Method for manufacturing positive plate of secondary battery and secondary battery

Abstract

Provided is a method for manufacturing a positive electrode plate of a lithium ion secondary battery and a secondary battery, which can suppress mixing of a boundary portion of a positive electrode composite material layer and an insulating protective layer even in a case where a paste for forming the positive electrode composite material layer and a paste for forming the insulating protective layer are simultaneously applied. The method for manufacturing the positive electrode plate of the lithium ion secondary battery includes: generating an insulating protective paste for forming an insulating protective layer, the insulating protective paste being adjusted to a pH at which Zeta potential of constituent insulating particles does not cause aggregation; generating a positive electrode composite material paste for forming a positive electrode composite material layer, the positive electrode composite material paste containing positive electrode active material particles, a conductive auxiliary material, a binder, and a solvent, and having acetic acid added as a pH adjuster to adjust the pH to Zeta potential at which the constituent insulating particles cause aggregation; and simultaneously applying the positive electrode composite material paste and the insulating protective paste on a positive electrode current collector.

Description

Technical Field

[0001] This invention relates to a method for manufacturing a positive electrode plate of a secondary battery and to a secondary battery, and more specifically, to a method for manufacturing a positive electrode plate of a secondary battery having an insulating protective layer that does not easily mix with the positive electrode composite material layer and to a secondary battery. Background Technology

[0002] Secondary batteries, such as lithium-ion secondary batteries, are lightweight and can achieve high energy density, making them a preferred choice for high-output power supplies used in vehicles. Such secondary batteries typically have a positive electrode with a positive composite material layer formed on the positive current collector, and a negative electrode with a negative composite material layer formed on the negative current collector. The positive and negative electrodes are insulated by a separator and are multi-layered. This layered energy storage element is wound into a cylindrical or elliptical cylinder to form a wound electrode body. This wound electrode body is housed in a battery casing. For the positive and negative electrodes of such secondary batteries, they are typically designed so that the negative electrode capacity is greater than the positive electrode capacity, with the width dimension of the negative composite material layer being wider than that of the positive composite material layer. In this case, the negative composite material layer is positioned opposite the positive current collector, which lacks a positive composite material layer and has exposed metal, separated by a separator. Therefore, if metal powder or other microparticles are mixed in, or if metal precipitates at the negative electrode, it may penetrate the separator and cause a small short circuit with the positive current collector, potentially generating heat.

[0003] Therefore, to prevent such short circuits, Patent Documents 1 and 2 disclose the provision of an insulating protective layer containing an inorganic insulator on the surface of the positive current collector along the end of the positive active material layer. By providing such an insulating protective layer, the metal plate constituting the positive current collector is covered by an insulator, effectively preventing short circuits with the negative electrode composite material layer even in the event of foreign matter such as metal powder intrusion.

[0004] Methods for forming an insulating protective layer are described in Patent Document 1 and Patent Document 2, but each has the following problems.

[0005] In the invention described in Patent Document 1, a paste for forming a positive electrode composite material layer is first applied before forming an insulating protective layer, and then dried to form a positive electrode composite material layer. After that, a paste for forming an insulating protective layer is applied to form an insulating protective layer.

[0006] In the method described in Patent Document 1, the coating process for the paste forming the insulating protective layer and the coating process for the paste forming the positive electrode composite layer are separate processes. This increases the number of processes and requires multiple coating machines, leading to increased labor time. Furthermore, to prevent gaps between the insulating protective layer and the positive electrode composite layer, the coating is performed with a partial overlap between the two layers. This overlap eliminates the possibility of conductivity between the positive electrode composite layer and the positive electrode current collector, or ion exchange between the positive electrode composite layer and the negative electrode composite layer. Therefore, this results in the creation of portions of the positive electrode composite layer that do not contribute to battery performance, leading to waste in the positive electrode composite material.

[0007] Furthermore, the increased thickness at the boundary between the insulating protective layer and the positive electrode composite material layer, especially in the invention described in Patent Document 2, may cause wear on the pressure roller due to inorganic insulators with high hardness such as boehmite and alumina.

[0008] Therefore, in Patent Document 2, electrode material is coated onto an electrode substrate supplied at a specific speed, and a first insulating material is coated onto the adjacent portions of the electrode material on both sides in a direction orthogonal to the supply direction of the electrode substrate. Furthermore, a second insulating material is coated onto the surfaces of the coated electrode material and the first insulating material. The coated electrode material and the first and second insulating materials are then dried / solidified.

[0009] In the invention described in Patent Document 2, the paste forming the insulating protective layer and the paste forming the positive electrode composite layer are applied approximately simultaneously, and then dried / solidified and pressed. Therefore, the coating process and equipment are simple, and the processing time is short. Furthermore, overlap or height differences are less likely to occur at the boundary between the insulating protective layer and the positive electrode composite layer.

[0010] Existing technical documents

[0011] Patent documents

[0012] Patent Document 1: Japanese Patent Application Publication No. 2015-222657

[0013] Patent Document 2: International Publication No. 2015 / 156213 Summary of the Invention

[0014] The problem that the invention aims to solve

[0015] However, in the invention described in Patent Document 2, the paste of the coated insulating protective layer and the paste of the positive electrode composite layer become mixed at the boundary. Therefore, the portion containing this positive electrode composite layer does not contribute to battery performance, resulting in waste in the positive electrode composite material.

[0016] The manufacturing method of the secondary battery of the present invention and the problem to be solved by the secondary battery are that, even when a paste for forming a positive electrode composite material layer and a paste for forming an insulating protective layer are coated simultaneously, mixing at the boundary between the positive electrode composite material layer and the insulating protective layer can be suppressed.

[0017] Methods for solving problems

[0018] In a method for manufacturing a positive electrode plate of a secondary battery according to one aspect of the present invention, the secondary battery includes an electrode body formed by laminating a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate is configured to have a positive electrode composite material layer formed on a positive electrode current collector, and an insulating protective layer formed on the positive electrode current collector at a position adjacent to the positive electrode composite material layer and opposite to the end of the negative electrode composite material layer. The negative electrode plate is configured to have a negative electrode composite material layer formed on a negative electrode current collector. The manufacturing method is characterized by the following step: generating an insulating protective paste for forming the insulating protective layer, the insulating protective paste containing insulating particles. The process includes: adjusting the pH of the insulating particles, binder, and solvent to a pH that constitutes a zeta potential that prevents the agglomeration of the insulating particles; generating a positive electrode composite paste for forming the positive electrode composite layer, the positive electrode composite paste containing a positive electrode active material, conductive auxiliary material, binder, and solvent, and adding a pH adjuster to adjust the pH to a zeta potential that causes the agglomeration of the insulating particles; and a coating process in which the positive electrode composite paste and the insulating protective paste are simultaneously coated on the positive electrode current collector, the coating of the insulating protective paste being performed in a manner adjacent to the end of the positive electrode composite paste.

