Patent Application
20220416225
The present disclosure relates to an electrode plate for non-aqueous electrolyte secondary battery and a non-aqueous electrolyte secondary battery.
Patent Literature 1 describes a configuration of a lithium ion secondary battery (non-aqueous electrolyte secondary battery), in which a slurry prepared by mixing carbon nanofibers with a solvent is applied to a surface of an aluminum foil (electrode core) constituting a positive electrode plate, which is an electrode plate, and the slurry is dried and then heated to fix the carbon nanofibers on the surface of the aluminum foil. The carbon nanofibers have an average fiber diameter of 5 to 80 nm, and an average fiber length of 50 to 5000 nm. Patent Literature 1 states that, with this configuration, the resistance at the surface of the aluminum foil is sufficiently reduced.
Patent Literature 2 describes forming, in a positive electrode plate for non-aqueous electrolyte secondary battery, a base layer formed of a conductive composition containing carbon nanotubes. The carbon nanotubes are such that the diameter, which is the number average value of the length of the short axis, is 5 nm or greater and 1000 nm or less, and the aspect ratio, which is defined as (the number average value of the length of the long axis)/(the number average value of the length of the short axis), is 1 or greater and 2000 or less.
In order to increase the output and to improve the durability performance of non-aqueous electrolyte secondary battery, it is desired to reduce the resistance at a surface of an electrode core of an electrode plate in the non-aqueous electrolyte secondary battery, or more specifically, it is desired to reduce the interfacial resistance, which is the resistance between the electrode core and an electrode mixture layer. According to the configuration of the carbon nanotubes or carbon nanofibers included in the positive electrode plate as described in Patent Literature 1 and Patent Literature 2, the effect of reducing the interfacial resistance is not sufficient. In particular, when the secondary battery is in use, the electrode plate is in a state swollen with a non-aqueous solvent, which is an electrolyte solution solvent, of a non-aqueous electrolyte. The electrode plate described in Patent Literature 1 and 2 does not have a sufficiently low interfacial resistance in the swollen state. Reduction in the interfacial resistance of the electrode plate in the swollen state is desired in terms of increasing the output and improving the durability performance in the actual state of use.
An electrode plate for non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode core having an undercoat layer formed on its surface, and an electrode mixture layer formed on the undercoat layer of the electrode core. A conductive auxiliary agent used for the undercoat layer is carbon nanotubes. The average diameter of the conductive auxiliary agent is 12 nm or smaller. The aspect ratio of the conductive auxiliary agent, which is defined as (the average length/the average diameter), is 4000 or higher. The thickness of the undercoat layer is 0.10 μm or smaller.
A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes a positive electrode plate, a negative electrode plate, and a non-aqueous electrolyte. At least one of the positive electrode plate and the negative electrode plate is the electrode plate for non-aqueous electrolyte secondary battery according to the present disclosure.
According to the electrode plate for non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery according to the present disclosure, the interfacial resistance of the electrode plate swollen with the non-aqueous electrolyte containing a non-aqueous solvent can be sufficiently reduced.
The inventors of the present disclosure have found that the interfacial resistance of an electrode plate that has been dried after being swollen with a non-aqueous solvent can be sufficiently reduced when the electrode plate for non-aqueous electrolyte secondary battery comprises: an electrode core having an undercoat layer formed on its surface; and an electrode mixture layer formed on the undercoat layer of the electrode core, wherein: a conductive auxiliary agent used for the undercoat layer is carbon nanotubes; the average diameter of the conductive auxiliary agent is 12 nm or smaller; the aspect ratio of the conductive auxiliary agent, which is defined as (the average length/the average diameter), is 4000 or higher; and the thickness of the undercoat layer is 0.10 μm or smaller. Based on this, the inventors of the present disclosure have found that, with the above-described electrode plate for non-aqueous electrolyte secondary battery, the interfacial resistance of an electrode plate that is swollen with a non-aqueous electrolyte containing a non-aqueous solvent can be sufficiently reduced.
