Secondary battery laminate and secondary battery

Abstract

This invention provides a laminate for a secondary battery, which is formed by laminating electrodes and spacers using an adhesive material. In this laminate, the shear peel strength between the electrodes and spacers, measured under temperature variations, is valued as A (mN / mm²). 2 The maximum thermal shrinkage force obtained from thermomechanical analysis of the spacer is B (mN / mm). 2 Furthermore, thermomechanical analysis of the spacer revealed that the thermal shrinkage force was reduced to a value lower than the thermal shrinkage force at 30°C (mN / mm). 2 ) Value 20% higher (mN / mm 2 When the temperature is the heat shrinkage end temperature α (°C), the value of A is above 25°C and below the heat shrinkage end temperature α (°C), satisfying the condition A > B.

Description

Technical Field

[0001] This invention relates to a laminate for a secondary battery and a secondary battery. Background Technology

[0002] Secondary batteries, such as lithium-ion batteries, are characterized by their small size, light weight, high energy density, and ability to be repeatedly charged and discharged, making them suitable for a wide range of applications. Furthermore, secondary batteries typically include battery components such as a positive electrode, a negative electrode, and a spacer that isolates the positive and negative electrodes to prevent short circuits between them.

[0003] In the manufacturing process of secondary batteries, sometimes electrodes immersed in electrolyte are pressed together with spacers to form a laminate (hereinafter sometimes referred to as "laminate for secondary batteries"). Sometimes it is cut to the desired size as needed, and sometimes it is laminated, folded or wound.

[0004] In recent years, various structures of rechargeable batteries and their manufacturing methods have been proposed. For example, Patent Document 1 discloses an electrochemical element (i.e., a rechargeable battery laminate) formed by bonding spacers and electrodes with a crystalline polymer. The spacers have a porous coating and a dot-patterned layer. The porous coating is formed on at least one side of a porous substrate and is composed of a mixture of inorganic particles and a binder polymer. The dot-patterned layer is formed on the surface of the porous coating, with multiple dots of crystalline polymer spaced apart from each other. Furthermore, Patent Document 2 discloses a laminate formed by stacking spacers and electrodes. The spacers have a defined thermoplastic polymer coating covering at least one surface of a polyolefin microporous membrane. In this defined thermoplastic polymer coating, portions containing a thermoplastic polymer having at least one glass transition temperature in a temperature range below 20°C and at least one glass transition temperature in a temperature range above 20°C, and portions not containing the thermoplastic polymer, exist in an island-like configuration.

[0005] Furthermore, Patent Document 3, for example, discloses a method for efficiently manufacturing a laminate for secondary batteries. The manufacturing method of Patent Document 3 includes: a step of forming an adhesive material in a predetermined amount on the mating surface of at least one of the electrodes and spacers; a step of transporting the electrodes and spacers to a mating start position without allowing other components to contact the mating surface on which the adhesive material is formed; and a step of mating the electrodes and spacers. According to this manufacturing method, a laminate for secondary batteries formed by mating spacers and electrodes with an adhesive material can be manufactured efficiently.

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: Japanese Patent No. 5572101;

[0009] Patent Document 2: Japanese Patent No. 5876577;

[0010] Patent document 3: International Publication No. 2019 / 163489. Summary of the Invention

[0011] The problem the invention aims to solve

[0012] Here, for the laminated body for secondary batteries, it is required that the electrodes and spacers be well bonded within the laminated body, and that it be able to form a secondary battery with low internal resistance and excellent stability. However, the laminated body for secondary batteries obtained according to the above-mentioned prior art cannot simultaneously achieve all of the above-mentioned properties at a high level.

[0013] Therefore, the object of the present invention is to provide a laminate for a secondary battery formed by laminating electrodes and spacers with an adhesive material, wherein the adhesion between the electrodes and spacers of the laminate for the secondary battery is excellent, and it is capable of forming a secondary battery with low internal resistance and excellent stability.

[0014] Furthermore, the present invention aims to provide a secondary battery with low internal resistance and excellent stability.

[0015] Solution for solving the problem

[0016] In order to solve the above-mentioned problems, the inventors conducted in-depth research. Then, the inventors discovered that when manufacturing a laminate for a secondary battery formed by stacking electrodes and spacers with adhesive materials, within a specified temperature range, the shear peel strength between the electrodes and spacers is greater than the maximum thermal shrinkage force of the spacers, thereby enabling the manufacture of a laminate for a secondary battery that achieves the above-mentioned objective, thus completing the present invention.

[0017] That is, the object of the present invention is to advantageously solve the above-mentioned problems. The feature of the rechargeable battery laminate of the present invention is that it is a rechargeable battery laminate formed by laminating electrodes and spacers via an adhesive material, and the shear peel strength between the electrodes and the spacers, measured by temperature change, is A (mN / mm²). 2 The maximum thermal shrinkage force obtained from the thermomechanical analysis of the above spacer is B (mN / mm). 2 Furthermore, thermomechanical analysis of the aforementioned spacer revealed that the thermal shrinkage force was reduced to a value lower than the thermal shrinkage force at 30°C (mN / mm). 2 ) 20% higher value (mN / mm 2When the temperature is the heat shrinkage end temperature α (°C), the value of A above 25°C and below the heat shrinkage end temperature α (°C) satisfies A > B. A secondary battery laminate that satisfies the condition that the shear peel strength A between the electrode and the spacer is greater than the maximum heat shrinkage force B of the spacer within a temperature range above 25°C and below the heat shrinkage end temperature α (°C) exhibits excellent adhesion between the electrode and the spacer, and can form a secondary battery with low internal resistance and excellent stability.

[0018] The values ​​of “shear peel strength A between the electrode and the spacer”, “maximum thermal shrinkage force B obtained from thermomechanical analysis of the spacer”, and “thermal shrinkage end temperature α (°C)” can be measured according to the methods described in the examples.

[0019] In this invention, the spacer in the secondary battery laminate preferably comprises a polyolefin resin. If the spacer comprises a polyolefin resin, the internal resistance of the resulting secondary battery can be further reduced, and its stability can be further improved.

[0020] Furthermore, the laminate for secondary batteries of the present invention preferably contains at least one of the following adhesive materials: a non-water-soluble polymer that does not have a glass transition temperature and melting point in a temperature range below 180°C, and a non-water-soluble polymer that has a glass transition temperature in a temperature range below 180°C but a melting point in a temperature range above 180°C. Using an adhesive material containing at least one of the following—a non-water-soluble polymer that does not have a glass transition temperature and melting point in a temperature range below 180°C, and a non-water-soluble polymer that has a glass transition temperature in a temperature range below 180°C but a melting point in a temperature range above 180°C—further improves the adhesion between the electrode and the spacer, and provides a secondary battery with even better stability.

[0021] Furthermore, "water-insoluble polymers" refers to polymers in which the insoluble component is 90% or more by mass when 0.5g of the polymer is dissolved in 100g of water at 25°C. In addition, the melting point and glass transition temperature of water-insoluble polymers can be analyzed according to JIS K 7121:2012.

[0022] Furthermore, in the laminated body for secondary batteries of the present invention, the water-insoluble polymer is preferably a particulate polymer with a volume average particle size D50 smaller than the average pore size of the spacer. The volume average particle size D50 is the particle size that accounts for 50% of the cumulative volume from the smallest particle size side in the particle size distribution based on a volume reference determined by dynamic light scattering. If the water-insoluble polymer is a particulate polymer with a volume average particle size D50 smaller than the average pore size of the spacer, the adhesion between the electrode and the spacer can be further improved.

[0023] Furthermore, the polymer being "particulate" means that its particle size distribution can be determined using dynamic light scattering. Additionally, the "volume average particle size D50" of the particulate polymer can be determined using the method described in the examples. Furthermore, the average pore size of the spacer is the numerical average of the diameters measured from 1000 randomly selected voids, which can be determined using the method described in the examples.

[0024] Furthermore, in the laminated body for secondary batteries of the present invention, the adhesive material preferably comprises a water-soluble polymer with a thermal decomposition temperature of 180°C or higher. Using an adhesive material comprising a water-soluble polymer with a thermal decomposition temperature of 180°C or higher further improves the adhesion between the electrode and the spacer, and provides a secondary battery with even better stability.

[0025] Here, "water-soluble polymer" refers to a polymer in which the insoluble component is less than 1.0% by mass when 0.5g of the polymer is dissolved in 100g of water at a temperature of 25°C. Furthermore, the "thermal decomposition temperature" of the water-soluble polymer can be determined according to JIS K 7120:1987.

[0026] The object of the present invention is to advantageously solve the above-mentioned problems. The secondary battery of the present invention is characterized by having a laminated body for a secondary battery as described above. The secondary battery having the laminated body for a secondary battery of the present invention has low internal resistance and excellent stability.

[0027] Invention Effects

[0028] According to the present invention, a laminate for a secondary battery is provided that exhibits excellent adhesion between the electrodes and spacers, and is capable of forming a secondary battery with low internal resistance and excellent stability.

