Positive electrode for secondary battery, and secondary battery

Abstract

A positive electrode (11) as an example of an embodiment is provided with a positive electrode core (30) and a positive electrode mixture layer (31) disposed on the positive electrode core (30). The positive electrode mixture layer (31) includes first regions (35) and second regions (36) arranged alternately in at least one of the longitudinal direction and the width direction of the positive electrode core (30). The porosity of the second region (36) is greater than the porosity of the first region (35).

Description

Technical Field

[0001] The present disclosure relates to a positive electrode for a secondary battery and a secondary battery using the same. Background Art

[0002] In recent years, secondary batteries such as lithium ion batteries have been widely used in applications that require high capacity, high durability, fast charging performance, etc., such as in-vehicle use and power storage use. The positive electrode, which is a main constituent element of the secondary battery, has a great influence on these performances, and thus a great deal of research has been conducted on the positive electrode. For example, Patent Document 1 discloses a positive electrode in which the physical properties of the binder layer are made different in the thickness direction of the positive electrode binder layer, and there are more active materials with a large specific surface area on the core side than on the surface side of the binder layer.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Patent No. 5929183 Summary of the Invention

[0006] In Patent Document 1, effects of improved discharge capacity and cycle characteristics are described. However, it is considered that if the specific surface area of the surface side of the binder layer is reduced, the penetration of the electrolyte into the core side becomes insufficient, and the fast charging performance is degraded. In particular, when the binder layer is formed at a high density in order to increase the energy density, the degradation of the fast charging performance becomes more significant. An object of the present disclosure is to provide a positive electrode for a secondary battery that can achieve high capacity and excellent fast charging performance.

[0007] The positive electrode for a secondary battery of the present disclosure includes a positive electrode core and a positive electrode binder layer disposed on the positive electrode core, and the positive electrode binder layer includes a first region and a second region alternately disposed in at least one of the length direction and the width direction of the positive electrode core, and the porosity of the second region is greater than the porosity of the first region.

[0008] The secondary battery of the present disclosure includes the above positive electrode, a negative electrode, and an electrolyte.

[0009] According to the positive electrode of the present disclosure, a secondary battery with high capacity and excellent fast charging performance can be provided. Brief Description of the Drawings

[0010] Figure 1 is a cross-sectional view of a secondary battery as an example of an embodiment.

[0011] Figure 2 is a front view of a positive electrode as an example of an embodiment.

[0012] Figure 3 is Figure 2 a cross-sectional view taken along line AA in

[0013] Figure 4 This is a diagram showing a modified example of the positive electrode.

[0014] Figure 5 This is a diagram showing a modified example of the positive electrode. Detailed implementation mode

[0015] The inventors of the present invention have conducted in-depth research on the above problems. As a result, by providing a first region and a second region with different porosity rates in the positive electrode mixture layer, and alternately arranging the first region and the second region in at least one of the length direction and the width direction of the positive electrode core, a secondary battery with high capacity and excellent fast charging performance has been successfully realized. Through the function of the second region with a large porosity rate, the permeability of the electrolyte in the entire mixture layer is greatly improved, and the electrolyte also rapidly penetrates in the thickness direction of the mixture layer. As a result, excellent fast charging performance can be obtained.

[0016] On the other hand, the first region of the mixture layer with a small porosity rate contributes to high capacity. In addition, the electrolyte is also supplied from the adjacent second region to the first region. According to the secondary battery using the positive electrode of the present disclosure, high capacity and excellent fast charging performance can be highly balanced. In addition, since the electrolyte is smoothly supplied to the entire mixture layer, a homogeneous battery reaction occurs in a wide range of the mixture layer, and the cycle characteristics are also improved.

[0017] Hereinafter, an example of an implementation mode of the positive electrode for a secondary battery of the present disclosure and a secondary battery using the positive electrode will be described in detail with reference to the drawings. It should be noted that a configuration formed by selectively combining the respective constituent elements of the following described multiple implementation modes and modified examples is included in the scope of the present disclosure.

[0018] In the implementation mode described below, as the secondary battery, a cylindrical battery 10 in which a wound electrode body 14 is housed in a bottomed cylindrical outer can 16 is exemplified, but the outer package of the battery is not limited to a cylindrical outer can. As other implementation modes of the secondary battery of the present disclosure, a square battery having a square outer can, a coin-shaped battery having a coin-shaped outer can, and a pouch-type battery having an outer package composed of a laminate including a metal layer and a resin layer can be cited. In addition, the electrode body is not limited to the wound type, and may also be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately laminated with a separator therebetween. In addition, the electrolyte may be an aqueous electrolyte, but a non-aqueous electrolyte is used in the present implementation mode.

[0019] Figure 1 This is a diagram schematically showing an axial cross-section of the cylindrical battery 10 as an example of the implementation mode. As Figure 1As shown, the cylindrical battery 10 includes a wound electrode body 14, a non-aqueous electrolyte, and an outer can 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 has a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape with the separator 13 interposed therebetween. The outer can 16 is a bottomed cylindrical metal container that is open at one end in the axial direction, and the opening of the outer can 16 is blocked by a sealing body 17. Hereinafter, for the sake of convenience of explanation, the side of the battery where the sealing body 17 is located is set as the upper side, and the bottom side of the outer can 16 is set as the lower side.

[0020] The non-aqueous electrolyte contains a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. As the non-aqueous solvent, for example, esters, ethers, nitriles, amides, and a mixed solvent of two or more of them can be used. As an example of the non-aqueous solvent, ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and a mixed solvent thereof can be cited. The non-aqueous solvent may contain a halogen-substituted product (for example, fluoroethylene carbonate, etc.) in which at least a part of the hydrogen of these solvents is substituted with a halogen atom such as fluorine. The electrolyte salt is, for example, a lithium salt such as LiPF 6 and so on.

[0021] The positive electrode 11, the negative electrode 12, and the separator 13 that constitute the electrode body 14 are all strip-shaped long bodies, and are alternately laminated in the radial direction of the electrode body 14 by being wound in a spiral shape. In order to prevent the precipitation of lithium, the negative electrode 12 is formed with a size that is one turn larger than the positive electrode 11. That is, the negative electrode 12 is formed to be longer than the positive electrode 11 in the length direction and the width direction. The separator 13 is formed with a size that is at least one turn larger than the positive electrode 11, and for example, two sheets are arranged so as to sandwich the positive electrode 11. The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 by welding or the like and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like.

