Method for manufacturing electrode, electrode, and nonaqueous electrode secondary battery

Abstract

Provided is a method for producing an electrode with which it is possible to obtain a composite material sheet having good stretchability. The method for manufacturing an electrode (10) is characterized by comprising: a composite material sheet manufacturing step for manufacturing a composite material sheet (12) by forming a powder (20) of an electrode composite material containing an active material and a fibrous binder and having a solid content concentration of substantially 100% into a sheet; and a bonding step in which the composite material sheet (12) is bonded to the surface of the core material (11), the binder having, as the main component, polytetrafluoroethylene having a shear bond stress of 40 kPa or less.

Description

Technical Field

[0001] The present disclosure relates to a method for producing an electrode, the electrode, and a nonaqueous electrolyte secondary battery including the electrode. Background Art

[0002] The electrode of a non-aqueous electrolyte secondary battery such as a lithium ion secondary battery is usually made by the following wet method: an electrode composite material slurry comprising an active material, a binder, etc. is applied to the surface of a core material as a metal foil, and the coating is dried and compressed. In this case, there is a problem of migration that easily causes the binder to move during the drying of the coating. If the migration of the binder occurs, the amount of binder at the surface side closer to the core material side of the coating (electrode composite material layer) increases, and the distribution of the binder in the thickness direction of the electrode composite material layer is offset.

[0003] In recent years, dry methods have been studied for producing electrodes by stretching and forming a powder of an electrode composite material into a sheet, then bonding this sheet to a core material. Patent Document 1 discloses an electrode composite material sheet produced by mixing an active material, a fibrillating binder such as polytetrafluoroethylene (PTFE), and a conductive material using a mill and fibrillating the PTFE.

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application No. 2019-512872 Summary of the Invention

[0007] However, when a composite material sheet is produced by a dry process, it is required to have good stretchability. If the sheet has poor stretchability, for example, the productivity of the electrode may be reduced or the strength of the electrode in the thickness direction may be reduced.

[0008] Therefore, an object of the present disclosure is to provide a method for producing an electrode that can obtain a composite material sheet exhibiting good stretchability.

[0009] The manufacturing method of the electrode disclosed in the present invention is characterized in that it includes: a composite material sheet preparation step, in which a powder of an electrode composite material containing an active material and a fibrous binder and having a solid content concentration of substantially 100% is formed into a sheet to prepare the composite material sheet; and a bonding step, in which the aforementioned composite material sheet is bonded to the surface of a core material, wherein the aforementioned binder has polytetrafluoroethylene with a shear bond stress of less than 40 kPa as a main component.

[0010] The electrode disclosed herein is characterized by comprising a core material and a composite material sheet bonded to the surface of the core material, wherein the composite material sheet contains an active material and a fibrous binder, wherein the binder mainly comprises polytetrafluoroethylene having a shear bonding stress of 40 kPa or less.

[0011] The nonaqueous electrolyte secondary battery disclosed herein includes the above-mentioned electrode. The above-mentioned electrode configuration is preferably used for a positive electrode.

[0012] According to the method for producing an electrode disclosed herein, it is possible to provide an electrode including a composite material sheet exhibiting good stretchability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 1 is a cross-sectional view of an electrode as an example of an embodiment.

[0014] Figure 2 A diagram showing the process of preparing an electrode composite material and the process of preparing a composite material sheet from the electrode mixture.

[0015] Figure 3 This is a diagram showing the process of bonding the composite material sheet to the surface of the core material. DETAILED DESCRIPTION

[0016] The following describes the embodiment of the electrode of the present disclosure in detail. The embodiment described below is only an example, and the present disclosure is not limited to the following embodiment. The drawings referred to in the description of the embodiment are schematically recorded, and the size ratios of the components depicted in the drawings should be judged with reference to the following description. In addition, the scheme formed by selectively combining multiple embodiments and modified examples described below is included in the present disclosure.

[0017] The electrode disclosed herein and its manufacturing method are suitable for non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries, but can also be used in storage devices such as batteries or capacitors containing aqueous electrolytes. It should be noted that, in the following, electrodes for non-aqueous electrolyte secondary batteries are cited as examples for explanation. The composition and manufacturing method of the electrode for non-aqueous electrolyte secondary batteries disclosed herein can also be used for negative electrodes, but are particularly preferably used for positive electrodes. The non-aqueous electrolyte secondary battery comprises an electrode body comprising a positive electrode and a negative electrode, and a non-aqueous electrolyte. The non-aqueous electrolyte, for example, comprises a non-aqueous solvent and a lithium salt dissolved in the non-aqueous solvent.

