Electrode for battery

Abstract

The invention relates to an electrode for a battery. The battery electrode includes a substrate and a negative electrode active material layer. The negative electrode active material layer is disposed on the surface of the substrate. The negative electrode active material layer contains graphite and a binder. The negative electrode active material layer has a mass per unit area of 25 mg / cm2 or more and a density of 1.2-1.6 g / cm3. The area fraction of the binder in the entire cross section parallel to the thickness direction of the negative electrode active material layer is 1.9% or more. The cross-section includes a first region and a second region. The first region is disposed between the second region and the substrate. And the relationships of 1.0 < (tau 1 / tau 2) < 4.4 and tau 2 < 2.1 are satisfied. [tau] 1 represents the curvature of the first region. '[tau] 2' represents the curvature of the second region.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an electrode for a battery. BACKGROUND

[0002] Japanese Laid-Open Patent Publication No. 2023-537139 discloses a negative electrode plate in which the degree of curvature of a first negative electrode active material layer (deep portion) is smaller than the degree of curvature of a second negative electrode active material layer (shallow portion). SUMMARY

[0003] An object of the present disclosure is to improve the rate characteristic.

[0004] 1. An electrode for a battery includes a substrate and a negative electrode active material layer. The negative electrode active material layer is disposed on a surface of the substrate. The negative electrode active material layer includes graphite and a binder. The negative electrode active material layer has a mass per unit area of 25 mg / cm 2 or more and a density of 1.2 to 1.6 g / cm 3 . In a cross section parallel to a thickness direction of the negative electrode active material layer as a whole, an area fraction of the binder is 1.9% or more. The cross section includes a first region and a second region. The first region is disposed between the second region and the substrate. A relationship of "1.0 < (τ1 / τ2) < 4.4" and "τ2 < 2.1" is satisfied. "τ1" represents the degree of curvature of the first region. "τ2" represents the degree of curvature of the second region.

[0005] When discharged for a long time, lithium (Li) ions move from the shallow portion to the deep portion of the negative electrode active material layer. The degree of curvature represents the complexity of the movement path (void) of the Li ions in the thickness direction of the negative electrode active material layer. It is considered that the closer the degree of curvature is to 1, the simpler (straight line) the movement path is. It is considered that the greater the degree of curvature is than 1, the more complex the movement path is. It is considered that the closer the degree of curvature is to 1, the more the supply of the Li ions in the thickness direction is promoted, and thus the rate characteristic is improved.

[0006] In order to increase the energy density, a negative electrode active material layer with a high mass per unit area and a high density is required. However, the high mass per unit area and the high density increase the degree of curvature. That is, the high mass per unit area and the high density decrease the rate characteristic. The negative electrode active material layer includes a binder in addition to a negative electrode active material (graphite). In order to alleviate the decrease in the rate characteristic caused by the high mass per unit area and the high density, a reduction in the binder is also considered. The reduction in the binder increases the void (movement path of the Li ions). That is, improvement in the rate characteristic is expected. However, on the other hand, the adhesion strength of the negative electrode active material layer to the substrate can also become insufficient due to the lack of the binder. In view of these actual situations, in the past, it has been difficult to achieve a degree of curvature of less than 2.1 under the conditions of a high mass per unit area of 25 mg / cm 2 or more, a high density of 1.2 g / cm 3 or more, and a binder amount of 1.9% or more.

[0007] The present disclosure maintains sufficient adhesion strength in a negative electrode active material layer having a high mass per unit area and a high density, while improving the rate characteristics, by providing two regions having different curvatures within the negative electrode active material layer. The first region can be referred to as a "deep portion", a "deep layer", or the like. The first region is disposed on a side relatively close to the substrate compared to the second region. The second region can be referred to as a "shallow portion", a "surface layer", or the like. The second region is disposed on a side relatively close to the surface of the negative electrode active material layer compared to the first region. The ratio "τ1 / τ2" of the curvature "τ1" of the first region to the curvature "τ2" of the second region is greater than 1.0 and less than 4.4. When the ratio "τ1 / τ2" of the curvatures is 1.0 or less, the movement distance of Li ions in the shallow portion is relatively long, and thus the utilization rate of the negative electrode active material in the deep portion can decrease. When the ratio "τ1 / τ2" of the curvatures is greater than 1, the movement distance of Li ions in the shallow portion is relatively short, and thus the utilization rate of the negative electrode active material in the deep portion can increase. With the increase in the utilization rate of the negative electrode active material in the deep portion, improvement in the rate characteristics is expected. However, if the ratio "τ1 / τ2" of the curvatures becomes 4.4 or greater, the movement of Li ions in the deep portion can become difficult. As a result, the utilization rate of the negative electrode active material in the deep portion can also decrease. Therefore, the present disclosure limits the ratio "τ1 / τ2" of the curvatures to be greater than 1.0 and less than 4.4.