[0029] Furthermore, according to the present invention, a secondary battery with low internal resistance and excellent stability can be provided. Attached Figure Description

[0030] Figure 1 A graph showing the thermal shrinkage curve obtained from a thermomechanical analysis of a spacer for an example.

[0031] Figure 2 This is an explanatory diagram illustrating a simplified configuration of an example of an apparatus for manufacturing a laminate for a secondary battery. Detailed Implementation

[0032] The embodiments of the present invention will now be described in detail.

[0033] Here, the laminate for secondary batteries of the present invention can be used in the manufacture of secondary batteries such as non-aqueous secondary batteries (e.g., lithium-ion secondary batteries).

[0034] (Laminated structure for secondary batteries)

[0035] The rechargeable battery laminate of the present invention is formed by laminating electrodes and spacers using an adhesive material. In this rechargeable battery laminate, the shear peel strength between the electrodes and spacers, measured under temperature variations, needs to be A (mN / mm²). 2 The maximum thermal shrinkage force obtained from thermomechanical analysis of the spacer is B (mN / mm). 2 Furthermore, thermomechanical analysis of the spacer revealed that the thermal shrinkage force was reduced to a value lower than the thermal shrinkage force at 30°C (mN / mm). 2 ) 20% higher value (mN / mm 2 When the temperature is the heat shrinkage end temperature α (°C), the value of A is above 25°C and below the heat shrinkage end temperature α (°C), satisfying A > B. A secondary battery laminate that satisfies the condition that the shear peel strength A between the electrode and the spacer is greater than the maximum heat shrinkage force B of the spacer within a temperature range above 25°C and below the heat shrinkage end temperature α (°C) exhibits excellent adhesion between the electrode and the spacer, and can form a secondary battery with low internal resistance and excellent stability.

[0036] While the reasoning is not clear, it is speculated as follows: First, as mentioned above, "A > B in the temperature range above 25°C and below the heat shrinkage end temperature α°C" means that in the temperature range from room temperature to the end of the spacer's heat shrinkage, i.e., from room temperature until the spacer's heat shrinkage force almost disappears, the shear peel strength A between the electrode and the spacer is greater than the maximum heat shrinkage force that the spacer can exert (i.e., the spacer's maximum heat shrinkage force B). More specifically, "the spacer's heat shrinkage force almost disappears" means that the gaps are blocked by the melting of the spacer, thus achieving the so-called "spacer shutdown performance." Therefore, if the relationship A > B is satisfied throughout the entire "temperature range above 25°C and below the heat shrinkage end temperature α°C," then the adhesion between the electrode and the spacer can be maintained in the temperature range above room temperature until the spacer shutdown is completed. If the adhesion between the electrode and the spacer can be maintained in the secondary battery laminate, the increase in the internal resistance of the secondary battery having the secondary battery laminate can be suppressed, and thermal runaway can be suppressed to improve stability. Furthermore, more specifically, the stability of the secondary battery can be evaluated through tests such as nail penetration and overcharge tests, as verified in the embodiments described later. In the nail penetration test, the performance in suppressing thermal runaway, such as fire or rupture, can be tested when the secondary battery is subjected to a simulated internal short circuit. In the overcharge test, the performance in suppressing thermal runaway can be tested when the secondary battery is continuously charged and discharged under high load conditions.

[0037] Furthermore, the secondary battery laminate of the present invention is a secondary battery laminate formed by laminating electrodes and spacers with an adhesive material. More specifically, the secondary battery laminate of the present invention is a secondary battery laminate formed by bonding electrodes and spacers together with a bonding surface and integrating them. Here, the electrode that is laminated with the spacer to form the secondary battery laminate can be only a positive electrode, only a negative electrode, or both a positive electrode and a negative electrode. In addition, when the positive electrode and the negative electrode are bonded to the spacer to form the secondary battery laminate, the number of positive electrode, negative electrode and spacer in the secondary battery laminate can be one or more.

[0038] That is, the structure of the secondary battery stack of the present invention can be any one of the following (1) to (6).

[0039] (1) Positive electrode / spacer

[0040] (2) Negative electrode / spacer

[0041] (3) Positive electrode / spacer / negative electrode

[0042] (4) Positive electrode / spacer / negative electrode / spacer

[0043] (5) Spacer / Positive electrode / Spacer / Negative electrode

[0044] (6) A structure in which multiple positive and negative electrodes are alternately stacked via spacers (e.g., “spacer / negative electrode / spacer / positive electrode / spacer / negative electrode… / spacer / positive electrode” etc.)

[0045] <Electrode>

[0046] There are no particular limitations on the electrode; for example, an electrode formed from an electrode substrate in which an electrode composite material layer is formed on one or both sides of the current collector, or an electrode in which a porous membrane layer is further formed on the electrode composite material layer of the electrode substrate, can be used.

[0047] Furthermore, there are no particular limitations on the current collector, electrode composite material layer, and porous membrane layer; any current collector, electrode composite material layer, and porous membrane layer that can be used in the field of secondary batteries, such as those described in Japanese Patent Application Publication No. 2013-145763, may be used. Here, a porous membrane layer refers to a layer containing non-conductive particles, such as those described in Japanese Patent Application Publication No. 2013-145763.

[0048] Here, the electrodes of the secondary battery laminate of the present invention preferably do not have a porous film layer containing non-conductive particles, which is mainly provided to improve the heat resistance of the secondary battery laminate. This is because, as described above, the temperature range of the secondary battery laminate of the present invention above 25°C and below the heat shrinkage end temperature α°C satisfies the relationship A > B. Therefore, even without a porous film layer mainly provided to improve the heat resistance of the secondary battery laminate, sufficient stability can be imparted to the obtained secondary battery. If the secondary battery laminate does not have a porous film layer or other constituent parts that do not directly contribute to the electrochemical reaction, the increase in internal resistance of the obtained secondary battery can be suppressed, and the energy density can be improved.

[0049] <spacer>

[0050] Furthermore, the porosity of the spacers in the secondary battery laminate of the present invention is preferably 5% or more, more preferably 20% or more, and even more preferably 40% or more. If the porosity of the spacers is 5% or more, substances that contribute to the battery reaction, such as lithium ions, can move through the spacers, thus suppressing an excessive increase in the internal resistance of the resulting secondary battery. Additionally, the porosity of the spacers is not particularly limited and can be, for example, 70% or less. Furthermore, "porosity of the spacers" is a value obtained by cross-sectional observation of the spacers included in the secondary battery laminate, expressed as a ratio (%) of the area of ​​voids in a randomly selected target area to the total area of ​​the target area.

[0051] Furthermore, the average diameter of the spacer pores (hereinafter also referred to as the average pore size of the spacer) is preferably 100 nm or more and 1000 nm or less. Furthermore, from the viewpoint of improving the adhesion between the spacer and the electrode, the average pore size of the spacer is preferably larger than the volume average particle size D50 of the particulate polymer, which is a non-water-soluble polymer, as described later. In this case, when the cross-sectional view of the laminate for the secondary battery is performed and the ratio of the area of ​​the particulate polymer contained in the pores of the spacer to the total area of ​​the particulate polymer is measured, the ratio is preferably 10% or more. This ratio can be controlled by various adjustments, such as adjusting the relative ratio between the average pore size of the spacer and the volume average particle size of the particulate polymer, and the heating and / or pressurization conditions when the spacer and the electrode are bonded.

[0052] In addition, the spacer may be, for example, a spacer formed from a spacer substrate, or a spacer with a porous membrane layer on one or both sides of the spacer substrate, without particular limitation.

[0053] There are no particular limitations on the spacer substrate and porous membrane layer; examples include any spacer substrate and porous membrane layer that can be used in the field of secondary batteries, such as those described in Japanese Patent Application Publication No. 2012-204303 and Japanese Patent Application Publication No. 2013-145763. Spacers comprising spacer substrates formed of polyolefin resins such as polyethylene and polypropylene are particularly preferred. If the spacer comprises a polyolefin resin, the internal resistance of the resulting secondary battery can be further reduced, and the stability can be further improved.

[0054] Furthermore, for the same reasons mentioned in the <Electrode> section, the spacers of the secondary battery laminate of the present invention preferably do not have a porous membrane layer provided primarily to improve the heat resistance of the secondary battery laminate.

[0055] <Maximum thermal shrinkage force B of the spacer>

[0056] "The value of the maximum thermal shrinkage force B obtained from the thermomechanical analysis of the spacer" refers to the value per unit area (mm²) of the test piece for the spacer determined by the thermomechanical analysis of the test piece. 2 The value of the maximum load (mN).

[0057] Figure 1 This shows the heat shrinkage force (mN / mm) 2 The curve (thermal shrinkage curve) is obtained by plotting the data from a thermomechanical analysis of a spacer for an example, with the vertical axis set to 0 and the horizontal axis set to temperature (°C). Figure 1 As shown, the maximum heat shrinkage force B of the spacer is the maximum value of the heat shrinkage force. Of course, the shape of the heat shrinkage curve varies depending on the physical properties of the spacer, but even in cases where the heat shrinkage curve has multiple maxima, the maximum value of the heat shrinkage force is equivalent to the maximum heat shrinkage force B of the spacer.