[0018] Figure 1 : is a cross-sectional view of an electrode as an example of an embodiment. Figure 1As shown, the electrode 10 includes a core material 11 and a composite material sheet 12 bonded to the surface of the core material 11. The composite material sheet 12 is preferably bonded to both surfaces of the core material 11. The composite material sheet 12 is produced by forming a powder of an electrode composite material (described later) into a sheet shape, and is bonded to the core material 11 to form an electrode composite material layer. The electrode 10 can be a long strip electrode constituting a wound electrode body or a rectangular electrode constituting a stacked electrode body.

[0019] Core material 11 may be made of metal foil or a film with a metal layer formed on its surface. The thickness of core material 11 is, for example, 5 μm to 20 μm. If electrode 10 is a positive electrode, core material 11 may be made of, for example, a metal foil of aluminum or an aluminum alloy. If electrode 10 is a negative electrode, core material 11 may be made of, for example, a metal foil of copper or a copper alloy.

[0020] The composite material sheet 12 contains an active material and a fibrous binder. The thickness of the composite material sheet 12 for a non-aqueous electrolyte secondary battery is, for example, 50 μm to 150 μm, preferably 80 μm to 140 μm, and more preferably 100 μm to 130 μm.

[0021] Composite material sheet 12 may further contain a conductive material. When composite material sheet 12 constitutes a positive electrode composite material layer, it is particularly preferable to contain a conductive material. Examples of conductive materials contained in composite material sheet 12 include carbon black such as acetylene black and Ketjen black, and carbon materials such as carbon nanotubes (CNTs) and graphite. When electrode 10 is a positive electrode, a suitable content of the conductive material in composite material sheet 12 is, for example, 0.2% by mass or more and 5.0% by mass or less.

[0022] Lithium transition metal composite oxides are generally used as the active material for the positive electrode. Examples of the metal elements contained in the lithium transition metal composite oxide include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among them, it is preferred to contain at least one selected from Ni, Co, and Mn. In particular, as a composition of the lithium transition metal composite oxide, the ratio of Ni in the metal elements other than lithium is preferably 70% or more and 99% or less, more preferably 80% or more and 95% or less. Relative to the mass of the composite material sheet 12, the content of the positive electrode active material is preferably 85% by mass or more and 99% by mass or less, more preferably 90% by mass or more and 99% by mass or less (the suitable content of the negative electrode active material is also the same as the content of the positive electrode active material).

[0023] The positive electrode active material is composed of, for example, secondary particles formed by the aggregation of a plurality of primary particles. The volume-based median particle size (D50) of the positive electrode active material is preferably 3 μm or more and 30 μm or less. D50 refers to the particle size at which the cumulative frequency of the volume-based particle size distribution from the particle with the smallest particle size becomes 50%, and is also called the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction particle size distribution measuring device (e.g., MT3000II manufactured by MicrotracBEL Corp.) using water as the dispersion medium.

[0024] The negative electrode active material may include natural graphites such as flake graphite, bulk graphite, and amorphous graphite, or artificial graphites such as bulk artificial graphite (MAG) and graphitized mesocarbon microbeads (MCMB). Alternatively, the negative electrode active material may contain Si, Sn, or other metals that alloy with lithium.

[0025] The fibrous binder contains polytetrafluoroethylene (PTFE) with a shear bond stress of 40 kPa or less as its main component. The fibrous binder is produced, for example, by fibrillating a granular binder containing PTFE as its main component. In this specification, the term "main component" refers to the constituent with the highest mass ratio.

[0026] However, there is a problem in electrodes that requires increasing the strength of the electrode composite material in the thickness direction of the electrode. By increasing the strength of the electrode composite material in the thickness direction of the electrode, it is sometimes possible to suppress damage to the composite material sheet caused by stress applied to the electrode when manufacturing a wound electrode body, for example. In the manufacturing method of the electrode 10 of the present embodiment described below, the composite material sheet 12 is produced by forming a powder of an electrode composite material having a solid content concentration of substantially 100% into a sheet, a so-called dry method. By making the powder of the electrode composite material contain a fibrous binder whose main component is polytetrafluoroethylene with a shear bonding stress of 40 kPa or less, a composite material sheet 12 with good stretchability is obtained, thereby increasing the strength of the electrode composite material in the thickness direction of the electrode 10. That is, according to the electrode 10 of the present embodiment, it has a composite material sheet 12 containing a fibrous binder whose main component is polytetrafluoroethylene with a shear bonding stress of 40 kPa or less, and therefore has high strength in terms of the strength of the electrode composite material in the thickness direction of the electrode 10.

