Secondary battery and method of manufacturing the same

Abstract

[Project] Provides a highly durable secondary battery. [Solution] A positive electrode and a negative electrode are positioned opposite each other with a separator in between. The negative electrode comprises a negative electrode current collector, a negative electrode composite layer provided on the negative electrode current collector and containing graphite particles, and an adhesive layer provided between the surface of the negative electrode composite layer and the separator. In the XRD profile of the negative electrode composite layer, the degree of orientation, which is the intensity ratio obtained by dividing the intensity of the (110) plane of the graphite crystal by the intensity of the (002) plane, is 0.03 or greater. The thickness of the adhesive layer is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer.

Description

Technology Field

[0001] The technology disclosed in this specification relates to a secondary battery and a method for manufacturing a secondary battery. Background Technology

[0002] The negative electrode used in secondary batteries comprises a conductive negative electrode current collector and a negative electrode composite layer provided on the negative electrode current collector. The negative electrode composite layer contains graphite particles having a layered crystal structure. Charge and discharge functions are realized through the absorption and release of metal ions between the layers of graphite particles. Accordingly, a technique has been proposed to orient the layer planes of the graphite particles approximately perpendicular to the negative electrode current collector by utilizing the magnetic field orientation of the graphite particles. The closer the layer planes of the graphite particles are to perpendicular to the negative electrode current collector, the more smoothly the absorption and release of metal ions between the layers of the graphite particles can be performed. Therefore, it becomes possible to improve the performance of the secondary battery.

[0003] In addition, the surface of the negative electrode composite layer and the separator are bonded. Also, Patent Document 1 can be cited as a related technology. Prior art literature

[0004] Japanese Patent Publication No. 2019-87422 The problem to be solved

[0005] As described above, when graphite particles included in the negative electrode composite layer are oriented by a magnetic field, the angle formed between the layer plane of the graphite particles and the surface of the negative electrode current collector becomes larger. Consequently, the surface roughness of the surface layer of the negative electrode composite layer increases when oriented by a magnetic field compared to when not oriented by a magnetic field. As a result, there is a concern that the adhesion between the surface layer of the negative electrode composite layer and the separator may deteriorate. means of solving the problem

[0006] The technology disclosed in this specification is implemented in a secondary battery. A first aspect of the technology is a secondary battery in which a positive electrode and a negative electrode face each other via a separator. The negative electrode comprises a negative electrode current collector, a negative electrode composite layer provided on the negative electrode current collector and containing graphite particles, and an adhesive layer provided between the surface of the negative electrode composite layer and the separator. In the XRD profile of the negative electrode composite layer, the degree of orientation, which is the intensity ratio obtained by dividing the intensity of the (110) plane of the graphite crystal by the intensity of the (002) plane, is 0.03 or greater. The thickness of the adhesive layer is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer.

[0007] According to the above structure, the thickness of the adhesive layer formed between the surface of the negative electrode composite layer and the separator is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer. Accordingly, fine concave areas on the surface of the negative electrode composite layer can be sufficiently filled by the adhesive layer. Since the adhesion between the surface of the negative electrode composite layer and the adhesive layer can be increased, it becomes possible to improve the adhesion between the surface layer of the negative electrode composite layer and the separator. Brief explanation of the drawing

[0008] Figure 1 is a perspective view of a secondary battery (1). Figure 2 is an exploded plan view of the electrode body (108). Figure 3 is a cross-sectional view of the negative electrode (114). Figure 4 is a flowchart describing the method of manufacturing a secondary battery (1). Figure 5 is a figure illustrating an example of the preparation process of the first paste. Figure 6 is a diagram illustrating steps S20-S50. Figure 7 is a diagram illustrating steps S100 and S110. Figure 8 is a diagram illustrating the heating press process. Figure 9 is a cross-sectional view of the negative electrode of the first comparative example. Specific details for implementing the invention

[0009] In a second embodiment of the present technology, in addition to the first embodiment above, the adhesive layer may have a first adhesive layer containing additive particles in contact with the separator. The adhesive layer may have a second adhesive layer that does not contain additive particles in contact with the negative electrode composite layer. The thickness of the second adhesive layer may be greater than the arithmetic mean roughness of the surface of the negative electrode composite layer.

