Electrode and method for manufacturing an electrode

Abstract

The present invention provides an electrode which is capable of reducing the interface resistance, while ensuring the strength of a core material by suppressing the amount of biting of an active material into the core material. An electrode according to one embodiment of the present disclosure comprises a core material, an electrode mixture that is superposed on the surface of the core material, and a conductive bonding layer that is formed between the core material and the electrode mixture; the electrode mixture comprises an active material and a fibrous binder; the active material bites into the core material; the maximum bite depth is 20% or less of the thickness of the core material; and the ratio of the density of the active material in the electrode mixture to the true density of the active material is 70% or more.

Description

Technical Field

[0001] The present disclosure relates to an electrode and a method for manufacturing the electrode.

Background Art

[0002] The electrodes of non-aqueous electrolyte secondary batteries such as lithium-ion batteries are generally produced by a wet method in which an electrode mixture slurry containing an active material, a binder, etc. is applied to the surface of a core material which is a metal foil, and the coating film is dried and compressed. In this case, there is a problem that migration in which the binder moves during drying of the coating film easily occurs. When migration of the binder occurs, the amount of the binder becomes larger on the surface side than on the core material side of the coating film (electrode mixture layer), and a bias occurs in the distribution of the binder in the thickness direction of the electrode mixture layer.

[0003] In recent years, a dry method has been studied in which an electrode mixture sheet is produced by rolling an electrode mixture and forming it into a sheet shape, and the sheet is bonded to a core material to manufacture an electrode. Patent Document 1 discloses an electrode film (electrode mixture) produced by fibrillating a binder by using a mill to mix an active material, a particulate binder, and a conductive material, and then applying a large shearing force to this mixture at a high pressure for a long time.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As a result of our investigations, we found that when bonding the electrode composite sheet disclosed in Patent Document 1 to a core material, increasing the linear pressure allows the active material contained in the electrode composite to penetrate the core material, thereby reducing the interfacial resistance of the electrode. However, we also found that this penetration of the active material reduces the strength of the core material. The technology disclosed in Patent Document 1 does not consider reducing the amount of penetration of the active material into the core material while ensuring the strength of the core material and reducing interfacial resistance, and there is still room for improvement.

[0006] Therefore, the purpose of this disclosure is to provide an electrode that can reduce interfacial resistance while ensuring the strength of the core material by reducing the amount of penetration of the active material into the core material. [Means for solving the problem]

[0007] An electrode according to one aspect of the present disclosure comprises a core material, an electrode composite laminated on the surface of the core material, and a conductive adhesive layer formed between the core material and the electrode composite, wherein the electrode composite comprises an active material and a fibrous binder, the active material is embedded in the core material, the maximum embedding depth is 20% or less of the thickness of the core material, and the ratio of the density of the active material in the electrode composite to the true density of the active material is 70% or more.

[0008] A method for manufacturing an electrode according to one aspect of the present disclosure is characterized by comprising: a mixing step of mixing an active material, a conductive material, and a fibrous binder to produce electrode composite particles having a solid content of substantially 100%; a rolling step of rolling the electrode composite particles into a sheet to produce an electrode composite sheet; a compression step of compressing the electrode composite sheet to produce a high-density electrode composite sheet; and a bonding step of bonding the high-density electrode composite sheet to a core material to produce an electrode. [Effects of the Invention]

[0009] According to one aspect of this disclosure, in an electrode, the interfacial resistance can be reduced while ensuring the strength of the core material. [Brief explanation of the drawing]

[0010] [Figure 1] This is a cross-sectional view of an electrode, which is an example of an embodiment. [Figure 2] Figure 1 is a schematic diagram showing a cross-section with the active material visible, and a magnified view of the area near the core material. [Figure 3] In an example of an electrode manufacturing process, (a) is a diagram showing the mixing step, and (b) is a diagram showing the rolling step. [Figure 4] This figure shows a compression step in the manufacturing process of an electrode, which is an example of an embodiment. [Figure 5] This figure shows a bonding step in the manufacturing process of an electrode, which is an example of an embodiment.