[0019] In the above-mentioned method for manufacturing the positive electrode plate of the secondary battery, the insulating particles can be composed of boehmite, and the pH of the insulating protective paste can be adjusted to 10-12.

[0020] In the above-mentioned method for manufacturing the positive electrode plate of the secondary battery, the average particle size of the boehmite in the insulating protective paste can be 1 to 3 μm, and no dispersant can be added to the insulating protective paste.

[0021] In the above-mentioned method for manufacturing the positive electrode plate of the secondary battery, the amount of Na contained in the insulating protective paste can be 50 to 500 ppm.

[0022] In the above-mentioned method for manufacturing the positive electrode plate of the secondary battery, the pH adjuster can be composed of acetic acid.

[0023] In the above-mentioned method for manufacturing the positive electrode plate of the secondary battery, the pH of the positive electrode composite paste can be adjusted to 7-9.

[0024] In the above-mentioned method for manufacturing the positive electrode plate of the secondary battery, the acid concentration of the positive electrode composite paste can be 300 to 800 ppm.

[0025] Furthermore, another aspect of the secondary battery of the present invention includes an electrode body formed by laminating a positive electrode plate, a negative electrode plate, and a separator. The positive electrode plate is configured to have a positive electrode composite material layer formed on a positive electrode current collector and an insulating protective layer containing insulating particles formed on the positive electrode current collector in a manner adjacent to the positive electrode composite material layer. The negative electrode plate is configured to have a negative electrode composite material layer formed on a negative electrode current collector. In this case, the insulating particles at the boundary of the insulating protective layer that contacts the positive electrode composite material layer are more aggregated than the insulating particles at other portions.

[0026] In the aforementioned secondary battery, the insulating particles may be composed of boehmite.

[0027] In the manufacturing method of the positive electrode plate of the above-mentioned secondary battery, the amount of Na contained in the above-mentioned insulating protective layer can be 150 to 1700 ppm.

[0028] The aforementioned secondary battery can be appropriately implemented in lithium-ion secondary batteries.

[0029] The effects of the invention

[0030] According to the manufacturing method of the positive electrode plate of the secondary battery of the present invention and the secondary battery, even when a paste for forming the positive electrode composite material layer and a paste for forming the insulating protective layer are coated simultaneously, the mixing at the boundary between the positive electrode composite material layer and the insulating protective layer can be suppressed. Attached Figure Description

[0031] Figure 1 This is a perspective view showing the outline of the structure of the lithium-ion secondary battery according to this embodiment.

[0032] Figure 2 This is a schematic diagram showing the configuration of the electrode body in this embodiment.

[0033] Figure 3 This is a partial cross-sectional view showing a portion of the structure of the electrode body in this embodiment.

[0034] Figure 4 This is a flowchart illustrating the manufacturing method of the positive electrode plate according to this embodiment.

[0035] Figure 5 This is a schematic diagram showing the boundary between the positive electrode composite material layer and the insulating protective layer in the coating process of this embodiment.

[0036] Figure 6 This is a schematic diagram showing the boundary between the positive electrode composite material layer and the insulating protective layer after the coating process of this embodiment.

[0037] Figure 7 This is a three-dimensional view showing the structure of the coating machine.

[0038] Figure 8 This is a schematic perspective view showing the first nozzle and the second nozzle.

[0039] Figure 9 This is a schematic diagram showing the boundary between the positive electrode composite material layer and the insulating protective layer in the coating process of the prior art.

[0040] Figure 10 This is a schematic diagram showing the boundary between the positive electrode composite material layer and the insulating protective layer after the coating process in the prior art. Detailed Implementation

[0041] (Summary of this implementation method)

[0042] The following is for reference Figures 1-8 The manufacturing method of the non-aqueous electrolyte secondary battery and the non-aqueous electrolyte secondary battery of the present invention will be described through embodiments of lithium-ion secondary batteries and their manufacturing methods.

[0043] <Principle of this implementation method>

[0044] <Existing topics>

[0045] Figure 9 This is a schematic diagram showing the boundary B between the positive electrode composite material layer 32 and the insulating protective layer 34 in the coating process of the prior art. Figure 10 This is a schematic diagram showing the boundary B between the positive electrode composite material layer 32 and the insulating protective layer 34 after the coating process in the prior art.

[0046] As described in the prior art, in the invention described in Patent Document 2, such as Figure 9 As shown, in the coating process, the positive electrode composite paste 32a and the insulating protective paste 34a are coated simultaneously, and the positive electrode composite layer 32 and the insulating protective layer 34 are formed simultaneously. However, in the invention described in Patent Document 2, as... Figure 10 As shown, a mixed portion M is generated at the boundary B between the coated insulating protective paste 34a and the positive electrode composite paste 32a. Therefore, the mixed portion M of the positive electrode composite layer 32 does not contribute to the battery performance, resulting in waste in the positive electrode composite material and causing a reduction in the original battery performance.

[0047] <Reasons for Existing Research Topics>

[0048] One reason for this is that both the freshly coated positive electrode composite paste 32a and the insulating protective paste 34a have high fluidity, making them prone to mixing at their boundary B. In particular, the average particle size of boehmite and other materials constituting the insulating protective paste 34a is 1–3 μm, which is smaller than the average particle size of the positive electrode active material particles 32b (3–6 μm). Therefore, the insulating particles 34b can easily penetrate between the positive electrode active material particles 32b, making mixing even easier. Furthermore, in the prior art, the dispersant is formulated in a way that prevents the insulating particles 34b from agglomerating, thus facilitating mixing even further.

[0049] <Principle of this implementation method>

[0050] Therefore, in this embodiment, during the simultaneous coating of the positive electrode composite paste 32a and the insulating protective paste 34a, when the positive electrode composite paste 32a and the insulating protective paste 34a are liquid-contacted at the boundary B, the insulating particles 34b composed of boehmite contained in the insulating protective paste 34a agglomerate, thereby increasing the apparent particle size. As a result, neither the positive electrode composite paste 32a nor the insulating protective paste 34a can easily penetrate the gaps between the insulating particles 34b or the gaps between the positive electrode active material particles 32b and the conductive auxiliary material 32c, thus suppressing mixing.

[0051] Therefore, acetic acid 32f, acting as a pH adjuster, was added to the positive electrode composite paste 32a so that when the positive electrode composite paste 32a and the insulating protective paste 34a were liquid-converted at the boundary B, boehmite aggregated and the apparent particle size increased. Due to the influence of acetic acid, the pH of the positive electrode composite paste 32a was low. Therefore, by allowing the positive electrode composite paste 32a and the insulating protective paste 34a to liquid-convert at the boundary B, the pH of the insulating protective paste 34a could be brought closer to its isoelectric point, thereby causing the boehmite to aggregate. This effectively suppressed the mixing of the positive electrode composite paste 32a and the insulating protective paste 34a.

[0052] <Conditions for the success of this implementation method>

[0053] Two conditions are necessary for this to be achieved.

