applied to the surface of the negative electrode current collector, dried, and pressed if necessary. A method of adjusting the thickness and density of the negative electrode mixture layer can be adopted. However, the method for producing the negative electrode of the present invention is not limited to the above method, and other methods may be adopted.

In the present invention, an adhesive layer containing an adhesive resin may be provided on the negative electrode mixture layer. As the adhesive resin, the adhesive resin (C) described later can be adopted. The adhesive layer can be obtained by pressing the negative electrode mixture layer, applying a slurry containing the adhesive resin (C), and drying the adhesive layer.

The thickness of the negative electrode mixture layer (when the negative electrode mixture layer is formed on both sides of the current collector, the thickness per one side thereof) is preferably 30 to 80 μm.

The current collector used for the negative electrode is not particularly limited as long as it is a substantially chemically stable electron conductor in a non-aqueous electrolyte secondary battery. Examples of the material constituting such a current collector include stainless steel, nickel and its alloy, copper and its alloy, titanium and its alloy, carbon, conductive resin, and the like, as well as carbon or carbon on the surface of copper or stainless steel. Those treated with titanium are used. Of these, copper and copper alloys are particularly preferred. These materials can also be used by oxidizing the surface. Further, it is preferable to make the surface of the current collector uneven by surface treatment. Examples of the shape of the current collector include a film, a sheet, a net, a punched body, a lath body, a porous body, a foam body, a molded body of a fiber group, and the like, in addition to the foil. The thickness of the current collector is not particularly limited, but is preferably 5 to 50 μm, for example.

As the non-aqueous electrolyte, for example, a solution (non-aqueous electrolyte solution) prepared by dissolving a lithium salt in the following non-aqueous solvent can be used.

Examples of the solvent include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (MEC), and γ-butyrolactone (γ-BL). ), 1,2-Dimethoxyethane (DME), tetrahydrofuran (THF), 2-methyltetrahydrofuran, dimethylsulfoxide (DMSO), 1,3-dioxolane, formamide, dimethylformamide (DMF), dioxolane, acetonitrile, nitromethane, Aprotonic organics such as methyl formic acid, methyl acetate, phosphate triester, trimethoxymethane, dioxolane derivatives, sulfolanes, 3-methyl-2-oxazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, diethyl ether, 1,3-propanesaltone. The solvent can be used alone or as a mixed solvent in which two or more kinds are mixed.

The lithium salt according to the non-aqueous electrolyte solution, for _{example, LiClO 4, LiPF 6, LiBF} 4, LiAsF 6, LiSbF 6, LiCF 3 SO 3, LiCF 3 CO 2, Li 2 C 2 F 4 (SO 3) 2, Select from lithium salts such as LiN (CF ₃ SO ₂ ) ₂ , LiC (CF ₃ SO ₂ ) ₃ , LiC _n F _{2n + 1} SO 3 (n ≧ 2), LiN (RfOSO ₂ ) ₂ [where Rf is a fluoroalkyl group]. At least one of these is mentioned. The concentration of these lithium salts in the non-aqueous electrolytic solution is preferably 0.6 to 1.8 mol / l, more preferably 0.9 to 1.6 mol / l.

Non-aqueous electrolytes Non-aqueous electrolytes used in secondary batteries include vinylene carbonate, vinylethylene carbonate, and anhydrous for the purpose of further improving charge / discharge cycle characteristics and improving safety such as high-temperature storage and prevention of overcharging. Additives (including derivatives thereof) such as acid, sulfonic acid ester, dinitrile, 1,3-propanesarton, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, and t-butylbenzene can also be added as appropriate.

Further, as the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery, a gelled product (gel-like electrolyte) obtained by adding a known gelling agent such as a polymer to the above-mentioned non-aqueous electrolyte solution can also be used.

[Rotating electrode body]
The wound electrode body of the present invention is characterized in that an adhesive layer containing an adhesive resin is provided between the positive electrode and the separator and one or both between the negative electrode and the separator. Since the electrode and the separator can be brought into close contact with each other by this adhesive layer, the distortion of the flat wound electrode body due to charging and discharging is suppressed. By suppressing the distortion of the electrode body, it is possible to prevent the positive electrode from breaking even when a positive electrode current collector having a low tensile strength is used.

Further, the positive electrode and the negative electrode can be maintained at a constant distance, the gas generated during charging / discharging is prevented from increasing the distance between the electrodes, and the thickness of the flat wound electrode body and the battery is prevented from increasing. Further, since the distance between the positive electrode and the negative electrode is constant, it is possible to suppress local Li precipitation. Further, since gas generation can be suppressed by the violent reaction between Li and the electrolytic solution accompanying Li precipitation, it is possible to prevent the thickness of the flat wound electrode body and the battery from increasing.

Further, by keeping the distance between the positive electrode and the negative electrode constant, even if charging and discharging are repeated, the charging and discharging reaction occurs uniformly without uneven reaction, and the cycle characteristics are improved.

[Adhesive layer]
From this point of view, the present invention can obtain the effects of the present invention if there is an adhesive layer containing an adhesive resin at least between the positive electrode and the separator and between the negative electrode and the separator. It is preferable that both of them have an adhesive layer containing an adhesive resin because the effect of the present invention is more exhibited.
As aspects of the present invention, there is an adhesive layer on one side of the separator, an adhesive layer on both sides of the separator, an adhesive layer on both sides of the negative electrode, an adhesive layer on the negative electrode side of the separator, and adhesion on both sides of the positive electrode. Having a layer, etc. can be adopted. Above all, it is particularly preferable to provide an adhesive layer containing an adhesive resin on both sides of the separator because it is easy to produce.

It is preferable that the adhesive layer contains an adhesive resin (C) that develops adhesiveness when heated.

The minimum temperature at which the adhesiveness of the adhesive resin (C) is exhibited needs to be a temperature lower than the temperature at which shutdown occurs in a layer other than the adhesive layer in the separator of the present invention. Specifically, 60. It is preferably ° C. or higher and 120 ° C. or lower. Further, when the layer other than the adhesive layer in the separator of the present invention includes the resin porous layer (I) and the heat-resistant porous layer (II) described later, the minimum temperature at which the adhesiveness of the adhesive resin (C) is exhibited is , The temperature needs to be lower than the melting point of the resin (A) (details will be described later) which is the main component of the resin porous layer (I).

By using such an adhesive resin (C), deterioration of the separator can be satisfactorily suppressed when the separator and the positive electrode and / or the negative electrode are heat-pressed and integrated.

