Electrode sheet and method for manufacturing the same

Abstract

To improve the conductivity of an electrode sheet while maintaining the tensile strength.SOLUTION: A method for manufacturing an electrode sheet includes the steps of: producing first coated active material particles by mixing at least a binder with a plurality of first active material particles; producing second coated active material particles by mixing at least a conductive additive with a plurality of second active material particles; producing an electrode mixture by mixing the first coated active material particles and the second coated active material particles; and forming the electrode mixture into a sheet shape. The average particle diameter of the second active material particles is larger than the average particle diameter of the first active material particles.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to an electrode sheet and a method for manufacturing an electrode sheet. [Background technology]

[0002] Patent Document 1 describes an electrode sheet for a battery cell and a method for manufacturing the electrode sheet. The electrode sheet includes active material particles and a binder. The method for manufacturing the electrode sheet includes a step of preparing an electrode composite mixture by mixing the active material particles and the binder, and a step of preparing an electrode sheet from the electrode composite mixture. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Special Publication No. 2021-504877 Summary of the Invention [Problem to be solved by the invention]

[0004] The conductivity of the electrode sheet can be improved by adding a conductive additive to the electrode sheet. The conductive additive is, for example, carbon black or carbon nanotubes, and forms conductive paths extending between active material particles. However, when the conductive additive and binder are mixed with the active material particles, there is a risk that the conductive additive will be incorporated into the binder. In this case, the amount of conductive additive extending between the active material particles will decrease, making it impossible to sufficiently improve the conductivity of the electrode sheet.

[0005] One possible solution to the above problem is to reduce the amount of binder mixed. However, reducing the amount of binder mixed may result in a decrease in the tensile strength of the electrode sheet. Therefore, to improve the tensile strength of the electrode sheet, it is possible to use a fibrillating binder, such as polytetrafluoroethylene (PTFE). However, when the binder is fibrillated, the conductive additive becomes more likely to become entangled in the binder. As a result, more conductive additive is absorbed into the binder, further reducing the amount of conductive additive extending between the active material particles.

[0006] In view of the above circumstances, the present specification provides a technique for improving the conductivity of an electrode sheet while maintaining the tensile strength. [Means for solving the problem]

[0007] The technology disclosed in this specification is embodied in a method for manufacturing an electrode sheet. In a first aspect, the method for manufacturing an electrode sheet includes the steps of: preparing first coated active material particles by mixing at least a binder with a plurality of first active material particles; preparing second coated active material particles by mixing at least a conductive additive with a plurality of second active material particles; mixing the first coated active material particles and the second coated active material particles to prepare an electrode mixture; and forming the electrode mixture into a sheet. The average particle diameter of the second active material particles is larger than the average particle diameter of the first active material particles.

[0008] The above-described manufacturing method includes a step of preparing first coated active material particles and a step of preparing second coated active material particles. The first coated active material particles and the second coated active material particles are mixed to prepare an electrode composite mixture. In the step of preparing the first coated active material particles, the first active material particles and the binder can be mixed without considering the influence on the conductive additive. On the other hand, in the step of preparing the second coated active material particles, the conductive additive can be attached to the second active material particles without being affected by the binder. This prevents the conductive additive from being incorporated into the binder when the first coated active material particles and the second coated active material particles are mixed in the step of preparing the electrode composite mixture. In this way, a relatively large amount of the conductive additive can be distributed between the active material particles to form conductive paths without reducing the amount of binder mixed, thereby producing an electrode sheet with excellent tensile strength and conductivity.

[0009] The inventors of the present invention also discovered that the adhesion of a conductive additive (e.g., carbon nanotubes) to active material particles varies depending on the particle size of the active material particles. Specifically, it was found that the conductive additive is more likely to adhere to active material particles with a relatively large particle size. Based on this, in the above-described manufacturing method, in the step of producing the second coated active material particles, the conductive additive is mixed with second active material particles with a relatively large average particle size. This allows a larger amount of conductive additive to adhere to the second active material particles, and further suppresses the conductive additive from being incorporated into the binder when the first coated active material particles and the second coated active material particles are mixed.