[0054] First, the first condition is that, during simultaneous coating, until the positive electrode composite paste 32a and the insulating protective paste 34a come into contact at the boundary B, the insulating particles 34b composed of boehmite contained in the insulating protective paste 34a do not agglomerate but are uniformly dispersed.

[0055] Secondly, the second condition is that during simultaneous coating, when the positive electrode composite paste 32a and the insulating protective paste 34a are liquid-contacted at the boundary B, the insulating particles 34b composed of boehmite contained in the insulating protective paste 34a agglomerate.

[0056] <Condition 1: "Dispersion" of Boehmite>

[0057] As a prerequisite, it is known that the aggregation / dispersion of the insulating particles 34b is determined by the Zeta potential.

[0058] <Zeta Potential>

[0059] The potential of the region where the particles are sufficiently separated and electrically neutral is defined as zero. The "Zeta potential" at this time is defined as the potential of the slip plane measured based on this zero point. In the case of fine particles, if the absolute value of the Zeta potential increases, the repulsive force between the particles increases, the stability of the particles increases, and they are easily dispersed. Conversely, if the Zeta potential approaches zero, the particles are likely to aggregate. Therefore, in the present embodiment, the Zeta potential is also adjusted as an index of the dispersion stability of the dispersed particles.

[0060] <Regarding the Isoelectric Point of Boehmite>

[0061] The boehmite, which is the insulating particle 34b in the present embodiment, needs to aggregate at the boundary portion B, but does not aggregate in other portions. Regarding inorganic oxide particles, when the pH of the solution changes, the Zeta potential changes. In boehmite, it is known that it has an isoelectric point with a surface potential of zero at pH = 7.7 to 9.4. If the pH approaches the isoelectric point, the electrostatic repulsive force disappears, and thus the particles are likely to aggregate. Therefore, in order to stabilize the dispersion state, it is necessary to make the pH far from the isoelectric point. That is, in the insulating protective paste 34a before coating, it is necessary to make the pH far from the pH = 7.7 to 9.4 close to the isoelectric point.

[0062] Especially, since the insulating protective paste 34a in the present embodiment does not contain a dispersant, this is an important condition.

[0063] <Setting to Meet Condition 1>

[0064] Regarding the state of the insulating protective paste 34a, in order to make the insulating protective paste 34a before contacting the positive electrode composite paste 32a at the boundary portion B have excellent dispersion stability and make the boehmite contained in the insulating protective paste 34a aggregate when contacting the positive electrode composite paste 32a at the boundary portion B, in the present embodiment, the average particle diameter of the boehmite is 1 to 3 μm in a manner that is not too small, and no dispersant is used in the insulating protective paste 34a. And, from the aspect of dispersion stability, the pH in the state of the insulating protective paste 34a is adjusted to 10 to 12.

[0065] <pH Adjustment of the Insulating Protective Paste 34a>

[0066] Various manufacturing methods of boehmite are provided, but usually, it is manufactured by hydrothermally treating aluminum hydroxide derived from bauxite raw materials. This manufacturing method consists of processes such as a stirring and mixing process of a slurry formed by adding water to aluminum hydroxide and a reaction promoter (metal compound), a hydrothermal treatment process in which the slurry is heated in a steam atmosphere using a pressure vessel while performing wet curing, a dehydration process of the reaction product, a water washing process, a filtration process, a drying process, etc. (for example, refer to Japanese Patent Laid-Open No. 6-263437, Japanese Patent Laid-Open No. 2000-86235). If the existing manufacturing method of boehmite based on hydrothermal treatment is used, hydroxides, oxides, chlorides, sulfates, etc. of alkaline earth metals or alkali metals as reaction promoters are added to aluminum hydroxide. Therefore, the water washing process is indispensable, and even after undergoing this water washing process, impurities such as Na and Ca derived from the reaction promoter are likely to remain.

[0067] Therefore, in the present embodiment, in order to adjust the pH of the insulating protective paste 34a in the state to 10 to 12, the Na amount of the insulating protective paste 34a is adjusted to 50 to 500 ppm, and more preferably adjusted to 260 to 355 ppm. For example, if the boehmite in the insulating protective paste 34a is 25 [wt%], the Na amount contained in the boehmite is adjusted to 200 to 2000 ppm. As a result, in the completed secondary battery, the Na amount of the insulating protective layer 34 is 150 to 1700 ppm.

[0068] <Condition 2: "Aggregation" of boehmite>

[0069] Condition 2 is that during coating, in the insulating protective paste 34a, the dispersed insulating particles 34b aggregate at the boundary portion B. As described above, the pH close to the isoelectric point of boehmite is pH = 7.7 to 9.4. Therefore, it is necessary to make the pH of the positive electrode composite paste 32a in contact with the insulating protective paste 34a highly acidic.

[0070] <pH adjuster>

[0071] Here, as a pH adjuster for making the pH of the positive electrode composite paste 32a highly acidic, an acidic substance is preferred, and for example, "acetic anhydride, formic acid, propionic acid, succinic acid", etc. can be exemplified.

[0072] In the present embodiment, as a method for aggregating boehmite, by adding acetic acid 32f to the positive electrode composite paste 32a, aggregation occurs due to the reduction of the electrostatic repulsive force of boehmite when in contact with the insulating protective paste 34a. Here, "acetic acid 32f" includes forms such as acetic anhydride and glacial acetic acid. The reason for selecting "acetic acid" in the present embodiment is as follows.

[0073] According to Japanese Patent Application Publication No. 2019-075273, the following objective is described: Regarding secondary batteries with non-aqueous electrolytes, it is known that their characteristics deteriorate due to the decomposition of the non-aqueous electrolyte. Therefore, the specific surface area (m²) of the positive electrode active material is increased. 2 The product of the mass ratio (%) of the positive electrode active material in the positive electrode composite layer 32 and the mass percentage (%) of the positive electrode active material is within a certain range. Simultaneously, the content of acetic anhydride in the positive electrode composite layer 32 is kept within a certain range. As a result, the positive electrode composite paste 32a exhibits a viscosity reduction effect during positive electrode plate fabrication, resulting in good paste stability and coatability, and improving the productivity of non-aqueous electrolyte secondary batteries. Furthermore, by promoting the decomposition of film-forming components (especially Li3PO4) on the surface of the positive electrode active material, the resistance of the positive electrode is reduced, resulting in improved output of the non-aqueous electrolyte secondary battery at low temperatures. Adding a certain amount of acetic acid 32f to the positive electrode composite paste 32a not only allows for pH adjustment but also enables the high-productivity production of non-aqueous electrolyte secondary batteries with excellent output at low temperatures. On the other hand, the problems associated with adding acetic acid 32f are also eliminated.