[0027] When using a positive electrode active material with a high Ni content of 70% or more relative to metal elements other than Li, which reduces the Co content, a cost-increasing factor in the positive electrode active material, the strength of the positive electrode composite sheet and the strength of the electrode composite in the thickness direction of the positive electrode are often insufficient. However, by incorporating a fibrous binder primarily composed of polytetrafluoroethylene with a shear bond stress of 40 kPa or less into the composite sheet, sufficient strength of the positive electrode composite sheet and the strength of the composite sheet in the thickness direction of the positive electrode are achieved. Therefore, when using a positive electrode active material with a high Ni content of 70% or more, using polytetrafluoroethylene with a shear bond stress of 40 kPa or less is extremely effective.

[0028] The method for adjusting the shear bond stress of polytetrafluoroethylene is not particularly limited. In terms of easily adjusting the shear bond stress to 40kPa or less, for example, the method of giving polytetrafluoroethylene a branched structure (also referred to as a branched structure), a cross-linked structure, and a modification thereof can be mentioned. A branched structure refers to a structure having a side chain branched from a main chain. The method of giving a branched structure to the molecules of polytetrafluoroethylene is not particularly limited. For example, the method of irradiating an electron beam or radiation to PTFE particles as a raw material or fibrillated fibrous PTFE can be mentioned. In addition, a cross-linked structure refers to a structure in which the molecules of polytetrafluoroethylene are cross-linked to each other. For example, when synthesizing polytetrafluoroethylene, a cross-linking agent is added to give the molecules of polytetrafluoroethylene a cross-linked structure. Modification refers to copolymerizing tetrafluoroethylene with other monomers.

[0029] The shear bonding stress of polytetrafluoroethylene only needs to be 40 kPa or less. In order to further improve the stretchability of the composite material sheet 12 and further improve the strength of the composite material sheet 12 in the thickness direction of the electrode 10, it is preferably 30 kPa or less, and more preferably 10 kPa or more and 30 kPa or less.

[0030] The shear adhesive stress of polytetrafluoroethylene is measured by the following procedure using, for example, a commercially available powder layer shear force measuring apparatus NS-S500 (manufactured by Nano Seeds Corporation).

[0031] (1) 10 g of a sample (polytetrafluoroethylene) was placed inside a cylindrical unit (upper fixed unit, lower movable unit) with an inner diameter of 15 mm. The upper pestle was lowered to apply a load such that the vertical load on the upper surface became 50 N, thereby forming a compacted powder layer.

[0032] (2) While maintaining the volume of the compacted powder layer while fixing the position of the upper pestle, the lower movable unit is gradually moved horizontally. After the shear stress reaches a maximum and stabilizes, the lower movable unit is lowered downward, gradually and slowly lowering until the shear stress reaches a minimum. The shear stress is plotted against the vertical stress of the bottom load detected at the bottom of the unit to obtain the powder layer failure envelope (PYL curve).

[0033] (3) In the powder layer failure envelope, a straight line is obtained by the least square method from the curve from the critical point where the shear stress becomes maximum to the final point where the shear stress becomes minimum in the measurement.

[0034] (4) The intercept of the obtained straight line becomes the shear adhesive stress of the sample (polytetrafluoroethylene).

[0035] The content of the fibrous binder is preferably 0.1 to 5.0 parts by mass, more preferably 0.2 to 3 parts by mass, and particularly preferably 0.3 to 2 parts by mass, relative to 100 parts by mass of the active material, in order to further improve the stretchability of the composite material sheet 12 and, in turn, to further improve the thickness-direction strength of the electrode 10. Furthermore, the binder has a crystallite size of, for example, 20 nm to 45 nm. The crystallite size of the binder is determined by X-ray diffraction measurement.

[0036] When the composite material sheet 12 is divided into three equal parts in the thickness direction and divided into a first region, a second region, and a third region from the core material 11 side, the content (a) of the binder 22 in the first region, the content (b) of the binder 22 in the second region, and the content (c) of the binder 22 in the third region preferably satisfy (ca) / (a+b+c) ≤ ±10%, and more preferably satisfy (ca) / (a+b+c) ≤ ±5%. According to the manufacturing method of the electrode 10 of this embodiment described later, the binder is prevented from being concentrated in a portion of the composite material sheet 12, and is thus substantially uniformly distributed throughout the composite material sheet 12. Therefore, the binder contents (a), (b), and (c) satisfy the above formula.