[0022] Insulating plates 18 and 19 are respectively arranged above and below the electrode body 14. In Figure 1 the example shown, the positive electrode lead 20 extends toward the sealing body 17 through the through hole of the insulating plate 18, and the negative electrode lead 21 extends toward the bottom side of the outer can 16 through the outside of the insulating plate 19. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 inside the sealing body 17 by welding or the like, and the lid 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive terminal. The negative electrode lead 21 is connected to the inner surface of the bottom of the outer can 16 by welding or the like, and the outer can 16 becomes the negative terminal.

[0023] A gasket 28 is provided between the outer can 16 and the sealing body 17 to ensure the hermeticity inside the battery. An insertion groove portion 22 for supporting the sealing body 17 is formed in the outer can 16, where a part of the side surface extends inward. The insertion groove portion 22 is preferably formed in a ring shape along the circumferential direction of the outer can 16, and the sealing body 17 is supported on its upper surface. The sealing body 17 is fixed to the upper part of the outer can 16 through the insertion groove portion 22 and the opening end portion of the outer can 16 that is caulked to the sealing body 17.

[0024] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a lid 27 are laminated in sequence from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and the members other than the insulating member 25 are electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is interposed between their respective peripheral portions. If the internal pressure of the battery rises due to abnormal heating, the lower valve body 24 is deformed and broken in a manner of pushing the upper valve body 26 toward the lid 27 side, whereby the current path between the lower valve body 24 and the upper valve body 26 is cut off. If the internal pressure further rises, the upper valve body 26 is broken, and gas is discharged from the opening portion of the lid 27.

[0025] Hereinafter, the positive electrode 11, the negative electrode 12, and the separator 13 constituting the electrode body 14 will be described in detail, particularly the positive electrode 11.

[0026] [Positive Electrode]

[0027] The positive electrode 11 has a positive electrode core 30 and a positive electrode mixture layer 31 disposed on the positive electrode core 30. The positive electrode core 30 can be a foil of a metal such as aluminum, aluminum alloy, stainless steel, or titanium that is stable within the potential range of the positive electrode 11, a film having the metal disposed on its surface, or the like. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent, and a binder, and is preferably disposed on both sides of the positive electrode core 30 except for the portion connected to the positive electrode lead 20. A protective layer containing inorganic particles and a binder can also be disposed between the positive electrode core 30 and the positive electrode mixture layer 31, or on the positive electrode mixture layer 31.

[0028] The positive electrode 11 can be produced, for example, by coating a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder on the positive electrode core 30, and forming the positive electrode mixture layer 31 on both sides of the positive electrode core 30 by drying the coating film and then compressing it. The dispersion medium of the positive electrode mixture slurry is, for example, N-methyl-2-pyrrolidone (NMP). The positive electrode mixture slurry can be prepared by adding a positive electrode active material to a conductive agent paste containing a conductive agent, a binder, and a dispersion medium. The positive electrode mixture slurry and the conductive agent paste can contain a dispersant.

[0029] As will be described in detail later, the positive electrode mixture layer 31 includes a first region and a second region that are alternately arranged in at least one of the length direction and the width direction of the positive electrode core 30 and have different physical properties. The positive electrode mixture layer 31 is formed using at least two types of positive electrode mixture slurries.

[0030] The positive electrode active material uses a lithium metal composite oxide. Examples of the metal elements contained in the lithium metal composite oxide include Li, Ni, Co, Mn, Al, Be, B, Na, Mg, Si, K, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, In, Sn, Sb, Ba, Ta, W, Pb, Bi, etc. Suitable lithium metal composite oxides contain Li, Ni, and Co, and contain at least one of Mn and Al.

[0031] The lithium metal composite oxide, for example, has a layered rock salt structure. Examples of the layered rock salt structure include a layered rock salt structure belonging to the space group R-3m, a layered rock salt structure belonging to the space group C2 / m, etc. Among them, from the viewpoints of high capacity and crystal structure stability, a layered rock salt structure belonging to the space group R-3m is preferred. It should be noted that the content ratio of the elements in the composite oxide can be measured by an inductively coupled plasma optical emission spectrometer (ICP-AES), an electron probe microanalyzer (EPMA), or an energy dispersive X-ray analyzer (EDX).

[0032] In the lithium metal composite oxide, the proportion of Ni relative to the total molar number of metal elements other than Li is preferably 50 mol% or more, more preferably 80 mol% or more. By making the Ni content ratio 50 mol% or more, a high-capacity battery can be obtained, and the effects brought about by the configuration of the present disclosure become more significant. The Ni content ratio relative to the total molar number of metal elements other than Li can be 85 mol% or more, or can be 90 mol% or more. The upper limit of the Ni content ratio is, for example, 95 mol%.

[0033] When the lithium metal composite oxide contains Co, the content ratio of Co relative to the total molar number of metal elements other than Li is preferably 1 mol% or more and 25 mol% or less, more preferably 2 mol% or more and 7 mol% or less. In this case, the material cost can be suppressed, and high capacity and high durability can be achieved at the same time. When the lithium metal composite oxide contains Mn, the content ratio of Mn, for example, relative to the total molar number of metal elements other than Li is 1 mol% or more and 20 mol% or less. In this case, it is easy to achieve both high capacity and high durability. When the lithium metal composite oxide contains Al, the content ratio of Al, for example, relative to the total molar number of metal elements other than Li is 0.1 mol% or more and 7 mol% or less.

[0034] Figure 2 is the front view of the positive electrode 11, schematically showing the state where the positive electrode 11 is unfolded. Figure 3 is Figure 2 the sectional view taken along line AA in Figure 2 and Figure 3 As shown in

[0035] In the positive electrode 11, the porosity of the second region 36 is larger than the porosity of the first region 35. As a result of the research by the present inventors, by providing the first region 35 and the second region 36 having different porosities in the positive electrode mixture layer 31 and alternately arranging these regions in the length direction of the positive electrode core 30, it is possible to realize the cylindrical battery 10 having high capacity and excellent rapid charging performance. It should be noted that, within the scope not impairing the object of the present disclosure, physical properties other than the porosities of the first region 35 and the second region 36 may also be different from each other. In addition, there may be three or more regions having different porosities in the positive electrode mixture layer.

[0036] According to the positive electrode 11, due to the second region 36 having a large porosity, the permeability of the electrolyte in the entire mixture layer is significantly improved, and thus excellent rapid charging performance can be obtained. In addition, the first region 35 having a small porosity contributes to high capacity. Further, the electrolyte is also supplied from the adjacent second region 36 to the first region 35. Therefore, according to the positive electrode 11, high capacity and excellent rapid charging performance can be highly balanced. The second region 36 functions as a supply path for the electrolyte, smoothly supplying the electrolyte to the entire positive electrode mixture layer 31. Therefore, a homogeneous battery reaction occurs in a wide range of the positive electrode mixture layer 31, and the cycle characteristics are also improved.

