Electrode sheet and method for manufacturing electrode sheet

Abstract

The invention relates to an electrode sheet and a method for manufacturing the electrode sheet. The present invention addresses the problem of improving conductivity while maintaining tensile strength in an electrode sheet. Disclosed is a method for manufacturing an electrode sheet, which comprises: a step for preparing first coated active material particles by mixing at least a binder among a plurality of first active material particles; a step for preparing second coated active material particles by mixing at least a conductive auxiliary agent into the plurality of second active material particles; a step in which the first coated active material particles and the second coated active material particles are mixed to produce an electrode mixture; and a step for molding 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.

Description

Technical Field

[0001] The technology disclosed in this specification relates to electrode sheets and methods for manufacturing electrode sheets. 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 mixing the active material particles and the binder to form an electrode composite material mixture; and a step of manufacturing the electrode sheet from the electrode composite material mixture.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2021-504877 Summary of the Invention

[0006] The problem that the invention aims to solve

[0007] By adding conductive additives to the electrode sheets described above, the conductivity of the electrode sheets can be improved. Conductive additives, such as carbon black or carbon nanotubes, form conductive pathways extending between the active material particles. However, if the conductive additive and binder are mixed together with the active material particles, the conductive additive may be absorbed into the binder. In this case, the amount of conductive additive extending between the active material particles is reduced, thus failing to sufficiently improve the conductivity of the electrode sheets.

[0008] To avoid the aforementioned problems, reducing the amount of adhesive mixed is considered. However, reducing the amount of adhesive mixed may decrease the tensile strength of the electrode sheet. Therefore, to improve the tensile strength of the electrode sheet, for example, fibrillable adhesives such as polytetrafluoroethylene (PTFE) are considered. However, when the adhesive is fibrillated, conductive additives tend to become entangled in the adhesive. As a result, more conductive additives are absorbed into the adhesive, further reducing the amount of conductive additives extending between the active material particles.

[0009] In view of the above-mentioned actual situation, this specification provides a technique for maintaining tensile strength and improving conductivity in an electrode sheet.

[0010] Methods for solving problems

[0011] The technology disclosed in this specification is embodied in a method for manufacturing an electrode sheet. In its first embodiment, the method for manufacturing the electrode sheet includes: a step of mixing at least a binder into a plurality of first active material particles to form first coated active material particles; a step of mixing at least a conductive additive into a plurality of second active material particles to form second coated active material particles; a step of mixing the first coated active material particles and the second coated active material particles to form an electrode composite; and a step of molding the electrode composite into a sheet shape. The average particle size of the second active material particles is larger than the average particle size of the first active material particles.

[0012] The aforementioned manufacturing method includes a step of producing first coated active material particles and a step of producing second coated active material particles. Then, an electrode composite is produced by mixing the first coated active material particles and the second coated active material particles. In the step of producing the first coated active material particles, the mixing of the first active material particles and the binder can be carried out without considering the influence on the conductive additive. On the other hand, in the step of producing the second coated active material particles, the conductive additive can be attached to the second active material particles without considering the influence of the binder. Therefore, in the step of producing the electrode composite, when the first coated active material particles and the second coated active material particles are mixed, the conductive additive is prevented from being absorbed into the binder. In this way, without reducing the amount of binder mixed, a greater amount of conductive additive can extend between the active material particles, forming conductive paths, thus enabling the manufacture of an electrode sheet with excellent tensile strength and conductivity.

[0013] Furthermore, the inventors of this invention have discovered that the ease with which conductive additives (such as carbon nanotubes) adhere to active material particles varies depending on the particle size of the active material particles. Specifically, it is known that conductive additives readily adhere to active material particles with relatively large particle sizes. Based on this, in the aforementioned manufacturing method, during the step of producing the second coated active material particles, a conductive additive is mixed into the second active material particles with a relatively large average particle size. This allows more conductive additive to adhere to the second active material particles, and further suppresses the entry of conductive additives into the adhesive when the first coated active material particles and the second coated active material particles are mixed.

