Laminated body for secondary battery and secondary battery

Abstract

A multilayer body for secondary batteries, said multilayer body being obtained by stacking an electrode and a separator, with a bonding material being interposed therebetween. With respect to the shear peel strength between the electrode and the separator of this multilayer body, if A (mN / mm2) is the value measured while changing the temperature, B (mN / mm2) is the maximum thermal shrinkage force of the separator as determined by means of thermomechanical analysis, and α (°C) is the thermal shrinkage end temperature at which the thermal shrinkage force of the separator as determined by means of thermomechanical analysis reaches a value (mN / mm2) that is higher, by 20%, than the value (mN / mm2) of the thermal shrinkage force at 30°C, the value of A satisfies A > B within the temperature range of from 25°C to the thermal shrinkage end temperature α°C.

Description

Technical Field

[0001] The present invention relates to a laminate for a secondary battery and a secondary battery.

Background Art

[0002] Secondary batteries such as lithium ion secondary batteries are small, lightweight, have a high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. And secondary batteries generally include battery members such as a positive electrode, a negative electrode, and a separator that separates the positive electrode and the negative electrode to prevent a short circuit between the positive electrode and the negative electrode.

[0003] Here, in the manufacturing process of a secondary battery, an electrode and a separator before being immersed in an electrolytic solution are pressure-bonded to form a laminate (hereinafter sometimes referred to as a "laminate for a secondary battery"), and if necessary, it may be cut into a desired size, laminated, folded, or wound.

[0004] In recent years, laminates for secondary batteries having various structures and manufacturing methods thereof have been proposed. For example, Patent Document 1 discloses an electrochemical element (that is, a laminate for a secondary battery) in which a separator including a porous coating layer formed of a mixture of inorganic particles and a binder polymer formed on at least one surface of a porous substrate and a dot pattern layer formed of a crystalline polymer in which a plurality of dots formed of the crystalline polymer are spaced apart from each other on the surface of the porous coating layer is bonded to an electrode via the crystalline polymer. Further, for example, Patent Document 2 discloses a laminate in which a separator including a predetermined thermoplastic polymer coating layer covering at least one surface of a polyolefin microporous membrane is laminated with an electrode. In such a predetermined thermoplastic polymer coating layer, a portion containing a thermoplastic polymer having at least one glass transition temperature in a temperature region of less than 20°C and at least one glass transition temperature in a temperature region of 20°C or more and a portion not containing such a thermoplastic polymer exist in a sea-island shape.

[0005] Furthermore, for example, Patent Document 3 proposes a method for efficiently manufacturing a laminate for a secondary battery. The manufacturing method according to Patent Document 3 includes a step of forming an adhesive material in a predetermined amount of formation on at least one bonding surface of an electrode and a separator, a step of transporting the electrode and the separator to a bonding start position without bringing another member into contact with the bonding surface on which the adhesive material is formed, and a step of bonding the electrode and the separator. According to such a manufacturing method, a laminate for a secondary battery in which a separator and an electrode are bonded via an adhesive material can be efficiently manufactured.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0007] Here, for a laminate for a secondary battery, it is required that the electrode and the separator are well adhered in the laminate, and that a secondary battery having a low internal resistance and excellent stability can be formed. However, in the laminate for a secondary battery obtained according to the above conventional technology, it has not been possible to achieve all of the above attributes at a high level simultaneously.

[0008] Therefore, an object of the present invention is to provide a laminate for a secondary battery in which an electrode and a separator are laminated via an adhesive material, which has excellent adhesiveness between the electrode and the separator and can form a secondary battery having a low internal resistance and excellent stability. Another object of the present invention is to provide a secondary battery having a low internal resistance and excellent stability.

Means for Solving the Problems

[0009] The inventors of the present invention have conducted intensive studies for the purpose of solving the above problems. And, when manufacturing a laminate for a secondary battery in which an electrode and a separator are laminated via an adhesive material, within a predetermined temperature range, when the value of the shear peel strength between the electrode and the separator is greater than the value of the maximum thermal shrinkage force of the separator, the inventors have found that a laminate for a secondary battery capable of achieving the above object can be manufactured, and have completed the present invention.

[0010] That is, the present invention aims to advantageously solve the above problems, and the laminate for a secondary battery of the present invention is a laminate for a secondary battery in which an electrode and a separator are laminated via an adhesive material. Regarding the shear peel strength between the electrode and the separator, the value measured by changing the temperature is A (mN / mm 2 ), the value of the maximum thermal shrinkage force obtained by performing thermomechanical analysis on the separator is B (mN / mm 2 ), and further, the temperature at which the thermal shrinkage force obtained by performing thermomechanical analysis on the separator drops to a value 20% higher than the value of the thermal shrinkage force at 30°C (mN / mm 2 ) (mN / mm 2 ) is defined as the thermal shrinkage end temperature α (°C). When the value of A satisfies A > B in the temperature range of 25°C or higher and the thermal shrinkage end temperature α°C or lower of the separator. Thus, a laminate for a secondary battery that satisfies the condition that the shear peel strength A between the electrode and the separator is greater than the maximum thermal shrinkage force B of the separator in the temperature range of 25°C or higher and the thermal shrinkage end temperature α°C or lower of the separator has excellent adhesiveness between the electrode and the separator, and can form a secondary battery with low internal resistance and excellent stability. The "value A of the shear peel strength between the electrode and the separator", the "value B of the maximum thermal shrinkage force obtained by performing thermomechanical analysis on the separator", and the "thermal shrinkage end temperature α (°C)" can be measured according to the methods described in the examples.

[0011] Here, it is preferable that the separator of the laminate for secondary battery of the present invention contains a polyolefin resin. If the separator contains a polyolefin resin, the internal resistance of the resulting secondary battery can be further reduced and the stability can be further enhanced.

[0012] In addition, it is preferable that the adhesive material of the laminate for secondary battery of the present invention contains at least one of a water-insoluble polymer having no glass transition temperature and melting point in a temperature range below 180°C and a water-insoluble polymer having a glass transition temperature in a temperature range below 180°C but having a melting point in a temperature range of 180°C or higher. By using an adhesive material containing at least one of a water-insoluble polymer having no glass transition temperature and melting point in a temperature range below 180°C and a water-insoluble polymer having a glass transition temperature in a temperature range below 180°C but having a melting point in a temperature range of 180°C or higher, the adhesiveness between the electrode and the separator can be further enhanced, and it becomes possible to provide a secondary battery having even better stability. Note that the "water-insoluble polymer" means that when 0.5 g of the polymer is dissolved in 100 g of water at 25°C, the insoluble content is 90% by mass or more. In addition, the melting point and glass transition temperature of the water-insoluble polymer can be analyzed according to JIS K7121:2012.

[0013] Furthermore, in the laminate for secondary battery of the present invention, the water-insoluble polymer is preferably a particulate polymer having a volume average particle diameter D50, which is the particle diameter at which the cumulative volume calculated from the small-diameter side is 50% in the volume-based particle size distribution measured by the dynamic light scattering method, smaller than the average pore diameter of the separator. If the water-insoluble polymer is a particulate polymer having a volume average particle diameter D50 smaller than the average pore diameter of the separator, the adhesiveness between the electrode and the separator can be further enhanced. Note that the polymer being "particulate" means that the particle size distribution can be measured by the dynamic light scattering method. Also, the "volume average particle diameter D50" of the particulate polymer can be measured by the method described in the examples. Further, the average pore diameter of the separator is the number average value of the diameters measured for 1000 randomly extracted voids, and can be measured by the method described in the examples.

[0014] Furthermore, in the laminate for secondary battery of the present invention, it is preferable that the adhesive material contains a water-soluble polymer having a thermal decomposition temperature of 180°C or higher. By using an adhesive material containing a water-soluble polymer having a thermal decomposition temperature of 180°C or higher, it is possible to further enhance the adhesiveness between the electrode and the separator and to provide a secondary battery having even better stability. Here, the "water-soluble polymer" refers to a polymer in which when 0.5 g of the polymer is dissolved in 100 g of water at a temperature of 25°C, the insoluble content is less than 1.0 mass%. Also, the "thermal decomposition temperature" of the water-soluble polymer can be measured according to JIS K 7120:1987.

[0015] This invention aims to advantageously solve the above problems, and the secondary battery of the present invention is characterized by including any one of the above-described laminates for secondary battery. A secondary battery including the laminate for secondary battery of the present invention has a low internal resistance and excellent stability.

Advantages of the Invention

[0016] According to the present invention, it is possible to provide a laminate for secondary battery that can form a secondary battery having excellent adhesiveness between the electrode and the separator, a low internal resistance, and excellent stability. Also, according to the present invention, it is possible to provide a secondary battery having a low internal resistance and excellent stability.

