Manufacturing method for secondary battery electrodes

Abstract

Reduce the variation in the through-plane resistance [Ω / cm 2 of the manufactured electrode plate according to the conductive material. 【Solution】In the method for manufacturing a positive electrode plate of a lithium-ion secondary battery, the specific surface area S [m 2 / g], the coating film resistance R S [Ω / cm], the rotational speed N [rpm] of the kneader NM, and the through-plane resistance R P [Ω / cm 2 are determined for their mutual relationship (S1). The specific surface area S [m 2 / g] of the positive electrode active material is measured (S2), the coating film resistance R S [Ω / cm] of the conductive material is measured (S3), and based on the specific surface area S [m 2 / g] and the coating film resistance R S [Ω / cm], the rotational speed N [rpm] of the kneader NM is adjusted so that the through-plane resistance R P [Ω / cm 2 becomes the set value (S4), and kneading is performed at the set rotational speed N [rpm] (S5). Therefore, according to the conductive material, the variation in the through-plane resistance [Ω / cm 2 of the positive electrode plate can be reduced, and a lithium-ion secondary battery with little variation in capacity can be manufactured.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing electrode plates of secondary batteries, and more specifically, to a method for manufacturing electrode plates of secondary batteries that reduces variations in the through-resistance of the electrode plates. [Background technology]

[0002] Non-aqueous secondary batteries, such as lithium-ion secondary batteries, have high voltage and large volumetric energy density [Wh / L] and gravimetric energy density [Wh / kg], and are therefore often installed as power sources for electric vehicles, including hybrid vehicles. Electric vehicles require high-current discharge during high-load operation, as well as high-current charging and discharging through rapid charging and regenerative current. Increasing the thickness of the composite material layer is advantageous to increase battery capacity. However, the lithium nickel-cobalt manganese oxide (LiNi) used as the positive electrode active material presents challenges. 1 / 3 C o1 / 3 Mn 1 / 3 Binding materials supporting lithium transition metal oxides, such as O2, do not have relatively high conductivity themselves. Therefore, when increasing the thickness of the composite layer, it is necessary to improve the input / output performance of lithium-ion secondary batteries at high currents. For this reason, highly conductive materials are sometimes added to the positive electrode composite layer of the positive electrode plate to reduce the electrical resistance between the numerous positive electrode active material particles and the non-aqueous electrolyte. Examples of conductive materials used in such cases include fibrous carbon materials, such as carbon nanotubes (CNTs), and granular acetylene black (AB), which have high conductivity. Carbon nanotubes, in particular, have a fibrous shape. Therefore, even a small amount can easily form a conductive network between the positive electrode active materials, which consist of lithium transition metal oxides dispersed in the positive electrode composite layer. Such a conductive network can reduce the electrical resistance between the positive electrode active materials.

[0003] Therefore, Patent Document 1 describes the following method for manufacturing electrodes for a non-aqueous electrolyte secondary battery. At least a portion of the surface of the electrode active material is coated with a mixture of a fine conductive material having an average primary particle size of 20 nm to 200 nm and a high molecular weight binder having an average molecular weight of 1 million to 5 million. The coated electrode active material is an electrode in which an electrode active material layer is formed by bonding together an anisotropic conductive material having shape anisotropy with an average primary particle size of 1 μm to 30 μm and a low molecular weight binder having an average molecular weight of 10,000 to 300,000.

[0004] According to this method for manufacturing electrodes for non-aqueous electrolyte secondary batteries, even when the porosity of the electrode active material layer is relatively high or the electron conductivity of the electrode active material surface is low, the reactivity at the interface between the electrode active material, the conductive material, and the electrolyte component of the electrode can be efficiently enhanced.

[0005] Incidentally, lithium transition metal oxides used as positive electrode active materials are first produced as crystalline primary particles. Furthermore, these primary particles are aggregated to form spherical secondary particles with cavities, which allows for efficient reaction on the surface of the positive electrode active material. In positive electrode active materials with this secondary particle shape, there is a problem that the degree of the voids on the surface communicates with the internal cavities, but the degree of these voids varies greatly depending on conditions such as firing.

[0006] Therefore, in Patent Document 2, the applicant disclosed an evaluation method for evaluating conductive materials used in secondary batteries by measuring the coating resistance, which is the surface resistance of a test coating film. This method allows for accurate evaluation of the conductivity and dispersibility of the conductive material itself used in secondary batteries. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2023-218895 [Patent Document 2] Japanese Patent No. 7535646

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0008] However, it is possible to accurately evaluate the conductivity and dispersibility of the conductive material used in the secondary battery. Even when using conductive materials with the same characteristics, there is a variation in the through-plane resistance [Ω / cm 2 of the completed electrode plate, and there is a problem that it does not achieve the same through-plane resistance [Ω / cm 2 .

[0009] Therefore, the problem to be solved by the method for manufacturing an electrode plate of a secondary battery according to the present invention is to reduce the variation in the through-plane resistance [Ω / cm 2 of the electrode plates manufactured according to different conductive materials.

MEANS FOR SOLVING THE PROBLEMS

[0010] To solve the above problems, in the method for manufacturing an electrode plate of a secondary battery according to the present invention, an active material, a conductive material, and a solvent are kneaded by a kneader to prepare a mixed material paste, and the mixed material paste is applied to a substrate to form a mixed material layer. The method for manufacturing an electrode plate of a secondary battery is characterized by including a step of obtaining the mutual relationship between the specific surface area S [m 2 / g] of the active material in advance, the coating film resistance R S [Ω / cm] of the conductive material, the rotation speed N [rpm] of the kneader, and the through-plane resistance R P [Ω / cm 2 of the mixed material layer; a step of measuring the specific surface area S [m 2 / g] of the specific surface area measurement; a step of measuring the coating film resistance R S [Ω / cm] of the conductive material resistance measurement; and a step of adjusting the rotation speed N [rpm] of the kneader so that the through-plane resistance R 2 / g] and the coating film resistance R S [Ω / cm] based on the mutual relationship, the through-plane resistance R P [Ω / cm 2 of the mixed material layer becomes the set value.

[0011] The aforementioned kneader may be a twin-shaft kneader. The rotational speed N [rpm] is determined by the threshold Th N The rotational speed can be adjusted within the range of [rpm]. The threshold Th N [rpm] can be in the range of 50[rpm] to 1000[rpm].

[0012] The step of measuring the specific surface area is to determine the specific surface area S[m²] of the active material. 2 The concentration [ / g] can be measured using the BET method. The steps for measuring the conductive material resistance include: a paste preparation step of preparing a paste containing simulated primary particles made of an insulator that simulates the active material of the secondary battery, and the conductive material; a test coating preparation step of coating and drying the paste prepared in the paste preparation step onto a simulated substrate that simulates the substrate of the secondary battery to prepare a test coating containing the simulated primary particles; and the coating resistance R, which is the surface resistance of the test coating. S This may include a measurement step that measures [Ω / cm].

[0013] In the step of determining the interrelationship, the specific surface area S[m 2 / g] and the coating film resistance R S [Ω / cm], the rotation speed N [rpm] of the kneader, and the penetration resistance R of the asphalt layer. P [Ω / cm 2 The relationship between ] and R is given by a, b, and c as coefficients and d as a constant. P =(R S It can be expressed as (x a) + (S × b) + (N × c) + d ... (Equation 1).

[0014] The above equation 1 is R P =(R S ×3.7×10 -2 ) + (S × -4.5 × 10 -1 ) + (N × -1.6 × 10 -4 It can be expressed as ) + 0.91…(Equation 1'). The aforementioned rotational speed adjustment step is N=(R P -R SThe rotational speed N [rpm] can be determined by the following equation: × aS × bd) / c…(Equation 2).

[0015] The above step of adjusting the rotation speed involves the penetration resistance R of the asphalt layer. P [Ω / cm 2 The rotation speed N [rpm] of the kneader can be adjusted so that the standard deviation σ of ] falls within the set threshold Thσ.

