Negative electrode and non-aqueous electrolyte secondary battery

Abstract

A negative electrode 6 according to the present disclosure comprises a long negative electrode mixture layer 6b. The negative electrode mixture layer 6b contains graphite as a negative electrode active material. The negative electrode mixture layer 6b includes a first end region 61 including a first end 64a in the width direction, a second end region 62 including a second end 64b in the width direction, and a central region 63 including a center 64c in the width direction. The Raman spectrum ID / IG ratio of the first end region 61 is greater than the Raman spectrum ID / IG ratio of the central region 63. The "Raman spectrum ID / IG ratio" as used herein is the ratio of a peak intensity ID of a D band appearing in the vicinity of Raman shift 1348 cm-1 to a peak intensity IG of a G band appearing in the vicinity of Raman shift 1575 cm-1 in a Raman spectrum that is obtained by analyzing the surface of the negative electrode mixture layer by Raman spectroscopy.

Description

Negative electrode and non-aqueous electrolyte secondary battery

[0001] This disclosure relates to a negative electrode and a non-aqueous electrolyte secondary battery.

[0002] In non-aqueous electrolyte secondary batteries such as lithium-ion secondary batteries, for example, an electrode group having a wound structure is used in which a positive electrode and a negative electrode are stacked with a separator made of a resin microporous membrane or the like placed between the positive and negative electrodes, and then wound in a spiral shape.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery using an electrode group having a wound structure. The negative electrode disclosed in Patent Document 1 has a configuration in which the degree of graphitization of graphite particles distributed on the surface side of the negative electrode active material layer is lower than the degree of graphitization of graphite particles distributed on the negative electrode current collector side, in order to suppress lithium deposition on the negative electrode surface and improve cycle characteristics.

[0004] Japanese Patent Publication No. 2010-267540

[0005] This disclosure provides a technology that can improve the cycle characteristics of a battery, for example, a negative electrode used in an electrode group having a wound structure, which is used in a non-aqueous electrolyte secondary battery.

[0006] This disclosure provides a negative electrode for use in an electrode group having a wound structure, wherein the negative electrode comprises a long negative electrode mixture layer, the negative electrode mixture layer contains graphite as a negative electrode active material, the negative electrode mixture layer includes a first end region including a first end in the width direction of the negative electrode mixture layer, a second end region including a second end in the width direction, and a central region including the center in the width direction of the negative electrode mixture layer, the Raman spectral ID / IG ratio of the first end region is greater than the Raman spectral ID / IG ratio of the central region. Here, the Raman spectral ID / IG ratio is defined as a Raman spectrum obtained by analysis of the surface of the negative electrode mixture layer by Raman method, with a Raman shift of 1575 cm⁻¹. -1 The Raman shift of 1348 cm is relative to the peak intensity IG of the G band appearing in the vicinity. -1 This is the ratio of the peak intensity IDs of the D-band that appear in the vicinity.

[0007] The technology described herein can improve the cycle characteristics of non-aqueous electrolyte secondary batteries.

[0008] Figure 1 is a schematic cross-sectional view showing the ends of the electrode group in the width direction to illustrate the mechanism of metallic lithium deposition. Figure 2 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the present disclosure. Figure 3A is a partial plan view of a long negative electrode. Figure 3B is a cross-sectional view of the negative electrode along the line III-III shown in Figure 3A.

[0009] (Knowledge forming the basis of this disclosure) In lithium-ion secondary batteries, which are an example of non-aqueous electrolyte secondary batteries, it is known that repeated charging and discharging causes lithium ions to deposit as metallic lithium on the surface of the negative electrode, reducing the battery capacity. Conventionally, technologies have been proposed to solve this metallic lithium problem and improve the cycle characteristics of batteries. For example, the negative electrode disclosed in Patent Document 1 has a configuration in which the degree of graphitization of graphite particles distributed on the surface side of the negative electrode active material layer is lower than the degree of graphitization of graphite particles distributed on the negative electrode current collector side, in order to suppress the deposition of lithium on the negative electrode surface and improve cycle characteristics.

[0010] However, in recent years, there has been a demand for further improvement in the cycle characteristics of batteries. Therefore, the inventors of this invention have diligently researched the mechanism of deposition of metallic lithium on the surface of the negative electrode in order to further improve the cycle characteristics of batteries.

[0011] The inventors of the present invention studied the structure of an electrode group having a wound structure, including a positive electrode, a negative electrode, and a separator placed between the positive and negative electrodes, when it is incorporated into a battery together with the electrolyte. As a result, the inventors found that the electrode group has a structural characteristic in which the distance between the positive and negative electrodes is greater at the ends in the width direction than at the center in the width direction, and that this structural characteristic is related to the deposition of metallic lithium. The details are as follows.

[0012] Figure 1 is a schematic cross-sectional view showing the ends of an electrode group in the width direction to explain the mechanism of metallic lithium deposition. As shown in Figure 1, in an electrode group 1000 in which a positive electrode 500 and a negative electrode 600 are superimposed with a separator 700 in between, the distance d between the positive electrode 500 and the negative electrode 600 at the ends in the width direction is greater than the distance between the positive electrode 500 and the negative electrode 600 at the center in the width direction. Because the distance d between the positive electrode 500 and the negative electrode 600 is large at the ends in the width direction of the electrode group 1000, and because the electrolyte between the positive electrode 500 and the negative electrode 600 is insufficient as a result, the resistance between the positive electrode 500 and the negative electrode 600 is locally high in the electrode group 1000. When the resistance between the positive electrode 500 and the negative electrode 600 is locally high in this way, the negative electrode potential on the surface of the negative electrode 600 decreases, creating conditions that make it easier for lithium to deposit. In fact, when the inventors removed the electrode group from a battery that had undergone repeated charging and discharging and examined the surface of the negative electrode, they found that a greater amount of metallic lithium had been deposited on the surface of the negative electrode, specifically in the portion corresponding to the end of the electrode group in the width direction. In Figure 1, reference numeral 500a denotes the positive electrode current collector, 500b denotes the positive electrode mixture layer, 600a denotes the negative electrode current collector, and 600b denotes the negative electrode mixture layer.

[0013] Based on the finding that a negative electrode capable of suppressing the deposition of metallic lithium at the edges in the width direction of the electrode group can effectively improve the cycle characteristics of a battery, the present inventors have come up with the non-aqueous electrolyte secondary battery of this disclosure.