[0074] <Adjustment of pH and acid concentration in positive electrode composite paste 32a>

[0075] As described above, the pH of the positive electrode composite paste 32a was adjusted to pH = 7-9 and the acid concentration was adjusted to 300-800 ppm using a pH adjuster (acetic acid 32f in this embodiment). As a result, when the positive electrode composite paste 32a and the insulating protective paste 34a were liquid-welded at the boundary B, boehmite aggregated, and the apparent particle size increased. By increasing the apparent particle size of the boehmite, the mixing of the positive electrode composite paste 32a and the insulating protective paste 34a can be suppressed.

[0076] <Composition of Lithium-ion Secondary Battery 1> Figure 1 This is a perspective view showing the outline of the structure of the lithium-ion secondary battery according to this embodiment. Next, the structure of the lithium-ion secondary battery according to this embodiment will be described.

[0077] like Figure 1 As shown, the lithium-ion secondary battery 1 is configured as a single-cell battery. The lithium-ion secondary battery 1 has a rectangular battery case 11 with an opening on the top. Electrode bodies 12 are housed inside the battery case 11. Electrolyte 13 is filled into the battery case 11 through the filling hole. The battery case 11 is made of a metal such as aluminum alloy, forming a sealed battery cell. Furthermore, the lithium-ion secondary battery 1 has a positive external terminal 14 and a negative external terminal 15 for charging and discharging. It should be noted that the shapes of the positive external terminal 14 and the negative external terminal 15 are not limited to... Figure 1 The shape shown.

[0078] <Electrode 12>

[0079] Figure 2 This is a schematic diagram showing the configuration of the wound electrode body 12. Regarding the electrode body 12, the negative electrode plate 2, the positive electrode plate 3, and the spacer 4 disposed between them are wound into a flat shape. In the negative electrode plate 2, a negative electrode composite material layer 22 is formed on the negative electrode current collector 21, which serves as a substrate. At one end, in the width direction W (winding axis direction) orthogonal to the winding direction (winding direction L), a negative electrode connection portion 23 is provided, where the negative electrode composite material layer 22 is not formed, and the negative electrode current collector 21 is exposed. That is, the winding direction of the electrode body 12 (negative electrode plate 2, positive electrode plate 3, and spacer 4) is referred to as the winding direction L of the electrode body 12. The direction orthogonal to the winding direction L of the electrode body 12 is referred to as the width direction W (winding axis direction) of the electrode body 12. The negative electrode plate 2 includes a negative electrode connection portion 23 at one end of the negative electrode plate 2 disposed in the width direction W (winding axis direction) of the electrode body 12. The negative electrode composite material layer 22 is not formed on the negative electrode current collector 21 of the negative electrode connection portion 23. As a result, the negative electrode current collector 21 is exposed at the negative electrode connection portion 23.

[0080] In the positive electrode plate 3, a positive electrode composite material layer 32 is formed on the positive electrode current collector 31, which serves as a substrate. A positive electrode connection portion 33 is provided at the other end (opposite to the negative electrode connection portion 23) in the width direction W (winding axis direction), which is orthogonal to the winding direction (winding direction L) of the positive electrode current collector 31. That is, the positive electrode plate 3 includes a positive electrode connection portion 33 at the end of the positive electrode plate 3 disposed in the width direction W (winding axis direction) of the electrode body 12, opposite to the negative electrode connection portion 23 of the negative electrode plate 2. The positive electrode composite material layer 32 is not formed on the positive electrode current collector 31 at the positive electrode connection portion 33, and the metal of the positive electrode current collector 31 is exposed.

[0081] In this embodiment, the positive electrode plate 3 is adjacent to the end of the positive electrode composite material layer 32 and has an insulating protective layer 34 at a position opposite to the negative electrode composite material layer 22. That is, the direction orthogonal to the winding direction L and the width direction W (winding axis direction) of the electrode body 12 is called the thickness direction of the electrode body 12. The positive electrode plate 3 includes an insulating protective layer 34 disposed on the positive electrode current collector 31. The insulating protective layer 34 is adjacent to the end of the positive electrode composite material layer 32 in the width direction W (winding axis direction) of the electrode body 12 and is opposite to the negative electrode composite material layer 22 in the thickness direction of the electrode body 12. In one example, the insulating protective layer 34 may be disposed adjacent to the two ends of the positive electrode composite material layer 32 in the width direction W of the electrode body 12 on two portions of the positive electrode current collector 31. In one example, the insulating protective layer 34 may be disposed on the positive electrode current collector 31 between the positive electrode connection portion 33 and the positive electrode composite material layer 32 in the width direction W of the electrode body 12. The insulating protective layer 34 is provided in such a way as to cover the exposed positive current collector 31.

[0082] <Laminated structure of electrode 12>

[0083] Figure 3 This is a schematic partial cross-sectional view showing the structure of the laminated electrode body 12 of the lithium-ion secondary battery 1. (See diagram below.) Figure 3 As shown, the basic structure (layered body) of the electrode body 12 of the lithium-ion secondary battery 1 includes a negative electrode plate 2, a positive electrode plate 3, and a separator 4.

[0084] The negative electrode plate 2 has negative electrode composite material layers 22 on both sides of the negative electrode current collector 21, which serves as the negative electrode substrate. One end of the negative electrode current collector 21 becomes a negative electrode connection portion 23 with exposed metal. That is, one end of the negative electrode current collector 21 in the width direction W of the electrode body 12 is used as a negative electrode connection portion 23 with exposed metal.

[0085] The positive electrode plate 3 has positive electrode composite material layers 32 on both sides of the positive electrode current collector 31, which serves as the positive electrode substrate. The other end of the positive electrode current collector 31 becomes a positive electrode connection portion 33 with exposed metal. That is, the end of the positive electrode current collector 31 on the opposite side of the negative electrode connection portion 23 of the negative electrode current collector 21 in the width direction W of the electrode body 12 is used as the positive electrode connection portion 33.

[0086] The negative electrode 2 and the positive electrode 3 are overlapped with a separator 4 to form a laminate. The laminate is wound along the length direction with a winding axis as the center and shaped into a flat shape to form a wound electrode body 12.

[0087] In this embodiment, an insulating protective layer 34 is provided on the positive current collector 31 adjacent to the positive electrode connection portion 33 side of the positive electrode composite material layer 32. That is, in this embodiment, the insulating protective layer 34 is provided on the positive current collector 31 adjacent to the positive electrode connection portion 33 in the width direction W of the electrode body 12. In the case of no insulating protective layer 34 as in the prior art, the positive current collector 31 is exposed on the positive electrode side starting from end a on the positive electrode connection portion 33 side of the positive electrode composite material layer 32. In this case, the positive current collector 31 and the negative electrode composite material layer 22 are facing each other across the separator 4 from end a to end b on the positive electrode side of the negative electrode composite material layer 22. At this time, metal powder may be mixed into this position, or dendrites of metallic Li may grow on the negative electrode composite material layer 22. When they penetrate the separator 4, a small short circuit occurs at the negative electrode composite material layer 22 and the positive current collector 31, which may generate heat or self-discharge. Therefore, in this embodiment, an insulating protective layer 34 is provided from end a to end c, which extends beyond end b. This insulating protective layer 34 can suppress such minor short circuits.