[0010] According to the above composition, the second adhesive layer has higher fluidity than the first adhesive layer because it does not contain additive particles. The thickness of this highly fluid second adhesive layer is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer. Accordingly, the second adhesive layer can have a sufficient volume to fill the concave areas present on the surface of the negative electrode composite layer. This makes it possible to improve the adhesion between the negative electrode composite layer and the separator.

[0011] In a third embodiment of the present technology, in addition to the first or second embodiment above, the adhesive layer may include a resin as a base material.

[0012] In the fourth embodiment of the present technology, in addition to the third embodiment above, the resin may include an acrylic resin or a polyvinylidene fluoride resin.

[0013] In the fifth embodiment of the present technology, in addition to the second to fourth embodiments above, the additive particles may include any of alumina, boehmite, and polyimide.

[0014] The technology disclosed in this specification is implemented as a method for manufacturing a secondary battery. A sixth aspect of the technology is a method for manufacturing a secondary battery in which a positive electrode and a negative electrode face each other via a separator. The manufacturing method comprises a process of forming a first adhesive layer containing additive particles on the surface of a separator. The manufacturing method comprises a process of forming a negative electrode composite layer by coating a paste containing graphite particles and a solvent onto the surface of a negative electrode current collector. The manufacturing method comprises a magnetic field orientation process of applying an external magnetic field to the negative electrode composite layer. The manufacturing method comprises a drying process of drying the negative electrode composite layer after the magnetic field orientation process. The manufacturing method comprises a process of forming a second adhesive layer not containing additive particles on the surface of the negative electrode composite layer or on the surface of the first adhesive layer after the drying process. The manufacturing method comprises a process of heating the first adhesive layer and the second adhesive layer while they are in contact with each other.

[0015] According to the above configuration, the first adhesive layer and the separator can be bonded by interposing a second adhesive layer with high fluidity. The second adhesive layer can be moved to flow into the concave portion formed by the magnetic field orientation of graphite particles. This makes it possible to improve the adhesion between the negative electrode composite layer and the separator.

[0016] In the seventh embodiment of the present technology, in addition to the sixth embodiment above, the thickness of the second adhesive layer may be greater than the arithmetic mean roughness of the surface of the negative electrode composite layer.

[0017] According to the above configuration, the second adhesive layer can have a sufficient volume to fill the concave portions existing on the surface of the negative electrode composite layer.

[0018] In the eighth embodiment of the present technology, in addition to the sixth or seventh embodiment above, the first adhesive layer and the second adhesive layer may comprise an acrylic resin or a polyvinylidene fluoride resin as a base material.

[0019] In the ninth embodiment of the present technology, in addition to the sixth to eighth embodiments above, the additive particles may include any of alumina, boehmite, and polyimide.

[0020] [Example]

[0021] Structure of the secondary battery (1)

[0022] FIG. 1 shows a perspective view of a secondary battery (1) related to the present embodiment. In the present embodiment, as one of the preferred embodiments of the secondary battery (1), it is described by embodying it as a lithium-ion secondary battery. As shown in FIG. 1, the secondary battery (1) comprises a housing (102), a positive electrode terminal (104), a negative electrode terminal (106), an electrode body (108), and a non-aqueous electrolyte (110). The housing (102) accommodates the electrode body (108) and the non-aqueous electrolyte (110). The housing (102) comprises a housing body (102a) and a cover plate (102b). The housing body (102a) is a box body having an opening (102c) at the top. The cover plate (102b) is mounted on the opening (102c) and blocks the opening (102c).

[0023] Each of the positive terminal (104) and the negative terminal (106) is mounted on a cover plate (102b). One end (104a) of the positive terminal (104) is exposed to the outside of the housing (102). The other end (104b) of the positive terminal (104) is connected to the positive connection part (112a) of the electrode body (108) inside the housing (102). One end (106a) of the negative terminal (106) is exposed to the outside of the housing (102). The other end (106b) of the negative terminal (106) is connected to the negative connection part (114a) of the electrode body (108) inside the housing (102).

