Electrode body and battery

Abstract

Provided are an electrode body including a positive electrode having improved electrolyte permeability, and a battery including the electrode body. An electrode body includes a current collector, a positive electrode layer, and a separator in this order, the positive electrode layer including positive electrode active material particles and graphite particles, and when the positive electrode layer is divided into two regions in the thickness direction, the number of graphite particles per unit area in the separator-side region is greater than the number of graphite particles per unit area in the current collector-side region.

Description

Technical Field

[0001] The present disclosure relates to an electrode body and a battery. Background Art

[0002] Lithium-ion secondary batteries are generally manufactured by injecting an electrolyte into an outer body, which contains an electrode body including an electrode and a separator. In order to increase the electrode density, the electrode body is subjected to a process such as high-pressure pressing and bonding the electrode and the separator with an adhesive. Due to this treatment, it becomes difficult for the electrolyte to penetrate into the electrode body, and improving the efficiency of the injection operation has become a problem.

[0003] As a method for improving the permeability of the electrolyte solution into the electrode body, for example, Japanese Patent Application Laid-Open No. 2002-15773 proposes providing a portion where the electrode and the separator are not bonded when bonding the electrode and the separator constituting the electrode body.

[0004] The method described in Japanese Patent Application Laid-Open No. 2002-15773 requires a step of providing a portion where the electrode and the separator are not bonded together in order to improve the permeability of the electrolyte, and thus there is room for improvement in terms of working efficiency.

[0005] In addition, the positive electrode tends to have lower permeability to the electrolyte than the negative electrode. Therefore, if the positive electrode and the separator are bonded, the movement speed of the electrolyte in the surface direction of the boundary between the positive electrode and the separator decreases, which tends to impair the permeability. Summary of the invention

[0006] In view of the above circumstances, an object of one embodiment of the present disclosure is to provide an electrode body including a positive electrode having improved electrolyte permeability, and a battery including the electrode body.

[0007] Means for solving the above-mentioned problems include the following embodiments.

[0008] <1> An electrode body comprises a current collector, a positive electrode layer and a separator in sequence,

[0009] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0010] When the positive electrode layer is divided into two regions in the thickness direction, the number of graphite particles per unit area in the separator side region is larger than the number of graphite particles per unit area in the collector side region.

[0011] <2> An electrode body comprises a current collector, a positive electrode layer and a separator in sequence,

[0012] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0013] 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 separator side region is larger than the area ratio of the region corresponding to the graphite particles in the collector side region.

[0014] <3> An electrode body comprises a current collector, a positive electrode layer and a separator in sequence,

[0015] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0016] When the positive electrode layer is divided into two regions in the thickness direction, the average particle size of graphite particles contained in the separator side region is larger than the average particle size of graphite particles contained in the collector side region.

[0017] <4> An electrode body comprises a current collector, a positive electrode layer and a separator in sequence,

[0018] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0019] 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 collector side region and greater than the number of graphite particles per unit area in the separator side region.

[0020] <5> An electrode body comprises a current collector, a positive electrode layer and a separator in sequence,

[0021] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0022] 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 greater than the area ratio of the region corresponding to the graphite particles in the collector side region, and is greater than the area ratio of the region corresponding to the graphite particles in the separator side region.

[0023] <6> An electrode body comprises a current collector, a positive electrode layer and a separator in sequence,

[0024] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0025] When the positive electrode layer is divided into three regions in the thickness direction, the average particle size of graphite particles in the central region is larger than that in the collector side region and larger than that in the separator side region.

[0026] <7> according to <1> ~ <6> In the electrode assembly described in any one of the above, at least a portion of the separator is bonded to the positive electrode layer.

[0027] <8> A battery comprising <1> ~ <6> The electrode body described in any one of the above.

[0028] According to the present disclosure, there are provided an electrode body including a positive electrode having improved electrolyte permeability, and a battery including the electrode body. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a cross-sectional view schematically showing an example of the structure of an electrode body.

[0030] Figure 2 This is a cross-sectional view schematically showing an example of the structure of an electrode body.

[0031] Figure 3 This is a diagram schematically showing an example of application of a battery in an electric vehicle.

[0032] Figure 4 This is a diagram schematically showing an example of the structure of a battery module.

[0033] Figure 5 This is a diagram schematically showing an example of the structure of a battery module.

[0034] Figure 6 This is a diagram schematically showing an example of the structure of a battery cell included in a battery module. DETAILED DESCRIPTION

[0035] In the present disclosure, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the minimum value and the maximum value, respectively.

