Negative electrode for secondary battery and method for manufacturing same

Abstract

To provide a negative electrode for a secondary battery that is more sufficiently excellent in rate characteristics and cycle characteristics.SOLUTION: A negative electrode 1 for the secondary battery includes a negative electrode layer 11 arranged on a surface of a negative electrode current collector 10; the negative electrode layer includes a first negative electrode layer 111 that is arranged on the surface of the negative electrode current collector, and a second negative electrode layer 112 that is arranged on a surface of the first negative electrode layer; the first negative electrode layer includes a first graphite, and the second negative electrode layer includes a second graphite that is more easily magnetically oriented than the first graphite; the first graphite is graphite in which a ratio Rs of the 002 peak to the 110 peak in X-ray diffraction is 90 or smaller, and the second graphite is graphite in which a ratio Rf of the 002 peak to the 110 peak in the X-ray diffraction is 100 or larger; an average orientation angle θs of the second graphite with respect to the surface of the negative electrode current collector in the longitudinal direction is larger than the average orientation angle θf of the first graphite with respect to the surface of the negative electrode current collector in the longitudinal direction; and a ratio Re of the 002 peak to the 110 peak in the X-ray diffraction of the negative electrode having the negative electrode current collector and the negative electrode layer is 320 or smaller.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a negative electrode for a secondary battery and a method for producing the same. [Background technology]

[0002] Secondary batteries that can be repeatedly charged and discharged have been used for various purposes. For example, secondary batteries are used as power sources for electronic devices such as smartphones and laptop computers.

[0003] The secondary battery has a structure in which an electrode assembly including a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes, and an electrolyte are housed in an exterior body. The electrodes include a current collector and an electrode layer provided on at least one main surface of the current collector. Specifically, the positive electrode includes a positive electrode current collector and a positive electrode layer provided on at least one main surface of the positive electrode current collector. The negative electrode includes a negative electrode current collector and a negative electrode layer provided on at least one main surface of the negative electrode current collector.

[0004] In recent years, attempts have been made to achieve both high power (for example, rate characteristics) and cycle characteristics of secondary batteries. For example, in Patent Document 1, graphite as a negative electrode active material is magnetically oriented, and a binder-rich layer is provided near the current collector. Specifically, a current collector foil on which a binder layer has been formed in advance is used. Furthermore, for example, in Patent Document 2, graphite is oriented by a magnetic field in either the layer near the current collector or the layer near the electrode surface in the negative electrode layer. In this technology, the same graphite particles are used in both layers, and when coating is performed twice, the first coating is performed and dried, and then the second drying and coating is performed, creating a structure with different orientations in the thickness direction. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2014-96386 [Patent Document 2] Patent No. 5783433 Summary of the Invention [Problem to be solved by the invention]

[0006] The inventors of the present invention have discovered a new problem that excellent rate characteristics and cycle characteristics cannot be sufficiently obtained when conventional secondary batteries (particularly negative electrodes) are used. For example, in Patent Document 1, a binder-rich layer is provided near the current collector, and the high binder concentration increases the interfacial resistance between the current collector and the electrode layer, resulting in a deterioration in rate characteristics. Furthermore, the additional step of applying a binder to the current collector increases the process cost of electrode production. For example, in Patent Document 2, the strength of the interface between the alignment layer and the non-alignment layer weakened, causing interfacial peeling due to expansion and contraction during cycling, resulting in poor cycle performance. Rate performance also deteriorated. Furthermore, the negative electrode layer required two coatings, and drying between the two coatings increased the process cost of electrode production.

[0007] The present invention has been devised in view of the above circumstances. Specifically, an object of the present invention is to provide a negative electrode for a secondary battery having sufficiently excellent rate characteristics and cycle characteristics, and a method for producing the same.

[0008] Another object of the present invention is to provide a negative electrode for a secondary battery that is not only sufficiently excellent in rate characteristics and cycle characteristics but also sufficiently excellent in process costs during production, and a method for producing the same. [Means for solving the problem]

[0009] The present invention provides a negative electrode current collector; a negative electrode layer disposed on the surface of the negative electrode current collector, the negative electrode layer includes a first negative electrode layer disposed on a surface of the negative electrode current collector and a second negative electrode layer disposed on a surface of the first negative electrode layer, the first negative electrode layer includes a first graphite; the second negative electrode layer includes second graphite that is more easily oriented by a magnetic field than the first graphite; the first graphite is graphite having an X-ray 002 / 110 peak ratio Rs of 90 or less; the second graphite is graphite having an X-ray 002 / 110 peak ratio Rf of 100 or more; an average orientation angle θs of the second graphite particle in the longitudinal direction with respect to the surface of the negative electrode current collector is larger than an average orientation angle θf of the first graphite particle in the longitudinal direction with respect to the surface of the negative electrode current collector, The present invention relates to a negative electrode for a secondary battery, wherein the negative electrode has the negative electrode current collector and the negative electrode layer and has an X-ray 002 / 110 peak ratio Re of 320 or less.

[0010] The present invention also provides (i) a preparation step of preparing a negative electrode current collector; (ii) a slurry preparation step of preparing a first negative electrode layer slurry containing a first graphite and a second negative electrode layer slurry containing a second graphite that is more easily oriented in a magnetic field than the first graphite; (iii) applying the first negative electrode layer slurry to the surface of the negative electrode current collector, and then, without drying, applying the second negative electrode layer slurry to the surface of the first negative electrode layer slurry coating, applying a magnetic field, and drying the coating to form a negative electrode precursor; and (iv) pressing the negative electrode precursor Including, the first graphite is graphite having an X-ray 002 / 110 peak ratio Rs of 90 or less as measured by compressing graphite powder, The present invention relates to a method for producing a negative electrode for a secondary battery, wherein the second graphite is graphite having an X-ray 002 / 110 peak ratio Rf of 100 or more. [Effects of the Invention]

[0011] The negative electrode for a secondary battery of the present invention is more sufficiently excellent in rate characteristics and cycle characteristics. The method for producing a negative electrode for a secondary battery of the present invention is significantly superior in terms of process cost. [Brief explanation of the drawings]

[0012] [Figure 1] 1 is a cross-sectional view schematically illustrating an example of a negative electrode for a secondary battery of the present invention. [Figure 2] FIG. 2 is a conceptual diagram for explaining the orientation angle of graphite contained in the negative electrode for a secondary battery of the present invention. [Figure 3A] FIG. 1 is a schematic plan view illustrating one step of a method for preparing a glass sample plate as a sample for determining (or measuring) the X-ray 002 / 110 peak ratio of graphite contained in a negative electrode for a secondary battery of the present invention. [Figure 3B] FIG. 1 is a schematic plan view illustrating one step of a method for preparing a glass sample plate as a sample for determining (or measuring) the X-ray 002 / 110 peak ratio of graphite contained in a negative electrode for a secondary battery of the present invention. [Figure 3C] FIG. 1 is a schematic plan view illustrating one step of a method for preparing a glass sample plate as a sample for determining (or measuring) the X-ray 002 / 110 peak ratio of graphite contained in a negative electrode for a secondary battery of the present invention. [Figure 3D] FIG. 1 is a schematic plan view illustrating one step of a method for preparing a glass sample plate as a sample for determining (or measuring) the X-ray 002 / 110 peak ratio of graphite contained in a negative electrode for a secondary battery of the present invention. [Figure 3E] FIG. 1 is a schematic plan view illustrating one step of a method for preparing a glass sample plate as a sample for determining (or measuring) the X-ray 002 / 110 peak ratio of graphite contained in a negative electrode for a secondary battery of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a negative electrode for a secondary battery according to one embodiment of the present invention will be described in detail with reference to the drawings. The various elements in the drawings are merely shown schematically and exemplarily to facilitate understanding of the present invention, and the appearance, dimensional ratio, etc. may differ from the actual ones.

[0014] Before specifically describing the negative electrode for a secondary battery according to one embodiment of the present invention, the basic structure of a secondary battery will be described. Note that, as used herein, the term "secondary battery" refers to a battery capable of repeated charging and discharging. The term "secondary battery" is not limited to its name and may also encompass electrochemical devices such as "energy storage devices." As used herein, a "planar view" refers to the state of an object placed on a horizontal surface with its main surface (e.g., the surface with the largest area) as the bottom and viewed from above or below along a direction perpendicular to the horizontal surface. Furthermore, as used herein, a "cross-sectional view" refers to the state of a secondary battery viewed from a direction approximately perpendicular to the thickness direction based on the stacking direction of the electrodes constituting the secondary battery (e.g., the direction perpendicular to the negative electrode current collector). The terms "vertical direction" and "horizontal direction" used directly or indirectly in this specification correspond to the vertical direction and horizontal direction in the drawings, respectively. Unless otherwise specified, the same symbols or symbols refer to the same components or parts or have the same meaning. In a preferred embodiment, the vertically downward direction (i.e., the direction in which gravity acts) can be considered to correspond to the "downward direction," and the opposite direction can be considered to correspond to the "upward direction."

[0015] The secondary battery (particularly the negative electrode) of the present invention will be described in detail below with reference to the drawings. Unless otherwise specified, each component constituting the secondary battery of the present invention is disposed in a positive electrode and a negative electrode, respectively. For example, the term "electrode" refers to a positive electrode and a negative electrode, the positive electrode refers to a positive electrode current collector and a positive electrode layer disposed on at least one surface of the positive electrode current collector, and the negative electrode refers to a negative electrode current collector and a negative electrode layer disposed on at least one surface of the negative electrode current collector. Also, for example, the term "electrode active material" refers to a positive electrode active material and a negative electrode active material. Also, for example, the term "conductive assistant" refers to a positive electrode conductive assistant and a negative electrode conductive assistant. Also, for example, the term "electrolyte" refers to a positive electrode electrolyte and a negative electrode electrolyte.