[0014] In the second embodiment, the first active material particle can be a single crystal, as in the first embodiment. In this case, the second active material particle can be a polycrystalline material. This is because the average particle size of a single crystal is smaller than that of a polycrystalline material.

[0015] In a third embodiment, in the first or second embodiment, the step of producing the first coated active material particles may include at least a step of applying shear force to the adhesive to fibrillate the adhesive. According to this configuration, a further improvement in the tensile strength of the electrode sheet can be achieved.

[0016] In the fourth embodiment, in any of the first to third embodiments, the shear force applied to the adhesive during the process of fibrillating the adhesive is greater than the shear force applied to the plurality of second active material particles and the conductive additive during the process of producing the second coated active material particles. According to this configuration, the adhesion between the first active material particles and the adhesive can be improved in the first coated active material particles. This results in an increase in the tensile strength of the electrode sheet.

[0017] In the fifth embodiment, in any of the first to fourth embodiments, the conductive additive may comprise at least one selected from carbon nanotubes and acetylene black. Carbon nanotubes have a tubular shape, and acetylene black has a chain-like structure. When a conductive additive with such a shape or structure is used, the conductive additives easily entangle with each other, facilitating the formation of conductive paths. On the other hand, when the conductive additive has a tubular shape or a chain-like structure, the conductive additive is easily incorporated into the adhesive. However, in this technology, during the process of producing the second coated active material particles, since the conductive additive is pre-attached to the second active material particles, the incorporation of the conductive additive into the adhesive is effectively suppressed.

[0018] In the sixth embodiment, in any of the first to fifth embodiments, the electrode sheet may be a self-supporting electrode sheet. This configuration improves the energy density of the electrode. It should be noted that a self-supporting electrode sheet refers to an electrode sheet that is supported by itself without requiring a support (e.g., a current collector).

[0019] The technology disclosed in this specification is also embodied in an electrode sheet. This electrode sheet can be manufactured using the manufacturing method described above. For example, according to a seventh embodiment, the electrode sheet includes a plurality of active material particles, a binder, and a conductive additive. The plurality of active material particles comprises 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. As described above, the electrode sheet manufactured using this technology has excellent tensile strength and conductivity.

[0020] In the eighth embodiment, in the seventh embodiment, the first active material particle can be a single crystal. In this case, the second active material particle can be a polycrystalline material.

[0021] In the ninth embodiment, in the seventh or eighth embodiment, the adhesive may be a fibrillated resin. With this configuration, a further increase in the tensile strength of the electrode sheet can be achieved.

[0022] In the tenth embodiment, in any one of the seventh to ninth embodiments, the conductive additive may comprise at least one selected from carbon nanotubes and acetylene black. According to this configuration, the conductivity of the electrode sheet is improved by the conductive additive having a tubular or chain-like structure.

[0023] In the eleventh embodiment, in any one of the seventh to tenth embodiments, the electrode sheet may be a self-standing electrode sheet. With this configuration, the energy density of the electrode can be increased. Attached Figure Description

[0024] Figure 1 A diagram is provided to schematically illustrate the configuration of the electrode body 100 employing the electrode sheet 10.

[0025] Figure 2 A diagram showing the general structure of electrode plate 10 is provided.

[0026] Figure 3 This is a flowchart illustrating the manufacturing method of electrode sheet 10.

[0027] Figure 4 This diagram illustrates the process of using mixer 104 to mix PTFE in an NCM single crystal to create first coated active material particles.

[0028] Figure 5 This diagram illustrates the process of using a kneader 110 to apply shear force to PTFE to fibrillate it.

[0029] Figure 6 This diagram illustrates the process of forming an electrode composite material mixture into a sheet using a pressing device 116.

[0030] Figure 7A This is a flowchart illustrating the manufacturing method of the electrode sheet 10 in Example 1.

