Secondary battery manufacturing method and secondary battery

Abstract

To provide a manufacturing method of a secondary battery, that has an excellent battery performance and a sufficient adhesion force between an electrode and a separator.SOLUTION: A manufacturing method of a secondary battery, disclosed here, includes: an assembling preparation step of housing an electrode body having a positive electrode comprising a positive electrode active material layer on a positive electrode collector foil, a negative electrode comprising a negative electrode active material layer onto a negative electrode collector foil, and a separator having an adhesive layer, and an electrolyte into a battery case, and preparing a battery assembly; a high temperature treatment step of restraining the battery assembly under a restraining pressure of at least 0.35 MPa or more, and retaining the battery assembly so that temperature of the battery assembly becomes at least 80°C or more. Herein, the high temperature treatment step is executed so as to satisfy Formula I of A≥B>C, where: A(N / m) represents peel strength at an interface surface between the separator and the negative electrode active material layer; B(N / m) represents peel strength at an interface surface between the negative electrode active layer and the negative electrode collector foil; and C(N / m) represents peel strength in the negative electrode active material layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a secondary battery and a secondary battery. [Background technology]

[0002] Secondary batteries such as lithium-ion secondary batteries are suitable for use as portable power sources for personal computers, mobile terminals, and the like, and as power sources for driving vehicles such as electric vehicles (BEVs), hybrid electric vehicles (HEVs), and plug-in hybrid electric vehicles (PHEVs). Such secondary batteries include, for example, an electrode assembly having a positive electrode, a negative electrode, and a separator, an electrolyte, and a battery case that houses the electrode assembly and the electrolyte. Patent Document 1, for example, discloses a method for manufacturing such secondary batteries, in which a positive electrode, a negative electrode, and a separator are stacked together and then pressed while being heated. It also discloses that this improves the adhesive strength between the electrode and the separator. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-23488 Summary of the Invention [Problem to be solved by the invention]

[0004] However, according to the results of the inventors' investigations, even if the positive electrode, negative electrode, and separator are bonded by pressing under heat, there is a risk that the adhesive strength may decrease if an electrolyte (e.g., a non-aqueous electrolyte) is subsequently injected. If the adhesive strength decreases, the inter-electrode distance may increase locally, which may cause uneven charge-discharge reactions. On the other hand, if the pressing pressure is increased to increase the adhesive strength between the electrode and separator, the air permeability of the separator increases, which may hinder ion migration and reduce high-rate characteristics. Therefore, there is still room for improvement from the perspective of such battery performance.

[0005] The present invention has been made in view of the above circumstances, and a main object of the present invention is to provide a method for manufacturing a secondary battery that has good battery performance and sufficient adhesive strength between the electrodes and the separator. Another object of the present invention is to provide a secondary battery having the above-mentioned characteristics. [Means for solving the problem]

[0006] The method for manufacturing a secondary battery disclosed herein includes an assembly preparation step of preparing a battery assembly by housing, in a battery case, an electrode body including a positive electrode having a positive electrode active material layer on a positive electrode current collector foil, a negative electrode having a negative electrode active material layer on a negative electrode current collector foil, and a separator having an adhesive layer, and an electrolyte, and a high-temperature treatment step of constraining the battery assembly at a confining pressure of at least 0.35 MPa or more and maintaining the battery assembly at a temperature of at least 80°C or more. The high-temperature treatment step of the manufacturing method is carried out so as to satisfy the formula I: A≧B>C; where A (N / m) is the peel strength at the interface between the separator and the negative electrode active material layer, B (N / m) is the peel strength at the interface between the negative electrode active material layer and the negative electrode current collector foil, and C (N / m) is the peel strength within the negative electrode active material layer.

[0007] By subjecting a battery assembly including an electrode body and an electrolyte to high-temperature treatment under the conditions described above, the adhesive contained in the adhesive layer of the separator is constrained in a swollen state, thereby exhibiting, for example, an anchoring effect. Therefore, even when constraining is performed at a relatively low pressure, the adhesive strength between the electrode and the separator can be improved. Furthermore, because the constraining is performed at a relatively low pressure, the air permeability of the separator is not excessively increased. Therefore, good ion mobility can be maintained. This configuration allows the manufacture of a secondary battery that has good battery performance (e.g., high-rate characteristics and input / output characteristics) and high adhesion between the electrode and the separator. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a secondary battery according to one embodiment. [Figure 2] FIG. 2 is a partial cross-sectional view schematically showing a secondary battery according to one embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the technology disclosed herein will be described with reference to the drawings. Matters other than those specifically mentioned in this specification that are necessary for implementing the technology disclosed herein (e.g., the general configuration and manufacturing process of a battery that do not characterize the technology disclosed herein) can be understood as design matters for a person skilled in the art based on conventional technology in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and common technical knowledge in the relevant field. In the following, components and parts that perform the same function will be assigned the same reference numerals, and redundant explanations may be omitted or simplified. In this specification, the expression "A to B (where A and B are arbitrary numerical values)" indicating a range is intended to include not only "A or more but not more than B," but also "greater than A but less than B," "greater than A but not more than B," and "greater than A but not more than B."

