Method of manufacturing positive electrode plate

Abstract

To provide a method of manufacturing a positive electrode plate, the method enabling manufacturing of a positive electrode plate with excellent peeling resistance strength between a positive electrode active material layer and a positive electrode foil.SOLUTION: A method of manufacturing a positive electrode plate includes a paste preparation step of mixing a positive electrode active material having an absolute value of zeta potential of 10 mV or less, a binder, and a solvent to prepare a positive electrode active material paste having a viscosity of 18,000 mPa s or less, a coating step of coating the positive electrode active material paste onto a positive electrode foil, a low-temperature drying step of drying the positive electrode active material paste after the coating step at a temperature equal to or higher than the freezing point of the solvent and equal to or lower than 40°C, and a high-temperature drying step of drying the positive electrode active material paste after the low-temperature drying step, at a temperature equal to or higher than 80°C and at a temperature equal to or lower than 130°C.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a method for manufacturing a positive electrode plate.

Background Art

[0002] Secondary batteries are widely used in fields such as in-vehicle, information and communication technology (e.g., personal computers, smartphones, etc.), and power storage. And various batteries such as these secondary batteries are configured to include a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery that includes a positive electrode, a negative electrode, and an electrolyte, the positive electrode includes a positive electrode substrate and a positive electrode active material layer, the positive electrode active material layer is disposed on the surface of the positive electrode substrate, the positive electrode active material layer includes a first layer and a second layer, the second layer is disposed between the first layer and the positive electrode substrate, the first layer contains a first particle group as a main active material, the second layer contains a second particle group as a main active material, the first particle group is composed of a plurality of first positive electrode active material particles, the second particle group is composed of a plurality of second positive electrode active material particles, the first positive electrode active material particles contain 1 to 10 single particles, and the second positive electrode active material particles are secondary particles in which 50 or more primary particles are aggregated.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, in the positive electrode plates used in various batteries, a binder is contained in the positive electrode active material layer in order to enhance the binding property between the positive electrode foil and the positive electrode active material layer. However, in the drying process (for example, a process of drying at a temperature of 80°C or higher and 130°C or lower) after applying the positive electrode active material paste for forming the positive electrode active material layer onto the positive electrode foil, migration of the binder occurs in the positive electrode active material paste, and the binder may be unevenly distributed on the side opposite to the positive electrode foil. As a result, the concentration of the binder on the positive electrode foil side in the dried positive electrode active material layer is relatively reduced, and the peel strength between the positive electrode active material layer and the positive electrode foil may be reduced.

[0006] In view of the above circumstances, an embodiment of the present disclosure aims to provide a method for manufacturing a positive electrode plate capable of obtaining a positive electrode plate having excellent peel strength between the positive electrode active material layer and the positive electrode foil.

Means for Solving the Problems

[0007] The means for solving the above problems include the following means. <1> A paste preparation step of mixing a positive electrode active material having an absolute value of zeta potential of 10 mV or less, a binder, and a solvent to prepare a positive electrode active material paste having a viscosity of 18,000 mPa·s or less, A coating step of applying the positive electrode active material paste onto a positive electrode foil, A low-temperature drying step of drying the positive electrode active material paste after the coating step at a temperature equal to or higher than the freezing point of the solvent and 40°C or lower, A high-temperature drying step of drying the positive electrode active material paste after the low-temperature drying step at a temperature of 80°C or higher and 130°C or lower, A method for manufacturing a positive electrode plate having the above steps. <2> The method for manufacturing a positive electrode plate according to <1>, wherein the solid content ratio of the positive electrode active material paste prepared in the paste preparation step is 50% by mass to 60% by mass.

Advantages of the Invention

[0008] According to an embodiment of the present disclosure, there is provided a method for manufacturing a positive electrode plate capable of obtaining a positive electrode plate excellent in the peel strength between a positive electrode active material layer and a positive electrode foil.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments which are an example of the present disclosure will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the present specification, a numerical range represented by “~” means a range including these numerical values as a lower limit value and an upper limit value. In the numerical ranges described stepwise in the present specification, the upper limit value of a certain stepwise numerical range may be replaced with the upper limit value of the numerical range described in other steps, or may be replaced with the value shown in the examples. Also, the lower limit value of a certain stepwise numerical range may be replaced with the lower limit value of the numerical range described in other steps, or may be replaced with the value shown in the examples. Also, “%” for the content means “mass %” unless otherwise specified.