[0031] Figure 7B This is a flowchart illustrating the manufacturing method of the electrode sheet in Comparative Example 1.

[0032] Figure 7C This is a flowchart illustrating the manufacturing method of the electrode sheet in Comparative Example 2.

[0033] Figure 7D This is a flowchart illustrating the manufacturing method of the electrode sheet in Comparative Example 3.

[0034] Figure 8A The evaluation results of tensile strength of Example 1 and Comparative Examples 1-3 are shown.

[0035] Figure 8B The evaluation results of the resistance of Example 1 and Comparative Examples 1-3 are shown.

[0036] Explanation of reference numerals in the attached figures

[0037] 10: Electrode sheet; 12: First active material particle; 14: Second active material particle; 16: Adhesive; 18: Conductive additive; 100: Electrode body; 102: Current collector; 104: Mixer; 106: Blade; 108: Container; 110: Kneader; 112: Blade; 114: Container; 116: Pressing device; 118: Roller Detailed Implementation

[0038] The electrode sheet 10 of this embodiment will be described with reference to the accompanying drawings. The electrode sheet 10 of this embodiment is used in the electrode body 100. The electrode body 100 is used, for example, as the positive electrode of a lithium-ion secondary battery.

[0039] like Figure 1 As shown, the electrode body 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 thickness of the current collector 102 is, 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 self-supporting electrode sheet. Here, "self-supporting electrode sheet" means an electrode sheet that does not require a support such as a current collector 102 and can be supported by itself. Therefore, the electrode body 100 may not necessarily include a current collector 102. That is, as another embodiment, the electrode sheet 10 can constitute the electrode body 100 independently. The thickness of the electrode sheet 10 is, for example, 10 μm or more and 500 μm or less.

[0040] like Figure 2 As shown, the electrode sheet 10 includes a plurality of active material particles 12 and 14, an adhesive 16, and a conductive additive 18. The plurality of active material particles 12 and 14 include 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 size of the second active material particles 14 is larger than the average particle size of the first active material particles 12. Thus, the smaller first active material particles 12 can enter the gaps between the larger second active material particles 14, thereby increasing 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 adhesive 16. At least a portion of the surface of each second active material particle 14 is coated with the conductive additive 18.

[0041] As described above, the electrode sheet 10 of this embodiment serves as the positive electrode of a lithium-ion secondary battery, therefore, each active material particle 12, 14 is a positive electrode active material particle. Examples of 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 / 2 O4), lithium nickel manganese cobalt composite oxides (e.g., LiNi) 1 / 3 Mn 1 / 3Co 1 / 3 O2), etc. Each active substance particle 12, 14 can be composed of one material or multiple materials. In addition, the compound used as the first active substance particle 12 can be the same as or different from the compound used as the second active substance particle 14.

[0042] The adhesive 16 binds the active material particles 12 and 14 together. Examples of adhesives 16 include carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), acrylic resins, and ultra-high molecular weight polyethylene. The adhesive 16 may be composed of one material or multiple materials. In this embodiment, the adhesive 16 is a fibrillable resin, which has been fibrillated in the electrode sheet 10. It should be noted that the term "fibrillable resin" here refers to a resin that can be fibrillated by applying shear force. Examples of fibrillable resins include cellulose, acrylic resins, ultra-high molecular weight polyethylene, and PTFE.

[0043] The conductive additive 18 can form conductive paths extending between the active material particles 12 and 14 within the electrode sheet 10. Examples of conductive additives 18 include carbon nanotubes, carbon black (e.g., acetylene black, furnace black, Ketjen black, etc.), coke, graphite, and other carbon materials. The conductive additive 18 can be composed of one material or multiple materials.

[0044] The inventors of this application have discovered that the ease with which the conductive additive 18 (e.g., carbon nanotubes) adheres to the active material particles 12 and 14 varies depending on the particle size of the active material particles 12 and 14. Specifically, it is known that the conductive additive 18 readily adheres to active material particles with a relatively large particle size. Therefore, in this embodiment, as described above, two active material particles 12 and 14 with different average particle sizes are used to fabricate the electrode sheet 10.

