Evaluation method for evaluating conductive material to be used for secondary battery

Abstract

To correctly evaluate the conductivity and dispersibility of a conductive material used for a secondary battery.SOLUTION: An evaluation method for evaluating a conductive material 322 used for a lithium ion secondary battery 1, comprises: a paste production step of producing paste containing a simulation primary particle 132a formed of an insulator simulating a cathode active material 321 of the lithium ion secondary battery 1 and a conductive material 132b; a test coating film production step of producing a test coating film 132 containing the simulation primary particle 132a by coating the paste to a simulation substrate 131 obtained by simulating a cathode substrate 31 of the lithium ion secondary battery 1 and drying them; and a conductive evaluation step of evaluating conductive materials 322 and 132b by measuring a coating membrane resistance RS as a surface electrical resistance of the test coating film 132.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to an evaluation method for evaluating a conductive material used in a secondary battery. More specifically, the present invention relates to an evaluation method for evaluating a conductive material used in a secondary battery that accurately evaluates the conductivity, dispersibility, etc. of the conductive material.

Background Art

[0002] Secondary batteries, for example, lithium-ion secondary batteries, have a high voltage and large volume energy density [Wh / L] and weight energy density [Wh / kg], and are often mounted as a power source for driving electric vehicles including hybrid vehicles. In electric vehicles, etc., large current charge and discharge are required due to large current discharge during high load operation, rapid charging, and regenerative current. However, a binder that supports a lithium transition metal oxide such as lithium nickel cobalt manganese oxide (LiNi 1 / 3 C o1 / 3 Mn 1 / 3 O2) has relatively low conductivity itself. Therefore, in order to improve the input / output performance of a lithium-ion secondary battery at a large current, a highly conductive material may be added to the positive electrode mixture layer of the positive electrode plate for the purpose of reducing the electrical resistance between a large number of positive electrode active material particles and a non-aqueous electrolyte, etc. As an example of such a conductive material in such a case, a fibrous carbon material such as carbon nanotubes (CNT) or a granular acetylene black (AB) having high conductivity may be used. In particular, carbon nanotubes have a fibrous shape and can easily form a conductive network even in a small amount between positive electrode active materials composed of lithium transition metal oxides dispersed in the positive electrode mixture layer, thereby reducing the electrical resistance between the non-aqueous electrolyte and the positive electrode active material.

[0003] For example, carbon nanotubes as described in Patent Document 1 are easily dispersed in a resin and exhibit high conductivity in the resin, and can reduce the electrical resistance (coating film resistance) in the positive electrode mixture layer by adding them to the positive electrode mixture layer.

Prior Art Documents

Patent Document

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, the lithium transition metal oxide used as the positive electrode active material is first made into primary particles that are crystals, and then these primary particles are aggregated to form spherical secondary particles with cavities, so that the reaction on the surface of the positive electrode active material can be efficiently carried out. Such a positive electrode active material having the shape of secondary particles has gaps on its surface that communicate with the internal cavities, but the degree varies greatly depending on conditions such as firing.

[0006] Conventionally, for the coating film resistance of the positive electrode mixture layer of the positive electrode plate, a positive electrode mixture layer was formed on a substrate made of an actual PET (polyethylene terephthalate) film or the like, and its surface was measured and its conductivity was evaluated as the coating film resistance. However, unlike the case of being dispersed in a homogeneous resin as described in Patent Document 1, in the case of the positive electrode mixture layer, when the conductive material enters the inside of the particles of the positive electrode active material from the gaps, the coating film resistance changes. For example, when the gaps between the particles of the positive electrode active material are large, a large amount of the conductive material enters, and the conductive material existing between the positive electrode active materials decreases. Then, it becomes difficult to form a conductive network by the conductive material, and the resistance increases. For these reasons, there has been a problem that even if the coating film resistance of the positive electrode mixture layer is accurately measured, the conductive material cannot be correctly evaluated.

[0007] The situation where such a conductive material cannot be correctly evaluated is not a problem limited to the hollow positive electrode active material of the positive electrode plate, but a problem that can occur in the negative electrode plate. Furthermore, it is not a problem limited to lithium ion secondary batteries, but a problem that also occurs in other non-aqueous electrolyte secondary batteries, alkaline secondary batteries, and other secondary batteries.

[0008] The problem to be solved by the evaluation method for evaluating the conductive material used in the secondary battery of the present invention is to accurately evaluate the conductivity, dispersibility, etc. of the conductive material of the secondary battery.

Means for Solving the Problem

[0009] In order to solve the above problems, in the evaluation method for evaluating the conductive material used in the secondary battery of the present invention, in a secondary battery including an electrode plate in which a composite material layer containing an active material and a conductive material is formed on a substrate, it is an evaluation method for evaluating the conductive material used in the secondary battery, including a paste preparation step of preparing a paste containing simulated primary particles made of an insulator simulating the active material of the secondary battery and the conductive material, and a test coating film preparation step of coating and drying the paste prepared in the paste preparation step on a simulated substrate simulating the substrate of the secondary battery to prepare a test coating film containing the simulated primary particles, and a conductivity evaluation step of evaluating the conductive material by measuring the surface resistance of the test coating film, that is, the coating film resistance [Ω·cm].

[0010] In this case, the compounding volume ratio R v [vol%] of the conductive material with respect to the simulated primary particles of the paste is preferably set based on the compounding volume ratio R v [vol%] of the active material and the conductive material.

[0011] The compounding mass ratio R W [wt%] of the conductive material with respect to the simulated primary particles can be set to a range including the portion with the largest curvature of the graph showing the change in the compounding mass ratio R W [wt%] and the coating film resistance [Ω·cm] of the test coating film from the graph.

[0012] Also, when the compounding mass ratio of the conductive material with respect to the simulated primary particles is R W [wt%], the compounding mass ratio R W [wt%] can be in the range of 1 [wt%] or more and 3 [wt%] or less.

[0013] The average particle diameter D of the simulated primary particles S (d50) [μm] is desirably substantially the same as the particle diameter of the active material of the secondary battery. In this case, the average particle diameter D of the simulated primary particles S (d50) [μm] can be 0.1 [μm] or more and 50 [μm] or less.

[0014] It is desirable that the test coating film has the same thickness [μm] as the thickness [μm] of the composite layer of the secondary battery. It can be preferably applied when the active material is secondary particles in which primary particles are aggregated. It can be preferably applied when the conductive material is made of fibrous carbon. Further, the simulated primary particles can be preferably applied when they are made of alumina.

[0015] It is desirable that the simulated substrate is formed of an insulator, and it is desirable that the simulated substrate is formed of a PET film. The average diameter D of the conductive material C (d50) [nm] is 1 [nm] or more and 100 [nm] or less, and the average length L of the conductive material C (d50) [nm] is desirably 100 [nm] or more and 10000 [nm] or less.