[0008] 2. The electrode for a battery described in the above "1" can include the following configuration, for example. The area fraction of the binder in the first region is 2.9% or more. The area fraction of the binder in the second region is 1.0% or less.

[0009] With the relatively large amount of the binder in the first region (deep portion), an increase in the adhesion strength is expected. With the relatively small amount of the binder in the second region (shallow portion), the ratio "τ1 / τ2" of the curvatures in the second region tends to easily take a value exceeding 1.

[0010] 3. The electrode for a battery described in the above "1" or "2" can include the following configuration, for example. The graphite includes artificial graphite. With respect to the total amount of the graphite, 80% or more of the graphite has an aspect ratio of 1.6 or less in terms of mass fraction.

[0011] With the proportion of the artificial graphite having an aspect ratio of 1.6 or less being 80% or more, improvement in the rate characteristics is expected.

[0012] 4. The electrode for a battery described in any one of the above "1" to "3" can include the following configuration, for example. The negative electrode active material layer satisfies the relationship "0.033 ≤ I (110) / I (002) ". The "I (110)" indicates the diffraction intensity of the (110) plane in the X-ray diffraction curve of the negative electrode active material layer. "I (002) " indicates the diffraction intensity of the (002) plane in the X-ray diffraction curve of the negative electrode active material layer.

[0013] The ratio of the diffraction intensities "I (110) / I (002) " is an index of the orientation state. Hereinafter, the ratio of the diffraction intensities "I (110) / I (002) " is also referred to as "degree of orientation". It is considered that the higher the degree of orientation, the more the long axis of the graphite particle is oriented in the thickness direction of the negative electrode active material layer. When the degree of orientation is 0.033 or more, improvement in the rate characteristics is expected. For example, by applying a magnetic field at the time of drying the slurry, the graphite can be oriented in the thickness direction of the negative electrode active material layer.

[0014] 5. The electrode for a battery according to any one of the above "1" to "4" can include the following configuration. In a cross section, the area fraction of the second region with respect to the entire negative electrode active material layer is 50 to 70%.

[0015] When the area fraction of the second region is 50 to 70%, improvement in the rate characteristics is expected.

[0016] Hereinafter, an embodiment of the present disclosure (hereinafter, can be referred to as "the present embodiment") and an example of the present disclosure (hereinafter, can be referred to as "the present example") will be described. However, the present embodiment and the present example do not limit the technical scope of the present disclosure. The present embodiment and the present example are illustrative in all respects. The present embodiment and the present example are not restrictive. The technical scope of the present disclosure includes all modifications equivalent to the recitations of the claims and within the meanings and scope of equivalents. For example, arbitrary configurations are extracted from the present embodiment, and they are arbitrarily combined, which is anticipated from the beginning. BRIEF DESCRIPTION OF DRAWINGS

[0017] Features, advantages, and technical and industrial significance of exemplary embodiments of the application will be described below with reference to the accompanying drawings, wherein the same reference numerals denote the same elements, and wherein:

[0018] Figure 1 is a schematic cross-sectional view to show an example of the electrode for a battery in the present embodiment.

[0019] Figure 2 is a table to show experimental results. DETAILED DESCRIPTION

[0020] TERMS AND EXPRESSIONS

[0021] Geometrical terms should not be interpreted in a strict sense. As geometrical terms, for example, "parallel," "perpendicular," "orthogonal," and the like can be exemplified. For example, directions, angles, distances, and the like can be relatively displaced (shifted) within a range where substantially the same or similar functions are obtained. Geometrical terms can include, for example, design, operational, manufacturing, and the like tolerances, errors, and the like. Dimensional relationships in the respective drawings are sometimes inconsistent with actual dimensional relationships. In order to facilitate the reader's understanding, dimensional relationships in the respective drawings are sometimes changed. For example, lengths, widths, thicknesses, and the like are sometimes changed. The constitution of a part is sometimes omitted.