[0011] The embodiments of the electrode and the method for manufacturing the electrode according to this disclosure will be described in detail below. The embodiments described below are merely examples, and this disclosure is not limited to these embodiments. Furthermore, the drawings referenced in the description of the embodiments are schematic, and the dimensional ratios of the components drawn in the drawings should be determined by referring to the following description.

[0012] [electrode] The electrodes described herein are suitable for non-aqueous electrolyte secondary batteries such as lithium-ion batteries, but can also be applied to batteries containing aqueous electrolytes or energy storage devices such as capacitors. In the following, an example of an electrode for a non-aqueous electrolyte secondary battery (particularly when applied to the positive electrode) will be given.

[0013] Figure 1 is a cross-sectional view of an electrode, which is an example of an embodiment. The electrode 10 includes a core material 11, an electrode composite material 12 laminated on the surface of the core material, and an adhesive layer 13 formed between the core material 11 and the electrode composite material 12. As shown in Figure 1, the electrode 10 may have the electrode composite material 12 and the adhesive layer 13 on both sides of the core material 11. The electrode 10 may be a long electrode constituting a wound electrode body, or a rectangular electrode constituting a laminated electrode body. The electrode 10 can be applied to the positive electrode, negative electrode, or both of the electrodes of a non-aqueous electrolyte secondary battery.

[0014] The core material 11 can be a metal foil or a film with a metal layer formed on its surface. The thickness of the core material 11 is, for example, 5 μm to 20 μm. In the case of the positive electrode, the core material 11 can be a metal foil mainly composed of aluminum. In the case of the negative electrode, a metal foil mainly composed of copper can be used. In this specification, "main component" means the component with the highest mass ratio. The core material 11 may be an aluminum foil that is substantially 100% aluminum, or a copper foil that is substantially 100% copper.

[0015] The electrode mixture 12 comprises an active material and a fibrous binder. The thickness of the electrode mixture 12 is, for example, 30 μm to 120 μm, preferably 50 μm to 100 μm. The electrode mixture 12 may also contain a conductive material. Examples of conductive materials included in the electrode mixture 12 include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), and graphite. The particle size of the conductive material is, for example, 0.01 μm to 0.1 μm. This allows it to penetrate and adhere to depressions on the surface of the positive electrode active material. The content of the conductive material in the electrode mixture 12 can be, for example, 0.5 mass% to 5.0 mass%.

[0016] Generally, lithium transition metal composite oxides are used as the active material for the positive electrode. Examples of metal elements contained in lithium transition metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, it is preferable to contain at least one of Ni, Co, and Mn. For the active material for the negative electrode, carbon-based active materials such as natural graphite such as flake graphite, lump graphite, and clay graphite, or artificial graphite such as lump graphite (MAG) and graphitized mesophase carbon microbeads (MCMB) are used. In addition, Si-based active materials that alloy with lithium may be used as the negative electrode active material. The active material is the main component of the electrode mixture 12, and the content of the active material in the electrode mixture 12 is preferably 85% to 99% by mass, and more preferably 90% to 99% by mass.

[0017] The positive electrode active material is, for example, secondary particles formed by aggregation of a plurality of primary particles. As a result, irregularities exist on the surface of the positive electrode active material, and as described above, the conductive material can enter and adhere to the concave portions in these irregularities. The particle size of the primary particles constituting the secondary particles is, for example, 0.05 μm to 1 μm. The particle size of the primary particles is measured as the diameter of the circumscribed circle in the particle image observed by a scanning electron microscope (SEM). The positive electrode active material is particles having a volume-based median diameter (D50) of, for example, 3 μm to 30 μm, preferably 5 μm to 25 μm, more preferably 7 μm to 15 μm. D50 means the particle size at which the cumulative frequency in the volume-based particle size distribution reaches 50% from the smaller particle size side, and is also called the median diameter. The particle size distribution of the positive electrode active material can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by Microtrac Bell Corporation) with water as the dispersion medium.

[0018] The fibrous binder is a powder in a dry state, not a powder in a dispersed state in a dispersion such as water. As a result, the electrode mixture can be produced by the dry process described later. In addition, the electrode mixture 12 may contain a binder such as polyvinylidene fluoride (PVdF) that does not fibrillate in addition to the fibrous binder.