[0010] In a second aspect, the first active material particles may be single crystals, and the second active material particles may be polycrystalline, since the average particle size of a single crystal is smaller than that of a polycrystalline material.

[0011] In a third aspect, in the first or second aspect, the step of preparing the first coated active material particles may include a step of fibrillating the binder by applying a shear force to the binder, thereby further improving the tensile strength of the electrode sheet.

[0012] In a fourth aspect, in any one of the first to third aspects, the shear force applied to at least the binder in the step of fibrillating the binder may be greater than the shear force applied to the plurality of second active material particles and the conductive additive in the step of producing the second coated active material particles. This configuration can increase the degree of binding between the first active material particles and the binder in the first coated active material particles, thereby improving the tensile strength of the electrode sheet.

[0013] In a fifth aspect, in any of the first to fourth aspects, the conductive additive may include at least one selected from the group consisting of carbon nanotubes and acetylene black. Carbon nanotubes have a tubular shape, and acetylene black has a chain structure. When a conductive additive having such a shape or structure is used, the conductive additives tend to become entangled with each other, facilitating the formation of a conductive path. On the other hand, when the conductive additive has a tubular shape or a chain structure, the conductive additive is easily incorporated into the binder. However, in the present technology, the conductive additive is pre-attached to the second active material particles in the step of preparing the second coated active material particles, thereby effectively preventing the conductive additive from being incorporated into the binder.

[0014] In a sixth aspect, in any one of the first to fifth aspects, the electrode sheet may be a free-standing electrode sheet. This configuration can improve the energy density of the electrode. Note that a free-standing electrode sheet refers to an electrode sheet that is self-supporting without requiring a support (e.g., a current collector).

[0015] The technology disclosed in this specification is also embodied in an electrode sheet. The electrode sheet can be manufactured by the manufacturing method described above. For example, in a seventh aspect, the electrode sheet includes a plurality of active material particles, a binder, and a conductive additive. The plurality of active material particles includes a plurality of first active material particles and a plurality of second active material particles. The average particle diameter of the second active material particles is larger than the average particle diameter of the first active material particles. At least a portion of the surface of the first active material particles is coated with the binder. At least a portion of the surface of the second active material particles is coated with the conductive additive. As described above, the electrode sheet manufactured by this technology has excellent properties in both tensile strength and conductivity.

[0016] In an eighth aspect, in the seventh aspect, the first active material particles may be single crystal, and in this case, the second active material particles may be polycrystalline.

[0017] In a ninth aspect, in the seventh or eighth aspect, the binder may be a fibrillated resin. With this configuration, the tensile strength of the electrode sheet can be further improved.

[0018] In a tenth aspect, in any one of the seventh to ninth aspects, the conductive additive may include at least one selected from the group consisting of carbon nanotubes and acetylene black. With this configuration, the conductive additive has a tubular or chain-like structure, thereby improving the conductivity of the electrode sheet.

[0019] In an eleventh aspect, in any one of the seventh to tenth aspects, the electrode sheet may be a free-standing electrode sheet. With this configuration, the energy density of the electrode can be improved. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram schematically illustrating the configuration of an electrode body 100 in which an electrode sheet 10 is used. [Figure 2]1 is a diagram schematically illustrating the configuration of an electrode sheet 10. FIG. [Figure 3] 4 is a flowchart illustrating a method for manufacturing the electrode sheet 10. [Figure 4] FIG. 10 is a diagram illustrating a process of preparing first coated active material particles by mixing PTFE with NCM single crystals using a mixer 104. [Figure 5] FIG. 1 is a diagram illustrating a process of fibrillating PTFE by applying shear force to the PTFE using a kneader 110. [Figure 6] FIG. 10 is a diagram illustrating a process of forming an electrode mixture into a sheet using a press device 116. [Figure 7A] 3 is a flowchart illustrating a method for manufacturing the electrode sheet 10 of the first embodiment. [Figure 7B] 10 is a flowchart illustrating a method for manufacturing an electrode sheet according to Comparative Example 1. [Figure 7C] 10 is a flowchart illustrating a method for manufacturing an electrode sheet according to Comparative Example 2. [Figure 7D] 10 is a flowchart illustrating a method for manufacturing an electrode sheet according to Comparative Example 3. [Figure 8A] The evaluation results of the electrical resistance for Example 1 and Comparative Examples 1 to 3 are shown below. [Figure 8B] The evaluation results of tensile strength for Example 1 and Comparative Examples 1 to 3 are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0021] An electrode sheet 10 of an embodiment will be described with reference to the drawings. The electrode sheet 10 of this embodiment is employed in an electrode assembly 100. The electrode assembly 100 is used, for example, as a positive electrode of a lithium ion secondary battery.