[0011] Each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition. “Step” includes not only an independent step, but also this term includes cases where it is not clearly distinguishable from other steps as long as the intended action of the step is achieved.

[0012] <Method for manufacturing positive electrode plate> The method for manufacturing a positive electrode plate according to an embodiment of the present disclosure includes the following steps. (1) Paste preparation step of preparing a positive electrode active material paste having a viscosity of 18,000 mPa·s or less by mixing a positive electrode active material having an absolute value of zeta potential of 10 mV or less, a binder, and a solvent. (2) Coating step of coating the positive electrode active material paste on a positive electrode foil. (3) Low-temperature drying step of drying the positive electrode active material paste after the coating step at a temperature equal to or higher than the freezing point of the solvent and equal to or lower than 40°C. (4) High-temperature drying step of drying the positive electrode active material paste after the low-temperature drying step at a temperature of 80°C or higher and 130°C or lower.

[0013] By having the above configuration, the method for manufacturing a positive electrode plate according to an embodiment of the present disclosure can obtain a positive electrode plate excellent in the peel strength between the positive electrode active material layer and the positive electrode foil. The reason for this effect is speculated as follows.

[0014] Conventionally, in a positive electrode plate used in various batteries such as lithium-ion batteries, a binder is mixed in the positive electrode active material paste for forming the positive electrode active material layer from the viewpoint of enhancing the binding property between the positive electrode foil and the positive electrode active material layer. However, in the drying step after coating the positive electrode active material paste on the positive electrode foil (for example, the step of drying at a temperature of 80°C or higher and 130°C or lower), migration of the binder may occur in the positive electrode active material paste. Migration refers to the phenomenon in which the temperature rises from the positive electrode foil side in the positive electrode active material paste during drying, so that the binder is unevenly distributed on the side opposite to the positive electrode foil. Therefore, in the dried positive electrode active material layer, the concentration of the binder on the positive electrode foil side relatively decreases, and the peel strength (that is, the difficulty of peeling) between the positive electrode active material layer and the positive electrode foil may decrease.

[0015] In contrast, in the method for manufacturing a positive electrode plate according to an embodiment of the present disclosure, a positive electrode active material paste having a zeta potential absolute value of 10 mV or less and a viscosity of 18,000 mPa·s or less is applied onto a positive electrode foil, and then a low-temperature drying step (drying at a temperature equal to or higher than the freezing point of the solvent and equal to or lower than 40°C) is provided before a high-temperature drying step (drying at a temperature of 80°C or higher and 130°C or lower). A positive electrode active material having a zeta potential absolute value of 10 mV or less can be said to be an active material with a small surface charge of the active material, that is, an active material that easily aggregates. Therefore, in the low-temperature drying step after the coating step, aggregates of the positive electrode active material are formed in the positive electrode active material paste. And since the viscosity of the positive electrode active material paste is as low as 18,000 mPa·s or less, that is, the fluidity of the positive electrode active material paste is high, the aggregates of the positive electrode active material easily settle and are unevenly distributed on the side of the positive electrode foil. Therefore, on the side of the positive electrode foil in the positive electrode active material paste where there are many aggregates of the positive electrode active material, the number density of the particles of the positive electrode active material becomes a state of decrease.

[0016] Here, it will be described with reference to FIG. 1. FIG. 1 is a schematic cross-sectional view showing a positive electrode plate obtained by the method for manufacturing a positive electrode plate according to an embodiment of the present disclosure. In the method for manufacturing a positive electrode plate according to an embodiment of the present disclosure, a positive electrode active material paste containing a positive electrode active material 2 having a zeta potential absolute value of 10 mV or less and a binder 4 and having a viscosity of 18,000 mPa·s or less is applied onto a positive electrode foil 42, and then a high-temperature drying step is performed after passing through the low-temperature drying step in the aforementioned temperature range. Therefore, in the low-temperature drying step, aggregates 2B of the positive electrode active material 2 are formed in the positive electrode active material paste, and these aggregates 2B settle and are unevenly distributed on the side of the positive electrode foil 42. As a result, in the positive electrode plate 10 obtained by the method for manufacturing a positive electrode plate according to an embodiment of the present disclosure, as shown in FIG. 1, the aggregates 2B of the positive electrode active material 2 are unevenly distributed on the side of the positive electrode foil 42 of the positive electrode active material layer, while on the side of the positive electrode active material layer opposite to the positive electrode foil 42, the non-aggregated positive electrode active material 2 (non-aggregated positive electrode active material 2A) is unevenly distributed. And on the side of the positive electrode foil 42 of the positive electrode active material layer where there are many aggregates 2B of the positive electrode active material 2, the number density of the positive electrode active material particles becomes a state of decrease.