Brief Description of the Drawings

[0017]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present invention will be described in detail. Here, the laminate for a secondary battery of the present invention can be used when manufacturing a secondary battery such as a non-aqueous secondary battery (for example, a lithium-ion secondary battery).

[0019] (Laminate for Secondary Battery) The laminate for a secondary battery of the present invention is formed by laminating an electrode and a separator via an adhesive material. In such a laminate for a secondary battery, regarding the shear peel strength between the electrode and the separator, the value measured by changing the temperature is A (mN / mm 2 ), the value of the maximum thermal shrinkage force obtained by performing thermomechanical analysis on the separator is B (mN / mm 2 ), and further, the temperature at which the thermal shrinkage force obtained by performing thermomechanical analysis on the separator drops to a value (mN / mm 2 ) 20% higher than the value of the thermal shrinkage force at 30°C (mN / mm 2 ) is defined as the thermal shrinkage end temperature α (°C). In this case, it is necessary that the value of A satisfies A > B in the temperature range of 25°C or higher and lower than the thermal shrinkage end temperature α°C. Thus, in the temperature range of 25°C or higher and lower than the thermal shrinkage end temperature α°C of the separator, a laminate for a secondary battery that satisfies the condition that the shear peel strength A between the electrode and the separator is greater than the maximum thermal shrinkage force B of the separator has excellent adhesion between the electrode and the separator, and can form a secondary battery with low internal resistance and excellent stability.

[0020] The reason is not clear, but it is presumed as follows. First, as described above, "in the temperature range of 25°C or higher and α°C or lower, the heat shrinkage end temperature, A > B" means that in the temperature range from room temperature to the temperature at which the heat shrinkage of the separator ends, that is, the temperature range until the heat shrinkage force of the separator is substantially lost, the shear peel strength A between the electrode and the separator is greater than the maximum heat shrinkage force that the separator can exhibit (i.e., the maximum heat shrinkage force B of the separator). More specifically, "the heat shrinkage force of the separator is substantially lost" means that the separator melts and the voids are blocked, resulting in a state where the so-called "shutdown performance by the separator" is exhibited and completed. Therefore, if the relationship A > B is satisfied in all of the "temperature range of 25°C or higher and α°C or lower, the heat shrinkage end temperature", the adhesion between the electrode and the separator will be maintained in the temperature region from normal temperature to the completion of shutdown by the separator. In the laminate for a secondary battery, if the adhesion between the electrode and the separator is maintained, it is possible to suppress an increase in the internal resistance of the secondary battery provided with such a laminate for a secondary battery, and to suppress thermal runaway and enhance stability. More specifically, the stability of the secondary battery can be evaluated by a nail penetration test and an overcharge test as verified in the examples described later. In the nail penetration test, when an internal short circuit is simulated in the secondary battery, the performance of suppressing thermal runaway such as ignition or rupture can be tested. Also, in the overcharge test, when the secondary battery is continuously charged and discharged to a high load state, the performance of suppressing thermal runaway can be tested.

[0021] The laminate for a secondary battery of the present invention is formed by laminating an electrode and a separator via an adhesive material. More specifically, the laminate for a secondary battery of the present invention may be formed by bonding and integrating an electrode and a separator via a bonding surface. Here, the electrode laminated with the separator to form the laminate for a secondary battery may be only a positive electrode, only a negative electrode, or both a positive electrode and a negative electrode. Further, when both the positive electrode and the negative electrode are bonded to the separator to form the laminate for a secondary battery, the number of the positive electrode, the negative electrode, and the separator included in the laminate for a secondary battery may each be one, or may be two or more. That is, the structure of the laminate for a secondary battery of the present invention may be any of the following (1) to (6). (1) Positive electrode / Separator (2) Negative electrode / Separator (3) Positive electrode / Separator / Negative electrode (4) Positive electrode / Separator / Negative electrode / Separator (5) Separator / Positive electrode / Separator / Negative electrode (6) A structure in which a plurality of positive electrodes and negative electrodes are alternately laminated via separators (for example, "Separator / Negative electrode / Separator / Positive electrode / Separator / Negative electrode ····· / Separator / Positive electrode", etc.)

[0022] <Electrode> The electrode is not particularly limited. For example, an electrode composed of an electrode substrate formed by forming an electrode mixture layer on one or both sides of a current collector, or an electrode formed by further forming a porous film layer on the electrode mixture layer of the electrode substrate can be used. Note that the current collector, the electrode mixture layer, and the porous film layer are not particularly limited, and any current collector, electrode mixture layer, and porous film layer that can be used in the field of secondary batteries, such as those described in JP-A-2013-145763, can be used. Here, the porous film layer refers to a layer containing non-conductive particles as described in, for example, JP-A-2013-145763.

[0023] Here, the electrode provided in the laminate for a secondary battery of the present invention preferably does not include a porous film layer mainly composed of non-conductive particles that can be provided to enhance the heat resistance of the laminate for a secondary battery. In the laminate for a secondary battery of the present invention, as described above, in the temperature range of 25°C or higher and α°C or lower of the heat shrinkage end temperature, since the relationship of A > B is satisfied, even if it does not include a porous film layer that can be mainly provided to enhance the heat resistance of the laminate for a secondary battery, sufficient stability can be imparted to the resulting secondary battery. If the laminate for a secondary battery does not include components such as a porous film layer that is a layer not directly contributing to the electrochemical reaction, it is possible to suppress an increase in the internal resistance of the resulting secondary battery and increase the energy density.

[0024] <Separator> Further, the separator provided in the laminate for a secondary battery of the present invention preferably has a porosity of 5% or more, more preferably 20% or more, and even more preferably 40% or more. If the porosity of the separator is 5% or more, it is possible to move substances contributing to battery reactions such as lithium ions through the separator, and it is possible to suppress an excessive increase in the internal resistance of the resulting secondary battery. Note that the porosity of the separator is not particularly limited and can be, for example, 70% or less. The "porosity of the separator" is a value obtained as the ratio (%) of the area of voids included in a randomly extracted target region by observing the cross-section of the separator included in the laminate for a secondary battery to the total area of the target region.

[0025] Furthermore, the average diameter of the pores in the separator (hereinafter also referred to as the average pore diameter of the separator) is preferably 100 nm or more and 1000 nm or less. Further, from the viewpoint of enhancing the adhesion between the separator and the electrode, the average pore diameter of the separator is preferably larger than the volume average particle diameter D50 of the particulate polymer as the water-insoluble polymer described later. In this case, when observing the cross section of the laminate for a secondary battery and measuring the ratio of the area of the particulate polymer contained in the pores of the separator to the total area of the particulate polymer, the ratio is preferably 10% or more. Such a ratio can be controlled by variously adjusting the relative ratio between the average pore diameter of the separator and the volume average particle diameter of the particulate polymer, the heating and / or pressurization conditions when bonding the separator and the electrode, and the like.

[0026] Note that the separator is not particularly limited, and for example, it can be a separator made of a separator base material or a separator having a porous film layer on one or both sides of the separator base material. The separator base material and the porous film layer are not particularly limited, and examples include any separator base material and porous film layer that can be used in the field of secondary batteries, such as those described in JP-A-2012-204303 and JP-A-2013-145763. Among them, the separator preferably includes a separator base material made of a polyolefin resin such as polyethylene and polypropylene. If the separator contains a polyolefin resin, the internal resistance of the resulting secondary battery can be further reduced and the stability can be further enhanced. Note that for the same reason as described in the item of <electrode>, the separator provided in the laminate for a secondary battery of the present invention preferably does not include a porous film layer, which can be mainly provided to enhance the heat resistance of the laminate for a secondary battery.

[0027] <The maximum heat shrinkage force B of the separator> The value B of the maximum heat shrinkage force obtained by performing thermomechanical analysis on the separator is the value of the maximum load (mN) per unit area (mm 2 ) of the test piece measured by performing thermomechanical analysis on the test piece of the separator. Figure 1 shows a curve (thermal shrinkage curve) plotted with the data obtained by performing a thermomechanical analysis on a separator according to an example, with the vertical axis representing the thermal shrinkage force (mN / mm 2 ), and the horizontal axis representing the temperature (°C). As shown in Figure 1, the maximum thermal shrinkage force B of the separator is the maximum value of the thermal shrinkage force. Naturally, depending on the physical properties of the separator, the shape of the thermal shrinkage curve varies. For example, even when the thermal shrinkage curve has multiple maximum values, the maximum value of the thermal shrinkage force corresponds to the maximum thermal shrinkage force B of the separator.