An example embodiment of the present disclosure will now be described in detail. Although the following describes a case in which the electrode plate having the undercoat layer of the present disclosure formed thereon is a positive electrode plate, the electrode plate having the undercoat layer formed thereon may alternatively be a negative electrode plate or both of a positive electrode plate and a negative electrode plate.
As illustrated for example in
The outer casing 1 has a bottom portion having a substantially rectangular shape as viewed from the bottom face, and a side wall portion erected on the peripheral edge of the bottom portion. The side wall portion is formed perpendicular to the bottom portion.
A positive electrode current collector 9 is connected to a laminated part of the positive electrode core exposed portion 4a of the positive electrode plate 4, and a negative electrode current collector 10 is connected to a laminated part of the negative electrode core exposed portion 8a of the negative electrode plate 8. A positive electrode terminal 11 comprises a positive electrode bolt portion 12 arranged on the battery outer side of the sealing plate 2, and a positive electrode insertion portion 13 that is electrically connected to the positive electrode bolt portion 12 and inserted into a through hole provided in the sealing plate 2. To this positive electrode terminal 11, the positive electrode current collector 9 is electrically connected. Further, a negative electrode terminal 14 comprises a negative electrode bolt portion 15 arranged on the battery outer side of the sealing plate 2, and a negative electrode insertion portion 18 that is electrically connected to the negative electrode bolt portion 15 and inserted into a through hole provided in the sealing plate 2. To this negative electrode terminal 14, the negative electrode current collector 10 is electrically connected.
The positive electrode terminal 11 and the positive electrode current collector 9 are respectively fixed to the sealing plate 2 via insulating members. The negative electrode terminal 14 and the negative electrode current collector 10 are respectively fixed to the sealing plate 2 via insulating members.
The electrode assembly 3 is housed in the outer casing 1. The sealing plate 2 is connected to an opening edge part of the outer casing 1 by laser welding or the like. The sealing plate 2 has an electrolyte injection port 19, and this electrolyte injection port 19 is sealed with a sealing plug after the non-aqueous electrolyte is injected into the outer casing 1.
The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, carbonates, lactones, ethers, ketones, esters, and the like can be used, and two or more of these solvents can be mixed and used. When mixing and using two or more kinds of solvents, it is preferable to use a mixed solvent containing a cyclic carbonate and a chain carbonate. For example, ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like can be used as the cyclic carbonate, and dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and the like can be used as the chain carbonate. The non-aqueous solvent may contain a halogen-substituted product obtained by substituting at least a part of the hydrogens in the above solvents with halogen atoms such as fluorine. As the electrolyte salt, LiPF6, LiBF4, LiCF3SO3, and the like and mixtures thereof can be used. The amount of the electrolyte salt dissolved in the non-aqueous solvent can be, for example, 0.5 to 2.0 mol/L. Further, an additive such as vinylene carbonate (VC) can be added as appropriate.
A detailed description will now be given regarding the positive electrode plate 4, the negative electrode plate 8, and the separator that constitute the electrode assembly 3, and in particular regarding the positive electrode plate 4.
[Positive Electrode Plate]
As shown in
The undercoat layer 6 is obtained by applying, on the surface of the positive electrode core 5, an undercoat dispersion liquid containing a conductive auxiliary agent 6a (
The average length of the conductive auxiliary agent 6a used for the undercoat layer 6 is not particularly limited, but is preferably 10 μm or longer, more preferably 40 μm or longer, and further preferably 100 μm or longer.
Further, the aspect ratio of the conductive auxiliary agent, which is defined as (the average length/the average diameter), is 4000 or higher.
In the present specification, the average diameter of the conductive auxiliary agent 6a is a value determined by observing 10 conductive auxiliary agent 6a pieces using a scanning electron microscope (SEM), measuring the diameters of the 10 conductive auxiliary agent 6a pieces, and calculating a number average value thereof. Further, the average length of the conductive auxiliary agent 6a is a value determined by observing 10 conductive auxiliary agent 6a pieces using a scanning electron microscope, measuring the lengths of the 10 conductive auxiliary agent 6a pieces, and calculating a number average value thereof. More specifically, the conductive auxiliary agent 6a was observed using a scanning electron microscope at an acceleration voltage of 5 kV, and an image (having 1024×1280 pixels) with a magnification of 50,000 times was captured. In the captured image, the diameter and length were measured respectively regarding 10 arbitrary conductive auxiliary agent 6a pieces, and number average values thereof were calculated to determine the average diameter and the average length. From these values, the aspect ratio was calculated.