[0024] FIG. 2 shows an exploded plan view of an electrode body (108). The electrode body (108) is provided with a positive electrode (112), a negative electrode (114), and a separator (116). Each of the positive electrode (112), the negative electrode (114), and the separator (116) is in the shape of a long sheet. The positive electrode (112) and the negative electrode (114) are stacked with the separator (116) interposed. The electrode body (108) is formed by winding the stack of the positive electrode (112) and the negative electrode (114). However, the electrode body (108) does not necessarily have to be a wound electrode body. The electrode body (108) may be, for example, a so-called stacked electrode body in which a plurality of positive electrodes (112) and a plurality of negative electrodes (114) are alternately stacked with the separator (116) interposed.

[0025] The positive electrode (112) is provided with a positive electrode current collector (118) and a positive electrode active material sheet (120). The positive electrode current collector (118) is a conductive sheet. The positive electrode current collector (118) is, for example, an aluminum foil. The positive electrode active material sheet (120) is disposed on the surface of the positive electrode current collector (118). The positive electrode active material sheet (120) is provided with a positive electrode active material. As a positive electrode active material, for example, a lithium composite oxide may be provided. On one side edge in the width direction of the positive electrode (112), a positive electrode exposed portion (118a) is provided in which the positive electrode current collector (118) is exposed. The positive electrode exposed portion (118a) forms a positive electrode connection portion (112a) by being wound and overlapped when forming the electrode body (108).

[0026] The negative electrode (114) is provided with a negative electrode current collector (122) and a negative electrode composite layer (10). The negative electrode current collector (122) is a conductive sheet. The negative electrode current collector (122) is, for example, a copper foil. The negative electrode composite layer (10) is disposed on the surface of the negative electrode current collector (122). Specific details regarding the negative electrode (114) will be described later. On one side edge in the width direction of the negative electrode (114), a negative electrode exposure portion (122a) is provided in which the negative electrode current collector (122) is exposed. When forming the electrode body (108), the negative electrode exposure portion (122a) is wound and overlapped to form a negative electrode connection portion (114a).

[0027] The separator (116) is configured to allow a charge carrier (here, lithium ions) to pass through. Examples of separators (116) include porous polymer membranes such as porous polyethylene membranes, porous polypropylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, as well as lithium ion conductive polymer electrolyte membranes. These separators (116) may be used alone or in combination with multiple types.

[0028] An adhesive layer (13) is formed on the surface of the separator (116). The specific details of the adhesive layer (13) will be described later.

[0029] The non-aqueous electrolyte (110) penetrates into the interior of the electrode body (108). The non-aqueous electrolyte (110) includes a non-aqueous solvent and a supporting salt. Examples of non-aqueous solvents include carbonates, ethers, esters, nitriles, sulfones, and lactones. Additionally, examples of supporting salts include lithium salts containing fluorine. Each of the non-aqueous solvent and the supporting salt may be composed of a single type of material or a plurality of types of materials.

[0030] Structure of the negative pole (114)

[0031] FIG. 3 shows a cross-sectional view of the negative electrode (114). FIG. 3 also shows a separator (116). In FIG. 3, the direction parallel to the negative electrode current collector (122) is defined as the x and y directions. Also, the direction perpendicular to the negative electrode current collector (122) (the thickness direction of the negative electrode (114)) is defined as the z direction. Additionally, for the purpose of clarity in illustration, only one of the components arranged in multiple places may be labeled. The same applies to subsequent drawings. The negative electrode (114) mainly comprises a negative electrode current collector (122), a negative electrode composite layer (10), and an adhesive layer (13).