[0016] The aforementioned secondary battery can be suitably applied to lithium-ion secondary batteries. Furthermore, the aforementioned electrode plate can be suitably applied to positive electrode plates. [Effects of the Invention]

[0017] According to the method for manufacturing electrode plates of the secondary battery of the present invention, the through-resistance of the manufactured electrode plate [Ω / cm] can be determined depending on the conductive material. 2 This can reduce the variation in [ ]. [Brief explanation of the drawing]

[0018] [Figure 1] (a) A schematic diagram showing the relationship with conductive materials when there is almost no void in the positive electrode active material. (b) A schematic diagram showing the relationship with conductive materials when there is a moderate void in the positive electrode active material. (c) A schematic diagram showing the relationship with conductive materials when there is a large void in the positive electrode active material. [Figure 2] (a) A schematic diagram of the simulated positive electrode plate of this embodiment. (b) A schematic diagram of the positive electrode plate of the lithium-ion secondary battery of this embodiment. [Figure 3] This is a schematic diagram showing the relationship between simulated primary particles and conductive materials. [Figure 4] This is a cross-sectional view showing an example of the kneader NM of this embodiment. [Figure 5] This is a perspective view showing a schematic representation of the external configuration of the lithium-ion secondary battery of this embodiment. [Figure 6] This is a schematic diagram showing the configuration of the wound electrode body. [Figure 7] This flowchart shows the procedure for manufacturing the positive electrode plate according to this embodiment. [Figure 8] This table shows the relationship between the measured penetration resistance RP [Ω / cm2] of the positive electrode plate, the predicted penetration resistance RP' [Ω / cm2], the coating resistance RS [Ω / cm] of the conductive material, the specific surface area S [m2 / g] of the positive electrode active material, and the rotation speed N [rpm] of the kneader NM. [Figure 9] This graph compares the measured penetration resistance RP [Ω / cm2] with the predicted penetration resistance RP' [Ω / cm2]. [Figure 10] This table summarizes the results of Experiment 2, showing the penetration resistance RP [Ω / cm2] when the rotational speed N [rpm] is fixed. [Figure 11] This is a histogram showing the frequency of each category of through-wall resistance RP [Ω / cm2] in Experiment 2. [Figure 12] This table summarizes the results of Experiment 3, in which the rotational speed N [rpm] of the kneader NM was determined when the penetration resistance RP [Ω / cm2] was fixed. [Figure 13] This table shows the penetration resistance RP [Ω / cm2] when the rotation speed N [rpm] of the mixing machine NM is adjusted within the range of 50 [rpm] to 1000 [rpm]. [Figure 14] Figure 11 shows a histogram of the frequency of each category of penetration resistance RP [Ω / cm2] for Experiment 2, with the histogram of the results shown in Figure 13 superimposed on it. [Modes for carrying out the invention]

[0019] Hereinafter, the method for manufacturing the electrode plate of the secondary battery of the present invention will be described with reference to Figures 1 to 14, with an embodiment as an example. In this embodiment, a positive electrode active material 321, a conductive material 322, and a solvent are kneaded in a kneader NM to produce a positive electrode composite paste, and the positive electrode composite paste is coated onto a positive electrode substrate 31 to form a positive electrode composite layer 32, thereby manufacturing the positive electrode plate 3 of the lithium-ion secondary battery 1.

[0020] This embodiment is merely one example of an implementation for the purpose of explaining the present invention and does not limit the present invention. For example, the electrode plate is not limited to the positive electrode plate 3, and the secondary battery is not limited to the lithium-ion secondary battery 1.

[0021] (Summary of this embodiment) <Background Art of This Embodiment> As described in the background information, the applicant proposed in Patent Document 2 a method for accurately evaluating the conductivity and dispersibility of a conductive material 322 used in a secondary battery. Here, as shown in Figures 2(b) and 3, a positive electrode composite paste is prepared in the paste preparation step, containing simulated primary particles 132a made of an insulator that simulates the positive electrode active material 321 of a lithium-ion secondary battery 1, and a conductive material 132b. In the test coating preparation step, the positive electrode composite paste is coated onto a simulated substrate 131 that simulates the positive electrode substrate 31 of a lithium-ion secondary battery 1, and dried to prepare a test coating 132 containing simulated primary particles 132a. In the conductivity evaluation step, the coating resistance R, which is the surface resistance of the test coating 132, is measured. S The conductive material 132b is evaluated by measuring its [Ω / cm]. In this way, the coating resistance R of the conductive material 132b itself is accurately determined. S It can measure [Ω / cm].

[0022] The through-resistance R directly affects the charge-discharge characteristics of the positive electrode plate 3. P [Ω / cm 2 ] is the through-resistance R P [Ω / cm 2 As its name suggests, ] is an index that indicates the magnitude of the resistance per unit area [Ω] that penetrates the surface of the positive electrode composite layer 32 and the positive electrode substrate 31. However, it is possible to accurately evaluate the conductivity and dispersibility of the conductive material 322 used in the lithium-ion secondary battery 1, and assuming that conductive material 322 with the same characteristics is used, the through-resistance R of the completed electrode plate P [Ω / cm 2 The problem was that ] would not be the same. According to the inventors, this through-resistance R P [Ω / cm 2 ] is the coating resistance R of the conductive material 132b itself. S Even when the [Ω·cm] value is the same, it fluctuates during the manufacturing process of the positive electrode composite paste. Specifically, this fluctuation is mainly due to the specific surface area S[m²]. 2 We found that it depends on the g / g and rotational speed N[rpm].

[0023] <Principle of this embodiment> In this embodiment, the coating resistance R of such conductive material 322 S [Ω / cm], specific surface area S[m 2 / g], the rotation speed N [rpm] of the kneader NM, and the through-resistance R of the positive electrode plate 3. P [Ω / cm 2 The relationship was derived through repeated experiments. This relationship was then expressed by a relational equation. Based on this relational equation, the rotation speed N [rpm] of the kneader NM was adjusted to obtain a predetermined coating resistance R. S [Ω / cm], specific surface area S[m 2 In / g], the through-resistance R P [Ω / cm 2 The standard deviation σ of ] was set to a certain range. In this way, the through-resistance R can be set with high accuracy and appropriateness. P [Ω / cm 2 By doing so, it is possible to manufacture lithium-ion secondary batteries 1 with stable quality.

[0024] <Premise of this embodiment> Next, the premise of this embodiment will be explained. <Specific surface area S[m 2 / g]> Here, the specific surface area S[m 2 The specific surface area S[m²] is expressed as the area per unit mass. 2 Analysis of the specific surface area of ​​a powder can be performed using methods such as adsorption, moist heat, and reaction. The adsorption method involves adsorbing molecules with a known adsorption area onto the surface of powder particles at the temperature of liquid nitrogen, and then determining the specific surface area of ​​the sample from the amount of adsorbed molecules. Adsorption methods include the BET method and the Langmuir method, but the BET method, which uses low-temperature, low-humidity physical adsorption of an inert gas, is the most commonly used for specific surface area analysis. In this embodiment, the specific surface area S[m²] of the powder is determined by the BET method (Berunauer Emmett and Teller's method, gas adsorption method). 2The method used to determine the [ / g] ratio is employed. Specifically, for example, a sample of a predetermined size is prepared by fixing conductive material 322 to a foil. A BET specific surface area measuring device (not shown) was used, for example, Quantasorb manufactured by Quantachrome, with nitrogen gas as the adsorption gas. A bulk solid cell was used as the sample cell, and the sample was rolled up and placed inside this cell. By using krypton as the adsorption gas, it is possible to measure even smaller samples.

[0025] <Coating film resistance R S [Ω / cm]> Coating film resistance R S [Ω / cm] is a value that measures the conductivity of the conductive material 322 in the positive electrode composite layer 32, while excluding the influence of the positive electrode active material 321. For this purpose, in this embodiment, it is measured using a special method that utilizes a simulated positive electrode plate 103. Below, the coating resistance R S The method for measuring [Ω / cm] will be explained in detail.