[0016] [Negative electrode] As shown in Fig. 1, the negative electrode 1 has a negative electrode current collector 10 and a negative electrode layer 11 disposed on the surface of the negative electrode current collector. In Fig. 1, the negative electrode layer 11 is disposed on only one side of the negative electrode current collector 10, but it may be disposed on both sides. From the viewpoint of increasing the capacity of the secondary battery, the negative electrode layer 11 is preferably disposed on both sides of the negative electrode current collector 10.

[0017] The negative electrode layer 11 typically has a first negative electrode layer 111 disposed on the surface of the negative electrode current collector 10 and a second negative electrode layer 112 disposed on the surface of the first negative electrode layer 111. The second negative electrode layer 112 typically constitutes (or provides) the negative electrode layer surface.

[0018] The first negative electrode layer 111 contains, as a negative electrode active material, graphite (hereinafter sometimes referred to as first graphite (Gr1)), which is relatively difficult to orient in a magnetic field, and typically further contains a binder (hereinafter sometimes referred to as first binder). The first negative electrode layer 111 may or may not contain a conductive additive (hereinafter sometimes referred to as first conductive additive). From the viewpoint of further improving rate characteristics, the first negative electrode layer 111 preferably contains the first conductive additive. In the first negative electrode layer, a plurality of first graphite particles are bound between them by a first binder. In this case, the first conductive additive may be bound to the first graphite particles by the first binder.

[0019] The second negative electrode layer 112 contains, as a negative electrode active material, graphite (hereinafter sometimes referred to as second graphite (Gr2)) that is more easily magnetically oriented than the first graphite, and typically further contains a binder (hereinafter sometimes referred to as second binder). The second negative electrode layer 112 may or may not contain a conductive additive (hereinafter sometimes referred to as second conductive additive). From the viewpoint of further improving rate characteristics, the second negative electrode layer 112 preferably contains a second conductive additive. In the second negative electrode layer, a plurality of second graphite particles are bound between them by a second binder. In this case, the second conductive additive may be bound to the second graphite particles by the second binder.

[0020] By including the first negative electrode layer 111 and the second negative electrode layer 112, which are difficult to magnetically orient, respectively, and including the second negative electrode layer 112 and the second negative electrode layer 112, which are easily magnetically orientated, respectively, as shown in FIG. 1, the first negative electrode layer 111 in contact with the negative electrode current collector 10 can be a non-oriented layer, and the second negative electrode layer 112 on the electrode surface side can be an oriented layer. The non-oriented layer is a layer in which the graphite is oriented in a relatively random direction. The oriented layer is a layer in which the graphite is oriented in a relatively more vertical direction. Here, the vertical direction refers to the direction perpendicular to the current collector 10 (particularly its surface). This increases the linearity of the voids in the thickness direction (or reduces the degree of curvature) in the negative electrode layer 11, while also ensuring the adhesive strength at the interface between the negative electrode layer 11 and the current collector 10. As a result, high power (particularly rate characteristics) and cycle characteristics can both be achieved. Specifically, increasing the linearity of the voids reduces the tortuosity of the voids, shortening the effective diffusion distance of lithium ions, thereby reducing ionic resistance during charge and discharge and improving rate characteristics. Furthermore, by forming the first anode layer 111 in contact with the anode current collector 10 as a non-oriented layer, interfacial delamination between them is sufficiently prevented, improving cycle characteristics. When the first anode layer contains the second graphite and the second anode layer contains the first graphite, the first anode layer becomes an oriented layer, resulting in poor cycle characteristics. When both the first anode layer and the second anode layer contain the first graphite, an oriented layer is not sufficiently formed, resulting in poor rate characteristics. When both the first anode layer and the second anode layer contain the second graphite, an oriented layer is not sufficiently formed at the interface with the current collector 10, resulting in insufficient adhesive strength at the interface with the current collector 10 and poor cycle characteristics. Graphite is a substance that contributes to the absorption and desorption of lithium ions. Therefore, the negative electrode 1 is an electrode that can absorb and release lithium ions.

[0021] With respect to graphite, "orientation" is a term that refers to the orientation of the graphite particles Gr, where the longitudinal direction L of the graphite particles Gr forms an orientation angle θ with respect to the current collector 10 (particularly its surface) in a cross section such as that shown in FIG. 2. The average value of the orientation angle θ in an oriented layer (i.e., the average orientation angle) is usually larger than the average orientation angle in a non-oriented layer. The longitudinal direction L of the graphite particles Gr is the direction that defines the maximum length of the graphite particles Gr in a cross section.

[0022] In the present invention, the first negative electrode layer 111 corresponds to a non-oriented layer, and the second negative electrode layer 112 corresponds to an oriented layer, and therefore the average orientation angle θs of the second graphite in the second negative electrode layer 112 is larger than the average orientation angle θf of the first graphite in the first negative electrode layer 111. If the average orientation angle θs of the second graphite in the second negative electrode layer is equal to or smaller than the average orientation angle θf of the first graphite in the first negative electrode layer, the rate characteristics and cycle characteristics will deteriorate.

[0023] From the viewpoint of further improving the rate performance and cycle performance, it is preferable that the average orientation angle θs of the second graphite and the average orientation angle θf of the first graphite satisfy the following relationship: 3 ≤ θs - θf; Preferably, 4≦θs-θf≦20; More preferably, 5≦θs-θf≦15; Furthermore, 5≦θs-θf≦10.

[0024] The average orientation angle θs of the second graphite is usually 35° or greater, and from the viewpoint of further improving the rate performance and cycle performance, it is preferably 35° or greater and 70° or less, more preferably 40° or greater and 60° or less, and even more preferably 40° or greater and 50° or less.

[0025] The average orientation angle θ of the first graphite is usually 60° or less, and from the viewpoint of further improving the rate performance and cycle performance, it is preferably 10° or more and 60° or less, more preferably 20° or more and 50° or less, and even more preferably 32° or more and 42° or less.

[0026] The average orientation angle is a value obtained by the following method. A cross section of the negative electrode layer is extracted from the negative electrode by ion milling, and the cross section is observed using an SEM to obtain an image. In the obtained cross section image, as shown in Figure 1, the negative electrode layer 11 is divided into five equal parts in the thickness T direction, which are designated as first to fifth regions (E1 to E5) in order from the current collector 10 side, and the average orientation angles θ1 to θ5 of the graphite in each region are determined. The average orientation angle is the average value of the orientation angles of 100 particles arbitrarily selected in each region. The average orientation angle θ1 of the first region E1 is defined as the average orientation angle θf of the graphite in the first negative electrode layer. The average orientation angle θ5 of the fifth region E5 is defined as the average orientation angle θs of the graphite in the second negative electrode layer.

[0027] In the present invention, from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferable that the average orientation angle of each region gradually changes from the first region E1 to the fifth region E5. Specifically, when the average orientation angle of each region and the orientation angle change rate between two adjacent regions are calculated for the first to fifth regions (E1 to E5) obtained by dividing the negative electrode layer 11 into five equal parts in the thickness direction T, all of the orientation angle change rates are preferably 25% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. The "all orientation angle change rates" refer to the orientation angle change rate between the first region E1 and the second region E2, the orientation angle change rate between the second region E2 and the third region E3, the orientation angle change rate between the third region E3 and the fourth region E4, and the orientation angle change rate between the fourth region E4 and the fifth region E5. The orientation angle change rate is calculated by dividing the average orientation angle θ in the lower region between two adjacent regions. L From the above, the average orientation angle θ H Specifically, the rate of change to {(θ H -θ L ) / θ L It is expressed as an absolute value of}×100(%).

[0028] The first graphite is a graphite having an X-ray 002 / 110 peak ratio Rs of 90 or less, particularly 50 or more and 90 or less, as measured by compressing graphite powder. From the viewpoint of further improving rate characteristics and cycle characteristics, the first graphite is a graphite having an X-ray 002 / 110 peak ratio Rs of preferably 60 or more and 85 or less, more preferably 70 or more and 85 or less, and even more preferably 75 or more and 85 or less.

[0029] Therefore, the first graphite can be selected from commercially available graphites and used if the X-ray 002 / 110 peak ratio falls within the above range. As such a first graphite, for example, artificial graphite can be used.

[0030] The average particle size of the first graphite is not particularly limited, and may be, for example, 1 μm or more and 30 μm or less, particularly 5 μm or more and 15 μm or less. In this specification, the average particle size of graphite can be determined by measuring the maximum lengths of any 100 graphite particles in a cross-sectional photograph (for example, an SEM photograph) of the negative electrode layer, and averaging the measured values.

[0031] The second graphite is a graphite having an X-ray 002 / 110 peak ratio Rf of 100 or more, particularly 100 or more and 150 or less, and from the viewpoint of further improving the rate characteristics and cycle characteristics, the second graphite is preferably 100 or more and 135 or less, more preferably 100 or more and 120 or less, and even more preferably 105 or more and 115 or less.

[0032] Therefore, the second graphite can be selected from commercially available graphites and used if the X-ray 002 / 110 peak ratio falls within the above range. As such a second graphite, for example, synthetic graphite can be used.

[0033] The average particle size of the second graphite is not particularly limited, and may be, for example, 1 μm or more and 30 μm or less, particularly 5 μm or more and 15 μm or less.