[0037] The BET specific surface areas of the first region 35 and the second region 36 may be substantially the same, for example, but it is preferable that the BET specific surface area of the second region 36 is larger than the BET specific surface area of the first region 35. The BET specific surface area of each region is measured by the BET method using nitrogen with the mixture layer (each region) peeled off from the positive electrode core 30 as a sample, and can be measured by a commercially available measuring device such as HM model-1201 of Macsorb Co., Ltd., for example.

[0038] The BET specific surface area of the second region 36 is preferably 1.1 times or more and 3.0 times or less, more preferably 1.2 times or more and 2.0 times or less, than the BET specific surface area of the first region 35. For example, the BET specific surface area of the first region 35 is 1.5 m 2 / g or more and 2.5 m 2 / g or less, and the BET specific surface area of the second region 36 is 2.0 m 2 / g or more and 3.0 m 2 / g or less.

[0039] As described above, the first region 35 and the second region 36 are alternately arranged in the length direction of the positive electrode core 30 to form a striped pattern. The front view shapes of the first region 35 and the second region 36 are not particularly limited, but in Figure 2 the example shown, they are formed in a rectangular shape in the front view. The shapes and sizes of the respective first regions 35 may also be different, but from the viewpoint of homogenizing the electrode reaction and the like, they are preferably substantially the same (the same applies to the second region 36). It should be noted that if the difference in the shapes and sizes of a very small part of the regions is small, the same effect as in the case where the shapes and sizes of the regions are uniform can be achieved.

[0040] The first region 35 and the second region 36 can be formed, for example, using different positive electrode mixture slurries. After intermittently coating the surface of the positive electrode core 30 with the first positive electrode mixture slurry for forming the first region 35 in the length direction of the positive electrode core 30, the second positive electrode mixture slurry for forming the second region 36 is intermittently coated on the portion where the first positive electrode mixture slurry is not coated, thereby forming Figure 2 the striped pattern exemplified. It should be noted that the first and second positive electrode mixture slurries can also be simultaneously coated on different places on the surface of the positive electrode core 30 to form a striped pattern. For example, a positive electrode active material with a porosity that is likely to become smaller is added to the first positive electrode mixture slurry, and a positive electrode active material with a porosity that is likely to become larger is added to the second positive electrode mixture slurry.

[0041] Among the plurality of first regions 35, physical properties such as porosity are preferably substantially the same. By forming each first region 35 using the same first positive electrode mixture slurry, the porosity of each first region 35 is substantially the same. Similarly, among the plurality of second regions 36, physical properties such as porosity are preferably substantially the same. In addition, the porosity is substantially the same in the thickness direction of the first region 35. For example, the porosity is substantially the same near the positive electrode core 30 of the first region 35 and near the surface of the first region 35 away from the positive electrode core 30 (the same applies to the second region 36). The thicknesses of the first region 35 and the second region 36 are preferably of the same degree.

[0042] The length of the first region 35 in the longitudinal direction of the positive electrode core 30 may be equal to or less than the length of the second region 36 in the longitudinal direction of the positive electrode core 30, but is preferably longer than the length of the second region 36. In this case, high capacity and excellent fast charging performance can be more highly balanced. In the present embodiment, the first region 35 and the second region 36 extend longer in the width direction than in the longitudinal direction of the positive electrode core 30. Hereinafter, the length of the first region 35 in the longitudinal direction of the positive electrode core 30 is defined as "width W1", and the length of the second region 36 in the longitudinal direction of the positive electrode core 30 is defined as "width W2".

[0043] The first region 35 and the second region 36 are preferably formed over the entire width of the positive electrode core 30. In this case, high capacity and excellent fast charging performance can be more highly balanced. The widths W1 and W2 of the respective regions may vary in the width direction of the positive electrode core 30, but in the present embodiment, the respective regions are formed with substantially the same width in the width direction of the positive electrode core 30. In addition, since the width W1 of each first region 35 is substantially the same and the width W2 of each second region 36 is also substantially the same, stripes formed by regularly repeating the first region 35 and the second region 36 are formed in the longitudinal direction of the positive electrode core 30.

[0044] The width W1 of the first region 35 is preferably 1.1 times or more, more preferably 1.5 times or more, and particularly preferably 2.0 times or more or 2.5 times or more the width W2 of the second region 36. There is no particular limitation on the upper limit of the ratio (W1 / W2) of the width W1 to the width W2. As an example, it is 10.0 times, 9.0 times, or 8.0 times. An example of a suitable range of the ratio (W1 / W2) is 1.1 times or more and 10.0 times or less, 1.5 times or more and 9.0 times or less, 1.5 times or more and 8.0 times or less, or 2.0 times or more and 8.0 times or less. The suitable ratio (W1 / W2) varies depending on the porosity of each region, etc., but if the ratio (W1 / W2) is approximately within this range, high capacity and excellent fast charging performance can be more highly balanced.

[0045] The width W1 of the first region 35 is, for example, 1 mm or more and 30 mm or less, more preferably 2 mm or more and 20 mm or less. The width W2 of the second region 36 is, for example, 0.5 mm or more and 20 mm or less, more preferably 1 mm or more and 15 mm or less. The length of the positive electrode 11 varies depending on the size of the cylindrical battery 10 and the like. As an example, it is 40 mm or more and 4000 mm or less. In this case, one or more and 2000 or less of the first region 35 and the second region 36 are respectively arranged on one side of the positive electrode core 30 in the length direction of the positive electrode 11. The number of each of the first region 35 and the second region 36 arranged in the length direction of the positive electrode 11 is obtained based on the above widths W1, W2 and the length of the positive electrode 11.

[0046] If the porosity of the positive electrode mixture layer 31 satisfies the condition that the porosity of the second region 36 > the porosity of the first region 35, it helps to achieve both high capacity and excellent fast charging performance. The lower limit of the porosity of each region is preferably greater than 11%, more preferably greater than 12%. That is, the porosity of the first region 35 is preferably greater than 11%. In addition, the upper limit of the porosity of each region is preferably 35%, more preferably 30%. That is, within the range where the porosity is 10% or more and 35% or less, it is preferably to satisfy the condition that the porosity of the second region 36 > the porosity of the first region 35.

[0047] The porosity of the first region 35 is preferably 10% or more and 30% or less, more preferably 12% or more and 25% or less, particularly preferably 15% or more and 20% or less. The porosity of the second region 36 is preferably 15% or more and 35% or less, more preferably 17% or more and 30% or less, particularly preferably 20% or more and 25% or less. If the porosity of each region is within this range and the ratio (W1 / W2) is within the above range, high capacity and excellent fast charging performance can be achieved more highly.