[0026] Figure 1(a) is a schematic diagram showing the relationship between the conductive material 322 and the positive electrode active material 321 when there is almost no gap 321c. Figure 1(b) is a schematic diagram showing the relationship between the conductive material 322 and the positive electrode active material 321 when there is a moderate amount of gap 321c. Figure 1(c) is a schematic diagram showing the relationship between the conductive material 322 and the positive electrode active material 321 when there is a large amount of gap 321c. When there is a large variation in the gap 321c of the conductive material 322, for example, when there is almost no gap 321c as shown in Figure 1(a), the conductive material 322 does not enter the cavity 321d of the positive electrode active material 321. In this case, the conductive material 322 will be present in the binder 323 between the secondary particles 321a of adjacent positive electrode active material 321. Consequently, in a positive electrode composite layer 32 containing the same amount [vol%] of conductive material 322, the density of conductive material 322 per unit volume of the positive electrode composite layer 32 increases. As a result, the conductive materials 322 become more likely to come into contact with each other, making it easier to form a conductive network. In other words, the coating resistance R of the positive electrode composite layer 32 S The [Ω / cm] value decreases.

[0027] On the other hand, as shown in Figure 1(c), if there are many gaps 321c, the conductive material 322 can easily penetrate the cavities 321d of the positive electrode active material 321 through the gaps 321c. In this case, the conductive material 322 will be present not only in the binder 323 between the secondary particles 321a of the positive electrode active material 321, but also in the cavities 321d. Consequently, even with a positive electrode composite layer 32 containing the same amount [vol%] of conductive material 322, the number of conductive material 322 per unit volume of the positive electrode composite layer 32 will decrease. As a result, the conductive material 322 will be less likely to come into contact with each other, making it difficult to form a conductive network. In other words, the coating resistance R of the positive electrode composite layer 32 S The [Ω / cm] value increases.

[0028] Furthermore, while gaps 321c exist as shown in Figure 1(b), if their number and area are smaller than those shown in Figure 1(c), the properties will be intermediate between those of Figure 1(a) and Figure 1(c). Figure 2(a) is a schematic diagram of the simulated positive electrode plate 103 of this embodiment. Figure 2(b) is a schematic diagram of the positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment. The simulated positive electrode plate 103 is a test configuration for accurately measuring the conductivity and dispersibility of the conductive material 322, which cannot be accurately measured on the positive electrode plate 3 of the lithium-ion secondary battery 1.

[0029] <Configuration of the positive electrode plate 3 of lithium-ion secondary battery 1> First, the positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment will be described with reference to Figure 2(b). The positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment comprises a positive electrode substrate 31 made of Al foil, and a positive electrode composite layer 32 is formed on this positive electrode substrate 31. The positive electrode composite layer 32 is a layer to which a positive electrode composite paste has been coated, dried, and press-molded. The positive electrode composite paste is made by kneading a positive electrode active material 321, a conductive material 322, and a binder 323 with a solvent.

[0030] In this positive electrode plate 3, as shown in Figures 1(a) to (c), the secondary particles 321a of the positive electrode active material 321 differ in the formation of a conductive network by the conductive material 322 depending on their shape, particularly the amount of gaps 321c.

[0031] <Configuration of the simulated positive electrode plate 103 in this embodiment> Here, the "coating film resistance R" of this embodiment S This document explains the Ω / cm value and the method for evaluating the conductive material 322. As shown in Figure 2(a), in the simulated positive electrode plate 103 of this embodiment, first, instead of the positive electrode substrate 31 made of Al foil, a positive electrode composite layer 32 is applied to a simulated substrate 131 made of PET (polyethylene terephthalate) film. Then, on the surface of the positive electrode composite layer 32, measurement points MP1 and MP2 are set at positions 1 cm apart. The probe of the resistance meter OM is brought into contact with these measurement points MP1 and MP2 to measure the coating resistance R, which is the surface resistance of the conductive material 322 between these points. S The [Ω / cm] value was measured. The measurement was performed using the 4-terminal method with an electrode resistance measurement system RM2610 using a 4-probe, for example, from HIOKI E.E. CORPORATION. This "coating film resistance R S The [Ω / cm] measurement allows for accurate evaluation of the conductivity and dispersibility of the conductive material 132b.

[0032] Conventionally, on the surface facing the measurement points MP1 and MP2 of the positive electrode composite layer 32, there was a positive electrode substrate 31 made of conductive Al foil, so in reality, only the resistance in the thickness direction of the positive electrode composite layer 32 could be determined. As a result, it was difficult to accurately evaluate the conductive material 322 itself used as the material. Therefore, as described above, instead of the positive electrode substrate 31 made of Al foil, a simulated substrate 131 made of highly insulating PET (polyethylene terephthalate) film was used to measure the coating resistance R S The effect of the positive electrode substrate 31, which is made of Al foil, was eliminated by measuring the [Ω / cm] value.

[0033] However, as described above, the secondary particles 321a of the positive electrode active material 321 not only possess conductivity themselves, but their shape, particularly the amount of voids 321c, affects the formation of the conductive network by the conductive material 322. For this reason, it was not possible to accurately observe the conductivity of the conductive material 322 itself or the state of the conductive network formed by dispersion. Therefore, in the simulated positive electrode plate 103 of this embodiment shown in Figure 2(a), the positive electrode active material 321 is replaced with simulated primary particles 132a.

[0034] Figure 3 is a schematic diagram showing the relationship between the simulated primary particles 132a and the conductive material 132b. As shown in Figure 3, the simulated primary particles 132a are particles made of an insulator that simulates the positive electrode active material 321 of the lithium-ion secondary battery 1 as shown in Figure 1(a). Here, "simulated" means that the external shape of the secondary particles 321a of the positive electrode active material 321 is approximated, and the structure imitates the positive electrode active material 321. For example, the average particle size (d50) [μm] is substantially the same. In this application, unless otherwise specified, "average particle size D S [μm] refers to the median diameter (d50) in the frequency distribution measured by laser diffraction. Also, the average diameter D of the conductive material 132b. C [nm] or average length L C [nm] refers to the value obtained through image analysis of electron microscope photographs.

[0035] The term "substantial" here means that, even with slight differences in shape such as unevenness, the mechanical function of the simulated primary particles 132a in the test coating 132 is equivalent to the mechanical function of the positive electrode active material 321 in the positive electrode composite layer 32. However, since the material is an insulator and alumina particles are used in this embodiment, the electrochemical function will be different.

[0036] Furthermore, the term "primary particle" here refers to the particle in its initial state when manufacturing particles, and in the case of the simulated primary particle 132a, the entire mass is a solid crystalline particle. On the other hand, in the positive electrode active material 321, numerous primary particles aggregate to form secondary particles 321a. As a result, the positive electrode active material 321, as shown in Figures 1(b) and 1(c), has cavities 321d and gaps 321c inside the secondary particles 321a. In contrast, the simulated primary particle 132a does not have such internal cavities 321d and gaps 321c.

[0037] <Conductive material 132b> Regarding the conductive material 132b, although the name is different, it is the same as the conductive material 322 of the positive electrode composite layer 32. That is, although carbon nanotubes are used as an example in this embodiment, their type, length, diameter, mass, and amount added are all the same. Also, the volume ratio R of conductive material 132b to simulated primary particles 132a in the inspection coating paste. V [vol%] is the volume ratio of the positive electrode active material 321 and the conductive material 322. V It is set based on [vol%]. In other words, it is to make the amount essentially the same. Note that this mixing volume ratio R V [vol%] represents the blending mass ratio R of conductive material 132b to simulated primary particles 132a. W This is replaced with [wt%]. This is the exact volume [mm²]. 3 This is because it is difficult to determine the mass due to the effects of bulk density and porosity, so it is replaced with mass [g] which is easier to measure beforehand.

[0038] The reason for doing so is as follows: The evaluation method for evaluating the conductive material 322 used in the lithium-ion secondary battery 1 of this embodiment aims to accurately evaluate the conductivity and dispersibility of the conductive material 322 itself contained in the positive electrode composite layer 32 of the lithium-ion secondary battery 1. To that end, it is necessary to strictly reproduce the actual state. Generally, in the field of engineering, conductivity is expressed in units of [S / m], but in this embodiment, such measurements are performed in order to analyze the actual dispersion state of the conductive material 322 in the lithium-ion secondary battery 1.

[0039] Specifically, in this embodiment, the average diameter D of the conductive material 132b is C (d50)[nm] is between 1[nm] and 100[nm]. Also, the average length L of the conductive material 132b is... C (d50)[nm] is between 100[nm] and 10000[nm].