[0022] A numerical range such as "m~n%" includes the upper limit value and the lower limit value unless otherwise specified. That is, "m~n%" indicates a numerical range of "m% or more and n% or less." In addition, "m% or more and n% or less" includes "more than m% and less than n%." "Or more" and "or less" are indicated by inequalities with equal signs "<, >." "More than" and "less than" are indicated by inequalities without equal signs "<, >." A value arbitrarily selected from a numerical range can be a new upper limit value or a new lower limit value. For example, by arbitrarily combining a value within a numerical range with a value described in another part of the specification, a table, a drawing, and the like, a new numerical range can be set.

[0023] All numerical values are modified by the term "about." The term "about" can mean, for example, ±5%, ±3%, ±1%, and the like. All numerical values can be approximate values that can vary depending on the usage form of the technology according to the present disclosure. All numerical values can be expressed with significant digits. A measured value can be an average value of a plurality of measurements unless otherwise specified. The number of measurements can be 3 or more, can be 5 or more, can be 10 or more. Generally, the more the number of measurements, the higher the reliability of the average value is expected. A measured value can be rounded off by rounding based on the number of significant digits. A measured value can include, for example, errors and the like associated with the detection limit of a measuring device and the like.

[0024] The "mass per unit area" of the negative electrode active material layer indicates the mass per unit area of the negative electrode active material layer. "mg / cm 2 " is used as the unit of the mass per unit area. The "density" of the negative electrode active material layer indicates the apparent density of the negative electrode active material layer. The apparent density is obtained by dividing the mass per unit area of the negative electrode active material layer by the thickness of the negative electrode active material layer. "g / cm 3 " is used as the unit of the density. The mass per unit area and the density are measured at 5 or more places in the negative electrode active material layer. The arithmetic mean of the measurements at 5 or more places is used.

[0025] The "bending degree" of each region is measured as follows. A FIB-SEM (Focused Ion Beam Scanning Electron Microscopy) is prepared. Using the FIB, slicing processing is performed once for every 50 nm thickness of the sample (negative active material layer), and SEM scanning is performed, thereby obtaining a cross-sectional SEM image (tomographic image). This operation is repeated a plurality of times. From all the tomographic images obtained, a three-dimensional structure is reconstructed, thereby obtaining a 3D image of the negative active material layer. Using a simulation software "GeoDict" (manufactured by Math2Market GmbH), the 3D image is analyzed, thereby calculating the bending degree "τ1, τ2" of each region.

[0026] The "area fraction" of the binder is measured as follows. For example, in the cross-sectional sample of the negative active material layer, staining treatment of the binder can be performed. For example, styrene butadiene rubber (SBR) can be stained using osmium oxide. Mapping analysis of the binder is performed in the cross-sectional sample using SEM-EDX (Energy dispersive X-ray spectrometry). The pixels corresponding to the binder are counted in the negative active material layer. The number of pixels corresponding to the binder is divided by the total number of pixels of the negative active material layer, thereby calculating the area fraction of the binder in the negative active material layer. The area fraction is expressed in percentage (%). The area fraction of the binder in each region can also be measured in the same manner.

[0027] The "aspect ratio" of the graphite is measured as follows. The negative active material layer is cut, thereby producing a cross-sectional sample. The cross-sectional sample includes a cross section parallel to the thickness direction of the negative active material layer. For example, the observation target portion can be cleaned using a Cross Section Polisher (registered trademark) or the like. By observing the cross-sectional sample using an SEM, a cross-sectional SEM image is obtained. In the cross-sectional SEM image, 10 or more graphites (particles) are randomly selected. In the selected particles, the major axis diameter and the minor axis diameter are measured. The major axis diameter "φ1" represents the diameter between the two points farthest apart on the outline of the particle. The minor axis diameter "φ2" represents the largest diameter among the diameters orthogonal to the major axis diameter. The aspect ratio is the ratio of the major axis diameter to the minor axis diameter "φ1 / φ2". The arithmetic mean of 10 or more aspect ratios is taken as the "aspect ratio".