[0088] <Electrolyte 13>

[0089] The electrolyte 13 of the lithium-ion secondary battery is a non-aqueous electrolyte, which is a composition formed by dissolving a lithium salt in an organic solvent. Examples of lithium salts include LiClO4, LiPF6, LiAsF6, LiBF4, and LiSO3CF3. Examples of organic solvents include cyclic carbonates such as ethylene carbonate, propylene carbonate, butyl carbonate, and propylene trifluorocarbonate; chain carbonates such as diethyl carbonate, dimethyl carbonate, methyl ethyl carbonate, and dipropyl carbonate; ether compounds such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethoxyethane; sulfur-containing compounds such as ethyl methyl sulfone and butane sulpholol; and phosphorus compounds such as triethyl phosphate and trioctyl phosphate. One of these compounds or a mixture of two or more can be used as the electrolyte. The composition of the electrolyte 13 is not limited to these.

[0090] <Components of Electrode 12>

[0091] Next, the negative electrode plate 2, the positive electrode plate 3, and the separator 4, which are the constituent elements of the electrode body 12, will be described.

[0092] It should be noted that in this embodiment, "average diameter," unless otherwise specified, refers to the median diameter (D50: 50% volume average particle size) in the volumetric particle size distribution that corresponds to the cumulative 50%. For average particle sizes of approximately 1 μm or larger, laser diffraction / light scattering can be used to determine them. For average particle sizes of approximately 1 μm or smaller, dynamic light scattering (DLS) can be used to determine them. The average particle size based on the DLS method can be measured according to JIS Z 8828:2013.

[0093] <Negative Plate 2>

[0094] A negative electrode plate 2 is formed by forming negative electrode composite material layers 22 on both sides of the negative electrode current collector 21, which serves as the negative electrode substrate. In this embodiment, the negative electrode current collector 21 is made of Cu foil. The negative electrode current collector 21 forms a substrate that serves as the aggregate of the negative electrode composite material layer 22, and functions as a current collector that collects electricity from the negative electrode composite material layer 22. In this embodiment, the negative electrode active material is a material capable of intercalating / deintercalating lithium ions, and a powdered carbon material such as graphite is used.

[0095] The negative electrode plate 2 is manufactured, for example, by mixing the negative electrode active material, solvent and binder (adhesive), applying the mixed negative electrode composite paste to the negative electrode current collector 21 and drying it.

[0096] <Positive Plate 3>

[0097] The positive electrode plate 3 is composed of a positive current collector 31, a positive composite material layer 32 coated thereon, and an insulating protective layer 34.

[0098] <Positive current collector 31>

[0099] A positive electrode plate 3 is formed by forming positive electrode composite material layers 32 on both sides of a positive electrode current collector 31, which serves as the positive electrode substrate. In this embodiment, the positive electrode current collector 31 is made of Al foil. The positive electrode current collector 31 forms a substrate that serves as the aggregate of the positive electrode composite material layer 32, and functions as a current collector that collects electricity from the positive electrode composite material layer 32.

[0100] First, an A1 foil is shown as an example of the positive electrode substrate constituting the positive current collector 31, but it can be made of a conductive material (formed from a metal with good conductivity). For example, a material containing aluminum or an aluminum alloy can be used as the conductive material. The structure of the positive current collector 31 is not limited to this.

[0101] <Positive electrode composite layer 32>

[0102] Figure 5 The boundary B between the positive electrode composite material layer 32 and the insulating protective layer 34 in the coating process (S3) of this embodiment is shown. Figure 3 The diagram is an enlarged representation of part A. (Refer to...) Figure 5 The positive electrode composite material layer 32 will be described below. The positive electrode composite material layer 32 is formed by coating the positive electrode composite material paste 32a onto the positive electrode current collector 3l and then drying it. In addition to the positive electrode active material particles 32b, the positive electrode composite material layer 32 also contains conductive auxiliary materials 32c, binders 32d, and additives such as dispersants.

[0103] <Positive Electrode Composite Material Paste 32a>

[0104] Regarding the positive electrode composite paste 32a, it is prepared by adding solvent 32e and acetic acid 32f to positive electrode active material particles 32b, conductive auxiliary material 32c, binder 32d, and dispersant, etc., to form a paste. As the positive electrode composite layer 32, in... Figure 4 In the coating process (S3) shown, the positive electrode composite paste 32a is coated onto the positive electrode current collector 31. Subsequently, in the drying process (S4), the positive electrode composite paste 32a is dried and solidified. Figure 5 In the stage of the positive electrode composite paste 32a shown, acetic acid 32f and solvent 32e are mixed in the positive electrode composite paste 32a. However, in the positive electrode composite layer 32 after the drying process (S4), acetic acid 32f and solvent 32e evaporate and disappear.

[0105] <Composition of positive electrode active material particles 32b>

[0106] The primary particles of the positive electrode active material particle 32b contain a lithium transition metal oxide with a layered crystal structure. In addition to Li (lithium), the lithium transition metal oxide contains one or more specified transition metal elements. The transition metal element contained in the lithium transition metal oxide is preferably at least one of Ni, Co, and Mn. As a preferred example of a lithium transition metal oxide, a lithium transition metal oxide containing all elements of Ni, Co, and Mn can be cited.

[0107] In addition to transition metal elements (i.e., at least one of Ni, Co, and Mn), the positive electrode active material particles 32b may also contain one or more additional elements. These additional elements may include any one of the following elements from the periodic table: Group 1 (alkali metals such as sodium), Group 2 (alkaline earth metals such as magnesium and calcium), Group 4 (transition metals such as titanium and zirconium), Group 6 (transition metals such as chromium and tungsten), Group 8 (transition metals such as iron), Group 13 (metals such as boron or aluminum as half-metals), and Group 17 (halogens such as fluorine).

[0108] In a preferred embodiment, the positive electrode active material particles 32b may have the composition (average composition) represented by the following general formula (1).

[0109] Li1+xNiyCozMn(1-yz)MAαMBβO2…(1)

[0110] In equation (1) above, x can be a real number satisfying 0 ≤ x ≤ 0.2. Y can be a real number satisfying 0.1 < y < 0.6. z can be a real number satisfying 0.1 < z < 0.6. MA is at least one metallic element selected from W, Cr, and Mo. α For a given condition, α must be a real number satisfying 0 < α ≤ 0.01 (representatively 0.0005 ≤ α ≤ 0.01, e.g., 0.001 ≤ α ≤ 0.01). MB is one or more elements selected from the group consisting of Zr, Mg, Ca, Na, Fe, Zn, Si, Sn, Al, B, and F, and β can be a real number satisfying 0 ≤ β ≤ 0.01. β can be substantially 0 (i.e., oxides that substantially do not contain MB). It should be noted that, for convenience, the composition ratio of O (oxygen) in the chemical formula representing layered lithium transition metal oxides is expressed as 2. However, this value should not be strictly interpreted, and slight variations in composition can be tolerated (representatively included in the range of 1.95 to 2.05).