[0037] The density of the composite material sheet 12 is not particularly limited. When the composite material sheet 12 constitutes the positive electrode composite material layer, it is preferably 2.5 g / cc to 4.5 g / cc, more preferably 3.0 g / cc to 4.2 g / cc, and particularly preferably 3.0 g / cc to 4.0 g / cc. It should be noted that an intermediate layer may be provided in the electrode 10, sandwiched between the core material 11 and the composite material sheet 12. The intermediate layer may contain, for example, a conductive material and a binder, to improve the bonding strength of the composite material sheet 12 to the core material 11 and reduce interfacial resistance.

[0038] Below, refer to Figure 2 and Figure 3 The following describes a method for manufacturing the electrode 10. Although a method for manufacturing a positive electrode is exemplified below, this method can also be used to manufacture a negative electrode. Figure 2 The process of making an electrode composite material and the process of making a composite material sheet from the electrode mixture are shown. Figure 3 The process of joining the composite material sheet to the core material is shown.

[0039] The electrode 10 is manufactured through the following steps.

[0040] (1) Electrode composite material preparation step: preparing a powder of an electrode composite material containing an active material and a fibrous binder and having a solid content concentration of substantially 100%

[0041] (2) Composite material sheet production step: forming the powder of the electrode composite material into a sheet to produce a composite material sheet 12

[0042] (3) Joining step: Joining the composite material sheet 12 to the surface of the core material 11

[0043] (Electrode composite material production process)

[0044] Figure 2 The electrode composite material powder 20 shown is obtained by, for example, stirring and mixing raw materials such as an active material, a granular binder, and a conductive material in a mixer 30. The solid content concentration of the electrode composite material powder 20 is substantially 100%. The granular binder in the raw materials is stirred and mixed in the mixer 30, thereby fibrillating into a fibrous binder. The content of the fibrous binder (i.e., the content of the granular binder) is as described above.

[0045] The granular binder used in the first process is based on polytetrafluoroethylene (PTFE) as a main component. In the granular binder, components other than PTFE such as polyvinylidene fluoride (PVdF) may also be included within the scope of not damaging the purpose of the present disclosure, but in fact, PTFE may also be included. The average particle size of the granular binder is not particularly limited, and is preferably more than 100 μm and less than 500 μm, more preferably more than 200 μm and less than 400 μm. The average particle size of the granular binder can be obtained by observing the PTFE particles with a scanning electron microscope (SEM). Specifically, on the basis of extracting 100 particles selected at random, the diameter of the circumscribed circle of 100 particles is measured, and each measured value is averaged to obtain.

[0046] As previously mentioned, the polytetrafluoroethylene (PTFE) serving as the main component of the binder has a shear bond stress of 40 kPa or less. For example, when the binder is irradiated with an electron beam or radiation to reduce the shear bond stress of the PTFE to 40 kPa or less, the irradiation can be performed on a granular binder or on a fibrillated fibrous binder. In either case, the shear bond stress of the PTFE contained in the powder 20 of the electrode composite material obtained in the electrode composite material production process is 40 kPa or less.

[0047] A conventionally known mechanical stirring mixer capable of imparting mechanical shearing force can be used as the mixer 30. Specific examples of the mixer 30 include a chopper (such as the Wonder crusher manufactured by OSAKA CHEMICAL Co., Ltd.), a pin mill, a bead mill, a kneading machine (such as a kneader and a Banbury mixer), a planetary mixer, and a microparticle compounding device (a device that generates shearing force between a specially shaped rotor rotating at high speed inside a tank and a collision plate).

[0048] The mixing time (the time during which shearing force is applied to the composite material raw material) in the mixer 30 varies depending on the type of mixer 30, but is preferably within a few minutes, for example, from 0.5 minutes to 10 minutes. The mixing in the mixer 30 may include the following steps: mixing the active material with the conductive material; and mixing the mixture of the active material and the conductive material with the binder.

[0049] The dry mixing of the active material and the conductive material can also be performed using a mechanical fusion method. By applying the mechanical fusion method, the binding force of the conductive material to the particle surface of the active material becomes stronger. Examples of mechanical fusion reaction devices include Nobilta (registered trademark) or Mechanofusion (registered trademark) manufactured by Hosokawa Micron Group, a hybridization system manufactured by Nara Machinery Manufacturing Co., Ltd., a balance gran manufactured by FREUND-TURBO CORPORATION, and a composi manufactured by NIPPON COKE & ENGINEERING.CO.,LTD.