[0010] In this specification, the term "battery" refers to any power storage device capable of extracting electrical energy, and is a concept that encompasses primary batteries and secondary batteries. Furthermore, in this specification, the term "secondary battery" refers to any power storage device that can be repeatedly charged and discharged by the movement of charge carriers between a positive electrode and a negative electrode via an electrolyte, and is a concept that encompasses so-called storage batteries (chemical batteries) such as lithium-ion secondary batteries and nickel-metal hydride batteries, and capacitors (physical batteries) such as electric double-layer capacitors.

[0011] Here, we will first explain the configuration of the secondary battery 100 disclosed herein, and then explain each step of the manufacturing method disclosed herein. FIG. 1 is a perspective view of the secondary battery 100 disclosed herein. FIG. 2 is a schematic longitudinal sectional view taken along line II-II in FIG. 1. In the following explanation, the symbols L, R, F, Rr, U, and D in the drawings represent left, right, front, rear, top, and bottom. In the drawings, the symbol X indicates the "short side direction of the battery," the symbol Y indicates the "long side direction of the battery," and the symbol Z indicates the "up-down direction of the battery." However, these directions are merely used for convenience of explanation and do not limit the installation form of the secondary battery 100 in any way.

[0012] 1 and 2, the secondary battery 100 includes a battery case 10, an electrode assembly 20, a positive electrode terminal 30, a negative electrode terminal 40, and an electrolyte (not shown). The specific configuration of the secondary battery 100 will be described below.

[0013] The battery case 10 is a housing that houses the electrode assembly 20 and the electrolyte. The battery case 10 has a rectangular parallelepiped (square) outer shape with a bottom. The material of the battery case 10 may be the same as that conventionally used, and is not particularly limited. The battery case 10 is preferably made of metal, and more preferably made of, for example, aluminum, an aluminum alloy, iron, an iron alloy, or the like. As shown in FIG. 2, the battery case 10 includes an exterior body 12 having an opening 12h, and a sealing plate (lid) 14 that closes the opening 12h.

[0014] As shown in FIG. 1, the exterior body 12 includes a bottom wall 12a, a pair of wide surfaces 12b extending from the bottom wall 12a and facing each other, and a pair of narrow surfaces 12c extending from the bottom wall 12a and facing each other. The bottom wall 12a is generally rectangular. The bottom wall 12a faces an opening 12h (see FIG. 2). The sealing plate 14 is attached to the exterior body 12 so as to close the opening 12h of the exterior body 12. The sealing plate 14 faces the bottom wall 12a of the exterior body 12. The sealing plate 14 is generally rectangular in plan view. The battery case 10 is integrated by joining (e.g., welding) the sealing plate 14 to the periphery of the opening 12h of the exterior body 12.

[0015] As shown in Fig. 2, sealing plate 14 is provided with injection hole 15 and gas release valve 17. Injection hole 15 is a through-hole for injecting an electrolyte into battery case 10 after sealing plate 14 is assembled to exterior body 12. Injection hole 15 is sealed with sealing member 16 after the electrolyte is injected. Gas release valve 17 is a thin-walled portion configured to break when the pressure inside battery case 10 reaches or exceeds a predetermined value, thereby releasing gas inside battery case 10 to the outside.

[0016] The electrolyte is accommodated inside the battery case 10 together with the electrode assembly 20. Any electrolyte used in conventionally known batteries can be used without any particular limitation. As an example, a non-aqueous electrolyte solution in which a supporting salt is dissolved in a non-aqueous solvent can be used. As the non-aqueous solvent, for example, a carbonate-based solvent such as ethylene carbonate (EC), dimethyl carbonate (DMC), or ethyl methyl carbonate (EMC) can be used. As the supporting salt, a fluorine-containing lithium salt such as LiPF6 can be used. The concentration of the supporting salt is not particularly limited, but can be, for example, 0.1 mol / L to 1.2 mol / L. The electrolyte is not limited to a liquid state, and may be a gel or a solid state.

[0017] The electrode assembly 20 is a power-generating element of the secondary battery 100 and includes a positive electrode having a positive electrode active material layer 22a fixed onto a positive electrode current collector foil 22c, a negative electrode having a negative electrode active material layer 24a fixed onto a negative electrode current collector foil 24c, and a separator with an adhesive layer. As shown in FIG. 2, the electrode assembly 20 is housed inside the exterior housing 12 while covered with an insulating film such as an electrode assembly holder 29. Here, the electrode assembly 20 is a zigzag-folded stacked electrode assembly formed by sandwiching multiple positive electrodes and multiple negative electrodes between zigzag-folded separators. However, the electrode assembly may also be a wound electrode assembly in which strip-shaped positive electrodes and strip-shaped negative electrodes are stacked in a state of being insulated by two strip-shaped separators and wound in the longitudinal direction around a winding axis. Alternatively, the electrode assembly may be a stacked electrode assembly in which rectangular positive electrodes and rectangular negative electrodes are alternately stacked with rectangular separators interposed therebetween.

