Electrode body and battery

Abstract

To provide an electrode body including a positive electrode in which the permeability of an electrolyte solution is improved, and a battery including this electrode body.SOLUTION: An electrode body includes a current collector, a positive electrode layer, and a separator in this order. The positive electrode layer includes a positive electrode active material particle and a graphite particle. When the positive electrode layer is divided into two regions in a thickness direction, the number of graphite particles per unit area in a region on the separator side is larger than the number of graphite particles per unit area in a region on the current collector side.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to an electrode assembly and a battery. [Background technology]

[0002] Lithium-ion secondary batteries are generally manufactured by injecting an electrolyte solution into an outer casing that houses an electrode assembly including electrodes and a separator. The electrode assembly is pressed under high pressure to increase electrode density, or the electrodes and separator are joined with adhesives or other adhesives. This makes it difficult for the electrolyte solution to penetrate the electrode assembly, making it necessary to improve the efficiency of the injection process.

[0003] As a method for improving the permeability of an electrolyte solution into an electrode assembly, for example, Patent Document 1 proposes providing a region where the electrode and separator are not bonded when bonding the electrodes and separator that constitute the electrode assembly. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-15773 Summary of the Invention [Problem to be solved by the invention]

[0005] The method described in Patent Document 1 requires a step of providing a region where the electrode and separator are not bonded to each other in order to increase the permeability of the electrolyte solution, and therefore leaves room for improvement in work efficiency. Furthermore, the positive electrode tends to have lower electrolyte permeability than the negative electrode, and therefore, when the positive electrode is adhered to the separator, the rate of in-plane movement of the electrolyte at the interface between the positive electrode and the separator decreases, and permeability is likely to be impaired. An object of the present disclosure is to provide an electrode assembly including a positive electrode with improved electrolyte permeability, and a battery including this electrode assembly. [Means for solving the problem]

[0006] The means for solving the above problems include the following embodiments. <1> A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, An electrode body, wherein when the positive electrode layer is divided into two regions in the thickness direction, the number of graphite particles per unit area in the region on the separator side is greater than the number of graphite particles per unit area in the region on the current collector side. <2> A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into two regions in the thickness direction, the area ratio of the region corresponding to the graphite particles in the region on the separator side is larger than the area ratio of the region corresponding to the graphite particles in the region on the current collector side. <3> A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, An electrode body, wherein, when the positive electrode layer is divided into two regions in the thickness direction, the average particle diameter of the graphite particles contained in the region on the separator side is larger than the average particle diameter of the graphite particles contained in the region on the current collector side. <4> A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into three regions in the thickness direction, the number of graphite particles per unit area in the central region is greater than the number of graphite particles per unit area in the region on the current collector side and the number of graphite particles per unit area in the region on the separator side. <5> A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body in which, when the positive electrode layer is divided into three regions in the thickness direction, the area ratio of the region corresponding to the graphite particles in the central region is larger than the area ratio of the corresponding region in the region on the current collector side and the area ratio of the region corresponding to the graphite particles in the region on the separator side. <6> A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into three regions in the thickness direction, the average particle diameter of the graphite particles in the central region is larger than the average particle diameter of the graphite particles in the region on the current collector side and the average particle diameter of the graphite particles in the region on the separator side. <7> At least a portion of the separator is in a state of being adhered to the positive electrode layer. <1> ~ <6> The electrode assembly according to any one of the preceding claims. <8> <1> ~ <6> A battery comprising the electrode assembly according to any one of claims 1 to 4. [Effects of the Invention]

[0007] According to the present disclosure, there is provided an electrode assembly including a positive electrode with improved electrolyte permeability, and a battery including this electrode assembly. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 2 is a cross-sectional view schematically showing an example of the configuration of an electrode body. [Figure 2] FIG. 2 is a cross-sectional view schematically showing an example of the configuration of an electrode body. [Figure 3] FIG. 1 is a diagram illustrating an example of application of a battery to an electric vehicle. [Figure 4] FIG. 2 is a diagram schematically illustrating an example of the configuration of a battery module. [Figure 5] FIG. 2 is a diagram schematically illustrating an example of the configuration of a battery module. [Figure 6] FIG. 2 is a diagram schematically illustrating an example of the configuration of a battery cell included in a battery module. DETAILED DESCRIPTION OF THE INVENTION

[0009] In the present disclosure, a numerical range indicated using "to" means a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In the numerical ranges described in this disclosure, the upper or lower limit value described in a certain numerical range may be replaced with the value shown in the examples. In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0010] First Embodiment The first embodiment of the present disclosure is A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, When the positive electrode layer is divided into two regions in the thickness direction, the number of graphite particles per unit area in the region on the separator side is greater than the number of graphite particles per unit area in the region on the current collector side.