[0028] <Thermal shrinkage end temperature α (°C) of the separator> As shown in Figure 1, the "thermal shrinkage end temperature α (°C) of the separator" is the temperature at which the thermal shrinkage force obtained by performing a thermomechanical analysis on the separator drops to a value 20% higher than the value F (30) (mN / mm 2 ) of the thermal shrinkage force at 30°C (mN / mm 2 ). At this temperature α (°C), the shutdown performance of the separator is fully exerted and completed. That is, at the temperature α (°C), the separator is melted and the voids are blocked. Since the mass transfer through the separator is inhibited, the battery reaction is stopped, and the thermal runaway of the secondary battery is stopped. The shutdown performance of the separator starts from the thermal shrinkage start temperature β shown in Figure 1. The thermal shrinkage start temperature β corresponds to the intersection of the tangent lines around the point where the slope of the tangent line of the thermal shrinkage curve first changes significantly after the start of temperature increase detected by the thermomechanical analysis.

[0029] The thermal shrinkage start temperature β of the separator is preferably 100°C or lower, more preferably 90°C or lower, and even more preferably 70°C or lower. If the thermal shrinkage start temperature β of the separator is below the above upper limit value, the stability of the obtained secondary battery can be further enhanced. More specifically, when the secondary battery is continuously charged and discharged to a high load state, the performance of suppressing thermal runaway (i.e., the characteristics that can be evaluated by an overcharge test) can be enhanced. The thermal shrinkage start temperature of the separator can be, for example, 45°C or higher.

[0030] <Peeling strength A between electrode and separator> The "value A of the shear peeling strength between the electrode and the separator" is for a test piece in which the separator and the electrode are adhered via an adhesive material. While varying the temperature, the tensile stress (mN) in the shear direction is measured and converted to a value per unit area (mm 2 ). It is a value converted to a value per unit area (mm). Such peeling strength can be adjusted based on the properties of the adhesive material used and the combination of the properties of the separator.

[0031] And in the laminate for a secondary battery according to the present invention, in the temperature range of 25°C or higher and α°C or lower at the end of thermal shrinkage, the relationship of A > B is satisfied. Therefore, in a secondary battery provided with such a laminate, within the temperature range until the shutdown by the separator is completed, thermal runaway can be suppressed and an excessive increase in internal resistance can be suppressed.

[0032] <Adhesive material> The adhesive material is a material for adhering the electrode and the separator. As the adhesive material, any adhesive material used in the field of secondary batteries can be used without particular limitation as long as it can adhere the electrode and the separator and does not inhibit the battery reaction. The polymer constituting the adhesive material may be only one type or two or more types. Among them, it is preferable that the adhesive material contains a water-insoluble polymer satisfying at least one of the following conditions (i) and (ii), or a water-soluble polymer having a thermal decomposition temperature of 180°C or higher, or both of them.

[0033] <<Water-insoluble polymer>> The adhesive material preferably contains at least one of (i) a water-insoluble polymer having no glass transition temperature and melting point in a temperature range below 180°C, and (ii) a water-insoluble polymer having a glass transition temperature in a temperature range below 180°C but having a melting point in a temperature range of 180°C or higher. The water-insoluble polymer corresponding to the above (i) preferably has no glass transition temperature and melting point in a temperature range below 190°C, and more preferably has no glass transition temperature and melting point in a temperature range below 200°C. Further, the water-insoluble polymer corresponding to the above (ii) preferably has a melting point in a temperature range of 190°C or higher, and more preferably has a melting point in a temperature range of 200°C or higher. By using the adhesive material containing the water-insoluble polymer corresponding to the above (i) or (ii), it is possible to further enhance the adhesiveness between the electrode and the separator and to provide a secondary battery having more excellent stability.

[0034] Here, when the water-insoluble polymer as the adhesive material is crystalline, both the glass transition temperature and the melting point can be detected. Therefore, among the crystalline water-insoluble polymers, those satisfying the above (i) have both the glass transition temperature and the melting point in a temperature range of 180°C or higher. Also, among the crystalline water-insoluble polymers, those satisfying the above (ii) have a glass transition temperature below 180°C but a melting point of 180°C or higher. On the other hand, when the water-insoluble polymer as the adhesive material is amorphous, the glass transition temperature is detected but the melting point is not detected. Therefore, for the amorphous water-insoluble polymers that satisfy the above (i), the glass transition temperature can be detected in a temperature range of 180°C or higher. Also, there are no amorphous water-insoluble polymers that satisfy the above (ii).

[0035] Here, the composition of the water-insoluble polymer satisfies the above-described "water-insoluble" conditions, and preferably, it can be any composition without particular limitation as long as it can satisfy the above conditions (i) or (ii) regarding the glass transition temperature and the melting point. Among them, as the water-insoluble polymer, a binder containing polyfunctional ethylenically unsaturated monomer units at a ratio of 20% by mass or more and 90% by mass or less (hereinafter, binder 1), a binder containing nitrile group-containing monomer units at 70% by mass or more and 95% by mass or less (hereinafter, binder 2), a silicone binder which is a polymer having a main chain composed of siloxane bonds, a polyamideimide which is a polymer containing an amide bond and an imide bond in the repeating unit, a fluorine-based binder such as polytetrafluoroethylene, a polyamide fine particle dispersion, an epoxy resin, a thermosetting urethane resin, etc. can be mentioned. Among them, as the water-insoluble polymer, the above binder 1, binder 2, silicone binder, and fluorine-based binder are preferable, binder 1 and binder 2 are more preferable, and binder 1 is even more preferable.

[0036] In addition, the polyfunctional ethylenically unsaturated monomer that can be used when forming the above binder 1 (a binder containing polyfunctional ethylenically unsaturated monomer units at a ratio of 20% by mass or more and 90% by mass or less) is not particularly limited, and includes polyfunctional (meth)acrylic acid ester monomers such as 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; polyfunctional aromatic vinyl monomers such as divinylbenzene and diisopropenylbenzene; Dipropylene glycol diallyl ether, polyglycol diallyl ether, triethylene glycol divinyl ether, hydroquinone diallyl ether, tetraallyloxyethane, trimethylolpropane - diallyl ether, allyl or vinyl ethers of polyfunctional alcohols other than those described above, triallylamine, methylenebisacrylamide; and the like. 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. Note that "(meth)acrylate" means acrylate and / or methacrylate. Also, the method for preparing such a binder 1 is not particularly limited. The polymerization mode when preparing binder 1 can be any method without particular limitation, such as solution polymerization method, suspension polymerization method, bulk polymerization method, emulsion polymerization method, etc. Also, as the polymerization reaction, any reaction such as ionic polymerization, radical polymerization, living radical polymerization, etc. can be used. And for emulsifiers, dispersants, polymerization initiators, chain transfer agents, etc. that can be used in the polymerization, those generally used can be used.

[0037] In addition, the nitrile group-containing monomer that can be used when forming the above binder 2 (a binder containing 70% by mass or more and 95% by mass or less of a nitrile group-containing monomer unit) is not particularly limited, and examples thereof include α,β-ethylenically unsaturated nitrile monomers. Specifically, examples of the α,β-ethylenically unsaturated nitrile monomer include acrylonitrile; α-halogenoacrylonitriles such as α-chloroacrylonitrile and α-bromoacrylonitrile; α-alkylacrylonitriles such as methacrylonitrile and α-ethylacrylonitrile; and the like. These can be used alone or in combination of two or more. Among them, acrylonitrile and methacrylonitrile are preferred, and acrylonitrile is more preferred. Further, the method for preparing such a binder 2 is not particularly limited, and the polymerization methods and polymerization conditions as exemplified above for the preparation method of binder 1 can be adopted.

[0038] Furthermore, the water-insoluble polymer is preferably a particulate polymer that satisfies a predetermined volume average particle diameter D50. Specifically, it is preferable that the volume average particle diameter D50 of the particulate polymer, which is a water-insoluble polymer, is smaller than the average pore diameter of the separator constituting the secondary battery laminate. If the volume average particle diameter D50 of the particulate polymer satisfies such a condition, the adhesiveness between the electrode and the separator can be further enhanced. Although the reason is not clear, it is presumed that this is because at least a part of the particulate polymer enters the pores of the separator, and the adhesive strength between the electrode and the separator can be increased by exhibiting the adhesive ability as an adhesive material.

[0039] The specific numerical value of the volume average particle diameter D50 of the particulate polymer as the water-insoluble polymer is preferably 100 nm or more, more preferably 150 nm or 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 diameter D50 of the particulate polymer is within the above range, the adhesive force between the electrode and the separator can be further enhanced. The volume average particle diameter D50 of the particulate polymer can be controlled by adjusting the formulation of the monomer composition and the polymerization conditions (for example, polymerization time, etc.) when preparing the particulate polymer.

