Energy storage device and method for manufacturing an energy storage device

Abstract

Providing energy storage devices with improved reliability. [Solution] A battery 100, which is one embodiment of the energy storage device disclosed herein, comprises a positive electrode 50 including a positive electrode current collector 52 and a positive electrode active material layer 54 disposed on the positive electrode current collector 52. The positive electrode 50 has a first layer 54A and a second layer 54B disposed on the first layer 54A. The positive electrode active material contained in the first layer 54A is mainly composed of single particles 57. The positive electrode active material contained in the second layer 54B is mainly composed of aggregated particles 58. The first layer 54A has a plurality of recesses 54A1. The second layer 54B has a plurality of protrusions 54B1. In the first layer 54A and the second layer 54B, the relationships Aave≧d2×1.3, Bave≧d1×3, d2×0.5≦Cave≦d2×2.5, and Dave≧d2 are satisfied. The mass ratio of aggregated particles 58 to single particles 57 is within the range of 30:70 to 50:50.

Description

[Technical Field]

[0001] This disclosure relates to an energy storage device and a method for manufacturing an energy storage device. [Background technology]

[0002] Japanese Patent Publication No. 2022-063677 discloses a non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode comprises a positive electrode substrate and a positive electrode active material layer, the positive electrode active material layer being disposed on the surface of the positive electrode substrate. The positive electrode active material layer comprises a first layer and a second layer, the second layer being disposed between the first layer and the positive electrode substrate. The first layer is described as comprising single particles, and the second layer as comprising secondary particles formed by the aggregation of primary particles. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-063677 [Overview of the project] [Problems that the invention aims to solve]

[0004] Incidentally, the inventors' research has shown that in the above-mentioned non-aqueous electrolyte secondary battery, the interfacial resistance between the positive electrode substrate and the positive electrode active material layer is reduced, which can increase the amount of heat generated during an internal short circuit. Therefore, there is a need to develop a technology that can reduce the amount of heat generated at the interface between the positive electrode substrate and the positive electrode active material layer, thereby providing an energy storage device with improved reliability. [Means for solving the problem]

[0005] The energy storage device disclosed herein is an energy storage device comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The positive electrode active material layer is divided in the thickness direction by an uneven boundary in an SEM cross-sectional view, and comprises a first layer disposed on the positive electrode current collector side and a second layer disposed on the first layer. The positive electrode active material contained in the first layer is mainly composed of single particles. The positive electrode active material contained in the second layer is mainly composed of aggregated particles. The first layer has a plurality of recesses that are recessed toward the positive electrode current collector side in the SEM cross-sectional view. The second layer has a plurality of protrusions that are filled with the aggregated particles in each of the recesses of the first layer and protrude toward the positive electrode current collector side. Here, Aave, Bave, Cave, Dave, d1, and d2 are defined as follows. Aave is the average value of the opening length A along the boundary excluding the recess in the SEM cross-sectional view. Bave is the average value of the distance B between adjacent recesses in the SEM cross-sectional view. Cave is the average value of the depth C of the recess in the SEM cross-sectional view. Dave is the average value of the thickness D from the boundary excluding the protrusion in the second layer in the SEM cross-sectional view. d1 is the average particle diameter of the single particles. d2 is the average particle diameter of the aggregated particles. In this case, Aave, Bave, Cave, and Dave satisfy the following relationships: Aave ≥ d2 × 1.3, Bave ≥ d1 × 3, d2 × 0.5 ≤ Cave ≤ d2 × 2.5, and Dave ≥ d2. The mass ratio of the aggregated particles to the single particles is in the range of 30:70 to 50:50. An energy storage device with such a configuration is an energy storage device with improved reliability.

[0006] The method for manufacturing an energy storage device disclosed herein is a method for manufacturing an energy storage device comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The method for manufacturing the energy storage device includes a preparation step, a first coating film formation step, an uneven shape formation step, a second coating film formation step, and a pressing step. In the preparation step, the positive electrode current collector is prepared. In the first coating film formation step, a first paste is applied onto the positive electrode current collector to form a first coating film consisting of the first paste. Here, the first paste mainly contains single particles as the positive electrode active material. In the uneven shape formation step, an uneven shape is formed on the surface of the first coating film. In the second coating film formation step, a second paste is applied to the surface of the first coating film on which the uneven shape has been formed to form a second coating film consisting of the second paste. Here, the second paste mainly contains aggregated particles as the positive electrode active material. The pressing process described above involves pressing the first coating film and the second coating film to form the positive electrode active material layer, which includes a first layer made of the first paste and a second layer made of the second paste. In the first coating film formation process and the second coating film formation process, the basis weight of the first coating film and the second coating film are adjusted so that the mass ratio of the aggregated particles in the second coating film to the single particles in the first coating film is within the range of 30:70 to 50:50. The pressing process described above is configured such that the first layer and the second layer are separated in the thickness direction by a boundary having irregularities, the first layer has a plurality of recesses that are recessed toward the positive electrode current collector, and the second layer has a plurality of protrusions that are filled in each of the recesses of the first layer and protrude toward the positive electrode current collector. According to the manufacturing method of the energy storage device with this configuration, it becomes easier to manufacture the energy storage device described above. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a schematic longitudinal cross-sectional view showing the internal structure of a battery according to one embodiment. [Figure 2] Figure 2 is a schematic perspective view showing the configuration of an electrode body according to one embodiment. [Figure 3]FIG. 3 is a schematic cross-sectional view along the thickness direction of the positive electrode according to one embodiment. [Figure 4] FIG. 4 is an explanatory diagram for explaining how to draw a boundary according to one embodiment. [Figure 5] FIG. 5 is a flowchart showing a method for manufacturing a battery according to one embodiment.

Embodiments for Carrying Out the Invention

[0008] Hereinafter, some embodiments of the technology disclosed herein will be described with reference to the drawings. In the drawings, members and parts having the same function are appropriately assigned the same reference numerals. Also, the dimensional relationships (length, width, thickness, etc.) in each figure do not reflect the actual dimensional relationships. Note that matters other than those specifically mentioned in this specification, which are necessary for implementing the technology disclosed herein (for example, the general configuration and manufacturing process of a power storage device that does not characterize the present disclosure), can be grasped as design matters of those skilled in the art based on the prior art in the relevant field. The technology disclosed herein can be implemented based on the content disclosed in this specification and the common technical knowledge in the relevant field. Also, the following description is not intended to limit the present disclosure to the following forms.

[0009] In this specification and the claims, the notation "A to B" indicating a range means "A or more and B or less", and also includes the meanings of "exceeding A" and "less than B". In this specification, a "power storage device" refers to a device that can perform charging and discharging. Power storage devices include batteries such as primary batteries and secondary batteries (for example, non-aqueous electrolyte secondary batteries such as lithium ion secondary batteries and nickel metal hydride batteries), and capacitors (physical batteries) such as electric double layer capacitors. Also, the electrolyte may be any of a liquid electrolyte (electrolyte solution), a gel electrolyte, and a solid electrolyte. Hereinafter, a lithium ion secondary battery (hereinafter also simply referred to as a "battery"), which is one embodiment of the power storage device disclosed herein, will be described as an example. Note that the following description is not intended to limit the power storage device to a lithium ion secondary battery.

[0010] In the drawings, reference signs X, Y, and Z represent the short side direction, the long side direction orthogonal to the short side direction, and the vertical direction of the battery 100, respectively. However, these directions are defined for convenience of explanation and do not limit the arrangement mode of the battery 100. In this specification, the "rectangular parallelepiped" can be a concept that includes a substantially rectangular parallelepiped having rounded corners together with the rectangular parallelepiped. Also, in this specification, the "rectangular shape" can be a concept that includes a substantially rectangular shape having rounded corners together with the rectangular shape. And, in this specification, the "paste" refers to a mixture in which part or all of the solid content is dispersed in a dispersion medium, and can be a concept that includes so-called "slurry", "ink", etc.

[0011] In this specification and the claims, the term "particle" means a population of a large number of particles (i.e., particles), unless it particularly refers to a single particle unit. In Japanese, since it is ambiguous whether it is singular or plural, it is defined as above to clarify the meaning of "particle".

[0012] <Configuration of Battery 100> Here, FIG. 1 is a longitudinal sectional view schematically showing the internal structure of the battery 100 according to an embodiment. FIG. 2 is a perspective view schematically showing the configuration of the electrode body 20 according to an embodiment. FIG. 3 is a schematic sectional view along the thickness direction of the positive electrode 50 according to an embodiment.

[0013] As shown in FIG. 1, in this embodiment, the battery 100 includes a case 10, an electrode body 20, and an electrolyte 80. Hereinafter, each component will be described.

[0014] <Case 10> The case 10 is the outer casing of the battery 100. The case 10 houses the electrode body 20 and the electrolyte 80. In this embodiment, the case 10 has a flattened rectangular parallelepiped shape. The case 10 also has a case body 12 having an opening 12h and a sealing plate 14 that closes the opening 12h. The sealing plate 14 is here a rectangular plate-shaped member (plate). In this embodiment, the sealing plate 14 has a safety valve 16 and an electrolyte injection hole (not shown). The safety valve 16 is a thin-walled portion that is set to release the internal pressure of the case 10 when the internal pressure rises above a predetermined level. The electrolyte injection hole is, for example, a place for injecting the electrolyte 80 into the case 10. Here, it is preferable that the case 10 is made of metal. Examples of such metal materials include aluminum, aluminum alloy, and stainless steel (SUS).

[0015] <Electrode body 20> In the configurations shown in Figures 1 and 2, the electrode body 20 is a wound electrode body in which a long rectangular sheet-like positive electrode 50 and a long rectangular sheet-like negative electrode 60 are superimposed with a long rectangular sheet-like separator 70 in between, and wound in the longitudinal direction of the sheet (hereinafter also simply referred to as the "longer direction"). The electrode body 20 here has a flattened rectangular parallelepiped shape. Although not particularly limited, "sheet-like" can mean, for example, a thickness in the range of 5 μm to 500 μm.