[0048] The porosity of the first region 35 and the second region 36 can be measured by the following method.

[0049] (1) Use an ion milling device to expose the cross-section of the positive electrode mixture layer 31.

[0050] (2) Use a scanning electron microscope (SEM) to take a backscattered electron image of the exposed cross-section of the positive electrode mixture layer 31. The magnification when taking the backscattered electron image is, for example, 1000 - 5000 times.

[0051] (3) Import the SEM image of the cross-section of the positive electrode mixture layer 31 into a computer, use image analysis software (for example, ImageJ manufactured by the National Institutes of Health, USA), distinguish it into three colors according to the contrast, and set the middle color as the void.

[0052] (4)Select a measurement target area from the processed image, calculate the total area of voids within this area, and compute the proportion (void fraction) of the voids in the measurement target area.

[0053] The void fractions of the first region 35 and the second region 36 can be adjusted to a target range, for example, by changing the compression force of each region using the same material, or by forming each region using mutually different materials. Specifically, in the first region 35 and the second region 36, at least one selected from the positive electrode active material, the conductive agent, and the binder is changed. Among them, from the viewpoints of battery performance, productivity, etc., it is preferable to use different types of positive electrode active materials in the first region 35 and the second region 36. Different positive electrode active materials can also be used in the first region 35 and the second region 36, and the compression force of the coating film can be made different.

[0054] In the positive electrode mixture layer 31, as the positive electrode active material, for example, it contains secondary particles formed by aggregation of primary particles with an average particle diameter of 50 nm or more and 5 μm or less, that is, the first lithium metal composite oxide, and non-aggregated particles, that is, the second lithium metal composite oxide. The first lithium metal composite oxide contains a plurality of primary particles. The second lithium metal composite oxide can be a single primary particle (a single crystal particle without grain boundaries inside), or secondary particles formed by aggregation of 5 or fewer primary particles. The second lithium metal composite oxide is characterized by having a smaller number of primary particles and harder particles compared to the first lithium metal composite oxide. For example, the first lithium metal composite oxide is easily crushed during the compression process of the positive electrode mixture layer 31 and is filled at a high density.

[0055] The first region 35 contains, for example, more of the first lithium metal composite oxide than the second lithium metal composite oxide. That is, in the first region 35, the content rate (mass ratio) of the first lithium metal composite oxide with respect to the total mass of the positive electrode active material is greater than the content rate of the second lithium metal composite oxide. On the other hand, the second region 36 contains, for example, more of the second lithium metal composite oxide than the first lithium metal composite oxide. As the positive electrode active material, the first region 35 may contain only the first lithium metal composite oxide, and the second region 36 may contain only the second lithium metal composite oxide.

[0056] The median particle size on a volume basis (hereinafter sometimes referred to as "D50") of the lithium metal composite oxide contained in the first region 35 is, for example, 7 μm or more and 30 μm or less. In this specification, D50 refers to the particle size at which the cumulative frequency in the volume-based particle size distribution reaches 50% starting from the smaller particle size side. The D50 of the lithium metal composite oxide contained in the second region 36 is, for example, 1 μm or more and 10 μm or less. It should be noted that when only the first lithium metal composite oxide is contained in the first region 35, the D50 of the first lithium metal composite oxide is equal to the D50 of the lithium metal composite oxide contained in the first region 35.

[0057] The particle size distribution of the positive electrode active material can be measured using a laser diffraction type particle size distribution measuring device (for example, MT3000II manufactured by MicrotracBEL Corporation) with water as the dispersion medium. It should be noted that the average particle size of the positive electrode active material can also be obtained by measuring the diameter of the circumscribed circle of the particles in the cross-sectional image of the positive electrode mixture layer 31. In the case where it is difficult to measure the above particle size distribution, this average particle size can be applied instead of D50. The cross-section of the positive electrode mixture layer 31 can be produced by the cross polishing (CP) method, and the cross-sectional image is taken by SEM. The average particle size can be calculated by averaging the particle sizes of any 100 particles based on the SEM image.

[0058] The average particle size of the primary particles constituting the positive electrode active material (lithium metal composite oxide) is, for example, 50 nm or more and 5.0 μm or less, preferably 50 nm or more and 1.0 μm or less. The average particle size of the primary particles is calculated as follows: The diameters of the circumscribed circles of 100 primary particles extracted by analyzing the SEM image of the cross-section of the secondary particles are measured, and the measured values are averaged.

[0059] The first region 35 can, for example, contain two types of lithium metal composite oxides with different D50s as the positive electrode active material. By mixing large particles and small particles, the packing density of the positive electrode active material becomes higher and the porosity of the first region 35 becomes smaller. In this case, the lithium metal composite oxide contained in the first region 35 has a particle size distribution with two peaks. On the other hand, the second region 36 contains, for example, one type of lithium metal composite oxide. In this case, the lithium metal composite oxide contained in the second region 36 has a particle size distribution with one peak. It should be noted that as long as the porosities of the first region 35 and the second region 36 can be adjusted to the target range, the combination of the positive electrode active materials used in each region is not particularly limited.

[0060] A lithium metal composite oxide can be synthesized, for example, by mixing a composite oxide raw material containing Ni and Co and at least one of Mn and Al, and a Li raw material such as lithium hydroxide (LiOH), and then firing the mixture. The fired product can be pulverized, classified, etc., and can also be washed with water. The composite oxide raw material containing Ni, Co, etc. is obtained, for example, by precipitating (co-precipitating) a composite hydroxide containing Ni, Co, etc. and then performing heat treatment on the composite hydroxide.

[0061] The above-mentioned composite hydroxide can be synthesized, for example, by adjusting the pH to the alkaline side (for example, 8.5 or more and 12.5 or less) by dropping an alkali solution such as sodium hydroxide while stirring a solution containing metal salts such as Ni and Co. The particle size of the composite hydroxide tends to be smaller as the pH during synthesis is higher, and can also be controlled by adjusting the amount of the added metal salt solution. Lithium metal composite oxides with different particle sizes can be produced by controlling the particle size of the composite hydroxide.

[0062] The firing process of the mixture of the composite oxide raw material and the Li raw material can be a multi-stage firing process including a first firing process and a second firing process with a temperature higher than that of the first firing process. The firing of the mixture is carried out in an oxygen atmosphere. At this time, for example, the oxygen concentration is set to 85% or more. The suitable first firing temperature varies slightly according to the composition of the mixture. As an example, it is 500 °C or more and 750 °C or less. The suitable second firing temperature is, for example, 800 °C or more and 1150 °C or less. The temperatures of each firing process preferably have a temperature difference of 50 °C or more.