[0014] The embodiments of this disclosure will be described in detail below with reference to the drawings. This disclosure is not limited to the embodiments described below.

[0015] (Embodiments of the Disclosure) Figure 2 is a cross-sectional view of a non-aqueous electrolyte secondary battery according to an embodiment of the Disclosure. Here, a lithium-ion secondary battery will be used as an example to describe the non-aqueous electrolyte secondary battery of the Disclosure.

[0016] The non-aqueous electrolyte secondary battery 100 comprises a container 1 and an electrode group 4. The electrode group 4 is housed in the container 1. The electrode group 4 has a wound structure. The electrode group 4 has a positive electrode 5, a negative electrode 6, and a pair of separators 7. That is, the electrode group 4 is formed by overlapping the positive electrode 5 and the negative electrode 6 with a separator 7 placed between them, and then winding them in a spiral shape. The electrode group 4 is impregnated with an electrolyte solution, which is a non-aqueous electrolyte. The opening of the container 1 is sealed with a sealing plate 2. The positive electrode 5 has a positive electrode current collector 5a and a positive electrode mixture layer 5b. One end of a positive electrode lead 5c is connected to the positive electrode 5. The other end of the positive electrode lead 5c is connected to the back surface of the sealing plate 2. An insulating packing 3 is arranged around the sealing plate 2. The negative electrode 6 has a negative electrode current collector 6a and a negative electrode mixture layer 6b. One end of the negative electrode lead 6c is connected to the negative electrode 6. The other end of the negative electrode lead 6c is connected to the bottom surface of the container 1. Insulating rings 8 are placed on the upper and lower surfaces of the electrode group 4, respectively.

[0017] In this embodiment, the container 1 has negative polarity and the sealing plate 2 has positive polarity. However, the container 1 may have positive polarity and the sealing plate 2 may have negative polarity.

[0018] When the electrode group 4 is unwound and viewed from above, the positive electrode 5 and the negative electrode 6 have an elongated (e.g., strip-shaped) form. The length of the elongated negative electrode 6 in the width direction is greater than the length of the elongated positive electrode 5 in the width direction. That is, the width of the negative electrode 6 is wider than the width of the positive electrode 5. The outer edge of the positive electrode 5 in the width direction overlaps with the negative electrode 6. In the width direction, the positive electrode 5 is contained inside the negative electrode 6. The width of the separator 7 is greater than the width of the positive electrode 5 and the width of the negative electrode 6. With this configuration, the safety of the battery 100 is improved.

[0019] When the winding of the electrode group 4 is unwound and viewed in plan view, as described above, the negative electrode 6 is in a long shape and includes a long negative electrode mixture layer 6b. FIG. 3A is a partial plan view of the long negative electrode 6. FIG. 3B is a cross-sectional view of the negative electrode 6 taken along line III-III shown in FIG. 3A. The negative electrode mixture layer 6b includes a first end region 61 including a first end 64a in the width direction of the negative electrode mixture layer 6b, a second end region 62 including a second end 64b in the width direction of the negative electrode mixture layer 6b, and a central region 63 including a center 64c in the width direction of the negative electrode mixture layer 6b. As shown in FIGS. 3A and 3B, the negative electrode mixture layer 6b may be composed of a first end region 61, a second end region 62, and a central region 63. That is, in the negative electrode mixture layer 6b, the first end region 61 and the second end region 62 may be regions provided in contact with the central region 63, respectively. Note that the first end region 61 in the width direction of the negative electrode mixture layer 6b corresponds to the region indicated by reference numeral 100a or 100b in FIG. 2. The first end region 61 may be either the end region 100a or the end region 100b shown in FIG. 2. The second end region 62 corresponds to the region different from the end portion corresponding to the first end region 61 among the end regions 100a and 100b shown in FIG. 2.

[0020] In the present embodiment, the negative electrode mixture layer 6b contains graphite as a negative electrode active material. The Raman spectrum ID / IG ratio of the first end region 61 is larger than the Raman spectrum ID / IG ratio of the central region 63. Here, the Raman spectrum ID / IG ratio is the ratio of the peak intensity ID of the D band appearing near a Raman shift of 1348 cm -1 to the peak intensity IG of the G band appearing near a Raman shift of 1575 cm -1 for the Raman spectrum obtained by analyzing the surface of the negative electrode mixture layer 6b by the Raman method. Note that the vicinity of 1575 cm -1 corresponds to a range of, for example, 1575 cm -1 ±50 cm -1 , and the vicinity of 1348 cm -1 corresponds to a range of, for example, 1348 cm[[ID=​​​​​The Raman spectrum ID / IG ratio is an indicator for evaluating the crystallinity of graphite. The G band originates from the crystal structure of the graphite, and the D band originates from defects in the crystal structure of the graphite (i.e., amorphousness). Therefore, a larger Raman spectrum ID / IG ratio indicates lower crystallinity and amorphousness. As described above, in this embodiment, the Raman spectrum ID / IG ratio of the first end region 61 is larger than that of the central region 63, so the first end region 61 contains more amorphous graphite than the central region 63. Amorphous graphite has better lithium ion acceptance than crystalline graphite. In the negative electrode 6 of this embodiment, the negative electrode mixture layer 6b contains more amorphous graphite with excellent lithium ion acceptance in the first end region 61 than in the central region 63, among the end regions where the resistance is high and the surface potential is low. With this configuration, in the negative electrode 6 in contact with the electrolyte, the resistance between it and the positive electrode 5 decreases in the first end region 61. As a result, the negative electrode potential increases on the surface of the negative electrode mixture layer 6b in the first end region 61, suppressing lithium deposition. Consequently, the deposition of metallic lithium on the surface of the negative electrode mixture layer 6b due to repeated charging and discharging is suppressed, preventing a decrease in capacity and thus improving the cycle characteristics of the battery 100.

[0022] The first end region 61 having a Raman spectrum ID / IG larger than that of the central region 63 can be formed, for example, by including amorphous carbon-coated graphite in the graphite contained in the first end region 61 as the negative electrode active material. This makes it easy to realize the first end region 61 having a desired Raman spectrum ID / IG by adjusting various factors such as the content ratio of amorphous carbon-coated graphite to the negative electrode active material and the coating ratio of amorphous carbon to the amorphous carbon-coated graphite. Therefore, the deposition of metallic lithium can be effectively suppressed and the cycle characteristics of the battery 100 can be effectively improved. Of the graphite contained in the first end region 61 as the negative electrode active material, for example, 40% by mass or more may be amorphous carbon-coated graphite, 60% by mass or more may be amorphous carbon-coated graphite, 80% by mass or more may be amorphous carbon-coated graphite, or all (i.e., 100% by mass) may be amorphous carbon-coated graphite.