[0011] In the electrode assembly of this embodiment, the positive electrode layer contains graphite particles, which form appropriate voids in the positive electrode layer that serve as paths for the electrolyte to move, making it easy for the electrolyte to permeate. On the other hand, increasing the voids in the positive electrode layer reduces the energy density of the battery. In particular, it is desirable for the portion of the positive electrode layer closest to the current collector to contain a high density of positive electrode active material. Therefore, in the electrode assembly of this embodiment, a larger number of graphite particles are arranged in the region of the positive electrode layer closer to the separator, thereby improving the permeability of the electrolyte while suppressing a decrease in energy density. The electrode assembly of this embodiment has good electrolyte permeability even when at least a portion of the separator is in a state of being bonded to the positive electrode layer.

[0012] In this embodiment, the number of graphite particles per unit area in the separator-side region of the positive electrode layer can be compared with the number of graphite particles per unit area in the current collector-side region by image analysis. Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope, etc. This cross-sectional image is divided into two regions in the thickness direction. The position of the boundary between the two regions is determined so that the thickness of the region on the separator side is within a range of 0.5 to 1.5 times (for example, 1.0 times) the thickness of the region on the current collector side. Next, the number of graphite particles per unit area in each region is measured and compared. The dimension of the positive electrode layer to be measured in the planar direction is at least 10 mm. To improve measurement accuracy, cross-sectional images in the thickness direction may be obtained at multiple locations (for example, 5 to 10 locations) of the positive electrode layer, and the number of graphite particles per unit area in each cross-sectional image may be compared.

[0013] The number N1 of graphite particles per unit area in the separator-side region and the number N2 of graphite particles per unit area in the current collector-side region are not particularly limited as long as they satisfy the relationship N1 / N2>1. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, N1 / N2 is preferably 1.5 or more, and more preferably 2.0 or more. The upper limit of N1 / N2 is not particularly limited, and may be ∞ (that is, N2 is 0). The positive electrode layer may be such that the separator-side region contains graphite particles as a conductive material, and the current collector-side region contains carbon black as a conductive material.

[0014] Second Embodiment A second embodiment of the present disclosure is A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, When the positive electrode layer is divided into two regions in the thickness direction, the area ratio of the region corresponding to the graphite particles in the region on the separator side is larger than the area ratio of the region corresponding to the graphite particles in the region on the current collector side.

[0015] In the electrode assembly of this embodiment, the positive electrode layer contains graphite particles, which form appropriate voids in the positive electrode layer that serve as paths for the electrolyte to move, making it easy for the electrolyte to permeate. On the other hand, increasing the voids in the positive electrode layer reduces the energy density of the battery. In particular, it is desirable for the portion of the positive electrode layer closest to the current collector to contain a high density of positive electrode active material. Therefore, in the electrode assembly of this embodiment, graphite particles are arranged at a higher density in the portion of the positive electrode layer closer to the separator, thereby improving the permeability of the electrolyte while suppressing a decrease in energy density. The electrode assembly of this embodiment has good electrolyte permeability even when at least a portion of the separator is in a state of being bonded to the positive electrode layer.

[0016] In this embodiment, the area ratio of the region corresponding to the graphite particles in the separator side region of the positive electrode layer and the area ratio of the region corresponding to the graphite particles in the current collector side region can be compared by image analysis. Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope, etc. This cross-sectional image is divided into two regions in the thickness direction. The position of the boundary between the two regions is determined so that the thickness of the region on the separator side is within a range of 0.5 to 1.5 times (for example, 1.0 times) the thickness of the region on the current collector side. Next, the area ratio of the region corresponding to the graphite particles in each region is measured and compared. The dimension of the positive electrode layer to be measured in the planar direction is at least 10 mm. The area ratio of the region corresponding to graphite particles is obtained by dividing the region corresponding to graphite particles in the measurement region of the positive electrode layer by the area of ​​the measurement target region (i.e., the total area of ​​the region corresponding to graphite particles and the region not corresponding to graphite particles). When determining the region corresponding to graphite particles, image processing such as binarization may be performed. To improve measurement accuracy, cross-sectional images in the thickness direction may be obtained at multiple locations (for example, 5 to 10 locations) of the positive electrode layer, and the area proportions of regions corresponding to graphite particles in each cross-sectional image may be compared.

