Non-aqueous electrolyte secondary battery

Abstract

The present invention is characterized by comprising an electrode body in which a positive electrode (11) and a negative electrode (12) are wound in a longitudinal direction with a separator (13) therebetween, wherein: the negative electrode (12) includes a negative electrode current collector (40) and a negative electrode mixture layer (41) disposed on the negative electrode current collector (40), and has a facing part (42) facing the positive electrode (11) with the separator (13) therebetween and a non-facing part (43) extending from the winding finish end of the facing part (42) toward the winding finish end of the electrode body (14); and the non-facing part (43) is folded back toward the winding start side within a range in which a longitudinal end portion (12A) of the negative electrode (12) does not face the positive electrode (11).

Description

Non-aqueous electrolyte secondary battery

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

[0002] Conventionally, a non-aqueous electrolyte secondary battery including an electrode body in which a positive electrode and a negative electrode are wound via a separator, and a bottomed cylindrical exterior can for housing the electrode body is known (see, for example, Patent Document 1). The non-aqueous electrolyte secondary battery of Patent Document 1 includes a biasing portion that biases radially outward in the vicinity of the winding center of the electrode body for the purpose of suppressing deformation of the electrode plate when charging and discharging are repeated.

[0003] Japanese Patent Application Laid-Open No. 2011-91020

[0004] In a non-aqueous electrolyte secondary battery having a wound electrode body, a gap that is not occupied by the negative electrode and the separator is formed in the vicinity of the end of the positive electrode where winding ends. Therefore, when charging and discharging are repeated, stress may concentrate on the electrode plate in the vicinity of the gap due to volume change (expansion and contraction) of the electrode plate, etc., and deformation of the electrode plate may occur. When deformation of the electrode plate occurs, the distance between the electrode plates between the positive electrode and the negative electrode becomes non-uniform, and unevenness in the charge and discharge reaction is likely to occur inside the electrode body. As a result, the cycle characteristics of the non-aqueous electrolyte secondary battery deteriorate.

[0005] A non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound along the longitudinal direction via a separator, a non-aqueous electrolyte, and a bottomed cylindrical exterior can for housing the electrode body and the non-aqueous electrolyte. The negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and has a facing portion facing the positive electrode via the separator, and a non-facing portion extending from the end of the facing portion to the winding end side of the electrode body. The non-facing portion is folded back toward the winding start side within a range where the longitudinal end of the negative electrode does not face the positive electrode.

[0006] According to the non-aqueous electrolyte secondary battery according to one aspect of the present disclosure, unevenness in the charge and discharge reaction inside the electrode body is suppressed, and the cycle characteristics can be improved.

[0007] This is an axial cross-sectional view of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. This figure shows a part of the radial cross-section of the electrode body of a non-aqueous electrolyte secondary battery, which is an example of an embodiment. This is a plan view of the positive electrode and negative electrode, which are an example of an embodiment.

[0008] In the following, an example of an embodiment of the non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings. In the following description, specific shapes, materials, numerical values, directions, etc., are examples to facilitate understanding of the present invention and can be appropriately modified according to the specifications of the non-aqueous electrolyte secondary battery. Furthermore, if the following description includes multiple embodiments and modifications, it is intended from the outset that their characteristic parts may be used in appropriate combinations.

[0009] Figure 1 is an axial cross-sectional view of a non-aqueous electrolyte secondary battery 10 (cylindrical battery), which is an example of an embodiment. As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte (not shown), and an outer casing 16 that houses the electrode body 14 and the non-aqueous electrolyte.

[0010] The electrode body 14 has a wound structure in which a positive electrode 11 and a negative electrode 12 are wound in a spiral shape via a separator 13. The positive electrode 11, the negative electrode 12, and the separator 13 are all elongated strip-shaped bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape. The negative electrode 12 is formed to be slightly larger in dimensions than the positive electrode 11 in order to prevent lithium deposition. That is, the negative electrode 12 is formed to be longer in the longitudinal and width directions than the positive electrode 11. The separator 13 is formed to be at least slightly larger in dimensions than the positive electrode 11, and for example, two separators are arranged so as to sandwich the positive electrode 11.