[0034] The 002 / 110 peak ratio of graphite is a value obtained by the following method. First, a measurement sample is prepared by the following method, which will be explained with reference to Figures 3A to 3E. A glass sample plate 50 having a groove 51 on one side is used. (1) As shown in FIG. 3A, the glass sample plate 50 is placed on a medicine wrapping paper or the like so that the surface having the grooves 51 faces upward, and graphite Gr is placed in the grooves 51. (2) Since the graphite is raised in the grooves 51, the surface of the graphite Gr is flattened using the back surface of another glass sample plate 55, as shown in FIGS. 3B and 3C. (3) As shown in FIG. 3D, the above step (2) is repeated until the surface of the graphite Gr becomes flat and is flush with the surface of the glass sample plate 50 (particularly the surface of the non-grooved portion). (4) Wipe each part of the glass sample plate 50 with alcohol or the like to complete the measurement sample. The measurement sample was then subjected to an XRD (X-ray diffractometer) to measure the 002 / 110 peak ratio, which is the ratio of the 002 plane peak intensity to the 110 plane peak intensity.

[0035] In the first negative electrode layer, the content of the first graphite is usually 80% by weight or more and 99% by weight or less, relative to the total amount of the first negative electrode layer, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 90% by weight or more and 99% by weight or less, more preferably 92% by weight or more and 98% by weight or less, and even more preferably 94% by weight or more and 98% by weight or less. In the second negative electrode layer, the content of the second graphite is typically 80% by weight or more and 99% by weight or less, relative to the total amount of the second negative electrode layer, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 90% by weight or more and 99% by weight or less, more preferably 92% by weight or more and 98% by weight or less, and even more preferably 94% by weight or more and 98% by weight or less.

[0036] The content of the first graphite in the first negative electrode layer and the content of the second graphite in the second negative electrode layer may be independently selected. From the viewpoint of further improving the rate characteristics and cycle characteristics, when the content of the first graphite in the first negative electrode layer is α (wt%), the content of the second graphite in the second negative electrode layer is preferably 0.8×α to 1.2×α, more preferably 0.9×α to 1.1×α, even more preferably 0.95×α to 1.05×α, and particularly preferably α.

[0037] In the negative electrode 11 of the present invention, it is preferable that the boundary surface between the first negative electrode layer 111 and the second negative electrode layer 112 is not clearly distinguishable. This makes it possible to more effectively prevent cracks from occurring at the boundary surface, thereby further improving the cycle characteristics.

[0038] The boundary between the first negative electrode layer 111 and the second negative electrode layer 112 cannot be clearly identified, which means that when a cross section of the obtained negative electrode is extracted by ion milling and the cross section is observed with an SEM, the boundary between the first negative electrode layer and the second negative electrode layer cannot be clearly identified.

[0039] In the present invention, when the boundary surface between the first negative electrode layer 111 and the second negative electrode layer 112 cannot be clearly identified, this corresponds to the case where all of the orientation angle change rates between two adjacent regions in the first to fifth regions (E1 to E5) described above are 25% or less, more preferably 20% or less, even more preferably 15% or less, and particularly preferably 10% or less. In contrast, when the boundary surface between the first negative electrode layer 111 and the second negative electrode layer 112 is clearly distinguishable, this coincides with the case where at least one of all the orientation angle change rates between two adjacent regions in the first to fifth regions (E1 to E5) described above exceeds 25%.

[0040] The total basis weight of the first negative electrode layer and the second negative electrode layer is not particularly limited, and may be, for example, 1 mg / cm 2 More than 30mg / cm 2 Below, especially 5 mg / cm 2 More than 20mg / cm 2The basis weight of each of the first negative electrode layer and the second negative electrode layer is not particularly limited, and may be a basis weight that achieves the thickness ratio (Tf / Ts) described below. The basis weight is the basis weight per side of the current collector.

[0041] The basis weight of the first negative electrode layer is not particularly limited, and is, for example, 1 mg / cm 2 More than 20mg / cm 2 From the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 1 mg / cm 2 More than 10mg / cm 2 Less than 1 mg / cm, more preferably 2 More than 5mg / cm 2 The following is the result. The basis weight of the second negative electrode layer is not particularly limited, and is, for example, 1 mg / cm 2 More than 20mg / cm 2 From the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 3 mg / cm 2 More than 13mg / cm 2 Less than 4 g / cm 2 Over 9mg / cm 2 The following is the result.

[0042] The ratio (Tf / Ts) of the thickness Tf of the first negative electrode layer 111 to the thickness Ts of the second negative electrode layer 112 is not particularly limited and may be, for example, 2.2 or less (particularly, 0.1 or more and 2.2 or less), and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 0.2 or more and 1.5 or less, more preferably 0.2 or more and 1.2 or less, and even more preferably 0.3 or more and 0.8 or less.

[0043] When the boundary surface between the first negative electrode layer 111 and the second negative electrode layer 112 cannot be clearly identified, the thickness ratio (Tf / Ts) is a value obtained by the following method. For a specific region among the second to fourth regions (E2 to E4) described above, if the orientation angle change rate with respect to both regions is 5% or more (particularly 7% or more), it is assumed that a boundary exists at the center of the thickness direction of the specific region. Based on the assumed boundary, the thicknesses of the first negative electrode layer and the second negative electrode layer are measured, and the thickness ratio between them is calculated. The thickness is measured using the average value of 10 arbitrary points on the SEM image.

[0044] The thickness Tf of the first negative electrode layer 111 is not particularly limited, and may be, for example, a value that achieves the above-mentioned basis weight of the first negative electrode layer. The thickness Ts of the second negative electrode layer 112 is not particularly limited, and may be, for example, a value that achieves the above-mentioned basis weight of the second negative electrode layer.

[0045] The negative electrode of the present invention has an X-ray 002 / 110 peak ratio Re of 320 or less (particularly, 100 or more and 320 or less), and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 120 or more and 320 or less, more preferably 140 or more and 300 or less, even more preferably 160 or more and 280 or less, and particularly preferably 170 or more and 220 or less.

[0046] The 002 / 110 peak ratio Re of the negative electrode is a parameter indicating the orientation of graphite throughout the negative electrode layer. For example, the larger the peak ratio Re, the more randomly oriented the graphite is throughout the negative electrode layer. For example, the smaller the peak ratio Re, the more perpendicularly oriented the graphite is throughout the negative electrode layer.

[0047] Therefore, the 002 / 110 peak ratio Re of the negative electrode can be controlled by adjusting the thickness ratio (Tf / Ts) of the first negative electrode layer and the second negative electrode layer. For example, increasing the thickness ratio (Tf / Ts) increases the peak ratio Re. Also, decreasing the thickness ratio (Tf / Ts) decreases the peak ratio Re.

[0048] The 002 / 110 peak ratio Re of the negative electrode can be measured in the same manner as the 002 / 110 peak ratio of graphite, except that the negative electrode is used as is as a measurement sample.

[0049] The first and second negative electrode layers may further contain other negative electrode active materials in addition to the first and second graphites, respectively. Such other negative electrode active materials may be, for example, one or more substances selected from various carbon materials other than graphite, oxides, lithium alloys, and the like.

[0050] Examples of various carbon materials other than graphite include soft carbon, hard carbon, and diamond-like carbon. The oxide of the negative electrode active material can be at least one selected from the group consisting of silicon oxide, tin oxide, indium oxide, zinc oxide, and lithium oxide. The lithium alloy of the negative electrode active material can be any metal capable of forming an alloy with lithium, such as a binary, ternary, or higher alloy of lithium with a metal such as Al, Si, Pb, Sn, In, Bi, Ag, Ba, Ca, Hg, Pd, Pt, Te, Zn, or La. Such oxides preferably have an amorphous structure, as this reduces degradation due to inhomogeneities such as grain boundaries or defects.

[0051] The content of the other negative electrode active material is not particularly limited, and is, for example, 50% by weight or less relative to the first graphite and the second graphite in the first negative electrode layer slurry and the second negative electrode layer slurry, respectively, and from the viewpoint of further improving the rate characteristics and cycle characteristics, is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 1% by weight or less, and most preferably 0% by weight.

[0052] The first binder and the second binder of the first negative electrode layer and the second negative electrode layer, respectively, are not particularly limited and may be, for example, at least one selected from the group consisting of carboxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polyvinylidene fluoride, polyimide resins, and polyamide-imide resins. From the viewpoint of further improving rate characteristics and cycle characteristics, the first binder and the second binder are preferably made of the same (particularly the same) material. For example, from the viewpoint of further improving rate characteristics and cycle characteristics, the first binder and the second binder may each independently be carboxymethyl cellulose, styrene-butadiene rubber, or a mixture thereof.

[0053] In the first negative electrode layer, the content of the first binder is usually 0.1% by weight to 10% by weight, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 1% by weight to 8% by weight, more preferably 1% by weight to 5% by weight. When two or more types of first binders are used, the total amount thereof may be within the above range. In the second negative electrode layer, the content of the second binder is usually 0.1% by weight to 10% by weight, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 1% by weight to 8% by weight, more preferably 1% by weight to 5% by weight. When two or more types of second binders are used, the total amount thereof may be within the above range.

[0054] The content of the first binder in the first negative electrode layer and the content of the second binder in the second negative electrode layer may be selected independently. From the viewpoint of further improving the rate characteristics and cycle characteristics, when the content of the first binder in the first negative electrode layer is β (wt%), the content of the second binder in the second negative electrode layer is preferably 0.8×β or more and 1.2×β or less, more preferably 0.9×β or more and 1.1×β or less, even more preferably 0.95×β or more and 1.05×β or less, and particularly preferably β.