There is almost no adhesiveness (adhesiveness) at room temperature (for example, 25 ° C.), and the ability to develop adhesiveness by heat-bonding is called delayed tackiness. In the separator of the present invention, the adhesive resin (C) is present. Therefore, it is preferable to have such a delayed tack property. More specifically, for example, the peel strength obtained when a peeling test is performed at 180 ° between an electrode (for example, a negative electrode) constituting an electrochemical element and a separator is preferable in a state before a heating press. Is 0.05 N / 20 mm or less, particularly preferably 0 N / 20 mm (state in which there is no adhesive force), and the delayed tack property is 0.2 N / 20 mm or more in the state after heat pressing at a temperature of 60 to 120 ° C. It is preferable to have.

However, if the peel strength is too strong, the mixture layer of the electrode (positive electrode mixture layer and negative electrode mixture layer) may be peeled from the current collector of the electrode, and the conductivity may decrease. Therefore, the 180. The peel strength by the peel test at ° is preferably 10 N / 20 mm or less in the state after being heat-pressed at a temperature of 60 to 120 ° C.

The peel strength at 180 ° between the electrode and the separator referred to in the present specification is a value measured by the following method. The separator and the electrode are cut into a size of 5 cm in length and 2 cm in width, respectively, and the cut-out separator and the electrode are overlapped with each other. When the peel strength in the state after heat pressing is obtained, a test piece is prepared by heat pressing a region of 2 cm × 2 cm from one end. The end of the test piece on the side where the separator and the electrode are not heat-pressed is opened, and the separator and the negative electrode are bent so that their angles are 180 °. Then, using a tensile tester, grasp one end side of the separator opened at 180 ° of the test piece and one end side of the electrode, pull at a tensile speed of 10 mm / min, and heat-press both the separator and the electrode in the region. Measure the strength when peeled off. In addition, the peel strength of the separator and the electrode before heat pressing is the same as above, except that each separator cut out as described above and the electrode are overlapped and pressed without heating. , Perform the peeling test by the same method as described above.

Therefore, the adhesive resin (C) has almost no adhesiveness (adhesiveness) at room temperature (for example, 25 ° C.), and the minimum temperature at which the adhesiveness develops is lower than the melting point of the resin (A), preferably 60 ° C. or higher 120. Those having a delayed tack property such as ° C or lower are desirable. The temperature of the heating press when integrating the separator and the electrode is more preferably 80 ° C. or higher and 100 ° C. or lower at which the heat shrinkage of the resin porous layer (I) constituting the separator does not occur so significantly. The minimum temperature at which the adhesiveness of the adhesive resin (C) is exhibited is more preferably 80 ° C. or higher and 100 ° C. or lower.

As the adhesive resin (C) having a delayed tack property, a resin having almost no fluidity at room temperature, exhibiting fluidity at the time of heating, and having a property of being adhered by pressing is preferable. Further, a resin of a type that is solid at room temperature, melts by heating, and exhibits adhesiveness by a chemical reaction can also be used as the adhesive resin (C).

The adhesive resin (C) preferably has a softening point in the range of 60 ° C. or higher and 120 ° C. or lower, with the melting point, glass transition point, or the like as an index. The melting point and glass transition point of the adhesive resin (C) are determined by, for example, JIS K 7121, and the softening point of the adhesive resin (C) is determined by, for example, the method specified in JIS K 7206. Can be measured.

Specific examples of such an adhesive resin (C) include low-density polyethylene (LDPE), poly-α-olefin [polypropylene (PP), polybutene-1, etc.], polyacrylic acid ester, and ethylene-vinyl acetate. Polymers (EVA), ethylene-methyl acrylate copolymers (EMA), ethylene-ethyl acrylate copolymers (EEA), ethylene-butyl acrylate copolymers (EBA), ethylene-methyl methacrylate copolymers (EMMA) , Ionomer resin and the like.

Further, each of the above resins and a resin having adhesiveness at room temperature such as styrene butadiene rubber (SBR), nitrile rubber (NBR), fluororubber, and ethylene-propylene rubber are used as the core, and the melting point and softening point are 60 ° C. or higher and 120. A resin having a core-shell structure having a resin in the range of ° C. or lower as a shell can also be used as the adhesive resin (C). In this case, various acrylic resins, polyurethane, and the like can be used for the shell. Further, as the adhesive resin (C), one-component polyurethane, epoxy resin, or the like, which exhibits adhesiveness within the range of 60 ° C. or higher and 120 ° C. or lower, can also be used.

As the adhesive resin (C), the above-exemplified resin may be used alone or in combination of two or more.

As commercial products of the adhesive resin (C) having delayed tackiness as described above, "Morescomelt Excel Peel (PE, trade name)" manufactured by Matsumura Petroleum Research Institute and "Aquatex (EVA) manufactured by Chuo Rika Kogyo Co., Ltd." , Product name) ”, EVA manufactured by Nippon Unicar Co., Ltd.,“ Heat Magic (EVA, product name) ”manufactured by Toyo Ink Co., Ltd.,“ Evaflex-EEA series (ethylene-acrylic acid copolymer) manufactured by Mitsui DuPont Polychemical Co., Ltd. , Trade name) ”,“ Arontac TT-1214 (acrylic acid ester, trade name) ”manufactured by Toa Synthetic Co., Ltd.,“ Hymilan (ethylene-based ionomer resin, trade name) ”manufactured by Mitsui DuPont Polychemical Co., Ltd., and the like.

When a layer made of the adhesive resin (C) and having substantially no pores is formed, it becomes difficult for the non-aqueous electrolytic solution of the battery to come into contact with the surface of the electrode integrated with the separator. Since there is a risk, it is preferable that a portion where the adhesive resin (C) is present and a portion where the adhesive resin (C) is not present are formed on the surface where the adhesive resin (C) is present. Specifically, for example, the presence and absence of the adhesive resin (C) may be alternately formed in a groove shape, and the adhesive resin (C) such as a circle in a plan view may be formed. There may be a plurality of discontinuously formed locations of the above. In these cases, the locations where the adhesive resin (C) is present may be arranged regularly or randomly.

In the surface where the adhesive resin (C) is present, when a portion where the adhesive resin (C) is present and a portion where the adhesive resin (C) is not present are formed, the adhesive resin (C) is formed on the surface where the adhesive resin (C) is present. The area (total area) of the portion where) is present may be set so that, for example, the peel strength at 180 ° after the separator and the electrode are heat-bonded to the above values, and the adhesiveness to be used is used. Although it may vary depending on the type of the resin (C), specifically, in a plan view, the adhesive resin (C) accounts for 10 to 60% of the area of the existing surface of the adhesive resin (C). It is preferable that it exists.