[0019] [[ID= (9)]] The content rate of the fibrous binder in the electrode mixture 12 is, for example, 0.5 mass% to 5.0 mass%. The fibrous binder adheres to the particle surface of the active material and is intertwined with the active material. In other words, the active material is held by the fibrous binder existing in a network form.

[0020] The fibrous binder can be produced by fibrillating PTFE raw materials (PTFE particles) belonging to fine powders capable of fibrillation (fiberization) using a dry grinder such as a jet mill grinder. The PTFE raw materials may be secondary particles. The average particle diameter of the PTFE raw materials is, for example, 100 μm to 700 μm, preferably 100 μm to 500 μm, and more preferably 100 μm to 400 μm. The average particle diameter of the PTFE raw materials can be determined by observing the particles of the PTFE raw materials with a SEM. Specifically, after identifying the outer shapes of 100 randomly selected particles, the major axis (longest diameter) of each of the 100 particles is determined, and the average value thereof is taken as the average particle diameter of the PTFE raw materials.

[0021] The median diameter of the fibrous binder is preferably 2 μm to 20 μm. The median diameter can be measured with a particle size distribution meter. The fact that the median diameter of the fibrous binder is 2 μm to 20 μm means that the fibrous binder has been micronized to a size relative to the PTFE particles of the PTFE raw materials.

[0022] When the electrode binder 12 is divided into three equal parts in the thickness direction and the first region, the second region, and the third region are defined starting from the core material 11 side, the content (a) of the fibrous binder in the first region, the content (b) of the fibrous binder in the second region, and the content (c) of the fibrous binder in the third region preferably satisfy (c - a) / (a + b + c) ≤ ±10%, and more preferably satisfy (c - a) / (a + b + c) ≤ ±5%. Thereby, the fibrous binder can be present substantially uniformly throughout the electrode binder 12 without being ubiquitous in a part of the electrode binder 12. By using the dry process described later, the fibrous binder can be made to be present substantially uniformly throughout the electrode binder 12.

[0023] The thickness of the adhesive layer 13 is, for example, 1 μm to 10 μm. The adhesive layer 13 has the function of bonding the core material 11 and the electrode composite material 12. The adhesive layer 13 is also conductive. The adhesive layer 13 may contain a conductive material and a binder. Examples of conductive materials included in the adhesive layer 13 include carbon materials such as carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), and graphite. It is preferable that the conductive material has a small particle size and a large specific surface area. This makes it easier for the adhesive layer 13 to form a structure. The specific surface area of ​​the conductive material is, for example, 100 m². 2 / g~150m 2 The range is / g. Examples of binders included in the adhesive layer 13 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyacrylonitrile (PAN), polyimide, acrylic resin, and polyolefin. PVdF is preferred as the binder included in the adhesive layer 13. The adhesive layer 13 can be produced, for example, by applying a slurry containing a conductive material, a binder, etc., to the surface of the core material 11, drying the coating film, and then compressing it. The adhesive layer 13 can also be produced on the surface of the core material 11 by dip coating or spray coating.

[0024] The content of the conductive material in the adhesive layer 13 is preferably 40% to 85% by mass, more preferably 45% to 75% by mass, and particularly preferably 50% to 71% by mass. By making the content of the conductive material in the adhesive layer 13 relatively high in this way, the interfacial resistance can be reduced. If the amount of conductive material is too high, the strength of the adhesive layer 13 itself decreases, and the layer structure becomes brittle, which inhibits conductivity between the electrode composite material 12 and the core material 11.

[0025] Next, the state near the core material 11 will be described with reference to Figure 2. Figure 2 schematically represents the area near the core material 11 while showing the active material 14. As shown in Figure 2, some of the active material 14 is embedded in the core material 11 via the adhesive layer 13. Since the amount of embedding of the active material 14 into the core material 11 can be reduced by the thickness of the adhesive layer 13, the decrease in the strength of the core material 11 can be suppressed.