[0040] <Simulated circuit board 131> The simulated positive electrode plate 103 of this embodiment has an external shape similar to that of the positive electrode substrate 31, but includes a simulated substrate 131 made of an insulator instead of Al foil. The material is not limited as long as it is insulating and can be coated with the test coating paste. For example, in this embodiment, PET (polyethylene terephthalate) film is used, which has high insulating properties and is easy to coat. A test coating film 132 is formed on this simulated substrate 131. The test coating film 132 is a layer to which the test coating paste has been applied, dried, and press-molded. The test coating paste is made by kneading simulated primary particles 132a, conductive material 132b, and binder 132c with a solvent. The conductive material 132b, binder 132c, and solvent are the same as those of the conductive material 322, binder 323, and solvent of the positive electrode composite paste. In other words, it is a configuration in which only the positive electrode active material 321 is replaced with simulated primary particles 132a.

[0041] <Coating film resistance R S Measurement in [Ω / cm] > In the evaluation method for evaluating the conductive material 322 used in the lithium-ion secondary battery 1 of this embodiment, the measurement is performed on the surface of the test coating 132 of the completed simulated positive electrode plate 103, similar to the conventional measurement method. Measurement points MP1 and MP2 are set at a distance of 1 cm from each other, and the probe of the resistance meter OM is brought into contact with these measurement points MP1 and MP2 to measure the coating resistance R of the conductive material 322 between them. S Measure [Ω / cm].

[0042] Here, the positive electrode active material 321 is replaced with insulating simulated primary particles 132a. The positive electrode substrate 31 is also replaced with an insulating simulated substrate 131. Therefore, the simulated primary particles 132a not only possess insulating properties themselves, but their shape, particularly the absence of gaps 321c, ensures that the conductive material 322 is always present at the same density. Consequently, the formation of the conductive network by the conductive material 322 remains consistent. This allows for accurate observation of the conductivity of the conductive material 322 itself and the state of the conductive network formed by the dispersion of the conductive material 322. Furthermore, a simulated substrate 131 made of insulating resin is present on the surface of the positive electrode composite layer 32 facing the measurement points MP1 and MP2. Therefore, the measurement is unaffected by the conductive positive electrode substrate 31, and only the resistance of the conductive network formed by the conductive material 132b in the test coating 132 can be measured. As a result, the conductive material 132b used as a raw material can be accurately evaluated.

[0043] <Penetration resistance R P [Ω / cm 2 ] Measurement > Penetration resistance R P [Ω / cm 2 ] A test piece of, for example, 1 × 1 cm is prepared from the completed positive electrode plate 3, and its electrical resistance [Ω] is measured from the thickness direction. The measurement is performed using the electrode resistance measurement system described above, 1 [cm 2 The resistance [Ω] per ] was calculated. This value actually reflects the charge and discharge characteristics of the positive electrode plate 3.

[0044] (Configuration of this embodiment) <Mixing Machine NM> Figure 4 is a cross-sectional view showing an example of the kneader NM of this embodiment. As shown in Figure 4, the kneader NM of this embodiment is a twin-shaft kneader and comprises a barrel 202 and a shaft unit 204 having a pair of rotating shafts 203.

[0045] The kneader NM produces a cathode composite paste by kneading the slurry of cathode materials introduced into the barrel 202 with the shaft unit 204. The barrel 202 has a housing chamber 206 that rotatably houses the shaft unit 204. The barrel 202 has an inlet 207 for introducing electrode material into the housing chamber 206 and an outlet 208 for discharging the electrode material kneaded by the shaft unit 204 inside the housing chamber 206. The inlet 207 and outlet 208 are located at one axial end of the barrel 202, with the inlet 207 located at the other axial end of the barrel 202.

[0046] The shaft unit 204 has a pair of rotating shafts 203, namely a first rotating shaft 209 and a second rotating shaft 211. The first rotating shaft 209 and the second rotating shaft 211 are arranged parallel to each other inside the barrel 202 so as to rotate in the same direction (the paddle rotation direction A1 indicated by the arrow in the figure). In this example, the first rotating shaft 209 rotates around axis L1, and the second rotating shaft 211 rotates around axis L2.

[0047] The shaft unit 204 has a plurality of paddle pairs 214 arranged in the axial direction of the shaft unit 204. Each paddle pair 214 includes a paddle 216 (first paddle 216a) attached to the shaft body of the first rotating shaft 209 and a paddle 216 (second paddle 216b) attached to the shaft body of the second rotating shaft 211. The paddles 216 have three projections that are evenly spaced in the circumferential direction, so that when viewed from the axis of rotation of the paddle 216, it is formed in a substantially triangular shape.

[0048] Screws 218 are formed at both ends of the rotating shaft 203 to guide the electrode material from the upstream to the downstream side. The screw 218 has an upstream screw 218a that guides the electrode material flowing in from the inlet 207 to the paddle 216, and a downstream screw 218b that dams and pushes back the electrode material flowing from the paddle 216 while sending it to the outlet 208.

[0049] The kneader NM forms a positive electrode composite paste by kneading the slurry of the positive electrode material, thereby shearing and dispersing it. Due to the rotation of the rotary shaft 3, the kneader NM shears and disperses the slurry of the positive electrode material, and the shearing and dispersion progress. Also, when comparing at the same time, increasing the rotation speed [rpm] of the kneader NM causes more shearing and dispersion to progress, and thus the through resistance R P [Ω / cm 2 is found to decrease. Therefore, in order to obtain a desired through resistance R P [Ω / cm 2 , the rotation speed [rpm] of the kneader NM can be adjusted to obtain the desired through resistance R P [Ω / cm 2 .

[0050] <Configuration of Lithium-Ion Secondary Battery 1> FIG. 5 is a perspective view showing an outline of the external configuration of the lithium-ion secondary battery 1 of the present embodiment.

[0051] As shown in FIG. 5, the lithium-ion secondary battery 1 is a cell battery that constitutes a battery module of a drive battery pack mounted on a vehicle. The lithium-ion secondary battery 1 includes a plate-shaped rectangular parallelepiped battery case 11 having an opening on the upper side. An electrode body 12 is housed inside the battery case 11. The battery case 11 is filled with a non-aqueous electrolyte 13 from a liquid injection hole. The battery case 11 is made of a metal such as an aluminum alloy and forms an electrolytic cell sealed by a lid. The lithium-ion secondary battery 1 also includes a positive electrode external terminal 14 and a negative electrode external terminal 15 used for charging and discharging electric power. The positive electrode external terminal 14 is electrically connected to a positive electrode current collector terminal 16 inside the battery case 11 through the lid. Also, the negative electrode external terminal 15 is electrically connected to a negative electrode current collector terminal 17 inside the battery case 11 through the lid. The positive electrode current collector terminal 16 is electrically connected to the positive electrode current collecting portion 33 (see FIG. 8) of the electrode body 12. Also, the negative electrode current collector terminal 17 is electrically connected to the negative electrode current collecting portion 23 (see FIG. 8) of the electrode body 12.

[0052] <Electrode Body 12> Figure 6 is a schematic diagram showing the configuration of the wound electrode body 12. The electrode body 12 is made up of a number of stacked negative electrode plates 2, positive electrode plates 3, and separators 4 placed between them. The stacked negative electrode plates 2, positive electrode plates 3, and separators 4 are wound together to form a flat shape. The negative electrode plate 2 has a negative electrode composite layer 22 formed on a negative electrode substrate 21 made of copper foil, which serves as the base material. A negative electrode current collector 23 is provided on one end in the width direction W (winding axis direction) perpendicular to the winding direction (winding direction L). The negative electrode current collector 23 has a configuration in which the negative electrode composite layer 22 is not formed and the negative electrode substrate 21 is exposed.

[0053] The positive electrode plate 3 has a positive electrode composite layer 32 formed on a positive electrode substrate 31 made of aluminum foil, which serves as the base material. As shown in Figure 6, the positive electrode current collector 33 is provided on the other end (opposite side from the negative electrode current collector 23) in the width direction W (winding axis direction) perpendicular to the winding direction (winding direction L) of the positive electrode substrate 31. The positive electrode composite layer 32 is not formed on the positive electrode current collector 33, and the metal of the positive electrode substrate 31 is exposed.