Further, in terms of the presence surface of the adhesive resin (C), the adhesive resin (C) has a good adhesion to the electrode, for example, at these 180 ° after pressure-bonding the separator and the electrode. to adjust peel strength of the value of said, preferably be 0.05 g / ^{m 2} or more, and more preferably set to 0.1 g / ^{m 2} or more. However, if the adhesive resin (C) is too large in terms of the presence of the adhesive resin (C), the thickness of the flat wound electrode body becomes too large, or the adhesive resin (C) is empty of the separator. There is a risk that the holes will be blocked and the movement of ions inside the electrochemical element will be hindered. Therefore, the existing surface of the adhesive resin (C), the basis weight of the adhesive resin (C) is preferably at 1 g / ^{m 2} or less, more preferably 0.5 g / ^{m 2} or less.

[Separator]
The separator of the present invention comprises a resin porous layer (I) containing a resin (A) having a melting point of 100 to 170 ° C. as a main component, a resin that does not melt at a temperature of 150 ° C. or lower, or a filler having a heat resistant temperature of 150 ° C. or higher. Having a heat-resistant porous layer (II) containing B) as a main component is preferable because it can prevent thermal shrinkage of the separator at high temperatures. The resin porous layer (I) is a layer having the original function of a separator that allows ions to pass through while preventing a short circuit between a positive electrode and a negative electrode in an electrochemical element using the separator of the present invention, and is a heat-resistant porous layer (a heat-resistant porous layer). II) is a layer that plays a role in imparting heat resistance to the separator.

The resin porous layer (I) has a melting point of 100 ° C. or higher and 170 ° C. or lower, that is, a melting temperature measured by a differential scanning calorimeter (DSC) according to JIS K 7121 is 100 ° C. or higher and 170 ° C. or higher. The main component is the resin (A) at ° C or lower. By using a separator having a resin porous layer (I) containing the resin (A) as a main component, the thermoplastic resin melts when the temperature inside the electrochemical element using the separator is high. It is possible to secure a so-called shutdown function that closes the hole of the separator.

The resin (A), which is the main component of the resin porous layer (I), has a melting point of 100 ° C. or higher and 170 ° C. or lower, has an electrochemical insulating property, is electrochemically stable, and will be described in detail later. The non-aqueous electrolyte solution of the electrochemical element and the medium used for the composition for forming the heat-resistant porous layer (II) are not particularly limited as long as they are stable thermoplastic resins, but polyethylene (PE) and polypropylene (PP). ), Polyethylene such as an ethylene-propylene copolymer and the like are preferable.

For the resin porous layer (I), for example, a microporous film made of polyolefin used in an electrochemical element such as a conventionally known lithium secondary battery, that is, a polyolefin mixed with an inorganic filler or the like is used. It is possible to use a film or sheet formed by subjecting the film or sheet to be uniaxially or biaxially stretched to form fine pores. Further, the above resin (A) and another resin are mixed to form a film or a sheet, and then these films or sheets are immersed in a solvent that dissolves only the other resin to form only the other resin. Can also be used as the resin porous layer (I) by dissolving the above to form pores.

The resin porous layer (I) may contain a filler for the purpose of improving the strength and the like. Examples of such a filler include various fillers described later as specific examples of the filler (B) used for the heat-resistant porous layer (II).

The phrase "mainly composed of the resin (A)" in the resin porous layer (I) includes the resin (A) in an amount of 70% by volume or more in the total volume of the constituent components of the resin porous layer (I). It means that. The amount of the resin (A) in the resin porous layer (I) is preferably 80% by volume or more, more preferably 90% by volume or more, based on the total volume of the constituent components of the resin porous layer (I). preferable.

The heat-resistant porous layer (II) contains a resin that does not melt at a temperature of 150 ° C. or lower or a filler (B) having a heat-resistant temperature of 150 ° C. or higher as a main component.

When the heat-resistant porous layer (II) contains a resin having a melting point of 150 ° C. or higher, for example, a microporous film formed of a resin that does not melt at a temperature of 150 ° C. or lower (for example, the above-mentioned microporous film for batteries made of PP). ) Is laminated on the resin porous layer (I), or a dispersion liquid containing resin particles that do not melt at a temperature of 150 ° C. or lower is applied to the porous layer (I) and dried to dry the porous layer (I). ), The form of the coating laminated type in which the porous layer (II) is formed on the surface thereof can be mentioned.

Examples of the resin that does not melt at a temperature of 150 ° C. or lower include PP; crosslinked polymethyl methacrylate, crosslinked polystyrene, crosslinked polydivinylbenzene, styrene-divinylbenzene copolymer crosslinked product, polyimide, melamine resin, phenol resin, and benzoguanamine-formaldehyde condensation. Various cross-linked polymer fine particles such as substances; polysulfone; polyether sulfone; polyphenylene sulfide; polytetrafluoroethylene; polyacrylonitrile; aramid; polyacetal and the like can be mentioned.

When resin particles that do not melt at a temperature of 150 ° C. or lower are used, the particle size thereof is preferably 0.01 μm or more, more preferably 0.1 μm or more, and more preferably 0.1 μm or more, in terms of average particle size. It is preferably 10 μm or less, and more preferably 2 μm or less. As described above, the average particle size of the various particles referred to in the present specification is measured by using, for example, a laser scattering particle size distribution meter "LA-920" manufactured by HORIBA, Ltd., by dispersing these fine particles in a medium that does not dissolve the resin. The average particle size is D50%.

When the heat-resistant porous layer (II) contains a filler (B) having a heat-resistant temperature of 150 ° C. or higher, the filler (B) has a heat-resistant temperature of 150 ° C. or higher and is electrochemically stable in the electrochemical element. Therefore, there is no particular limitation as long as it is stable with respect to the non-aqueous electrolytic solution in the electrochemical element. The term "heat-resistant temperature of 150 ° C. or higher" in the filler (B) referred to in the present specification means that shape changes such as deformation are not visually confirmed at at least 150 ° C. The heat resistant temperature of the filler (B) is preferably 200 ° C. or higher, more preferably 300 ° C. or higher, and even more preferably 500 ° C. or higher.

The filler (B) is preferably inorganic fine particles having electrical insulating properties, and specifically, inorganic oxidation of iron oxide, silica (SiO ₂ ), alumina (Al ₂ O ₃ ), TiO ₂ , BaTiO _{3, and the} like. Fine particles; Inorganic nitride fine particles such as aluminum nitride and silicon nitride; Poorly soluble ion crystal fine particles such as calcium fluoride, barium fluoride and barium sulfate; Covalent crystal fine particles such as silicon and diamond; Clay fine particles such as montmorillonite ; And so on. Here, the inorganic oxide fine particles may be fine particles derived from mineral resources such as boehmite, zeolite, apatite, kaolin, mullite, spinel, olivine, and mica, or artificial products thereof. Further, the inorganic compounds constituting these inorganic fine particles may be elementally substituted or solid-solved, if necessary, and the inorganic fine particles may be surface-treated. Further, the inorganic fine particles have _{electrical insulating properties on the surface of a conductive material exemplified by a metal, a conductive oxide such as SnO 2} , tin-indium oxide (ITO), and a carbonaceous material such as carbon black and graphite. The particles may be electrically insulating by being coated with a material having (for example, the above-mentioned inorganic oxide or the like).

