Positive electrode for secondary battery, secondary battery, and method for producing positive electrode for secondary battery

Abstract

A positive electrode for a secondary battery is provided with a strip-shaped positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The positive electrode current collector has a first region and a second region. The first regions are edge regions extending in the longitudinal direction of the positive electrode current collector at both edge portions in the width direction of the positive electrode current collector. The second region is a central region extending in the longitudinal direction of the positive electrode current collector at a central portion in the width direction of the positive electrode current collector. The positive electrode mixture layer has a first positive electrode mixture layer supported in the first region and a second positive electrode mixture layer supported in the second region. The positive electrode mixture layer has a first positive electrode mixture layer supported in the first region and a second positive electrode mixture layer supported in the second region. The first positive electrode mixture layer contains a first positive electrode active material, and the second positive electrode mixture layer contains a second positive electrode active material. The first positive electrode active material has an average particle diameter D1 of 1 [mu] m or more and 7 [mu] m or less. The second positive electrode active material has an average particle diameter D2 of 9 [mu] m or more and 30 [mu] m or less.

Description

Technical Field

[0001] The present disclosure relates to a positive electrode for a secondary battery, a secondary battery, and a method for manufacturing the positive electrode for a secondary battery. Background Art

[0002] Secondary batteries, especially lithium-ion secondary batteries, have high output power and high energy density, and therefore are expected to be used as power sources for small consumer applications, power storage devices, and electric vehicles.

[0003] Patent document 1 proposes: "A lithium ion secondary battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte, wherein the positive electrode comprises a positive electrode collector and a positive electrode mixture layer fixed to the surface of the positive electrode collector with a predetermined width L, and the negative electrode comprises a negative electrode collector and a negative electrode mixture layer fixed to the surface of the negative electrode collector with a width wider than the positive electrode mixture layer, the positive electrode mixture layer having a central region including a center in a width direction and a pair of end regions including both ends in a width direction, the central region comprising a first positive electrode active material and a conductive material, and the end regions comprising a second positive electrode active material and a conductive material, wherein, when the average primary particle size of the first positive electrode active material is set to d1 (μm), the average primary particle size of the second positive electrode active material is set to d2 (μm), and the width of the pair of end regions is set to L2, the d1, d2, L and L2 satisfy the following conditions: d1<d2; 1.5μm≤d2; (2×L2)≤(L / 3)".

[0004] Prior art literature

[0005] Patent Literature

[0006] Patent Document 1: Japanese Patent Application Publication No. 2018-181543 Summary of the invention

[0007] Problems to be solved by the invention

[0008] From the perspective of productivity, a strip-shaped positive electrode is usually produced by slitting a laminated intermediate having a positive electrode mixture layer on the surface of a wide current collector into a predetermined width. However, during the slitting process, particles of the positive electrode active material bite into the slitting blade, which causes damage to the blade and requires replacement of the slitting blade in a short time, which sometimes results in a decrease in the productivity of the positive electrode. In addition, in order to exhibit battery performance (such as charge and discharge performance), the positive electrode produced by slitting, etc. requires a predetermined liquid circulation of the electrolyte.

[0009] Means for solving problems

[0010] One aspect of the present disclosure relates to a positive electrode for a secondary battery, which comprises a strip-shaped positive electrode collector and a positive electrode mixture layer carried on the surface of the positive electrode collector, the positive electrode collector having a first region and a second region, the first region being an end region extending along the length direction of the positive electrode collector at two end edges in the width direction of the positive electrode collector, the second region being a central region extending along the length direction of the positive electrode collector at the central portion in the width direction of the positive electrode collector, the positive electrode mixture layer comprising a first positive electrode mixture layer carried on the surface of the first region and a second positive electrode mixture layer carried on the surface of the second region, the first positive electrode mixture layer comprising a first positive electrode active material, the second positive electrode mixture layer comprising a second positive electrode active material, the first positive electrode active material having an average particle size D1 of not less than 1 μm and not more than 7 μm, and the second positive electrode active material having an average particle size D2 of not less than 9 μm and not more than 30 μm.

[0011] Another aspect of the present disclosure relates to a secondary battery including a positive electrode, a negative electrode, and an electrolyte, wherein the positive electrode is the positive electrode for the secondary battery.

[0012] Another aspect of the present disclosure relates to a method for manufacturing a positive electrode for a secondary battery, comprising: a first step of preparing a collector sheet having a first region and a second region alternately having stripes; a second step of preparing a first positive electrode slurry containing a first positive electrode active material; a third step of preparing a second positive electrode slurry containing a second positive electrode active material; a fourth step of applying the first positive electrode slurry on the surface of the first region and drying it to form a first positive electrode mixture layer; a fifth step of applying the second positive electrode slurry on the surface of the second region 2 positive electrode slurry and drying it to form a second positive electrode mixture layer; and a sixth step, in the stacked intermediate of the first positive electrode mixture layer, the second positive electrode mixture layer and the collector sheet, cutting it together with the first positive electrode mixture layer in the first region along the length direction of the first region to obtain a plurality of strip-shaped positive electrodes, the average particle size D1 of the first positive electrode active material is greater than 1 μm and less than 7 μm, and the average particle size D2 of the second positive electrode active material is greater than 9 μm and less than 30 μm.

[0013] Effects of the Invention

[0014] According to the present disclosure, it is possible to ensure the liquid circulation property of the positive electrode and suppress a decrease in the productivity of the positive electrode.

[0015] The novel features of the present invention are described in the attached technical claims, but both the structure and content of the present invention, together with other objects and features of the present invention, can be better understood through the following detailed description with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1It is a plan view schematically showing an example of a positive electrode for a secondary battery according to an embodiment of the present disclosure.

[0017] Figure 2 This is a cross-sectional view schematically showing an example of a positive electrode for a secondary battery according to an embodiment of the present disclosure.

[0018] Figure 3 This is a plan view of the main parts schematically showing an example of a current collector sheet prepared in the first step of the method for producing a secondary battery positive electrode according to an embodiment of the present disclosure.

[0019] Figure 4 This is a plan view of the main parts schematically showing an example of a stacked intermediate body obtained in the fourth step and the fifth step of the method for producing a secondary battery positive electrode according to an embodiment of the present disclosure.

[0020] Figure 5 This is a schematic perspective view in which a part of a secondary battery according to an embodiment of the present disclosure is cut away. DETAILED DESCRIPTION

[0021] Hereinafter, the embodiments of the present disclosure will be described with examples, but the present disclosure is not limited to the examples described below. In the following description, specific numerical values ​​and materials are sometimes exemplified, but other numerical values ​​and materials may also be applied as long as the effects of the present disclosure can be obtained. In this specification, a description such as "numerical value A to numerical value B" includes numerical value A and numerical value B, and can be replaced by "numerical value A or more and numerical value B or less". In the following description, when a lower limit and an upper limit are exemplified for numerical values ​​of specific physical properties, conditions, etc., as long as the lower limit is not above the upper limit, any one of the exemplified lower limits can be arbitrarily combined with any one of the exemplified upper limits. When multiple materials are exemplified, one can be selected from them and used alone, or two or more can be used in combination.