[0016] It can be particularly preferably carried out when the secondary battery is a lithium-ion secondary battery. Further, it can be particularly preferably carried out when the electrode plate is a positive electrode plate.

Advantages of the Invention

[0017] According to the evaluation method for evaluating the conductive material used in the secondary battery of the present invention, the conductivity, dispersibility, etc. of the conductive material can be accurately evaluated.

Brief Description of the Drawings

[0018]

Figure 1

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Figure 12

Mode for Carrying Out the Invention

[0019] Hereinafter, an embodiment of an evaluation method for evaluating the conductive material used in the secondary battery of the present invention will be described with reference to FIGS. 1 to 12, taking as an example the evaluation method for evaluating CNT (carbon nanotube), which is the conductive material 322 of the positive electrode plate 3 used in the lithium-ion secondary battery 1.

[0020] Note that this embodiment is an example, and the electrode plate is not limited to the positive electrode plate, and the secondary battery is not limited to the lithium-ion secondary battery. (Overview of this Embodiment) <Background Art of this Embodiment> FIG. 1 is an enlarged perspective schematic view of the positive electrode active material 321. FIG. 2 is an enlarged schematic cross-sectional view of the positive electrode active material 321. As shown in FIGS. 1 and 2, the lithium transition metal oxide used as the positive electrode active material 321 first forms primary particles 321b that are crystals. If left as they are, they tend to aggregate. Therefore, in order to improve dispersibility, the primary particles 321b are further aggregated to form spherical secondary particles 321a having cavities 321d. By doing so, a material that efficiently performs reactions on the surface of the positive electrode active material 321 is used. In the positive electrode active material 321 having a shape with cavities 321d in such secondary particles 321a, it has gaps 321c on its surface that communicate with the internal cavities 321d. The number and degree of the area of these gaps 321c vary greatly depending on conditions such as firing.

[0021] FIG. 3(a) is a schematic view showing the relationship with the conductive material 322 when there are few gaps 321c in the positive electrode active material 321. FIG. 3(b) is a schematic view showing the relationship with the conductive material 322 when the gaps 321c in the positive electrode active material 321 are of medium degree. FIG. 3(c) is a schematic view showing the relationship with the conductive material 322 when there are many gaps 321c in the positive electrode active material 321. The conductive material 322 has a large variation in the gaps 321c. For example, when there are few gaps 321c as shown in FIG. 3(a), the conductive material 322 does not enter the cavities 321d of the positive electrode active material 321. In this case, the conductive material 322 will exist in the binder 323 between the secondary particles 321a of the adjacent positive electrode active materials 321. Then, in the positive electrode composite layer 32 in which the same amount [vol%] of the conductive material 322 is blended, the density of the conductive material 322 per volume of the positive electrode composite layer 32 increases. As a result, the conductive materials 322 are likely to come into contact with each other and are likely to form a conductive network. That is, the coating resistance R S [Ω·cm] becomes small.

[0022] On the other hand, as shown in Fig. 3(c), when there are many gaps 321c, the conductive material 322 can easily enter the cavities 321d of the positive electrode active material 321 through the gaps 321c. In this case, the conductive material 322 will exist not only in the binder 323 between the secondary particles 321a of the positive electrode active material 321 but also in the cavities 321d. Then, even for the positive electrode composite layer 32 with the same amount [vol%] of the conductive material 322 blended, the number of the conductive material 322 per unit volume of the positive electrode composite layer 32 will be reduced. As a result, it becomes difficult for the conductive materials 322 to contact each other, making it difficult to form a conductive network. That is, the coating resistance R S [Ω·cm] of the positive electrode composite layer 32 increases.

[0023] Also, when there are gaps 321c as shown in Fig. 3(b), but the number and area thereof are smaller than those shown in Fig. 3(c), it will exhibit properties intermediate between those of Fig. 3(a) and Fig. 3(c). Fig. 4 is a schematic cross-sectional view showing the variation in the mode of the positive electrode active material 321 in the positive electrode composite layer 32. The actual positive electrode active material 321 as a raw material is not homogeneous as shown in Fig. 4, and there are differences in the number of gaps 321c as shown in Figs. 3(a) to (c).

[0024] Furthermore, in the actual positive electrode composite layer 32, the positive electrode composite paste of the positive electrode composite layer 32 before being coated on the positive electrode substrate 31 is compressed in the press forming process after being coated on the positive electrode substrate 31. For this reason, there are cases where the secondary particles 321a of the positive electrode active material 321 are disintegrated or single primary particles 321b. Therefore, in the completed lithium-ion secondary battery 1, the state of the positive electrode active material 321 is not homogeneous. For this reason, no matter how accurately the coating resistance R S [Ω·cm] of the positive electrode composite layer 32 is measured, there is a problem that the conductivity of the conductive material 322 itself and the evaluation of the quality of the positive electrode composite layer 32 itself cannot be performed.

[0025] <The positive electrode plate 3 of the lithium-ion secondary battery 1 and the simulated positive electrode plate 103> Fig. 5(a) is a schematic diagram of the simulated positive electrode plate 103 of the present embodiment. Fig. 5(b) is a schematic diagram of the positive electrode plate 3 of the lithium-ion secondary battery 1 of the present embodiment. The simulated positive electrode plate 103 is a test configuration for accurately measuring the conductivity and dispersibility of the conductive material 322 that cannot be accurately measured in the positive electrode plate 3 of the lithium-ion secondary battery 1.

[0026] <Configuration of the positive electrode plate 3 of the lithium-ion secondary battery 1> First, the positive electrode plate 3 of the lithium-ion secondary battery 1 of the present embodiment will be described with reference to Fig. 5(b). The positive electrode plate 3 of the lithium-ion secondary battery 1 of the present embodiment includes a positive electrode substrate 31 made of Al foil, and a positive electrode composite layer 32 is formed on the positive electrode substrate 31. The positive electrode composite layer 32 is a layer formed by coating a positive electrode composite paste and drying and press-molding it. The positive electrode composite paste is prepared by kneading a positive electrode active material 321, a conductive material 322, and a binder 323 with a solvent.