[0055] The first and second conductive additives in the first and second negative electrode layers are each independently and not particularly limited, and may be at least one selected from the group consisting of carbon blacks such as graphite, thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers; metal powders such as copper, nickel, aluminum, and silver; and polyphenylene derivatives. The first and second conductive additives are preferably the same (particularly the same) material from the viewpoint of further improving rate characteristics and cycle characteristics. For example, the first and second conductive additives may each independently be graphite (particularly flake-shaped graphite) from the viewpoint of further improving rate characteristics and cycle characteristics. The graphite used as the first and second conductive additives has a different average particle size from the first and second graphites described above, and the X-ray 002 / 110 peak ratio is not particularly limited. Specifically, the graphite serving as the first conductive additive has an average particle size smaller than that of the first graphite, and the graphite serving as the second conductive additive has an average particle size smaller than that of the second graphite.

[0056] The average particle size of the first conductive assistant and the second conductive assistant is not particularly limited, and may be, for example, 0.01 μm or more and 10 μm or less, particularly 0.1 μm or more and 5 μm or less. In this specification, the average particle size of the conductive additive can be determined by measuring the maximum lengths of any 100 conductive additives in a cross-sectional photograph (for example, an SEM photograph) of the negative electrode layer, and averaging the results.

[0057] In the first negative electrode layer, the content of the first conductive additive is 0.1 wt % or more and 10 wt % or less, relative to the total amount of the first negative electrode layer, and from the viewpoint of further improving the rate characteristics and cycle characteristics, is preferably 0.5 wt % or more and 5 wt % or less, and more preferably 0.5 wt % or more and 2 wt % or less, In the second negative electrode layer, the content of the second conductive additive is 0.1% by weight or more and 10% by weight or less, relative to the total amount of the second negative electrode layer, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 0.5% by weight or more and 5% by weight or less, and more preferably 0.5% by weight or more and 2% by weight or less.

[0058] The content of the first conductive additive in the first negative electrode layer and the content of the second conductive additive in the second negative electrode layer may be selected independently. From the viewpoint of further improving the rate characteristics and cycle characteristics, when the content of the first conductive additive in the first negative electrode layer is γ (wt%), the content of the second conductive additive in the second negative electrode layer is preferably 0.8×γ or more and 1.2×γ or less, more preferably 0.9×γ or more and 1.1×γ or less, even more preferably 0.95×γ or more and 1.05×γ or less, and particularly preferably γ.

[0059] The first negative electrode layer and the second negative electrode layer may each independently further contain any additive conventionally known as an additive for negative electrode layers in the field of secondary batteries.

[0060] [Method of manufacturing negative electrode] The negative electrode can be produced by a method including the following steps. (i) a preparation step of preparing a negative electrode current collector; (ii) a slurry preparation step of preparing a first negative electrode layer slurry containing a first graphite and a second negative electrode layer slurry containing a second graphite that is more easily oriented in a magnetic field than the first graphite; (iii) applying the first negative electrode layer slurry to the surface of the negative electrode current collector, and then, without drying, applying the second negative electrode layer slurry to the surface of the first negative electrode layer slurry coating, applying a magnetic field, and drying the coating to form a negative electrode precursor; and (iv) pressing the negative electrode precursor;

[0061] In the preparation process, the negative electrode current collector is a member that contributes to collecting and supplying electrons generated in the active material due to the battery reaction. Such a current collector may be a sheet-like metal member and may be porous or perforated. For example, the current collector may be a metal foil, punched metal, mesh, expanded metal, or the like. The negative electrode current collector used in the negative electrode is preferably made of a metal foil containing at least one selected from the group consisting of copper, stainless steel, nickel, and the like, and may be, for example, copper foil.

[0062] In the slurry preparation step, a slurry for a first negative electrode layer and a slurry for a second negative electrode layer are prepared. The slurry for the first negative electrode layer can usually be prepared by mixing and dispersing a first binder and a solvent (hereinafter sometimes referred to as the first solvent) together with a first graphite as the negative electrode active material, and usually further contains a first conductive assistant as an optional component. The slurry for the second negative electrode layer can usually be prepared by mixing and dispersing a second binder and a solvent (hereinafter sometimes referred to as the second solvent) together with second graphite as the negative electrode active material, and usually further contains a second conductive additive as an optional component.

[0063] The first graphite, the second graphite, the first binder, the second binder, the first conductive additive, and 2 are as described above. The concentrations of these components in each slurry may be any concentration that achieves the above-described content of the component in each of the first negative electrode layer and the second negative electrode layer.

[0064] The first solvent and the second solvent are not particularly limited as long as they are solvents capable of dissolving (or dispersing) the first binder and the second binder, respectively, and may each independently be, for example, at least one selected from water, NMP, alcohols, etc. From the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferable that the first solvent and the second solvent are the same type (particularly the same) of material. For example, from the viewpoint of further improving the rate characteristics and cycle characteristics, the first solvent and the second solvent may each independently be water.

[0065] The solids concentrations of the first and second negative electrode layer slurries are each independently not particularly limited and may be, for example, 35% by weight to 60% by weight, particularly 40% by weight to 55% by weight. From the viewpoint of further improving rate performance and cycle performance, the solids concentration of the second negative electrode layer slurry is preferably 0.8×η to 1.2×η, more preferably 0.9×η to 1.1×η, even more preferably 0.95×η to 1.05×η, where η is the solids concentration of the first negative electrode layer slurry (wt %).

[0066] In the negative electrode precursor formation process, a first negative electrode layer slurry is applied to the surface of a negative electrode current collector, and then, without drying, a second negative electrode layer slurry is applied to the surface of the first negative electrode layer slurry coating, followed by application of a magnetic field and drying to form a negative electrode precursor. In the present invention, the first negative electrode layer and the second negative electrode layer each contain a first graphite and a second graphite, respectively. In addition, during the manufacturing process, after application of the first negative electrode layer slurry, a second negative electrode layer slurry is applied, without drying, and then oriented in a magnetic field and dried. This allows the relationship between the average orientation angle θf of the first graphite and the average orientation angle θs of the second graphite and the X-ray 002 / 110 peak ratio Re of the negative electrode to fall within the aforementioned ranges. As a result, high power (particularly rate performance) and cycle performance can be achieved simultaneously. Without application of a magnetic field, the average orientation angle θs of the second graphite decreases, resulting in a decrease in rate performance.

[0067] In this process, the second negative electrode layer slurry is applied without drying after the first negative electrode layer slurry is applied. This allows for a wet-on-wet method, allowing two types of slurries to be applied consecutively in one process. Preferably, two types of slurries can be applied consecutively using one application device. Therefore, the negative electrode manufacturing method of the present invention is significantly superior in terms of process cost.

[0068] The method for applying the first negative electrode layer slurry and the second negative electrode layer slurry is not particularly limited as long as it is possible to apply the first negative electrode layer slurry and the second negative electrode layer slurry, and examples thereof include die coating, dip coating, brush coating, roller coating, etc. When two types of slurries are applied continuously in one step (particularly when two types of slurries are applied continuously using one coating device), it is usually preferable to adopt the die coating method for both applications.

[0069] The application amounts of the first negative electrode layer slurry and the second negative electrode layer slurry are not particularly limited, and may be, for example, amounts that achieve the above-mentioned thickness ratio (Tf / Ts) and / or basis weight.

[0070] The magnetic flux density of the applied magnetic field is not particularly limited and is usually 0.1 Tesla or more and 10 Tesla or less, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably 0.5 Tesla or more and 5 Tesla or less, more preferably 0.5 Tesla or more and 2 Tesla or less.

[0071] The magnetic field application time is not particularly limited and is usually from 0.1 seconds to 1 minute, and from the viewpoint of further improving the rate characteristics and cycle characteristics, it is preferably from 0.1 seconds to 30 seconds, more preferably from 0.5 seconds to 10 seconds, and even more preferably from 0.5 seconds to 5 seconds.

[0072] The drying method is not particularly limited as long as the drying of the first negative electrode layer slurry coating film and the second negative electrode layer slurry coating film is achieved, and examples of the drying method that can be used include hot air drying, far-infrared drying, etc. The drying temperature and drying time are also not particularly limited as long as the drying of the first negative electrode layer slurry coating film and the second negative electrode layer slurry coating film is achieved, and for example, the drying temperature may be 50°C or higher and 130°C or lower, and the drying time may be 1 minute or higher and 10 minutes or lower.

[0073] In the pressing step, for example, a roll press is used to consolidate the mixture so that the porosity is 10% or more and 40% or less, particularly 20% or more and 30% or less.

[0074] The various numerical ranges referred to in this specification are intended to include both the lower and upper limits. For example, a numerical range such as 1 to 10 can be interpreted as including the lower limit of "1" and the upper limit of "10."

[0075] The method for producing an anode of the present invention does not preclude the application of a magnetic field and drying after the application of the first anode layer slurry and before the application of the second anode layer slurry. In the method for producing an anode of the present invention, from the viewpoints of further improving the rate characteristics and cycle characteristics (particularly further improving the cycle characteristics) based on the blurring of the boundary between the first anode layer 111 and the second anode layer 112 and further reducing the process cost during production, it is preferable to apply the second anode layer slurry after the application of the first anode layer slurry without applying a magnetic field or drying.

[0076] [Basic structure of secondary batteries] The secondary battery of the present invention includes the above-described negative electrode. Specifically, the secondary battery of the present invention has a structure in which an electrode assembly and an electrolyte are housed and sealed inside an outer casing. The electrode assembly may include a positive electrode, a negative electrode, and a separator disposed between the positive and negative electrodes. The electrode assembly may be a stacked electrode assembly or a wound (jelly roll) electrode assembly. A stacked electrode assembly is formed by stacking multiple electrode constituent layers, each including a positive electrode, a negative electrode, and a separator. A wound electrode assembly is formed by winding an electrode constituent layer, each including a positive electrode, a negative electrode, and a separator. Furthermore, for example, the electrode assembly may have a so-called stack-and-fold structure in which a positive electrode, a separator, and a negative electrode are stacked on a long film and then folded.