[0017] The area ratio R1 of the region corresponding to graphite particles in the region on the separator side and the area ratio 2 of the region corresponding to graphite particles in the region on the current collector side are not particularly limited as long as they satisfy the relationship R1 / R2>1. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, R1 / R2 is preferably 1.5 or more, and more preferably 2.0 or more. The upper limit of R1 / R2 is not particularly limited, and may be ∞ (that is, R2 is 0). The positive electrode layer may be such that the separator-side region contains graphite particles as a conductive material, and the current collector-side region contains carbon black as a conductive material.

[0018] Third Embodiment A third embodiment of the present disclosure is A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, When the positive electrode layer is divided into two regions in the thickness direction, the average particle size of the graphite particles contained in the region on the separator side is larger than the average particle size of the graphite particles contained in the region on the current collector side.

[0019] In the electrode assembly of this embodiment, the positive electrode layer contains graphite particles, which form appropriate voids in the positive electrode layer that serve as paths for the electrolyte to move, making it easy for the electrolyte to permeate. On the other hand, increasing the voids in the positive electrode layer reduces the energy density of the battery. In particular, it is desirable for the portion of the positive electrode layer closest to the current collector to contain a high density of positive electrode active material. Therefore, in the electrode assembly of this embodiment, larger graphite particles are arranged in the positive electrode layer in a region closer to the separator, thereby improving the permeability of the electrolyte while suppressing a decrease in energy density. The electrode assembly of this embodiment has good electrolyte permeability even when at least a portion of the separator is in a state of being bonded to the positive electrode layer.

[0020] In this embodiment, the average particle size of the graphite particles in the separator-side region of the positive electrode layer can be compared with the average particle size of the graphite particles in the current collector-side region by image analysis. Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope, etc. This cross-sectional image is divided into two regions in the thickness direction. The position of the boundary between the two regions is determined so that the thickness of the region on the separator side is within a range of 0.5 to 1.5 times (for example, 1.0 times) the thickness of the region on the current collector side. Next, the average particle size of the graphite particles in each region is measured and compared. The dimension in the planar direction of the positive electrode layer to be measured is at least 10 mm. The average particle size of graphite particles is the arithmetic mean value of the measured particle sizes of 100 graphite particles randomly selected in the measurement area of ​​the positive electrode layer. The particle size of graphite particles can be determined based on the length of the major axis, the equivalent circle diameter (the diameter of a circle with the same area as the projected image of the particle), etc. To improve measurement accuracy, cross-sectional images in the thickness direction may be obtained at multiple locations (for example, 5 to 10 locations) of the positive electrode layer, and the average particle diameter of the graphite particles may be compared in each cross-sectional image.

[0021] The values ​​of the average particle diameter D1 of the graphite particles in the separator-side region and the average particle diameter D2 of the graphite particles in the current collector-side region are not particularly limited as long as they satisfy the relationship D1 / D2>1. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, D1 / D2 is preferably 1.5 or more, and more preferably 2.0 or more. The upper limit of D1 / D2 is not particularly limited, and may be ∞ (that is, D2 is 0). The positive electrode layer may be such that the separator-side region contains graphite particles as a conductive material, and the current collector-side region contains carbon black as a conductive material.

[0022] <Fourth embodiment> A fourth embodiment of the present disclosure is A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, When the positive electrode layer is divided into three regions in the thickness direction, the number of graphite particles per unit area in the central region is greater than the number of graphite particles per unit area in the region on the current collector side and the number of graphite particles per unit area in the region on the separator side.

[0023] In the electrode assembly of this embodiment, the positive electrode layer contains graphite particles, which form appropriate voids in the positive electrode layer that serve as paths for the electrolyte to move, making it easy for the electrolyte to permeate. On the other hand, increasing the porosity of the positive electrode layer leads to a decrease in the energy density of the battery. In particular, it is desirable for the portion of the positive electrode layer close to the current collector to contain a high density of positive electrode active material. Furthermore, from the viewpoint of minimizing the electrolyte migration path in the thickness direction of the positive electrode layer, it is effective to increase the permeability of the electrolyte near the center of the positive electrode layer. Therefore, in the electrode body of this embodiment, by arranging more graphite particles in the area near the center of the positive electrode layer, the permeability of the electrolyte is improved while suppressing a decrease in energy density. The electrode assembly of this embodiment has good electrolyte permeability even when at least a portion of the separator is in a state of being bonded to the positive electrode layer.

