Manufacturing method for positive electrode plates for lithium-ion secondary batteries

Abstract

To effectively suppress the formation of mixed layers. [Solution] Insulator paste 24A contains chloride ions Cl - It contains 24C, and by bringing the insulating paste 24A into contact with the positive electrode composite paste 23A, the chloride ions Cl contained in the insulating paste 24A are absorbed. - When 24C comes into contact with the positive electrode composite paste 23A, the viscosity of the positive electrode composite paste 23A at the boundary 25 with the insulator paste 24A increases, suppressing mixing between the positive electrode composite paste 23A and the insulator paste 24A.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a positive electrode plate for a lithium-ion secondary battery, and more particularly to a method for manufacturing a positive electrode plate for a lithium-ion secondary battery that suppresses the formation of a mixed layer in which a positive electrode composite paste and an insulating paste are mixed. [Background technology]

[0002] In electric vehicles and hybrid vehicles, lithium-ion secondary batteries are sometimes used as the power source for propulsion. A lithium-ion secondary battery comprises electrode plates having a positive electrode plate and a negative electrode plate. The electrode plate comprises a long positive electrode substrate and an asphalt layer formed by coating the positive electrode substrate with an asphalt paste. The positive electrode substrate has exposed portions along its side edges in the width direction where the asphalt paste is not coated and the positive electrode substrate is exposed. These exposed portions are used as current collectors to connect to external terminals. In addition, an insulating layer made of insulating paste is formed at the boundary between the positive electrode asphalt layer and the exposed portion of the positive electrode plate. From the viewpoint of manufacturing efficiency, it is common to coat the positive electrode asphalt paste and insulating paste simultaneously onto the positive electrode substrate as a method for forming the positive electrode asphalt layer and the insulating layer. In this case, a mixed layer may be formed at the boundary between the positive electrode asphalt paste and the insulating paste, where the positive electrode asphalt paste and insulating paste are mixed. The mixed layer has lower conductivity than the asphalt layer because it contains insulating particles derived from the insulating paste. As the mixed layer expands, the reaction of the positive electrode active material that contributes to charging and discharging is suppressed in the mixed layer, leading to a decrease in battery capacity and deterioration of charging and discharging characteristics at high currents.

[0003] Patent Document 1 describes the following invention for suppressing the formation of such mixed layers: At least one of the positive electrode binder and the insulating resin is a gelling agent. By bringing the insulating paste into contact with the positive electrode composite paste, the lithium-containing alkaline component reacts with an acid to produce alkaline water. Furthermore, by bringing the alkaline water into contact with the gelling agent, a gel layer is formed at the boundary between the positive electrode composite paste and the insulating paste. According to this invention, the formation of mixed layers can be suppressed. [Prior art documents]

Patent Document

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, in the invention described in Patent Document 1, it is necessary that at least one of the positive electrode binder and the insulating resin is a gelling agent in the positive electrode composite paste. Further, a gel layer cannot be formed at the boundary unless the positive electrode composite paste and the insulator paste are mixed.

[0006] The problem to be solved by the method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to the present invention is to effectively suppress the formation of a mixed layer.

Means for Solving the Problems

[0007] To solve the above problems, the method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to the present invention uses a positive electrode composite paste containing a positive electrode active material and a positive electrode solvent, and an insulator paste containing an insulating material and a solvent for the insulator, and applies the positive electrode composite paste and the insulator paste to a positive electrode substrate so that the insulator paste contacts the positive electrode composite paste, thereby forming a positive electrode composite layer and an insulator layer adjacent to the positive electrode composite layer on the positive electrode substrate. The insulator paste contains Cl - By bringing the insulator paste into contact with the positive electrode composite paste, Cl - contained in the insulator paste contacts the positive electrode composite paste, increasing the viscosity of the positive electrode composite paste at the boundary with the insulator paste, and suppressing mixing of the positive electrode composite paste and the insulator paste.

[0008] The insulator paste contains 0.0050 [%] or more and 0.0620 [%] or less of the Cl -It may be made to include this. The positive electrode mixture paste may contain a dispersant, and the amount of the dispersant contained may be 0.15% or less of the mass of the positive electrode mixture paste.

[0009] The Cl contained in the insulating paste - The mass of the dispersant may be 5.0% or more of the mass of the dispersant. The viscosity of the positive electrode composite paste facing the boundary after coating may be set to 1 [Pa·s] or more and 15 [Pa·s] or less.

[0010] The specific surface area of ​​the positive electrode active material in the positive electrode composite paste is 1.7 [m²] 2 / g] or more, 2.5[m 2 It may be less than or equal to [ / g]. Preferably, the specific surface area of ​​the positive electrode active material in the positive electrode composite paste is 2.0 [m²]. 2 / g] or more, 2.4[m 2 It is less than or equal to [ / g].

[0011] The solid content of the positive electrode composite paste may be 55% or more and 70% or less. The positive electrode composite paste and the insulating paste may be applied to the positive electrode substrate simultaneously.