[0028] The "degree of orientation" of the negative electrode active material layer is determined by the following method. The XRD curve of the negative electrode active material layer is determined by XRD (X-ray diffraction). The X-ray source is Cu Kα ray. The measurement range is "10° ≤ 2θ ≤ 90°". In the XRD curve, the diffraction peak of the (002) plane can be detected in the range of "25° ≤ 2θ ≤ 30°". The area (integrated intensity) of the diffraction peak of the (002) plane is the diffraction intensity "I (002) ". The diffraction peak of the (110) plane can be detected in the range of "75° ≤ 2θ ≤ 80°". The area of the diffraction peak of the (110) plane is the diffraction intensity "I (110) ". The diffraction intensity "I (110) " is divided by the diffraction intensity "I (002) ", and thus the degree of orientation "I (110) / I (002) " is determined.

[0029] -Electrode for battery-

[0030] One aspect of the present disclosure is an electrode for battery. Another aspect of the present disclosure is a battery including the electrode for battery. The present disclosure can be applied to any battery. The battery can be, for example, a single-pole battery, a double-pole battery, a non-aqueous battery, or a lithium ion battery, and the like.

[0031] Figure 1 A schematic cross-sectional view showing one example of the electrode for battery of the present embodiment is shown in FIG. 1. Hereinafter, the electrode for battery can be simply referred to as "electrode". The electrode 200 can be, for example, in a sheet shape. The electrode 200 can be, for example, a negative electrode of a single-pole lithium ion battery. Figure 1 The cross section of the electrode 200 is parallel to the thickness direction (Z direction) of the electrode 200. The electrode 200 includes a substrate 210 and a negative electrode active material layer 220.

[0032] The substrate 210 supports the negative electrode active material layer 220. The substrate 210 can be, for example, in a sheet shape. The thickness of the substrate 210 can be, for example, 1 to 50 μm, 3 to 30 μm, or 5 to 15 μm. The substrate 210 has conductivity. The substrate 210 can include, for example, a metal foil or the like. The substrate 210 can include, for example, at least one selected from the group consisting of Cu, Ni, Zn, Pb, Al, Ti, Fe, Ag, Au, and a conductive resin. The substrate 210 can include, for example, a Cu foil, a Cu alloy foil, or the like. The substrate 210 can have, for example, a multi-layer structure. For example, the substrate 210 can be formed by laminating a Cu foil and an Al foil.

[0033] A negative electrode active material layer 220 is disposed on the surface of the substrate 210. The negative electrode active material layer 220 may be disposed on only one side of the substrate 210. Alternatively, the negative electrode active material layer 220 may be disposed on both sides of the substrate 210. In the case where the electrode 200 is used for a bipolar battery, the negative electrode active material layer 220 may be disposed on one side (surface) of the substrate 210, and a positive electrode active material layer (not shown) may be disposed on the other side (back side).

[0034] The thickness of the negative electrode active material layer 220 can be, for example, 10 μm or more, 50 μm or more, 100 μm or more, 150 μm or more, 200 μm or more, 300 μm or more, 400 μm or more, or 500 μm or more. The thickness of the negative electrode active material layer 220 can be, for example, less than 1000 μm, less than 500 μm, less than 400 μm, less than 300 μm, or less than 200 μm.

[0035] The surface area mass of the negative electrode active material layer 220 is 25 mg / cm². 2 The above. The mass per unit area of ​​the negative electrode active material layer 220 can be, for example, 30 mg / cm³. 2 Above, 35mg / cm 2 Above, 40mg / cm 2 Above, 45mg / cm 2 Above, or 50mg / cm 2 The above. The mass per unit area of ​​the negative electrode active material layer 220 can be, for example, 100 mg / cm³. 2 Below, 75mg / cm 2 Below, 50mg / cm 2 Below, 40mg / cm 2 Below, or 30mg / cm 2 the following.

[0036] The density of the negative electrode active material layer 220 is 1.2–1.6 g / cm³. 3 When the density exceeds 1.6 g / cm³ 3 At this time, it may be difficult to achieve the desired curvature. The density of the negative electrode active material layer 220 can be, for example, 1.3 g / cm³. 3 Above, 1.4g / cm 3 Above, or 1.5g / cm 3 The density of the negative electrode active material layer 220 can be, for example, 1.5 g / cm³. 3 Below, 1.4g / cm 3 Below, or 1.3g / cm 3 the following.