[0058] <Heat shrinkage end temperature α (°C) of spacer>

[0059] like Figure 1 As shown, "the heat shrinkage end temperature α (°C) of the spacer" is the value F of the heat shrinkage force obtained from the thermomechanical analysis of the spacer, which is reduced to below 30°C. (30) (mN / mm 2 ) 20% higher value (mN / mm 2 At temperature α (°C), the spacer's cutting-off performance is achieved and completed. That is, at temperature α (°C), the spacer melts and the voids are blocked. Material movement through the spacer is hindered, thereby terminating the battery reaction and stopping the thermal runaway of the secondary battery. Furthermore, the spacer's cutting-off performance... Figure 1The heat shrinkage onset temperature β is shown. The heat shrinkage onset temperature β corresponds to the intersection of the tangents before and after the point where the slope of the tangent to the heat shrinkage curve begins to change significantly after the start of heating, as detected by thermomechanical analysis.

[0060] The thermal shrinkage initiation temperature β of the spacer is preferably 100°C or less, more preferably 90°C or less, and even more preferably 70°C or less. If the thermal shrinkage initiation temperature β of the spacer is below the above-mentioned upper limit, the stability of the resulting secondary battery can be further improved. More specifically, when the secondary battery is continuously charged and discharged under high load conditions, the performance in suppressing thermal runaway (i.e., the characteristics that can be evaluated by overcharge tests) can be improved. In addition, the thermal shrinkage initiation temperature of the spacer can be, for example, 45°C or more.

[0061] <Peel strength A between electrode and spacer>

[0062] The "shear peel strength A between the electrode and the spacer" is the tensile stress (mN) measured in the shear direction while varying the temperature of the test piece formed by bonding the spacer and electrode with adhesive material, and then converted to a value per unit area (mm²). 2 The value of the peel strength is [value missing]. This peel strength can be adjusted based on a combination of the properties of the adhesive material used and the properties of the spacers.

[0063] Furthermore, the temperature range of the secondary battery laminate of the present invention, which is above 25°C and below the thermal shrinkage end temperature α°C, satisfies the relationship A > B. Therefore, in the secondary battery having this laminate, thermal runaway can be suppressed within the temperature range until the spacer is cut off, and excessive increase in internal resistance can be suppressed.

[0064] <Adhesive Materials>

[0065] Adhesive material refers to material used to bond electrodes and spacers. There are no particular limitations on adhesive materials, as long as they can bond electrodes and spacers without hindering the battery reaction; any adhesive material applicable to the field of secondary batteries can be used. The polymer constituting the adhesive material can be only one type or two or more types. Particularly preferred adhesive materials include a non-water-soluble polymer satisfying at least one of the following conditions (i) and (ii), or a water-soluble polymer with a thermal decomposition temperature of 180°C or higher, or both.

[0066] <<Non-water-soluble polymers>>

[0067] The adhesive material preferably comprises at least one of (i) a non-water-soluble polymer that does not have a glass transition temperature and melting point in a temperature region below 180°C, and (ii) a non-water-soluble polymer that has a glass transition temperature in a temperature region below 180°C but a melting point in a temperature region above 180°C. The non-water-soluble polymer corresponding to (i) above preferably does not have a glass transition temperature and melting point in a temperature region below 190°C, and more preferably does not have a glass transition temperature and melting point in a temperature region below 200°C. Furthermore, the non-water-soluble polymer corresponding to (ii) above preferably has a melting point in a temperature region above 190°C, and more preferably has a melting point in a temperature region above 200°C. Using an adhesive material comprising a non-water-soluble polymer belonging to (i) or (ii) above can further improve the adhesion between the electrode and the spacer, and can provide a secondary battery with further superior stability.

[0068] Here, when the water-insoluble polymer used as an adhesive is crystalline, both its glass transition temperature and melting point can be detected. Therefore, among crystalline water-insoluble polymers, those satisfying (i) above have both a glass transition temperature and melting point in a temperature range of 180°C or higher. Furthermore, among crystalline water-insoluble polymers, those satisfying (ii) above have a glass transition temperature less than 180°C but a melting point of 180°C or higher. On the other hand, when the water-insoluble polymer used as an adhesive is non-crystalline, its glass transition temperature can be detected, but its melting point cannot be detected. Therefore, among non-crystalline water-insoluble polymers, those satisfying (i) above have a glass transition temperature detectable in a temperature range of 180°C or higher. Furthermore, among non-crystalline water-insoluble polymers, there are no polymers satisfying (ii) above.

[0069] Here, the composition of the water-insoluble polymer is not particularly limited as long as it satisfies the above-mentioned condition of "water-insoluble," and preferably satisfies the above-mentioned conditions (i) or (ii) regarding the glass transition temperature and melting point; any composition is acceptable. Examples of water-insoluble polymers include binders containing polyfunctional olefinic unsaturated monomer units in a proportion of 20% to 90% by mass (hereinafter referred to as binder 1), binders containing nitrile-containing monomer units in a proportion of 70% to 95% by mass (hereinafter referred to as binder 2), silicone binders as polymers whose main chain is formed by siloxane bonds, polyamide-imide and fluorinated binders such as polytetrafluoroethylene as polymers whose repeating units contain amide and imide bonds, polyamide microparticle dispersions, epoxy resins, thermosetting polyurethane resins, etc. Among these, binders 1, binder 2, silicone binders, and fluorinated binders are preferred as water-insoluble polymers; binders 1 and binder 2 are more preferred; and binder 1 is even more preferred.

[0070] Furthermore, the polyfunctional olefin unsaturated monomers that can be used in forming the above-mentioned binder 1 (binder containing polyfunctional olefin unsaturated monomer units in a proportion of 20% by mass or more and 90% by mass or less) are not particularly limited, and examples include: allyl (meth)acrylate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, trimethylolpropane-tri(meth)acrylate, and other polyfunctional (meth)acrylate monomers;

[0071] Multifunctional aromatic vinyl monomers such as divinylbenzene and diisopropenylbenzene;

[0072] Dipropylene glycol diallyl ether, polyethylene glycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane-diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those mentioned above, triallylamine, methylenediacrylamide, etc. These can be used alone or in combination of two or more. Among them, polyfunctional (meth)acrylate monomers and polyfunctional aromatic vinyl monomers are preferred, polyfunctional (meth)acrylate monomers are more preferred, ethylene glycol dimethacrylate and trimethylolpropane-trimethacrylate are even more preferred, and ethylene glycol dimethacrylate is particularly preferred.

[0073] Furthermore, "(meth)acrylate" means acrylate and / or methacrylate. In addition, there are no particular limitations on the preparation method of this binder 1. There are no particular restrictions on the polymerization method used to prepare binder 1; any of the following methods can be used: solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. Furthermore, as the polymerization reaction, any of the following reactions can be used: ionic polymerization, free radical polymerization, living radical polymerization, etc. Moreover, the emulsifiers, dispersants, polymerization initiators, chain transfer agents, etc., used in the polymerization can be those commonly used.

[0074] Furthermore, the nitrile monomers that can be used in forming the aforementioned binder 2 (a binder containing nitrile monomer units in a proportion of 70% to 95% by mass or less) are not particularly limited, and α,β-olefinic unsaturated nitrile monomers can be cited as examples. Specifically, examples of α,β-olefinic unsaturated nitrile monomers include: acrylonitrile; α-haloacrylonitrile, α-bromoacrylonitrile, and other α-haloacrylonitrile; α-alkylacrylonitrile, α-methacrylonitrile, and other α-alkylacrylonitrile. These can be used alone or in combination of two or more. Acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. Furthermore, the preparation method of the binder 2 is not particularly limited, and the polymerization methods and polymerization conditions listed above as the preparation method of binder 1 can be used.

[0075] Furthermore, the water-insoluble polymer is preferably a particulate polymer that meets the specified volume average particle size D50. Specifically, it is preferable that the volume average particle size D50 of the particulate polymer, which is a water-insoluble polymer, is smaller than the average pore size of the spacers that together form the laminate for the secondary battery. If the volume average particle size D50 of the particulate polymer meets this condition, the adhesion between the electrode and the spacer can be further improved. Although the reason is not clear, it is speculated that by having at least a portion of the particulate polymer enter the pores of the spacer and perform its adhesive function as an adhesive material, the adhesion strength between the electrode and the spacer can be improved.

[0076] Regarding the specific value of the volume average particle size D50 of the particulate polymer, which is a water-insoluble polymer, it is preferably 100 nm or more, more preferably 150 nm or more, more preferably 5000 nm or less, more preferably 3000 nm or less, and even more preferably 2000 nm or less. If the volume average particle size D50 of the particulate polymer is within the above range, the adhesion between the electrode and the spacer can be further improved. In addition, the volume average particle size D50 of the particulate polymer can be controlled by adjusting the formulation of the monomer composition and the polymerization conditions (e.g., polymerization time) during the preparation of the particulate polymer.