[0018] As shown in FIG. 2 , at the upper end of the electrode body 20 in the vertical direction Z, there is a positive current collector foil exposed portion where the positive active material layer 22a is not fixed and a portion of the positive current collector foil 22c is exposed. A positive current collector member 34 is attached to the positive current collector foil exposed portion. The positive current collector member 34 can be made of the same metal material as the positive current collector foil 22c, for example, a conductive metal such as aluminum or an aluminum alloy. Furthermore, at the upper end of the electrode body 20 in the vertical direction Z, there is a negative current collector foil exposed portion where the negative active material layer 24a is not fixed and a portion of the negative current collector foil 24c is exposed. A negative current collector member 44 is attached to the negative current collector foil exposed portion. The negative current collector member 44 can be made of the same metal material as the negative current collector foil 24c, for example, a conductive metal such as copper or a copper alloy.

[0019] The positive electrode terminal 30 is attached to one end of the sealing plate 14 in the long side direction Y (the left end in FIG. 2 ). The positive electrode terminal 30 is electrically connected to the electrode assembly 20 inside the battery case 10 via a positive electrode current collector 34. The negative electrode terminal 40 is attached to the other end of the sealing plate 14 in the long side direction Y (the right end in FIG. 2 ). The negative electrode terminal 40 is electrically connected to the electrode assembly 20 inside the battery case 10 via a negative electrode current collector 44. The positive electrode terminal 30 is preferably formed from a metal with excellent conductivity, such as aluminum or an aluminum alloy. The negative electrode terminal 40 is preferably formed from a metal with excellent conductivity, such as copper or a copper alloy. The positive electrode terminal 30 and the negative electrode terminal 40 are insulated from the sealing plate 14 by a gasket 50 and an insulator 60, respectively. The gasket 50 and the insulator 60 may be made of an electrically insulating resin material, such as a fluorinated resin such as perfluoroalkoxy fluororesin (PFA) or polytetrafluoroethylene (PTFE), polyphenylene sulfide resin (PPS), or polypropylene (PP).

[0020] The positive electrode includes a strip-shaped positive electrode current collector foil 22c and a positive electrode active material layer 22a fixed to at least one surface of the positive electrode current collector foil 22c. Conventional materials that can be used in general batteries (e.g., lithium-ion secondary batteries) can be used for the components constituting the positive electrode without any particular restrictions. For example, the positive electrode current collector foil 22c is preferably made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The positive electrode active material layer 22a contains a positive electrode active material (e.g., a lithium transition metal composite oxide such as lithium-nickel-cobalt-manganese composite oxide) that can reversibly store and release charge carriers. The positive electrode active material layer 22a may contain optional components other than the positive electrode active material, such as a conductive material, a binder, and various additives. Examples of the conductive material include carbon materials such as acetylene black (AB). Examples of the binder include polyvinylidene fluoride (PVdF).

[0021] The negative electrode includes a strip-shaped negative electrode current collector foil 24c and a negative electrode active material layer 24a fixed to at least one surface of the negative electrode current collector foil 24c. Conventional materials that can be used in general batteries (e.g., lithium-ion secondary batteries) can be used for each component of the negative electrode without any particular restrictions. For example, the negative electrode current collector foil 24c is preferably made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel. The negative electrode active material layer 24a contains a negative electrode active material (e.g., a carbon material such as graphite) that can reversibly store and release charge carriers. The negative electrode active material layer 24a may contain optional components other than the negative electrode active material, such as a conductive material, a binder, a dispersant, a thickener, and various additives. Examples of binders that can be used include rubbers such as styrene butadiene rubber (SBR). Examples of dispersants that can be used include celluloses such as carboxymethyl cellulose (CMC).

[0022] The positive electrode and negative electrode are arranged opposite each other in an insulated state via a separator. The separator is an insulating sheet having a plurality of fine through-holes through which charge carriers can pass. The separator includes a substrate and an adhesive layer. The separator may further include a heat-resistant layer in addition to the substrate and adhesive layer. For example, the separator includes a substrate and a heat-resistant layer provided on one side of the substrate in the thickness direction, and further includes an adhesive layer on at least one side, preferably both sides.

[0023] The substrate of the separator is not particularly limited, but is preferably made of a porous substrate containing at least one material selected from the group consisting of polyolefin, polyvinylidene fluoride, polytetrafluoroethylene, polyimide, polyamide, polyamideimide, polyethersulfone, polyetherimide, and aramid as a main component. Such a substrate is preferably made of polyolefin, and more preferably made of polyethylene (PE) or polypropylene (PP).

[0024] The adhesive layer of the separator is bonded to the electrodes (positive and / or negative electrodes) by, for example, heating or pressing (typically, press molding). The adhesive layer contains an adhesive. Examples of adhesives include acrylic resins, fluorine-based resins, epoxy resins, urethane resins, and ethylene vinyl acetate resins. Among these, fluorine-based resins and acrylic resins are preferred because they have high flexibility and can more suitably exhibit adhesive properties. Examples of fluorine-based resins include polyvinylidene fluoride (PVdF) and polytetrafluoroethylene (PTFE). Examples of acrylic resins include polyacrylic acid (PAA) and polymethyl methacrylate (PMMA).