[0022] In addition, the present disclosure includes a combination of matters recorded in two or more technical solutions arbitrarily selected from a plurality of technical solutions recorded in the attached technical solutions. That is, as long as no technical contradiction occurs, matters recorded in two or more technical solutions arbitrarily selected from a plurality of technical solutions recorded in the attached claimed scope may be combined.

[0023] [Positive electrode for secondary battery]

[0024] The positive electrode for a secondary battery of the embodiment of the present disclosure comprises a strip-shaped positive electrode collector and a positive electrode mixture layer carried on the surface of the positive electrode collector. The positive electrode for a secondary battery is produced by slitting a laminated intermediate having a positive electrode mixture layer carried on the surface of a wide current collector into a predetermined width. The positive electrode mixture layer is carried on one or both surfaces (main surfaces) of the positive electrode collector. The positive electrode mixture layer is usually a layer (including a membrane or a film) composed of a positive electrode mixture. The positive electrode mixture (layer) contains a particulate positive electrode active material as an essential component.

[0025] The positive electrode current collector has a first region and a second region. The first region is an edge region extending along the length direction of the positive electrode current collector at two end edges in the width direction of the positive electrode current collector. The edge region is formed by slitting. The second region is a central region extending along the length direction of the positive electrode current collector at the central portion in the width direction of the positive electrode current collector. The positive electrode mixture layer has a first positive electrode mixture layer carried on the surface of the first region and a second positive electrode mixture layer carried on the surface of the second region. The first positive electrode mixture layer contains a first positive electrode active material, and the second positive electrode mixture layer contains a second positive electrode active material. The average particle size D1 of the first positive electrode active material is greater than 1 μm and less than 7 μm, and the average particle size D2 of the second positive electrode active material is greater than 9 μm and less than 30 μm.

[0026] The first region includes a region 1a and a region 1b extending along the length direction of the positive electrode collector at one end and the other end in the width direction of the positive electrode collector, respectively. The first positive electrode mixture layer includes a positive electrode mixture layer 1a carried on the surface of the region 1a and a positive electrode mixture layer 1b carried on the surface of the region 1b.

[0027] The positive electrode current collector may have a third region in addition to the first region and the second region. The third region is a region that does not carry the positive electrode mixture layer and is provided along the width direction of the positive electrode current collector at the end of the length direction of the positive electrode current collector or at a predetermined position near the center. The third region can be used, for example, for connection with a positive electrode lead.

[0028] The inventors of the present invention have conducted in-depth research focusing on the particle size of the positive electrode active material. As a result, they have obtained the following new insights: when the positive electrode active material contained in the positive electrode mixture layer is a small particle with an average particle size of 7 μm or less, the damage to the slitting knife caused by the bite of the particles is suppressed, but on the other hand, the liquid circulation of the positive electrode mixture layer (liquid absorption of the positive electrode) is reduced.

[0029] Based on the above insights, the inventors of the present invention have further conducted in-depth research. As a result, it has been newly discovered that by forming a portion of the positive electrode mixture layer (the edge region formed by slitting) with a first positive electrode mixture layer containing small particles of a first positive electrode active material, and forming the remaining portion (central region) with a second positive electrode mixture layer containing large particles of a second positive electrode active material having an average particle size of 9 μm or more, it is possible to suppress a decrease in productivity while ensuring the performance (liquid circulation) of the positive electrode.

[0030] From the perspective of improving productivity (extending the life of the slitting knife), the widths of the 1a region (1a positive electrode mixture layer) and the 1b region (1b positive electrode mixture layer) are preferably 1% or more (or 4% or more) of the width of the positive electrode collector (positive electrode mixture layer). From the perspective of improving the liquid circulation of the positive electrode mixture layer, the widths of the 1a region (1a positive electrode mixture layer) and the 1b region (1b positive electrode mixture layer) are preferably 20% or less (or 15% or less) of the width of the positive electrode collector (positive electrode mixture layer). It should be noted that the width of the positive electrode collector (positive electrode mixture layer) refers to the width obtained by adding the first region (first positive electrode mixture layer) and the second region (second positive electrode mixture layer).

[0031] (Average particle size D1 and D2)

[0032] The end faces of the first positive electrode mixture layer (the 1a positive electrode mixture layer and the 1b positive electrode mixture layer) at both ends in the width direction of the positive electrode are formed by slitting. When the average particle size D1 of the first positive electrode active material in the first positive electrode mixture layer is less than 7 μm, the particles of the first positive electrode active material are small, and the particles are inhibited from biting into the slitting knife. The damage to the slitting knife caused by the biting of particles is suppressed, the replacement frequency of the slitting knife can be reduced, and the reduction in productivity can be suppressed. From the perspective of further improving productivity, D1 is more preferably less than 4 μm. However, when D1 is less than 1 μm, the handleability of the positive electrode active material is reduced, which is disadvantageous in terms of the productivity of the positive electrode.

[0033] When the average particle size D2 of the second positive electrode active material in the second positive electrode mixture layer is 9 μm or more, the voids in the second positive electrode mixture layer are large, and the liquid circulation of the positive electrode mixture layer is improved. From the viewpoint of improving the liquid circulation of the positive electrode mixture layer, D2 is preferably 10 μm or more, and more preferably 20 μm or more. However, when D2 is greater than 30 μm, the productivity of the positive electrode is disadvantageous due to the reduced coating of the positive electrode slurry and the reduced compressibility of the positive electrode mixture layer.

[0034] D1 and D2 can be calculated as follows.

[0035] The positive electrode mixture layer and the positive electrode current collector are cut simultaneously along the width direction of the positive electrode to obtain a cross-sectional sample of the positive electrode in the thickness direction. At this time, the cross section can also be processed using a cross-sectional polisher (CP) to obtain a cross-sectional sample. Next, a scanning electron microscope (SEM) is used to observe the cross section of the positive electrode mixture layer in the cross-sectional sample.

[0036] Specifically, for the cross section of the positive electrode mixture layer, the distance from one end surface in the width direction of the positive electrode mixture layer is less than 1% of the width direction of the positive electrode mixture layer by SEM. More than 10 positive electrode active material particles are randomly selected in the edge region. The equivalent circle diameter of the cross section of the positive electrode active material particles is obtained by image processing, and their average value is obtained as D1.

[0037] Next, for the cross section of the positive electrode mixture layer, observe the central area of ​​the positive electrode mixture layer in the width direction of which the distance from one end surface is 40% to 60% of the width direction of the positive electrode mixture layer by SEM. Randomly select 10 or more positive electrode active material particles in the central area. Calculate the equivalent circle diameter of the cross section of the positive electrode active material particles by image processing, and calculate their average value as D2.

[0038] D1 and D2 can be obtained using multiple cross-sectional samples. It should be noted that the above-mentioned equivalent circle diameter is the diameter of a circle having the same area as the cross-sectional area of ​​the positive electrode active material particle. The positive electrode active material particle may include secondary particles formed by agglomeration of multiple primary particles. In the case of secondary particles, the above-mentioned equivalent circle diameter is the diameter of a circle having the same area as the cross-sectional area of ​​the secondary particles.