[0024] In this embodiment, the number of graphite particles per unit area in the central region of the positive electrode layer, the number of graphite particles per unit area in the region on the separator side, and the number of graphite particles per unit area in the region on the current collector side can be compared by image analysis. Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope, etc. This cross-sectional image is divided into three regions in the thickness direction. The positions of the boundaries of the three regions are determined so that the thickness of the central region is within a range of 0.5 to 1.5 times (for example, 1.0 times) the thickness of each of the separator-side region and the current collector-side region. Next, the number of graphite particles per unit area in each region is measured and compared in the same manner as in the first embodiment.

[0025] The values ​​of the number of graphite particles per unit area in the central region N0, the number of graphite particles per unit area in the separator-side region N1, and the number of graphite particles per unit area in the current collector-side region N2 are not particularly limited as long as they satisfy the relationships N0 / N1>1 and N0 / N2>1. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, N0 / N1 and N0 / N2 are each preferably 1.5 or more, and more preferably 2.0 or more. The upper limit of N0 / N1 is not particularly limited, and may be ∞ (that is, N1 is 0). The upper limit of N0 / N2 is not particularly limited, and may be ∞ (that is, N2 is 0). The positive electrode layer may have a central region containing graphite particles as a conductive material, and a separator-side region and a current collector-side region containing carbon black as a conductive material.

[0026] Fifth Embodiment A fifth embodiment of the present disclosure is A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, When the positive electrode layer is divided into three regions in the thickness direction, the area ratio of the region corresponding to the graphite particles in the central region is larger than the area ratio of the corresponding region in the region on the current collector side and the area ratio of the region corresponding to the graphite particles in the region on the separator side.

[0027] In the electrode assembly of this embodiment, the positive electrode layer contains graphite particles, which form appropriate voids in the positive electrode layer that serve as paths for the electrolyte to move, making it easy for the electrolyte to permeate. On the other hand, increasing the porosity of the positive electrode layer leads to a decrease in the energy density of the battery. In particular, it is desirable for the portion of the positive electrode layer close to the current collector to contain a high density of positive electrode active material. Furthermore, from the viewpoint of minimizing the electrolyte migration path in the thickness direction of the positive electrode layer, it is effective to increase the permeability of the electrolyte near the center of the positive electrode layer. Therefore, in the electrode body of this embodiment, graphite particles are arranged at a higher density near the center of the positive electrode layer, thereby improving the permeability of the electrolyte while suppressing a decrease in energy density. The electrode assembly of this embodiment has good electrolyte permeability even when at least a portion of the separator is in a state of being bonded to the positive electrode layer.

[0028] In this embodiment, the area ratio of the region corresponding to the graphite particles in the central region of the positive electrode layer, the area ratio of the region corresponding to the graphite particles in the region on the separator side, and the area ratio of the region corresponding to the graphite particles in the region on the current collector side can be compared by image analysis. Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope, etc. This cross-sectional image is divided into three regions in the thickness direction. The positions of the boundaries of the three regions are determined so that the thickness of the central region is within a range of 0.5 to 1.5 times (for example, 1.0 times) the thickness of each of the separator-side region and the current collector-side region. Next, the area ratio of the regions corresponding to graphite particles in each region is measured and compared in the same manner as in the second embodiment.

[0029] The values ​​of the area ratio R0 of the region corresponding to graphite particles in the central region, the area ratio R1 of the region corresponding to graphite particles in the separator-side region, and the area ratio R2 of the region corresponding to graphite particles in the current collector-side region are not particularly limited as long as they satisfy the relationships R0 / R1>1 and R0 / R2>1. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, R0 / R1 and R0 / R2 are each preferably 1.5 or more, and more preferably 2.0 or more. The upper limit of R0 / R1 is not particularly limited, and may be ∞ (that is, R1 is 0). The upper limit of R0 / R2 is not particularly limited, and may be ∞ (i.e., R2 is 0). The positive electrode layer may have a central region containing graphite particles as a conductive material, and a separator-side region and a current collector-side region containing carbon black as a conductive material.

[0030] Sixth Embodiment A sixth embodiment of the present disclosure is A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into three regions in the thickness direction, the average particle diameter of the graphite particles in the central region is larger than the average particle diameter of the graphite particles in the region on the current collector side and the average particle diameter of the graphite particles in the region on the separator side. is.