[0011] The positive electrode 11 comprises a long positive electrode current collector 30 and a positive electrode mixture layer 31 disposed on the positive electrode current collector 30. The positive electrode current collector 30 can be made of a metal foil that is stable within the potential range of the positive electrode 11, such as aluminum, aluminum alloy, stainless steel, or titanium, or a film with such metal on its surface. The positive electrode mixture layer 31 contains a positive electrode active material, a conductive agent such as acetylene black, and a binder such as polyvinylidene fluoride (PVdF), and is preferably formed on both sides of the positive electrode current collector 30. For example, a lithium transition metal composite oxide containing Ni, Co, Mn, Al, etc., can be used as the positive electrode active material.

[0012] The thickness of the positive electrode 11 is, for example, 100 μm or more and 250 μm or less. In this embodiment, the thickness of the positive electrode 11 is substantially constant except for the region to which the positive electrode lead 20 is connected. The thickness of the positive electrode current collector 30 is, for example, 10 μm or more and 50 μm or less. The thickness of the positive electrode mixture layer 31 is, for example, 50 μm or more and 100 μm or less on one side of the positive electrode current collector 30. The positive electrode 11 can be manufactured by applying a positive electrode mixture slurry containing a positive electrode active material, a conductive agent, and a binder onto the positive electrode current collector 30, drying the coating film, and then compressing it to form the positive electrode mixture layer 31 on the surface of the positive electrode current collector 30.

[0013] The negative electrode 12 comprises a long negative electrode current collector 40 and a negative electrode mixture layer 41 disposed on the negative electrode current collector 40. The negative electrode current collector 40 can be made of a metal foil that is stable within the potential range of the negative electrode 12, such as copper, copper alloy, stainless steel, nickel, or nickel alloy, or a film with such metal on its surface. The negative electrode mixture layer 41 contains a negative electrode active material and a binder such as styrene-butadiene rubber (SBR).

[0014] The thickness of the negative electrode 12 is, for example, 100 μm or more and 300 μm or less. The thickness of the negative electrode current collector 40 is, for example, 5 μm or more and 30 μm or less. The thickness of the negative electrode mixture layer 41 is, for example, 50 μm or more and 150 μm or less on one side of the negative electrode current collector 40. The negative electrode 12 can be manufactured in the same way as the positive electrode 11 by applying a negative electrode mixture slurry containing a negative electrode active material and a binder onto the negative electrode current collector 40, drying the coating film, and then compressing it to form the negative electrode mixture layer 41 on the surface of the negative electrode current collector 40.

[0015] The negative electrode active material preferably contains a silicon-containing material in addition to the carbon material. Including a silicon-containing material makes it easier to achieve both high capacity and excellent cycle characteristics. From the viewpoint of increasing capacity, the silicon-containing material content is preferably 5% by mass or more, and more preferably 10% by mass or more, relative to the total mass of the negative electrode active material. In general, silicon-containing materials undergo a larger volume change during charging and discharging compared to carbon materials. Therefore, when a silicon-containing material is included as the negative electrode active material, deformation of the electrode plate is likely to occur at the end of the winding of the electrode body 14. Thus, when a silicon-containing material is included as the negative electrode active material, the effect of improving the cycle characteristics described later is significantly exhibited.

[0016] The carbon material that functions as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. In particular, it is preferable to use at least artificial graphite such as bulk artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, bulk graphite, or earthy graphite, or a mixture thereof as the carbon material.

[0017] The silicon-containing material can be any material containing Si, and examples include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The volume-based average particle size (D50) of the composite material is generally smaller than that of graphite. The volume-based D50 of the composite material is, for example, 1 μm or more and 15 μm or less. One type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0018] A suitable silicon-containing material (composite material) is a composite particle comprising an ionic conductive phase and a Si phase dispersed within the ionic conductive phase. The ionic conductive phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ionic conductive phase is a continuous phase composed of an aggregate of particles finer than those of the Si phase. The silicon-containing material may also have a conductive layer covering the surface of the ionic conductive phase. The conductive layer is composed of a material with higher conductivity than the ionic conductive phase and forms good conductive paths in the negative electrode mixture layer 41.