[0026] The maximum penetration ratio (P / T), defined as the ratio of the maximum penetration depth P of the active material 14 into the core material 11 to the thickness T of the core material 11, is 20% or less. P / T is preferably 15% or less, and more preferably 10% or less. This ensures the strength of the core material 11. The maximum penetration depth P is determined by observing the cross-section of the electrode 10 with a scanning electron microscope (SEM), as shown in Figure 2. More specifically, if the cross-section of the electrode 10 is magnified 1500 times with an SEM and five or more pieces of active material 14 embedded in the core material 11 are observed, the maximum penetration depth is determined for any five pieces of active material 14, and the average value of these is taken as the maximum penetration depth P. If, when the cross-section of the electrode 10 is magnified 1500 times with an SEM, there are fewer than five pieces of active material 14 embedded in the core material 11, the maximum penetration depth is determined for each piece of active material 14, and the average value of these is taken as the maximum penetration depth P. In the example shown in Figure 2, since the four active materials 14 are embedded in the core material 11, the maximum embedment depth is determined for each embedded active material 14, and the average of these values ​​is P.

[0027] The electrode 10 has a conductive adhesive layer 13, and since the P / T ratio is adjusted to a suitable range, it is possible to ensure the strength of the core material 11 and reduce the interfacial resistance. The interfacial resistance of the electrode 10 is 0.12 Ωcm. 2 The following is preferable. Furthermore, the P / T ratio is preferably 1% or more, more preferably 3% or more, and particularly preferably 5% or more.

[0028] The ratio of the density Dm of the active material 14 in the electrode mixture 12 to the true density Dt of the active material 14 (Dm / Dt) is 70% or more. If Dm / Dt is 72% or more, it can be said that the packing rate of the active material in a given volume of the mixture is high. The density Dm of the active material 14 in the electrode mixture 12 can be calculated by multiplying the electrode mixture density, which is calculated by dividing the mass of the electrode mixture 12 by the volume of the electrode mixture 12, by the mass ratio of the active material 14 in the electrode mixture.

[0029] [Method for manufacturing electrodes] The manufacturing method for electrode 10 will be explained in more detail below. The manufacturing method for the positive electrode is given as an example, but this method can also be applied to the manufacturing of the negative electrode. In the case of the negative electrode, a negative electrode active material is used instead of the positive electrode active material.

[0030] Figures 3, 4, and 5 schematically show the manufacturing process of an electrode 10, which is an example of an embodiment. The manufacturing method of the electrode 10 includes a mixing step shown in Figure 3(a), a rolling step shown in Figure 3(b), a compression step shown in Figure 4, and a bonding step shown in Figure 5. In the mixing step, the active material and a fibrous binder are mixed to produce electrode composite particles 12a with a solid content concentration of substantially 100%. In the rolling step, the electrode composite particles 12a are rolled and formed into a sheet to produce an electrode composite sheet 12b. In the compression step, the electrode composite sheet 12b is compressed to produce a high-density electrode composite sheet 12c. In the bonding step, the high-density electrode composite sheet 12c is bonded to a core material 11 to produce an electrode.

[0031] The method for manufacturing the electrode 10 is a dry process in which the electrode 10 is manufactured using an electrode mixture 12 having a solid content concentration of substantially 100%. A dry process is a process in which active material particles and binder particles are mixed without using a solvent, that is, the active material and binder are mixed in a state in which the solid content concentration is substantially 100%. The method for manufacturing the electrode 10 according to this disclosure does not require the use of a solvent, as in conventional methods for manufacturing the electrode 10. The fact that a solvent is not required means not only that it is not needed as a raw material, but also that the solvent drying process is unnecessary, and thus exhaust equipment and other equipment related to the drying process can also be eliminated.

[0032] In the mixing step, raw materials such as active material, fibrous binder, and conductive material are mixed in a mixer 20 to produce electrode composite particles 12a. For example, a conventionally known mechanical stirring mixer can be used as the mixer 20. Specific examples of suitable mixers 20 include devices that can apply mechanical shear force, such as cutter mills, pin mills, bead mills, microparticle compounding devices (devices that generate shear force between a rotor with a special shape that rotates at high speed inside a tank and a collision plate), granulators, twin-screw extruders, and planetary mixers, with cutter mills, microparticle compounding devices, granulators, and twin-screw extruders being preferred. This allows for further fibrillation of the fibrous binder while mixing the raw materials. The processing time in the mixing step (the time for applying shear force to the materials) is preferably within a few minutes, for example, 0.5 to 10 minutes. If the processing time is too long, the amount of conductive material incorporated into the fibrous binder increases. In this case, the conductivity of the electrode composite sheet decreases significantly, leading to an increase in resistance and other adverse effects on the battery characteristics.