[0054] <Laminated structure of electrode body 12> As shown in Figure 6, the basic configuration of the electrode body 12 of the lithium-ion secondary battery 1 includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0055] The negative electrode plate 2 has a negative electrode composite material layer 22 on both sides of a negative electrode substrate 21, which serves as the negative electrode base material. One end of the negative electrode substrate 21 is a negative electrode current collector portion 23 where metal is exposed. The positive electrode plate 3 has a positive electrode composite material layer 32 on both sides of a positive electrode substrate 31, which serves as the positive electrode base material. The other end of the positive electrode substrate 31 is a positive electrode current collector portion 33 where metal is exposed.

[0056] The negative electrode plate 2 and the positive electrode plate 3 are stacked on top of each other via a separator 4 to form a laminate. As shown in Figure 6, this laminate is wound longitudinally around a winding axis to form a wound electrode body 12 that is flattened as shown in Figure 5.

[0057] <Nonaqueous electrolyte 13> The non-aqueous electrolyte 13 of the lithium-ion secondary battery 1 of this embodiment shown in Figure 5 is a composition obtained by dissolving a lithium salt in an organic solvent. Examples of lithium salts that can be used include LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and trifluoropropylene carbonate; linear carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur compounds such as ethylmethylsulfone and butanesultone; or phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One or more of these can be mixed and used as the non-aqueous electrolyte 13. However, the composition of the non-aqueous electrolyte 13 is not limited to these.

[0058] In this embodiment, EC (ethylene carbonate) is used as the organic solvent. Furthermore, in this embodiment, an additive such as LiBOB (lithium bisoxalate borate, LiB(C2O4)2) may be added as a film-forming material.

[0059] <Components of electrode body 12> Next, we will describe the components that make up the electrode body 12: the negative electrode plate 2, the positive electrode plate 3, and the separator 4.

[0060] <Negative electrode plate 2> As shown in Figure 6, the negative electrode plate 2 is constructed by forming negative electrode composite material layers 22 on both sides of the negative electrode substrate 21, which is the negative electrode base material. In the source process, the negative electrode composite material paste is applied to the negative electrode substrate 21. Subsequently, the negative electrode plate 2 is completed through drying, pressing, and cutting processes.

[0061] In this embodiment, the negative electrode substrate 21 is made of Cu foil. The negative electrode substrate 21 serves as a base for the aggregate of the negative electrode composite layer 22 and also functions as a current collector that collects electricity from the negative electrode composite layer 22. One end of the negative electrode substrate 21 is a negative electrode current collector section 23 where the metal surface is exposed and the negative electrode composite layer 22 is not formed thereon. In other words, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 via the negative electrode substrate 21, the negative electrode current collector section 23, and the negative electrode current collector terminal 17.

[0062] The negative electrode composite layer 22 consists of a negative electrode active material as the raw material, and a binder (binding agent) and additives as auxiliary materials. The raw material and auxiliary materials are mixed with an organic solvent to produce a negative electrode composite paste. This negative electrode composite paste is coated onto the negative electrode substrate 21. The coated negative electrode composite paste is dried and then molded and pressed to complete the negative electrode plate 2.

[0063] In this embodiment, the negative electrode active material is powdered graphite particles GP, which consist of graphite having a layered structure, and lithium ions Li + It is a material capable of absorbing and releasing substances. <Positive plate 3> As shown in Figures 2(b) and 6, the positive electrode plate 3 is composed of a positive electrode substrate 31, which is the positive electrode base material, and a positive electrode composite layer 32 coated thereon. The positive electrode composite layer 32 is formed when a positive electrode composite paste is applied to the positive electrode substrate 31 in the source process, and the positive electrode plate 3 is completed through drying, pressing, and cutting processes.

[0064] The positive electrode plate 3 is constructed by forming a positive electrode composite layer 32 on both sides of a positive electrode substrate 31. In this embodiment, the positive electrode substrate 31 is made of Al foil. The positive electrode substrate 31 serves as a base for the aggregate of the positive electrode composite layer 32 and also functions as a current collector that collects electricity from the positive electrode composite layer 32.

[0065] First, although Al foil was used as an example for the positive electrode substrate 31, it can be made of a conductive material 322 made of a metal with good conductivity, for example. As a material with good conductivity, for example, in addition to Al foil, materials containing Al alloys can be used. The composition of the positive electrode substrate 31 is not limited to this.

[0066] The positive electrode composite layer 32 is formed by coating the positive electrode composite paste onto the positive electrode substrate 31 and drying it. The positive electrode composite layer 32 contains secondary particles 321a of the positive electrode active material 321, a conductive material 322, a binder 323, and additives such as a dispersant.

[0067] The positive electrode active material 321 contains a lithium transition metal oxide having a layered crystalline structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. Preferably, the transition metal elements contained in the lithium transition metal oxide are at least one of Ni, Co, and Mn. The positive electrode active material 321 of this embodiment is exemplified by a ternary system called NCM, which has a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0068] Furthermore, the positive electrode active material 321 in this embodiment is not limited to having a lithium transition metal oxide containing all of Ni, Co, and Mn. It may also have a composition containing, for example, Al.

[0069] <Separator 4> The separator 4 is a highly insulating nonwoven fabric, such as polypropylene, which is a porous resin, for insulating the negative electrode plate 2 and the positive electrode plate 3 and for holding the non-aqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. The separator 4 may also be a porous polymer membrane such as a porous polyethylene membrane, a porous polyolefin membrane, or a porous polyvinyl chloride membrane, or a lithium ion Li + Alternatively, ion-conductive polymer electrolyte membranes can be used alone or in combination.

[0070] (Operation of this embodiment) <Manufacturing method for positive electrode plate 3> Next, a method for manufacturing the lithium ion secondary battery 1 of the present embodiment will be described.

[0071] FIG. 7 is a flowchart showing the procedure of the method for manufacturing the positive electrode plate 3 of the present embodiment. First, a positive electrode active material 321, a conductive material 322, a binder 323, and a solvent, which are raw materials of the positive electrode mixture paste, are prepared. And in advance, the specific surface area S [m 2 / g] of the positive electrode active material 321, the coating film resistance R S [Ω / cm] of the conductive material 322, the rotation speed N [rpm] of the kneader NM, and the through - resistance R P [Ω / cm 2 of the positive electrode mixture layer 32 are obtained (S1). This procedure corresponds to the "step of obtaining the correlation" of the present invention. Next, the specific surface area S [m 2 / g] of the positive electrode active material 321 of the positive electrode plate 3 to be manufactured is measured (S2). This procedure corresponds to the "step of measuring the specific surface area" of the present invention. Also, using the above - mentioned simulated positive electrode plate 103, the coating film resistance R S [Ω / cm] of the conductive material 322 of the positive electrode plate 3 to be manufactured is measured (S3). This procedure of measuring the coating film resistance corresponds to the "step of measuring the resistance of the conductive material" of the present invention.

[0072] Next, in the rotation speed adjustment procedure (S4), in the procedure of obtaining the correlation (S1), the formula "R P =(R S ×3.7×10 [[ID=2,5]] -2 )+(S× - 4.5×10 -1 )+(N× - 1.6×10 -4 )+0.91…(Equation 1´)" has already been obtained. Transforming this formula, the formula "N=(R P -R SThe rotation speed N [rpm] of the kneader NM is adjusted from the formula (×aS×bd) / c…(Equation 2) (S4). This procedure corresponds to the "rotation speed adjustment step" of the present invention. Once the rotation speed N [rpm] is determined, the positive electrode active material 321, conductive material 322, binder 323, and solvent are put into the kneader NM and kneaded (S5). Once kneading is complete and the positive electrode composite paste is finished, the positive electrode composite paste is coated onto the positive electrode substrate 31. After that, a drying process is performed with hot air to solidify the positive electrode composite paste and form the positive electrode composite layer 32. Then, it is pressed to a predetermined thickness with a shaping press (not shown) and the surface is shaped (S6). The completed positive electrode plate 3 has a through-resistance R P [Ω / cm 2 The through-resistance R of the positive electrode plate 3 is measured (S7). P [Ω / cm 2 ] is the resistance [Ω / cm] of the positive electrode substrate 31 made of Al foil. 2 By pre-measuring the through-resistance R of the positive electrode composite layer 32 and dividing by that value, the through-resistance R of the positive electrode composite layer 32 is determined. P [Ω / cm 2 The through-resistance R of the positive electrode composite layer 32 can be calculated. Based on this result, the through-resistance R of the positive electrode composite layer 32 can be calculated. P [Ω / cm 2 The standard deviation σ of [ ] is calculated. It is then determined whether the calculated standard deviation σ falls within the set threshold Thσ (S8).