[0019] An example of a suitable composite material containing Si is one having a sea-island structure in which fine Si particles are dispersed substantially uniformly in an amorphous silicon oxide phase, and the overall general formula is SiO ｘ These are composite particles represented by (0 < x ≤ 2). The main component of silicon oxide may be silicon dioxide. The oxygen content ratio (x) to Si is, for example, 0.5 ≤ x < 2.0, and preferably 0.8 ≤ x ≤ 1.5.

[0020] The electrode body 14 has a positive electrode lead 20 connected to the positive electrode 11 and a negative electrode lead 21 connected to the negative electrode 12. The positive electrode lead 20 is, for example, an aluminum tab, and the negative electrode lead 21 is, for example, a nickel tab. In this embodiment, the positive electrode lead 20 is connected to the approximate center of the longitudinal direction of the positive electrode 11. The negative electrode lead 21 is provided at one longitudinal end of the negative electrode 12, which is located on the winding start side of the electrode body 14.

[0021] As will be described in more detail later, in this embodiment, the negative electrode 12 is arranged on the outermost outer surface of the electrode body 14, and the outer surface of the negative electrode current collector 40 is exposed. At least a portion of the exposed surface of the negative electrode current collector 40 is in contact with the inner surface of the outer casing 16. By the negative electrode current collector 40 in contact with the inner surface of the outer casing 16, both ends of the negative electrode 12 in the longitudinal direction and the outer casing 16 are electrically connected, ensuring good current collection performance.

[0022] Non-aqueous electrolytes are lithium ion conductive. Non-aqueous electrolytes may be liquid electrolytes (electrolytes) or solid electrolytes.

[0023] A liquid electrolyte (electrolyte solution) comprises a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles, amides, and mixtures of two or more of these. Examples of non-aqueous solvents include ethylene carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), and mixtures thereof. The non-aqueous solvent may also contain halogen-substituted solvents (e.g., fluoroethylene carbonate) in which at least some of the hydrogen atoms of the solvent are replaced with halogen atoms such as fluorine. Examples of electrolyte salts include LiPF4. ６ Lithium salts such as these are used.

[0024] As the solid electrolyte, for example, a solid or gel-like polymer electrolyte, an inorganic solid electrolyte, etc., can be used. As the inorganic solid electrolyte, materials known for all-solid-state lithium-ion secondary batteries, etc. (for example, oxide-based solid electrolytes, sulfide-based solid electrolytes, halogen-based solid electrolytes, etc.) can be used. The polymer electrolyte includes, for example, a lithium salt and a matrix polymer, or a non-aqueous solvent, a lithium salt and a matrix polymer. As the matrix polymer, for example, a polymer material that absorbs a non-aqueous solvent and gels is used. Examples of polymer materials include fluororesins, acrylic resins, polyether resins, etc.

[0025] The outer container 16 is a bottomed cylindrical metal container with one end open in the axial direction, and the opening of the outer container 16 is sealed by a sealing body 17. For the sake of explanation, the side of the non-aqueous electrolyte secondary battery 10 with the sealing body 17 will be referred to as "upper," and the bottom side of the outer container 16 will be referred to as "lower."

[0026] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends through a through-hole in the insulating plate 19 towards the bottom of the outer can 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the inner bottom surface of the outer can 16 by welding or the like, and the outer can 16 becomes the negative electrode terminal.

[0027] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has a grooved portion 22 formed on its side surface, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0028] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are stacked in order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each component except the insulating member 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected at their respective centers, with the insulating member 25 interposed between their respective peripheries. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 deforms and ruptures, pushing the upper valve body 26 towards the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure rises further, the upper valve body 26 ruptures, and gas is discharged from the vent hole in the cap 27. Note that the configuration of the sealing body 17 is not limited to the above form.

[0029] Next, the electrode body 14 will be described in detail with reference to Figures 2 and 3. Figure 2 is a schematic diagram showing a portion of the winding end side of the radial cross-section of the electrode body 14. Note that in Figure 2, the positive electrode current collector 30 and the positive electrode mixture layer 31 are omitted from the illustration for clarity. Figure 3 is a plan view of the inner surface of the winding of the positive electrode 11 and negative electrode 12 before and after the negative electrode 12 is folded back, and is a diagram for explaining the positional relationship between the positive electrode 11 and the negative electrode 12.