[0033] The mixing step may include a step of mixing the active material and the conductive material to produce a coated active material, and a step of mixing the coated active material and the fibrous binder. By using a coated active material produced by mixing the active material and the conductive material, the mixing time between the coated active material and the fibrous binder can be shortened. This reduces the amount of conductive material incorporated into the fibrous binder. It is preferable that the surface of the coated active material has irregularities, and that the conductive material penetrates and adheres to the depressions in these irregularities. This makes it less likely for the conductive material on the surface of the coated active material to be taken up by the fibrous binder during the mixing process between the coated active material and the fibrous binder.

[0034] As a method for dry mixing the active material and the conductive material, for example, the mechanofusion method may be used. The mechanofusion method is a dry processing method performed in a mechanofusion reactor having a cylindrical chamber equipped with a compression device and rotating at high speed. The conductive material and the active material are placed in the chamber and the chamber is rotated, causing the particles to be pressed against each other and against the chamber wall. By using a compression device and generating centrifugal force through high-speed rotation, the adhesion and bonding between the conductive material and the active material are promoted. Examples of mechanofusion reactors include the "Nobilta" (registered trademark) pulverizer or "Mechanofusion" (registered trademark) pulverizer manufactured by Hosokawa Micron Corporation (Japan), the "Hybridicer" (trademark) pulverizer manufactured by Nara Machinery Works Co., Ltd., "Balance Gran" manufactured by Freund Turbo K.K., and "COMPOSI" manufactured by Nippon Coke Industries Co., Ltd.

[0035] Next, in the rolling step, as shown in Figure 3(b), the electrode composite particles 12a are rolled using two rolls 22 to form a sheet. The two rolls 22 are positioned with a predetermined gap between them and rotate in the same direction. The electrode composite particles 12a are fed into the gap between the two rolls 22 and compressed and stretched into a sheet by the two rolls 22. The two rolls 22 have, for example, the same roll diameter. The resulting electrode composite sheet 12b may be passed through the gap between the two rolls 22 multiple times, or it may be stretched one or more times using other rolls with different roll diameters, peripheral speeds, gaps, etc. Alternatively, the rolls may be heated to hot press the electrode composite particles 12a.

[0036] The thickness of the electrode composite sheet 12b can be controlled, for example, by the gap between the two rolls 22, the peripheral speed, the number of stretching cycles, etc. In the rolling step, it is preferable to form the electrode composite particles 12a into a sheet using two rolls 22 with a peripheral speed ratio that differs by more than twice. By making the peripheral speed ratios of the two rolls 22 different, for example, it becomes easier to make the electrode composite sheet 12b thinner, and productivity is improved.

[0037] Next, in the compression step, as shown in Figure 4, the electrode composite sheet 12b is compressed using two rolls 24 to produce a high-density electrode composite sheet 12c. The two rolls 24, for example, have the same roll diameter, are positioned with a predetermined gap between them, and rotate in the same direction at the same peripheral speed. The two rolls 24 may be subjected to a linear pressure of, for example, 1 t / cm to 3 t / cm. The temperature of the two rolls 24 is not particularly limited and may be, for example, room temperature. The active material density of the high-density electrode composite sheet 12c is, for example, 3.6 g / cm³. 3 ~4.0g / cm 3 That is the case.

[0038] Next, in the bonding step, as shown in Figure 5, the high-density electrode composite sheet 12c is bonded to the core material 11 via the adhesive layer 13, thereby obtaining an electrode 10 in which an composite layer made of electrode composite 12 is provided on the surface of the core material 11. In Figure 5, the electrode composite 12 is shown to be bonded to only one side of the core material 11, but it is preferable that the electrode composite 12 be bonded to both sides of the core material 11. The two electrode composite sheets 12 may be bonded to both sides of the core material 11 simultaneously, or one may be bonded to one side of the core material 11 and then the other may be bonded to the other side.