[0077] The positive electrode is composed of at least a positive electrode current collector and a positive electrode layer, with the positive electrode layer being provided on at least one side of the positive electrode current collector. A positive electrode side lead tab is positioned at a portion of the positive electrode current collector where the positive electrode layer is not provided, i.e., at an end of the positive electrode current collector. The positive electrode layer contains a positive electrode active material as an electrode active material. The negative electrode is the above-described negative electrode of the present invention. In the negative electrode, a negative electrode side lead tab is positioned at a portion of the negative electrode current collector where the negative electrode layer is not provided, i.e., at an end of the negative electrode current collector.

[0078] The positive electrode active material contained in the positive electrode layer is a material directly involved in the transfer of electrons in a secondary battery, and is the main material of the positive electrode responsible for charge and discharge, i.e., the battery reaction. More specifically, ions are introduced into the electrolyte due to the "positive electrode active material contained in the positive electrode layer" and the "first graphite and second graphite contained in the negative electrode layer." These ions then move between the positive electrode and negative electrode, transferring electrons and causing charge and discharge. The positive electrode layer and negative electrode layer are preferably layers capable of absorbing and releasing lithium ions. In other words, a secondary battery in which lithium ions move between the positive electrode and negative electrode via the electrolyte to charge and discharge the battery is preferred. When lithium ions are involved in charge and discharge, the secondary battery corresponds to a so-called "lithium ion battery."

[0079] The positive electrode layer may contain a binder, for example, a granular positive electrode active material, to ensure sufficient contact between the particles and maintain their shape. Furthermore, the positive electrode layer may contain a conductive additive to facilitate the transfer of electrons that drive the battery reaction. Because the positive electrode layer contains multiple components, it may also be referred to as a "positive electrode composite layer."

[0080] The positive electrode active material is preferably a material that contributes to the absorption and desorption of lithium ions. From this perspective, the positive electrode active material is preferably, for example, a lithium-containing composite oxide. More specifically, the positive electrode active material is preferably a lithium transition metal composite oxide containing lithium and at least one transition metal selected from the group consisting of cobalt, nickel, manganese, and iron. In other words, such a lithium transition metal composite oxide is preferably contained as the positive electrode active material in the positive electrode layer of the secondary battery. For example, the positive electrode active material may be lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium iron phosphate, or a material in which part of the transition metal is replaced with another metal. Such positive electrode active materials may be contained alone or in combination of two or more types. In a more preferred embodiment, the positive electrode active material contained in the positive electrode layer is lithium cobalt oxide.

[0081] The binder that can be contained in the positive electrode layer is not particularly limited, but can include at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, vinylidene fluoride-tetrafluoroethylene copolymer, and polytetrafluoroethylene. The conductive additive that can be contained in the positive electrode layer is not particularly limited, but can include at least one selected from the group consisting of carbon black such as thermal black, furnace black, channel black, ketjen black, and acetylene black; carbon fibers such as graphite, carbon nanotubes, and vapor-grown carbon fibers; metal powders such as copper, nickel, aluminum, and silver; and polyphenylene derivatives. For example, the binder of the positive electrode layer can be polyvinylidene fluoride. By way of example only, the conductive additive of the positive electrode layer can be carbon black. Furthermore, the binder and conductive additive of the positive electrode layer can be a combination of polyvinylidene fluoride and carbon black.

[0082] The separator is a component provided to prevent short circuits due to contact between the positive and negative electrodes and to maintain electrolyte integrity. In other words, the separator is a component that allows ions to pass through while preventing electronic contact between the positive and negative electrodes. Preferably, the separator is a porous or microporous insulating component, and has a membrane shape due to its small thickness. By way of example only, a microporous membrane made of polyolefin may be used as the separator. In this regard, the microporous membrane used as the separator may contain, for example, only polyethylene (PE) or only polypropylene (PP) as the polyolefin. Furthermore, the separator may be a laminate composed of a "microporous membrane made of PE" and a "microporous membrane made of PP." The surface of the separator may be covered with an inorganic particle coating layer and / or an adhesive layer, etc. The surface of the separator may have adhesive properties.

[0083] The separator should not be limited to a specific name, and may be a solid electrolyte, a gel electrolyte, insulating inorganic particles, or the like, which have similar functions. From the viewpoint of further improving the ease of handling of the electrodes, it is preferable that the separator and the electrodes (positive electrode / negative electrode) are bonded together. The adhesion between the separator and the electrodes can be achieved by using an adhesive separator as the separator, or by applying and / or thermocompressing an adhesive binder onto the electrode layer (positive electrode layer / negative electrode layer). Examples of adhesive binder materials that provide adhesiveness to the separator or electrode layer include polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene polymer, and acrylic resin. The thickness of the adhesive layer formed by applying an adhesive binder, etc., may be 0.5 μm or more and 5 μm or less.

[0084] When the positive and negative electrodes have layers capable of absorbing and releasing lithium ions, the electrolyte is preferably a "non-aqueous" electrolyte such as an organic electrolyte and / or an organic solvent (i.e., the electrolyte is preferably a non-aqueous electrolyte). The metal ions released from the electrodes (positive and negative electrodes 1) are present in the electrolyte, and therefore the electrolyte assists the migration of the metal ions in the battery reaction.

[0085] The nonaqueous electrolyte is an electrolyte containing a solvent and a solute. A specific solvent for the nonaqueous electrolyte preferably contains at least a carbonate. Such carbonate may be a cyclic carbonate and / or a chain carbonate. Although not particularly limited, the cyclic carbonate may include at least one selected from the group consisting of propylene carbonate (PC), ethylene carbonate (EC), butylene carbonate (BC), and vinylene carbonate (VC). The chain carbonate may include at least one selected from the group consisting of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dipropyl carbonate (DPC). By way of example only, a combination of a cyclic carbonate and a chain carbonate may be used as the nonaqueous electrolyte, such as a mixture of ethylene carbonate and ethyl methyl carbonate. As a specific solute of the non-aqueous electrolyte, a Li salt such as LiPF6, LiBF4, etc. is preferably used. As a specific solute of the non-aqueous electrolyte, a Li salt such as LiPF6 and / or LiBF4 is preferably used.

[0086] The exterior body may be in the form of a conductive hard case or a flexible case (e.g., a pouch). When the exterior body is in the form of a flexible case (e.g., a pouch), each of the multiple positive electrodes is connected to a positive electrode external terminal via a positive electrode current collecting lead. The positive electrode external terminal is fixed to the exterior body by a seal portion, which prevents leakage of the electrolyte. Similarly, each of the multiple negative electrodes is connected to a negative electrode external terminal via a negative electrode current collecting lead. The negative electrode external terminal is fixed to the exterior body by a seal portion, which prevents leakage of the electrolyte. However, this is not limited thereto, and the positive electrode current collecting lead connected to each of the multiple positive electrodes may have the function of a positive electrode external terminal, and the negative electrode current collecting lead connected to each of the multiple negative electrodes may have the function of a negative electrode external terminal. When the exterior body is in the form of a conductive hard case, each of the multiple positive electrodes is connected to a positive electrode external terminal via a positive electrode current collecting lead. The positive electrode external terminal is fixed to the exterior body by a seal portion, and the seal portion prevents leakage of the electrolyte.

[0087] The conductive hard case consists of a main body and a lid. The main body consists of a bottom and side sections that form the bottom surface of the exterior body. The main body and lid are sealed together after housing the electrode assembly, electrolyte, current collecting leads, and external terminals. The sealing method is not particularly limited, and examples include laser irradiation. Any material capable of forming a hard case-type exterior body in the field of secondary batteries can be used as the material for the main body and lid. Such materials may be any material that allows electron transfer, including conductive materials such as aluminum, nickel, iron, copper, and stainless steel. The dimensions of the main body and lid are determined primarily based on the dimensions of the electrode assembly. For example, it is preferable that the dimensions are large enough to prevent the electrode assembly from moving (shifting) within the exterior body when the electrode assembly is housed. Preventing movement of the electrode assembly prevents damage to the electrode assembly and improves the safety of the secondary battery.

[0088] The flexible case is composed of a soft sheet. The soft sheet is only required to be flexible enough to allow the sealing portion to be folded, and is preferably a plastic sheet. The plastic sheet is a sheet that maintains its deformation due to an external force when the external force is applied and then removed, and for example, a so-called laminated film can be used. A flexible pouch made of a laminated film can be produced, for example, by overlapping two laminated films and heat-sealing their periphery. A typical laminated film is a film made by laminating a metal foil and a polymer film, and a specific example is a three-layer structure consisting of an outer layer polymer film / metal foil / inner layer polymer film. The outer layer polymer film is intended to prevent moisture penetration and damage to the metal foil due to contact, and polymers such as polyamide and polyester are suitable for use. The metal foil is intended to prevent moisture and gas penetration, and foils such as copper, aluminum, and stainless steel are suitable for use. The inner layer polymer film protects the metal foil from the electrolyte contained inside and serves to melt and seal the opening during heat sealing, and polyolefin or acid-modified polyolefin can be suitably used.

[0089] Any current collecting leads used in the field of secondary batteries can be used as the positive electrode current collecting lead and the negative electrode current collecting lead. Such current collecting leads may be made of any material that allows electron transfer, such as conductive materials such as aluminum, nickel, iron, copper, and stainless steel. The positive electrode current collecting lead is preferably made of aluminum, and the negative electrode current collecting lead is preferably made of nickel. The shape of the positive electrode current collecting lead and the negative electrode current collecting lead is not particularly limited and may be, for example, wire-like or plate-like.