[0077] Furthermore, when the non-water-soluble polymer is a particulate polymer, the particulate polymer can be a single-phase structure particle formed from a single polymer, or a heterogeneous structure particle formed by the physical or chemical combination of two or more different polymers. Specific examples of heterogeneous structures include: core-shell structures formed from polymers that are different in the central part (core) and outer shell (shell) of spherical particles; and side-by-side structures where two or more polymers are arranged side-by-side. In this specification, "core-shell structure" includes not only structures where the shell completely covers the outer surface of the core, but also structures where the shell partially covers the outer surface of the core. Moreover, in this invention, even when the outer surface of the core appears to be completely covered by the shell, if a hole is formed connecting the inside and outside of the shell, then the shell is a shell that partially covers the outer surface of the core.

[0078] Furthermore, when the particulate polymer has a core-shell structure, it is preferable that, among the glass transition temperature and melting point of the core and the glass transition temperature and melting point of the shell, at least the glass transition temperature and melting point of the shell satisfy the above-described condition (i) or (ii). Moreover, it is preferable that both the glass transition temperature and melting point of the core and the glass transition temperature and melting point of the shell satisfy the above-described condition (i) or (ii).

[0079] <<Water-soluble polymers>>

[0080] The adhesive material preferably contains a water-soluble polymer with a thermal decomposition temperature of 180°C or higher, more preferably 190°C or higher, and even more preferably 200°C or higher. Using an adhesive material containing a water-soluble polymer with a thermal decomposition temperature of 180°C or higher further improves the adhesion between the electrode and the spacer, and provides a secondary battery with even better stability. Furthermore, the thermal decomposition temperature of the water-soluble polymer used as the adhesive material is not particularly limited and can be, for example, 450°C or lower.

[0081] Here, the composition of the water-soluble polymer is not particularly limited as long as it meets the above-mentioned conditions of "water solubility" and thermal decomposition temperature; any composition is acceptable. Examples of water-soluble polymers include carboxymethyl cellulose, xanthan gum, alginate, polyamide-imide, polyacrylamide, polyacrylic acid, polysulfonic acid, polyvinyl alcohol, polyvinylpyrrolidone, poly-2-acrylamide-2-methylpropanesulfonic acid, and aromatic amide compounds. Carboxymethyl cellulose and polyamide-imide are preferred.

[0082] <<Ratio of insoluble to water-soluble polymers in adhesive materials>>

[0083] As described above, the adhesive material used in the laminate for secondary batteries to bond the electrodes and spacers together is preferably composed of at least one of a non-water-soluble polymer and a water-soluble polymer. Furthermore, from the viewpoint of further improving the electrolyte injection properties when forming a secondary battery using the laminate for secondary batteries, the adhesive material is more preferably composed of both a non-water-soluble polymer and a water-soluble polymer. This is presumably because maintaining an appropriate distance between the electrodes and spacers is advantageous from the viewpoint of improving electrolyte injection properties. When using a non-water-soluble polymer (particulate polymer), such an "appropriate distance" can be ensured by the volume of the particulate polymer, whereas such an "appropriate distance" cannot be ensured when the adhesive material is formed solely of a water-soluble polymer. Furthermore, when the adhesive material comprises both a non-water-soluble polymer and a water-soluble polymer, it is preferable that the content of the non-water-soluble polymer is 100% by mass and the content of the water-soluble polymer is 1 part by mass or more and 20 parts by mass or less.

[0084] Furthermore, the secondary battery laminate of the present invention needs to be formed by laminating electrodes and spacers with adhesive materials. Without hindering the effect of the present invention, inorganic particles such as fumed alumina that can penetrate the pores of the spacers may be present between the electrodes and the spacers.

[0085] (Manufacturing method of laminated body for secondary batteries)

[0086] The aforementioned laminate for secondary batteries of the present invention can be efficiently manufactured according to a manufacturing method exemplified below. The exemplary manufacturing method is a method for manufacturing a laminate for secondary batteries by bonding electrodes and spacers. In the exemplary manufacturing method, after step (A) of applying adhesive material to the bonding surface of at least one of the electrodes and spacers, step (B) is performed to prevent the bonding surface with applied adhesive material from contacting other components and to transport the electrodes and spacers to a bonding start position. Then, step (C) is performed to bond the electrodes and spacers via the bonding surfaces, thereby manufacturing a laminate for secondary batteries. Furthermore, the "bonding start position" refers to the position where the bonding surfaces of the electrodes and spacers abut against each other during bonding of the electrodes and spacers.

[0087] <Process (A)>

[0088] In step (A), the aforementioned adhesive material is applied to the bonding surface of at least one of the electrodes and spacers. Furthermore, the electrodes used in manufacturing the secondary battery laminate can be rolled into a roll or pre-cut. Similarly, the spacer material used in manufacturing the secondary battery laminate can be rolled into a roll or pre-cut. From the viewpoint of efficiently and continuously manufacturing the secondary battery laminate, it is preferable to use a spacer material that is rolled into a roll. Furthermore, it is preferable to use a spacer material with a porosity of at least 5%. Moreover, the porosity of the spacer material is preferably 20% or more, more preferably 40% or more. Furthermore, the average diameter of the voids in the spacer material (hereinafter also referred to as the average pore size of the spacer material) is preferably 100 nm or more and 1000 nm or less. Furthermore, from the viewpoint of improving the adhesion between the spacer and the electrode, the average pore size of the spacer material is preferably larger than the volume average particle size D50 of the adhesive material. Furthermore, from the viewpoint of improving the energy density of the obtained secondary battery, the thickness of the spacer material used is preferably 20 μm or less, and more preferably 15 μm or less. Alternatively, the thickness of the spacer material can be, for example, 4 μm or more.

[0089] As an adhesive material, the adhesive material described in the (laminated body for secondary batteries) section is preferably used. Furthermore, the adhesive material can be supplied to the bonding surface in any state, such as a solid state, a molten state, a state dissolved in a solvent, or a state dispersed in a solvent. Preferably, the adhesive material is supplied in a state dissolved in a solvent or a state dispersed in a solvent.

[0090] Furthermore, in step (A), when the adhesive material is supplied to the bonding surface in a state of being dissolved in a solvent or dispersed in a solvent, that is, when the adhesive composition containing the adhesive material and the solvent is supplied to the bonding surface, the solvent for the adhesive composition is not particularly limited, and can be, for example, water, organic solvents, and mixtures thereof. Additionally, the organic solvent is not particularly limited, and examples include: cyclic aliphatic hydrocarbons such as cyclopentane and cyclohexane; aromatic hydrocarbons such as toluene and xylene; ketones such as ethyl methyl ketone and cyclohexanone; esters such as ethyl acetate, butyl acetate, γ-butyrolactone, and ε-caprolactone; nitriles such as acetonitrile and propionitrile; ethers such as tetrahydrofuran and ethylene glycol diethyl ether; and alcohols such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, and ethylene glycol monomethyl ether. From the viewpoint of efficiently manufacturing laminates for secondary batteries, water and alcohols are preferred as solvents. In addition, the concentration of the adhesive material in the adhesive composition is not particularly limited, and may be, for example, 1% by mass or more and 40% by mass or less.

[0091] Furthermore, there are no particular limitations on the method for applying the adhesive material to the bonding surface; methods such as inkjet printing, spraying, drop coating, gravure coating, and screen printing can be used. From the viewpoint of high productivity and freedom of shape formation, inkjet printing is the preferred method for applying the adhesive material. When applying the adhesive material to the bonding surface, it is sufficient to apply the adhesive material to at least one of the electrodes and spacers. The electrodes can be either positive or negative.

[0092] Furthermore, the adhesive material can be applied to the entire bonding surface or only to a portion of the bonding surface. Moreover, when applying the adhesive material only to a portion of the bonding surface, it can be applied in any top-view shape, such as stripes, dots, or a mesh, without particular limitation. From the viewpoint of improving the electrolyte injection properties when manufacturing secondary batteries using a laminated secondary battery assembly, it is preferable to apply the adhesive material in a dotted pattern. Furthermore, when arranging the tiny dots of adhesive material into a predetermined pattern, from the viewpoint of facilitating the application and arrangement of the adhesive material, it is preferable to apply the adhesive composition in the desired pattern using an inkjet printing method.

[0093] <Process (B)>

[0094] In process (B), the electrodes and spacers are transported to the bonding start position without allowing the bonding surfaces with applied adhesive to come into contact with other components. If the bonding surfaces with applied adhesive are not allowed to come into contact with other components in this way, problems such as adhesion will not occur. Therefore, adhesive materials with excellent adhesion can be used, and laminates for secondary batteries can be manufactured efficiently.

[0095] Furthermore, there are no particular limitations on the transport of the electrodes and spacers; any transport mechanism such as rollers, belt conveyors, robotic arms, or suction belts can be used. However, from the viewpoint of further improving the manufacturing efficiency of the laminate for secondary batteries, it is preferable to use rollers to transport at least one of the electrodes and spacers.