[0036] In the numerical ranges recorded in stages in the present disclosure, the upper limit or lower limit recorded in a certain numerical range may also be replaced by the upper limit or lower limit of another numerical range recorded in stages. In the numerical ranges recorded in the present disclosure, the upper limit or lower limit recorded in a certain numerical range may also be replaced by the value shown in the embodiments.

[0037] 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 can be achieved.

[0038] In the present disclosure, when an embodiment is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the sizes of components in each figure are conceptual, and the relative relationship between the sizes of the components is not limited to this.

[0039] <First Embodiment>

[0040] A first embodiment of the present disclosure is an electrode body including a current collector, a positive electrode layer, and a separator in this order.

[0041] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0042] When the positive electrode layer is divided into two regions in the thickness direction, the number of graphite particles per unit area in the separator side region is larger than the number of graphite particles per unit area in the collector side region.

[0043] In the electrode body of the present embodiment, the positive electrode layer contains graphite particles, thereby forming appropriate gaps that serve as electrolyte movement paths in the positive electrode layer, thereby achieving a state in which the electrolyte can easily permeate.

[0044] On the other hand, if the voids in the positive electrode layer are increased, the energy density of the battery will decrease. In particular, it is desirable that the positive electrode active material is contained at a high density in the portion of the positive electrode layer close to the current collector.

[0045] Therefore, in the electrode body of the present embodiment, more graphite particles are arranged in the portion of the positive electrode layer close to the separator, thereby improving the permeability of the electrolyte and suppressing a decrease in energy density.

[0046] The electrode assembly of the present embodiment has good permeability of the electrolyte even in a state where at least a portion of the separator is bonded to the positive electrode layer.

[0047] In the present embodiment, the number of graphite particles per unit area in the separator-side region of the positive electrode layer and the number of graphite particles per unit area in the collector-side region can be compared by image analysis.

[0048] Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope or the like. The cross-sectional image is divided into two regions in the thickness direction.

[0049] The boundary position between the two regions is determined, for example, so that the thickness of the separator-side region is within a range of 0.5 to 1.5 times (eg, 1.0 times) the thickness of the collector-side region.

[0050] Next, the number of graphite particles per unit area in each region was measured and compared. The dimension of the positive electrode layer to be measured in the surface direction was at least 10 mm.

[0051] From the viewpoint of improving the measurement accuracy, cross-sectional images in the thickness direction may be obtained at a plurality of locations (eg, 5 to 10 locations) of the positive electrode layer, and the number of graphite particles per unit area may be compared in each cross-sectional image.

[0052] The values ​​of 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 collector side region are not particularly limited as long as the relationship N1 / N2>1 is satisfied.

[0053] From the viewpoint of suppressing a decrease in energy density and improving the permeability of the electrolyte, N1 / N2 is preferably 1.5 or more, and more preferably 2.0 or more.

[0054] The upper limit value of N1 / N2 is not particularly limited and may be ∞ (ie, N2 is 0).

[0055] The positive electrode layer may contain graphite particles as a conductive material in the separator side region and carbon black as a conductive material in the collector side region.

[0056] <Second Embodiment>

[0057] A second embodiment of the present disclosure is an electrode body including a current collector, a positive electrode layer, and a separator in this order.

[0058] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0059] 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 separator side region is larger than the area ratio of the region corresponding to the graphite particles in the collector side region.

[0060] In the electrode body of the present embodiment, the positive electrode layer contains graphite particles, thereby forming appropriate gaps that serve as electrolyte movement paths in the positive electrode layer, thereby achieving a state in which the electrolyte can easily permeate.

[0061] On the other hand, if the voids in the positive electrode layer increase, the energy density of the battery decreases. It is particularly desirable that the positive electrode active material is contained at a high density in the portion of the positive electrode layer close to the current collector.

[0062] Therefore, in the electrode body of the present embodiment, graphite particles are arranged at a higher density in the portion of the positive electrode layer close to the separator, thereby improving the permeability of the electrolyte and suppressing a decrease in energy density.

[0063] The electrode assembly of the present embodiment has good permeability of the electrolyte even in a state where at least a portion of the separator is bonded to the positive electrode layer.

[0064] In the present embodiment, the comparison between 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 collector side region can be performed by image analysis.

[0065] Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope or the like. The cross-sectional image is divided into two regions in the thickness direction.

[0066] The boundary position between the two regions is determined, for example, so that the thickness of the separator-side region is within a range of 0.5 to 1.5 times (eg, 1.0 times) the thickness of the collector-side region.

[0067] 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 surface direction is at least 10 mm.