[0037] The negative electrode active material layer 220 includes a first region 221 and a second region 222. The negative electrode active material layer 220 can be composed of the first region 221 and the second region 222. Each region can form a layer. The first region 221 is disposed between the second region 222 and the substrate 210. The first region 221 can be in direct contact with the substrate 210, for example. The first region 221 can include an interface of the substrate 210 and the negative electrode active material layer 220, for example. The second region 222 can include a surface of the negative electrode active material layer 220, for example. That is, the second region 222 can be exposed on the surface of the negative electrode active material layer 220.

[0038] In a cross section of the negative electrode active material layer 220, the area fraction of the second region 222 with respect to the entire negative electrode active material layer 220 can be 50 to 70%, for example. The area fraction of the second region 222 can be 60% or more and can be 60% or less, for example. In the cross section, the area fraction of the first region 221 with respect to the entire negative electrode active material layer 220 can be 30 to 50%, for example. The area fraction of the first region 221 can be 40% or more and can be 40% or less, for example. Note that the area fraction of each region with respect to the entire negative electrode active material layer 220 in the cross section of the negative electrode active material layer 220 is considered to be equal to the ratio of the thickness of each region with respect to the thickness of the negative electrode active material layer 220 in the cross section.

[0039] The negative electrode active material layer 220 can further include an additional region (a third region, a fourth region, or the like) in addition to the first region 221 and the second region 222. The additional region can be distinguished from the first region 221 and the second region 222, for example, in terms of at least one of the composition and the structure. For example, the additional region can be disposed between the substrate 210 and the first region 221. For example, the additional region can be disposed between the first region 221 and the second region 222. For example, the additional region can be disposed between the surface of the negative electrode active material layer 220 and the second region 222.

[0040] The second region 222 has a smaller curvature than the first region 221. The ratio "τ1 / τ2" of the curvature "τ1" of the first region 221 to the curvature "τ2" of the second region 222 is greater than 1.0 and less than 4.4. The ratio "τ1 / τ2" of the curvatures can be 1.2 or more, 1.6 or more, 2.0 or more, 2.4 or more, 2.8 or more, 3.2 or more, 3.6 or more, or 4.0 or more, for example. The ratio "τ1 / τ2" of the curvatures can be 4.0 or less, 3.6 or less, 3.2 or less, 3.0 or less, less than 3.0, 2.8 or less, 2.4 or less, 2.0 or less, 1.6 or less, or 1.2 or less, for example.

[0041] However, the curvature "τ2" of the second region 222 is less than 2.1. The curvature "τ2" of the second region 222 may, for example, be 2.0 or less, 1.9 or less, 1.8 or less, 1.7 or less, 1.6 or less, 1.5 or less, 1.4 or less, 1.3 or less, 1.2 or less, or 1.1 or less. The curvature "τ2" of the second region 222 may, for example, be 1 or more, 1.1 or more, 1.2 or more, 1.3 or more, 1.4 or more, 1.5 or more, 1.6 or more, 1.7 or more, 1.8 or more, 1.9 or more, or 2.0 or more.

[0042] The curvature "τ1" of the first region 221 may, for example, be 2.1 or more, 2.5 or more, 3.0 or more, 3.5 or more, 4.0 or more, 4.5 or more, 5.5 or more, 6.0 or more, 6.5 or more, 7.0 or more, 7.5 or more, or 8.0 or more. The curvature "τ1" of the first region 221 may, for example, be less than 8.5, 8.0 or less, 7.5 or less, 7.0 or less, 6.5 or less, 6.0 or less, 5.5 or less, 5.0 or less, 4.5 or less, 4.0 or less, 3.5 or less, 3.0 or less, or 2.5 or less.

[0043] The curvature of each region can be adjusted by any method. For example, "split coating (layered coating)" can be performed. That is, two kinds of slurry having different compositions can be used to perform multi-layer coating. The less the amount of binder, the more the curvature tends to decrease. For example, a magnetic field can be applied to the coating film (slurry). The graphite is oriented by the magnetic field, thereby having a tendency to decrease the curvature. For example, the drying temperature of the coating film can be adjusted. The lower the drying temperature (the slower the drying speed), the more the curvature tends to decrease. For example, by appropriately combining these methods, the negative electrode active material layer 220 that satisfies the relationship "1.0 < (τ1 / τ2) < 4.4" and "τ2 < 2.1" can be formed.