[0040] Furthermore, when the water-insoluble polymer is a particulate polymer, such a particulate polymer may be particles having a single-phase structure formed from a single polymer, or may be particles having a heterogeneous structure formed by physically or chemically bonding two or more different polymers to each other. Here, specific examples of the heterogeneous structure include a core-shell structure in which spherical particles are formed from different polymers in the central part (core part) and the outer shell part (shell part); a side-by-side structure in which two or more polymers are juxtaposed; and the like. In the present specification, the "core-shell structure" includes not only a structure in which the outer surface of the core part is completely covered by the shell part, but also a structure in which the outer surface of the core part is partially covered by the shell part. And in the present invention, even when the outer surface of the core part appears to be completely covered by the shell part in appearance, if pores communicating the inside and outside of the shell part are formed, the shell part is a shell part that partially covers the outer surface of the core part.

[0041] When the particulate polymer has a core-shell structure, it is preferable that at least the glass transition temperature and melting point of the shell part satisfy the above-described condition (i) or (ii) among the glass transition temperature and melting point of the core part and the glass transition temperature and melting point of the shell part. Further, it is preferable that both the glass transition temperature and melting point of the core part and the glass transition temperature and melting point of the shell part satisfy the above-described condition (i) or (ii).

[0042] <<Water-soluble polymer>> The water-soluble polymer that can be preferably contained in the adhesive material preferably has a thermal decomposition temperature of 180°C or higher, more preferably 190°C or higher, and even more preferably 200°C or higher. When an adhesive material containing a water-soluble polymer with a thermal decomposition temperature of 180°C or higher is used, the adhesiveness between the electrode and the separator can be further enhanced, and a secondary battery with even better stability can be provided. Note that the thermal decomposition temperature of the water-soluble polymer as the adhesive material is not particularly limited and can be, for example, 450°C or lower.

[0043] Here, the composition of the water-soluble polymer is not particularly limited as long as it satisfies the above-described "water-soluble" condition and the condition of the thermal decomposition temperature, and can be any composition. Among them, examples of the water-soluble polymer include carboxymethyl cellulose, xanthan gum, alginic acid, polyamideimide, polyacrylamide, polyacrylic acid, polysulfonic acid, polyvinyl alcohol, polyvinyl pyrrolidone, poly-2-acrylamido-2-methylpropanesulfonic acid, and aromatic amide compounds, etc. Among them, carboxymethyl cellulose and polyamideimide are preferred.

[0044] <<Ratio of the amounts of the water-insoluble polymer and the water-soluble polymer in the adhesive material>> In the laminate for secondary batteries, an adhesive material that can adhere and integrate the electrode and the separator by intervening therebetween preferably contains at least one of a water-insoluble polymer and a water-soluble polymer as described above. Further, from the viewpoint of further enhancing the liquid injection property of the electrolytic solution when a secondary battery is formed using the laminate for secondary batteries, it is more preferable that the adhesive material contains a water-insoluble polymer and a water-soluble polymer. This is because, from the viewpoint of enhancing the liquid injection property of the electrolytic solution, it is advantageous that an appropriate distance is maintained between the electrode and the separator. When a water-insoluble polymer (particulate polymer) is used, such an "appropriate distance" can be ensured by the volume of the particulate polymer. However, when the adhesive material consists only of a water-soluble polymer, such an "appropriate distance" is not ensured. Furthermore, when the adhesive material contains a water-insoluble polymer and a water-soluble polymer, it is preferable that the content of the water-insoluble 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.

[0045] Note that the laminate for secondary batteries of the present invention requires that the electrode and the separator are laminated via an adhesive material. However, inorganic fine particles that can penetrate into the pores of the separator such as fumed alumina may optionally be interposed between the electrode and the separator within a range that does not inhibit the effects of the present invention.

[0046] (Method for manufacturing a laminate for secondary batteries) The laminated body for secondary battery of the present invention described above can be efficiently manufactured according to, for example, a manufacturing method according to the following example. The manufacturing method according to the example is a method of manufacturing a laminated body for secondary battery by laminating an electrode and a separator. In the manufacturing method according to the example, after performing step (A) of applying an adhesive material to at least one bonding surface of the electrode and the separator, the electrode and the separator are transported to the bonding start position without contacting another member with the bonding surface to which the adhesive material is applied. Then, step (C) of bonding the electrode and the separator through the bonding surface is performed to manufacture a laminated body for secondary battery. Here, the "bonding start position" refers to the position where the bonding surface of the electrode and the bonding surface of the separator are brought into contact when bonding the electrode and the separator.

[0047] <Step (A)> In step (A), the above-described adhesive material is applied to at least one bonding surface of the electrode and the separator. Note that the electrode used for manufacturing the laminated body for secondary battery may be wound in a roll shape or may be pre-cut. Also, the separator material used for manufacturing the laminated body for secondary battery may be wound in a roll shape or may be pre-cut. Among them, from the viewpoint of efficiently and continuously manufacturing the laminated body for secondary battery, it is preferable to use a separator material wound in a roll shape. Also, as the separator material to be used, it is preferable to use at least one having a porosity of 5% or more. Further, the porosity of the separator material is preferably 20% or more, and more preferably 40% or more. Also, the average diameter of the voids in the separator material (hereinafter also referred to as the average pore diameter of the separator material) is preferably 100 nm or more and 1000 nm or less. Further, from the viewpoint of enhancing the adhesiveness between the separator and the electrode, the average pore diameter of the separator material is preferably larger than the volume average particle diameter D50 of the adhesive material. Furthermore, from the viewpoint of increasing the energy density of the obtained secondary battery, the separator material to be used preferably has a thickness of 20 μm or less, and more preferably 15 μm or less. Note that the thickness of the separator material can be, for example, 4 μm or more.

[0048] As the bonding material, those described above in the item (laminated body for secondary battery) can be preferably used. The bonding 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. Among these, it is preferable to supply the bonding material in a state dissolved in a solvent or a state dispersed in a solvent.

[0049] And when the bonding material is supplied to the bonding surface in a state dissolved in a solvent or a state dispersed in a solvent in step (A), that is, when a bonding composition containing the bonding material and a solvent is supplied to the bonding surface, the solvent of the bonding composition is not particularly limited, and for example, water, an organic solvent, and a mixture thereof can be used. 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; alcohols such as methanol, ethanol, isopropanol, ethylene glycol, propylene glycol, and ethylene glycol monomethyl ether; and the like. Among these, from the viewpoint of efficiently manufacturing a laminated body for a secondary battery, water and alcohol are preferable as the solvent. The concentration of the bonding material in the bonding composition is not particularly limited and can be, for example, 1% by mass or more and 40% by mass or less.

[0050] And the application of the adhesive material to the bonding surface is not particularly limited, and for example, it can be carried out using methods such as the inkjet method, spray method, dispenser method, gravure coating method, screen printing method, etc. Among them, from the viewpoints of productivity and high degree of freedom in the formed shape, the application method of the adhesive material is preferably the inkjet method. When applying the adhesive material to the bonding surface, the adhesive material may be applied to at least one of the electrode and the separator. The electrode may be a positive electrode or a negative electrode.

[0051] In addition, the adhesive material may be applied to the entire bonding surface or only to a part of the bonding surface. And when applying the adhesive material only to a part of the bonding surface, the adhesive material is not particularly limited and can be applied in an arbitrary planar shape such as stripe shape, dot shape, lattice shape, etc. Among them, from the viewpoint of enhancing the liquid injection property of the electrolytic solution when manufacturing a secondary battery using the laminated body for secondary battery, the adhesive material is preferably applied in a dot shape. When arranging minute dot-shaped adhesive materials in a predetermined pattern, from the viewpoints of ease of application and arrangement of the adhesive material, it is preferable to coat the adhesive composition in a desired pattern by the inkjet method.

[0052] <Step (B)> In step (B), the electrode and the separator are conveyed to the bonding start position without bringing other members into contact with the bonding surface to which the adhesive material has been applied. In this way, if other members are not brought into contact with the bonding surface to which the adhesive material has been applied, problems such as blocking do not occur, so that an adhesive material with excellent adhesiveness can be used and the laminated body for secondary battery can be efficiently manufactured.

[0053] In addition, the conveyance of the electrode and the separator is not particularly limited, and for example, it can be carried out using any conveyance mechanism such as a roller, a belt conveyor, a manipulator, an adsorption band, etc. Among them, from the viewpoint of further enhancing the manufacturing efficiency of the laminated body for secondary battery, it is preferable to convey at least one of the electrode and the separator using a roller.