[0068] The area ratio of the region corresponding to the graphite particles is obtained by dividing the region corresponding to the graphite particles in the measurement region of the positive electrode layer by the area of ​​the measurement object region (i.e., the total area of ​​the region corresponding to the graphite particles and the region not corresponding to the graphite particles). When determining the region corresponding to the graphite particles, image processing such as binarization can also be performed.

[0069] From the viewpoint of improving measurement accuracy, cross-sectional images in the thickness direction may be obtained at a plurality of locations (eg, 5 to 10 locations) of the positive electrode layer, and the area ratios of regions corresponding to graphite particles may be compared in each cross-sectional image.

[0070] The values ​​of the area ratio R1 of the region corresponding to the graphite particles in the separator side region and the area ratio R2 of the region corresponding to the graphite particles in the collector side region are not particularly limited as long as the relationship R1 / R2>1 is satisfied.

[0071] From the viewpoint of suppressing a decrease in energy density and improving the permeability of the electrolyte, R1 / R2 is preferably 1.5 or more, and more preferably 2.0 or more.

[0072] The upper limit of R1 / R2 is not particularly limited and may be ∞ (ie, R2 is 0).

[0073] The positive electrode layer may contain graphite particles as a conductive material in the separator side region and carbon black as a conductive material in the collector side region.

[0074] <Third Embodiment>

[0075] A third embodiment of the present disclosure is an electrode body including a current collector, a positive electrode layer, and a separator in this order.

[0076] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0077] When the positive electrode layer is divided into two regions in the thickness direction, the average particle size of graphite particles contained in the separator side region is larger than the average particle size of graphite particles contained in the collector side region.

[0078] In the electrode body of the present embodiment, the positive electrode layer contains graphite particles, thereby forming appropriate gaps that serve as electrolyte movement paths in the positive electrode layer, thereby achieving a state in which the electrolyte can easily permeate.

[0079] On the other hand, if the voids in the positive electrode layer are increased, the energy density of the battery will decrease. In particular, it is desirable that the positive electrode active material is contained at a high density in the portion of the positive electrode layer close to the current collector.

[0080] Therefore, in the electrode body of the present embodiment, by arranging larger graphite particles in the portion of the positive electrode layer close to the separator, the permeability of the electrolyte is improved while suppressing a decrease in energy density.

[0081] The electrode assembly of the present embodiment has good permeability of the electrolyte even in a state where at least a portion of the separator is bonded to the positive electrode layer.

[0082] In the present embodiment, the average particle size of the graphite particles in the separator-side region of the positive electrode layer and the average particle size of the graphite particles in the collector-side region can be compared by image analysis.

[0083] Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope or the like. The cross-sectional image is divided into two regions in the thickness direction.

[0084] The boundary position between the two regions is determined, for example, so that the thickness of the separator-side region is within a range of 0.5 to 1.5 times (eg, 1.0 times) the thickness of the collector-side region.

[0085] Next, the average particle size of the graphite particles in each region was measured and compared. The dimension of the positive electrode layer to be measured in the surface direction was at least 10 mm.

[0086] The average particle size of the graphite particles is the arithmetic mean of the measured values ​​of the particle sizes of 100 graphite particles randomly selected in the measurement target area of ​​the positive electrode layer. The particle size of the graphite particles can be determined based on the length of the major axis, the equivalent circle diameter (the diameter of a circle having an area equal to the projection image of the particle), etc.

[0087] From the viewpoint of improving the measurement accuracy, cross-sectional images in the thickness direction may be obtained at a plurality of locations (eg, 5 to 10 locations) of the positive electrode layer, and the average particle diameters of the graphite particles may be compared in the respective cross-sectional images.

[0088] The values ​​of the average particle size D1 of the graphite particles in the separator side region and the average particle size D2 of the graphite particles in the current collector side region are not particularly limited as long as the relationship D1 / D2>1 is satisfied.

[0089] From the viewpoint of suppressing a decrease in energy density and improving the permeability of the electrolyte, D1 / D2 is preferably 1.5 or more, and more preferably 2.0 or more.

[0090] The upper limit of D1 / D2 is not particularly limited and may be ∞ (ie, D2 is 0).

[0091] The positive electrode layer may contain graphite particles as a conductive material in the separator side region and carbon black as a conductive material in the collector side region.

[0092] <Fourth Implementation Method>

[0093] A fourth embodiment of the present disclosure is an electrode body including a current collector, a positive electrode layer, and a separator in this order.

[0094] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0095] 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 collector side region and greater than the number of graphite particles per unit area in the separator side region.