[0044] The negative electrode active material layer 220 contains graphite 2 and a binder 4. The negative electrode active material layer 220 may, for example, be composed of 0.1 to 10% of the binder 4 and the remaining graphite 2 in terms of mass ratio. The cross section of the negative electrode active material layer 220 may, for example, be composed of 1.9% or more of the binder 4 and the remaining graphite 2 in terms of area ratio. The negative electrode active material layer 220 may, for example, further contain a conductive material, an adhesion-improving material, an inorganic filler, or the like in addition to the graphite 2 and the binder 4.

[0045] The first region 221 and the second region 222 each independently contain graphite 2 and a binder 4. The graphite 2 contained in the first region 221 can be the same as or different from the graphite 2 contained in the second region 222. The binder 4 contained in the first region 221 can be the same as or different from the binder 4 contained in the second region 222. The graphite is a negative electrode active material. The first region 221 and the second region 222 each can further contain an additional negative electrode active material other than the graphite. The first region 221 and the second region 222 each can contain, for example, at least one selected from the group consisting of silicon (Si), silicon oxide (SiO), silicon-carbon composite (Si-C), silicon-based alloy, tin, tin oxide, and lithium titanate. The mass fraction of the other negative electrode active material can be, for example, 50% or less, 40% or less, 30% or less, 20% or less, 10% or less, 5% or less, or 1% or less, with respect to the total of the negative electrode active materials.

[0046] The graphite can be natural graphite or artificial graphite. The surface of the graphite can be coated with a carbon material. The carbon material can contain, for example, soft carbon, hard carbon, amorphous carbon, low-crystallinity carbon, or the like. The D50 of the graphite can be, for example, 1 μm or more, 5 μm or more, or 10 μm or more. The D50 of the graphite can be, for example, 30 μm or less, 20 μm or less, 15 μm or less, or 10 μm or less. The "D50" indicates the particle diameter that accumulates to 50% in the particle size distribution (cumulative distribution) on a volume basis. The particle size distribution can be measured by a laser diffraction method.

[0047] The aspect ratio of the graphite can be, for example, 1 to 4. The aspect ratio of the graphite can be, for example, 1.2 or more, 1.4 or more, 1.6 or more, 2.0 or more, 2.3 or more, 2.8 or more, 3.2 or more, or 3.6 or more. The aspect ratio of the graphite can be, for example, 3.6 or less, 3.2 or less, 2.8 or less, 2.3 or less, 2.0 or less, 1.6 or less, 1.4 or less, or 1.2 or less. For example, 80% or more of the graphite can have an aspect ratio of 1.6 or less, in terms of mass fraction, with respect to the total amount of the graphite. The proportion of the graphite having an aspect ratio of 1.6 or less can be, for example, 85% or more, 90% or more, or 95% or more. The proportion of the graphite having an aspect ratio of 1.6 or less can be, for example, 100% or less, 95% or less, 90% or less, or 85% or less.

[0048] The orientation degree "I (110) / I (002) " of the graphite can be, for example, 0.033 or more. The orientation degree can be, for example, 0.050 or more or 0.075 or more. The orientation degree can be, for example, 0.100 or less, 0.075 or less, or 0.050 or less.

[0049] The binder 4 may, for example, include at least one selected from SBR, acrylate butadiene rubber (ABR), polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), polytetrafluoroethylene (PTFE), an acrylic resin (acrylate copolymer), a methacrylic resin (methacrylate copolymer), polyvinyl alcohol (PVA), and derivatives thereof.

[0050] In the cross section of the negative electrode active material layer 220, the area fraction of the binder 4 is 1.9% or more with respect to the entire negative electrode active material layer 220. The area fraction may, for example, be 2.5% or more, 3.0% or more, 3.5% or more, 4.0% or more, 4.5% or more, or 5.0% or more. The area fraction may, for example, be 10% or less, 7.5% or less, 7.0% or less, 6.5% or less, 6.0% or less, 5.5% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, or 2.5% or less.