The BET specific surface area of the conductive auxiliary agent 6a for the undercoat layer 6 is not particularly limited, but is preferably 100 m2/g or larger, more preferably 200 m2/g or larger, and further preferably 400 m2/g or larger. The content of the conductive auxiliary agent 6a in the undercoat layer 6 is preferably 75 to 97.5%. The bulk density of the conductive auxiliary agent 6a is not particularly limited, but is preferably 0.008 to 0.01 g/cm3.
Examples of the binder used for the undercoat layer 6 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, polyolefin resins, and the like. These may be used alone or by combining two or more thereof. As the binder used for the undercoat layer 6, polyvinylidene fluoride (PVDF) is preferably used. The molecular weight of the binder for the undercoat layer 6 is not particularly limited, but is preferably 900,000 or higher, and more preferably 1.4 million or higher. The binder content in the undercoat layer 6 is preferably 2.5 to 22.5%. A dispersant may also be added to the undercoat layer 6. The solid content ratio (NV) of the undercoat layer 6 is preferably 0.5 to 2.5%.
When forming the above-described undercoat layer 6 on the surface of the positive electrode core 5, a slurry for forming the undercoat layer is prepared as the undercoat dispersion liquid by dispersing the conductive auxiliary agent 6a in a solvent. Examples of the solvent for dispersing the conductive auxiliary agent 6a include N-methyl-2-pyrrolidone (NMP). Next, the prepared slurry is applied to the surface of the positive electrode core 5 by a gravure coating method or the like, and then dried to form the undercoat layer 6. For this drying, heat treatment in a hot air circulation path can for example be used, but the drying method is not limited to this method.
The thickness of the undercoat layer 6 is 0.10 μm or smaller. In the present specification, the thickness of the undercoat layer 6 is a value determined by measuring, using a scanning electron microscope, thicknesses in a cross section of the undercoat layer 6 processed by a cross-section processing apparatus (CP), and calculating a number average value thereof. More specifically, for the thickness of the undercoat layer 6, a cross section was observed using a scanning electron microscope at an acceleration voltage of 5 kV, and an image (having 1024×1280 pixels) with a magnification of 50,000 times was captured. In the captured image, the length from a top part of the positive electrode core 5 to the top part of the undercoat layer 6 was measured respectively regarding five arbitrary positions, and a number average value thereof was calculated to determine the thickness of the undercoat layer 6. The weight per unit area of the undercoat layer 6 is not particularly limited, but is preferably 110 mg/m2 or less, more preferably 80 mg/m2 or less, and further preferably 50 mg/m2 or less, while the lower limit of the weight per unit area is preferably 10 mg/m2. By using the undercoat layer 6 as described above, the interfacial resistance of the positive electrode plate 4 in the swollen state can be reduced. The coverage of the undercoat layer 6 on the surface of the positive electrode core 5 is preferably 20 to 100%.
The positive electrode plate 4 can be produced by, for example, having the undercoat layer 6 formed on the surface of the positive electrode core 5, applying a positive electrode mixture slurry containing the positive electrode active material, the binder, the conductive auxiliary agent, and the like onto the undercoat layer 6 of the positive electrode core 5, drying the applied slurry to form the positive electrode mixture layer 7, and then rolling this positive electrode mixture layer 7.
Examples of the positive electrode active material include lithium transition metal oxides containing transition metal elements such as Co, Mn, and Ni. Lithium transition metal oxides are, for example, LixCoO2, LixNiO2, LixMnO2, LixCoyNi1−yO2, LixCoyM1−yOz, LixNi1−yMyOz, LixMn2−yMyO4, LixMn2−yMyO4, LiMPO4, and Li2MPO4F (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x<1.2, 0<y<0.9, and 2.0≤z≤2.3). The foregoing may be used alone or by mixing a plurality thereof. In terms of enabling an increase in the capacity of the secondary battery 100, the positive electrode active material preferably contains a lithium-nickel composite oxide such as LixNiO2, LixCoyNi1−yO2, LixNi1−yMyOz (where M is at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, and B, 0<x≤1.2, 0≤y≤0.9, and 2.0≤z≤2.3), and the like.