[0012] The viscosity [Pa·s] of the coated positive electrode composite paste and the insulating paste may be equal. The insulating paste may contain at least one of HCl, LiCl, NaCl, and KCl. [Effects of the Invention]

[0013] According to the method for manufacturing a positive electrode plate for a lithium-ion secondary battery of the present invention, the formation of a mixed layer can be effectively suppressed. [Brief explanation of the drawing]

[0014] [Figure 1] This is a schematic diagram illustrating the principle of this embodiment. [Figure 2]This is a perspective view of the lithium-ion secondary battery cell of this embodiment. [Figure 3] This is a diagram of the electrode body of this embodiment, with a part of it unfolded. [Figure 4] This is a cross-sectional view of the electrode body of this embodiment in an unfolded state. [Figure 5] This graph shows the relationship between the concentration of chloride ions (Cl-) [ppm] and the adsorption rate of the dispersant and the positive electrode active material [%]. [Figure 6] This is a cross-sectional view showing the state immediately after coating the positive electrode substrate with the positive electrode composite paste and the insulating paste in the manufacturing process of the positive electrode plate of this embodiment. [Figure 7] This is a cross-sectional view of a key part illustrating the function at the boundary between the positive electrode composite paste and the insulating paste in the positive electrode plate of this embodiment. [Figure 8] This is a comparison table of the diffusion coefficients of chloride ions (Cl-), positive electrode active material, and insulating particles. [Figure 9] This graph compares the viscosity of different types of dispersants. [Figure 10] This graph shows the relationship between paste viscosity index and the thickness [mm] of the mixed layer. [Figure 11] This graph shows the relationship between the concentration of chloride ions (Cl-) in the paste [ppm] and the paste viscosity index. [Figure 12] This is a cross-sectional view of a key part showing a state in which a mixed layer has formed at the boundary between the positive electrode composite paste and the insulating paste in the manufacturing process of a conventional positive electrode plate. [Modes for carrying out the invention]

[0015] Referring to Figures 1 to 11, the method for manufacturing a positive electrode plate for a lithium-ion secondary battery of the present invention will be explained using the manufacturing method of the positive electrode plate 21 of a lithium-ion secondary battery 10 as an example. (Outline of this embodiment) FIG. 1 is a schematic diagram for explaining the formation of the high-viscosity layer 25B of the present embodiment. The positive electrode plate 21 of the lithium-ion secondary battery 10 of the present embodiment is manufactured (see FIGS. 2 and 3). The object is to suppress the formation of the mixed layer 25A that occurs at the boundary 25 between the positive electrode mixture paste 23A and the insulator paste 24A as shown in FIG. 12.

[0016] In Patent Document 1, the formation of the mixed layer 25A was suppressed by having a gelling agent in the positive electrode mixture paste 23A. In the present embodiment, even if the positive electrode mixture paste 23A does not contain a gelling agent, the formation of the mixed layer 25A can be suppressed. In the manufacturing method of the positive electrode plate 21 of the lithium-ion secondary battery 10 of the present embodiment, the chloride ion Cl - 24C in the insulator paste 24A aggregates the components of the positive electrode mixture paste 23A to increase the viscosity [Ps·s]. Thereby, the mixing of the positive electrode mixture paste 23A and the insulator paste 24A is suppressed, and the formation of the mixed layer 25A is suppressed.

[0017] In Patent Document 1, mixing occurs at the boundary 25 between the positive electrode mixture paste 23A and the insulator paste 24A, and the formation of the mixed layer 25A is suppressed by the gelling agent gelling. Here, the chloride ion Cl - 24C aggregates particles such as the positive electrode active material 23B. Especially when the positive electrode mixture paste 23A contains a dispersant 23C, the repulsive action due to the static electricity is effectively reduced, and the positive electrode mixture paste 23A is aggregated to form a high-viscosity layer 25B, thereby suppressing the formation of the mixed layer 25A.

[0018] FIG. 5 is a graph showing the relationship between the concentration [ppm] of the chloride ion Cl - 24C and the adsorption rate [%] of the dispersant 23C to the positive electrode active material 23B. According to the experiments of the present inventors, it was demonstrated that by increasing the concentration [ppm] of the chloride ion Cl - 24C, the adsorption rate [%] of the dispersant 23C to the positive electrode active material 23B increases. As shown in FIG. 5, the chloride ion Cl -When the concentration of 24C [ppm] was 20 [ppm], the adsorption rate of the dispersant 23C to the positive electrode active material 23B was approximately 80 [%]. In contrast, the adsorption rate of chloride ions Cl - When the concentration of 24C [ppm] was 50 [ppm], the adsorption rate of the dispersant 23C to the positive electrode active material 23B was approximately 83.8 [%]. That is, chloride ions Cl - We verified that when the concentration of 24C [ppm] is 50 [ppm], the adsorption rate [%] of the dispersant 23C and the positive electrode active material 23B is significantly higher compared to when the concentration is 20 [ppm]. In other words, chloride ions Cl - It was found that adding 24C can suppress dispersion even when the dispersant 23C is added.

[0019] Also, chloride ions (Cl) - 24C is extremely diffusive compared to the positive electrode active material 23B and insulating particles 24B. After coating, the positive electrode composite paste 23A and the insulating paste 24A move and mixing occurs at the boundary 25. However, before that, chloride ions Cl - 24C reaches the boundary 25 with the positive electrode composite paste 23A more quickly, and suppresses the effect of the dispersant 23C. Therefore, even in the presence of the dispersant 23C, it aggregates the positive electrode active material 23B, binder 23D, and conductive additive 23E in a short time. As a result, the viscosity [Pa·s] of the portion of the positive electrode composite paste 23A facing the boundary 25 increases rapidly, forming a high-viscosity layer 25B and suppressing the formation of the mixed layer 25A.

[0020] By suppressing the formation of the mixed layer 25A in this way, the amount of inactive positive electrode active material 23B in the mixed layer 25A is not increased. As a result, the decrease in the capacitance of the positive electrode plate 21 is suppressed.

[0021] (Configuration of this embodiment) The lithium-ion secondary battery 10, which is the basis for the manufacturing method of the positive electrode plate 21 for the lithium-ion secondary battery 10 of this embodiment, will be described in detail below. It goes without saying that the lithium-ion secondary battery 10 of this embodiment is presented for illustrative purposes only, and the lithium-ion secondary battery 10 is not limited to those illustrated in the embodiment.