[0051] In the negative electrode active material layer 220, the binder 4 may, for example, be uniformly distributed. In the negative electrode active material layer 220, the distribution of the binder 4 may, for example, also have a concentration. For example, the area fraction of the binder 4 in the first region 221 may be higher than the area fraction of the binder 4 in the second region 222. The area fraction of the binder 4 in the first region 221 may, for example, be 2.9% or more. The area fraction of the binder 4 in the first region 221 may, for example, be 3.0% or more, 3.5% or more, 4.0% or more, 4.5% or more, or 5.0% or more. The area fraction of the binder 4 in the first region 221 may, for example, be 10% or less, 7.5% or less, 7.0% or less, 6.5% or less, 6.0% or less, 5.5% or less, 5.0% or less, 4.5% or less, 4.0% or less, 3.5% or less, 3.0% or less, or 2.5% or less. The area fraction of the binder 4 in the second region 222 may, for example, be 1.0% or less. The area fraction of the binder 4 in the second region 222 may, for example, be 0.9% or less, 0.8% or less, 0.7% or less, 0.6% or less, 0.5% or less, 0.4% or less, 0.3% or less, or 0.2% or less. The area fraction of the binder 4 in the second region 222 may, for example, be 0.1% or more, 0.2% or more, 0.3% or more, 0.4% or more, 0.5% or more, 0.6% or more, 0.7% or more, 0.8% or more, or 0.9% or more.

[0052] Manufacture of Electrode (Negative Electrode)

[0053] No. 1

[0054] The following materials were prepared.

[0055] Negative active material: artificial graphite (SG), aspect ratio: 1.6

[0056] Binder: SBR

[0057] Tackifier: carboxymethyl cellulose (CMC)

[0058] Dispersion medium: water

[0059] Substrate: Cu foil (thickness: 15 μm)

[0060] In No. 1, "split coating" was performed. The SG, SBR, CMC, and water were mixed to prepare a first slurry. The composition of the solid components was "SG / CMC / SBR = 97 / 0.6 / 2.4 (mass ratio)". The first slurry was applied to the substrate to form a first region (deep portion). The first region was formed so that the mass per unit area after drying was 14 mg / cm 2 .

[0061] The SG, SBR, CMC, and water were mixed to prepare a second slurry. The composition of the solid components was "SG / CMC / SBR = 98.6 / 0.6 / 0.8 (mass ratio)". The second slurry was applied to overlap the first slurry to form a second region (shallow portion). The second region was formed so that the mass per unit area after drying was 14 mg / cm 2 . That is, the total mass per unit area was 28 mg / cm 2 .

[0062] A magnetic field was applied to the coating film (first and second regions). After the application of the magnetic field, the coating film was dried to form a negative active material layer. The drying temperature (hot air temperature) was 50°C. The negative active material layer was compressed to manufacture an electrode (negative electrode). After the compression, the density of the negative active material layer was 1.2 g / cm 3 .

[0063] No. 2

[0064] The electrode was manufactured in the same manner as in No. 1 except that the magnetic field was not applied to the coating film.

[0065] No. 3

[0066] In No. 3, the negative active material layer was formed without performing split coating. The SG, SBR, CMC, and water were mixed to prepare a slurry. The composition of the solid components was "SG / CMC / SBR = 98.8 / 0.6 / 1.6 (mass ratio)". The slurry was applied to the substrate to form a coating film. A magnetic field was applied to the coating film. After the application of the magnetic field, the coating film was dried to form a negative active material layer. The mass per unit area after drying was 28 mg / cm 2After drying, the negative active material layer was compressed, thereby manufacturing an electrode. After compression, the density of the negative active material layer was 1.2 g / cm 3 .

[0067] No. 4

[0068] An electrode was manufactured in the same manner as No. 1 except that SG having an aspect ratio of 2.3 was used.

[0069] No. 5

[0070] An electrode was manufactured in the same manner as No. 3 except that a magnetic field was not applied to the coating film.

[0071] No. 6

[0072] An electrode was manufactured in the same manner as No. 5 except that the drying temperature was changed to 25°C.

[0073] No. 7

[0074] An electrode was manufactured in the same manner as No. 1 except that the binder in the first slurry was not increased.