[0027] In this positive electrode plate 3, the secondary particles 321a of the positive electrode active material 321 as described above will have differences in the formation of the conductive network by the conductive material 322 depending on the shape, especially the amount of gaps 321c. Here, the "coating film resistance R S [Ω·cm]" of the present embodiment will be described, and the evaluation method of the conductive material 322 will be described. For the "coating film resistance R S [Ω·cm]" of the present embodiment, first, the positive electrode composite layer 32 is coated on a simulated substrate 131 made of a PET (polyethylene terephthalate) film instead of the positive electrode substrate 31 made of Al foil. Then, measurement points MP1 and MP2 are provided at positions 1 [cm] apart on the surface of the positive electrode composite layer 32. The probes of a resistance meter OM are brought into contact with these measurement points MP1 and MP2 to measure the coating film resistance R S [Ω·cm], which is the surface resistance of the conductive material 322 between them. The measurement was performed by the four-terminal method using a resistance meter with a four-probe probe of, for example, Hioki E.E. Corporation. With this "coating film resistance R S [Ω·cm]", the conductivity and dispersibility of the conductive material can be accurately evaluated.

[0028] Conventionally, on the surface facing the surfaces of measurement points MP1 and MP2 of the positive electrode composite layer 32, there was a positive electrode substrate 31 made of conductive Al foil. Therefore, in reality, only the resistance in the thickness direction of the positive electrode composite layer 32 was known. 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, the coating resistance R S [Ω·cm] was measured using a simulated substrate 131 made of a PET (polyethylene terephthalate) film to eliminate the influence of the positive electrode substrate 31 made of Al foil.

[0029] However, as described above, the secondary particles 321a of the positive electrode active material 321 not only have conductivity themselves, but also differ in the formation of the conductive network by the conductive material 322 depending on their shape, particularly the amount of gaps 321c. For this reason, it has not been possible to accurately observe the conductivity of the conductive material 322 itself and the state of the conductive network formed by dispersion.

[0030] <Configuration of the simulated positive electrode plate 103 of the present embodiment> Next, the simulated positive electrode plate 103 of the present embodiment will be described with reference to FIG. 5(a). In the simulated positive electrode plate 103 of the present embodiment shown in FIG. 5(a), the positive electrode active material 321 is replaced with simulated primary particles 132a.

[0031] FIG. 6 is a schematic diagram showing the relationship between the simulated primary particles 132a and the conductive material 132b. As shown in FIG. 6, the simulated primary particles 132a are particles made of an insulator produced by simulating the positive electrode active material 321 of the lithium ion secondary battery 1 as shown in FIG. 3(a). Here, "simulation" means approximating the outer shape of the secondary particles 321a of the positive electrode active material 321 and imitating the positive electrode active material 321 structurally. For example, its average particle diameter (d50) [μm] and the like are substantially the same. In the present application, unless otherwise specified, "the average particle diameter D of the simulated primary particles 132a S [μm]" refers to the median diameter (d50) in the frequency distribution measured by the laser diffraction method, and the average diameter D of the conductive material 132b C [nm] or the average length L C[nm] refers to the value obtained by image analysis of electron micrographs.

[0032] Here, "substantially" means that even if there are some shape differences such as slight unevenness, the mechanical function of the simulated primary particles 132a in the test coating film 132 is equivalent to the mechanical function of the positive electrode active material 321 in the positive electrode composite layer 32. However, since its material is made of an insulator and alumina particles are used in this embodiment, the electrochemical function is different.

[0033] Also, the "primary particles" mentioned here are the particles in the state formed first when manufacturing the particles. In the simulated primary particles 132a, the whole is a solid mass of crystal particles. On the other hand, in the positive electrode active material 321, a large number of primary particles aggregate to form secondary particles 321a. As a result, in the positive electrode active material 321 as shown in FIGS. 3(b) and 3(c), it has cavities 321d and gaps 321c inside the secondary particles 321a. In contrast, the simulated primary particles 132a do not have such internal cavities or gaps.

[0034] <Conductive material 132b> Regarding the conductive material 132b, although the name is different, it is the same as the conductive material 322 in the positive electrode composite layer. That is, in this embodiment, carbon nanotubes are exemplified, but all of its type, length, diameter, mass, addition amount, etc. are the same. Also, the compounding volume ratio R of the conductive material 132b to the simulated primary particles 132a in the test coating paste V [vol%] is based on the compounding volume ratio R of the positive electrode active material 321 and the conductive material 322 V [vol%]. That is, it is for making the amount substantially the same. Note that this compounding volume ratio R V [vol%] can be replaced by the compounding mass ratio R of the conductive material 132b to the simulated primary particles 132a W [wt%]. This is because it is difficult to specify the exact volume [mm 3 due to the influence of bulk density and porosity, so it is replaced with the mass [g] that is easy to measure in advance for implementation.

[0035] The reason for doing so is as follows. That is, the evaluation method for evaluating the conductive material 322 used in the lithium ion secondary battery 1 of the present embodiment aims to accurately evaluate the conductivity, dispersibility, etc. of the conductive material 322 itself contained in the positive electrode mixture layer 32 of the lithium ion secondary battery 1. Therefore, it is to strictly reproduce the actual state. Generally, in the field of engineering, conductivity is expressed in units of [S / m], but in the present embodiment, such measurements are performed to analyze the dispersion state of the actual conductive material 322 in the lithium ion secondary battery 1.

[0036] In the present embodiment, fibrous carbon, specifically CNT (carbon nanotube), is exemplified as the conductive materials 322 and 132b. However, other conductive materials, such as fibrous carbon microfibers or even granular AB (acetylene black), may be used. Even if it is a granular conductive material, similar to the fibrous conductive material, it enters the cavity 321d through the gap 321c of the positive electrode active material 321 or enters gaps, etc. And the problem of changing the configuration of the conductive network by the conductive material in the binder 323 is the same.

[0037] Specifically, in the present embodiment, the average diameter D C (d50) [nm] of the conductive material 132b is 1 [nm] or more and 100 [nm] or less. Also, the average length L C (d50) [nm] of the conductive material is 100 [nm] or more and 10000 [nm] or less.

[0038] <simulation substrate 131> The simulated positive electrode plate 103 of this embodiment has the same external shape as the positive electrode substrate 31, but includes a simulated substrate 131 made of an insulator instead of an Al foil. The material is not limited as long as it is insulating and the test coating paste can be applied. For example, in this embodiment, a PET (polyethylene terephthalate) film is used, which has high insulation 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 formed by applying a test coating paste and drying and press-molding it. The test coating paste is prepared by kneading simulated primary particles 132a, a conductive material 132b, and a binder 132c with a solvent. The conductive material 132b, the binder 132c, and the solvent are the same as those of the conductive material 322, the binder 323, and the 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 the simulated primary particles 132a.

[0039] <Coating resistance R S [Ω·cm] measurement> In the evaluation method for evaluating the conductive material used in the lithium-ion secondary battery 1 of this embodiment, similar to the conventional measurement method, the measurement is performed on the surface of the test coating film 132 of the completed simulated positive electrode plate 103. For the measurement, measurement points MP1 and MP2 are provided at a position 1 [cm] apart, and the probes of the resistance meter OM are brought into contact with these measurement points MP1 and MP2 to measure the coating resistance R S [Ω·cm] of the conductive material between them.