[0063] Non-aggregated single particles can be synthesized, for example, by increasing the pH of the alkaline aqueous solution used in the synthesis of the composite hydroxide compared to the case of synthesizing secondary particles formed by aggregating a plurality of primary particles. Alternatively, non-aggregated single particles can also be synthesized by increasing the firing temperature instead of increasing the pH of the alkaline aqueous solution, or by increasing the firing temperature on the basis of increasing the pH of the alkaline aqueous solution. An example of the suitable pH of the alkaline aqueous solution during the synthesis of single particles is 10 to 11, and an example of the suitable firing temperature is 950 to 1100 °C. When synthesizing secondary particles, for example, an alkaline aqueous solution with a pH of 9 to 10 is used, and the firing temperature is 950 °C or less.

[0064] Examples of the conductive agent contained in the positive electrode binder layer 31 include carbon blacks such as acetylene black and Ketjen black, graphite, carbon nanotubes (CNT), carbon nanofibers, graphene, metal fibers, metal powders, conductive whiskers, etc. The conductive agent can be used alone or in combination of multiple kinds. The first region 35 and the second region 36 contain, for example, the same conductive agent, but may also contain different conductive agents.

[0065] Examples of the binder contained in the positive electrode mixture layer 31 include fluororesins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF), olefin resins such as polyethylene, polypropylene, ethylene-propylene-isoprene copolymer, and ethylene-propylene-butadiene copolymer, acrylic resins such as polyacrylonitrile (PAN), polyimide, polyamide, and ethylene-acrylic acid copolymer. In addition, these resins can be used in combination with carboxymethyl cellulose (CMC) or its salts, polyethylene oxide (PEO), etc. The binder can be used alone or in combination of multiple kinds. The first region 35 and the second region 36 contain, for example, the same kind of binder, but may also contain different binders.

[0066] The content rates of the conductive agent and the binder relative to the mass of the positive electrode mixture layer 31 are, for example, 0.1% by mass or more and 5% by mass or less, respectively. The amounts of the conductive agent in the first region 35 and the second region 36 are substantially the same, for example, but the content rates of the conductive agent in each region may also be different. As an example, it can be mentioned that the content rate of the conductive agent in the second region 36 is made larger than that in the first region 35. The same applies to the binder. The amounts of the binder in each region are substantially the same, for example, but the content rates of the binder in each region may also be different.

[0067] Figure 4 and Figure 5 is a front view showing a modified example of the positive electrode 11. In Figure 2 the example shown, the first region 35 and the second region 36 are alternately arranged only along the length direction of the positive electrode core 30, but may also be arranged as in Figure 4 and Figure 5 shown, the first region 35 and the second region 36 are alternately arranged in both the length direction and the width direction of the positive electrode core 30. The first region 35 and the second region 36 can be arranged in a random and irregular pattern, but from the viewpoints of stabilizing the battery performance and homogenizing the battery reaction, etc., it is preferable to arrange them in a regular pattern.

[0068] It should be noted that the first region 35 and the second region 36 can be alternately arranged only along the width direction of the positive electrode 11, but in the case of a stripe shape, it is preferably the Figure 2 shape exemplified. In the cylindrical battery 10, if the volume change of the charge-discharge electrode body 14 becomes large, there is a case where the electrolyte is extruded in the axial direction of the electrode body 14. Therefore, according to the stripe shape formed in such a manner that the second region 36 having a high porosity and good electrolyte permeability is along the axial direction, the supply of the electrolyte to the electrode body 14 becomes smoother.

[0069] As Figure 4 shown, the second region 36 can be arranged in a lattice shape when viewed from the front of the positive electrode 11. In Figure 4In the example shown, the cells of the second region 36 are along the width direction and the length direction of the positive electrode 11, but the cells can also be formed along a direction inclined with respect to the width direction and the length direction. The first region 35 surrounded by the cells of the second region 36 has a square shape when viewed from the front, but can also be a rectangular shape. In this case, the lattice-like second region 36 also functions as a supply path for the electrolyte, and a part of the electrolyte is supplied to the first region 35 via the second region 36.

[0070] As Figure 5 shown, the first region 35 can be configured to be dot-shaped when viewed from the front of the positive electrode 11. The first region 35 has, for example, a perfect circular shape when viewed from the front. In Figure 5 the example shown, the first regions 35 are arranged at equal intervals in the length direction of the positive electrode 11 with the same size as each other. They are arranged densely in the width direction of the positive electrode 11 to fill the depressions at the points of two first regions 35. And the second region 36 is formed in such a way as to fill the spaces between the points of the first region 35. In this case, the second region 36 also functions as a supply path for the electrolyte.

[0071] It should be noted that the second region 36 can be formed in a honeycomb shape (hexagonal shape) when viewed from the front of the positive electrode 11, or can have a shape other than circular, square, and hexagonal. In addition, the first region 35 can be formed in a lattice shape or a honeycomb shape, or the second region 36 can be formed in a dot shape.

[0072] [Negative electrode]

[0073] As Figure 1 shown, the negative electrode 12 has a negative electrode core 40 and a negative electrode mixture layer 41 disposed on the negative electrode core 40. The negative electrode core 40 can use a foil of a metal such as copper, copper alloy, stainless steel, nickel, nickel alloy, etc. that is stable within the potential range of the negative electrode 12, a film having such a metal disposed on its surface, etc. Preferably, the negative electrode mixture layer 41 contains a negative electrode active material and a binder, and is provided on both sides of the negative electrode core 40 except for the part where the negative electrode lead 21 is connected. A protective layer containing inorganic particles and a binder can also be disposed between the negative electrode cores 40 or on the negative electrode mixture layer 41.

[0074] The negative electrode 12 can be manufactured, for example, by coating a negative electrode mixture slurry containing a negative electrode active material and a binder on the surface of the negative electrode core 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on both sides of the negative electrode core 40. The dispersion medium of the negative electrode mixture slurry uses water, for example. The negative electrode mixture layer 41 can contain a conductive agent such as CNT, and the conductive agent can use the same conductive agent as in the case of the positive electrode 11. The negative electrode mixture slurry can contain a dispersant.

[0075] The negative electrode active material generally uses a carbon material that can reversibly absorb and release lithium ions. As the negative electrode active material, elements alloyed with Li such as Si and Sn, materials containing such elements, etc. can be used. Among them, a material containing Si is preferred. In addition, as the negative electrode active material, lithium titanate, etc. with a potential for charge and discharge relative to metallic lithium higher than that of the carbon material can also be used. The negative electrode active material can be used alone or in combination of multiple kinds.