[0096] In the electrode body of the present embodiment, the positive electrode layer contains graphite particles, thereby forming appropriate gaps that serve as electrolyte movement paths in the positive electrode layer, thereby achieving a state in which the electrolyte can easily permeate.

[0097] On the other hand, if the voids in the positive electrode layer are increased, the energy density of the battery is reduced. In particular, it is desirable that the portion of the positive electrode layer close to the current collector contains the positive electrode active material at a high density. In addition, from the viewpoint of minimizing the moving path of the electrolyte 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.

[0098] Therefore, in the electrode body of the present embodiment, more graphite particles are arranged in the vicinity of the center of the positive electrode layer, thereby improving the permeability of the electrolyte and suppressing a decrease in energy density.

[0099] The electrode assembly of the present embodiment has good permeability of the electrolyte even in a state where at least a portion of the separator is bonded to the positive electrode layer.

[0100] 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 separator side region, and the number of graphite particles per unit area in the collector side region can be compared by image analysis.

[0101] Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope or the like. The cross-sectional image is divided into three regions in the thickness direction.

[0102] The boundary positions of the three regions are determined, for example, so that the thickness of the central region is within a range of 0.5 to 1.5 times (eg, 1.0 times) the thickness of each of the separator side region and the collector side region.

[0103] Next, the number of graphite particles per unit area in each region is measured and compared in the same manner as the method described in the first embodiment.

[0104] There is no particular restriction on the values ​​of the number N0 of graphite particles per unit area in the central region, the number N1 of graphite particles per unit area in the diaphragm side region, and the number N2 of graphite particles per unit area in the collector side region as long as the relationship N0 / N1>1 and N0 / N2>1 is satisfied.

[0105] From the viewpoint of suppressing a decrease in energy density and improving the permeability of the electrolyte, N0 / N1 and N0 / N2 are preferably 1.5 or more, more preferably 2.0 or more, respectively.

[0106] The upper limit value of N0 / N1 is not particularly limited and may be ∞ (ie, N1 is 0).

[0107] The upper limit value of N0 / N2 is not particularly limited and may be ∞ (ie, N2 is 0).

[0108] The positive electrode layer may contain graphite particles as a conductive material in the central region, and carbon black as a conductive material in the separator side region and the collector side region.

[0109] <Fifth Implementation Method>

[0110] A fifth embodiment of the present disclosure is an electrode body including a current collector, a positive electrode layer, and a separator in this order.

[0111] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0112] 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 greater than the area ratio of the region corresponding to the graphite particles in the collector side region, and is greater than the area ratio of the region corresponding to the graphite particles in the separator side region.

[0113] In the electrode body of the present embodiment, the positive electrode layer contains graphite particles, thereby forming appropriate gaps that serve as electrolyte movement paths in the positive electrode layer, thereby achieving a state in which the electrolyte can easily permeate.

[0114] On the other hand, if the voids in the positive electrode layer are increased, the energy density of the battery is reduced. In particular, it is desirable that the portion of the positive electrode layer close to the current collector contains the positive electrode active material at a high density. In addition, from the viewpoint of minimizing the moving path of the electrolyte 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.

[0115] Therefore, in the electrode body of the present embodiment, by arranging the graphite particles at a higher density in the vicinity of the center of the positive electrode layer, the permeability of the electrolyte is improved and the decrease in energy density is suppressed.

[0116] The electrode assembly of the present embodiment has good permeability of the electrolyte even in a state where at least a portion of the separator is bonded to the positive electrode layer.

[0117] In this embodiment, comparison of the area ratio of the region corresponding to graphite particles in the central region of the positive electrode layer, the area ratio of the region corresponding to graphite particles in the separator side region, and the area ratio of the region corresponding to graphite particles in the collector side region can be performed by image analysis.

[0118] Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope or the like. The cross-sectional image is divided into three regions in the thickness direction.

[0119] The boundary positions of the three regions are determined, for example, so that the thickness of the central region is within a range of 0.5 to 1.5 times (eg, 1.0 times) the thickness of each of the separator side region and the collector side region.

[0120] Next, the area ratio of the region corresponding to the graphite particles in each region is measured and compared in the same manner as the method described in the second embodiment.

[0121] The values ​​of the area ratio R0 of the area equivalent to the graphite particles in the central area, the area ratio R1 of the area equivalent to the graphite particles in the diaphragm side area, and the area ratio R2 of the area equivalent to the graphite particles in the collector side area are not particularly limited as long as the relationship R0 / R1>1 and R0 / R2>1 is satisfied.