[0022] <Lithium-ion secondary battery 10> Figure 2 is a perspective view of the cell battery of the lithium-ion secondary battery 10 of this embodiment. As shown in Figure 2, the lithium-ion secondary battery 10 of this embodiment is configured as a cell battery. Although not shown in the figure, the lithium-ion secondary battery 10 is combined with the cell batteries of other lithium-ion secondary batteries 10 with a similar configuration to form a battery pack. The battery pack is further combined and sealed in a resin case or the like to form a battery pack. The battery pack is used as a power source for hybrid vehicles and electric vehicles.

[0023] The lithium-ion secondary battery 10 comprises a battery case 11 and a cover 12. The battery case 11 has a rectangular parallelepiped shape with an opening on its upper side. The cover 12 seals the opening of the battery case 11. The battery case 11 and the cover 12 are made of a metal such as an aluminum alloy. The lithium-ion secondary battery 10 is formed as a sealed battery case by attaching the cover 12 to the battery case 11.

[0024] The cover 12 is provided with two external terminals 13A and 13B. These external terminals 13A and 13B are used for charging and discharging power. The electrode body 20 is housed inside the battery case 11. The positive electrode side current collector 20A, which is the positive electrode end of the electrode body 20, is electrically connected to the positive electrode external terminal 13A via the positive electrode side current collector 14A. The negative electrode side current collector 20B, which is the negative electrode end of the electrode body 20, is electrically connected to the negative electrode external terminal 13B via the negative electrode side current collector 14B. In addition, a non-aqueous electrolyte is injected into the battery case 11 through an injection port (not shown).

[0025] Figure 3 shows an unfolded view of a portion of the electrode body 20 of this embodiment. As shown in Figure 3, the electrode body 20 is a flat wound body formed by winding a laminate in which a long positive electrode plate 21 and a negative electrode plate 26 are stacked with a separator 29 in between. Before winding, the laminate is stacked in the order of positive electrode plate 21, separator 29, negative electrode plate 26, separator 29, with the longitudinal directions aligned.

[0026] <Positive plate 21> Figure 4 is a cross-sectional view of the electrode body 20 of this embodiment in an unfolded state. As shown in Figures 3 and 4, the positive electrode plate 21 comprises a sheet-like positive electrode base material 22 formed in an elongated shape, a positive electrode composite material layer 23 provided on both sides of the positive electrode base material 22, and an insulating layer 24 adjacent to the positive electrode composite material layer 23. In addition, an exposed portion 22A is provided at one end of the positive electrode plate 21 in the width direction, where neither the positive electrode composite material layer 23 nor the insulating layer 24 is formed, and the positive electrode base material 22 is exposed. The insulating layer 24 is provided on the positive electrode plate 21 along the exposed portion 22A. That is, the insulating layer 24 is provided on the positive electrode plate 21 at a position spaced apart from the side edge along the longitudinal direction of the positive electrode base material 22. The positive electrode composite material layer 23 is provided from the end of the positive electrode plate 21 opposite to the exposed portion 22A in the width direction to the position of the insulating layer 24. The positive electrode composite layer 23 and the insulating layer 24 are in contact with each other at their boundary 25.

[0027] <Positive electrode substrate 22> The positive electrode substrate 22 is a thin film made of aluminum or an alloy mainly composed of aluminum. The positive electrode substrate 22 functions as a current collector in the positive electrode. In the wound state, the exposed portion 22A of the positive electrode substrate 22 is pressed against each other by opposing surfaces to form the positive electrode side current collector 20A.

[0028] <Cathode active material 23B> Positive electrode active material 23B is an example of an active material contained in positive electrode composite paste 23A. Positive electrode active material 23B is lithium ion Li + A lithium-containing composite metal oxide capable of intercalating and releasing lithium is used. The lithium-containing composite oxide is an oxide containing lithium and other metal elements other than lithium. The other metal elements other than lithium are, for example, at least one selected from the group consisting of nickel, cobalt, manganese, vanadium, magnesium, molybdenum, niobium, titanium, tungsten, aluminum, and iron contained as iron phosphate in the lithium-containing composite oxide.

[0029] For example, lithium-containing composite oxides include lithium cobaltate (LiCoO2), lithium nickelate (LiNiO2), and lithium manganeseate (LiMn2O4). Another example is lithium-containing composite oxide, a ternary lithium-containing composite oxide containing nickel, cobalt, and manganese, which is lithium nickel-cobalt-manganate (LiNiCoMnO2). Yet another example is lithium iron phosphate (LiFePO4). Furthermore, the positive electrode composite paste 23A contains lithium-containing alkaline components as unreacted residues and by-products during the production of lithium-containing composite metal oxides. These lithium-containing alkaline components include, for example, lithium hydroxide (LiOH), and lithium carbonate (Li2CO3), a carbonate produced when LiOH reacts with carbon dioxide in the air.

[0030] <Binding material 23D> The binder 23D is an example of a binder included in the positive electrode composite paste 23A. Examples of binders 23D include polyvinylidene fluoride (PVDF) and polyvinyl alcohol (PVA).

[0031] <Conductive additive 23E> The conductive additive 23E is incorporated in the positive electrode composite layer 23 to form a conductive network and enhance conductivity between positive electrode active materials 23B and with the non-aqueous electrolyte. For example, carbon black such as acetylene black and Ketjenblack, carbon fibers such as carbon nanotubes and carbon nanofibers, and graphite are used. In particular, carbon nanotubes tend to aggregate, so the addition of a dispersant 23C is effective.