Examples of the conductive auxiliary agent used for the positive electrode mixture layer 7 include carbon-based particles such as carbon black (CB), acetylene black (AB), Ketjen black, carbon nanotubes (CNT), and graphite. These may be used alone or by combining two or more thereof. As the conductive auxiliary agent used for the positive electrode mixture layer, carbon black is preferably used.
Examples of the binder used for the positive electrode mixture layer 7 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These may be used alone or by combining two or more thereof. As the binder used for the positive electrode mixture layer 7, polyvinylidene fluoride is preferably used. The molecular weight of the binder for the positive electrode mixture layer 7 is not particularly limited, but is preferably 900,000 or higher, and more preferably 1.4 million or higher.
In the positive electrode plate 4 produced as described above, the undercoat layer 6 contains the conductive auxiliary agent 6a which is carbon nanotubes having an average diameter of 12 nm or smaller, and the aspect ratio of the conductive auxiliary agent 6a is 4000 or higher. Further, the thickness of the undercoat layer 6 is 0.10 μm or smaller.
With these features, the interfacial resistance of the positive electrode plate 4 swollen with the non-aqueous electrolyte containing the non-aqueous solvent can be sufficiently reduced. An explanation in this regard is given below by reference to
Further, with the thickness of the undercoat layer 6 being 0.10 μm or smaller, the distance between the surface of the positive electrode core 5 after swelling and the positive electrode mixture layer 7 again tends to be small, and it is therefore presumed that the interfacial resistance can be reduced in the same manner as described above.
In addition, when the molecular weight of the binder used respectively for the undercoat layer 6 and the positive electrode mixture layer 7 is 900,000 or higher, swelling of the binder that occurs when the positive electrode plate 4 is immersed in the electrolyte solution is suppressed. Since this also tends to result in a reduced distance between the surface of the positive electrode core 5 after swelling and the positive electrode mixture layer 7, it is presumed that the interfacial resistance can be reduced in the same manner as described above.
[Negative Electrode]
The negative electrode plate 8 comprises a negative electrode core and a negative electrode mixture layer formed on a surface of the negative electrode core. For the negative electrode core, it is possible to use, for example, a foil of a metal that is stable in the potential range of the negative electrode such as copper, a film having such a metal disposed on its surface layer, or the like. The negative electrode mixture layer contains a negative electrode active material. The negative electrode plate 8 can be produced by applying a negative electrode mixture slurry containing the negative electrode active material onto the negative electrode core, drying the applied slurry to form a negative electrode mixture layer, and then rolling this negative electrode mixture layer.
The negative electrode active material is not particularly limited so long as it can reversibly occlude and release lithium ions, and it is possible to use, for example, a carbon material such as natural graphite or artificial graphite, a metal that forms an alloy with lithium such as silicon (Si) or tin (Sn), an alloy or composite oxide containing a metal element such as Si or Sn, or the like. As the negative electrode active material, a carbon material is preferable, and natural graphite is more preferable. The negative electrode active material may be used alone or by combining two or more thereof
[Separator]
For the separator, for example, a porous sheet having ion permeability and insulating property is used. Specific examples of the porous sheet include a microporous thin film, a woven fabric, and a non-woven fabric. As the material of the separator, olefin resins such as polyethylene and polypropylene, cellulose, and the like are preferred. The separator may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer made of olefin resin or the like. The separator may alternatively be a multilayer separator including a polyethylene layer and a polypropylene layer, and a separator having a surface coated with a material such as aramid resin or ceramic may be used.
While Examples will be used below to further explain the positive electrode plate 4, which is an electrode plate for non-aqueous electrolyte secondary battery according to the present disclosure, the present disclosure is not limited to these Examples.