[0054] <Engineering (C)> In Engineering (C), the electrode and the separator are bonded together through the bonding surface. Here, the bonding is not particularly limited, and for example, it can be performed by pressing and / or heating a laminate of the electrode and the separator superposed through the bonding surface. Here, when the adhesive composition is used in Engineering (A), it is preferable that the time interval from the completion of Engineering (A) to the start of Engineering (C) is shorter than the time required for the adhesive composition to completely dry. That is, it is preferable that the adhesive composition has not completely dried at the time of starting Engineering (C). If Engineering (C) can be started at the timing when the adhesive composition is undried, the adhesive force between the separator and the electrode can be further increased, and the stability of the obtained secondary battery can be further enhanced. More specifically, by firmly bonding between the separator and the electrode, when an internal short circuit occurs, the short-circuited portion can be held so as not to spread, and the stability of the secondary battery can be further enhanced.

[0055] Note that the pressure applied to the laminate in Engineering (C), the temperature at the time of bonding the electrode and the separator, and the time for pressing and / or heating the laminate can be appropriately adjusted according to the type and amount of the adhesive material used, etc.

[0056] (Secondary battery) The secondary battery of the present invention is characterized by including the laminate for secondary battery of the present invention. And since the secondary battery of the present invention includes the laminate for secondary battery of the present invention, it has a low internal resistance and excellent stability. Note that, in one example, when manufacturing a secondary battery using the laminate for secondary battery of the present invention, a process of assembling the secondary battery using the laminate for secondary battery and an electrolytic solution (assembly process) is performed.

[0057] <Assembly process> Here, as the electrolytic solution, an organic electrolytic solution in which a supporting electrolyte is dissolved in an organic solvent is usually used. For example, when the secondary battery is a lithium-ion secondary battery, a lithium salt is used as the supporting electrolyte. Examples of the lithium salt include LiPF6, LiAsF6, LiBF4, LiSbF6, LiAlCl4, LiClO4, CF3SO3Li, C4F9SO3Li, CF3COOLi, (CF3CO)2NLi, (CF3SO2)2NLi, (C2F5SO2)NLi, and the like. Among them, LiPF6, LiClO4, and CF3SO3Li are preferable because they are easily soluble in the solvent and exhibit a high degree of dissociation, and LiPF6 is particularly preferable. Note that the electrolyte may be used alone or in combination of two or more in any ratio. Usually, the higher the degree of dissociation of the supporting electrolyte used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted according to the type of the supporting electrolyte.

[0058] Furthermore, the organic solvent used in the electrolytic solution is not particularly limited as long as it can dissolve the supporting electrolyte. For example, carbonates such as dimethyl carbonate (DMC), ethylene carbonate (EC), diethyl carbonate (DEC), propylene carbonate (PC), butylene carbonate (BC), ethyl methyl carbonate (EMC), vinylene carbonate (VC); esters such as γ-butyrolactone and methyl formate; ethers such as 1,2-dimethoxyethane and tetrahydrofuran; sulfur-containing compounds such as sulfolane and dimethyl sulfoxide; and the like are preferably used. Also, a mixture of these solvents may be used. Among them, it is preferable to use carbonates because they have a high dielectric constant and a wide stable potential region. Usually, the lower the viscosity of the solvent used, the higher the lithium ion conductivity tends to be, so the lithium ion conductivity can be adjusted according to the type of the solvent. Note that the concentration of the electrolyte in the electrolytic solution can be adjusted as appropriate. Also, known additives may be added to the electrolytic solution.

[0059] Then, for the secondary battery, after further laminating additional battery members (such as electrodes and / or separators) on the laminate for the secondary battery of the present invention as required, the obtained laminate is wound, folded, etc. according to the battery shape as required and placed in a battery container, and the battery container is filled with an electrolytic solution and sealed to assemble the secondary battery. In addition, in order to prevent an increase in the internal pressure of the secondary battery, the occurrence of overcharge / discharge, etc., an overcurrent prevention element such as a fuse or a PTC element, an expandable metal, a lead plate, etc. may be provided as required. Also, the shape of the secondary battery may be, for example, any of a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, etc.

Examples

[0060] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, the measurement and evaluation of various attributes were carried out as follows.

[0061] <Volume average particle diameter D50> For the aqueous dispersion containing the particulate polymer which is the water-insoluble polymer to be measured, the particle size distribution (volume basis) was measured by a laser diffraction particle size distribution measuring device (manufactured by Shimadzu Corporation, product name “SALD-3100”). Then, in the measured particle size distribution, the particle size at which the cumulative volume calculated from the small diameter side becomes 50% was defined as the volume average particle diameter (D50) of each particle. <Glass transition temperature (Tg) and melting point> Measurement was carried out using a differential scanning calorimeter (manufactured by Nanotechnology Co., Ltd., DSC6220SII) in accordance with JIS K7121:2012 at a measurement temperature of -100°C to 180°C and a heating rate of 5°C / min. <Thermal decomposition temperature> Measurement was carried out in accordance with JIS K 7120:1987.

[0062] <Void fraction and average pore diameter of the separator> In the Examples and Comparative Examples, the separator materials used in manufacturing the secondary battery laminate, and the secondary battery laminates (after electrolyte injection) manufactured in the Examples and Comparative Examples were cut using an argon ion beam while cooling with liquid nitrogen as a refrigerant to prepare a cross-section, which was observed with a scanning electron microscope (SEM) to obtain a cross-sectional image of the secondary battery laminate. The obtained cross-sectional image was binarized, and the ratio (%) of the area of voids included in a randomly extracted target region to the total area of the target region was calculated to obtain the porosity of the separator. Further, for 1000 voids randomly extracted in the cross-sectional image, the diameter when an circumscribed circle was set was measured, and the number average value was obtained to obtain the average pore diameter of the separator, and it was determined whether the relationship "average pore diameter of separator > volume average particle diameter D50 of the water-insoluble polymer" was satisfied. Note that the values (porosity and average pore diameter) obtained for the separator material and the laminate were the same. Note that the average pore diameter of the separator obtained by measurement was 250 nm for the separator base material of 12 μm thickness made of polyethylene (PE) used in Example 1 etc., and 300 nm for the separator made of polypropylene (PP) of 18 μm thickness used in Example 3 etc. <Thermomechanical Analysis of Separator Material> Using the separator materials used in the Examples and Comparative Examples as measurement samples, a tensile load (mN) was measured under the following conditions by setting a thermomechanical analyzer (manufactured by SII NanoTechnology Inc., "TMA / SS6100") in the constant displacement mode. The measured value of the tensile load was divided by the cross-sectional area (mm 2 ) of the measurement sample to obtain the value (mN / mm 2 ) of the thermal shrinkage force, which is the value of the tensile load per unit cross-sectional area. · Measurement temperature range: 20°C to up to the displacement detection limit · Heating rate: 5°C / min · Measurement atmosphere: Nitrogen Then, corresponding to each temperature, the value (mN / mm 2 ) of the thermal shrinkage force was plotted to obtain a thermal shrinkage curve, and the maximum value (mN / mm 2 ) of the thermal shrinkage force was defined as "the maximum thermal shrinkage force B of the separator", and the thermal shrinkage force was the value F of the thermal shrinkage force at 30°C (30) (mN / mm 2) a value 20% higher than (mN / mm 2 ) The temperature at which it decreases to is defined as the "thermal shrinkage end temperature α (°C) of the separator", and after the start of temperature increase detected by thermomechanical analysis, the temperature corresponding to the intersection of the tangents before and after the point where the slope of the tangent of the thermal shrinkage curve first changes significantly is defined as the "thermal shrinkage start temperature β". The results are shown in Table 1.