[0023] In the negative electrode mixture layer 6b, in the region 65 from the center 64c to the first end 64a, the ratio B (W1:W2a) of the length W1 of the first end region 61 in the width direction to the length W2a of the central region 63 in the width direction may be, for example, in the range of 5:95 to 60:40, or in the range of 10:90 to 50:50. By setting the ratio B, in other words, the ratio of the width of the first end region 61 to the central region 63 in the half of the region 65 on the first end region 61 side in the width direction of the negative electrode 6, within the above range, the deposition of metallic lithium can be effectively suppressed, and the cycle characteristics of the battery 100 can be effectively improved.

[0024] The ratio of the Raman spectral ID / IG ratio of the first end region 61 to the Raman spectral ID / IG ratio of the central region 63 ((Raman spectral ID / IG ratio of the first end region 61) / (Raman spectral ID / IG ratio of the central region 63)) may be, for example, 2 or more, or 3 or more and 20 or less. By adjusting the amorphous nature of the graphite contained in the first end region 61 so that such a Raman spectral ID / IG ratio is obtained, the deposition of metallic lithium can be effectively suppressed and the cycle characteristics of the battery 100 can be effectively improved.

[0025] The Raman spectral ID / IG ratio of the first end region 61 may be, for example, 0.8 or more, or 0.8 or more and 3 or less. By adjusting the amorphous nature of the graphite contained in the first end region 61 so that such a Raman spectral ID / IG ratio is achieved, the deposition of metallic lithium can be effectively suppressed, and the cycle characteristics of the battery 100 can be effectively improved.

[0026] In the negative electrode 6 of this embodiment, it is desirable that the Raman spectral ID / IG ratio of the second end region 62 is greater than that of the central region 63, similar to the first end region 61. As a result, the negative electrode 6 of this embodiment can suppress the deposition of metallic lithium on the surface of the negative electrode mixture layer 6b due to repeated charge and discharge in the second end region 62, similar to the first end region 61, thereby further suppressing the decrease in capacity due to repeated charge and discharge. Therefore, the cycle characteristics of the battery 100 can be further improved.

[0027] The second end region 62, which has a Raman spectrum ID / IG larger than that of the central region 63, can be realized in the same manner as the first end region 61. That is, for example, the graphite included in the second end region 62 as the negative electrode active material may include amorphous carbon coated graphite. Of the graphite included in the second end region 62 as the negative electrode active material, 40% by mass or more may be amorphous carbon coated graphite, 60% by mass or more may be amorphous carbon coated graphite, 80% by mass or more may be amorphous carbon coated graphite, or all (i.e., 100% by mass) may be amorphous carbon coated graphite.

[0028] When the Raman spectral ID / IG ratio of the second end region 62 is greater than the Raman spectral ID / IG ratio of the central region 63, that is, when the Raman spectral ID / IG ratio of both end regions is greater than the Raman spectral ID / IG ratio of the central region 63, the ratio A ((W1+W3):W2) of the length of the end region (W1+W3), which is the sum of the length W1 of the first end region 61 and the length W3 of the second end region in the width direction, and the length W2 of the central region 63 in the width direction, may be, for example, in the range of 5:95 to 60:40, or in the range of 10:90 to 50:50. In this way, when the Raman spectral ID / IG ratio of both end regions is greater than the Raman spectral ID / IG ratio of the central region 63, by setting the ratio A within the above range, the deposition of metallic lithium can be effectively suppressed, and the cycle characteristics of the battery 100 can be effectively improved.

[0029] If the Raman spectral ID / IG ratio of the second end region 62 is greater than the Raman spectral ID / IG ratio of the central region 63, the ratio of the Raman spectral ID / IG ratio of the second end region 62 to the Raman spectral ID / IG ratio of the central region 63 ((Raman spectral ID / IG ratio of the second end region 62) / (Raman spectral ID / IG ratio of the central region 63)) may be, for example, 2 or more, or 3 or more and 20 or less. By adjusting the amorphous nature of the graphite contained in the second end region 62 so that such a Raman spectral ID / IG ratio is achieved, the deposition of metallic lithium can be effectively suppressed, and the cycle characteristics of the battery 100 can be effectively improved.

[0030] The Raman spectral ID / IG ratio of the second end region 62 may be, for example, 0.8 or more, or 0.8 or more and 3 or less. By adjusting the amorphous nature of the graphite contained in the second end region 62 so that such a Raman spectral ID / IG ratio is achieved, the deposition of metallic lithium can be effectively suppressed, and the cycle characteristics of the battery 100 can be effectively improved.

[0031] The negative electrode active material contained in the negative electrode mixture layer 6b includes graphite, as described above. Typically, a carbon material containing graphite having a graphite-type crystalline structure can be used as the negative electrode active material. Examples of such graphite carbon materials include natural graphite, spherical or fibrous artificial graphite, hard carbon (difficult to graphitize), and soft carbon (easily graphitizable). As described above, graphite coated with amorphous carbon may be used as the negative electrode active material in the first end region 61 and the second end region 62.

[0032] Amorphous carbon-coated graphite is, for example, a core-shell particle having graphite and an amorphous carbon coating formed on the surface of the graphite. The amorphous carbon coating is, for example, a carbon coating in an amorphous or microcrystalline, randomly layered state in which the graphite crystal structure is not well developed, and is composed of carbon with a d(002) interplanar spacing greater than 0.340 nm as determined by X-ray diffraction. It is preferable that the amorphous carbon coating is formed over the entire surface of the graphite particles. The amorphous carbon coating has functions such as reducing the decomposition of electrolytes and improving the hardness of amorphous carbon-coated graphite. Amorphous carbon-coated graphite is harder and less prone to crushing during the rolling process than graphite that is not amorphous carbon-coated.

[0033] Specific examples of amorphous carbon coatings include hard carbon, soft carbon, carbon black such as acetylene black, Ketjen black, thermal black, and furnace black, as well as carbon fibers and activated carbon. A suitable range for the thickness of an amorphous carbon coating is 10 nm or more and 200 nm or less. The thickness of an amorphous carbon coating can be measured by observing a cross-section of graphite particles coated with amorphous carbon using a scanning electron microscope (SEM).