[0090] Any external terminal used in the field of secondary batteries can be used as the external terminal. Such external terminals may be made of any material that allows electron transfer, typically a conductive material such as aluminum, nickel, iron, copper, or stainless steel. The external terminals 5 may be electrically connected directly to the substrate or electrically connected indirectly to the substrate via another device. However, this is not a limitation. A positive electrode current collecting lead connected to each of the multiple positive electrodes may function as a positive electrode external terminal, and a negative electrode current collecting lead connected to each of the multiple negative electrodes may function as a negative electrode external terminal.

[0091] Although one embodiment of the present invention has been described above, it is merely a typical example within the scope of application of the present invention. Therefore, it will be readily understood by those skilled in the art that the present invention is not limited to this embodiment and that various modifications can be made. [Example]

[0092] Examples of the present invention will be described below.

[0093] [Cathode manufacturing] A positive electrode slurry was obtained by dispersing lithium cobalt oxide (LCO) with an average particle size of 15 μm as the positive electrode active material, carbon black (HS-100 manufactured by Denka) as a conductive additive, and PVdF (polyvinylidene fluoride: #7200 manufactured by Kureha) as a binder in NMP (N-methyl-2-pyrrolidone) at a weight ratio of 96:2:2. The positive electrode slurry was produced by dissolving PVdF in NMP using a disper mill, then adding carbon black and dispersing using a disper mill, finally adding LCO and dispersing using a disper mill, and finally mixing with NMP to achieve a predetermined viscosity. Next, a die coater was used to coat the film so that the weight per side was 18.9 mg / cm 2 After applying the mixture to both sides of a 12 μm thick Al foil and drying it, the mixture was compressed using a roll press to a porosity of 16%, and then cut into a predetermined shape to obtain a positive electrode plate.

[0094] [Manufacturing of negative electrodes] (Reference example 1) The negative electrode active material was artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). The binders were CMC (carboxymethyl cellulose) and SBR (styrene-butadiene rubber) in a weight ratio of 96:1:3 (=1.5 + 1.5) and dispersed in water to obtain a negative electrode slurry (solids concentration 45 wt%). The negative electrode slurry was then coated using a die coater to a single-sided coating weight of 10.0 mg / cm. 2 After applying the mixture to both sides of a 10 μm thick Cu foil and drying it, the foil was compressed using a roll press to a porosity of 25%, and then cut into a predetermined shape to obtain a negative electrode plate.

[0095] (Comparative Example 1) As the negative electrode active material, artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm, flake graphite (average particle size 3 μm) as a conductive additive, and CMC and SBR as binders were dispersed in water in a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain a negative electrode slurry (solid concentration 45 wt%). Next, using a die coater, the negative electrode slurry was coated to a single-sided coating weight of 10.0 mg / cm. 2 The negative electrode coating was obtained by applying the coating to both sides of a 10 μm-thick Cu foil, which had previously been coated with an undercoat layer on both sides. A magnetic field (magnetic flux density 1 Tesla) was then applied perpendicular to the Cu foil for 1 second, followed by drying. The foil was then compressed using a roll press to a porosity of 25% and cut into the desired shape to obtain a negative electrode plate. The undercoat layer had a composition of AB (acetylene black) / CMC / SBR=40 / 30 / 30, and was formed using a microgravure coater to a thickness of 3 μm on each side.

[0096] (Comparative Example 2) As the negative electrode active material, artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm, flake graphite (average particle size 3 μm) as a conductive additive, and CMC and SBR as binders were dispersed in water in a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain a negative electrode slurry (solid concentration 45 wt%). Next, the negative electrode slurry was coated using a die coater to a single-sided coating weight of 5.0 mg / cm. 2 The electrode layer was then coated on both sides of a 10 μm thick Cu foil and dried, with a weight of 5.0 mg / cm on one side. 2 A magnetic field (magnetic flux density 1 tesla) was applied perpendicular to the Cu foil for 1 second, and then the foil was dried to produce a graphite sheet with a surface area of ​​10 mg / cm on one side, in which only the upper layer of graphite was magnetically oriented. 2 Thereafter, the negative electrode coating film was compressed using a roll press to a porosity of 25%, and then cut into a predetermined shape to obtain a negative electrode plate.

[0097] (Comparative Example 3) As the negative electrode active material, artificial graphite (first graphite) with an X-ray 002 / 110 peak ratio of 80 and an average particle size of approximately 10 μm, flake graphite (average particle size 3 μm) as a conductive additive, and CMC and SBR as binders were dispersed in water in a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain a negative electrode slurry (solid concentration 45 wt%). Next, using a die coater, the negative electrode slurry was coated with a coating weight of 10.0 mg / cm on one side. 2 The negative electrode slurry was applied to both sides of a 10 μm thick Cu foil so that the negative electrode slurry was oriented in a uniform manner. A magnetic field (magnetic flux density 1 tesla) was applied perpendicular to the Cu foil for 1 second, and then the foil was dried to obtain a negative electrode coating in which all graphite was uniformly oriented. The negative electrode coating was then compressed using a roll press to a porosity of 25% and cut to the desired shape to obtain a negative electrode plate.

[0098] Comparative Example 4 The negative electrode active material was artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were also used as binders, and the resulting mixture was dispersed in water in a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain a negative electrode slurry (solid concentration 45 wt%). The resulting mixture was then coated with a die coater to a surface area of ​​10.0 mg / cm2. 2 The negative electrode slurry was applied to both sides of a 10 μm thick Cu foil so that the negative electrode slurry was oriented in a uniform manner. A magnetic field (magnetic flux density 1 tesla) was applied perpendicular to the Cu foil for 1 second, and then the foil was dried to obtain a negative electrode coating in which all graphite was uniformly oriented. The negative electrode coating was then compressed using a roll press to a porosity of 25% and cut to the desired shape to obtain a negative electrode plate.

[0099] Example 1 The negative electrode active material was artificial graphite (first graphite) with an X-ray 002 / 110 peak ratio of 80 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were used as binders, and the resulting mixture was dispersed in water at a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain negative electrode slurry 1 (solid concentration 45 wt%). The negative electrode active material was artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were used as binders, and the resulting mixture was dispersed in water at a weight ratio of 96:1:3 (=1.5 + 1.5). This result also obtained negative electrode slurry 2 (solid concentration 45 wt%). Next, a die coater was used to coat the film so that the weight per side was 5.0 mg / cm 2 The negative electrode slurry 1 was applied to both sides of a 10 μm thick Cu foil so that the weight per side was 5.0 mg / cm on the surface of the coating film (undried). 2 Next, a magnetic field (magnetic flux density 1 tesla) was applied to the Cu foil in the perpendicular direction for 1 second, and then the foil was dried to form a negative electrode having a surface area of ​​10 mg / cm2 on one side, with different degrees of graphite orientation between the upper and lower layers. 2Thereafter, the negative electrode coating film was compressed using a roll press to a porosity of 25%, and then cut into a predetermined shape to obtain a negative electrode plate.

[0100] Example 2 The negative electrode active material was artificial graphite (first graphite) with an X-ray 002 / 110 peak ratio of 80 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were used as binders, and the resulting mixture was dispersed in water at a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain negative electrode slurry 1 (solid concentration 45 wt%). The negative electrode active material was artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were used as binders, and the resulting mixture was dispersed in water at a weight ratio of 96:1:3 (=1.5 + 1.5). This result also obtained negative electrode slurry 2 (solid concentration 45 wt%). Next, a die coater was used to coat the film so that the weight per side was 6.66 mg / cm 2 The negative electrode slurry 1 was applied to both sides of a 10 μm thick Cu foil so that the weight per side was 3.33 mg / cm on the surface of the coating film (undried). 2 Next, a magnetic field (magnetic flux density 1 tesla) was applied to the Cu foil in the perpendicular direction for 1 second, and then the foil was dried to obtain a negative electrode having a surface area of ​​10 mg / cm2 on one side, with the thickness and degree of orientation of the graphite in the upper and lower layers being different. 2 Thereafter, the negative electrode coating film was compressed using a roll press to a porosity of 25%, and then cut into a predetermined shape to obtain a negative electrode plate.

[0101] Example 3 The negative electrode active material was artificial graphite (first graphite) with an X-ray 002 / 110 peak ratio of 80 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were used as binders, and the resulting mixture was dispersed in water at a weight ratio of 96:1:3 (=1.5 + 1.5) to obtain negative electrode slurry 1 (solid concentration 45 wt%). The negative electrode active material was artificial graphite (second graphite) with an X-ray 002 / 110 peak ratio of 110 and an average particle size of approximately 10 μm. The conductive additive was flake graphite (average particle size 3 μm). CMC and SBR were used as binders, and the resulting mixture was dispersed in water at a weight ratio of 96:1:3 (=1.5 + 1.5). This result also obtained negative electrode slurry 2 (solid concentration 45 wt%). Next, a die coater was used to coat the film so that the weight per side was 3.33 mg / cm 2 The negative electrode slurry 1 was applied to both sides of a 10 μm thick Cu foil so that the weight per side was 6.66 mg / cm on the surface of the coating film (undried). 2 Next, a magnetic field (magnetic flux density 1 tesla) was applied to the Cu foil in the perpendicular direction for 1 second, and then the foil was dried to obtain a negative electrode having a surface area of ​​10 mg / cm2 on one side, with the thickness and degree of orientation of the graphite in the upper and lower layers being different. 2 Thereafter, the negative electrode coating film was compressed using a roll press to a porosity of 25%, and then cut into a predetermined shape to obtain a negative electrode plate.