[0096] <Process (C)>

[0097] In step (C), the electrodes and spacers are bonded together via the bonding surfaces. Bonding can be performed, for example, by pressurizing and / or heating the laminate of electrodes and spacers overlapping via the bonding surfaces, without particular limitation. When an adhesive composition is used in step (A), it is preferable that the time interval between the end of step (A) and the start of step (C) is shorter than the time required for the adhesive composition to dry completely. That is, it is preferable that the adhesive composition is not completely dry at the start of step (C). If step (C) can be started while the adhesive composition is not dry, the adhesion between the spacers and electrodes can be further improved, and the stability of the resulting secondary battery can be further improved. More specifically, by firmly bonding the spacers and electrodes, the short circuit portion can be prevented from expanding in the event of an internal short circuit, further improving the stability of the secondary battery.

[0098] In addition, in process (C), the pressure applied to the laminate, the temperature when bonding the electrodes and spacers, and the time for pressurizing and / or heating the laminate can be appropriately adjusted according to the type and amount of adhesive material used.

[0099] (Secondary battery)

[0100] The secondary battery of the present invention is characterized by having the laminated body for secondary batteries of the present invention. Furthermore, because the secondary battery of the present invention has the laminated body for secondary batteries of the present invention, it exhibits low internal resistance and excellent stability. Additionally, in the example, when manufacturing a secondary battery using the laminated body for secondary batteries of the present invention, a step of assembling the secondary battery using the laminated body for secondary batteries and an electrolyte is performed (assembly step).

[0101] Assembly Process

[0102] Here, as the electrolyte, an organic electrolyte in which the supporting electrolyte is dissolved in an organic solvent is typically used. For example, in the case of a lithium-ion secondary battery, a lithium salt can be used as the supporting electrolyte. Examples of lithium salts include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, and (C2F5SO2)NLi. Among these, LiPF6, LiClO4, and CF3SO3Li are preferred due to their high degree of dissociation, with LiPF6 being particularly preferred. Furthermore, a single electrolyte can be used, or two or more can be combined in any ratio. Generally, since there is a tendency for higher lithium-ion conductivity to be achieved by using a supporting electrolyte with a higher degree of dissociation, the lithium-ion conductivity can be adjusted by the type of supporting electrolyte.

[0103] Furthermore, the organic solvent used as the electrolyte is not particularly limited as long as it can dissolve the supporting electrolyte. Preferably, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butyl carbonate (BC), methyl ethyl carbonate (EMC), and vinylene carbonate (VC) can be used; esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; and sulfur-containing compounds such as sulfolane and dimethyl sulfoxide can be used. Mixtures of these solvents can also be used. Among these, carbonates are preferred due to their high dielectric constant and wide stable potential range. Generally, since there is a tendency for lower solvent viscosity to result in higher lithium-ion conductivity, the lithium-ion conductivity can be adjusted by the type of solvent used.

[0104] Furthermore, the concentration of the electrolyte in the electrolyte solution can be appropriately adjusted. Additionally, known additives can be added to the electrolyte solution.

[0105] Furthermore, the secondary battery can be assembled by further stacking additional battery components (electrodes and / or spacers, etc.) onto the secondary battery laminate of the present invention as needed. Then, the resulting laminate is wound, bent, etc., according to the battery shape, placed in a battery container, electrolyte is injected into the battery container, and the container is sealed. Additionally, to prevent internal pressure rise, overcharging, or over-discharging of the secondary battery, overcurrent protection components such as fuses and PTC elements, porous metal mesh, and guide plates can be provided as needed. Moreover, the shape of the secondary battery can be any of, for example, coin-shaped, button-shaped, sheet-shaped, cylindrical, square, or flat.

[0106] Example

[0107] The present invention will now be specifically described based on embodiments, but the present invention is not limited to these embodiments. Furthermore, in the following description, unless otherwise specified, "%" and "parts" refer to quantities based on mass.

[0108] In the examples and comparative examples, the determination and evaluation of various properties were carried out as follows.

[0109] <Volume Average Particle Size D50>

[0110] The particle size distribution (volume basis) of an aqueous dispersion of a particulate polymer containing the non-water-soluble polymer being measured was determined using a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, product name "SALD-3100"). Then, the cumulative volume calculated from the smallest particle size side of the measured particle size distribution was taken as the 50% of the particle size as the volume average particle size (D50) of each particle.

[0111] <Glass transition temperature (Tg) and melting point>

[0112] According to JIS K 7121:2012, the measurements were performed using a differential scanning calorimeter (manufactured by NanoTechnology Inc., DSC6220SII) with a temperature range of -100℃ to 180℃ and a heating rate of 5℃ / min.

[0113] <Thermal Decomposition Temperature>

[0114] The determination was performed according to JIS K 7120:1987.

[0115] <Porosity and average pore size of spacers>

[0116] For the spacer material used in manufacturing the secondary battery laminate in the examples and comparative examples, and the secondary battery laminate manufactured in the examples and comparative examples (after electrolyte injection), cross-sections were prepared by cutting with an argon ion beam while cooling with liquid nitrogen as a refrigerant. The cross-sectional images of the secondary battery laminate were observed using a scanning electron microscope (SEM). The obtained cross-sectional images were binarized, and the ratio (%) of the area of ​​voids contained in randomly selected object regions to the total area of ​​the object regions was calculated to obtain the porosity of the spacer. Furthermore, the diameter of 1000 randomly selected voids in the cross-sectional images was measured with a circumscribed circle set, and the average value was obtained to obtain the average pore size of the spacer. It was then determined whether the relationship "average pore size of the spacer > volume average particle size D50 of the water-insoluble polymer" was satisfied. Additionally, the values ​​(porosity and average pore size) obtained for the spacer material and the laminate were the same. In addition, regarding the average pore size of the spacers obtained by measurement, the spacer material made of polyethylene (PE) with a substrate thickness of 12 μm used in Example 1, etc., has a pore size of 250 nm, while the spacer material made of polypropylene (PP) with a substrate thickness of 18 μm used in Example 3, etc., has a pore size of 300 nm.

[0117] <Thermomechanical Analysis of Spacer Materials>

[0118] The spacer material used in the examples and comparative examples was used as the test specimen. A thermomechanical analysis apparatus (manufactured by SII Nano Technology Inc., "TMA / SS6100") was set to constant displacement mode, and the tensile load (mN) was measured under the following conditions. The measured tensile load value was divided by the cross-sectional area of ​​the test specimen (mm²). 2 This yields the value of the thermal contraction force (mN / mm²) as the tensile load per unit cross-sectional area. 2 ).

[0119] • Measurement temperature range: 20℃ to outside the displacement detection range

[0120] • Heating rate: 5℃ / minute

[0121] • Measurement environment: nitrogen

[0122] Then, the values ​​of thermal shrinkage force (mN / mm) are plotted corresponding to each temperature. 2 The heat shrinkage curve is obtained, and the value of the maximum heat shrinkage force (mN / mm) is calculated. 2 As the "maximum heat shrinkage force B of the spacer", the heat shrinkage force is reduced to a value F lower than the heat shrinkage force at 30°C. (30) (mN / mm 2 ) 20% higher value (mN / mm 2 The temperature of the spacer was taken as the "end temperature α (°C) of heat shrinkage" and the temperature of the intersection of the tangents before and after the point where the slope of the tangent to the heat shrinkage curve begins to change significantly after the start of heating, as detected by thermomechanical analysis, was taken as the "start temperature β of heat shrinkage". The results are shown in Table 1.

[0123] <Shear peel strength>

[0124] The lithium-ion secondary battery, after being filled with electrolyte and left for a period of time, was disassembled. The secondary battery, which was formed by laminating a negative electrode (positive electrode in Example 5) with a spacer using adhesive material, was cut into a laminate with an adhesive area of ​​3 cm². After clamping the spacer and electrode along the shear direction, the tensile stress was observed using a tensile testing machine (Autograph) in a constant temperature bath (tensile speed: 5 mm / min). The peak value of the initial response of the obtained data was taken as the shear peel strength. The test temperature was plotted at 20°C increments from room temperature (25°C) up to 200°C. The minimum value of the temperature range from room temperature to the end temperature α (°C) of the heat shrinkage of the spacer material used in each example and comparative example was taken as the shear peel strength.

[0125] A: Shear peel strength is 3 mN / mm 2 above

[0126] B: Shear peel strength greater than 1.3 mN / mm 2 And less than 3mN / mm 2

[0127] C: Shear peel strength is 1 mN / mm 2 Above and 1.3 mN / mm 2 the following

[0128] D: Shear peel strength less than 1 mN / mm 2

[0129] <Adhesion between electrode and spacer>

[0130] The laminate (i.e., a laminate formed by bonding an electrode and a spacer together with an adhesive material) was used as the test piece under the same conditions as in the embodiments and comparative examples.

[0131] With the current collector side of the electrode of the test piece facing down, cellophane tape is adhered to the surface of the current collector side of the negative electrode (positive electrode in Example 5). Cellophane tape as specified in JIS Z1522 is used. Furthermore, the cellophane tape is pre-fixed on a horizontal test bench. Then, the stress is measured when one end of the spacer is stretched vertically upwards at a tensile speed of 50 mm / min and then peeled off.