[0034] Amorphous carbon coatings can be formed by mixing coal tar, tar pitch, naphthalene, anthracene, phenanthrone, etc., with graphite and heat-treating it at a temperature of 800°C or higher and 1200°C or lower, or by chemical vapor deposition (CVD) using hydrocarbon gas, etc. In graphite coated with amorphous carbon, the proportion of the amorphous carbon coating may be in the range of, for example, 0.5% by mass or more and 15% by mass or less.

[0035] The negative electrode binder layer 6b may contain, as a negative electrode active material, other materials than graphite coated with amorphous carbon. It is desirable that the other materials be, for example, 20% by mass or less based on the total negative electrode active material. Examples of other materials than graphite that can be included in the negative electrode binder layer 6b as a negative electrode active material include Si-based materials. Here, the Si-based material means a material containing Si. Examples of the Si-based material include Si, Si alloys, Si compounds, etc. Further, the Si-based material may be, for example, composite particles including an ion conductive phase and a silicon phase (silicon particles from one viewpoint) dispersed in the ion conductive phase. The ion conductive phase is a phase that conducts ions and includes, for example, at least any one selected from the group consisting of a silicate phase, an aluminate phase, a carbon phase, and a silicon oxide phase. One kind selected from these negative electrode active materials may be used, or two or more kinds may be used in combination.

[0036] In addition to the negative electrode active material, the negative electrode binder layer 6b may further contain a conductive assistant, an ion conductor, a binder, etc.

[0037] The conductive assistant and the ion conductor are used to reduce the resistance of the negative electrode 6. Examples of the conductive assistant include carbon materials, conductive polymer compounds, etc. Examples of the carbon material include carbon black, graphite, acetylene black, carbon nanotubes, carbon nanofibers, graphene, fullerenes, oxidized graphite, etc. Examples of the conductive polymer compound include polyaniline, polypyrrole, polythiophene, etc. Examples of the ion conductor include gel electrolytes, organic solid electrolytes, inorganic solid electrolytes, etc. Examples of the gel electrolyte include polymethyl methacrylate, methyl polymethacrylate, etc. Examples of the organic solid electrolyte include polyethylene oxide, etc. Examples of the inorganic solid electrolyte include Li7La3Zr2O 12 and the like.

[0038] The binder is used to improve the binding property of the materials constituting the negative electrode 6. As the binder, polymer materials such as polyvinylidene fluoride, vinylidene fluoride - hexafluoropropylene copolymer, vinylidene fluoride - tetrafluoroethylene copolymer, polytetrafluoroethylene, carboxymethyl cellulose, polyacrylic acid, styrene - butadiene copolymer rubber, polypropylene, polyethylene, and polyimide can be used.

[0039] The negative electrode binder layer 6b is supported on the negative electrode current collector 6a. As the negative electrode current collector 6a, a sheet or film made of a metal material such as stainless steel, nickel, copper, or their alloys can be used. The sheet or film may be porous or non - porous. As the sheet or film, a metal foil, a metal mesh, etc. are used. A carbon material such as carbon may be coated as a conductive auxiliary material on the surface of the negative electrode current collector 6a.

[0040] As the positive electrode current collector 5a, a sheet or film made of a metal material such as aluminum, stainless steel, titanium, or their alloys can be used. Aluminum and its alloys are suitable as the material for the positive electrode current collector 5a because they are inexpensive and easy to form into thin films. The sheet or film may be porous or non - porous. As the sheet or film, a metal foil, a metal mesh, etc. are used. A carbon material such as carbon may be coated as a conductive auxiliary material on the surface of the positive electrode current collector 5a.

[0041] The positive electrode mixture layer 5b is supported on the positive electrode current collector 5a. The positive electrode mixture layer 5b contains a positive electrode active material. Possible positive electrode active materials include lithium-containing transition metal oxides, lithium-containing transition metal phosphates, transition metal fluorides, polyanionic materials, fluorinated polyanionic materials, transition metal sulfides, transition metal oxysulfides, and transition metal oxynitrides. In particular, when lithium-containing transition metal oxides or lithium-containing transition metal phosphates are used as the positive electrode active material, the manufacturing cost of the battery can be reduced and the average discharge voltage can be increased. Examples of lithium-containing transition metal oxides include lithium cobalt oxide, lithium nickel cobalt aluminate, lithium nickel cobalt manganese oxide, and lithium nickel manganese oxide. Examples of lithium-containing transition metal phosphates include lithium iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

[0042] The positive electrode mixture layer 5b may further contain other materials in addition to the positive electrode active material, such as conductive additives, ion conductors, and binders. The same materials that can be used in the negative electrode mixture layer 6b can be used in the positive electrode mixture layer 5b as conductive additives, ion conductors, and binders.

[0043] The separator 7 is permeable to lithium ions. The material of the separator 7 is not particularly limited as long as the passage of lithium ions is permitted. The material of the separator 7 may be at least one selected from the group consisting of gel electrolytes, ion exchange resin membranes, semipermeable membranes, and porous membranes. If the separator 7 is made of these materials, the safety of the non-aqueous electrolyte secondary battery 100 can be sufficiently ensured. Examples of gel electrolytes include gel electrolytes containing fluororesins such as PVdF. Examples of ion exchange resin membranes include cation exchange membranes and anion exchange membranes. Examples of porous membranes include porous membranes made of polyolefin resin and porous membranes containing glass paper obtained by weaving glass fibers into a nonwoven fabric.

[0044] The electrolyte is a non-aqueous electrolyte impregnated into the positive electrode 5, the negative electrode 6, and the separator 7. The electrolyte may fill the internal space of the container 1. Lithium ions can move between the positive electrode 5 and the negative electrode 6 through the action of the electrolyte.

[0045] The electrolyte contains a non-aqueous solvent and a lithium salt.

[0046] Examples of non-aqueous solvents include cyclic carbonate solvents, linear carbonate solvents, cyclic ether solvents, linear ether solvents, cyclic ester solvents, linear ester solvents, or fluorinated solvents. Examples of cyclic carbonate solvents are ethylene carbonate, propylene carbonate, or butylene carbonate. Examples of linear carbonate solvents are dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate. Examples of cyclic ether solvents are tetrahydrofuran, 1,4-dioxane, or 1,3-dioxolane. Examples of linear ether solvents are 1,2-dimethoxyethane, or 1,2-diethoxyethane. An example of a cyclic ester solvent is γ-butyrolactone. An example of a linear ester solvent is methyl acetate. Examples of fluorinated solvents are fluoroethylene carbonate, methyl fluoropropionate, fluorobenzene, fluoroethyl methyl carbonate, or fluorodimethylene carbonate. One non-aqueous solvent selected from these may be used alone. Alternatively, a mixture of two or more non-aqueous solvents selected from these may be used.