[0050] By stirring and mixing the raw materials using a mixer 30, a powder 20 of an electrode composite material is obtained, which contains an active material, a fibrous binder with polytetrafluoroethylene having an internal friction angle of 45 degrees or more as the main component, and a solid content concentration of substantially 100%. The powder 20 of the electrode composite material obtained by the mixer 30 can be used to make a composite sheet 12, but the powder 20 of the electrode composite material obtained by the mixer 30 can also be supplied to a pair of rollers (not shown) for sheeting, thereby promoting the fibrillation of PTFE. Specifically, the powder 20 of the electrode composite material is supplied to a gap formed between a pair of rollers, thereby being rolled and sheeted by a pair of rollers. By supplying the powder 20 of the electrode composite material to a pair of rollers and sheeting it, the unfibrillated granular binder can be fibrillated in the electrode composite material. The obtained sheet of the electrode composite material is crushed, for example, by a grinder, and restored to the powder 20 of the electrode composite material. The grinder used is a conventionally known one.

[0051] (Composite material sheet production process)

[0052] In the composite material sheet production step, the composite material sheet 12 is produced by a dry process using the electrode composite material powder 20 obtained in the electrode composite material production step.

[0053] In the process of making composite sheets, Figure 2 As shown, the powder 20 of the electrode composite material is supplied to a pair of rollers 31 and rolled through the gap formed between the pair of rollers 31 to produce the positive electrode composite material sheet 12. Figure 2 The rotation axes of the rollers shown are parallel, and the arrows drawn on the rollers indicate the rotation directions of the rollers.

[0054] The thickness of the composite material sheet 12 can be controlled, for example, by adjusting the gap between the rollers, the circumferential speed of the rollers, the number of times the sheet passes through the rollers, and the like. During the composite material sheet production process, different rollers with a circumferential speed ratio of 2 or more can be used to form the electrode composite material powder 20 into a sheet. By varying the circumferential speed ratio of the rollers, thinning the composite material sheet 12 is facilitated, improving productivity. Furthermore, during the composite material sheet production process, the composite material sheet 12 can be compressed at the end. The linear pressure in this case is, for example, from 1 t / cm to 3 t / cm.

[0055] (Joining process)

[0056] The composite material sheet 12 and the core material 11 are joined using, for example, Figure 3 The composite material sheet 12 and the core material 11 are passed between the pair of rollers 32 to obtain the electrode 10 in which the composite material sheet 12 is bonded to the surface of the core material 11. Figure 3In the embodiment, the composite material sheet 12 is bonded to only one surface of the core material 11, but it may be bonded to both surfaces of the core material 11. In this case, the two composite material sheets 12 may be bonded to both surfaces of the core material 11 at the same time, or the first composite material sheet 12 may be bonded to one surface of the core material 11 and then the second composite material sheet 12 may be bonded to the other surface of the core material 11.

[0057] At least one of the pair of rollers 32 may be heated. The temperature of these rollers is preferably between room temperature and 300°C or lower, more preferably between room temperature and 200°C or lower. The linear pressure between the pair of rollers 32 is, for example, between 0.1 t / cm and 2 t / cm or lower. An intermediate layer such as an adhesive layer may be formed on both surfaces of the core material 11 supplied to this joining step.

[0058] The thus obtained electrode 12 may also be subjected to a compression step as needed. Specifically, the electrode 12 may be conveyed to a predetermined gap between a pair of opposing rollers and compressed within this gap. The linear pressure between the pair of rollers compressing the electrode 12 may be, for example, 1 t / cm to 3 t / cm.

[0059] As in the manufacturing method of the electrode 10 of this embodiment, the powder of the electrode composite material having a solid content concentration of substantially 100% used when preparing the composite material sheet 12 by a dry method contains a fibrous binder having polytetrafluoroethylene with a shear bonding stress of less than 40 kPa as the main component, thereby obtaining a composite material sheet 12 with good stretchability, and further improving the strength of the electrode composite material in the thickness direction of the electrode 10.

[0060] Example

[0061] Hereinafter, the present disclosure will be further described based on examples, but the present disclosure is not limited to these examples.