[0045] The average particle size of the second active material particle 14 is, for example, more than twice the average particle size of the first active material particle 12, or, for example, more than three times the average particle size of the first active material particle 12. The average particle size of the first active material particle 12 is not particularly limited, and may be, for example, 0.5 μm or more and 6 μm or less, or, for example, 1 μm or more and 5 μm or less, or, for example, 2 μm or more and 4 μm or less. The average particle size of the second active material particle 14 is not particularly limited, and may be, for example, 7 μm or more and 13 μm or less, or, for example, 8 μm or more and 12 μm or less, or, for example, 9 μm or more and 11 μm or less. It should be noted that the average particle size referred to herein means the particle size (D50) at the 50% cumulative value in the volumetric particle size distribution determined by laser diffraction and scattering.

[0046] Secondly, refer to Figure 3-6 The manufacturing method of electrode sheet 10 will be described. In this manufacturing method, electrode sheet 10 can be manufactured without the use of solvents. That is, this manufacturing method is a so-called dry process.

[0047] like Figure 3 As shown, the manufacturing method includes a step (S10) of mixing an adhesive 16 into a plurality of first active material particles 12 to form first coated active material particles. In this step, as... Figure 4 As shown, mixer 104 is used, for example. Mixer 104 mixes the first active material particles 12 and adhesive 16 fed into container 108 by rotating blades 106. This creates a first coated active material particle to which adhesive 16 is attached. That is, in the first coated active material particle, at least a portion of the surface of the first active material particle 12 is coated with adhesive 16. In this process, other desired materials besides the first active material particles 12 and adhesive 16 can be mixed together. However, conductive additive 18 is not mixed in this process. Since conductive additive 18 is absent, the mixing of the first active material particles 12 and adhesive 16 can be performed without considering the effect on conductive additive 18.

[0048] In this embodiment, the mixer 104 can increase the rotational speed of the blades 106 in stages, using two different rotational speeds to mix the first active material particles 12 and the binder 16. However, the mixer 104 may not necessarily increase the rotational speed of the blades 106 in two stages. As another embodiment, the rotational speed of the blades 106 may be constant or increased in three or more stages. Furthermore, the mixer 104 may not be used in S10. In other embodiments, other mixers such as blenders or mills may be used instead of the mixer 104.

[0049] like Figure 3As shown, the manufacturing method further includes a step (S12) of applying shear force to the first coated active material particles to fibrillate the adhesive 16. In this step, as... Figure 5 As shown, a kneader 110 is used, for example. The kneader 110 applies shear force to the first coated active material particles existing between the blades 112 and the wall 114a of the container 114 by rotating the blades 112. As described above, the adhesive 16 in this embodiment is a fibrillable resin; therefore, by applying shear force to the adhesive 16 constituting the first coated active material particles, the adhesive 16 is fibrillated. This allows for a further increase in the tensile strength of the electrode sheet 10. It should be noted that the kneader 110 is not necessarily used in S12. In another embodiment, a mixer, mill, or other mixer can be used instead of the kneader 110. It should be noted that, without particular limitation, the processing in S12 can be performed while the container 114 of the kneader is heated at a specified temperature.

[0050] like Figure 3 As shown, the manufacturing method further includes a step (S14) of mixing a conductive additive 18 into the second active material particles 14 to form second coated active material particles. In this step, as... Figure 4 As shown, a mixer is used, for example. The mixer mixes the second active material particles 14 and the conductive additive 18 placed in the container by rotating the blades. This creates a second coated active material particle to which the conductive additive 18 is attached. That is, in the second coated active material particle, at least a portion of the surface of the second active material particle 14 is coated with the conductive additive 18. In this process, other desired materials besides the second active material particles 14 and the conductive additive 18 can be mixed together. As an example, PVdF is mixed together in this embodiment. PVdF is an additive used to bind the second active material particles 14 and the conductive additive 18 together in the mixing of the second active material particles 14 and the conductive additive 18. That is, the PVdF used in this process is not intended for bonding the active material particles 12 and 14 in the electrode sheet 10, as the adhesive 16 used in S10. Therefore, the amount of PVdF mixed is relatively small, and the conductive additive 18 is not absorbed into the PVdF. As such an additive, materials other than PVdF can be used, and it is preferable to avoid fibrillable resins such as PTFE. In addition, since the second active material particles 14 have a relatively large average particle size, more conductive additives 18 can be attached to the second active material particles 14.