[0040] Here, the positive electrode active material 321 has been replaced by insulating simulated primary particles 132a. Also, the positive electrode substrate 31 has been replaced by an insulating simulated substrate 131. For this reason, the simulated primary particles 132a not only have insulating properties themselves, but also, due to their shape, especially the absence of gaps 321c, the conductive material 322 always exists at the same density. Therefore, the formation of the conductive network by the conductive material 322 is always in the same state. As a result, it is possible to accurately observe the conductivity of the conductive material 322 itself and the state of the conductive network formed by the dispersion of the conductive material 322. Further, on the surface of the positive electrode composite layer 32 facing the surfaces of the measurement points MP1 and MP2, there is a simulated substrate 131 made of an insulating resin. For this reason, the measurement can be performed to measure only the resistance of the conductive network formed by the conductive material 132b in the test coating film 132 without being affected by the conductive positive electrode substrate 31. As a result, the evaluation of the conductive material 132b used as a raw material can be made accurate.

[0041] (Configuration of this Embodiment) Here, an example of the lithium-ion secondary battery 1 that is a premise for the evaluation method for evaluating the CNT, which is the conductive material 322 used in the lithium-ion secondary battery 1 of this embodiment, will be described. Note that the intention is not to limit the type of battery targeted.

[0042] <Configuration of Lithium-Ion Secondary Battery 1> FIG. 7 is a perspective view showing an outline of the external configuration of the lithium-ion secondary battery 1 of this embodiment.

[0043] As shown in FIG. 7, 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 electric 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 via 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 via the lid. The positive electrode current collector terminal 16 is electrically connected to a 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 a negative electrode current collecting portion 23 (see FIG. 8) of the electrode body 12.

[0044] <Electrode body 12> FIG. 8 is a schematic diagram showing the configuration of the wound electrode body 12. The electrode body 12 is formed by laminating a large number of negative electrode plates 2, positive electrode plates 3, and separators 4 disposed therebetween. The laminated negative electrode plates 2, positive electrode plates 3, and separators 4 are wound to form a flat shape. The negative electrode plate 2 has a negative electrode composite material layer 22 formed on a negative electrode substrate 21 made of a copper foil serving as a base material. A negative electrode current collecting portion 23 is provided on one end side in the width direction W (winding axis direction) orthogonal to the winding direction L. The negative electrode current collecting portion 23 has a configuration in which the negative electrode composite material layer 22 is not formed and the negative electrode substrate 21 is exposed.

[0045] The positive electrode plate 3 has a positive electrode composite material layer 32 formed on a positive electrode substrate 31 made of an aluminum foil serving as a base material. As shown in FIG. 8, a positive electrode current collecting portion 33 is provided on the other end side (opposite side to the negative electrode current collecting portion 23) in the width direction W (winding axis direction) orthogonal to the direction (winding direction L) in which the positive electrode substrate 31 is wound. The positive electrode current collecting portion 33 has a configuration in which the positive electrode composite material layer 32 is not formed and the metal of the positive electrode substrate 31 is exposed.

[0046] <Laminated Structure of Electrode Body 12> As shown in Fig. 8, 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.

[0047] The negative electrode plate 2 is provided with negative electrode composite material layers 22 on both sides of a negative electrode substrate 21 serving as a negative electrode base material. One end portion of the negative electrode substrate 21 serves as a negative electrode current collector portion 23 where the metal is exposed. The positive electrode plate 3 is provided with positive electrode composite material layers 32 on both sides of a positive electrode substrate 31 serving as a positive electrode base material. The other end portion of the positive electrode substrate 31 serves as a positive electrode current collector portion 33 where the metal is exposed.

[0048] The negative electrode plate 2 and the positive electrode plate 3 are stacked via the separator 4 to form a laminate. As shown in Fig. 4, this laminate is wound in the longitudinal direction around a winding axis to form a wound-type electrode body 12 that is formed flat as shown in Fig. 7.

[0049] <Non-aqueous Electrolyte 13> The non-aqueous electrolyte 13 of the lithium-ion secondary battery 1 according to the present embodiment shown in Fig. 7 is a composition in which a lithium salt is dissolved in an organic solvent. As the lithium salt, LiClO4, LiPF6, LiAsF6, LiBF4, LiSO3CF3, etc. can be used. As the organic solvent, cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, trifluoropropylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, dimethoxyethane, sulfur compounds such as ethyl methyl sulfone, butane sultone, or phosphorus compounds such as triethyl phosphate, trioctyl phosphate, etc. can be mentioned. As the non-aqueous electrolyte 13, these can be mixed and used in one or more types. Note that the composition of the non-aqueous electrolyte 13 is not limited to this.

[0050] In the present embodiment, EC (ethylene carbonate) is used as the organic solvent. In addition, in this embodiment, as an additive for the film-forming material, for example, LiBOB (lithium bisoxalate borate, LiB(C2O4)2) may be added.

[0051] <Constituent elements of the electrode body 12> Next, the negative electrode plate 2, the positive electrode plate 3, and the separator 4, which are the constituent elements of the electrode body 12, will be described.

[0052] <Negative electrode plate 2> As shown in FIG. 8, negative electrode composite material layers 22 are formed on both surfaces of a negative electrode substrate 21, which is a negative electrode base material, to constitute the negative electrode plate 2. In the source process, a negative electrode composite material paste is applied to the negative electrode substrate 21 for the negative electrode composite material layer 22. Then, through a drying process, a pressing process, and a cutting process, the negative electrode plate 2 is completed.

[0053] In this embodiment, the negative electrode substrate 21 is composed of a Cu foil. The negative electrode substrate 21 serves as a base as an aggregate of the negative electrode composite material layer 22 and has a function of a current collecting member that collects electricity from the negative electrode composite material layer 22. One end portion of the negative electrode substrate 21 becomes a negative electrode current collecting portion 23 where the metal surface is exposed without the negative electrode composite material layer 22 being formed. That is, the negative electrode active material particles are electrically connected to the negative electrode external terminal 15 through the negative electrode substrate 21, the negative electrode current collecting portion 23, and the negative electrode current collecting terminal 17.

[0054] The negative electrode composite material layer 22 is composed of, as raw materials, a negative electrode active material, a binder (binding material) as a secondary material here, an additive, and the like. An organic solvent and the like are added to the raw materials and the secondary materials and kneaded to produce a negative electrode composite material paste. This negative electrode composite material paste is applied to the negative electrode substrate 21. The applied negative electrode composite material paste is dried and formed by pressing, whereby the negative electrode plate 2 is completed.