[0122] From the viewpoint of suppressing a decrease in energy density and improving the permeability of the electrolyte, R0 / R1 and R0 / R2 are each preferably 1.5 or more, and more preferably 2.0 or more.

[0123] The upper limit of R0 / R1 is not particularly limited and may be ∞ (ie, R1 is 0).

[0124] The upper limit of R0 / R2 is not particularly limited and may be ∞ (ie, R2 is 0).

[0125] The positive electrode layer may contain graphite particles as a conductive material in the central region, and carbon black as a conductive material in the separator side region and the collector side region.

[0126] <Sixth Implementation Method>

[0127] A sixth embodiment of the present disclosure is an electrode body including a current collector, a positive electrode layer, and a separator in this order.

[0128] The positive electrode layer includes positive electrode active material particles and graphite particles.

[0129] When the positive electrode layer is divided into three regions in the thickness direction, the average particle size of graphite particles in the central region is larger than that in the collector side region and larger than that in the separator side region.

[0130] In the electrode body of the present embodiment, the positive electrode layer contains graphite particles, thereby forming appropriate gaps that serve as electrolyte movement paths in the positive electrode layer, thereby achieving a state in which the electrolyte can easily permeate.

[0131] On the other hand, if the voids in the positive electrode layer are increased, the energy density of the battery is reduced. In particular, it is desirable that the portion of the positive electrode layer close to the current collector contains the positive electrode active material at a high density. In addition, from the viewpoint of minimizing the moving path of the electrolyte 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.

[0132] Therefore, in the electrode body of the present embodiment, by arranging larger graphite particles in the vicinity of the center of the positive electrode layer, the permeability of the electrolyte is improved and a decrease in energy density is suppressed.

[0133] The electrode assembly of the present embodiment has good permeability of the electrolyte even in a state where at least a portion of the separator is bonded to the positive electrode layer.

[0134] In the present disclosure, the average particle size of graphite particles in the central region of the positive electrode layer, the average particle size of graphite particles in the separator side region, and the average particle size of graphite particles in the collector side region can be compared by image analysis.

[0135] Specifically, a cross-sectional image of the positive electrode layer in the thickness direction is obtained using a scanning electron microscope or the like. The cross-sectional image is divided into three regions in the thickness direction.

[0136] The boundary positions of the three regions are determined, for example, so that the thickness of the central region is within a range of 0.5 to 1.5 times (eg, 1.0 times) the thickness of each of the separator side region and the collector side region.

[0137] Next, the average particle size of the graphite particles in each region is measured and compared in the same manner as the method described in the third embodiment.

[0138] The average particle size D0 of the graphite particles in the central region, the average particle size D1 of the graphite particles in the separator side region, and the average particle size D2 of the graphite particles in the collector side region are not particularly limited as long as the relationship D0 / D1>1 and D0 / D2>1 are satisfied.

[0139] From the viewpoint of suppressing a decrease in energy density and improving the permeability of the electrolyte, D0 / D1 and D0 / D2 are each preferably 1.5 or more, and more preferably 2.0 or more.

[0140] The upper limit of D0 / D1 is not particularly limited and may be ∞ (ie, D1 is 0).

[0141] The upper limit of D0 / D2 is not particularly limited and may be ∞ (ie, D2 is 0).

[0142] The positive electrode layer may contain graphite particles as a conductive material in the central region, and carbon black as a conductive material in the separator side region and the collector side region.

[0143] (Various characteristics of electrode body)

[0144] The electrode body of the present disclosure corresponds to at least one selected from the above-mentioned first embodiment to sixth embodiment.

[0145] In the electrode body 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.

[0146] From the viewpoint of suppressing a decrease in energy density and improving electrolyte permeability, the amount (g) of graphite particles contained in the positive electrode layer may be in the range of 1% to 10% of the amount (g) of the positive electrode active material particles.

[0147] The graphite particles can function as a conductive material in the positive electrode layer.

[0148] The thickness of the positive electrode layer is not particularly limited and can be selected from common thicknesses of positive electrode layers.

[0149] For example, the thickness of the positive electrode layer can be selected from the range of 10 μm to 200 μm.

[0150] The electrode body may include a plurality of positive electrode layers. In this case, some of the plurality of positive electrode layers may satisfy the conditions of the above-mentioned embodiments, or all of the positive electrode layers may satisfy the conditions of the above-mentioned embodiments.

[0151] The particle size of the graphite particles contained in the positive electrode layer is not particularly limited, and can be selected from a range of 5 μm to 30 μm, for example. The shape of the graphite particles is not particularly limited, and can also be flaky, spherical, or secondary particles that are aggregates of primary particles. When the graphite particles are secondary particles, the above particle size is the particle size of the secondary particles.