[0051] like Figure 3 As shown, the manufacturing method further includes a step (S16) of mixing first coated active material particles with second coated active material particles to form an electrode composite. In this step, as... Figure 4As shown, a mixer is used, for example. By rotating the blades of the mixer, the first coated active material particles and the second coated active material particles, which are introduced into the container, are mixed. This produces an electrode composite mixture. When producing the electrode composite mixture in this way, for example compared to mixing the active material particles 12, 14, the binder 16, and the conductive additive 18 together to produce the electrode composite mixture, the conductive additive 18 is less likely to be absorbed into the binder 16.

[0052] like Figure 3 As shown, the manufacturing method further includes a step (S18) of molding the electrode composite mixture into a sheet shape. In this step, as... Figure 6 As shown, for example, a pressing device 116 is used. The pressing device 116 includes a pair of rollers 118, configured to calender the electrode compound mixture passing between the pair of rollers 118. Therefore, the electrode compound mixture is calendered by the pair of rollers 118, thereby forming a sheet. Thus, an electrode sheet 10 is produced. As described above, the produced electrode sheet 10 is a self-standing electrode sheet. It should be noted that, without particular limitation, the processing in S18 can be performed while the pair of rollers 118 are heated at a specified temperature.

[0053] According to the manufacturing method described above, a greater amount of conductive additive 18 can be extended between the active material particles 12 and 14 to form a conductive path without reducing the amount of binder 16 mixed, thus enabling the manufacture of an electrode sheet 10 with excellent tensile strength and conductivity. Furthermore, since more conductive additive 18 can be attached to the second active material particles 14 during the process of producing the second coated active material particles (S14), the mixing of the first coated active material particles and the second coated active material particles further inhibits the conductive additive 18 from being absorbed into the binder 16.

[0054] 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, and also, 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, and also, 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, and also, for example, 1:1 or 1:1.1.

[0055] The content of binder 16 in the electrode composite mixture is, for example, 0.5% by weight or more and 5% by weight or less, and also, for example, 1% by weight or more and 3% by weight or less. The content of conductive additive 18 in the electrode composite mixture is, for example, 0.25% by weight or more and 3% by weight or less, and also, for example, 0.5% by weight or more and 2% by weight or less. The content of additive in the electrode composite mixture is, for example, 0.1% by weight or more and 2% by weight or less, and also, for example, 0.25% by weight or more and 1% by weight or less.

[0056] In the above manufacturing method, the shear force applied to the adhesive 16 in the fibrillation step (S12) is greater than the shear force applied to the plurality of second active material particles 14 and the conductive additive 18 in the step of producing the second coated active material particles (S14). With this configuration, the adhesion between the first active material particles 12 and the adhesive 16 can be improved in the first coated active material particles. Therefore, the tensile strength of the electrode sheet 10 can be increased.

[0057] As an example, the conductive additive 18 used in the above manufacturing method comprises at least one selected from carbon nanotubes and acetylene black. Carbon nanotubes have a tubular shape, and acetylene black has a chain-like structure. When a conductive additive 18 with such a shape or structure is used, the conductive additive 18 is easily entangled with each other, making the formation of conductive paths easier. On the other hand, when the conductive additive 18 has a tubular shape or a chain-like structure, the conductive additive 18 is easily incorporated into the adhesive 16. However, in this technology, in the step (S14) of producing the second coated active material particles, the conductive additive 18 is pre-attached to the second active material particles 14, thus effectively preventing the conductive additive 18 from being incorporated into the adhesive 16.