[0017] By reducing the number density of particles on the positive electrode foil side in the positive electrode active material paste in this way, the amount of binder required to maintain the peel strength between the positive electrode active material layer and the positive electrode foil can also be reduced. As a result, even when binder migration occurs in the high-temperature drying process and the concentration of the binder on the positive electrode foil side in the positive electrode active material layer relatively decreases, excellent peel strength between the positive electrode active material layer and the positive electrode foil can be obtained. As described above, according to the method for manufacturing a positive electrode plate according to the embodiment of the present disclosure, a positive electrode plate excellent in peel strength between the positive electrode active material layer and the positive electrode foil can be obtained.

[0018] Hereinafter, the method for manufacturing a positive electrode plate according to the embodiment of the present disclosure will be described step by step.

[0019] (1) Paste preparation step In the paste preparation step, a positive electrode active material having an absolute value of zeta potential of 10 mV or less, a binder, and a solvent are mixed to prepare a positive electrode active material paste having a viscosity of 18,000 mPa·s or less.

[0020] · Positive electrode active material In the paste preparation step, a positive electrode active material having an absolute value of zeta potential of 10 mV or less (that is, a zeta potential of -10 mV or more and 10 mV or less) is used. A positive electrode active material having an absolute value of zeta potential of 10 mV or less has a small surface charge of the active material, that is, it can be said that the active material is easy to aggregate. Therefore, in the low-temperature drying step after the coating step, aggregates of the positive electrode active material can be generated in the positive electrode active material paste, and as a result, a positive electrode plate excellent in peel strength between the positive electrode active material layer and the positive electrode foil can be obtained. From the viewpoint of increasing the peel strength between the positive electrode active material layer and the positive electrode foil, the absolute value of the zeta potential of the positive electrode active material is preferably further 8 mV or less, and more preferably 6 mV or less.

[0021] The zeta potential of the positive electrode active material can be measured by the following method. By using a dispersion liquid in which a positive electrode active material is dispersed at a predetermined concentration (0.1 mass% to 0.2 mass%) in a solvent such as N-methylpyrrolidone (NMP) as a sample for measurement by laser Doppler electrophoresis, measurement can be performed.

[0022] Examples of the particles of the positive electrode active material include particles composed of a lithium composite oxide. Examples of the lithium composite oxide include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganate (LiMn2O4), lithium nickel cobalt aluminum oxide (NCA), lithium nickel cobalt manganate (NCM), lithium iron phosphate (LiFePO4), and the like.

[0023] The method for controlling the zeta potential of the positive electrode active material within the above-mentioned range is not particularly limited. For example, a method of adjusting the amounts of hydroxyl groups (-OH) and carbonate groups (-CO3) on the surface of the particles of the positive electrode active material can be mentioned. In addition, as a method of adjusting the amounts of hydroxyl groups (-OH) and carbonate groups (-CO3) on the surface of the positive electrode active material particles, specifically, a method of adding an oxo acid or the like that can react with the hydroxyl groups and carbonate groups to the positive electrode active material can be mentioned.

[0024] ·Binder The binder is not particularly limited, and a known binder conventionally used for the positive electrode active material layer can be used. Examples of the binder include polyvinylidene fluoride (PVDF), modified polyvinylidene fluoride (modified PVDF), and polytetrafluoroethylene (PTFE). Among them, polyvinylidene fluoride (PVDF) is preferable as the binder.

[0025] From the viewpoint of the peel strength resistance between the positive electrode active material layer and the positive electrode foil, in the formed positive electrode active material layer, the content ratio of the binder to the amount of the positive electrode active material is preferably 0.5 mass% or more and 5 mass% or less, and more preferably 1 mass% or more and 3 mass% or less.

[0026] ·Solvent The solvent is not particularly limited, and known solvents conventionally used in the positive electrode active material paste can be used. Examples of the solvent include N-methylpyrrolidone (NMP) and the like.