[0025] The adhesive layer of the separator is formed by applying an adhesive to the surface of the separator substrate or heat-resistant layer using a known method such as vapor deposition. The adhesive layer may be applied in a solid form or in a predetermined pattern. In plan view, the adhesive layer may have a dotted, striped, wavy, banded (stripe), dashed line, or a combination thereof. The adhesive layer is formed, for example, by providing a heat-resistant layer on the entire surface of one of the separator's thickness directions, and then disposing adhesive dots (dot-shaped portions) on the entire surface of the separator with the heat-resistant layer and the entire surface of the separator without the heat-resistant layer by printing or the like. The area density of the adhesive dots may be adjusted to be approximately constant. The amount of adhesive in each of the multiple adhesive dots may be approximately the same. The number density of the adhesive dots may be approximately constant on both the entire surface of the separator and the entire surface of the other separator. The adhesive may be arranged so that the area density is substantially constant over at least one of the entire one surface and the entire other surface of the separator, and an adhesive layer may be provided on at least one surface of the separator.

[0026] The heat-resistant layer is provided for purposes such as protecting the separator when, for example, the positive electrode and the negative electrode are short-circuited and heat is generated. The heat-resistant layer may be provided directly on the surface of the substrate, or may be provided on the substrate via another layer. However, the heat-resistant layer is not essential and may be omitted in other embodiments. The heat-resistant layer preferably contains inorganic particles such as aluminum oxide and a heat-resistant layer binder. Examples of heat-resistant layer binders include acrylic resins, fluorine-based resins, epoxy resins, urethane resins, and ethylene vinyl acetate resins. The type of heat-resistant layer binder may be the same as or different from the adhesive used in the adhesive layer of the separator described above.

[0027] As described above, the separator is disposed between the positive electrode and the negative electrode (more specifically, between the positive electrode active material layer 22a and the negative electrode active material layer 24a). The separator is porous to allow charge carriers contained in the electrolyte to pass through. The separator retains an electrolyte (e.g., a non-aqueous electrolyte) in its pores, forming an ion conduction path between the positive electrode active material layer 22a and the negative electrode active material layer 24a. The separator's air permeability (Gurley value, a value measured in accordance with JIS P8117:2009; the same applies hereinafter) is preferably 200 sec / 100 ml or less, and more preferably 180 sec / 100 ml or less. This allows for smooth movement of charge carriers within the separator, and can suitably suppress an increase in internal resistance, even in a configuration in which high-rate charging and discharging are repeated. The lower limit of the air permeability is not particularly limited, but is preferably, for example, about 30 sec / 100 ml or more.

[0028] The secondary battery 100 disclosed herein satisfies the formula I: A≧B>C; where A (N / m) is the peel strength at the interface between the separator and the negative electrode active material layer 24a, B (N / m) is the peel strength at the interface between the negative electrode active material layer 24a and the negative electrode current collector foil 24c, and C (N / m) is the peel strength within the negative electrode active material layer 24a. Here, in this specification, "peel strength (N / m)" refers to the 90° peel strength measured in accordance with JIS K6854-1:1999 (ISO 8519-1:1990). The peel strength A at the interface between the separator and the negative electrode active material layer 24a is equal to or greater than the peel strength B at the interface between the negative electrode active material layer 24a and the negative electrode current collector foil 24c, and the peel strength A is greater than the peel strength C within the negative electrode active material layer 24a, thereby preventing the separator and the negative electrode active material layer 24a from separating. This appropriately improves the adhesion between the negative electrode and the separator in the secondary battery 100.

[0029] Furthermore, in the secondary battery 100 disclosed herein, the peel strength A at the interface between the separator and the negative electrode active material layer 24a is 10 N / m or more. This peel strength ensures favorable adhesion between the negative electrode and the separator, ensuring adhesion between the negative electrode and the separator even after repeated high-rate charge and discharge. The upper limit of the peel strength is not particularly limited, but is preferably 20 N / m or less, and more preferably 18 N / m or less.

[0030] <Secondary battery manufacturing method> Next, a method for manufacturing the secondary battery 100 disclosed herein will be described. The manufacturing method disclosed herein includes an assembly preparation step of preparing a battery assembly by housing an electrode body 20 including a positive electrode, a negative electrode, and a separator, and an electrolyte in a battery case 10, and a high-temperature treatment step of constraining the battery assembly at a confining pressure of at least 0.35 MPa and maintaining the temperature of the battery assembly at at least 80°C. The high-temperature treatment step is characterized by being carried out so that the peel strength A (N / m) at the interface between the separator and the negative electrode active material layer 24a, the peel strength B (N / m) at the interface between the negative electrode active material layer 24a and the negative electrode current collector foil 24c, and the peel strength C (N / m) within the negative electrode active material layer 24a satisfy the formula I: A≧B>C. The manufacturing method disclosed herein makes it possible to manufacture a secondary battery 100 that has good battery characteristics (e.g., high-rate characteristics and input / output characteristics) and improved adhesion between the electrode and the separator. The manufacturing method disclosed herein is characterized by the high-temperature treatment step described above, and other manufacturing processes may be the same as conventional ones. In addition, the manufacturing method may further include other steps at any stage.

[0031] In the assembly preparation step, a battery assembly is prepared. In this specification, the term "battery assembly" refers to a secondary battery before initial charging and aging. The battery assembly prepared in this step includes a battery case 10, an electrode assembly 20, and an electrolyte.