[0058] The following describes embodiments related to this technology, but it is not intended to limit this technology to the content shown in these embodiments.

[0059] (Example 1)

[0060] <Preparation of Raw Materials>

[0061] As the first active material particle 12, LiCo was used. 1 / 3 Ni 1 / 3 Mn 1 / 3 O2 single crystal (hereinafter referred to as NCM single crystal, average particle size: 3μm). LiCo was used as the second active material particle 14. 1 / 3 Ni 1 / 3 Mn 1 / 3O2 polycrystalline material (hereinafter referred to as NCM polycrystalline material, average particle size: 10 μm). Polytetrafluoroethylene (PTFE, Chemours) powder was used as the binder 16. Carbon nanotube (CNT, LG Chem) powder was used as the conductive agent 18. Polyvinylidene fluoride (PVdF, Arkema SA) powder was used as the additive. The weight ratio of NCM single crystal / NCM polycrystalline material / PTFE / CNT / PVdF was 48.7 / 48.7 / 1.4 / 0.75 / 0.5.

[0062] <Preparation of the first coated active material particles and fibrillation of PTFE>

[0063] like Figure 7A As shown, firstly, NCM single crystals and PTFE were fed into a mixer (MP5B, manufactured by Nippon Kogyo Kogyo Co., Ltd.) and mixed at 300 rpm for 180 seconds, followed by mixing at 5000 rpm for 500 seconds. This produced the first coated active material particles. The first coated active material particles were then fed into a kneader (DSI-5, manufactured by Spindle Manufacturing Co., Ltd., Japan) and kneaded at 100°C and 10 rpm for 180 seconds. This imparted a relatively large shear force to the first coated active material particles, fibrillating the PTFE.

[0064] <Preparation of the Second Coated Active Material Particles>

[0065] NCM polycrystalline material, CNT, and PVdF were fed into a mixer (MP5B, manufactured by Nippon Kogyo Co., Ltd.) and mixed at 10,000 rpm for 10 minutes. This produced second-coated active material particles.

[0066] <Preparation of Electrode Material Mixture>

[0067] The first and second coated active material particles were fed into a mixer (manufactured by Nippon Kogyo Co., Ltd., MP5B) and mixed at 300 rpm for 1 minute. This produced an electrode composite material mixture.

[0068] <Electrode Fabrication>

[0069] Electrode sheet 10 was fabricated by calendering the electrode composite material mixture using a roll forming device (Tester Sangyo SA-602) at 160°C and a linear pressure of 0.4 t / cm. The thickness of electrode sheet 10 is 110 μm.

[0070] (Comparative Example 1)

[0071] <Preparation of Raw Materials>

[0072] 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-described NCM single crystal and the above-described NCM polycrystalline material (hereinafter referred to as NCM mixture) was used as the active material particles 12 and 14. It should be noted that the other raw materials and weight ratios were the same as in Example 1.

[0073] <From the fabrication of electrode composite materials to the fabrication of electrode sheets>

[0074] In Comparative Example 1, the raw materials were mixed together to prepare an electrode composite material. That is, as shown... Figure 7B As shown, the NCM mixture, PTFE, CNT, and PVdF were added to the aforementioned mixer (MP5B, manufactured by Nippon Kogyo Co., Ltd.), and mixed at 300 rpm for 180 seconds, followed by mixing at 5000 rpm for 500 seconds. This produced an electrode composite material mixture. The method for fabricating electrode sheets from the electrode composite material mixture was the same as in Example 1.

[0075] (Comparative Example 2)

[0076] <From the fabrication of electrode composite materials to the fabrication of electrode sheets>

[0077] Comparative Example 2 adds a kneading process to Comparative Example 1. That is, as... Figure 7C As shown, in Comparative Example 2, the mixture prepared using a mixer was fed into the aforementioned kneader and kneaded at 100°C and 10 rpm for 180 seconds. This produced an electrode material mixture. The method for preparing electrode sheets from the electrode material mixture was the same as in Example 1.

