Negative electrode material sheet for non-aqueous secondary battery, negative electrode for non-aqueous secondary battery, non-aqueous secondary battery, and method for manufacturing negative electrode material sheet for non-aqueous secondary battery

Abstract

To provide a negative electrode material sheet for a nonaqueous secondary battery, which enables the formation of a high-density negative electrode mixture layer, and allows a secondary battery to exhibit a superior rate characteristic.SOLUTION: A negative electrode material sheet has a first principal surface and a second principal surface, and it contains a granular carbon material. The negative electrode material sheet has a first region where a distance from the first principal surface in its thickness direction is 10 to 20% of a thickness of the negative electrode material sheet, and a second region where a distance from the second principal surface is 10 to 20% in the thickness direction in section view in the thickness direction; supposing that a center line of the negative electrode material sheet in the thickness direction is 0°, the average value of angles θ1 formed by the center line of the thickness direction and long axis lines of the granular carbon material in the first region is from 40° up to 80°, and the average value of angles θ2 formed by the center line of the thickness direction and the long axis lines of the granular carbon material in the second region is from -40° up to -80°.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a negative electrode material sheet for a non-aqueous secondary battery, a negative electrode for a non-aqueous secondary battery, a non-aqueous secondary battery, and a method for manufacturing the negative electrode material sheet for a non-aqueous secondary battery.

Background Art

[0002] Non-aqueous secondary batteries such as lithium-ion secondary batteries (hereinafter sometimes simply abbreviated as "secondary batteries") are small, lightweight, have a high energy density, and can be repeatedly charged and discharged, and are used in a wide range of applications. Therefore, conventionally, improvements to battery components such as electrodes (positive electrodes, negative electrodes) have been studied for the purpose of further improving the performance of secondary batteries.

[0003] Here, a negative electrode used in a secondary battery such as a lithium-ion secondary battery usually includes an electrode mixture layer (negative electrode mixture layer) containing a negative electrode active material capable of occluding and releasing charge carriers such as lithium ions, and a current collector are laminated.

[0004] Therefore, in recent years, attempts have been made to further improve the performance of secondary batteries by improving the negative electrode mixture layer provided in the negative electrode. For example, in Patent Document 1, for the purpose of improving the input / output characteristics (rate characteristics) etc. of a secondary battery, by applying a magnetic field when forming the negative electrode mixture layer, the orientation state of graphite as the negative electrode active material contained in the negative electrode mixture layer is controlled.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, in the above conventional technology, while exhibiting excellent rate characteristics in a secondary battery, it has been required to increase the density of the negative electrode composite material layer from the viewpoints of reducing the size and increasing the capacity of the secondary battery.

[0007] Therefore, an object of the present invention is to provide a new technology capable of exhibiting excellent rate characteristics in a secondary battery and increasing the density of the negative electrode composite material layer.

Means for Solving the Problems

[0008] The present inventor conducted intensive studies to achieve the above object. Then, when using a non-aqueous secondary battery negative electrode material sheet containing a particulate carbon material such as graphite (hereinafter, may be abbreviated as "negative electrode material sheet") as the negative electrode composite material layer, if the particulate carbon material is controlled to a predetermined orientation state in the thickness direction cross section of the negative electrode material sheet, the negative electrode composite material layer made of the negative electrode material sheet can be densified, and it was newly found that a negative electrode provided with the negative electrode composite material layer can exhibit excellent rate characteristics in a secondary battery, and the present invention was completed.

[0009] That is, the present invention aims to advantageously solve the above problems. The negative electrode material sheet for a non-aqueous secondary battery of the present invention is a negative electrode material sheet for a non-aqueous secondary battery having a first main surface and a second main surface located on the opposite side of the first main surface. The negative electrode material sheet for a non-aqueous secondary battery contains a particulate carbon material. In a cross-sectional view in the thickness direction, a region located between the first main surface and the second main surface and having a thickness direction distance from the first main surface of 10% or more and 20% or less of the thickness of the negative electrode material sheet for a non-aqueous secondary battery is defined as a first region, and a region located between the first main surface and the second main surface and having a thickness direction distance from the second main surface of 10% or more and 20% or less is defined as a second region. When the center line in the thickness direction of the negative electrode material sheet for a non-aqueous secondary battery is set to 0°, the average value of the angle θ1 formed by the center line in the thickness direction and the major axis line of the particulate carbon material in the first region is 40° or more and 80° or less, and the average value of the angle θ2 formed by the center line in the thickness direction and the major axis line of the particulate carbon material in the second region is -80° or more and -40° or less. Thus, when the cross-section in the thickness direction is confirmed, with the center line in the thickness direction set to 0°, according to the negative electrode material sheet in which the average value of the angle θ1 formed by the center line in the thickness direction and the major axis line of the particulate carbon material in the first region and the average value of the angle θ2 formed by the center line in the thickness direction and the major axis line of the particulate carbon material in the second region are within the above ranges, a high-density negative electrode composite layer can be formed, and excellent rate characteristics can be exhibited by the secondary battery including the negative electrode composite layer.

[0010] In the present invention, the "main surface" (the first main surface and the second main surface) of the negative electrode material sheet means the surface having the largest area in the negative electrode material sheet and the surface facing the said surface, and the areas of the two main surfaces may be equal. In the present invention, the "particulate carbon material in the first region" means a particulate carbon material, a part or all of which is included in the first region, and the "particulate carbon material in the second region" means a particulate carbon material, a part or all of which is included in the second region. In the present invention, the "positive / negative (+ / -)" of the angle formed by the major axis line of the particulate carbon material and the center line in the thickness direction in a cross-sectional view in the thickness direction is not particularly limited as long as the "average value of the angle θ1" in the first region is set to a positive value. The clockwise angle may be defined as "positive" and the counterclockwise angle as "negative", or the clockwise angle may be defined as "negative" and the counterclockwise angle as "positive". And in the present invention, the average value of the above-described angle θ1 and the average value of the angle θ2 can be specified by the method described in the examples.

[0011] Here, for the negative electrode material sheet for a non-aqueous secondary battery of the present invention, the ratio I(110) / I(004) of the diffraction intensity of the (110) plane to the diffraction intensity of the (004) plane in the X-ray diffraction of at least one of the first main surface and the second main surface is preferably 10 or more. Thus, if the ratio I(110) / I(004) of the diffraction intensity in the X-ray diffraction of the first main surface and / or the second main surface is the above value or more, the rate characteristics of the secondary battery can be further improved. In the present invention, the "ratio I(110) / I(004) of the diffraction intensity of the (110) plane to the diffraction intensity of the (004) plane in the X-ray diffraction" of the main surface of the negative electrode material sheet can be measured by the method described in the examples.

[0012] And the negative electrode material sheet for a non-aqueous secondary battery of the present invention has a density of 1.20 g / cm 3 or more and 1.70 g / cm 3 or less, which is preferable. If the density of the negative electrode material sheet is within the above range, a sufficiently high-density negative electrode composite layer can be formed using the negative electrode material sheet, and the rate characteristics of the secondary battery can be further improved. In the present invention, the "density" of the negative electrode material sheet can be measured using the method described in the examples.

[0013] Furthermore, the present invention aims to advantageously solve the above problems, and the negative electrode for a non-aqueous secondary battery of the present invention is characterized by comprising any one of the non-aqueous secondary battery negative electrode material sheets described above. The negative electrode obtained by using any one of the negative electrode material sheets of the present invention described above can achieve a good balance between the densification of the negative electrode composite layer and the improvement of the rate characteristics of the secondary battery.

[0014] And the present invention aims to advantageously solve the above problems, and the non-aqueous secondary battery of the present invention is characterized by comprising the non-aqueous secondary battery negative electrode described above. The secondary battery of the present invention is excellent in battery characteristics such as rate characteristics.