[0152] 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.

[0153] As the type of positive electrode active material particles, composite oxides composed of lithium and transition metals and other metals that may be optionally contained (hereinafter also referred to as lithium transition metal composite oxides) can be cited. As transition metals and other metals, Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, W, etc. can be cited. Among them, lithium transition metal composite oxides containing at least one selected from Ni, Co and Mn are preferred, and lithium transition metal composite oxides (NCM, nickel cobalt manganese oxides) containing Ni, Co and Mn are more preferred.

[0154] Specific examples of lithium transition metal composite oxides include lithium cobalt oxide (LiCoO2), lithium nickel oxide (LiNiO2), lithium manganese oxide (LiMnO2), and composite oxides thereof (LiCo x Ni y Mn z O2, x+y+z=1), a composite oxide containing an additive element M' (LiCo a Ni b Mn c M' d O2, a+b+c+d=1, M': Al, Mg, Ti, Zr or Ge), spinel lithium manganese oxide (LiMn2O4), olivine LiMPO4 (M: Co, Ni, Mn, Fe), etc.

[0155] The positive electrode active material particles contained in the positive electrode layer may be a single type or two or more types.

[0156] The particle size of the positive electrode active material particles is not particularly limited, and can be selected from a range of 5 μm to 30 μm, for example. The shape of the positive electrode active material particles is not particularly limited, and can also be flaky, spherical, or secondary particles that are aggregates of primary particles. When the positive electrode active material particles are secondary particles, the above particle size is the particle size of the secondary particles.

[0157] The positive electrode layer may contain a conductive material other than graphite particles as necessary.

[0158] Specific examples of the conductive material include carbon materials such as carbon black (acetylene black, thermal black, furnace black, etc.) and carbon nanotubes.

[0159] The conductive material contained in the positive electrode layer may be a single type or two or more types.

[0160] The positive electrode layer may contain a binder as necessary.

[0161] Specific examples of the binder 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, polytetrafluoroethylene (PTFE), and the like.

[0162] The binder contained in the positive electrode layer may be a single type or two or more types.

[0163] (Current Collector)

[0164] The type of current collector contained in the electrode body of the present disclosure is not particularly limited and can be selected from current collectors commonly used as current collectors for electrodes. For example, a current collector containing copper can be used as a negative electrode current collector, and a current collector containing aluminum can be used as a positive electrode current collector.

[0165] The thickness of the current collector can be selected from the range of 5 μm to 50 μm, for example.

[0166] (Method for producing positive electrode layer)

[0167] The method for producing the positive electrode layer is not particularly limited and can be selected from known methods.

[0168] For example, the positive electrode layer can also be formed by applying a composition for forming a positive electrode layer on one or both sides of the collector. At this time, by preparing a mixture of more than two kinds of graphite particles, such as the amount and particle size contained in the composition, and applying them to the collector in sequence, a positive electrode layer satisfying the conditions of the present disclosure can be made.

[0169] (Example of Configuration of Electrode Body)

[0170] An example of the structure of the electrode body disclosed in the present invention is shown in Figure 1 and Figure 2 .

[0171] Figure 1 The electrode body 10 shown includes a current collector 11 , a positive electrode layer 12 , and a separator 13 in this order.

[0172] 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 divided by a clear boundary.

[0173] When the positive electrode layer 12 is composed of a plurality of layers having different compositions, the boundary between them may or may not coincide with the boundary between the region 12 a and the region 12 b .

[0174] The electrode body 10 may further include a negative electrode layer and a current collector (not shown) disposed on the surface of the separator 13 opposite to the positive electrode layer 12 .

[0175] Figure 2 The electrode body 20 shown includes a current collector 21 , a positive electrode layer 22 , and a separator 23 in this order.

[0176] 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 collector 21 side. The regions 22a, 22b, and 22c may or may not be divided by clear boundaries.

[0177] When the positive electrode layer 22 is composed of a plurality of layers having different compositions, the boundaries between them may or may not coincide with the boundaries between the region 22 a , the region 22 b , and the region 22 c .

[0178] The electrode body 20 may further include a negative electrode layer and a current collector (not shown) disposed on the surface of the separator 23 opposite to the positive electrode layer 22 .

[0179] <Seventh Implementation Method>

[0180] A seventh embodiment of the present disclosure is a battery including the electrode assembly of the present disclosure described above.

[0181] The battery of this embodiment includes, for example, an electrode body, an outer casing for housing the electrode body, 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.