[0027] · Viscosity of the positive electrode active material paste The viscosity (20 °C) of the positive electrode active material paste shall be 18,000 mPa·s or less. Since the viscosity of the positive electrode active material paste is within the above range, that is, the fluidity of the positive electrode active material paste is high, the aggregates of the positive electrode active material generated in the low-temperature drying process can easily settle and be unevenly distributed on the positive electrode foil side. As a result, a positive electrode plate excellent in the peel strength between the positive electrode active material layer and the positive electrode foil can be obtained. From the viewpoint of increasing the peel strength between the positive electrode active material layer and the positive electrode foil, the absolute value of the viscosity of the positive electrode active material paste is preferably 10,000 mPa·s or less, and more preferably 7,000 mPa·s or less. On the other hand, the lower limit value of the viscosity of the positive electrode active material paste is not particularly limited, but from the viewpoint of ease of coating, it is preferably 3,000 mPa·s or more, and more preferably 4,000 mPa·s or more.

[0028] Note that the viscosity of the positive electrode active material paste at 20 °C can be adjusted by, for example, the selection of the type of binder, the amount of binder, the type of solvent, and the amount of solvent.

[0029] The viscosity of the positive electrode active material paste at 20 °C complies with JIS K7117 (1999), and the viscosity measured at a measurement temperature of 20 °C using a B-type viscometer is adopted.

[0030] · Solids content ratio of the positive electrode active material paste The solids content ratio (mass ratio) of the positive electrode active material paste is preferably 50% by mass to 60% by mass. When the solids content ratio of the positive electrode active material paste is 50% by mass or more, it is possible to easily cause aggregation of the positive electrode active material. On the other hand, when the solids content ratio of the positive electrode active material paste is 60% by mass or less, the occurrence of migration of the positive electrode active material particles in the high-temperature drying process can be suppressed. The solid content ratio of the positive electrode active material paste is more preferably 52% by mass to 58% by mass.

[0031] · Other conditions in the paste preparation process The kneading method for preparing the positive electrode active material paste is not particularly limited and may be performed by a known method. For example, it can be kneaded using a planetary mixer, a sand mill, a ball mill, a planetary mill, a roll mill, an extruder, etc.

[0032] The positive electrode active material paste may further contain other additives, for example, it may contain a conductive agent. In addition, it may also contain a thickener, a surfactant, a dispersant, a wetting agent, an antifoaming agent, etc. Examples of the conductive agent include carbon materials such as acetylene black, ketjen black, vapor grown carbon fiber (VGCF (registered trademark)), and carbon nanotube (CNT). Among them, carbon nanotube (CNT) is preferable as the conductive agent. The ratio of the conductive agent can be such that the content ratio of the conductive agent to the amount of the positive electrode active material in the formed positive electrode active material layer is 0.5% by mass or more and 5% by mass or less.

[0033] (2) Coating process In the coating process, the positive electrode active material paste is coated on the positive electrode foil. As the coating method, it can be performed by a known method such as knife coating or gravure coating.

[0034] (3) Low-temperature drying process In the low-temperature drying process, the positive electrode active material paste after the coating process is dried at a temperature equal to or higher than the freezing point of the solvent and equal to or lower than 40°C. By providing a low-temperature drying process at a temperature equal to or higher than the freezing point of the solvent and equal to or lower than 40°C, aggregates of the positive electrode active material are generated in the positive electrode active material paste at a stage prior to the high-temperature drying process where migration of the binder may occur, and these aggregates are sedimented and unevenly distributed on the positive electrode foil side. As a result, on the positive electrode foil side in the positive electrode active material paste, the number density of the particles of the positive electrode active material is in a reduced state, and a positive electrode plate excellent in the peel strength between the positive electrode active material layer and the positive electrode foil can be obtained. From the perspective of enhancing the peel strength between the positive electrode active material layer and the positive electrode foil, the drying temperature in the low-temperature drying process is preferably 35°C or lower, more preferably 30°C or lower. On the other hand, the lower limit of the drying temperature in the low-temperature drying process is not particularly limited as long as it is above the freezing point of the solvent.

[0035] From the perspective of enhancing the peel strength between the positive electrode active material layer and the positive electrode foil, the drying time in the low-temperature drying process is preferably 10 minutes or longer, more preferably 15 minutes or longer. On the other hand, from the perspective of process simplification and the time when the applied positive electrode active material paste cannot be completely dried, the upper limit of the drying time in the low-temperature drying process is preferably 60 minutes or shorter, more preferably 45 minutes or shorter.

[0036] Note that the drying temperature means the maximum temperature reached by the positive electrode active material paste in the low-temperature drying process. The drying can be appropriately selected from natural drying, vacuum drying, and heat drying.