[0039] When the first positive electrode active material and the second positive electrode active material can be recovered from the positive electrode mixture layer (or the second step and the third step in the manufacturing method of the positive electrode described later), the median particle size (particle size at 50% cumulative volume) in the volume-based particle size distribution of the first positive electrode active material and the second positive electrode active material can be obtained as D1 and D2. The volume-based particle size distribution can be measured by a laser diffraction scattering method. For example, the measurement device "LA-750" manufactured by HORIBA Co., Ltd. can be used for the measurement.

[0040] (Positive electrode active material)

[0041] The positive electrode active material may be a material that can absorb and release lithium ions (for example, a composite oxide containing lithium and a transition metal described later). From the perspective of improving productivity, the first positive electrode active material and the second positive electrode active material are preferably of the same type (chemical structure or composition). In this case, the first positive electrode active material and the second positive electrode active material can easily adjust the single particle breaking strength to be approximately equal.

[0042] In the case where the single particle breaking strength of the first positive electrode active material and the second positive electrode active material is approximately equal, by adjusting the average particle diameters of D1 and D2 to within a specific range, it is easy to simultaneously achieve a longer life of the slitting blade and an improvement in the liquid absorption of the positive electrode (liquid circulation of the positive electrode mixture layer). In addition, it is possible to reduce the deviation in the degree of crack formation of the positive electrode active material particles in the positive electrode mixture layer accompanying the charge and discharge cycle.

[0043] When the first positive electrode active material and the second positive electrode active material have substantially the same single particle fracture strength, they may be of different types (chemical structures or compositions).

[0044] It should be noted that the above “single particle fracture strength is substantially equal” means that when the single particle fracture strength of the first positive electrode active material and the second positive electrode active material are respectively F1 and F2, F1 / F2 is greater than 0.8 and less than 1.2. F1 / F2 may also be greater than 0.9 and less than 1.1.

[0045] In addition, from the viewpoint of extending the life of the slitting blade, the single particle fracture strength of the first positive electrode active material may be smaller than that of the second positive electrode active material. F1 / F2 may be less than 1.0, or may be 0.8 or less.

[0046] The single particle fracture strength can be measured by the following procedure using a commercially available measuring device (for example, a micro compression tester (MCT-W201) manufactured by Shimadzu Corporation).

[0047] (1) Particles of the positive electrode active material are spread on the lower pressure plate (SKS plate) of the measuring device.

[0048] (2) Using an optical microscope, select particles of the measurement object and measure the particle size. The particle size here refers to an equivalent circle diameter (the diameter of a circle having the same area as the area of ​​the particle) obtained using an image of the particle obtained using an optical microscope.

[0049] (3) A diamond flat indenter with a diameter of 50 μm was used as an upper indenter so that only one particle selected as a sample existed between the upper indenter and the lower press plate.

[0050] (4) The upper indenter is slowly lowered, and a load is applied at a constant acceleration (specifically, a displacement speed of 2.7 mN / sec) from the moment it contacts the sample (the lowering speed changes).

[0051] (5) The relationship between the load and the deformation of the sample was measured, and the point where the deformation of the sample changed sharply (the inflection point of the load-deformation curve) was taken as the breaking point. The breaking strength was calculated based on the load and particle size at that time using the following formula. The breaking strength was measured 5 times and the average value was obtained.

[0052] St=2.8P / πd 2

[0053] St: Fracture strength [MPa or N / mm 2 ]

[0054] P: Load [N]

[0055] d: particle size [mm]

[0056] (Positive electrode mixture layer)

[0057] From the viewpoint of extending the life of the slitting blade, the amount of the positive electrode mixture layer supported on the surface of the positive electrode current collector is preferably 450 mg / 10 cm 2 Below, more preferably 400mg / 10cm 2 Below, more preferably 300 mg / 10 cm 2 In addition, from the viewpoint of high energy density, the loading amount of the positive electrode mixture layer is preferably 100 mg / 10 cm 2 It should be noted that the loading amount of the positive electrode mixture layer is the loading amount per 10 cm on one surface of the positive electrode current collector. 2 The mass of the positive electrode mixture layer carried.

[0058] The density of the positive electrode mixture layer is preferably 2 g / cm 3 Above (or 2.5g / cm 3 Above) and 4g / cm 3 The density of the positive electrode mixture layer is 2 g / cm 3 In the case of the above, it is easy to increase the energy density. The density of the positive electrode mixture layer is 4 g / cm 3 In the following cases, it is easy to extend the life of the slitting blade. The density of the positive electrode mixture layer can be 3.5 g / cm 3 the following.

[0059] The positive electrode mixture layer preferably contains a binder. The binder may be the binder exemplified below. From the viewpoint of extending the life of the slitting knife, the content of the binder in the positive electrode mixture layer is preferably 0.2% by mass or more and 7% by mass or less. From the viewpoint of extending the life of the slitting knife and ensuring the filling amount of the positive electrode active material, the content of the binder in the positive electrode mixture layer is more preferably 0.2% by mass or more and 5% by mass or less, and more preferably 2% by mass or more and 5% by mass or less. It should be noted that the content of the binder refers to the ratio (percentage) of the mass of the binder to the overall mass of the positive electrode mixture layer.

[0060] From the perspective of the uniformity of the positive electrode mixture layer and the productivity of the positive electrode, the first positive electrode mixture layer and the second positive electrode mixture layer preferably have approximately the same loading amount, binder content, and density on the positive electrode collector. From the same perspective, the first positive electrode mixture layer and the second positive electrode mixture layer preferably have the same materials such as the binder contained in the positive electrode mixture. From the same perspective, the proportions of the positive active material, binder, and other materials contained in the positive electrode mixture are preferably approximately the same.

[0061] Here, Figure 1 It is a plan view schematically showing an example of a positive electrode for a secondary battery according to an embodiment of the present disclosure. Figure 2 This is a cross-sectional view schematically showing an example of a positive electrode for a secondary battery according to an embodiment of the present disclosure. Figure 1 In FIG. 1 , X and Y respectively represent the length direction and the width direction of the strip-shaped positive electrode. Figure 2 express Figure 1 The cross section along the II-II direction.

[0062] The positive electrode 10 includes a strip-shaped positive electrode collector 20 and a positive electrode mixture layer 30 carried on both surfaces (main surfaces) of the positive electrode collector 20. The positive electrode collector 20 includes a first region 21 and a second region 22. The first region 21 is an edge region extending along the length direction of the positive electrode collector 20 at both end edges in the width direction of the positive electrode collector 20. The second region 22 is a central region extending along the length direction of the positive electrode collector 20 at the central portion in the width direction of the positive electrode collector 20. The positive electrode mixture layer 30 includes a first positive electrode mixture layer 31 ( Figure 1 ) and the second positive electrode mixture layer 32 carried on both surfaces of the second region 22.

[0063] The first region 21 includes a 1a region 21a and a 1b region 21b extending along the length direction of the positive electrode collector 20 at one end edge and the other end edge in the width direction of the positive electrode collector 20, respectively. The first positive electrode mixture layer 31 includes a 1a positive electrode mixture layer 31a carried on both surfaces of the 1a region 21 and a 1b positive electrode mixture layer 31b carried on both surfaces of the 1b region 21.

[0064] The positive electrode current collector 20 (positive electrode mixture layer 30 ) has a width L0 . The 1a region 21 a (1a positive electrode mixture layer 31 a ) has a width L1a , and the 1b region 21 b (1b positive electrode mixture layer 31 b ) has a width L1b .