Organic fine particles can also be used as the filler (B). Specific examples of the organic fine particles include polyimide, melamine resin, phenol resin, crosslinked polymethylmethacrylate (crosslinked PMMA), crosslinked polystyrene (crosslinked PS), polydivinylbenzene (PDVB), benzoguanamine-formaldehyde condensate and the like. Examples thereof include fine particles of molecules; fine particles of heat-resistant polymers such as thermoplastic polyimide. The organic resin (polymer) constituting these organic fine particles is a mixture, a modified product, a derivative, or a copolymer (random copolymer, alternate copolymer, block copolymer, graft copolymer) of the above-exemplified materials. ), A crosslinked body (in the case of the above-mentioned heat-resistant polymer).

As the filler (B), one of the above-exemplified ones may be used alone, or two or more kinds of the fillers (B) may be used in combination. Is more preferably at least one selected from alumina, silica, and boehmite.

The particle size of the filler (B) is an average particle size, preferably 0.001 μm or more, more preferably 0.1 μm or more, preferably 15 μm or less, and more preferably 1 μm or less. The average particle size of the filler (B) is, for example, a numerical average measured by using a laser scattering particle size distribution meter (for example, “LA-920” manufactured by HORIBA) and dispersing the filler (B) in an insoluble medium. It can be specified as a particle size.

The shape of the filler (B) may be, for example, a shape close to a spherical shape or a plate shape, but from the viewpoint of preventing a short circuit, plate-shaped particles are preferable. Typical examples of the plate-shaped particles include plate-shaped Al ₂ O ₃ and plate-shaped boehmite.

When the filler (B) is a plate-like particle, the aspect ratio is preferably 5 or more, more preferably 10 or more, preferably 100 or less, and 50 or less. It is more preferable to have. Further, the average value of the ratio of the length in the major axis direction to the length in the minor axis direction (length in the major axis direction / length in the minor axis direction) of the flat plate surface of the particles is preferably 3 or less, and preferably 2 or less. Is more preferable, and a value close to 1 is particularly preferable.

The average value of the ratio of the length in the major axis direction to the length in the minor axis direction of the flat plate surface in the plate-shaped filler (B) is, for example, an image analysis of an image taken by a scanning electron microscope (SEM). Can be obtained by. Further, the aspect ratio of the plate-shaped particles can also be obtained by image analysis of the image taken by SEM.

The presence form of the plate-shaped filler (B) in the separator is preferably such that the flat plate surface is substantially parallel to the surface of the separator, and more specifically, the plate-shaped filler (B) in the vicinity of the surface of the separator. ), The average angle between the flat plate surface and the separator surface is preferably 30 ° or less [most preferably, the average angle is 0 °, that is, the plate-shaped flat plate surface in the vicinity of the surface of the separator is the separator. Parallel to the plane]. The term "near the surface" as used herein refers to a range of about 10% from the surface of the separator to the total thickness. When the existence form of the plate-shaped filler (B) is as described above, the heat shrinkage of the resin porous layer (I) can be prevented more effectively, and a separator having a particularly small heat shrinkage rate is formed as a whole. can do.

Further, in a non-aqueous electrolytic solution secondary battery using the resin porous layer (I) and the heat-resistant porous layer (II), when high output characteristics are required, the filler (B) contains primary particles. It is preferable to use a filler having a secondary particle structure in which the particles are aggregated. By using the tufted filler, the voids of the heat-resistant porous layer (II) can be enlarged, and an electrochemical element having high output characteristics can be formed.

"Containing as a main component" of the heat-resistant porous layer (II) means that it is contained in an amount of 70% by volume or more in the total volume of the constituent components of the heat-resistant porous layer (II). The amount of the filler (B) in the heat-resistant porous layer (II) is preferably 80% by volume or more, more preferably 90% by volume or more, based on the total volume of the constituents of the heat-resistant porous layer (II). preferable. By setting the filler (B) in the heat-resistant porous layer (II) to a high content as described above, it is possible to satisfactorily suppress the heat shrinkage of the entire separator and impart high heat resistance.

Further, the heat-resistant porous layer (II) contains an organic binder for binding the filler (B) to each other and the heat-resistant porous layer (II) and the resin porous layer (I). From this point of view, the preferable upper limit of the amount of the filler (B) in the heat-resistant porous layer (II) is, for example, 99% by volume in the total volume of the constituents of the heat-resistant porous layer (II). Is. If the amount of the filler (B) in the heat-resistant porous layer (II) is less than 70% by volume, for example, it is necessary to increase the amount of the organic binder in the heat-resistant porous layer (II). The pores of the heat-resistant porous layer (II) may be filled with an organic binder, and the function as a separator may be lost, for example.

As the organic binder used for the heat-resistant porous layer (II), the fillers (B) can be adhered to each other and the heat-resistant porous layer (II) and the resin porous layer (I) can be adhered well, and the electrochemical stability is achieved. There is no particular limitation as long as it is stable with respect to the non-aqueous electrolyte solution for electrochemical elements. Specifically, fluororesin [polyvinylidene fluoride (PVDF), etc.], fluororubber, SBR, carboxymethyl cellulose (CMC), hydroxyethyl cellulose (HEC), polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyralidone ( PVP), polyN-vinylacetamide, crosslinked acrylic resin, polyurethane, epoxy resin and the like can be mentioned. These organic binders may be used alone or in combination of two or more.

Among the above-exemplified organic binders, a heat-resistant resin having a heat resistance of 150 ° C. or higher is preferable, and a highly flexible material such as fluorine-based rubber or SBR is more preferable. Specific examples of these include "Dayl Latex Series (fluororubber, product name)" manufactured by Daikin Industries, Ltd., "TRD-2001 (SBR, product name)" manufactured by JSR Corporation, and "EM-" manufactured by Nippon Zeon Corporation. 400B (SBR, product name) "and the like. Further, a crosslinked acrylic resin (self-crosslinked acrylic resin) containing butyl acrylate as a main component and having a structure in which the butyl acrylate is crosslinked and having a low glass transition temperature is also preferable.

When these organic binders are used, they may be used in the form of an emulsion which is dissolved or dispersed in a medium of a composition (slurry or the like) for forming a heat-resistant porous layer (II) described later.

The porosity of the heat-resistant porous layer (II) is 40% or more in a dry state in order to secure the liquid retention amount of the non-aqueous electrolytic solution possessed by the electrochemical element and improve the ion permeability. It is preferably 50% or more, and more preferably 50% or more. On the other hand, from the viewpoint of ensuring strength and preventing internal short circuits, the porosity of the heat-resistant porous layer (II) is preferably 80% or less, more preferably 70% or less in a dry state. .. For the porosity: P (%), the sum of each component i is calculated from the thickness of the heat-resistant porous layer (II), the mass per area, and the density of the constituent components using the following formula (1). Can be calculated by.