[0037] (4) High-temperature drying process In the high-temperature drying process, the positive electrode active material paste after the low-temperature drying process is dried at a temperature of 80°C or higher and 130°C or lower. By drying at a temperature of 80°C or higher, the solvent can be evaporated well. On the other hand, from the perspective of process simplification, the upper limit of the drying temperature in the high-temperature drying process is set to 130°C or lower. The drying temperature in the high-temperature drying process is preferably further 90°C or higher and 120°C or lower, more preferably 100°C or higher and 110°C or lower.

[0038] The drying time in the high-temperature drying process can be, for example, 10 minutes or longer and 60 minutes or shorter. Note that the drying temperature means the maximum temperature reached by the positive electrode active material paste in the high-temperature drying process. The drying can be appropriately selected from vacuum drying and heat drying.

[0039] The basis weight (g / cm 2) is not particularly limited as long as it does not interfere with the effects of the present disclosure. For example, it may be 1 g / cm 2 ~10 g / cm 2 .

[0040] After drying, the positive electrode active material layer is pressed, if necessary, by roll pressing, cold isostatic pressing (CIP), etc., to adjust to a predetermined thickness or electrode density (g / cm 3 ). Further, after pressing, it may be further cut by a slitter and adjusted to a predetermined size.

[0041] <Battery> The positive electrode plate obtained by the method for manufacturing a positive electrode plate according to an embodiment of the present disclosure can be used in various batteries. Examples of the battery include a structure having a positive electrode, a negative electrode, and a separator interposed between the positive electrode and the negative electrode.

[0042] Here, an example of the battery will be described with reference to FIG. 1. A secondary battery 100, which is an example of the battery, has a positive electrode including a positive electrode current collector 32 (e.g., aluminum foil, etc.) as a positive electrode foil and a positive electrode active material layer 34 containing a positive electrode active material formed on both surfaces of the positive electrode current collector 32. The secondary battery 100 also has a negative electrode including a negative electrode current collector 22 (e.g., copper foil, etc.) as a negative electrode foil and a negative electrode active material layer 24 containing a negative electrode active material formed on both surfaces of the negative electrode current collector 22. The secondary battery 100 has a structure in which the positive electrode and the negative electrode are laminated via a separator 60. The secondary battery 100 is configured to include predetermined battery constituent materials (active materials for the positive and negative electrodes, current collectors for the positive and negative electrodes, separator, etc.), similar to a typical lithium secondary battery. And, as the positive electrode plate composed of the positive electrode current collector 32 and the positive electrode current collector 32, it includes the positive electrode plate obtained by the method for manufacturing a positive electrode plate according to the above-described embodiment of the present disclosure.

[0043] For the positive electrode current collector as the positive electrode foil, for example, a metal foil (specifically, aluminum foil, etc.) is used. Details of the positive electrode active material layer are as described above, and the description here is omitted.

[0044] As the negative electrode current collector as the negative electrode foil, for example, a metal foil (specifically, a copper foil or the like) is used. The negative electrode active material layer contains, for example, a negative electrode active material and a binder. Examples of the negative electrode active material include substances capable of occluding and releasing lithium ions (for example, carbon materials (for example, natural graphite, artificial graphite, etc.)). Examples of the binder include fluororesins (for example, polyvinylidene fluoride (PVdF), tetrafluoroethylene-hexafluoropropylene copolymer, etc.), polyvinyl acetate, and the like. The negative electrode active material layer may contain, as necessary, a conductive agent (for example, acetylene black, carbon nanotubes, etc.), a thickener, a surfactant, a dispersant, a wetting agent, an antifoaming agent, and the like.

[0045] Examples of the separator include a porous resin flat plate. Examples of the material of the resin flat plate include resins (for example, polyethylene, polypropylene, etc.).

[0046] As the electrolytic solution used in the battery, for example, a non-aqueous electrolytic solution is preferred. The non-aqueous electrolytic solution contains an electrolyte and a non-aqueous solvent. Examples of the electrolyte include lithium salts containing fluorine (for example, lithium hexafluorophosphate, lithium tetrafluoroborate, etc.), lithium salts not containing fluorine (for example, lithium perchlorate, lithium aluminum tetrachloride, etc.). Examples of the non-aqueous solvent include cyclic carbonates (for example, ethylene carbonate, etc.), and chain carbonates (for example, dimethyl carbonate, ethyl methyl carbonate, etc.). The non-aqueous electrolytic solution may further contain an additive (for example, lithium bisoxalate borate, etc.).

Examples

[0047] Examples will be described below, but the present invention is not limited to these examples at all.