[0015] In addition, the present invention aims to advantageously solve the above problems, and the method for manufacturing a non-aqueous secondary battery negative electrode material sheet of the present invention includes a primary sheet forming step of pressing a composition containing a resin and a particulate carbon material into a sheet shape to obtain a primary sheet, a laminate forming step of laminating a plurality of the primary sheets in the thickness direction, or folding or winding the primary sheet to obtain a laminate, a slicing step of slicing the laminate at an angle of 45° or less with respect to the lamination direction to obtain a secondary sheet, a firing step of firing the secondary sheet to obtain a fired sheet, and a pressing step of pressing the fired sheet in the thickness direction. According to the negative electrode material sheet obtained through the above-described steps, a high-density negative electrode composite layer can be formed, and the secondary battery including the negative electrode composite layer can exhibit excellent rate characteristics.

[0016] Here, in the method for manufacturing a non-aqueous secondary battery negative electrode material sheet of the present invention, it is preferable that the sheet compression ratio in the pressing step is 1% or more and 40% or less. If the fired sheet is compressed at a sheet compression ratio within the above-described range in the pressing step, a sufficiently high-density negative electrode composite layer can be formed using the obtained negative electrode material sheet, and the rate characteristics of the secondary battery can be further improved. Note that in the present invention, the "sheet compression ratio" in the pressing step can be specified by the method described in the examples.

Effects of the Invention

[0017] According to the present invention, it is possible to provide a negative electrode material sheet for a non-aqueous secondary battery that can form a high-density negative electrode composite layer and can exhibit excellent rate characteristics in a secondary battery. Further, according to the present invention, it is possible to provide a negative electrode for a non-aqueous secondary battery including the negative electrode material sheet for a non-aqueous secondary battery, a non-aqueous secondary battery including the negative electrode for a non-aqueous secondary battery, and a method for manufacturing the negative electrode material sheet for a non-aqueous secondary battery.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described in detail. The negative electrode material sheet for a non-aqueous secondary battery of the present invention can be used as a negative electrode composite layer of a negative electrode for a non-aqueous secondary battery. Note that the negative electrode material sheet of the present invention can be manufactured using the method for manufacturing the negative electrode material sheet of the present invention. And, the negative electrode for a non-aqueous secondary battery of the present invention includes the negative electrode material sheet of the present invention as a negative electrode composite layer. For example, the negative electrode of the present invention can be manufactured by bonding the negative electrode material sheet of the present invention to a current collector. Furthermore, the non-aqueous secondary battery of the present invention includes the negative electrode of the present invention.

[0020] (Negative electrode material sheet for non-aqueous secondary battery) The negative electrode material sheet of the present invention is a sheet having a first main surface and a second main surface. And the negative electrode material sheet of the present invention contains a particulate carbon material and optionally further contains other components such as a resin, a silicon active material, and a fibrous carbon material.

[0021] Here, when checking the cross-section in the thickness direction of the negative electrode material sheet of the present invention, in the first region located between the first main surface and the second main surface and having a thickness direction distance from the first main surface of 10% or more and 20% or less, with the center line in the thickness direction of the negative electrode material sheet being 0°, it is necessary that the average value of the angle θ1 formed by the center line in the thickness direction and the major axis line of the particulate carbon material is 40° or more and 80° or less. In addition, when checking the cross-section in the thickness direction of the negative electrode material sheet of the present invention, in the second region located between the first main surface and the second main surface and having a thickness direction distance from the second main surface of 10% or more and 20% or less, with the center line in the thickness direction of the negative electrode material sheet being 0°, it is necessary that the average value of the angle θ2 formed by the center line in the thickness direction and the major axis line of the particulate carbon material is -40° or more and -80° or less.

[0022] The cross-section in the thickness direction of the negative electrode material sheet of the present invention represented as described above will be described with reference to the drawings. FIG. 1 is an explanatory diagram schematically showing an example of the cross-section in the thickness direction of the negative electrode material sheet 1 according to the present invention. In FIG. 1, the upper main surface of the negative electrode material sheet 1 is defined as the first main surface 11, and the lower main surface is defined as the second main surface 12. Here, taking the thickness of the negative electrode material sheet 1 (the distance between the first main surface 11 and the second main surface 12) as 100%, the region where the thickness direction distance from the first main surface 11 is 10% or more and 20% or less (that is, the region sandwiched between the straight line A parallel to the center line C in the thickness direction and separated from the first main surface by 10% of the thickness of the negative electrode material sheet and the straight line B separated by 20%) is the first region 21, and taking the thickness of the negative electrode material sheet as 100%, the region where the thickness direction distance from the second main surface 12 is 10% or more and 20% or less (that is, the region sandwiched between the straight line D parallel to the center line C in the thickness direction and separated from the second main surface by 10% of the thickness of the negative electrode material sheet and the straight line E separated by 20%) is the second region 22. Then, centering on the intersection point P1 between the thickness-direction center line C and the major axis line L1 of the particulate carbon material 2 in the first region 21, the clockwise angle (positive angle) from the thickness-direction center line C to the major axis line L1 is the angle θ1. Also, centering on the intersection point P2 between the thickness-direction center line C and the major axis line L2 of the particulate carbon material 2 in the second region 22, the counterclockwise angle (negative angle) from the thickness-direction center line C to the major axis line L2 is the angle θ2.

[0023] Since the average value of the angle θ1 in the first region is 40° or more and the average value of the angle θ2 in the second region is -40° or less, the movement of charge carriers such as lithium ions in the thickness direction of the negative electrode composite layer made of the negative electrode material sheet becomes easy. On the other hand, since the average value of the angle θ1 in the first region is 80° or less and the average value of the angle θ2 in the second region is -80° or more, the ratio of the particulate carbon material that takes a perpendicular orientation or an orientation close to it with respect to the thickness-direction center line in the negative electrode material sheet can be reduced. Therefore, the reduction in thickness and the increase in density of the negative electrode material sheet are not excessively inhibited by such a particulate carbon material. Although it is presumed to be due to the above contributions, according to the negative electrode material sheet of the present invention in which the average value of the angle θ1 and the average value of the angle θ2 are within the above-described ranges respectively, a high-density negative electrode composite layer can be formed, and the secondary battery including the negative electrode composite layer can exhibit excellent rate characteristics.

[0024] <Particulate carbon material> The particulate carbon material functions as a negative electrode active material in the negative electrode composite layer made of the negative electrode material sheet. Here, the particulate carbon material as the negative electrode active material is not particularly limited, and for example, graphite such as artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, expanded graphite; carbon black; etc. can be used. These may be used alone or in combination of two or more.

[0025] Among the above, as the particulate carbon material, it is preferable to use flaky graphite. If flaky graphite is used as the particulate carbon material, the rate characteristics of the secondary battery can be further improved. Examples of the flaky graphite include "UP20α" manufactured by Nippon Graphite Industries, Ltd.

[0026] <<Average value of angle θ1 in the first region>> In the first region, it is necessary that the average value of the angle θ1 from the center line in the thickness direction of the negative electrode material sheet to the major axis line of the particulate carbon material is 40° or more and 80° or less as described above, preferably 45° or more, more preferably 50° or more, and still more preferably 55° or more. If the average value of the angle θ1 is less than 40°, the rate characteristics of the secondary battery will be impaired, and if the average value of the angle θ1 exceeds 80°, it will be difficult to increase the density of the negative electrode composite layer composed of the negative electrode material sheet.

[0027] <<Average value of angle θ2 in the second region>> In the second region, it is necessary that the average value of the angle θ2 from the center line in the thickness direction of the negative electrode material sheet to the major axis line of the particulate carbon material is -80° or more and -40° or less as described above, preferably -45° or less, more preferably -50° or less, and still more preferably -55° or less. If the average value of the angle θ2 is less than -80°, it will be difficult to increase the density of the negative electrode composite layer composed of the negative electrode material sheet, and if it exceeds -40°, the rate characteristics of the secondary battery will be impaired.