[0016] (positive electrode 50) In the configurations shown in Figures 1 and 2, the positive electrode 50 comprises a positive electrode current collector 52 and a positive electrode active material layer 54 disposed on the positive electrode current collector 52. In the configuration shown in Figure 2, the positive electrode current collector 52 is in the form of a long rectangular sheet. The positive electrode active material layer 54 is also in the form of a long rectangular sheet. The positive electrode current collector 52 is made of a conductive metal such as aluminum, aluminum alloy, nickel, or stainless steel. In this case, the positive electrode current collector 52 is a metal foil, specifically aluminum foil. The thickness of the positive electrode current collector 52 is, for example, 5 μm to 35 μm, and may be 7 μm to 20 μm. The thickness of the positive electrode active material layer 54 is, for example, 10 μm to 200 μm, and may be 20 μm to 150 μm, and may be 50 μm to 100 μm. In this embodiment, the positive electrode current collector 52 has a region where a positive electrode active material layer 54 is provided, and a portion 56 where the surface of the positive electrode current collector 52 is exposed and the positive electrode active material layer is not provided. The positive electrode active material layer 54 is provided, for example, in a strip shape on one or both sides (here, one side) of the positive electrode current collector 52, along the longitudinal direction of the positive electrode 50. In the embodiment shown in Figure 2, the positive electrode active material layer 54 is not provided at the end in the longitudinal direction Y (the left end in the figure). The portion 56 where the positive electrode active material layer is not provided is, here, a strip-shaped region at the end in the longitudinal direction Y (the left end in the figure).

[0017] The positive electrode active material layer 54 contains a positive electrode active material capable of reversibly intercepting and releasing charge carriers. When the total solid content of the positive electrode active material layer 54 is considered to be 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The positive electrode active material layer 54 may also contain optional components other than the positive electrode active material, such as conductive materials, binders, and various additives. As conductive materials, for example, carbon black such as acetylene black (AB), graphite, graphite, and other carbon materials can be used. As binders, for example, polyvinylidene fluoride (PVdF) can be used.

[0018] As shown in Figure 3, in this embodiment, the positive electrode active material layer 54 has a first layer 54A located on the positive electrode current collector 52 side and a second layer 54B located on the first layer 54A. The first layer 54A and the second layer 54B are two layers separated in the thickness direction of the electrode plate (short side direction X in the definition of paragraph 0010) by an uneven boundary P in an SEM cross-sectional view. In such an SEM cross-sectional view, the cross-section of the rectangular sheet-like positive electrode 50 (positive electrode active material layer 54) cut along its short side direction (hereinafter also simply referred to as the "SEM cross-section of the positive electrode active material layer") is observed by an SEM (Scanning Electron Microscope). Any commercially available device can be used as the SEM without any particular restrictions. The positive electrode current collector 52, the first layer 54A, and the second layer 54B are stacked in this order in the thickness direction. Each layer will be described below.

[0019] As shown in Figure 3, in this embodiment, the first layer 54A has a plurality of recesses 54A1 that are recessed toward the positive electrode current collector 52 side in an SEM cross-sectional view. In this embodiment, in an SEM cross-section, the first layer 54A has recesses 54A1 and protrusions 54A2 that are alternately arranged along the long side direction Y. Here, the number of recesses 54A1 in the SEM cross-section of the positive electrode active material layer 54 (hereinafter also simply referred to as "number of recesses 54A1") is not particularly limited as long as the effects of the technology disclosed herein are achieved. The number of recesses 54A1 is, for example, 100 or more, preferably 1000 or more, and more preferably 2000 or more, from the viewpoint of more favorably reducing the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54. The upper limit of the number of recesses 54A1 is, for example, 5000 or less, preferably 4000 or less, and more preferably 3000 or less, from the viewpoint of suitably ensuring the mechanical strength of the first layer 54A.

[0020] As shown in Figure 3, in this embodiment, the positive electrode active material contained in the first layer 54A is mainly composed of single particles 57. In this embodiment, aggregated particles 58, described later, are filled in the recesses 54A1 of the first layer 54A. Also, single particles 57 are filled in the protrusions 54A2 of the first layer 54A. Here, when we say that the positive electrode active material contained in the first layer 54A is mainly composed of single particles 57, it may mean that when the total positive electrode active material contained in the first layer 54A is considered to be 100% by mass, it contains, for example, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass (it may also be 100% by mass). The first layer 54A may further contain other particles as long as it mainly contains single particles 57. The other particles may be aggregated particles 58, or particles other than aggregated particles 58 that can be used as positive electrode active material.

[0021] Here, the single particle 57 is a primary particle that has grown relatively larger compared to the primary particle 59 contained in the aggregated particle 58 described later. Here, a primary particle refers to a particle in which no grain boundaries can be observed externally in the SEM image of the particle. A primary particle may be a particle in which no grain boundaries can be observed inside in the SEM image of the particle. The single particle 57 may be a single crystal. The single particle 57 may have any shape. For example, the single particle 57 may be spherical, columnar, or massive. The single particle 57 may form positive electrode active material particles on its own. Alternatively, the single particle 57 may form positive electrode active material particles by aggregating.

[0022] The number of individual particles 57 contained in the positive electrode active material particles can be measured in the SEM image of the positive electrode active material particles. The magnification of the SEM image can be adjusted as appropriate according to the particle size. The magnification of the SEM image may be, for example, 10,000x to 30,000x.

[0023] In addition, in SEM images of particles, for example, if two single particles 57 overlap, the particle further back may not be visible. In such cases, the number of single particles 57 that can be seen in the SEM image is considered to be the number of single particles 57 contained in the positive electrode active material particle. The same applies to the aggregated particles 58 described later. The positive electrode active material particle may consist of, for example, 1 to 10 single particles 57. The positive electrode active material particle may consist of, for example, 1 to 5 single particles 57. The positive electrode active material particle may consist of, for example, 1 to 3 single particles 57. The positive electrode active material particle may consist of, for example, 1 single particle 57.

[0024] A single particle 57 has a first maximum diameter. Here, in this specification, "first maximum diameter" refers to the distance between the two furthest points on the contour line of the single particle 57. The "contour line of the particle" may be confirmed in a two-dimensional projection image of the particle or in a cross-sectional image of the particle. The contour line of the particle may be confirmed, for example, in an SEM image of the powder or in a cross-sectional SEM image of the particle. The same applies to the second and third maximum diameters, which will be described later, regarding the "contour line of the particle". The first maximum diameter is, for example, 1.5 μm or more, but may be 2 μm or more, or 3 μm or more. The upper limit of the first maximum diameter is, for example, 10 μm or less, but may be 9 μm or less, 8 μm or less, 7 μm or less, or 6 μm or less.

[0025] The average value of the first maximum diameter is, for example, 1.5 μm or more, but may be 2 μm or more, or 3 μm or more. The upper limit of the average value of the first maximum diameter is, for example, 10 μm or less, but may be 9 μm or less, 8 μm or less, 7 μm or less, or 6 μm or less. Note that the "average value of the first maximum diameter" is the arithmetic mean of the first maximum diameters of 100 or more single particles 57. 100 or more single particles 57 are randomly selected.

[0026] The average particle diameter d1 of the single particle 57 is, for example, 1.5 μm or more, preferably 2 μm or more, and more preferably 3 μm or more. The upper limit of the average particle diameter d1 of the single particle 57 is, for example, 10 μm or less, preferably 8 μm or less or 7 μm or less, and more preferably 6 μm or less.

[0027] In this specification and in the claims, "average particle diameter" means the particle diameter (D) corresponding to 50% of the cumulative particle size distribution from the fine particle side, measured by particle size distribution measurement based on laser diffraction / light scattering. 50 This refers to the particle size. The average particle size can be obtained, for example, by preparing a sample by dispersing the particles to be measured (about 1 g) in about 50 g of water, and then introducing the sample into a conventionally known particle size distribution analyzer to obtain the particle size distribution. Any commercially available particle size distribution analyzer can be used without any particular restrictions. An example of such a commercially available device is the laser diffraction particle size distribution analyzer "Product name: MT3000II" manufactured by Microtrac-Bell Corporation.

[0028] While not particularly limited, when the total solid content of the first layer 54A is considered to be 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more.

[0029] As shown in Figure 3, in this embodiment, the second layer 54B has multiple protrusions 54B1 that project toward the positive electrode current collector 52, with aggregated particles 58 filling each of the recesses 54A1 of the first layer 54A. In the positive electrode active material layer 54, the aggregated particles 58 of the second layer 54B did not accidentally enter the recesses 54A1 of the first layer 54A; rather, the aggregated particles 58 were intentionally inserted by the formation of the uneven shape. In this embodiment, in the SEM cross-section, the second layer 54B has protrusions 54B1 and recesses 54B2 that are alternately arranged along the long side direction Y. The protrusions 54B1 of the second layer 54B correspond to the recesses 54A1 of the first layer 54A described above. Therefore, the number of protrusions 54B1 of the second layer 54B can refer to the range of the number of recesses 54A1 of the first layer 54A described above.

[0030] As shown in Figure 3, in this embodiment, the positive electrode active material contained in the second layer 54B is mainly composed of aggregated particles 58. In this embodiment, the protrusions 54B1 of the second layer 54B are filled with aggregated particles 58, which will be described later. In addition, the recesses 54B2 of the second layer 54B are filled with single particles 57. Here, when we say that the positive electrode active material contained in the second layer 54B is mainly composed of aggregated particles 58, it means that when the total positive electrode active material contained in the second layer 54B is considered to be 100% by mass, it contains, for example, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass (it may also be 100% by mass). The second layer 54B may further contain other particles as long as it mainly contains aggregated particles 58. The other particles may be single particles 57, or particles other than single particles 57 that can be used as positive electrode active material.

[0031] Here, as shown in Figure 3, in this embodiment, the aggregated particle 58 is a particle formed by the aggregation of a plurality of primary particles 59. The aggregated particle 58 can also be described as a composite of a plurality of primary particles 59. The primary particles 59 may be single crystals. The number of primary particles 59 contained in the aggregated particle 58 can be measured in an SEM image of the aggregated particle 58. The magnification of the SEM image may be, for example, 10,000 to 30,000 times. The aggregated particle 58 may be formed by the aggregation of, for example, 100 or more primary particles 59. There is no upper limit to the number of primary particles 59 in the aggregated particle 58. The aggregated particle 58 may be formed by the aggregation of, for example, 10,000 or fewer primary particles 59. The aggregated particle 58 may be formed by the aggregation of, for example, 1,000 or fewer primary particles 59. The primary particles 59 can have any shape. The primary particles 59 may be, for example, spherical, columnar, or lumpy.