[0032] The adhesive layer (13) is provided between the surface (10s) of the negative electrode composite layer (10) and the separator (116), and the two are bonded together. The adhesive layer (13) has an average thickness (AT). The adhesive layer (13) comprises a first adhesive layer (13_1) and a second adhesive layer (13_2). The first adhesive layer (13_1) is in contact with the separator (116). The first adhesive layer (13_1) is a layer containing resin (16) and additive particles (17). That is, the first adhesive layer (13_1) is a layer containing resin (16) as a base material. The second adhesive layer (13_2) is in contact with the negative electrode composite layer (10). The second adhesive layer (13_2) is composed mainly of resin (16) and is a layer that does not contain additive particles (17). In addition, in FIG. 3, for the sake of clarity, the resin (16) is similarly represented by a small white circle. Also, the additive particles (17) are similarly represented by a gray circle.

[0033] The first adhesive layer (13_1) has an average thickness (AT1). The second adhesive layer (13_2) has an average thickness (AT2). The average thickness (AT2) of the second adhesive layer (13_2) is greater than the surface roughness (Ra2) of the surface (10s) of the negative electrode composite layer (10). For example, if the surface roughness (Ra2), defined as the arithmetic mean roughness, is 1.5 μm, the average thickness (AT2) is greater than 1.5 μm. The surface roughness (Ra2) will be described later.

[0034] The composition of the resin (16) may vary, and, for example, may be the same as the composition of the binder (14) described later. In this embodiment, the composition of the resin is PVdF, which is the same as the binder (14).

[0035] The material of the additive particle (17) is preferably heat-resistant and insulating, and also highly durable against the electrolyte. Examples of the material of the additive particle (17) include metal compounds or polymer compounds such as polyimide. Suitable examples of metal compounds include α-alumina (Al2O3), boehmite (Al2O3·H2O), magnesium hydroxide (Mg(OH)2), and magnesium carbonate (MgCO3). Additionally, one or more of these materials may be used for the additive particle (17).

[0036] The additive particles (17) included in the first adhesive layer (13_1) are bonded together by the resin (16). Accordingly, since a heat-resistant porous layer can be formed, it is possible to prevent an internal short circuit of the secondary battery (1).

[0037] The negative electrode composite layer (10) is provided on the negative electrode current collector (122). The negative electrode composite layer (10) comprises graphite particles (11), a binder (14), and a conductive agent not shown. For the graphite particles (11), a graphite-based carbon material such as natural graphite, artificial graphite, or an amorphous form thereof may be used. For example, the graphite particles (11) may be flat, flaky graphite, or spheroidized graphite formed by spheroidizing flaky graphite. In this embodiment, flaky graphite is used as the graphite particles (11). This is because flaky graphite is flat and can be stably oriented by applying a magnetic field.

[0038] In FIG. 3, graphite particles (11) are shown as hatching. The median diameter of the graphite particles (11) is, for example, within the range of 15 to 40 micrometers. Furthermore, the median diameter referred to here means the particle size (D50) at 50% of the cumulative value in the volume-based particle size distribution measured by the laser diffraction and scattering method. In this embodiment, the graphite particles (11) have a median diameter of 20 micrometers.

[0039] The binder (14) is a component for binding graphite particles (11) together. The binder (14) is mixed into the negative electrode composite layer (10). The binder (14) contains a resin in the form of particles. In FIG. 3, the binder (14) is similarly represented by a white circle. Examples of binders (14) include polyvinylidene fluoride (PVdF), various acrylic resins, carboxymethylcellulose (CMC), styrene butadiene rubber (SBR), polytetrafluoroethylene (PTFE), etc.

[0040] As an acrylic resin, a homopolymer obtained by polymerizing monomers such as acrylic acid, methacrylic acid, acrylamide, methacrylamide, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, methacrylate, methyl methacrylate, ethylhexyl acrylate, and butyl acrylate into one type may be used. Additionally, the acrylic resin may be a copolymer obtained by polymerizing two or more of the above monomers.

[0041] The binder (14) may be composed of a single type of material or a plurality of types of materials. In this embodiment, the binder (14) is made of PVdF.