[0022] As shown in FIG. 1 , the electrode assembly 100 includes an electrode sheet 10 and a current collector 102. The current collector 102 is a conductive sheet. The current collector 102 is, for example, an aluminum foil or a copper foil. The current collector 102 has a thickness of, for example, 5 μm or more and 50 μm or less. The electrode sheet 10 is disposed on the current collector 102. The electrode sheet 10 is a free-standing electrode sheet. The free-standing electrode sheet here refers to an electrode sheet that is self-supporting without requiring a support such as the current collector 102. Therefore, the electrode assembly 100 does not necessarily need to include the current collector 102. That is, in another embodiment, the electrode sheet 10 may constitute the electrode assembly 100 by itself. The thickness of the electrode sheet 10 is, for example, 10 μm or more and 500 μm or less.

[0023] As shown in FIG. 2 , the electrode sheet 10 includes a plurality of active material particles 12, 14, a binder 16, and a conductive additive 18. The plurality of active material particles 12, 14 includes a plurality of first active material particles 12 and a plurality of second active material particles 14. In this embodiment, the first active material particles 12 are single crystals, and the second active material particles 14 are polycrystalline. Therefore, the average particle diameter of the second active material particles 14 is larger than the average particle diameter of the first active material particles 12. This allows the first active material particles 12, which have a smaller particle diameter, to enter the gaps between the second active material particles 14, which have a larger particle diameter, thereby improving the electrode density of the electrode sheet 10. At least a portion of the surface of each first active material particle 12 is coated with the binder 16. At least a portion of the surface of each second active material particle 14 is coated with the conductive additive 18.

[0024] As described above, the electrode sheet 10 of this embodiment is used as a positive electrode of a lithium ion secondary battery, and therefore the active material particles 12, 14 are positive electrode active material particles. Examples of the active material particles 12, 14 include lithium composite oxides. Examples of lithium composite oxides include lithium nickel composite oxides, lithium cobalt composite oxides, lithium manganese composite oxides, and lithium nickel manganese composite oxides (e.g., LiNi 1 / 2 Mn 3 / 2O4), lithium nickel manganese cobalt composite oxides (e.g., LiNi 1 / 3 Mn 1 / 3 Co 1 / 3 O2). Each of the active material particles 12, 14 may be composed of a single material or a plurality of materials. The compound used as the first active material particles 12 may be the same as or different from the compound used as the second active material particles 14.

[0025] The binder 16 can bind the active material particles 12 and 14 together. Examples of the binder 16 include carboxymethyl cellulose (CMC), styrene butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), acrylic resin, and ultra-high molecular weight polyethylene. The binder 16 may be composed of a single material or multiple materials. In this embodiment, the binder 16 is a fibrillizable resin, and in the electrode sheet 10, the resin is fibrillated. Note that the fibrillizable resin here refers to a resin that can be fibrillated by applying a shear force. Examples of the fibrillizable resin include cellulose, acrylic resin, ultra-high molecular weight polyethylene, and PTFE.

[0026] The conductive additive 18 can form conductive paths extending between the active material particles 12, 14 within the electrode sheet 10. Examples of the conductive additive 18 include carbon materials such as carbon nanotubes, carbon black (e.g., acetylene black, furnace black, ketjen black, etc.), coke, and graphite. The conductive additive 18 may be composed of a single type of material or multiple types of materials.