[0182] (outer body)

[0183] The type of the outer casing for housing the electrode assembly is not particularly limited and can be selected according to the type of battery.

[0184] In one embodiment, a sheet-like outer casing may be used.

[0185] As the sheet-like outer casing, an outer casing containing metal can be cited. Specifically, a laminate having a metal layer containing a metal such as aluminum and a heat-sealing layer containing a resin melted by heating (so-called laminated film) can be cited. That is, the battery of the present disclosure can also be a battery using a laminated film as an outer casing (so-called laminated battery).

[0186] The outer casing may be a single member or may be composed of two or more members. For example, when the outer casing is a sheet-like object, the outer casing may be composed of a single sheet-like object or may be composed of two sheet-like objects.

[0187] If necessary, a recessed portion for housing the electrode assembly may be formed in the sheet-like exterior body by embossing.

[0188] As a method of housing the electrode assembly in the outer casing using the sheet-like outer casing, for example, the following method 1 and method 2 can be cited.

[0189] Method 1: A method of joining the outer casing around the electrode body while placing the electrode body between one outer casing folded in half or between two outer casings stacked together

[0190] Method 2: The electrode assembly is placed in a bag made by joining the peripheries of a folded outer casing or two overlapped outer casings.

[0191] (Electrolyte)

[0192] The type of electrolyte is not particularly limited and can be selected according to the type of battery.

[0193] As the electrolyte solution, for example, an electrolyte solution obtained by dissolving an electrolyte such as LiPF 6 in a non-aqueous solvent can be used.

[0194] The battery of the present disclosure can be mounted on an electric vehicle. Hereinafter, an example of applying the battery of the present disclosure to an electric vehicle will be described with reference to the accompanying drawings. In the following description, "battery unit 20" is equivalent to the battery of the present disclosure.

[0195] Figure 3 1 is a schematic top view showing the main parts of a vehicle 100 to which the battery pack 10 according to the embodiment is applied. Figure 3 As shown, the vehicle 100 is an electric vehicle (BEV) equipped with a battery pack 10 under the cab. In addition, the arrows UP, FR, and LH in each figure respectively indicate the upper side in the vehicle vertical direction, the front side in the vehicle front-back direction, and the left side in the vehicle width direction. When the directions of front, back, left, right, up, and down are used for description, unless otherwise specified, they indicate the front and back in the vehicle front-back direction, the left and right in the vehicle width direction, and the up and down in the vehicle vertical direction.

[0196] As an example of a vehicle 100 of the present embodiment, a DC / DC converter 102, an electric compressor 104, and a PTC (Positive Temperature Coefficient) heater 106 are arranged on the front side of the vehicle relative to the battery pack 10. In addition, a motor 108, a gear box 110, an inverter 112, and a charger 114 are arranged on the rear side of the vehicle relative to the battery pack 10.

[0197] The DC current output from battery pack 10 is regulated in voltage by DC / DC converter 102 and then supplied to electric compressor 104, PTC heater 106, inverter 112, etc. In addition, by supplying power to motor 108 via inverter 112, rear wheels are rotated and vehicle 100 travels.

[0198] A charging port 116 is provided on the right side of the rear portion of the vehicle 100 . By connecting a charging plug of an external charging device (not shown) to the charging port 116 , electric power can be stored in the battery pack 10 via the charger 114 .

[0199] The configuration and structure of each component constituting the vehicle 100 are not limited to the above-mentioned configuration. For example, it can also be applied to a hybrid vehicle (HV: Hybrid Vehicle) or a plug-in hybrid vehicle (PHEV: Plug-in Hybrid Electric Vehicle) equipped with an engine. In addition, in the present embodiment, the motor 108 is mounted on the rear of the vehicle to drive the rear wheels, but it is not limited to this. It can also be a front-wheel drive vehicle with the motor 108 mounted on the front of the vehicle, and a pair of motors 108 can be mounted on the front and rear of the vehicle. In addition, it can also be a vehicle with an in-wheel motor on each wheel.

[0200] The battery pack 10 is composed of a plurality of battery modules 11. In the present embodiment, as an example, 10 battery modules 11 are provided. Specifically, five battery modules 11 are arranged along the front-rear direction of the vehicle on the right side of the vehicle 100, and five battery modules 11 are arranged along the front-rear direction of the vehicle on the left side of the vehicle 100. In addition, each battery module 11 is electrically connected.