[0065] From the viewpoint of improving productivity, L1a / L0 and L1b / L0 are each preferably 1 / 100 or more, and more preferably 4 / 100 or more.

[0066] From the viewpoint of ensuring liquid circulation of the positive electrode mixture layer (ensuring the second region 22 and the second positive electrode mixture layer 32 region), L1a / L0 and L1b / L0 are each preferably 20 / 100 or less, and more preferably 15 / 100 or less.

[0067] L1a is preferably substantially the same as L1b, but may be different from L1b. L1a / L1b is, for example, 0.90 or more and 1.1 or less.

[0068] The second region 22 is a central region extending in the longitudinal direction of the positive electrode current collector 20 at the central portion in the width direction of the positive electrode current collector 20. The second region 22 (second positive electrode mixture layer 32) has a width L2, which is a value obtained by subtracting the sum of L1a and L1b from L0.

[0069] The first positive electrode mixture layer 31 (the 1a positive electrode mixture layer 31a and the 1b positive electrode mixture layer 31b) contains a first positive electrode active material, and the second positive electrode mixture layer 32 contains a second positive electrode active material. The average particle size D1 of the first positive electrode active material is 1 μm or more and 7 μm or less. The average particle size D2 of the second positive electrode active material is 9 μm or more and 30 μm or less.

[0070] The thickness of the positive electrode mixture layer 30 carried on one surface of the positive electrode current collector 20 ( Figure 2 The T in ( ) may be 80 μm or more, or 100 μm or more. The upper limit of the thickness of the positive electrode mixture layer 30 is, for example, about 300 μm, but is not limited thereto. The thickness of the positive electrode current collector 20 ( Figure 2 T0 in FIG. 1 is, for example, not less than 1 μm and not more than 50 μm.

[0071] [Method for producing positive electrode for secondary battery]

[0072] The method for producing a secondary battery positive electrode according to an embodiment of the present disclosure includes the following first to sixth steps.

[0073] First step: preparing a current collector sheet having first regions and second regions alternately having stripes.

[0074] Second step: preparing a first positive electrode slurry containing a first positive electrode active material. The first positive electrode active material has an average particle size D1 of 1 μm or more and 7 μm or less.

[0075] Step 3: Prepare a second positive electrode slurry containing a second positive electrode active material. The average particle size D2 of the second positive electrode active material is 9 μm or more and 30 μm or less.

[0076] Step 4: Apply the first positive electrode slurry to the surface of the first region and dry it to form a first positive electrode mixture layer.

[0077] Step 5: Apply the second positive electrode slurry on the surface of the second region and dry it to form a second positive electrode mixture layer.

[0078] Step 6: Cutting the stacked intermediate of the first positive electrode mixture layer, the second positive electrode mixture layer, and the current collector sheet together with the first positive electrode mixture layer in the first region along the longitudinal direction of the first region to obtain a plurality of strip-shaped positive electrodes.

[0079] (Step 1: Preparation of current collector)

[0080] Figure 3 This is a plan view schematically showing an example of the current collector sheet prepared in the first step. Figure 3 Indicates a portion of the current collector. Figure 3 In FIG. 1 , X and Y represent the length direction and width direction of the current collector, respectively.

[0081] The current collector sheet 50 has strip-shaped first regions 51 ( Figure 3 The first area 51 includes Figure 3 The cut portion 53 is shown by the dashed line in FIG. The cut portion 53 extends in the first region 51 along the longitudinal direction of the first region and is a portion cut during the slitting process in the sixth step. The first region 51 has a width (L1a+L1b). The second region 52 has a width L2. L0 is the sum of L1a, L1b, and L2.

[0082] The collector sheet 50 may be a conductive sheet that can be used as a positive electrode collector, for example, a non-porous conductive substrate (metal foil, etc.), a porous conductive substrate (mesh, mesh, punching sheet, etc.). Examples of the material of the collector sheet 50 include aluminum, aluminum alloy, stainless steel, titanium, etc. The thickness of the collector sheet 50 may be, for example, not less than 1 μm and not more than 50 μm.

[0083] (Step 2 and Step 3: Preparation of positive electrode slurry)

[0084] A first (second) positive electrode slurry containing a first (second) positive electrode active material is prepared. The first positive electrode active material has an average particle size D1 of 1 μm or more and 7 μm or less. The second positive electrode active material has an average particle size D2 of 9 μm or more and 30 μm or less.

[0085] The first (second) positive electrode slurry is prepared, for example, by dispersing the first (second) positive electrode mixture in a dispersion medium. The first (second) positive electrode mixture contains the first (second) positive electrode active material as an essential component, and may contain a binder, a conductive agent, etc. as an arbitrary component. The binder and the conductive agent may be the binders and conductive agents exemplified below. The dispersion medium may be alcohol, ether, N-methyl-2-pyrrolidone (NMP), etc.

[0086] (Step 4 and Step 5: Formation of Positive Electrode Mixture Layer)

[0087] The first (second) positive electrode slurry is applied to the surface of the first (second) region and dried to form the first (second) positive electrode mixture layer. The dried coating can be rolled as needed. The density of the formed positive electrode mixture layer can also be adjusted by rolling. The first (second) positive electrode slurry can be applied to one surface of the first (second) region or to both surfaces of the first (second) region. From the perspective of productivity, the fourth step and the fifth step can be performed in parallel. The first positive electrode slurry and the second positive electrode slurry can be applied to the surface of the positive electrode collector at the same time using a two-fluid nozzle.

[0088] Through the fourth and fifth steps, a stacked intermediate of the current collector sheet and the positive electrode mixture layer (the first positive electrode mixture layer supported on the surface of the first region and the second positive electrode mixture layer supported on the surface of the second region) is obtained.

[0089] Figure 4 It is a plan view schematically showing an example of a laminated intermediate body produced in the fourth step and the fifth step. Figure 4 Represents a portion of a stacked intermediate. Figure 4 In FIG. 1 , X and Y represent the length direction and the width direction of the laminated intermediate, respectively.

[0090] The laminated intermediate body 70 includes a current collector sheet 50 and positive electrode mixture layers 60 carried on both surfaces of the current collector sheet 50. The positive electrode mixture layers 60 include first positive electrode mixture layers 61 ( Figure 4) and the second positive electrode mixture layer 62 carried on both surfaces of the second region 52 of the collector sheet 50. The striped first positive electrode mixture layer 61 and the second positive electrode mixture layer 62 are arranged alternately. The first positive electrode mixture layer 61 is formed by applying the first positive electrode slurry to both surfaces of the first region 51 and drying the coating. The second positive electrode mixture layer 62 is formed by applying the second positive electrode slurry to both surfaces of the second region 52 and drying the coating. The first positive electrode mixture layer 61 has a width (L1a+L1b). The second positive electrode mixture layer 62 has a width L2. L0 is the sum of L1a, L1b and L2. The first positive electrode mixture layer 61 includes Figure 4 The cut portion 63 is indicated by the dashed line in FIG. The cut portion 63 extends in the first positive electrode mixture layer 61 along the longitudinal direction of the first positive electrode mixture layer 61 and is a portion that is cut during the slitting process in the sixth step.