[0055] In this embodiment, the negative electrode active material is powdery graphite particles GP made of graphite (graphite) having a layered structure, etc., and is a material capable of occluding and releasing lithium ions Li + and releasing. <Positive electrode plate 3> As shown in FIGS. 5(b) and 8, the positive electrode plate 3 is composed of a positive electrode substrate 31, which is a positive electrode base material, and a positive electrode mixture layer 32 coated thereon. The positive electrode mixture layer 32 is formed by coating the positive electrode substrate 31 with a positive electrode mixture paste in the source process, and the positive electrode plate 3 is completed through a drying process, a pressing process, and a cutting process.

[0056] The positive electrode mixture layer 32 is formed on both sides of the positive electrode substrate 31 to constitute the positive electrode plate 3. In the embodiment, the positive electrode substrate 31 is composed of an Al foil. The positive electrode substrate 31 serves as a base as an aggregate of the positive electrode mixture layer 32 and has a function of a current collecting member for collecting electricity from the positive electrode mixture layer 32.

[0057] First, although the positive electrode base material constituting the positive electrode substrate 31 is exemplified by an Al foil, for example, it may be composed of a conductive material made of a metal having good conductivity. As a material having good conductivity, for example, in addition to an Al foil, a material containing an Al alloy can be used. The configuration of the positive electrode substrate 31 is not limited to this.

[0058] The positive electrode mixture layer 32 is formed by coating and drying a positive electrode mixture paste on the positive electrode substrate 31. The positive electrode mixture layer 32 contains secondary particles 321a of a positive electrode active material 321, a conductive material 322, a binder 323, and additives such as a dispersant.

[0059] The positive electrode active material 321 contains a lithium transition metal oxide having a layered crystal structure. The lithium transition metal oxide contains one or more predetermined transition metal elements in addition to Li. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. The positive electrode active material 321 of the present embodiment exemplifies a ternary system called so-called NCM having a lithium transition metal oxide containing all of Ni, Co, and Mn.

[0060] Note that the positive electrode active material 321 of the present embodiment is not limited to having a lithium transition metal oxide containing all of Ni, Co, and Mn. Further, for example, a composition containing Al may be used in addition to these.

[0061] <Separator 4> Separator 4 is a highly insulating non-woven fabric made of polypropylene or the like, which is a porous resin for holding the non-aqueous electrolyte 13 between the negative electrode plate 2 and the positive electrode plate 3. As the separator 4, a porous polymer film such as a porous polyethylene film, a porous polyolefin film, and a porous polyvinyl chloride film, or a lithium ion or ion conductive polymer electrolyte membrane can be used alone or in combination.

[0062] <Evaluation Method for Evaluating Conductive Materials Used in Lithium Ion Secondary Battery 1> Hereinafter, experimental examples of an evaluation method for evaluating a conductive material used in the lithium ion secondary battery 1 of the present embodiment will be described.

[0063] <Simulated Primary Particle 132a> The average particle diameter D (d50) [μm] of the simulated primary particles 132a is substantially the same as the particles of the positive electrode active material 321 of the lithium ion secondary battery 1. Specifically, in the present embodiment, the average particle diameter D (d50) [μm] of the simulated primary particles 132a is 0.1 [μm] or more and 50 [μm] or less.

[0064] <Measurement Conditions for Alumina Coating Resistance> The composition of the test coating paste 30 [g] in this experimental example is 7.41 [g] of alumina, 3.96 [g] of CNT 3% solution, and 18.63 [g] of NMP (N-methyl-2-pyrrolidone). Among these, CNT is 0.1188 [g], which corresponds to 1.6 [wt%] of alumina.

[0065] The paste preparation process is performed as follows. The paste is kneaded as follows. After stirring at 2000 [rpm] for 30 [seconds] using a stirring and defoaming machine, the inside of the container is stirred with a spatula to visually check for lumps. If there are lumps, they are crushed with a spatula. Stir at 2000 [rpm] for 5 [minutes] using a stirring and defoaming machine to prepare a slurry for coating film production. As the stirring and defoaming machine, for example, a rotation / revolution type mixer Awatori Renkotoru (registered trademark) atmospheric pressure type ARE-312 of Shinki Co., Ltd. can be used.

[0066] The test coating film preparation process is carried out as follows. The test coating film 132 has the same thickness [μm] as the thickness [μm] of the positive electrode composite layer 32 of the lithium-ion secondary battery 1. The preparation of the test coating film 132 consists of a coating process and a drying process, and is carried out as follows. Place 4 to 5 [ml] of the test coating film paste on the PET film which is the simulated substrate 131, and apply it using a bar coater and a 300 [μm] applicator. After application, heat and dry it in a hot air dryer at 120 [°C] for 15 [minutes] to prepare the test coating film 132. The thickness of the test coating film 132 was measured with a film thickness gauge (digital micrometer). The coating film resistance R which is the surface resistance of the test coating film 132 S [Ω·cm] is measured by the four-probe method.

[0067] Figure 9 is a table showing the conditions of Examples 1 to 4 of the experimental examples. The conditions are the particle composition of the simulated primary particles 132a or the positive electrode active material 321, and whether the particle structure is primary particles or secondary particles. Also, the “oil supply amount [ml / 100g]” was measured. This oil supply amount [ml / 100g] indicates the amount of linseed oil absorbed. By using linseed oil with high permeability, linseed oil penetrates from the gap 321c into the cavity 321d. If this oil supply amount [ml / 100g] is large, it can be seen that the conductive material 322 made of CNT easily enters from the gap 321c into the cavity 321d.

[0068] The conductivity evaluation process is carried out as follows. By the method shown in Fig. 5(a), the coating film resistance R of the test coating film 132 S [Ω·cm] was measured. Also, by the method shown in Fig. 5(b), the coating film resistance R of the positive electrode composite layer 32 S [Ω·cm] was measured. In the measurement, in order to make the conditions uniform, the positive electrode substrate 31 shown in Fig. 5(b) is replaced with the PET-made simulated substrate 131 shown in Fig. 5(a). In the table, these are collectively referred to as “coating film resistance R S [Ω·cm]”.

[0069] “σ” represents the standard deviation, which is the standard deviation of the coating film resistance R S [Ω·cm]. The "Coefficient of Variation (CV)" is a numerical value indicating variation, and the coefficient of variation CV = standard deviation σ ÷ mean value. It is a dimensionless numerical value without a unit used when relatively evaluating the variation of data with different units and the relationship between the data and the variation relative to the mean value. Here, it is expressed as a percentage [%].