[0030] As shown in Figures 2 and 3, the negative electrode 12 extends toward the winding end side of the electrode body 14 beyond the position facing the winding end end 11X of the positive electrode 11. Therefore, the negative electrode 12 has a facing portion 42 whose inner surface faces the positive electrode 11 via the separator 13, and a non-facing portion 43 that extends from the winding end end 42X of the facing portion 42 toward the winding end side of the electrode body 14 and does not face the positive electrode 11 via the separator 13.

[0031] In this embodiment, a double-sided coated portion 44 is provided in the region of the opposing portion 42 that faces the positive electrode 11 on both sides via the separator 13, where a negative electrode mixture layer 41 is formed on both sides of the negative electrode current collector 40. In addition, a single-sided coated portion 45 is provided in the region of the opposing portion 42 that faces the positive electrode 11 on one side (the inner surface of the winding) via the separator 13, where a negative electrode mixture layer 41 is formed on one side (the inner surface of the winding) of the negative electrode current collector 40. A part of the outer surface of the single-sided coated portion 45 constitutes the outermost outer surface of the electrode body 14 and abuts against the inner surface of the outer can 16. A part of the single-sided coated portion 45 on the winding end side may be provided in the non-opposing portion 43. The length of the portion of the single-sided coated portion 45 provided in the non-opposing portion 43 is, for example, a length of 0.01 turns or more and 0.25 turns or less.

[0032] In the non-opposing portion 43, in the region on the winding end side of the winding end end of the single-sided coated portion 45, the negative electrode mixture layer 41 is not formed on the negative electrode current collector 40, and a negative electrode current collector exposed portion 46 is provided where both sides of the negative electrode current collector 40 are exposed. The negative electrode current collector exposed portion 46, except for the folded region described later, constitutes the outermost outer surface of the electrode body 14 and is in contact with the inner surface of the outer can 16.

[0033] As shown in Figure 2, a gap is formed near the end 11X of the positive electrode 11 that is not occupied by the negative electrode 12 and the separator 13. Therefore, when charging and discharging are repeated, stress may concentrate on the electrode plate near this gap due to volume changes (expansion and contraction) of the electrode plate, which may cause deformation of the electrode plate. Furthermore, the larger the gap, the more likely the electrode plate deformation is to occur. When electrode plate deformation occurs, for example, the distance between the positive electrode 11 and the negative electrode 12 becomes uneven, making it easier for unevenness in the charging and discharging reaction to occur inside the electrode body 14. As a result, the cycle characteristics of the non-aqueous electrolyte secondary battery 10 deteriorate.

[0034] Therefore, in this embodiment, the non-facing portion 43 of the negative electrode 12 is folded back toward the winding start side in the range where the longitudinal end 12A of the negative electrode 12 does not face the positive electrode 11. This makes it possible to reduce the gap formed near the winding end 11X of the positive electrode 11. As a result, deformation of the electrode plate near the gap is suppressed, unevenness in the charge-discharge reaction inside the electrode body 14 is less likely to occur, and the cycle characteristics are improved.

[0035] In the example shown in Figure 2, the non-opposing portion 43 is folded radially inward of the electrode body 14 so as to sandwich the two separators 13. By folding the non-opposing portion 43 so as to sandwich the separators 13, the thickness of the folded portion is increased, and the gap formed near the winding end 11X of the positive electrode 11 can be made smaller. As a result, deformation of the electrode plate near the gap is further suppressed, and the cycle characteristics are further improved. Furthermore, by folding the non-opposing portion 43 radially inward of the electrode body 14, in addition to making the gap formed near the winding end 11X of the positive electrode 11 smaller, it becomes easier to insert the electrode body 14 into the outer casing 16 during the manufacturing of the non-aqueous electrolyte secondary battery 10. The folded portion of the non-opposing portion 43 may be joined to the opposing negative electrode 12 or separator 13 by an adhesive member or the like.