[0062] <Example 1>

[0063] [Production of positive electrode composite material sheet]

[0064] Using a NOB300-Nobilta (registered trademark) manufactured by Hosokawa Micron Group, 1000 g of a lithium transition metal composite oxide containing 89% Ni as a positive electrode active material was mixed with 10 g of carbon black for 5 minutes to produce a carbon-coated positive electrode active material with carbon black attached to the surface of the positive electrode active material particles. This carbon-coated positive electrode active material and PTFE particles (CD097, manufactured by AGC Corporation) with a shear bond stress of 39.0 kPa were placed in a Wonder crusher manufactured by OSAKA Chemical Co., Ltd. at a mass ratio of 101:0.8 and mixed for 2 minutes at room temperature and a rotation speed of 3 on the scale. The Wonder crusher's rotation speed was set to a maximum of 28,000 rpm, with a rotation speed of 10 on the scale being the maximum.

[0065] The mixed mixture is rolled using a pair of opposing rollers to form a sheet, which is then pulverized using a grinder. This process fibrillates the PTFE particles into fibrous PTFE, resulting in a positive electrode composite material in which the carbon-coated positive electrode active material and fibrous PTFE are uniformly dispersed. The resulting positive electrode composite material is a powder with a solids concentration of 100%.

[0066] use Figure 2 The pair of rollers 31 shown here are used to roll the powder of the positive electrode composite material into a sheet to produce a positive electrode composite material sheet. The peripheral speed ratio of the pair of rollers 31 at this time is set to 1:1, and the linear pressure between the pair of rollers 31 is set to 0.1 t / cm. The tensile strength of the positive electrode composite material sheet obtained by the first roll rolling was evaluated. The composite material sheet obtained by the first roll rolling was stretched using a pair of rollers 31 to produce a stretched positive electrode composite material sheet. The peripheral speed ratio of the pair of rollers 31 at this time is set to 1:2, the linear pressure between the pair of rollers 31 is set to 0.5 t / cm, and the gap between the pair of rollers 31 is set to half the film thickness of the positive electrode composite material sheet before stretching, and the stretchability at this time is evaluated. Finally, the obtained positive electrode composite material sheet is passed between two rollers at room temperature and repeatedly stretched until a desired film thickness is reached, thereby obtaining a positive electrode composite material sheet for the positive electrode.

[0067] The stretchability of the positive electrode material sheet obtained by the first roll rolling by the pair of rollers 31 was evaluated based on the following criteria. The results are shown in Table 1.

[0068] ○: The sheet does not break during the process of forming the powder of the positive electrode composite material into a sheet

[0069] ×: The sheet breaks during the process of forming the powder of the positive electrode composite material into a sheet

[0070] The tensile strength of the positive electrode composite material sheet obtained by the first roll rolling was also measured. The tensile strength was measured using a universal testing machine with a transverse tensile fixture at a tensile speed of 2 cm / min. The tensile strength results are shown in Table 1.

[0071] [Production of positive electrode]

[0072] like Figure 3 As shown, the positive electrode composite material sheet and the core material are pressed (linear pressure: 1 t / cm) using a pair of opposing rollers 32 to obtain a positive electrode in which the positive electrode composite material sheet is bonded to both sides of the core material. It should be noted that when the positive electrode composite material sheet (positive electrode composite material layer) is divided into three equal parts along the thickness direction and divided into a first region, a second region, and a third region from the core material side, the fibrous PTFE content (a) in the first region, the fibrous PTFE content (b) in the second region, and the fibrous PTFE content (c) in the third region is (ca) × 100 / (a ​​+ b + c) = 0.01 (1%).

[0073] <Example 2>

[0074] In the preparation of the positive electrode composite material sheet, a positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles with a shear bond stress of 35.4 kPa (DF681, manufactured by Solvay S.A.) were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. Subsequently, the tensile properties of the positive electrode composite material sheet were evaluated and the tensile strength of the positive electrode composite material sheet was measured in the same manner as in Example 1. These results are shown in Table 1.

[0075] <Example 3>

[0076] In the preparation of the positive electrode composite material sheet, a positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles with a shear bond stress of 28.8 kPa (manufactured by Daikin Industries, Ltd., 208) were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. The tensile properties of the positive electrode composite material sheet were evaluated and the tensile strength of the positive electrode composite material sheet was measured in the same manner as in Example 1. These results are shown in Table 1.

[0077] <Example 4>

[0078] In the preparation of the positive electrode composite material sheet, a positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles with a shear bond stress of 22.4 kPa (manufactured by Juhua Group Corporation, JF4DE1201) were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. The tensile properties of the positive electrode composite material sheet were evaluated and the tensile strength of the positive electrode composite material sheet was measured in the same manner as in Example 1. These results are shown in Table 1.