[0091] (Step 6: Slitting)

[0092] In the sixth step, in the stacked intermediate, the first positive electrode mixture layer containing small particles of the first positive electrode active material is cut along the length direction of the first region in the first region. In the sixth step, the stacked intermediate is continuously cut using a slitting device (cutting of the first positive electrode mixture layer and the first region using a slitting knife). By cutting in the first region and in the first positive electrode mixture layer, the stacked intermediate is divided into strips of a specified width. Thus, a plurality of strip-shaped positive electrodes are obtained. In the slitting process, since the first positive electrode mixture layer in the positive electrode mixture layer is cut, damage to the slitting knife is suppressed.

[0093] exist Figure 4 In the stacked intermediate 70, the cut portion 63 in the first positive electrode mixture layer 61 and the cut portion 53 in the first region 51 are cut simultaneously by the slitting process. The stacked intermediate 70 is transported to the slitting process device, and the cutting in the first positive electrode mixture layer 61 and the first region 51 is continuously performed. Accompanying this cutting, the first region 51 is divided into the 1a region 51a and the 1b region 51b, and the first positive electrode mixture layer 61 is divided into the 1a positive electrode mixture layer 61a carried on both surfaces of the 1a region 51a and the 1b positive electrode mixture layer 61b carried on both surfaces of the 1b region 51b. The 1a region 51a and the 1a positive electrode mixture layer 61a have a width L1a. The 1b region 51b and the 1b positive electrode mixture layer 61b have a width L1b. L1a / L0 and L1b / L0 are preferably within the ranges exemplified above.

[0094] [Secondary battery]

[0095] The secondary battery of the embodiment of the present disclosure has a positive electrode, a negative electrode and an electrolyte. The positive electrode is the positive electrode for the above-mentioned secondary battery. The secondary battery can obtain good load characteristics (fast charging characteristics) by the good liquid circulation of the positive electrode. In addition, by improving the productivity of the positive electrode, the productivity of the secondary battery is also improved. The secondary battery includes at least non-aqueous electrolyte secondary batteries such as lithium ion batteries and lithium metal secondary batteries. The secondary battery is described in detail below.

[0096] (positive electrode)

[0097] The positive electrode includes a positive electrode current collector and a positive electrode mixture layer supported on the surface of the positive electrode current collector. The positive electrode mixture layer can be formed by applying a positive electrode slurry formed by dispersing a positive electrode mixture in a dispersion medium to the surface of the positive electrode current collector and drying it. The dried coating film can be rolled as needed. The positive electrode mixture layer can be formed on one surface of the positive electrode current collector or on both surfaces.

[0098] The positive electrode mixture may contain a positive electrode active material as an essential component, and a binder, a conductive agent, etc. as optional components.

[0099] The positive electrode active material may be a material that can absorb and release lithium ions, and a known material may be used. As the positive electrode active material, a composite oxide containing lithium and a transition metal may be exemplified. As the composite oxide, for example, Li a CoO 2 , Li a NiO 2 , Li a MnO 2 , Li a Co b Ni 1-b O 2 , Li a Co 1-b M b O c , Li a Ni 1-b M b O c , Li a Mn 2 O 4 , Li a Mn 2- b M b O 4 、LiMePO 4 , Li 2 MePO 4F. Here, M is at least one selected from Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb and B. Me contains at least a transition element (for example, contains at least one selected from Mn, Fe, Co, Ni). Here, 0≤a≤1.2, 0≤b≤0.9, 2.0≤c≤2.3. It should be noted that the value a indicating the molar ratio of lithium increases or decreases due to charge and discharge.

[0100] Examples of the binder include fluororesins, polyolefin resins, polyamide resins, polyimide resins, vinyl resins, styrene-butadiene copolymer rubber (SBR), polyacrylic acid and its derivatives, etc. Examples of the fluororesins include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymers, and vinylidene fluoride-hexafluoropropylene copolymers.

[0101] As the conductive agent, the same conductive agent as exemplified for the negative electrode can be used. As the conductive agent, graphite such as natural graphite and artificial graphite can be used.

[0102] The shape and thickness of the positive electrode current collector can be selected based on the shape and range of the negative electrode current collector. Examples of the material of the positive electrode current collector include stainless steel, aluminum, aluminum alloy, titanium, and the like.

[0103] (negative electrode)

[0104] The negative electrode, for example, comprises a negative electrode current collector and a negative electrode mixture layer carried on the surface of the negative electrode current collector. The negative electrode mixture layer can be formed, for example, by applying a negative electrode slurry obtained by dispersing a negative electrode mixture in a dispersion medium to the surface of the negative electrode current collector and drying it. The dried coating can be rolled as needed. The negative electrode mixture layer can be formed on one surface of the negative electrode current collector or on both surfaces. In addition, the negative electrode can comprise a negative electrode current collector and a lithium metal foil or a lithium alloy foil carried on the surface of the negative electrode current collector.

[0105] The negative electrode mixture may contain a negative electrode active material as an essential component, and may contain a binder, a conductive agent, a thickener, and the like as optional components.

[0106] The negative electrode active material includes materials that can absorb and release lithium ions, lithium metal, lithium alloys, etc. As materials that can absorb and release lithium ions, carbon materials, alloy materials, etc. can be used. As carbon materials, for example, graphite, easily graphitized carbon (soft carbon), and difficultly graphitized carbon (hard carbon) can be exemplified. Among them, graphite with excellent charge and discharge stability and low irreversible capacity is preferred. As alloy materials, alloys containing at least one metal that can form an alloy with lithium can be cited, and silicon, tin, silicon alloys, tin alloys, silicon compounds, etc. can be cited. Silicon oxide, tin oxide, etc. formed by combining them with oxygen can also be used.

[0107] The alloy material containing silicon can be a composite material having a lithium ion conductive phase and a silicon phase (silicon particles) dispersed in the lithium ion conductive phase. As the lithium ion conductive phase, for example, a silicon oxide phase, a silicate phase, a carbon phase, etc. can be used. The main component of the silicon oxide phase (for example, 95 to 100% by mass) can be silicon dioxide. The carbon phase can be composed of, for example, amorphous carbon (i.e., non-crystalline carbon) with low crystallinity. Amorphous carbon can be, for example, hard carbon, soft carbon, or carbon other than these. The composite material can be used together with the carbon material.

[0108] From the perspective of small irreversible capacity and high initial charge and discharge efficiency, a silicate phase containing lithium (lithium silicate phase) is preferred. The lithium silicate phase can be an oxide phase containing lithium (Li), silicon (Si) and oxygen (O), and can also contain other elements. Examples of other elements include iron (Fe), chromium (Cr), nickel (Ni), manganese (Mn), copper (Cu), molybdenum (Mo), zinc (Zn), and aluminum (Al). The lithium silicate phase can have the formula: Li 2z SiO 2＋z The lithium silicate phase may contain Li 2 SiO 3 , Li 2 Si 2 O 5 wait.

[0109] As the binder, the binders exemplified for the positive electrode can be used. As the conductive agent, carbon black, conductive fibers, carbon fluoride, organic conductive materials, etc. can be exemplified. As the thickener, carboxymethyl cellulose (CMC), polyvinyl alcohol, etc. can be exemplified.