[0073] Here, the through-resistance R of the positive electrode composite layer 32 P [Ω / cm 2 If the standard deviation σ of ] is within the set threshold Thσ (S8: YES), then this positive electrode composite layer 32 is considered a good product and proceeds to the next process (end). If the through-resistance R of the positive electrode composite layer 32 P [Ω / cm 2 If the standard deviation σ of ] falls outside the set threshold Thσ (S8:NO), this positive electrode composite layer 32 is excluded as a defective product (S9).

[0074] (experiment) <Experiment 1> Figure 8 shows the measured through-resistance R of the positive electrode plate 3. P [Ω / cm 2 ] and the predicted penetration resistance R P ´[Ω / cm2 ] and the coating resistance R of the conductive material 322 S [Ω / cm], specific surface area S of positive electrode active material 321 [m 2 This table shows the relationship between [g] and the rotation speed N [rpm] of the kneader NM. Here, as Experiment 1, the coating resistance R of conductive material 322 was measured. S [Ω / cm], specific surface area S of positive electrode active material 321 [m 2 / g], the rotation speed N [rpm] of the kneader NM gives the penetration resistance R P [Ω / cm 2 We investigated whether ] was predictable or not.

[0075] Therefore, using this data, we can approximate the specific surface area S[m²] using regression analysis. 2 / g] and coating resistance R S [Ω / cm], the rotation speed N of the kneader NM [rpm], and the through-resistance R of the positive electrode composite layer 32. P [Ω / cm 2 The relationship between ] was found. The approximation formula (Equation 1) is given by, when a, b, and c are coefficients and d is a constant, R P =(R S ×a)+(S×b)+(N×c)+d…(Formula 1) I decided to represent it as such.

[0076] The results of the analysis showed that the partial regression coefficients were as follows: Coating film resistance R of conductive material 322 S The coefficient a = 3.7 × 10 -2 The specific surface area S[m²] of the positive electrode active material 321 was determined to be the specific surface area of ​​the positive electrode active material 321. 2 The coefficient b of [ / g] = -4.5 × 10 -1 The coefficient c = -1.6 × 10⁻¹⁰ of the rotational speed N [rpm] of the mixing machine NM. -4 The result was d = 0.91.

[0077] In other words, R P =(R S ×3.7×10 -2 ) + (S × -4.5 × 10 -1 ) + (N × -1.6 × 10 -4 )+0.91…(Formula 1´) It could be expressed as follows.

[0078] Figure 9 shows the measured through-wall resistance R. P [Ω / cm 2 ] and predicted penetration resistance R P ´[Ω / cm 2 This graph compares the measured penetration resistance R. The dotted line represents the measured penetration resistance R. P [Ω / cm 2 ] and predicted penetration resistance R P ´[Ω / cm 2 The plotted points indicate the position when ] is equal to R. P ´[Ω / cm 2 ] and the measured through-resistance R at that time P [Ω / cm 2 This point indicates the penetration resistance R predicted by this (Equation 1'). P ´[Ω / cm 2 ] and the measured through-wall resistance R P [Ω / cm 2 When compared with ], the plotted points appear to be roughly in the vicinity of the dotted line, and in reality R 2 Penetration resistance R with an accuracy of =0.95 P [Ω / cm 2 It was found that ] can be predicted.

[0079] <Experiment 2> Next, the through-resistance R P [Ω / cm 2 We investigated whether it is possible to control the variation in [ ]. Resistance R of the coating film of conductive material 322 S Ten types of [Ω / cm], and the specific surface area S[m] of the positive electrode active material 321. 2 Ten samples of positive electrode plates 3 were prepared using 10 different combinations of [ / g] and one combination of the rotation speed N [rpm] of the kneader NM, and each was designated as Experimental Example 1 to 10, with a through-resistance R P [Ω / cm 2 ] was measured.

[0080] Figure 10 shows the coating resistance R when the rotation speed N [rpm] is fixed. S [Ω / cm], specific surface area S[m 2 When the [g] changes, the penetration resistance R P [Ω / cm 2This table summarizes the results of Experiment 2, which shows [the following]. As shown in Figure 10, the through-resistance R of 10 samples of positive electrode plate 3. P [Ω / cm 2 The standard deviation of the variation is σ = 0.121, and the penetration resistance R P [Ω / cm 2 The average value of ] is R P = 0.77 [Ω / cm] 2 ] was.

[0081] Figure 11 shows the through-resistance R of Experiment 2. P [Ω / cm 2 This is a histogram showing the frequency for each category of ]. As shown in Figure 11, at a glance, the penetration resistance P [Ω / cm 2 It can be seen that there is a large variation in [ ].

[0082] <Experiment 3> Next, the through-resistance R of experimental examples 1-10 P [Ω / cm 2 We investigated whether the variation in [ ] could be suppressed by adjusting the rotation speed N [rpm] of the kneader NM.

[0083] As mentioned above, the through-resistance R P [Ω / cm 2 ] can be found using (Equation 1). R P =(R S ×a)+(S×b)+(N×c)+d…(Formula 1) In this embodiment, regression analysis is performed R P =(R S ×3.7×10 -2 ) + (S × -4.5 × 10 -1 ) + (N × -1.6 × 10 -4 )+0.91…(Formula 1´) It could be expressed as follows.

[0084] By rearranging (Equation 1), we get the through-resistance R P [Ω / cm 2 ], coating resistance R S [Ω / cm], specific surface area S[m 2From [ / g], the rotational speed N [rpm] of the kneader NM can be determined (Equation 2).

[0085] N=(R P -R S ×aS×bd) / c…(Formula 2) In this embodiment, N={R P -(R S ×3.7×10 -2 )-S×(-4.5×10 -1 )-0.91} / (-1.6×10 -4 )...(Equation 2')

[0086] Through-hole resistance R of Comparative Examples 1-10 P [Ω / cm 2 The average value of ] is R P = 0.77 [Ω / cm] 2 Therefore, this value represents the penetration resistance R P [Ω / cm 2 Set this as the target value for ]. Then, R P = 0.77 [Ω / cm] 2 Substituting ] into (Equation 2') we found the rotational speed N [rpm] of the kneader NM.

[0087] Figure 12 shows the through-resistance R P [Ω / cm 2 This table summarizes the results of Experiment 3, in which the rotational speed N [rpm] of the kneader NM was determined when [ ] was fixed. The penetration resistance R of Experimental Examples 1-10 P [Ω / cm 2 The average value is R P = 0.77 [Ω / cm] 2 Therefore, this value represents the penetration resistance R P [Ω / cm 2 ] is fixed as (Equation 2') and the through-resistance R P [Ω / cm 2 Substituting 0.77 into the value, the rotational speed N [rpm] was calculated. Naturally, the penetration resistance R P = 0.77 [Ω / cm] 2 Since ] is common, there is no variation and the standard deviation σ = 0.

[0088] From these calculations, by adjusting the rotational speed N [rpm] in experimental examples 1 to 10 from N = -219 [rpm] to N = 1897 [rpm], the theoretical penetration resistance R can be increased. P [Ω / cm 2 ] is 0.77[Ω / cm 2 It was found that it could be adjusted to ].

[0089] <Optimization of rotational speed N [rpm]> However, in a real-world mixing machine NM, the rotational speed N [rpm] cannot take a negative value. Also, if the rotational speed N [rpm] is too low, the particles of the positive electrode mixture paste will not disperse, and a conductive network will not be formed. On the other hand, if the rotational speed N [rpm] is too high, the shear force will be too great, destroying the particles of the positive electrode mixture paste or placing an excessive load on the mixing machine NM itself.