[0036] In the radial cross-section of the electrode body 14, the length of the folded region of the non-opposing portion (corresponding to the length L in Figure 3) is preferably 0.25 turns or less, and more preferably 0.20 turns or less. If the length of the folded region of the non-opposing portion exceeds 0.25 turns, a step due to the folding is likely to form on the outermost circumference of the electrode body 14, and deformation of the electrode plate may occur near the step. The lower limit of the length of the folded region of the non-opposing portion is, for example, 0.01 turns.

[0037] Furthermore, as shown in Figure 2, in the radial cross-section of the electrode body 14, the angle θ formed by a straight line X1 extending radially along the electrode body 14 from the winding center Z of the electrode body 14 through the winding end 11X of the positive electrode 11 and a straight line X2 extending radially along the electrode body 14 through the longitudinal end 12A of the negative electrode 12, which is folded back from the winding center Z of the electrode body 14, is preferably 60° or less, and more preferably 45° or less. The smaller the angle θ, the smaller the gap formed near the winding end 11X of the positive electrode 11 that is not occupied by the negative electrode 12 and the separator 13. As a result, deformation of the electrode plate near the gap is suppressed, unevenness in the charge-discharge reaction inside the electrode body 14 is less likely to occur, and the cycle characteristics are improved. The lower limit of the angle θ is as long as the longitudinal end 12A of the negative electrode 12 does not face the positive electrode 11, taking into account manufacturing variations, for example, 3°.

[0038] The above embodiments can be modified within the scope of the purpose of this disclosure. For example, in the above embodiments, the non-opposing portion 43 is folded back radially inward of the electrode body 14, but it may also be folded back radially outward of the electrode body 14. Even in this case, when the electrode body 14 is inserted into the outer can 16, the thickness of the folded portion can reduce the gap formed near the end 11X of the winding of the positive electrode 11.

[0039] In addition, in the above-described embodiment, only the negative electrode current collector exposed portion 46 among the non-opposing portions 43 is folded back, but in addition to the negative electrode current collector exposed portion 46, a part of the single-sided coating portion 45 may also be folded back. Further, in the example shown in FIG. 2, the two separators 13 are also folded back while being sandwiched by the non-opposing portion 43, but at least one of the two separators 13 may not be folded back.

[0040] In addition, in the above-described embodiment, the negative electrode 12 has the double-sided coating portion 44 and the single-sided coating portion 45, but may not have the single-sided coating portion 45. That is, the double-sided coating portion 44 may be formed in the region where the single-sided coating portion 45 of FIG. 2 is formed.

[0041] Hereinafter, the present disclosure will be further described by way of examples, but the present disclosure is not limited to these examples.

[0042] <Example 1> [Production of positive electrode] As the positive electrode active material, a composite oxide represented by the composition formula LiNi ０．９ Co ０．０４ Mn ０．０５ Al ０．０１ O ２ was used. The positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed at a solid content mass ratio of 98:1:1, and a positive electrode mixture slurry was prepared using N-methylpyrrolidone (NMP) as a dispersion medium. The slurry was applied to both sides of a positive electrode current collector made of a long aluminum foil with a thickness of 15 μm, and the coating film was dried and compressed to obtain a positive electrode having positive electrode mixture layers formed on both sides of the positive electrode current collector. Note that a region where no positive electrode mixture layer exists was provided at the central portion in the length direction of the positive electrode, and a positive electrode lead made of aluminum was ultrasonically welded to the region.

[0043] [Fabrication of Negative Electrode] As the negative electrode active material, a mixture of graphite and silicon oxide with a mass ratio of 95:5 was used. The negative electrode active material, a dispersion of styrene-butadiene rubber, and sodium carboxymethyl cellulose were mixed at a solid content mass ratio of 98:1:1, and a negative electrode binder slurry was prepared using water as the dispersion medium. The slurry was applied to a negative electrode current collector made of a long copper foil with a thickness of 8 μm, and the coating film was dried and compressed to obtain a negative electrode with a negative electrode binder layer formed on the negative electrode current collector. At this time, as shown in FIG. 2, a single-sided coating portion and a current collector exposed portion were provided on the winding end side of the negative electrode. In addition, a region where no negative electrode binder layer exists was provided at one end in the longitudinal direction of the negative electrode located on the winding start side of the negative electrode, and a negative electrode lead made of nickel was ultrasonically welded to the region.