[0063] <Shear peel strength> After the passage of time after electrolyte injection, the lithium-ion secondary battery was disassembled, and the secondary battery laminate in which the negative electrode (in Example 5, the positive electrode) - separator was laminated via an adhesive material was cut out to a size with an adhesive area of 3 cm square. After chucking the separator and the electrode in the shear direction, the tensile stress was observed with an autograph in a thermostatic bath (tensile speed: 5 mm / min). The peak value of the initial response of the obtained data was defined as the shear peel strength. The test measurement temperature was plotted from room temperature (25 °C) to 200 °C every 20 °C, and the minimum value in the temperature range from room temperature to the thermal shrinkage end temperature α (°C) of the separator material used in each example and comparative example was defined as the shear peel strength. A: Shear peel strength is 3 mN / mm 2 or more B: Shear peel strength is 1.3 mN / mm 2 exceeding, 3 mN / mm 2 less than C: Shear peel strength is 1 mN / mm 2 or more and 1.3 mN / mm 2 or less D: Shear peel strength is 1 mN / mm 2 less than

[0064] <Adhesion between electrode and separator> Under the same conditions as in each example and comparative example, the laminate after lamination (that is, a laminate in which one electrode and one separator are laminated via an adhesive material) was taken as a test piece. This test piece was placed with the surface on the current collector side of the electrode facing downwards, and cellophane tape was attached to the surface on the current collector side of the negative electrode (in Example 5, the positive electrode). At this time, the cellophane tape specified in JIS Z1522 was used. Also, the cellophane tape was fixed to a horizontal test bench. Then, the stress when one end of the separator was pulled vertically upwards at a pulling speed of 50 mm / min and peeled off was measured. This measurement was performed a total of six times, and the average value of the stress was determined as the peel strength, and the adhesiveness between the negative electrode and the separator was evaluated according to the following criteria. The higher the peel strength, the higher the adhesiveness between the electrode (negative electrode / positive electrode) and the separator in a state not immersed in the electrolyte, that is, in a dry state. A: Peel strength is 1.5 N / m or more B: Peel strength is 1.0 N / m or more and less than 1.5 N / m C: Peel strength is 0.5 N / m or more and less than 1.0 N / m D: Peel strength is less than 0.5 N / m <Electrolyte injection property> The electrolyte was injected into the lithium-ion secondary batteries prepared in the examples and comparative examples. Then, the inside of the lithium-ion secondary battery was depressurized to -100 kPa and held in that state for 1 minute. Then, heat sealing was performed. Then, after 10 minutes, the electrode (negative electrode, positive electrode in Example 5) was disassembled, and the impregnation state of the electrolyte in the electrode was visually confirmed. And it was evaluated according to the following criteria. In the electrode, the more the portion impregnated with the electrolyte, the higher the electrolyte injection property. A: The electrolyte is impregnated on all surfaces of the electrode. B: In the electrode, the portion not impregnated with the electrolyte remains less than 5% in terms of area conversion (excluding the case where it is impregnated on all surfaces). C: In the electrode, the portion not impregnated with the electrolyte remains 5% or more and less than 10% in terms of area conversion. D: In the electrode, the portion not impregnated with the electrolyte remains 10% or more in terms of area conversion.

[0065] <Battery thickness> To measure the thickness of the lithium-ion secondary batteries fabricated in the examples and comparative examples, measurements were performed using a thickness gauge (Mitutoyo Corporation, "547-321 Thickness Gauge"). Ten random measurement points were set on the same battery for measurement, and the arithmetic mean value was taken as the battery thickness. A: Battery thickness is less than 8 mm B: Battery thickness is 8 mm or more <Internal Resistance> The lithium-ion secondary batteries fabricated in the examples and comparative examples were charged at 1C (where C is the value represented by the rated capacity (mA) / 1h (hour)) to 50% of the SOC (State Of Charge, depth of charge) under the condition of 25°C. After that, with 50% of the SOC as the center, charging and discharging were each performed for 15 seconds at 0.5C, 1.0C, 1.5C, and 2.0C. The battery voltage 10 seconds after each case (charging side and discharging side) was plotted against the current value, and the value obtained by dividing the slope by the area of the positive electrode of the fabricated lithium-ion battery was taken as the IV resistance (Ω·cm 2 )(IV resistance during charging and IV resistance during discharging). Regarding the obtained IV resistance values (Ω·cm 2 ), evaluation was performed according to the following criteria. The smaller the value of the IV resistance, the less the internal resistance and the lower the DC resistance. A: IV resistance is 22 Ω·cm 2 or less B: IV resistance is more than 22 Ω·cm 2 and 25 Ω·cm 2 or less C: IV resistance is more than 25 Ω·cm 2 and 28 Ω·cm 2 or less D: IV resistance is more than 28 Ω·cm 2 exceeding <Nail Piercing Test> The lithium-ion secondary batteries fabricated in the examples and comparative examples were evaluated by a nail piercing test. The nail piercing test was carried out using a nail with a diameter of 6 mm at a lifting speed of 1 mm / min with the laminated lithium-ion secondary battery as the test sample under the condition of variable temperature in a thermostatic bath. After the nail was pierced, those that led to thermal runaway and ignition were regarded as NG, and those that did not ignite were regarded as OK. Five test samples were evaluated, and if even one reached NG, it was determined that the stability of the test sample could not be maintained under that temperature condition. A: All test samples passed under the condition of 60 °C temperature. B: All test samples passed under the condition of 50 °C temperature. C: All test samples passed under the condition of 40 °C temperature. D: There were test samples that failed under the condition of 40 °C temperature. <Overcharge Test> The laminated lithium-ion secondary batteries fabricated in the examples and comparative examples were used as test samples and evaluated through overcharge tests. The test samples were continuously charged in a constant current mode with variable rates, and the upper limit of the charging voltage was set to 20 V for test safety. In the evaluation at each rate, those that led to thermal runaway and ignition were regarded as NG, and those that did not ignite were regarded as OK. Five test samples were evaluated, and if any one of them reached NG, it was determined that the stability of the test samples could not be maintained under that rate condition. The evaluation temperature was set to 25 °C. A: All test samples passed at a rate of 1.5C. B: All test samples passed at a rate of 1.0C. C: There were test samples that failed at a rate of 1.0C.