[Production of Positive Electrode Plate]
As the positive electrode active material, a composite oxide represented by LiNi0.35Co0.35Mn0.30O2, which is a lithium-nickel-cobalt-manganese composite oxide, was used. The positive electrode active material, PVDF serving as a binder, and carbon black were mixed together at a mass ratio of 90.3:2.7:7.0, and the mixture was kneaded while adding N-methyl-2-pyrrolidone to thereby prepare a positive electrode mixture slurry. The molecular weight of the PVDF for the mixture layer was 1.1 million. Further, an undercoat dispersion liquid containing carbon nanotubes as the conductive auxiliary agent 6a was applied to both sides of an elongate positive electrode core 5 made of an aluminum foil having a thickness of 13 μm, and the applied films were dried to obtain a positive electrode core 5 having an undercoat layer 6 formed on its surfaces. Here, the average diameter of the conductive auxiliary agent 6a was 7.5 nm, and the aspect ratio of the conductive auxiliary agent 6a was 13333. Further, as the binder for the undercoat layer 6, PVDF having a molecular weight of 1.1 million was used. The undercoat layer 6 had a weight per unit area of 50 mg/m2 and a thickness of 0.07 μm. Further, the mixture layer had a weight per unit area of 109 mg/10cm2 on each of both sides of the positive electrode core 5, and a thickness of 45 μm on each of both sides of the positive electrode core 5. Table 1 shows the conductive auxiliary agent 6a of the undercoat layer 6, the PVDF, and properties of the undercoat layer 6 for Example 1. Table 1 also shows such information regarding Examples 2 to 8 and Comparative Examples 1 to 7 described further below. In Table 1, the average diameter of the conductive auxiliary agent is indicated as “diameter”.
Next, the positive electrode mixture slurry was applied onto the undercoat layers 6 of the positive electrode core 5, and the applied films were dried. The dried applied films were compressed to a packing density of 2.5 g/cm3, and the product was cut to a predetermined electrode size. A positive electrode plate 4 having positive electrode mixture layers 7 formed on both sides of the positive electrode core 5 was thereby produced.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the undercoat layer 6 had a weight per unit area of 13 mg/m2 and a thickness of 0.06 μm. The produced positive electrode plate 4 was used as Example 2.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the aspect ratio of the conductive auxiliary agent 6a used for the undercoat layer 6 was 8000, and the thickness of the undercoat layer 6 was 0.08 μm. The produced positive electrode plate 4 was used as Example 3.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the aspect ratio of the conductive auxiliary agent 6a used for the undercoat layer 6 was 5333, and the thickness of the undercoat layer 6 was 0.09 μm. The produced positive electrode plate 4 was used as Example 4.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the conductive auxiliary agent 6a used for the undercoat layer 6 had an average diameter of 12 nm and an aspect ratio of 6667. The produced positive electrode plate 4 was used as Example 5.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the conductive auxiliary agent 6a used for the undercoat layer 6 had an average diameter of 12 nm and an aspect ratio of 5000. The produced positive electrode plate 4 was used as Example 6.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the aspect ratio of the conductive auxiliary agent 6a used for the undercoat layer 6 was 4000. The produced positive electrode plate 4 was used as Example 7.
A positive electrode plate 4 was produced in the same manner as in Example 1 except that the weight per unit area of the undercoat layer 6 was 80 mg/m2, PVDF having a molecular weight of 900,000 was used as the binder for the undercoat layer 6 and the mixture layer, and the thickness was 0.09 μm. The produced positive electrode plate 4 was used as Example 8.
A positive electrode plate was produced in the same manner as in Example 1 except that the undercoat layer had a weight per unit area of 105 mg/m2 and a thickness of 0.15 μm. The produced positive electrode plate was used as Comparative Example 1.
A positive electrode plate was produced in the same manner as in Example 1 except that the conductive auxiliary agent used for the undercoat layer had an average diameter of 12 nm and an aspect ratio of 833, and the undercoat layer had a weight per unit area of 80 mg/m2 and a thickness of 0.09 μm. The produced positive electrode plate was used as Comparative Example 2.
A positive electrode plate was produced in the same manner as in Example 1 except that the undercoat layer had a weight per unit area of 130 mg/m2 and a thickness of 0.32 μm. The produced positive electrode plate was used as Comparative Example 3.