P = 100- (Σai / ρi) × (m / t) (1)
Here, in the above formula, ai: the ratio of the component i expressed in% by mass, ρi: the density of the component i (g / cm ³ ), m: the mass per unit area of the heat-resistant porous layer (II) (g / g / cm ² ), t: Thickness (cm) of the heat-resistant porous layer (II).

The separator may have one resin porous layer (I) and one heat-resistant porous layer (II), or may have a plurality of each. Specifically, the heat-resistant porous layer (II) is arranged only on one side of the resin porous layer (I) to serve as a separator. For example, the porous layer (II) is arranged on both sides of the resin porous layer (I). May be arranged and used as a separator. However, if the number of layers of the separator is too large, the thickness of the separator may be increased, which may lead to an increase in the internal resistance of the electrochemical element and a decrease in the energy density, which is not preferable, and the number of layers in the separator is 5 or less. Is preferable.

The separator in the present invention is, for example, after applying a composition for forming a heat-resistant porous layer (II) containing a filler (B) or the like (a liquid composition such as a slurry) to the resin porous layer (I). After drying at a predetermined temperature, a solution containing an adhesive resin (C), an emulsion, or the like is applied, and then the resin porous layer (I) and the heat-resistant porous layer (II) are separated from each other by drying at a predetermined temperature. It can be produced by a method in which the adhesive resin (C) is present on the surface of the separator having the separator.

The composition for forming the heat-resistant porous layer (II) contains an organic binder and the like in addition to the filler (B), and these are dispersed in a solvent (including a dispersion medium; the same applies hereinafter). The organic binder can also be dissolved in a solvent. The solvent used in the composition for forming the heat-resistant porous layer (II) may be any solvent as long as it can uniformly disperse the filler (B) and the like, and can uniformly dissolve or disperse the organic binder, but for example, toluene and the like. In general, organic solvents are preferably used, such as aromatic hydrocarbons, furans such as tetrahydrofuran, and ketones such as methyl ethyl ketone and methyl isobutyl ketone. Alcohol (ethylene glycol, propylene glycol, etc.) or various propylene oxide-based glycol ethers such as monomethyl acetate may be appropriately added to these solvents for the purpose of controlling the interfacial tension. When the organic binder is water-soluble or used as an emulsion, water may be used as a solvent, and alcohols (methyl alcohol, ethyl alcohol, isopropyl alcohol, ethylene glycol, etc.) may be added as appropriate. It is also possible to control the interfacial tension.

The composition for forming the heat-resistant porous layer (II) preferably has a solid content of, for example, 10 to 80% by mass, which contains the filler (B) and the organic binder.

It should be noted that plate-shaped particles are used as the filler (B), and in order to enhance the orientation of the plate-shaped particles and allow their functions to work more effectively, the heat-resistant porous layer (II) containing the plate-shaped particles is formed. After applying the composition to the resin porous layer (I), a method such as applying a shear or a magnetic field to the composition may be used. For example, a composition for forming a heat-resistant porous layer (II) containing a plate-shaped filler (B) is applied to the resin porous layer (I) and then passed through a certain gap to give a share to the composition. You can call.

A solution or emulsion containing the adhesive resin (C) is applied to the laminate of the resin porous layer (I) and the heat-resistant porous layer (II) formed as described above to form an adhesive layer. And the separator can be manufactured. In this case, as described above, the heat-resistant porous layer (II) can be formed on one side or both sides of the resin porous layer (I), and the adhesive resin (C) can be formed on the resin porous layer (C). It can be present on one or both sides of the laminate of I) and the heat-resistant porous layer (II).

Of these, those in which the first adhesive layer, the resin porous layer (I), the heat-resistant porous layer (II), and the second adhesive layer are laminated in this order are preferable. With this configuration, since the adhesive layer is also present on the negative electrode side on the positive electrode side, the shape change due to charging and discharging of the flat wound electrode body can be further suppressed, and the initial thickness can be maintained.

Further, in order to more effectively exert the action of the constituents such as the filler (B), the constituents are unevenly distributed so that the constituents are gathered in layers in parallel or substantially parallel to the film surface of the separator. May be.

The method for producing the separator of the present invention is not limited to the above method, and may be produced by another method. For example, the composition for forming the heat-resistant porous layer (II) is applied to the surface of a substrate such as a liner, dried to form the heat-resistant porous layer (II), and then peeled off from the substrate. The heat-resistant porous layer (II) is layered on a microporous film or the like to be the resin porous layer (I) and integrated by a hot press or the like to form a laminate, and then one or both sides of the laminate are subjected to the same procedure as described above. The separator can also be manufactured by a method in which the adhesive resin (C) is present.

Since the separator manufactured in this manner is used for a separator for an electrochemical element, the thickness is preferably 6 μm or more, and more preferably 10 μm or more, from the viewpoint of more reliably separating the positive electrode and the negative electrode. preferable. On the other hand, if the separator is too thick, the energy density of the electrochemical element may decrease. Therefore, the thickness thereof is preferably 50 μm or less, more preferably 30 μm or less.

Further, when the thickness of the resin porous layer (I) constituting the separator is X (μm) and the thickness of the heat-resistant porous layer (II) is Y (μm), the ratio X / Y of X and Y is. It is preferably 5 or less, more preferably 4 or less, more preferably 1 or more, and even more preferably 2 or more. In the separator of the present invention, even if the thickness ratio of the resin porous layer (I) is increased and the heat-resistant porous layer (II) is thinned, the thermal shrinkage of the entire separator can be suppressed, and the inside of the electrochemical element can be suppressed. It is possible to highly suppress the occurrence of a short circuit due to the thermal shrinkage of the separator in the above. When the separator has a plurality of resin porous layers (I), the thickness X is the total thickness, and when a plurality of heat-resistant porous layers (II) are present, the thickness Y is the total thickness. Is.

Expressed as a specific value, the thickness of the resin porous layer (I) [if there are multiple resin porous layers (I), the total thickness. ] Is preferably 5 μm or more, and more preferably 30 μm or less. Then, the thickness of the heat-resistant porous layer (II) [if there are a plurality of heat-resistant porous layers (II), the total thickness thereof. ] Is preferably 1 μm or more, more preferably 2 μm or more, further preferably 4 μm or more, further preferably 20 μm or less, still more preferably 10 μm or less, and more preferably 6 μm or less. Is more preferable. If the resin porous layer (I) is too thin, the shutdown characteristics may be weakened, and if it is too thick, the energy density of the electrochemical element may be lowered, and the force for heat shrinkage may be exerted. There is a risk that the size will increase and the effect of suppressing heat shrinkage of the entire separator will decrease. Further, if the heat-resistant porous layer (II) is too thin, the effect of suppressing heat shrinkage of the entire separator may be reduced, and if it is too thick, the thickness of the entire separator may increase.