[0032] The primary particle 59 has a second maximum diameter. Here, the "second maximum diameter" indicates the distance between the two furthest points on the contour line of the primary particle 59. For information on how to measure the second maximum diameter, please refer to the section describing the first maximum diameter above. In this embodiment, the second maximum diameter of the primary particle 59 is smaller than the first maximum diameter of the single particle 57. Here, the ratio of the first maximum diameter to the second maximum diameter (first maximum diameter / second maximum diameter) is, for example, greater than 1, and may be 2 or more, 3 or more, 4 or more, or 5 or more. The upper limit of the above (first maximum diameter / second maximum diameter) is, for example, 20 or less, and may be 15 or less, or 10 or less.

[0033] The second maximum diameter of the primary particle 59 is, for example, less than 1.5 μm, and may be 1.2 μm or less, or 1 μm or less. The upper limit of the second maximum diameter of the primary particle 59 is, for example, 0.1 μm or more, and may be 0.5 μm or more, or 0.7 μm or more. For example, when 10 or more primary particles 59 randomly sampled from an SEM image of one aggregated particle 58 have a second maximum diameter between 0.1 μm and 1 μm, all primary particles 59 contained in the aggregated particle 58 may be considered to have a second maximum diameter between 0.1 μm and 1 μm.

[0034] The average value of the second largest diameter is, for example, less than 1.5 μm, and may be 1.2 μm or less, or 1 μm or less. The upper limit of the average value of the second largest diameter is, for example, 0.1 μm or more, and may be 0.5 μm or more, or 0.7 μm or more. The average value of the second largest diameter is the arithmetic mean of the second largest diameters of 100 or more primary particles 59. 100 or more primary particles 59 are randomly selected. Here, the ratio of the average value of the first largest diameter to the average value of the second largest diameter (average value of the first largest diameter / average value of the second largest diameter) is, for example, greater than 1, and may be 2 or more, 3 or more, 4 or more, or 5 or more. The upper limit of the above (average value of the first largest diameter / average value of the second largest diameter) is, for example, 20 or less, and may be 15 or less, or 10 or less.

[0035] The aggregated particle 58 has a third maximum diameter. Here, the "third maximum diameter" refers to the distance between the two furthest points on the contour line of the aggregated particle 58. For information on how to measure the third maximum diameter, please refer to the section describing the first maximum diameter above. The third maximum diameter is, for example, 5 μm or more, and may be 6 μm or more or 7 μm or more, preferably 8 μm or more or 9 μm or more, and more preferably 10 μm or more. The upper limit of the third maximum diameter of the aggregated particle 58 is, for example, 20 μm or less, preferably 19 μm or less or 18 μm or less, and more preferably 17 μm or less.

[0036] The average value of the third maximum diameter is, for example, 5 μm or more, but may be 6 μm or more or 7 μm or more, preferably 8 μm or more or 9 μm or more, and more preferably 10 μm or more. The upper limit of the third maximum diameter of the agglomerated particles 58 is, for example, 20 μm or less, preferably 19 μm or less or 18 μm or less, and more preferably 17 μm or less. Note that the "average value of the third maximum diameter" is the arithmetic mean of the third maximum diameters of 100 or more agglomerated particles 58. 100 or more agglomerated particles 58 are randomly selected.

[0037] The average particle diameter d2 of the aggregated particles 58 is, for example, 5 μm or more, may be 6 μm or more or 7 μm or more, preferably 8 μm or more or 9 μm or more, and more preferably 10 μm or more. The upper limit of the average particle diameter d2 of the aggregated particles 58 is, for example, 20 μm or less, preferably 19 μm or less or 18 μm or less, and more preferably 17 μm or less.

[0038] While not particularly limited, when the total solid content of the second layer 54B is considered to be 100% by mass, the positive electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more.

[0039] In Figure 3, A shows the opening length of the recess 54A1 in the SEM cross-sectional view along the boundary Q excluding the recess 54A1 from boundary P. B shows the distance B between adjacent recesses 54A1 in the SEM cross-sectional view. C shows the depth of the recess 54A1 in the SEM cross-sectional view. D shows the thickness of the second layer 54B from the boundary Q excluding the protrusion 54B1 from boundary P to the surface S1 of the second layer 54B in the SEM cross-sectional view. In this embodiment, the average values ​​Aave, Bave, Cave, and D of A, B, C, and D described above satisfy the following relationships: Aave ≥ d2 × 1.3, Bave ≥ d1 × 3, d2 × 0.5 ≤ Cave ≤ d2 × 2.5, and Dave ≥ d2.

[0040] As described above, in this embodiment, the average opening length Aave satisfies Aave ≥ d2 × 1.3. If the average opening length Aave is too small, it becomes difficult for the aggregated particles 58 to enter the recess 54A1, so this lower limit is set. On the other hand, from the viewpoint of more favorably reducing the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54, the average opening length Aave is preferably d2 × 2 or more (for example, d2 × 2.3 or more). Furthermore, the upper limit of the average opening length Aave is, for example, d2 × 6 or less (for example, d2 × 5.4 or less), and from the viewpoint of more favorably obtaining the above effect, it is preferably d2 × 4.3 or less. By setting an upper limit on the average opening length Aave in this way, contact between aggregated particles 58 with low volume resistivity is suppressed, and the effect of more favorably increasing volume resistivity can be obtained. As a result, the amount of heat generated between the positive electrode current collector 52 and the positive electrode active material layer 54 can be more favorably reduced. While not particularly limited, the average aperture length Aave can be, for example, 5 μm to 100 μm, or 10 μm to 55 μm. The average aperture length Aave can be obtained, for example, as follows: First, five or more (for example, 10) SEM cross-sectional images of the positive electrode active material layer 54 are randomly acquired. Next, the average value of the aperture length A of all recesses 54A1 in the first layer 54A is calculated for each of the five or more acquired SEM cross-sectional images. The arithmetic mean of the measurement results of the five or more SEM cross-sectional images can then be adopted as the average aperture length Aave.

[0041] As described above, in this embodiment, the average distance Bave satisfies Bave ≥ d1 × 3. If the average distance Bave is too small, the uneven structure is prone to collapse, and the electrode structure becomes unstable, so this lower limit is set. The upper limit of the average distance Bave may be d1 × 20 or less (for example, d1 × 19 or less), d1 × 10 or less, or d1 × 8 or less. Although not particularly limited, the above average distance Bave may be, for example, 5 μm to 100 μm, or 10 μm to 95 μm. The above average distance Bave can be obtained, for example, as follows. First, five or more (for example, 10) SEM cross-sectional images of the positive electrode active material layer 54 are randomly acquired. Next, the average value of the distance B between all the recesses 54A1 in the first layer 54A is calculated for each of the five or more acquired SEM cross-sectional images. Furthermore, the arithmetic mean of the measurement results from the five or more SEM cross-sectional images mentioned above can be used as the average distance Bave.

[0042] As described above, in this embodiment, the average depth Cave satisfies d2 × 0.5 ≤ Cave ≤ d2 × 2.5. If the average depth Cave is too small, it becomes difficult for aggregated particles 58 to enter the recesses 54A1. Also, if the average depth Cave is too large, the effect of increasing the volume resistivity of the positive electrode active material layer 54 due to the uneven structure is reduced. Therefore, upper and lower limits are set for the average depth Cave. On the other hand, from the viewpoint of more favorably reducing the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54, the average depth Cave is preferably d2 × 1 or more, and more preferably d2 × 1.1 or more. Also, from the viewpoint of more favorably obtaining the above effect, the upper limit of the average depth Cave is preferably d2 × 2 or less (for example, d2 × 1.8 or less). Although not particularly limited, the average depth Cave may be, for example, 5 μm to 50 μm, or 10 μm to 30 μm. The average depth Cave mentioned above can be obtained, for example, as follows: First, five or more (for example, 10) SEM cross-sectional images of the positive electrode active material layer 54 are randomly acquired. Next, the average value of the depth C of all recesses 54A1 in the first layer 54A is calculated for each of the five or more acquired SEM cross-sectional images. Then, the arithmetic mean of the measurement results of the five or more SEM cross-sectional images can be adopted as the average depth Cave.

[0043] As described above, in this embodiment, the average thickness Dave satisfies Dave ≥ d2. This lower limit is set because the average thickness Dave must be at least the thickness of one layer of aggregated particles 58. On the other hand, from the viewpoint of more favorably reducing the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54, the average thickness Dave is preferably d2 × 1.2 or more. Furthermore, from the viewpoint of more favorably obtaining the above effect, the upper limit of the average thickness Dave is preferably d2 × 2 or less (for example, d2 × 1.7 or less). Although not particularly limited, the average thickness Dave may be, for example, 10 μm to 50 μm, or 15 μm to 40 μm. The average thickness Dave can be obtained, for example, as follows. First, five or more (for example, 10) SEM cross-sectional images of the positive electrode active material layer 54 are randomly acquired. Next, for the five or more SEM cross-sectional images obtained above, the average value of the thickness D from the boundary Q, excluding the protrusion 54B1 of the second layer 54B, is measured at five or more points (for example, 10 points). The arithmetic mean of the measurement results of the five or more SEM cross-sectional images above can then be adopted as the average thickness Dave.