[0027] The inventors of the present invention have found that the adhesion of the conductive additive 18 (e.g., carbon nanotubes) to the active material particles 12, 14 varies depending on the particle size of the active material particles 12, 14. Specifically, it has been found that the conductive additive 18 adheres more easily to active material particles having a relatively large particle size. For this reason, in this embodiment, as described above, the electrode sheet 10 is produced using two active material particles 12, 14 having different average particle sizes.

[0028] The average particle diameter of the second active material particles 14 is, for example, at least twice the average particle diameter of the first active material particles 12, and for example, at least three times the average particle diameter of the first active material particles 12. The average particle diameter of the first active material particles 12 is not particularly limited, but is, for example, 0.5 μm to 6 μm, for example, 1 μm to 5 μm, or for example, 2 μm to 4 μm. The average particle diameter of the second active material particles 14 is not particularly limited, but is, for example, 7 μm to 13 μm, for example, 8 μm to 12 μm, or for example, 9 μm to 11 μm. The average particle diameter here refers to the particle size at 50% cumulative value (D50) in a volume-based particle size distribution measured by a laser diffraction / scattering method.

[0029] 3-6, a method for manufacturing the electrode sheet 10 will be described. This manufacturing method makes it possible to produce the electrode sheet 10 without using a solvent. In other words, this manufacturing method is a so-called dry process.

[0030] As shown in FIG. 3, the manufacturing method includes a step of mixing a plurality of first active material particles 12 with a binder 16 to produce first coated active material particles (S10). In this step, for example, a mixer 104 is used, as shown in FIG. 4. The mixer 104 mixes the first active material particles 12 and the binder 16 introduced into a container 108 by rotating a blade 106. This produces first coated active material particles in which the binder 16 adheres to the first active material particles 12. That is, in the first coated active material particles, at least a portion of the surface of the first active material particles 12 is coated with the binder 16. In this step, in addition to the first active material particles 12 and the binder 16, other necessary materials may be mixed. However, the conductive additive 18 is not mixed in this step. The absence of the conductive additive 18 allows the first active material particles 12 and the binder 16 to be mixed without considering the influence of the conductive additive 18.

[0031] In this embodiment, the mixer 104 increases the rotation speed of the blades 106 in stages, and mixes the first active material particles 12 and the binder 16 at two different rotation speeds. However, the mixer 104 does not necessarily have to increase the rotation speed of the blades 106 in two stages. In other embodiments, the rotation speed of the blades 106 may be constant or may be increased in three or more stages. Furthermore, it is not necessarily required to use the mixer 104 in S10. In other embodiments, other mixers such as a blender or a mill may be used instead of the mixer 104.

[0032] As shown in FIG. 3, the manufacturing method further includes a step of fibrillating the binder 16 by applying a shear force to the first coated active material particles (S12). In this step, as shown in FIG. 5, for example, a kneader 110 is used. The kneader 110 rotates a blade 112 to apply a shear force to the first coated active material particles present between the blade 112 and the wall surface 114a of the container 114. As described above, since the binder 16 in this embodiment is a fibrillizable resin, the binder 16 constituting the first coated active material particles is fibrillated by applying a shear force to the binder 16. This further improves the tensile strength of the electrode sheet 10. Note that the kneader 110 does not necessarily have to be used in S12. In other embodiments, other mixers such as a blender or mill may be used instead of the kneader 110. Although not particularly limited, the process of S12 may be performed while the container 114 of the kneader is heated to a predetermined temperature.