[0031] In the electrode assembly of this embodiment, the positive electrode layer contains graphite particles, which form appropriate voids in the positive electrode layer that serve as paths for the electrolyte to move, making it easy for the electrolyte to permeate. On the other hand, increasing the porosity of the positive electrode layer leads to a decrease in the energy density of the battery. In particular, it is desirable for the portion of the positive electrode layer close to the current collector to contain a high density of positive electrode active material. Furthermore, from the viewpoint of minimizing the electrolyte migration path in the thickness direction of the positive electrode layer, it is effective to increase the permeability of the electrolyte near the center of the positive electrode layer. Therefore, in the electrode body of this embodiment, larger graphite particles are arranged in the area near the center of the positive electrode layer, thereby improving the permeability of the electrolyte while suppressing a decrease in energy density. The electrode assembly of this embodiment has good electrolyte permeability even when at least a portion of the separator is in a state of being bonded to the positive electrode layer.

[0032] In the present disclosure, the average particle size of the graphite particles in the central region of the positive electrode layer, the average particle size of the graphite particles in the region on the separator side, and the average particle size of the graphite particles in the region on the current collector side can be compared by image analysis. Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope, etc. This cross-sectional image is divided into three regions in the thickness direction. The positions of the boundaries of the three regions are determined so that the thickness of the central region is within a range of 0.5 to 1.5 times (for example, 1.0 times) the thickness of each of the separator-side region and the current collector-side region. Next, the average particle size of the graphite particles in each region is measured and compared in the same manner as in the third embodiment.

[0033] The values ​​of the average particle diameter D0 of the graphite particles in the central region, the average particle diameter D1 of the graphite particles in the separator-side region, and the average particle diameter D2 of the graphite particles in the current collector-side region are not particularly limited as long as they satisfy the relationships D0 / D1>1 and D0 / D2>1. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, D0 / D1 and D0 / D2 are each preferably 1.5 or more, and more preferably 2.0 or more. The upper limit of D0 / D1 is not particularly limited, and may be ∞ (that is, D1 is 0). The upper limit of D0 / D2 is not particularly limited, and may be ∞ (that is, D2 is 0). The positive electrode layer may have a central region containing graphite particles as a conductive material, and a separator-side region and a current collector-side region containing carbon black as a conductive material.

[0034] (Electrode body characteristics) The electrode assembly of the present disclosure corresponds to at least one selected from the first to sixth embodiments described above. In the electrode assembly of the present disclosure, the amount of graphite particles contained in the positive electrode layer is not particularly limited, and can be selected within a range that does not impair the function of the positive electrode layer. From the viewpoint of improving the permeability of the electrolyte while suppressing a decrease in energy density, the amount (g) of graphite particles contained in the positive electrode layer may be within the range of 1% to 10% of the amount (g) of the positive electrode active material particles. The graphite particles can function as a conductive material in the positive electrode layer.

[0035] The thickness of the positive electrode layer is not particularly limited and can be selected from the thicknesses of common positive electrode layers. For example, the thickness of the positive electrode layer can be selected from the range of 10 μm to 200 μm.

[0036] The electrode assembly may include a plurality of positive electrode layers. In this case, some or all of the positive electrode layers may satisfy the conditions of the above-described embodiments.

[0037] The particle size of the graphite particles contained in the positive electrode layer is not particularly limited and can be selected, for example, from the range of 5 μm to 30 μm. The shape of the graphite particles is not particularly limited and may be flaky, spherical, or a secondary particle which is an aggregate of primary particles. When the graphite particles are secondary particles, the particle size mentioned above is the particle size of the secondary particles.

[0038] The type of positive electrode active material particles contained in the positive electrode layer is not particularly limited, and can be selected from those generally used as positive electrode active materials for batteries. The positive electrode active material particles may be of a lithium transition metal composite oxide. Examples of the transition metal include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Among these, a lithium transition metal composite oxide containing at least one selected from Ni, Co, and Mn is preferred, and a lithium transition metal composite oxide (NCM, nickel cobalt manganese oxide) containing Ni, Co, and Mn is more preferred. Specific examples of lithium transition metal composite oxides include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and their composite oxides (LiCo x Ni y Mn z O2, x+y+z=1), and a double oxide containing an additional element M' (LiCo a Ni b Mn c M' d O2, a+b+c+d=1, M': Al, Mg, Ti, Zr or Ge), spinel-type lithium manganese oxide (LiMn2O4), olivine-type LiMPO4 (M: Co, Ni, Mn, Fe), etc. The positive electrode layer may contain one type of positive electrode active material particles or two or more types of particles.

[0039] The particle diameter of the positive electrode active material particles is not particularly limited and can be selected, for example, from the range of 5 μm to 30 μm. The shape of the positive electrode active material particles is not particularly limited and may be flaky, spherical, or a secondary particle which is an aggregate of primary particles. When the positive electrode active material particles are secondary particles, the particle diameter described above is the particle diameter of the secondary particles.