[0032] The electrode assembly 20 includes a positive electrode, a negative electrode, and a separator. The positive electrode can be produced, for example, by applying a positive electrode slurry, which is obtained by kneading the above-described positive electrode active material, a conductive material, and a binder in an appropriate solvent, to the surface of the positive electrode current collector foil 22c and then drying the slurry. The negative electrode can be produced, for example, by applying a negative electrode slurry, which is obtained by kneading the above-described negative electrode active material, a binder, and a thickener in an appropriate solvent, to the surface of the negative electrode current collector foil 24c and then drying the slurry. The separator, as described above, is prepared by providing at least a substrate and an adhesive layer. The electrode assembly 20 can be produced by stacking multiple positive electrodes and multiple negative electrodes sandwiched between separators folded in a zigzag pattern.

[0033] As shown in Fig. 2, at the upper end of the electrode body 20 in the vertical direction Z, a positive current collecting member 34 is welded to the exposed portion of the positive current collecting foil. The positive terminal 30 is electrically connected to the electrode body 20 via the positive current collecting member 34. Furthermore, at the upper end of the electrode body 20 in the vertical direction Z, a negative current collecting member 44 is welded to the exposed portion of the negative current collecting foil. The negative terminal 40 is electrically connected to the electrode body 20 via the negative current collecting member 44. This integrates the sealing plate 14, the electrode body 20, the positive terminal 30, and the negative terminal 40.

[0034] Next, electrode body 20 integrated with sealing plate 14 is inserted through opening 12h of exterior body 12. Then, the periphery of sealing plate 14 and opening 12h of exterior body 12 are joined by laser welding or the like. Thereafter, electrolyte is poured through filling hole 15, and filling hole 15 is closed with sealing member 16 to hermetically seal the battery assembly. In this manner, the battery assembly can be prepared.

[0035] In the high-temperature treatment step, a battery assembly including the electrode body 20 and the electrolyte is held under a predetermined confining pressure and a predetermined temperature. Specifically, the battery assembly prepared in the assembly preparation step is confined under a pressure of at least 0.35 MPa and held in a high-temperature environment so that the battery assembly reaches a temperature of at least 80°C. The high-temperature treatment step is carried out so that the relationship between the peel strength A (N / m) at the interface between the separator and the negative electrode active material layer 24a, the peel strength B (N / m) at the interface between the negative electrode active material layer 24a and the negative electrode current collector foil 24c, and the peel strength C (N / m) within the negative electrode active material layer satisfies the following formula I: A≧B>C. This ensures favorable adhesion between the electrodes and the separator in the completed secondary battery 100.

[0036] In conventional manufacturing methods, electrodes (positive and / or negative electrodes) and separators are bonded together by heating and pressing after the electrode assembly is assembled. However, the inventors have found that injecting an electrolyte (e.g., a non-aqueous electrolyte) after bonding the electrodes and separator reduces the adhesive strength between the electrodes and separator in the completed battery (i.e., reduces the peel strength). Therefore, in the manufacturing method disclosed herein, after the non-aqueous electrolyte is injected, the electrodes and separator are bonded together at a predetermined confining pressure and temperature. This allows the adhesive contained in the separator's adhesive layer to absorb the non-aqueous electrolyte and be pressed in a swollen state. Therefore, even at a relatively low confining pressure, it is presumed that the adhesive deforms between the electrode and separator's adhesive layer, thereby favorably exerting adhesive strength due to the anchor effect. Furthermore, by adjusting the peel strength between the separator, the negative electrode active material layer 24a, and the negative electrode current collector foil 24c to satisfy the above-mentioned formula I, sufficient adhesive strength between the electrodes and separator is ensured in the completed secondary battery 100. Furthermore, this manufacturing method allows the electrodes and separator to be bonded together using a relatively low confining pressure, preventing excessive increases in the separator's air permeability. This maintains favorable ion mobility, allowing the secondary battery 100 to be manufactured with favorable high-rate and input-output characteristics. Therefore, the manufacturing method disclosed herein can realize a secondary battery 100 with improved adhesion between the electrodes and separator while maintaining favorable high-rate and input-output characteristics.

[0037] By performing a high-temperature treatment step so that peel strength A at the interface between the separator and the negative electrode active material layer 24a is equal to or greater than peel strength B at the interface between the negative electrode active material layer 24a and the negative electrode current collector foil 24c, and so that peel strength A is greater than peel strength C within the negative electrode active material layer, separation between the separator and the negative electrode active material layer 24a is prevented in the completed secondary battery 100. Therefore, the negative electrode and the separator are favorably bonded in the completed secondary battery 100, and it is possible to prevent, for example, uneven interelectrode distances from occurring.

[0038] In the high-temperature treatment step, as described above, the battery assembly is constrained at a confining pressure of at least 0.35 MPa. The confining pressure can be adjusted appropriately depending on, for example, the size of the battery assembly and the number of layers (or windings) of the electrode body 20. The confining pressure is preferably, for example, 0.35 MPa or more and 1.20 MPa or less, or may be 0.35 MPa or more and 0.85 MPa or less, and more preferably 0.35 MPa or more and 0.60 MPa or less. According to the manufacturing method disclosed herein, the electrodes and separators can be appropriately bonded even at a relatively low confining pressure.

[0039] Furthermore, as described above, in the high-temperature treatment step, the battery assembly is maintained at a temperature of at least 80°C or higher. The temperature in the high-temperature treatment step may be maintained so that the temperature of the battery assembly is 85°C or higher. However, if the temperature of the battery assembly becomes too high, it is undesirable because there is a concern that unintended side reactions may occur inside the battery assembly, deteriorating the battery characteristics. For this reason, the temperature of the heat treatment is preferably maintained so that the temperature of the battery assembly is, for example, 100°C or lower, and more preferably 90°C or lower.