[0028] <<Absolute value of the sum of the average value of angle θ1 and the average value of angle θ2>> Here, the absolute value of the sum of the average value of the angle θ1 and the average value of the angle θ2 described above (that is, |average value of angle θ1 + average value of angle θ2|) is preferably 0° or more and 10° or less, and more preferably 0° or more and 5° or less. If the absolute value of the sum of the average value of the angle θ1 and the average value of the angle θ2 is within the above range, it is presumed that the movement of charge carriers in the thickness direction of the negative electrode composite layer composed of the negative electrode material sheet becomes easy, and the rate characteristics of the secondary battery can be further improved.

[0029] <<Volume-average particle diameter>> The volume-average particle diameter of the particulate carbon material is preferably 3 μm or more, more preferably 5 μm or more, still more preferably 8 μm or more, yet more preferably 12 μm or more, even more preferably 16 μm or more, and preferably 200 μm or less, more preferably 150 μm or less, still more preferably 100 μm or less, and yet more preferably 50 μm or less. If the volume-average particle diameter of the particulate carbon material is 3 μm or more, the movement of charge carriers in the thickness direction of the negative electrode composite layer made of the negative electrode material sheet becomes easy, so that the rate characteristics of the secondary battery can be further improved. On the other hand, if the volume-average particle diameter of the particulate carbon material is 200 μm or less, further densification of the negative electrode composite layer made of the negative electrode material sheet becomes possible. In the present invention, the "volume-average particle diameter" can be measured in accordance with JIS Z8825, and represents the particle diameter at which the cumulative volume calculated from the small-diameter side is 50% in the particle size distribution (volume basis) measured by the laser diffraction method.

[0030] <<Aspect ratio>> Further, the particulate carbon material preferably has an aspect ratio (major axis / minor axis) of more than 1.2, more preferably more than 2, still more preferably more than 4, yet more preferably more than 6, and preferably 20 or less, more preferably 15 or less, and still more preferably 10 or less. If the aspect ratio of the particulate carbon material is within the above range, the average value of the angle θ1 and the average value of the angle θ2 can be easily made to fall within the desired ranges described above, so that further densification of the negative electrode composite layer made of the negative electrode material sheet becomes possible, and the rate characteristics of the secondary battery can be further improved.

[0031] In the present invention, the "aspect ratio" of the particulate carbon material can be determined by observing the particulate carbon material with an SEM (scanning electron microscope), measuring the maximum diameter (major axis) and the particle diameter (minor axis) in the direction perpendicular to the maximum diameter for any 50 particulate carbon materials, and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis). In the above, for example, when observing a particulate carbon material having a scale shape with an SEM, the "major axis" refers to the length in the direction of the major axis of the main surface of the scale shape, and the "minor axis" refers to the length in the direction perpendicular to the major axis of the main surface on the same plane as the main surface.

[0032] <<Content ratio>> The content ratio of the particulate carbon material in the negative electrode material sheet is preferably 92% by mass or more, more preferably 95% by mass or more, still more preferably 97% by mass or more, and can be 100% by mass or less, with the total mass of the negative electrode material sheet being 100% by mass. If the content ratio of the particulate carbon material in the negative electrode material sheet is within the above range, further densification of the negative electrode composite layer made of the negative electrode material sheet becomes possible, and the rate characteristics of the secondary battery can be further improved.

[0033] <Other components> The negative electrode material sheet of the present invention may further contain components other than the above-described particulate carbon material. As other components, for example, resins, silicon active materials, and fibrous carbon materials can be used.

[0034] <<Resin>> The resin optionally contained in the negative electrode material sheet is not particularly limited, and examples thereof include resins described later in the section "Method for manufacturing negative electrode material sheet". In the negative electrode material sheet obtained by using the "Method for manufacturing negative electrode material sheet" described later, it may contain a resin, may contain the combustion residue of the resin, or may contain both the resin and its combustion residue.

[0035] Here, the content ratio of the resin in the negative electrode material sheet determined by thermogravimetric measurement is preferably 8% by mass or less, more preferably 3% by mass or less, and still more preferably 1% by mass or less, with the total mass of the negative electrode material sheet being 100% by mass. If the content ratio of the resin in the negative electrode material sheet determined by thermogravimetric measurement is 8% by mass or less, the amount of resin that can impede the movement of charge carriers decreases, so that the rate characteristics of the secondary battery can be further improved. In addition, the content ratio of the resin in the negative electrode material sheet determined by thermogravimetric measurement is not particularly limited and can be 0% by mass or more. From the viewpoint of further improving the rate characteristics of the secondary battery, the content ratio of the resin in the negative electrode material sheet is particularly preferably 0% by mass. Note that the content ratio of the resin in the negative electrode material sheet can be adjusted, for example, by the steps implemented in the method for manufacturing the negative electrode material sheet described later, the type and amount of the resin used, and the firing conditions (for example, temperature and time). In the present invention, the "thermogravimetric measurement" for obtaining the "content ratio of the resin in the negative electrode material sheet" can be carried out by the method described in the examples.

[0036] <<Silicon active material>> The silicon active material functions as a negative electrode active material in the negative electrode composite material layer composed of the negative electrode material sheet, similar to the above-described particulate carbon material. Examples of the silicon active material include silicon (Si), an alloy containing silicon, SiO, SiO x , and a composite of a Si-containing material and conductive carbon obtained by coating or compounding a Si-containing material with conductive carbon. These may be used alone or in combination of two or more. Examples of the alloy containing silicon include an alloy composition containing silicon and at least one element selected from the group consisting of titanium, iron, cobalt, nickel, and copper. Examples of the silicon-containing alloy include an alloy composition containing silicon, aluminum, and a transition metal such as iron, and further containing rare earth elements such as tin and yttrium. SiO x is a compound containing at least one of SiO and SiO2 and Si, and x is usually not less than 0.01 and less than 2. And SiO x can be formed, for example, by utilizing the disproportionation reaction of silicon monoxide (SiO). Specifically, SiO x can be prepared by heat-treating SiO in the presence of an optional polymer such as polyvinyl alcohol to produce silicon and silicon dioxide. The heat treatment can be carried out at a temperature of 900 °C or higher, preferably 1000 °C or higher, in an atmosphere containing an organic gas and / or vapor after pulverizing and mixing SiO and an optional polymer. Examples of the composite of the Si-containing material and the conductive carbon include a compound obtained by heat-treating a pulverized mixture of SiO, an optional polymer such as polyvinyl alcohol, and an optional carbon material in an atmosphere containing an organic gas and / or vapor. The composite can also be obtained by known methods such as a method of coating the surface of SiO particles by chemical vapor deposition using an organic gas or the like, and a method of forming composite particles (granulation) of SiO particles and graphite or artificial graphite by a mechanochemical method. From the viewpoint of increasing the capacity of the secondary battery, as the silicon active material, an alloy containing silicon and SiO x are preferred.

[0037] <<Fibrous carbon material>> The fibrous carbon material optionally contained in the negative electrode material sheet is a material that can improve the strength of the negative electrode material sheet. The fibrous carbon material is not particularly limited, and for example, carbon nanotubes (hereinafter may be abbreviated as "CNT"), vapor-grown carbon fibers, carbon fibers obtained by carbonizing organic fibers, and cut products thereof can be used. These may be used alone or in combination of two or more. In addition, the fibrous carbon material preferably has an aspect ratio (major axis / minor axis) exceeding 20, more preferably exceeding 50. If the aspect ratio of the fibrous carbon material exceeds 20, the strength of the negative electrode material sheet can be further improved. In the present invention, the "aspect ratio" of the fibrous carbon material can be measured in the same manner as the "aspect ratio" of the particulate carbon material described above.