[0042] Orientation of graphite particles

[0043] As described above, the graphite particle (11) is flat, flake-like graphite. The flake-like graphite is composed of a number of stacked plate-shaped (graphene) structures having hexagonal crystals. Therefore, the graphite particle (11) has a roughly plate-like shape. The graphite particle (11) has a (002) plane and a (110) plane. The (002) plane is a layer plane (a plane horizontal to the graphite layer) of the layered graphite particle. The (002) plane is a plane horizontal to the carbon network of the graphene sheet constituting the graphite particle (11). The (110) plane is a cross-section (a plane perpendicular to the graphite layer) of the layered graphite particle. The (110) plane is a plane perpendicular to the (002) plane of the graphite particle. That is, as shown in FIG. 3, the graphite particles (11) have a long, slender shape such that the length in the direction parallel to the layer plane is longer than the length in the direction perpendicular to the layer plane.

[0044] Here, the “orientation degree” of the graphite particle (11) is defined. The peak intensity originating from the (110) plane of the graphite particle (11) by powder X-ray diffraction measurement is denoted as PI1. Also, the peak intensity originating from the (002) plane is denoted as PI2. The peak intensity (PI1) originates from the ab-axis direction of the graphite crystal. The peak intensity (PI2) originates from the c-axis direction of the graphite crystal. Furthermore, the intensity ratio of the peak intensity (PI1) divided by the peak intensity (PI2) is defined as the orientation degree. That is, it is defined as “orientation degree = PI1 / PI2”.

[0045] The greater the degree of orientation, the more graphite particles (11) are oriented in the negative electrode composite layer (10) such that the c-axis is parallel to the negative electrode current collector (122) (the xy plane direction of Fig. 3). That is, the greater the degree of orientation, the higher the proportion of graphite particles (11) that are upright with an angle relative to the surface of the negative electrode current collector (122).

[0046] And according to the inventors' research, it was found that when the magnetic field orientation described below is not performed, the degree of orientation of the negative electrode composite layer (10) becomes less than 0.03. And, it was found that by performing magnetic field orientation, the degree of orientation of the negative electrode composite layer (10) can be made greater than 0.03. That is, it is possible to determine whether magnetic field orientation is being performed depending on whether the degree of orientation of the negative electrode composite layer (10) is greater than 0.03.

[0047] <Method for manufacturing secondary battery (1)>

[0048] Using the flowchart of FIG. 4 and the schematic diagrams of FIG. 5 to 8, the method for manufacturing the secondary battery (1) described above will be explained. In step S2, a first adhesive layer (13_1) is formed on the surface of the separator (116) (process for forming the first adhesive layer). The paint for forming the first adhesive layer (13_1) is a paste-like paint in which a resin (16), additive particles (17), and a solvent are mixed and dispersed. This paint is applied to the surface of the separator (116). Conventional general coating devices may be used for the coating process. Examples of coating devices include a gravure coater, a slit coater, a die coater, a comma coater, a dip coater, etc. After coating, the solvent is removed from the coated material using a suitable drying means. Accordingly, the first adhesive layer (13_1) is completed.

[0049] In step S4, a second adhesive layer (13_2) is formed on the surface of the first adhesive layer (13_1) (process for forming the second adhesive layer). A resin (16) and a solvent are mixed and dispersed in the paint for forming the second adhesive layer (13_2). This paint is applied to the surface of the first adhesive layer (13_1). If necessary, a drying process is performed after application. Furthermore, since conventional general devices can be used for the application process and the drying process in step S4, a detailed description is omitted.

[0050] In step S10, a first paste is prepared (paste preparation process). The first paste is a paste containing graphite particles (11). The paste may be in the form of a slurry or an ink.

[0051] Using FIG. 5, an example of the preparation process for the first paste is described. Graphite particles (11), a binder (14), and a conductive agent (15) are each supplied to a mixing machine (210) in predetermined amounts. A solvent is added to the materials supplied to the mixing machine (210), and the mixture is mixed. Accordingly, the first paste is completed. The mixing machine (210) may be of various types, and, for example, a planetary mixer may be used.