[0044] Furthermore, Eave shown in Figure 3 represents the average thickness E from the boundary Q of the first layer 54A to the bottom surface S2 of the first layer 54A. Here, the ratio of the average thickness Eave to the average thickness Dave (Eave / Dave) is, for example, 1 or more, and may be 1.2 or more, or 1.3 or 1.4 or more. Also, the upper limit of the ratio (Eave / Dave) is, for example, 2 or less, and may be 1.5 or less. Although not particularly limited, the average thickness Eave may be, for example, 10 μm to 100 μm, or 20 μm to 60 μm. The average thickness Eave can be obtained, for example, as follows. First, five or more (for example, 10) SEM cross-sectional images of the positive electrode active material layer 54 are randomly acquired. Next, the average value of the thickness E from the boundary Q of the first layer 54A is measured at five or more points (for example, 10 points) in the five or more acquired SEM cross-sectional images is calculated for each. Furthermore, the arithmetic mean of the measurement results from the five or more SEM cross-sectional images mentioned above can be used as the average thickness, Eave.

[0045] The above SEM cross-sectional images can be obtained, for example, as follows. For example, in this embodiment, five or more cross-sectional samples are prepared, each cut along the Y direction in Figure 2 from a rectangular sheet-shaped positive electrode 50 (positive electrode active material layer 54). Each cross-sectional sample is taken from a randomly selected position. Then, the collected cross-sectional samples are subjected to cross-sectional processing. Such cross-sectional processing may be, for example, CP (Crosssection Polisher) processing, FIB (Focused Ion Beam) processing, etc. Each cross-sectional sample is observed by SEM. In this way, five or more SEM images can be obtained.

[0046] Here, Figure 4 is an explanatory diagram illustrating how to draw a boundary P according to one embodiment. In the SEM cross-sectional image, the boundary P having irregularities between the first layer 54A and the second layer 54B can be drawn, for example, as described below. As shown in Figure 4, first, a single particle 57A located at the furthest position in the thickness direction (corresponding to the X direction in Figure 3; the same applies hereinafter) on the electrode plate is extracted from the bottom surface S2 on the positive electrode current collector 52 side of the first layer 54A. Then, a line L1 is drawn passing through the outermost point of the single particle 57A in the thickness direction and along the short side direction (corresponding to the Y direction in Figure 3; the same applies hereinafter) on the electrode plate. Next, an aggregated particle 58A that fills the recess 54A1 is extracted. Then, a line L2 is drawn passing through the outermost point on one side Y1 in the short side direction of the aggregated particle 58A and along the thickness direction. Subsequently, a line L3 is drawn passing through the outermost point on one side X1 in the thickness direction of the aggregated particle 58A and along the short side direction. Next, a line L4 is drawn along the thickness direction, passing through the outermost point of the aggregated particle 58A on the other side Y2 in the short-side direction. Subsequently, near line L4, a single particle 57B is extracted that is located at the position furthest in the thickness direction from the bottom surface S2 on the positive electrode current collector 52 side of the first layer 54A. Then, a line L5 is drawn along the short-side direction, passing through the outermost point of the single particle 57B in the thickness direction. By repeating these steps, a boundary P with irregularities can be drawn.

[0047] However, in Figure 4, for example, the isolated particle 60 is excluded from the extraction target. The isolated particle 60 represents a particle surrounded by another type of particle. Here, the isolated particle 60 is a single particle. For example, the isolated particle 60 in Figure 4 is surrounded by another type of particle (here, aggregated particle 58). The isolated particle 60 may have moved during cross-sectional processing, for example. Alternatively, it may have been scattered during the fabrication of the positive electrode active material layer 54.

[0048] While not particularly limited, in the measurements A, B, C, and D described above, the magnification of the SEM image can be, for example, 10,000x to 30,000x.

[0049] In this embodiment, the mass ratio of single particles 57 contained in the first layer 54A to aggregated particles 58 contained in the second layer 54B is within the range of 30:70 to 50:50. If the mass ratio of aggregated particles 58 is 30% or less, the energy density decreases due to deterioration of packing performance. If the mass ratio of aggregated particles 58 exceeds 50%, it is difficult to ensure the safety of the battery 100 even with the heat generation reduction effect of the uneven structure. Therefore, such a range is set. By keeping the mass ratio of single particles 57 to aggregated particles 58 within the above range, it is possible to reduce the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54, and to improve the safety of the battery 100.

[0050] The single particles 57 and the aggregated particles 58 may each independently have any crystal structure. The single particles 57 and the aggregated particles 58 may each independently have, for example, a layered structure, a spinel structure, an olivine structure, etc. The single particles 57 may, for example, have the same crystal structure as the aggregated particles 58. Alternatively, the single particles 57 may, for example, have a different crystal structure from the aggregated particles 58.

[0051] The single particles 57 and the aggregated particles 58 can each have any composition independently. For example, the single particles 57 may have the same composition as the aggregated particles 58. Alternatively, the single particles 57 may have a different composition from the aggregated particles 58. Examples of materials constituting the single particles 57 and the aggregated particles 58 include lithium composite oxides and lithium transition metal phosphate compounds.

[0052] As the lithium composite oxide, a lithium transition metal composite oxide containing at least one of Ni, Co, and Mn as a transition metal element is preferable. Examples of the lithium transition metal composite oxide include lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel manganese-based composite oxides, lithium nickel cobalt manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, lithium iron nickel manganese-based composite oxides, and the like. These positive electrode active materials may be used alone or in combination of two or more.

[0053] In addition, in this specification, the term "lithium nickel cobalt manganese-based composite oxide" includes oxides containing one or two or more additional elements other than those in addition to the oxides composed of Li, Ni, Co, Mn, and O as constituent elements. Examples of the additional elements include transition metal elements such as Mg, Ca, Al, Ti, V, Cr, Y, Zr, Nb, Mo, Hf, Ta, W, Na, Fe, Zn, Sn, and typical metal elements. The additional elements may be semi-metal elements such as B, C, Si, P, and non-metal elements such as S, F, Cl, Br, I. This also applies to the above-mentioned lithium nickel-based composite oxides, lithium cobalt-based composite oxides, lithium manganese-based composite oxides, lithium nickel manganese-based composite oxides, lithium nickel cobalt aluminum-based composite oxides, lithium iron nickel manganese-based composite oxides, and the like.

[0054] Examples of the above lithium composite oxide include LiCoO2, LiMnO2, LiMn2O4, Li(NiCoMn)O2, Li(NiCoAl)O2, and the like. Further, the above lithium composite oxide is LiNi 0.6 Co 0.3 Mn 0.1 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.6 Co 0.1 Mn 0.3It may also be O2. These positive electrode active materials may be used individually or in combination of two or more. Note that in compositional formulas such as "Li(NiCoMn)O2", the notation "(NiCoMn)" indicates that the sum of the compositional ratios in parentheses is 1.

[0055] Examples of lithium transition metal phosphate compounds include lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), and lithium manganese iron phosphate. These cathode active materials may be used individually or in combination of two or more.

[0056] In one preferred embodiment, the single particles 57 and aggregated particles 58 are given by the following general formula (1): Li(Li a Ni x Mn y M z )O2(1) It is composed of materials represented by [this]. In the above general formula (1), it is preferable that a, x, y, and z satisfy the following relationships: -0.1 ≤ a ≤ 0.1, 0.7 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, and a + x + y + z = 1. Furthermore, examples of M include Co, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr, and Ge.

[0057] An example of a material represented by the above general formula (1) is LiNi 0.8 Co 0.1 Mn 0.1 O2, LiLiLi 0.7 Co 0.2 Mn 0.1 O2, LiLiLi 0.7 Co 0.1 Mn 0.2 Examples include O2 and LiNiO2. These can be layered metal oxides. These positive electrode active materials may be used individually or in combination of two or more.

[0058] (Negative electrode 60) In the embodiments shown in Figures 1 and 2, the negative electrode 60 comprises a long, sheet-like negative electrode current collector 62 and a negative electrode active material layer 64. The negative electrode current collector 62 is made of a conductive metal such as copper, copper alloy, nickel, or stainless steel. In this embodiment, the negative electrode current collector 62 is a metal foil, specifically a copper foil. The thickness of the negative electrode current collector 62 is, for example, 5 μm to 35 μm, preferably 7 μm to 20 μm. The thickness of the negative electrode active material layer 64 is, for example, 10 μm to 300 μm, preferably 20 μm to 200 μm. In this embodiment, the negative electrode current collector 62 has a region where the negative electrode active material layer 64 is provided and a portion 66 where the surface of the negative electrode current collector 62 is exposed without the negative electrode active material layer 64. The negative electrode active material layer 64 is provided in a strip-like shape along the longitudinal direction of the negative electrode 60, for example, on one or both sides (in this case, both sides) of the negative electrode current collector 62. In the configuration shown in Figure 2, the negative electrode active material layer 64 is not provided at the end in the longitudinal direction Y (the right end in the figure). The portion 66 where the negative electrode active material layer is not formed is, in this case, a strip-like region at the end in the longitudinal direction Y (the right end in the figure).

[0059] The negative electrode active material layer 64 contains a negative electrode active material (e.g., a carbon material such as graphite) capable of reversibly intercalating and releasing charge carriers. When the total solid content of the negative electrode active material layer 64 is taken as 100% by mass, the negative electrode active material may account for approximately 80% by mass or more, typically 90% by mass or more, for example, 95% by mass or more. The negative electrode active material layer 64 may also contain optional components other than the negative electrode active material, such as conductive materials, binders, dispersants, and various additives. As conductive materials, for example, carbon nanotubes such as single-walled carbon nanotubes (SWCNTs), double-walled carbon nanotubes (DWCNTs), and multi-walled carbon nanotubes (MWCNTs), carbon black such as acetylene black (AB), and carbon fibers can be used. Among these, from the viewpoint of improving the cycle characteristics of the lithium-ion secondary battery 100, carbon nanotubes are preferred as the conductive material, and single-walled carbon nanotubes are more preferred. Examples of binders that can be used include carboxymethylcellulose (CMC), polyacrylic acid (PAA), styrene-butadiene rubber (SBR), and polyvinylidene fluoride (PVdF). Among these, carboxymethylcellulose (CMC), polyacrylic acid (PAA), and styrene-butadiene rubber (SBR) are particularly preferred.