[0132] A total of six measurements were performed, and the average stress was calculated as the peel strength. The adhesion between the negative electrode and the spacer was evaluated using the following criteria. A higher peel strength indicates a stronger adhesion between the electrode (negative / positive electrode) and the spacer in the dry state, i.e., when not immersed in the electrolyte.

[0133] A: Peel strength is above 1.5 N / m

[0134] B: Peel strength is above 1.0 N / m and less than 1.5 N / m

[0135] C: Peel strength is ≥0.5 N / m and <1.0 N / m

[0136] D: Peel strength less than 0.5 N / m

[0137] <Electrolyte injection properties>

[0138] Electrolyte was injected into the lithium-ion secondary batteries prepared in the examples and comparative examples. Then, the internal pressure of the lithium-ion secondary battery was reduced to -100 kPa and maintained at this state for 1 minute. Subsequently, heat sealing was performed. Then, after 10 minutes, the electrodes (negative electrode, positive electrode in Example 5) were disassembled to visually confirm the electrolyte impregnation state within the electrodes. Then, the following criteria were used for evaluation: The greater the portion of the electrode impregnated with electrolyte, the higher the electrolyte infusion performance.

[0139] A: All surfaces of the electrode are impregnated with electrolyte.

[0140] B: In the electrode, the portion not impregnated with electrolyte is less than 5% remaining on an area basis (excluding impregnation on all surfaces).

[0141] C: In the electrode, the portion not impregnated with electrolyte has a residual area of ​​more than 5% but less than 10% based on area.

[0142] D: In the electrode, more than 10% of the portion not impregnated with electrolyte remains, calculated by area.

[0143] <Battery Thickness>

[0144] To determine the thickness of the lithium-ion secondary batteries manufactured in the examples and comparative examples, a thickness gauge (Mitutoyo Corporation, Japan, "547-321 Thickness Gauge") was used. Measurements were performed at 10 randomly selected measurement points on identical batteries, and the arithmetic mean was taken as the battery thickness.

[0145] A: Battery thickness is less than 8mm

[0146] B: Battery thickness is 8mm or more

[0147] <Internal Resistance>

[0148] The lithium-ion secondary batteries fabricated in the examples and comparative examples were charged to 50% of their SOC (State of Charge) at 25°C at 1C (C is a value expressed in rated capacity (mA) / 1h). Then, using 50% SOC as the center, the batteries were charged and discharged for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C, respectively. The battery voltage after 10 seconds (charging side and discharging side) was plotted relative to the current value. The slope of this plot was divided by the area of ​​the positive electrode of the fabricated lithium-ion secondary battery, and the resulting value was used as the IV resistance (Ω·cm). 2 (IV resistance during charging and IV resistance during discharging) are calculated. The obtained IV resistance value (Ω·cm) is then compared to the following reference. 2 The value of the IV resistor is used for evaluation. The smaller the IV resistor value, the smaller the internal resistance and the lower the DC resistance.

[0149] A: The resistance of IV is 22Ω·cm 2 the following

[0150] B: IV resistance greater than 22Ω·cm 2 And it is 25Ω·cm 2 the following

[0151] C: IV resistance greater than 25Ω·cm 2 And it is 28Ω·cm 2 the following

[0152] D: IV resistance greater than 28Ω·cm 2

[0153] <Needle prick test>

[0154] The lithium-ion secondary batteries prepared in the examples and comparative examples were evaluated using a nail penetration test. In the nail penetration test, a stacked lithium-ion secondary battery was used as the test specimen in a constant temperature bath under variable temperature conditions. A 6mm diameter needle was used, and the test was performed at a lifting and lowering speed of 1mm / min. A battery that experienced thermal runaway and ignition after being punctured was considered NG (Not Good), while one that did not ignite was considered OK. Five test specimens were evaluated; even if only one specimen met the NG standard, it was determined that the stability of the test specimen could not be maintained under that temperature condition.

[0155] A: All test samples were OK at a temperature of 60℃.

[0156] B: All test specimens are OK under the condition of 50℃.

[0157] C: All test specimens are OK at a temperature of 40℃.

[0158] D: There are NG test specimens at a temperature of 40℃.

[0159] <Overcharge Test>

[0160] The stacked lithium-ion secondary batteries fabricated in the examples and comparative examples were used as test specimens and evaluated using an overcharge test. The test specimens were continuously charged in a constant current mode with a variable rate. For safety reasons, the upper limit of the charging voltage was set to 20V. In the evaluation at each rate, thermal runaway leading to fire was considered NG (Not Acceptable), while no fire was considered OK. Five test specimens were evaluated; even if only one specimen met the NG standard, it was determined that the stability of the test specimen could not be maintained under that rate condition. The evaluation temperature was 25°C.

[0161] A: All test samples were OK at the 1.5C magnification.

[0162] B: All test samples were OK at the 1.0C magnification.

[0163] C: Test specimens with NG at 1.0C magnification.

[0164] (Example 1)

[0165] <Preparation of adhesive material (adhesive 1)>

[0166] In reactor A equipped with a stirrer, 0.20 parts of sodium dodecyl sulfate, 0.30 parts of ammonium persulfate, and 180 parts of deionized water were added and mixed to form a mixture, which was then heated to 65°C. Meanwhile, in another container, 88.0 parts of n-butyl acrylate (a monofunctional (meth)acrylate monomer), 6.0 parts of acrylic acid (an acidic monomer), 6.0 parts of acrylonitrile (a nitrile monomer), 0.8 parts of sodium dodecyl sulfate, and 40 parts of deionized water were mixed to prepare a monomer composition for seed particles.

[0167] The monomer composition for seed particles was continuously added to reactor A for 4 hours to carry out the polymerization reaction. The temperature inside the reactor was maintained at 65°C during the continuous addition of the monomer composition for seed particles. After the continuous addition was completed, the polymerization reaction was further continued at 80°C for 3 hours. This yielded an aqueous dispersion of seed particles. Furthermore, the volume average particle size D50 of the seed particles was measured and found to be 120 nm.

[0168] Next, in a reactor equipped with a stirrer, an aqueous dispersion of the aforementioned seed particles (16.7 parts by solids equivalent, including 14.7 parts of n-butyl acrylate, 1 part of acrylic acid, and 1 part of acrylonitrile) was added, along with 80.8 parts of ethylene glycol dimethacrylate (Kyoei Chemical Co., Ltd., product name "LIGHT ESTER EG") as a polyfunctional olefinic unsaturated monomer, 2.5 parts of acrylic acid as an acidic monomer, 0.8 parts of sodium dodecylbenzenesulfonate, 3.2 parts of tert-butyl peroxide-2-ethylhexanoate (Nippon Oil Co., Ltd., product name "PERBUTYL O") as a polymerization initiator, and 160 parts of deionized water. The mixture was stirred at 35°C for 12 hours, thereby allowing the seed particles to completely absorb the polyfunctional olefinic unsaturated monomer, the acidic monomer, and the polymerization initiator. The temperature inside the reactor was then maintained at 90°C for 5 hours for polymerization (seed polymerization).

[0169] Next, steam was introduced to remove unreacted monomers and initiator decomposition products, yielding an aqueous dispersion of binder 1. Then, the volume average particle size D50 of the obtained binder 1 was measured according to the method described above. The results are shown in Table 1. Furthermore, it was confirmed according to the method described above that binder 1 does not have a glass transition temperature or melting point in the temperature range below 180°C.

[0170] Furthermore, binder 1 is granular in both the aqueous dispersion and the dry state. Additionally, binder 1 was confirmed to be a non-water-soluble polymer with an insoluble content of 90% by mass or more when 0.5 g of the polymer is dissolved in 100 g of water at 25°C.

[0171] <Preparation of Adhesive Compositions>

[0172] A mixture of 100 parts by weight of binder 1 (a particulate polymer) and 2 parts by weight of carboxymethyl cellulose (manufactured by Daicel Co., Ltd., product number "1220") was added, with the content ratio shown in Table 1. Then, the mixture was mixed for 100 minutes at 3000 rpm using an ultra-high-speed emulsifying disperser (manufactured by PRIMIX Co., Ltd., Japan, "ROBOMIX"). Finally, 45 parts of propylene glycol (a polyol compound used as a solvent) were added to obtain a slurry-like adhesive composition.

[0173] In addition, regarding carboxymethyl cellulose, when 0.5g of carboxymethyl cellulose is dissolved in 100g of water at a temperature of 25°C, the insoluble component is less than 1.0g by mass.

[0174] <Formation of the Negative Electrode>

[0175] In a 5 MPa pressure vessel equipped with a stirrer, 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 parts of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of deionized water, and 0.5 parts of potassium persulfate as a polymerization initiator were added. After thorough stirring, the mixture was heated to 50°C to initiate polymerization. The reaction was terminated by cooling at the point where the polymerization conversion reached 96%, yielding a mixture containing a binder material for the negative electrode composite layer (SBR). A 5% aqueous solution of sodium hydroxide was added to the mixture containing the binder material for the negative electrode composite layer to adjust the pH to 8. Unreacted monomers were removed by heated vacuum distillation. Subsequently, the mixture was cooled to below 30°C to obtain an aqueous dispersion containing the desired binder material for the negative electrode composite layer.