[0040] The positive electrode layer may contain a conductive material other than graphite particles as needed. Specific examples of the conductive material include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.) and carbon nanotubes. The conductive material contained in the positive electrode layer may be one type alone or two or more types.

[0041] The positive electrode layer may contain a binder as needed. Specific examples of binders include polyvinylidene fluoride (PVdF), polyethylene, polypropylene, polyethylene terephthalate, cellulose, nitrocellulose, carboxymethyl cellulose, polyethylene oxide, polyepichlorohydrin, polyacrylonitrile, styrene-butadiene rubber (SBR), acrylonitrile-butadiene rubber (NBR), polyacrylate, polymethacrylate, and polytetrafluoroethylene (PTFE). The binder contained in the positive electrode layer may be one type alone or two or more types.

[0042] (current collector) The type of current collector contained in the electrode assembly of the present disclosure is not particularly limited and can be selected from those commonly used as electrode current collectors. For example, a current collector containing copper may be used as the negative electrode current collector, and a current collector containing aluminum may be used as the positive electrode current collector. The thickness of the current collector can be selected, for example, from the range of 5 μm to 50 μm.

[0043] (Method for producing positive electrode layer) The method for producing the positive electrode layer is not particularly limited and can be selected from known methods. For example, a positive electrode layer may be formed by applying a composition for forming the positive electrode layer to one or both surfaces of a current collector. In this case, two or more composite materials containing different amounts of graphite particles, particle diameters, etc., are prepared, and these composite materials are sequentially applied to the current collector, thereby producing a positive electrode layer that satisfies the requirements of the present disclosure.

[0044] (Example of electrode structure) An example of the configuration of the electrode assembly of the present disclosure is shown in FIGS. The electrode assembly 10 shown in FIG. 1 includes a current collector 11, a positive electrode layer 12, and a separator 13 in this order. The positive electrode layer 12 is divided in the thickness direction into a region 12a on the separator 13 side and a region 12b on the current collector 11 side. The region 12a and the region 12b may or may not be separated by a clear boundary. When the positive electrode layer 12 is made up of multiple layers with different compositions, the boundary between these layers may or may not coincide with the boundary between the region 12a and the region 12b. The electrode assembly 10 may further include a negative electrode layer and a current collector (not shown) disposed on the surface of the separator 13 opposite the positive electrode layer 12.

[0045] The electrode assembly 20 shown in FIG. 2 includes a current collector 21, a positive electrode layer 22, and a separator 23 in this order. The positive electrode layer 22 is divided in the thickness direction into a region 22a on the separator 23 side, a central region 22b, and a region 22c on the current collector 21 side. The regions 22a, 22b, and 22c may or may not be separated by clear boundaries. When the positive electrode layer 22 is made up of a plurality of layers with different compositions, the boundaries between these layers may or may not coincide with the boundaries between the region 22a, the region 22b, and the region 22c. The electrode assembly 20 may further include a negative electrode layer and a current collector (not shown) disposed on the surface of the separator 23 opposite the positive electrode layer 22.

[0046] Seventh Embodiment A seventh embodiment of the present disclosure is a battery including the electrode assembly of the present disclosure described above. The battery of this embodiment includes, for example, an electrode assembly, an exterior housing that houses the electrode assembly, and an electrolyte. Specific examples of the battery include secondary batteries such as lithium ion secondary batteries, sodium ion secondary batteries, and potassium ion secondary batteries.

[0047] (exterior body) The type of exterior body that houses the electrode assembly is not particularly limited and can be selected depending on the type of battery. In some embodiments, a sheet-like outer covering may be used. The sheet-like outer casing may include a metal-containing one. Specifically, a laminate (a so-called laminate film) having a metal layer containing a metal such as aluminum and a heat-seal layer containing a resin that melts when heated may be used. That is, the battery of the present disclosure may be a battery that uses a laminate film as an outer casing (a so-called laminate battery).

[0048] The exterior body may be made of one member or two or more members. For example, if the exterior body is a sheet-like material, the exterior body may be made of one sheet-like material or two sheet-like materials. If necessary, the sheet-like outer casing may be embossed to form recesses for accommodating the electrode assembly.

[0049] Examples of methods for housing the electrode assembly in a sheet-like exterior body include the following methods 1 and 2. Method 1: A method in which the electrode body is placed between one exterior body folded in half or between two overlapping exterior bodies, and then the exterior body around the electrode body is joined. Method 2: The electrode assembly is placed in a bag made by joining the periphery of one outer casing folded in half or two overlapping outer casings.