[0066] (Example 1) <Preparation of Adhesive Material (Binder 1)> Into reactor A equipped with a stirrer, 0.20 parts of sodium dodecyl sulfate, 0.30 parts of ammonium persulfate, and 180 parts of ion-exchanged water were added and mixed to form a mixture, which was heated to 65 °C. On the other hand, in another container, 88.0 parts of n-butyl acrylate, which is a monofunctional (meth)acrylate monomer, 6.0 parts of acrylic acid, which is an acidic group-containing monomer, 6.0 parts of acrylonitrile, which is a nitrile group-containing monomer, 0.8 part of sodium dodecyl sulfate, and 40 parts of ion-exchanged water were mixed to prepare a monomer composition for seed particles. This monomer composition for seed particles was continuously added to the above-mentioned reactor A over 4 hours to conduct a polymerization reaction. The temperature inside the reactor during the continuous addition of the monomer composition for seed particles was maintained at 65 °C. After the continuous addition was completed, the polymerization reaction was further continued at 80 °C for 3 hours. As a result, an aqueous dispersion of seed particles was obtained. When the volume average particle diameter D50 of the seed particles was measured, it was 120 nm. Next, into a reactor equipped with a stirrer, add the aqueous dispersion of the above-mentioned seed particles in an amount equivalent to 16.7 parts by solid content (among which, the n-butyl acrylate unit is 14.7 parts, the acrylic acid unit is 1 part, and the acrylonitrile unit is 1 part), 80.8 parts of ethylene glycol dimethacrylate (manufactured by Kyoeisha Chemical Co., Ltd., product name "Light Ester EG") as a polyfunctional ethylenically unsaturated monomer, 2.5 parts of acrylic acid as an acidic group-containing monomer, 0.8 part of sodium dodecylbenzenesulfonate, 3.2 parts of t-butyl peroxy-2-ethylhexanoate (manufactured by NOF Corporation, product name "Perbutyl O") as a polymerization initiator, and 160 parts of ion-exchanged water, and stir at 35°C for 12 hours to completely absorb the polyfunctional ethylenically unsaturated monomer, the acidic group-containing monomer, and the polymerization initiator into the seed particles. Then, maintain the temperature in the reactor at 90°C and carry out a polymerization reaction (seed polymerization) for 5 hours. Next, steam was introduced to remove unreacted monomers and initiator decomposition products, and an aqueous dispersion of Binder 1 was obtained. Then, according to the above, the volume average particle diameter D50 of the obtained Binder 1 was measured. The results are shown in Table 1. Also, according to the above, it was confirmed that for Binder 1, the glass transition temperature and the melting point do not exist in the temperature range below 180°C. Note that Binder 1 exhibited a particulate state in both the aqueous dispersion and the dry state. Also, it was confirmed that Binder 1 is a water-insoluble polymer with an insoluble content of 90 mass% or more when 0.5 g of the polymer is dissolved in 100 g of water at 25°C. <Preparation of Adhesive Composition> Based on 100 parts by solid content of the aqueous dispersion of Binder 1, which is a particulate polymer, add 2 parts by solid content of carboxymethyl cellulose (manufactured by Daicel Corporation, product number "1220"), and add ion-exchanged water so as to have the content ratio shown in Table 1. Then, using an ultra-high-speed emulsifying disperser (manufactured by Primix Corporation, "Robomix"), mix at 3000 rpm for 100 minutes, and then add 45 parts of propylene glycol, which is a polyhydric alcohol compound as a solvent, to obtain a slurry-like adhesive composition. In addition, carboxymethyl cellulose had less than 1.0 mass% of insoluble matter when 0.5 g of carboxymethyl cellulose was dissolved in 100 g of water at a temperature of 25°C. <Formation of negative electrode> Into a 5 MPa pressure-resistant container equipped with a stirrer, 33 parts of 1,3-butadiene, 3.5 parts of itaconic acid, 63.5 parts of styrene, 0.4 part of sodium dodecylbenzenesulfonate as an emulsifier, 150 parts of ion-exchanged water, and 0.5 part of potassium persulfate as a polymerization initiator were put. After sufficiently stirring, the mixture was heated to 50°C to initiate polymerization. When the polymerization conversion rate reached 96%, it was cooled to stop the reaction, and a mixture containing a binder (SBR) for the negative electrode composite layer was obtained. To the mixture containing the binder for the negative electrode composite layer, an aqueous solution of 5% sodium hydroxide was added, adjusted to pH 8, and then unreacted monomers were removed by heating under reduced pressure distillation. Thereafter, it was cooled to 30°C or lower to obtain an aqueous dispersion containing a desired binder for the negative electrode composite layer. Next, 100 parts of artificial graphite (volume average particle diameter: 15.6 μm) as a negative electrode active material, 1 part in terms of solid content of a 2% aqueous solution of sodium carboxymethyl cellulose (manufactured by Nippon Paper Industries Co., Ltd., product name "MAC350HC") as a viscosity modifier, and ion-exchanged water were mixed and adjusted to a solid content concentration of 68%, and then further mixed at 25°C for 60 minutes. Further, after adjusting the solid content concentration to 62% with ion-exchanged water, it was further mixed at 25°C for 15 minutes. To the obtained mixed liquid, 1.5 parts in terms of solid content of the aqueous dispersion containing the binder for the negative electrode composite layer described above and ion-exchanged water were added, adjusted so that the final solid content concentration became 52%, and further mixed for 10 minutes. This was defoamed under reduced pressure to obtain a slurry composition for a secondary battery negative electrode having good fluidity. The obtained slurry composition for a secondary battery negative electrode was applied onto a 20-μm-thick copper foil as a current collector with a comma coater so that the film thickness after drying was about 150 μm, and then dried. This drying was performed by conveying the copper foil through an oven at 60°C at a speed of 0.5 m / min for 2 minutes. Thereafter, heat treatment was performed at 120°C for 2 minutes to obtain a negative electrode raw sheet before pressing. The negative electrode raw sheet before pressing was rolled with a roll press to obtain a negative electrode raw sheet after pressing with a thickness of 80 μm for the negative electrode composite layer. <Formation of positive electrode> 100 parts of LiCoO₂ with a volume average particle diameter of 12 μm as the positive electrode active material, 2 parts of acetylene black (manufactured by Denki Kagaku Kogyo Co., Ltd., product name "HS-100") as the conductive material, and 2 parts of polyvinylidene fluoride (manufactured by Kureha Corporation, product name "#7208") as the binder in terms of solid content were mixed with N-methylpyrrolidone as the solvent to make the total solid content concentration 70%. These were mixed by a planetary mixer to obtain a slurry composition for a secondary battery positive electrode. The obtained slurry composition for a secondary battery positive electrode was applied onto a 20-μm-thick aluminum foil serving as a current collector by a comma coater so that the film thickness after drying would be about 150 μm, and then dried. This drying was carried out by transporting the aluminum foil through an oven at 60 °C for 2 minutes at a speed of 0.5 m / min. Then, it was heat-treated at 120 °C for 2 minutes to obtain a positive electrode precursor. Then, the obtained positive electrode precursor was rolled and cut out using a roll press machine to obtain a positive electrode having a positive electrode composite layer. <Preparation of Separator Material> A separator precursor made of polyethylene (PE) was prepared. Various attributes regarding the separator material were measured according to the above. The results are shown in Table 1. <Manufacture of Laminate for Secondary Battery> Using the prepared adhesive composition, negative electrode precursor, and separator precursor, a laminate for a secondary battery was manufactured using the manufacturing apparatus 100 shown in FIG. 2. In FIG. 2, reference numeral 91 indicates a conveying roller, and reference numeral 92 indicates a heat roller. Specifically, while conveying the negative electrode raw sheet 20A fed from the negative electrode raw sheet roll at a speed of 10 m / min, an adhesive composition was supplied from the inkjet head of an inkjet coater 52 (manufactured by Konica, KM1024 (Cyan mode type)) onto one surface of the negative electrode raw sheet 20A, and the second separator raw sheet 30A fed from the separator raw sheet roll and the negative electrode raw sheet 20A were bonded together by pressure rollers 61 and 62. Further, an adhesive composition was supplied from the inkjet head of an inkjet coater 51 (manufactured by Konica, KM1024 (Cyan mode type)) onto the other surface of the negative electrode raw sheet 20A, and the first separator raw sheet 10A fed from the separator raw sheet roll and the laminate of the negative electrode raw sheet 20A and the first separator raw sheet 30A were bonded together by pressure rollers 61 and 62. Note that the bonding conditions using the pressure rollers 61 and 62 were the conditions shown in Table 1. Also, regarding the coating shape of the adhesive amount, it was a dot shape, and the dot interval was 200 μm both in the TD (Transverse Direction) and MD (Machine Direction). The laminate of the first separator raw sheet - negative electrode raw sheet - first separator raw sheet obtained through bonding using the pressure rollers 61 and 62 was cut by a cutting machine 70 to obtain a laminate for a secondary battery in which the first separator, negative electrode, and first separator were laminated in this order, and the negative electrode and the separator were adhesively bonded to each other by the amount of adhesive. <Manufacture of secondary battery> Twenty sets of the laminate for a secondary battery obtained above and the cut positive electrode were stacked to form a stacked body. In the stacked body, the positive electrode and the laminate for a secondary battery were not bonded to each other. The fabricated stacked body was wrapped with an aluminum packaging as the exterior of the battery, and an electrolytic solution (solvent: ethylene carbonate / diethyl carbonate / vinylene carbonate = 68.5 / 30 / 1.5 (volume ratio), electrolyte: 1 M LiPF6) was injected. Then, the opening of the aluminum packaging was closed by heat sealing at 150 °C to manufacture a laminated lithium ion secondary battery with a capacity of 8000 mAh. Then, various evaluations were performed on the secondary battery according to the above. The results are shown in Table 1.

[0067] (Example 2) All kinds of operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a separator base fabric made of polyethylene (PE) with a heat shrinkage start temperature, a heat shrinkage end temperature, and a maximum heat shrinkage force as shown in Table 1 was used as the separator material. The results are shown in Table 1.

[0068] (Example 3) All kinds of operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a separator base fabric made of polypropylene (PP) (product name "Celgard 2500") with a heat shrinkage start temperature, a heat shrinkage end temperature, and a maximum heat shrinkage force as shown in Table 1 was used as the separator material. The results are shown in Table 1.

[0069] (Example 4) In the step of <Preparation of the Adhesive Composition>, all kinds of operations, measurements, and evaluations were carried out in the same manner as in Example 1, except that a silicone binder (manufactured by Shin-Etsu Silicone Co., Ltd., model number "KM-9729") was used as the particulate polymer which is a water-insoluble polymer. The results are shown in Table 1. The volume average particle diameter D50 and the glass transition temperature of the silicone binder are as shown in Table 1. Note that the silicone binder exhibited a particulate state in water and in the dry state. Also, it was confirmed that the silicone binder is a water-insoluble polymer in which the insoluble content is 90 mass% or more when 0.5 g of the polymer is dissolved in 100 g of water at 25°C. Furthermore, it was confirmed that the glass transition temperature and the melting point of the silicone binder do not exist in the temperature range below 180°C according to the above.

[0070] (Example 5) In the step of <Preparation of Composition>, as the particulate polymer which is a water-insoluble polymer, polytetrafluoroethylene (manufactured by Asahi Glass Co., Ltd., "Lumiflon (registered trademark) FE4300"), which is a fluorine-based binder, was used. Further, in the step of <Formation of Negative Electrode>, after rolling the negative electrode raw sheet using a roll press and then cutting it out, a negative electrode provided with a negative electrode composite material layer was obtained. Furthermore, in the step of <Formation of Positive Electrode>, the positive electrode raw sheet was not cut out. Still further, in the step of <Manufacture of Laminate for Secondary Battery>, a laminate for secondary battery was formed using the positive electrode raw sheet instead of the negative electrode raw sheet. Then, in the step of <Manufacture of Secondary Battery>, the laminate for secondary battery and the negative electrode cut out in the step of <Formation of Negative Electrode> were superposed to obtain a superposed body. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. The volume average particle diameter D50 and glass transition temperature of the fluorine-based binder are as shown in Table 1. The fluorine-based binder exhibited a particulate state in water and in the dry state. Also, it was confirmed that the fluorine-based binder is a water-insoluble polymer in which the insoluble content is 90 mass% or more when 0.5 g of the polymer is dissolved in 100 g of water at 25°C. Still further, in accordance with the above, it was confirmed that the fluorine-based binder does not exist in the temperature range where the glass transition temperature and melting point are less than 180°C.