[0033] As shown in FIG. 3 , the manufacturing method further includes a step of preparing second coated active material particles by mixing the second active material particles 14 with the conductive additive 18 (S14). In this step, as shown in FIG. 4 , for example, a mixer is used. The mixer rotates its blades to mix the second active material particles 14 and the conductive additive 18 placed in a container. This produces second coated active material particles in which the conductive additive 18 is attached to the second active material particles 14. That is, in the second coated active material particles, at least a portion of the surface of the second active material particles 14 is coated with the conductive additive 18. In this step, other necessary materials may be mixed in addition to the second active material particles 14 and the conductive additive 18. As an example, in the present embodiment, PVdF is also mixed in. PVdF is an additive that bonds the second active material particles 14 and the conductive additive 18 when mixing the second active material particles 14 and the conductive additive 18. That is, the PVdF used in this step is not intended to bind the active material particles 12, 14 together in the electrode sheet 10, as is the binder 16 used in S10. Therefore, the amount of PVdF mixed is relatively small, and the conductive additive 18 is not incorporated into the PVdF. Materials other than PVdF may be used as such additives, but it is advisable to avoid fibrillating resins such as PTFE. Furthermore, because the second active material particles 14 have a relatively large average particle diameter, a larger amount of conductive additive 18 can be attached to the second active material particles 14.

[0034] As shown in FIG. 3, the manufacturing method further includes a step of mixing the first coated active material particles and the second coated active material particles to prepare an electrode mixture (S16). In this step, for example, a mixer is used, as shown in FIG. 4. By rotating the mixer blades, the first coated active material particles and the second coated active material particles introduced into the container are mixed together. This produces an electrode mixture. When the electrode mixture is produced in this manner, the conductive additive 18 is less likely to be incorporated into the binder 16, compared to when, for example, the active material particles 12, 14, the binder 16, and the conductive additive 18 are mixed at once to produce an electrode mixture.

[0035] As shown in FIG. 3, the manufacturing method further includes a step of forming the electrode mixture into a sheet (S18). In this step, for example, a press device 116 is used, as shown in FIG. 6. The press device 116 includes a pair of rollers 118 and is configured to roll the electrode mixture passing between the pair of rollers 118. Therefore, the electrode mixture is rolled by the pair of rollers 118 to be formed into a sheet. In this way, an electrode sheet 10 is produced. As described above, the produced electrode sheet 10 is a self-supporting electrode sheet. Note that, although not particularly limited, the process of S18 may be performed in a state in which the pair of rollers 118 is heated at a predetermined temperature.

[0036] According to the above-described manufacturing method, a relatively large amount of the conductive additive 18 can be spread between the active material particles 12, 14 to form conductive paths without reducing the amount of the binder 16 mixed, thereby manufacturing an electrode sheet 10 that is excellent in both tensile strength and conductivity. In addition, since a larger amount of the conductive additive 18 can be attached to the second active material particles 14 in the step (S14) of preparing the second coated active material particles, it is possible to further prevent the conductive additive 18 from being incorporated into the binder 16 when the first coated active material particles and the second coated active material particles are mixed.

[0037] The content of the first active material particles 12 in the electrode mixture is, for example, 45% by weight or more and 49.5% by weight or less, or, for example, 47% by weight or more and 49% by weight or less. The content of the second active material particles 14 in the electrode mixture is, for example, 45% by weight or more and 49.5% by weight or less, or, for example, 47% by weight or more and 49% by weight or less. In the electrode mixture, the weight ratio of the content of the first active material particles 12 to the content of the second active material particles 14 is, for example, 1.1:1, or, for example, 1:1, or, for example, 1:1.1.

[0038] The content of the binder 16 in the electrode mixture is, for example, 0.5% by weight to 5% by weight, or for example, 1% by weight to 3% by weight. The content of the conductive additive 18 in the electrode mixture is, for example, 0.25% by weight to 3% by weight, or for example, 0.5% by weight to 2% by weight. The content of the additive in the electrode mixture is, for example, 0.1% by weight to 2% by weight, or for example, 0.25% by weight to 1% by weight.

[0039] In the above-described manufacturing method, the shear force applied to the binder 16 in the step (S12) of fibrillating the binder 16 is greater than the shear force applied to the plurality of second active material particles 14 and the conductive assistant 18 in the step (S14) of producing the second coated active material particles. With this configuration, the degree of binding between the first active material particles 12 and the binder 16 in the first coated active material particles can be increased. This can improve the tensile strength of the electrode sheet 10.