[0050] (electrolyte) The type of electrolyte is not particularly limited and can be selected depending on the type of battery. As the electrolytic solution, for example, a solution in which an electrolyte such as LiPF6 is dissolved in a non-aqueous solvent can be used.

[0051] The battery of the present disclosure may be installed in an electric vehicle. An example in which the battery of the present disclosure is applied to an electric vehicle will be described below with reference to the drawings. In the following description, "battery cell 20" corresponds to the battery of the present disclosure.

[0052] Fig. 3 is a schematic plan view showing a main part of a vehicle 100 to which a battery pack 10 according to an embodiment is applied. As shown in Fig. 3, the vehicle 100 is a battery electric vehicle (BEV) with the battery pack 10 mounted under the floor. Note that the arrows UP, FR, and LH in each figure indicate the upper side in the vehicle vertical direction, the front side in the vehicle longitudinal direction, and the left side in the vehicle width direction, respectively. When describing using the front-rear, left-right, up-down directions, these directions refer to the front and rear in the vehicle longitudinal direction, the left and right in the vehicle width direction, and the up-down in the vehicle vertical direction, unless otherwise specified.

[0053] In the vehicle 100 of this embodiment, for example, a DC / DC converter 102, an electric compressor 104, and a PTC (Positive Temperature Coefficient) heater 106 are arranged on the vehicle front side of the battery pack 10. In addition, a motor 108, a gearbox 110, an inverter 112, and a charger 114 are arranged on the vehicle rear side of the battery pack 10.

[0054] The DC current output from the battery pack 10 has its voltage adjusted by a DC / DC converter 102 and is then supplied to an electric compressor 104, a PTC heater 106, an inverter 112, etc. Furthermore, power is supplied to a motor 108 via the inverter 112, causing the rear wheels to rotate and causing the vehicle 100 to travel.

[0055] A charging port 116 is provided on the right side at the rear of the vehicle 100, and by connecting a charging plug of an external charging facility (not shown) to the charging port 116, power can be stored in the battery pack 10 via the on-board charger 114.

[0056] The arrangement and structure of each component constituting vehicle 100 are not limited to the above-described configuration. For example, the present invention may be applied to a hybrid vehicle (HV) or a plug-in hybrid electric vehicle (PHEV) equipped with an engine. In addition, in this embodiment, the vehicle is a rear-wheel drive vehicle in which motor 108 is mounted at the rear of the vehicle, but the present invention is not limited to this. The vehicle may be a front-wheel drive vehicle in which motor 108 is mounted at the front of the vehicle, or a pair of motors 108 may be mounted at the front and rear of the vehicle. Furthermore, the vehicle may be equipped with an in-wheel motor on each wheel.

[0057] The battery pack 10 is configured to include a plurality of battery modules 11. In this embodiment, as an example, ten battery modules 11 are provided. Specifically, five battery modules 11 are arranged on the right side of the vehicle 100 in the longitudinal direction of the vehicle, and five battery modules 11 are arranged on the left side of the vehicle 100 in the longitudinal direction of the vehicle. The battery modules 11 are electrically connected to each other.

[0058] Fig. 4 is a schematic perspective view of the battery module 11. As shown in Fig. 4, the battery module 11 is formed in a substantially rectangular parallelepiped shape with the vehicle width direction as the longitudinal direction. The outer shell of the battery module 11 is formed from an aluminum alloy. For example, the outer shell of the battery module 11 is formed by joining aluminum die-casting to both ends of an extruded aluminum alloy material by laser welding or the like.

[0059] A pair of voltage terminals 12 and a connector 14 are provided at each end of the battery module 11 in the vehicle width direction. A flexible printed circuit board 21, which will be described later, is connected to the connector 14. In addition, bus bars (not shown) are welded to each end of the battery module 11 in the vehicle width direction.

[0060] The length MW of the battery module 11 in the vehicle width direction is, for example, 350 mm to 600 mm, the length ML in the vehicle front-rear direction is, for example, 150 mm to 250 mm, and the height MH in the vehicle up-down direction is, for example, 80 mm to 110 mm.

[0061] Fig. 5 is a plan view of the battery module 11 with the top cover removed. As shown in Fig. 5, a plurality of battery cells 20 are housed in an array inside the battery module 11. In this embodiment, as an example, 24 battery cells 20 are arranged in the front-rear direction of the vehicle and bonded to one another.

[0062] A flexible printed circuit (FPC) 21 is disposed on top of the battery cells 20. The flexible printed circuit 21 is formed in a strip shape with its longitudinal direction aligned with the vehicle width direction, and a thermistor 23 is provided at each end of the flexible printed circuit 21. The thermistor 23 is not bonded to the battery cells 20, but is pressed toward the battery cells 20 by the upper lid of the battery module 11.