[0032] <Dispersant 23C> The dispersant 23C disperses the conductive additive 23E, which is prone to aggregation, and the positive electrode active material 23B. Dispersants 23C can utilize either steric hindrance or electrostatic repulsion. "Steric hindrance" involves functional adsorption onto the particle surface, preventing aggregation due to steric hindrance caused by the particle's physical shape. "Electrostatic repulsion," on the other hand, prevents aggregation by utilizing the repulsive force of static electricity. In this embodiment, the positive electrode mixture paste 23A contains the dispersant 23C, and its content is 0.15% or less of the mass of the positive electrode mixture paste 23A, specifically, 0.10%.

[0033] <Positive electrode solvent 23F> The positive electrode solvent 23F is an example of a non-aqueous solvent for the positive electrode mixture paste 23A, which is included in the positive electrode mixture paste 23A. The positive electrode solvent 23F is an example of an organic solvent, such as NMP (N-methyl-2-pyrrolidone) solution.

[0034] <Insulating layer 24> As shown in Figure 4, the insulating layer 24 is formed to contact the widthwise end of the positive electrode composite layer 23 on the exposed portion 22A side of the positive electrode plate 21. In the case of a lithium-ion secondary battery 10, the capacity of the positive electrode composite layer 23 is set to a positive electrode regulation, which sets the capacity to be smaller than that of the negative electrode composite layer 28. For this reason, the width of the negative electrode composite layer 28 is also larger than that of the positive electrode composite layer 23, and it is configured to protrude beyond the opposing portion of the positive electrode composite layer 23 and the negative electrode composite layer 28. For this reason, if the insulating layer 24 shown in Figure 4 is not present, the exposed portion 22A of the positive electrode substrate 22 and the negative electrode composite layer 28 of the negative electrode plate 26 will be in a position to face each other via the separator 29. In this state, if foreign matter such as a small piece of metal gets mixed between the exposed portion 22A of the positive electrode substrate 22 and the separator 29 and damages the separator 29, a small short circuit may occur. In such cases, rapid battery degradation will occur.

[0035] Therefore, an insulating layer 24 is formed between the exposed portion 22A of the positive electrode substrate 22 and the separator 29. The insulating layer 24 is a hardened form of the liquid insulating paste 24A (see Figure 6). The insulating paste 24A consists of insulating particles 24B, which are insulating materials, and chloride ions Cl -The mixture contains 24C, a binder 24D made of insulating resin, and an insulating solvent 24E. The insulating particles 24B are powdered boehmite or alumina. The insulating solvent 24E is either an aqueous insulating solvent or a non-aqueous insulating solvent. The aqueous insulating solvent contains water. As an example of an organic solvent, NMP solution is used as the non-aqueous insulating solvent.

[0036] The binder 24D is selected from polymer materials soluble in the insulating solvent 24E, depending on the type of insulating solvent 24E used. For example, when water is used as the insulating solvent 24E, water-soluble polymer materials such as styrene-butadiene rubber (SBR) and PVA (polyvinyl alcohol) derivatives are used as insulating resins. Alternatively, when NMP is used as the insulating solvent 24E, polymer materials soluble in NMP such as PVDF and PVA are used as insulating resins. In this embodiment, water is used as the insulating solvent 24E, and SBR is used as the insulating resin.

[0037] <Chloride (chloride ions Cl - 24C)> The insulating paste 24A of this embodiment contains chloride as a compounding material. The chloride dissociates in the insulating solvent 24E, forming chloride ions Cl - 24C is supplied to the insulating solvent 24E. The mass of 24C is between 0.0050% and 0.0620% of chloride ions (Cl) relative to the insulating paste 24A. - Add the solution so that it contains 24C. Examples of chlorides include hydrochloric acid (HCl), lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl).

[0038] <Negative electrode plate 26> Figure 4 is a cross-sectional view of the electrode body 20 of this embodiment in an unfolded state. As shown in Figures 3 and 4, the negative electrode plate 26 comprises a sheet-like negative electrode base material 27 formed in a long shape and a negative electrode composite material layer 28 provided on both sides of the negative electrode base material 27. The negative electrode plate 26 is manufactured by kneading the materials constituting the negative electrode composite material layer 28, coating the kneaded negative electrode composite paste onto the negative electrode base material 27, and drying it.

[0039] The negative electrode substrate 27 functions as a current collector at the negative electrode. The negative electrode substrate 27 can be a thin film made of copper or an alloy mainly composed of copper. At one end of the negative electrode plate 26 in the width direction, an exposed portion 27A is provided where the negative electrode substrate 27 is exposed without the negative electrode composite layer 28 being formed. In the wound state, the exposed portion 27A has opposing surfaces pressed against each other to form the negative electrode side current collector 20B.

[0040] The negative electrode composite layer 28 is a hardened body of a liquid negative electrode composite paste. The negative electrode composite layer 28 is provided on the surface of the negative electrode substrate 27. The negative electrode composite layer 28 contains lithium ions Li + The negative electrode active material is a material capable of intercalating and releasing a certain substance. The negative electrode active material can be, for example, carbon materials such as graphite, non-graphitizable carbon, or easily graphitizable carbon. In addition to the negative electrode active material, the negative electrode composite material includes a conductive agent, a binder, and the like.

[0041] <Separator 29> The separator 29 prevents contact between the positive electrode plate 21 and the negative electrode plate 26, and holds the non-aqueous electrolyte between the positive electrode plate 21 and the negative electrode plate 26. When the electrode body 20 is immersed in the non-aqueous electrolyte, the non-aqueous electrolyte permeates from the edges of the separator 29 toward the center.