[0201] Figure 4 1 is a schematic three-dimensional diagram of the battery module 11. Figure 4 As shown, the battery module 11 is formed into a substantially rectangular parallelepiped shape with the vehicle width direction as the long side direction. In addition, the outer shell of the battery module 11 is formed of an aluminum alloy. For example, an aluminum die casting is joined to both ends of an aluminum alloy pressing member by laser welding or the like, thereby forming the outer shell of the battery module 11.

[0202] A pair of voltage terminals 12 and a connector 14 are provided at both ends of the battery module 11 in the vehicle width direction. A flexible printed circuit board 21 described later is connected to the connector 14. Bus bars (not shown) are welded to both ends of the battery module 11 in the vehicle width direction.

[0203] The battery module 11 has a length MW in the vehicle width direction of, for example, 350 mm to 600 mm, a length ML in the vehicle front-rear direction of, for example, 150 mm to 250 mm, and a height MH in the vehicle vertical direction of, for example, 80 mm to 110 mm.

[0204] Figure 5 FIG. 1 is a top view of the battery module 11 with the upper cover removed. Figure 5 As shown, a plurality of battery cells 20 are housed in an aligned state inside the battery module 11. In the present embodiment, as an example, 24 battery cells 20 are aligned in the vehicle front-rear direction and bonded to each other.

[0205] A flexible printed circuit (FPC) 21 is disposed on the battery cell 20. The flexible printed circuit 21 is formed in a strip shape with the vehicle width direction as the long side direction, and thermistors 23 are provided at both ends of the flexible printed circuit 21. The thermistors 23 are not bonded to the battery cell 20, but are pressed toward the battery cell 20 by the upper cover of the battery module 11.

[0206] In addition, one or more buffers (not shown) are stored inside the battery module 11. For example, the buffer is a thin plate-shaped member that can be elastically deformed, and is 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, buffers are arranged at both ends and the center of the battery module 11 in the long side direction.

[0207] Figure 6 2 is a schematic diagram of the battery cell 20 housed in the battery module 11 as viewed from the thickness direction. Figure 6 As shown, the battery cell 20 is formed in a substantially rectangular plate shape, and an electrode body (not shown) is accommodated therein. The electrode body is formed by laminating a positive electrode, a negative electrode, and a separator, and is sealed by a laminate film 22 .

[0208] In this embodiment, as an example, the storage part of the electrode body is formed by folding and laminating the embossed sheet-shaped laminate film 22. In addition, two structures, a single cup embossed structure with embossing at one place and a double cup embossed structure with embossing at two places, can be adopted, but in this embodiment, a single cup embossed structure with a drawing depth of about 8 mm to 10 mm is adopted.

[0209] The upper ends of both ends of the battery cell 20 in the longitudinal direction are bent to form an angular shape. In addition, the upper end of the battery cell 20 is bent, and a fixing band 24 is wound around the upper end of the battery cell 20 along the longitudinal direction.

[0210] Here, terminals (tabs) 26 are provided at both ends in the longitudinal direction of the battery cell 20. In this embodiment, as an example, the terminals 26 are arranged below the vertical center of the battery cell 20. The terminals 26 are joined to a bus bar (not shown) by laser welding or the like.

[0211] 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 where the electrode body is stored 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, and the height CH of the battery cell 20 is, for example, 80 mm to 110 mm, 110 mm to 140 mm. In addition, 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, and the height TH of the terminal 26 is 40 mm to 50 mm, 50 mm to 60 mm, or 60 mm to 70 mm.

Claims

1. An electrode body comprising a current collector, a positive electrode layer and a separator in sequence, 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 separator side region is larger than the number of graphite particles per unit area in the collector side region.

2. An electrode body comprising a current collector, a positive electrode layer and a separator in sequence, 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 separator side region is larger than the area ratio of the region corresponding to the graphite particles in the collector side region.

3. An electrode body comprising a current collector, a positive electrode layer and a separator in sequence, 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 graphite particles contained in the separator side region is larger than the average particle size of graphite particles contained in the collector side region.

4. An electrode body comprising, in order, a current collector, a positive electrode layer and a separator, 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 collector side region and greater than the number of graphite particles per unit area in the separator side region.

5. An electrode body comprising, in order, a current collector, a positive electrode layer and a separator, 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 greater than the area ratio of the region corresponding to the graphite particles in the collector side region, and is greater than the area ratio of the region corresponding to the graphite particles in the separator side region.

6. An electrode body comprising, in order, a current collector, a positive electrode layer and a separator, 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 average particle size of graphite particles in the central region is larger than that in the collector side region and larger than that in the separator side region. 7 . The electrode body according to claim 1 , wherein at least a portion of the separator is bonded to the positive electrode layer. 8 . A battery comprising the electrode body according to claim 1 .

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