[0052] In steps S20-S50, a process of forming a negative electrode composite layer (10) on the first surface (122s1) of the negative electrode current collector (122) is performed. This will be explained in detail using FIG. 6. In step S20, a first coating process is performed. In the first coating process, a first paste containing graphite particles (11) is coated onto the surface of the negative electrode current collector (122). Specifically, the negative electrode current collector (122) is sent out at a constant speed in the conveying direction (T1) from a roll (122R) on which the negative electrode current collector (122) is wound. Then, the first paste is applied onto the negative electrode current collector (122) using a first coater (211). Accordingly, a first layer (L1) is formed. Various types of coaters may be used for the first coater (211). For example, the first coater (211) may be a slot die coater.

[0053] In step S40, an external magnetic field is applied to the first layer (L1) (magnetic field orientation process). Specifically, a magnetic field generating means (221) is used to apply a magnetic field such that the direction of the magnetic field lines (MF) is approximately perpendicular to the surface of the negative current collector (122). The magnetic field generating means (221) may be a permanent magnet or an electromagnet. Accordingly, the (002) plane of the graphite particles (11) can be oriented so that it is approximately parallel to the direction of the magnetic field lines.

[0054] In step S50, the first layer (L1) is dried (drying process). Specifically, it is dried by irradiating it with hot air (HA). Furthermore, the means used in the drying process are not limited to hot air, and drying by low humidity air, vacuum, infrared rays, far infrared rays, electron beams, etc., can be used alone or in combination. Through the drying process, the solvent can be removed from the first layer (L1). Accordingly, a negative electrode composite layer (10) can be formed on the first surface (122s1) of the negative electrode current collector (122).

[0055] In steps S60-S90, a process of forming a negative electrode composite layer (10) on the second surface (122s2) of the negative electrode current collector (122) is performed. Additionally, since the contents of steps S60, S80, and S90 are the same as the contents of steps S20, S40, and S50 described above, the explanation is omitted. Accordingly, a negative electrode (114) is formed. The negative electrode (114) has a configuration in which a negative electrode composite layer (10) is disposed on both sides of the negative electrode current collector (122).

[0056] In step S100, the negative electrode (114) is pressed (press process). As shown in FIG. 7, for example, a roll press device (230) is used in the press process. The roll press device (230) is configured to roll the negative electrode (114) passing between a pair of rollers (231). Accordingly, the density and thickness of the negative electrode composite layer (10) can be adjusted.

[0057] In step S110, slit processing is performed. As shown in FIG. 7, in slit processing, the negative electrode (114) being sent in the feed direction (T1) is cut by a cutter (240). Accordingly, the width of the negative electrode (114) in the short length direction can be made to a width corresponding to the size of the secondary battery (1).

[0058] In step S120, an electrode body (108) is manufactured (electrode body manufacturing process). As shown in FIG. 2, in the electrode body manufacturing process, a positive electrode (112), a negative electrode (114), and a separator (116) are stacked so that the positive electrode (112) and the negative electrode (114) face each other with a separator (116) interposed. Specifically, the stack of the positive electrode (112) and the negative electrode (114) is wound.

[0059] In step S130, the electrode body (108) is pressed while being heated (heating press process). As shown in FIG. 8, for example, a flat plate press device (250) is used in the heating press process. Accordingly, the electrode body (108) can be compressed into a flat shape having a predetermined thickness. In addition, in the heating press process, as shown in FIG. 3, the first adhesive layer (13_1) and the second adhesive layer (13_2) can be heated while in contact with each other. Thus, the separator (116) and the negative electrode composite layer (10) can be bonded together with the additive particles (17) interposed. Furthermore, this heating press process may be performed after the electrolyte injection process (S150) described later.

[0060] In step S140, an electrode housing process is performed. Specifically, as shown in FIG. 1, a positive electrode terminal (104) and a negative electrode terminal (106) mounted on a cover plate (102b) are welded to each end of the electrode body (108). The electrode body (108) is housed inside the housing body (102a) through an opening (102c). After that, the housing body (102a) and the cover plate (102b) are joined together using laser welding or the like.