[0044] [Fabrication of Electrode Assembly] The above positive electrode, the above negative electrode, and a separator made of polyethylene were wound in a spiral shape using a cylindrical winding core member to obtain an electrode assembly. At this time, as shown in FIG. 2, the non-opposing portion (current collector exposed portion) on the winding end side of the negative electrode was folded back radially inward so as to sandwich two separators. The length of the folded-back region of the non-opposing portion was set to the length wound around 0.1 turns, and the angle θ formed by the straight line X1 and the straight line X2 shown in FIG. 2 was set to about 30°.

[0045] [Preparation of Non-aqueous Electrolyte] 5 parts by mass of vinylene carbonate (VC) was added to 100 parts by mass of a mixed solvent obtained by mixing ethylene carbonate (EC) and dimethyl carbonate (DMC) at a volume ratio of 3:7, and LiPF ６ was dissolved at 1.5 mol / liter to prepare a non-aqueous electrolyte.

[0046] [Fabrication of Test Cell (Non-aqueous Electrolyte Secondary Battery)] After insulating plates were arranged above and below the above electrode assembly, the negative electrode lead was welded to the inner surface of the bottom of a bottomed cylindrical exterior can, and the positive electrode lead was welded to the internal terminal plate of the sealing body, and the electrode assembly was housed in the exterior can. Then, a non-aqueous electrolyte solution was injected into the exterior can by a decompression method, and the opening of the exterior can was sealed with a sealing body through a gasket to obtain a cylindrical battery.

[0047] [Evaluation of Cycle Characteristics (Capacity Retention Rate)] The fabricated test cell was charged to 4.2V with a constant current of 1.0C at a temperature of 25°C, and then charged at a constant voltage of 4.2V until the current value was equivalent to 0.02C. After that, it was discharged with a constant current of 1.0C until it reached 2.5V. This was considered one cycle, and the discharge capacity at 1.0C after 500 cycles was measured. The capacity retention rate was then calculated using the following formula: Capacity retention rate [%] = (Discharge capacity after 500 cycles / Discharge capacity in the first cycle) × 100

[0048] <Example 2> A test cell was fabricated and evaluated in the same manner as in Example 1, except that the length of the folded region of the non-opposing part was set to a length that would be wound around 0.25 times, and the electrode body was fabricated so that the angle θ between the straight lines X1 and X2 shown in Figure 2 was approximately 30°.

[0049] <Example 3> A test cell was fabricated and evaluated in the same manner as in Example 1, except that the length of the folded region of the non-opposing part was set to a length that would be wound around 0.33 times, and the electrode body was fabricated so that the angle θ between the straight lines X1 and X2 shown in Figure 2 was approximately 30°.

[0050] <Comparative Example 1> A test cell was prepared and evaluated in the same manner as in Example 1, except that the non-facing portion was not folded back.

[0051] Table 1 shows the volume retention rates of the test cells for Examples 1-3 and Comparative Example 1.

[0052]

[0053] As shown in Table 1, the test cells of Examples 1 to 3 showed improved capacity retention compared to the test cell of Comparative Example 1. This is presumed to be because folding back the non-opposing portion of the negative electrode reduced the gap formed near the end of the positive electrode winding, thereby suppressing deformation of the electrode plate near the gap and reducing unevenness in the charge-discharge reaction inside the electrode body. Furthermore, the test cells of Examples 1 and 2, in which the length of the folded portion was 0.25 turns or less, showed improved capacity retention compared to the test cell of Example 3, in which the length of the folded portion exceeded 0.25 turns.