[0078] (Comparative Example 3)

[0079] <Preparation of Raw Materials>

[0080] In Comparative Example 3, compared with Example 1, the active material particles 12 and 14 were changed. Specifically, in Comparative Example 3, the above-described NCM polycrystalline material was used as the first active material particle 12, and the above-described NCM single crystal was used as the second active material particle 14. It should be noted that the other raw materials and weight ratios were the same as in Example 1.

[0081] <From the fabrication of electrode composite materials to the fabrication of electrode sheets>

[0082] like Figure 7D As shown, in Comparative Example 3, the electrode sheet was fabricated using the same method as in Example 1.

[0083] (Tensile strength)

[0084] Electrode sheets prepared using the methods of Example 1 and Comparative Examples 1-3 were punched using a punching tool to produce dog-bone shaped sample sheets with a width of 4 mm. The thickness of the sample sheets was approximately 5.6 mm. As the measuring apparatus, a Shimadzu AGS-X sensor, a 50 N force sensor, and a 50 N clamp-type fixture were used. The measurement was performed with a clamp spacing of approximately 4.0 mm and an initial strain rate of 0.33 mm / s (tensile speed 1.3 mm / s). The measurement results are shown below. Figure 8A .

[0085] Depend on Figure 8A The results show that the tensile strength of the electrode sheet 10 in Example 1 is higher than that of the electrode sheet in Comparative Example 1. Furthermore, the tensile strength of the electrode sheet in Comparative Example 2 is higher than that of the electrode sheet in Comparative Example 1. Therefore, it can be said that by including fibrillated PTFE in the electrode composite mixture, the tensile strength of the electrode sheet made from the electrode composite mixture is improved.

[0086] The tensile strength of the electrode sheet in Comparative Example 3 was lower than that of the electrode sheets in Examples 1 and 2, but to the same extent as that of the electrode sheet in Comparative Example 1. That is, although Comparative Example 3 underwent a kneading process similar to Examples 1 and 2, it resulted in the same outcome as Comparative Example 1, which did not undergo the kneading process. Therefore, it can be said that using active material particles with a small average particle size (in this case, NCM single crystals) as the first active material particle 12 and using active material particles with a large average particle size (in this case, NCM polycrystals) as the second active material particle 14 is advantageous from the viewpoint of tensile strength.

[0087] (resistance)

[0088] The resistance of sample electrode sheets (φ11.25 mm) prepared using the methods of Examples 1 and Comparative Examples 1-3 was measured using an electrode resistance measurement system (Hioki Electric Co., Ltd., RM2610). The measurement results are shown below. Figure 8B .

[0089] Depend on Figure 8B The results shown indicate that the resistance of electrode sheet 10 in Example 1 is lower than that of electrode sheet in Comparative Example 2. Therefore, it can be said that when PTFE is fibrillated during the fabrication of the electrode composite, mixing NCM single crystals and PTFE, as well as NCM polycrystals, CNTs, and PVdF separately, is advantageous from the viewpoint of electrode sheet 10's conductivity compared to mixing them together. This is believed to be because the incorporation of CNTs into PTFE is suppressed, resulting in more CNTs extending between NCM particles, thereby forming sufficient conductive paths within electrode sheet 10.

[0090] Furthermore, it is known that the resistance of the electrode sheet in Example 1 is lower than that of the electrode sheet in Comparative Example 3. Therefore, it can be said that using active material particles with a small average particle size (in this case, NCM single crystals) as the first active material particle 12 and using active material particles with a large average particle size (in this case, NCM polycrystals) as the second active material particle 14 is advantageous from the viewpoint of electrode sheet conductivity. This is believed to be because CNTs are more likely to adhere to NCM polycrystals with a relatively large average particle size than to NCM single crystals with a relatively small particle size. This can be confirmed from the SEM-EDS (Scanning Electron Microscope-Energy Dispersive X-ray Spectrometry) images of the fabricated electrode sheet, which show that CNTs readily adhere to NCM polycrystals with a relatively large particle size.