[0038] Here, as described above, the fibrous carbon material can improve the strength of the negative electrode material sheet. From the viewpoint of improving the strength of the negative electrode material sheet, the content ratio of the fibrous carbon material in the negative electrode material sheet is preferably 0.1% by mass or more and 5% by mass or less, more preferably 0.2% by mass or more and 5% by mass or less, and still more preferably 0.4% by mass or more and 5% by mass or less, with respect to the total mass of the negative electrode material sheet being 100% by mass. On the other hand, from the viewpoint of further enhancing the rate characteristics of the secondary battery, it is preferable to reduce the amount of the fibrous carbon material contained in the negative electrode material sheet. From the viewpoint of improving the rate characteristics of the secondary battery, the content ratio of the fibrous carbon material in the negative electrode material sheet is more preferably 1% by mass or less, still more preferably 0.5% by mass or less, particularly preferably 0.1% by mass or less, and most preferably 0% by mass (that is, the negative electrode material sheet does not contain the fibrous carbon material), with respect to the total mass of the negative electrode material sheet being 100% by mass.

[0039] <Ratio of diffraction intensity of main plane I(110) / I(004)> In the negative electrode material sheet of the present invention, the ratio I(110) / I(004) of the diffraction intensity of the (110) plane to the diffraction intensity of the (004) plane in the X-ray diffraction of at least one of the first main plane and the second main plane is preferably 10 or more, more preferably 20 or more. Here, in the X-ray diffraction pattern of the above-described particulate carbon material, peaks attributable to the (004) plane and peaks attributable to the (110) plane are detected. Since the (110) plane in the crystal structure of the particulate carbon material is a plane perpendicular to the plane composed of carbon six-membered rings (i.e., a plane equivalent to the (004) plane), the ratio of the peak intensity of the (110) plane to the peak intensity of the (004) plane in X-ray diffraction indicates the crystal orientation of the particulate carbon material. And a high value of I(110) / I(004) in the X-ray diffraction of the main surface of the negative electrode material sheet means that the orientation of the (004) plane in the direction perpendicular to the main surface of the negative electrode material sheet (typically, it coincides with the direction perpendicular to the main surface of the current collector of the negative electrode provided with the negative electrode material sheet) is high. Therefore, if the ratio of diffraction intensities I(110) / I(004) is equal to or greater than the above-mentioned predetermined value, the orientation of the (004) plane in the direction perpendicular to the main surface of the negative electrode material sheet is enhanced. As a result, the movement of charge carriers in the thickness direction of the negative electrode composite layer made of the negative electrode material sheet becomes easy, and the rate characteristics of the secondary battery can be further improved. Also, the ratio of diffraction intensities I(110) / I(004) is not particularly limited, but it is preferably 90 or less.

[0040] The I(110) / I(004) of the diffraction intensity can be adjusted, for example, by the steps carried out in the method for manufacturing the negative electrode material sheet described later, the properties of the particulate carbon material used (e.g., aspect ratio), the molding conditions including the film thickness of the primary sheet described later, and the firing conditions (e.g., temperature and time).

[0041] <Density> The negative electrode material sheet of the present invention preferably has a density of 1.20 g / cm 3 or more, more preferably 1.30 g / cm 3 or more, still more preferably 1.40 g / cm 3 or more, and preferably 1.70 g / cm 3 or less, and preferably 1.50 g / cm 3It is more preferable that the following conditions are met. If the density of the negative electrode material sheet is within the above range, a negative electrode composite layer with a sufficiently high density can be formed using the negative electrode material sheet, and the rate characteristics of the secondary battery can be further improved.

[0042] <Thickness> The thickness of the negative electrode material sheet is preferably 70 μm or more, more preferably 80 μm or more, still more preferably 90 μm or more, preferably 500 μm or less, more preferably 300 μm or less, and still more preferably 200 μm or less. If the thickness of the negative electrode material sheet is 70 μm or more, the secondary battery can have a higher capacity. On the other hand, if the thickness of the negative electrode material sheet is 500 μm or less, the secondary battery can be made thinner. In the present invention, the "thickness" of the negative electrode material sheet can be measured by the method described in the examples.

[0043] (Method for manufacturing the negative electrode material sheet) The negative electrode material sheet of the present invention described above can be manufactured using the method for manufacturing the negative electrode material sheet of the present invention. The method for manufacturing the negative electrode material sheet of the present invention includes: (A) a primary sheet forming step of pressing a composition containing a resin and a particulate carbon material into a sheet shape to obtain a primary sheet; (B) a laminate forming step of laminating a plurality of the primary sheets in the thickness direction, or folding or winding the primary sheet to obtain a laminate; (C) a slicing step of slicing the laminate at an angle of 45° or less with respect to the lamination direction to obtain a secondary sheet; (D) a firing step of firing the secondary sheet to obtain a fired sheet; and (E) a pressing step of pressing the fired sheet in the thickness direction. Note that the method for manufacturing the negative electrode material sheet described above may optionally further include steps other than the above (A) to (E).

[0044] <(A) Primary sheet forming step> In the primary sheet forming step, a composition containing a resin and a particulate carbon material is pressed into a sheet shape to obtain a primary sheet.

[0045] <<Composition>> The above composition contains a resin and a particulate carbon material. The composition may further contain components other than the above-mentioned resin and particulate carbon material (other components).

[0046] [Resin] The resin is not particularly limited, and any resin can be used. For example, as the resin, either a liquid resin or a solid resin can be used. Note that the resin may be used alone or in combination of two or more. For example, both a liquid resin and a solid resin can be used as the resin. When a liquid resin and a solid resin are used in combination as the resin, the mass ratio of the liquid resin to the solid resin can be adjusted within the range in which the desired effects of the present invention can be obtained. Note that the higher the content ratio of the liquid resin in the total resin, the easier it is to increase the filling rate of the particulate carbon material in the primary sheet. On the other hand, the higher the content ratio of the solid resin in the total resin, the higher the strength of the primary sheet can be increased.

[0047] ―Liquid resin― And, as the liquid resin, as long as it is liquid under normal temperature and pressure, it is not particularly limited. For example, a thermoplastic resin that is liquid under normal temperature and pressure can be used. In the present invention, "normal temperature" refers to 23°C, and "normal pressure" refers to 1 atm (absolute pressure). Examples of the liquid resin include fluororesin, silicone resin, acrylic resin, epoxy resin, and nitrile rubber (acrylonitrile-butadiene copolymer). These may be used alone or in combination of two or more.

[0048] ―Solid resin― As the solid resin, as long as it is not liquid under normal temperature and pressure, it is not particularly limited. For example, a thermoplastic resin that is solid under normal temperature and pressure, a thermosetting resin that is solid under normal temperature and pressure, etc. can be used.

[0049] Examples of thermoplastic resins that are solid under normal temperature and pressure include acrylic resins such as poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, and polyacrylic acid or its esters; silicone resins; fluorine resins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymers; nitrile rubber; acrylonitrile-butadiene-styrene copolymers (ABS resins); styrene-butadiene block copolymers or their hydrogenated products; styrene-isoprene block copolymers or their hydrogenated products; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamideimide; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyether nitrile; polyether ketone; polyketone; polyurethane; liquid crystal polymer; ionomer; etc. These may be used alone or in combination of two or more. In the present invention, rubber is included in "resin".

[0050] Examples of thermosetting resins that are solid under normal temperature and pressure include natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene-propylene rubber; chlorinated polyethylene; chlorosulfonated polyethylene; butyl rubber; halogenated butyl rubber; polyisobutylene rubber; epoxy resin; polyimide resin; bismaleimide resin; benzocyclobutene resin; phenol resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting modified polyphenylene ether; etc. These may be used alone or in combination of two or more.