[0102] Example 4 (Reference example) A negative electrode plate was obtained in the same manner as in Example 1, except that after applying the negative electrode slurry 1 and before applying the negative electrode slurry 2, a magnetic field (magnetic flux density 1 tesla) was applied for 1 second in the perpendicular direction to the Cu foil to dry it.

[0103] [Cell production] Positive and negative electrode plates were stacked alternately with separators between them, and the positive and negative electrodes were bundled and tab-welded. The resulting electrode assembly was placed in an aluminum laminate cup, and after pouring in electrolyte (1M LiPF6, EC:EMC = 25:75 vol), a temporary vacuum seal was performed and charging and discharging were carried out at 0.2 CA. After that, degassing and full vacuum sealing were performed to prepare various cells (capacity 2 Ah). After that, the cells were charged to 70% SOC and aged at 55°C for 24 hours, completing the various cells.

[0104] [Cell Evaluation] (rate characteristics) The completed cell was discharged at 2 CA at 25° C., and the capacity retention rate (0.2 CA discharge capacity ratio) was measured. ◎: 90% or more (best); ○; 88% or more but less than 90% (good); △: 78% or more but less than 88% (no practical problems); ×: Less than 78% (unacceptable) (problems in practical use).

[0105] (Cycle characteristics) The completed cells were subjected to 300 cycles of full charge and discharge (3.00 V to 4.35 V) at a current of 0.5 CA at 35° C., and then the capacity retention rate (ratio to initial discharge capacity) was measured. ◎: 89% or more (best); ○; 85% or more but less than 89% (good); △: 74% or more but less than 85% (no practical problems); ×: Less than 74% (unacceptable) (problems in practical use).

[0106] (Overall judgment) The lower evaluation result of the rate characteristics and cycle characteristics was used as the overall evaluation result.

[0107] (process cost) Using Reference Example 1 as a reference, examples in which the number of electrode manufacturing processes increases were judged as examples in which the process cost increases as follows. ○: The number of electrode manufacturing processes is the same as Reference Example 1 ×: The number of electrode manufacturing processes exceeds that of Reference Example 1

[0108] [Measurement method] (average orientation angle) Cross sections of the obtained electrodes were extracted by ion milling, and the cross sections were observed using an SEM to obtain images. In the obtained cross-sectional images, as shown in FIG. 1, the negative electrode layer 11 was divided into five equal parts in the thickness T direction, which were designated as first to fifth regions (E1 to E5) from the current collector side, and the average orientation angles θ1 to θ5 of the graphite in each region were determined. The average orientation angle was the average value of the orientation angles of 100 particles arbitrarily selected in each region. As shown in FIG. 2, the orientation angle is the angle θ of the longitudinal direction L of the graphite particles Gr with respect to the surface of the current collector 10. The average orientation angle θ1 of the first region E1 was defined as the average orientation angle θf of the graphite in the first negative electrode layer. The average orientation angle θ5 of the fifth region E5 was defined as the average orientation angle θs of the graphite in the second negative electrode layer.

[0109] (Orientation angle change rate) The rate of change in orientation angle is the average orientation angle θ in the lower region between two adjacent regions. L From the above, the average orientation angle θ H The rate of change of the orientation angle is specifically expressed as {(θ H -θ L ) / θ L It is expressed as an absolute value of}×100(%).

[0110] (Identifying the boundary between the first and second negative electrode layers) A cross section of each of the obtained negative electrodes was taken out by ion milling, and the cross section was observed with an SEM to visually check whether the boundary surface between the first negative electrode layer and the second negative electrode layer was distinguishable. In the negative electrodes in which the boundary surface was visually identifiable, at least one of the orientation angle change rates between adjacent regions in the first to fifth regions (E1 to E5) exceeded 25% among all the orientation angle change rates. In the negative electrodes in which the boundary surface was not visually identifiable, the orientation angle change rate between adjacent regions in the first to fifth regions (E1 to E5) was 25% or less (particularly 20% or less or 15% or less) for all of them.

[0111] (Thickness ratio of first negative electrode layer / second negative electrode layer) For negative electrodes that were "identifiable" in the evaluation of "first negative electrode layer / second negative electrode layer boundary identification," the thicknesses of the first negative electrode layer and the second negative electrode layer were measured based on the identified boundary, and their thickness ratio was calculated.

[0112] For negative electrodes that were "unidentifiable," the thickness ratio was determined by the following method. For a specific region among the second to fourth regions (E2 to E4), if the orientation angle change rate with respect to the regions on both sides is 5% or more (particularly 7% or more), it was assumed that a boundary exists at the center of the specific region in the thickness direction. Based on this assumed boundary, the thicknesses of the first negative electrode layer and the second negative electrode layer were measured, and their thickness ratio was calculated. The thickness was measured using the average value of 10 arbitrary points in the SEM image.

[0113] (002 / 110 peak ratio of graphite) First, a measurement sample was prepared by the following method: A glass sample plate 50 having a groove 51 on one side was used. (1) As shown in FIG. 3A, a glass sample plate 50 was placed on a medicine wrapping paper or the like so that the surface having the grooves 51 faced upward, and graphite Gr was placed in the grooves 51. (2) Since the graphite was raised in the grooves 51, the surface of the graphite Gr was flattened using the back surface of another glass sample plate 55, as shown in FIGS. 3B and 3C. (3) As shown in FIG. 3D, the above step (2) was repeated until the surface of the graphite Gr became flat and was flush with the surface of the glass sample plate 50 (particularly the surface of the non-grooved portion). (4) Each part of the glass sample plate 50 was wiped with alcohol or the like to complete the measurement sample. Next, the measurement sample was subjected to an XRD device (X-ray diffraction device: manufactured by Rigaku Corporation) to measure the 002 / 110 peak ratio, which is the ratio of the 002 plane peak intensity to the 110 plane peak intensity.

[0114] (Electrode after pressing: 002 / 110 peak ratio Re) The negative electrode was directly subjected to an XRD (X-ray diffractometer) to measure the 002 / 110 peak ratio.

[0115] [Table 1]

[0116] [Table 2]

[0117] Comparative Example 1 The need to form an undercoat layer on the current collecting foil increases the process cost. Furthermore, although the formation of the undercoat layer improved the foil interface strength, and thus the capacity retention rate after cycling was maintained at the same level as Reference Example 1, the 2C capacity retention rate was low considering the magnetic field orientation due to the influence of binder diffusion in the undercoat layer. Therefore, the overall rating was ×.

[0118] Comparative Example 2 The need for two coating and drying processes increases the process cost. Furthermore, the magnetic field alignment effect is only achieved in the upper layer, resulting in relatively poor rate characteristics. Furthermore, because the upper and lower layers are formed separately by two coatings, the boundary between the non-aligned layer (first anode layer) and the aligned layer (second anode layer) is clearly defined, and interfacial peeling occurs due to expansion and contraction during cycling, resulting in a decline in cycle characteristics. Therefore, the overall rating is "Fail."

[0119] Regarding Comparative Example 3 The two types of slurries can be applied wet on wet and dried simultaneously, which does not significantly increase process costs. Furthermore, because graphite, which is difficult to orient, is used, the deterioration of cycle characteristics due to foil interface peeling caused by expansion and contraction during cycling is suppressed, but the degree of orientation is low, so the effect of improving rate characteristics is relatively small. Therefore, the overall rating is ×.

[0120] Regarding Comparative Example 4 The two types of slurries can be applied wet on wet and dried simultaneously, so there is no significant increase in process costs. Furthermore, the use of graphite, which is easily oriented, improves rate characteristics, but the foil interface peeling caused by expansion and contraction during cycling significantly reduces cycle characteristics. Therefore, the overall rating is ×.

[0121] Regarding Example 1 The two types of slurries can be applied wet on wet and dried simultaneously, eliminating any significant increase in process costs. Furthermore, by using graphite that is more likely to orient in the upper layer and graphite that is less likely to orient in the lower layer, the rate characteristics are significantly improved, and the deterioration of cycle characteristics due to foil interface peeling caused by expansion and contraction during cycling is also suppressed. Therefore, the overall rating is good.

[0122] Regarding Example 2 The two types of slurries can be applied wet on wet and dried simultaneously, so there is no significant increase in process costs. Furthermore, by increasing the thickness ratio of the graphite in the lower layer, which is difficult to orient, the deterioration of cycle characteristics is suppressed, but the improvement in rate characteristics is reduced within a range that does not pose a problem in practical use. Therefore, the overall rating is fair.

[0123] Regarding Example 3 The two types of slurries can be applied wet on wet and dried simultaneously, which does not significantly increase process costs. Furthermore, by reducing the thickness ratio of the graphite in the lower layer, which is difficult to orient, a decrease in cycle performance is suppressed while achieving higher rate performance. Therefore, the overall rating is excellent.