[0079] In addition, in Example 4, the strength of the positive electrode composite material in the thickness direction of the positive electrode was measured according to the following method. The positive electrode was adhered to a 120mm×30mm acrylic plate with the help of double-sided tape to prepare a measurement sample. Using a tacking tester (TACII) manufactured by RHESCA Co., Ltd., a measuring probe with a diameter of 2mm adhered to a double-sided tape was pressed on the surface of the horizontally placed and fixed measurement sample with 400gf for 10 seconds, and then the measuring probe was lifted upward at a speed of 600mm / min to measure the strength of the positive electrode composite material when peeled off. The measured value is used as the strength of the positive electrode composite material in the thickness direction of the positive electrode.

[0080] <Example 5>

[0081] In the preparation of the positive electrode composite material sheet, a positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles (manufactured by The Chemours Company, 640) with a shear bond stress of 16.4 kPa were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. The tensile properties of the positive electrode composite material sheet were evaluated and the tensile strength of the positive electrode composite material sheet was measured in the same manner as in Example 1. These results are shown in Table 1.

[0082] <Example 6>

[0083] In the preparation of the positive electrode composite material sheet, a positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles with a shear bond stress of 15.9 kPa (TF2073Z, manufactured by 3M Co., Ltd.) were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. Subsequently, the tensile properties of the positive electrode composite material sheet were evaluated and the tensile strength of the positive electrode composite material sheet was measured in the same manner as in Example 1. Furthermore, the strength of the positive electrode composite material in the thickness direction of the positive electrode was measured in the same manner as in Example 4. These results are shown in Table 1.

[0084] Comparative Example 1

[0085] In the preparation of the positive electrode composite material sheet, PTFE particles (AGC Co., Ltd., CD123E) with a shear bonding stress of 69.4 kPa were used instead of PTFE particles with a shear bonding stress of 39.0 kPa. A positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1. Then, the tensile properties of the positive electrode composite material sheet were evaluated in the same manner as in Example 1. In addition, the strength of the positive electrode composite material in the thickness direction of the positive electrode was measured in the same manner as in Example 4. These results are shown in Table 1.

[0086] Comparative Example 2

[0087] A positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles with a shear bond stress of 62.5 kPa (TF2035Z, manufactured by 3M Co., Ltd.) were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. The tensile properties of the positive electrode composite material sheet were then evaluated in the same manner as in Example 1. The results are shown in Table 1.

[0088] Comparative Example 3

[0089] A positive electrode composite material sheet and a positive electrode were prepared in the same manner as in Example 1, except that PTFE particles with a shear bond stress of 56.2 kPa (GN7040, manufactured by GFL Co., Ltd.) were used instead of the PTFE particles with a shear bond stress of 39.0 kPa. The positive electrode composite material sheet and the positive electrode were then evaluated for tensile properties in the same manner as in Example 1. The results are shown in Table 1.

[0090] [Table 1]

[0091]

[0092] As shown in Table 1, the tensile properties of the positive electrode composite material sheets of the embodiments are all good. On the other hand, the positive electrode composite material sheets of the comparative examples are all broken and have poor tensile properties. From these results, it can be said that by using a fibrous binder having a shear bonding stress of 40 kPa or less polytetrafluoroethylene as the main component as the binder contained in the powder of the electrode composite material used when making the composite material sheet by a dry method, a composite material sheet showing good tensile properties is obtained. In addition, the strength of the positive electrode composite material in the thickness direction of the positive electrode is higher than that of Comparative Example 1 in Examples 4 and 6. From these results, it can be said that by making the composite material sheet contain a fibrous binder having a shear bonding stress of 40 kPa or less polytetrafluoroethylene as the main component, the strength of the composite material sheet in the thickness direction of the electrode can be improved.

[0093] As for the tensile strength of the composite material sheet, the results of Examples 1 to 6 show that the lower the shear bond stress of polytetrafluoroethylene, the more improved the tensile strength of the composite material sheet.

[0094] [Note]

[0095] Option 1:

[0096] A method for manufacturing an electrode, comprising:

[0097] a composite material sheet production step of forming a powder of an electrode composite material containing an active material and a fibrous binder and having a solid content concentration of substantially 100% into a sheet to produce a composite material sheet; and

[0098] The bonding step is to bond the composite material sheet to the surface of the core material.

[0099] The adhesive contains polytetrafluoroethylene having a shear bonding stress of 40 kPa or less as a main component.