[0060] (Separator 70) The separator 70 is an insulating member that separates the positive electrode active material layer 54 of the positive electrode 50 from the negative electrode active material layer 64 of the negative electrode 60. For example, the separator 70 can be a porous sheet (film) made of a resin material such as polyethylene (PE), polypropylene (PP), polyester, cellulose, or polyamide. The porous sheet may have a single-layer structure or a laminated structure of two or more layers (for example, a three-layer structure with PP layers laminated on both sides of a PE layer). A heat-resistant layer (HRL) containing an inorganic filler may be provided on the surface of the separator 70. Examples of inorganic fillers include alumina, boehmite, aluminum hydroxide, and titania. While not particularly limited, the thickness of the separator 70 is, for example, 5 μm to 35 μm, or 7 μm to 20 μm.

[0061] In the configuration shown in Figure 1, the positive electrode terminal 30 and the negative electrode terminal 40 are arranged on the sealing plate 14. The positive electrode terminal 30 is an external connection terminal on the positive electrode side. Here, the positive electrode terminal 30 is electrically connected to the portion 56 of the electrode body 20 that does not have a positive electrode active material layer via the positive electrode current collector plate 32. Here, the positive electrode terminal 30 is preferably made of metal, and more preferably of aluminum or an aluminum alloy. The positive electrode current collector plate 32 may be made of a conductive metal such as aluminum, an aluminum alloy, nickel, or stainless steel. The negative electrode terminal 40 is an external connection terminal on the negative electrode side. Here, the negative electrode terminal 40 is electrically connected to the portion 66 of the electrode body 20 that does not have a negative electrode active material layer via the negative electrode current collector plate 42. Here, the negative electrode terminal 40 is preferably made of metal, and more preferably of copper or a copper alloy. The negative electrode current collector plate 42 may be made of a conductive metal such as copper, a copper alloy, nickel, or stainless steel.

[0062] <Electrolyte 80> Electrolyte 80 is, for example, a non-aqueous electrolyte containing a non-aqueous solvent and a supporting salt. Examples of non-aqueous solvents include organic solvents such as various carbonates, ethers, esters, nitriles, sulfones, and lactones used in this type of application. Among these, carbonates are preferably used. Examples of carbonates include ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), fluoroethylene carbonate (FEC) (preferably monofluoroethylene carbonate), monofluoromethyldifluoromethyl carbonate (F-DMC), and trifluorodimethyl carbonate (TFDMC). The non-aqueous solvent may be used alone or in combination of two or more. Examples of supporting salts include lithium salts such as LiPF6, LiBF4, and LiClO4. The supporting salt may be used alone or in combination of two or more types. The concentration of the supporting salt is preferably, for example, 0.7 mol / L to 1.4 mol / L. The electrolyte 80 may contain additives used for this type of application as needed. Examples of additives may include film-forming agents such as LiB(C2O4)2 (LiBOB) and LiBF2 (C2O4), gas-generating agents such as biphenyl (BP) and cyclohexylbenzene (CHB), and thickeners.

[0063] An example of a manufacturing method for the battery 100 according to this embodiment will be described below. The following description is not intended to limit the manufacturing method of the battery 100 disclosed herein to the following configuration. The steps described below can be carried out in any order as long as the effects of the disclosed technology are obtained. In addition, some of the steps described below can be omitted as needed. Alternatively, other steps may be added in addition to the steps described below. Note that the manufacturing method of the battery 100 according to this embodiment is characterized by the manufacturing method of the positive electrode 50, and the other steps can be carried out based on conventionally known manufacturing methods for this type of battery. Therefore, the following description will focus on the manufacturing method of the positive electrode 50.

[0064] <Method for manufacturing battery 100> Figure 5 is a flowchart illustrating a method for manufacturing a battery according to one embodiment. As shown in Figure 5, the method for manufacturing the battery 100 according to this embodiment includes a preparation step S1, a first coating film forming step S2, an uneven shape forming step S3, a second coating film forming step S4, and a pressing step S5. Each step will be described below.

[0065] <Preparation Step S1> In this process, a positive electrode current collector 52 is prepared. For example, the positive electrode current collector 52 can be one of those described in the (positive electrode 50) section above.

[0066] <First coating film formation step S2> In this step, the first paste is applied onto the prepared positive electrode current collector 52 to form a first coating film consisting of the first paste.

[0067] Specifically, first, a first paste is prepared. This first paste mainly contains single particles 57 as the positive electrode active material. Here, when we say that the first paste mainly contains single particles 57 as the positive electrode active material, it means that when the total positive electrode active material contained in the first paste is considered to be 100% by mass, single particles 57 are present in amounts of, for example, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass (it may also be 100% by mass). The first paste may further contain other particles as long as it mainly contains single particles 57. The other particles may be aggregated particles 58, or particles other than aggregated particles 58 that can be used as positive electrode active material.

[0068] The first paste is prepared by mixing, for example, single particles 57 as a positive electrode active material, a conductive material, a binder, and a dispersant using a mixing device. For example, the conductive material and binder described in the (positive electrode 50) section above can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used as the dispersion medium. While not particularly limited, the proportions of each material can be set as follows: for example, when the positive electrode active material is 100 parts by mass, the conductive material can be 1 to 5 parts by mass, the binder 0.5 to 3 parts by mass, and the dispersion medium 10 to 40 parts by mass. As the mixing device, any conventionally known mixing device used for this type of application can be used without particular limitation. While not particularly limited, the viscosity of the first paste can be, for example, 10 mPa·s to 500 mPa·s. For example, a value measured at 25°C using a commercially available rotational viscometer can be adopted.

[0069] For the range of the average particle diameter d1 of the single particles 57 contained in the first paste, please refer to the relevant section in <Battery 100 Configuration>.

[0070] The single particle 57 may be a commercially available product or a manufactured product. When manufacturing the single particle 57, it can be manufactured according to conventionally known manufacturing methods for this type of single particle. One example of a method for manufacturing the single particle 57 is to calcine the precursor of the single particle 57 at 500°C, add lithium hydroxide (LiOH), calcine at 900°C for about 72 hours, then wet grind it in a ball mill, and calcine at 750°C for about 10 hours.

[0071] Next, the first paste prepared above is applied to the surface (in this case, one side) of the positive electrode current collector 52. This application can be carried out using a gravure coater, comma coater, slit coater, die coater, etc. Then, the applied material is dried at a predetermined temperature (for example, 40°C to 80°C). In this way, the first coating film can be formed on the positive electrode current collector 52.

[0072] <Uneven shape formation process S3> In this process, an uneven surface is formed on the surface of the first coating film prepared as described above. Specifically, first, a mold having a predetermined uneven surface is prepared. Then, the first coating film is rolled to a predetermined thickness while sandwiching this mold between the press rolls of a roll press machine. In this way, recesses can be formed on the surface of the first coating film with a predetermined pattern and a constant pitch. Although not particularly limited, the press pressure of the press rolls can be, for example, 10 MPa to 100 MPa. Conventional molds and roll press machines used for this type of application can be used without any particular limitations.

[0073] The mold described above has protrusions with dimensions corresponding to the recesses formed on the surface of the first coating film. In this embodiment, the dimensions of these protrusions are designed so that the recesses 54A of the positive electrode active material layer 54 obtained after the pressing process S5 described later satisfy Aave≧d2×1.3, Bave≧d1×3, and d2×0.5≦Cave≦d2×2.5. The dimensions of the protrusions on the mold can be determined, for example, by combining preliminary tests using computer simulations with actual compression tests using the electrode plate and the mold.

[0074] For preferred ranges of the average values ​​of the opening length A (Aave), distance B (Bave), depth C (Cave), and thickness D (Dave), please refer to the relevant section in <Battery 100 Configuration>.

[0075] <Second coating film formation step S4> In this process, a second paste is applied to the surface of the first coating film, which has the above-mentioned uneven shape formed on it, to form a second coating film consisting of the second paste.

[0076] Specifically, first, a second paste is prepared. This second paste mainly contains aggregated particles 58 as the positive electrode active material. Here, "the second paste mainly contains aggregated particles 58 as the positive electrode active material" means that, when the total positive electrode active material contained in the second paste is considered to be 100% by mass, aggregated particles 58 are present in amounts of, for example, 70% or more by mass, 80% or more by mass, 90% or more by mass, 95% or more by mass, 99% or more by mass (it may also be 100% by mass). The second paste may further contain other particles as long as it mainly contains aggregated particles 58. The other particles may be single particles 57, or particles other than single particles 57 that can be used as positive electrode active material.

[0077] The second paste is prepared by mixing, for example, aggregated particles 58 as a positive electrode active material, a conductive material, a binder, and a dispersant using a mixing device. While not particularly limited, the proportions of each material can be set as follows: for example, when the aggregated particles 58 are 100 parts by mass, the conductive material can be 1 to 5 parts by mass, the binder 0.5 to 3 parts by mass, and the dispersion medium 10 to 40 parts by mass. Here, the proportion of aggregated particles 58 is adjusted so that the mass ratio of aggregated particles 58 to single particles 57 in both the first and second pastes is within the range of 30:70 to 50:50. For example, the conductive material and binder described in the (positive electrode 50) section above can be used. For example, N-methyl-2-pyrrolidone (NMP) can be used as the dispersion medium. As the mixing device, conventionally known mixing devices used for this type of application can be used without particular limitation. While not particularly limited, the viscosity of the first paste can be, for example, between 10 mPa·s and 500 mPa·s. For example, a value measured at 25°C using a commercially available rotational viscometer can be used to determine such viscosity.

[0078] For the range of the average particle diameter d2 of the aggregated particles 58 contained in the second paste, please refer to the relevant section in <Battery 100 Configuration>.

[0079] The aggregated particles 58 may be commercially available or manufactured. When manufacturing the aggregated particles 58, they can be manufactured according to conventionally known methods. One example of a method for manufacturing the aggregated particles 58 is to add lithium hydroxide (LiOH) to the precursor of the aggregated particles 58 and calcine it at 800°C for about 10 hours.

[0080] Next, the second paste prepared above is applied to the surface of the first coating film on the side where the recess is formed. This application can be carried out using a gravure coater, comma coater, slit coater, die coater, etc. Then, the coated material is dried at a predetermined temperature (for example, 40°C to 80°C). In this way, the second coating film can be formed on the positive electrode current collector 52.