[0111] <Conductive auxiliary material 32c>

[0112] The conductive auxiliary material 32c is a material used to form conductive paths in the positive electrode composite layer 32. By mixing an appropriate amount of the conductive auxiliary material into the positive electrode composite layer 32, the conductivity inside the positive electrode can be improved, as well as the charge-discharge efficiency and output characteristics of the battery. Examples of conductive auxiliary materials that can be used include carbon black such as acetylene black (AB) or other carbon materials such as graphite or carbon nanotubes. The average particle size of the conductive auxiliary material is, for example, 0.1–0.15 μm.

[0113] <Adhesive 32d>

[0114] In the adhesive 32d, for example, polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid, polyacrylate, etc. can be used.

[0115] <Dispersant>

[0116] Examples of dispersants include polyvinyl alcohol (PVA), polyvinyl butyral (PVB), polyvinylpyrrolidone (PVP), polyacrylate, polymethyl methacrylate, polyoxyethylene alkyl ether, polyalkylene polyamine, benzimidazole, etc.

[0117] <Composition of Insulating Protective Layer 34>

[0118] like Figure 2 As shown, in the positive electrode plate 3, a positive electrode composite material layer 32 is formed on the positive electrode current collector 31, and an insulating protective layer 34 is formed adjacent to the positive electrode composite material layer 32 and opposite the end of the negative electrode composite material layer 22 on the positive electrode current collector 31. That is, the insulating protective layer 34 is adjacent to the end of the positive electrode composite material layer 32 in the width direction W of the electrode body 12 and opposite to the end of the negative electrode composite material layer 22 in the thickness direction of the electrode body 12. In the insulating protective layer 34, insulating particles 34b are fixed in a dispersed state using an adhesive 32d. The insulating protective layer 34 is formed by applying an insulating protective paste 34a along the end of the positive electrode composite material layer 32 to the surface of the positive electrode current collector 31 and drying it. This insulating protective layer 34 contains 150 to 1700 ppm of Na.

[0119] <Insulating Protective Paste 34a>

[0120] The insulating protective paste 34a is a liquid paste made by adding solvent 34d to binder 34c to disperse insulating particles 34b. In addition, although dispersants are usually added to ensure uniform dispersion of insulating particles 34b in the paste, no dispersant is added in this embodiment, which is a characteristic feature.

[0121] As an insulating protective layer 34, in Figure 4In the coating process (S3) shown, the insulating protective paste 34a is coated onto the positive electrode current collector 31, and in the drying process (S4), the insulating protective paste 34a is dried and solidified. Figure 5 In the stage of insulating protective paste 34a shown, solvent 32e is mixed into insulating protective paste 34a. However, in the insulating protective layer 34 after the drying process (S4), solvent 32e evaporates and disappears.

[0122] <Insulating Particles 34b>

[0123] Insulating particles 34b are disposed between the negative electrode composite material layer 22 and the positive electrode current collector 31 to achieve electrical insulation. For example, particles made of insulators such as boehmite and alumina are used. In this embodiment, boehmite is used.

[0124] <Boehmite>

[0125] Boehmite is an aluminum hydroxide (γ-AlO(OH)) mineral, a component of bauxite ore. It exhibits a vitreous to pearly luster, with a Mohs hardness of 3–3.5 and a specific gravity of 3.00–3.07. Due to its high insulation, heat resistance, and hardness, boehmite is used industrially as a low-cost flame-retardant additive for refractory polymers.

[0126] Boehmite is represented by the chemical composition AlO(OH) or Al2O3·H2O, and is usually a chemically stable monohydrate of alumina produced by heating or hydrothermally treating alumina trihydrate in air. Boehmite has a high dehydration temperature, ranging from 450 to 530°C. By adjusting the manufacturing conditions, it can be controlled to produce various shapes such as tabular boehmite, acicular boehmite, and hexagonal tabular boehmite. Furthermore, the aspect ratio and particle size can be controlled by adjusting the manufacturing conditions.

[0127] Various methods for manufacturing boehmite have been provided in the past, but it is usually produced by hydrothermal treatment of aluminum hydroxide, a raw material derived from bauxite. This manufacturing method includes a stirring and mixing step of a slurry obtained by adding water to aluminum hydroxide and a reaction promoter (metal compound). It also includes a hydrothermal treatment step of wet curing under a steam atmosphere in a pressure vessel. The process is further comprised of steps such as dehydration of the reaction products, washing, filtration, and drying. For example, see Japanese Patent Application Publication Nos. 6-263437 and 2000-86235.

[0128] According to existing methods for manufacturing boehmite based on hydrothermal treatment, alkaline earth metals or alkali metal hydroxides, oxides, chlorides, sulfates, etc., are added to aluminum hydroxide as reaction promoters. Therefore, a water washing process is indispensable, but even after this process, impurities such as Na and Ca from the reaction promoters can easily remain.

[0129] In boehmite, pH can be managed by controlling the Na component derived from the raw material.

[0130] <Particle size of insulating particle 34b>

[0131] As mentioned above, if the average particle size [μm(D50)] is too large, the dispersibility deteriorates. On the other hand, if the average particle size [μm(D50)] is too small, aggregation will occur. In particular, in this embodiment, since no dispersant is used, the average particle size [μm(D50)] is set to 1 to 3 μm in order to prevent aggregation.

[0132] <pH Adjustment of Insulating Protective Paste 34a>

[0133] In this embodiment, in order to adjust the pH of the insulating protective paste 34a to 10-12, the Na content of the insulating protective paste 34a is adjusted to 50-500 ppm, more preferably 260-355 ppm. For example, if the boehmite in the insulating protective paste 34a is 25 [wt%], the Na content in the boehmite is adjusted to 200-2000 ppm, more preferably 1040-1420 ppm. As a result, in the completed secondary battery, the Na content of the insulating protective layer 34 is 150-1700 ppm, more preferably 800-1200 ppm.

[0134] <Adhesive 34c>

[0135] Adhesive 34c may use materials such as polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), polyacrylic acid, polyacrylate, etc.

[0136] <Separator 4>

[0137] The separator 4 can be a porous resin sheet made of resins such as polyethylene (PE) and polypropylene (PP) used to hold the electrolyte 13 between the positive electrode plate 3 and the negative electrode plate 2. Such a porous resin sheet can be a single-layer structure using various materials individually, or a multi-layer structure composed of various materials combined.

[0138] <Manufacturing Method of Positive Plate 3>

[0139] Figure 4 This is a flowchart illustrating the manufacturing method of the positive electrode plate 3 according to this embodiment. (Refer to...) Figure 4 The manufacturing method of the positive electrode plate 3 in this embodiment will be described.