[0054] This disclosure is further illustrated by the following embodiments. Configuration 1: A non-aqueous electrolyte secondary battery comprising an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally via a separator, a non-aqueous electrolyte, and a bottomed cylindrical outer casing for housing the electrode body and the non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and has a facing portion facing the positive electrode via the separator, and a non-facing portion extending from the winding end end of the facing portion toward the winding end side of the electrode body, wherein the non-facing portion is folded back toward the winding start side in a manner in which the longitudinal end of the negative electrode does not face the positive electrode. Configuration 2: The non-aqueous electrolyte secondary battery according to Configuration 1, wherein the non-facing portion is folded back radially inward of the electrode body. Configuration 3: The non-aqueous electrolyte secondary battery according to Configuration 1 or 2, wherein the non-facing portion is folded back so as to sandwich the separator. Configuration 4: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 3, wherein the length of the folded region of the non-opposing portion is a length that is wound 0.25 times or less. Configuration 5: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 4, wherein in the radial cross-section of the electrode body, the angle between a straight line extending radially along the electrode body from the winding center of the electrode body through the winding end of the positive electrode and a straight line extending radially along the electrode body from the winding center of the electrode body through the folded longitudinal end of the negative electrode is 45° or less. Configuration 6: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 5, wherein the non-opposing portion includes a negative electrode current collector exposed portion in which the negative electrode mixture layer is not formed on the negative electrode current collector and both sides of the negative electrode current collector are exposed, and the negative electrode current collector exposed portion is folded back. Configuration 7: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 6, wherein a negative electrode lead is provided at the winding start end of the negative electrode to electrically connect the negative electrode and the outer casing. Configuration 8: A non-aqueous electrolyte secondary battery according to any one of Configurations 1 to 7, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5% by mass or more relative to the total mass of the negative electrode active material.

[0055] 10 Non-aqueous electrolyte secondary battery (cylindrical battery), 11 Positive electrode, 11X End of winding, 12 Negative electrode, 12A Longitudinal end, 13 Separator, 14 Electrode body, 16 Outer can, 17 Sealing body, 18 Insulating plate, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 21Y Lead end, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket, 30 Positive electrode current collector, 31 Positive electrode mixture layer, 40 Negative electrode current collector, 41 Negative electrode mixture layer, 42 Opposing section, 42X End of winding, 43 Non-opposing section, 44 Double-sided coated section, 45 Single-sided coated section, 46 Negative electrode current collector exposed section, Z Winding center.

Claims

1. A non-aqueous electrolyte secondary battery comprising: an electrode body in which a strip-shaped positive electrode and a strip-shaped negative electrode are wound longitudinally via a separator; a non-aqueous electrolyte; and a bottomed cylindrical outer casing for housing the electrode body and the non-aqueous electrolyte, wherein the negative electrode includes a negative electrode current collector and a negative electrode mixture layer disposed on the negative electrode current collector, and has a facing portion facing the positive electrode via the separator, and a non-facing portion extending from the winding end end of the facing portion toward the winding end side of the electrode body, wherein the non-facing portion is folded back toward the winding start side in a manner in which the longitudinal end of the negative electrode does not face the positive electrode.

2. The non-opposing portion is folded back radially inward of the electrode body, as described in claim 1, for the non-aqueous electrolyte secondary battery.

3. The non-opposing portion is folded back so as to sandwich the separator, as described in claim 1.

4. The non-aqueous electrolyte secondary battery according to claim 1, wherein the length of the folded region of the non-opposing portion is a length that is wound around 0.25 turns or less.

5. In the radial cross-section of the electrode body, the angle between a straight line extending radially along the electrode body from the winding center of the electrode body through the winding end of the positive electrode and along the electrode body, and a straight line extending radially along the electrode body from the winding center of the electrode body through the folded longitudinal end of the negative electrode, is 45° or less, as described in claim 1.

6. The non-facing portion includes a negative electrode current collector exposed portion in which the negative electrode mixture layer is not formed on the negative electrode current collector and both sides of the negative electrode current collector are exposed, and the negative electrode current collector exposed portion is folded back, the non-aqueous electrolyte secondary battery according to claim 1.

7. The non-aqueous electrolyte secondary battery according to claim 1, wherein a negative electrode lead is provided at the winding start end of the negative electrode for electrically connecting the negative electrode and the outer casing.

8. The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode mixture layer contains a silicon-containing material as a negative electrode active material, and the content of the silicon-containing material is 5% by mass or more relative to the total mass of the negative electrode active material.

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