[0070] <Regarding Examples 1 to 4> · Example 1: It uses simulated primary particles 132a, the particle composition is alumina, and the particle structure is solid primary particles. Therefore, the fuel supply amount [ml / 100g] is as low as 16 [ml / 100g]. This means that there are extremely few cavities 321d and gaps 321c like those in the positive electrode active material 321 in the simulated primary particles 132a of Example 1.

[0071] The coating resistance R of Example 1 S The average value of [Ω·cm] was 11.2 [Ω·cm]. Also, the standard deviation σ was 0.26 [Ω·cm]. Therefore, the coefficient of variation CV was 2.7%, indicating that the variation was small.

[0072] · Example 2: It uses a positive electrode active material with relatively few gaps 321c as shown in Fig. 3(b), and here it is called the positive electrode active material (b). The particle composition is the positive electrode active material 321, and the particle structure is hollow secondary particles 321a. Therefore, the fuel supply amount [ml / 100g] is 41 [ml / 100g], which is approximately 2.5 times more than that of the simulated primary particles 132a in Example 1. This means that there are cavities 321d and gaps 321c in the positive electrode active material (b) of Example 2.

[0073] The coating resistance R of Example 2 S The average value of [Ω·cm] was 9.1 [Ω·cm]. Also, the standard deviation σ was 0.62 [Ω·cm]. Therefore, the coefficient of variation CV was 5.2%, indicating that the variation was larger compared to Example 1.

[0074] ·Example 3: A positive electrode active material with a relatively large number of gaps 321c as shown in Fig. 3(c) is used, and here it is referred to as the positive electrode active material (c). The particle composition is the positive electrode active material 321, and the particle structure is the hollow secondary particle 321a. Therefore, the fuel supply amount [ml / 100g] is 47 [ml / 100g], which is also larger compared to Example 2. This means that there are more cavities 321d and gaps 321c than in the positive electrode active material (b) of Example 2.

[0075] The coating film resistance R of Example 3 S [Ω·cm] had an average value of 20.5 [Ω·cm]. Also, the standard deviation σ was 1.36 [Ω·cm]. Therefore, the coefficient of variation CV was 6.7%, indicating that the variation was slightly larger compared to Example 2.

[0076] ·Example 4: A mixture of the positive electrode active material (b) using a positive electrode active material with relatively few gaps 321c as shown in Fig. 3(b) and the positive electrode active material (c) using a positive electrode active material with relatively many gaps 321c as shown in Fig. 3(c), and here it is referred to as the positive electrode active material (b + c). The particle composition is the positive electrode active material 321, and the particle structure is the hollow secondary particle 321a. Therefore, the fuel supply amount [ml / 100g] is 46 [ml / 100g], showing a value intermediate between Example 2 and Example 3. This indicates the intermediate properties between the positive electrode active material (b) of Example 2 and the positive electrode active material (c) of Example 3.

[0077] The coating film resistance R of Example 4 S [Ω·cm] had an average value of 14.8 [Ω·cm]. This indicates the intermediate properties between the positive electrode active material (b) of Example 2 and the positive electrode active material (c) of Example 3. Also, the standard deviation σ was 5.78 [Ω·cm]. Therefore, the coefficient of variation CV was 39.1%, indicating that the variation was extremely large compared to Example 2 and Example 3.

[0078] <Evaluation of the coefficient of variation CV> FIG. 10 is a diagram showing the coefficient of variation CV indicating the variations of the positive electrode active material 321 and the simulated primary particles 132a, respectively. The simulated primary particles 132a made of alumina in Example 1 have relatively little variation from their production process, and the coefficient of variation CV = 2.7 [%].

[0079] On the other hand, in the positive electrode active material (b) of Example 2, the coefficient of variation CV = 5.2 [%] is large. This is because variations occur in the positive electrode active material (b) at the stage of firing the primary particles 321b to produce the secondary particles 321a. Further, in the positive electrode active material (c) of Example 3, the number of gaps 321c increases, and the variation becomes even larger. In addition, although the conductive material 132b moves from the gaps 321c into the positive electrode active material (c), it is considered that variations are likely to occur in its arrangement. And in the positive electrode active material (b + c) of Example 4, it becomes a mixture of the positive electrode active material (b) and the positive electrode active material (c). For this reason, the coating film resistance R S of the positive electrode active material (b) with a coating film resistance R S [Ω·cm] and the influence of the positive electrode active material (c) are likely to change, and the standard deviation σ = 5.78 becomes large. That is, the fuel supply amount [ml / 100g] and the coating film resistance R S [Ω·cm] become the average values of Example 2 and Example 3. However, regarding the variation, as shown in FIG. 10, between the positive electrode active material (b) with a small coating film resistance R S [Ω·cm] and the positive electrode active material (c) with a large coating film resistance R S [Ω·cm], variations occur, so the coefficient of variation CV = 39.1% becomes large.

[0080] <Optimization of the blending mass ratio R [wt%] of the conductive material 132b with respect to the simulated primary particles 132a> FIG. 11 is a graph showing the change in the blending mass ratio R W [wt%] of the conductive material 132b with respect to the simulated primary particles 132a and the coating film resistance R S [Ω·cm] of the test coating film 132. As shown in FIG. 11, when the blending mass ratio R W [wt%] of the conductive material 132b with respect to the simulated primary particles 132a is changed from zero, at first, the coating film resistance R Sis shown in [Ω·cm]. Then, the compounding mass ratio R W [wt%] rapidly decreases around 0.1 to 0.2. This is presumably because the amount has reached a sufficient level to form a conductive network by the conductive material 132b between adjacent simulated primary particles 132a.

[0081] Also, FIG. 12 is an enlarged graph of a part (0 ≤ R W ≤ 5, 0 ≤ R S ≤ 100) of the graph shown in FIG. 11. As shown in FIG. 12, there is a significant change in the slope of the graph in the range of 0 ≤ R W ≤ 5, 0 ≤ R S ≤ 100. Here, the compounding mass ratio R W [wt%] of the conductive material 132b with respect to the simulated primary particles 132a was varied from 0.8 to 3 [wt%], and the behavior of the coating resistance R S [Ω·cm] of the test coating film was confirmed.

[0082] Then, it can be seen that the conductive material 132b may be compounded at a ratio in the range where the compounding mass ratio R W [wt%] of the conductive material 132b with respect to the simulated primary particles 132a is generally 1 [wt%] or more and 3 [wt%] or less. In particular, from the graph shown in FIG. 12, it was found that the sensitivity to dispersibility appears in the vicinity of 1.6 [wt%] where the curvature of the graph is maximum. More specifically, when the compounding mass ratio R W [wt%] exceeds 3 [wt%], there is no change in the coating resistance R S [Ω·cm], and it can be seen that the compounding mass ratio R W [wt%] of the conductive material 132b is excessive. On the other hand, when the compounding mass ratio R W [wt%] is less than 1 [wt%], it can be seen that the compounding mass ratio R W [wt%] of the conductive material 132b is not sufficient to form a conductive network. As a result, it was found that the conductive material 132b may be compounded at a ratio in the range where the compounding mass ratio R W [wt%] of the conductive material 132b with respect to the simulated primary particles 132a is generally 1 [wt%] or more and 3 [wt%] or less.