[0110] As the negative electrode current collector, a nonporous conductive substrate (metal foil, etc.) or a porous conductive substrate (mesh, net-like body, punched sheet, etc.) can be used. Examples of the material of the negative electrode current collector include stainless steel, nickel, nickel alloy, copper, copper alloy, etc.

[0111] (Electrolyte)

[0112] The electrolyte solution contains a solvent and a solute dissolved in the solvent. The solute is an electrolyte salt that undergoes ion dissociation in the electrolyte solution. The solute may contain, for example, a lithium salt. The components of the electrolyte solution other than the solvent and the solute are additives. The electrolyte solution may contain various additives.

[0113] The solvent uses an aqueous solvent or a non-aqueous solvent. As the non-aqueous solvent, for example, cyclic carbonates, chain carbonates, cyclic carboxylates, chain carboxylates, etc. can be used. As cyclic carbonates, propylene carbonate (PC), ethylene carbonate (EC), vinylene carbonate (VC), etc. can be mentioned. As chain carbonates, diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), etc. can be mentioned. In addition, as cyclic carboxylates, γ-butyrolactone (GBL), γ-valerolactone (GVL), etc. can be mentioned. As chain carboxylates, methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), ethyl propionate (EP), etc. can be mentioned. The non-aqueous solvent can be used alone or in combination of two or more.

[0114] As the lithium salt, for example, a lithium salt of a chlorine-containing acid (LiClO 4 、LiAlCl 4 , LiB 10 Cl 10 etc.), lithium salts of fluorinated acids (LiPF 6 、LiPF 2 O 2 , LiBF 4 、LiSbF 6 、LiAsF 6 、LiCF 3 SO 3 、LiCF 3 CO 2 etc.), lithium salts of fluorinated imides (LiN(FSO 2 ) 2 、LiN(CF 3 SO 2 ) 2 、LiN(CF 3 SO 2 )(C 4 F 9 SO 2 )、LiN(C 2 F 5 SO 2 ) 2 etc.), lithium halides (LiCl, LiBr, LiI, etc.), etc. The lithium salt may be used alone or in combination of two or more.

[0115] The concentration of the lithium salt in the electrolyte may be 1 mol / liter or more and 2 mol / liter or less, or 1 mol / liter or more and 1.5 mol / liter or less. By controlling the lithium salt concentration within the above range, an electrolyte having excellent ion conductivity and appropriate viscosity can be obtained. However, the lithium salt concentration is not limited to the above range.

[0116] (Diaphragm)

[0117] Preferably, a separator is sandwiched between the positive electrode and the negative electrode. The separator has high ion permeability and has appropriate mechanical strength and insulation. As the separator, a microporous film, a woven fabric, a non-woven fabric, etc. can be used. As the material of the separator, polyolefins such as polypropylene and polyethylene are preferred.

[0118] As an example of the structure of a secondary battery, an electrode group in which a positive electrode and a negative electrode are wound across a separator and housed in an outer body together with an electrolyte can be cited. However, it is not limited to this, and other forms of electrode groups can also be applied. For example, it can also be a laminated electrode group in which a positive electrode and a negative electrode are laminated across a separator. The form of the battery is also not limited, for example, it can be cylindrical, square, coin-shaped, button-shaped, laminated, etc.

[0119] Below, refer to Figure 5 The structure of a rectangular secondary battery as an example of the secondary battery of the present disclosure will be described.

[0120] The battery comprises a battery case 4 having a square bottom, an electrode group 1 housed in the battery case 4, and an electrolyte (not shown). The electrode group 1 comprises a long strip-shaped negative electrode, a long strip-shaped positive electrode, and a separator therebetween. The negative electrode collector of the negative electrode is electrically connected to a negative terminal 6 provided on a sealing plate 5 via a negative electrode lead 3. The negative terminal 6 is insulated from the sealing plate 5 by a resin gasket 7. The positive electrode collector of the positive electrode is electrically connected to the back of the sealing plate 5 via a positive electrode lead 2. That is, the positive electrode is electrically connected to the battery case 4 which also serves as a positive terminal. The periphery of the sealing plate 5 is fitted with the open end of the battery case 4, and the fitting portion is laser welded. The sealing plate 5 has an injection hole for the electrolyte, which is blocked by a seal 8 after the injection.

[0121] Postscript

[0122] The following techniques are disclosed through the description of the above embodiments.

[0123] (Technique 1)

[0124] A positive electrode for a secondary battery, comprising a strip-shaped positive electrode current collector and a positive electrode mixture layer carried on the surface of the positive electrode current collector.

[0125] The positive electrode current collector has a first region and a second region.

[0126] The first region is an edge region extending along the longitudinal direction of the positive electrode current collector at both edge portions in the width direction of the positive electrode current collector.

[0127] The second region is a central region extending in the longitudinal direction of the positive electrode current collector at the central portion in the width direction of the positive electrode current collector.

[0128] The positive electrode mixture layer includes a first positive electrode mixture layer carried on the surface of the first region and a second positive electrode mixture layer carried on the surface of the second region.

[0129] The first positive electrode mixture layer includes a first positive electrode active material.

[0130] The second positive electrode mixture layer contains a second positive electrode active material.

[0131] The average particle size D1 of the first positive electrode active material is 1 μm or more and 7 μm or less.

[0132] The second positive electrode active material has an average particle size D2 of 9 μm or more and 30 μm or less.

[0133] (Technique 2)

[0134] The secondary battery positive electrode according to the first aspect, wherein the positive electrode mixture layer on the surface of the positive electrode current collector has a loading amount of 100 mg / 10 cm 2 More than 400mg / 10cm 2 the following.

[0135] (Technique 3)

[0136] The secondary battery positive electrode according to the technique 1 or 2, wherein the density of the positive electrode mixture layer is 2.5 g / cm 3 Above 4g / cm 3 the following.

[0137] (Technique 4)

[0138] The secondary battery positive electrode according to any one of techniques 1 to 3, wherein the positive electrode mixture layer contains 0.2 mass % or more and 5 mass % or less of a binder.

[0139] (Technique 5)

[0140] A secondary battery positive electrode according to any one of techniques 1 to 4, wherein the first region includes a region 1a and a region 1b extending along the length direction of the positive electrode current collector at one end edge and the other end edge in the width direction of the positive electrode current collector, respectively;

[0141] The widths of the region 1a and the region 1b are each not less than 1% and not more than 20% of the width of the positive electrode current collector.

[0142] (Technique 6)

[0143] A secondary battery comprising a positive electrode, a negative electrode and an electrolyte,

[0144] The positive electrode is the positive electrode for a secondary battery described in any one of Techniques 1 to 5.

[0145] (Technique 7)

[0146] A method for manufacturing a positive electrode for a secondary battery, comprising:

[0147] In a first step, a current collector sheet having first and second regions in a strip shape alternately is prepared;

[0148] The second step is to prepare a first positive electrode slurry containing a first positive electrode active material;

[0149] The third step is to prepare a second positive electrode slurry containing a second positive electrode active material;

[0150] In a fourth step, the first positive electrode slurry is applied to the surface of the first region and dried to form a first positive electrode mixture layer.