[0042] The separator 29 is a nonwoven fabric made of polypropylene or the like. As the separator 29, for example, porous polymer membranes such as porous polyethylene membranes, porous polyolefin membranes, and porous polyvinyl chloride membranes, and ion-conductive polymer electrolyte membranes can be used.

[0043] <Nonaqueous electrolyte> A non-aqueous electrolyte is a composition containing a supporting salt in a non-aqueous solvent. As the non-aqueous solvent, one or more materials selected from the group consisting of propylene carbonate, ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, etc., can be used. As the supporting salt, one or more lithium compounds (lithium salts) selected from LiPF6, LiBF4, LiClO4, LiAsF6, LiCF3SO3, LiC4F9SO3, LiN(CF3SO2)2, LiC(CF3SO2)3, LiI, etc., can be used.

[0044] In this embodiment, ethylene carbonate is used as the non-aqueous solvent. Lithium bisoxalate borate (LiBOB), as a lithium salt, is added to the non-aqueous electrolyte as an additive. For example, LiBOB is added to the non-aqueous electrolyte so that the concentration of LiBOB [mol / L] in the non-aqueous electrolyte is between 0.001 and 0.1 [mol / L].

[0045] (Effect of the embodiment) Next, a method for manufacturing the positive electrode plate 21 for the lithium-ion secondary battery 10 of this embodiment will be described.

[0046] <Formation of positive electrode composite paste 23A> For coating, a positive electrode composite paste 23A is produced. The positive electrode composite layer 23 is a cured form of the liquid positive electrode composite paste 23A. In this embodiment, the positive electrode composite paste 23A is prepared by adding a positive electrode solvent 23F to a positive electrode active material 23B, a dispersant 23C, a binder 23D, and a conductive additive 23E, and kneading these together.

[0047] The positive electrode composite paste 23A is to which a dispersant 23C is added in an amount of 0.15% or less of the mass of the positive electrode composite paste 23A. The viscosity of the positive electrode composite paste 23A facing the boundary portion 25 after coating is adjusted to be between 1 [Pa·s] and 15 [Pa·s].

[0048] Furthermore, the specific surface area of ​​the positive electrode active material 23B of the positive electrode composite paste 23A is 1.7 [m²]2 / g] or more, 2.5[m 2 Adjusted to less than / g. Preferably, 2.0[m 2 / g] or more, 2.4[m 2 It is considered to be less than or equal to [ / g].

[0049] Furthermore, the solid content of the positive electrode composite paste 23A is adjusted to be between 55% and 70%. <Generation of insulating paste 24A> An insulating paste 24A is prepared for coating. The insulating paste 24A in this embodiment contains chloride. When water, which is the insulating solvent 24E, is added, the chloride dissociates in the insulating solvent 24E, forming chloride ions (Cl). - 24C is supplied to the insulating solvent 24E. The insulating paste 24A contains chloride ions Cl with a mass of 0.0050% or more and 0.0620% or less. - It contains 24C. In this embodiment, the amount is 0.050%. Examples of chlorides include hydrochloric acid (HCl), lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl).

[0050] Chloride ions (Cl) contained in insulating paste 24A - The mass of 24C should preferably be 5.0% or more of the mass of the dispersant 23C. Furthermore, it is desirable to make the viscosity [Pa·s] of the coated positive electrode composite paste 23A and the insulator paste 24A equal.

[0051] <Coating Process> Figure 6 is a cross-sectional view showing the state immediately after coating the positive electrode substrate 22 with the positive electrode composite paste 23A and the insulating paste 24A in the manufacturing process of the positive electrode plate 21 of this embodiment. As shown in Figure 6, in the manufacturing process of the positive electrode plate 21, first, the positive electrode composite paste 23A, which is the material for the positive electrode composite layer 23, and the insulating paste 24A, which is the material for the insulating layer 24, are simultaneously coated on one surface of the positive electrode substrate 22. Specifically, the positive electrode composite paste 23A is coated in the central part of the short side of the positive electrode substrate 22, at a position spaced apart from both side edges in the width direction of the positive electrode substrate 22. The insulating paste 24A is simultaneously coated between the width direction edge of the positive electrode substrate 22 and the positive electrode composite paste 23A, at a position spaced apart from the side edges of the positive electrode substrate 22, so as to be in contact with each end of the positive electrode composite paste 23A. The positive electrode composite paste 23A and the insulating paste 24A are simultaneously discharged from adjacent nozzles in a direction perpendicular to the coating direction of a coating machine (not shown). At this time, as shown in Figure 6, a boundary portion 25 is formed where the positive electrode composite paste 23A and the insulating paste 24A come into contact.

[0052] <Formation of conventional mixed layer 25A> Figure 12 is a cross-sectional view of a key part showing the state in which a mixed layer 25A is formed at the boundary 25 between the positive electrode composite paste 23A and the insulating paste 24A during the manufacturing process of a conventional positive electrode plate 21. Conventionally, as shown in Figure 12, at the boundary 25 where the positive electrode composite paste 23A and the insulating paste 24A come into contact, the positive electrode composite paste 23A and the insulating paste 24A mix due to osmotic pressure, and a mixed layer 25A is formed.

[0053] In the mixed layer 25A, the positive electrode active material 23B is mixed with insulating particles 24B, resulting in extremely poor conductivity around the positive electrode active material 23B, rendering it unable to function as such. Consequently, the positive electrode active material 23B in the mixed layer 25A cannot contribute to the battery capacity [Ah] of the positive electrode, resulting in a decrease in battery capacity [Ah].

[0054] <Formation of the high-viscosity layer 25B in this embodiment> Figure 7 is a cross-sectional view of a key part illustrating the function at the boundary portion 25 between the positive electrode composite paste 23A and the insulating paste 24A in the positive electrode plate 21 of this embodiment.