[0076] The carbon material that functions as the negative electrode active material is, for example, at least one selected from natural graphite, artificial graphite, soft carbon, and hard carbon. Among them, as the carbon material, it is preferred to use at least artificial graphite such as massive artificial graphite (MAG) and graphitized mesophase carbon microspheres (MCMB), natural graphite such as flake graphite, massive graphite, and earthy graphite, or a mixture thereof. The volume-based D50 of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0077] An example of the silicon-containing material that functions as the negative electrode active material can be a silicon alloy, a silicon compound, and a composite material containing Si. Among them, a composite material containing Si is preferred. A suitable composite material is composite particles containing an ion conduction phase and an Si phase dispersed in the ion conduction phase. The ion conduction phase is, for example, at least one selected from a silicate phase, a carbon phase, a silicide phase, and a silica phase. The Si phase is formed by dispersing Si into fine particle form. The ion conduction phase is a continuous phase composed of a collection of finer particles than the Si phase. The volume-based D50 of the silicon-containing material is, for example, 1 μm or more and 20 μm or less, or 1 μm or more and 15 μm or less.

[0078] The binder contained in the negative electrode mixture layer 41 can be the same as that of the positive electrode 11, and fluororesin, olefin resin, PAN, polyimide, polyamide, acrylic resin, etc. can be used. Usually, polyvinyl acetate, styrene-butadiene rubber (SBR), etc. are used. Among them, it is preferred to use SBR. The binder can be used alone or in combination of multiple kinds. In addition, the negative electrode mixture layer 41 preferably contains CMC or its salt, polyacrylic acid (PAA) or its salt, polyvinyl alcohol (PVA), etc. They also function as thickeners in the negative electrode mixture slurry.

[0079] [Separator]

[0080] The separator 13 uses a porous sheet having ion permeability and insulation. Specific examples of the porous sheet include microporous films, woven fabrics, non-woven fabrics, etc. As the material of the separator 13, polyolefins such as polyethylene and polypropylene, cellulose, etc. are suitable. The separator 13 can be a single-layer structure or a multi-layer structure. For example, the separator 13 can have a multi-layer structure including a thermoplastic resin layer such as polyolefin and a cellulose fiber layer, a double-layer structure of polyethylene (PE) / polypropylene (PP), or a triple-layer structure of PE / PP / PE.

[0081] A filler layer containing an inorganic filler can be disposed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. As the inorganic filler, for example, oxides containing metal elements such as Ti, Al, Si, Mg, phosphate compounds, etc. can be cited. The filler layer can be formed by coating a slurry containing the filler on the surface of the positive electrode 11, the negative electrode 12, or the separator 13. In addition, a resin layer with high heat resistance such as an aromatic polyamide resin (heat-resistant layer) can be disposed on the surface of the separator 13. For example, the separator 13 can have a substrate made of a porous sheet and a filler layer or a heat-resistant layer disposed on the substrate.

[0082] Examples

[0083] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0084] <Example 1>

[0085] [Synthesis of the first lithium metal composite oxide]

[0086] A composite hydroxide containing Ni, Co, and Al in a molar ratio of 85:10:5 was synthesized by a coprecipitation method and heat-treated at 600 °C to obtain a composite oxide. In the synthesis of the composite hydroxide, the pH and the amount of the metal salt solution were adjusted so that the D50 of the finally obtained lithium metal composite oxide was about 15 to 20 μm. The obtained composite oxide and lithium hydroxide were mixed so that the molar ratio of the metal element (Me) in the composite oxide to Li of lithium hydroxide (Li / Me ratio) was 1:1.020. This mixture was put into a firing furnace and fired in two stages.

[0087] In the firing process, under an oxygen flow with an oxygen concentration of 95% (per 10 cm 3at a flow rate of 2 mL / min and 5 L / min per 1 kg of the mixture), and heated from room temperature to 650 °C (the first firing temperature) at a heating rate of 3 °C / min (the first heating rate). Then, it was heated from 650 °C to 750 °C (the second firing temperature) at a heating rate of 1 °C / min (the second heating rate) and held at 750 °C for 3 hours. After crushing the fired product, it was washed with water to obtain the first lithium metal composite oxide.

[0088] Using MT3000II manufactured by MicrotracBEL Co., Ltd., the volume-based D50 of the first lithium metal composite oxide measured with water as the dispersion medium was 17 μm. It was confirmed from the SEM image that this composite oxide was secondary particles formed by the aggregation of primary particles with an average particle size of 500 nm.

[0089] [Preparation of the first positive electrode mixture paste]

[0090] As the positive electrode active material, the above-mentioned first lithium metal composite oxide was used. The positive electrode active material, acetylene black, and polyvinylidene fluoride (PVdF) were mixed at a solid component mass ratio of 98:1:1, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare the first positive electrode mixture paste.

[0091] [Synthesis of the second lithium metal composite oxide]

[0092] The pH during the synthesis of the composite hydroxide and the amount of the metal salt solution were adjusted so that the D50 of the finally obtained lithium metal composite oxide would be about 1 to 5 μm, and 10% by mass of KOH was added to the composite oxide that had been fired in two stages, and it was fired in an oxygen stream at 750 °C for 40 hours. Except for this, the second lithium metal composite oxide was obtained by the same method as the first lithium metal composite oxide.

[0093] Using MT3000II manufactured by MicrotracBEL Co., Ltd., the volume-based D50 of the second lithium metal composite oxide measured with water as the dispersion medium was 3 μm. From the SEM image, this composite oxide was single primary particles or non-aggregated single particles composed of 5 or fewer primary particles.

[0094] [Preparation of the second positive electrode mixture paste]

[0095] Using the above-mentioned second lithium metal composite oxide as the positive electrode active material, except for this, the second positive electrode mixture paste was prepared by the same method as the first positive electrode mixture paste.

[0096] [Fabrication of the positive electrode]

[0097] The first positive electrode mixture slurry is intermittently coated on both sides of a positive electrode core made of aluminum foil to form a first coating film, and the coating film is dried. Then, the second positive electrode mixture slurry is coated on the part where the first coating film does not exist to form a second coating film, and the coating film is dried. At this time, the first and second positive electrode mixture slurries are coated so that the first and second coating films are alternately formed in the length direction of the positive electrode core, that is, it becomes Figure 2 the striped pattern as shown. It should be noted that the first coating film becomes the first region of the positive electrode mixture layer, and the second coating film becomes the second region of the positive electrode mixture layer. In this embodiment, the ratio of the width of the first region to the width of the second region is adjusted to 75:25. The average value of the width of the first region is 7.5 mm, and the average value of the width of the second region is 2.5 mm.