[0081] In the first coating film formation step S2 and the second coating film formation step S3, the basis weight of the first coating film and the basis weight of the second coating film are adjusted so that the mass ratio of aggregated particles 58 in the second coating film to the single particles 57 in the first coating film is within the range of 30:70 to 50:50. That is, the mass of the single particles 57 in the first coating film and the mass of aggregated particles 58 in the second coating film are adjusted by adjusting the basis weight of the first coating film and the basis weight of the second coating film. In this specification and in the claims, "basis weight of the first layer" means the value obtained by dividing the mass of the first layer by the area of ​​the forming region (mass of the first layer / area of ​​the forming region). "Basis weight of the second layer" means the value obtained by dividing the mass of the second layer by the area of ​​the forming region (mass of the second layer / area of ​​the forming region).

[0082] <Pressing process S5> In this process, the first and second coating films formed above are pressed together to form a positive electrode active material layer 54 containing a first layer 54A made of the first paste and a second layer 54B made of the second paste. Specifically, the first and second coating films are rolled to a predetermined thickness while sandwiched between the press rolls of a roll press machine. Any conventionally known roll press machine used for this type of application can be used without any particular limitations.

[0083] In this embodiment, after pressing, it is preferable to press with a press pressure such that the average value Dave of the thickness D of the second layer 54B satisfies Dave ≥ d2. This press pressure can be determined, for example, by combining preliminary tests using computer simulations and condition studies using actual electrode plates. Although not particularly limited, the press pressure of the press roll can be, for example, 10 MPa to 100 MPa.

[0084] As described above, the positive electrode 50 according to this embodiment can be manufactured. Furthermore, in the positive electrode active material layer 54 after the pressing process S5, the first layer 54A and the second layer 54B are separated in the thickness direction by a boundary P having irregularities. The first layer 54A has a plurality of recesses 54A1 that are recessed toward the positive electrode current collector 52 side. The second layer 54B has a plurality of protrusions 54B1 that are filled with aggregated particles 58 in each of the recesses 54A1 of the first layer 54A and protrude toward the positive electrode current collector 52 side. In other words, the pressing process is configured to realize an irregular shape with such a configuration.

[0085] The positive electrode 50 prepared as described above and the negative electrode 60 prepared by a conventionally known method are superimposed with a separator 70 in between, wound up, and then pressed with a predetermined pressure. In this way, an electrode body 20 having a flat rectangular parallelepiped shape can be obtained. Next, a sealing plate 14 having a positive electrode terminal 30 and a negative electrode terminal 40 is prepared. Then, a positive electrode current collector plate 32 and a negative electrode current collector plate 42 are attached to the positive electrode terminal 30 and the negative electrode terminal 40, respectively. Then, the portion 56 of the electrode body 20 that does not have a positive electrode active material layer is electrically connected to the positive electrode current collector plate 32. Also, the portion 66 of the electrode body 20 that does not have a negative electrode active material layer is electrically connected to the negative electrode current collector plate 42. Next, the opening 12h of the case body 12 is sealed with the sealing plate 14 and the area around the opening 12h is joined. Finally, the inside of the case 10 is depressurized and the electrolyte 80 is injected through the injection hole of the sealing plate 14. As described above, the battery 100 according to this embodiment can be manufactured.

[0086] Battery 100 can be used for various applications. Suitable applications include plug-in hybrid electric vehicles (PHEVs), hybrid electric vehicles (HEVs), and battery electric vehicles (BEVs). Battery 100 can be used, for example, as a storage battery for small-scale power storage devices. Battery 100 can also be used, for example, in the form of a battery pack in which multiple batteries are connected in series and / or parallel.

[0087] As described above, the battery 100 according to this embodiment includes a positive electrode 50 comprising a positive electrode current collector 52 and a positive electrode active material layer 54 disposed on the positive electrode current collector 52. The positive electrode active material layer 54 has a first layer 54A disposed on the positive electrode current collector 52 side and a second layer 54B disposed on the first layer 54A. The positive electrode active material contained in the first layer 54A is mainly composed of single particles 57. The positive electrode active material contained in the second layer 54B is mainly composed of aggregated particles 58. The mass ratio of aggregated particles 58 to single particles 57 is adjusted to be within the range of 30:70 to 50:50. For example, conventionally, soft aggregated particles 58 were disposed on the positive electrode current collector 52 side, so the adhesion of the positive electrode active material layer 54 to the positive electrode current collector 52 was high. In contrast, in this technology, hard single particles 57 are placed on the positive electrode current collector 52 side, thereby reducing the adhesion of the positive electrode active material layer 54 to the positive electrode current collector 54. This increases the interfacial resistance between the positive electrode current collector 52 and the positive electrode active material layer 54. The first layer 54A has multiple recesses 54A1 that are recessed on the positive electrode current collector 52 side. The second layer 54B has multiple protrusions 54B1 that are filled with aggregated particles 58 in each of the recesses 54A1 of the first layer 54A, and protrude on the positive electrode current collector 52 side. The aforementioned uneven surfaces are formed to satisfy Aave≧d2×1.3, Bave≧d1×3, 0.5×d2≦Cave≦2.5×d2, and Dave≧d2. In this way, a predetermined uneven structure is formed at the two-layer interface, and aggregated particles 58 are placed in the protrusions 54B1 and single particles 57 are placed in the recesses 54B2. As a result, some of the aggregated particles 58 with low volume resistivity are surrounded by single particles 57 with high volume resistivity, thus increasing the volume resistivity. In other words, the overall volume resistivity of the positive electrode active material layer 54 increases. Therefore, according to the battery 100 of this embodiment, the interfacial resistance and the volume resistivity of the positive electrode active material layer 54 are increased, which reduces the amount of heat generated at the terminals of the battery 100 during an internal short circuit, thereby improving safety. Furthermore, a battery 100 with such a configuration can be manufactured, for example, by the manufacturing method described above.

[0088] As described above, in one preferred embodiment, the battery 100 comprises materials that make up the single particles 57 and aggregated particles 58, and the following general formula (1): Li(Lia Ni x Mn y M z )O2(1) It is represented by [this]. In the general formula (1) above, it is preferable that a, x, y, and z satisfy the following relationships: -0.1 ≤ a ≤ 0.1, 0.7 ≤ x ≤ 1.0, 0 ≤ y ≤ 0.3, 0 ≤ z ≤ 0.3, and a + x + y + z = 1. Also, M is at least one of Co, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr, and Ge. For example, the materials described above have a high nickel (Ni) content. These are also called "high-nickel materials". Such high-nickel materials have a relatively large specific capacity among materials that satisfy the composition of (1). Therefore, single particles 57 and aggregated particles 58 made from such materials can be preferably used in this type of battery 100 from the viewpoint of energy density.

[0089] As described above, in one preferred embodiment, the average particle diameter d1 is 3 μm to 6 μm, and the average particle diameter d2 is 10 μm to 17 μm. Single particles 57 and aggregated particles 58 having such a configuration can be preferably used in this type of battery 100.

[0090] As described above, in one preferred embodiment, the average opening length Aave satisfies 2.3 × d² ≤ Aave ≤ 4.3 × d². With this configuration, the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54 can be more preferably reduced.

[0091] As described above, in one preferred embodiment, the average depth Cave satisfies d2 ≤ Cave ≤ 2 × d2. With this configuration, the amount of heat generated at the interface between the positive electrode current collector 52 and the positive electrode active material layer 54 can be more preferably reduced.

[0092] <Other Embodiments> The embodiments of the technology disclosed herein have been described above. However, the above description is illustrative and does not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated in the above description.

[0093] For example, in the above embodiment, the battery 100 is a flat rectangular parallelepiped shape, but it is not limited to this. In other embodiments, the battery 100 may be cylindrical or laminated.

[0094] For example, in the above embodiment, the electrode body 20 is a wound electrode body, but it is not limited to this. In other embodiments, the battery 20 may be a laminated electrode body in which a plurality of positive electrodes and negative electrodes are stacked with a separator in between. Such a laminated electrode body may have a rectangular sheet-shaped positive electrode, a rectangular sheet-shaped negative electrode, and a rectangular sheet-shaped separator. In this case, in the SEM cross-sectional view, the cross-section of the rectangular sheet-shaped positive electrode active material layer cut along its short side direction is observed by SEM.

[0095] For example, in the above embodiment, the electrode body 20 has a portion 56 where the positive electrode active material layer is not formed and a portion 66 where the negative electrode active material layer is not formed, but it is not limited thereto. In other embodiments, the electrode body 20 may have a positive electrode tab and a negative electrode tab. Furthermore, for example, in the above embodiment, the electrode body 20 has a flattened rectangular parallelepiped shape, but it is not limited thereto. For example, if the battery 100 is cylindrical, the electrode body 20 can be cylindrical.

[0096] For example, in the above embodiment, the positive electrode active material layer 54 has a two-layer structure consisting of a first layer 54A and a second layer 54B, but is not limited thereto. In other embodiments, any layer may be provided between the first layer 54A and the positive electrode current collector 52, insofar as the effects of the technology disclosed herein can be realized. Alternatively, any layer may be provided on the second layer 54B. The above-mentioned arbitrary layer is preferably a layer containing positive electrode active material.

[0097] For example, in the above embodiment, the shape and size of the multiple recesses 54A1 of the first layer 54A are the same, but are not limited to this. In other embodiments, the shape and size of the multiple recesses 54A1 may differ, as long as Aave, Bave, Cave, and Dave satisfy the above range. Also, for example, in the above embodiment, the shape and size of the multiple protrusions 54A2 of the first layer 54A are the same, but are not limited to this. In other embodiments, the shape and size of the multiple protrusions 54A2 may differ, as long as Aave, Bave, Cave, and Dave satisfy the above range.

[0098] For example, in the above embodiment, the positive electrode active material contained in the first layer 54A exists as single particles 57, and the positive electrode active material contained in the second layer 54B exists as aggregated particles 58, but the embodiment is not limited to this. In other embodiments, the first layer 54A may partially contain other particles (e.g., aggregated particles 58) insofar as the effects of the disclosed technology are achieved. Similarly, the second layer 54B may partially contain other particles (e.g., single particles 57) insofar as the effects of the disclosed technology are achieved.