[0051] Particulate carbon material As the particulate carbon material, the particulate carbon material described above in the section of "Negative electrode material sheet for non-aqueous secondary battery" can be used.

[0052] And the content of the particulate carbon material in the composition is preferably 50 parts by mass or more, more preferably 80 parts by mass or more, still more preferably 120 parts by mass or more, even more preferably 180 parts by mass or more, particularly preferably 250 parts by mass or more, preferably 500 parts by mass or less, more preferably 450 parts by mass or less, and still more preferably 400 parts by mass or less with respect to 100 parts by mass of the resin. When the content of the particulate carbon material in the composition is 50 parts by mass or more per 100 parts by mass of the resin, the strength of the produced negative electrode material sheet can be improved, and the secondary battery produced using the negative electrode provided with the negative electrode material sheet can be made to have a higher capacity. On the other hand, when the content of the particulate carbon material in the composition is 500 parts by mass or less per 100 parts by mass of the resin, the rate characteristics of the secondary battery produced using the negative electrode provided with the negative electrode material sheet can be further improved.

[0053] [Other components] The composition may further contain other components other than the resin and the particulate carbon material described above. Examples of the other components include the fibrous carbon material described above in the section of "Negative electrode material sheet for non-aqueous secondary battery" and a dispersant used for the dispersion of the fibrous carbon material. The dispersant is not particularly limited, and known ones can be used. Also, the content of the dispersant in the composition can be adjusted within a range in which the desired effects of the present invention can be obtained.

[0054] [Preparation of the composition] The composition is not particularly limited and can be prepared by mixing the components described above. The mixing of the above-described components can be carried out without particular limitation using known mixing devices such as a kneader; mixers such as a Henschel mixer, a Hobart mixer, and a high-speed mixer; a twin-screw kneader; rolls; and the like. Further, the mixing may be carried out in the presence of a solvent such as ethyl acetate. The resin may be previously dissolved or dispersed in the solvent to form a resin solution, which is then mixed with the particulate carbon material, the fibrous carbon material optionally added, and other components. When using CNT as the fibrous carbon material, after preparing a dispersion obtained by dispersing CNT and a dispersant in a solvent such as methyl ethyl ketone, a small amount of resin is added to the dispersion, and the solvent is distilled off to obtain a masterbatch, which may be mixed with the resin and the particulate carbon material. The mixing time can be, for example, 5 minutes or more and 60 minutes or less. Further, the mixing temperature can be, for example, 5°C or more and 150°C or less.

[0055] [Molding of the Composition] Then, the composition prepared as described above can be molded into a sheet by pressing after being optionally defoamed and crushed. The sheet-like product obtained by pressure-molding the composition in this way can be used as a primary sheet. When a solvent is used during mixing, it is preferably removed before molding into a sheet. For example, if vacuum defoaming is used for defoaming, the solvent can be removed simultaneously during defoaming.

[0056] Here, the composition can be molded into a sheet without particular limitation using known molding methods such as press molding, rolling molding, or extrusion molding as long as it is a molding method in which pressure is applied. Among them, the composition is preferably molded into a sheet by rolling molding (primary processing), and more preferably passed between rolls while sandwiched between protective films to be molded into a sheet. As the protective film, a polyethylene terephthalate (PET) film or the like subjected to sandblasting treatment can be used without particular limitation. Further, the roll temperature can be 5°C or more and 150°C or less, the roll gap can be 50 μm or more and 2500 μm or less, the roll linear pressure can be 1 kg / cm or more and 3000 kg / cm or less, and the roll speed can be 0.1 m / min or more and 20 m / min or less.

[0057] <(B) Laminated body forming step> In the laminated body forming step, a plurality of primary sheets obtained in the primary sheet forming step are laminated in the thickness direction, or the primary sheet is folded or wound so as to obtain a laminated body in which a plurality of primary sheets containing a resin and a particulate carbon material are formed in the thickness direction. Here, the formation of the laminated body by folding the primary sheet can be carried out without particular limitation by folding the primary sheet with a folding machine at a constant width. Further, the formation of the laminated body by winding the primary sheet can be carried out without particular limitation by winding the primary sheet around an axis parallel to the short side direction or the long side direction of the primary sheet. Further, the formation of the laminated body by laminating the primary sheets can be carried out without particular limitation using a laminating device. For example, by using a sheet laminating device (manufactured by Nikkiso Co., Ltd., product name "Hi-Stacker"), it is possible to suppress the entry of air between the layers, and thus a good laminated body can be efficiently obtained.

[0058] Note that in the lamination step, it is preferable to press the obtained laminated body in the lamination direction while heating (secondary pressing). By performing secondary pressing in which the laminated body is pressed in the lamination direction while heating, the fusion between the laminated primary sheets can be promoted.

[0059] Here, the pressure when pressing the laminated body in the lamination direction can be 0.05 MPa or more and 0.50 MPa or less. Further, the heating temperature of the laminated body is not particularly limited, but is preferably 50°C or more and 170°C or less. Furthermore, the heating time of the laminated body can be, for example, 10 seconds or more and 30 minutes or less.

[0060] Note that in the laminated body obtained by laminating, folding or winding the primary sheet, it is presumed that the particulate carbon material is oriented in a direction substantially orthogonal to the lamination direction. For example, when the particulate carbon material has a scale shape, it is presumed that the major axis direction of the main surface of the scale shape is substantially orthogonal to the lamination direction.

[0061] <(C) Slicing Process> In the slicing process, the laminate is sliced at an angle of 45° or less with respect to the lamination direction to obtain a secondary sheet composed of slices of the laminate. Here, the method of slicing the laminate is not particularly limited, and examples include the multi-blade method, laser processing method, water jet method, knife processing method, etc. Among them, the knife processing method is preferable in terms of easily making the thickness of the secondary sheet uniform. Further, as the cutting tool for slicing the laminate, without particular limitation, a slicing member having a smooth disk surface with a slit and a blade portion protruding from the slit portion (for example, a cutter or slicer equipped with a sharp blade) can be used.

[0062] Note that the angle at which the laminate is sliced is preferably 30° or less with respect to the lamination direction, more preferably 15° or less with respect to the lamination direction, and preferably substantially 0° with respect to the lamination direction (that is, the direction along the lamination direction). In the secondary sheet thus obtained, the particulate carbon material is favorably oriented in the thickness direction. For example, when the particulate carbon material has a flake shape, the direction of the major axis of the main surface of the flake shape substantially coincides with the thickness direction of the secondary sheet.

[0063] <(D) Firing Process> In the firing process, the secondary sheet is fired to burn and remove the resin contained in the secondary sheet, thereby obtaining a fired sheet. The obtained fired sheet is a sheet obtained by removing at least a part of the resin from the above-described secondary sheet. Therefore, in the fired sheet, the particulate carbon material is favorably oriented in the thickness direction. For example, when the particulate carbon material has a flake shape, the direction of the major axis of the main surface of the flake shape substantially coincides with the thickness direction of the secondary sheet.

[0064] Here, when firing the secondary sheet, the heating temperature is preferably T - 50°C or higher, more preferably T - 40°C or higher, still more preferably T - 20°C or higher, preferably T + 2000°C or lower, more preferably T + 1500°C or lower, and still more preferably T + 1000°C or lower, where T°C is the decomposition start temperature of the resin contained in the secondary sheet. If the heating temperature when firing the secondary sheet is at or above the above lower limit, the content ratio of the resin in the manufactured negative electrode material sheet can be reduced, and the rate characteristics of the secondary battery can be further improved. On the other hand, if the heating temperature when firing the secondary sheet is at or below the above upper limit, it is possible to suppress the structure and the like of the manufactured negative electrode material sheet from being damaged due to excessive heating, and to ensure that the strength of the negative electrode material sheet is sufficiently high. In the present invention, the "decomposition start temperature" of the resin can be measured by the method described in the examples. And in the present invention, when two or more kinds of resins are used, among the decomposition start temperatures obtained by measuring each of the two or more kinds of resins by the method described in the examples of this specification, the lowest value is taken as the decomposition start temperature T of the resin.