[0075] - Evaluation of Cell Manufacturing -

[0076] The following materials were prepared.

[0077] Positive active material: LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM)

[0078] Conductive material: acetylene black (AB)

[0079] Binder: PVdF

[0080] Dispersing medium: N-methylpyrrolidone (NMP)

[0081] Substrate: Al foil (thickness: 30 μm)

[0082] Separator: PE-made porous sheet

[0083] Electrolyte: LiPF6(concentration: 1.0 mol / L), EC + DMC + EMC

[0084] Outer packaging body: bag made of Al laminated film

[0085] The NCM, the AB, the PVdF, and the NMP were mixed, whereby a slurry was prepared. The compounding of the solid components was "NCM / AB / PVdF = 97.8 / 0.8 / 1.4 (mass ratio)". The slurry was applied to a substrate, whereby a positive electrode active material layer was formed. The positive electrode active material layer was dried. The positive electrode active material layer was compressed, whereby a positive electrode was manufactured.

[0086] The positive electrode, the separator, and the negative electrode were sequentially stacked, whereby a power generation element was formed. The power generation element and an electrolyte were enclosed in an outer packaging body, whereby an evaluation battery cell (rated capacity: 155 mA) was manufactured.

[0087] -Evaluation-

[0088] Figure 2 A table showing the experimental results. The discharge capacity of the evaluation battery cell was measured at a rate of 0.1 C and a rate of 1 C, respectively. "C" is a symbol indicating the rate. At a rate of 1 C, the rated capacity flowed out for 1 hour. The discharge capacity at a rate of 1 C (1 C discharge capacity) was divided by the discharge capacity at a rate of 0.1 C (0.1 C discharge capacity), whereby "1 C discharge capacity / 0.1 C discharge capacity" was calculated. The greater "1 C discharge capacity / 0.1 C discharge capacity", the better the rate characteristics.

[0089] -Results-

[0090] No. 3

[0091] By the application of a magnetic field (the orientation of graphite), a tendency of the degree of curvature to decrease was seen. However, a degree of curvature of less than 2.1 was not achieved.

[0092] No. 6

[0093] By improving the binder migration through the reduction of the drying temperature, a tendency of the degree of curvature to decrease was seen. However, a degree of curvature of less than 2.1 was not achieved.

[0094] No. 2

[0095] By partial coating, the degree of curvature could be locally decreased. However, a degree of curvature of less than 2.1 was not achieved.

[0096] No. 1

[0097] When the conditions "1.0 < (τ1 / τ2) < 4.4" and "τ2 < 2.1" were satisfied, a tendency of the rate characteristics to improve was seen.

Claims

1. A battery electrode comprising a substrate and a negative electrode active material layer, the negative electrode active material layer being disposed on the surface of the substrate. The negative electrode active material layer comprises graphite and a binder. The negative electrode active material layer has a concentration of 25 mg / cm³. 2 The above are unit area mass and 1.2~1.6g / cm³. 3 density, In a cross-section parallel to the thickness direction of the negative electrode active material layer, the area fraction of the adhesive is 1.9% or more. The cross-section includes a first region and a second region, the first region being disposed between the second region and the substrate, satisfying the relationship 1.0 < (τ1 / τ2) < 4.4 and τ2 < 2.1, where τ1 represents the curvature of the first region and τ2 represents the curvature of the second region.

2. The battery electrode according to claim 1, wherein, The area fraction of the adhesive in the first region is 2.9% or more, and the area fraction of the adhesive in the second region is 1.0% or less.

3. The battery electrode according to claim 1 or 2, wherein, The graphite comprises artificial graphite, and more than 80% of the graphite, by mass fraction, has an aspect ratio of less than 1.6 relative to the total amount of graphite.

4. The battery electrode according to claim 1 or 2, wherein, The negative electrode active material layer satisfies 0.033≤I (110) / I (002) Relationship, The I (110) The diffraction intensity of the (110) plane in the X-ray diffraction curve of the negative electrode active material layer is represented, and the I (002) The intensity of the diffraction of the (002) plane in the X-ray diffraction curve of the negative electrode active material layer is indicated.

5. The battery electrode according to claim 1 or 2, wherein, In the cross-section, the area fraction of the second region is 50-70% relative to the entire negative electrode active material layer.

Images