[0063] One or more cushioning materials (not shown) are housed inside the battery module 11. For example, the cushioning materials are elastically deformable thin plate-like members, and are arranged between adjacent battery cells 20 with the arrangement direction of the battery cells 20 as the thickness direction. In this embodiment, as an example, cushioning materials are arranged at both ends of the battery module 11 in the longitudinal direction and in the center portion in the longitudinal direction.

[0064] Fig. 6 is a schematic diagram of a battery cell 20 housed in a battery module 11 as viewed from the thickness direction. As shown in Fig. 6, the battery cell 20 is formed in a substantially rectangular plate shape and houses an electrode body (not shown) inside. The electrode body is configured by laminating a positive electrode, a negative electrode, and a separator, and is sealed with a laminate film 22.

[0065] In this embodiment, as an example, the housing portion for the electrode body is formed by folding and pasting an embossed sheet-like laminate film 22. Note that although both a single-cup embossed structure in which embossing is performed in one place and a double-cup embossed structure in which embossing is performed in two places can be employed, the present embodiment employs a single-cup embossed structure with a drawing depth of approximately 8 mm to 10 mm.

[0066] The upper ends of both longitudinal ends of the battery cells 20 are bent to form corners. The upper end of the battery cells 20 is also bent, and a fixing tape 24 is wrapped around the upper end of the battery cells 20 along the longitudinal direction.

[0067] Terminals (tabs) 26 are provided at both longitudinal ends of the battery cell 20. In this embodiment, as an example, the terminals 26 are provided at positions offset downward from the center of the battery cell 20 in the up-down direction. The terminals 26 are joined to a bus bar (not shown) by laser welding or the like.

[0068] The length CW1 of the battery cell 20 in the vehicle width direction is, for example, 530 mm to 600 mm, 600 mm to 700 mm, 700 mm to 800 mm, 800 mm to 900 mm, or 1000 mm or more. The length CW2 of the region housing the electrode assembly is, for example, 500 mm to 520 mm, 600 mm to 700 mm, 700 mm to 800 mm, 800 mm to 900 mm, or 1000 mm or more. The height CH of the battery cell 20 is, for example, 80 mm to 110 mm, or 110 mm to 140 mm. The thickness of the battery cell 20 is 5.0 mm to 7.0 mm, 7.0 mm to 9.0 mm, or 9.0 mm to 11.0 mm. The height TH of the terminal 26 is 40 mm to 50 mm, 50 mm to 60 mm, or 60 mm to 70 mm. [Explanation of symbols]

[0069] 10, 20: Electrode body 11, 21: Current collector 12, 22: Positive electrode layer 13, 23: Separator

Claims

1. A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body for a secondary battery, wherein, when the positive electrode layer is divided into two regions in the thickness direction, the value of N1 / N2, obtained by dividing the number of graphite particles per unit area in the separator-side region by N1 and the number of graphite particles per unit area in the current collector-side region by N2, is 2.0 or more.

2. A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body for a secondary battery, wherein, when the positive electrode layer is divided into two regions in the thickness direction, the value of R1 / R2, obtained by dividing the area ratio of the region corresponding to graphite particles in the separator side region by R1 and the area ratio of the region corresponding to graphite particles in the current collector side by R2, is 2.0 or more.

3. A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into two regions in the thickness direction, the average particle diameter of the graphite particles contained in the region on the separator side is larger than the average particle diameter of the graphite particles contained in the region on the current collector side.

4. A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into three regions in the thickness direction, the number of graphite particles per unit area in the central region is greater than the number of graphite particles per unit area in the current collector side region and the number of graphite particles per unit area in the separator side region.

5. A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into three regions in the thickness direction, the area ratio of the region corresponding to the graphite particles in the central region is larger than the area ratio of the corresponding region in the region on the current collector side and the area ratio of the region corresponding to the graphite particles in the region on the separator side.

6. A current collector, a positive electrode layer, and a separator are included in this order, the positive electrode layer includes positive electrode active material particles and graphite particles, an electrode body, wherein, when the positive electrode layer is divided into three regions in a thickness direction, the average particle diameter of the graphite particles in the central region is larger than the average particle diameter of the graphite particles in the current collector side region and the average particle diameter of the graphite particles in the separator side region.

7. 7. The electrode assembly according to claim 1, wherein at least a portion of the separator is in a state of being adhered to the positive electrode layer.

8. A battery comprising the electrode assembly according to any one of claims 1 to 6.

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