[0039] In the bonding step, the high-density electrode composite sheet 12c is bonded to the surface of the core material 11 using two rolls 26. The two rolls 26 have, for example, the same roll diameter, are positioned with a predetermined gap between them, and rotate in the same direction at the same peripheral speed. The temperature of the two rolls 26 is, for example, 50°C to 300°C. The linear pressure applied by the two rolls 26 is preferably 0.1 t / cm to 2 t / cm, and more preferably 0.2 t / cm to 1 t / cm. [Examples]

[0040] The present disclosure will be further illustrated by the following examples, but the present disclosure is not limited to these examples.

[0041] <Example 1> [Formation of the adhesive layer] A slurry was prepared by mixing carbon black (CB) as a conductive material and polyvinylidene fluoride (PVdF) as a binder in a mass ratio of 50:50, and then mixing this with N-methyl-2-pyrrolidone (NMP). Next, the slurry was applied to a core material made of aluminum foil with a thickness of 14.4 μm, and after the coating film was dried, the coating film was rolled using a rolling mill, cut to a predetermined electrode size, and an adhesive layer was formed on both sides of the core material.

[0042] [Preparation of positive electrode composite particles (mixing step)] Using NOB300™ Novilta™ manufactured by Hosokawa Micron Corporation, 1000 g of lithium transition metal composite oxide and 10 g of carbon black (CB) were mixed in a Novilta™ pulverizer for 5 minutes to prepare a carbon-coated cathode active material.

[0043] The carbon-coated cathode active material and the fibrous binder were placed in a mixer (Osaka Chemical Co., Ltd., Wonder Crusher) in a mass ratio of 101:4 and mixed at room temperature at a rotation speed of 5 (setting 5 on the scale) for 5 minutes. The Wonder Crusher's rotation speed is 28,000 rpm (maximum setting 10 on the scale). This mixing process yielded cathode composite particles in which the carbon-coated cathode active material and fibrous binder were uniformly dispersed. The resulting cathode composite had a solid content concentration of 100%.

[0044] [Preparation of positive electrode composite sheet (rolling step)] The obtained cathode composite particles were passed between two rolls and rolled to produce a cathode composite sheet. The peripheral speed ratio of the two rolls was set to 1:3, and the thickness of the cathode composite sheet was adjusted to 100-120 μm.

[0045] [Preparation of high-density cathode composite sheet (compression step)] The resulting cathode composite sheet was compressed by passing it between two rolls at room temperature to produce a high-density cathode composite sheet.

[0046] [Fabrication of the positive electrode (bonding step)] The high-density cathode composite sheets described above were placed on the front and back surfaces of the core material, and the laminate of the high-density cathode composite sheets and the core material was pressed (linear pressure: 0.2 t / cm) using two rolls heated to 200°C to obtain the cathode. The ratio of the density Dm of the active material in the electrode composite to the true density Dt of the active material (Dm / Dt) was 73.7%. The combined thickness of the core material and the cathode composite sheets placed on both sides of the core material was adjusted to 170 μm to 180 μm.

[0047] [Measurement of interfacial resistance] The interface resistance of the positive electrode prepared as described above was measured using an electrode resistance meter (device name: XF057) manufactured by HIOKI E.E. CORPORATION. The measurement current was set to 100 μA and the voltage range to 0.5 V.

[0048] [Evaluation of peel strength] A 10mm x 90mm positive electrode composite layer was bonded to double-sided tape (Nichiban NW-20) attached to the sample stage. Under 25°C conditions, one end of the positive electrode was pulled vertically relative to the sample stage at a constant speed of 20mm / min using an A&D material testing machine (ORIENTEC RTC-1150A), and the peel strength was defined as the load at which the positive electrode composite layer peeled away from the core material.

[0049] <Example 2> The cathode was prepared and evaluated in the same manner as in Example 1, except that the mixing ratio of CB and PVdF in the formation of the adhesive layer was set to 71:29 by mass.

[0050] <Example 3> The positive electrode was prepared and evaluated in the same manner as in Example 1, except that the mixing ratio of CB and PVdF in the formation of the adhesive layer was set to 71:29 by mass, and the linear pressure in the bonding step was set to 1.0 t / cm.