[0061] In step S150, a non-aqueous electrolyte is injected into the housing (102) through an injection port not shown (electrolyte injection process). Then, the injection port is hermetically sealed using a sealing member. By the above, the secondary battery (1) is completed.

[0062] Assignment

[0063] The problem is explained using the first comparative example of FIG. 9 and the present embodiment of FIG. 3. FIG. 9 is a cross-sectional view similar to FIG. 3. The first comparative example ( FIG. 9) is different from the present embodiment ( FIG. 3) in that magnetic field orientation is not performed on the negative electrode composite layer (310).

[0064] In the negative electrode composite layer (310) of the first comparative example (Fig. 9), magnetic field orientation is not performed. Therefore, the layer surface (longer side) of the graphite particles (11) is not oriented in a direction (z-direction) that is approximately perpendicular to the negative electrode current collector (122). Because of this, the path length (PL1) of the pores reaching from the separator (116) to the negative electrode current collector (122) increases. As a result, the curvature of the negative electrode composite layer (310) increases. Here, the curvature is the ratio of the path length (PL1) to the straight distance (SD) connecting the separator (116) to the negative electrode current collector (122). As the curvature increases, the absorption and release of Li ions between the layers of graphite particles (11) are not performed smoothly. Therefore, as the degree of curvature increases, the internal resistance of the secondary battery (1) increases, and the performance of the secondary battery (1) deteriorates.

[0065] Meanwhile, in the negative electrode composite layer (10) of the present embodiment (Fig. 3), magnetic field orientation is performed. Accordingly, the layer surface (longer length surface) of the graphite particles (11) is oriented in a direction (z-direction) that is approximately perpendicular to the negative electrode current collector (122). Because of this, the path length (PL2) of the pores in the present embodiment can be made shorter than the path length (PL1) of the pores in the first comparative example. Therefore, in the present embodiment, the curvature is smaller than in the first comparative example, so the internal resistance can be reduced. However, when the graphite particles (11) are magnetically oriented, the angle formed between the layer surface of the graphite particles (11) and the surface of the negative electrode current collector (122) becomes larger. Accordingly, the pointed tip surface ((110) surface) of the graphite particle (11) ends up protruding upward from the surface of the negative electrode composite layer (10) (see region (A2)). As a result, the surface roughness (Ra2) of the negative electrode composite layer (10) of this embodiment becomes larger than the surface roughness (Ra1) of the negative electrode composite layer (310) of the first comparative example. There is a risk that the adhesion between the surface of the negative electrode composite layer that is magnetically oriented and the separator (116) will deteriorate compared to the adhesion between the surface of the negative electrode composite layer that is magnetically oriented and the separator (116).

[0066] In addition, various indicators can be used for surface roughness (Ra1 and Ra2). In this embodiment, arithmetic mean roughness is used as the surface roughness. Arithmetic mean roughness can be measured in accordance with the JIS B 0601:2001 standard.

[0067] <Effect>

[0068] In the negative electrode composite layer (10) of the present embodiment (Fig. 3), the degree of orientation is 0.03 or greater. That is, the negative electrode composite layer (10) is magnetically oriented. Therefore, since the curvature of the negative electrode composite layer (10) is small, the internal resistance can be reduced. In addition, an adhesive layer (13) is provided between the surface (10s) of the negative electrode composite layer (10) and the separator (116). Furthermore, the average thickness (AT) of the adhesive layer (13) is greater than the surface roughness (Ra2) of the surface (10s) of the negative electrode composite layer (10). Accordingly, the fine concave portions of the surface (10s) of the negative electrode composite layer (10) can be sufficiently filled by the adhesive layer (13). Since the adhesion between the surface (10s) of the negative electrode composite layer (10) and the adhesive layer (13) can be increased, it is possible to improve the adhesion between the negative electrode composite layer (10) and the separator (116).