[0055] In this embodiment, the insulating paste 24A contains chloride ions (Cl) at the stage shown in Figure 6. - 24C exists in an ionized state in the insulating solvent 24E. Figure 8 shows the chloride ion Cl - This is a comparison table of the diffusion coefficients of 24C, the positive electrode active material 23B, and the insulating particles 24B. It is known that the diffusion of a substance in a paste can be calculated using Einstein's relation (kinetics). The diffusion rate depends on the particle size. In this embodiment, chloride ions (Cl) - The diffusion coefficients of 24C, the positive electrode active material 23B, and the insulating particles 24B were 0.09 to 0.63 for the positive electrode active material 23B and 0.39 to 1.00 for the insulating particles 24B. On the other hand, chloride ions Cl - 24C has an extremely small particle size and a diffusion coefficient of 2762.43, which is more than four orders of magnitude higher. Therefore, the chloride ions Cl present in the insulating paste 24A, as shown in Figure 1, are present in the state immediately after coating, as shown in Figure 6. - 24C moves quickly. And chloride ions Cl - 24C reaches the area around the dispersant 23C, positive electrode active material 23B, binder 23D, and conductive additive 23E in the positive electrode composite paste 23A. Therefore, chloride ions Cl - In 24C, the electrostatic repulsion effect of the dispersant 23C decreases due to the increase in ionic species. As a result, the distance between the dispersed positive electrode active material 23B decreases, and the viscosity [Pa·s] increases due to intermolecular forces.

[0056] In this embodiment, once the boundary portion 25 is formed by coating as shown in Figure 6 through this action, immediately before the mixed layer 25A shown in Figure 12 is formed, chloride ions Cl present in the insulating paste 24A are released. - 24C reaches the positive electrode composite paste 23A. As a result, the viscosity of the positive electrode composite paste 23A along the boundary 25 is rapidly increased, forming a high-viscosity layer 25B as shown in Figure 7, which suppresses the mixing of the insulator paste 24A and the positive electrode composite paste 23A.

[0057] Therefore, even if the positive electrode composite paste 23A contains a dispersant 23C, its effect is suppressed, and sufficient mixing is inhibited. In the high-viscosity layer 25B formed in the positive electrode composite paste 23A, insulating particles 24B are almost absent, and the positive electrode active material 23B can contribute to charging and discharging because the conductive additive 23E ensures conductivity, thus not reducing the capacity of the positive electrode.

[0058] <Post-process> Next, the positive electrode composite paste 23A and the insulating paste 24A are coated onto one surface of the positive electrode substrate 22, and then a drying process is performed to dry the positive electrode composite paste 23A and the insulating paste 24A in a high-temperature environment. Similarly, on the positive electrode substrate 22, the positive electrode composite paste 23A and the insulating paste 24A are coated onto the surface opposite to the surface to which they were coated, and then a drying process is performed. Through the drying process, the positive electrode composite paste 23A hardens to become the positive electrode composite layer 23. The insulating paste 24A also hardens to become the insulating layer 24.

[0059] Subsequently, a pressing process is used to adjust the thickness of the positive electrode composite paste 23A and insulating paste 24A applied to both sides of the positive electrode substrate 22. Finally, the positive electrode substrate 22 after the pressing process is cut in half along the center in the short direction. Through these steps, the positive electrode plate 21 is manufactured.

[0060] Furthermore, the mixed layer 25A formed in the process of coating the positive electrode composite paste 23A and the insulating paste 24A loses its water during the drying process. As a result, in the positive electrode plate 21 after the drying process, the high-viscosity layer 25B may not be observed partially or entirely at the boundary 25 between the positive electrode composite layer 23 and the insulating layer 24.

[0061] (Example of experiment) <Experiment 1: Comparison of effects depending on the type of dispersant 23C> In Example 1 and Comparative Example 1, a dispersant 1 having a steric hindrance function was added to the insulating paste 24A. In Example 2 and Comparative Example 2, a dispersant 2 having an electrostatic repulsion function was added to the insulating paste 24A.

[0062] Figure 9 is a graph comparing the viscosity [Pa·s] of different types of dispersant 23C. The vertical axis represents the viscosity ratio. The viscosity ratio is shown with the viscosity [Pa·s] of Comparative Examples 1 and 2 set to 1, and the viscosity [Pa·s] of Examples 1 and 2 expressed as a ratio. As shown in Figure 9, the chloride ion Cl of this embodiment - The viscosity ratios of the insulating paste 24A containing 24C in Examples 1 and 2 were approximately 4.0 for Example 1 and approximately 3.2 for Example 2.

[0063] The results of this experiment showed that the viscosity [Pa·s] could be sufficiently increased regardless of the type of dispersant 23C. Specifically, dispersant 23C showed a more effective effect on dispersant 1, which has a steric hindrance function.

[0064] <Experiment 2: Chloride ions Cl> - Relationship between the concentration of 24C [ppm] and the thickness of the mixed layer 25A [mm] > Figure 10 is a graph showing the relationship between the paste viscosity index and the width [mm] of the mixed layer 25A. The horizontal axis represents the paste viscosity index. The vertical axis represents the width [mm] (thickness) of the mixed layer 25A in Figure 12, corresponding to the paste viscosity index. Individual explanations for each plotted point are omitted, but a paste viscosity index of 0.4 corresponds to a width of 0.68 [mm] of the mixed layer 25A. From this, as the paste viscosity index increases, the width [mm] of the mixed layer 25A decreases. Regression analysis from these plotted points yielded a downward-sloping graph G1, as shown by the dotted line.