[0040] In the high-temperature treatment step, the time (retention time) for which the battery assembly is held at the above-mentioned confining pressure and temperature is not particularly limited, but is preferably held for 6 hours or more. For example, the retention time is preferably about 6 to 100 hours, and may be, for example, about 6 to 72 hours, about 12 to 48 hours, or about 12 to 24 hours. Although it cannot be generally defined because it varies depending on the size of the battery assembly, for example, it is preferable to constrain the battery assembly at a confining pressure of 0.35 MPa to 0.60 MPa and hold it in a temperature environment of 80°C to 90°C for about 6 to 24 hours.

[0041] The method for restraining the battery assembly is not particularly limited, but it is preferable to restrain the battery assembly by placing a pair of restraining plates in the stacking direction of the electrode assemblies and pressing the battery assembly from both sides in the stacking direction. Here, the battery assembly can be restrained by sandwiching the wide surface 12b of the battery assembly between a pair of restraining plates and connecting the pair of restraining plates with a bridging member. In this case, it is preferable to restrain the battery assembly so that the restrained area is at least 60% or more. In other words, when the area of ​​one wide surface 12b of the battery assembly is 100%, it is preferable to arrange the restraining plates so that at least 60% or more of the area is restrained. The restrained area is, for example, 60% or more, preferably 80% or more, and may be 90% or more, or may be 100% (i.e., the entire wide surface 12b of the battery assembly).

[0042] Although not particularly limited, it is preferable to perform the high-temperature treatment process on the battery assembly when its SOC (State of Charge) is less than 5%. The SOC of the battery assembly is preferably lower, for example, less than 3%, less than 1%, or even 0%. In other words, it is preferable to perform the high-temperature treatment process on the battery assembly before performing the initial charge. This can prevent deterioration of battery characteristics due to side reactions.

[0043] After the high-temperature treatment step, the secondary battery 100 can be provided by performing initial charging and aging. The initial charging is a process of charging the secondary battery 100 over the voltage range in which the manufactured (completed) secondary battery 100 will be used. This allows the battery assembly to be electrochemically activated. The initial charging can be performed using a general procedure that has been conventionally used in secondary battery manufacturing methods. The conditions for the initial charging are not particularly limited. For example, the initial charging can be constant-current-constant-voltage charging (CC-CV charging) in which, in a room temperature environment (e.g., 25°C), charging is performed at a constant current of about 0.1 C to 10 C until the terminal voltage between the positive electrode terminal 30 and the negative electrode terminal 40 reaches 2.5 V to 4.2 V (preferably 3.0 V to 4.1 V), and then charging at a constant voltage until the SOC reaches 60% to 100% (e.g., 80% to 100%).

[0044] Aging is performed by holding the battery assembly, which has been initially charged, at a temperature of 35°C or higher for 6 hours or longer (preferably 10 hours or longer, e.g., 20 hours or longer). This increases the stability of the SEI (Solid Electrolyte Interphase) coating that may form on the surface of the negative electrode during initial charging, and reduces internal resistance. The aging temperature is preferably about 45°C to 85°C (more preferably 50°C to 80°C, and even more preferably 60°C to 70°C).

[0045] As described above, the manufacturing method disclosed herein can provide a secondary battery 100 that has good high-rate characteristics and input / output characteristics and has high adhesion between the electrodes and the separator. The secondary battery 100 can be used for a variety of purposes, and can be suitably used, for example, as a power source (driving power source) for a motor mounted on a vehicle such as a passenger car or truck. The type of vehicle is not particularly limited, and examples include a plug-in hybrid electric vehicle (PHEV), a hybrid electric vehicle (HEV), and an electric vehicle (BEV). The secondary battery 100 can also be suitably used to construct a battery pack.

[0046] <Other embodiments> Although the technology disclosed herein has been described above, the technology disclosed herein is not limited to the above-described embodiments, and various modifications and changes can be made.

[0047] For example, initial charging may be performed before the high-temperature treatment step described above. The initial charging may be performed under the conditions of constant current-constant voltage charging (CC-CV charging) as described above. After the initial charging, the high-temperature treatment step may be performed while maintaining the charged state. This allows, for example, the SEI film formed on the negative electrode to be modified at the same time. Therefore, the aging treatment described above can be omitted, which is preferable from the viewpoint of manufacturing efficiency.