[0090] Therefore, in this embodiment, in the rotation speed adjustment procedure (S3), the rotation speed N [rpm] is limited by determining an upper and lower limit. In this case, the penetration resistance R of the positive electrode composite layer 32 P [Ω / cm 2 We confirmed whether the rotation speed N [rpm] of the kneader NM could be adjusted so that the standard deviation σ of ] falls within the set threshold Thσ. Specifically, in this embodiment, the rotation speed N [rpm] of the kneader NM is adjusted to a range of 50 [rpm] or more and 1000 [rpm] or less. Also, the penetration resistance R P [Ω / cm 2 The threshold Thσ for the standard deviation σ of [ ] was set to the standard deviation before adjustment σ = 0.121.

[0091] Figure 13 shows the penetration resistance R when the rotation speed N [rpm] of such a kneader NM is adjusted within the range of 50 [rpm] to 1000 [rpm]. P [Ω / cm 2 This is a table showing the pass-through resistance R. As shown in Figure 13, P [Ω / cm 2 ] is 0.74~0.90 [Ω / cm 2 The result was within the range of ], and the standard deviation was σ = 0.054.

[0092] As a result, even when the rotation speed N [rpm] of the kneader NM is adjusted to a range of 50 [rpm] or more and 1000 [rpm] or less, the penetration resistance R P [Ω / cm 2 The variation of [ ] had a standard deviation of σ = 0.054. This is a significant reduction in the standard deviation σ compared to the standard deviation before adjustment, which was σ = 0.121. In other words, the penetration resistance R P [Ω / cm 2 We were able to reduce the variability of [ ].

[0093] Figure 14 shows the through-resistance R of Experiment 2 shown in Figure 11. P [Ω / cm 2 This figure shows a histogram of the frequency for each category, with the histogram of the results shown in Figure 13 superimposed on it. The open histogram is the histogram in Figure 11, and the filled histogram is the histogram of the results shown in Figure 13. As shown in Figure 14, the adjusted through-resistance R P [Ω / cm 2 The variation in ] is, at first glance, the pre-adjustment through-resistance R P [Ω / cm 2 It can be seen that it is smaller compared to [ ].

[0094] (Operation of this embodiment) In the manufacturing method of the positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment, the specific surface area S[m²] is determined in advance in the procedure for obtaining the interrelationship (Figure 7: S1). 2 / g] and coating resistance R S [Ω / cm], the rotation speed N [rpm] of the kneader NM, and the penetration resistance R P The relationship with [Ω] is obtained. Then, the specific surface area S[m] of the positive electrode active material 321 is obtained. 2 The [ / g] value is measured (S2). Also, the coating resistance R of the conductive material 322 is measured. S [Ω / cm] is measured (S3). Based on these, the through-resistance R of the positive electrode composite layer 32 is measured in the rotation speed adjustment procedure (S4). P [Ω / cm 2The rotation speed N [rpm] of the kneader NM is adjusted so that the value of ] becomes the set value. Therefore, by adjusting the rotation speed N [rpm] of the kneader NM according to the raw materials, such as the positive electrode active material 321 and the conductive material 322, the penetration resistance R can be reduced. P [Ω / cm 2 The variation in ] can be adjusted to be small. Based on this, the through-resistance R P [Ω / cm 2 This allows for the manufacture of a positive electrode plate 3 with small variations in [the specified value]. As a result, it is possible to manufacture a lithium-ion secondary battery 1 with small variations in input / output characteristics.

[0095] (Effects of this embodiment) (1) According to the manufacturing method of the positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment, the through-resistance R of the manufactured electrode plate depends on the conductive material 322 with different properties. P [Ω / cm 2 This has the effect of being able to adjust the variation in [ ] to a smaller size.

[0096] (2) In this embodiment, the specific surface area S[m 2 / g] and coating resistance R S [Ω / cm], the rotation speed N of the kneader NM [rpm], and the through-resistance R of the positive electrode composite layer 32. P [Ω / cm 2 The relationship with ] is obtained (S1). Therefore, the specific surface area S[m 2 / g] and coating resistance R S Based on [Ω / cm], the through-resistance R of the positive electrode composite layer 32 P [Ω / cm 2 This has the effect of allowing you to adjust the rotation speed N[rpm] of the kneader NM so that ] becomes the precisely set value.

[0097] (3) In this embodiment, in the procedure for measuring the specific surface area (S2), the specific surface area S[m²] of the positive electrode active material 321 is 2 The through-resistance R is measured. P [Ω / cm 2 This has the effect of allowing for accurate estimation of [the value].

[0098] (4) In addition, the coating resistance R of the conductive material 322 is measured in advance using the coating resistance measurement procedure (S2). S The [Ω / cm] value is measured. Therefore, the through-resistance R P [Ω / cm 2 This has the effect of allowing for accurate estimation of [the value].

[0099] (5) Since the kneader NM is a twin-shaft kneader, it has the effect of being able to produce a homogeneous cathode composite paste in a stable state according to the rotation speed N [rpm]. (6) The rotational speed N [rpm] is a threshold Th between 50 [rpm] and 1000 [rpm]. N The rotation speed is adjusted within the range of [rpm]. This allows for the production of a cathode composite paste of stable quality while also preventing excessive load on the kneader NM.

[0100] (7) Specific surface area S[m²] of positive electrode active material 321 2 The specific surface area S[m² / g] is measured by the BET method. Therefore, even with the porous positive electrode active material 321, the specific surface area S[m² / g] is accurately measured. 2 It has the effect of being able to measure [ / g].

[0101] (8) The procedure for measuring the coating resistance includes the following steps: A paste preparation step is performed to prepare a paste containing simulated primary particles 132a made of an insulator that simulates the positive electrode active material 321 of the lithium-ion secondary battery 1, and a conductive material 322. A test coating preparation step is performed to prepare a test coating 132 containing simulated primary particles 132a by coating the paste prepared in the paste preparation step onto a simulated substrate 131 that simulates the positive electrode substrate 31 of the lithium-ion secondary battery 1 and drying it. Then, the coating resistance R, which is the surface resistance of the test coating 132, is measured. S A measurement process is performed to measure [Ω / cm]. This has the effect of accurately obtaining the properties of the conductive material 322 itself without being affected by other factors.

[0102] (9) In the procedure for determining the interrelationship (S1), the specific surface area S [m 2 / g] and coating resistance R S[Ω / cm], the rotation speed N of the kneader NM [rpm], and the through-resistance R of the positive electrode composite layer 32. P [Ω / cm 2 The relationship with ] is found using the following (Equation 1). a, b, and c are coefficients, and d is a constant. (Equation 1) is "R P =(R S It is expressed as (x a) + (S × b) + (N × c) + d. Therefore, the specific surface area S [m 2 / g] and coating resistance R S From [Ω / cm] and rotational speed N [rpm], the through-resistance R P [Ω / cm 2 This has the effect of allowing us to estimate [ ].

[0103] (10) In this embodiment, (Equation 1) is "R P =(R S ×3.7×10 -2 ) + (S × -4.5 × 10 -1 ) + (N × -1.6 × 10 -4 It can be expressed as ) + 0.91…(Equation 1'). Therefore, it has the effect of allowing us to precisely identify these relationships.

[0104] (11) In the procedure for adjusting the rotation speed (S3), "N=(R P -R S The rotational speed N [rpm] is calculated using the formula × aS × bd) / c…(Equation 2). Therefore, the specific surface area S [m 2 / g] and coating resistance R S [Ω / cm], penetration resistance R P [Ω / cm 2 This has the effect of allowing for easy estimation of the rotational speed N [rpm] from [the given data].

[0105] (12) The procedure for adjusting the rotation speed (S3) is to control the through-resistance R of the positive electrode composite layer 32. P [Ω / cm 2 The rotation speed N [rpm] of the kneader NM is adjusted so that the standard deviation σ of ] falls within the set threshold Thσ. Therefore, the penetration resistance R P [Ω / cm 2 This has the effect of allowing the rotational speed N [rpm] to be set without variation in [ ].