[0140] <Cathode Composite Material Paste Manufacturing Process (S1)>

[0141] First, the positive electrode composite paste 32a is manufactured. Details have been explained above.

[0142] <Insulating protective paste manufacturing process (S2)>

[0143] In addition, insulating protective paste 34a is manufactured. Details of this process have been described above.

[0144] <Coating process (S3)>

[0145] Next, the coating process (S3) will be described. The coating process (S3) is a process in which the positive electrode composite material paste 32a manufactured by the positive electrode composite material paste manufacturing process (S1) and the insulating protective paste 34a manufactured by the insulating protective paste manufacturing process (S2) are simultaneously applied to a specified position on the positive electrode current collector 31.

[0146] <Composition of Coating Machine 5>

[0147] Figure 7 This is a perspective view showing the structure of the coating machine 5. Figure 8 This is a schematic perspective view showing the first nozzle 53 and the second nozzle 55, including a cross-section viewed from the CC section of the coating machine 5. (Refer to...) Figure 7 and Figure 8 The coating machine 5 will be described.

[0148] like Figure 7 As shown, the coating machine 5 includes a platform 57 serving as a base. The platform 57 includes a positioning guide 58 for conveying a strip-shaped positive current collector 31 made of Al foil before cutting. The positive current collector 31 is drawn from a supply reel (not shown) and conveyed on the platform 57 by a conveying means. A gate-shaped mold nozzle 51, spanning the positive current collector 31, is provided at the upstream end of the platform 57 in the conveying direction of the positive current collector 31, in a direction orthogonal to the conveying direction. The mold nozzle 51 includes a first mold 52 for storing the positive composite material paste 32a. The first mold 52 is a space located at a position corresponding to the location where the positive composite material layer 32 is formed. The positive composite material paste 32a is supplied by a supply means (not shown) and stored in the first mold 52. Additionally, a second mold 54 is a space located at a position corresponding to the location where the insulating protective layer 34 is formed. The insulating protective paste 34a is supplied by a supply means (not shown) and stored in the second mold 54. The first mold 52 and the second mold 54 are arranged in a straight line adjacent to each other.

[0149] The first nozzle 53 is a nozzle that connects from the lower part of the first mold 52 to the position on the stage 57 where the positive current collector 31 forms the positive composite material layer 32. When the internal pressure of the first mold 52 is increased by a pressurization means not shown, a predetermined amount of positive composite material paste 32a is ejected from the first nozzle 53 to the position on the positive current collector 31 where the positive composite material layer 32 is formed.

[0150] The second nozzle 55 is a nozzle that connects from the lower part of the second mold 54 to the position on the stage 57 where the insulating protective layer 34 is formed on the positive current collector 31. When the internal pressure of the second mold 54 is increased by a pressurizing means not shown, a predetermined amount of insulating protective paste 34a is dispensed from the second nozzle 55 to the position on the positive current collector 31 where the insulating protective layer 34 is formed.

[0151] like Figure 8 As shown, the first nozzle 53 and the second nozzle 55 are isolated from each other. Furthermore, the positive electrode composite material paste 32a dispensed from the first nozzle 53 and the insulating protective paste 34a dispensed from the second nozzle 55 are immediately brought into contact with liquid in a mutually sealed manner after being dispensed. While in the liquid-contact state, the positive electrode composite material paste 32a is applied to the location where the positive electrode current collector 31 forms the positive electrode composite material layer 32. Additionally, while in the liquid-contact state, the insulating protective paste 34a is applied to the location where the positive electrode current collector 31 forms the insulating protective layer 34. Subsequently, the surfaces of the coated positive electrode composite material layer 32 and the insulating protective layer 34 are shaped using the roller 56. It should be noted that when the insulating protective layer 34 is thinner than the positive electrode composite material layer 32, only the positive electrode composite material layer 32 is shaped.

[0152] Figure 5 In the coating process (S3) of this embodiment shown, the boundary B between the positive electrode composite material layer 32 and the insulating protective layer 34 is subjected to liquid contact in this state. During liquid contact, as... Figure 6 As shown, the positive electrode composite paste 32a and the insulating protective paste 34a are mixed to form a mixed portion M. At this time, the acetic acid 32f in the positive electrode composite paste 32a causes the pH value around the insulating particles 34b of the insulating protective paste 34a to decrease from pH 10-12. Consequently, the pH around the insulating particles 34b is close to the isoelectric point of boehmite, pH = 7.7-9.4. At pH = 7.7-9.4, boehmite begins to agglomerate, and the apparent particle size of the boehmite increases. Thus, the mixed portion M does not expand further.

[0153] <Drying Process (S4)>

[0154] As described above, when the mixing of the positive electrode composite material paste 32a and the insulating protective paste 34a is suppressed immediately after the coating process (S3), a drying process (S4) is performed in this state. Through the drying process (S4), the solvent 32e and acetic acid 32f of the positive electrode composite material layer 32 evaporate, and the paste-like positive electrode composite material layer 32 becomes solid and no longer mixes with the insulating protective layer 34. Furthermore, the solvent 34d of the insulating protective layer 34 also evaporates, and the paste-like insulating protective layer 34 becomes solid, which also no longer mixes with the positive electrode composite material layer 32. The system is stable in this state.

[0155] <Shaping and Pressing Process (S5)>

[0156] When the drying process is completed, the positive electrode composite material layer 32 and the insulating protective layer 34 have reached a certain hardness. In the shaping and pressing process (S6), they are shaped into a plane of uniform thickness using a press (not shown). It should be noted that in this embodiment, since the solid content NV of the insulating protective paste 34a is less than the solid content NV of the positive electrode composite material paste 32a, the volume shrinkage rate due to the volatilization of volatile components during the drying process (S4) is greater. That is, after the drying process (S4), the thickness of the insulating protective layer 34 is thinner than the thickness of the positive electrode composite material layer 32. As a result, in the shaping and pressing process (S5), only the positive electrode composite material layer 32 is shaped using the press.

[0157] <Cutting process (S6)>

[0158] In the shaping and pressing process (S5), after shaping a flat surface with uniform thickness, the electrode body 12 is cut into lengths corresponding to the electrode body 12 by the cutting process (S6).

[0159] This completes the positive electrode plate 3.

[0160] <Manufacturing Methods for Vehicle Battery Packs>

[0161] After the positive electrode plate 3 is manufactured using this method, the negative electrode plate 2 and the positive electrode plate 3 are laminated in multiple sections with the separator 4 in between. The laminated body is then wound to manufacture the electrode body 12. Next, the positive electrode external terminal 14 and the negative electrode external terminal 15 are installed on the electrode body 12 through the cover of the battery casing 11. The electrode body 12 is then housed in the battery casing 11, and the cover is hermetically joined using laser welding or similar methods. After a drying process, electrolyte 13 is filled into the battery casing 11 during the electrolyte filling process, and the battery casing 11 is sealed. After initial charging and other adjustments, OCV checks, internal resistance checks, and aging, the unit cell is completed. Multiple unit cells are stacked to form a battery pack. These battery packs are further housed in a battery array, and charging and discharging are monitored. Control devices are installed to control these processes, completing the battery as a lithium-ion secondary battery for automotive use.