[0065] From graph G1, it can be seen that when the paste viscosity index is 3.0, the width of the mixed layer 25A is approximately 0.06 [mm], which is sufficiently thin, and the desired effect can be achieved. Also, when the paste viscosity index is near 3.0, the change in the width of the mixed layer 25A is small. Therefore, in this embodiment, the paste viscosity index was set to 3.0.

[0066] Figure 11 shows chloride ions (Cl) in insulating paste 24A. - This graph shows the relationship between the concentration [ppm] of 24C and the paste viscosity index. The horizontal axis represents chloride ions (Cl). - The concentration of 24C [ppm] is shown. The vertical axis represents chloride ions (Cl). - This shows the paste viscosity index corresponding to the concentration [ppm] of 24C.

[0067] Chloride ions (Cl) in insulating paste 24A - The paste viscosity index was 1.5 when the concentration of 24C was approximately 6 ppm. Similarly, the paste viscosity index was 2.3-2.4 when the concentration was 19 ppm. The paste viscosity index was 3.9 when the concentration was 25 ppm. The paste viscosity index was 3.9 when the concentration was 32 ppm. When these plotted points were represented as a quadratic curve using regression analysis, a dotted line graph G2, which slopes upward to the right, was derived.

[0068] From this, as shown in Figure 10, it is known that the width of the mixed layer 25A can be reduced to 0.06 [mm] by setting the paste viscosity index to 3.0. According to graph G2 in Figure 11, in order to set the paste viscosity index to 3.0, chloride ions Cl - It can be seen that the concentration of 24C [ppm] should be approximately 23 [ppm]. Therefore, in this embodiment, for safety reasons, chloride ions Cl - The threshold concentration [ppm] for 24C was set to 25 [ppm] or higher.

[0069] Next, chloride ions (Cl) are added to the insulating paste 24A. - The amount of 24C added will be explained. In this embodiment, the high viscosity layer 25B that suppresses the mixed layer 25A is formed by chloride ions Cl - It was found that the concentration of 24C [ppm] should be set to 25 [ppm]. For the formation of the high viscosity layer 25B, chloride ions Cl -The insulating paste 24A containing 24C needs to be mixed with the positive electrode composite paste 23A to some extent. Therefore, the chloride ions Cl are present in the mixture of the insulating paste 24A and the positive electrode composite paste 23A. - The concentration of 24C [ppm] must be 25 [ppm]. It is presumed that the mixing of the insulating paste 24A and the positive electrode composite paste 23A is carried out in approximately a 1:1 ratio. Therefore, the chloride ions Cl are present in the mixture of the insulating paste 24A and the positive electrode composite paste 23A. - The concentration of 24C [ppm] needs to be 25 [ppm]. To achieve this, chloride ions Cl are needed in the insulating paste 24A. - It is clear that the concentration of 24C [ppm] must be 50 [ppm] or higher.

[0070] (Effects of this embodiment) (1) The method for manufacturing the positive electrode plate 21 for the lithium-ion secondary battery 10 of this embodiment has the effect of effectively suppressing the formation of the mixed layer 25A even if the positive electrode mixture paste 23A does not contain a gelling agent.

[0071] (2) Insulator paste 24A contains chloride ions Cl - It contains 24C, and by bringing the insulating paste 24A into contact with the positive electrode composite paste 23A, chloride ions Cl are produced. - 24C comes into contact with the positive electrode composite paste 23A. This increases the viscosity of the positive electrode composite paste 23A at the boundary 25, which has the effect of suppressing the mixing of the positive electrode composite paste 23A and the insulator paste 24A.

[0072] (3) The insulating paste 24A contains chloride ions Cl with a mass of 0.0050% (50 ppm) or more. - It contains 24C. This has the effect of enabling the formation of a high-viscosity layer 25B in the positive electrode composite paste 23A. In addition, by keeping the mass of the insulating paste 24A to 0.0620[%] or less, the viscosity [Pa·s] does not rise more than necessary.

[0073] (4) The dispersant 23C contained in the positive electrode mixture paste 23A is adjusted to 0.15% or less of the mass of the positive electrode mixture paste 23A. Therefore, chloride ions Cl - 24C has the effect of suppressing dispersion and forming a high-viscosity layer 25B.

[0074] (5) Chloride ions Cl contained in insulating paste 24A - The mass of 24C was set to 5.0% or more of the mass of the dispersant 23C. This has the effect of sufficiently suppressing the dispersing force of the dispersant 23C.

[0075] (6) The viscosity of the positive electrode composite paste 23A facing the boundary portion 25 after coating was set to 1 [Pa·s] or higher. This prevents the initial paste viscosity from becoming too low, and has the effect of suppressing mixing by increasing the viscosity of the positive electrode paste at the contact surface. It was also set to 15 [Pa·s] or lower. This prevents the initial paste viscosity from becoming too high, and has the effect of achieving the desired effect.

[0076] (7) The specific surface area of ​​the positive electrode active material 23B of the positive electrode composite paste 23A is 1.7 [m² 2 The viscosity was set to be 2.5 [m] or higher. This prevents the initial paste viscosity from becoming too low, and has the effect of suppressing mixing by increasing the viscosity of the positive electrode paste at the contact surface. 2 The viscosity was kept below [ / g]. This has the effect of preventing the initial paste viscosity from becoming too high, allowing it to exert the desired effect.

[0077] Furthermore, the specific surface area of ​​the positive electrode active material 23B of the positive electrode composite paste 23A is 2.0 [m²] 2 / g] or more, 2.4[m 2 By setting it to less than [ / g], the above-mentioned effects can be further achieved.