[0091] The results above show that the electrode sheet 10 of Example 1 has superior tensile strength and conductivity (resistance) compared with the electrode sheets of Comparative Examples 1-3.

[0092] The specific examples of the present invention have been described in detail above, but these are merely illustrative and do not limit the scope of the patent claims. The technology described in the patent claims includes various modifications and alterations to the specific examples described above. The following are examples of modifications to the above embodiments.

[0093] In the above embodiments, the present technology has been described using electrode 100, which is used as the positive electrode of a lithium-ion secondary battery, as an example. However, the technology disclosed in this specification is not necessarily limited to the positive electrode of a lithium-ion secondary battery; it can also be used as the negative electrode of a lithium-ion secondary battery. In this case, the active material particles 12 and 14 described above can be used as 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 100 of the present technology is not limited to lithium-ion secondary batteries; it can be used in the same way for electrode bodies (positive or negative electrodes) of any type of secondary battery.

[0094] In the above embodiments, the first active material particle 12 is a single crystal, and the second active material particle 14 is a polycrystalline material. However, as long as the average particle size of the second active material particle 14 is larger than the average particle size of the first active material particle 12, there is no particular limitation on the crystallization state of each active material particle 12 and 14.

[0095] In the above implementation methods, such as Figure 3As shown, the manufacturing method of electrode body 100 includes a step of fibrillating adhesive 16 (S12). However, in a modified example, the step of fibrillating adhesive 16 can be omitted. In this case, a material that cannot be fibrillated can be used for adhesive 16.

[0096] In the above implementation methods, such as Figure 3 As shown, in the method for manufacturing the electrode body 100, after the first coated active material particles are formed (S10), the second coated active material particles are formed (S14). However, in a modified example, the first coated active material particles can be formed after the second coated active material particles are formed. That is, in Figure 3 In the manufacturing method of the electrode body 100 shown, S14 can be performed before S10.

[0097] Furthermore, the technical elements described in this specification or drawings may be technically useful individually or in various combinations, and are not limited to the combinations recited in the claims at the time of application. Additionally, the technologies illustrated in this specification or drawings can simultaneously achieve multiple objectives, and achieving one of these objectives is itself technically useful.

Claims

1. A method for manufacturing an electrode sheet, comprising: a process of mixing at least a binder in a plurality of first active material particles to produce first coated active material particles; a process of mixing at least a conductive aid in a plurality of second active material particles to produce second coated active material particles; a process of mixing the first coated active material particles and the second coated active material particles to produce an electrode mixture; a process of molding the electrode mixture into a sheet shape, wherein an average particle diameter of the second active material particles is larger than an average particle diameter of the first active material particles.

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

3. The manufacturing method according to claim 1, wherein, The process of producing the first coated active material particles includes a process of at least applying a shear force to the binder to fibrillate the binder.

4. The manufacturing method according to claim 3, wherein, The shear force applied to the binder in the process of fibrillating the binder is larger than a shear force applied to the plurality of second active material particles and the conductive aid in the process of producing the second coated active material particles.

5. The manufacturing method according to claim 1, wherein, The conductive aid includes at least one selected from a carbon nanotube and acetylene black.

6. The production method according to claim 1, wherein The electrode sheet is a self-supporting electrode sheet.

7. An electrode sheet, comprising a plurality of active material particles, a binder, and a conductive aid, the plurality of active material particles including a plurality of first active material particles and a plurality of second active material particles, an average particle diameter of the second active material particles being larger than an average particle diameter of the first active material particles, at least a portion of a surface of the first active material particles being coated with the binder, at least a portion of a surface of the second active material particles being coated with the conductive aid.

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