[0162] (The function of this implementation method)

[0163] In the lithium-ion secondary battery of this embodiment, simultaneous coating is performed during the coating process (S3). At this time, when the positive electrode composite paste 32a and the insulating protective paste 34a come into contact with the liquid at the boundary portion B, the insulating particles 34b composed of boehmite contained in the insulating protective paste 34a agglomerate, thereby increasing the apparent particle size. As a result, neither material can easily penetrate the gaps between the insulating particles 34b, nor between the positive electrode active material particles 32b and the conductive auxiliary material 32c, suppressing the occurrence of mixed portions M.

[0164] Therefore, acetic acid 32, acting as a pH adjuster, was added to the positive electrode composite paste 32a so that when the positive electrode composite paste 32a and the insulating protective paste 34a were liquid-converted at the boundary B, boehmite aggregated and the apparent particle size increased. By adjusting the pH of the insulating protective paste 34a at the boundary B to near its isoelectric point due to the influence of acetic acid 32f in the positive electrode composite paste 32a, boehmite aggregation was achieved, and impurities were suppressed.

[0165] (Effects of this implementation method)

[0166] (1) In this embodiment, even when the positive electrode composite material paste 32a and the insulating protective paste 34a are coated at the same time, it is possible to manufacture a positive electrode plate 3 in which the mixing of the boundary portion B of the positive electrode composite material layer 32 and the insulating protective layer 34 is suppressed.

[0167] (2) An insulating protective paste 34a is generated to form an insulating protective layer 34 (the pH is adjusted to a zeta potential that prevents the insulating particles 34b from agglomerating). Therefore, in the coating process (S3), coating can be performed with the insulating particles 34b uniformly dispersed.

[0168] (3) Since the insulating particles 34b are composed of boehmite and the pH of the insulating protective paste is adjusted to 10-12, the equipotentiality of boehmite aggregation can be effectively avoided.

[0169] (4) The average particle size of the boehmite in the insulating protective paste 34a is 1 to 3 μm, and no dispersant is added to the insulating protective paste 34a. Therefore, by making it a particle size that is not prone to agglomeration, agglomeration can be reliably suppressed up to the coating process (S3). On the other hand, after the coating process (S3), agglomeration will not be hindered by the dispersant.

[0170] (5) The amount of Na contained in the insulating protective paste 34a is 50 to 500 ppm. Therefore, the pH can be adjusted appropriately and agglomeration before the coating process (S3) can be appropriately suppressed.

[0171] (6) The pH adjuster of the positive electrode composite paste 32a is composed of acetic acid 32f. Therefore, when it is wetted with the insulating protective paste 34a, the insulating particles 34b can be reliably aggregated. In addition, acetic acid 32f also has the effect of enabling the production of non-aqueous electrolyte secondary batteries with excellent output at low temperatures with high productivity in the positive electrode composite paste 32a.

[0172] (7) The pH of the positive electrode composite paste 32a is adjusted to 7-9. Therefore, when it is wetted with the insulating protective paste 34a, the insulating particles 34b can be reliably aggregated.

[0173] (8) The acid concentration of the positive electrode composite paste 32a is 300 to 800 ppm. Therefore, when it is wetted with the insulating protective paste 34a, the insulating particles 34b can be reliably aggregated.

[0174] (9) It can be appropriately applied in the case of lithium-ion secondary battery 1.

[0175] (Modified Example)

[0176] The accompanying drawings are for illustrative purposes only and do not accurately show the actual size, thickness, number of particles, etc.

[0177] · Figure 4 The flowchart shown is an example of the manufacturing method of the positive electrode plate 3. Of course, the order of the process can be changed or the process can be eliminated, added or replaced.

[0178] The examples of positive electrode active material particles 32b, conductive auxiliary material 32c, binder 32d, acetic acid 32f (pH adjuster), insulating particles 34b, and binder 34c are provided, but are not limited to the specific implementation method.

[0179] • A lithium-ion secondary battery 1 is illustrated in the example of a secondary battery, but the present invention can be implemented for any other secondary battery as long as the same electrode body can be used.

[0180] The lithium-ion secondary battery described in this embodiment is one embodiment of the present invention. As long as it does not depart from the claims, those skilled in the art can certainly add, remove, or modify its structure to implement it, and it is not limited to this embodiment.

Claims

1. A method for manufacturing a positive electrode plate of a secondary battery, the secondary battery comprising an electrode body formed by laminating a positive electrode plate, a negative electrode plate, and a separator, wherein the positive electrode plate is configured to have a positive electrode composite material layer formed on a positive electrode current collector, and an insulating protective layer formed on the positive electrode current collector adjacent to the positive electrode composite material layer and opposite to the end of the negative electrode composite material layer, and the negative electrode plate is configured to have a negative electrode composite material layer formed on a negative electrode current collector, characterized in that... The manufacturing method includes the following steps: The process of generating an insulating protective paste for forming the insulating protective layer, the insulating protective paste containing insulating particles, a binder and a solvent, and adjusted to a pH that constitutes a zeta potential that prevents the insulating particles from agglomerating; The step of generating a positive electrode composite paste for forming the positive electrode composite layer, the positive electrode composite paste containing a positive electrode active material, a conductive auxiliary material, a binder, and a solvent, and adding a pH adjuster to adjust the pH to the zeta potential at which the insulating particles aggregate; and In the coating process, the positive electrode composite material paste and the insulating protective paste are simultaneously coated on the positive electrode current collector. The coating of the insulating protective paste is carried out in a manner that is adjacent to the end of the positive electrode composite material paste.

2. The method for manufacturing the positive electrode plate of the secondary battery according to claim 1, characterized in that, The insulating particles are composed of boehmite, and the pH of the insulating protective paste is adjusted to 10-12.

3. The method for manufacturing the positive electrode plate of the secondary battery according to claim 2, characterized in that, The average particle size of the boehmite in the insulating protective paste is 1 μm to 3 μm. No dispersant was added to the insulating protective paste.

4. The method for manufacturing the positive electrode plate of the secondary battery according to claim 2 or 3, characterized in that, The amount of Na contained in the insulating protective paste is 50ppm to 500ppm.

5. A method for manufacturing the positive electrode plate of a secondary battery according to any one of claims 1 to 3, characterized in that, The pH adjuster is composed of acetic acid.

6. A method for manufacturing the positive electrode plate of a secondary battery according to any one of claims 1 to 3, characterized in that, The pH of the positive electrode composite paste was adjusted to 7-9.

7. A method for manufacturing the positive electrode plate of a secondary battery according to any one of claims 1 to 3, characterized in that, The acid concentration of the positive electrode composite paste is 300ppm to 800ppm.

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