[0098] Next, a roller is used to calender the coating film (positive electrode mixture layer) so that the mixture density of the first region becomes 3.4 g / cc and the mixture density of the second region becomes 3.3 g / cc. The positive electrode core is cut into a specified electrode size, and a positive electrode having a positive electrode mixture layer formed on both sides of the positive electrode core is obtained. It should be noted that an exposed portion where the surface of the positive electrode core is exposed is provided in a part of the positive electrode. The porosity of the first region of the positive electrode mixture layer measured by the above method is 17%, and the porosity of the second region is 21%. In addition, the BET specific surface area of the first region is 1.9 m 2 / g, and the BET specific surface area of the second region is 2.3 m 2 / g.

[0099] [Fabrication of negative electrode]

[0100] As the negative electrode active material, a substance obtained by mixing natural graphite and a silicon-containing material (a composite material in which fine Si phases are dispersed in a silicon oxide phase) at a mass ratio of 98:2 is used. A dispersion of the negative electrode active material, sodium carboxymethylcellulose (CMC-Na), and styrene-butadiene rubber (SBR) is mixed at a solid component mass ratio of 100:1:1, and water is used as a dispersion medium to prepare a negative electrode mixture slurry. The negative electrode mixture slurry is coated on both sides of a negative electrode core made of copper foil. After the coating film is dried, the coating film is calendered using a roller and cut into a specified electrode size, and a negative electrode having a negative electrode mixture layer formed on both sides of the negative electrode core is obtained. It should be noted that an exposed portion where the surface of the negative electrode core is exposed is provided in a part of the negative electrode.

[0101] [Preparation of non-aqueous electrolyte]

[0102] LiPF is dissolved in a mixed solvent obtained by mixing ethylene carbonate (EC), ethyl methyl carbonate (MEC), and dimethyl carbonate (DMC) at a volume ratio of 3:3:4 (25 °C) at a concentration of 1.2 mol / L 6 , and a non-aqueous electrolyte is prepared.

[0103] [Fabrication of Test Battery (Non-aqueous Electrolyte Secondary Battery)]

[0104] Aluminum leads were respectively installed on the exposed portions of the above positive electrodes, and nickel leads were installed on the exposed portions of the above negative electrodes. The positive and negative electrodes were wound into a spiral shape with a polyolefin separator in between to fabricate a wound electrode body. This electrode body was housed in a bottomed cylindrical outer can, and after injecting the above non-aqueous electrolyte, the opening of the outer can was blocked with a sealing body to obtain a test battery.

[0105] <Example 2>

[0106] The ratio of the width of the first region to the width of the second region of the positive electrode mixture layer was changed to 25:75, and otherwise, the operation was the same as in Example 1 to fabricate a test battery.

[0107] <Example 3>

[0108] The ratio of the width of the first region to the width of the second region of the positive electrode mixture layer was changed to 50:50, and otherwise, the operation was the same as in Example 1 to fabricate a test battery.

[0109] <Example 4>

[0110] The ratio of the width of the first region to the width of the second region of the positive electrode mixture layer was changed to 90:10, and otherwise, the operation was the same as in Example 1 to fabricate a test battery.

[0111] <Example 5>

[0112] The first coating film and the second coating film were respectively calendered, and the second coating film was calendered so that the mixture density of the second region became 3.1 g / cc. Otherwise, the operation was the same as in Example 1 to fabricate a test battery.

[0113] <Example 6>

[0114] Only the first positive electrode mixture slurry was used to form the coating films of the first region and the second region, and the coating films of each region were respectively calendered so that the mixture density of the first region became 3.4 g / cc and the mixture density of the second region became 3.6 g / cc. Otherwise, the operation was the same as in Example 1 to fabricate a test battery.

[0115] <Comparative Example 1>

[0116] Only the first positive electrode mixture slurry was used to form the positive electrode mixture layer, and otherwise, the operation was the same as in Example 1 to fabricate a test battery. The porosity of the positive electrode mixture layer was 17%.

[0117] <Comparative Example 2>

[0118] A test battery was fabricated by forming the positive electrode mixture layer using only the second positive electrode mixture slurry and operating in the same manner as in Example 1. The porosity of the positive electrode mixture layer was 20%.

[0119] For each test battery of the examples and comparative examples, the discharge capacity (initial discharge capacity per unit mass of the positive electrode active material), fast charging performance (electrolyte permeability), and cycle characteristics (capacity retention rate after the cycle test) were evaluated by the following methods, and the evaluation results are shown in Table 1. The fast charging performance shown in Table 1 is a relative value with the evaluation result of the positive electrode of Comparative Example 1 set to 100. The smaller the value, the more excellent the fast charging performance.

[0120] [Evaluation of Discharge Capacity]

[0121] The test battery was charged at a constant current of 0.3It until the battery voltage reached 4.2V in a temperature environment of 25°C, and then charged at a constant voltage of 4.2V until the current value reached 0.02It. Then, it was discharged at a constant current of 0.5It until the battery voltage reached 2.5V, and the discharge capacity was determined.

[0122] [Evaluation of Fast Charging Performance]

[0123] Ethylene carbonate (EC) with a particle size of 3μm was dropped onto the surface of the positive electrode mixture layer, and the time (penetration time) until the EC penetrated from the surface of the mixture layer into the interior and disappeared was measured. The shorter the penetration time, the more excellent the electrolyte permeability of the positive electrode mixture layer. The electrolyte permeability is closely related to the fast charging performance of the battery. The more excellent the permeability, the higher the fast charging performance.

[0124] [Evaluation of Cycle Characteristics]

[0125] The test battery was charged at a constant current of 0.3It until the battery voltage reached 4.2V in a temperature environment of 25°C, and then charged at a constant voltage of 4.2V until the current value reached 0.02It. Then, it was discharged at a constant current of 0.5It until the battery voltage reached 2.5V. This charge-discharge process was regarded as one cycle, and 400 cycles were performed. The discharge capacity of the first cycle and the discharge capacity of the 300th cycle were determined, and the capacity retention rate was calculated by the following formula.