[0065] More specifically, when firing the secondary sheet, the heating temperature is preferably 300°C or higher, more preferably 500°C or higher, still more preferably 700°C or higher, preferably 2000°C or lower, more preferably 1500°C or lower, and still more preferably 1200°C or lower. If the heating temperature when firing the secondary sheet is at or above the above lower limit, the content ratio of the resin in the manufactured negative electrode material sheet can be reduced, and the rate characteristics of the secondary battery can be further improved. On the other hand, if the heating temperature when firing the secondary sheet is at or below the above upper limit, it is possible to suppress the structure and the like of the manufactured negative electrode material sheet from being damaged due to excessive heating, and to ensure that the strength of the negative electrode material sheet is sufficiently high.

[0066] Note that the heating time when firing the secondary sheet can be adjusted according to the heating temperature. For example, it can be 30 minutes or more and 72 hours or less.

[0067] <(E) Pressing Process> In the pressing process, the fired sheet is pressed and compressed in the thickness direction to obtain a negative electrode material sheet. By compressing the fired sheet in the thickness direction in this way, the particulate carbon material oriented in the thickness direction can be toppled. And according to the present inventor, it has been clarified that by pressing the fired sheet obtained through the above-described predetermined process in particular in the thickness direction, the particulate carbon material can be toppled in a characteristic manner. Specifically, when the above-described fired sheet in which the particulate carbon material is oriented in the thickness direction is pressed in the thickness direction, the particulate carbon material topples in opposite directions near one main surface (for example, the first main surface) and the other main surface (for example, the second main surface), and in a cross-sectional view in the thickness direction of the obtained negative electrode material sheet, it has been found that the particulate carbon material forms an overall "く" shape ("<", less-than sign) or "reverse く" shape (">", greater-than sign). Using the SEM image of the cross-section in the thickness direction of the negative electrode material sheet shown in FIG. 2, it will be described more specifically. In the example of FIG. 2, in the upper part of the cross-section, the particulate carbon material is inclined to the right side, and in the lower part, it is inclined to the left side, forming an overall "reverse く" shape. That is, according to the method for manufacturing a negative electrode material sheet of the present invention in which the above-described pressing is performed on a predetermined fired sheet, the negative electrode material sheet of the present invention in which the average value of the angle θ1 and the average value of the angle θ2 of the particulate carbon material are each within a predetermined range can be efficiently manufactured.

[0068] Here, the sheet compression ratio in the above-described pressing is preferably 1% or more, more preferably 2% or more, preferably 40% or less, more preferably 30% or less, and still more preferably 25% or less. If the fired sheet is compressed at a sheet compression ratio within the above-described range in the pressing process, a sufficiently high-density negative electrode composite layer can be formed using the obtained negative electrode material sheet, and the rate characteristics of the secondary battery can be further improved.

[0069] Note that the method for pressing the fired sheet in the thickness direction is not particularly limited, and it can be performed using a known press machine.

[0070] Negative electrode for non-aqueous secondary battery The negative electrode for non-aqueous secondary battery of the present invention is characterized by comprising the negative electrode material sheet of the present invention described above. For example, the negative electrode of the present invention comprises the negative electrode material sheet of the present invention as a negative electrode composite layer on a current collector. And the negative electrode of the present invention obtained by using the negative electrode material sheet of the present invention described above can achieve a good balance between the densification of the negative electrode composite layer and the improvement of the rate characteristics of the secondary battery.

[0071] The negative electrode of the present invention is not particularly limited. For example, it can be manufactured by laminating a current collector and the negative electrode material sheet of the present invention. Here, as the current collector, for example, a current collector made of a material such as iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, platinum, etc. can be used. Among them, a copper foil is particularly preferable as the current collector used for the negative electrode. Note that the above-described materials may be used alone or in combination of two or more in any ratio. Note that the current collector and the negative electrode material sheet are not particularly limited and can be laminated by a known method. When laminating the current collector and the negative electrode material sheet, an adhesive or the like may be used.

[0072] (Non-aqueous secondary battery) The secondary battery of the present invention is characterized by comprising the negative electrode of the present invention described above. For example, the secondary battery of the present invention comprises a positive electrode, a negative electrode, an electrolytic solution, and a separator, and uses the negative electrode for non-aqueous secondary battery of the present invention as the negative electrode. And since the secondary battery of the present invention uses the negative electrode of the present invention, it has excellent battery characteristics such as rate characteristics. Hereinafter, taking the case where the secondary battery of the present invention is a lithium-ion secondary battery as an example, the positive electrode, the electrolytic solution, and the separator will be described, but the present invention is not limited to these examples.

[0073] <Positive electrode> As the positive electrode, a known positive electrode used for a positive electrode of a lithium-ion secondary battery can be used. Specifically, as the positive electrode, for example, a positive electrode formed by forming a positive electrode composite layer on a current collector can be used. As the current collector, one made of a metal material such as aluminum can be used. Further, as the positive electrode composite layer, a layer containing a known positive electrode active material, a conductive material, and a binder can be used.

[0074] <Electrolyte> As the electrolyte, an electrolyte in which an electrolyte is dissolved in a solvent can be used. Here, as the solvent, an organic solvent capable of dissolving the electrolyte can be used. Specifically, as the solvent, an alkyl carbonate-based solvent such as ethylene carbonate, propylene carbonate, γ-butyrolactone, to which a viscosity-adjusting solvent such as 2,5-dimethyltetrahydrofuran, tetrahydrofuran, diethyl carbonate, ethyl methyl carbonate, dimethyl carbonate, methyl acetate, dimethoxyethane, dioxolane, methyl propionate, methyl formate is added can be used. As the electrolyte, a lithium salt can be used. As the lithium salt, for example, those described in JP-A-2012-204303 can be used. Among these lithium salts, LiPF6, LiClO4, and CF3SO3Li are preferable as the electrolyte in terms of being easily dissolved in an organic solvent and showing a high degree of dissociation.

[0075] <Separator> The separator is not particularly limited, and a known one can be used. For example, those described in JP-A-2012-204303 can be used. Among these, a microporous membrane made of a polyolefin-based resin (polyethylene, polypropylene, polybutene, polyvinyl chloride) is preferable in that the film thickness of the entire separator can be reduced, and thereby the ratio of the positive electrode active material in the lithium-ion secondary battery can be increased and the capacity per unit volume can be increased.

[0076] <Method for manufacturing a secondary battery> The secondary battery of the present invention can be manufactured, for example, by superposing a positive electrode and a negative electrode with a separator interposed therebetween, winding or folding the same according to the battery shape as necessary, placing the same in a battery container, and injecting an electrolytic solution into the battery container and sealing the same. In order to prevent the occurrence of an increase in the internal pressure of the secondary battery, overcharging / discharging, etc., an overcurrent prevention element such as a fuse or a PTC element, an expandable metal, a lead plate, etc. may be provided as necessary. The shape of the secondary battery may be, for example, a coin type, a button type, a sheet type, a cylindrical type, a rectangular type, a flat type, etc., any of which is acceptable.

Example

[0077] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified. In addition, various measurements and evaluations in the examples were performed according to the following methods.