[0151] A fifth step of coating the second positive electrode slurry on the surface of the second region and drying the slurry to form a second positive electrode mixture layer; and

[0152] In the sixth step, in the stacked intermediate of the first positive electrode mixture layer, the second positive electrode mixture layer and the collector sheet, the first positive electrode mixture layer is cut along the length direction of the first region in the first region together with the first positive electrode mixture layer to obtain a plurality of strip-shaped positive electrodes.

[0153] The average particle size D1 of the first positive electrode active material is 1 μm or more and 7 μm or less.

[0154] The second positive electrode active material has an average particle size D2 of 9 μm or more and 30 μm or less.

[0155] (Technique 8)

[0156] According to the method for producing a positive electrode for a secondary battery described in the seventh aspect, the fourth step and the fifth step are performed in parallel.

[0157] Hereinafter, the present disclosure will be specifically described based on Examples and Comparative Examples, but the present disclosure is not limited to the following Examples.

[0158] 《Example 1》

[0159] Follow the steps below to make the positive electrode.

[0160] (Step 1: Preparation of current collector)

[0161] A current collector sheet having alternately striped first and second regions was prepared. A wide aluminum foil (thickness T0: 15 μm) was used as the current collector sheet. The width of the first region: the width of the second region = 2:8.

[0162] (Step 2 and Step 3: Preparation of positive electrode slurry)

[0163] 100 parts by mass of the first positive electrode active material, 1.0 parts by mass of acetylene black as a conductive agent, 2 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) were mixed to prepare a first positive electrode slurry.

[0164] 100 parts by mass of the second positive electrode active material, 1.0 parts by mass of acetylene black as a conductive agent, 2 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of NMP were mixed to prepare a second positive electrode slurry.

[0165] The first positive electrode active material and the second positive electrode active material use composite oxides having different average particle sizes, layered rock salt type crystal structures, and containing Li, Ni, Co, and Al. The atomic ratio of the total of Li, Ni, Co, and Al to O is 1:1:2. Among Ni, Co, and Al, Ni has the largest atomic ratio.

[0166] The average particle size D1 of the first positive electrode active material and the average particle size D2 of the second positive electrode active material, measured as median diameters in a volume-based particle size distribution by a laser diffraction scattering method, were 4 μm and 20 μm, respectively.

[0167] (Step 4 and Step 5: Formation of Positive Electrode Mixture Layer)

[0168] The first positive electrode slurry is applied to both surfaces of the first region of the collector sheet, and the first coating is dried. The second positive electrode slurry is applied to both surfaces of the second region of the collector sheet, and the second coating is dried. The application of the first positive electrode slurry and the second positive electrode slurry is performed by die coating. Then, the stack of the first coating, the second coating and the collector sheet is rolled to form positive electrode mixture layers (the first positive electrode mixture layer and the second positive electrode mixture layer) on both surfaces of the collector sheet. The density of the rolled positive electrode mixture layers (the first positive electrode mixture layer and the second positive electrode mixture layer) is set to 3.5 g / cm 3 The loading amount of the positive electrode mixture layer (the first positive electrode mixture layer and the second positive electrode mixture layer) on the surface of the collector sheet was set to 300 mg / 10 cm 2 .

[0169] (Step 6: Slitting)

[0170] In the stacked intermediate of the first positive electrode mixture layer and the second positive electrode mixture layer and the collector sheet, the first positive electrode mixture layer is continuously cut along the length direction of the first region in the first region to obtain a plurality of strip-shaped positive electrodes A1. That is, by slitting, the first region is divided into the 1a region and the 1b region, and the first positive electrode mixture layer is divided into the 1a positive electrode mixture layer and the 1b positive electrode mixture layer. A positive electrode having a second positive electrode mixture layer supported on the surface of the second region of the positive electrode collector, and the 1a positive electrode mixture layer and the 1b positive electrode mixture layer supported on the 1a region and the 1b region of the positive electrode collector, respectively, is obtained. The widths of the 1a region and the 1b region are each 10% of the width of the positive electrode collector (the width of the 1a region, the 1b region and the 2nd region combined).

[0171] The positive electrode was cut along the width direction to form a cross section in the thickness direction, and the cross section was processed using a cross section polisher (CP) to obtain a sample cross section. An SEM image of the sample cross section was taken, and the average value of the first equivalent circle diameter of more than 10 first positive electrode active materials was obtained as D1 by the above method, and the average value of the second equivalent circle diameter of more than 10 cross sections of the second positive electrode active materials was obtained as D2. As a result, the average values ​​D1 and D2 are basically consistent with D1 and D2 (i.e., 4μm and 20μm) obtained as the median particle size in the volume-based particle size distribution.

[0172] 《Examples 2 to 9 and Comparative Examples 1 to 7》

[0173] Positive electrodes A2 to A9 of Examples 2 to 9 and B1 to B7 of Comparative Examples 1 to 7 were produced in the same manner as battery A1 of Example 1 except that the average particle sizes D1 and D2 of the first and second positive electrode active materials were set to the values ​​shown in Table 1.

[0174] The following evaluations were performed on each positive electrode of the example and the comparative example.

[0175] (Evaluation 1: Life of the slitting knife)

[0176] The stacked intermediate is cut continuously by slitting, and the time when a defect (curling) and a scratch are confirmed on the appearance of the slitting knife is regarded as the life. The length of the positive electrode produced until the slitting knife reaches the end of its life is measured. The measured value of each positive electrode is expressed as a relative value when the measured value of positive electrode A1 is set to 100. When the measured value is large, the life of the knife is long and the productivity of the positive electrode is high.

[0177] (Evaluation 2: Liquid absorption of the positive electrode)

[0178] The positive electrode is fixed on a horizontal surface, and 0.3 μL of propylene carbonate (PC) as a solvent is dripped on the surface of the positive electrode mixture layer, and the time from the dripping of the solvent to the complete absorption of the solvent into the positive electrode mixture layer is measured. The liquid absorption is evaluated based on the measured value of the positive electrode A1. Specifically, when the measured value T of the positive electrode is greater than {T0 + (60 × n) - 30} seconds and less than {T0 + (60 × n) + 30} seconds, {100 - (10 × n)} is calculated as a numerical value representing the liquid absorption. It should be noted that T0 (seconds) is the measured value of A1, and n is an integer. For example, when T is greater than (T0-90) seconds and less than (T0-30) seconds, n = -1, and the numerical value representing the liquid absorption is 110. When T is (T0+30) seconds or more and less than (T0+90) seconds, n=1, and the numerical value indicating the liquid absorption is 90. When the numerical value indicating the liquid absorption is large, the liquid absorption (liquid circulation) of the positive electrode is high.

[0179] Table 1 shows the evaluation results.

[0180] [Table 1]

[0181]

[0182] In positive electrodes A1 to A9 in which the average particle size D1 of the first positive electrode active material in the first positive electrode mixture layer is less than 7 μm and the average particle size D2 of the second positive electrode active material in the second positive electrode mixture layer is greater than 9 μm, liquid absorption is improved, the life of the slitting blade is prolonged, and productivity is improved.