[0071] (Example 6) In the step of <Preparation of Adhesive Composition>, as the adhesive material, binder 1 which is a particulate polymer was not blended, and a carboxymethyl cellulose which is a water-soluble polymer and the content ratios of propylene glycol and water which are solvents were made as shown in Table 1, and an adhesive composition was prepared. Except for such points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0072] (Example 7) In the <Preparation of Composition> step, as an adhesive material, binder 1 which is a particulate polymer was not blended, and as a water-soluble polymer, instead of carboxymethyl cellulose, polyamideimide (manufactured by Solvay, "Torlon (registered trademark) AI-30") was used, and an adhesive composition was prepared such that the content ratio of propylene glycol and water as solvents was as shown in Table 1. Except for this point, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. Note that for polyamideimide, when 0.5 g of polyamideimide was dissolved in 100 g of water at a temperature of 25°C, the insoluble matter was less than 1.0 mass%.

[0073] (Comparative Example 1) In the <Preparation of Adhesive Composition> step, as an adhesive material, instead of binder 1, binder 3 whose glass transition temperature and melting point measurement results are as shown in Table 1 and which was prepared as follows was used, and an adhesive composition was prepared without blending propylene glycol. Further, prior to the <Manufacture of Secondary Battery Laminate> step, a separator made of polyethylene (PE) whose surface was coated with the adhesive composition on the entire surface as a coated surface using a gravure roll and dried and wound up was prepared. Then, in the <Manufacture of Secondary Battery Laminate> step, the negative electrode raw material and the separator were bonded under the conditions shown in Table 1 using the manufacturing apparatus shown in Fig. 1 without using the adhesive material supply machines 51 to 52. Except for these points, various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1. <Binder 3> 70 parts of ion-exchanged water, 0.15 part of sodium lauryl sulfate (manufactured by Kao Chemical Co., Ltd., product name "Emal 2F") as an emulsifier, and 0.5 part of ammonium persulfate were respectively supplied to a reactor equipped with a stirrer, the gas phase part was replaced with nitrogen gas, and the temperature was raised to 60°C. On the other hand, in a separate container, 50 parts of ion-exchanged water, 0.5 part of sodium dodecylbenzenesulfonate as an emulsifier, and 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 above-mentioned reactor over 2 hours for polymerization. During the addition, the reaction was carried out at 60°C. After the addition was completed, the mixture was further stirred at 70°C for 2 hours to terminate the reaction, and an aqueous dispersion containing a binder 3 which is a particulate polymer was produced. The volume average particle diameter D50, glass transition temperature, and melting point of the obtained binder 3 were measured. The results are shown in Table 1. Note that the binder 3 exhibited a particulate form both in the aqueous dispersion and in the dry state. Also, it was confirmed that the binder 3 is a water-insoluble 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.

[0074] (Comparative Example 2) <Manufacture of the laminate for secondary battery> In the process, various operations, measurements, and evaluations were carried out in the same manner as in Comparative Example 1, except that the adhesive composition was applied onto the surface of the separator in a dot-like coating shape using a gravure coater. The results are shown in Table 1.

[0075] (Comparative Example 3) <Preparation of the separator material> In the process, a separator stock was prepared by coating 5 μm thick of ceramic (alumina) on one side of a polyethylene separator. Except for this point, various operations, measurements, and evaluations were carried out in the same manner as in Comparative Example 2. The results are shown in Table 1. Note that Table 1 shows the attributes of the separator material before alumina coating.

[0076] (Comparative Example 4) <Manufacture of the laminate for secondary battery> In the process, various operations, measurements, and evaluations were carried out in the same manner as in Comparative Example 2, except that the bonding conditions were changed as shown in Table 1 (the bonding roll temperature was changed to 50°C). The results are shown in Table 1.

[0077] (Comparative Example 5) <Preparation of Composition> Except for using a silicone binder (manufactured by Shin-Etsu Silicone Co., Ltd., model number "KM-9729") as the adhesive material in the <Subsequent Preparation of Composition> step, various operations, measurements, and evaluations were carried out in the same manner as in Comparative Example 1. The results are shown in Table 1.

[0078] (Comparative Example 6) <Manufacture of Laminate for Secondary Battery> Except for changing the lamination conditions in the step as shown in Table 1 (changing the conveyance speed to 2.5 m / min and setting the time from coating to lamination to 10 seconds), various operations, measurements, and evaluations were carried out in the same manner as in Example 1. The results are shown in Table 1.

[0079] (Comparative Example 7) Except for using a separator raw sheet made of polypropylene (PP) (product name "Celgard 2500") with the heat shrinkage start temperature, heat shrinkage end temperature, and maximum heat shrinkage force as shown in Table 1 as the separator material, various operations, measurements, and evaluations were carried out in the same manner as in Example 4. The results are shown in Table 1.

[0080] In Table 1, "Tg" represents the glass transition temperature, "EDMA" represents ethylene glycol dimethacrylate, "AA" represents acrylic acid, "BA" represents n-butyl acrylate, "AN" represents acrylonitrile, "PTFE" represents polytetrafluoroethylene, "CMC" represents carboxymethyl cellulose, "PG" represents propylene glycol, "PE" represents polyethylene, "PP" represents polypropylene, "MAA" represents methacrylic acid, "ST" represents styrene, "DVB" represents divinylbenzene, Each is shown.

[0081] [Table 1]

[0082] From Table 1, it can be seen that in Examples 1 to 7, it was possible to manufacture a laminate for a secondary battery that has excellent adhesion between the electrode and the separator, low internal resistance, and excellent stability. On the other hand, from Table 1, it can be seen that in Comparative Examples 1 to 7, it was not possible to manufacture a laminate for a secondary battery in which all of the above attributes could be achieved at a high level simultaneously.

Industrial Applicability

[0083] According to the present invention, it is possible to provide a laminate for a secondary battery that has excellent adhesion between the electrode and the separator, low internal resistance, and excellent stability. Further, according to the present invention, it is possible to provide a secondary battery that has low internal resistance and excellent stability.

Explanation of Signs

[0084] 10A First separator raw sheet 20A Negative electrode raw sheet 30A Second separator raw sheet 51, 52 Coating machines 61, 62 Pressing rollers 70 Cutting machine 91 Conveyor roller 92 Heat roller 100 Manufacturing apparatus

Claims

1. A laminate for a secondary battery in which an electrode and a separator are laminated via an adhesive material, Regarding the shear peel strength between the electrode and the separator, the value measured by changing the temperature is defined as A (mN / mm 2 ), and Let the value of the maximum thermal shrinkage force obtained by performing thermomechanical analysis on the separator be B (mN / mm 2 ), and further The temperature at which the thermal shrinkage force obtained by performing thermomechanical analysis on the separator drops to a value (mN / mm 2 ) that is 20% higher than the value of the thermal shrinkage force at 30°C (mN / mm 2 ) is defined as the thermal shrinkage end temperature α (°C). When this is the case, wherein the value of A satisfies A > B in a temperature range of 25°C or higher and lower than the heat shrinkage end temperature α°C, the separator contains a polyolefin resin, and further, the adhesive material contains at least one of a water-insoluble polymer having no glass transition temperature and melting point in a temperature region below 180°C and a water-insoluble polymer having a glass transition temperature in a temperature region below 180°C but having a melting point in a temperature region of 180°C or higher, A laminate for a secondary battery.

2. The laminate for a secondary battery according to claim 1, wherein the water-insoluble polymer is a particulate polymer having a volume average particle diameter D50, which is the particle diameter at which the cumulative volume calculated from the small-diameter side in the volume-based particle size distribution measured by the dynamic light scattering method is 50%, smaller than the average pore diameter of the separator.

3. The laminate for a secondary battery according to claim 1 or 2, wherein the adhesive material contains a water-soluble polymer having a thermal decomposition temperature of 180°C or higher.

4. A secondary battery comprising the laminate for a secondary battery according to any one of claims 1 to 3.

Images