[0048] As described above, specific aspects of the technology disclosed herein include those described in the following sections. Item 1: A method for producing a secondary battery, comprising: an assembly preparation step of preparing a battery assembly by housing, in a battery case, an electrode body having a positive electrode comprising a positive electrode active material layer on a positive electrode current collector foil, a negative electrode comprising a negative electrode active material layer on a negative electrode current collector foil, and a separator comprising an adhesive layer; and an electrolyte; and a high-temperature treatment step of constraining the battery assembly at a constraining pressure of at least 0.35 MPa or more and maintaining the battery assembly at a temperature of at least 80°C or more, wherein the high-temperature treatment step is carried out so as to satisfy the formula I: A≧B>C; where A (N / m) is the peel strength at the interface between the separator and the negative electrode active material layer, B (N / m) is the peel strength at the interface between the negative electrode active material layer and the negative electrode current collector foil, and C (N / m) is the peel strength within the negative electrode active material layer. Item 2: The manufacturing method according to Item 1, wherein the high-temperature treatment step comprises constraining the battery assembly at a constraining pressure of at least 0.35 MPa and heating the battery assembly to at least 80°C for 6 hours or more. Item 3: The manufacturing method according to Item 1 or 2, wherein the high-temperature treatment step restricts an area of ​​at least 60% or more of the wide surface of the battery assembly, assuming the area of ​​the wide surface to be 100%. Item 4: The manufacturing method according to any one of items 1 to 3, wherein the high-temperature treatment step is carried out in a state where the SOC of the battery assembly is less than 5%. Item 5: A secondary battery comprising: an electrode assembly including a positive electrode, a negative electrode, and a separator; an electrolyte; and a battery case that houses the electrode assembly and the electrolyte, wherein the positive electrode comprises a positive electrode active material layer on a positive electrode current collector foil, the negative electrode comprises a negative electrode active material layer on a negative electrode current collector foil, and the separator comprises an adhesive layer on a surface of the separator, and wherein, when the peel strength at the interface between the separator and the negative electrode active material layer is A (N / m), the peel strength at the interface between the negative electrode active material layer and the negative electrode current collector foil is B (N / m), and the peel strength within the negative electrode active material layer is C (N / m), the secondary battery satisfies formula I: A≧B>C; and formula II: A≧10. Item 6: The secondary battery according to Item 5, wherein a peel strength A at the interface between the separator and the negative electrode active material layer is 10 N / m or more and 18 N / m or less. Item 7: The secondary battery according to Item 5 or 6, wherein the adhesive layer includes an adhesive, and the adhesive is either an acrylic resin adhesive or a fluororesin adhesive. Item 8: The secondary battery according to any one of Items 5 to 7, wherein the separator has an air permeability of 180 sec / 100 ml or less.

[0049] Test examples relating to the present invention will be described below. Note that the contents of the test examples described below are not intended to limit the present invention.

[0050] Lithium nickel cobalt manganese composite oxide (NCM) was prepared as the positive electrode active material, polyvinylidene fluoride (PVdF) as the binder, and acetylene black (AB) as the conductive material. These were weighed out to a mass ratio of NCM:PVdF:AB = 98:1:1 and mixed in N-methylpyrrolidone (NMP) to prepare a positive electrode slurry. This positive electrode slurry was applied to the surface of aluminum foil as a positive electrode current collector foil. The mixture was then dried and pressed to a predetermined thickness to produce a positive electrode.

[0051] Graphite powder (C) was prepared as the negative electrode active material, styrene butadiene rubber (SBR) as the binder, and carboxymethyl cellulose (CMC) as the thickener. These were weighed out to a mass ratio of C:SBR:CMC = 98:1:1 and mixed in ion-exchanged water to prepare a negative electrode slurry. This negative electrode slurry was applied to the surface of copper foil as a negative electrode current collector foil. It was then dried and pressed to a predetermined thickness to produce a negative electrode.

[0052] A separator was prepared, with a porous polyethylene (PE) substrate surface (both surfaces) and an adhesive layer containing polyvinylidene fluoride (PVdF). The prepared positive and negative electrodes were sandwiched between zigzag separators to produce a stacked electrode assembly. The stacked electrode assembly, positive electrode terminal, negative electrode terminal, and sealing plate were connected, and the assembly was inserted into the exterior body of a battery case. The sealing plate and the exterior body were then welded. A nonaqueous electrolyte was then injected through the injection hole in the sealing plate. The nonaqueous electrolyte was prepared by dissolving LiPF6 as a supporting electrolyte at a concentration of 1.0 mol / L in a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 30:40:30. In this manner, a battery assembly for evaluation was prepared.

[0053] <Example 1> The wide surface of the test battery assembly was constrained at a confining pressure of 0.35 MPa, and the assembly was placed in a thermostatic chamber set at 80°C for 12 hours for high-temperature treatment. After that, initial charging and aging treatment were performed. Thus, the test secondary battery of Example 1 was produced.

[0054] <Example 2> A separator was prepared by providing an adhesive layer containing an acrylic resin on the surface (both sides) of a porous substrate made of polyethylene (PE). Except for this, a secondary battery for evaluation of Example 2 was produced in the same manner as Example 1.

[0055] <Example 3 to Example 7> Secondary batteries for evaluation of Examples 3 to 7 were fabricated in the same manner as in Example 1, except that the confining pressure and temperature conditions were varied as shown in Table 1.