[0183] In the positive electrodes B1 to B4 whose second positive electrode active material average particle size D2 in the second positive electrode mixture layer is less than 9 μm, the liquid absorption is reduced. In the positive electrodes B4 to B7 whose first positive electrode active material average particle size D1 in the first positive electrode mixture layer exceeds 7 μm, the life of the slitting blade is reduced.

[0184] 《Examples 10-12》

[0185] The positive electrodes A10 to A12 of Examples 10 to 12 were prepared and evaluated in the same manner as the battery A1 of Example 1, except that the coating amount of the positive electrode slurry (the first positive electrode slurry and the second positive electrode slurry) was adjusted so that the loading amount of the positive electrode mixture layer (the first positive electrode mixture layer and the second positive electrode mixture layer) on the surface of the current collector sheet was the value shown in Table 2. The evaluation results are shown in Table 2. The results of the positive electrode A1 are also shown in Table 2.

[0186] [Table 2]

[0187]

[0188] The positive electrode material layer loading is 100-450 mg / 10 cm2 The liquid absorption of positive electrodes A1, A10-A12 is improved, the life of the slitting knife is long, and the productivity is improved. The loading amount in the positive electrode mixture layer is 100-400 mg / 10 cm 2 In the positive electrodes A1, A10 to A11, the life of the slitting blade becomes longer and higher productivity can be obtained.

[0189] 《Examples 13-14》

[0190] Positive electrodes A13 to A14 of Examples 13 to 14 were prepared and evaluated in the same manner as battery A1 of Example 1, except that the degree of compression during rolling was adjusted so that the density of the positive electrode mixture layer (the first positive electrode mixture layer and the second positive electrode mixture layer) was set to the value shown in Table 3. The evaluation results are shown in Table 3. The results of positive electrode A1 are also shown in Table 3.

[0191] [Table 3]

[0192]

[0193] The density of the positive electrode mixture layer is 2.5 to 4.0 g / cm 3 The liquid absorption of positive electrodes A1, A13 and A14 is improved, and the life of the slitting knife is long, and the productivity is improved. Among them, the density of the positive electrode mixture layer is 2.5 to 3.5 g / cm 3 In the positive electrodes A1 and A13, excellent liquid absorption and productivity can be obtained.

[0194] 《Examples 15 to 17》

[0195] Positive electrodes A15 to A17 of Examples 15 to 17 were prepared and evaluated in the same manner as battery A1 of Example 1, except that the contents of the binder (polyvinylidene fluoride) in the positive electrode mixture layers (the first positive electrode mixture layer and the second positive electrode mixture layer) were set to the values ​​shown in Table 4. The evaluation results are shown in Table 4. The results of positive electrode A1 are also shown.

[0196] [Table 4]

[0197]

[0198] The liquid absorption of positive electrodes A1, A15 to A17 with a binder content of 0.2 to 7% by mass was improved, and the life of the slitting blade was long, and the productivity was improved. Among them, in positive electrodes A1 and A16 with a binder content of 2 to 5% by mass, the life of the slitting blade became longer, and higher productivity could be obtained.

[0199] Industrial Applicability

[0200] The secondary battery of the present disclosure is useful as a main power source for mobile communication devices, electric vehicles, hybrid vehicles, portable electronic devices, and the like.

[0201] The present invention has been described with respect to currently preferred embodiments, but such disclosure is not interpreted restrictively. By reading the above disclosure, various deformations and changes are undoubtedly obvious to those skilled in the art of the technical field to which the present invention belongs. Therefore, the attached technical scheme should be interpreted as including all deformations and changes without departing from the true spirit and scope of the present invention.

[0202] Description of Reference Numerals

[0203] 1: electrode group, 2: positive electrode lead, 3: negative electrode lead, 4: battery case, 5: sealing plate, 6: negative electrode terminal, 7: gasket, 8: seal, 10: positive electrode, 20: positive electrode collector, 21, 51: first region, 21a, 51a: first a region, 21b, 51b: first b region, 22, 52: second region, 30: positive electrode mixture layer, 31: first positive electrode mixture layer, 31a, 61a: first a positive electrode mixture layer, 31b, 61b: first b positive electrode mixture layer, 32, 62: second positive electrode mixture layer, 53, 63: cut portion, 70: collector sheet

Claims

1. A positive electrode for a secondary battery, comprising a strip-shaped positive electrode current collector and a positive electrode mixture layer carried on a surface of the positive electrode current collector, The positive electrode current collector has a first region and a second region, The first region is an edge region extending along the longitudinal direction of the positive electrode current collector at both edge portions in the width direction of the positive electrode current collector. The second region is a central region extending in the longitudinal direction of the positive electrode current collector at the central portion in the width direction of the positive electrode current collector. The positive electrode mixture layer includes a first positive electrode mixture layer carried on the surface of the first region and a second positive electrode mixture layer carried on the surface of the second region. The first positive electrode mixture layer includes a first positive electrode active material. The second positive electrode mixture layer includes a second positive electrode active material. The average particle size D1 of the first positive electrode active material is greater than or equal to 1 μm and less than or equal to 7 μm. The second positive electrode active material has an average particle size D2 of 9 μm or more and 30 μm or less.

2. The positive electrode for a secondary battery according to claim 1, wherein The positive electrode mixture layer loading amount on the surface of the positive electrode current collector is 100 mg / 10 cm 2 More than 400mg / 10cm 2 the following.

3. The positive electrode for a secondary battery according to claim 1, wherein The density of the positive electrode mixture layer is 2.5 g / cm 3 Above 4g / cm 3 the following.

4. The positive electrode for a secondary battery according to claim 1, wherein The positive electrode mixture layer contains 0.2 mass % or more and 5 mass % or less of a binder.

5. The positive electrode for a secondary battery according to claim 1, wherein The first region includes a region 1a and a region 1b extending along the longitudinal direction of the positive electrode current collector at one end edge portion and the other end edge portion in the width direction of the positive electrode current collector, respectively. The widths of the region 1a and the region 1b are each not less than 1% and not more than 20% of the width of the positive electrode current collector.

6. A secondary battery comprising a positive electrode, a negative electrode and an electrolyte, The positive electrode is the positive electrode for a secondary battery according to claim 1.

7. A method for manufacturing a positive electrode for a secondary battery, comprising: In a first step, a current collector sheet having first and second regions in a strip shape alternately is prepared; The second step is to prepare a first positive electrode slurry containing a first positive electrode active material; The third step is to prepare a second positive electrode slurry containing a second positive electrode active material; In a fourth step, the first positive electrode slurry is applied to the surface of the first region and dried to form a first positive electrode mixture layer. a fifth step of applying the second positive electrode slurry on the surface of the second region and drying the slurry to form a second positive electrode mixture layer; and In a sixth step, in the stacked intermediate of the first positive electrode mixture layer, the second positive electrode mixture layer and the current collector sheet, the first positive electrode mixture layer is cut along the length direction of the first region in the first region together with the first positive electrode mixture layer to obtain a plurality of strip-shaped positive electrodes. The average particle size D1 of the first positive electrode active material is greater than or equal to 1 μm and less than or equal to 7 μm. The second positive electrode active material has an average particle size D2 of 9 μm or more and 30 μm or less.

8. The method for producing a positive electrode for a secondary battery according to claim 7, wherein: The fourth step and the fifth step are performed in parallel.

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