[0176] Next, 100 parts of artificial graphite (volume average particle size: 15.6 μm) as the negative electrode active material, 1 part of sodium carboxymethyl cellulose (manufactured by Nippon Paper Corporation, product name "MAC350HC") as a viscosity modifier (based on the solids content), and deionized water were mixed to adjust the solids content concentration to 68%, and then mixed further at 25°C for 60 minutes. Then, the solids content concentration was adjusted to 62% with deionized water, and mixed further at 25°C for 15 minutes. To the resulting mixture, 1.5 parts of the above-mentioned aqueous dispersion containing the binder material for the negative electrode composite layer (based on the solids content), and deionized water were added, adjusting the final solids content concentration to 52%, and then mixed further for 10 minutes. The mixture was then degassed under reduced pressure to obtain a slurry composition for a secondary battery negative electrode with good flowability.

[0177] The obtained secondary battery negative electrode slurry composition was coated onto a 20 μm thick copper foil (serving as a current collector) with a dried film thickness of approximately 150 μm using a corner-cutting roller coating machine, and then dried. This drying was performed by conveying the copper foil at a speed of 0.5 m / min in an oven at 60°C for 2 minutes. Subsequently, it was heat-treated at 120°C for 2 minutes to obtain the negative electrode raw material before pressing. This unpressed negative electrode raw material was then calendered using a roller press to obtain a pressed negative electrode raw material with a negative electrode composite layer thickness of 80 μm.

[0178] <The Formation of the Positive Electrode>

[0179] 100 parts of LiCoO2 with a volume average particle size of 12 μm, used as the positive electrode active material, 2 parts of acetylene black (manufactured by Denka Co., Ltd., product name "HS-100"), used as the conductive material, 2 parts of polyvinylidene fluoride (manufactured by Kureha Co., Ltd., Japan, product name "#7208"), used as the binder, and N-methylpyrrolidone, used as the solvent, were mixed to bring the total solid content concentration to 70%. These were then mixed using a planetary mixer to obtain a slurry composition for the positive electrode of a secondary battery.

[0180] The obtained secondary battery positive electrode slurry composition was coated onto a 20 μm thick aluminum foil (serving as a current collector) with a dried film thickness of approximately 150 μm using a corner-shaped coating machine, and then dried. This drying was performed by conveying the aluminum foil at a speed of 0.5 m / min in an oven at 60°C for 2 minutes. Subsequently, it was heat-treated at 120°C for 2 minutes to obtain the positive electrode raw material.

[0181] Then, the cathode raw material obtained by rolling is calendered using a roller press and cut to obtain a cathode with a cathode composite material layer.

[0182] <Preparation of Spacer Materials>

[0183] Prepare the raw materials for the spacer made of polyethylene (PE). Determine the properties of the spacer material according to the method described above. The results are shown in Table 1.

[0184] <Manufacturing of Laminated Structures for Secondary Batteries>

[0185] Using the prepared adhesive composition, negative electrode raw material, and spacer raw material, Figure 2 The manufacturing apparatus 100 shown is used to manufacture a laminated body for secondary batteries. Additionally, Figure 2 In the figure, reference numeral 91 indicates the conveying roller, and reference numeral 92 indicates the heating roller.

[0186] Specifically, while conveying the negative electrode raw material 20A from the negative electrode raw material roller at a speed of 10 m / min, an adhesive composition is supplied from the inkjet head of an inkjet coating machine 52 (manufactured by Konica Corporation, KM1024 (shear mode type)) to one surface of the negative electrode raw material 20A, and the second spacer raw material 30A fed from the spacer raw material roller and the negative electrode raw material 20A are bonded together using pressing rollers 61 and 62. Furthermore, an adhesive composition is supplied from the inkjet head of the inkjet coating machine 51 (manufactured by Konica Corporation, KM1024 (shear mode type)) to another surface of the negative electrode raw material 20A, and the laminate of the first spacer raw material 10A fed from the spacer raw material roller and the negative electrode raw material 20A and the second spacer raw material 30A are bonded together using pressing rollers 61 and 62.

[0187] In addition, the bonding conditions using pressing rollers 61 and 62 are as shown in Table 1. Furthermore, the adhesive coating is applied in a dotted pattern, with a dot spacing of 200 μm in both the TD (transverse) and MD (longitudinal) directions.

[0188] The first spacer material, negative electrode material, and first spacer material obtained by bonding with pressing rollers 61 and 62 are cut by cutting machine 70 to obtain a laminate for secondary batteries in which the first spacer, negative electrode, and first spacer are sequentially stacked and the negative electrode and spacer are bonded to each other by adhesive.

[0189] <Manufacturing of Secondary Batteries>

[0190] The aforementioned secondary battery laminate and the cut positive electrode were stacked 20 times to form an overlapped body. In the overlapped body, the positive electrode and the secondary battery laminate were not bonded together. The overlapped body was packaged in an aluminum packaging material, which serves as the outer packaging of the battery, and an electrolyte was injected (solvent: ethylene carbonate / diethyl carbonate / ethylene carbonate = 68.5 / 30 / 1.5 (volume ratio), electrolyte: 1M LiPF6). Subsequently, the opening of the aluminum packaging material was sealed by heat sealing at 150°C, thus manufacturing a laminated lithium-ion secondary battery with a capacity of 8000mAh.

[0191] Then, various evaluations were performed on the secondary batteries using the methods described above. The results are shown in Table 1.

[0192] (Example 2)

[0193] As the spacer material, a polyethylene (PE) spacer raw material was used, with heat shrinkage start temperature, heat shrinkage end temperature, and maximum heat shrinkage force as shown in Table 1. Otherwise, the same procedures, measurements, and evaluations were performed as in Example 1. The results are shown in Table 1.

[0194] (Example 3)

[0195] As the spacer material, a polypropylene (PP) spacer raw material (product name "Celgard 2500") with heat shrinkage start temperature, heat shrinkage end temperature, and maximum heat shrinkage force as shown in Table 1 was used. Otherwise, the same procedures, measurements, and evaluations were performed as in Example 1. The results are shown in Table 1.

[0196] (Example 4)

[0197] In the <Preparation of Adhesive Composition> step, a silicone binder (manufactured by Shin-Etsu Silicone Co., Ltd., model "KM-9729") was used as the particulate polymer of the non-water-soluble polymer. Otherwise, the procedure was the same as in Example 1, with various operations, measurements, and evaluations performed. The results are shown in Table 1. The volume average particle size D50 and glass transition temperature of the silicone binder are shown in Table 1.

[0198] Furthermore, the silicone binder is granular in both water and dry states. Moreover, it has been confirmed that the silicone binder is a non-water-soluble polymer with an insoluble content of 90% by mass or more when 0.5g of the polymer is dissolved in 100g of water at 25°C. Furthermore, it has been confirmed, according to the above method, that the silicone binder does not have a glass transition temperature or melting point in the temperature range below 180°C.

[0199] (Example 5)

[0200] In the <Preparation of Adhesive Composition> step, polytetrafluoroethylene (manufactured by Asahi Glass Co., Ltd., "LUMIFLON (registered trademark) FE4300") is used as a fluorine-based binder, which is a particulate polymer that is not water-soluble. Furthermore, in the <Forming of Negative Electrode> step, the negative electrode raw material is calendered using a roll press and then cut to obtain a negative electrode with a negative electrode composite layer. In the <Forming of Positive Electrode> step, the positive electrode raw material is not cut. Furthermore, in the <Manufacturing of Laminate for Secondary Battery> step, the positive electrode raw material is used instead of the negative electrode raw material to form a laminate for secondary battery. Then, in the <Manufacturing of Secondary Battery> step, the laminate for secondary battery and the negative electrode cut in the <Forming of Negative Electrode> step are overlapped to obtain an overlapped body.

[0201] Apart from these aspects, the same procedures, measurements, and evaluations were performed as in Example 1. The results are shown in Table 1. Additionally, the volume average particle size D50 and glass transition temperature of the fluorinated binder are shown in Table 1.

[0202] Furthermore, the fluorinated binder is granular in both water and dry states. Moreover, it has been confirmed that the fluorinated binder is a non-water-soluble polymer with an insoluble content of 90% by mass or more when 0.5 g of the polymer is dissolved in 100 g of water at 25°C. Furthermore, it has been confirmed, using the methods described above, that the fluorinated binder does not have a glass transition temperature or melting point in the temperature range below 180°C.