[0047] Examples of lithium salts include lithium hexafluoride phosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bisperfluoroethylsulfonylimide (LiN(SO2C2F5)2), LiAsF6, LiCF3SO3, and lithium difluoro(oxalato)borate. One of these lithium salts may be used, or two or more may be used in combination.

[0048] Container 1 is, for example, a metal container such as aluminum or stainless steel. Container 1 may have a cylindrical shape or a rectangular tube shape.

[0049] The electrode group 4 may be wound in a cylindrical shape or in an elliptical shape.

[0050] The shape of the non-aqueous electrolyte secondary battery 100 is not particularly limited. Various shapes such as cylindrical and rectangular can be used for the non-aqueous electrolyte secondary battery 100.

[0051] Next, a method for manufacturing a non-aqueous electrolyte secondary battery 100 will be described.

[0052] First, the electrode group 4 is fabricated. Specifically, a positive electrode 5, a negative electrode 6, and a separator 7 are prepared. The positive electrode 5, the negative electrode 6, and a pair of separators 7 are stacked and wound together to form a spiral-shaped electrode group 4. This gives rise to the electrode group 4.

[0053] The positive electrode 5 can be manufactured by applying a slurry-like positive electrode mixture (positive electrode mixture slurry) to one or both sides of the positive electrode current collector 5a, drying it, and rolling it. The positive electrode 5 has a thickness of, for example, 30 μm to 200 μm and is preferably highly flexible. The positive electrode mixture slurry is obtained by kneading and uniformly dispersing materials such as positive electrode active material, conductive additive, and binder using a dispersion medium.

[0054] The method for applying the positive electrode mixture slurry to the positive electrode current collector 5a is not particularly limited. The positive electrode mixture slurry can be applied to the positive electrode current collector 5a using a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater, dip coater, etc. The applied positive electrode mixture may be air-dried or dried using a drying device.

[0055] After drying, the positive electrode 5 is rolled so that the positive electrode mixture layer 5b reaches a predetermined thickness. Rolling may be performed multiple times using a roll press, or multiple times while varying the pressing pressure of the roll press. After rolling, the positive electrode lead 5c for power extraction is welded to the positive electrode current collector 5a.

[0056] The negative electrode 6 can be manufactured by applying a slurry-like negative electrode mixture (negative electrode mixture slurry) to one or both sides of the negative electrode current collector 6a, drying it, and rolling it. In this embodiment, as described above, the negative electrode mixture layer 6b has different types, combinations, and composition ratios of graphite materials used as the negative electrode active material in at least the first end region 61 and the central region 63. Therefore, at least two types of slurry are prepared for manufacturing the negative electrode mixture layer 6b: a slurry for the first end region and a slurry for the central region. If the negative electrode mixture in the second end region 62 is not the same as the negative electrode mixture in the first end region 61 or the negative electrode mixture in the central region, a slurry for the second end region is also prepared. The slurry for the first end region is applied to one end region in the width direction of the negative electrode current collector 6a, the slurry for the central region is applied to the central region, and the slurry for the second end region is applied to the other end region in the width direction of the negative electrode current collector 6a. The coating film, formed in a pattern using an appropriate negative electrode slurry for each region, is then dried and rolled. The negative electrode 6 has a thickness of, for example, 30 μm to 210 μm and is preferably highly flexible. The negative electrode slurry for producing the negative electrode layer 6b is obtained by kneading and uniformly dispersing materials such as the negative electrode active material, conductive additive, and binder using a dispersion medium.

[0057] The method for applying the negative electrode mixture slurry to the negative electrode current collector 6a is not particularly limited. The negative electrode mixture slurry can be applied to the negative electrode current collector 6a using a slit die coater, reverse roll coater, lip coater, blade coater, knife coater, gravure coater, dip coater, etc. The applied negative electrode mixture slurry may be air-dried or dried using a drying device.

[0058] Next, the electrode group 4 is placed in container 1, and then the electrolyte solution is poured into container 1. Finally, container 1 is sealed.

[0059] Through the above process, a non-aqueous electrolyte secondary battery 100, as shown in Figure 2, is obtained, which includes an electrode group including the negative electrode 6 shown in Figures 3A and 3B.

[0060] (Other Embodiments) (Note) The above description of embodiments discloses the following technologies.

[0061] (Technical 1) A negative electrode used in an electrode group having a wound structure, wherein the negative electrode comprises a long negative electrode mixture layer, the negative electrode mixture layer contains graphite as a negative electrode active material, the negative electrode mixture layer includes a first end region including a first end in the width direction of the negative electrode mixture layer, a second end region including a second end in the width direction, and a central region including the center in the width direction of the negative electrode mixture layer, the Raman spectral ID / IG ratio of the first end region is greater than the Raman spectral ID / IG ratio of the central region. Here, the Raman spectral ID / IG ratio is defined as the Raman spectrum obtained by analysis of the surface of the negative electrode mixture layer by Raman method, with a Raman shift of 1575 cm⁻¹. -1 The Raman shift of 1348 cm is relative to the peak intensity IG of the G band appearing in the vicinity. -1 This is the ratio of the peak intensity IDs of the D-band that appear in the vicinity.

[0062] This configuration allows the negative electrode of technology 1 to improve the battery's cycle characteristics.

[0063] (Technical 2) The negative electrode according to Technical 1, wherein the Raman spectral ID / IG ratio of the second end region is greater than the Raman spectral ID / IG ratio of the central region.

[0064] This configuration allows the negative electrode of technology 2 to further improve the battery's cycle characteristics.

[0065] (Technical 3) The negative electrode according to Technical 2, wherein the ratio A (length of the end region:length of the central region) of the length of the end region, which is the sum of the lengths of the first end region and the second end region in the width direction, to the length of the central region in the width direction is within the range of 5:95 to 60:40.

[0066] This configuration allows the negative electrode of technology 3 to effectively improve the battery's cycle characteristics.

[0067] (Technical 4) The negative electrode according to Technical 3, wherein the ratio A (length of the end region: length of the central region) is in the range of 10:90 to 50:50.