[0099] [Example Test] The following describes examples of tests related to the technology disclosed herein. Note that the content of the test examples described below is not intended to limit the scope of the technology disclosed herein.

[0100] [Manufacturing of test cells] <Test Example 1> As the positive electrode active material, single particles (first positive electrode active material) and aggregated particles (second positive electrode active material) were prepared. Here, the composition of both the single particles and aggregated particles was LiNi 0.8 Co 0.1 Mn 0.1The material was O2. The average particle size d1 of the single particles was 5 μm. The average particle size d2 of the aggregated particles was 13 μm. Graphite was prepared as a conductive material, and powdered polyvinylidene fluoride (PVdF) was prepared as a binder. The above prepared materials were mixed with N-methyl-2-pyrrolidone (NMP) as a dispersant to prepare a first paste and a second paste. Specifically, the first paste was prepared by mixing 100 parts by mass of single particles, 1.5 parts by mass of graphite, 1 part by mass of PVdF, and an appropriate amount of NMP. The second paste was prepared by mixing 100 parts by mass of aggregated particles, 1.5 parts by mass of graphite, 1 part by mass of PVdF, and an appropriate amount of NMP.

[0101] Next, the first paste prepared above was applied to one side of a 13 μm thick aluminum foil, which was to be used as the positive electrode current collector, and dried to produce a coating of the first paste (i.e., the first coating). Then, a mold having a predetermined uneven shape was prepared, and the mold was sandwiched between the press rolls of a roll press machine and rolled. In this way, an uneven surface was formed on the surface of the first coating. Subsequently, the second paste prepared above was applied to the surface of the first coating with the uneven shape formed on it and dried to produce a coating of the second paste (i.e., the second coating). The basis weight of the second coating was adjusted to 30 / 70 of the basis weight of the first coating. Then, the first and second coatings formed on the surface of the positive electrode current collector were rolled to a predetermined thickness to produce a positive electrode including the first and second layers. Furthermore, in the positive electrode active material layer, the average value Aave of the opening length A of the recess in the first layer, the average value Bave of the distance B between adjacent recesses, the average value Cave of the recess depth, and the average value Dave of the thickness D from the boundary of the second layer excluding the protrusions were adjusted to match the corresponding column in Table 1.

[0102] Graphite particles were prepared as the negative electrode active material. The average particle size of the graphite particles was 16 μm. Carboxymethylcellulose (CMC) and styrene-butadiene rubber (SBR) were prepared as binders. The prepared materials were mixed with water as a dispersion medium to prepare a negative electrode paste. Specifically, the negative electrode paste was prepared by mixing 98.3 parts by mass of graphite particles, 0.7 parts by mass of CMC, 1 part by mass of SBR, and an appropriate amount of water. The prepared negative electrode paste was applied to both sides of an 8 μm thick copper foil to be used as the negative electrode current collector, dried, pressed to the desired thickness, and processed to the desired dimensions to manufacture the negative electrode.

[0103] The positive and negative electrodes manufactured as described above were cut to predetermined dimensions and interposed with a separator consisting of a polyethylene / heat-resistant layer two-layer structure. The heat-resistant layer and the positive electrode active material layer were then brought into contact, and the electrodes were laminated so that the positive electrode current collector was exposed to create the electrode body. The aluminum foil of the positive electrode current collector was welded to an aluminum plate for external current collection. The negative electrode was welded to a copper plate for external current collection. This integrated assembly was inserted into an aluminum laminate film casing, a non-aqueous electrolyte was injected, and the assembly was left to stand for 12 hours. The outside of the casing was then sealed to create the test cell for this example. The non-aqueous electrolyte used was a mixed solvent containing ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) in a volume ratio of EC:EMC:DMC = 3:3:4, with LiPF6 as a supporting salt dissolved at a concentration of 1.15 mol / L.

[0104] <Examples of tests 2-4, 8, 9> The test cells for Test Examples 2-4, 8, and 9 were prepared in the same manner as in Test Example 1, except that the average values ​​Aave (opening length A of the recess in the first layer), Bave (distance B between adjacent recesses), Cave (depth C of the recess), and Dave (thickness D from the boundary excluding the protrusions of the second layer) were adjusted to match the corresponding columns in Table 1. In Test Example 9, however, the desired positive electrode could not be obtained.

[0105] <Test Example 5> The test cell for this example was prepared in the same manner as in Test Example 1, except that no uneven surface was formed in the first layer.

[0106] <Test Example 6> A test cell for this example was prepared in the same manner as in Test Example 5, except that aggregated particles were used as the first positive electrode active material and single particles as the second positive electrode active material, and the basis weight ratio was adjusted to first positive electrode active material / second positive electrode active material = 30 / 70.

[0107] <Test Example 7> A test cell for this example was prepared in the same manner as in Test Example 6, except that it had the same dimensions as in Test Example 1 and the first layer was made to have irregularities.

[0108] <Test Example 10> The test cell for this example was prepared in the same manner as in Test Example 1, except that the ratio of basis weight was adjusted so that the first positive electrode active material / second positive electrode active material = 50 / 50, and Aave, Bave, Cave, and Dave were adjusted to match the corresponding columns in Table 1.

[0109] <Test Example 11> The test cell for this example was prepared in the same manner as in Test Example 1, except that the ratio of basis weight was adjusted to 40 / 60 for the first positive electrode active material and the second positive electrode active material, and Aave, Bave, Cave, and Dave were adjusted to match the corresponding columns in Table 1.

[0110] [Evaluation of test cells] <Measuring input resistance> Each test cell (counter electrode: graphite) prepared as described above was charged at 0.5C to a State of Charge (SOC) of 50% in an environment of -10°C. After this charging, a 15-minute rest period was followed by a 10-second discharge at 0.1C. The voltage and discharged current values ​​were recorded at 0.1 seconds and 10 seconds after the start of discharge. Then, the cells were charged again at 0.1C for 10 seconds, and the voltage and current values ​​were recorded at 0.1 seconds and 10 seconds after the start of charge. The same procedure was repeated, varying only the current rate at 0.33C, 0.5C, 1C, and 1.5C. The discharge resistance between 0.1 seconds and 10 seconds after the start of discharge (charging) was calculated from the relationship between the voltage at 0.1 seconds, the voltage at 10 seconds after the start of discharge (charging), and the current values. The results are shown in the corresponding column of Table 1. In this test example, the input resistance of the cell is considered to be within the appropriate range if the input resistance is 600 mΩ or higher. Furthermore, in Test Example 8, the input resistance was not measured because aggregated particles did not enter the convex portion, making it impossible to manufacture electrodes to the correct dimensions.

[0111] <Measurement of interfacial resistance and volume resistivity of the positive electrode active material layer> The positive electrodes for each of the above-described examples were analyzed using a conventionally known electrode resistance measuring device (for example, the RM2610 electrode resistance measuring system from HIOKI E.E. CORPORATION) to obtain various resistance values. These measurements were performed by referring to the method described in the catalog of the electrode resistance measuring device. Here, "interfacial resistance of the positive electrode active material layer" refers to the resistance that occurs at the interface between the positive electrode current collector and the first layer. Also, "volume resistance of the positive electrode active material layer" refers to the volume resistance of the entire positive electrode active material layer. The results are shown in the corresponding column of Table 1. In this test example, the interfacial resistance is expressed as a ratio with the interfacial resistance value of Test Example 6 set to 100. Similarly, the volume resistance is expressed as a ratio with the volume resistance values ​​of Test Examples 5 and 6 set to 100. In this test example, if the interfacial resistance is greater than 100, the interfacial resistance of the positive electrode is evaluated as being within the appropriate range. Similarly, if the volume resistance is greater than 100, the volume resistance of the positive electrode is evaluated as being within the appropriate range.

[0112] <Fusing test (measurement of heat generation)> Each test cell prepared as described above was charged with a constant current to a voltage of 4.2V. After charging, each test cell was confined to a constant voltage. While measuring the voltage with a data logger, a metal nail was inserted into the center of each test cell, penetrating through the positive and negative electrodes in the thickness direction of the cell, thereby causing an internal short circuit. At this time, each test cell was connected in parallel to a constant voltage power supply with a maximum current of 200A, so that a current simulating that of a large cell flowed. The amount of heat generated for each time interval was calculated using the cell voltage at the time of the short circuit, the current that flowed (short circuit current), and the elapsed time after the short circuit, and the cumulative heat generation (J) was obtained by integrating these values. Hereafter, the amount of heat generation will refer to this cumulative heat generation. The results are shown in the corresponding column of Table 1. In this test example, if the amount of heat generation exceeds 6J, it will be evaluated as having a high risk of thermal runaway. Here, if the amount of heat generation is below a certain value, there is a high possibility that the area near the short circuit will melt before thermal runaway occurs, and the safety of the cell is more easily maintained. On the other hand, if the amount of heat generated exceeds a certain value, there is a high probability that thermal runaway will occur due to the heat generation before melting occurs. This makes the cell prone to becoming unstable.

[0113] [Table 1]

[0114] As shown in Table 1, in Test Examples 1-4 and 10, where single particles are present in the first layer and aggregated particles are present in the second layer, and the conditions Aave≧d2×1.3, Bave≧d1×3, d2×0.5≦Cave≦d2×2.5, and Dave≧d2 are satisfied, and the mass ratio of aggregated particles to single particles is within the range of 30:70 to 50:50, it was confirmed that the interfacial resistance and the volume resistivity of the positive electrode active material layer can be increased, and the amount of heat generated by the cell can be suppressed, while keeping the input resistance of the cell within an appropriate range (in other words, while ensuring cell performance). On the other hand, in Test Example 5, where no irregularities were formed in the first layer; Test Example 6, where no irregularities were formed in the first layer and the positions of single particles and aggregated particles were reversed; Test Example 7, where irregularities were formed in the first layer but the positions of single particles and aggregated particles were reversed; Test Example 8, where Aave was outside the range of Aave≧d2×1.3; Test Example 9, where Bave was outside the range of Bave≧d1×3; and Test Example 11, where the mass ratio of aggregated particles to single particles was outside the range of 30:70~50:50, the heat generation of the cell could not be suppressed.