[0051] <Comparative Example 1> A positive electrode was fabricated and evaluated in the same manner as in Example 1, except that an adhesive layer was not formed, the compression step was not performed, and the positive electrode composite sheet was bonded to the core material with a linear pressure of 3.0 t / cm during the bonding step.

[0052] <Comparative Example 2> The positive electrode was prepared and evaluated in the same manner as in Example 1, except that an adhesive layer was not formed.

[0053] <Comparative Example 3> The cathode was prepared and evaluated in the same manner as in Example 1, except that the mixing ratio of CB and PVdF in the formation of the adhesive layer was set to 33:67 by mass.

[0054] Table 1 shows the evaluation results (interfacial resistance, peel strength) for the examples and comparative examples. Table 1 also shows the conductive material content of the adhesive layer, the roll temperature and linear pressure in the compression step, the roll temperature and linear pressure in the bonding step, the maximum penetration depth P, P / T, and Dm / Dt. Table 2 shows the fibrous binder content in the first region (a), the fibrous binder content in the second region (b), the fibrous binder content in the third region (c), and the (ca) / (a+b+c) values ​​for the examples and comparative examples.

[0055] [Table 1]

[0056] [Table 2]

[0057] As shown in Table 1, the positive electrode of the example had lower interfacial resistance compared to the positive electrode of the comparative example. Furthermore, the positive electrode of the example had a lower P / T ratio compared to the positive electrode of the comparative example, ensuring the strength of the core material. Therefore, according to the electrode of this embodiment, it is possible to reduce interfacial resistance while ensuring the strength of the core material by reducing the amount of active material embedded in it. The peel strength of the example was approximately the same as that of Comparative Example 1, which was bonded using conventional methods. The Dm / Dt ratio of the comparative example is the same as that of the example (73.7%), so it can be said that the positive electrode composite sheet of the comparative example itself has increased capacity. However, the interfacial resistance of the comparative example is higher than that of the example. Since the battery of the example has lower interfacial resistance than the battery of the comparative example, it can be seen that the battery characteristics have been improved compared to the battery of the comparative example. [Explanation of Symbols]

[0058] 10 Electrode, 11 Core material, 12 Electrode mixture, 12a Electrode mixture particles, 12b Electrode mixture sheet, 12c High-density electrode mixture sheet, 13 Adhesive layer, 14 Active material, 20 Mixer, 22, 24, 26 Rolls

Claims

1. An electrode comprising a metal core, an electrode composite laminated on the surface of the core, and a conductive adhesive layer formed between the core and the electrode composite, The adhesive layer comprises a conductive material and a binder. The content of the conductive material in the adhesive layer is 40% by mass to 85% by mass. The electrode composite material comprises an active material and a fibrous binder. The active material is embedded in the core material, and the maximum embedding depth is 1% or more and 20% or less of the thickness of the core material. The ratio of the density of the active material in the electrode composite to the true density of the active material is 70% or more. An electrode in which, when the electrode composite is divided into three equal parts in the thickness direction, and the core material side is divided into a first region, a second region, and a third region, the content of the fibrous binder in the first region (a), the content of the fibrous binder in the second region (b), and the content of the fibrous binder in the third region (c) satisfy -10% ≤ (c - a) / (a ​​+ b + c) ≤ 10%.

2. The electrode according to claim 1, wherein in the adhesive layer, the conductive material is a carbon material and the binder is polyvinylidene fluoride.

3. A method for manufacturing an electrode according to claim 1 or 2, A mixing step in which an active material, a conductive material, and a fibrous binder are mixed to produce electrode composite particles with a solid content of 100%, A rolling step to produce an electrode composite sheet by rolling the electrode composite particles into a sheet, A compression step to compress the electrode composite sheet to produce a high-density electrode composite sheet, A method for manufacturing an electrode, comprising a bonding step of manufacturing an electrode by bonding the high-density electrode composite sheet to a core material.

4. The mixing step is, The steps include: mixing the active material and the conductive material to produce a coated active material; A method for manufacturing an electrode according to claim 3, comprising the step of mixing the coating active material and the fibrous binder.

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