[0106] (Another example) ○This embodiment is one example for explaining the present invention, and it goes without saying that the present invention is not limited to this embodiment and can be implemented in various ways, for example, as follows.

[0107] ○Specific surface area [m 2 While the BET method was used as an example for measuring [ / g], other methods such as the moist heat method and reaction method can also be used. ○The measurement of the resistance value [Ω] of the conductive material 322 was illustrated using the method with the simulated positive electrode plate 103, but it is not limited to this method and can be carried out by other methods as well.

[0108] ○In this embodiment, a lithium-ion secondary battery 1 is given as an example of a secondary battery, but its shape, configuration, and purpose are not limited. It can also be implemented with other non-aqueous electrolyte secondary batteries, and even with alkaline aqueous solution secondary batteries. Furthermore, it can be applied to resin batteries, all-solid-state batteries, and the like. The electrode plate configuration can also be implemented, for example, with bipolar electrodes.

[0109] ○In addition, although a positive electrode plate 3 is shown as an example in this embodiment, it can also be implemented with a negative electrode plate 2. Furthermore, the positive electrode active material 321, conductive material 322, binder 323, solvent, etc., are not limited to those exemplified, and other materials can be used. The other exemplified materials are merely examples and are not limited to them; they can be appropriately selected by those skilled in the art. For example, in this embodiment, fibrous carbon, specifically CNT (carbon nanotube), is exemplified as the conductive material 322, 132b, but other conductive materials, such as fibrous carbon microfibers or granular AB (acetylene black), may be used.

[0110] ○The numerical values, ranges, etc., in this embodiment are examples only and can be optimized by those skilled in the art, and are not limited to these. ○The drawings are schematic diagrams for explaining the manufacturing method of the positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment, and the quantities, shapes, dimensions, etc. do not reflect the actual form.

[0111] ○The flowchart shown in Figure 7 is an example of the procedure for manufacturing the positive electrode plate 3 of the lithium-ion secondary battery 1 of this embodiment. The order of the procedure can be changed, and steps can be added or deleted. For example, steps S2 and S3 can be swapped, or steps S7 and S8 can be omitted.

[0112] Furthermore, it goes without saying that the present invention can be implemented by those skilled in the art by adding, deleting, or modifying its configuration, as long as it does not deviate from the scope of the claims. [Explanation of Symbols]

[0113] N[rpm]... Rotational speed (of the kneader NM) Th N [rpm]... (threshold for rotational speed N) R S [Ω / cm]...Coating film resistance (of conductive materials) S[m 2 / g]...Specific surface area (of the positive electrode active material) R P [Ω / cm 2 ]...(Measured) Through-hole resistance R P ´[Ω / cm 2 ]...(Predicted) Penetration resistance σ...Standard deviation Thσ...threshold 1…Lithium-ion rechargeable battery (cell battery) 11…Battery case 12...Electrode body 13...Nonaqueous electrolyte 14…Positive external terminal 15…Negative external terminal 16…Positive current collection terminal 17... Negative current collection terminal 2… Negative plate 21... Negative electrode substrate 22...Negative electrode composite material layer 23... Negative electrode current collector 3...Positive plate (electrode plate) 31…Positive electrode substrate (substrate) 32...Positive electrode composite material layer (compound material layer) 321...Cathode active material (active material) 321a…Secondary particle 321b…Primary particle 321c…Gap 321d…Cavity 322... Conductive materials 323…Binding material 33…Positive electrode current collector 103... Simulated positive electrode plate 131... Simulated circuit board 132...Test coating 132a...Simulated primary particle 132b…Conductive material 132c... Binding material 133... Positive electrode current collector 4... Separator OM…Resistance meter MP1, MP2... Measurement points R S [Ω cm]…Coating film resistance (surface resistance) NM... Mixing machine (twin-shaft mixer) 202... Barrel 203... Rotation axis 204... Axis unit 206... Confinement Room 207... Inlet 208…Discharge port 209...First rotation axis L1…axis 211...Second rotation axis 214...Paddle vs 216... Paddle 216a...First paddle 216b... Second paddle 218... Screw 218a... Upstream screw 218b... Downstream screw

Claims

1. A method for manufacturing an electrode plate of a secondary battery, comprising kneading an active material, a conductive material, and a solvent in a kneader to produce a composite paste, and then coating the composite paste onto a substrate to form a composite layer, The specific surface area S [m²] of the active material is determined in advance. ２ / g] and the coating film resistance R of the conductive material Ｓ [Ω / cm], the rotational speed N [rpm] of the kneader, and the penetration resistance RP [Ω / cm] of the asphalt layer. ２ The steps include obtaining the relationship with ], The specific surface area S [m ２ The steps for measuring the specific surface area by measuring [ / g], The coating film resistance R Ｓ The steps for measuring the resistance of a conductive material by measuring [Ω / cm], Based on the above mutual relationship, the specific surface area S [m ２ / g] and the coating film resistance R Ｓ [Ω / cm], from which the through resistance R Ｐ of the composite layer [Ω / cm ２ becomes the set value, a step of adjusting the rotational speed N [rpm] of the kneader A method for manufacturing electrode plates of a secondary battery, characterized by comprising the following:

2. The method for manufacturing electrode plates of a secondary battery according to claim 1, characterized in that the kneader is a twin-shaft kneader.

3. The rotational speed N [rpm] is the threshold Th Ｎ A method for manufacturing an electrode plate of a secondary battery according to claim 2, characterized in that the rotational speed is adjusted within the range of [rpm].

4. The aforementioned threshold Th Ｎ The method for manufacturing an electrode plate of a secondary battery according to claim 3, characterized in that [rpm] is in the range of 50 [rpm] to 1000 [rpm].

5. The step of measuring the specific surface area is as follows: The specific surface area S [m²] of the active material ２ A method for manufacturing an electrode plate of a secondary battery according to claim 1, characterized in that the [ / g] is measured by the BET method.

6. The step of measuring the resistance of the conductive material is: A paste-making step for making a paste comprising simulated primary particles made of an insulator that simulates the active material of the secondary battery, and the conductive material, A test coating preparation step involves applying the paste prepared in the paste preparation step to a simulated substrate that simulates the substrate of the secondary battery and drying it to prepare a test coating containing the simulated primary particles. The coating resistance R is the surface resistance of the test coating film. Ｓ Measurement process for measuring [Ω / cm] and A method for manufacturing an electrode plate of a secondary battery according to claim 1, characterized by including the following:

7. In the step of determining the aforementioned interrelationship, the specific surface area S [m²] ２ / g] and the coating film resistance R Ｓ [Ω / cm], the rotational speed N [rpm] of the kneader, and the penetration resistance RP [Ω / cm] of the asphalt layer. ２ The relationship between ] is given by, when a, b, and c are coefficients and d is a constant, R Ｐ = (R) Ｓ ×a)+(S×b)+(N×c)+d…(Equation 1) A method for manufacturing an electrode plate of a secondary battery according to claim 1, characterized by being represented by

8. The above formula 1 is, R Ｐ = (R) Ｓ ×3.7×10 －２ ) + (S × - 4.5 × 10 －１ ) + (N×-1.6×10 －４ ) + 0.91…(Equation 1') A method for manufacturing an electrode plate of a secondary battery according to claim 7, characterized by being represented by [this].

9. The aforementioned step of adjusting the rotational speed is: N = (R) Ｐ -R Ｓ ×a-S×b-d) / c…(Equation 2) The method for manufacturing an electrode plate of a secondary battery according to claim 7, characterized in that the rotational speed N [rpm] is determined by this method.

10. The aforementioned step of adjusting the rotational speed is: The penetration resistance RP [Ω / cm] of the aforementioned composite layer ２ The method for manufacturing an electrode plate of a secondary battery according to claim 9, characterized in that the rotation speed N [rpm] of the kneader is adjusted so that the standard deviation σ of ] falls within a set threshold Thσ.

11. A method for manufacturing an electrode plate of a secondary battery according to any one of claims 1 to 10, characterized in that the secondary battery is a lithium-ion secondary battery.

12. A method for manufacturing an electrode plate of a secondary battery according to any one of claims 1 to 10, characterized in that the electrode plate is a positive electrode plate.

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