[0040] As an example, the conductive additive 18 used in the above-described manufacturing method includes at least one selected from the group consisting of carbon nanotubes and acetylene black. Carbon nanotubes have a tubular shape, and acetylene black has a chain structure. When conductive additives 18 having such a shape or structure are used, the conductive additives 18 tend to become entangled with each other, facilitating the formation of conductive paths. On the other hand, when the conductive additives 18 have a tubular shape or a chain structure, the conductive additives 18 tend to be easily incorporated into the binder 16. However, in the present technology, in the step (S14) of preparing second coated active material particles, the conductive additives 18 are pre-attached to the second active material particles 14, thereby effectively preventing the conductive additives 18 from being incorporated into the binder 16.

[0041] Examples of the present technology will be described below, but it is not intended that the present technology be limited to those shown in these examples.

[0042] Example 1 <Ingredient preparation> The first active material particles 12 are LiCo 1 / 3 Ni 1 / 3 Mn 1 / 3 The second active material particles 14 were made of LiCoO2 single crystals (hereinafter referred to as NCM single crystals, average particle diameter: 3 μm). 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 polycrystalline body (hereinafter referred to as NCM polycrystalline body, average particle size: 10 μm) was used. Polytetrafluoroethylene (PTFE, manufactured by Chemours) powder was used as the binder 16. Carbon nanotube (CNT, manufactured by LG Chem) powder was used as the conductive additive 18. Polyvinylidene fluoride (PVdF, manufactured by Arkema) powder was used as the additive. The weight ratio of NCM single crystal body / NCM polycrystalline body / PTFE / CNT / PVdF was 48.7 / 48.7 / 1.4 / 0.75 / 0.5.

[0043] <Preparation of first coated active material particles and fibrillation of PTFE> As shown in FIG. 7A, first, the NCM single crystal and PTFE were placed in a mixer (MP5B, manufactured by Nippon Coke Co., Ltd.) and mixed at 300 rpm for 180 seconds, and then at 5000 rpm for 500 seconds. This produced first coated active material particles. The first coated active material particles were placed in a kneader (DSI-5, manufactured by Nihon Spindle Mfg. Co., Ltd.) and kneaded at 100°C and 10 rpm for 180 seconds. This applied a relatively large shear force to the first coated active material particles, causing the PTFE to fibrillate.

[0044] <Preparation of second coated active material particles> The NCM polycrystalline body, CNT, and PVdF were placed in a mixer (MP5B, manufactured by Nippon Coke Co., Ltd.) and mixed at 10,000 rpm for 10 minutes, thereby producing second coated active material particles.

[0045] <Preparation of electrode mixture> The first coated active material particles and the second coated active material particles were placed in a mixer (MP5B, manufactured by Nippon Coke Co., Ltd.) and mixed at 300 rpm for 1 minute, thereby producing an electrode mixture.

[0046] <Preparation of electrode sheet> The electrode mixture was rolled in a roll press device (SA-602, manufactured by Tester Sangyo Co., Ltd.) at 160°C and a linear pressure of 0.4 t / cm to produce an electrode sheet 10. The thickness of this electrode sheet 10 was 110 μm.

[0047] (Comparative Example 1) <Ingredient preparation> In Comparative Example 1, the active material particles 12 and 14 were changed compared to Example 1. Specifically, in Comparative Example 1, a mixture of the above-mentioned NCM single crystal and the above-mentioned NCM polycrystalline material (hereinafter referred to as the NCM mixture) was used as the active material particles 12 and 14. The other raw materials and weight ratios were the same as those in Example 1.

[0048] <From preparing the electrode mixture to producing the electrode sheet> In Comparative Example 1, the raw materials were mixed at once to prepare an electrode mixture. Specifically, as shown in FIG. 7B, the NCM mixture, PTFE, CNT, and PVdF were placed in the mixer (MP5B, manufactured by Nippon Coke Co.) and mixed at 300 rpm for 180 seconds, followed by mixing at 5000 rpm for 500 seconds. This produced an electrode mixture. The electrode sheet was prepared from the electrode mixture in the same manner as in Example 1.