[0068] This configuration allows the negative electrode of technology 4 to effectively improve the battery's cycle characteristics.

[0069] (Technical 5) The negative electrode according to any one of Technical 1 to 4, wherein in the region of the negative electrode mixture layer from the center to the first end, the ratio B (length of the first end region: length of the central region) in the width direction to the length of the central region in the width direction is in the range of 5:95 to 60:40.

[0070] This configuration allows the negative electrode of technology 5 to effectively improve the battery's cycle characteristics.

[0071] (Technical 6) The negative electrode according to Technical 5, wherein the ratio B (length of the first end region: length of the central region) is in the range of 10:90 to 50:50.

[0072] This configuration allows the negative electrode of technology 6 to effectively improve the battery's cycle characteristics.

[0073] (Technical 7) The negative electrode according to any one of Technical 1 to 6, wherein the ratio of the Raman spectral ID / IG ratio of the first end region to the Raman spectral ID / IG ratio of the central region is 2 or more.

[0074] This configuration allows the negative electrode of technology 7 to effectively improve the battery's cycle characteristics.

[0075] (Technical 8) The negative electrode according to Technical 7, wherein the ratio of the Raman spectral ID / IG ratio of the first end region to the Raman spectral ID / IG ratio of the central region is 3 or more and 20 or less.

[0076] This configuration allows the negative electrode of technology 7 to effectively improve the battery's cycle characteristics.

[0077] (Technical 9) The negative electrode according to any one of Technical 1 to 8, wherein the Raman spectral ID / IG ratio of the first end region is 0.8 or more.

[0078] This configuration allows the negative electrode of technology 9 to effectively improve the battery's cycle characteristics.

[0079] (Technical 10) The negative electrode according to Technical 9, wherein the Raman spectrum ID / IG ratio of the first end region is 0.8 or more and 3 or less.

[0080] This configuration allows the negative electrode of technology 10 to effectively improve the battery's cycle characteristics.

[0081] (Technical 11) The negative electrode according to any one of Technical 1 to 10, wherein the graphite in the first end region includes graphite coated with amorphous carbon.

[0082] This configuration facilitates the realization of the first end region having the desired Raman spectrum ID / IG.

[0083] (Technical 12) The negative electrode according to Technical 2, wherein the ratio of the Raman spectral ID / IG ratio of the second end region to the Raman spectral ID / IG ratio of the central region is 2 or more.

[0084] With this configuration, the negative electrode of technology 12 can effectively improve the battery's cycle characteristics.

[0085] (Technical 13) The negative electrode according to Technical 12, wherein the ratio of the Raman spectral ID / IG ratio of the second end region to the Raman spectral ID / IG ratio of the central region is 3 or more and 20 or less.

[0086] With this configuration, the negative electrode of technology 13 can effectively improve the battery's cycle characteristics.

[0087] (Technical 14) The negative electrode according to Technical 2, wherein the Raman spectrum ID / IG ratio of the second end region is 0.8 or more.

[0088] With this configuration, the negative electrode of technology 14 can effectively improve the battery's cycle characteristics.

[0089] (Technical 15) The negative electrode according to Technical 14, wherein the Raman spectrum ID / IG ratio of the second end region is 0.8 or more and 3 or less.

[0090] This configuration allows the negative electrode of technology 15 to effectively improve the battery's cycle characteristics.

[0091] (Technical 16) The negative electrode according to Technical 2, wherein the graphite in the second end region includes graphite coated with amorphous carbon.

[0092] This configuration facilitates the realization of the second-end region having the desired Raman spectrum ID / IG.

[0093] (Technical 17) A non-aqueous electrolyte secondary battery comprising: an electrode group having a winding structure, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the negative electrode is the negative electrode described in any one of Technical 1 to 16.

[0094] This configuration allows the non-aqueous electrolyte secondary battery of technology 17 to improve its cycle characteristics.

[0095] [Example 1] (Preparation of negative electrode mixture slurry) As the graphite constituting the negative electrode active material, graphite A1 coated with amorphous carbon and graphite B not coated with amorphous carbon were used. Then, graphite A1 and silicon oxide represented by SiO were mixed in a mass ratio of 94:6 to obtain negative electrode active material A mainly composed of graphite A1. Similarly, for graphite B, graphite B and SiO were mixed in a mass ratio of 94:6 to obtain negative electrode active material B mainly composed of graphite B.

[0096] Graphite A1 was produced by mixing graphite (artificial graphite) and pitch, depositing the pitch onto the surface of the graphite particles, and then firing the mixture at 1000°C.

[0097] A negative electrode mixture was prepared by mixing negative electrode active material A (a mixture of graphite A1 coated with amorphous carbon and SiO), carboxycellulose sodium (CMC-Na), and styrene-butadiene rubber (SBR) in a mass ratio of negative electrode active material A:CMC-Na:SBR = 100:1:1. Water was added as a dispersion medium to this mixture, and then the mixture was stirred using a mixer to prepare a slurry for the edge region.

[0098] A negative electrode mixture was prepared by mixing negative electrode active material B (a mixture of graphite B and SiO), sodium carboxycellulose (CMC-Na), and styrene-butadiene rubber (SBR) in a mass ratio of negative electrode active material B:CMC-Na:SBR = 100:1:1. Water was added as a dispersion medium to this mixture, and then the mixture was stirred using a mixer to prepare a slurry for the central region.

[0099] (Fabrication of the negative electrode) A long copper foil, the kind used for cylindrical cells, was used as the negative electrode current collector. On both sides of this long negative electrode current collector, a slurry for the end regions was applied to the regions at both ends in the width direction, and a slurry for the central region was applied to the central region including the center in the width direction. Each slurry was applied so that the ratio of the width direction lengths W1 of the first end region, W2 of the central region, and W3 of the second end region was W1:W2:W3 = 16.5:67:16.5. That is, the ratio A ((W1+W3):W2) of the length of the end regions (W1+W3), which is the sum of the lengths W1 of the first end region and W3 of the second end region in the width direction, to the length W2 of the central region in the width direction was 33:67. The coating was dried and then rolled to produce the negative electrode mixture layer. An exposed portion was provided on a part of the negative electrode where the surface of the negative electrode current collector was exposed.

[0100] For the anodes prepared as described above, the Raman spectral ID / IG ratios of each region on the surface of the anode mixture layer were determined using the method described later. The results are shown in Table 1.