[0083] (Operation of this Embodiment) When measuring the conductivity of the conductive material 322 incorporated in the positive electrode plate 3 of the completed lithium ion secondary battery 1 as shown in Fig. 5(b), it is affected by the conductivity of the positive electrode active material 321 itself. Also, due to the cavities 321d and gaps 321c formed in the positive electrode active material 321 as shown in Fig. 3, the density in the binder 323 changes. Furthermore, it is affected by the conductive positive electrode substrate 31. Therefore, no matter how accurately the coating film resistance R S [Ω·cm] of the surface of the positive electrode plate 3 is measured, it is impossible to correctly evaluate the conductivity, dispersibility, formation of the conductive network, etc. of the conductive material 322 itself.

[0084] Therefore, in the simulated positive electrode plate 103 shown in Fig. 5(a), only the positive electrode active material 321 that affects such measurement is replaced with the simulated primary particles 132a that are insulators while keeping its mechanical configuration unchanged. Also, the positive electrode substrate 31 is replaced with the simulated substrate 131 that is an insulator while keeping its mechanical configuration unchanged.

[0085] As a result, in the completed lithium ion secondary battery 1, it has become possible to correctly evaluate the conductivity, dispersibility, formation of the network, etc. of the conductive material 322 itself that could not be accurately evaluated before.

[0086] Also, by conducting experiments using this simulated positive electrode plate 103, it is possible to derive the appropriate addition amount of the original conductive material 322, etc. (Effect of this Embodiment) (1) The evaluation method for evaluating the conductive material 322 used in the lithium ion secondary battery 1 of this embodiment has the effect that it can accurately evaluate the conductivity, dispersibility, etc. of the conductive material 322.

[0087] (2) This embodiment is an evaluation method for evaluating the conductive material 322 used in the lithium-ion secondary battery 1, which includes a positive electrode plate 3 in which a positive electrode composite layer 32 containing a positive electrode active material 321 and a conductive material 322 is formed on a positive electrode substrate 31. Therefore, when manufacturing the lithium-ion secondary battery 1 which is the actual production target, there is an effect that the addition amount and the like of the conductive material 322 can be appropriately set.

[0088] (3) The simulated positive electrode plate 103 contains simulated primary particles made of an insulator that simulates the positive electrode active material 321 of the lithium-ion secondary battery 1. Therefore, by accurately reproducing the dispersion state and the like of the conductive material 322, there is an effect that the conductivity and dispersibility of the conductive material 322 can be accurately evaluated.

[0089] (4) Further, in the simulated positive electrode plate 103, a test coating film 132 containing simulated primary particles 132a is produced by coating and drying on a simulated substrate 131 that simulates the positive electrode substrate 31 of the lithium-ion secondary battery 1. Therefore, there is an effect that the conductivity and dispersibility of the conductive material 322 can be accurately evaluated by eliminating the influence of the conductivity of the positive electrode substrate 31 and the like.

[0090] (5) The coating film resistance R S [Ω·cm] which is the surface resistance of the test coating film 132 is measured. Therefore, there is an effect that the conductivity and dispersibility of the conductive material 322 can be accurately evaluated.

[0091] (6) The compounding volume ratio Rv [vol%] of the conductive material 132b to the simulated primary particles 132a of the test coating film paste is set based on the compounding volume ratio R V [vol%] of the positive electrode active material 321 and the conductive material 322. Therefore, in the simulated positive electrode plate 103, there is an effect that the action of the conductive material 132b of the lithium-ion secondary battery 1 can be accurately reproduced.

[0092] (7) The compounding mass ratio R of the conductive material 132b to the simulated primary particles 132a WLet [wt%] be the compounding mass ratio as R W In the graph showing the change in [wt%] and the film resistance R S [Ω·cm], the range including the portion with the largest curvature of the graph is defined. Thus, there is an effect that the action of the conductive material 132b can be accurately analyzed.

[0093] According to the experiments of the present inventors, the compounding mass ratio R W [wt%] of the conductive material 132b with respect to the simulated primary particles 132a was analyzed to be appropriately in the range of 1 [wt%] or more and 3 [wt%] or less. Thus, there is an effect that the appropriate addition amount of the conductive material 132b can be derived.

[0094] (8) The average particle diameter D S (d50) [μm] of the simulated primary particles 132a was made substantially the same diameter as the particles of the positive electrode active material 321 of the lithium ion secondary battery 1. Thus, there is an effect that the action of the conductive material 132b of the lithium ion secondary battery 1 can be accurately reproduced in the simulated positive electrode plate 103.

[0095] According to the experiments of the present inventors, it was analyzed that the average particle diameter D S (d50) [μm] of the simulated primary particles is appropriate when it is 0.1 [μm] or more and 50 [μm] or less. (9) The test film 132 was made to have the same thickness [μm] as the thickness [μm] of the positive electrode mixture layer 32 of the lithium ion secondary battery 1. Thus, there is an effect that the action of the conductive material 132b of the lithium ion secondary battery 1 can be accurately reproduced in the simulated positive electrode plate 103.

[0096] (10) In this embodiment, it was applied when the positive electrode active material 321 is secondary particles of a lithium transition metal oxide. In such a case, the problems can be solved by this embodiment. Also, there is an effect that it can be preferably applied when the conductive material 322 is made of fibrous carbon.

[0097] (11) The simulated primary particles 132a were applied with alumina. Alumina has high insulation, is mechanically stable, and does not cause unnecessary electrochemical reactions. The simulated substrate 131 is preferably formed of an insulator. In this embodiment, the simulated substrate 131 is formed of a PET film. The PET film has high insulation, is mechanically stable, and does not cause unnecessary electrochemical reactions. Therefore, there is an effect that the conductivity and dispersibility of the conductive material 322 can be accurately evaluated.

[0098] (12) The average diameter D C (d50) [nm] of the conductive materials 322 and 132b is 1 [nm] or more and 100 [nm] or less, and the average length L C (d50) [nm] is 100 [nm] or more and 10,000 [nm] or less. Since such a material is easily affected by the shape of the positive electrode active material 321, there is an effect that the conductivity and dispersibility of the conductive material 322 can be accurately evaluated.

[0099] (Another example) ○ The description in this embodiment is an example of the present invention and does not limit the present invention. It can be implemented as in the following other examples, and in these other examples, the invention will be optimized by those skilled in the art.