The porosity of the entire separator is preferably 30% or more in a dry state from the viewpoint of ensuring the retention amount of the non-aqueous electrolytic solution and improving the ion permeability. On the other hand, from the viewpoint of ensuring the strength of the separator and preventing an internal short circuit, the porosity of the separator is preferably 70% or less in a dry state. The porosity of the separator: P (%) is determined by using m as the mass per unit area of the separator (g / cm ² ) and t as the thickness of the separator (cm) in the above equation (1). , Can be obtained using the above equation (1).

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

Further, the separator of the present invention is carried out by a method according to JIS P 8117, and the Garley value indicated by the number of seconds that 100 ml of air permeates the membrane under a pressure of ^{0.879 g / mm 2 is 30 to 300 sec.} It is desirable to have. If the air permeability is too large, the ion permeability may be small, while if it is too small, the strength of the separator may be small. Further, as the strength of the separator, it is desirable that the piercing strength using a needle having a diameter of 1 mm is 50 g or more. If the piercing strength is too small, a short circuit may occur due to the breakthrough of the separator when lithium dendrite crystals are generated. By adopting the above configuration, the separator having the above-mentioned air permeability and piercing strength can be obtained.

In the non-aqueous electrolyte secondary battery of the present invention, as described above, the positive electrode and the negative electrode are overlapped with each other via the separator, wound in a spiral shape, and crushed to flatten the cross section. Although it depends on the resin of the separator, a flat wound electrode body manufactured through a process such as pressing by applying heat is used.

Then, the flat wound electrode body is enclosed in the outer body together with the non-aqueous electrolyte to form the non-aqueous electrolyte secondary battery of the present invention.

As the exterior body of the present invention, conventionally known ones can be used as long as the flat wound electrode body can be inserted. For example, a laminated film exterior (see FIG. 4) may be used. In addition, a metal battery composed of a bottomed tubular (square tubular) outer can and a lid, which face each other on the side surfaces and have two wide surfaces that are wider than the other surfaces when viewed from the side. Cases (see Figures 1 to 3) may be used.

When using a metal battery case, the electrode body of the present invention has an excellent swelling suppressing effect as described above, so the outer can should be thinner than before and have a thickness of 0.22 mm or less. Can be used.

The thickness of the outer can is obtained by measuring the thickness at the point corresponding to the intersection of the two diagonal lines in the projected shape of the wide surface (square in FIGS. 1 to 3).

The non-aqueous electrolyte secondary battery of the present invention can be applied to the same applications as the conventionally known non-aqueous electrolyte secondary batteries. According to the present invention, since the thickness of the flat wound electrode body can be made smaller, it becomes possible to contain more material that contributes to charge / discharge with respect to a limited volume, and it is possible to contain more material per volume of the battery. Energy density can be improved. Therefore, it is particularly effective for devices that require high capacity for a limited volume, such as mobile devices, small devices, and robot applications in which multiple cells are combined in series.

Hereinafter, the present invention will be described in detail based on examples. However, the following examples do not limit the present invention.

Example 1
<Manufacturing of positive electrode>
_{LiCoO 2} : a positive electrode active material: 97.3 parts by mass, acetylene black as a conductive auxiliary agent: 1.5 parts by mass, and PVDF as a binder: 1.2 parts by mass are mixed to form a positive electrode mixture. NMP, which is a solvent, is added to the positive electrode mixture, and the mixture is treated with "Clairemix CLM0.8 (trade name)" manufactured by M-Technique ^{for 30 minutes at a rotation speed of 10,000 min-1} to form a paste-like mixture. And said. NMP, which is a solvent, was further added to this mixture, and the mixture was ^{treated at a rotation speed of 10000 min-1} for 15 minutes to prepare a positive electrode mixture-containing composition.

The above-mentioned positive electrode mixture-containing composition is applied to both sides of an arnimium alloy foil (No. 1100, thickness: 10.0 μm, tensile strength: 2.5 N / mm) which is a current collector, and vacuum dried at 80 ° C. for 12 hours. And further pressed, a positive electrode having a positive electrode mixture layer having a thickness of 59 μm was prepared on both sides of the current collector.
<Manufacturing of negative electrode>
A mixture of natural graphite (average particle size: 19.3 μm) and a surface-treated carbon material having an average particle size of 10 μm in which amorphous carbon is supported on the surface of natural graphite is mixed at a mass ratio of 1: 1. Obtained. This mixture (negative electrode active material): 97.5% by mass, SBR: 1.5% by mass, and carboxymethyl cellulose (thickener): 1% by mass are mixed with water to contain a slurry-like negative electrode mixture. The composition was prepared. This negative electrode mixture-containing composition is applied to both sides of a copper foil (thickness: 8 μm) which is a current collector, vacuum dried at 120 ° C. for 12 hours, and further pressed to be applied to both sides of the current collector. A negative electrode having a negative electrode mixture layer having a thickness of 71 μm was prepared.

<Preparation of non-aqueous electrolyte solution>
_{LiPF 6} was dissolved in a mixed solvent having a volume ratio of ethylene carbonate and diethyl carbonate at a volume ratio of 3: 7 at a concentration of 1.1 mol / L, and 2% by mass of vinylene carbonate and 2% by mass of fluoroethylene carbonate were added to each of them to make them non-aqueous. The electrolyte was prepared.

<Making a separator>
To 5 kg of plate-shaped boehmite (average particle size 1 μm, aspect ratio 10), 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) were added, and an internal volume of 20 L was added. A dispersion was prepared by crushing with a ball mill having a number of inversions of 40 times / min for 10 hours. A part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM). As a result, the shape of boehmite was almost plate-like. The average particle size of boehmite after the treatment was 1 μm.

To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added, and the mixture is stirred with a three-one motor for 3 hours to achieve uniform heat resistance. A slurry for forming the porous layer (II) (solid content ratio: 50% by mass) was prepared.

Corona discharge treatment (discharge amount 40 W / min / min) on one side of a microporous film made of PE (thickness 10 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.) which is the resin porous layer (I). m2) is applied, the slurry for forming the heat-resistant porous layer (II) is applied to the treated surface with a microgravia coater, dried, and the heat-resistant porous layer (II) having a thickness of 2 μm is formed into a resin porous layer (I). Formed on one side above.