[0069] The adhesive layer (13) is provided with a second adhesive layer (13_2) in contact with the surface (10s) of the negative electrode composite layer (10). Since the second adhesive layer (13_2) does not contain additive particles (17), it has higher fluidity than the first adhesive layer (13_1). Furthermore, the average thickness (AT2) of this highly fluid second adhesive layer (13_2) is greater than the surface roughness (Ra2) of the surface (10s) of the negative electrode composite layer (10). Accordingly, the second adhesive layer (13_2) can have a sufficient volume to fill the concave portions present on the surface (10s). Thus, a state can be created in which the second adhesive layer (13_2) is sufficiently filled into the gap formed by the magnetic field orientation of the graphite particles (11) (see region (A0)). It is possible to improve the adhesion between the negative electrode composite layer (10) and the separator (116).

[0070] Although embodiments have been described in detail above, they are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and alterations of the specific embodiments exemplified above. The technical elements described in this specification or drawings exhibit technical utility either individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings achieves multiple objectives simultaneously, and possesses technical utility in itself by achieving one of those objectives.

[0071] <Variation Example>

[0072] In step S4, although the form of forming the second adhesive layer (13_2) on the surface of the first adhesive layer (13_1) has been described, it is not limited to this form. The second adhesive layer (13_2) may be formed on the surface (10s) of the negative electrode composite layer (10). For example, after the drying process of step S50 or S90, a paint for forming the second adhesive layer (13_2) may be applied to the surface of the negative electrode composite layer (10). Explanation of the symbols

[0073] 1: Secondary battery 10: Poison composite layer 11: Graphite particles 13: Adhesive layer 13_1: First adhesive layer 13_2: Second adhesive layer 17: Added particles 112: Straight Drama 114: Buguk 116: Separator 122: Buguk entire house AT, AT1, AT2: Average thickness Ra1, Ra2: Surface roughness

Claims

Claim 1 A secondary battery having a positive electrode and a negative electrode facing each other via a separator, wherein the negative electrode comprises a negative electrode current collector, a negative electrode composite layer provided on the negative electrode current collector and containing graphite particles, and an adhesive layer provided between the surface of the negative electrode composite layer and the separator, wherein in the XRD profile of the negative electrode composite layer, the degree of orientation, which is the intensity ratio of the (110) plane of the graphite crystal divided by the intensity of the (002) plane, is 0.03 or greater, and the thickness of the adhesive layer is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer. Claim 2 A secondary battery according to claim 1, wherein the adhesive layer comprises a first adhesive layer containing additive particles in contact with the separator and a second adhesive layer not containing additive particles in contact with the negative electrode composite layer, and the thickness of the second adhesive layer is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer. Claim 3 In claim 2, the adhesive layer comprises a resin as a base material, in a secondary battery. Claim 4 In claim 3, the resin comprises an acrylic resin or a polyvinylidene fluoride resin, in a secondary battery. Claim 5 In claim 2, the additive particles comprise any one of alumina, boehmite, and polyimide, in a secondary battery. Claim 6 A method for manufacturing a secondary battery in which a positive electrode and a negative electrode face each other via a separator, comprising: a process of forming a first adhesive layer containing additive particles on the surface of the separator; a process of forming a negative electrode composite layer by coating a paste containing graphite particles and a solvent on the surface of a negative electrode current collector; a magnetic field orientation process of applying an external magnetic field to the negative electrode composite layer; a drying process of drying the negative electrode composite layer after the magnetic field orientation process; a process of forming a second adhesive layer not containing additive particles on the surface of the negative electrode composite layer after the drying process, or on the surface of the first adhesive layer; and a process of heating the first adhesive layer and the second adhesive layer in a state where they are in contact with each other. Claim 7 A method for manufacturing a secondary battery according to claim 6, wherein the thickness of the second adhesive layer is greater than the arithmetic mean roughness of the surface of the negative electrode composite layer. Claim 8 A method for manufacturing a secondary battery according to claim 7, wherein the first adhesive layer and the second adhesive layer comprise an acrylic resin or a polyvinylidene fluoride resin as a base material. Claim 9 A method for manufacturing a secondary battery according to claim 6, wherein the additive particles comprise any one of alumina, boehmite, and polyimide.

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