[0100] Option 2:

[0101] According to the method for manufacturing an electrode described in the above-mentioned scheme 1, when the above-mentioned composite material sheet bonded to the surface of the above-mentioned core material is divided into three equal parts in the thickness direction and set as the first region, the second region and the third region from the side of the above-mentioned core material, the content (a) of the above-mentioned binder in the above-mentioned first region, the content (b) of the above-mentioned binder in the above-mentioned second region and the content (c) of the above-mentioned binder in the above-mentioned third region satisfy (ca) / (a+b+c)≤±10%.

[0102] Option 3:

[0103] The method for producing an electrode according to the above embodiment 1 or 2, wherein the content of the binder is 0.1 parts by mass or more and 5.0 parts by mass or less relative to 100 parts by mass of the active material.

[0104] Option 4:

[0105] The method for producing an electrode according to any one of aspects 1 to 3, wherein the active material is a positive electrode active material, and the ratio of Ni in the metal elements other than lithium in the positive electrode active material is 70% or more.

[0106] Option 5:

[0107] An electrode comprising a core material and a composite material sheet bonded to a surface of the core material.

[0108] The composite material sheet comprises an active material and a fibrous binder.

[0109] The adhesive contains polytetrafluoroethylene having a shear bonding stress of 40 kPa or less as a main component.

[0110] Option 6:

[0111] According to the electrode described in the above-mentioned scheme 5, when the above-mentioned composite material sheet is divided into three equal parts along the thickness direction and set as the first region, the second region and the third region from the above-mentioned core material side, the content (a) of the above-mentioned binder in the above-mentioned first region, the content (b) of the above-mentioned binder in the above-mentioned second region and the content (c) of the above-mentioned binder in the above-mentioned third region satisfy (ca) / (a+b+c)≤±10%.

[0112] Option 7:

[0113] The electrode according to the above embodiment 5 or 6, wherein the content of the binder is 0.1 parts by mass or more and 5.0 parts by mass or less relative to 100 parts by mass of the active material.

[0114] Option 8:

[0115] A non-aqueous electrolyte secondary battery comprising the electrode according to any one of the above aspects 5 to 7.

[0116] Description of Reference Numerals

[0117] 10 Electrode, 11 Core material, 12 Composite material sheet, 20 Powder of electrode composite material, 30 Mixer, 31 Roller, 40 1st Roller, 41 2nd Roller, 42 3rd Roller, 43 4th Roller, 44 5th Roller, 45 6th Roller, 46 7th Roller, 47 8th Roller.

Claims

1. A method for manufacturing an electrode, comprising: a composite material sheet production step of forming a powder of an electrode composite material containing an active material and a fibrous binder and having a solid content concentration of substantially 100% into a sheet to produce a composite material sheet; as well as a bonding step of bonding the composite material sheet to the surface of the core material, The adhesive contains polytetrafluoroethylene having a shear bonding stress of 40 kPa or less as a main component.

2. The method for manufacturing an electrode according to claim 1, wherein: When the composite material sheet bonded to the surface of the core material is divided into three equal parts in the thickness direction and is set as the first region, the second region and the third region from the core material side, the content of the adhesive in the first region (a), the content of the adhesive in the second region (b) and the content of the adhesive in the third region (c) satisfy (ca) / (a+b+c)≤±10%.

3. The method for manufacturing an electrode according to claim 1 or 2, wherein: The content of the binder is 0.1 parts by mass or more and 5.0 parts by mass or less relative to 100 parts by mass of the active material.

4. The method for manufacturing an electrode according to claim 1 or 2, wherein: The active material is a positive electrode active material, and a ratio of Ni in metal elements other than lithium in the positive electrode active material is 70% or more.

5. An electrode comprising a core material and a composite material sheet bonded to a surface of the core material. The composite sheet comprises an active substance and a fibrous binder, The adhesive contains polytetrafluoroethylene having a shear bonding stress of 40 kPa or less as a main component.

6. The electrode according to claim 5, wherein When the composite material sheet is divided into three equal parts in the thickness direction and is divided into a first region, a second region, and a third region from the core material side, the content of the binder in the first region (a), the content of the binder in the second region (b), and the content of the binder in the third region (c) satisfy (ca) / (a+b+c)≤±10%.

7. The electrode according to claim 5 or 6, wherein The content of the binder is 0.1 parts by mass or more and 5.0 parts by mass or less relative to 100 parts by mass of the active material. 8 . A non-aqueous electrolyte secondary battery comprising the electrode according to claim 5 .

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