[0049] (Comparative Example 2) <From preparing the electrode mixture to producing the electrode sheet> Comparative Example 2 is a comparison example in which a kneader treatment was added to Comparative Example 1. That is, as shown in FIG. 7C, the mixture mixed in the mixer in Comparative Example 1 was put into the above-mentioned kneader and kneaded at 100°C and 10 rpm for 180 seconds. In this way, an electrode mixture was produced. The method for producing an electrode sheet from the electrode mixture was the same as in Example 1.

[0050] (Comparative Example 3) <Ingredient preparation> In Comparative Example 3, the active material particles 12 and 14 were changed compared to Example 1. Specifically, in Comparative Example 3, the first active material particles 12 were made of the above-described NCM polycrystalline body, and the second active material particles 14 were made of the above-described NCM single crystal body. The other raw materials and weight ratios were the same as those in Example 1.

[0051] <From preparing the electrode mixture to producing the electrode sheet> As shown in FIG. 7D, in Comparative Example 3, an electrode sheet was produced in the same manner as in Example 1.

[0052] (tensile strength) The electrode sheets prepared by the methods of Example 1 and Comparative Examples 1-3 were punched with a punching die to prepare 4 mm wide dogbone-shaped sample pieces. The sample pieces had a thickness of approximately 5.6 mm. Measurements were performed using a Shimadzu AGS-X, a 50 N load cell, and a 50 N clip-type clamp, with a clamp distance of approximately 4.0 mm and an initial strain rate of 0.33 / s (tensile rate of 1.3 mm / s). The measurement results are shown in Figure 8A.

[0053] 8A, it was found that the tensile strength of the electrode sheet 10 of Example 1 was higher than that of the electrode sheet of Comparative Example 1. Furthermore, the tensile strength of the electrode sheet of Comparative Example 2 was higher than that of the electrode sheet of Comparative Example 1. This suggests that the inclusion of fibrillated PTFE in the electrode mixture improves the tensile strength of the electrode sheet produced from the electrode mixture.

[0054] The tensile strength of the electrode sheet of Comparative Example 3 was lower than the tensile strength of the electrode sheets of Example 1 and Comparative Example 2, and was approximately the same as the tensile strength of the electrode sheet of Comparative Example 1. That is, in Comparative Example 3, although treatment with a kneader was performed as in Example 1 and Comparative Example 2, the results were similar to those of Comparative Example 1, in which treatment with a kneader was not performed. This suggests that, from the perspective of tensile strength, it is advantageous to use active material particles with a small average particle size (NCM single crystal in this case) as the first active material particles 12 and active material particles with a large average particle size (NCM polycrystalline in this case) as the second active material particles 14.

[0055] (electrical resistance) The electrical resistance of sample pieces (φ11.25 mm) of the electrode sheets prepared by the methods of Example 1 and Comparative Examples 1-3 was measured using an electrode resistance measurement system (RM2610, manufactured by Hioki E.E. Corporation). The measurement results are shown in Figure 8B.

[0056] 8B, it was found that the electrical resistance of the electrode sheet 10 of Example 1 was lower than that of the electrode sheet of Comparative Example 2. This indicates that when fibrillating PTFE in the preparation of an electrode composite mixture, mixing NCM single crystal and PTFE, and NCM polycrystalline, CNT, and PVdF separately is more advantageous in terms of the conductivity of the electrode sheet 10 than mixing them all at once. This is thought to be because the incorporation of CNT into PTFE is suppressed, and a relatively large number of CNTs extend between the NCMs, thereby forming sufficient conductive paths within the electrode sheet 10.

[0057] In addition, it was found that the electrical resistance of the electrode sheet of Example 1 was lower than that of the electrode sheet of Comparative Example 3. This suggests that using active material particles (here, NCM single crystals) with a small average particle size as the first active material particles 12 and active material particles (here, NCM polycrystalline) with a large average particle size as the second active material particles 14 is advantageous in terms of the conductivity of the electrode sheet. This is thought to be because CNTs adhere more easily to NCM polycrystalline bodies with a relatively large average particle size than to NCM single crystals with a relatively small particle size. The fact that CNTs adhere more easily to NCM polycrystalline bodies with a relatively large particle size was confirmed by SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectrometry) images of the produced electrode sheet.