[0124] Regarding Example 4 The upper layer uses graphite that is easy to orient, while the lower layer uses graphite that is difficult to orient. However, because the upper and lower layers are formed separately by applying two coats, the boundary between the non-oriented layer (first anode layer) and the oriented layer (second anode layer) is clearly defined. As a result, the improvement in rate characteristics and cycle characteristics is reduced within a range that is not problematic for practical use. Therefore, the overall rating is △. Furthermore, the process costs increase because two coating and drying steps are required. [Explanation of symbols]

[0125] 1 negative electrode 10 Current collector 11 negative electrode layer 111 First negative electrode layer 112 second negative electrode layer 50 Glass sample plate 51 Groove 55 Another glass sample plate Gr Graphite (or graphite grains)

Claims

1. a negative electrode current collector; a negative electrode layer disposed on the surface of the negative electrode current collector, the negative electrode layer includes a first negative electrode layer disposed on a surface of the negative electrode current collector and a second negative electrode layer disposed on a surface of the first negative electrode layer, the first negative electrode layer includes a first graphite; the second negative electrode layer includes second graphite that is more easily oriented by a magnetic field than the first graphite; the first graphite is graphite having an X-ray 002 / 110 peak ratio Rs of 90 or less; the second graphite is graphite having an X-ray 002 / 110 peak ratio Rf of 100 or more; an average orientation angle θs of the second graphite particle in the longitudinal direction with respect to the surface of the negative electrode current collector is larger than an average orientation angle θf of the first graphite particle in the longitudinal direction with respect to the surface of the negative electrode current collector, an X-ray 002 / 110 peak ratio Re of a negative electrode having the negative electrode current collector and the negative electrode layer is 320 or less; a negative electrode for a secondary battery, wherein when an average orientation angle of each region and an orientation angle change rate between two adjacent regions are calculated for first to fifth regions obtained by dividing the negative electrode layer into five equal regions in a thickness direction, all of the orientation angle change rates are 25% or less.

2. 2. The negative electrode for a secondary battery according to claim 1, wherein an average orientation angle θs of the second graphite and an average orientation angle θf of the first graphite satisfy the following relationship: 3≦θs−θf

3. the first graphite has an average orientation angle θf of 10° or more and 60° or less; 3. The negative electrode for a secondary battery according to claim 2, wherein the average orientation angle θs of the second graphite is 35° or more and 70° or less.

4. the peak ratio Rs of the first graphite is 50 or more and 90 or less, 4. The negative electrode for a secondary battery according to claim 1, wherein the peak ratio Rf of the second graphite is 100 or more and 150 or less.

5. 5. The negative electrode for a secondary battery according to claim 1, wherein the peak ratio Re of the negative electrode is 140 or more and 300 or less.

6. 6. The negative electrode for a secondary battery according to claim 1, wherein a ratio (Tf / Ts) of a thickness Tf of the first negative electrode layer to a thickness Ts of the second negative electrode layer is 2.2 or less.

7. 7. The negative electrode for a secondary battery according to claim 1, wherein a ratio (Tf / Ts) of a thickness Tf of the first negative electrode layer to a thickness Ts of the second negative electrode layer is 0.2 or more and 1.5 or less.

8. The negative electrode for a secondary battery according to any one of claims 1 to 7, wherein a ratio (Tf / Ts) of a thickness Tf of the first negative electrode layer to a thickness Ts of the second negative electrode layer is 0.3 or more and 0.8 or less.

9. 9. The negative electrode for a secondary battery according to claim 1, wherein the average orientation angle θs of the second graphite and the average orientation angle θf of the first graphite satisfy the following relationship: 5≦θs−θf≦10

10. the first negative electrode layer includes the first graphite and a first binder; 10. The negative electrode for a secondary battery according to claim 1, wherein the second negative electrode layer comprises the second graphite and a second binder.

11. In the first negative electrode layer, a content of the first graphite is 80% by weight or more and 99% by weight or less with respect to a total amount of the first negative electrode layer, 11. The negative electrode for a secondary battery according to claim 10, wherein a content of the second graphite in the second negative electrode layer is 80% by weight or more and 99% by weight or less with respect to a total amount of the second negative electrode layer.

12. the first negative electrode layer further includes a first conductive additive; 12. The negative electrode for a secondary battery according to claim 1, wherein the second negative electrode layer further contains a second conductive additive.

13. In the first negative electrode layer, the content of the first conductive additive is 0.1 wt % or more and 10 wt % or less with respect to the total amount of the first negative electrode layer, 13. The negative electrode for a secondary battery according to claim 12, wherein the content of the second conductive additive in the second negative electrode layer is 0.1 wt % or more and 10 wt % or less with respect to the total amount of the second negative electrode layer.

14. 14. The negative electrode for a secondary battery according to claim 1, wherein the negative electrode is an electrode capable of absorbing and releasing lithium ions.

15. A secondary battery comprising the negative electrode for secondary batteries according to any one of claims 1 to 14.

16. The following steps: (i) a preparation step of preparing a negative electrode current collector; (ii) a slurry preparation step of preparing a first negative electrode layer slurry containing a first graphite and a second negative electrode layer slurry containing a second graphite that is more easily oriented in a magnetic field than the first graphite; (iii) applying the first negative electrode layer slurry to the surface of the negative electrode current collector, and then, without drying, applying the second negative electrode layer slurry to the surface of the first negative electrode layer slurry coating, applying a magnetic field, and drying the resulting coating to form a negative electrode precursor; and (iv) pressing the negative electrode precursor Including, the first graphite is graphite having an X-ray 002 / 110 peak ratio Rs of 90 or less as measured by compressing graphite powder, the second graphite is graphite having an X-ray 002 / 110 peak ratio Rf of 100 or more.

17. The negative electrode for the secondary battery is a negative electrode current collector; a negative electrode layer disposed on the surface of the negative electrode current collector, the negative electrode layer includes a first negative electrode layer disposed on a surface of the negative electrode current collector and a second negative electrode layer disposed on a surface of the first negative electrode layer, the first negative electrode layer includes a first graphite; the second negative electrode layer includes second graphite that is more easily oriented by a magnetic field than the first graphite; the first graphite is graphite having an X-ray 002 / 110 peak ratio Rs of 90 or less; the second graphite is graphite having an X-ray 002 / 110 peak ratio Rf of 100 or more; an average orientation angle θs of the second graphite particle in the longitudinal direction with respect to the surface of the negative electrode current collector is larger than an average orientation angle θf of the first graphite particle in the longitudinal direction with respect to the surface of the negative electrode current collector, 17. The method for producing a negative electrode for a secondary battery according to claim 16, wherein an X-ray 002 / 110 peak ratio Re of a negative electrode having the negative electrode current collector and the negative electrode layer is 320 or less.

18. A method for manufacturing a negative electrode for a secondary battery described in claim 16 or 17, wherein the average orientation angle θs of the second graphite and the average orientation angle θf of the first graphite satisfy the following relationship: 3≦θs−θf

19. The first graphite has an average orientation angle θf of 10° or more and 60° or less, 19. The method for producing a negative electrode for a secondary battery according to claim 16, wherein the average orientation angle θs of the second graphite is 35° or more and 70° or less.

20. The peak ratio Rs of the first graphite is 50 or more and 90 or less, 20. The method for producing a negative electrode for a secondary battery according to claim 16, wherein the peak ratio Rf of the second graphite is 100 or more and 150 or less.

21. A method for manufacturing a negative electrode for a secondary battery according to claim 16, wherein the peak ratio Re of the negative electrode is 140 or more and 300 or less.

22. A method for manufacturing a negative electrode for a secondary battery described in any of claims 16 to 21, wherein the ratio (Tf / Ts) of the thickness Tf of the first negative electrode layer to the thickness Ts of the second negative electrode layer is 2.2 or less.

23. A method for manufacturing a negative electrode for a secondary battery described in any of claims 16 to 22, wherein the ratio (Tf / Ts) of the thickness Tf of the first negative electrode layer to the thickness Ts of the second negative electrode layer is 0.2 or more and 1.5 or less.

24. A method for manufacturing a negative electrode for a secondary battery described in any of claims 16 to 23, wherein the ratio (Tf / Ts) of the thickness Tf of the first negative electrode layer to the thickness Ts of the second negative electrode layer is 0.3 or more and 0.8 or less.

25. A method for manufacturing a negative electrode for a secondary battery described in any of claims 16 to 24, wherein when the average orientation angle of each region and the orientation angle change rate between two adjacent regions are calculated for the first to fifth regions obtained by dividing the negative electrode layer into five equal parts in the thickness direction, all orientation angle change rates are 25% or less.

26. A method for manufacturing a negative electrode for a secondary battery described in any of claims 16 to 25, wherein the average orientation angle θs of the second graphite and the average orientation angle θf of the first graphite satisfy the following relationship. 5≦θs−θf≦10 27. The first negative electrode layer comprising the first graphite and a first binder; 27. The method for producing a negative electrode for a secondary battery according to claim 16, wherein the second negative electrode layer comprises the second graphite and a second binder.

28. In the first negative electrode layer, the content of the first graphite is 80% by weight or more and 99% by weight or less with respect to the total amount of the first negative electrode layer, 28. The method for manufacturing a negative electrode for a secondary battery according to claim 27, wherein the content of the second graphite in the second negative electrode layer is 80% by weight or more and 99% by weight or less with respect to the total amount of the second negative electrode layer.

29. The first negative electrode layer further comprises a first conductive additive; The method for manufacturing a negative electrode for a secondary battery according to any one of claims 16 to 28, wherein the second negative electrode layer further contains a second conductive additive.

30. In the first negative electrode layer, the content of the first conductive additive is 0.1 wt% or more and 10 wt% or less with respect to the total amount of the first negative electrode layer, 30. The method for manufacturing a negative electrode for a secondary battery according to claim 29, wherein the content of the second conductive additive in the second negative electrode layer is 0.1 wt % or more and 10 wt % or less with respect to the total amount of the second negative electrode layer.

31. A method for manufacturing a negative electrode for a secondary battery according to any one of claims 16 to 30, wherein the negative electrode is an electrode capable of absorbing and releasing lithium ions.

32. The method for producing the negative electrode for a secondary battery according to claim 16, which comprises producing the negative electrode for a secondary battery according to any one of claims 1 to 14.

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