[0115] Furthermore, from Test Examples 1-4 and 10, it was confirmed that, from the viewpoint of suppressing the heat generation of the cell, it is preferable for Aave to satisfy 2.3 × d² ≤ Aave ≤ 4.3 × d². And from Test Examples 1-4 and 10, it was confirmed that, from the viewpoint of suppressing the heat generation of the cell, it is preferable for Cave to satisfy d² ≤ C ≤ 2 × d².

[0116] Based on the above, this disclosure provides a highly reliable energy storage device with suppressed heat generation.

[0117] As described above, specific embodiments of the technology disclosed herein include those described in the following sections.

[0118] Section 1: A power storage device comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, The positive electrode active material layer, in SEM cross-sectional view, is divided in the thickness direction by an uneven boundary, and comprises a first layer located on the positive electrode current collector side and a second layer located on the first layer. The positive electrode active material contained in the first layer is mainly composed of single particles. The positive electrode active material contained in the second layer is mainly composed of aggregated particles. The first layer has a plurality of recesses that are recessed toward the positive electrode current collector side in the SEM cross-sectional view, and The second layer has a plurality of protrusions that project toward the positive electrode current collector, with the aggregated particles filled in each of the recesses of the first layer. Aave is the average value of the opening length A along the boundary excluding the recess in the aforementioned SEM cross-sectional view. The average value of the distance B between adjacent recesses in the SEM cross-sectional view is Bave. The average value of the depth C of the recess in the SEM cross-sectional view is Cave. Dave is the average value of the thickness D from the boundary of the second layer, excluding the protrusions, in the SEM cross-sectional view. The average particle diameter of the single particle is d1, When the average particle diameter of the aggregated particles is denoted as d2, the following relationship exists: Aave ≥ d2 × 1.3, Bave ≥ d1 × 3, d2 × 0.5 ≤ Cave ≤ d2 × 2.5, Dave ≥ d2 Satisfying the conditions, An energy storage device in which the mass ratio of aggregated particles to single particles is within the range of 30:70 to 50:50.

[0119] Section 2: The material constituting the single particle and the aggregated particle is given by the following general formula (1): Li(Li a Ni x Mn y M z )O2(1) Represented by, In the above general formula (1), the following relationship exists: -0.1≦a≦0.1, 0.7≦x≦1.0, 0≦y≦0.3, 0≦z≦0.3, a+x+y+z=1 Satisfying the conditions, M is at least one selected from the group consisting of Co, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr, and Ge. The energy storage device described in item 1.

[0120] Section 3: The energy storage device according to item 1 or 2, wherein d1 is 3 μm to 6 μm and d2 is 10 μm to 17 μm.

[0121] Section 4: The Aave is an energy storage device described in any one of items 1 to 3, satisfying d2 × 2.3 ≤ Aave ≤ d2 × 4.3.

[0122] Section 5: The aforementioned Cave is an energy storage device described in any one of items 1 to 4, satisfying d2 ≤ Cave ≤ d2 × 2.

[0123] Item 6: A method for manufacturing an energy storage device comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, comprising the following steps; Preparation step of preparing the positive electrode current collector; A first coating film forming step is to apply a first paste onto the positive electrode current collector to form a first coating film consisting of the first paste, wherein the first paste mainly contains single particles as the positive electrode active material; A process for forming an uneven surface on the surface of the first coating film; A second coating film forming step is to apply a second paste to the surface of the first coating film on which the aforementioned uneven shape is formed, thereby forming a second coating film consisting of the second paste, wherein the second paste mainly contains aggregated particles as a positive electrode active material; and A pressing step of pressing the first coating film and the second coating film to form the positive electrode active material layer, which includes a first layer made of the first paste and a second layer made of the second paste; It includes, Here, in the first coating film formation step and the second coating film formation step, The basis weight of the first coating and the second coating are adjusted so that the mass ratio of aggregated particles in the second coating to the single particles in the first coating is within the range of 30:70 to 50:50. The aforementioned pressing process is The first layer and the second layer are separated in the thickness direction by a boundary having irregularities, the first layer has a plurality of recesses that are recessed toward the positive electrode current collector, and the second layer is configured such that the aggregated particles are filled into each of the recesses of the first layer and the second layer has a plurality of protrusions that are projected toward the positive electrode current collector. A method for manufacturing energy storage devices.

[0124] Section 7: The material constituting the single particle and the aggregated particle is given by the following general formula (1): Li(Li a Ni x Mn y M z )O2(1) Represented by, In the above general formula (1), the following relationship exists: -0.1≦a≦0.1, 0.7≦x≦1.0, 0≦y≦0.3, 0≦z≦0.3, a+x+y+z=1 Satisfying the conditions, M is at least one selected from the group consisting of Co, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr, and Ge. A method for manufacturing the energy storage device described in item 6.

[0125] Section 8: A method for manufacturing an energy storage device according to item 6 or 7, wherein the average particle diameter of the single particles is 3 μm to 6 μm, and the average particle diameter of the aggregated particles is 10 μm to 17 μm. [Explanation of Symbols]

[0126] 10 cases 12 Case body 12h opening 14 Sealing plate 16 Safety valve 20 Electrode body 30 Positive terminal 32 Positive electrode current collector plate 40 Negative terminal 42 Negative electrode current collector plate 50 Positive electrode (Positive electrode sheet) 52 Positive electrode current collector 54 Cathode active material layer 54A 1st layer 54A1 Recess 54B 2nd layer 54B1 protrusion 56 Portion where positive electrode active material layer is not formed 57 Single Particle 58 Agglomerated particles 59 Primary particles 60 Negative electrode (negative electrode sheet) 62 Negative electrode current collector 64 Negative electrode active material layer 66 Part where negative electrode active material layer is not formed 70 Separators (Separator Sheets) 80 Electrolytes 100 batteries

Claims

1. A power storage device comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, The positive electrode active material layer, in SEM cross-sectional view, is divided in the thickness direction by an uneven boundary, and comprises a first layer located on the positive electrode current collector side and a second layer located on the first layer. The positive electrode active material contained in the first layer is mainly composed of single particles. The positive electrode active material contained in the second layer is mainly composed of aggregated particles. The first layer has a plurality of recesses that are recessed toward the positive electrode current collector in the SEM cross-sectional view, and The second layer has the aggregated particles filled in each of the recesses of the first layer, and has a plurality of protrusions that project toward the positive electrode current collector. Aave is the average value of the opening length A along the boundary excluding the recess in the aforementioned SEM cross-sectional view. The average value of the distance B between adjacent recesses in the SEM cross-sectional view is Bave. The average value of the depth C of the recess in the SEM cross-sectional view is Cave. Dave is the average value of the thickness D from the boundary of the second layer, excluding the protrusions, in the SEM cross-sectional view. The average particle diameter of the single particle is d1, When the average particle size of the aggregated particles is denoted as d2, the following relationship exists: Aave ≥ d² × 1.3, Bave ≥ d1 × 3, d² × 0.5 ≤ Cave ≤ d² × 2.5, Dave ≥ d² Satisfying the conditions, An energy storage device in which the mass ratio of the aggregated particles to the single particles is in the range of 30:70 to 50:

50.

2. The material constituting the single particle and the aggregated particle is given by the following general formula (1): Li(Li ａ Ni ｘ Mn ｙ M ｚ )O ２ (1) Represented by, In the above general formula (1), the following relationship exists: -0.1≦a≦0.1, 0.7≦x≦1.0, 0≦y≦0.3, 0≦z≦0.3, a+x+y+z=1 Satisfying the conditions, M is at least one selected from the group consisting of Co, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr, and Ge. The energy storage device according to claim 1.

3. The energy storage device according to claim 1 or 2, wherein d1 is 3 μm to 6 μm and d2 is 10 μm to 17 μm.

4. The energy storage device according to claim 1 or 2, wherein Aave satisfies d2 × 2.3 ≤ Aave ≤ d2 × 4.

3.

5. The energy storage device according to claim 1 or 2, wherein the Cave satisfies d2 ≤ Cave ≤ d2 × 2.

6. A method for manufacturing an energy storage device comprising a positive electrode including a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the following steps: Preparation step of preparing the positive electrode current collector; A first coating film forming step is to apply a first paste onto the positive electrode current collector to form a first coating film consisting of the first paste, wherein the first paste mainly contains single particles as the positive electrode active material; A process for forming an uneven surface on the surface of the first coating film; A second coating film forming step, in which a second paste is applied to the surface of the first coating film on which the aforementioned uneven shape is formed, thereby forming a second coating film consisting of the second paste, wherein the second paste mainly contains aggregated particles as a positive electrode active material; and A pressing step of pressing the first coating film and the second coating film to form the positive electrode active material layer, which includes a first layer made of the first paste and a second layer made of the second paste; It includes, Here, in the first coating film formation step and the second coating film formation step, The basis weight of the first coating and the second coating are adjusted so that the mass ratio of aggregated particles in the second coating to the single particles in the first coating is within the range of 30:70 to 50:

50. The aforementioned pressing process is The first layer and the second layer are separated in the thickness direction by a boundary having irregularities, the first layer has a plurality of recesses that are recessed toward the positive electrode current collector, and the second layer has a plurality of protrusions that are filled in each of the recesses of the first layer toward the positive electrode current collector. A method for manufacturing energy storage devices.

7. The material constituting the single particle and the aggregated particle is given by the following general formula (1): Li(Li ａ Ni ｘ Mn ｙ M ｚ )O ２ (1) Represented by, In the above general formula (1), the following relationship exists: -0.1≦a≦0.1, 0.7≦x≦1.0, 0≦y≦0.3, 0≦z≦0.3, a+x+y+z=1 Satisfying the conditions, M is at least one selected from the group consisting of Co, Al, Zr, B, Mg, Fe, Cu, Zn, Sn, Na, K, Ba, Sr, Ca, W, Mo, Nb, Ti, Si, V, Cr, and Ge. A method for manufacturing an energy storage device according to claim 6.

8. The method for manufacturing an energy storage device according to claim 6 or 7, wherein the average particle diameter of the single particles is 3 μm to 6 μm, and the average particle diameter of the aggregated particles is 10 μm to 17 μm.

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