[0078] <Decomposition start temperature of resin> For each resin used in the examples and comparative examples, thermogravimetric measurement (TGA measurement) was performed in an air atmosphere in the temperature range of 30 to 1000°C at a heating rate of 10°C / min. At this time, the temperature at which the weight decreased by 5% was defined as the decomposition start temperature of the resin. <Sheet compression ratio> The “sheet compression ratio” in the pressing step was calculated using the thickness T0 (μm) of the sheet before pressing and the thickness T1 (μm) of the sheet after pressing by the formula: sheet compression ratio (%) = (1 - T1 / T0) × 100 (%). Note that both the sheet thickness T0 before pressing and the sheet thickness T1 after pressing were measured using a film thickness gauge (manufactured by Mitutoyo, product name “Digital Indicator ID-C112XBS”) at a total of five points including the approximate center point and the four corners (square) of the sheet, and the value obtained as the average value (μm) of the measured thicknesses was used. <Average value of angle θ1 in the first region and average value of angle θ2 in the second region> A test sheet having a regular octagon shape in plan view was cut out from the negative electrode material sheet. Regarding the obtained test sheet having a regular octagonal column shape, eight side surfaces (cross-sections in the thickness direction) were observed with a scanning electron microscope (SEM, "SU-3500" manufactured by Hitachi High-Technologies Corporation) at a magnification (600 times in the examples and comparative examples described later) that allows the entire length from the upper end to the lower end of the sheet to be captured. Regarding the SEM image of the side surface, the angle θ1 formed between the center line in the thickness direction of the negative electrode material sheet and the major axis line of randomly selected particulate carbon materials within the first region was measured. This operation was performed on a total of 25 particulate carbon materials, and the average value of the 25 angles θ1 was determined. This operation was performed on all eight side surfaces, and the average value with the largest absolute value was taken as the "average value of angle θ1" for the negative electrode material sheet. Also, regarding the SEM image of the side surface, the angle θ2 formed between the center line in the thickness direction of the negative electrode material sheet and the major axis line of randomly selected particulate carbon materials within the second region was measured. This operation was performed on a total of 25 particulate carbon materials, and the average value of the 25 angles θ2 was determined. This operation was performed on all eight side surfaces, and the average value with the largest absolute value was taken as the "average value of angle θ2" for the negative electrode material sheet. Here, the center line in the thickness direction of the negative electrode material sheet can be specified as a line that passes through the center in the thickness direction of the observed negative electrode material sheet and is parallel (or substantially parallel) to both main surfaces in the SEM image. In the case where it is difficult to specify a proper center line in the thickness direction due to unevenness in the thickness of the negative electrode material sheet, etc., 20 line segments that connect the two main surfaces at the shortest distance in the SEM image (in FIGS. 1 and 2, the line segments that cut the negative electrode material sheet in the vertical direction) are arbitrarily specified, and a straight line for which the sum of the lengths of the perpendiculars dropped from the midpoints of each of these 20 line segments is minimized can also be taken as the center line in the thickness direction. <Thickness> Using a film thickness gauge (manufactured by Mitutoyo, product name "Digimatic Indicator ID-C112XBS"), the thicknesses at a total of five points, namely, the approximate center point and the four corners (quadrangles) of the negative electrode material sheet were measured, and the average value (μm) of the measured thicknesses was taken as the thickness of the negative electrode material sheet. <Density> The mass, the area of the main surface, and the thickness of the negative electrode material sheet were measured, and the density (g / cm 3 ) of the negative electrode material sheet was calculated by dividing the mass by the volume (= area × thickness). The value of this density was evaluated according to the following criteria. <<Evaluation Criteria>> A: The density is 1.40 g / cm 3 or more B: The density is 1.30 g / cm 3 or more and less than 1.40 g / cm 3 C: The density is 1.20 g / cm 3 or more and less than 1.30 g / cm 3 D: The density is less than 1.20 g / cm 3 <X-ray Diffraction> X-ray diffraction of one main surface of the negative electrode material sheet was performed using "X' Pert PRO MPD" manufactured by PANalytical. From the obtained peaks, using the peak height (diffraction intensity) at 2Θ = 77 degrees corresponding to the (110) plane and the peak height (diffraction intensity) at 2Θ = 54.5 degrees corresponding to the (004) plane, the value of the ratio I(110) / I(004) of the diffraction intensity of the (110) plane to the diffraction intensity of the (004) plane was calculated. <Content of Resin> The negative electrode material sheet was subjected to thermogravimetric measurement (TGA measurement) in a nitrogen atmosphere in the temperature range of from 30 to 1000°C at a heating rate of 10°C / min. At this time, the ratio of the weight decreased between 30°C and 1000°C was taken as the content of the resin in the negative electrode material sheet. <Rate Performance> <<Manufacture of Cell for Electrode Evaluation>> A half-cell of a lithium-ion secondary battery for evaluation was fabricated with the configuration shown below. The fabrication of the half-cell was carried out in a dry box with a dew point of -80°C or lower after punching out each member to a size of 17 mmφ and vacuum drying (120°C × 10 hours). 〔Configuration of Half-Cell〕 Working electrode: Negative electrode (negative electrode formed by attaching a negative electrode material sheet to a copper foil) Counter electrode: Li metal Reference electrode: Li metal ​​​Separator: Glass non-woven fabric, polyethylene (PE) microporous membrane Electrolyte: 1.0 M LiPF6 solution (the solvent is a mixed solvent of ethylene carbonate (EC) / methyl ethyl carbonate (MEC) = 3 / 7 (volume ratio), containing 1 volume% (solvent ratio) of vinylene carbonate (VC) as an additive) <<Charge-discharge test>> For the obtained half-cells for evaluation, a charge-discharge test was conducted under the following Condition 1. (Condition 1) Charging condition: 0.2C charging voltage 0.01V - CCCV (0.05C cut) Discharging condition: 0.2C cut-off voltage 2.5V - CC Number of cycles: 10 cycles Test temperature: 25°C Next, a further charge-discharge test was conducted under the following Condition 2. (Condition 2) Charging condition: 0.2C charging voltage 0.01V - CCCV (0.05C cut) Discharging condition: 2.0C cut-off voltage 2.5V - CC Number of cycles: 10 cycles Test temperature: 25°C Then, the ratio (discharge capacity ratio) of the discharge capacity at 2.0C (measured under Condition 2) to the discharge capacity at 0.2C (measured under Condition 1) was calculated as a percentage (=(discharge capacity at 2.0C / discharge capacity at 0.2C) × 100%), and evaluated according to the following criteria. The larger the value of the discharge capacity ratio, the smaller the internal resistance and the more capable of high-speed charge and discharge (i.e., excellent rate characteristics). <<Evaluation criteria>> A: Discharge capacity ratio is 65% or more B: Discharge capacity ratio is more than 47.5% and less than 65% C: Discharge capacity ratio is more than 30% and less than 47.5% D: Discharge capacity ratio is less than 30%