Next, as the adhesive resin (C), acrylic acid (containing 20% by mass of solid content ratio), which is a delayed tack type adhesive resin, is applied to the resin porous layer (I) side and the heat-resistant porous layer in the laminate. It was applied to both sides of II) using a microgravia coater and dried to obtain a separator (thickness 22 μm) in which the adhesive resin (C) was present on both sides. The total area of the locations where the adhesive resin (C) is present on the surface where the adhesive resin (C) is present in this separator is 30% of the area where the adhesive resin (C) is present in the separator, and is adhered. The texture of the sex resin (C) was 0.5 g / m ² .

<Assembly of lithium secondary battery>
The separators obtained as described above were stacked while being interposed between the positive electrode and the negative electrode, and wound in a spiral shape to prepare a wound electrode group. The obtained wound electrode group was crushed into a flat shape, and a heat press was applied at 80 ° C. for 1 minute at a pressure of 0.5 Pa to prepare a flat wound electrode body. Then, it was placed in an aluminum outer can having a thickness of 6 mm, a height of 80 mm, and a width of 34 mm, and after injecting a non-aqueous electrolytic solution, sealing was performed. The thickness of the can was 0.20 mm at a point corresponding to the intersection of two diagonal lines (the intersection of the broken lines in FIG. 2) in the projected shape of the wide surface of the metal constituting the outer can. A non-aqueous electrolyte secondary battery having the appearance shown in FIG. 1 and having the structure shown in FIG. 2 was manufactured.

Here, the non-aqueous electrolyte secondary battery will be described with reference to FIGS. 1, 2 and 3. FIG. 3 is a partial vertical sectional view schematically showing a non-aqueous electrolyte secondary battery. In the non-aqueous electrolyte secondary battery 1, the positive electrode 31 and the negative electrode 32 are spirally wound via the separator 33 and then pressed so as to be flat to form a square wound electrode body 30 (square). It is housed together with a non-aqueous electrolyte in the outer can 11 (square cylinder). However, in FIG. 3, in order to avoid complication, a metal foil or a non-aqueous electrolytic solution as a current collector used in manufacturing the positive electrode 31 and the negative electrode 32 is not shown. Further, in FIG. 3, the portion on the inner peripheral side of the flat wound electrode body 30 is not shown in a cross section.

The outer can 11 is made of an aluminum alloy and also serves as a positive electrode terminal. An insulator 40 made of a polyethylene sheet is arranged at the bottom of the outer can 11, and a flat wound electrode body 30 made of a positive electrode 31, a negative electrode 32 and a separator 33 is connected to one end of each of the positive electrode 31 and the negative electrode 32. The positive electrode lead body 51 and the negative electrode lead body 52 are pulled out. Further, a stainless steel terminal 21 is attached to the aluminum alloy lid plate 20 that seals the opening of the outer can 11 via an insulating packing 22 made of polypropylene, and the terminal 21 is attached to the terminal 21 via an insulator 24. A lead plate 25 made of stainless steel is attached.

The lid plate 20 is inserted into the opening of the outer can 11, and the joint between the two is welded to seal the opening of the outer can 11 and seal the inside of the battery. Further, in the battery of FIG. 3, a non-aqueous electrolyte injection port 23 is provided in the lid plate 20, and a sealing member is inserted into the non-aqueous electrolyte injection port 23, for example, laser welding or the like. The battery is hermetically sealed by welding to ensure the airtightness of the battery.

In the battery of the first embodiment, the outer can 11 and the lid plate 20 function as positive electrode terminals by directly welding the positive electrode lead body 51 to the lid plate 20, and the negative electrode lead body 52 is welded to the lead plate 25. The terminal 21 functions as a negative electrode terminal by conducting the negative electrode lead body 52 and the terminal 21 via the lead plate 25.

Further, in the battery of the first embodiment, as shown in FIGS. 1 and 2, the wide surface 111 of the outer can 11 is provided with a cleavage groove 12 for opening when the internal pressure becomes larger than the threshold value. ing.

Example 2
A flat wound electrode body was produced in the same manner as in Example 1, and the exterior body was changed to a laminated film to produce a non-aqueous electrolyte secondary battery of Example 2.

Hereinafter, the non-aqueous electrolyte secondary battery of Example 2 will be described with reference to FIG. FIG. 4 is a plan view of the battery of the second embodiment. The laminated film 510 is made of a material obtained by laminating aluminum with nylon and polypropylene, has a substantially quadrangular planar shape, and houses a flat wound electrode body 530 inside. (The portion raised from the laminated film 510 corresponds to the portion where the electrode body 530 is present.) The edge portion 511 of the laminated film 510 is sealed. One end of the positive electrode tab 511 is connected to the positive electrode of the wound electrode body, and the other end is drawn out via the laminated film 510. One end of the negative electrode tab 552 is connected to the negative electrode of the wound electrode body, and the other end is drawn out via the laminated film 510.

Example 3
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode current collector was changed to an arnimium alloy foil (No. 1100, thickness: 12.0 μm, tensile strength: 3.2 N / mm).

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 4
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode current collector was changed to an arnimium alloy foil (No. 1100, thickness: 15.0 μm, tensile strength: 3.6 N / mm). A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Example 5
<Making a separator>
To 5 kg of plate-shaped boehmite (average particle size 1 μm, aspect ratio 10), 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) were added, and an internal volume of 20 L was added. A dispersion was prepared by crushing with a ball mill having a number of inversions of 40 times / min for 10 hours. A part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM). As a result, the shape of boehmite was almost plate-like. The average particle size of boehmite after the treatment was 1 μm.

To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added, and the mixture is stirred with a three-one motor for 3 hours to achieve uniform heat resistance. A slurry for forming the porous layer (II) (solid content ratio: 50% by mass) was prepared.

Corona discharge treatment (discharge amount 40 W / min / min) on one side of a microporous film made of PE (thickness 10 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.) which is the resin porous layer (I). m2) is applied, the slurry for forming the heat-resistant porous layer (II) is applied to the treated surface with a microgravia coater, dried, and the heat-resistant porous layer (II) having a thickness of 2 μm is formed into a resin porous layer (I). Formed on one side above.

Next, acrylic acid (containing 20% by mass of solid content ratio), which is a delayed tack type adhesive resin, is applied as the adhesive resin (C) on the surface of the laminate on the resin porous layer (I) side. It was applied using a coater and dried to obtain a separator (thickness 22 μm) in which the adhesive resin (C) was present on one side. The total area of the locations where the adhesive resin (C) is present on the surface where the adhesive resin (C) is present in this separator is 30% of the area where the adhesive resin (C) is present in the separator, and is adhered. The texture of the sex resin (C) was 0.5 g / m ² .

With the above separator, a wound body electrode group was prepared with the adhesive layer facing the negative electrode side. A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this wound body electrode group was used.

Comparative Example 1
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode current collector was changed to an arnimium alloy foil (No. 3003, thickness: 15.0 μm, tensile strength: 4.0 N / mm). A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that this positive electrode was used.