[0056] <Evaluation of peel strength> The peel strength of the evaluation secondary battery prepared above was measured. The peel strength was measured in accordance with the 90-degree peel adhesion strength test method (JIS K6854-1:1999). Specifically, the evaluation secondary battery that had been subjected to high-temperature treatment was disassembled to remove the laminated electrode assembly. A test piece was cut out from the electrode assembly, and the negative electrode current collector foil was fixed to a fixture with double-sided tape. Next, the separator was pulled vertically (at a 90° angle) using a peel strength meter (Tensilon, manufactured by A&D Corporation). The peel strength when the negative electrode active material layer peeled off from the negative electrode current collector foil or separator was measured. The results are shown in Table 1. Furthermore, after the peel strength test, the surfaces of the negative electrode and separator were observed. When the negative electrode active material layer was attached to the side of the separator that had been in contact with the negative electrode active material layer, it can be said that the peel strength A at the interface between the separator and the negative electrode active material layer was greater than the peel strength C within the negative electrode active material layer. It can also be said that the peel strength A at the interface between the separator and the negative electrode active material layer was approximately the same as or greater than the peel strength B at the interface between the negative electrode current collector foil and the negative electrode active material layer. On the other hand, when the negative electrode active material layer was not attached to the side of the separator that had been in contact with the negative electrode active material layer, it can be said that the peel strength A at the interface between the separator and the negative electrode active material layer was smaller than the peel strength C within the negative electrode active material layer. The results of the peel strength permutations are shown in Table 1.

[0057] <Air permeability measurement> The air permeability of each separator was also measured. Specifically, a test piece was first prepared by cutting out the separator from each example. The test piece was placed in a Gurley tester (Type A), and air pressure was applied in accordance with JIS P8117:2009. The time (sec) required for 100 ml of air to pass through the test piece was then measured. The results are shown in Table 1.

[0058] [Table 1]

[0059] As shown in Table 1, regardless of the type of adhesive, a secondary battery with sufficient adhesion between the electrode and separator can be fabricated by constraining the battery assembly at a constraining pressure of at least 0.35 MPa and maintaining the battery assembly at a temperature of at least 80°C. A high-temperature treatment is performed so that the relationship between the peel strength A at the interface between the separator and the negative electrode active material layer, the peel strength B at the interface between the negative electrode active material layer and the negative electrode current collector foil, and the peel strength C within the negative electrode active material layer satisfies the formula I: A > B > C. Furthermore, as shown in Table 1, this manufacturing method does not excessively increase the separator's air permeability, thereby maintaining a state in which ions can move favorably. Therefore, a secondary battery with excellent battery characteristics can be fabricated.

[0060] In addition, in Examples 1 and 2, the peel strength upon peeling was 10 N / m, and the negative electrode active material layer was attached to the separator side, which indicates that the peel strength A at the interface between the separator and the negative electrode active material layer was at least 10 N / m or more.

[0061] While specific examples of the technology disclosed herein have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology disclosed herein includes various modifications and variations of the above specific examples. [Explanation of symbols]

[0062] 10 Battery case 12 Exterior body 14 Sealing plate 20 Electrode body 22a Cathode active material layer 22c positive electrode current collector foil 24a Negative electrode active material layer 24c Negative current collector foil 30 Positive terminal 40 Negative terminal 50 gaskets 60 insulator 100 Secondary battery

Claims

1. an assembly preparation step of preparing a battery assembly by housing an electrode body having a positive electrode comprising a positive electrode active material layer on a positive electrode current collector foil, a negative electrode comprising a negative electrode active material layer on a negative electrode current collector foil, and a separator comprising an adhesive layer, and an electrolyte in a rectangular battery case made of aluminum or an aluminum alloy; a high-temperature treatment step of constraining the battery assembly at a confining pressure of 0.35 MPa or more and 1.20 MPa or less and maintaining the battery assembly at a temperature of at least 80°C or more; Including, Here, the high-temperature treatment step is The peel strength at the interface between the separator and the negative electrode active material layer is A (N / m), The peel strength at the interface between the negative electrode active material layer and the negative electrode current collector foil is B (N / m), When the peel strength in the negative electrode active material layer is C (N / m), Formula I: A≧B>C; The implementation will be carried out to satisfy the following: The method for manufacturing a secondary battery, wherein the high-temperature treatment step is carried out for 6 hours or more.

2. The manufacturing method according to claim 1 , wherein the high-temperature treatment step restricts an area of ​​at least 60% or more of the broad surface of the battery assembly, assuming the area of ​​the broad surface of the battery assembly to be 100%.

3. The manufacturing method according to claim 1 or 2, wherein the high-temperature treatment step is performed when the SOC of the battery assembly is less than 5%.

4. an electrode assembly including a positive electrode, a negative electrode, and a separator; Electrolytes, a rectangular battery case made of aluminum or an aluminum alloy that houses the electrode assembly and the electrolyte; A secondary battery comprising: the positive electrode includes a positive electrode active material layer on a positive electrode current collector foil, the negative electrode includes a negative electrode active material layer on a negative electrode current collector foil, the separator has an adhesive layer on a surface of the separator, The peel strength at the interface between the separator and the negative electrode active material layer is A (N / m), The peel strength at the interface between the negative electrode active material layer and the negative electrode current collector foil is B (N / m), When the peel strength in the negative electrode active material layer is C (N / m), Formula I: A≧B>C; and Formula II: A≧10; Fulfilling The separator has an air permeability of 180 sec / 100 ml or less.

5. 5. The secondary battery according to claim 4, wherein a peel strength A at the interface between the separator and the negative electrode active material layer is 10 N / m or more and 18 N / m or less.

6. the adhesive layer comprises an adhesive; 6. The secondary battery according to claim 4, wherein the adhesive is either an acrylic resin adhesive or a fluororesin adhesive.

Images