[0058] From the above results, it was found that the electrode sheet 10 of Example 1 was superior in both tensile strength and conductivity (herein referred to as electrical resistance) compared to the electrode sheets of Comparative Examples 1-3.

[0059] Although specific examples of the present invention have been described above in detail, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Modifications of the above embodiments are listed below.

[0060] In the above-described embodiment, the present technology has been described using the electrode assembly 100 employed as a positive electrode of a lithium-ion secondary battery as an example. However, the technology disclosed in this specification is not necessarily limited to positive electrodes of lithium-ion secondary batteries, and can also be employed in electrode assemblies employed as negative electrodes of lithium-ion secondary batteries. In this case, the above-described active material particles 12, 14 may be replaced with negative electrode active material particles. Examples of negative electrode active material particles include carbon materials such as graphite, hard carbon, and soft carbon. Furthermore, the electrode assembly 100 of the present technology is not limited to lithium-ion secondary batteries, and can similarly be employed in electrode assemblies (positive or negative electrodes) of any type of secondary battery.

[0061] In the above-described embodiment, the first active material particles 12 are single crystals, and the second active material particles 14 are polycrystalline. However, the crystalline state of each active material particle 12, 14 is not particularly limited as long as the average particle size of the second active material particles 14 is larger than the average particle size of the first active material particles 12.

[0062] 3, the manufacturing method of the electrode assembly 100 includes a step of fibrillating the binder 16 (S12). However, in one modified example, the step of fibrillating the binder 16 may be omitted, in which case a material that cannot be fibrillated may be used for the binder 16.

[0063] In the above-described embodiment, as shown in Fig. 3, in the method for manufacturing the electrode body 100, after the first coated active material particles are produced (S10), the second coated active material particles are produced (S14). However, in one variation, the first active material particles 12 may be produced after the second coated active material particles are produced. That is, in the method for manufacturing the electrode body 100 shown in Fig. 3, S14 may be performed before S10.

[0064] Furthermore, the technical elements described in this specification or drawings exhibit technical utility either alone or in various combinations, and are not limited to the combinations set forth in the claims at the time of filing. Furthermore, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of those objectives is itself technically useful. [Explanation of symbols]

[0065] 10: electrode sheet, 12: first active material particles, 14: second active material particles, 16: binder, 18: conductive additive, 100: electrode body, 102: current collector, 104: mixer, 106: blade, 108: container, 110: kneader, 112: blade, 114: container, 116: press device, 118: roller

Claims

1. A method for manufacturing an electrode sheet, a step of preparing first coated active material particles by mixing a plurality of first active material particles with at least a binder; a step of preparing second coated active material particles by mixing at least a conductive additive with a plurality of second active material particles; mixing the first coated active material particles and the second coated active material particles to prepare an electrode mixture; forming the electrode mixture into a sheet; Equipped with the average particle size of the second active material particles is larger than the average particle size of the first active material particles; Manufacturing method.

2. the first active material particles are single crystals, The manufacturing method according to claim 1 , wherein the second active material particles are polycrystalline.

3. The manufacturing method according to claim 1 , wherein the step of preparing the first coated active material particles includes a step of fibrillating the binder by applying a shear force to the binder.

4. 4. The manufacturing method according to claim 3, wherein in the step of fibrillating the binder, a shear force applied to at least the binder is greater than a shear force applied to the plurality of second active material particles and the conductive additive in the step of producing the second coated active material particles.

5. The method according to claim 1 , wherein the conductive additive comprises at least one selected from the group consisting of carbon nanotubes and acetylene black.

6. The manufacturing method according to claim 1 , wherein the electrode sheet is a free-standing electrode sheet.

7. A battery comprising a plurality of active material particles, a binder, and a conductive additive; the plurality of active material particles include a plurality of first active material particles and a plurality of second active material particles, the average particle size of the second active material particles is larger than the average particle size of the first active material particles; At least a portion of the surface of the first active material particles is coated with the binder, At least a portion of the surface of the second active material particles is coated with the conductive additive. Electrode sheet.

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