A positive electrode plate was produced in the same manner as in Example 1 except that the conductive auxiliary agent used for the undercoat layer had an average diameter of 50 nm and an aspect ratio of 200, and the undercoat layer had a weight per unit area of 80 mg/m2 and a thickness of 1.34 μm. The produced positive electrode plate was used as Comparative Example 4.
<Comparative Example 5
A positive electrode plate was produced in the same manner as in Example 1 except that the conductive auxiliary agent used for the undercoat layer had an average diameter of 50 nm and an aspect ratio of 200, and the undercoat layer had a weight per unit area of 25 mg/m2 and a thickness of 0.18 μm. The produced positive electrode plate was used as Comparative Example 5.
A positive electrode plate was produced in the same manner as in Example 1 except that the aspect ratio of the conductive auxiliary agent used for the undercoat layer was 2667. The produced positive electrode plate was used as Comparative Example 6.
A positive electrode plate was produced in the same manner as in Example 1 except that the conductive auxiliary agent used for the undercoat layer had an average diameter of 12 nm and an aspect ratio of 1667, and the thickness of the undercoat layer was 0.06 μm. The produced positive electrode plate was used as Comparative Example 7.
In each of the above Examples and Comparative Examples, the aspect ratio was adjusted by changing agitation conditions of a dispersion agitator.
[Measurement of Interfacial Resistance]
In the positive electrode plate 4 of each of the Examples and Comparative Examples, the interfacial resistance (sheet resistance Ωcm 2) was measured, which is the resistance between the positive electrode core 5 and the positive electrode mixture layer 7. The interfacial resistance was measured at a point after the positive electrode plate 4 was compressed as described above, and at a point after the positive electrode plate 4 was swelled and dried subsequent to compression (i.e., after swelling and drying). For measuring the interface resistance, an electrode resistance measuring instrument (device name: RM2610) manufactured by Hioki E.E. Corporation was used.
Here, the interfacial resistance of the electrode plate that has been dried after being swollen with a non-aqueous solvent was evaluated. Difficulties exist in measuring the interfacial resistance of an electrode plate that remains swollen with a non-aqueous solvent. Accordingly, the electrode plate was evaluated by measuring the interfacial resistance in a state after swelling and drying, which is close to the swollen state and which enables measurement of the interfacial resistance. In order to place the positive electrode plate 4 in a state after swelling and drying, after the positive electrode plate 4 was compressed as described above, the positive electrode plate 4 was placed in a solution of dimethyl carbonate and left overnight at a temperature of 85° C., and then taken out from the solution and dried in a dryer at a temperature of 130° C. for 3 to 4 hours. After the drying, the interfacial resistance was measured. Table 1 shows the results obtained by measuring the interfacial resistance after compressing and the interfacial resistance after swelling and drying in each of the Examples and Comparative Examples.
According to the results shown in Table 1, the interfacial resistance of the positive electrode plate 4 after swelling and drying could be significantly reduced in Examples 1 to 8 as compared with Comparative Examples 1 to 7. It is presumed that the interfacial resistance value is significantly reduced also when the electrode plate is in a state swollen with the non-aqueous solvent, and based on this, the advantageous effect of the present disclosure could be confirmed. For example, when comparing Examples 1 and 2 with Comparative Examples 1 and 3, while the aspect ratio of the conductive auxiliary agent 6a was likewise 4000 or higher in all these cases, it is considered that the interfacial resistance of the positive electrode plate 4 after swelling and drying could be reduced in Examples 1 and 2 because the thickness of the undercoat layer 6 was 0.10 μm or less, which was smaller than that in Comparative Examples 1 and 3.
When comparing Examples 1 to 8 with Comparative Examples 2, 6, and 7, while the thickness of the undercoat layer 6 was 0.10 μm or less in all these cases, it is considered that the interfacial resistance of the positive electrode plate 4 after swelling and drying could be reduced in Examples 1 to 8 because the aspect ratio of the conductive auxiliary agent 6a was 4000 or higher, which was higher than that in Comparative Examples 2, 6, and 7.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-216873 | Nov 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/042219 | 11/12/2020 | WO |