[0126] Capacity retention rate (%) = (Discharge capacity of the 300th cycle ÷ Discharge capacity of the first cycle) × 100

[0127] [Table 1]

[0128]

[0129] As shown in Table 1, the electrolyte permeability of the test batteries of the examples is good compared to that of the test battery of Comparative Example 1. Therefore, the test batteries of the examples have excellent fast charging performance. In addition, the test batteries of the examples have higher capacities compared to the test battery of Comparative Example 2. It should be noted that the test battery of Comparative Example 1 has a high capacity but poor fast charging performance, and the test battery of Comparative Example 2 has excellent fast charging performance but a low capacity. From this result, it can be understood that by providing at least two regions with different porosity in the positive electrode mixture layer, for example, by alternately arranging the first region and the second region in the length direction of the positive electrode core, a secondary battery with high capacity and excellent fast charging performance can be achieved.

[0130] The present disclosure will be further described by the following embodiments.

[0131] Configuration 1: A positive electrode for a secondary battery, comprising a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, the positive electrode mixture layer including a first region and a second region alternately arranged in at least one of the length direction and the width direction of the positive electrode core, and the porosity of the second region being greater than the porosity of the first region.

[0132] Configuration 2: The positive electrode for a secondary battery according to Configuration 1, wherein the BET specific surface area of the second region is greater than the BET specific surface area of the first region.

[0133] Configuration 3: The positive electrode for a secondary battery according to Configuration 1 or 2, wherein the first region and the second region are alternately arranged in the length direction of the positive electrode core.

[0134] Configuration 4: The positive electrode for a secondary battery according to Configuration 3, wherein the length of the first region along the length direction of the positive electrode core is longer than the length of the second region along the length direction of the positive electrode core.

[0135] Configuration 5: The positive electrode for a secondary battery according to Configuration 3 or 4, wherein the first region and the second region are formed over the entire width of the positive electrode core.

[0136] Configuration 6: The positive electrode for a secondary battery according to Configuration 1 or 2, wherein, when viewed from the front of the positive electrode mixture layer, at least one of the first region and the second region is arranged in a striped, grid-like, dot-like, or honeycomb-like pattern.

[0137] Configuration 7: The positive electrode for a secondary battery according to any one of Configurations 1 to 6, wherein the porosity of the first region is greater than 11%.

[0138] Configuration 8: The positive electrode for a secondary battery according to any one of Configurations 1 to 7, wherein the positive electrode mixture layer contains a first lithium metal composite oxide and a second lithium metal composite oxide, the first lithium metal composite oxide is secondary particles formed by aggregation of primary particles having an average particle diameter of 50 nm or more and 5 μm or less, the second lithium metal composite oxide is non-aggregated primary particles, the first region contains more of the first lithium metal composite oxide than the second lithium metal composite oxide, and the second region contains more of the second lithium metal composite oxide than the first lithium metal composite oxide.

[0139] Configuration 9: The positive electrode for a secondary battery according to any one of Configurations 1 to 8, wherein the median particle diameter on a volume basis of the lithium metal composite oxide contained in the first region is 10 μm or more and 30 μm or less, and the median particle diameter on a volume basis of the lithium metal composite oxide contained in the second region is 2 μm or more and 10 μm or less.

[0140] Configuration 10: The positive electrode for a secondary battery according to any one of Configurations 1 to 9, wherein the positive electrode mixture layer contains a lithium metal composite oxide, the lithium metal composite oxide contains Li, Ni, and Co, and contains at least one of Mn and Al, and the proportion of Ni relative to the total molar amount of metal elements other than Li is 80 mol% or more.

[0141] Configuration 11: A secondary battery including the positive electrode for a secondary battery according to any one of Configurations 1 to 10, a negative electrode, and an electrolyte.

[0142] Explanation of Reference Numerals

[0143] 10: Cylindrical battery, 11: Positive electrode, 12: Negative electrode, 13: Separator, 14: Electrode body, 16: Outer can, 17: Sealing body, 18, 19: Insulating plate, 20: Positive electrode lead, 21: Negative electrode lead, 22: Insertion groove portion, 23: Internal terminal board, 24: Lower valve body, 25: Insulating member, 26: Upper valve body, 27: Cover, 28: Gasket, 30: Positive electrode core, 31: Positive electrode mixture layer, 35: First region, 36: Second region, 40: Negative electrode core, 41: Negative electrode mixture layer

Claims

1. A positive electrode for a secondary battery, comprising a positive electrode core and a positive electrode mixture layer disposed on the positive electrode core, The positive electrode mixture layer includes a first region and a second region alternately disposed in at least one of the length direction and the width direction of the positive electrode core, The porosity of the second region is greater than the porosity of the first region.

2. The positive electrode for a secondary battery according to claim 1, Wherein, The BET specific surface area of the second region is greater than the BET specific surface area of the first region.

3. The positive electrode for a secondary battery according to claim 1, Wherein, The first region and the second region are alternately disposed in the length direction of the positive electrode core.

4. The positive electrode for a secondary battery according to claim 3, Wherein, The length of the first region along the length direction of the positive electrode core is longer than the length of the second region along the length direction of the positive electrode core.

5. The positive electrode for a secondary battery according to claim 3, Wherein, The first region and the second region are formed over the entire length in the width direction of the positive electrode core.

6. The positive electrode for a secondary battery according to claim 1, Wherein, When viewed from the front of the positive electrode mixture layer, at least one of the first region and the second region is arranged in a striped, grid-like, dot-like or honeycomb-like pattern.

7. The positive electrode for a secondary battery according to claim 1, Wherein, The porosity of the first region is greater than 11%.

8. The positive electrode for a secondary battery according to claim 1, Wherein, The positive electrode mixture layer includes a first lithium metal composite oxide and a second lithium metal composite oxide. The first lithium metal composite oxide is secondary particles formed by aggregation of primary particles with an average particle diameter of 50 nm or more and 5 μm or less, and the second lithium metal composite oxide is non-aggregated primary particles, The first region contains more of the first lithium metal composite oxide than the second lithium metal composite oxide, The second region contains more of the second lithium metal composite oxide than the first lithium metal composite oxide.

9. The positive electrode for a secondary battery according to claim 1, Wherein, The median particle diameter of the lithium metal composite oxide contained in the first region is 10 μm or more and 30 μm or less based on volume, The median particle diameter of the lithium metal composite oxide contained in the second region is 2 μm or more and 10 μm or less based on volume.

10. The positive electrode for a secondary battery according to claim 1, Wherein, The positive electrode mixture layer includes a lithium metal composite oxide, The lithium metal composite oxide contains Li, Ni, and Co, and contains at least one of Mn and Al. The proportion of Ni relative to the total molar amount of metal elements other than Li is 80 mol% or more.

11. A secondary battery, comprising the positive electrode for a secondary battery according to any one of claims 1 to 10, a negative electrode, and an electrolyte.

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