[0101] (Preparation of positive electrode mixture slurry) Lithium cobaltate, graphite, and polyvinylidene fluoride (PVdF) were mixed in a mass ratio of lithium cobaltate:graphite:PVdF = 90:5:5, and an appropriate amount of N-methyl-2-pyrrolidone (NMP) was added to prepare the positive electrode mixture slurry.

[0102] (Preparation of the positive electrode) A positive electrode mixture slurry was applied to both sides of a positive electrode current collector made of aluminum foil (15 μm thick) using the doctor blade method, the coating was dried, and then compressed using a rolling roller. The positive electrode current collector was then cut to a predetermined electrode size to obtain a positive electrode in which positive electrode active material layers were formed on both sides of the positive electrode current collector.

[0103] (Preparation of non-aqueous electrolyte) Ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed in a volume ratio of EC:PC:EMC = 10:10:80. LiPF6 was dissolved in this mixed solvent to a concentration of 1 mol / L to prepare a non-aqueous electrolyte.

[0104] (Preparation of test cell (secondary battery)) Aluminum leads were attached to the exposed part of the positive electrode and nickel leads were attached to the predetermined position of the negative electrode. The positive and negative electrodes were then wound in a spiral shape via a polyolefin separator to create a wound electrode group. This electrode group was placed inside a bottomed cylindrical outer container, the non-aqueous electrolyte was injected, and a sealing body was attached to the opening of the outer container via a gasket to create a cylindrical test cell.

[0105] [Example 2] (Preparation of negative electrode mixture slurry) For the slurry for the end region, graphite A2 coated with amorphous carbon was used as the graphite constituting the negative electrode active material. Graphite A2 was prepared in the same manner as graphite A1 in Example 1, except that the mixing ratio of graphite (artificial graphite) and pitch was changed. The slurry for the end region was prepared in the same manner as in Example 1, except that graphite A2 was used instead of graphite A1. The slurry for the central region was prepared in the same manner as in Example 1.

[0106] (Preparation of the negative electrode) The negative electrode was prepared in the same manner as in Example 1, except that the slurry prepared in Example 2 was used as the slurry for the edge region.

[0107] For the anodes prepared as described above, the Raman spectral ID / IG ratios of each region on the surface of the anode mixture layer were determined using the method described later. The results are shown in Table 1.

[0108] (Preparation of positive electrode slurry and preparation of positive electrode) The positive electrode slurry and the positive electrode were prepared in the same manner as in Example 1.

[0109] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 2 was used.

[0110] [Example 3] (Preparation of negative electrode mixture slurry) A slurry for the edge region and a slurry for the central region were prepared in the same manner as in Example 1.

[0111] (Fabrication of the negative electrode) The negative electrode was fabricated in the same manner as in Example 1, except that the slurry for the end region and the slurry for the central region were applied so that the ratio of the widthwise length W1 of the first end region, the widthwise length W2 of the central region, and the widthwise length W3 of the second end region was W1:W2:W3 = 5:90:5. In other words, in Example 3, the ratio A ((W1+W3):W2) of the length of the end region (W1+W3), which is the sum of the widthwise length W1 of the first end region and the widthwise length W3 of the second end region, to the widthwise length W2 of the central region was 10:90.

[0112] For the anodes prepared as described above, the Raman spectral ID / IG ratios of each region on the surface of the anode mixture layer were determined using the method described later. The results are shown in Table 1.

[0113] (Preparation of positive electrode slurry and preparation of positive electrode) The positive electrode slurry and the positive electrode were prepared in the same manner as in Example 1.

[0114] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 3 was used.

[0115] [Example 4] (Preparation of negative electrode mixture slurry) A slurry for the edge region and a slurry for the central region were prepared in the same manner as in Example 1.

[0116] (Preparation of the negative electrode) The negative electrode was prepared in the same manner as in Example 1, except that the slurry for the end region and the slurry for the central region were applied so that the ratio of the widthwise length W1 of the first end region, the widthwise length W2 of the central region, and the widthwise length W3 of the second end region was W1:W2:W3 = 25:50:25. In other words, in Example 4, the ratio A ((W1+W3):W2) of the length of the end region (W1+W3), which is the sum of the widthwise length W1 of the first end region and the widthwise length W3 of the second end region, to the widthwise length W2 of the central region was 50:50.

[0117] For the anodes prepared as described above, the Raman spectral ID / IG ratios of each region on the surface of the anode mixture layer were determined using the method described later. The results are shown in Table 1.

[0118] (Preparation of positive electrode slurry and preparation of positive electrode) The positive electrode slurry and the positive electrode were prepared in the same manner as in Example 1.

[0119] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Example 4 was used.

[0120] [Comparative Example 1] (Preparation of negative electrode mixture slurry) In Example 1, only the slurry prepared as the slurry for the central region was prepared as the negative electrode mixture slurry.

[0121] (Fabrication of the negative electrode) The same copper foil as in Example 1 was used as the negative electrode current collector. The slurry for the central region was applied to both sides of the negative electrode current collector without distinguishing between regions. That is, the entire region, including both ends and the central region, was fabricated using the slurry for the central region prepared in Example 1. The coating was dried and then rolled to produce the negative electrode mixture layer. An exposed portion of the negative electrode was provided, in which the surface of the negative electrode current collector was exposed.

[0122] For the anodes prepared as described above, the Raman spectral ID / IG ratios of each region on the surface of the anode mixture layer were determined using the method described later. The results are shown in Table 1.

[0123] (Preparation of positive electrode slurry and preparation of positive electrode) The positive electrode slurry and the positive electrode were prepared in the same manner as in Example 1.

[0124] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Comparative Example 1 was used.

[0125] [Comparative Example 2] (Preparation of negative electrode mixture slurry) The slurry for the central region of Example 1 was used as the slurry for the edge region of Comparative Example 2, and the slurry for the edge region of Example 1 was used as the slurry for the central region of Comparative Example 2.

[0126] (Preparation of the negative electrode) The negative electrode was prepared in the same manner as in Example 1, except that the slurry for the edge region and the slurry for the central region of Comparative Example 2 were used.

[0127] For the anodes prepared as described above, the Raman spectral ID / IG ratios of each region on the surface of the anode mixture layer were determined using the method described later. The results are shown in Table 1.

[0128] (Preparation of positive electrode slurry and preparation of positive electrode) The positive electrode slurry and the positive electrode were prepared in the same manner as in Example 1.