[0100] ○ In this embodiment, the positive electrode active material 321 having a hollow structure with the gap 321c and the cavity 321d is exemplified. However, the present invention can also be implemented even when it is composed only of a solid positive electrode active material 321 that does not have the gap 321c or the cavity 321d. In such a case, CNT does not enter the gap 321c or the cavity 321d. However, even when the surface unevenness is large or the size is not uniform, the conductivity and dispersibility of the conductive material can be more accurately evaluated by using the simulated primary particles 132a as in the present invention.

[0101] ○ Similarly, the electrode plate is not limited to the positive electrode plate 3 and can also be implemented in the negative electrode plate 2. For example, even when graphite is used as the negative electrode active material or silicon is used as the active material of the lithium-ion secondary battery 1, verification of the conduction path can be carried out.

[0102] ○ Furthermore, the secondary battery is not limited to the lithium-ion secondary battery and can be implemented in other non-aqueous electrolyte secondary batteries, alkaline secondary batteries, and other secondary batteries.

[0103] ○ In this embodiment, fibrous carbon, specifically CNT (carbon nanotube), is exemplified as the conductive materials 322 and 132b, but other conductive materials, such as fibrous carbon microfibers or even granular AB (acetylene black), may be used.

[0104] ○ The drawings are schematic drawings for explaining an evaluation method for evaluating the conductive materials used in the lithium-ion secondary battery of this embodiment, and their quantity, shape, dimensions, etc. do not reflect the actual form.

[0105] ○ Each numerical value, numerical range, shape, material, etc., such as quantity, shape, and dimensions, are examples and do not limit the present invention. Needless to say, it will be appropriately optimized by those skilled in the art. ○ The procedure of the evaluation method for evaluating the conductive materials used in the lithium-ion secondary battery is an example, and the order can be changed, and procedures can be added or deleted.

[0106] ○ Needless to say, the present invention can be implemented by adding, deleting, or changing its configuration by those skilled in the art without departing from the description of the claims.

Explanation of Reference Numerals

[0107] 1... Lithium-ion secondary battery (cell battery) 11... Battery case 12... Electrode body 13... Non-aqueous electrolyte 14… Positive electrode external terminal 15… Negative electrode external terminal 16… Positive electrode current collector terminal 17… Negative electrode current collector terminal 2… Negative electrode plate 21… Negative electrode substrate 22… Negative electrode composite layer 23… Negative electrode current collector part 3… Positive electrode plate 31… Positive electrode substrate 32… Positive electrode composite layer 321… Positive electrode active material 321a… Secondary particle 321b… Primary particle 321c… Gap 321d… Void 322… Conductive material 323… Binder 33… Positive electrode current collector part 103… Simulated positive electrode plate 131… Simulated substrate 132… Test coating film 132a… Simulated primary particle 132b… Conductive material 132c… Binder 133… Positive electrode current collector part 4… Separator OM… Resistance meter MP1,MP2… Measurement points R S [Ω·cm]… Coating film resistance (surface resistance) R V [vol%]… Blended volume ratio of conductive material to primary particles, or blended volume ratio of positive electrode active material and conductive material R W [wt%]… Blended mass ratio of conductive material to simulated primary particles, or blended mass ratio of positive electrode active material and conductive material D S (d50)[μm]… Average particle size of simulated primary particles D C (d50)[nm]… Average diameter of conductive material L C (d50)[nm]… Average length of conductive material

Claims

1. In a secondary battery including an electrode plate having a composite material layer containing an active material and a conductive material formed on a substrate, an evaluation method for evaluating the conductive material used in the secondary battery, comprising: a paste preparation step of preparing a paste containing simulated primary particles made of an insulator simulating the active material of the secondary battery and the conductive material; a test coating film preparation step of coating and drying the paste prepared in the paste preparation step on a simulated substrate simulating the substrate of the secondary battery to prepare a test coating film containing the simulated primary particles; The coating film resistance R, which is the surface resistance of the test coating film Ｓ A conductivity evaluation step of evaluating the conductive material by measuring [Ω·cm], and An evaluation method for evaluating a conductive material used in a secondary battery, characterized by including the above steps.

2. The compound volume ratio R of the conductive material to the simulated primary particles of the paste ｖ [vol%] is set based on the compound volume ratio R ｖ [vol%] of the active material and the conductive material, and the evaluation method for evaluating the conductive material used in the secondary battery according to claim 1, characterized in that it is set.

3. The blending mass ratio R of the conductive material to the simulated primary particles Ｗ [wt%], the blending mass ratio R Ｗ [wt%] change and the coating film resistance R of the test coating film Ｓ [Ω·cm], and the evaluation method for evaluating the conductive material used in the secondary battery according to claim 1, wherein the range includes the portion having the largest curvature of the graph.

4. When the compounding mass ratio of the conductive material to the simulated primary particles is R Ｗ [wt%], the compounding mass ratio R Ｗ The evaluation method for evaluating the conductive material used in the secondary battery according to claim 1, characterized in that [wt%] is in the range of 1 [wt%] or more and 3 [wt%] or less.

5. The average particle diameter D of the simulated primary particles Ｓ (d50) [μm] is substantially the same as the particles of the active material of the secondary battery, and is an evaluation method for evaluating a conductive material used in the secondary battery according to claim 1.

6. The average particle diameter D of the simulated primary particles Ｓ (d50) [μm] is 0.1 [μm] or more and 50 [μm] or less, and an evaluation method for evaluating a conductive material used in the secondary battery according to claim 1, characterized in that it is as follows.

7. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 1, wherein the test coating film has the same thickness [μm] as the thickness [μm] of the composite material layer of the secondary battery.

8. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 1, wherein the active material is secondary particles in which primary particles are aggregated.

9. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 1, wherein the conductive material is made of fibrous carbon.

10. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 1, wherein the simulated primary particles are made of alumina.

11. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 1, wherein the simulated substrate is formed of an insulator.

12. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 11, wherein the simulated substrate is formed of a PET film.

13. The average diameter D Ｃ (d50) [nm] of the conductive material is 1 [nm] or more and 100 [nm] or less, and the evaluation method for evaluating the conductive material used in the secondary battery according to claim 1, characterized in that.

14. The average length L of the conductive material Ｃ (d50) [nm] is 100 [nm] or more and 10,000 [nm] or less, and the evaluation method for evaluating the conductive material used in the secondary battery according to claim 1, characterized in that it is as described above.

15. The evaluation method for evaluating a conductive material used in a secondary battery according to any one of Claims 1 to 14, wherein the secondary battery is a lithium ion secondary battery.

16. The evaluation method for evaluating a conductive material used in a secondary battery according to Claim 15, wherein the electrode plate is a positive electrode plate.

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