[0078] (8) The solid content of the positive electrode mixture paste 23A was set to 55% or more. This prevents the initial viscosity [Pa·s] of the positive electrode mixture paste 23A from becoming too low, and has the effect of suppressing mixing by increasing the viscosity [Pa·s] of the positive electrode mixture paste 23A at the boundary 25.

[0079] Furthermore, the solid content of the positive electrode mixture paste 23A was set to 70% or less. This has the effect of preventing the initial viscosity [Pa·s] of the positive electrode mixture paste 23A from becoming too high, allowing it to exert the desired effect.

[0080] (9) The positive electrode composite paste 23A and the insulating paste 24A are applied to the positive electrode substrate 22 simultaneously. This allows the boundary portion 25 to be positioned precisely. (10) The viscosity [Pa·s] of the coated positive electrode composite paste 23A and the insulating paste 24A are made equal. This allows the boundary portion 25 to be positioned precisely.

[0081] (Another example) The above embodiment is an example of the present invention and can be implemented with the following modifications. ○In this embodiment, chloride ions Cl - Focusing only on 24C, chloride ions Cl - Although only 24C was shown, the present invention can also be implemented in cases where other ions are present.

[0082] The various formulations and other details provided are examples, and those skilled in the art can optimize and implement them as appropriate depending on the composition and structure of the secondary battery in question. For example, the insulating particles 24B contained in the insulating paste 24A may be resin, and the binder 24D is not an essential component.

[0083] ○In this embodiment, the binder 23D and conductive additive 23E contained in the positive electrode composite paste 23A are not essential components. Similarly, the dispersant 23C is shown as an example to clarify the effects of the present invention, but it is also not an essential component.

[0084] Although lithium-ion secondary battery 10 was given as an example, the invention can also be implemented using solid-state batteries, semi-solid-state batteries, or lithium-ion secondary batteries of other configurations, as long as the invention is feasible. ○Although the electrode plate group in this embodiment is exemplified as a wound type, a laminated type electrode plate group may also be used. Furthermore, the raw materials are illustrative and not limited to these.

[0085] ○The lithium-ion secondary battery 10 shown as an example has a plate-shaped case, but its shape is not limited to cylindrical or other shapes. ○The method for manufacturing the positive electrode plate 21 for the positive electrode of the lithium-ion secondary battery 10 in this embodiment is one embodiment of the invention, and it goes without saying that, as long as it does not depart from the scope of the claims, it is not limited to this embodiment and can be implemented by those skilled in the art by adding, deleting, or modifying its configuration. [Explanation of Symbols]

[0086] 10…Lithium-ion rechargeable battery 11…Battery case 12... Lid 13A,13B…External terminal 20...Electrode body 21…Positive plate 22…Positive electrode substrate 22A, 27A…Exposed part 23…Positive electrode composite layer 23A... Positive electrode composite paste 23B…Cathode active material 23C…Dispersant 23D…Binding material 23E... Conductive additive 23F... Cathode solvent 24…Insulator layer 24A...Insulator paste 24B...Insulating particles 24C…Chloride ion Cl - 24D…Binding material 24E... Solvent for insulators 25... Boundary 25A... Mixed layer 25B…High viscosity layer 26... Negative electrode plate 27…Negative electrode substrate 28...Negative electrode composite material layer 29... Separator

Claims

1. Using a positive electrode composite paste containing a positive electrode active material and a positive electrode solvent, and an insulating paste containing an insulating material and an insulating solvent, A method for manufacturing a positive electrode plate for a lithium-ion secondary battery, comprising coating the positive electrode composite paste and the insulating paste onto a positive electrode substrate so as to bring the insulating paste into contact with the positive electrode composite paste, thereby forming a positive electrode composite layer and an insulating layer adjacent to the positive electrode composite layer on the positive electrode substrate, The aforementioned insulating paste is Cl － It contains, By bringing the insulating paste into contact with the positive electrode composite paste, the Cl contained in the insulating paste － A method for manufacturing a positive electrode plate for a lithium-ion secondary battery, characterized in that, by contacting the positive electrode composite paste, the viscosity of the positive electrode composite paste at the boundary with the insulating paste increases, thereby suppressing mixing between the positive electrode composite paste and the insulating paste.

2. The insulating paste contains Cl with a mass of 0.0050% or more and 0.0620% or less. － A method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized by containing the following:

3. The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the positive electrode mixture paste contains a dispersant, and the amount of the dispersant contained is 0.15% or less of the mass of the positive electrode mixture paste.

4. The Cl contained in the aforementioned insulating paste － The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 3, characterized in that the mass of is 5.0% or more of the mass of the dispersant.

5. The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the viscosity of the positive electrode composite paste facing the boundary after coating is 1 [Pa·s] or more and 15 [Pa·s] or less.

6. The specific surface area of ​​the positive electrode active material in the positive electrode composite paste is 1.7 [m²] ２ / g] or more, 2.5[m ２ A method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that it is less than or equal to [ / g].

7. The specific surface area of ​​the positive electrode active material in the positive electrode composite paste is 2.0 [m²] ２ / g] or more, 2.4[m ２ A method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 6, characterized in that it is less than or equal to [ / g].

8. The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 6, characterized in that the solid content of the positive electrode composite paste is 55% or more and 70% or less.

9. The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the positive electrode composite paste and the insulating paste are simultaneously coated onto the positive electrode substrate.

10. The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the viscosity [Pa·s] of the coated positive electrode composite paste and the insulating paste are equal.

11. The method for manufacturing a positive electrode plate for a lithium-ion secondary battery according to claim 1, characterized in that the insulating paste contains at least one of HCl, LiCl, NaCl, and KCl.

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