[0079] (Example 1) <Preparation of composition> 175 parts of nitrile rubber (NBR) that is liquid at normal temperature and pressure (manufactured by Zeon Corporation, trade name "Nipol 1312", decomposition start temperature: 336 °C), 75 parts of nitrile rubber (NBR) that is solid at normal temperature and pressure (manufactured by Zeon Corporation, trade name "Nipol 3350", decomposition start temperature: 375 °C), and 700 parts of flaky graphite as a particulate carbon material (manufactured by Nippon Graphite Industry Co., Ltd., trade name "UP20α", volume average particle diameter: 20 μm, aspect ratio: 10) were stirred and mixed at a temperature of 150 °C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the obtained mixture was put into a crusher (manufactured by Osaka Chemical Co., Ltd., trade name "Wonder Crush Mill D3V-10") and crushed for 10 seconds to obtain a composition. <Formation of primary sheet> Next, 50 g of the obtained composition was sandwiched between sandblasted PET films (protective films) with a thickness of 50 μm, and roll-formed (primary pressing) under the conditions of a roll gap of 1000 μm, a roll temperature of 50 °C, a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min to obtain a primary sheet with a thickness of 0.8 mm. <Formation of laminate> Subsequently, the obtained primary sheet was cut into a size of 150 mm in length × 150 mm in width × 0.8 mm in thickness, 188 sheets were laminated in the thickness direction of the primary sheet, and further pressed (secondary pressing) in the lamination direction at a temperature of 120 °C and a pressure of 0.1 MPa for 3 minutes to obtain a laminate with a height of about 150 mm. <Formation of secondary sheet> After that, while pressing the laminated side surface of the secondarily pressed laminate at a pressure of 0.3 MPa, a woodworking slicer (manufactured by Marunaka Iron Works Co., Ltd., trade name "Super Finishing Plane Super Meka S") was used to slice at an angle of 0° with respect to the lamination direction (in other words, in the normal direction of the main surface of the laminated primary sheet) to obtain a secondary sheet with a size of 150 mm in length × 150 mm in width × 0.10 mm in thickness. <Production of fired sheet> The obtained secondary sheet was fired at 1000 °C for 8 hours in a nitrogen atmosphere to burn and remove the resin, thereby obtaining a fired sheet (thickness: 103 μm). <Production of negative electrode material sheet> Then, using a precision hot press machine (manufactured by Shin-Tokyo Industries Co., Ltd., product name "CYPT-20"), the fired sheet was pressed and compressed in the thickness direction until the thickness of the sheet became from 103 μm to 100 μm, to obtain a negative electrode material sheet. The resin content ratio of this negative electrode material sheet was 0% by mass (the same applies to Examples 2 to 4, Comparative Examples 1 and 2). Also, various evaluations were performed using this negative electrode material sheet. The results are shown in Table 1.

[0080] (Examples 2 to 4) When obtaining a negative electrode material sheet by pressing the fired sheet, except that the thickness of the sheet after pressing (i.e., the negative electrode material sheet) was changed to 96 μm (Example 2), 84 μm (Example 3), and 74 μm (Example 4) respectively, in the same manner as in Example 1, a composition, a primary sheet, a laminate, a secondary sheet, a fired sheet, and a negative electrode material sheet were produced, and various evaluations were performed. The results are shown in Table 1.

[0081] (Comparative Example 1) In the same manner as in Example 1, a composition, a primary sheet, a laminate, a secondary sheet, and a fired sheet were produced. Then, the fired sheet was used as the negative electrode material sheet without pressing, and various evaluations were performed. The results are shown in Table 1.

[0082] (Comparative Example 2) (Preparation of Composition, Primary Sheet, and Laminate) In the same manner as in Example 1, a composition, a primary sheet, and a laminate were prepared. (Formation of Secondary Sheet) Thereafter, while pressing the laminated side surface of the secondarily pressed laminate at a pressure of 0.3 MPa, using a woodworking slicer (manufactured by Marunaka Iron Works Co., Ltd., product name "Super Finishing Plane Super Meka S"), slicing at an angle of 50° with respect to the lamination direction, a secondary sheet having a length of 150 mm × width of 150 mm × thickness of 0.10 mm was obtained. (Production of Fired Sheet (Negative Electrode Material Sheet)) The obtained secondary sheet was fired at 1000°C for 8 hours in a nitrogen atmosphere to burn and remove the resin, thereby obtaining a fired sheet (thickness: 101 μm). Then, various evaluations were performed on the fired sheet as the negative electrode material sheet without pressing it. The results are shown in Table 1.

[0083]

Table 1

[0084] From Table 1, in Examples 1 to 4 using a negative electrode material sheet in which the average value of the angle θ1 formed by the major axis line of the particulate carbon material and the center line in the thickness direction and the average value of the angle θ2 are within predetermined ranges in the first region and the second region in the cross-section view in the thickness direction, it can be seen that a high-density negative electrode composite layer can be formed, and the secondary battery provided with the negative electrode composite layer can exhibit excellent rate characteristics. On the other hand, in Comparative Example 1 in which the average value θ1 of the above-described angle exceeds the predetermined upper limit value (80°) and the average value θ2 of the above-described angle is less than the predetermined lower limit value (-80°), and in Comparative Example 2 in which the average value θ2 of the above-described angle is less than the predetermined lower limit value (-80°), it can be seen that the density of the negative electrode composite layer is relatively low.

Industrial Applicability

[0085] According to the present invention, it is possible to provide a negative electrode material sheet for a non-aqueous secondary battery that can form a high-density negative electrode composite layer and can exhibit excellent rate characteristics in a secondary battery. Further, according to the present invention, it is possible to provide a negative electrode for a non-aqueous secondary battery including the negative electrode material sheet for a non-aqueous secondary battery, a non-aqueous secondary battery including the negative electrode for a non-aqueous secondary battery, and a method for manufacturing the negative electrode material sheet for a non-aqueous secondary battery.

[0086] 1 Negative electrode material sheet 2 Particulate carbon material 11 First major surface 12 Second major surface 21 First region 22 Second region A, B, D, E Straight lines C Thickness-direction center line L1 Long axis line of the particulate carbon material 2 in the first region 21 L2 Long axis line of the particulate carbon material 2 in the second region 22 P1 Intersection point of the thickness-direction center line C and the long axis line L1 P2 Intersection point of the thickness-direction center line C and the long axis line L2 θ1 Angle from the thickness-direction center line C to the long axis line L1 θ2 Angle from the thickness-direction center line C to the long axis line L2

Claims

1. A negative electrode material sheet for a non-aqueous secondary battery having a first main surface and a second main surface located on the opposite side of the first main surface, The negative electrode material sheet for a non-aqueous secondary battery contains a particulate carbon material, In a cross-sectional view in the thickness direction, a region located between the first main surface and the second main surface and having a thickness direction distance from the first main surface of 10% or more and 20% or less with respect to the thickness of the negative electrode material sheet for a non-aqueous secondary battery is defined as a first region, and a region located between the first main surface and the second main surface and having a thickness direction distance from the second main surface of 10% or more and 20% or less is defined as a second region. When, With the center line in the thickness direction of the negative electrode material sheet for the non-aqueous secondary battery being 0°, the angle θ formed by the center line in the thickness direction and the major axis line of the particulate carbon material in the first region １ has an average value of 40° or more and 80° or less, and the angle θ formed by the center line in the thickness direction and the major axis line of the particulate carbon material in the second region ２ has an average value of -80° or more and -40° or less. A negative electrode material sheet for a non-aqueous secondary battery.

2. The negative electrode material sheet for a non-aqueous secondary battery according to claim 1, wherein the ratio I(110) / I(004) of the diffraction intensity of the (110) plane to the diffraction intensity of the (004) plane in the X-ray diffraction of at least one of the first main surface and the second main surface is 10 or more.

3. The density is 1.20 g / cm ３ or more and 1.70 g / cm ３ or less, the non-aqueous secondary battery negative electrode material sheet according to claim 1 or 2.

4. A negative electrode for a non-aqueous secondary battery comprising the negative electrode material sheet for a non-aqueous secondary battery according to any one of claims 1 to 3.

5. A non-aqueous secondary battery comprising the negative electrode for a non-aqueous secondary battery according to claim 4.

6. A primary sheet forming step of pressing a composition containing a resin and a particulate carbon material into a sheet shape to obtain a primary sheet; A laminate forming step of laminating a plurality of the primary sheets in the thickness direction, or folding or winding the primary sheet to obtain a laminate; A slicing step of slicing the laminate at an angle of 45° or less with respect to the lamination direction to obtain a secondary sheet; A firing step of firing the secondary sheet to obtain a fired sheet; A pressing step of pressing the fired sheet in the thickness direction; A method for manufacturing a negative electrode material sheet for a non-aqueous secondary battery, comprising:

7. The method for manufacturing a negative electrode material sheet for a non-aqueous secondary battery according to claim 6, wherein the sheet compression ratio in the pressing step is 1% or more and 40% or less.

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