Comparative Example 2
A positive electrode was produced in the same manner as in Example 1 except that the positive electrode current collector was changed to an arnimium alloy foil (No. 3003, thickness: 10.0 μm, tensile strength: 3.0 N / mm).

<Making a separator>
To 5 kg of plate-shaped boehmite (average particle size 1 μm, aspect ratio 10), 5 kg of ion-exchanged water and 0.5 kg of a dispersant (aqueous polycarboxylic acid ammonium salt, solid content concentration 40% by mass) were added, and an internal volume of 20 L was added. A dispersion was prepared by crushing with a ball mill having a number of inversions of 40 times / min for 10 hours. A part of the treated dispersion was vacuum dried at 120 ° C. and observed with a scanning electron microscope (SEM). As a result, the shape of boehmite was almost plate-like. The average particle size of boehmite after the treatment was 1 μm.

To 500 g of the above dispersion, 0.5 g of xanthan gum as a thickener and 17 g of a resin binder dispersion (modified polybutyl acrylate, solid content 45% by mass) as a binder are added, and the mixture is stirred with a three-one motor for 3 hours to achieve uniform heat resistance. A slurry for forming the porous layer (II) (solid content ratio: 50% by mass) was prepared.

Corona discharge treatment (discharge amount 40 W / min / min) on one side of a microporous membrane made of PE (thickness 16 μm, porosity 40%, average pore diameter 0.08 μm, PE melting point 135 ° C.) which is the resin porous layer (I). m ² ) is applied, the slurry for forming the heat-resistant porous layer (II) is applied to the treated surface with a microgravia coater, dried, and the heat-resistant porous layer (II) having a thickness of 6 μm is formed into a resin porous layer (I). ) It was formed on one side of the upper surface to prepare a separator.

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the above positive electrode and separator were used.

Comparative Example 3
The positive electrode current collector was changed to an arnimium alloy foil (No. 3003, thickness: 15.0 μm, tensile strength: 4.0 N / mm).

The separator was changed to the same as that of Comparative Example 2.

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 1 except that the above positive electrode and separator were used.

Comparative Example 4
The positive electrode current collector was changed to an arnimium alloy foil (No. 3003, thickness: 15.0 μm, tensile strength: 4.0 N / mm).

A non-aqueous electrolyte secondary battery was produced in the same manner as in Example 2 except that this positive electrode was used.

The configurations of the non-aqueous electrolyte secondary batteries of Examples and Comparative Examples and their evaluations are summarized in Tables 1 and 2. In addition, the dimensions of the flat electrode body used in Examples and Comparative Examples and the non-aqueous electrolyte secondary battery were evaluated as follows.

<Insert defect rate>
For Examples 1, 2 to 4 and Comparative Examples 1 to 3, the insertion failure rate into the outer body (metal outer can + lid) was determined. In Examples 1, 2 to 4 and Comparative Examples 1 to 3, 1000 wound electrode bodies and exterior bodies before assembly were prepared, respectively.

When the wound electrode body was inserted into the exterior body, the case where the surface of the wound electrode body was damaged was regarded as the occurrence of insertion failure, and the rate of occurrence of insertion failure when 1000 batteries were manufactured was determined as a percentage.

<Initial thickness of non-aqueous electrolyte secondary battery>
For each of the batteries of Examples and Comparative Examples, the thickness of the batteries was measured. The measurement points were Examples 1, 2 to 4, and for Comparative Examples 1 to 3, the thickness of the battery at the intersection of the alternate long and short dash lines shown in FIG. 2 was measured, and Examples 2 to 4 and Comparative Examples 1 to 3 were Example 1. The relative dimensions when the thickness of 100 is 100 are shown in Table 1.

In Example 2 and Comparative Example 4, the thickness of the battery at the intersection of the alternate long and short dash lines shown in FIG. 4 was measured. In Comparative Example 4, the relative dimensions when the thickness of Example 2 is 100 are shown in Table 2.

<Thickness of non-aqueous electrolyte secondary battery after charge / discharge cycle>
For each of the batteries of Examples and Comparative Examples used for the initial thickness measurement, after charging with a constant current of 1.0 C up to 4.4 V in an environment of 45 ° C., a constant voltage until the total charging time reaches 2.5 hours. A series of operations of charging and then discharging at a constant current of 1.0 C to a battery voltage of 2.75 V was set as one cycle, and these were repeated 700 times.

Then, the post-cycle thickness of each of the batteries of Examples and Comparative Examples was measured by the same means as the initial thickness.

The difference between the thickness after the cycle of the batteries of Examples and Comparative Examples and the initial thickness (hereinafter referred to as thickness increase) is calculated, and the thickness increase for Examples 2 to 4 and Comparative Examples 1 to 3 is the thickness increase of Example 1. Table 1 shows the relative values when the value is 100. Table 2 shows the relative values of the thickness increase in Comparative Example 4 when the thickness increase in Example 2 is 100.

1 Non-aqueous electrolyte secondary battery 10 Battery case 11 Exterior can 111 Wide surface on the side surface of the exterior can 12 Cleft groove 20 Lid 21 Terminal 30 Flat winding electrode body 31 Positive electrode 32 Negative electrode 33 Separator 501 Non-aqueous electrolyte secondary battery 510 Laminated film

Claims (6)

A non-aqueous electrolyte secondary battery in which a wound electrode body in which a positive electrode, a negative electrode, and a separator are stacked and wound in a spiral shape to form a flat cross section, and a non-aqueous electrolyte are housed in an exterior body.
The positive electrode has a current collector made of an aluminum alloy and positive electrode mixture layers on both sides of the current collector.
The positive electrode current collector has a tensile strength of 3.2 N / mm or less and has a tensile strength of 3.2 N / mm or less.
A non-aqueous electrolyte secondary battery comprising an adhesive layer containing an adhesive resin between the positive electrode and the separator and one or both between the negative electrode and the separator. The non-aqueous electrolyte secondary battery according to claim 1, wherein the separator has an adhesive layer on one side or both sides. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein the current collector of the positive electrode has a tensile strength of 2.5 N / mm or less. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3, wherein the exterior body is a laminated film. The non-water according to any one of claims 1 to 3, wherein the exterior body has a bottomed tubular metal outer can and a lid for sealing the opening of the metal outer can. Electrolyte secondary battery. The side surface portions of the outer can have two wide surfaces that face each other and are wider than the other surfaces when viewed from the side.
The wide surface has a rectangular projection shape from the side surface.
The non-water according to claim 5, wherein the metal constituting the outer can has a thickness of 0.22 mm or less at a portion corresponding to an intersection of two diagonal lines in the projected shape of the wide surface. Electrolyte secondary battery.

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