[0048] (Example 1) The following positive electrode active material, conductive agent, and binder were mixed at a ratio (mass ratio) of positive electrode active material:conductive agent:binder = 98.0:1.0:1.0, and further, a solvent (N-methylpyrrolidone (NMP)) was added so that the solid content ratio became 50% by mass and kneaded to obtain a positive electrode active material paste A. The viscosity of the paste is shown in Table 1. · Positive electrode active material (material: lithium transition metal oxide), zeta potential -10 mV · Conductive agent: carbon nanotube (product name: multi-walled carbon nanotube) · Binder: (polyvinylidene fluoride: PVdF)

[0049] Regarding the obtained positive electrode active material paste A, the maximum value of the particle gauge (μm) and the value in the group were measured by the following method. The paste was drawn using a grind meter (for 0 μm to 100 μm, in 10 μm increments), irradiated with light, and observed to measure. The particle gauge at the maximum depth on the scale was defined as the maximum value, and the median value of the region where the particles were concentrated was defined as the group.

[0050] The positive electrode active material paste A was applied to both sides of a positive electrode foil (aluminum foil) (coating step). Subsequently, it was dried under the conditions of normal temperature (25 °C) for 30 minutes (low-temperature drying step). Furthermore, it was dried under the conditions of 110 °C for 15 minutes (high-temperature drying step) to form a positive electrode active material layer, and a positive electrode plate was obtained.

[0051] (Comparative Example 1) In Example 1, the positive electrode active material used was changed to one with a zeta potential of -30 mV (material: lithium transition metal oxide), and a positive electrode plate was obtained in the same manner as in Example 1 except that the low-temperature drying step (that is, drying under the conditions of normal temperature (25 °C) for 30 minutes) was not performed and the high-temperature drying step was performed immediately after the coating step. The viscosity of the paste, the maximum value of the particle gauge (μm), and the group are shown in Table 1.

[0052] (Comparative Example 2) In Example 1, a positive electrode plate was obtained in the same manner as in Example 1, except that the low-temperature drying step (i.e., drying under normal temperature (25 °C) for 30 minutes) was not performed, and the high-temperature drying step was performed immediately after the coating step. The viscosity of the paste, the maximum value of the particle gauge (μm), and the group are shown in Table 1.

[0053] - Evaluation: Peel Strength Ratio - Evaluation was performed by a 90-degree peel test method using a tensile tester in accordance with JIS Z0237:2009. Specifically, a double-sided tape of a predetermined size was attached to a steel plate, and the positive electrode active material layer of the positive electrode plate cut out to a width of 10 mm × a length of 80 mm was brought into close contact with the surface of the double-sided tape opposite to the steel plate side, and peeled while pulling in the 90° direction at a speed of 40 mm / min. The average value of the stress at this time was taken as the peel strength (N / m), and the results of the ratio (peel strength ratio) when the value of the peel strength (N / m) in "Comparative Example 1" was set to 1.0 are shown in Table 1.

[0054]

Table 1

[0055] As shown in Table 1, in Example 1 using a positive electrode active material with a zeta potential in a specific range, a positive electrode active material paste with a viscosity in a specific range, and providing a low-temperature drying step (drying at a temperature not lower than the freezing point of the solvent and not higher than 40 °C) before the high-temperature drying step, excellent peel strength was obtained. On the other hand, in Comparative Example 2 without a low-temperature drying step and in Comparative Example 1 using a positive electrode active material outside the specific range of the zeta potential and without a low-temperature drying step, the peel strength was inferior.

Explanation of Signs

[0056] 2 Positive electrode active material 2A Unaggregated positive electrode active material 2B Aggregate 4 Binder 10 Positive electrode plate 22 Negative electrode current collector 24 Negative electrode active material layer 32 Secondary battery 34 Positive electrode active material layer 60 Separator 100 Secondary battery

Claims

1. A paste preparation step of preparing a positive electrode active material paste having a viscosity of 18,000 mPa·s or less by mixing a positive electrode active material having an absolute value of the zeta potential of 10 mV or less, a binder, and a solvent; A coating step of coating the positive electrode active material paste on a positive electrode foil; A low-temperature drying step of drying the positive electrode active material paste after the coating step at a temperature equal to or higher than the freezing point of the solvent and equal to or lower than 40°C; A high-temperature drying step of drying the positive electrode active material paste after the low-temperature drying step at a temperature of 80°C or higher and 130°C or lower; A method for manufacturing a positive electrode plate having the above steps.

2. The method for manufacturing a positive electrode plate according to claim 1, wherein the solid content ratio of the positive electrode active material paste prepared in the paste preparation step is 50% by mass to 60% by mass.

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