[0129] (Preparation of test cell (secondary battery)) A secondary battery to be used as a test cell was prepared in the same manner as in Example 1, except that the negative electrode prepared in Comparative Example 1 was used.

[0130] [Measurement of Raman Spectrum ID / IG Ratio in Each Region] Measurements were performed using a JASCO NRS-5100 laser from JASCO Corporation, with a laser wavelength of 532 nm and an output of 4.4 mW. Measurements were performed at a minimum of 3 or 4 locations until the range of intensity fluctuations could be determined. The IG peak had a Raman shift of 1575 cm⁻¹. -1 This is the peak intensity of the peak appearing in the vicinity, and the ID is a Raman shift of 1348 cm. -1 These are the peak intensities of the peaks appearing in the vicinity. These intensities were determined from Raman spectral measurements, and the ID / IG ratio was obtained.

[0131] [Initial Low-Rate Cycle Conditions] Under a temperature environment of 25°C, each test cell for the examples and comparative examples was charged with a constant current at 0.2C until the cell voltage reached 4.2V, and then charged with a constant voltage at 4.2V until the C / 50. Subsequently, a constant current discharge was performed at 0.2C until the cell voltage reached 2.5V.

[0132] [Evaluation of Cycle Characteristics (Capacity Retention Rate)] Under a temperature environment of 25°C, each test cell for the example and comparative example was charged with a constant current at 1C until the cell voltage reached 4.2V, and then charged with a constant voltage at 4.2V to C / 50. Subsequently, a constant current discharge was performed at 0.5C until the cell voltage reached 2.5V. This charge-discharge cycle was repeated 100 times, and the capacity retention rate was calculated using the following formula: Capacity Retention Rate = (Discharge Capacity at 100 Cycles / Discharge Capacity at 1 Cycle) × 100

[0133] The obtained capacity retention rate was defined as the cycle retention rate. The results are shown in Table 1. Table 1 also shows the relative values ​​when the cycle retention rate of Comparative Example 1 is set as the baseline (100%).

[0134]

[0135] As shown in Table 1, the batteries of Examples 1 to 4, which had negative electrodes in which the Raman spectral ID / IG ratio in both end regions, including the first end region, was greater than the Raman spectral ID / IG ratio in the central region, had a higher cycle retention rate compared to the battery of Comparative Example 1, which had a negative electrode in which the entire negative electrode mixture layer had the same Raman spectral ID / IG ratio, and the battery of Comparative Example 2, which had a negative electrode in which the Raman spectral ID / IG ratio in both end regions was smaller than the Raman spectral ID / IG ratio in the central region. Thus, negative electrodes in which the Raman spectral ID / IG ratio in both end regions, including the first end region, is greater than the Raman spectral ID / IG ratio in the central region were able to improve the cycle characteristics of the battery.

[0136] The technology disclosed herein is useful for non-aqueous electrolyte secondary batteries, such as lithium-ion secondary batteries, which require excellent cycle characteristics.

Claims

1. A negative electrode used in an electrode group having a wound structure, wherein the negative electrode comprises a long negative electrode mixture layer, the negative electrode mixture layer contains graphite as a negative electrode active material, the negative electrode mixture layer includes a first end region including a first end in the width direction of the negative electrode mixture layer, a second end region including a second end in the width direction, and a central region including the center in the width direction of the negative electrode mixture layer, the Raman spectral ID / IG ratio of the first end region is greater than the Raman spectral ID / IG ratio of the central region. Here, the Raman spectral ID / IG ratio is defined as the Raman spectrum obtained by analysis of the surface of the negative electrode mixture layer by Raman method, with a Raman shift of 1575 cm⁻¹. -1 The Raman shift of 1348 cm is relative to the peak intensity IG of the G band appearing in the vicinity. -1 This is the ratio of the peak intensity IDs of the D-band that appear in the vicinity.

2. The negative electrode according to claim 1, wherein the Raman spectral ID / IG ratio of the second end region is greater than the Raman spectral ID / IG ratio of the central region.

3. The negative electrode according to claim 2, wherein the ratio A (length of the end region : length of the central region) of the length of the end region, which is the sum of the length of the first end region and the length of the second end region in the width direction, is within the range of 5:95 to 60:

40.

4. The negative electrode according to claim 3, wherein the ratio A (length of the end region : length of the central region) is in the range of 10:90 to 50:

50.

5. The negative electrode according to claim 1, wherein in the region of the negative electrode mixture layer from the center to the first end, the ratio B (length of the first end region : length of the central region) in the width direction to the length of the central region in the width direction is within the range of 5:95 to 60:

40.

6. The negative electrode according to claim 5, wherein the ratio B (length of the first end region : length of the central region) is in the range of 10:90 to 50:

50.

7. The negative electrode according to claim 1, wherein the ratio of the Raman spectral ID / IG ratio of the first end region to the Raman spectral ID / IG ratio of the central region is 2 or more.

8. The negative electrode according to claim 7, wherein the ratio of the Raman spectral ID / IG ratio of the first end region to the Raman spectral ID / IG ratio of the central region is 3 or more and 20 or less.

9. The negative electrode according to claim 1, wherein the Raman spectral ID / IG ratio of the first end region is 0.8 or greater.

10. The negative electrode according to claim 9, wherein the Raman spectral ID / IG ratio of the first end region is 0.8 or more and 3 or less.

11. The negative electrode according to claim 1, wherein the graphite in the first end region comprises graphite coated with amorphous carbon.

12. The negative electrode according to claim 2, wherein the ratio of the Raman spectral ID / IG ratio of the second end region to the Raman spectral ID / IG ratio of the central region is 2 or more.

13. The negative electrode according to claim 12, wherein the ratio of the Raman spectral ID / IG ratio of the second end region to the Raman spectral ID / IG ratio of the central region is 3 or more and 20 or less.

14. The negative electrode according to claim 2, wherein the Raman spectral ID / IG ratio of the second end region is 0.8 or greater.

15. The negative electrode according to claim 14, wherein the Raman spectral ID / IG ratio of the second end region is 0.8 or more and 3 or less.

16. The negative electrode according to claim 2, wherein the graphite in the second end region comprises graphite coated with amorphous carbon.

17. A non-aqueous electrolyte secondary battery comprising: an electrode group having a winding structure, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode; and a non-aqueous electrolyte, wherein the negative electrode is the negative electrode described in any one of claims 1 to 16.

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