[0203] (Example 6)

[0204] In the step of <Preparation of Adhesive Composition>, instead of using binder 1 as a particulate polymer, the adhesive composition was prepared by using carboxymethyl cellulose as a water-soluble polymer, and propylene glycol and water as solvents, in the amounts shown in Table 1. Apart from these aspects, various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0205] (Example 7)

[0206] In the step of <Preparation of Adhesive Composition>, instead of using binder 1 as a particulate polymer, polyamide-imide (manufactured by Solvay SA, "Torlon (registered trademark) AI-30") was used as the water-soluble polymer instead of carboxymethyl cellulose. The contents of polyamide-imide, propylene glycol as a solvent, and water were as shown in Table 1, thereby preparing the adhesive composition. Apart from these aspects, various operations, measurements, and evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0207] In addition, regarding polyamide-imide, when 0.5g of polyamide-imide is dissolved in 100g of water at a temperature of 25°C, the insoluble component is less than 1.0g by mass.

[0208] (Comparative Example 1)

[0209] In the step of <Preparation of Adhesive Composition>, as the adhesive material, adhesive 3, whose glass transition temperature and melting point are as shown in Table 1, is used instead of adhesive 1, and propylene glycol is not incorporated, thereby preparing the adhesive composition. Furthermore, before the step of <Manufacturing of the Laminate for Secondary Batteries>, the adhesive composition is applied to the entire surface of the spacer made of polyethylene (PE) as the coating surface using a gravure roller, and then dried to prepare the wound spacer. Then, in the step of <Manufacturing of the Laminate for Secondary Batteries>, adhesive material feeders 51-52 are not used; instead, adhesive 3 is used instead of adhesive 3. Figure 1 The manufacturing apparatus shown was used to bond the negative electrode raw material and spacer under the conditions shown in Table 1. Except for these aspects, the same procedures, measurements, and evaluations were performed as in Example 1. The results are shown in Table 1.

[0210] <Adhesive 3>

[0211] 70 parts of ion-exchanged water, 0.15 parts of sodium dodecyl sulfate (manufactured by Kao Chemical Co., Ltd., product name "Emal 2F") as an emulsifier, and 0.5 parts of ammonium persulfate were supplied to a reactor equipped with a stirrer. The gas phase was replaced with nitrogen and the temperature was raised to 60°C.

[0212] On the other hand, in a separate container, 50 parts of deionized water, 0.5 parts of sodium dodecylbenzenesulfonate as an emulsifier, 40 parts of n-butyl acrylate, 1 part of methacrylic acid, 58 parts of styrene, and 1 part of divinylbenzene were mixed to obtain a monomer mixture. This monomer mixture was continuously added to the reactor described above over a period of 2 hours for polymerization. The reaction was carried out at 60°C during the addition. After the addition was completed, the reaction was further stopped by stirring at 70°C for 2 hours to produce an aqueous dispersion containing binder 3 as a particulate polymer.

[0213] The volume average particle size D50, glass transition temperature, and melting point of the obtained binder 3 were determined. The results are shown in Table 1.

[0214] Furthermore, binder 3 is granular in both the aqueous dispersion and the dry state. Additionally, binder 3 was confirmed to be a non-water-soluble polymer with an insoluble content of 90% by mass or more when 0.5 g of the polymer is dissolved in 100 g of water at 25°C.

[0215] (Comparative Example 2)

[0216] In the manufacturing process of the laminate for secondary batteries, the adhesive composition was applied to the surface of the spacer in a dotted pattern using a gravure coating machine. Otherwise, the same procedures, measurements, and evaluations were performed as in Comparative Example 1. The results are shown in Table 1.

[0217] (Comparative Example 3)

[0218] In the <Preparation of Spacer Material> step, ceramic (alumina) was coated onto each single side of the polyethylene spacer to a thickness of 5 μm to prepare the spacer raw material. Apart from these aspects, the same procedures, measurements, and evaluations were performed as in Comparative Example 2. The results are shown in Table 1.

[0219] Additionally, Table 1 shows the properties of the spacer material before alumina coating.

[0220] (Comparative Example 4)

[0221] The bonding conditions in the <Manufacturing of Laminated Body for Secondary Batteries> process were changed as shown in Table 1 (the bonding roller temperature was changed to 50°C). Otherwise, the same procedures, measurements, and evaluations were performed as in Comparative Example 2. The results are shown in Table 1.

[0222] (Comparative Example 5)

[0223] In the <Preparation of Adhesive Composition> step, an organosilicon adhesive (manufactured by Shin-Etsu Silicone Co., Ltd., model "KM-9729") was used as the adhesive material. Otherwise, the same procedures, measurements, and evaluations were performed as in Comparative Example 1. The results are shown in Table 1.

[0224] (Comparative Example 6)

[0225] The bonding conditions in the <Manufacturing of Laminated Body for Secondary Batteries> process were changed as shown in Table 1 (the transport speed was changed to 2.5 m / min and the time from coating to bonding was set to 10 seconds). Otherwise, the same procedures as in Example 1 were followed, and various operations, measurements, and evaluations were performed. The results are shown in Table 1.

[0226] (Comparative Example 7)

[0227] As the spacer material, a polypropylene (PP) spacer raw material (product name "Celgard 2500") with heat shrinkage start temperature, heat shrinkage end temperature, and maximum heat shrinkage force as shown in Table 1 was used. Otherwise, the same procedures, measurements, and evaluations were performed as in Example 4. The results are shown in Table 1.

[0228] In Table 1,

[0229] "Tg" represents the glass transition temperature.

[0230] "EDMA" stands for ethylene glycol dimethacrylate.

[0231] "AA" indicates acrylic acid.

[0232] "BA" indicates n-butyl acrylate.

[0233] “AN” represents acrylonitrile.

[0234] "PTFE" stands for polytetrafluoroethylene.

[0235] "CMC" stands for carboxymethyl cellulose.

[0236] “PG” represents propylene glycol.

[0237] "PE" stands for polyethylene.

[0238] "PP" stands for polypropylene.

[0239] "MAA" stands for methacrylic acid.

[0240] "ST" stands for styrene.

[0241] “DVB” stands for divinylbenzene.

[0242] [Table 1]

[0243]

[0244] As shown in Table 1, in Examples 1 to 7, it is possible to manufacture a laminate for a secondary battery that exhibits excellent adhesion between the electrodes and spacers, and can form a secondary battery with low internal resistance and excellent stability. On the other hand, as shown in Table 1, in Comparative Examples 1 to 7, it is not possible to manufacture a laminate for a secondary battery that can simultaneously achieve all of the above-mentioned properties at a high level.

[0245] Industrial availability

[0246] According to the present invention, a laminate for a secondary battery is provided that exhibits excellent adhesion between the electrodes and spacers, and is capable of forming a secondary battery with low internal resistance and excellent stability.

[0247] Furthermore, according to the present invention, a secondary battery with low internal resistance and excellent stability can be provided.

[0248] Explanation of reference numerals in the attached figures

[0249] 10A: Raw material for the first spacer

[0250] 20A: Anode raw material

[0251] 30A: Raw material for the second spacer

[0252] 51, 52: Coating machine

[0253] 61, 62: Pressing rollers

[0254] 70: Cutting machine

[0255] 91: Conveyor Roller

[0256] 92: Heating roller

[0257] 100: Manufacturing equipment

Claims

1. A laminated body for a secondary battery, formed by laminating electrodes and spacers with an adhesive material. The spacer comprises a polyolefin resin. The adhesive material comprises at least one of the following: a non-water-soluble polymer that does not have a glass transition temperature and melting point in a temperature range below 180°C; and a non-water-soluble polymer that has a glass transition temperature in a temperature range below 180°C but a melting point in a temperature range above 180°C. The shear peel strength between the electrode and the spacer, measured by temperature variation, is A mN / mm. 2 , The maximum thermal shrinkage force obtained from the thermomechanical analysis of the spacer is B mN / mm. 2 ,and then When the thermomechanical analysis of the spacer shows that the thermal shrinkage force decreases to a value 20% higher than the thermal shrinkage force value at 30°C, the thermal shrinkage termination temperature α°C is defined as the temperature at which the thermal shrinkage ends. The temperature range where the value of A is above 25°C and the heat shrinkage end temperature α°C is below α°C satisfies A > B. The shear peel strength is obtained by the following method: after the electrolyte is injected and a period of time has passed, the secondary battery is disassembled, and the secondary battery formed by the electrode-spacer laminated by the adhesive material is cut into a laminate with an adhesive area of ​​3 cm square. After clamping the spacer and the electrode along the shear direction, the tensile stress is observed by a tensile testing machine in a constant temperature bath. The peak value of the initial response of the obtained data is taken as the shear peel strength.

2. The laminated body for secondary batteries according to claim 1, wherein, The non-water-soluble polymer is a particulate polymer with a volume average particle size D50 smaller than the average pore size of the spacer. The volume average particle size D50 is the particle size that accounts for 50% of the cumulative volume from the smallest particle size side in the particle size distribution of the volume reference determined by dynamic light scattering.

3. The laminated body for secondary batteries according to claim 1 or 2, wherein, The adhesive material comprises a water-soluble polymer with a thermal decomposition temperature of 180°C or higher.

4. A secondary battery having a laminate for a secondary battery as described in any one of claims 1 to 3.

Images